Wheel hub motor


The wheel hub motor is an electric motor that is incorporated into the hub of a wheel and drives it directly.

History

The electric wheel hub motor was raced by Ferdinand Porsche in 1897 in Vienna, Austria. Porsche's first engineering training was electrical, not internal combustion based. As a result, he developed his first cars as electric cars with electric wheel hub motors that ran on batteries. The Lohner Porsche, fitted with one wheel motor in each of the front wheels, appeared at the World Exhibition in Paris in 1900 and created a sensation in the young automobile world. In the following years, 300 Lohner Porsches were made and sold to wealthy buyers.
Eventually the growth in power of the gasoline engine overtook the power of the electric wheel hub motors and this made up for any losses through a transmission. As a result, autos moved to gasoline engines with transmissions, but they were never as efficient as electric wheel hub motors. A potential exception to this history occurred on 17 January 2012 with the granting of, The General Wheel Rotation Power Motor, a pressure driven three cylinder wheel motor contained in the hub that applies this force through crank wheels directly to the rotating rim surrounding the hub.

Uses in current and future vehicles

Several concept cars have been developed using in-wheel motors:
Hub motor electromagnetic fields are supplied to the stationary windings of the motor. The outer part of the motor follows, or tries to follow, those fields, turning the attached wheel. In a brushed motor, energy is transferred by brushes contacting the rotating shaft of the motor. Energy is transferred in a brushless motor electronically, eliminating physical contact between stationary and moving parts. Although brushless motor technology is more expensive, most are more efficient and longer-lasting than brushed motor systems.
A hub motor typically is designed in one of three configurations. Considered least practical is an axial-flux motor, where the stator windings are typically sandwiched between sets of magnets. The other two configurations are both radial designs with the motor magnets bonded to the rotor; in one, the inner rotation motor, the rotor sits inside the stator, as in a conventional motor. In the other, the outer-rotation motor, the rotor sits outside the stator and rotates around it. The application of hub motors in vehicular uses is still evolving, and neither configuration has become standard.
Electric motors have their greatest torque at startup, making them ideal for vehicles as they need the most torque at startup too. The idea of "revving up" so common with internal combustion engines is unnecessary with electric motors. Their greatest torque occurs as the rotor first begins to turn, which is why electric motors do not require a transmission. A gear-down arrangement may be needed, but unlike in a transmission normally paired with a combustion engine, no shifting is needed for electric motors.
Wheel hub motors are increasingly common on electric bikes and electric scooters in some parts of the world, especially Asia.

Comparison with conventional EV design in automobiles

Compared with the conventional electric vehicle design with one motor situated centrally driving two wheels by axles, the wheel motor arrangement has certain advantages and disadvantages:

Drive by wire

Cars with electronic control of brakes and acceleration for each individual wheel provide more opportunities for computerized vehicle dynamics such as:
However, these benefits also accrue to vehicles with an in-board motor for each wheel. Wheel assemblies with in-wheel motors can pivot through greater angles than a conventional steering rack allows, and the Protean and REE "corner modules" add steering motors that allow vehicle motion in any direction, called crab steering.
As wheel motors brake and accelerate a vehicle with a single solid state electric/electronic system many of the above features can be added as software upgrades rather than requiring additional systems/hardware be installed. This should lead to cheaper active dynamic safety systems for road vehicles equipped with wheel motors.

Weight savings

Eliminating mechanical transmission, including gearboxes, differentials, drive shafts, and axles, provides a significant weight and manufacturing cost saving, while also decreasing the environmental impact of the product.

Unsprung weight concerns

The major disadvantage of a wheel hub motor is that the weight of the electric motor increases the unsprung weight, which adversely affects handling and ride. The wheels are more sluggish in responding to road conditions, especially fast motions over bumps, and transmit the bumps to the chassis instead of absorbing them.
Most conventional electric motors include ferrous material composed of laminated electrical steel. This ferrous material contributes most of the weight of electric motors. To minimize this weight, several recent wheel-motor designs have minimized the electrical steel content of the motor by using a coreless design with Litz wire coil windings to reduce eddy current losses. This significantly reduces wheel motor weight and therefore unsprung weight.
Another method used is to replace the cast iron friction brake assembly with a wheel motor assembly of similar weight. This results in no net gain in unsprung weight and provides a car capable of braking up to 1G.
A good example of this is the Michelin Active Wheel motor as fitted to the Heuliez Will, the first electric car with an Active Wheel drive, which results in an unsprung weight of 35 kg on the front axle and which compares favorably to a small car such as a Renault Clio that has 38 kg of unsprung weight on its front axle.