① Introduction
The brake caliper assembly mainly consists of brake disc, brake caliper, friction plate and other parts. The function of the brake caliper is to convert the hydraulic pressure of the brake master cylinder into the clamping force of the friction plate on the brake disc, so that The vehicle decelerates to a stop.
②. Investigation of friction lining wear status
A certain model was undergoing a durable road test at the Yancheng Proving Ground in Jiangsu. At 25,000 kilometers, it was found that the friction plate of the left rear caliper was worn to the limit, accompanied by scratches on the brake disc. After replacing the friction plate, the road test continued. The friction plate of the left rear caliper is abnormally worn. See Figure 1 for the wear picture of the friction plate. In response to this abnormal problem, the researchers conducted an on-site investigation of the actual vehicle problem. Before dismantling the vehicle, the stroke margin of the cable, the gap between the pull arm and the limit screw, and the dragging moment were measured. The test results are shown in Table 1. From the data in the table, it can be determined that the drag torque of the left rear brake caliper does not meet the standard requirements and the drag torque of the left and right calipers is inconsistent, which is the cause of abnormal wear of the friction plate.
Table 1 Measurement results of rear brake caliper drag torque
Figure 1 Schematic diagram of the wear of the left rear friction plate
③Cause analysis of friction plate eccentric wear
The brake caliper mechanism is complex, including calipers, brake discs, friction plates, hub bearings, parking mechanisms and other parts. Failure or abnormality of any component may cause abnormal wear of the friction plate. Therefore, it is necessary to analyze the impact of the above components one by one. At the same time, the adjustment process of the parking cable also has an impact on the eccentric wear of the friction plate, which needs to be studied simultaneously. This paper analyzes the structure of the components and the adjustment process of the parking cable.
3.1 Abnormal parts such as brake calipers
After the actual vehicle inspection, the researchers in this paper disassembled the rear brake calipers for inspection, and the inspection results are shown in Table 2. From the test data, it can be analyzed that the basic performance of the parts related to the drag torque deviation of the assembly meets the design requirements, and the problem of eccentric wear of the friction plate caused by product consistency can be preliminarily eliminated.
3.2 Improper adjustment of parking cable technology
If the process of parking cable is not adjusted properly, the caliper self-adjusting mechanism may be over-adjusted. Because the initial clearance between the left and right caliper friction plates and the brake disc is inconsistent, over-adjustment of the clearance will cause inconsistent adjustment of the clearance on both sides and cannot be adjusted back. As a result, one side of the caliper friction plate drags the brake disc, causing the friction plate to wear out in advance. After the actual vehicle inspection, the problems related to the abnormality of the parking cable are as follows: ① The balance weight is tilted, ② The distance between the left and right caliper arms and the limit bolt is inconsistent. See Table 2 for statistics on differences. According to experience, this problem is related to the adjustment process of the parking cable.
Table 2 Basic performance test results of product parts and components
④. Improper adjustment of the parking cable leads to the mechanism of eccentric wear of the friction plate
4.1 The principle of caliper parking
The driver pulls up the parking handle to drive the cable to generate displacement. The displacement of the cable causes the caliper pull arm to rotate, and the steel ball sleeve screw produces axial displacement, thereby pushing the self-adjusting screw sleeve, piston, friction plate and brake disc to generate parking force. . In order to facilitate the assembly of the production line, the gap between the friction plate and the brake disc will be kept between 0.5-1.0mm when the caliper assembly is assembled (Figure 2).
figure 2
1 Pull arm; 2 Brake caliper; 3 Control shaft; 4 Screw; 5 Regulator; 6 Piston; 7 Friction plate
4.2 Adjustment process of parking cable
According to the instructions provided by the base, the adjustment process of the parking cable is as follows:
① Pull the parking handle to the 8th tooth, and operate 6 times in total;
② Pre-tighten the cable nut with a torque wrench. parking force.
Due to the inconsistency of the initial gap between the left and right caliper friction plates and the brake disc, when the parking handle is pulled, the angle at which the parking cable drives the left and right caliper arms will be different. The strokes are all smaller than the side with a large disc gap. Although after repeated operations, the self-adjusting mechanism will be activated to reduce the disc gap, but the disadvantage of this adjustment process is that it cannot eliminate the inconsistency of the left and right gaps. The intuitive performance is that the balance weight is tilted, and the self-adjusting mechanism on one side is over-adjusted, resulting in a large drag torque. The corresponding measured data of the faulty vehicle also shows that the partial friction mechanism of the friction plate is caused by the improper adjustment process of the parking cable.
Table 3 The actual measurement results of the caliper pull arm and the position of the limit bolt
⑤Improvement measures
The above analysis determined that the improper adjustment process of the parking cable caused the gap between the left and right discs to be inconsistent after the adjustment of the parking cable, and the over-adjustment of the gap on one side caused the drag torque to be too large, resulting in abnormal wear of the friction plate on one side. In order to ensure the same disc gap on both sides, it is necessary to use the same force to make the caliper self-adjusting mechanism work. The best choice for this force is the brake fluid pressure. The oil pressure on the left and right sides is output through the master cylinder. In the caliper piston, it drives the deformation of the rectangular sealing ring to automatically adjust the disc clearance. To achieve the purpose of consistent gaps on both sides. Therefore, in view of the problem of the cable process adjustment, the process improvement is carried out:
① After the brake fluid is filled, pre-tighten the brake cable adjustment nut;
② Repeatedly step on the brake pedal, the number of times should reach 10;
③ Pull the parking When the handle reaches the 8th tooth, tighten the adjusting nut with a torque wrench.
When the torque reaches 1.5N.m, the adjustment is completed. Through this method, the parking cable of the Yancheng test vehicle was adjusted. After the subsequent road test of the real vehicle, there was no partial friction of the friction plate, and there was no abnormality in the positions of the balance weight, pull arm and limit bolt. Prove that the measure is effective.
⑥ Summary
Partial friction of the friction plate will lead to insufficient parking force of the vehicle, making it impossible to park under the standard requirements, which may easily cause problems such as slippery slopes, premature wear, and abnormal noise. If this problem occurs in the market, customers will complain a lot. Prevention needs to be done. This paper analyzes the parking principle of the brake caliper mechanism and the adjustment process of the cable, summarizes the shortcomings of the cable adjustment process, and makes improvements to completely solve the problem.