SMOOTHING ALGORITHM FOR VEHICLE AND ENGINE SPEED DETECTION THAT REMOVES GEARBOX AND SENSOR JITTER
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-12
Existing speed measuring systems suffer from noise in the alignment of the sensor poles and in gearbox induced cyclic variations (most people are familiar with the sudden jittery movement of the speedometer under acceleration or the gentle sway- ing of the pointer at constant speed). Modem sys- tems use multi-pole sensors that produce rectangular waveforms, the period of which is dependent on the road speed (one example produces one edge every 20cm of vehicle travel). Examples 1 and 2 below illustrate the typical output of these sensors with no jitter or cyclic variations. Example 3 below illus- trates typical 8 pole jitter. This is caused by the 8 sensors around the shaft not being evenly spaced. The result is that for constant speed, some edges are too early and some too late, however the cycle is accurate for a full rotation from any given angle round to that same angle.