JP2006022724A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain deterioration of an exhaust gas property with the usage of a negative pressure generated in an intake air passage while maintaining the negative pressure in a brake booster high. <P>SOLUTION: This control device is provided with a spark ignition type internal combustion engine 1, a fuel injection valve 11 for directly injecting fuel to a combustion chamber 5 of the internal combustion engine, and the brake booster 60. When the negative pressure in the brake booster is equal to or lower than a reference negative pressure, negative pressure control is carried out in order to raise the negative pressure in the brake booster, and expansion stroke injection for injecting the fuel into the combustion chamber in the expansion stroke or the exhaust stroke is carried out in addition to main injection for injecting the fuel into the combustion chamber in the intake stroke or the compression stroke of the internal combustion engine when it is under the expansion stroke injection execution condition. When the negative pressure in the brake booster is equal to or lower than the reference negative pressure even under the expansion stroke injection execution condition, the expansion stroke injection is prohibited and negative pressure control is carried out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In general, a brake booster is used in an automobile to increase the braking force. The brake booster has a first chamber and a second chamber separated by a power piston, and the first chamber is connected to a negative pressure source. Further, when the braking action is not performed, the second chamber is connected to the first chamber. Therefore, at this time, negative pressure is introduced into the first chamber and the second chamber from the negative pressure source. On the other hand, when the brake pedal is depressed, the communication between the first chamber and the second chamber is blocked, and at the same time, the second chamber is opened to the atmosphere. Accordingly, at this time, a large pressure difference is generated between the first chamber and the second chamber, and the power piston is driven by this pressure difference, thereby generating a large braking force.

  Thus, when using a brake booster, a negative pressure source is required. In the spark ignition type internal combustion engine, when performing homogeneous combustion, a large negative pressure is generated in the intake passage, so the negative pressure generated in the intake passage is used as a negative pressure source. On the other hand, when performing stratified combustion, since the negative pressure generated in the intake passage is small, a sufficient negative pressure may not be obtained. Therefore, when a sufficient negative pressure cannot be obtained during stratified combustion, it is necessary to take measures to positively generate a large negative pressure in the intake passage.

  In the internal combustion engine described in Patent Document 1, a compression auto-ignition internal combustion engine is used instead of a spark ignition internal combustion engine. However, when the negative pressure generated in the intake passage is small and sufficient negative pressure cannot be obtained. Reduces the opening of the throttle valve and the opening of the EGR valve to positively generate a large negative pressure in the intake passage. As a result, the necessary negative pressure can be generated in the intake passage at any time, thereby preventing the negative pressure from being insufficient in the brake booster.

JP 2000-135939 A JP 2000-328984 A JP 2001-27145 A JP 2001-355494 A JP 2002-21604 A JP 2002-188500 A

  By the way, in the internal combustion engine, various exhaust purification catalysts are employed to purify the exhaust gas. However, in order to maintain the exhaust purification performance, it is necessary to always maintain the temperature above a certain temperature. When the temperature becomes lower than a certain temperature, it is necessary to raise the temperature of the exhaust purification catalyst. As one of such temperature raising processes, an expansion stroke or an exhaust stroke (hereinafter referred to as “expansion stroke or the like”) separate from main injection for injecting fuel into the combustion chamber during the intake stroke or compression stroke of the internal combustion engine. ) Is an expansion stroke injection in which fuel is injected into the combustion chamber. The fuel injected in the expansion stroke or the like raises the temperature of the exhaust gas, thereby raising the temperature of the exhaust purification catalyst. Such temperature raising processing is often performed during stratified combustion, but the air-fuel ratio of the gas during stratified combustion is basically large and the degree of leanness is high, so most of the fuel injected in the expansion stroke etc. is in the combustion chamber. It is unlikely that it will burn and deteriorate the exhaust gas properties.

  However, as in the internal combustion engine described in Patent Document 1, if the throttle valve opening is made small and the EGR valve opening is made small in order to generate a large negative pressure in the intake passage, the combustion chamber of the internal combustion engine While the stratified combustion is performed, the air-fuel ratio of the gas during the stratified combustion is relatively low. Therefore, if the expansion stroke injection is performed at this time, the air-fuel ratio of the exhaust gas (that is, the ratio of the air flowing into the combustion chamber and the fuel injected in both the main injection and the expansion stroke injection) becomes the stoichiometric air-fuel ratio or rich. Thus, the fuel does not completely burn in the combustion chamber, and therefore, the unburned fuel is contained in the exhaust gas flowing into the exhaust purification catalyst. However, since the expansion stroke injection is performed when the temperature of the exhaust purification catalyst is low as described above, sufficient oxidation performance is not exhibited in the exhaust purification catalyst. For this reason, the unburned fuel passes through the exhaust purification catalyst, and hence the exhaust gas properties deteriorate.

  Accordingly, an object of the present invention is to suppress deterioration of exhaust gas properties while maintaining a high negative pressure in the brake booster by using a negative pressure generated in the intake passage.

In order to solve the above-described problems, the first invention includes a spark ignition internal combustion engine, a fuel injection valve that directly injects fuel into a combustion chamber of the internal combustion engine, and a brake booster. When the negative pressure falls below the reference negative pressure, negative pressure control is performed to increase the negative pressure in the brake booster. When the expansion stroke injection execution condition is satisfied, fuel is injected into the combustion chamber during the intake stroke or compression stroke of the internal combustion engine. In a control device for an internal combustion engine that performs an expansion stroke injection that injects fuel into the combustion chamber in an expansion stroke or an exhaust stroke separately from the main injection for injecting When the negative pressure becomes equal to or lower than the reference negative pressure, the expansion stroke injection is prohibited and the negative pressure control is executed.
If the expansion stroke injection and the negative pressure control are performed simultaneously as described above, the exhaust gas properties deteriorate. On the other hand, according to the first invention, the expansion stroke injection and the negative pressure control are not performed at the same time, and deterioration of the exhaust gas properties is prevented. Further, when the time when the expansion stroke injection should be executed and the time when the negative pressure control should be executed overlap, the negative pressure control is performed first. As a result, the negative pressure in the intake passage, and hence in the brake booster, can be increased, thereby preventing a reduction in brake force.
The term “expansion stroke injection execution condition” refers to the case where the temperature of the exhaust gas purification catalyst of the internal combustion engine has dropped below a certain temperature, or the case where the pressure of the exhaust gas has fallen below a certain pressure. “Negative pressure control” includes, for example, reducing the opening of a throttle valve provided in the intake passage to a small value or reducing the opening of an EGR valve that opens and closes an exhaust gas recirculation passage (EGR passage). Further, the “reference negative pressure” means a negative pressure that reduces the effect of the brake booster when the negative pressure in the brake booster further decreases.

  According to a second aspect, in the first aspect, when the negative pressure in the brake booster is equal to or lower than a predetermined negative pressure higher than the reference negative pressure when the expansion stroke injection execution condition is met, Even if the negative pressure in the booster is higher than the reference negative pressure, negative pressure control is executed and the start of the expansion stroke injection is delayed until the negative pressure in the brake booster becomes higher than the predetermined negative pressure.

In order to solve the above problems, in the third invention, a spark ignition internal combustion engine capable of performing both stratified combustion and homogeneous combustion, a fuel injection valve for directly injecting fuel into the combustion chamber of the internal combustion engine, and a brake booster And an expansion stroke for injecting fuel into the combustion chamber in the expansion stroke or the exhaust stroke separately from the main injection for injecting the fuel into the combustion chamber during the intake stroke or compression stroke of the internal combustion engine when the expansion stroke injection execution condition is satisfied In a control device for an internal combustion engine that performs injection, when the negative pressure in the brake booster becomes equal to or lower than the reference negative pressure when the expansion stroke injection is performed during the stratified combustion of the internal combustion engine, the expansion The stroke injection is prohibited and the combustion mode of the internal combustion engine is switched from stratified combustion to homogeneous combustion.
If the expansion stroke injection and the negative pressure control are performed simultaneously as described above, the exhaust gas properties deteriorate. On the other hand, according to the third invention, when the time when the expansion stroke injection should be executed and the time when the negative pressure control should be executed overlap, the combustion mode of the internal combustion engine changes from stratified combustion to homogeneous combustion. Neither expansion stroke injection nor negative pressure control is executed. When performing homogeneous combustion, unlike when performing stratified combustion, negative pressure is generated in the intake passage and the temperature of the exhaust gas is high.

  According to a fourth aspect, in the third aspect, when the negative pressure in the brake booster is equal to or lower than a predetermined negative pressure higher than the reference negative pressure when the expansion stroke injection execution condition is satisfied, Even if the negative pressure in the booster is higher than the reference negative pressure, the combustion mode of the internal combustion engine is switched from stratified combustion to homogeneous combustion, and the expansion stroke is continued until the negative pressure in the brake booster becomes higher than the predetermined negative pressure. Delay the start of injection.

  According to the first and second inventions, since the expansion stroke injection and the negative pressure control are not performed at the same time and the negative pressure control is performed first, the negative pressure in the brake booster is maintained high, and the exhaust gas properties deteriorate. Can be suppressed.

  According to the third and fourth inventions, switching from stratified combustion to homogeneous combustion generates a large negative pressure in the intake passage and increases the temperature of the exhaust gas. Therefore, the negative pressure in the brake booster is increased. While maintaining, it is possible to prevent deterioration of the exhaust gas properties.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The engine body 1 schematically shown in FIG. 1 represents a direct injection spark ignition type internal combustion engine. However, the present invention may be applied to other spark ignition internal combustion engines and compression ignition internal combustion engines. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a piston that reciprocates in the cylinder block 2, 4 is a cylinder head fixed on the cylinder block 2, and 5 is a piston 3 and a cylinder head 4. A combustion chamber formed therebetween, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, and 9 is an exhaust port. As shown in FIG. 1, a spark plug 10 is arranged at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is arranged around the inner wall surface of the cylinder head 4. A cavity 12 extending from the lower side of the fuel injection valve 11 to the lower side of the spark plug 10 is formed on the top surface of the piston 3.

  The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to a supercharger such as a compressor 18 of an exhaust turbocharger 17 via an intake duct 15 and an intercooler 16. It is connected with the exit part of. An inlet portion of the compressor 18 is connected to an air cleaner 20 via an air suction pipe 19, and a throttle valve 22 driven by a step motor 21 is disposed in the air suction pipe 19.

  On the other hand, the exhaust port 9 is connected to an inlet portion of an exhaust turbine 25 of the exhaust turbocharger 17 via an exhaust manifold 23 and an exhaust pipe 24, and an outlet portion of the exhaust turbine 25 is an exhaust for purifying exhaust gas via an exhaust pipe 26. It is connected to a catalytic converter 28 incorporating a purification catalyst 27. The exhaust purification catalyst 27 is provided with a temperature sensor 29 for detecting the temperature of the exhaust purification catalyst 27.

  The exhaust pipe 30 connected to the outlet portion of the catalytic converter 28 and the air suction pipe 19 downstream of the throttle valve 22 are connected to each other via an EGR passage 31, and EGR control driven by a step motor 32 in the EGR passage 31. A valve 33 is arranged. Further, an EGR cooling device 34 for cooling the EGR gas flowing in the EGR passage 31 is disposed in the EGR passage 31. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooling device 34, and the EGR gas is cooled by the engine cooling water.

  The electronic control unit (ECU) 40 is a digital computer, and is connected to each other by a bidirectional bus 41, a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, and An output port 46 is provided. The output signal of the temperature sensor 29 is input to the input port 45 via the corresponding AD converter 47. An air flow meter 37 for detecting the flow rate of intake air is disposed in the air suction pipe 19 upstream of the throttle valve 22, and an output signal of the air flow meter 37 is input to the input port 45 via the corresponding AD converter 47. Is done.

  A load sensor 51 that generates an output voltage proportional to the amount of depression of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. For example, the crank angle sensor 52 generates an output pulse every time the crankshaft rotates 30 degrees, and the output pulse is input to the input port 45. The CPU 44 calculates the engine speed from the output pulse of the crank angle sensor 52. On the other hand, the output port 46 is connected to the spark plug 10, the fuel injection valve 11, the throttle valve control step motor 21 and the EGR control valve control step motor 32 via a corresponding drive circuit 48.

  The air suction pipe 19 downstream of the throttle valve 22 is connected to the brake booster 60 via a negative pressure conduit 61. 2, the brake booster 60 includes a power piston 63, a first chamber 64 and a second chamber 65 formed on both sides of the power piston 63, an operating rod 67 having a plunger 66, and an operating valve 68. It comprises. A push rod 69 is fixed to the power piston 63, and a master cylinder 70 that generates a brake hydraulic pressure is driven by the push rod 69. Further, the operating rod 67 is connected to the brake pedal 71.

  The negative pressure conduit 61 is connected to the first chamber 64, and a check valve 62 that can flow only from the first chamber 64 toward the air suction pipe 19 is disposed in the negative pressure conduit 61. When a negative pressure greater than the negative pressure in the first chamber 64 is generated in the air suction pipe 19, the check valve 62 is opened, and thus the negative pressure in the first chamber 64 is generated in the air suction pipe 19. The maximum negative pressure is maintained.

  As shown in FIG. 2, when the brake pedal 71 is released, the first chamber 64 and the second chamber 65 communicate with each other via a pair of communication passages 72 and 73. The same negative pressure is generated in the two chambers 65. Next, when the brake pedal 71 is depressed, the operation valve 68 moves to the left together with the operation rod 67. As a result, the communication path 72 is blocked by the operation valve 68, and the plunger 66 is separated from the operation valve 68, so that the second chamber 65 is opened to the atmosphere via the atmosphere communication path 74. Atmospheric pressure. Accordingly, a pressure difference is generated between the first chamber 64 and the second chamber 65, and the power piston 63 is moved to the left by this pressure difference.

  On the other hand, when the brake pedal 71 is released, the atmosphere communication passage 74 is closed by the plunger 66 and the communication passages 72 and 73 are opened, so that the first chamber 64 and the second chamber 65 are connected again via the communication passages 72 and 73. Communicate with each other. A pressure sensor 75 for detecting the absolute pressure in the first chamber 64 is attached to the brake booster 60, and an output signal of the pressure sensor 75 is input to the input port 45 via the corresponding AD converter 47.

  By the way, in the in-cylinder injection type spark ignition type internal combustion engine as in the present invention, two combustion modes of homogeneous combustion and stratified combustion can be selectively performed. Homogeneous combustion is performed by injecting fuel during the intake stroke to make the air-fuel ratio of the air-fuel mixture substantially uniform over the entire combustion chamber and then igniting the air-fuel mixture. The homogeneous combustion is performed when the air-fuel ratio of the intake gas is close to the stoichiometric air-fuel ratio, and a large output can be obtained.

  On the other hand, stratified combustion is combustion at a very high air-fuel ratio for the combustion chamber as a whole, and fuel is injected in the compression stroke just before ignition, and the fuel is unevenly distributed only in the vicinity of the spark plug. This is done by igniting. In stratified combustion, the opening degree of the throttle valve and the EGR control valve is increased, so that the pumping loss caused by the small opening degree of the throttle valve can be reduced even in a low load operation state with a small fuel injection amount. it can. Further, in stratified combustion, combustion is mainly performed only in the vicinity of the spark plug, so that a cooling loss can be reduced, and as a result, fuel efficiency can be greatly improved. However, in stratified combustion, the pumping loss can be reduced, but conversely, almost no negative pressure is generated in the intake air intake pipe 19.

  On the other hand, as described above, the negative pressure in the first chamber 64 of the brake booster 60 is maintained at the maximum negative pressure generated in the air suction pipe 19. However, if the negative pressure generated in the intake suction pipe 19 is continuously low, the maximum negative pressure in the air suction pipe 19 is also low, and as a result, the negative pressure in the first chamber 64 is also low. Further, in the brake booster 60, the braking force at the time of braking increases as the pressure difference between the absolute pressure in the first chamber 64 and the absolute pressure in the second chamber 65 increases. In other words, the smaller the absolute pressure in the first chamber 64, that is, the greater the negative pressure in the first chamber 64, the higher the braking force during braking, and vice versa. That is, as the negative pressure in the first chamber 64 becomes smaller, the braking force at the time of braking action becomes lower. Therefore, if the negative pressure in the air suction pipe 19 is continuously small, the braking force is reduced.

  Therefore, in the present embodiment, when the negative pressure in the first chamber 64 becomes equal to or lower than the reference negative pressure during stratified combustion, a large negative pressure is forcibly generated in the air suction pipe 19. Perform negative pressure control. Here, the “reference negative pressure” is a negative pressure at which the brake force decreases greatly when the negative pressure in the first chamber 64 becomes smaller, that is, the brake boosting effect of the brake booster 60 is greatly reduced. This negative pressure is defined in advance by experiments or the like. By executing the negative pressure control in this way, the negative pressure in the first chamber 64 is kept higher than the reference negative pressure even when stratified combustion is being performed, so that the braking force is greatly reduced. Is prevented.

  In addition, as negative pressure control, when performing stratified combustion, reducing the opening degree of the throttle valve 22 or the EGR control valve 33 which is normally fully opened or close to it is mentioned. That is, when the opening degree of the throttle valve 22 is reduced, the flow resistance to the air flowing into the air suction pipe 19 downstream of the throttle valve 22 through the throttle valve 22 is increased, and when the opening degree of the EGR control valve 22 is reduced, EGR is reduced. The flow resistance to the EGR gas flowing into the air suction pipe 19 downstream of the EGR control valve 33 through the control valve 33 increases. On the other hand, even if the opening degree of the throttle valve 22 and the EGR control valve 33 is reduced, the amount of intake gas required in the combustion chamber 5 does not change. As a result, the negative pressure in the air suction pipe 19 downstream of the throttle valve 22 is reduced. growing.

In order to brake the vehicle satisfactorily, the higher the vehicle speed, the greater the braking force required. Therefore, the minimum required negative pressure in the first chamber 64 increases as the vehicle speed increases. Therefore, in the embodiment according to the present invention, the reference negative pressure P ₁ in the first chamber 64 is reduced as the vehicle speed SP increases as shown in FIG.

On the other hand, the exhaust gas discharged from the combustion chamber 5 of the internal combustion engine contains harmful substances such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO _x ). In the present embodiment, an exhaust purification catalyst 27 is provided in the exhaust passage in order to remove these harmful substances. As the exhaust purification catalyst 27, various forms such as an oxidation catalyst, a three-way catalyst, and an NO _x storage reduction catalyst can be adopted.

  Such an exhaust purification catalyst 27 needs to be at a certain temperature (hereinafter referred to as “activation temperature”) in order to exhibit its exhaust purification ability. This is because a catalyst noble metal such as platinum is supported on the exhaust purification catalyst 27, but this catalyst noble metal needs to be at a certain high temperature in order to exhibit oxidation ability.

  However, when the internal combustion engine is performing stratified combustion, the temperature of the exhaust gas is relatively low. Therefore, when the internal combustion engine is performing stratified combustion, the temperature of the exhaust purification catalyst 27 tends to decrease. is there. In some cases, the temperature of the exhaust purification catalyst 27 becomes lower than the activation temperature, and the exhaust purification capability of the exhaust purification catalyst 27 may not be fully exhibited.

  Therefore, in the present embodiment, when the temperature of the exhaust purification catalyst 27 is lower than its activation temperature, the fuel is injected from the fuel injection valve 11 into the combustion chamber 5 during the intake stroke or the compression stroke of the internal combustion engine. Auxiliary fuel injection (hereinafter referred to as “expansion stroke or the like”) performed after the main injection (or after ignition by the spark plug 10) during the expansion stroke or exhaust stroke (hereinafter referred to as “expansion stroke or the like”) separately from the main injection to be injected. , Referred to as “expansion stroke injection”). Since the fuel injected by the expansion stroke injection is combusted in the combustion chamber 5 in the latter stage of the expansion stroke or during the exhaust stroke, the temperature of the exhaust gas becomes high. Therefore, the temperature of the exhaust purification catalyst 27 is raised to the activation temperature in a short time. be able to.

  In addition, since the temperature and pressure of the exhaust gas are increased by performing the expansion stroke injection, in addition to the temperature increase of the exhaust purification catalyst 27, the work of the turbine 25 of the exhaust turbocharger 17 is increased to accelerate the boost pressure. Effects such as improved performance can be obtained.

  By the way, almost all of the fuel injected into the combustion chamber 5 by the expansion stroke injection is basically combusted during stratified combustion. That is, normally, during stratified combustion, the air-fuel ratio of the intake gas combusted in the combustion chamber 5 is very high, and a large amount of oxygen remains in the combustion chamber 5 during the expansion stroke injection. The injected fuel reacts with these oxygens in the combustion chamber 5. Therefore, basically, there is almost no unburned fuel or the like in the exhaust gas during stratified combustion, so that HC or the like is released into the atmosphere even when the exhaust purification catalyst 27 has not reached the activation temperature. There is nothing.

  However, even during stratified combustion, the air-fuel ratio of the intake gas in the combustion chamber 5 is relatively low during execution of the negative pressure control, and in some cases, is close to the theoretical air-fuel ratio. This is because the amount of intake air into the combustion chamber 5 is reduced by reducing the opening of the throttle valve 22 and the like, while the fuel injection amount from the fuel injection valve 11 in the main injection is maintained. Therefore, in this case, only a small amount of oxygen remains in the combustion chamber 5 at the time of expansion stroke injection, and thus a part of the fuel injected by the expansion stroke injection remains unreacted with oxygen. That is, even during stratified combustion, if negative pressure control is being performed, the fuel injected into the combustion chamber 5 by the expansion stroke injection flows into the exhaust purification catalyst 27 without burning. When the expansion stroke injection is executed, the temperature of the exhaust purification catalyst 27 is lower than the activation temperature, so that the unburned fuel that has flowed into the exhaust purification catalyst 27 is not easily purified by the exhaust purification catalyst 27 and remains in the atmosphere. Will be released.

  As described above, if the expansion stroke injection and the negative pressure control are performed simultaneously, the properties of the exhaust gas deteriorate. Therefore, from the viewpoint of exhaust gas purification, the expansion stroke injection and the negative pressure control should not be performed simultaneously.

  Therefore, in the embodiment of the present invention, even when the execution conditions for the expansion stroke injection are satisfied and the execution conditions for the negative pressure control are satisfied, the expansion stroke injection and the negative pressure control are performed. Are not executed simultaneously, and either one of the expansion stroke injection and the negative pressure control is prohibited. Thereby, it is suppressed that unburned fuel is discharged | emitted from the combustion chamber 5, As a result, the quality deterioration of the exhaust gas discharge | released in air | atmosphere is prevented.

  Further, in the embodiment of the present invention, when the execution conditions of the expansion stroke injection and the negative pressure control are both established, the expansion stroke injection is prohibited and the negative pressure control is preferentially executed. That is, if the negative pressure in the first chamber 64 of the brake booster 60 is left unattended, the braking force is extremely reduced, and the operation of the vehicle becomes difficult, which is extremely dangerous for the driver. On the other hand, since the exhaust purification catalyst 27 does not completely lose its oxidizing ability even at an activation temperature or lower, it has an exhaust gas purification ability although it is in a very small amount. For this reason, the more important negative pressure control is prioritized over the expansion stroke injection.

FIG. 4 shows various parameters relating to the control device of the first embodiment of the present invention (temperature of exhaust purification catalyst 27, absolute pressure in first chamber 64 of brake booster 60, execution status of negative pressure control, execution of expansion stroke injection). It is a time chart of the situation. Prior to time t ₀ , stratified combustion is performed in the internal combustion engine. At time t ₀ , the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature T ₁ , and the conditions for executing the expansion stroke injection are satisfied. On the other hand, at this time, the absolute pressure in the first chamber 64 is smaller than the reference absolute pressure (absolute pressure corresponding to the reference negative pressure) P ₁ and is a high negative pressure, and therefore the negative pressure control execution condition is satisfied. Not. Since both the execution conditions for the expansion stroke injection and the execution conditions for the negative pressure control are not satisfied, the expansion stroke injection is executed as usual from time t ₀ .

When the absolute pressure in the first chamber 64 rises to the reference absolute pressure P ₁ or more due to repeated braking operation during the expansion stroke injection, and the negative pressure decreases, the negative pressure control execution condition is satisfied. At this time, since the temperature of the exhaust purification catalyst 27 is still lower than the activation temperature T _{1, the} conditions for executing the expansion stroke injection are simultaneously satisfied. Therefore, in this case, the expansion stroke injection is prohibited and only the negative pressure control is executed. Thereby, the absolute pressure in the first chamber 64 is reduced, that is, the negative pressure is recovered. On the other hand, since the expansion stroke injection is prohibited, the temperature increase of the exhaust purification catalyst 27 becomes slight or hardly increases.

When the absolute pressure in the first chamber 64 becomes lower than the reference absolute pressure P ₁ again by the execution of the negative pressure control, the execution condition for the negative pressure generation control is not satisfied, and the negative pressure control is terminated (time t ₂ ). On the other hand, since the temperature of the exhaust purification catalyst 27 is still below the activation temperature T ₁ at this time, the conditions for executing the expansion stroke injection remain established. Accordingly, the execution of the expansion stroke injection is started again simultaneously with the end of the negative pressure control, and the temperature of the exhaust purification catalyst 27 is raised. Then, when the temperature of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ , the expansion stroke injection is terminated (time t ₃ ).

In the above embodiment, at time t _2, the has been decided to resume execution at the same time the expansion stroke injection and the negative pressure control exit, a low air-fuel ratio of the intake gas negative pressure control ends after the combustion chamber 5 Since the state is considered to continue slightly, the execution of the expansion stroke injection may be resumed after a short time has elapsed after the negative pressure control is completed.

  FIG. 5 is a control routine related to the execution of the expansion stroke injection and the negative pressure control in the first embodiment of the present invention, and this routine is performed by interruption at regular time intervals.

First, in step 101, whether absolute pressure Pbra in the first chamber 64 detected by the pressure sensor 75 is the reference absolute pressure P ₁ or more is determined. When it is determined that the absolute pressure Pbra is equal to or higher than the reference absolute pressure P ₁ (Pbra ≧ P ₁ ), that is, when the negative pressure control execution condition is satisfied, the routine proceeds to step 102 and step 103. In step 102 and step 103, negative pressure control is executed and expansion stroke injection is not executed. That is, when the absolute pressure Pbra in the first chamber 64 is equal to or higher than the reference absolute pressure P ₁ , negative pressure control is executed regardless of the temperature of the exhaust purification catalyst 27.

On the other hand, when it is determined in step 101 that the absolute pressure Pbra in the first chamber 64 is smaller than the reference absolute pressure P ₁ (Pbra <P ₁ ), that is, when the negative pressure control execution condition is not satisfied. Proceed to step 104. In step 104, whether or not the temperature Tcat of the exhaust purification catalyst 27 detected by the temperature sensor 29 is active temperature T ₁ of less is determined. When it is determined that the temperature Tcat is equal to or lower than the activation temperature T ₁ (Tcat ≦ T ₁ ), that is, when the expansion stroke injection execution condition is satisfied, the process proceeds to steps 105 and 106. In Step 105 and Step 106, negative pressure control is not executed, but expansion stroke injection is executed. If it is determined in step 104 that the temperature Tcat is higher than the activation temperature T ₁ (Tcat> T ₁ ), that is, if the expansion stroke injection execution condition is not satisfied, the process proceeds to step 107 and step 108. In Step 107 and Step 108, neither negative pressure control nor expansion stroke injection is executed.

In the first embodiment, the execution start condition and the execution end condition are the same for both the negative pressure control and the expansion stroke injection. For example, for the negative pressure control, both the execution start and the execution end of the negative pressure control are performed. The reference absolute pressure P ₁ is used as a reference. However, a hysteresis may be provided between the execution start condition and the execution end condition for both the negative pressure control and the expansion process injection. That is, the reference for starting execution of the negative pressure control is the reference absolute pressure P ₁ , whereas the reference for ending the execution of the negative pressure control may be an absolute pressure lower than the reference absolute pressure P ₁ .

  Next, the control apparatus of 2nd embodiment of this invention is demonstrated. The configuration of the control device of the second embodiment is basically the same as the configuration of the first embodiment. However, in the second embodiment, the expansion stroke injection is started only when the negative pressure in the first chamber 64 of the brake booster 60 is higher than a predetermined negative pressure higher than the reference negative pressure. Therefore, when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature, the expansion stroke injection is not executed if the negative pressure in the first chamber 64 is equal to or lower than the predetermined negative pressure. In this case, the expansion stroke injection is executed after the negative pressure control is executed and the negative pressure in the first chamber 64 reaches the predetermined negative pressure.

  As described above, the expansion stroke injection is started after the negative pressure in the first chamber 64 becomes higher than the predetermined negative pressure, so that the driver operates the brake while the expansion stroke injection is being executed. Even if the negative pressure in 64 is reduced, it is difficult to reduce it to below the reference negative pressure. Therefore, the possibility that the negative pressure control has to be executed during the expansion stroke injection is reduced. The “predetermined negative pressure” is a negative pressure that is slightly higher than the reference negative pressure and is predetermined.

FIG. 6 is a time chart of various parameters related to the control device of the second embodiment of the present invention. Prior to time t ₀ , stratified combustion is performed in the internal combustion engine. At time t ₀ , the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature T ₁ , and the conditions for executing the expansion stroke injection are satisfied. On the other hand, even if the absolute pressure Pbra in the first chamber 64 of the brake booster 60 is lower than the reference absolute pressure P ₁ at this time, it corresponds to a predetermined absolute pressure (a predetermined negative pressure) lower than the reference absolute pressure P _1. If it is absolute pressure) P ₂ or more, the expansion stroke injection is not executed with negative pressure control is executed. Therefore, the temperature of the exhaust purification catalyst 27 is not increased, but the absolute pressure Pbra in the first chamber 64 is reduced.

Then, at time t _4, the absolute pressure Pbra in the first chamber 64 becomes lower than the predetermined absolute pressure P _2, the negative pressure control of the execution is made to finished therewith execution of expansion stroke injection is started at the same time. That is, the start of execution of expansion stroke injection is caused to delay until an absolute pressure Pbra in the first chamber 64 is lower than the predetermined absolute pressure P _2. When the execution of the expansion stroke injection is started, the temperature of the exhaust purification catalyst 27 is raised, and when the temperature of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ , the expansion stroke is terminated (t ₅ ).

  FIG. 7 is a control routine relating to the execution of the expansion stroke injection and the negative pressure control in the second embodiment of the present invention, and this routine is performed by interruption at regular time intervals.

First, in step 121, whether or not the temperature Tcat of the exhaust purification catalyst 27 detected by the temperature sensor 29 is active temperature T ₁ of less is determined. When it is determined that the temperature Tcat is equal to or lower than the activation temperature T ₁ (Tcat ≦ T ₁ ), that is, when the expansion stroke injection execution condition is satisfied, the routine proceeds to step 122. In step 122, it is determined whether or not the expansion stroke injection is being performed. If the expansion stroke injection has not been executed yet, that is, if the expansion stroke injection is to be started, the routine proceeds to step 123.

In step 123, the absolute pressure Pbra in the first chamber 64 detected by the pressure sensor 75 whether the predetermined absolute pressure P ₂ or more is determined. When it is determined that the absolute pressure Pbra in the first chamber 64 detected by the pressure sensor 75 is equal to or higher than the predetermined absolute pressure P ₂ (Pbra ≧ P ₂ ), the process proceeds to steps 124 and 125 to control the negative pressure. Is executed and the expansion stroke injection is not executed. In this case, since the expansion stroke injection is not performed, it is determined in step 122 that the expansion stroke injection is not being performed. When the absolute pressure Pbra becomes lower than the predetermined absolute pressure by the negative pressure control, it is determined in step 123 that the absolute pressure Pbra is lower than the predetermined absolute pressure P ₂ (Pbra <P ₂ ), and the process proceeds to steps 126 and 127. In steps 126 and 127, negative pressure control is not executed, and expansion stroke injection is executed.

When the expansion stroke injection is executed in step 127, it is determined that the expansion stroke injection is being executed in step 122 from the next routine, and the routine proceeds to step 128. In step 128, whether absolute pressure Pbra in the first chamber 64 is the reference absolute pressure P ₁ or more is determined. While the absolute pressure Pbra is lower than the reference absolute pressure P ₁ (Pbra <P ₁ ), the routine proceeds to steps 126 and 127, and negative pressure control is not executed and only the expansion stroke injection is executed. On the other hand, when the absolute pressure Pbra becomes equal to or higher than the reference absolute pressure P ₁ due to repeated braking operation by the driver (Pbra ≧ P ₁ ), the process proceeds to steps 129 and 130, negative pressure control is executed again, and expansion stroke injection is performed. Is not executed. As a result, in the next routine, it is determined in step 122 that the expansion stroke injection is not being executed, so the routine proceeds to step 123.

On the other hand, when the temperature Tcat of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ (Tcat> T ₁ ), the routine proceeds to step 131. In step 131, whether absolute pressure Pbra in the first chamber 64 is the reference pressure P ₁ or more is determined, when it is determined that the reference pressure P ₁ or more (Pbra ≧ P _1), step 132, Proceed to 133. In steps 132 and 133, negative pressure control is executed and expansion stroke injection is not executed. On the other hand, when it is determined in step 131 that the absolute pressure Pbra in the first chamber 64 is lower than the reference pressure P ₁ (Pbra <P ₁ ), the process proceeds to steps 134 and 135. In steps 134 and 135, neither negative pressure control nor expansion stroke injection is executed.

  Next, the control apparatus of 3rd embodiment of this invention is demonstrated. The configuration of the control device of the third embodiment is basically the same as the configuration of the first embodiment. However, in the third embodiment, when the temperature of the exhaust purification catalyst 27 is lower than the activation temperature and the negative pressure in the first chamber 64 of the brake booster 60 is lower than the reference negative pressure, that is, the expansion stroke injection execution condition is If the condition is satisfied and the negative pressure control execution condition is satisfied, the combustion mode in the internal combustion engine is changed from stratified combustion to homogeneous combustion instead of executing the expansion stroke injection or the negative pressure control. Yes.

  When the homogeneous combustion is performed, the opening degree of the throttle valve 22 and the EGR control valve 33 is small, so that a large negative pressure is generated in the intake gas in the intake suction pipe 19 downstream of the throttle valve 22. Therefore, the negative pressure in the first chamber 64 can be increased as in the case where the negative pressure control is executed. Further, the temperature of the exhaust gas during the homogeneous combustion is higher than that during the stratified combustion, and the temperature of the exhaust purification catalyst 27 can be increased. In addition, since fuel injection is performed from the fuel injection valve 11 before ignition by the spark plug 10, unburned fuel hardly remains in the exhaust gas. However, in the case of performing homogeneous combustion, the fuel consumption is slightly worse than in the case of performing negative pressure control during stratified combustion.

  From the above, according to the homogeneous combustion, it is possible to simultaneously solve the shortage of the negative pressure of the brake booster 60, the temperature rise of the exhaust purification catalyst 27, and the prevention of deterioration of the exhaust gas properties. Therefore, from this point of view, it is considered to be very effective to perform homogeneous combustion when the execution conditions for the expansion stroke injection are satisfied and the execution conditions for the negative pressure control are satisfied.

FIG. 8 is a time chart of various parameters related to the control device of the third embodiment of the present invention. Prior to time t ₀ , stratified combustion is performed in the internal combustion engine. At time t ₀ , the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature T ₁ , and the conditions for executing the expansion stroke injection are satisfied. On the other hand, the absolute pressure in the first chamber 64 is lower than P ₁ , and the negative pressure control execution condition is not satisfied. Therefore, only the expansion stroke injection is executed at time t ₀ . Thereafter, when the absolute pressure in the first chamber 64 rises to P ₁ or more at time t ₆ , the negative pressure control execution condition is satisfied. Thus, at time t _6, the expansion stroke injection and the negative pressure control execution condition is satisfied together. In this case, the expansion stroke injection is stopped and the negative pressure control is not executed. Instead, the combustion mode of the internal combustion engine is switched from stratified combustion to homogeneous combustion. As a result, the absolute pressure in the first chamber 64 is decreased and the temperature of the exhaust purification catalyst 27 is increased simultaneously.

When the absolute pressure in the first chamber 64 becomes lower than the reference absolute pressure P ₁ again by executing the homogeneous combustion, the negative pressure generation control execution condition is not satisfied, and the combustion mode of the internal combustion engine is returned from the homogeneous combustion to the stratified combustion. (Time t ₇ ). Moreover, since the execution conditions for the expansion stroke injection are still satisfied, the expansion stroke injection is started again. Then, when the temperature of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ , the expansion stroke injection is terminated (time t ₈ ).

  FIG. 9 is a control routine relating to the execution of expansion stroke injection and negative pressure control in the third embodiment of the present invention, and this routine is performed by interruption at regular time intervals.

First, in step 151, whether or not the temperature Tcat of the exhaust purification catalyst 27 detected by the temperature sensor 29 is active temperature T ₁ of less is determined. When it is determined that the temperature Tcat of the exhaust purification catalyst 27 is equal to or lower than the activation temperature T ₁ (Tcat ≦ T ₁ ), the routine proceeds to 152. In step 152, whether absolute pressure Pbra in the first chamber 64 detected by the pressure sensor 75 is the reference absolute pressure P ₁ or more is determined. When it is determined that the absolute pressure Pbra is equal to or higher than the reference absolute pressure P ₁ (Pbra ≧ P ₁ ), that is, when both the expansion stroke injection execution condition and the negative pressure control execution condition are satisfied, Steps 153 to 153 are performed. Proceed to 155. In Steps 153 to 155, the combustion mode of the internal combustion engine is set to homogeneous combustion, and neither the negative pressure control nor the expansion stroke injection is executed. When it is determined in step 152 that the absolute pressure Pbra is smaller than the reference absolute pressure P ₁ (Pbra <P ₁ ), that is, the expansion stroke injection execution condition is satisfied, but the negative pressure control execution condition is not satisfied. In this case, the process proceeds to step 156 to step 158. In Steps 156 to 158, the combustion mode of the internal combustion engine is stratified combustion, negative pressure control is not performed, and expansion stroke injection is performed.

If it is determined in step 151 that the temperature Tcat of the exhaust purification catalyst 27 is higher than the activation temperature T ₁ (Tcat> T ₁ ), the routine proceeds to 159. In step 159, whether absolute pressure Pbra in the first chamber 64 is the reference absolute pressure P ₁ or more is determined as in step 152. When it is determined that the absolute pressure Pbra is equal to or higher than the reference absolute pressure P ₁ (Pbra ≧ P ₁ ), that is, when the expansion stroke injection execution condition is not satisfied but the negative pressure control execution condition is satisfied, Proceed to step 160 to step 162. In step 160 to step 162, the combustion mode of the internal combustion engine is stratified combustion, negative pressure control is executed, and expansion stroke injection is not executed. When it is determined in step 159 that the absolute pressure Pbra is smaller than the reference absolute pressure P ₁ (Pbra <P ₁ ), that is, when the expansion stroke injection execution condition and the negative pressure control execution condition are not satisfied, It progresses to step 163-step 165. In Steps 163 to 165, the combustion mode of the internal combustion engine is stratified combustion, and neither negative pressure control nor expansion stroke injection is executed.

  Next, the control apparatus of 4th embodiment of this invention is demonstrated. The configuration of the control device of the fourth embodiment is basically the same as the configuration of the third embodiment. However, in the fourth embodiment, when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature, the negative pressure in the first chamber 64 is higher than the reference negative pressure but lower than the predetermined negative pressure. In this case, the expansion stroke injection is not executed, and the combustion mode is switched from stratified combustion to homogeneous combustion. That is, when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than its activation temperature, the combustion mode is switched from stratified combustion to homogeneous combustion if the negative pressure in the first chamber 64 is equal to or lower than the predetermined negative pressure. The homogeneous combustion is continued until the temperature of the exhaust purification catalyst 27 becomes higher than its activation temperature. In other words, the expansion stroke injection is executed only when the negative pressure in the first chamber 64 is higher than the predetermined negative pressure when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature.

  As described above, when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature and the negative pressure in the first chamber 64 is equal to or lower than the predetermined negative pressure, the temperature of the exhaust purification catalyst 27 is higher than the activation temperature. By continuing the homogeneous combustion until it becomes higher, it becomes unnecessary to repeat the execution and stop of the negative pressure control and the expansion stroke injection during that time, and the control becomes easy. If the negative pressure in the first chamber 64 is higher than the predetermined negative pressure when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature, the first chamber 64 even if the expansion stroke injection is executed. The possibility that the internal negative pressure becomes lower than the reference negative pressure is low, and the deterioration of fuel consumption can be prevented by executing the expansion stroke injection without performing homogeneous combustion.

FIG. 10 is a time chart of various parameters related to the control device of the fourth embodiment of the present invention. Prior to time t ₀ , stratified combustion is performed in the internal combustion engine. At time t ₀ , the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature T ₁ . At this time, the absolute pressure in the first chamber 64 of the brake booster 60 is equal to or higher than the predetermined absolute pressure P _2, and neither the expansion stroke injection nor the negative pressure control is executed, and the combustion mode of the internal combustion engine is stratified combustion. To homogeneous combustion. Thereafter, even if the absolute pressure in the first chamber 64 becomes lower than the predetermined absolute pressure P ₂ , the homogeneous combustion is continued as it is, and the expansion stroke injection and the negative pressure control are not executed. When the temperature of the exhaust purification catalyst 27 is higher than the activation temperatures T ₁ at time t _9, the combustion mode of the internal combustion engine is switched to stratified combustion from homogeneous combustion.

Next, a modification of the fourth embodiment of the present invention will be described with reference to FIG. In the control device of the fourth embodiment, after the combustion mode of the internal combustion engine is switched from stratified combustion to homogeneous combustion when the temperature of the exhaust purification catalyst 27 becomes equal to or lower than the activation temperature T ₁ , Even if the absolute pressure becomes lower than the predetermined absolute pressure P ₂ , the homogeneous combustion is continued as it is. On the other hand, in this modified example, when the internal combustion engine is performing homogeneous combustion, if the absolute pressure in the first chamber 64 becomes lower than the predetermined absolute pressure P ₂ , the combustion mode of the internal combustion engine Is returned from the homogeneous combustion to the stratified combustion, and the execution of the expansion stroke injection is started (time t _{10 in} FIG. 11). Thereafter, when the temperature of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ , the execution of the expansion stroke injection is terminated (time t ₁₁ ).

When homogeneous combustion is performed in an internal combustion engine, fuel efficiency is worse than when stratified combustion is performed, but this is the same as when performing expansion stroke injection during stratified combustion. I can say that. Therefore, when the temperature of the exhaust purification catalyst 27 becomes higher than the activation temperature T ₁ , the fuel consumption can be improved by stopping the execution of the homogeneous combustion and performing the expansion stroke injection.

1 is an overall view of a cylinder injection type spark ignition internal combustion engine. It is an expanded side sectional view of a brake booster. It is a figure which shows the relationship between a vehicle speed and a reference | standard negative pressure. It is a time chart of the various parameters regarding the apparatus of 1st embodiment of this invention. It is a flowchart of the control routine regarding execution of expansion stroke injection and negative pressure control in the first embodiment of the present invention. It is a time chart of the various parameters regarding the apparatus of 2nd embodiment of this invention. It is a flowchart of the control routine regarding execution of expansion stroke injection and negative pressure control in the second embodiment of the present invention. It is a time chart of the various parameters regarding the apparatus of 3rd embodiment of this invention. It is a flowchart of the control routine regarding execution of expansion stroke injection and negative pressure control in a third embodiment of the present invention. It is a time chart of the various parameters regarding the apparatus of 4th embodiment of this invention. It is a time chart of the various parameters regarding the apparatus of 5th embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 5 Combustion chamber 10 Spark plug 11 Fuel injection valve 19 Air suction pipe 27 Exhaust purification catalyst 29 Temperature sensor 40 Electronic control unit (ECU)
60 Brake Booster 61 Negative Pressure Pipe 64 First Chamber 65 Second Chamber 75 Pressure Sensor

Claims (4)

A spark ignition type internal combustion engine, a fuel injection valve for directly injecting fuel into a combustion chamber of the internal combustion engine, and a brake booster, and the brake booster when the negative pressure in the brake booster falls below a reference negative pressure When the negative pressure control for increasing the negative pressure in the booster is executed and the expansion stroke injection execution condition is satisfied, in the expansion stroke or the exhaust stroke separately from the main injection that injects fuel into the combustion chamber during the intake stroke or the compression stroke of the internal combustion engine In a control device for an internal combustion engine that performs expansion stroke injection for injecting fuel into a combustion chamber,
Even when the expansion stroke injection execution condition is satisfied, if the negative pressure in the brake booster becomes equal to or lower than the reference negative pressure, the spark ignition for prohibiting the expansion stroke injection and executing the negative pressure control is performed. Control device for an internal combustion engine.   If the negative pressure in the brake booster is equal to or lower than a predetermined negative pressure higher than the reference negative pressure when the expansion stroke injection execution condition is met, the negative pressure in the brake booster is higher than the reference negative pressure. 2. The control device for an internal combustion engine according to claim 1, wherein the negative pressure control is executed even when the pressure is high and the start of the expansion stroke injection is delayed until the negative pressure in the brake booster becomes higher than the predetermined negative pressure. A spark ignition type internal combustion engine capable of performing both stratified combustion and homogeneous combustion, a fuel injection valve for directly injecting fuel into the combustion chamber of the internal combustion engine, and a brake booster, and when the expansion stroke injection is in an execution condition In a control apparatus for an internal combustion engine that performs expansion stroke injection that injects fuel into a combustion chamber in an expansion stroke or an exhaust stroke separately from main injection that injects fuel into the combustion chamber during an intake stroke or compression stroke of the engine,
If the negative pressure in the brake booster falls below the reference negative pressure when the expansion stroke injection is being executed during stratified combustion of the internal combustion engine, the expansion stroke injection is prohibited and the internal combustion engine A control device for an internal combustion engine that switches the combustion mode from stratified combustion to homogeneous combustion.   If the negative pressure in the brake booster is equal to or lower than a predetermined negative pressure higher than the reference negative pressure when the expansion stroke injection execution condition is met, the negative pressure in the brake booster is higher than the reference negative pressure. The combustion mode of the internal combustion engine is switched from stratified combustion to homogeneous combustion even if it is high, and the start of expansion stroke injection is delayed until the negative pressure in the brake booster becomes higher than the predetermined negative pressure. Control device for internal combustion engine.

Images