New cooling technology ‘shrinks motor sizes by 75%’
Two US companies have announced plans to produce electric motors with a novel cooling technology that results in them being 75% smaller, and much lighter, than conventional motors with a similar power rating. They say that the motors, aimed principally at automotive applications, will deliver the power and torque to drive a passenger car from a package the size of a one-gallon can of paint.
The motor technology has been developed by Georgia-based DHX Electric Machines. It has granted the automotive specialist, DeltaWing Technology Group, worldwide rights to make, use and sell the motors and allied components.
The key to the new motor’s design is a cooling system that removes heat directly from its stator windings. Most of the thermal losses in a high-torque electric motor are generated in the windings, with the heat typically dissipating through the stator to the frame using air or liquid cooling.
DHX Electric Machines’ patented cooling system uses a technology that it calls a Direct-Winding Heat Exchanger (DWHX) to remove the heat at the source. Tiny channels in the heat exchanger increase the cooling surface area by up to four times that of conventional cooling channels. They also help to increase the coolant flow rates through an effect known as “localised turbulence”. DHX claims that the technology can remove more than ten times as much heat as conventional cooling channels.
The improved heat removal allows the motor to carry four times more current than usual, and to deliver four times more torque, according to DHX. Alternatively, the motor can be made a quarter of the size of a conventional motor, yet deliver a similar performance.
“Our DHX Falcon electric motor features standard materials, not exotic steels and magnets,” says Rhett Mayor, DHX Electric Machines’ president and co-founder. He claims that it achieves power densities of 25kW/litre (120hp/gallon) and “extraordinary” torque levels of 70Nm/litre (195ft-lb/gallon). “In simple terms, it delivers the power and torque of the standard sedan's powertrain in the space of a one-gallon can of paint.”
The motors are said to operate with efficiencies of up to 96%. For an 80hp (60kW) motor weighing 30lb (13.6kg), a 96% efficiency is equivalent to a loss of about 2.4hp (1.8kW) – half as much as a standard high-efficiency induction motor that is four times the size, according to DHX. This could result in extended ranges for battery-powered vehicles.
If a motor is produced using exotic steels and best-in-class materials, power densities approaching 250hp/gallon (41kW/litre) are possible, DHX adds. Such motors could put out 400 ft-lb (542Nm) and two of them in a vehicle – one on each axle – could create a 500hp (370kW), 800 ft-lb (1,084Nm) powertrain with a 96% conversion efficiency.