Bi Ye's thesis
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20 12 May 18
Fault analysis and maintenance of automobile steering system
The steering system is the compass of the car, and its quality is related to whether the car can drive safely. Firstly, this paper introduces the overall structure of automobile power steering system; Its function is introduced in detail. Classification and working principle. Then, several common faults of automobile power steering system are analyzed in detail: heavy steering, noise during steering, excessive free travel of steering wheel, different weights during left and right steering, strong steering wheel jitter during steering, and steering wheel drift or deviation during straight driving. Finally, the free stroke of the steering wheel, the liquid level of the steering reservoir, the pumping pressure of the hydraulic pump, the sealing of the hydraulic system, the inspection method of the steering column and the progress of the fault phenomenon of the automobile power steering system are expounded.
Diagnosis, analysis and maintenance were carried out. It is very realistic to use and maintain cars.
Automobile, steering gear, fault analysis, inspection and maintenance
introduce
The trend of automobile development is safety, energy saving and environmental protection. Steering system is an important system related to active safety, and its handling stability has a great influence on automobile performance. Mobility means that the car accurately tracks the driver's driving intention; Stability requires dangerous working conditions (high speed driving, large lateral acceleration, large centrifugal force, exceeding tire cornering force, causing large sideslip; Side slip of pavement with small adhesion coefficient; Under the condition that the left and right bias forces of tires are not equal on the open road and the crosswind causes yaw, the car still runs stably. In order to improve the handling stability, ESP (electronic stability program), active steering and 4WS (four-wheel steering) appeared. ESP judges that when understeer or oversteer occurs, the rear wheel and front wheel generate braking force and yaw moment. The rear wheels of four-wheel steering also participate in steering. At low speed, the rear wheel and the front wheel turn in opposite directions, reducing the turning radius and improving the maneuverability. At high speed, the rear wheel and the front wheel rotate in the same direction, which improves the stability of the car. The control objective is that the sideslip angle of the center of mass is zero. However, these automobile steering systems are in the mechanical transmission stage. Because the steering transmission ratio is fixed, the steering response characteristics of the automobile change with the vehicle speed. Therefore, the driver must compensate the amplitude and phase changes of the steering characteristics of the car in advance, so as to control the car to drive according to its wishes. If the driver's steering operation can be connected with the steering wheel through the signal and the controller, then the driver's steering operation only inputs his own driving instructions to the vehicle, and the controller can determine the reasonable front wheel angle according to the driver's instructions, the current vehicle state and road conditions, so as to realize the intelligent control of the steering system, which will greatly improve the vehicle handling stability, reduce the driver's handling burden and improve the performance of the closed-loop system for people and vehicles.
analyse
It consists of a steering oil pump, a steering oil pipe, a steering oil tank, a steering control valve and a steering power cylinder located in an integral steering gear. When the driver turns the steering wheel, the steering rocker swings, and the steering wheel deflects through the steering straight tie rod, tie rod and knuckle arm, thus changing the driving direction of the car. At the same time, the input shaft of the steering gear also drives the steering control valve inside the steering gear to rotate, so that the steering power cylinder generates hydraulic pressure to help the driver steer. In this way, in order to overcome the steering resistance torque acting on the steering wheel on the ground, the steering torque that the driver needs to add to the steering wheel is much smaller than that needed when using the mechanical steering system.
1. Working principle of automobile power steering system
(1) When the car runs straight, the rotary valve is in the middle position, and the working fluid from the steering oil pump flows from the oil inlet of the steering gear housing to the middle oil ring groove of the valve body. Through the through hole at the bottom of the groove, it enters between the valve body and the rotary valve. At this time, because the rotary valve is in
In the middle position, the incoming oil flows to the upper and lower oil ring grooves of the outer circle of the valve body through the equilateral gap formed by the shoulder of the longitudinal groove of the valve body and the rotary valve, and then flows to the upper and lower chambers of the power cylinder through two oil passages in the shell, namely the left steering power chamber L and the right steering power chamber R, but the oil pressure of the upper and lower chambers is equal and small. At this time, the rack piston is not affected by the axial thrust generated by the steering screw, nor by the axial thrust generated by the pressure difference between the upper and lower chambers, so the rack piston is in the middle position and the power steering does not work. The oil flowing into the inner cavity of the valve body flows to the upper and lower oil ring grooves of the valve body through the longitudinal groove of the rotary valve, flows to the gap between the rotary valve and the torsion bar shaft assembly through the radial oil hole on the shoulder of the rotary valve groove, flows to the oil return port through the gap between the valve body assembly and the adjusting plug, and returns to the oil tank through the oil pipe, thus forming a constant-flow oil circulation.
(2) When the car turns left, turn the steering wheel to make the short shaft rotate counterclockwise, and drive the rotary valve to rotate synchronously through its lower shaft pin. This torque is also transmitted to the lower shaft cover through the elastic torsion bar shaft. The notch on the edge of the lower shaft cover drives the valve body to rotate through the pin fixed on the valve body, and the valve body transmits the steering torque to the screw through its lower notch and pin. Due to the existence of steering resistance, enough steering torque is needed to make the steering screw rotate. This torque makes the torsion bar shaft elastically twist, making the rotation angle of the valve body smaller than that of the rotary valve, resulting in relative angular displacement. The oil inlet clearance of the lower power chamber decreases (or closes), the oil return clearance increases and the oil pressure decreases; The oil inlet gap passing through the upper power chamber increases, while the oil return gap decreases (or closes), and the oil pressure increases, resulting in the oil pressure difference between the upper power chamber and the lower power chamber. The rack piston moves under the action of the oil pressure difference between the upper chamber and the lower chamber, thus generating a power-assisted effect. At this time, the pressure oil from the steering oil pump flows to the upper cavity of the power cylinder through the groove, and the oil in the lower cavity of the power cylinder flows to the oil storage tank through the radial hole of the valve body, the groove, the radial hole of the rotary valve and the oil return port.
(3) Turning right is basically similar. The difference is that because the steering direction is opposite, the angular displacement of the valve body and the rotary valve is opposite, the pressure in the lower cavity of the rack-piston increases, and the oil pressure in the upper cavity decreases, resulting in right steering assistance.
(4) When the steering wheel stops at a certain position and does not continue to rotate: at this time, under the action of hydraulic pressure and the elastic force of the torsion bar shaft, the valve body rotates an angle along the steering wheel rotation direction with the screw, so that the relative angular displacement with the rotary valve is reduced, and the oil pressure difference between the upper and lower power chambers is reduced. However, it still has a certain boosting effect. At this time, the assist torque is balanced with the righting torque of the wheel to keep the wheel in a certain steering position.
(5) Progressive follow-up principle: During steering, if the steering wheel rotates fast, the relative angular displacement between the valve body and the rotary valve is also large, the oil pressure difference between the upper and lower power chambers increases correspondingly, and the front wheel deflection speed is also accelerated, such as the steering wheel rotates slowly and the front wheel deflects slowly; If the steering wheel rotates in a certain position, the corresponding front wheel also rotates in a certain position. This is called "the principle of gradual follow-up", that is, the principle of "helping quickly when you turn around, helping greatly when you turn around, and not helping".
(6) After steering, it is necessary to reset the timing. If the driver releases the steering wheel, the rotary valve will return to the middle position and the power-assisted function will be lost. At this time, the steering wheel will automatically return under the action of return torque; If the driver turns the steering wheel at the same time, the steering booster will help the car turn around.
(7) When the car runs in a straight line and encounters external resistance, the steering wheel deflects: the resistance moment acts on the valve body through the steering transmission mechanism, the steering screw, the screw locking pin and the valve body, so that it has relative angular displacement with the rotary valve, thus
The oil pressure of the upper and lower cavities of the power cylinder is not equal, which produces the power-assisted effect opposite to that of the steering wheel. Under this force, the steering wheel quickly returns to the right, ensuring the stability of the car driving in a straight line.
Once the hydraulic booster fails, the power steering gear becomes a mechanical steering gear. At this time, turning the steering wheel drives the short shaft to rotate, and the flange edge at the lower end of the short shaft has an arc gap. After rotating for a certain angle, the screw is driven to rotate by the lug of the flange at the upper end of the screw to ensure the steering of the automobile. But at this time, the free travel of the steering wheel is increased and the steering is heavy. Fault diagnosis and analysis of automobile power steering system
This chapter introduces several common faults of automobiles, and makes diagnosis and analysis. The first steering is heavy, the second steering is noisy, the free travel of the steering wheel is too large for the third steering, the weight of the fourth steering is different, the steering wheel shakes strongly for the fifth steering, and the steering wheel floats or deviates for the sixth straight driving.
2. 1 heavy steering
2. 1. 1 failure phenomenon
A car with variable hydraulic power steering, which was originally light, suddenly felt heavy steering or the steering wheel could not turn.
2. 1.2 Cause of failure
The oil tank is short of oil or the oil level is insufficient.
There is a lot of air mixed in the system.
The oil tank screen is blocked or the pipeline is blocked.
Wear of hydraulic pump, internal leakage or slip, and wear of driving parts.
Parts of oil spill valve and safety valve in booster are worn, and the spring is too soft or improperly adjusted.
The gap between the slide valve and the sliding wall in the booster is too large or not closed correctly.
Poor sealing of system joints and gaskets, resulting in hydraulic oil leakage; Internal leakage is caused by the damage of sealing elements in the system.
2. 1.3 fault diagnosis and elimination
Check the working condition of the driving part of the hydraulic pump. Check whether the transmission belt slips or whether the gear transmission of other transmission forms is damaged.
Check the oil level in the oil tank to see if it reaches the specified height. If the oil level is too low, it should be supplemented to make the oil level reach the height mark on the dipstick. Check whether the filter in the oil tank is blocked or damaged. If it is blocked, clean it. If it is damaged, it should be replaced.
Check whether there is air in the system. If foam (or turbid hydraulic oil) is found in the hydraulic oil, it may be that there is air in the oil circuit (generally, it can be judged by observing whether there are bubbles in the oil return pipe when returning oil). Air intake is usually caused by the rupture of the oil inlet pipe of the hydraulic pump, the looseness of the joint and the damage of the sealing ring on the shaft of the hydraulic pump. If the above damage occurs, it should be repaired first, and then the air in the system should be removed.
Check whether the flow of hydraulic pump and the functions of overflow valve and safety valve are good. The pressure gauge can be connected to the pipeline for inspection. If the effect is not good, the valve and spring should be removed, cleaned and inspected, and new parts should be replaced if necessary.
Check the slide valve in the control valve to see if it works properly. If the clearance is too large or the sealing is not tight, replace the steering screw and slide valve with new ones.
Check whether the sealing ring on the booster piston and the middle sealing function of the radial ring groove of the valve chamber are good, and replace them if necessary. At the same time, check whether the surface of the hydraulic cylinder is damaged.
Check whether the ball valve of the check valve is in close contact with the valve seat. If the valve is not closed properly due to dirt, it should be cleaned. If the valve itself is not closed correctly, it must be replaced with a new one.
2.2 There is noise when turning.
2.2. 1 failure phenomenon
The hydraulic pump is noisy when steering.
failure cause
There is noise in the driving part of the hydraulic pump, such as the belt is too loose and the driving gear transmission part is damaged.
The mixed hydraulic oil and air in the system are insufficient.
The fuel tank filter element is blocked or damaged.
Loose pipe joint or broken or blocked oil pipe.
2.2.3 Fault diagnosis and elimination
First check the oil level in the oil tank. If the oil level is too low, please replenish the hydraulic oil.
Check the working condition of the transmission part, check whether the belt is too loose and whether the transmission gear and other parts are damaged. If there is any abnormality, it should be adjusted and repaired according to the specified requirements.
Check the oil return of the oil return pipe and observe whether there are bubbles (oil turbidity) in the hydraulic oil. If there are bubbles, first find out the leaking place, and then exclude the air.
Check whether the oil tank filter and oil circuit are blocked or damaged, and if so, repair them.
2.3 steering wheel free travel is too large
2.3. 1 failure phenomenon
Turn the steering wheel and find that the free travel is too large.
failure cause
The clearance between the ball pin and the pin seat at both ends of the tie rod is too large.
The gap between the rack and the sector teeth is too large.
The gap between the steering screw and the steering nut and the steel ball is too large.
2.3.3 Fault diagnosis and elimination
Check whether the above gaps are too large one by one and take corresponding measures.
2.4 When turning left and right, the weight varies.
2.4. 1 failure phenomenon
When the car turns left and right, the feeling of turning the steering wheel left and right is different.
failure cause
The slide valve in the control valve deviates from the middle position, or although it is in the middle position, it is inconsistent with the gap size of the valve body shoulder. There are burrs, bumps or dirt on the shoulder of the slide valve or valve body, which hinders the circulation of hydraulic oil and leads to unbalanced afterburner. There is air on one side of the power cylinder, which leads to excessive pressure difference between the two sides of the piston, resulting in different weights in the left and right directions.
2.4.3 Fault diagnosis and elimination