Currently, none of the conventional transmission designs provide an ideal option for electric vehicles. Conventional manual transmissions interrupt the drive to the wheels during gear shifting and require a clutch, adding cost and bulk to the tightly packaged powertrain of an EV. Conventional automatic transmissions, meanwhile, add bulk and also introduce a significant efficiency loss.

British transmission specialist Zeroshift has now devised a multi-speed gearbox for EVs that needs no clutch--a damper inside the gear hubs and electronic control of the motor make ratio changes seamless. Having more than one gear ratio and the ability to shift without interrupting torque means the motor runs at higher efficiency, extending battery life and driving range by as much as 10 percent.

Additionally, the clutchless multi-speed gearbox also prevents any torque interruptions during gear changes, an issue that’s so far deterred EV manufacturers from fitting multi-speed gearboxes. Current EVs instead use a single-speed transmission, but the motor then spends more of its time outside of its optimum efficiency range.

The design essentially replaces the synchromesh in a conventional manual gearbox with paired interlocking rings that change gears without interrupting the torque. To provide the required levels of shift refinement, Zeroshift’s concept uses electronic control of the electric motor or motors to match the shaft speeds and an integrated passive damper system within the drive hub to isolate any vibrations.

Zeroshift is currently developing its innovative transmission with several major automakers.