JP2012197674A - Combustion control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control device capable of suppressing the increase of unburnt HC at a low water temperature and the change of the tone of combustion noise when an engine is operated at a very low load.SOLUTION: The combustion control device is provided with an ECU having an injector control part. The injector control part decides first fuel injection timing for first main fuel injection timing and second fuel injection timing for second main fuel injection executed after the first main fuel injection, and when the water temperature of the engine is lower than the upper side reference temperature, decides fuel injection timing of pre-fuel combustion injection to be executed before the first main fuel injection. The injector control part advances each of the fuel injection timing of the pre fuel injection and the main fuel injection timing of the first main fuel when the load of the engine is lower than the predetermined value and the water temperature of the engine is lower than the lower side reference temperature. The injector control part controls the injector to sequentially execute the pre fuel injection, the first main fuel injection and the second main fuel injection.

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. When the engine fuel injection device described in Patent Document 1 is operated at a low load, the first and second fuel injections are performed at a timing at which premix combustion is possible. The fuel injection amount in this fuel injection is 60% of the total injection amount in the first fuel injection and 40% of the total injection amount in the second fuel injection. By such fuel injection, the heat generation rate forms two peaks on the graph, and the generation of CO and smoke is suppressed.

JP 2009-264332 A

  However, if the premixed compression ignition combustion as in the prior art is applied to an extremely low load where the engine operating state is close to, for example, an idling state, the total fuel injection amount, particularly the first fuel injection amount is reduced. The combustion by the first fuel injection is weakened. For this reason, at the time of low water temperature, the ignition timing by the first fuel injection is delayed, and the heat generation rate becomes one peak on the graph, which greatly differs from the combustion waveform in the warm-up state. This not only makes it difficult to sufficiently suppress the increase in unburned HC, but the tone of the combustion sound may be extremely different from that in the warm-up state.

  An object of the present invention is to provide a combustion control device capable of suppressing an increase in unburned HC and a change in timbre of combustion noise at a low water temperature when the engine is operating at an extremely low load. .

  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 water temperature detection means that detects a water temperature of the engine, and a load that detects a load of the engine. A first injection timing determining means for determining a fuel injection timing of the first fuel injection and a fuel injection timing of the second fuel injection performed after the first fuel injection; A load determination means for comparing and determining the load with a first predetermined value and a second predetermined value less than or equal to the first predetermined value, and when the load determination means determines that the engine load is lower than the first predetermined value In addition, the second fuel injection timing determining means for determining the fuel injection timing of the third fuel injection performed before the first fuel injection, and the load determination means cause the engine load to exceed the second predetermined value. When it is determined to be low, Injection timing advance means for advancing the fuel injection timing of the third fuel injection and the fuel injection timing of the first fuel injection in accordance with the water temperature of the engine, and the fuel injection timing and the first fuel injection timing of the first fuel injection First control means for controlling the fuel injection valve so as to sequentially perform the first fuel spray and the second fuel injection according to the fuel injection timing of the second fuel injection, and the fuel of the third fuel injection And a second control unit for controlling the fuel injection valve so as to perform the third fuel spray before the first fuel spray according to the injection timing.

  As described above, in the combustion control apparatus of the present invention, the third fuel injection is first performed, and then the first fuel injection and the second fuel injection are sequentially performed. The ignition timing is advanced by preheating by the third fuel injection, and the heat generation rate waveform (combustion waveform) comes closer to the warm-up state. However, the present inventors have found the fact that when the engine operating state is an extremely low load, the combustion waveform at the low water temperature may be significantly different from the combustion waveform at the warm air state. Therefore, the present inventors have conducted further intensive studies, and paid attention to the advance angles of the fuel injection timing of the third fuel injection and the fuel injection timing of the first fuel injection, and have completed the present invention.

  That is, when it is determined that the engine load is lower than the second predetermined value, the fuel injection timing of the third fuel injection and the fuel injection timing of the first fuel injection are advanced, respectively. The ignition timing due to the fuel injection of 1 is further advanced. However, since the fuel injection timing of the second fuel spray is not changed, a two-peaked combustion waveform is maintained. Therefore, when the engine is operating at an extremely low load, even when the water temperature is low, a combustion waveform that is almost the same as that in the warm air state can be obtained, so that combustion due to fuel spray is stabilized. As a result, an increase in unburned HC is sufficiently suppressed and a timbre change in combustion noise is prevented.

  Preferably, the apparatus further comprises water temperature determining means for determining whether or not the water temperature of the engine is lower than the first predetermined temperature, and the second injection timing determining means is configured such that the water temperature of the engine is lower than the first predetermined temperature by the water temperature determining means. Is determined to be low, the fuel injection timing of the third fuel injection is determined, and the second control means determines that the water temperature of the engine is lower than the first predetermined temperature by the water temperature determination means. In addition, the fuel injection valve is controlled to implement the third fuel spray.

  In this case, the third fuel injection is performed when the engine water temperature is lower than the first predetermined temperature, and the third fuel injection is performed when the engine water temperature is higher than the first predetermined temperature. Since this is not performed, it is possible to prevent unnecessary fuel injection in a warm air state, for example.

  In this case, it is preferable that the injection timing advance means is a second engine in which the engine water temperature is lower than the first predetermined temperature when the load determination means determines that the engine load is lower than the second predetermined value. If the engine water temperature is determined to be lower than the second predetermined temperature, the fuel injection timing of the third fuel injection and the fuel injection timing of the first fuel injection are determined. Each is advanced.

  When the engine operating state is an extremely low load, the combustion waveform in the warm-up state becomes significantly different as the engine water temperature decreases. Accordingly, when the water temperature of the engine is lower than the second predetermined temperature which is lower than the first predetermined temperature, the fuel injection timing of the third fuel injection and the fuel injection timing of the first fuel spray are respectively advanced. Is effective.

  According to the present invention, when the operating state of the engine is an extremely low load, it is possible to suppress an increase in unburned HC and a change in timbre of combustion noise at a low water temperature. Thereby, it is possible to realize excellent premixed compression ignition combustion.

It is a schematic block diagram which shows the diesel engine provided with one Embodiment of the combustion control apparatus concerning this invention. It is a block diagram which shows the structure of the combustion control apparatus shown in FIG. It is a flowchart which shows the detail of the injector control processing procedure performed by the injector control part shown in FIG. It is a figure which shows the fuel-injection quantity and fuel-injection timing of the pre fuel injection, the 1st main fuel injection, and the 2nd main fuel injection in the time of a warm air state, the state where water temperature is low, and the state where water temperature is still lower. It is a graph which shows an example of the heat release rate waveform at the time of not having advanced the fuel injection timing of pre fuel injection and the 1st main fuel injection at the time of low water temperature when it is a warm air state, and when it advanced.

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

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

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

  An intake passage 7 for sucking air into the combustion chamber 4 is connected to the engine body 2 via an intake manifold 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 is a valve that adjusts the amount of air sucked into the combustion chamber 4. In the exhaust passage 9, a turbine 16 of the turbocharger 12 and a DPF 17 with a catalyst are provided.

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

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

  Here, the engine water temperature is directly detected by the water temperature sensor 28, but the present invention is not limited to this. For example, the engine water temperature is indirectly detected such as the cylinder block temperature outside the water jacket and the cylinder head temperature outside the water jacket. Sensors that detect what is shown may be used.

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

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

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

  The injector control unit 31 determines the number of fuel injections, the fuel injection amount, and the fuel injection timing based on the engine load calculated by the engine load calculation unit 30 and the engine water temperature detected by the water temperature sensor 28, and sets each injector 5. Control.

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

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

  Subsequently, it is determined whether or not the engine water temperature detected by the water temperature sensor 28 is lower than the upper reference temperature (for example, 80 ° C.) and the engine load calculated by the engine load calculation unit 30 is lower than the upper reference value ( Step S102).

  When the procedure S102 is not satisfied, the injector 5 is controlled so that the first main fuel injection is performed according to the fuel injection amount and the fuel injection timing set in the procedure S101 (procedure S108). Subsequently, the injector 5 is controlled so as to perform the second main fuel injection in accordance with the fuel injection amount and fuel injection timing set in step S101 (step S109).

  When the above-described procedure S102 is satisfied, that is, when it is determined that the engine water temperature is lower than the upper reference temperature and the engine load is lower than the upper reference value, based on the engine load and the engine water temperature, FIG. As shown in FIG. 5, the fuel injection amount and fuel injection timing of the pre-fuel injection (third fuel injection) performed before the first main fuel injection are determined (step S103).

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

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

  Subsequently, it is determined whether or not the engine load is lower than the lower reference value (step S104). The lower reference value is a value lower than the above upper reference value, for example, a value at which the engine torque is 5N. When it is determined that the engine load is lower than the lower reference value, it is subsequently determined whether the engine water temperature is lower than a lower reference temperature (for example, 40 ° C.) lower than the upper reference temperature (step S105).

  When it is determined that the engine water temperature is lower than the lower reference temperature, as shown in FIG. 4C, the fuel injection timing of the pre-fuel injection set in step S103 and the first time set in step S101 The fuel injection timing of the main fuel injection is advanced by the same amount (step S106). At this time, it is preferable to advance the fuel injection timing of each fuel injection by an ignition delay (for example, several degrees Celsius A to several tens of degrees Celsius A) due to the low engine water temperature. The fuel injection timing of the second main fuel injection is not advanced.

  Subsequently, the injector 5 is controlled so as to perform the pre-fuel injection according to the fuel injection amount set in step S103 and the fuel injection timing advanced in step S106 (step S107). Subsequently, the injector 5 is controlled to perform the first main fuel injection according to the fuel injection amount set in step S101 and the fuel injection timing advanced in step S106 (step S108). Subsequently, the injector 5 is controlled so as to perform the second main fuel injection in accordance with the fuel injection amount and fuel injection timing set in step S101 (step S109).

  If it is determined in step S104 that the engine load is not lower than the lower reference value, or if it is determined in step S105 that the engine water temperature is not lower than the lower reference value, step S106 is not executed and step S103 is performed. The injector 5 is controlled so that the pre-fuel injection is performed in accordance with the fuel injection amount and fuel injection timing set in (Step S107). Subsequently, the injector 5 is controlled to perform the first main fuel injection according to the fuel injection amount and fuel injection timing set in step S101 (step S108). Subsequently, the injector 5 is controlled so as to perform the second main fuel injection in accordance with the fuel injection amount and fuel injection timing set in step S101 (step S109).

  In the above, the accelerator opening sensor 25, the engine rotation sensor 26, and the engine load calculation unit 30 constitute a load detection unit that detects the load of the engine 1. The procedure S101 of the injector control unit 31 includes a first injection timing for determining a fuel injection timing for the first fuel injection and a fuel injection timing for the second fuel injection performed after the first fuel injection, respectively. The determination means is configured. The procedures S102 and S104 constitute load determining means for comparing and determining the engine load with a first predetermined value and a second predetermined value equal to or lower than the first predetermined value. In step S103, when the load determining means determines that the engine load is lower than the first predetermined value, the fuel injection timing of the third fuel injection that is performed before the first fuel spray is determined. A second injection timing determining means for determining is configured. In steps S105 and S106, when the load determining means determines that the load of the engine 1 is lower than the second predetermined value, the fuel injection timing of the third fuel injection and the first The fuel injection timing advance means for advancing the fuel injection timing of each fuel spray is configured. In steps S108 and S109, the fuel injection is performed so that the first fuel injection and the second fuel injection are sequentially performed according to the fuel injection timing of the first fuel injection and the fuel injection timing of the second fuel injection. The 1st control means which controls the injection valve 5 is comprised. The procedure S107 is a second control means for controlling the fuel injection valve 5 so as to perform the third fuel spray before the first fuel spray according to the fuel injection timing of the third fuel injection. Configure.

  The procedure S102 of the injector control unit 31 constitutes a water temperature determining unit that determines whether the water temperature of the engine 1 is lower than the first predetermined temperature.

  By the way, when the engine 1 is in an extremely low load such as idling and the engine 1 is in a normal warm-up state (for example, 80 ° C. or higher), as shown in FIG. Without performing the fuel injection, the first main fuel injection and the second main fuel injection are sequentially performed. Then, since the ignition of the premixed mixture of fuel and air is started after a predetermined period after the first and second main fuel injections are completed, as shown by the broken line P in FIG. A mountain-shaped heat release rate waveform (combustion waveform) is obtained.

  However, in an extremely low load state, the amount of one injection is reduced, and the initial combustion becomes weak. For this reason, when the engine 1 is in a low water temperature state (for example, 40 ° C. or less) in an extremely low load state, as shown in FIG. 4B, the pre-fuel injection, the first main fuel injection, and the second time If the main fuel injections are simply performed in sequence, the combustion waveform is greatly different from that in the warm-up state, as indicated by the one-dot chain line Q in FIG.

  In this case, combustion becomes unstable due to a delay in the ignition timing, and it becomes difficult to sufficiently suppress the generation of unburned HC and unburned CO. In addition, since the first and second main fuel injections are ignited almost simultaneously, the combustion noise may become louder than necessary, or the tone of the combustion noise may be extremely different from that in the warm air state. As a result, the driver feels uncomfortable.

  On the other hand, in this embodiment, when the engine 1 is in an extremely low load and the engine 1 is in a low water temperature state, as shown in FIG. 4C, the pre-fuel injection and the first main fuel injection are performed. Each of the fuel injection timings of the fuel injection is advanced. At this time, each fuel injection timing is advanced by an amount corresponding to the ignition delay due to the decrease in the engine water temperature, so that the ignition timings of the first and second main fuel injections are warm as shown by the solid line R in FIG. It almost coincides with the state (see the broken line P). Further, since the fuel injection timing of the second main fuel injection is not changed, a double-flank combustion waveform is maintained as in the warm-up state.

  As described above, when the engine 1 is in an extremely low load state, even if the engine 1 is in a low water temperature state, a combustion waveform similar to that in the warm air state is obtained. Generation of fuel HC and unburned CO can be sufficiently suppressed. Further, since ignition by the first and second main fuel injections is prevented from being performed almost simultaneously, an increase in combustion noise and a timbre change due to a change in the combustion waveform can be suppressed. As a result, it is possible to reduce the driver's uncomfortable feeling.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, when the engine load is lower than a predetermined value and the engine water temperature is lower than the lower reference temperature, the fuel injection timing of the pre-fuel injection and the first main fuel injection is advanced by a certain amount. However, the present invention is not limited to this, and when the engine load is lower than a predetermined value, for example, the advance amount of the fuel injection timing of the pre-fuel injection and the first main fuel injection is changed according to the engine water temperature. Also good.

  In the above embodiment, when the engine water temperature is lower than the upper reference temperature, the pre-fuel injection is performed before the first main fuel injection. However, the present invention is not limited to this, and the engine water temperature is not limited. The pre-fuel injection may always be performed.

  Furthermore, in the above-described embodiment, the lower reference value is lower than the upper reference value for the upper reference value and the lower reference value used for engine load comparison determination. However, the lower reference value is not particularly limited thereto. May be equal to the upper reference value.

  Moreover, in the said embodiment, although the main fuel injection is implemented 2 times for every cycle, you may implement the main fuel injection 3 times or more for every cycle.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 24 ... ECU, 25 ... Accelerator opening degree sensor (load detection means), 26 ... Engine rotation sensor (load detection means), 28 ... Water temperature sensor (Water temperature detection means), 29 ... combustion control device, 30 ... engine load calculation section (load detection means), 31 ... injector control section (first injection timing determination means, second injection timing determination means, load determination means, Injection timing advance means, first control means, second control means, water temperature judgment means).

Claims (3)

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;
Water temperature detecting means for detecting the water temperature of the engine;
Load detecting means for detecting the load of the engine;
First injection timing determining means for respectively determining a fuel injection timing of the first fuel spray and a fuel injection timing of the second fuel injection performed after the first fuel spray;
Load determination means for comparing and determining the load of the engine with a first predetermined value and a second predetermined value equal to or lower than the first predetermined value;
When the load determining means determines that the engine load is lower than the first predetermined value, the fuel injection timing of the third fuel injection to be performed before the first fuel spray is determined. Second injection timing determining means for
When the load determining means determines that the engine load is lower than the second predetermined value, the fuel injection timing of the third fuel injection and the first fuel tank are determined according to the water temperature of the engine. Injection timing advance means for advancing each fuel injection timing,
The fuel injection valve performs the first fuel injection and the second fuel injection sequentially in accordance with the fuel injection timing of the first fuel injection and the fuel injection timing of the second fuel injection. First control means for controlling
Second control means for controlling the fuel injection valve so as to perform the third fuel spray before the first fuel spray according to the fuel injection timing of the third fuel injection; A combustion control device comprising: Water temperature judging means for judging whether the water temperature of the engine is lower than a first predetermined temperature;
The second injection timing determining means determines the fuel injection timing of the third fuel injection when the water temperature determining means determines that the water temperature of the engine is lower than the first predetermined temperature,
The second control unit is configured to perform the third fuel spray when the water temperature determining unit determines that the water temperature of the engine is lower than the first predetermined temperature. The combustion control device according to claim 1, wherein the combustion control device is controlled.   The injection timing advance means has a second coolant temperature lower than the first predetermined temperature when the load determination means determines that the engine load is lower than the second predetermined value. If the engine water temperature is determined to be lower than the second predetermined temperature, the fuel injection timing of the third fuel injection and the first fuel injection are determined. 3. The combustion control apparatus according to claim 2, wherein the fuel injection timings of each are advanced.

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