The unit urgently sent the author to drive a Japanese Mitsubishi Jeep from Duanzhou District of Zhaoqing City on a business trip to Guangzhou, on the way back.

First, the cause analysis of the accident:

There are many factors that cause automobile braking deviation. The impact of human factors, road conditions and environmental changes, as well as the impact of brake system failure factors or changes in vehicle geometry. To sum up, there are mainly:

(A) the impact of human factors

For people with rich driving experience, when encountering an emergency, they can basically make a correct response calmly and quickly to avoid this disaster as much as possible. If you are not skilled in driving, you will be in danger. As a driver, you must clearly understand the driving performance and braking performance of the car, but you must also master the speed; Know that overload or light load is going on; What is the road condition; Also pay attention to the changes in the weather; Whether people and animals are walking on the road.

If you hit the direction, then brake urgently; Or when braking in an emergency, the accelerator pedal is mistakenly used as a brake pedal, resulting in the car losing control; Or when a large car approaches a small car and overtakes it at high speed, the small car will brake, and the small car will slide to the side of the large car under the influence of airflow. These factors will pose a threat to the driver's driving safety, and it is easy for the vehicle to stop due to excessive speed and operational errors, which will easily lead to serious traffic accidents.

(B) the impact of road conditions

The current traffic situation is complex and changeable, which is influenced by many factors. Asphalt pavement is prone to unevenness because it is softened by sunlight and affected by wheel pressure for a long time. Cement pavement, which is used for a long time, is prone to crack subsidence and inclination; When braking, the friction between each wheel and the ground is bound to be different, or a lateral force will be generated, which will cause the vehicle to slip and run off. When the car is driving on a gravel road, or on an inclined, slippery, uphill, downhill or curved road, it is also easily affected by the lateral force and centrifugal force of the center of gravity deviation, which leads to the car braking and running deviation.

The influence of weather change

The sudden change of weather has also brought difficulties to the driving of seat belts. On rainy and snowy days, the road surface is slippery. There are water, grease, silt, sand, snow, thin ice or small sundries on the road surface, which will form a layer of friction medium between the brake wheel and the ground, which will reduce the friction between the brake wheel and the ground when the car brakes, and it is easy to cause braking deviation; When there is windy weather, give a lateral force to the moving car; It is also easy to cause side slip and deviation when braking.

On the day of the incident, the weather was clear and windless, and there was no obvious depression and inclination on the cement pavement where the car was driving, only a little sand, so the brake marks were not obvious. Due to the timely braking, although the children crossing the road are avoided, the phenomenon of braking deviation causes the vehicle to slide into the left lane, which is extremely dangerous. Excluding these factors, it should be reasonable that the car itself has problems. The vehicle should be overhauled to find out the real cause of the accident.

Second, the solution to the problem:

(a), the brake system inspection

Whether the technical performance of automobile driving is brought into full play is directly related to the braking performance of automobile, especially the safety of automobile driving depends on the working reliability of automobile braking system to a great extent. In fact, due to the hidden danger of the brake system, it is common for the car to slip and run off when braking, so we first made a comprehensive and serious inspection of the brake system.

The braking system of this car belongs to the conventional braking system (without ABS system), which is mainly composed of main brake cylinder and brake booster, front disc brake cylinder, rear drum brake cylinder and related pipelines. If there is moisture and air in the braking system, or the brake master cylinder, brake booster and brake cylinder are worn, it will cause braking failure and deviation.

Check the brake system pipeline first, and no signs of oil leakage are found. The braking stroke of the pedal (the standard value is 186 ~ 19 1 mm) and the gap between the brake pedal and the floor (the standard value is 100mm or more) are basically within the normal range. Check the brake booster in three steps: First, the engine stops after running for 1 ~ 2 minutes. If the brake pedal is fully depressed for the first time, and then gradually rises several times, it is good; Secondly, when the engine is turned off, step on the brake pedal several times with the same foot force, and then step on the brake pedal to start the engine, and the pedal moves down slightly, indicating good; Third, start the engine, step on the brake pedal, turn off the engine, keep the pedal for 30 seconds, and the pedal height remains unchanged, indicating that the brake booster has good performance. Otherwise, the brake booster is damaged, which will also affect the braking effect. Press and hold the brake pedal for a period of time, and the brake pedal will not sink, indicating that there is no problem with the brake master cylinder.

Then check the front disc brake cylinder and the rear drum brake cylinder. First, remove the tire and brake drum, and check whether there are signs of oil leakage in the front disc brake cylinder and the rear drum brake cylinder. However, it is found that the piston of the right front disc brake cylinder is inflexible. Remove the right disc brake, remove the piston dust cover, and press out the brake piston with a compressed air pipe. It is found that there are rust and impurities in the brake fluid in the piston, which is caused by the oxidation of water in the brake system, which makes the piston of the brake cylinder stuck. Then thoroughly clean the brakes; The rear drum brake cylinder has also been thoroughly cleaned and maintained; The front brake friction plate is worn, please replace it. The thickness of the rear brake shoe is ok. It is understood that the car has been used for more than two years and the brake fluid has not been replaced. Failure to meet the maintenance technical requirements of changing the brake fluid once a year will deteriorate the brake fluid, accelerate the wear of the brake cylinder and bring hidden dangers to safe driving. After modification and adjustment, for the sake of safety, replace the brake fluid of the whole vehicle, completely eliminate the air in the braking system, and the braking force detected by the brake instrument meets the standard requirements. After many road tests, there is still a phenomenon of leaning to the left. Why? We have to check other systems.

(2) Inspection of the geometric structure of the automobile.

1) suspension system inspection

Automobile suspension system is the basic component of automobile chassis. It supports the weight of the vehicle and ensures the normal running of the vehicle. At the same time, it not only transmits traction, but also bears braking force, impact force from the road surface and centrifugal force generated when the car turns. The problem of automobile suspension system will affect the center of gravity deviation during braking, resulting in braking sideslip.

The front suspension belongs to double wishbone independent suspension, its elastic element is torsion bar spring, and the shock absorber is double-acting cylinder shock absorber. The rear suspension is dependent, and the elastic element is leaf spring. Both front and rear suspensions are equipped with lateral stabilizer bars, which produce resistance when the vehicle rolls, reduce the inclination angle of the vehicle body and improve cornering passability.

If the suspension torsion bar spring is used for a long time, it is easy to produce fatigue deformation, reduce its elasticity and make the vehicle unbalanced; The front upper and lower suspension arms are impacted and deformed by external force; Buffer rubber is worn and loose, or cracked, displaced or loose; Excessive wheelbase deviation of front and rear axles, fatigue deformation of front and rear axles, frame deformation and shock absorber failure; It will make the center of gravity of the car deviate from the original standard and produce lateral force during the movement; If the leaf spring of rear suspension is used for a long time, it is easy to produce fatigue deformation, reduce its elasticity and make the vehicle unbalanced; Or the U-bolt of the steel plate pin and the steel plate spring seat is broken, displaced, worn or loosened; When the car is driving normally, the direction is deviated when braking. After a detailed inspection of the suspension system, no such abnormality was found.

2) Inspection of steering system

The function of the automobile steering system is to change the direction of the automobile and keep the stable state of the automobile driving in a straight line, so as to adapt to the complicated and changeable roads and change the direction of the automobile at any time. The technical condition of automobile steering system has a great influence on the portability of driver's operation and driving safety, so we should check the steering system first.

The steering system of this car belongs to hydraulic power steering system. Through inspection, it is found that the steering wheel clearance is about 15o, which meets the standard requirements. The fixed bracket of the steering gear is installed firmly, and the bearing of the steering gear transmission shaft is not found loose; The clearance between worm wheel and worm of steering gear also meets the basic requirements; The hub bearing is not loose or too tight; Upon inspection, no looseness was found in the upper and lower suspension shaft rubber, the upper and lower suspension ball heads and the front, rear, left and right hub bearings. However, the left tie rod shows signs of collision, and the tie rod is deformed, which will cause the front wheel positioning to change value, leading to the phenomenon of side slip and deviation when the car brakes, so the left tie rod assembly is replaced. The air pressure of the four tires basically meets the standard requirements, but the rear tires are seriously worn. In order to ensure the braking effect, the front and rear tires were replaced with new ones, and the dynamic balance test was carried out.

If the front wheel alignment value does not meet the standard, the toe-in is too large or too small, and the inclination angle of the steering kingpin axis changes, the car will definitely run off. Finally, the front wheel alignment is tested, and it is found that the measured data basically meet the standard requirements (the standard values are: front wheel toe-in 3.5±3.5mm, kingpin camber 14o 52'', kingpin caster 3o 1'), which can prove that the steering system is normal. After many road tests, the results show that the braking performance is good, no deviation phenomenon is found, the direction is smooth and light, and the fault is completely eliminated.

Third, the conclusion:

The quality of the braking system seriously affects the driving safety, and skidding, traffic accidents and even serious car accidents occur from time to time due to braking failure. If the automobile braking system is not maintained for a long time, the braking performance will gradually deteriorate and it will not work normally. Once there is a problem, it will lead to traffic accidents, and the consequences will be unimaginable. Long-term abnormal wear of the brake cylinder of the braking system leads to the phenomenon of sticking and card issuing, which seriously affects the braking effect, easily causes serious traffic accidents and causes unnecessary heavy losses to people's lives and property. A fault phenomenon may be caused by many reasons, so before troubleshooting, it is necessary to comprehensively consider and conduct a comprehensive inspection of the relevant systems of the automobile.

Therefore, as an excellent car driver, you must have good technical quality. While accumulating driving skills and experience, we should strengthen the study of traffic safety regulations and theoretical knowledge of automobile maintenance technology, and also understand the structure, working principle and troubleshooting of the braking system of this vehicle. So as to understand the driving performance and braking performance of the vehicle, and carry out regular maintenance and repair of the vehicle in strict accordance with the requirements of the automobile maintenance manual. Before leaving the car, carry out routine safety inspection on the vehicle to ensure that it is safe and reliable when driving.