JP2013060922A - Combustion control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control device capable of establishing a proper pre-mixing, compressive ignition combustion even if the suction pressure to inside a combustion chamber is lowered.SOLUTION: After deciding the fuel injection amount of the first fuel injection and its timing and those of the second time fuel injection executed following the first fuel injection, an ECU determines whether the suction pressure sensed by a suction pressure sensor is lower than the reference pressure, controls, when the suction pressure is lower than the reference pressure, so that the air-fuel ratio in the combustion chamber may be maintained at the value which is set when the pressure is at the reference, and further advances the fuel injection timings of the first fuel injection and the second fuel injection. Additionally, the ECU controls an injector so that the first time fuel injection and the second fuel injection may be executed one after the other according to the given fuel injection amount and fuel injection timing.

Description

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

  As a combustion control device for an engine that performs premixed compression ignition combustion, for example, as described in Patent Document 1, by injecting fuel into a plurality of times by an injector from the middle to the latter half of a cylinder compression stroke, It is known that an air-fuel mixture that is as homogeneous as possible is formed and burned by self-ignition.

JP 2003-286879 A

  However, when premixed compression ignition combustion is performed as in the above prior art, if the intake pressure into the combustion chamber of the engine decreases, an appropriate combustion waveform (heat generation rate waveform) cannot be obtained, and appropriate premixing is performed. Realizing compression ignition combustion may be difficult. In this case, the combustion noise increases and the emission deteriorates.

  An object of the present invention is to provide a combustion control device capable of realizing appropriate premixed compression ignition combustion even when the intake pressure into the combustion chamber decreases.

  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, a determination unit that determines a fuel injection amount and a fuel injection timing, a fuel injection amount, Injecting control means for controlling the fuel injection valve so as to perform fuel injection according to the fuel injection timing, an intake passage for sucking air into the combustion chamber, and exhausting exhaust gas after combustion from the combustion chamber The exhaust passage, the intake pressure detecting means for detecting the intake pressure into the combustion chamber, and the ignition timing by the fuel injection is advanced when the intake pressure detected by the intake pressure detecting means is lower than a predetermined pressure. And a correction means for correcting.

  When the intake pressure into the combustion chamber of the engine decreases, the amount of air taken into the combustion chamber decreases, so that when the fuel is injected into the combustion chamber by the fuel injection valve, the oxidation reaction between the fuel and air is delayed. A correct combustion waveform cannot be obtained. Therefore, in the present invention, the intake pressure into the combustion chamber is detected, and when the intake pressure is lower than the predetermined pressure, correction is made to advance the ignition timing by fuel injection, so that the combustion waveform at that time is at the predetermined pressure. It approaches the resulting combustion waveform. Thereby, appropriate premixed compression ignition combustion can be realized. As a result, an increase in combustion noise and a deterioration in emissions can be suppressed.

  In the combustion process in premixed compression ignition combustion, the fuel injected into the combustion chamber causes a low temperature oxidation reaction (cool flame reaction) in which heat generation occurs slowly, and a high temperature oxidation reaction in which heat generation increases rapidly after the low temperature oxidation reaction. Accompanied by (hot flame reaction). Here, the ignition timing by fuel injection is the timing when a high-temperature oxidation reaction in which heat generation rapidly increases starts.

  Preferably, the determining means determines the fuel injection amount and the fuel injection timing of the first fuel injection and the second fuel injection performed thereafter, and the injection control means is responsive to the fuel injection amount and the fuel injection timing. The fuel injection valve is controlled so as to sequentially perform the first fuel injection and the second fuel injection, and the correction unit is configured to perform the first operation when the intake pressure detected by the intake pressure detection unit is lower than a predetermined pressure. The ignition timing by the fuel injection is corrected so as to advance.

  If the fuel is divided and injected, the combustion period of the fuel in the combustion chamber becomes longer. Therefore, when the intake pressure becomes lower than a predetermined pressure, the combustion waveform tends to deviate from an appropriate combustion waveform. Therefore, when the detected intake pressure is lower than the predetermined pressure, correction is made to advance the ignition timing by the first fuel injection so that the combustion waveform at that time approaches the combustion waveform obtained at the predetermined pressure. Become. The first fuel injection and the second fuel injection are performed by dividing the main fuel injection for generating the required engine output, and are performed before the main fuel injection. A small amount of fuel injection called injection or pre-injection is not included.

  At this time, preferably, the correction means includes an air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber, and an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. The air-fuel ratio control means controls the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio set at the predetermined pressure when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure.

  Since the ignition timing by the first fuel injection is advanced by advancing the fuel injection timing of the first fuel injection in this way, the ignition timing at which the ignition timing by the first fuel injection is obtained at a predetermined pressure. Will definitely come closer to. Further, by controlling the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio set at a predetermined pressure, the combustion waveform can be brought close to the combustion waveform obtained at the predetermined pressure. Therefore, since the combustion of the premixed mixture of fuel and air is appropriately performed, an increase in unburned HC and CO can be suppressed.

  At this time, it is preferable to further include load detection means for detecting the engine load, and the injection timing advance means detects the intake pressure detected by the intake pressure detection means lower than a predetermined pressure and is detected by the load detection means. When the engine load is higher than the first predetermined value, the fuel injection timing of the first fuel injection is advanced, and the air-fuel ratio control means causes the intake pressure detected by the intake pressure detection means to be a predetermined pressure. When the engine load detected by the load detecting means is higher than the first predetermined value, the air-fuel ratio in the combustion chamber is controlled to be maintained at the air-fuel ratio set at the predetermined pressure.

  Generally, when the engine load is low, the intake air amount is smaller than when the engine load is high. Therefore, when the engine load is lower than the first predetermined value, the ignition timing due to the first fuel injection is hardly advanced even if the fuel injection timing of the first fuel injection is advanced. Therefore, by narrowing the ignition timing by the first fuel injection to a region where it is easy to advance, the ignition timing by the first fuel injection can be efficiently brought close to the ignition timing obtained at a predetermined pressure.

  In this case, preferably, the air-fuel ratio control means is such that the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure, and the engine load detected by the load detection means is lower than a first predetermined value. Sometimes, the air-fuel ratio in the combustion chamber is controlled to be lean with respect to the air-fuel ratio set at a predetermined pressure.

  As described above, when the engine load is lower than the first predetermined value, the air-fuel ratio in the combustion chamber is controlled to be lean with respect to the air-fuel ratio set at the predetermined pressure, thereby being sucked into the combustion chamber. The amount of air becomes large enough. For this reason, even if the fuel injection timing of the first fuel injection is not advanced, the ignition timing by the first fuel injection is advanced, so that the combustion waveform reliably approaches the combustion waveform obtained at the predetermined pressure. It becomes like this. Therefore, since the combustion of the premixed mixture of fuel and air is appropriately performed, an increase in unburned HC and CO can be suppressed.

  Preferably, the exhaust passage and the intake passage are connected to each other, and an exhaust gas recirculation passage for returning a part of the exhaust gas after combustion as an exhaust gas recirculation gas into the combustion chamber and an exhaust gas recirculation passage are provided. And a valve means for adjusting the recirculation amount of the exhaust gas recirculation gas. The air-fuel ratio control means controls the valve means so that the recirculation amount of the exhaust gas recirculation gas decreases, thereby Control the fuel ratio.

  Thus, by using the valve means for adjusting the recirculation amount of the exhaust gas recirculation gas, the air-fuel ratio in the combustion chamber can be reliably maintained at the air-fuel ratio set at a predetermined pressure with a simple configuration.

  Further preferably, when the engine load detected by the load detecting means is higher than a second predetermined value larger than the first predetermined value, the correcting means preferably performs the first fuel injection and the second fuel injection. There is further provided an injection pressure control means for controlling the fuel injection pressure to be reduced.

  When the intake pressure into the combustion chamber of the engine becomes low, ignition by the first fuel injection is delayed, so the temperature in the combustion chamber rises at the time of performing the second fuel injection thereafter, and the ignition delay by the second fuel injection is delayed. This shortens the premixing time of fuel and air. In particular, when the engine load is increased, the ignitability is improved, so that such a problem appears remarkably. Therefore, when the engine load is higher than the second predetermined value that is larger than the first predetermined value, the second fuel injection is reduced by reducing the fuel injection pressures of the first fuel injection and the second fuel injection. Therefore, the premixing time of the fuel and the air becomes long, and the premixing shortage is prevented. Thereby, the increase in smoke can be suppressed.

  The correction means reduces the fuel injection quantity of the second fuel injection when the engine load detected by the load detection means is higher than a second predetermined value that is larger than the first predetermined value. You may further have a weight reduction means.

  Thus, when the engine load is higher than the second predetermined value that is larger than the first predetermined value, the fuel injection pressure of the second fuel injection is reduced by decreasing the fuel injection amount of the second fuel injection. As in the case of lowering, since ignition due to the second fuel injection is less likely to occur, the premixing time of the fuel and air is lengthened, and insufficient premixing is prevented. Thereby, the increase in smoke can be suppressed.

  According to the present invention, appropriate premixed compression ignition combustion can be realized even if the intake pressure into the combustion chamber decreases. Thereby, it is possible to suppress an increase in combustion noise and a deterioration in emissions.

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 graph which compares and shows an example of the heat release rate waveform in the condition where an engine load is in a low load region under various conditions. It is a graph which compares and shows an example of the level of combustion noise in the situation where an engine load is in a low load region, and the exhaust concentration of HC and CO under various conditions. It is a graph which compares and shows an example of the heat release rate waveform in the condition where an engine load is in a middle load region under various conditions. It is a graph which compares and shows an example of the generation amount of NOx and the level of a combustion noise in the condition where an engine load is in a middle load region. It is a graph which compares and shows an example of the heat release rate waveform in the condition where the engine load is in a high load region under various conditions. It is a graph which compares and shows an example of the premixing time by the incidence rate of smoke in the situation where an engine load is in a high load region, and the second fuel injection under various conditions. An image of the combustion waveform when only the fuel injection timing of the first fuel injection is advanced is an image of the combustion waveform when the fuel injection timing of the first fuel injection and the second fuel injection is advanced It is a graph shown in comparison.

  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 that performs premixed compression ignition (PCCI) combustion, and includes 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. The common rail 6 is connected to a high pressure pump 8 through a fuel supply pipe 7. The common rail 6 stores the high-pressure fuel supplied from the high-pressure pump 8 and supplies it uniformly to the injectors 5. The fuel supply pipe 7 is provided with a rail pressure adjusting valve 9 for adjusting the fuel pressure (common rail pressure) in the common rail 6.

  An intake passage 10 for sucking air into the combustion chamber 4 is connected to the engine body 2 via an intake manifold 11. Further, an exhaust passage 12 for exhausting exhaust gas after combustion is connected to the engine body 2 via an exhaust manifold 13.

  In the intake passage 10, an air cleaner 14, a compressor 16 of the turbocharger 15, an intercooler 17, and a throttle valve 18 are provided from the upstream side toward the downstream side. The throttle valve 18 restricts the passage area of the intake passage 10 and generates negative pressure downstream, thereby enabling exhaust gas recirculation (EGR), which will be described later. In the exhaust passage 12, a turbine 19 of the turbocharger 15 and a DPF 20 with a catalyst are provided.

  The diesel engine 1 also includes an exhaust gas recirculation (EGR) device 21 that recirculates a part of the exhaust gas after combustion into the combustion chamber 4 as exhaust gas recirculation gas (EGR gas). The EGR device 21 is provided so as to connect the intake passage 10 and the exhaust manifold 13, and an EGR passage 22 for recirculating the EGR gas, and an EGR that adjusts the recirculation amount of the EGR gas from the exhaust manifold 13 to the intake passage 10. A valve (valve means) 23, an EGR cooler 24 for cooling EGR gas passing through the EGR passage 22, a bypass passage 25 connected to the EGR passage 22 so as to bypass the EGR cooler 24, and an EGR gas passage And a switching valve 26 for switching to the EGR cooler 24 side or the bypass passage 25 side.

  Each injector 5, rail pressure adjusting valve 9, throttle valve 18, EGR valve 23 and switching valve 26 are controlled by an electronic control unit (ECU) 27. A crank angle sensor 28, an accelerator opening sensor 29, and an intake pressure sensor 30 are connected to the ECU 27.

  The crank angle sensor 28 is a sensor that enables calculation of the rotational speed (engine rotational speed) of the engine body 2 by detecting the rotational angle (crank angle) of a crankshaft to which a piston (not shown) is coupled. The accelerator opening sensor 29 is a sensor (load detection means) that detects the depression angle (accelerator opening) of the accelerator pedal as an alternative value for 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 intake pressure sensor 30 is a sensor (intake pressure detection means) for detecting the pressure of air sucked into the combustion chamber 4 (intake pressure detection means), for example, at the downstream end of the intake passage 10. It is attached.

  The ECU 24 receives detection signals from the crank angle sensor 28, the accelerator opening sensor 29, and the intake pressure sensor 30, performs predetermined processing, and performs the injector 5, the rail pressure adjustment valve 9, the throttle valve 18, the EGR valve 23, and the switching valve. 26 is controlled.

  Here, the injector 5, common rail 6, fuel supply pipe 7, high-pressure pump 8, rail pressure adjustment valve 9, intake passage 10, exhaust passage 12, throttle valve 18, exhaust recirculation device 21, ECU 27 and sensors 28 to 30 are The combustion control device 31 of the present embodiment is configured. Such a combustion control device 31 draws air into the combustion chamber 4 and divides the fuel from each injector 5 into the combustion chamber 4 in a plurality of times in one cycle of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. To perform premixed compression ignition combustion.

  FIG. 2 is a flowchart showing a processing procedure executed by the ECU 27. This process is a process of controlling the injector 5, the rail pressure adjusting valve 9, and the EGR valve 23 based on the detection signals of the sensors 28-30.

  In the figure, firstly, based on the engine speed detected by the crank angle sensor 28 and the accelerator opening (engine load) detected by the accelerator opening sensor 29, the first fuel injection and thereafter 2 are carried out. The fuel injection amount and fuel injection timing for the second fuel injection are determined (step S101).

  Subsequently, it is determined whether or not the intake pressure detected by the intake pressure sensor 30 is lower than a reference pressure (for example, atmospheric pressure) (step S102). When it is determined that the intake pressure is lower than the reference pressure, it is determined whether or not the engine load detected by the accelerator opening sensor 29 is lower than the low load side threshold (step S103). The low load side threshold is, for example, an opening of 30% with respect to the accelerator fully open.

  When it is determined that the engine load is lower than the low load side threshold, the air-fuel ratio (A / F) in the combustion chamber 4 at that time is leaned (increased) with respect to the air-fuel ratio set at the reference pressure. ), The EGR valve 23 is controlled (step S104). Specifically, the EGR valve 23 is controlled so as to increase the intake air amount into the combustion chamber 4 by decreasing the recirculation amount of the EGR gas to the intake passage 10. When the air-fuel ratio is made lean, the intake air amount into the combustion chamber 4 is increased without changing the fuel injection amount into the combustion chamber 4. At this time, for example, the amount of lean air-fuel ratio is increased as the intake pressure and engine load are lowered.

  By making the air-fuel ratio lean in this way, the amount of intake air into the combustion chamber 4 increases, so that when the fuel is injected into the combustion chamber 4 by the injector 5, the premixed air and fuel are mixed. The ignition timing of will advance.

  On the other hand, when it is determined that the engine load is not lower than the low load side threshold, the EGR valve 23 is controlled so that the air-fuel ratio in the combustion chamber 4 at that time is maintained at the air-fuel ratio set at the reference pressure. (Step S105). Specifically, when the intake pressure into the combustion chamber 4 decreases, the amount of intake air into the combustion chamber 4 decreases, so the amount of intake air into the combustion chamber 4 is increased accordingly, that is, the intake passage. The EGR valve 23 is controlled so as to reduce the recirculation amount of the EGR gas to 10.

  Subsequently, the fuel injection timings of the first fuel injection and the second fuel injection determined in step S101 are advanced (step S106). At this time, the advance amount of the fuel injection timing may be, for example, an amount corresponding to the intake pressure and the engine load, or may be a predetermined constant amount.

  By advancing the fuel injection timing of the fuel injection in this way, when the fuel is injected into the combustion chamber 4 by the injector 5, the ignition timing of the premixed air / fuel mixture is advanced. .

  Subsequently, it is determined whether or not the engine load detected by the accelerator opening sensor 29 is higher than a high load side threshold (step S107). The high load side threshold value is larger than the above low load side threshold value, and is, for example, an opening degree of 60% with respect to the accelerator fully open.

  When it is determined that the engine load is higher than the high load side threshold value, the rail pressure adjusting valve 9 is controlled so as to lower the common rail pressure from a preset value (step S108). Thereby, the fuel injection pressure from the injector 5 falls. At this time, the amount of decrease in the common rail pressure may be, for example, an amount corresponding to the intake pressure and the engine load, or may be a predetermined constant amount.

  Subsequently, the fuel injection amount of the second fuel injection determined in step S101 is decreased, and the fuel injection amount of the first fuel injection determined in step S101 is increased by an amount corresponding to the decrease in the fuel injection amount. (Procedure S109). At this time, the amount of decrease in the fuel injection amount may be, for example, an amount corresponding to the intake pressure and the engine load, or may be a predetermined constant amount.

  When it is determined at step S102 that the intake pressure is not lower than the reference pressure, when step S104 is executed, when it is determined at step S107 that the engine load is not higher than the high load side threshold value, step S109 is executed. At this time, each injector 5 is controlled so that the first fuel injection and the second fuel injection are sequentially performed (step S110).

  At this time, when it is determined in step S102 that the intake pressure is not lower than the reference pressure, when step S104 is executed, the first fuel injection and the fuel injection timing and the fuel injection timing determined in step S101 are performed. The second fuel injection is performed sequentially. When it is determined in step S107 that the engine load is not higher than the high load side threshold, the first and second fuel injections are performed according to the fuel injection amount determined in step S101 and the fuel injection timing corrected in step S106. The fuel injection is performed sequentially. When step S109 is executed, the first fuel injection and the second fuel injection are sequentially performed according to the fuel injection amount corrected in step S109 and the fuel injection timing determined in step S101.

  In the above, the procedure S101 constitutes a determination unit that determines the fuel injection amount and the fuel injection timing. The procedure S110 constitutes an injection control means for controlling the fuel injection valve 5 so as to perform fuel injection according to the fuel injection amount and the fuel injection timing. The steps S102 to S109 constitute correction means for correcting the ignition timing by fuel injection to advance when the intake pressure detected by the intake pressure detection means 30 is lower than a predetermined pressure.

  At this time, the steps S102 to S105 constitute air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber 4. Step S106 constitutes an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. The above steps S107 and S108 are performed when the engine load detected by the load detecting means 29 is higher than a second predetermined value that is larger than the first predetermined value. An injection pressure control means for controlling to reduce the fuel injection pressure is configured. The above steps S107 and S109 reduce the fuel injection amount of the second fuel injection when the engine load detected by the load detecting means 29 is higher than a second predetermined value larger than the first predetermined value. An injection amount reducing means is configured.

  By the way, when the intake pressure into the combustion chamber 4 decreases due to a change in atmospheric pressure or the like, the amount of air sucked into the combustion chamber 4 decreases, so when the fuel is injected into the combustion chamber 4 by the injector 5, Since the oxidation reaction between fuel and air is delayed, the heat generation rate waveform (combustion waveform) at that time deviates from the heat generation rate waveform obtained at the reference pressure, and the premixed compression ignition combustion similar to that at the reference pressure is realized. It becomes difficult. In this case, combustion noise increases, and unburned HC and CO are likely to be generated due to deterioration of combustion.

  On the other hand, in the present embodiment, when the intake pressure into the combustion chamber 4 is lower than the reference pressure, the combustion chamber 4 is in a state where the engine load is in the middle load region from the low load side threshold value to the high load side threshold value. The fuel injection timing of the first fuel injection and the second fuel injection is advanced while maintaining the air-fuel ratio set at the reference pressure so as to secure the intake air amount into the fuel. The ignition timing of the premixed mixture of air and air almost coincides with the reference pressure. For this reason, the heat generation rate waveform comes closer to the heat generation rate waveform obtained at the reference pressure. Accordingly, since the premixed gas is appropriately burned, an increase in combustion noise and an increase in unburned HC and CO can be suppressed. Further, NOx can be reduced as compared with the case where the air-fuel ratio in the combustion chamber 4 is made lean.

  When the intake pressure into the combustion chamber 4 is lower than the reference pressure, the intake air amount into the combustion chamber 4 is ensured in a situation where the engine load is in a high load region higher than the high load side threshold. In addition to advancing the fuel injection timing of the first fuel injection and the second fuel injection while maintaining the air-fuel ratio set at the reference pressure, the fuel injection from the injector 5 is reduced by reducing the common rail pressure. While reducing the pressure, the fuel injection amount of the second fuel injection is reduced. As a result, the heat generation rate waveform approaches the heat generation rate waveform obtained at the reference pressure as described above.

  Further, when the intake pressure into the combustion chamber 4 becomes low, the ignition in the first fuel injection is delayed, so that the temperature in the combustion chamber 4 (cylinder temperature) increases when the second fuel injection is performed. For this reason, especially in a situation where the engine load is in a high load region, the ignition quality of the premixed mixture of fuel and air is improved, so that the ignition delay due to the second fuel injection is easily shortened. However, as described above, since the fuel injection pressure from the injector 5 is reduced and the fuel injection amount of the second fuel injection is reduced, the ignition delay due to the second fuel injection can be suppressed. Accordingly, the premixing time by the second fuel injection becomes longer, and insufficient premixing of fuel and air is prevented, so that an increase in smoke can be suppressed.

  In a situation where the engine load is in a low load region, the ignitability of the premixed mixture of fuel and air deteriorates. Therefore, when the intake pressure into the combustion chamber 4 decreases, the pressure in the combustion chamber 4 (cylinder pressure) Thus, the first fuel injection is performed at an early stage where the value is low. Under the circumstances, the fuel of the first fuel injection and the second fuel injection is maintained while maintaining the air-fuel ratio set at the reference pressure so as to ensure the intake air amount into the combustion chamber 4 as described above. When the injection timing is advanced, the first fuel injection is performed at a stage where the in-cylinder pressure is further lowered. In this case, since the fuel spray reach distance is extended and the amount of spray adhering to the wall surface of the combustion chamber 4 is increased, the effect of suppressing the increase in HC and CO may be reduced.

  Therefore, when the intake pressure into the combustion chamber 4 is lower than the reference pressure, the air-fuel ratio in the combustion chamber 4 is set at the reference pressure in a situation where the engine load is in a low load region lower than the low load side threshold. By making the air-fuel ratio lean, the amount of air sucked into the combustion chamber 4 becomes sufficiently large, so that the fuel and air can be mixed without advancing the fuel injection timing of the first fuel injection. The ignition timing of the premixed gas becomes earlier. For this reason, similarly to the above, since the ignition timing of the premixed gas substantially coincides with that at the reference pressure, the heat generation rate waveform approaches the heat generation rate waveform obtained at the reference pressure. Accordingly, since the premixed gas is appropriately burned, an increase in combustion noise and an increase in unburned HC and CO can be suppressed.

  FIG. 3 shows an example of a heat release rate waveform in a situation where the engine load is in a low load region, compared with various conditions. The broken line P represents the heat generation rate waveform when the intake pressure is the reference pressure, the thin solid line Q represents the heat generation rate waveform when the intake pressure is 20 kPa lower than the reference pressure, and the thick solid line R represents the absorption rate. It shows a heat release rate waveform when the air-fuel ratio is leaned with respect to the reference pressure when the atmospheric pressure is lower by 20 kPa than the reference pressure.

  As can be seen from FIG. 3, when the intake pressure is lower than the reference pressure by 20 kPa, the heat release rate waveform is greatly deviated from that at the reference pressure due to the ignition delay (see broken line P and thin solid line Q). However, when the intake pressure is lower than the reference pressure by 20 kPa, the air-fuel ratio is made lean relative to the reference pressure, so that the heat generation rate waveform approaches that at the reference pressure (broken lines P and (See thick solid line R).

  FIG. 4 shows an example of the combustion noise level and the HC and CO emission concentrations in a situation where the engine load is in a low load region, under the same conditions as in FIG. As can be seen from FIG. 4, even when the intake pressure is lower than the reference pressure by 20 kPa, the air-fuel ratio is made lean with respect to the reference pressure, so that the combustion noise level and the HC and CO generation rates are at the reference pressure. Compared with almost no change. In particular, the exhaust concentrations of HC and CO are sufficiently lower than when the air-fuel ratio is not made lean when the intake pressure is lower than the reference pressure by 20 kPa.

  FIG. 5 shows an example of the heat generation rate waveform in a situation where the engine load is in the middle load region, compared under various conditions. The broken line P represents the heat generation rate waveform when the intake pressure is the reference pressure, the alternate long and short dash line Q represents the heat generation rate waveform when the intake pressure is lower by 20 kPa than the reference pressure, and the thin solid line R is When the intake pressure is lower than the reference pressure by 20 kPa, the heat generation rate waveform when the air-fuel ratio is leaned with respect to the reference pressure is shown. A thick solid line S indicates when the intake pressure is lower by 20 kPa than the reference pressure. The heat release rate waveform when the fuel injection timing of the first fuel injection and the second fuel injection is advanced is shown.

  As can be seen from FIG. 5, when the intake pressure is lower than the reference pressure by 20 kPa, the heat release rate waveform is greatly deviated from the reference pressure due to the ignition delay (see the broken line P and the one-dot chain line Q). However, when the intake pressure is lower than the reference pressure by 20 kPa, the heat generation rate waveform by the first fuel injection is obtained by making the air-fuel ratio leaner than the reference pressure or by advancing the fuel injection timing. It comes close to that at the time of the reference pressure (see broken line P, thin solid line R, and thick solid line S).

  FIG. 6 shows an example of the amount of NOx generated and the level of combustion noise in a situation where the engine load is in the middle load region under the same conditions as in FIG. As can be seen from FIG. 6, even if the intake pressure is lower than the reference pressure by 20 kPa, the combustion noise level is hardly changed by advancing the fuel injection timing as compared with the reference pressure. Further, when the fuel injection timing is advanced when the intake pressure is lower than the reference pressure by 20 kPa, the amount of NOx generated is sufficiently smaller than when the air-fuel ratio is made lean relative to the reference pressure. It has become.

  FIG. 7 shows an example of a heat release rate waveform in a situation where the engine load is in a high load region and compared under various conditions. The broken line P represents the heat generation rate waveform when the intake pressure is the reference pressure, the one-dot chain line Q represents the heat generation rate waveform when the intake pressure is lower by 30 kPa than the reference pressure, and the thin solid line R is When the intake pressure is lower than the reference pressure by 30 kPa, the heat generation rate waveform when the fuel injection timing of the first fuel injection and the second fuel injection is advanced is shown. The thick solid line S indicates the intake pressure is the reference When the fuel injection timing of the first fuel injection and the second fuel injection is advanced and the common rail pressure is lowered and the fuel injection amount of the second fuel injection is reduced when the pressure is lower by 30 kPa than the pressure Represents the heat release rate waveform.

  As can be seen from FIG. 7, when the intake pressure is lower than the reference pressure by 30 kPa, the heat release rate waveform is greatly deviated from the reference pressure due to the ignition delay (see the broken line P and the one-dot chain line Q). However, when the intake pressure becomes 30 kPa lower than the reference pressure, the fuel injection timing is advanced so that the heat generation rate waveform by the first fuel injection approaches that at the reference pressure (dashed line). P, thin solid line R and thick solid line S).

  FIG. 8 shows an example of the smoke generation rate in the situation where the engine load is in a high load region and an example of the premix time for the second fuel injection under the same conditions as in FIG. As can be seen from FIG. 8, even when the intake pressure is lower than the reference pressure by 30 kPa, the fuel injection timing is advanced, the common rail pressure is reduced, and the fuel injection amount of the second fuel injection is reduced. Therefore, the smoke generation rate hardly changes compared with the reference pressure. In addition, when the common rail pressure is reduced and the fuel injection amount of the second fuel injection is reduced, the premixing time by the second fuel injection becomes longer than when these processes are not performed. The incidence of smoke is low.

  As described above, according to the present embodiment, even if the intake pressure into the combustion chamber 4 becomes lower than the reference pressure, the combustion waveform by the first fuel injection is the one at the reference pressure regardless of the engine load. Since it comes closer, premixed compression ignition combustion similar to that at the reference pressure can be realized. As a result, it is possible to suppress an increase in combustion noise and a deterioration in emissions.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, when the engine load is higher than the low load side threshold, the fuel injection timing of the first fuel injection and the second fuel injection is advanced, but the fuel of the second fuel injection Instead of advancing the injection timing, only the fuel injection timing of the first fuel injection may be advanced. The combustion waveform in this case is as shown by the solid line X in FIG. A broken line Y in FIG. 9 shows a waveform when the fuel injection timing of the second fuel injection is advanced. As a result, the heat release rate waveforms due to the first fuel injection and the second fuel injection become closer to those at the reference pressure, and the timbre change when the intake pressure changes is reduced.

  Further, in the above embodiment, when the engine load is higher than the high load side threshold, the common rail pressure is reduced and the fuel injection amount of the second fuel injection is decreased. Only one of the decrease in the common rail pressure and the decrease in the fuel injection amount of the second fuel injection may be performed.

  In the above embodiment, when the engine load is higher than the high load side threshold, the advance amount of the fuel injection timing of the first fuel injection is not changed when the common rail pressure is reduced. However, the present invention is not limited thereto, and when the common rail pressure is reduced, the fuel injection timing of the first fuel injection may be further advanced. Thereby, the heat generation rate waveform can be made closer to the heat generation rate waveform obtained at the reference pressure. In this case, when the amount of decrease in the common rail pressure is variable, the advance amount of the fuel injection timing of the first fuel injection may be an amount corresponding to the amount of decrease in the common rail pressure.

  Furthermore, 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 23. However, the air-fuel ratio control method is not particularly limited, for example, You may make it raise the supercharging pressure of a turbocharger.

  In the above-described embodiment, the main fuel injection is controlled to be performed by dividing the fuel injection into the first fuel injection and the second fuel injection. However, the present invention is not limited to this, and the main fuel injection is performed only once. You may carry out. In this case, when the engine load is lower than the low load threshold, the air-fuel ratio is controlled to be leaner than that at the reference pressure, and when the engine load is higher than the low load threshold, the air-fuel ratio at the reference pressure is set. The main fuel injection timing is advanced while maintaining it.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 10 ... Intake passage, 12 ... Exhaust passage, 22 ... EGR passage (exhaust recirculation passage), 23 ... EGR valve (valve means), 27 ... ECU (determination means, injection control means, correction means, air-fuel ratio control means, injection timing advance means, injection pressure control means, injection amount reduction means), 29 ... accelerator opening sensor (load detection means), 30 ... suction Barometric pressure sensor (intake pressure detecting means), 31... Combustion control device.

At this time, preferably, the correction means includes an air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber, and an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. And the injection timing advance means advances the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means is lower than a predetermined pressure, and the air-fuel ratio control means When the intake pressure detected by the atmospheric pressure detection means is lower than a predetermined pressure, control is performed so that the air-fuel ratio in the combustion chamber is maintained at the air-fuel ratio set at the predetermined pressure.

Preferably, the correction unit is configured to perform the first fuel injection and the second fuel injection when the engine load detected by the load detection unit is higher than a second predetermined value which is larger than the first predetermined value. further have the injection pressure control means for controlling to reduce the fuel injection pressure.

When the intake pressure into the combustion chamber of the engine becomes low, ignition by the first fuel injection is delayed, so the temperature in the combustion chamber rises at the time of performing the second fuel injection thereafter, and the ignition delay by the second fuel injection is delayed. This shortens the premixing time of fuel and air. In particular, when the engine load is increased, the ignitability is improved, so that such a problem appears remarkably. Therefore, when the engine load is higher than the second predetermined value that is larger than the first predetermined value, the second fuel injection is reduced by reducing the fuel injection pressures of the first fuel injection and the second fuel injection. Therefore, the premixing time of the fuel and the air becomes long, and the premixing shortage is prevented. Thereby, the increase in smoke can be suppressed.

Further, the correction means reduces the fuel injection amount of the second fuel injection when the engine load detected by the load detection means is higher than a second predetermined value that is larger than the first predetermined value. You may further have a weight reduction means.

Thus, when the engine load is higher than the second predetermined value that is larger than the first predetermined value, the fuel injection pressure of the second fuel injection is reduced by decreasing the fuel injection amount of the second fuel injection. As in the case of lowering, since ignition due to the second fuel injection is less likely to occur, the premixing time of the fuel and air is lengthened, and insufficient premixing is prevented. Thereby, the increase in smoke can be suppressed.

Preferably, the exhaust passage and the intake passage are connected to each other, and an exhaust gas recirculation passage for returning a part of the exhaust gas after combustion as an exhaust gas recirculation gas into the combustion chamber and an exhaust gas recirculation passage are provided. And a valve means for adjusting the recirculation amount of the exhaust gas recirculation gas. The air-fuel ratio control means controls the valve means so that the recirculation amount of the exhaust gas recirculation gas decreases, thereby Control the fuel ratio.

Thus, by using the valve means for adjusting the recirculation amount of the exhaust gas recirculation gas, the air-fuel ratio in the combustion chamber can be reliably maintained at the air-fuel ratio set at a predetermined pressure with a simple configuration .

The present invention relates to a combustion control apparatus for an engine that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into a combustion chamber of the engine, a fuel for a first fuel injection and a second fuel injection that is performed thereafter. Determination means for determining the injection amount and the fuel injection timing, and injection control means for controlling the fuel injection valve so as to sequentially perform the first fuel injection and the second fuel injection according to the fuel injection amount and the fuel injection timing An intake passage for sucking air into the combustion chamber, an exhaust passage for discharging exhaust gas after combustion from the combustion chamber, an intake pressure detection means for detecting the intake pressure into the combustion chamber, and an intake pressure detection Correction means for correcting the ignition timing by the first fuel injection to advance when the intake pressure detected by the means is lower than a predetermined pressure , and the correction means controls the air-fuel ratio in the combustion chamber. Air-fuel ratio control And an injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means, and the air-fuel ratio control means has a predetermined intake pressure detected by the intake pressure detection means. When the pressure is lower than the pressure, the air-fuel ratio in the combustion chamber is controlled to be maintained at the air-fuel ratio set at a predetermined pressure .

Further, since the ignition timing of the first fuel injection is advanced by advancing the fuel injection timing of the first fuel injection, the ignition timing of the first fuel injection is obtained at an ignition timing obtained at a predetermined pressure. It will come closer. Further, by controlling the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio set at a predetermined pressure, the combustion waveform can be brought close to the combustion waveform obtained at the predetermined pressure. Therefore, since the combustion of the premixed mixture of fuel and air is appropriately performed, an increase in unburned HC and CO can be suppressed.

Claims (8)

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;
Determining means for determining the fuel injection amount and fuel injection timing;
Injection control means for controlling the fuel injection valve so as to perform fuel injection according to the fuel injection amount and the fuel injection timing;
An intake passage for sucking air into the combustion chamber;
An exhaust passage for exhausting exhaust gas after combustion from the combustion chamber;
Intake pressure detection means for detecting intake pressure into the combustion chamber;
A combustion control apparatus, comprising: a correction unit that corrects the ignition timing by the fuel injection to advance when the intake pressure detected by the intake pressure detection unit is lower than a predetermined pressure. The determining means determines the fuel injection amount and fuel injection timing of the first fuel injection and the second fuel injection performed thereafter,
The injection control means controls the fuel injection valve so as to sequentially perform the first fuel injection and the second fuel injection according to the fuel injection amount and the fuel injection timing;
The correction means corrects the ignition timing by the first fuel injection to advance when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure. Item 4. The combustion control device according to Item 1. The correction means includes air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber, and injection timing advance means for advancing the fuel injection timing of the first fuel injection determined by the determination means. ,
The air-fuel ratio control means maintains the air-fuel ratio in the combustion chamber at the air-fuel ratio set at the predetermined pressure when the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure. The combustion control device according to claim 2, wherein the combustion control device is controlled. A load detecting means for detecting the load of the engine;
The injection timing advance means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the engine load detected by the load detection means is lower than a first predetermined value. When high, advance the fuel injection timing of the first fuel injection,
The air-fuel ratio control means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the engine load detected by the load detection means is lower than the first predetermined value. 4. The combustion control apparatus according to claim 3, wherein when the fuel pressure is high, control is performed so that the air-fuel ratio in the combustion chamber is maintained at the air-fuel ratio set at the predetermined pressure.   The air-fuel ratio control means is configured such that the intake pressure detected by the intake pressure detection means is lower than the predetermined pressure, and the engine load detected by the load detection means is lower than the first predetermined value. 5. The combustion control device according to claim 4, wherein when the temperature is low, the air-fuel ratio in the combustion chamber is controlled to be lean with respect to the air-fuel ratio set at the predetermined pressure. An exhaust gas recirculation passage provided so as to connect the exhaust passage and the intake passage, and for returning a part of the exhaust gas after combustion as exhaust gas recirculation gas into the combustion chamber;
Valve means for adjusting a recirculation amount of the exhaust gas recirculation gas provided in the exhaust gas recirculation passage;
The air-fuel ratio control means controls the air-fuel ratio in the combustion chamber by controlling the valve means so that the recirculation amount of the exhaust gas recirculation gas decreases. A combustion control device according to claim 1.   The correction means includes the first fuel injection and the second fuel when the engine load detected by the load detection means is higher than a second predetermined value that is larger than the first predetermined value. The combustion control device according to any one of claims 4 to 6, further comprising injection pressure control means for controlling the fuel injection pressure of the injection to be lowered.   The correction means reduces the fuel injection amount of the second fuel injection when the engine load detected by the load detection means is higher than a second predetermined value that is larger than the first predetermined value. The combustion control device according to any one of claims 4 to 6, further comprising injection amount reduction means for performing the injection amount reduction.

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