WO1993009393A1

WO1993009393A1 - Method and apparatus for determining position of a body in cyclic movement

Info

Publication number: WO1993009393A1
Application number: PCT/AU1992/000595
Authority: WO
Inventors: Mark Raymond Kitson
Original assignee: Orbital Engine Company (Australia) Pty. Limited
Priority date: 1991-11-06
Filing date: 1992-11-06
Publication date: 1993-05-13

Abstract

Apparatus for determining the position of a body in movement. A member (5) moves in a fixed cyclic relation to the cyclic movement of the body. The member has a set of first position indicators (P1, P2, P3) and a specific second position indicator (P4) arranged to correspond to a predetermined position of the body in cyclic movement. Sensor means (A, B) detect the duty cycles of the first and second position indicators to provide a detection signal sequence. Processor means receive and analyse the detection signal sequence to determine the duty cycle of each position indicator to thereby identify in the position of the body in cyclic motion. Application to ignition and fuel injection systems in multicombustion chamber engines, where the member moves in fixed cyclic relation to the engine cycle.

Description

METHOD AND APPARATUS FOR DETERMINING POSITION OF A BODY IN CYCLIC MOVEMENT

This invention relates generally to determining the position of a body in a cyclic movement, for example, in a rotational or circular movement. More specifically, it relates to determining a predetermined position of the body and also to the rate of cyclic movement thereof. In particular, the present invention relates to determining the time at which an engine, for example, an electric motor or combustion engine, is at a particular angular position in its cyclic revolution. In this regard, it also relates to determining the angular position and the rate of revolution of the engine at a particular time.

Generally, a specific reference marker which is subject to a corresponding cyclic movement as the body and corresponds to the predetermined position of the body, is provided to be detected. The detection of the specific reference marker determines the body being at the predetermined position, and repeated detections of the specific reference marker allow the rate of cyclic movement to be calculated and the position of the body at any one time, as well as the time at which the body is at any one position, to be estimated or predicted. This detection of the position of a body is particularly useful in the control of the operation of internal combustion engines and examples of such use are described in United States Patent No. 4352345 Menard, 4783627 Pagel and 4941445 Deutsch.

Due to the fact that the rate of cyclic movement of the body may vary during each cycle, in particular between successive detections of the specific reference marker, it is known to provide a large number of reference markers arranged together with the specific reference marker for detection. All the reference markers are in general spaced a predetermined distance apart from one another with the specific reference marker being made to be distinguishable from other markers. The detection of adjacent reference markers enables the rate of cyclic movement to be determined and also the position of the body with respect to the predetermined position at a particular time as well as the time of different body positions with reference to the predetermined position. However, in practice, with continuing and substantial variations in the rate of cyclic movement during each cycle, it has been difficult in detecting the reference markers to distinguish the specific reference marker from all the other reference markers and thus to determine the body being at the predetermined position in its cyclic movement.

In order to improve the ability to distinguish the specific reference marker from all the other reference markers, it is known to provide the specific reference marker as a "missing tooth", that is, one less marker or as a "double tooth", that is, one extra marker. Neither the missing tooth nor the double tooth has proved completely satisfactory.

It has also been known to detect the specific reference marker separately from the detection of other reference markers adjacent thereto. Two sets of reference markers are provided for simultaneous detection with respective sensors, one set having all identical reference markers and the other set having the specific reference marker. In this regard, the provision of two sets of reference markers, and of the respective sensors therefor, increases production costs. Further, with at least one set having a large number of reference markers, the closely spaced apart arrangement thereof requires relatively narrow beam sensors to effect detection. These narrow beam sensors are generally more expensive and more susceptible to adverse environments than a corresponding wider beam sensor.

It is an object of the present invention to provide an apparatus and for determining the position of a body in a cyclic movement.

In accordance with one aspect of the present invention, there is provided an apparatus for determining the position of a body in a cyclic movement, comprising: a member adapted to be in a cyclic movement having a fixed relation to the cyclic movement of the body; said member also having a set of position indicators each having a first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, said member having a specific position indicator arranged to correspond to a predetermined position of the body in said cyclic movement and having a second duty cycle different to said first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, sensor means arranged to detect the duty cycle of said position indicators in said set of position indicators and of said specific position indicator of the member when in said related cyclic movement and to provide a detection signal sequence, and processor means arranged to receive and to analyse said detection signal sequence for determining the position of the body in said cyclic movement with reference to said predetermined position.

The provision of the set of position indicators having a first duty cycle and the specific position indicator having a different second duty cycle ensures that a detectable difference exists between the position indicators of the set and the specific position indicator that can be sensed independently of the speed of the member.

Conveniently, the specific position indicator can be distinguished from the position indicators of the set by having a difference in its dimension in a part thereof being sensed and a corresponding opposite difference in its distance apart from a like part of an adjacent position indicator. Conveniently, the combined dimension of the part of each position indicator being sensed and the distance apart thereof in the direction or line of sensing is equal.

Preferably, each position indicator can comprise a reference spacing and a reference marker. The detection time of the position indicator, that is represented by the dimension of the position indicator in the direction of corresponding cyclic movement, is termed the period of the position indicator. The ratio of the detection time of the reference marker to the detection time of the reference spacing, that is represented by the dimension of the reference marker in the direction of corresponding cyclic movement to the dimension of the reference spacing in the direction of corresponding cyclic movement in a position indicator, is termed the duty cycle of the position indicator. The specific position indicator can be distinguished from the other position indicators by its specific duty cycle. Typically, the first duty cycle is of the order of 1 to 2 with the specific duty cycle being of an order of 2 to 1.

Preferably, two sensor means are provided that will generate two detection signal sequences from detecting the same position indicators, the two detection signal sequences in all respects being substantially identical save for a phase difference or lag proportional to a separation distance or space between the two sensor means. Further, each detection signal sequence is necessarily a cyclic sequence, with each cycle appearing over varying lengths of time. The related cyclic movement of the member may actually be a corresponding cyclic movement to the body. The phase difference between the two detection signal sequences produces a constant detection signal relationship therebetween for the detection of each position indicator, that is for between the detection of adjacent reference markers, save for where the specific position indicator is detected. Thus, a change in the detection signal relationship in detecting a position indicator may be used to determine the body being at the predetermined position in its cyclic movement.

Further, the detection of successive position indicators with reference to the specific position indicator can be used to determine the rate of cyclic movement of the body and in particular, the position of the body with respect to the predetermined position at a particular time or the time at which the body is at a particular position with reference to the predetermined position.

The two sensor means may be suitably mounted at respective locations fixed with respect to the disc member. The respective locations may preferably be spaced one half, or a whole number multiple and one half, of the dimension of a position indicator apart. Accordingly, the two sensor means may be mounted collectively in proximity without having to use separate mounting devices.

The apparatus as proposed by the present invention may be particularly adopted for determining the angular position of a shaft of an engine or motor such as a crankshaft of an internal combustion engine in its cyclic revolution. The member can be made in the form of a ring or disc, and mounted o the engine or motor, such as to an output shaft thereof for rotational movement therewith. The disc member can have an axis of rotation aligned with the axis of the shaft of the engine or motor.

Each position indicator is arranged on the disc member at substantially the same radial distance from the axis of rotation and can preferably be arranged about the periphery of the disc member, extending over an arc of a preset angle. The specific position indicator can correspond to an absolute position of the engine.

In broad terms in relation to internal combustion engines, there is provided an apparatus for determining in a multi-combustion chamber internal combustion engine the occurrence of a selected point in each combustion chamber cycle and a further selected point in each engine cycle comprising; a member adapted to be in a cyclic movement having a fixed relation to the engine cycle, said member carrying a first specific position indicator for the selected point of each combustion chamber cycle each having a first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, said member carrying a second specific position indicator for the further selected point of the engine cycle having a second duty cycle different to said first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, sensor means arranged to detect the duty cycle of said first and second specific position indicators when the member is moving in said related cyclic movement and to provide a detection signal sequence, and processor means arranged to receive and to analyse said detection signal sequence for determining the duty cycle of each specific position indicator to thereby identify in sequence the selected points of each combustion chamber cycle and the selected position in the engine cycle.

With a multi-combustion chamber engines such as a multi-cylinder internal combustion engine, the disc member is conveniently mounted to or formed in a flywheel connected to the crankshaft of the engine. Further, the disc member may have one particular position indicator for each combustion chamber or cylinder of the engine to indicate the top dead centre (TDC) position thereof. Conveniently, the disc member can also have two consecutive specific position indicators, one to indicate the TDC of a cylinder the and other the absolute position of the engine. Alternatively, the specific position indicator may be distinguished from the particular position indicator by having a different duty cycle therefrom, that is, having a specific reference marker of a different dimension from that of the particular reference markers of a particular position indicator.

The two sensor means may be suitably mounted at respective locations fixed with respect to the disc member. The respective locations may preferably be spaced one half, or a whole number multiple and one half, of the dimension of a position indicator apart. Accordingly, the two sensor means may be mounted collectively in proximity without having to use separate mounting devices. The presently proposed apparatus is preferably operable with only one sensor means, and is operable when one sensor means of a two sensor means system has been disabled.

In such an arrangement the processor means is arranged to receive and to analyse the single detection signal sequence for determining the position of the body in said cyclic movement with reference to said predetermined position. In particular, the processor means can include movement tracking means arranged to identify when the specific position indicator is detected and to register the position thereof and to count the number of position indicators therefrom to locate in sequence each position indicator of the set.

Conveniently, for a two sensor system where one sensor means has become disabled, the processor means can further include compensation means to compensate for any phase difference appearing in the single detection signal sequence due to the offset location of the one operating sensor means. In practice, the movement tracking means can be arranged to generate for the period between detections of each adjacent position indicator being detected, a preselected number of step movement signals at a rate derived from the period between detections of the period of the last position indicator detected, that is, at the immediate prevailing rate of cyclic movement. The generation of the step movement signals can allow the position of the body to be determined more efficiently. More particularly, the particular position indicators corresponding to the top dead centre positions of the cylinders can each be arranged the same number of position indicators apart and the movement tracking means can be arranged to generate a top dead centre signal when a particular position indicator is detected or when the same number of position indicators have been detected since the last top dead centre signal was generated. Further, the movement tracking means can be designed to count the number of position indicators being detected and reset itself for each top dead centre position when the same number of position indicators have been counted or for an absolute position, when the preset number of position indicators have been counted. The present invention is described in detail with reference to embodiments of the apparatus particularly adopted for determining the angular position of a two-stroke three-cylinder internal combustion engine. To determine accurately the angular position of the engine in its cyclic revolution at a particular time and precisely the moment of time at which the engine will be at a particular angular position in its cyclic revolution are important in the efficient control of engine management, for example, for the events of fuel injection and ignition. The generality and application of the present invention are not limited by the detailed description nor by the accompanying drawings, in which:

Figure 1 shows diagrammatically the layout of an encoder member with two operating sensors A and B, and the signal waveform derived therefrom; Figure 2 shows the physical layout of the encoder member of Figure 1 with a single operating sensor C, and the signal waveform therefrom; and

Figure 3 is a diagram illustrating the possible effects of acceleration or deceleration of the engine on the sensing of the engine position. The apparatus illustrated is specifically for use on a three-cylinder two-stroke cyclic engine wherein the encoder is mounted to rotate with the engine crankshaft. The encoder is in the form of a circular ring having a number of teeth thereon. The ring is adapted to be mounted to or formed in the engine flywheel or like disc, preferably adjacent the periphery thereof.

The disc or flywheel is mounted to rotate with the engine crankshaft so that the encoder has a cyclic rotation corresponding to that of the engine crankshaft and thus, the angular position and movement of the encoder also represents the engine revolution and the cycle of each cylinder. With a four- stroke engine, the disc may be suitably connected to the camshaft of the engine, which is being driven at half the crankshaft speed, but at a speed of one revolution per cylinder cycle.

Referring to Figures 1 and 2, wherein the circular encoder 5 is shown in a flat form with a leading end 10 and its trailing end 20, the encoder has one set of 24 position indicators P arranged to rotate in the direction indicated by the arrows at each end of the flattened out encoder. Each position indicator P consists of a reference spacing S followed by a reference marker M. The reference markers M are in the form of teeth separated apart from each other by the reference spacings S in the form of gaps.

The dimension of each position indicator P in the direction of movement is substantially equal; that is, the combined dimension of the tooth M and the gap S within each position indicator P is uniform. The ratio of the dimension of the tooth M to the dimension of the gap S in a position indicator P is generally referred to as the angular duty cycle of the position indicator.

It is to be understood that the angular duty cycle is substantially constant independent of speed and acceleration or deceleration conditions and throughout the specification and claims the term "duty cycle" is to be understood to mean angular duty cycle. However, under severe acceleration and deceleration conditions, the duty cycle, with respect to time, can vary. The duty cycle with respect to time is the ratio of the time for the tooth M to pass a fixed point to the time for the gap S to pass the same point.

The teeth are in general of equal dimensions in the direction of movement and arranged equally spaced apart. However, with an increase in the width of the tooth M in a position indicator P and a corresponding reduction in the gap S, or vice versa, the duty cycle of the position indicator is changed. The position indicators of the encoder as shown include a number of distinguishable position indicators P1 , P2, P3 and P4, each having a different duty cycle from the basic position indicators P. Each distinguishable position indicator as shown comprises a distinguishable reference marker having a predetermined dimension providing a specific duty cycle of 2 to 1 whereas the other position indicators have a general duty cycle of 1 to 2. It is to be understood that different values of specific and general duty cycles could be used.

The distinguishable position indicators of the encoder are arranged to correspond to predetermined angular positions of the three-cylinder engine in its two-stroke cyclic revolution. The indicator P1 corresponds to the top dead centre position of cylinder one (TDC #1), indicator P2 to the top dead centre position of cylinder two (TDC #2), indicator P3 to the top dead centre position of cylinder three (TDC #3), and indicator P4 to an absolute position of the engine in its cyclic revolution.

Each of the three distinguishable position indicators P1 , P2 and P3 are separated from each other by a same number of position indicators; that is, with a total of 24 position indicators, every eighth position indicator is a distinguishable position indicator. The absolute position indicator P4 follows immediately the TDC position indicator for cylinder three P3. With this arrangement, one distinguishable position indicator indicates a top dead centre position and two consecutive distinguishable position indicators P3 and P4 indicate the absolute position of the engine.

Alternatively, the absolute position of the engine could be indicated by a different arrangement of the absolute position indicator P4 in the encoder to provide an individual angular duty cycle or by any other arrangement of at least two distinguishable position indicators. When the encoder disc is connected to the crankshaft of the engine for rotational movement therewith, the position indicators P are subject to a cyclic movement corresponding to the engine cyclic revolution. Each of the 24 position indicators P is arranged an equal radial distance from the axis of rotation and extends over an arc of 15° angle in the direction of cyclic movement. This arrangement provides the position indicators P including the teeth M for detection by one or more sensors to determine the angular position of the engine, for example, the absolute position or top dead centre positions, and the rate of cyclic revolution of the engine.

Referring to Figure 1 , two sensors A and B are arranged to detect the cyclic movement of the position indicators P. The sensors are mounted at respective locations fixed with respect to the encoder, and are spaced apart in the direction of rotation. The preferred spacing distance as shown is one-half of the dimension of a position indicator P, that is 7.5° of rotation, or any whole number multiple plus one-half of the position indicator dimension. However, other convenient separation distances can also be used, say for example, where different values of specific and general duty cycles are used. With a small separation distance therebetween, the sensors A and

B are suitably mounted collectively and in proximity to one another, using a single mounting device. Alternatively, the two sensors can be provided in a single unit.

As shown in Figure 1 , the sensors A and B would detect different parts of the encoder at any one particular time and would each generate a respective detection signal sequence. The waveforms of the detection signal sequence of the sensors A and B are shown in a timed relation in the waveforms

12 and 13 of Figure 1.

The two detection signal sequences generated from detecting the position indicators P including the gaps S and teeth M, are each signal sequences of low and high levels, for example, "0"s and Ts. The detection of a gap would generate a low level O" signal and a tooth, a high level "I" signal. It will be seen that since the two sensors A and B detect the same one set of position indicators P, the two signal sequences are identical in all respects except by a phase difference or lag proportional to the separation distance between the two sensors. As shown, the sensor A signal waveform 12 has a 7.5° phase lag to the sensor B signal waveform 13. In the waveform summary, each signal sequence is similar in shape as the encoder and is necessarily a cyclic sequence. The period of each cycle will vary according to the engine rate of cyclic revolution.

Processor 25 are arranged to receive and to analyse the detection signal sequences from the sensors A and B. In general, the processor means generates a position pulse signal upon the complete detection of a positron indicator P or a tooth M by sensor A, that is upon each transition of high level to low level in the sensor A signal sequence as shown at 15, to track or note the rate of cyclic movement of the position indicators P or the teeth M. The rate of cyclic revolution of the engine can be derived using the period or detection time of the last position indicator detected or the rate of detection of the last adjacent teeth, that is the frequency of the position pulse signals.

Further, in particular, the processor analyses the two, out of phase signal sequences relative to each other to determine the angular position of the engine crankshaft. More specifically, the processor is adapted to determine the top dead centre (TDC) positions and the absolute position of the engine in its cyclic revolution.

The phase difference between the two signal sequences produces a definite signal relationship between the two signal sequences for the detection of each position indicator. The signal relationship maintains a general pattern from one position indicator to the next position indicator; but the general pattern is changed or altered when a distinguishable position indicator or a distinguishable reference marker thereof is detected. The change in the general pattern, that is in the signal relationship, is used to determine the angular position of the engine. As shown in Figure 1 , generally for each signal sequence, both the transitions from low level to high level and then back to low level occur whilst the other signal sequence remains in the low level, except where a distinguishable position indicator or a distinguishable reference marker thereof is detected. The processor means generates a top dead centre signal when a distinguishable position indicator P1 , P2 or P3 or a distinguishable reference marker thereof, is detected by sensor A. As shown, when a transition of high level to low level in the sensor A signal sequence occurs whilst the sensor B signal sequence is at the high level, a TDC signal is generated and registered or recorded. The TDC signal is set to last the full period of the TDC position indicator, that is, until the next transition of high level to low level. Further, the processor generates an absolute position signal when the distinguishable position indicator P4 is detected by sensor A. As shown, when a consecutive transition of high level to low level in the sensor A signal sequence also occurs whilst the sensor B signal sequence is at the high level, an absolute position signal, rather than a consecutive TDC signal, is generated and registered or recorded. The absolute position signal is set to last the full period of the distinguishable position indicator P4.

In the embodiment as described and shown, the absolute position signal is used as an angular reference signal, with the next TDC signal designated as the TDC signal for cylinder one (TDC #1) of the three-cylinder engine and, together with the tracking of position pulse signals, for deriving the angular position of the engine at any particular time and also the time at which the engine is at any particular angular position.

In practice, the processor means includes a movement tracking capability to count the number of position pulse signals being generated after each registration of the absolute position signal. With the absolute position as an angular reference position and knowing the number of position pulse signals that have been counted, that is knowing the number of position indicators that have been detected, the angular position of the engine crankshaft can be determined. In this regard, when the full one set of 24 position indicators have been detected and the corresponding 24 position pulse signals generated and counted since the last registration of the absolute position signal, the next absolute position signal is generated and registered, and the counting for the absolute position is reset.

Conveniently, the movement tracking capability also generates a preselected number of step movement signals, preferably 32 high data rate degree signals, for the period of each position indicator to be detected, as well as generating the position pulse signals, the top dead centre signals and the absolute position signal. The step movement signals are generated at a rate derived from the period of the last position indicator detected. In this regard, the movement tracking capability also counts the number of step movement signals being generated as well as the position pulse signals to track with more accuracy and efficiency the angular position of the engine crankshaft in its cyclic revolution.

Preferably, the movement tracking capability counts the number of position pulse signals being generated after each registration of a TDC signal. With every 8th position pulse signal being counted, the next TDC signal is generated and registered, and the counting means for the top dead centre position is reset. Further, the movement tracking capability also counts the number of TDC signals being generated after each registration of the absolute position signal. When all three TDC signals are generated and counted, the next absolute position signal is generated and registered, and the counting means for the absolute position is reset.

In one embodiment, the processor includes engine position memory capability which records the angular position at which the engine had last stopped and provides the information for the next engine start-up. Thus, at start-up, the engine is not required to run an initial cycle for the apparatus to determine its angular position and the fuel and spark can be selectively delivered to the correct cylinder of the engine. Further, during manufacture, the engine position memory is preset in accordance to the angle of the engine crankshaft.

The memory capability and count down facility as previously referred to enables the processor to store information as to the position within the engine cycle, relative to the absolute position indicator, upon engine shut¬ down. As a result, upon next starting up the engine the processor has available the position of the engine within the engine cycle, and thus knows which cylinder is to be first fired after start-up. This enables improved start up time as in some prior art systems the engine must be cranked until a single absolute position marker is sensed, which could be up to near one complete crankshaft revolution or even near two revolutions in a four stroke cycle engine. Referring to Figure 2, there is illustrated, an embodiment of the apparatus with only one sensor C, which may be the basic form of the apparatus or the form as shown in Figure 1 with either one of the sensors disabled or non- functioning.

As shown in Figure 2, with the encoder of the same general form, the single sensor C is arranged to detect the one set of 24 position indicators P, each having a gap S and a tooth M.

As shown, only a single detection signal sequence, waveform 18, is detected by the sensor C. The processor means receives and analyses the single signal sequence.

The processor means is arranged to generate duty cycle pulse signals for each duty cycle variation from the general duty cycle of 1 to 2. Four duty cycle pulse signals, each corresponding to the distinguishable duty cycle of 2 to 1 of the four distinguishable position indicators P1, P2, P3 and P4 are generated.

The processor is further arranged to generate a TDC signal when a distinguishable duty cycle is detected, and also to generate the absolute position signal when consecutive distinguishable duty cycles are detected, that is, when consecutive duty cycle pulse signals are generated.

However, as shown in Figure 2, each duty cycle pulse signal is generated only after the distinguishable position indicator P1 , P2, P3 or P4 has passed and thus, the generation of the subsequent TDC signals and absolute position signal are necessarily offset from the correct moment of time. The amount of offset in time is dependent upon the location of the operating sensor. For the arrangement as shown in Figure 2 with sensor C being the only sensor and positioned as shown, the offset is a 15° phase lag, equal to one period of the position indicator behind.

It is to be understood that if only one sensor means of a normal two sensor means system is operating, there are two different possible offsets of the generation of the TDC signals and absolute position from the correct moment of time. For the arrangement as shown in Figure 1 , when sensor A is the single operating sensor, the offset is a 15° phase lag, equal to one period of the position indicator behind. For sensor B as the single operating sensor, the offset is a 7.5° phase lag, equal to one-half period of the position indicator behind.

Accordingly, the processor means is preferred to include compensation means arranged to compensate for the phase difference appearing in the single signal sequence and the offset in time in detecting the TDC and absolute position indicators.

It will be appreciated that the movement tracking means as described provides particular advantages in operating the apparatus when only one sensor is employed or when a two sensor system is functioning in a limp- home mode, that is when one sensor thereof has been disabled.

With sudden and rapid acceleration and deceleration of the engine and hence of the engine crankshaft, it may become difficult to identify duty cycles and to distinguish the specific duty cycle from the general duty cycle where the difference therebetween is insufficient for the purpose of effectively detecting the TDC and absolute position indicators by the processor. The detection of position indicators and the generation and counting of position pulse signals allow the movement tracking means to continuously track the angular position of the engine crankshaft in its cyclic revolution and to generate and register at the correct moment of time the TDC and absolute position signals independently of having to detect the TDC and absolute position indicators.

During the acceleration and deceleration of the engine, the detection time or period of successive position indicators could vary substantially and in particular, the duty cycle on a time basis as seen by the sensor may be significantly different from the norm and cause incorrect TDC or absolute position signal to be generated.

During acceleration, the duty cycle would in general decrease in value. Thus, the specific position indicators may give a duty cycle of around 1 to

2, rather than 2 to 1. During deceleration, the duty cycle would in general increase in value and thus , the general position indicators may give a duty cycle of around 2 to 1 , rather than 1 to 2.

Figure 3 illustrated the effects of rapid acceleration and declaration on the duty cycle when considered on a time basis.

It is to be understood that the duty cycle of the general position indicators and the distinguishable position indicators measured on a dimensional basis previously referred to as angular duty cycle does not change, but on a time basis as seen by sensor C, change does occur. Where the rate change on a time basis, as would arise when an engine is accelerating or decelerating, is gradual, the change in duty cycle from one position indicator to the next is not significant and typically cannot give rise to a false detection signal sequence to the processor. However under rapid acceleration or deceleration, the rate of change of the duty cycle on a time basis as detected by sensor C can result in false detection signal sequences being sent to the processor.

The portion of the waveform shown at A in Figure 3 is the waveform at constant engine speed wherein ^"a distinguishable position indicator corresponding to atop dead centre position of a cylinder is nearing detection by the sensor means. The duty cycle of the general position indicators is T^ where Tι T₂ and the angular duty cycle of the distinguishable position indicator is T3/T₄ where T₃<T₄. In this case, T-i, T₂, T₃ and T₄ are measured on a time basis where the encoder has a constant speed.

If the engine is subjected to rapid acceleration, as is illustrated in waveform B, just prior to the distinguishable position indicator being detected, the marker portion 20 of the distinguishable position indicator is reduced on a time basis so the sensor will tell the processor that T₃>T₄. Thus the TDC position will not be identified by the processor and is therefore the function of the engine related to that TDC position will not be performed. During rapid deceleration of the engine, the waveform may be as shown at C in Figure 3 wherein the duty cycle 21 immediately prior deceleration is normal having T-ι>T₂, but the following general position indicator prior to the

TDC position as detected by the sensor means as a result of the rapid deceleration is seen to have a duty cycle where T₃<T₄ and hence, a false TPC position is indicated to the processor.

In one embodiment, the movement tracking capacity is arranged to generate an array of 256 high data rate (HDR) degree signals for each cylinder cycle of the engine, that is between top-dead-centres, and to count each 32 HDR degree signals at a self-adjusting rate derived from the detection time of the last position indicator detected. The HDR degree signals may be generated and counted at the immediate prevailing rate. Further, the value of a duty cycle is determined by the tooth and gap detection times whilst the HDR degree signals are being counted; and a duty cycle pulse signal to indicate the detection of a distinguishable position indicator is generated when the duty cycle is greater than 1.

Thus, during acceleration, the HDR degree signals are counted at a slower rate than the actual rate of engine revolution. The general position indicators would always provide a duty cycle of less than 1 , but the distinguishable position indicators may not always provide a duty cycle greater than 1 , thus missing a duty cycle pulse signal. Upon generating the next position pulse signal, the remaining HDR degree signals yet to be counted are disregarded, and the next 32 HDR degree signals will then be counted for th© next position indicator.

Similarly, during deceleration, the HDR degree signals would be counted at a faster rate than the actual rate of engine revolution. When the complete 32 HDR degree signals are counted, no further HDR degree signals will be counted until the next position pulse signal is generated to start the next position indicator. In this regard, although the general position indicators may have provided a duty cycle greater than 1 , thus creating an incorrect duty cycle pulse signal, for duty cycle purposes, the detection time of the tooth would be shortened by the completion of counting the 32 HDR degree signals and the duty cycle would always be less than 1 , thus avoiding an incorrect duty cycle pulse signal.

However, the shortening of the detection time of the tooth may sometimes in detecting the distinguishable position indicators also provide a duty cycle less than 1 , thus missing a duty cycle pulse signal. The particular method of determining the value of a duty cycte using the HDR degree signals ensures that no false TDC or absolute position signal is added but rather a true TDC or absolute position signal may occasionally be missed.

It will be appreciated that the counting of the HDR degree signals at the immediate prevailing rate contribute to ensure that no incorrect TDC and absolute position signals are generated in detecting the period and duty cycle of the position indicators. Further, the correct TDC and absolute position signals may be internally generated and registered by the movement tracking capacity rather than by direct detection of the distinguishable position indicators.

The number of position indicators provided in the encoder is suitably chosen having regard to at least the acceptable error or workable accuracy and also the design and production costs of the apparatus. Decreasing the number may increase the working errors and increasing the number would reduce the dimension of each position indicator, thus requiring the use of more expensive narrow beam sensors. Preferably, for the encoder as described and shown, there is provided at least 18 position indicators and the known Hall Effect sensors may be used. The wider beam sensors would be less susceptible to be covered up by dirt.

The general and specific duty cycles can be chosen as appropriate so that a specific duty cycle can be effectively distinguished from a general duty cycle, for example, by a substantial difference. Further, having regard to the values of the specific and general duty cycles and the separation distance between the two sensors, the processor means can be suitably programmed with the appropriate criteria to analyse the two signal sequences relative to each other to determine the top dead centre and absolute positions of the engine cyclic revolution. As seen in Figures 1 and 2, the signals generated by the sensor A,

B or C are fed to the processor 25 which is conveniently an integral part of a conventional ECU controlled engine management system, as widely used in internal combustion engine propelled vehicles. The inputs from the sensor enable the processor 25 to determine the engine speed, the TDC or other fixed position in the cycle of each cylinder of the engine, and the absolute position of the crankshaft in the engine cycle, that is the total of one cycle of each cylinder of the engine. These determinations are then applied by the processor in the management of the operation of the engine including the control of the fuel and/or air supply, the ignition timing, and in a fuel injected engine, the injection timing.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. Apparatus for determining the position of a body in a cyclic movement, comprising: a member adapted to be in a cyclic movement having a fixed relation to the cyclic movement of the body; said member having a set of position indicators each having a first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, said member also having a specific position indicator arranged to correspond to a predetermined position of the body in said cyclic movement and having a second duty cycle different to said first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, sensor means arranged to detect the duty cycle of said position indicators in said set of position indicators and of said specific position indicator of the member when in said related cyclic movement and to provide a detection signal sequence, and processor means arranged to receive and to analyse said detection signal sequence for determining the position of the body in said cyclic movement with reference to said predetermined position.

2. Apparatus as claimed in claim 1 wherein the cyclic movement of the body is rotation about a fixed axis.

3. Apparatus as claimed in claim 2 wherein said body is a component of an engine that rotates at a speed directly related to the speed of rotation of the engine.

4. Apparatus as claimed in claim 3 wherein the engine is a multi¬ combustion chamber engine, each combustion chamber having a cycle, and said member having a chamber position indicator having a third duty cycle for each combustion chamber adapted to be detected to indicate a selected position in each combustion chamber cycle.

5. Apparatus as claimed in claim 4 wherein said specific position indicator is located to indicate a specific position within the cycle of one specific combustion chamber.

6. Apparatus as claimed in claim 4 or 5 wherein the specific position indicator and one or more of the chamber position indicators each have the same duty cycle and the specific position indicator is located in a fixed relation to a selected one of the chamber position indicators, and the processor being arranged to respond to sensing said two duty cycles in said fixed relation to determine the position of the member.

7. Apparatus as claimed in any one of the preceding claims wherein the processor means includes movement tracking means arranged to identify when the specific position indicator is detected and register the position thereof, and to count the number of position indicators therefrom to locate in sequence each of the position indicators of said set of position indicators.

8. Apparatus as claimed in any one of the preceding claims wherein the processor means includes memory means to store positional information of the member upon cessation of said cyclic movement for retrieval upon recommencement of said movement of the member.

9. Apparatus for determining in a multi-combustion chamber internal combustion engine the occurrence of a selected point in each combustion chamber cycle and a further selected point in each engine cycle comprising; a member adapted to be in a cyclic movement having a fixed relation to the engine cycle, said member carrying a first specific position indicator for the selected point of each combustion chamber cycle each having a first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, said member also carrying a second specific position indicator for the further selected point of the engine cycle having a second duty cycle different to said first duty cycle and adapted to be detected when said member is subject to said related cyclic movement, sensor means arranged to detect the duty cycle of said first and second specific position indicators when the member is moving in said related cyclic movement and to provide a detection signal sequence, and processor means arranged to receive and to analyse said detection signal sequence for determining the duty cycle of each specific position indicator to thereby identify in sequence the selected points of each combustion chamber cycle and the selected position in the engine cycle.

10. Apparatus as claimed in claim 9 wherein said member is arranged to rotate on fixed axis at a rotational speed having a fixed relation to the engine cycle.

11. Apparatus as claimed in claim 9 or 10 wherein said engine is a multi-cylinder internal combustion engine having a crankshaft interconnected to a piston of each cylinder and the member is supported to rotate at a speed directly proportional to the rotational speed of the crankshaft.

12. Apparatus as claimed in claim 11 wherein said selected point in each combustion chamber cycle is the top dead centre position of the piston in the respective cylinder.

13. Apparatus for determining in a multi-combustion chamber internal combustion engine the occurrence of a selected point in each combustion chamber cycle and a further selected point in each engine cycle comprising a member adapted to rotate at a speed having a fixed relation to the engine cycle, said member having a set of position indicators each having a first duty cycle and arranged in a circular array co-axial with the axis of rotation of the member, said position indicators being adapted to be detected in sequence when said member is rotated, said member also having a specific position indicator arranged to correspond to a predetermined position in the engine cycle and having a second duty cycle different to said first duty cycle, said specific position indicator being interposed in said array and adapted to be detected when said member is rotated, sensor means arranged to detect the duty cycle of said position indicators in said set of position indicators and of said specific position indicator as the member is rotated to provide a detection signal sequence, and processor means arranged to receive and to analyse said detection signal sequence for determining the duty cycle of each position indicator to thereby identify in sequence the selected point of each combustion chamber cycle and the selected position in the engine cycle.

14. Apparatus as claimed in claim 1 wherein said member also has one or more second specific position indicators arranged to correspond to different predetermined positions of the body in said cyclic movement and adapted to be detected when said member is subject to said related cyclic movement.

15. Apparatus as claimed in claim 14 wherein said second position indicators have duty cycles equal to the duty cycle of said second specific position indicator.

16. Apparatus as claimed in claim 14 wherein said second specific position indicators have duty cycles different to the duty cycle of said second specific position indicator.

17. Apparatus for determining the position of a body in a cyclic movement, comprising: a member adapted to be in a cyclic movement related to the cyclic movement of the body; said member having one set of position indicators adapted to be detected when said member is in said related cyclic movement, said position indicators being in general arranged a predetermined distance apart and including a specific position indicator arranged to correspond to a predetermined position of the body in the cyclic movement; two sensor means, each arranged to detect said one set of position indicators with reference to said specific position indicators, of the member when in said related cyclic movement and to provide a respective detection signal sequence, said two sensor means being arranged a separation distance apart; processor means arranged to receive and to analyse relative to each other said two detection signal sequences for determining the position of the body, with reference to said predetermined position, in said cyclic movement.

18. Apparatus as claimed in claim 17 wherein the phase difference between the two detection signal sequences is arranged to produce a constant detection signal relationship therebetween for the detection of each position indicator.