abstract
Firstly, this paper introduces the phenomenon, causes, diagnosis, troubleshooting and system maintenance of Shanghai GM's braking system. This paper also introduces the general series of automobile braking system-ABS, including the composition of ABS, system maintenance, reading and diagnosis of fault codes and system maintenance. Then, the importance of fault diagnosis and maintenance of braking system is introduced by briefly introducing the diagnosis case of ABS system.
Keywords: ABS fault diagnosis, troubleshooting and troubleshooting of GM brake system
Diagnosis and maintenance of Shanghai GM series brake system
abstract
Firstly, the fault, fault reason, fault diagnosis, fault elimination and system maintenance of Shanghai GM brake system are introduced. This paper also introduces the general series of automobile braking system-ABS, including the composition of ABS, system maintenance, fault code reading and diagnosis maintenance; Then the case of ABS system diagnosis is summarized, which leads to the importance of brake system fault diagnosis and maintenance.
Keywords: general motors ABS brake system fault diagnosis and troubleshooting
catalogue
Abstract ... 1
Abstract 2
Chapter 1 Overview of Automobile Braking System
1. 1 concept of braking system ........................................................ 1
1. 1 concept of braking system ....................................................................................... 1
1. 1.2 Function of braking system ..................................... 1
1. 1.3 composition of braking system .......................................... 1
Chapter II Fault Diagnosis of Shanghai Universal Brake System
2. 1 Brake system test
2. 1. 1 brake system test
2. 1.2 Inspection of brake fluid
2. 1.3 brake hose inspection
2. 1.4 operation of warning light
2. 1.5 Common faults and maintenance of Shanghai GM Buick braking system .........................................................................................................................................................
Chapter III ABS Fault Diagnosis and Maintenance of Shanghai General Brake System
3. 1 Structure and working principle of anti-lock braking system
3. 1. 1 concept of anti-lock braking system
3. 1.2 Composition of anti-lock braking system
3.1.3 Functions of ABS system components
3.2 Case Analysis of ABS Fault Diagnosis and Maintenance of Brake System
conclusion
Reference 8
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The first chapter is an overview of automobile braking system.
1. 1 the concept of braking system
1. 1. 1 the concept of braking system
Brake system is a series of special devices used to make the outside world (mainly the road surface) exert a certain force on some parts of the car (mainly the wheels), so as to brake it to a certain extent.
1. 1.2 Function of braking system
The function of that brake system are: according to the requirement of the driver, the moving car is slowed down or even stop; Make parking stable under various road conditions (including on ramps); Keep the speed of the car downhill stable.
Only the external force acting on the car in the opposite direction to the direction of the car can make the car brake, and the magnitude of these external forces is random and uncontrollable, so a series of special devices must be installed on the car to realize the above functions.
1. 1.3 composition of braking system
Includes application system, brake light system, hydraulic system and wheel braking system.
The application system is mainly composed of brake pedal, brake connecting rod and brake booster.
Brake light system is mainly composed of brake switch, wire and brake light.
The hydraulic system is mainly composed of brake master cylinder, hydraulic valve, combined valve, proportional valve and metering valve.
The wheel brake is mainly composed of a rotating part, a fixed part and an adjusting mechanism, wherein the rotating part is a brake drum; The fixed part comprises a brake shoe and a brake bottom plate; The adjusting mechanism consists of eccentric support pin and adjusting cam, which is used to adjust the gap between brake shoe and brake drum.
Chapter II Fault Diagnosis of Shanghai General Brake System
2. 1 Brake system test
2. 1. 1 brake system test
The brake must be tested on a dry, clean and flat road. If the road surface is wet or unclean, the adhesion performance of each tire is different, so the braking performance tested is not true. The central convex pavement is also not conducive to testing. Because of the uneven distribution of gravity, wheels are easy to bounce.
Test the brakes at different speeds, lightly and heavily; But I feel that I can't lock the brakes and let the tires slip on the road. Just because the brakes are locked and the tires slip on the road doesn't mean that the braking efficiency is high. Press the brake pedal again, but keep the wheels turning, which is shorter than stopping braking. Step on the brake pedal again, but the friction between the tire and the road surface is greater than the tire slipping when the wheel rotates. Due to the high deceleration of stepping on the brake pedal again, I feel that the vehicle decelerates quickly. The external conditions that affect the braking performance are: 1) Different contact area and adhesion between the tire and the road surface will lead to uneven braking. The tire pressure must be the same, and the ratio of left and right tread depth must be similar. 2) Uneven vehicle load also affects the braking performance. Heavy-duty wheels need more braking force than other wheels. 3) Dislocation of wheels, especially when camber angle and main inclination angle are too large, will lead to braking deviation.
2. 1.2 brake fluid inspection
Check whether the brake fluid leaks, the engine is idling, put the gear lever in neutral, and then press the pedal with constant foot force. If the pedal drops gradually under the condition of constant foot force, it indicates that the hydraulic system may leak. Confirm the suspected leakage site by visual inspection.
Check the master cylinder liquid level. Although the normal wear fluid of the lining will cause the liquid level of the liquid storage tank to drop slightly, if the liquid level is too low, it indicates that the system has leaked. Internal leakage or external leakage of hydraulic system. Check the master cylinder according to the following procedure. In addition, minor system leaks can also pass the test. If the liquid level is normal, check the length of the vacuum booster push rod. If the length of the push rod is found to be incorrect, adjust and replace the push rod. Check the master cylinder as follows: 1) Check whether the casting shell of the master cylinder is cracked or whether there is brake fluid leakage around the master cylinder. As long as there is a little brake fluid, it means there is leakage and the humidity is normal. 2) Check whether the pedal connecting rod is stuck and whether the push rod length is abnormal. If these two parts are normal, remove the master cylinder and check whether the master cylinder or piston seal is extended or expanded. If the seal expands, it is suspected that the brake fluid is unqualified or contaminated. If brake fluid pollution is found, all parts must be removed and cleaned, and all rubber parts must be replaced. All pipe fittings must also be cleaned.
2. 1.3 brake hose inspection
Hydraulic brake hoses should be inspected at least twice a year. Check the brake hose cover for damage, cracking, wear, leakage or expansion. Check whether the laying and installation of hoses are normal. Brake hoses that rub against suspension components will soon wear out and eventually fail. You need a flashlight and a lens to check. If any of the above conditions are observed on the brake hose, the hose must be adjusted or replaced.
2. 1.4 operation of warning light
The braking system uses the "brake" warning light in the instrument panel cluster. When the ignition switch is in the "start" position, the "brake" warning light should be on, and when the ignition switch is returned to the "run" position, the warning light will be off. When the parking brake is applied, the following conditions will illuminate the "Brake" light: 1. As long as the parking brake is applied and the ignition switch is in the on position, the warning light will light up. 2) When the brake fluid level is too low. If the brake fluid level in the master cylinder is too low, the "Brake" light will light up. 3) When 3)EBD system function fails. When the function of EBD system fails, the brake lamp lights up.
2. 1.5 Common faults and maintenance of Shanghai GM Buick braking system
1) Failure phenomenon: When the brake pedal is stepped, the pedal does not rise and there is no resistance; Judge the reason: check whether the brake fluid is missing; Whether the brake cylinder, pipeline and joint leak oil; Whether the master cylinder and slave cylinder parts are damaged. 2) Failure phenomenon: the braking effect is not good when the brake pedal is pressed to the bottom; Continuous braking, the effect has not improved, and the pedal is gradually raised; Cause: There is gas in the braking system. 3) Failure phenomenon: after continuous braking, the pedal returns to a higher position and the braking effect is improved; Cause: The clearance between friction plate and brake drum is too large. 4) Failure phenomenon: the pedal position rises when the brake is continuously applied, and there is a sinking feeling; Judge the cause: oil leakage. 5) Failure phenomenon: the pedal position is very low; One more step, the position can't be raised, and it feels hard; Cause: The master cylinder is blocked.
Chapter III ABS Fault Diagnosis and Maintenance of Shanghai General Brake System
3. 1 Structure and working principle of anti-lock braking system
3. 1. 1 the concept of anti-lock braking system
ABS (Anti-lock Brake System) is a kind of automobile safety control system, which has the advantages of anti-skid and anti-lock. Modern cars are equipped with a large number of anti-lock braking systems. ABS not only has the braking function of ordinary braking system, but also can prevent the wheel from locking, so that the car can still turn under braking conditions, ensure the stability of the braking direction of the car and prevent side slip and deviation. It is the most advanced braking device with the best braking effect in the car at present.
3. 1.2 Composition of anti-lock braking system
ABS system is mainly composed of sensors, electronic control devices and actuators.
3.1.3 Functions of ABS system components
Vehicle speed sensor: detects vehicle speed and provides vehicle speed signal to ECU for slip rate control mode.
Wheel speed sensor: detects wheel speed and provides wheel speed signal to ECU. Various control methods are adopted.
Deceleration sensor: it detects the deceleration of the car when braking and identifies whether it is a slippery road such as ice and snow. Only used in four-wheel drive control system.
Brake pressure regulator: receives the instruction of ECU, and increases, maintains and decreases the pressure of the brake system through the action of solenoid valve.
Hydraulic pump: under the control of ECU, the control oil pressure is established in the control oil circuit of variable displacement brake pressure regulator; In the process of adjusting the pressure of the circulating brake pressure regulator, the brake fluid flowing out of the wheel cylinder is pumped back to the master cylinder through the accumulator to prevent the brake pedal stroke from changing when ABS works.
ABS warning light: When ABS fails, EUC will control it to light up and give an alarm to the driver, and ECU will control it to flash and display the fault code.
ECU: It receives signals from sensors such as vehicle speed, wheel speed and deceleration, calculates vehicle speed, wheel speed, slip rate, wheel deceleration and acceleration, analyzes, discriminates and amplifies these signals, and the output stage outputs control instructions to control the work of each actuator.
3.2 ABS brake system fault diagnosis and maintenance case analysis
3.2. 1 Fault symptom: A Sail SLX-AT sedan produced in 2003 with a mileage of 26000km. According to the owner, when braking, you need to step on the brake pedal to a very low position to have braking force.
Overhaul process: Let the engine idle in place, and slowly press the brake pedal, and the pedal will drop continuously. Press the brake pedal quickly, and you will feel the braking force when the pedal is in a lower position. If the pedal force is continuously applied, the brake pedal will drop and the pedal will feel soft.
Conduct a road test. When the vehicle speed is about 30 km/h, slowly step on the brake pedal, and the vehicle still moves forward, obviously feeling that the braking effect is not good. If you press the brake pedal quickly, the vehicle can stop, but the position of the brake pedal is low. In order to eliminate the possibility of air in the brake system, the brake system was deflated, but no bubbles were found, and the brake pedal could not return after deflation, indicating that the brake master cylinder could not establish oil pressure.
Troubleshooting: Carry out road test and troubleshooting after replacing the brake master cylinder.
Review and summary: The brake master cylinder is the core component of the braking system, which compresses the brake fluid into the brake cylinders of each wheel for braking. According to the author's maintenance experience, the most common fault of the brake master cylinder is the poor sealing of the piston (commonly known as the cup), which leads to the failure to establish or release the brake pressure. There are two common fault phenomena when the brake master cylinder releases pressure.
(1) Press the brake pedal slowly, the brake pedal will drop to the lowest position, and the brake oil pressure cannot be established. The performance of the road test is: when driving at low speed, you can brake by stepping on the brake pedal quickly, but you won't brake by stepping on the brake pedal slowly.
(2) When the brake system is deflated, the brake pedal can't return after being put down, and the oil pressure can't be established after being pressed repeatedly, so the brake fluid can't be released or is released very little.
When the master cylinder breaks down, besides the master cylinder's own problems, brake fluid is also an important factor that cannot be ignored. Brake fluid has different brands and grades, and even the same model will use different types of brake fluid due to production batches and technical improvements. If the brake fluid is mixed or deteriorated, the brake master cylinder will be damaged quickly, or gas will be generated in the brake system. It should be noted that the bleeder valve on the brake cylinder should be located at the highest position of the cylinder to ensure that the gas can be discharged when bleeding. Some models can also install the left and right auxiliary cylinders upside down, but at this time, the exhaust valve is at the lowest position of the auxiliary cylinder, so it can't release gas and can only drain oil.
3.2.2 Fault phenomenon: A Buick GL sedan produced in 2004 with a mileage of 32000km. It is normal for the car to step on the brake pedal in situ, and it is difficult to drive after driving for a while.
Maintenance process: when lifting the vehicle, it was found that all four wheels were delayed due to braking, and it was almost impossible to turn the wheels by hand. Check whether the brake pedal position is abnormal, and whether there is any abnormality such as seizure. Because it is very unlikely that the four brake cylinders will be misaligned at the same time, the author thinks that the fault point should be the brake master cylinder or the brake booster.
Loosen the connecting bolt between the brake master cylinder and the booster, and all four wheels can rotate, indicating that the fault lies in the booster, not the braking delay caused by poor piston return in the master cylinder.
Troubleshooting: Replace the vacuum booster and troubleshoot.
3.2.3 Fault phenomenon: A Sail SRV-AT sedan produced in 2004 has a mileage of 56000km, and the owner complains that the braking distance of the vehicle is too long.
Maintenance process: after debugging, the maintenance personnel found that the braking distance was obviously too long and felt that the braking force was insufficient. Bleed the brake system and the fault still exists. Look at the brake disc of this car, it has been modified, and the brake disc has been replaced by a large-size brake disc with a vent hole. Switching back to the original brake disc road test, the braking performance has not been significantly improved. When the brake friction plate was removed, it was found that there were only a few contact marks on the friction plate.
Troubleshooting: Remove the brake friction plate and carefully polish the convex points with fine sandpaper to make the brake friction plate run in quickly. After the vehicle was used for a period of time, the braking performance was obviously improved, and the fault was finally eliminated.
Review and summary: Brake friction plate and brake disc are the direct components that generate braking force, and their common faults include body shaking caused by warping of brake disc during braking, abnormal noise of brake friction plate, poor contact between brake friction plate and brake disc, and reduced braking force. In the actual maintenance work, it is important to check whether the friction plates and brake discs have been modified and whether the accessories are qualified.
3.2.4 Failure phenomenon: A Excelle 1.6 car produced in 2009 has a mileage of 58000km, and the brake pads on the right front wheel are seriously worn.
Maintenance process: the car comes to the service station for maintenance. During the test run, lightly step on the brake, and the right front wheel will make a grinding sound, then prop up the car and unload the two front wheels. It is found that the right front brake pad has been worn out, the brake disc has a groove, and the left front wheel brake pad has been worn out by half. Judging from this, it may be that the right front wheel brake has stopped, or there is a problem with the quality of the brake pads. According to the computer files of the car, the brake pads were replaced during the maintenance of 45,000 kilometers, and the quality of the brake pads was fine, so the serious wear of the brake pads may be caused by the strike.
Braking force refers to the phenomenon that the brakes are ineffective, the tires can't turn, and the brake pads are close to the brake disc. This phenomenon is generally caused by the poor oil return of the brake master cylinder and the rusty piston inside the brake master cylinder being stuck. According to the above two conditions, the oil pressure gauge is used to check, which proves that the oil return of the brake master cylinder is normal and the pump piston moves normally when the brake is applied. Later, the old brake discs and discs were reinstalled. After several brake inspections, it is found that there is a return pin on the brake cylinder bracket, which walks inward when braking and does not move when lifting the foot. Remove the brake cylinder bracket, pull out the return pin, and find that the return pin is bent. It turned out that the front brake cylinder bracket was deformed, resulting in serious wear of brake pads. Replace the brake cylinder bracket and troubleshoot.
Cause of failure: After asking the owner, the car had an accident six months ago. The right front wheel hit the pier and the hub was damaged. At that time, the insurance company only changed tires, wheels and lower arms. According to the owner, the wheel hub collided with the brake cylinder when it was deformed, which caused the return pin of the brake bracket to bend. When the damage was determined, the adjuster did not see it.