Zero is Developing Liquid-Cooled Electric Motors

Dennis Chung
by Dennis Chung

Patent filing points to a liquid-cooled future

Since its inception, Zero has been powering its motorcycles with its proprietary Z-Force motor. The motor has evolved over the years, but at its core, it has remained an air-cooled interior permanent magnet brushless motor. That might soon change, as recently-published patent filings reveal Zero has been working on a liquid-cooled motor.

The patent application, first submitted to the U.S. Patent and Trademark Office in late 2021 but only made public last week, is for a liquid cooled motor, and more specifically, for the design of the motor enclosure, or water jacket.

Figure 2 shows a schematic exploded view of the motor as a series of concentric cylinders. From left to right, it illustrates an outer shell, an inner shell, a stator, and a rotor with a drive shaft.

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.

Raised nubs between the inner and outer shells increases the surface area to improve heat transfer.

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.

Zero uses an SR/F to illustrate a motorcycle with an electric motor. The radiator (#118) would be in a conventional position behind the front wheel, where a protective cover currently sits on the production SR/F.

Zero’s patent focuses primarily for use on a motorcycle, but it doesn’t rule out other applications. An electric RZR model, or a Polaris snowmobile may warrant increased performance or range that a liquid-cooling system could offer.

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Dennis Chung
Dennis Chung

Dennis has been a part of the team since 2008, and through his tenure, has developed a firm grasp of industry trends, and a solid sense of what's to come. A bloodhound when it comes to tracking information on new motorcycles, if there's a new model on the horizon, you'll probably hear about it from him first.

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2 of 3 comments
  • Paulévalence Paulévalence on Jul 03, 2023

    Hopefully these becomes their new "top" of the line models, and they make their current models cheaper. For their performance, they still feel about 8-10k overpriced at the moment. And I would looovvvee to switch to an easy maintenance electric for my daily commuting bike

  • Todd Todd on Aug 26, 2023

    Electric motor for me would would be a Yamaha... ..of course!!