The automatic transmission is arranged according to the traditional planetary scheme with friction braking and is connected to the engine crankshaft through a torque converter 7 (see fig. 6.5 a). The torque converter uses a lock-up mechanism that reduces mechanical slip losses between the pump and turbine wheels at medium to high speeds.
Gears in an automatic transmission are shifted using an electronic control unit, which receives information about the state of the engine, driving conditions and selects the moment of gear shifting according to road conditions and driving style. The result is improved fuel economy and improved transmission performance. In addition, the electronic transmission control system provides a function for diagnosing malfunctions and switching to emergency operation when they occur.
torque converter (pic. 6.6) plays the role of a clutch and serves to smoothly connect the engine and the gearbox mechanism and increase torque when the car starts to move. The torque converter housing is connected to the engine crankshaft through the drive plate and rotates constantly when the engine is running. The internal cavity of the torque converter is filled with a working fluid for automatic transmissions. The engine rotates the torque converter and drives the pump wheel, which creates flows of working fluid in the direction of the turbine wheel. The latter begins to rotate due to the flow of the working fluid created by the pump wheel. With a large difference in the speeds of rotation of the turbine and pump wheels, the reactor changes the direction of the fluid flow, increasing the torque. As the speed difference decreases, it becomes unnecessary and is therefore installed on the overrunning clutch.
Hydraulic control system automatic transmission includes pump, pressure regulator, automatic transmission range selection spool valve, auxiliary valves (solenoids), hydraulic accumulators, clutches and brakes. The pressure in the hydraulic system is generated by a pump installed in front of the gearbox housing. The pump ensures the operation of the torque converter, blocking clutches, brakes and lubrication of the gearbox parts. The pressure generated by the pump is adjusted according to vehicle speed and engine load.
planetary gears correspond to the gear block in a manual transmission and serve to change the gear ratio in an automatic transmission when shifting gears.
Planetary reductor Ravinier systems (pic. 6.7) is a gear train with external and internal meshing of gears, which provides various ways of connecting its elements to obtain various gear ratios.
Principle of operation multi-disc clutches (pic. 6.8) And disc brakes (pic. 6.9) very similar, the difference lies in the fact that the multi-plate clutch connects the gearbox links to each other, and the disc brake connects to the gearbox crankcase. The working fluid supplied to the clutch actuates the piston, and the friction discs are compressed. The links blocked by the clutch begin to rotate as one.
When the disc brakes are released, the working fluid stops flowing into the clutch and the piston returns to its original position under the action of a return spring.
The design feature of the multi-plate clutch is that it is in constant rotation and under the action of centrifugal force acting on the working fluid, pressure is created that prevents the clutch from unlocking. Additionally, a ball valve is installed in the coupling. It is located as close as possible to the edge from the center of the coupling. When the pressure of the working fluid in the chamber of the multi-plate clutch increases, the ball valve closes the drain hole, and when the pressure in the chamber decreases, the ball valve opens the drain hole under the action of centrifugal force and the clutch unlocks.
The automatic transmission selector is installed in the same place on the floor tunnel as the manual transmission control lever, and is connected to the lever of the combined multifunctional selector switch installed in the transmission by a control cable.
A feature of the automatic transmissions of the 2011 Chevrolet Aveo is the ability to switch from fully automatic control mode to manual mode (so-called sequential gearbox), in which the driver, during the acceleration of the car, independently chooses the moment of switching to overdrive. This allows, if desired, to achieve more intensive acceleration compared to automatic mode, artificially delaying the upshift, and bring the engine speed to the maximum torque range. At the same time, the electronic control system constantly monitors the vehicle speed and engine load, eliminates driver error by not allowing him to shift into a higher gear at low speed to avoid engine overload, or downshift at too high a speed, which eliminates the possibility of exceeding the maximum allowable engine speed. When the vehicle speed decreases, the gears automatically switch to lower gears without the participation of the driver. When the car comes to a complete stop, 1st gear is automatically engaged. Features of automatic transmission control are described in «Vehicle device» (see «Gearbox control»).
The automatic transmission differential is similar in design to the manual transmission differential.
To repair an automatic transmission, a large set of special tools and appropriate training of the performer are required, therefore, in this section, only the removal and installation of the gearbox, the replacement of its seals, and the repair of the drive are considered. If necessary, repair the gearbox at a specialized service.