Garrard, M. and Edwards, W., "Unique Variable Reluctance System for Improved Noise Immunity," SAE Technical Paper 2012-32-0053, 2012, doi:10.4271/2012-32-0053.
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.