Vehicle control device, vehicle, vehicle control method, and program

Abstract

To provide a technique capable of allowing a vehicle to exhibit stable driving performance over a longer period of time.SOLUTION: A vehicle control device 30 according to the present disclosure reduces second driving force at a first reduction rate when the second driving force is limited in a state where second driving force limitation processing is not being executed, and reduces the second driving force at a second reduction rate smaller than the first reduction rate when a second determination unit determines that a second condition is satisfied in a state where the second driving force limitation processing is being executed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a vehicle control device, a vehicle, a vehicle control method, and a program. [Background technology]

[0002] Patent Document 1 discloses a motor control device for an electric vehicle. According to Patent Document 1, the electric vehicle is equipped with a front motor and a rear motor. The motor control device can also distribute required torque between the drive torque of the front motor and the drive torque of the rear motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-95378 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, there has been a demand for technology that allows vehicles to exhibit stable driving performance for a longer period of time.

[0005] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0006] A first aspect of the present invention is a vehicle control device that controls a vehicle equipped with a first drive source that drives first drive wheels and a second drive source that drives second drive wheels, and that includes a first judgment unit that determines whether a predetermined first condition is met, a second judgment unit that determines whether a second condition different from the first condition is met, and a control unit that executes a second drive force limiting process that limits a second drive force output from the second drive source when the first judgment unit determines that the first condition is met, and further limits the second drive force when the second judgment unit determines that the second condition is met while the second drive force limiting process is being executed.When limiting the second drive force when the second drive force limiting process is not being executed, the control unit reduces the second drive force at a first reduction rate, and when the second judgment unit determines that the second condition is met while the second drive force limiting process is being executed, the control unit reduces the second drive force at a second reduction rate that is smaller than the first reduction rate.

[0007] A second aspect of the present invention is a vehicle including the vehicle control device according to the first aspect of the present invention.

[0008] A third aspect of the present invention is a vehicle control method executed by a computer to control a vehicle equipped with a first drive source that drives first drive wheels and a second drive source that drives second drive wheels, the vehicle control method comprising: a first determination step of determining whether a predetermined first condition is met; a first control step of executing a second drive force limiting process that limits a second drive force output from the second drive source when it is determined in the first determination step that the first condition is met; a second determination step of determining whether a second condition different from the first condition is met; and a second control step of further limiting the second drive force when it is determined in the second determination step that the second condition is met while the second drive force limiting process is being executed, wherein in the second control step, the second drive force is reduced by a second reduction rate that is smaller than a first reduction rate used to reduce the second drive force when limiting the second drive force when the second drive force limiting process is not being executed.

[0009] A fourth aspect of the present invention is a program for causing a computer to execute the vehicle control method according to the third aspect of the present invention. [Effects of the Invention]

[0010] According to the present invention, a vehicle can exhibit stable driving performance for a longer period of time. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a vehicle according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a cooling device provided in a vehicle. [Figure 3] FIG. 3 is a block diagram of a vehicle control device according to an embodiment. [Figure 4] FIG. 4 is a graph illustrating an example of changes over time in the first driving force and the second driving force when the drive distribution ratio is changed. [Figure 5]FIG. 5 is a graph illustrating the correlation between the required driving force and the second reduction rate defined in a predetermined setting map. [Figure 6] FIG. 6 is a flowchart of a vehicle control method according to an embodiment. [Figure 7] FIG. 7 is a graph illustrating the temporal changes of the first driving force and the second driving force. DETAILED DESCRIPTION OF THE INVENTION

[0012] Patent Document 1 proposes to prevent overheating of one of two drive sources (front motor, rear motor) by changing the drive distribution ratio between the two drive sources.

[0013] However, there is a problem that the driving stability of the vehicle is affected due to a sudden drop in the drive distribution ratio of one of the two drive sources. In other words, the conventional technologies including Patent Document 1 have a problem in that it is difficult to maintain the driving stability of the vehicle while preventing overheating of the multiple drive sources provided in the vehicle.

[0014] Based on the above preliminary explanation, one embodiment will be described below.

[0015] (One embodiment) FIG. 1 is a schematic diagram showing a vehicle 10 according to one embodiment.

[0016] The vehicle 10 is, for example, an AWD (all-wheel drive) type automobile. In this embodiment, the vehicle 10 is described as a hybrid AWD vehicle. The vehicle 10 includes first drive wheels 12, second drive wheels 14, a first drive device 16, a second drive device 18, a battery 20, a power conversion device 22, a cooling device 24, an air-cooling device 26, a sensor group (plurality of sensors) 28, and a vehicle control device 30.

[0017] The first drive wheels 12 are either the front wheels or the rear wheels of the vehicle 10. In this embodiment, the first drive wheels 12 are the front wheels, but are not limited to this. In contrast, the second drive wheels 14 are the other of the front wheels or the rear wheels of the vehicle 10. In this embodiment, the second drive wheels 14 are the rear wheels, but are not limited to this.

[0018] The first drive device 16 is a device that drives the first drive wheels 12. The first drive device 16 includes a power generation unit 32 and a first drive source 34. The power generation unit 32 includes a generator 36, which is an electric power generator, and an engine 38, which is an internal combustion engine. The engine 38 (output shaft of the engine 38) can drive the generator 36. The generator 36 generates electricity by being driven by the engine 38. The power generation unit 32 can supply electric power to the first drive source 34 and a second drive source 42 (second drive device 18), which will be described later.

[0019] The first drive source 34 is an electric motor that can be driven by electric power supplied from a generator 36. The first drive source 34 can transmit driving force to the first drive wheels 12 via a first transmission mechanism 40. The first transmission mechanism 40 is equipped with, for example, a transmission (not shown).

[0020] The engine 38 can supply driving force to the first drive wheels 12 via a first transmission mechanism 40. The first drive wheels 12 may be driven by driving force supplied from the first drive source 34 via the first transmission mechanism 40, or by driving force supplied from the engine 38 via the first transmission mechanism 40.

[0021] The driving force output by the first driving device 16 toward the first drive wheels 12 is also referred to as the first driving force DRV1 in the following description. In addition, unless otherwise specified, the first driving force DRV1 is output by the first driving source 34.

[0022] The second drive device 18 is a device that drives the second drive wheels 14. The second drive device 18 includes a second drive source 42 and a second transmission mechanism 44 connected to the second drive source 42. The second drive source 42 is an electric motor separate from the first drive source 34. The shaft of the second drive source 42 is connected to the second drive wheels 14 via the second transmission mechanism 44. Therefore, the second drive source 42 can transmit driving force to the second drive wheels 14 via the second transmission mechanism 44. The second transmission mechanism 44 may include, for example, a transmission (not shown). The second drive source 42 can be driven by electric power supplied from the generator 36 (first drive device 16). Electric power can be supplied from the generator 36 to the second drive source 42 via the power conversion device 22. When the first drive wheels 12 are driven by the first drive device 16, the second drive source 42 may be used to generate regenerative electric power.

[0023] The driving force output by the second driving device 18 (second driving source 42) toward the second driving wheels 14 is also referred to as second driving force DRV2 in the following description.

[0024] The power conversion device 22 is connected to the first drive device 16, the second drive device 18, and the battery 20. The power conversion device 22 includes, for example, a converter, an inverter, etc. The power conversion device 22 is capable of converting the electric power supplied from the first drive device 16 to the second drive source 42.

[0025] The battery 20 is a chargeable and dischargeable secondary battery. The battery 20 includes, for example, a plurality of battery cells (not shown). Each of the plurality of battery cells is, for example, a lithium-ion battery, a nickel-metal hydride battery, or the like, but is not limited to these. The battery 20 is charged using power generated by the generator 36, for example. The battery 20 may also be charged using the regenerated power described above. In this case, the power conversion device 22 described above may convert the power supplied to the battery 20.

[0026] The battery 20 that stores the electric power can supply the electric power to at least one of the first drive device 16 (first drive source 34) and the second drive device 18 (second drive source 42) as needed. In this case, the above-mentioned power conversion device 22 may convert the electric power supplied from the battery 20 to at least one of the first drive device 16 and the second drive device 18.

[0027] FIG. 2 is a schematic diagram showing the cooling device 24 provided in the vehicle 10. As shown in FIG.

[0028] The cooling device 24 is a device that cools the power conversion device 22 with a refrigerant RF1 and cools the first drive source 34 with a refrigerant RF2. The refrigerant RF1 is a liquid refrigerant. The liquid refrigerant may be water or oil. The refrigerant RF2 is preferably a liquid refrigerant, but is not limited to this.

[0029] As shown in FIG. 2 , the cooling device 24 includes a radiator 46, a first pump 48, a heat exchanger 50, a valve device 52, and a second pump 54. The radiator 46 cools the refrigerant RF1. The first pump 48 can circulate the refrigerant RF1 between the radiator 46 and the power conversion device 22. The first pump 48 can also circulate the refrigerant RF1 between the radiator 46 and the heat exchanger 50. Thus, the refrigerant RF1 cooled by the radiator 46 can be supplied to the power conversion device 22 and the heat exchanger 50 by the first pump 48. The amount of refrigerant RF1 supplied to the power conversion device 22 and the amount of refrigerant RF1 supplied to the heat exchanger 50 can be adjusted by the valve device 52. The power conversion device 22 is cooled by the refrigerant RF1 supplied to the power conversion device 22. The second pump 54 circulates the refrigerant RF2 between the heat exchanger 50 and the first driving source 34. The refrigerant RF2 exchanges heat with the refrigerant RF1 via the heat exchanger 50. As described above, the refrigerant RF1 supplied to the heat exchanger 50 is cooled by the radiator 46. Therefore, the refrigerant RF2 can be cooled (liquid-cooled) by the refrigerant RF1 via the heat exchanger 50.

[0030] According to the cooling device 24, the power conversion device 22 (refrigerant RF1) and the first driving source 34 (refrigerant RF2) are cooled substantially by a single radiator 46. Furthermore, according to the cooling device 24, the refrigerant RF2 that cools the first driving source 34 is liquid-cooled by the refrigerant RF1, which is a liquid refrigerant. In general, the cooling efficiency of liquid cooling is better than the cooling efficiency of air cooling.

[0031] As shown in FIG. 1 , the air-cooling device 26 may be provided in the second drive unit 18 of the vehicle 10. The air-cooling device 26 is a device that air-cools the refrigerant RF3. The refrigerant RF3 is a refrigerant for cooling the second drive source 42. The refrigerant RF3 is preferably, but not limited to, a liquid refrigerant. The air-cooling device 26 cools the refrigerant RF3 using, for example, outside air. Although a specific illustration is omitted, the air-cooling device 26 may include, for example, a housing that houses the second drive source 42 and the refrigerant RF3. A heat dissipation unit is formed in the housing. The heat dissipation unit has, for example, a fin shape. The heat dissipation unit actively exchanges heat when air passes through the housing while the vehicle is running. The heat dissipation unit causes the refrigerant RF3 to exchange heat with the outside air. This allows the refrigerant RF3 to be air-cooled. The air-cooled refrigerant RF3 can cool the second drive source 42.

[0032] As shown in FIG. 1 , the sensor group 28 includes, for example, an outside air temperature sensor 56, a vehicle speed sensor 58, an accelerator pedal sensor 60, and a temperature sensor 62. The outside air temperature sensor 56 is a sensor for detecting the outside air temperature. The vehicle speed sensor 58 is a sensor for detecting the vehicle speed, which is the traveling speed of the vehicle 10. The accelerator pedal sensor 60 is a sensor for detecting the accelerator opening (AP opening) of the vehicle 10. The temperature sensor 62 is a sensor for detecting the second driving source temperature. The second driving source temperature is the temperature of the second driving source 42. The temperature sensor 62 may detect the temperature of the refrigerant RF3 as the second driving source temperature. Various detection signals output from the sensor group 28 are input to the vehicle control device 30.

[0033] FIG. 3 is a block diagram of a vehicle control device 30 according to an embodiment.

[0034] The vehicle control device 30 is an electronic device (computer) that controls the vehicle 10. The vehicle control device 30 is included in, for example, an ECU (Electronic Control Unit). The vehicle control device 30 includes a calculation unit 64 and a storage unit 66.

[0035] The arithmetic unit 64 includes a predetermined processing circuit (not shown). The processing circuit includes one or more processors, such as a central processing unit (CPU) or a graphics processing unit (GPU). The processing circuit may include a predetermined integrated circuit, such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0036] The storage unit 66 includes one or more memories. The one or more memories include non-volatile memories. Non-volatile memories are recording media that non-temporarily store programs, tables, maps, etc. For example, non-volatile memories include ROM (Read Only Memory), flash memory, etc. The storage unit 66 (one or more memories) may include volatile memories. For example, volatile memories include RAM (Random Access Memory).

[0037] The calculation unit 64 includes an information acquisition unit 68, a required driving force calculation unit 70, a control unit 72, a first determination unit 74, a second determination unit 76, and a reduction rate adjustment unit 78. The information acquisition unit 68, the required driving force calculation unit 70, the control unit 72, the first determination unit 74, the second determination unit 76, and the reduction rate adjustment unit 78 are realized by the calculation unit 64 (processor) executing a program stored in the storage unit 66 (memory). At least some of the information acquisition unit 68, the required driving force calculation unit 70, the control unit 72, the first determination unit 74, the second determination unit 76, and the reduction rate adjustment unit 78 may be realized by an integrated circuit such as the ASIC or FPGA described above.

[0038] The information acquisition unit 68 acquires various pieces of information based on various detection signals supplied from the sensor group 28 (FIG. 1). For example, the information acquisition unit 68 can acquire information indicating the outside air temperature based on the detection signal of the outside air temperature sensor 56. The information acquisition unit 68 can acquire information indicating the vehicle speed based on the detection signal of the vehicle speed sensor 58. The information acquisition unit 68 can acquire information indicating the AP opening degree based on the detection signal of the accelerator pedal sensor 60. The information acquisition unit 68 can acquire information indicating the second drive source temperature based on the detection signal of the temperature sensor 62.

[0039] The required driving force calculation unit 70 calculates the required driving force (a numerical value indicating the required driving force). The required driving force is the driving force required of the vehicle 10. The required driving force is calculated based on, for example, the vehicle speed and the AP opening degree.

[0040] The control unit 72 executes a drive distribution ratio determination process and a driving control process.

[0041] The drive distribution ratio determination process is a process for determining the drive distribution ratio between the first drive wheels 12 and the second drive wheels 14 that are driven to satisfy the required drive force. The control unit 72 determines the drive distribution ratio based on, for example, the required drive force (AP opening) and the vehicle speed. The control unit 72 may determine the drive distribution ratio using a control map that defines the relationship between the required drive force, the vehicle speed, and the drive distribution ratio. The control map is stored in advance in, for example, the storage unit 66.

[0042] The drive distribution ratio may be determined (changed) in response to an operation instruction from the driver who drives the vehicle 10. For example, the driver may instruct the control unit 72 to set the drive distribution ratio to "first drive wheels 12:second drive wheels 14=100:0." When the drive distribution ratio is "first drive wheels 12:second drive wheels 14=100:0," the entire requested drive force is borne by only the first drive wheels 12 out of the first drive wheels 12 and the second drive wheels 14. In this case, the second drive wheels 14 essentially function as driven wheels that follow the first drive wheels 12.

[0043] Fig. 4 is a graph showing an example of changes over time in the first driving force DRV1 and the second driving force DRV2 when the drive distribution ratio is changed. The vertical axis of Fig. 4 represents each driving force (first driving force DRV1, second driving force DRV2). The horizontal axis of Fig. 4 represents time.

[0044] Time point ta is shown in Figure 4. Time point ta is the time when the drive distribution ratio between the first drive wheels 12 and the second drive wheels 14 is changed to "first drive wheels 12:second drive wheels 14 = 90:10." If the drive distribution ratio of the second drive wheels 14 is reduced while the required drive force is maintained constant, the second drive force DRV2 output based on that drive distribution ratio also decreases. That is, as shown in Figure 4, second drive force DRV2 decreases after time point ta. Furthermore, as second drive force DRV2 decreases, first drive force DRV1 increases.

[0045] In the following description, for illustrative purposes, an example will be described in which the drive distribution ratio is determined to be "first drive wheels 12:second drive wheels 14=50:50" by the drive distribution ratio determination process.

[0046] The driving control process is a process for controlling the first drive unit 16 and the second drive unit 18 to drive the vehicle 10. The control unit 72 controls the first drive unit 16 and the second drive unit 18 based on the required drive force calculated by the required drive force calculation unit 70 and the drive distribution ratio determined by the drive distribution ratio determination process.

[0047] It should be noted that the processes that can be executed by the control unit 72 are not limited to the drive distribution ratio determination process and the driving control process. Other processes that can be executed by the control unit 72 will be described later as appropriate.

[0048] The first determination unit 74 determines whether a predetermined first condition is met. The first condition includes a period during which the required driving force exceeds the driving force threshold value, continuing for a predetermined time or longer. The driving force threshold value and the predetermined time are each determined, for example, based on experiments. The driving force threshold value can be determined, for example, by assuming the required driving force when the vehicle 10 is caused to climb a slope with a certain degree of inclination at a certain vehicle speed (acceleration). Information indicating the driving force threshold value and information indicating the predetermined time are stored in advance in the memory unit 66. The length of the period (time) can be measured, for example, using a timer. The timer can be realized, for example, by a processing circuit provided in the calculation unit 64, but is not limited to this.

[0049] When the first determination unit 74 determines that the first condition is met, the control unit 72 executes the second driving force limiting process. The second driving force limiting process is a process for limiting the second driving force DRV2. By limiting the second driving force DRV2, the temperature rise of the second driving source 42 is suppressed.

[0050] The control unit 72 limits the second driving force DRV2, for example, by reducing the drive distribution ratio allocated to the second driving wheels 14. For example, a drive distribution ratio of "first driving wheels 12:second driving wheels 14 = 50:50" can be changed to "first driving wheels 12:second driving wheels 14 = 70:30" by executing the second driving force limiting process. As described above, if the drive distribution ratio of the second driving wheels 14 is reduced while the required driving force is maintained constant, the second driving force DRV2 output based on that drive distribution ratio also decreases.

[0051] The amount of reduction (reduction rate) of the second driving force DRV2 when the second driving force limiting process is executed may be constant or may vary depending on the required driving force. The control unit 72 may limit the second driving force DRV2 by reducing the upper limit of the second driving force DRV2, rather than the drive distribution ratio of the second drive wheels 14.

[0052] Note that when the second driving force limiting process reduces the drive distribution ratio of the second drive wheels 14, the lower limit of the drive distribution ratio is greater than zero. In other words, the second driving force limiting process does not set the drive distribution ratio of the second drive wheels 14 to zero. Therefore, even when the second driving force limiting process is executed, if the required driving force is greater than zero, the second drive device 18 continues to drive the second drive wheels 14.

[0053] The second determination unit 76 determines whether a second condition, which is different from the first condition, is satisfied. The second determination unit 76 can determine whether the second condition is satisfied when the second driving force limiting process is being executed. The second condition includes the second driving source temperature exceeding a temperature threshold. As described above, the second driving source temperature is the temperature of the second driving source 42. Information indicating the second driving source temperature is acquired by the information acquisition unit 68. The temperature threshold is determined, for example, based on experiments. In this case, the temperature threshold is determined in consideration of the overheating prevention process and the second reduction rate R2, which will be described later, so as to prevent the second driving source 42 from overheating. The information indicating the temperature threshold is stored in advance by the storage unit 66.

[0054] If the second determination unit 76 determines that the second condition is met while the second driving force limiting process is being executed, the control unit 72 executes the overheating prevention process. The overheating prevention process is a process for further limiting the second driving force DRV2 that is limited by the second driving force limiting process described above. The overheating prevention process limits the second driving force DRV2 to a level that is expected to sufficiently prevent the second driving source 42 from overheating. The overheating prevention process may reduce the second driving force DRV2 to zero. Execution of the overheating prevention process prevents the second driving source 42 from overheating.

[0055] When the overheating prevention process is executed, the control unit 72 reduces the second driving force DRV2 at a second reduction rate R2 that is smaller than the first reduction rate R1.

[0056] The first reduction rate R1 is the amount of reduction in the second driving force DRV2 per unit time when the second driving force DRV2 is limited when the second driving force limiting process is not being executed. More specifically, the first reduction rate R1 is the amount of reduction in the second driving force DRV2 per unit time when the second driving force DRV2 is limited when the second condition is not satisfied. Therefore, for example, when the control unit 72 reduces the second driving force DRV2 (the drive distribution ratio of the second drive wheels 14) in response to an operation instruction from the driver when the second condition is not satisfied, the control unit 72 reduces the second driving force DRV2 based on the first reduction rate R1 (see also FIG. 4).

[0057] As described above, the second reduction rate R2 is smaller than the first reduction rate R1. Therefore, the rate at which the second driving force DRV2 is reduced when the overheating prevention process is performed is slower than the rate at which the second driving force DRV2 is reduced based on the first reduction rate R1.

[0058] The second reduction rate R2 is adjusted (determined) by the reduction rate adjustment unit 78. The reduction rate adjustment unit 78 adjusts the second reduction rate R2 based on information indicating the required driving force and a predetermined setting map. The predetermined setting map is a map that defines the correspondence relationship between the required driving force and the second reduction rate R2. The predetermined setting map can be determined based on experiments. The predetermined setting map is also stored in advance in the storage unit 66.

[0059] 5 is a graph showing an example of the correlation between the required driving force and the second reduction rate R2 defined in a predetermined setting map. The vertical axis of FIG. 5 represents the second reduction rate R2. The horizontal axis of FIG. 5 represents the required driving force.

[0060] The predetermined setting map is created so that the second reduction rate R2 increases as the required driving force increases. For example, the predetermined setting map can be created so that the second reduction rate R2 is proportional to the required driving force. FIG. 5 shows y1, which is the second reduction rate R2 when the required driving force is x1, and y2, which is the second reduction rate R2 when the required driving force is x2. x2 is greater than x1, and y2 is greater than y1 (x2>x1; y2>y1). By using such a predetermined setting map, the reduction rate adjustment unit 78 can increase the second reduction rate R2 as the required driving force increases. However, the maximum value of the second reduction rate R2 in the predetermined setting map is smaller than the first reduction rate R1.

[0061] Fig. 6 is a flowchart of a vehicle control method according to one embodiment. Fig. 7 is a graph illustrating an example of changes over time in first driving force DRV1 and second driving force DRV2. The graph format of Fig. 7 is similar to that of Fig. 4.

[0062] A vehicle control method that can be executed by the above-mentioned vehicle control device 30 (computer) and the operation of the vehicle 10 during execution of the vehicle control method are described below. The vehicle control method of FIG. 6 is executed, for example, by having the calculation unit 64 (processor) execute a program stored in the storage unit 66 (memory). The vehicle control method includes an information acquisition step S1, a required driving force calculation step S2, a first determination step S3, a first control step S4, a second determination step S5, a reduction rate adjustment step S6, and a second control step S7. In the following description, the vehicle 10 is traveling throughout the execution of the vehicle control method.

[0063] In the information acquisition step S1, the information acquisition unit 68 acquires various pieces of information from the sensor group 28. The various pieces of information include, for example, information indicating the vehicle speed, information indicating the AP opening degree, and information indicating the second drive source temperature.

[0064] In the required driving force calculation step S2, the required driving force calculation unit 70 calculates the required driving force based on, for example, information indicating the vehicle speed and information indicating the AP opening degree.

[0065] In the first determination step S3, the first determination unit 74 determines whether a first condition is met. The first condition includes a period during which the requested driving force exceeds the driving force threshold continuing for a predetermined time or longer. Therefore, in the first determination step S3, the first determination unit 74 determines whether the period during which the requested driving force exceeds the driving force threshold continuing for a predetermined time or longer.

[0066] Time t1 and time t2 are shown in Figure 7. Time t1 is an example of the time when the required driving force exceeds the driving force threshold. Time t2 is an example of the time when the period during which the required driving force exceeds the driving force threshold reaches a predetermined time.

[0067] If the first determination unit 74 determines that the first condition is not met (S3: NO), the information acquisition step S1 is executed again. If the first determination unit 74 determines that the first condition is met (S3: YES), the first control step S4 is executed.

[0068] In the first control step S4, the control unit 72 executes a second driving force limiting process. As a result, the second driving force DRV2 decreases after time t2 in FIG. 7. Furthermore, the first driving force DRV1 increases after time t2. By executing the second driving force limiting process, the temperature of the second driving source 42 is prevented from rising.

[0069] The first control step S4 may be executed when the first condition is not satisfied. Therefore, in the first control step S4, the control unit 72 may reduce the second driving force DRV2 based on the first reduction rate R1 described above.

[0070] In the second determination step S5, the second determination unit 76 determines whether or not a second condition is met. The second condition includes the second driving source temperature exceeding a temperature threshold value. Therefore, in the second determination step S5, the second determination unit 76 determines whether or not the second driving source temperature has exceeded the temperature threshold value. Note that information indicating the second driving source temperature can be acquired in the information acquisition step S1 described above.

[0071] If the second determination unit 76 determines that the second condition is not met (S5: NO), the first control step S4 continues. If the second determination unit 76 determines that the second condition is met (S5: YES), the reduction rate adjustment step S6 and the second control step S7 are executed.

[0072] In the reduction rate adjustment step S6, the reduction rate adjustment unit 78 adjusts the second reduction rate R2 described above. In the second control step S7, the control unit 72 executes an overheating prevention process based on the second reduction rate R2 adjusted in the reduction rate adjustment step S6. This prevents the second drive source 42 from overheating. The vehicle 10 can continue traveling while the second control step S7 is being executed.

[0073] Time t3 is shown in FIG. 7. Time t3 indicates the time when the overheating prevention process is initiated. After time t3, the second driving force DRV2 gradually decreases based on the second decrease rate R2. As the second driving force DRV2 decreases, the first driving force DRV1 gradually increases. This ends the vehicle control method of FIG. 7. The vehicle 10 can continue to travel while the overheating prevention process is being executed.

[0074] The above-described vehicle control device 30 (vehicle control method) and the vehicle 10 equipped with the vehicle control device 30 can achieve the effects described below, for example.

[0075] The vehicle control device 30 includes a control unit 72. The control unit 72 executes a second driving force limiting process and an overheating suppression process, thereby suppressing the second driving source 42 from rising in temperature (overheating).

[0076] The driving stability of the vehicle 10 changes in response to a change in the difference between the first driving force DRV1 and the second driving force DRV2. In this regard, according to the present embodiment, the control unit 72 gradually reduces the second driving force DRV2 in response to the establishment of multiple conditions (first condition, second condition). This prevents the difference between the first driving force DRV1 and the second driving force DRV2 from increasing suddenly. As a result, the driving stability of the vehicle 10 is prevented from changing suddenly.

[0077] The second condition includes the second driving source temperature exceeding a temperature threshold. When the second condition is met, the vehicle control device 30 reduces the second driving force DRV2 based on a second reduction rate R2 that is smaller than the first reduction rate R1. As a result, the second driving force DRV2 gradually reduces over a relatively long period of time. In other words, even when the difference between the first driving force DRV1 and the second driving force DRV2 increases, the rate at which the difference increases is relatively slow. As a result, both overheating of the second driving source 42 and a sudden change in the driving stability of the vehicle 10 are suppressed.

[0078] As described above, the control unit 72 can suppress an increase in temperature of the second driving source 42 by executing the second driving force limiting process. That is, the control unit 72 can suppress the second condition from being satisfied by executing the second driving force limiting process. This suppresses the difference between the first driving force DRV1 and the second driving force DRV2 from being widened by the overheating suppression process. As a result, changes in the driving stability of the vehicle 10 are further suppressed.

[0079] In the first control step S4 described above, the control unit 72 can execute the second driving force limiting process by reducing, by a predetermined percentage, the driving force distribution ratio of the second drive wheels 14. This allows the control unit 72 to dynamically adjust the second driving force DRV2 based on the driving force distribution ratio, even if, for example, the required driving force changes while the second driving force limiting process is being executed.

[0080] In the first control step S4 described above, the control unit 72 may execute the second driving force limiting process by lowering the upper limit of the second driving force DRV2. This upper limit does not change in response to changes in the required driving force. By setting the upper limit of the second driving force DRV2 regardless of changes in the required driving force, it becomes easier to manage the temperature of the second driving source. In this case, the control unit 72 can dynamically adjust the drive distribution ratio of the first driving wheels 12 and the drive distribution ratio of the second driving wheels 14 based on the required driving force and the second driving force DRV2 (the upper limit).

[0081] The greater the required driving force, the more likely the second driving source 42 is to heat up. In this regard, according to the present embodiment, the reduction rate adjustment unit 78 increases the second reduction rate R2 within a range less than the first reduction rate R1 as the required driving force increases. This allows the control unit 72 to reduce the second driving force DRV2 relatively quickly in the overheating prevention process while maintaining the driving stability of the vehicle 10 for a relatively long period of time. As a result, overheating of the second driving source 42 is suppressed.

[0082] The vehicle control device 30 suppresses overheating of the second driving source 42, thereby improving the design flexibility of the vehicle 10 with respect to the cooling mechanism of the second driving source 42. That is, according to the present embodiment, the cooling efficiency of the second driving source 42 can be made lower than the cooling efficiency of the first driving source 34. For example, as described above, the refrigerant RF3 can be air-cooled, whereas the refrigerant RF2 is liquid-cooled. In this case, the air-cooling device 26 can be configured relatively simply compared to the cooling device 24. By deliberately using the simple air-cooling device 26 as the cooling device for the refrigerant RF3, an increase in the manufacturing cost of the vehicle 10 can be suppressed.

[0083] One embodiment may be modified as follows. In the following modifications, descriptions that overlap with the embodiment will be omitted as appropriate. In addition, in the drawings used in the following modifications, the same reference numerals are used for the same components as those described in the embodiment.

[0084] (Variation 1) The vehicle 10 is not limited to a hybrid AWD vehicle, and may be, for example, an electric vehicle.

[0085] (Variation 2) The overheating prevention process, which is a process of reducing the second driving force DRV2 at the second reduction rate R2, may be interpreted as reducing the drive distribution ratio of the second drive wheels 14 based on the second reduction rate R2. In other words, the second reduction rate R2 may be the amount of reduction per unit time in the drive distribution ratio of the second drive wheels 14 when the second driving force DRV2 is limited. The control unit 72 may limit the second driving force DRV2 by reducing the drive distribution ratio of the second drive wheels 14 based on the second reduction rate R2.

[0086] (Variation 3) The first condition may include the presence of snow (accumulated snow, snowfall) around the vehicle 10. The first determination unit 74 can determine whether or not there is snow around the vehicle 10 based on, for example, image information acquired by an imaging device that captures images of the surroundings of the vehicle 10. The imaging device can be provided in the vehicle 10 as appropriate.

[0087] In an environment cold enough to cause snow accumulation or snowfall, the temperature of the first drive source 34 is relatively low. In other words, in an environment cold enough to cause snow accumulation or snowfall, it is expected that overheating of the first drive source 34 will be suppressed.

[0088] According to this modification, the control unit 72 can increase the drive distribution ratio of the first drive wheels 12 through the second drive force limiting process only when the environment around the vehicle 10 is relatively cold. This prevents the first drive source 34 from overheating.

[0089] (Variation 4) The first condition may include that the outside air temperature is equal to or higher than an outside air temperature threshold. The outside air temperature threshold is determined in advance, for example, based on experiments. Information indicating the outside air temperature threshold is stored in the storage unit 66 in advance.

[0090] The cold outside air prevents the second driving source 42 from rising in temperature. Therefore, even if the required driving force exceeds the driving force threshold for a predetermined period of time or longer, if the outside air temperature is relatively low, the second driving source 42 can be prevented from overheating without the second driving force limiting process.

[0091] According to this modification, the vehicle 10 can be driven based on the drive distribution ratio determined by the drive distribution ratio determination process while preventing the second drive source 42 from overheating for as long a period as possible.

[0092] (Combination of multiple modifications) The above-described multiple modifications may be combined as appropriate within a range that does not contradict each other.

[0093] According to the embodiment and each of the modifications described above, the vehicle 10 can exhibit stable driving performance for a longer period of time by the vehicle control device 30 (vehicle control method).

[0094] The following additional notes are further disclosed regarding the above embodiment.

[0095] (Appendix 1) A vehicle control device (30) according to the present disclosure is a vehicle control device for controlling a vehicle (10) equipped with a first drive device (16) that drives first drive wheels (12) and a second drive source (42) that drives second drive wheels (14), and includes a first determination unit (74) that determines whether a predetermined first condition is met, a second determination unit (76) that determines whether a second condition different from the first condition is met, and, when the first determination unit determines that the first condition is met, executes a second drive force limiting process that is a process that limits a second drive force (DRV2) output from the second drive source, and a control unit (72) that further limits the second driving force when the second determination unit determines that the second condition is met while the second driving force limiting process is being executed, wherein when limiting the second driving force while the second driving force limiting process is not being executed, the control unit reduces the second driving force at a first reduction rate (R1), and when the second determination unit determines that the second condition is met while the second driving force limiting process is being executed, the control unit reduces the second driving force at a second reduction rate (R2) that is smaller than the first reduction rate (R1). This allows the vehicle to exhibit stable driving performance for a long period of time.

[0096] (Appendix 2) In the vehicle control device described in Supplementary Note 1, the first condition may include a state in which a required driving force of the vehicle exceeds a predetermined driving force threshold value for a predetermined period of time or more. This allows the vehicle control device to prevent the second driving source from overheating in a situation in which the temperature of the second driving source is likely to increase.

[0097] (Appendix 3) In the vehicle control device according to Supplementary Note 2, the first condition may further include an outside air temperature being equal to or higher than a predetermined outside air temperature threshold. This allows the vehicle control device to prevent the second drive source from overheating in a situation where the temperature of the second drive source is likely to rise.

[0098] (Appendix 4) In the vehicle control device according to any one of Supplementary Notes 1 to 3, the second condition may include a second driving source temperature exceeding a predetermined temperature threshold, thereby enabling the vehicle control device to more reliably prevent the second driving source from overheating.

[0099] (Appendix 5) The vehicle control device according to any one of Supplementary Notes 1 to 4 may further include a reduction rate adjustment unit (78) that adjusts the second reduction rate based on a required driving force of the vehicle, and the reduction rate adjustment unit may increase the second reduction rate as the required driving force of the vehicle increases. This allows the vehicle control device to quickly prevent the second drive source from overheating while preventing a sudden change in the running stability of the vehicle.

[0100] (Appendix 6) In the vehicle control device according to any one of Supplementary Notes 1 to 5, the control unit may execute the second driving force limiting process by reducing the drive distribution ratio to the second drive wheels, thereby enabling the vehicle control device to suppress abrupt changes in vehicle running stability in response to changes in the required driving force.

[0101] (Appendix 7) In the vehicle control device according to any one of Supplementary Notes 1 to 5, the control unit may execute the second driving force limiting process by lowering an upper limit value of the second driving force, thereby enabling the vehicle control device to easily manage the temperature of the second driving source.

[0102] (Appendix 8) The vehicle control device according to any one of Supplementary notes 1 to 7 may be a vehicle control device in which the cooling efficiency of the second drive source is lower than the cooling efficiency of the first drive device.

[0103] (Appendix 9) The vehicle control device according to any one of Supplementary notes 1 to 8 may be configured such that the vehicle is provided with an air-cooling device (26) that air-cools a refrigerant for cooling the second drive source.

[0104] (Appendix 10) A vehicle (10) according to the present disclosure is a vehicle equipped with the vehicle control device according to any one of Supplementary Notes 1 to 9. This allows the vehicle to exhibit stable driving performance for a longer period of time.

[0105] (Appendix 11) A vehicle control method according to the present disclosure is a computer-executed vehicle control method for controlling a vehicle (10) equipped with a first drive device (16) that drives first drive wheels (12) and a second drive source (42) that drives second drive wheels (14), the method including a first determination step (S3) of determining whether a predetermined first condition is met, a first control step (S4) of executing a second drive force limiting process that is a process of limiting a second drive force (DRV2) output from the second drive source when it is determined in the first determination step that the first condition is met, and This vehicle control method includes a second determination step (S5) of determining whether a second condition different from the first condition is satisfied, and a second control step (S7) of further restricting the second driving force if the second determination step determines that the second condition is satisfied while the second driving force limiting process is being executed, where the second control step reduces the second driving force at a second reduction rate (R2) that is smaller than the first reduction rate R1 used to reduce the second driving force when the second driving force limiting process is not being executed. This enables the vehicle to exhibit stable driving performance for a longer period of time.

[0106] (Appendix 12) A program according to the present disclosure is a program for causing the computer to execute the vehicle control method described in Supplementary Note 11. This enables the vehicle to exhibit stable driving performance for a longer period of time.

[0107] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present disclosure. [Explanation of symbols]

[0108] 10...Vehicle 12...First drive wheel 14...Second drive wheel 26...Air cooling device 30...Vehicle control device 34...First driving source 42...Second driving source 72...Control unit 74...1st judgment section 76…Second judgment part 78...Decrease rate adjustment section DRV2: Second driving force R1…1st reduction rate R2…Second decline rate

Claims

1. A vehicle control device that controls a vehicle equipped with a first drive source that drives first drive wheels and a second drive source that drives second drive wheels, a first determination unit that determines whether a predetermined first condition is met; a second determination unit that determines whether a second condition different from the first condition is satisfied; a control unit that, when the first determination unit determines that the first condition is met, executes a second driving force limiting process that limits a second driving force output from the second driving source, and, when the second determination unit determines that the second condition is met while the second driving force limiting process is being executed, further limits the second driving force; Equipped with When the second driving force is to be limited in a state in which the second driving force limiting process is not being executed, the control unit reduces the second driving force at a first reduction rate, When the second determination unit determines that the second condition is met while the second driving force limiting process is being executed, the control unit reduces the second driving force at a second reduction rate that is smaller than the first reduction rate.

2. The vehicle control device according to claim 1, The vehicle control device, wherein the first condition includes a state in which a required driving force of the vehicle exceeds a predetermined driving force threshold value for a predetermined period of time or more.

3. The vehicle control device according to claim 2, The vehicle control device, wherein the first condition further includes that the outside air temperature is equal to or greater than a predetermined outside air temperature threshold.

4. The vehicle control device according to any one of claims 1 to 3, The vehicle control device, wherein the second condition includes a second driving source temperature exceeding a predetermined temperature threshold.

5. The vehicle control device according to any one of claims 1 to 3, a reduction rate adjustment unit that adjusts the second reduction rate based on a required driving force of the vehicle, The reduction rate adjustment unit increases the second reduction rate as the required driving force of the vehicle increases.

6. The vehicle control device according to any one of claims 1 to 3, The control unit executes the second driving force limiting process by reducing a drive distribution ratio to the second drive wheels.

7. The vehicle control device according to any one of claims 1 to 3, The control unit executes the second driving force limiting process by reducing an upper limit value of the second driving force.

8. The vehicle control device according to any one of claims 1 to 3, A vehicle control device, wherein the cooling efficiency of the second driving source is lower than the cooling efficiency of the first driving source.

9. The vehicle control device according to any one of claims 1 to 3, The vehicle control device is provided with an air-cooling device that air-cools a refrigerant for cooling the second drive source.

10. A vehicle comprising the vehicle control device according to any one of claims 1 to 3.

11. A vehicle control method executed by a computer to control a vehicle equipped with a first drive source that drives first drive wheels and a second drive source that drives second drive wheels, comprising: a first determination step of determining whether a predetermined first condition is met; a first control step of executing a second driving force limiting process, which is a process of limiting a second driving force output from the second driving source, when it is determined in the first determination step that the first condition is satisfied; a second determination step of determining whether a second condition different from the first condition is satisfied; a second control step of further limiting the second driving force when it is determined in the second determination step that the second condition is satisfied while the second driving force limiting process is being executed; and In the second control step, the second driving force is reduced at a second reduction rate that is smaller than a first reduction rate used to reduce the second driving force when limiting the second driving force when the second driving force limiting process is not being executed.

12. A program for causing the computer to execute the vehicle control method according to claim 11.

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