Application of TMR sensors in vehicles

Introduction to TMR Technology

TMR (Tunnel Magneto Resistance) is a new technology that uses magnetoresistive effect sensors in industrial applications in recent years. Its tunnel magnetoresistive effect is caused by magnetic multilayer film materials, and the resistance change rate of TMR is better than AMR and GMR. We usually call TMR a magnetic tunnel junction (MTJ). Compared with Hall elements, MTJ elements have better thermal stability, higher sensitivity, lower power consumption, better linearity, and no additional polyethylene magnetic ring structure is required. Compared with AMR, TMR has better temperature stability, higher sensitivity, wider linear range, and no need for additional set/reset coil structure; compared with GMR, TMR has higher temperature stability, higher sensitivity, lower power consumption, and wider linear range.

1. Engine speed (crankshaft) sensor

Measures the engine speed and determines the crankshaft position (piston position) for the engine management system. Reference marks are used to define the crankshaft position and the synchronization control unit.

2. Engine phase (camshaft) sensor

Indicates piston (compression or exhaust) stroke to trigger ignition and fuel injection.

a: 1, electrical connection (plug) 2, sensor housing 3, crankcase 4, seal 5, permanent magnet 6, sensor 7, pulse wheel with teeth/segments (Z) and space (L)
b: output signal

3. Transmission speed sensor

AT detects turbine/output shaft speed, CVT detects primary and secondary pulleys, DKG detects input/drive shifting, and high-end products require steering.

Due to the diversity of transmission, custom designs include ASIC, packaging, mechanical and magnetic interfaces.

Trigger wheel type

Multi-pole wheel

Differential signal btw R/C

Differential signal btw C/L

CW output signal

Counterclockwise output signal

4. Wheel speed sensor

Measures wheel speed to control braking force at each wheel individually to prevent wheel lock (with ABS) or skidding (with TCS or ESP) and to calculate speed/distance travelled.

5. Accelerator pedal sensor

Records the travel or angle position of the accelerator pedal for Electronic Throttle Control (ETC).

6. Electronic throttle sensor

The throttle angle position information is responded to the ECU to adjust the intake amount of a specific mixture.

7. Steering angle sensor

The driver's input is monitored by continuously measuring the position and rotation rate of the steering wheel and reporting this information to the ECU which, together with information from other sensors, controls various driver assistance systems such as ESP, EPS and active steering.

The steering wheel of a passenger car rotates ±720° (4 turns in total). Traditional angle position sensors can only measure a maximum of 360°, so two angle sensors are required.

8. Axle sensor

Two angle sensors on the front/end axle register the body tilt angle due to vehicle load, braking/acceleration and can automatically adjust the vehicle's headlight range or the chassis height via active suspension.

1, Pivot rod 2, Shaft 3, Housing 4, Rotor with magnet 5, Stator with sensor 6, Magnet

1. Body mount 2. Axle sensor 3. Pivot rod 4. Link 5. Axle

9. Magnetic encoders for BLDC motors

Measuring rotor position for current commutation in the stator to achieve high power efficiency and low torque ripple.