Apparatus and method for controlling ignition timing of internal combustion engines

Abstract: An ignition timing control apparatus (15) for an internal combustion engine (7) is constructed such that a predetermined amount of correction for the ignition timing of the engine is set beforehand in accordance with directions of change (dN(dt) in the revolutional speed (N) of the engine (7) in such a manner that, during a predetermined period of time after the detection of an operation to accelerate the engine (7), the predetermined amount of correction for the ignition timing is added to standard ignition timing of the engine to suppress the change (dN/dt) in the revolutional speed (N) of the engine (7). The ignition timing control unit (15) is provided with a revolution speed change rate detector (151) for detecting the actual rate of change (dN/dt) in the revolutional speed (N) and means (152) for detecting the direction of the rate of change (dN/dt). The predetermined amount of correction for the ignition timing is controlled in accordance with the sign and magnitude of the rate of change (dN/dt) in the revolutional speed (N) of the engine (7), thereby preventing surging in the revolutional speed of the engine when the load is changed suddenly.

Description: The present invention relates to a method and an apparatus for controlling the ignition timing in an internal combustion engine according to the preambles of the independent claims. Such a method and apparatus are known from EP-A-0 233 449. In particular the invention may be used for engines of electric ignition type, such as gasoline engines and is suitable for preventing occurrence of irregular surge in acceleration operation. In a vehicle such as an automobile equipped with the gasoline engine, for example, when an accelerating operation is performed by suddenly stepping on an accelerator pedal, there is accompanied in some cases with a great change in running speed, that is, an acceleration surging resulting in what is called awkward operation. In order to suppress the occurrence of such awkward operation, there has hitherto been known a method in which engine torque is controlled by changing the ignition timing when an accelerating operation is detected, for instance, as disclosed in Japanese Patent Unexamined Publication No. 62-159771. Thus, according to this conventional method, a predetermined correction is constantly made on the standard ignition timing so as to suppress the change in the number of revolutions of the engine. This conventional method, however, gives no consideration to the point that the change in the number of revolutions of the engine caused due to surging appears in an asymmetric form in some cases. This gives rise to a problem in the viewpoint of ensuring the satisfactory prevention of the irregular awkward operation at all times. More specifically, in the above-described method, no consideration is taken on a phenomenon that, in some cases, the change in the number of revolutions of the engine appears in the asymmetric form in respect of the period and amplitude thereof in the increasing and decreasing directions. Accordingly, it is impossible to suppress the irregular operation satisfactorily when applied to an automobile or the like of the type that exhibits such asymmetric characteristic in the change in the number of revolutions of the engine. Prior art document EP-A-0 233 449 discloses an apparatus and a method for controlling the ignition timing in internal combustion engines. According to the method, the ignition timing is controlled in that a change in engine speed is detected from a differentiated value dN/dt, and when dN/dt is larger than a predetermined value and when a value of dN/dt is positive, the ignition timing is retarded by a predetermined value from a fundamental ignition timing, and further, when the dN/dt is larger than a predetermined value and when the value of dN/dt is negative, the ignition timing is advanced by the predetermined value from the fundamental ignition timing. Prior art document EP-A- 0 109 535 discloses an apparatus for dampening the searching of an internal combustion engine within a vehicle. For actively attenuating the searching of an internal combustion engine, the ignition engine and the torque corresponding thereto is adjusted such that ignition is retarded when the engine speed increases and ignition is advanced, when the engine speed decreases. An object of the present invention is to provide an apparatus and a method for controlling ignition timing of internal combustion engines, which is applied to a vehicle of having an asymmetrical characteristic in terms of the change in the number of revolutions of the engine so as to constantly ensure satisfactory suppression of irregular awkward operation. This object is solved in accordance with the features of the independent claims. Dependent claims are directed on preferred embodiments of the present invention. The proposed method has the effect that the amount of correction of the ignition timing is changed in accordance with the sign of the detected change rate. Therefore, even if the change in the number of revolutions of the engine appears asymmetrically, and adequate correction for the ignition timing can be made at all times in response to that change, thereby ensuring the satisfactory suppression of the irregular operation. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram for explanation of the controlling function of an ignition timing control unit for internal combustion engine according to the present invention; Figure 2 is a block diagram of an engine system to which an embodiment of the present invention is applied; Figure 3 is a block diagram showing an example of a control unit for use in the embodiment of the invention; Figures 4a to 4c are flow charts showing the operation of the embodiment of the invention; Figure 5 is an explanatory diagram of an example of tables for ignition timing correction for use in the embodiment of the invention; Figure 6 is a diagram showing the operating characteristics obtained by the embodiment of the invention; Figure 7 is a characteristic view for explanation of effects of a conventional control unit; and Figure 8 is a characteristic view for explanation of effects of the embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Description will be given below of an ignition timing control unit for internal combustion engine according to the present invention in more detail in connection with a preferred embodiment illustrated in the drawings. Figure 2 illustrates an example of an engine system to which the invention is applied. Referring to Figure 2, air to be sucked into an engine is introduced from an inlet portion 2 of an air cleaner 1 and passes through a hot-wire air flow sensor 3 for detecting the quantity of suction air, a duct 4, and a throttle body 5 having a throttle valve for controlling the air flow rate, and then enters into a collector 6. In the collector 6, air is distributed to intake pipes 8 communicated directly with the internal combustion engine 7 so as to be sucked into cylinders thereof. On the other hand, fuel is fed from a fuel tank 9 and pressurized by means of a fuel pump 10 and then supplied to a fuel system which includes a fuel damper 11, a fuel filter 12, injection valves 13 and a fuel pressure regulator 14. The fuel thus supplied to the fuel system is regulated to be at a constant pressure by means of the regulator 14 and then injected into the intake pipes 8 through the injection valves (injectors) 13 provided on the intake pipes. The air flow sensor 3 is adapted to output a signal representing the quantity of suction air. This output signal is inputted in a control unit 15. Furthermore, the throttle body 5 is equipped with a throttle sensor 18 for detecting the degree of opening of the throttle valve. A signal from this sensor is also inputted in the control unit 15. A reference numeral 16 denotes a distributor which incorporates a crank angle sensor so as to produce a standard signal for the injection timing and ignition timing and a signal representing the number of revolutions, these signals being inputted into the control unit 15. Figure 3 shows the details of the control unit 15. As seen from Figure 3, the control unit 15 is constituted by an arithmetic unit including an MPU (microprocessing unit), a ROM (read-only memory), an A/D (analog-digital) converter, and an input/output circuit. In this control unit, a predetermined arithmetic operation is performed on the basis of the output signal from the air flow sensor 3, those from the distributor 16, etc. so as to produce an output signal indicative of the result of this operation. This output signal serves to actuate the injectors 13 so as to allow a required quantity of fuel to be injected into the respective intake pipes 8. Meanwhile, control of the ignition timing is effected by sending another signal from the control unit to a power transistor of an ignition coil 17. With the arrangement described above, controlling operation of the ignition timing control unit for internal combustion engine in accordance with the embodiment of the invention will be explained in the following. Figures 4a to 4c are flow charts showing the process for controlling the ignition timing according to the embodiment of the invention. The controlling process shown in Figures 4 is executed by the microcomputer including the MPU, the ROM and other like means in the control unit 15. As understood from Figures 4a to 4c, in the present embodiment, the controlling process comprises three kinds of tasks, that is, a [BGJ] task serving as background job, a [10mS] task which is executed periodically every ten milliseconds, and an [REF interrupt] task which is executed each time an REF signal is produced. These tasks will be explained below in order. First, the [BGJ] task is a background job in which retrieval of an ignition timing map ADVMAP is carried out on the basis of the number N of revolutions of the engine and the degree  TH of opening of the throttle, and then read of a standard ignition timing TADVM is carried out, as shown in Figure 4a. Secondly, in the [REF interrupt] task, process for setting a corrected ignition timing TADVM 1 in a predetermined register of I/O (input/output), shown in Figure 3, is executed as shown in Figure 4c. Accordingly, this corrected ignition timing TADVM 1 is an actual ignition timing of the engine. It is noted that the data required for the above tasks, such as N,  TH , TADVM 1 and the like, are given by the [10mS] task to be described below. Finally, the [10mS] task shown in Figure 4b will be explained. Explanation of this task will be made for every step. Step 100: In this step, read of the number N of revolutions of the engine, a standard pulse width T P , and the degree  TH of opening of the throttle is performed. Step 101: In this step, the rate of change dN/dt in the number N of revolutions of the engine is investigated so that the direction of change is determined from the sign of the thus investigated rate of change to detect the point of inflection thereof, thereby detecting whether the number N of revolutions is being increased or decreased. Step 102: In this step, investigation is performed for judging whether or not the number N of revolutions is being increased. Step 103: In this step, correction for the standard ignition timing is made when the number N of revolutions of the engine is being increased. The amount of correction is retrieved from a table ΔADV U shown in Figure 5. Accordingly, the amount of correction is given in such a manner that it is 0°, 1°, 2°, 1°, and 0° at the first ignition, the second ignition, the third ignition, the fourth ignition and the subsequent ignition, respectively, after the number N of revolutions has changed its direction from the decreasing one to the increasing one. Incidentally, the amount of correction and the number of correcting operations mentioned above are set beforehand in correspondence with the pattern of the change in the number of revolutions. Step 104: In this step, correction for the standard ignition timing is made when the number N of revolutions of the engine is being decreased. The amount of correction is retrieved from a table ΔADV D shown in Figure 5. Accordingly, the amount of correction in this case is 0°, 1°, and 0° at the first ignition, the second ignition and the third and subsequent ignitions, respectively, after the number N of revolutions has changed its direction from the increasing one to the decreasing one. The amount of correction and the number of correcting operations in this case are also set to the values corresponding to the pattern of the change in the number of revolutions. Next, description will be given of the operation of the described embodiment obtained as a result of execution of the process referred above. As mentioned before, there is caused surging when a sudden accelerating operation is carried out by, for example, stepping on the accelerator pedal. Figure 6 shows the characteristic of the ignition timing ADV provided by the described embodiment at the time when the surging is occurred. As seen from the drawing, in this example of the surging, the change in the number of revolutions of the engine is such that the number of revolutions is increased gradually while it is decreased relatively steeply. Accordingly, since the correction for the standard ignition timing TADVM taken as a MAP value makes use of the tables shown in Figure 5, retarding corrections are made at three ignition timing points, after the number of revolutions being to increase, during the period of increase which continues for a relatively long time. On the other hand, an advancing correction is made at one ignition timing point during the period of decrease which is finished in a short time. The manner of correction described above can be expressed as shown in Figure 1 by way of a functional block diagram representing the controlling function of the ignition time unit (151,152,153,154,155). Subsequently, effects of the present embodiment will be described with reference to Figures 7 and 8. Both these Figures 7 and 8 show what difference exists between the characteristics of the conventional method and the embodiment of the invention after the surging has been made to occur intentionally by suddenly stepping on the accelerator pedal for a short time (an accelerating operation effected by once stepping instantaneously). Figure 7 shows the results of a test conducted by making use of the conventional method, while Figure 8 shows the results of a test conducted in accordance with the present invention. It is understood from Figure 7 that, according to the conventional method, although the magnitude of the change in the number N of revolutions of the engine can be made smaller in comparison with the case where no correction is made for the ignition timing, the change itself does not come to be prevented. This is because the change in the number N of revolutions of the engine appears in the same form as shown in Figure 6. On the other hand, it is understood from Figure 8 that, by adopting the present invention, the change in the number of revolutions of the engine comes to disappear after a lapse of T sec from the point at which the accelerating operation is started, so that the surging can be prevented effectively. This is because also the correction for the ignition timing is given to show an asymmetric form in agreement with the change in the number N of revolutions of the engine which appears in an asymmetric form with respect to the increasing and decreasing portions thereof as shown in Figure 6. In consequence, according to the present embodiment, it is possible to constantly suppress the irregular awkward operation with sureness merely by setting the data for the tables shown in Figure 5 in agreement with the characteristic of change in the number of revolutions of the engine. Meanwhile, as preferred embodiments of the invention, there are two methods of setting the amount of correction and the number of correcting operations shown in Figure 5. Namely, in the first method, upon confirming the pattern of the change in the number of revolutions of the engine, values which are capable of minimizing the magnitude of the change in the number of revolutions are set beforehand. In the second method, upon calculating the time periods during which the number of revolutions of the engine is being changed to increase and decrease, the magnitude of the change is checked at regular time intervals in relation to the thus calculated time periods so that, when it is judged that the magnitude of the change in the number of revolutions does not become small, the amount of correction and the number of correcting operations automatically undergo a feedback control to alter the set values. The same effect of preventing the surging can be attained whichever the first or second method referred above is used when the invention is put into practice. According to the second method, however, since the amount of correction can be determined automatically although the necessary program capacity becomes large, it is possible to obtain a control unit of an extremely with use. Incidentally, in the described embodiments of the invention, the correction for the ignition timing is made by increasing or decreasing both the amount of correction per one correcting operation and the number of correcting operations. However, modification can be made such that the correction is made by changing either of the above factors alone. According to the present invention, the amounts of correction for the ignition timing, which correction is made for the control of torque, can be given as independent optimum values in correspondence with the cases that the number of revolutions of the engine is being changed to increase and decrease, respectively. Therefore, it becomes possible to make adequate correction for the ignition timing in agreement with the pattern of the change in the number of revolutions of an engine, irrespectively of difference in types of the vehicles, such as automobiles, to which the present invention is applied. Consequently, it is possible to prevent any irregular awkward operation surely and easily at all times without distinction of the type of the vehicles.

Claims: A method for controlling the ignition timing in an internal combustion engine, comprising the steps of determining a standard ignition timing in accordance with engine parameters, determining the sign of the change rate of the engine speed, correcting the standard ignition timing in accordance with correction values retrieved from a table so as to obtain a corrected ignition timing, and outputting the corrected ignition timing, characterized in that the step of correcting the standard ignition timing comprises correcting the standard ignition timing for a predetermined first number of ignitions by adding first correction values retrieved from a first table, when the engine speed decreases, or correcting the standard ignition timing for a predetermined second number of ignitions by adding second correction values retrieved from a second table different from said first table, when the engine speed increases. The method according to claim 1, characterized in that the absolute value of the values stored in the second table is larger than those of the values stored in the first table. The method according to claim 1, characterized in further comprising the step of controlling the frequency of correction of the ignition timing made within a period of time during which the engine speed changes and/or the amount of change of the ignition timing per one correction operation. The method according to one of the claims 1 to 3, characterized in that said amounts of correction of the standard ignition timing are calculated through a feedback control in accordance with the detected change rate of the engine speed. An apparatus for controlling the ignition timing in an internal combustion engine, the apparatus particularly being adapted to carry out the method according to one of the claims 1 to 3, comprising sensors (3, 18) for detecting operational parameters of the engine, a control unit (15, 151, 152, 153, 154, 155) adapted to determine the sign of the change rate of the engine speed, to determine a standard ignition timing in accordance with the engine parameters and to correct the standard ignition timing in accordance with correction values retrieved from a table, characterized in that the control unit (15, 151, 152, 153, 154, 155) comprises a first table for storing first correction values for the standard ignition timing for a predetermined first number of ignitions, the correction values being used when the engine speed decreases, and a second table different from said first table for storing second correction values for the standard ignition timing for a predetermined second number of ignitions, the values being used when the engine speed increases. The apparatus according to claim 5, characterized in further comprising means (153, 154) for controlling the frequency of correction of the ignition timing made within a period of time during which the engine speed changes and/or the amount of change of the ignition timing per one correcting operation. The apparatus according to claim 5 or 6, characterized in further comprising a feedback control for the amount of correction of the ignition timing, the feedback control operating in accordance with the change rante of the engine speed.

Inventors: ATAGO TAKESHI, NAGANO MASAMI, ATAGO, TAKESHI, NAGANO, MASAMI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: F02P5
IPC codes: F02P5, F02B1