Method and apparatus for control of engine fuel injection

Abstract: A method and an apparatus for control of engine fuel injection are characterized by detecting the state of the acceleration of the engine and also judging whether or not the engine is in a specific acceleration state, by, when the engine is judged to be in a specific state of acceleration, using such a value as a crank angle obtained in advance in order to predict the air mass flow rate of the air flowing into a specific cylinder having undergone a fuel injection, by using the predicted air mass flow rate or the crank angle to determine a proper asynchronous fuel injection quantity for the above-mentioned acceleration state for the specific cylinder, and then by performing an asynchronous injection. Thus, they make it possible to calculate the shortage of fuel occurring with the synchronous injection even at the early stage of acceleration by using various variables so as to determine a proper supplemental fuel supply quantity (asynchronous injection quantity) for achieving a desired air fuel ratio in various drive modes.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a method of controlling engine fuel injection, and is particularly concerned with a method and apparatus for asynchronous injection in an electronic controller of an automobile engine. DESCRIPTION OF THE PRIOR ART An electronic controller of an automobile engine controls the quantity of a gasoline injection in accordance with the air mass which flows into the engine in response to the angle of the accelerator pedal so as to obtain a theoretical air fuel ratio. In other words, it obtains the air mass flow rate of the air flowing into the cylinder, uses an electric circuit such as a microprocessor to obtain a required fuel quantity and then controls the quantity of fuel injection. In the fuel injection control by conventional electronic engine controllers, especially in their fuel injection control during the acceleration of the automobile, to make up for the shortage of fuel occurring with a synchronous injection during acceleration, an asynchronous injection is performed by using a compensation coefficient obtained by table lookup whose parameter is the throttle opening angle variation, as described on pages 116 to 117 of "Electronic Controlled Gasoline Injection," Sankaido, May 5, 1987. According to the technique shown in the above-mentioned text, for every engine model a table must be produced by the trial-and-error finding of table data with throttle opening angle variations being parameters. Therefore, such a technique has the disadvantage that a large number of processes are needed for producing the table. But in the first place, the shortage of fuel to be made up for by an asynchronous injection should be specified as a value equivalent to the difference between the air mass flow rate of the air actually drawn into the engine and the air mass flow rate of the air used for calculating the synchronous injection. For this purpose, it is necessary to directly or indirectly use the time of acceleration and the responding air mass flow rate at the inlet port during the early stage of acceleration. However, conventionally no attention has been paid to the time of acceleration in relation to an induction stroke, and the quantity of asynchronous injection has been calculated in most cases by using only an opening angle variation, with the result that excessive or insufficient asynchronous injections still occur with the shifty time of acceleration. Therefore, prior art attempts have the disadvantage that it is impossible to determine a proper asynchronous injection quantity for achieving a desired air fuel ratio in various drive modes. A conventional fuel injection controller which performs asynchronous fuel injection is disclosed in JP-A-1-313639. This apparatus calculates the asynchronously injected fuel quantity not from the air mass flow rate but from a predicted future suction pipe pressure, when acceleration start is detected. A further fuel injection controlling apparatus is described in EP-A-391 385 constituting prior art under Art. 54(3) EPC. This apparatus calculates the amount of fuel to be injected asynchronously on the basis of a momentary change of the throttle valve angle and engine speed. The change of these values is measured a number of times during one engine revolution and it is judged each time whether to effect asynchronous injection or not. According to said document the demanded fuel quantity is computed based on the estimated sucked air quantity. The demanded fuel quantity is corrected so as to produce a state of a phase advanced by a predetermined time over the change of the demanded fuel quantity corresponding substantially to the actual engine load. and the additional fuel supply at every unit time is effected based on the change quantity per said unit time of the demanded fuel quantity computed by said correction. SUMMARY OF THE INVENTION It is an object of the present invention to provide an engine fuel injection control method and apparatus for determining a proper air fuel ratio in every drive mode. This object is solved by the method of claim 1 and the apparatus of claim 10. Preferred embodiments and implementations of the invention are set forth in the subclaims. According to an implementation of the present invention the quantity of a fuel supply to a cylinder is controlled according to the air mass flowing into the cylinder, the state of the acceleration of the engine is detected and also it is judged whether or not the engine is in a specific acceleration state, and, when the engine is judged to be in a specific state of acceleration, the air mass flow rate of the air flowing into a specific cylinder having undergone a fuel injection is predicted, the predicted air mass flow rate is used for determining a proper asynchronous fuel injection quantity for the above-mentioned acceleration state for the above-mentioned specific cylinder, and then the determined quantity of fuel is injected asynchronously into the above-mentioned specific cylinder. Note that the above-mentioned proper asynchronous fuel injection quantity may be determined according to a crank angle detected in advance. In a preferred embodiment of the above-mentioned method and apparatus, the above-mentioned asynchronous fuel injection quantity is determined so that it can be a supplemental fuel supply quantity necessary for achieving a proper air fuel ratio for the above-mentioned predicted air mass flow rate. Note that the above-mentioned specific cylinder is a cylinder having the latest fuel injection. It is desirable that an asynchronous injection quantity should be determined by fuel supply quantity calculation with regard to the difference between the predicted air mass flow rate of the air flowing into the cylinder having the latest fuel injection and the air mass flow rate used for calculating the fuel supply quantity so that a desired air fuel ratio can be achieved. Concerning the characteristic effects of the present invention, it is possible to judge acceleration to calculate the shortage of fuel occurring to a cylinder with the synchronous injection at the early stage of acceleration by using a predicted air mass flow rate, the time of acceleration and other various variables. Therefore, a proper supplemental fuel supply quantity (asynchronous injection quantity) for achieving a desired air fuel ratio in various drive modes can be determined. Besides, a proper asynchronous fuel injection quantity can be determined without using a table requiring matching, so the processes of developing a fuel injection system can be decreased in number. The foregoing and other objects, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a flowchart of an engine fuel injection control method which embodies the present invention; Fig. 2 is a block diagram of an engine fuel injection control apparatus for carrying out an engine fuel injection control method which embodies the present invention; Fig. 3 is an explanatory representation concerning the necessity of asynchronous injection in an engine; Figs. 4 and 5 are illustrations of the timing of air mass flow rate calculation, fuel injection and an induction stroke in relation to the angle of an engine crank; Fig. 6 is a view of the course of fuel in an intake manifold; and Fig. 7 is a flow diagram of the calculation processes in an engine fuel injection control method which embodies the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figs. 1 and 2 of the drawing, there are shown a flowchart of an engine fuel injection control method which embodies the present invention and a block diagram of a fuel injection control apparatus for carrying out the method of Fig. 1 in a multi-point fuel injection engine respectively. Before description of these embodiments, why asynchronous injection is necessary will be explained to ease the understanding of the embodiment. Fig. 3 is graphs illustrating the timing of fuel injections, the angle of the throttle and the responding air mass flow rate at the inlet port during the acceleration of a vehicle. They show how fuel is injected by the input of the timing signal REF for timing a synchronous injection and causes acceleration immediately after that. Ordinary engines have a fuel injection (synchronous injection) one stroke before their induction stroke. Thus, their fuel injection time is shown to be to the left of the induction stroke in Fig. 3. Qa represents the air mass flow rate used for calculation of synchronous fuel injection quantity. When acceleration starts immediately after a synchronous injection, the air mass flow rate Q anda at inlet port in the induction stroke when fuel will be flowing into the cylinder the mass flow rate of the air actually drawn into the cylinder is much greater than the air mass flow rate used for calculating the quantity of the synchronous injection quantity. Fuel being supplied only with synchronous injection, such an engine lacks the quantity of fuel corresponding to this air mass flow rate error ΔQa (= Q anda - Qa), and the air fuel ratio has a temporary rise, generating a lean spike. As acceleration is more rapid, the air mass flow rate error ΔQa becomes larger along with the lean spike. To compensate for a great shortage of fuel due to rapid acceleration, it is necessary to perform an asynchronous injection before an induction stroke. As shown in Fig. 3, an air mass flow rate error depends on the time of acceleration in relation to that of an induction stroke and the responding air mass flow rate at the inlet port, namely the responding change of the air mass flow rate at the inlet port for a unit of time. Therefore, an asynchronous fuel injection quantity must be determined in compliance with the time of acceleration in relation to an induction stroke and with the air mass flow rate at the inlet port. Otherwise, proper control of fuel injection is impossible. Now, the embodiments of the present invention which are shown in Figs. 1 and 2 will be described. In the apparatus for control of engine fuel injection which is shown in Fig. 2, a control unit 3 is composed of a CPU 4, ROM 5, RAM 6, timer 7, an I/O LSI 8 and a bus for connecting them electrically. The information resulting from the detection by a throttle angle sensor 10, an air flow sensor 9, a water temperature sensor 13, a crank angle sensor 14 and an oxygen sensor 12 is sent to the RAM 6 through the I/O LSI 8 installed in the control unit 3. The I/O LSI 8 issues an injection valve drive signal to an injector 11. The timer 8 sends an interruption request to the CPU 4 at a certain interval. The CPU 4 executes a control program, which is stored in the ROM 5, for performing the processes which will be described in detail below. Note that the reference numeral 1 denotes a cylinder, 2 a crank, 15 an intake manifold, 16 an exhaust manifold, 17 an intake valve, and 18 an exhaust valve. Now, in reference to the flowchart in Fig. 1, the calculation of synchronous and asynchronous injection quantities by the above-mentioned control unit 3 and the process of synchronous injection will be described in detail. These processes are performed in a 10 msc cycle. First, at step 101, the control unit obtains information from the air flow sensor 9, throttle angle sensor 10, crank angle sensor 14 and water temperature sensor 13. The unit stores values which are output from the throttle angle sensor 10 till after 20 msec in order to use the values for the judgment of acceleration at the next step 102. The unit also calculates in a specific manner the air mass flow rate at the inlet port after one stroke or the present air mass flow rate at the inlet port by using information obtained by the measurement by these sensors. The unit also stores values of the air mass flow rate till after a specific length of time in order to use the values for the calculation at step 105. At step 102, acceleration is judged. How this process is performed will be described from now. The state of acceleration can be detected most swiftly by using the angle of the opening of the throttle. Therefore, it is judged that, when the change of the throttle opening angle within a specific length of time exceeds a specific value, the engine goes into the state of acceleration. For instance, it is judged that the engine goes into acceleration when the following equation is satisfied, the current time being i: th(i) - th(i - 2) > k 1 where th(i) is a sample of the throttle opening angle at time i (the sampling period is 10 ms), and k 1 is a positive constant. When the engine is judged to be in the state of acceleration, the control unit 3 performs the processes at steps 104 to 109 for asynchronous injection and the calculation processes at steps 110 to 113 for synchronous injection. When the engine is judged to be not in the state of acceleration, only the calculation processes at steps 110 to 113 for synchronous injection are performed. At step 103, the rate ratio x' for the deposition of asynchronously injected fuel on the intake manifold wall is calculated by using the information obtained by the measurement at step 101. Tne method of calculating the rate ratio x' will be described later in detail. At step 104, it is judged which cylinder has the latest synchronous injection. Step 105 is for predicting and calculating the air mass flow rate Q anda of the air flowing into the cylinder judged at step 104 to have the latest synchronous injection. Step 106 is for calculating an air mass error ΔQa (= Q anda - Qa) by using the calculated air mass flow rate Qa, which was used for calculating the fuel quantity injected into the above-mentioned cylinder having the latest synchronous injection, and by using Q anda calculated at step 105. The unit 3 stores a rate Q anda for each cylinder by using a program wnich will be described later. At step 107, an asynchronous fuel injection quantity ΔG f is calculated by using the above-mentioned air mass error ΔQa and the rate x' for the deposition of asynchronously injected fuel on the intake manifold wall, as described later. At step 108, the above-mentioned asynchronous fuel injection quantity ΔG f is converted into an asynchronous injection pulse width ΔTi by using the following equation (2) in order to perform an asynchronous injection. ΔTi = K · ΔG f + Ts where Ts is an idle injection period. Step 109 is for using the following equation (3) to update the fuel film quantity M f for the cylinder judged to have the latest synchronous injection at step 104: M f ← M f + x' · ΔG f This update equation expresses the increase of the fuel film quantity by x'·ΔG f due to the asynchronous injection. The update of a fuel film quantity by synchronous injection is performed by another program. At the steps following step 109, a synchronous injection quantity is calculated. Step 110 is, as described later, for calculating the rate x of the deposition of injected fuel on the intake manifold wall and the ratio α of the sucking off of a fuel film by a cylinder during an induction stroke. At step 111, it is judged in which cylinder the next synchronous injection is performed. Step 112 is for calculating a synchronous fuel injection quantity G f by using the latest fuel film quantity M f (= M fold ) calculated for the cylinder judged to have the next synchronous injection and by using the information obtained from the measurement at step 101. At step 113, the synchronous injection pulse width Ti for the cylinder judged to have the next synchronous injection at step 111 is calculated by using the following equation (4): Ti = k · G f + Ts The processes performed by the control unit 3 are thus completed, and the unit 3 waits for the next interruption request. Fig. 1b is a flowchart of the update of a fuel film quantity by the program referred to in the description of the above-mentioned step 108. This program is executed immediately after a synchronous injection is performed. Step 114 is for judging in which cylinder the latest synchronous injection is performed. At step 115, the fuel film quantity for a cylinder judged to have the latest synchronous injection is updated by using the following equation (5): M f ← M f + (x · G f - α · M f ) where x, α, G f and M f are latest values. Step 116 is for storing the latest air mass flow rate Qa used for calculating a synchronous fuel injection quantity G f in order to use the information to calculate the air mass error ΔQa at the above-mentioned step 106 shown in Fig. 1a. Now, the above-mentioned steps will be described in detail. To begin with, in reference to Fig. 4, a first method will be described for predicting the air mass flow rate Q anda for the cylinder which has the latest synchronous injection after acceleration is detected at step 103. In this first method, the angle of the crank is used. Fig. 4 is an illustration of the timing of air mass flow rate calculation, fuel injection and an induction stroke in relation to the angle of the crank. The air mass flow rate Q anda is represented by the air mass which flows into the cylinder when the crank is in the middle of an induction stroke. Let the time for calculating the air mass flow rate at inlet port be i - 1, i ... and the cycle of this calculation be Δt and the air mass flow rate at inlet port at the time i, which has been calculated in a specific manner, be Qa(i). If acceleration is detected at the time i, the air mass flow rate Q anda, which is assumed to change linearly with time, is given by the following equation, the number of the revolutions and the crank angle between the position of crank in the time i and the position of the crank in the middle of an induction stroke being N (rpm) and  (deg) respectively: Q a = Qa (i) +  6NΔt (Qa (i) - Qa (i-1)) The use of  for predicting Q anda means that the prediction is performed indirectly by using the time of the acceleration. A second method for predicting the air mass flow rate Q anda is related to a throttle and speed method, namely, one of using the angle of the opening of the throttle and the number N of the revolutions in the below way. Since engines in ordinary vehicles inject fuel one stroke (a crank angle of about 180 degrees) before the induction stroke, the air mass flow rate after one stroke is needed for determining a proper fuel injection quantity at the time of its calculation. In this throttle and speed method, a throttle opening angle is applied to the prediction of the angle after one stroke, and thus using the predicted value for the same calculation of the air mass as specified earlier obtains the air mass flow rate after one stroke. For throttle opening angle prediction, such an equation as the following is used:  th(i) = th(i) + T Δt (th(i) - th(i-1)) where th(i) is a detected throttle opening angle,  andth(i) is a predicted throttle opening angle, Δt is a throttle opening angle detection cycle and T is the time for one stroke (time required for a half revolution of the engine). When the angle of the throttle changes smoothly in a transient condition, the equation (7) works accurately, and so it is possible to predict the air mass flow rate after one stroke. However, when the angle of the throttle changes abruptly from a certain constant condition during rapid acceleration, the equation (7) does not work accurately as far as the early stage of acceleration is concerned, and so it is impossible to predict the air mass flow rate after one stroke. The reason is that with the angle of the throttle in a certain constant condition it is impossible to predict such an abrupt change of the angle. Therefore, an asynchronous fuel injection is necessary also for this throttle and speed method. Now, how the air mass flow rate Q anda is predicted in this throttle and speed method will be explained. Fig. 5 is an illustration of the timing of air mass calculation, fuel injection and an induction stroke in relation to the angle of the crank. i - 2, i - 1 and i each are the time for calculating the air mass flow rate at the inlet port, Δt is the cycle of the calculation of the air mass, N is the number of revolutions,  is the crank angle between the time i and the position of the crank in the middle of an induction stroke and Qa'(j) (j = i - 2, i - 1, i) is the calculated air mass flow rate at the inlet port one stroke after time j. If acceleration is detected at the time i after fuel is injected, Qa'(i) can be considered to be a value after one stroke since the angle of the throttle has already changed. This value represents the air mass flow rate at the inlet port with the crank in the position for it in Fig. 5. On the other hand, no acceleration occurs at the time i - 2, so Qa'(i - 2) represents the value of the air mass flow rate at the inlet port at the time i - 2, namely, when the crank is in the position for it in the illustration. Therefore, the air mass flow rate Q anda with the crank positioned in the middle of an induction stroke is assuming that the air mass flow rate changes linearly with respect to time, given by the following proportional distribution equation using Qa'(i) and Qa'(i - 2): Q a = (180-)Qa'(i-2)+180Qa'(i) 360- where it is assumed that in the middle of an induction stroke the crank is positioned a crank angle of 90 degrees after the top dead center (TDC), that fuel injection time is a crank angle of 90 degrees before the TDC and that fuel injection time REF and the time for calculating Qa (i - 2) used for calulating the fuel injection quantity almost coincide with each other. There may be a third method for predicting the air mass flow rate Q anda. This method is a throttle and speed method and also is, in the system for calculating the air mass flow rate Qa(i) in a specific cycle, to predict the air mass flow rate Qa'(i) after one stroke by using the following equation (9) and then to calculate Q anda by using the equation (8): Qa' (i)=Qa (i) + T Δt {Qa(i) - Qa(i-1)} where Δt is the cycle of the calculation of the air mass flow rate, and T is the time for one stroke. According to the above methods, it is possible to calculate Q anda almost at the same time that acceleration is detected and thus to supply fuel promptly. Now, the method of calculating a fuel shortage G f0 corresponding to the air mass flow rate error ΔQ anda handled at step 107 shown in Fig. 1 will be described. The fuel shortage G f0 is given by the following equation (9), the objective air fuel ratio being (A/F) 0 : G fo = ΔQa (A/F) 0 If all injected fuel flew into the cylinder, the fuel quantity given by the equation (10) could be injected asynchronously. In reality, however, part of injected fuel is deposited on the inlet port, causing fuel transport delay. It is necessary, therefore, to take this delay into account in order to determine a proper fuel injection quantity. A method of compensating for such a fuel transport delay will be described from now. In this method, the following equations are used as models for compensating for fuel transport delay: G fe =(1-x) · G f + α · M fold M fnew =M fold + ( x ·G f - α · M fold ) where G fe is the quantity (g) of the fuel coming into the cylinder, G f is a synchronous fuel injection quantity (g), M fold is the fuel film quantity (g) before fuel injection, M fnew is the fuel film quantity (g) at the end of an induction stroke after fuel injection, x is the rate of the deposition of injected fuel on the intake manifold wall and α is the ratio of the sucking off of a fuel film by the cylinder during an induction stroke. Fig. 6 is a view of a cylinder and the intake manifold of an engine for explaining how the equations (11) and (12) work. The equation (11) expresses the flow into the cylinder 1 of the fuel (1 - x) G f not deposited on the intake manifold wall which are part of the fuel G f injected by an injector 11 and the fuel α·M fold whose port is sucked off by the cylinder. The equation (12) expresses the increase of the quantity of fuel film from M fold by x·G f due to fuel injection and its decrease into M fnew by α·M fold during an induction stroke. When an asynchronous injection is performed, the equations (11) and (12) are written as the following: G fe =(1-x) G f +(1-x' ) Δ G f + α · M fold M fnew =M fOℓd +(x · G f +x' ΔG f -α M fOℓd ) where ΔG f is an asynchronous fuel injection quantity (g), x' is the rate of the deposition of asynchronously injected fuel on the intake manifold wall. Let the air mass flow rate which has been calculated in a specific manner be Qa (g/s), then the air mass Q a (g) flowing into the cylinder is given by: Q a = k · Qa N where k is a constant and N is the number of revolutions. With regard to the air mass Q a flowing into the cylinder, a desired air fuel ratio (A/F) 0 can be achieved by satisfying the following equation: Q a G fe = (A/F) 0 The equations (11) and (16) combined, the following equation is derived for the synchronous fuel injection quantity G f : G f = Q a (A/F) 0 -α · M fOℓd 1-x In this equation, when Q a is a correct air mass flowing into the cylinder, the synchronous fuel injection quantity G f is a proper fuel injection quantity. However, as stated earlier, just before acceleration it is impossible to correctly obtain the air mass flowing into the cylinder, and the resulting shortage of fuel due to G f is the reason why an asynchronous injection is necessary. After acceleration is detected according to the above-mentioned method, the predicted air mass flow rate at the inlet port being Q anda, its air mass a is given by the following equation: A desired air fuel ratio can be achieved by satisfying the following equation (19): From the equations (13) and (19), the following equation for the asynchronous injection quantity ΔG f is obtained: where G f is a synchronous fuel injection quantity calculated by using the equation (17). Here, substituting the equation (17) into the equation (20) simplifies the latter into: Note that determining a fuel injection quantity by using the equations (17) and (20) necessitates the values of x, x', α and M fold . x, x' and α are formulated in advance by a particular experiment. They are after all given by such equations as: x = f 1 (Qa, N) x' = f 2 (Qa, N,  ) α = g (Qa, N , Tw) where f 1 , f 2 and g are specific operators, Qa is an air mass flow rate, N is the number of revolutions, Tw is the temperature of water and  is the crank angle during asynchronous injection. The reason why x' has a crank angle is that asynchronous injection is not so constant in respect of injection timing as synchronous injection with the result that there is a difference between them in fuel deposition condition. The injection quanti ty M f is updated by using the equation (14) so that a latest value can be used for determining a synchronous injection quantity. In a multi-point fuel injection system, since each cylinder has fuel films, fuel is controlled by determining a fuel film quantity for each cylinder. Fig. 7 illustrates the calculation processes for the fuel control by synchronous and asynchronous injection for a cylinder of such a multi-point fuel injection engine. The parenthesized numbers attached to the blocks in the illustration are those of the equations so far used for description. Block 51 is for calculating the deposition rate x and the sucking-off ratio by using the calculated air mass flow rate Qa'(i) at the inlet port after one stroke, the number N of engine revolutions, the water temperature Tw. In block 52, the fuel film quantity M f is updated by using the fuel deposition rates x and x' and the sucking-off ratio α, the synchronous injection quantity G f and the asynchronous injection quantity ΔG. The fuel film quantity M f is updated every time fuel injection is completed. This update is performed every cycle. In block 53, the quantity of an injection is calculated by using the fuel deposition rate x, the sucking-off ratio α, the latest fuel film quantity M f , the number N of revolutions and the air mass flow rate Qa'(i) at the inlet port after one stroke. Block 54 is for calculating the synchronous injection pulse width Ti by using the injection quantity G f . In the equation, k is a constant, and Ts is an idle injection period. The calculation in blocks 51 and 53 is performed at a specific interval only when the cylinder subject to the fuel control system is a cylinder where the next injection is carried out. In response to an REF signal, fuel is injected with the latest synchronous injection pulse width Ti. Blocks 55 to 58 work when the engine changes from the stationary driving status into the acceleration status when though the cylinder subject to the system has undergone a synchronous injection no synchronous injection is yet applied to any other cylinders. In block 55, the air mass flow rate Q anda during an induction stroke of the subject cylinder is calculated by using Qa'(i),  and the number N of revolutions (by the throttle and speed method for detecting the air mass flow rate which has been described as the third method for step 105 shown in Fig. 1). In block 56, the fuel deposition rate x' is calculated by using the calculated air mass flow rate Qa'(i) at the inlet port after one stroke, the number N of engine revolutions, the crank angle  between the time and the position of the crank in the middle of an induction stroke. In block 57, the asynchronous injection pulse width ΔTi is calculated by using the air mass error ΔQa, the number N of revolutions, the fuel deposition rate x' and the asynchronous injection quantity ΔG f . Immediately after the calculation of ΔTi, asynchronous injection is performed. [Effects of the Invention] According to the present invention, asynchronous fuel injection quantity can be determined without using a table whose matching would be required for each engine model, so the processes of developing an engine fuel injector can be decreased in number. Besides, according to the present invention, the shortage of fuel occurring with the synchronous injection at the early stage of acceleration is determined logically in compliance with the time of acceleration so as to provide a proper quantity of asyn chronously injected fuel in various drive modes to make up for the shortage. This allows air fuel ratio control to be more accurate.

Claims: A method of controlling the quantity of fuel supplied to a cylinder of an engine according to an air mass flow rate, comprising the steps of: detecting the start time of an acceleration of the engine, detecting the crank angle of the engine, when said start time has been detected, predicting, in compliance with said starting time and for a predetermined crank angle in an induction stroke, the air mass flow rate of the air flowing into a specific cylinder that has received a fuel injection, determining an asynchronous further fuel injection quantity for said specific cylinder on the basis of the predicted air mass flow rate and then asynchronously injecting the determined quantity of fuel into said specific cylinder. An engine control method according to claim 1, wherein in said step of determining an asynchronous injection quantity, a supplemental fuel supply quantity is determined which is necessary for achieving a proper air fuel ratio for said predicted air mass flow rate. An engine control method according to claim 1, wherein said specific cylinder has received the latest fuel injection. An engine control method according to claim 1, wherein said determination of the asynchronous injection quantity is made according to the value of the difference between the air mass flow rate used for determining the quantity of the latest injection into said specific cylinder and said predicted air mass flow rate. An engine control method according to claim 1, wherein the acceleration start time is detected when the variation of the angle of the throttle of said engine for a unit of time exceeds a specific value. An engine control method according to claim 1, wherein when the acceleration start time has been detected, said detected crank angle is used to predict the air mass flow rate of the air flowing into said specific cylinder. An engine control method according to claim 1, wherein said prediction of the air mass flow rate depends on a value calculated in a specific cycle of the air mass flow rate of the air flowing into the cylinder. An engine control method according to claim 1, wherein said prediction of the air mass flow rate depends on a predicted value of said air mass flow rate of the air which flows into a specific cylinder after a specific length of time. An engine control method according to claim 4, wherein in said step of determining an asynchronous fuel injection quantity, the fuel supply quantity is determined so that the ratio of said value of air mass flow rate difference to the sum of the quantity of injected fuel flowing directly into said specific cylinder and that of fuel deposited on the intake manifold wall and then sucked off by the cylinder is a desired air fuel ratio. An apparatus for controlling the quantity of fuel supplied to a cylinder (1) of an engine according to an air mass flow rate, comprising: means (3, 10) for detecting the start time of an acceleration of the engine, means (14) for detecting a crank angle of the engine, means (3) for predicting, when the start time has been detected, the air mass flow rate of the air flowing into a specific cylinder (1) that has received a fuel injection, said prediction being made for a predetermined crank angle in an induction stroke and in compliance with said start time, means (3) for determining a proper asynchronous further fuel injection quantity for said specific cylinder (1) on the basis of the predicted air mass flow rate, and means (3, 11) for asynchronously injecting the determined quantity of fuel into said specific cylinder (1).

Inventors: ASANO SEIJI, SEKOZAWA TERUJI, SHIOYA MAKOTO, TAKAHASHI SHINSUKE, ASANO, SEIJI, SEKOZAWA, TERUJI, SHIOYA, MAKOTO, TAKAHASHI, SHINSUKE
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1991
Main classification: F02D41
IPC codes: F02D45, F02D41