Zero is Developing Liquid-Cooled Electric Motors

The patent describes an electric motor packaged inside an inner and outer shell, with coolant flowing between the two shells. As with liquid-cooled internal combustion engines, heat transfers from the motor through the inner shell to the coolant fluid, which is circulated by a pump to a radiator where the heat gets released to the outside environment.

Liquid-cooled electric motors aren’t a new concept for motorcycles; Energica and LiveWire both use liquid cooling to draw heat from motors to improve performance. Zero’s patent application aims to improve upon the idea, both in the way the liquid-cooling system is packaged and to improve cooling efficiency.

The patent describes a series of raised nubs, located either on the convex surface of the inner shell as depicted in Figure 5 above, or on the concave surface of the outer shell. These protrusions increase the surface area that comes in contact with the coolant, improving heat transfer. These structures also improve heat transfer by adding turbulence to the flow of the coolant between the two shells. The patent further describes how the nubs could be concentrated in areas requiring more cooling.

Adding a liquid cooling system sounds like a natural move for Zero, even if the company has long touted the advantage of air cooling being simpler and requiring no routine maintenance. We also have to consider that Zero has been trying to expand beyond producing just motorcycles to being a supplier of electric powertrains. Most notably, Zero signed a 10-year partnership with Polaris to provide electric powertrain technology for off-road vehicles and snowmobiles. The first product of this partnership, the Polaris Ranger XP Kinetic, began shipping in April. A utility vehicle, the Ranger XP Kinetic’s motor produces a claimed 110 hp and 140 lb-ft. of torque and a range of 45 miles.