Method for adapting mechanical tolerances when performing time measurements on rotating shafts

#The invention relates to a method for adapting mechanical tolerances when performing time measurements on rotating shafts, in particular on internal combustion engine crankshafts or shafts connected thereto.

#One possible way of measuring time is by providing the shaft itself, or preferably a sensor wheel connected thereto, with marks and scanning the marks through the use of a sensor. The time within which the shaft rotates through a specific angle of rotation or through a specific segment is measured. In that way, fluctuations in rotational speed are sensed to a very high resolution, in addition to the rotational speed, as a function of the distance between the marks on the periphery of the shaft or the sensor wheel.

#Such measurements are used, for example, in internal combustion engines, in order to detect combustion misfires by reference to a brief slowing down of the angular speed of the crankshaft. However, if the marks or the sensor wheel have mechanical faults or inaccuracies, such as, for example, angular faults of the segments or faults in marking teeth on the sensor wheel, eccentricity of the disk or deviations in the tooth shape, the measurement of the angular speed is falsified. As a consequence thereof, misdiagnoses may be made when detecting combustion misfires.

#FIG. 1 is a diagrammatic, elevational view of a sensor wheel with an associated sensor for a 6-cylinder internal combustion engine;

#FIG. 2 is a table showing deviations of adaptation values assigned to segments relative to those for a reference segment; and

#FIG. 3 is a flowchart for an adaptation method according to the invention.

#Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a sensor wheel which has ferromagnetic teeth, is mounted on a non-illustrated crankshaft of a 6-cylinder internal combustion engine and is designated by reference symbol GR. During the rotary movement of the crankshaft, an inductive sensor SE generates a voltage signal which fluctuates with the distance from the front surface of the gearwheel. The sensor wheel GR thus forms a modulator for converting an input variable of the angular speed, which is analogous with the amplitude, into a signal which is analogous with the frequency. Zero crossover points of this signal also contain information on the instantaneous angle. A magnetic field changes as a result of a sequence of tooth gaps and of teeth of the sensor wheel GR.

#Removing one or more teeth on the sensor wheel GR makes it is possible to obtain a region for an angular reference which can be used to determine an absolute angle. Sixty teeth minus a gap of two teeth has become established as the standard for pulse transmitters on the crankshaft of internal combustion engines.

#The sensor wheel GR illustrated in FIG. 1 for a 6-cylinder internal combustion engine is divided into three segments which each include 120.degree. corresponding to a complete working cycle of two crankshaft revolutions (720.degree.). In this case, the cylinders 1 and 6 are assigned to a segment SEG 1+6, the cylinders 2 and 5 are assigned to a segment SEG 2+5, and the cylinders 3 and 4 are assigned to a segment SEG 3+4. This division of the segments applies to a 6-cylinder internal combustion engine with an ignition sequence 1-5-3-6-2-4. The direction of rotation of the sensor wheel GR is indicated with an arrow symbol.