Continental’s New E-Motor Rotor Position Sensor: More Efficiency and Smoother Operations for Electric Vehicles

The eRPS was specially developed to control synchronous motors (where the rotor rotates at the same speed as the revolving field in the machine). To achieve maximum motor efficiency, the motor control unit needs to know the exact position of the rotor, which makes this type of sensor an essential part of synchronous motor applications. While the resolver is a comparatively massive sensor, the eRPS is very flat and supports compact motor designs with a small overall length. The sensor design is based on eddy current principle and is optimized to increase robustness to mechanical tolerances. State-of-the-art integrated circuits (ICs) are used for signal processing. The IC has been designed according to ISO 26262 functional safety automotive standards to reach ASIL C. As an option, two ICs can be embedded in the eRPS to ensure the redundancy that is an integral part of functional safety.

Though the traction motor of an electric or hybrid vehicle is a prominent use case, there are many more synchronous motors in electrified vehicles. Future dry-brake systems (without hydraulics), for instance, will also be actuated electrically and will require rotation sensors. When developing the eRPS, Continental took on existing knowledge and experience with inductive technology. For example, the brake-by-wire system MK C2 uses an Inductive Motor Position Sensor and has been a benchmark for the sensing concept development with increased speed and accuracy, as is the case with the eRPS. 

The new eRPS is an inductive rotor position sensor covering several integration configurations. The sensor can be mounted through the shaft, or it could be integrated at the end of the rotor shaft, including in this case the sealing function. The module contains excitation and reception coils embedding one or two ICs that detects directly the electrical angular position of the metallic encoder on the rotor shaft. This straightforward and weight efficient solution delivers an output in a format that requires minimal signal post processing. The electrical angular position data is required for an efficient e-machine torque control and to achieve the maximum service life of a motor.

“The signal pattern of the eRPS is much easier to work with than that of a resolver. The measurement principle is very fast, extremely robust and is suited for high motor speeds and acceleration. It is very compact and works with a minimal number of parts,” said Murali Srinivasan, Head of Passive Safety and Sensorics, Continental North America.

With a maximum current consumption of 15mA, the eRPS offers an electrical accuracy of ±0,5° for a four pole pairs motor. It is designed to cover rotational speed requirements needed for future electric vehicle platforms (~24.000 rpm). The sensor’s operating temperature range is very wide and falls within -40 °C to 140 °C and peaks up to 155 °C.