Control device for internal combustion engine

Abstract

To accurately calculate a value which is referred to when estimating a wall surface temperature of a cylinder bore.SOLUTION: A control device 100 executes processing for calculating a wall surface temperature of a cylinder bore 4b on the basis of a cooling water flow rate in a water jacket 70 provided in a cylinder block 2 of an internal combustion engine 1, a cooling water temperature in the water jacket 70 and a heat generation amount when fuel supplied to a cylinder of the internal combustion engine 1 is burned. The control device 100 executes flow rate calculation processing for calculating the cooling water flow rate on the basis of engine speed of the internal combustion engine 1 and an opening variable related to an opening of a thermostat 68.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 is configured to estimate the wall surface temperature of the cylinder bore based on the coolant temperature and the accumulated air volume. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-231948 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, it is possible to calculate the wall temperature of the cylinder bore by referring to the flow rate of the cooling water in a water jacket provided in the cylinder block of the internal combustion engine, the temperature of the cooling water in the water jacket, and the amount of heat generated when fuel supplied to the cylinder of the internal combustion engine is burned. In this case, when estimating any of the values ​​to be referenced when calculating the wall temperature of the cylinder bore, it is desirable to calculate the estimated value with high accuracy. [Means for solving the problem]

[0005] The control device for an internal combustion engine that solves the above problem is applied to an internal combustion engine that includes a coolant flow path having a radiator, a bypass flow path that bypasses the radiator, a thermostat that adjusts the flow rate of coolant passing through the radiator according to the temperature of the coolant, and a mechanical water pump connected to a crankshaft. The control device executes a process of calculating a wall temperature of a cylinder bore based on the coolant flow rate and the coolant temperature in a water jacket provided in a cylinder block of the internal combustion engine, and the amount of heat generated when fuel supplied to a cylinder of the internal combustion engine is burned. The control device then executes a flow rate calculation process that calculates the coolant flow rate based on an engine speed of the internal combustion engine and an opening degree variable related to the opening degree of the thermostat.

[0006] Since the opening degree of the thermostat changes depending on the temperature of the cooling water, the temperature of the cooling water can be used as the opening degree variable related to the opening degree of the thermostat. Also, the opening degree of the thermostat itself can be used as the opening degree variable. Effect of the Invention

[0007] This control device for an internal combustion engine can accurately calculate a value to be referenced when estimating the wall surface temperature of the cylinder bore. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an internal combustion engine according to one embodiment. [Diagram 2] FIG. 2 is a flowchart showing a procedure of a process executed by the control device of the embodiment. [Diagram 3] FIG. 3 is a block diagram showing a flow rate calculation process executed by the control device of the embodiment. [Figure 4] FIG. 4 is a block diagram showing a temperature calculation process executed by the control device of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, one embodiment of a control device for an internal combustion engine will be described 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.

[0010] A water jacket 70 through which cooling water flows is formed in the cylinder block 2. A cylinder head 3 is attached to the upper part of the cylinder block 2. A water jacket through which cooling water flows is formed in the cylinder head 3.

[0011] The water jacket 70 of the cylinder block 2 and the water jacket of the cylinder head 3 are connected by a cooling water passage 62 formed by external piping. A mechanical water pump 60 connected to the crankshaft 7 and a radiator 64 serving as a heat sink are provided midway along the cooling water passage 62. A bypass passage 66 through which the cooling water flows, bypassing the radiator 64, is also connected to the cooling water passage 62.

[0012] At the connection between the cooling water passage 62 and the bypass passage 66, a thermostat 68 is provided which adjusts the flow rate of the cooling water passing through the radiator 64 in accordance with the temperature of the cooling water. The opening degree of the thermostat 68 gradually increases when the temperature of the cooling water reaches or exceeds a predetermined temperature, and finally reaches a fully open state. Also, as the opening degree of the thermostat 68 increases, the flow rate of the cooling water passing through the bypass passage 66 out of the cooling water flowing through the cooling water passage 62 decreases, and thus the flow rate of the cooling water passing through the radiator 64 increases.

[0013] The flow path diameter of the bypass flow path 66 is smaller than the flow path diameter of the cooling water flow path 62. Therefore, the cooling water flow path 62 is a flow path in which the pressure loss is larger when the cooling water flows through the bypass flow path 66 than when the cooling water flows through the radiator 64.

[0014] In the internal combustion engine 1, a cooling water inlet is provided in the water jacket 70 of the cylinder block 2, and a cooling water outlet is provided in the water jacket of the cylinder head 3. Therefore, the cooling water pumped by the water pump 60 flows into the water jacket 70 of the cylinder block 2, and then flows into the water jacket of the cylinder head 3. The cooling water then flows from the water jacket of the cylinder head 3 into the cooling water flow passage 62.

[0015] A combustion chamber 8 is formed in the cylinder 4 between the top surface of the piston 5 and the cylinder head 3. In addition, the cylinder head 3 is provided with an in-cylinder injection valve 35 that directly injects fuel into the combustion chamber 8, and an ignition plug 11 that spark-ignites the mixture in the combustion chamber 8, for each cylinder of the internal combustion engine 1.

[0016] Furthermore, the cylinder head 3 is 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 for adjusting the amount of intake air. The intake port 9 is also provided with an intake valve 12 for opening and closing the intake port 9. The cylinder head 3 is also provided with a port injection valve 36 for injecting fuel into the intake port 9, for each cylinder of the internal combustion engine 1.

[0017] An exhaust valve 13 that opens and closes the exhaust port 10 is provided in 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.

[0018] The control device 100 includes a 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 thereby perform various engine controls.

[0019] 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 coolant temperature Tw corresponds to the outlet temperature, which is the temperature of the coolant flowing out from 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.

[0020] 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 steadily operated with the throttle valve fully open at the current engine speed Ne. The cylinder inflow air amount is the amount of air that flows into each cylinder during the intake stroke.

[0021] <Estimation of bore temperature Tb> The bore temperature Tb, which is the wall surface temperature of the cylinder bore 4b, can be calculated based on the amount of heat Qburn generated when fuel supplied into the cylinder of the internal combustion engine 1 is burned, the bore peripheral water temperature Twb, which is the temperature of the coolant in the water jacket 70, and the thermal resistance R between the cylinder 4 and the coolant. Here, the thermal resistance R correlates with the coolant flow rate V in the water jacket 70. Therefore, in this embodiment, the bore temperature Tb is calculated based on the coolant flow rate V in the water jacket 70, the bore peripheral water temperature Twb, and the amount of heat Qburn generated when fuel is burned.

[0022] 2 shows the procedure of the process of calculating the bore temperature Tb executed by the control device 100. The control device 100 repeatedly executes this process at each predetermined calculation cycle. In the following, step numbers are represented by numbers preceded by "S."

[0023] 2 starts, the control device 100 acquires the bore-surrounding water temperature Twb, the cooling water flow rate V, and the fuel injection amount Q (S100). The bore-surrounding water temperature Twb and the cooling water flow rate V are values ​​calculated by the control device 100 in a separate process, which will be described later. The fuel injection amount Q is the amount of fuel injected from the port injection valve 36 or the in-cylinder injection valve 35 at a preset injection timing.

[0024] Next, the control device 100 calculates the thermal resistance R based on the cooling water flow rate V (S110). The thermal resistance R is the thermal resistance between the cylinder bore 4b and the cooling water in the water jacket 70.

[0025] The thermal resistance R is a value that correlates with the coolant flow rate V in the water jacket 70. In this embodiment, the relationship between the coolant flow rate V and the thermal resistance R is stored in advance as map data in the memory 120. Then, the control device 100 calculates the thermal resistance R based on the map data. In the map data of the thermal resistance R, the value of the thermal resistance R is set so that the larger the coolant flow rate V, the smaller the calculated value of the thermal resistance R becomes.

[0026] Next, the control device 100 calculates the amount of heat generated per unit time Qburn when the fuel supplied into the cylinder of the internal combustion engine 1 is burned, based on the following formula (1) (S120). Qburn = Ne Q LC α … (1) Ne: Engine speed Q: Fuel injection amount LC: Lower heating value of fuel α: A constant for adjusting the units The lower heating value LC is a preset value.

[0027] Next, the control device 100 calculates the heat flow rate Qw (S130). The heat flow rate Qw is the amount of heat transferred per unit time from the cylinder bore 4b to the cooling water in the water jacket 70. The control device 100 multiplies the heat generation amount Qburn by a coefficient K and assigns the result to the heat flow rate Qw. The coefficient K is an adaptation value for converting the heat generation amount Qburn to the heat flow rate Qw. Note that while the coefficient K is a fixed value in this embodiment, it may be a variable value that changes depending on, for example, the engine operating state.

[0028] Next, the control device 100 calculates the bore temperature Tb from the following formula (2) based on the thermal resistance R, the heat flow rate Qw, and the bore peripheral water temperature Twb (S140). Tb = R Qw + Twb … (2) R: Thermal resistance Qw: heat flow rate Twb: Water temperature around the bore Then, after executing the process of S140, the control device 100 ends the execution of this process in the current calculation cycle.

[0029] <Estimation of cooling water flow rate V> The control device 100 executes a flow rate calculation process for calculating the above-mentioned cooling water flow rate V in the water jacket 70.

[0030] FIG. 3 shows a flow rate calculation process that the control device 100 executes at each predetermined calculation cycle. The basic flow rate calculation process M1 is a process for calculating a basic flow rate Vb, which is a base value of the coolant flow rate V when the thermostat 68 is in a fully open state. In the basic flow rate calculation process M1, the control device 100 acquires the engine rotation speed Ne. Then, the control device 100 calculates the basic flow rate Vb so that the higher the acquired engine rotation speed Ne, the larger the value of the basic flow rate Vb becomes.

[0031] The first coefficient setting process M2 is a process for setting a first coefficient K1. The first coefficient K1 is the following value set within a range greater than "0" and equal to or less than "1". That is, when the opening degree variable relating to the opening degree of the thermostat 68 is a value that increases the flow rate of the cooling water in the bypass passage 66, the coefficient is set so that the calculated cooling water flow rate V is smaller than when the opening degree variable is a value that decreases the flow rate of the cooling water. In the first coefficient setting process M2, the control device 100 acquires an opening degree variable relating to the opening degree of the thermostat 68. Here, the opening degree of the thermostat 68 changes according to the temperature of the cooling water. Therefore, in this embodiment, the above-mentioned cooling water temperature Tw is acquired as the opening degree variable relating to the opening degree of the thermostat 68. Then, the control device 100 sets the first coefficient K1 based on the acquired cooling water temperature Tw. More specifically, the first coefficient K1 is set so that the value of the first coefficient K1 approaches "1" as the opening degree of the thermostat 68 increases with the rise in the cooling water temperature Tw.

[0032] The flow rate calculation process M3 is a process for calculating the cooling water flow rate V. In the flow rate calculation process M3, the control device 100 acquires a basic flow rate Vb and a first coefficient K1. Then, the control device 100 calculates the cooling water flow rate V by substituting a value obtained by multiplying the basic flow rate Vb by the first coefficient K1 into the cooling water flow rate V.

[0033] <Estimation of the water temperature around the bore Twb> The control device 100 executes a temperature calculation process for calculating the bore peripheral water temperature Twb. FIG. 4 shows a temperature calculation process that the control device 100 executes at each predetermined calculation cycle.

[0034] The conversion value calculation process M4 is a process for calculating a heat capacity conversion value Cs of the coolant in the water jacket 70. In the conversion value calculation process M4, the control device 100 multiplies the calculated coolant flow rate V by the specific heat c of the coolant and the density ρ of the coolant, and assigns the result to the heat capacity conversion value Cs. The heat capacity conversion value Cs calculated in this manner indicates the amount of heat required to raise the temperature of the coolant flowing through the water jacket 70 by 1 degree per unit time. Note that the specific heat c of the coolant and the density ρ of the coolant are preset values.

[0035] The first temperature difference calculation process M5 is a process for calculating the first temperature difference ΔTw1. When the temperature difference ΔTw is a value obtained by subtracting the inlet temperature, which is the temperature of the cooling water flowing into the internal combustion engine 1, from the outlet temperature, which is the temperature of the cooling water flowing out from the internal combustion engine 1, the first temperature difference ΔTw1 is a base value of the temperature difference ΔTw. In the first temperature difference calculation process M5, the control device 100 acquires the heat flow rate Qw and the heat capacity conversion value Cs. Then, the control device 100 assigns the value obtained by dividing the heat flow rate Qw by the heat capacity conversion value Cs to the first temperature difference ΔTw1 (ΔTw1=Qw / Cs).

[0036] The second coefficient setting process M6 is a process for setting the second coefficient K2. The second coefficient K2 is the following value set within a range greater than "0" and equal to or less than "1". That is, when the opening degree variable relating to the opening degree of the thermostat 68 is a value that increases the flow rate of the cooling water in the bypass passage 66, the second coefficient K2 is a coefficient for making the calculated temperature difference ΔTw smaller than when the opening degree variable is a value that decreases the flow rate of the cooling water. In the second coefficient setting process M6, the control device 100 acquires an opening degree variable relating to the opening degree of the thermostat 68. Here again, in this embodiment, the control device 100 acquires the cooling water temperature Tw as the opening degree variable relating to the opening degree of the thermostat 68. Then, the control device 100 sets the second coefficient K2 based on the acquired cooling water temperature Tw. More specifically, the second coefficient K2 is set so that the value of the second coefficient K2 approaches "1" as the opening degree of the thermostat 68 increases with the rise in the cooling water temperature Tw.

[0037] The second temperature difference calculation process M7 is a process for calculating the second temperature difference ΔTw2. In the second temperature difference calculation process M7, the control device 100 acquires the first temperature difference ΔTw1 and the second coefficient K2. Then, the control device 100 multiplies the first temperature difference ΔTw1 by the second coefficient K2 and assigns the result to the second temperature difference ΔTw2 (ΔTw2=ΔTw1·K2). The second coefficient setting process M6 and the second temperature difference calculation process M7 are correction processes for correcting the first temperature difference ΔTw1 based on an opening degree variable related to the opening degree of the thermostat 68.

[0038] The third coefficient setting process M8 is a process for setting the third coefficient K3. The third coefficient K3 is a time constant for compensating for a first-order delay occurring between the calculated second temperature difference ΔTw2 and the actual temperature difference. In the third coefficient setting process M8, the control device 100 acquires the cooling water temperature Tw and the cooling water flow rate V. Then, the control device 100 calculates the third coefficient K3 based on the cooling water temperature Tw and the cooling water flow rate V. More specifically, when the cooling water flow rate V is large, the third coefficient K3 is calculated so that the amount of change per unit time of the second temperature difference ΔTw2 is larger than when the cooling water flow rate V is small. In addition, when the thermostat 68 is in an open state, the cooling water flows via the radiator 64, so the flow path length through which the cooling water flows is longer than when the thermostat 68 is in a closed state. When the flow path length of the cooling water is longer, the amount of change per unit time of the actual temperature difference tends to be smaller. Therefore, it is desirable to calculate the third coefficient K3 so that the amount of change per unit time of the second temperature difference ΔTw2 becomes smaller as the flow path length of the cooling water becomes longer. Here, the flow path length of the coolant changes depending on whether the thermostat 68 is open or closed. The opening degree of the thermostat 68 changes depending on the temperature of the coolant. Therefore, in this embodiment, the third coefficient K3 is calculated based on the coolant temperature Tw, which is an opening degree variable related to the opening degree of the thermostat 68. More specifically, when the coolant temperature Tw is a value when the flow path length of the coolant is long, the third coefficient K3 is calculated so that the amount of change per unit time of the second temperature difference ΔTw2 is smaller than when the flow path length is short.

[0039] The first-order delay process M9 is a value for calculating the third temperature difference ΔTw3, which is a value obtained by subjecting the second temperature difference ΔTw2 to first-order delay processing. In the first-order delay process M9, the control device 100 acquires the second temperature difference ΔTw2, the third coefficient K3, and the predetermined calculation cycle time TIM. Then, based on these respective values, the value obtained by subjecting the second temperature difference ΔTw2 to first-order delay processing is substituted for the third temperature difference ΔTw3.

[0040] The fourth temperature difference calculation process M10 is a process for calculating a fourth temperature difference ΔTw4. The fourth temperature difference ΔTw4 is a value indicating the temperature difference between the outlet temperature, which is the temperature of the cooling water flowing out from the internal combustion engine 1, and the bore peripheral water temperature Twb. In other words, the fourth temperature difference ΔTw4 is a value indicating the temperature difference between the cooling water temperature Tw and the bore peripheral water temperature Twb. In the fourth temperature difference calculation process M10, the control device 100 acquires the third temperature difference ΔTw3 and a fourth coefficient K4. The fourth coefficient K4 is a weighting coefficient for converting the third temperature difference ΔTw3 into the temperature difference between the cooling water temperature Tw and the bore peripheral water temperature Twb, and is a preset adaptation value. Then, the control device 100 substitutes a value obtained by multiplying the third temperature difference ΔTw3 by the fourth coefficient K4 into the fourth temperature difference ΔTw4.

[0041] When the value of the fourth coefficient K4 approaches "0", the bore-surrounding water temperature Twb calculated in the bore-surrounding water temperature calculation process M11 described later approaches the outlet temperature, which is the temperature of the coolant flowing out from the internal combustion engine 1, that is, the coolant temperature Tw. On the other hand, when the value of the fourth coefficient K4 approaches "1", the bore-surrounding water temperature Twb calculated in the bore-surrounding water temperature calculation process M11 described later approaches the inlet temperature, which is the temperature of the coolant flowing into the internal combustion engine 1.

[0042] The bore-periphery water temperature calculation process M11 is a process for calculating the bore-periphery water temperature Twb. In the bore-periphery water temperature calculation process M11, the control device 100 acquires the fourth temperature difference ΔTw4 and the cooling water temperature Tw. The control device 100 then calculates a value obtained by subtracting the fourth temperature difference ΔTw4 from the cooling water temperature Tw, and assigns the calculated value to the bore-periphery water temperature Twb to calculate the bore-periphery water temperature Twb.

[0043] <Actions and Effects of the Present Embodiment> The operation and effects of this embodiment will be described below. (1) In this embodiment, when the bore temperature Tb is calculated, the cooling water flow rate V in the water jacket 70 provided in the cylinder block 2 is referred to. Here, in the mechanical water pump 60 connected to the crankshaft 7, the flow rate of the cooling water changes according to the engine rotation speed Ne. Also, the cooling water flow rate V in the water jacket 70 changes according to the opening degree of the thermostat 68 of the cooling water flow passage 62. Therefore, in the above-mentioned flow rate calculation process, the cooling water flow rate V is calculated based on the engine rotation speed Ne related to the cooling water flow rate V in the water jacket 70 and the cooling water temperature Tw, which is an opening degree variable related to the opening degree of the thermostat 68. Therefore, the cooling water flow rate V, which is a value referred to when estimating the bore temperature Tb, can be calculated with high accuracy.

[0044] (2) In the case of a cooling water flow passage in which the pressure loss is larger when the cooling water flows through the bypass flow passage 66 than when the cooling water flows through the radiator 64, the following is true. That is, when the flow rate of the cooling water in the bypass flow passage 66 is larger, the flow rate of the cooling water flowing through the cooling water flow passage 62 is smaller than when the flow rate of the cooling water in the bypass flow passage 66 is smaller. Here, the flow rate of the cooling water in the bypass flow passage 66 changes according to the opening degree of the thermostat 68. The cooling water flow passage 62 of this embodiment is a cooling water flow passage in which the pressure loss is larger when the cooling water flows through the bypass flow passage 66 than when the cooling water flows through the radiator 64. Therefore, when the cooling water temperature Tw is a value that increases the flow rate of the cooling water in the bypass flow passage 66, the cooling water flow rate V calculated in the flow rate calculation process is calculated so that the cooling water flow rate V is smaller than when the flow rate of the cooling water in the bypass flow passage 66 is a value that decreases. Specifically, the cooling water flow rate V is calculated by multiplying the basic flow rate Vb by a first coefficient K1 that is set based on the cooling water temperature Tw. Therefore, the cooling water flow rate V can be calculated accurately according to the opening degree of the thermostat 68.

[0045] (3) The temperature difference ΔTw between the outlet temperature, which is the temperature of the cooling water flowing out from the internal combustion engine 1, and the inlet temperature, which is the temperature of the cooling water flowing into the internal combustion engine 1, is generated by the rise in the temperature of the cooling water due to heat received from the cylinder bore 4b. Therefore, the temperature difference ΔTw is a value that correlates with the bore surrounding water temperature Twb, which is the cooling water temperature in the water jacket 70. The bore surrounding water temperature Twb can be estimated based on the outlet temperature, which is the cooling water temperature Tw, and the temperature difference ΔTw.

[0046] Here, the temperature rise of the cooling water caused by the heat received from the cylinder bore 4b can be calculated from the heat capacity conversion value Cs of the cooling water calculated from the cooling water flow rate V, the density ρ of the cooling water, and the specific heat c of the cooling water, and the heat flow rate Qw. In the first temperature difference calculation process M5 in the temperature calculation process, the first temperature difference ΔTw1 is calculated based on these values. In the bore surrounding water temperature calculation process M11 in the temperature calculation process, the bore surrounding water temperature Twb is calculated based on the fourth temperature difference ΔTw4 obtained by performing various processes on the first temperature difference ΔTw1 and the cooling water temperature Tw. Therefore, the bore surrounding water temperature Twb, which is a value to be referred to when estimating the bore temperature Tb, can be calculated with high accuracy.

[0047] (4) When the coolant flows through the coolant passage 62 via the radiator 64, the coolant that has received heat in the internal combustion engine 1 is cooled by the radiator 64 before flowing into the internal combustion engine 1, so that the temperature difference ΔTw is large. On the other hand, when the coolant flows through the bypass passage 66, the coolant that has received heat in the internal combustion engine 1 flows into the internal combustion engine 1 without being cooled by the radiator 64, so that the temperature difference ΔTw is small. Therefore, the temperature difference ΔTw changes depending on the opening degree of the thermostat 68. Therefore, in the second coefficient setting process M6 and the second temperature difference calculation process M7 in the temperature calculation process, the first temperature difference ΔTw1 is corrected based on the coolant temperature Tw, which is an opening degree variable related to the opening degree of the thermostat 68. Therefore, the accuracy of the first temperature difference ΔTw1 is improved.

[0048] (5) The temperature difference ΔTw decreases as the flow rate of the cooling water flowing through the bypass flow passage 66 increases among the cooling water flowing through the cooling water flow passage 62. Therefore, the second coefficient setting process M6 and the second temperature difference calculation process M7 in the temperature calculation process execute the following process. That is, when the cooling water temperature Tw, which is the opening degree variable, is a value that increases the flow rate of the cooling water in the bypass flow passage 66, the first temperature difference ΔTw1 is corrected so that the first temperature difference ΔTw1 is smaller than when the flow rate of the cooling water is a value that decreases. Specifically, the first temperature difference ΔTw1 is multiplied by the second coefficient K2, which is set based on the cooling water temperature Tw, to calculate the second temperature difference ΔTw2, which is the temperature difference ΔTw after correcting the first temperature difference ΔTw1, as the cooling water flow rate V. Therefore, the correction of the first temperature difference ΔTw1 described above can be performed appropriately.

[0049] (6) The degree of the first-order lag occurring between the calculated second temperature difference ΔTw2 and the actual temperature difference varies depending on the flow rate of the coolant and the flow path length of the coolant, which varies depending on the open / close state of the thermostat 68, as described above. Therefore, in the third coefficient setting process M8 in the temperature calculation process, the third coefficient K3, which is a time constant for compensating for the first-order lag, is calculated based on the coolant temperature Tw, which is related to the coolant flow rate V and the flow path length of the coolant. Then, in the first-order lag process M9 in the temperature calculation process, the third coefficient K3 is used to perform first-order lag processing of the second temperature difference ΔTw2. Therefore, the third temperature difference ΔTw3, which is a value obtained by performing first-order lag processing on the second temperature difference ΔTw2, can be calculated with high accuracy.

[0050] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0051] In the bore surrounding water temperature calculation process M11, the value obtained by subtracting the fourth temperature difference ΔTw4 from the cooling water temperature Tw, which is the outlet temperature, is substituted for the bore surrounding water temperature Twb. Alternatively, if the inlet temperature, which is the temperature of the cooling water flowing into the internal combustion engine 1, is detected by a sensor instead of the outlet temperature, the value obtained by adding the fourth temperature difference ΔTw4 to the inlet temperature detected by the sensor may be substituted for the bore surrounding water temperature Twb. However, in this case, the fourth coefficient K4 is set to a value obtained by subtracting the above-mentioned fourth coefficient K4 from "1".

[0052] When the opening degree of the thermostat 68 is detected, the detected opening degree may be used as an opening degree variable relating to the opening degree of the thermostat 68. The amount of heat generated per unit mass of fuel changes depending on the air-fuel ratio of the mixture. Therefore, when calculating the heat generation amount Qburn, the amount of heat generated per unit mass of fuel according to the change in the air-fuel ratio of the mixture may be taken into consideration. In this case, the accuracy of estimating the heat generation amount Qburn is improved, and therefore the accuracy of estimating the bore temperature Tb is also improved.

[0053] When a mixed fuel in which alcohol fuel and gasoline fuel are mixed is used as fuel for the internal combustion engine 1, the lower heating value LC changes according to the alcohol concentration AD. Therefore, when such a mixed fuel is used, the alcohol concentration AD is estimated or detected. When calculating the above-mentioned heating value Qburn, the lower heating value LC may be variably set based on the ascertained alcohol concentration AD. In this case, the estimation accuracy of the heating value Qburn is improved, and therefore the estimation accuracy of the bore temperature Tb is improved.

[0054] 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, etc.) that processes at least a part of the software processing executed in the above embodiment. That is, the control device 100 may have any of the following configurations (a) to (c). (a) It includes a processing device that executes all of the above processing according to a program, and a program storage device such as a memory that stores the program. (b) It includes a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) It includes a dedicated hardware circuit that executes all of the above processing. Here, the software processing circuit including the processing device and the program storage device and the dedicated hardware circuit may be multiple. That is, the above processing may be executed by a processing circuit that includes at least one of one or more software processing circuits and one or more dedicated hardware circuits. [Explanation of symbols]

[0055] 1. Internal combustion engine 2...Cylinder block 3. Cylinder head 4...Cylinder 4b…Cylinder bore 7…Crankshaft 8…Combustion chamber 9…Intake port 10…Exhaust port 20…Intake passage 30…Exhaust passage 35…In-cylinder injection valve 36…Port injection valve 41...Crank angle sensor 45...Water temperature sensor 60…Water pump 62...cooling water passage 64…Radiator 66...Bypass flow path 68…Thermostat 70…Water jacket 100...Control device 110…CPU 120…Memory

Claims

1. A control device is applied to an internal combustion engine having a cooling water passage including a radiator, a bypass passage that bypasses the radiator, a thermostat that adjusts a flow rate of cooling water passing through the radiator in accordance with a temperature of the cooling water, and a mechanical water pump that is connected to a crankshaft, and executes a process of calculating a wall surface temperature of a cylinder bore based on a cooling water flow rate and a cooling water temperature in a water jacket provided in a cylinder block of the internal combustion engine, and an amount of heat generated when fuel supplied to a cylinder of the internal combustion engine is combusted, A flow rate calculation process is executed to calculate the cooling water flow rate based on an engine speed of the internal combustion engine and an opening degree variable related to an opening degree of the thermostat. A control device for an internal combustion engine.

2. the cooling water flow passage is a passage in which a pressure loss is larger when the cooling water flows through the bypass flow passage than when the cooling water flows through the radiator, The flow rate calculation process executes a process of calculating the cooling water flow rate so that, when the opening degree variable is a value that increases the flow rate of the cooling water in the bypass flow path, the cooling water flow rate is reduced compared to when the opening degree variable is a value that decreases the flow rate of the cooling water. The control device for an internal combustion engine according to claim 1.

3. A temperature difference between an outlet temperature, which is the temperature of the cooling water flowing out from the internal combustion engine, and an inlet temperature, which is the temperature of the cooling water flowing into the internal combustion engine, is calculated based on the heat flow rate calculated based on the heat generation amount, the cooling water flow rate, the cooling water density, and the specific heat of the cooling water, and a temperature calculation process is performed to calculate the cooling water temperature in the water jacket based on either one of the outlet temperature and the inlet temperature and the temperature difference. The control device for an internal combustion engine according to claim 1.

4. The temperature calculation process executes a correction process for correcting the temperature difference based on the opening degree variable. The control device for an internal combustion engine according to claim 3.

5. The correction process is a process of correcting the temperature difference so that, when the opening degree variable is a value that increases the flow rate of the cooling water in the bypass flow path, the temperature difference is smaller than when the opening degree variable is a value that decreases the flow rate of the cooling water. The control device for an internal combustion engine according to claim 4.

Images