Oxford YASA Motors is finding that a TorqSense non-contact speed and torque sensor from Sensor Technology is an invaluable aid in the refinement of its motor designs. Used in a test rig to evaluate prototype motors, the sensor provides accurate and dependable real time information in a readily accessible format.

Oxford YASA Motors is engaged in the development and manufacture of a new type of axial flux motor that features Yokeless and Segmented Armature (YASA) topology. Compared with conventional axial flux motors, the new YASA types offer a step-change improvement in torque density, making them ideal for applications such as electric vehicles where the highest possible torque-to-weight ratio is a key requirement.

The YASA topology is based around a series of magnetically separated segments that form the stator of the machine. The step-change improvement in the specific torque of the motor, which at around 20 Nm/kg is at least twice that of the best currently available alternatives, results from a combination of patented improvements in the magnetics, cooling and packaging of the motor.

A 500 Nm YASA motor has already been developed specifically for use in electric and hybrid vehicles. This motor is compact – just 340 mm in diameter and 70 mm wide – and is, therefore, able to fit easily within the space that would normally be occupied by the front or rear differential in typical vehicle. With the YASA motors, no differential is needed. 

Since these motors have an output of 500 Nm per “slice”, and a peak power of around 75 kW, two of them provide sufficient power for most vehicles. This has been verified in practice by the Westfield iRacer, a pioneering electric racing car fitted with two YASA motors, which accelerates from 0 to 60 mph in less than five seconds, and is capable of reaching an electronically limited top speed of 110 mph.

For the Oxford YASA Motors application, a type RWT321 sensor with integral electronics was chosen. Like all TorqSense sensors, this combines high accuracy and resolution with a large overload capacity and the ability to operate equally well with clockwise and anti-clockwise rotation. In addition to torque data, the sensor also provides information about shaft speed, power and temperature, with all of the data made available in real time.

A further benefit for Oxford YASA Motors is that the RWT321 incorporates a CANopen interface. This is directly compatible with the company’s data acquisition and analysis systems and, therefore, made interfacing the sensor very straightforward.