Control device for vehicle

Abstract

To provide a control device for a vehicle, which can suppress a hindrance to traveling while suppressing a discomfort feeling from being imparted to a driver.SOLUTION: There is provided a control device for a vehicle that is equipped with a viscous coupling for transmitting engine torque to auxiliary drive wheels by utilizing shear resistance of a viscous fluid. The control device comprises: a coupling temperature acquisition unit that acquires a coupling temperature Tc; and a control unit that executes first fail-safe processing to suppress a rise in the coupling temperature when the coupling temperature Tc acquired by the coupling temperature acquisition unit exceeds a threshold value TH1. When the coupling temperature Tc becomes higher than a threshold value TH2 that is higher than the threshold value TH1 during execution of the first fail-safe processing, the control unit executes second fail-safe processing that can suppress the rise in the coupling temperature more than the first fail-safe processing.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Patent Document 1 discloses a control for the purpose of preventing overheating of the coupling mechanism, in which when the coupling oil temperature rises above an oil temperature threshold, the engine output torque is reduced to slow down the vehicle speed, thereby reducing friction generated within the controlled coupling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-276575 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the control described in Patent Document 1, when the coupling oil temperature exceeds the oil temperature threshold, control is suddenly executed to reduce the friction generated within the control coupling, which is likely to cause discomfort to the driver and may also cause a sudden reduction in engine output due to this control, resulting in impaired driving.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a vehicle control device that can suppress any disruption to driving while suppressing any discomfort felt by the driver. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a control device for a vehicle equipped with a viscous coupling that transmits a driving force of a power source to a driving wheel by utilizing the shear resistance of a viscous fluid, comprising: a coupling temperature acquisition unit that acquires a coupling temperature, which is the temperature of the viscous coupling; and a control unit that executes a first fail-safe processing to suppress an increase in the coupling temperature when the coupling temperature acquired by the coupling temperature acquisition unit exceeds a first threshold value, and the control unit is configured to execute a second fail-safe processing that can suppress the increase in the coupling temperature more than the first fail-safe processing when the coupling temperature becomes higher than a second threshold value that is higher than the first threshold value during the execution of the first fail-safe processing. Effect of the Invention

[0007] According to the present invention, it is possible to provide a vehicle control device that can suppress any discomfort felt by the driver while suppressing any disruption to driving. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a vehicle equipped with a vehicle control device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart showing the flow of fail-safe control executed by a fail-safe control device of a vehicle equipped with a vehicle control device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A vehicle control device according to one embodiment of the present invention is a control device for a vehicle equipped with a viscous coupling that transmits the driving force of a power source to a drive wheel by utilizing the shear resistance of a viscous fluid, and includes a coupling temperature acquisition unit that acquires a coupling temperature, which is the temperature of the viscous coupling, and a control unit that executes a first fail-safe processing to suppress an increase in the coupling temperature when the coupling temperature acquired by the coupling temperature acquisition unit exceeds a first threshold value, and is characterized in that, during execution of the first fail-safe processing, when the coupling temperature becomes higher than a second threshold value that is higher than the first threshold value, the control unit executes a second fail-safe processing that can suppress the increase in the coupling temperature more than the first fail-safe processing.

[0010] As a result, the vehicle control device according to one embodiment of the present invention can suppress any discomfort felt by the driver while suppressing any disruption to driving. EXAMPLES

[0011] Hereinafter, with reference to Figs. 1 and 2, a vehicle control device according to an embodiment of the present invention will be described by taking a vehicle equipped with the control device as an example.

[0012] (Vehicle configuration) As shown in FIG. 1, the vehicle 1 is a four-wheel drive vehicle including an engine 2 as a power source, a transmission 3, a transfer 4, main drive wheels 5 and auxiliary drive wheels 10 as drive wheels, and a fail-safe control device 12 as a vehicle control device.

[0013] The engine 2 has a plurality of cylinders (not shown), and is configured to perform a series of four strokes, including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, for each cylinder.

[0014] A radiator 40 that cools the coolant for the engine 2 is disposed in front of the engine 2. A radiator fan 41 serving as a blower fan is provided behind the radiator 40, and blows air that has passed through the radiator 40 toward the rear of the vehicle. The radiator fan 41 is connected to an engine control device (hereinafter referred to as "ECM") 13, and its drive is controlled by the ECM 13.

[0015] The transmission 3 is connected to the engine 2, and changes the speed of the rotation transmitted from the engine 2 at a desired gear ratio and outputs it to the main drive shaft 6 and the transfer 4. Left and right main drive wheels 5 arranged on the front side of the vehicle 1 are connected to the main drive shaft 6. The left and right main drive wheels 5 are each provided with a brake device 24 as a braking device.

[0016] One end of a propeller shaft 7 is connected to the transfer 4 via a viscous coupling 8 serving as a viscous coupling. In other words, the viscous coupling 8 is provided between the transfer 4 and the propeller shaft 7.

[0017] The other end of the propeller shaft 7 is connected to a differential 9. An auxiliary drive shaft 11 is connected to the differential 9. Left and right auxiliary drive wheels 10 arranged on the rear side of the vehicle 1 are connected to the auxiliary drive shaft 11. The left and right auxiliary drive wheels 10 are each provided with a brake device 25 as a braking device.

[0018] The viscous coupling 8 has an inner plate and an outer plate in an operating chamber (not shown) filled with a viscous fluid such as silicon oil. When the inner plate and the outer plate rotate differentially, the viscous coupling 8 generates a transmission torque by utilizing the shear resistance that occurs in the viscous fluid according to the rotation difference.

[0019] The viscous coupling 8 utilizes the shear resistance of a viscous fluid to transmit the driving force of the engine 2 to the auxiliary drive wheels 10. Note that the viscous coupling is not limited to the viscous coupling.

[0020] The fail-safe control device 12 is composed of a computer unit including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, and an output port.

[0021] The ROM of the fail-safe control device 12 stores various control constants, various maps, and the like, as well as a program for causing the computer unit to function as the fail-safe control device 12. That is, in the fail-safe control device 12, the CPU executes the program stored in the ROM, causing the computer unit to function as the fail-safe control device 12.

[0022] The fail-safe control device 12 is connected to an ECM 13, a brake control device 14, and a transmission control device (hereinafter referred to as "TCM") 15.

[0023] An accelerator position sensor 23 that detects the accelerator position, which is the depression state of the accelerator pedal 22, is connected to the ECM 13. The ECM 13 calculates a required engine torque by referring to a map (not shown) based on the accelerator position detected by the accelerator position sensor 23 and the engine speed. The ECM 13 controls the engine 2 so that the required engine torque is output by the engine 2.

[0024] The brake control device 14 has a brake operation unit including a brake pedal, a brake booster, a master cylinder, etc., all of which are not shown, and a brake actuator that controls the hydraulic pressure in accordance with a control signal from a brake controller, all of which are not shown.

[0025] In this embodiment, the brake control device 14 can generate a braking force in response to, for example, depression of the brake pedal, as well as in response to a signal from the fail-safe control device 12.

[0026] The TCM 15 is connected to the transmission 3 and is configured to obtain shift position information. When the transmission 3 is configured as an automatic transmission, the TCM 15 controls gear shifting in the transmission 3.

[0027] Additionally, the fail-safe control device 12 is connected to a coupling temperature sensor 8a and a combination meter 19 serving as an informing unit.

[0028] The coupling temperature sensor 8a detects the internal temperature of the viscous coupling 8 (hereinafter referred to as the “coupling temperature”), specifically, the temperature of the viscous fluid in the differential chamber, and outputs the detection result to the fail-safe control device 12.

[0029] The combination meter 19 is provided in front of the driver's seat and is configured to display various warning lights, etc., in addition to displaying the speed and engine RPM. The combination meter 19 is capable of displaying various warning lights, such as a warning light (notice) indicating that a first fail-safe process or a second fail-safe process, which will be described later, may be executed, a warning light (executing) indicating that the first fail-safe process is being executed, and a warning light (executing) indicating that the second fail-safe process is being executed.

[0030] In this embodiment, the warning light (notice) and the warning light (in progress) are configured as separate warning lights, but the warning light (notice) and the warning light (in progress) may be integrated into one warning light by using a single warning light with different lighting forms, such as the way it is turned on or the color it is lit in. Also, in this embodiment, separate warning lights (in progress) are configured to indicate that the first fail-safe process and the second fail-safe process are being executed, but a single warning light (in progress) may indicate that either the first fail-safe process or the second fail-safe process, or both, are being executed by using different lighting forms.

[0031] The fail-safe control device 12 includes a coupling temperature acquisition unit 30 and a control unit 31.

[0032] The coupling temperature acquisition unit 30 acquires the coupling temperature input from the coupling temperature sensor 8a.

[0033] The control unit 31 is configured to perform fail-safe control to execute at least one of a first fail-safe process and a second fail-safe process, which will be described later, according to the state of the viscous coupling 8. The first fail-safe process and the second fail-safe process are processes for suppressing an increase in the coupling temperature.

[0034] (Fail-safe control) Next, the flow of the fail-safe control executed by the fail-safe controller 12 will be described with reference to FIG.

[0035] The fail-safe controller 12 acquires the coupling temperature Tc from the coupling temperature sensor 8a (step S1).

[0036] Next, the fail-safe controller 12 calculates the gradient ΔTc of the coupling temperature (step S2). Specifically, when the coupling temperature Tc is rising, the fail-safe controller 12 calculates the amount of rise of the coupling temperature Tc per unit time, that is, the rate of rise of the coupling temperature Tc, as the gradient ΔTc.

[0037] Thereafter, the fail-safe controller 12 judges whether or not the coupling temperature Tc is higher than a threshold value TH0 (step S3). The threshold value TH0 is a value lower than a threshold value TH1 serving as a first threshold value, which will be described later.

[0038] If the fail-safe controller 12 determines in step S3 that the coupling temperature Tc is not higher than the threshold value TH0, the fail-safe controller 12 returns the process to step S1.

[0039] When the fail-safe control device 12 determines in step S3 that the coupling temperature Tc is higher than the threshold value TH0, it displays, for example, lights or blinks a warning light (notice) on the combination meter 19 (step S4). This notifies the driver that there is a possibility that a first fail-safe process or a second fail-safe process, which will be described later, will be executed before the execution of these fail-safe processes.

[0040] Next, the fail-safe controller 12 judges whether the coupling temperature Tc acquired in step S1 is higher than a threshold value TH1 (step S5). The threshold value TH1 is a value higher than the threshold value TH0, and is an upper limit value of the coupling temperature at which it is judged that there is no problem with the viscous coupling 8 even if the coupling temperature is not lowered. The threshold value TH1 is experimentally obtained in advance and stored in the ROM of the fail-safe controller 12.

[0041] When it is determined in step S5 that the coupling temperature Tc is not higher than the threshold value TH1, the fail-safe controller 12 determines whether or not the coupling temperature Tc is equal to or lower than a threshold value TH0 (step S6).

[0042] When the fail-safe controller 12 determines in step S6 that the coupling temperature Tc is not equal to or lower than the threshold value TH0, the fail-safe controller 12 returns the process to step S1.

[0043] When the fail-safe control device 12 determines in step S6 that the coupling temperature Tc is equal to or lower than the threshold value TH0, it turns off the warning light (notice) displayed in step S4 (step S19) and ends this fail-safe control. As a result, when there is no possibility that the driver who has confirmed the warning light (notice) will drive in a manner that will lower the coupling temperature Tc and thus cause the fail-safe process to be executed, the unnecessary warning light (notice) is turned off.

[0044] When the fail-safe controller 12 determines in step S5 that the coupling temperature Tc is higher than the threshold value TH1, the fail-safe controller 12 determines whether or not a predetermined time has elapsed since it was determined in step S5 that the coupling temperature Tc is higher than the threshold value TH1 (step S7).

[0045] If the fail-safe controller 12 determines in step S7 that the predetermined time has not elapsed, it returns the process to step S1.

[0046] When it is determined in step S7 that the predetermined time has elapsed, the fail-safe control device 12 determines whether the gradient ΔTc of the coupling temperature calculated in step S2 is greater than a predetermined gradient Δth (step S8). The predetermined gradient Δth is, for example, an upper limit of the gradient of the coupling temperature at which it can be determined that the coupling temperature Tc can be lowered by performing the first fail-safe process, and is experimentally obtained in advance and stored in the ROM of the fail-safe control device 12.

[0047] When it is determined in step S8 that the gradient ΔTc of the coupling temperature is not larger than the predetermined gradient Δth, the fail-safe controller 12 executes a first fail-safe process (step S9).

[0048] Specifically, as a first fail-safe process, the fail-safe control device 12 controls the brake control device 14 to activate at least one of the brake device 24 and the brake device 25, and executes a process to suppress the difference in rotation speed between the main drive wheel 5 which is the input side of the viscous coupling 8 and the auxiliary drive wheel 10 which is the output side of the viscous coupling 8. This reduces the friction resistance in the viscous coupling 8, and suppresses an increase in the coupling temperature.

[0049] Next, the fail-safe control device 12 displays, for example lights up or blinks, a warning light (in execution) indicating that the first fail-safe process is being executed (step S10), thereby making the driver aware that the first fail-safe process is being executed.

[0050] After that, the fail-safe controller 12 acquires the coupling temperature Tc from the coupling temperature sensor 8a (step S11).

[0051] Next, the fail-safe controller 12 judges whether the coupling temperature Tc acquired in step S11 is equal to or lower than a threshold value TH2 as a second threshold value (step S12). The threshold value TH2 is a value higher than the above-mentioned threshold value TH1, and is an upper limit value of the coupling temperature at which it is possible to determine that the coupling temperature Tc can be reduced by performing the first fail-safe processing as it is. The threshold value TH2 is experimentally obtained in advance and stored in the ROM of the fail-safe controller 12.

[0052] If the fail-safe control device 12 determines in step S12 that the coupling temperature Tc acquired in step S11 is not equal to or lower than the threshold value TH2, it determines that it is difficult to suppress the increase in the coupling temperature unless the second fail-safe processing is executed, and transfers the processing to step S14.

[0053] When the fail-safe controller 12 determines in step S12 that the coupling temperature Tc acquired in step S11 is equal to or lower than the threshold value TH2, the fail-safe controller 12 determines whether or not the coupling temperature Tc acquired in step S11 is lower than a threshold value TH1_h (step S13).

[0054] The threshold value TH1_h is a threshold value that provides a hysteresis characteristic to the above-mentioned threshold value TH1, and is set to a value obtained by subtracting a predetermined hysteresis width from the threshold value TH1. In this manner, the use of the threshold value TH1_h suppresses chattering.

[0055] When the fail-safe controller 12 determines in step S13 that the coupling temperature Tc acquired in step S11 is not lower than the threshold value TH1_h, the fail-safe controller 12 returns the process to step S2 and continues the first fail-safe process.

[0056] If the fail-safe controller 12 determines in step S13 that the coupling temperature Tc acquired in step S11 is lower than the threshold value TH1_h, it moves the process to step S18.

[0057] If the fail-safe controller 12 determines in step S8 that the gradient ΔTc of the coupling temperature is greater than the predetermined gradient Δth, it executes a second fail-safe process (step S14).

[0058] Specifically, as a second fail-safe process, the fail-safe control device 12 executes a process of reducing the engine torque, which is the torque of the engine 2 relative to the accelerator opening, through the ECM 13. The fail-safe control device 12 can reduce the engine torque actually output from the engine 2, for example, by reducing a required engine torque calculated based on the accelerator opening and the engine speed.

[0059] The second fail-safe process is a fail-safe process that can suppress an increase in the coupling temperature more effectively than the above-described first fail-safe process.

[0060] In this embodiment, the second fail-safe process is executed in, for example, the following three situations.

[0061] The first case is when the coupling temperature Tc becomes higher than the threshold value TH2 during the execution of the first fail-safe processing. That is, in FIG. 2, after the processing of steps S1 to S5 and steps S7 to S11 is executed, the result becomes NO in step S12. In this first case, the fail-safe processing is executed in stages, such that the first fail-safe processing is executed first, and then the second fail-safe processing is executed in addition to the first fail-safe processing. At this time, the second fail-safe processing may be executed instead of the first fail-safe processing.

[0062] The second is a case where the gradient ΔTc of the coupling temperature becomes larger than a predetermined gradient Δth during execution of the first fail-safe process. That is, in FIG. 2, after the processes of steps S1 to S5 and steps S7 to S13 are executed, the process returns to step S2, and step S8 becomes YES again. In this second case, the fail-safe process is also executed in stages, as in the first case. At this time, the second fail-safe process may be executed instead of the first fail-safe process.

[0063] The third is a case where the gradient ΔTc of the coupling temperature becomes larger than a predetermined gradient Δth before the first fail-safe process is executed. That is, in FIG. 2, after the processes of steps S1 to S5 and step S7 are executed, the result becomes YES in step S8. In this third case, since the coupling temperature Tc is high and the gradient ΔTc of the coupling temperature is large, it is determined that suppression of an increase in the coupling temperature has a higher priority than suppression of discomfort felt by the driver, and the second fail-safe process is executed without going through the first fail-safe process. At this time, the first fail-safe process may be executed together with the second fail-safe process.

[0064] Thereafter, the fail-safe control device 12 displays, for example lights up or blinks, a warning light (in execution) indicating that the second fail-safe process is being executed (step S15). This allows the driver to recognize that the second fail-safe process, which can suppress the increase in coupling temperature more effectively than the first fail-safe process, is being executed, that is, that the fail-safe process has been switched.

[0065] Next, the fail-safe controller 12 acquires the coupling temperature Tc from the coupling temperature sensor 8a (step S16).

[0066] Thereafter, the fail-safe controller 12 determines whether or not the coupling temperature Tc acquired in step S16 is lower than a threshold value TH1_h (step S17).

[0067] If the fail-safe controller 12 determines in step S17 that the coupling temperature Tc acquired in step S16 is not lower than the threshold value TH1_h, it returns the process to step S14 and continues the second fail-safe process.

[0068] If the fail-safe controller 12 determines in step S17 that the coupling temperature Tc acquired in step S16 is lower than the threshold value TH1_h, it moves the process to step S18.

[0069] In step S18, the fail-safe controller 12 cancels the first fail-safe process or the second fail-safe process, or both of the fail-safe processes that are being executed.

[0070] Thereafter, the fail-safe control device 12 turns off all warning lights that have been displayed, for example, lit or flashing, on the combination meter 19 (step S19), and ends this fail-safe control.

[0071] (Action and effect) As described above, the vehicle control device of this embodiment is configured to execute a first fail-safe process to suppress an increase in the coupling temperature when the coupling temperature Tc exceeds the threshold value TH1, and to execute a second fail-safe process that can suppress the increase in the coupling temperature more effectively than the first fail-safe process if the coupling temperature Tc becomes higher than the threshold value TH2 that is higher than the threshold value TH1 during execution of the first fail-safe process.

[0072] With this configuration, the control device of the vehicle in this embodiment can gradually perform fail-safe processing to suppress an increase in coupling temperature, thereby suppressing any discomfort felt by the driver due to the execution of the fail-safe processing while suppressing any disruption to driving.

[0073] In addition, as a first fail-safe processing, the vehicle control device of this embodiment executes a process of activating at least one of the brake devices 24 and 25 to suppress the difference in rotation speed between the input side and the output side of the viscous coupling 8, thereby reducing the frictional resistance in the viscous coupling 8 and suppressing an increase in the coupling temperature.

[0074] In addition, the vehicle control device according to this embodiment executes a process of reducing the engine torque relative to the accelerator opening as a second fail-safe process, thereby suppressing the transmission torque in the viscous coupling 8 and suppressing an increase in the coupling temperature.

[0075] Furthermore, the vehicle control device according to this embodiment notifies the driver via the combination meter 19 that there is a possibility that the first fail-safe processing or the second fail-safe processing, or both, will be executed before the first fail-safe processing is executed, so that the possibility of executing the fail-safe processing can be communicated to the driver in advance. This can eliminate the sense of incongruity felt by the driver due to the execution of the fail-safe processing. In addition, it is also possible for the driver to make adjustments so that the fail-safe processing is not executed. For example, in preparation for the need for four-wheel drive driving, the accelerator can be operated so that excessive torque transmission does not occur in the viscous coupling 8.

[0076] Furthermore, the vehicle control device according to this embodiment executes the second fail-safe processing when the gradient ΔTc of the increase in coupling temperature is greater than a predetermined gradient Δth. Therefore, regardless of whether the first fail-safe processing is being executed or not, when suppression of an increase in coupling temperature has a high priority, the second fail-safe processing is executed to quickly suppress an increase in coupling temperature.

[0077] (Modification) In this embodiment, the coupling temperature acquisition unit 30 acquires the coupling temperature from the coupling temperature sensor 8a, but the coupling temperature acquisition unit 30 may estimate the coupling temperature. In this case, the coupling temperature acquisition unit 30 obtains a rotation difference between the main drive wheels 5 and the auxiliary drive wheels 10 based on information from a wheel speed sensor (not shown), for example, and estimates the coupling temperature from the rotation difference.

[0078] In this embodiment, it is determined whether or not the gradient ΔTc of the coupling temperature is larger than a predetermined gradient Δth in step S8 of the fail-safe control in Fig. 2, but when moving to step S8 during execution of the first fail-safe processing, it may be determined whether or not the gradient ΔTc of the coupling temperature has decreased compared to before the execution of the first fail-safe processing. In this case, if no decrease in the gradient ΔTc of the coupling temperature is observed even after the first fail-safe processing is executed, the second fail-safe processing is executed in step S14.

[0079] In addition, in this embodiment, the brake control device 14 is controlled to suppress the difference in rotation speed between the main drive wheels 5 and the auxiliary drive wheels 10 as the first fail-safe process, but in addition to this, a process may be executed in which the radiator fan 41 is operated to send air toward the viscous coupling 8. In this case, a blower fan other than the radiator fan 41 may be provided near the viscous coupling 8 to send air to the viscous coupling 8. Such a blower fan such as the radiator fan 41 can blow cooling air onto the viscous coupling 8, and the temperature rise of the viscous coupling 8 can be further suppressed.

[0080] In the second fail-safe processing of the present embodiment, the amount of engine torque reduction may be switched in stages. For example, the fail-safe control device 12 switches the amount of engine torque reduction in stages in response to a change in the gradient ΔTc of the coupling temperature.

[0081] In this case, when the gradient ΔTc of the coupling temperature exceeds a predetermined gradient Δth, the amount of engine torque reduction in the previous second fail-safe processing is reduced, and if the gradient ΔTc of the coupling temperature does not change or increases after the previous second fail-safe processing is executed, the amount of engine torque reduction in the next second fail-safe processing is increased. This allows the amount of engine torque reduction to be increased stepwise without a large reduction in engine torque from the beginning, thereby further reducing the discomfort felt by the driver.

[0082] Although an embodiment of the invention has been disclosed, it will be apparent to one of ordinary skill in the art that modifications may be made therein without departing from the spirit and scope of the invention, and it is intended that all such modifications and equivalents be included in the following claims. [Explanation of symbols]

[0083] 1 vehicle 2 Engine (power source) 3. Gearbox 4 Transfer 5 Main drive wheels (drive wheels) 7 Propeller shaft 8 Viscous coupling (viscous coupling) 8a Coupling temperature sensor 10 Secondary drive wheel (drive wheel) 12 Fail-safe control device 13 ECM 14 Brake control device 15 TCM 19 Combination meter (alarm section) 22 Accelerator pedal 23 Accelerator opening sensor 24, 25 Brake device 30 Coupling temperature acquisition unit 31 Control Unit 40 Radiator 41 Radiator fan (blower fan) Tc coupling temperature ΔTc Coupling temperature slope Δth given slope TH0 Threshold TH1 Threshold (First Threshold) TH2 Threshold (Second Threshold) TH1_h threshold

Claims

1. A control device for a vehicle equipped with a viscous coupling that transmits a driving force of a power source to a driving wheel by utilizing the shear resistance of a viscous fluid, A coupling temperature acquisition unit that acquires a coupling temperature, which is a temperature of the viscous coupling; a control unit that executes a first fail-safe process to suppress an increase in the coupling temperature when the coupling temperature acquired by the coupling temperature acquisition unit exceeds a first threshold value, The control unit of the vehicle control device executes a second fail-safe processing that can suppress an increase in the coupling temperature more than the first fail-safe processing when the coupling temperature becomes higher than a second threshold value that is higher than the first threshold value during execution of the first fail-safe processing.

2. The vehicle control device according to claim 1 , wherein the control unit executes, as the first fail-safe process, a process of suppressing a difference in rotation speed between an input side and an output side of the viscous coupling by activating a braking device of the driving wheels.

3. The vehicle control device according to claim 2 , wherein the control unit executes, as the first fail-safe process, a process of blowing air toward the viscous coupling by a blower fan disposed in the vicinity of the viscous coupling.

4. the vehicle is provided with a radiator that cools the cooling water of the power source, and a radiator fan that blows air that has passed through the radiator to a rear of the vehicle, 4. The vehicle control device according to claim 3, wherein the radiator fan is used as the blower fan.

5. The vehicle control device according to claim 1 , wherein the control unit executes, as the second fail-safe process, a process of reducing a driving force of the power source relative to an accelerator opening degree.

6. 5. The vehicle control device according to claim 1, wherein the control unit notifies a driver via an alarm unit that there is a possibility that the first fail-safe processing will be executed before the first fail-safe processing is executed.

7. The vehicle control device according to claim 5 , wherein the control unit notifies a driver via a notification unit that there is a possibility that the first fail-safe processing will be executed before the first fail-safe processing is executed.

8. The vehicle control device according to claim 1 , wherein the control unit executes the second fail-safe process when a gradient of an increase in the coupling temperature is greater than a predetermined gradient.

9. The vehicle control device according to claim 5 , wherein the control unit executes the second fail-safe process when a gradient of an increase in the coupling temperature is greater than a predetermined gradient.

10. The vehicle control device according to claim 6 , wherein the control unit executes the second fail-safe process when a gradient of an increase in the coupling temperature is greater than a predetermined gradient.

11. The vehicle control device according to claim 7 , wherein the control unit executes the second fail-safe process when a gradient of an increase in the coupling temperature is greater than a predetermined gradient.

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