Could In-Wheel Motors be the Next Big Thing?

As advanced technology vehicles evolve, we’re likely to see a full range of evolutionary changes in the technologies used in these vehicles. One example was presented by Honda’s FCX fuel cell concept that debuted at the Tokyo Motor Show, which provided a high-profile example with its integration of rear in-wheel motors. By the time the FCX Concept made its way from show floor display to drivable concept, though, its in-wheel motors were left behind in favor of more conventional electric drive, ostensibly because of the high voltage that must pass through cables powering each wheel motor and the friction challenges presented by the constant motion these cables endure.

That’s not to say in-wheel motors aren’t a contender. Developmental challenges are inherent in most advanced technologies as they make their way to real-world use and this is likely no exception. Plus, there’s plenty of interest out there. This efficient electric drive system has also shown up in other hybrid and fuel cell concepts.

The advantage of in-wheel motors, you ask? The concept can be adapted to create hybrids out of almost any internal combustion engine vehicle model. With internal combustion-driven wheels up front and electric motors motivating rear wheels, drivetrain losses decrease and all-wheel drive – plus all-wheel steering – are a natural. Adding in-wheel motors to an existing hybrid instantly creates a high-performance model. When used in an all-electric car, in-wheel motors also do away with all the conventional driveline apparatus and its associated weight.

GM’S IN-WHEEL MOTOR DEVELOPMENT
While in-wheel motor technology has been in the works at Honda for some time, it’s also been under development at the Canadian company Technologies M4 for many years and also at GM. In the very early 1990s, when GM was in the midst of translating its one-off Impact electric vehicle prototype into a car that could be readily manufactured, the automaker toyed with a variety of power schemes. The concept vehicle that Southern California-based Aerovironment created for GM’s 1990 L.A. Auto Show debut was nothing less than stunning, leaping far forward of the electric concepts that came before it and forcefully ushering the electric vehicle into a more modern age. This concept did not lend itself to mass production, though, so all of its major systems and subsystems were closely evaluated. Of special interest was the vehicle’s electric propulsion.

We experienced first-hand GM’s focus on developing a practical electric powerplant for its soon-to-come EV1 electric car. Some 15 years ago, at the GM Desert Proving Grounds in Phoenix, Arizona, Green Car editors drove several test cars for the EV program including an electrically-powered Chevrolet Lumina APV minivan and an electric Geo Storm. What was unusual about the vehicles was the application of individual electric propulsion at each front wheel using a pair of inboard motors. Clearly, there was work to be done since synchronization problems subtly jinked the steering wheel back and forth, but the engineering direction was there. The EV1 eventually made its way to limited production but with a single electric drive motor.

GM?s work with individual wheel motors did not end there. The next time this technology surfaced was in a Chevrolet S-10 equipped with motor-in-wheel units at each rear wheel, supplementing the considerable front-wheel drive power provided by the pickup’s 120 horsepower, 2.2-liter internal combustion engine. Developed by GM’s Advanced Technology Center and made in Italy, these motors generated about 34 hp (25 kilowatts) of power each and added some 80 pounds total to the rear wheels. Quantum Technologies, a noted Southern California vehicle integrator, built the concept truck, modified the vehicle’s coolant, power, and electrical systems, and developed its special electronic controller and related software.

We test drove a motor-in-wheel equipped S-10 in Los Angeles and the result was complete affirmation of GM’s strategy. The S-10 exhibited significantly more power than a stock variant and acceleration was definitely impressive. According to GM engineers, these hub motors added about 60% more torque at launch with that torque available instantly, a power scheme that enabled a four-cylinder engine to perform like a six-cylinder.

This motor-in-wheel concept is not necessarily viewed by GM as an electric vehicle drive system, but a hybrid electric drive system that could potentially be added to any number of vehicles to provide both increased fuel efficiency and higher levels of performance. In fact, GM execs point out that this technology could make it possible to build some pretty exciting future vehicles that have the potential to be as quick as a sports car, while providing significant fuel economy improvements.

SIEMENS VDO eCORNER
An interesting effort involving in-wheel drive motors is also being developed by automotive electronics supplier Siemens VDO. This company’s eCorner concept integrates the drivetrain, steering, shock absorbers, and brakes into a vehicle’s wheels, along the way replacing conventional shock absorbers, mechanical steering, hydraulic brakes, and a vehicle’s internal combustion engine. This forms the basis of drive-by-wire automobiles that the company anticipates will be widely produced in 15 years.

Plus, there are efficiency advantages. While today’s gasoline and diesel engines utilize less than 50 percent of their available energy, wheel hub motors are projected to use up to 96 percent of the provided electrical energy for vehicle propulsion, with a large part of this efficiency increase due to the electric motors’ regenerative braking capability under deceleration. If further braking power is needed, electronic brakes can decelerate each wheel individually to allow for better vehicle control. In a setup like the eCorner, individual wheels can also be moved to their own specific steering angles with a greater degree of freedom, making cars that can park sideways with pivoting wheels a real possibility. By eliminating hydraulic and mechanical systems and reducing the number of components, in-wheel motor systems could reduce costs for car buyers as well.

The integration of electric drive motors and various vehicle components into a vehicle’s wheels allows further modularization of future cars. In-wheel motors also have the potential to allow for completely new vehicle designs by freeing up the space traditionally occupied by the engine, transmission, and all of a drivetrain’s associated accessories. Offering the potential for improved fuel efficiency, better performance, greater design freedom, and integration with many advanced vehicle platforms including those powered by fuel cells, hybrids, and batteries, in-wheel motors seem to have a bright future, indeed.