METHOD OF AND APPARATUS FOR FUEL CONTROL

Abstract: An amount of fuel fed to an engine and determined by the rpm of the engine (2) and a suction air flow rate is increased by a predetermined amount of fuel upon detection of acceleration. When the engine is suddenly accelerated from a low-speed operational region to enter a power zone, the above-mentioned predetermined amount of fuel is corrected based on the rpm of the engine (2) and the amount of change in the throttle valve (4) opening degree.

Description: Background of the Invention This invention relates to a method of and apparatus for fuel control of an automobile internal combustion engine and, more particularly, to a method of and apparatus for fuel control, which are capable of supplying an engine with fuel of a suitable amount when an operational condition of the engine has been changed from a low-speed regime to a sudden acceleration such that a throttle valve is fully opened. In general, a flow rate of air flowing into an engine varies in proportion to the opening degree of a throttle valve. However, when the throttle valve in a fully-closed state is operated to fully open, the air flow does not respond since the air suction passage has a length from the engine to the throttle valve and an air flow rate sensor is provided on the upstream side of the throttle valve. When the throttle valve is moved in an opening direction thereof, the engine is accelerated, and the A/F (air-fuel) ratio must be reduced. However, due to the above arrangement, the air flow passing at the air flow rate sensor has not reached to an air flow rate corresponding to the throttle opening as yet. Therefore, when a flow rate of sucked air is detected by the air flow rate sensor, an optimum fuel supply amount is calculated based on this flow rate and the fuel is ejected by an injector. Therefore, the A/F (air-fuel) ratio increases (fuel is lean), and the engine is not sufficiently accelerated. In order to eliminate this inconvenience, a method of correcting the control delay has been employed, in which the fuel feed rate is determined by the air flow rate sensor in accordance with the degree of opening of the throttle valve. In the conventional acceleration correcting system using a throttle sensor disclosed in JP-A- 185949/1983, the so-called fuel increment correction for acceleration is carried out, in which, when the amount variation per predetermined period of time, i.e. differentiation amount, of an output from the throttle sensor is detected and the amount of variation of the throttle sensor output exceeds a predetermined level, the fuel feed rate which is computed based on the air suction rate detected by the air flow rate sensor is multiplied by a certain coefficient (for example, 1.1) to increase the fuel feed rate. However, the conventional acceleration correction system has the following drawbacks. Namely, when the engine is suddenly accelerated to such an extent that the throttle valve is fully opened while the engine is in a low-speed operation, for example, at 800-1000rpm, the air suction rate increases in accordance with the increase in the degree of opening of the throttle valve but the fuel feed rate does not sufficiently increase in spite of increase of fuel for the acceleration because the fuel is deposited on the inner surface of the manifold. Consequently, desired acceleration characteristics cannot be obtained. If the fuel increase for acceleration is increased on every occasion when the engine is accelerated so as to eliminate these inconveniences, the mixing ratio of the fuel in an operational region other than the fuel injection rate increasing operational region, a so-called power zone increases, so that emissions in the exhaust gas become worse. Summary of the Invention An object of the present invention is to provide a fuel control method and apparatus capable of improving the operational characteristics of the engine when the engine is suddenly accelerated from a low-speed operational region. According to the present invention, in a fully-opened low-speed operational region, fuel is injected more than a regular increment of fuel for acceleration by an amount of fuel deposited on an inner wall of the suction passage, in particular, of the manifold thereby to improve operational characteristics when the engine is suddenly accelerated from the low-speed operational region. Namely, the present invention provides a fuel control method and apparatus, wherein an amount of fuel fed to the engine and determined by the number of revolutions of the engine and a suction air flow rate is increased by a predetermined amount of fuel upon detection of acceleration, and which are characterized in that when a load has exceeded a predetermined level while the engine runs at a rpm lower than the predetermined value, the above-mentioned predetermined amount of fuel is corrected based on the rpm of the engine and a quantity of change in load. Brief Description of the Drawings: Fig. 1 is a schematic view of a fuel injection system to which the present invention is applied; Fig. 2 is a characteristic diagram showing the correction starting conditions; Fig. 3(A) to 3(C) characteristic diagrams showing fuel feed rate correction factors; Fig. 4 is a flow chart of a control operation for determining a power zone fuel-increasing correction coefficient K mr ; and Fig. 5 is a flow chart of a control operation for determining a fuel injection pulse width Ti. Detailed Description of the Invention Fig. 1 shows a fuel injection system of an internal combustion engine for automobiles to which the invention is applied. In Fig. 1, the engine 2 communicates with an air cleaner 1 by an intake passage 3 to suck therein air from the air cleaner 1. The intake passage 3 has a portion formed in manifold through which air is supplied to respective engine cylinders (not shown) according to suction stroke thereof. A throttle valve 4 is provided in the intake passage 3 in which a fuel injector 5 is disposed on the upstream side of the throttle valve 4. In this construction, the throttle valve 4 is actuated by an accelerator pedal (not shown) to open and close. As the throttle valve 4 is opened, the engine 2 sucks air through the intake passage 3 according to suction stroke of the respective cylinders. The flow rate of the air sucked into the engine is measured with an air flow rate sensor 7. A value determined by this air flow rate sensor 7 is inputted into a control unit 10. In this control unit 10, pulses outputted from a crank angle sensor 9 are counted to determine the rpm N of the engine 2, a fed rate of the fuel is calculated based on the air flow rate and the rpm and output pulses corresponding to this feed rate are outputted to the injector 5. The fuel is then ejected from the injector 5 at a rate corresponding to the number of the pulses supplied thereto. Let Qa equal a suction rate of the air, and N rpm of the engine. A basic width Tp of a pulse supplied to the injector 5 can then be expressed by the following equation: Tp = k × Qa/N ............... (1) wherein k is a constant. On the other hand, outputs, which represent the degree of opening of the throttle valve 4, from a throttle sensor 8 are inputted to the control unit 10 every tl msec (for example, 10 msec) to examine an amount of change in the throttle opening at an interval of t msec. Let ϑx equal the latest degree of opening of the throttle valve, and ϑx-1 the degree opening of the throttle valve at an instant t₁ msec before. When ϑx - ϑ x-1 ≧Δϑ₃, the condition of the engine is regarded as the accelerated condition, and an acceleration correction coefficient Kd is set. This coefficient Kd serves to correct injection pulse width during the acceleration of the automobile according to the following equation; Ti = Tp × (1 + Kmr + Kd) ............... (2) wherein Ti is the injection pulse width; Tp the basic pulse width obtained by the equation (1); and Kmr a fully opening fuel feed rate increasing correction coefficient which is a fuel increment coefficient for increasing fuel more than a magnitude determined depending upon the suction rate of air Q a and the rpm N of the engine when the engine is in conditions such that the throttle valve is fully opened in normal operational conditions other than acceleration, for example. In operational conditions of the engine, Given if fuel corrected according to the acceleration correction coefficient Kd is injected, a power zone depending on the rpm N of the engine and a load, as outside the area enclosed by a solid line A of Fig. 2 exists. This power zone is a zone in which a sufficient engine power is not generated unless a fuel/air mixing ratio is set higher (fuel rich) than on a regular occasion. In such a case, fuel is increased depending on the fully opening full feed rate coefficient or a power zone fuel feed rate increasing correction coefficient K mr . When the automobile in a regular travelling condition enters this power zone, the fuel runs short if it is fed at a regular rate. Especially, when an automobile running in an operational region of less than 2000 rpm is suddenly accelerated, with the throttle valve fully opened, to enter the power zone which is shown by hatching in Fig. 2, according to a conventional fuel control apparatus, the acceleration injection is simply carried out, i.e., a fuel increment for the acceleration is injected in addition to a fuel amount necessary for regular speed running. Namely, the fuel is supplied according to the equation (2).However, some of the fuel is increment for the acceleration is deposited on the inner surface of the intake manifold, and does not serve to generate substantial power of the engine. The fuel deposition amount increases as the engine load increases, and the fuel deposition amount remarkably increases in a low speed fully-opened operational region. In the embodiment of the present invention, the fuel is controlled so as to increase further fuel injection rate on the basis of correction factors shown in Fig. 3. As shown in Fig. 3(A), one of them is a fuel increment correction coefficient K₁ which varies depending upon the rpm N of the engine, and, when the rpm N of the engine is large, the fuel increment correction coefficient K1 may be small because a fuel deposition amount on the manifold is small when the engine runs at a large rpm. Another factor is a fuel increment correction coefficient K₂ the magnitude of which varies (refer to Fig. 3(B)) depending upon a variation of a load, for example, a variation of the degree of opening of the throttle valve. The suction vacuum may be used as a variation of the load. The time T₁ for which the correction pulses are applied differs with this correction coefficient. This correction pulse application time T₁ has characteristics such as shown in Fig. 3(C), which changes with respect to the rpm N of the engine. This correction pulse application time T₁ is a period of time for increasing the feed rate of the fuel until the fuel deposited on the inner surface of the manifold has entered the combustion chamber. When the operational conditions for the engine enter the power zone after the starting of the acceleration has been ascertained, the product K ac (=K1 × K2) of the correction coefficients K1, K2 is added to the power zone fuel feed rate increasing correction coefficient Kmr. Namely, in such a case, fuel is injected according to the following equation: T i = T p × (1 + K mr + K d + K ac ) ............... (3) K mr + K ac can be given as follows: K mr + K ac = K mr′ = K mr (1 + K ac′ ) wherein K ac′ = K ac /K mr . Namely, during the time T₁ fuel is corrected by Kmr′ = Kmr × (1 + Kac′). The time T₁ starts to be measured at an instant at which the operation of the engine enters the power zone during the acceleration thereof. K mr is obtained through experiments. For example the engine under the conditions of a certain load and a certain rpm is operated so that the engine will be in an optimum operational condition. In this case, K mr is calculated based on the fuel injection according to the equation (2). Such experiments are conducted all over the operational regions and the K mr obtained is stored as a map in the control unit in advance. the map is as shown in Fig. 2 (in which data is not plotted), K mr is easily read out by indexing the rpm and the load (or throttle valve opening degree ϑ). K₁, K₂ and T₁ also are obtained through experiments and stored as maps as shown in Fig. 3. (K ac also maybe obtained through experiments). Fig. 4 and 5 show the flow charts of control operations which are carried out in the control unit 10. Referring to Fig. 4, the degree of opening ϑx of the throttle valve 4, the rpm N of the engine 2 and an air suction rate Qa are read in a step 101, and a difference Δϑ₂ between this degree of opening ϑx and the preceding read value ϑ x-1 of the degree of opening of the throttle valve 4 is calculated in a step 102, the power zone fuel feed rate increasing correction coefficient Kmr being calculated or read out in a step 103 on the basis of the rpm N of the engine and air suction rate Qa (or the degree of opening ϑ of the throttle valve 4). In a step 104, a comparison is made to ascertain that Kmr=0. When Kmr=0, the engine is not in the power zone as shown in Fig. 2 and a coefficient Kac is set to zero in a step 115. When Kmr≠0, a comparison is made in a step 105 to ascertain that a counted value t is zero. When t=0, a comparison is made in a step 106 to ascertain that Δϑ₂ is larger than a predetermined value Δϑ₁. When Δϑ₂ is smaller than Δϑ₁, Kac is set to zero in a step 115. When Δϑ₂ is larger than Δϑ₁, the correction pulse application time T₁ is read out in a step 107 with reference to the map shown in Fig. 3 (C), and a comparison is made in a step 108 to ascertain that the counted value t is smaller than the value of the correction pulse application time T₁. When the counted value t is larger than the value of T₁, the counted value t is set to zero in a step 114, and Kac to zero in a step 115. When the counted value t is smaller than the value of the correction pulse application time T₁, the correction coefficient K₁, K₂ are determined in a step 109 with reference to the maps shown in Figs. 3A and 3B, and Kac is calculated in a step 110 in accordance with the equation Kac=K₁×K₂, the counted value t being increased by t in a step 111, ϑ x being set equal to ϑ x-1 in a step 112 to calculate Δϑ₂ for the subsequent routine an make preparations therefor, the power zone fuel feed rate increasing coefficient being corrected in a step 113 in accordance with the equation Kmr=Kmr × (1 + Kac). When the counted value t is not zero in the step 105, T₁ is read from the map in the step 107. Fig. 5 shows a flow of a control operation for determining the fuel injection pulse width T₁. The number of revolutions per minute N of the engine, air suction rate Qa, degree of opening ϑx of the throttle valve 4 and Kmr′ determined in the flow of the control operation of Fig. 4 are read in a step 201, and a comparison is made in a step 202 to ascertain that a difference between the actual degree of opening ϑ x and the preceding degree of opening ϑ x-1 is larger than a predetermined value Δϑ₃. When this difference is not more than Δϑ₃, the acceleration correction coefficient Kd is set to zero in a step 203, and the injection pulse width Ti is determined in a step 204 in accordance with the equation Ti = K (1 + Kmr′ + Kd) to set the injector so that the fuel is injected at a predetermined crank angle, ϑ x being set equal to ϑ x-1 in a step 205 to make preparations for the subsequent computation. When the above-mentioned difference is larger than Δϑ₃, Kd is set to 0.1, for example, in a step 206, and Ti is determined in the step 204, ϑ x being set equal to ϑ x-1 . According to the present invention described above, the operational characteristics of the engine at the time of sudden acceleration thereof from a low-speed operational region can be improved.

Claims: 1. A method of fuel control which includes a step of fuel increment for acceleration, wherein a fuel feed rate which is determined depending upon the number of revolutions per unit time of the engine (2) and an air suction rate is increased by a predetermined degree when acceleration is detected, characterized in that when a load of the engine (2) has exceeded a predetermined level while an automobile travels with the number of revolutions per unit time of the engine (2) not more than a predetermined level, said predetermined degree of increase in the fuel feed rate is corrected on the basis of the number of revolutions per unit time of the engine (2) in practical operation and a quantity of variation of the load. 2. The method of fuel control according to claim 1, wherein whether or not the load on the engine (2) has exceeded a predetermined level is detected through detection of a predetermined quantity in variation of the through valve (4) opening degree. 3. The method of fuel control according to claim 1, wherein said predetermined degree of increase in the fuel feed rate is corrected when an operational condition of the engine (2) is changed from a low-speed operational condition to a suddenly-accelerated condition such as a throttle valve (4) is fully opened. 4. The method of fuel control according to claim 3, wherein said predetermined degree of increase in fuel feed rate is corrected during a period of time from a time of deposition of fuel on an inner surface of the manifold until the time that the fuel deposited on the inner surface has entered the combustion chambers of the engine. 5. A fuel injection system comprising an intake passage (3) including a manifold portion, and communicating with on air cleaner (1) and an internal combustion engine (2) for an automobile, a throttle valve (4) provided to control a flow rate of air sucked into the engine (2) through the intake passage (3), an air flow rate sensor (7) adapted to detect a flow rate of air passing through said intake passage (3), a sensor(9) provided to detect the number of revolution per unit time of the engine (2), a throttle sensor provided to detect an opening degree of said throttle (4), and fuel control apparatus (10) adapted to increase by a predetermined degree when the acceleration is detected a fuel feed rate which is determined depending upon the number of revolutions per unit time of the engine (2) and an air suction rate, said fuel control apparatus (10) characterized in that, when a load has exceeded a predetermined level while a vehicle travels with the number of revolutions per unit time of the engine (2) not more than a predetermined level, said predetermined degree of increase in the fuel feed rate is corrected on the basis of the number of revolutions per unit time of the engine (2) in practical operation and a quantity of variation of the load.

Inventors: HATANAKA, KEIJI, MIYAKE, JUNJI, MORITA, KIYOMI, SAKUMA, KIYOTOSHI
Applicants: HITACHI, LTD.
Application year: 1987
Main classification: F02D41
IPC codes: F02D41