The electric hub motor has been around for a long time. Ferdinand Porsche’s first automobile in 1898 was the Lohner-Porsche with two electric motors in the front wheel hubs. Initially, electricity was supplied from batteries and later by batteries and a gasoline engine-driven generator, in what is considered the first hybrid electric vehicle. While there has been on-and-off interest in hub drive systems, there are currently two programs underway that could lead to production vehicles within a couple of years.
One of the big challenges has been the substantial unsprung weight that can degrade ride quality and handling. This can be overcome by lighter weight motors and other components that are now available. For example, Ford has shown its Fiesta eWheelDrive prototype developed with Schaeffler Technologies in Germany. The two Schaeffler eWheelDrives are housed within the 16-inch rear wheel rims. Each highly-integrated wheel hub drive contains an electric motor, power electronics, controller, brake system, and liquid cooling system.
Each motor supplies a peak 54 horsepower or 44 horsepower continuous output to a rear wheel. The motor produces 516 lb-ft of torque. The highly-integrated wheel hub drive has a total weight of 117 pounds, only 17.6 pounds more than a conventional wheel including its wheel bearing and brake components.
The Fiesta eWheelDrive installation is just a technology demonstrator. Ford and Schaeffler feel the ideal application is in city cars for use in crowded urban areas with limited parking. Everything, with the exception of batteries, needed to propel and brake the car is located in the wheel. Thus, the space now needed for the engine and transmission or electric motor in an EV can be used for passengers and luggage. Indeed, it could mean a four-person car that takes up no more parking space than a current two-person car. The eWheel- Drive steering system could even allow moving sideways into parking spaces.
Despite its somewhat higher wheel-sprung masses, extensive testing has shown the Fiesta eWheelDrive exhibiting driving behavior equal to a conventional Fiesta in terms of comfort and safety. The two wheel hub drive motors also allow torque vectoring for enhanced maneuverability in tight spaces. Ford, Schaeffler, and other partners plan on producing two more drivable vehicles by 2015.
Protean Electric, based in Britain, has been developing hub drive motors for years and plans volume production of its Protean Drive system in China this year. It showed its in-wheel electric drive system on a BRABUS hybrid vehicle at Auto Shanghai 2013. The BRABUS Hybrid, based on the Mercedes-Benz E-Class, is powered by an internal combustion engine driving a generator and two Protean electric drive motors, one in each of the rear wheels. Protean had also demonstrated Protean Drive in a Vauxhall Vivaro cargo van, Guangzhou Trumpchi sedan, Ford F150 pick-up, and a BRABUS full electric vehicle also based on the Mercedes-Benz E-Class.
The Protean PD18, designed to fit inside an 18 x 18 inch wheel rim, provides 735 lb-ft torque and 100 horsepower. This is a 25 percent increase in peak torque compared with the previous generation design. Thus, it is powerful enough to be the only source of traction drive in electric vehicles. The unit only weighs 68 pounds per motor.
Each Protean Drive has a built-in inverter, control electronics, and software. The design can be used in small- to full-size vehicles including application in current vehicle platforms, retrofits to existing vehicles, or in all new vehicles. Protean says it recoups up to 85 percent of the available kinetic energy during regenerative braking. Compared to other electric vehicle drive systems, in-wheel motors apply regenerative braking directly at each wheel independently, similar to standard friction brakes.
BMW's Concept Active Tourer, a through-the-road plug-in hybrid, uses a front-mounted engine to drive the front wheels and an electric motor to drive the rear, with no mechanical connection between the two. In most hybrids the output of the engine and motor are combined. The Concept Active Tourer is the first additional application of the eDrive system used in the i8, which incorporates an electric motor, lithium-ion battery, and intelligent engine control. BMW will use the eDrive designation for all its electric and plug-in hybrid vehicles.
Like BMW’s latest four- and six-cylinder engines, the BMW Concept Active Tourer’s 1.5-liter three-cylinder gasoline engine uses BMW TwinPower turbo technology. Even though it has only three-cylinders, BMW claims it is very smooth running even at low speeds and emits the sporty sound expected of a BMW.
The synchronous electric motor can power the car for up to 18 miles exclusively on a fully charged battery. It also augments the gasoline engine to provide over 190 horsepower when maximum power is required. BMW expects it will get an impressive 94 mpg, achieved partly through automatic engine start/stop and regenerative braking energy supplied the rear axle during deceleration. A high-voltage generator connected to the 1.5-engine also charges the battery while driving.
BMW’s Concept Active Tourer has an ECO PRO mode to help reduce fuel consumption. When appropriate, it reduces air conditioning and other electrically powered creature comforts to increase fuel efficiency. Linked to the navigation system, ECO PRO mode gives drivers advice on how to reach a destination using minimum fuel. ECO PRO mode also completely shuts off the engine at speeds up to nearly 80 mph, and then decouples the engine from the drivetrain up to 100 mph to make full use of the kinetic energy already generated.
The Efficient Dynamics strategy uses information from the navigation system to optimize electric motor and battery efficiency. For example, it calculates in advance the most suitable driving situations and sections of a route for electric-only operation or to charge the battery. This optimized charging strategy can achieve an energy savings up to 10 percent and thus increase electric range.
While small on the outside, the Tourer is very roomy on the inside. It rides on a long 105 inch wheelbase and has an overall length of 171 inches. A tall roof allows a raised seating position for an excellent all-around view. Batteries are located entirely beneath the floor so there’s no intrusion into passenger or cargo space.
Will the BMW Concept Active Tourer appear in dealer showrooms? BMW has a good track record for putting concept vehicles into production, so here’s hoping.