JP5477498B2 - Control device for internal combustion engine - Google Patents

Description

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

  Under the conditions before the warm-up is completed, such as when the engine is started, the air-fuel ratio is leaner than the stoichiometric mixture in the entire combustion chamber by the fuel injection in the intake stroke, and the fuel is injected into the combustion chamber in the compression stroke. There is known a direct injection internal combustion engine in which an air-fuel ratio is formed around a spark plug and an air-fuel ratio is richer than stoichiometric, and stratified combustion is performed to increase the exhaust gas temperature (Patent Document 1).

  In this internal combustion engine, air-fuel ratio feedback control is performed in which the average air-fuel ratio in the combustion chamber is stoichiometrically corrected by increasing and decreasing both the fuel injection amount during the intake stroke and the fuel injection amount during the compression stroke using a feedback correction coefficient. Is called.

JP 2001-82220 A

  However, the conventional control method for an internal combustion engine has a problem that a torque step is generated because the fuel injection amount during the compression stroke with high torque sensitivity is also corrected.

  The problem to be solved by the present invention is to provide a control device for an internal combustion engine that can suppress the occurrence of a torque step.

  The present invention sets the injection amount of the first injection so that the air-fuel mixture in the combustion chamber becomes the target air-fuel ratio in a state where the change amount per unit time of the injection amount of the second injection performed in the compression stroke is zero. After executing the control step, the above problem is solved by executing the step of correcting the injection amount of the second injection so that the injection amount ratio of the first injection and the second injection becomes the target injection amount ratio.

  According to the present invention, after controlling the injection amount of the first injection in a state where the change amount per unit time of the injection amount of the second injection having high torque sensitivity is zero, the injection of the first injection and the second injection Since the injection amount of the second injection is corrected so that the amount ratio becomes the target injection amount ratio, occurrence of a torque step can be suppressed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in the case where the present invention is applied to a control device for an internal combustion engine will be described below with reference to the drawings. In addition, the internal combustion engine system common to 1st Embodiment-3rd Embodiment mentioned later is demonstrated first, and each embodiment is described after that.

  FIG. 1 is a block diagram showing an embodiment of a control device for an internal combustion engine according to the present invention. In an intake passage 11 of the internal combustion engine 1, an air filter 12, an air flow meter 13 for detecting an intake air flow rate Qa, A throttle valve 14 and an intake manifold 15 for controlling the intake air flow rate Qa are provided.

  The throttle valve 14 is provided with a throttle valve control device 31 that can control the opening degree of the throttle valve 14 by an actuator such as a DC motor. The throttle valve control device 31 electronically controls the opening degree of the throttle valve 14 based on the drive signal from the control unit 50 so as to achieve the required torque calculated based on the driver's accelerator pedal operation amount and the like.

  Further, a fuel injection valve 17 is provided facing the combustion chamber 16 of each cylinder of the internal combustion engine 1. The fuel injection valve 17 is driven to open by a drive pulse signal set in a control unit 50 to be described later, and fuel that is pumped from the fuel pump 18 and controlled to a predetermined pressure by the pressure regulator 19 is directly injected into the combustion chamber 16. To do.

  The spark plug 20 is mounted facing the combustion chamber 16 of each cylinder, and ignites the intake air-fuel mixture based on an ignition signal from the control unit 50.

  On the other hand, the exhaust passage 21 is provided with an air-fuel ratio sensor 22 that detects exhaust gas by detecting a specific component in the exhaust gas, for example, oxygen concentration, and thus the air-fuel ratio of the intake air-fuel mixture, and the detection signal is sent to the control unit 50. Is output. The air-fuel ratio sensor 22 may be an oxygen sensor that performs rich / lean output, or a wide-area air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide area.

  The exhaust passage 21 is provided with an exhaust purification catalyst 24 for purifying the exhaust. The exhaust purification catalyst 24 oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust in the vicinity of stoichiometric (theoretical air-fuel ratio, λ = 1, air weight / fuel weight = 14.7), and nitrogen oxide NOx. It is possible to use a three-way catalyst that can purify the exhaust gas by reducing the above, or an oxidation catalyst that oxidizes carbon monoxide CO and hydrocarbon HC in the exhaust gas.

  On the downstream side of the exhaust purification catalyst 24 in the exhaust passage 21, there is provided a downstream oxygen sensor 25 that detects a specific component in the exhaust gas, for example, oxygen concentration, and performs rich and lean output, and the detection signal is output to the control unit 50. Is done. Here, in order to suppress a control error associated with deterioration of the air-fuel ratio sensor 22 or the like by correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 22 based on the detection value of the downstream oxygen sensor 25. Although the downstream oxygen sensor 25 is provided (in order to adopt a so-called double air-fuel ratio sensor system), if the air-fuel ratio feedback control based on the detected value of the air-fuel ratio sensor 22 only needs to be performed, the downstream side oxygen sensor 25 is provided. The oxygen sensor 25 can be omitted.

  The crankshaft 26 of the internal combustion engine 1 is provided with a crank angle sensor 27, and the control unit 50 counts a crank unit angle signal output from the crank angle sensor 27 in synchronization with the engine rotation for a predetermined time, or By measuring the cycle of the crank reference angle signal, the engine speed Ne can be detected.

  The cooling jacket 28 of the internal combustion engine 1 is provided with a water temperature sensor 29 facing the cooling jacket 28, detects the cooling water temperature Tw in the cooling jacket 28, and outputs it to the control unit 50.

  Further, a throttle sensor 30 for detecting the opening of the throttle valve 14 is provided, and the detection signal is output to the control unit 50. The throttle sensor 30 can also function as an idle switch.

  In FIG. 1, 32 is a muffler.

  As described above, the detection signals from the various sensors 13, 22, 25, 27, 29, and 30 include a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The control unit 50 controls the opening degree of the throttle valve 14 via the throttle valve control device 31 according to the operation state detected based on the signals from the sensors. The fuel injection valve 17 is driven to control the fuel injection amount, the ignition timing is set, and the ignition plug 20 is ignited at the ignition timing.

  In a predetermined operation state such as a low / medium load region, fuel is injected into the combustion chamber 16 during the compression stroke, and a flammable air-fuel mixture is formed in the vicinity of the spark plug 20 in the combustion chamber 16 to form a stratified combustion. On the other hand, in other operating conditions such as a high load region, the fuel is injected into the combustion chamber 16 during the intake stroke to form an air-fuel mixture having a substantially uniform mixing ratio over the entire cylinder, thereby performing homogeneous combustion. As can be done, the fuel injection timing can also be changed according to the operating state.

  The fuel injection valve 17 corresponds to the fuel injection means of the present invention, and the control unit 50 corresponds to the control means of the present invention.

  Now, the control unit 50 according to the present embodiment activates the exhaust purification catalyst 24 at an early stage while suppressing the emission of hydrocarbons HC to the atmosphere between the start of starting and the activation of the exhaust purification catalyst 24. In order to achieve the above, input signals from various sensors such as the key switch 33 are received, and for example, the following control is executed. In this example, when the stratified combustion for raising the exhaust gas temperature is performed, the average air-fuel ratio in the combustion chamber 16 is almost stoichiometric, and this combustion mode is called stratified stoichiometric combustion. However, the average air-fuel ratio in the combustion chamber 16 may be an air-fuel mixture that is leaner than stoichiometric.

  FIG. 2 is a cross-sectional view showing a state of the first injection performed in the intake stroke in the stratified stoichiometric combustion stroke, and FIG. 3 is a cross-sectional view showing a state of the second injection performed in the compression stroke in the stratified stoichiometric combustion stroke. 4 is a cross-sectional view showing a state immediately before ignition after the first injection and the second injection are performed in the stratified stoichiometric combustion stroke.

  That is, the stratified stoichiometric combustion according to the present example is, for example, of the total fuel amount that can be almost completely combusted with the intake air amount per combustion cycle, in other words, out of the fuel weight necessary to achieve almost stoichiometric, for example, A fuel weight of about 50% to about 90% is injected into the combustion chamber 16 in the intake stroke (corresponding to the first injection of the present invention) as shown in FIG. A relatively lean homogeneous mixture is formed and the remaining fuel weight of about 50% to about 10% is injected into the combustion chamber 16 in the compression stroke as shown in FIG. 3 (in the second injection of the present invention). The air-fuel mixture that is relatively richer than the stoichiometric gas is layered around the spark plug 20 and burned by ignition after compression top dead center (see FIG. 4).

  In place of this, this stratified stoichiometric combustion mode sets the air-fuel ratio of the air-fuel mixture leaner than stoichiometric (A / F = 14.7) formed in the combustion chamber 16 during the intake stroke to 16 to 28, The fuel injection amount during the intake stroke and the fuel injection during the compression stroke are set so that the air-fuel ratio of the air-fuel mixture richer than the stoichiometry formed around the spark plug 20 by the fuel injection during the compression stroke becomes 9-13. A ratio to the amount (hereinafter referred to as a division ratio) may be set. Further, the first injection may be injected in the first half of the compression stroke, or the second injection may be injected in the expansion stroke before the ignition timing.

  Then, based on the detection value of the air-fuel ratio sensor 22 and further the downstream oxygen sensor 25 so that the average air-fuel ratio in the combustion chamber 16 becomes stoichiometric while the air-fuel ratio of each air-fuel mixture is in the above range. Then, air-fuel ratio feedback control is performed.

  According to such stratified stoichiometric combustion, it is possible not only to raise the exhaust gas temperature but also to reduce the amount of unburned hydrocarbon HC discharged from the combustion chamber 16 to the exhaust passage 21 as compared with the conventional homogeneous stoichiometric combustion. Can do.

  That is, according to the stratified stoichiometric combustion, the conventional combustion mode, that is, only the homogeneous combustion, only the stratified combustion, or further, additional fuel is injected after the later combustion stage (after the expansion stroke after the ignition timing or during the exhaust stroke). Compared to the case where the engine is warmed up in a combustion mode or the like, the exhaust purification catalyst 24 is activated early while suppressing the emission of HC into the atmosphere between the start of start and the activation of the exhaust purification catalyst 24. Can be promoted.

  Next, the control until the start of stratified stoichiometric combustion according to this example and the control of the stratified stoichiometric combustion will be described based on the flowcharts shown in FIGS.

  FIG. 5 is a flowchart showing a control procedure from the start of the internal combustion engine in a cold state until the exhaust purification catalyst 24 reaches the activation temperature and performs steady combustion, and FIG. 6 is a flowchart showing a subroutine of step S7 in FIG. is there. Up to this point, the control procedure is common to the first embodiment and the second embodiment.

  First, in step S1 of FIG. 5, it is determined whether or not the ignition signal of the key switch 33 is turned on. If it is turned on, the process proceeds to step S2, and if it is turned off, this flow is terminated. In the subsequent step S2, it is determined whether or not the start signal of the key switch 33 is turned on. That is, it is determined whether or not there is a cranking request by the starter motor. If the start signal is ON, it is determined that there is a start cranking request and the process proceeds to step S3. Then, the process returns to step D1. In step S3, the starter motor is started to crank the internal combustion engine 1.

  In step S4, the internal combustion engine 1 is operated by performing fuel injection for starting. In this step S4, for example, direct fuel injection in the intake stroke shown in FIG. 2 is performed (direct injection homogeneous combustion), and the internal combustion engine 1 is started. Alternatively, stratified stoichiometric combustion (step S7) can be performed from the beginning of the internal combustion engine 1.

  In the next step S5, it is determined whether or not the exhaust purification catalyst 24 has reached the activation temperature. This determination can be made by directly detecting the temperature or outlet temperature of the exhaust purification catalyst 24 with a temperature sensor. In this example, the downstream oxygen sensor 25 provided facing the exhaust passage 21 is activated. It is substituted by judging whether or not it has become. That is, whether or not the exhaust purification catalyst 24 is activated is determined based on the change in the detection value number of the downstream oxygen sensor 25.

  Alternatively, the engine water temperature is detected by the water temperature sensor 29 or the oil temperature of the engine oil is detected by the oil temperature sensor to estimate the temperature of the exhaust purification catalyst 24 or the outlet temperature, and the exhaust purification is performed based on the result. The activation of the catalyst 24 can also be determined.

  If the temperature of the exhaust purification catalyst 24 is lower than the activation temperature and inactive, the process proceeds to step S6. On the other hand, when the exhaust purification catalyst 24 is activated higher than the activation temperature as in the case where the internal combustion engine 1 is restarted, control for accelerating the activation of the catalyst is not necessary, so that the process proceeds to step S9 and fuel consumption is increased. For improvement and the like, combustion is performed in the same combustion mode as in the past according to the operation state, and this flow is finished.

  If the exhaust purification catalyst 24 is inactive, it is determined in step S6 whether a condition for permitting transition to stratified stoichiometric combustion is satisfied. Specifically, even if the temperature state of the combustion chamber 16 is estimated and the combustion chamber temperature becomes equal to or higher than a predetermined temperature and stratified stoichiometric combustion is performed to promote catalyst activation or the like, good ignitability, combustibility, and elongation are achieved. If it is determined that engine stability (engine operability) or the like is obtained, it is determined that the condition for permitting transition to stratified stoichiometric combustion is satisfied.

  If the determination in step S6 is YES, it is assumed that even if stratified stoichiometric combustion for promoting catalyst activation, which will be described later, is performed, good ignitability, combustibility, and engine stability are obtained. Proceed to S7.

  On the other hand, when the determination in step S6 is NO, if stratified stoichiometric combustion for promoting catalyst activation described later is performed, the temperature of the combustion chamber is lower than a predetermined value, so that the stratified mixture is atomized.・ Vaporization promotion etc. will not be performed well, and this may reduce ignitability, combustion stability and eventually engine stability, etc., prohibiting the transition to stratified stoichiometric combustion, and in the intake stroke In order to continue the direct fuel injection (direct injection homogeneous combustion), the process returns to step S4.

  When the permission condition for the stratified stoichiometric combustion in step S6 is satisfied, that is, when the catalyst is not activated, the catalyst activation needs to be promoted, and the combustion chamber temperature is equal to or higher than the predetermined temperature, so that the stratified mixture is generated well. If yes, in step S7, the shift to the stratified stoichiometric combustion for promoting the catalyst activation is permitted and the stratified stoichiometric combustion is performed. Details of the stratified stoichiometric combustion will be described later.

  Next, in step S8, similarly to step S5, it is determined whether the exhaust purification catalyst 24 has been activated, that is, whether warm-up has been completed. If the exhaust purification catalyst 24 is activated, the process proceeds to step S9, and if not activated, the process returns to step S7, and stratified stoichiometric combustion is continued until the exhaust purification catalyst 24 is activated.

  In step S9, after shifting to a combustion mode that can achieve desired exhaust performance, fuel efficiency performance, driving performance (output performance, stability, etc.) or the like according to the operating state, this flow is ended. Examples of the combustion mode in this case include homogeneous stoichiometric combustion, homogeneous lean combustion, and stratified lean combustion.

  Next, the fuel injection amount control during the stratified stoichiometric combustion in step S7 will be described with reference to FIGS. FIG. 9 is a time chart showing temporal displacements of the first injection performed in the intake stroke and the second injection performed in the compression stroke.

  First, the stratified stoichiometric combustion of this example is the second injection while performing the fuel injection in the intake stroke, which is the first injection, at the predetermined fuel injection amount V1 in order to ensure the stability at the start of the control. Fuel injection in the compression stroke is performed with a predetermined fuel injection amount V2 (step S71). These initial fuel injection amounts V1 and V2 are fixed values, and the fuel injection amount ratio V1 / V2 is preferably set to be an appropriate division ratio (injection amount ratio) according to the internal combustion engine 1. . The stratified stoichiometric combustion with the fixed fuel injection amounts V1 and V2 corresponds to the first step of the present invention, and is continued until permission of air-fuel ratio feedback control is established in step S72. The conditions for establishing the air-fuel ratio feedback control in step S72 are not particularly limited, but can be defined by elapse of a predetermined time during which the air-fuel ratio sensor 22 is activated.

  When the air-fuel ratio feedback control is permitted, the process proceeds to step S73, and the process proceeds to the air-fuel ratio feedback control which is the second step of the present invention. In step S 73, the basic fuel injection amount Tp is calculated by Equation 1 from the intake air flow rate Qa obtained from the output signal of the air flow meter 13 and the engine speed Ne obtained from the output signal of the crank angle sensor 27.

[Formula 1] Tp = c × Qa / Ne (c is a constant)
In the next step S74, a water temperature correction coefficient Kw for correcting the basic fuel injection amount Tp calculated in step S73 to the rich side for engine stability at a low water temperature, an increase correction coefficient Kas after starting and starting, etc. Using various correction coefficients COEF included, correction is made as shown in Equation 2 to calculate the effective fuel injection amount CTi.

[Formula 2] CTi = Tp × COEF
In the next step S75, the effective fuel injection amount CTi (HB) in the intake stroke that is the first injection is set by Equation 3 using the division ratio (injection amount ratio) Ksp.

[Formula 3] CTi (HB) = CTi × Ksp
Here, the division ratio Ksp is a total fuel injection amount (= CTiH + CTiS) obtained by summing the fuel injection amount CTiH in the intake stroke as the first injection and the fuel injection amount CTiS in the compression stroke as the second injection. It is set as a ratio of the fuel injection amount CTiH in the intake stroke. Therefore, the division ratio of the fuel injection amount CTiS in the compression stroke that is the second injection to the total fuel injection amount is 1-Ksp. The division ratio Ksp may be a fixed value or may be variably set according to the operating state. In the following description, the division ratio Ksp is a fixed value.

  In step S76, the effective fuel injection amount CTi (SB) in the compression stroke that is the second injection is set according to the equation 4 as described above.

[Formula 4] CTi (SB) = CTi × (1−Ksp)
In the next step S77, whether or not the effective fuel injection amount CTi (SB) in the compression stroke, which is the second injection with the smaller fuel injection amount, is equal to or greater than the minimum injection amount TImin that can be injected by the fuel injection valve 17. Determine. When the fuel injection amount of the effective fuel injection amount CTi (HB) in the intake stroke as the first injection is smaller, it is determined whether or not this value CTi (HB) is equal to or greater than the minimum injection amount TImin. To do.

  If it is determined in step S77 that the injection amount is less than the minimum injection amount TImin, it is determined that fuel injection in the compression stroke cannot be substantially performed, and normal stratified stoichiometric combustion cannot be performed, and the routine proceeds to step S78 to stop stratified stoichiometric combustion. Then, switch to another combustion.

  On the other hand, when it is determined in step S77 that the fuel injection amount is not less than the minimum injection amount TImin, the process proceeds to step S79, where the air-fuel ratio detection result of the air-fuel ratio sensor 22 provided upstream of the exhaust purification catalyst 24 is determined. The fuel ratio feedback correction coefficient α is set to be increased or decreased by proportional integral (PI) control or the like.

  In step S80, the effective fuel injection amount CTi (HB) in the intake stroke as the first injection is corrected by the air-fuel ratio feedback correction coefficient α set in step S79, and the fuel injection amount in the final intake stroke is corrected. CTiH is calculated by Equation 5.

  As will be described later, since the amount of change per unit time is limited for the fuel injection amount in the compression stroke that is the second injection, a feedback gain for the fuel injection amount in the intake stroke that is the first injection is set. It is desirable to make it larger than usual to shorten the convergence time to stoichiometry.

[Formula 5] CTiH = CTi (HB) × α
In step S81, the fuel injection amount CTiS in the final compression stroke is calculated by Equation 6.

  Here, from the viewpoint of torque sensitivity regarding the first injection and the second injection, the injection amount of the second injection has higher torque sensitivity than the injection amount of the first injection. That is, when the amount of change per unit time of the injection amount of the second injection is large, the torque level difference experienced is also relatively large compared to the first injection. In order to suppress this torque step, in the present invention, the amount of change per unit time of the injection amount of the second injection is limited.

<< First Embodiment >>
FIG. 7 shows a control procedure according to the first embodiment for limiting the amount of change per unit time of the injection amount of the second injection. FIG. 7 is a flowchart showing a subroutine of step S81 in FIG.

  In step S811 of this example, the effective fuel injection amount CTi (SB) in the compression stroke that is the second injection is corrected by the air-fuel ratio feedback correction coefficient α, and the fuel injection amount CTiS in the final compression stroke is calculated by the equation. 6 is calculated.

[Formula 6] CTiS = CTi (SB) × α
In the next step S812, the fuel injection amount CTiSn calculated in step S811 is compared with the previous fuel injection amount CTiSn-1 to calculate the injection amount change amount ΔCTiS per unit time.

  In step S813, it is determined whether or not the change amount ΔCTiS of the injection amount per unit time calculated in step S812 is greater than a predetermined value K1, and the change amount ΔCTiS is equal to or less than the predetermined value K1. In this case, the process proceeds to step S815, and the second injection is performed with the injection amount CTiS calculated in step S811.

  On the other hand, if it is determined in step S813 that the change amount ΔCTiS is greater than the predetermined value K1, the process proceeds to step S814.

  In step S814, the change amount ΔCTiS of the injection amount of the second injection exceeds the predetermined value K1, and the second injection is performed with an injection amount that is limited to the predetermined value K1. That is, in the second injection, no matter how the change amount ΔCTiS per unit time varies, the maximum injection amount of the second injection is determined by limiting to the maximum K1.

  The second step of FIG. 9 shows the temporal displacement of the injection amounts of the first injection and the second injection. The first injection may have a large change amount of the injection amount per unit time, whereas the second injection The change amount of the injection amount per unit time is limited to the maximum K1.

  As a result, the injection amount of the first injection and the injection amount of the second injection maintain a predetermined division ratio (injection amount ratio), while the second injection gradually approaches a stoichiometric change. Thereby, since the variation | change_quantity of 2nd injection with high torque sensitivity becomes small, generation | occurrence | production of a torque level | step difference can be suppressed.

<< Second Embodiment >>
FIG. 8 shows a control procedure according to the second embodiment for limiting the amount of change per unit time of the injection amount of the second injection. FIG. 8 is a flowchart showing a subroutine of step S81 in FIG. 10 and 11 are time charts showing temporal displacements of the first injection and the second injection of the control according to the second embodiment, and FIG. 10 shows a case where the fuel injection amount decreases with respect to the initial value. FIG. 11 shows a case where the fuel injection amount increases with respect to the initial value.

  In step S8110 of this example, the second injection is continued from time t1 to time t2 in a state where the fuel injection amount CTiS in the compression stroke that is the second injection is fixed at, for example, a constant value V2. On the other hand, the fuel injection amount CTiH in the intake stroke, which is the first injection, is calculated by the air-fuel ratio feedback control in step S78 of FIG. 6 described above, and the first injection is performed with the calculated injection amount from time t1 to time t2. If it continues, the sum of the fuel injection amounts of the first injection and the second injection becomes the target air-fuel ratio (stoichiometric) at time t2.

  In step S8120, it is determined whether or not stoichiometric has occurred due to air-fuel ratio feedback control by the first injection. If stoichiometric, the process proceeds to step S8130.

  In step S8130, since the total injection amount of the first injection and the second injection achieved at time t2 is the stoichiometric injection amount, the split ratio between this injection amount and the first injection and the second injection From the (injection amount ratio), the injection amount CTiS of the second injection, specifically, the increase / decrease amount with respect to the current injection amount is calculated.

  In step S 8140, it is determined whether the increase / decrease amount of the second injection calculated in step S 8130 is an increase or decrease. If it is an increase as shown in FIG. 11, the process proceeds to step S 8150 and is decreased as shown in FIG. In that case, the process advances to step S8160.

  Here, when the increase / decrease amount of the second injection is increased, the mixture is controlled to shift from the lean state to the rich side from the stoichiometric state. When the increase / decrease amount of the second injection is decreased, that is, the mixture is The torque sensitivity is relatively small compared to the control to shift from the richer state to the lean side than stoichiometric. Therefore, even if the increase amount (correction amount) of the injection amount per unit time of the second injection is increased, the torque step does not occur so much.

  In this example, from this point of view, if the increase / decrease amount of the second injection is decreased in step S8140, that is, if the increase / decrease amount per unit time is negative, the increase amount per unit time is set to ΔK3 in step S8160. 2 injections are performed.

  On the other hand, if the increase / decrease amount of the second injection is increased in step S8140, that is, if the increase / decrease amount per unit time is positive, the increase amount per unit time is set to ΔK2 larger than ΔK3 in step S8150. The second injection is performed. As a result, the time required to reach the stoichiometric ratio and the target split ratio (fuel injection ratio) is shortened.

  As described above, according to the control apparatus for an internal combustion engine according to the present example, the amount of change per unit time of the fuel injection amount in the compression stroke that is the second injection is limited, so that the occurrence of a torque step is suppressed. be able to.

  Since this restriction is executed immediately after the air-fuel ratio feedback control, which is the second step of stratified stoichiometric combustion, is started, the occurrence of a torque step can be suppressed over the entire time axis.

  Further, the amount of change per unit time of the second injection is made zero by only the injection amount control of the first injection, and the injection amount of the second injection is set to the target injection amount ratio while maintaining this stoichiometry. By correcting based on the above, generation of a torque step can be further suppressed. In addition, the control flow is simplified and the calculation load is reduced.

  Furthermore, by setting the correction amount per unit time in accordance with the increase / decrease amount of the correction, it is possible to shorten the time until the stoichiometry is reached.

1 is a block diagram showing an embodiment of a control device for an internal combustion engine according to the present invention. It is sectional drawing which shows the state of the 1st injection performed by an intake stroke among the stratified stoichiometric combustion stroke performed with the control apparatus of the internal combustion engine which concerns on this invention. It is sectional drawing which shows the state of the 2nd injection performed by a compression stroke among the stratified stoichiometric combustion strokes performed with the control apparatus of the internal combustion engine which concerns on this invention. It is sectional drawing which shows the state just before ignition after 1st injection and 2nd injection are performed among the stratified stoichiometric combustion strokes performed with the control apparatus of the internal combustion engine which concerns on this invention. It is a flowchart which shows the control procedure performed with the control unit shown in FIG. It is a flowchart which shows the subroutine of step S7 of FIG. It is a flowchart which shows the control procedure which concerns on 1st Embodiment of this invention, and shows the subroutine of FIG.6 S81. It is a flowchart which shows the control procedure which concerns on 2nd Embodiment of this invention, Comprising: The subroutine of step S81 of FIG. It is a time chart which shows the time displacement of the 1st injection of control and the 2nd injection concerning a 1st embodiment of the present invention. It is a time chart which shows the time displacement (the amount of injection decreases) of the 1st injection of control and the 2nd injection concerning a 2nd embodiment of the present invention. It is a time chart which shows the time displacement (injection amount) of the 1st injection and the 2nd injection of control concerning a 2nd embodiment of the present invention to increase.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 11 ... Intake passage 12 ... Air filter 13 ... Air flow meter 14 ... Throttle valve 15 ... Intake manifold 16 ... Combustion chamber 17 ... Fuel injection valve (fuel injection means)
DESCRIPTION OF SYMBOLS 18 ... Fuel pump 19 ... Pressure regulator 20 ... Spark plug 21 ... Exhaust passage 22 ... Air-fuel ratio sensor 24 ... Exhaust gas purification catalyst 25 ... Downstream oxygen sensor 26 ... Crankshaft 27 ... Crank angle sensor 28 ... Cooling jacket 29 ... Water temperature sensor 30 ... Throttle sensor 31 ... Throttle valve control device 32 ... Muffler 50 ... Control unit

Claims (4)

A fuel injection means for directly injecting fuel into a combustion chamber of an internal combustion engine performs a first injection that forms an air-fuel mixture in the entire combustion chamber before the completion of warm-up, and around an ignition plug attached to the combustion chamber A control device that executes control for performing the second injection to form the air-fuel mixture in layers,
In the first step before the warm-up is completed, the injection amount of the first injection and the injection amount of the second injection are set to constant values, respectively.
In a second step following the first step, control means is provided for controlling the injection amount of the first injection and the injection amount of the second injection so that the air-fuel mixture in the combustion chamber becomes a target air-fuel ratio. In a control device for an internal combustion engine,
The control means includes
In the second step,
The step of controlling the injection amount of the first injection so that the air-fuel mixture in the combustion chamber becomes the target air-fuel ratio in a state where the amount of change per unit time of the injection amount of the second injection is zero is executed. Later
A control apparatus for an internal combustion engine, wherein a step of correcting an injection amount of the second injection so that an injection amount ratio between the first injection and the second injection becomes the target injection amount ratio is executed. The control apparatus for an internal combustion engine according to claim 1,
The control device for an internal combustion engine, wherein the control means sets the change amount per unit time of the injection amount of the second injection to zero immediately after the transition from the first step to the second step. The control device for an internal combustion engine according to claim 1 or 2,
The control means determines a change amount per unit time of correction of the injection amount of the second injection according to an increase / decrease amount per unit time of the injection amount of the first injection and the second injection with respect to the target air-fuel ratio. A control device for an internal combustion engine, characterized by being changed. The control apparatus for an internal combustion engine according to claim 3,
The control means increases the amount of change per unit time of the correction when the amount of increase / decrease per unit time is positive compared to when the amount of increase / decrease per unit time is negative. A control device for an internal combustion engine.

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