Zero Motorcycles

Zero Patent Points to Liquid Cooled Future By Ben Purvis

Electric motors need to be prevented from overheating, and just like combustion engines, there's a clear choice for their designers between air-cooling and liquid-cooling. Zero - undeniably a leader in electric motorcycles - has been in the air-cooled school so far, but a new patent shows the company is considering a switch to liquid-cooling in the future.

As with combustion engines, there are pros and cons to both technologies. The benefits of air-cooled designs are that they're lighter and simpler, with fewer components and potential points of failure. But when it comes to outright performance, liquid-cooled electric vehicles tend to have the edge because it's easier to keep components within the small temperature range that maximizes their performance.

For example, the Ducati MotoE race bikes used in the series that supports MotoGP have not one but two liquid-cooling systems, with completely separate pumps and radiators for the cooling of the batteries and the motor. Why? Because their optimum operating temperatures are different - the batteries need to be kept cooler than the motor - and with two cooling systems, those temperatures can both be maintained.

So far, Zero has stuck with air-cooling for both its batteries and motors, but the company has filed a patent application for a liquid-cooled motor that could be the next step up for its bikes' performance. The design uses a series of layers for its motor housing, with a water-filled cooling jacket sandwiched between the stator and an outer housing. The cooling jacked features manifolds that allow hot water to be pumped out to a radiator and cooler water to come in to replace it.

"Water-cooled motors for future Zero electric bikes"

Inside the cooling jacket, the patent illustrates a pattern of bumps that are used to increase its surface area - ensuring better transfer of heat - and to create turbulence in the water that's running through the jacket, improving the heat transfer from the motor to the coolant.

Outside, the system is much like that of a liquid-cooled combustion engine bike, with a radiator mounted behind the front wheel and a water pump - electrically powered, of course - to keep the fluid flowing between the radiator and the motor.

As the patent says, "the amount of work that an electric motor may perform may be proportional to the amount of heat that can be removed" - suggesting that by shifting to a liquid-cooled motor, Zero hopes to be able to make a bike that's more powerful than its current range-toppers.