A PROCESS FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE

Abstract: According to the process for controlling an internal combust­ ion engine having a fuel injection control system (34) the detected number of revolutions is so modified that it becomes higher than an actual number of revolutions when a changing rate of the number of revolutions is larger than a pre­ determined value and the actual number of revolutions tends upward, the lower than the actual one when the changing rate is larger than the predetermined value and the actual number of revolutions tends downward. The quantity of fuel to be injected is calculated on the basis of the thus modified number of revolutions. According to the present invention, the deceleration shock or surging occurring during the low speed running of an automobile can be effectively diminished without any deterior­ ation of the exhaust gas.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for controlling an internal combustion engine for use in an autmobile, which is capable of preventing shock or surging occurring duing the automobile runs in the low speed region. Description of The Related Art In an internal combustion engine for use in an automobile, which has a fuel injection control system and an injection time, i.e., the amount of the fuel to be injected, is determined according to the load of the engine (intake of air or pressure in a suction pipe) and the number of revolutions of the engine, it is known that deceleration shock or surging (fluctuation of acceleration) occurs at an automobile body, when a throttle valve is abruptly closed for the purpose of decelerating the automobile running at the low speed. This phenomenon results from the fact that the intake of air (or the pressure in the suction pipe) is sharply reduced due to the abrupt closing of the throttle valve and accordingly the injection time, which is originally calculated based on the intake of air, is also extremely reduced. As a result, the air/fuel ratio of mixture within a combustion chamber becomes large and the condition of over-lean is brought about, so that the necessary torque is not generated and a so called minus torque is caused. This minus torque resonates with the characteristic frequency of the automobile to make the shock or surging to occur. To prevent this, in the Japanese Patent Laid-open Publication No.59-231144, for example, when a throttle valve is closed under a certain operational condition, the injection time is maintained at the value just before the closure of the throttle valve for the predetermined duration, and after that the injection time is slowly shortened. Further, there is an internal combustion engine, in which, upon engine brake, fuel is cut if the number of revolutions of the engine is higher than the predetermined value. When the injection of fuel is restarted, the control of decreasing fuel is undertaken in order to prevent the acceleration shock caused by the abrupt increase of fuel. In such a control, fuel adhered to an inner wall of a suction pipe is perfectly evaporated during the fuel cut and, after restart of injection, injected fuel is consumed to wet the inner wall of the suction pipe, so that the condition of over-lean is temporarily caused in a combustion chamber. This also resuls in occurrence of the shock or surging. To prevent the shock or surging of this kind, in the Japanese Patent Laid-open Publication No.60-30446, for example, the injection time is increased by the predetermined rate, after it was once decreased upon restart of the injection. US-A 4 442 812 and US-A 4 508 075 describe a process for controlling an internal combustion engine, in which the amount of fuel to be injected and/or the timing of ingition is varied in accordance with parameters representative of the operation conditional of the engine, including at least the number of revolutions of the engine, so as to decreasingly adjust the output power of the engine, when a positive changing rate of the number of revolutions is larger in its absolute value than a predetermined value and to increasingly adjust it when a negative changing rate of the number of revolution is larger in its absolute value than a predetermined value, whereby the shock or surging of the engine is prevented, so as to stably control engine rotational speeds at the time of iding and a low speed operation of the engine. But in contrast to the present invetion said process does not relate to a control process capable of preventing the shock or surging, which occurs when the fuel mixture falls in the over-lean condition. In the prior art as described above, whether the shock or surging is actually occurring or not, the control for preventing the shock or surging, i.e., the enrichment of fuel, is always executed in the deceleration process of the automobile. Therefore, the prior art is in danger of deteriorating the performance of purification of exhaust gas. Besides, the prior art is of no effect against the surging which occurs during a constant speed running of the automobile, which is caused by the irregular combustion in the engine, the condition of a road surface and so on. SUMMARY OF THE INVENTION An object of the present invention is to provide a process for controlling an internal combustion engine, which can prevent deceleration shock or surging occurring during the low speed running of an automobile, without deteriorating the performance of purification of exhaust gas. According to the present invention this object is achieved by providing a process for controlling an internal combustion engine comprising the features indicated in the characterizing part of claim 1. According to the present invention, the control for diminishing the deceleration shock or surging is executed only when it is actually detected and at the early time of its occurrence. Therefore, the deterioration of the purification of exhaust gas can be avoided, since mixture supplied for the engine is not enriched more than necessary. In addition, the present invention functions effectively against the surging which occurs when an automobile is running at the constant speed. Other objects, featurs and advantages of the present invention will become apparent upon reading the specification and inspection of the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows the construction of an internal combustion engine to which the present invention is applied; Fig. 2 is a block diagram roughly showing the construction of a control unit shown in Fig. 1; Fig. 3 is a drawing for explaining the method of detecting the surging according to the present invention; Fig. 4 is a timing chart for explaining the filtering operation used in an embodiment of the present invention; Fig. 5 is a drawing showing the relationship between the number of revolutions and the fuel injection period, when the compensation operation according to the embodiment of the present invention is conducted; Fig. 6 is a drawing showing the relationship between the number of revolutions and the compensated ignition angle, when the compensation operation according to another embodiment of the present invention is conducted; Fig. 7 shows an example of the way of compensation according to the another embodiment; Fig. 8 is a flow chart showing the operation of a control apparatus according to the another embodiment of the present invention, also the operation of this flow chart being executed in the control unit shown in Fig. 2; Fig. 9 is a drawing for showing the effect of the present invention at the time of the deceleration of an automobile, compared with the prior art; and Fig. 10 is a drawing for showing the effect of the present invention during the constant speed running of an automobile, compared with the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring at first to Fig. 1, the brief explanation will be made of the whole construction of an internal combustion engine, to which the present invention is applied. In the figure, reference numeral 10 denotes an engine, in which a combustion chamber 14 is defined by a cylinder 12 and a piston 16. To the combustion chamber 14 coupled are one end of a suction pipe 18 and one end of an exhaust pipe 20. The other end of the suction pipe 18 is coupled through a collector portion 22 to a throttle body 24, in which a throttle valve is equipped. The throttle body 24 is coupled to an air cleaner 28 through a duct 26. Reference muneral 30 denotes an inlet of the air cleaner 28. The quantity of air sucked into the engine 10 is measured by an airflow meter 32 attached to a part of te duct 26. As the airflow meter 32, a hot wire type airflow meter can be employed, for example. A signal representative of the intake of air measured by the airflow meter 32 is sent to a control unit 34. To a part of the suction pipe 18 attached is a fuel injecting valve (injector) 36, which injects fuel, which is sent by a fuel pump 40 from a fuel tank 38 through a dumper 42 and a filter 44, into the air sucked by the engine 10 for the opening duration thereof, which is varied in response to a signal from the control unit 34. By adjusting this opening duration (injection time), the air/fuel ratio of a mixture of air and fuel sucked into the combustion chamber 14 can be controlled. Further, there is provided a fuel pressure regulator 46, by which a part of fuel is returned to the tank 38 when the pressure of fuel supplied to the injector 36 exceeds a predetermined value. To the control unit 34 are given the following signals, in addition to the aforesaid signal of the quantity of air. One of them is, at first, a signal of the number of revolutions of the engine, which is sent from a crank angle sensor assembled within a distributor 48. Next one is a signal from an idle switch attached to the throttle body 24, which represents that the throttle valve is closed. The control unit 34 also receives a signal from a cooling water temperature sensor 50, whereby the temperature of the engine 10 is taken into the control unit 10. Receiving these signals, the control unit 34 produces signals to the injector 36, the fuel pump 40 and an ignition coil 52. The signal to the ignition coil 52 controls the timing of generation of the high voltage which supplied to the distributor 48, i.e., this signal adjusts the output of the engine 10 by varying the ignition timing. Fig. 2 roughly shows the construction of the control unit 34 mentioned above. As is apparent from the drawing, the control unit 34 is formed by a known microprocessor comprising a processing unit (MPU), a read-only memory (ROM) and a random access memory (RAM) which are connected through busses. Further, to the MPU, an input/output (I/O) circuit is connected through a bus. Through this circuit, the MPU receives signals from a startor switch, an oxygen sensor and a battery voltage sensor, as well as the signals from the airflow meter, the crank angle sensor, the idle switch and the cooling water temperature sensor, which have been already described referring to Fig. 1. Further, sensors or devices to be connected with the I/O circuit should not be construed in such a manner that they are limited to those described here or they all are required for the implementation of the present invention. Receiving the signals from those sensors and devices, the MPU executes the predetermined processing and outputs the signals to the injectors, the ignition coil and the fuel pump through the I/O circuit. Although only one injector 36 is indicated in Fig. 1, it is to be understood that there are provided in this case one injector for every cylinder of a four cylinder engine. Referring next to Figs. 3 to 5, the explanation will be made of the principle of the detection of the shock or surging and the diminishing method thereof according to an embodiment of the present invention. If the surging occurs, the number of revolutions of the engine 10 fluctuates. Further, as is apparent from Figs.3(A) and 3(B), when the fluctuation at the time of the loaded condition of the engine is compared with that under the non-loaded condition, the degree of the fluctuation is different to a great extent. Namely, a changing rate ΔN of the number of revolutions of the engine under the loaded condition is much larger than that of the engine under the non-loaded condition. Then, the fluctuation in the number of revolutions caused by the surging can be discriminated by providing an appropriate threshold ΔN R . Fig. 4 is a chart showing the timing of the detection of the surging and the operation for diminishing it. Assuming that the number of revolutions fluctuates as shown in Fig. 4(a) due to the surging, the signal as shown in Fig. 4(b) appears for the duration of ΔN ≧ ΔN R . The filtering operation, which is described in detail later, starts simultaneously with the appearance of the signal of Fig. 4(b) and continues until the time T1 after the disappear of the signal of Fig. 4(b). Next, the filtering operation will be explained, referring to Fig. 5. The filtering operation is executed by a so called recursive digital filter as indicated by the following formula. N = N y + G(N y - N y-1 ) wherein N represents the number of revolutions modified by this filtering processing, which is utilized for the calculation for the fuel injection period (the width of the fuel injection pulse) of this time, N y denotes an actual number of revolutions taken for the filtering operation of this time, N y-1 represents the modified number of revolutions, which has been used for the calculation of the fuel injection period of the last time, and G denotes a constant. Here let us assume that the number of revolutions of the engine fluctuates as shown by a solid line in Fig. 5. In the figure, the number of revolutions fluctuates stepwise, because it is shown in the form of the signal taken into the control unit 34, i.e., the solid line represents the change in sampling values, which is taken into the control unit 34 every sampling period. If the filtering processing as described above is applied to the signal of the number of revolutions as shown by the solid line in Fig. 5, the signal is changed as shown by a broken line in Fig. 5. The value indicated by the broken line is N obtained by the aforesaid formula. As apparent from the figure, when the actual number of revolution changes decreasingly, the modified number of revolutions is made lower than the actual one. To the contrary, when the actual number of revolutions changes increasingly, the modified number of revolutions is made higher than the actual one. This is the meaning of the filtering operation indicated by the aforesaid formula. The filtering processing is executed y times (this appears as the number of steps in the figure) from the instances when the number of revolution changes from increase to decrease the vice versa. The number y of times of the filtering processing depends on the characteristic frequency of the automobile. Therefore, it must be finally fixed by the experiment. In the following will be explained an embodiment with reference to Figs. 6 to 9. As is well known, the output of the internal combustion engine can be also adjusted by controlling the ignition timing. The ignition is usually conducted at the angle read out from an ignition timing map stored in the storage in accordance with detected parameters indicative of the operational condition of the engine. Then, assuming that, when the engine is operated with the ignition timing ADVM read out from the map, the fluctuation of the number of revolutions occurs as shown in Fig. 6(a). In this embodiment, when the number of revolutions of the engine changes decreasingly, the ignition timing is advanced with respect to ADVM, whereby the output of the engine is increased and the fall of the number of revolutions is moderated. When the number of revolutions of the engine changes increasingly, the ignition timing is delayed with respect to ADVM, whereby the output of the engine is decreased and the increase of the number of revolutions is moderated. Fig. 7 shows an example of the compensation amount. In the figure, the abscissa indicates the order of the compensating operations counted from their commencement. Namely, the amount of the compensation is varied in accordance with the order of the compensating operation. Further, the ordinate indicates the absolute value ΔADV of the compensating amount. When the number of revolutions changes decreasingly, the values ΔADV corresponding to the respective orders of compensation are added to the present ignition angle ADVM read out from the ignition timing map. To the contrary, when the number of revolutions changes increasingly, the values ΔADV corresponding to the respective orders of compensation are subtracted from the present ignition angle ADVM. The relation as shown in Fig. 7 can be stored in the form of a table in the storage. Further, the compensating amount shown in Fig. 7 is decreased every time of the compensation. However, the manner of selecting the compensating amounts for respective times is not limited thereto. For example, the compensating amount of the second time can be selected larger than that of the first time. It is desirable that the largest amount is made to correspond to the compensation of the time at which the changing rate of the number of revolutions indicates its maximal value. According to this, the largest compensation is added, when the number of revolutions is changing most sharply, so that the effect of diminishing the shock or surging is enhanced. The above mentioned operation is executed by the MPU in the control unit 34 in accordance with an operation flow shown in Fig. 8. After the operation starts, the number N of revolutions and the present ignition angle ADVM are sampled at a predetermined sampling time and is read into the PMU at step 100. At step 102, a changing rate ΔN is calculated from N read at this sampling time and N′ read at the last sampling time, and it is discriminated at step 102 whether ΔN≧ ΔN R . If ΔN < ΔN R , the operation jumps to step 110, and N r at this sampling time is stored into the predetermined address of the storage. When ΔN ≧ ΔN R , it is discriminating at step 104 whether the sign of the changing rate ΔN changed. If not, the operation jumps to step 110. When the sign of the changing rate N has turned, the operation enters into the process consisting of steps 105 to 108. In this process, the operation is repeated Y times. It is easily understood that the operation of this step 106′ is as described above. After accomplishing the process, the operation goes to step 110, at which the ignition angle is stored. Figs. 9 and 10 show the effect of the present invention, compared with the prior art, in which Fig. 9 shows the effect at the time of the deceleration of an automobile and Fig. 10 shows the effect in the constant speed running. It will be understood that, according to the present invention, the surging is diminished in both cases of the deceleration and the constant speed running. Further, it is to be understood that the embodiments mentioned above can be effectively used independently or in combination thereof. For example, upon detection of the occurrence of the shock or surging, if the compensation for both the fuel injection and the ignition timing is conducted, the effect of diminishing the shock or surging is further enhanced.

Claims: A process for controlling an internal combustion engine, in which the amount of fuel to be injected and/or the timing of ignition is varied in accordance with parameters representative of the operational condition of the engine, including at least the number of revolutions of the engine, so as to decreasingly adjust the output power of the engine when a positive changing rate of the number of revolutions is larger in its absolute value than a predetermined value and to increasingly adjust it when a negative changing rate of the number of revolutions is larger in its absolute value than a predetermined value, whereby the shock or surging of the engine is prevented, characterized in that said adjustment of the output power of the engine is intitiated when the sign of the changing rate of the number of revolutions of the engin turns; and in that the output power of the engine is adjusted by compensating the ignition timing for a predetermined number of ignitions after the turn of the sign of the changing rate of the number of revolutions in such a manner that the timing of ignition is delayed, when the positive changing rate of the number of revolutions is larger in its absolute value than the predetermined value, and advanced, when the negative changing rate of the number of revolutions is larger in its absolute value than the predetermined value. A process for controlling an internal combustion engine as defined in claim 1 characterized in that the amount of compensating the ignition timing is changed for every time of compensation of the ignition timing.

Inventors: ATAGO, TAKESHI, NAGANO, MASAMI, SAKAMOTO, MASAHIDE, SUDA, SEIJI
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: F02D31
IPC codes: F02D45, F02D41, F02P5, F02D43