Position and angle sensors are used in several electric vehicle (EV) components, including the traction motor and drivetrain, heating, ventilation, air-conditioning (HVAC) compressor, steer-by-wire, brake-by-wire, regenerative braking, accelerator position, active headlight aiming, active suspension systems, and more.
This FAQ reviews some position and angle sensing technologies and how the use cases differ between internal combustion engine (ICE) vehicles and EVs. It closes with a brief overview of a few applications for position and angle sensors in EVs.
Magnetic position sensors
Typical magnetic sensor technologies used for position and angle sensors include Hall effect, AMR (anisotropic magnetoresistive), GMR (giant magnetoresistive), and TMR (tunnel magnetoresistive) (Figure 1). In many applications, Hall effect sensors can provide a good combination of accuracy and low cost.
The various magnetoresistive technologies have higher sensitivities, offering more reproducible measurements than Hall effect sensors. However, they can suffer from nonlinearity, hysteresis, and a temperature-dependent output that can reduce measurement accuracy.
Inductive
Magnetic position and angle sensing technologies are well-established in ICE vehicles. The electrical environment in an EV is different and can make it more challenging to use sensors based on magnetic technologies (Figure 2). Those sensors induce a current in a metal plate. An oscillator generates a magnetic field picked up by the sensor.
Two pickup coils are used and physically separated to generate different voltages that can be used to determine the position of the object being monitored. Inductive sensors use active demodulation to increase their immunity to external magnetic fields. And, since they don’t use magnets, they can have better high-temperature performance.
Resolvers
Resolvers are electromagnetic sensors that operate like a transformer. There are several ways to implement a resolver. A variable reluctance (VR) resolver is commonly used in EV traction motors, consisting of a ferromagnetic rotor and a stator with multiple secondary coils. These resolvers work well in harsh environments and are used for generating rotational position signals.
Other types of resolvers include magnetic resolvers that use Hall effect sensors and inductive resolvers that measure the position of a metallic target rotating in front of a set of inductive coils.
Encoders
Encoders involve disks with coded slots with a single track or quadrature resolution. The disk spins in front of an IR LED, and the light is interrupted by the rotation of the disk. A receiver on the opposite side of the disk from the IR source converts the resulting light pulses into an output signal. Encoders can measure the speed and direction of rotation.
In addition to optical technology, other less common encoder implementations include magnetic and resistive. Encoders can be designed to provide relative or absolute measurements.
Steering angle and torque
Frictionless inductive angle sensors are used in some steer-by-wire systems. They’re compact assemblies that can be integrated into the steering mechanism. Some of these sensors measure torque and angle. The torque measures the force needed to turn the steering wheel, which varies based on driving speed, steering angle, and other factors.
In addition, the sensor enables the steering wheel to provide feedback to the driver through dynamic steering force requirements.
Braking and angular position
Contactless magnetic sensor technology measures the brake pedal angles in electric brake assemblies in some EVs (Figure 3). These sensors record the required level of braking and send that information to an electronic control unit (ECU) that determines the necessary combination of hydraulic and regenerative braking. The sensors in these brake assemblies include redundant signal recording to enhance reliability.
Throttle and motor control
Mechanical throttle potentiometers have mainly been replaced by contactless Hall effect or inductive angular position sensors that measure the distance and speed of movement of the gas pedal (throttle). In addition, the system usually includes a resolver on the motor shaft to provide feedback on motor speed to the traction inverter controller.
Optical encoders and LIDAR
Optical encoders are used in mechanical LIDAR (Light Detection and Ranging) systems to provide the accurate position information needed by autonomous vehicles.
Mechanical LIDAR provides a wide field of view (up to 360°) and is typically used in prototype vehicle systems. LIDAR systems in the production of EVs and autonomous vehicles are generally based on solid-state LIDAR implementations that are more compact and consume less power.
References
Angular position sensor for electric brake pedals, Bosch
Angular position sensor: Functioning and areas of application, Hella
Automotive-qualified position & angle sensors, ams Osram
Motor Position Sensors in EVs: Enhancing Performance and Efficiency, Lambda Geeks
Rethinking Position Sensing in the Age of the Electric Vehicle, Microchip
TMR Sensors, TDK
xMR Sensor Signal Conditioner, Renesas
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