The gearbox can be removed without removing the engine. It is necessary to remove the gearbox when replacing or repairing it. It is not recommended to repair the gearbox at home.
Transmission control is described in detail in Chapter Controls and safe operation techniques.
The removal and installation procedures are similar to the removal and installation of a manual transmission, the description is given in Section Removal and installation of gearbox.
An automatic transmission, when starting off, performs the function of a regular clutch, and during movement, it performs the work of shifting gears.
The main units of the AT are: torque converter, planetary gearbox and hydraulic or electronic control system. To switch to another gear ratio in the planetary gearbox, hydraulically driven disc brakes and disc clutch are used.
The torque converter functions like a hydraulic clutch. Its job is to provide clutch when starting off and changing gears.
The switching control is performed by an electronic unit. At the same time, the electronic unit uses various information for correct control, which allows for each mode of the car's movement and depending on the driver's desire to select the most optimal gear ratio.
Program switches such as "Economy" or "Sport" are not required, as the control unit automatically sets the switching points based on the driving mode. When determining the switching points, driving resistances such as uphill or downhill, towing a trailer and the presence of a headwind are also taken into account.
The control system can operate in a special safe mode, which it switches to when any malfunction is detected. In this case, the transmission operating modes are limited, and the car can be driven to a repair shop under its own power. When the control system switches to safe mode, a control lamp lights up on the instrument panel (refer to Chapter Controls and safe operation techniques).
By analyzing information coming from various sensors (not only sensors that are directly related to the transmission), the control system selects the optimal gearbox operating mode in terms of economy, smoothness, etc. At a certain position of the throttle valve, the control system can block the torque converter in such a way that only the fourth and fifth gears are engaged. This achieves a significant reduction in fuel consumption.
The only regular maintenance procedure for the box is checking the working fluid level (refer to Section Checking the Automatic Transmission Oil Level). There is no need to change the transmission fluid regularly.
A transmission fluid cooler is installed next to the cooling system radiator.
There are several transmission operating modes, each of which can be engaged by moving the selector to one of the following positions: P, R, N, D, S (refer to Chapter Controls and safe operation techniques).
The engine can only be started if the selector is in position P or N. This is done to prevent the car from moving when trying to start it (if the selector is set to one of the other positions). By analyzing the information coming from the sensors, the control system allows or prohibits the engine from starting. The locations of the various relays are indicated in Chapter On-board electrical equipment.
The 5-speed AT Tiptronic selector has a second step-by-step track next to the automatic shift position track (consistent) switching. The sports steering wheel can be equipped with the corresponding keys. This switching is accepted in sports cars.
With the Tiptronic gearbox, the driver can perform forced upshifts and downshifts. Compared to manual shifting, Tiptronic is more comfortable and protected against erroneous control. For example, downshifts are only performed if the revs do not exceed certain limits.
If there are any faults in the input signals or electromagnetic valves, the system switches to the emergency program. The fault that occurs at the same time is recorded in the fault memory. Information from the memory can be read with a special device.
Automatic transmission Multitronic with continuously variable gear shifting
Stepless AT Multitronic
Multitronic is a continuously variable transmission CTV with a smoothly variable gear ratio, which ensures not only efficient use of engine power, but also provides good dynamics and driving comfort.
The core element of the Multitronic system is the V-chain variator. The variator changes the gear ratios between the starting mode and the final drive smoothly. This ensures that the engine operates in its optimal mode, regardless of whether it is a high-performance or economical drive. The variator consists of two bevel pairs connected to each other by a plate chain. Since each pair of discs shifts the bevel disk by an electrohydraulic drive, the working diameter of the chain and, as a result, the gear ratio changes smoothly. In addition, the Multitronic uses an oil-cooled clutch, which not only eliminates the typical disadvantages of the torque converter, but also enables various starting modes. The variant is selected by the electronic control system in accordance with the driver's wishes, which are recognized by the nature of the movement of the gas pedal. In addition, the electronically controlled clutch implements a stable creeping mode, which is an element of comfort. The electronic control system also ensures recognition of the driver and the state of the environment and works with the dynamic control program DRP. The specified program determines, based on the nature of the gas pedal movement, whether the driver wants to drive in dynamic or economical mode.
If the driver gives full throttle (kick-down), the electronic control system immediately switches to the sports mode and downshifts, which ensures the required high engine speed. In normal driving mode, the optimal gear ratio is selected, and all its changes, unlike the step-by-step switching of the automatic transmission, are carried out smoothly, without jerks and unnoticeably. The electronics also recognize ascents and descents and compensate for the additional load or increase the engine braking torque.
In manual shift mode, 6 fixed gear ratios (gears) stored in the control unit's memory can be smoothly shifted using the selector lever or buttons on the steering wheel.
[The original text of the material can be found on the website audimanual.ru]