Control device and control method for controlling a vehicle capable of switching between two-wheel drive and four-wheel drive

Abstract

To provide a technique which can improve the balance between fuel consumption and traction performance.SOLUTION: A control device of a vehicle comprises: an area setting unit which sets a driving area including a two-wheel driving area where two-wheel driving is executed and a four-wheel driving area where four-wheel driving is executed according to a driving state parameter; and a switching execution unit which changes between the two-wheel driving and the four-wheel driving, when the vehicle travels in the two-wheel driving area, based on a switching condition set in advance. The area setting unit expands the two-wheel driving area at the time of automatic driving compared to manual driving.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a control device and a control method for controlling a vehicle that is switchable between two-wheel drive and four-wheel drive. [Background technology]

[0002] Conventionally, there has been known a driving control that switches between two-wheel drive and four-wheel drive in consideration of the vehicle's driving state, etc. For example, Patent Document 1 proposes a technology for switching between two-wheel drive and four-wheel drive in consideration of the vehicle's driving plan in a vehicle that executes automatic driving control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-082896 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, four-wheel drive vehicles have lower fuel economy than two-wheel drive vehicles, but they offer superior traction performance. Therefore, there has long been a demand for a better balance between fuel economy and traction performance. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a control device for controlling a vehicle capable of automatic driving and capable of switching between two-wheel drive and four-wheel drive. The control device includes a region setting unit that sets a driving region including a two-wheel drive region where the two-wheel drive is performed and a four-wheel drive region where the four-wheel drive is performed according to a driving state parameter, and a switching execution unit that switches between the two-wheel drive and the four-wheel drive according to a preset switching condition when the vehicle is traveling in the two-wheel drive region. The region setting unit expands the two-wheel drive region during automatic driving compared to when the vehicle is manually driven. and reduce the four-wheel drive range without eliminating it. do.

[0006] This control device expands the two-wheel drive range during autonomous driving, thereby ensuring traction performance through four-wheel drive while suppressing a decrease in fuel efficiency.

[0007] According to a second aspect of the present disclosure, a vehicle capable of automatic driving and capable of switching between two-wheel drive and four-wheel drive is controlled. The control device executes A control method is provided, which includes the steps of: (a) setting a driving region including a two-wheel drive region in which the two-wheel drive is performed and a four-wheel drive region in which the four-wheel drive is performed in accordance with a driving state parameter; and (b) switching between the two-wheel drive and the four-wheel drive in accordance with a preset switching condition when the vehicle is traveling in the two-wheel drive region. The step (a) expands the two-wheel drive region during the automatic driving compared to during manual driving. and reduce the four-wheel drive range without eliminating it. The method includes the step of:

[0008] This control method expands the two-wheel drive range during autonomous driving, thereby ensuring traction performance through four-wheel drive while suppressing a decrease in fuel efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a four-wheel drive system of a vehicle. [Figure 2] FIG. 1 is a block diagram showing the configuration of a vehicle control system. [Figure 3] FIG. 3 is an explanatory diagram showing an example of a driving region used in the first embodiment. [Figure 4] FIG. 10 is an explanatory diagram showing another example of the driving region. [Figure 5] 10 is a graph showing a method for estimating the coefficient of friction between the road and the wheels from the history of the wheel slip ratio. [Figure 6] 4 is a timing chart showing an example of an operation for switching from two-wheel drive to four-wheel drive according to a slip ratio. [Figure 7] 4 is a timing chart showing an example of an operation for switching from two-wheel drive to four-wheel drive depending on the friction coefficient of the road. [Figure 8] 4 is a flowchart showing a procedure for selecting a drive control mode in the first embodiment. [Figure 9] 10 is a flowchart showing a procedure for selecting a drive control mode in a second embodiment. [Figure 10] FIG. 10 is an explanatory diagram showing an example of a driving region used in the second embodiment. [Figure 11] 10 is a flowchart showing a procedure for selecting a drive control mode in a third embodiment. [Figure 12] FIG. 11 is an explanatory diagram showing an example of a driving region used in the third embodiment. [Figure 13] 10 is a flowchart showing a procedure for selecting a drive control mode in a fourth embodiment. [Figure 14] FIG. 13 is an explanatory diagram showing an example of a driving region used in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A. First embodiment: FIG. 1 is an explanatory diagram showing the configuration of a four-wheel drive system of a vehicle 10. The vehicle 10 includes an internal combustion engine 12, a transmission 14, a first differential 16, a first disconnect mechanism 18, a front axle 20, a propeller shaft 30, a second differential 40, a rear axle 50, front wheels 60f, rear wheels 60r, and a four-wheel drive control unit 100. The second differential 40 includes a second disconnect mechanism 42, a first coupling mechanism 44, and a second coupling mechanism 46. The disconnect mechanisms 18, 42 are configured, for example, by dog ​​clutches. The coupling mechanisms 44, 46 are configured, for example, by electronically controlled couplings.

[0011] The four-wheel drive control unit 100 can switch between two-wheel drive and four-wheel drive by controlling the disconnect mechanisms 18, 42 and the second differential 40. When performing two-wheel drive, the two disconnect mechanisms 18, 42 are disconnected. Since the vehicle 10 is a front-wheel drive vehicle, only the front wheels 60f are driven in two-wheel drive. That is, the front wheels 60f are drive wheels and the rear wheels 60r are driven wheels. On the other hand, when performing four-wheel drive, the two disconnect mechanisms 18, 42 are connected.

[0012] During two-wheel drive, the power of the engine 12 is not transmitted to the propeller shaft 30 or rear axle 50, improving fuel efficiency. On the other hand, during four-wheel drive, traction performance (the ability to move forward without slipping due to the frictional force of the tires) is excellent. The four-wheel drive control unit 100 can distribute torque between the front wheels 60f and the rear wheels 60r by controlling the coupling mechanisms 44, 46. The four-wheel drive control unit 100 corresponds to the "control device" of this disclosure.

[0013] It should be noted that the four-wheel drive system may have any configuration other than that shown in FIG. 1. For example, a viscous coupling type four-wheel drive system or a dual pump type four-wheel drive system may be used. Furthermore, an electric four-wheel drive system may be used in which the main drive wheels are driven by an engine (internal combustion engine) and the secondary drive wheels are driven by an electric motor. Also, a system in which the rear wheels 60r are the drive wheels in two-wheel drive may be used.

[0014] FIG. 2 is a block diagram showing the configuration of a control system for the vehicle 10. In addition to the four-wheel drive control unit 100 shown in FIG. 1, the vehicle 10 also includes a vehicle control unit 200, an automatic driving control unit 300, a surroundings detection unit 400, an assistance information acquisition unit 500, and sensors 600. In this disclosure, the vehicle 10 is also referred to as the "host vehicle 10." The four-wheel drive control unit 100, the vehicle control unit 200, and the automatic driving control unit 300 can each be configured using one or more ECUs (Electronic Control Units). The ECU has a processor, RAM, and ROM, and a computer program is stored in the ROM. The functions of the control units 100, 200, and 300 can be realized by the processor executing a computer program stored in a non-volatile storage medium. Some of the functions of the control units 100, 200, and 300 may be realized by hardware circuits.

[0015] The vehicle control unit 200 executes various controls such as drive control, brake control, and steering angle control for driving the vehicle 10. The vehicle control unit 200 is used in both automatic driving and manual driving.

[0016] The autonomous driving control unit 300 performs autonomous driving using information relating to the driving state of the vehicle 10 provided by sensors 600 including a vehicle speed sensor 610, and information provided by the periphery detection unit 400 and the assistance information acquisition unit 500. Specifically, the autonomous driving control unit 300 transmits to the vehicle control unit 200 a driving force command value indicating the driving force of the drive unit (engine and motor), a brake command value indicating the operating state of the brake mechanism, and a steering angle command value indicating the steering angle of the wheels. The vehicle control unit 200 controls each of the mechanisms to be controlled in accordance with the provided command values.

[0017] In this disclosure, "autonomous driving" means driving in which drive control, brake control, and steering angle control are all performed automatically without the driver (operator) performing any driving operation. Therefore, in autonomous driving, the operating state of the drive unit, the operating state of the brake mechanism, and the steering angle of the wheels are automatically determined. "Manual driving" means driving in which the driver operates the accelerator pedal to control the drive unit, the brake pedal to control the brakes, and the steering wheel to control the steering angle.

[0018] The periphery detection unit 400 uses on-board sensors such as a camera 410 and a radar 420 to acquire information about various objects present around the vehicle 10, such as objects and road facilities (lanes, intersections, traffic lights, etc.).

[0019] The assistance information acquisition unit 500 acquires various pieces of assistance information for autonomous driving. The assistance information acquisition unit 500 includes a GNSS receiver 510, a navigation device 520, and a wireless communication device 530. The GNSS receiver 510 measures the longitude and latitude of the current position of the vehicle 10 based on navigation signals received from artificial satellites constituting the GNSS (Global Navigation Satellite System). The navigation device 520 has a function of determining a planned route for autonomous driving based on a destination and the vehicle's position detected by the GNSS receiver 510. The wireless communication device 530 acquires various pieces of information related to the roadway of the vehicle 10 by communicating with various external devices 700. For example, the wireless communication device 530 can acquire information related to the roadway conditions by performing vehicle-to-vehicle communication with another vehicle 710 or road-to-vehicle communication with a wireless roadside device 720 installed on road facilities. The wireless roadside device 720 is, for example, a wireless device constituting an Intelligent Transport System.

[0020] The four-wheel drive control unit 100 includes a region setting unit 110, a slip ratio calculation unit 120, a friction coefficient estimation unit 130, and a switching execution unit 140.

[0021] The region setting unit 110 sets a driving region including a two-wheel drive region and a four-wheel drive region. The two-wheel drive region is a region where the driving mode is switched from two-wheel drive to four-wheel drive depending on the slip ratio of the wheels. The four-wheel drive region is a region where the driving mode is four-wheel drive regardless of the slip ratio.

[0022] 3 is an explanatory diagram showing an example of a driving range. Here, a driving range MP1 for manual driving and a driving range MP2 for automatic driving are shown. These driving ranges MP1 and MP2 are two-dimensional maps defined by vehicle speed Vv and accelerator pedal position Pa. Vehicle speed Vv is a value detected by vehicle speed sensor 610, and accelerator pedal position Pa is a value indicating the amount of accelerator pedal depression detected by accelerator pedal position sensor 630.

[0023] The manual driving region MP1 is divided into a two-wheel drive region R2-1 and a four-wheel drive region R4-1. When the vehicle 10 is traveling in the two-wheel drive region R2-1 and a preset first switching condition is met, the vehicle is switched from two-wheel drive to four-wheel drive. On the other hand, when the vehicle 10 is traveling in the four-wheel drive region R4-1 and a preset second switching condition is met, the vehicle is switched from four-wheel drive to two-wheel drive. The first and second switching conditions will be described later.

[0024] The two-wheel drive region R2-1 is a region extending between a region lower limit speed Vmin and a region upper limit speed Vmax. The region lower limit speed Vmin is set to a value greater than 0. In the example of FIG. 3, the accelerator opening degree Pa at the upper end of the two-wheel drive region R2-1 is set to a value less than 100%.

[0025] The four-wheel drive region R4-1 is located outside the two-wheel drive region R2-1. The four-wheel drive region R4-1 is a region where the combination of vehicle speed Vv and accelerator opening Pa is likely to cause wheel slip. In the four-wheel drive region R4-1, four-wheel drive is applied regardless of whether or not slip actually occurs. This reduces the possibility of slippage and achieves stable driving with high traction performance.

[0026] The boundaries between the two-wheel drive region R2-1 and the four-wheel drive region R4-1 are defined as a first boundary line B1 when switching from two-wheel drive to four-wheel drive, and a second boundary line B2 when switching from four-wheel drive to two-wheel drive. The second boundary line B2 is set inside the first boundary line B1. This is to provide hysteresis to prevent an unstable state caused by frequent switching between two-wheel drive and four-wheel drive. In this disclosure, the size of the two-wheel drive region R2-1 is defined as being determined by the first boundary line B1 when switching from two-wheel drive to four-wheel drive.

[0027] Similarly, the driving range MP2 for autonomous driving is divided into a two-wheel drive range R2-2 and a four-wheel drive range R4-2. This two-wheel drive range R2-2 is wider than the two-wheel drive range R2-1 of the driving range MP1 for manual driving. On the other hand, the four-wheel drive range R4-2 is narrower than the four-wheel drive range R4-1 of the driving range MP1 for manual driving. In this way, by expanding the two-wheel drive range during autonomous driving, it is possible to ensure the traction performance of four-wheel drive while suppressing a decrease in fuel efficiency.

[0028] The driving ranges MP1 and MP2 may be created using driving state parameters other than the vehicle speed Vv and the accelerator opening Pa. Examples of other driving state parameters that can be used include vehicle acceleration and the engagement / disengagement state (disconnection rate) of the dog clutch. In general, the driving range that separates the two-wheel drive range and the four-wheel drive range can be set in a driving state space defined by one or more driving state parameters. In other words, the driving range that separates the two-wheel drive range and the four-wheel drive range is set according to the driving state parameters.

[0029] FIG. 4 is an explanatory diagram showing another example of a driving region. The horizontal axis of the driving region MPa shown in the upper part of FIG. 4 is the friction coefficient between the road surface of the road and the wheels, and the vertical axis is the engagement / disconnection state (disconnection rate) of the dog clutch. The friction coefficient between the road surface of the road and the wheels is also simply referred to as the "friction coefficient of the road" or the "friction coefficient of the road surface." In this driving region MPa, the region with a high friction coefficient is set as the two-wheel drive region R2, and the region with a low friction coefficient is set as the four-wheel drive region R4. The higher the disconnection rate of the dog clutch, the wider the width of the four-wheel drive region R4 is set. The horizontal axis of the driving region MPb shown in the lower part of FIG. 4 is the lateral acceleration Gx of the vehicle, and the vertical axis is the forward acceleration Gy of the vehicle. In this driving region MPb, the circular region with low acceleration is set as the two-wheel drive region R2, and the ring-shaped region with high acceleration is set as the four-wheel drive region R4. Even when using either of these driving ranges MPa and MPb, it is preferable to extend the two-wheel drive range during automatic driving compared to manual driving. In the first embodiment, the driving ranges MP1 and MP2 described in Figure 3 are used.

[0030] The first condition for switching from two-wheel drive to four-wheel drive can be considered to be met when, for example, at least one of the following conditions C1a to C1c is met. <First switching condition C1> (C1a) The coordinate position on the driving area determined by the current value of the driving state parameter has moved from inside to outside the first boundary line B1 between the two-wheel drive area and the four-wheel drive area. (C1b) The slip ratio of the wheel becomes equal to or greater than a preset first slip ratio threshold Ts1. (C1c) The friction coefficient of the road surface becomes less than a predetermined first friction coefficient threshold Tμ1. An example of the operation of switching from two-wheel drive to four-wheel drive will be described later.

[0031] The second condition for switching from four-wheel drive to two-wheel drive is considered to be met when, for example, all of the following conditions C2a to C2c are met. <Second switching condition C2> (C2a) The coordinate position on the driving area determined by the current value of the driving state parameter has moved from outside to inside the second boundary line B2 between the two-wheel drive area and the four-wheel drive area. (C2b) The slip ratio of the wheel becomes less than a second slip ratio threshold Ts2 that is set to a value smaller than the first slip ratio threshold Ts1. (C2c) The friction coefficient of the road surface becomes equal to or greater than a second friction coefficient threshold Tμ2, which is set to a value greater than the first friction coefficient threshold Tμ1.

[0032] The first switching condition C1 may be any one or two of the above-described conditions C1a to C1c. A condition other than these may also be used as the first switching condition C1. The second switching condition C2 is set appropriately in accordance with the first switching condition C1. Various thresholds may be set to different values ​​for manual driving and automatic driving, or may be set to the same values. When using the above-described switching conditions C1 and C2, it is preferable to use a parameter other than the wheel slip ratio and the road surface friction coefficient as the driving state parameter that defines the driving region.

[0033] The slip ratio calculation unit 120 calculates the slip ratio Sr of the wheels using the vehicle speed Vv (vehicle speed) measured by the vehicle speed sensor 610 and the wheel speed Vw of each wheel measured by the wheel speed sensor 620 according to the following equation. Sr = max |Vv - Vw| / Vv … (1) Here, max means the calculation of taking the maximum value of the slip ratios for the four wheels. It should be noted that the slip ratio may be calculated using any one of the wheel speeds Vw of the four wheels instead of the vehicle speed Vv.

[0034] The friction coefficient estimation unit 130 estimates the friction coefficient of the road surface of the road on which the vehicle 10 is currently traveling. The friction coefficient may be estimated using a slip ratio history. This method will be described later. Alternatively, the friction coefficient of the road surface may be estimated using road surface information obtained through communication with an external device 700 such as another vehicle 710 or a wireless roadside device 720. The friction coefficient of the road surface may also be estimated using road surface information obtained from an image captured by a camera 410 mounted on the vehicle 10. Furthermore, the friction coefficient of the road surface may be estimated using one or more of these pieces of information. In this way, by using various pieces of information, the friction coefficient of the road surface can be estimated with high accuracy.

[0035] FIG. 5 is a graph showing a method for estimating the friction coefficient of a road surface from the history of the wheel slip ratio. The horizontal axis of FIG. 5 represents the slip ratio Sr, and the vertical axis represents the friction coefficient μ of the road surface. Since the slip ratio Sr changes while the vehicle is traveling, the current friction coefficient μ can be estimated from the history of the slip ratio Sr using the graph of FIG. 5. However, in reality, the value of the friction coefficient μ cannot be uniquely estimated depending on the value of the slip ratio Sr, and the estimated value of the friction coefficient μ changes depending on other driving state parameters such as the vehicle acceleration. Therefore, the friction coefficient estimation unit 130 can estimate the friction coefficient μ using the history of the slip ratio Sr and taking other driving state parameters into consideration.

[0036] The switching execution unit 140 switches between two-wheel drive and four-wheel drive in accordance with the above-mentioned switching conditions C1 and C2 using one or more of the driving region set by the region setting unit 110, the slip ratio calculated by the slip ratio calculation unit 120, and the friction coefficient estimated by the friction coefficient estimation unit 130.

[0037] 6 is a timing chart showing an example of switching from two-wheel drive to four-wheel drive depending on the slip ratio Sr during autonomous driving. As the thresholds for the slip ratio Sr, a first slip ratio threshold Ts1 used under the first switching condition C1 and a second slip ratio threshold Ts2 used under the second switching condition C2 are shown. As the thresholds for the friction coefficient μ, a first friction coefficient threshold Tμ1 used under the first switching condition C1 and a second friction coefficient threshold Tμ2 used under the second switching condition C2 are shown.

[0038] In FIG. 6, the vehicle is running in two-wheel drive before time t1. When the slip ratio Sr becomes equal to or greater than the first slip ratio threshold Ts1 at time t1, the switching execution unit 140 accordingly determines to change from two-wheel drive to four-wheel drive, and the drive system is switched to four-wheel drive at a subsequent time t2. That is, at time t2, the two disconnect mechanisms 18, 42 are each switched from a disconnected state to a connected state. The time delay between the time t1 when the switching is determined and the time t2 when the switching is executed is to synchronize the rotations of the shafts connected by the disconnect mechanisms 18, 42 before connection to mitigate impact at the time of connection. Thereafter, when the slip ratio Sr becomes less than the second slip ratio threshold Ts2 at time t3, the switching execution unit 140 accordingly switches the drive system from four-wheel drive to two-wheel drive. When switching from four-wheel drive to two-wheel drive, there is no need to provide a time delay between the time when the switching is determined and the time when the switching is executed. In the example of FIG. 6, the friction coefficient μ of the road is equal to or greater than the first friction coefficient threshold Tμ1 in the first switching condition C1, so the friction coefficient μ is not used to determine whether to switch the drive state.

[0039] FIG. 7 is a timing chart showing an example of an operation in which the vehicle is switched from two-wheel drive to four-wheel drive in response to the road surface friction coefficient μ during autonomous driving. In this example, the slip ratio Sr is less than the first slip ratio threshold Ts1. When the friction coefficient μ becomes less than the first friction coefficient threshold Tμ1 at time t11, the switching execution unit 140 determines that the vehicle should be switched from two-wheel drive to four-wheel drive. At a subsequent time t12, the drive system is switched to four-wheel drive. Then, when the friction coefficient μ becomes equal to or greater than the second friction coefficient threshold Tμ2 at time t13, the switching execution unit 140 switches the drive system from four-wheel drive to two-wheel drive. In this way, when the friction coefficient μ is determined to be less than the first friction coefficient threshold Tμ1, four-wheel drive may be executed regardless of the value of the slip ratio Sr. This can suppress slippage when the road surface friction coefficient μ is small.

[0040] Figure 8 is a flowchart showing the procedure for selecting a drive control mode in the first embodiment. The process in Figure 8 is repeatedly executed at regular intervals. In step S10, the region setting unit 110 determines whether the vehicle 10 is in autonomous driving. This determination can be made based on a driving state signal provided from the autonomous driving control unit 300 to the four-wheel drive control unit 100.

[0041] If the vehicle is being driven manually, the process proceeds to step S21, where the region setting unit 110 selects the manual driving mode as the drive control mode. The manual driving mode is a mode that uses the driving region MP1 for manual driving shown in Figure 3. The switching execution unit 140 uses the selected driving region MP1 to switch between two-wheel drive and four-wheel drive in accordance with the switching conditions C1 and C2 described above.

[0042] If the vehicle is in autonomous driving, the process proceeds to step S22, where the region setting unit 110 selects the autonomous driving mode as the drive control mode. The autonomous driving mode is a mode that uses the driving region MP2 for autonomous driving shown in Figure 3. The switching execution unit 140 uses the selected driving region MP2 to switch between two-wheel drive and four-wheel drive in accordance with the switching conditions C1 and C2 described above.

[0043] As described above, in the first embodiment, the two-wheel drive range is expanded during automatic driving compared to manual driving, so that traction performance by four-wheel drive can be ensured while suppressing a decrease in fuel efficiency.

[0044] B. Second embodiment: Fig. 9 is a flowchart showing the drive control mode selection procedure in the second embodiment, and Fig. 10 is an explanatory diagram showing an example of a drive region used in the second embodiment. The procedure in Fig. 9 is the same as the procedure in Fig. 8 in the first embodiment, with steps S12 and S23 added, and the contents of steps S10, S21, and S22 are almost the same as the contents of steps S10, S21, and S22 in Fig. 8. In addition, the configuration of vehicle 10 and drive state switching conditions C1 and C2 are the same as those in the first embodiment.

[0045] If the vehicle is in manual driving, the process proceeds to step S21, where the region setting unit 110 selects the manual driving mode as the drive control mode. The manual driving mode is a mode that uses the driving region MP1 for manual driving shown in Fig. 10. This driving region MP1 is the same as the driving region MP1 shown in Fig. 3. However, a driving region different from the driving region MP1 in Fig. 3 may be used.

[0046] If the vehicle is in autonomous driving, the process proceeds to step S12, where the area setting unit 110 determines whether the vehicle 10 is traveling without a driver, i.e., whether one or more people are on board. This determination can be made based on the passenger status signal provided to the four-wheel drive control unit 100 from the passenger sensor 640.

[0047] If the vehicle is in automatic driving mode and is manned, in step S22, the region setting unit 110 selects the manned automatic driving mode as the drive control mode. The manned automatic driving mode is a mode that uses the driving region MP2 in FIG. 10. This driving region MP2 is the same as the driving region MP2 shown in FIG. 3. However, a driving region different from the driving region MP2 in FIG. 3 may be used.

[0048] If the vehicle is in automatic driving and traveling unmanned, in step S23, the region setting unit 110 selects the unmanned automatic driving mode as the drive control mode. The unmanned automatic driving mode is a mode that uses the drive region MP3 in FIG. 10. The drive region MP3 does not have a two-wheel drive region, and is entirely four-wheel drive region R4-3. In other words, the unmanned automatic driving mode is a mode in which four-wheel drive is always performed. However, other drive control modes, such as a mode in which two-wheel drive is always performed, may also be set as the unmanned automatic driving mode.

[0049] The second embodiment also achieves the same effects as the first embodiment. Furthermore, in the second embodiment, one of a plurality of different driving ranges is selected and used depending on selection conditions including whether the vehicle 10 is running unmanned, so drive control can be performed according to the appropriate driving range depending on whether the vehicle is running unmanned.

[0050] C. Third embodiment: Fig. 11 is a flowchart showing the drive control mode selection procedure in the third embodiment, and Fig. 12 is an explanatory diagram showing an example of a drive region used in the third embodiment. The procedure in Fig. 11 adds steps S12, S14, S24, and S25 to the procedure in Fig. 8 in the first embodiment, and the contents of steps S10, S21, and S22 are almost the same as the contents of steps S10, S21, and S22 in Fig. 8. In addition, the configuration of vehicle 10 and drive state switching conditions C1 and C2 are the same as those in the first embodiment.

[0051] If the vehicle is in manual driving, the process proceeds to step S21, where the region setting unit 110 selects the manual driving mode as the drive control mode. The manual driving mode is a mode that uses the driving region MP1 for manual driving shown in FIG. 12. This driving region MP1 is the same as the driving region MP1 shown in FIG. 3. However, a driving region different from the driving region MP1 in FIG. 3 may be used.

[0052] If the vehicle is in autonomous driving, the process proceeds to step S12, where the area setting unit 110 determines whether the vehicle 10 is traveling without a driver, i.e., whether one or more people are on board. This determination can be made based on the passenger status signal provided to the four-wheel drive control unit 100 from the passenger sensor 640.

[0053] If the vehicle is in automatic driving mode and is manned, in step S22, the region setting unit 110 selects the manned automatic driving mode as the drive control mode. The manned automatic driving mode is a mode that uses the driving region MP2 in FIG. 12. This driving region MP2 is the same as the driving region MP2 shown in FIG. 3. However, a driving region different from the driving region MP2 in FIG. 3 may be used.

[0054] If the vehicle is in automatic driving and unmanned, the process proceeds to step S14, where the region setting unit 110 determines whether the friction coefficient μ of the road surface is equal to or less than a predetermined judgment value μd. The judgment value μd is preferably set to a value greater than the friction coefficient threshold values ​​Tμ1 and Tμ2 used in the switching conditions C1 and C2 described in the first embodiment.

[0055] If the friction coefficient μ is equal to or greater than the preset reference value μd, the process proceeds to step S24, where the region setting unit 110 selects the unmanned high μ driving mode as the drive control mode. The unmanned high μ driving mode is a mode that uses the driving region MP4 in Figure 12. This driving region MP4 has a smaller two-wheel drive region R2-4 and a larger four-wheel drive region R4-4 than the driving region MP2 used in the manned automatic driving mode.

[0056] If the friction coefficient μ is less than the reference value μd, the process proceeds to step S25, where the region setting unit 110 selects the unmanned low μ driving mode as the drive control mode. The unmanned low μ driving mode is a mode that uses the driving region MP5 in FIG. 12. This driving region MP4 has a smaller two-wheel drive region R2-5 and a larger four-wheel drive region R4-5 than the driving region MP4 used in the unmanned high μ driving mode. In this way, if the four-wheel drive region is made larger when the friction coefficient μ is less than the reference value μd than when the friction coefficient μ is equal to or greater than the reference value μd, the possibility of wheel slippage can be reduced, and high traction performance can be ensured.

[0057] It is preferable that the driving range MP4 used in the unmanned high-μ driving mode and the driving range MP5 used in the unmanned low-μ driving mode have an expanded two-wheel drive range R2 compared to the driving range MP1 used in the manual driving mode. In this way, the driving ranges MP2, MP4, and MP5 for autonomous driving all have an expanded two-wheel drive range R2 compared to the driving range MP1 for manual driving, which makes it possible to ensure traction performance through four-wheel drive while suppressing a decrease in fuel efficiency during autonomous driving.

[0058] The third embodiment also achieves the same effects as the first embodiment. Furthermore, in the third embodiment, as in the second embodiment, one of a plurality of driving ranges is selected according to selection conditions including whether or not the vehicle 10 is running unmanned, so that drive control can be performed according to the driving range that is appropriate for whether or not the vehicle is running unmanned.

[0059] D. Fourth embodiment: Fig. 13 is a flowchart showing the drive control mode selection procedure in the fourth embodiment, and Fig. 14 is an explanatory diagram showing an example of the drive range used in the fourth embodiment. The procedure in Fig. 13 is the same as Fig. 11 in the third embodiment, except that steps S24 and S25 are replaced with steps S26 and S27, and the contents of the other steps are almost the same as Fig. 11. Furthermore, the configuration of vehicle 10 and drive state switching conditions C1 and C2 are the same as those in the first embodiment.

[0060] If the vehicle is in automatic driving mode and unmanned, and the road surface friction coefficient μ is equal to or greater than a preset threshold μd, the process proceeds to step S26, where the unmanned high μ driving mode is selected as the drive control mode. In the unmanned high μ driving mode of the fourth embodiment, the drive range MP6 of FIG. 14 is used. This drive range MP6 does not include a four-wheel drive range, and all of the drive ranges are two-wheel drive range R2-6. However, if the first switching condition C1 described in the first embodiment is met, the drive mode is switched from two-wheel drive to four-wheel drive.

[0061] If the vehicle is in automatic driving mode and unmanned, and the road surface friction coefficient μ is less than the reference value μd, the process proceeds to step S27, where the unmanned low μ driving mode is selected as the drive control mode. In the unmanned low μ driving mode of the fourth embodiment, the drive range MP7 in FIG. 14 is used. In this drive range MP7, no two-wheel drive range is set, and all are in the four-wheel drive range R4-7.

[0062] 3, 10, 12, and 14, it is not necessary for the two-wheel drive region R2 to be wider than the driving region MP1 for manual driving for all of the driving regions for automatic driving, but it is sufficient that the two-wheel drive region R2 is wider for at least one driving region for automatic driving. In this disclosure, the phrase "the two-wheel drive region is wider during automatic driving than during manual driving" is used in a broad sense to include such cases.

[0063] Other forms: The present disclosure is not limited to the above-described embodiments and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following aspects. The technical features in the above embodiments corresponding to the technical features in each aspect described below can be appropriately replaced or combined to solve some or all of the problems of the present disclosure or to achieve some or all of the effects of the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0064] (1) According to a first aspect of the present disclosure, there is provided a control device for controlling a vehicle capable of autonomous driving and capable of switching between two-wheel drive and four-wheel drive. The control device includes a region setting unit that sets a driving region including a two-wheel drive region where the two-wheel drive is performed and a four-wheel drive region where the four-wheel drive is performed in accordance with a driving state parameter, and a switching execution unit that switches between the two-wheel drive and the four-wheel drive in accordance with a preset switching condition when the vehicle is traveling in the two-wheel drive region. The region setting unit expands the two-wheel drive region during the autonomous driving compared to when the vehicle is manually driven. This control device expands the two-wheel drive range during autonomous driving, thereby ensuring traction performance through four-wheel drive while suppressing a decrease in fuel efficiency.

[0065] (2) The control device may further include a slip ratio calculation unit that calculates the slip ratio of the wheels of the vehicle, and the switching execution unit may switch from the two-wheel drive to the four-wheel drive when the slip ratio becomes equal to or greater than a predetermined slip ratio threshold while the two-wheel drive is being executed in the automatic driving mode. This control device can maintain traction performance by switching to four-wheel drive when wheel slip occurs.

[0066] (3) The control device may further include a friction coefficient estimation unit that estimates a friction coefficient between the vehicle's roadway and the wheels, and the switching execution unit may switch from the two-wheel drive to the four-wheel drive regardless of the slip ratio if the friction coefficient becomes less than a predetermined friction coefficient threshold while the two-wheel drive is being performed in the automatic driving mode. According to this control device, when the coefficient of friction of the road is small, the occurrence of slippage can be suppressed by implementing four-wheel drive.

[0067] (4) In the above control device, the friction coefficient estimation unit may estimate the friction coefficient of the driving path using one or more of the following information: slip ratio information indicating the slip ratio, first road surface information obtained by communication with an external device, and second road surface information obtained from an image captured by a camera mounted on the vehicle. This control device can estimate the coefficient of friction of the road from various pieces of information.

[0068] (5) According to a second aspect of the present disclosure, there is provided a control method for controlling a vehicle capable of autonomous driving and capable of switching between two-wheel drive and four-wheel drive. This control method includes: (a) setting a driving region including a two-wheel drive region in which the two-wheel drive is performed and a four-wheel drive region in which the four-wheel drive is performed in accordance with a driving state parameter; and (b) switching between the two-wheel drive and the four-wheel drive in accordance with a preset switching condition while the vehicle is traveling in the two-wheel drive region. The step (a) includes expanding the two-wheel drive region during the autonomous driving compared to when the vehicle is manually driven. This control method expands the two-wheel drive range during autonomous driving, thereby ensuring traction performance through four-wheel drive while suppressing a decrease in fuel efficiency.

[0069] (6) The above control method may further include a step of calculating a slip ratio of the wheels of the vehicle, and step (b) may include a step of switching from the two-wheel drive to the four-wheel drive when the slip ratio becomes equal to or greater than a predetermined slip ratio threshold while the two-wheel drive is being performed in the automatic driving mode. This control method allows traction performance to be maintained by switching to four-wheel drive when wheel slip occurs.

[0070] (7) The above control method may further include a step of estimating a friction coefficient between the vehicle's roadway and the wheels, and step (b) may include a step of switching from two-wheel drive to four-wheel drive regardless of the slip ratio if the friction coefficient becomes less than a predetermined friction coefficient threshold while two-wheel drive is being performed in the automatic driving mode. According to this control method, when the friction coefficient of the road is small, the occurrence of slippage can be suppressed by implementing four-wheel drive.

[0071] (8) In the above control method, the step of estimating the friction coefficient may include a step of estimating the friction coefficient of the road using one or more pieces of information: slip ratio information indicating the slip ratio, first road surface information obtained by communication with an external device, and second road surface information obtained from an image captured by a camera mounted on the vehicle. According to this control method, the friction coefficient of the road can be estimated from various information.

[0072] The present disclosure may be realized in various forms other than a vehicle control device or a control method, such as a computer program for controlling a vehicle, or a non-transitory storage medium on which a computer program is recorded. [Explanation of symbols]

[0073] 10...vehicle, 12...engine, 14...transmission, 16...first differential, 18...first disconnect mechanism, 20...front axle, 30...propeller shaft, 40...second differential, 42...second disconnect mechanism, 44...first coupling mechanism, 46...second coupling mechanism, 50...rear axle, 60f...front wheels, 60r...rear wheels, 100...four-wheel drive control unit, 110...area setting unit, 120...slip ratio calculation unit, 130...friction coefficient estimation unit, 140...switching execution unit, 200...vehicle control unit, 300...autonomous driving control unit, 400...periphery detection unit, 410...camera, 420...radar, 500...assistance information acquisition unit, 510...GNSS receiver, 520...navigation device, 530...wireless communication device, 600...sensors, 610...vehicle speed sensor, 620...wheel speed sensor, 630...accelerator opening sensor, 640...occupant sensor, 700...external device, 710...other vehicle, 720...wireless roadside device

Claims

1. A control device for controlling a vehicle that is capable of automatic driving and is capable of switching between two-wheel drive and four-wheel drive, a region setting unit that sets a driving region including a two-wheel drive region in which the two-wheel drive is performed and a four-wheel drive region in which the four-wheel drive is performed according to a driving state parameter; a switching execution unit that switches between the two-wheel drive and the four-wheel drive in accordance with a preset switching condition when the vehicle is traveling in the two-wheel drive region; Equipped with The control device wherein the region setting unit expands the two-wheel drive region during the automatic driving compared to when the vehicle is being driven manually, and reduces the four-wheel drive region without reducing it to zero.

2. The control device according to claim 1, further comprising: a slip ratio calculation unit that calculates a slip ratio of a wheel of the vehicle; The control device, wherein the switching execution unit switches from the two-wheel drive to the four-wheel drive when the slip ratio becomes equal to or greater than a preset slip ratio threshold while the two-wheel drive is being executed in the automatic driving mode.

3. The control device according to claim 2, further comprising: a friction coefficient estimation unit that estimates a friction coefficient between a roadway and the wheels of the vehicle; The control device wherein the switching execution unit switches from two-wheel drive to four-wheel drive regardless of the slip ratio when the friction coefficient becomes less than a predetermined friction coefficient threshold while the two-wheel drive is being performed in the automatic driving mode.

4. The control device according to claim 3, A control device in which the friction coefficient estimation unit estimates the friction coefficient of the driving path using one or more of slip ratio information indicating the slip ratio, first road surface information obtained through communication with an external device, and second road surface information obtained from images captured by a camera mounted on the vehicle.

5. A control method executed by a control device that controls a vehicle that is capable of automatic driving and is capable of switching between two-wheel drive and four-wheel drive, (a) setting a driving region including a two-wheel drive region in which the two-wheel drive is performed and a four-wheel drive region in which the four-wheel drive is performed according to a driving state parameter; (b) switching between the two-wheel drive and the four-wheel drive in accordance with a preset switching condition while the vehicle is traveling in the two-wheel drive region; Equipped with The control method, wherein the step (a) includes a step of expanding the two-wheel drive region during the automatic driving compared to when the vehicle is being driven manually, and reducing the four-wheel drive region without reducing it to zero.

6. The control method according to claim 5, further comprising: calculating a slip ratio of a wheel of the vehicle; The control method, wherein step (b) includes a step of switching from two-wheel drive to four-wheel drive when the slip ratio becomes equal to or greater than a predetermined slip ratio threshold while the two-wheel drive is being performed in the automatic driving mode.

7. The control method according to claim 6, further comprising: estimating a coefficient of friction between a roadway and the wheels of the vehicle; The control method includes a step of switching from two-wheel drive to four-wheel drive regardless of the slip ratio when the friction coefficient becomes less than a predetermined friction coefficient threshold while the two-wheel drive is being performed in the automatic driving mode.

8. 8. The control method according to claim 7, A control method, wherein the step of estimating the friction coefficient includes a step of estimating the friction coefficient of the road using one or more pieces of information selected from slip ratio information indicating the slip ratio, first road surface information obtained by communication with an external device, and second road surface information obtained from an image captured by a camera mounted on the vehicle.

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