The modern automatic gearbox is certainly the most complex mechanical component in the car. The automatic gearbox contains mechanical systems, hydraulic systems, electric systems and computer control, all systems work together in complete harmony, which is almost imperceptibly, until the problem arises. This article will help you understand what processes occur inside the box and what is needed for repair in case of breakdown.
This article is divided into five sections:
What is a gearbox in the simplest form, what is the purpose of the gearbox.
The transmission components describe the general principles of each system in simple words to help you understand how an automatic gearbox works.
Visual inspection and detection of problems to prevent automatic transmission breakdown.
The maintenance tells about preventive maintenance, everyone should know this.
The repair describes the types of repair, which are usually performed on the gearbox.
What is a gearbox?
The gearbox is a device connected to the rear of the engine and transfers the engine power to the drive wheels. The automobile engine works most efficiently in a certain range and the transmission function so that the power is transmitted to the wheels, while maintaining the engine operation in this range. The gearbox does this using various transmission combinations. In the first gear, engine speed is much faster in relation to the drive wheels. In addition to the front gears, the transmission also has a neutral position that turns off the engine from the drive wheels, and the rear gear so that the car moves back. Finally, there is a parking position. In this, II, the mechanism blocks the steering mechanism, thereby preventing the vehicle from theft, and includes the parking brake.
There are two main types of automatic gearboxes, depending on whether the rear -wheel drive or front -wheel drive car.
On a car with rear -wheel drive, the gearbox, as a rule, is attached to the rear of the engine and is located under the bottom in the center next to the gas pedal. The drive shaft connects the back of the gearbox with the gearbox, which is located on the rear axle and is used to transmit power to the rear wheels. Power transmission in this system is simple, from the engine through the hydrotransformer, and then through the gearbox, drive shaft, gearbox and on the rear wheels.
In the front -wheel drive car, in the gearbox, as a rule, a gearbox is mounted. The checkpoint is mounted in the side of the car from the rear of the engine. The front bridges are connected directly to the checkpoint and power to the front wheels. For this layout, power transmission comes from the engine through the automatic transmission of the automatic transmission, the gearbox further through the drive shafts to the wheels.
There are a number of other layouts, but these two systems, today, are the most popular
The modern automatic gearbox consists of many components and systems that are designed for collaboration; mechanical, hydraulic and electric, which have developed over the years.
The main components that make up the automatic gearbox include:
Planetary transmissions, which are mechanical systems, provide various gear rates.
A hydraulic system that uses a special liquid sent under the pressure of an oil pump through the valve to control the couplings to control planetary gears.
Seals and gaskets are used to prevent oil leaks.
Gidrotransformer, which works as a clutch, so that the car stands still while the engine still works.
Controller and modulator to control the speed and position of the throttle.
On new vehicles, the movement of the car is under the control of the computer, which controls the electric solenoids to redirect the oil flow at the right time.
Automatic gearboxes contain many gears in various combinations. In the selection of gears, on a mechanical box, when moving the switching lever from one position to another, the gear slide along the shafts, switching various gears to ensure the correct ratio of transmission numbers. In an automatic gearbox, this function is taken by the planetary transmission.
The main components of the planetary series are the sunny gear, gear crown and two or more sattellite. Planetary gears are connected to each other through the Ob.
In one example, the way that this system can be used this connection of the gear crown to the primary shaft connecting the central gear with the secondary shaft, and the solar gear lock so that it could not move. In this case, when we turn to a gear crown, the Sattelaites will “rotate” along the sunny gear (which is motionless), forcing the drive to turn the output shaft in the same direction as the entrance shaft, but at a lower speed (by analogy with the car which moves in first gear).
If we unlock the solar gear and block any two elements together, this will cause the rotation of all three elements, at the same speed, so that the output and entrance shaft will rotate at the same speed. It is like a car that is in the third or higher gear. Another way that we can use in the functions of the planetary series, blocking the drive from the movement, using the gear wheel, which will force the solar gear to turn in the opposite direction, which gives us the reverse.
Illustrations on the right shows how simple systems described above will look in a real gearbox. The input shaft is connected to a gear crown (blue), the output shaft is connected to the drive (green), which is also associated with a set of clutches. The solar gear is connected to the drum (yellow), which is also connected to the other half of the set of clutches. The strip brake (red), which can drag out around the drum, when this is required to prevent the drum flowering with attached sunny gear.
A set of clutches is used, in this case, to fix the drive from the solar gear, forcing both elements to rotate at the same speed. If both clutch and group packages are released, the system will be in a neutral position. Included in the entrance shaft will free the planetary gear from the sunny gear, but since the sunny gear holds nothing, it will simply be free and does not affect the output shaft. To turn on the first speed, satellites are motionless and the solar gear rotates. To transition from the first to increased, the sattellites rotate forcing the output shaft to rotate at the same speed as the entrance shaft.
Modern automatic transmissions already have up to eight speeds. The computer’s computer monitors and controls these processes so that they are almost invisible.
Clutch packages .
The clutch package consists of alternating discs that are placed in the clutch drum. Half of steel disks and have protrusions that enter the grooves on the internal side of the drum. The other half of the friction material.
There are pistons in the drum, which is driven under the pressure of the oil at the appropriate time to squeeze the clutch package, so that these two components are contacted and turned as a single whole.
Free stroke coupes .
Free stroke coupes are a device that allows you to freely rotate the toothache in one direction. This effect is like that of a bicycle, where the pedals will turn the wheel forward when rotating the pedals, when the rotation stops, the free move and slow down when the pedal is pressed.
Typically, one -sided coupling is used in the first gear. When you start accelerating in the first gear. You someday noticed what is happening if you release the gas, in the first gear? The car continued to move, as if you were on neutral gear. When you release gas in this case, you will feel that the engine slows down the same as a standard car. The reason for this is that in Drive, free clutch couplings are used at that time, the clutch package or strip brake is used in lower gears
Street of steel tape with friction material associated with the inner surface. One end of the tape is attached against the transfer while the other end is connected to the servo. At the right time, the oil is supplied to the servo under pressure to tighten the tape around the drum to stop the drum from the turn.
On automatic transmission, hydrotransformer stands instead of adhesion. The hydrotransformer allows the engine to work at idle when the car stops. The principle of operation of the hydrotransformer, like the receiving fan, which takes the air flow from another fan that is connected to the network. If you hold the impeller of the disconnected fan, you can hold it from rotation, but as soon as you let go, it will begin to rotate until it spins until the fan is turned on. The difference with the torque converter is that instead of air, it uses oil or transmission fluid to be more accurate.
The hydrotransformer has the shape of a large donut (10 “up to 15” in diameter), which is installed between the engine and the gearbox. It consists of three internal elements that work together to transmit power to transmission. Three elements of the hydrotransformer are a pump, turbine, and stator. The pump is installed directly on the converter case, in turn is attached directly to the crankshaft of the engine. The turbine inside the case and is connected directly to the input shaft of the gearbox. The stator is attached to a one -sided clutch so that he can freely rotate in one direction. Each of the three elements have blades to accurately direct the oil flow through the converter
When the engine is running, the transmission fluid is drawn into the pump section and pushes out under the influence of centrifugal force until it reaches the turbine section that triggers its turn. The liquid continues the circular movement back to the center of the turbine, where it is part of the stator. If the turbine moves much slower than the pump, the liquid will come into contact with the front of the stator of the blade of which the stator is pushed in one direction of the clutch and prevents its rotation. The fluid is directed from the stator’s bubbles for re -entering the pump thereby increasing the torque. Since the speed of the turbine catches up with the speed of the pump, the liquid begins to beat the stator’s shoulder blades on the back of the stator rotation in the same direction as the pump and turbine. So with an increase in speed, all three elements begin to rotate at about the same speed.
Since the 80s, in order to save fuel, the hydrotransformers were equipped with a locking coupling (not shown), which blocks the turbine to the pump, as soon as the car speed reaches about 70-80 kilometers per hour. These locks are controlled by a computer.
The hydraulic system is a complex labyrinth of passages and tubes that sends a transmission fluid under pressure so that all parts of the transmission and hydrotransformer are functioning. Using transmission oil, all automatic transmission functions include: gear shift, general lubrication and cooling of automatic transmission parts. Unlike the engine, which uses primarily for lubrication of oil, each aspect of the transmission function depends on the constant fluid supply under pressure. This is not much different from the human circulation system (even red liquid), where even several minutes of work without pressure can be harmful or even fatal for the life of automatic transmission. In order to maintain the temperature regime of the gearbox, part of the fluid is supplied through one of two steel pipes within the radiator. The liquid passing through the radiator is cooled, and then returns to the gearbox., Most of the transmission components are constantly immersed in transmission oil, including clutches.
Oil pump .
The transmission oil pump (not to be confused with the pump inside the hydrotransformer) is responsible for the pressure of the oil, which is required in the gearbox. The oil pump is mounted on the front of the giving box and is directly related to the flange on the body of the torque converter. The pump creates pressure constantly when the engine works. The oil enters the pump through the filter, which is located in the lower part of the oil submarine and moves up the tube directly to the oil pump. The oil pressure is controlled by the pressure regulator, valve body and other components as necessary.
Valve Corps Center for Updating Automatic gearbox. It contains the labyrinth of channels and passes to provide a flow of hydraulic fluid for numerous valves, which then activate the corresponding clutch packages or servo drives for smooth gear. Each of the many valves in the case has a specific goal and is called the switching gear, respectively. For example, 2-3 switching valve activates the transmission from the 2nd to the third.
The most important valve is the one that carries out direct control is a manual valve that is directly related to the gear handle and reveals various passages depending on the position of the gear lever. For example, when you place the gearbox in D, the manual valve directs the liquid to the clutch package that activates the first gear. He also establishes the control of the speed of the vehicle and the position of the throttle so that it can determine the optimal time and power for switching 1 – 2 of the transfer. With computer control of the gearbox, you will also have electric solenoids that are attached in the valves body to direct the liquid to the corresponding clutch packages for more accurate control of the shift points.
Management computer .
The computer uses sensors on the engine and transmission to identify things such as the position of the throttle, the speed of the car, the engine speed, the load on the engine, the position of the brake pedal, etc. D. control the exact points of the shift, as well as smooth or sharp transmissions. As soon as the computer receives this information, he sends signals to a package of solenoids. The solenoid package contains several electrically controlled solenoids, which redirect the liquid to the appropriate clutch package or servo drive to control the gear. The computerized gearbox even knows your driving style and is constantly adapting to switch exactly when you think about it.
Computer automatic transmission also have the ability to manually control with steering wheel switches.
Another advantage of these “smart” programs is that they have a self -diagnosis mode that can detect problems at an early stage and warn you with an indicator on the dashboard. The mechanic can then, using diagnostic equipment, get error codes and determine where the problem arose.
Control valve, vacuum modulator, gas cable.
These three components play an important role in non-comprehensive transmission. They provide transmission shift inputs. The control valve is connected to the output shaft and regulates the hydraulic pressure that creates the speed of the car. This is achieved by the use of centrifugal force.
Of course, the speed of the vehicle is not the only thing that controls when the transmission should be changed, the load on the engine also matters. The larger the load on the engine, the longer the transmission.
There are two types of devices that serve to control the load on the engine: gas cable and vacuum modulator. The program will use one or another element. Each works in their own way to control the load on the engine.
The gas cable simply monitors the position of the gas pedal through the cable connecting the gas pedal to the throttle.
Vacuum modulator is connected with the engine using a vacuum hose. The vacuum created by the engine reacts very accurately, with a high load, the vacuum value is large. The modulator is attached to the outer side of the gearbox from the shaft side, which passes through the case and connects to the throttle in the valve body. When the engine is under a small load or without a load, the vacuum acts on the modulator, which moves the throttle in one direction to switch the transmission to a lower. With an increase in the load on the engine, the vacuum decreases which drives the valve in another direction by switching the gear to a higher.
Basons and gaskets .
The automatic gearbox has many seals and gaskets to control the flow of working fluid and to prevent leaks. There are two main external seals: compaction of the front and rear cover of the automatic transmission. The front laying seals the part where the hydrotransformer is located. The rear gasket holds the liquid from the leakage from the output shaft side.
Essle, as a rule, are made of rubber and is used to compact the box at the output points of rotating parts, such as a rotating shaft.
Gaskets are used to seal two stationary parts that are fastened to each other. The material of the cushioning materials are: paper, cork, rubber, silicone and soft metal.
Visual examination of automatic transmission.
Follow leaks or spots under the car
If you notice the red liquid under your car, you must check that it is dripping from your automatic transmission or, possibly, from the steering system (for the most part, transmission fluid is also used in the steering wheel amplifier system and leaks may appear in about the same areas At the gearbox.) If you see everything, a few drops on the ground, you can postpone the repair, but the fluid level must be checked constantly. If the automatic transmission fluid level drops below the minimum level, then this can lead to a serious repair of your automatic transmission.
Flip check for color and smell
Most manufacturers require you to check the level of transmission fluid when the car engine operates and in an even place. Pull out the probe from the automatic transmission and check the liquid for the color and smell. The automatic transmission fluid should be transparent red, which looks like cherry cough syrup. If the liquid is muddy or dirty, or has a burning smell, you must check the automatic transmission per service station, where most likely it is recommended to change the oil. (Cm. Section maintenance below details about this service).
You need to be attentive to new noises, vibration and change of automatic transmission behavior.
In modern gearboxes under a slight acceleration of transmission, they change smoothly and silently. With intensive acceleration of automatic transmission should be made more rigid transmission. If the automatic transmission switches erroneously or you hear noise when switching, you must check the box immediately. If you find a problem in time, many problems can be resolved without expensive transmission repair. Even if you cannot afford repairs, you must at least check the automatic transmission. The master can give you some tips on what to do and not to do to extend the life of automatic transmission before repair.
Periodically, transmission oil should be changed. The user manual should have recommended intervals that range from 20,000 to 100,000 kilometers. Most experts recommend changing liquid and filter every 25,000 km.
Just drain the oil through the drain plug. In order to check the spent liquid, the master removes the automatic transmission tray. This very dirty work is not recommended to do it with your own hands. When the pallet is removed, the master can check the presence of metal chips and other garbage, which are indicators of the impending problems of the box.
In most cases, only about half of the oil can be merged. This is because most of the oil is located in the hydrotransformer and cooler and cannot be removed without serious disassembly. Fluid replacement intervals are based on the fact that the old liquid remains in the system.
When servicing the box, make sure that you have chosen the right oil to replace. Each automatic transmission manufacturer has its own recommendations for using a particular fluid and internal components are designed for this particular formula. Automatic transmission will not work properly or will switch with jerks, can even lead to repair due to improper liquid. In the user manual, it will tell you which liquids need to be used. Naturally, in the operating instructions, they will try to convince you only to the manufacturer’s branded liquids, but they will also provide you with the technical characteristics of the oil. If the secondary market of the product indicates that they correspond or exceed the technical characteristics of a particular type of transmission fluid, then as a rule, this product can be used.
Automatic transmission repair.
Adjustments and minor repairs.
There are several problems that can be solved by adjustment (simple adjustment can be done without removing the box from the car.) or minor repairs. If the automatic transmission of the later model (with computer control of the box became popular in the early 90s) does not switch properly, then this is often the result of the wrong signal of the sent to the computer and due to the faulty sensor is a faulty electromagnetic package or due to poor connection. These problems can be fixed for a small fee. On older automatic transmission, not controlled by a computer, the programs switch too sooner or too late, then the gas cable adjustment may be required. Since the gas cable rarely dumps the adjustment by itself, as a rule, is associated with the restoration after the accident. If the box is equipped with a vacuum modulator instead of a gas cable, there are adjustments that can be made using a control screw (in some design design). In cars with modulators, it is very important that there are no vacuum leaks and the engine works with maximum efficiency. The engine vacuum is very sensitive to how the engine works. Many problems of the gearbox disappears after the engine configuration.
Replacement of seals and gaskets.
If you see red oil spots on the ground under the car, you must check the gearbox for leaks. The master will put the car on the lift and study the box for the presence of signs of oil leaks. If the leak is noticed on any of the external seals or gaskets, and the automatic transmission works well, it most likely recommends changing the oil seal or gasket.
Most external seals can be replaced without removing the box, but if the front oil seal has flowed, then the box will have to be removed from the car to access the oil seal (such work will cost more).