All modern vehicles must sense the position and movement of automotive control functions such as turn signal indicators and gear selectors. However, engineers face challenges here with conventional sensor technologies as the requirement is for sensing movement in the three axes simultaneously. The challenge lies in the physical size of the device, its reliability, power consumption, and its cost. However, 3-D magnetic sensing technology, recently introduced, could be helping engineers to address these challenges.
It is well known that electro-mechanical switching is a common source of failures in the several applications, including in automobiles. Contacts usually corrode or burn out over a period, causing inconveniences and failure to the owner of the vehicle, also potentially damaging the reputation of the manufacturer of the car. Therefore, most car manufacturers prefer using solid-state technology, such as switching based on Hall-Effect detection of magnetic signals. This method increases the reliability, saves space, and is inexpensive.
When driving a car, among the most common things people do is to signal for a turn and change gears. In the past, most cars used heavy current wiring harnesses around the vehicle for transmitting signals and power. Lately, using a turn indicator or a gearshift is more likely to send a high-impedance signal to a central processing unit rather than physically switching something over.
Vehicular control is becoming more sophisticated and multi-functional, with the trend moving towards sensing in more than one plane. For instance, most modern cars using automatic gearboxes now have sequential controls and move the gear lever into a different plane. That makes the task of sensing position more complex than ever.
Magnetic 3-D Sensing
Hall Effect sensing for implementing 3-D position sensing is actually possible in several ways. One can place individual Hall sensors at the multiple fixed positions where the movement has to be sensed—just as in the case of a turn signal or a gear lever. This may result in as many as seven sensor elements, and the controller will know the position by locating the live sensor.
Another method could be to use flux concentrators. Although this method also uses Hall sensors, the number of sensors used is lower. This is because two pairs of orthogonal sensing elements are integrated into a CMOS IC, whose surface has a deposit of a ferromagnetic film to enhance the magnetic field, increase the sensitivity, and increase the signal-to-noise ratio.
Several algorithms in subtraction and addition make it possible to accurately sense the magnetic field components present in the horizontal (X and Y) and the vertical (Z) directions to the IC. Analog to digital converters then convert these analog voltages from the sensors to digital values and the digital signal processors then compute the final, absolute position.
However, none of the above is a viable solution in the automotive sector, as these are not suitable for mass production, because multiple sensors are involved. However, there is another alternative, also based on Hall-Effect sensors—the TLE493D-A1B6 3-D sensor. This simultaneously determines the x, y, and z coordinates of the magnetic source, while building a 3-D image of the magnetic field that surrounds the sensor.