Control device

Abstract

To provide a control device and a control method capable of appropriately controlling a flow rate of a cooling medium.SOLUTION: A control device controls a flow rate of a cooling medium flowing and circulating a cooling flow passage of an internal combustion engine. The control device includes: acquisition means for acquiring a detection value of a temperature of the cooling medium at an outlet of the cooling flow passage; and calculation means for calculating, on the basis of a correlation between a difference between temperatures of the cooling medium at an inlet and the outlet of the cooling flow passage and an inverse number of the flow rate, the inverse number of the flow rate so that a difference between the temperature of the cooling medium at the inlet of the cooling flow passage and the detection value compensates delay before arrival at a target value in accordance with the control of the flow rate, and calculating the flow rate from the inverse number of the flow rate.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a control device. [Background technology]

[0002] For example, a control device for an internal combustion engine such as an engine controls the flow rate of a cooling medium (e.g., cooling water) discharged from a pump to the internal combustion engine (see, for example, Patent Document 1). For example, the control device needs to quickly reduce the flow rate of the cooling medium to increase the temperature of the internal combustion engine in order to reduce cooling loss and mechanical loss of the internal combustion engine and improve combustion efficiency, and also needs to quickly increase the flow rate of the cooling medium to reduce the temperature of the internal combustion engine in order to suppress an increase in exhaust loss due to knocking of the internal combustion engine and abnormalities due to boiling of the cooling medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-209792 A Summary of the Invention [Problem to be solved by the invention]

[0004] The control device controls the flow rate of the cooling medium so that the temperature reaches a target value based on the temperature of the cooling medium detected by a water temperature sensor at the outlet of the cooling passage of the internal combustion engine (hereinafter, outlet temperature). However, due to a delay in the response to the control of the control device, the flow rate of the cooling medium may be higher or lower than the control value.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a control device and a control method capable of appropriately controlling the flow rate of a cooling medium. [Means for solving the problem]

[0006] The control device of the present invention is a control device for controlling the flow rate of a cooling medium circulating through a cooling passage of an internal combustion engine, and has an acquisition means for acquiring a detection value of the temperature of the cooling medium at an outlet of the cooling passage, and a calculation means for calculating the reciprocal of the flow rate based on a correlation between the temperature difference of the cooling medium at the inlet and outlet of the cooling passage and the reciprocal of the flow rate so as to compensate for the delay until the difference between the temperature of the cooling medium at the inlet of the cooling passage and the detected value reaches a target value in accordance with the control of the flow rate, and for calculating the flow rate from the reciprocal of the flow rate.

[0007] In the above configuration, the calculation means may calculate a rate of change of the temperature difference with respect to the reciprocal of the flow rate in the correlation as a parameter related to the amount of heat the cooling medium receives from the internal combustion engine.

[0008] In the above configuration, the calculation means may perform a filtering process using a low-pass filter on the difference between the temperature of the cooling medium at the inlet of the cooling flow passage and the detected value.

[0009] In the above configuration, the present invention may further include a correction means for predicting the delay from the inverse of the flow rate calculated by the calculation means based on the correlation, and correcting the difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value based on the prediction result.

[0010] In the above configuration, the correcting means may predict the delay including a dead time of a response to control of the flow rate from an inverse number of the flow rate calculated by the calculating means.

[0011] In the above configuration, a circulation flow path through which the cooling medium circulates is provided with a radiator that cools the cooling medium, and a thermostat that opens so that the cooling medium passes through the radiator when the temperature of the cooling medium is equal to or higher than a threshold value, and the circulation flow path has an estimation means that estimates a temperature of the cooling medium at an inlet of the cooling flow path from the detection value based on a transfer function corresponding to the circulation flow path, and the calculation means may limit the flow rate to a first lower limit value or higher when the estimated value of the temperature estimated by the estimation means is equal to or higher than the threshold value.

[0012] In the above configuration, the present invention may further include an estimation means for estimating a temperature of the cooling medium at an inlet of the cooling flow passage from the detection value based on a transfer function corresponding to a circulation flow passage through which the cooling medium circulates, and the calculation means may calculate a second lower limit value of the flow rate from a heat generation state of the internal combustion engine and a difference between the boiling point of the cooling medium in the cooling flow passage and the temperature estimated by the estimation means, and limit the flow rate to equal to or greater than the second lower limit value.

[0013] The control method of the present invention is a method for controlling the flow rate of a cooling medium circulating through a cooling passage of an internal combustion engine, in which a computer executes processing to obtain a detection value of the temperature of the cooling medium at an outlet of the cooling passage, calculate the reciprocal of the flow rate based on a correlation between the temperature difference of the cooling medium at the inlet and outlet of the cooling passage and the reciprocal of the flow rate so as to compensate for the delay until the difference between the temperature of the cooling medium at the inlet of the cooling passage and the detection value reaches a target value in response to control of the flow rate, and calculate the flow rate from the reciprocal of the flow rate.

[0014] In the above configuration, in the process of calculating the reciprocal of the flow rate, the reciprocal of the flow rate may be calculated as a parameter relating to the amount of heat that the cooling medium receives from the internal combustion engine, using the rate of change of the temperature difference with respect to the reciprocal of the flow rate in the correlation.

[0015] In the above configuration, in the process of calculating the reciprocal of the flow rate, a filtering process may be performed using a low-pass filter on a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detected value.

[0016] In the above configuration, the computer may further execute a process of predicting the delay from the inverse of the calculated flow rate based on the correlation, and correcting the difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value based on the prediction result.

[0017] In the above configuration, in the process of correcting the difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value, the delay including the dead time of the response to the control of the flow rate may be predicted from the inverse of the calculated flow rate.

[0018] In the above configuration, a circulation flow path through which the cooling medium circulates is provided with a radiator that cools the cooling medium, and a thermostat that opens so that the cooling medium passes through the radiator when the temperature of the cooling medium is equal to or higher than a threshold value, and the computer further executes a process of estimating a temperature of the cooling medium at an inlet of the cooling flow path from the detected value based on a transfer function corresponding to the circulation flow path, and in a process of calculating the reciprocal of the flow rate, if the estimated value of the estimated temperature is equal to or higher than the threshold value, the flow rate may be limited to equal to or higher than a first lower limit value.

[0019] In the above configuration, the computer may further execute a process of estimating a temperature of the cooling medium at the inlet of the cooling flow passage from the detected value based on a transfer function corresponding to a circulation flow passage through which the cooling medium circulates, and in the process of calculating the reciprocal of the flow rate, a second lower limit value of the flow rate may be calculated from the heat generation state of the internal combustion engine and the difference between the boiling point of the cooling medium in the cooling flow passage and the estimated temperature, and the flow rate may be limited to be equal to or greater than the second lower limit value. Effect of the Invention

[0020] According to the present invention, the flow rate of the cooling medium can be appropriately controlled. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a configuration diagram showing an example of an engine control system. [Diagram 2] FIG. 2 is a configuration diagram showing an example of an ECU (Electronic Control Unit). [Diagram 3] FIG. 4 is a diagram showing an example of the correlation between the flow rate of cooling water and the inlet / outlet water temperature difference in a thermal equilibrium state. [Figure 4] FIG. 4 is a diagram showing an example of a correlation between the inverse of the flow rate of cooling water and the inlet / outlet water temperature difference. [Diagram 5] FIG. 2 is a block diagram illustrating an example of a feedback control system of a plant. [Figure 6] FIG. 6 is a block diagram embodying the inverse plant model and each transfer function of the low-pass filter in FIG. 5. [Figure 7] FIG. 6 is a block diagram that is an equivalent representation of the block diagram in FIG. 5. [Figure 8] FIG. 8 is a block diagram embodying the inverse plant model and each transfer function of the low-pass filter in FIG. [Figure 9] 4 is a flowchart showing an example of a flow rate control operation of an ECU. [Figure 10] FIG. 11 is a diagram showing the change over time in outlet water temperature in a comparative example. [Figure 11] FIG. 4 is a graph showing the change over time in outlet water temperature in an embodiment. [Figure 12] 7 is a diagram showing an example of changes over time in the detected value of the outlet water temperature sensor and the estimated value of the inlet water temperature. FIG. [Figure 13] FIG. 4 is a configuration diagram showing another example of the ECU. [Figure 14] FIG. 4 is a block diagram illustrating an example of an inlet water temperature estimating unit. [Figure 15] 6 is a flowchart showing an example of a flow rate limiting process based on a valve opening determination of a thermostat. [Figure 16]10 is a flowchart showing an example of a flow rate limiting process for preventing the cooling water in the drill path from boiling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] (Control system configuration) 1 is a configuration diagram showing an example of a control system 9 for an engine 2. The control system 9 is mounted on a vehicle that uses the engine 2 as a drive source. The control system 9 has an ECU 1, the engine 2, a cooling system 3, and a sensor system 4.

[0023] The engine 2 is an example of an internal combustion engine, and has a cylinder head 2a and a cylinder block 2b. Water jackets 20, 23 through which cooling water flows to cool the engine 2 are provided inside the cylinder head 2a and the cylinder block 2b, respectively. The water jacket 20 also includes a drill path between the bores. The cooling water is an example of a cooling medium, and the water jackets 20, 23 are examples of cooling flow paths.

[0024] An inlet 24 of a water jacket 23 is provided in the cylinder block 2b, and outlets 21, 22 of a water jacket 20 are provided in the cylinder head 2a. Cooling water circulates between the cooling system 3 and the water jackets 20, 23. The cooling water flows from the cooling system 3 through the inlet 24 into the water jacket 23, and from the water jacket 23 into the water jacket 20 of the cylinder head 2a. The cooling water flows from the water jacket 20 into the cooling system 3 through the outlets 21, 22.

[0025] The cooling system 3 has an electric water pump (EWP) 30, a thermostat (T / S) 31, a radiator 32, a heater 33, a transmission thermal fluid exchanger (ATF / W) 34, an EGR (Exhaust Gas Recirculation) cooler (EGR / C) 35, and an outlet water temperature sensor 36. The cooling system 3 also has an EGR passage 37, a distribution passage 38, return passages 390 and 391, an ATF passage 380, a heater passage 381, and a radiator passage 382 as circulation passages through which the coolant circulates.

[0026] The EWP 30 delivers cooling water to the water jackets 20 and 23. The cooling water flows from the EWP 30 through the inlet 24 into the water jacket 23.

[0027] Cooling water flows into the EGR cooler 35 from the outlet 22 of the water jacket 20. The EGR cooler 35 cools the exhaust gas of the engine 2 with the cooling water. The EGR cooler 35 is provided in an EGR flow path 37, and the cooling water is discharged from the EGR cooler 35 to the EGR flow path 37.

[0028] The cooling water flows into the outlet water temperature sensor from the outlet 22 of the water jacket 20. The outlet water temperature sensor detects the temperature of the cooling water at the outlet 22 (hereinafter referred to as the “outlet water temperature”). The outlet water temperature sensor is provided in the distribution flow path .

[0029] The distribution passage 38 branches into an ATF passage 380, a heater passage 381, and a radiator passage 382. The ATF / W 34, the heater 33, and the radiator 32 are respectively provided in the ATF passage 380, the heater passage 381, and the radiator passage 382. The coolant flows from the outlet water temperature sensor 36 through the distribution passage 38, and is divided into the ATF passage 380, the heater passage 381, and the radiator passage 382.

[0030] The ATF / W 34 exchanges heat between the transmission cooling oil or the like and the cooling water in the ATF flow path 380. The heater 33 exchanges heat between the air in the passenger compartment of the vehicle equipped with the control system 9 and the cooling water in the heater flow path 381. The radiator 32 exchanges heat between the outside air of the vehicle and the cooling water in the radiator flow path 382.

[0031] The EGR passage 37, the ATF passage 380, and the heater passage 381 merge into one return passage 390. The coolant cooled by the radiator 32 is discharged into the other return passage 391. That is, the EGR passage 37, the ATF passage 380, and the heater passage 381 function as bypass passages that bypass the radiator 32. The coolant that has flowed through the EGR passage 37, the ATF passage 380, and the heater passage 381 flows back from the return passage 390 to the EWP 30. The coolant that has flowed through the radiator passage 382 flows back from the return passage 391 to the EWP 30 when an opening / closing valve 311 of the thermostat 31 is opened as described below.

[0032] The return passages 390 and 391 are provided with a thermostat 31. The thermostat 31 is provided with a temperature detection unit 310 and an on-off valve 311. The temperature detection unit 310 detects the temperature of the cooling water flowing in from the EGR passage 37, the ATF passage 380, and the heater passage 381. The on-off valve 311 blocks the flow of the cooling water flowing in from the radiator 32 or allows it to pass.

[0033] The temperature detection unit 310 includes, for example, wax that expands in response to the temperature of the cooling water. When the cooling water reaches a predetermined temperature (hereinafter referred to as the "valve opening determination water temperature"), the opening / closing valve 311 is opened by an opening / closing mechanism (not shown) in response to the expansion of the wax.

[0034] Therefore, when the temperature of the coolant flowing from the EGR passage 37, the ATF passage 380, and the heater passage 381 is lower than the valve opening judgment water temperature, the on-off valve 311 is closed, so that the coolant cooled by the radiator 32 is not returned to the EWP 30, and only the coolant in the EGR passage 37, the ATF passage 380, and the heater passage 381 is returned to the EWP 30. When the temperature of the coolant flowing from the EGR passage 37, the ATF passage 380, and the heater passage 381 is equal to or higher than the valve opening judgment water temperature, the on-off valve 311 is open, so that the coolant cooled by the radiator 32 is returned to the EWP 30 together with the coolant in the EGR passage 37, the ATF passage 380, and the heater passage 381. In this case, the on-off valve 311 opens so that the coolant passes through the radiator. The valve opening judgment water temperature is an example of a threshold value.

[0035] The ECU 1 controls the torque of the engine 2. The ECU 1 sets a target value for the outlet water temperature of the coolant depending on the state of the engine 2. The ECU 1 obtains a detection value of the outlet water temperature sensor 36, and controls the discharge amount of the EWP 30 based on the detection value so that the outlet water temperature approaches the target value. In other words, the ECU 1 controls the flow rate of the coolant circulating through the distribution passage 38 and the EGR passage 37. The ECU 1 is an example of a control device.

[0036] The sensor system 4 outputs various detection values ​​to the ECU 1. The sensor system 4 includes, for example, an air flow meter (AFM) 40, a throttle opening sensor (TA) 41, an intake pressure sensor 42, and an exhaust pressure sensor 43. The AFM 40 detects the flow rate of air taken into the engine 2. The TA 41 detects the opening of a throttle (not shown) provided in the engine 2. The intake pressure sensor 42 and the exhaust pressure sensor 43 detect the intake pressure and exhaust pressure, respectively, of the engine 2. The ECU 1 controls the torque and the flow rate of coolant of the engine 2 based on the detection values ​​of the sensor system 4.

[0037] (ECU configuration) 2 is a configuration diagram showing an example of the ECU 1. The ECU 1 has a CPU (Central Processing Unit) 10, a ROM (Read Only Memory) 11, a RAM (Random Access Memory) 12, a storage memory 13, and an input / output port 14. The CPU 10 is electrically connected to the ROM 11, the RAM 12, the storage memory 13, and the input / output port 14 via a bus 19 so as to be able to input and output signals to and from each other. The ECU 1 is an example of a computer.

[0038] The ROM 11 stores a program that drives the CPU 10. The RAM 12 functions as a working memory for the CPU 10. The input / output port 14 inputs and outputs various signals between, for example, the sensor system 4, the outlet water temperature sensor 36, and the EWP 30. In this way, the CPU 10 communicates with the sensor system 4, the outlet water temperature sensor 36, and the EWP 30.

[0039] When the CPU 10 reads a program from the ROM 11, it functions as an operation control unit 100, a detection value acquisition unit 101, a torque control unit 102, a flow rate calculation unit 103, and a water temperature difference correction unit 104. Also, a heat quantity map data table 130 is stored in the storage memory 13. The storage memory 13 is realized by, for example, a flash memory.

[0040] The operation control unit 100 controls the overall operation of the ECU 1. The operation control unit 100 instructs the detection value acquisition unit 101, the torque control unit 102, the flow rate calculation unit 103, and the water temperature difference correction unit 104 to operate in accordance with a predetermined sequence. At this time, the operation control unit 100 relays variables related to various processes between the detection value acquisition unit 101, the torque control unit 102, the flow rate calculation unit 103, and the water temperature difference correction unit 104.

[0041] The detection value acquisition unit 101 acquires various detection values ​​from the sensor system 4 and acquires a detection value of the outlet water temperature from the outlet water temperature sensor 36 in accordance with instructions from the operation control unit 100. The detection value acquisition unit 101 acquires the detection values ​​at different periods for each detection value, for example. The detection value acquisition unit 101 is an example of an acquisition means for acquiring a detection value of the outlet water temperature.

[0042] The torque control unit 102 controls the torque of the engine 2 in accordance with instructions from the operation control unit 100. At this time, the torque control unit 102 uses various detection values ​​of the sensor system 4 for the control.

[0043] The flow rate calculation unit 103 calculates the flow rate of the cooling water based on the detection value of the outlet water temperature sensor 36. As described later, the flow rate calculation unit 103 calculates the reciprocal of the flow rate based on the correlation between the temperature difference of the cooling water at the inlet 24 and the outlet 21 of the cooling water (hereinafter referred to as the "inlet / outlet water temperature difference") and the reciprocal of the flow rate so as to compensate for the delay until the difference between the temperature of the cooling water at the inlet 24 (hereinafter referred to as the "inlet water temperature") and the detection value of the outlet water temperature (hereinafter referred to as the "water temperature difference detection value") reaches a target value in response to the flow rate control. The flow rate calculation unit 103 calculates the flow rate from the reciprocal of the flow rate and controls the output of the EWP 30 so that the cooling water flows at that flow rate. Note that, as the inlet water temperature of the cooling water, for example, a design value of the adjustment temperature of the thermostat 31 is used, but an estimated value may be used as described later.

[0044] Based on the correlation between the inlet / outlet water temperature difference and the reciprocal of the flow rate, the water temperature difference correction unit 104 predicts the above delay from the reciprocal of the flow rate calculated by the flow rate calculation unit 103, and corrects the detected water temperature difference value based on the prediction result. The flow rate calculation unit 103 calculates the reciprocal of the flow rate from the detected water temperature difference corrected by the water temperature difference correction unit 104. Therefore, the flow rate calculation unit 103 can reduce the deviation between the response delay of the actual flow rate control and the response delay assumed by the flow rate calculation unit 103 and calculate an appropriate reciprocal of the flow rate.

[0045] In the heat quantity map data table 130, for example, heat quantity parameters Kq are registered in advance in association with various detection values ​​of the sensor system 4.

[0046] Kp = Qw / ρc (1)

[0047] The heat quantity parameter Kp is expressed, for example, by the above formula (1). In formula (1), the variable Qw indicates the amount of heat (J / s) per unit time received by the cooling water from the engine 2, and the constant ρ indicates the density of the cooling water (g / cm 3 ), and constant c indicates the heat capacity (J / K) of the coolant. The heat quantity parameter Kp is an example of a parameter related to the amount of heat that the coolant receives from the engine 2.

[0048] The flow rate calculation unit 103 calculates the reciprocal of the flow rate as a heat quantity parameter Kp, which is the rate of change of the temperature difference with respect to the reciprocal of the flow rate in the correlation between the reciprocal of the flow rate and the temperature difference of the coolant at the inlet 24 and outlet 21 of the coolant. Therefore, the flow rate calculation unit 103 can appropriately calculate the reciprocal of the flow rate according to the heat generation state of the engine 2.

[0049] (Correlation between cooling water flow rate and inlet / outlet water temperature difference) 3 is a diagram showing an example of the correlation between the coolant flow rate V (L / min.) and the inlet / outlet water temperature difference ΔTw (K) in a thermal equilibrium state. Characteristic Fr shows the correlation between the actual coolant flow rate V and the inlet / outlet water temperature difference ΔTw, while characteristic Fb shows the correlation between the coolant flow rate V and the inlet / outlet water temperature difference ΔTw when there is no deviation α in the inlet coolant temperature due to disturbance. Characteristic Fp shows the correlation between the coolant flow rate V and the inlet / outlet water temperature difference ΔTw assumed when ECU1 controls the flow rate based on characteristic Fb.

[0050] In each of the characteristics Fr, Fb, and Fp, a nonlinear relationship (effectively an inverse proportional relationship) is established between the flow rate V of the cooling water and the inlet / outlet water temperature difference ΔTw. Here, the proportionality constant is assumed to be the product (Vb×ΔTwb) of a predetermined flow rate Vb and the inlet / outlet water temperature difference ΔTwb in the characteristic Fp (see point Pc).

[0051] ΔTwact is a detected water temperature difference obtained from the detection value of the outlet water temperature sensor 36, and Vact is a flow rate corresponding to the detected water temperature difference ΔTwact in the characteristic Fr. ΔTwtgt is a control target inlet / outlet water temperature difference, and Vtgt is a flow rate corresponding to the control target inlet / outlet water temperature difference ΔTwtgt in the specific Fp.

[0052] Here, the difference between the control target inlet / outlet water temperature difference ΔTwtgt and the inlet / outlet water temperature difference corresponding to the flow rate Vtgt in the characteristic Fb is defined as γ. Also, the difference between the water temperature difference detected value ΔTwact and the inlet / outlet water temperature difference corresponding to the flow rate Vtgt in the characteristic Fr is defined as ε. Therefore, the difference err between the control target inlet / outlet water temperature difference ΔTwtgt and the water temperature difference detected value ΔTwact is (α+γ+ε).

[0053] The flow rate Vcrc for controlling the inlet / outlet water temperature difference to the target inlet / outlet water temperature difference ΔTwtgt is calculated as follows.

[0054] Vcrc(ΔTwtgt-α)=Vact(ΔTwtgt+γ+ε)···(2) Vcrc=Vact{(ΔTwtgt+γ+ε) / (ΔTwtgt-α)} =Vact{1-err / (ΔTwtgt-α)} ···(3)

[0055] In the characteristic Fb, the product of the inlet / outlet water temperature difference and the flow rate is equal for point Pa corresponding to the flow rate Vact and point Pb corresponding to the flow rate Vcrc, so the above formula (2) is established. The flow rate Vcrc is calculated from formula (2) and the above definition of the difference err using formula (3).

[0056] In this way, when the flow rate V and the inlet / outlet water temperature difference ΔTw have a nonlinear relationship, it is difficult to compensate for the delay in response to flow rate control. If a control means is used that outputs the flow rate V from the inlet / outlet water temperature difference ΔTw, integral control (I control) using a nonlinear gain is required, making it difficult to perform rapid control and vulnerable to disturbances.

[0057] Therefore, the flow rate calculation unit 103 controls the flow rate V based on the linear relationship between the inverse of the flow rate V and the inlet / outlet water temperature difference ΔTw, instead of the nonlinear relationship between the flow rate V and the inlet / outlet water temperature difference ΔTw.

[0058] (Correlation between the inverse of the cooling water flow rate and the difference in water temperature between the inlet and outlet) FIG. 4 is a diagram showing an example of the correlation between the inverse v (=1 / V) (min. / L) of the cooling water flow rate and the inlet / outlet water temperature difference ΔTw (K). The characteristics fr, fb, and fp correspond to the characteristics Fr, Fb, and Fp in FIG. 3, respectively. Here, the slope of the straight line of each characteristic Fr, Fb, and Fp coincides with the proportionality constant (Vb×ΔTwb) mentioned above. Furthermore, for vcrc, vff, and vact, vcrc=1 / Vcrc, vff=1 / Vtgt, and vact=1 / Vact hold.

[0059] ΔTw = Vb × ΔTwb × v (4)

[0060] The linear relationship shown in the above formula (4) is established between the reciprocal v of the coolant flow rate and the inlet / outlet water temperature difference ΔTw. Therefore, it is possible to treat the engine 2 and the cooling system 3, which are the plants to be controlled, as a linear behavior model.

[0061] ΔTw = Kp × v (5)

[0062] If the proportionality constant in equation (4), that is, the rate of change of the inlet / outlet water temperature difference ΔTw with respect to the reciprocal of the flow rate, is taken as the heat quantity parameter Kp, then the above equation (5) is established.

[0063]

number

[0064] Therefore, when the control value vcmd is the reciprocal of the flow rate Vcmd, the detected water temperature difference ΔTwact is expressed as the plant response by the above formula (6), where 1 / (Ts-1) represents the transfer function of the first-order lag element of the plant, and the constant T is the time constant of the plant.

[0065] By treating the plant as a model of linear behavior in this way, it becomes possible to express the control system by a transfer function, and therefore it is possible to compensate for the delay in the response of the plant to flow rate control.

[0066] (Block diagram) FIG. 5 is a block diagram showing an example of a feedback control system for a plant P. The feedback control system includes transfer functions F, Pn -1 ,LIM,Pn, where F,Pn is the transfer function -1 , LIM are processed by a flow rate calculation unit 103, and the process of the transfer function Pn and the process of calculating the feedback water temperature difference ΔTwfb from the water temperature difference detected value ΔTwact are executed by a water temperature difference correction unit 104.

[0067] Transfer function Pn -1 outputs the inverse vcmd of the cooling water flow rate to compensate for the first-order lag element of the response of the plant P. The transfer function Pn outputs the estimated inlet / outlet water temperature difference ΔTwcmd based on the first-order lag element of the response of the plant P from the inverse vcmd of the flow rate. -1 The transfer element of the transfer function Pn is denoted as the "inverse plant model", and the transfer element of the transfer function Pn is denoted as the "plant response assumption model".

[0068] Pn -1 =(Ts+1) / Kp (7) Pn = Kp / (Ts + 1) (8)

[0069] Based on the linear relationship between the inverse of the flow rate v and the inlet / outlet water temperature difference ΔTw, the transfer function Pn -1 is expressed by the above equation (7), and the transfer function Pn is expressed by the above equation (8).

[0070] The detected water temperature difference ΔTwact, which is the plant response, is subtracted by the assumed inlet / outlet water temperature difference ΔTwcmd calculated by the plant response assumption model before being fed back. In this way, the water temperature difference correction unit 104 predicts a delay in the response of the plant P from the reciprocal vcmd of the flow rate based on the above linear relationship, and corrects the detected water temperature difference ΔTwact based on the prediction result.

[0071] Therefore, the flow rate calculation unit 103 can calculate an appropriate reciprocal vcmd of the flow rate by reducing the response delay of the plant P and the deviation of the response delay assumed by the inverse plant model. This absorbs disturbances and modeling errors and improves the stability and responsiveness of the flow rate control. Note that the plant response assumption model, i.e., the water temperature difference correction unit 104, does not need to be provided if the stability and responsiveness of the flow rate control are sufficient.

[0072] The flow rate calculation unit 103 determines a target inlet / outlet water temperature difference ΔTwtgt based on, for example, various detection values ​​of the sensor system 4. The control target inlet / outlet water temperature difference ΔTwtgt is subtracted by the corrected water temperature difference detection value ΔTwact′ and input to the transfer element of the transfer function F as the feedback water temperature difference ΔTwfb.

[0073] F = 1 / (T F s+1) (9)

[0074] The transfer function F corresponds to a low-pass filter and is expressed, for example, by the above formula (9). F is the time constant of the low-pass filter. The feedback water temperature difference ΔTwfb is filtered by the transfer function F before being input to the inverse plant model. In other words, the flow rate calculation unit 103 performs filtering processing on the feedback water temperature difference ΔTwfb using a low-pass filter. This suppresses fluctuations in the feedback water temperature difference ΔTwfb caused by noise, etc. This suppresses fluctuations in the reciprocal vcmd of the flow rate, which is the command value, improving the stability of the flow rate control. Note that this filtering processing does not need to be provided if the fluctuations in the feedback water temperature difference ΔTwfb are sufficiently small.

[0075] The transfer function LIM limits the flow rate (1 / vcmd), which is a command value. As described later, the transfer function LIM sets, for example, a lower limit of the flow rate when the on-off valve 311 of the thermostat 31 is determined to be open, or a lower limit of the flow rate for preventing the cooling water in the drill path of the water jacket 23 from boiling.

[0076] FIG. 6 shows the inverse plant model and the transfer function Pn -1 ,F. By applying the above equations (7) and (9) to the block diagram in Fig. 5, it can be rewritten as shown in Fig. 6.

[0077] Figure 7 is a block diagram that is an equivalent representation of the block diagram in Figure 5. The transfer function Pn of the plant response assumption model is integrated into the transfer function F of the filtering process. The transfer function after integration is (F / (1-F)).

[0078] FIG. 8 shows the inverse plant model and the transfer function Pn -1 ,F. If we apply the above equations (7) and (9) to the block diagram in Figure 7, it can be rewritten as in Figure 6.

[0079] The transfer function (T / Tf) represents proportional control (P control), and the transfer function (1 / Tfs) represents integral control (I control). Therefore, the ECU 1 can control the flow rate (its inverse vcmd) by PI control that feeds back the water temperature difference detection value ΔTwact.

[0080] (ECU flow control operation)

[0081] 9 is a flowchart showing an example of the flow rate control operation of the ECU 1. The following operation is an example of a control method.

[0082] First, the detection value acquisition unit 101 acquires each detection value from the outlet water temperature sensor 36 and the sensor system 4 (step St1). Next, the flow rate calculation unit 103 acquires the heat quantity parameter Kp by referring to the heat quantity map data table 130 based on each detection value of the sensor system 4 (step St2). Next, the flow rate calculation unit 103 determines the target value To of the outlet water temperature (target outlet water temperature) based on each detection value of the sensor system 4 (step St3).

[0083] ΔTwtgt = To - Tin (10)

[0084] Next, the flow rate calculation unit 103 calculates the target inlet / outlet water temperature difference ΔTwtgt from the above formula (10) (step St4). Here, Tin is a predetermined inlet water temperature, but may be an estimated value of the inlet water temperature as described later.

[0085] ΔTwact = Tout - Tin (11)

[0086] Next, the flow rate calculation unit 103 calculates the water temperature difference detection value ΔTwact from the above formula (11) (step St5), where Tout is the detection value of the outlet water temperature sensor 36. Note that the subsequent processing is performed according to the block diagram of FIG.

[0087] ΔTwcmd = Pn vcmd (12)

[0088] Next, the water temperature difference correction unit 104 calculates the assumed inlet / outlet water temperature difference ΔTwcmd from the reciprocal vcmd of the flow rate calculated in the previous step St9 and the transfer function Pn of the plant response assumption model according to the above formula (12) (step St6). In this way, the water temperature difference correction unit 104 predicts the delay until the water temperature difference detection value ΔTwact reaches the target inlet / outlet water temperature difference ΔTwtgt, that is, the response delay of the plant P.

[0089] ΔTwact'=ΔTwact-ΔTwcmd ···(13)

[0090] Next, the water temperature difference correction unit 104 calculates the corrected water temperature difference detected value ΔTwact' from the difference between the water temperature difference detected value ΔTwact and the assumed inlet / outlet water temperature difference ΔTwcmd according to the above formula (13) (step St7). As a result, the water temperature difference correction unit 104 corrects the water temperature difference detected value ΔTwact based on the predicted result of the response delay of the plant P.

[0091] ΔTwfb=ΔTwtgt-ΔTwact' (14)

[0092] Next, the flow rate calculation unit 103 calculates the feedback water temperature difference ΔTwfb from the difference between the target inlet / outlet water temperature difference ΔTwtgt and the corrected water temperature difference detected value ΔTwact′ in accordance with the above equation (14) (step St8).

[0093] vcmd=F·Pn -1 ΔTwfb (15)

[0094] Next, the flow rate calculation unit 103 calculates the inverse plant model and each transfer function Pn -1 , F and the feedback water temperature difference ΔTwfb are used to calculate the reciprocal of the flow rate vcmd (step St8).

[0095] Next, the flow rate calculation unit 103 calculates the flow rate Vcmd from the reciprocal vcmd of the flow rate (step St10). Next, the flow rate calculation unit 103 issues a command for the flow rate Vcmd to the EWP 30 (step St11).

[0096] Next, the flow rate calculation unit 103 judges whether or not it has received an instruction to end the flow rate control from the operation control unit 100 (step St12). If the flow rate calculation unit 103 has not received the instruction to end (No in step St12), the operation from step St1 onwards is executed again. On the other hand, if the flow rate calculation unit 103 has received the instruction to end (Yes in step St12), this operation ends.

[0097] In this way, the ECU 1 controls the flow rate of the cooling water circulating through the water jackets 20, 23 of the engine 2. The detection value acquisition unit 101 acquires the detection value Tout of the outlet water temperature of the water jacket 20. The flow rate calculation unit 103 calculates the reciprocal vcmd of the flow rate based on the correlation between the inlet / outlet water temperature difference ΔTw and the reciprocal v of the flow rate so as to compensate for the delay until the difference between the inlet water temperature Tin of the water jacket 23 and the detection value Tout reaches the target inlet / outlet water temperature difference ΔTwtgt in response to the flow rate control.

[0098] Therefore, the ECU 1 can construct a control system using the transfer function Pn by treating the plant P as a model of linear behavior, and can appropriately control the flow rate of the cooling water by compensating for the delay in the response of the plant P to the flow rate control.

[0099] (Plant response model assuming dead time) In the above embodiment, the plant response expected model uses a transfer function Pn assuming a first-order delay element as the response delay of the plant P, but is not limited to this and may further use a transfer function Pn assuming a dead time of the plant P. Examples of the dead time of the plant P include, but are not limited to, a delay time in the calculation of the detection value Tout of the outlet water temperature sensor 36 and a delay time in the transportation of the cooling water.

[0100] Pn = Kp e -Ls / (Ts+1) (16)

[0101] When a dead time is assumed, the transfer function Pn of the plant response expected model is expressed by the above formula (16). In formula (18), L is the dead time of the plant P. The block diagram in this example is as shown in Figures 5 and 6.

[0102] Fig. 10 is a diagram showing the change over time of the outlet water temperature in a comparative example. In this example, a case is shown in which the plant response assumption model does not assume the dead time of the plant P. Fig. 9 shows the target value of the outlet water temperature corresponding to the target inlet / outlet water temperature difference ΔTwtgt, the command value of the outlet water temperature corresponding to the reciprocal of the flow rate vcmd, the assumed value of the outlet water temperature corresponding to the assumed inlet / outlet water temperature difference ΔTwcmd, and the actual outlet water temperature as a response to the flow rate control.

[0103] If no dead time is assumed, the expected value will rise at substantially the same time as the target value. The actual water temperature will start to rise after the command time, but due to deviation from the expected value, the actual water temperature is controlled to rise excessively, as shown by arrow A1. This increases the dead time.

[0104] Fig. 11 is a diagram showing a change over time in the outlet water temperature in the embodiment. In this example, a case is shown in which the plant response assumption model assumes a dead time of the plant P. Note that in Fig. 10, the description of parameters common to Fig. 9 is omitted.

[0105] When dead time is assumed, the expected value rises with a delay of time X from the rise in the target value due to the transfer function Pn in the above equation (16). The actual water temperature starts to rise with a delay from the command value, but because the delay is a value close to time X, it acts to lower the actual water temperature that has exceeded the target value, as shown by arrow A1. This results in an optimal relationship between the control timing and the response timing.

[0106] In this way, the water temperature difference correction unit 104 predicts the delay including the dead time of the response to the flow rate control from the reciprocal vcmd of the flow rate calculated by the flow rate calculation unit 103. Therefore, the relationship between the control timing and the response timing is appropriately adjusted, and the dead time is reduced.

[0107] (Thermostat opening judgment) The cooling water is divided into a distribution passage 38 extending from one outlet 21 of the cylinder head 2a and an EGR passage 37 extending from the other outlet 22 of the cylinder head 2a. A temperature detection unit 310 of the thermostat 31 detects the temperature of the cooling water that flows together from the distribution passage 38 and the EGR passage 37.

[0108] For example, when the flow rate of the cooling water is low, high-temperature cooling water from the distribution passage 38 and the EGR passage 37 may unevenly impinge on the temperature detection unit 310, which may cause the on-off valve 311 of the thermostat 31 to erroneously open. Therefore, when the estimated value Tin' of the inlet water temperature is equal to or higher than the valve opening determination water temperature TH of the on-off valve 311, the flow rate calculation unit 103 sets a lower limit value Vmin of the flow rate so that the high-temperature cooling water does not unevenly impinge on the temperature detection unit 310. The lower limit value Vmin of the flow rate is set to the transfer function LIM shown in FIG.

[0109] In contrast, if the flow rate calculation unit 103 uses the detection value Tout of the outlet water temperature sensor 36 instead of the estimated value Tin' of the inlet water temperature, the lower limit value of the flow rate cannot be set in a timely manner as described below.

[0110] 12 is a diagram showing an example of changes over time in the detected value Tout of the outlet water temperature sensor 36 and the estimated value Tin' of the inlet water temperature. During the warm-up operation of the engine 2, the detected value Tout of the outlet water temperature sensor 36 and the estimated value Tin' of the inlet water temperature increase over time.

[0111] However, since the detection value Tout of the outlet water temperature sensor 36 is higher than the estimated value Tin' of the inlet water temperature, it reaches the valve-opening judgment water temperature TH sooner. In other words, the time Ta required for the detection value Tout of the outlet water temperature sensor 36 to reach the valve-opening judgment water temperature TH is shorter than the time Tb required for the estimated value Tin' of the inlet water temperature to reach the valve-opening judgment water temperature TH.

[0112] Therefore, if the flow rate calculation unit 103 sets the lower limit Vmin of the flow rate at the timing when the detection value Tout of the outlet water temperature sensor 36 becomes equal to or higher than the valve opening judgment water temperature TH, the error between the setting timing and the timing when the on-off valve 311 of the thermostat 31 actually opens will be large. In other words, the period during which the flow rate restriction by the lower limit Vmin can be lifted will be shorter than the actual period during which it can be lifted. For this reason, the flow rate of the coolant will start to be restricted to equal to or higher than the lower limit earlier than appropriate, and the temperature of the coolant may drop before the engine 2 is sufficiently warmed up.

[0113] In response to this, the flow rate calculation unit 103 sets the lower limit value Vmin of the flow rate at the timing when the estimated value Tin' of the inlet water temperature becomes equal to or higher than the valve opening judgment water temperature TH, thereby reducing the error between the timing of setting the lower limit value Vmin of the flow rate and the timing when the opening / closing valve 311 of the thermostat 31 actually opens.

[0114] Fig. 13 is a configuration diagram showing another example of the ECU 1. In Fig. 13, components common to Fig. 2 are given the same reference numerals, and their description will be omitted. When the CPU 10 reads a program from the ROM 11, it forms, as functions, an operation control unit 100, a detection value acquisition unit 101, a torque control unit 102, a flow rate calculation unit 103a, a water temperature difference correction unit 104, and an inlet water temperature estimation unit 105.

[0115] The inlet water temperature estimation unit 105 is an example of an estimation means, and estimates the inlet water temperature of the coolant from the detection value Tout of the outlet water temperature sensor 36 based on a transfer function corresponding to the coolant circulation flow paths, i.e., the distribution flow path 38, the EGR flow path 37, the ATF flow path 380, the heater flow path 381, and the return flow path 391. In calculating the reciprocal vcmd of the flow rate, the flow rate calculation unit 103a uses the estimated value Tin′ calculated by the inlet water temperature estimation unit 105 instead of the predetermined inlet water temperature Tin.

[0116] 14 is a block diagram showing an example of the inlet water temperature estimation unit 105. The inlet water temperature estimation unit 105 has transfer functions of first-order lag elements {k / (T1s+1)}, {(1-k) / (T2s+1)}, and {1 / (T3s+1)}.

[0117] The transfer function {k / (T1s+1)} represents a temperature transfer element of the route Ra, which is one of the coolant circulation routes and includes the distribution route 38, the ATF route 380, and the heater route 381. Here, the constant T1 is determined from various design values ​​related to the temperature transfer of the route Ra.

[0118] The transfer function {(1-k) / (T2s+1)} represents the temperature transfer element of the path Rb, which includes the EGR path 37, among the coolant circulation paths. Here, the constant T2 is determined from various design values ​​related to the temperature transfer of the path Rb. The outputs from the transfer functions {k / (T1s+1)}, {(1-k) / (T2s+1)} are added together and input to the transfer function {1 / (T3s+1)}.

[0119] The transfer function {1 / (T3s+1)} represents a temperature transfer element of the return flow passage 391 where the paths Ra and Rb join among the cooling water circulation passages. Here, the constant T3 is determined from various design values ​​related to the temperature transfer of the return flow passage 391.

[0120] Furthermore, the constant k is the ratio of the flow rate of the cooling water in the distribution passage 38 extending from one outlet 21 of the cylinder head 2a and the EGR passage 37 extending from the other outlet 22 of the cylinder head 2a. The constant k is set in advance to an appropriate value based on the results of previous experiments, simulations, etc.

[0121] 15 is a flowchart showing an example of a flow rate limiting process based on a valve opening determination of the thermostat 31. This process is executed repeatedly at a constant cycle, for example. Note that this process is an example of a control method performed by the ECU 1.

[0122] The inlet water temperature estimation unit 105 estimates the inlet water temperature from the detection value Tout of the outlet water temperature sensor 36 (step St21). At this time, the inlet water temperature estimation unit 105 calculates the estimated value Tin' of the inlet water temperature by the above-mentioned transfer functions {k / (T1s+1)}, {(1-k) / (T2s+1)}, and {1 / (T3s+1)}.

[0123] Next, the flow rate calculation unit 103a compares the estimated value Tin’ of the inlet water temperature with the valve opening determination water temperature TH of the thermostat 31 (step St22). When Tin’ < TH holds (No in step St22), the flow rate calculation unit 103a determines that the on-off valve 311 is closed and ends the process without restricting the flow rate Vcmd to the lower limit value Vmin.

[0124] Also, when Tin’ ≥ TH holds (Yes in step St22), the flow rate calculation unit 103a determines that the on-off valve 311 is open and compares the flow rate Vcmd with the lower limit value Vmin (step St23). Here, the lower limit value Vmin is preset according to various design values of the circulation flow path, for example, as a sufficient flow rate to prevent high-temperature cooling water from hitting the temperature detection unit 310 unevenly. When Vcmd ≥ Vmin holds (No in step St23), since the flow rate is sufficient, the process ends.

[0125] Also, when Vcmd < Vmin holds (Yes in step St23), the flow rate calculation unit 103a controls the flow rate Vcmd to the lower limit value Vmin (step St24). Therefore, when there is a possibility that high-temperature cooling water hits the temperature detection unit 310 unevenly due to a low flow rate, the flow rate increases to the lower limit value Vmin.

[0126] In this way, when the estimated value Tin’ of the inlet water temperature estimated by the inlet water temperature estimation unit 105 is equal to or higher than the valve opening determination water temperature TH, the flow rate calculation unit 103a restricts the flow rate Vcmd to be equal to or higher than the lower limit value Vmin. Therefore, compared with the case where the detection value Tout of the outlet water temperature sensor 36 itself is used, the flow rate calculation unit 103a can perform the valve opening determination of the thermostat 31 with high accuracy based on the estimated value Tin’ and restrict the flow rate Vcmd in a timely manner. Note that the lower limit value Vmin is an example of the first lower limit value.

[0127] (Prevention of boiling of cooling water in the drill pass) As described below, the above-mentioned estimated value Tin' may be used to set a lower limit value Fewp for preventing boiling of the cooling water in the drill path of the water jacket 23. The lower limit value Fewp is an example of a second lower limit value, and is set to the transfer function LIM shown in FIG.

[0128] Fewp=(A / ΔTewp) · G+B / ΔTewp ···(17) ΔTewp=Td-ΔTin' (18)

[0129] The flow rate calculation unit 103a calculates the lower limit value Fewp according to the above formula (17). In formula (17), the variable G is a parameter related to the heat generation state of the engine 2. The flow rate calculation unit 103a calculates the variable G as the intake amount (L) per 1 (L) of the displacement of the engine 2 from, for example, various detection values ​​of the sensor system 4.

[0130] In addition, the flow rate calculation unit 103a calculates the variable ΔTewp according to the above formula (18). In formula (18), the predetermined value Td is the water temperature at which the cooling water boils in the drill path (i.e., the boiling point). The predetermined value Td is set in advance based on various design values ​​of the drill path. The flow rate calculation unit 103a calculates the variable ΔTewp as the difference between the predetermined value Td and the estimated value Tin'. Moreover, the constants A and B are appropriately determined in advance from the linear relationship between the variable G and the variable ΔTewp obtained from a previous experiment or simulation, and the minimum flow rate at which boiling of the cooling water in the drill path can be prevented.

[0131] 16 is a flowchart showing an example of a flow rate limiting process for preventing the boiling of the cooling water in the drill path. This process is executed repeatedly at a constant cycle, for example. Note that this process is an example of a control method by the ECU 1.

[0132] The inlet water temperature estimation unit 105 estimates the inlet water temperature from the detection value Tout of the outlet water temperature sensor 36 by the above-mentioned method (step St31). Next, the flow rate calculation unit 103a calculates the lower limit value Fewp according to the formula (17) (step St32).

[0133] Next, the detection value acquisition unit 101 acquires various detection values from the sensor system 4 (step St33). Next, the flow rate calculation unit 103a calculates the variable G from each detection value (step St34).

[0134] Next, the flow rate calculation unit 103a calculates the lower limit value Fewp of the flow rate for preventing boiling according to formula (17) (step St35). Next, the flow rate calculation unit 103a compares the flow rate Vcmd with the lower limit value Fewp (step St36).

[0135] When Vcmd≥Fewp holds (No in step St36), the flow rate calculation unit 103a determines that there is no possibility of boiling of the cooling water in the drill path, and ends the process. When Vcmd<Fewp holds (Yes in step St36), the flow rate calculation unit 103a determines that there is a possibility of boiling of the cooling water in the drill path, and sets the flow rate Vcmd to the lower limit value Fewp (step St37).

[0136] In this way, the flow rate calculation unit 103a calculates the lower limit value Fewp of the flow rate Vcmd from the heat generation state of the engine 2 and the difference between the boiling point of the cooling water in the drill path and the estimated value Tin’ of the inlet water temperature, and limits the flow rate Vcmd to be equal to or higher than the lower limit value Fewp. Thereby, boiling of the cooling water in the drill path is suppressed.

[0137] The above-described embodiments are preferred examples of the present invention. However, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

Explanation of Reference Numerals

[0138] 1 ECU (computer) 2 Engine (internal combustion engine) 9 Control system 10 CPU 20, 23 Water jacket (cooling flow path) 21, 22 Outlet 24 Inlet 30 EWP 31 Thermostat 32 Radiator 36 Outlet water temperature sensor 37 EGR passage (circulation passage) 38 Distribution channel (circulation channel) 101 Detection value acquisition unit (acquisition means) 103,103a Flow rate calculation unit (calculation means) 104 Water temperature difference correction section (correction means) 105 Inlet water temperature estimation section (estimation means) 380 ATF flow path (circulation flow path) 381 Heater flow path (circulation flow path) 382 Radiator flow path (circulation flow path) 390,391 Return flow path (circulation flow path)

Claims

1. A control device for controlling a flow rate of a cooling medium circulating through a cooling passage of an internal combustion engine, an acquisition means for acquiring a detection value of the temperature of the cooling medium at an outlet of the cooling flow path; a calculation means for calculating the reciprocal of the flow rate based on a correlation between a temperature difference of the cooling medium at the inlet and outlet of the cooling flow path and the reciprocal of the flow rate so as to compensate for a delay until a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value reaches a target value in response to control of the flow rate, and for calculating the flow rate from the reciprocal of the flow rate. Control device.

2. the calculation means calculates a rate of change of the temperature difference with respect to the inverse of the flow rate in the correlation as a parameter related to the amount of heat received by the cooling medium from the internal combustion engine, the inverse of the flow rate. The control device according to claim 1 .

3. the calculation means performs a filtering process using a low-pass filter on the difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detected value. The control device according to claim 1 or 2.

4. a correction means for predicting the delay from the inverse of the flow rate calculated by the calculation means based on the correlation, and correcting a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value based on the prediction result. A control device according to any one of claims 1 to 3.

5. The correction means predicts the delay including a dead time of a response to control of the flow rate from the inverse of the flow rate calculated by the calculation means. The control device according to claim 4.

6. a radiator that cools the cooling medium and a thermostat that opens to allow the cooling medium to pass through the radiator when the temperature of the cooling medium is equal to or higher than a threshold value, an estimation means for estimating a temperature of the cooling medium at an inlet of the cooling flow path from the detected value based on a transfer function corresponding to the circulation flow path; The calculation means limits the flow rate to a first lower limit value or more when the estimated value of the temperature estimated by the estimation means is equal to or more than the threshold value. A control device according to any one of claims 1 to 5.

7. an estimation means for estimating a temperature of the cooling medium at an inlet of the cooling flow passage from the detected value based on a transfer function corresponding to a circulation flow passage through which the cooling medium circulates; the calculation means calculates a second lower limit value of the flow rate based on a heat generation state of the internal combustion engine and a difference between a boiling point of the cooling medium in the cooling flow passage and a temperature estimated by the estimation means, and limits the flow rate to equal to or greater than the second lower limit value. A control device according to any one of claims 1 to 5.

8. A method for controlling a flow rate of a cooling medium circulating through a cooling passage of an internal combustion engine, comprising: obtaining a detection value of the temperature of the cooling medium at an outlet of the cooling flow path; a reciprocal of the flow rate is calculated based on a correlation between a temperature difference of the cooling medium at the inlet and the outlet of the cooling flow path and the reciprocal of the flow rate so as to compensate for a delay until a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value reaches a target value in response to control of the flow rate, and the flow rate is calculated from the reciprocal of the flow rate. Control methods.

9. In the process of calculating the reciprocal of the flow rate, a rate of change of the temperature difference with respect to the reciprocal of the flow rate in the correlation is calculated as a parameter related to the amount of heat that the cooling medium receives from the internal combustion engine. The control method according to claim 8.

10. In the process of calculating the reciprocal of the flow rate, a filtering process is performed using a low-pass filter on a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value.

10. The control method according to claim 8 or 9.

11. The computer further executes a process of predicting the delay from the reciprocal of the calculated flow rate based on the correlation, and correcting a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detection value based on the prediction result. A control method according to any one of claims 8 to 10.

12. and in a process of correcting a difference between the temperature of the cooling medium at the inlet of the cooling flow path and the detected value, predicting the delay including a dead time of a response to control of the flow rate from the reciprocal of the calculated flow rate. The control method according to claim 11.

13. a radiator that cools the cooling medium and a thermostat that opens to allow the cooling medium to pass through the radiator when the temperature of the cooling medium is equal to or higher than a threshold value, The computer further executes a process of estimating a temperature of the cooling medium at an inlet of the cooling flow path from the detected value based on a transfer function corresponding to the circulation flow path; In the process of calculating the reciprocal of the flow rate, when the estimated value of the temperature is equal to or greater than the threshold value, the flow rate is limited to a first lower limit value or greater. A control method according to any one of claims 8 to 12.

14. the computer further executes a process of estimating a temperature of the cooling medium at an inlet of the cooling flow path from the detected value based on a transfer function corresponding to a circulation flow path through which the cooling medium circulates; In the process of calculating the reciprocal of the flow rate, a second lower limit value of the flow rate is calculated based on a heat generation state of the internal combustion engine and a difference between the boiling point of the cooling medium in the cooling flow passage and the estimated temperature, and the flow rate is limited to be equal to or greater than the second lower limit value. A control method according to any one of claims 8 to 12.

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