The vehicle is equipped with power steering combined in one unit with a steering gear

Power steering reduces the amount of force required to turn the front wheels, absorbs shock from bumps in the road, and improves driving safety by allowing you to maintain control of your vehicle's direction of travel in the event of a front tire blowout.

ZIL-131 steering

Scheme of power steering is given in fig. 2.

ZIL-131 power steering schematic

The steering mechanism (fig. 3) has a screw with a nut on circulating balls and a rack with a gear sector. The steering gear ratio is 20 : 1.

The steering gear is attached to the frame and connected to the steering column shaft by a cardan shaft with two joints.

The crankcase 4 of the steering mechanism is simultaneously a hydraulic booster cylinder in which the piston-rack 5 moves.

A plug 3 is rolled in the piston-rack. The piston-rack engages with the toothed sector of the shaft 31 of the steering arm.

The teeth of the rack and bipod shaft have a variable thickness along the length, which allows you to adjust the engagement gap by means of axial displacement of the bipod shaft.

The steering shaft rotates in bronze bushings 33 pressed into the crankcase and into the hole in the side cover 24 of the crankcase.

The axial position of the bipod shaft is determined by the adjusting screw 30, the head of which enters the hole of the bipod shaft and rests on the thrust washer 26.

The axial movement of the adjusting screw in the bipod shaft, which is maintained during assembly within 0.02–0.08 mm, is limited by the adjusting washer 27 and the retaining ring 28.

A ball nut 8 is located in the piston rail, reinforced with set screws 42, which are centered after assembly.

The nut is pre-assembled with the screw 7 in such a way that 31 balls 10 are inserted into the screw grooves and the groove.

In the groove of the ball nut, connected by two holes to its helical groove, two stamped grooves 9 are inserted, forming a tube along which the balls, rolling out when the screw is turned from one end of the nut, return to its other end.

The screw 7 passes through the intermediate cover 12, to which the body 17 of the control valve is attached.

The screw has two thrust ball bearings 13 with a spool 16 of the control valve between them.

The large ball bearing rings face the spool.

The ball bearings and the spool are fixed with a nut 19, the thinned shoulder of which is pressed into the groove on the screw.

A conical spring washer 18 is placed under the nut, which ensures uniform compression of the thrust ball bearings.

The spring is installed with the concave side towards the ball bearing.

The length of the spool is greater than the length of the hole for it in the control valve body. As a result, the spool and screw can move in the axial direction by 1.1 mm in each direction from the middle position.

They return to the middle position under the action of six springs 39 and jet plungers 40, which are under oil pressure in the supply line from the pump.

The screw 7 rotates in the needle bearing 21 located in the top cover 20 of the steering mechanism.

Two hoses from the hydraulic booster pump are connected to the control valve body: high pressure hose 4 (see Fig. 1), through which oil is supplied from pump 1, and low pressure hose 3 (drain), through which oil returns to the pump.

When the screw 7 (Fig. 3) rotates in one direction or another, due to the resistance that occurs when the wheels turn, a force is created that tends to move it in the axial direction in the corresponding direction.

If this force exceeds the precompression force of the springs 39, then the screw moves and displaces the spool 16. In this case, one cavity of the hydraulic booster cylinder communicates with the pressure line, and the other with the drain.

The oil coming from the pump into the cylinder presses on the piston rail, creating additional force on the sector of the steering bipod shaft, and contributes to the rotation of the wheels.

The pressure in the working cavity of the cylinder increases with increasing resistance to turning the wheels.

At the same time, the pressure under the jet plungers 40 also increases.

The screw and spool tend to return to the middle position under the action of springs 39 and reactive plungers.

The greater the resistance to turning the wheels and the higher the pressure in the working cavity of the cylinder, the greater the force with which the spool seeks to return to the middle position and set the thrust ball bearings and the screw to the middle position, the greater the force on the steering wheel.

When the effort is and the steering wheel increases with increasing resistance to turning the wheels, the driver gets a "sense of the road".

ZIL-131 steering gear

The force on the steering wheel rim corresponding to the start of the hydraulic booster is about 2 kg, and the maximum force is about 10 kg.

When the steering wheel stops turning, the oil entering the cylinder acts on the piston rail with the screw, shifts the spool to the middle position, which causes a decrease in pressure in the cylinder to the level necessary to keep the wheels in the turned position, and stops the piston from moving, and therefore turning the wheels.

In the body of the control valve there is a ball valve 15, which connects the high pressure and drain lines when the pump is not running.

In this case, the valve ensures the operation of the steering mechanism as a conventional steering mechanism without hydraulic booster.

The cavity in which the thrust ball bearings are located is connected to the drain and sealed with 14 rubber O-rings.

The rest of the fixed joints are sealed with similar rings 2, 25 and 41.

The steering arm shaft 31 is sealed with a rubber gland 34, which has a thrust ring 35 that prevents it from turning out under pressure.

External rubber cuff 36 prevents dirt and dust from entering the shaft.

The piston-rack is sealed with two cast-iron elastic split rings 11

The screw 7 of the steering mechanism has two seals in the intermediate cover and in the piston-rack. The seal is made by cast iron elastic split rings 6.

In the top cover 20, the screw is sealed with a rubber gland 38 with a thrust ring 22 and an outer cuff 23.

The adjusting screw 30 is sealed with a rubber O-ring 29.

When the screw 7 of the steering is rotated in one direction or another from the middle position, the free play in the steering mechanism increases, as a result of which the width of the cavity between the teeth of the piston-rack 5, which is engaged with the middle tooth of the sector of the shaft 31 of the bipod, is reduced compared to the width of the remaining depressions, and the steering screw 7 has a barrel-shaped shape with a slight decrease in the diameter of the helical groove towards its ends.

The steering housing has a plug 32 with a magnet that traps steel and cast iron particles from the oil.

The steering screw 7 is connected to the steering column of the cardan shaft.