Unique Variable Reluctance System for Improved Noise Immunity

Accurate knowledge of crank angle is essential to the correct operation of both ignition and fuel injection systems, yet the interface is one of the most problematic in a fuel injection system. The problems are well known to car manufacturers, but for many small engine manufacturers they are yet to be encountered. This paper describes a semiconductor circuit solution as integrated into the MC33813 and MC33814 Application Specific ICs for small engines. A circuit has been developed that uses the mathematical properties of VR sensor signals to create a robust interface that makes the fewest possible mistakes in the counting of crank position teeth. Validation pictures show a high level of noise immunity thus demonstrating suitability for the variation present in high volume manufacturing.