JP4534914B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

In an internal combustion engine (hereinafter also referred to as “engine”) provided with a fuel injection valve (hereinafter referred to as “port injection valve”) that injects fuel into an intake passage upstream of the intake valve. In general, a part of the fuel injected from the port injection valve adheres to the intake system (specifically, the wall surface of the intake pipe, the umbrella portion of the intake valve, etc., hereinafter collectively referred to as “intake passage constituent member”). To do. For this reason, for example, a fuel injection control device for an internal combustion engine described in Patent Document 1 below estimates a fuel adhesion amount that is the amount of fuel adhering to the intake passage constituting member, and uses the estimated fuel adhesion amount. Accordingly, the amount of fuel injected from the port injection valve is determined.
JP-A-5-2321221

  On the other hand, in order to reduce fuel consumption, for example, when a predetermined fuel cut execution condition including an accelerator pedal operation amount including “0” or the like is satisfied, the combustion chamber (hereinafter also referred to as “in-cylinder”) may be used. Is stopped (hereinafter referred to as “fuel cut”).

  When the fuel cut is started, the fuel that flows into the cylinder from the intake passage is only the fuel that separates from the intake passage constituent member and flows into the cylinder (hereinafter referred to as “attached inflow fuel”). . Hereinafter, the amount of attached inflow fuel is referred to as “attached inflow fuel amount”. This amount of adhering inflow fuel is smaller than the amount of fuel corresponding to the misfire limit. Therefore, misfire occurs, and the amount of attached inflow fuel is discharged to the exhaust passage as unburned fuel.

  Here, the amount of fuel adhering inflow increases as the fuel adhering amount increases. Accordingly, there is a problem that a relatively large amount of unburned fuel is discharged to the exhaust passage when the fuel adhesion amount at the time when the fuel cut is started is large.

  By the way, in recent years, in order to improve combustion efficiency, lower fuel consumption, and ensure startability at the time of engine start, the port injection valve and a fuel injection valve that directly injects fuel into the cylinder (hereinafter referred to as “in-cylinder injection”). Internal combustion engines that have both been called “valves” have been developed. Hereinafter, a system including two fuel injection valves, that is, a port injection valve and an in-cylinder injection valve for each cylinder, is referred to as a “dual injection system”.

  In this dual injection system, let us consider a case where the injection by the port injection valve and the in-cylinder injection valve is stopped simultaneously after the fuel cut execution condition is established. In this case, the fuel supplied into the cylinder immediately after the stop of injection becomes only the attached inflow fuel, and misfire occurs. Therefore, as described above, there is a problem that a relatively large amount of unburned fuel is discharged to the exhaust passage if the amount of fuel adhering at the start of injection stop is large.

  Accordingly, an object of the present invention is to provide a fuel injection control device for an internal combustion engine applied to a dual injection system, which can reduce the amount of unburned fuel that is discharged to an exhaust passage due to fuel cut. There is.

  The fuel injection control device according to the present invention includes an injection amount that determines a port injection amount that is an amount of fuel injected from the port injection unit and an in-cylinder injection amount that is an amount of fuel injected from the in-cylinder injection unit. And a fuel cut means for stopping the injection by the port injection means and the injection by the in-cylinder injection means when a fuel cut execution condition, which is a condition for stopping the fuel supply to the combustion chamber, is satisfied. With.

  The fuel injection control device according to the present invention is characterized in that, after the fuel cut execution condition is satisfied, the fuel cut means first stops the injection by the port injection means, and the injection by the port injection means is stopped. The present invention is configured to stop the injection by the in-cylinder injection means after a predetermined period has elapsed from the time. Hereinafter, the injection by the port injection means and the injection by the in-cylinder injection means are referred to as “port injection” and “in-cylinder injection”, respectively.

  According to this, in-cylinder injection is continued for a predetermined period from the time point when the port injection is stopped. That is, in addition to the attached inflow fuel, fuel by in-cylinder injection is also supplied into the cylinder. Therefore, since combustion can be continued for a predetermined period, discharge of unburned fuel into the exhaust passage can be suppressed.

  When the in-cylinder injection is stopped after a lapse of a predetermined period, the fuel supplied into the cylinder immediately after that becomes only the adhering inflow fuel and misfire occurs. Here, after the time when the port injection is stopped, the fuel adhesion amount decreases with the passage of time by the amount of the adhering inflow fuel. Therefore, by setting the predetermined period to an appropriate length, it is possible to reduce the amount of fuel adhering (accordingly, the amount of adhering inflow fuel) when in-cylinder injection is stopped.

  As a result, it is possible to suppress the discharge of unburned fuel into the exhaust passage even after the time when in-cylinder injection is stopped. As described above, according to the above configuration, it is possible to reduce the amount of unburned fuel discharged to the exhaust passage along with the fuel cut by setting the predetermined period to an appropriate length.

Specifically, the fuel injection control device according to the present invention is configured to estimate a fuel adhesion amount that estimates a fuel adhesion amount that is an amount of fuel adhering to a member constituting the intake passage by the injection by the port injection means. further comprising means, the fuel cut means, as the predetermined time period, configuration from the time when injection by the port injection means is stopped, so that the fuel adhesion amount to use time to become less than the first predetermined value Is done .

  According to this, in-cylinder injection is stopped when the fuel adhesion amount is equal to or less than the first predetermined value. That is, the amount of attached inflow fuel at the time when the in-cylinder injection is stopped is determined depending on the first predetermined value, and becomes smaller as the first predetermined value is smaller. Therefore, if the first predetermined value is set to a sufficiently small value for suppressing the discharge of unburned fuel, the discharge of unburned fuel after the point in time when in-cylinder injection is stopped can be reliably suppressed. . In other words, the predetermined period can be set to an appropriate length.

  In this case, when a catalyst device for purifying unburned fuel or the like (hereinafter simply referred to as “catalyst”) is provided in the exhaust passage of the engine, the fuel cut means sets the first predetermined value to It is more preferable to determine a smaller value as the temperature of the catalyst provided in the exhaust passage of the internal combustion engine is higher. Here, the catalyst temperature may be physically detected by a sensor that detects the catalyst temperature, or may be estimated using a known function, model, or the like for estimating the catalyst temperature.

  When unburned fuel flows into the catalyst, it burns by a catalytic reaction. The greater the amount of unburned fuel that flows into the catalyst, the greater the heat of reaction generated in the catalyst and the higher the catalyst temperature. On the other hand, when the catalyst temperature becomes excessively high, the deterioration of the catalyst is promoted, so that it is necessary to suppress the catalyst temperature from becoming excessively high. Therefore, it is preferable that the amount of unburned fuel flowing into the catalyst is smaller as the catalyst temperature is higher.

  The above configuration is based on such knowledge. According to this, the higher the catalyst temperature, the smaller the amount of attached inflow fuel at the time when the in-cylinder injection is stopped, so that the amount of unburned fuel flowing into the catalyst can be further reduced. Accordingly, it is possible to suppress the deterioration of the catalyst from being accelerated by excessively increasing the catalyst temperature. In addition, when the catalyst temperature is low, the predetermined period (thus, the period during which the in-cylinder injection is continued) can be shortened, so that the reduction in fuel consumption can be achieved more reliably.

In addition, the fuel injection control device engine according to the present invention is directed to an internal combustion engine in which an exhaust passage is provided with a catalyst having an oxygen storage function, and the fuel cut means sets the first predetermined value to configured to determine a smaller value as the oxygen storage amount of the catalyst provided in an exhaust passage of the internal combustion engine is small. Here, the oxygen storage amount of the catalyst can be estimated using a known function, model, or the like for estimating the oxygen storage amount of the catalyst.

  The smaller the amount of oxygen stored in the catalyst, the smaller the amount of unburned fuel that the catalyst can purify (combust). Therefore, it is preferable that the amount of unburned fuel flowing into the catalyst is made smaller as the oxygen storage amount of the catalyst is smaller.

  The above configuration is based on such knowledge. According to this, the smaller the oxygen storage amount of the catalyst, the smaller the amount of unattached fuel flowing into the catalyst because the amount of attached inflow fuel at the time when the in-cylinder injection is stopped becomes smaller. it can. Therefore, when the oxygen storage amount of the catalyst is small, unburned fuel can be suppressed from being discharged from the catalyst as it is. In addition, when the oxygen storage amount of the catalyst is large, the predetermined period (and hence the period in which the in-cylinder injection is continued) can be shortened, so that fuel consumption can be achieved more reliably.

  By the way, an internal combustion engine applied to a dual injection system usually has an in-cylinder in order to make the air-fuel ratio of an air-fuel mixture supplied to the engine (hereinafter simply referred to as “air-fuel ratio”) coincide with the target air-fuel ratio. A required fuel amount determining means for determining a required fuel amount that is the amount of fuel to be burned is provided, and the injection amount determining means is a port injection so that the total amount of fuel supplied into the cylinder matches the required fuel amount. The amount and the in-cylinder injection amount are determined.

  In this case, it is preferable that the injection amount determination means is configured to determine the in-cylinder injection amount based on the required fuel amount and the fuel adhesion amount during the predetermined period. According to this, the in-cylinder injection amount during the predetermined period can be determined in consideration of the attached inflow fuel amount calculated based on the fuel adhering amount in addition to the required fuel amount, and is thus supplied into the cylinder. The total amount of fuel can be matched with the required fuel amount.

  Specifically, if the injection amount determining means is configured to determine the in-cylinder injection amount to a value obtained by subtracting the attached inflow fuel amount from the required fuel amount during the predetermined period. The total amount of fuel supplied inside can be matched with the required fuel amount, and as a result, the air-fuel ratio during the predetermined period can be matched with the target air-fuel ratio.

  By the way, an internal combustion engine usually has a throttle valve for adjusting an opening cross-sectional area of an intake passage and an opening cross-sectional area of the throttle valve (hereinafter referred to as “throttle valve opening”) as an operating state of the internal combustion engine ( Specifically, a throttle valve control means for controlling to a value corresponding to an accelerator pedal operation amount or the like is provided.

  In general, the fuel cut execution condition can be satisfied when the accelerator pedal operation amount is changed from a value larger than “0” to “0”. Therefore, the fuel cut execution condition is often satisfied when the throttle valve opening is suddenly reduced. When the throttle valve opening decreases rapidly, the air pressure in the intake pipe decreases rapidly, and the fuel adhering to the intake passage constituting member rapidly evaporates. As a result, the fuel adhesion amount decreases rapidly.

  Here, when the value of the fuel adhesion amount suddenly fluctuates (decreases), the estimation accuracy of the fuel adhesion amount tends to decrease. Therefore, the estimation accuracy of the attached inflow fuel amount is also lowered. Furthermore, the larger the fuel adhering amount (and hence the adhering inflow fuel amount) itself, the larger the error in the adhering inflow fuel amount itself. Therefore, if the fuel cut execution condition is satisfied when the fuel adhesion amount is large, the in-cylinder injection amount and the air-fuel ratio are set as targets during the predetermined period if the throttle valve opening is immediately decreased rapidly according to the operating state. It becomes difficult to accurately determine a value for matching the air-fuel ratio.

  From the above, when the internal combustion engine includes the throttle valve and the throttle valve control means, the throttle valve control means is configured such that the fuel adhesion amount at the time when the fuel cut execution condition is satisfied is the first predetermined value. When the fuel cut execution condition is satisfied, the throttle valve opening is changed to a value corresponding to the operation state of the internal combustion engine and changed to the operation state of the internal combustion engine. It is preferable to be configured to control to a value obtained by performing delay processing on the corresponding value.

  According to this, when the fuel adhering amount at the time when the fuel cut execution condition is satisfied is large, it is possible to prevent the throttle valve opening from being rapidly decreased. As a result, it is possible to reduce the error of the adhering inflow fuel amount, and as a result, it is possible to accurately determine the in-cylinder injection amount to a value for making the air-fuel ratio coincide with the target air-fuel ratio during the predetermined period. .

  Examples of the delay processing include response delay processing (for example, first-order delay processing), delay processing, and the like. When response delay processing is performed, since a rapid decrease in the throttle valve opening (and hence a sharp decrease in the amount of fuel adhering) is avoided, a decrease in the estimation accuracy of the amount of fuel adhering can be suppressed. The error of the adhering inflow fuel amount can be reduced.

  Further, when the delay process is performed, the throttle valve opening rapidly decreases after a delay period from the time when the fuel cut execution condition is satisfied. However, the fuel adhesion amount is small when the throttle valve opening decreases rapidly. Therefore, it is possible to reduce an error in the amount of adhering inflow fuel generated when the throttle valve opening is rapidly decreased.

  Embodiments of an internal combustion engine fuel injection control apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of a system in which a fuel injection control device according to an embodiment of the present invention is applied to a spark ignition type multi-cylinder (four-cylinder) internal combustion engine 10 having a dual injection system. The internal combustion engine 10 includes a cylinder block unit 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head unit 30 fixed on the cylinder block unit 20, and a gasoline mixture in the cylinder block unit 20. And an exhaust system 50 for releasing exhaust gas from the cylinder block 20 to the outside.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The heads of the cylinder 21 and the piston 22 form a combustion chamber 25 together with the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and continuously changes the phase angle of the intake camshaft. The variable intake timing device 33, the actuator 33 a of the variable intake timing device 33, the exhaust port 34 communicating with the combustion chamber 25, the exhaust valve 35 that opens and closes the exhaust port 34, the exhaust camshaft 36 that drives the exhaust valve 35, and the spark plug 37 , An igniter 38 including an ignition coil that generates a high voltage to be applied to the spark plug 37, a port injection valve 39P for injecting fuel into the intake port 31, and an in-cylinder injection valve 39C for injecting fuel directly into the combustion chamber 25. Yes.

  The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. A throttle valve 43 having a variable opening cross-sectional area of the intake passage and a throttle valve actuator 43a as a throttle valve control means comprising a DC motor constituting the throttle valve driving means are provided. Hereinafter, the value of the opening cross-sectional area of the throttle valve 43 is referred to as a throttle valve opening TA.

  The throttle valve actuator 43a has a throttle valve opening determination table MapTAt (Accp) in which the throttle valve opening TA defines an accelerator pedal operation amount Accp, which will be described later, and the relationship between the accelerator pedal operation amount Accp and the target throttle valve opening TAt. ), The throttle valve 43 is adjusted so as to coincide with the target throttle valve opening degree TAt obtained in principle. Here, the target throttle valve opening degree TAt is determined so as to increase as the accelerator pedal operation amount Accp increases. Therefore, in principle, the throttle valve opening TA is also determined so as to increase as the accelerator pedal operation amount Accp increases.

  The exhaust system 50 includes an exhaust manifold 51 that communicates with the exhaust port 34, and an exhaust pipe (exhaust pipe) that is connected to the exhaust manifold 51 (actually, a collection portion of the exhaust manifolds 51 that communicate with each exhaust port 34). ) 52. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Further, the exhaust system 50 includes a three-way catalyst 53 having an oxygen storage function disposed (intervened) in the exhaust pipe 52.

  On the other hand, this system includes a hot-wire air flow meter 61, a cam position sensor 62, a crank position sensor 63, a water temperature sensor 64, and an exhaust passage upstream of the three-way catalyst 53 (in this example, a set in which the exhaust manifolds 51 are gathered. An air-fuel ratio sensor 65, a catalyst temperature sensor 66, a pressure sensor 67, and an accelerator opening sensor 68.

  The hot-wire air flow meter 61 outputs a voltage corresponding to the mass flow rate per unit time of the intake air flowing through the intake pipe 41. An intake air amount (flow rate) Ga is calculated from this output. The cam position sensor 62 generates a signal (G2 signal) having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). This signal also represents the opening / closing timing VT of the intake valve 32.

  The crank position sensor 63 outputs a signal having a narrow pulse every time the crankshaft 24 rotates 10 ° and a wide pulse every time the crankshaft 24 rotates 360 °. This signal represents the operating speed NE. The water temperature sensor 64 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The air-fuel ratio sensor 65 outputs a current corresponding to the air-fuel ratio of the exhaust gas, and outputs a voltage vabyfs corresponding to this current. The exhaust gas air-fuel ratio abyfs is calculated from the output vabyfs. The catalyst temperature sensor 66 detects the temperature of the three-way catalyst 53 and outputs a signal indicating the catalyst temperature Tc.

  The pressure sensor 67 detects the pressure of air (gas) in the intake pipe 41 and outputs a signal representing the intake pipe pressure Pm. The accelerator opening sensor 68 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81.

  The electric control device 70 includes a CPU 71 connected by a bus, a routine (program) executed by the CPU 71, a table (look-up table, map), a ROM 72 in which constants and the like are stored in advance, and the CPU 71 temporarily stores data as necessary. This is a microcomputer comprising a RAM 73 for storing data, a backup RAM 74 for storing data while the power is turned on and holding the stored data while the power is shut off, an interface 75 including an AD converter, and the like. .

  The interface 75 is connected to the sensors 61-68, supplies signals from the sensors 61-68 to the CPU 71, and in response to commands from the CPU 71, the actuator 33a, the igniter 38, and the port injection valve 39P of the variable intake timing device 33. A drive signal is sent to the in-cylinder injection valve 39C and the throttle valve actuator 43a. As a result, the opening / closing timing VT of the intake valve 32 is changed according to the operating state of the engine.

(Fuel behavior (adhesion) model)
Next, determination of the fuel injection amount, that is, the port injection amount fip and the in-cylinder injection amount fic by the fuel injection control device (hereinafter also referred to as “this device”) configured as described above, and Before describing fuel injection control (actual operation), a fuel behavior (attachment) model used by the present apparatus to determine the port injection amount fip will be described.

  As conceptually shown in FIG. 2, part of the fuel injected from the port injection valve 39P of the cylinder into which the fuel is injected is partly the wall surface of the intake pipe 41, the umbrella portion of the intake valve 32, etc. Adhering to the intake passage component.

  More specifically, as shown in FIG. 3 focusing on the port-injected cylinder, fip is the port injection amount that is the amount of fuel that is port-injected from the port injection valve 39P for the current intake stroke, fw (fw (k)) after the previous port injection and immediately before the current port injection, the amount of fuel adhering to the intake passage component (fuel adhering amount), Pv (0 ≦ Pv <1) The ratio (residual rate) of the amount of fuel remaining attached to the intake passage component in the fuel adhesion amount fw (k), Rv (0 ≦ Rv <1), is assigned to the intake passage component of the port injection amount fip. Assuming that the amount of adhering fuel (adhesion rate), the amount of fuel remaining in the intake passage component after the current port injection and immediately before the next port injection in the fuel adhering amount fw (k) is Pv fw (k), which is newly added to the intake passage component of the fuel with the port injection amount fip The amount of fuel that will be Rv · fip. Therefore, the following equation (1) is established for the fuel attachment amount fw (k + 1), which is the amount of fuel attached to the intake passage constituting member immediately after the current port injection and immediately before the next port injection. The following equation (1), which is a recurrence formula, describes the fuel behavior model.

fw (k + 1) = Pv · fw (k) + Rv · fip (1)

(Actual operation)
Next, the actual operation of this device (electric control device 70) will be described with reference to the series of flowcharts shown in FIGS. 4 and 5 and the time chart of FIG. Hereinafter, for convenience of explanation, “MapX (a1, a2,...)” Represents a table for obtaining a value X having a1, a2,.

  The CPU 71 performs a series of routines for calculating the port injection amount fip, the in-cylinder injection amount fic, and the fuel injection command shown in the flowcharts of FIGS. 4 and 5, and determining that the crank angle of each cylinder is before the intake top dead center. Each time a predetermined crank angle (for example, BTDC 90 ° CA) is reached, it is repeatedly executed for each cylinder.

  The fuel cut execution flag XFC used in the routine of FIG. 4 is set to “1” when the fuel cut execution condition is satisfied by a routine not shown separately, and when the fuel cut execution condition is not satisfied, “ "0" is set. The fuel cut execution condition is satisfied, for example, when the accelerator operation amount Accp is “0” and the operation speed NE is equal to or higher than a predetermined low speed. Hereinafter, first, a case where the fuel cut execution condition is not satisfied (that is, XFC = 0, refer to the time before time t1 in FIG. 6) will be described.

<When fuel cut execution condition is not satisfied>
When the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts the process from step 400 in FIG. 4 and proceeds to step 402, where the intake air of the cylinder that reaches the intake stroke using MapMc (NE, Ga). The in-cylinder intake air amount Mc that is the amount is obtained. Here, the current value measured by the air flow meter 61 is used as the value of the intake air flow rate Ga, and the current value obtained based on the output of the crank position sensor 63 is used as the value of the operating speed NE. Is used.

  Next, the CPU 71 proceeds to step 404, and multiplies the value obtained by dividing the obtained in-cylinder intake air flow rate Mc by the current target air-fuel ratio abyfr by a coefficient α to set the air-fuel ratio to the target air-fuel ratio abyfr. Obtain the required fuel amount Fbase. The coefficient α is a coefficient that is appropriately changed by air-fuel ratio feedback control or the like based on the output vabyfs of the air-fuel ratio sensor 65. This step 404 corresponds to the required fuel amount determining means.

  Next, the CPU 71 proceeds to step 406 and obtains the port injection ratio R (= fip / (fip + fic)) using MapR (THW, NE, Mc), and at the next step 408, MapPv (Pm, THW, NE) , VT) and MapRv (Pm, THW, NE, VT) are used to determine the residual rate Pv and the adhesion rate Rv, respectively. Here, as the intake pipe pressure Pm, the cooling water temperature THW, and the opening / closing timing VT of the intake valve 32, current values obtained from outputs of the pressure sensor 67, the water temperature sensor 64, and the cam position sensor 62 are used. .

  Subsequently, the CPU 71 proceeds to step 410 to determine whether or not the value of the fuel cut execution flag XFC is “1”. At this time, since the fuel cut execution condition is not satisfied, the CPU 71 makes a “No” determination at step 410 and proceeds to step 412 in FIG. 5 to determine the required fuel amount Fbase determined above and the above determined amount. A required port inflow fuel amount Fc (see FIG. 3) is obtained based on the port injection ratio R and the formula described in step 412.

  Next, the CPU 71 proceeds to step 414, where the required port inflow fuel amount Fc determined in step 412, the residual rate Pv and the deposition rate Rv determined in step 408, and the fuel deposition amount fw (k) The port injection amount fip is obtained based on the formula described in step 414. When the port injection amount fip is a negative value, the port injection amount fip is set to “0”. As the fuel adhesion amount fw (k), the latest value already updated in step 422, which will be described later, at the time of the previous execution of this routine is used.

  The equation described in step 414 is an equation representing an inverse model of the fuel behavior model. The inverse model of this fuel behavior model is the amount of fuel (1-Rv) / fip that flows into the cylinder without adhering to the intake passage components among the fuel injected into the port for the current intake stroke, and the intake air Calculated in step 412 in consideration of the amount (1-Pv) · fw (k) of fuel that flows into the cylinder out of the fuel adhering to the passage component (that is, the adhering inflow fuel amount). This is a model for calculating a port injection amount fip that is required to cause the required port inflow fuel amount Fc to flow into the cylinder.

  Next, the CPU 71 proceeds to step 416, determines the in-cylinder injection amount fic based on the calculated required fuel amount Fbase, the determined port injection ratio R, and the formula described in step 416, and the following step At 418, a command for injecting the fuel of the obtained port injection amount fip and in-cylinder injection amount fic at a predetermined timing is given to the port injection valve 39P and the in-cylinder injection valve 39C of the cylinder that reaches the intake stroke. For each. These steps 414 and 416 correspond to the injection amount determining means.

  Subsequently, the CPU 71 proceeds to step 420, and based on the residual rate Pv and the deposition rate Rv determined in step 408, the fuel deposition amount fw (k), and the above equation (1), Update fw (k + 1). Here, as the fuel adhesion amount fw (k), the latest value already updated in the next step 422 at the time of the previous execution of this routine is used as in step 414. That is, when the CPU 71 proceeds to step 422, it updates the value of fw (k) to the value of fw (k + 1) updated in step 420 when this routine is executed. This step 420 corresponds to the fuel adhesion amount estimation means.

  Then, the CPU 71 proceeds to step 595 and once ends this routine. As described above, when the fuel cut execution condition is not satisfied, the port fuel injection amount fip and the in-cylinder injection amount fic are set so that the total fuel amount combusted in the cylinder (Fc + fic) matches the required fuel amount Fbase. It will be decided. Thereby, the air-fuel ratio can be matched with the target air-fuel ratio abyfr. Thereafter, as long as the fuel cut execution condition is not satisfied, the CPU 71 repeatedly executes steps 400 to 410, 412 to 422, and 595 shown in FIGS. 4 and 5 in order.

<When fuel cut execution conditions are met>
Next, a case where the fuel cut execution condition is satisfied in this state (see time t1 in FIG. 6) will be described. In this case, the value of the fuel cut execution flag XFC is changed from “0” to “1”. Accordingly, when the CPU 71 proceeds to step 410, it determines “Yes”, proceeds to step 424, and determines whether or not the value of the fuel cut execution flag XFC has changed from “0” to “1”.

  Since the present time is immediately after the value of the fuel cut execution flag XFC is changed from “0” to “1”, the CPU 71 determines “Yes” in Step 424 and proceeds to Step 426 to proceed to Step 426 to determine the fuel adhesion amount fw ( It is determined whether the value of k) is larger than the second predetermined value fwlim2. Here, the second predetermined value fwlim2 is larger than a first predetermined value fwlim1 described later. As the fuel adhesion amount fw (k), the latest value updated in step 422 at the previous execution of this routine is used as in step 414 and the like. A case where the value of the fuel adhesion amount fw (k) is larger than the second predetermined value fwlim2 will be described later.

  Now, assuming that the value of the fuel adhesion amount fw (k) is equal to or smaller than the second predetermined value fwlim2, the CPU 71 makes a “No” determination at step 426 to proceed to step 428 of FIG. The amount fip is set to “0”, and in the next step 430, Mapfwlim1 (Tc, OSA) is used to determine the first predetermined value (small value) to be compared with the fuel adhesion amount fw (k) in the next step 432 determination. Value) Find fwlim1.

  As a result, the first predetermined value fwlim1 is determined to be smaller as the catalyst temperature Tc is higher, and to be smaller as the oxygen storage amount OSA of the catalyst 53 is smaller. Here, the current value obtained from the output of the catalyst temperature sensor 66 is used as the catalyst temperature Tc. As the oxygen storage amount OSA, the current value calculated by the following equations (2) and (3) is used.

ΔOSA = 0.23 ・ Fbase ・ (abyfs−stoich) (2)

OSA = ΣΔOSA (3)

  In the above equations (2) and (3), ΔOSA is an excess amount of oxygen (hereinafter referred to as “oxygen storage amount change”) contained in the gas discharged to the exhaust passage (and hence the gas flowing into the catalyst 53) in each combustion cycle. Referred to as “quantity”). The value “0.23” is the weight ratio of oxygen contained in the atmosphere. abyfs is the exhaust air-fuel ratio obtained from the output of the air-fuel ratio sensor 65, and stoich is the stoichiometric air-fuel ratio (for example, 14.7). As shown in the above equation (2), by multiplying the total amount of fuel combusted in the cylinder for each combustion cycle (that is, the required fuel amount Fbase) by the deviation (abyfs-stoich) from the theoretical air-fuel ratio, The excess amount of air flowing into the catalyst 53 is obtained for each combustion cycle, and the oxygen storage amount change amount ΔOSA is obtained by multiplying the excess amount of air by the value “0.23” which is the weight ratio of oxygen. Then, as shown in the above equation (3), the oxygen storage amount OSA of the catalyst 53 is calculated by accumulating ΔOSA for each combustion cycle.

  Further, when the value of the oxygen storage amount OSA of the catalyst 53 calculated as described above is less than “0”, OSA = 0, and on the other hand, the value of OSA is appropriately calculated by a routine not shown separately. If the maximum oxygen storage amount Cmax, which is the maximum allowable oxygen storage amount of the catalyst 53, is exceeded, OSA = Cmax. The above is the calculation method of the oxygen storage amount OSA of the catalyst 53.

  The first predetermined value fwlim1 is an exhaust passage in which fuel that departs from the intake passage constituting member and flows into the cylinder during each intake stroke when the port injection is stopped (fip = 0) (that is, the attached inflow fuel) is unburned fuel. The amount of fuel adhering to the inflow is such that the deterioration of the catalyst 53 is promoted due to an excessive increase in the catalyst temperature Tc, and that unburned fuel can be sufficiently prevented from being discharged from the catalyst 53 as it is. This is a value of the fuel adhesion amount fw (k) for making (1−Pv) · fw (k) ”(see FIG. 3) a small value, and is a value obtained through experiments and simulations.

  Subsequently, the CPU 71 proceeds to step 432, and determines whether or not the value of the fuel adhesion amount fw (k) is equal to or less than the first predetermined value fwlim1 obtained above. As the fuel adhesion amount fw (k), the latest value already updated in step 422 at the previous execution of this routine is used. Now, if the description is continued assuming that “fw (k)> fwlim1” (see time t1 in FIG. 6), the CPU 71 determines “No” and proceeds to step 434 to determine the required fuel amount obtained above. The in-cylinder injection amount fic is determined based on Fbase, the determined residual rate Pv, the fuel adhesion amount fw (k), and the formula described in step 434. That is, the in-cylinder injection amount fic is set to a value obtained by subtracting the adhering inflow fuel amount (1-Pv) · fw (k) from the required fuel amount Fbase. Then, the CPU 71 executes the processes of steps 418 to 422 in order, and then proceeds to step 595 to end the present routine tentatively.

  Thereby, since the port injection amount fip is set to “0”, the stop of the port injection is started (see after time t1 in FIG. 6). However, misfire does not occur due to the continuation of the in-cylinder injection of the fuel of the obtained in-cylinder injection amount fic. Therefore, it is possible to prevent the adhering inflow fuel from being discharged to the exhaust passage as unburned fuel. In addition, the sum of the adhering inflow fuel amount (1−Pv) · fw (k) and the in-cylinder injection amount fic (= Fbase− (1−Pv) · fw (k)) (that is, the required fuel amount Fbase) Since this fuel is combusted in the cylinder, the air-fuel ratio can be matched with the target air-fuel ratio abyfr.

  Thereafter, as long as “fw (k)> fwlim1” (see times t1 to t2 in FIG. 6), the CPU 71 performs steps 400 to 410, 424, 428 to 432, 434 shown in FIG. 4 and FIG. , 418 to 422, 595 are repeatedly executed in order. Thereby, in-cylinder injection is continued. During this period, since the port injection amount fip is set to “0”, the fuel adhesion amount fw (k + 1) (fw (k)) updated in step 420 in FIG. 5 becomes smaller for each intake stroke. .

  Thereafter, when the fuel adhesion amount fw (k), which is updated to a smaller value for each intake stroke, becomes equal to or smaller than the first predetermined value fwlim1 (see time t2 in FIG. 6), the CPU 71 proceeds to step 432 in FIG. At this time, it is determined as “Yes” and the routine proceeds to step 436 where the in-cylinder injection amount fic is set to “0”. Thereby, the stop of in-cylinder injection is started. That is, fuel cut is started. These steps 428 to 432, 436 correspond to the fuel cut means.

  Thereafter, as long as the fuel cut execution condition is satisfied (XFC = 1) (see times t2 to t3 in FIG. 6), the CPU 71 performs steps 400 to 410, 424, 428 to 432, 436, 418 to 422,595. Are repeatedly executed in order. Thereby, fuel cut is continued.

  After the fuel cut is started in this way, the fuel supplied into the cylinder becomes only the attached inflow fuel and misfire occurs. In other words, the adhering inflow fuel is discharged into the exhaust passage as unburned fuel. However, after this time, the fuel adhesion amount fw is equal to or less than the first predetermined value fwlim1 described above. Therefore, even if the adhering inflow fuel amount (1-Pv) · fw (k) is sufficiently small and the adhering inflow fuel is discharged to the exhaust passage as unburned fuel, the catalyst temperature Tc is excessively increased. It is possible to suppress the deterioration of 53 and to prevent the unburned fuel from being discharged from the catalyst 53 as it is.

  In addition, as described above, since the first predetermined value fwlim1 is determined to be smaller as the catalyst temperature Tc is higher, the fuel adhesion amount fw (k) after the fuel cut is started (that is, The amount of attached inflow fuel (1-Pv) · fw (k)) also becomes smaller as the catalyst temperature Tc is higher. Therefore, the higher the catalyst temperature Tc, the smaller the amount of unburned fuel that flows into the catalyst 53. Therefore, even if the catalyst temperature Tc is high, the catalyst 53 is excessively high, so that the catalyst It can be suppressed that the deterioration of the is accelerated. Further, the first predetermined value fwlim1 is determined to be smaller as the oxygen storage amount OSA of the catalyst 53 is smaller. Therefore, even when the oxygen storage amount OSA of the catalyst 53 is small, the unburned fuel can be suppressed from being discharged from the catalyst 53 as it is.

  When the fuel cut execution condition is not satisfied (see time t3 in FIG. 6), the value of the fuel cut execution flag XFC is changed from “1” to “0”. Accordingly, the CPU 71 thereafter determines “No” when it proceeds to step 410, and again executes the processing of steps 412 to 416. Thereby, the fuel injection control of the port injection amount fip and the in-cylinder injection amount fic corresponding to the port injection ratio R obtained in step 406 is resumed.

<Throttle valve opening delay processing>
Finally, the delay process of the throttle valve opening TA will be described. As described above, the throttle valve actuator 43a is controlled by a routine (not shown) so that the throttle valve opening TA basically matches the target throttle valve opening TAt obtained using the table MapTAt (Accp). ing.

  Now, the fuel cut execution condition is satisfied when the accelerator operation amount Accp suddenly changes from a value larger than “0” to “0” in a state where the fuel adhesion amount fw (k) is larger than the second predetermined value fwlim2. (XFC value is changed from “0” to “1”). In this case, when the CPU 71 proceeds to step 410, it determines “Yes” and proceeds to step 424. After determining “Yes”, the fuel adhesion amount fw (k) is determined from the second predetermined value fwlim2 in subsequent step 426. It is also determined whether or not the

  At present, the fuel adhesion amount fw (k) is larger than the second predetermined value fwlim2. Therefore, the CPU 71 makes a “Yes” determination at step 426 to proceed to step 438, and the CPU 71 determines that the throttle valve opening degree TA is equal to the above only while the fuel cut execution condition is satisfied (during XFC = 1). Instruct the throttle valve actuator 43a to match the target throttle valve opening TAt obtained by performing the delay process of the delay period T1 instead of the target throttle valve opening TAt obtained using the table MapTAt (Accp). Then, the processing after step 428 in FIG. 5 is executed.

  As a result, when the fuel adhesion amount fw (k) at the time when the fuel cut execution condition is satisfied is large (fw (k)> fwlim2), the throttle valve opening is delayed by the delay period T1 from the time when the fuel cut execution condition is satisfied. Degree TA decreases rapidly. In other words, during the delay period T1 from the time when the fuel cut execution condition is satisfied, the rapid decrease in the throttle valve opening TA (and hence the rapid decrease in the intake pipe pressure Pm) can be avoided. It can be avoided that (k) evaporates rapidly. That is, an increase in the estimation error of the attached inflow fuel amount (1-Pv) · fw (k) can be avoided.

  In addition, since the port injection amount fip is maintained at “0”, the fuel adhesion amount fw (k + 1) (fw (k)) updated in step 420 in FIG. It gets smaller with each stroke. Therefore, since the fuel adhesion amount fw (k) is sufficiently small at the time when the delay period T1 has elapsed from the time when the fuel cut execution condition is satisfied, it occurs when the throttle valve opening TA rapidly decreases at that time. The error of the adhering inflow fuel amount (1-Pv) · fw (k) can be reduced. As described above, the in-cylinder obtained based on the attached inflow fuel amount (1-Pv) · fw (k) during the in-cylinder injection after the fuel cut execution condition is satisfied (see times t1 to t2 in FIG. 6). It is possible to avoid a situation in which it is difficult to accurately determine the injection amount fic (see step 434) to a value for making the air-fuel ratio coincide with the target air-fuel ratio abyfr.

  As described above, according to the embodiment of the fuel injection control device for an internal combustion engine according to the present invention, when the fuel cut execution condition is not satisfied, the port injection amount fip and the in-cylinder injection amount fic are Is determined in accordance with the port injection ratio R so that the total amount of fuel combusted in step 1 matches the required fuel amount Fbase. As a result, the air-fuel ratio can be matched with the target air-fuel ratio abyfr.

  On the other hand, when the fuel cut execution condition is satisfied, first, the port injection is stopped, and during the period from when the port injection is stopped until the fuel adhesion amount fw (k) becomes equal to or less than the first predetermined value fwlim1 In-cylinder injection of fuel with an injection amount fic is continued. Thereby, misfire can be avoided during the period, and the adhering inflow fuel can be prevented from being discharged into the exhaust passage as unburned fuel. Further, during the above period, the in-cylinder injection amount fic is determined to be an amount obtained by subtracting the attached inflow fuel amount from the required fuel amount Fbase. As a result, the air-fuel ratio can be matched with the target air-fuel ratio abyfr.

  When the fuel adhesion amount fw (k) that gradually decreases after the port injection stops becomes equal to or less than the first predetermined value fwlim1, the in-cylinder injection is also stopped (that is, the fuel cut is started). Therefore, after that, the fuel supplied into the cylinder becomes only the adhering inflow fuel and misfire occurs, and the adhering inflow fuel is discharged to the exhaust passage as unburned fuel. However, the attached inflow fuel amount (1-Pv) · fw (k) after this point is sufficiently small. Therefore, even if the adhering inflow fuel is discharged to the exhaust passage as unburned fuel, deterioration of the catalyst 53 is promoted due to excessive increase in the catalyst temperature Tc, and unburned fuel is discharged from the catalyst 53 as it is. Can be suppressed.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above embodiment, the first predetermined value fwlim1 is obtained using the catalyst temperature Tc, the oxygen storage amount OSA of the catalyst 53, and the table Mapfwlim1 using Tc and OSA as arguments. fwlim1 may be a constant value. As a result, it is not necessary to perform a table search for obtaining the first predetermined value fwlim1, and the calculation load on the CPU 71 can be reduced. In this case, it is desirable that the value of the first predetermined value fwlim1 be a minimum value that can be taken by the table Mapfwlim1 in order to reliably suppress the amount of unburned fuel discharged to the exhaust passage.

  Further, in the above embodiment, when the delay process of the throttle valve opening TA is performed, the delay period T1 is configured to be a constant time, but the delay period T1 is set at the time when the fuel cut execution condition is satisfied. The fuel adhering amount fw (k) may be changed. According to this, the delay period T1 is set longer as the fuel adhesion amount fw (k) is larger, so that the fuel adhesion amount fw (k) after the delay period T1 elapses from the time when the fuel cut execution condition is satisfied. Can be small. In other words, the delay period T1 can be appropriately set by the above configuration.

  In the above embodiment, the delay process is performed as the delay process of the throttle valve opening degree TA. However, a first-order lag process with a time constant T2 may be performed. According to this, it is possible to avoid a sudden change (decrease) in the throttle valve opening TA after the fuel cut execution condition is satisfied, and hence a sudden change in the intake pipe pressure Pm can be avoided (that is, adhering to the intake passage constituting member). The fuel that is being used can be prevented from evaporating rapidly). Accordingly, an increase in the error of the adhering inflow fuel amount can be avoided, so that the in-cylinder injection amount fic is matched with the target air-fuel ratio abyfr while the in-cylinder injection is continued after the fuel cut execution condition is satisfied. Can be accurately determined. Here, the time constant T2 may be a constant value, or may be configured to be set according to the fuel adhesion amount fw (k).

  In the above embodiment, the port injection is stopped immediately after the fuel cut execution condition is satisfied. However, the port injection is stopped after a predetermined time has elapsed after the fuel cut execution condition is satisfied. You may comprise.

  In addition, in the above embodiment, the port injection ratio R (= fip / (fip + fic)) is adopted as the injection ratio, but the in-cylinder injection ratio (fic / (fip + fic)) ) May be adopted. Further, the value “fip / fic” or the value “fic / fip” may be adopted as the injection ratio.

1 is a schematic configuration diagram of a system in which a fuel injection control device according to an embodiment of the present invention is applied to a spark ignition type multi-cylinder internal combustion engine. It is the figure which showed notionally the mode that the fuel injected from the port injection valve adheres to an intake passage structural member. The amount of fuel injected from the port injection valve (port injection amount), the amount of fuel adhering to the intake passage component (fuel adhering amount), the amount of fuel flowing into the cylinder (necessary port inflow fuel amount), It is a figure for demonstrating the relationship of these. 3 is a flowchart showing a first half of a program for determining a port injection amount and in-cylinder injection amount and for executing port injection and in-cylinder injection, which is executed by the CPU shown in FIG. 1. 3 is a flowchart illustrating a second half of a program for determining a port injection amount and in-cylinder injection amount, and for executing port injection and in-cylinder injection, which is executed by the CPU shown in FIG. 1. 6 is a time chart showing an example of changes in the value of a fuel cut execution flag, a port injection amount, an in-cylinder injection amount, and a fuel adhesion amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Spark ignition type multi-cylinder internal combustion engine, 25 ... Combustion chamber, 39C ... In-cylinder injection valve, 39P ... Port injection valve, 41 ... Intake pipe, 43 ... Throttle valve, 53 ... Catalyst, 70 ... Electric control device, 71 ... CPU

Claims (5)

Port injection means for injecting fuel into the intake passage upstream of the intake valve of the internal combustion engine;
In-cylinder injection means for injecting fuel into the combustion chamber;
Applied to an internal combustion engine with
An injection amount determining means for determining a port injection amount that is an amount of fuel injected from the port injection means and an in-cylinder injection amount that is an amount of fuel injected from the in-cylinder injection means;
Fuel cut means for stopping injection by the port injection means and injection by the in-cylinder injection means when a fuel cut execution condition, which is a condition for stopping fuel supply into the combustion chamber, is established;
In a fuel injection control device for an internal combustion engine comprising:
A fuel adhesion amount estimating means for estimating a fuel adhesion amount that is an amount of fuel adhering to a member constituting the intake passage by injection by the port injection means;
The fuel cut means is
After the fuel cut execution condition is satisfied, first, the injection by the port injection unit is stopped, and the injection by the in-cylinder injection unit is stopped after a predetermined period has elapsed since the injection by the port injection unit was stopped. is configured to,
The fuel cut means, as the predetermined period,
It is configured to use a period from when the injection by the port injection means is stopped until the fuel adhesion amount becomes a first predetermined value or less,
The fuel cut means is
A fuel injection control device for an internal combustion engine configured to determine the first predetermined value to be smaller as the oxygen storage amount of the catalyst provided in the exhaust passage of the internal combustion engine is smaller . A fuel injection control device for an internal combustion engine according to claim 1 ,
A required fuel amount determining means for determining a required fuel amount that is an amount of fuel to be burned in the combustion chamber in order to make the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine coincide with the target air-fuel ratio;
The injection amount determining means includes
A fuel injection control device for an internal combustion engine configured to determine the in-cylinder injection amount based on the required fuel amount and the fuel adhesion amount during the predetermined period. The fuel injection control device for an internal combustion engine according to claim 2 ,
The injection amount determining means includes
During the predetermined period, the in-cylinder injection amount is determined from the required fuel amount, and the amount of fuel flowing out of the member constituting the intake passage calculated based on the fuel adhesion amount and flowing into the combustion chamber is determined. An internal combustion engine fuel injection control device configured to determine a reduced value. A fuel injection control device for an internal combustion engine according to claim 3 ,
The internal combustion engine includes a throttle valve for adjusting an opening cross-sectional area of the intake passage,
Throttle valve control means for controlling the opening cross-sectional area of the throttle valve to a value according to the operating state of the internal combustion engine,
The throttle valve control means includes
When the fuel adhesion amount at the time when the fuel cut execution condition is satisfied exceeds a second predetermined value that is larger than the first predetermined value, an opening cross-sectional area of the throttle valve after the fuel cut execution condition is satisfied A fuel injection control device for an internal combustion engine configured to control a value obtained by performing a delay process on a value corresponding to the operating state of the internal combustion engine instead of a value corresponding to the operating state of the internal combustion engine. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 4 ,
The fuel cut means is
A fuel injection control device for an internal combustion engine configured to determine the first predetermined value to be a smaller value as a temperature of a catalyst provided in an exhaust passage of the internal combustion engine is higher.

Images