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ZF brings energy-saving "by-wire" manual clutch system

24 Sep 2015

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Clutch-by-wire actuator system

ZF has brought vehicle manufacturers new scope for designing much more efficient passenger car drivelines with manual transmissions. The clutch-by-wire (CBW) actuator system enables control of the clutch independently of the driver's left foot, even without a mechanical connection to the pedal.

Compared to automatic or automated systems, the market share of manual transmissions will continue to contract slightly. However, current forecasts also show that the overall sales curve for manual transmissions will continue to point upward for a long time. This applies to vehicle segments from the medium class down, and especially to emerging markets. This and steadily tougher emission and consumption regulations worldwide make it imperative to exploit efficiency potential in conventional drivelines as well. With this in mind, ZF has developed the CBW system wherein the clutch is actuated electronically by an integrated electric motor.

Because of automatic disengagement and engine switch-off in driving situations, known as the coasting function, the CBW system cuts fuel consumption and carbon dioxide emissions by up to 10 per cent.

Anti-stalling feature

The option of controlling the clutch by control unit and actuator alone with no mechanical connection to the pedal also opens up a raft of new comfort and safety benefits for manual transmissions. This includes start-up without operating the clutch pedal, as well as an anti-stall function that kicks in when the clutch pedal is released too soon or during emergency braking. The anti-stall feature then fully or partly opens the clutch before the engine speed drops below a critical level. Added to this is the creep function where controlled slipping makes manoeuvring and driving in traffic jams easier.

Because the pedal is independent of the driveline, the design possibilities for different models are almost limitless. For instance, the pedal could be made easy to press even if it comes with a sporty characteristic curve. A sensor detects actuating speeds and paths, and the electronic and mechanical systems translate these into the clutch action the driver wants. Once set, the pedal feedback remains constant throughout the vehicle's entire service life. Even clutch wear doesn't affect it because the CBW actuator automatically balances this out.

In this context, it is crucial that, although car drivers benefit from lower fuel consumption, new functions, and an ultraprecise coupling feel, they still control the vehicle in the familiar way. Vehicle manufacturers, on the other hand, can continue to install the same volume production transmissions as before.

Designed by experts

The CBW actuator comes with a brushless DC motor that actuates the clutch in place of a cable-controlled or hydraulic system. The integrated CCU (Clutch Control Unit) controls the system depending on the pedal parameters and the function requirements in each case. When designing both actuators and software, the developers benefited from the profound ZF expertise in automated manual transmissions that has been applied in passenger cars since 1994. That is how the engineers also managed to combine effectiveness with low electricity consumption in the CBW actuator as well as uniting the system components in a compact design that saves installation space. As a result, the CBW from ZF can be integrated into most common manual-control drive concepts easily and cost-efficiently.

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