According to an IHS report, semiconductor magnetic sensors used in automotive motors will grow by about 38% in 2012. Magnetic sensors help improve car safety, convenience and fuel efficiency. As a result, IHS expects revenue derived from the use of magnetic sensors in automotive motors will reach $160.3 million next year (compared to $116.0 million this year). By 2015, magnetic sensor revenue in automotive motors will grow to about $193.6 million.
Source: IHS iSuppli Research
Automotive motors generally use Hall integrated circuit (IC) sensors in a three-phase motor for commutation. A three-phase motor typically has six states, measured by three digital Hall ICs for closed-loop regulation. In some cases, magnetic sensors may not be required, and Hall ICs may be replaced by simple current measurement in the circuit. For example, DC motors that operate in an environment with constant speed and no load changes (such as a fan that constantly rotates) can infer the required knowledge of speed without the need for sensors.
In advanced motors where load changes and knowledge of torque is needed, the use of Hall ICs or anisotropic magnetoresistive (AMR) sensors is required in order to measure the motor position of the shaft. As a result, the use of AMR will increase in the next five years. An example of its use is for the tachometer motors used to indicate speed and RPM instruments, for reasons of motor quietness.
NXP Semiconductors of the Netherlands is a major provider of AMR sensors, while Hall sensor IC alternatives are supplied by Micronas of Switzerland, Infineon Technologies of Germany, U.S.-based Allegro Microsystems, Melexis N.V. of Belgium and Japan’s Asahi Kasei Microsystems.
The automotive industry currently accounts for half of semiconductor magnetic sensor market revenue. Each low-end to midrange car includes over ten electric motors on average. They are used for fan cooling, the alternator and front and rear wipers. Luxury cars have almost 100 motors (for HVAC blowers, electronic steering and throttle control, and transmission sensors for automatics and new double-clutch systems). Other uses include seat positioning, sunroof, tachometer, headlight positioning, headrests and even control of air input flaps based on air quality information.
Magnetic sensors are also used in shaft position encoding (ie: power windows). The sensors are used to determine how many complete turns a shaft has made in order to control the length of travel of the window lifter. Unusual loading conditions due to the presence of a hand also can be detected by the sensor to provide anti-pinch functionality, which results in the motor turning backward if an obstruction is encountered.
Electronic power steering is also a fast-growing direct motor application. It replaces electro-hydraulic alternatives that use a pump to build pressure in order to provide for greater fuel efficiency. The sensor requirement is in commutation of the motor and also in sensors that detect current.
In hybrid electric vehicles, magnetic sensors are used to monitor auxiliary motor inverters, where the battery direct current needs to be changed to the motor alternating current. Such a conversion requires the use of three current sensors — one for each phase of the motor.