Engine position sensor

Abstract: Apparatus for developing a series of square-wave pulses (112) from an alternating voltage (110) generated in the pick-up coil (20) of a variable reluctance sensor (16-20) associated with a slotted wheel (10) driven by the crankshaft of an internal combustion engine (12). The system has an adaptive control which comprises a peak detector (52-58) including a capacitor (56) and a voltage comparator (Q1-Q7). The capacitor (56) is charged to a peak voltage that corresponds to the peak value of the positive half-cycles (110A) of the alternating voltage (110). The comparator (Q1-Q7) is connected to compare the peak voltage and a voltage that corresponds to the magnitude of the positive half-cycles. A diode (44) is connected between the pick-up coil (20) and the peak detector (52-58) which prevents charging of the capacitor (56) and accordingly prevents adaptive control until the voltage induced in the pick-up coil (20) is high enough to cause the diode (44) to conduct in the forward direction.

Description: ENGINE POSITION SENSOR This invention relates to an engine position sensor for developing square-wave pulses from an alternating voltage that is developed by a variable reluctance sensor. Systems for developing square-wave pulses as a function of the angular position of the crankshaft of an internal combustion engine are well known. In some of these systems a wheel which has a plurality of angularly spaced slots is driven by the crankshaft of an internal combustion engine. The wheel rotates past a variable reluctance sensor that has a pick-up coil. An alternating voltage is induced in the pick-up coil each time a slot in the wheel passes by the sensor. The alternating voltage is converted to a series of square-wave pulses which can be used as timing pulses for a digital electronic ignition system. A problem associated with systems of the type described is that imperfections in the wheel may cause noise voltages to be induced in the pick-up coil which may be converted into false square-wave pulses. As one possible solution to this problem, so-called adaptive controls have been developed. In one known type of adaptive control, a capacitor is charged to the peak voltage developed in the pick-up coil by a peak detector. This peak voltage is then used as a threshold voltage for a voltage comparator and when the voltage induced in the pick-up coil has a certain relationship with the threshold voltage, the comparator switches states to cause a voltage transition that defines the leading edge of a square-wave pulse to be developed. The system is an adaptive system because it adapts to the fact that the peak amplitude of the voltage induced in the pick-up coil varies with changes in the speed of rotation of the engine driven wheel. Thus, the amplitude of the peak voltage increases as the speed of rotation of the wheel increases. EP-A-0,282,732 discloses a circuit arrangement for evaluating the output signals of an inductive sensor such as a needle-stroke sensor which senses the nozzle needle of a fuel injection nozzle of an internal combustion engine. The circuit arrangement includes a peak detector including a capacitor and a diode. The diode prevents operation of the peak detector circuit when the output of the sensor is below a predetermined level. The output of the peak detector is used to adjust the operation of the circuit arrangement to account for sensor tolerances and temperature changes. It is an object of this invention to provide an improved engine position sensor. According to an aspect of the present invention, there is provided an engine position sensor as specified in claim 1. Preferably, an adaptive control is provided which does not come into operation until engine speed exceeds some value. More specifically, the adaptive control may include a diode connected between the pick-up coil of the sensor and a peak detector for charging a capacitor. The control can prevent energizing the peak detector from the alternating voltage induced in the pick-up coil until the voltage induced in the pick-up coil is high enough to forward bias the diode. In effect, the control can prevent adaptive operation over a low speed range of the engine. In a preferred embodiment, a voltage comparator forming part of the adaptive control, has three inputs and one output. The voltage of the first input is compared to the voltages of the second and third inputs. The first input is connected to the pick-up coil. The second input has a voltage, when engine speed is high enough to cause the diode to be forward biased, that is related to the voltage of the capacitor that has been charged by the peak detector. The third input may have a low or high state which is dependent upon the switching state of the comparator. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawing, in which: Figure 1 is a schematic circuit diagram of an embodiment of adaptive control system; and Figure 2 illustrates voltage waveforms derived from the system of Figure 1. It is to be understood that the values of the components of the circuit described below are given by way of example only. As will be fully apparent to the skilled person, in practice the values of the components are chosen in dependence upon the particular application of the circuit. Referring to Figure 1, a wheel 10 that is driven by the crankshaft of an internal combustion engine 12 has six radially extending slots 14, which are spaced from each other by sixty angular degrees. The number of slots and their angular spacing is given by way of example and the number of slots and their angular spacing can be varied to suit a particular application. Disposed adjacent the outer periphery of wheel 10 is a variable reluctance magnetic pick-up. This pick-up comprises a permanent magnet 16 and a core 18 formed of magnetic material. A pick-up coil 20 is wound on core 18. As a slot 14 rotates past the end of core 18, an alternating voltage is induced or generated in pick-up coil 20. The voltage waveform 22 generated in coil 20 is formed of a series of alternating voltages. Waveform 22 shows three consecutively occurring alternating voltages which represent the passage of three slots past the end of the sensor. Each alternating voltage generated occurs at a predetermined angularly spaced position of the engine crankshaft. One end of coil 20 is grounded, while the other end is connected to conductor 24. Conductor 24 is connected to a junction 26 through a 40kΩ resistor 28. A resistor 30 of 14kΩ and a 1000pf capacitor 32 are connected between conductor 24 and ground. A 16kΩ resistor 36 and a p-n junction semiconductor diode 38 are connected in series between junction 26 and ground. Junction 26 is connected to conductor 40 which, in turn, is connected to one input of a voltage comparator described hereinafter. Junction 26 is connected to a junction 42 through a p-n junction semiconductor diode 44 and a 15kΩ resistor 46. A 12kΩ resistor 48 is connected between junction 42 and ground. Junction 42 is connected to a conductor 50 which, in turn, is connected to the input of a peak detector, to be described. The peak voltage of the alternating voltage generated in coil 20 may go as high as 200 volts. The positive half-cycles of the alternating voltage is attenuated or scaled down by voltage divider circuits. Thus, the voltage at junction 26 and conductor 40 is scaled down by a voltage divider formed from the resistor 28 and the resistor 36. The voltage at junction 26 is further attenuated or scaled down by a voltage divider formed by the resistors 46 and 48. On the basis of the resistor values given above, the voltage at junction 42 and conductor 50 will be about 12/(12+15) or about 0.44 times the voltage at junction 26. The circuit includes a peak detector for detecting the peak alternating voltage on conductor 50. This peak detector comprises a unity gain amplifier 52 having a input connected to conductor 50. The output of amplifier 52 is connected to a conductor 54. A capacitor 56, which may have a capacitance of about one microfarad, is connected between conductor 54 and ground. A resistor 58, of about 500kΩ resistance, is connected between conductor 54 and ground and therefore in parallel with capacitor 56. The conductor 54 is also connected to a conductor 60 through two series connected p-n junction semiconductor diodes 61 and 63. During the positive half-cycles of the voltage generated in coil 22, the peak detector charges the capacitor 56 to substantially the peak positive voltage at junction 42, which in this example will be about 0.44 times the peak voltage at junction 26. As the positive half-cycle goes from its peak voltage towards zero, the capacitor will discharge through the resistor 58. The peak detector may take the form of a voltage comparator. The conductor 60 forms one input to a voltage comparator, which will be described. Conductor 60 is connected to a junction 62 through a 17kΩ resistor 64. A 2.4kΩ resistor 66 is connected between junction 62 and ground. A 19.2kΩ resistor 68 is connected between junction 62 and a conductor 70. The conductor 70 is connected to a junction or terminal 72 which has a positive direct voltage of about 2.1 volts applied thereto in a manner to be described. The voltage at junction 62 from the positive 2.1 volts on line 70 will be about (2.1 x 2.4)/(19.2 + 2.4), or about 0.24 volts. The voltage on conductor 60 will be the voltage on capacitor 56 less the voltage drops across diodes 61 and 63. The voltage on conductor 60 therefore represents the peak positive peak voltage to which capacitor 56 has been charged less any voltage caused by the discharge of capacitor 56 through resistor 58. The circuit also includes a voltage comparator which comprises PNP transistors Q1, Q2, Q3, Q4 and Q5 and NPN transistors Q6 and Q7. The emitters of transistors Q2 and Q3 are connected together and to a conductor 74. The collector of transistor Q2 is connected to the collector of transistor Q6, which is connected to form a diode. The collector of transistor Q3 is connected to the collector of NPN transistor Q7. The emitters of transistors Q6 and Q7 are connected together and to ground. The base electrodes of transistors Q6 and Q7 are connected together. The base of transistor Q2 is connected to the emitter of transistor Q1 by conductor 76, the collector of transistor Q1 being grounded. The base of transistor Q3 is connected to the emitters of transistors Q4 and Q5. The collector of transistor Q7 is connected to the base of an NPN transistor Q8 by conductor 78. The emitter of transistor Q8 is grounded. Conductor 76 is connected to one of the collectors of a PNP transistor Q9. The other collector of this transistor Q9 is connected to the emitters transistors Q4 and Q5. The emitter of transistor Q9 is connected to a power supply conductor 80 through a resistor 82. The base of transistor Q9 is connected to the bases of PNP transistors Q10, Q11 and Q12. Transistor Q12 is connected as a diode and its collector is connected to the collector of an NPN transistor Q13. The emitter of transistor Q13 is connected to ground through a 14kΩ resistor 85. Transistors Q9, Q10, Q11 and Q12 provide a current source function. Transistor Q13 is a current generator. The base of transistor Q5 is connected to a junction 84 on conductor 86. Conductor 86 is connected to the emitter of an NPN transistor Q14 and it can be seen that the base of transistor Q5 is connected to the emitter of transistor Q14. The collector of transistor Q14 is connected to conductor 80. The base of transistor Q14 is connected to the collector of transistor Q8 through conductor 88. The base of transistor Q14 and the collector of transistor Q8 are connected to the collector of transistor Q10. The conductor 86 is connected in series with two 20kΩ resistors 90 and 92. The junction 94 of these resistors is connected to the base of an NPN transistor Q15. The emitter of transistor Q15 is connected to ground. The collector of transistor Q15 is connected to conductor 96 through a current source 100. Conductor 96 is connected to junction 102 which has a positive direct voltage of five volts applied thereto. The collector of transistor Q15 is also connected to an output terminal 98 for the system. Transistor Q15 is part of an output circuit for the system that develops square-wave pulses on terminal 98 at certain angular positions of the crankshaft of the engine. When transistor Q15 is biased conductive, the voltage at terminal 98 is low or near ground potential. When transistor Q15 is biased non-conductive, the voltage at terminal 98 is high or, in other words, at a positive direct voltage level of about five volts higher than ground. The power supply for the system will now be described. The system is powered by the twelve volt storage battery 104 of a motor vehicle. The negative side of battery 104 is connected to ground. The positive side of battery 104 is connected to conductor 80 through a resistor 106. The voltage on conductor 80 is about 12 volts. The battery 104 feeds a voltage regulator 108 which has two outputs connected respectively to terminals 102 and 72. The regulator 108 develops a positive direct voltage of five volts on terminal 102 and 2.1 volts on terminal 72. These voltages are applied to the system in the manner described above. In this regard, terminals designated by the same reference numeral are connected together. Before proceeding to a detailed description of the operation of this circuit, a general description of this operation will now be given with reference to Figure 2. In Figure 2, reference numeral 110 designates an alternating voltage that is induced in coil 20 as a slot 14 passes the sensor. This voltage has a positive half-cycle 110A and a negative half-cycle 110B. Figure 2 also shows a square wave pulse 112 which has a leading rising edge 112A and a trailing falling edge 112B. Pulse 112 appears at terminal 98 and is caused by the on-off switching of transistor Q15. Also shown in Figure 2 is a trigger or threshold voltage level shown as dotted line 114. Level 114 corresponds to a voltage on capacitor 56 and represents peak voltage. This level 114 will vary in dependence upon the peak amplitude of alternating voltage 110. The waveforms of Figure 2 are not to be taken as indicative of the actual magnitude or shapes of the voltages developed by the circuit but are generalized waveforms to aid in explaining the operation of the circuit. As an alternating voltage 110 is generated, the beginning of the positive half-cycle 110A increases in a positive direction and when it reaches the trigger or threshold level 114 the transistor Q15 is biased non-conductive, thereby to cause the rising edge 112A of square-wave 112 to be developed. Square-wave 112 now remains at a high level 112C until the positive half-cycle 110A goes through zero at point 116. When this happens, transistor Q15 is biased conductive to cause the falling edge 112B of square-wave 112 to be developed. The falling edge 112B is used in digital ignition systems for timing purposes. In more detail, the voltage comparator has three inputs, namely the bases of transistors Q1, Q4 and Q5, and an output 78 which controls the switching of transistors Q8, Q14 and Q15. A high level voltage on line 78 causes transistor Q8 to be biased on which, in turn, causes transistors Q14 and Q15 to be biased off. A low level voltage on line 78 causes transistor Q8 to be biased off which, in turn, causes transistors Q14 and Q15 to be biased on. The comparator input at the base of transistor Q1 has a voltage applied thereto from junction 26 and conductor 40 which is a scaled down version of the voltage induced in coil 22. This voltage at the base of transistor Q1 is compared to the voltages, respectively, at the bases of transistors Q4 and Q5. When the engine is running above a predetermined speed, the voltage at the base of transistor Q4 will follow the voltage on capacitor 56. This capacitor voltage varies as a function of the peak amplitude of alternating voltage induced in coil 20. In general, the dotted line 114 in Figure 2 represents the variable peak voltage attained by capacitor 56. When the voltage at the base of transistor Q1 reaches a value that exceeds the peak-related voltage on the base of transistor Q4, the voltage comparator switches to a state where the voltage on conductor 78 biases transistor Q8 on. With transistor Q8 biased on, transistors Q14 and Q15 are biased off causing the rising edge of pulse 112A in Figure 2 to be developed. When transistor Q14 is biased off, the voltage at junction 84 drops, from a positive value above ground, substantially to ground potential, due to the path to ground through resistors 90 and 92, and is applied to the base of transistor Q5, which is one of the comparator inputs. The voltage at the base of transistor Q5 (ground potential) is now compared to the voltage at the base of transistor Q1. When the voltage at transistor Q1, which corresponds to the decreasing part of the positive half-cycle 110A shown in Figure 2 drops to ground potential, the comparator switches to a state that causes transistor Q8 to be biased off. With transistor Q8 biased off, transistors Q14 and Q15 are biased on causing the falling edge of pulse 112B (Figure 2) to be developed. This happens at point 116 in Figure 2, where the positive half-cycle of the alternating voltage crosses zero. The above description has assumed that the engine speed is higher than a predetermined speed. At low engine speeds, a different mode of operation takes place which disables the peak detector 52 so that the system no longer operates in an adaptive manner, such that the voltage at the base of transistor Q4 no longer varies and remains substantially constant. In this regard, the p-n junction semiconductor diode 44 will not conduct in a forward direction (anode to cathode) until a voltage of about 700 millivolts is applied across it. At low engine speeds, the peak voltage induced in coil 20 may be as low as 250 millivolts. When the voltage induced in coil 20 is below a value that will cause the forward conduction of diode 44, the peak detector 52 is not energized and capacitor 56 is not charged. Accordingly, there is no voltage applied to the base of transistor Q4 that can be attributable to the voltage on capacitor 56, since it was not charged. Under this condition, the voltage at the base of transistor Q4 will be substantially equal to the voltage at junction 62, which is about 0.24 volts, as explained above. A fixed trigger or threshold voltage of about 0.24 volts at the base of transistor Q4 is now compared to the voltage at the base of transistor Q1 and when the voltage at the base of transistor Q1 exceeds this fixed threshold voltage, the comparator switches state to cause the rising edge 112A of Figure 2 to be developed. In effect, at low engine speeds the peak detector 52 is disabled by diode 44 to ensure that adaptive control, including the charging of capacitor 56, does not start until the voltage induced in pick-up coil 20 is high enough to cause diode 44 to conduct in a forward direction. As will be apparent to the skilled person, a circuit of the type described above could also be used to measure the position of the engine camshaft(s).

Claims: An engine position sensor for producing a series of square-wave pulses related to the angular position of an engine, comprising a variable reluctance sensor which includes a pick-up coil (20) and a wheel (10) driven by the engine, the wheel comprising a plurality of slots (14) adapted to induce an alternating voltage in the pick-up coil on the passage of the slots across the sensor; a voltage comparator including at least first and second inputs (Q1,Q4) and an output (78), the first input (Q1) being coupled to the pick-up coil; square-wave voltage developing means (Q15) coupled to the output (78) for developing the square-wave pulses; a peak detector (52) including a capacitor (56), the peak detector being connected to the pick-up coil for charging the capacitor to a voltage related to the peak voltage of the alternating voltage induced in the pick-up coil, the capacitor (60) being coupled to the second input (Q4) of the comparator and being adapted to cause the output of the comparator to drive the square-wave voltage developing means so as to develop a first voltage transition when the voltage at the first input of the comparator reaches a predetermined value related to the voltage at said second input of said comparator and a second voltage transition opposite to the first voltage transition when the voltage at the first input of the comparator is less than a second predetermined value; charge preventing means for preventing charging of the capacitor until the amplitude of the alternating voltage induced in the pick-up coil exceeds a predetermined amplitude; and means (62-72) for maintaining the voltage applied to the second input of the comparator at a fixed amplitude when there is no voltage across the capacitor; the comparator including a third input (Q5) responsive to the output (78) of the comparator, the third input having a low potential when the output (78) causes the square-wave developing means (Q5) to develop the first voltage transition; the comparator being adapted, when the third input (Q5) is at a low potential, to compare the voltages at the first and third inputs (Q1,Q5) and to switch to a second state when the voltage at the first input (Q1) becomes less than the low potential, so as to cause the square-wave developing means to develop the second voltage transition. An engine position sensor according to claim 1, wherein the comparator is adapted to switch to the second state when the alternating voltage induced in the pick-up coil crosses through a zero level. An engine position sensor according to claim 1 or 2, wherein the first voltage transition is a rising edge of a square-wave and the second voltage transition is a falling edge of a square-wave. An engine position sensor according to any preceding claim, wherein one end of the pick-up coil (20) is connected to ground, and the low potential is substantially ground potential. An engine position sensor according to any preceding claim, wherein the charge preventing means comprises a diode (44) connected between the pick up coil and the peak detector.

Inventors: CHRISTENSON REBECCA ANN, GOOD BRIAN KEITH, CHRISTENSON, REBECCA ANN, GOOD, BRIAN KEITH
Applicants: DELCO ELECTRONICS CORP, DELCO ELECTRONICS CORPORATION
Application year: 1992
Main classification: G01D5
IPC codes: G01P3, F02D35, F02P5, F02P7, F02D45