JP3838299B2 - Diesel engine control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a diesel engine for maintaining good conversion efficiency of a catalyst for purifying NOx contained in exhaust gas.
[0002]
[Prior art]
In order to purify NOx discharged from the diesel engine, it is known to install a NOx reduction catalyst in the exhaust system. However, in order to reduce NOx by the catalyst, an appropriate amount of HC is required as a reducing agent. Under normal operating conditions, the concentration of HC contained in the exhaust gas of a diesel engine is small to reduce NOx. For this reason, as disclosed in Japanese Patent Laid-Open No. 8-270433, what is the main injection of fuel into the combustion chamber? Separately, fuel is supplied in the exhaust stroke, and the shortage of HC is compensated by this fuel.
[0003]
This uses an accumulator fuel injection device and injects fuel into the cylinder even during the exhaust stroke. Since the accumulator fuel injection device always accumulates high-pressure fuel, multiple fuel injections are performed. You can do it freely.
[0004]
However, the amount of fuel supplied by this sub-injection needs to be supplied so that the HC concentration becomes a predetermined value with respect to the NOx concentration, but if the sub-injection amount is too large, HC is released into the atmosphere as it is. The amount of release increases and fuel consumption deteriorates.
[0005]
Therefore, in the above-described conventional example, the amount of fuel to be sub-injected is set in advance in a map according to the engine speed and load, and control is performed so as to maintain the set injection amount while detecting the operating state.
[0006]
[Problems to be solved by the invention]
However, when the amount of HC required by the NOx reduction catalyst is converted into the fuel injection amount, it is in the range of about 1/20 to 1/500 of the fully opened injection amount at full throttle, and the injection period is very short. Because there are variations between cylinders of the fuel injection injector and variations in the operation cycle of the solenoid valve for controlling the fuel injection timing, how much pressure is accumulated to accurately and accurately inject such a small amount of fuel. Even a fuel injection device of the type is very difficult.
[0007]
For this reason, there have been problems such as an increase in HC and fuel consumption due to an excessive sub-injection amount, or incomplete NOx reduction due to an excessive sub-injection amount.
[0008]
The present invention has been proposed to solve such a problem, and the injection amount of the sub-injection is set to a minimum range that can be accurately controlled to the target value, and the injection timing is changed according to the operating state. Unnecessary fuel is burned and only an appropriate amount of HC can be supplied at all times.
[0009]
[Means for Solving the Problems]
The first aspect of the invention is a sub-injection in the late combustion stage separately from the NOx purification catalyst provided in the exhaust passage, the fuel injection injector that injects the accumulated fuel into the combustion chamber, and the main injection that is performed near the compression top dead center. In the control device for a diesel engine comprising: an injection timing control device for controlling the engine; a means for detecting the operating state of the engine; and a sub-timer that sets the basic timing for performing the sub-injection according to the load so as to be delayed as the engine load increases. And a sub-injection correcting unit that corrects the basic time to be delayed as the unburned rate is lower based on the relationship with the unburned rate of the sub-injected fuel .
[0011]
In the second invention, the sub-injection correcting means delays the sub-injection timing as the cooling water temperature is higher.
[0012]
In the third invention, the sub-injection correcting means delays the sub-injection timing as the supercharging pressure is higher.
[0013]
In a fourth aspect of the invention, the sub injection correction means delays the sub injection timing as the exhaust gas recirculation rate is small.
[0014]
In a fifth aspect of the invention, the sub injection correction means delays the sub injection timing as the intake gas temperature is higher.
[0015]
In a sixth aspect of the invention, the sub injection correction means delays the sub injection timing as the in-cylinder maximum pressure is higher.
[0016]
In a seventh aspect of the invention, the NOx purification catalyst provided in the exhaust passage, the fuel injection injector that injects the accumulated fuel into the combustion chamber, and the main injection that performs the fuel injection near the compression top dead center are separated in the second combustion stage. In a control apparatus for a diesel engine having an injection timing control device for injecting , a means for detecting an operating state of the engine and a basic timing for performing the sub-injection are set according to the load so as to be delayed as the engine load is higher Based on the relationship between the sub-injection setting means, the basic timing and the unburned rate of the fuel to be sub-injected, the sub-injection correcting unit for correcting the basic timing to be delayed as the unburned rate is lower, and the activation state of the catalyst And means for stopping the sub-injection when the catalyst is in an inactive state.
[0017]
According to an eighth aspect of the present invention, the catalyst activity determining means is configured to estimate the activity state of the catalyst from the operating state, or to determine the active state by directly or indirectly measuring the temperature of the catalyst.
[0018]
[Operation and effect of the invention]
In the first invention, the amount of fuel sub-injected at the end of combustion is set as small as possible within a range that can be controlled to the target value in the accumulator fuel injection device, and the amount of sub-injection is determined according to the state of NOx generation. Change the injection timing of the injection.
[0019]
When the amount of NOx generated is small relative to the sub-injection amount, the sub-injection timing is advanced, so that a part of the sub-injected fuel is burned, and at that time, only the minimum fuel required by the catalyst has not been consumed. The fuel is discharged from the engine in the state of HC and flows into the catalyst.
[0020]
Conversely, when the amount of NOx generated is large, the injection timing is delayed so that much of the sub-injected fuel is discharged without being burned.
[0021]
Thus, a necessary amount of HC is supplied to the catalyst, and NOx can be reduced efficiently, while the amount of HC released to the outside can be reduced.
[0023]
Also, from the second, including the invention of the sixth, by correcting the change in the non-燃排fraction of auxiliary injection fuel by their respective operating conditions, it is always possible to supply a proper amount of HC.
[0024]
In other words, when the cooling water temperature rises and the unburned emission rate falls, the injection timing is delayed to ensure the required amount of HC. Similarly, when the supercharging pressure rises and the unburned emission rate falls, When the recirculation rate is low and the unburned exhaust rate decreases, when the intake gas temperature increases and the unburned exhaust rate decreases, when the in-cylinder maximum pressure increases and the unburned exhaust rate decreases, the injection timing The required amount of HC can be supplied accurately.
[0025]
On the other hand, in the seventh aspect, since the sub-injection control is stopped when the catalyst is not activated, the fuel consumption caused by the wasteful sub-injection when NOx in the catalyst is insufficiently reduced. Deterioration of HC and release of HC to the outside can be avoided.
[0026]
In the eighth invention, the inactive state of the catalyst can be accurately determined based on the engine operating state and the catalyst temperature.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0028]
FIG. 1 shows a configuration of a fuel supply system. A fuel supply pump 1 includes a plunger 3 that reciprocates by a cam 2 that is rotationally driven in synchronization with engine rotation. As the plunger 3 reciprocates, fuel is sucked. It is sucked from the passage 4 and stored in the pressure accumulating chamber 7 through the check valve 5 and the discharge passage 6 in a high pressure state.
[0029]
The suction passage 4 is provided with an effective stroke control valve 8 for the plunger 3, and fuel pumping starts when the effective stroke control valve 8 is closed during the compression stroke of the plunger 3, and the pump discharge amount is determined accordingly. . The pressure accumulating chamber 7 is provided with a pressure sensor 9 for detecting the fuel pressure.
[0030]
The high-pressure fuel in the pressure accumulating chamber 7 is guided through the supply passage 10 to the nozzle chamber 12 of the fuel injector 11 and the pressure chamber 14 above the nozzle piston 13 through the suction orifice 18.
[0031]
Normally, the nozzle piston 13 pushes down the needle valve 16 together with the spring 19 to close the valve. However, when the electromagnetic valve 15 that connects the pressure chamber 14 to the drain side opens, the pressure in the pressure chamber 14 passes through the discharge orifice 17. Therefore, the needle valve 16 is lifted upward by the fuel pressure acting on the nozzle chamber 12, and fuel is injected. When the solenoid valve 15 is closed, the pressure chamber 14 is filled with high-pressure fuel through the suction orifice 18, and the needle valve 16 is pushed down by the nozzle piston 13 whose pressure receiving area is set larger than the pressure receiving area of the needle valve 12. Then, the fuel injection stops.
[0032]
Therefore, by controlling the energization timing and period of the electromagnetic valve 15, the fuel injection timing and injection period can be freely controlled.
[0033]
A control unit 22 is provided to adjust the fuel pressure in the pressure accumulating chamber 7, and the opening / closing timing of the effective stroke control valve 8 is controlled by a signal from the control unit 22 in accordance with the pressure detected by the pressure sensor 9 to supply fuel. The discharge amount of the pump 1 is changed.
[0034]
The effective stroke control valve 8 opens when the fuel is inhaled, that is, when the plunger 3 is lowered, and closes only the stroke required for the ascending (compression stroke) for discharging the fuel, thereby controlling the fuel discharge amount. When the fuel pressure in the pressure accumulating chamber 7 is lower than the target value, the pressure is recovered by increasing the effective stroke amount. Conversely, when the fuel pressure is high, the pressure can be decreased by decreasing the effective stroke amount.
[0035]
The control unit 22 receives signals from a sensor 19 for determining the engine cylinder, a sensor 20 for detecting the engine speed and the crank angle, a sensor 21 for detecting the accelerator opening, and the like. The target pressure accumulation chamber pressure, the target fuel injection amount, and the target injection timing are searched based on the engine speed, and the opening / closing timing of the solenoid valve 15 is determined so as to be the target fuel injection amount and injection timing, and the pressure accumulation The opening / closing timing of the effective stroke control valve 8 is controlled so that the fuel pressure in the chamber 7 becomes the target pressure.
[0036]
FIG. 2 shows the overall configuration. The high-pressure fuel in the pressure accumulating chamber (common rail) 7 is injected into the cylinder by a fuel injection injector 11 provided in each cylinder of the diesel engine 30. An exhaust gas recirculation passage 36 branched from the exhaust passage 34 is connected to the intake air passage 35 connected to the intake manifold 31, and the exhaust gas recirculation amount is controlled by an exhaust gas recirculation control valve 37 interposed in the middle. Further, a turbocharger 38 that pressurizes intake air using exhaust energy is provided, and a catalyst 39 that reduces and purifies NOx in the exhaust is installed downstream of the turbocharger 38 in the exhaust passage 34.
[0037]
Then, the control unit 22 performs combustion in the fuel injector 11 separately from the main fuel injection performed near the compression top dead center in order to obtain the amount of HC necessary for reducing NOx in the catalyst 39. A fuel sub-injection is performed at the end of the stroke. In the present invention, at this time, the concentration of HC contained in the exhaust gas is always a minimum amount necessary for the reduction of NOx by the catalyst 39, so that the injection timing from the fuel injection injector 11 is set according to the operating state. It is adjusted.
[0038]
The injection amount required for the sub-injection is very small compared to the main injection and varies depending on the operating state. It is extremely difficult to always control the injection amount from the fuel injection injector 11 to this minute required flow rate with high accuracy. Therefore, the injection amount from the fuel injector 11 is set to the smallest possible injection amount within a range that can be accurately controlled to the target value, and at that time NOx in which the HC concentration in the exhaust gas is reduced is reduced. Therefore, the amount of HC required to reduce NOx is obtained by adjusting the sub-injection timing in accordance with the concentration of NOx generated, that is, by combusting some unnecessary fuel. As a result, the unburnt rate of the fuel is appropriately controlled.
[0039]
For this reason, the control unit 22 receives not only a detection signal representative of the above-described operation state but also a detection signal of the engine cooling water temperature or the in-cylinder pressure, although not shown, and further, the intake gas temperature from the intake air temperature sensor 32, the supercharging Detection signals such as the supercharging pressure from the pressure sensor 33 and the exhaust gas recirculation amount by the valve lift of the exhaust gas recirculation control valve (EGR valve) 37 are input, and the control unit 22 determines the generation state of NOx based on these detection signals. Then, the injection timing of the sub-injection is controlled so that the amount of unburned HC required to reduce this NOx is included in the exhaust gas.
[0040]
Next, the contents of this control executed by the control unit 22 will be described in more detail with reference to the flowchart of FIG.
[0041]
In step S1, the engine speed Ne, the accelerator opening Acc, the supercharging pressure Pb, the in-cylinder maximum pressure Pe, the EGR valve lift Legr, the cooling water temperature Tw, the intake gas temperature Ta, and the like are read. In step S2, a target fuel injection amount (main injection amount) Qs is retrieved from a map stored in the control unit based on the engine speed Ne and the accelerator opening Acc. In step S3, a target EGR valve lift Legrs is obtained by searching a predetermined map from the engine speed Ne, the fuel injection amount Qs, and the engine coolant temperature Tw.
[0042]
Next, in step S4, the basic injection timing ITps of the sub-injection performed separately from the main injection at the end of the combustion stroke is searched from the map based on the engine speed Ne at that time. In step S5, the basic sub-injection timing ITps is changed from the fuel injection amount Qs, the cooling water temperature Tw, the supercharging pressure Pb, the in-cylinder maximum pressure Pe, the intake gas temperature Ta, the target and actual EGR valve lift difference Legr-Legrs. Make corrections based on the above.
[0043]
These correction characteristics are shown in FIGS. 4 to 8, and are set based on the relationship with the generated NOx and the combustion conditions of the sub-injected fuel.
[0044]
If the timing of sub-injection performed at the end of combustion is delayed, the in-cylinder temperature decreases, so the amount of HC discharged without combustion increases, and conversely, the amount of sub-injected fuel that burns in the combustion chamber increases. Thus, the amount of HC discharged is reduced.
[0045]
Therefore, in the present invention, the basic injection amount of sub-injection performed in the latter half of combustion is as small as possible within a range in which there is little variation for each cylinder and cycle, and even a small injection amount can be accurately controlled to the target value. By adjusting the sub-injection timing according to the condition of the unburned rate of the sub-injected fuel at that time, and corresponding to the amount of NOx generated that differs depending on the operation state This makes it possible to supply the minimum necessary amount of HC for the catalyst.
[0046]
For this correction, first, as shown in FIG. 4, as for the fuel injection amount Qs, the retard amount is increased as the fuel injection amount Qs in which the NOx generation amount increases is increased, and is necessary for the reaction at the catalyst 39. Increase HC emissions.
[0047]
On the other hand, in FIG. 5, it correct | amends so that retardation amount may be enlarged, so that cooling water temperature rises. This is because the lower the cooling water temperature, the more the injected fuel adheres to the inner wall of the cylinder and the unburned fuel is discharged at a higher rate. On the contrary, the discharge amount decreases as the cooling water temperature increases. In order to ensure, it is retarded as the cooling water temperature increases.
[0048]
The supercharging pressure is retarded as the supercharging pressure increases as shown in FIG. The higher the supercharging pressure, the later the timing at which the in-cylinder temperature decreases until the later stage of combustion, and the higher the in-cylinder temperature, the lower the unburned rate of the sub-injected fuel. Therefore, even if the injection is performed at the same time, if the boost pressure is increased, the HC emission amount is reduced. In order to correct this, the sub-injection time is delayed.
[0049]
FIG. 7 shows correction characteristics according to the EGR state, and the sub-injection timing is corrected to the retard side as the actual EGR rate is lower than the target EGR rate, that is, as Legr-Legrs is smaller. The lower the actual EGR rate, the higher the oxygen concentration in the working gas in the cylinder, the lower the fuel unburnt rate, and the higher the amount of NOx generated. Therefore, the sub injection timing is retarded as the actual EGR rate falls below the target value.
[0050]
Further, the intake gas temperature in FIG. 8 is corrected so as to be retarded as the intake gas temperature into the cylinder increases. The in-cylinder gas temperature in the later stage of combustion becomes higher as the intake gas temperature becomes higher, and thus the unburned rate decreases. Therefore, the sub-injection timing is delayed as the intake gas temperature becomes higher.
[0051]
FIG. 9 shows correction characteristics in relation to the in-cylinder maximum pressure. The higher the in-cylinder maximum pressure, the better the combustion is performed, the more NOx is generated, and the higher the in-cylinder gas temperature at the later stage of combustion. Therefore, the required discharge amount of HC is ensured by retarding the sub-injection timing as the in-cylinder maximum pressure increases.
[0052]
When the correction value for the sub-injection timing is obtained in this way, the fuel main injection, sub-injection, and further the EGR valve lift are controlled in step S6 of FIG.
[0053]
Next, the overall operation will be described.
[0054]
The NOx generated varies depending on the engine operating conditions. Generally, the amount of NOx generated increases as the engine load increases. Therefore, the amount of HC required for the catalyst 39 for reducing this NOx varies depending on the amount of NOx generated.
[0055]
At the end of the engine combustion stroke, a small amount of fuel is sub-injected from the fuel injector 11, which becomes unburned HC and is supplied to the catalyst 39. The amount of fuel required at this time is much smaller than that of main injection, and it is extremely difficult to accurately inject such a minute amount of fuel in consideration of variations between cylinders and cycles.
[0056]
Therefore, in the present invention, the amount of fuel for sub-injection is set to the smallest possible amount within the range that can be controlled by the fuel injector 11, and the amount of HC discharged is adjusted by changing the injection timing. is doing.
[0057]
That is, part of the fuel injected in the latter half of the combustion burns in the cylinder, and the rest is discharged as it is as unburned HC. If the timing of sub-injection is advanced at this time, the gas temperature in the cylinder will be high and the residence time will also be long, so that most of the injected fuel will be burned, and the discharge ratio in the unburned state will be low. The proportion of fuel discharged while burning increases.
[0058]
Therefore, basically, the injection timing of the sub-injection is changed according to the operating state of the engine, that is, according to the generation state of NOx, and as the amount of NOx generated increases, the injection timing is retarded and the required amount is not yet increased. Fuel HC is discharged.
[0059]
In contrast to controlling the injection amount to be minute, it is not so difficult to advance or delay the injection timing, and it is possible to control with high accuracy.
[0060]
Therefore, the fuel injection amount is set in advance in the minimum range that can be controlled accurately, and the injection timing is advanced or retarded, so that the minimum amount of HC necessary for reducing NOx in the catalyst 39 is accurately supplied. Thus, the reduction reaction is always maintained best by the catalyst 39, and NOx can be suppressed and emission of unburned HC to the outside can be surely reduced.
[0061]
In the present invention, as described above, regarding the injection timing of the sub-injection, not only the fuel injection amount (engine load) but also the relationship with the unburned rate of the sub-injected fuel, specifically, the cooling water temperature, By making corrections based on the relationship between the supercharging pressure, EGR state, intake gas temperature, maximum cylinder pressure, etc., appropriate sub-injection corresponding to the operating conditions can be performed, and the amount of HC supplied to the catalyst 39 can be reduced. Therefore, it is possible to always make an appropriate amount without excess or deficiency for the reduction reaction of NOx.
[0062]
It goes without saying that all of these corrections are not necessarily performed, and one or several of them can be selected as necessary.
[0063]
Next, another embodiment shown in FIG. 10 will be described.
[0064]
In this embodiment, until the catalyst 39 is activated, the above-described sub-injection control is stopped, and wasteful fuel consumption and HC emission are suppressed.
[0065]
For this reason, in FIG. 10, in step S1, the engine speed Ne and the target fuel injection amount (main injection) Qs are read, and in step S2, based on these speed Ne and injection amount Qs, the catalyst as shown in FIG. Search the active area map.
[0066]
In step S3, it is determined whether or not the catalyst is in an active state. If the catalyst is in the active state, the process proceeds to step S4 and sub injection is permitted. On the other hand, when the catalyst is inactive, the process proceeds to step S5 and the sub-injection is not permitted.
[0067]
Therefore, when the sub-injection is permitted, the sub-injection control as shown in FIG. 3 is executed, but when the permission is denied, the sub-injection is not performed.
[0068]
This is because when the engine speed and load are small and the catalyst 39 is not sufficiently raised to the temperature required for the reaction, that is, when the catalyst 39 is inactive, the NOx reduction reaction is performed even if the fuel is sub-injected. Not only that, but the unburned HC is released to the outside as it is, and the fuel consumption is also deteriorated. Therefore, the sub-injection control in such a state is stopped.
[0069]
In order to determine the active state of the catalyst 39, a method in which the temperature in the vicinity of the catalyst is directly or indirectly measured or determined from the history of the engine operating state may be used.
[0070]
Further, regarding the various parameter detection means for correcting the sub-injection timing, for example, the EGR rate is estimated while measuring the intake air amount at that time according to the engine speed and load, etc. Of course, other methods may be used.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a fuel supply system according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram showing the overall configuration.
FIG. 3 is a flowchart of a control operation.
FIG. 4 is a characteristic diagram showing a correction characteristic of a sub-injection timing with respect to a fuel injection amount.
FIG. 5 is a characteristic diagram showing correction characteristics of sub-injection timing for cooling water temperature.
FIG. 6 is a characteristic diagram showing a correction characteristic of sub-injection timing for supercharging pressure.
FIG. 7 is a characteristic diagram showing a correction characteristic of sub injection timing with respect to an EGR rate.
FIG. 8 is a characteristic diagram showing correction characteristics of sub-injection timing with respect to intake gas temperature.
FIG. 9 is a characteristic diagram showing correction characteristics of sub-injection timing for in-cylinder pressure.
FIG. 10 is a flowchart of a control operation according to another embodiment.
FIG. 11 is an explanatory view showing a sub injection region.
[Explanation of symbols]
1 Fuel Injection Pump 7 Fuel Accumulation Chamber 11 Fuel Injection Injector 15 Solenoid Valve 20 Revolution Sensor 21 Acceleration Opening Sensor 22 Control Unit 37 Exhaust Recirculation Control Valve 39 NOx Reduction Catalyst

Claims (8)

A catalyst for purifying NOx provided in the exhaust passage, a fuel injection injector for injecting the pressure-accumulated fuel into the combustion chamber, and an injection timing control device for sub-injecting the fuel at a later stage of combustion separately from the main injection performed near the compression top dead center In the control device for a diesel engine, the sub-injection setting unit that sets the basic timing for performing the sub-injection according to the load so as to delay the basic timing for performing the sub-injection, A control device for a teasel engine, comprising: a sub-injection correcting unit that corrects the basic time so as to be delayed as the unburned rate is lower based on the relationship with the unburned rate of fuel to be sub-injected . The control device for a diesel engine according to claim 1 , wherein the sub-injection correcting means delays the sub-injection timing as the cooling water temperature is higher. The diesel engine control device according to claim 1 or 2 , wherein the sub-injection correcting means delays the sub-injection timing as the supercharging pressure is higher. The control device for a diesel engine according to any one of claims 1 to 3 , wherein the sub-injection correcting means delays the sub-injection timing as the exhaust gas recirculation rate becomes smaller. The diesel engine control device according to any one of claims 1 to 4 , wherein the sub-injection correcting means delays the sub-injection timing as the intake gas temperature is higher. The control device for a diesel engine according to any one of claims 1 to 5 , wherein the sub-injection correcting means delays the sub-injection timing as the cylinder maximum pressure is higher. An NOx purification catalyst provided in the exhaust passage, a fuel injection injector for injecting pressure-accumulated fuel into the combustion chamber, and an injection timing control device for performing sub-injection in the late combustion stage separately from the main injection in which fuel injection is performed near the compression top dead center And a diesel engine control device comprising: a means for detecting the operating state of the engine; and a sub-injection setting means for setting the basic timing for performing the sub-injection according to the load so as to delay as the engine load increases, Sub-injection correction means for correcting the basic time based on the relationship with the unburned ratio of the sub-injected fuel so that the lower the unburned ratio , the means for determining the activation state of the catalyst; A control device for a teal engine, comprising: means for stopping the sub-injection in an active state. 8. The teasel according to claim 7 , wherein the catalyst activity determination means is configured to estimate the activity state of the catalyst from the operating state, or to determine the activity state by directly or indirectly measuring the temperature of the catalyst. Engine control device.

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