Strictly speaking, it is completely unnecessary with an electric drive, but at Zero they apparently see advantages in it. The American electric motorcycle manufacturer has filed a patent for a clutch lever that modulates torque and regenerative braking force to mimic the feel and control of a combustion engine clutch.
We could dismiss Zero’s idea of a fake clutch as a gimmick to win over entrenched motorcyclists for whom the combustion engine is still sacred, but that would be too easy and would not do the idea justice. After all, the clutch on a combustion engine is much more than just an on/off switch to transmit power to the rear wheel. It’s also a tool we all tend to use to add finesse when riding, creating an extra dimension of control.
Whether modulating torque when pulling away from a stop or harmonizing with downshifts to add a variable level of engine braking, the clutch is an integral part of driving, and for those new to an electric bicycle steps, this is a check that is mainly noticeable by its absence.
Zero seems to recognize the subtle control a clutch provides, as evidenced by this patent application, which shows a completely normal-looking “clutch lever” and explains how it would interface with the bike’s electronics to provide familiar feedback to the rider.
As for feel, the patent says: “To mimic the feel of a traditional clutch, the kinematic relationship between the left lever, clutches, rotation sensor, yoke, etc. can be configured so that the rider initially experiences a sharp increase in the resistance felt when moving the lever from its rest position, followed by a peak stay or plateau, followed by significant relief as the lever approaches its fully retracted position. As the rider then reduces pressure on the lever, it returns to its rest position pushed by a spring.” In other words, it will give you exactly the same feeling as you are used to from a bicycle with a combustion engine.
Also in use, the results of using the lever will be familiar, even if it does not actually connect or disconnect the drive through a set of clutch plates. The patent explains that: “By reducing the torque delivered by the engine, the left lever mimics the action and feel, e.g. slip, of a multi-speed clutch found in motorcycles and other vehicles powered by internal combustion engines. ”
However, we do not use the clutch purely and simply to reduce torque, but also, for example, to allow the engine to rotate more revolutions and therefore reach a stronger part of the power band than the selected gear would allow – very common with two-strokes. Or to pull the engine onto the rear wheel, something we would obviously never do. Zero realized this and programmed her fake clutch lever to respond in the same way as a clutch lever on a combustion engine does.
The patent says: “For example, quickly releasing the left lever can cause the controller to briefly transmit more torque from the electric motor than is appropriate for the throttle grip position, to recreate the ‘clutch release’ sensation on a vehicle with multi-speed gearbox and clutch.”
The same ideas apply during deceleration, when the pseudo-clutch can be used to soften or amplify the effect of the bike’s regenerative braking. The patent explains that “the controller causes the motor to act as a generator to supply electrical energy to the battery and brake the vehicle as a function of the rotational position, angular displacement, force and/or pressure applied to the left lever.
In addition, the controller may take into account the rate of change in rotational position, angular displacement, force and/or pressure applied to the left lever when determining the amount of regenerative braking to apply. For example, a rapid movement of the lever may indicate that the driver of the vehicle is demanding a very high level of regenerative braking, e.g. during an emergency stop, while a slower movement of the left lever may indicate less drastic demands for regenerative braking.”
While Kawasaki has already shown an electric motor with a gearbox in promotional videos and Kymco has also applied for a patent for a similar idea, it is not clear whether Zero is also going in that direction. Zero’s patent leaves the possibility open, saying the system can be used in conjunction with an automatic, clutchless transmission, but the document makes no mention of giving control of fake gears to your left foot.
Zero’s fake clutch is shown in the drawings mounted on an SR/F, which would suggest that when the clutch goes into production, the SR/F will be the first model to see it applied.
– Thanks for information from Motorfreaks.