Rotor heat sensor could cut use of rare-earths and protect magnets
6 June 2025 
Continental Automotive has developed a technology that directly measures the temperature of rotors in permanently excited synchronous motors “for the first time”. It says that the e-Motor Rotor Temperature Sensor (eRTS) will deliver much more precise results than the software-based temperature simulation techniques currently used. The technology, aimed at EV motor applications, reduces the temperature tolerance range from 15°C for simulations, to just 3°C. This will allow motor manufacturers to reduce the amount of rare-earth elements they need to increase the magnets’ heat resistance, and improve the performance of the motors.
The sensor consists of two components: a wireless sensor located close to a magnet in the motor; and a transmitter located outside the motor, which sends the temperature data to the motor controller via a cable connection. The two elements communicate via piezo ultrasound, which also supplies energy to the sensor.
Synchronous motors can operate at temperatures of up to 150°C. Monitoring and controlling these temperatures is crucial. Currently, they are cannot be measured directly, but are calculated combining information from a sensor in the stator, phase current measurements, and environmental variables. This method results in a temperature tolerance range of up to 15°C.
To protect motor magnets from demagnetisation due to high temperatures, motor manufacturers use costly rare-earth materials that cover the entire temperature tolerance range. These help to ensure that the magnet is heat-resistant.
By reducing the tolerance range to 3°C, manufacturers will have more freedom when designing permanent magnet synchronous motors, according to Continental. They can also reduce their use of rare-earth materials, and improve motor performance by pushing the limits of the temperature tolerance range.
“Our E-Mobility Sensors product centre aims to increase efficiency and sustainability in electric vehicles,” says Christoph Busch, who heads the centre. “The eRTS technology is a good example of this: reducing the use of rare earths contributes to a more sustainable supply chain, especially given that the number of EVs is expected to greatly increase in the coming years and decades. In combination with other sensor technologies, such as the e-Motor rotor position sensor, it can even act as a system solution to create synergies that can save car manufacturers money and effort.”
