A new differential magnetoresistive gear wheel sensor with high suppression of external magnetic fields

Abstract

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. In the last years, the general demand for less fuel consumption and less exhaust emissions has yielded harsher requirements particularly for crankshaft sensors. 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 cause 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. INTRODUCTIONThe property of a current-carrying magnetic material to change its resistivity ρ in the presence of an external magnetic field H is called the magnetoresistive (MR) effect. The effect has been described previously [1]. Because the magnetoresistive effect is a nonlinear effect by nature, a number of magnetoresistive sensors use a 'barber-pole' construction to linearize the R − H relationship, incorporating slanted stripes of a good conductor to rotate the current. This type of sensor has the widest range of linearity and the least associated distortion than any other form of linearization. The characteristic of a magnetoresistive element with barberpole-stripes is plotted in figure 1 (curve a)). It can be seen, that for small values of the magnetic field strength H, the R − H dependence is quasi-linear. By rotation of the barberpole stripes the characteristic of the resistor can be inverted (curve b). For the realisation of a rotational speed sensor, typically four

Investigation on the Output Signal of Rotational Speed Sensor for Different Flux Surfaces between Gear Wheel and Sensor

“…Fig. 5 Magnetic Wheel Speed Sense Options; magnet in x-direction [3] Left : Magnetic field provided by a multipole Wheel, Right : Altering the bias field provided by a permanent magnet [4] High-precision speed sensors in cars are widely used to meet the requirements of security and environmental protection. One of the application area is tracking control system (TCS).…”

“…Fig. 3 Output of sensor in front of a moving gear wheel [3] Sensitivity of the sensor structure is reduced and prevented from operating in saturation with by increasing of the biasing permanent magnet angle mag φ [3].…”