Automobile Inspection Technology

Chapter 29 Vehicle Inspection Technology (5)
Automobile operating conditions can be divided into several types such as constant speed, acceleration, deceleration and idling. In actual operation, it is often a combination of the above-mentioned operating conditions, which determines the fuel consumption of the vehicle.Therefore, countries have formulated different test cycles according to the common working conditions of different types of vehicles, which not only makes the test results closer to the actual situation, but also shortens the test cycle.

The method of multi-working condition fuel consumption test is to measure the fuel consumption of vehicles of different models strictly according to their respective test cycles.In the idling condition, the clutch should be engaged, and the transmission should be placed in neutral. When changing from idling to accelerating, disengage the clutch 5 seconds before the transition, and change the transmission gear to a low gear. The shift should be quick and smooth.In the deceleration condition, the accelerator pedal should be completely released, the clutch is still engaged, when the vehicle speed drops to 10km/h, the clutch should be disengaged, and if necessary, the brake of the vehicle is allowed to be used in the deceleration condition.

When the vehicle is undergoing multi-working condition tests, when accelerating, maintaining a constant speed and decelerating with the vehicle's brakes, in each test condition unless specified separately, the vehicle speed deviation is ±2km/h.In the process of changing working conditions, the deviation of the vehicle speed is allowed to be greater than the specified value, but the time exceeding the deviation of the vehicle speed under any condition is not more than 1s, that is, the time deviation is ±1s.

After each cycle test, the fuel consumption and passing time of the cycle test shall be recorded.After completing a test according to each test cycle, the vehicle should turn around quickly.The test is repeated, and the test is carried out twice, and the arithmetic mean of the four test results is taken as the measured value of the fuel consumption test in multiple working conditions.

In order to improve the test accuracy, generally, the fuel consumption test of each vehicle should be carried out four times, and the arithmetic mean value of the results of the four tests should be taken as the measured value of the fuel consumption test of the multi-working conditions.

2. Side slip caused by steering wheel camber

The existence of the camber angle of the steering wheel makes the steering wheel try to open outwards during the rolling process, but because the steering bridge cannot be elongated, it cannot really roll outwards in the actual rolling process.However, the resulting external tension will inevitably become a hidden danger of aggravating tire wear and the like.

Assuming that two steering wheels with only camber and no toe-in are driven forward at the same time through two sliding plates that can slide left and right relative to the ground, it can be seen that the sliding plates under the left and right steering wheels are pushed by the reaction force of the external tension of the steering wheels Down.

sliding board

(Section [-]) Vehicle Side Slip Test
[-]. The occurrence and harm of vehicle sideslip
Practice has proved that the side slip of the wheel will cause the car to deviate, increase the rolling resistance, and aggravate the normal wear and tear of the steering mechanism and steering tires, which will eventually lead to an increase in fuel consumption and a decline in power performance of the car, which will easily cause the potential for driving accidents. Danger.Therefore, the alignment value of automobile steering wheel is one of the key inspection items in automobile safety inspection.

The national standard GB7258-2004 "Technical Conditions for Motor Vehicle Operation Safety" and GB18565-2001 "Comprehensive Performance Requirements and Inspection Methods for Commercial Vehicles" stipulate the following regulations on the detection of steering wheel alignment parameters of automobiles:
①The steering wheel of the motor vehicle should be able to automatically return to the center after turning, so that the motor vehicle has a stable straight-line driving ability.

② The alignment value of the front wheel of a motor vehicle should meet the relevant technical conditions of the vehicle.

③For the lateral side slip of the steering wheel of the motor vehicle, when the side slip meter is used to detect the side slip, the value of the side slip should be between ±5m/km.

There are two kinds of detection methods for the alignment parameters of automobile front wheels: static detection method and dynamic detection method.

The static detection method is to detect the front wheel alignment value with a wheel aligner when the car is stationary.

The dynamic detection method is to make the car pass through the sideslip test bench at a certain driving speed, so as to measure the lateral side of the steering wheel.
slippage.

The side slip refers to the lateral displacement of the steering wheel when the straight-line displacement of the car is 1km.

1. Side slip caused by steering wheel toe-in
After the steering wheel has a toe-in, it tries to draw inward during the rolling process, but because the steering bridge cannot be shortened, the steering wheel does not really roll inward during the actual rolling process.But the resulting inward force is bound to become an intensifying wheel.
Hazards such as tire wear.

Assuming that two steering wheels with only toe-in but no camber are driven forward, the sliding plate shown in the figure can also be seen that the sliding plates under the left and right steering wheels are pushed by the reaction force of the steering wheel’s inward force, The phenomenon of slipping to the outside as shown by the dotted line in Figure 5-24 appears, and the side slip test bench of the factory's side slip of the unilateral steering wheel is to use the above sliding plate principle to detect the side slip of the steering wheel.

[-]. Automobile sideslip test bench
1. Structural principle of slide-type sideslip test bench

Automobile sideslip inspection equipment can be divided into two categories according to its measurement parameters: one is a skateboard type sideslip test bench for measuring the amount of wheel sideslip; the other is for measuring the sideslip caused by wheel camber in Figure 5-25 Forced roller side-slip test bench.The above two test rigs belong to the dynamic sideslip test rig.

According to its structure, the slide-type side-slip test bench can be divided into two types: single-plate side-slip test bench and double-plate side-slip test bench.The former has only one side skateboard, and only one wheel of the car passes through the side skateboard during the inspection; the latter has two left and right side skateboards, and the left and right wheels of the car pass through the side skateboard at the same time during the inspection.They are generally composed of measuring devices, indicating devices and alarm devices.The roller side slip test bench measures the lateral force of the wheel when the car is running, so as to determine the amount of side slip of the car.The following mainly introduces the double-plate sideslip test bench.

(1) Measuring device
It consists of a frame, two left and right sliding plates, a lever mechanism, a return device, a roller device, a guide device, a locking device, a displacement sensor and a signal transmission device.The device can measure the side slip of the front wheel and transmit it to the indicating device.

The length of the sliding plate generally has three types: 500mm, 800mm and 1000mm.The upper surface of the sliding plate is made with "D" or "+" pattern to increase the adhesion between the tire and the tire.The bottom of the slide plate is equipped with a roller device and a guide device, and a crank mechanism, a return device and a locking device are connected between the two slide plates.Under the action of lateral force, the two sliding plates can only do equal displacements in the left and right directions, and they must be all inwards and outwards, and cannot be displaced in the front and rear directions.

When the positive toe-in (IN) of the front wheel is too large, the sliding plate slides outward; when the negative toe-in (OUT) of the front wheel is too large, the sliding plate slides inward; when the lateral force disappears, the two The sliding plates return to the zero position; when the locking device is closed, the two sliding plates are locked.

According to the difference in the way the displacement of the sliding plate is transmitted to the indicating device, the measuring device can be divided into two types: mechanical and electrical.

①Mechanical measuring device is a structural form in which the sliding plate and the indicating device are mechanically connected together, and the displacement of the sliding plate is directly transmitted to the indicating device through connecting rods and "L" shaped levers and other parts.A side-slip test bench with a mechanical measuring device is generally called a mechanical side-slip test bench. The indicating device is set up at one end of the measuring device. It is convenient for long-distance transmission and has been gradually used in recent years.

②Electrical measuring device is a structural form that converts the displacement of the sliding plate into an electrical signal through a displacement sensor, and then transmits it to the indicating device after amplification and processing. The measurement result can be transmitted over a long distance by means of a wire, or It is very convenient to connect with the computer.Displacement sensors have various forms such as self-aligning motor type, potentiometer type and differential transformer type.

Steering wheel moving direction

a.自整角电动机式测量装置如图5-26所示。测量装置上的自整角电动机7通过齿轮齿条机构、杠杆和连杆等与滑动板连接在一起。指示装置中也装备有同一规格的自整角电动机9。当滑动板发生位移时，自整角电动机7(产生信号的自整角电动机）回转一定角度并产生电信号传输给自整角电动机9(接受信号的自整角电动机），自整角电动机9接到电信号后回转同一角度并通过指针指示出滑动板位移量的大小和方向。

The measurement principle is shown in Figure 5-27. The auto-alignment motor that generates the signal and the auto-alignment motor that receives the signal, the rotor coil is connected with a certain voltage of alternating current, and the three terminals of the stator coil are connected correspondingly.Therefore, when one motor rotates by a certain angle, the other motor will also rotate by the same angle, realizing that the two motors have different axes but rotate at the same angle.

The self-aligning motor that generates the signal The self-aligning motor that receives the signal Figure 5-27 Schematic diagram of the self-aligning motor measuring device
b. The potentiometer measuring device is shown in Figure 5-28, and the measuring principle is shown in Figure 5-29.It can be seen that the displacement of the sliding plate can be converted into the movement of the potentiometer contact on the resistance coil, resulting in a change in the resistance value of the circuit, which in turn causes a change in the circuit voltage.By transmitting this change to the indicating device (voltmeter), the magnitude and direction of the displacement of the sliding plate can be indicated.

c. The differential transformer measuring device is shown in Figure 5-30, and the measuring principle is shown in Figure 5-31.The primary winding and the secondary winding share an iron core, and an alternating current is passed through the primary winding, and an induced current is generated in the secondary winding through the iron core.When the sliding plate is displaced, the contact drives the iron core in the differential transformer coil to move, changing the magnetic flux and causing the voltage of the secondary winding circuit to change.By transmitting this change to the indicating device (voltmeter), the magnitude and direction of the displacement of the sliding plate can be indicated.

(2) Indicating device
There are two types of pointer and digital.The pointer-type indicating device is shown in Figure 5-32. The indicating device can set the amount of side slip of the sliding plate transmitted by the measuring device as a scale of 1 m for every 1 km of the vehicle.The positive toe-in (IN) of the front wheel and the negative toe-in (OUT) of the front wheel are each engraved with a scale of 10 grids.Therefore, when the length of the sliding plate is 1000mm and the sliding plate slides sideways by 1mm, the indicating device indicates 1 scale, which means that the vehicle slides sideways by 1m every 1km traveled.Similarly, when the length of the sliding plate is 800mm, the sliding plate slides sideways by 0.8mm and the length of the sliding plate is 500mm, and the sliding plate slides sideways by 0.5mm, the indicating device can also indicate a scale.In this way, the inspector can obtain the specific value of the amount of sideslip of the front wheel from the indicating device, and determine the direction of the sideslip according to the direction in which the pointer deviates to IN or OUT.

In addition to marking the sideslip amount and sideslip direction with numbers and symbols on the dial of the indicating device, some are also divided into three areas by color and English, that is, the side slip is green within the range of 0-3mm, indicating a good area ;The side slip of 3-5mm is yellow, which means the usable area; the side slip is more than 5mm, which is red, which means the bad area.

In recent years, the sideslip test benches produced by various domestic manufacturers adopt digital indicating devices, and mostly use single-chip computers for data collection and processing, so they have the advantages of convenient operation, reliable operation, strong anti-interference, etc., and can also monitor the test results. Analysis, judgment, storage, printing and digital display, etc.When the sliding plate slides sideways, the displacement is converted into an electrical signal by the displacement sensor, which becomes an analog quantity of 0-5V after amplification and signal processing, and then converted into a digital quantity by the A/D converter, which is input into the computer for calculation and processing, and then The test results are displayed on a digital display or printed out by a printer.The digital indicating device is shown in Figure 5-33.

(3) Alarm device
When detecting the side slip of the front wheel, in order to quickly display whether the test result is qualified or not, the side slip of the front wheel exceeds the specified value (five-grid scale)

Finally, the alarm device of the sideslip test bench can use the buzzer or signal light to alarm according to the signal sent by the limit switch of the measuring device, so there is no need to read the specific value on the indicating instrument, which saves time for the detection work.

[-]. Detection method of vehicle sideslip

The type, structure, and allowable axle load of the sideslip test bench are different, and their use methods are also different.Be sure to read the instruction manual carefully before use to master the correct method of use.The general usage method of the sideslip test bench is as follows.

1. Preparation before detection

(1) Preparation of the test bench
① Check the wire connection of the sideslip test bench, turn on the power switch when the wire is well connected, and check whether the pointer of the pointer instrument is at the mechanical zero point, or check whether the brightness of the digital tube is normal and is at the zero position, if any fault is found , should be removed in time.

② Check the cleanliness of the sideslip test bench and its surroundings, and remove any oil, mud, sand and gravel.

③Open the locking device of the sideslip test bench, check whether the sliding plate can slide freely left and right under the action of external force, whether the external force disappears and returns to the original position, and the indicating device points to the zero point.

④ Check whether the alarm device can send out an alarm signal when it is at the specified value, and adjust and repair if necessary.

(2) Preparation of the car to be inspected

①The tire pressure should meet the requirements of the automobile manufacturer.

② When there is oil, mud, water or stones embedded in the tread groove on the tire, it should be cleaned up.

③The tire tread depth must comply with the provisions of GB7258-2004 "Technical Conditions for Safety in Motor Operation".

2. Detection method

① Pull out the locking pin of the slide plate and turn on the power.

②The car drives perpendicular to the slide plate to the sideslip test stand at a speed of 3-5km/h, so that the front wheels pass the slide plate smoothly.

③ After the front wheel passes the sliding plate completely, observe the side slip direction from the indicating device and read and print the maximum side slip amount.

④ After the test is completed, cut off the power and lock the sliding plate.

3. Precautions for use
① Vehicles exceeding the allowable axle load of the test stand cannot pass through the sideslip test stand.

②The car cannot turn or brake on the sideslip test bench.

③Keep the inside, outside and surrounding environment of the sideslip test bench clean.

④ Non-test vehicles cannot stay on the sideslip test bench.

4. Detect the technical condition of the rear axle

Except that the rear wheels of some cars also have toe-in and camber (such as Shanghai Santana), the rear wheels of a considerable number of cars are not positioned.For the latter, the sideslip test bench can be used to detect whether the rear axle is bent and deformed and whether the hub bearing is loose according to the following methods.

① Make the rear wheels of the car pass forward and backward on the sliding plate of the sideslip test bench. If the two sideslip readings are all zero, it means that the rear axle has no bending deformation.

②If the two sideslip readings are not zero, and the sideslip readings are equal and the sideslip direction is opposite after the forward and reverse passes the sliding plate, it indicates that the rear axle is bent in the horizontal plane.

a. If the sliding plate slides outward when moving forward, and slides inward when moving backward, it means that the end of the rear axle is bent forward in the horizontal plane.

b. If the sliding plate slides inward when moving forward, and slides outward when moving backward, it means that the end of the rear axle is backward in the horizontal plane
bending.

③ If the two sideslip readings are not zero, and the sideslip readings are equal and the sideslip direction is the same after driving forward and backward over the sliding plate, it indicates that the rear axle is bent in the vertical plane.

a. If the sliding plate slides outward, it means that the end of the rear axle is bent upward in the vertical plane.

b. If the sliding plate slides inward, it means that the end of the rear axle is bent downward in the vertical plane.

④The rear wheel has passed the sliding plate of the sideslip test bench for many times, and the readings are not equal each time, indicating that the hub bearing is loose.

For cars with rear wheels that have been positioned, it is still possible to detect whether the rear axle is bent and deformed and whether the hub bearing is loose according to the above method, but the positioning value is subtracted from the detection result, and the remaining value is caused by the bending deformation of the rear axle.

(Section [-]) Vehicle Braking Performance Testing

The braking performance of the car directly affects the driving of the car. The safety of parking is an important factor for the safe driving of the car, so it is also an important content of the car inspection.

According to the latest national standard GB18565-2001 "Comprehensive Performance Requirements and Inspection Methods for Commercial Vehicles", the braking performance can be tested by bench test or road test.

[-]. Evaluation parameters of automobile braking performance

Automobile braking is mainly evaluated by the following three aspects:

① Braking efficiency (including braking force, braking deceleration, braking distance, braking time).

②Consistency of braking performance (including heat decay resistance and water decay resistance).

③ Directional stability during braking (braking deviation, braking sideslip).

1. Braking efficiency
Braking efficiency refers to the ability of a car to brake at a certain initial speed until it stops on a good road surface.Braking efficiency is the most basic evaluation index of automobile braking performance.It mainly includes braking force, braking deceleration, braking distance and braking time.

(1) Braking force

The external force required to stop a running car is provided by the ground in contact with it (except for air resistance). This external force is called the ground braking force. The ground braking force depends on the friction of two friction pairs: one is the friction between the brake friction pairs Force (that is, the braking force of the brake; the other is the friction force (adhesion force) between the tire and the ground.

The ground braking force of a car depends first on the braking force of the brakes, but at the same time it is limited by the ground attachment conditions.Sufficient ground braking force can only be obtained when the car has sufficient brake braking force and good ground adhesion conditions.

(2) Braking deceleration
Braking deceleration is related to brake braking force and ground adhesion.

When testing vehicles, the average deceleration or maximum deceleration is usually used to evaluate the braking performance. Our country uses the fully issued average deceleration MFDD (MeanFullyDevelopmentDeceleration).

(3) Braking distance
The braking distance is directly related to the driving safety of the car. It refers to the distance traveled by the car from the time the driver steps on the brake pedal to the stop of the car. It is related to many factors such as pedal force, attachment conditions, load, and vehicle speed.Different models have very different specific requirements for this braking performance index.

(End of this chapter)