Vehicle control device

Abstract

To achieves optimal driving on sand.SOLUTION: A control device 100 executes subsidence amount acquisition processing to acquire the subsidence amount of drive wheels 11 and physical property value acquisition processing to acquire physical property values of sand in a sand area. The control device 100 also executes processing to calculate driving force and resistance force of the drive wheels 11 based on the acquired subsidence amount of the drive wheels 11 and the acquired physical property values of the sand. The control device 100 also executes target slip ratio calculation processing to calculate, as a target slip ratio, a slip ratio of the drive wheels 11 that maximizes tractive force, which is the difference between the driving force and the resistance force. The control device 100 then executes drive torque control processing to control drive torque applied to the drive wheels 11 so that the acquired actual slip ratio of the drive wheels 11 becomes the calculated target slip ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, the vehicle described in Patent Document 1 sets the target slip ratio to the slip ratio of the drive wheels that maximizes acceleration on a road such as sand, and then controls the drive torque of the drive wheels to achieve the target slip ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-111368 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the slip ratio at which acceleration becomes maximum varies depending on the condition of the road, it may be difficult to achieve optimal driving on sand in some cases. [Means for solving the problem]

[0005] A vehicle control device that solves the above problem controls drive torque applied to drive wheels when traveling on sand. The control device executes a slip ratio acquisition process to acquire a slip ratio of the drive wheels, a subsidence amount acquisition process to acquire an amount of subsidence of the drive wheels into the sand, a physical property value acquisition process to acquire physical property values ​​of sand in the sand, a drive force calculation process to calculate a drive force that is a force generated between the drive wheels and the sand and corresponds to the slip ratio based on the acquired amount of subsidence of the drive wheels and the acquired physical property values ​​of the sand, a resistance calculation process to calculate a resistance force that is a force that the drive wheels receive from the sand in the vehicle's traveling direction and corresponds to the slip ratio based on the acquired amount of subsidence of the drive wheels and the acquired physical property values ​​of the sand, a target slip ratio calculation process to calculate a target slip ratio for the drive wheels that maximizes tractive force, which is the difference between the drive force and the resistance force, and a drive torque control process to control the drive torque so that the acquired slip ratio of the drive wheels becomes the calculated target slip ratio. [Effects of the Invention]

[0006] According to the present invention, optimal running on sand can be achieved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a vehicle according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the forces acting on the drive wheels on sandy ground. [Figure 3] FIG. 3 is a schematic diagram showing normal stress and shear stress acting on the surface of a driving wheel on sandy soil. [Figure 4] FIG. 4 is a flowchart showing the procedure of the process executed by the control device of the embodiment. [Figure 5] FIG. 5 is a graph showing the relationship between the driving torque and the engine rotation speed when traveling on sand. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a specific embodiment of a vehicle control device will be described with reference to FIGS. <Vehicle configuration> As shown in Fig. 1, a vehicle 10 runs as a four-wheel drive vehicle with two front wheels 11F and two rear wheels 11R as drive wheels 11. Power is transmitted to the front wheels 11F and rear wheels 11R from an internal combustion engine 13, which is a prime mover mounted on the vehicle 10. As is well known, the output of the internal combustion engine 13 is adjusted by controlling the amount of intake air, the amount of fuel injected from a fuel injection valve, and the like.

[0009] The internal combustion engine 13 is connected to an automatic transmission 30 via a torque converter 21 . The vehicle 10 is provided with a transfer 40 that is connected to the output side of the automatic transmission 30 and distributes the power transmitted from the automatic transmission 30 to the front wheels 11F and the rear wheels 11R.

[0010] The transfer 40 is connected to the two front wheels 11F via a front propeller shaft 22 and a front differential 23. The transfer 40 is also connected to the two rear wheels 11R via a rear propeller shaft 24 and a rear differential 25.

[0011] The control device 100 controls the output of the internal combustion engine 13, the shifting of the automatic transmission 30, and the like, thereby controlling the drive torque T applied to the drive wheels 11. The control device 100 is equipped with a CPU 110 and a memory 120 configured from a ROM, a RAM, and the like, and performs various controls by the CPU 110 executing programs stored in the memory 120.

[0012] When performing various controls, the control device 100 refers to the intake air amount GA detected by the air flow meter 32 and the engine rotation speed NE detected by the crank angle sensor 33. The control device 100 also refers to the wheel speed ω detected by the wheel speed sensors 34 provided on the drive wheels 11, and the subsidence amount X of the drive wheels 11 detected by the laser displacement meters 35. The subsidence amount X is the amount of subsidence of the drive wheels 11 in the sand. The control device 100 also acquires current position information LI of the vehicle 10 from a GPS (Global Positioning System) 50 provided on the vehicle 10. The control device 100 also calculates the vehicle speed V, which is the horizontal moving speed of the vehicle 10, based on the wheel speed ω of each drive wheel 11, etc.

[0013] <Control of driving torque on sandy ground> The control device 100 sets a target value for the slip ratio S when traveling on sand. Then, the control device 100 controls the drive torque T applied to the drive wheels 11 so that the target value for the slip ratio S matches the actual slip ratio S. Such control will be described below.

[0014] First, the slip ratio S is a value calculated based on the vehicle speed V and the wheel speed ω using the following equation (1).

[0015]

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[0016] As shown in Figure 2, when traveling on sand, in addition to the driving force FX generated between the sand and the driving wheel 11, the driving wheel 11 sinks into the sand by an amount X, resulting in a resistance force FR from the sand in front of the driving wheel 11. The difference obtained by subtracting the resistance force FR from the driving force FX is the tractive force FDP, which is the force that accelerates the vehicle 10. As is well known, the driving force FX and the resistance force FR are values ​​that change depending on the slip ratio S. Therefore, the tractive force FDP, which is the difference between these values, also changes depending on the slip ratio S.

[0017] As shown in FIG. 3, shear stress τ(θ) and normal stress σ(θ) are generated between the surface of the drive wheel 11 and the sand. The driving force FX is calculated by integrating the horizontal component of the shear stress τ from the contact start angle θf to the contact departure angle θr, as shown in the following equation (2). The contact start angle θf is the angle at which the drive wheel 11 starts to contact the ground. The contact departure angle θr is the angle at which the drive wheel 11 separates from the ground. The vertical downward direction is θ0 = 0.

[0018]

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[0019] On the other hand, the resistance force FR can be calculated by integrating the horizontal component of the normal stress σ(θ) from the contact start angle θf to the contact departure angle θr, as shown in the following equation (3).

[0020]

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[0021] In each equation, "r" is the radius of the drive wheel 11, i.e., the tire radius, and "b" is the width of the drive wheel 11, i.e., the tire width. The contact start angle θf is calculated using the amount of sinking X from the following equation (4).

[0022]

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[0023] The ground separation angle θr can be detected by a sensor or the like, but in this embodiment, it is simply set to "θr=0". The normal stress σ(θ) can be calculated from the following equation (5), which is a well-known normal stress model in terramechanics.

[0024]

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[0025] Note that "kc" is the adhesion coefficient of sand, "kφ" is the internal friction coefficient of sand, and "n" is the settlement coefficient of sand, and each of these values ​​is a physical property of sand. The shear stress τ(θ) can be calculated using the following equation (6):

[0026]

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[0027] "C" is the cohesion of the sand, "φ" is the internal friction angle of the sand, and "kx" is the soil deformation coefficient, all of which are physical properties of the sand. "j(θ)" is the amount of soil deformation, which can be calculated using the following equation (7).

[0028]

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[0029] It should be noted that "S" is the slip ratio calculated from the above formula (1). "μ" in equation (6) is the coefficient of friction between the sand and the surface of the drive wheel 11. The ratio A in equation (6) is a value within the range of "0≦A≦1" and indicates the ratio of the force due to sand deformation to the force due to friction between the surface of the drive wheel 11 and the sand in the shear stress τ(θ). The value of this ratio A varies depending on the condition of the sand.

[0030] The first term on the right side of equation (6) represents the force due to deformation of the sand caused by the sand flowing on the surface of the drive wheel 11. The second term on the right side of equation (6) represents the force due to friction between the surface of the drive wheel 11 and the sand.

[0031] From these equations (1) to (7), the tractive force FDP can be calculated at any slip ratio S. Therefore, the control device 100 calculates the slip ratio S at which the tractive force FDP becomes maximum, and sets this calculated value as the target slip ratio St. The control device 100 then controls the drive torque T so that the target slip ratio St is obtained.

[0032] <About the flowchart> FIG. 4 shows a processing procedure that the control device 100 executes at predetermined intervals to control the drive torque T. The execution conditions for this processing can be set as appropriate. For example, the processing may be executed when the vehicle driver requests that the vehicle 10 travel on sand. Alternatively, the processing may be executed when the control device 100 detects, based on the position information LI, that the vehicle 10 is traveling on sand. In the following, the step number of each processing step will be represented by a number preceded by "S."

[0033] When the series of processes shown in FIG. 4 is started, the control device 100 executes a subsidence amount acquisition process for acquiring the subsidence amount X (S100). Next, the control device 100 calculates the contact start angle θf based on the above equation (4) (S110).

[0034] Next, the control device 100 sets the ground contact departure angle θr (S120). In this embodiment, the ground contact departure angle θr is simply set to "0". Next, the control device 100 acquires the physical properties of the sand, the friction coefficient μ, and the ratio A (S130). The physical properties of the sand acquired in the process of S130 are the adhesion coefficient kc of the sand, the internal friction coefficient kφ of the sand, the settlement coefficient n of the sand, the cohesion C of the sand, the internal friction angle φ of the sand, and the soil deformation coefficient kx. The physical properties of the sand, the friction coefficient μ, and the ratio A are pre-stored in the memory 120 in association with the position information LI. In the process of S130, the control device 100 acquires the physical properties of the sand, the friction coefficient μ, and the ratio A of the sand for the current travel path by reading them from the memory 120 based on the current position information LI. The physical properties of the sand, the friction coefficient μ, and the ratio A associated with the position information LI are stored in an external server or the like. In the process of S130, the physical properties of the sand, the friction coefficient μ, and the ratio A associated with the position information LI may be acquired from the external server or the like via a communication line. The process of S130 corresponds to a physical property value acquisition process for acquiring the physical property values ​​of the sand in the sandy area.

[0035] Next, the control device 100 executes a resistance force calculation process to calculate the resistance force FR based on the adhesion coefficient kc, internal friction coefficient kφ, subsidence coefficient n obtained in the process of S130, the above formula (3), and the above formula (5) (S150).

[0036] Next, the control device 100 executes a driving force calculation process (S170) to calculate the driving force FX based on the adhesion force C, internal friction angle φ, soil deformation coefficient kx, friction coefficient μ, ratio A, and the above equations (2), (5), (6), and (7) obtained in the process of S130.

[0037] Next, the control device 100 calculates a value obtained by subtracting the resistance force FR from the driving force FX, and substitutes the calculated difference for the tractive force FDP (S180). Next, the control device 100 executes a target slip ratio calculation process (S190) to calculate the target slip ratio St. In S190, the control device 100 calculates the tractive force FDP according to the slip ratio S. The control device 100 then calculates the target slip ratio St by substituting the slip ratio S that maximizes the calculated tractive force FDP into the target slip ratio St.

[0038] Next, the control device 100 executes a slip ratio acquisition process to acquire the actual slip ratio S calculated based on the above formula (1) (S200). Next, the control device 100 executes a drive torque control process to control the drive torque T applied to the drive wheels 11 so that the acquired actual slip ratio S becomes the calculated target slip ratio St (S210). In this S210, the control device 100 calculates a target wheel speed ωt, which is a target value of the wheel speed ω required to make the acquired actual slip ratio S match the target slip ratio St. Then, the control device 100 executes a process to adjust the drive torque T so that the actual wheel speed ω matches the target wheel speed ωt.

[0039] Then, when the process of S210 is completed, the control device 100 ends the execution of this process in the current execution cycle. <Actions and Effects of This Embodiment> (1) The control device 100 executes a subsidence amount acquisition process to acquire the subsidence amount X of the drive wheels 11 on sandy ground. The control device 100 also executes a physical property value acquisition process to acquire the physical properties of sand in sandy ground, including the adhesion coefficient kc, the internal friction coefficient kφ, the subsidence coefficient n, the adhesion force C, the internal friction angle φ, and the soil deformation coefficient kx. The control device 100 also executes a driving force calculation process to calculate the driving force FX generated between the drive wheels 11 and the sand based on the acquired subsidence amount X of the drive wheels 11 and the acquired physical properties of the sand. The control device 100 also executes a resistance force calculation process to calculate the resistance force FR that the drive wheels 11 receive from the sand in the vehicle's traveling direction based on the acquired subsidence amount X of the drive wheels 11 and the acquired physical properties of the sand. The control device 100 also executes a target slip ratio calculation process to calculate, as the target slip ratio St, the slip ratio S of the drive wheels 11 at which the tractive force FDP, which is the difference between the driving force FX and the resistance force FR, is maximized. Then, the control device 100 executes a driving torque control process for controlling the driving torque T so that the acquired actual slip ratio S of the driving wheels 11 becomes the calculated target slip ratio St.

[0040] Therefore, the driving force FX and the resistance force FR are calculated based on the sinking amount X of the drive wheels 11, which indicates the road condition, and the physical properties of the sand, so the tractive force FDP calculated from the driving force FX and the resistance force FR appropriately reflects the condition of the sand. This improves the accuracy of calculating the target slip ratio St that maximizes the tractive force FDP. Furthermore, the driving torque T is controlled to obtain the target slip ratio St with improved calculation accuracy, enabling optimal driving on sand.

[0041] (2) The inventor discovered that the shear stress τ(θ) of the sand involved in the driving force FX when the driving wheel 11 slips on sandy ground is affected not only by the deformation of the sand caused by the sand flowing over the surface of the driving wheel 11, but also by the slippage that occurs between the surface of the driving wheel 11 and the sand.

[0042] Therefore, in the driving force calculation process, the driving force FX is calculated using a ratio A that indicates the proportion of the shear stress τ(θ) in the sand that is due to the force caused by the deformation of the sand to the proportion that is due to the force caused by the friction between the surface of the drive wheels 11 and the sand. Therefore, when calculating the driving force FX, not only the deformation of the sand but also the slippage that occurs between the surface of the drive wheels 11 and the sand is taken into consideration, improving the calculation accuracy of the driving force FX. When the calculation accuracy of the driving force FX is improved in this way, the calculation accuracy of the tractive force FDP also improves, and therefore the calculation accuracy of the target slip ratio St at which the tractive force FDP is maximized also improves.

[0043] (3) As the drive torque control process, a process is executed to adjust the drive torque T by controlling the wheel speed ω, which is the rotation speed of the drive wheels 11. Therefore, the wheel speed ω is controlled by adjusting the drive torque T. Therefore, the actual slip ratio S can be controlled so that the target slip ratio St is obtained.

[0044] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0045] The internal friction angle φ of the sand may be calculated while the vehicle 10 is traveling. That is, the strength at which the sand collapses due to shear can be calculated from the following equation (8).

[0046]

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[0047] Here, "τ" is the shear stress, "C" is the adhesion of the sand, "σ" is the normal stress, and "φ" is the angle of internal friction of the sand. Here, the product of the contact area Y of the drive wheel 11 that is in contact with the sand and the shear stress τ is equal to the drive torque T applied to the drive wheel 11. Therefore, by multiplying both sides of the above equation (8) by the contact area Y, the following equation (9) is obtained.

[0048]

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[0049] On a sandy road surface such as a completely dry desert, the adhesion force C is "0." Also, "Yσ" is equal to the wheel load W applied to one of the drive wheels 11 under static load conditions. Therefore, the above formula (9) can be approximated as the following formula (10).

[0050]

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[0051] The wheel load W is a known value and can be stored in memory 120. Then, by substituting the driving torque T when shear failure of the sand occurs and the sand collapses into the following equation (11), which is a modification of equation (10), the internal friction angle φ of the sand during travel can be calculated.

[0052]

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[0053] As shown in Figure 5, when shear failure of sand occurs, a point D (Ta, NEa) is observed where the amount of change in engine speed NE with respect to change in driving torque T changes suddenly. Therefore, by obtaining the driving torque Ta when such point D is detected, it is possible to determine the driving torque T when shear failure of sand occurs.

[0054] Therefore, the control device 100 executes a torque acquisition process to acquire the drive torque T when shear failure of sand occurs on the roadway. Then, the control device 100 may execute a process to calculate the arc tangent of the quotient obtained by dividing the acquired drive torque T by the wheel load W applied to one of the drive wheels 11 as the internal friction angle φ, as shown in the above formula (11).

[0055] In this case, the internal friction angle φ of the sand is calculated based on the driving torque T when shear failure of the sand occurs on the roadway. Therefore, an appropriate internal friction angle φ can be obtained according to the actual state of the sand on the roadway, thereby improving the calculation accuracy of the driving force FX.

[0056] The above-described subsidence amount X may be obtained by other methods. For example, the subsidence amount X may be obtained by using GPS position information or image diagnosis. The vehicle 10 may be a front-wheel drive vehicle or a rear-wheel drive vehicle.

[0057] The vehicle 10 may be equipped with a manual transmission instead of the automatic transmission 30. The prime mover installed in the vehicle 10 may be a motor. Also, the prime mover installed in the vehicle 10 may be an internal combustion engine and a motor.

[0058] The control device 100 is not limited to a device equipped with a CPU and memory and executing software processing. For example, the control device 100 may be equipped with a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of the software processing performed in the above embodiments. That is, the control device 100 may include a processing circuit having any of the following configurations (a) to (c): (a) a processing circuit equipped with one or more processing devices that execute all of the above processing according to a program and one or more program storage devices, such as ROM, that store the program; (b) a processing circuit equipped with one or more processing devices and one or more program storage devices that execute part of the above processing according to a program, and one or more dedicated hardware circuits that execute the remaining processing; (c) a processing circuit equipped with one or more dedicated hardware circuits that execute all of the above processing. Program storage devices, i.e., computer-readable media, include any available media that can be accessed by a general-purpose or dedicated computer. [Explanation of symbols]

[0059] 10...Vehicle 11...Drive wheels 11F...front wheel 11R…Rear wheel 13...Internal combustion engine 21...Torque converter 22...Front propeller shaft 23…Front differential 24...Rear propeller shaft 25…Rear differential 30...Automatic transmission 32...Air flow meter 33...Crank angle sensor 34...Wheel speed sensor 35...Laser displacement meter 40...Transfer 50...GPS 100...Control device 110...CPU 120...Memory

Claims

1. A vehicle control device that controls a drive torque applied to a drive wheel when traveling on sand, a slip ratio acquisition process for acquiring a slip ratio of the drive wheels; a subsidence amount acquisition process for acquiring a subsidence amount of the drive wheels on the sandy ground; a physical property value acquisition process for acquiring physical property values ​​of sand in the sandy area; a driving force calculation process for calculating a driving force that is generated between the driving wheels and the sand and corresponds to the slip ratio, based on the acquired sinking amount of the driving wheels and the acquired physical property values ​​of the sand; a resistance calculation process for calculating a resistance force that corresponds to the slip ratio and is a force that the drive wheels receive from the sand in the vehicle traveling direction based on the acquired sinking amount of the drive wheels and the acquired physical property values ​​of the sand; a target slip ratio calculation process for calculating, as a target slip ratio, a slip ratio of the driving wheels at which a tractive force, which is a difference between the driving force and the resistance force, is maximized; a driving torque control process for controlling the driving torque so that the obtained slip ratio of the driving wheels becomes the calculated target slip ratio; Vehicle control device.

2. The driving force calculation process calculates the driving force using a ratio indicating a ratio of a force due to deformation of the sand to a force due to friction between the surface of the drive wheel and the sand in the shear stress of the sand involved in the driving force. The vehicle control device according to claim 1 .

3. The physical property values ​​of the sand acquired by the physical property value acquisition process include the adhesion coefficient of the sand, the internal friction coefficient of the sand, the settlement coefficient of the sand, the cohesion force of the sand, the internal friction angle of the sand, and the soil deformation coefficient. The vehicle control device according to claim 1 .

4. The physical properties of the sand include an internal friction angle of the sand, a torque acquisition process for acquiring the driving torque when shear failure of the sand occurs on the travel path; and calculating the arc tangent of a value obtained by dividing the acquired driving torque by a wheel load applied to one of the driving wheels as the internal friction angle. The vehicle control device according to claim 1 .

5. The drive torque control process is a process for adjusting the drive torque by controlling the rotation speed of the drive wheels. The vehicle control device according to claim 1 .

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