Automobile inspection and maintenance specialty

Fault analysis and maintenance technology of automobile automatic transmission

Department: Department of Biological and Environmental Engineering.

Student name: Pu Chunlin

Student number: 2006030630 14

Instructor: Li Minhe

Grade: 06 steam inspection

Fault analysis and maintenance technology of automobile automatic transmission

Qiandongnan National Vocational and Technical College, Kaili 556000, Guizhou, Pu Chunlin

Abstract: Transmission is one of the most important components in the automobile transmission system, and its quality is related to whether the automobile can change the driving speed smoothly, whether it can reverse smoothly and realize neutral. This paper mainly studies the structural principle and common faults of automatic transmission, and analyzes and solves them. It has important practical significance for the use and maintenance of automobiles.

Keywords: automatic transmission; Renault landscape automatic transmission; Fault analysis

I. Introduction

With the rapid development of national economy, the output of automobiles has increased year by year, reaching 7.2 million in 2006. There are more and more cars in China, and their models are becoming more and more complicated. Especially with the rapid development of high technology and the wide application of some new technologies and materials in automobiles, it is more difficult to diagnose and eliminate automobile faults. This paper mainly introduces the fault analysis and maintenance methods of automobile transmission. Transmission is an important part of automobile. Without the transmission, the car can't run normally, and it is difficult to shift gears. In the process of using the car, the transmission will inevitably have such and such faults, which will directly affect people's life safety. Nowadays, cars are rapidly entering families, and the degree of privatization of cars has increased. Car failures will affect everyone. It is of great practical significance to analyze and study the phenomena and causes of transmission faults and explore the troubleshooting methods and maintenance skills of transmission faults.

Two. Overview of automobile automatic transmission

As we all know, the torque and speed of the vehicle engine change in a small range, and the complex use conditions require that the driving force and speed of the vehicle wheels can change in a considerable range, so it is necessary to set a transmission in the vehicle power transmission system.

There are generally two forms of automobile transmission, one is a common manual transmission and the other is an automatic transmission.

With the help of ordinary manual gearbox, although the driver can also shift gears as needed, that is, choose the most suitable gear combination to adapt to the specific driving conditions, every shift is inevitably accompanied by the operation of the clutch. Statistics show that under urban driving conditions, trucks need to start and stop 80 ~ 100 times per km, while buses need 400 ~ 500 times. Considering the clutch operation during gear shifting, a bus can work 800 ~ 1000 times per1000 km under urban working conditions. In the case of increasingly busy urban traffic and congested roads, frequent gear shifting is a great burden for car drivers, both mentally and physically. At the same time, it is also an unfavorable factor for road traffic safety.

Because the automatic transmission can automatically shift gears according to the speed of the vehicle and the degree of the driver's stepping on the accelerator pedal, the driver of the automobile is freed from a series of heavy driving operations such as selecting transmission gears, manipulating clutches and implementing gear shifting, thus ensuring the power of the automobile, improving the driving safety and increasing the comfort of driving and riding.

Third, the structure, advantages and disadvantages of automatic transmission

There are three common types of automobile automatic transmission: hydraulic automatic transmission (AT), mechanical continuously variable automatic transmission (CVT) and electronically controlled mechanical automatic transmission (AMT). AT present, AT is the most widely used, and AT has almost become synonymous with automatic transmission.

AT is composed of hydraulic torque converter, hydraulic torque converter, planetary gear and hydraulic control system, and variable speed torque converter is realized by means of hydraulic transmission and gear combination. Among them, hydraulic torque converter is the most important component, which consists of pump wheel, turbine and guide wheel, and has the function of transmitting torque.

Compared with AT, CVT saves complex and bulky gear combination variable speed transmission, but adopts two sets of pulleys for variable speed transmission. The speed is changed by changing the contact radius between the driving wheel and the driven wheel drive belt. Because the gear transmission is cancelled, its transmission ratio can be changed at will, and the speed change is smoother, and there will be no sudden shift feeling.

AMT is a stepped automatic transmission, just like automatic hydraulic transmission (AT). On the basis of ordinary manual transmission, it replaces the separation and engagement of clutch and gear selection and shift of transmission by adding an electric device controlled by microcomputer, thus realizing automatic shift.

(1) Advantages of automatic transmission:

1. The most suitable gear can be automatically selected according to the driving speed and accelerator pedal position;

2. The clutch operation and frequent gear shifting are cancelled, which makes the driving operation simple and labor-saving, and at the same time improves the driving safety;

3. The dynamic load of automobile transmission system is greatly reduced, and the service life of engine, transmission system related parts and tires is greatly improved;

4. When the external load suddenly increases, it can prevent the engine from overloading or flameout, thus protecting the engine and reducing exhaust pollution;

5. Effectively, stably and continuously transmit the torque generated by the engine, start smoothly, reduce vibration and noise, and improve ride comfort.

Compared with ordinary manual transmission, automatic transmission has some disadvantages, such as complex structure, high process requirements and manufacturing cost, and slightly low transmission efficiency, which makes the manufacturing cost of the whole vehicle and the running fuel consumption of the vehicle slightly higher in some situations and occasions, and makes the maintenance more difficult. However, because its advantages far outweigh its disadvantages, automatic transmission is more and more widely used in automobiles.

(B) the shortcomings of automatic transmission

1. Slow response to speed change, not as sensitive as manual shift;

2. Compared with oil consumption, the transmission efficiency is low and the torque range is limited. In recent years, the introduction of electronic control technology has improved this problem;

3. The structure is complex and difficult to repair. The hydraulic oil circulating at high speed in the torque converter will produce high temperature, so the specified high temperature resistant hydraulic oil should be used.

4. If the car can't be started due to insufficient battery, it can't be started by cart or trailer. When hauling the faulty vehicle, the driving wheel must also be off the ground, otherwise it will be damaged.

Four, automatic transmission common fault analysis

(a) The car cannot run.

Symptoms: No matter whether the shift control handle is in reverse gear, forward gear or low-speed forward gear, the car can't run; The car can travel a short distance after starting, but it can't travel after a little preheating.

Reason for failure:

1. The oil pan of automatic transmission is damaged, and all automatic transmission oil leaks;

2. Loosen the connecting rod or zipper between the shift operating handle and the rocker arm of the manual valve, and keep the manual valve in neutral or parking position;

3. The oil inlet screen of the oil pump is blocked;

4. Serious oil leakage in the main oil circuit;

5. The oil pump is damaged.

(2) Troubleshooting of automatic transmission slippage

Symptoms: When the accelerator pedal is pressed during automatic start, the engine speed increases rapidly, but the vehicle speed increases slowly. When the car is stepping on the accelerator to accelerate, the engine speed increases but the speed increases slowly; The car basically runs normally on a flat road, with weak uphill and abnormally high engine speed.

Reason for failure:

1. Automatic transmission oil level is too low;

2. The oil level of the automatic transmission is too high, and a large number of bubbles are generated after being violently stirred by the planetary gear mechanism during operation;

3. Clutch or brake friction plate and brake band are worn or even burned;

4. The oil pump is worn or even the main oil circuit leaks oil, resulting in low oil pressure in the oil circuit;

5. The one-way overrunning clutch slips;

6. The seal ring of clutch or brake piston is damaged, resulting in oil leakage.

(3) Troubleshooting of shift impact of automatic transmission

Failure phenomenon: When the vehicle is automatically started, the vehicle vibrates seriously when it is engaged into reverse gear (R gear) or forward gear (D gear) from parking gear (P gear) or neutral gear (N gear); When the car is driving, the automatic gear upshifts or there is obvious sudden noise in an instant.

Reason for failure:

1. Engine idle speed is too high;

2. Improper adjustment of the throttle zipper or throttle position sensor makes the oil pressure in the main oil circuit too high;

3. The upshift is too late;

4. There is a fault in the pressure adjustment of the main oil circuit, which leads to the high pressure of the main oil circuit;

5. The check valve steel ball is missing, and the shift actuator (clutch or brake) is combined too fast;

6. The shift actuator slips;

7. The oil pressure solenoid valve does not work;

There is something wrong with this computer.

(4) Troubleshooting of automatic transmission upshift too late

Fault phenomenon: When the car is driving, the upshift speed is obviously higher than the standard value, and the engine speed is slightly higher before the upshift. Therefore, it is necessary to adopt the operation method of upshifting the accelerator pedal in advance (that is, release the accelerator pedal for a few seconds and then press it), so that the automatic transmission can move into the high-speed or overdrive gear.

Reason for failure:

1. Improper adjustment of throttle cable or throttle position sensor;

2. The throttle position sensor is damaged;

3. The oil pressure of main oil circuit or throttle valve is too high;

4. Forced downshift switch is short-circuited;

5. There is something wrong with the computer or sensor.

(5) Troubleshooting of Automatic Transmission Failure to Upshift

Fault phenomenon: the automatic gear is always in 1 gear when the car is driving, and it cannot be upgraded to second gear or high gear; When driving, the automatic transmission can shift to second gear, but it cannot shift to third gear or overdrive gear.

Reason for failure:

1. Improper adjustment of throttle cable or throttle position sensor;

2. The speed sensor is faulty;

3. The corresponding brake or clutch is faulty;

4. The shift valve is stuck;

5. The gear switch is faulty.

(6) Troubleshooting of frequent tripping and shutdown.

Fault phenomenon: when the car is driving in the forward gear, even if the accelerator pedal remains stationary, the automatic transmission will often downshift suddenly, and the engine speed will increase abnormally after the downshift, resulting in shift impact.

Reason for failure:

1. The throttle position sensor is faulty;

2. The speed sensor is faulty;

3. The control system circuit is poorly grounded;

4. Poor contact of the shift solenoid valve;

There is something wrong with this computer.

(7) Troubleshooting of automatic transmission that cannot be forced to downshift

Fault phenomenon: When the car is driving in the third gear or overspeed gear, the accelerator pedal suddenly steps to the bottom, and the automatic transmission can't immediately downshift, resulting in weak acceleration of the car.

Reason for failure:

1. Improper adjustment of throttle cable or throttle position sensor;

2. The forced downshift switch is damaged or improperly installed;

3. The forced downshift solenoid valve is damaged or the line is short-circuited or disconnected;

4. The forced downshift control valve in the valve plate is stuck.

(8) Troubleshooting of engine idling and easy flameout after gear shifting.

Symptoms: When the engine is idling, the engine stops when the shift control handle is changed from P or N to R, D, 3rd, 2nd and 1. When driving in forward gear or reverse gear, press the brake pedal and the engine will stop running.

Reason for failure:

1. Engine idle speed is too low;

2. The locking control valve in the valve plate is stuck;

3. The gear switch is faulty;

4. The input shaft speed sensor is faulty.

(9) Troubleshooting of unlocked automatic transmission

Fault phenomenon: The vehicle speed and gear have met the working conditions of the lock-up clutch, but the lock-up clutch still has no locking effect, and the vehicle consumes a lot of fuel.

Reason for failure:

1. Automatic transmission oil temperature sensor is faulty;

2. The throttle position sensor is faulty;

3. The locking solenoid valve fails or the line is short-circuited or disconnected;

4. The locking control valve is faulty;

5. The locking clutch in the hydraulic torque converter is damaged.

(10) Troubleshooting of Engine-free Braking for Automatic Transmission Vehicles

Fault symptom: When the vehicle is running, when the shift control handle is in the forward low position (3 or 2, 1), release the accelerator pedal, and the engine speed drops to idle speed, but the vehicle does not obviously slow down; When the car goes downhill, the shift control handle is in the forward gear, but it cannot produce engine braking effect.

Reason for failure:

1. Improper adjustment of gear switch;

2. Improper adjustment of the shift control handle;

3.2 forced brake slips or is low, and reverse brake slips;

4. The solenoid valve for controlling engine braking is faulty;

5. The valve plate is faulty;

6. The automatic transmission slips;

There is something wrong with this computer.

(1 1) Troubleshooting of Abnormal Sound in Automatic Transmission

Fault phenomenon: the automatic transmission always has abnormal sound during the operation of the car; When the car is driving, the automatic transmission has abnormal noise, and the abnormal noise disappears after neutral parking.

Reason for failure:

1. The oil pump is worn or even the oil level of automatic transmission is too low or too high, resulting in abnormal sound;

2. The hydraulic torque converter makes abnormal sound due to the damage of the lock-up clutch and the one-way clutch of the guide wheel;

3. Abnormal sound of planetary gear mechanism;

4. Abnormal sound of shift actuator;

(12) Troubleshooting for Deterioration of Automatic Transmission Oil

Fault phenomenon: the new automatic transmission oil after replacement will deteriorate soon after use; The automatic transmission temperature is too high, and the oil filler is smoking.

Reason for failure:

1. The car is often overloaded due to improper use, for example, it is often used in a trailer or suddenly accelerates speeding;

2. The pipeline of automatic transmission oil radiator is blocked;

3. The pressure limiting valve leading to the automatic transmission oil radiator is stuck;

4. The free clearance of clutch or brake is too large;

5. The oil pressure in the main oil circuit is too low, and the clutch or brake slips during operation.

Five, Renault scenery automatic transmission fault maintenance example

When the shift lever of a Renault scenic car is set to 1, the transmission will immediately enter the fail-safe mode and lock in the third gear after the throttle exceeds the medium load. If the throttle continues, the transmission will not enter the safety protection mode. When the shift lever is set to the second gear, the accelerator with medium load or above will have the impact of 1 gear shifting to the second gear, and will not shift to the third gear after refueling, and will immediately enter the fail-safe mode; When the shift lever is set to the D position, the test run is carried out with a medium load above the throttle. The fault phenomenon is that the 1 gear is upgraded to the second gear, and the valve will enter the third gear of the safety protection mode after continuing to refuel.

Troubleshooting:

The electronic control system of the transmission was tested with a scan tool, and no fault code was found. After repeated trial operation, it is found that when the throttle is very small, 1 gear rises to the second gear or impacts, the second gear rises to the third gear normally, and the third gear slides to the fourth gear for 800r/min before impacting. Because there is no special diagnostic instrument, this fault can only be roughly analyzed according to experience. The change of load will directly affect the shift of transmission and the working pressure of hydraulic system. When the engine load is small, the shift process can be completed when the shift and working oil pressure are around 200kPa. Due to the increase of engine load under heavy load, the shift and working oil pressure cannot be met at this time, and the transmission control unit will enter the safety protection mode after being monitored by the oil pressure sensor.

Because this transmission has some common problems, such as the filter screen of the transmission is easy to be dirty, especially the filter screen with poor quality is easy to be dirty, and the two pulse control oil pressure solenoid valves are usually easy to wear. So we decided to carry out maintenance from these two points first, so we replaced the new filter screen and solenoid valve and inspected the inside of the transmission in detail. After installation, the fault still existed.

Because the valve body was replaced when repairing the car elsewhere, it was decided to test the resistance of the input and output sensor, the flow solenoid valve and the oil pressure sensor first, and the test results were normal. Next, the valve body with solenoid valve was replaced, and the fault still exists. After that, the throttle was adjusted, but the fault symptoms remained unchanged.

Although the control unit of the transmission may also fail, we will focus on the peripheral components of the transmission, because the preliminary detection of the diagnostic instrument did not find any related faults of the control unit, and both the control unit and the vehicle control unit used CAN data bus to communicate, and no related faults of the transmission control unit were found in other systems. Under normal circumstances, the abnormal operation of the oil pressure sensor will give an error signal to the control unit, which will make the transmission enter the safety protection mode, and the abnormal adjustment of the flow solenoid valve will also make the system enter the safety protection mode because of the low working oil pressure. For this reason, we first tested the oil pressure sensor and found no abnormality. Later, when testing the flow solenoid valve with the resistance of 1.8, it was occasionally found that the solenoid valve was stuck during power-on and power-off. We found a 1 2.5 bulb to replace the resistance of the solenoid valve, and directly supplied the battery voltage to the solenoid valve for trial operation. During the trial operation, it was found that the other gears were in good condition, except that 1 occasionally impacted when it rose to the second gear. After repeated trial operation, it was found that the transmission occasionally entered the safety protection mode. Because the control mode of this solenoid valve is duty cycle control, it is unreasonable to replace it with battery voltage, so remove the flow solenoid valve and clean it carefully. Test run again after restoring the line. 1 When the gear rises to the second gear, there is still occasional impact, and everything else is normal. At this point, the distance from completion is getting closer and closer. If the impact feels less, the car can be delivered.

At this stage, there is nothing to do with maintenance, so calm down and sum up the problem of occasional impact of 1 gear 2. The possibility of failure of external components of the transmission has been ruled out one after another. At this time, the possibility of mechanical, hydraulic and electronic control of the transmission is extremely small. Therefore, it is necessary to find a good road surface and carefully test it to find the root cause of the occasional impact of 1 gear 2. When we test drive on roads with few vehicles and good road conditions, it is found that the impact of the first gear transmission 1 will occur immediately when the vehicle knocks on the cylinder. When there is no knocking sound from the engine, the transmission 1 shifts to 2nd gear, and the response is good. At this time, the problem will suddenly become clear. The engine sent the wrong working condition information to the transmission control unit through CAN bus, so the transmission control unit gave the wrong shift oil pressure. At the same time, the abnormal operation of the engine also affects the function of reducing torque when the engine shifts gears.

After a 2.5-hour road test with the user, it was confirmed that there were no other problems and the engine was thoroughly inspected. It is found that the coolant temperature is slightly higher than the normal temperature. Considering that the engine has been repaired and there is knocking sound, it is suspected that there is something wrong with the engine valve timing. Therefore, mainly check the valve train. After careful observation of the timing marks, it is found that the valve timing toothed belt has a difference of 1 tooth compared with the correct assembly. So far, it is certain that this is the cause of the car failure.

After reassembling the valve train correctly, we disassembled and cleaned the water tank, and the faults found in the trial operation were completely eliminated.

Any model should be thoroughly tested before maintenance, because "road test" is the most important link in fault diagnosis and maintenance of new automatic transmission. For vehicles equipped with automatic transmission and continuously variable transmission with high degree of electronic control, it is necessary not only to test drive on good road surface, but also to have a clear understanding of the common faults of the repaired vehicles, because it is sometimes difficult to find the fault points by principle analysis, but it is not difficult to explain them by principle after troubleshooting.

Vi. Precautions for Transmission Maintenance

When we overhaul any automatic transmission, we should start with a preliminary inspection, which can often solve many potential problems. Only when the preliminary inspection results show that all prerequisites for the normal operation of the automatic transmission are qualified can the manual shift test be carried out. For automatic transmission, this step can determine whether the fault is in the electronic control system or the mechanical mechanism. Only when all external conditions are met can the fault of automatic transmission be correctly judged. Among them, the performance of the engine has a great influence on the operation of the automatic transmission, so it is necessary to ensure the good performance of the engine before maintaining the automatic transmission. It is best to test the engine with a professional diagnostic instrument. If a fault code is found, it should be diagnosed according to the fault code prompt to completely eliminate the engine fault.

Before diagnosing the specific faults of the transmission, the transmission should be visually inspected, such as whether the vehicle is damaged, whether the transmission oil pan is damaged and whether there is oil leakage, whether the transmission oil cooler or cooler oil pipe is damaged, etc. If the above situation is found, it should be ruled out first. After that, check the oil level and oil quality of the automatic transmission. The correct inspection steps are: firstly, start the engine and run the transmission oil 15 minutes until the working temperature is 82 ~ 93℃. Then park the vehicle on a level ground and tighten the parking brake. When the engine is idling, press the brake pedal, hang the transmission shift lever in each gear and stop at P gear. Then check the oil level and color of the transmission, and pay attention to whether the oil color is opaque pink. When the transmission is not used normally, the oil will turn black, which is usually caused by oxidation or pollution. When confirming the oil quality, oil should be drained to determine whether the oil is polluted. It is normal to find a lot of small particles in the oil pan. If there are large pieces of metal or other materials in it, the transmission needs to be disassembled for inspection, and the transmission oil and filter should be replaced if necessary.

After checking the oil level and oil quality, you can measure the oil pressure of the transmission. When measuring the oil pressure, the oil pressure gauge should be correctly installed on the corresponding transmission oil pressure test hole and operated according to the correct measurement steps. Refer to the maintenance manual for specific measurement data.

Seven. Concluding remarks

This paper introduces the function, function, structure and common faults of automobile automatic transmission, and taking a typical transmission as an example, analyzes the principle, fault causes, solutions and maintenance methods of automobile transmission, and how to use and maintain automobile transmission correctly, so as to avoid the faults of transmission as much as possible and prolong its service life.

In the future, continuously variable transmission is the development trend of automobile transmission system. Although manual transmission still accounts for the majority of passenger cars in China, in recent years, automatic transmission has also occupied a considerable part of the market in the field of cars, while in other developed countries or regions, automatic transmission has long been its mainstream product. However, no matter how it develops, the transmission, as an important part of the car, will not change.

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[3] Huang Zhu. Principle and design of modern automobile automatic transmission. Shanghai. Tongji University Press. 2006

[4] Zhang Jianjun. Automobile testing technology. Version 1. Beijing. Higher education press. 2003.338+02.

[5] Pan Rongwei. Tan Benzhong. Advanced course of automobile automatic transmission maintenance. Beijing. Machinery industry press. 2007.

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Express gratitude/gratitude

I sincerely thank my tutor for his careful guidance. What he says and does will benefit me for life.

I am very grateful to him for his warm guidance and help. Thanks to the teachers and students of Qiandongnan Vocational College for Nationalities for their concern and support!

Thanks to all those who have helped me!