Method and apparatus for detecting reference rotational angle for each cylinder in an internal combustion engine

Abstract: Disclosed is an apparatus for detecting the reference rotational angle for each cylinder in a multiple-cylinder internal combustion engine, in which a reference pulse signal is output at a position of a predetermined rotational angle of the engine at a specific stroke of each cylinder synchronously with the revolution of the engine, a cylinder-­ discriminating pulse signal is put out just after termination of specific one of the reference pulse signal, the precedent and present values of elements, concerning the time, of the pulse signal are detected, and when the present value is smaller than the precedent value by at least a predetermined value, discrimination of cylinders is performed.

Description: The present invention relates to a method and apparatus for detecting reference rotational angles in a multiple-cylinder internal combustion engine. More particularly, the present invention relates to a method and apparatus for detecting the reference rotational angles, by which it is possible to judge that a specific cylinder is at a specific stroke. A crank angle sensor has heretofore been used for making various controls, for example, the control of the ignition timing, in an internal combustion engine. There are known various systems for making various controls for the engine, for example, the control of the ignition timing, in cylinders by using crank angle sensors, and recently, there is often adopted a system in which a crank angle sensor having only a function of outputting a reference pulse signal at a specific crank angle (a reference rotational angle) position during a specific stroke of each cylinder synchronously with the revolution of the engine is used and the ignition timing is computed based on the detected reference pulse signal by a microcomputer (see Japanese Utility Model Application No. 62-133304). The reason for adoption of this system is that it is not necessary to impart a function of generating a unit signal at every crank angle of 1 to 2 degrees to the crank angle sensor and the cost can be advantageously reduced. However, in the case where an electric current for ignition is electronically applied to each cylinder without using a mechanical distributer or in the case where not only the ignition timing control system but also a system for injecting a fuel to respective cylinders independently is adopted, it is necessary to obtain not only a reference pulse signal but also a signal for judging that a specific cylinder is at a specific stroke (hereinafter referred to as "independent judgement for each cylinder") and therefore, at least two systems become necessary for a group comprising a pickup device and a signal-processing circuit. Accordingly, reduction of the cost is limited. WO-83/04283 discloses an optically read sensor disk in an apparatus for detecting a reference rotational angle for each cylinder in a multiple-cylinder internal combustion engine which performs a cylinder discrimination by making use of marked segments for each cylinder provided at the circumferential surface of the disk, wherein one of the segments is shorter than the others so as to indicate a specific cylinder. In other words, one of the segments is foreshortened so that its leading edge is detected at a later time than that of the remaining segments. The trailing edges or flanks of all segments are identical or regularly spaced so that signals derived from the trailing edges can be used as a reference basis. Clock pulses are stored as a representation of the length of the respective elements. The stored count representing a previous length is compared with a subsequent count. A cylinder discrimination is made on the basis of whether or not the counts are identical. If the counts are not identical or do not match, it is judged that the actual detected segment of the disk is the foreshortened one and thus indicates a specific cylinder to allow the cylinder discrimination. To summarize, WO-83/04283 teaches to perform the cylinder discrimination on the basis of whether or not the precedent count and the present count are identical. Similarly, GB-A-2 058 358 discloses a system for detecting the angular position of a shaft comprising a shaft disk having segmented marker teeth and an additional tooth or additional teeth for synchronisation. All teeth with the exception of the synchronisation tooth are regularly spaced. The system comprises a memory, two counters and a comparator. The counters are incremented during the time periods occurring between the detection of two subsequent teeth. An actual counter signal is stored in the memory. At time T₁ indicated in Figure 3 of this reference, the memory has a count which corresponds to the precedent count stored therein as indicated by the horizontal broken line in Figure 3. The count of the counters are increased as shown in the figure and, upon occurrence of the next sensor pulse at the time T₁, the content of the first counter is transferred to the memory and this counter is set to 0. Since the memory value is changed at each pulse, the reference value clearly changes as illustrated by lines 34 and 37 and thus is not constant. Therefore, the presence of a tooth indicative of a specific cylinder is detected by detection of the pulse before either counter reaches a temporary reference value stored in the memory. Thus, this reference teaches to conduct the cylinder discrimination on the basis of a comparison to a variable reference value stored in the memory. It is an object of the invention to provide a method and an apparatus for detecting a reference rotational angle in a multi-cylinder internal combustion engine establishing an enhanced degree of reliability even in case of abrupt changes of the rotational speed of the motor. This object is achieved by a method for detecting a reference rotational angle in a multi-cylinder internal combustion engine in accordance with claim 1 and by an apparatus for detecting a reference rotational angle in a multi-cylinder internal combustion engine in accordance with claim 5. Embodiments of the present invention will now be described with reference to the accompanying drawings. The present invention will be understood from these embodiments, but the scope of the present invention is not limited by these embodiments. Brief Description of the Drawings Fig. 1 is a diagram of a crank angle sensor and a single-processing circuit, which illustrates one embodiment of the present invention. Fig. 2 is a diagram showing waveforms of signals. Fig. 3 is a flow chart of a cylinder-discriminating routine of the present invention. Fig. 4 is a diagram illustrating the ignition control according to the time control system. Fig. 5 is a flow chart of another cylinder-discriminating routine of the present invention. Fig. 6 is a flow chart of still another cylinder-discriminating routine of the present invention. Detailed Description of the Preferred Embodiments Fig. 1 is an apparatus for detection of the rotational angle in a spark-ignition reciprocating multiple-cylinder internal combustion engine. In case of, for example, a four-cylinder engine, a crank angle sensor 10 for picking up the rotational angle of the engine comprises a signal disk plate 12 as the rotary body, which is attached to a rotation shaft making 1/2 rotation per rotation of the engine, for example, a distributer shaft or cam shaft 11, so that the signal disk plate 12 rotates in the plane orthogonal to the rotation shaft integrally with the rotation shaft. Fan-shaped slits 13 are formed at equal angle intervals in the circumferential direction on the signal disk plate 12 in the same number as the number of cylinders (four slits in this embodiment because the engine is a four-cylinder engine), and the same radius distance from the rotation axis. A light emitter (LED) 15 and a light receiver (phtodiode) 16, which constitute a photoelectric pickup 14, are arranged adjacently to rotation loci of slits 13, i.e., on both the sides of the signal disk plate 12 which is interposed between the projector and light receiver. When the slit 13 passes between the projector and receiver, the light emitted from the projector 15 is received by the light receiver 16, and in other case, the light is intercepted by the signal disk plate 12. When the light receiver 16 receives the light, a pulse signal is emitted by the light receiver 16. Accordingly, reference pulse signals are generated at predetermined crank angle positions at a specific stroke synchronously with the revolution of the engine at the same period as the period of ignitions of cylinders by the ignition plugs. In the present embodiment, each reference pulse signal REF is generated in the region of 70° from the point of 75° to the point of 5° before the compression top dead center (TDC) in each cylinder (see Fig. 2). In addition to the reference pulse signal-generating slits 13, one cylinder-discriminating signal-generating slit 17 is formed on the signal disk plate 12 at a just rear portion of the specific one of slits 13 and at the same radius position from the rotation axis as that of the slits 13. More specifically, the fan-shaped slit 17 is formed so that the cylinder-discriminating pulse signal SGC is output on the same output line as of the reference pulse signals REF just after termination of one of the reference pulse signals REF (Fig. 2). This slit 17 constitutes the cylinder-discriminating pulse signal output means. In this embodiment, the crank angle from the point of termination of the reference pulse signal REF to the point of emission of the cylinder-discriminating pulse signal SGC is adjusted to 2°. The crank angle corresponding to the pulse time width of the cylinder-discriminating pulse signal SGC is adjusted to 3° (see Fig. 2). The signals from the crank angle sensor(pickup device) 10 are shaped by a waveform-shaping circuit 20 and input to a microcomputer 30 comprising an input-processing device, CPU, a store device and the like, and the signals are processed by the microcomputer 30. A timer (timer counter) 40 for counting clock signals output the counted signals to the microcomputer 30, and the count value is reset by the microcomputer 30. Timer means to be used instead of the timer can be constructed by software. Fig. 3 shows a routine of discrimination of the cylinders performed by the microcomputer 30. The cylinder-discriminating operation of this routine is performed when rising or falling of the pulse signal from the crank angle sensor 10 is detected. At step 1 (indicated as "S1" in the drawings; the same will apply hereinafter), the pulse signal from the crank angle sensor 10 is received and it is judged whether the pulse signal is in the rising state or in the falling state. When the pulse signal is in the rising stage, the routine goes to step 2 then the timer (timer counter) 40 is reset and restarted, and the operation of this routine is completed. When it is judged that the pulse signal is in the falling state, the routine goes to step 3, and the value of the timer 40 is read as Ta in the memory. Thus, the pulse width (the time of H level) of the pulse signal is stored as Ta in the memory. Then the routine goes to step 4, and the ratio Ta/Ta old of the present pulse time width Ta to the precedent pulse time width is determined and compared with the predetermined value K. If the falling of the pulse signal is the falling of the reference pulse signal REF, because of Ta≧Ta old , the value of Ta/Ta old becomes large. If the falling of the pulse signal is the falling of the cylinder-discriminating pulse signal SGC, because of Ta<Ta old the value of Ta/Ta old becomes small. Accordingly, if Ta/Ta old >K is judged at step 4, the falling signal is regarded as the falling signal of the reference pulse signal REF, and the routine goes to step 5and the value of the cylinder-discriminating coutnter Ccyl is increased by 1. The count value n of the cylinder-discriminating counter Ccyl indicates that the n-th cylinder is at a specific stroke, for example, at the compression stroke. When the count value of the cylinder-discriminating counter Ccyl exceeds the number of the cylinders, the count value is restored to 1. Then the routine goes to step 6 and the precedent value Ta old in the memory is substituted for the present value Ta. In case of Ta/Ta old ≦K, the falling signal is regarded as the cylinder-discriminating pulse signal SGC, and it is judged that the first cylinder is judged at a specific stroke, for example, the compression stroke, and the routine goes to step 7 and the value of the cylinder-discriminating counter Ccyl is set at 1. When the cylinder-discriminating pulse signal SGC is thus detected, at subsequent step 8 the pulse signal SGC is subjected to mask processing, and a mask-processed waveform (see Fig. 2) of only the reference pulse signal REF skipping this pulse signal SGC is formed by the microcomputer. After the passage of a predetermined time from the pulse signal, the known-control of ignition of the corresponding cylinder by the ignition plug is carried out based on the mask processed waveform. More specifically, for example, as shown in Fig. 4, the period of the reference pulse signal is computed based on the rising and falling times of the reference pulse signal detected by the routine, and the change ratio of the period is determined from the precedent period Tn-1 and the present frequency Tn and the subsequent period TF is estimated. Based on the subsequent period TF, the required ignition angle is converted to the time, and the reference point tn, that is, the time τ1 from the point of rising of the reference pulse signal of the corresponding cylinder in the present embodiment. When the time of τ2 has passed from the reference point tn, application of electricity is started and after the lapse of the time of τ1, the application of electricity is stopped, whereby ignition of the corresponding cylinder is effected. As is apparent from the foregoing description, in the present embodiment, the precedent value and the present value of the pulse widths (the time of H level) of the pulse signal are measured, and the ratio of the two widths is determined and compared with the predetermined value K. Thus, it is judged whether the pulse signal is the reference pulse signal or the cylinder-discriminating pulse signal. Alternatively, there can be adopted a method in which another element of the pulse signal concerning the time, for example, the pulse width or pulse frequency, is computed at the time of rising of the pulse signal, the present value is compared with the precedent value, and when the ratio of the two values is smaller than a predetermined value K, it is judged that the pulse signal giving the present value is the cylinder-discriminating pulse signal. The cylinder-discriminating operation of this routine is shown in Fig. 5 and is performed when rising of the pulse signal from the crank angle sensor 10 is detected. The pulse signal from crank angle sensor 10 is received and when the pulse signal is in the falling stage, the value of the timer 40 counting the clock signals is read in step 11 as the present period T of the pulse signal in the memory. Then, at step 12, the timer 40 is reset and restarted. Then, the routine goes to step 13, and the ratio T/T old of the present pulse time width to the precedent pulse time width of the pulse signal is determined and compared with the predetermined value K. If the rising of the pulse signal is the rising of the reference pulse signal REF, because of T≒T old , the value of T/T old becomes large to approximately be 1. If the rising of the pulse signal is the rising of the cylinder-discriminating pulse signal SGC, because of T old »T, the value of T/T old becomes small. Accordingly, if T/T old >K is judged at step 13, the rising signal is regarded as the rising signal of the reference pulse signal REF, and the routine goes to step 14 and the value of the cylinder-discriminating counter Ccyl is increased by 1. The count value n of the cylinder-discriminating counter Ccyl indicates that the n-th cylinder is at a specific stroke, for example, at the compression stroke. When the count value of the cylinder-discriminating counter Ccyl exceeds the number of the cylinders, the count value is restored to 1. In case of T/T old ≦K, the rising signal is regarded as the cylinder-discriminating pulse signal SGC, and it is judged that the first cylinder is judged at a specific stroke, for example, the compression stroke, and the routine goes to step 15 and the value of the cylinder-discriminating counter Ccyl is set at 1. When the cylinder-discriminating pulse signal SGC is thus detected, at subsequent step 16 the pulse signal SGC is subjected to mask processing, and a mask-processed waveform (see Fig. 2) of only the reference pulse signal REF skipping this pulse signal SGC is formed by the microcomputer. After the passage of a predetermined time from the pulse signal, the well-known control of ignition of the corresponding cylinder by the ignition plug is carried out based on the mask-processed waveform. In these cases of the cylinder-discriminating routines shown in Figs. 3 and 4, since the pulse width or period of the pulse signal is time-sequentially decreased by the maximum rotation variation ratio (about 30%) at abrupt change of the revolution of the engine, for example, at abrupt acceleration of the engine by no-load racing or the like, this reduction should be taken into consideration. In the case where the judgement is made by using the pulse width of the pulse signal, the rotational angle of the engine (crank angle) corresponding to the pulse width of the cylinder-discriminating pulse signal, that is, the angle of the slit 17 about the rotational axis, is made smaller than the angle (crank angle) corresponding to the pulse width of the reference pulse signal by at least the maximum rotation variation ratio (at least 30%), or in the case where discrimination of the cylinders is carried out by using the period of pulse signals, the angle about the rotational axis corresponding to the frequency of the precedent reference pulse signal and the cylinder-discriminating pulse signal, that is, the respective angle between the start or end of the slit 13 and the start or end of the slit 17, is made smaller than the angle corresponding to the period of the reference pulse signals by at least the maximum rotation variation ratio (at least 30%). In this case, even if the engine rotation variation ratio shows a maximum value, the pulse width of the sequent reference pulse signal or the period of the sequent reference pulse signals is decreased from the same at the constant revolution of the engine only by the maximum engine rotation variation ratio, and therefore, the pulse width or the period of the subsequent reference pulse signal does not become smaller than the pulse width of the cylinder-discriminating pulse signal or the period between the reference pulse signal and the subsequent cylinder-discriminating signal. Accordingly, erroneous judgement of the cylinder-discriminating pulse signal for the reference pulse signal is not made at all. Further, in the precedent discussion, the judgement whether the pulse signal is the reference pulse signal or the cylinder-discriminating pulse signal is performed by using the element of the pulse signal concerning the time, for example, the pulse width or pulse period. Alternatively, however there can be adopted a method in which the pulse width (the time of H level --- precedent value) of the pulse signal and the time width (the time of L level --- present value) between the pulse signals are measured, and the ratio of the two widths is determined and compared with the predetermined value. And when the ratio of the two values is smaller than a predetermined value, it is judged that the pulse signal giving the present value is the cylinder-discriminating pulse signal. The cylinder-discriminating operation of this routine is shown in Fig. 6. This routine is performed when rising or falling of the pulse signal from the crank angle sensor 10 is detected. At step 21, the pulse signal from the crank angle sensor 10 is received and it is judged whether the pulse signal is in the rising state or in the falling state. When the pulse signal is in the falling stage, the routine goes to step 22 and the value of the timer (timer counter) 40 counting the clock signals is read as Ta in a memory. Then, at step 23, the timer 40 is reset and restarted, and the operation of this routine is completed. When it is judged that the pulse signal is in the rising state, the routine goes to step 24, and the value of the timer 40 is read as Tb in the memory. Then, at step 25, the timer 40 is reset and restarted. Thus, the pulse width (the time of H level) of the pulse signal is stored as the precedent value Ta in the memory, and the time with (the time of L level) between the present and subsequent pulse signals is stored as the present value Tb in the memory. In the case where the pulse signal is in the rising state, the routine goes to step 26, and the ratio Tb/Ta of the time width (the time of L level) Tb between the pulse signals to the pulse width (the time of H level) ta of the pulse signal is determined and compared with the predetermined value K1. If the rising of the pulse signal is the rising of the reference pulse signal REF, because of Ta<Tb, the value of Tb/Ta becomes large. If the rising of the pulse signal is the rising of the cylinder-discriminating pulse signal SGC, because of Ta≧Tb, the value of Tb/Ta becomes small. Accordingly, if Tb/Ta>K is judged at step 26, the rising signal is regarded as the rising signal of the reference pulse signal REF, and the routine goes to step 27 and the value of the cylinder-discriminating counter Ccyl is increased by 1. The count value n of the cylinder-discriminating counter Ccyl indicates that the n-th cylinder is at a specific stroke, for example, at the compression stroke. When the count value of the cylinder-discriminating counter Ccyl exceeds the number of the cylinders, the count value is restored to 1. In case of Tb/Ta≦K1, the rising signal is regarded as the cylinder-discriminating pulse signal SGC, and it is judged that the first cylinder is judged at a specific stroke, for example, the compression stroke, and the routine goes to step 28 and the value of the cylinder-discriminating counter Ccyl is set at 1. When the cylinder-discriminating pulse signal SGC is thus detected, at subsequent step 29 the pulse signal SGC is subjected to mask processing, and a mask-processed waveform (see Fig. 2) of only the reference pulse signal REF skipping this pulse signal SGC is formed by the microcomputer. After the passage of a predetermined time from the pulse signal, the known control of ignition of the corresponding cylinder by the ignition plug is carried out based on the mask-processed waveform. In the present embodiment, reference pulse signals and cylinder-discriminating signals are generated by slits 13 and 17 formed on the signal disk plate in cooperation with the photoelectric pickup device. Projections can be formed instead of the slits for generation of these pulse signals. In short, it is sufficient if deformed portions are formed on the rotary body for picking up pulse signals. Incidentally, the same deformed elements, for example, space elements such as slits, or protrusions, are preferably formed for both of reference pulse signals and cylinder-discriminating pulse signals. As is apparent from the foregoing description, according to the present invention, there can be provided a method an apparatus for detecting the reference rotational angle of the engine, in which signals for discrimination of cylinders can easily be obtained by a simple structure of one pickup system. Especially, this can be accomplished by merely adding a cylinder-discriminating pulse signal-generating deformed portion consisting of the same element as that of the reference pulse signal-generating deformed portion to the conventional disk plate after one of the reference pulse signal-generating deformed portions. Accordingly, the conventional system can be improved very easily and simply and detection of the reference rotational angle of the engine to be used for control of ignition or the like and discrimination of cylinders can be accomplished by one pickup device. Therefore, the cost can be reduced and the present invention is very advantageous from the economical viewpoint.

Claims: A method for detecting a reference rotational angle for each cylinder in a multiple-cylinder internal combustion engine, comprising the steps of: outputting a reference pulse signal at a position of a predetermined rotational angle of the engine at a specific stroke of each cylinder synchronously with the revolution of the engine; outputting a cylinder-discriminating pulse signal of a predetermined amplitude in the same output line as the reference pulse signal just after termination of one of said reference pulse signals; detecting and storing time period values of the pulse signals; characterized by the steps of: calculating the ratio of an actual time period value to a precedent time period value; and performing a discrimination of the cylinder if the ratio is smaller than a predetermined constant value, said constant value being predetermined on the basis of the maximum expected variation ratio of the rotational speed of the engine between subsequent engine cycles in case of an abrupt acceleration of the engine under a no-load condition. A method according to claim 1, characterized in that the maximum expected variation ratio is about 30%. A method according to claim 1 or 2, characterized in that the time period value is derived from the pulse width of the pulse signal. A method according to claim 1 or 2, characterized in that the time period value is derived from the ratio of the pulse width of the pulse signal to the spacing between the trailing edge of the actual pulse and the leading edge of the subsequent pulse of the pulse signal. An apparatus for detecting a reference rotational angle for each cylinder in a multiple-cylinder internal combustion engine comprising: reference signal output means for putting out a reference pulse signal at a position of a predetermined rotational angle of the engine at a specific stroke of each cylinder synchronously with the revolution of the engine; cylinder-discriminating signal output means for outputting a cylinder-discriminating pulse signal on the same output line as said reference pulse signal just after termination of one of said reference pulse signals; and means for detecting and storing time period values of the pulse signal; characterized by means for calculating the ratio of a present time period value to a precedent time period value; and cylinder-discriminating means for performing a discrimination of the cylinder if the ratio is smaller than a predeterimined constant value, said constant value being predetermined on the basis of the maximum expected variation ratio of the rotational speed of the engine between subsequent engine cycles in case of an abrupt acceleration of the engine under the no-load condition. An apparatus according to claim 5, characterized in that the maximum expected variation ratio is about 30%. An apparatus according to claim 5 or 6, characterized in that the time period value is derived from the pulse width of the pulse signal. An apparatus according to claim 5 or 6, characterized in that the time period value is derived from the ratio of the pulse width of the pulse signal to the spacing between the trailing edge of the actual pulse and the leading edge of the subsequent pulse of the pulse signal.

Inventors: MOGI TAKAAKI JAPAN ELECTRONIC, TOMISAWA NAOKI JAPAN ELECTRONI, MOGI, TAKAAKI JAPAN ELECTRONIC, TOMISAWA, NAOKI JAPAN ELECTRONIC
Applicants: ATSUGI UNISIA CORP, NISSAN MOTOR, NISSAN MOTOR COMPANY, LTD., UNISIA JECS CORPORATION
Application year: 1989
Main classification: F02P7
IPC codes: F02P7