What are the sensors used in EV?

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.

**Figure 1.** Basic structures and operation of AMR, GMR, and TMR sensors. (Image: TDK)

Inductive

Magnetic position and angle sensing technologies are well-established in ICE vehicles. However, the electrical environment in an EV is different, making 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. Since they don’t use magnets, they can have better high-temperature performance.

position and angle sensors — **Figure 2.** Examples of magnetic field sources in electric vehicles. (Image: Microchip)

Resolvers

Resolvers are electromagnetic sensors that operate like transformers. There are several ways to implement a resolver. A variable reluctance (VR) resolver, consisting of a ferromagnetic rotor and a stator with multiple secondary coils, is commonly used in EV traction motors. These resolvers work well in harsh environments and generate rotational position signals.

Other 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, interrupting the light. 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

Some steer-by-wire systems use frictionless inductive angle sensors, compact assemblies that can be integrated into the steering mechanism. 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 producing EVs and autonomous vehicles are generally based on solid-state LIDAR implementations that are more compact and consume less power.