GB1566396A

GB1566396A - Electrical displacement transducer

Info

Publication number: GB1566396A
Application number: GB12330/78A
Authority: GB
Original assignee: Hughes Microelectronics Ltd
Current assignee: Hughes Microelectronics Ltd
Priority date: 1978-03-29
Filing date: 1978-03-29
Publication date: 1980-04-30
Also published as: FR2421365A1; DE2911420C2; IT7921387A0; IT1113050B; JPS54133363A; JPH0115803B2; DE2911420A1; FR2421365B1

Description

(54) AN ELECTRICAL DISPLACEMENT TRANSDUCER (71) We, HUGHES MICROELECTRONICS LIMITED, a British Company, of Queensway Industrial Estate, Glenrothes, Fife, Scotland, KY7 5PY, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to an electrical displacement transducer which has particular but not exclusive application to use with an internal combustion engine, to provide an electrical signal indicative of the angular rotational position of the engine crankshaft, for use in controlling spark ignition of the engine.

Conventionally, spark ignition of an internal combustion engine is controlled by mechanical contact breaker points which are operated by a rotary cam driven from the crankshaft of the engine. Timing of the spark ignition is controlled by moving the angular position of the contact breaker points relative to the cam's axis of rotation in dependence upon the level of partial vacuum obtaining in the inlet manifold to the engine.

Recently, electronic ignition systems for internal combustion engines have been developed. The electronic systems permit the timing of the spark ignition to be controlled in dependence not only upon the aforementioned vacuum level but also in dependence upon a plurality of other engine operating parameters and consequently permit the engine to operate more efficiently. The electronic ignition systems do not require the conventional contact breaker and cam arrangement, but some means is required to provide to the system an electrical signal indicative of the angular position of rotation of the engine in order that the system can control the timing of the spark ignition. Moreover, the angular position of rotation of the engine crankshaft needs to be monitored much more accurately than is possible with the conventional cam and contact breaker arrangement if the advantages of efficiency of engine operation made possible by the electronic ignition systems are to be maximised.

Accordingly, it is an object of the present invention to provide an improved electrical displacement transducer which has particular but not exclusive application to providing an electrical signal indicative of the angular position of rotation of an internal combustion engine.

In accordance with the present invention there is provided an electrical displacement transducer comprising spaced apart transmitting and receiving means for respectively transmitting energy and receiving said energy, a member for being moved between said transmitting and receiving means, said member being adapted to interrupt repetitively the passage of said energy from the transmitting means to the receiving means as a function of the movement of the member between said means, said receiving means being adapted to produce an electrical output signal which assumes a first magnitude during said repetitive interruptions and a second different magnitude for periods between said interruptions, and means arranged to produce an output indicative of when said signal exceeds a magnitude representative of an average of said first and second magnitudes whereby to provide an indication of the commencement and cessation of said interruptions.

The transducer of the present invention has the advantage that the output provides an accurate indication of the commencement and cessation of the interruptions, even in the event that a variation occurs in the first and second magnitudes of the signal from the receiving means.

Preferably, the transmitting and receiving means comprise coils spaced apart for inductive coupling therebetween, and the movable member comprises a rotary disc having a castellated periphery, the coils being so positioned that upon rotation of the disc, the castellations thereof interrupt the inductive coupling between the coils. With this preferred arrangement, the disc can be mounted to rotate with the crankshaft of an internal combustion engine. The edges of the castellations can be positioned to define predetermined positions prior to top dead centre for the respective pistons of the engine, so that in use, the signal produced by the comparator provides an indication of the positions, which can be used in an electronic ignition timing system as a reference for use in computing appropriate timings for ignition sparks.

In order that the invention may be more fully understood and readily carried into effect, a preferred embodiment of the invention will now be described by way of illustrative example with reference to the accompanying drawings in which: Figure 1 is a schematic perspective view of an electrical displacement transducer of the present invention installed on an internal combustion engine.

Figure 2 is a perspective view in more detail of a part of the transducer shown in Figure 1, Figure 3 is a schematic circuit diagram of the transducer, and Figure 4 illustrates several electrical waveforms developed in use of the circuit of Figure 3.

Referring firstly to Figure 1, there is shown a six cylinder automobile internal combustion engine 1 fitted with an electrical displacement transducer in accordance with the invention.

The transducer comprises a member to be rotated by the engine, the member comprising a metal disc 2 mounted on the engine's crankshaft and having a castellated periphery.

Mounted on the engine's casing is an electrical sensing arrangement 3 which provides electrical signals indicative of the angular position of rotation of the disc 2. The arrangement 3 is driven by electrical signals from a control circuit shown-schematically at 4, and output signals from the arrangement 3 are fed to the circuit 4.

The circuit 4 provides signals on line 5 which are accurately indicative of the angular position of rotation of the disc 2 and these signals are applied to a computing circuit 6 which uses the signals as a reference in computing the appropriate timing of ignition sparks for the engine, the timing being computed in response to sensed operating parameters of the engine. Such computing circuits are known, one such circuit being described in our British Patent Specification No. 1,481,683.

The output of the computing circuit is applied to a spark generating and spark distributor arrangement 7 which can be of any of the well known types and will not be described in detail herein. The arrangement 7 feeds high voltage electrical sparks to conventional spark plugs 8 installed in the engine 1.

The disc 2 and the sensing arrangement 3 of the transducer are shown in more detail in Figure 2. The disc 2 has three castellations 9 which define six radially extending edges 10 each of which is for defining a predetermined position in the angular rotational cycle of the engine. More particularly, the edges are so arranged that as they pass the sensing arrangement 3, the appropriate edges define a predetermined angle prior to top dead centre for the six pistons of the engine. The sensing arrangements 3 is arranged to detect the passage of the edges 10 and comprises a transmitting means and a receiving means disposed on opposite sides of the disc 2, the transmitting means comprising a coil 11 wound on a U-shaped ferrite core 12 having its pole pieces 12a, b disposed in a line extending radially of the disc, and the receiving means comprising a similarly arranged in this example, centre tapped coil 13 on a ferrite core 14.

As will be explained in more detail hereinafter, the coil 11 is energised by an oscillatory electrical signal for inducing an electrical output signal in the coil 13. Upon rotation of the disc 2, the castellations 9 interrupt repetitively the passage of magnetic flux from the coil 11 to the coil 13 and thus the output signal induced in the coil 13, upon rotation of the disc 2, alternates between two peak amplitudes a first of which is of a relatively small magnitude and occurs during the periods that the castellations 9 interrupt the inductive coupling between the coils 11, 13, and the second of which is of a relatively large magnitude and occurs for periods between the interruptions. Thus, it will be appreciated that the transitions between the two peak amplitudes- in the signal induced in the coil 13, are indicative of the passage of the edges 10 of the disc 2 through the sensing arrangement 3.

The control circuit 4 is adapted to detect these transitions between the two peak signal amplitudes.

The control circuit 4 will now be described in detail with reference to Figure 3 and is shown therein in dotted outline. The circuit is driven by a system clock (not shown) which applies clock pulses to a terminal 15. The clock pulses typically are of a frequency of 100 kHz or greater and are fed to a drive circuit which produces at the frequency of the clock pulses, a rectangular or sinusoidal waveform which is used to energize the coil 11. The waveform of the signal fed to the coil 11 is shown in Figure 4a. The waveform of the signal induced in the coil 13 as the disc 2 is rotated, is shown in Figure 4b and it will be seen that the induced signal comprises the signal of Figure 4a amplitude modulated repetitively to a first peak signal amplitude whilst the castellations 9 interrupt the inductive coupling between the coils, and amplitude modulated to a second higher peak signal amplitude for periods between the interruptions produced by the castellations 9. It will also be noted that at the transitions between the two peak signal levels, a finite rise or fall time occurs as a result of the time taken for the edges 10 to pass the coils 11, 13.

The modulated signal induced in the centre tapped coil 13 is fed on lines 17, 18 to a full wave demodulator 19 to remove the carrier frequency of the clock waveform and thereby derive a signal indicative of the amplitude modulation effected by rotation of the disc 2.

The demodulator comprises two CMOS transmission gates 20, 21 connected to the lines 17, 18 respectively, and an inverter 22. The gate electrodes of the MOS transistors of the gates 20, 21 are driven either by the clock waveform or by an inverse thereof produced by the inverter 22, in such a manner as to recover the amplitude modulation envelope produced by rotation of the disc 2. The output of the demodulator 19 is fed to a filter comprising a resistor R1 and a capacitor C1 arranged to filter out harmonics produced by the demodulator.

The filtered output of the demodulator 19 is shown in Figure 4c and it will be seen that the filtered output signal repetitively changes between a first signal level of a magnitude V1 and a second signal level of magnitude V2 each time one of the edges 10 of the disc passes between the coils 11, 13, the signal having finite rise and fall times tr ts as the edges 10 pass between the coils.

In order to detect the timing of the transitions in the waveform of Figure 4c accurately, the filtered output of the demodulator 19 is fed to one input of a differential amplifier 24 which operates as a squaring comparator. The other input of the amplifier 24 receives a d.c.

level Va produced from the output of the demodulator by a filtering network comprising a resistor R2 and a capacitor C2. The d.c. level Va is arranged to be an average of the magnitudes of the signal levels V1, V2 and is preferably related as follows: Va = 1/2 (V1 + V2) Thus, the comparator 24 will only produce an output on line 23 when the signal level shown in Figure 4c exceeds the magnitude Va, which results in a rectangular waveform on line 23 as shown in Figure 4d. The leading and trailing edges of the rectangular waveform are accurately indicative of the passage of the edges 10 of the disc 2 between the coils 11, 13, since the magnitude of the filtered output of the demodulator 19 becomes equal to Va half way through the rise times tr, ts. The arrangement of the comparator 22 and the averaging filter network R2, C2 provides a substantial advantage in that the timing of the leading and trailing edges of the pulses of the waveform of Figure 4d is not deleteriously affected by long term drifts in the magnitudes of V1 and/or V2, since the filtered output from the demodulator 19 is always compared with an average of V1 and V2, and the average will be commensurately affected by the long term drifts in V1 and/or V2 so that the leading and trailing edges of the waveform of Figure 4d will always occur midway through the transitions between V1 and V2.

Also, it will be seen that variations in the frequency of the clock waveform applied to terminal 15 will not affect substantially the accuracy of the output on line 23.

Moreover, the design of the filter network C2, R2 can be arranged so that the transducer will operate accurately over the normal range of engine speeds associated with an internal combustion engine.

The circuit 4 also has the advantage that it can readily be formed by CMOS integrated circuit techniques and can be integrated into the circuit component(s) of the computing circuit 6.

Whilst in the described embodiment, the transmitting and receiving means comprise coils arranged in ferrite cores, other devices such as an l.e.d. and a photodetector could be used.

However, we especially prefer to use the described coil arrangement because it permits a wide spacing of typically Smm between the cores, is not affected substantially by dirt or other accumulated deposits thereon, and is capable of withstanding the vibration, shock and temperature variations that occur in the vicinity of an internal combustion engine.

Whilst the above described embodiment of the invention is used in an engine spark ignition system, the transducer has other applications and can be used in fuel injection, exhaust gas recirculation and other engine management systems.

WHAT WE CLAIM IS: 1. An electrical displacement transducer comprising spaced apart transmitting and receiving means for respectively transmitting energy and receiving said energy, a member for being moved between said transmitting and receiving means, said member being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

induced in the coil 13 as the disc 2 is rotated, is shown in Figure 4b and it will be seen that the induced signal comprises the signal of Figure 4a amplitude modulated repetitively to a first peak signal amplitude whilst the castellations 9 interrupt the inductive coupling between the coils, and amplitude modulated to a second higher peak signal amplitude for periods between the interruptions produced by the castellations 9. It will also be noted that at the transitions between the two peak signal levels, a finite rise or fall time occurs as a result of the time taken for the edges 10 to pass the coils 11, 13.

The modulated signal induced in the centre tapped coil 13 is fed on lines 17, 18 to a full wave demodulator 19 to remove the carrier frequency of the clock waveform and thereby derive a signal indicative of the amplitude modulation effected by rotation of the disc 2.

The demodulator comprises two CMOS transmission gates 20, 21 connected to the lines 17, 18 respectively, and an inverter 22. The gate electrodes of the MOS transistors of the gates 20, 21 are driven either by the clock waveform or by an inverse thereof produced by the inverter 22, in such a manner as to recover the amplitude modulation envelope produced by rotation of the disc 2. The output of the demodulator 19 is fed to a filter comprising a resistor R1 and a capacitor C1 arranged to filter out harmonics produced by the demodulator.

The filtered output of the demodulator 19 is shown in Figure 4c and it will be seen that the filtered output signal repetitively changes between a first signal level of a magnitude V1 and a second signal level of magnitude V2 each time one of the edges 10 of the disc passes between the coils 11, 13, the signal having finite rise and fall times tr ts as the edges 10 pass between the coils.

In order to detect the timing of the transitions in the waveform of Figure 4c accurately, the filtered output of the demodulator 19 is fed to one input of a differential amplifier 24 which operates as a squaring comparator. The other input of the amplifier 24 receives a d.c.

level Va produced from the output of the demodulator by a filtering network comprising a resistor R2 and a capacitor C2. The d.c. level Va is arranged to be an average of the magnitudes of the signal levels V1, V2 and is preferably related as follows: Va = 1/2 (V1 + V2) Thus, the comparator 24 will only produce an output on line 23 when the signal level shown in Figure 4c exceeds the magnitude Va, which results in a rectangular waveform on line 23 as shown in Figure 4d. The leading and trailing edges of the rectangular waveform are accurately indicative of the passage of the edges 10 of the disc 2 between the coils 11, 13, since the magnitude of the filtered output of the demodulator 19 becomes equal to Va half way through the rise times tr, ts. The arrangement of the comparator 22 and the averaging filter network R2, C2 provides a substantial advantage in that the timing of the leading and trailing edges of the pulses of the waveform of Figure 4d is not deleteriously affected by long term drifts in the magnitudes of V1 and/or V2, since the filtered output from the demodulator 19 is always compared with an average of V1 and V2, and the average will be commensurately affected by the long term drifts in V1 and/or V2 so that the leading and trailing edges of the waveform of Figure 4d will always occur midway through the transitions between V1 and V2.

Also, it will be seen that variations in the frequency of the clock waveform applied to terminal 15 will not affect substantially the accuracy of the output on line 23.

Moreover, the design of the filter network C2, R2 can be arranged so that the transducer will operate accurately over the normal range of engine speeds associated with an internal combustion engine.

The circuit 4 also has the advantage that it can readily be formed by CMOS integrated circuit techniques and can be integrated into the circuit component(s) of the computing circuit 6.

Whilst in the described embodiment, the transmitting and receiving means comprise coils arranged in ferrite cores, other devices such as an l.e.d. and a photodetector could be used.

However, we especially prefer to use the described coil arrangement because it permits a wide spacing of typically Smm between the cores, is not affected substantially by dirt or other accumulated deposits thereon, and is capable of withstanding the vibration, shock and temperature variations that occur in the vicinity of an internal combustion engine.

Whilst the above described embodiment of the invention is used in an engine spark ignition system, the transducer has other applications and can be used in fuel injection, exhaust gas recirculation and other engine management systems.

WHAT WE CLAIM IS: 1. An electrical displacement transducer comprising spaced apart transmitting and receiving means for respectively transmitting energy and receiving said energy, a member for being moved between said transmitting and receiving means, said member being

adapted to interrupt repetitively the passage of said energy from the transmitting means to the receiving means as a function of the movement of the member between said means, said receiving means being adapted to produce an electrical output signal which assumes a first magnitude during said repetitive interruptions and a second different magnitude for periods between said interruptions, and means arranged to produce an output indicative of when said signal exceeds a magnitude representative of an average of said first and second magnitudes whereby to provide an indication of the commencement and cessation of said interruptions.
2. An electrical displacement transducer in accordance with claim 1 wherein said member comprises a rotary disc having a castellated periphery, the transmitting and receiving means being so positioned that upon rotation of the disc the castellations thereof produce said repetitive interruptions.
3. An electrical displacement transducer in accordance with claim 1 or claim 2, wherein said transmitting and receiving means comprise coils spaced apart from one another for inductive coupling therebetween.
4. An electrical displacement transducer in accordance with claim 3 including a drive circuit arranged to feed an oscillatory electrical signal to one of said coils, a demodulator connected to receive the signal induced in the other of said coils and arranged to provide a demodulated signal indicative of an amplitude modulation effected by movement of said member to the signal induced in said second coil.
5. An electrical displacement transducer in accordance with claim 4, wherein said drive circuit has an input to receive clock pulses and is adapted to produce said oscillatory signal at a frequency controlled by the frequency of said pulses, and said demodulator is connected to receive said clock pulses.
6. An electrical displacement transducer in accordance with claim 5, wherein said demodulator comprises CMOS transmission gates, the gate electrodes of the transistors thereof being connected to receive said clock pulses or the inverse thereof.
7. An electrical displacement transducer according to any one of claims 4 to 6 wherein said output producing means comprises means responsive to said signal from the receiving means and adapted to produce a control signal of a magnitude which is representative of an average of said first and second magnitudes, and a comparator arranged to compare the magnitude of said signal from the receiving means with the magnitude of the control signal so as to provide said output.
8. An electrical displacement transducer in accordance with claim 7 and including a filtering network connected to the demodulator and arranged to produce said control signal.
9. An electrical displacement transducer in accordance with claim 8, wherein the comparator comprises a differential amplifier having a first input connected to receive said control signal from said filtering network and having a second input connected to receive the demodulated signal from the demodulator.
10. A displacement transducer in accordance with any preceding claim wherein said member is mounted for rotational movement with the crankshaft of an internal combustion engine.
11. A displacement transducer substantially as herein described with reference to the accompanying drawings.