阅读说明：本技术 内燃机的控制装置及控制方法 (Control device and control method for internal combustion engine ) 是由 西田健太郎 于 2019-08-16 设计创作，主要内容包括：提供内燃机的控制装置及控制方法。控制装置具备阀控制部及目标算出部。阀控制部构成为,以通过主喷射而喷射到汽缸内的燃料的着火延迟与着火延迟目标值的背离变小的方式,控制燃料喷射阀。目标算出部构成为,在扩散燃烧和预混合燃烧混合存在的区域中的内燃机运转时,以推定的汽缸内的燃料的着火性越高则着火延迟目标值越小的方式,算出着火延迟目标值。(Provided are a control device and a control method for an internal combustion engine. The control device includes a valve control unit and a target calculation unit. The valve control unit is configured to control the fuel injection valve such that a deviation between an ignition delay of fuel injected into the cylinder by the main injection and an ignition delay target value is reduced. The target calculation unit is configured to calculate the ignition delay target value such that the ignition delay target value becomes smaller as the estimated ignitability of the fuel in the cylinder is higher during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.)

1. A control device for an internal combustion engine configured to control a compression self-ignition type internal combustion engine provided with a fuel injection valve for injecting fuel into a cylinder, the control device being configured to cause the fuel injection valve to perform main injection after causing the fuel injection valve to perform pre-injection, the control device comprising:

a valve control unit configured to control the fuel injection valve such that a deviation between an ignition delay of the fuel injected into the cylinder by the main injection and an ignition delay target value that is a target of the ignition delay is reduced; and

the target calculation unit is configured to calculate the ignition delay target value such that the ignition delay target value becomes smaller as the ignition quality of the fuel in the cylinder estimated based on the parameter for changing the ignition quality of the fuel in the cylinder is higher during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.

2. The control apparatus of an internal combustion engine according to claim 1,

the parameter includes a partial pressure of fuel in the cylinder, and the target calculation unit is configured to estimate that the higher the partial pressure of fuel in the cylinder is, the higher the ignitability of fuel in the cylinder is.

3. The control apparatus of an internal combustion engine according to claim 1 or 2,

the parameter includes an oxygen partial pressure in the cylinder, and the target calculation unit is configured to estimate that the higher the oxygen partial pressure in the cylinder is, the higher the ignitability of the fuel in the cylinder is.

4. The control device for an internal combustion engine according to any one of claims 1 to 3,

the parameter includes a temperature in the cylinder, and the target calculation unit is configured to estimate that the higher the temperature in the cylinder is, the higher the ignitability of the fuel in the cylinder is.

5. The control apparatus of an internal combustion engine according to claim 1,

the parameters including a partial pressure of fuel within the cylinder, a partial pressure of oxygen within the cylinder, and a temperature within the cylinder,

the control device includes an index calculation unit configured to calculate an index of ignitability of the fuel based on a partial pressure of the fuel in the cylinder, a partial pressure of oxygen in the cylinder, and a temperature in the cylinder,

the target calculation unit is configured to calculate the ignition delay target value based on the index calculated by the index calculation unit,

the index calculation unit is configured to calculate the index using an equation shown below when τ 0 is defined as the index, Pfuel is defined as a fuel partial pressure in the cylinder, O2 is defined as an oxygen partial pressure in the cylinder, T is defined as a temperature in the cylinder, m (T) is defined as a function having the temperature in the cylinder as a variable, and A, B and C are defined as model constants:

6. the control device for an internal combustion engine according to any one of claims 1 to 5,

the valve control unit is configured to adjust at least one of a fuel injection amount in the pre-injection and a start timing of the pre-injection to cause the ignition delay to approach the ignition delay target value.

7. A method of controlling a compression self-ignition type internal combustion engine including a fuel injection valve for injecting fuel into a cylinder, the method comprising:

performing a pre-injection using the fuel injection valve;

performing a main injection with the fuel injection valve after the pre-injection;

controlling the fuel injection valve in such a manner that a deviation between an ignition delay of the fuel injected into the cylinder by the main injection and an ignition delay target value that is a target of the ignition delay becomes smaller; and

the ignition delay target value is calculated so that the ignition delay target value becomes smaller as the ignition quality of the fuel in the cylinder estimated based on the parameter for changing the ignition quality of the fuel in the cylinder is higher during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.

Technical Field

The present disclosure relates to a control device and a control method for an internal combustion engine configured to control a compression self-ignition type internal combustion engine.

Background

International publication No. 2013/051109 discloses an example of a control device for an internal combustion engine. In this internal combustion engine, the control device causes the fuel injection valve to perform the pre-injection before the piston reaches compression top dead center, and thereafter causes the fuel injection valve to perform the main injection when the piston reaches the vicinity of compression top dead center. When fuel is injected into the cylinder by the pre-injection, the premixed combustion is performed in the cylinder, and the temperature in the cylinder increases. When the main injection is performed in a state where the temperature in the cylinder is sufficiently high, diffusion combustion is performed in the cylinder.

In the control device, the ignition delay is estimated as a length of a period from a start time point of fuel injection from the fuel injection valve to a start of combustion of the fuel. The ignition delay target value, which is a target of the ignition delay, is derived using a predetermined arithmetic expression having the engine speed and the engine load factor as variables. Then, the opening degree of the nozzle vanes of the supercharger is adjusted so that the ignition delay becomes the target ignition delay value.

Here, when the opening degree of the nozzle vane of the supercharger is increased, the supercharging pressure of the supercharger can be decreased. Further, by reducing the boost pressure, the ignition delay can be extended.

Therefore, the control device described above increases the opening degree of the nozzle vanes when the ignition delay is shorter than the target ignition delay value. In contrast, the control device decreases the opening degree of the nozzle vanes when the ignition delay is longer than the target ignition delay value.

When the internal combustion engine is operated, combustion noise, which is noise generated by combustion in the cylinder, is generated. In addition, during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed, the magnitude of the combustion noise may vary even if the ignition delay is maintained to be equal to the target ignition delay value by adjusting the supercharging pressure.

The region where the diffusion combustion and the premixed combustion are mixed is a region where the premixed combustion starts earlier than the diffusion combustion, but the diffusion combustion starts during the process of the premixed combustion.

Disclosure of Invention

The 1 st aspect provides a control device configured to control a compression self-ignition internal combustion engine provided with a fuel injection valve for injecting fuel into a cylinder, and configured to cause the fuel injection valve to perform main injection after causing the fuel injection valve to perform pilot injection. The control device includes a valve control unit and a target calculation unit. The valve control unit is configured to control the fuel injection valve such that a deviation between an ignition delay of fuel injected into the cylinder by the main injection and an ignition delay target value, which is a target of the ignition delay, is reduced. The target calculation unit is configured to calculate the ignition delay target value such that the ignition delay target value becomes smaller as the ignition quality of the fuel in the cylinder estimated based on the parameter for changing the ignition quality of the fuel in the cylinder is higher, during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.

It is known that the higher the premixed combustion speed, the greater the combustion noise, which is the noise caused by the combustion of the fuel in the cylinder.

Further, the inventors have carried out various experiments and simulations, and as a result, have newly obtained the following findings.

The lower the ignitability of the fuel in the "cylinder" the lower the premixed combustion speed.

Based on the conventional findings and the new findings of the inventors, the higher the ignitability of the fuel in the cylinder, the higher the premixed combustion speed, and therefore the higher the combustion noise.

Here, the inventors have also obtained the following findings.

When the internal combustion engine is operated in a region where the diffusion combustion and the premixed combustion are mixed, the ignition delay of the fuel in the cylinder is longer, and the proportion of the premixed combustion in the diffusion combustion and the premixed combustion is larger. As a result, combustion noise increases.

In the above configuration, the ignition delay target value of the fuel injected into the cylinder by the main injection is calculated based on the ignition property of the fuel in the cylinder estimated based on the parameter for changing the ignition property of the fuel in the cylinder. That is, the ignition delay target value is calculated so that the ignition delay target value becomes smaller as the estimated ignitability of the fuel in the cylinder becomes higher. The fuel injection valve is controlled so that the deviation between the ignition delay of the fuel injected into the cylinder by the main injection and the ignition delay target value is reduced.

As described above, the higher the ignitability of the fuel, the higher the premixed combustion speed, and the larger the combustion noise tends to be. In this regard, according to the above configuration, the ignition delay target value is smaller as the ignitability of the fuel is higher. Therefore, by reducing the ignition delay target value even when the ignitability of the fuel is high, it is possible to suppress an increase in the ratio of the premixed combustion in the diffusion combustion and the premixed combustion. That is, even if the ignitability of the fuel increases, the combustion noise can be suppressed from increasing. As a result, it is possible to suppress a change in the magnitude of combustion noise due to a change in the premixed combustion speed, that is, the ignitability. As a result, even if the parameter for changing the ignitability of the fuel in the cylinder is changed while the engine operating state is maintained at a certain state, the change in the magnitude of the combustion noise can be suppressed.

Therefore, according to the above configuration, it is possible to suppress variation in the magnitude of combustion noise during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.

Further, the higher the partial pressure of fuel in the cylinder, the higher the ignitability of fuel in the cylinder tends to be. That is, the partial pressure of fuel in the cylinder is an example of the above parameter. Therefore, the target calculation unit may be configured to estimate that the ignitability of the fuel in the cylinder is higher as the partial pressure of the fuel in the cylinder is higher.

Further, the higher the partial pressure of oxygen in the cylinder, the higher the ignitability of the fuel in the cylinder tends to be. That is, the partial pressure of oxygen in the cylinder is an example of the above parameter. The target calculation unit may be configured to estimate that the ignitability of the fuel in the cylinder is higher as the oxygen partial pressure in the cylinder is higher.

Further, the higher the temperature in the cylinder, the higher the ignitability of the fuel in the cylinder tends to be. That is, the temperature in the cylinder is an example of the above parameter. Therefore, the target calculation unit may be configured to estimate that the ignitability of the fuel in the cylinder is higher as the temperature in the cylinder is higher.

The control device for an internal combustion engine may further include an index calculation unit that calculates an index of ignitability of the fuel based on a partial pressure of the fuel in the cylinder, a partial pressure of oxygen in the cylinder, and a temperature in the cylinder. In this case, the target calculation unit preferably calculates the ignition delay target value based on the index calculated by the index calculation unit.

"τ 0" is defined as the index, "Pfuel" as the partial pressure of fuel in the cylinder, "O2" as the partial pressure of oxygen in the cylinder, "T" as the temperature in the cylinder, "m (T)" as a function having the temperature in the cylinder "T" as a variable, and "a", "B" and "C" as model constants. The index calculation unit can calculate the index reflecting the parameter by using, for example, an equation shown below. The index thus calculated is the length of the ignition delay of the fuel when the single injection is performed, and the higher the ignitability of the fuel is, the smaller the ignition delay is. By calculating the ignition delay target value based on the index, it is possible to reduce the ignition delay target value as the ignitability of the fuel increases.

By reducing the fuel injection amount in the pre-injection, the ignition delay of the fuel injected into the cylinder by the main injection can be extended. Therefore, the valve control unit may be configured to adjust the fuel injection amount in the pre-injection so that the ignition delay of the fuel injected into the cylinder by the main injection approaches the ignition delay target value.

Further, by retarding the start timing of the pre-injection, that is, by shortening the interval between the pre-injection and the main injection by adjusting the start timing of the pre-injection, the ignition delay of the fuel injected into the cylinder by the main injection can be lengthened. Therefore, the valve control unit may be configured to adjust the start timing of the pilot injection so that the ignition delay of the fuel injected into the cylinder by the main injection approaches the ignition delay target value.

The 2 nd aspect provides a method of controlling a compression self-ignition type internal combustion engine provided with a fuel injection valve that injects fuel into a cylinder. The method comprises the following steps: performing a pre-injection using the fuel injection valve; performing a main injection with the fuel injection valve after the pre-injection; controlling the fuel injection valve in such a manner that a deviation between an ignition delay of the fuel injected into the cylinder by the main injection and an ignition delay target value that is a target of the ignition delay becomes smaller; and calculating the ignition delay target value such that the ignition delay target value becomes smaller as the ignition quality of the fuel in the cylinder estimated based on the parameter for changing the ignition quality of the fuel in the cylinder is higher, during operation of the internal combustion engine in a region where the diffusion combustion and the premixed combustion are mixed.

Drawings

Fig. 1 is a schematic diagram showing a configuration of a control device that is an embodiment of a control device for an internal combustion engine and a configuration of the internal combustion engine controlled by the control device.

Fig. 2 is a diagram in which the spray of fuel injected from a fuel injection valve of the internal combustion engine is modeled.

Fig. 3 is a flowchart showing processing steps when driving the fuel injection valve.

Fig. 4 is a graph showing a relationship between the premixed combustion speed and the magnitude of combustion noise.

Fig. 5 is a graph showing the relationship between the ignitability of the fuel in the cylinder and the premixed combustion speed.

Fig. 6 is a graph showing a relationship between ignition delay of fuel in a cylinder and magnitude of combustion noise.

Fig. 7 is a graph showing the relationship between the index of ignitability of the fuel and the ignition delay target value.

Fig. 8 is a graph showing the relationship between the index of the ignitability of the fuel and the ignition delay target value in the modified example.

Detailed Description

An embodiment of a control device for an internal combustion engine will be described below with reference to fig. 1 to 7.

Fig. 1 shows a control device 60 of the present embodiment and an internal combustion engine 10 controlled by the control device 60. The control device 60 includes processing circuitry. 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 gas driven supercharger 12. An air cleaner 22, a compressor 13 of a supercharger 12, an intercooler 23, and a throttle valve 24 are arranged in this order from the upstream side in the air flow direction in an intake passage 21 of the internal combustion engine 10. In the intake passage 21, the air filtered by the air cleaner 22 is sent out in a state of being compressed by the compressor impeller 13a disposed in the compressor 13. The air thus compressed is cooled by the intercooler 23. The amount of air introduced into the cylinder 11 through the intake passage 21, that is, the intake air amount, is adjusted by controlling the opening degree of the throttle valve 24.

The internal combustion engine 10 is provided with the same number of fuel injection valves 26 as the number of cylinders 11. Each fuel injection valve 26 directly injects fuel into the corresponding cylinder 11. Fuel is supplied to each fuel injection valve 26 by a fuel supply device 27. The fuel supply device 27 includes a supply pump 29 that draws up fuel accumulated in a fuel tank through a supply passage 28, and a common rail 30 that temporarily accumulates the fuel pressurized by the supply pump 29. The fuel in the common rail 30 is supplied to each fuel injection valve 26. When fuel is injected from the fuel injection valve 26 into the cylinder 11, the compressed air is brought into contact with the fuel and burned.

Exhaust gas generated by 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 gas purification device 37 are arranged in this order from the upstream side 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.

A turbine wheel 14a incorporated in the turbine 14 is connected to the compressor wheel 13a via a connecting shaft 15. Thus, when the turbine wheel 14a is rotated by the flow force of the exhaust gas, the compressor wheel 13a is rotated in synchronization with the rotation of the turbine wheel 14 a. As a result, the compressor 13 pressurizes the air. Further, the exhaust gas blowing port to the turbine impeller 14a in the turbine 14 is provided with a variable nozzle 16 that changes the opening area of the exhaust gas blowing port in accordance with a change in the nozzle opening degree. By adjusting the nozzle opening of the variable nozzle 16, the flow rate of the exhaust gas blown to the turbine impeller 14a can be adjusted.

The internal combustion engine 10 includes an EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust passage 36 to the intake passage 21 as EGR gas. The EGR device 40 includes an EGR passage 41 that takes out exhaust gas from a portion of the exhaust passage 36 on the upstream side of the turbine 14, and an EGR flow rate adjustment device 42 that adjusts the flow rate of EGR gas to the intake passage 21 via the EGR passage 41. The EGR passage 41 connects a portion of the intake passage 21 on the downstream side of the throttle valve 24 to 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 that cools the EGR gas flowing through the EGR passage 41. When the valve of the EGR flow rate adjustment device 42 is opened, the EGR gas flowing from the exhaust passage 36 into the EGR passage 41 is cooled by the EGR cooler 43 and introduced into the intake passage 21 via the EGR flow rate adjustment device 42.

Signals are input to the control device 60 from various sensors such as an intake air pressure sensor 101, an intake air 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 a pressure of air in the intake passage 21 at a portion downstream of the throttle valve 24, and outputs a signal corresponding to the detected intake pressure Pim. The intake temperature sensor 102 detects an intake temperature Thim, which is the temperature of air in the intake passage 21 downstream of the intercooler 23, and outputs a signal corresponding to the detected intake temperature Thim. The airflow meter 103 detects an intake air amount GA, which is a flow rate of air in a 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 a water temperature Thw, which is the temperature of engine cooling water flowing through the cylinder of the internal combustion engine 10, and outputs a signal corresponding to the detected water temperature Thw. The boost pressure sensor 105 detects the boost pressure BP achieved by the supercharger 12, and outputs a signal corresponding to the detected boost pressure BP. The boost pressure sensor 105 detects a gauge pressure with reference to the atmospheric pressure as the boost pressure BP. The crank angle sensor 106 detects an engine speed NE, which is the rotational speed of the output shaft of the internal combustion engine 10, and outputs a signal corresponding to the detected engine speed NE. The fuel pressure sensor 107 detects a common rail pressure Pcr that is the pressure of the fuel in the common rail 30, and outputs a signal corresponding to the detected common rail pressure Pcr.

The control device 60 controls the engine operation based on the output signals of the various sensors 101 to 107.

The control device 60 includes a valve control unit 61, an index calculation unit 62, and a target calculation unit 63 as functional units.

The valve control portion 61 controls the driving of the fuel injection valve 26. Specifically, when fuel is combusted in the cylinder 11, the fuel injection valve 26 is caused to perform pilot injection and main injection. The pre-injection refers to fuel injection performed before the piston reciprocating in the cylinder 11 reaches the compression top dead center. The main injection is a fuel injection performed after the pilot injection and is performed when the piston reaches the vicinity of the compression top dead center. When fuel is injected into the cylinder 11 by the preliminary injection, the premixed combustion is performed in the cylinder 11, and the temperature in the cylinder 11 rises. The main injection is performed in a state where the temperature in the cylinder 11 is increased in this manner. Then, diffusion combustion is performed in the cylinder 11. In this case, diffusion combustion may be started in a state where premixed combustion started earlier is also performed. The region where diffusion combustion is started in a state where premix combustion is also performed in this manner is referred to as a region where premix combustion and diffusion combustion are mixed.

When the internal combustion engine is operated in a region where the premixed combustion and the diffusion combustion are mixed, the valve control unit 61 controls the fuel injection valve 26 so that the ignition delay τ of the fuel injected into the cylinder 11 by the main injection approaches the ignition delay target value τ trg. The ignition delay τ is the length of a period from the start time point of fuel injection from the fuel injection valve 26 to the actual start of combustion of the fuel. The ignition delay target value τ trg is a target for ignition delay.

The index calculation unit 62 is configured to calculate the index τ 0 of the ignitability of the fuel in the cylinder 11 based on the parameter that changes the ignitability of the fuel in the cylinder 11. The "ignitability of fuel" as used herein refers to the easiness of ignition of fuel. The index τ 0 calculated by the index calculation unit 62 is a length of ignition delay of the fuel when the fuel injection valve 26 performs single injection. The index τ 0 becomes smaller as the ignitability of the fuel in the cylinder 11 is higher.

The parameters for changing the ignitability of the fuel in the cylinder 11 include, for example, an intake air temperature Thim, an intake air pressure Pim, a recirculation amount of EGR gas, a supercharging pressure BP, a temperature of engine coolant, that is, a water temperature Thw, an outside air temperature, and an outside air pressure.

For example, the index calculation unit 62 calculates the index τ 0 using an arrhenius equation (equation 1) shown below. In equation 1, "Pfuel" is the partial pressure of fuel in the cylinder 11 at the end time point of the main injection, "O2" is the partial pressure of oxygen in the cylinder 11 at the end time point of the main injection, and "T" is the temperature in the cylinder 11 at the start of the main injection. "M (T)" is a function of the temperature "T" in the cylinder 11 as a variable. That is, the function "m (T)" is a function that can derive a larger value as the temperature "T" in the cylinder 11 is higher. For example, as the function "m (t)", an exponential function of the following formula 2 can be employed. In this case, the model constant "D" is set to a value that increases as the temperature "T" in the cylinder 11 increases, as the calculation result of expression 2 increases. For example, the model constant "D" is set to a negative value. In formula 1, "a", "B", and "C" are model constants and are values set in advance by experiments and simulations. Specifically, the model constant "B" is set to a value such that the index τ 0 can be made smaller as the fuel partial pressure "Pfuel" is higher. The model constant "C" is set to a value such that the index τ 0 can be made smaller as the oxygen partial pressure "O2" is higher. For example, the model constants "B" and "C" are set to positive values. The model constant "a" is set to a value such that the index τ 0 can be made smaller as the product of the power "B" of the fuel partial pressure "Pfuel", the power "C" of the oxygen partial pressure "O2", and "m (t)". For example, the model constant "a" is set to a positive value.

The fuel partial pressure "Pfuel" is calculated as the product of the fuel concentration Cfuel in the cylinder 11 and the in-cylinder pressure Pcy that is the pressure in the cylinder 11. The fuel concentration Cfuel is a value corresponding to the in-spray equivalence ratio Φ at the end time point of the main injection. The in-spray equivalence ratio Φ at the time point of the end of the main injection is calculated based on the instruction value of the injection amount when the fuel injection valve 26 is caused to perform the main injection.

The in-spray equivalence ratio Φ refers to the equivalence ratio in the spray of fuel injected from the fuel injection valve 26 into the cylinder 11. For example, the in-spray equivalence ratio Φ can be derived by dividing the stoichiometric air-fuel ratio by the in-spray air-fuel ratio. The in-spray air-fuel ratio refers to an air-fuel ratio in the spray of the fuel injected from the fuel injection valve 26 into the cylinder 11. The in-spray fuel ratio 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 time point of the main injection and the oxygen concentration Cox in the cylinder 11.

Here, a method of calculating the volume V of the spray will be described with reference to fig. 2. As shown in fig. 2, it is assumed that the spray of fuel injected from the fuel injection valve 26 into the cylinder 11 is conical. In this case, the volume V of the spray can be calculated by using a known guang' an equation. The following relational expression (expression 3) or (expression 4) is a calculation expression of the spray penetration S. The relational expression (expression 3) is an expression used when the injection time "t" of the fuel is smaller than the split time "tc". The relational expression (expression 4) is an expression used when the injection time "t" of the fuel is equal to or longer than the split time "tc". The split time "tc" refers to a time required for the fuel injected from the fuel injection valve 26 to change its state from liquid to gas.

In the relational expressions (expression 3) and (expression 4), "Δ P" is the difference between the common rail pressure Pcr and the cylinder internal pressure Pcy. The in-cylinder pressure Pcy can be estimated based on the amount of air charged into 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 in the cylinder 11, the detection value of the sensor may be used as the cylinder pressure Pcy. In the relational expressions (expression 3) and (expression 4), "ρ f" is the fuel density, and "ρ a" is the air density. "d 0" is the diameter of the nozzle hole of the fuel injection valve 26.

The following relational expression (expression 5) is an expression for calculating the spray angle θ. In the relational expression (expression 5), "μ a" is a viscosity coefficient of air, and is set in advance.

The following relational expression (expression 6) is an expression for calculating the volume V of the spray.

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, an intake air amount GA detected by the air flow meter 103 can be used. 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 as to decrease as the amount of EGR gas recirculated to the intake passage 21 via the EGR device 40 increases.

Further, when the valve opening degree of the EGR flow rate adjustment device 42 and the flow rate of the exhaust gas in the exhaust passage 36 are kept constant, the amount of EGR gas recirculated to the intake passage 21 via the EGR device 40, that is, the recirculation amount 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 adjustment device 42. The flow rate of the exhaust GAs becomes a value corresponding to the intake air amount GA and the engine speed NE.

When at least one of the valve opening degree of the EGR flow rate adjustment device 42 and the flow rate of the exhaust gas changes, a response delay occurs in a change in the recirculation amount of the EGR gas with respect to the change. In the present embodiment, a map is prepared for estimating to what extent the change in the recirculation flow rate is delayed when at least one of the valve opening degree and the flow rate of the exhaust gas changes. Therefore, when at least one of the valve opening degree and the flow rate of the exhaust gas changes, the return flow rate is estimated using the map.

The partial pressure "O2" of oxygen in the cylinder 11 in the relational expression (expression 1) is calculated as the product of the oxygen concentration Cox in the cylinder 11 and the in-cylinder pressure Pcy.

The temperature "T" in the cylinder 11 at the start of the main injection can be estimated based on the intake air temperature Thim and the water temperature Thw. Of course, when a sensor for detecting the temperature in the cylinder 11 is provided in the cylinder 11, the detection value of the sensor may be used as the temperature "T" in the cylinder 11.

As described above, "Pfuel", "O2", and "T" in the relational expression (expression 1) vary depending on the temperature of the air flowing through the intake passage 21, the pressure of the air flowing through the intake passage 21, the recirculation amount of the EGR gas, and the water temperature Thw. Accordingly, the fuel partial pressure "Pfuel", the oxygen partial pressure "O2", and the temperature "T" in the cylinder 11 can be said to be examples of parameters for changing the ignitability of the fuel in the cylinder 11. The index τ 0 calculated using the above equation 1 is a value based on a parameter that changes the ignitability of the fuel in the cylinder 11.

The target calculation unit 63 is configured to estimate the ignitability of the fuel in the cylinder 11 based on the index τ 0 calculated by the index calculation unit 62. The target calculation unit 63 calculates the ignition delay target value τ trg so that the ignition delay target value τ trg becomes smaller as the ignition quality estimated based on the index τ 0 becomes higher. In the present embodiment, the ignition delay target value τ trg is calculated using the relational expression (expression 7) shown below. Therefore, the ignition delay target value τ trg can be monotonically increased with respect to the increase in the index τ 0. That is, the ignition delay target value τ trg can be monotonously decreased with respect to the increase in ignition performance estimated based on the index τ 0. In the relational expression (expression 7), "F11" and "F12" are constants and values set based on experiments and simulations. For example, the constant "F11" is a positive value.

τ trg ═ F11 · τ 0+ F12 · (formula 7)

Next, referring to fig. 3, a flow of a process of fuel injection during engine operation in a region where diffusion combustion and premixed combustion are mixed will be described.

Before the description of the flow of the processing shown in fig. 3, a description will be given of a method of estimating whether or not the internal combustion engine is operating in a region where diffusion combustion and premixed combustion are mixed. In the present embodiment, this estimation is performed based on the ignition delay of the fuel injected into the cylinder 11 by the main injection. For example, as shown in fig. 6, when the ignition delay τ, which is an estimated value of the ignition delay of the fuel injected into the cylinder 11 by the main injection, is smaller than the predetermined time τ Th, it can be estimated that the internal combustion engine is operated in a region where the diffusion combustion and the premixed combustion are mixed. In contrast, when the ignition delay τ is equal to or longer than the predetermined time τ Th, it can be estimated that the engine operation is performed not in a region where diffusion combustion and premixed combustion are mixed but in a region where only premixed combustion is performed. Therefore, when the ignition delay τ is smaller than the predetermined time τ Th, it can be estimated that the engine operation is performed in a region where the diffusion combustion and the premixed combustion are mixed, and therefore a series of processes shown in fig. 3 is executed.

The ignition delay τ can be calculated based on, for example, the boost pressure BP, the intake air amount GA, the water temperature Thw, the intake air temperature Thim, the start timing of the main injection, and the fuel injection amount of the main injection.

As shown in fig. 3, in step S11, various parameters necessary for calculating the index τ 0 are acquired. In the next step S12, the index calculation unit 62 calculates the index τ 0 using the above equation 1. Next, in step S13, the target calculation unit 63 calculates the ignition delay target value τ trg using the above relational expression (expression 7).

Then, in the next step S14, the valve control unit 61 controls the driving of the fuel injection valve 26 so that the ignition delay τ becomes the ignition delay target value τ trg. In the present embodiment, in step S14, the fuel injection amount in the pre-injection performed prior to the main injection, that is, the energization time to the fuel injection valve 26 at the time of the pre-injection is adjusted. For example, when the ignition delay τ is shorter than the ignition delay target value τ trg, the valve control unit 61 decreases the fuel injection amount during the preliminary injection. In contrast, for example, when the ignition delay τ is longer than the ignition delay target value τ trg, the valve control unit 61 increases the fuel injection amount during the preliminary injection. Then, the series of processes is once ended.

Next, the operation and effect of the present embodiment will be described with reference to fig. 4 to 7.

Fig. 4 shows the relationship between the premixed combustion speed and the magnitude of combustion noise, which is noise caused by combustion of fuel in the cylinder 11. As shown in fig. 4, the higher the premixed combustion speed, the greater the combustion noise. This is because the higher the premixed combustion speed is, the more the flame spreads into the cylinder 11 at a stroke. The higher the speed at which the flame expands within the cylinder 11, the greater the combustion noise tends to be.

Fig. 5 shows the ignitability of the fuel injected into the cylinder 11 in relation to the premixed combustion speed. The graph shown in fig. 5 is a result obtained by experiment and simulation. As can be understood from the graph shown in fig. 5, the lower the ignitability of the fuel in the cylinder 11, the lower the premixed combustion speed. That is, it can be said that the larger the index τ 0, the lower the premixed combustion speed.

Fig. 6 shows the relationship between the ignition delay τ and the magnitude of combustion noise. As shown in fig. 6, when the ignition delay τ is smaller than the predetermined time τ Th, the diffusion combustion and the premixed combustion are mixed in the cylinder 11. On the other hand, when the ignition delay τ is equal to or longer than the predetermined time τ Th, only the premixed combustion is performed in the cylinder 11. As can be understood from the graph shown in fig. 6, when the internal combustion engine is operated in a region where the diffusion combustion and the premixed combustion are mixed, the combustion noise becomes larger as the ignition delay τ becomes longer. This is presumably because, during the operation of the internal combustion engine in the region where the diffusion combustion and the premixed combustion are mixed, the longer the ignition delay of the fuel in the cylinder is, the greater the proportion of the premixed combustion in the diffusion combustion and the premixed combustion becomes, and as a result, the greater the combustion noise becomes. Specifically, the lower the ignitability of the fuel in the cylinder 11, the longer the ignition delay of the fuel in the cylinder is likely to be. Further, the lower the ignitability of the fuel in the cylinder 11, the lower the premixed combustion speed tends to be. Further, the lower the premixed combustion speed, the larger the proportion of premixed combustion in diffusion combustion and premixed combustion tends to be. Therefore, the longer the ignition delay, the lower the premixed combustion speed, and therefore the larger the proportion of premixed combustion in diffusion combustion and premixed combustion. As a result, combustion noise increases.

The relationship between the combustion noise and the ignition delay τ during the operation of the internal combustion engine in the region where the diffusion combustion and the premixed combustion are mixed can be expressed by an approximate expression shown in the following expression 8. In addition, in formula 8, "P1", "P2", and "P3" are constants.

Combustion noise. varies to P1. tau^P2+ P3 (formula 8)

As described above, the relationship between the index τ 0 and the premixed combustion speed is an inverse proportional relationship, and the relationship between the combustion noise and the ignition delay τ can be expressed by the above equation 8. Therefore, the relationship between the combustion noise, the ignition delay τ, and the index τ 0 can be expressed by the following equation 9.

Combustion noise. varies (P1. tau.)^P2+ P3)/τ 0 · (formula 9)

When the combustion noise is assumed to be a constant value "Const", equation 9 can be expressed as equation 10. When the ignition delay τ when the combustion noise becomes a constant value "Const" is set as the ignition delay target value τ trg, the ignition delay target value τ trg can be expressed by the following expression 11.

Const＝(P1·τ^P2+ P3)/τ 0 · (formula 10)

As is apparent from equation 11, the ignition delay target value τ trg is increased as the index τ 0 is increased, and the combustion noise level can be kept constant. The above relational expression (expression 7) can be derived by setting the constant "P2" in expression 11 to "1".

In the present embodiment, the ignition delay target value τ trg is calculated using the relational expression (expression 7) derived in this way. The solid line in fig. 7 shows the relationship between the ignition delay target value τ trg calculated using the relational expression (expression 7) and the index τ 0. The broken line in fig. 7 shows comparative example 1 in which the ignition delay target value τ trg is set regardless of the index τ 0, which is the ignitability of the fuel.

In the case of comparative example 1, even if the ignition quality indicator τ 0, which is a parameter for changing the ignition quality of the fuel, is changed when the engine speed NE and the engine load factor KL, which are the operating states of the internal combustion engine 10, are constant, the ignition delay target value τ trg is not changed. As a result, when the parameter changes, the magnitude of the combustion noise changes.

In contrast, in the present embodiment, the ignition quality of the fuel is estimated based on the index τ 0, and the ignition delay target value τ trg is calculated so that the ignition quality is higher and the ignition delay target value τ trg is smaller. The fuel injection valve 26 is controlled so that the ignition delay τ of the fuel injected into the cylinder 11 by the main injection approaches the ignition delay target value τ trg. That is, the fuel injection valve 26 is controlled so that the ignition delay τ of the fuel injected into the cylinder 11 by the main injection is less apart from the ignition delay target value τ trg. As a result, the variation in the magnitude of the combustion noise due to the variation in the parameter can be suppressed.

Therefore, according to the present embodiment, it is possible to suppress variation in the magnitude of combustion noise during operation of the internal combustion engine in a region where diffusion combustion and premixed combustion are mixed.

The above embodiment can be modified and implemented as follows. The above-described embodiments and the following modifications can be implemented in combination with each other within a range not technically contradictory to the technology.

The ignition delay τ of the fuel injected into the cylinder 11 in the main injection also changes in accordance with the start timing of the pre-injection. Specifically, by retarding the start timing of the pre-injection to narrow the interval between the timing of the pre-injection and the timing of the main injection, the ignition delay of the fuel injected into the cylinder 11 by the main injection can be extended. Therefore, the timing of the pre-injection may be retarded when the ignition delay τ is shorter than the ignition delay target value τ trg, and advanced when the ignition delay τ is longer than the ignition delay target value τ trg.

When the ignition delay τ of the fuel injected into the cylinder 11 in the main injection is different from the ignition delay target value τ trg, both the fuel injection amount of the pre-injection and the start timing of the pre-injection may be adjusted.

The deviation of the ignition delay τ of the fuel injected into the cylinder 11 by the main injection from the ignition delay target value τ trg may also be reduced by the modification of the start timing of the main injection. In this case, the adjustment of the fuel injection amount of the pre-injection and the adjustment of the start timing of the pre-injection for adjusting the deviation of the ignition delay τ from the ignition delay target value τ trg may be omitted.

In the above embodiment, the ignition delay target value τ trg is calculated using the relational expression (expression 7) which is a linear function. However, the ignition delay target value τ trg may be calculated using an expression different from the above-described relational expression (expression 7) as long as the ignition delay target value τ trg can be monotonically decreased with respect to the decrease in the index τ 0. For example, the ignition delay target value τ trg may be calculated using a quadratic function such as the following relational expression (expression 12). "F21", "F22", and "F23" in the relational expression (expression 12) are constants and values set based on experiments and simulations. The relational expression (expression 12) can be derived by setting the constant "P2" in expression 11 to "0.5".

τtrg＝F21·τ0²+ F22. tau 0+ F23. cndot. (formula 12)

When the ignition delay target value τ trg is calculated using the relational expression (expression 9), the ignition delay target value τ trg changes as shown in fig. 8 with respect to the change in the index τ 0.

The higher the temperature "T" in the cylinder 11, the larger the value of the calculation result can be made, and the function "m (T)" in the arrhenius equation (equation 1) may be a function different from the above equation 2.

In the above embodiment, the index τ 0 is calculated using an arrhenius equation (equation 1). However, if the index τ 0 can be set to a value corresponding to the ignitability of combustion in the cylinder 11, equation 1 may not be used in calculating the index τ 0.

For example, the index τ 0 may be calculated without using equation 1, as the index τ 0 can be made smaller as the fuel partial pressure "Pfuel" in the cylinder 11 at the end time point of the main injection is higher.

Note that, the index τ 0 may be made smaller as the oxygen partial pressure "O2" in the cylinder 11 at the end time of the main injection is higher, and the index τ 0 may be calculated without using equation 1.

Note that, if the temperature "T" in the cylinder 11 at the start of main injection can be made smaller than the index τ 0, the index τ 0 may be calculated without using equation 1.

Instead of estimating the ignitability of the fuel based on the index τ 0, the ignitability may be directly estimated from a parameter that changes the ignitability of the fuel in the cylinder 11. For example, the ignitability may also be estimated based on the fuel partial pressure "Pfuel" in the cylinder 11 at the end time point of the main injection. The ignitability may be estimated based on the oxygen partial pressure "O2" in the cylinder 11 at the end time of the main injection. Further, the ignitability may be estimated based on the temperature "T" in the cylinder 11 at the start of the main injection.

The control device 60 is not limited to being provided with a CPU and a memory and executing software processing. For example, a dedicated hardware circuit (e.g., ASIC) may be provided for performing hardware processing on at least a part of the software processing in each of the above embodiments. That is, the control device may be configured as any one of the following (a) to (c). (a) The processing device includes a processing device for executing all the above-described processing according to a program, and a program storage device such as a ROM for storing the program. (b) The apparatus includes a processing device and a program storage device for executing a part of the above-described processing in accordance with a program, and a dedicated hardware circuit for executing the remaining processing. (c) The apparatus includes a dedicated hardware circuit for executing all of the above-described processing. Here, a plurality of software processing circuits and dedicated hardware circuits may be provided, each of which includes a processing device and a program storage device. That is, the above processing may be executed by a processing circuit including at least one of 1 or more software processing circuits and 1 or more dedicated hardware circuits.