JP2008025445A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To alleviate the change of combustion noise when the number of times of pilot injection is changed accompanied by the change of an operation state in relation to a control device for an internal combustion engine. <P>SOLUTION: When the operation state is transferred from a low speed side multiple pilot region in which a plurality of times of pilot injection are performed to a high speed side single pilot region in which only one pilot injection is performed, an injection pattern is changed over. At the changeover, an internal EGR ratio is temporally increased. Consequently, since ignition timing is advanced, the increase of combustion noise caused by changeover from multiple pilot injection to single pilot injection can be inhibited. A swirl ratio is also increased simultaneously. Consequently, the increase of smoke accompanied by the increase of the internal EGR ratio can be inhibited. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device in which pilot injection is performed prior to main injection.

  Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 2001-342877, there is known a control device for a diesel engine that performs pilot injection prior to main injection during one cycle of the diesel engine. By performing pilot injection, there is an advantage that combustion noise can be reduced.

  In the invention disclosed in the above publication, when the diesel engine is in an idle state, the intake throttle valve is closed to reduce the intake air amount, thereby reducing vibration and noise, and increasing the external EGR amount to increase the pilot injection fuel. It is said that the ignition delay period of pilot injection can be reduced by warming up. Further, at that time, the larger the amount of external EGR, the shorter the interval between the pilot injection and the main injection, thereby making it possible to appropriately continue the combustion of the pilot injected fuel and the combustion of the main injected fuel. .

JP 2001-342877 A JP 2004-116446 A JP 2005-146960 A JP-A-60-162018

  In recent years, a technique for performing pilot injection a plurality of times is also known. Combustion noise is further reduced when pilot injection is performed a plurality of times (hereinafter referred to as “multi-pilot injection”) compared to when the pilot injection is performed once (hereinafter referred to as “single pilot injection”). can do.

  However, depending on the operating condition of the diesel engine, multi-pilot injection cannot be performed due to some restrictions, and there is a case where it is unavoidable to use single pilot injection. For this reason, switching between multi-pilot injection and single pilot injection is performed according to the operating state of the diesel engine. In that case, when switching from multi-pilot injection to single-pilot injection, combustion noise increases, which may make the driver feel uncomfortable.

  In particular, when switching from multi-pilot injection to single-pilot injection during rapid acceleration, combustion noise tends to increase rapidly. This is due to the following reason. During rapid acceleration, the fuel injection pressure (rail pressure) increases as the load increases. In general, the combustion noise increases as the fuel injection pressure increases. For this reason, when switching from multi-pilot injection to single-pilot injection during rapid acceleration, the factors that increase the combustion noise overlap, so the combustion noise tends to increase rapidly.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine that can mitigate changes in combustion noise when the number of pilot injections is changed in accordance with changes in operating conditions. An object is to provide a control device.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
Number of times changing means for changing the number of pilot injections performed prior to the main injection according to the operating state of the internal combustion engine;
When the number of pilot injections is changed, the ignition timing is temporarily set to a parameter that is different from the normal value so that the change in combustion noise caused by the change is reduced. Control means;
It is characterized by providing.

The second invention is the first invention, wherein
The ignition timing control means is characterized in that, when the number of pilot injections is reduced, the parameter is temporarily changed so that the ignition timing is advanced.

The third invention is the second invention, wherein
It further comprises injection timing retarding means for delaying the main injection timing from the normal time while the parameter is changed by the ignition timing control means so that the ignition timing becomes earlier.

Moreover, 4th invention is 2nd or 3rd invention,
An internal EGR ratio variable means for changing the internal EGR ratio of the internal combustion engine;
The parameter is a parameter correlated with the internal EGR rate;
The direction in which the ignition timing is advanced is a direction in which the internal EGR ratio is increased.

The fifth invention is the fourth invention, wherein
Swirl ratio varying means for varying the swirl ratio of the internal combustion engine;
Swirl control means for controlling the swirl ratio variable means so that the swirl ratio becomes larger than normal when the parameter is changed by the ignition timing control means in a direction in which the internal EGR ratio increases;
Is further provided.

The sixth invention is the second or third invention, wherein
Further comprising compression ratio varying means for varying the compression ratio or the actual compression ratio of the internal combustion engine,
The parameter is the compression ratio or the actual compression ratio,
The direction in which the ignition timing is advanced is a direction in which the compression ratio or the actual compression ratio is increased.

According to a seventh invention, in any one of the first to sixth inventions,
The number changing means divides the operating region of the internal combustion engine into a relatively low speed region and a high speed region, and determines the number of pilot injections in the high speed region in the low speed region. The number of pilot injections is less than the number of pilot injections.

The eighth invention is the seventh invention, wherein
The ignition timing control means functions when the engine rotational speed shifts from the low speed region to the high speed region as the engine load increases, and does not function otherwise.

The ninth invention is the seventh or eighth invention, wherein
The engine further comprises a shift means for shifting the engine rotational speed at the boundary for switching the number of pilot injections to a higher speed side than in the steady state when the engine rotational speed increases with an increase in engine load. And

According to a tenth invention, in any one of the first to ninth inventions,
The ignition timing control means sets the parameter to a value different from the normal value, and then gradually returns the parameter to the normal value.

  According to the first invention, when the number of pilot injections is changed in accordance with the operating state of the internal combustion engine, it is involved in the ignition timing so that the change in combustion noise caused by the change is alleviated. The parameter can be temporarily different from the normal value. For this reason, the change of the combustion noise resulting from the change of the frequency | count of pilot injection can be suppressed. Therefore, even if the number of pilot injections is changed with a change in the operating state of the internal combustion engine, it is possible to make the driver feel as uncomfortable as possible.

  According to the second invention, when the number of pilot injections is reduced, the parameter can be temporarily changed in a direction in which the ignition timing is advanced. Reducing the number of pilot injections generally increases combustion noise. On the other hand, if the ignition timing is advanced (ignition delay is shortened), combustion noise can be reduced. Therefore, according to the second aspect, even if the injection pattern is switched in the direction in which the number of pilot injections decreases, the increase in combustion noise can be mitigated. For this reason, it is possible to prevent the driver from feeling as uncomfortable as possible.

According to the third aspect of the invention, the main injection timing can be made later than the normal time while the parameter is changed in a direction in which the ignition timing is advanced. While the above parameters are changed so that the ignition timing is advanced, the ignition performance is improved, so that the main injection timing can be delayed without causing adverse effects such as misfiring or an increase in HC emission amount. When the main injection timing is delayed, the maximum in-cylinder pressure P _max is reduced, so that combustion noise can be further reduced. For this reason, according to the third invention, it is possible to further suppress an increase in combustion noise when the injection pattern is switched in a direction in which the number of pilot injections decreases.

  According to the fourth invention, when the injection pattern is switched in the direction in which the number of pilot injections decreases, the ignition timing is advanced by increasing the internal EGR ratio, thereby effectively suppressing the increase in combustion noise. Can do. For this reason, it is possible to more effectively suppress the driver from feeling uncomfortable.

  According to the fifth aspect, when the internal EGR ratio is increased, the swirl ratio can be made larger than usual. For this reason, the increase in smoke accompanying the increase in the internal EGR ratio can be reduced or offset.

  According to the sixth aspect of the invention, when the injection pattern is switched in the direction in which the number of pilot injections decreases, the ignition timing is advanced by increasing the compression ratio or the actual compression ratio, thereby effectively increasing the combustion noise. Can be suppressed. For this reason, it is possible to more effectively suppress the driver from feeling uncomfortable.

  According to the seventh aspect, the number of pilot injections in the relatively high speed region can be made smaller than the number of pilot injections in the relatively low speed region. As a result, it is possible to prevent an adverse effect (for example, an increase in smoke) from occurring when the number of pilot injections is increased in a relatively high speed region.

  According to the eighth invention, when the engine rotational speed shifts from the low speed region to the high speed region as the engine load increases, the ignition timing control for mitigating the increase in combustion noise is performed. Can be implemented and otherwise not implemented. When the injection pattern is switched in the direction in which the number of pilot injections decreases with an increase in the engine load, the increase in combustion noise tends to become significant. According to the eighth aspect of the invention, only in such a case, by performing the ignition timing control to alleviate the increase in combustion noise, it is possible to minimize the implementation of the control and eliminate waste.

  According to the ninth aspect, when the engine rotational speed increases with an increase in the engine load, the engine rotational speed at the boundary for switching the number of pilot injections is shifted to the high speed side compared to the steady state. be able to. The higher the engine rotational speed, the greater the mechanical noise of the internal combustion engine, and other noises such as the wind noise and road noise of the vehicle, so the combustion noise becomes relatively small. Therefore, according to the ninth aspect, the engine rotational speed at the boundary for switching the number of pilot injections is shifted to the high speed side, thereby more reliably suppressing the driver from feeling uncomfortable with an increase in combustion noise. be able to.

  According to the tenth aspect, after the parameter related to the ignition timing is set to a value different from the normal value, the parameter can be gradually returned to the normal value. For this reason, the change of combustion noise can be made milder and it can suppress more reliably that a driver feels uncomfortable.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine (compression ignition internal combustion engine) 10. It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source. Although the diesel engine 10 of the present embodiment is an in-line four-cylinder type, the number of cylinders and the cylinder arrangement of the diesel engine in the present invention are not limited to this.

  Each cylinder of the diesel engine 10 is provided with an injector 12 that injects fuel directly into the cylinder. The injectors 12 of each cylinder are connected to a common common rail 14. In the common rail 14, high-pressure fuel pressurized by the supply pump 16 is stored. Then, fuel is supplied from the common rail 14 to each injector 12. In the diesel engine 10 of the present embodiment, the fuel pressure in the common rail 14 (hereinafter referred to as “rail pressure”) corresponds to the fuel injection pressure from the injector 12.

  The injector 12 can inject fuel into the cylinder a plurality of times during one cycle. That is, the injector 12 can perform pilot injection once or a plurality of times prior to main injection during one cycle. Further, after the main injection, after injection, post injection, or the like may be performed.

  An exhaust passage 18 of the diesel engine 10 is branched by an exhaust manifold 20 and connected to an exhaust port 22 (see FIG. 2) of each cylinder. The diesel engine 10 of this embodiment includes a turbocharger 24. The exhaust passage 18 is connected to the exhaust turbine of the turbocharger 24.

  A catalyst (exhaust gas purification device) 26 for purifying exhaust gas is provided in the exhaust passage 18 downstream of the turbocharger 24. Examples of the catalyst 26 include an oxidation catalyst, a NOx storage reduction type or selective reduction type NOx catalyst, a DPF (Diesel Particulate Filter), a DPNR (Diesel Particulate-NOx-Reduction system), or a combination thereof. Can be used.

  An air cleaner 30 is provided near the inlet of the intake passage 28 of the diesel engine 10. The air drawn through the air cleaner 30 is compressed by the intake compressor of the turbocharger 24 and then cooled by the intercooler 32. The intake air that has passed through the intercooler 32 is distributed by the intake manifold 34 to the intake ports 35 (see FIG. 2) of the respective cylinders.

  An intake throttle valve 36 is installed between the intercooler 32 and the intake manifold 34 in the intake passage 28. An air flow meter 38 for detecting the amount of intake air is installed in the vicinity of the intake passage 28 downstream of the air cleaner 30.

  One end of an external EGR passage 40 is connected to the intake passage 28 in the vicinity of the intake manifold 34. The other end of the external EGR passage 40 is connected to the vicinity of the exhaust manifold 20 of the exhaust passage 18. In this system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 28 through the external EGR passage 40, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  In the middle of the external EGR passage 40, an EGR cooler 42 for cooling the external EGR gas is provided. An EGR valve 44 is provided downstream of the EGR cooler 42 in the external EGR passage 40. By changing the opening degree of the EGR valve 44, the amount of exhaust gas passing through the external EGR passage 40, that is, the amount of external EGR can be adjusted.

  In this system, the external EGR amount can be adjusted not only by the opening degree of the EGR valve 44 but also by the opening degree of the intake throttle valve 36. When the opening of the intake throttle valve 36 is reduced to throttle the intake air, the intake pressure decreases, so the differential pressure from the back pressure (exhaust pressure) increases. That is, the differential pressure before and after the external EGR passage 40 increases. For this reason, the amount of external EGR can be increased.

  The system of this embodiment further includes an accelerator opening sensor 48 that detects the amount of depression of the accelerator pedal (accelerator opening) and an ECU (Electronic Control Unit) 50. The ECU 50 is connected to the various sensors and actuators described above. The ECU 50 controls the operating state of the diesel engine 10 by operating each actuator according to a predetermined program based on the output of each sensor.

  FIG. 2 is a view showing a cross section of one cylinder of the diesel engine 10 in the system shown in FIG. Hereinafter, the diesel engine 10 will be further described. As shown in FIG. 2, a crank angle sensor 62 that detects the rotation angle of the crankshaft 60 is attached in the vicinity of the crankshaft 60 of the diesel engine 10. The crank angle sensor 62 is connected to the ECU 50. The crank angle sensor 62 can detect the engine speed.

  The diesel engine 10 includes an intake variable valve mechanism 54 that continuously varies the valve timing (opening / closing timing) of the intake valve 52, and an exhaust variable valve that continuously varies the valve timing of the exhaust valve 56. Mechanism 58 is provided. The intake variable valve mechanism 54 and the exhaust variable valve mechanism 58 are each connected to the ECU 50.

  The specific structures of the intake variable valve mechanism 54 and the exhaust variable valve mechanism 58 are not particularly limited, and even when a mechanical mechanism such as a cam mechanism is used, an electromagnetic that can be opened and closed at an arbitrary time is used. A drive valve or a hydraulic drive valve may be used.

  The diesel engine 10 is provided with a cooling water temperature sensor 68 that detects the temperature of the cooling water. This cooling water temperature sensor 68 is connected to the ECU 50.

(Control of internal EGR)
In the diesel engine 10 of the present embodiment, the magnitude of the negative valve overlap between the intake valve 52 and the exhaust valve 56 can be continuously changed by the intake variable valve mechanism 54 and the exhaust variable valve mechanism 58. . FIG. 3 is a diagram for explaining negative valve overlap. As shown in FIG. 3, the negative valve overlap is a period during which both the intake valve 52 and the exhaust valve 56 are closed after the exhaust valve 56 is closed until the intake valve 52 is opened.

  3 is a valve lift diagram of the intake valve 52 and the exhaust valve 56 when no negative valve overlap is provided. From this state, the closing timing of the exhaust valve 56 is advanced and the opening timing of the intake valve 52 is delayed, so that a negative valve overlap can be caused. A thick curve in FIG. 3 is a valve lift diagram of the intake valve 52 and the exhaust valve 56 when a negative valve overlap is generated. The magnitude of the negative valve overlap can be changed according to the degree to which the closing timing of the exhaust valve 56 and the opening timing of the intake valve 52 are changed.

  When a negative valve overlap is generated, the exhaust valve 56 is closed before the burned gas in the cylinder completely flows out to the exhaust port 22. The burned gas that has not been discharged to the exhaust port 22 remains in the cylinder as it is, or once exits to the intake port 35 when the intake valve 52 is opened, and then the piston 64 descends together with fresh air. Inhaled. When a negative valve overlap occurs, internal EGR can be performed in this way. The larger the negative valve overlap, the greater the internal EGR.

  The internal EGR ratio (the ratio of the internal EGR gas to the in-cylinder gas when the intake valve 52 is closed) greatly affects the state of combustion. The optimum internal EGR ratio varies depending on the engine speed and the engine load. In the system of the present embodiment, the relationship between the valve timing of the intake valve 52 and the exhaust valve 56 for obtaining the optimum internal EGR ratio, the engine speed and the engine load is mapped and stored in the ECU 50 in advance. And When the diesel engine 10 is in a normal steady operation state, the internal EGR ratio is controlled by controlling the intake variable valve mechanism 54 and the exhaust variable valve mechanism 58 according to the map. .

  In the present embodiment, it is assumed that the internal EGR is performed by generating a negative valve overlap. However, in the present invention, the positive valve overlap, that is, the state where both the intake valve 52 and the exhaust valve 56 are opened. Alternatively, the internal EGR may be performed by generating a normal valve overlap, and the internal EGR ratio may be adjusted by changing the size of the positive valve overlap.

(Control of swirl ratio)
FIG. 4 is a schematic plan view of one cylinder of the diesel engine 10. As shown in the figure, the diesel engine 10 is provided with two intake ports 35 of a helical port 35a and a tangential port 35b per cylinder. The helical port 35 a and the tangential port 35 b are opened and closed by separate intake valves 52. The helical port 35a allows air to flow into the cylinder while swirling in a spiral. That is, the helical port 35a is the intake port 35 having a large swirl ratio. On the other hand, the tangential port 35b allows air to flow toward the tangential direction of the cylinder bore. The tangential port 35b is an intake port 35 that allows a larger amount of air to flow into the cylinder, although the swirl ratio is smaller than that of the helical port 35a.

  The intake variable valve mechanism 54 performs an operation of closing the intake valve 52 on the tangential port 35b side earlier than the intake valve 52 on the helical port 35a side (hereinafter referred to as “one valve early closing of the intake valve 52”). Can be done.

  When the intake valve 52 on the helical port 35a side and the intake valve 52 on the tangential port 35b side are both open, the strong swirl created by the air flowing in from the helical port 35a is weakened by the flow from the tangential port 35b. End up. On the other hand, when the intake valve 52 on the tangential port 35b side is closed early, air flows from only the helical port 35a thereafter, so that a strong swirl can be generated. Therefore, the swirl ratio can be increased as the closing timing of the intake valve 52 on the tangential port 35b side is earlier. In the diesel engine 10, when the intake valve 52 is quickly closed by the intake variable valve mechanism 54, the swirl ratio is increased by continuously changing the closing timing of the intake valve 52 on the tangential port 35b side. It can be adjusted freely.

  The swirl ratio greatly affects the state of combustion. The optimum swirl ratio varies depending on the engine speed and the engine load. In the system of the present embodiment, the relationship between the valve timing (closing timing) of the intake valve 52 on the helical port 35a side and the tangential port 35b side for obtaining the optimum swirl ratio, the engine rotation speed and the engine load is mapped. It is assumed that it is stored in the ECU 50 in advance. When the diesel engine 10 is in a normal steady operation state, the swirl ratio is controlled by controlling the intake variable valve mechanism 54 according to the map.

  In the present embodiment, the swirl ratio is changed by the above method. However, in the present invention, the method of changing the swirl ratio is not limited to the above method. For example, the swirl ratio may be changed by adjusting the opening of the swirl control valve provided in the intake port 35.

[Features of Embodiment 1]

  FIG. 5 is a diagram for explaining pilot injection performed in the diesel engine 10. In the diesel engine 10, one or two pilot injections can be performed before the main injection. The upper side in FIG. 5 is a diagram showing a drive signal to the injector 12 when pilot injection is performed twice (hereinafter also referred to as “multi-pilot injection”). In the example shown in this figure, the first pilot injection and the second pilot injection are relatively distant from each other, and the second pilot injection and the main injection are relatively close to each other.

  On the other hand, the lower side in FIG. 5 is a diagram showing a drive signal to the injector 12 when the pilot injection is performed once (hereinafter also referred to as “single pilot injection”). As shown in this figure, in the case of single pilot injection, the injection mode is such that the second pilot injection in multi-pilot injection is omitted.

  In general, the combustion noise of the diesel engine 10 is likely to increase as the ignition delay period is longer, that is, as the ignition timing is later. If the ignition delay period is long, the amount of combustible air-fuel mixture generated during that period increases by that amount, so that a large amount of combustible air-fuel mixture burns at a time after ignition. As a result, the in-cylinder pressure rises rapidly, and the combustion noise increases.

  Combustion noise can be reduced by performing pilot injection. When pilot injection is performed, a small amount of fuel injected by the pilot injection burns to create a fire type, and main injection is performed when the temperature in the cylinder becomes high. For this reason, the ignition timing of the fuel injected by the main injection is advanced. That is, by performing pilot injection, the ignition delay period can be shortened. Therefore, combustion noise can be reduced.

  When the multi-pilot injection is performed, the ignition delay period can be further shortened and the increase in the in-cylinder pressure can be made smoother than in the case of the single pilot injection. For this reason, combustion noise can be further reduced. In other words, in the case of single pilot injection, combustion noise is slightly larger than in the case of multi pilot injection. Therefore, from the viewpoint of suppressing combustion noise, it is preferable to perform multi-pilot injection in all operating regions.

  However, due to restrictions on the injection system such as the injector 12, there is a limit to shortening the time interval of each injection. For this reason, it is difficult to perform multi-pilot injection in a high speed region where the time interval between the second pilot injection and the main injection is extremely short. Further, if the second pilot injection is intentionally performed, the main injection is performed before the rail pressure reduced by the injection cannot be recovered. As a result, the injection pressure of the main injection becomes low and smoke is likely to increase. In other words, in the high speed range, the suppression of smoke is a restriction and multi-pilot injection cannot be performed.

  For this reason, in this system, in the region where the engine speed is higher than a certain speed, multi-pilot injection is not performed but single pilot injection is performed. FIG. 6 is a diagram showing an operation region in which multi-pilot injection is performed (hereinafter referred to as “multi-pilot region”) and an operation region in which single pilot injection is performed (hereinafter referred to as “single pilot region”). It is. In the diesel engine 10, multi-pilot injection is performed in the multi-pilot region on the lower speed side than the broken line in FIG. 6, and single pilot injection is performed in the single pilot region on the higher speed side than the broken line. In the example shown in FIG. 6, the boundary between the multi-pilot region and the single pilot region is a constant engine speed regardless of the engine load (injection amount). It may change according to the engine load. That is, the broken line in FIG. 6 may be diagonal.

  When the operation state of the diesel engine 10 shifts from the multi-pilot region to the single pilot region, switching from the multi-pilot injection to the single pilot injection is performed, so that combustion noise increases. In particular, when switching from multi-pilot injection to single-pilot injection during acceleration, an increase in combustion noise tends to be noticeable. The reason is as follows.

  FIG. 7 is a diagram showing the relationship between the engine rotational speed and the engine load, and the rail pressure. As shown in FIG. 7, in this system, the rail pressure is controlled to increase as the engine speed increases. This is because the fuel injection period needs to be shortened in time as the engine speed increases. The rail pressure is controlled to be lower as the engine load is smaller. This is because the combustion noise tends to be annoying in the low load region, and therefore it is necessary to sufficiently suppress the combustion noise.

  As can be seen from FIG. 7, the increase in rail pressure is greater when the engine load is increased than when the engine speed is increased. As the rail pressure increases, the combustion noise tends to increase. At the time of acceleration, switching from multi-pilot injection to single-pilot injection is performed while the engine load increases as in the change from point A to point B in FIG. For this reason, the increase in combustion noise due to an increase in rail pressure, that is, the fuel injection pressure, and the increase in combustion noise due to switching of pilot injection from two times to one time tend to be particularly loud. As a result, when switching from multi-pilot injection to single-pilot injection, the driver or passenger may feel uncomfortable with the engine sound.

  Therefore, in this embodiment, when switching from multi-pilot injection to single-pilot injection during acceleration, the internal EGR ratio is temporarily set to 2 (in this embodiment, 2) in order to suppress an increase in combustion noise. (Second) to increase. The internal EGR gas is a high-temperature burned gas. For this reason, if the internal EGR ratio is increased, the in-cylinder temperature near the compression top dead center (hereinafter referred to as “compression end temperature”) increases, so that the ignition timing of the main injection is advanced (the ignition delay is shortened). Can do. Therefore, it is possible to sufficiently suppress an increase in combustion noise when switching from multi-pilot injection to single pilot injection.

  In the present embodiment, when the internal EGR ratio is increased as described above, the swirl ratio is also increased. When the internal EGR ratio is increased, the amount of air in the cylinder (the amount of fresh air) decreases accordingly, and smoke tends to increase easily. On the other hand, when the swirl ratio is increased, mixing of fuel and air is promoted, so that smoke can be reduced. In the present embodiment, by increasing the swirl ratio together with the increase in the internal EGR ratio, it is possible to effectively suppress the increase in smoke.

[Specific Processing in Embodiment 1]
FIG. 8 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. According to the routine shown in FIG. 8, it is first determined whether or not the current engine speed is in the low speed region, that is, the multi-pilot region (step 100). In the present embodiment, it is assumed that the rotation speed for switching between the multi-pilot region and the single pilot region is 2000 rpm. Therefore, in this step 100, when the current engine speed is 2000 rpm or less, it is determined that the engine is in the low speed range.

  The control of this routine is control for suppressing combustion noise at the time of acceleration from the low speed region, that is, the multi-pilot region, for example, acceleration from point A to point B in FIG. Therefore, if it is determined in step 100 that the engine speed is in the low speed range, it is next determined whether or not the engine is in an accelerated state (step 102). That is, when the accelerator opening is detected and the accelerator pedal is depressed, it is determined that the vehicle is in an acceleration state.

  If it is determined in step 100 that the engine speed is not in the low speed range, or if it is determined in step 102 that the engine speed is not in an acceleration state, it can be determined that it is not necessary to perform control of this routine. The current processing cycle is terminated as it is.

  On the other hand, if it is determined in step 102 that the vehicle is in the acceleration state, it is determined whether or not switching from multi-pilot injection to single pilot injection is necessary (step 104). Specifically, it is determined whether or not the engine rotational speed has switched to reach the rotational speed of 2000 rpm. As a result, when it is determined that the engine rotational speed has reached 2000 rpm, switching from multi-pilot injection to single pilot injection is performed by processing of another routine. Along with this switching, a process of increasing the internal EGR ratio is performed (step 106). Specifically, the intake variable valve mechanism 54 and the exhaust variable valve mechanism 58 are controlled so that the negative valve overlap becomes larger than the value set in the normal steady operation state. As a result, the internal EGR ratio is increased and the ignition delay is shortened. For this reason, it is possible to effectively suppress an increase in combustion noise due to switching to single pilot injection.

  In addition, the swirl ratio is increased together with the increase in the internal EGR ratio in step 106 (step 108). Specifically, the intake variable valve mechanism 54 is controlled so that the closing timing of the intake valve 52 on the tangential port 35b side is earlier than the timing set in the normal steady operation state. As a result, the swirl ratio can be increased and smoke can be reduced.

  According to the routine shown in FIG. 8, it is subsequently determined whether or not 2 seconds have elapsed since switching to the single pilot injection (step 110). If it is determined that 2 seconds have not elapsed, the process returns to step 106. That is, the control to increase the internal EGR ratio from the normal time and the control to increase the swirl ratio from the normal time are continued. On the other hand, if it is determined in step 110 that 2 seconds have elapsed, the processing of this routine is terminated. As a result, the control returns to the normal control, and the internal EGR ratio and the swirl ratio are controlled to normal values. At this time, when the internal EGR ratio and the swirl ratio are returned to the normal values, the combustion noise increases. However, this does not cause a problem for the following reason.

  When about 2 seconds elapse after switching to single pilot injection, the engine speed and vehicle speed are higher than when switching. For this reason, other noises such as mechanical noise of the diesel engine 10, wind noise of the vehicle, and road noise are also increasing. Therefore, even if the combustion noise increases slightly, the driver is not so concerned about it. For this reason, in this embodiment, an increase in combustion noise when the internal EGR ratio and the swirl ratio are returned to normal values after 2 seconds after switching to the single pilot injection does not become a problem. Note that the time until the internal EGR ratio and the swirl ratio are returned to the normal values is not limited to 2 seconds, and may be any number of seconds.

  Moreover, when returning the internal EGR ratio increased with the switching to the single pilot injection to the normal value, it may be returned at once, but it may be gradually brought closer to the normal value. FIG. 9 is a diagram showing the change over time in the internal EGR ratio in such a case. As shown in this figure, immediately after the time point when switching from multi-pilot injection to single pilot injection (t = 0), the increase range of the internal EGR ratio is increased, and the internal EGR ratio is usually increased as time passes. You may make it gradually approach the value of time. In this case, since the increase in the combustion noise when the internal EGR ratio is returned to the normal value gradually occurs, it is possible to more reliably suppress the driver from noticing the increase in the combustion noise. In this case, the swirl ratio may be gradually returned to the normal value in the same manner.

  In step 106, the increase range of the internal EGR ratio may be changed according to the degree of acceleration determined in step 102. For example, the increase range of the internal EGR rate may be made relatively small during rapid acceleration, and the increase range of the internal EGR rate may be made relatively large when acceleration is not so rapid. Thereby, it is possible to suppress an increase in smoke even at the time of rapid acceleration in which the fuel injection amount increases.

  In the first embodiment described above, the number of pilot injections is two in the low speed range and once in the high speed range, but the number of pilot injections is not limited to this. For example, the number of pilot injections may be 3 times in the low speed range and 2 times in the high speed range.

  Further, the increase in the swirl ratio in step 108 may be performed only in a part of the operation region, or may not be performed in the entire region.

  Further, in the first embodiment described above, the control for suppressing the increase in combustion noise is performed only at the time of acceleration, that is, only when the engine rotational speed shifts from the multi-pilot region to the single pilot region with an increase in engine load. I am doing so. On the other hand, in the present invention, control for suppressing an increase in combustion noise may be performed even when the engine rotational speed shifts from the multi-pilot region to the single pilot region while the engine load remains constant.

  Further, in the first embodiment described above, the internal EGR ratio corresponds to the “parameter relating to the ignition timing” in the first invention. Further, when the ECU 50 performs the switching of the injection pattern according to the map shown in FIG. 6, the “number of times changing means” in the first and seventh inventions executes the processing of the step 106, thereby The “ignition timing control means” in the second and eighth aspects of the invention is realized.

  The ECU 50 controls the intake variable valve mechanism 52 and the exhaust variable valve mechanism 58 to change the magnitude of the negative valve overlap, whereby the “internal EGR ratio variable means” in the fourth invention is By controlling the intake variable valve mechanism 52 to change the closing timing of the intake valve 52 on the tangential port 35b side, the “swirl ratio varying means” in the fifth aspect of the invention executes the processing of step 108 above. Thus, the “swirl control means” in the fifth invention gradually returns the increased internal EGR ratio to the normal value as shown in FIG. 9, thereby “ignition timing control means” in the tenth invention. Are realized.

  In the first embodiment described above, a method of increasing the internal EGR ratio is adopted as a method of increasing the ignition timing (shortening the ignition delay) in order to suppress combustion noise, but a method for controlling the ignition timing. Is not limited to this. For example, in the case of a diesel engine equipped with a variable compression ratio mechanism that makes the compression ratio variable, if the compression ratio is increased, the compression end temperature increases and the ignition delay can be shortened, thereby reducing combustion noise. be able to. Further, even when the actual compression ratio is increased by bringing the closing timing of the intake valve 52 closer to the bottom dead center by the intake variable valve mechanism 54, the combustion noise can be similarly reduced.

  FIG. 10 is a diagram illustrating the lift characteristics of the intake valve 52 when the actual compression ratio is increased. The solid line graph in FIG. 10 is the lift curve of the intake valve 52 at the normal time. In this lift curve, the closing timing (IVC) of the intake valve 52 is after the bottom dead center (BDC). On the other hand, the broken line graph in FIG. 10 is a lift curve of the intake valve 52 when the actual compression ratio is increased. As shown in this lift curve, when the closing timing of the intake valve 52 is made closer to the bottom dead center than normal, the effective compression stroke becomes longer, so that the actual compression ratio (substantial compression ratio) can be increased. . As a result, the ignition delay can be shortened and the combustion noise can be reduced.

  Therefore, in the above step 106, instead of increasing the internal EGR ratio, a process for increasing the compression ratio or the actual compression ratio from the normal time may be performed. Even in this case, the same effect as described above can be obtained. In this case, the compression ratio or the actual compression ratio corresponds to the “parameter related to the ignition timing” in the first invention, and the ECU 50 controls the intake variable valve mechanism 54 to set the closing timing of the intake valve 52. By changing it, the “compression ratio varying means” in the sixth aspect of the invention is realized.

  Note that each modification described in the first embodiment can be similarly applied to each embodiment described later.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 11 and FIG. 12. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit. The present embodiment can be realized by causing the ECU 50 to execute a routine process shown in FIG. 12 described later using the hardware configuration shown in FIGS. 1 and 2 described above.

[Features of Embodiment 2]
In the first embodiment described above, when switching the injection pattern from multi-pilot injection to single pilot injection during acceleration, switching is performed with 2000 rpm as the boundary according to the map in the steady operation state shown in FIG. .

  On the other hand, in the present embodiment, at the time of acceleration, the engine rotation speed for switching the injection pattern from the multi-pilot injection to the single pilot injection is set to a higher speed side (for example, 2500 rpm) than the normal value (2000 rpm here). It was decided to shift to.

  In the present embodiment, as in the first embodiment, when the injection pattern is switched during acceleration, the swirl ratio is increased. As described above, when multi-pilot injection is performed when the engine speed is high, smoke is likely to increase, but by increasing the swirl ratio, it is possible to suppress the increase in smoke. . For this reason, in the present embodiment, the engine rotation speed at which the injection pattern is switched can be shifted to the high speed side without increasing the smoke.

  Switching from multi-pilot injection to single-pilot injection can make the increase in combustion noise less noticeable by the driver as the engine speed is increased. The higher the engine speed, the greater the mechanical noise of the diesel engine 10, and the higher the vehicle speed, the greater the wind noise and road noise. For this reason, the combustion noise is relatively smaller than other noises. Therefore, according to the present embodiment, it is possible to more reliably suppress the driver from feeling uncomfortable with the increase in combustion noise by shifting the switching speed of the injection pattern to the high speed side during acceleration.

Furthermore, in this embodiment, after switching from multi-pilot injection to single-pilot injection, the timing of main injection is made later than normal. FIG. 11 is a diagram for comparing the main injection timing at normal time and the main injection timing when switching from multi-pilot injection to single pilot injection at the time of acceleration. In general, when the main injection timing is delayed, the maximum in-cylinder pressure P _max is reduced, so that combustion noise can be reduced. However, if the main injection timing is delayed, the injected fuel becomes difficult to ignite, and the HC emission amount increases or misfires easily occur. For this reason, there is a limit to the retard of the main injection timing.

  On the other hand, in this embodiment, after switching from multi-pilot injection to single-pilot injection, the internal EGR ratio is increased from the normal time. Increasing the internal EGR ratio increases the compression end temperature and improves the ignition performance, so that the retard limit of the main injection timing can be set later. For this reason, in this embodiment, as shown in FIG. 11, it is possible to perform retarding of the main injection timing after switching from multi-pilot injection to single-pilot injection. And since the combustion noise can be further suppressed by the retard at the main injection timing, it is possible to further reliably suppress the driver from feeling uncomfortable with the increase in the combustion noise.

[Specific Processing in Second Embodiment]
FIG. 12 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. In FIG. 12, the same steps as those shown in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified. The routine shown in FIG. 12 is the same as the routine shown in FIG. 8 except that step 112 is inserted between steps 102 and 104 and step 114 is inserted between steps 108 and 110, respectively.

  According to the routine shown in FIG. 12, when it is determined in steps 100 and 102 that the diesel engine 10 is in the acceleration state from the low speed region, the switching speed of the injection pattern is the value at the steady state (in this embodiment, 2000 rpm) is shifted to a higher speed side (for example, 2500 rpm). Then, when the engine speed reaches the shifted switching speed, switching from multi-pilot injection to single pilot injection is performed (step 104).

  In addition, according to the routine shown in FIG. 12, when switching to single pilot injection is performed, the main injection timing is set to normal when the internal EGR ratio is increased (step 106) and the swirl ratio is increased (step 108). Further processing is performed to make the time later (step 114).

  According to the routine shown in FIG. 12 as described above, the driver increases the combustion noise when switching from multi-pilot injection to single-pilot injection is performed due to the addition of the processing of steps 112 and 114 described above. It is possible to very effectively suppress a sense of discomfort. Note that either one of the processes in steps 112 and 114 may be performed. Even in that case, it is possible to effectively suppress the driver from feeling uncomfortable with the increase in combustion noise.

  In the second embodiment described above, the ECU 50 executes the process of step 114, so that the “injection timing retarding means” in the third invention executes the process of step 112, so that the ninth invention is executed. The “shifting means” in FIG.

  In each of the embodiments described above, the case where the combustion noise at the time of switching is suppressed in the system in which the number of pilot injections is changed according to the engine rotation speed has been described as an example. It is also possible to apply to a system that changes according to other operating conditions other than the engine speed.

  For example, a system in which the number of pilot injections is changed in accordance with the coolant temperature detected by the coolant temperature sensor 68 during the warm-up after the cold start of the diesel engine 10 is also conceivable. When the diesel engine 10 is cold, the combustion noise tends to be large, and therefore, it is preferable to perform multi-pilot injection from the viewpoint of reducing the combustion noise. On the other hand, after the diesel engine 10 is warmed up, it is preferable to perform single pilot injection in order to reduce the NOx emission amount. Therefore, at the time of warm-up, it is conceivable to perform a control to switch to single pilot injection after initially reaching multi-pilot injection and reaching a certain coolant temperature. In that case, an increase in combustion noise when switching from multi-pilot injection to single-pilot injection may be suppressed by the same method as in the above-described embodiment. In this case, the cooling water temperature corresponds to the “operating state” in the first invention.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the diesel engine shown in FIG. It is a figure for demonstrating a negative valve overlap. FIG. 2 is a schematic plan view of one cylinder of the diesel engine shown in FIG. 1. It is a figure for demonstrating the pilot injection implemented with the system shown in FIG. It is a figure which shows a multi-pilot area | region and a single pilot area | region. It is a figure which shows the relationship between an engine rotational speed and an engine load, and rail pressure. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows a time-dependent change of an internal EGR ratio. It is a figure which shows the lift characteristic of the intake valve when making a real compression ratio high. It is a figure which shows the main injection time at the time of normal, and the main injection time at the time of injection pattern switching. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

10 diesel engine 12 injector 14 common rail 18 exhaust passage 20 exhaust manifold 22 exhaust port 24 turbocharger 26 catalyst 28 intake passage 34 intake manifold 35 intake port 35a helical port 35b tangential port 36 intake throttle valve 38 air flow meter 40 external EGR passage 44 EGR valve 48 Accelerator opening sensor 50 ECU
52 Intake valve 54 Intake variable valve mechanism 56 Exhaust valve 58 Exhaust variable valve mechanism 62 Crank angle sensor 64 Piston 68 Cooling water temperature sensor

Claims (10)

Number of times changing means for changing the number of pilot injections performed prior to the main injection according to the operating state of the internal combustion engine;
When the number of pilot injections is changed, the ignition timing is temporarily set to a parameter that is different from the normal value so that the change in combustion noise caused by the change is reduced. Control means;
A control device for an internal combustion engine, comprising:   2. The control apparatus for an internal combustion engine according to claim 1, wherein the ignition timing control means temporarily changes the parameter in a direction in which the ignition timing is advanced when the number of pilot injections is reduced.   3. The internal combustion engine according to claim 2, further comprising injection timing retarding means for delaying the main injection timing from the normal time while the parameter is changed by the ignition timing control means so that the ignition timing is advanced. Engine control device. An internal EGR ratio variable means for changing the internal EGR ratio of the internal combustion engine;
The parameter is a parameter correlated with the internal EGR rate;
The control apparatus for an internal combustion engine according to claim 2 or 3, wherein the direction in which the ignition timing is advanced is a direction in which the internal EGR ratio is increased. Swirl ratio varying means for varying the swirl ratio of the internal combustion engine;
Swirl control means for controlling the swirl ratio variable means so that the swirl ratio becomes larger than normal when the parameter is changed by the ignition timing control means in a direction in which the internal EGR ratio increases;
The control apparatus for an internal combustion engine according to claim 4, further comprising: Further comprising compression ratio varying means for varying the compression ratio or the actual compression ratio of the internal combustion engine,
The parameter is the compression ratio or the actual compression ratio,
The control device for an internal combustion engine according to claim 2 or 3, wherein the direction in which the ignition timing is advanced is a direction in which the compression ratio or the actual compression ratio is increased.   The number changing means divides the operating region of the internal combustion engine into a relatively low speed region and a high speed region, and determines the number of pilot injections in the high speed region in the low speed region. 7. The control device for an internal combustion engine according to claim 1, wherein the number of pilot injections is less than the number of pilot injections.   The ignition timing control means functions when the engine rotational speed shifts from the low speed region to the high speed region with an increase in engine load, and does not function otherwise. Item 8. A control device for an internal combustion engine according to Item 7.   The engine further comprises a shift means for shifting the engine rotational speed at the boundary for switching the number of pilot injections to a higher speed side than in the steady state when the engine rotational speed increases with an increase in engine load. The control device for an internal combustion engine according to claim 7 or 8.   The internal combustion engine according to any one of claims 1 to 9, wherein the ignition timing control means gradually returns the parameter to a normal value after setting the parameter to a value different from a normal value. Engine control device.

Images