IGNITION TIMING CONTROL METHOD AND APPARATUS FOR AN INTERNAL COMBUSTION ENGINE HAVING A PLURALITY OF CYLINDERS

Abstract: The invention relates to an ignition timing control method and apparatus for an internal combustion engine having a plurality of cylinders. The apparatus includes a knock sensor (401) for detect­ ing a knocking condition in the engine, sensors (40, 50, 60) for detecting other operating conditions of the engine, a microprocessor unit (12) for receiving signals from the sen­ sors (40, 50, 60) to determine a basic ignition timing of the engine and generate an ignition timing control signal, and a power transistor circuit (74) responsive to the ignition tim­ ing control signal from the microprocessor unit (12) to switch on and off the primary current in an ignition coil and generate a high-voltage ignition signal. The microprocessor unit (12) has a control function of retarding the basic ignition timing a predetermined amount in response to a knock de­ tected during an ignition operation at the basic ignition tim­ ing and another control function of gradually restoring the retarded ignition timing to the basic ignition timing in re­ sponse to a knock detected during an ignition operation at the retarded ignition timing from the basic ignition timing. The apparatus includes control means (12) responsive to the occurrence of a knock to correct the basic ignition timing for each cylinder of the engine whereby the basic ignition timing of each cylinder is controlled to be retarded in re­ sponse to the detection of a knock in each cylinder.

Description: BACKGROUND OF THE INVENTION The present invention relates to an ignition timing control apparatus for gasoline engines as referred to in the main claim of the present invention. Such an apparatus is known from FR-A25 50 825. It discloses an ignition timing control apparatus for an internal combustion engine having one or more cylinders comprising: a knock sensor for detecting a knocking condition in an engine; sensors for detecting other operating conditions of said engine; and control means including computing means and memory means for receiving signals from said sensors to determine a basic ignition timing of said engine and generate an ignition timing control signal whereby in accordance with said ignition timing control signal from said control means a primary current in an ignition coil is switched on and off to enerate a high-voltage ignition signal, said control means having a control function of retarding said basic ignition timing a predetermined amount in accordance with a knock detected during an ignition operation at said basic ignition timing and another control function of gradually restoring said retarded ignition timing to said basic ignition timing in accordance with a knock detected during an ignition operation at an ignition timing retarded from said basic ignition timing. These types of knock control devices are disadvantageous in that the variations in knocking characteristics among the cylinders are not accomodated and the desired engine performance is not ensured fully. EP-A-47 394 discloses an ignition timing control apparatus for an internal combustion engine comprising: a knock sensor for detecting a knocking condition in an engine; sensors for detecting other operating conditions of said engine; and control means including computing means and memory means for receiving signals from said sensors to determine a basic ignition timing of said engine and generate an ignition timing control signal whereby in accordance with said ignition timing control signal from said control means a primary current in an ignition coil is switched on and off to generate a high-voltage ignition signal, said control means having a control function of retarding said basic ignition timing a predetermined amount in accordance with a knock detected during an ignition operation at said basic ignition timing and another control function of gradually restoring said retarded ignition timing to said basic ignition timing in accordance with a knock detected during an ignition operation at an ignition timing retarded from said basic ignition timing. SUMMARY OF THE INVENTION It is an object of the present invention to provide an ignition timing control apparatus for an internal combustion engine which overcomes the foregoing deficiencies in the prior art and is capable of always ensuring satisfactory engine performance and satisfactorily preventing the occurrence of knocking even if there are variations in knocking characteristics among the cylinders of an engine, so that the occurrence of knocking positively is always detected and the occurrence of knocking is satisfactorily prevented irrespective of the variations in knocking characteristics among the engine cylinders and the aging of the sensor. To accomplish the first object, in accordance with the invention the basic ignition timing of each cylinder is controlled in response to the knocking conditions in each cylinder. To accomplish the second object, in accordance with the invention the level of a detection signal corresponding to the detection of knock with no ignition timing retard is compared with the level of a detection signal generated at the retarded ignition timing so that when the level of the later is higher than the former, the knock detection level is corrected. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an embodiment of an ignition timing control apparatus according to the invention. Fig. 2 is a block diagram showing an embodiment of the input/output interface according to the invention. Fig. 3 is a time chart for explaining the operation of the invention. Fig. 4 is a block diagram showing an embodiment of the knock detecting device. Fig. 5 illustrates a plurality of signal waveforms useful for explaining the operation of the knock detecting device. Fig. 6 is a general flow chart for the embodiment of the invention. Fig. 7 is a diagram showing an ignition timing control routine. Fig. 8 is a diagram showing a rotation synchronization routine. Fig. 9 is a timing chart for explaining the operation of the first embodiment of the invention. Fig. 10 is a diagram for explaining the operating regions according to the first embodiment of the engine. DESCRIPTION OF THE PREFERRED EMBODIMENTS An ignition timing control apparatus for an internal combustion engine according to the invention will now be described in detail with reference to the illustrated embodiments. Referring to Fig. 1 illustrating an embodiment of the invention, a central processing unit or CPU 12 performs digital computations of various data such as the ignition timing of the engine. An ROM 14 stores an ignition timing control program and fixed data. An RAM 16 is a read/write memory device. A back-up RAM 17 is an RAM for holding the data even when the engine is stopped. The CPU 12 receives a signal from each of various sensors (this embodiment uses a knock detecting device 30, a crank angle sensor 40, a load sensor 50, a water temperature sensor 60 and a load switch 80) through an input/output interface circuit 20, so that in accordance with the program stored in the ROM 14 an ignition timing is computed on the basis of these signals and an ignition signal IGN is generated through the input/output interface circuit 20. The ignition signal IGN is applied to a base 70 of a power transistor 74 through an amplifier 72 and the power transistor 74 is turned on. When the power transistor 74 is turned off, an ignition current is produced in the secondary winding of an ignition coil 76. Fig. 2 shows a detailed construction of a portion of the input/output interface circuit 20 operatively associated with the ignition timing control. The crank angle sensor 40 applies position pulse signals POS to AND circuits 216 and 220. The crank angle sensor 40 also applies a reference crank angle signal REF to the reset terminal of a first counter register 210 and the set terminal of an R-S flip-flop 218. The first counter register 210 is responsive to the leading edge of the signal REF to start counting the signals POS through the AND circuit 216 and the R-S flip-flop 218 and the resulting count is applied to a comparator 206. The comparator 206 compares the count of the first counter register 210 and the ignition timing data ϑ ig computed by the CPU 12 and stored in an advance register 202, so that when the two are equal, a set pulse is applied to an R-S flip-flop 214 and the R-S flip-flop 218 is reset. When the set pulse is applied to the R-S flip-flop 214, its Q output is interrupted and the ignition power transistor 74 is turned off thus supplying a discharge current to the secondary winding of the ignition coil 76. The timing of starting current supply to the ignition coil 76 will now be described. In response to the set pulse generated from the comparator 206 to set an R-S flip-flop 222, a second counter register 212 starts the counting of position pulses POS through the AND circuit 220 and the resulting count is applied to a comparator 208. The comparator 208 compares this count and the value computed by the CPU 12 and stored in a dwell register 204 so that when the two are equal, a reset pulse is applied to the R-S flip-flop 214 and the R-S flip-flop 222 is reset. In response to the reset pulse, the R-S flip-flop 214 generates an output at its Q terminal so that the power transistor 74 is turned on and the flow of current to the primary winding of the ignition coil 76 is started. Next, the introduction of a knock signal KNCKP into the CPU 12 will be described. The knock signal KNCKP generated from the knock detecting device 30 is applied to a counter register 234 and a number of knock pulses proportional to the intensity of the knock produced are counted. The CPU 12 receives the count of the counter register 234 through a bus 18. The pulse count NP thus applied to the CPU 12 is the data corresponding to the knock intensity and it is used for the computation of an ignition timing correction amount. Fig. 3 is a timing chart showing the operation of the above-mentioned circuits of Fig. 2. In Fig. 3, (A) shows a reference crank angle signal, (B) a position pulse signal, (C) the count of the first counter register 210, and C₁ the preset value in the advance register 202. (D) shows the output signal of the comparator 206 showing that the output signal is generated when the count of the first counter register 210 attains the preset value in the advance register 202. (E) shows the count of the second counter register 212, and (E₁) the preset value in the dwell register 204. (F) shows the output of the comparator 208 which is the same in operation with the comparator 206, and (G) the Q output of the R-S flip-flop 214 which is responsive to the outputs of the comparators 206 and 208 or the signals D and F. (H) shows the current in the ignition coil 76 which is supplied in response to the Q output, and (I) the ignition timing. Referring now to Fig. 4, there is illustrated a block diagram of the knock detecting device 30 which is responsive to the occurrence of knocking to generate a number of pulses corresponding to the intensity of the knock. In the Figure, a knock sensor 401 comprises a piezoelectric element to convert the knocking vibrations of the engine cylinder to an electric signal. The output signal V IN of the knock sensor 401 is applied to a band-pass filter 403 through an input processing circuit 402. The band-pass filter 403 is provided to remove the parasitic oscillations of the engine and efficiently take out a knock signal and its band width is selected to correspond with those frequencies at which a knock signal is generated. The knock signal passed through the band-pass filter 403 is first half-wave rectified by a half-wave rectifier circuit 404 and then it is branched into two paths. Thus, one is amplified as a knock representative signal by a dc amplifier circuit 405 and the other is amplified as a discrimination level for knock detection by a dc amplifier circuit 407 after it has been smoothed by a smoothing circuit 406. A comparator 409 compares the two signals so that a knock detection signal is generated and applied to an I/O circuit 410. Fig. 5 shows the signal waveforms generated at various points in the block diagram shown in Fig. 4. (1) shows the output waveform of the knock sensor 401, (2) the output waveform of the input processing circuit 402, (3) the output waveform of the band-pass filter 403, (4) the output waveform of the half-wave rectifier circuit 404, (5) the output waveform of the amplifier circuit 405, (6) the output waveform of the smoothing circuit 406, (7) the output waveform of the amplifier circuit 407, and (8) the knock detection signal KNCKP or the output waveform of the comparator 409. Fig. 6 shows a general flow chart of the ignition timing control apparatus according to the present embodiment. In the Figure, when an interrupt request 600 is generated, whether it is a reference (REF) or timer interrupt is determined by the interrupt request analytic processing of the next step 602. If it is the timer interrupt (TIMER), tasks including an input signal A/D conversion and engine speed inputting task (606), a basic ignition timing and dwell time computing task (608) a digital input signal processing task (610) and a correction task (612) are performed. Fig. 7 shows an ignition timing and dwell time control routine corresponding to the task 608 in Fig. 6 and this routine computes a basic ignition timing ϑ ADV (base) from an equation ϑ ADV (base) = f (N, L) . Here, N represents the engine speed and L the engine load (e.g., the intake manifold vacuum). First a basic ignition timing processing is performed at steps 701 and 702. At a step 703, the counter data for advancing after the ignition retard is determined. If the counter content is zero, it is determined that a given period of time (e.g., a second) has elapsed and a transfer is made to a step 706. Thus, an advancing data Δϑ ADV2 is set at the step 706. Then, since the given time has elapsed, a lapse of given time confirming data is set in the counter at a step 707 and a transfer is made to a step 708. On the contrary, if the counter data is not zero at the step 703, it is an indication that the given time has not elapsed and the advance data Δϑ ADV2 is set to 0. This is done at a step 704. At a step 705, the counter data is decreased by 1 so as to measure the passage of time. Then, a transfer is made to the step 708. Fig. 8 shows a rotation synchronization processing routine corresponding to a task 606 of Fig. 6. At a step 801, the counter data (the number of pulses NP) is inputted. After the inputting, the counter is cleared. At a step 802, the corresponding cylinder is discriminated and the knock discrimination level (the number of pulses) corresponding to the current cylinder is searched. This discrimination level is a function of the engine speed and load. At a step 803, the counter data NP and the searched knock discrimination level N SI are compared. This discrimination level N SI is used for performing the ordinary ignition timing control. If the counter data NP is greater than the discrimination level N SI , the presence of knock is determined and a transfer is made to a step 804 thereby retarding the ignition timing. Here, Δϑ ADV1 represents the current correction amount and Δϑ ADV (t-1) represents the preceding correction amount (the amount of retard). At a step 805, in accordance with the current engine speed N and load L, corresponding one of the regions shown in Fig. 10 (while the four regions are provided in accordance with the engine speeds N and loads L, they may be provided in accordance with only the speeds or the loads and alternatively a greater number of regions may be provided) is discriminated and a maximum advance angle determining data α₁ is searched. At a step 806, the value NP of the counter is compared with a discrimination level N S2 for controlling the maximum advance angle. If the value of NP is greater than N S2 at the step 806, it is determined that the current knock is middle knock and a computation of α₁(t) = α₁(t-1) + α₁ for correcting the maximum advance angle (the maximum value of the advance after the ignition retard) is performed at a step 807. Also, when the counter value NP is smaller than N S2 at the step 806, it is predetermined that the maximum advance angle needs not be corrected and the previous value is used as α₁(t) = α₁(t-1) . Then, a transfer is made to a step 809. The step 809 sets in the advance counter the data for advancing after the ignition timing has been retarded upon the occurrence of the knock (in this embodiment data corresponding to 1 second is set). Note that the counter is operated by a TIMER interrupt to determine whether a predetermined time has elapsed. Then, a transfer is made to a step 811. On the other hand, if the step 803 determines that NP < N S1 , the absence of knock is determined and a transfer is made to a step 810. The step 810 performs the ignition advance after the retard. However, since the data Δϑ ADV2 is set to 0 at the step 704 if the predetermined time (1 second) has not elapsed, no ignition advance is made and the data Δϑ ADV (t) assumes the previous value. ϑ ADV (t) = ϑ ADV (base) + Δϑ ADV (t) At a step 811, the basic ignition timing ϑ ADV (base) and the ignition timing correction amount are added up and thus the ignition timing ϑ ADV (t) is determined. At a step 812, the current operating region (Fig. 10) is searched and the maximum advance angle correction amount α₁(t) corresponding to the region is obtained. At a step 813, the maximum advance angle ϑ max is controlled in accordance with the current basic ignition timing ϑ ADV (base) and the correction amount α₁(t), as follows ϑ max = ϑ ADV (base) - α₁(t) . At a step 814, the maximum advance angle ϑ max and the current ignition timing ϑ ADV (t) are compared. If the step 814 determines that ϑ max < ϑ ADV (t), a transfer is made to a step 815 and the maximum advance angle is set to ϑ max . If the step 814 determines that ϑ max > ϑ ADV (t), the current ignition timing still leaves margine for further advance and the current value is set in the ADV register at a step 816. As the result of the foregoing control, the advance angle after the retard is controlled at ϑ max at the most. If there is no occurrence of knock, the ignition timing for this cylinder is maintained at ϑ max so that the basic ignition timing is controlled as shown by the following equation ϑ max = ϑ ADV (base) - α₁(t) As described hereinabove, the above basic ignition timing is corrected for each cylinder and this prevents the frequent occurrence of middle knock. Referring to Fig. 9 showing a timing chart for explaining the operation of this embodiment, if middle knock occurs at A ○ in one cylinder operating at the basic ignition timing ϑ ADV (base) (when NP of the step 801 of Fig. 8 is NP > N S2 ), the ignition timing is retarded by Δϑ ADV1 so that if the knock no longer occurs, the ignition timing is advanced at the rate of Δϑ ADV2 per Δt (1 second). At this time the advance angle is controlled at ϑ ADV (base) - α₁ in accordance with ϑ max = ϑ ADV (base) - α₁(t) . If middle knock occurs at B ○ in the same cylinder in the same operating region, the advance angle is controlled at ϑ max = ϑ ADV (base) - 2α₁ . If middle knock occurs at C ○, the maximum advance angle is controlled at the following ϑ max = ϑ ADV (base) - 3α₁ At this time, if trace knock occurs at D ○, the ignition timing is first retard by Δϑ ADV1 and then advanced at the rate of Δϑ ADV2 per Δt (1 second) until finally attaining ϑ max = ϑ ADV (base) - 3α₁ . In other words, this means that in this operating region, the basic ignition timing of this cylinder is changed to ϑ ADV (base) - 3α₁ and the knock is reduced to a suitable level. This control is performed in all the same manner on the ignition timing of the remaining cylinders. Thus, in accordance with this embodiment, the desired retard control of the basic ignition timing is provided for each cylinder in accordance with the occurrence of knocking in the cylinder thus enhancing the engine performance to the utmost extent while satisfactorily reducing the ill effects of knocking. As described hereinabove, in accordance with the invention, by virtue of the fact that the desired corrective control of the basic ignition timing is provided for each cylinder in accordance with the occurrence of knocking in the cylinder, there is easily provided an ignition timing control apparatus which overcomes the deficiencies in the prior art and is capable of always accurately providing the desired retard control of the ignition timing in accordance with the occurrence of knocking in each cylinder and ensuring full play of the engine performance.

Claims: An ignition timing control apparatus for an internal combustion engine having one or more cylinders comprising: a knock sensor (401) for detecting a knocking condition in an engine; sensors (40, 50, 60) for detecting other operating conditions of said engine; and control means including computing means (12) and memory means (14, 16) for receiving signals from said sensors (40, 50, 60) to determine a basic ignition timing of said engine and generate an ignition timing control signal whereby in accordance with said ignition timing control signal from said control means a primary current in an ignition coil is switched on and off to generate a high-voltage ignition signal, said control means having a control function of retarding said basic ignition timing a predetermined amount in accordance with a knock detected by first comparing means when comparing a knock signal with a first discrimination level during an ignition operation at said basic ignition timing and another control function of gradually restoring said retarded ignition timing to said basic ignition timing in accordance with a knock detected during an ignition operation at an ignition timing retarded from said basic ignition timing, characterized in that said control means comprises a second comparing means for comparing a knock intensity with a second discrimination level higher than said first discrimination level so as to provide signals for a maximum advance angle setting means for setting a maximum advance angle ϑ max for each cylinder on the basis of said comparison result; and advance angle limiting means for limiting the advance angle of the ignition timing of each cylinder so that it does not exceed the maximum advance angle ϑ max set for each cylinder. An apparatus according to claim 1, characterized in that said maximum advance angle setting means is adapted to advance the maximum advance angle ϑ max each when said knock intensity exceeds said second discrimination level. An apparatus according to claim 1, characterized in that said correcting control means (12, 14, 16) is operable in accordance with a knock intensity. An apparatus according to claim 1, characterized in that the control means (12, 14, 16) responsive to a knock signal from said knock sensor (401) correct said basic ignition timing in accordance with knocking conditions for each cylinder of said engine separately. An apparatus according to claim 5, characterized in that each of said retard control means, said basic ignition timing restoring means and said correcting means is operable in response to an intensity of a knock signal from said knock sensor (401). An apparatus according to claim 1, characterized in that said control means comprise means for responding to a knock signal detected at said retarded ignition timing from said basic ignition timing to gradually restore said retarded ignition timing to said basic ignition timing.

Inventors: ISHII, TOSHIO, KASHIMURA, YUICHI, MOURI, YASUNORI, SHIDA, MASAMI, SUGIURA, NOBORU, TERAGAKIUCHI, AKIRA
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: F02P5
IPC codes: F02P5, F02B1