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A sensor first: New unit measures heat in EV motors
Automotive tech company Continental has developed a new sensor technology that measures the temperature inside permanently excited synchronous motors in electric vehicles (EVs) directly on the rotor for the first time.
eRTS contains two separate components: the wireless mote temperature sensor unit located close to the magnet in the EV motor, and the wired transducer element located outside the EV motor, which is connected to the inverter control. [Credit: Image courtesy of Continental]
The e-Motor Rotor Temperature Sensor (eRTS) delivers significantly more precise measurement results than the current software-based temperature simulation -- with a tolerance range reduced from 15 C to just 3 C.
The new technology enables vehicle manufacturers to reduce the amount of rare earth elements used to increase the magnets' heat resistance and to improve potential motor performance, which also means greater sustainability. The eRTS is one of several sensor technologies for EVs developed by the E-Mobility Sensors (EMS) product center at Continental.
How it works
Rotors operate under extreme conditions, for example in temperatures up to 150 C. For this reason, monitoring and controlling temperature development in EV motors is crucial. Currently, heat development is not measured directly but calculated based on the information from the stator temperature sensor, phase current measurements, and environmental variables. This comes with a tolerance range up to 15 C.
To protect the magnet from demagnetization due to excessive temperature, expensive rare earth elements are used to cover the entire tolerance range and ensure the magnet is heat resistant. With greater measuring accuracy reducing the tolerance range to 3 C, car manufacturers profit from new possibilities and freedom of choice in permanent magnet synchronous EV motor design, meaning a significant portion of costly rare earth materials, which would normally have to exceed the higher tolerance range for safety reasons, can be saved. Another interesting variable is the possibility to improve motor performance by pushing the limits of the tolerance range.
In "harvesting mode," the transducer emits ultrasonic waves to supply the integrated temperature unit in the electric motor with energy inductively. In "listening mode," the ultrasound transmission is stopped, whereby the temperature unit is activated, measures the temperature, and transmits the data back to the transducer by means of coded ultrasonic pulses. [Credit: Image courtesy of Continental]
eRTS contains two separate components: the mote element and the transducer element. The mote temperature sensor unit measures the temperature directly at the target area, as close as possible to the magnet. The wireless mote draws its energy only from the wired transducer that is connected to the ECU, providing the transducer with its measuring data. The transducer is located outside the EV motor on the chassis. It is connected to the inverter control, transmitting temperature information through a communication interface. Mote and transducer communicate via Piezo ultrasound, which also provides for the energy supply.
A wide range of sensing solutions
The Passive Safety and Sensorics (PSS) segment at Continental Automotive has a long tradition of sensor technologies. It offers an extensive portfolio of around 50 different sensors for a multitude of purposes such as tire pressure monitoring, chassis position determination, wheel speed sensing, and even battery impact detection, providing key information on a whole range of vehicle conditions. More than two years ago, a product center for E-Mobility Sensors was dedicated specifically to this area, resulting in a fast-growing portfolio of sensors specifically for EVs.
"Our E-Mobility Sensors product center aims to increase efficiency and sustainability in electric vehicles," says Christoph Busch, who heads the center. "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."
Source: Continental
Published June 2025
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