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Zeroshift Developing Clutchless Multi-speed Transmission for EVs

Zeroshift’s multi-speed transmission concept changes gear without interrupting the torque, allowing EVs to run for longer at peak efficiency. Click to enlarge.

UK-based transmission specialist Zeroshift has devised a multi-speed gearbox 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 enables the motor to run at higher efficiency, extending range and batteries’ life expectancy by up to 10%, according to the company.

The company’s 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 or motors to match the shaft speeds and an integrated a 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. Zeroshift has carried out extensive damper optimization using simulation tools correlated against development test results.

By varying parameters such as fluid properties, peak pressures and end-of-travel speeds, we can tune the damper’s performance to suit different applications.

—Bill Martin, Zeroshift’s managing director

Development of the concept is underway using Zeroshift’s proprietary gear-shifting system. The new gearbox could enable manufacturers to downsize EVs’ electric motors, keeping them running longer at the medium loads and speeds where peak efficiency of more than 95% is possible.

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. However, with a single-speed transmission prevalent in EVs, the motor spends more of its time outside of its optimum efficiency range.

The improved efficiency offered by Zeroshift’s concept could also extend EVs’ in-service battery 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 batteries’ 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.

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.

The benefits of Zeroshift’s transmission would be greatest for electric delivery vehicles where the compromises in efficiency are greatest. To be able to pull away fully laden on hills requires low gearing, but the motor then runs too fast and too inefficiently on the highway.

—Bill Martin

Zeroshift is developing its compact transmission with several vehicle manufacturers. The company is also working with consultancy firms and manufacturers on the integration of its technology into the next generation of seamless layshaft automatic transmissions for hybrid medium-duty trucks, buses and passenger cars.



Is is rally the way of solvng high spead related issues? High spead electric trains do not have any gear boxes and never intended to have. May be AC motor powertrain would be alternative vs. DC+gear box?


This may help EVs to get started, to pull heavier loads and/or to go up hill. However, on rather flat highways, it will not make much difference.

Motorizing all four wheels would give equivalent/sufficient flexibility and may be a better all-seasons compromise.


@ Darius:
My friend, you're comparing potatoes with apples. Trains are connected to a grid supply and not to a battery like an EV. When high current drain surges occur, that is literally poison for the battery and limits its total life and cycle capability. A transmission (e.g. CVT) provides high torque at low drain and eases the load on the battery subsequently improving its cycle capability and total life. It doesn't matter if the power train is comprised of a DC or AC motor (DC applications are "for the birds" for various reasons). Hopefully, you understand the difference between potatoes and apples.


I agree with you that I do not understand all this completely. But I understand that in case you want high torque you need high power or high current and this is realy very little to do with gear box. In order to store high power for short time you need capacitors. Gear box is related not to the battery properties but to the electric motor dynamic features. So I do not agree with the rest of your statement.


This is why Tesla started out with a 2-speed gearbox, so they could run the motor in a more efficient zone and get more range.


Actually, Tesla started out with 2-speed to get both a sub-4 0-60 time and an unembarrassing top speed. Despite their "up to 10%" claims, multiple ratios does not provide a large efficiency gain for an electric motor. It could provide a large performance gain in some configurations.


The Michelin motorized wheel (2 smaller motors per wheel) or equivalent could negate the need of a mechanical transmission. Sufficient power levels could be obtained via adequate electronic control of all motors.

Ideally, all wheels could be designed with built-in, fully integrated, e-motors/generators with variable power levels. No separate autonomous motors would be required. If the motor/generator fails, just change the wheel and send it to repair depot or to the scrap yard if you live in a high consumption country.


There may be need for multi-speed gearboxes in electric drives for at least two types of applications:

a) Racing cars that require very strong acceleration - the reason Tesla Roadster used it initially.
It's apparently more practical than having a stronger (and heavier) el motor that provides more torque.

b) Hauling trucks and other vehicles that have high ratio of Max Loaded vs Empty ratio (often up to 3:1), or when such vehicles have to drive up steep hills.

I'd say multi-speed gearboxes with electric drives are mostly for performance gains.
For ordinary passenger vehicles existing electric motors (induction or AC synchronous PM motors) are flexible enough so they only need single-speed gearbox (reducer).
Induction motors (with max rpm over 8,000 - like those used in some cars) are usually inefficient below 1,000 rpm, but operate in that range for short time, mostly during start-ups.

Henry Gibson

There are ways to build a very highspeed lightweight motor that can be used with a single reduction gear. Motors and Engines and Turbines have always had higher horsepower per pound when they operated at high speeds, but there are the very low speed ship diesel engines that need no gears at all and are very efficient; they might even be more efficient than many fuel cells and use cheaper fuel. These ship engines could implement combined cycle heat recovery with a steam turbine and then definately be more efficient than a fuel cell whilst still burning the cheapest liquid fuels. It may even be true that purefied coal with the ash removed can be used as fuel in such machines when combined with some cheap petroleum liquid.

People can use a small electric car for most uses and it does not have to be a race car, but can be a weak hybrid. Tiny OPOC engine generators can be available for occasional range extension as can other engines. ..HG..


Yoatmon has a good explanation. The huge current required for acceleration takes a lot out of the electro chemistry of batteries. You can get 10-20C current surges, but the chemistry does not last a long time for 1000s of deep cycles. A good efficient CVT would help give good performance and last many years for 1000s of deep charge/discharge cycles.

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