Control system for internal combustion engines

Abstract: A control system for an internal combustion engine (1) estimates an amount of fuel adhering to the inner surface of the intake passage (2), as well as an amount of fuel evaporated from fuel adhering to the inner surface of the intake passage (2) and carried into the combustion chambers, determines an amount of supply fuel to be supplied to the engine (1), based upon operating conditions of the engine (1), the estimated adherent fuel amount, and the estimated carried-off fuel amount, and supplies the determined supply fuel amount into the intake passage (2). The control system corrects the estimated adherent fuel amount and the estimated carried-off fuel amount, in response to an intake parameter which is changeable within the intake passage (2).The intake parameter includes an amount of evaporative fuel purged, valve operating characteristics of intake valves and/or exhaust valves, and an amount of assist air supplied to fuel injection valves (6).

Description: This invention relates to a control system for internal combustion engines, and more particularly to a control system which controls the supply of fuel injected into an intake pipe in a manner compensating for a fuel amount adhering to the inner surface of the intake pipe. In conventional internal combustion engines of the type that fuel is injected into an intake pipe, there is a problem that some of injected fuel adheres to the inner surface of the intake pipe, so that a required amount of fuel cannot be drawn into the combustion chamber. To solve this problem, there has been proposed a fuel supply control method which estimates a fuel amount which is to adhere to the inner surface of the intake pipe and one which is to be drawn into the combustion chamber by evaporation from the fuel adhering to the intake pipe, and determines a fuel injection amount in dependence on the estimated fuel amounts (Japanese Provisional Patent Publication (Kokai) No. 61-126337). GB-A-2228592 also relates to a similar system in which an adherent fuel amount is estimated based on the quantity of fuel injected and the fuel adhesion and evaporation rates, the fuel adhesion rate being derived from throttle opening and coolant temperature, and the evaporation rate being derived from coolant temperature, intake air quantity and engine speed. On the other hand, conventionally, evaporative fuel emission control systems have been widely used in internal combustion engines, which operate to prevent evaporative fuel from being emitted from a fuel tank into the atmosphere, by temporarily storing evaporative fuel from the fuel tank in a canister, and purging same into the intake system of the engine. Purging of evaporative fuel into the intake system causes fluctuations in the air-fuel ratio of a mixture supplied to the combustion chamber. To prevent such fluctuations in the air-fuel ratio or a deviation thereof from a desired value due to purging of evaporative fuel, it has also been proposed to estimate an amount of evaporative fuel to be purged, and determine a fuel injection amount based on the estimated evaporative fuel amount (Japanese Provisional Patent Publications (Kokai) Nos. 1-148043 and 2-27167). The above proposed or known systems or methods are intended to solve their respective problems alone. However, in actuality, unless all the problems are solved at the same time, the air-fuel ratio of a mixture supplied to an internal combustion engine cannot be accurately controlled to a desired value. In any event, at least the problem of adherence of fuel to the inner surface of the intake pipe has to be taken into consideration in solving the problems mentioned above. However, a mere combination of two or more of the above-mentioned systems or methods cannot lead to successful control of the air-fuel ratio. It is a feature of the invention to provide a control system for an internal combustion engine, which is capable of accurately controlling the air-fuel ratio by taking into consideration the amount of fuel adhering to the inner surface of the intake pipe as well as the amount of evaporative fuel purged. The present invention provides a control system for an internal combustion engine having a fuel tank, at least one combustion chamber, and an intake passage having an inner surface, the control system comprising: operating condition detecting means for detecting operating conditions of the engine; adherent fuel amount estimating means for estimating an amount of adherent fuel adhering to the inner surface of the intake passage; carried-off fuel amount estimating means for estimating an amount of carried-off fuel evaporated from fuel adhering to the inner surface of the intake passage and carried into the combustion chamber; supply fuel amount determining means for determining an amount of supply fuel to be supplied to the engine, based upon operating conditions of the engine detected by the operating condition detecting means, the adherent fuel amount estimated by the adherent fuel amount estimating means, and the carried-off fuel amount estimated by the carried-off fuel amount estimating means; and fuel supply means for supplying the supply fuel amount determined by the supply fuel amount determining means into the intake passage; characterised in that the engine further comprises a canister for adsorbing evaporative fuel generated from the fuel tank, and a purging passage connecting between the canister and the intake passage; and in that said control system further comprises estimated fuel amount correcting means for correcting the adherent fuel amount estimated by the adherent fuel amount estimating means, and the carried-off fuel amount estimated by the carried-off fuel amount estimating means, in response to an amount of the evaporative fuel supplied to the intake passage from the canister via the purging passage. Preferably, the estimated fuel amount correcting means corrects the adherent fuel amount and the carried-off fuel amount in response to concentration of hydrocarbon in the evaporative fuel supplied to the intake passage via the purging passage and a flow rate of the evaporative fuel. The above and other objects, features, and advantages of the invention will be more apparent from the following detailed description of various embodiment given by way of example only taken in conjunction with the accompanying drawings. Fig. 1 is a block diagram showing the whole arrangement of a fuel supply control system for an internal combustion engine, according to a preferred embodiment of the invention; Fig. 2 is a flowchart of a program for calculating a fuel injection period Tout; Fig. 3 is a flowchart of a program for calculating an intake pipe-adherent fuel amount TWP(N); and Figs. 4 (a), (b), and (c) show tables for calculating correction coefficients for correcting a direct supply ratio A and a carry-off ratio B. Referring first to Fig. 1, there is illustrated the whole arrangement of a fuel supply control system of an internal combustion engine, according to a preferred embodiment of the invention. In the figure, reference numeral 1 designates an internal combustion engine for automotive vehicles. The engine is a four-cylinder type, for instance. Connected to the cylinder block of the engine 1 is an intake pipe 2 across which is arranged a throttle body 3 accommodating a throttle valve 301 therein. A throttle valve opening ( TH ) sensor 4 is connected to the throttle valve 301 for generating an electric signal indicative of the sensed throttle valve opening and supplying same to an electronic control unit (hereinafter called "the ECU") 5. Fuel injection valves 6, only one of which is shown, are inserted into the interior of the intake pipe 2 at locations intermediate between the cylinder block of the engine 1 and the throttle valve 301 and slightly upstream of respective intake valves, not shown. The fuel injection valves 6 are connected to a fuel tank 8 via a fuel pump 7, and electrically connected to the ECU 5 to have their valve opening periods controlled by signals therefrom. On the other hand, an intake pipe absolute pressure (PBA) sensor 10 is provided in communication with the interior of the intake pipe 2 via a conduit 9 at a location immediately downstream of the throttle valve 301 for supplying an electric signal indicative of the sensed absolute pressure within the intake pipe 2 to the ECU 5. An engine coolant temperature (TW) sensor 11 is mounted in the cylinder block of the engine 1, for supplying an electric signal indicative of the sensed engine coolant temperature TW to the ECU 5. An engine rotational speed (NE) sensor 12 is arranged in facing relation to a camshaft or a crankshaft of the engine 1, not shown. The engine rotational speed sensor 12 generates a pulse as a TDC signal pulse at each of predetermined crank angles whenever the crankshaft rotates through 180 degrees, the pulse being supplied to the ECU 5. An O 2 sensor 13 as an exhaust gas ingredient concentration sensor is mounted in an exhaust pipe 14 connected to the cylinder block of the engine 1, for sensing the concentration of oxygen present in exhaust gases emitted from the engine 1 and supplying an electric signal indicative of the detected value of the oxygen concentration to the ECU 5. An evaporative fuel emission control system is arranged between the fuel tank 8 and the intake pipe 2. More specifically, a conduit line (purging passage) 21 extends from an upper space in the fuel tank 8 which has an enclosed body and opens into the interior of a canister 23 having an adsorbent 231. A two-way valve 22 is arranged across the conduit line 21. A purging passage 24 extends from the canister 23 and opens into the interior of the intake pipe 2 at a location downstream of the throttle valve 3. Arranged across the purging passage 24 are a purge control valve 25, which is a linear control valve (EPCV) having a solenoid for actuating a valve element thereof, a flowmeter 26 which detects a flow rate VP of an air-fuel mixture containing evaporative fuel, flowing through the purge passage 24 (hereinafter referred to as "purging flow rate"), and a HC (hydrocarbon) concentration sensor 27 for sensing the concentration of HC in the air-fuel mixture. The solenoid of the purge control valve 25 is electrically connected to the ECU 5 to be controlled by a control signal therefrom to linearly vary its valve opening. Evaporative fuel or gas (hereinafter merely referred to as "evaporative fuel") generated within the fuel tank 8 forcibly opens a positive pressure valve, not shown, of the two-way valve 22 when the pressure of the evaporative fuel reaches a predetermined level, to flow through the valve 22 into the canister 23, where the evaporative fuel is adsorbed by the adsorbent 231 in the canister and thus stored therein. The purge control valve 25 is a so-called on-off control type solenoid valve, which has its valve opening linearly variable in response to the duty ratio of a control signal from the ECU 5, i.e. the ratio between the valve opening period and the valve closing period. Thus, the purge control valve 25 is opened to a valve opening corresponding to the duty ratio of the control signal from the ECU 5, whereby evaporative fuel temporarily stored in the canister 23 flows therefrom together with fresh air introduced through an outside air-introducing port 232 of the canister 23 at the flow rate determined by the valve opening of the purge control valve 25, through the purging passage 24 into the intake pipe 2 to be supplied to the cylinders. When the fuel tank 8 is cooled due to low ambient temperature etc. so that negative pressure increases within the fuel tank 8, a negative pressure valve, not shown, of the two-way valve 22 is opened to return evaporative gas temporarily stored in the canister 23 into the fuel tank 8. In the above described manner, the evaporative fuel generated within the fuel tank 8 is prevented from being emitted into the atmosphere. The ECU 5 comprises an input circuit having the functions of shaping the waveforms of input signals from various sensors, shifting the voltage levels of sensor output signals to a predetermined level, converting analog signals from analog-output sensors to digital signals, and so forth, a central processing unit (hereinafter called "the CPU") which executes programs for controlling the fuel injection valves 6 and the purge control valve 25, etc., memory means storing maps and tables, referred to hereinafter, and various operational programs which are executed in the CPU and for storing results of calculations therefrom, etc., and an output circuit which outputs control or driving signals to the fuel injection valves 6 and the purge control valves 25. The CPU operates in response to the above-mentioned signals from the sensors to determine operating conditions in which the engine 1 is operating, such as an air-fuel ratio feedback control region in which the fuel supply is controlled in response to the detected oxygen concentration in the exhaust gases, and open-loop control regions, and calculates, based upon the determined operating conditions, the valve opening period or fuel injection period Tout over which the fuel injection valves 6 are to be opened, by the use of the program of Fig. 2 in synchronism with inputting of TDC signal pulses to the ECU 5. The CPU supplies via the output circuit the driving signals based upon the fuel injection period Tout determined as above to the fuel injection valves 6 to open same over the fuel injection period Tout. The fuel injection period Tout is proportional to the fuel injection amount, and therefore will be hereinafter referred to as the fuel injection amount. Fig. 2 shows the program for calculating the fuel injection amount Tout. This program is executed upon generation of each TDC signal pulse and in synchronism therewith. At a step S1, a direct supply ratio A and a carry-off ratio B are calculated. The direct supply ratio A is defined as a ratio of a fuel amount directly or immediately drawn into a combustion chamber to the whole fuel amount injected in a cycle, the direct supply ratio including a fuel amount carried off the inner surface of the intake pipe 2 by evaporation etc., in the same cycle. The carry-off ratio B is defined as a ratio of a fuel amount carried off the inner surface of the intake pipe 2 by evaporation etc. and drawn into the combustion chamber in the present cycle to the whole fuel amount which adhered to the inner surface of the intake pipe 2 in the last or immediately preceding cycle. The direct supply ratio A and the carry-off ratio B are read, respectively, from an A map and a B map set in accordance with coolant temperature TW and intake pipe absolute pressure PBA, in response to the detected TW and PBA values. The direct supply ratio A and the carry-off ratio B may be calculated by interpolation, if required. At the next step S2, first, second and third correction coefficients KA1 to KA3 and KB1 to KB3, which correct the direct supply ratio A and the carry-off ratio B, are calculated. The first correction coefficients KA1 and KB1 are determined in response to the HC concentration β detected by the HC concentration sensor 27, as shown in Fig. 4 (a). The second correction coefficients KA2 and KB2 are determined in response to the purging flow rate VP detected by the flowmeter 26, as shown in Fig. 4 (b). Therefore, (KA1 x KA2) and (KB1 x KB2) assume values representing (β x VP), i.e. an amount of evaporative fuel flowing through the purging passage 24. According to Fig. 4 (a), as the HC concentration β increases, the first correction coefficients KA1 and KB1 are increased. This is because, when the evaporative fuel amount which is supplied to the intake pipe 2 increases, the direct supply ratio A and the carry-off ratio B apparently increase. The setting of the second correction coefficients KA2 and KB2 in Fig. 4 (b) is based upon a similar ground. The third correction coefficients KA3 and KB3 are determined in response to the engine rotational speed NE, as shown in Fig. 4 (c). Specifically, according to Fig. 4 (c), the correction coefficient KA3 for correcting the direct supply ratio A is set such that it increases as the engine rotational speed NE increases. The third correction coefficient KB3 for correcting the carry-off ratio B is set likewise. The reason why the third correction coefficients KA3 and KB3 are thus increased as the engine rotational speed NE increases is that the direct supply ratio A and the carry-off ratio B apparently increase as the intake air flow speed in the intake pipe increases with an increase in the engine rotational speed NE. Next, at a step S3, corrected values Ae and Be of the direct supply ratio and the carry-off ratio are calculated by the use of the following equations (1) and (2): Ae = A x KA1 x KA2 x KA3 Be = B x KB1 x KB2 x KB3 Further, (1 - Ae) and (1 - Be) are calculated at a step S4, where the values Ae, (1 - Ae) and (1 - Be) thus calculated are stored into a RAM of the ECU 5 for use in a program shown in Fig. 3, which will be described hereinafter followed by the program proceeding to step S5. At step S5, it is determined whether or not the engine is being started. If the answer is affirmative (YES), the fuel injection amount Tout is calculated based upon a basic fuel amount Ti for use at the start of the engine, and then the program is terminated. If the answer to the question of the step S5 is negative (NO), i.e. if the engine is not being started, a required fuel amount TCYL(N) for each cylinder, which does not include an additive correction term Ttotal, referred to hereinafter, is calculated by the use of the following equation (3), at a step S6: Tcyl(N) = TiM x Ktotal(N) where (N) represents a number allotted to the cylinder for which the required fuel amount Tcyl is calculated. TiM represents a basic fuel amount to be applied when the engine is under normal operating conditions (other than the starting condition) and is calculated in response to the rotational speed NE and the intake pipe absolute pressure PBA. Ktotal(N) represents the product of all correction coefficients (e.g. a coolant temperature-dependent correction coefficient KTW and a leaning correction coefficient KLS) which are calculated based upon engine operating parameter signals from various sensors excluding an air-fuel ratio correction coefficient KO2 which is calculated based on an output signal from the O 2 sensor 13. At a step S7, the required fuel amount TCYL(N) calculated above is corrected by applying a purging correction variable Tpurge to the following equation (4). The purging correction variable Tpurge represents a fuel injection period corresponding to an evaporative fuel amount calculated based upon outputs from the flowmeter 26 and the HC sensor 27 Tcyl(N) = Tcyl(N) - Tpurge At a step S8, a combustion chamber supply fuel amount TNET, which should be supplied to the corresponding combustion chamber in the present injection cycle, is calculated by the use of the following equation (5): TNET = Tcyl(N) + Ttotal - Be x TWP(N) where Ttotal is the sum of all additive correction terms (e.g. an acceleration fuel-increasing correction term TACC), which is calculated based on engine operating parameter signals from various sensors. The value Ttotal does not include an ineffective time correction term TV, refered to later. TWP(N) represents an intake pipe-adherent fuel amount (estimated value), which is calculated by the program of Fig. 3. (Be x TWP(N)) corresponds to an amount of fuel, which is evaporated from fuel adhering to the inner surface of the intake pipe 2 and carried into the combustion chamber. A fuel amount corresponding to the fuel amount carried off the intake pipe inner surface need not be injected, and, therefore, is to be subtracted from the value Tcyl(N) in the equation (5). At a step S9, it is determined whether or not the value TNET calculated by the equation (5) is larger than a value of O. If the answer is negative (NO), i.e., if TNET ≦ 0, the fuel injection amount Tout is set to 0, followed by terminating the program. If the answer at the step S9 is affirmative (YES), i.e., if TNET > 0, the TOUT value is calculated by the use of the following equation (6): Tout = TNET(N)/Ae x KO2 + TV where KO2 is the aforementioned air fuel ratio correction coefficient calculated in response to the output from the O 2 sensor 13. TV is the ineffective time correction term. Thus, a fuel amount corresponding to TNET(N) X KO2 + Be x TWP(N) is supplied to the combustion chamber by opening the fuel injection valve 6 over the time period Tout calculated by the equation (6). Fig. 3 shows the program for calculating the intake pipe-adherent fuel amount TWP(N), which is executed upon generation of each crank angle pulse which is generated whenever the crankshaft rotates through a predetermined angle (e.g. 30 degrees). At a step S21, it is determined whether or not the present loop of execution of this program falls within a time period after the start of the calculation of the fuel injection amount Tout and before the fuel injection is completed (hereinafter referred to as the injection control period). If the answer is affirmative (YES), a first flag FCTWP(N) is set to a value of O at a step S32, followed by terminating the program. If the answer at the step S21 is negative (NO), i.e., if the present loop is not within the injection control period, it is determined at a step S22 whether or not the first flag FCTWP(N) is equal to 1. If the answer is affirmative (YES), that is, if FCTWP(N) = 1, the program jumps to a step S31, whereas if the answer is negative (NO), i.e., if FCTWP(N) = 0, it is determined at a step S23 whether or not the engine is under fuel cut (the fuel supply is interrupted). If the engine is not under fuel cut, the intake pipe-adherent fuel amount TWP(N) is calculated at a step S24 by the use of the following equation (7), then a second flag FTWPR(N) is set to a value of O, and the first flag FCTWP(N) is set to a value of 1 at steps S30 and S31, followed by terminating the program: TWP(N) = (1 - Be) x TWP(N)(n - 1) + (1 - Ae) x (Tout(N) - TV) where TWP(N)(n - 1) represents a value of TWP(N) obtained on the last occasion, and Tout(N) an updated or new value of the fuel injection amount Tout which has been calculated by the program of Fig. 2. The first term on the right side corresponds to a fuel amount remaining on the inner surface of the intake pipe 2 without being carried into the combustion chamber, out of the fuel previously adhering to the inner surface of the intake pipe 2, and the second term on the right side corresponds to a fuel amount newly adhering to the inner surface of the intake pipe 2 out of newly injected fuel. If the answer at the step S23 is affirmative (YES), i.e., if the engine is under fuel out, it is determined at a step S25 whether or not the second flag FTWPR(N) has been set to a value of 1. If the answer is affirmative (YES), i.e., if FTWPR(N) = 1, the program jumps to the step S31. If the answer is negative (NO), i.e., if FTWPR(N) = 0, the adherent fuel amount TWP(N) is calculated by the use of the following equation (8) at a step S26, and then the program proceeds to a step S27: TWP(N) = (1 - Be) x TWP(N)(n -1) The equation (8) is identical with the equation (7), except that the second term on the right side is omitted. The reason for the omission is that there is no fuel newly adhering to the intake pipe inner surface, due to fuel cut. At the step 27, it is determined whether or not the calculated TWP(N) value is larger than a very small predetermined value TWPLG. If the answer is affirmative (YES), i.e., if TWP(N) > TWPLG, the program proceeds to the next step S30. If the answer at the step S27 is negative (NO), i.e., if TWP(N) ≦ TWPLG, the TWP(N) value is set to a value of 0 at a step S28, and then the second flag FTWPR(N) is set to a value of 1 at a step S29, followed by the program proceeding to the step, at a step S31. According to the program of Fig. 3 described above, the intake pipe-adherent fuel amount TWP(N) can be accurately calculated. Moreover, an appropriate fuel amount can be supplied to the combustion chamber of each cylinder, which reflects the fuel amount adhering to the inner surface of the intake pipe 2 as well as the fuel amount carried off the adherent amount. Further, according to the embodiment the direct supply ratio A and the carry-off ratio B are corrected by the correction coefficients KA1, KB1, KA2 and KB2 which depend upon the amount of evaporative fuel supplied from the canister 23. Therefore, the calculated fuel injection amount reflects the evaporative fuel amount. As a result, the air-fuel ratio of the mixture supplied to the combustion chamber of each cylinder can be accurately controlled to a desired value. Although in the present embodiment, the second correction coefficients KA2, KB2 for correcting the direct supply ratio A and the carry-off ratio B are set in accordance with the purging flow rate VP, they may be set in accordance with the valve opening of the purge control valve 25 or the duty ratio of the on-off control signal for the purge control valve 25. According to the preferred embodiment described above, an amount of evaporative fuel supplied from the canister to the intake pipe is detected, and the intake pipe-adherent fuel amount and the carried-off fuel amount are corrected in response to the detected evaporative fuel amount. Therefore, the resulting calculated fuel injection amount can reflect the intake pipe-adherent fuel amount as well as the evaporative fuel amount, to thereby enable accurately controlling the air-fuel ratio of the mixture supplied to the combustion chamber of each cylinder to a desired value.

Claims: A control system for an internal combustion engine (1) having a fuel tank, at least one combustion chamber, and an intake passage (2) having an inner surface, said control system comprising: operating condition detecting means for detecting operating conditions of said engine (1); adherent fuel amount estimating means for estimating an amount of adherent fuel adhering to said inner surface of said intake passage; carried-off fuel amount estimating means for estimating an amount of carried-off fuel evaporated from fuel adhering to said inner surface of said intake passage (2) and carried into said combustion chamber (1); supply fuel amount determining means for determining an amount of supply fuel to be supplied to said engine (1), based upon operating conditions of said engine (1) detected by said operating condition detecting means, said adherent fuel amount estimated by said adherent fuel amount estimating means, and said carried-off fuel amount estimated by said carried-off fuel amount estimating means; and fuel supply means for supplying said supply fuel amount determined by said supply fuel amount determining means into said intake passage (2); characterised in that said engine further comprises a canister (23) for adsorbing evaporative fuel generated from said fuel tank (8), and a purging passage (24) connecting between said canister (23) and said intake passage (24); and in that said control system further comprises estimated fuel amount correcting means for correcting said adherent fuel amount estimated by said adherent fuel amount estimating means, and said carried-off fuel amount estimated by said carried-off fuel amount estimating means, in response to an amount of said evaporative fuel supplied to said intake passage (2) from said canister (23) via said purging passage (24). A control system as claimed in claim 1, wherein said estimated fuel amount correcting means corrects said adherent fuel amount and said carried-off fuel amount in response to concentration of hydrocarbon in said evaporative fuel supplied to said intake passage (2) via said purging passage (24) and a flow rate of said evaporative fuel.

Inventors: HARA YOSHIHISA, MIYASHITA KOTARO, OGAWA KEN, HARA, YOSHIHISA, MIYASHITA, KOTARO, OGAWA, KEN, Hara, Yoshihisa c/o Honda R &amp; D, Co., Ltd., Miyashita, Kotaro c/o Honda R &amp; D, Co., Ltd., Ogawa, Ken c/o Honda R &amp; D, Co., Ltd.
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F02D35
IPC codes: F02D13, F02M25, F01L9, F02D41