JP2009121389A - Combustion control system of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the discharge of NOx during transition time of switching between a premix combustion mode and a normal combustion mode. <P>SOLUTION: A combustion control system of a diesel engine controls fuel injection timing to enable switching to the normal combustion mode, the premix combustion mode, and a transition mode of between these modes. During the transition mode, by switching to a low emission mode suppressing the discharge of nitrogen oxide according to an engine operation state and a low smoke mode suppressing the discharge of smoke, the system controls the fuel injection timing corresponding to intake oxygen density, and when an NOx catalyst is in an inactive state, forcibly selects the low emission mode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a diesel engine combustion control device, and more particularly to a technique for controlling fuel injection so as to be switchable between a premixed combustion mode and a normal combustion mode.

In the combustion control of diesel engines, fuel is injected near the compression top dead center of the piston, the normal combustion mode is ignited during fuel injection, and the fuel injection is completed before the fuel self-ignition timing, and then ignites A technique for switching to the premixed combustion mode is known.
In the normal combustion mode, additional fuel is supplied even after ignition, so the amount of fuel supplied into the cylinder is increased and high output can be secured. On the other hand, in the premixed combustion mode, after the fuel injection is completed, the air-fuel mixture is sufficiently diluted and homogenized and ignited, so the local combustion temperature rise is suppressed and NOx (nitrogen oxide) generation is reduced. To do. Therefore, combustion control is generally performed by selecting the premixed combustion mode in consideration of the exhaust performance at low rotation and low load or idling, and selecting the normal combustion mode in consideration of the output performance in other cases. ing.

In the premixed combustion mode and the normal combustion mode, the target values of the control parameters such as the fuel injection timing are set in the map, etc., and at the time of transition between the premixed combustion mode and the normal combustion mode, each mode is supported. Some control is performed such that the target value of the control parameter is gradually changed so that the two maps are connected (Patent Document 1).
JP 2006-105046 A

  However, in the combustion control described in the above-mentioned Patent Document 1, control is performed so as to simply connect the map of the premixed combustion mode and the map of the normal combustion mode. For example, in an engine having an EGR device, these At the time of switching to the switching of the combustion mode (during the transition mode), proper fuel injection becomes difficult due to the delay in operation of the EGR device, and smoke or NOx may be generated.

By the way, the exhaust passage of the diesel engine is widely equipped with an exhaust purification catalyst that captures NOx in the exhaust and reduces and removes it. However, when the exhaust purification catalyst is in an inactive state, such as immediately after the cold start, there is a problem that NOx is not sufficiently removed in the exhaust purification catalyst and exhausted to the outside.
The present invention has been made to solve such problems. The object of the present invention is to suppress the generation of smoke in the transition mode and to reduce the NOx even when the exhaust purification catalyst is in an inactive state. It is in providing the combustion control apparatus which can suppress discharge | emission of.

  In order to achieve the above object, the first aspect of the present invention provides a normal combustion mode that ignites within a fuel injection period, a premix combustion mode that ignites through a premix period after completion of fuel injection, a normal combustion mode, and a premix As a map in which the fuel injection timing corresponding to the intake oxygen concentration in the transition mode is set in the diesel engine combustion control device that controls the fuel injection timing by switching to any one of the transition modes that transition between the combustion modes The low emission mode map that suppresses the emission of nitrogen oxides and the low smoke mode map that suppresses the emission of smoke, and the low emission mode map and the low smoke mode map based on the engine operating state in the transition mode Control means for controlling the fuel injection timing by selecting any of the above, and in the exhaust of the diesel engine Catalyst state estimating means for estimating whether or not the exhaust purification catalyst for removing elemental oxide is in an inactive state, and the control means estimates that the exhaust purification catalyst is in an inactive state by the catalyst state estimating means. In this case, the low emission mode map is selected.

Further, in claim 2, when it is estimated by the catalyst state estimating means that the exhaust purification catalyst is in an inactive state, the control means selects the low emission mode based on the engine operating state. Further, a limiting means for limiting the accelerator opening is further provided.
According to a third aspect of the present invention, the control means according to the first or second aspect of the present invention provides the low emission mode map based on the accelerator operation rate change rate, the intake oxygen concentration change rate, and the catalyst temperature of the exhaust purification catalyst as the engine operating state. And a map for low smoke mode is selected.

  According to the combustion control apparatus for a diesel engine according to claim 1 of the present invention, during the transition mode, the fuel injection timing is controlled by switching between the low emission mode and the low smoke mode based on the engine operating state, so that the nitrogen oxide is controlled. It is possible to achieve both the suppression of the emission of smoke and the suppression of the emission of smoke. Further, when the exhaust purification catalyst is in an inactive state, the generation of nitrogen oxides is suppressed by selecting the low emission mode, so that the exhaust purification catalyst is in an inactive state just after the cold start. Even if it exists, discharge | emission of a nitrogen oxide can be suppressed.

According to the combustion control device for a diesel engine of claim 2 of the present invention, when the exhaust purification catalyst is in an inactive state, the accelerator opening is limited so that the low emission mode is selected in the control means. Rapid changes in the intake state are suppressed, and generation of nitrogen oxides caused by fuel injection delay can be reliably suppressed.
According to the combustion control apparatus for a diesel engine of claim 3 of the present invention, the low emission mode map or the low smoke mode map is based on the accelerator opening change rate, the intake oxygen concentration change rate, and the catalyst temperature of the exhaust purification catalyst. Therefore, it is possible to achieve both the suppression of nitrogen oxide emission and the suppression of smoke emission accurately in the transition mode.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A NOx catalyst (exhaust gas purification) that captures NOx (nitrogen oxides) in exhaust gas and reduces it to harmless substances in an exhaust passage of a diesel engine (hereinafter simply referred to as an engine) equipped with the combustion control device of the present embodiment. Catalyst). Further, the engine is provided with an EGR system and a common rail system. The EGR system has an EGR passage that communicates an exhaust passage and an intake passage, and controls the opening and closing of an EGR valve that is interposed in the EGR passage, whereby a part of the exhaust gas is circulated to the intake air to lower the combustion temperature. Thus, it has a function of suppressing the generation of NOx.

  In the common rail system, fuel whose pressure is increased by a fuel pump is stored in a common rail, and high pressure fuel is supplied from the common rail to an injector provided in each cylinder and injected into the cylinder. The pressure in the common rail can be adjusted by controlling the operation of the fuel pump. Each injector is controlled by a combustion control device, and the amount of fuel injected into the cylinder and the fuel injection timing are controlled.

The combustion control device has a function of inputting various operating states of the engine and switching the fuel injection by the injector to the normal combustion mode or the premixed combustion mode.
In the normal combustion mode, it is controlled to inject fuel near the compression top dead center of the piston, and additional fuel is supplied even after ignition, so that the amount of fuel supplied into the cylinder increases and high output can be obtained. . In the premixed combustion mode, the fuel injection is controlled to be completed before the fuel self-ignition timing, and after the fuel injection is completed, the mixture is sufficiently diluted and homogenized to ignite, so the local combustion temperature rises. Is suppressed, and the amount of NOx generated is reduced. Further, a transition mode that is a transition period between these two modes is provided between the normal combustion mode and the premixed combustion mode.

FIG. 1 is a flow chart showing a combustion mode switching determination procedure. This routine is repeatedly executed while the engine is operating.
As shown in FIG. 1, first in step S10, an engine speed Ne and a load L (for example, fuel injection amount) are input, and a premixed combustion mode is determined by a combustion mode determination map stored in advance as shown in FIG. It is determined whether or not the driving state is suitable for. If it is determined that the operation state is suitable for the premixed combustion mode, the process proceeds to step S20. This map is set so that the premixed combustion (PCI) mode is selected at low rotation and low load, and the normal combustion (Conventional) mode is selected in other regions. The region between the premixed combustion mode and the normal combustion mode corresponds to the transition mode.

In step S20, the premixed combustion mode is selected. Then, this routine is returned.
If it is determined in step S10 that the engine operating condition is not suitable for the premixed combustion mode, the process proceeds to step S30.
In step S30, it is determined whether or not the intake oxygen concentration is greater than a predetermined value. If larger than the predetermined value, the process proceeds to step S40. This predetermined value may be set to a lower limit value at which normal combustion is possible, for example.

In step S40, the normal combustion mode is selected. Then, this routine is returned.
If it is determined in step S30 that the intake oxygen concentration is equal to or lower than the predetermined value, the transition mode is selected, and the process proceeds to step S50.
In step S50, it is determined whether or not the NOx catalyst is in an active state. If it is in the active state, the process proceeds to step S60.

In step S60, the normal transition mode is selected from the transition modes. Then, this routine is returned.
If it is determined in step S50 that the NOx catalyst is not in an active state, that is, if it is in an inactive state, the process proceeds to step S70.
In step S70, the restricted transition mode is selected from the transition modes. Then, this routine is returned.

Next, how to calculate the fuel injection timing and the accelerator opening in the transition mode will be described with reference to the block diagram of FIG.
The combustion control device sets the fuel injection timing in the transition mode based on the intake oxygen concentration. Specifically, there are two types of maps in which the fuel injection timing corresponding to the intake oxygen concentration is set, and control is performed to switch these maps based on the operating state of the engine (control means). Further, the combustion control device has a function of limiting the accelerator opening (limit means).

  As shown in FIG. 3, the first injection timing calculation unit 10 inputs the intake oxygen concentration and the engine rotation speed and calculates the fuel injection timing in the low smoke mode. The fuel injection timing in the low smoke mode is performed using a map as shown in FIG. On the other hand, the second injection timing calculation unit 20 inputs the intake oxygen concentration and the engine speed, and calculates the fuel injection timing in the low emission mode. The fuel injection timing in the low emission mode is performed using a map as shown in FIG. 4 and 5, both are set so that the fuel injection timing is delayed as the intake oxygen concentration increases, and the fuel injection timing is changed according to the change in the engine speed.

The NOx catalyst state determination unit 30 (catalyst state estimation means) inputs the NOx catalyst determination information and determines whether or not the NOx catalyst is in an active state. The NOx catalyst determination information may be information that can be used to estimate whether the NOx catalyst is in an inactive state, such as the catalyst temperature of the NOx catalyst or the supply state of the reducing agent to the NOx catalyst.
The mode selection unit 40 inputs the determination result of the catalyst state of the NOx catalyst from the NOx catalyst active state determination unit 30, and also inputs the accelerator opening change rate and the intake oxygen concentration change rate, so that the low emission mode and the low smoke mode are input. To select one of them. Here, when the change rate of the accelerator opening and the intake oxygen concentration is small, when the NOx catalyst is in an inactive state, the low emission mode is selected. When the change rate of the accelerator opening and the intake oxygen concentration is large, the NOx catalyst is In the active state, the low smoke mode may be selected.

The first switching unit 50 outputs the value calculated by the injection timing calculation unit 10 or 20 corresponding to the mode selected by the mode selection unit 40 as the final fuel injection timing.
The accelerator opening limit value calculation unit 60 inputs the accelerator opening and the engine speed, and calculates a corrected accelerator opening. The corrected accelerator opening is obtained using a map as shown in FIG. In FIG. 6, the upper limit value of the accelerator opening based on the engine speed is set so that the low emission mode is selected by the mode selection unit 40.

  The second switching unit 70 inputs the determination result of the catalyst state of the NOx catalyst from the NOx catalyst state determination unit 30 through the mode selection unit 40, and when the NOx catalyst is in an active state, the accelerator opening is not corrected. The final accelerator opening is output as it is. When it is determined that the NOx catalyst is in an inactive state, the corrected accelerator opening calculated by the accelerator opening limit value calculation unit 60 is output as the final accelerator opening.

  FIG. 7 is a graph showing the relationship between the intake oxygen concentration and the fuel injection timing, and is a reference diagram showing the difference in the transition path between the low emission mode and the low smoke mode. In the figure, the smoke concentration is shown as a contour line for reference, and the smoke concentration is high in the center of the figure. FIG. 8 is a graph showing the relationship between the intake oxygen concentration and the fuel injection timing and the smoke concentration. The larger the number in the figure, the higher the smoke concentration. FIG. 9 is a graph showing the relationship between the intake oxygen concentration and fuel injection timing and the NOx concentration. The larger the number in the figure, the higher the NOx concentration. FIG. 10 is a graph showing the relationship between the intake oxygen concentration and the fuel injection timing and the output torque. The larger the number in the figure, the larger the output torque.

  As shown in FIG. 7, during the transition mode, the transition is made between the region of the premixed combustion mode in the lower part of the figure and the region of the normal combustion mode in the upper right part of the figure. Different from smoke mode. In the low smoke mode, in consideration of the smoke concentration characteristics shown in FIG. 8, the premixed combustion mode region and the normal combustion mode region are set to be connected by a substantially straight line so as to avoid the region where the smoke concentration is high. ing. In the low emission mode, in consideration of the characteristics of the NOx concentration shown in FIG. 9, the region where the NOx concentration is low is set to shift as much as possible. Further, as shown in FIG. 10, the engine output torque is a characteristic that changes little depending on the fuel injection timing without being substantially affected by the intake oxygen concentration between the premixed combustion mode and the normal combustion mode. Therefore, as shown in the figure, in the low smoke mode, the inclination (fuel injection timing / intake oxygen concentration) is set smaller than in the low emission mode, so that the change in the fuel injection timing is small with respect to the change in the intake oxygen concentration. Therefore, the change in output torque is also reduced. The engine output torque also increases when the fuel injection timing is early (advanced), and the combustion injection timing is set earlier in the low smoke mode than in the low emission mode at the same intake oxygen concentration. The engine output torque can be kept high during the transition between the premixed combustion mode and the normal combustion mode.

As described above, in this embodiment, the switching between the normal combustion mode and the transition mode, and further, the fuel injection timing in the transition mode is set based on the intake oxygen concentration. For example, the response of the EGR device is delayed. However, it is possible to set an accurate fuel injection timing in accordance with the intake air state, and the occurrence of smoke can be suppressed.
In addition, two maps, the low emission mode and the low smoke mode, are prepared as the maps used to set the fuel injection timing. When the accelerator opening changes suddenly, the catalyst temperature of the NOx catalyst is sufficient. When the engine speed is increased, the low smoke mode is selected to suppress the generation of smoke, and the output torque fluctuation is also suppressed to enable a smooth transition. On the other hand, when there is little change in the accelerator opening or the intake oxygen concentration, it is difficult for smoke to occur and output torque does not fluctuate, so it is possible to suppress the generation of NOx by selecting the low emission mode as described above. it can.

  In particular, in the present embodiment, when the NOx catalyst is in an inactive state during the transition mode, the low emission mode is forcibly selected. Therefore, since the generation of NOx is suppressed in the engine, NOx emission can be suppressed even when the NOx catalyst is in an inactive state. Further, when the NOx catalyst is in an inactive state during the transition mode, the accelerator opening is suppressed so that the low emission mode is maintained, so a sudden change in the intake state is suppressed, and the optimum for the intake oxygen concentration is suppressed. Generation of nitrogen oxides caused by a deviation from a proper injection timing can be reliably suppressed.

In this embodiment, when the exhaust purification catalyst is in an inactive state, both the forced switching to the low emission mode and the limitation on the accelerator opening are performed, but the present invention is not limited to this. Any one of these may be implemented.
In the present embodiment, the mode selection unit 40 selects the low emission mode map or the low smoke mode map based on the accelerator opening change rate, the intake oxygen concentration change rate, and the catalyst temperature as the NOx catalyst state. However, the present invention is not limited to this, and may be appropriately selected based on information that can be used to estimate whether the engine is in a transient operation state or whether the NOx catalyst is in an active state.

It is a flowchart which shows the switching determination procedure of the combustion mode in the combustion control apparatus which concerns on this invention. It is a map for combustion mode determination. It is a block diagram which shows the calculation point of the fuel injection timing at the time of transfer mode, and an accelerator opening. It is a map for fuel injection timing calculation in the low smoke mode. It is a map for fuel injection timing calculation in the low emission mode. It is a map for corrected accelerator opening calculation. It is a reference figure which shows the relationship between a fuel-injection time and intake oxygen concentration, and shows the difference in the transition path | route of fuel-injection time in a low smoke mode and a low emission mode. It is a graph which shows the relationship between fuel injection timing, intake oxygen concentration, and smoke concentration in exhaust gas. It is a graph which shows the relationship between fuel injection timing, intake oxygen concentration, and NOx concentration in exhaust gas. It is a graph which shows the relationship between a fuel-injection timing, intake oxygen concentration, and an engine output torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 1st injection timing calculating part 20 2nd injection timing calculating part 30 NOx catalyst state determination part 40 Mode selection part 50 1st switching part 60 Accelerator opening degree limit value calculating part 70 2nd switching part

Claims (3)

Any of a normal combustion mode that ignites within the fuel injection period, a premix combustion mode that ignites through a premixing period after completion of fuel injection, and a transition mode that transitions between the normal combustion mode and the premixed combustion mode In a diesel engine combustion control device that controls the fuel injection timing by switching between
As a map in which the fuel injection timing corresponding to the intake oxygen concentration in the transition mode is set, a low emission mode map for suppressing emission of nitrogen oxides and a map for low smoke mode for suppressing emission of smoke, Control means for controlling the fuel injection timing by selecting and using either the low emission mode map or the low smoke mode map based on the engine operating state during the transition mode;
Catalyst state estimating means for estimating whether or not the exhaust purification catalyst for removing nitrogen oxides in the exhaust of the diesel engine is in an inactive state,
The diesel engine combustion control apparatus, wherein the control means selects the low emission mode map when the catalyst state estimating means estimates that the exhaust purification catalyst is in an inactive state.   Limiting means for limiting the accelerator opening so that the control means selects the low emission mode based on the engine operating state when the exhaust gas purification catalyst is estimated to be in an inactive state by the catalyst state estimating means. The combustion control device for a diesel engine according to claim 1, further comprising:   The control means selects either the low emission mode map or the low smoke mode map as the engine operating state based on the accelerator opening change rate, the intake oxygen concentration change rate, and the catalyst temperature of the exhaust purification catalyst. The combustion control device for a diesel engine according to claim 1 or 2, wherein

Images