JP2015078615A - Combustion control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control system which can suppress increase of combustion noise when an intake pressure into a combustion chamber decreases.SOLUTION: ECU determines fuel injection amounts and fuel injection timings of a first fuel injection and a second fuel injection which is carried out after the first fuel injection. Thereafter, the ECU determines whether or not an intake pressure detected by an intake pressure sensor is lower than a reference pressure. When the intake pressure is lower than the reference pressure, the fuel injection timing of the first fuel injection is advanced, and the fuel injection timing of the second fuel injection is advanced so that an advance amount of the fuel injection timing of the second fuel injection is smaller than an advance amount of the fuel injection timing of the first fuel injection. Then, the ECU controls an injector to successively carry out the first fuel injection and the second fuel injection in accordance with the fuel injection amount and the 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 is formed as homogeneous as possible 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 heat generation rate waveform (combustion waveform) cannot be obtained, which increases combustion noise. There is a problem of being connected.

  The objective of this invention is providing the combustion control apparatus which can suppress the increase in a combustion noise when the intake pressure in a combustion chamber falls.

  The present invention relates to an engine combustion control apparatus that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into a combustion chamber of the engine, and a second fuel injection after the first fuel injection is performed. As described above, the injection valve control means for controlling the fuel injection valve and the intake pressure detection means for detecting the intake pressure into the combustion chamber are provided, and the injection valve control means includes the first fuel injection and the second fuel injection. Determination means for determining fuel injection timing, and first injection timing advance means for advancing the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means is lower than the reference pressure When the intake pressure detected by the intake pressure detection means is lower than the reference pressure, the advance amount of the fuel injection timing of the second fuel injection is larger than the advance amount of the fuel injection timing of the first fuel injection. During the fuel injection of the second fuel injection so as to reduce It is characterized in that a second injection timing advance means for the advance.

  When the intake pressure into the combustion chamber of the engine decreases, the amount of air taken into the combustion chamber decreases, so when the fuel is injected into the combustion chamber by the fuel injection valve, the air-fuel ratio in the combustion chamber becomes rich and the fuel and Combustion of the premixed air with air slows down, and as a result, the heat generation rate waveform (combustion waveform) becomes significantly different from that at the reference pressure. Therefore, in the present invention, when the intake pressure into the combustion chamber is lower than the reference pressure, the fuel injection timing of the first fuel injection and the second fuel injection performed thereafter is advanced and the second fuel injection timing is advanced. By making the advance amount of the fuel injection timing of the fuel injection smaller than the advance amount of the fuel injection timing of the first fuel injection, the heat generation rate waveform can be made closer to that at the reference pressure. As a result, an increase in combustion noise when the intake pressure into the combustion chamber decreases can be suppressed.

  Preferably, the first injection timing advance means advances the fuel injection timing of the first fuel injection so that the ignition timing by the first fuel injection is equivalent to the ignition timing at the reference pressure. In this case, since the heat generation rate waveform by the first fuel injection is substantially the same as that at the reference pressure, combustion noise can be reliably reduced.

  Preferably, the second injection timing advance means is configured to reduce the maximum sound pressure at the time of combustion by the first fuel injection by the sound pressure at the time of combustion by the second fuel injection. Advance the fuel injection timing of fuel injection. In this case, since the maximum value of the sound pressure during combustion by the first fuel injection is reduced, the combustion noise can be reliably reduced.

  At this time, the second injection timing advance means uses the pressure wave of the sound pressure in the frequency band in which the sound pressure during combustion by the first fuel injection is a maximum value as the sound pressure during combustion by the second fuel injection. It is preferable to advance the fuel injection timing of the second fuel injection so as to cancel out by the pressure wave. In this case, since the sound pressure in a specific frequency band becomes low, combustion noise in a specific frequency band can be reduced. As a result, overall (all frequency band) combustion noise can be reduced.

  Further preferably, it further comprises air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio at the reference pressure when the intake pressure detected by the intake pressure detection means is lower than the reference pressure. . In this case, since the combustion of the fuel / air premixed gas is appropriately performed, it is possible to suppress an increase in smoke and unburned HC and CO.

  According to the present invention, it is possible to suppress an increase in combustion noise when the intake pressure into the combustion chamber decreases. Thereby, it is possible to realize excellent premixed compression ignition combustion.

It is a schematic structure figure showing a diesel engine provided with one embodiment of a combustion control device concerning the present invention. It is a flowchart which shows the detail of the process sequence performed by ECU shown in FIG. It is a graph which shows the concept which makes the pressure wave of the sound pressure at the time of the combustion by the 2nd fuel injection interfere with the pressure wave of the sound pressure at the time of the combustion by the 1st fuel injection. It is a graph which compares and shows an example of a heat release rate waveform. It is a graph which compares and shows an example of the frequency characteristic (spectrum) of a sound pressure. It is a graph which compares and shows an example of a combustion noise.

  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 provided 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. 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 exhaust passage 9 is provided with a turbine 16 of the turbocharger 12 and a DPF 17 with a catalyst from the upstream side toward the downstream side.

  The diesel engine 1 also includes an exhaust gas recirculation (EGR) unit 18 that recirculates a part of the exhaust gas after combustion into the combustion chamber 4 as exhaust gas recirculation gas (EGR gas). The EGR unit 18 is provided so as to connect the intake passage 7 and the exhaust manifold 10, and an EGR passage 19 that recirculates the EGR gas, and an EGR that adjusts the recirculation amount of the EGR gas from the exhaust manifold 10 to the intake passage 7. The EGR cooler 21 that cools the EGR gas that passes through the valve 20, the EGR passage 19, the bypass passage 22 that is connected to the EGR passage 19 so as to bypass the EGR cooler 21, and the EGR gas passage on the EGR cooler 21 side Or it has the switching valve 23 switched to the bypass channel | path 22 side.

  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 opening sensor 26, and an intake pressure sensor 27 are connected to the ECU 24.

  The crank angle sensor 25 is a sensor that detects 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 26 is a sensor that detects a depression angle (accelerator opening) of an accelerator pedal as a load (engine load) of the engine body 2. The intake pressure sensor 27 is a sensor (intake pressure detection means) for detecting the pressure of air sucked into the combustion chamber 4 (intake pressure into the combustion chamber 4), for example, at the downstream end of the intake passage 7. It is attached.

  Here, the injector 5, the throttle valve 15, the EGR unit 18, the ECU 24 and the sensors 25 to 27 constitute the combustion control device 28 of the present embodiment. The combustion control device 28 sucks air into the combustion chamber 4 and injects fuel from each injector 5 into the combustion chamber 4 in a plurality of times for each cycle of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. (Split injection) and control to perform premixed compression ignition combustion.

  FIG. 2 is a flowchart showing details of a processing procedure executed by the ECU 24. This process is a process for inputting the detection signals of the sensors 25 to 27 and performing predetermined steps to control the injector 5 and the EGR valve 20.

  In the figure, first, the first fuel injection (first fuel injection) is performed based on the engine speed detected by the crank angle sensor 25 and the accelerator opening (engine load) detected by the accelerator opening sensor 26. Then, the fuel injection amount and fuel injection timing of the second fuel injection (second fuel injection) to be performed thereafter are determined (step S101). Here, the first fuel injection and the second fuel injection are main fuel injections for performing premixed compression ignition combustion.

  Subsequently, it is determined whether or not the intake pressure detected by the intake pressure sensor 27 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, the EGR valve 20 is controlled so that the air-fuel ratio in the combustion chamber 4 is maintained at the air-fuel ratio obtained at the reference pressure (step S103).

  Specifically, when the intake pressure into the combustion chamber 4 decreases, the amount of intake air into the combustion chamber 4 decreases, so the EGR valve 20 is controlled to reduce the recirculation amount of EGR gas to the intake passage 7. By doing so, the intake air amount into the combustion chamber 4 is increased. As a result, the combustion of the premixed mixture of fuel and air is appropriately performed in the combustion chamber 4, so that smoke and unburned HC and CO can be reduced.

  Subsequently, the fuel injection timing of the first fuel injection determined in step S101 is advanced (procedure S104). At this time, it is desirable to advance the fuel injection timing of the first fuel injection so that the ignition timing of the pre-mixture by the first fuel injection is equivalent to the ignition timing of the pre-mixture obtained at the reference pressure. .

  Subsequently, the fuel injection timing of the second fuel injection determined in step S101 is advanced (procedure S105). At this time, the fuel injection timing of the second fuel injection is advanced so that the advance amount of the fuel injection timing of the second fuel injection becomes smaller than the advance amount of the fuel injection timing of the first fuel injection. .

  Specifically, as shown in FIG. 3, the pressure wave of the sound pressure at the time of combustion caused by the first fuel injection is made to interfere with the pressure wave of the sound pressure at the time of combustion caused by the second fuel injection. The fuel of the second time so that the pressure wave of the sound pressure is canceled by the pressure wave of the sound pressure of the second fuel injection in the frequency band where the sound pressure during the combustion by the fuel injection is the maximum value. It is desirable to set the fuel injection timing of the injection.

  For example, the fuel injection timing data of the optimal second fuel injection corresponding to the fuel injection amount and the intake pressure of the first and second fuel injections are prepared in advance as an injection timing correction table, and the injection timing is prepared. The fuel injection timing of the second fuel injection is set using the correction table.

  In FIG. 3, a one-dot chain line L indicates a pressure wave of sound pressure during combustion by the first fuel injection, a broken line M indicates a pressure wave of sound pressure during combustion by the second fuel injection, and a solid line N indicates the interference between the pressure waves of the two.

  After step S105 is executed, each injector 5 is controlled to perform the first fuel injection according to the fuel injection amount determined in step S101 and the fuel injection timing changed in step S104 (step S106). Then, each injector 5 is controlled so as to perform the second fuel injection according to the fuel injection amount determined in step S101 and the fuel injection timing changed in step S105 (step S107).

  On the other hand, when it is determined in step S102 that the intake pressure is not lower than the reference pressure, steps S103 to S105 are not executed, and the first fuel injection is performed according to the fuel injection amount and fuel injection timing determined in step S101. Each injector 5 is controlled so as to be executed (step S106). Then, each injector 5 is controlled so as to perform the second fuel injection according to the fuel injection amount and the fuel injection timing determined in step S101 (step S107).

  In the above, the ECU 24 constitutes the injection valve control means for controlling the fuel injection valve 5 so that the second fuel injection is performed after the first fuel injection is performed. The EGR unit 18 and the ECU 24 control the air-fuel ratio so that the air-fuel ratio in the combustion chamber 4 is maintained at the air-fuel ratio at the reference pressure when the intake pressure detected by the intake-pressure detecting means 27 is lower than the reference pressure. The control means is configured.

  At this time, steps S101, S102, and S104 to S107 shown in FIG. 2 function as the injection valve control means, and the steps S102 and S103 function as a part of the air-fuel ratio control means. More specifically, step S101 functions as a determination unit that determines the fuel injection timings of the first fuel injection and the second fuel injection. Steps S102 and S104 function as first injection timing advance means for advancing the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means 27 is lower than the reference pressure. . In steps S102 and S105, when the intake pressure detected by the intake pressure detection means 27 is lower than the reference pressure, the advance amount of the fuel injection timing of the second fuel injection is equal to the fuel injection timing of the first fuel injection. It functions as a second injection timing advance means for advancing the fuel injection timing of the second fuel injection so as to be smaller than the advance amount.

  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 significantly from the heat generation rate waveform obtained at the reference pressure, realizing premixed compression ignition combustion similar to that at the reference pressure. Difficult to do. In order to solve such a problem, it is conceivable to advance the fuel injection timings of the first fuel injection and the second fuel injection. However, even if the fuel injection timing of the first fuel injection and the second fuel injection is advanced by the same amount, the heat generation rate waveform obtained at that time does not match the heat generation rate waveform obtained at the reference pressure, The combustion noise level becomes higher than that at the reference pressure.

  On the other hand, in this embodiment, when the intake pressure into the combustion chamber 4 is lower than the reference pressure, the ignition timing of the premixed gas by the first fuel injection is the ignition timing of the premixed gas obtained at the reference pressure. In order to be equivalent, the fuel injection timing of the first fuel injection is advanced, and the pressure wave of the sound pressure is applied to the second time in the frequency band in which the sound pressure at the time of combustion by the first fuel injection is the maximum value. The fuel injection timing of the second fuel injection is advanced so as to cancel out by the pressure wave of the sound pressure at the time of combustion by fuel injection. By doing in this way, the advance amount of the fuel injection timing of the second fuel injection becomes smaller than the advance amount of the fuel injection timing of the first fuel injection, and the heat generation rate waveform almost coincident with the reference pressure Can be obtained. Thereby, the combustion noise when the intake pressure to the combustion chamber 4 falls can be reduced.

  FIG. 4 shows a comparison of examples of heat release rate waveforms. In the figure, a broken line P indicates a heat release rate waveform at the reference pressure. A one-dot chain line Q indicates a heat generation rate waveform in the conventional control in which the advance amount of the fuel injection timing of the first and second fuel injections is equal when the pressure is 20 kPa lower than the reference pressure. The solid line R represents the heat generation rate in the present control in which the advance amount of the fuel injection timing of the second fuel injection is smaller than the advance amount of the fuel injection timing of the first fuel injection when it is 20 kPa lower than the reference pressure. The waveform is shown. In any case, the engine speed is 1300 rpm.

  Here, in the conventional control and the main control, the advance amount of the fuel injection timing of the first main fuel injection is the ignition timing of the pre-mixture obtained when the ignition timing of the pre-mixture by the first fuel injection is the reference pressure. The amount is equivalent to. Thereby, as can be seen from FIG. 4, the first peak of the heat generation rate waveform in the conventional control and the main control substantially coincides with the first peak of the heat generation rate waveform at the reference pressure.

At the reference pressure, the combustion peak interval of the heat release rate waveform (interval between the first combustion peak and the second combustion peak) is X ₁ (about 4.0 ° CA≈0.51 ms). In the conventional control, the combustion peak interval of the heat generation rate waveform is X ₂ (about 2.5 ° CA≈0.32 ms), which is shorter than the combustion peak interval of the heat generation rate waveform at the reference pressure. On the other hand, in this control, by making the advance amount of the fuel injection timing of the second fuel injection smaller than the advance amount of the fuel injection timing of the first fuel injection, the combustion peak interval of the heat release rate waveform is X ₃ (about 3.5 ° CA≈0.45 ms), approaching the combustion peak interval of the heat release rate waveform at the reference pressure.

  FIG. 5 shows a comparison of examples of frequency characteristics (spectrums) of sound pressure generated in the combustion chamber 4 (inside the cylinder). In the figure, the broken line P indicates the frequency characteristic at the time of the reference pressure. A one-dot chain line Q indicates a frequency characteristic in the conventional control in which the advance amount of the fuel injection timing of the first and second fuel injections is equal when the pressure is 20 kPa lower than the reference pressure. The solid line R shows the frequency characteristic in this control in which the advance amount of the fuel injection timing of the second fuel injection is smaller than the advance amount of the fuel injection timing of the first fuel injection when it is 20 kPa lower than the reference pressure. Show. In any case, the engine speed is 1300 rpm. In the conventional control and the main control, the advance amount of the fuel injection timing of the first main fuel injection is the same as that shown in FIG.

  In the conventional control, the frequency band in which combustion noise is canceled is greatly different from that at the reference pressure, and the maximum value of the sound pressure is high. As a result, as shown in FIG. 6, the combustion noise is higher than that at the reference pressure.

  In this control, so that the pressure wave of the sound pressure at the time of combustion by the first fuel injection is offset by the pressure wave of the sound pressure at the time of combustion by the second fuel injection, The fuel injection timing of the second fuel injection is advanced. As a result, the frequency band in which combustion noise is canceled is shifted to the lower frequency side, and the maximum value of the sound pressure is reduced. Specifically, as shown in FIG. 3, the pressure wave of the sound pressure at the time of combustion by the second fuel injection is, for example, 1/2 cycle with respect to the pressure wave of the sound pressure at the time of combustion by the first fuel injection. It is adjusted to shift. Thereby, the combustion noise of overall (all frequency bands) can be reduced. As a result, as shown in FIG. 6, the combustion noise can be reduced to a level equivalent to that at the reference pressure.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, an injection timing correction table is prepared in advance, and the fuel injection timing of the second fuel injection is advanced using the injection timing correction table. Absent. For example, an in-cylinder pressure sensor that detects the pressure in the combustion chamber 4 (in-cylinder) is provided, and the frequency band in which the sound pressure during combustion by the first fuel injection becomes the maximum value based on the detection value of the in-cylinder pressure sensor. It is also possible to calculate the fuel injection timing of the second fuel injection that cancels the fuel injection.

  In the above embodiment, the pressure wave of the sound pressure is canceled by the pressure wave of the sound pressure at the time of combustion by the second fuel injection in the frequency band in which the sound pressure at the time of combustion by the first fuel injection is the maximum value. As described above, the fuel injection timing of the second fuel injection is calculated, but the method is not particularly limited. For example, in a frequency band other than the frequency band where the sound pressure during combustion by the first fuel injection is the maximum value, the pressure wave of the sound pressure is canceled by the pressure wave of the sound pressure during combustion by the second fuel injection. Even if the fuel injection timing of the second fuel injection is calculated so as to reduce the maximum value of the sound pressure at the time of combustion by the first fuel injection, the effect of this embodiment is exhibited. Furthermore, the fuel injection timing of the second fuel injection is calculated so as to reduce the maximum value of the sound pressure at the time of combustion by the first fuel injection using the sound pressure at the time of combustion by the second fuel injection. You may do it.

  Further, in the above embodiment, the air-fuel ratio in the combustion chamber 4 is maintained at the air-fuel ratio at the reference pressure by adjusting the flow rate of the EGR gas by the EGR valve 20, but as a method for controlling the air-fuel ratio, In particular, the invention is not limited thereto, and for example, the supercharging pressure of the turbocharger may be adjusted.

  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 fuel injection, and the main fuel injection immediately before corresponds to the first fuel injection.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 18 ... EGR unit (air-fuel ratio control means), 24 ... ECU (injection valve control means, determination means, first injection timing advance means) , Second injection timing advance means, air-fuel ratio control means), 27 ... intake pressure sensor (intake pressure detection means), 28 ... combustion control device.

Claims (5)

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;
Injection valve control means for controlling the fuel injection valve so that the second fuel injection is performed after the first fuel injection is performed;
An intake pressure detecting means for detecting the intake pressure into the combustion chamber,
The injection valve control means includes
Determining means for determining fuel injection timings of the first fuel injection and the second fuel injection;
First injection timing advance means for advancing the fuel injection timing of the first fuel injection when the intake pressure detected by the intake pressure detection means is lower than a reference pressure;
When the intake pressure detected by the intake pressure detection means is lower than the reference pressure, the advance amount of the fuel injection timing of the second fuel injection is the advance angle of the fuel injection timing of the first fuel injection. And a second injection timing advance means for advancing the fuel injection timing of the second fuel injection so as to be smaller than the amount.   The first injection timing advance means advances the fuel injection timing of the first fuel injection so that the ignition timing by the first fuel injection is equivalent to the ignition timing at the reference pressure. The combustion control device according to claim 1.   The second injection timing advance means is configured to reduce the maximum value of sound pressure at the time of combustion by the first fuel injection by the sound pressure at the time of combustion by the second fuel injection. 3. The combustion control device according to claim 1, wherein the fuel injection timing of injection is advanced.   The second injection timing advance means converts the pressure wave of the sound pressure into a sound pressure at the time of combustion by the second fuel injection in a frequency band where the sound pressure at the time of combustion by the first fuel injection becomes a maximum value. 4. The combustion control apparatus according to claim 3, wherein the fuel injection timing of the second fuel injection is advanced so as to cancel out by the pressure wave.   Air-fuel ratio control means for controlling the air-fuel ratio in the combustion chamber to be maintained at the air-fuel ratio at the reference pressure when the intake pressure detected by the intake pressure detection means is lower than the reference pressure. The combustion control device according to any one of claims 1 to 4, wherein

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