METHOD AND APPARATUS FOR MONITORING ROTATION

Abstract: To monitor the rotation of a disc with normal marks and a reference mark, respective pulses P are produced upon passage of the marks, a first stored value being increased at a steady rate during the spaces between pulses and decreased during the pulses themselves, and a second stored value being increased at a lower steady rate throughout a whole cycle, whereby a comparison of the two stored values at the end of the cycle depends upon the time between the pulses and thus serves to distinguish between the passage of a normal mark and the passage of a reference mark. The stored value may be the charge on a capacitor (C1, C2) or the content of a counter. The disc may be attached to the camshaft of the engine of a motor vehicle and the results of the comparison may be used to determine the point of ignition and the point of fuel injection.

Description: Method and Apparatus for monitoring rotation The present invention relates to the monitoring of rotation and more particularly to monitoring the rotation of a member such as a disc, the circumference of which has a series of regularly spaced normal markings and additionally at least one reference marking. Such arrangements are used to monitor the rotation of the crankshaft of a motor vehicle engine so that a signal processing unit can be used to determine the point of ignition and the point of fuel injection. Such arrangements are disclosed in DE-A-3423664, and in DE-A-2933516. The introductory part of the present claim 1 corresponds to the latter document. In an existing system of the type in whicn a plurality of equally-spaced normal grooves are provided around the circumference of a disc, the reference groove may be an additional one following shortly after one of the other grooves. The output signal of an associated inductive pick-up is sinusoidal for each groove. A pulse generator produces a square wave signal during the positive amplitude, the mark/space ratio being relatively constant. If the relationship between a high time (mark) and the preceding low time (space) is substantially higher, this means that it is a reference pulse. In order to recognise with confidence the difference between normal pulses and reference pulses in all cases, even during acceleration and slowing down and in spite of component tolerances, the groove width ana the inductive pick-up must be so selected that no overlapping or cross-over occurs. The present invention seeks to provide an improved arrangement for identifying reference marks. According to the present invention there is provided an arrangement for monitoring the rotation of a member having a plurality of substantially regularly spaced marks and at least one reference mark wherein the reference mark is distinguished by being of greater or smaller length than the other marks or by being directly adjacent to a spacing of greater or smaller length than the regular spacings between the other marks, comprising sensing means for detecting the marks and producing corresponding electrical output signals of a first and of a second type corresponding respectively to the start and finish of a mark r two storage means the contents of which are dependent upon said electrical output signals, and comparison means for comparing the contents of the storage means, characterised in that the contents of one of the storage means are increased at a substantially constant rate between receipt of a signal of the first type and the immediately following signal of the second type and are steadily decreased between receipt of a signal of the second type and the immediately following signal of the first type, and the contents of the other storage means are steadily increased at a lower rate between receipt of successive signals of the same type, and in that the comparison means compares the contents of the two storage means at the moment of receipt of a signal of- the second type whereby to determine whether the relevant mark is a reference mark. An advantage of such an arrangement is that a simple comparison of the contents of the two storage means permits an unambiguous determination of whether a particular mark is a reference mark. The storage means may operate in an analogue manner and may comprise first and second capacitors which are charged, and in one case discharged, by respective steady currents. Means may be provided for adjusting the magnitudes . of the respective currents; this has the advantage of maintaining the capacitor voltage high compared to noise and other disturbances even at high speeds. Alternatively the storage means may operate in a digital manner and may comprise first and second counters which are counted in one direction, and in one case both directions, at respective steady rates. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Fig 1 shows a pulse-processing circuit of an arrangement in accordance with the present invention; and Fig 2 shows a voltage diagram indicating the voltages at various points in the circuit of Fig 1. In an arrangement according to the present invention a disc is attached coaxially with the camshaft of the engine of a motor vehicle. The circumference of the disc has a plurality of equally-spaced reference marks in the form of rectangular grooves. Between two of these regularly-spaced "normal grooves" there is provided an additional, "reference" groove of substantially the same size and shape as the normal grooves. This may correspond to the top dead-centre position of a first cylinder of the engine, with reference to which fuel injection and electronic ignition are conventionally timed. An inductive pick-up 20 is located next to the disc to detect the passage of the grooves and provides an output voltage indicated at S in 2 Figure. Each groove gives rise to a substantially sinusoidal curve having both a positive and a negative half-cycle. The output from the -pick-up is fed to a pulse generator 30 which produces the pulsed signal P. The pulses have relatively short "high" times and relatively long "low" times. The leading and trailing edges of the pulses are used to control the charging and discharging of first and second capacitors Cl and C2. The control of the charging and discharging is effected by a first logic circuit 40 associated with current sources and sinks 50. Upon occurrence of a trailing pulse edge 12, charging of the first capacitor is initiated at a constant rate and charging of the second capacitor is initiated at a lower constant rate. The voltages across the first and second capacitors are respectively indicated at ϋ^ Upon occurrence of a leading pulse edge 11, discharging of the first capacitor is initiated at a constant rate, whereas uniform charging of the second capacitor continues. At the following trailing edge 12, both capacitors are substantially instantaneously completely discharged, and charging recommences at the respective constant rates. Upon the occurrence of a trailing edge 12 and before complete discharge of the capacitors is initiated, the voltages ϋ^ and U2 are compared by comparison means 60. In Figure 2, pulses Pi and P2 are normal pulses and P3 is a reference pulse following shortly after pulse P2. Between the trailing edge of pulse Pi at time t 2 and the leading edge of pulse P2 at time t3 # ϋ^ has reached such a high value relative to U2 that, ' even after partial discharge of the first capacitor, ϋ^ still exceeds l^. Thus U j _ > ϋ 2 unambiguously identifies a normal pulse. Between the trailing edge of pulse P2 at time t 4 and the leading edge of pulse P3 at time t 5 , U } has not obtained a substantially higher value, so mat at the time 6 of the trailing edge of pulse P3, ϋ^ lies oelow u 2 . Thus U > O unambiguously identifies a reference pulse eg a top dead-centre pulse. The output of the comparison means 60 is supplied to a second logic circuit 70 and then via output 80 to suitable signal-processing apparatus. An advantage of the above-described arrangement is that it provides definite identification of a reference mark even with quick changes of rotational speed of the disc. In a modification of the above arrangement, means are provided for adjusting the values of the charging and discharging currents. Thus for high disc rotation speeds, high current levels may be selected so that the capacitor voltages U and U 2 are kept higher than noise and other disturbing signals. Instead of the capacitors two counters can be employed which are triggered at different rates. The first counter counts upwards during the low part of the pulse generator output and downwards during the high part. If at the high-low transition of the pulse generator (trailing-edge) the count of the first generator is higher than that of a second counter which only counts upwards, it represents a normal pulse. If the count of the second counter is greater than the first, it represents a reference pulse. After tms opip isor. the counters are reset and can begin a new cycle of counting. The counting rates can be adjusted to maintain discrimination at high disc rotating speeds. In another modification, the reference groove is separated from the preceding normal groove by an increased spacing. In this case the charging and discharging currents are selected so that the criteria for recognition of a reference pulse are reversed, i.e. ϋ 2 > ϋ^ normal pulse. D l > ϋ 2 reference pulse. Any suitable marking may be used; for example instead of grooves, teeth , slots or holes may be provided. The reference marking may be in the form of an extra marking, a missing marking, or a marking of different size. Instead of inductively, the detector may operate in any suitable way, e.g. optically, capacitatively or ultra-sonically.

Claims: Claims 1. An arrangement for monitoring the rotation of a member having a plurality of substantially regularly spaced marks and at least one reference mark wherein the reference mark is distinguished by being of greater or smaller length than the other marks or by being directly adjacent to a spacing of greater or smaller length than the regular spacings between the other marks, comprising sensing means (20,30) for detecting the marks and producing corresponding electrical output signals (P) of a first (12) and of a second type (11) corresponding to the ends of a mark, two storage means (Cl,C2) the contents of which are dependent upon said electrical output signals, and comparison (60) means for comparing the contents of the storage means, characterised in that the contents U^ of one of the storage means are increased at a substantially constant rate between receipt of a signal of the first type and the immediately following signal of the second type and are steadily decreased between receipt of a signal of the second type and the immediately following signal of the first type, and the contents U of the other storage means are steadily increased at a lower rate between receipt of successive signals of the same type, and in that the comparison means compares the contents of the two storage means at the moment of receipt of a signal of the second type whereby to determine whether the relevant mark is a reference mark. 2. An arrangement according to claim 1 wherein the sensing means provides output pulses, a signal of the first type being the trailing edge (12) of a pulse and a signal of the second type being the leading edge (11) of a pulse. 3. An arrangement according to claim 1 or 2 wherein the storage means- operate in an analogue manner. 4. An arrangement according to claim 3 wherein the storage means are first and second capacitors which are charged, and in one case discharged, by respective steady currents. 5. An arrangement according to claim 4 wherein means are provided for adjusting the magnitudes of the respective currents. 6. An arrangement according to claim 1 or 2 wherein the storage means operate in a digital manner. 7. An arrangement according to claim 6 wherein the storage means are first and second counters which are counted in one direction, and in one case both directions, at respective steady rates. 8. An arrangement according to any preceding claim wherein the marks are grooves in the circumference of a conductive disc, the grooves being narrower than the spaces between them, and the sensing means comprise an inductive pick-up. 9. An arrangement according to any preceding claim wherein the rotating member is a disc attached to the camshaft of a motor vehicle engine. 10. A method of monitoring the rotation of a member having a plurality of substantially regularly spaced marks and at least one reference mark wherein the reference mark is distinguished by being of greater or smaller length than the other marks or by being directly adjacent to a spacing of greater or smaller length than the regular spacings between the other marks, comprising detecting the marks and producing corresponding electrical output signals of a first and of a second type corresponding respectively to the start and finish of a mark, the method being characterised in that a first stored value is increased at a substantially constant rate between receipt of a signal of the first type and the immediately following signal of the second type and is steadily decreased oetween receipt of a signal of the second type and the immediately following signal of the first type, and a second stored value is steadily increased εt a lower rate oetween receipt of. successive signals of the same type, and the two stored values are compared at the moment of receipt of a signal of the second type whereby to determine whether the relevant mark is a reference mark.

Inventors: VOGEL WOLFGANG, VOGEL, WOLFGANG
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02P7
IPC codes: F02D41, F02D45, F02P7, H03K5