Semi-automatic transmission

An automatic clutch system ( AKS ) English Automatic Clutch System (ACS ) is an independent clutch system for motor vehicle transmission in which the opening ( disengagement ) and engaging the clutch ( engagement ) is triggered by the sensor signals and effected by auxiliary drives. The coupling procedure eliminated directly by the driver, a clutch pedal is no longer necessary.

Components of the clutch system

• Clutch: Self- diaphragm spring clutch with hydraulic central slave
• Sensors for switching intention recognition, gait recognition, disengagement and disengagement
• The control unit of the clutch system
• Actuators: electric motor, worm gear, master cylinder, slave cylinder

Circuit tripping

The intention of the driver circuit for triggering is detected by a sensor ( potentiometer ) on the shift lever.

Further the control operation influencing sensor signals are:

• Ignition switch
• Engine speed
• Crossing detection
• Switching intention recognition
• Disengagement
• Accelerator pedal position
• Speed
• Signals of antilock braking system (ABS)
• Signals of the acceleration skid control ( ASR)
• Signals the Electronic Stability Program ( ESP)
• Disengagement

Crossing detection

It is recorded by two contactless rotary position sensors on the shift linkage in the transmission. In addition to the sensor signals for switching intention and gait recognition the control unit receives signals up via the CAN -BUS in front of the control devices of the motor controller and the ABS/ASR- and ESP systems.

Operation

For detecting the respective state of the system the control unit processes the input signals under software control of the sensors and transmits output signals to the actuator means ( actuators ). Corresponding to the signals of the clutch is opened or closed.

Approach

From the information released by the sensors for the starting state input signals and the maps contained in the software, the controller calculates the optimum slip for the start.

Gear changes

The sensor on the shift lever indicates the driver's intention to shift. The control device causes an electric motor with a worm gear a pressure generation in the master cylinder. This pressure opens on the hydraulic central ( slave cylinder ) the clutch.

After shifting Report the transition detection sensors which gear has been switched. Now the control device sends a signal to the electric motor with worm gear, which causes the closing of the clutch with a specified slip.

The accelerator pedal may not necessarily be withdrawn during switching. The injection quantity is automatically reduced by the control unit, and then increased again.

Normal driving

In order to dampen torsional vibrations, the control unit calculates, from the signals of the engine speed and transmission input speed, the difference, so that if necessary a controlled slip is set.

Load change

When sudden actuation of the accelerator pedal, the swaying of the vehicle ( Bonanza effect) is kept in check because the clutch opens for a short time. This can be smoothly accelerated.

Downshifting on slippery surfaces

The signal of the blocking drive wheels is processed by the control unit, that the clutch opens when the start lock, and the wheels are free.

Features

• No clutch pedal available
• Cheap wear process for clutch lining and clutch release bearing
• No " stalling " of the motor during acceleration and braking
• Torsional vibrations of the engine are absorbed by slippage in the clutch.
• Less disruptive load-change reactions.

History

A solution completely mechanically constructed was the mid -1950s by Fichtel & Sachs developed " Saxomat ". It was offered as an extra, for example, in the DKW F93, the VW Beetle and the Taunus 12 M ( " Globe Taunus " ) from Ford. From 1959 the system under the name " Olymat " was available in the Opel Rekord P1. At Daimler Benz, there was also a similar coupling point of Fichtel & Sachs named Hydrak, in the Mercedes 219 sedan, 450 DM surcharge, however, was only available in the six- cylinder models. Starting from August 1957

With a similar system from 1965 to 1990 the Trabant P601 H ( Hycomat ) was produced. The clutch actuation was electro-hydraulic, but there was also a " Notpedal ".

While in Saxomat / Olymat a centrifugally controlled clutch was installed, had " Hydrak " a hydraulic clutch, which was technically more complex and somewhat more comfortable. To switch the additional mechanical dry clutch was available. The actuated by the vacuum of the engine stop cycle is electrically activated by touching the shift lever.

Today

Examples of vehicles with here -described modern electronic semi-automatic gearboxes are the Renault Twingo 'Easy', Ecomatic Golf, the Mercedes -Benz A-Class or the Lexus SC. Examples of this type clutch systems are eg the EKS (Electronic Clutch System) or the ECM (electronic clutch management ).

In vehicles with automatic transmissions, manual gear selection is sometimes referred to as a semi- automatic mode. Here, the shift request is ( up - or downshift ) the transmission electronics communicated eg via steering wheel buttons, but the clutch and shift takes ultimately the (full - ) automatic transmission (such as Tiptronic ).