Method and apparatus for controlling supply of fuel in internal combustion engine

Abstract

 In the control of the supply of a fuel in an internal combustion engine, the quantity of the change of the demanded fuel quantity corresponding to the quantity of air sucked in the engine is computed at every unit time, and every time an increase change of the demanded fuel quantity is detected, the fuel in a quantity corresponding to this increase is additionally supplied into the engine. According to this control, after the start of the fuel supply synchronous with the revolution of the engine, the fuel can be supplied precisely in conformity with the increase change of the demanded fuel quantity.

Description

Background of the Invention

(1) Field of the Invention

[0001] The present invention relates to a method and apparatus for controlling the supply of a fuel in an internal combustion engine. More particularly, the present invention relates to an apparatus for improving acceleration driving performances by carrying out at a high precision correction and control of the quantity of a fuel supplied to an engine at the time of acceleration.

(2) Description of the Related Art

[0002] The following apparatus is known as the apparatus for controlling the supply of a fuel in an internal combustion engine.

[0003] The flow quantity of sucked air or the intake pressure is detected as the quantity of the state participating in the quantity of air sucked in the engine, and the basic fuel supply quantity Tp is computed based on this detected value and the detected value of the revolution speed of the engine. This basic fuel supply quantity Tp is corrected according to various correction coefficients COEF set based on driving state factors such as the engine temperature, an air-fuel ratio feedback correction coefficient LAMBDA set by the air-­fuel ratio determined through the oxygen concentration in the exhaust gas and a correction portion Ts for correcting a change of an effective valve-opening time of the fuel injection valve by the battery voltage as the driving power source, and the final fuel supply quantity Ti is thus computed (Ti ← Tp X COEF X LAMBDA + Ts) and the computed quantity of the fuel is intermittently supplied at a timing synchronous with the revolution of the engine by the fuel injection valve or the like (see, for example, Japanese Unexamined Patent Publication No. 57-8328).

[0004] In this electronic control apparatus for thus computing and setting the fuel supply quantity, at the transient driving, the detection delay in various sensors and the computation delay in the control apparatus are caused, and there is a time difference between the detection of the sucked air flow quantity or the intake pressure and the intake stroke. Accordingly, for example, at the time of acceleration, the fuel supply quantity smaller than the quantity actually demanded by the engine is set and the air-­fuel ratio becomes lean, with the result that such troubles as increase of the amounts of discharged nitrogen oxide NO_x and hydrocarbon HC in the exhaust gas and the acceleration shock or reduction of the response characteristic to acceleration by the response delay of the average effective pressure are caused.

[0005] Under this background, we proposed the system in which the change of the demanded fuel quantity to the target position of the fuel control is estimated based on the variation quantity of the engine load determined from the opening degree of the throttle valve (the open area of the intake system of the engine) and the revolution speed of the engine and also on the time of up to the predetermined crank angle position of the intake stroke, and the quantity of the correction of the fuel supply quantity is set based on the result of this estimation (see Japanese Unexamined Patent Publication No. 1-237333).

[0006] Supposing that the predetermined crank angle position of the intake stroke as the target position of the fuel control is intake BDC and the timing of initiation of the fuel supply synchronous with the revolution of the engine is 360° of the crank angle before intake BDC in each cylinder, in order to correct the ordinary fuel supply quantity, the change of the engine load during 360° revolution of the engine should be estimated. However, it is difficult to precisely estimate the quantity of the change of the engine load over such a long period as the period required for 360° revolution, and hence, an error of the estimated value is produced to reduce the precision of setting of the correction quantity. From the viewpoint of driving performances, this reduction of the setting precision is serious problem at the acceleration for which a high-precision air-fuel ratio control is required.

[0007] Especially, at the initial stage of acceleration where the change of the demanded fuel quantity rises or at the latter stage of acceleration where the change of the demanded fuel quantity reaches the ceiling, the above-mentioned estimation error becomes large, and if the estimation period is prolonged, the estimation error becomes larger. If the injection timing is delayed and brought close to the intake stroke, the estimation error can be decreased, but the properties of the exhaust gas and the engine performances such as the fuel consumption are influenced by the timing of the fuel supply and the best timing of the fuel supply differs according to the engine. Accordingly, in a certain engine, it is necessary to start the fuel supply at a position distant from the intake stroke, and in this case, it is necessary to estimate the change of the engine load over a long period and it is sometimes impossible to maintain a high precision for the estimation and control.

[0008] Furthermore, in the region where the quantity of the fuel supplied by the fuel injection valve is small, the difference of the actual injection quantity from the set injection quantity is generally large, and therefore, especially in case of an engine of a small displacement, by adopting, for example, a method in which a fuel is simultaneously injected and supplied into all of cylinders at every two revolutions of the engine, the quantity of the fuel to be injected and supplied one time from the fuel injection valve is secured so as to obtain a good precision in the supply quantity. Accordingly, also in this case, the period of the estimation of the quantity of the change of the engine load becomes long, and it is impossible to perform the estimation and control at a high precision.

Summary of the Invention

[0009] The present invention is to solve the foregoing problems. It is therefore a primary object of the present invention to provide a method and apparatus for controlling the fuel supply, in which against the increase change of the demanded fuel quantity from the ordinary fuel supply quantity set synchronously with the revolution of the engine, the fuel supply quantity is corrected in real time at a high precision, whereby the air-fuel ratio controllability at the acceleration driving of the engine can be improved.

[0010] Another object of the present invention to provide a fuel supply control method and apparatus in which the additional supply for coping with the increase change of the demanded fuel quantity can be performed at a high precision according to the set additional supply fuel quantity.

[0011] Still another object of the present invention to provide a fuel supply control method and apparatus in which the above-mentioned additional fuel supply is not excessively performed but is carried out assuredly.

[0012] In accordance with one fundamental aspect of the present invention, the foregoing objects can be attained by a method for controlling the supply of a fuel into an internal combustion engine, which comprises computing a fuel supply quantity corresponding to the quantity of air sucked into the engine and carrying out the main fuel supply based on the computed fuel supply quantity intermittently at a timing synchronous with the revolution of the engine, wherein a quantity of an engine state participating in the quantity of air sucked into the engine is detected, the fuel quantity demanded by the engine and the quantity of the change per unit time of the demanded fuel quantity are computed based on said state quantity, and separately from the fuel supply conducted synchronously with the revolution of the engine, the fuel is additionally supplied based on said change quantity at every said unit time, whereby every time the change of the demanded fuel quantity is determined at every unit time, the fuel is additionally supplied in a quantity corresponding to the quantity of said change and the change of the demanded fuel quantity, that cannot be followed up by the main fuel supply synchronous with the revolution of the engine, can be precisely coped with.

[0013] In this method for controlling the supply of a fuel into an internal combustion engine, the quantities of states participating in the variably controlled open area of the intake system of the engine and the revolution speed of the engine, respectively, are detected as the quantity of the state participating in the quantity of air sucked into the engine, the sucked air quantity in the engine is estimated from the detected open area and engine revolution speed and the demanded fuel quantity is computed based on the estimated sucked air quantity, whereby the fuel is additionally supplied based on the change of the demanded fuel quantity computed from the open area and engine revolution speed.

[0014] In the above-mentioned method, there is preferably adopted a structure in which 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 said unit time is effected based on the change quantity per said unit time of the demanded fuel quantity computed by said correction If the phase of the demanded fuel quantity is thus advanced by a predetermined time over the actual engine load, the fuel can be supplied precisely in conformity with the change of the demanded fuel quantity with good response characteristics.

[0015] Furthermore, in the above-mentioned control method, there is preferably adopted a structure in which when the quantity of the fuel to be additionally supplied based on said change quantity at every said unit time is smaller than a predetermined minimum fuel quantity, the additional supply is carried over to the next fuel supply timing, and the quantity of the fuel to be additionally supplied is added to the quantity of the fuel to be supplied at the next timing to avoid the additional supply of the fuel in the quantity smaller than the minimum fuel quantity, the quantity of the carried-over fuel is added to the quantity of the fuel to be supplied at the next timing, and when the added quantity is larger than said minimum fuel quantity, the supply of the fuel is effected.

[0016] Furthermore, in the above-mentioned control method, there can be adopted a structure in which the additional supply at every said unit time is allowed only within a predetermined range of the crank angle, and even when the quantity of the fuel to be additionally supplied is set based on the change of the demanded fuel quantity, if the crank angle is not within the predetermined angle, the additional supply of the fuel corresponding to the change of the demanded fuel quantity is not performed.

[0017] Moreover, there can be adopted a structure in which the quantity of the fuel additionally supplied at every said unit time within the predetermined crank angle range is subtracted from the quantity of the fuel to be supplied by the next main fuel supply synchronous with the engine revolution, whereby the main fuel supply is prevented from being made excessive by the additional fuel supply.

[0018] Still further, there can be adopted a structure in which when the timing of the additional fuel supply at every said unit time is during the main fuel supply synchronous with the engine revolution, the additional fuel supply carried out after termination of the main fuel supply, and even if the main fuel supply is being conducted at the time when the additional fuel supply is desired, the fuel to be additionally supplied is supplied afterward subsequently to the main fuel supply.

[0019] In accordance with another fundamental aspect of the present invention, there is provided an apparatus for controlling the supply of a fuel into an internal combustion engine, which comprises engine driving state-detecting means for detecting the quantity of an engine state participating in the quantity of air sucked in the engine, demanded fuel quantity-computing means for computing a demanded fuel quantity of the engine based on the state quantity detected by the engine driving state-detecting means, change quantity-­computing means for computing the quantity of the change per unit time of the demanded fuel quantity computed by the demanded fuel quantity-computing means, and additional fuel supply-controlling means for additionally supplying the fuel at every said unit time according to the change quantity computed by the change quantity-computing means, separately from the main fuel supply conducted synchronously with the revolution of the engine.

[0020] If the apparatus having the above-mentioned structure is used, the quantity of the change of the demanded fuel quantity of the engine can be determined at every unit time and the fuel is additionally supplied according to the quantity of the change of the demanded fuel quantity per unit time, and therefore, in the case where increase of the fuel quantity is demanded after initiation of the main fuel supply, the increase portion is additionally supplied at every unit time and the demand for increase of the fuel quantity is satisfied.

[0021] In the above-mentioned apparatus, there is preferably adopted a structure in which the engine driving state-­detecting means detects the quantities of states participating in a variably controlled open area of the intake system of the engine and a revolution speed of the engine, respectively, and the demanded fuel quantity-­computing means estimates a quantity of air sucked into the engine from the detected open area and engine revolution speed and computing the demanded fuel quantity speed and computes the demanded fuel quantity based on the estimation.

[0022] Furthermore, in the above-mentioned apparatus, there can be disposed phase advance correction computing means for correcting and computing the demanded fuel quantity computed by said demanded fuel quantity-computing means so as to produce a phase state advanced by a predetermined time over the change of the demanded fuel quantity corresponding substantially to the actual engine load, and causing the change quantity-computing means to compute the change quantity according to the demanded fuel quantity determined by said correction computation.

[0023] If the demanded fuel quantity of the phase advanced over the change of the demanded fuel quantity corresponding substantially to the actual engine load is thus computed, by controlling the additional fuel supply based on the change of said demanded fuel quantity, correction of the fuel supply can be performed with a good response characteristic.

[0024] In the above-mentioned apparatus, there is preferably disposed additional supply carry-over means for carrying over the additional fuel supply to the next timing of the main fuel supply when the quantity of the fuel to be additionally supplied by the additional fuel supply-controlling means is smaller than a predetermined minimum fuel quantity, and adding the quantity of the additional fuel to the quantity of the fuel to be supplied at the next fuel supply timing.

[0025] In a fuel supply device such as a fuel injection valve, if the quantity of the fuel to be supplied is small, there is produced a great difference between the quantity of the actually supplied fuel and the set quantity of the fuel, and it is impossible to control the fuel supply at a high precision. Therefore, when the quantity of the fuel to be additionally supplied is smaller than the above-mentioned minimum fuel quantity, the additional supply is not effected but carried over to the next supply. If the added quantity is larger than the above-mentioned minimum fuel quantity, the fuel supply is practiced.

[0026] Furthermore, in the above-mentioned apparatus, there can be disposed additional supply timing-limiting means for allowing the additional fuel supply-controlling means to perform the additional fuel supply only when the crank angle is within a predetermined range. If the timing of the additional fuel supply is at such a crank angle position that if the supply is effected, the supplied fuel is not sucked but is kept resident, the supplied fuel does not participate in formation of an air-fuel mixture to be burnt at this time, and therefore, this additional supply is inhibited and excessive additional supply is avoided.

[0027] Still further, in the above-mentioned apparatus, there can be disposed main fuel quantity-reducing means for subtracting the quantity of the fuel additionally supplied within the predetermined crank angle range by the additional fuel supply-controlling means from the quantity of the fuel supplied by the next main fuel supply conducted synchronously with the revolution of the engine. In this case, even if the additional supply is carried out to such a degree that the fuel is carried over to the next suction stroke, at the next main fuel supply conducted synchronously with the revolution of the engine, this excessive fuel to be carried over is subtracted and the fuel is supplied in an appropriate quantity.

[0028] Still in addition, in the above-mentioned apparatus, there is preferably disposed means for controlling the additional supply subsequent to the main supply, which exerts the function of performing the additional fuel supply after termination of the main fuel supply when the additional fuel supply timing determined by the additional fuel supply-­controlling means is during the main fuel supply conducted synchronously with the revolution of the engine. In the case where the additional fuel supply timing is during the main fuel supply, the additional fuel supply cannot be performed unless another fuel supply device is disposed, and in this case, the quantity of the fuel actually supplied is smaller than the demanded fuel quantity. Therefore, when the main fuel supply is terminated and the additional fuel supply becomes possible, the additional fuel which has been restrained from being supplied is supplied.

[0029] The present invention will now be described in detail with reference to one embodiment illustrated in the accompanying drawings.

Brief Description of the Drawings

[0030] 

Fig. 1 is a block diagram illustrating the structure of the fuel supply control apparatus of the present invention.

Fig. 2 is a system diagram illustrating one embodiment of the present invention.

Figs. 3 through 6 are flow charts showing the contents of controls in the embodiment shown in Fig. 2.

Fig. 7 is a time chart illustrating the characteristics in the computation of the weighted mean of the demanded fuel quantity in the embodiment shown in Fig. 2.

Figs. 8 and 9 are time charts illustrating the control characteristics in the embodiment shown in Fig. 2.

Fig. 10 is a graph illustrating the change of the error of the injection quantity of a fuel injection valve according to the fuel injection quantity.

Detailed Description of the Preferred Embodiment

[0031] The outline of the apparatus for controlling the supply of a fuel into an internal combustion engine according to the present invention is as shown in Fig. 1, and an embodiment of the method and apparatus for controlling the supply of a fuel into an internal combustion according to the present invention is illustrated in Figs. 2 through 10.

[0032] Referring to Fig. 2 illustrating the system structure of this embodiment, air is sucked into an internal combustion engine through an air cleaner 2, a suction duct 3, a throttle chamber 4 and a suction manifold 5.

[0033] In the throttle chamber 4, a throttle valve 7 co­operating with an accelerator pedal not shown in the drawings is arranged to control the flow quantity Q of sucked air. A throttle sensor 8 comprising a potentiometer for detecting the opening degree TVO of the throttle valve 7 and an idle switch 8A to be turned on at the fully closed position (idle position) of the throttle valve 7 is attached to the throttle valve 7.

[0034] An intake pressure sensor 9 for detecting the intake pressure PB is arranged on the intake manifold 5 located downstream of the throttle valve 7, and an electromagnetic fuel injection valve 10 is disposed for each cylinder.

[0035] The electromagnetic fuel injection valve 10 is intermittently driven and opened by a driving pulse signal put out from a control unit 11 having a microcomputer, described below, installed therein, and a fuel fed under compression from a fuel pump not shown in the drawings and controlled to have a predetermined pressure by a pressure regulator is supplied and injected into the suction manifold 5. Namely, the quantity of the fuel supplied by the fuel injection valve 10 is controlled based on the driving time for opening the fuel injection valve 10.

[0036] Furthermore, a water temperature sensor 12 is arranged to detect the cooling water temperature Tw in a cooling jacket of the engine 1, and an oxygen sensor 14 is arranged to detect the air-fuel ratio of an air-fuel mixture sucked in the engine by detecting the oxygen concentration in the exhaust gas in an exhaust gas passage 13.

[0037] The control unit 11 counts, for a certain time, a unit crank angle signal POS put out from a crank angle sensor 15 synchronously with the revolution of the engine or measures the frequency of a reference crank angle signal REF put out at every predetermined crank position (every 180° in case of a four-cylinder engine; BTDC 120° in the present embodiment) to detect the revolution speed N of the engine.

[0038] Furthermore, a car speed sensor 16 for detecting the car speed and a neutral sensor 17 for detecting the neutral position are arranged in a transmission attached to the engine 1, and signals from these sensors are put into the control unit 11.

[0039] An electromagnetic idle control valve 19 for controlling the idle revolution speed through the quantity of auxiliary air is arranged on the auxiliary air passage 18 bypassing the throttle valve 7.

[0040] The control unit 11 computes the fuel injection quantity Ti (the pulse width of the injection pulse signal) based on detection signals from the above-mentioned various sensors and drives and opens each fuel injection valve 10 at a predetermined timing synchronous with the revolution of the engine based on the set fuel injection Ti to control the ordinary fuel supply according to the timing of the intake stroke of each cylinder, and simultaneously, the control unit 11 controls the additional supply (interruption) of the fuel, separately from the ordinary fuel supply, according to an increase change of the demanded fuel quantity. Furthermore, the control unit 11 performs feedback control of the idle revolution speed to a target idle revolution speed by controlling the opening degree of an idle control valve 19 at the idle driving detected based on signals from the idle switch 8A and neutral sensor 17.

[0041] Various computing processings conducted by the control unit 11 for controlling the fuel supply will now be described with reference to routines shown in flow charts of Figs. 3 through 6.

[0042] In the present embodiment, demanded fuel quantity-­computing means, change quantity-computing means, additional fuel supply-controlling means, phase advance correction computing means, additional supply carry-over means, additional supply timing-limiting means, main fuel quantity-­reducing means and means for controlling the additional supply subsequent to the main fuel supply are arranged to exert their functions as softwares as shown in flow charts of Figs. 3 through 6. In the present embodiment, the throttle sensor 8 for detecting the opening degree TVO of the throttle valve 7 and the crank angle sensor 15 for putting out a detection signal synchronous with the revolution of the engine correspond to the engine driving state-detecting means.

[0043] Incidentally, the internal combustion engine 1 of the present embodiment is a four-cylinder engine which is constructed so that the fuel injection valves 10 arranged for the respective cylinders are independently driven according to the intake strokes of the respective cylinders to effect the supply of the fuel.

[0044] The routine shown in the flow chart of Fig. 3 is practiced at every 10 ms.

[0045] At first, at step 1, the suction pressure PB detected by the suction pressure sensor 9, the engine revolution speed N computed based on the detection signal from the crank angle sensor 15 and the opening degree TVO of the throttle valve detected by the throttle sensor 8 are put into the control unit.

[0046] At step 2, the open area A (mm²) (of the intake system of the engine) of the throttle chamber 4 variably controlled by the throttle valve 7 is retrieved from a map preliminarily set based on the opening degree TVO of the throttle valve put in the control unit at step 1.

[0047] At step 3, the basic volume efficiency QH0̸ (%) of the engine 1 corresponding to the stationary driving is retrieved from a map based on the value obtained by dividing the open area A determined at step 2 by the engine revolution speed N. Namely, the intake air quantity of the engine is estimated from the open area A and the engine revolution speed N.

[0048] At step 4, the weighting load X used for weight-­averaging the basic volume efficiency QH0̸ determined at step 1 for making it substantially in correspondence to the true engine load change at the transient driving of the engine 1 is set according to the engine revolution speed N and the open area A. More specifically, a constant a set according to the engine revolution speed N is added to the value obtained by multiplying a constant b set according to the engine revolution speed N by the open area A to finally set the weighting load X. This weighting load X is the weighting load on the newest basic volume efficiency QH0̸ . Since the time change of the engine load is made quicker than the change of the opening degree of the throttle valve in a higher-­revolution-speed and heavier-load region, the weighting load X is increased in a higher-revolution-speed and heavier-load region.

[0049] At step 5, the basic volume efficiency QH0̸ determined at the step 3 and the volume efficiency QCYL computed at step 5 at the previous practice of the present routine are weight-­averaged by using the above-mentioned weighting load X according to the following equation, and the obtained value is set as the newest volume efficiency QCYL:
QCYL←(1-X)QCYL + X x QH0̸

[0050] If the volume efficiency QCYL is determined by the above-mentioned computation equation, at the stationary driving, the relation of QH0̸ = QCYL is established and the volume efficiency QCYL is kept constant. However, at the transient driving of the engine 1, the change of the volume efficiency QCYL is made slower than the change of the basic volume efficiency QH0̸ according to the driving state of the engine, whereby the volume efficiency QCYL corresponding substantially to the true change of the engine load, which falls behind the changes of the open area A and engine revolution speed N, is set.

[0051] At step 6, the basic fuel injection quantity (the demanded fuel quantity of the engine) ANTp is computed based on the volume efficiency QCYL conformable to the open area A and engine revolution speed N according to the following equation:
ANTp←KCONA X QCYL

[0052] In the above equation, the basic fuel injection quantity ANTp is computed based on the volume efficiency QCYL corresponding substantially to the true change of the engine load at the transient driving of the engine 1, but as shown in Fig. 7, this value is of the phase advanced by scores of ms over the basic fuel injection quantity TpPB set based on the suction pressure PB detected by the suction pressure sensor 9 described hereinafter.

[0053] The above-mentioned basic fuel injection quantity ANTp is set for determining the change of the demanded fuel quantity of the engine 1 at the transient driving of the engine, and the reason why the basic fuel injection quantity ANTp is set as the value of the phase advanced by scores of ms over the basic fuel injection quantity TpPB is that the travel time of the fuel injected from the fuel injection valve 10 to the point of the suction into the cylinder is taken into consideration. Namely, if the change of the demanded fuel quantity is determined based on this basic fuel injection quantity ANTp and the fuel in a quantity corresponding to the change of the demanded fuel quantity is additionally supplied (interruption injection), separately from the ordinary injection, as described hereinafter, since the travel time of the fuel is taken into consideration in advance, the change of the demanded fuel quantity can be coped with while maintaining good response characteristics.

[0054] Since the suction pressure pulsates under the influence of the pulsation of the pressure generated in the intake passage, also the basic fuel injection quantity TpPB pulsates and the change of the basic fuel injection quantity TpPB is, sometimes, not in agreement with the true change of the demanded fuel quantity. However, if the change of the demanded fuel quantity is detected based on the basic fuel injection quantity ANTp determined from the open area A and the engine revolution speed N as described hereinbefore, the detection is not influenced by the pulsation of the pressure and the detection response characteristics are improved, and therefore, the change of the demanded fuel quantity can be grasped at a high precision.

[0055] Then, at step 7, the basic fuel injection quantity ANTpold computed at step 6 at the previous practice of the present routine is subtracted from the basic fuel injection quantity presently computed at step 6 to compute the change quantity ΔANTp of the basic fuel injection quantity ANTp during the practice frequency of the present routine, that is, 10 ms (the change per unit time). This change quantity ΔANTp is a value corresponding to the change of the demanded fuel quantity of the engine 1 during the period of 10 ms, and when the engine 1 is accelerated and the demanded fuel quantity increases, the value ΔANTp is positive value.

[0056] At step 8, the basic fuel injection quantity ANTp presently computed at step 6 is set at the preceding value ANTpold, so that the set value ANTp will be used for computing the change quantity ΔANTp at step 7 at the next practice of the present routine.

[0057] Next, at step 9, the value obtained by doubling the change quantity ΔANTp determined at step 7 is regarded as the change quantity of the demanded fuel injection quantity in one cylinder during the period of recent 10 ms, and the voltage correction portion Ts set based on the battery voltage is added to this change quantity, and the obtained value is set as the interruption injection quantity Y for the additional supply interruption the ordinary fuel injection.

[0058] In the present invention, for convenience, the value obtained by doubling the basic fuel injection quantity Tp computed based on the driving state of the engine is set as the basic fuel supply quantity to one cylinder, and also at the ordinary fuel supply control conducted synchronously with the revolution of the engine, the final fuel injection quantity Ti is computed by doubling the basic fuel injection quantity TpPB determined from the suction pressure PB. Therefore, the change quantity ΔANTp is doubled, as described hereinbefore. Even if the fuel injection valve 10 is driven and controlled based on this value of 2 X ΔANTp, there is practically produced a response delay time in the fuel injection valve and this delay is changed according to the voltage of the battery as the driving source for the fuel injection valve 10. Accordingly, the voltage correction portion Ts set based on the battery voltage is added, so that the fuel in a quantity corresponding to 2 X ΔANTp is actually injected from the fuel injection valve 10.

[0059] At step 10, the change quantity 2 X ΔANTp of the demanded fuel quantity during 10 ms, which is the value obtained by subtracting the voltage correction portion Ts from the interruption quantity Y, is set as the change quantity Z.

[0060] Then, at step 11, the value obtained by adding the integration value ΣQ4, which is the carried-over interruption injection quantity in #4 cylinder, not interruption-injected at the preceding practice but integrated, to the interruption quantity Y (←2 X ΔANTp + Ts) set at step 9, is compared with the minimum injection quantity (minimum fuel quantity) Timin allowing the interruption injection.

[0061] If (Y + ΣQ4) is smaller than Timin, the interruption injection is not carried out but routine goes into step 12, and the integration value ΣQ4 at the preceding practice is added to Z set at step 10, and the obtained value is newly set as the integration value ΣQ4. Accordingly, the integration value ΣQ4 is the interruption injection quantity which is to be additionally injected based on the change quantity ΔANTp in #4 cylinder but is not injected at the present and carried over.

[0062] The minimum injection quantity Timin is defined to indicate the region where if the fuel injection valve 10 is driven and controlled based on the injection quantity smaller than Timin, the dispersion of the fuel actually injected from the fuel injection valve (F/I) 10 during the valve-opening time is large and the injection quantity cannot be controlled at a high precision by the control of the valve-opening time (see Fig. 10).

[0063] Accordingly, when it is judged at step 11 that the sum of the interruption injection quantity Y and the integration value ΣQ4 is smaller than Timin, the interruption injection (additional injection) is not carried out at the present practice but is carried over to the next practice (this carried-over portion corresponds to ΣQ4). At the next practice, the interruption injection quantity Y is added to this carried-over portion, and if the obtained value exceeds the minimum injection quantity Timin, the interruption injection is carried out.

[0064] Namely, if the interruption injection quantity is smaller than the minimum injection quantity Timin, even when the interruption injection is carried out, the control of the fuel supply is not carried out at a high precision, and therefore, the interruption injection at the present practice is carried over to the next practice and when the value obtained by the integration exceeds the minimum injection quantity Timin, the interruption injection is carried out. In the case where the integration value ΣQ4 is not injected but is left to the point of initiation of the ordinary fuel injection in #4 cylinder, the carried-over portion ΣQ4 is added to the quantity of the ordinary fuel supply conducted synchronously with the engine revolution and the fuel in the quantity corresponding to this sum is injected and the integration value ΣQ4 is reset at zero. If the interruption quantity Y set at step 9 exceeds the minimum injection quantity Timin at every practice, the interruption injection is carried out at every 10 ms (see Fig. 9).

[0065] If it is judged at step 11 that the sum of the interruption injection quantity Y and the integration value ΣQ4 is larger that Timin, the routine goes into step 13, and a flag F100d4 for judging the crank angle range allowing the interruption injection in #4 cylinder is judged. As described hereinafter, this flag F100d4 is set at zero in the range of from the point at which the cylinder-discriminating value ncyl is 4 (the point at which the reference angle signal REF is the ignition reference signal of #1 cylinder and the ordinary injection is started in #4 cylinder) to the intake BDC of #4 cylinder (or the predetermined crank angle between intake ATDC 100° to intake BDC), and the flag F100d4 is set at 1 in other range. Within the crank angle range where the flag F100d4 is at zero, the interruption injection is allowed (see Fig. 8).

[0066] The crank angle range where the flag F100d4 is set at zero (the range of from intake BTDC 120° to intake ATDC 100° or intake BDC) indicates the range of from the point of initiation of the ordinary fuel supply in #4 cylinder to the last injection point of the intake of the fuel during the intake stroke for sucking the supplied fuel (intake valve open: INT/V OPEN). Even if the interruption injection is effected at the point outside this crank angle range, the fuel is not sucked in the cylinder during the intake stroke at the present practice but is kept resident upstream of the intake valve till the next intake stroke where the ordinary fuel injection quantity is newly set. In the present embodiment, since the change of the demanded fuel quantity during the period of from the initiation (setting) of the ordinary fuel injection to the intake stroke is coped with, the interruption injection to #4 cylinder effected when the flag F100d4 is set at 1 results in excessive supply in #4 cylinder.

[0067] Accordingly, when it is judged at step 13 that the flag F100d4 is set at zero, the interruption injection of the quantity (2 X ΔANTp + Ts + ΣQ4) determined based on the change quantity ΔANTp is effected, but when it is judged that the flag F100d4 is set at 1, the interruption injection is inhibited, or even if the interruption injection is effected, the injected fuel is not immediately sucked but carried over to the next intake stroke, the integration value Σq4 of the interruption injection quantity to be carried over to the next intake stroke is determined, and at the next ordinary injection in #4 cylinder conducted at every reference angle signal REF, the fuel is injected in a quantity corresponding to the value obtained by subtracting the integration value Σq4 from the ordinary fuel injection quantity Ti.

[0068] Namely, if it is judged at step 13 that the flag F100d4 is at zero, the routine goes into step 15, and a driving pulse having a pulse width corresponding to (2 X ΔANTp + Ts + ΣQ4) is put out to the fuel injection valve 10 arranged in #4 cylinder to effect the interruption injection of the fuel in a quantity corresponding to the change of the demanded fuel quantity to #4 cylinder, separately from the ordinary injection conducted at every reference angle signal REF. Then, at step 16, the integration value ΣQ4 is reset at zero, because the interruption injection inclusive of the fuel corresponding to the integration value ΣQ4 has been effected at step 15.

[0069] Incidentally, in the case where the timing of the interruption injection is during the ordinary fuel injection in #4 cylinder, after termination of this ordinary fuel injection, a interruption driving pulse signal having a pulse width corresponding to (α X ΔANTp + ΣQ4) is emitted.

[0070] On the other hand, when it is judged at step 13 that the flag F100d4 is at 1, even if the interruption injection is effected in #4 cylinder, the injected fuel is not sucked during the recent intake stroke. Therefore, in the case where the interruption injection is allowed, the present interruption injection quantity (2 X ΔANTp + ΣQ4) is added to the integration value Σq4 of the interruption quantity not sucked at the preceding practice to determine the sum of the interruption injection quantity not sucked during the recent intake stroke in #4 cylinder but kept resident upstream of the intake valve till the next intake stroke.

[0071] The integration value Σq4 set here represents the quantity of the fuel not sucked till the next intake stroke in #4 cylinder but is kept resident upstream of the intake valve in #4 cylinder. Accordingly, as described hereinafter, this integration value Σq4 is subtracted from the next ordinary injection quantity in #4 cylinder to make a correction coping with the resident portion, and excessive supply into the cylinder by the portion kept resident upstream of the intake valve by the interruption injection is avoided.

[0072] When the integration value Σq4 is renewed and set at step 14, the routine goes into step 15, and as in the case where it is judged that the flag F100d4 is at zero, an interruption driving pulse signal having a pulse width corresponding to (2 X ΔANTp + Ts + ΣQ4) is emitted to the fuel injection valve 10 of #4 cylinder, and at step 16, the integration valve ΣQ4 is reset at zero.

[0073] When it is judged at step 13 that the flag F100d4 is at 1, even if the interruption injection is effected, the fuel is not immediately sucked in #4 cylinder, and therefore, as indicated by the dot line in Fig. 3, the routine advances from step 13 while skipping steps 14 through 16 and the interruption injection is inhibited. In this case, the fuel interruption-injected is completely sucked in the cylinder during the recent intake stroke and therefore, the above-­mentioned setting of the integration value Σq4 is not necessary.

[0074] The above-mentioned steps 11 through 16 are for the computing processing for controlling the interruption injection. This computing processing is similarly and simultaneously carried out in other #2, #1 and #3 cylinders.

[0075] Namely, in the respective cylinders, interruption injection quantities ΣQ1 to ΣQ4 not interruption-injected but carried over are set, and when the sum of the carried-over portion and the newly computed interruption injection quantity Y is larger than the minimum injection quantity Timin, the interruption injection is caried out. If it is judged by the flags F100d1 through F100d4 that the interruption injection timing is not within the interruption injection-allowing crank angle range in the corresponding cylinder, in order to subtract the interruption-injected portion from the quantity of the ordinary injection conducted synchronously with the next reference angle signal REF, the interruption integration quantities Σq1 to Σq4 are integrated for the respective cylinders. This interruption injection quantity control is effected at steps 17 through 22 in #2 cylinder, at steps 23 through 28 in #1 cylinder and at steps 29 through 34 in #3 cylinder, so that the interruption injection is simultaneously effected in a plurality of cylinders (see Fig. 9).

[0076] Accordingly, in the present embodiment, if the condition of Y + ΣQ1 - Q4 ≧ Timin is satisfied in all of the cylinders, the interruption injection is simultaneously effected in all of the cylinders at every 10 ms, that is, the practicing frequency of this routine. In the case where the demanded fuel quantity increases and changes after the starting of the fuel supply (main fuel supply) synchronous with the revolution of the engine, that is, after the final setting of the ordinary fuel supply quantity, the fuel in a quantity corresponding exactly to the increased demanded quantity can be additionally supplied, and therefore, the air-fuel ratio controllability at the acceleration of the engine is highly improved. Furthermore, the above-mentioned control of the interruption injection does not estimate a long-period change of the demanded fuel quantity but directly computes the quantity of the change of the demanded fuel quantity per unit time (10 ms). Accordingly, the error of the correction and control of the fuel is hardly caused and the step of matching the interruption injection quantity with the demand by the engine, which is indispensable in the case where the interruption injection quantity is set based on the change of the opening degree TVO of the throttle valve or the like, is not necessary at all.

[0077] If the interruption injection is controlled based on the change of the demanded fuel quantity in each cylinder in the above-mentioned manner, at subsequent step 35, the volume efficiency correction coefficient KQCYL used for computing the basic fuel injection quantity TpPB based on the suction pressure PB is set. The volume efficiency KQCYL is obtained by multiplying the basic correction coefficient KBP set based on the suction pressure PB by a minute correction coefficient KFLAT set based on the suction pressure PB and the engine revolution speed N at step 41 of the background job shown in Fig. 4.

[0078] At next step 36, the basic fuel injection quantity TpPB for the ordinary fuel supply based on the suction pressure PB is computed according to the following equation:
TpPB←KCOND X PB X KQCYL X KTA

[0079] In the above equation, KCOND is a constant determined based on the injection characteristics of the fuel injection valve 10, and KTA is an intake air temperature (intake air density) correction coefficient set based on the intake air temperature TA detected by the intake air sensor 6 at step of the background job shown in Fig. 4.

[0080] Then, at step 37, the fuel injection quantity Ti, common to the respective cylinders, of the fuel supplied synchronously with the engine revolution is computed according to the equation:
Ti←2 X TpPB X LAMBDA X COEF + Ts

[0081] In the above equation, LAMBDA is an air-fuel ratio feedback correction coefficient for the feedback control of the air-fuel ratio detected through the oxygen concentration in the exhaust gas detected by the oxygen sensor 14 to the target air-fuel ratio, COEF represents various correction coefficients set according to the driving state, such as the cooling water temperature Tw detected by the water temperature sensor 12, and Ts is the same battery voltage correction portion as used for carrying out the interruption injection based on the change of the demanded fuel quantity during 10 ms.

[0082] The routine shown in the flow chart of Fig. 5 is practiced every time a reference angle signal REF is put out from the crank angle sensor 15.

[0083] In the present embodiment, the reference angle signal REF is emitted at every BTDC 120°. This reference angle signal REF indicates the reference position for the control of the ignition timing for each cylinder, and synchronously with this reference angle signal REF, the ordinary fuel injection is carried out in conformity with the intake stroke in each cylinder. The reference angle signal REF can discriminate the cylinder which is at the ignition reference position. For example, when the reference angle signal REF is at the ignition reference position of #1 cylinder, the fuel injection is started in #4 cylinder, and when the reference angle signal REF is at the ignition reference position of #3 cylinder, the fuel injection is started in cylinder #2 (see Fig. 8).

[0084] At first, at step 51, it is judged whether or not the present reference angle signal REF corresponds to the ignition reference position of #1 cylinder. If it is judged that the signal REF corresponds to the ignition reference position of #1 cylinder, the routine goes into step 52, a driving pulse signal having a pulse width corresponding to (Ti + ΣQ4 - ΣQ4) is emitted to the fuel injection valve 10 of #4 cylinder where the ordinary fuel injection should be started synchronously with the engine revolution.

[0085] ΣQ4 is a value corresponding to the change of the demanded fuel quantity, which is not interruption-injected in #4 cylinder till the emission of the present reference signal REF, and Σq4 is the quantity of the fuel which is interruption-injected into #4 cylinder till the present reference signal REF but is not sucked in the cylinder and is kept resident. Accordingly, the ordinary fuel injection quantity Ti is corrected by addition and subtraction of these values. Furthermore, the fuel injection quantity Ti used at step 52 is a newest value of the fuel injection quantity Ti computed at every 10 ms according to the flow chart of Fig. 3.

[0086] At next step 53, the flag F100d4 for determining whether or not the fuel interruption-injected in #4 cylinder is sucked in the cylinder is set at zero, and it is possible to judge from the recent angle signal REF that the fuel injected in #4 cylinder is in the state sucked in the cylinder during the recent intake stroke.

[0087] Incidentally, the flag F100d4 set at zero is constructed so that the flag is set at 1 at the intake BDV of #4 cylinder according to the flow chart of Fig. 6 described hereinafter, and the flag F100d4 is set at zero during the period of from the ignition reference position of #1 cylinder (the timing of the starting of the ordinary injection in #4 cylinder) to the intake BDC of #4 cylinder.

[0088] At step 54, ΣQ4 and Σq4 used for the correction of the ordinary fuel injection quantity Ti at step 52 are reset at zero, and ΣQ4 and ΣQ4 are newly set before the reference angle signal REF corresponding to the ignition reference position of #1 cylinder is next emitted.

[0089] At step 55, the cylinder discrimination value ncyl is set at 4, and based on the cylinder discrimination value ncyl, the period of from the point of the start of the ordinary injection in #4 cylinder to the point before the start of the ordinary injection in #2 cylinder where the injection is next to the effected is discriminated.

[0090] When it is judged at step 51 that the present reference angle signal REF does not correspond to the ignition reference position of #1 cylinder, the routine goes into step 56 and it is judged whether or not the present reference angle signal REF corresponds to the ignition reference position of #3 cylinder.

[0091] When the present reference angle signal REF corresponds to the ignition reference position of #3 cylinder, as at steps 52 through 55, a driving pulse signal having a pulse width corresponding to (Ti + ΣQ2 + Σq2) is put out to the fuel injection valve 10 of #2 cylinder for the control of the ordinary injection quantity (step 57) and the flag 100d2 is reset at zero (step 58), or the data of ΣQ2 and Σq2 used for the control of the ordinary fuel injection are reset at zero (step 59) and the cylindrical discrimination value ncyl is set at 2 (step 60).

[0092] On the other hand, it is judged at step 56 that the reference angle signal REF does not correspond to the ignition reference position of #3 cylinder, the routine goes into step 61 and it is judged whether or not the reference angle signal REF corresponds to the ignition reference position of #4 cylinder. When it is judged that the reference angle signal REF corresponds to the ignition reference position of #4 cylinder, in the same manner as described above, the ordinary fuel injection to #1 cylinder and the setting of various data concerning #1 cylinder are carried out (steps 62 through 65).

[0093] When it is judged at step 61 that the reference angle signal REF does not correspond to the ignition reference position of #4 cylinder, the present reference angle signal REF should correspond to the ignition reference position of #2 cylinder. Accordingly, the ordinary fuel injection to #3 cylinder and the setting of various data concerning #3 cylinder are carried out at steps 66 through 69.

[0094] The routine shown in the flow chart of Fig. 6 is interruption-practiced at the TDC position of each cylinder. For example, a counter is disposed so that the reference angle signal REF and unit angle signal POS from the crank angle sensor 15 are put into this counter. By counting the reference angle signal REF emitted at BTDC 120° and the unit angle signal POS by this counter, the TDC position is detected, and when an interruption signal is emitted to an external interruption terminal of CPU at the TDC, the interruption routine shown in Fig. 6 is practiced.

[0095] At first, at step 81, it is judged whether or not the cylinder discrimination value ncyl is 2, and when the cylinder discrimination value ncyl is 2, the routine goes into step 82 and the flag F100d4 is set at 1. When the cylinder discrimination value ncyl is 2, as shown in Fig. 8, #2 cylinder is in the range of from intake BTDC 120° to intake BTDC 180° , and TDC at this point is either intake TDC of #2 cylinder or intake BDC of #4 cylinder. Accordingly, at TDC where the cylinder discrimination value ncyl is 2, it is detected that #4 cylinder is at intake BDC, and even if the fuel injection is carried out in #4 cylinder over this point, the fuel is not sucked but is kept resident till the next intake stroke. Therefore, the flag F100d4 is set at 1, so that the time when the fuel injected to #4 cylinder is not sucked but is kept resident is discriminated.

[0096] If it is judged at step 81 that the cylinder discrimination value ncyl is not 2, the routine goes into step 83, and it is judged whether or not the cylinder discrimination value ncyl is 1. If the cylinder discrimination value ncyl is 1, as shown in Fig. 8, present TDC corresponds to intake BDC of #2 cylinder, and therefore, the routine goes into step 84 and flag F100d2 is set at 1.

[0097] When it is judged at step 83 that the cylinder discrimination value ncyl is not 1, the routine goes into step 85 and it is judged whether or not the cylinder discrimination value ncyl is 3. If it is judged that the cylinder discrimination value ncyl is 3, in the same manner as described above, the routine goes into step 86 and the flag F100d1 is set at 1, because present TDC corresponds to intake BDC of #1 cylinder.

[0098] If it is judged at step 85 that the cylinder discrimination value ncyl is not 3, the cylinder discrimination value should be 4, and therefore, the routine goes into step 87 and the flag F100d3 is set at 1.

[0099] Namely, when each cylinder is at intake BDC, the flags F100d1 to F100d4 are set at 1, and by the flags F100d1 to F100d4, it is judged whether or not the corresponding cylinder is in the state where if the fuel injection is conducted, the fuel can be sucked within the nearest intake stroke.

[0100] In the present embodiment, the fuel supply quantity in the main fuel supply control synchronous with the revolution of the engine is computed based on the suction pressure. However, there can be adopted a modification in which an air flow meter for detecting the sucked air flow quantity Q is disposed instead of the suction pressure sensor 9 and the ordinary fuel supply quantity is computed based on the sucked air flow quantity Q detected by this air flow meter.

[0101] In the present embodiment, the fuel is injected individually in the respective cylinders at timings corresponding to the intake strokes of the respective cylinders. However, in the case where fuel injection valves 10 of all of the cylinders are simultaneously driven and controlled, or the cylinders are divided into groups, each consisting of a plurality of cylinders, and fuel injection valves 10 of cylinders of each group are simultaneously driven and controlled, if the interruption injection is carried out in the same manner as in the present embodiment, the above-mentioned effects can be similarly attained. Furthermore, even in the case where the ordinary fuel supply in each cylinder is carried out at a timing corresponding to the intake stroke of the cylinder, the time of the start of the injection is not limited. For example, the time of the start of the injection can be variably controlled so that the injection is terminated at a certain crank position.

Claims

1. A method for controlling the supply of a fuel into an internal combustion engine, which comprises computing a fuel supply quantity corresponding to the quantity of air sucked into the engine and carrying out the main fuel supply based on the computed fuel supply quantity intermittently at a timing synchronous with the revolution of the engine, wherein a quantity of an engine state participating in the quantity of air sucked into the engine is detected, the fuel quantity demanded by the engine and the quantity of the change per unit time of the demanded fuel quantity are computed based on said state quantity, and separately from the fuel supply conducted synchronously with the revolution of the engine, the fuel is additionally supplied based on said change quantity at every said unit time.

2. A method for controlling the supply of a fuel into an internal combustion engine according to claim 1, wherein the quantities of states participating in the variably controlled open area of the intake system of the engine and the revolution speed of the engine, respectively, are detected as the quantity of the state participating in the quantity of air sucked into the engine, the sucked air quantity in the engine is estimated from the detected open area and engine revolution speed and the demanded fuel quantity is computed based on the estimated sucked air quantity.

3. A method for controlling the supply of a fuel into an internal combustion engine according to claim l, wherein 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 said unit time is effected based on the change quantity per said unit time of the demanded fuel quantity computed by said correction.

4. A method for controlling the quantity of a fuel into an internal combustion engine according to claim 1, wherein when the quantity of the fuel to be additionally supplied based on said change quantity at every said unit time is smaller than a predetermined minimum fuel quantity, the additional supply is carried over to the next fuel supply timing, and the quantity of the fuel to be additionally supplied is added to the quantity of the fuel to be supplied at the next timing.

5. A method for controlling the quantity of a fuel into an internal combustion engine according to claim 1, wherein the additional supply at every said unit time is allowed only within a predetermined range of the crank angle.

6. A method for controlling the quantity of a fuel into an internal combustion engine according to claim 1, wherein the quantity of the fuel additionally supplied at every said unit time within the predetermined crank angle range is subtracted from the quantity of the fuel to be supplied by the next main fuel supply synchronous with the engine revolution.

7. A method for controlling the quantity of a fuel into an internal combustion engine according to claim 1, wherein when the timing of the additional fuel supply at every said unit time is during the main fuel supply synchronous with the engine revolution, the additional fuel supply is carried out after termination of the main fuel supply.

8. An apparatus for controlling the supply of a fuel into an internal combustion engine, which comprises engine driving state-detecting means for detecting the quantity of an engine state participating in the quanti ty of air sucked in the engine, demanded fuel quantity-computing means for computing a demanded fuel quantity of the engine based on the state quantity detected by the engine driving state-­detecting means, change quantity-computing means for computing the quantity of the change per unit time of the demanded fuel quantity computed by the demanded fuel quantity-computing means, and additional fuel supply-­controlling means for additionally supplying the fuel at every said unit time according to the change quantity computed by the change quantity-computing means, separately from the main fuel supply conducted synchronously with the revolution of the engine.

9. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, wherein the engine driving state-detecting means detects the quantities of states participating in a variably controlled open area of the intake system of the engine and a revolution speed of the engine, respectively, and the demanded fuel quantity-computing means estimates a quantity of air sucked into the engine from the detected open are and engine revolution speed and computes the demanded fuel quantity based on the estimation.

10. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, which further comprises phase advance correction computing means for correcting and computing the demanded fuel quantity computed by said demanded fuel quantity-computing means so as to produce a phase state advanced by a predetermined time over the change of the demanded fuel quantity corresponding substantially to the actual engine load, and causing the change quantity-computing means to compute the change quantity according to the demanded fuel quantity determined by said correction computation.

11. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, which further comprises additional supply carry-over means for carrying over the additional fuel supply to the next timing of the main fuel supply when the quantity of the fuel to be additionally supplied by the additional fuel supply-­controlling means is smaller than a predetermined minimum fuel quantity, and adding the quantity of the additional fuel to the quantity of the fuel to be supplied at the next fuel supply timing.

12. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, which further comprises additional supply timing-limiting means for allowing the additional fuel supply-controlling means to perform the additional fuel supply only when the crank angle is within a predetermined range.

13. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, which further comprises main fuel quantity-reducing means for subtracting the quantity of the fuel additionally supplied within the predetermined crank angle range by the additional fuel supply-controlling means from the quantity of the fuel supplied by the next main fuel supply conducted synchronously with the revolution of the engine.

14. An apparatus for controlling the supply of a fuel into an internal combustion engine according to claim 8, which further comprises means for controlling the additional supply subsequent to the main supply, which exerts the function of performing the additional fuel supply after termination of the main fuel supply when the additional fuel supply timing determined by the additional fuel supply-­controlling means is during the main fuel supply conducted synchronously with the revolution of the engine.

Drawing