JP2007002795A - Controller for direct injection spark controller for cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To substantialize early activation of a catalyst and HC reduction due to after-burning by drastic delay of ignition timing, and to improve combustion stability. <P>SOLUTION: At cold start of an internal combustion engine requiring early temperature rise of a catalytic convertor, ignition timing is set to be after a compression top dead center, and super retard combustion for injecting fuel before the ignition timing and after the compression top center is performed. Since turbulence inside a cylinder is improved due to high-pressure fuel injection immediately before the ignition timing and flame spread is promoted, stable combustion can be realized. The internal combustion engine is equipped with a compression ratio variable mechanism which controls the compression ratio high at the time of super retard combustion. By the high compression ratio, penetration of injection is made short, injection becomes compact, and combustion stability is further improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an in-cylinder direct injection type spark ignition internal combustion engine that directly injects fuel into a cylinder, and in particular, at a cold start in which early temperature rise (early activation) of an exhaust system catalytic converter is required. It relates to control of injection timing and ignition timing.

  In Patent Document 1, as a catalyst warm-up method for a direct injection spark-ignition internal combustion engine, a period from the intake stroke to the ignition timing when the exhaust gas catalytic converter is in an unwarmed state lower than the activation temperature. In this case, it is possible to spread the fuel by the late injection in which the air-fuel mixture having a partial air-fuel ratio concentration is formed in the combustion chamber, the fuel is injected before this late injection, and the fuel of the late injection and the combustion of the late injection And at least two split injections of early injection for generating an air-fuel mixture leaner than the stoichiometric air-fuel ratio in the combustion chamber, and retarding the ignition timing by a predetermined amount from the MBT point, and no engine load A technique is described in which the ignition timing is set before the compression top dead center in the region, and the ignition timing is retarded until the compression top dead center in the low speed and low load region excluding the no-load region. The latter-stage injection is performed, for example, at 120 ° BTDC to 45 ° BTDC after the middle of the compression stroke.

A variable compression ratio mechanism that can change the mechanical compression ratio of the engine, that is, the nominal compression ratio, in order to improve the thermal efficiency of the internal combustion engine in the low and medium load ranges and at the same time avoid knocking in the high load range. Various proposals have been made. Patent Document 2 previously proposed by the applicant of the present application discloses a variable compression ratio mechanism in which the top dead center position of a piston is changed using a multi-link type piston-crank mechanism.
Japanese Patent No. 3325230 JP 2001-342859 A

  For early activation of the catalyst when the internal combustion engine is cold and HC reduction due to afterburning, retarding the ignition timing is effective. To obtain a greater effect, ignition after compression top dead center (ATDC) Ignition) is desirable. In order to perform stable combustion by ATDC ignition, it is necessary to shorten the combustion period. For this reason, it is necessary to increase the combustion speed (flame propagation speed) by strengthening the turbulence in the cylinder.

  In order to strengthen such disturbance, it is conceivable that the disturbance is generated in the cylinder by the energy of the fuel spray injected at a high pressure in the cylinder.

  However, in Patent Document 1, the first fuel injection (early injection) is performed during the intake stroke, and the second fuel injection (late injection) is performed from 120 ° BTDC to 45 ° BTDC during the compression stroke. Yes. As described above, before the last fuel injection is before the compression top dead center, even if the spray generates turbulence in the cylinder, the turbulence is attenuated after the compression top dead center, and the flame propagation in ATDC ignition Does not contribute to speed increase.

  For example, FIG. 9 shows the magnitude of turbulence in the cylinder when a gas flow control valve (for example, a tumble control valve) provided in the intake port is operated and when such a gas flow control valve is not provided. As shown, the turbulence (part A) generated during the intake stroke by operating the gas flow control valve is attenuated as the compression stroke progresses, and is temporarily accompanied by the collapse of the tumble flow in the latter half of the compression stroke. Although the turbulence increases (the portion indicated by reference symbol B), after the compression top dead center, as shown by the reference symbol C, it rapidly attenuates, and combustion improvement (improving flame propagation) using the turbulence cannot be expected so much. The same applies to turbulence caused by fuel spray, and even if turbulence is generated by fuel injection before compression top dead center, it does not contribute to ignition combustion after compression top dead center.

  For this reason, ATDC ignition is more advantageous for increasing exhaust temperature and reducing HC, but combustion stability is not established. Therefore, in Patent Document 1, the ignition timing is set to before compression top dead center (BTDC ignition) in the no-load region. Yes.

  The present invention aims to improve the combustion stability in ATDC ignition for early activation of the catalyst, reduction of HC, and the like based on such a situation.

  The present invention provides a control device for a direct injection type spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug. When the exhaust gas temperature needs to be raised, such as when the engine is cold, the ignition timing is set after the compression top dead center, and super retard combustion is performed to inject fuel before the ignition timing and after the compression top dead center. . In the NOx trap catalyst that adsorbs NOx, the sulfur component (SOx) adheres to the catalyst, so that the NOx adsorption performance deteriorates. However, it is also possible to raise the temperature of the exhaust gas during the SOx release process using the above-mentioned super retard combustion. In particular, the present invention includes a variable compression ratio mechanism that changes the mechanical compression ratio of the internal combustion engine. During operation in the above-described super retard combustion, the variable compression ratio mechanism allows a high compression ratio state to be obtained. To do.

  In other words, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but the in-cylinder turbulence is generated and strengthened by the fuel injection performed during the expansion stroke after the compression top dead center. Flame propagation with ATDC ignition is facilitated. Therefore, super retard combustion with the ignition timing after the compression top dead center is established stably.

  Further, by increasing the compression ratio during super retard combustion, the penetration of the spray, that is, the spray reach distance is shortened and the spray becomes compact, so that the diffusion of the spray is suppressed and the combustion stability is improved. Moreover, since the in-cylinder temperature rises with the compression ratio, fuel vaporization is promoted, and the combustion stability is also improved from this point. Therefore, it is possible to perform super retard combustion in which the ignition timing is more retarded than when the compression ratio is low.

  Furthermore, by increasing the compression ratio, the thermal efficiency is improved, and the amount of air and fuel required for equal torque are relatively reduced, so that the amount of HC generated itself is reduced.

  The exhaust temperature is relatively lowered by increasing the compression ratio, but the ignition timing is further retarded by improving the combustion stability as described above, thereby offsetting the decrease in the exhaust temperature accompanying the increase in the compression ratio. Is possible.

  As the variable compression ratio mechanism, a mechanism that changes the mechanical compression ratio by changing the piston position up and down when the crank angle is at a predetermined compression top dead center position can be used.

  For example, the variable compression ratio mechanism has an upper link whose one end is connected to a piston via a piston pin, and the other end of the upper link is connected via a first connection pin, and is connected to the crank pin of the crankshaft. A lower link that is rotatably mounted, and a control link that is connected to the lower link via a second connecting pin and that has the other end swingably supported with respect to the internal combustion engine body. The engine compression ratio can be variably controlled by displacing the swing support position of the control link with respect to the internal combustion engine body.

  According to the present invention, it is possible to sufficiently ensure the combustion stability of the super retard combustion in which the ignition timing is set after the compression top dead center. For example, at the time of cold start, the catalyst is activated early and the HC due to the afterburning. Reduction can be achieved. In particular, at the same time, by controlling the mechanical compression ratio to be high, combustion stability can be improved and ignition timing can be significantly retarded.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration explanatory view showing a system configuration of a direct injection type spark ignition internal combustion engine to which the present invention is applied.

  An intake passage 4 is connected to the combustion chamber 3 formed by the piston 2 of the internal combustion engine 1 via an intake valve (not shown), and an exhaust passage 5 is connected via an exhaust valve (not shown). Has been. The intake passage 4 is provided with an air flow meter 6 for detecting the amount of intake air, and an electronically controlled throttle valve 7 whose opening degree is controlled via an actuator 8 by a control signal. The exhaust passage 5 is provided with a catalytic converter 10 for purifying exhaust gas, and air-fuel ratio sensors 11 and 12 are provided on the upstream side and the downstream side, respectively. Further, the upstream air-fuel ratio sensor 11 is provided. Is provided with an exhaust gas temperature sensor 13 for detecting the exhaust gas temperature at the inlet side of the catalytic converter 10. The piston 2 is linked to the crankshaft 26 via a multi-link piston-crank mechanism that becomes a variable compression ratio mechanism 100 described later.

  A spark plug 14 is disposed at the central top of the combustion chamber 3. A fuel injection valve 15 that directly injects fuel into the combustion chamber 3 is disposed on the side of the combustion chamber 3 on the intake passage 4 side. The fuel that has been regulated to a predetermined pressure by the high-pressure fuel pump 16 and the pressure regulator 17 is supplied to the fuel injection valve 15 via the high-pressure fuel passage 18. Therefore, when the fuel injection valve 15 of each cylinder is opened by the control pulse, an amount of fuel corresponding to the valve opening period is injected. Reference numeral 19 denotes a fuel pressure sensor that detects the fuel pressure, and 20 denotes a low-pressure fuel pump that sends fuel to the high-pressure fuel pump 16.

  In addition, the internal combustion engine 1 is provided with a water temperature sensor 21 for detecting the engine cooling water temperature and a crank angle sensor 22 for detecting a crank angle. Further, an accelerator opening sensor 23 is provided for detecting the amount of depression of the accelerator pedal by the driver.

  The fuel injection amount, injection timing, ignition timing, and the like of the internal combustion engine 1 are controlled by the control unit 25 together with a compression ratio described later. The control unit 25 receives detection signals from the various sensors described above. The control unit 25 determines the combustion method, that is, the homogeneous combustion or the stratified combustion, in accordance with the engine operating conditions detected by these input signals, and according to this, the electronic control throttle valve 7 is opened. The fuel injection timing and fuel injection amount of the fuel injection valve 15, the ignition timing of the spark plug 14, and the like are controlled.

  FIG. 2 shows a configuration of a variable compression ratio mechanism 100 that variably controls the mechanical compression ratio (nominal compression ratio) of the internal combustion engine. The variable compression ratio mechanism itself is known from the above-mentioned Patent Document 2 and the like.

  The variable compression ratio mechanism 100 uses a multi-link type piston-crank mechanism. An upper link 105 having one end connected to the piston 2 via a piston pin 104, and a connecting pin connected to the other end of the upper link 105 106, and a lower link 109 rotatably connected to the crankpin 108 of the crankshaft 26, and a further connecting pin 110 for the lower link 109 in order to limit the degree of freedom of the lower link 109. A control link 111 having one end connected to the internal combustion engine body and the other end swingably supported by the internal combustion engine main body, and the swing support position of the control link 111 is an eccentric cam portion 113 of the control shaft 112. It is configured to be variably controlled by.

  The control shaft 112 is disposed in parallel with the crankshaft 26 and is rotatably supported by the cylinder block 107. The control shaft 112 is driven in the rotation direction by an actuator 115 made of an electric motor via a gear mechanism 114, and its rotation position is controlled.

  In the variable compression ratio mechanism 100 configured as described above, the swing support position of the lower end of the control link 111 changes depending on the rotational position of the control shaft 112, that is, the position of the eccentric cam portion 113, and the initial posture of the lower link 109 changes. Along with this, the top dead center position of the piston 2, and hence the compression ratio, changes. As shown in FIG. 2, the rotational position of the actuator 115 is controlled by the control unit 25 based on the engine operating conditions.

  In the above configuration, after the warm-up is completed, in a predetermined region on the low speed and low load side, fuel injection is performed at an appropriate time in the compression stroke as a normal stratified combustion operation, and the time before the compression top dead center Is ignited. The fuel spray is collected in the vicinity of the spark plug 14, thereby achieving extremely lean stratified combustion with an air-fuel ratio of about 30 to 40. Further, in a predetermined region on the high speed and high load side, as normal homogeneous combustion operation, fuel injection is performed during the intake stroke, and ignition is performed in the vicinity of the MBT point before the compression top dead center. In this case, the fuel becomes a homogeneous mixture in the cylinder. As the homogeneous combustion operation, there are homogeneous stoichiometric combustion in which the air-fuel ratio is the stoichiometric air-fuel ratio and homogeneous lean combustion in which the air-fuel ratio is lean about 20 to 30 depending on the operating conditions.

  Note that the compression ratio control in these normal stratified combustion operation mode and homogeneous combustion operation mode basically corresponds to the load as shown in FIG. 3 in order to improve the thermal efficiency at the partial load. It is controlled to a high compression ratio, and at a high load, it is controlled to a low compression ratio to avoid knocking.

  The present invention performs super retard combustion so that the exhaust gas temperature becomes high at the time of cold start of the internal combustion engine 1 where early temperature rise of the catalytic converter 10 is required. The fuel injection timing and ignition timing will be described with reference to FIG.

  FIG. 4 shows three examples of super retard combustion. In Example 1, the ignition timing is set to 15 ° to 30 ° ATDC (for example, 20 ° ATDC), and the fuel injection timing (specifically, the fuel injection start timing) is shown. Is set after the compression top dead center and before the ignition timing. At this time, the air-fuel ratio is set to the stoichiometric air-fuel ratio or slightly lean (about 16 to 17).

  That is, in order to promote catalyst warm-up and reduce HC, ignition timing retardation is effective, and ignition after top dead center (ATDC ignition) is desirable, but in order to perform stable combustion with ATDC ignition, It is necessary to shorten the combustion period, and for this purpose, flame propagation due to turbulence must be promoted. As described above, after the compression top dead center, the turbulence generated in the intake stroke and the compression stroke is attenuated, but in the present invention, by the high pressure fuel injection performed during the expansion stroke after the compression top dead center. The gas flow is generated, and thereby the turbulence in the cylinder can be generated and strengthened. Therefore, flame propagation by ATDC ignition is promoted and stable combustion is possible.

  Example 2 of FIG. 4 is an example in which fuel injection is divided into two times, and the first fuel injection is performed during the intake stroke, and the second fuel injection is performed after the compression top dead center. The ignition timing and the air-fuel ratio (the air-fuel ratio obtained by combining the two injections) are the same as those in the first embodiment.

  As described above, when fuel injection (intake stroke injection) is performed during the intake stroke prior to fuel injection after the compression top dead center (expansion stroke injection), disturbance due to fuel spray in the intake stroke injection is attenuated in the latter half of the compression stroke. However, since the injected fuel is diffused throughout the combustion chamber and contributes to the promotion of HC afterburning by ATDC ignition, the HC reduction and It is effective for raising the exhaust temperature.

  In the third embodiment shown in FIG. 4, the fuel injection is divided into two, the first fuel injection is performed in the compression stroke, and the second fuel injection is performed after the compression top dead center. As described above, when the fuel injection (compression stroke injection) is performed during the compression stroke prior to the fuel injection after the compression top dead center (expansion stroke injection), the compression stroke injection is compared with the intake stroke injection of the second embodiment. However, since the disturbance of the turbulence due to the fuel spray is delayed, the turbulence due to the first fuel injection remains, and the second fuel injection is performed after the compression top dead center, which is generated by the first fuel injection. The turbulence can be strengthened to promote the turbulence, and the gas flow can be further strengthened near the compression top dead center.

  In the case of Example 3, the first compression stroke injection may be in the first half of the compression stroke, but if it is set in the second half of the compression stroke (after 90 ° BTDC), the disturbance near the top dead center can be further increased. In particular, if the first compression stroke injection is 45 ° BTDC or later, more desirably 20 ° BTDC or later, the gas flow after compression top dead center can be further enhanced.

  As described above, according to the super retarded combustion of the first to third embodiments, the turbulence in the cylinder can be generated and strengthened by the fuel spray immediately before the ignition, and the flame propagation is promoted to perform stable combustion. be able to. In particular, by retarding the ignition timing from 15 ° to 30 ° ATDC, a sufficient afterburning effect for early activation of the catalyst and reduction of HC can be obtained. In other words, even if the ignition timing is greatly delayed in this way, the fuel injection is delayed until just before that, and the generation time of the turbulence is also delayed, so that the combustion improvement by improving the flame propagation can be achieved. In the present invention, during such super retard combustion, the combustion stability is further improved by simultaneously setting the compression ratio to a high compression ratio as shown in FIG.

  FIG. 5 is an example of the super retarded combustion of the first embodiment described above, and the in-cylinder pressure, gas flow, turbulence strength, in-cylinder temperature, fuel injection period IT, ignition timing ADV, during the compression stroke to the expansion stroke, Each of which is shown. For the in-cylinder pressure and the in-cylinder temperature, the characteristics at the time of the low compression ratio are indicated by solid lines, and the characteristics at the time of the high compression ratio are indicated by broken lines.

  Further, FIG. 6 shows spray penetration (spray reach distance), piston position at top dead center, S / V ratio of combustion chamber, exhaust temperature, thermal efficiency, rotational fluctuation (combustion stability) with respect to compression ratio change. Each characteristic is shown. Note that the smaller the rotational fluctuation, the higher the combustion stability.

  As is clear from these figures, by increasing the compression ratio during super retard combustion, the spray reach distance (penetration) is shortened and the spray becomes compact, so the turbulence in the combustion chamber is relatively large. Even in the later stage, diffusion of the spray is suppressed and combustion stability is improved. Moreover, since the in-cylinder temperature rises with the compression ratio, fuel vaporization is promoted, and the combustion stability is also improved from this point. Therefore, it is possible to perform super retard combustion in which the ignition timing is more retarded than when the compression ratio is low.

  In addition, the amount of HC generated in the combustion chamber itself correlates with the amount of fuel and the amount of air, but increasing the compression ratio improves thermal efficiency, and the required amount of air and fuel relative to equal torque are relatively Therefore, the amount of HC generated itself becomes smaller.

  On the other hand, the exhaust temperature is relatively lowered by increasing the compression ratio. However, as shown in FIG. 7, the exhaust temperature increases as the ignition timing is retarded. By further retarding the ignition timing, it is possible to cancel the exhaust temperature decrease (for example, ΔT) accompanying the increase in the compression ratio.

  FIG. 8 shows the piston stroke characteristics of the multi-link piston-crank mechanism constituting the variable compression ratio mechanism 100 described above, and shows a general single-link piston-crank mechanism (a piston link and a crank pin are connected to a single link ( This is shown in contrast to the piston stroke characteristics (shown by broken lines) of the mechanism connected by connecting rods). As shown in this figure, in the multi-link type piston-crank mechanism, each link is set appropriately. It is possible to reduce the piston speed around the top dead center and increase the piston speed around the bottom dead center. That is, as indicated by the solid line, the piston speed before and after the top dead center is made smaller and the piston speed around the bottom dead center is made larger than the characteristic of the single link type piston-crank mechanism shown by the broken line. be able to. Therefore, in the configuration combined with the above-described multi-link type piston-crank mechanism, the movement of the piston 2 near the compression top dead center where fuel is injected in the case of super retard combustion becomes much slower and more stable. Therefore, the spray diffusion is suppressed, which is more advantageous in terms of combustion stability.

  The super retarded combustion of the present invention can also be used for releasing sulfur poisoning when a NOx trap catalyst is used as the exhaust system catalytic converter 10. The NOx trap catalyst adsorbs NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releases the adsorbed NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is rich, and purifies by catalytic action. However, when the sulfur component (SOx) in the fuel is bound to the catalyst, the NOx adsorption performance is lowered. For this reason, it is necessary to perform a process (so-called sulfur poisoning release) for forcibly raising the temperature of the catalyst and releasing SOx at an appropriate time. The super retarded combustion according to the present invention can obtain a very high exhaust temperature, and therefore is suitable for the sulfur poisoning release processing of this NOx trap catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Structure explanatory drawing which shows the structure of a variable compression ratio mechanism. The characteristic view which shows the characteristic of the compression ratio by this variable compression ratio mechanism. The characteristic view which shows the fuel injection timing and ignition timing of the super retard combustion of this invention. FIG. 5 is a characteristic diagram collectively showing in-cylinder pressure, gas flow, turbulence intensity, in-cylinder temperature, fuel injection period, and ignition timing with respect to a crank angle. FIG. 5 is a characteristic diagram collectively showing penetration, piston position at top dead center, S / V ratio, exhaust temperature, thermal efficiency, and rotational fluctuation with respect to compression ratio change. The characteristic view which shows the relationship between ignition timing and exhaust gas temperature. The characteristic view which shows the piston stroke characteristic of a multilink type piston-crank mechanism in contrast with the thing of a single link type piston-crank mechanism. Explanatory drawing which shows the change of the disturbance in a cylinder in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Combustion chamber 10 ... Catalytic converter 14 ... Spark plug 15 ... Fuel injection valve 25 ... Control unit 100 ... Variable compression ratio mechanism

Claims (10)

  Control of an in-cylinder direct injection spark ignition internal combustion engine having a variable compression ratio mechanism for changing the mechanical compression ratio of the internal combustion engine, a fuel injection valve for directly injecting fuel into the cylinder, and an ignition plug In the device, the ignition timing is set after the compression top dead center in a predetermined operating state, and super retard combustion is performed before the ignition timing and after the compression top dead center, and the variable compression ratio mechanism A control device for an in-cylinder direct injection spark-ignition internal combustion engine, characterized by having a high compression ratio state.   The control apparatus for an in-cylinder direct injection spark-ignition internal combustion engine according to claim 1, wherein the super retard combustion is executed when a temperature increase of the exhaust gas is required as a predetermined operation state.   The in-cylinder direct injection spark according to claim 2, wherein the temperature of the exhaust gas is required to be raised during a cold start of the internal combustion engine that requires an early temperature increase of the exhaust system catalytic converter. Control device for an ignition internal combustion engine.   3. The control device for a direct injection type spark ignition internal combustion engine according to claim 2, wherein the exhaust gas temperature is required to be raised when performing SOx release processing of the exhaust system catalytic converter.   5. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing in the super retard combustion is 15 ° to 30 ° CA after compression top dead center.   6. The direct in-cylinder fuel injection according to claim 1, wherein in super retard combustion, fuel injection is further performed during an intake stroke or a compression stroke prior to fuel injection after compression top dead center. A control device for an injection spark ignition internal combustion engine.   The in-cylinder direct injection spark ignition internal combustion engine control device according to any one of claims 1 to 6, wherein the air-fuel ratio in the super retard combustion is a stoichiometric air-fuel ratio or slightly lean.   8. The variable compression ratio mechanism according to claim 1, wherein the mechanical compression ratio is changed by changing the piston position up and down when the crank angle is at a predetermined compression top dead center position. The control device for a direct injection type spark ignition internal combustion engine according to claim 1.   9. The control device for a direct injection type spark ignition internal combustion engine according to claim 8, wherein the variable compression ratio mechanism comprises a multi-link type piston-crank mechanism.   The multi-link type piston-crank mechanism includes an upper link whose one end is connected to the piston via a piston pin, and the other end of the upper link is connected via a first connection pin. A lower link rotatably attached to the lower link, and a control link having one end connected to the lower link via a second connecting pin and the other end supported to be swingable with respect to the internal combustion engine body. 10. The control device for a direct injection type spark ignition internal combustion engine according to claim 9, wherein the engine compression ratio is variably controlled by displacing the swing support position of the control link with respect to the internal combustion engine body.

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