Accurate position sensor helps BLDC motor in transmission control unit to run smoothly

January 16, 2013 // By Paul Buckley
Automotive systems manufacturer Continental has started to use the robust, accurate AS5134 angular position sensor from ams to help the high-speed brushless DC (BLDC) motor in Continental’s transmission control unit run smoothly and efficiently.

The AS5134, as well as the newer AS5132, which are fully qualified to the AEC-Q100 automotive standard, are contactless magnetic position sensors optimized for use in high-speed brushless DC (BLDC) motors. The AS5134 is used to sense the position of the rotor in motors in transmission control units for new double-clutch transmissions (DCTs), providing angle measurements that support an optimized, efficient commutation scheme. Requirements for the device included accuracy at high rotation speed and reliability.

A DCT is an advanced form of automatic gearbox for passenger cars. In some newly developed DCTs, BLDC motors are used to shift the gears and to control the dual clutch. As many as four BLDC motors may be used in one DCT.

An integrated module designed by Continental controls the motors through field-oriented commutation, a technique in which the input current to each stator is determined by reference to the angular displacement of the rotor. More accurate measurement of the rotor’s angle results in lower torque jitter, smoother operation and higher power efficiency. A particular benefit of the AS5134’s high accuracy is that the start-up torque of the motor is increased. This enables the motor to reach its optimal operating speed faster, resulting in reduced energy consumption.

The AS5134 magnetic position sensor features a low propagation delay – the delay between the input from the sense magnet and the angle calculation output leaving the chip – of 22 μs. This enables highly accurate measurement of rotors turning at high speed: the AS5134 is specified for angular measurements in 1° steps accurate to ±2° at rotation speeds up to 82,000rpm.

The control module in the Continental transmission is a complete integrated unit that cannot easily be accessed for repair or replacement, and so the reliability of components in the module, such as the position sensor, is very important. Like all magnetic position sensors from ams, the AS5134 features patented differential input technology developed by ams