Electronic clutch control

In a vehicle fitted with a manual transmission (MT), the clutch engagement and disengagement is decided and performed by the driver, through the clutch pedal. The clutch actuation system links directly the motion of the clutch pedal with the position of the clutch.

In a vehicle with electronic clutch control, there is no more a direct connection between the clutch pedal and the clutch itself. The engagement/disengagement of the clutch is done with an actuator (electric or hydraulic), controlled by an electronic control module.

There are two types of vehicles using an electronic clutch control system:

• with manual transmission (MT) and clutch pedal: the driver is deciding when to engagement/disengage the clutch through a clutch pedal position sensor, but the actuation of the clutch is controlled by an electrical or hydraulic actuator (clutch-by-wire systems)
• with automated manual transmission (AMT) or double clutch transmission (DCT) and without clutch pedal: the engagement/disengagement of the clutch is decided by an electronic control module and the actuation of the clutch by an electric or hydraulic actuator

An electronic clutch control (ECC) system, also called electronic clutch management (ECM) system, contains a clutch which is engaged/disengaged by an actuator (electric or hydraulic), based on the position of a clutch pedal (with position sensor) or function of the control signals send independently by an electronic control module.

1. accelerator pedal
2. brake pedal
3. clutch pedal
4. clutch position sensor
5. wire (electric)
6. electrohydraulic actuator with control module and reservoir
7. pipe (hydraulic)
8. concentric slave cylinder
9. clutch cover

How the electronic clutch control works? When the driver presses the clutch pedal (3), the clutch position sensor (4) sends an electrical signal to the control module (6). Depending to how much the clutch pedal is pressed, the control module regulates the pressure in the concentric slave cylinder (8) engaging and disengaging the clutch.

Engine torque tracking (torque follow-up system)

A driver actuated clutch used in manual transmissions, when fully closed, is designed to transmit between two and three times the maximum engine torque. This is the result of design safety factors and tolerances, which have to make sure that the clutch doesn’t slip.

In most cases, during driving, the engine operates at partial loads, where the torque output is only a fraction of the maximum torque.

In an engine with torque tracking (also called follow-up) clutch system, the clutch is closed enough to transmit slightly more than the current engine torque and not the maximum possible clutch torque.

This feature is only possible with an electronic clutch control system and has several benefits in terms of comfort and driveability.

One advantage is a faster clutch opening/closing during a gear shift. When the driver releases the accelerator pedal, the engine torque is reduced and the “torque follow-up system” function automatically adjusts the clutch by opening it slightly. This means that when the system recognizes the drivers desire to shift gears, the clutch is already partly open, leading to faster disengagement/engagement times and faster overall gear changes.

Another advantage is a higher quality gear shift. Since the clutch torque can be precisely controlled by the electronic control module, at the end of the shift, the clutch is let to slip for a limited period. This procedure will filter out the driveline oscillations, leading to a smoother gear shift and an enhanced comfort of the passengers.

Fuel consumption benefit

A vehicle with manual transmission and electronic clutch control can inherit some of the fuel consumption reduction function seen in hybrid electric vehicles, such as Coasting (or Sailing).

During motion, when the driver releases the accelerator pedal, the engine is disconnected from the driveline and shut down (or kept at idle). The vehicle will travel thanks to its inertia and fuel consumption reduced. This functionality is only possible on a manual transmission vehicle if it’s fitted with an electronic clutch control system.

According to Schaeffler, using a 1.2 liter petrol engine demonstrator vehicle, tests conducted using the WLTP consumption measurement cycle and realistic customer cycles have recorded reductions in fuel consumption from 2% (engine goes to idle) to 6% (engine switches off). Also, it is possible to achieve savings of up to 8% in urban driving conditions.

Advantages of a electronic clutch control system

A full integration of the electronic clutch operation into the overall powertrain control system brings several advantages at the vehicle level:

• improved driveability thanks to a faster and smoother gear shift and clutch operation
• automatic engine restart in case of unwanted stall (anti-stall protection)
• easier clutch operation, especially on vehicles with high engine torque
• improved passive safety (crash protection) due to the absence of the mechanical components
• clutch maintenance scheduling possible due to data acquisition of the usage factor
• improved fuel economy of the vehicle due to vehicle coasting (sailing) functions
• improved passenger comfort due to less vibration being transmitted from the powertrain into the cabin (no mechanical link between clutch and clutch pedal)