High-accuracy magnetic position encoder concept

Position sensors based on the detection of magnetic flux densities by Hall sensors or magnetoresistors are used in automotive applications for crankshaft and camshaft position sensing, which are needed for engine control. This paper identifies the limitations of traditional designs, which introduce an angular error between the position signal pulse and the actual location of the corresponding triggering feature on the sensor target wheel. It proposes a solution ensuring that the position signal pulse coincides with a point of symmetry in the triggering target wheel feature, thus eliminating the angular error. Two interesting implementations are described in this paper. One of them is analyzed in full detail, and a methodology for its design is provided. In particular, specific design rules are derived which link some of the design parameters to relevant dimensional specifications. These rules are established on the basis of a geometrical method developed for this particular type of problem which necessitates the calculation of flux densities in a few specific locations, namely, where the sensing elements are located. The overall approach, including these design rules, is validated by finite-element analysis, as well as by experimental data.