Original Lao Hou unpacking the car I want to share
The performance is undoubtedly one of the most important active safety features, and its function is to slow down according to the driver’s will until it stops. According to different functions, it can be divided into driving, parking and auxiliary (emergency); according to different structural types, it can be divided into drum and disc types; according to different media, it can be divided into hydraulic and pneumatic types. Generally, hydraulic disc type is used in small, while pneumatic drum type is generally used in medium and large and passenger cars. We can’t simply use good or bad to evaluate them. Although hydraulic disc type has fast response and good heat dissipation, its force is not as large as that of pneumatic drum type, so air pressure is still used more on heavy loads or passenger cars.
The three parameters for evaluating the pros and cons of a car are:, the constancy of, and the directional stability of time. For ordinary people, it is generally used to measure the performance. But for medium and large or passenger cars, the constancy and the directional stability of time are also very important indicators. The most common unqualified items encountered by many cars during annual inspections are unevenness, which actually refers to the imbalance of forces on both sides, and the phenomenon of deviation will occur at time. The whole process is as follows, which can be divided into six stages: driver reaction time, mechanism reaction time, force growth time, device action time, duration, and release time.
The current "Motor Vehicle Safety Technical Inspection Items and Methods" is the national mandatory standard GB21861-2014 that was implemented in 2015. Among them, there are very clear inspection items and inspection standards for the performance of motor vehicles. The inspection items are divided into no-load and parking. For models with more than three axles, the loading is also inspected. The reaction time, constancy, and blocking force are not tested. The inspection instrument is generally a drum-type or skateboard-type force detector. The inspection standards are: single-axis force and not less than 60% of the axle load, the whole vehicle force and not less than 60%, the parking force shall not be less than 20%, the left and right force imbalance of one axis (steering shaft) shall not exceed 20%, and the left and right force imbalance of two axes and three axes (driving and load-bearing axes) shall not exceed 24%. Here are some examples to illustrate the meaning of these parameters.
1. Axle load: also called axle load, which is the load on the axle, which can be understood as the weight borne on the axle. Add the axle load of all axles together. For example, the axle load of one axle is 2829kg, and the axle load of two axles is 6244kg, then the axle load of this car is 2829 + 6244 = 9073kg.
2. Force and force sum: The force here refers to the maximum force generated by each process, and this maximum force is not necessarily generated at the same time. The ratio of the maximum force of the left and right on each axle to the axle load is the axle force sum, and the ratio of all the maximum forces together is the total force sum. They must meet relevant standards. Force sum is also called rate.
For example, in a certain car, the revolver force of one axle is 1017kgf, the right wheel force of one axle is 960kgf, the two-axle revolver force is 1698kgf, and the right wheel force of two axles is 1604kgf. Calculate the force and:
The force sum of one axis: (1017 + 960)/2829 = 69% > 60%, qualified;
The force sum of the two axes: (1698 + 1604)/6244 = 53% < 60%, unqualified;
Total vehicle power: (1017 + 960 + 1698 + 1604)/(2829 + 6244) = 58%, unqualified.
Because the car’s two-axis force and the whole vehicle force are unqualified, the car’s force is determined to be unqualified. It can be seen from the test data that its unqualified force is mainly caused by the small force of the two axles, so we need to focus on repairing the pipeline and device of the two axles. First check whether there are leaks in the pipeline of the two axles. If there are any leaks, we need to deal with them in time. Then check whether the pressure leading to the two axles is normal. If the pressure is obviously too low, it may be a fault or the air pressure of the two-axis air reservoir is insufficient, which should be dealt with separately. If the pipeline fault is dealt with and the force is still too small, the disassembler needs to be disassembled. Generally speaking, it is caused by the wear of the basin and the friction area between the two. It needs to be replaced and the basin is
3. Parking force and parking force sum: Parking force refers to the force generated by pulling up the hand, and parking force sum refers to the sum of the maximum parking force of the left and right wheels. According to relevant standards, the parking force sum shall not be less than 20%.
For example, for a car, the left rear wheel parking force is 1110kgf, the right rear wheel parking force is 949kgf, which is 11514kg, then the parking force of the car is:
(1110 + 949)/11514 = 18% < 20%, unqualified.
The current medium and large and passenger cars generally use the strong pump as a parking, and the parking force is also generated by the two rear wheels. Therefore, the unqualified parking force is generally caused by the unqualified force of the two rear wheels. Generally, the vehicle devices of the two rear wheels need to be overhauled. In addition, the internal fracture of the strong pump, the failure of the hand switch, and the failure of the hand relay valve will also cause the strong pump to fail to fully eject, resulting in too little force. In this case, the relevant pipelines and valves need to be overhauled. Some models use central parking. If the force fails, it is generally caused by the poor contact surface with the basin and needs to be disassembled and repaired.
4. Unbalance rate: The so-called force imbalance rate is also called the left and right force imbalance, which refers to the maximum value of the left and right wheel force difference during the force growth process, and the ratio of the maximum force of the left and right wheels of the shaft measured during the whole process. Generally, it is required that the left and right force imbalance of one axis (steering shaft) shall not exceed 20%, and the left and right force imbalance of two axes and three axes (driving and load-bearing axes) shall not exceed 24%.
For example, the revolver force of one axle of a car is 1312kgf, the right wheel force of one axle is 858kgf, the two axle revolver force is 2360kgf, and the right wheel force of two axles is 2505kgf. Calculations show that the unbalance rate of one axle of the car is 35.6%, which is unqualified; the unbalance rate of two axles is 17.3%, which is qualified.
It is important to note that the maximum force difference does not occur when the maximum force appears at the same time, but occurs during the process of force rise, so its calculation is not simple addition, subtraction, multiplication and division, but is automatically calculated by the detection equipment.
The main reason for the imbalance of the left and right forces is that the difference between the left and right forces is too large or the reaction time is not synchronized. For example, if one side of the device is new and the other side is old, the forces of the two may be very different, and the imbalance rate will be unqualified. There is also a difference in the performance of the left and right pump, resulting in a large difference in the reaction time. In addition, the rust of the shoe shaft can also lead to an imbalance of the left and right forces.
In addition, for multi-axle, it is also necessary to detect its loading rate and unbalance rate. Its detection method is to apply a load to the detected axle to simulate the force under actual driving conditions. It can more accurately detect the force and better fit the actual driving state. Generally, only semi-trailers or four-axle bicycles are detected, and only the second and third bridges are detected. The specific parameters are that the loading rate of the second bridge is greater than 50%, and the unbalance rate is less than 10%; the loading rate of the third bridge is greater than 50%, and the unbalance rate is less than 30%. The reasons for its failure are similar to the above, all due to insufficient force.
Overall, it is very difficult to pass the force test of medium and large or passenger cars at one time. This is mainly because many times, the test line is a quantitative test, and the specific force of each one will be tested, and then whether it is qualified according to the relevant standards is determined. When we drive the vehicle ourselves, it is more of a perceptual cognition. Many times we feel that the performance is good, but as soon as we get on the test line, it fails. Some people do four-wheel maintenance before the inspection, and replace the basin with a new one, but it still fails. This is mainly because the newly replaced basin has burrs on the surface, and the contact surface is not good at first. It takes some time to achieve the best results (more than 75% of the contact surface).
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