Transmission specialist Zeroshift has devised a multi-speed transmission for electric vehicles (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 range and battery life by up to 10 percent.
Development of the concept is underway using Zeroshift's proprietary gear-shifting system. The innovation could enable manufacturers to downsize EV electric motors, keeping them running longer at the medium loads and speeds where peak efficiency of over 95 percent is possible. For drivers, that could mean more performance, greater range and longer lasting batteries.
Zeroshift's managing director Bill Martin says: "Our studies suggest that by using a compact, multi-speed transmission and a smaller electric motor, manufacturers can gain an operating efficiency of up to 10 percent. You can use that 10 percent to improve EVs' range or reduce the size, weight and cost of battery packs."
Zeroshift's concept prevents any torque interruptions during ratio changes and does not require a clutch, issues that have 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 improved efficiency offered by Zeroshift's concept could also extend battery service life. Current range limitations often lead EV drivers to drain the cells to the maximum allowable level of discharge in order to reach their destination; the deeper cycling affects battery life expectancy. Improving the motor efficiency uses less of the energy stored for a given journey, easing the discharge-recharge cycles and reducing recharge time.
The technology replaces the synchromesh in a conventional manual gearbox with paired, interlocking rings that change ratios without interrupting the torque. To provide the required levels of shift refinement, Zeroshift's concept uses electronic control of the electric motor to match the shaft speeds and an integrated passive damper system within the drive hub to isolate any vibrations. The combination of sealed pockets of silicone fluid and mechanical compression springs make shifts virtually unnoticeable to occupants.