Steering is used to ensure the movement of the car in the direction set by the driver. The steering control consists of a steering gear and a steering gear.
The steering mechanism serves to increase and transfer to the steering gear the effort applied by the driver to the steering wheel. IN passenger cars mainly used are worm and rack and pinion steering mechanisms.
The advantages of the "worm-roller" mechanism include: low tendency to transmit shocks from road irregularities, large angles of rotation of the wheels, the ability to transmit large forces. The disadvantages are a large number of rods and articulated joints with ever-accumulating backlash, "heavy" and uninformative steering wheel. The cons in the end turned out to be more significant than the pros. On modern cars such devices are practically not used.
The most common today is a rack and pinion steering gear. Low weight, compactness, low price, minimum number of rods and joints - all this has led to widespread use. The rack-and-pinion mechanism is ideal for front-wheel drive configurations and McPherson suspension, providing greater ease and precision in steering. However, there are also disadvantages: due to the simplicity of the design, any push from the wheels is transmitted to the steering wheel. And such a mechanism is not entirely suitable for heavy machines.
The steering gear is designed to transfer the force from the steering mechanism to the steered wheels, while ensuring their rotation at unequal angles. If both wheels are turned the same amount, the inner wheel will criss-cross on the road (slide sideways) and reduce steering efficiency. This slip, which also creates additional heat and wear on the wheel, can be eliminated by turning the inner wheel at a greater angle than the outer wheel. When cornering, each of the wheels describes its own circle, which is different from the other, and the outer (farthest from the center of the turn) wheel moves along a larger radius than the inner one. And, since they have a common center of rotation, respectively, the inner wheel must be turned at a greater angle than the outer one. This is ensured by the design of the so-called "steering link", which includes pivot arms and steering rods with joints. The required ratio of the angles of rotation of the wheels is ensured by the selection of the angle of inclination of the steering levers relative to the longitudinal axis of the vehicle and the length of the steering levers and the transverse link.
Steering gear worm-type comprises:
- a steering wheel with a shaft,
- crankcase of the worm gear,
- pairs "worm-roller",
- steering arm.
In the crankcase of the steering gear, there is a pair of worm-roller in constant engagement. The worm is nothing more than the lower end of the steering shaft, and the roller, in turn, is located on the steering shaft. When the steering wheel rotates, the roller begins to move along the screw thread of the worm, which leads to the rotation of the steering arm shaft.
The worm pair, like any other gear connection, requires lubrication, and therefore oil is poured into the steering gear crankcase, the brand of which is indicated in the instructions for the car. The result of the interaction of the "worm-roller" pair is the transformation of the steering wheel rotation into the steering arm turn in one direction or the other. And then the effort is transmitted to the steering gear and from it to the steered (front) wheels. Modern cars use a safe steering shaft that can fold or break when the driver hits wheel during an accident to avoid serious chest injury.
The steering gear used with a worm-type mechanism includes:
- right and left side rods,
- medium thrust,
- pendulum arm,
- right and left swivel wheel arms.
Each tie Rod has hinges at its ends so that the moving parts of the steering gear can
freely rotate relative to each other and the body in different planes.
Rack and pinion steering gear
In the “pinion-rack” steering mechanism, the force is transmitted to the wheels by means of a spur or helical gear, installed in bearings, and a toothed rack moving in guide bushings. To ensure backlash-free engagement, the rack is pressed against the gear by springs. The steering gear is connected by a shaft to the steering wheel, and the rack is connected to two transverse rods, which can be attached in the middle or at the ends of the rack. These mechanisms have little ratio, which makes it possible to quickly turn the steered wheels to the required position. A full turn of the steered wheels from one extreme position to another is carried out in 1.75 ... 2.5 turns of the steering wheel.
The steering gear consists of two horizontal rods and swing arms of the telescopic front suspension struts. The rods are connected to the pivot arms by means of ball joints. The swing arms are welded to the front suspension struts. The rods transmit the force to the pivoting levers of the telescopic wheel suspension struts and accordingly turn them to the right or left.
The main malfunctions of the steering
Increased backlash of the steering wheel, as well as knocking, may be the result of a loosening of the steering housing, steering arm or swingarm bracket, excessive wear of the steering rod joints or swingarm bushings, wear of the transmission pair ("worm-roller" or "gear-rack") or violation of the adjustment of its engagement. To eliminate the malfunction, tighten all fasteners, adjust the engagement in the transmission pair, replace worn parts.
Tight rotation of the steering wheel may be due to improper adjustment of the gearing in the transmitting pair, lack of lubrication in the steering gear housing, violation of the angles of the front wheels. To eliminate the malfunction, it is necessary to adjust the engagement in the transmission pair of the steering mechanism, check the level and, if necessary, add lubricant to the crankcase, adjust the angles of the front wheels in accordance with the manufacturer's recommendations.
Steering care
Everyone knows the expression: "The best treatment is prevention." Therefore, each time, communicating with your car from below (on inspection pit or overpass), one of the first things to do is to check the elements of the steering drive and mechanism. All protective rubber bands must be intact, the nuts must be pinned, the levers in the hinges must not dangle, the steering elements must not have mechanical damage or deformation. Backlash in the drive joints is easily determined when the assistant shakes the steering wheel, and you find the faulty unit by touch, by the mutual movement of the articulated parts. Fortunately, the times of general shortage have passed, and it is possible to purchase high-quality parts, and not those numerous fakes that fail after a week of operation, as it was in the recent past.
Driving style, road conditions and timely maintenance play a decisive role in the durability of car parts and assemblies. All this also affects the service life of the steering parts. When the driver constantly jerks the steering wheel, turns it on the spot, jumps over holes and arranges off-road races, there is intense wear of all the pivot joints of the drive and parts of the steering mechanism. If, after a "hard" ride, your car began to drift to the side while driving, then at best you will get by with adjusting the front wheel alignment angles, but at worst - the costs will be more tangible, since you will have to replace damaged parts. After replacing any of the steering drive parts or when moving the car away from straight-line movement, it is necessary to adjust the camber of the front wheels. Work on these adjustments should be carried out at the car service stand using special equipment.
It allows steering wheels to be steered with little steering effort. This can be achieved by increasing the steering gear ratio. However, the gear ratio is limited by the number of turns of the steering wheel. If you choose a gear ratio with the number of revolutions of the steering wheel more than 2-3, then the time required to turn the car significantly increases, and this is unacceptable due to driving conditions. Therefore, the gear ratio in the steering mechanisms is limited to 20-30, and to reduce the effort on the steering wheel, an amplifier is built into the steering mechanism or drive.
The limitation of the gear ratio of the steering mechanism is also associated with the property of reversibility, i.e. the ability to transfer reverse rotation through the mechanism to the steering wheel. With large gear ratios, the friction in the engagement of the mechanism increases, the reversibility property disappears and self-return of the steered wheels after turning into a straight-line position turns out to be impossible.
Steering mechanisms, depending on the type of steering gear, are divided into:
worm,
screw,
gear.
The steering gear with a worm-type transmission - the roller has a worm as a driving link, fixed on the steering shaft, and the roller is mounted on a roller bearing on the same shaft with the bipod. To make full engagement at a large angle of rotation of the worm, the worm is cut along an arc of a circle - a globoid. Such a worm is called globoid.
In the screw mechanism, the rotation of the screw connected to the steering shaft is transferred to the nut, which ends with a rack meshed with the toothed sector, and the sector is installed on the same shaft with the bipod. Such a steering mechanism is formed by a screw-nut-sector steering gear.
In gear steering mechanisms, the steering gear is formed by cylindrical or bevel gears, which also include a gear-rack transmission. In the latter, the cylindrical gear is connected to the steering shaft, and the rack, meshed with the gear teeth, acts as a transverse thrust. Rack and pinion gears and worm-roller type gears are mainly used on passenger cars, since they provide a relatively small gear ratio. For trucks, steering gears of the worm-sector and screw-nut-sector type are used, equipped either with amplifiers built into the mechanism, or amplifiers placed in the steering gear.
3.2. Steering drive.
The design of the steering gear differs in the arrangement of the levers and rods that make up the steering linkage in relation to the front axle. If the steering linkage is in front of the front axle, then this design of the steering drive is called the front steering linkage, with the rear positioning - the rear linkage. The design of the front wheels' suspension has a great influence on the design and layout of the steering linkage.
With a dependent suspension (Fig. 2. (a)), the steering gear has a simpler design, since it consists of a minimum of parts. The transverse tie rod in this case is made in one piece, and the bipod swings in a plane parallel to the longitudinal axis of the vehicle. You can make a drive with a bipod swinging in a plane parallel to front axle... Then the longitudinal thrust will be absent, and the force from the bipod is transmitted directly to the two lateral rods associated with the wheel journals.
With independent suspension of the front wheels (Fig. 2. (b)), the steering drive circuit is structurally more complicated. In this case, additional drive parts appear that are not in the scheme with dependent wheel suspension. The design of the tie rod is changed. It is splitted, consisting of three parts: the main transverse link and two side links - left and right. The main thrust is supported by a pendulum arm, which corresponds in shape and size to the bipod. The connection of the lateral transverse rods with the pivot levers of the pins and with the main transverse rod is made using hinges that allow independent movement of the wheels in the vertical plane. The considered steering drive scheme is used mainly on passenger cars.
The steering drive, being a part of the vehicle's steering, provides not only the ability to turn the steered wheels, but also allows the wheels to oscillate when they hit the bumps in the road. In this case, the drive parts receive relative displacements in the vertical and horizontal planes and, when turning, transmit the forces that turn the wheels. The connection of parts for any drive scheme is carried out using ball or cylindrical hinges.
The task of the steering gear is to change the direction of movement of the vehicle. In most cars, you can only change the direction of the front wheels, but there are modern models, which are controlled by changing the direction of all four wheels.
The steering system consists of a steering gear and a drive. As a result of the rotation of the steering wheel, the engine begins to move forward. Then the steer wheels turn and the car changes direction.
During this process, the initial movement of the driver is amplified several times. The steering gear diagram shows which parts and mechanisms are involved in the process of driving a car. Hydraulic boosters are additionally installed on modern cars and trucks designed for the transportation of large loads. The hydraulic boosters make driving easier and increase driving safety.
Steering device
Worm-type steering gear
This is the oldest type of steering. The system consists of a crankcase with a built-in screw called "worm". The "worm" is directly connected to the steering shaft. In addition to the screw, the system has one more shaft with a roller sector. The rotation of the steering wheel leads to the rotation of the "worm" and the subsequent rotation of the roller sector. A steering arm is attached to the sector roller, connected by means of a hinged control with a linkage system.
As a result of the operation of this linkage system, the steered wheels turn and the vehicle changes direction. The worm-type steering mechanism has several disadvantages. First is big loss energy due to high friction inside the mechanism. Secondly, there is no rigid connection between the wheels and the steering wheel. Thirdly, in order to change the direction of movement, you need to turn the steering wheel several times, which not only looks out of date, but also does not meet the existing management standards in the world. Currently, worm-type devices are used only in russian UAZs, VAZs with rear wheel drive and GASakh.
Screw type steering gear
The screw mechanism is also called "ball screw nut". In developing this system, the designers replaced the "worm" with a special screw with a ball nut attached to it. On outside the nuts are located teeth, which come into contact with the same as in the previous system, the roller sector.
In order to reduce friction, the developers proposed to place ball channels between the sector roller and the nut. Thanks to this solution, it was possible to significantly reduce friction, increase recoil and facilitate handling. However, the presence of the same complex system of rods, large dimensions and inconvenient shape of the screw mechanism led to the fact that the screw system was also recognized as unadapted to modern conditions. However, some well-known car manufacturers still use the "screw-ball nut" mechanism in the manufacture of cars with longitudinal motor... Such mechanisms have nissan cars Patrol, Mitsubishi Pajero other.
Rack type steering mechanism
- tie rod end;
- ball joint of the tip;
- swing arm;
- lock-nut;
- traction;
- bolts of fastening of steering rods to the rack;
- inner tips of steering rods;
- steering gear mounting bracket;
- steering gear support;
- protective case;
- connecting plate;
- lock plate;
- damping ring;
- support sleeve of the rail;
- rail;
- steering gear housing;
- coupling pinch bolt;
- bottom flange of elastic coupling;
- the upper part of the cladding casing;
- damper;
- wheel;
- ball bearing;
- steering shaft;
- the lower part of the cladding casing;
- steering shaft mounting bracket;
- protective cap;
- roller bearing;
- drive gear;
- ball bearing;
- retaining ring;
- protective washer;
- sealing ring;
- bearing nut;
- anther;
- stop O-ring;
- retaining ring of the stop nut;
- rail stop;
- spring;
- stop nut;
- ball joint pin;
- protective cap;
- ball pin liner;
A. mark on the boot;
B. mark on the steering box;
C. surface of the ball joint;
D. Swing arm surface
Rack and pinion is the most common steering device. The strength of this design lies in its simplicity. This simple and progressive mechanism is used in the production of 90% of cars. The steering rack device is based on the main element - the shaft-rack. The rack-shaft is equipped with transverse teeth. A gear is located on the steering shaft, which engages the teeth of the steering shaft and moves the rack.
By using this system, it was possible to minimize the number of pivot joints and save significant energy. Each wheel is "supposed" to have two hinges and one rod. For comparison: in the "screw-ball nut" system, the wheel corresponds to three rods, in the "worm" mechanism - five rods. Steering rack provided an almost direct connection between the steering wheel and the wheels, which means that it several times increased the ease of driving. Such steering gear the car made it possible to change the direction of travel with a minimum number of turns of the steering wheel.
Another advantage of the rack and pinion design is the size and shape of the crankcase. With its small size and elongated shape, the crankcase can fit anywhere in the car. Automakers place the crankcase above the engine, below the engine, in front or behind, based on the vehicle model. The rack and pinion mechanism made it possible to achieve an almost instant reaction of the wheels to the steering wheel turn. This system made it possible to create high-speed cars with a modern, improved control system.
Amplifier
The amplifier is used to facilitate control. Thanks to the amplifier, it is possible to achieve greater control accuracy, to increase the speed of transferring movement from the steering wheel to the wheel. A car with an amplifier is easier to control, easier, faster. The amplifier can be electric, pneumatic or hydraulic. Most modern vehicles use a hydraulic booster that is powered by an electric motor.
The hydraulic booster consists of a rotary valve and a vane pump. Due to the movement of the vane pump, hydraulic energy is supplied to the steering gear. The pump is powered by electric motor car. It moves hydraulic fluid. The pressure is regulated by a safety valve built into the pump. It is not hard to guess that what more speed the movement of the engine, the more fluid enters the pumping mechanism.
New technologies
Recently, automakers have begun to produce models with electric amplifier... Such cars are driven by " on-board computer", i.e electronic systemworking in automatic mode... Most of all, this system resembles a computer game in which special sensors installed on the steering wheel provide information on all changes to the central computer and change the position of the mechanisms.
Weak links in steering
Like any other mechanism, the steering system breaks down from time to time. Experienced driver listens to his car and can determine the presence of a particular malfunction by characteristic sounds.
For example, knocks or increased play in the steering wheel may indicate that the crankcase, swingarm bracket, or steering arm is loose in the steering gear. It can also be a sign that the steering rod joints, transmission pair, or swingarm bushing have become unusable. These malfunctions can be eliminated using simple manipulations: replacing worn parts, adjusting gearing or fasteners.
In the event that excessive resistance is felt when the steering wheel rotates, we can say that the ratio of the angles of the front wheels or the engagement of the transmitting pair has been violated. Also, the steering wheel can move tightly if there is no lubricant in the crankcase. These disadvantages should be eliminated: add lubricant, balance the installation angles, adjust the engagement.
Prevention
In order for the car's steering device to serve for a long time, attention must be paid to its prevention. Thorough inspection of steering parts and mechanisms can protect against breakdowns that require lengthy and costly repairs. Besides prevention, driving style is of great importance.
Timely maintenance, which includes diagnostics of the state of the steering mechanism and other important parts and elements of the car.
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There are several types of steering gear You are aware that when you turn the steering wheel, the wheels of your car turn. But between turning the steering wheel and turning the wheels, certain actions take place.
In this article we will look at the features of the two most common types of steering gear: rack and pinion steering gear and ball nut steering gear. We will also talk about power steering and learn about interesting technologies for the development of steering systems that can reduce fuel consumption. But first of all, we'll look at how the turn occurs. Not everything is as simple as it might seem.
Turning the car
You may be surprised to learn that the wheels on the front axle follow different paths when turning. To ensure smooth turning, each wheel should circle a different circle. Due to the fact that the inner wheel describes a wheel with a smaller radius, it makes a sharper turn than the outer one. If you draw a perpendicular to each wheel, the lines will intersect at the center pivot point. The steering geometry makes the inner wheel turn more than the outer.
There are several types of steering gear. The most common are rack and pinion steering and ball nut steering.
Rack and pinion steering gear
The rack and pinion steering gear is widely used in passenger cars, light trucks and SUVs. In fact, this mechanism is quite simple. The rack gears are located in a metal tube with a rack protruding from each side. The steering end connects to each side of the rack. The pinion gear is mated to the steering shaft. When you turn the steering wheel, the gear starts to rotate and sets the rack in motion. The steering tip at the end of the rack connects to the steering bipod on the spindle (see illustration).
The functions of the pinion rack are as follows:
- It converts the rotational motion of the steering wheel into the linear motion required to turn the wheels.
- It provides a gear ratio to facilitate turning the wheels.
The steering gear ratio is the ratio of the degree of steering to the degree of steering. For example, if one full turn The steering wheel (360 degrees) turns the wheel 20 degrees, then the steering gear ratio is 18: 1 (360 divided by 20). The higher the ratio, the greater the degree of steering. Moreover, the higher the ratio, the less effort is required.
Typically in the lungs sports cars steering gear ratio is lower than that of large vehicles and trucks. With a low gear ratio, the steering response is quicker, so you don't have to turn the steering wheel hard to make a turn. Than smaller car, the less its mass, and, even with a low gear ratio, does not require additional effort to turn.
There are also cars with variable steering gear ratio. In this case, a rack with pinion has a different pitch (teeth per inch) in the center and sides. As a result, the car reacts to a steering wheel turn faster (the rack is located closer to the center), and the effort when turning the steering wheel to the stop is also reduced.
Rack and pinion power steering
In the presence of a rack and pinion power steering, the rack has a slightly different design.
Part of the rack includes a cylinder with a piston in the middle. The piston is connected to the rack. There are two holes on both sides of the piston. Liquid supply under high pressure on one side of the piston sets the piston in motion, it turns the rack, providing power steering. Steering gear with ball nut
Ball nut steering gear can be found on many trucks and SUVs. This system is slightly different from the rack and pinion mechanism.The ball nut steering gear includes a worm gear. Conventionally, the worm gear can be divided into two parts. The first part is a metal block with a threaded hole. This block has teeth on the outside, which mate with a gear that drives steering bipod (see figure). The steering wheel is connected to a threaded rod, similar to a bolt, installed in a threaded hole in the block. When the steering wheel turns, the bolt turns with it. Rather than screwing into a block like conventional bolts, this bolt is secured so that when it rotates, it drives the block, which in turn drives the worm gear. 
The bolt does not come into contact with the thread on the block, as it is filled with ball bearings circulating through the mechanism. Ball bearings are used for two purposes: They reduce friction and wear on the transmission, and they also reduce contamination of the mechanism. If there are no balls in the steering gear, the teeth will not touch each other for some time and you will feel that the steering wheel has lost its rigidity.
The power steering in the ball nut steering box functions in the same way as in the rack and pinion steering box. Strengthening is provided by supplying high pressure fluid to one side of the block.
Power steering
In addition to the steering mechanism itself, the power steering includes several main components. Pump
The vane pump supplies the steering gear with hydraulic power (see illustration). The motor drives the pump using a belt and pulley. The pump includes recessed vanes rotating in an oval chamber.As the vanes rotate, they push the low pressure hydraulic fluid from the return line to the high pressure outlet. The flow rate depends on the number of revolutions of the car engine. The design of the pump provides the required head even on idle... As a result, the pump moves more fluid when the engine is running for more high revs.
The pump has a relief valve to ensure proper pressure, which is especially important at high engine speeds when a large volume of fluid is being supplied.
Rotary valve
The power steering should only assist the driver when force is applied to the steering wheel (when cornering). In the absence of effort (eg driving in a straight line), the system should not provide assistance. The device that senses the force applied to the steering wheel is called a rotary valve.The main component of the rotary valve is the torsion bar. A torsion bar is a thin metal bar that rotates under the action of a torque. The upper end of the torsion bar is connected to the steering wheel, and the lower end is connected to a gear or worm gear (which turns the wheels), while the torque of the torsion bar is equal to the torque applied by the driver to turn the wheels. The higher the applied torque, the more the torsion bar turns. The inlet portion of the steering shaft forms the inside of the rotary valve. It is also connected to the top of the torsion bar. The lower part of the torsion bar is connected to the outside of the rotary valve. The torsion bar also rotates the steering gear, mating with the pinion or worm gear, depending on the type of steering gear.
When turning, the torsion bar rotates the inside of the rotary valve, while the outside remains stationary. Due to the fact that the inside of the valve is also connected to the steering shaft (and therefore to the steering wheel), the number of revolutions of the inside of the valve depends on the torque applied by the driver.
When the handlebars are stationary, both hydraulic tubes provide equal pressure to the gear. But when the valve is turned, the channels open to supply high pressure fluid to the corresponding tube.
Practice has shown not the highest efficiency of this type of power steering.
Innovative power steering
Because the power steering pump on most vehicles continuously pumps fluid, it wastes power and fuel. It is logical to count on a number of innovations that will improve fuel economy. One of the most successful ideas is a computer-controlled system. This system completely eliminates the mechanical connection between the steering wheel and the steering mechanism, replacing it with an electronic control system.In fact, the steering wheel works in the same way as the steering wheel for computer games. The steering wheel will be equipped with sensors to send signals to the car about the direction of travel of the wheels and motors, providing a response to the actions of the car. The output from these sensors will be used to control the power steering. In this case, the need for a steering shaft is eliminated, which increases the free space in engine compartment.
General Motors has unveiled the Hy-wire concept car, which already has such a system. Distinctive feature such a system with electronic control from GM is that you can customize the handling of the car yourself using a new computer software without replacing mechanical components. In the electronically controlled cars of the future, you can customize the control system to your liking with just a few buttons. Everything is very simple! The steering system hasn't changed much over the past fifty years. But the next decade will be an era of more fuel efficient cars.
The following requirements are imposed on the steering mechanism:
- the optimal gear ratio, which determines the ratio between the required angle of rotation of the steering wheel and the effort on it; - insignificant energy losses during operation (high efficiency);
- the possibility of spontaneous return of the steering wheel to the neutral position after the driver has ceased to hold the steering wheel in the rotated position;
- slight clearances in moving joints to ensure low backlash or freewheel steering wheel;
- high reliability.
Rack and pinion steering mechanisms are most widely used in passenger cars today.
Rack and pinion steering gear without power steering:
1 - cover;
2 - insert;
3 - spring;
4 - ball pin;
5 - ball joint;
6 - emphasis;
7 - steering rack;
8 - gear
The design of such a mechanism includes a gear mounted on the steering wheel shaft and a gear rack associated with it. When the steering wheel rotates, the rack moves to the right or left and through the steering rods attached to it turns the steered wheels.
The reasons for the widespread use of just such a mechanism in passenger cars are: simplicity of design, low weight and manufacturing cost, high efficiency, a small number of rods and hinges. In addition, the rack and pinion housing located across the vehicle leaves enough space in the engine compartment to accommodate the engine, transmission and other vehicle components. Rack and pinion steering is highly rigid, which provides more precise control of the vehicle during harsh maneuvers.
At the same time, the rack and pinion steering mechanism also has a number of disadvantages: increased sensitivity to shocks from road irregularities and the transmission of these shocks to the steering wheel; a tendency to vibroactivity of the steering, increased load on parts, the difficulty of installing such a steering mechanism on cars with dependent suspension of steered wheels. This limited the scope of application of this type of steering mechanisms only to passenger cars (with a vertical steering axle load of up to 24 kN) vehicles with independent steering wheel suspension.
Rack and pinion steering gear with hydraulic booster:
1 - high pressure liquid;
2 - piston;
3 - liquid under low pressure;
4 - gear;
5 - steering rack;
6 - hydraulic booster distributor;
7 - steering column;
8 - power steering pump;
9 - reservoir for liquid;
10 - suspension element
The steering gear of the "globoidal worm-roller" type without hydraulic booster:
1 - roller;
2 - worm
Cars with dependent suspension of steering wheels, light trucks and buses, cars high cross-country ability are equipped, as a rule, with steering mechanisms of the "globoidal worm-roller" type. Previously, such mechanisms were also used on passenger cars with independent suspension (for example, the VAZ-2105, -2107 family), but now they are practically supplanted by rack and pinion steering mechanisms.
Mechanism type "Globoidal worm-roller" is a type of worm gear and consists of a globoidal worm (a worm with a variable diameter) connected to the steering shaft and a roller mounted on the shaft. On the same shaft, outside the steering mechanism housing, a lever (bipod) is installed, with which the steering rods are connected. The rotation of the steering wheel ensures the rolling of the roller over the worm, the swing of the bipod and the rotation of the steered wheels.
In comparison with rack and pinion steering mechanisms, worm gears are less sensitive to the transmission of shocks from road irregularities, provide greater maximum angles turning the steered wheels (better maneuverability of the car), are well combined with dependent suspension, allow the transfer of large forces. Sometimes worm gears are used on cars high class and a large unladen weight with an independent suspension of steered wheels, but in this case the design of the steering drive becomes more complicated - an additional steering rod and a pendulum arm are added. In addition, the worm gear requires adjustment and is expensive to manufacture.
Steering gear of the type "screw-ball nut-rack-toothed sector" without hydraulic booster (a):
1 - crankcase;
2 - a screw with a ball nut;
3 - shaft-sector;
4 - filler plug;
5 - shims;
6 - shaft;
7 - steering shaft seal;
8 - bipod;
9 - cover;
10 - shaft-sector seal;
11 - outer ring of the shaft-sector bearing;
12 - retaining ring;
13 - a sealing ring;
14 - side cover;
15 - cork;
with built-in hydraulic booster (b):
1 - adjusting nut;
2 - bearing;
3 - a sealing ring;
4 - screw;
5 - crankcase;
6 - piston rack;
7 - hydraulic distributor;
8 - cuff;
9 - sealant;
10 - input shaft;
11 - shaft-sector;
12 - protective cover;
13 - retaining ring;
14 - a sealing ring;
15 - outer ring of the shaft-sector bearing;
16 - side cover;
17 - nut;
18 - bolt
The most common steering gear for heavy duty trucks and buses is a screw-ball-nut-rack-toothed-sector mechanism. Sometimes steering mechanisms of this type can be found on large and expensive passenger cars (Mercedes, Range rover and etc.).
When the steering wheel is turned, the shaft of the mechanism with a helical groove rotates and the nut put on it moves. In this case, the nut, which has a toothed rack on the outside, turns the toothed sector of the bipod shaft. To reduce friction in a screw-nut pair, the transfer of forces in it occurs by means of balls circulating in the helical groove. This steering mechanism has the same advantages as the worm gear discussed above, but it has high efficiency, allows you to effectively transfer large forces and is well combined with the hydraulic power steering.
Earlier on trucks it was possible to find other types of steering mechanisms, for example, "worm-side sector", "screw-crank", "screw-nut-connecting rod-lever". On modern cars, such mechanisms, due to their complexity, the need for adjustment and low efficiency, are practically not used.
