JP5056966B2 - Combustion control device - Google Patents

Description

  The present invention relates to a combustion control device for an engine that performs premixed compression ignition (PCCI) combustion.

  As an engine combustion control device that performs premixed compression ignition combustion, for example, the one described in Patent Document 1 is known. The combustion control device described in Patent Document 1 corrects the fuel injection timing to the advance side and lowers the injection pressure when the ignition delay period is prolonged in cold when performing low temperature premixed combustion. By correcting the fuel injection period in such a way as to extend the fuel injection period, the fuel is prevented from excessively diffusing into the combustion chamber and the increase in unburned HC is suppressed.

JP 2003-184609 A

  However, even if the fuel injection period is extended as in the prior art described above, the time for diffusing the fuel injected earlier becomes longer. For this reason, since it becomes difficult to fully prevent overdiffusion of fuel, the increase in unburned HC / CO may not be sufficiently suppressed.

  An object of the present invention is to provide a combustion control device that can sufficiently suppress an increase in unburned HC / CO even at a low water temperature.

The present invention relates to an engine combustion control apparatus that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into a combustion chamber of the engine, and a second fuel injection after the first fuel injection is performed. The first injection valve control means for controlling the fuel injection valve, the water temperature detection means for detecting the engine water temperature, the load detection means for detecting the engine load, and the engine water temperature detected by the water temperature detection means A determination unit that determines whether the temperature is lower than the predetermined temperature, and a third fuel injection is performed before the first fuel injection is performed when the determination unit determines that the engine water temperature is lower than the predetermined temperature. and a second injection valve control means for controlling the fuel injection valve such that, ene second injection valve control means, which is detected by the water temperature and the load detecting means of the engine detected by the coolant temperature detecting means Means for determining the fuel injection amount by the third fuel injection according to the load of the engine, means for comparing and determining the engine load with the first predetermined value and the second predetermined value, and the engine load being the first Is determined to be greater than the predetermined value, the fuel injection amount by the third fuel injection is reduced from the fuel injection amount by the first fuel injection, and the engine load is smaller than the second predetermined value. When the determination is made, there is provided means for reducing the fuel injection amount by the third fuel injection from the fuel injection amount by the second fuel injection . For example, the first predetermined value and the second predetermined value are equal.

  As described above, in the combustion control device of the present invention, when it is determined that the engine water temperature is lower than the predetermined temperature, the third fuel injection is performed before the first fuel injection is performed, and then the first fuel injection is performed. By sequentially performing the first fuel injection and the second fuel injection, the ignition timing is advanced by preheating by the third fuel injection, and the heat generation rate waveform (combustion waveform) comes closer to the warm-up state. Combustion is activated. Thereby, even at the time of low water temperature, the increase in unburned HC / CO can be sufficiently suppressed.

  In this case, ignition can be performed at an appropriate time even at a low water temperature by increasing the fuel injection amount by the third fuel injection as the water temperature of the engine becomes lower. Moreover, excessive combustion at the time of high load can be suppressed by decreasing the fuel injection amount by the third fuel injection as the engine load increases.

  When it is determined that the engine load is greater than the first predetermined value, the first fuel injection is performed by reducing the fuel injection amount by the third fuel injection from the fuel injection amount by the first fuel injection. Excessive combustion due to is suppressed, so that combustion noise can be reduced. On the other hand, when it is determined that the engine load is smaller than the second predetermined value, the fuel injection amount by the third fuel injection is subtracted from the fuel injection amount by the second fuel injection, so that the first Since active combustion is ensured by fuel injection, unburned HC / CO can be reduced. The second fuel injection has a lower degree of premixing than the first fuel injection, but the amount of fuel injection by the second fuel injection is reduced, so that NOx and smoke can be reduced.

  Preferably, the apparatus further comprises air-fuel ratio control means for controlling the ratio of air and fuel existing in the combustion chamber according to the engine water temperature detected by the water temperature detection means.

  In this case, the ignition delay time is shortened by controlling the ratio of the air and fuel (air-fuel ratio) existing in the combustion chamber to a lean state as the water temperature of the engine becomes lower. As a result, the combustion waveform can be made closer to the warm-up state.

  Further preferably, an exhaust gas recirculation passage connecting the intake portion and the exhaust portion of the combustion chamber, an exhaust gas recirculation cooler provided in the exhaust gas recirculation passage for cooling the exhaust gas recirculation gas passing through the exhaust gas recirculation passage, A bypass passage connected to the exhaust gas recirculation passage so as to bypass the recirculation cooler, and an exhaust gas recirculation gas flow path on the exhaust gas recirculation cooler side or the bypass passage according to the engine water temperature detected by the water temperature detection means And a flow path switching means for switching to the side.

  In this case, when the engine water temperature is lower than the set temperature, the exhaust gas recirculation gas in a high temperature state is introduced into the combustion chamber by switching the flow path of the exhaust gas recirculation gas from the exhaust gas recirculation cooler side to the bypass passage side. Therefore, the ignition delay time is shortened. As a result, the combustion waveform can be made closer to the warm-up state.

  According to the present invention, an increase in unburned HC / CO can be sufficiently suppressed even at a low water temperature. Thereby, it is possible to realize excellent premixed compression ignition combustion.

It is a schematic block diagram which shows the diesel engine provided with one Embodiment of the combustion control apparatus concerning this invention. It is a block diagram which shows the structure of the combustion control apparatus shown in FIG. It is a flowchart which shows the detail of the injector control processing procedure performed by the injector control part shown in FIG. It is a figure which shows the fuel injection quantity and fuel injection timing of the pre fuel injection at the time of high load and low load, the 1st main fuel injection, and the 2nd main fuel injection. It is a graph showing an example of a heat generation rate waveform when pre-fuel injection and EGR gas reduction are not performed at a low water temperature, when pre-injection and EGR gas reduction are performed at a low water temperature in a warm air state. is there. It is a graph which shows an example of an in-cylinder average temperature waveform and a heat release rate waveform at the time of high load and low load when pre-fuel injection is performed at the time of low water temperature. It is a figure which shows the modification of the fuel injection quantity of the pre fuel injection at the time of high load, the 1st main fuel injection, and the 2nd main fuel injection, and fuel injection timing.

  Hereinafter, a preferred embodiment of a combustion control device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a diesel engine equipped with an embodiment of a combustion control device according to the present invention. In the figure, a diesel engine 1 according to this embodiment is a premixed compression ignition (PCCI) type four-cylinder in-line diesel engine. The diesel engine 1 includes an engine body 2, and the engine body 2 is provided with four cylinders 3.

  Each cylinder 3 is provided with an injector (fuel injection valve) 5 for injecting fuel into the combustion chamber 4. The injector 5 has a plurality of injection holes (not shown) and injects fuel radially from each injection hole. Each injector 5 is connected to a common rail 6, and high-pressure fuel stored in the common rail 6 is constantly supplied to each injector 5.

  An intake passage 7 for sucking air into the combustion chamber 4 is connected to the engine body 2 via an intake manifold (intake portion) 8. Further, an exhaust passage 9 for discharging exhaust gas after combustion is connected to the engine body 2 via an exhaust manifold (exhaust portion) 10.

  In the intake passage 7, an air cleaner 11, a compressor 13 of the turbocharger 12, an intercooler 14, and a throttle valve 15 are provided from the upstream side toward the downstream side. The throttle valve 15 restricts the passage area of the intake passage 7 and generates a negative pressure on the downstream side, thereby enabling exhaust gas recirculation (EGR) described later. In the exhaust passage 9, a turbine 16 of the turbocharger 12 and a DPF 17 with a catalyst are provided.

  The diesel engine 1 also includes an exhaust gas recirculation (EGR) device 18 that recirculates part of the exhaust gas after combustion into the combustion chamber 4. The EGR device 18 includes an EGR passage 19 that connects the intake passage 7 and the exhaust manifold 10, an EGR valve 20 that adjusts the recirculation amount of exhaust recirculation gas (EGR gas) from the exhaust manifold 10 to the intake passage 7, and an EGR passage. The EGR cooler 21 that cools the EGR gas passing through the EGR 19, the bypass passage 22 connected to the EGR passage 19 so as to bypass the EGR cooler 21, and the EGR gas flow path to the EGR cooler 21 side or the bypass passage 22 side And a switching valve 23 for switching.

  Each injector 5, throttle valve 15, EGR valve 20 and switching valve 23 are controlled by an electronic control unit (ECU) 24. As shown in FIG. 2, the ECU 24 includes an accelerator opening sensor 25 for detecting the accelerator opening, an engine rotation sensor 26 for detecting the engine speed, and a crankshaft angle (crank angle) of a piston (not shown). A crank angle sensor 27 for detecting and a water temperature sensor (water temperature detecting means) 28 for detecting the engine water temperature are connected.

  Here, the injector 5, the throttle valve 15, the EGR valve 20, the switching valve 23, the ECU 24, and the sensors 25 to 28 constitute the combustion control device 29 of the present embodiment. Such a combustion control device 29 is controlled so as to perform premixed compression ignition combustion of split injection in which fuel is injected in a plurality of times from each injector 5 in one cycle of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. To do.

  FIG. 2 is a block diagram showing the configuration of the combustion control device 29. In the figure, the ECU 24 has an engine load calculation unit 30, an injector control unit 31, and an EGR control unit 32.

  The engine load calculation unit 30 calculates the engine load based on the accelerator opening detected by the accelerator opening sensor 25, the engine speed detected by the engine rotation sensor 26, and other conditions.

  The injector control unit 31 determines the basic values of the number of fuel injections, the fuel injection amount, and the fuel injection timing from the engine load and engine speed calculated by the engine load calculation unit 30. Further, the injector control unit 31 performs correction based on the engine water temperature detected by the water temperature sensor 28, determines the number of fuel injections, the fuel injection amount, and the fuel injection timing, and controls each injector 5.

  FIG. 3 is a flowchart showing details of the injector control processing procedure executed by the injector control unit 31.

  In FIG. 4, first, based on the engine load calculated by the engine load calculating unit 30, as shown in FIG. 4, the first main fuel injection (first fuel injection) and the second main fuel injection performed thereafter are performed. A fuel injection amount and fuel injection timing for fuel injection (second fuel injection) are determined (step S101). At this time, the fuel injection amount of the second main fuel injection is made smaller than the fuel injection amount of the first main fuel injection, for example. The second main fuel injection starts, for example, at a time when the crank angle is immediately before the compression top dead center (TDC).

  Subsequently, it is determined whether or not the engine water temperature detected by the water temperature sensor 28 is lower than a predetermined temperature (for example, 80 ° C.) (step S102).

  When it is determined that the engine water temperature is not lower than the predetermined temperature, the injector 5 is controlled so that the first main fuel injection is performed in accordance with the fuel injection amount determined in step S101 (step S108). Subsequently, the injector 5 is controlled so that the second main fuel injection is performed according to the fuel injection amount determined in step S101 (step S109).

  When it is determined in step S102 that the engine water temperature is lower than the predetermined temperature, based on the engine load and the engine water temperature, as shown in FIG. The fuel injection amount and fuel injection timing of the third fuel injection) are determined (procedure S103).

  At this time, the fuel injection amount of the pre-fuel injection is made smaller than the fuel injection amounts of the first and second main fuel injections. Further, the fuel injection amount of the pre-fuel injection is increased as the engine water temperature becomes lower, and the fuel injection amount of the pre-fuel injection is reduced as the engine load becomes higher.

  Further, the interval between the pre-fuel injection and the first main fuel injection is determined based on the bore, stroke, number of injection holes of the injector 5, swirl ratio, etc. in order to prevent spray overlap and gaps from adjacent injection holes of the injector 5. Set the appropriate interval to be calculated. As a result, local rich and local lean are avoided, and generation of unburned fuel is suppressed.

  Subsequently, it is determined whether the engine load is higher than a predetermined value (step S104). When it is determined that the engine load is higher than the predetermined value, as shown in FIG. 4A, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the first main fuel injection (step S105). . Therefore, the fuel injection amount of the first main fuel injection set in step S101 is corrected. On the other hand, when it is determined that the engine load is not higher than the predetermined value, as shown in FIG. 4B, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the second main fuel injection ( Procedure S106). Therefore, the fuel injection amount of the second main fuel injection set in step S101 is corrected.

  After executing steps S105 and S106, the injector 5 is controlled so that the pre-fuel injection is performed according to the fuel injection amount set in step S103 (step S107). Subsequently, the injector 5 is controlled to perform the first main fuel injection according to the fuel injection amount set in step S101 or the fuel injection amount corrected in step S105 (step S108). Subsequently, the injector 5 is controlled to perform the second main fuel injection according to the fuel injection amount set in step S101 or the fuel injection amount corrected in step S106 (step S109).

  Returning to FIG. 2, the EGR control unit 32 controls the EGR valve 20 and the switching valve 23 according to the engine water temperature. Specifically, the EGR control unit 32 controls the EGR valve 20 so that the flow rate of the EGR gas decreases as the engine water temperature decreases. Further, the EGR control unit 32 determines whether or not the engine water temperature is equal to or lower than a preset reference temperature, and when the engine water temperature is higher than the reference temperature, the switching valve 23 allows the EGR gas to pass through the EGR cooler 21. When the engine water temperature is below the reference temperature, the switching valve 23 is controlled so that the EGR gas passes through the bypass passage 22.

  In the above, the steps S101, S108, and S109 of the injector control unit 31 of the ECU 24 perform the first injection for controlling the fuel injection valve 5 so as to perform the second fuel injection after performing the first fuel injection. The valve control means is configured. The procedure S102 constitutes determination means for determining whether or not the engine water temperature detected by the water temperature detection means 28 is lower than a predetermined temperature. In steps S103 to S107, the fuel injection valve 5 is configured to perform the third fuel injection before the first fuel injection when the determination means determines that the water temperature of the engine is lower than the predetermined temperature. The second injection valve control means for controlling the engine is configured.

  The accelerator opening sensor 25, the engine rotation sensor 26, and the engine load calculation unit 30 of the ECU 24 constitute load detection means for detecting the engine load. The EGR control unit 32 and the EGR valve 20 of the ECU 24 constitute air-fuel ratio control means for controlling the ratio of air and fuel existing in the combustion chamber 4 in accordance with the engine water temperature detected by the water temperature detection means 28. To do. The EGR control unit 32 and the switching valve 23 of the ECU 24 are configured to switch the flow path of the exhaust recirculation gas to the exhaust recirculation cooler 21 side or the bypass passage 22 side according to the engine water temperature detected by the water temperature detection means 28. A path switching means is configured.

  In the present embodiment configured as described above, when the engine 1 is in a normal warm-up state (for example, 80 ° C. or higher), the pre-fuel injection is not performed and the first main fuel injection and the second main fuel are performed. Injection is performed in order. Then, since the ignition of the premixed mixture of fuel and air is started after a predetermined period after the first and second main fuel injections are finished, as shown by the broken line P in FIG. A heat release rate waveform (combustion waveform) is obtained.

  On the other hand, when the first main fuel injection and the second main fuel injection are sequentially performed without performing the pre-fuel injection when the engine 1 is in a low water temperature state, the fuel and air are premixed. Since the ignition timing of the ki is delayed as compared with the warm-air state, the combustion waveform is as indicated by a one-dot chain line Q in FIG.

  On the other hand, as in the present embodiment, when the engine 1 is in a low water temperature state, the first main fuel injection and the second main fuel injection are sequentially performed after the pre-fuel injection, and the EGR gas When the flow rate is decreased, the combustion waveforms almost coincide with each other in the warm-up state, as indicated by the solid line R in FIG. The reason is as follows.

  That is, when pre-fuel injection is performed, the ignition timing is advanced by preheating of the pre-fuel injection. Further, by reducing the flow rate of EGR gas, the ratio of air to fuel (air-fuel ratio) becomes lean, and good combustibility is ensured, so that the ignition delay period is shortened. As described above, since the ignition timing is appropriate, the combustion waveform almost coincides with that in the warm-up state.

  At this time, when the engine 1 is in a low load state, as described above, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the second main fuel injection to reduce the fuel injection amount of the pre-fuel injection. The total amount with the fuel injection amount of the first main fuel injection increases. On the other hand, when the engine 1 is in a high load state, as described above, the fuel injection amount of the pre-fuel injection is reduced to 1 from the fuel injection amount of the first main fuel injection. The total amount with the fuel injection amount of the second main fuel injection does not change.

  The effect of this difference in control will be described with reference to FIG. When the same amount of fuel is injected in the low load state control pattern (broken line X), the in-cylinder average temperature is higher than in the case of the high load state control pattern (solid line Y). As a result, the heat generation rate is increased. Therefore, unburned HC / CO can be reduced by injecting fuel with a control pattern in a low load state.

  As described above, in the present embodiment, when the engine water temperature is lower than the predetermined temperature, the pre-fuel injection is performed before the first main fuel injection, and then the first main fuel injection and the second main fuel injection are performed. Since the main fuel injection is sequentially performed, the ignition timing is advanced by preheating by the pre-fuel injection, and the combustion waveform comes closer to the warm-up state. At this time, since the fuel injection amount corresponding to the engine water temperature is set in the pre-fuel injection, combustion by the pre-fuel injection and the first main fuel injection is activated. Thereby, unburned HC / CO can be reduced.

  When the engine load is lower than a predetermined value when the engine water temperature is low, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the second main fuel injection. Combustion is activated. Thereby, unburned HC / CO can be reduced. In addition, since the fuel injection amount of the second main fuel injection with a low premixing degree decreases and the total fuel injection amount of the prefuel injection with a high premixing degree and the first main fuel injection increases, NOx and Smoke can be reduced.

  Further, when the engine load is higher than a predetermined value when the engine water temperature is low, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the first main fuel injection. Excessive activation of combustion is suppressed. Therefore, an increase in combustion noise can be suppressed.

  Further, as the engine water temperature becomes lower, the flow rate of the EGR gas is decreased and the air-fuel ratio is made lean, so that combustion is activated. Further, when the engine water temperature is lower than the reference temperature, the switching valve 23 is switched from the EGR cooler 21 side to the bypass passage 22 side, so that the EGR gas passes through the bypass passage 22 and is not cooled by the EGR cooler 21. The EGR gas is recirculated into the combustion chamber 4 to stabilize the combustion. As described above, the ignition delay is reduced, and the combustion waveform becomes closer to the warm-up state. As a result, an increase in unburned HC / CO can be further suppressed.

  As described above, according to the present embodiment, even when the water temperature is low, premixed compression ignition combustion similar to that after warming-up can be realized, and increases in HC, CO, combustion noise, and emissions can be sufficiently suppressed.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, when the engine load is higher than a predetermined value, the fuel injection amount of the pre-fuel injection is reduced from the fuel injection amount of the first main fuel injection (see FIG. 4A). However, if an increase in combustion noise can be allowed even when the engine load is higher than a predetermined value, as shown in FIG. 7, the fuel injection amount of the pre-fuel injection is calculated from the fuel injection amount of the second main fuel injection. You may lose weight. In this case, since the fuel injection amount of the second main fuel injection with a low premixing degree is reduced, it is possible to contribute to the reduction of smoke.

  In the above embodiment, when the fuel injection amount for the pre-fuel injection is reduced from the fuel injection amount for the main fuel injection, the first or second main fuel injection is based on the comparison result between the engine load and one predetermined value. Although it has been determined from which side of the fuel injection amount of the fuel injection the amount of the fuel injection amount of the pre-fuel injection is reduced, the predetermined value used for comparison with the engine load is not limited to one. For example, a first predetermined value and a second predetermined value smaller than the first predetermined value are determined, and when the engine load is a high load larger than the first predetermined value, the fuel of the first main fuel injection When the engine load is reduced to a low load smaller than the second predetermined value, the fuel injection amount of the second main fuel injection is decreased and the engine load is equal to or lower than the first predetermined value and the second predetermined value. At the above medium load, the fuel injection amount may be reduced from both the first and second main fuel injection amounts. In other words, at least a region for reducing the fuel injection amount of the first main fuel injection is set on the high load side, and a region for reducing the fuel injection amount of the second main fuel injection is set on the low load side. good. In addition, when the fuel injection amount is reduced from both the first and second main fuel injections at a medium load, the same amount may be reduced uniformly, or from the fuel injection amount of each main fuel injection. The amount to be reduced may be gradually changed.

  Furthermore, in the above embodiment, the flow path of the exhaust gas recirculation gas is switched to the exhaust gas recirculation cooler 21 side or the bypass passage 22 side by the switching valve 23, but is not limited to simple switching, for example, the flow rate of the exhaust gas recirculation gas These gradually changing regions may be provided.

  In the above embodiment, the air-fuel ratio in the combustion chamber 4 is controlled by adjusting the flow rate of the EGR gas by the EGR valve 20 in accordance with the engine water temperature. The air-fuel ratio in the combustion chamber 4 may be controlled by adjusting the air intake amount by the throttle valve 15 according to the engine water temperature. Further, both the EGR valve 20 and the throttle valve 15 may be controlled according to the engine water temperature.

  Further, in the above embodiment, the main fuel injection is performed twice per cycle, but the main fuel injection may be performed three times or more per cycle.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 8 ... Intake manifold (intake part), 10 ... Exhaust manifold (exhaust part), 15 ... Throttle valve (air-fuel ratio control means), 19 ... EGR passage (exhaust recirculation passage), 20 ... EGR valve (air-fuel ratio control means), 21 ... EGR cooler (exhaust recirculation cooler), 22 ... bypass passage, 23 ... switching valve (flow passage switching means), 24 ... ECU (Control means), 25 ... accelerator opening sensor (load detection means), 26 ... engine rotation sensor (load detection means), 28 ... water temperature sensor (water temperature detection means), 29 ... combustion control device, 30 ... engine load calculation section (Load detection means), 31... Injector control section (first injection valve control means, determination means, second injection valve control means), 32... EGR control section ( Ratio control means, the flow path switching means).

Claims (4)

In an engine combustion control device that performs premixed compression ignition combustion,
A fuel injection valve for injecting fuel into the combustion chamber of the engine;
First injection valve control means for controlling the fuel injection valve so as to perform the second fuel injection after the first fuel injection;
Water temperature detecting means for detecting the water temperature of the engine;
Load detecting means for detecting the load of the engine;
Determining means for determining whether the water temperature of the engine detected by the water temperature detecting means is lower than a predetermined temperature;
When the determination means determines that the water temperature of the engine is lower than the predetermined temperature, the fuel injection valve is controlled so that a third fuel injection is performed before the first fuel injection is performed. Second injection valve control means ,
The second injection valve control means determines a fuel injection amount by the third fuel injection in accordance with the water temperature of the engine detected by the water temperature detection means and the engine load detected by the load detection means. A means for determining, a means for comparing and determining the load of the engine with a first predetermined value and a second predetermined value, and when it is determined that the load of the engine is greater than the first predetermined value, When the fuel injection amount by the third fuel injection is reduced from the fuel injection amount by the first fuel injection, and it is determined that the load of the engine is smaller than the second predetermined value, the second injection And a means for reducing a fuel injection amount by the third fuel injection from a fuel injection amount by the fuel injection . Combustion control device according to claim 1, wherein the equal to the second predetermined value and said first predetermined value. Depending on the water temperature of the engine detected by the coolant temperature detecting means, according to claim 1 or 2, wherein said further comprising air-fuel ratio control means for controlling the ratio of air and fuel present in the combustion chamber Combustion control device. An exhaust gas recirculation passage connecting an intake portion and an exhaust portion of the combustion chamber;
An exhaust gas recirculation cooler provided in the exhaust gas recirculation passage for cooling the exhaust gas recirculation gas passing through the exhaust gas recirculation passage;
A bypass passage connected to the exhaust gas recirculation passage to bypass the exhaust gas recirculation cooler;
A flow path switching means for switching the flow path of the exhaust gas recirculation gas to the exhaust gas recirculation cooler side or the bypass passage side according to the water temperature of the engine detected by the water temperature detection means. The combustion control device according to any one of claims 1 to 3 .

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