Automobile Inspection Technology

Chapter 13 Automobile Chassis Inspection Technology (2)
When the steering measuring instrument is aligned with the center of the steering wheel under test, and the length of the three movable claws is adjusted to be firmly connected with the steering wheel, the steering force of the steering wheel is transmitted to the steering wheel under test through the base plate, torque sensor, and connecting fork, so that The steering wheel turns to steer the car.At this time, the torque sensor converts the steering torque into an electrical signal, and the photoelectric device connected to the inner end of the positioning rod converts the change of the rotation angle into an electrical signal.These two electrical signals are automatically completed by the microcomputer for data collection, rotation angle coding, calculation, analysis, storage, display and printing, so the instrument can measure both the steering torque (or steering force) and the steering wheel angle. The amount of free rotation of the steering wheel can be measured.

When testing the steering force, install the steering parameter detector on the steering wheel under test, align the parameter measuring instrument with the center of the steering wheel under test, adjust the length of the telescopic jaws of the three connecting forks, connect and fix the steering wheel .Press the "turning force" button and input the radius of the steering wheel, and then turn the steering wheel slowly according to the specified conditions, then the steering force of the steering wheel can be measured.

2. Empirical testing method
Without a parameter measuring device, the steering force can also be measured by pulling the rim of the steering wheel tangentially with a spring balance.There are many methods for detecting steering force, and the following two methods are most widely used in practice.

(1) In situ steering force detection

① Install the force-measuring spring scale on the steering wheel of the vehicle under test.

②Put the steering wheel of the car on the corner plate.

③Turn the steering wheel through the force measuring device so that the steering wheel can reach the maximum rotation angle specified by the original factory.

④ During the whole process of turning the steering wheel, the maximum value measured by the force measuring device is the steering force of the steering wheel turning the wheel in situ.

This detection method is the method specified in GB18565-2001 "Comprehensive Performance Requirements and Inspection Methods for Commercial Vehicles". The detection standard for commercial vehicles using this method is: the maximum steering force of the steering wheel should be less than or equal to 120N.

Road test steering force detection

Install the steering parameter measuring instrument on the steering wheel to be tested, and let the car transition from a straight line to a diameter of 10m circular driving, measure the maximum tangential force value applied to the outer edge of the steering wheel, and this value is the steering force of the steering wheel.

This detection method is the method recommended by GB7258-1997 "Technical Conditions for Motor Vehicle Operation Safety", and its detection standard is: the maximum steering force of turning the steering wheel should be less than or equal to 245N.

[-]. Detection of minimum turning diameter

1. The function of minimum turning diameter detection and its national standard
The minimum turning diameter and channel circle of the car are the maneuverability parameters of the car, and their size affects the passability of the car.

When the front wheels of the car are running at the maximum turning angle,

The diameter of the track circle formed on the ground by the center of the tire tread that is farthest from the front axle of the vehicle from the steering center is called the minimum turning diameter of the front outer wheel.As shown in Figure 3-6.

When the front wheels of the car are running at the maximum turning angle,

The diameter of the track circle formed on the ground by the center of the tire tread on the ground from the rear axle of the car closest to the steering center must be called the minimum turning diameter of the rear inner wheel.

When the front wheels of the car are running at the maximum turning angle, the diameter of the track circle formed by the farthest point of the car body from the steering center is called the minimum turning diameter of the farthest point.

When the front wheels of the car are running at the maximum turning angle, the diameter of the trajectory circle formed by the closest point of the car body to the steering center is called the minimum turning diameter of the closest point.

1/2 of the difference between the minimum turning diameter at the furthest point and the minimum turning diameter at the closest point of the car is called the maximum aisle width B.

The National Standard of the People's Republic of China GB17675-1999 "Automotive Steering System - Basic Requirements" stipulates that when the car is moving forward and turning left or right, the turning angle and turning force of the steering wheel must not have significant differences.

Article 7258 of the national standard GB2004-6.10 of the People's Republic of China "Technical Conditions for Motor Vehicle Operation Safety" stipulates that the minimum turning diameter of a motor vehicle shall not be greater than 25m when measured from the center line of the front outer wheel rail apodization.

2. Minimum turning diameter detection method

The national standard GB/T12540-1990 "Measurement Method for the Minimum Turning Diameter of Automobiles" stipulates the measurement method for the minimum turning diameter of automobiles applicable to various types of vehicles with front wheel steering.

(1) Test condition requirements
① The test site is a flat, hard, dry, clean concrete or asphalt ground, and its size should allow the car to run in a full circle.

②The maximum turning angle of the front wheels of the car shall comply with the technical requirements of the car.

③The car should be evenly loaded and fully loaded, and at the same time, ensure that all wheels are on the ground.

④ Test equipment: driving track display device, steel tape measure.

(2) Test method
①Above the center of the front outer wheel and rear inner tire surface, and in the direction perpendicular to the ground at the closest point of the car body to the farthest point from the steering center, respectively install a driving track display device (generally use a water spray needle, the distance between the needle and the ground is less than 50mm) .

②The car is running at a low speed, the steering wheel is turned to the limit position, keep it still, and after the speed is stable, start the display device (spray water on the ground with water), so that each measuring point shows a closed movement track on the ground, Drive the car off the track.

③ Use a steel tape to measure the diameter of the track circle formed by each measuring point on the ground. It should be measured in two directions perpendicular to each other, and the arithmetic mean value should be taken as the test result.

④The car turns left and turns right once respectively.

(Section III) Detection of driving system

The technical status of the vehicle driving system not only affects the comfort of the vehicle and the handling stability of the vehicle, but also directly affects the driving safety of the vehicle.Therefore, enough attention should be paid to the detection and diagnosis of the driving system.The main contents of the detection and diagnosis of the driving system include the detection of wheel balance, the detection of the suspension performance, the detection of the wheel alignment and the diagnosis of the fault of the driving system.

[-]. Detection of wheel balance

With the improvement of road quality and the advancement of automobile technology, the speed of automobiles is getting higher and higher.speeding car,

If the wheel is unbalanced, it will cause the beating and shimmy of the wheel, which not only affects the ride comfort and handling stability of the car, but also makes the vehicle difficult to control, which seriously affects the safety of the car, and also aggravates the damage of tires and tires. The wear and impact of related parts make the related parts of the car vulnerable to damage and shorten the service life of the car.The study found that the wear rate of the wheel is 10 times that of normal use when the wheel is out of position or the imbalance is serious.Therefore, the detection of wheel balance has become one of the important items of automobile detection.

1. The concept of wheel balance and the cause of imbalance
Wheel balance can be divided into wheel static balance and wheel dynamic balance.

(1) Wheel static balance and static unbalance
Support the axle, adjust the tightness of the hub bearing, and turn the wheel lightly by hand to make it stop naturally.Make a mark at the closest point to the ground after the wheels stop, and then repeat the above test several times.If the position of the marks is different after the wheel stops naturally after several rotations, or the wheel does not rotate even after being forced to stop, the wheel is statically balanced.A statically balanced wheel has its center of rotation coincident with the center of the wheel.

If the marks for each test stop at the closest point to the ground, the wheel is statically unbalanced.A statically unbalanced wheel whose center of rotation does not coincide with the center of the wheel.

(2) Wheel dynamic balance and dynamic unbalance
In (a), the wheel is statically balanced. On the radially opposite position of the wheel's rotation axis, there is an unbalance point and W2 with the same radius and mass, and they are not in the same plane.For such a wheel, the resultant centrifugal force at the unbalanced point is zero, but the resultant moment of the centrifugal force is not zero, and a force couple M whose direction changes repeatedly occurs during rotation, making the wheel in a dynamic unbalance.The unbalanced front wheel swings around the kingpin.If the same mass mi and m2 are arranged in the opposite direction of the same radius of action of rni and m2, the wheel is in dynamic balance, as shown in Figure 3-7(b).Dynamically balanced wheels must be statically balanced, so the wheel should mainly be tested for dynamic imbalance.

(3) Causes of wheel imbalance
The main causes of wheel imbalance are:
① Inaccurate centering and positioning of hubs and brake drums (discs) during processing, large processing errors, large casting errors on non-processed surfaces, heat treatment deformation, deformation or uneven wear during use.

②The quality of tire bolts is not equal, the mass distribution of the rim is uneven, or the radial circular runout and the end face circular runout are too large.

③ Uneven distribution of tire mass, large size or shape error, deformation or uneven wear during use, retreaded tires or tire repairs.

④ The inflation nozzles of the twin tires are not installed 180° apart, and the inflation nozzles of the single tires are not marked with the unbalance point (new tires that have passed the balance test are often marked with red, yellow, white or light blue or - symbol, used to indicate the position of the unbalanced point) installed 180° apart.

⑤ When the wheel hub, brake drum (disk), tire bolts, rim, inner tube, lining belt, tire, etc. are disassembled and reassembled into wheels, the accumulated unbalanced mass or shape deviation is too large, which destroys the original balance.

2. Types of wheel balancers
3. Structure and usage of off-car wheel balancer
(1) Brief introduction to the structure of off-vehicle wheel balancer

The display and control devices of wheel dynamic balancing machines produced in recent years are mostly microcomputer type, with automatic diagnosis and automatic system, which can display the unbalance and phase after the electrical signal of the sensor is calculated, analyzed and judged by the microcomputer.

In order to make the displayed unbalance exactly equal to the mass of the balance weight added to the edge of the rim, the measured rim diameter A, rim width b and the distance a from the rim edge to the balancing machine chassis (rim overhang size) must be obtained through the keyboard or by selecting The device knob is input into the microcomputer.

(2) How to use off-vehicle wheel balancer

①Remove dirt, stones and old balance weights from the wheel under test.

② Check the tire pressure and charge it to the specified value if necessary.

③ Select the cone according to the size of the center hole of the rim, carefully install the wheel, and tighten it with a large pitch nut.

④Turn on the power switch, and check whether the indication and the panel of the control device indicate correctly.

⑤ Use a caliper to measure the rim width b and rim diameter (can also be read from the sidewall), measure the distance a from the edge of the rim to the chassis with the ruler on the balancing machine, align the measured values ​​with the key or the selector knob, and set a and b , d is directly input into the instruction and control device.In order to adapt to different measurement systems, all scales on the balancing machine are generally marked with both imperial and metric scales.

⑥ Put down the wheel guard, press the start button, the wheel rotates, the balance test starts, and the microcomputer automatically collects data.

⑦The wheels stop automatically or when a "beep" sound is heard, press the stop button and operate the brake device to stop the wheels, then read the inner and outer unbalanced amounts and unbalanced positions of the wheels from the indicating device.

⑧ Lift the wheel guard and turn the wheel slowly by hand.Stop rotating when the indicating device gives an indication (sound, indicator light is on, braking, displaying dot matrix or displaying detection data, etc.).The quality of the side balance weight displayed by an indicator device is installed on the inner or outer upper part of the rim (12 o'clock position of the clock).The inner and outer sides should be carried out separately, and the balance block should be firmly installed.

⑨After the balance weight is installed, new unbalance may occur, and the balance test should be carried out again until the unbalanced amount is <5g (0.3oz), and the indicating device shows "00" or "OK".When the difference in unbalance is about 10g, if the balance weight can be moved left and right along the edge of the rim for a certain angle, satisfactory results will be obtained.

4. On-board wheel balancer and its usage method
The car-type wheel balancer can be used directly on the vehicle, which is very convenient. It can not only perform dynamic balance detection, but also static balance detection. The components to be corrected include wheels, brake drums (discs), hub bearings, etc. that rotate at high speeds. body.

(1) Brief introduction to the structure of the car-type wheel balancer

Using the on-board wheel balancer, the balance of the wheel can be measured on the car without removing the wheel from the car.The on-car wheel dynamic balancing machine is generally composed of a driving device, a measuring device, an indicating and controlling device, a braking device and a trolley, etc. The driving device is composed of a motor, a runner, etc., which can drive the wheels off the ground to rotate.The measuring device is composed of a sensing head, an adjustable pole, a base and a sensor.It can convert the vibration generated by the unbalanced amount of the wheel into an electrical signal and send it to the indicating and controlling device.

The indication and control device is composed of strobe light, unbalance meter or digital display, etc.The strobe light is used to indicate the position of the unbalanced point of the wheel, and the unbalance meter or digital display is used to indicate the unbalanced amount of the wheel.There are generally two gears for unbalanced volume.The first gear is often used for the indication during the preliminary inspection, and the second gear is often used for the indication during the re-inspection after the balance weight is installed.Brakes are used to stop the wheels.Except for the measuring device, the other devices of the wheel dynamic balancing machine are installed on the trolley, which can be easily moved.

(2) The method of detecting and correcting the dynamic balance of the wheel on the vehicle-type wheel balancer

①Preparation work:
a. Before testing, prop up the front of the car with a jack, and keep the front axle level so that the ground clearance of the wheels on both sides is equal.

b. Remove the dirt, stones and old balance weights on the wheel under test.

c. Check the tire pressure and adjust it to the specified value if necessary.

d. Turn the wheel by hand to check whether the hub bearing is loose, and adjust it to the specified value if necessary.

e. Use white chalk or white tape to mark any position on the outside of the tire.

② Detection and calibration of wheel static balance:
a. Use triangular skids or other methods to fix the other front wheel and two rear wheels, attach the sensor head to the suspension or steering knuckle, adjust the height of the adjustable strut and lock it.

b. Push the wheel dynamic balancer to the side or front of the wheel (depending on the type of wheel balancer), check whether the strobe light is working normally, and check whether the rotation direction of the wheel can make the rotation direction of the wheel coincide with the direction of the car's forward movement unanimous.
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Manipulate the wheel of the wheel dynamic balancing machine to contact the tire, start the motor to drive the wheel to rotate to the specified speed.

d. Observe the position of the tire mark under the strobe light, and read the unbalance value from the indicating device (displayed in the first gear).

e. Manipulate the brake device on the wheel balancer to stop the wheel from rotating.

Turn the wheel by hand so that the mark on it is still at the above observation position. At this time, the uppermost part of the rim is the position where the balance weight is installed.

g. Select the balance weight according to the static unbalance amount displayed by the indicating device, and firmly install it on the edge of the rim.

h. Re-drive the wheels for a retest, at this time the indicator will display in 2nd gear.Adjust the quality and position of the balance weight until it meets the balance requirements.

③ Detection and calibration of wheel dynamic balance:
Attach the sensor head to the flat edge of the wiped brake bottom plate, so that the head is at the same level as the center of rotation of the wheel.

b. Drive the wheel to rotate to the specified speed, observe the position of the tire mark according to the above detection method, and read the dynamic unbalance value.

C. Stop the wheel, select the balance weight and the installation position on the wheel according to the unbalance value, and install the balance weight.

④Notes:
a. The tires must be installed correctly and locked with quick nuts at the same time.

b. Safely operate the tire dynamic balancer.

Second, the detection of suspension performance

Suspension device is an important device of automobile chassis, which usually consists of three parts: elastic element, guide device and shock absorber.The failure of the automobile suspension system will directly affect the ride comfort, handling stability and driving safety of the automobile.Therefore, the technical status and working performance of the suspension device have an important impact on the overall performance of the car.Therefore, it is very important to detect the working performance of the suspension device.

There are three types of detection methods for the working performance of automobile suspension devices: empirical method, body pressing method and test bench detection method.

The empirical method is through manual visual inspection, mainly to check from the outside whether there are cracks in the spring of the suspension device, whether the connecting bolts between the spring and the guide device are loose, whether the shock absorber is leaking, lacking oil, and damaged.

The method of pressing the car body can either manually press the car body or press the car body with the power of the test bench.Press to make the car body move up and down, observe the working condition of the shock absorber and various components of the suspension device, and judge whether the shock absorber and other components need to be replaced or repaired based on experience.

The test bench can quickly detect and diagnose the working performance of the suspension device, and can conduct quantitative analysis.According to different excitation methods, the suspension device testing platform can be divided into two types: drop type and resonance type.Among them, the resonant suspension device testing platform can be divided into force-measuring type and displacement-measuring type according to different detection parameters.

1. Types and working principles of suspension device testing benches

(1) Drop suspension device test bench
As shown in Figure 3-12, in the test, the car is first raised to a certain height by the lifting device, and then the support mechanism is suddenly released, and the car falls to produce free vibration.Use the measuring device to measure the vibration amplitude of the car body or the pressure sensor to measure the impact pressure of the wheel on the platform, and after analyzing the amplitude or pressure, evaluate the working performance of the automobile suspension device.

(2) The resonant suspension device testing platform is shown in Figure 3-13. The vibration exciter composed of the motor, eccentric wheel, energy storage flywheel and spring of the test platform forces the test platform and the suspension of the vehicle under inspection on it. The device vibrates.

Disconnect the power supply of the motor after starting for a few seconds, so that the energy-storage flywheel swing-down suspension testing platform generates frequency-sweeping excitation.Because the frequency of the motor is higher than the natural frequency of the wheel, the frequency-sweeping excitation process of the energy storage flywheel can always sweep to the natural vibration frequency of the wheel during the gradual deceleration of the energy storage flywheel, thereby causing the table-vehicle system to resonate.By detecting the vibration curve of the force or displacement during the vibration attenuation process after excitation, and obtaining the frequency and attenuation characteristics, the working performance of the shock absorber of the suspension device can be judged.

(3) Force-measuring suspension device testing platform and displacement-measuring suspension device testing platform
One is to measure the force during the vibration attenuation process, and the other is to measure the displacement during the vibration attenuation process. Their structures are shown in the figure
(End of this chapter)