JP7077871B2 - 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. In this control device, the fuel injection amount at the time of pilot injection is adjusted so that the ignition delay of the fuel injected into the cylinder by the main injection becomes the target ignition delay. The ignition delay is the length of the period from the injection of fuel from the fuel injection valve to the start of combustion of the fuel. The target ignition delay is the target value of the ignition delay.

In the control device described in Patent Document 1, the relational expression (Equation 1) shown below is used to estimate and calculate the ignition delay τ1 of the fuel injected into the cylinder by the main injection. In the following relational expression (Equation 1), "P1" is the pressure in the cylinder at the compression top dead center at the time of non-combustion, and "T1" is the cylinder at the compression top dead center at the time of non-combustion. The temperature inside. Further, "NE1" is the engine rotation speed, and "CCLD" is the oxygen concentration in the cylinder before combustion. Further, "A1", "B1", "C1", "D1" and "E1" are constants, respectively.

Japanese Unexamined Patent Publication No. 2016-701922

Here, the actual ignition delay of the fuel injected into the cylinder changes depending on the amount of heat generated in the cylinder (that is, the temperature), the amount of oxygen in the cylinder, and the like.
The main injection is done after the pilot injection. Therefore, the ignition delay of the fuel injected into the cylinder by the main injection is accurately calculated without considering the heat generation and oxygen consumption in the cylinder caused by the combustion of the fuel injected into the cylinder by the pilot injection. Can't.

The above relational expression (Equation 1) does not include parameters related to heat generation and oxygen consumption in the cylinder due to combustion of fuel injected into the cylinder by pilot injection. Therefore, even if the ignition delay of the fuel injected into the cylinder by the main injection is calculated using the relational expression (Equation 1), it cannot be said that the accuracy is high.

Therefore, there is a need for a technique for modeling the transition of the heat generation rate in the cylinder due to the combustion of the fuel injected into the cylinder.

The control device for an internal combustion engine 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 cylinder. This control device has an air-fuel ratio calculation unit in the spray that calculates the air-fuel ratio in the spray, which is the air-fuel ratio in the spray of the fuel injected from the fuel injection valve, and an equivalent ratio distribution in the spray as a normal distribution. When, the first equivalent ratio, which is the median value of the distribution of the equivalent ratio, is defined as the value obtained by dividing the theoretical air-fuel ratio by the air-fuel ratio in the spray, which is larger than the first equivalent ratio and the first equivalent. An equivalent ratio calculation unit in which a value smaller than twice the ratio is used as the second equivalent ratio, and a value smaller than the first equivalent ratio and larger than "0" is used as the third equivalent ratio. The first ignition delay, which is the ignition delay of the fuel injected from the fuel injection valve, is calculated using the first equivalent ratio, and the second ignition delay is calculated using the second equivalent ratio. , The ignition delay calculation unit that calculates the third ignition delay using the third equivalent ratio, and the time when the first ignition delay elapses from the start time of fuel injection of the fuel injection valve is the first time. When the time when the second ignition delay elapses from the start time is set as the second time, and the time when the third ignition delay elapses from the start time is set as the third time, the second time is set. The heat generation rate in the period and the heat generation rate in the third period are set to "0", respectively, and the heat generation rate increases from the second period to the first period, and from the first period to the first period. It is provided with an estimation unit for estimating the transition of the heat generation rate after the fuel injection so that the heat generation rate decreases toward the third period. Then, the estimation unit is based on the difference between the third period and the second period and the amount of heat generated in the cylinder due to the combustion of the fuel injected from the fuel injection valve. The heat generation rate in the first period is calculated.

Within the spray of fuel injected from the fuel injection valve, there are variations in the equivalent ratio. According to the above configuration, assuming that the distribution of the equivalent ratio in the spray is a normal distribution, the first equivalent ratio, which is the median value of the distribution of the equivalent ratio, is the value obtained by dividing the stoichiometric air-fuel ratio by the air-fuel ratio in the spray. It is calculated. In addition, a second equivalent ratio larger than the first equivalent ratio and a third equivalent ratio smaller than the first equivalent ratio are also calculated. Then, by using the first equivalent ratio, the second equivalent ratio, and the third equivalent ratio, the first ignition delay, the second ignition delay, and the third ignition delay are calculated, respectively.

Then, the first time, which is the time when the first ignition delay has passed from the start time of the fuel injection of the fuel injection valve, and the second time, which is the time when the second ignition delay has passed from the start time, and the start. The third time, which is the time when the third ignition delay has passed from the time, is specified. Then, it is possible to estimate the transition of the heat generation rate after fuel injection, with the heat generation rate in the first period, the heat generation rate in the second period, and the heat generation rate in the third period at the vertices. At this time, the heat generation rate in the second period and the heat generation rate in the third period are set to "0", respectively, and the heat generation rate in the first period is defined as the third ignition delay and the second ignition delay. It is calculated based on the difference and the amount of heat of the fuel injected from the fuel injection valve.

By performing various estimation calculations as described above, it is possible to model the transition of the heat generation rate in the cylinder due to the combustion of the fuel injected into the cylinder.

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. The figure which modeled the spray of the fuel injected from the fuel injection valve of the internal combustion engine. A graph showing the relationship between the frequency and the equivalent ratio in the normalized spray. The figure which shows the heat generation rate model. Schematic diagram when the main injection is executed after the pilot injection. A flowchart illustrating a process flow when controlling a fuel injection valve. A flowchart explaining the flow of processing when creating a heat generation rate model.

Hereinafter, an embodiment of the control device for an internal combustion engine will be described with reference to FIGS. 1 to 7.
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. 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 cylinder 11 from the fuel injection valve 26, the fuel comes into contact with the compressed air and ignites and burns.

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 flow direction of the exhaust gas. 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, 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. 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 an intake pressure Pim, which is the pressure of air in a 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 output shaft of the internal combustion engine 10, 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.
The control device 60 has a valve control unit 61, an in-spray air-fuel ratio calculation unit 62, an equivalent ratio calculation unit 63, an ignition delay calculation unit 64, an estimation unit 65, and a main ignition delay calculation unit 66 as functional units.

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 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 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. In this case, diffusion combustion may be started while the previously started premixed combustion is still being performed. The region where the diffusion combustion is started while the premixed combustion is still performed is called the region where the premixed combustion and the diffused combustion coexist.

When engine operation is performed in a region where premixed combustion and diffusion combustion coexist, the valve control unit 61 sets the ignition delay target value of the main ignition delay τm, which is the ignition delay of the fuel injected into the cylinder 11 by the main injection. The fuel injection valve 26 is controlled so as to approach τtrg. The ignition delay is the length of the period from the start point of fuel injection of the fuel injection valve 26 to the actual start of combustion of the fuel. The ignition delay target value τtrg is the target of the main ignition delay τm.

For example, the valve control unit 61 can control the length of the main ignition delay τm by adjusting at least one of the fuel injection amount in the pilot injection and the start timing of the pilot injection. In the present embodiment, the length of the main ignition delay τm is controlled by adjusting the fuel injection amount in the pilot injection.

The air-fuel ratio calculation unit 62 in the spray calculates the air-fuel ratio AFsp in the spray, which is the air-fuel ratio in the spray of the fuel injected into the cylinder 11 by the pilot injection. The air-fuel ratio in the spray AFsp is the air-fuel ratio in the spray of the fuel injected into the cylinder 11 from the fuel injection valve 26. The air-fuel ratio in the spray AFsp can be derived by dividing the amount of air in the spray by the amount of fuel in the spray. The amount of air in the spray is calculated based on the volume V of the spray at the end of the pilot injection, the oxygen concentration Cox in the cylinder 11, and the like.

Here, a method of calculating the volume V of the spray will be described with reference to FIG. As shown in FIG. 2, the spray of fuel injected into the cylinder 11 from the fuel injection valve 26 is assumed to have a conical shape. In this case, the volume V of the spray can be calculated by using the known Guang'an formula. That is, the following relational expression (Equation 2) or (Equation 3) is a calculation expression of the spray penetration S. The relational expression (Equation 2) is an expression used when the fuel injection time "t" is less than the splitting time "tk", and the relational expression (Equation 3) is the equation in which the fuel injection time "t" is the splitting time. It is an equation used when it is "tc" or more. The split time "ct" is the time required for the fuel injected from the fuel injection valve 26 to change state from a liquid to a gas.

In the relational expressions (Equation 2) and (Equation 3), "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 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 2) and (Equation 3), "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.

また、以下の関係式（式４）は、噴霧角θの算出式である。関係式（式４）において、「μａ」は、空気の粘性係数であり、予め設定されている。

Further, the following relational expression (Equation 4) is an expression for calculating the spray angle θ. In the relational expression (Equation 4), “μa” is the viscosity coefficient of air and is preset.

そして、以下の関係式（式５）は、噴霧の体積Ｖの算出式である。

The following relational expression (Equation 5) is an expression for calculating the volume V of the spray.

酸素濃度Ｃｏｘは、気筒１１内に導入される空気の量と、気筒１１内に導入されるＥＧＲガスの量とを基に算出する。気筒１１内に導入される空気の量として、例えば、エアフロメータ１０３によって検出される吸入空気量ＧＡを採用することができる。空気のうちの酸素が占める割合は、ＥＧＲガスのうちの酸素が占める割合よりも大きい。そのため、酸素濃度Ｃｏｘは、ＥＧＲ装置４０を介して吸気通路２１に還流するＥＧＲガスの量が多いほど低くなるように算出される。

The oxygen concentration Cox is calculated based on the amount of air introduced into the cylinder 11 and the amount of EGR gas introduced into the cylinder 11. As the amount of air introduced into the cylinder 11, for example, the intake air amount GA detected by the air flow meter 103 can be adopted. The proportion of oxygen in the air is greater than the proportion of oxygen in the EGR gas. Therefore, the oxygen concentration Cox is calculated so that the larger the amount of EGR gas recirculated to the intake passage 21 via the EGR device 40, the lower the oxygen concentration Cox.

When the valve opening of the EGR flow rate adjusting device 42 and the flow rate of the exhaust gas in the exhaust passage 36 are kept constant, the recirculation amount, which is the amount of EGR gas recirculated to the intake passage 21 via the EGR device 40, is the recirculation amount. It can be calculated based on the flow rate of the exhaust gas in the exhaust passage 36 and the valve opening degree of the EGR flow rate adjusting device 42. The flow rate of the exhaust becomes a value corresponding to the intake air amount GA and the engine rotation speed NE.

On the other hand, when at least one of the valve opening degree of the EGR flow rate adjusting device 42 and the exhaust flow rate changes, a response delay occurs in the change in the recirculation amount of the EGR gas in response to the change. In the present embodiment, a map is prepared for estimating how much the change in the recirculation amount is delayed when at least one of the valve opening degree and the exhaust flow rate changes. Therefore, when at least one of the valve opening and the exhaust flow rate changes, the map is used to estimate the recirculation amount.

The equivalent ratio calculation unit 63 calculates the first equivalent ratio Φpt1, the second equivalent ratio Φpt2, and the third equivalent ratio Φpt3. That is, the equivalent ratio calculation unit 63 sets the first equivalent ratio Φpt1, which is the median value of the distribution of the equivalent ratio, as the stoichiometric air-fuel ratio AFst when the distribution of the equivalent ratio in the spray is a normal distribution as shown in FIG. Is calculated as a value divided by the air-fuel ratio in spray AFsp calculated by the air-fuel ratio calculation unit 62 in spray. Further, the equivalent ratio calculation unit 63 sets a value larger than the first equivalent ratio Φpt1 and smaller than twice the value of the first equivalent ratio Φpt1 as the second equivalent ratio Φpt2. Further, the equivalent ratio calculation unit 63 sets a value smaller than the first equivalent ratio Φpt1 and larger than “0” as the third equivalent ratio Φpt3. For example, the second equivalent ratio Φpt2 and the second equivalent ratio Φpt2 so that the difference between the first equivalent ratio Φpt1 and the second equivalent ratio Φpt2 is larger than the difference between the first equivalent ratio Φpt1 and the third equivalent ratio Φpt3. The equivalent ratio Φpt3 of 3 is calculated respectively.

The ignition delay calculation unit 64 calculates the first ignition delay τp1, which is the ignition delay of the fuel injected into the cylinder 11 by the pilot injection, using the first equivalent ratio Φpt1. Further, the ignition delay calculation unit 64 calculates the second ignition delay τp2, which is the ignition delay of the fuel injected from the fuel injection valve 26 by the pilot injection, using the second equivalent ratio Φpt2. Further, the ignition delay calculation unit 64 calculates the third ignition delay τp3, which is the ignition delay of the fuel injected from the fuel injection valve 26 by the pilot injection, using the third equivalent ratio Φpt3.

The ignition delay τ is calculated using the following Arrhenius equation (Equation 6). In the formula (formula 6), "Fuel" is the partial pressure of fuel in the cylinder 11 at the end of the pilot injection, "O2" is the partial pressure of oxygen in the cylinder 11 at the end of the pilot injection, and "T". Is the temperature in the cylinder 11 at the start of pilot injection. Further, "A", "B", "C" and "D" are model constants, which are preset values through experiments and simulations. Specifically, the model constant "B" is set to a value such that the higher the fuel partial pressure "Fuel", the smaller the ignition delay τ. The model constant "C" is set to a value such that the higher the oxygen partial pressure "O2", the smaller the ignition delay τ. The model constant "D" is set to a value such that the higher the temperature "T" in the cylinder 11, the smaller the ignition delay τ can be. For example, the model constants "B" and "C" are set to positive values, and the model constants "D" are set to negative values. The model constant "A" is ignited as the product of the fuel partial pressure "Fuel" to the "B" power, the oxygen partial pressure "O2" to the "C" power, and "exp (D / T)" is larger. It is set to a value that can reduce the delay τ. For example, the model constant "A" is set to a positive value.

燃料分圧「Ｆｕｅｌ」は、気筒１１内における燃料濃度Ｃｆｕｅｌと気筒１１内の圧力である筒内圧力Ｐｃｙとの積として算出される。燃料濃度Ｃｆｕｅｌは、パイロット噴射の終了時点における噴霧内当量比Φａに応じた値となる。パイロット噴射の終了時点における噴霧内当量比Φａは、パイロット噴射を燃料噴射弁２６に行わせる際における噴射量の指示値を基に算出される。

The fuel partial pressure "Fuel" is calculated as the product of the fuel concentration Cfuel in the cylinder 11 and the in-cylinder pressure Pcy which is the pressure in the cylinder 11. The fuel concentration Cfuel is a value corresponding to the in-spray equivalent ratio Φa at the end of the pilot injection. The in-spray equivalent ratio Φa at the end of the pilot injection is calculated based on the indicated value of the injection amount when the pilot injection is performed by the fuel injection valve 26.

The oxygen partial pressure "O2" in the cylinder 11 is calculated as the product of the oxygen concentration Cox in the cylinder 11 and the in-cylinder pressure Pcy.
Further, the temperature "T" in the cylinder 11 at the start of the pilot injection can be estimated based on the intake air temperature Tim and the water temperature Thw. Of course, when a sensor for detecting the temperature in the cylinder 11 is provided, the detected value of the sensor may be adopted as the temperature "T" in the cylinder 11.

Then, when calculating the first ignition delay τp1, the ignition delay calculation unit 64 calculates the fuel concentration Cfuel with the first equivalent ratio Φpt1 as the in-spray equality ratio Φa, and sets the fuel concentration Cfeel and the in-cylinder pressure Pcy. The fuel partial pressure "Fuel" is calculated as the product of. Then, the ignition delay calculation unit 64 calculates the first ignition delay τp1 by substituting the fuel partial pressure “Fuel” calculated in this way into the above equation (Equation 6).

When calculating the second ignition delay τp2, the ignition delay calculation unit 64 calculates the fuel concentration Cfuel with the second equivalent ratio Φpt2 as the in-spray equality ratio Φa, and the product of this fuel concentration Cfeel and the in-cylinder pressure Pcy. The fuel partial pressure "Fuel" is calculated as. Then, the ignition delay calculation unit 64 calculates the second ignition delay τp2 by substituting the fuel partial pressure “Fuel” calculated in this way into the above equation (Equation 6).

When calculating the third ignition delay τp3, the ignition delay calculation unit 64 calculates the fuel concentration Cfuel with the third equivalent ratio Φpt3 as the in-spray equality ratio Φa, and the product of this fuel concentration Cfeel and the in-cylinder pressure Pcy. The fuel partial pressure "Fuel" is calculated as. Then, the ignition delay calculation unit 64 calculates the third ignition delay τp3 by substituting the fuel partial pressure “Fuel” calculated in this way into the above equation (Equation 6).

Of the respective equivalent ratios Φpt1, Φpt2, Φpt3, the second equivalent ratio Φpt2 is the largest, the first equivalent ratio Φpt1 is the second largest, and the third equivalent ratio Φpt3 is the smallest. Therefore, of the ignition delays τp1, τp2, τp3, the second ignition delay τp2 is the shortest, the first ignition delay τp1 is the second shortest, and the third ignition delay τp3 is the longest.

The estimation unit 65 creates a heat generation rate model MDhgr, which is a transition of the heat generation rate Hgr in the cylinder 11 after the pilot injection. That is, as shown in FIG. 4, the time when the first ignition delay τp1 has elapsed from the start time t0 of the pilot injection is defined as the first time t1, and the time when the second ignition delay τp2 has elapsed from the start time t0 is the second. The time t2 of 2 is set, and the time when the third ignition delay τp3 has elapsed from the start time t0 is set as the third time t3. Of each period t1, t2, t3, the second period t2 is the closest to the start time t0, the first period t1 is the second closest to the start time t0, and the third period t3 is the farthest from the start time t0. ing. In this case, the estimation unit 65 sets the heat generation rate Hgr in the second period t2 and the heat generation rate Hgr in the third period t3 to “0”, respectively. Further, in the estimation unit 65, the heat generation rate Hgr increases from the second period t2 to the first period t1, and the heat generation rate Hgr decreases from the first period t1 to the third period t3. As described above, the transition of the heat generation rate Hgr after the pilot injection is estimated, that is, the heat generation rate model MDhgr is created.

The estimation unit 65 calculates the amount of heat Q generated in the cylinder 11 due to the combustion of the fuel based on the amount of fuel injected by the pilot injection. That is, the calorific value Q increases as the fuel injection amount increases. Then, the estimation unit 65 is the first based on the difference between the third period t3 and the second period t2 and the amount of heat Q generated in the cylinder 11 due to the combustion of the fuel injected by the pilot injection. The heat generation rate Hgr at the time t1 is calculated. The calorific value Q corresponds to the area of the triangle formed by connecting the three points in FIG. Therefore, the estimation unit 65 calculates the heat generation rate Hgr at the first time t1 by using the relational expression (Equation 7) shown below.

メイン着火遅れ算出部６６は、メイン噴射によって気筒１１内に噴射された燃料の着火遅れであるメイン着火遅れτｍを算出する。メイン着火遅れτｍは、メイン噴射の開始時期における気筒１１内の温度や圧力に応じた値となる。すなわち、メイン噴射の開始時期における気筒１１内の温度が高いほど、メイン着火遅れτｍが短くなる。また、メイン噴射の開始時期における気筒１１内の圧力が高いほど、メイン着火遅れτｍが短くなる。そして、メイン噴射の開始時期における気筒１１内の温度は、パイロット噴射によって気筒１１内に噴射された燃料の燃焼によって気筒１１内で生じた熱量が多いほど高くなる。また、メイン噴射の開始時期における気筒１１内の圧力は、パイロット噴射によって気筒１１内に噴射された燃料の燃焼によって気筒１１内で生じた熱量が多いほど高くなる。

The main ignition delay calculation unit 66 calculates the main ignition delay τm, which is the ignition delay of the fuel injected into the cylinder 11 by the main injection. The main ignition delay τm is a value corresponding to the temperature and pressure in the cylinder 11 at the start time of the main injection. That is, the higher the temperature in the cylinder 11 at the start time of the main injection, the shorter the main ignition delay τm. Further, the higher the pressure in the cylinder 11 at the start time of the main injection, the shorter the main ignition delay τm. The temperature inside the cylinder 11 at the start time of the main injection becomes higher as the amount of heat generated in the cylinder 11 by the combustion of the fuel injected into the cylinder 11 by the pilot injection increases. Further, the pressure in the cylinder 11 at the start time of the main injection increases as the amount of heat generated in the cylinder 11 due to the combustion of the fuel injected into the cylinder 11 by the pilot injection increases.

Therefore, in the present embodiment, the main ignition delay calculation unit 66 uses the heat generation rate model MDhgr to calculate the amount of heat Q1 generated in the cylinder 11 from the pilot injection to the start time tm of the main injection. .. That is, in the main ignition delay calculation unit 66, when the start time tm of the main injection is between the second time t2 and the third time t3, the closer the start time tm is to the second time t2, the more heat is generated. The calorific value Q1 is calculated so that Q1 is reduced. Further, the main ignition delay calculation unit 66 calculates the calorific value Q1 so that the calorific value Q1 increases as the start time tm is closer to the third time t3. That is, the calorific value Q1 is calculated so that the area of the hatched region in FIG. 5 is the calorific value Q1.

The main ignition delay calculation unit 66 calculates the temperature and pressure in the cylinder 11 at the start time of the main injection based on the calculated calorific value Q1 by using the known energy conservation law and the ideal gas state equation. Then, the main ignition delay calculation unit 66 calculates the main ignition delay τm by using the temperature and pressure in the cylinder 11 at the start time of the main injection calculated in this way. Thereby, the main ignition delay τm can be calculated in consideration of the influence of the combustion of the fuel injected into the cylinder 11 by the pilot injection.

Next, with reference to FIGS. 6 and 7, a processing procedure for injecting fuel from the fuel injection valve 26 will be described.
As shown in FIG. 6, in the first step S11, a model creation process for creating a heat generation rate model MDhgr is executed.

Specifically, as shown in FIG. 7, in step S111, the air-fuel ratio in the spray AFsp is calculated by the air-fuel ratio calculation unit 62 in the spray. In the next step S112, the equivalent ratio calculation unit 63 calculates the first equivalent ratio Φpt1, the second equivalent ratio Φpt2, and the third equivalent ratio Φpt3. Subsequently, in step S113, the ignition delay calculation unit 64 calculates the first ignition delay τp1, the second ignition delay τp2, and the third ignition delay τp3. In the next step S114, the estimation unit 65 creates a heat generation rate model MDhgr. When the heat generation rate model MDhgr is created in this way, the model creation process of step S11 shown in FIG. 6 is completed, and the process proceeds to the next step S12.

In step S12, the main ignition delay τm is calculated by the main ignition delay calculation unit 66 using the created heat generation rate model MDhgr. Subsequently, in step S13, the valve control unit 61 corrects the fuel injection amount in the pilot injection based on the calculated main ignition delay τm and the ignition delay target value τtrg. That is, when the fuel injection amount assumed when calculating the heat generation rate model MDhgr is used as the reference injection amount, and the main ignition delay τm is longer than the ignition delay target value τtrg, the fuel injection amount increases from the reference injection amount. Will be done. This makes it possible to shorten the actual main ignition delay. On the other hand, when the main ignition delay τm is shorter than the ignition delay target value τtrg, the fuel injection amount is reduced from the reference injection amount. As a result, the actual main ignition delay can be lengthened.

When the start time t0 of the pilot injection is reached, the process shifts to step S14. In this step S14, pilot injection is executed by the valve control unit 61 based on the corrected fuel injection amount. Then, when the start time tm of the main injection is reached, the process is shifted to step S15. In this step S15, the valve control unit 61 executes the main injection. After that, a series of processes is temporarily terminated.

The operation and effect of this embodiment will be described.
Within the spray of fuel injected into the cylinder 11 by pilot injection, the equivalent ratio Φ varies. In the present embodiment, the distribution of the equivalent ratio Φ in the spray is assumed to be a normal distribution, and the first equivalent ratio Φpt1, which is the median value of the distribution of the equivalent ratio Φ, is calculated. Further, a second equivalent ratio Φpt2 larger than the first equivalent ratio Φpt1 and a third equivalent ratio Φpt3 smaller than the first equivalent ratio Φpt1 are also calculated. Then, by using the first equivalent ratio Φpt1, the second equivalent ratio Φpt2, and the third equivalent ratio Φpt3, the first ignition delay τp1, the second ignition delay τp2, and the third ignition delay τp3 are calculated, respectively. Will be done.

Then, based on the start time t0 of the pilot injection and the first ignition delay τp1, the second ignition delay τp2, and the third ignition delay τp3, the first period t1, the second period t2, and the third period The time t3 can be obtained. Then, the heat generation rate Hgr after the pilot injection is peaked at the heat generation rate Hgr of the first period t1, the heat generation rate Hgr of the second period t2, and the heat generation rate Hgr of the third period t3. It is possible to estimate the transition of. That is, the heat generation rate model MDhgr can be created. Therefore, it is possible to model the transition of the heat generation rate Hgr in the cylinder 11 due to the combustion of the fuel injected into the cylinder 11 by the pilot injection.

By using the heat generation rate model MDhgr created in this way, it is possible to calculate the main ignition delay τm in consideration of the influence of the combustion of the fuel injected into the cylinder 11 by the pilot injection. Compared with the case where the main ignition delay is calculated without considering the influence of the combustion of the fuel injected into the cylinder 11 by the pilot injection, the main ignition delay τm is actually the fuel injected into the cylinder 11 by the main injection. It is possible to approach the main ignition delay of.

As a result, fuel injection control for bringing the actual main ignition delay closer to the ignition delay target value τtrg can be appropriately performed.
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.

When the main ignition delay τm calculated in step S12 deviates from the ignition delay target value τtrg, the actual main ignition delay is adjusted to approach the ignition delay target value τtrg by adjusting the pilot injection start time t0. You may.

-In the above embodiment, the created heat generation rate model MDhgr can be used for other than the calculation of the main ignition delay τm. For example, based on the heat generation rate model MDhgr, it is possible to predict the transition of the pressure in the cylinder 11 due to the combustion of fuel. By using such a transition of the pressure in the cylinder 11, it is possible to predict the transition of the magnitude of the combustion noise in the cylinder 11.

When the heat generation rate model MDhgr is used in this way, even when the main injection is performed, the heat generation rate model due to the combustion of the fuel injected into the cylinder 11 by the main injection may be created. good.

Further, even when single injection is performed instead of multi-stage injection, a heat generation rate model due to combustion of fuel injected into the cylinder 11 by the injection may be created.

10 ... Internal combustion engine, 11 ... Cylinder, 26 ... Fuel injection valve, 60 ... Control device, 62 ... Air-fuel ratio calculation unit in spray, 63 ... Equivalent ratio calculation unit, 64 ... Ignition delay calculation unit, 65 ... Estimating unit, 66 ... Main ignition delay calculation 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 cylinder.
An air-fuel ratio calculation unit in the spray that calculates the air-fuel ratio in the spray, which is the air-fuel ratio in the spray of the fuel injected from the fuel injection valve, and
When the distribution of the equivalent ratio in the spray is a normal distribution, the first equivalent ratio, which is the median value of the distribution of the equivalent ratio, is defined as the theoretical air fuel ratio divided by the air fuel ratio in the spray, and the first A value that is larger than the equivalent ratio and smaller than twice the value of the first equivalent ratio is defined as the second equivalent ratio, and is smaller than the first equivalent ratio and larger than "0". Equivalent ratio calculation unit with the third equivalent ratio,
The first ignition delay, which is the ignition delay of the fuel injected from the fuel injection valve, is calculated using the first equivalent ratio, and the second ignition delay is calculated using the second equivalent ratio. An ignition delay calculation unit that calculates the third ignition delay using the third equivalent ratio, and an ignition delay calculation unit.
The time when the first ignition delay has elapsed from the start time of fuel injection of the fuel injection valve is defined as the first period, and the period when the second ignition delay has elapsed from the start time is defined as the second period. When the time when the third ignition delay has elapsed from the start time is set as the third time, the heat generation rate in the second time and the heat generation rate in the third time are set to "0", respectively, and the first time. The heat generation rate after fuel injection increases so that the heat generation rate increases from the second period to the first period, and the heat generation rate decreases from the first period to the third period. Equipped with an estimation unit that estimates the transition of
The estimation unit is based on the difference between the third period and the second period and the amount of heat generated in the cylinder due to the combustion of the fuel injected from the fuel injection valve. A control device for an internal combustion engine that calculates the heat generation rate at the time of.

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