A new differential magnetoresistive gear wheel sensor with high suppression of external magnetic fields [automotive applications]

Rotational speed detection is one of the most essential sensor tasks in today´s cars. It is used to determine the position of the crank- and camshaft as well as for the control of the wheel speed in ABS applications. One of the most promising approaches for rotational speed detection is the use of magnetoresistive sensors in front of a turning gear wheel. These sensors offer a high sensitivity to magnetic fields. Furthermore, the high signal-to-noise-ratio results in a very small phase error due to phase jitter. This makes the use of MR-technology very attractive for revolution counting with the parallel implementation of additional features, such as misfire detection, for example. In the proximity of new engine components like the integrated starter generator which causes large disturbing magnetic fields, these sensors require magnetic shielding in order to produce a correct output signal. For this reason, a new generation of engine speed sensors is under development, which combines the described advantages of magnetoresistive technology with a high robustness against disturbances caused by external magnetic fields due to neighbouring engine components.