A 'clutch-by-wire' system is one that does away with the mechanical or hydraulic connection between the clutch pedal and clutch itself.
Instead, the position of the clutch pedal is monitored by sensors and an electromechanical actuator is used to remotely operate the clutch.
Consequently, in a car equipped with a 'CBW' system, the driver is presented with a familiar-looking pedal and transmission arrangement - and the car otherwise drives just like any other manual transmission-equipped vehicle.
However, the CBW system can also automatically operate the clutch or alter the behaviour of its actuation. This automatic clutch control capability grants a wide range of additional safety, efficiency and assistance benefits.
For example, automotive CBW systems - such as those unveiled by Bosch in 2013 and ZF in 2015 - can automate clutch control at low speeds. This means the driver can creep in traffic, in first gear, without having to operate the clutch.
How do clutch-by-wire systems work?
In a clutch-by-wire set-up, the pedal assembly is replaced with one that features a sensor which monitors the pedal position - just like the pedal assemblies used in many electronically controlled throttle systems.
Signals from the pedal are then transmitted to a control unit which triggers the electrically driven actuator that operates the clutch. Because there is no direct link between the pedal and the clutch, the overseeing control system can ensure that the driver's inputs are translated into the most appropriate clutch action.
If a driver were to release the clutch pedal too quickly, for example, the overseeing control system can slow the engagement of the clutch - preventing judder, lurching or a stall.
A further benefit of such a configuration is that the pedal travel and clutch actuation will remain consistent throughout the life of the clutch, as the actuator can automatically take up any slack caused by wear in the system.
Similarly, the use of CBW also makes it easier to integrate hybrid technology into a conventional manual transmission-equipped car - which can help keep costs down while boosting efficiency.
What are the benefits of a clutch-by-wire system?
The motivation behind developing clutch-by-wire systems was one of cost and functionality. A manual transmission with a CBW reportedly costs 50 per cent less than a conventional torque converter-based automatic while offering many similar advantages - such as the ability to coast with the engine off and reduced driver workload.
German manufacturer Schaeffler claims its CBW system, among other benefits, can reduce fuel consumption and CO2 emissions by up to 10 per cent thanks to the coasting function alone. This enables the engine to be automatically decoupled from the transmission, and then shut off, when the car is coasting - reducing fuel consumption.
There are also myriad assistance-related functions which are enabled by CBW systems, including an anti-stall feature, complete clutch automation at low speeds and emergency braking aids. The behaviour of the clutch could also be altered depending on the conditions.
One of the potential pitfalls, however, is the potential lack of meaningful feedback through the pedal - which has been a reported issue with prototype CBW setups, as well as other similar 'X-by-wire' systems. The pedal itself could be engineered to deliver suitable feedback, though, in order to emulate the feel of a conventional hydraulic assembly.
CBW systems have seemingly met with little success so far, though, perhaps due to ever-advancing, increasingly inexpensive fully automatic transmissions and more efficient engines. That said, some manufacturers - such as GM - are beginning to develop and test their own systems. As safety and efficiency demands continue to rise, some may subsequently start to use CBW set-ups in their vehicles.
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