JP2013068134A - Combustion control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control device capable of reducing HC and CO in low rotation/low load regions of an engine.SOLUTION: An ECU of a combustion control device determines fuel injection amounts and fuel injection timings of main fuel injection the first time and subsequent main fuel injection the second time, and then determines a fuel injection amount and a fuel injection timing of auxiliary after fuel injection performed after the main fuel injection the second time when an engine rotation speed detected by a crank angle sensor is lower than a predetermined rotation speed and when an engine load detected by an acceleration sensor is lower than a predetermined load. The ECU controls an injector so that the main fuel injection the first time, the main fuel injection the second time, and the after fuel injection are sequentially performed in accordance with the determined fuel injection amounts and the fuel injection timings.

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. In the combustion control device described in Patent Document 1, after a first injection amount of fuel is injected by the fuel injection valve at a relatively early stage of the compression stroke in the low load region of the engine, the cooling of the premixed gas at the end of the compression stroke is performed. When the flame reaction starts, fuel injection of the second injection amount is performed by the fuel injection valve.

JP 2004-100603 A

  By the way, since the fuel injection amount is relatively small in the low rotation region and low load region of the engine, the temperature in the combustion chamber does not rise so much, and unburned HC and CO are likely to be generated. However, in the above prior art, although soot and NOx are reduced, no consideration is given to such suppression of generation of HC and CO.

  The objective of this invention is providing the combustion control apparatus which can reduce HC and CO in the low rotation area and low load area of an engine.

  The present invention relates to an engine combustion control apparatus that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into the combustion chamber of the engine, and a second main fuel injection after the first main fuel injection is performed. As detected, the first injection valve control means for controlling the fuel injection valve, the rotation speed detection means for detecting the engine rotation speed, the load detection means for detecting the engine load, and the rotation speed detection means. Determining means for determining whether the engine speed detected is lower than the predetermined engine speed and the engine load detected by the load detecting means is lower than the predetermined load; And after the second main fuel injection is performed, the auxiliary after fuel injection is performed when it is determined that the engine load is lower than the predetermined load. It is characterized in further comprising a second injector control means for controlling the fuel injection valve.

  As described above, in the combustion control apparatus of the present invention, after the first main fuel injection and the second main fuel injection are sequentially performed, the engine speed is lower than the predetermined speed and the engine load is higher than the predetermined load. Is lower, further auxiliary after-injection is performed, so that combustion by after-fuel injection is performed and the temperature in the combustion chamber rises, so that the oxidation reaction of unburned fuel is promoted and HC and CO are reduced. Less likely to occur. Thereby, HC and CO can be reduced in a low engine speed and low load range.

  Preferably, the second injection valve control means performs the after fuel injection at a timing when the second main fuel injection can be ignited while the fuel existing in the combustion chamber undergoes a high temperature oxidation reaction. In addition, the fuel injection valve is controlled. By performing after fuel injection at an appropriate time in this way, combustion by after fuel injection is activated, and the temperature in the combustion chamber is sufficiently increased. As a result, HC and CO can be further reduced in the low engine speed / low load range of the engine.

  Preferably, the second injection valve control means has injection amount setting means for setting a fuel injection amount by after-fuel injection, and performs after-fuel injection according to the fuel injection amount set by the injection amount setting means. The fuel injection valve is controlled to perform. In this case, after-fuel injection can be appropriately performed by setting an optimal fuel injection amount according to the conditions.

  In this case, preferably, the second injection valve control means reduces the fuel injection quantity by the second main fuel injection when the fuel injection quantity by the after fuel injection is set by the injection quantity setting means. Have means. When the second main fuel injection is performed, the oxidation reaction of the first main fuel injection is suppressed by the endothermic reaction at that time. However, by reducing the fuel injection amount by the second main fuel injection, the suppression effect by such endothermic reaction is reduced, so that the combustion by the first main fuel injection becomes active.

  At this time, the injection amount reducing means preferably reduces the fuel injection amount by the after fuel injection set by the injection amount setting means from the fuel injection amount by the second main fuel injection. In this case, since the fuel injection amount by the second main fuel injection is sufficiently reduced, the combustion by the first main fuel injection becomes more active.

  Preferably, the apparatus further comprises a water temperature detecting means for detecting the cooling water temperature of the engine, and the injection amount setting means determines whether or not the engine cooling water temperature detected by the water temperature detecting means is lower than the first predetermined temperature. Means for determining whether the engine coolant temperature detected by the water temperature detector is higher than a second predetermined temperature equal to or higher than the first predetermined temperature, and the engine coolant temperature is the first predetermined temperature. When it is determined that the fuel injection amount is lower than that, the fuel injection amount by the after fuel injection is increased, and when it is determined that the engine coolant temperature is higher than the second predetermined temperature, the fuel injection amount by the after fuel injection is decreased. Means. When the air-fuel ratio is corrected to the lean side when the engine coolant temperature is low, smoke does not easily occur due to an increase in the air amount. Therefore, when the engine coolant temperature is lower than the first predetermined temperature, the amount of fuel injection by after-fuel injection is increased, thereby reducing the generation of smoke and reducing the HC in the low engine speed range and low load range of the engine. And CO can be reduced. On the other hand, when the air-fuel ratio is corrected to the rich side when the engine coolant temperature is high, smoke is likely to occur due to a decrease in the air amount or the like. Therefore, when the engine coolant temperature is higher than the second predetermined temperature, the generation of smoke can be suppressed by reducing the fuel injection amount by the after fuel injection.

  According to the present invention, HC and CO can be reduced in a low engine speed and low load range. 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 flowchart which shows the process sequence performed by ECU shown in FIG. It is a figure which shows an example of the fuel injection quantity of 1st main fuel injection, 2nd main fuel injection, and after fuel injection, and fuel injection timing. It is a flowchart which shows the detail of the determination processing procedure of the fuel injection quantity of the after fuel injection shown in FIG. It is a graph which shows an example of the heat release rate waveform when the after fuel injection is performed and when the after fuel injection is not performed. It is a graph which shows an example of the relationship between the fuel injection timing of after fuel injection, CO generation amount, HC generation amount, and a smoke generation rate. It is a graph which shows an example of the relationship between the fuel injection quantity of after fuel injection, CO generation amount, and a smoke generation rate.

  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 four-cylinder in-line diesel engine equipped with a common rail fuel injection device. 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 injects fuel radially from the injection nozzle 5a. 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 8. In addition, an exhaust passage 9 for discharging exhaust gas after combustion is connected to the engine body 2 via an exhaust manifold 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 negative pressure downstream, thereby enabling exhaust gas recirculation (EGR), which will be 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. A crank angle sensor 25, an accelerator sensor 26, and a water temperature sensor 27 are connected to the ECU 24.

  The crank angle sensor 25 constitutes rotation speed detection means that can calculate the rotation speed (engine rotation speed) of the engine body 2 by detecting the rotation angle (crank angle) of a crankshaft to which a piston (not shown) is coupled. doing. The accelerator sensor 26 constitutes load detecting means for detecting the depression angle (accelerator opening) of the accelerator pedal as an alternative value of the load (engine load) of the engine body 2. In a diesel engine equipped with a common rail fuel injection device, the fuel injection amount is electronically controlled, and the fuel injection amount can be used as an alternative value for the engine load. The water temperature sensor 27 constitutes a water temperature detecting means for detecting the cooling water temperature of the engine body 2 (engine cooling water temperature). For example, the water temperature sensor 27 is attached to the cylinder head of the engine body 2 and detects the water temperature of the water jacket in the cylinder head. ing.

  The ECU 24 inputs detection signals from the crank angle sensor 25, the accelerator sensor 26, and the water temperature sensor 27, performs predetermined processing, and controls the injector 5, the throttle valve 15, the EGR valve 20, and the switching valve 23.

  Here, the injector 5, the ECU 24, and the sensors 25 to 27 constitute a combustion control device 28. Further, in this embodiment, the combustion control device 28 includes a throttle valve 15, an EGR valve 20, and a switching valve 23. Such a combustion control device 28 performs premixed compression ignition (PCCI) combustion of split injection in which fuel is injected from each injector 5 in a plurality of times in one cycle of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. Control to do.

  In the present embodiment, as described above, premixed compression ignition combustion is performed in the diesel engine by controlling the amount and timing of fuel to be dividedly injected. Here, the premixed compression ignition combustion will be supplemented. Premixed compression ignition combustion is accompanied by a low temperature oxidation reaction in which heat generation occurs more slowly than the fuel injected into the combustion chamber 4 in the combustion process, and a high temperature oxidation reaction in which heat generation increases rapidly after the low temperature oxidation reaction. In this embodiment, the case where the high temperature oxidation reaction occurs after the completion of fuel injection, that is, the case where the premixing time exists before the high temperature oxidation reaction is referred to as premixed compression ignition combustion. The main fuel injection described below is a fuel injection for performing premixed compression ignition combustion.

  FIG. 2 is a flowchart showing a processing procedure executed by the ECU 24. This process is a process for controlling the injector 5 and the EGR valve 20 based on the detection signals of the sensors 25 to 27.

  In the figure, first, an after fuel injection flag F is initially set to 0 (step S101). Subsequently, based on the engine speed detected by the crank angle sensor 25 and the engine load detected by the accelerator sensor 26, as shown in FIG. 3, the first main fuel injection and the second time executed thereafter are performed. The fuel injection amount and fuel injection timing of the main fuel injection are determined (step S102). 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. In addition, the start timing of the second main fuel injection is, for example, the crank angle immediately before the compression top dead center (TDC).

  Subsequently, it is determined whether or not the engine speed detected by the crank angle sensor 25 is lower than a predetermined speed (step S103). Here, the predetermined rotational speed is set to a rotational speed lower than ½ of the maximum rotational speed (for example, about 2000 rpm). When it is determined that the engine speed is lower than the predetermined speed, it is determined whether the engine load detected by the accelerator sensor 26 is lower than the predetermined load (step S104). Here, when the predetermined load is replaced by the depression angle of the accelerator pedal, for example, the predetermined load is a depression angle of about 20% with respect to the maximum depression angle.

  When it is determined that the engine load is lower than the predetermined load, as shown in FIG. 3, the fuel injection timing of the auxiliary after fuel injection that is performed after the second main fuel injection is determined (step S105). . Specifically, the fuel injection timing of the after fuel injection is such that the premixed mixture of fuel and air can be ignited while the injected fuel existing in the combustion chamber 4 is combusted by performing the second main fuel injection. It is preferable that the time be such that.

  Subsequently, the fuel injection amount of the after fuel injection is determined (procedure S106). FIG. 4 shows details of the procedure for determining the fuel injection amount for the after fuel injection.

  In the figure, first, the fuel injection amount of the after fuel injection is set (step S201). The fuel injection amount of the after fuel injection may be obtained based on the engine speed detected by the crank angle sensor 25 and the engine load detected by the accelerator sensor 26, or may be determined as a constant value in advance. .

  Subsequently, it is determined whether or not the engine coolant temperature detected by the water temperature sensor 27 is lower than the first predetermined temperature (step S202). When it is determined that the engine coolant temperature is lower than the first predetermined temperature, the recirculation amount of the EGR gas to the intake passage 7 is set to correct the air-fuel ratio (A / F) in the combustion chamber 4 to the lean side. The EGR valve 20 is controlled so as to increase the amount of intake air into the combustion chamber 4 by decreasing (step S203). When the air-fuel ratio is corrected to the lean side, the amount of intake air into the combustion chamber 4 is increased without changing the fuel injection amount into the combustion chamber 4.

  Subsequently, the after-injection fuel injection amount set in step S201 is increased according to the engine coolant temperature (step S204). At this time, for example, the fuel injection amount of the after fuel injection is increased as the engine coolant temperature becomes lower.

  If it is determined in step S202 that the engine coolant temperature is not lower than the first predetermined temperature, it is determined whether the engine coolant temperature is higher than the second predetermined temperature (step S205). The second predetermined temperature is preferably higher than the first predetermined temperature, but may be the same as the first predetermined temperature.

  When it is determined that the engine coolant temperature is higher than the second predetermined temperature, combustion is performed by increasing the recirculation amount of EGR gas to the intake passage 7 in order to correct the air-fuel ratio in the combustion chamber 4 to the rich side. The EGR valve 20 is controlled so as to reduce the amount of intake air into the chamber 4 (step S206). When the air-fuel ratio is corrected to the rich side, the amount of intake air into the combustion chamber 4 is reduced without changing the fuel injection amount into the combustion chamber 4.

  Note that the air-fuel ratio in the combustion chamber 4 is also in a lean environment by the procedure S203 and the procedure S206. The correction to the lean side or the correction to the rich side described above is the value of the air-fuel ratio (A / F) set when the engine coolant temperature is between the first predetermined temperature and the second predetermined temperature. Means that the correction is made to the lean side or the rich side with respect to the standard.

  Subsequently, the fuel injection amount of the after fuel injection set in step S201 is decreased according to the engine coolant temperature (step S207). At this time, for example, the fuel injection amount of the after fuel injection is decreased as the engine coolant temperature becomes higher.

  When it is determined in step S205 that the engine coolant temperature is not higher than the second predetermined temperature, the after-injection fuel injection amount set in step S201 is not changed.

  Thereafter, as shown in FIG. 3, the fuel injection amount of the second main fuel injection determined in the procedure 102 is reduced by subtracting the fuel injection amount of the after fuel injection from the fuel injection amount of the second main fuel injection. The amount is changed (procedure S208).

  However, when the fuel injection amount of the after fuel injection is reduced from the fuel injection amount of the second main fuel injection, the fuel injection amount of the second main fuel injection is lower than the minimum injection amount of the injection nozzle 5a of the injector 5. In this case, the remaining fuel injection amount of the after fuel injection is reduced from the fuel injection amount of the first main fuel injection. If the fuel injection amount of the after fuel injection is still insufficient, the fuel injection amount of the after fuel injection is reduced within a range that does not fall below the minimum injection amount of the injection nozzle 5a of the injector 5. Thereby, the total fuel injection amount is kept constant.

  Returning to FIG. 2, after determining the fuel injection amount of the after fuel injection as described above, the after fuel injection flag F is set to 1 (step S107).

  Then, after step S107 is executed, or when it is determined in step S103 that the engine speed is not lower than the predetermined speed, if it is determined in step S104 that the engine load is not lower than the predetermined load. Then, at the fuel injection timing determined in step S102, the injector 5 is controlled so that the first main fuel injection is performed in accordance with the fuel injection amount determined in step S102 (step S108).

  Subsequently, at the fuel injection timing determined in step S102, the injector 5 is controlled so that the second main fuel injection is performed according to the fuel injection amount determined in step S102 or the fuel injection amount changed in step S208. (Step S109). Specifically, when the subsequent after fuel injection is not performed, the second main fuel injection is performed according to the fuel injection amount determined in step S102, and when the subsequent after fuel injection is performed, in step S208. A second main fuel injection is performed according to the changed fuel injection amount.

  Subsequently, it is determined whether or not the after fuel injection flag F is 1 (procedure S110). If the after fuel injection flag F is not 1, this processing is terminated without performing after fuel injection. When the after fuel injection flag F is 1, the injector 5 is controlled to perform after fuel injection according to the fuel injection amount determined in step S106 at the fuel injection timing determined in step S105 (step S111). ), This process is terminated.

  Here, when the second main fuel injection is performed, the high temperature oxidation reaction of the first main fuel injection is suppressed by the endothermic reaction of the fuel. However, when the after fuel injection is performed, the fuel injection amount of the second main fuel injection is reduced by the amount of the fuel injection of the after fuel injection, so the first end due to the endothermic reaction of the fuel in the second main fuel injection. The suppression effect of the main fuel injection is reduced, and the high temperature oxidation reaction of the first main fuel injection becomes active.

  In the above, the first injection valve control means for controlling the fuel injection valve 5 so as to perform the second main fuel injection after the first main fuel injection is made up of the ECU 24, and the procedure S102, S108 and S109 correspond to the function. The judging means for judging whether or not the engine speed detected by the speed detecting means 25 is lower than the predetermined speed and whether the engine load detected by the load detecting means 26 is lower than the predetermined load comprises the ECU 24. The above steps S103 and S104 correspond to the function. When the determination means determines that the engine speed is lower than the predetermined speed and the engine load is lower than the predetermined load, an auxiliary after-fuel injection is performed after the second main fuel injection is performed. As described above, the second injection valve control means for controlling the fuel injection valve 5 comprises the ECU 24, and the above-described procedures S105, S106, and S111 correspond to the function thereof.

  Further, the injection amount setting means for setting the fuel injection amount by the after fuel injection includes the ECU 24, and the above steps S201 to S207 correspond to the function. The injection amount reducing means for reducing the fuel injection amount by the second main fuel injection when the fuel injection amount by the after fuel injection is set by the injection amount setting means is composed of the ECU 24, and the above-described procedure S208 corresponds to the function.

  In the present embodiment configured as described above, when the engine speed is lower than the predetermined speed and the engine load is lower than the predetermined load, following the first main fuel injection and the second main fuel injection. Since the after fuel injection is performed, the combustion by the after fuel injection is performed in the later stage of the combustion in the combustion chamber 4 (in the cylinder), and the temperature in the combustion chamber 4 (the in-cylinder temperature) rises. Therefore, the oxidation reaction of unburned matter is promoted, and HC and CO are hardly generated. Thereby, HC and CO can be reduced in the low rotation range and low load range of the engine 1.

  FIG. 5 shows an example of the heat release rate waveform when the after fuel injection is performed and when the after fuel injection is not performed. In FIG. 5, the broken line P indicates the heat generation rate waveform when the after fuel injection is not performed, and the one-dot chain line Q and the solid line R indicate the heat generation rate waveform when the after fuel injection is performed at different timings. Yes. When the after fuel injection is performed, a heat generation region (mountain shape) corresponding to the after fuel injection occurs around 10 ° ATDC in the one-dot chain line Q, and around 15 ° ATDC in the solid line R. ing. In addition, when the after fuel injection is performed, the amount of fuel injection of the second main fuel injection is reduced by the amount of the fuel injection of the after fuel injection, so that heat is generated compared to the case where the after fuel injection is not performed. The rate peak is suppressed.

  FIG. 6A shows an example of the relationship between the fuel injection timing of the after fuel injection and the CO generation amount, and FIG. 6B shows an example of the relationship between the fuel injection timing of the after fuel injection and the HC generation amount. FIG. 6C shows an example of the relationship between the fuel injection timing of the after fuel injection and the smoke occurrence rate. As shown in FIGS. 6A and 6B, when after-fuel injection is performed (see the solid line S), CO and HC are reduced compared to when no after-fuel injection is performed (see the broken line T). It is clear that

  At this time, by performing the after fuel injection at a time when the premixed gas can be ignited while the fuel injected by the second main fuel injection is combusting, the combustion by the after fuel injection is activated, and the cylinder The internal temperature rises sufficiently. Accordingly, the oxidation reaction of the unburned portion is promoted, and HC and CO are further hardly generated, so that HC and CO can be further reduced.

  In FIG. 5, an alternate long and short dash line Q indicates a case where the fuel injection timing of the after fuel injection is set to a timing (5 ° ATDC) at which ignition is possible while the injected fuel is burned by performing the second main fuel injection. A heat generation rate waveform is shown, and a solid line R represents a case where the fuel injection timing of the after fuel injection is set to a timing (8 ° ATDC) at which ignition is possible after the combustion of the injected fuel by the second main fuel injection is completed. The heat release rate waveform is shown.

  As shown in FIGS. 6A and 6B, when the fuel injection timing of after fuel injection is set to 5 ° ATDC, it is clear that CO and HC are reduced compared to the case where 8 ° ATDC is set. It is. Further, as shown in FIG. 6C, when the fuel injection timing of the after fuel injection is 5 ° ATDC, the smoke generation rate is lower than when the fuel injection timing is 8 ° ATDC. Therefore, by setting the fuel injection timing of the after fuel injection to a timing at which ignition can be performed while the fuel injected by the second main fuel injection is combusting, the increase in smoke is suppressed and HC and CO are reduced. Can be reduced.

  Further, when the engine coolant temperature is lower than the first predetermined temperature, the amount of air taken into the combustion chamber 4 increases by correcting the air-fuel ratio to the lean side as described above, so that smoke is generated. It becomes difficult to do. Therefore, when the engine cooling water temperature is lower than the first predetermined temperature, it is possible to reduce HC and CO while suppressing the generation of smoke by increasing the fuel injection amount of the after fuel injection.

  FIG. 7A shows an example of the relationship between the fuel injection amount of the after fuel injection and the CO generation amount, and FIG. 7B shows an example of the relationship between the fuel injection amount of the after fuel injection and the smoke generation rate. Show. Both graphs show the characteristics when the engine coolant temperature is 20 ° C. The fuel injection amount when the engine coolant temperature is 80 ° C. is about 1.1 mm 3 / st.

  As can be seen from FIG. 7A, the CO decreases as the fuel injection amount of the after fuel injection is increased from 1.1 mm 3 / st. Further, as can be seen from FIG. 7B, even if the fuel injection amount of the after fuel injection is increased from 1.1 mm 3 / st to 2.0 mm 3 / st, the smoke hardly increases. Therefore, by increasing the fuel injection amount of the after fuel injection within the range of 1.1 to 2.0 mm 3 / st, it becomes possible to reduce CO while suppressing the generation of smoke.

  On the other hand, when the engine coolant temperature is higher than the second predetermined temperature, the amount of air sucked into the combustion chamber 4 is reduced by correcting the air-fuel ratio to the rich side as described above, and the premixed gas Since the ignition delay is shortened, smoke is likely to occur. Therefore, when the engine coolant temperature is higher than the second predetermined temperature, the generation of smoke can be suppressed by reducing the fuel injection amount of the after fuel injection.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, when the engine speed is lower than the predetermined speed and the engine load is lower than the predetermined load, the first main fuel injection, the second main fuel injection, and the after fuel injection are sequentially performed. However, an auxiliary pre-fuel injection may be performed before the first main fuel injection is performed.

  In the above embodiment, when the after fuel injection is performed, the fuel injection amount of the after fuel injection is basically reduced from the fuel injection amount of the second main fuel injection. The fuel decrease amount of the main fuel injection is not particularly limited to the fuel injection amount of the after fuel injection.

  Furthermore, in the above embodiment, the fuel injection amount of the after fuel injection is increased or decreased according to the engine cooling water temperature detected by the water temperature sensor 27. However, in addition to the water temperature sensor 27, the outside air temperature for detecting the outside air temperature. A sensor may be provided to increase or decrease the fuel injection amount of the after fuel injection based on the engine coolant temperature and the outside air temperature. For example, a correction coefficient is set in advance for each of the engine cooling water temperature and the outside air temperature, and the larger one of the engine cooling water temperature correction coefficient and the outside air temperature correction coefficient is selected based on the engine cooling water temperature and the outside air temperature. By multiplying the previously obtained basic fuel injection amount by the correction coefficient, the fuel injection amount of the after fuel injection is obtained.

  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. When the main fuel injection is performed three times or more, the last main fuel injection corresponds to the second main fuel injection, and the immediately preceding main fuel injection corresponds to the first main fuel injection.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 24 ... ECU (1st injection valve control means, judgment means, 2nd injection valve control means, injection amount setting means, injection amount reduction) Means), 25 ... crank angle sensor (rotation speed detection means), 26 ... accelerator sensor (load detection means), 27 ... water temperature sensor (water temperature detection means), 28 ... combustion control device.

The present invention relates to an engine combustion control apparatus that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into the combustion chamber of the engine, and a second main fuel injection after the first main fuel injection is performed. As detected, the first injection valve control means for controlling the fuel injection valve, the rotation speed detection means for detecting the engine rotation speed, the load detection means for detecting the engine load, and the rotation speed detection means. Determining means for determining whether the engine speed detected is lower than the predetermined engine speed and the engine load detected by the load detecting means is lower than the predetermined load; And after the second main fuel injection is performed, the auxiliary after fuel injection is performed when it is determined that the engine load is lower than the predetermined load. And a second injection valve control means for controlling the fuel injection valve, the second injection valve control means, while the fuel present in the combustion chamber by the practice of the second main fuel injection occurs a high temperature oxidation reaction The fuel injection valve is controlled so that after-fuel injection is performed at a time when ignition is possible .

In addition, by performing the after fuel injection at the appropriate time described above, the combustion by the after fuel injection is activated, and the temperature in the combustion chamber is sufficiently increased. As a result, HC and CO can be further reduced in the low engine speed / low load range of the engine.

Claims (6)

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 that the second main fuel injection is performed after the first main fuel injection is performed;
A rotational speed detection means for detecting the rotational speed of the engine;
Load detecting means for detecting the load of the engine;
Determining means for determining whether the engine speed detected by the engine speed detecting means is lower than a predetermined engine speed and whether the engine load detected by the load detecting means is lower than a predetermined load;
When it is determined by the determination means that the engine speed is lower than the predetermined speed and the engine load is lower than the predetermined load, an auxiliary is performed after the second main fuel injection is performed. And a second injection valve control means for controlling the fuel injection valve so as to perform the after-fuel injection.   The second injection valve control means performs the after fuel injection at a time when ignition is possible while the fuel existing in the combustion chamber undergoes a high-temperature oxidation reaction by performing the second main fuel injection. The combustion control apparatus according to claim 1, wherein the fuel injection valve is controlled as described above.   The second injection valve control means has an injection amount setting means for setting a fuel injection amount by the after fuel injection, and performs the after fuel injection according to the fuel injection amount set by the injection amount setting means. The combustion control apparatus according to claim 1, wherein the fuel injection valve is controlled.   The second injection valve control means includes an injection amount reducing means for reducing the fuel injection quantity by the second main fuel injection when the fuel injection quantity by the after fuel injection is set by the injection quantity setting means. The combustion control device according to claim 3, wherein the combustion control device is provided.   5. The fuel injection amount reduction unit according to claim 4, wherein the injection amount reduction unit reduces a fuel injection amount by the after-fuel injection set by the injection amount setting unit from a fuel injection amount by the second main fuel injection. Combustion control device. A water temperature detecting means for detecting a cooling water temperature of the engine;
The injection amount setting means determines whether the engine cooling water temperature detected by the water temperature detecting means is lower than a first predetermined temperature, and the engine cooling water temperature detected by the water temperature detecting means. Is determined to be higher than a second predetermined temperature equal to or higher than the first predetermined temperature, and when it is determined that the cooling water temperature of the engine is lower than the first predetermined temperature, Means for increasing the amount of fuel injected by after-fuel injection and reducing the amount of fuel injected by after-fuel injection when it is determined that the engine coolant temperature is higher than the second predetermined temperature. The combustion control device according to any one of claims 3 to 5, wherein

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