Opel Astra and Zafira have four-speed automatic transmissions (AKP).
The design of the automatic transmission includes a torque converter, an oil pump, planetary gears, friction clutches and brakes. The gearbox is controlled by an electronic unit.
The torque converter acts as a clutch. During operation, it is filled with a working fluid and, rotating at a sufficient speed, transmits torque from the transmission engine, absorbs and smoothes vibrations and jerks from the operation of the engine and gearbox. The torque converter consists of three wheels: pump, reactor and turbine, as well as its blocking clutch. The impeller is integrated with the torque converter housing and fixed to the engine flywheel. The turbine wheel is splined to the gearbox input shaft. When a certain speed is reached, the torque converter is blocked by the clutch, thus providing a rigid connection between the engine crankshaft and the transmission. This significantly reduces power losses and has a positive effect on driving dynamics and fuel consumption.
The oil pump is driven by the engine and is designed to create the necessary pressure of the working fluid for the operation of the automatic transmission. With this, the impossibility of starting the engine of a car with automatic transmission is connected «from the pusher». In the absence of working fluid pressure, the torque from the transmission cannot be transmitted in any way to the engine crankshaft. Also, the lack of working fluid pressure imposes certain restrictions on towing a car (see «Operation and driving»), since there is no proper lubrication of the automatic transmission units.
The planetary mechanisms are installed directly in the automatic transmission case and are designed to provide a change in gear ratio and reverse gear engagement. planetary gear (broadcast) consists of four main elements: sun gear, planet carrier and ring gear. Changing the gear ratio and direction of rotation occurs by locking or unlocking two of the three elements (sun gear, carrier, ring gear) in various combinations. In modern automatic transmissions, several planetary gears are installed, depending on the number of gears and design.
Friction clutches and brakes are designed to block various elements of planetary mechanisms. They are triggered by the pressure of the working fluid when the corresponding valve is opened. The valves are opened in a certain sequence by the electronic control unit, depending on the speed, degree of opening of the throttle valve, on the frequency of rotation of the crankshaft, etc.
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