CONTROL METHOD FOR A FUEL INJECTION ENGINE

Abstract: The fuel injection quantity required for maintaining the air-fuel ratio of the mixture supplied to each cylinder of an engine (10) at a desired value is determined by calculating from sensor data a deposition rate X at which injected fuel deposits and forms film mass on an intake manifold wall (21) of the engine and a vaporization rate 1/τ at which the film mass vaporizes from the manifold wall, calculating a current film mass quantity M f from the calculated X and 1/τ and the fuel quantity by the preceding injection, calculating a de­ sired fuel quantity Q a /(A/F) to be supplied to the cylinder from an intake air flow Q a and a desired air-fuel ratio A/F and determining a current fuel injection quantity G f from the calculation results in accordance with the following equa­ tion Also, an accurate film mass quantity estimation is ac­ complished by subtracting a calculated value of a carry-over fuel quantity to be delivered to the cylinder from the film mass quantity estimated during the preceding period and adding a calculated value of a wall deposition fuel quantity per period obtained on the basis of an actual fuel injection quantity per stroke of the engine to the remaining film mass quantity thereby estimating a current film mass quantity.

Description: CONTROL METHOD FOR A FUEL INJECTION ENGINE BACKGROUND OF THE INVENTION The present invention relates to a control method for fuel injection engines of the type used in vehicles such as automobiles and more particularly to a fuel injection control method so designed that the film mass deposited on the wall of the intake manifold is estimated and the desired fuel injection quantity is determined on the basis of the estimated film mass. The fuel injected from the fuel injection valve is partly deposited on the intake manifold wall or the fuel deposited as the film mass is vaporized and fed into each cylinder thus failing to wholly supply the injected fuel into the cylinder and in particular the quantity of fuel supplied to the engine deviates considerably from the fuel quantity required from moment during the engine acceleration or deceleration. Conventional techniques heretofore proposed for solving this problem include methods in which the quantity of deposited fuel is estimated and the desired fuel injection quantity is determined on the basis of the estimated deposited fuel (e.g., a fuel injection quantity control method for fuel injection engines disclosed in Japanese Patent Publication No. 58-8238 by Toyota Jidosha Co., Ltd.). In this method, a basic fuel injection pulse width to injector is determined in accordance with the manifold pressure and the engine speed and the quantity of film mass in the intake manifold is estimated on the assumption that the fuel is injected for the duration of the pulse width. However, the actual quantity of fuel injected into the intake manifold is the quantity of fuel injected during the time that the injection valve or injector is opened for the duration of an actual fuel injection pulse width calculated in accordance with the fuel quantity carried over to the engine cylinder, the deposited fuel quantity, a feedback correction factor, etc., as well as the basic fuel injection pulse width. As a result, it is impossible to correctly estimate the actual quantity of film mass unless the method of estimating the quantity of film mass deposited in the intake manifold is such that the actually injected fuel quantity is fed back and a part of the injected fuel quantity is deposited on the intake manifold wall. For these reasons, the conventional estimating method cannot accurately estimate the quantity of film mass and therefore there is a disadvantage that the quantity of fuel supplied to the engine deviates from the required fuel quantity at the moment despite the fact that the fuel injection quantity also takes the quantity of film mass into consideration. Also included among the conventional fuel injection quantity control methods of controlling the fuel injection quantity by estimating the quantity of film mass are methods in which the desired fuel injection quantity is determined by subtracting the quantity delivered to the cylinder or the carry-over quantity from the quantity of film mass and adding the deposited quantity on the manifold wall to the basic fuel injection quantity (e.g., Japanese Patent Publication No. 58-8238). In this case, of the quantity of fuel injected the quantity of fuel deposition on the manifold wall is of such a nature that it can be accurately determined only after the actual fuel injection quantity has been determined. While this conventional method determines the deposition quantity of fuel supposed to deposit on the manifold wall on the basis of a basic fuel injection pulse width, there is a disadvantage that the fuel deposited on the intake manifold wall does not represent a part of the actually injected fuel quantity and therefore it is impossible to accurately determine the quantity of film mass (the quantity of fuel deposition). SUMMARY OF THE INVENTION It is a first object of the present invention to provide a control method for a fuel injection engine which controls the quantity of fuel injected in such a manner that the air-fuel ratio of the mixture supplied to each cylinder attains a desired value when the quantity of film mass deposited on the intake manifold wall, the deposition rate or the rate of the film mass deposited on the manifold wall to the injected fuel and the vaporization rate or the rate of vaporization of the film mass from the manifold wall have been calculated from various sensor data. It is a second object of the invention to provide a method of accurately estimating the quantity of film mass deposited on the intake manifold wall of an engine so as to control the quantity of fuel injected such that the quantity of fuel supplied to the engine always coincides with the required fuel quantity. To accomplish the first object, the quantity of injected fuel entering the cylinder of an engine without depositing on the intake manifold wall is added to the quantity of fuel entering the cylinder as a result of the vaporization of the deposited film mass and this fuel quantity is injected as the actual fuel supply to the cylinder to attain the desired air-fuel ratio in accordance with the mass of air flow to the engine. Also, to accomplish the second object, the calculated value of a carry-over fuel quantity delivered to the engine cylinder during the current cycle is subtracted from the intake manifold wall film mass fuel quantity estimated during the preceding cycle and then the value of an intake manifold wall fuel deposition per cycle calculated on the basis of the actual injection quantity per stroke of the engine injected at the latest moment during the preceding cycle is added to the remaining film mass fuel quantity. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a schematic diagram showing the construction of a fuel injection control apparatus to which the present invention is applied. Fig. 1B is a flow chart showing the fuel injection control procedure of the computer 1. Fig. 2 is a diagram showing the behavior of the inducted air and fuel in the intake manifold. Fig. 3 is a block diagram of the fuel injection control system. Fig. 4 is a flow chart of the ordinary computing processing and interrupt processing. Figs. 5A to 5C are time charts illustrating the time relationship between the strokes and the cycle periods. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control method for a fuel injection engine according to the invention will now be described with reference to Figs. 1A to 2. Fig. 1A illustrates a schematic diagram of a fuel injection control apparatus. In the Figure, the mass of air flow in the intake manifold of an engine is detected by a hot-wire air flow meter 2 and applied to a computer 1. The computer 1 receives the throttle position from a throttle position sensor 3, the intake manifold pressure from a manifold pressure sensor 4, the cooling water temperature from a water temperature sensor 5, the engine speed from a crank angle sensor 6 and the binary airfuel ratio signal from an O2 sensor 7. The computer 1 directs the desired fuel injection quantity to an injector 8. As shown in Fig. 1B, at a step 1, the computer 1 calculates the rate of deposition of the fuel injection quantity on the intake manifold wall and the rate of vaporization of the film mass deposited on the intake manifold wall from the following equations (1) and (2), respectively, according to the inputted data. If the deposition rate is represented by X and the vaporization rate by 1/T, the deposition rate X is simply given for example as a function of the throttle position ath as follows X = 0.3 + 0.7 6th (1) 90 On the other hand, the vaporization rate l/T is given as a function of the water temperature Tw as follows EMI6.1 Here, it is assumed so that l/T = 0.026 when Tw S 230C. Then, at a step 102, in accordance with the resulting deposition rate X and vaporization rate 1/T, the current film mass quantity is calculated from the film mass quantity obtained during the preceding cycle and the actually injected fuel quantity as follows Mf + (1 - T AT)Mf + XATGf.T (3) where AT is the computing cycle period, Mf is the film mass quantity, Gf is the fuel injection quantity and GfT is the actually injected fuel quantity in terms of the fuel quantity per unit time. Then, at a step 103, the fuel injection quantity per unit time is determined in accordance with the deposition rate and the film mass quantity in the following manner. The fuel injection quantity of the engine must correspond to the intake air flow and therefore the desired value of the fuel quantity to be supplied to each cylinder is given as follows. Qa (4) Gfe* = (A/F) (4) where a is the intake air flow, (A/F) is the desired air-fuel ratio and Gfe* is the desired value of the quantity of fuel injected into the engine cylinder. Fig. 2 shows the behavior within the intake manifold of the fuel quantity entering the engine cylinder. As shown in the Figure, if Gf represents the injected fuel quantity, XeGf represents the quantity of the fuel deposited on an intake manifold wall 21 and (1 - X)Gf represents the quantity of the fuel supplied to the cylinder without deposition. Also, Mf/T represents the quantity of fuel supplied to the cylinder by the vaporization of the previously deposited fuel quantity (film mass quantity) on the intake manifold wall 21. As a result, if the quantity of fuel supplied to the cylinders is repreaented by Gfer then the following equation holds Gfe = (1 - X) Gf + 1 Mf (5) # If the value of Gfe is equal to the fuel quantity Gfe* to be supplied to the cylinder, the desired air-fuel ratio will be attained. Thus, assuming that the equations (4) and (5) are equal, Qa (A/F) = (1 - X) Gf + # Mf (6) Then, it is only necessary to determine the fuel injection quantity Gf such that the above equation holds. Thus, the following equation holds EMI8.1 The equation (7) is obtained as follows. The fuel quantity Qa/(A/F) to be supplied to the cylinder to attain the desired air-fuel ratio is obtained in accordance with the intake air flow Q and the fuel quantity Mf to be a carried over to the cylinder is obtained in accordance with the vaporization rate l/T and the film mass quantity Mf. The fuel quantity Mf is subtracted from the fuel quantity Q (A/F) and the difference is divided by the non-deposition rate (1 - X) of the injection fuel to be supplied to the cylinder without deposition thereby determining the desired fuel quantity per unit time. Since the value of Gf obtained at the step 103 is the fuel injection quantity per unit time, it is then converted to a fuel injection pulse width per stroke of the engine at a step 104, as follows Gf Ti = ki N T + T (8) S where N is the engine speed, k. is a coefficient determined by the characteristics of the injector, T is the correction factor fed back by the O2 sensor signal and T5 is a dead fuel injection time. The fuel injection pulse width per stroke T. is renewed at intervals of the computing cycle and therefore the actual fuel injection takes place for the duration of the fuel injection pulse width T. existing at the time of arrival of an interrupt signal generated for every stroke. Therefore, as the fuel injection quantity data required for the computer to calculate the quantity of film mass during the next cycle, the actual fuel injection pulse width in terms of the following quantity corresponding to the fuel quantity per unit time is fed back Gf#T (9) The expression (9) is used during the next computing cycle as shown by the equation (3). Fig. 3 illustrates a block diagram of the fuel injection control system in the computer 1 of Fig. 1A. In the Figure, a fuel injection quantity per unit time Gf is calculated by computing means 12 in accordance with the film mass estimated by computing means 13 for estimating the film mass quantity Mf deposited on the intake manifold wall and the mass of air flow. In response to the signal generated from the 2 sensor 7, computing means 14 calculates an air-fuel ratio feedback correction factor 6 = f(O2) aiming at a stoichiometric air fuel ratio. Computing means 11 calculates the quantity of fuel injected per stroke as shown by the following equation T-G T. = k N + T8 (10) 1 N S where k is a coefficient which is used in the conversion to the fuel injection quantity per stroke and dependent on the injector characteristics and T5 is a dead injection time. The computing means 13 computes the quantity of film mass in the intake manifold as follows Mf < - (1 - -1AT)M + X*AT-T-Gf (11) T f Here, the right member Mf represents the film mass quantity for the preceding cycle and the left member Mf is the newly estimated film mass quantity. Also, l/T represents the rate of vaporization of the film mass and X represents the rate of fuel deposition on the intake manifold wall to the injected fuel quantity (referred to as a deposition rate). Represented by AT is one cycle period of the computation by the blocks of Fig. 3. Thus, the following in the right member represents the quantity of fuel delivered to the cylinder by the vaporization of the film mass during one cycle period T ATMf (12) Also, of the quantity of fuel actually injected per unit time the quantity of fuel deposition during the cycle period is given by the second term of the right member in the equation (11) or the following expression X AT TwGf (13) While a description will be made later of T go in consideration of the time relationship between the time per stroke and the cycle period of computation, the fuel injection quantity per unit time TeGf resulting from the integration of the feedback correction factor T represents the quantity of fuel injected per unit time which is renewed in response to the application of a stroke start signal from the crank angle sensor. While the deposition rate X and the vaporization rate l/T CT is a vaporization time constant) are obtained by experiments in accordance with the throttle position etch, the water temperature Tw, the manifold pressure P, the mass air flow Qa etc., in this embodiment the deposition rate X is given as a function of the throttle position for purposes of simplicity, as follows X = 0.3 + ¯Rr- 6th (14) Also, the vaporization rate is given as a function of the water temperature as follows EMI12.1 Here, it is assumed that l/T = 0.0266 when Tw= < 230C. As described hereinabove, a feature of the construction of the control system resides, as will also be seen from Fig. 3, in the fact that the feedback loop for feeding back the correction factor T in response to the O2 sensor signal and the loop of the fuel injection quantity T#Gf for calculating the deposited quantity or the deposited part of the injected fuel overlap doubly. Next, the timing of the injection per stroke and the timing of the computing cycle will be described. The computational operations shown in Fig. 3 are performed at intervals of a given period T and the injection pulse width is renewed by injection timing adjusting means 16 of Fig. 3 at a step 31 of Fig. 4 for every period. The actual injection is initiated by an interrupt signal INT generated for every stroke. As a result, the fuel is actually injected for the duration of the most lately calculated injection pulse width Ti as shown in Figs. 5A to 5C. Figs. 5A to 5C respectively show interrupt signals each generated for every stroke, injection pulse widths and calculated T*Gf with the lapse of time. In accordance with the embodiment, when an interrupt signal is applied, the timely existing T-Gf is stored in a TGf memory. This operation is performed by injection synchronizing means 15 of Fig. 3 and its timing corresponds to the application of the interrupt signal as shown at a step 32 of Fig. 4. By performing these operations, the actually injected fuel quantity is fed back and used for the accurate estimation of the quantity of film mass. In accordance with the present invention, the occurrence of lean spikes during the engine acceleration and the occurrence of rich spikes during the engine deceleration are eliminated as compared with the conventional method in which a basic fuel injection quantity is determined in accordance with the flow of intake air. This has the effect of improving the engine performance during the acceleration and ensuring effective removal of the harmful gases during the deceleration. Thus, it is possible to reduce the amount of the three-way catalyst by this method making it also effective economically. Further, while it has been necessary in the past to prepare various memory maps for providing acceleration and deceleration corrections on the basis of changes in the throttle position, etc., and search for the corresponding map values, in accordance with the present invention the desired acceleration and deceleration corrections can be provided by matching only the deposition rate of the fuel injection and the vaporization rate of the film mass in accordance with the acceleration and deceleration air-fuel ratios and thus the invention has the effect of providing more efficient manufacturing steps. Further, in accordance with the invention, by virtue of the fact that the quantity of the film mass deposited on the intake manifold wall is estimated by newly estimating the film mass quantity by using the actually injected fuel quantity, it is possible to estimate an accurate film mass quantity closer to the actual film mass quantity. By using the method which determines the desired fuel injection quantity in consideration of such estimated film mass, the air-fuel ratio of the mixture supplied to the engine can be controlled at around the stoichiometric air-fuel ratio even during the engine acceleration and deceleration. Thus, the invention has the effect of improving the exhaust gas purification and the engine performance.

Claims: CLAIMS: 1. In a control method for a fuel injection engine (10) in which the quantity of fuel injected into the engine is controlled in accordance with the flow of intake air, the improvement comprising the steps of: calculating a deposition rate X of injected fuel on an intake manifold wall (21) of said engine and a vaporization rate l/T of a deposited film mass; calculating a current film mass quantity Mf from said calculated X and l/T and a fuel injection quantity Gf by a preceding injection; calculating a desired fuel quantity Qa/(A/F) to be supplied to each cylinder of said engine from an intake air flow Q and a desired air-fuel ratio A/F; and determining a current fuel injection quantity Gf in accordance with the following EMI15.1 2. In a control method for a fuel injection engine (10), an intake manifold wall film mass fuel quantity estimating method of a fuel injection quantity feedback type comprising the steps: determining a fuel injection quantity per stroke of said engine at intervals of a predetermined period; subtracting a calculated value of a carry-over fuel quantity delivered to an engine cylinder during a current period from an intake manifold wall film mass fuel quantity estimated during a preceding period; and estimating an intake manifold wall deposition quantity per period in accordance with an actual fuel injection quantity per stroke and adding the same to said remaining film mass fuel quantity thereby estiminating a current intake manifold wall film mass fuel quantity.

Inventors: FUNABASHI, MOTOHISA, ONARI, MIKIHIKO, SEKOZAWA, TERUJI, SHIDA, MASAMI, SHIOYA, MAKOTO
Applicants: HITACHI, LTD.
Application year: 1985
Main classification: F02D41
IPC codes: F02D41