The car, regardless of whether it is moving or stationary, is subject to gravity (weight), directed vertically downward.
Gravity pushes the wheels of the car against the road. The resultant of this force is located in the center of gravity. The distribution of the vehicle's weight along the axles depends on the location of the center of gravity. The closer the center of gravity is to one of the axes, the greater the load on that axle. On passenger cars the axle load is distributed approximately equally.
The location of the center of gravity not only in relation to the longitudinal axis, but also in height is of great importance for the stability and handling of the vehicle. The higher the center of gravity, the less stable the vehicle will be. If the car is on a horizontal surface, then the force of gravity is directed downward. On an inclined surface, it is decomposed into two forces (see figure): one of them presses the wheels to the road surface, and the other seeks to overturn the car. The higher the center of gravity and the greater the lean angle of the vehicle, the sooner stability will be compromised and the vehicle may tip over.
During movement, in addition to gravity, a number of other forces act on the car, to overcome which the engine power is spent.
The figure shows a diagram of the forces acting on the vehicle while driving. These include:
- rolling resistance force spent on deformation of the tire and the road, on the friction of the tire against the road, friction in the bearings of the driving wheels, etc .;
- the force of resistance to lifting (not shown in the figure), depending on the weight of the vehicle and the angle of ascent;
- the force of air resistance, the value of which depends on the shape (streamline) of the car, the relative speed of its movement and the density of the air;
- centrifugal force arising during the movement of the car on a bend and directed in the direction opposite to the bend;
- the force of inertia of movement, the value of which consists of the force required to accelerate the mass of the vehicle in its forward motion, and the force required for the angular acceleration of the rotating parts of the vehicle.
The movement of the car is possible only on condition that its wheels have sufficient adhesion to the road surface.
If the traction force is insufficient (less than the traction force on the driving wheels), then the wheels slip.
Traction power depends on the weight on the wheel, the condition of the road surface, the air pressure in the tires and the tread pattern.
To determine the influence of road conditions on traction force, the coefficient of adhesion is used, which is determined by dividing the traction force of the driving wheels of the car by the weight of the car falling on these wheels.
The adhesion coefficient depends on the type of road surface and on its condition (presence of moisture, mud, snow, ice); its value is given in the table (see figure).
On asphalt roads, the coefficient of adhesion decreases dramatically if the surface is covered with wet dirt and dust. In this case, the dirt forms a film that dramatically reduces the adhesion coefficient.
On roads with asphalt concrete, in hot weather, an oily film of protruding bitumen appears on the surface, which reduces the coefficient of adhesion.
A decrease in the coefficient of adhesion of wheels to the road is also observed with an increase in speed. So, with an increase in the speed of movement on a dry road with asphalt concrete pavement from 30 to 60 km / h, the friction coefficient decreases by 0.15.
Acceleration, acceleration, roll forward
Engine power is spent on driving the driving wheels of the vehicle and overcoming the frictional forces in the transmission mechanisms.
If the value of the force with which the driving wheels rotate, creating a traction force, is greater than the total force of resistance to movement, then the car will move with acceleration, i.e. with overclocking.
Acceleration is the increase in speed per unit of time. If the tractive effort is equal to the forces of resistance to motion, then the car will move without acceleration at a uniform speed. The higher maximum power engine and the lower the value of the total resistance forces, the faster car reaches the set speed.
In addition, the amount of acceleration is affected by the weight of the vehicle, ratio gearbox, final drive, number of gears and car streamlining.
During the movement, a certain amount of kinetic energy is accumulated, and the car acquires inertia. Due to inertia, the car can move for some time with the engine off - coasting. Coasting is used to save fuel.
Car braking
Braking a car is of great importance for driving safety and depends on its braking qualities. The better and more reliable the brakes, the faster you can stop a moving car and the faster you can move, and therefore the higher its average speed will be.
When the vehicle is in motion, the accumulated kinetic energy is absorbed during braking. Braking is assisted by the forces of air resistance, rolling resistance and lifting resistance. On a slope, there are no upward resistance forces, and a component of gravity is added to the vehicle's inertia, which makes braking difficult.
When braking, a braking force is generated between the wheels and the road, which is opposite to the direction of the traction force. Braking depends on the relationship between braking force and traction. If the force of adhesion of the wheels to the road is greater than the braking force, then the car brakes. If the braking force is greater than the adhesion force, then when the wheels are braked, they will slip relative to the road. In the first case, when braking, the wheels roll, gradually slowing down the rotation, and the kinetic energy of the car is converted into heat energy, heating the brake pads and discs (drums). In the second case, the wheels will stop rotating and will slide along the road, so most of the kinetic energy will be converted into friction heat from the tires on the road. Stopping braking impairs the vehicle's handling, especially on slippery roads, and leads to accelerated tire wear.
The greatest braking force can be obtained only when the braking moments on the wheels are proportional to the loads on them. If this proportionality is not observed, then the braking force on one of the wheels will not be fully used.
Braking performance is assessed by braking distance and the amount of deceleration.
The braking distance is the distance that the vehicle travels from the start of braking to a complete stop. Vehicle deceleration is the amount by which the vehicle speed decreases per unit of time.
Vehicle handling
Vehicle handling is understood as its ability to change the direction of travel.
When driving in a straight line, it is very important that the steered wheels do not turn randomly and the driver does not need to expend effort to keep the wheels in the right direction. The car provides stabilization of the steered wheels in the forward direction, which is achieved by the longitudinal tilt angle of the steering axis and the angle between the plane of rotation of the wheel and the vertical. Thanks to longitudinal tilt the wheel is installed so that its fulcrum in relation to the pivot axis is pulled back by an amount and and its work is similar to a roller (see picture).
When tilting laterally, turning the wheel is always more difficult than returning it to its original position - driving in a straight line. This is due to the fact that when the wheel is turned, the front of the car rises by an amount b (the driver applies relatively more force to the steering wheel).
To return the steered wheels to a straight-ahead position, the weight of the vehicle helps the wheels turn and the driver applies a small amount of force to the steering wheel.
On cars, especially those with low tire pressure, side slip occurs. Lateral slip occurs primarily due to lateral forces that cause lateral deflection of the tire; in this case, the wheels do not roll in a straight line, but are shifted to the side under the action of a lateral force (see figure).
Both wheels on the front axle have the same slip angle. When the wheels are shifted, the turning radius changes, which increases, reducing the steering of the car, while driving stability does not change.
When the wheels of the rear axle are shifted, the turning radius decreases, this is especially noticeable if the steering angle rear wheels more than in the front ones, the stability of movement is disturbed, the car begins to "yaw" and the driver has to correct the direction of movement all the time. To reduce the effect of slip on the vehicle's handling, the air pressure in the tires of the front wheels should be slightly less than that of the rear. The greater the lateral force acting on the car, for example, at a sharp turn, where large centrifugal forces arise, the more the wheel slip will be.
Car skid
Skidding is the lateral slip of the rear wheels as the vehicle continues to move forward. Sometimes skidding can cause the vehicle to turn around its vertical axis.
Skidding can occur for a number of reasons. If you turn the steered wheels sharply, it may turn out that the inertial forces will become greater than the adhesion force of the wheels with the road, especially often on slippery roads.
With unequal traction or braking forces applied to the wheels on the right and left sides, acting in the longitudinal direction, a turning moment occurs, leading to a skid. The immediate cause of skidding during braking is unequal braking forces on the wheels of one axle, unequal adhesion of the wheels of the right or left side to the road, or incorrect placement of the load relative to the longitudinal axis of the vehicle. The reason for the car skidding when cornering can also be its braking, since this adds a longitudinal force to the lateral force and their sum can exceed the adhesion force that prevents the skidding (see figure).
To prevent the vehicle skidding that has begun, it is necessary: \u200b\u200bto stop braking without disengaging the clutch (on vehicles with manual transmission); turn the wheels towards the skid.
These techniques are performed as soon as the skid begins. After stopping the skid, you need to align the wheels so that the skid does not start in the other direction.
Most often, a skid is obtained when braking suddenly on a wet or icy road, skid increases especially quickly at high speed, therefore, on a slippery or icy road and when cornering, you need to reduce the speed without applying braking.
Passage of the car
The passability of a car is its ability to drive on bad roads and off-road conditions, as well as overcome various obstacles on the way. Passage is determined:
- the ability to overcome rolling resistance using traction forces on the wheels;
- overall dimensions of the vehicle;
- the ability of the car to overcome obstacles on the road.
The main factor that characterizes flotation is the ratio between the greatest traction force used on the drive wheels and the force of resistance to motion. In most cases, the vehicle's cross-country ability is limited by insufficient traction of the wheels with the road and, therefore, the inability to use the maximum traction force. To assess the passability of a car on the ground, use the coefficient of adhesion weight, determined by dividing the weight of the driving wheels by the total weight of the car. The greatest cross-country ability is found in cars with all wheels driving. In the case of using trailers that increase the total weight, but do not change the coupling weight, the passability is sharply reduced.
The grip of the driving wheels with the road is significantly influenced by the specific tire pressure on the road and the tread pattern. Specific pressure is determined by the pressure of the weight on the wheel on the tire footprint. On loose soils, the vehicle's permeability will be better if the specific pressure is less. On hard and slippery roads, flotation improves at higher specific pressure. A tire with a large tread pattern on soft soils will have a larger footprint and less specific pressure, while on hard soils the tire will have a smaller footprint and more specific pressure.
Passage of the car on overall dimensions determined by:
- longitudinal radius of passability;
- transverse radius of passability;
- the smallest distance between the lowest points of the car and the road;
- front and back corner cross-country ability (angles of entry and exit);
- radius of turns of horizontal passability;
- overall dimensions of the car;
- the height of the vehicle's center of gravity.
A lot of novice drivers, especially female drivers, are afraid to drive with mechanical transmission... Especially now, when technical progress reaches the point that machines with automatic transmission gear.
Many car enthusiasts simply do not want to associate their lives with difficulties in learning and using mechanics. Since in the process of learning to drive, there are many difficulties with gear shifting. And this distracts from the road and makes an unprepared driver and all road users nervous.
But the automatic transmission is also not perfect and has many disadvantages. A large and very important one, this is not a budget option. Therefore, in spite of the inconvenience, most drivers choose mechanics. And then the question immediately arises, how to properly change gears on the mechanics while driving? In this article, we will help you deal with this issue.
Errors made by newbies when shifting gears
With the help of this pedal, the mechanics undergoes the process of mechanically disconnecting the engine drive from the wheel drive. Therefore, on the mechanics, when switching from a low speed to a high speed, or vice versa, you need to depress the clutch pedal. If you do not master the correctness of working with this mechanism, then you are guaranteed not only the fastest repair of the car, but also the likelihood of getting into a traffic accident increases.
The main mistakes that most often occur when changing gears for beginners are the following:
- Re-gasing or diving of the car (short-term engine braking) when the gas pedal is released and the clutch is pressed. This is due to the fact that the student releases the gas faster than depressing the clutch in the event of a dive. Or, on the contrary, quickly presses the clutch, while not releasing the gas pedal, as a result, overgassing occurs.
- Transfer the emphasis to the hand with which the student holds the steering wheel (pulls the steering wheel to the left) at the moment the gear is turned on. This habit can easily lead you astray.
- Incorrect operation with the gear lever. The transmission is switched on not according to the scheme, but obliquely. This leads to the fact that instead of the desired gear, a completely different speed is included. For example, instead of the first gear, the third is turned on, and instead of the second, the fourth. The location of each gear should be known before driving for the first time. And it is better to train in gear shifting on an uncooked car and exactly according to the scheme. Thus, it is possible to avoid various problems, for example, associated with incorrect shifting while driving.
- Also, novice drivers often divert attention to the gear lever when shifting, instead of watching the road. This is strictly prohibited and can lead to an accident, try not to look at it.
- As practice shows, it also becomes difficult to choose the moment for the subsequent shift or not knowing which gear to include at a given speed. Let's talk about this in more detail below.
You can also learn about the mistakes of novice drivers from the following video:
Correct shifting while driving
Often there are situations when inexperienced drivers start to switch without gaining the required speed. Ultimately, this ruins not only the transmission, but also the car engine. When driving on highways or highways, shifting should be smooth, gears should be changed as the vehicle speed increases.
You should not have a goal to reach the highest gear at a low speed of the car, as well as vice versa, constantly drive high revs engine. You should only choose the right gearcorresponding to the current vehicle speed. Since each gear has its own optimal speed modeat which the engine works most efficiently and economically.
We are watching a useful video on how to change gears using a speedometer or tachometer while driving:
Feature of driving a car on mechanics
For novice drivers, some of the nuances of driving a car with a manual transmission may be surprising news. For example, that when changing speeds in a gearbox, the car loses a certain speed. And the longer you delay shifting, the more speed the car loses.
If you need to upshift, you need to shift the lever quickly, without wasting time thinking about this step. But this does not mean that you need to sharply "stick" the lever into the wrong position. Try to prepare in advance for the inclusion of a particular gear, even before changing the speed. Since your car will suffer greatly from abrupt and incorrect shifts.
Remember that you should not switch when overtaking a car unless you guarantee to do it quickly and correctly. This is especially true in those cases when the maneuver needs to be done in a minimum period of time or in an extreme situation.
How to properly shift gears on the mechanics while driving?
In fact, the actions are simple, in the process of driving everything is worked out to automatism:
- First of all, remove your foot from the accelerator pedal and, at the same time, depress the clutch pedal all the way.
- Next, you need to switch to the lower or top gear, depending on what you want to accomplish.
- After that, you need to very slowly and smoothly release the clutch pedal, while adding gas.
Almost every driver faced such an unpleasant situation when the car began to twitch during acceleration, at low speed, or even at the very beginning of the movement. Experienced car enthusiasts they say with confidence that such a nuisance can happen to any car, regardless of age and brand. Jerks in motion can be traced both in the Chevrolet Niva and in any other car. If your car starts to show jerks on the move, it is recommended to find the cause as soon as possible and eliminate it in time.
Often, every driver can eliminate such an ailment without the help of specialists in the service station. Ignoring the problem can not only aggravate the situation, which in the future will require expensive repairs, but also jerking the vehicle often leads to an accident. A faulty car is unable to start a smooth ride followed by acceleration. Twitching transport not only brings fear and horror to other road users, but also confuses them. Next, let's try to figure out what can cause the uneven course of the car.
At the first stage, the machine is diagnosed. Let's say that you have a Niva in your garage with carburetor engine... Your car already at the first stage of movement from a standstill shows signs of "illness". Or the car started moving without hassle, and when a certain number of revolutions were reached, the engine malfunctioned. All this will not give answers, but only create questions, because anything can break. Anyway, if seen unstable work power unit car while pressing the accelerator pedal, first of all, you should:
- Check air and fuel filters... The supply of air and fuel to form a combustible mixture will be difficult if these elements are heavily contaminated.
- Check the fuel pump. Its incorrect operation leads to an unstable fuel supply.
- Check fuel pressure. The intake of a fuel-air mixture under insufficient pressure often leads to jerks of the car. The pressure while the engine is running should not exceed 3 kgf / cm2.
Most of the reasons lie precisely in fuel system car.
do not write off the ignition system, and sometimes even the transmission can cause discomfort while driving. There can be many reasons. To narrow the circle of suspicion, measure the conditions during which the car begins to "be capricious." To do this, while driving, watch the dashboard and remember at what moment the steady motion stopped. Do this several times to confirm the observation is correct.
Eliminate jerks when the car starts moving
According to the number of reviews from the owners of the Chevrolet Niva with a carburetor engine, it is the motor power system that most often conceals a problem. Due to the breakdown of absolutely any element of the system, the stable process of fuel combustion in the cylinders can be disrupted. If an insufficient amount of mixture enters the cylinders, then the car in such conditions will not be able to deliver the required power. Against the background of this problem, twitching will begin to appear.
Check the pipes, determine if there is a leak in the system. Measure the fuel pressure. If the indicator does not correspond to the norm, then further search for the cause should be sought in the pressure regulator, fuel pump. These actions must be done not only with the carburetor system, but also with the injection system. If an injector is installed on the Niva 21214, then in this version the ignition system is also connected. Any sensor that is out of order can cause the car to jerk. Perhaps, in this case, the help of specialists will be needed, because all the work is complicated by the presence of an electronic unit.
Eliminate jerks when accelerating a car
If the Niva 21214 begins to show twitching when accelerating, then in this case it is necessary to carefully check the engine power system. The driver presses the speed pedal while driving, but the vehicle does not accelerate. By pressing the accelerator pedal, the driver provokes an increase in the amount of fuel mixture supplied to the cylinders. If this does not happen, breakdowns occur in a uniform course.
We check all filters: fuel, air. Carburetor motor has 2-3 filters. We will not take into account the mesh in the throat, since it is capable of preventing the penetration of only large particles. Carefully check the filter that goes to fuel pump... It is often clogged with impurities, which ultimately prevents free running fuel, because of this, the motor begins to "starve".
Eliminate jerks with stable car movement
If the Chevrolet Niva or Niva 21214 shows twitching during stable movement, then this most often happens due to problems with the ignition system. You can often hear complaints from car owners that, they say, they just put new candles on, and the engine has already malfunctioned. Detonation can occur even with new spark plugs due to incompatibility with the engine. If the plug is out of order, then in this case the fuel will not burn completely, and breakdowns will begin in the operation of the power unit.
Checking the candles is easy enough. The first step is to:
- Check the level of the gaps on the unscrewed plugs. Check for violations in the process sparking.
- A working candle gives off a dark blue spark.
- If there is black carbon deposits on the plug, then the problem may lie in the downed ignition or faulty mixture formation.
If checking the spark plugs does not bring any results, you should check all the wiring for oxidation and breakdowns. Do not forget about the coil, the toggle switch. All elements of the ignition system, as in the case of a problem in the power supply system, are thoroughly examined and checked for correct operation.
Conclusion
It is in the interest of every car owner to keep his car running like a clock. But sometimes problems arise. If your car began to twitch, then start diagnostics from simple to complex... Sometimes the problem can be on the surface. But it is not uncommon and difficult cases when serious car repairs are required. The least common problem is the transmission. In cars with manual transmission the clutch may be the cause of the twitching, namely the driven disc wears out.
Lack of oil in an automatic transmission also often brings such troubles. These are the main reasons that most often bring headache owners of Chevrolet Niva, Niva 21214. If, after doing all the above operations, it was not possible to find and eliminate the cause, then in this case it is best to contact a specialist for a deeper diagnosis of the car.
Unfortunately, most drivers can quickly panic when there is an emergency on the road, which can eventually lead to an accident. Many people think that the more driving experience, the more prepared the driver is for the dangerous situations that may arise while driving. But according to statistics, it turns out that a large number of experienced people, faced with an emergency situation on the road, panicked and, making mistakes, end up in an accident. Yes, indeed, when a wheel suddenly goes down in your car, or when a dog, moose or any other animal runs out onto the road, or your brakes are missing, this will cause panic in most drivers, which will increase the risk of an accident. Therefore, every driver, regardless of driving experience, must be prepared for any emergency situation on the road and clearly understand what needs to be done under certain circumstances.
There are many scary and dangerous things that can happen while you are driving.
But knowing how to respond to emergency situations, you can either completely avoid an accident, or minimize the consequences of a traffic accident as much as possible. Here's what you should do in the most common driving situations while driving.
The car stalls while driving
If your car suddenly stalls while driving, immediately turn on alarm ("Emergency gang") to warn about problems the cars behind you. Remember that even though the engine stalls, the vehicle will still roll on the road. Your task is to slow down and come to a complete stop on the side of the road or in the extreme right lane. Remember that after the engine has stalled in your car, the power steering is completely disabled. So while driving will not disappear, wheel will be hard to rotate. So just expect that if the car stalls on the move, then you will need to make more effort to drive the car.
If you stalled on a highway where there is no shoulder, then stop in the far right lane and do not get out of the car. Buckle up, turn on the emergency light and call for help.
Attention! By no means try to lead renovation work being in the rightmost lane. It is very dangerous.
Unexpectedly flat tire while driving
If, while driving, your car suddenly starts to pull to the side, then there is a high probability that one of the tires is damaged and the pressure in the wheel has dropped to a critical level. At this point, many start to panic. Especially if the wheel is not just flat, but burst. Never press the brake pedal sharply. This is mistake. You need to take your foot off the accelerator first. Also, hold the steering wheel firmly with both hands and steer the vehicle to the side of the curb, or hold the steering wheel so that the vehicle continues straight ahead until it slows down to safely change lanes or onto the shoulder. If you are going to install yourself spare wheel, make sure you can do this in safe place... Remember that if the place of your forced stop is not safe and you do not have the financial ability to call road assistance, then you will have to continue driving on a flat tire (at a slow speed).
Yes, it will completely ruin the tire and possibly damage your wheel rim, but your personal safety is worth the extra expense.
Car aquaplaning (planing)
On wet road, especially when the tread of your tires is worn out, a thin water film forms between the road and the rubber (the tread of the worn rubber does not have time to drain off excess water). In fact, when such a film forms, the tire does not drive on the road, but floats, since it does not push the water to the side. If the car starts aquaplaning, it will begin to deviate from the course of travel. In this case, do not apply the brake and jerk the steering wheel sharply, as this can lead to a skid of the car. Instead, take your foot off the gas pedal and keep the steering wheel straight until you feel like you've regained control of the car.
Danger on the roadside (sand, gravel, etc.)
Many accidents occur due to improper actions of drivers when driving onto an unpaved shoulder from the asphalt.
Many novice drivers may suddenly pull over to the side of the road when they hear the sound of gravel on the underside of a car. This can cause driver panic. As a result, many drivers make the mistake of abruptly trying to get back onto the asphalt road. But this often leads to the fact that the car can fly into the ditch. Remember that if you pull over to the side of the road with only a few wheels, never turn the steering wheel abruptly, as the car can lose traction and lose control, leading to a serious accident. Therefore, if you pull over to the side of the road, in order to get back on the normal road, slow down by pressing the brake pedal and taking your foot off the accelerator. Then smoothly and safely return to the right lane of the road.
The brakes are missing while driving! What to do?
Imagine that while driving you, as always, press the brake pedal to slow down or stop, but it goes to the floor and the car does not slow down. This is a sign of complete failure brake system... Your task is not to panic, but to accept emergency measures by stopping the car. To do this, go as quickly as possible to downshift (if your car is equipped with mechanical box gears, shift the transmission down). This way you will perform engine braking. This will definitely slow down the car. If your car is equipped with an automatic transmission, then shift the transmission to neutral. Also, with any transmission, you must raise the car's handbrake (handbrake) as quickly as possible. If all your actions are useless, you should direct the car to a place on the road where it will receive as little damage as possible. For example, instead of a tree, it is better to direct the car into a fence. Also, your task is to direct the car to a place where there are no pedestrians or other vehicles nearby.
Gas pedal problem
If, while driving, you, removing your foot from the gas pedal, notice that the car has not started to slow down and continues to accelerate, then most likely the floor mat in the car blocked the gas pedal.
In no case try to correct the mat on the go to unlock the gas pedal. You will be wasting your time. In this case, there is only one way out, put the gearbox in neutral and then press the brake pedal. This should help. But if your actions do not help, then turn off the ignition. If your car is equipped with a system for starting the engine from the button (Stop / Start), then in order to turn off the ignition while driving, you will have to hold the Stop / Start button for a few seconds.
Remember that turning off the ignition while driving will make your steering heavy, since the power steering will turn off, and the brakes will become hard and you will need more physical effort required to drive the car.
An animal suddenly ran out onto the road
We all love animals. But nevertheless, people have the main priority anyway. Imagine that while driving a car, an animal suddenly runs out in front of you. What are you going to do? Will you try to stop abruptly? Or try to make a sharp maneuver trying to avoid the animal? We advise each driver to think in advance about the answers to these questions. After all, on the road you will not have time for this. Be aware that in some cases, trying to avoid colliding with an animal could jeopardize your own safety and the safety of other road users. We cannot tell you the exact advice on what to do if an animal ran out onto the road. Your actions should depend on the situation. But so that such cases do not come as a complete surprise to you, you need to pay attention to road signsindicating the danger of animals on the road. Remember that these signs are installed on the road for a reason. So if there is a warning, then you must slow down. Also, if you are driving outside the city, be careful. Especially in the countryside at night. Pay attention to the side of the road where you may see your headlights reflected in the eyes of the animal at night. Also, in areas where there is a lot of wildlife, expect elk, deer, wild boar and other wild animals to run into the road. Therefore, drive at a slow speed in such places.
Suddenly, a car drove into the intersection. What to do?
Imagine a typical situation on Russian roads... You enter an intersection strictly according to the rules of the road and a car suddenly leaves in front of you. In this case, you press the brake pedal sharply in order to avoid a collision. But in most cases, you will not have enough time to completely stop the car. In this case, your task is to minimize the consequences of the accident by directing your car to the rear of the traffic violation vehicle. Thus, you will soften the impact (the rear of any car is lighter, since the front is overloaded with the engine, gearbox and drives, and steering). Also, a blow to the back of the car will possibly reduce the risks for the driver and passengers of the vehicle that has driven out to the intersection.
What to do if an accident occurs
More than once, on the pages of our online edition, the site has published various tips and recommendations on how to behave in accident case... You can read more about this here.
We will briefly recap what you should do immediately after the accident. First, immediately after the accident, it is necessary to find out if the victims are in an accident. If there are casualties, you are obliged to provide first aid to the participants in the accident and call ambulanceby calling 112. Then use our instruction-algorithm of action in the event of an accident.
The car started to roll in the parking lot
If you, having parked the car, got out of the car, but forgot to put it on the manual parking brake, and if the car is equipped with a manual transmission did not put the gearbox into gear, then there is a risk of the vehicle rolling away in your absence. But if it happened before your eyes, then you should try to stop the car. Unfortunately, there are not many options for this. Remember, the main thing is your safety. You may be trying to stop the vehicle with your hands. This is possible if the car starts rolling at a slow speed on a practically level surface. But if vehicle rolling down and picking up speed, you should not try as a stuntman to do anything. You risk getting hit by the wheels of a moving car.
Never stand in front of a moving vehicle while trying to stop it. Remember that he is not superman and the car will not scare you or drive around you. The vehicle is very heavy and can easily damage you.
If the car catches fire
Are you afraid that your car might explode on the road? In fact, in life it happens quite rarely, unlike Hollywood blockbusters. But unfortunately, vehicle fires occur on the roads quite often. Therefore, every driver must know and be prepared for a car fire.
If your car catches fire, then you should stop and get out of the car as soon as possible. Do not under any circumstances open the hood and do not try to go back to the salon to save any things. Your task is to get a fire extinguisher out of the trunk and extinguish the fire as quickly as possible. If you fail, then do not approach the car, leaving a safe distance and wait for the firemen.
Remember not to risk your life for an unsuccessful attempt to extinguish a vehicle or to save any personal belongings or documents. You should prioritize your own safety and the safety of passengers and other road users.
There is one more important aspect that deserves attention. Modern cars have such a high level of comfort that feedback in them is minimal and is reduced to zero. The driver is immersed in a virtual space: the windshield turns into a computer screen, and the steering wheel becomes a joystick. Such sensations are provoked by the car itself, confidently, as if on rails, flying along the road, which seems to be possible to pass a turn of any steepness at any speed. In fact, this is a very deceiving feeling. Sooner or later, the laws of physics come into force, pushing the car into a ditch or into oncoming traffic.
Consider the forces acting on a car in such a situation.
Any moving body has its own mass. To slow down or change the direction of movement of this mass, a force must be applied to it. The more change in the nature of motion we want from the mass, the more force is required to be applied.
Forces acting on a moving vehicle pass through three axles (fig. 2).The horizontal transverse axis is the one along which the weight is redistributed in the turn. In the left turn the car rolls to the right, in the right - to the left. Every driver and passenger always feels this force when cornering. The laden vehicle weighs at least one ton. Even a small subcompact with four passengers on board will weigh that much. Medium and executive class weigh about two tons, and SUVs easily pull three, three and a half tons. This weight rests on four suspension springs. It is clear that he will be unstable, he will definitely "want" to tilt. Why one side of the body rises - moves up, while the opposite falls - moves down, it's very easy to understand: the body is located on springs that can compress and expand. Car roll in a corner is a natural and understandable movement of the car body relative to the wheels. As a result of the movement of weight towards the outer wheels in a turn, a large force begins to press on them (fig. 3).Does this mean that their grip is increased? Of course yes! But the weight pressing on the inner wheels decreased, as part of it moved to the outer side - there was a dynamic movement of weight. This means that the grip of the inner wheel with the road surface has decreased. The roll of a car depends on the location of its center of gravity, tire width, shock absorber stiffness and suspension design. For example, Formula 1 race cars practically do not heel even at high speeds in corners. They are specially designed to move at great speed, and although the dynamic movement of weight is exactly the same as that of ordinary car, the roll is almost invisible. This is due to the ultra-short-travel suspension, very wide wheels, stiff springs and the work of special devices called stabilizers. lateral stability (fig. 4).From the name it is clear that they are just invented to prevent the body from lurching. Similar devices are available on ordinary city cars and SUVs, only they, of course, cannot be as tough as on racing and sports cars... Conventional cars need to be comfortable, which means that their springs and stabilizers are selected to provide a smooth ride on bumps. And their tires are not so wide, and the center of gravity due to the large ground clearance located much higher. Although serial cars have already appeared, which almost do not roll in corners. Their shock absorbers are equipped with a special hydraulic systemcontrolled by electronics, which gives commands to lift outside body in corners. The idea of \u200b\u200bmaking one side of the car stiffer by having to turn in one direction all the time is not new. This is exactly what American racing engineers do when preparing their cars for racing on ovals, for example in Indianapolis.
Figure: 2. AXIS OF ROTATION OF THE CAR:
A - horizontal,
B - vertical,
B - longitudinal.
Car roll in a corner is a natural and understandable movement of the car body relative to the wheels.
Figure: 4. DIAGRAM OF STABILIZER OPERATION
Anti-roll bars prevent the car body from rolling too much in a corner. The U-shaped metal bar works for twisting, resisting body roll in corners. On modern cars there are front and rear stabilizers.
Now consider the longitudinal axis (fig. 5).With a sharp start, the hood of the car rises. The driver sees this from his seat, but in fact the entire front part of the car rises, the front springs are unloaded, the weight moves back - rear springs shrink. The weight of the car naturally remains unchanged, and we are only talking about dynamic, short-term weight transfer. How much weight is moving? If the weight of the car is 100% and the acceleration is 0.5 G, which corresponds to an acceleration of 18 km / h, then the rear of the car will be 15% heavier. Little? Yes, but the effect is great! On rear-wheel drive vehicles, it translates into a better start of the car due to more pressure on the drive wheels, and, consequently, improved grip. Does this mean that if the driver turns on the gas in the second half of the turn, due to the improved traction of the rear wheels, the car will be more stable? Of course yes (fig. 6).But do not forget that the front-wheel drive will start worse due to unloading of the front wheels, and in the turn any addition of gas reduces the grip of its driving wheels. When braking (take the example of a deceleration of 9.81 m / s2), the transfer of weight becomes truly dramatic. For example, on a front-wheel drive car, where the motor with a gearbox is in front (and this is additional weight on the front axle), when braking rear wheels unload so much that the slightest turn of the steering wheel causes them to skid (fig. 7),since at this moment only 12% of the total weight of the car presses on the rear tires. If you just suddenly release the accelerator pedal, the weight will also move forward, relieving the rear wheels.
With a sharp start, the entire front of the machine rises, the front springs are unloaded, the weight moves back - the rear springs are compressed.
Figure: 6. DYNAMIC WEIGHT DISTRIBUTION WHEN SPEEDING THE VEHICLE
During acceleration, the weight moves backward and loads the rear of the vehicle. The rear tire grip is increased. With this knowledge, racers are adept at using rear wheel loading to stabilize the vehicle in order to neutralize oversteer or understeer.
Figure: 7. DYNAMIC WEIGHT DISPLACEMENT DURING BRAKING
The weight acting on the front of the vehicle is increased and the rear of the vehicle is unloaded accordingly. Riders use this lightening effect on the rear axle to artificially cause the vehicle to skid to aid in cornering at high speed.
The line drawn through the roof to the road itself through the vehicle's center of gravity is called the vertical axis. At the moment of skidding, the car begins to rotate around this vertical axis. For most drivers, this situation often comes as a complete surprise. (fig. 8).
Figure: 8. ROTATION OF THE CAR
At the moment of skidding, the car begins to rotate around this vertical axis. For most drivers, this situation often comes as a complete surprise.
One day my friend wanted to take me for a ride with the breeze on his new car, and at the same time surprise with the skill of driving on a suburban highway. He immediately rushed to overtake the long tail of cars, but too late included a lower gear, went from fourth to third. I noticed this at once. But the distance between the cars on the right did not allow him to squeeze the car, and we inevitably approached the sharp right turn ahead. The friend decided that he would have time to overtake the next two cars and duck into that saving free space that was in front of them. Almost in time, but his return to the right lane after overtaking almost coincided with the beginning of the turn. He threw the gas abruptly, and as soon as he began to turn the steering wheel, our car swam with the rear axle to the side. Gas, gas, I shouted. My friend obeyed and caught the car out of control. If he began to brake at this critical moment at the entrance to the turn, as they do, alas, at any emergency most drivers (and many of them consider themselves aces), the chance of getting out of this situation would be reduced to zero.
What forces were acting on the car at that moment, and how was it possible to change their arrangement. Rear axle tires lost grip due to sudden weight shifting. The deceleration was caused by the throttle release, which caused the weight to move forward. Turning the steering wheel caused the weight to move to the outer wheels. This means that the pressure on certain wheels has changed, therefore, their grip has changed. In our case, the weight moved simultaneously in two directions: longitudinal and transverse. The ideal situation, as a result of which the car almost always strives to get out of control. The driver wanted to change direction, by all means force the car to turn, while it was leaning almost all its weight on a single front wheel outside to turn. And to slow down or change the direction of movement of the mass of the car, force must be applied to it. But the contact area with the road of a single wheel for this force to act is clearly not enough. What happened when the driver turned on the gas? The weight was redistributed back, and the rear wheels gained traction (outer more, inner less), which stopped the beginning of the rear axle skidding. By adding throttle, the driver, purely intuitively, turned the steering wheel back a little - "let go" the car, added loads on the inner wheels to turn.
Racers in similar situations do the same. They know exactly how the car will react to the weight transfer, and the average driver often does not think about weight transfer. And any change in direction or nature of movement, be it acceleration or deceleration, turn left or right, is necessarily accompanied by a shift in weight, which changes the grip of the tires with the road. Of course, a car enthusiast does not need to be able to finely steer his car into corners at breakneck speed, as does a race car driver who skillfully uses weight shifting to his advantage. But he is obliged to know the elementary laws of physics that accompany a car in motion.
If we assume that we have to drive on an absolutely smooth surface, such as the cloth of a billiard table or the surface of an ice rink, then there is no need to talk about the vertical displacement of the car's weight. In practice, the road is undulating asphalt, bumps, steep ascents and descents, holes and other irregularities.
Imagine the situation: the car entered with high speed on the hillock. The body rushes up, the suspension is unloaded, and at this moment the driver decided to change the direction of travel. This is mistake. It was at this moment that the contact of the car's tires with the road is very weak. And literally in a second, when the car body is lowered, the tires will regain traction, and even more than before the jump. At this moment, the car will sensitively respond to the steering wheel (fig. 9).
The car drove onto a hillock at high speed: the body rushes up, the suspension is unloaded - at this moment the contact of the car's tires with the road is very weak or absent altogether.
The behavior of the car on the bumps was very well studied by the rally drivers. They sweep along them at such a speed that the car takes off high into the air, and therefore they call such irregularities nothing more than jumps.
The behavior of the car in cornering, its stability is also influenced by the design principle of the car: front, rear or four-wheel drive, engine location. The weight distribution of the machine also plays an important role - in what proportion the weight is distributed between the front and rear axles. Of course, cars with modern multi-link suspension more willingly fulfill the will of the driver in corners than those with outdated suspension. But it's clean technical reasons... The magnitude of the forces acting on the car when cornering plays a huge role. Drivers, without going into details, talk in this case about how the tires are kept - good or bad? Affects stability and additional weight - whether the driver is traveling alone or with passengers, whether there is heavy luggage, whether there is a lot of fuel in the tank. Cornering acceleration, suspension design, tire pressure, braking - all of these can most directly affect which tires - front or rear - start losing traction first? This is a very important question.
Remember what we said about demolition or skidding? If the front tires are slipping, it is drift or understeer. If the rear, then we are dealing with a skid, and this is called oversteer. If all four tires slip at the same time, this is neutral steering. (fig. 10).It is clear that the latter option is preferable, since it does not provide for the rotation of the car around the vertical axis. If the car turns in a corner, while the driver does not turn the steering wheel, then this will be called steering. Let's consider in more detail what it is.
Figure: 10. THIS DIAGRAM SHOWS VARIOUS TYPES OF ROTATION:
1. Understeer occurs when the slip angle of the front tires is greater than that of the rear. This is front wheel drift, characterized by the reluctance of the car to turn. The trajectory of movement in a corner is straightened.
2. Oversteer occurs when the rear tire slip angle is greater than that of the front tires. This is rear wheel skid when the car turns more than the driver wants.
3. With neutral steering, the slip angles of the front and rear tires are the same.
at first small excursion into the theory of the movement of the car, or rather into the subsection where wheel slip in a turn is considered. Imagine that the driver turns the wheels at a certain angle in a corner. At low speed, the car went along a given radius. If you describe a circle, then it will have a certain diameter, regardless of how many circles you roll over it (the angle of rotation of the wheels remains unchanged). Let's start increasing the speed and see that the diameter of our circle began to increase. This increase causes tire drift, the direction of the contact patch with the surface of the site began to shift relative to the wheel disk. The theoretical direction of rolling of the tire began to differ from the real one, given by a certain turn of the steering wheel. In simple words, the direction of the tire began to differ from the direction of the wheel disc (fig. 11).It is this angle, which determines the difference between the theoretical and real directions of the tire, and shows the amount of slip, which led to an increase in the radius of our circle. Let's go even faster. At some point, the grip of the tires will reach a critical value and they will begin to slip. All four at the same time? This is not the worst option, as in this case, sliding will simply increase the diameter of the circle even more, but will not cause the car to rotate around the vertical axis. This behavior of the car at the moment of loss of grip and slip of all four tires is called neutral steering. It is characterized by the fact that all four wheels have the same slip angle. This is how racers try to tune their cars, which allows them to completely control their behavior on high speeds in turns.
Figure: 11. TIRE ANGLE
A - straight
B - direction of movement
B - direction of the steering wheel
As the cornering speed increases, there comes a point where the direction the tire is facing is slightly different from where the wheel rim is actually oriented. The angle between the rolling direction of the tire and the plane of rotation of the wheel is called the slip angle.
In practice, it is often different: the front wheels will start to slide first, then the rear. In the first case, the slip angle of the front wheels will be greater than that of the rear wheels. The car will no longer obey the turned front wheels and will tend to move away from the circle tangentially. This is a typical example of a front axle drift, and the car's behavior in this situation is called understeer.
If the rear wheels slip first, it will cause oversteer, which is characterized by a greater rear wheel slip angle. This is a classic example of a skid, when the rear of the car tries to overtake the front wheels, turning it with its nose to the top of the turn.
It is possible to simulate different manifestations of understeer on site in the same vehicle. To do this, before starting to drive in a circle, you must first release half the pressure in the front tires so that they quickly lose grip and start demolition of the front end. Then re-pressurize the front tires and deflate the rear tires by half, causing a skid.
Why would an ordinary driver know this? Any vehicle with a normal load and average grip will be programmed to behave in a critical cornering situation. Suppose, if we are talking about front wheel drive - understeer will appear. The same car, but under different conditions, for example, with a full load and on slippery surface if the critical speed is exceeded, it will demonstrate the oversteer characteristic of a rear-wheel drive. The main thing to understand is that a driver who does not know how the car will behave in a critical situation, what responses will help him not to lose control of the situation, cannot be called safe. The driver must know exactly what can happen on the road and how to deal with it.
Designers try to give their creations neutral qualities in critical situations... This is what journalists mean when they describe temper automotive news, telling the reader: "Controllability is beyond praise." But not all manufacturers "implant" the nature of neutral understeer into their products, such as the sports models of BMW and Porsche.
How to insure against inept actions of drivers while driving a powerful and fast car? Most likely, it will look like this: flying into a turn at an overestimated speed, an inexperienced driver will get scared, suddenly drop the gas pedal and turn the steering wheel even more abruptly, which will cause the tailgate to skid. That is why engineers are trying to give sports cars tendency to understeer, at least during the first moment of tire slip. This behavior of the car will somewhat resist the tendency to skid the rear axle under these conditions. But in general, rear-wheel drive cars maintain neutral steering at the beginning of sliding, which in limiting modes will still result in oversteer or skid. Likewise, front-wheel drive cars may initially show neutral behavior in sliding, but deeper sliding will still result in a bright manifestation of understeer or drift. (fig. 12).
Circular movement is a litmus test for the manifestation of the individual characters of machines with different types of drives. Rear drive tends to oversteer, front - to understeer.
Neutral steering is characteristic of all-wheel drive vehicles.
How and where to check the character of your car, its tendency to drift and skid? This requires a fenced-off area on which a circle of at least 30 m in diameter can be safely drawn. To drive fast in a racing car, a rider must check the behavior of his car in training. He can, using certain piloting techniques, influence the behavior of the car or change the settings of the suspensions to achieve the desired controllability. Why the overwhelming majority of drivers do not want to check how their cars will behave in a critical situation ?
But the main problems begin when several forces act on the car at once. For example: the car brakes, then turns, and the top of the turn is on a hill. This means that the forces of negative longitudinal acceleration act on the tires, that is, braking, lateral acceleration in a turn, and even vertical, since the car was thrown up. And not strictly along the indicated vectors, but in all directions. The forces acting on the tire when cornering can be represented graphically.
But first, to make it clearer, consider the following situation: the hostess poured borscht into your plate, and you should proceed with the plate to the dining room. "It's good that I haven't poured it to the brim yet!" - you mutter and carefully look at the plate so as not to spill the soup. And he just strives to spill over the edge in the forward and left direction. Stop! Why forward and left? Because you just pulled up at the end of the corridor and turned right. Likewise, the tire grip reserve rushes forward and to the right when braking and turning left in our graphical image. See, as soon as you go again, the soup rushes backward, just like a car pulling away has a load on the rear axle, which increases the grip of the rear tires.
Professor Wunibald Kamm (1893–1966), who worked at the Technical University in Stuttgart, Germany, was the first to suggest using a circle to graphically depict the work of a tire in a corner. Probably before Mr. Kamm came to the conclusion that it was possible to graphically depict the tire's grip in a corner, he also circled around with a bowl of soup in hand. Only it was not borscht, but a German eintopf, but this did not affect the results of the experiment.
So, the forces acting on the tire in a corner can be represented by vectors. This strength can be high, medium, or zero. There is no need to measure it, it doesn't matter for our chart (fig. 13).It is only important that the length of the arrow represents the maximum, half of the arrow represents the middle of the maximum and zero represents nothing. The direction of the arrow is possible in any direction, so draw a circle around it. The distance from the center to the circumference in this case represents the maximum lateral or longitudinal acceleration. What happens on the circle line? This is the zone of turbulence, where the adhesion forces dry up and give way to sliding forces. In this area, maximum grip of the tire with road surface, the tires are in a state of controlled instability. Professor Kamm's circle clearly shows that it is possible to brake and accelerate in a corner, it is only important to correctly distribute the ratio of the forces of longitudinal and lateral accelerations. Of course, in practice, everything is much more complicated, but it helps to understand how the tire works in a corner. I'll tell you a secret that thanks to this theory, it was invented anti-lock braking system brakes.
The graph shows that in a given corner with lateral accelerations "C", we can brake so intensively "B" that the resulting vector "B" is no more than the circumference that determines the tire adhesion limit.
At the circumference, the tire loses grip and the vehicle becomes unstable.
Surface of Professor Kamm's hemisphere (fig. 14)shows vertical acceleration. We talked about the fact that the top of the turn can be on a hill or on a bend. At this moment, the car will become lighter, and the vector will rush towards the surface of the hemisphere, reducing the adhesion of the tire to the road surface. At this point, the tire's ability to turn, accelerate or brake is severely limited. Unloading the suspension will be compressed, and downforce will inevitably arise - the weight of the car will increase, the grip of the tires will improve. This is shown graphically by an enlargement of the circle pushing the sliding start zone. This is the perfect moment to brake or turn.
When driving over a hillock, the car becomes lighter and its ability to brake and turn is reduced.
When driving through a depression, on the contrary, the circumference of the hemisphere becomes larger, which means that the grip of the tires increases under the influence of additional load.
Let's summarize and summarize the above. Driving while driving creates forces acting on the vehicle. The driver can increase or decrease these forces in the process of "fighting" with the road and the car, but they will still obey the laws of physics. Competent driving is the driver's ability to understand and not violate these laws, but skillfully use them. Fast but safe driving means skillfully balancing on the edge of Professor Kamm's circle (fig. 15)... And in balance, the main thing is to feel the weight movement and not overdo it with it. Otherwise, your borscht will spill out of the plate!
Fast but safe driving means skillfully balancing on the edge of the circle. And in balance, the main thing is to feel the transfer of weight.
