Automobile Inspection Technology

Chapter 12 Automobile Chassis Inspection Technology (1)
Knowledge points
1. Understand the manifestations of common faults in automobile transmission system, steering system, driving system and other systems;

2. Familiar with the basic structure and working principle of the testing instruments of each system of the automobile chassis;

3. Be able to correctly use various testing instruments to test the performance of each system of the chassis, and be able to make correct adjustments to the corresponding mechanisms according to the test results.

Learn
1. Able to correctly judge the fault location according to the manifestations of the common faults of each system of the chassis;
2. Able to measure the swimming angle of the transmission system by using the transmission system swimming angle detector, and analyze the technical status of the transmission system according to the inspection results;
3. Master the wheel balance detection method of the off-car wheel balancer and the on-car wheel balancer, and install the balance block at the correct position of the wheel;
4. Able to use automobile four-wheel aligner and other instruments to detect the alignment parameters of the wheels, and adjust them to meet the requirements of driving safety.

(Section [-]) Inspection of the drive train

The transmission system of the automobile chassis includes clutches, transmissions, universal transmissions, final reducers and differential half shafts, and vehicles such as off-road vehicles and engineering vehicles also include transfer cases.The change of the technical status of the automobile transmission system has a direct impact on the performance of the automobile such as power performance, fuel economy and light handling.

Therefore, the overall performance of the automobile transmission system should be checked frequently, and the faults of the transmission system should be diagnosed and eliminated in time to ensure that the transmission system has a good technical condition.

The national standard GB7258-2004 "Technical Conditions for Motor Vehicle Operation Safety" puts forward the following requirements for the drive train:

1. Clutch

The clutch of the motor vehicle should be stable and completely separated, and no abnormal noise, vibration or abnormal slippage should be allowed during operation; the free travel of the pedal should meet the relevant regulations of the technical conditions of the whole vehicle; when the clutch is completely separated, the pedal force should not exceed 300N , the hand grip should not be greater than 200N.

2. Transmission and transfer case
When shifting gears, the gears mesh easily, and the locking device is effective, and there must be no disordered gears and self-jumping phenomena; there is no abnormal sound during operation; the gear lever must not interfere with other components when shifting gears.

3. Universal transmission device
The transmission shaft is not allowed to vibrate and make abnormal noise during operation, and the intermediate support and universal joint are not allowed to have cracks and looseness.

4. Drive axle

The drive axle casing and the axle tube are not allowed to have deformation and cracks, and the drive axle should work normally and no abnormal noise is allowed.

The pros and cons of the technical condition of the transmission system can be checked by empirical methods or by testing instruments.The detection of the transmission system with modern automobile testing equipment mainly includes the detection of the transmission efficiency of the transmission system, the detection of the sliding distance, the detection of the swimming angle of the transmission system and other items, which are introduced as follows.

[-]. Detection and Analysis of Swimming Angle of Drive Train
The driveline play angle is the sum of the play clearances of the clutch, transmission, cardan drive and transaxle.It can indicate the wear and adjustment of the entire drive train.Usually, when the play angle exceeds the allowable value, the related parts will be worn and loose, so the play angle of the drive train can be used as a diagnostic parameter to evaluate the technical status of the automobile drive train.

1. Detection method

The detection of the swimming angle of the drive train should be carried out with the engine hot and the engine turned off.The detection methods include experience inspection method and instrument inspection method.

(1) Empirical inspection method
When checking the driving train’s swimming angle, it can be carried out in sections, and then the total swimming angle of the driving system can be obtained by summing the traveling angles of each section. The steps are as follows:
①Inspection of the swimming angle of clutch and transmission.The clutch is engaged, the transmission is in the gear to be checked, release the parking brake, and then turn the transmission output shaft flange disc or the parking brake (drum) disc from one limit position to another limit position, The angle turned in this process is the swimming angle from the clutch to the output end of the transmission.Engage each gear in turn, which is the swimming angle of the clutch and transmission under each gear.

② Check the swimming angle of the universal transmission device.Support the drive axle, tighten the parking brake, and then turn the flange plate of the transmission shaft from one limit position to another limit position, and the angle turned during this process is the play angle of the universal joint transmission.

③ Inspection of the driving axle's swimming angle.Release the parking brake, put the transmission in the neutral position, and brake the driving axle, then the maximum angle that the flange plate of the driving axle can turn at this time is the swimming angle of the driving axle.

④ Inspection of the drive train's swimming angle. The sum of the three angles of ①, ②, and ③ is the swimming angle of the drive train of the car.

(2) Instrument detection method
The swimming angle of the automobile transmission system is usually detected by a pointer type swimming angle detector and a digital swimming angle detector.

①Pointer swimming angle detector and its detection method:
The pointer-type swimming angle detector is composed of a measuring wrench, a pointer, a dial and a bayonet.When measuring, the pointer is fixed on the driving shaft of the drive axle, and the dial is fixed on the final reducer shell, as shown in (a).One end of the measuring wrench is provided with a U-shaped clip for clamping on the cross universal joint, and the replaceable jaws on the clip are adapted to different models.The other end of the measuring wrench has a pointer and a dial to indicate the torque value turned to the wrench.

(a) Installation of pointer dial
(b) Setting wrench
When detecting the running angle of the transmission system, clamp the measuring wrench on the universal joint, and turn it from one extreme position to the other with a torque of not less than 30Nm. The measured swim angle value.

The measurement steps are as follows:

a. Detect the swimming angle of the driving axle.Put the transmission in neutral, release the parking brake, brake the drive wheel, and use a measuring wrench to clamp the driven fork of the driving shaft universal joint of the drive axle to measure the wandering angle of the drive axle.

b. Detect the swimming angle of the universal transmission device.Similar to the measurement method of the drive axle, just clamp the measuring wrench on the active fork of the universal joint at the rear end of the transmission, and the travel angle obtained at this time minus the travel angle of the drive axle is the travel angle of the universal transmission .

c. Detect the swimming angle of the clutch and the transmission.Loosen the wheel brakes to keep the clutch in a combined state. If necessary, support the drive axle. The measuring wrench is still stuck on the active fork of the universal joint at the rear end of the transmission. The play angle of the transmission.

②Digital swimming angle detector and detection method:
The digital swimming angle detector is mainly composed of two parts: an inclination sensor and a measuring instrument, which are connected by cables.

a. Inclination sensor.The function of the inclination sensor is to convert the inclination angle of its casing swimming with the rotating shaft into electrical oscillation of corresponding frequency.The sensor housing is a rectangular housing with a V-shaped notch on its upper part and a nylon belt with a buckle, so it can be easily fixed on the transmission shaft.The device inside the sensor housing is shown in Figure 3-2.In the figure, the arc-shaped coil is fixed on the splint in the shell, and the arc-shaped ferrite magnetic rod is supported on the two bearings of the splint through the swing rod and the mandrel, so it can swing around the axis of the mandrel.Under the action of gravity, the pendulum and the direction of gravity always maintain a certain angle. When the inclination angle of the sensor shell is different, the length of the arc-shaped ferrite magnetic rod in the arc-shaped coil is also different, and the inductance generated is also different. It also changes the oscillation frequency of the circuit.It can be seen that the sensor is actually an inclination-frequency converter.In order to keep the movable part of the sensor in a balanced state quickly after swinging, the sensor housing is equipped with transformer oil.

b. Measuring instrument.The measuring instrument is a dedicated digital frequency meter, which can directly display the inclination angle of the sensor due to the use of the gate time and the initial setting measures corresponding to the characteristics of the sensor.The measuring instrument adopts PMOS digital integrated circuit.

The oscillating signal sent by the inclination sensor enters the main counter through the counting gate, and the number of pulses is accumulated on the basis of the set complement number.After the counting is over, under the action of the latch receiving the pulse, the result of the counter is sent to the register, and the result is displayed by the fluorescent digital tube.In use, read out the inclination angles of the two extreme positions within the swimming range, and the difference is the swimming angle.

The measurement steps are as follows:

Connect the measuring instrument to the power supply, connect the measuring instrument and the inclination sensor with a cable, first perform self-calibration of the instrument according to the requirements of the instrument manual, and then turn the switch to the "measurement" position, and then the actual measurement can be carried out.In the car drive train, the most convenient place to fix the inclination sensor is the drive shaft.Therefore, during the whole detection process, the inclination sensor is always fixed on the transmission shaft.

a. Swimming angle of universal transmission.Place the transmission shaft in the middle of the drive axle's travel range or support the drive axle, and tighten the parking brake.Rotate the transmission shaft left and right to extreme positions, and the measuring instrument directly displays the inclination angle of the inclination sensor fixed on the transmission shaft.Write down the inclination angles of the two extreme positions, and the difference is the swimming angle of the universal joint transmission.This angle does not include the angle of play of the universal joint between the drive shaft and the transaxle.

b. Swimming angles of the clutch and each gear of the transmission.Release the parking brake, put the transmission in the selected gear, the clutch is in the engaged state, and the transmission shaft is placed in the middle of the travel range of the driving axle or the driving axle is supported.Rotate the transmission shaft left and right to extreme positions, and the measuring instrument will display the inclination angle of the inclination sensor.The value of the swimming angle can be obtained by calculating the difference of the inclination angles of the two extreme positions.The travel angle minus the measured travel angle of the universal transmission is the travel angle of the clutch and the transmission in this gear.According to the same method, put people in each gear in turn, and then measure the swimming angle of the clutch and transmission in each gear.
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The travel angle of the drive axle.Put the transmission in neutral, release the parking brake, and depress the brake pedal to brake the drive wheels.Rotate the transmission shaft left or right to the extreme position, then the swimming angle of the drive axle can be measured.This angle includes the angle of play of the universal joint between the drive shaft and the transaxle.

For vehicles driven by multiple axles, when it is necessary to detect the swimming angle of each section, the inclination sensor should be respectively fixed on the drive shaft between the transmission and the transfer case, the front axle drive shaft, the middle axle drive shaft and the rear axle drive shaft .

在测量仪上读取数值时应注意，其显示的角度值在0°-30°内有效。出现大于30°的情况，可将固定在传动轴上的传感器适当转过一定角度。若其中一极限位置为0°，另一极限位置超过30。说明该段游动角度已大于30。超出了仪器的测量范围。

Up to now, there is no specific detection standard for the swimming angle in my country. For the reference standard of the driving train angle of medium-sized trucks and the swimming angle of each segment, generally refer to Table 3-1.

2. Fault phenomenon and cause analysis caused by drive train swimming angle

(1) Fault phenomenon
When the car starts and the speed changes suddenly, the transmission system makes a "squeak" sound; when the car is running slowly, the transmission system makes a "fox, fox" sound; the car is stationary, the transmission is in gear, and the clutch pedal is lifted , Release the parking brake, and when you turn the transmission shaft left and right with your hands under the car, you feel that the rotation direction is very large.

Cause Analysis
① The splines of the clutch driven plate and the first shaft of the transmission are loosely matched.

②The meshing clearance of each transmission gear in the transmission is too large or the cooperation between the sliding gear and the spline shaft is loose.

③ The telescopic joints of the universal transmission device and the universal joints are loose.

④The meshing gap between the bevel gear of the main reducer in the drive axle, the planetary gear of the differential and the ten-axis gear, and the half-shaft gear and the half-shaft spline is too large.

[-]. Detection of clutch slippage

Clutch slippage refers to the phenomenon that the friction plate of the clutch driven disc slips between the pressure plate and the flywheel when the clutch is combined to transmit force, which will make the power of the engine unable to be effectively transmitted to the driving wheels.The failure performance of clutch slipping is as follows:
Difficulty walking; the speed of the car cannot increase with the increase of the engine speed during driving, and the driving feels weak; especially when going uphill with a full load, the power is insufficient, and you can smell the burnt smell of the clutch friction plate.

1. Empirical testing method
Start the engine, tighten the parking brake, put in low gear, slowly release the clutch pedal and slowly step on the accelerator pedal, if the body does not move but the engine does not turn off, it means the clutch is slipping; when driving the car and accelerating, If the engine speed increases, but the vehicle speed does not increase accordingly, the clutch is slipping.

2. Instrument detection method
Use a clutch stroboscope to detect clutch slippage.The stroboscope consists of a flash lamp, electrodes, resistors, capacitors and batteries, as shown in Figure 3-3.During the inspection, the high-voltage electrode of the instrument is fed with electric pulses by the spark plug of the engine.The spark plug receives an electric pulse once, and the flashlight lights up once, and the frequency of the flashlight should be proportional to the engine speed.

The detection of clutch slippage can be carried out on the chassis dynamometer test stand or the speedometer test stand, and the driving wheel can be supported without a test stand.When testing, mark the transmission shaft, put the transmission in direct gear and step on the accelerator pedal to make the wheels rotate. It may be considered to apply a certain external load (such as reverse gear starting torque) to the driving wheel or transmission system.Project the light point of the tester onto a certain point on the transmission shaft. If the light point of the flashlight can be accurately irradiated on this point each time, it means that the clutch performance is good; if it cannot be accurately irradiated on this point, but If it follows this point in turn, it means that the clutch is slipping.

(Section [-]) Detection of Steering System

The steering system is used to change the driving direction of the car and determine whether the car maintains a stable straight-line steering performance, which directly affects the safety and maneuverability of the car.Therefore, after the technical condition of the steering system deteriorates, fault diagnosis and maintenance should be carried out in time.

The free travel of the steering wheel refers to the angle at which the steering wheel can rotate freely when the steering wheel of the car remains in a straight-line driving position.The steering force of the steering wheel refers to the circumferential force acting on the outer edge of the steering wheel under certain driving conditions.These two parameters are mainly used to diagnose the coordination status of the parts in the steering system.The matching condition directly affects the handling stability and driving safety of the car.

[-]. Detection of steering wheel free travel

The free travel of the steering wheel is the total reflection of the gaps between the transmission connectors inside the steering system. Excessive free rotation of the steering wheel will directly lead to insensitive steering of the car and affect driving safety; The large transmission gap weakens the constraint on the steering wheel, which leads to the instability of the straight-line driving of the car.Therefore, the amount of free rotation of the steering wheel should be checked and adjusted to meet the requirements.

The amount of free rotation of the steering wheel can be detected with a steering parameter measuring instrument, and the inspection method is as follows:
① Install the steering parameter measuring instrument on the steering wheel to be tested.

②Park the car so that the front wheels are in the straight-line driving position, and connect the power supply of the instrument.

③Turn the steering wheel to the limit position of one side of free rotation, press the "angle measurement" button, and then slowly turn the steering wheel in the opposite direction until the other side stops at the limit position of free rotation, and the angle displayed by the detection instrument is The amount of free rotation of the steering wheel.

In the absence of a steering parameter measuring instrument, a simple steering wheel free rotation measuring instrument (Fig. 3-4) can be used for detection, but it can only detect the free travel of the steering wheel.The instrument is mainly composed of a dial and a pointer. The dial and pointer are respectively fixed on the steering wheel shaft tube and the edge of the steering wheel. There are mechanical and magnetic types.

Measuring method: keep the two steering wheels of the car in the straight-line driving position, turn the steering wheel slightly to the left (or right) to the extreme position on the side of the empty stroke (feel resistance), and adjust the pointer to the zero scale of the dial; Then, turn the steering wheel slightly to the extreme position of the idle travel on the other side, and the scale indicated by the pointer is the free rotation amount of the steering wheel.

[-]. Detection of steering wheel steering force

Since the driver controls the driving direction of the car by manipulating the steering wheel, if the steering is heavy, it will not only increase the driver's labor intensity, but also cannot turn quickly and timely, which will affect driving safety; Losing the "road sense", feeling "fluttering", and having difficulty controlling the driving direction of the car are also detrimental to driving safety.Therefore, a car with good handling stability should have moderate steering portability.

1. Instrument detection method
Steering convenience can be expressed by the magnitude of the steering force acting on the steering wheel (that is, the tangential force acting on the outer edge of the steering wheel) under certain driving conditions.Its steering force can be detected with a steering parameter measuring instrument.

The instrument is mainly composed of four parts: control panel, main box, connection fork and positioning rod, as shown in Figure 3-5.The steering wheel is fixed on the three-jaw bottom plate by bolts, and the bottom plate is connected with the connection fork through the torque sensor. Each connection fork has a movable claw with a retractable length so as to connect with the steering wheel under test.The main chassis is a circular structure, which is fixed in the center of the bottom plate, and is equipped with an interface board, a microcomputer board, a rotary encoder, a printer, a battery, etc., and a torque sensor is also installed in it.The positioning rod protrudes from under the base plate, and is adsorbed on the instrument panel in the cab through the magnetic seat.The inner end of positioning rod is connected with photoelectric device, and photoelectric device is contained in the bottom in the main frame.

(End of this chapter)