I think that no one will doubt that the car poses a great danger to others and road users. And since it is not yet possible to completely avoid road traffic accidents, the car is being improved in the direction of reducing the likelihood of an accident and minimizing its consequences. This is facilitated by the tightening of requirements for vehicle safety on the part of organizations engaged in analysis and practical experiments (crash tests). And such events give their positive "fruits". Every year the car becomes safer - both for those who are inside it and for pedestrians. To understand the components of the concept of "car safety", we first divide it into two parts - ACTIVE and PASSIVE safety.
ACTIVE SECURITY
What is ACTIVE CAR SAFETY?
Scientifically speaking, it is a set of structural and operational properties of a car aimed at preventing road accidents and eliminating the prerequisites for their occurrence associated with the design features of the car.
Simply put, these are the systems in the car that help prevent accidents.
Below - more about the parameters and systems of the car that affect its active safety.
1. RELIABILITY
Reliability of components, assemblies and systems of a car is a determining factor in active safety. Particularly high demands are placed on the reliability of elements related to the implementation of the maneuver - the braking system, steering, suspension, engine, transmission, and so on. Improving reliability is achieved by improving the design, using new technologies and materials.
2. CAR LAYOUT
There are three types of vehicle layout:
and) Front-engine - vehicle layout in which the engine is located in front of the passenger compartment. It is the most common and has two options: rear-wheel drive (classic) and front wheel drive... The last type of layout is front-engine front-wheel drive - has now become widespread due to a number of advantages over rear-wheel drive:
- better stability and handling when driving at high speed, especially on wet and slippery roads;
- ensuring the required weight load on the driving wheels;
- lower noise level, which is facilitated by the absence of a cardan shaft.
At the same time, front-wheel drive cars have a number of disadvantages:
- under full load, acceleration on the rise and on wet roads is reduced;
- at the moment of braking, too uneven distribution of weight between the axles (the wheels of the front axle account for 70% -75% of the vehicle weight) and, accordingly, braking forces (see Braking Properties);
- the tires of the front driving steered wheels are loaded more, respectively, are more prone to wear;
- the drive to the front wheels requires the use of complex narrow joints - constant velocity joints (SHRUS)
- the combination of the power unit (engine and gearbox) with the main gear complicates access to individual elements.
b) Layout with central location of the engine - the engine is located between the front and rear axles, it is quite rare for cars. It allows you to get the most spacious interior for the given dimensions and good distribution along the axes.
in) Rear-engined - the engine is located behind the passenger compartment. This arrangement was common in small cars. When transmitting torque to the rear wheels, it made it possible to obtain an inexpensive power unit and the distribution of such a load along the axles, in which the rear wheels accounted for about 60% of the weight. This had a positive effect on the cross-country ability of the car, but negatively on its stability and handling, especially at high speeds. Cars with this layout, at present, are practically not produced.
3. BRAKE PROPERTIES
The ability to prevent accidents is most often associated with heavy braking, therefore, it is necessary that the braking properties of the car provide its effective deceleration in all traffic situations.
To fulfill this condition, the force developed by the braking mechanism should not exceed the adhesion force with the road, which depends on the weight load on the wheel and the condition of the road surface. Otherwise, the wheel will block (stop rotating) and begin to slip, which can lead (especially when several wheels are blocked) to the car skidding and a significant increase in the braking distance. To prevent blocking, the forces generated by the brakes must be proportional to the weight load on the wheel. This is realized by using more efficient disc brakes.
Modern cars use anti-lock braking system (ABS), which corrects the braking force of each wheel and prevents them from slipping.
In winter and summer, the condition of the road surface is different, therefore, for the best implementation of the braking properties, it is necessary to use tires appropriate for the season.
4. TRACTION PROPERTIES
Traction properties (traction dynamics) of a car determine its ability to intensively increase its speed. The confidence of the driver when overtaking, driving through prerekrests largely depends on these properties. Traction dynamics is especially important for getting out of emergency situations, when it is too late to brake, difficult conditions do not allow maneuvering, and an accident can be avoided only by anticipating the event.
As in the case of braking forces, the traction force on the wheel should not be greater than the traction force, otherwise it will start to slip. This is prevented by the traction control system (PBS). When the car accelerates, it slows down the wheel, the rotation speed of which is greater than that of the others, and, if necessary, reduces the power developed by the engine.
5. STABILITY OF THE CAR
Stability is the ability of a car to keep moving along a given trajectory, counteracting the forces that cause it to skid and roll over in various road conditions at high speeds.
The following types of resistance are distinguished:
- transverse with straight motion (directional stability).
Its violation manifests itself in yawing (changing the direction of movement) of the car on the road and can be caused by the action of the lateral wind force, different values \u200b\u200bof traction or braking forces on the wheels of the left or right side, their slipping or sliding. large backlash in the steering, incorrect wheel alignment angles, etc.;
- transverse with curvilinear movement.
Its violation leads to skidding or overturning under the influence of centrifugal force. Stability is especially impaired by an increase in the position of the center of mass of the vehicle (for example, a large mass of cargo on a removable roof rack);
- longitudinal.
Its violation is manifested in the slipping of the driving wheels when overcoming prolonged icy or snow-covered ups and downs of the car. This is especially true for road trains.
6. CAR CONTROL
Handling is the ability of the vehicle to move in the direction given by the driver.
One of the characteristics of handling is understeer - the ability of a car to change the direction of travel when the steering wheel is stationary. Depending on the change in the turning radius under the influence of lateral forces (centrifugal force when cornering, wind force, etc.), steering can be:
- insufficient - the car increases the turning radius;
- neutral - the turning radius does not change;
- redundant - the turning radius decreases.
Distinguish between tire and roll steering.
Tire steering
Tire understeer is associated with the property of tires to move at an angle to a given direction during lateral pull (displacement of the contact patch with the road relative to the plane of rotation of the wheel). If tires of a different model are fitted, steering may change and the vehicle will behave differently when cornering at high speeds. In addition, the amount of lateral slip depends on the tire pressure, which must correspond to that specified in the vehicle's operating instructions.
Heel steering
Heel steering is associated with the fact that when the body tilts (roll), the wheels change their position relative to the road and the car (depending on the type of suspension). For example, if the suspension is double wishbone, the wheels tilt to the roll sides, increasing the slip.
7. INFORMATIVITY
Informativeness - the property of a car to provide the driver and other road users with the necessary information Insufficient information from other vehicles on the road about the condition of the road surface, etc. often causes an accident. The information content of the car is divided into internal, external and additional.
Internal provides an opportunity for the driver to perceive the information necessary for driving.
It depends on the following factors:
- Visibility should allow the driver to receive all the necessary information about the traffic situation in a timely manner and without interference. Faulty or ineffective washers, windshield blowing and heating systems, windshield wipers, and the absence of standard rear-view mirrors drastically impair visibility under certain road conditions.
- Instrument panel position, buttons and control keys, gear lever, etc. should provide the driver with a minimum time to monitor indications, operating switches, etc.
External information content - providing other traffic participants with information from the car, which is necessary for the correct interaction with them. It includes an external light alarm system, a sound signal, dimensions, shape and color of the body. The information content of cars depends on the contrast of their color relative to the road surface. According to statistics, cars painted in black, green, gray and blue are twice as likely to get into accidents due to the difficulty of distinguishing them in poor visibility conditions and at night. Defective direction indicators, brake lights, side lights will not allow other road users to recognize the driver's intentions in time and make the right decision.
Additional information content - the property of the car, allowing it to operate in conditions of limited visibility: at night, in fog, etc. It depends on the characteristics of the lighting system and other devices (for example, fog lamps) that improve the driver's perception of traffic information.
8. COMFORTABLE
The comfort of the car determines the time during which the driver is able to drive the car without fatigue. The increase in comfort is facilitated by the use of automatic transmission, speed controllers (cruise control), etc. Currently, cars are produced with adaptive cruise control. It not only automatically maintains the speed at a given level, but also, if necessary, reduces it to a complete stop of the car.
PASSIVE SECURITY
Passive vehicle safety must ensure the survival and minimization of the number of injuries to the passengers of the vehicle involved in a road traffic accident.
In recent years, passive vehicle safety has become one of the most important elements from the point of view of manufacturers. Huge funds are invested in the study of this topic and its development, and not only because firms care about the health of customers, but because safety is a sales lever. And firms love to sell.
I will try to explain a few definitions hidden under the broad definition of "passive safety".
It is subdivided into external and internal.
External is achieved by eliminating sharp corners, protruding handles, etc. on the outer surface of the body. With this, everything is clear and quite simple.
To level up internal security uses a lot of different design solutions:
1. BODY STRUCTURE or "SECURITY GRILLE"
It provides acceptable loads on the human body from a sharp deceleration in an accident and preserves the space of the passenger compartment after body deformation.
In a severe accident, there is a danger that the engine and other components can enter the driver's cab. Therefore, the cab is surrounded by a special "safety cage", which is an absolute protection in such cases. The same ribs and stiffening bars can be found in car doors (in case of side collisions).
This also includes energy dissipation areas.
In a severe accident, a sudden and sudden deceleration occurs until the vehicle comes to a complete stop. This process causes huge overloads on the bodies of passengers, which can be fatal. It follows that it is necessary to find a way to "slow down" the deceleration in order to reduce the load on the human body. One way to accomplish this is to design collision dampening areas in the front and rear of the body. The destruction of the car will be more severe, but the passengers will remain intact (and this is in comparison with the old "thick-skinned" cars, when the car got off with a "slight fright", but the passengers were seriously injured).
2. SEAT BELTS
The harness system, so familiar to us, is undoubtedly the most effective way to protect a person during an accident. After many years, during which the system has remained unchanged, in recent years there have been significant changes that have increased the degree of passenger safety. Thus, in the event of an accident, the belt pretensioner pulls the body of the person to the back of the seat, thereby preventing the body from moving forward or slipping under the belt. The effectiveness of the system is due to the fact that the belt is in a tensioned position, and not loosened by the use of various clips and clothespins, which practically cancel the action of the pretensioner. An additional element of the pretensioner seat belts is the maximum body load limiting system. When triggered, the belt will loosen slightly, thereby reducing the load on the body.
3. INFLATABLE AIRBAGS (airbag)
One of the most common and effective safety systems in modern cars (after seat belts) is airbags. They began to be widely used already in the late 70s, but only a decade later they really took their rightful place in the safety systems of cars of most manufacturers.
They are placed not only in front of the driver, but also in front of the front passenger, as well as from the sides (in doors, body pillars, etc.). Some car models have their forced shutdown due to the fact that people with heart problems and children may not withstand their false alarms.
4. SEATS WITH HEADRESTS
I don't think anyone doubts the role of the headrest is to prevent sudden movement of the head during an accident. Therefore, you should adjust the height of the headrest and its position to the correct position. Modern head restraints have two degrees of adjustment to prevent injuries to the cervical vertebrae when moving "with an overlap", so characteristic of rear collisions.
5. CHILD SAFETY
Today, there is no longer any need to rack your brains over fitting the child seat to the original seat belts. An increasingly common device Isofix allows you to attach the child safety seat directly to the connection points prepared in the car without using a seat belt. You just need to check that the car and the child seat are adapted to the mountings Isofix.
Safety depends on three important characteristics of the vehicle: size and weight, passive safety equipment to help you survive an accident and avoid injury, and active safety equipment to help avoid road accidents.
However, in a collision, heavier cars with relatively poor crash test scores may perform better than lighter cars with excellent scores. Twice as many people die in compact and small cars as in large ones. This should always be remembered.
Passive safety equipment helps the driver and passengers to survive an accident and remain without serious injury. The size of the car is also a means of passive safety: bigger \u003d safer. But there are other important points as well.
Seat belts have become the best driver and passenger protection device ever invented. The sane idea of \u200b\u200btying a person to a seat to save his life in an accident dates back to 1907. Then the driver and passengers were fastened only at the waist level. The first belts for production cars were supplied by the Swedish company Volvo in 1959. Belts in most cars are three-point, inertial, in some sports cars, four-point and even five-point are used to better keep the driver in the saddle. One thing is clear: the tighter you are pressed against the chair, the safer. Modern seat belt systems have automatic pretensioners that, in the event of an accident, select the sagging belts, increasing the protection of the person, and retaining space for the deployment of airbags. It is important to know that while airbags protect against serious injury, seat belts are absolutely essential to ensure the complete safety of the driver and passengers. The American Traffic Safety Organization NHTSA, based on its research, reports that using seat belts reduces the risk of death by 45-60%, depending on the type of vehicle.
Without airbags in the car it is impossible, now only the lazy does not know this. They will save us from a blow and from broken glass. But the first pillows were like an armor-piercing projectile - they opened up under the influence of impact sensors and fired towards the body at a speed of 300 km / h. A survival attraction, and only, not to mention the horror that a person experienced at the time of the clap. Now pillows are found even in the cheapest little cars and can unfold at different speeds depending on the force of the collision. The device has gone through many modifications and has been saving lives for 25 years. However, the danger still remains. If you forgot or were too lazy to buckle up, then the pillow can easily ... kill. During an accident, even at low speed, the body flies forward by inertia, the opened pillow will stop it, but the head kicks back with great speed. Surgeons call this "whiplash." In most cases, this threatens a fracture of the cervical vertebrae. At its best, it is an eternal friendship with vertebral neurologists. These are the kind of doctors who sometimes manage to put your vertebrae in place. But, as you know, it is better not to touch the cervical vertebrae, they pass under the category of untouchables. That is why in many cars a nasty squeak is heard, which does not so much remind us to buckle up as informs that the pillow will NOT open if the person is not fastened. Listen carefully to what your car is singing to you. Airbags are specially designed to work in conjunction with seat belts and in no way eliminate the need to use them. According to the American organization NHTSA, the use of airbags reduces the risk of death in an accident by 30-35%, depending on the type of vehicle.
During a collision, the seat belts and airbags work together. The combination of their work is 75% more effective in preventing serious head injuries and 66% more effective in preventing chest injuries. Side airbags also significantly improve driver and passenger protection. Car manufacturers also use two-stage airbags, which are deployed in stages one after the other to avoid possible injury to children and short adults from the use of single-stage, cheaper airbags. In this regard, it is more correct to put children only in the rear seats in cars of any type.
Headrests designed to prevent injury from sudden sudden movement of the head and neck in a collision with the rear of the car. In reality, head restraints often provide little or no protection against injury. Effective protection when using a head restraint can be achieved if it is exactly in line with the center of the head at the level of its center of gravity and no further than 7 cm from the back of the head. Please be aware that some seat options change the size and position of the headrest. Significantly improve safety active head restraints... Their principle of operation is based on simple physical laws, according to which the head is tilted back a little later than the body. Active head restraints use the pressure of the body against the seat back at the moment of impact, which causes the head restraint to move up and forward, preventing injury-causing sudden head tilt back. When hitting the rear of the car, the new head restraints are triggered simultaneously with the seat back to reduce the risk of injury to the vertebrae not only in the cervical, but also in the lumbar spine. After the impact, the lower back of the person sitting in the chair involuntarily moves into the depth of the back, while the built-in sensors instruct the headrest to move forward and up in order to evenly distribute the load on the spine. Extending on impact, the headrest reliably fixes the back of the head, preventing excessive bending of the cervical vertebrae. Bench tests have shown that the new system is 10-20% more effective than the existing one. At the same time, however, a lot depends on the position of the person at the moment of impact, his weight, and also whether he is wearing a seat belt.
Structural integrity (the integrity of the car frame) is another important component of the passive safety of the car. For each car, it is tested before going into production. The parts of the frame must not change their shape upon collision, while other parts must absorb the energy of the impact. The crumple zones in the front and rear were perhaps the most significant achievement here. The better the hood and trunk are crumpled, the less the passengers will get. The main thing is that the engine goes to the floor during an accident. Engineers are developing more and more new combinations of materials to absorb impact energy. The results of their activities can be very clearly seen on the horror stories of crash tests. As you know, there is a salon between the hood and the trunk. So this is how it should become a safety capsule. And this rigid frame should not be crumpled under any circumstances. The strength of the hard capsule makes it possible to survive even in the smallest car. If the front and rear of the frame is protected by a hood and trunk, then on the sides only metal bars in the doors are responsible for our safety. At the worst impact, a side one, they cannot protect, therefore they use active systems - side airbags and curtains, which also watch our interests.
Also passive safety elements include:
-the front bumper, which absorbs part of the kinetic energy in a collision;
-trauma-safe parts of the interior of the passenger compartment.
Active vehicle safety
In the arsenal of active car safety, there are many emergency systems. Among them are old systems and newfangled inventions. To name just a few: Anti-lock braking system (ABS), traction control, electronic stability control (ESC), night vision and automatic cruise control are trendy technologies that help the driver on the road today.
Anti-lock braking system (ABS) helps to stop faster and not lose control of the vehicle, especially on slippery surfaces. In the event of an emergency stop, ABS works differently than conventional brakes. With conventional brakes, a sudden stop often causes the wheels to lock, causing skidding. Anti-lock braking system detects when the wheel is locked and releases it, applying the brakes 10 times faster than the driver can do. When ABS is applied, a characteristic sound is heard and vibration is felt on the brake pedal. To use ABS effectively, the braking technique must be changed. It is not necessary to release and depress the brake pedal again, as this will deactivate the ABS system. In case of emergency braking, press the pedal once and gently hold it until the vehicle stops.
Traction Control (TCS) It is used to prevent slipping of the driving wheels, regardless of the degree of pressing the accelerator pedal and the road surface. Its principle of operation is based on a decrease in engine output power with an increase in speed.
driving wheels. The computer controlling this system learns about the rotational speed of each wheel from the sensors installed at each wheel and from the acceleration sensor. Exactly the same sensors are used in ABS and torque control systems.
moment, so these systems are often used simultaneously. Based on the signals from the sensors indicating that the drive wheels are starting to slip, the computer decides to reduce the engine power and has an effect on it similar to
a decrease in the degree of pressing the gas pedal, and the degree of gas release is the stronger, the higher the rate of increase in slip.
ESC (electronic stability control) - she's ESP. The task of the ESC is to maintain the stability and controllability of the vehicle in the extreme turning modes. By monitoring the vehicle's lateral acceleration, the steering vector, braking force and individual wheel speed, the system detects situations that threaten the vehicle with skidding or overturning, and automatically releases the gas and brakes the corresponding wheels. The figure clearly illustrates the situation when the driver exceeded the maximum corner entry speed and began to drift (or drift). The red line is the trajectory of the vehicle without ESC. If its driver starts to brake, he has a serious chance to turn around, and if not, then fly off the road. ESC, on the other hand, will selectively brake the desired wheels so that the car stays on the desired trajectory. ESC is the most sophisticated device that works with anti-lock braking (ABS) and traction control (TCS) systems to control traction and throttle control. The ESС system on a modern car is almost always disabled. This can help in unusual situations on the road, for example, when the vehicle is stuck rocking.
Cruise control is a system that automatically maintains a given speed, regardless of changes in the road profile (ascents, descents). The operation of this system (fixing the speed, decreasing or increasing) is controlled by the driver by pressing the buttons on the steering column switch or steering wheel after accelerating the car to the required speed. When the driver presses the brake or accelerator pedal, the system is instantly deactivated. Cruise control significantly reduces driver fatigue on long journeys by allowing the feet to be relaxed. In most cases, cruise control reduces fuel consumption by maintaining a stable engine operation; the service life of the engine increases, since at constant speeds maintained by the system, there are no variable loads on its parts.
In addition to maintaining a constant driving speed, it simultaneously monitors the observance of a safe distance to the vehicle in front. The main element of active cruise control is an ultrasonic sensor installed in the front bumper or behind the radiator grille. Its principle of operation is similar to parking radar sensors, only the range is several hundred meters, and the angle of coverage, on the contrary, is limited to a few degrees. By sending an ultrasonic signal, the sensor waits for a response. If the beam finds an obstacle in the form of a car moving at a lower speed and returns, then it is necessary to reduce the speed. As soon as the road is cleared again, the car accelerates to its original speed.
Tires are another important safety feature of a modern car. Think: they are the only thing that connects the car to the road. A good set of tires has a big advantage in how the car reacts to emergency maneuvers. The quality of the tires also significantly affects the handling of the cars.
Consider, for example, the equipment of the Mercedes S-Class. The basic vehicle is equipped with the Pre-Safe system. When there is a threat of an accident, which the electronics detects by hard braking or too much wheel slip, Pre-Safe tightens the seat belts and inflates
airbags in the multi-contour front and rear seats to better secure passengers. In addition, Pre-Safe "battens down hatches" - closes the windows and sunroof. All these preparations should reduce the severity of the possible accident. An excellent contractor from the S-class is made by all kinds of electronic driver assistants - the ESP stabilization system, the ASR traction control system, the Brake Assist emergency braking system. The emergency braking assistance system in the S-Class is combined with a radar. Radar detects
distance to cars ahead.
If it becomes alarmingly short, and the driver brakes less than necessary, the electronics begin to help him. During emergency braking, the vehicle's brake lights flash. On request, the S-Class can be equipped with the Distronic Plus system. It is an automatic cruise control, very convenient in traffic jams. The device, using the same radar, monitors the distance to the vehicle in front, if necessary, stops the car, and when the flow resumes movement, automatically accelerates it to its previous speed. Thus, Mercedes relieves the driver of any manipulation besides turning the steering wheel. Distronic works
at speeds from 0 to 200 km / h. The S-class anti-disaster parade is completed by an infrared night vision system. She snatches objects out of the darkness from powerful xenon headlights.
Car safety rating (EuroNCAP crash tests)
The main beacon of passive safety is the European New Car Test Association, or EuroNCAP for short. Founded in 1995, this organization is committed to regularly destroying brand new cars, giving ratings on a five-star scale. The more stars the better. So, if safety is your primary concern when choosing a new car, choose the model that has received the maximum possible five stars from EuroNCAP.
All test series follow the same scenario. First, the organizers select cars of the same class and model year that are popular on the market and purchase two cars of each model anonymously. The tests are carried out at two renowned independent research centers - English TRL and Dutch TNO. From the first tests in 1996 until mid-2000, the EuroNCAP safety rating was "four stars" and included an assessment of the car's behavior in two types of tests - in frontal and side crash tests.
But in the summer of 2000, EuroNCAP experts introduced another, additional, test - an imitation of a side impact on a pole. The car is placed transversely on a mobile trolley and at a speed of 29 km / h directed by the driver's door into a metal post with a diameter of about 25 cm. Only those cars that are equipped with special head protection for the driver and passengers - “high” side airbags or inflatable “curtains” pass this test ".
If the vehicle passes three tests, a star-shaped halo appears around the head of the dummy on the side impact safety pictogram. If the halo is green, it means that the car has passed the third test and received additional points that could move it into the five-star category. And those cars that do not have "high" side airbags or inflatable "curtains" as standard equipment are tested according to the usual program and cannot claim the highest Euro-NCAP rating.
It turned out that effectively triggered protective devices can more than an order of magnitude reduce the risk of injury to the driver's head in the event of a side impact on a pole. For example, without “high” pillows or “curtains,” the Head Injury Criteria (HIC) can be as high as 10,000 on a “pole” test! (The threshold value of HIC, beyond which the area of \u200b\u200bmortally dangerous head injuries begins, doctors consider 1000.) But with the use of "high" pillows and "curtains", HIC drops to safe values \u200b\u200b- 200-300.
A pedestrian is the most defenseless road user. However, EuroNCAP was concerned about its safety only in 2002, having developed an appropriate methodology for assessing cars (green stars). Having studied the statistics, experts have come to the conclusion that the majority of pedestrian collisions occur according to one scenario. First, the car hits the legs with a bumper, and then the person, depending on the speed of movement and the design of the car, hits his head either on the hood or on the windshield.
Before the test, the bumper and the front edge of the bonnet are drawn into 12 sections, and the bonnet and the lower part of the windshield are divided into 48 sections. Then, successively, each area is hit with simulators of legs and head. The impact force corresponds to a collision with a person at a speed of 40 km / h. Sensors are placed inside the simulators. After processing their data, the computer assigns a certain color to each marked area. The safest areas are indicated in green, the most dangerous areas are in red, and the intermediate ones are in yellow. Then, based on the aggregate scores, an overall star rating is given to the vehicle for pedestrian safety. The maximum possible score is four stars.
In recent years, there has been a clear trend - more and more new cars receive "stars" in the pedestrian test. Only large off-road vehicles remain problematic. The reason is in the high front part, which is why, in the event of a collision, the blow falls not on the legs, but on the body.
And one more innovation. More and more cars are equipped with seat belt reminder systems (SNRB) - for the presence of such a system in the driver's seat, EuroNCAP experts award one additional point, for equipping both front seats - two points.
The American National Highway Traffic Safety Association (NHTSA) conducts crash tests using its own method. In a frontal impact, the vehicle crashes into a rigid concrete barrier at a speed of 50 km / h. Side impact conditions are also more severe. The trolley weighs almost 1,400 kg and the vehicle travels at a speed of 61 km / h. This test is carried out twice - blows are made to the front door and then to the rear door. In the United States, another organization, the Transport Research Institute for Insurance Companies, IIHS, beats cars professionally and officially. But her methodology is not significantly different from the European one.
Factory crash tests
Even a non-specialist understands that the tests described above do not cover all possible types of accidents and, therefore, do not allow a sufficiently complete assessment of the vehicle's safety. Therefore, all major car manufacturers conduct their own, non-standard, crash tests, sparing no time or money. For example, every new Mercedes model goes through 28 tests before production starts. On average, one test takes about 300 man-hours. Some of the tests are carried out virtually on a computer. But they play the role of auxiliary, for the final fine-tuning of cars they are broken only in “real life.” The most serious consequences occur as a result of head-on collisions. Therefore, most of the factory tests simulate this type of accident. In this case, the car crashes into deformable and rigid obstacles at different angles, with different speeds and different overlap values. However, even such tests do not give the whole picture. Manufacturers began to push cars against each other, and not only "classmates", but also cars of different "weight categories" and even cars with trucks. Thanks to the results of such tests, underruns have become mandatory on all trucks since 2003.
Factory safety experts are also fancy for side impact testing. Different angles, speeds, places of impacts, participants of equal and different sizes - everything is like with frontal tests.
Convertibles and large off-road vehicles are also tested for a coup, because according to statistics, the death toll in such accidents reaches 40%
Manufacturers often test their cars with a rear impact at low speeds (15-45 km / h) and overlaps of up to 40%. This allows you to assess how protected passengers are from whiplash injuries (damage to the cervical vertebrae) and how protected the gas tank is. Frontal and side impacts at speeds up to 15 km / h help determine the extent of damage (i.e. repair costs) in minor accidents. Seats and seat belts are tested separately.
What are automakers doing to protect pedestrians? The bumper is made of softer plastic, and as few reinforcing elements as possible are used in the bonnet design. But the main danger to human life is engine compartment units. When hitting, the head punches the hood and bumps into them. Here they go in two ways - they try to maximize the free space under the hood, or they supply the hood with squibs. A sensor located in the bumper, upon impact, sends a signal to the mechanism that triggers the igniter. The latter, firing, raises the hood by 5-6 centimeters, thereby protecting the head from hitting the hard protrusions of the engine compartment.
Dolls for adults
Everyone knows that dummies are used to conduct crash tests. But not everyone knows that they did not come to such a seemingly simple and logical decision right away. In the beginning, human corpses, animals were used for the tests, and living people - volunteers - took part in less dangerous tests.
The pioneers in the fight for the safety of a person in a car were the Americans. It was in the USA that the first mannequin was made in 1949. In his "kinematics", he looked more like a large doll: his limbs moved in a completely different way from that of a person, and his body was whole. It wasn't until 1971 that GM created a more or less "humanoid" dummy. And modern "dolls" differ from their ancestor, approximately like a man from a monkey.
Now mannequins are made by whole families: two versions of the "father" of different heights and weights, a lighter and smaller "wife" and a whole set of "children" - from one and a half to ten years of age. The weight and proportions of the body completely mimic that of a human. The metal "cartilage" and "vertebrae" work like the human spine. Flexible plates replace ribs, and hinges replace joints, even the feet are mobile. From above, this "skeleton" is covered with a vinyl covering, the elasticity of which corresponds to the elasticity of human skin.
Inside, the dummy is stuffed from head to toe with sensors that, during testing, transmit data to a memory unit located in the "chest". As a result, the cost of the mannequin is - hold on to the chair - over 200 thousand dollars. That is, several times more expensive than the overwhelming majority of tested cars! But such "dolls" are universal. Unlike their predecessors, they are suitable for both frontal and side tests, and rear collisions. Preparing a dummy for testing requires fine tuning of the electronics and can take several weeks. In addition, immediately before the test, paint marks are applied to various parts of the "body" to determine which parts of the passenger compartment are in contact during an accident.
We live in a computer world, and therefore security specialists actively use virtual simulation in their work. This allows much more data to be collected and, moreover, such mannequins are practically eternal. Toyota programmers, for example, have developed more than a dozen models that simulate people of all ages and anthropometric data. And Volvo even created a digital pregnant woman.
Conclusion
Every year around 1.2 million people die in road traffic accidents worldwide, and half a million are injured or injured. In an effort to draw attention to these tragic figures, the United Nations in 2005 declared every third Sunday in November as World Day of Remembrance for Road Traffic Victims. Carrying out crash tests can improve the safety of cars and thereby reduce the above sad statistics.
Vehicle safety.Vehicle safety includes a set of design and operational properties that reduce the likelihood of road accidents, the severity of their consequences and negative impact on the environment.
The concept of safety of the vehicle structure includes active and passive safety.
Active safety Structures are constructive measures aimed at preventing accidents. These include measures that ensure controllability and stability while driving, effective and reliable braking, easy and reliable steering, low driver fatigue, good visibility, effective operation of external lighting and signaling devices, as well as improving the dynamic qualities of the car.
Passive safety Structures are constructive measures that eliminate or minimize the consequences of an accident for the driver, passengers and cargo. They provide for the use of injury-free steering column structures, energy-intensive elements on the front and rear of cars, soft cab and body upholstery and soft linings, seat belts, safety glasses, a sealed fuel system, reliable fire-fighting devices, locks for the hood and body with locking devices, safe arrangement of parts and all cars.
In recent years, much attention has been paid to improving the safety of vehicle construction in all countries that produce them. More generally in the United States of America. The active safety of a vehicle is understood as its properties that reduce the likelihood of a road traffic accident.
Active safety is provided by several operational properties that allow the driver to confidently drive the car, accelerate and brake with the required intensity, and maneuver on the roadway, which is required by the road situation, without significant expenditure of physical forces. The main of these properties are: traction, braking, stability, handling, cross-country ability, information content, habitability.
Under the passive safety of the vehiclewe understand its properties that reduce the severity of the consequences of a road traffic accident.
Distinguish between external and internal passive vehicle safety. The main requirement of external passive safety is to ensure such a constructive implementation of the outer surfaces and elements of the car, in which the probability of human injury by these elements in the event of a road traffic accident would be minimal.
As you know, a significant number of accidents are associated with collisions and collisions with a fixed obstacle. In this regard, one of the requirements for the external passive safety of vehicles is to protect drivers and passengers from injury, as well as the vehicle itself from damage by external structural elements.
Figure 8.1 - Scheme of forces and moments acting on the car
Figure 8.1 - Vehicle safety structure
An example of a passive safety element can be a crash-proof bumper, the purpose of which is to soften the impact of the car on obstacles at low speeds (for example, when maneuvering in a parking area).
The endurance limit of G-forces for a person is 50-60g (g-acceleration of gravity). The endurance limit for an unprotected body is the amount of energy perceived directly by the body, corresponding to a speed of about 15 km / h. At 50 km / h, the energy exceeds the permissible by about 10 times. Therefore, the task is to reduce the acceleration of the human body in a collision due to prolonged deformations of the front of the car body, which would absorb as much energy as possible.
That is, the greater the deformation of the car and the longer it occurs, the less overload the driver experiences when colliding with an obstacle.
External passive safety is related to body decorative elements, handles, mirrors and other parts fixed to the car body. On modern cars, tired door handles are increasingly used, which do not cause injury to pedestrians in the event of a traffic accident. The protruding emblems of the manufacturers on the front of the vehicle are not used.
There are two main requirements for the internal passive safety of a car:
Creation of conditions under which a person could safely withstand any overload;
Elimination of traumatic elements inside the body (cab). The driver and passengers in a collision, after an instant stop of the car, still continue to move, maintaining the speed that the car had before the collision. It is at this time that most of the injuries occur as a result of hitting the head on the windshield, chest on the steering wheel and steering column, knees on the lower edge of the instrument panel.
An analysis of road traffic accidents shows that the vast majority of those killed were in the front seat. Therefore, when developing measures for passive safety, attention is primarily paid to ensuring the safety of the driver and passenger in the front seat.
The design and rigidity of the car body are made in such a way that in collisions the front and rear parts of the body are deformed, and the deformation of the passenger compartment (cabin) is as minimal as possible to preserve the life support zone, that is, the minimum required space, within which the body of a person inside the body is excluded ...
In addition, the following measures should be taken to reduce the severity of the consequences of a collision:
The need to move the steering wheel and steering column and absorb impact energy by them, as well as evenly distribute the impact over the surface of the driver's chest;
Elimination of the possibility of ejection or loss of passengers and the driver (reliability of door locks);
Availability of personal protective and restraining equipment for all passengers and the driver (seat belts, head restraints, air bags);
Lack of traumatic elements in front of passengers and the driver;
Body equipment with safety glass. The effectiveness of using seat belts in combination with other measures is confirmed by statistical data. Thus, the use of belts reduces the number of injuries by 60 - 75% and reduces their severity.
One of the effective ways to solve the problem of limiting the movement of the driver and passengers in a collision is the use of pneumatic cushions, which, when the car collides with an obstacle, are filled with compressed gas in 0.03 - 0.04 s, absorb the impact of the driver and passengers and thereby reduce the severity of injury.
Under post-crash vehicle safetyits properties are understood in the event of an accident not to interfere with the evacuation of people, not to cause injury during and after evacuation. The main post-accident safety measures are fire-prevention measures, measures for the evacuation of people, and emergency signaling.
The most serious consequence of a traffic accident is a car fire. Fire most often occurs during severe accidents, such as collisions between cars, collisions with fixed obstacles, and rollovers. Despite the low probability of fire (0.03 -1.2% of the total number of incidents), their consequences are severe.
They cause almost complete destruction of the car and, if it is impossible to evacuate, the death of people. In such incidents, fuel is poured out of the damaged tank or from the filler neck. Ignition occurs from hot parts of the exhaust system, from a spark with a faulty ignition system or from friction of body parts on the road or on the body of another car. There may be other causes of fire.
Under the environmental safety of the vehicleits property is understood to reduce the degree of negative impact on the environment. Environmental safety covers all aspects of using the car. The following are the main environmental aspects associated with the operation of the car.
Loss of usable land area... The land necessary for the movement and parking of cars is excluded from the use of other sectors of the national economy. The total length of the global network of hard-surface roads exceeds 10 million km, which means a loss of over 30 million hectares. The expansion of streets and squares leads to "an increase in the territory of cities and the lengthening of all communications. In cities with a developed road network and car service enterprises, areas allocated for traffic and car parking occupy up to 70% of the entire territory.
In addition, vast territories are occupied by factories for the production and repair of cars, services for ensuring the functioning of road transport: gas stations, service stations, campings, etc.
Air pollution... Most of the harmful impurities dispersed in the atmosphere are the result of the operation of vehicles. A medium-power engine emits into the atmosphere in one day of operation about 10 m 3 of exhaust gases, which include carbon monoxide, hydrocarbons, nitrogen oxides and many other toxic substances.
In our country, the following norms have been established for the average daily maximum permissible concentration of toxic substances in the atmosphere:
Hydrocarbons - 0.0015 g / m;
Carbon monoxide - 0.0010 g / m;
Nitrogen dioxide - 0.00004 g / m
Use of natural resources.Millions of tons of high quality materials are used for the production and operation of cars, which leads to the depletion of their natural reserves. With the exponential growth of energy consumption per capita, characteristic of industrialized countries, the moment will soon come when existing energy sources will not be able to meet human needs.
A significant share of the consumed energy is consumed by cars, efficiency motors of which is 0.3 0.35, Therefore, 65 - 70% of the energy potential is not used.
Noise and vibration.The noise level, long-term tolerated by humans without harmful effects, is 80 - 90 dB On the streets of large cities and industrial centers, the noise level reaches 120-130 dB. Ground vibrations caused by vehicle movements have a detrimental effect on buildings and structures. To protect a person from the harmful effects of vehicle noise, various techniques are used: improving the design of vehicles, noise protection structures and green spaces along busy city highways, organizing such a traffic regime when the noise level is lowest.
The magnitude of the tractive force is the greater, the greater the engine torque and the gear ratios of the gearbox and final drive. But the amount of traction force cannot exceed the traction force of the driving wheels on the road. If the traction force exceeds the traction force of the wheels with the road, then the drive wheels will slip.
Adhesion forceequal to the product of the coefficient of adhesion and the adhesion weight. For a traction vehicle, the adhesion weight is equal to the normal load on the braked wheels.
Adhesion coefficientdepends on the type and condition of the road surface, on the design and condition of the tires (air pressure, tread pattern), on the load and vehicle speed. The value of the coefficient of adhesion decreases on wet and damp road surfaces, especially when the speed increases and the tire tread is worn out. For example, on a dry road with asphalt concrete, the friction coefficient is 0.7 - 0.8, and for a wet road - 0.35 - 0.45. On an icy road, the coefficient of adhesion decreases to 0.1 - 0.2.
The force of gravitythe car is attached at the center of gravity. In modern passenger cars, the center of gravity is located at a height of 0.45 - 0.6 m from the road surface and approximately in the middle of the car. Therefore, the normal load of a passenger car is distributed approximately equally along its axles, i.e. adhesion weight is 50% of normal load.
The height of the center of gravity for trucks is 0.65 - 1 m. For fully loaded trucks, the adhesion weight is 60–75% of the normal load. For four-wheel drive vehicles, the grip weight is equal to the vehicle's normal load.
When the car is moving, these ratios change, since there is a longitudinal redistribution of the normal load between the axles of the cars when the driving wheels transfer traction force, the rear wheels are more loaded, and when the car is braking, the front wheels are loaded. In addition, the redistribution of the normal load between the front and rear wheels occurs when the vehicle is moving downhill or uphill.
The redistribution of the load, by changing the value of the adhesion weight, affects the amount of adhesion of the wheels to the road, the braking properties and the stability of the car.
Movement resistance forces... Traction force on the driving wheels of the vehicle. When the vehicle moves uniformly on a horizontal road, such forces are: rolling resistance force and air resistance force. When the car is moving uphill, a resistance force arises to rise (Fig. 8.2), and when the car accelerates, a resistance force to acceleration (inertia force) arises.
Rolling resistance forceoccurs due to deformation of tires and road surface. It is equal to the product of the vehicle's normal load and the rolling resistance coefficient.
Figure 8.2 - Scheme of forces and moments acting on the car
The rolling resistance coefficient depends on the type and condition of the road surface, tire design, tire wear and air pressure, and vehicle speed. For example, for a road with an asphalt concrete surface, the rolling resistance coefficient is 0.014 0.020, for a dry dirt road it is 0.025-0.035.
On hard road surfaces, the rolling resistance coefficient increases sharply with decreasing tire pressure, and increases with an increase in driving speed, as well as an increase in braking and torque.
The air resistance force depends on the air resistance coefficient, frontal area and vehicle speed. The air resistance coefficient is determined by the type of vehicle and its body shape, and the frontal area is determined by the wheel track (distance between the tire centers) and the vehicle height. The force of air resistance increases in proportion to the square of the vehicle speed.
Lift resistance forcethe more, the greater the mass of the vehicle and the steepness of the rise of the road, which is estimated by the angle of rise in degrees or the value of the slope, expressed as a percentage. On the other hand, when the vehicle is moving downhill, the force of resistance to upward movement accelerates the movement of the vehicle.
On roads with asphalt concrete pavement, the longitudinal slope usually does not exceed 6%. If the coefficient of rolling resistance is taken equal to 0.02, then the total resistance of the road will be 8% t of the normal load of the car.
The force of resistance to acceleration(inertial force) depends on the mass of the car, its acceleration (increase in speed per unit of time) and the mass of rotating parts (flywheel, wheels), the acceleration of which also requires traction.
When the car accelerates, the force of resistance to acceleration is directed in the direction opposite to the movement. When the vehicle is braking and decelerating, the inertia force is directed towards the vehicle.
Car braking.Braking performance is characterized by the vehicle's ability to quickly decelerate and stop. A reliable and efficient braking system allows the driver to confidently drive the car at high speed and, if necessary, stop it on a short distance.
Modern cars have four braking systems: working, spare, parking and auxiliary. Moreover, the drive to all circuits of the brake system is separate. The most important for handling and safety is the service braking system. With its help, service and emergency braking of the car is carried out.
Service braking is called braking with a slight deceleration (1-3 m / s 2). It is used to stop the car at a previously marked place or to smoothly reduce speed.
Emergency braking is called deceleration with a large deceleration, usually maximum, reaching 8 m / s2. It is used in a hazardous environment to prevent an unexpected obstacle.
When braking the car, not the traction force acts on and on the wheels, but the braking forces Pt1 and Pt2, as shown in (Fig. 8.3). The force of inertia in this case is directed towards the movement of the vehicle.
Consider the emergency braking process. The driver, having noticed an obstacle, assesses the road situation, makes a decision on braking and transfers his foot to the brake pedal. The time t required for these actions (the driver's reaction time) is shown in (Fig. 8.3) by the segment AB.
During this time, the car travels the path S without reducing speed. Then the driver presses the brake pedal and the pressure from the main brake cylinder (or the brake valve) is transferred to the wheel brakes (the response time of the brake drive tpt - segment of the aircraft. The time tt depends mainly on the design of the brake drive. It is on average 0.2-0, 4s for vehicles with a hydraulic drive and 0.6-0.8 s with pneumatic ones. For road trains with a pneumatic brake drive, the time tt can reach 2-3 s. During the time tt, the car travels the path St, also without reducing speed.
Figure 8.3 - Stopping and braking distances of the car
After the expiration of the time trt, the braking system is fully engaged (point C), and the vehicle speed begins to decrease. In this case, the deceleration first increases (segment CD, the time of rise of the braking force tнт), and then remains approximately constant (steady) and equal to jset (time t mouth, segment DE).
The duration of the period tнт depends on the mass of the vehicle, the type and condition of the road surface. The greater the mass of the vehicle and the coefficient of adhesion of the tires to the road, the longer the time t. The value of this time is in the range of 0.1-0.6 s. During the time tнт, the car moves to the distance Sнт, and its speed decreases slightly.
When driving with a steady deceleration (time tset, segment DE), the vehicle speed decreases by the same amount for every second. At the end of braking, it drops to zero (point E), and the car, having passed the path Sust, stops. The driver removes his foot from the brake pedal and the braking occurs (braking time toт, section EF).
However, under the action of inertia, the front axle is loaded during braking, while the rear axle, on the contrary, is unloaded. Therefore, the response on the front wheels Rzl increases, and on the rear wheels Rz2 decreases. Accordingly, the adhesion forces change, therefore, in most cars, full and simultaneous use of the clutch by all the wheels of the car is extremely rare and the actual deceleration is less than the maximum possible.
To take into account the decrease in deceleration, a correction factor for the braking efficiency K.e has to be introduced into the formula for determining jst, equal to 1.1-1.15 for passenger cars and 1.3-1.5 for trucks and buses. On slippery roads, the braking forces on all wheels of the vehicle almost simultaneously reach the traction value.
The braking distance is less than the stopping distance, because during the driver's reaction time, the car moves a considerable distance. Stopping and braking distances increase with increasing speed and decreasing traction. The minimum permissible braking distances at an initial speed of 40 km / h on a horizontal road with a dry, clean and even surface are normalized.
The effectiveness of the braking system depends to a large extent on its technical condition and the technical condition of the tires. If oil or water enters the brake system, the coefficient of friction between the brake linings and the drums (or discs) decreases and the braking torque decreases. When the tire treads wear, the grip coefficient decreases.
This entails a decrease in braking forces. In operation, the braking forces of the left and right wheels of a car are often different, which causes it to turn around a vertical axis. The reasons can be different wear of the brake linings and drums or tires or the penetration of oil or water into the brake system on one side of the car, which reduces the coefficient of friction and reduces the braking torque.
Vehicle stability.Stability is understood as the properties of a car to resist skidding, sliding, overturning. Distinguish between longitudinal and lateral stability of the vehicle. Loss of lateral stability is more likely and dangerous.
Vehicle directional stability is called its property to move in the desired direction without corrective actions from the driver, i.e. with a constant steering wheel position. A car with poor directional stability all the time suddenly changes direction.
This poses a threat to other vehicles and pedestrians. The driver, driving an unstable car, is forced to especially carefully monitor the road situation and constantly adjust the movement to prevent going off the road. With long-term driving of such a car, the driver quickly gets tired, and the possibility of an accident increases.
Violation of directional stability occurs as a result of disturbing forces, for example, gusts of side wind, impacts of wheels on uneven roads, as well as due to a sharp turn of the steering wheels by the driver. Loss of stability can also be caused by technical malfunctions (incorrect adjustment of the brakes, excessive play in the steering or its jamming, tire puncture, etc.)
Loss of directional stability at high speed is especially dangerous. The car, having changed the direction of movement and deviated even at a small angle, may after a short time find itself in the lane of oncoming traffic. So, if a car moving at a speed of 80 km / h deviates from the straight-line direction of movement by only 5 °, then after 2.5 seconds it will move to the side by almost 1 m and the driver may not have time to return the car to the previous lane.
Figure 8.4 - Diagram of the forces acting on the car
Often the car loses stability when driving on a road with a side slope (slope) and when turning on a horizontal road.
If the car moves along a slope (Figure 8.4, a), the gravity force G makes an angle β with the road surface and it can be decomposed into two components: the force P1 parallel to the road and the force P2 perpendicular to it.
Force P1, strive to move the vehicle downhill and overturn it. The larger the slope angle β, the greater the force P1, therefore, the more likely the loss of lateral stability. When turning the car, the cause of loss of stability is the centrifugal force Pc (Fig. 8.4, b), directed from the center of rotation and applied to the center of gravity of the car. It is directly proportional to the square of the vehicle speed and inversely proportional to the radius of curvature of its trajectory.
The sideways sliding of the tires on the road is counteracted by traction forces, as noted above, which depend on the coefficient of traction. On dry, clean surfaces, the traction forces are strong enough to keep the vehicle stable even with high lateral forces. If the road is covered with a layer of wet mud or ice, the car can skid even if it is moving at low speed along a relatively gentle curve.
The maximum speed at which it is possible to move along a curved section of radius R without cross-sliding of tires is So, performing a turn on a dry asphalt surface (jx \u003d 0.7) at R \u003d 50m, you can move at a speed of about 66 km / h. Overcoming the same turn after rain (jx \u003d 0.3) without slipping, you can only move at a speed of 40-43 km / h. Therefore, before turning, the speed must be reduced the more, the smaller the radius of the upcoming turn. The formula determines the speed at which the wheels of both axles of the vehicle slide laterally simultaneously.
This phenomenon is extremely rare in practice. Much more often the tires of one of the axles - front or rear - begin to slip. Front axle cross-slip occurs infrequently and also stops quickly. In most cases, the wheels of the rear axle slide, which, starting to move in the lateral direction, slide faster and faster. This accelerating cross slip is called skid. To extinguish the skid that has begun, you need to turn the steering wheel towards the skid. In this case, the car will begin to move along a flatter curve, the turning radius will increase, and the centrifugal force will decrease. You need to turn the steering wheel smoothly and quickly, but not at a very large angle, so as not to cause a turn in the opposite direction.
As soon as the skid stops, you must also smoothly and quickly return the steering wheel to neutral position. It should also be noted that to get out of the skid of a rear-wheel drive car, the fuel supply must be reduced, and on a front-wheel drive, on the contrary, increased. Skid often occurs during emergency braking when the tire's grip has already been used to generate the braking force. In this case, immediately stop or release braking and thereby increase the vehicle's lateral stability.
Under the action of lateral force, the car can not only slide on the road, along and topple over on its side or onto the roof. The possibility of overturning depends on the position of the center, the weight of the vehicle. The higher the center of gravity is from the surface of the vehicle, the more likely it is to roll over. Especially often buses, as well as trucks engaged in the transportation of light, bulky goods (hay, straw, empty containers, etc.) and liquids are overturned. Under the action of lateral force, the springs on one side of the vehicle are compressed and the body tilts, increasing the risk of rollover.
Vehicle handling.Controllability is understood as the property of a car to provide movement in the direction given by the driver. The handling of a car, more than its other performance properties, is related to the driver.
To ensure good handling, the design parameters of the car must correspond to the psychophysiological characteristics of the driver.
The handling of a car is characterized by several indicators. The main ones are: the limiting value of the curvature of the trajectory in the circular motion of the car, the limiting value of the rate of change in the curvature of the trajectory, the amount of energy spent on driving the car, the amount of spontaneous deviations of the car from the given direction of movement.
The steered wheels constantly deviate from the neutral position under the influence of unevenness of the road. The ability of the steered wheels to maintain a neutral position and return to it after a turn is called steer stabilization. Weight stabilization is provided by the lateral inclination of the front suspension pins. When the wheels are turned, due to the lateral inclination of the pivots, the car rises, but its weight tends to return the turned wheels to their original position.
The high-speed stabilizing torque is due to the longitudinal tilt of the pivots. The king pin is located so that its upper end is directed backwards and the lower end is directed forward. The pivot pin crosses the road surface in front of the wheel-to-road contact patch. Therefore, when the vehicle is moving, the rolling resistance force creates a stabilizing moment relative to the pivot axis. If the steering gear and the steering mechanism are in good working order, after turning the car, the steered wheels and the steering wheel must return to the neutral position without the participation of the driver.
In the steering mechanism, the worm is located relative to the roller with a slight bias. In this regard, in the middle position, the gap between the worm and the roller is minimal and close to zero, and when the roller and bipod deviate in any direction, the gap increases. Therefore, when the wheels are in neutral position, increased friction is created in the steering mechanism, which contributes to the stabilization of the wheels and high-speed stabilizing moments.
Incorrect adjustment of the steering mechanism, large gaps in the steering gear can cause poor stabilization of the steered wheels, the cause of fluctuations in the course of the car. A car with poor steering wheel stabilization spontaneously changes direction of travel, as a result of which the driver is forced to continuously turn the steering wheel in one direction or the other in order to return the car to his lane.
Poor stabilization of the steering wheels requires a significant expenditure of physical and mental energy of the driver, increases the wear of tires and steering parts.
When the car moves around a bend, the outer and inner wheels roll in circles of various radii (Fig. 8.4). In order for the wheels to roll without sliding, their axes must intersect at one point. To fulfill this condition, the steered wheels must turn at different angles. The steering linkage provides steering wheel rotation at different angles. The outer wheel always turns at a smaller angle than the inner one, and this difference is the greater, the greater the angle of rotation of the wheels.
The elasticity of the tires has a significant influence on the steering behavior of the car. When a lateral force acts on the car (it does not matter, the forces of inertia or side wind), the tires deform and the wheels along with the car are displaced in the direction of the lateral force. The greater the lateral force and the higher the elasticity of the tires, the greater this displacement. The angle between the plane of rotation of the wheel and the direction of its movement is called the withdrawal angle 8 (Fig. 8.5).
With the same slip angles of the front and rear wheels, the car retains the given direction of movement, but rotated relative to it by the amount of the slip angle. If the wheel slip angle of the front axle is greater than the wheel slip angle of the rear bogie, then when the car moves around a corner, it will tend to move along an arc of a larger radius than that set by the driver. This property of the car is called understeer.
If the wheel slip angle of the rear axle is greater than the wheel slip angle of the front axle, then when the car moves around a corner, it will tend to move along an arc with a smaller radius than that specified by the driver. This property of the car is called oversteer.
The car's steering can be controlled to some extent by using tires of different plasticity, changing the pressure in them, changing the distribution of the car's mass along the axles (due to the placement of the load).
Figure 8.5 - Kinematics of car turning and wheel slip scheme
An oversteer car is more agile, but requires more attention and professional skill from the driver. An understeer car requires less attention and skill, but makes it difficult for the driver, as it requires turning the steering wheel at large angles.
The influence of steering and on the movement of the vehicle becomes noticeable and significant only at high speeds.
Vehicle handling depends on the technical condition of its chassis and steering. Decreasing the pressure in one of the tires increases its rolling resistance and decreases lateral stiffness. Therefore, a car with a flat tire constantly deviates from its side. To compensate for this drift, the driver turns the steered wheels in the direction opposite to the drift, and the wheels begin to roll with side slip, intensively wearing out.
The wear of the parts of the steering drive and the pivot joint leads to the formation of gaps and the occurrence of arbitrary oscillations of the wheels.
With large gaps and high travel speeds, the oscillation of the front wheels can be so significant that their grip is impaired. The reason for the oscillation of the wheels can be their imbalance due to tire imbalance, a patch on the tube, dirt on the wheel rim. To prevent wheel vibrations, they must be balanced on a special stand by installing balancing weights on the disk.
Passage of the car.Cross-country ability is understood as the property of a car to move on uneven and difficult terrain without touching the unevenness of the lower contour of the body. The vehicle's cross-country ability is characterized by two groups of indicators: geometric indicators of cross-country ability and fifth-wheel cross-country indicators. Geometric indicators characterize the likelihood of touching the car for irregularities, and the coupling ones characterize the ability to move on difficult road sections and off-road.
By passability, all cars can be divided into three groups:
General purpose vehicles (wheel arrangement 4x2, 6x4);
Off-road vehicles (wheel arrangement 4x4, 6x6);
Off-road vehicles with a special layout and design, multi-axle with all drive wheels, tracked or half-tracked, amphibious vehicles and other vehicles specially designed for work only in off-road conditions.
Consider the geometric indicators of permeability. Ground clearance is the distance between the lowest point of the vehicle and the road surface. This indicator characterizes the ability of the vehicle to move without touching obstacles located in the path of movement (Figure 8.6).
Figure 8.6 - Geometric indicators of permeability
The radii of the longitudinal and transverse passability are the radii of the circles tangent to the wheels and the lowest point of the car located inside the base (track). These radii characterize the height and shape of an obstacle that a vehicle can overcome without hitting it. The smaller they are, the higher the car's ability to overcome significant irregularities without touching them with its lowest points.
The front and bottom angles of the overhang, respectively, αп1 and αп2, are formed by the road surface and a plane tangent to the front or rear wheels and to the protruding lower points of the front or rear of the vehicle.
The maximum height of the threshold that the car can overcome for the driven wheels is 0.35 ... 0.65 of the wheel radius. The maximum height of the threshold overcome by the drive wheel can reach the radius of the wheel and is sometimes limited not by the traction capabilities of the vehicle or the grip properties of the road, but by the small values \u200b\u200bof the overhang or clearance angles.
The maximum required passage width at the minimum turning radius of the vehicle characterizes the ability to maneuver on small areas, therefore the vehicle's cross-country ability in the horizontal plane is often considered as a separate operational property of maneuverability. The most maneuverable vehicles are those with all steerable wheels. In the case of towing by a trailer or semi-trailers, the vehicle's maneuverability deteriorates, since when the road train turns, the trailer will mix to the center of the turn, which is why the width of the road train's lane is greater than that of a single vehicle.
The following are the cross-linking indicators of permeability. Maximum traction force - the greatest traction force that a car can develop in the lowest gear. Coupling weight is the vehicle's gravity applied to the drive wheels. The more scenes and weight, the higher the vehicle's cross-country ability.
Among the cars with a 4x2 wheel arrangement, rear-engine rear-wheel drive and front-engine front-wheel drive vehicles have the highest cross-country ability, since with this arrangement, the drive wheels are always loaded by the engine mass. The specific tire pressure on the supporting surface is defined as the ratio of the vertical load on the tire to the contact area measured along the contour of the tire-to-road contact patch q \u003d GF.
This indicator is of great importance for the vehicle's cross-country ability. The lower the specific pressure, the less the soil is destroyed, the less the depth of the track formed, the lower the rolling resistance and the higher the vehicle's permeability.
The track coincidence ratio is the ratio of the front wheel track to the rear wheel track. When the tracks of the front and rear wheels completely coincide, the rear wheels roll on the soil compacted by the front wheels, and the rolling resistance is minimal. If the track of the front and rear wheels does not coincide, additional energy is spent on the destruction of the sealed walls of the track formed by the front wheels by the rear wheels. Therefore, in cross-country vehicles, single tires are often installed on the rear wheels, thereby reducing rolling resistance.
The cross-country ability of a car largely depends on its design. So, for example, in off-road vehicles, limited slip differentials, lockable interaxle and cross-wheel differentials, wide-profile tires with developed lugs, self-pulling winches and other devices that facilitate the vehicle's cross-country ability in off-road conditions are used.
Informativeness of the car.Informativeness is understood as the property of a car to provide the driver and other road users with the necessary information. In all conditions, the information the driver receives is essential for safe driving. With insufficient visibility, especially at night, information content, among other operational properties of the car, has a particular impact on traffic safety.
Distinguish between internal and external information content.
Internal information content - this is the property of a car to provide the driver with information about the operation of units and mechanisms. It depends on the design of the instrument panel, visibility devices, handles, pedals and vehicle control buttons.
The location of the instruments on the panel and their arrangement should allow the driver to spend the minimum time to observe the instrument readings. Pedals, handles, buttons and control keys should be located so that the driver can find them easily, especially at night.
Visibility depends mainly on the size of windows and wipers, the width and location of the cab pillars, the design of the windscreen washers, the windscreen blowing and heating system, the location and design of the rear-view mirrors. Visibility also depends on the comfort of the seat.
External information content is the property of a car to inform other road users about its position on the road and the driver's intentions to change direction and speed. It depends on the size, shape and color of the body, the location of the reflectors, external light alarm, sound signal.
Medium and heavy duty trucks, road trains, buses due to their dimensions are more visible and better distinguishable than cars and motorcycles. Cars painted in dark colors (black, gray, green, blue), due to the difficulty of distinguishing them, are 2 times more likely to get into an accident than cars painted in light and bright colors.
The external light signaling system must be reliable and provide an unambiguous interpretation of signals by road users in any visibility conditions. Low and high beam headlights, as well as other additional headlights (spotlight, fog lights) improve the vehicle's internal and external information content when driving at night and in poor visibility conditions.
Car habitability.The habitability of a vehicle is the properties of the environment surrounding the driver and passengers, which determine the level of comfort and aesthetic i and places of their work and rest. The habitability is characterized by a microclimate, ergonomic characteristics of the cabin, noise and vibrations, gas pollution and smooth running.
The microclimate is characterized by a combination of temperature, humidity and air velocity. The optimum air temperature in the car cab is considered to be 18 ... 24 ° C. A decrease or increase in temperature, especially for a long period of time, affects the psychophysiological characteristics of the driver, leads to a slowdown) in reaction and mental activity, to physical fatigue and, as a result, to a decrease in labor productivity and traffic safety.
Humidity and air speed greatly affect the thermoregulation of the body. At low temperatures and high humidity, heat transfer increases and the body is subjected to more intense cooling. At high temperature and humidity, heat transfer decreases sharply, which leads to overheating of the body.
The driver begins to feel the movement of air in the cab at a speed of 0.25 m / s. The optimum air speed in the cabin is about 1m / s.
Ergonomic properties characterize the correspondence of the seat and vehicle controls to the anthropometric parameters of a person, i.e. the size of his body and limbs.
The design of the seat should facilitate the seating of the driver behind the controls, ensuring minimum energy consumption and constant availability over a long period of time.
The color scheme inside the passenger compartment also has a certain amount of attention to the driver's psyche, which naturally affects the driver's performance and traffic safety.
The nature of noise and vibration is the same - mechanical vibrations of car parts. Sources of noise in a car are the engine, transmission, exhaust system, suspension. The effect of noise on the driver is the reason for an increase in his reaction time, a temporary deterioration in vision characteristics, a decrease in attention, a violation of coordination of movements and functions of the vestibular apparatus.
Domestic and international regulatory documents establish the maximum permissible noise level in the cabin within 80 - 85 dB.
Unlike noise heard by the ear, vibrations are picked up by the driver's body surface. Just like noise, vibration causes great harm to the condition of the driver, and with constant exposure for a long time, it can affect his health.
Gas contamination is characterized by the concentration of exhaust gases, fuel vapors and other harmful impurities in the air. A particular danger to the driver is carbon monoxide, a colorless and odorless gas. Getting into the human blood through the lungs, it deprives it of the ability to deliver oxygen to the cells of the body. A person dies from suffocation, not feeling anything and not understanding what is happening to him.
In this regard, the driver must carefully monitor the tightness of the engine exhaust tract, prevent the suction of gases and vapors from the engine compartment into the cab. It is strictly forbidden to start up and most importantly warm up the engine in the garage when people are in it.
Today we will talk about active. Scientists and programmers specializing in promising developments in various fields of human knowledge: materials science, electronics, physics, biology, and many others are working to improve the reliability and efficiency of security systems for modern cars.
This is due to both the complexity of the tasks assigned to the security system in the event of an accident, and the need to equip the car with devices that can "predict" and prevent accidents. For a long time after the inception of the automotive industry, the main attention of the developers was directed to improving the characteristics of the passive safety system, that is, the designers sought to provide maximum protection for the driver and passenger from the consequences of the accident. But now no one in the world questions the assertion that a more important direction in the development of security systems is the development of an effective complex of means for detecting and recognizing emergency traffic situations, as well as the creation of executive devices capable of taking control of a car and preventing an accident. Such a complex of technical means installed on a passenger car is called an active safety system. The word "active" means that the system independently (without the participation of the driver) assesses the current traffic situation, makes a decision and starts controlling the car's devices in order to prevent the development of events in a dangerous scenario.
Today, the following elements of the active safety system are widely used on cars:
- Anti-lock braking system (ABS). Prevents complete blocking of one or more wheels during braking, thereby maintaining vehicle control. The principle of operation of the system is based on a cyclic change in the pressure of the brake fluid in the circuit of each wheel according to signals from the angular velocity sensors. ABS is a non-disconnectable system;
- Traction control system (PBS). It works in conjunction with the ABS elements and is designed to exclude the possibility of slipping of the driving wheels of the car by controlling the brake pressure value or changing the engine torque (for this function, the PBS interacts with the engine control unit). PBS can be forcibly disabled by the driver;
- Brake force distribution system (SRTU). Designed to exclude the onset of blocking of the rear wheels of the car before the front wheels and is a kind of software extension of the ABS functionality. Therefore, the sensors and actuators of the SRTU are elements of the anti-lock braking system;
- Electronic blocking of differential (EBD). The system prevents the drive wheels from slipping when starting off, accelerating on a wet road, driving in a straight line and in bends by activating the forced braking algorithm. In the process of braking a slipping wheel, an increase in torque occurs on it, which, due to a symmetrical differential, is transmitted to the other wheel of the car, which has better adhesion to the road surface. To implement the EBD mode, two valves have been added to the ABS hydraulic unit: a changeover valve and a high pressure valve. These two valves, together with a return pump, are capable of independently creating high pressure in the brake circuits of the drive wheels (which is absent in the functionality of a conventional ABS). EBD is controlled by a special program recorded in the ABS control unit;
- Dynamic Stability System (SDS). Another name for SDS is exchange rate stability system. This system combines the functionality and capabilities of the previous four systems (ABS, PBS, SRTU and EBD) and therefore is a device of a higher level. The main purpose of the SDS is to keep the car on a given trajectory in various driving modes. During operation, the SDS control unit interacts with all controlled active safety systems, as well as with engine and automatic transmission control units. VTS is a disconnectable system;
- Emergency braking system (SET). Designed to effectively use the capabilities of the braking system in critical situations. Allows to reduce the braking distance by 15-20%. Structurally, ETS are divided into two types: providing assistance in emergency braking and carrying out fully automatic braking. In the first case, the system is connected only after the driver has pressed the brake pedal sharply (a high speed of pressing the pedal is a signal to turn on the system) and realize the maximum brake pressure. In the second, the maximum brake pressure is generated completely automatically, without the participation of the driver. In this case, information for making a decision is supplied to the system by a vehicle speed sensor, a video camera and a special radar that determines the distance to the obstacle;
- Pedestrian Detection System (SOP). To some extent, the SOP is a derivative of the emergency braking system of the second type, since all the same video cameras and radars act as information providers, and the car brakes act as an actuator. But within the system, the functions are implemented differently, since the primary task of the SOP is to detect one or more pedestrians and prevent a vehicle from hitting or colliding with them. So far, SOPs have a pronounced drawback: they do not work at night and in poor visibility conditions.
According to the available statistics, most of this happens with the involvement of cars, therefore, it is safety considerations that designers and car manufacturers pay increased attention to. A large amount of work in this direction is carried out at the design stage, where modeling of all types of dangerous moments that can occur on the road is carried out.
Modern systems of active and passive vehicle safety include both separate auxiliary devices and rather complex technological solutions. The use of all this complex of tools is designed to help car drivers and all other road users to make life safer.
Active safety systems
The main task of the installed active safety systems is to create conditions to exclude the occurrence of any kind. At the moment, the electronic systems of the car are mainly responsible for ensuring active safety.
It should be borne in mind that the main link ensuring the absence of accidents on the road is still the driver. All available electronic systems should only help him in this and facilitate driving, correcting minor errors.
Anti-lock braking system (ABS)
Anti-lock braking devices are currently installed on most of all vehicles. Such safety systems help to exclude wheel blocking during braking. This makes it possible to maintain control over the vehicle in all difficult situations.
The greatest need for ABS systems usually arises when moving on slippery roads. If during icy conditions the vehicle control unit receives information that the rotation speed of one of the wheels is lower than that of the others, then ABS regulates the pressure of the braking system on it. As a result, the speed of rotation of all wheels is equalized.
Traction Control (ASC)
This type of active safety can be considered one of the varieties of the anti-lock braking system, and it is designed to ensure vehicle control during acceleration or ascent on a road with slippery surfaces. In this case, slipping is prevented due to the redistribution of torque between the wheels.
Vehicle Stability Program (ESP)
An active vehicle safety system of this kind allows you to maintain the stability of the vehicle and prevent emergencies. At its core, ESP uses traction control and anti-lock braking systems to stabilize vehicle movement. In addition, ESP is responsible for drying the brake pads, which greatly facilitates the situation when driving on a wet track.
Brake force distribution (EBD)
It is necessary to distribute braking forces in order to exclude the possibility of a vehicle skidding during braking. EBD is a type of anti-lock braking system and redistributes the pressure in the braking system between the front and rear wheels.
Differential lock system
The main task of the differential is to transfer torque from the gearbox to the drive wheels. Such a safety complex ensures the transfer of power to all consumers in the event that one of the driving wheels has poor adhesion to the surface, is in the air or on a slippery road.
Descent or ascent assistance systems
The inclusion of such systems greatly facilitates the control of the vehicle when driving downhill or uphill. The purpose of the electronic assistance system is to maintain the required speed by braking one of the wheels when necessary.
Parking system
Parking sensors are used when maneuvering a car in order to prevent it from colliding with other objects. In order to warn the driver, a sound signal is given, sometimes the display shows the remaining distance to the obstacle.
Hand brake
The main purpose of the parking brake is to hold the vehicle in a static position while stationary.
Passive vehicle safety systems
The goal that any passive vehicle safety system must fulfill is to reduce the severity of the possible consequences in the event that an emergency does occur. The applied methods of passive protection can be as follows:
- safety belt;
- airbag;
- headrest;
- parts of the front panel of the machine made of soft material;
- front and rear bumpers that absorb energy upon impact;
- folding steering column;
- safe pedal assembly;
- suspension of the engine and all main units, leading it to the bottom of the car in case of an accident;
- production of glasses using a technology that prevents the occurrence of sharp fragments.
Safety belt
Among all passive safety systems used in a car, belts are considered one of the main elements.
In the event of a traffic accident, seat belts help keep the driver and passengers in place.
Airbag
Along with the restraint straps, the airbag also belongs to the main elements of passive protection. In the event of an accident, the rapidly filling with gas airbags protect occupants from injury from the steering wheel, glass or dashboard.
Headrest
Head restraints allow you to protect the cervical region of a person in some types of accidents.
Conclusion
Active and passive vehicle safety systems in many cases help to prevent the occurrence of accidents, but only responsible behavior on the road can largely guarantee the absence of serious consequences.
