The main components of the AT are: torque converter (torque converter), planetary gearbox, hydraulic or electronic control units. To switch to another gear ratio in the planetary gearbox, hydraulically driven disc and band brakes and disc clutches are used.
The torque converter corresponds to the hydraulic clutch in its functions. Its task is to implement the clutch when starting the movement and changing gears. The torque converter is equipped with a locking clutch, which directly couples the engine to the AT.
The automatic transmission control system is connected to the engine control system via the CAN bus and based on the analysis of data received from various information sensors (not necessarily directly related to the functioning of the AT itself), selects the optimal mode of operation of the AT in terms of economy, smoothness of switching, etc. The AT has its own control unit (TCM). When a malfunction is detected, a corresponding code is written into the memory of the control unit (see Specifications to the Head Engine electrical systems).
The only AT maintenance procedures that must be performed on a regular basis are checking the level of its working fluid (ATF) and replacing the ATF. The order of performing these procedures is described in Sections Checking fluid levels, leak control and AT transmission oil change (respectively) Chapters Vehicle settings and routine maintenance.
Thanks to the use of D/V modes "P" / "N" (pNP sensor) the engine can only be started when the AT selector lever is in the "P" or "N" position, which prevents accidental movement of the vehicle when attempting to start.
If the sensors used by the TCM fail, the AT switches to emergency mode. In this case, the car can only forward the engine in 4th gear. The electromagnetic gear shift valves are de-energized.
This Chapter provides only general information on the operation and design of the AT.
Repairs to the AT that involve disassembling it should be entrusted to specialists.
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