System and apparatus to determine the angular position, and speed of a rotating shaft, particularly crank shaft of an internal combustion engine

Claim 1

Sensing system to determine angular position of a rotary shaft (W) having a disk element (S,S') rotating with a shaft, the disk element being subdivided into a plurality of successive zones of equal radial distance (r) from the center of the disk, and separated from each other by a plurality of circumferentially positioned angle position marker elements (21-32; 41-47) separating said zones, which angle marker elements are narrow with respect to the circumferential extent of the zones and which are formed with abrupt flanks to result in sharp change of a physical parameter upon rotation of the disk past a fixed pick-up sensor (35) and comprising, in accordance with the invention an additional marker element (33) forming a reference marker located in at least one of the zones and between two angle position marker elements, the angular distance of said additional reference marker element to a first angle position neighboring marker element (21) at one side of said reference marker element being substantially larger than the angular distance to a second neighboring marker element (32) at the opposite side of said reference marker element (33); a fixed sensor (35) positioned in sensing relation to said disk element and sensing passing both the angle position marker element and the additional reference elements past the sensor upon rotation of the shaft and providing needle-pulse type output signals; two counters (Z 1 , Z 12 , Z 1n ; Z2) connected to and controlled by the sensor to start counting upon receipt of an output signal from the sensor; means generating a first frequency (f 1 ), said first frequency being applied to the first counter as a counting clock frequency therefor; means generating a second frequency (f 2 ) which is higher than said first frequency (f 1 ), said second frequency being applied to the second counter as a counting clock frequency therefor; a memory (Sp) connected to the first counter (Z 1 ), Z 12 , Z 1n ) and receiving the count state thereof which said first counter has reached in the period of time from a preceding output signal; a comparator (V) connected to the memory (Sp) and to said second counter (Z 2 ) and comparing whether the count state of the second counter, counting at the higher frequency, has a value which is greater, or less than the value stored in the memory; and a transfer switch, operated by the comparator to route the signal from the sensor (35) (a) to a first output line (39) indicative of a marker pulse if the comparator determines that the count state of the second counter, (Z 2 ) upon termination of its counting period due to occurrence of a subsequent output signal from the sensor, has not reached the count state stored in the memory based on the preceding stored count state derived from the first lower frequency counter; and, (b) to a second output line (40) if the count state of the second counter (Z2) reaches the count state stored in the memory (S p ) based on the preceding stored count state derived from the first, lower frequency counter.