JP2006283684A - Direct injection type internal combustion engine and combustion method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate warming up by retard combustion without deteriorating combustion stability and exhaust emission performance in a spark ignition type direct injection type internal combustion engine. <P>SOLUTION: Main combustion is performed by igniting first injection fuel injected and supplied toward a first cavity 31 and second injection fuel injected and supplied toward a second cavity 32 is ignited and burned after that. Since sufficient oxygen necessary for combustion remains in the second cavity zone after main combustion, fuel additionally supplied by second injection is easily ignited in high temperature atmosphere accompanying the main combustion and sufficiently burns. Consequently, warming up or activation of the catalyst 5 is accelerated. Since injected fuel is retained in spray lump shape by the cavity, discharge of unburned fuel accompanying adhesion of fuel on a cylinder wall surface or the like does not happen. Since variation of spray lumps of each cycle is small, combustion stability is not deteriorated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in a spark ignition direct injection internal combustion engine or a combustion method thereof.

  In an internal combustion engine equipped with an exhaust purification catalyst, in order to improve exhaust emission performance after cold start, there is a problem of how quickly the temperature of the catalyst is raised to the activation temperature after start. In response to this problem, in a spark ignition type direct injection internal combustion engine, taking advantage of the feature that the fuel supply into the cylinder can be controlled relatively freely, the temperature of the exhaust is increased by supplying secondary additional fuel. There has been proposed one that promotes activation of the catalyst.

For example, in Patent Document 1, in addition to the injected fuel for main combustion, additional fuel is injected and supplied during the expansion stroke or exhaust stroke, and the additional fuel is ignited and burned, or provided in the exhaust pipe. With the spark plug, the additional fuel mixed in the exhaust gas is ignited and burned. Moreover, in the thing of patent document 2, what was made to raise exhaust gas temperature by performing additional supply of fuel in the middle stage-latter stage of an expansion stroke so that the thermal energy of additional fuel may not be lost as expansion work. .
JP 4-183922 A JP 2000-145511

  With the thing of patent document 1, since it is necessary to perform ignition twice within a short time after the latter stage of the compression stroke, in addition to complication of ignition control, it can only deal with two close ignition opportunities. High energy type ignition coil is required, which raises cost and durability concerns. In addition, since the fuel from the main injection is almost completely burned in the expansion stroke and the exhaust stroke, there are few chemically active species to be fired in the exhaust including the additional fuel. High energy is required, and the existing ignition device cannot obtain sufficient energy necessary for ignition and combustion may not be established. Further, in Patent Document 2, the fuel injected from the middle stage to the latter stage of the expansion stroke overflows to the outside of the piston cavity because the piston descends to the vicinity of the bottom dead center, and as a result, the spray diffuses and propagates the flame. The cycle variation increases, and the stability of the engine deteriorates. In addition, when fuel is injected into the already burned region, there is a possibility that since the remaining oxygen is low, the oxidation reaction of the injected fuel does not proceed and the fuel is discharged as unburned fuel.

The present invention is based on a direct injection internal combustion engine provided with a fuel injection valve for supplying fuel to a cavity formed on the piston crown surface and an ignition plug so as to face the combustion chamber. Or the combustion method is the gist.
An operation state detection device that detects an engine operation state, and a control device that controls a fuel injection timing by the fuel injection valve, a fuel injection amount, and an ignition timing by the spark plug based on the detected operation state, A cavity is formed from a plurality of cavity regions, and the control device is configured to cause the fuel injection valve to perform a first injection before ignition and a second injection after ignition in a cold state, and The fuel injection valve is configured so that the fuel sprays of the first injection and the second injection are directed to different cavity regions.
In a cold state, after performing the first injection toward the first cavity region of the plurality of cavity regions before ignition by the fuel injection valve, and igniting the injected fuel by the first injection, A second injection is performed toward the second cavity region, and the fuel injected by the second injection is combusted in a combustion chamber region having a relatively high oxygen concentration.

  According to the direct injection internal combustion engine or the combustion method according to the present invention, the fuel of the first injection injected and supplied toward the first cavity region is ignited to cause main combustion, and then the second cavity region. The fuel of the second injection injected and supplied toward is ignited and burned. Since the second cavity region is different from the first cavity region where the main combustion is performed, oxygen necessary for the combustion is sufficiently left. Therefore, the fuel additionally supplied by the second injection is not subjected to the main combustion. It is easily ignited in a high-temperature atmosphere that accompanies it, and combustion is sufficiently performed. As a result, the high-temperature exhaust gas is discharged, so that the engine warm-up or the temperature increase of the catalytic converter provided in the exhaust passage can be completed quickly.

  On the other hand, the shape of the spray lump is held to some extent by the second cavity region, or the diffusion of the spray lump is suppressed, so that the unburned fuel is discharged due to the fuel adhering to the cylinder wall surface or the like. Absent. Moreover, since the dispersion | variation in the spray lump for every cycle decreases for the same reason as described above, the combustion stability is not impaired by the second injection.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, common parts are denoted by the same reference numerals. FIG. 1 shows a schematic configuration of an internal combustion engine to which the present invention is applicable. In the figure, 1 is an internal combustion engine body, 2 is an intake passage, 3 is a throttle valve, 4 is an exhaust passage, 5 is a catalytic converter, 6 is an intake valve, 7 is an exhaust valve, 8 is a fuel injection valve, and 9 is a spark plug. is there. 10 is a control unit, 11 is an intake air amount sensor, 12 is an accelerator opening sensor, 13 is a crank angle sensor, 14 is a coolant temperature sensor, and 15 is an exhaust oxygen sensor. Reference numeral 17 denotes a fuel pump that pumps fuel to the fuel injection valve 8 by cam driving, and 16 is a pressure sensor that detects the fuel pressure. Reference numeral 21 denotes a combustion chamber, and 24 denotes a piston.

  The control unit 10 corresponds to a control device according to the present invention, and is constituted by a microcomputer including a CPU and its peripheral devices. The control unit 10 is an internal combustion engine based on inputs from various sensors 11 to 16 as the operating state detection device. The operation state of the engine is judged, and the operation of the fuel pump 17, the fuel injection nozzle 8 and the spark plug 9 is controlled so that the fuel injection timing, the injection amount, and the ignition timing respectively match predetermined target values.

  This internal combustion engine is a four-valve type provided with two intake valves 6 and two exhaust valves 7, and a fuel injection valve 8 and a spark plug 9 are respectively disposed near the center of the combustion chamber surrounded by the four valves. is there. The fuel injection valve 8 is attached so that the center of the fuel spray is substantially parallel to the cylinder axis.

  As shown in FIG. 2-1 or FIG. 2-2, a first cavity 31 having a relatively small diameter and a circular concave shape is surrounded on the crown surface of the piston 24 so as to face the fuel injection valve 8. In this way, a second cavity 32 having an annular shape with a relatively large diameter is formed. The combustion chamber space region immediately above the first cavity 31 and the second cavity 32 is referred to as a first cavity region and a second cavity region, respectively.

  The centers of the first and second cavities 31 and 32 and the center of the fuel injection valve 8 are set so as to substantially coincide with the cylinder axis, whereby the fuel spray from the fuel injection valve 8 is approximately cavities 31. Colliding with the center of the. On the other hand, the spark plug 9 has a spray guide arrangement in which the discharge electrode portion 9 a is positioned close to the fuel spray from the fuel injection valve 8.

  The fuel injection valve 8 inclines the fuel spray with respect to the cylinder axis so that the fuel spray moves between the first cavity 31 and the second cavity 32 according to the position of the piston 24. . Therefore, in this embodiment, a multi-hole nozzle or an outward type nozzle that injects fuel along a virtual conical surface having the nozzle portion at the top is applied as the fuel injection valve 8. As a result, the fuel spray is inclined with respect to the cylinder axis. Therefore, as shown in FIG. 3A, when the piston 24 is located near the top dead center, the fuel is sprayed only in the first cavity 31 having a small diameter. As the piston 24 descends, the diameter of the fuel spray is relatively increased. Therefore, as shown in FIG. 3B, most of the injected fuel is second cavity 32 having a relatively large diameter. It becomes possible to supply only to. In addition, the fuel spraying by the hole nozzle or the outward type nozzle has an advantage that even when the in-cylinder pressure rises in the latter half of the compression stroke, the squeezing or shape change of the spray mass is small.

  Next, an embodiment of a combustion system under the above configuration will be described. In general, in a direct injection internal combustion engine, fuel is injected and supplied during the compression stroke to stratify the mixture, and a stratified combustion operation mode in which operation is performed at a lean air-fuel ratio, and fuel is injected and supplied during the intake stroke. The mode of the homogeneous combustion operation in which the operation with the relatively rich premixed gas near the air-fuel ratio is performed is switched according to the operation state. The operation mode according to the present invention is basically a stratified combustion operation in which fuel injection is performed after the compression stroke, and in particular in the cold state before the exhaust purification catalyst is activated, fuel injection is performed twice with the ignition timing interposed therebetween. It is characterized by that. In the configuration shown in FIG. 1, the control unit 10 makes a determination based on a signal from the cooling water temperature sensor 14, and when the actual cooling water temperature is lower than a predetermined reference temperature, the cooling unit state is determined. And the combustion control according to the present invention is applied.

  FIG. 4 is a basic timing chart based on the control. In the figure, Pf is an injection pulse signal output from the controller 10 to the fuel injection device, Pi is an ignition pulse signal also output to the ignition device, and D1 or D2 is the amount of residual oxygen in the first cavity region and the second cavity region, respectively. Represents. The injection pulse signal Pf indicates that the rising edge of the pulse opens the nozzle of the fuel injection valve 8 to start fuel injection, and the falling edge closes the nozzle to end fuel injection. It is injected into the combustion chamber. The ignition pulse signal Pi is supplied with a discharge current to the spark plug 9 as the pulse is generated.

  In the present invention, as shown, the first injection F1 is performed before ignition and the second injection F2 is performed after ignition. In this embodiment, as shown in FIG. 3, the first injection injects fuel toward the first cavity 31 at the end of the compression stroke in which the piston 24 is located near the top dead center. In the second injection, the fuel is injected into the second cavity 32 after the middle stage of the expansion stroke in which the piston 24 is away from the top dead center. By doing so, the fuel of the first injection burns almost only in the first cavity region (residual oxygen amount D1), so that residual oxygen is secured in the second cavity region until the second injection (residual oxygen amount D2). ), The fuel of the second injection is ignited and combusted in the second cavity region having the residual oxygen. In this way, as a result of extending or delaying the combustion period until the middle of the expansion stroke, it is possible to increase the temperature by supplying much of the combustion energy to the exhaust, and to quickly increase the temperature of the catalyst It becomes.

  More specifically, since there is little gas flow in the cylinder near the compression top dead center and the back pressure is high, the influence of disturbance due to gas flow can be reduced by performing the first injection at this time, and the spray penetration is also reduced. Therefore, the fuel can be reliably supplied into the small-diameter first cavity 31 to improve the combustion stability. In addition, since the interval from the first injection to the ignition timing is shorter than the case where the injection is performed relatively early in the first half to the middle of the compression stroke, it is also possible to reduce the diffusion of the air-fuel mixture and the deviation of the mixing ratio. Contributes to combustion. On the other hand, by performing the second injection so that the fuel is introduced into the second cavity 32 having a relatively large diameter during the expansion stroke, the diffusion of the fuel in the second injection is also suppressed, and the discharge of unburned fuel is prevented. , Stable combustion can be maintained. As a result, the combustion period can be significantly retarded, so that the exhaust gas temperature can be effectively increased to activate the catalyst at an early stage.

  Further, in this case, since the circular or annular cavities 31 and 32 are formed concentrically, the fuel injected and supplied to any of the cavities diffuses in a cylindrical or annular manner in an isotropic manner in the combustion chamber. For this reason, a region that is excessively rich or lean is not generated in the air-fuel mixture, and there is no combustion failure or smoke due to a deviation in the air-fuel mixture concentration.

  In order to obtain the effect, the timing of the first injection and ignition is not limited to before the top dead center, but the first injection, that is, the main combustion injection fuel is reduced in diameter to a relatively early stage prior to the ignition timing. By performing the process toward the first cavity 31, it is possible to form a stratified air-fuel mixture that is compact and that remains stable in the cavity and the combustion chamber space above it and that does not diffuse easily. By igniting, stable main combustion is possible. Further, by performing the second injection toward the second cavity 32 having a large diameter at a relatively later stage thereafter, a large-diameter annular mixture is formed, and the discharge electrode of the spark plug located near the center of the combustion chamber Since the portion 9a is not exposed to the rich air-fuel mixture, the smoldering of the spark plug that tends to occur when ignited in a rich atmosphere can be avoided. Moreover, since this spray lump is contained in the inner region of the second cavity 32, it is possible to prevent discharge of unburned fuel and a decrease in combustion stability due to fuel adhering to the cylinder wall surface.

  In the above-described embodiment, the first injection is performed on the first cavity 31 having a small diameter and the second injection is performed on the second cavity 32 having a large diameter. Unlike this, as shown in FIG. The first injection may be performed on the second cavity 32 having a large diameter, and the second injection may be performed on the first cavity 31 having a small diameter. That is, as shown in FIG. 5A, the first injection is performed toward the outer second cavity 32 when the piston is relatively far from the top dead center during the compression stroke. Is performed toward the first inner cavity 31 when the piston is located at a position relatively close to the top dead center during the expansion stroke, as shown in FIG.

  Usually, stable combustion is possible by performing the first injection toward the second cavity 32 in the middle of the compression stroke where the piston is relatively far from the top dead center. Also, in this case, the second injection is performed at a time when the fuel is surely introduced into the first cavity 31 having a small diameter, for example, at the beginning of the expansion stroke where the piston is relatively close to the top dead center, thereby diffusing the air-fuel mixture. Therefore, it is possible to prevent unburned fuel from being discharged, and to avoid a decrease in combustion stability associated with the execution of the second injection.

  If fuel is injected and supplied to the small-diameter first cavity 31 while the engine speed or load is high to some extent, the rich air-fuel mixture concentrates in the vicinity of the discharge electrode portion 9a of the spark plug, resulting in excessive rich combustion. Plug smoldering or combustion stability may be impaired. Under such conditions, the first injection is performed on the second cavity 32 having a large diameter, so that the above-described problem can be avoided by setting the vicinity of the discharge electrode portion 9a as a relatively lean atmosphere. In this case, by performing the second injection toward the first cavity 31 having a small diameter, it is possible to effectively increase the exhaust temperature by effectively using the residual oxygen.

  In the embodiment, the fuel injection amount is set so that the sum of the fuel injection amount of the first injection and the fuel injection amount of the second injection constitutes the theoretical air-fuel ratio (approximately 14.5 to 15) with respect to the cylinder intake air amount. By setting, the input heat amount can be maximized and the activation of the catalyst can be achieved in the minimum time.

  However, if the retarding of the combustion period is performed by the second injection, the exhaust temperature becomes excessive and the durability of the catalyst may be impaired. On the other hand, by making the injection amount of the second injection smaller than that of the first injection, it is possible to shorten the time until activation while preventing overheating of the catalyst. In addition, even when the warm-up is completed or during the warm-up process, even if the fuel injection amount increases due to an increase in the load, the exhaust temperature may be excessively increased as an effect of retarding the combustion period by the second injection. Arise. This can be dealt with by reducing the injection amount of the second injection as the load increases, or by stopping the second injection when the load is higher than a predetermined reference load. it can. That is, it is possible to avoid the disadvantage that the exhaust temperature rises excessively by suppressing the retard of the combustion period by reducing the injection amount of the second injection or stopping the injection, and promote the activation while protecting the catalyst.

  In the above-described embodiment, after the warm-up is completed (after the catalyst is activated), basically, fuel injection into the first cavity 31 having a small diameter is performed, so that a compact stratified mixture is formed in the vicinity of the discharge electrode portion 9a of the spark plug. A lump may be formed to perform lean operation. As a result, the fuel consumption can be greatly reduced as compared with the case of performing a homogeneous operation. Even in the region where the load or the rotational speed is relatively high even in the stratified combustion operation region, the same effect as described above can be expected even if the first injection is performed on the second cavity 32 having a large diameter. FIG. 6 shows the operation region, where A in the drawing is an operation region in which fuel is injected into the first cavity 31 having a small diameter, and B in the drawing is an operation region in which fuel is injected into the second cavity 32 having a large diameter. Is shown. The region of higher speed or higher load than the region B is the above-described homogeneous combustion operation region.

  In the above-described embodiment, the fuel injection valve 8 is a multi-hole nozzle or an outward type nozzle, so that the injected fuel can be transferred between the first and second cavity regions with a single nozzle per cylinder. However, the present invention is not limited to this, and a configuration in which a fuel injection valve is provided for each cavity region, that is, a first fuel injection valve that injects fuel toward the first region of the cavity and a fuel that is injected toward the second region. A second fuel injection valve may be provided.

  The cavities are not limited to the concentric circles as described above. For example, as shown in FIG. 7-1 or FIG. 7-2, the first circular cavity 33 forming the first region and the second region The second circular cavity 34 to be formed may be arranged in series in the piston radial direction. In this configuration, two fuel injection valves corresponding to each cavity region are provided as described above, or a single fuel injection valve is moved between the respective regions depending on the piston position. As described above, by setting the fuel spray so as to be inclined with respect to the cylinder axis, it is possible to realize the same effect as that of the above-described embodiment.

1 is an overall configuration diagram of an embodiment of a direct injection internal combustion engine to which the present invention is applied. The top view of 1st Embodiment which concerns on the piston of this invention. The principal part longitudinal cross-sectional view of 1st Embodiment which concerns on the piston of this invention. Explanatory drawing of 1st Embodiment which concerns on the combustion method of this invention. The timing chart of 1st Embodiment which concerns on the said combustion method. Explanatory drawing of 2nd Embodiment which concerns on the combustion method of this invention. Explanatory drawing of the stratified combustion area | region which concerns on embodiment of this invention. The top view of 2nd Embodiment which concerns on the piston of this invention. The principal part longitudinal cross-sectional view of 2nd Embodiment which concerns on the piston of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body of direct injection type internal combustion engine 2 Intake passage 3 Throttle valve 4 Exhaust passage 5 Catalytic converter 6 Intake valve 7 Exhaust valve 8 Fuel injection valve 9 Spark plug 9a Discharge electrode part of spark plug 10 Control unit 21 Combustion chamber 24 Piston 31, 33 First cavity 32, 34 Second cavity

Claims (14)

A fuel injection valve for injecting fuel toward a cavity formed on the piston crown surface and an ignition plug are provided so as to face the combustion chamber, and an operating state detecting device for detecting an engine operating state, based on the detected operating state In a direct injection internal combustion engine comprising a control device for controlling the fuel injection timing by the fuel injection valve, the fuel injection amount, and the ignition timing by the spark plug,
Forming the cavity from a plurality of cavity regions;
The control device is configured to cause the fuel injection valve to perform a first injection before ignition and a second injection after ignition under a cold condition,
The direct injection type internal combustion engine, wherein the fuel injection valve is configured to direct the fuel sprays of the first injection and the second injection to different cavity regions. The cavity includes an inner first cavity that forms the first region, and an annular second cavity that forms the second region so as to surround the first cavity;
2. The direct injection type according to claim 1, wherein the fuel injection valve is set to form a fuel spray inclined with respect to a cylinder axis such that the fuel spray moves between the regions in accordance with a piston position. Internal combustion engine.   3. The direct injection internal combustion engine according to claim 2, wherein the control device is configured so that the first injection is performed toward an inner first cavity and the second injection is performed toward an outer second cavity. organ.   The controller performs the first injection toward the first inner cavity when the piston is relatively close to the top dead center during the compression stroke, and the second injection is performed during the expansion stroke of the piston. The direct injection internal combustion engine according to claim 2, wherein the direct injection internal combustion engine is configured to be directed toward the outer second cavity when being relatively far from the top dead center.   3. The direct injection internal combustion engine according to claim 2, wherein the control device is configured such that the first injection is performed toward an outer second cavity, and the second injection is performed toward an inner first cavity. organ.   The controller performs the first injection toward the second outer cavity when the piston is relatively far from the top dead center during the compression stroke, and the second injection is performed during the expansion stroke of the piston. The direct injection internal combustion engine according to claim 2, wherein the direct injection internal combustion engine is configured to be directed toward the first inner cavity when the position is relatively close to the top dead center.   3. The direct injection internal combustion engine according to claim 2, wherein the control device is configured to perform only the first injection toward the inner first cavity after the warm-up is completed.   2. The direct injection internal combustion engine according to claim 1, wherein the control device is configured to decrease an injection amount of the second injection in accordance with an increase in load.   2. The direct injection internal combustion engine according to claim 1, wherein the control device is configured to stop the second injection when the load is higher than a predetermined reference load.   2. The control device according to claim 1, wherein the control device sets the fuel injection amount so that a sum of a fuel injection amount of the first injection and a fuel injection amount of the second injection constitutes a theoretical air-fuel ratio with respect to a cylinder intake air amount. Direct injection internal combustion engine.   The direct injection type internal combustion engine according to claim 1, wherein the control device sets the injection amount of the second injection to be smaller than the injection amount of the first injection.   The said fuel injection valve consists of a 1st fuel injection valve which injects a fuel toward the 1st area | region of a cavity, and a 2nd fuel injection valve which injects a fuel toward a 2nd area | region. Direct injection internal combustion engine.   2. The direct injection internal combustion engine according to claim 1, wherein a first cavity that forms a first region and a second cavity that forms a second region are arranged in series in the piston radial direction. A combustion method for a direct injection internal combustion engine comprising a fuel injection valve for injecting fuel toward a cavity composed of a plurality of cavity regions formed on a piston crown surface and an ignition plug so as to face the combustion chamber,
Under cold conditions
Performing a first injection toward the first cavity region before ignition by the fuel injection valve;
After igniting the injected fuel from the first injection,
A direct injection internal combustion engine characterized in that the second injection is performed toward the second cavity region, and the fuel injected by the second injection is burned in a combustion chamber region having a relatively high oxygen concentration. Combustion method.

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