How does a worm gear work. Steering gear in a car

19.07.2019

Rice. 1

Steering gear worm type comprises:

steering wheel with shaft,

Carter worm pair,

Pairs of "worm-roller",

Pilot bipod.

In the crankcase of the steering mechanism, a pair of "worm-roller" is 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 arm shaft. When the steering wheel is rotated, the roller begins to move along the screw thread of the worm, which leads to the rotation of the steering arm shaft. Worm pair, like any other gear connection, requires lubrication, and therefore oil is poured into the crankcase of the steering mechanism, 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 rotation of the steering wheel into the rotation of the steering arm in one direction or another. And then the force is transferred to the steering drive and from it to the steered (front) wheels.

The steering gear used with the worm type mechanism includes:

Right and left side traction,

medium thrust,

pendulum lever,

Right and left wheel swivel 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.

The advantages of the worm-roller mechanism include:

Low propensity to pass blows from road bumps

Large steering angles

Possibility of high power transfer

The disadvantages are:

A large number of rods and articulations with ever-accumulating backlash

- “heavy” and uninformative steering wheel

Difficulties in manufacturing technology

Steering gear type “screw-nut-sector”

Rice. 2 Steering gear type "screw - ball nut - rack - sector"

1 - distributor;

3 - balls with a recirculation tube;

4 - piston rail;

5 -- toothed sector;

6 - bipod shaft;

7 -- restrictive valve

The full name is "screw-ball nut-rail-sector". The screw 2, which ends the steering shaft, pushes the piston-rack 4 along its axis through the balls 3 circulating along the thread. And that, in turn, turns the gear sector 5 of the steering arm. Because of the ability to transfer big moments, installed on trucks, pickups and large SUVs working in extreme conditions.

Advantages of the “screw-ball nut-rack-sector” steering mechanism:

Possibility of high gear ratio design

Disadvantages of the steering mechanism “screw-ball nut-rail-sector”:

Non-technological

Expensive

Large dimensions

Heavy

Steering gear rack type

In the steering mechanism rack and pinion» the force is transmitted to the wheels by means of a spur or helical gear mounted in bearings and a gear 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 mounted in the middle or at the ends of the rack. 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 gear ratios of the mechanism are determined by the ratio of the number of revolutions of the gear wheel, equal to the number of revolutions of the steering wheel, to the distance of movement of the rack.

The rack and pinion steering mechanism consists of a crankcase cast from an aluminum alloy. A drive gear is installed in the crankcase cavity on ball and roller bearings. Marks are made on the crankcase and on the anther for the correct assembly of the steering mechanism. The toothed wheel is engaged with the toothed rack, which is pressed against the toothed wheel by a spring through a ceramic-metal stop. The spring is pressed by a nut with a retaining ring, creating resistance to loosening the nut. The spring-loaded stop facilitates backlash-free engagement of the gear wheel with the gear rack over the entire stroke. The rail rests at one end on the stop, and at the other end on a split plastic sleeve. The travel of the rack is limited in one direction by a ring pressed onto the rack, and in the other direction by a bushing of the rubber-metal hinge of the left steering rod. The cavity of the crankcase of the steering mechanism is protected from contamination by a corrugated cover.

The steering shaft is connected to the drive gear with an elastic coupling. The upper part of the shaft rests on a deep groove ball bearing pressed into the bracket tube. On upper end shaft on the splines through the damping element is fastened with a nut steering wheel.

Variable ratio steering

Near the zero position of the steering wheel, when driving in a straight line at high speed, excessive steering sharpness is undesirable, it makes the driver tense up. And when parking or turning around, on the contrary, I would like to have gear ratio smaller - to turn the steering wheel at the smallest possible angle. To do this, there are several schemes of rack and pinion steering mechanisms.

This is how the ZF variable ratio rack and pinion steering works. Here the profile of the rack teeth and the gearing shoulder are changed

The Honda VGR (Variable Gear Ratio) rack and pinion steering was used on Honda cars NSX

The ZF company uses rack teeth with a variable profile: in the near-zero zone, the teeth are triangular, and closer to the edges, they are trapezoidal. The gear engages with them with a different shoulder, which helps to slightly change the gear ratio. And another, more complex, option was used by Honda on their NSX supercar. Here the rack and pinion teeth are made with variable pitch, profile and curvature. True, the gear has to be moved up and down, but the gear ratio can be varied over a much wider range.

The steering gear consists of two horizontal rods and rotary levers. telescopic racks front suspension. The rods are connected to the swing arms using ball joints. The swing arms are welded to the front suspension struts. The rods transmit the force to the pivot arms of the telescopic wheel suspension struts and respectively turn them to the right or left.

The benefits of rack and pinion steering include:

Light weight

compactness

low price

Minimum number of rods and hinges

Ease of connection of the steering gear with the steered wheels

Direct transmission of force

High rigidity and efficiency

Easy to equip with hydraulic booster

Flaws:

Due to the simplicity of the design, any push from the wheels is transmitted to the steering wheel.

Difficulties in the manufacture of a mechanism with a high gear ratio, therefore, such a mechanism is not suitable for heavy machines.

Selection and justification of the chosen design

In terms of its technological, price, and design qualities, the rack-and-pinion steering mechanism is most suitable for the front-wheel drive layout and McPherson suspension, providing greater ease and steering precision.

When designing the VAZ-2123 car, they tried to take as many nodes as possible from the VAZ-2121 model, so a “worm-roller” type mechanism was installed on the car. However, the Chevrolet Niva is not powerful SUV so that it would be advisable to put this mechanism on it. It is more expensive, technologically complex, heavier. The possibilities that the worm gear gives the car are not fully used. When using reykm, the concentration of stress from the steering mechanism on the side member is excluded, there is no need to strengthen it at the place where the mechanism is attached.

For all these reasons, I consider it necessary to replace the worm-roller mechanism with a cheaper, lighter, more technologically advanced rack and pinion mechanism, which in necessary measure provides ease and precision of a steering.

Due to the fact that the type of mechanism will be replaced, it is necessary to make a number of changes to the design of other components and assemblies:

Since it is not possible to place the rack and pinion behind the axle of the front wheels, we put it in front of the axle;

In order to free up space between the engine tray and the differential for the rack, we shift the cross-axle differential by the same distance (20.5 mm) back, which does not change the balance of the entire assembly;

Since the rail is located in front of the axle, then stopping support wheels must be placed at the rear.

The most important part of the steering of any car is the steering mechanism, which we will abbreviate as RM. Its main function is to increase the applied to car steering wheel effort, as well as its transmission to the steering gear. From the point of view of mechanics, this process looks like a transformation of the rotational movements of the steering wheel into translational movements of the steering rods.

To ensure smooth and accurate flow this process, a modern RM must meet the following requirements:

have a high degree reliability;
have small technological gaps to ensure free rotation of the steering wheel;
have the ability to arbitrarily return the steering wheel to a neutral position after the driver's hands stop exerting force on it;
have optimal gear ratio, which defines the relationship between the steering angle and the force applied to it.

Steering device

The steering mechanism (RM) has a rather complex device, and its most important part is a gearbox consisting of gears. Depending on the make and model of the vehicle, the gearbox can be enclosed in a housing made of welded high-strength steel or cast iron. In addition to gears, other elements are also placed in it: bearings, shafts. In some types of gearboxes, devices for independent lubrication of gears and bearings can also be placed inside the housing.

There are quite a few varieties of gearboxes these days. Some of them should be given, taking into account the classification criterion:

transmission type - "worm" and gear
the shape of the gears - bevel, cylindrical and bevel-cylindrical;
shaft arrangement - horizontal and vertical;
a feature of the kinematic scheme is a bifurcated stage and a deployed coaxial scheme;
number of steps - one- and two-stage.

Types of steering mechanisms:

Rack RM

The most common type of RM in our time is rack and pinion. The reason for this popularity lies in the relative simplicity of the design, its low weight, low production cost, high efficiency and a small number of hinges and rods, which significantly reduces the frequency of breakdowns. In addition, the location of this type of steering mechanism across the body of the car frees up space in engine compartment to accommodate other mechanisms and components in it, for example, transmission, engine, etc. Rack and pinion control is quite rigid, therefore, it provides a fairly high maneuverability of the car.

It has a rack and pinion mechanism and a number of disadvantages. Among them, the most serious are:

the complexity of the installation technology on cars with dependent suspension of steered wheels;
high vibration activity of the steering;
increased susceptibility to suspension shocks.

The rack and pinion steering mechanism consists of an insert, a cover, springs, a ball pin, a ball joint, stops, gears and the steering rack itself. The rack and pinion gears are located in a metal tube, on each side of which the rack itself protrudes. The steering tip is connected to each of its sides. The drive gear of the steering mechanism is associated with the steering column shaft, which, when the steering wheel rotates, also begins to turn, and thereby sets the rack in motion.

Worm RM

For passenger cars with dependent suspension of steered wheels, as well as light trucks and buses, cars with cross-country ability install another type of steering gear - "worm". Its modern version consists of a roller, a “worm”, which has a variable diameter (it is also called a globoid “worm”) and is connected to the steering shaft. Outside the body of the mechanism is a lever (bipod), which is connected to the steering rods. During the rotation of the steering wheel, the roller rolls along the “worm” and the lever (bipod) swings, which sets in motion steered wheels.

The main differences between the "worm" mechanism and the rack and pinion are its lower sensitivity to suspension shocks and large maximum angles turning wheels. The disadvantages of such a mechanism are its high cost of manufacture and the need for constant adjustment.

Screw RM

On large trucks, big buses and some cars executive class a screw steering mechanism is used. It consists of the following structural elements:

screw, which is located on the steering shaft;
nuts moving along the shaft;
gear rack, which is threaded on a nut;
toothed sector connected to the rail;
steering arm, which is located on the sector shaft.

The main feature of the mechanism is the connection of the screw and nut with the help of balls, which leads to a serious reduction in friction and wear. The very principle of operation is in many ways similar to the principle of operation of the "worm" steering mechanism. During the rotation of the steering wheel, the steering shaft and the screw located on it turn, which drives the nut, all this is accompanied by the circulation of balls. The nut, through the gear rack, shifts the gear sector, and with it the steering arm.

The screw steering gear is highly efficient and can transmit high forces.

How to check the performance of the RM?

As with other steering controls regular check the efficiency of the steering mechanism is the most important task of every car owner, because the safety of movement by car will directly depend on this.

First of all, you should check the play of the steering wheel. The check is carried out both manually and using a special device - a backlash dynamometer. It must be fixed on the wheel rim and a force equal to 10 N must be applied. It is necessary to measure the clearances in the steering rod joints and "worm" bearings. In the event that the car is equipped with a power steering (the so-called power steering), then such a check should be carried out with the engine running.

Visual inspection is also an important component of RM performance diagnostics. In its course it is necessary Special attention pay attention to the condition of the protective covers of the ball joints, since dirt penetrates into the steering mechanism through cracks in them, which can lead to its incorrect operation, breakage and even destruction. At the slightest doubt about the proper operation of the RM, you must contact a specialized car service.

How to remove the steering gear and how to install it?

We will consider the process of removing and installing the steering mechanism using the example of the VAZ 2106, which uses the "worm" type. To do this, you need the following tool:

2 keys "for 13";
key "on 22";
pliers;
ball pin puller.

The process of removing the mechanism will be as follows:

The first step is to remove the steering shaft.
After that, disconnect the left side and middle tie rods and take them to the sides.
Further, with one “13” wrench, holding the steering gear mounting bolts from turning, unscrew the nuts with the second and remove them together with the washers.
After that, holding the mechanism with your hand, you need to remove the mounting bolts, while leaving the steering mechanism to lie on the side member.
Pull it out through the engine compartment.

The new RM is installed in the reverse order, but taking into account some nuances: do not tightly tighten the bolts of the steering shaft bracket and nuts on the compensator, as well as the bolts of the steering gear housing to the side members. This is done in order to install a new mechanism in correct position.

This is done by turning the steering wheel two or three times in different sides, in this case, the mechanism and the steering shaft will self-align.

After that, you can proceed to the control tightening of all fasteners. The final step will be to check the presence of oil in the steering gear of the car.

After that, it is necessary to adjust the mechanism.

Steering gear adjustment

The most popular type of steering gear (rack and pinion) needs to be adjusted from time to time. The reason for this, as mentioned above, is the high susceptibility of the mechanism to bumps, pits and potholes, which are quite a lot on our roads. On most models of modern cars, rail adjustment can be done on your own.

The adjustment process is carried out using the adjusting screw, which, most often, is located on the end cap of the PM. For easier access to it, it is better to use viewing hole, overpass or lift, otherwise you will have to lie down a little on the ground. If the adjustment is made on jacks, then before lifting, the front wheels should be set in a level position.

After carrying out the preparatory measures, it is necessary to measure the backlash, the maximum indicator of which should not exceed 10 degrees. Next, you need to tighten the adjusting screw, and this must be done smoothly and slowly, all the time controlling the backlash with the help of a backlash dynamometer. After completing the adjustment, you should check the steering wheel travel in motion, and if it is too tight, you need to slightly loosen the adjusting screw.

How to repair the steering mechanism yourself?

Some malfunctions in the RM can be eliminated without resorting to replacing it. Some of the methods will be discussed next. If a leak is observed, this may indicate a lack of tightness in the connections of the cylinder tubes or a malfunction of the stuffing box, as well as corrosion of the gearbox shaft. To eliminate this malfunction, it is necessary to make a complete bulkhead of the unit. If the reason is in the seals and gaskets, then it is necessary to replace them with new ones, and if the matter is serious corrosion of the shaft, then it should be ground and restored to its original dimensions using thermal spraying.

Strong play may indicate failure and wear of such parts of the PM as, for example, the crankcase, hinges or propeller bearing. The cause of the backlash may be a crooked crankcase or shaft. To eliminate this malfunction, again, a complete overhaul of the assembly is needed, during which the replacement of worn parts will be required.

A strong knock in the RM gearbox usually indicates wear on the impact bearings. That is, they will need to be replaced with new ones. But this may also be evidence of such a malfunction as a shaft curvature or serious wear of the hinges. For a more accurate diagnosis, a complete reassembly of the assembly may again be required.

Average prices for repair of RM in Russia and the CIS

However, there is not always free time to troubleshoot the steering mechanism, and many of the repair operations require quite serious skills in car mechanic business, so the appeal to the services of specialists in car services is seen the right choice.

Final cost service work will depend not only on the severity of the breakdown, but also on the brand / model of the car, urgency and some other factors. On average, the cost (excluding the cost of replaced elements) of some work related to the maintenance of steering mechanisms in auto repair shops in Russia and neighboring countries in terms of rubles is as follows:

replacement of the steering gear with power steering - from 700 rubles;
replacement of the power cylinder - from 500 rubles;
repair of the power cylinder - from 300 rubles;
replacement of steering tips - from 400 rubles;
replacement of the fingers of the liner - from 100 rubles;
replacement of the steering rack - from 2,000 rubles;
steering rack adjustment - from 200 rubles;
repair of the steering rack without removing the mechanism from the car - from 1000 rubles;
replacement of the steering trapezoid - from 1,000 rubles;
replacement of anthers of the steering mechanism - from 1,800 rubles.

Average prices for new RM in Russia and CIS countries

Sometimes it is impractical to repair the steering mechanism, and sometimes it is simply impossible, for example, after serious accident, therefore, it may be necessary to purchase a new node to replace the old one. Naturally, the cost of a new steering mechanism depends not only on its type, but also on the brand and model of the car, the originality of the mechanism itself, because many popular models large (and not so) auto parts manufacturers produce non-original steering gears.

The average cost for new steering mechanisms in Russia and neighboring countries in terms of domestic currency is as follows:

on rear wheel drive vehicles domestic production(VAZ 2105, 2107, 2106, IZH Oda) - from 2,000 rubles;
on front wheel drive cars domestic production (VAZ 2109, 2114, Priora, Grant, Kalina, Largus) - from 2,500 rubles;
on budget cars foreign production(Kia Ria, Renault Logan, Toyota Corolla, Hyundai Accent(Solaris) Ford Fiesta,) - from 7,000 rubles;
for foreign-made business class cars ( Ford Mondeo, Toyota Camry, Volvo S40) - from 12,000 rubles;
for foreign-made premium cars (Mercedes S-classe, BMW 7, Audi A8) - from 22,000 rubles;
for trucks of domestic production (KamAZ, GAZ) - from 25,000 rubles.

It is worth adding that due to changes in the exchange rates of major foreign currencies, the cost of steering mechanisms for foreign-made cars can change up or, oddly enough, down.

The basis of the steering of any car is the steering mechanism. It is designed to convert the rotational movements of the steering wheel into reciprocating movements of the steering gear. In other words, this device turns the steering turns into the necessary movements of the rods and the rotation of the steered wheels. The main parameter of the mechanism is the gear ratio. And the device itself, in fact, is a gearbox, i.e. mechanical transmission.

Movement functions

steering rack

The main functions of the device are:

conversion of effort from the steering wheel (steering wheel);
transmission of the received force to the steering gear.

Types of steering mechanisms

The device of the steering mechanism differs depending on the method of converting torque. According to this parameter, worm and rack types mechanisms. There is also a screw type, the principle of operation of which is similar to a worm gear, but it has a greater efficiency and implements more effort.

Worm steering mechanism: device, principle of operation, advantages and disadvantages

This steering mechanism is one of the "obsolete" devices. They are equipped with almost all models of domestic "classics". The mechanism is used on vehicles with increased cross-country ability with dependent suspension steerable wheels, as well as in light trucks and buses.

Worm gear diagram

Structurally, the device consists of the following elements:

steering shaft;
transmission "worm-roller";
crankcase;
steering column.

A pair of "worm-roller" is in constant engagement. The globoidal worm is the lower part of the steering shaft, and the roller is mounted on the bipod shaft. When the steering wheel is rotated, the roller moves along the teeth of the worm, due to which the steering arm shaft also rotates. The result of this interaction is the transfer translational movements for drive and wheels.

The worm gear steering has the following advantages:

the ability to turn the wheels at a greater angle;
shock absorption from road bumps;
transfer of great effort;
providing better maneuverability of the machine.

The manufacture of the structure is quite complicated and expensive - this is its main disadvantage. Steering with such a mechanism consists of many connections, the periodic adjustment of which is simply necessary. Otherwise, you will have to replace damaged items.

Rack and pinion steering mechanism: device, principle of operation, advantages and disadvantages

Rack-and-pinion mechanism

The rack and pinion steering mechanism is considered more modern and convenient. Unlike the previous node, this device is applicable on vehicles with independent wheel suspension.

The rack and pinion steering mechanism includes the following elements:

mechanism body;
rack and pinion transmission.

The gear is mounted on the steering shaft and is in constant engagement with the rack. During the rotation of the steering wheel, the rack moves in a horizontal plane. As a result, the steering rods connected to it also move and set the steered wheels in motion.

The gear-rack mechanism is distinguished by its simple design and high efficiency. Its advantages also include:

fewer hinges and rods;
compactness and low price;
reliability and simplicity of design.

On the other hand, this type of gearbox is sensitive to bumps from road bumps - any push from the wheels will be transmitted to the steering wheel.

screw gearbox

Screw gear device

A feature of this mechanism is the connection with the help of balls of a screw and a nut. Due to which there is less friction and wear of the elements. The mechanism consists of the following elements:

steering wheel shaft with screw
screw nut
rack, chopped on a nut
toothed sector to which the rack is connected
steering arm

Helical steering gear is used in buses, heavy trucks and some cars executive class.

Device adjustment

Steering gear adjustment is used to compensate for gaps in the worm-roller and pinion-rack mechanisms. During operation, play may appear in these mechanisms, which can lead to rapid wear elements. It is necessary to adjust the steering mechanism only in accordance with the recommendations of the manufacturer and at specialized service stations. Excessive "clamping" of the mechanism can lead to jamming when turning the steering wheel to the extreme positions, which is fraught with loss of control of the car with corresponding consequences.

The steering gear is a part of the steering that makes driving a car easier due to a significant gear ratio in the gearbox. The following requirements are imposed on the design of steering mechanisms:

ensuring the specified nature of the change in the gear ratio of the steering mechanism;
high efficiency when transferring force from the steering wheel to the bipod;
the ability of the steering mechanism to perceive forces from the steered wheels to the steering wheel, which is necessary to stabilize the steered wheels.

Steering mechanisms are carried out with sufficiently large gear ratios. The gear ratio (m m) is determined by the ratio of the angles of rotation of the steering wheel and the shaft of the bipod of the steering mechanism. For passenger cars, the gear ratio is from 16 to 20, and for trucks 20-25. Usually the gear ratio of the steering mechanism is a constant value (Table 20.1).

Table 20.1. Steering ratios

Cars	Trucks	Buses

The designs of some steering gears allow you to change the gear ratio while turning the steering wheel either upwards (for trucks) or downwards (for cars). This is done to improve traffic safety. high speeds and make it easier to control the car when maneuvering.

Three types of steering gears are most used: worm, screw And rack. In the worm and rack and pinion steering mechanisms, one pair of parts is involved in the transfer of force to the bipod shaft, and in the screw steering mechanism, due to the low efficiency of the screw pair, another additional pair is introduced. Therefore, such steering mechanisms are called combined.

Worm gears used on cars, trucks and buses. They differ in the shape of the worm and the design of the driven element mated with the worm. Most widespread got worm-roller steering mechanisms. The steering pair consists of a globoidal worm and a two- or three-ridged roller. The worm is called globoidal because it has a concave shape, i.e., the shape of a one-sheeted hyperboloid of revolution. Such a gear has a high load capacity due to the simultaneous engagement of a large number of teeth and low friction losses, since the sliding friction in this gear is replaced by rolling friction.

In the engagement of the worm with the roller, a variable gap is provided: from almost backlash-free engagement in the middle position of the roller, corresponding to rectilinear motion, to a significantly increased gap in extreme positions. Such a change in clearances is achieved by shifting the center of the bipod shaft towards the worm. It is necessary to prevent jamming of the steering mechanism in the extreme positions after adjustment, resulting from the wear of the gap in the middle part of the worm pair.

On fig. 20.5 shows the worm gear of the GAZ-66-11 car. It consists of a crankcase /, inside of which there is a worm 6, engaging with a three-ridged roller 2. The worm is pressed onto a hollow shaft 7 and installed in the crankcase on two tapered bearings 5 and 8. Between bottom cover 4 and the steering housing installed several thin paper gaskets 3 for adjusting worm bearings.

Rice. 20.5. The worm gear of the car GAZ-66-11: 1 - crankcase; 2 - video clip; 3 - adjusting gaskets; 4- bottom cover; 5, 8, 11, 17, 18- bearings; 6- worm; 7 - shaft; 9 - dowel; 10 - axis; 12 - screw; 13 - pin; 14 - bipod shaft; 15 - sealing cuff; 16 - bipod; 19 - lock washer; 20 - screw

Roller mounted on axle 10 on bearings 77 in the cheeks of the bipod shaft head. The bipod shaft rotates in two bearings 77 and 18. A sealing cuff is installed at the exit point of the bipod shaft 15. A bipod is planted on the splined part of the shaft 16. The correct installation of the bipod is achieved by the presence of four double slots on it.

The engagement of the worm with the roller is adjusted using screw 72, which is screwed into the side cover of the crankcase. The screw is fixed with a lock washer /9, a pin 13 and nuts 20.

Worm shaft with key 9 connected to the lower fork of the steering shaft. The steering gear shaft consists of an upper steering shaft and an intermediate shaft connected to each other and to the steering gear reducer by means of cardan joints. A steering wheel hub is installed at the end of the steering shaft.

A variation of the worm gear is worm-but-spiroid steering gear with side sector, which is used on the Ural-4320 car (Fig. 20.6). The steering pair consists of a two-way cylindrical worm 2 and a side sector 3 with spiral bevel teeth. The worm is fixed on the shaft 4 , which rotates on bearings 7, allowing a small axial movement. Sector 3 made integral with the shaft 6, on the slots of which a bipod is installed 5.

The angles of the spirals of the worm and the sector are different. With a trapezoidal cross-sectional profile of the turns of the worm and the teeth of the sector, they are in contact along the line, so the teeth perceive the transmitted load along the entire axial length. This reduces the load on the teeth, reduces contact stress and increases the wear resistance of the transmission. bipod shaft 6 installed with great precision on elongated needle bearings 7. The deflection of the worm is limited by a special stop 8 installed in the steering gear housing. Similar emphasis 9 limits the deflection of the sector on the opposite side. Behind-

Rice. 20.6. The steering mechanism of the car Ural-4320: 1 - bearing; 2 - worm; 3 - sector; 4 - worm shaft; 5 - bipod; 6 - bipod shaft; 7 - needle bearing; 8, 9 - stops; 10 -

shim

the engagement of the worm with the sector is regulated by the selection of the thickness of the bronze washer 10 located between the crankcase cover and sector. The gap in the engagement increases when the worm is turned in both directions from the middle position in order to prevent jamming of the steering mechanism in the extreme positions.

Screw steering mechanisms used on cars heavy duty and, as a rule, they have two working pairs: a screw-nut and a rack-toothed sector. They differ from a conventional screw pair in that the moment is not transmitted directly from the screw to the nut, but through balls. In this case, the helical grooves made on the body of the screw and in the nut serve as the raceways for them. When the screw is turned, the balls circulate in the nut in a closed circle, rolling out of the screw channel through the hole on one side of the nut and returning to the nut through the bypass channel on the opposite side. The use of circulating balls makes it possible to replace sliding friction in a screw-nut pair with rolling friction, which increases the transmission efficiency both in forward direction, and vice versa. This improves the conditions for stabilizing the steered wheels, but also makes the mechanism quite sensitive to shocks from the side of the road. Therefore, shock absorbers or power steering should be installed to smooth out shocks. The depth of the helical groove is variable, and the thickness of the middle tooth of the sector is increased compared to other teeth to prevent jamming in extreme positions.

The gap in the engagement of the piston-rack with the bipod shaft sector is adjusted by axial movement of the bipod shaft using a special adjusting screw. The gap in the screw-nut pair is not adjustable, therefore high reliability and the required service life in this engagement is ensured by the use of high quality alloy steels.

The steering mechanism of the ZIL-431410 car is shown in fig. 20.7. The gearbox is connected to the steering wheel shaft with cardan shaft with two hinges. Carter 3 the gearbox is cast from cast iron and has a lower /, intermediate 9, top 14 and lateral 19 covers. Piston rack is located in the crankcase 4, in which the ball nut is fixed 6. The ball nut is assembled with the screw in such a way that helical grooves are formed into which the balls are inserted. 8. Two stamped grooves 7 are inserted into the groove of the ball nut, connected by two holes to its helical groove, forming a tube along which the balls, rolling out when the screw 5 is turned from one end of the nut, return to its other end.

Piston rack 4 is in engagement with the gear sector 18 shaft 21 bipod, which rotates on bronze bushings pressed into the crankcase. Axial movement of the bipod shaft is made by rotating the adjusting screw 20, the head of which enters the hole in the bipod shaft. When wrapping adjusting bolt decreases over-

Rice. 20.7. Screw-rack steering mechanism of the car ZIL-431410: 1 - bottom cover; 2 - stub; 3 - crankcase; 4 - piston rail; 5 - screw; 6 - screw; 7 - gutter; 8 - ball; 9 - intermediate cover; 10 - thrust bearing; 11 - ball valve; 12 - spool; 13 - control valve body; 14 - top cover; 15 -spring; 16 - jet plunger; 17 - set screw; 18 - toothed sector; 19 - side cover; 20 - adjusting screw; 21 - bipod shaft; 22 - magnetic stopper; 23 - fry

the gap in the engagement of the rack-toothed sector, which increases due to this moment of resistance to rotation should not exceed 500 N. A bipod is installed on the outer splined end of the shaft 23.

When the steering wheel is turned, the driver's force is transmitted through the steering wheel shaft and cardan transmission screw 5. Ball nut 6 moves along the axis of the screw, drags the piston-rail along with it 4 , which rotates the gear sector 18 with shaft 21 bipod around its axis. bipod force 23 is transmitted to the steering gear, which turns the steered wheels.

The steering mechanisms of cars of the KamAZ, KrAZ, MAZ brands work according to a similar scheme.

Rack and pinion steering mechanisms simple in design and compact, have a high efficiency, so they are widely used in passenger cars. Recently, such mechanisms have been used on light trucks with independent suspension. The working pair is a gear-rack, with a normal gear and rack tooth profile, the gear ratio of the mechanism is constant. Modern rack and pinion steering mechanisms can have a variable gear ratio, which is achieved by cutting the rack teeth of a special profile.

Increased sensitivity to external influences due to low friction, sensitivity to steering vibrations necessitate the installation of shock absorbers or amplifiers to absorb shocks.

The rack and pinion steering mechanism (Fig. 20.8) consists of a crankcase 2, in which on two bearings 6 And? a drive gear 7 is installed, which is engaged with the rack 10. The rack is pressed against the gear wheel by a spring 12 through metal-ceramic stop 11. Adjustment of the gap in the engagement is carried out by a nut 13.

Rice. 20.8. Rack and pinion steering mechanism of the VAZ-2109 car: 1 - protective case; 2 - steering gear housing; 3 - elastic coupling; 4 - rotary lever; 5 - tie rod; 6 - roller bearing; 7 - gear wheel; 8 - ball bearing; 9 - steering shaft; 10 - rail; 11 - rail emphasis; 12 - spring; 13 - stop nut

When turning the shaft 9, connected to the steering wheel, gear 7 moves the rack 10, from which the force is transmitted to the steering rods and further through the swing arms 4 on wheels.

Steering columns and shafts. IN general case the transmission of rotation from the steering wheel to the steering mechanism is carried out by a shaft, which is located inside the column. On trucks (Fig. 20.9, a, b) steering column 3, installed inside the driver's cab, is attached with the middle part to the inner panel and front shield cabins. The steering column can be fitted with a current collector sound signal and turn signal switch. Shaft 8 installed in a column 3 on bearings 7, and the steering wheel 4 connected to the shaft with a key or splines and fastened with a nut. The lower end of the shaft has a groove for attaching the cardan fork. Located in the center of the steering wheel contact device signal buttons.

The steering shaft and steering gear screw are not always aligned due to the layout of the vehicle and the need correct installation steering wheel. In addition, the angle between the shaft and the propeller may vary, since the cabin has the ability to move slightly relative to the frame. Therefore, the shaft is connected to the screw through a cardan drive 2. On some cab-over-engine vehicles, the driveline allows the cab to be raised to provide access to the engine. The cardan transmission of the steering mechanism has

Rice. 20.9. Steering columns of trucks: A- KAMAZ-5320; b- GAZ-66-11; V- angular reducer; 1 - power steering control valve; 2 - cardan transmission; 3 - steering column; 4 - steering wheel; 5 - steering gear; 6 - angular reducer; 7 - bearing; 8 - steering shaft; 9 - mounting bracket; 10 - driving gear; 11 - lid; 12 - drive gear shaft; 13, 14 - bearings; 15 - driven gear

there are two unequal hinges angular velocities, which are similar in design to those used in the transmission of a car.

In the case of a cab above the engine, the steering column is located almost vertically and an angular gearbox is used to transmit rotation at a large angle to the screw in the steering mechanism. 6 (Fig. 20, V) with gear ratio 1. Shaft 12 with drive gear 10 installed in the housing ball bearings 13, secured by a nut with a lock washer. driven gear 15 connected to the screw with splines, which makes it possible to move the screw relative to the gear wheel in the longitudinal direction.

On passenger cars (Fig. 20.10, A) the steering column includes a shaft 7 placed in a pipe, which is attached to the front panel. The connection of the steering shaft with the shaft with the drive gear of the steering mechanism is carried out through an elastic coupling. The shaft rotates on a bearing 3, a steering wheel is mounted on the splines at the upper end of the shaft. On modern vehicles, the steering column may have several vertical and longitudinal adjustment positions for ease of control, which complicates its design.

Rice. 20.10. Steering columns of passenger cars: A- steering column; b- deformable steering shaft; / - steering shaft; 2 - steering column with mounting bracket; 3 - bearing; 4 - perforated tubular steering shaft

Steering columns can cause serious injury to the driver in an accident. To reduce the dangerous impact of the steering column on the driver, the steering wheel is used, which deforms upon impact and absorbs part of the impact energy. The steering wheel shaft must bend or disengage in an accident without moving more than 127 mm into the passenger compartment. This is done by installing safety steering columns, which are elements passive safety car.

On a VAZ-2121 car, the shaft is folded, as it has a cardan drive, and the impact energy is absorbed by a specially designed steering column mounting bracket.

On a GAZ-3102 car, the energy-absorbing element is a rubber clutch installed between two parts of the steering shaft.

A deformable steering shaft can also absorb impact energy in a collision. 4 installed on foreign cars(Fig. 20.10, b). Such a shaft is a perforated pipe, which can be significantly shortened when a force is applied to it in the axial direction.

The steering shaft can also consist of two parts and be connected by several longitudinal plates, which will bend upon impact, absorbing energy.

It provides turning of the steered wheels with little effort on the steering wheel. 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 steering wheel revolutions greater than 2-3, then the time required to turn the car significantly increases, and this is unacceptable due to traffic conditions. Therefore, the gear ratio in the steering mechanisms is limited within 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 transmit reverse rotation through the mechanism to the steering wheel. With large gear ratios, friction in the gearing of the mechanism increases, the reversibility property disappears, and self-return of the steered wheels after turning to a straight position is impossible.

Steering mechanisms, depending on the type of steering gear, are divided into:

worm,

screw,

gear.

The steering mechanism with a worm-type transmission - the roller has a worm fixed on the steering shaft as a leading link, and the roller is mounted on roller bearing on the same shaft with the bipod. To make a complete engagement with high angle turning the worm, cutting the worm is performed along an arc of a circle - a globoid. Such a worm is called a globoid.

In the screw mechanism, the rotation of the screw associated with the steering shaft is transmitted to the nut, which ends with a rack engaged with the gear sector, and the sector is mounted on the same shaft with the bipod. Such a steering mechanism is formed by a steering gear of the screw-nut-sector type.

In gear steering mechanisms, the steering gear is formed by cylindrical or bevel gears, they also include a rack-and-pinion gear. In the latter, the spur 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 gears are mainly used in passenger cars, as they provide a relatively small gear ratio. For trucks, steering gears of the worm-sector and screw-nut-sector types are used, equipped with either amplifiers built into the mechanism or amplifiers placed in the steering gear.

3.2 Steering gear.

Steering drive designs differ in the location of the levers and rods that make up the steering linkage in relation to the front axle. If the steering trapezoid is in front of the front axle, then this steering drive design is called the front steering trapezoid, with a rear location - rear trapezoid. Big influence the design of the front wheel suspension has a bearing on the design and layout of the steering trapezoid.

With dependent suspension (Fig. 2. (a)) the steering gear has a simpler design, since it consists of a minimum of parts. The tie rod in this case is made integral, and the bipod oscillates 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 there will be no longitudinal thrust, and the force from the bipod is transmitted directly to two transverse thrusts connected to the wheel trunnions.

With independent suspension of the front wheels (Fig. 2. (b)) the steering drive scheme is structurally more complicated. In this case, additional drive parts appear that are not in the dependent wheel suspension scheme. The design of the transverse steering rod is being changed. It is made dissected, consisting of three parts: the main transverse rod and two side rods - left and right. To support the main thrust, a pendulum lever is used, which in shape and size corresponds to the bipod. Side connection transverse rods with swivel trunnion levers and with the main transverse link is made with the help of hinges that allow independent movement of the wheels in the vertical plane. The considered scheme of the steering gear is used mainly in passenger cars.

The steering drive, being part of the steering control of the car, provides not only the ability to turn the steered wheels, but also allows the wheels to oscillate when they run into bumps in the road. In this case, the drive parts receive relative movements in the vertical and horizontal planes and, when turning, transmit forces that turn the wheels. The connection of parts for any drive scheme is carried out using spherical or cylindrical joints.