JP2005113885A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder direct injection type engine capable of suppressing increase of an amount of smoke generation at the time of catalyst warming up operation and the like. <P>SOLUTION: The engine 1 is equipped with a combustion chamber 7, an ignition plug 9, a fuel injection valve 10, a piston 8 and a control unit 21. The ignition plug 9 and the fuel injection valve 10 are positioned in the approximately center of an upper part of the combustion chamber 7. An inside cavity 8b is formed in the approximately center of a crown face of the piston 8. At the time of catalyst warming up operation, the control unit 21 injects fuel from the fuel injection valve 10 toward the inside cavity 8b in a compression stroke, forms predetermined air fuel mixture at an air fuel ratio richer than a theoretical air fuel ratio, only in a region inside and above the inside cavity 8b, performs ignition combustion by the ignition plug 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine, and more particularly to an in-cylinder direct injection internal combustion engine.

  In general, the thermal efficiency of an engine (internal combustion engine) is generally sufficient in a low-speed rotation / high-load operation region, and becomes worse as a low-load operation region or a high-speed rotation operation region. As a method for improving the thermal efficiency of such an engine, the throttle opening is increased to reduce pump loss (loss due to throttling), and the air-fuel ratio of the air-fuel mixture is made lean to increase the specific heat ratio of the working gas. A method for increasing the theoretical thermal efficiency by increasing the size is known.

  However, in the conventional engine, when the air-fuel ratio is made lean, the combustion period is prolonged and the combustion stability is deteriorated, so that there is a limit to making the air-fuel ratio lean.

An in-cylinder direct injection engine has been put to practical use as an engine that makes the air-fuel ratio lean while avoiding such deterioration in combustion stability. In this engine, fuel is injected directly into the cylinder (combustion chamber) in the latter half of the compression stroke, thereby forming a stratified mixture, bringing the air-fuel ratio in the vicinity of the spark plug to a combustible level, Reduce the air / fuel ratio in the region. As a result, stable combustion is performed, and a drastic air-fuel ratio reduction is realized when the cylinder interior is viewed in total. By adopting such an engine, it is possible to improve the thermal efficiency in the low-speed rotation / low-load operation region. For example, Patent Document 1 discloses an in-cylinder direct injection engine.
JP-A-10-169488

  In the in-cylinder direct injection engine disclosed in Patent Document 1, when it is necessary to raise the temperature of the exhaust gas, an air-fuel mixture that is richer than the stoichiometric air-fuel ratio is locally provided around the spark plug. This mixture is ignited and burned. By doing so, incomplete combustion of the air-fuel mixture occurs, and in the process in which the generated CO diffuses around, the surrounding oxygen (the oxygen in the air surrounding the air-fuel mixture that is locally rich) ) And react again. Then, heat generated by re-combustion with a late generation time increases the temperature of the exhaust gas without being converted into engine output.

  As described above, when the technique of Patent Document 1 is used, in a direct injection type engine, when performing a catalyst warm-up operation for warming up an exhaust purification device (hereinafter referred to as a catalyst) disposed in an exhaust passage. In addition, the temperature of the exhaust gas can be raised well.

  By the way, in the engine disclosed in Patent Document 1, the fuel injection valve is disposed in the upper peripheral portion of the combustion chamber, and the air-fuel ratio mixture that is locally richer than the stoichiometric air-fuel ratio around the spark plug. When the fuel cell is formed, it is necessary to extremely shorten the time from fuel injection to ignition. That is, fuel is injected from the fuel injection valve arranged in the upper peripheral portion of the combustion chamber toward the crown surface of the piston, and the fuel is directly sprayed into the vicinity of the spark plug by the shape of the piston crown surface. In an injection engine, the fuel after injection is likely to diffuse over time, so in order to burn the air-fuel mixture in a locally rich air-fuel ratio state, the time from fuel injection to ignition must be extremely short. Arise.

  However, when the time from fuel injection to ignition is shortened, there is a problem that the vaporization of the fuel adhering to the crown surface of the piston is not in time for ignition and the amount of smoke generated increases.

  An object of the present invention is to provide an engine (internal combustion engine) that can suppress the problem of an increase in the amount of smoke generated.

  An internal combustion engine according to the present invention includes a combustion chamber, a spark plug, a fuel injection valve, a piston, and a control device. The spark plug ignites the air-fuel mixture in the combustion chamber. The combustion injection valve is located substantially at the center of the upper part of the combustion chamber and injects fuel directly into the combustion chamber. The piston reciprocates due to the explosion of the air-fuel mixture in the combustion chamber, and a cavity is formed in the approximate center of the crown surface. The control device injects fuel from the fuel injection valve toward the cavity in the compression stroke during a predetermined operation required to increase the temperature of the exhaust gas exhausted from the combustion chamber, and in the cavity and the area above the cavity. Therefore, a predetermined air-fuel mixture richer than the stoichiometric air-fuel ratio is formed. In addition, the control device ignites and burns the predetermined air-fuel mixture thus formed by means of a spark plug.

  As described above, in the configuration of the internal combustion engine in which the fuel injection valve is arranged in the approximate center of the upper portion of the combustion chamber and the fuel is injected toward the cavity formed in the approximately center of the crown surface of the piston, The fuel can be held in this region for a relatively long time. For this reason, even when a predetermined air-fuel ratio richer than the stoichiometric air-fuel ratio is formed during a predetermined operation, the time from fuel injection to ignition can be increased and smoke can be suppressed. It becomes like this.

  In addition, when a predetermined air-fuel mixture richer than the stoichiometric air-fuel ratio is formed only in a region inside the inner cavity and above the inner cavity during the predetermined operation, the predetermined air-fuel mixture As a result, a sufficient amount of oxygen can be left in the region around the gas, so that CO generated in the combustion of a predetermined air-fuel ratio richer than the stoichiometric air-fuel ratio can be recombusted satisfactorily. . Thereby, the temperature of the exhaust gas discharged from the combustion chamber can be increased more effectively.

  In the internal combustion engine according to the present invention, the fuel is injected from the substantially central fuel injection valve in the upper part of the combustion chamber toward the substantially central cavity of the crown surface of the piston. Even when a predetermined air-fuel ratio rich air-fuel mixture is formed, it is possible to increase the time from fuel injection to ignition, and to suppress the occurrence of smoke.

  In addition, if the configuration is such that a predetermined air / fuel ratio richer than the stoichiometric air / fuel ratio is formed not only in the outer cavity but in the inner cavity and in the region above the inner cavity during the predetermined operation, the exhaust gas is discharged from the combustion chamber. It is possible to increase the temperature of the exhaust gas that is produced more effectively.

<Schematic configuration and operation of the engine>
FIG. 1 shows an engine (internal combustion engine) and a control device thereof according to an embodiment of the present invention.

  The engine 1 includes an intake passage 2, a combustion chamber 7, an exhaust passage 12, an electric throttle 5, an intake valve 6, an exhaust valve 11, a spark plug 9, a fuel injection valve 10, a control unit (control device) 21, and the like. Yes.

  The intake passage 2 is a passage for sucking air into the combustion chamber 7, and an air cleaner 3, an air flow meter 4, and an electric throttle 5 are arranged. When the signal from the air flow meter 4 is sent to the control unit 21, the control unit 21 calculates the amount of intake air to be taken into the combustion chamber 7 and sends a command to the electric throttle 5. The electric throttle 5 is a throttle valve for adjusting the amount of intake air into the combustion chamber 7, and adjusts the amount of air entering the combustion chamber 7 based on a command from the control unit 21.

  The intake valve 6 introduces air flowing through the intake passage 2 into the combustion chamber 7 at a predetermined timing. The intake valve 6 is driven by an intake cam 16 that rotates according to the rotation of a crankshaft (not shown).

  A piston 8 is disposed in the combustion chamber 7 so as to be capable of reciprocating vertically. An outer cavity 8 a and an inner cavity 8 b are provided on the crown surface of the piston 8. The two cavities 8a and 8b have a substantially circular cross-sectional shape orthogonal to the piston center axis A1. The centers of the two cavities 8a and 8b are both on the piston center axis A1.

  An ignition plug 9 and a fuel injection valve 10 are disposed in the upper part of the combustion chamber 7. The fuel injection valve 10 is a device that directly injects fuel into the cylinder (combustion chamber), and is located on the cylinder center axis A1 (the same axis as the piston center axis A1). That is, the fuel injection valve 10 is located substantially in the center in the upper part of the combustion chamber 7. The fuel injection valve 10 injects fuel in a hollow conical shape toward the crown surface of the piston 8.

  A high-pressure fuel pump 18 for increasing the fuel pressure (fuel pressure) is arranged on the cam shaft of the intake cam 16 so that fuel can be directly injected into the combustion chamber 7 from the fuel injection valve 10. Driven by rotation. The high-pressure fuel pump 18 may be driven by a rotational force other than the cam shaft of the intake cam 16 or may be driven by an electric motor that does not utilize the rotational force of the engine 1. The fuel boosted by the high-pressure fuel pump 18 is guided to the fuel injection valve 10 through the high-pressure fuel pipe 19.

  A fuel pressure sensor 20 is disposed in the high-pressure fuel pipe 19, and a signal from the fuel pressure sensor 20 is sent to the control unit 21. Since the required fuel pressure changes according to the operating state, the control unit 21 controls the operation of the high-pressure fuel pump 18. The control unit 21 receives signals from an accelerator opening sensor 25, a crank angle sensor 26, and a coolant temperature sensor 27. Based on the accelerator signal, the crank angle signal, and the coolant temperature sensor signal, the control unit 21 calculates the required torque, the engine speed, and the engine temperature, respectively, and determines the fuel according to the operating state and the required torque of the engine 1. The injection valve 10 and the spark plug 9 are operated.

  Depending on the timing of fuel injection from the fuel injection valve 10, the movement of the injected fuel in the combustion chamber 7 varies as follows.

  First, when the fuel injection valve 10 performs fuel injection relatively early in the compression stroke (when the position of the piston 8 is low) and the injected fuel collides with the bottom surface of the outer cavity 8a, the fuel after the collision Rises along the side of the outer cavity 8a. Due to such movement of the fuel, a relatively large mixture of air-fuel mixtures is formed in the outer cavity 8a and in the region above it.

  Next, when the fuel injection valve 10 performs fuel injection at a relatively late time during the compression stroke (when the position of the piston 8 is high), the injected fuel collides with the bottom surface of the inner cavity 8b. The fuel rises along the side surface of the inner cavity 8b. Due to such a movement of the fuel, a relatively small mixture of air-fuel mixtures is formed in the inner cavity 8b and the region above it.

  When the fuel injection valve 10 performs fuel injection during the intake stroke, a homogeneous air-fuel mixture is formed throughout the combustion chamber 7.

  An ignition plug 9 located substantially in the center of the upper portion of the combustion chamber 7 is disposed adjacent to the fuel injection valve 10 so that the above three types of air-fuel mixture can be ignited satisfactorily. . Specifically, the spark plug 9 can provide a good ignition even when the injected fuel collides with the bottom surface of the inner cavity 8b and a relatively small air-fuel mixture mass is formed only in the inner cavity 8b and the region above it. In order to be able to do so, it is located in the region above the inner cavity 8b where the air-fuel mixture mass exists. The ignition timing by the spark plug 9 is adjusted by the control unit 21.

  The exhaust passage 12 is a passage for discharging the gas burned in the combustion chamber 7 from the combustion chamber 7. The exhaust valve 11 disposed between the exhaust passage 12 and the combustion chamber 7 is driven by an exhaust cam 17 that rotates in accordance with the rotation of the crankshaft. When the exhaust valve 11 is opened, the gas in the combustion chamber 7 is guided to the exhaust passage 12 and discharged. An exhaust air / fuel ratio sensor 13 and an exhaust purification catalyst 14 are disposed in the exhaust passage 12. A temperature sensor 15 is installed in the exhaust purification catalyst 14. The exhaust air / fuel ratio and catalyst temperature data detected by these sensors 13 and 15 are sent to the control unit 21 as needed. The control unit 21 calculates the amount of fuel injected from the fuel injection valve 10 so that the output value of the exhaust air / fuel ratio sensor 13 becomes the air / fuel ratio necessary for exhaust purification. Further, the control unit 21 determines the catalyst activation state of the exhaust purification catalyst 14 according to the catalyst temperature detected by the temperature sensor 15 of the exhaust purification catalyst 14.

<Catalyst warm-up control and normal control by control unit>
Next, the catalyst warm-up control by the control unit 21 will be described according to the flow shown in FIGS. 2 to 4, and the normal control to be compared with the catalyst warm-up control will be briefly described. The catalyst warm-up control is a control for performing the catalyst warm-up operation when it is required to increase the temperature of the exhaust gas discharged from the combustion chamber 7 to promote the activation of the exhaust purification catalyst 14. The flowcharts shown in FIGS. 2 to 4 are calculated for each reference crank angle signal Ref.

  In step S1, the engine load L, the engine speed Ne, the water temperature Tw, and the catalyst temperature Tcat are calculated from various sensor outputs. The engine speed Ne is calculated from the output of the crank angle sensor, and the engine load L is calculated as a load required from the accelerator position.

  In step S2, it is determined whether or not the catalyst temperature Tcat has reached a predetermined temperature Tcatk. The predetermined temperature Tcatk is a temperature at which the exhaust purification catalyst 14 is completely activated. If the catalyst temperature Tcat has not reached the predetermined temperature Tcatk, the routine proceeds to step S3, where it is determined whether or not to perform catalyst warm-up control. Here, the activity determination of the exhaust purification catalyst 14 is performed based on the catalyst temperature Tcat, but other methods such as the activity determination of the exhaust purification catalyst 14 based on the water temperature Tw may be used.

  In step S3, it is determined whether or not the current operation state of the engine 1 is an operation state in which catalyst warm-up control is possible. Since the stratified charge combustion operation is performed in the catalyst warm-up control, specifically, in step S3, it is determined whether or not the operation of the engine 1 is performed in a region where the stratified charge combustion operation is possible. The region where the stratified combustion operation can be performed is determined in advance by experiments or the like.

  When the current operation of the engine 1 is in a region where the stratified charge combustion operation is possible, the routine proceeds to step S31, where catalyst warm-up control is performed.

  FIG. 3 shows the flow of the catalyst warm-up control in step S31. First, in step S4, a basic fuel injection amount Tp0 corresponding to the engine load L and the engine speed Ne is calculated from a map M5 held by the control unit 21. The map M5 of the basic fuel injection amount Tp0 is, for example, a map as shown in FIG. 5, and the basic fuel injection amount Tp0, which is a fuel injection amount required to generate the engine load L required for the engine 1, It can be determined by the engine speed Ne.

  In step S5, the fuel injection amount Tp for increasing the CO generation amount by enriching the air-fuel mixture at the time of ignition with respect to the catalyst air temperature Tcat is determined. Specifically, in step S5, a fuel increase correction value Hosco corresponding to the catalyst temperature Tcat is calculated, and the fuel injection amount Tp is obtained by multiplying the basic fuel injection amount Tp0 by the fuel increase correction value Hosco. That is, the fuel injection amount Tp is determined by the following equation.

Formula: Tp = Tp0 × Hosco
As shown in FIG. 6, the fuel increase correction value Hosco corresponding to the catalyst temperature Tcat is basically the amount of CO generated as the oxidation reaction rate of CO in the exhaust purification catalyst 14 increases, that is, together with the catalyst temperature Tcat. It is assumed that the value increases. Therefore, first, the fuel increase correction value Hosco is increased together with the catalyst temperature Tcat from the catalyst temperature Tcatk0 to Tcatk. When the catalyst temperature Tcat approaches the complete activation temperature Tcatk, the fuel increase correction value Hosco is decreased. However, at a catalyst temperature Tcatk0 or lower, the exhaust purification catalyst 14 is not activated even if CO is generated. Therefore, the fuel increase correction value Hosco is set to 1 so that the fuel increase correction is not substantially performed. Note that, when the catalyst temperature Tcat becomes equal to or higher than the complete activation temperature Tcatk, the control shifts from step S2 to the normal control of step S32, and thus the flow of the catalyst warm-up control does not enter. The fuel increase correction value Hosco based on the catalyst temperature Tcat shown in FIG. 6 is an example, and the curve in FIG. 6 is optimized according to the characteristics of the catalyst used, or the curve in FIG. It is also possible to change.

  In step S6, a target intake air amount Q is calculated. The target intake air amount Q is the amount of air that forms a stoichiometric air-fuel mixture with the fuel of the basic fuel injection amount Tp0 only in the region inside the inner cavity 8b and the region above the inner cavity 8b. When the ratio of the total volume of the combustion chamber 7 to the volume of the region forming the air-fuel mixture at the time of ignition (when the piston 8 is near the top dead center) is α, the air existing in the region forming the air-fuel mixture The quantity is expressed as [Q × α]. By making the ratio of the air amount [Q × α] and the basic fuel injection amount Tp0 equal to the theoretical air-fuel ratio, the target intake air amount Q can be obtained by the following equation.

Formula: Q = Theoretical air-fuel ratio x Tp0 / α
By setting the target intake air amount Q in this way, the air-fuel ratio of the air-fuel mixture formed in the inner cavity 8b and in the region above the inner cavity 8b is theoretically equivalent to the amount increased by the fuel increase correction value Hosco at the time of ignition. Richer than the air-fuel ratio.

  The average air-fuel ratio of the entire combustion chamber 7 is [Q / Tp], that is, [theoretical air-fuel ratio / (α × Hosco)]. Therefore, if [α × Hosco] is made smaller than 1, the average air-fuel ratio of the entire combustion chamber 7 can be made leaner than the stoichiometric air-fuel ratio. In general, it has been found that if the air-fuel ratio of the exhaust gas flowing into the catalyst (= the average air-fuel ratio of the entire combustion chamber 7) is set to a lean air-fuel ratio of about 15 to 17, the catalyst can be warmed up efficiently. The above fuel increase correction value Hosco may be set in consideration of the above.

  In step S7, the electric throttle 5 is driven and controlled so as to realize the target intake air amount Q set in step S6.

  In step S8, the ignition timing ADV retarded according to the fuel increase correction is calculated so that the output torque of the engine 1 does not become excessive due to the fuel increase correction in step S5. Specifically, first, the basic ignition timing ADV0 is calculated from a map (not shown) corresponding to the basic fuel injection amount Tp0 and the engine speed Ne. Then, the basic ignition timing ADV0 is corrected by the ignition timing retard amount Hosret corresponding to the fuel increase correction value Hosco, and the ignition timing ADV is obtained by the following equation.

Formula: ADV = ADV0−Hosret
The relationship between the fuel increase correction value Hosco and the ignition timing retard amount Hosret is, for example, as shown in FIG. Basically, as the fuel increase correction value Hosco increases and the fuel increase increases, the ignition timing retard amount Hosret increases.

  In step S9, it is determined whether or not the entire fuel injection amount Tp calculated in step S5 can be injected during the compression stroke. In order to form the air-fuel mixture only in the inner cavity 8b and the region above the inner cavity 8b, it is necessary to perform fuel injection when the position of the piston 8 is high. The range of the position is limited. Therefore, in step S9, the maximum fuel amount Tpmax that can be injected within a limited period in the compression stroke is compared with the fuel injection amount Tp, and when the fuel injection amount Tp is equal to or less than the maximum fuel amount Tpmax, fuel injection is performed. It is determined that the entire amount Tp can be injected during the compression stroke. Since the fuel injection period varies depending on the engine speed Ne, the control unit 21 uses the maximum fuel amount Tpmax corresponding to the engine speed Ne in the above comparison.

  If it is determined in step S9 that the entire fuel injection amount Tp can be injected during one compression stroke, the process proceeds to step S10. In step S10, the fuel injection amount Tp is set to the compression stroke fuel injection amount Tpa, and zero (0) is set to the intake stroke fuel injection amount Tpk. The compression stroke fuel injection amount Tpa is the amount of fuel injected from the fuel injection valve 10 during the compression stroke. The intake stroke fuel injection amount Tpk will be described later.

  On the other hand, if it is determined in step S9 that the entire fuel injection amount Tp cannot be injected during one compression stroke, the process proceeds to step S11. In step S11, the maximum fuel amount Tpmax is set as the compression stroke fuel injection amount Tpa, and the amount obtained by subtracting the compression stroke fuel injection amount Tpa from the total fuel injection amount Tp is set as the intake stroke fuel injection amount Tpk.

  The intake stroke fuel injection amount Tpk is the amount of fuel injected from the fuel injection valve 10 toward the inner cavity 8b in the intake stroke before the compression stroke. Even in the fuel injection during the intake stroke, if the injection timing is set near the top dead center of the piston 8, the injected fuel adheres to the bottom surface of the inner cavity 8b, and the fuel stays in the inner cavity 8b for a relatively long time. Will be held. In view of this, in the engine 1, when the entire fuel injection amount Tp cannot be injected during one compression stroke, it is the first (first) in the vicinity of the top dead center during the previous intake stroke. The injection is performed, and the second injection is performed during the compression stroke. When the ignition is performed by the spark plug 9, the air-fuel ratio richer than the stoichiometric air-fuel ratio is obtained only in the area inside the inner cavity 8b and above the inner cavity 8b. An air-fuel mixture is formed. Thereby, even when the required fuel increase correction is large, the increased fuel amount (fuel injection amount Tp) is ensured. Note that by making the average air-fuel ratio of the entire combustion chamber 7 equal to or higher than the stoichiometric air-fuel ratio, the air-fuel ratio richer than the stoichiometric air-fuel ratio only in the inner cavity 8b and the area above the inner cavity 8b during ignition by the spark plug 9 When the air / fuel mixture is formed, an air / fuel mixture leaner than the stoichiometric air / fuel ratio is formed around the air / fuel mixture.

  In step S12, the fuel injection timing IT in each of the fuel injection by the fuel injection valve 10 in the intake stroke and the fuel injection by the fuel injection valve 10 in the compression stroke is calculated from a map (not shown).

  In step S13, the compression stroke fuel injection time Tia and the intake stroke fuel injection time Tik are set in consideration of the invalid pulse width (the time until the fuel injection valve 10 actually opens after the operation instruction to the fuel injection valve 10). It calculates from the compression stroke fuel injection amount Tpa and the intake stroke fuel injection amount Tpk, respectively. Thereby, the fuel injection timing and the fuel injection time in the compression stroke and the intake stroke are determined, and the flow of the catalyst warm-up control is ended.

  In the above catalyst warm-up control, the fuel increase correction is performed. However, the catalyst warm-up control may be performed by changing only the fuel injection timing while setting the fuel injection amount and the like in the normal control described later. Is possible. For example, in the case of normal control, when the fuel injection timing is delayed and fuel is injected toward the inner cavity 8b when the fuel injection amount is to be injected toward the outer cavity 8a, the inside of the inner cavity 8b and the inner cavity 8b It is possible to form a mixture of air-fuel mixtures richer than the stoichiometric air-fuel ratio only in the region above the air.

  The above is the flow of catalyst warm-up control. On the other hand, if it is determined in step S2 or step S3 that the catalyst warm-up control is not performed or that the catalyst warm-up control is not possible, the process proceeds to step S32 and normal control is performed.

  The normal control flow in step S32 is shown in FIG. First, in step S14, the target equivalent ratio TFBYA is calculated from the target equivalent ratio map M9 corresponding to the engine load L and the engine speed Ne shown in FIG. The equivalence ratio is a ratio of the stoichiometric air fuel ratio to the air fuel ratio (= theoretical air fuel ratio / air fuel ratio). The target equivalent ratio TFBYA set in step S14 is a value obtained by dividing the stoichiometric air-fuel ratio by the target value of the average air-fuel ratio of the entire combustion chamber 7.

  In step S15, the electric throttle 5 is driven and controlled so that the target intake air amount Q obtained from the required engine load L and the target equivalent ratio TFBYA is secured. The target intake air amount Q is calculated by the following equation.

Formula: Q = L / TFBYA x Kt (Kt is a constant that matches the unit)
In step S16, the fuel injection amount Tp is calculated by the following equation from the target intake air amount Q, the engine speed Ne, and the target equivalent ratio TFBYA.

Formula: Tp = Q / Ne x TFBYA x Ktc (Ktc is a constant that matches the unit)
In step S17, the fuel injection timing IT is calculated from the fuel injection amount Tp and the engine speed Ne using a map. Since the fuel injection timing IT differs greatly between the stratified combustion operation and the homogeneous combustion operation, the control unit 21 has a plurality of maps of the fuel injection timing IT corresponding to the target equivalence ratio TFBYA (see FIG. 1).

  When the target equivalent ratio TFBYA is 1 or more (that is, when the air-fuel ratio is the stoichiometric air-fuel ratio or an air-fuel ratio richer than that), homogeneous combustion is performed, so the fuel injection timing IT is set during the intake stroke. Reference is made to the homogeneous combustion operation map M0.

  When the target equivalent ratio TFBYA is smaller than 1 (that is, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio), stratified combustion is performed, so stratified combustion in which the fuel injection timing IT is set during the compression stroke The operation map M1 or the stratified combustion operation map M2 is referred to. Here, two types of stratified combustion operation maps are prepared. When the target equivalent ratio TFBYA is relatively large (the amount of fuel injection is large), fuel injection is performed at a relatively early time during the compression stroke, and in the area above the outer cavity 8a and the outer cavity 8a and the inner cavity 3b. Reference is made to a stratified combustion operation map M1 for forming a relatively large mixture of air-fuel mixtures. On the other hand, when the target equivalent ratio TFBYA is relatively small (the amount of fuel injection is small), fuel is injected at a relatively late time during the compression stroke, and is relatively small in the inner cavity 8b and the area above the inner cavity 8b. Reference is made to a stratified combustion operation map M2 for forming an air-fuel mixture mass.

  In step S18, the ignition timing ADV is calculated from the fuel injection amount Tp and the engine speed Ne using a map (not shown).

  In step S19, the fuel injection time Ti is calculated from the fuel injection amount Tp in consideration of the invalid pulse width. Thus, the fuel injection timing and the fuel injection time are determined, and the normal control flow is completed.

<Engine features>
(1)
In the engine 1, the temperature of the exhaust gas discharged from the combustion chamber 7 is increased to promote the activation of the exhaust purification catalyst 14, and during the catalyst warm-up operation, the crown of the piston 8 from the fuel injection valve 10 during the compression stroke is required. Fuel is injected toward the inner cavity 8b on the surface, and an air-fuel mixture richer than the stoichiometric air-fuel ratio (hereinafter referred to as a rich air-fuel mixture) is only in the inner cavity 8b and the region above the inner cavity 8b. It is formed. A rich air-fuel mixture is formed only in the area inside the inner cavity 8b and above the inner cavity 8b. In the state where an air-fuel mixture leaner than the stoichiometric air-fuel ratio is formed around the rich air-fuel mixture. Then, ignition by the spark plug 9 is performed.

  Here, in order to inject fuel from the fuel injection valve 10 at the approximate center of the upper portion of the combustion chamber 7 toward the inner cavity 8b formed at the approximate center of the crown surface of the piston 8, The rich air-fuel mixture can be held for a relatively long time only in the area above 8b. For this reason, the time from the fuel injection by the fuel injection valve 10 to the ignition by the spark plug 9 can be made long, and the generation of smoke is almost eliminated.

  Further, during the catalyst warm-up operation, the rich mixture is formed not only in the outer cavity 8a but in the region inside the inner cavity 8b and above the inner cavity 8b, so that a sufficient amount is provided in the region around the rich mixture. The remaining oxygen can be made to remain, and the CO generated by the combustion of the rich mixture can be reburned well. Thereby, the temperature of the exhaust gas discharged from the combustion chamber 7 is effectively increased.

(2)
In the engine 1, during the stratified combustion operation in the normal control, it is necessary to completely burn the stratified mixture. Therefore, the control unit 21 performs control so that the air-fuel ratio of the stratified mixture becomes a value close to the theoretical air-fuel ratio. Yes. For this reason, the fuel injection timing is set so that a large stratified mixture is formed when the fuel injection amount is large and a small stratified mixture is formed when the fuel injection amount is small (FIG. 8A). reference). That is, when the fuel injection amount is large, the fuel injection timing is early, and the fuel is injected into both cavities 8a and 8b of the piston 8, whereby a large stratified mixture is formed in the area above both cavities 8a and 8b. When the injection amount is small, the fuel injection timing is late, and the fuel is injected into the inner cavity 8b of the piston 8, so that a small stratified mixture is formed only in the region above the inner cavity 8b.

  On the other hand, during the catalyst warm-up control, the control unit 21 controls the air-fuel ratio of the small stratified mixture to be richer than the stoichiometric air-fuel ratio. For this reason, even if the fuel injection amount forms a large stratified mixture during normal control, a small stratified mixture may be formed during the catalyst warm-up operation (see FIG. 6A). For example, as shown in FIGS. 8A and 8B, in the range of fuel injection amounts Tpz1 to Tpz2, fuel is injected into the outer cavity 8a during normal operation, whereas fuel injection is performed during catalyst warm-up operation. The fuel is injected into the inner cavity 8b at a delayed time. In other words, when compared with the same fuel injection amount (and the same engine speed), the fuel injection timing during the catalyst warm-up control is set to be delayed from the fuel injection timing during the normal control.

  Thus, when the amount of fuel injection required for generating CO due to incomplete combustion in the catalyst warm-up operation is large, the ignition plug at the time of ignition is retarded by retarding the fuel injection timing in addition to the increase in fuel. A high degree of richness of the rich air-fuel mixture in the vicinity of 9 can be secured.

(3)
In the catalyst warm-up operation, the control unit 21 of the engine 1 changes the rich degree of the rich mixture according to the warm-up degree of the exhaust purification catalyst 14. Specifically, as shown in FIG. 6, by changing the fuel increase correction value Hosco in accordance with the catalyst temperature Tcat, the richness of the air-fuel ratio of the rich air-fuel mixture formed in the vicinity of the spark plug 9 at the time of ignition is changed. It is changing.

  As a result, the amount of CO generated due to the incomplete combustion of the rich air-fuel mixture is changed according to the warm-up state of the exhaust purification catalyst 14, and the exhaust gas is discharged while reducing the warm-up time of the exhaust purification catalyst 14. Can be suppressed.

  As described above, the fuel increase correction value Hosco based on the catalyst temperature Tcat shown in FIG. 6 is an example, and the curve in FIG. 6 is optimized according to the characteristics of the catalyst used, or depending on the degree of deterioration of the catalyst. It is effective to change the curve of FIG.

For example, in the case of using a normal temperature active catalyst oxidation reaction of CO Excluding moisture and HC occur from room temperature as the exhaust purification catalyst 14, immediately after the start of the exhaust purification catalyst 14 is not activated and a large amount of CO 0 ₂ and Is preferably sent to the exhaust purification catalyst 14 to quickly warm up the exhaust purification catalyst 14. After that, since warming up becomes unnecessary as the catalyst temperature Tcat increases, it is desirable to reduce the rich degree.

In the case of using the conventional three-way catalyst or the like as an exhaust purification catalyst 14 instead of the normal temperature active catalyst, until the catalyst temperature Tcat rises to a certain extent, be sent to the CO and 0 ₂ in the exhaust purification catalyst 14 oxidation exhaust since the reaction does not occur, performs the normal operation at a temperature where the catalyst temperature Tcat such as immediately after starting of the engine 1 does not occur oxidation reaction, from the catalyst temperature Tcat is equal to or higher than the temperature of occurrence of the oxidation reaction, a CO and 0 ₂ It is desirable to send it to the purification catalyst 14. Thereafter, as the temperature rises, the oxidation reaction becomes faster. Therefore, by increasing the rich mixture rich degree and increasing the oxidation reaction heat of the exhaust purification catalyst 14, the time until the exhaust purification catalyst 14 is completely warmed up is shortened. It is desirable to make it.

(4)
In the engine 1, during the catalyst warm-up operation, the average air-fuel ratio of the entire combustion chamber 7 is made leaner than the stoichiometric air-fuel ratio, specifically, the average air-fuel ratio of the entire combustion chamber 7 is made a lean air-fuel ratio of about 15-17. Thus, the exhaust purification catalyst 14 is efficiently warmed up. In this way, by controlling the intake air amount so that the air-fuel ratio (exhaust air-fuel ratio) of the exhaust gas flowing into the exhaust purification catalyst 14 becomes 15 to 17, CO generated from the rich mixture near the spark plug 9 As a result, the oxygen concentration required for the oxidation reaction is ensured around the rich air-fuel mixture, and a decrease in exhaust gas temperature due to unnecessary working air can be suppressed.

<Other embodiments>
(A)
In the above embodiment, the fuel injection valve 10 has a constant spray angle when spraying fuel (vertical angle of the hollow cone spray), but the spray angle as shown in FIG. 10 can be changed. When the fuel injection valve 50 is used, it is possible to perform injection from the fuel injection valve 50 to the inner cavity 8b of the piston 8 in a wider range. Specifically, for example, if the spray angle is decreased, the maximum fuel amount Tpmax that appears in step S9 can be increased, and the catalyst warm-up control is performed only by fuel injection in the compression stroke without using fuel injection in the intake stroke. The range that can be used becomes wider. In addition, while setting the fuel injection timing in the same manner as during normal control, only the spray angle can be changed, and a rich air-fuel mixture can be formed in the inner cavity 8b and the region above it during ignition. In other words, even during the normal operation, even when the fuel injection amount is to be injected toward the outer cavity 8a, if the spray angle is reduced, the fuel is injected toward the inner cavity 8b without changing the fuel injection timing. The catalyst can be warmed up by injecting.

  Below, the fuel injection valve 50 with a variable spray angle is demonstrated with reference to FIG. 10 and FIG.

  FIG. 10 is a longitudinal sectional structure of an injection portion of the fuel injection valve 50 having a variable spray angle. The fuel injection valve 50 includes a main body 51 and a needle valve 52. In the main body 51, a main channel 50a, a first branch channel 50c, and a second branch channel 50d are formed. A nozzle hole 50 b is formed on the lower surface of the main body 51. The first branch channel 50c and the second branch channel 50d are channels that connect the main channel 50a and the nozzle hole 50b. However, the first branch channel 50c and the second branch channel 50d are in different positions at which the main channel 50a communicates with the main channel 50a. It extends from the flow path 50a to the nozzle hole 50b. In the fuel injection valve 50, the fuel can be shut off or the fuel can be injected from the injection hole 50b by the lift of the needle valve 52. Further, the fuel injection valve 50 has a structure in which the amount of fuel flowing to the first branch channel 50c and the amount of fuel flowing to the second branch channel 50d can be changed depending on the lift amount of the needle valve 52.

  The operation of the fuel injection valve 50 will be described with reference to FIG.

  When the needle valve 52 is at the lowest position with respect to the main body 51, the first branch flow path 50c and the second branch flow path 50d are blocked by the needle valve 52, and fuel is not injected from the injection hole 50b.

  When the needle valve 52 moves upward (lifts), first, fuel flows from the main flow path 50a to the first branch flow path 50c, and the fuel is injected from the injection holes 50b. In this case, since the fuel is injected through the first branch channel 50c, the spray angle is determined by the angle of the first branch channel 50c.

  When the needle valve 52 further moves upward, the fuel flows not only through the first branch channel 50c but also through the second branch channel 50d. Then, the fuel is injected from the nozzle hole 50b, but the injected fuel collides due to the difference between the angle of the first branch channel 50c and the angle of the second branch channel 50d, and flows through both channels 50c and 50d. The spray angle varies depending on the fuel amount ratio.

  When the needle valve 52 moves up to the maximum lift amount, fuel is injected from the injection hole 50b only through the second branch channel 50d, and the spray angle is determined by the angle of the second branch channel 50d. The

  As apparent from the operation of the fuel injection valve 50, the spray angle (spray direction) of the fuel from the fuel injection valve 50 can be changed by adjusting the lift amount of the needle valve 52. In order to set the lift amount of the needle valve 52 to a desired value, for example, a piezo-type fuel injection valve using a piezo element whose deformation amount changes depending on the voltage as the actuator of the needle valve 52 is employed as the fuel injection valve 50. That's fine.

(B)
The catalyst warm-up control in the embodiment described above is not only immediately after engine start, which is required to increase the temperature of the exhaust gas for activation of the exhaust purification catalyst 14, or during low load operation in an environment where the outside air temperature is low, For example, it can also be employed when performing an operation of raising the temperature of the exhaust purification catalyst 14 in order to remove SOx adhering to the exhaust purification catalyst 14.

  In the internal combustion engine according to the present invention, when a predetermined mixture having an air-fuel ratio richer than the stoichiometric air-fuel ratio is formed during a predetermined operation in which it is necessary to raise the temperature of the exhaust gas such as a catalyst warm-up operation, The time until ignition can be increased, and the occurrence of smoke can be suppressed. Therefore, the internal combustion engine according to the present invention is useful as an in-cylinder direct injection internal combustion engine.

1 is a schematic configuration diagram of an engine according to the present invention. It is a flowchart of the control performed for every reference | standard crank angle signal Ref. It is a flowchart of catalyst warm-up control. It is a flowchart of normal control. It is a map which shows the basic fuel injection quantity with respect to engine load and rotation speed. It is a graph which shows the fuel increase correction value with respect to catalyst temperature. It is a graph which shows the retard amount of ignition timing correction | amendment with respect to a fuel increase correction value. (A) It is a graph which shows the fuel-injection time at the time of the compression stroke in normal driving | operation.

(B) It is a graph which shows the fuel-injection time at the time of the compression stroke in catalyst warm-up operation.
It is a map which shows the target equivalence ratio with respect to engine load and rotation speed. It is sectional drawing of the fuel injection valve in other embodiment. It is a figure which shows the action | operation of the fuel injection valve in other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 7 Combustion chamber 8 Piston 8a Outer cavity 8b Inner cavity 9 Spark plug 10 Fuel injection valve 14 Exhaust gas purification catalyst 21 Control unit 50 Fuel injection valve

Claims (12)

A combustion chamber;
A spark plug for igniting the air-fuel mixture in the combustion chamber;
A fuel injection valve that is located substantially in the center of the upper portion of the combustion chamber and injects fuel directly into the combustion chamber;
A piston with a cavity formed substantially in the center of the crown surface;
During a predetermined operation required to increase the temperature of exhaust gas discharged from the combustion chamber, fuel is injected from the fuel injection valve toward the cavity in a compression stroke, and the regions in the cavity and above the cavity A control device that only forms a predetermined air-fuel ratio richer than the stoichiometric air-fuel ratio and ignites and burns the predetermined air-fuel mixture with the spark plug;
An internal combustion engine. The cavity is divided into at least an inner cavity and an outer cavity located around the inner cavity;
In the predetermined operation, the control device injects fuel from the fuel injection valve toward the inner cavity in a compression stroke, and forms the predetermined air-fuel mixture only in the area inside the inner cavity and above the inner cavity. ,
The internal combustion engine according to claim 1. The spark plug is disposed substantially at the center of the upper portion of the combustion chamber, and is located in a region where the predetermined air-fuel mixture formed during the predetermined operation exists.
The internal combustion engine according to claim 1 or 2. The control device, during the predetermined operation, injects fuel from the fuel injection valve toward the cavity in a compression stroke, and has an air-fuel ratio richer than the stoichiometric air-fuel ratio only in the cavity and in the region above the cavity. Forming a predetermined air-fuel mixture, and forming an air-fuel mixture leaner than the stoichiometric air-fuel ratio or air containing no fuel around the predetermined air-fuel mixture.
The internal combustion engine according to any one of claims 1 to 3. Even when the amount of fuel is such that fuel is injected from the fuel injection valve into the outer cavity during normal operation, the control device supplies fuel from the fuel injection valve into the inner cavity during the predetermined operation. Spray,
The internal combustion engine according to claim 2. The control device makes the air-fuel ratio of the predetermined air-fuel mixture richer than the stoichiometric air-fuel ratio by increasing the amount of fuel during the predetermined operation and injecting fuel into the cavity from the fuel injection valve compared to the normal operation. To
The internal combustion engine according to any one of claims 1 to 5. The control device, during the predetermined operation, retards the timing of fuel injection compared to during normal operation and injects fuel into the cavity from the fuel injection valve, thereby reducing the air-fuel ratio of the predetermined air-fuel mixture to the stoichiometric air-fuel ratio. Make it richer than the fuel ratio,
The internal combustion engine according to any one of claims 1 to 6. The combustion injection valve can change the spray direction of fuel to be sprayed,
The control device changes the spray direction of the fuel by the combustion injection valve during the predetermined operation and injects the fuel into the inner cavity from the fuel injection valve as compared with the normal operation, so that the air-fuel ratio of the predetermined mixture is increased. To make it richer than the theoretical air-fuel ratio,
The internal combustion engine according to claim 2. During the predetermined operation, the control device injects fuel from the fuel injection valve toward the inner cavity in a compression stroke, and further injects fuel from the fuel injection valve toward the inner cavity in an intake stroke. The predetermined air-fuel mixture is formed only in the area inside the inner cavity and above the inner cavity at the time of ignition by the spark plug.
The internal combustion engine according to claim 2. The predetermined operation is a time when it is necessary to warm up the catalyst for purifying the exhaust gas.
The internal combustion engine according to any one of claims 1 to 9. The controller changes the rich degree of the air-fuel ratio of the predetermined mixture according to the warm-up degree of the catalyst during the predetermined operation.
The internal combustion engine according to claim 10. The control device controls the intake air amount so that the average air-fuel ratio in the combustion chamber is about 15 to 17 during the predetermined operation.
The internal combustion engine according to any one of claims 1 to 11.

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