How does an automated manual transmission work

The automated manual transmission (MTA transmission "Easytronic") consists of the gear actuator for automated gear actuation and the clutch actuator for automated clutch actuation. Compared to a vehicle with a conventional, foot-operated clutch, there is no clutch pedal, which is replaced by an electromechanical actuator.

Furthermore, there is no manual shift: the gear change is carried out by two actuators (shifting and selecting). This system combines the advantages of a

  • The automated operating mode.

In this operating mode, the control unit shifts the gears. In the automated operating mode, the MTA transmission behaves similarly to a conventional AT transmission. The shifts are carried out automatically as a function of the accelerator pedal position and the vehicle speed. In contrast to the AT transmission, with the MTA transmission there is a design-related "traction interruption" during a shifting process.

  • The semi-automatic operating mode.

Here the driver decides which gear is to be shifted by operating the selector lever.

  • Manual upshift Tip + 

  • manual downshift Tip -

The change from the automated operating mode to the semi-automatic operating mode is possible at any time, even while driving.

The advantages of an MTA gearbox are:

Free choice between manual and automatic switching. The dry clutch reacts spontaneously to the driver's request. Sporty driving experience.

Lower consumption compared to a conventional AT transmission. Lower weight compared to a conventional AT transmission. "High Tech" - but affordable.

The creep function makes maneuvering easier. The elimination of the shift-by-wire clutch pedal improves vehicle acoustics.

Relief of the driver. Automatic disengagement in the event of emergency braking and vehicle standstill.



The MTA system, the basic structure of which is shown in Figure 1, consists of the following components:

  • Self-adjusting clutch (SAC clutch)

  • Clutch actuator with integrated control unit

  • Gear actuator consisting of shift and selector motor

  • Selector lever

Figure 1MTA gearbox with SAC clutch, selector lever, clutch actuator with control unit and gearbox actuator

The clutch actuator with integrated transmission control unit

  • The clutch actuator consists of an electric motor, a transmission mechanism for actuating the hydraulic cylinder and an integrated displacement sensor that measures the piston rod displacement.

  • The clutch is actuated electro-hydraulically. The master cylinder is housed in the clutch actuator. The system must be carefully "vented" in order to ensure that it functions properly.

    The reprogrammable control unit is housed in the clutch actuator. The clutch actuator and control unit form a single unit. In the event of an error, only the entire unit can be changed.

The control unit contains a vehicle type-dependent transmission software, which takes over the control / regulation of the overall system.

The control unit has the following tasks

  • Reading in the signals (position of the actuators, vehicle parameters, selector lever position, accelerator pedal position, etc.).

  • Signal check or plausibility check.

  • Determine the target gear.

  • Status detection (transmission, shift and clutch status)

  • Calculation of the output variables.

  • Output of the signals.

The MTA control unit is responsible for the entire sequence of a shift (gear change).

  • Reduce engine torque

  • Disengage the clutch

  • Select target gear

  • synchronization

  • Engage target gear

  • Apply clutch

  • Increase engine torque

1) Integrated electronics (control unit / output stage clutch motor / output stage switch motor / output stage selector motor)

2) worm drive

3) worm wheel

4) worm gear shaft

5) bolts

6) Distance sensor

7) Compensation spring

8) plunger

9) Master cylinder

10) rotor

(When moving the mouse over the number becomes visible)

Clutch actuator with integrated control unit:

The task of the clutch actuator:

The clutch actuator takes over all tasks that are performed by the driver with the help of the clutch pedal in a vehicle with a conventional transmission.

  • Dosed application of the clutch when starting up.

  • Disengage and engage during gear changes.

  • Disengage when stopping.

  • Disengage during an ABS situation.

The gear actuator

The gear actuator consists of two gear motors and an actuation mechanism. The switching actuator executes the switching movement, the selector motor the movement for selecting the aisle (selection movement).

The actuation mechanism of the transmission actuator has a shift finger that is inserted into the

Functional description of the SAC clutch (Self Adjusting Clutch)

With conventional clutches, the actuating force increases with increasing lining wear. With the SAC, the lining wear is compensated for by an automatic wear adjustment system so that there is no change in the actuation force.

The main difference between the SAC and the conventional clutch pressure plate is that it adjusts the disc spring when it is worn. The tracking takes place in such a way that regardless of wear (mainly lining wear), the angular position of the disc spring and thus the actuation and contact forces remain constant. This wear compensation is achieved in that the main diaphragm spring is not riveted firmly to the clutch cover, as is the case with the conventional clutch pressure plate, or hooked onto the clutch cover by means of brackets, but only axially clamped against the cover with a defined force (sensor force). Between the plate spring and the clutch cover there is a ramp ring which engages in the ramps of the cover and is driven in the circumferential direction via compression springs.

Image SAC

The sensor force is dimensioned so that it can normally withstand the actuation force. If the actuation force increases when the linings wear and if the sensor force is no longer sufficient as a counterforce on the main diaphragm spring, the main diaphragm spring moves axially away from the cover surface in the direction of the motor. The resulting play is compensated for by the preloaded ramp mechanism, which is arranged between the plate spring and the clutch cover. The readjustment process lasts until the actuating force has decreased to the sensor force and thus to the desired level, and the original diaphragm spring angular position has been reached again.

Main advantages of the SAC

  • Low release forces that remain constant over the service life. This results in a high level of driving comfort over the entire service life.

  • Increased wear reserve and thus longer service life through wear adjustment.

  • In connection with the MTA transmission, faster gear changes can be achieved.

Electronic selector lever

The driver uses the selector lever to give the MTA system his desired driving / gear. The system converts this request to a corresponding gear in the transmission (shift-by-wire system). The selector lever signal is recorded both via a serial data line and via analog redundancy. The selector lever (electronic component) has no mechanical connection to the MTA transmission.

The MTA is a joint development by Luk and Opel

Source: Luk

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Johannes Wiesinger

edited: 02/19/2015
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