Control device for internal combustion engine

Abstract

To improve estimation accuracy of a piston temperature.SOLUTION: A control device 100 executes processing for: calculating heat generation amount of a piston 5 when fuel supplied into a cylinder of an internal combustion engine 1 is burned; acquiring thermal resistance related to a temperature of the piston 5; acquiring a cooling water temperature that is a temperature of cooling water of the internal combustion engine 1; and calculating the temperature of the piston 5 on the basis of heat reception amount, the thermal resistance and the cooling water temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] For example, the control device described in Patent Document 1 estimates the temperature of the piston based on the cooling loss that occurs from the combustion chamber to the piston and the temperature of the combustion gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-131941 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is difficult to accurately estimate the combustion gas temperature required to estimate the piston temperature. Therefore, there is a limit to the accuracy of estimating the piston temperature, and further improvement in accuracy is required. [Means for solving the problem]

[0005] The control device for an internal combustion engine that solves the above problem comprises: The present invention is applied to an internal combustion engine that is equipped with an in-cylinder injection valve that directly injects fuel into a combustion chamber and a port injection valve that injects fuel into an intake port, and that can use a mixed fuel that is a mixture of alcohol fuel and gasoline fuel as fuel, and that includes: a process for calculating a calorific value when fuel supplied into a cylinder of the internal combustion engine is burned, based on an engine rotation speed, a fuel injection amount, a target air-fuel ratio, an intake air amount, and an alcohol concentration of the fuel; a process for calculating a calorific value correction coefficient, based on an engine load factor, an ignition timing, a target EGR rate, the fuel injection amount, and an in-cylinder injection rate that is a rate of the amount of fuel injected from the in-cylinder injection valve within the fuel injection amount; The amount of heat received by a piston of the internal combustion engine when fuel supplied into a cylinder is burned, By multiplying the calorific value by the heat reception correction coefficient, The system executes a process of calculating the combustion gas temperature without relying on an estimated value, a process of acquiring the thermal resistance related to the temperature of the piston, a process of acquiring the cooling water temperature, which is the temperature of the cooling water of the internal combustion engine, and a process of calculating the temperature of the piston based on the amount of heat received, the thermal resistance, and the cooling water temperature.

[0006] The temperature of the piston correlates with the amount of heat received by the piston when fuel supplied to the cylinder of the internal combustion engine is burned, the thermal resistance related to the piston temperature, and the temperature of the coolant. Therefore, in this configuration, the piston temperature is calculated based on the amount of heat received, the thermal resistance, and the coolant temperature. Therefore, the piston temperature can be calculated without estimating the combustion gas temperature, thereby improving the accuracy of estimating the piston temperature. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of an internal combustion engine according to one embodiment; [Figure 2] FIG. 2 is a block diagram showing a process executed by a control device according to the embodiment. [Figure 3] 4 is a flowchart showing a procedure of a process executed by the control device of the embodiment. [Figure 4] 10 is a graph showing the relationship between the equivalence ratio and the fuel correction coefficient. [Figure 5] 1 is a graph showing the relationship between alcohol concentration and lower heating value. [Figure 6] FIG. 4 is a diagram showing the relationship between a first correction coefficient and a retardation rate. [Figure 7] FIG. 10 is a diagram showing the relationship between a second correction coefficient and an advance angle rate. [Figure 8] FIG. 10 is a diagram illustrating the relationship between a third correction coefficient and an in-cylinder ratio. [Figure 9] FIG. 4 is a diagram showing the relationship between the engine rotation speed and the flow rate of the cooling water and the combined thermal resistance. [Figure 10] FIG. 10 is a diagram showing the relationship between oil pressure and a fourth thermal resistance. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a control device for an internal combustion engine will be described below with reference to FIGS. <Configuration of an internal combustion engine> As shown in Fig. 1, a cylinder 4 is provided in a cylinder block 2 of an internal combustion engine 1. The inner wall of the cylinder 4 is hereinafter referred to as a cylinder bore 4b. A piston 5 is provided in the cylinder 4, and the piston 5 is connected to a crankshaft 7 via a connecting rod 6.

[0009] The cylinder block 2 is also formed with a water jacket 70 through which coolant supplied from the water pump 60 flows. A cylinder head 3 is attached to the top of the cylinder block 2. A combustion chamber 8 is formed in each cylinder 4 between the top surface of the piston 5 and the cylinder head 3. The cylinder head 3 is also provided with an in-cylinder injection valve 35 that directly injects fuel into the combustion chamber 8, and a spark plug 11 that spark-ignites the air-fuel mixture in the combustion chamber 8, for each cylinder of the internal combustion engine 1.

[0010] The cylinder head 3 is also provided with an intake port 9 that introduces intake air into the combustion chamber 8 and an exhaust port 10 that discharges exhaust gas from the combustion chamber 8. The intake port 9 is connected to an intake passage 20 provided with a throttle valve 14 that adjusts the amount of intake air. The intake port 9 is also provided with an intake valve 12 that opens and closes the intake port 9. The cylinder head 3 is also provided with a port injection valve 36 for each cylinder of the internal combustion engine 1 that injects fuel into the intake port 9.

[0011] An exhaust valve 13 is provided in the exhaust port 10 to open and close the exhaust port 10. The exhaust port 10 is connected to an exhaust passage 30. A catalyst 32 that purifies the exhaust gas is provided in the exhaust passage 30. The catalyst 32 purifies the exhaust gas by controlling the air-fuel ratio of the mixture to a target air-fuel ratio.

[0012] The internal combustion engine 1 is provided with an oil jet 80 that injects lubricating oil toward the piston 5. The internal combustion engine 1 can use only alcohol fuel (fuel with an alcohol content of "100%), only gasoline fuel (fuel with an alcohol content of "0%), or a blended fuel that is a mixture of alcohol fuel and gasoline fuel.

[0013] The internal combustion engine 1 is provided with an EGR passage 50 that recirculates exhaust gas as EGR gas to the intake passage 20. The EGR passage 50 connects a portion of the intake passage 20 downstream of the throttle valve 14 to the exhaust passage 30. An EGR valve 51 is provided in the EGR passage 50. By controlling the opening degree of the EGR valve 51, the flow rate of EGR gas flowing from the exhaust passage 30 into the intake passage 20 is adjusted.

[0014] <About the control device> The control device 100 includes a central processing unit (hereinafter referred to as CPU) 110, a memory 120 in which control programs and data are stored, etc. The CPU 110 executes the programs stored in the memory 120 to perform various engine controls.

[0015] Various sensors are connected to the control device 100. For example, the control device 100 is connected to a crank angle sensor 41 that detects the rotation angle of the crankshaft 7, an air flow meter 44 that detects the intake air amount GA, and a water temperature sensor 45 that detects the coolant temperature Tw, which is the temperature of the coolant after heat exchange in the internal combustion engine 1. The control device 100 is also connected to an air-fuel ratio sensor 46 that is provided in the exhaust passage 30 upstream of the catalyst 32 and detects the air-fuel ratio AF, and a pump speed sensor 47 that detects the pump rotation speed Np, which is the rotation speed of the water pump 60. The control device 100 is also connected to an oil temperature sensor 48 that detects the oil temperature To, which is the temperature of the lubricating oil supplied to the oil jet 80, and an oil pressure sensor 49 that detects the oil pressure Po of the lubricating oil supplied to the oil jet 80.

[0016] The control device 100 calculates the engine speed Ne based on the output signal Scr of the crank angle sensor 41. The control device 100 also calculates an engine load factor KL based on the engine speed Ne and the intake air amount GA. The engine load factor KL represents the ratio of the current cylinder inflow air amount to the cylinder inflow air amount when the internal combustion engine 1 is operated steadily with the throttle valve fully open at the current engine speed Ne. The cylinder inflow air amount is the amount of air flowing into each cylinder during the intake stroke. The control device 100 also calculates the flow rate V of the cooling water flowing through the water jacket 70 based on the pump rotation speed Np.

[0017] <Fuel injection distribution> As one of various controls of the internal combustion engine 1, the control device 100 executes a process of switching between three types of fuel injection modes depending on the engine operating state. One of the fuel injection modes that can be switched in this embodiment is an in-cylinder injection mode in which fuel is injected only from the in-cylinder injection valve 35. Another fuel injection mode that can be switched in this embodiment is a port injection mode in which fuel is injected only from the port injection valve 36. And another fuel injection mode that can be switched in this embodiment is a dual injection mode in which fuel is injected from both the in-cylinder injection valve 35 and the port injection valve 36.

[0018] The above-mentioned switching of the fuel injection mode is performed by variously changing the port injection ratio Rpf, which indicates the ratio of the amount of fuel injected from the port injection valve 36 out of the fuel injection amount Q that is set based on the engine operating state.

[0019] The port injection ratio Rpf is variably set within the range of "0 ≦ Rpf ≦ 1" based on the engine operating conditions such as the engine load factor KL and the engine rotational speed Ne. The fuel amount obtained by multiplying the fuel injection amount Q by the port injection ratio Rpf is set as the fuel injection amount of the port injection valve 36. On the other hand, the value obtained by subtracting the port injection ratio Rpf from "1" is calculated as the in-cylinder injection ratio Rd indicating the ratio of the fuel amount injected from the in-cylinder injection valve 35 among the fuel injection amount Q (Rd = 1 - Rp). Then, the fuel amount obtained by multiplying the fuel injection amount Q by the in-cylinder injection ratio Rd is set as the fuel injection amount of the in-cylinder injection valve 35.

[0020] <Regarding EGR control> As one of various controls of the internal combustion engine 1, the control device 100 performs EGR control for adjusting the recirculation amount, that is, the EGR amount, of EGR gas (external EGR gas) which is the exhaust gas recirculated to the intake passage 20. In this EGR control, the control device 100 calculates a target EGR rate EGp, which is a command value for adjusting the EGR amount flowing into the intake passage 20 via the EGR passage 50, based on the engine operating conditions such as the engine rotational speed Ne and the engine load factor KL. Note that the EGR rate is the ratio of the EGR amount to the total amount of the in-cylinder filling gas. Then, the control device 100 calculates a target opening degree EAt of the EGR valve 51 at which the target EGR rate EGp can be obtained, based on the target EGR rate EGp, the intake air amount GA, etc. Then, the opening degree of the EGR valve 51 is adjusted so that the opening degree of the EGR valve 51 becomes the target opening degree EAt. In this embodiment, the valve opening degree EA when the EGR valve 51 is fully opened is set as "100%", and the valve opening degree EA when the EGR valve 51 is in the fully closed state where it is completely closed is set as "0%".

[0021] <Regarding air-fuel ratio feedback control> The control device 100 performs air-fuel ratio feedback control as one of various controls of the internal combustion engine 1. This air-fuel ratio feedback control corrects the fuel injection amount Q based on the air-fuel ratio AF detected by the air-fuel ratio sensor 46 in order to make the air-fuel ratio of the mixture equal to a target air-fuel ratio AFt (e.g., a stoichiometric air-fuel ratio). The control device 100 calculates an air-fuel ratio correction value FAF so as to reduce the deviation between the air-fuel ratio AF and the target air-fuel ratio AFt. Specifically, the control device 100 calculates the air-fuel ratio correction value FAF as the sum of a proportional element, an integral element, and a derivative element, which have the deviation between the target air-fuel ratio AFt and the air-fuel ratio AF as input. Then, the control device 100 corrects the fuel injection amount Q with the air-fuel ratio correction value FAF, thereby converging the air-fuel ratio of the mixture to the target air-fuel ratio AFt.

[0022] <About estimating alcohol concentration> The control device 100 executes a process for estimating the alcohol concentration AD of the fuel. That is, the internal combustion engine 1 performs the above-described air-fuel ratio feedback control. Here, the higher the alcohol concentration in the fuel, the richer the value of the air-fuel ratio correction value FAF required to achieve the target air-fuel ratio AFt tends to be. Therefore, for example, the control device 100 of this embodiment executes a process for estimating the alcohol concentration AD of the fuel based on the air-fuel ratio correction value FAF calculated to maintain the target air-fuel ratio AFt. During this estimation, the control device 100 calculates the alcohol concentration AD so that the calculated alcohol concentration AD becomes higher as the value of the air-fuel ratio correction value FAF becomes richer. Incidentally, when estimating the alcohol concentration AD, the accuracy of the estimation of the alcohol concentration AD can be improved by performing the process when the degree of deviation between the actual air-fuel ratio AF and the target air-fuel ratio AFt is sufficiently small and this state has continued for a certain period of time.

[0023] The alcohol concentration AD of the fuel may be estimated in other ways, or may be directly detected using a sensor that detects the alcohol concentration based on the electrical conductivity or capacitance of the fuel, for example.

[0024] <About knocking control> As one of various controls of the internal combustion engine 1, the control device 100 performs so-called knocking control, in which, when the occurrence of knocking is detected by a sensor or the like, the ignition timing is retarded until the occurrence of knocking subsides. In this knocking control, a basic ignition timing AOPb is calculated based on the engine speed Ne and the engine load factor KL. The basic ignition timing AOPb is a value calculated as the most advanced ignition timing that can suppress the occurrence of knocking. Note that, when the amount of EGR flowing into the intake passage 20 increases, the combustion of the air-fuel mixture slows, making knocking less likely to occur, but engine torque decreases. Therefore, as the target EGR rate EGp is ​​set to a larger value, the basic ignition timing AOPb is set more advanced, thereby suppressing the decrease in engine torque. In addition, a knocking correction amount KH is calculated depending on the occurrence status of knocking. Then, the basic ignition timing AOPb is retarded by the knocking correction amount KH, and the retarded timing is set as the final ignition timing AOP, thereby performing feedback control of the ignition timing according to the occurrence of knocking.

[0025] <About estimating piston temperature> The control device 100 executes a process for calculating a piston temperature Tp, which is the temperature of the top surface of the piston 5. Hereinafter, this process will be described with reference to FIG.

[0026] FIG. 2 shows the processing that is realized by the CPU 110 executing the program stored in the memory 120. <Heat generation calculation process> The heat generation amount calculation process M10 is a process for calculating the heat generation amount Qburn when fuel supplied into the cylinder of the internal combustion engine 1 is burned.

[0027] 3 shows the procedure for the calculation process of the heat generation amount Qburn executed by the control device 100. The control device 100 repeatedly executes this process at predetermined calculation intervals. Note that, below, step numbers are represented by numbers preceded by "S."

[0028] When the process shown in FIG. 3 starts, the control device 100 acquires the coolant temperature Tw, the flow rate V, the target air-fuel ratio AFt, the intake air amount GA, the fuel injection amount Q, and the alcohol concentration AD (S100).

[0029] Next, the control device 100 calculates an equivalence ratio ER based on the target air-fuel ratio AFt, the intake air amount GA, and the fuel injection amount Q (S120). The fuel injection amount Q is the final fuel injection amount corrected by air-fuel ratio feedback control. The equivalence ratio ER is a value obtained by dividing the fuel injection amount Q by the fuel injection amount required to obtain the stoichiometric air-fuel ratio at the current intake air amount GA. Therefore, when the target air-fuel ratio AFt is smaller than the stoichiometric air-fuel ratio, the equivalence ratio ER becomes a value smaller than "1." Note that the equivalence ratio ER may also be calculated by dividing the stoichiometric air-fuel ratio by the air-fuel ratio AF, which is the detected value of the air-fuel ratio.

[0030] Next, the control device 100 calculates a fuel correction coefficient Kf based on the equivalence ratio ER (S130). Generally, the amount of heat generated per unit mass when fuel is burned varies depending on the air-fuel ratio of the mixture. Therefore, the control device 100 calculates the fuel correction coefficient Kf as a correction value to be multiplied by the fuel injection amount Q in order to correct for differences in the amount of heat generated due to differences in air-fuel ratio, based on the amount of heat generated per unit mass when a mixture of a stoichiometric air-fuel ratio is burned.

[0031] In this embodiment, the relationship between the equivalence ratio ER and the fuel correction coefficient Kf is stored in advance as map data in the memory 120. Then, the control device 100 calculates the fuel correction coefficient Kf based on the map data.

[0032] As shown in FIG. 4, in the map data of the fuel correction coefficient Kf, a value is set so that the fuel correction coefficient Kf is "1" when the equivalence ratio ER is "1." Furthermore, the value of the fuel correction coefficient Kf is set so that it gradually becomes smaller than "1" as the equivalence ratio ER becomes smaller than "1." Furthermore, the value of the fuel correction coefficient Kf is set so that it gradually becomes larger than "1" as the equivalence ratio ER becomes larger than "1." Due to the correction of the fuel injection amount Q using the fuel correction coefficient Kf, when the equivalence ratio ER is smaller than "1," that is, when the air-fuel ratio of the mixture is leaner than the stoichiometric air-fuel ratio, the fuel amount used to calculate the calorific value of the fuel is less than the fuel injection amount Q. On the other hand, when the equivalence ratio ER is greater than "1," that is, when the air-fuel ratio of the mixture is richer than the stoichiometric air-fuel ratio, the fuel amount used to calculate the calorific value of the fuel is greater than the fuel injection amount Q.

[0033] Next, the control device 100 calculates the lower heating value LC of the fuel based on the alcohol concentration AD (S140). In this embodiment, the relationship between the alcohol concentration AD and the lower heating value LC is stored in advance as map data in the memory 120. Then, the control device 100 calculates the lower heating value LC based on the map data.

[0034] As shown in FIG. 5, in the map data of the lower heating value LC, the value of the calculated lower heating value LC is set so that the value of the lower heating value LC decreases as the alcohol concentration AD increases.

[0035] Next, the control device 100 calculates the amount of heat Qburn per unit time when the fuel supplied into the cylinder of the internal combustion engine 1 is burned, based on the following equation (1) (S150). Qburn=Ne (Q Kf) LC α…(1) Ne: Engine rotation speed Q: Fuel injection amount Kf: Fuel correction factor LC: Low heating value α: constant for adjusting units As mentioned above, the value obtained by "Q·Kf" in equation (1) is a value obtained by correcting the fuel injection amount Q when calculating the calorific value in order to correct the calorific value per unit mass of fuel, which changes depending on the air-fuel ratio of the mixture.

[0036] After executing the process of S150, the control device 100 ends the execution of this process in the current calculation cycle. <Correction coefficient calculation process> The correction coefficient calculation process M20 shown in FIG. 2 is a process for calculating a heat reception correction coefficient K. The heat reception correction coefficient K is a value by which the heat generation amount Qburn is multiplied to calculate a piston heat reception amount Qp, which is the amount of heat received by the piston 5 when fuel supplied into the cylinder of the internal combustion engine 1 is burned. In this correction coefficient calculation process M20, the control device 100 first calculates a basic correction coefficient Kb. In this embodiment, the relationship between the engine load factor KL and the basic correction coefficient Kb is stored in advance in the memory 120 as basic correction coefficient map data. The control device 100 then calculates the basic correction coefficient Kb based on the basic correction coefficient map data and the acquired engine load factor KL. The basic correction coefficient Kb is a value greater than "0" and equal to or less than "1." Basically, the basic correction coefficient Kb is set to be smaller when the engine load factor KL is large than when it is small. The basic correction coefficient Kb is a value adapted based on an engine operating state in which the knocking correction amount KH is "0", the target EGR rate EGp is ​​"0", and the port injection rate Rpf is "1".

[0037] In this embodiment, three basic correction coefficient map data are prepared that are selected depending on the engine operating state in order to calculate the optimal basic correction coefficient Kb. The first basic correction coefficient map data is map data that is suitable for idling operation of the internal combustion engine 1. The second basic correction coefficient map data is map data that is suitable for steady operation of the internal combustion engine 1, i.e., operation other than idling. The third basic correction coefficient map data is map data that is suitable when rapid warm-up control of the catalyst 32 is being executed in the internal combustion engine 1. Examples of rapid warm-up control of the catalyst 32 include a significant ignition timing retard that is not executed during steady operation.

[0038] Furthermore, in a correction coefficient calculation process M20, the control device 100 acquires a first correction coefficient K1, a second correction coefficient K2, and a third correction coefficient K3. The first correction coefficient K1 is a value calculated in a first correction coefficient calculation process M22, which will be described later. The second correction coefficient K2 is a value calculated in a second correction coefficient calculation process M24, which will be described later. The third correction coefficient K3 is a value calculated in a third correction coefficient calculation process M26, which will be described later. Then, the control device 100 calculates the multiplication value of the basic correction coefficient Kb, the first correction coefficient K1, the second correction coefficient K2, and the third correction coefficient K3. Then, the control device 100 substitutes the calculated value for the received heat amount correction coefficient K (K = Kb · K1 · K2 · K3).

[0039] <First correction coefficient calculation process> The first correction coefficient calculation process M22 calculates a first correction coefficient K1 based on the acquired ignition timing AOP. The first correction coefficient K1 is a correction coefficient for reflecting a decrease in combustion gas temperature due to retarding the ignition timing in the heat generation amount Qburn. In this embodiment, the relationship between the retard rate RED calculated from the ignition timing AOP and the first correction coefficient K1 is stored in advance in the memory 120 as first correction coefficient map data. The control device 100 then calculates the first correction coefficient K1 based on the first correction coefficient map data and the retard rate RED. The first correction coefficient K1 is a value greater than "0" and equal to or less than "1." However, when either the first basic correction coefficient map data or the third basic correction coefficient map data is selected as the map data for calculating the basic correction coefficient Kb, the value of the first correction coefficient K1 is set to "1." In other words, no correction using the first correction coefficient K1 is performed.

[0040] The retardation ratio RED is a value defined by "ignition retard combustion period (CA) / MBT combustion period (CA) × 100 (%)." The ignition retard combustion period is the combustion period of the mixture when the mixture is ignited at the ignition timing AOP, expressed in crank angle. The MBT combustion period is the combustion period of the mixture when the mixture is ignited at the MBT, expressed in crank angle. Therefore, when the set ignition timing AOP is MBT, that is, when the ignition timing retard amount is "0," the retardation ratio RED is 100%. As the ignition timing retard amount increases, the start timing of combustion of the mixture becomes later, and therefore the ignition retard combustion period becomes shorter than the MBT combustion period. Therefore, the more the ignition timing AOP is retarded, the smaller the retardation ratio RED becomes. The control device 100 calculates the ignition retard combustion period based on the ignition timing AOP. The control device 100 also calculates the MBT combustion period based on the engine operating conditions such as the engine speed Ne. Incidentally, by calculating the retardation rate RED, the value related to the retardation of the ignition timing is made dimensionless. Therefore, the first correction coefficient map data can be applied to internal combustion engines with a different displacement from that of the internal combustion engine 1.

[0041] 6, the first correction coefficient map data is set so that when the retardation ratio RED is 100%, the first correction coefficient K1 is 1. As the retardation ratio RED becomes smaller than 100%, the value of the first correction coefficient K1 is set to gradually become smaller than 1.

[0042] <Second correction coefficient calculation process> The second correction coefficient calculation process M24 calculates a second correction coefficient K2 based on the acquired target EGR rate EGp. The second correction coefficient K2 is a correction coefficient for reflecting a decrease in combustion gas temperature due to external EGR in the heat generation amount Qburn. In this embodiment, the relationship between the advance rate ADD calculated from the target EGR rate EGp and the second correction coefficient K2 is stored in advance in the memory 120 as second correction coefficient map data. The control device 100 then calculates the second correction coefficient K2 based on the second correction coefficient map data and the advance rate ADD. The second correction coefficient K2 is a value greater than "0" and equal to or less than "1." However, when either the first basic correction coefficient map data or the third basic correction coefficient map data is selected as the map data for calculating the basic correction coefficient Kb, the value of the second correction coefficient K2 is set to "1." In other words, no correction using the second correction coefficient K2 is performed.

[0043] The advance rate ADD is a value defined as "MBT combustion period (CA) with EGR gas recirculation / MBT combustion period (CA) without EGR gas recirculation × 100 (%)." The MBT combustion period is the combustion period of the air-fuel mixture when the mixture is ignited at MBT, expressed in crank angle. Therefore, when EGR gas recirculation is not performed, that is, when the target EGR rate EGp is ​​"0%, " the advance rate ADD is 100%. As the target EGR rate EGp increases, the MBT timing shifts toward the advance side, so the "MBT combustion period with EGR gas recirculation" becomes longer toward the advance side compared to the "MBT combustion period without EGR gas recirculation." Therefore, as the target EGR rate EGp increases, the value of the advance rate ADD exceeds "100%." ​​The control device 100 calculates the advance rate ADD based on engine operating conditions such as the target EGR rate EGp and the engine speed Ne. Incidentally, by calculating the advance rate ADD, the value related to the external EGR is made dimensionless. Therefore, the second correction coefficient map data can be applied to an internal combustion engine having a displacement different from that of the internal combustion engine 1.

[0044] 7, the second correction coefficient map data is set so that when the advance rate ADD is 100%, the second correction coefficient K2 is 1. As the advance rate ADD becomes greater than 100%, the value of the second correction coefficient K2 gradually becomes smaller than 1.

[0045] <Third correction coefficient calculation process> The third correction coefficient calculation process M26 is a process for calculating a third correction coefficient K3 based on the acquired in-cylinder injection ratio Rd, fuel injection amount Q, and intake air amount GA. The third correction coefficient K3 is a correction coefficient for reflecting the decrease in combustion gas temperature due to the latent heat of vaporization of fuel injected into the cylinder in the heat generation amount Qburn. In this embodiment, the relationship between the in-cylinder ratio DD calculated from the in-cylinder injection ratio Rd and the fuel injection amount Q and the third correction coefficient K3 is stored in advance in the memory 120 as third correction coefficient map data. The control device 100 then calculates the third correction coefficient K3 based on the third correction coefficient map data and the in-cylinder ratio DD. The third correction coefficient K3 is a value greater than "0" and equal to or less than "1."

[0046] The in-cylinder ratio DD is a value defined as "in-cylinder injection amount (mg / st) / theoretical fuel injection amount (mg / st) when the engine load factor KL is 100%," and is calculated by the control device 100. The in-cylinder injection amount is the product of the in-cylinder injection ratio Rd and the fuel injection amount Q, and is calculated by the control device 100. The theoretical fuel injection amount is the fuel injection amount required to obtain a theoretical air-fuel ratio. The theoretical fuel injection amount when the engine load factor KL is 100% is calculated by the control device 100 based on the engine rotation speed Ne, predetermined map data, and the like. Therefore, when the in-cylinder injection amount is "0," that is, when the in-cylinder injection ratio Rd is "0" and the port injection ratio Rpf is "1," the in-cylinder ratio DD is 0%. Since the in-cylinder injection amount increases as the value of the in-cylinder injection ratio Rd increases, the value of the in-cylinder ratio DD increases as the in-cylinder injection ratio Rd increases. Incidentally, by calculating the in-cylinder ratio DD, the value related to the in-cylinder injection amount is made dimensionless. Therefore, the third correction coefficient map data can be applied to an internal combustion engine having a different displacement from that of the internal combustion engine 1.

[0047] 8, in the third correction coefficient map data, a value is set so that when the in-cylinder ratio DD is "0%," the third correction coefficient K3 is "1". Then, as the in-cylinder ratio DD increases, the value of the third correction coefficient K3 is set to gradually become smaller than "1".

[0048] <Calculation of received heat amount> The received heat amount calculation process M30 is a process for calculating the piston received heat amount Qp when the piston 5 receives heat due to the combustion of fuel. In this received heat amount calculation process M30, the control device 100 acquires the heat generation amount Qburn and the received heat amount correction coefficient K. Then, the value obtained by multiplying the heat generation amount Qburn by the received heat amount correction coefficient K is assigned to the piston received heat amount Qp.

[0049] <Convergence destination piston temperature calculation process> The convergence piston temperature calculation process M40 calculates the convergence piston temperature Tpc, which is the temperature to which the piston temperature Tp in the current heat balance state converges. In this convergence piston temperature calculation process M40, the control device 100 acquires the piston heat quantity Qp, the coolant temperature Tw, the jet oil temperature Tpj, which is the temperature of the lubricating oil injected from the oil jet 80, the composite thermal resistance Rcr, and the fourth thermal resistance Rpj. The control device 100 acquires the oil temperature To as a value indicating the jet oil temperature Tpj. The composite thermal resistance Rcr and the fourth thermal resistance Rpj are values ​​calculated in the thermal resistance calculation process M45, which will be described later.

[0050] When lubricating oil is being injected from the oil jet 80, the control device 100 calculates the convergence piston temperature Tpc using the following equation (2) obtained based on the thermal circuit model. When lubricating oil is not being injected from the oil jet 80, the control device 100 calculates the convergence piston temperature Tpc using the following equation (3) obtained based on the thermal circuit model.

[0051]

number

[0052]

number

[0053] <Thermal resistance calculation process> The thermal resistance calculation process M45 calculates the composite thermal resistance Rcr and the fourth thermal resistance Rpj. The composite thermal resistance Rcr is the sum of the second thermal resistance Rb, which is the thermal resistance related to heat transfer between the piston 5 and the cylinder bore 4b, and the third thermal resistance Rw, which is the thermal resistance related to heat transfer between the cylinder bore 4b and the cooling water in the water jacket 70. The fourth thermal resistance Rpj is the thermal resistance related to heat transfer between the piston 5 and the lubricating oil sprayed from the oil jet 80.

[0054] Here, as the engine rotation speed Ne increases, the number of times the piston 5 slides against the cylinder bore 4b increases, and the amount of heat transferred from the piston 5 to the cylinder bore 4b increases. Therefore, the second thermal resistance Rb tends to decrease as the engine rotation speed Ne increases. Also, the amount of heat transferred from the cylinder bore 4b to the coolant increases as the flow rate V of the coolant flowing through the water jacket 70 increases. Therefore, the third thermal resistance Rw tends to decrease as the flow rate V increases. Therefore, the composite thermal resistance Rcr tends to decrease as the engine rotation speed Ne increases or the flow rate V of the coolant increases.

[0055] Therefore, in this embodiment, the relationship between the engine rotation speed Ne and the flow rate V and the composite thermal resistance Rcr is stored in advance as composite thermal resistance map data in the memory 120. Then, the control device 100 acquires the engine rotation speed Ne and the flow rate V. Then, the control device 100 calculates the composite thermal resistance Rcr based on the acquired engine rotation speed Ne, flow rate V and the composite thermal resistance map data.

[0056] 9, the composite thermal resistance map data is set so that the value of the composite thermal resistance Rcr decreases as the engine rotation speed Ne increases. Also, the composite thermal resistance map data is set so that the value of the composite thermal resistance Rcr decreases as the flow rate V increases.

[0057] Furthermore, as the oil pressure Po increases, the flow rate of the lubricating oil supplied from the oil jet 80 to the piston 5 increases, and therefore the amount of heat transferred from the piston 5 to the lubricating oil increases. Therefore, the fourth thermal resistance Rpj tends to decrease as the oil pressure Po increases.

[0058] Therefore, in this embodiment, the relationship between the hydraulic pressure Po and the fourth thermal resistance Rpj is stored in advance in the memory 120 as fourth thermal resistance map data. Then, the control device 100 acquires the hydraulic pressure Po. Then, the fourth thermal resistance Rpj is calculated based on the acquired hydraulic pressure Po, flow rate V, and the fourth thermal resistance map data. Note that if the amount of lubricating oil supplied from the oil jet 80 to the piston 5 can be determined, the fourth thermal resistance Rpj may be calculated based on the lubricating oil supply amount instead of the hydraulic pressure Po.

[0059] As shown in FIG. 10, in the fourth thermal resistance map data, the value of the fourth thermal resistance Rpj is set so that the higher the hydraulic pressure Po, the smaller the value of the fourth thermal resistance Rpj. <Piston temperature calculation process> The piston temperature calculation process M50 is a process for calculating the piston temperature Tp. In this piston temperature calculation process M50, the control device 100 acquires the convergence piston temperature Tpc and the second thermal resistance Rb. The second thermal resistance Rb is a value calculated in the second thermal resistance calculation process M55 described below.

[0060] Here, the piston temperature Tp is a first-order lag of the convergence piston temperature Tpc. Therefore, the control device 100 calculates the piston temperature Tp based on the following equation (4) that performs first-order lag processing on the convergence piston temperature Tpc.

[0061]

number

[0062] The value of "Rpb" in equation (4) is the harmonic mean of the first thermal resistance Rp and the second thermal resistance Rb. The first thermal resistance Rp is the thermal resistance related to the heat transfer between the combustion gas and the piston 5, and is a predetermined value. The value of "Cp" in equation (4) is the heat capacity of the piston 5, and is a predetermined value.

[0063] <Second thermal resistance calculation process> The second thermal resistance calculation process M55 calculates the second thermal resistance Rb, i.e., the thermal resistance related to the heat transfer between the piston 5 and the cylinder bore 4b. As described above, the second thermal resistance Rb tends to decrease as the engine rotation speed Ne increases.

[0064] Therefore, in this embodiment, the relationship between the engine rotation speed Ne and the second thermal resistance Rb is stored in advance in the memory 120 as second thermal resistance map data. In the second thermal resistance map data, the value of the second thermal resistance Rb is set so that the value of the second thermal resistance Rb decreases as the engine rotation speed Ne increases. The control device 100 then acquires the engine rotation speed Ne. The control device 100 then calculates the second thermal resistance Rb based on the acquired engine rotation speed Ne and the second thermal resistance map data. Incidentally, the second thermal resistance Rb may also be calculated using the above-described composite thermal resistance map data. For example, the value of the composite thermal resistance Rcr calculated based on the engine rotation speed Ne when the flow rate V is set to "0" may be substituted for the value of the second thermal resistance Rb.

[0065] <Action and effect> The operation and effects of this embodiment will be described. (1) The temperature of the piston 5 correlates with the amount of heat received by the piston 5, the thermal resistances related to the temperature of the piston 5, and the temperature of the coolant. Therefore, in this embodiment, the piston temperature Tp is calculated based on the amount of heat received by the piston Qp, the first to fourth thermal resistances, and the coolant temperature Tw. In this way, the temperature of the piston 5 can be calculated without estimating the combustion gas temperature, thereby improving the accuracy of estimating the piston temperature Tp.

[0066] (2) The first correction coefficient K1 is calculated to reflect the decrease in combustion gas temperature due to ignition timing retardation in the heat generation amount Qburn. Therefore, the calculation accuracy of the heat generation amount Qburn is improved compared to when the first correction coefficient K1 is not calculated. Furthermore, the improved calculation accuracy of the heat generation amount Qburn further improves the estimation accuracy of the piston temperature Tp.

[0067] (3) The second correction coefficient K2 is calculated to reflect the decrease in combustion gas temperature due to external EGR in the calorific value Qburn. Therefore, the calorific value Qburn is calculated more accurately than when the second correction coefficient K2 is not calculated. The improved calculation accuracy of the calorific value Qburn further improves the estimation accuracy of the piston temperature Tp.

[0068] (4) The third correction coefficient K3 is calculated to reflect the decrease in combustion gas temperature due to the latent heat of vaporization of fuel injected into the cylinder in the calorific value Qburn. Therefore, the calorific value Qburn is calculated more accurately than when the third correction coefficient K3 is not calculated. This improved calculation accuracy of the calorific value Qburn further improves the accuracy of estimating the piston temperature Tp.

[0069] (5) When calculating the calorific value Qburn, the fuel injection amount Q is corrected by the fuel correction coefficient Kf. Therefore, the calorific value Qburn is calculated taking into account the calorific value per unit mass of fuel, which changes depending on the air-fuel ratio of the mixture. As a result, the accuracy of estimating the bore temperature Tb is improved compared to when correction by the fuel correction coefficient Kf is not performed.

[0070] (6) When calculating the calorific value Qburn, the lower calorific value LC of the fuel is calculated based on the alcohol concentration AD of the fuel. Therefore, the calorific value Qburn is calculated taking into account the lower calorific value that changes depending on the alcohol concentration AD. Therefore, the estimation accuracy of the bore temperature Tb is improved compared to when the lower calorific value according to the alcohol concentration AD is not calculated.

[0071] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0072] The procedures of each process shown in FIG. 2 and FIG. 3 may be changed as appropriate. Each value obtained from map data may be calculated using a function. The calculation of the first correction coefficient K1 may be omitted. Even in this case, the same effects and advantages as those described in (2) above can be obtained.

[0073] The calculation of the second correction coefficient K2 may be omitted. Even in this case, the same effects and advantages as those described in (3) above can be obtained. The calculation of the third correction coefficient K3 may be omitted. Even in this case, the same effects and advantages as those described in (4) above can be obtained.

[0074] The correction of the fuel injection amount Q by the fuel correction coefficient Kf may be omitted. Even in this case, the effects and advantages other than those of (5) above can be obtained. The calculation of the lower calorific value LC according to the alcohol concentration AD may be omitted. Even in this case, the effects and advantages other than those of (6) above can be obtained.

[0075] The control device 100 includes a CPU 110 and a memory 120, and is not limited to executing software processing. For example, it may include a dedicated hardware circuit (e.g., ASIC) that processes at least part of the software processing executed in the above embodiments. That is, the control device 100 may have any of the following configurations (a) to (c): (a) A processing device that executes all of the above processing in accordance with a program, and a program storage device such as a memory that stores the program; (b) A processing device and program storage device that executes part of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing; or (c) A dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software processing circuits and dedicated hardware circuits that include a processing device and a program storage device. That is, the above processing may be executed by a processing circuit that includes at least one software processing circuit and one or more dedicated hardware circuits. [Explanation of symbols]

[0076] 1...Internal combustion engine 2...Cylinder block 3...Cylinder head 4...Cylinder 4b...Cylinder bore 9...Intake port 10...Exhaust port 11...Spark plug 11...Internal combustion engine 12...Intake valve 13...Exhaust valve 14...Throttle valve 20...Intake passage 22...Port injection valve 30...Exhaust passage 35...In-cylinder injection valve 36...Port injection valve 41...Crank angle sensor 44...Air flow meter 45...Water temperature sensor 46...Air-fuel ratio sensor 47...Pump speed sensor 60...Water pump 70...Water jacket 80...Oil jet 100...Control device

Claims

[Claim 1] An internal combustion engine equipped with an in-cylinder injection valve that injects fuel directly into a combustion chamber and a port injection valve that injects fuel into an intake port, capable of using a mixed fuel of alcohol fuel and gasoline fuel, a process of calculating a heat value generated when fuel supplied into a cylinder of the internal combustion engine is burned based on the engine rotation speed, the fuel injection amount, the target air-fuel ratio, the intake air amount, and the alcohol concentration of the fuel; a process of calculating a heat reception correction coefficient based on an engine load factor, an ignition timing, a target EGR rate, the fuel injection amount, and an in-cylinder injection rate which is a rate of the amount of fuel injected from the in-cylinder injection valve within the fuel injection amount; a process of calculating the amount of heat received by a piston of the internal combustion engine when the fuel supplied into the cylinder is combusted, by multiplying the heat generation amount by the heat reception correction coefficient, without relying on an estimated value of the combustion gas temperature; obtaining a thermal resistance related to the temperature of the piston; A process of acquiring a coolant temperature, which is a temperature of the coolant for the internal combustion engine; and calculating a temperature of the piston based on the amount of heat received, the thermal resistance, and the cooling water temperature. Control device for internal combustion engines.

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