JP7099183B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to an internal combustion engine control device applied to a compression self-ignition type internal combustion engine.

Patent Document 1 causes the fuel injection valve to perform pilot injection before the piston reaches the compression top dead center, and then causes the fuel injection valve to perform the main injection when the piston reaches the vicinity of the compression top dead center. An example of a control device for an internal combustion engine is described.

Further, in the control device described in Patent Document 1, the change in the pressure in the cylinder is changed in order to suppress the combustion of the fuel injected into the cylinder by the pilot injection, that is, the increase in the combustion noise caused by the premixed combustion. Pilot injection is performed after the time when the rate is maximum.

Japanese Unexamined Patent Publication No. 2017-180140

When the fuel injected into the cylinder by pilot injection burns, heat generated by the combustion of the fuel is generated in the cylinder. As a result of various experiments and simulations, the inventor of the present invention states that the higher the peak value of the heat generation rate associated with the combustion of the fuel injected into the cylinder by the pilot injection, the greater the combustion noise associated with the pilot injection. I got the knowledge. According to this knowledge, even if the pilot injection is performed after the time when the rate of change of the pressure in the cylinder becomes maximum, the peak value of the heat generation rate due to the combustion of the fuel injected into the cylinder by the pilot injection is If it is high, the combustion noise cannot be reduced.

The internal combustion engine control device for solving the above problems is applied to a compression self-ignition type internal combustion engine provided with a fuel injection valve for injecting fuel into a combustion chamber partitioned in a cylinder. Further, this control device is a device that causes the fuel injection valve to perform pilot injection and then causes the fuel injection valve to perform main injection. When the time when the piston reaches the compression top dead point, the time corresponding to the time, or the time when the combustion of the fuel injected into the combustion chamber by the main injection is set as the specified time, the control device performs the pilot injection. A valve control unit is provided for causing the fuel injection valve to perform the pilot injection so that the pilot arrival time, which is the time when the fuel injected into the combustion chamber reaches the wall surface of the combustion chamber, is the specified time.

The ignition delay is the length of the period from the start of fuel injection by pilot injection to the start of combustion of the fuel injected into the combustion chamber by pilot injection. In this case, the inventor of the present invention states that the longer the ignition delay, the smaller the peak value of the heat generation rate associated with the combustion of the fuel injected into the combustion chamber by the pilot injection, that is, the smaller the combustion noise associated with the pilot injection. I got the knowledge.

By advancing the start time of the pilot injection, the ignition delay of the fuel injected into the combustion chamber by the pilot injection can be lengthened. However, if the start timing of the pilot injection is advanced too much, the exhaust properties may deteriorate. That is, if the start time of the pilot injection is advanced, the fuel injected into the combustion chamber by the pilot injection can easily reach the wall surface of the combustion chamber. The more the amount of fuel adhered to the wall surface at the time when the combustion of the fuel injected into the combustion chamber by the main injection is started, the more likely the exhaust property is deteriorated.

Therefore, in the above configuration, the fuel injection valve is made to perform the pilot injection so that the pilot arrival time becomes the specified time. As a result, while setting the start time of the pilot injection to the advance side, among the fuel injected into the combustion chamber by the pilot injection, the fuel injected by the main injection adheres to the wall surface at the start of combustion. It is possible to suppress an increase in the amount of fuel.

Therefore, it is possible to reduce the combustion noise caused by the pilot injection while suppressing the deterioration of the exhaust property.

The figure which shows the functional structure of the control device which is one Embodiment of the control device of the internal combustion engine, and the schematic structure of the internal combustion engine controlled by the control device. Schematic diagram of the internal combustion engine. A graph showing the relationship between the peak value of heat generation rate and combustion noise. A graph showing the relationship between the ignition delay and the peak value of the heat generation rate. The graph which shows the relationship between the start time of a pilot injection and the hydrocarbon concentration in an exhaust gas. A flowchart illustrating a processing routine executed when a pilot injection is performed on a fuel injection valve.

Hereinafter, an embodiment of the control device for an internal combustion engine will be described with reference to FIGS. 1 to 6.
FIG. 1 illustrates the control device 60 of the present embodiment and the internal combustion engine 10 controlled by the control device 60. The internal combustion engine 10 is a compression self-ignition type internal combustion engine. The internal combustion engine 10 includes a plurality of cylinders 11 and an exhaust-driven turbocharger 12. In the intake passage 21 of the internal combustion engine 10, an air cleaner 22, a compressor 13 of a supercharger 12, an intercooler 23, and a throttle valve 24 are arranged in order from the upstream in the air flow direction. In the intake passage 21, the air filtered by the air cleaner 22 is sent out in a compressed state by the compressor wheel 13a built in the compressor 13. The air compressed in this way is cooled by the intercooler 23. Then, the intake air amount, which is the amount of air introduced into the cylinder 11 through the intake passage 21, is adjusted through the control of the opening degree of the throttle valve 24.

The internal combustion engine 10 includes the same number of fuel injection valves 26 as the number of cylinders 11. Each fuel injection valve 26 injects fuel directly into the corresponding cylinder 11. Specifically, as shown in FIG. 2, the fuel injection valve 26 injects fuel into the combustion chamber 50 partitioned in the cylinder 11. The combustion chamber 50 is partitioned by the peripheral wall of the cylinder 11 and the top surface of the piston 51. The wall surface 50a of the combustion chamber 50 is formed by the peripheral wall of the cylinder 11 and the top surface of the piston 51 that partition the combustion chamber 50.

Returning to FIG. 1, fuel is supplied to each fuel injection valve 26 by the fuel supply device 27. The fuel supply device 27 has a supply pump 29 for pumping the fuel stored in the fuel tank through the supply passage 28, and a common rail 30 for temporarily storing the fuel pressurized by the supply pump 29. There is. The fuel in the common rail 30 is supplied to each fuel injection valve 26. Then, when the fuel is injected into the combustion chamber 50 from the fuel injection valve 26, the fuel comes into contact with the compressed air and ignites and burns. When the fuel burns in the combustion chamber 50 in this way, the piston 51 shown in FIG. 2 moves in the cylinder 11 in the direction of expanding the volume of the combustion chamber 50. As a result, the crank shaft 53 connected to the piston 51 via the connecting rod 52 rotates.

Returning to FIG. 1, the exhaust gas generated by the combustion of fuel in each cylinder 11 is discharged to the exhaust passage 36. In the exhaust passage 36, the turbine 14 of the supercharger 12 and the exhaust purification device 37 are arranged in order from the upstream in the exhaust flow direction. The exhaust gas purification device 37 collects particulate matter in the exhaust gas and purifies the exhaust gas.

The turbine wheel 14a incorporated in the turbine 14 is connected to the compressor wheel 13a via the connecting shaft 15. Therefore, when the turbine wheel 14a rotates due to the flow of the exhaust gas, the compressor wheel 13a rotates in synchronization with the rotation of the turbine wheel 14a. As a result, the air is pressurized by the compressor 13. The exhaust spray port to the turbine wheel 14a of the turbine 14 is provided with a variable nozzle 16 that changes the opening area of the exhaust spray port according to a change in the nozzle opening degree. By adjusting the nozzle opening degree of the variable nozzle 16, the flow force of the exhaust gas blown to the turbine wheel 14a can be adjusted.

The internal combustion engine 10 is provided with an EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust passage 36 as EGR gas to the intake passage 21. The EGR device 40 is an EGR flow rate adjusting device that adjusts the flow rate of EGR gas to the EGR passage 41 that takes out exhaust gas from the portion of the exhaust passage 36 upstream of the turbine 14 and the intake passage 21 via the EGR passage 41. It has 42 and. The EGR passage 41 connects a portion of the intake passage 21 on the downstream side of the throttle valve 24 and a portion of the exhaust passage 36 on the upstream side of the turbine 14. The EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas flowing through the EGR passage 41. When the valve of the EGR flow rate adjusting device 42 is open, the EGR gas flowing from the exhaust passage 36 into the EGR passage 41 is cooled by the EGR cooler 43 and then passed through the EGR flow rate adjusting device 42 to the intake passage 21. Will be introduced to.

Signals are input to the control device 60 from various sensors such as an intake pressure sensor 101, an intake temperature sensor 102, an air flow meter 103, a water temperature sensor 104, a boost pressure sensor 105, a crank angle sensor 106, and a fuel pressure sensor 107. ..

The intake pressure sensor 101 detects the intake pressure Pim, which is the air pressure in the portion downstream of the throttle valve 24 in the intake passage 21, and outputs a signal corresponding to the detected intake pressure Pim. The intake air temperature sensor 102 detects the intake air temperature Tim, which is the temperature of the air in the portion downstream of the intercooler 23 in the intake passage 21, and outputs a signal corresponding to the detected intake air temperature Tim. The air flow meter 103 detects the intake air amount GA, which is the flow rate of air in the portion upstream of the compressor 13 in the intake passage 21, and outputs a signal corresponding to the detected intake air amount GA. The water temperature sensor 104 detects the water temperature Thw, which is the temperature of the engine cooling water flowing in the cylinder block of the internal combustion engine 10, and outputs a signal corresponding to the detected water temperature Thw. The supercharging pressure sensor 105 detects the supercharging pressure BP by the supercharger 12 and outputs a signal corresponding to the detected supercharging pressure BP. The boost pressure sensor 105 detects the gauge pressure based on the atmospheric pressure as the boost pressure BP. The crank angle sensor 106 detects the engine rotation speed NE, which is the rotation speed of the crank shaft 53, and outputs a signal corresponding to the detected engine rotation speed NE. The fuel pressure sensor 107 detects the common rail pressure Pcr, which is the pressure of the fuel in the common rail 30, and outputs a signal corresponding to the detected common rail pressure Pcr.

Then, the control device 60 controls the engine operation based on the output signals of various sensors 101 to 107. Such a control device 60 has a valve control unit 61 as a functional unit.
The valve control unit 61 controls the drive of the fuel injection valve 26. Specifically, when the fuel is burned in the cylinder 11, the fuel injection valve 26 is made to perform the pilot injection and the main injection. The pilot injection is a fuel injection performed before the piston 51 reciprocating in the cylinder 11 reaches the compression top dead center. The main injection is a fuel injection executed after the pilot injection, and is a fuel injection performed when the piston 51 reaches the vicinity of the compression top dead center. When fuel is injected into the cylinder 11 by pilot injection, premixed combustion is performed in the cylinder 11 and the temperature in the cylinder 11 rises. In this way, the main injection is performed in a state where the temperature inside the cylinder 11 is high. Then, diffusion combustion is performed in the cylinder 11.

It should be noted that such multi-stage injection is also performed when raising the exhaust temperature for the purpose of regenerating the filter (DPF) provided in the exhaust passage 36. In such a case, the main injection is performed after the piston 51 reaches the compression top dead center. Even when the main injection is performed after the piston 51 reaches the compression top dead center in this way, the pilot injection is performed before the piston 51 reaches the compression top dead center.

The length of the period from the start of fuel injection of the fuel injection valve 26 to the actual start of combustion of the fuel is called the ignition delay τ.
In the present embodiment, when the pilot injection is performed by the fuel injection valve 26, the valve control unit 61 sets the fuel injection valve 26 so that the combustion noise during the premixed combustion accompanying the pilot injection does not increase. Control. The combustion noise is noise caused by the combustion of fuel in the cylinder 11.

When fuel is injected into the cylinder 11 by pilot injection, the heat generation rate in the cylinder 11 at this time gradually increases with the passage of time when the combustion of the fuel is started. Then, the heat generation rate gradually decreases with the passage of time after reaching the peak value Pk.

As a result of conducting various experiments and simulations, the inventor of the present invention obtained the following findings.
(Knowledge 1) As shown in FIG. 3, the higher the peak value Pk of the heat generation rate, the larger the combustion noise.
(Knowledge 2) When premixed combustion is performed in the cylinder 11 by executing the pilot injection, but diffusion combustion is not performed, ignition of the fuel injected into the cylinder 11 by the pilot injection is performed as shown in FIG. The longer the delay τ, the lower the peak value Pk of the heat generation rate.

The ignition delay τ becomes longer as the pilot injection start timing TC is set to the advance side. Therefore, by setting the start timing TC to the advance side timing, it is possible to reduce the combustion noise when the premixed combustion accompanying the pilot injection is performed. However, if the pilot injection start time TC is set to the advance side, as shown in FIG. 5, the concentration of hydrocarbons in the exhaust gas discharged from the inside of the cylinder 11 to the exhaust passage 36 becomes high, and the exhaust properties may deteriorate. There is.

When the start time TC of the pilot injection is on the advance side of the predetermined time TCTh, the amount of fuel adhering to the wall surface tends to increase as the start time TC is set to the advance side. The start time of combustion of the fuel injected into the cylinder 11 by the main injection is defined as the main combustion time. The amount of fuel adhered to the wall surface referred to here is the amount of the spray of fuel injected into the cylinder 11 by pilot injection that reaches the wall surface 50a of the combustion chamber 50 by the main combustion time. The fuel adhering to the wall surface 50a is cooled by cooling water or the like flowing in the cylinder block. Therefore, the fuel adhering to the wall surface 50a is difficult to burn in the combustion chamber 50. That is, the larger the amount of adhesion to the wall surface, the more likely it is that incomplete combustion will occur. Therefore, the larger the amount of adhesion to the wall surface, the higher the concentration of hydrocarbons in the exhaust gas discharged from the inside of the cylinder 11 to the exhaust passage 36, that is, the more easily the exhaust properties deteriorate.

Therefore, the valve control unit 61 sets the start time TC within a range in which the start time TC of the pilot injection does not become the time on the advance side of the predetermined time TCTh, and starts the pilot injection from the set start time TC. The predetermined time TCTh in FIG. 5 is a time slightly retarded from the main combustion time.

Next, with reference to FIG. 6, a processing routine executed by the valve control unit 61 when the fuel injection valve 26 is to perform the pilot injection will be described. This processing routine is executed when the fuel injection valve 26 is made to perform pilot injection.

In the first step S11 in this processing routine, the tentative start time TCa of the pilot injection is determined. That is, the start time TC determined at the time of the previous execution of this processing routine is determined as the provisional start time TCa. If this processing routine is executed for the first time after the start of engine operation, the provisional start time TCa is set as a preset reference time.

Subsequently, in step S12, the spray arrival time TSR, which is a predicted value of the time when the fuel spray injected from the fuel injection valve 26 reaches the wall surface 50a of the combustion chamber 50, is calculated. The spray arrival time TSR is a predicted value of the time when the spray reaches the wall surface 50a when the fuel injection of the fuel injection valve 26 is started at the temporary start time TCa.

For example, by using the following relational expression (Equation 1) or (Equation 2), it is the time required for the fuel spray to reach the wall surface 50a of the combustion chamber 50 after the fuel injection of the fuel injection valve 26 is started. The fuel injection time "t" is calculated. The relational expression (Equation 1) is an expression used when the injection time "t" is less than the split time "tk", and the relational expression (Equation 2) is an expression in which the injection time "t" is equal to or more than the split time "tk". It is an expression that is sometimes used. The split time "ct" is the time required for the fuel injected from the fuel injection valve 26 to change its state from a liquid to a gas.

In the relational expressions (Equation 1) and (Equation 2), "S" is a linear distance from the injection hole of the fuel injection valve 26 to the wall surface 50a of the combustion chamber 50 in the traveling direction of the fuel injected from the fuel injection valve 26. Is. Further, "ΔP" is the difference between the common rail pressure Pcr and the in-cylinder pressure Pcy. The in-cylinder pressure Pcy can be estimated based on the amount of air filled in the cylinder 11 and the position of the piston 51 in the cylinder 11. Of course, when a sensor for detecting the pressure in the cylinder 11 is provided, the detected value of this sensor may be adopted as the in-cylinder pressure Pcy. Further, in the relational expressions (Equation 1) and (Equation 2), "ρf" is the fuel density and "ρa" is the air density. “D0” is the diameter of the injection hole of the fuel injection valve 26.

そして、関係式（式１）又は（式２）を用いて噴射時間「ｔ」を算出した場合、仮の開始時期ＴＣａに噴射時間「ｔ」を加算した値が、噴霧到達時期ＴＳＲとして算出される。

When the injection time "t" is calculated using the relational expression (Equation 1) or (Equation 2), the value obtained by adding the injection time "t" to the provisional start time TCa is calculated as the spray arrival time TSR. To.

Then, in the next step S13, the time deviation ΔT, which is the deviation between the preset predetermined time Ttdc and the spray arrival time TSR, is calculated. Specifically, the value obtained by subtracting the spray arrival time TSR from the specified time Ttdc is calculated as the time deviation ΔT. In the present embodiment, the specified time Ttdc is set in advance at the time when the piston 51 reaches the compression top dead center. Therefore, when the main injection is performed when the piston 51 reaches the vicinity of the compression top dead center, the specified time Ttdc is the main combustion which is the start time of combustion of the fuel injected into the cylinder 11 by the main injection. It will be close to the time.

Subsequently, in step S14, it is determined whether or not the absolute value of the timing deviation ΔT is within a predetermined range. The predetermined range is a range set for determining that there is almost no deviation between the specified time Ttdc and the spray arrival time TSR. Therefore, when it is determined that the absolute value of the timing deviation ΔT is within a predetermined range (S14: YES), the process is shifted to the next step S15. In step S15, the start time TC of the pilot injection is set as the provisional start time TCa. Then, in the next step S16, when the start time TC set in step S15 is reached, the pilot injection is executed. After that, this processing routine is temporarily terminated.

On the other hand, if it is not determined in step S14 that the absolute value of the timing deviation ΔT is within a predetermined range (NO), the process is shifted to the next step S17. In step S17, it is determined whether or not the timing deviation ΔT is smaller than “0”. That is, it is determined whether or not the spray arrival time TSR is on the retard side of the specified time Ttdc. When the timing deviation ΔT is larger than “0”, assuming that the tentative start timing TCa starts the pilot injection, when the combustion of the fuel injected into the cylinder 11 by the main injection starts, the pilot injection causes the pilot injection into the cylinder 11. It can be inferred that the spray of the injected fuel reaches the wall surface 50a of the combustion chamber 50. On the other hand, when the timing deviation ΔT is smaller than “0”, even if the pilot injection is started by the temporary start timing TCa, the fuel spray injected into the cylinder 11 by the pilot injection does not reach the wall surface 50a. It can be inferred that the combustion of the fuel injected into the cylinder 11 is started by the main injection. That is, it can be determined that the exhaust property is hardly deteriorated even if the start time TC of the pilot injection is set to the time on the advance side of the temporary start time TCa.

Therefore, when it is determined that the timing deviation ΔT is smaller than “0” (S17: YES), the process proceeds to step S18. In step S18, an advance angle process is executed in which the start timing TC of the pilot injection is changed to a timing on the advance angle side of the provisional start timing TCa. In this advance processing, for example, a value obtained by subtracting a preset unit change amount from the provisional start time TCa is calculated as the start time TC. In the advance angle processing, for example, the time on the advance angle side of the provisional start time TCa may be calculated as the start time TC for the time corresponding to the time deviation ΔT or the time deviation ΔT.

Then, in the next step S16, when the start time TC set in step S18 is reached, the pilot injection is executed. After that, this processing routine is temporarily terminated.
On the other hand, if it is not determined in step S17 that the timing deviation ΔT is smaller than “0” (YES), the process is shifted to step S19. In step S19, a retarding process is executed in which the pilot injection start timing TC is changed to a timing on the retard side of the provisional start timing TCa. In this retard processing, for example, a value obtained by adding only a preset unit change amount to the provisional start time TCa is calculated as the start time TC. In the advance angle processing, for example, the time on the retard side of the provisional start time TCa may be calculated as the start time TC for the time corresponding to the time deviation ΔT or the time deviation ΔT.

Then, in the next step S16, when the start time TC set in step S19 is reached, the pilot injection is executed. After that, this processing routine is temporarily terminated.
The operation and effect of this embodiment will be described.

When the time when the spray of fuel injected into the combustion chamber 50 by the pilot injection reaches the wall surface 50a of the combustion chamber 50 is set as the pilot arrival time, the pilot injection is the fuel injection valve so that the pilot arrival time becomes the specified time Ttdc. It is executed at 26. Specifically, when the spray arrival time TSR calculated based on the provisional start time TCa is on the retard side of the specified time Ttdc, the pilot injection start time TC is higher than the provisional start time TCa. It is set at the time on the advance side. Then, the pilot injection is started from the set start time TC.

On the other hand, when the spray arrival time TSR calculated based on the provisional start time TCa is on the advance side of the specified time Ttdc, the pilot injection start time TC is on the retard side of the provisional start time TCa. It is set at the time of. Then, the pilot injection is started from the set start time TC.

By adjusting the start time TC in this way, the pilot arrival time can be brought closer to the specified time Ttdc. As a result, while setting the start timing TC of the pilot injection to the advance side, among the fuels injected into the combustion chamber 50 by the pilot injection, the wall surface 50a is reached at the start of combustion of the fuel injected by the main injection. It is possible to suppress an increase in the amount of attached fuel. When the specified time Ttdc is almost the same time as the actual main combustion time, the combustion of the fuel injected into the combustion chamber 50 by the main injection can be started with almost no fuel adhering to the wall surface 50a. It will be possible.

Therefore, it is possible to reduce the combustion noise caused by the pilot injection while suppressing the deterioration of the exhaust properties.
The above embodiment can be modified and implemented as follows. The above embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

The specified time Ttdc may be a time different from the time when the piston 51 reaches the compression top dead center as long as it corresponds to the time when the piston 51 reaches the compression top dead center. For example, a time slightly deviated from the time when the piston 51 reaches the compression top dead center may be set as a specified time Ttdc.

-The main combustion timing actually changes depending on the operating condition of the internal combustion engine 10. For example, the main combustion time changes depending on the start time of the main injection and the state in the combustion chamber 50 (temperature, pressure, oxygen concentration, etc. in the combustion chamber 50). Therefore, if the main combustion time can be estimated, the estimated value of the main combustion time may be set to the specified time Ttdc.

The pilot arrival time varies depending on the engine rotation speed NE, the fuel injection amount in the pilot injection, the amount of air filled in the cylinder 11, and the difference "ΔP" between the common rail pressure Pcr and the cylinder pressure Pcy at the time of fuel injection. Therefore, a map for calculating the correction coefficient of the pilot arrival time is prepared in advance for each parameter that affects the pilot arrival time in this way, and the pilot arrival time is based on the correction coefficient derived using each of these maps. May be calculated. Then, based on the pilot arrival time calculated in this way, the pilot injection start time TC may be determined and the pilot injection may be executed.

For example, in a map showing the relationship between the engine rotation speed NE and the correction coefficient, the correction coefficient changes so that the higher the engine rotation speed NE, the longer the pilot arrival time.
Further, in the map showing the relationship between the fuel injection amount and the correction coefficient in the pilot injection, the correction coefficient changes so that the pilot arrival time becomes shorter as the fuel injection amount increases.

Further, in the map showing the relationship between the amount of air filled in the cylinder 11 and the correction coefficient, the correction coefficient changes so that the pilot arrival time becomes longer as the amount of air increases.
Further, in the map showing the relationship between the difference “ΔP” between the common rail pressure Pcr and the in-cylinder pressure Pcy and the correction coefficient, the larger the difference “ΔP”, the shorter the correction coefficient changes so that the pilot arrival time becomes shorter.

10 ... Internal combustion engine, 11 ... Cylinder, 26 ... Fuel injection valve, 50 ... Combustion chamber, 50a ... Wall surface, 51 ... Piston, 60 ... Control device, 61 ... Valve control unit.

Claims (1)

It is applied to a compression self-ignition type internal combustion engine equipped with a fuel injection valve that injects fuel into the combustion chamber partitioned in the cylinder.
A control device for an internal combustion engine that causes the fuel injection valve to perform pilot injection and then causes the fuel injection valve to perform main injection.
When the specified time is the time when the piston reaches the compression top dead center or the time when the combustion of the fuel injected into the combustion chamber by the main injection is set as the specified time.
A valve control unit that causes the fuel injection valve to perform the pilot injection so that the pilot arrival time, which is the time when the fuel injected into the combustion chamber by the pilot injection reaches the wall surface of the combustion chamber, is the specified time. The control device of the internal combustion engine.

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