More than a century after a young Ferdinand Porsche used them on his first car, and after decades of their use in giant off-road vehicles, are electric wheel motors finally ready for light-duty applications? A small U.K.-based engineering company with some unique technology and plenty of dedication is betting they are.
Protean Electric has been developing electric motor technologies since the 1960s and built its first wheel motor for automotive use in 2003. In recent years the company has fitted the innovative pancake-shaped motors to various concepts and prototypes, including a Volvo C30-based series hybrid, a Ford F-150 EV with an individual motor at each wheel, and a Mini EV, among others.
The company is seeking customers who would license its design for production, and CEO Craig Knight believes the U.S. market is the ideal place to find them.
“We’re appealing to the U.S.’s love of larger vehicles—SUVs, minivans, pickups—for which we think wheel motors are the perfect fit for vehicle electrification to improve efficiency,” said Knight. “With four wheel motors, we can deliver more torque directly to the drive wheels."
He said that by employing the Protean motors, an OEM or Tier 1 can create a simpler, lower cost drivetrain and improve vehicle control and overall efficiencies by eliminating the losses typical in mechanical power transfer. Also, it can increase output by increasing wheel diameter.
He said wheel motors are more than 90% efficient in terms of converting energy into vehicle propulsion, enabled in large part by their capability to regenerate most of the vehicle’s braking energy under deceleration.
Better wheel control, grip
The simplest wheel motors integrate an e-motor into the wheel hub, creating a stator-rotor arrangement to generate torque when power is applied to the stationary coils. More sophisticated designs (including Protean’s) are liquid-cooled, and some even include suspension components. Michelin’s Active Wheel, Siemens’ eCorner, and developments from Canada’s M4 Technologies and General Motors are recent examples of interest in the technology.
In 2003, AEI drove a prototype hybrid-electric Chevrolet S-10 equipped with two 25 kW (33 hp) wheel motors sourced from Italy-based motor specialist Lucchi R. Elettromeccanica. The motors fit neatly within the truck’s 18-in-diameter (457-mm) road wheels. The rear-drive system was engineered by GM and partner Quantum Technologies with dedicated power control and coolant solutions.
In the S-10, the wheel motors provided nearly 60% more torque to the drive wheels than was available from the truck’s combustion engine and gave it prodigious acceleration, traction, and grip—wheelspin was eliminated—when tested on a drag strip and slalom course. Reporters who sampled the e-drive S-10 were impressed by its performance. Development did not proceed, however, nixing the logical next step: electric all-wheel drive.
Knight noted similar potential benefits of Protean Electric’s wheel motors, plus the capability to precisely control the amount of torque to each wheel, aiding traction in varying road-surface conditions and providing greater maneuverability.
Submotor architecture is key IP
Protean’s three-phase permanent-magnet motors are scaled for vehicle curb weights of 5000-6000 lb (2268-2722 kg). They are rated at 84 kW (113 hp) peak power for 20 s, and 54 kW (72 hp) continuous, depending on battery power.
According to Knight, the company’s key intellectual property is in the submotor architecture and its integration with the microinverter technology. Each motor features distributed architecture, incorporating one inverter and eight power-electronics modules within the motor, rather than residing in a separate unit. Each module handles one-eighth of the input power.
The wheel motors are designed to operate using open-source control software and integrated with the vehicle via CAN. Profiles of the copper-wire windings are proprietary, and Protean has developed a robotic winding process. “The entire unit is designed for manufacturability,” Knight noted.
The motor’s stator and power electronics are liquid-cooled. Knight noted that the company’s 72 engineers (out of a total staff of 86) have put much of their development focus on increasing cooling efficiency.
The design integrates the brake rotor on the back side of the electric motor’s cast-aluminum rotor. It fits an 18-in wheel and is intended to use the OEM’s existing bearing set.
A disadvantage of wheel hub motors that has yet to be fully solved is added unsprung weight, which negatively affects the vehicle’s handling and steering. GM’s wheel hub motors added 33 lb (15 kg) to each 18-in wheel, which GM engineers said could be offset by tweaking suspension damping and spring rates. Knight acknowledges that unsprung weight is a potential issue that is being addressed through design.
The integration of electric drive motors and various vehicle components into a vehicle’s wheels has the potential to enable fresh, unique new vehicle designs by freeing up the space traditionally occupied by the powertrain and related accessories. They are also one of the major components of a true “by wire” electrified propulsion system.
The F-150 fitted with Protean’s wheel motors has racked up thousands of test miles and recently received upgrades, including an integrated braking system, at the company’s Romulus, MI, facility. Knight said he welcomes OEMs or suppliers to collaborate with Protean on an SUV or minivan to demonstrate the technology's performance potential.