Automobile Inspection Technology

Chapter 14 Automobile Chassis Inspection Technology (3)
3-14 shown.Due to the stable performance and reliable data of the resonant suspension device testing platform, it is widely used.

(a) Displacement measuring type (b) Force measuring type

2. The structure and testing method of the resonant suspension device testing platform

(1) Structural composition
The resonant suspension device test bench is generally composed of a mechanical part and an electronic and electrical control part.

①Mechanical part: The mechanical part of the resonant suspension device testing platform is composed of a box body and two sets of the same vibration system on the left and right. The structure is shown in Figure 3-15.Each set of vibration system is composed of upper swing arm, middle swing arm, lower swing arm, support table, excitation spring, driving motor, energy storage flywheel and sensors.One end of the sensor is fixed on the box, and the other end is fixed on the table.

The upper swing arm, the middle swing arm and the lower swing arm are installed on the box through three swing arm shafts and six bearings.The upper swing arm and the middle swing arm are connected with the support platform and form a parallelogram four-bar linkage mechanism to ensure parallel movement when moving up and down and keep the platform level when loaded.A spring is installed between the ends of the middle swing arm and the bottom swing arm.One end of the drive motor is equipped with an energy storage flywheel, and the other end is equipped with a flange with an eccentric shaft on the flange.One end of the connecting rod is connected with the eccentric shaft through a bearing, and the other end is connected with the end of the lower swing arm.

When testing, drive the car onto the support platform, start the test program, and drive the motor to drive the eccentric mechanism to vibrate the entire car surface system.After a few seconds of excitation to achieve a stable forced vibration with an angular frequency of 0, the power supply of the drive motor is disconnected, and then the energy storage flywheel performs frequency sweep excitation with the angular frequency as the initial frequency.Since the natural frequency of the wheel parked on the platform is between kiss and zero, the frequency sweep excitation of the energy storage flywheel can always make the vehicle platform system resonate.While disconnecting the power supply of the driving motor, start the sampling test device, record the data and waveform, and then analyze, process and evaluate.

②Electronic and electrical control part: The electronic and electrical control part of the resonant suspension device testing platform is mainly composed of microcomputer, sensor, A/D converter, electromagnetic relay and control software.The control software is the bridge between the electronic and electrical control part of the suspension device test bench and the mechanical part.The software not only controls the test process of the suspension device test bench, but also analyzes and processes the data collected by the suspension device test bench, and finally displays and prints the test results.

(2) Detection method

①The specifications and air pressure of automobile tires should meet the specified values, and the vehicle should be empty without passengers.

②Drive the wheels of each axle of the vehicle onto the suspension testing platform, make the tires at the center of the platform, and the driver leave the vehicle.

③Start the testing platform, and the exciter forces the vehicle suspension to vibrate, increasing the vibration frequency to exceed the resonance frequency of the oscillation.

④ After the resonance point, the excitation source is cut off to reduce the vibration frequency and pass the resonance point.

⑤ Record the attenuation vibration curve, the ordinate is the dynamic wheel load, and the abscissa is time, and measure the dynamic wheel load at resonance.Calculates and displays the percentage of dynamic and static wheel loads and the difference between the percentages of left and right wheels on the same axis.

3. Diagnostic criteria for suspension device performance

GB18565-2001 "Comprehensive Performance Requirements and Inspection Methods for Commercial Vehicles" stipulates that for passenger vehicles with a maximum design speed of >100km/h and an axle load mass of <1500kg, the suspension characteristics shall be tested by the suspension testing platform according to the specified method. The absorption rate measured by the wheels of the tested vehicle under external excitation vibration, that is, the percentage value of the minimum dynamic wheel vertical load and the static wheel vertical load (also known as the wheel grounding index) at the time of resonance of the tested vehicle, should not be less than 40 %, the difference between the absorption rate of the coaxial left and right wheels shall not be greater than 15%.

The wheel ground contact index can characterize the working performance of the suspension device, and the wheel ground contact index indicates the minimum ability of the suspension device to ensure that the wheels are in contact with the road surface when the vehicle is running.When the car is running, the grounding index of all wheels is different, which is caused by the different working performance of the suspension device of each wheel, the different load of each wheel, and the different air pressure of each wheel.If the load on each wheel is artificially consistent with the tire pressure on the testing platform, then the wheel ground contact index is mainly determined by the performance of the suspension device.Therefore, the wheel ground contact index can be used to evaluate the performance of the suspension device.

In some European and American countries, the suspension device testing platform has been widely used in testing the working performance of the automobile suspension device.The main manufacturers of suspension device testing benches used in Europe include HOFMANN in Germany and CEMB in Italy.During the inspection of the suspension inspection table produced by them, the suspension inspection table plate and the inspected car on it vibrate vertically according to the sinusoidal law, and the excitation amplitude is fixed and the frequency changes.The force sensor senses the vertical force exerted by the wheel on the platen, and stores the force signal in the memory.After the detection of all the wheel suspension devices of the whole vehicle, the microcomputer analyzes and processes the force signals to obtain the grounding index of the wheels.

The reference standards for evaluating the wheel grounding index recommended by the European Shock Absorber Manufacturers Association (EUSAMA) are listed in Table 3-2, which can be used as a reference when testing the performance of suspension devices in my country.

(Section [-]) Detection of wheel alignment

The detection of wheel alignment refers to the detection of a set of geometric angles and size data formed after the static installation of the wheels, including the detection of steering wheel (front wheel) positioning and non-steering wheel (rear wheel) positioning, collectively referred to as four-wheel Location detection.In order to ensure the handling stability and steering portability of the car, as well as the safety during driving, the wheel alignment must meet the design requirements.During the use of the car, due to the deformation and wear of the steering mechanism, axle, frame and other mechanisms, the wheel alignment will gradually become out of alignment, the handling performance of the car will deteriorate, and driving accidents will easily occur; at the same time, the misalignment of the wheel will also cause the wheel to roll The resistance increases, the power of the car decreases, and the fuel consumption increases; in addition, the abnormal wear of the tires caused by this also reduces the economy of the car.Therefore, it is necessary to timely carry out wheel alignment detection on vehicles in use, and make adjustments according to the detection results to ensure their performance.
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, wheel alignment parameters

The parameters of wheel alignment mainly contain parameters such as caster angle, kingpin inclination angle, wheel camber angle, toe-in of wheel, retraction angle, thrust angle.

1. Kingpin caster angle
The kingpin axis or imaginary kingpin axis (some independent suspension cars have no actual kingpin) tilts backward in the longitudinal plane, and the angle formed with the plumb line is called the caster angle.The role of the caster angle is to form a stable torque and automatically return to alignment when the wheel is affected by an external force and deviates from the straight-line driving direction.The larger the kingpin caster angle, the higher the vehicle speed, the greater the centering torque, and the stronger the ability of the wheel to automatically return to the center after deflection, but the kingpin caster angle should not be too large, otherwise, in order to overcome this moment when turning, the driver will have to The high force required on the steering wheel makes the steering heavy.

2. Kingpin inclination
The steering knuckle kingpin axis or the imaginary kingpin axis is inclined inward in the transverse plane, and the angle formed with the vertical line is called the kingpin inclination angle.The inclination angle of the kingpin also has the function of automatically returning the wheel and making the steering easy at the same time.Appropriate kingpin inclination can reduce the moment applied to the steering wheel when turning, making the steering easy, and also reducing the impact force transmitted from the steering wheel to the steering wheel.

The kingpin inclination should neither be too large nor too small.If the inclination angle of the kingpin is too large, when turning, the wheel will slide a lot with the road surface while rolling, which will increase the friction resistance between the tire and the road surface, which not only makes the steering heavy, but also accelerates the wear of the tire, so the inclination angle of the kingpin Generally not more than 8°; if the inclination angle of the kingpin is too small (the offset increases), the driving stability and braking stability of the car will deteriorate.

3. Wheel camber
When the wheel is installed, it is not perpendicular to the road surface, but tilted outward at an angle. The angle between the center plane of the wheel and the plumb line is called the camber angle of the wheel.

The camber angle can further reduce the offset distance of the kingpin, so it has the function of making the steering light; at the same time, it can make the wheel adapt to the arch of the road surface and prevent the uneven wear of the tire surface inside and outside; in addition, it can also prevent the axle from being deformed under load. In case of inclination of the wheel, reduce the load on the small bearing at the axle end and the confining nut of the hub to prolong its service life.

4. Toe-in
The two wheels on the same axis are not all installed in parallel, the distance B from the front edge of the two wheels is smaller than the distance A from the rear edge, and the value of A-B is the toe-in.The function of the toe-in is to overcome the adverse effects caused by wheel camber and prevent the steering wheel from rolling and slipping on the ground when the car is driving straight, thereby reducing wear and rolling resistance.When the size of the toe value does not match the size of the wheel camber, the steering wheel will produce sideslip.In some cars with front-mounted engine and front-wheel drive, in order to make the car have good driving stability, especially braking stability, the kingpin inclination angle is relatively large, see Table 3-3.

[-]. Four-wheel aligner and detection method

There are two types of vehicle wheel alignment detection methods: static detection method and dynamic detection method.The static detection method is to use a measuring instrument to measure the geometric angle of the wheel alignment when the car is stopped.Dynamic detection is to use measuring instruments to detect the lateral force generated by wheel alignment or the resulting wheel slippage when the car is running at a certain speed.

(End of this chapter)