This invention relates to a knocking suppression apparatus for an internal combustion engine which suppresses knocking by adjusting the ignition timing of the engine. More particularly, it relates to a knocking suppression apparatus which can distinguish between noise due to engine knocking and high-level noise due to other causes and adjust the ignition timing only when knocking is taking place.
A knocking suppression apparatus is a device which suppresses knocking of an internal combustion engine by adjusting the ignition timing of the engine. FIG. 1 is a block diagram of a conventional knocking suppression apparatus for an internal combustion engine. As shown in this figure, an acceleration sensor 1 which is mounted on an unillustrated engine senses accelerations due to engine vibrations and generates a corresponding output signal which is input to a band-pass filter 2. The band-pass filter 2 passes only that component of the output signal of the acceleration sensor 1 lying in a frequency band corresponding to engine knocking, and this component is input to an analog gate 3 which can be turned on and off in order to block noise which is an impediment to the detection of knocking signals. The opening and closing of the analog gate 3 is controlled by a gate controller 4. The output of the analog gate 3 is provided to a noise level sensor 5 which generates an output signal having a DC voltage which is proportional to the average amplitude of the rectified output of the analog gate 3.
The output of the analog gate 3 and the output of the noise level sensor 5 are input to a comparator 6, which generates output pulses when the input signal from the analog gate 3 is higher than the input signal from the noise level sensor 5. The output pulses from the comparator 6 are integrated by an integrator 7, which generates an output signal whose voltage corresponds to the strength of the knocking of the engine.
A signal generator 9 generates pulses at a frequency corresponding to the rotational speed of the engine. These pulses are shaped by a waveform shaper 10 and input to a phase shifter 8. The output signal of the integrator 7 is also provided to the phase shifter 8. The phase shifter 8 generates output pulses having a phase which is shifted from that of the output of the waveform shaper 10 by an amount corresponding to the magnitude of the output signal of the integrator 7. The output pulses of the phase shifter 8 operate a switching circuit 11 which controls the supply of current to an ignition coil 12.
FIG. 2 illustrates the frequency characteristics of the output signal of the acceleration sensor 1. In the figure, curve A shows the characteristics of the output signal when there is no knocking, and curve B shows the characteristics of the output signal when knocking is occurring. In addition to a knocking signal (a signal which is generated by knocking), the output signal of the acceleration sensor 1 contains various other noise components such as components due to mechanical noise of the engine, ignition noise, and noise due to the signal transmission pathway.
Comparing curve A and curve B of FIG. 8, it can be seen that the knocking signal has unique frequency characteristics.
Accordingly, although the frequency distribution of the knocking signal will differ from engine to engine and in accordance with differences in the location in which the acceleration sensor 1 is mounted, there is always a clear difference in the characteristics of the output of the acceleration sensor 1 when knocking is taking place.
By passing only the frequency component corresponding to the knocking signal, noise having other frequency components is suppressed and the knocking signal can be efficiently detected.
The operation of the conventional apparatus of FIG. 1 will be explained while referring to FIGS. 3 and 4, which illustrate the waveforms of the output signals of various portions of the conventional knocking suppression apparatus of FIG. 1. FIG. 3 illustrates the case when there is no knocking and FIG. 4 illustrates the case when knocking is taking place in the engine. When the engine is operating, the ignition signal which is generated by the signal generator 9 in accordance with previously-determined ignition timing characteristics undergoes waveform shaping in the waveform shaping circuit 10 to form pulses which are input to the phase shifter 8. The pulses drive the switching circuit 11 via the phase shifter 8 and switch the current to the ignition coil 12 on and off. When the current to the ignition coil 12 is cut off, the ignition coil 12 generates a high voltage which is applied to unillustrated spark plugs of the engine.
The engine vibrations which occur during engine operation are detected by the acceleration sensor 1, which generates an output signal as shown by FIG. 3a. When the engine is not knocking, the output signal of the acceleration sensor 1 does not include a component due to knocking but it includes components due to other mechanical vibrations or due to ignition noise which is superimposed on the signal transmission pathway at the time of firing F of the cylinders.
This signal is passed through the band-pass filter 2, and a large part of the mechanical noise component is suppressed, as shown in FIG. 3b. However, as the ignition noise component is strong, it has a high level even after passing through the band-pass filter 2, as shown by the spikes in FIG. 3b.
In order to prevent the ignition noise from being misidentified as knocking signals, the analog gate 3 is closed for a prescribed length of time each time one of the cylinders is fired. The analog gate 3 is closed by a pulse (FIG. 3c) which is output by the gate controller 4, which is triggered by the output of the phase shifter 8, and as a result, the ignition noise is removed. Therefore, only low-level mechanical noise remains in the output of the analog gate 3, as shown by curve (i) of FIG. 3d. This output signal is provided to the noise level sensor 5 and the comparator 6.
The noise level sensor 5 responds to changes in the peak level of the output signal of the analog gate 3. It can respond to a relatively gradual change in the peak value of normal mechanical noise, and it generates an output signal having a DC voltage which is slightly higher than the peak of the mechanical noise (curve (ii) in FIG. 3d). This output signal is also provided to the comparator 6.
The comparator 6 generates an output signal when the input signal from the analog gate 3 is higher than the input signal from the noise level sensor 5. As shown in FIG. 3d, when knocking is not taking place, the output of the noise level sensor 5 is higher than the average peak value of the output signal of the analog gate 3, so that as shown in FIG. 3e, nothing is output from the comparator 6.
The integrator 7 integrates the output signal from the comparator 6, and when knocking is not taking place, the output signal of the integrator 7 is zero as shown in FIG. 3f.
The phase shifter 8 shifts the phase of the input signal from the waveform shaper 10 (shown by FIG. 3g) in accordance with the voltage of the output signal of the integrator 7. When there is no knocking, the integrator 7 output voltage is zero, so the phase shifter 8 does not produce a phase shift, and the output signal of the phase shifter 8 (FIG. 3h) is in phase with the output signal of the waveform shaper 10. As a result, the engine is operated with a reference ignition timing.
However, when knocking takes place, the output of the acceleration sensor 1 contains a knocking signal which is delayed from the ignition timing by a certain amount, as shown in FIG. 4a. After this signal passes through the band-pass filter 2 and the analog gate 3, it consists of mechanical noise on which the knocking signal is superimposed, as shown by curve (i) in FIG. 4d.
Of the signals which pass through the analog gate 3, the knocking signal is particularly steep, so the response of the output voltage of the noise level comparator 5 is delayed with respect to the knocking signal. As a result, the inputs to the comparator 6 are as shown by curves (i) and (ii) in FIG. 4d, and the comparator 6 generates output pulses, as shown in FIG. 4e.
The integrator 7 integrates the pulses from the comparator 6 and generates a voltage corresponding to the amount of knocking, as shown in FIG. 4f. Then, the phase shifter 8 generates an output signal (FIG. 4h) which is delayed with respect to the output signal of the waveform shaper 10 (FIG. 4h) by a prescribed amount corresponding to the output voltage of the integrator 7. Therefore, the ignition timing is retarded by the prescribed amount, and knocking is suppressed.
The time constant of the apparatus of FIG. 1 (the number of seconds per degree of engine rotation) which expresses the speed at which the output of the integrator 7 is decreased, and therefore the speed at which the ignition timing returns towards the reference timing after the occurrence of knocking, is a large value. This time constant is an important control characteristic, since if the lag angle is decreased too rapidly after the occurrence of knocking, the engine will abruptly enter a knocking region and knocking will again occur.
Therefore, in order to ensure an appropriate time constant, it is necessary to determine the amount of knocking each time knocking occurs by measuring the output of the integrator 7 immediately before and immediately after each time that knocking is detected, and then to find the change in the amount of knocking. This procedure involves complicated calculations, and it is not sufficient merely to read the value of the integrator 7 at the time of knocking detection.
It is therefore necessary to store the output of the integrator 7 before the occurrence of knocking and after the occurrence of knocking and to find the difference between the two stored values.
Recently, engine control is tending to become increasingly sophisticated. There is a tendency to control each cylinder individually so as to improve the combustion conditions of all the cylinders and increase the engine output.
In order to perform such control, it is necessary to detect the amount of knocking each time knocking occurs and to find the amount of knocking of individual cylinders.
However, complicated calculations are necessary to determine the amount of knocking each time knocking occurs based on the output of the integrator 7 in the above-described conventional apparatus. Furthermore, in order to determine the amount of knocking of each cylinder, the scale of the circuit has to be further increased, which is not easy.
FIG. 5 is a block diagram of an example of another type of knocking suppression apparatus for an internal combustion engine which can easily detect the amount of knocking each time knocking occurs and which can easily determine the amount of knocking of individual cylinders.
In FIG. 5, elements numbers 1-6, 11, and 12 are the same as in FIG. 1, so an explanation thereof will be omitted. This apparatus is further equipped with a cylinder pulse generator 21 which generates pulses corresponding to the ignition of each cylinder of the engine. These pulses are input to a circuit closing controller 22 which outputs an ignition pulse which guarantees the conducting time of the ignition coil 12. The output of the circuit closing controller 22 is provided to a phase shifter 23 which controls the phase of ignition pulses which are provided to the switching circuit 11 so as to obtain a desired ignition timing.
The output signal of the comparator 6 is provided to an integrator 24 which generates an output signal having a voltage which is proportional to the number of pulses from the comparator 6 per unit time. This integrator 24 also differs from the integrator 7 of FIG. 1 in that its output voltage is not made to gradually decrease over time. The integrator 24 receives the output signal of the phase shifter 23 and resets itself each time one of the cylinders of the engine is fired.
The output signal, of the integrator 24 is converted into a digital signal by an A/D converter 25, and the resulting digital signal is provided to a distribution circuit 26. According to which cylinder is knocking, the distribution circuit 26 provides the digital signal to one of four different memories 27-30, each of which corresponds to one of the four cylinders of the engine. The memories 27-30 store the digital signals from the distribution circuit 26.
A clock signal generator 31 generates output pulses at prescribed intervals and provides these pulses to the memories to cause a decrease in the values stored in the memories 27-30.
Each of the memories is connected to a selector 32 which selects the memory containing data corresponding to the cylinder which is firing.
A reference pulse generator 33 generates reference pulses corresponding to a reference cylinder of the four cylinders of the engine and provides the reference pulses to a cylinder selection pulse generator 34. Based on the reference pulses and the output of the circuit closing controller 22, the cylinder selection pulse generator 34 successively generates cylinder selection pulses which control the operation of the distribution circuit 26 and the selector 32 so that the appropriate memory will be accessed.
The output signals of the acceleration sensor 1 and the noise level sensor 5 are provided to a failure sensor 40 which detects failures in the form of breakage of signal wires between the acceleration sensor 1 and the band-pass filter 2, shorts to ground, and abnormal output voltages of the noise level sensor 5. When a failure is sensed, the failure sensor 40 generates failure signals KF which are sent in parallel to the integrator 24, a fuel controller, a vehicle diagnosis apparatus, and other unillustrated members.
The operation of the apparatus of FIG. 5 will be explained while referring to FIGS. 6 and 7, which are waveform diagrams similar to FIGS. 3 and 4 and respectively illustrate the case in which there is no knocking and when there is knocking. When engine knocking is not taking place, the two input signals to the comparator 6 are as shown by curves (i) and (ii) in FIG. 6d. Since in this case the input signal from the analog gate 3 is always less than the input signal from the noise level sensor 5, the comparator 6 does not generate an output signal (FIG. 6e). Accordingly, the output signal of the integrator 24 is zero, as shown by FIG. 6f. Therefore, no value is stored in memories 27-30, and the selector 32 does not produce any output, so there is no phase difference between the input signal of the phase shifter 23 (FIG. 6g) and its output signal (FIG. 6h). As a result, the ignition coil 12 is driven with the reference ignition timing
Next, the case in which knocking occurs will be explained while referring to FIG. 7. In this case, the output signal of the analog gate 3 (curve (i) of FIG. 7d) contains knocking signals which exceed the level of the output of the noise level sensor 5 (curve (ii). Therefore, the comparator 6 generates pulses as shown in FIG. 7e, and these pulses are integrated by the integrator 24, which generates an output signal having a magnitude K as shown in FIG. 7f.
Knocking detection is carried out with respect to each cylinder, so upon each ignition, the output of the integrator 24 is reset by the output of the phase shifter 23. The output of the integrator 24 remains constant from the time of the last output pulse of the comparator 6 until the integrator 24 is reset.
The above-described process is carried out upon each ignition at intervals equal to the ignition period. The output of the integrator 24 is converted into a digital signal by the A/D converter 25. Based on the cylinder selection pulse from the cylinder selection pulse generator 34, the distribution circuit 26 discriminates which cylinder is knocking, and it inputs the digital output of the A/D converter 25 to the memory corresponding to the cylinder which is knocking. For example, if the third cylinder is knocking, the output of the A/D converter 25 is stored in memory 29.
Memory 29 stores the output signal from the distribution circuit 26. Based on the cylinder selection pulse from the cylinder selection pulse generator 34, the selector 32 selects memory 29 and provides its output to the phase shifter 23. As a result, the phase shifter 23 delays its output signal (FIG. 7h) with respect to its input signal (FIG. 7g) by an angle .theta. corresponding to the output voltage of the integrator 24.
As can be seen from FIG. 7b, knocking also occurs in the cylinder which is fired immediately after the third cylinder, which in a normal four-cylinder engine is the fourth cylinder. Therefore, the output of the integrator 24 is stored in memory 30 by the distribution circuit 26. Then, upon the next firing of the fourth cylinder, the output of memory 30 which was selected by the selector 32 is input to the phase shifter 23.
Next, the manner in which the ignition timing of each cylinder is individually controlled will be explained while referring to FIG. 8, which shows the signals which are generated by various portions of the apparatus of FIG. 5 and the contents of the four memories 27-30. In FIG. 8, (s) indicates the number of the cylinder which is firing, (e) is the output of the comparator 6, (f) is the output of the integrator 24, (j), (k), (1), and (m) are the values stored in memories 27-30, (p) is the output of the selector 32, and (g) and (h) are respectively the input and the output of the phase shifter 23.
As shown in FIG. 8e, knocking pulses appear in the output of the comparator 6 due to knocking which occurs successively in the third cylinder, the second cylinder, the third cylinder, the fourth cylinder, and the second cylinder. The output pulses of the comparator 6 are integrated by the integrator 24, which generates the output signals shown in FIG. 8f.
Here, K1, K2, K3, and K5 indicate the voltages of the output signals of the integrator 24 and correspond to the amount of knocking which was detected. In order of small to large, they are ranked K1, K2, K3 and K5.
At time t1, knocking begins to occur in the third cylinder, and the output of the integrator 24 becomes voltage K5. This voltage K5 is converted into a digital signal by the A/D converter 25 and is input to the distribution circuit 26.
The distribution circuit 26 selectively outputs the digitalized voltage K5 to memory 29, corresponding to the third cylinder, at the time of firing t2 of the fourth cylinder, and at this time, K5 is stored in memory 29 (FIG. 81).
Next, at time t3, the second cylinder begins to knock, and the resulting output pulses of the comparator 6 are converted into a voltage K5 by the integrator 24. This voltage K5 is converted into a digital signal by the A/D converter 25, it is selectively input to memory 28, corresponding to the second cylinder, by the distribution circuit 26, and at time t4, which is the firing time for the first cylinder, this value is stored in memory 28 (FIG. 8k).
Also at time t4, voltage K5 which is stored in memory 29 is output from the selector 32 (FIG. 8p) and is input to the phase shifter 23.
As a result, the phase shifter 23 delays its next output pulse (FIG. 8h) with respect to the input pulse (FIG. 8g) by an angle .theta.5, corresponding to voltage K5. Therefore, firing takes place at time t5 and is delayed by angle .theta.5 with respect to the reference ignition timing.
At time t6, knocking again occurs in the third cylinder, but this time the knocking is of a lower level, and the integrator 24 generates an output voltage K2. At time t7, which is the firing time of the fourth cylinder, voltage K2 is added to voltage K5 which is already stored in memory 29, and the content of memory 29 becomes a new voltage K7, as shown in FIG. 81.
Knocking takes place in the fourth cylinder beginning at time t8, and so the integrator 24 outputs a corresponding voltage K3. This voltage K3 is stored in memory 30, corresponding to the fourth cylinder, at the firing time t9 of the second cylinder.
At time t7, memory 28 corresponding to the second cylinder is selected by the selector 32 and the voltage K5 stored therein is input to the phase shifter 23. As a result, the time of the next firing becomes time t9 which is delayed from the reference timing by an angle .theta.5 corresponding to the voltage K5.
Knocking again takes place in the second cylinder at time t10, and the integrator 24 generates a corresponding voltage K1. At the time t11 of the next cylinder firing, this voltage K1 is added to the voltage K5 already in memory 28 and the value stored in memory 28 becomes voltage K6, as shown in FIG. 8k.
At time t11, the selector 32 selects memory 29 corresponding to the third cylinder, the voltage K7 which is stored in memory 29 is input to the phase shifter 32, and the next firing time is delayed from the reference timing by a corresponding angle .theta.7.
Thereafter, the same type of lag angle control is repeated, the next firing time (time t13) of the fourth cylinder is delayed from the reference timing by an angle .theta.3, and the next firing time of the second cylinder is delayed by an angle .theta.6.
In the above manner, the firing time is delayed in accordance with the detected amount of knocking (the output voltage of the integrator 24). If knocking stops occurring in the engine, the firing time is advanced at a prescribed rate back towards the reference timing. Namely, the values stored in memories 27-30 are decreased at a prescribed rate based on the clock pulses from the clock signal generator 31. As the values stored in the memories decrease, the voltages which are input to the phase shifter 23 also decrease, so the delay angle is decreased, and the reference timing is approached.
The most common type of failure which is detected by the failure sensor 40 is severing of a signal path. This can be caused by poor contact between connectors. When the failure sensor 40 detects a failure due to this or other cause, it generates a failure signal KF which is input to the integrator 24. The failure signal KF causes the integrator 24 to generate a prescribed output having no relation to the input signal from the comparator 6.
FIGS. 9 and 10 illustrate two examples of the output which could be generated by the integrator 24 when it receives a failure signal KF from the failure sensor 40. In the example of FIG. 9, a failure signal KF causes the integrator 24 to generate an output pulse having the maximum voltage Vo.sub.MAX which can be output by the integrator 24. Each time the phase shifter 23 generates an ignition signal (at time F), the integrator 24 is reset and its output falls to zero.
In the example of FIG. 10 as well, the integrator 24 outputs a voltage Vo.sub.MAX when a failure signal KF is generated, but the ignition signal from the phase shifter 23 is made ineffective and the output of the integrator 24 is not reset each time one of the cylinders is fired.
The output voltage of the integrator 24 at the time of failure need not be the maximum output Vo.sub.MAX of the integrator 24 but can be a lower value, selected in accordance with the knocking characteristics or other characteristics of the engine.
In this manner, Vo.sub.MAX will be stored in all of memories 27-30, and the engine will operate with a predetermined failure ignition timing which prevents knocking from occurring.
The failure signal KF can also be input to a fuel controller so that the fuel supply can be controlled in accordance with the failure timing, and it can be input to a diagnostic apparatus which generates a warning to indicate that a failure has occurred.
If the phase shifter 23, the integrator 24--selector 32, and the cylinder selection pulse generator 34 of FIG. 5 are constituted by a computer, a sophisticated system can be obtained which can perform fine control not only of the ignition timing but also of the fuel supply.
The apparatus of FIG. 5 can be used to individually control the ignition timing of each of the cylinders. However, if the distribution circuit 26 and the selector 32 are suitably controlled, the apparatus can be made to perform either individual control of the cylinders or to uniformly control all the cylinders so as to have the same ignition timing.
While the apparatus of FIG. 5 is able to perform adequate knocking suppression in certain circumstances, it has the problem that it is unable to distinguish between knocking signals an high-level noise due to other causes. Therefore, high-level noise signals can cause the apparatus to retard the ignition timing more than is necessary, and suitable timing control can not be performed.
This problem will be explained in more detail with reference to FIG. 11, which illustrates the output of the analog gate 3 (lower curve) and of the noise level sensor 5 (upper curve) of the apparatus of FIG. 5 during the operation of an actual engine. FIG. 11a shows the case in which the output of the analog gate 3 contained only low-level noise, and FIG. 11b shows the case in which it included high-level noise not due to knocking.
In the case of FIG. 11a, the output signal of the analog gate 3 was always lower than the output of the noise level sensor 5, so the integrator 24 did not generate any output signal.
However, in the case of FIG. 11b, the output of the analog gate 3 contained high-level noise which exceeded the output of the noise level sensor 5. When this high-level noise was generated, the integrator 24 generated an output voltage.
FIG. 12 shows a portion of the waveforms of FIG. 11b with an expanded time scale. As shown in this figure, high-level noise was produced during the firing of the first cylinder, the fourth cylinder, and the second cylinder. As the level of this high-level noise exceeded the level of the output of the noise level sensor 5, the integrator 24 generated a corresponding output voltage each time the high-level noise was produced.
If the high-level noise is a momentary phenomenon, the output of the integrator 24 will not be large enough to significantly disturb the engine timing, and the high-level noise will not be a problem. However, in the case of the engine tested by the present inventors, if a large amount of noise was once generated, the output of the integrator 24 was high enough to disturb the engine timing, it continued long enough to lead to an excessive fall in output, and an excessive lag angle was produced in the engine timing. This high-level noise was repeatedly generated by specific cylinders each time they were fired.
It was found that this high-level noise was higher in level than usual noise, but that for the most part it was lower in level than signals due to knocking.
The integrator 24 can be prevented from generating an output due to this high-level noise simply by increasing the level of the output of the noise level sensor 5, but this is not a satisfactory solution to the problem since many knocking signals which should be detected would become impossible to detect, and adequate knocking suppression would become impossible.
FIG. 13 shows the output of the analog gate and the integrator 24 for a somewhat longer period of time than that illustrated in FIG. 12. For three successive ignitions of the first cylinder, the integrator 24 generated an output due to high-level noise.