Cooling water temperature control method for hybrid vehicle and cooling water temperature control device for hybrid vehicle

Abstract

A cooling water temperature control method for a hybrid vehicle equipped with an internal combustion engine comprises: calculating the required workload for traveling from the position of the hybrid vehicle to the highest elevation point within a predetermined distance range; executing first control for cooling the cooling water so that the temperature of the cooling water of the internal combustion engine reaches a first target temperature when the value obtained by subtracting a possible workload of the internal combustion engine from the required workload does not exceed a threshold; and executing second control for cooling the cooling water so that the temperature of the cooling water reaches a second target temperature lower than the first target temperature with cooling capacity higher than that of the first control even if the temperature of the cooling water is lower than the first target temperature when the value obtained by subtracting the possible workload of the internal combustion engine from the required workload exceeds the threshold.

Description

Coolant temperature control method for hybrid vehicle and coolant temperature control device for hybrid vehicle

[0001] The present invention relates to a method for controlling the temperature of coolant in a hybrid vehicle and a coolant temperature control device for a hybrid vehicle.

[0002] 2. Description of the Related Art A method for controlling the temperature of coolant in a vehicle equipped with an internal combustion engine is known (see, for example, Patent Document 1).

[0003] Special Publication No. 2003-513191

[0004] While Patent Literature 1 describes using information from a navigation system to adjust the target coolant temperature, it does not disclose any specific method, and depending on the vehicle's driving load, the coolant may not be sufficiently cooled, causing the coolant temperature to rise. In the case of a hybrid vehicle, a rise in the coolant temperature can cause abnormal combustion in the internal combustion engine, reducing the efficiency of power generation powered by the internal combustion engine and the generated power.

[0005] An object of the present invention is to provide a method and a device for controlling the coolant temperature of a hybrid vehicle that can suppress a decrease in the efficiency of power generation powered by an internal combustion engine and a decrease in the generated power.

[0006] In one aspect of the present invention, when the value obtained by subtracting the amount of work that the internal combustion engine can do from the amount of work required while traveling from the hybrid vehicle to the highest altitude point within a specified distance range exceeds a threshold value, a second control is implemented to cool the cooling water of the internal combustion engine with a cooling capacity higher than that of the first control so that the temperature of the cooling water reaches a second target temperature that is lower than the first target temperature, even if the temperature of the cooling water of the internal combustion engine is lower than a first target temperature.

[0007] 1 is a schematic diagram showing the general configuration of a hybrid vehicle; FIG. 2 is a diagram showing a first cooling circuit that cools the coolant of an internal combustion engine; FIG. 3 is a diagram showing a second cooling circuit; FIG. 4 is a control block diagram of a controller; FIG. 5 is a flowchart of a coolant temperature control method executed by the controller; FIG. 6 is a diagram showing the relationship between altitude, coolant temperature, and the output of the internal combustion engine; FIG. 7 is a diagram showing an area within a predetermined distance range centered on the vehicle; and FIG. 8 is a time chart showing changes in the vehicle state and altitude from flat ground driving to uphill driving.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a diagram showing a schematic configuration of a vehicle 10. The vehicle 10 is a so-called series hybrid vehicle in which electric power generated by a generator 43 using the power of an internal combustion engine (hereinafter referred to as "engine") 41 is supplied to a battery 31, and the electric power from the battery 31 is used to rotate electric motors 34, 35 to drive wheels 38.

[0009] The vehicle 10 includes a navigation device 20, a drive system 30, a power generation system 40, a first cooling circuit 50 and a second cooling circuit 60 (see FIG. 2), and a coolant temperature control device 70.

[0010] The navigation device 20 includes a position sensor 21 such as a Global Navigation Satellite System (GNSS). The navigation device 20 acquires map information and driving environment information within a predetermined distance around the vehicle 10, and displays the map information and driving environment information on a display and outputs the map information and driving environment information through a speaker. For example, when the navigation device 20 sets a driving route at the request of the driver of the vehicle 10, the navigation device 20 displays the current position of the vehicle 10 detected by the position sensor 21 and the driving route to the destination or an intermediate destination on a map displayed on the display, and provides driving route guidance through audio output from the speaker. The driving environment information includes, for example, the speed of the vehicle 10 (hereinafter referred to as vehicle speed), traffic volume and congestion information on the driving route including the driving route, weather conditions, and driving route conditions. The driving route conditions include the degree of inclination of the driving route and the unevenness of the road surface.

[0011] The drive system 30 includes a battery 31 , inverters 32 and 33 , electric motors 34 and 35 , reducers 36 and 37 , and wheels 38 .

[0012] The inverter 32 is provided corresponding to the electric motor 34 for the front wheels, and the inverter 33 is provided corresponding to the electric motor 35 for the rear wheels. The inverters 32, 33 convert the direct current input from the battery 31 into alternating current and output it to the electric motors 34, 35. The inverters 32, 33 also convert the alternating current input from the electric motors 34, 35 into direct current and input it to the battery 31.

[0013] The electric motors 34 and 35 are driven in response to inputs from the corresponding inverters 32 and 33 to generate driving force and regenerative braking force for the vehicle 10 .

[0014] The reducers 36 and 37 are equipped with differential gears and transmit the outputs of the electric motors 34 and 35 to the left and right wheels 38 after reducing the speed.

[0015] The power generation system 40 includes an engine 41 , a gearbox 42 , a generator 43 , and an inverter 44 .

[0016] The engine 41 is mechanically connected to the generator 43 via a speed increaser 42. The engine 41 is used not as a power source for propelling the vehicle 10, but as a power source for driving the generator 43 to generate electricity.

[0017] The generator 43 is configured to generate electricity by rotating using power from the engine 41 and charge the battery 31. Using the power of the battery 31, the generator 43 can rotate the output shaft of the engine 41 to crank the engine 41 when it is started, consume energy by rotating the engine 41 as a load when the SOC (State of Charge) of the battery 31 is high, and close the throttle valve of the engine 41 to generate negative pressure in the intake passage when negative pressure for brake pedal assist is required.

[0018] 2 is a diagram showing the first cooling circuit 50. The first cooling circuit 50 circulates a first coolant serving as a first coolant for cooling the engine 41, thereby cooling the first coolant. The first cooling circuit 50 includes a first circuit 51, a second circuit 52, a third circuit 53, a fourth circuit 54, a fifth circuit 55, a first pump 56, a second pump 57, a multi-flow control valve (hereinafter referred to as MCV) 58, and a radiator 59. The cooling capacity of the first cooling circuit 50 can be changed by controlling the pumps 56, 57 and the MCV 58 by a controller 80 (see FIG. 1) of the coolant temperature control device 70.

[0019] The first circuit 51 is a circuit that runs from the first pump 56 through the engine 41, the MCV 58, the interior heater 51A, the second pump 57, the EGR cooler 51B, and returns to the inlet 56A of the first pump 56.

[0020] The second circuit 52 is a circuit that runs from the first pump 56 through the engine 41, but does not pass through the MCV 58 and the second pump 57, but passes through the turbocharger 52A and EGR cooler 51B, and returns to the inlet 56A of the first pump 56.

[0021] The third circuit 53 is a circuit that runs from the first pump 56 , passes through a throttle chamber 53A that includes a throttle valve for adjusting the intake amount of the engine 41 , and returns to an inlet 56A of the first pump 56 .

[0022] The fourth circuit 54 is a circuit that runs from the first pump 56 through an oil cooler 54A of the engine 41 and returns to an inlet 56A of the first pump 56 .

[0023] The fifth circuit 55 is a circuit that runs from the first pump 56 through the engine 41, the MCV 58, and the high-temperature side radiator 59, and returns to the inlet 56A of the first pump 56.

[0024] The MCV 58 is a valve for switching the circuits in the first cooling circuit 50, and is controlled by the controller 80. In response to a command from the controller 80, the MCV 58 can shut off both the first circuit 51 and the fifth circuit 55, shut off only one of the first circuit 51 and the fifth circuit 55 and allow circulation through the other, or allow circulation through both the first circuit 51 and the fifth circuit 55.

[0025] 3 is a diagram showing the second cooling circuit 60. The second cooling circuit 60 circulates second cooling water as a second cooling medium that cools the inverters 32, 33, the electric motors 34, 35, the generator 43, and the inverter 44, thereby cooling the second cooling water. The second cooling circuit 60 includes a first circuit 61, a second circuit 62, a first pump 63, three-way valves 64, 65, 66, a radiator 67, a bypass valve 68, and a second pump 69.

[0026] The first circuit 61 is a circuit that runs from the first pump 63 through the three-way valve 64, the low-temperature side radiator 67, the bypass valve 68, the three-way valve 65, the electric motor 34 for the front wheels, the inverter 32 for the front wheels, the generator 43, the inverter 44 for the generator 43, the three-way valve 66, the second pump 69, the water-cooled intercooler 61A, and the reservoir tank 61B, and returns to the inlet of the first pump 63.

[0027] The second circuit 62 is a circuit that runs from the first pump 63 through the three-way valve 64, the low-temperature side radiator 67, the bypass valve 68, the three-way valve 65, the electric motor 35 for the rear wheels, the inverter 33 for the rear wheels, the three-way valve 66, the second pump 69, the water-cooled intercooler 61A, and the reservoir tank 61B, and returns to the inlet of the first pump 63.

[0028] The three-way valves 64 , 65 , 66 are valves for switching the circuits within the second cooling circuit 60 , and are controlled by the controller 80 .

[0029] The bypass valve 68 is a valve for bypassing the low-temperature side radiator 67 from the three-way valve 64 and connecting it to the upstream side of the three-way valve 65 , and is controlled by the controller 80 .

[0030] Returning to FIG. 1, the coolant temperature control device 70 includes a coolant temperature sensor 70A, an outside air temperature sensor 70B, and a controller 80.

[0031] The coolant temperature sensor 70A detects the temperatures of the first coolant and the second coolant.

[0032] The outside air temperature sensor 70B detects the outside air temperature of the vehicle 10 .

[0033] 4 is a control block diagram of the controller 80. The controller 80 controls the temperatures of the first coolant and the second coolant. The controller 80 is realized by, for example, a microcomputer including an arithmetic unit such as a CPU (Central Processing Unit) or a GPU (Central Graphics Processing Unit), a storage unit 81 such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and an input / output unit such as an input / output interface. The navigation device 20, the inverters 32, 33, 44, the coolant temperature sensor 70A, and the outside air temperature sensor 70B are electrically or communicatively connected to the controller 80.

[0034] The controller 80 includes a memory unit 81 , a required work amount calculation unit 82 , a control switching determination unit 83 , and a cooling control unit 84 .

[0035] The storage unit 81 stores a computer program for causing the controller 80 to function, various maps used for control, various parameter values, etc. The map stored in the storage unit 81 includes, for example, a map that defines the value of the driving force required for the vehicle speed. The parameter values ​​stored in the storage unit 81 include, for example, various threshold values ​​for the outside air temperature, altitude difference, workload, predicted average speed, etc. when determining whether to switch control.

[0036] The required workload calculation unit 82 calculates the workload required to travel from the vehicle 10 to the highest elevation point within a predetermined distance range based on the position of the vehicle 10 and map information. In this embodiment, when a navigation-based travel route is set, the required workload calculation unit 82 sets the highest elevation point on the travel route within a predetermined distance range as the highest elevation point and calculates the required workload based on the travel route. Furthermore, when a navigation-based travel route is not set, the required workload calculation unit 82 calculates the required workload assuming that the vehicle 10 is heading to the highest elevation point.

[0037] The control switching determination unit 83 determines whether to switch the cooling water temperature control based on the difference in altitude between the position of the vehicle 10 and the highest point, the amount of work required while traveling to the highest point, the amount of work that the engine 41 can perform, and the outside air temperature.

[0038] Based on the determination result of the control switching determination unit 83, the cooling control unit 84 switches between a first control in which the engine coolant (hereinafter referred to as engine coolant) that cools the engine 41 is cooled to a first target temperature, and a second control in which the engine coolant is cooled with a higher cooling capacity than the first control to a second target temperature that is lower than the first target temperature or a third target temperature that is lower than the second target temperature. The cooling control unit 84 performs the first control when the value obtained by subtracting the available work load of the engine 41 from the required work load does not exceed a threshold, and performs the second control when the value obtained by subtracting the available work load of the engine 41 from the required work load exceeds a threshold, even if the temperature of the engine coolant is lower than the first target temperature. However, the cooling control unit 84 does not perform the second control when the outside air temperature is lower than the threshold. When the outside air temperature is lower than the threshold value, the temperature of the engine coolant does not rise much, and the impact of the decrease in engine 41 output due to the high temperature of the engine coolant is small. In addition, the low temperature of the engine coolant may increase the amount of unburned fuel and generate more particulates than expected.

[0039] In this embodiment, the first target temperature is set to a coolant temperature at which the temperature of the engine 41 rises and abnormal combustion (knocking) begins to occur. Abnormal combustion in the engine 41 may cause deterioration or damage to the engine 41. Therefore, in order to protect the engine 41, retarded combustion is performed to delay the ignition timing of the engine 41 so as to prevent the temperature of the engine 41 from rising further. Retarded combustion not only reduces the fuel economy of the engine 41 compared to normal, but also reduces the efficiency of power generation powered by the engine 41. For this reason, when the value obtained by subtracting the available work load of the engine 41 from the required work load exceeds a threshold, the cooling control unit 84 performs second control to cool the engine coolant to a second target temperature or a third target temperature lower than the first target temperature, even if the temperature of the engine coolant is below the first target temperature. This cools the engine coolant to a lower temperature at an earlier timing than when the first control is performed.

[0040] 5 is a flowchart of the control executed by the controller 80. The control routine shown in the flowchart is pre-programmed, and this program is installed in the controller 80. In accordance with the program, the controller 80 repeatedly executes the following control routine at an operation cycle of, for example, about 10 to 100 milliseconds.

[0041] In step S1 of FIG. 5, the controller 80 acquires the outputs of the navigation device 20 and the sensors 70A and 70B, that is, the map information, the temperature of the engine coolant, and the outside air temperature.

[0042] In step S2, the control switching determination unit 83 determines whether the outside air temperature is lower than the threshold value. If it is determined in step S2 that the outside air temperature is lower than the threshold value, the cooling control unit 84 sets the target temperature of the engine coolant to a first target temperature and performs the first control in step S3.

[0043] On the other hand, if it is determined in step S2 that the outside air temperature is not lower than the threshold value, the control switching determination unit 83 determines in step S4 whether or not a travel route has been set by navigation by the navigation device 20.

[0044] If it is determined in step S4 that a driving route has been set, the control switching determination unit 83 determines in step S5 whether there is a point on the driving route within a predetermined distance range where the elevation difference is equal to or greater than a threshold. If it is determined in step S5 that there is a point on the driving route where the elevation difference is equal to or greater than the threshold, the required work amount calculation unit 82 calculates in step S6 the amount of work required to drive to the highest elevation point on the driving route. At this time, the required work amount calculation unit 82 adds the amount of work required for driving and the amount of work required for power generation by the generator 43 to calculate the amount of work required to drive to the highest elevation point.

[0045] The amount of work required for traveling is calculated, for example, by calculating the driving force required for traveling from the predicted average vehicle speed of the traveling route, adding the average grade resistance calculated from the weight of the vehicle 10 and the average grade of the traveling route to the required driving force, and multiplying the result by the traveling distance. The driving force required for traveling can be determined, for example, using a map that specifies the value of the driving force required for each vehicle speed. The map specifies the driving force according to the vehicle speed, taking into account, for example, losses due to traveling resistance, losses due to acceleration resistance, losses in the transmission, and electrical losses when driving the electric motors 34, 35 and the generator 43. The predicted average speed is set, for example, by multiplying the speed limit of the traveling route by a coefficient corresponding to the congestion level of the traveling route. The average grade resistance is calculated by multiplying the weight of the vehicle 10 in W [kg] and the acceleration of gravity in g [m / s ２ ], and the average gradient of the travel route is θ, it can be calculated as W·g·sin θ.

[0046] The amount of work required for power generation is calculated, for example, by multiplying the power generated when the generator 43 is driven by the output of the engine 41 by the driving time. As shown in Figure 6, the output of the engine 41 is affected by a decrease in air density due to an increase in altitude and an increase in the temperature of the engine coolant, and decreases as the altitude and the temperature of the engine coolant increase. Therefore, the output of the engine 41 taking the altitude and the temperature of the engine coolant into consideration is used to calculate the amount of work required for power generation.

[0047] If it is determined in step S4 of FIG. 5 that a driving route has not been set, the control switching determination unit 83 determines in step S7 whether there is a point within a predetermined distance range where the elevation difference is equal to or greater than a threshold. The threshold used in this determination is either a first elevation difference threshold or a second elevation difference threshold greater than the first elevation difference threshold, as shown in Table 1 below, depending on which region of FIG. 7 the highest elevation point is located in relative to the vehicle 10. In contrast, if a driving route has been set, the first elevation difference threshold is used regardless of the region. Note that in FIG. 7 , regions 1A and 1B are regions within a circle with a radius r1 representing the distance from the vehicle 10, and regions 2A and 2B are regions within a circle with a radius r2 representing the distance from the vehicle 10 that is greater than the radius r1. Regions 1B and 2B are regions behind the vehicle 10, and regions 1A and 2A are other regions, including the region ahead of the vehicle 10.

[0048]

[0049] If it is determined in step S7 that there is a point within the specified distance range where the elevation difference is greater than or equal to the threshold, the required work volume calculation unit 82 calculates in step S8 the amount of work required to travel to the highest elevation point, assuming that the vehicle 10 is heading towards the highest elevation point within the specified distance range.

[0050] In step S9 following steps S6 and S8, the control switching determination unit 83 determines whether the value obtained by subtracting the possible workload of the engine 41 from the required workload exceeds a threshold value. In this embodiment, the threshold value is a value obtained by multiplying the SOC of the battery 31 by a predetermined rate and converting the value into an amount of power, which is the workload. That is, the control switching determination unit 83 in this embodiment determines whether the value obtained by subtracting the possible workload of the engine 41 from the required workload exceeds the workload obtained by multiplying the SOC by the predetermined rate.

[0051] The work capacity of the engine 41 is calculated, for example, by multiplying the output of the engine 41 by the driving time. The work capacity of the engine 41 is calculated using the maximum output of the engine 41, taking into account the altitude and the temperature of the engine coolant.

[0052] In the next step S10, the control switching determination unit 83 determines whether the predicted average speed to the highest point is equal to or less than a threshold value. The threshold value used in this determination differs depending on whether a travel route has been set. If a travel route has been set, the first speed threshold value is used. If a travel route has not been set, the first speed threshold value or a second speed threshold value greater than the first speed threshold value is used, depending on which region shown in FIG. 7 the highest point is in, as shown in Table 1.

[0053] If it is determined in step S10 that the predicted average speed is below the threshold, the cooling control unit 84 sets the target temperature of the engine coolant to a second target temperature lower than the first target temperature in step S11; if not, it sets the target temperature of the engine coolant to a third target temperature lower than the second target temperature in step S12.

[0054] In the following step S13, the cooling control unit 84 performs the second control so that the temperature of the engine coolant becomes the target temperature.

[0055] FIG. 8 is a time chart showing changes in the state and altitude of the vehicle 10 as the vehicle moves from flat ground to uphill. First, we will explain the changes in the state of the vehicle 10 when only the first control is performed. In FIG. 8 , the first control is performed while the vehicle is traveling on flat ground, and the engine coolant temperature is approximately at the first target temperature TE1. Then, when the vehicle speed is increased at time T4 and uphill traveling begins, the engine coolant temperature begins to rise after a short time at time T5, as shown by the dotted line in FIG. 8 , and the maximum output of the engine 41 decreases accordingly. Thereafter, at time T7, the maximum output of the engine 41 falls below the required value, and the SOC of the battery 31 begins to decrease. In this case, if the vehicle continues traveling in the same manner, the SOC of the battery 31 may reach the allowable lower limit, as shown by the dotted line in FIG. 8 . Once the allowable lower limit is reached, the vehicle 10 will travel with an output lower than the driver's request.

[0056] Next, a description will be given of changes in the state of the vehicle 10 when the second control is performed. When the start condition for the second control is satisfied while the vehicle is traveling on flat ground, the controller 80 controls the pumps 56, 57, and the MCV 58 to start the second control at time T1. After a short delay, the engine coolant temperature begins to decrease at time T2 and reaches approximately the second target temperature TE2, which is lower than the first target temperature TE1, at time T3. Furthermore, as the engine coolant temperature decreases, the maximum output of the engine 41 increases. Thereafter, the engine coolant temperature begins to increase at time T6. However, because the engine coolant temperature has already decreased to the second target temperature TE2, the rate and level of decrease in the maximum output of the engine 41 are suppressed compared to when the second control is not performed. This minimizes the risk of the SOC of the battery 31 reaching the allowable lower limit, allowing the vehicle 10 to continue traveling at the output desired by the driver.

[0057] According to the above-described embodiment, when the value obtained by subtracting the work capacity of the engine 41 from the work required while traveling from the vehicle 10 to the highest altitude point within a predetermined distance range exceeds a threshold, even if the temperature of the engine coolant is below the first target temperature, the second control is executed to cool the engine coolant with a cooling capacity higher than that of the first control so that the temperature of the engine coolant reaches a second target temperature lower than the first target temperature. This prevents the temperature of the engine coolant from rising, avoids abnormal combustion in the engine 41, and suppresses a decrease in the efficiency of power generation powered by the engine 41 and the generated power.

[0058] According to this embodiment, when a driving route is set by navigation, the point on the driving route where the altitude is the highest within a predetermined distance is set as the highest altitude point, and the required workload is calculated based on the driving route. As a result, the workload required while driving to the highest altitude point can be calculated with high accuracy, and switching between the first control and the second control can be performed appropriately.

[0059] According to the embodiment, if a driving route is not set by navigation, the required workload is calculated on the assumption that the vehicle 10 is heading to the highest point in altitude. Therefore, even if a driving route is not set, the second control can be implemented, and a decrease in the efficiency of power generation powered by the engine 41 and the generated power can be suppressed.

[0060] According to this embodiment, when the outside air temperature is lower than the threshold value, the controller 80 does not perform the second control, thereby suppressing an increase in unburned fuel and generation of particulates due to a low engine coolant temperature.

[0061] As described above, the best configurations, methods, and the like for implementing the present invention have been disclosed in the above description, but the present invention is not limited thereto. That is, although the present invention has been particularly illustrated and described mainly with reference to specific embodiments, those skilled in the art can make various modifications to the above-described embodiments in terms of shape, material, quantity, and other detailed configurations without departing from the scope of the technical idea and purpose of the present invention. Furthermore, the above-disclosed descriptions limiting the shape, material, and the like are provided as examples to facilitate understanding of the present invention and are not intended to limit the present invention. Therefore, descriptions using names of components that are free from some or all of the limitations on shape, material, and the like are included in the present invention.

[0062] The vehicle 10 may be a so-called parallel hybrid vehicle in which the wheels 38 are driven by the electric motors 34, 35 and the engine 41. The vehicle 10 may be an all-wheel drive vehicle, a front-wheel drive vehicle, or a rear-wheel drive vehicle.

[0063] The speed reducers 36, 37 may be configured to be able to switch between a plurality of gear ratios in a stepwise manner, or may be configured to be able to switch between gear ratios continuously like a CVT (Continuously Variable Transmission).

[0064] The first cooling medium and the second cooling medium may be cooling water, cooling oil, or other materials.

[0065] 10... vehicle, 41... engine (internal combustion engine), 50... first cooling circuit (cooling circuit), 70... cooling water temperature control device, 80... controller

Claims

1. A coolant temperature control method for a hybrid vehicle equipped with an internal combustion engine, comprising: calculating a required amount of work for traveling from the hybrid vehicle to a highest altitude within a predetermined distance range; and, if a value obtained by subtracting the required amount of work capable of being done by the internal combustion engine from a required amount of work does not exceed a threshold, implementing a first control to cool the coolant so that the temperature of the coolant for the internal combustion engine reaches a first target temperature; and, if a value obtained by subtracting the required amount of work capable of being done by the internal combustion engine from a required amount of work exceeds a threshold, implementing a second control to cool the coolant with a cooling capacity higher than that of the first control so that the temperature of the coolant reaches a second target temperature lower than the first target temperature, even if the temperature of the coolant is below the first target temperature.

2. A cooling water temperature control method as claimed in claim 1, wherein, when a driving route is set by navigation, the point on said driving route whose elevation is the highest within said specified distance range is set as said highest elevation point, and said required workload is calculated based on said driving route.

3. A cooling water temperature control method according to claim 1, wherein, when a driving route is not set by navigation, the required amount of work is calculated on the assumption that the hybrid vehicle is heading towards the highest altitude point.

4. A cooling water temperature control method according to any one of claims 1 to 3, wherein the second control is not performed when the outside air temperature is lower than a threshold value.

5. A coolant temperature control device for a hybrid vehicle equipped with an internal combustion engine, comprising a cooling circuit that cools the coolant of the internal combustion engine and a controller that controls the temperature of the coolant of the internal combustion engine, wherein the controller calculates the amount of work required for traveling from the hybrid vehicle to the highest altitude within a predetermined distance range, and if the value obtained by subtracting the amount of work that the internal combustion engine can do from the amount of work does not exceed a threshold, performs a first control that cools the coolant so that the temperature of the coolant of the internal combustion engine becomes a first target temperature, and if the value obtained by subtracting the amount of work that the internal combustion engine can do from the amount of work exceeds a threshold, performs a second control that cools the coolant with a cooling capacity higher than that of the first control so that the temperature of the coolant becomes a second target temperature that is lower than the first target temperature, even if the temperature of the coolant is below the first target temperature.

Images