In wheel motor development

The YASA Axial motor
(Image courtesy of Mercedes)

YASA is working with Domin on an in-wheel motor system that weighs under 2 kg, writes Nick Flaherty. The project with Cranfield University in the UK will create a patented in-wheel motor design using YASA’s axial flux motor and Domin’s digitally controlled hydraulic active suspension. The aim is to develop a motor system that is ten times lighter than the current 12 kg motor package design.

The Mercedes Vision One-Eleven Hypercar concept already uses YASA’s motor technology, which generates 250 bhp for it. Cranfield University will provide digital twin modelling and vehicle powertrain design optimisation alongside simulation of the design. The digital twin is a detailed digital model of the motor and suspension that allows engineers to tweak different parameters to see how the performance can be improved by boosting the power of the motor or reducing the weight.

Putting the motor in the wheel reduces the need for a driveshaft, reducing the overall weight, but this changes the suspension requirements for the wheel. Domin uses electrically controlled distributed movement with electrified hydraulic power generation systems for a compact electrical motor and pump unit.

Servovalves are sophisticated devices used for precise control of fluid flow and pressure in hydraulic systems and are typically made using traditional manufacturing methods such as machining, casting, or forging. Using additive manufacturing, or 3D printing, for the valves and other parts of the hydraulic system provides advantages such as design freedom, less parts and more efficient manufacturing processes for a lighter suspension system.

The additive manufacturing enables the creation of intricate internal passages, channels, and fluid flow paths that are challenging or impossible to achieve using traditional manufacturing techniques. This enhances the performance and efficiency of servovalves by optimising fluid dynamics and reducing pressure losses.

Digital control using a proportional–integral–derivative (PID) algorithm allows for precise and variable control of the fluid flow and pressure in servovalves while digital signal processing algorithms developed by Domin enable real-time monitoring, filtering, and adjustment of control signals, improving the overall performance and stability of the servovalves.

The valves also use a brushless DC (BLDC) electric motor. Rather than using brushes and commutators, brushless DC motors use electronic controllers and permanent magnets to create rotational motion. This type is generally not used in hydraulics components, with manufacturers preferring to use cheaper options like solenoids or limited angle torque motors.

Domin uses brushless DC motors for high-precision applications such as the in-wheel motor as it provides uninterrupted rotational movement with tight control over both speed and position, unlike solenoids, which become less efficient with prolonged use. Brushless DC motors also have a longer lifespan by eliminating brush-wear and minimising maintenance requirements.

These BLDC motors also use magnetic position sensors to measure the position or movement of the rotor using magnetic fields. The non-contact position sensors eliminate mechanical wear and tear, minimising maintenance requirements and extending the sensor’s lifespan. This approach also reduces the risk of sensor malfunction due to debris, contaminants, or vibrations present in the hydraulic system.

The digital control allows the use of a CAN (Controller Area Network) interface for integration with other electronic systems, controllers, and supervisory systems, reducing the need for an additional electronic control unit. The digital controller monitors various parameters, such as temperature, current draw, motor faults, and voltage, to detect faults or anomalies.

Advanced diagnostic algorithms and built-in self-diagnostic features enable real-time fault detection and this has the potential to deliver notification and preventive maintenance. This analysis data can be included in the digital twin to provide more visibility of the performance of the motor and to highlight if a part of the system is failing.