What Is a Wheel Motor?

Wheel motors are in direct contact with the road and thus subject to a lot of wear. That’s why they are equipped with bearing and driving functions.

The traction control system works the same way as in conventional vehicles, controlling loss of traction by applying a brake to the wheel that is losing traction. This also prevents one wheel from becoming unloaded during cornering.

Reduced weight

The wheel motor is a type of electric motor that is built into the wheels of a vehicle. It has been around for some time, and is of interest to designers who are looking for ways to reduce the weight of a vehicle while maintaining power output. The wheel motor can be used in a variety of applications, including powering rear and front-wheel drive vehicles. It also offers a compact footprint and can be integrated into a number of different chassis configurations.

A wheel motor has several benefits over a traditional engine-based system, including reduced energy losses and lower weight. These advantages can help to improve the fuel efficiency of a vehicle and allow for increased range. It can also be used to provide a smoother ride for passengers and cargo. The technology is particularly useful for electric-powered vehicles, as it can eliminate the need for transmission systems and their associated energy loss.

In addition, a wheel motor can be used to create a system that can deliver torque vectoring, which is capable of turning the vehicle at different angles. This can be especially beneficial when driving on a road with uneven surface conditions. The motor can be used to distribute torque evenly between the two wheels, allowing each wheel to maintain its traction capability even when the vehicle is cornering.

Simpler drivetrain

In a traditional car engine the power produced by the internal combustion engine is mechanically connected to each of the wheels via a transmission and drive shaft. This requires complex gearing to match the operating speed of the engine to the wheel wheel motor speeds required for efficient operation. It also introduces significant mechanical losses that erode vehicle efficiency.

In contrast, an in-wheel motor provides a much simpler and more effective solution. With an in-wheel motor each wheel is powered by a separate electric motor, with each having its own inverter and controller. This eliminates the need for a transmission and reduces overall system complexity. It is even possible to use a single axis of motoring, known as 1x drivetrain or 2x drivetrain.

The direct drive distributed architecture of the in-wheel motor enables faster and more dynamic control of the wheel/tyre force with 15x the bandwidth of traditional powertrains. This enables features like torque vectoring, which enhances steering response by distributing power across the front and rear of the vehicle.

In-wheel motors have a number of other benefits too, such as reduced weight and packaging, and increased interior space because the motors are in the corners of the vehicle where there is more room. They also offer the ability to use a wider range of battery technology, making them a more flexible and adaptable solution.

Enhanced vehicle handling

A central trend propelling the global in-wheel motor market is the seamless integration of power electronics within each in-wheel motor unit. This reduces energy losses from cable runs between centralized drive electronics and each individual wheel motor unit. This streamlines the electric vehicle powertrain and also minimizes unsprung weight that can negatively impact ride quality and handling stability.

Another key benefit of in-wheel motors is their ability to control relative wheel speed. With the motor located inside the wheel, relative wheel speeds can be managed in a similar manner to a conventional differential system. This makes it possible to perform torque vectoring (also known as yaw control), which improves vehicle handling by adding additional traction to one side of the vehicle.

Torque vectoring requires sophisticated motor control software to make 16,000 decisions per second about which windings of each motor should be charged with voltage based on the condition of the motor, wheel position and driver command. It’s a challenge that many in-wheel technology developers, including Protean Electric, claim to have overcome.

The simplest implementation of such a system would demand equal torque from each motor every millisecond. This behaviour would then mimic that of a mechanical open differential, with the added benefit of eliminating wheel spin and the need for a drive-shaft. More advanced systems can be implemented that add further advantages such as brake-based traction and stability control systems to prevent wheels from spinning up on low-traction surfaces.

Reduced energy losses

A traditional EV/HEV drive system uses a central motor to power the wheels through mechanical transmission components which generate unwanted energy losses. By directly powering the wheel via an in-wheel motor, this 250w hub motor loss is eliminated. Combined with energy-saving technologies such as regenerative braking, this can provide significant savings in both cost and weight compared to the conventional setup.

By using a single-stator single-rotor (SSSR) design, wheel motors have lower magnetic losses than AC inverter-based systems. This is achieved by implementing SMC stator materials that feature an iron-based powder coated with an electrically insulating layer, allowing the motor to operate more efficiently. The motor also has a compact shape that minimises the size of its core, reducing the amount of air it needs to cool and further lowering its losses.

As the wheel motor is so close to where the vehicle’s tyre meets the road, it is particularly important that it be robust and efficient. It must be able to absorb the pounding of the road and still provide sufficient power for acceleration, roadholding and braking.

It must do so while being able to be precisely controlled. Software makes 16,000 decisions per second on what voltages to apply to the motor windings, based on information delivered by sensors that deliver data on thermal and electric conditions as well as the position and speed of the motor.