Control device for four-wheel drive vehicle

Abstract

To provide a control device for a four-wheel drive vehicle which permits travelling in a proper driving state in accordance with a situation even when malfunction of a switch for drive mode switching occurs.SOLUTION: A control device 100 includes a drive mode setting part 102 which sets a drive mode of a vehicle 10 on the basis of a signal outputted from a driving mode selection switch 140 provided in the vehicle 10, and a first clutch control part 104 and a second clutch control part 106 which operate and control a clutch 46 for driving front wheels and an engagement-type clutch 94 in accordance with the drive mode set on the drive mode setting part 102. The control device 100 performs such driving mode changing processing that a drive mode setting part 102 changes a driving mode from a two-wheel drive fixed mode to a driving type variable mode when malfunction of a driving mode selection switch 140 occurs in such a state that the vehicle 10 drives in the two-wheel drive fixed mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a four-wheel drive vehicle. [Background technology]

[0002] Conventionally, a control system for an all-wheel drive vehicle, such as that disclosed in Patent Document 1 below, has been provided as a control device for a four-wheel drive vehicle. The control system of Patent Document 1 controls the connection between a first axle that is driven by a prime mover in a timed manner, a second axle that is constantly connected to the prime mover via a propeller shaft, and a sub-shaft that drivingly connects the propeller shaft to the first axle. This control system includes a first clutch that disconnectably connects the propeller shaft to the sub-shaft, a second clutch that disconnectably connects the sub-shaft to the first axle, a synchronization determination means that determines whether the second clutch is connectable, and an engagement determination means that determines whether the second clutch is engaged. By adopting this configuration, the control system of Patent Document 1 aims to quickly switch between 2WD mode and 4WD mode while preventing shock or vibration fluctuations in transmission torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-032773 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the inventors have studied four-wheel drive vehicles that can be operated in drive modes (two-wheel drive fixed mode) that transmit power only to the main drive wheels, such as the 2WD mode described above, and drive modes (four-wheel drive fixed mode) that transmit drive power not only to the main drive wheels but also to the auxiliary drive wheels, such as the 4WD mode, as well as drive modes (drive system variable mode) that perform drive control to increase the distribution of drive power transmitted to the auxiliary drive wheels and change to four-wheel drive state, provided that slippage is detected in two-wheel drive state, such as a drive mode called 4WD AUTO.

[0005] As a result of the above-mentioned investigation, it was discovered that if a malfunction occurs in the switch provided for switching the drive mode, continuing the drive mode before the malfunction occurred may cause the vehicle to be unable to travel in four-wheel drive mode at the appropriate time. After further intensive investigation, the inventors discovered that, for example, if a malfunction occurs in the switch when the drive mode is in two-wheel drive mode, it may be possible to cause problems such as being unable to switch the drive mode to four-wheel drive mode when travel in four-wheel drive mode is required.

[0006] Therefore, the present invention aims to provide a control device for a four-wheel drive vehicle that enables driving in an appropriate driving state depending on the situation, even if a malfunction occurs in the switch for switching the driving mode. [Means for solving the problem]

[0007] Here, in order to solve the above-mentioned problems, the inventors conducted extensive research and came up with the idea of ​​switching the drive mode from two-wheel drive fixed mode to either four-wheel drive fixed mode or variable drive system mode, provided that a malfunction of the switch occurs when the drive mode is in two-wheel drive state.

[0008] As a result, it was discovered that if the drive mode is switched from two-wheel drive fixed mode to four-wheel drive fixed mode, there is a concern that tight corner braking may occur when attempting to turn at low speeds, and that if this occurs, it is highly likely that a user who intends to drive in two-wheel drive fixed mode will feel uncomfortable.

[0009] On the other hand, by switching the drive mode from fixed two-wheel drive mode to variable drive system mode, the vehicle can normally be driven in two-wheel drive mode, and the drive mode is switched to four-wheel drive mode if slippage occurs. This allows the user to drive without discomfort even when they intend to drive in fixed two-wheel drive mode, and also allows the vehicle to drive in four-wheel drive mode when slippage needs to be suppressed. Therefore, it was discovered that if the drive mode is switched from fixed two-wheel drive mode to variable drive system mode on the condition that a switch malfunction occurs while the drive mode is in two-wheel drive mode, it is possible to drive in four-wheel drive mode in appropriate situations.

[0010] (1) The control device for a four-wheel drive vehicle of the present invention, which is provided based on such findings, includes a first clutch that selectively connects or disconnects a power transmission path between a driving force source and a power transmission member, and a second clutch that selectively connects or disconnects a power transmission path between the power transmission member and auxiliary drive wheels, and has three modes: a two-wheel drive fixed mode in which driving force is transmitted from the driving force source to the left and right main drive wheels by disengaging at least one of the first clutch and the second clutch; a four-wheel drive fixed mode in which driving force is also transmitted from the driving force source to the left and right auxiliary drive wheels by engaging the first clutch and the second clutch, respectively; and a drive control mode in which, while engaging the second clutch, the degree of engagement of the first clutch is changed when a predetermined condition is satisfied, thereby increasing the distribution of driving force transmitted to the auxiliary drive wheels relative to the driving force transmitted to the main drive wheels. a variable drive system mode, and a drive mode setting unit that sets the drive mode of the four-wheel drive vehicle based on a signal output from the drive mode selection switch; and a clutch control unit that controls the operation of the first clutch and the second clutch according to the drive mode set by the drive mode setting unit. The control device for a four-wheel drive vehicle is used in a four-wheel drive vehicle that can be driven in a drive mode selected from a plurality of drive modes including a variable drive system mode, and a variable drive system mode, and is equipped with a drive mode selection switch that accepts the selection of the drive mode. The control device comprises: a drive mode setting unit that sets the drive mode of the four-wheel drive vehicle based on a signal output from the drive mode selection switch; and a clutch control unit that controls the operation of the first clutch and the second clutch according to the drive mode set by the drive mode setting unit, and is characterized in that when the four-wheel drive vehicle is driven in the fixed two-wheel drive mode, the drive mode setting unit performs a drive mode change process that changes the drive mode from the fixed two-wheel drive mode to the variable drive system mode, using an occurrence of a malfunction of the drive mode selection switch as part or all of the start conditions.

[0011] Based on the above findings, the control device for a four-wheel drive vehicle of the present invention performs a drive mode change process in which the drive mode setting unit switches the drive mode from a fixed two-wheel drive mode to a variable drive system mode on the condition that a malfunction occurs in the switch when the drive mode is in two-wheel drive. Therefore, even if a malfunction occurs in the drive mode switching switch when the drive mode is in two-wheel drive, the control device for a four-wheel drive vehicle of the present invention can control the operation of the four-wheel drive vehicle so that it can run in an appropriate drive system depending on the situation.

[0012] (2) The control device for a four-wheel drive vehicle of the present invention described above may be characterized in that it has a stability determination unit that determines the stability of the four-wheel drive vehicle, and the drive mode setting unit performs the drive mode change process using the stability determination unit's determination that the vehicle is in a stable state as one of the start conditions.

[0013] As described above, the control device for a four-wheel drive vehicle of the present invention performs drive mode change processing with the starting condition being that the stability of the four-wheel drive vehicle is ensured, so that the drive mode change processing can be performed reliably in preparation for situations where four-wheel drive driving is required.

[0014] (3) The control device for a four-wheel drive vehicle of the present invention described above may be characterized in that the drive mode setting unit performs the drive mode change process using as one of the start conditions at least one of the following being satisfied: (α) tire slippage has occurred, (β) the vehicle is traveling on a low μ road, and (γ) the outside air temperature is below a predetermined temperature.

[0015] By being configured in this manner, the control device for a four-wheel drive vehicle of the present invention can enable driving in four-wheel drive mode in situations where four-wheel drive mode is required, such as (α) to (γ) above, even if a malfunction occurs in the switch for switching drive modes.

[0016] (4) The control device for a four-wheel drive vehicle of the present invention described above may be characterized in that, when the four-wheel drive vehicle is being driven in the variable drive system mode, the drive mode setting unit maintains the drive mode in the variable drive system mode on the condition that a malfunction of the drive mode selection switch occurs.

[0017] By adopting such a configuration, the control device for a four-wheel drive vehicle of the present invention can enable the vehicle to travel in an appropriate drive state depending on the situation.

[0018] (5) The above-described control device for a four-wheel drive vehicle of the present invention may be characterized in that, when the four-wheel drive vehicle is being driven in the four-wheel drive fixed mode, the drive mode setting unit maintains the drive mode in the four-wheel drive fixed mode on the condition that a malfunction of the drive mode selection switch occurs.

[0019] By maintaining the drive state in the four-wheel drive fixed mode even after a malfunction of the drive mode selection switch occurs, the control device for a four-wheel drive vehicle of the present invention can prevent the drive mode from being unexpectedly changed to the two-wheel drive fixed mode or the drive system variable mode, and switching to the two-wheel drive state against the user's intention.

[0020] (6) The control device for a four-wheel drive vehicle of the present invention described above may be characterized in that the stability determination unit determines that the four-wheel drive vehicle is in a stable state based on at least one of the following criteria: (A) the vehicle is stopped; (B) both the gravitational accelerations acting on the vehicle in the longitudinal and lateral directions are within predetermined ranges; and (C) the yaw rate sensor value is within a predetermined range.

[0021] By being configured in this manner, the control device for a four-wheel drive vehicle of the present invention can accurately grasp the stability of the four-wheel drive vehicle and perform drive mode change processing when the stability of the four-wheel drive vehicle is high, in preparation for situations where four-wheel drive driving is necessary.

[0022] (7) The control device for a four-wheel drive vehicle of the present invention described above may be characterized in that, when the four-wheel drive vehicle is being driven in the four-wheel drive fixed mode, the drive mode setting unit changes the drive mode from the four-wheel drive fixed mode to the drive system variable mode on the condition that a malfunction of the drive mode selection switch occurs and the vehicle enters a state that is estimated to be a tight corner braking state.

[0023] By configuring the control device for a four-wheel drive vehicle of the present invention in this way, if a malfunction of the drive mode selection switch occurs while the vehicle is being driven in fixed four-wheel drive mode, and a state that is expected to be a tight corner braking state occurs, the control device can control the operation of the four-wheel drive vehicle so that the tight corner braking state can be eliminated and the vehicle can continue driving by changing to variable drive mode. [Effects of the Invention]

[0024] According to the present invention, a control device for a four-wheel drive vehicle can be provided that enables driving in an appropriate driving state depending on the situation, even if a malfunction occurs in the switch for switching the driving mode. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is an explanatory diagram showing a control device according to an embodiment of the present invention and a vehicle equipped with the control device; [Figure 2] 4 is a flowchart showing an example of control performed in a state where the drive mode selection switch in the vehicle shown in FIG. 1 does not operate normally. [Figure 3] 10(a) to 10(c) are timing charts showing changes in the drive mode when the drive mode selection switch does not operate normally. [Figure 4] FIG. 10(a) is a block diagram showing a control device according to a second modified example, and FIG. 10(b) is a block diagram showing a control device according to a third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, a four-wheel drive vehicle control device (control device 100) according to an embodiment of the present invention will be described with reference to the drawings, taking a four-wheel drive vehicle (vehicle 10) that employs the same as an example. In the following description, before describing the specific configuration of the control device 100 and the control performed by the control device 100, a general configuration of the vehicle 10 will be described.

[0027] Fig. 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied. As shown in Fig. 1, the vehicle 10 includes a driving force source 12, a pair of left and right front wheels 14L, 14R, a pair of left and right rear wheels 16L, 16R, a power transmission device 18, and a control device 100. The vehicle 10 is a four-wheel drive vehicle that can be switched as needed between a two-wheel drive state in which driving force is transmitted to the rear wheels 16L, 16R, and a four-wheel drive state in which driving force is transmitted to the front wheels 14L, 14R in addition to the rear wheels 16L, 16R.

[0028] The driving force source 12 generates driving force for the vehicle 10. The driving force source 12 can be configured, for example, by an engine or a motor. The front wheels 14L, 14R constitute auxiliary driving wheels of the vehicle 10. The front wheels 14L, 14R function as driving wheels in four-wheel drive mode and as driven wheels in two-wheel drive mode. The rear wheels 16L, 16R constitute main driving wheels of the vehicle 10. The rear wheels 16L, 16R function as driving wheels in both four-wheel drive mode and two-wheel drive mode.

[0029] As shown in FIG. 1, the power transmission device 18 includes a speed change device 20, a transfer case 22, a front propeller shaft 24 (power transmission member), a rear propeller shaft 26, a front wheel differential gear device 28, a rear wheel differential gear device 30, a pair of left and right front wheel axles 32L, 32R, and a pair of left and right rear wheel axles 34L, 34R.

[0030] The power transmission device 18 can transmit the power generated in the driving force source 12 to the rear wheels 16L, 16R via a power transmission path that sequentially passes from the transmission 20 to the transfer 22, the rear propeller shaft 26, the rear wheel differential gear device 30, and the rear axles 34L, 34R, etc., before reaching the rear wheels 16L, 16R. The power transmission device 18 can also configure a power transmission path that distributes and transmits a portion of the driving force transmitted from the driving force source 12 to the transfer 22 to the front wheels 14L, 14R. That is, by adjusting the engagement state of the front wheel drive clutch 46, which will be described in detail later, the power transmission device 18 can transmit a portion of the power generated in the driving force source 12 to the front wheels 14L, 14R via a power transmission path that sequentially passes from the transmission 20 to the transfer 22, the front propeller shaft 24, the front wheel differential gear device 28, the front axles 32L, 32R, etc., before reaching the front wheels 14L, 14R.

[0031] The transmission 20 operates by receiving output from the driving force source 12, and is configured by, for example, a conventionally known MT (manual transmission), AT (automatic transmission), CVT (continuously variable transmission), or the like.

[0032] The transfer case 36 houses an input shaft 38, a rear-wheel-side output shaft 40, a front-wheel-drive drive sprocket 42, and a front-wheel-drive clutch 46 (first clutch) around a first rotational axis C1. The transfer case 36 also houses a front-wheel-side output shaft 48 and a front-wheel-drive driven sprocket 50 around a second rotational axis C2 extending in a direction along the first rotational axis C1 (substantially parallel to the first rotational axis C1 in this embodiment). The transfer case 22 also houses a front-wheel-drive chain 52 wound around the front-wheel-drive drive sprocket 42 and the front-wheel-drive driven sprocket 50.

[0033] The input shaft 38 is connected to the transmission 20. This allows the input shaft 38 to receive power transmitted from the driving power source 12. The rear-wheel output shaft 40 is connected to the rear propeller shaft 26 so as to be capable of transmitting power. A front-wheel drive drive sprocket 42 is supported on the rear-wheel output shaft 40 so as to be rotatable relative to the rear-wheel output shaft 40.

[0034] By engaging the front-wheel drive clutch 46, the front-wheel drive sprocket 42 can rotate integrally with the rear-wheel output shaft 40, and can transmit power to the front-wheel output shaft 48 via the front-wheel drive chain 52. Therefore, by engaging the front-wheel drive clutch 46, a portion of the driving force transmitted from the driving power source 12 to the rear propeller shaft 26 via the rear-wheel output shaft 40 can be distributed and transmitted to the front-wheel output shaft 48 via the front-wheel drive drive sprocket 42 and the front-wheel drive chain 52. On the other hand, by disengaging the front-wheel drive clutch 46, the driving force transmitted from the driving power source 12 to the rear-wheel output shaft 40 can be transmitted to the rear propeller shaft 26 without being transmitted (distributed) to the front-wheel drive drive sprocket 42.

[0035] The front-wheel drive clutch 46 is configured as a wet multi-plate clutch. The front-wheel drive clutch 46 is capable of adjusting the degree of engagement (degree of engagement) to adjust the transmission torque transmitted from the rear-wheel output shaft 40 to the front-wheel drive drive sprocket 42. In other words, the front-wheel drive clutch 46 functions as a clutch (first clutch) for selectively disconnecting or connecting the power transmission path between the driving power source 12 and the front propeller shaft 24, which functions as a power transmission member to the front wheels 14L, 14R. The front-wheel drive clutch 46 is actuated by the action of hydraulic pressure, and the degree of engagement can be adjusted by controlling the magnitude of the hydraulic pressure.

[0036] The front-wheel-side output shaft 48 is connected to the front propeller shaft 24 so as to be able to transmit power. The front-wheel-drive driven sprocket 50 is provided so as to be able to rotate integrally with the front-wheel-side output shaft 48. In addition, a front-wheel-drive chain 52 is wound around the front-wheel-drive drive sprocket 42 and the front-wheel-drive driven sprocket 50, so that power can be transmitted between the two sprockets.

[0037] The front wheel differential gear device 28 includes a differential case 80, a pinion shaft 82, a pair of side gears 84L, 84R, a pair of pinions 86a, 86b, and a ring gear 90. The pinions 86a, 86b are attached to the differential case 80, with the pinions 86a, 86b disposed at both ends of the pinion shaft 82. The side gears 84L, 84R are disposed opposite each other within the differential case 80 and mesh with the pinions 86a, 86b, respectively. The side gears 84L, 84R are connected to the front wheels 14L, 14R via the front axles 32L, 32R. The ring gear 90 is attached integrally to the differential case 80. A front drive pinion 25 connected to the front propeller shaft 24 meshes with the ring gear 90. The front wheel differential gear device 28 also includes a mesh clutch 94 (second clutch). The mesh clutch 94 can be engaged by applying pressure (negative pressure). The mesh clutch 94 functions as a second clutch that selectively connects or disconnects the power transmission path between the front propeller shaft 24, which functions as a power transmission member to the front wheels 14L, 14R, and the front axles 32L, 32R, which are auxiliary drive wheels.

[0038] The rear wheel differential gear device 30 includes a differential case 120, a pinion shaft 122, a pair of side gears 124L and 124R, a pair of pinions 126a and 126b, and a ring gear 130. The pinions 126a and 126b are attached to the differential case 120, with the pinions 126a and 126b disposed at both ends of the pinion shaft 122. The side gears 124L and 124R are disposed opposite each other within the differential case 120 and mesh with the pinions 126a and 126b, respectively. The side gears 124L and 124R are connected to the rear wheels 16L and 16R via rear wheel axles 34L and 34R. The ring gear 130 is attached integrally to the differential case 120. A rear drive pinion 27 connected to the rear propeller shaft 26 meshes with the ring gear 130.

[0039] Because the vehicle 10 is configured as described above, when both the front-wheel drive clutch 46 and the dog clutch 94 are connected (engaged) to transmit torque, the vehicle 10 is in a state (four-wheel drive state) in which power generated in the driving force source 12 can be transmitted not only to the rear wheels 16L, 16R but also to the front wheels 14L, 14R. On the other hand, when at least one of the front-wheel drive clutch 46 and the dog clutch 94 is disconnected (disengaged), the power transmission path to the front wheels 14L, 14R is cut off, and the vehicle 10 is in a state in which torque transmission is disabled. As a result, the vehicle 10 is in a state (two-wheel drive state) in which power generated in the driving force source 12 can be transmitted to the rear wheels 16L, 16R but cannot be transmitted to the front wheels 14L, 14R.

[0040] The vehicle 10 is equipped with a drive mode selection switch 140 for switching the drive state. The drive mode selection switch 140 can be set to any one of three drive modes: "2WD," "4WD LOCK," and "4WD AUTO." When the drive mode selection switch 140 is set to "2WD," one or both of the front-wheel drive clutch 46 and the dog clutch 94 are disengaged. This places the vehicle 10 in a drive mode in which the vehicle is driven in two-wheel drive mode (two-wheel drive fixed mode). When the drive mode selection switch 140 is set to "4WD LOCK," the dog clutch 94 is engaged and the front-wheel drive clutch 46 is fully engaged. This places the vehicle 10 in a drive mode in which the vehicle is driven in four-wheel drive mode (four-wheel drive fixed mode).

[0041] Furthermore, when the drive mode selection switch 140 is set to "4WD AUTO," a drive mode (drive system variable mode) is selected in which drive control using a standby control system is possible, in which the degree of engagement of the front-wheel drive clutch 46 is changed while the dog clutch 94 is engaged, provided that slippage is detected, thereby increasing the distribution of drive power transmitted to the auxiliary drive wheels 14L, 14R relative to the drive power transmitted to the rear wheels 16L, 16R, which are the main drive wheels. Specifically, when the drive mode selection switch 140 is set to "4WD AUTO," the dog clutch 94 is engaged, and the front-wheel drive clutch 46 is engaged at a predetermined standby engagement degree S in preparation for slippage. When the drive mode selection switch 140 is set to "4WD AUTO," if slippage occurs in the rear wheels 16L, 16R, which are the main drive wheels, the drive state of the vehicle 10 is switched by fully engaging the front wheel drive clutch 46 while the dog clutch 94 is maintained in an engaged state.

[0042] The control device 100 is capable of controlling the connection state (engagement state) of the front-wheel drive clutch 46 and the dog clutch 94. The control device 100 is configured to include a microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc. The control device 100 is equipped with a drive mode setting unit 102. The control device 100 also has a first clutch control unit 104 and a second clutch control unit 106 as clutch control units for controlling the operation of the front-wheel drive clutch 46 and the dog clutch 94 in accordance with the drive mode set in the drive mode setting unit 102.

[0043] The drive mode setting unit 102 sets the drive mode of the vehicle 10 based on a signal output from the drive mode selection switch 140. Here, when the drive mode selection switch 140 is operating normally, the drive mode setting unit 102 can set the drive mode of the vehicle 10 by reflecting the user's operation of the drive mode selection switch 140. However, when the drive mode selection switch 140 is malfunctioning or a communication failure occurs between the drive mode selection switch 140 and the drive mode setting unit 102, and the drive mode selection switch 140 is not operating normally, the setting of the drive mode selection switch 140 cannot be reflected. Therefore, the drive mode setting unit 102 performs a drive mode change process and automatically sets the drive mode on the condition that the drive mode selection switch 140 is not operating normally.

[0044] Specifically, when the vehicle 10 is being driven in the two-wheel drive fixed mode, the drive mode setting unit 102 performs a process (drive mode change process) to change the drive mode from the two-wheel drive fixed mode to the variable drive system mode on the condition that the drive mode selection switch 140 malfunctions. On the other hand, when the four-wheel drive vehicle is being driven in the variable drive system mode, the drive mode setting unit 102 maintains the drive mode in the variable drive system mode on the condition that the drive mode selection switch 140 malfunctions. Furthermore, when the vehicle 10 is being driven in the four-wheel drive fixed mode, the drive mode setting unit 102 maintains the drive mode in the four-wheel drive fixed mode on the condition that the drive mode selection switch 140 malfunctions.

[0045] The first clutch control unit 104 controls the transmission torque (degree of engagement of the first clutch) transmitted to the front propeller shaft 24 via the front-wheel drive clutch 46. The first clutch control unit 104 controls the operation of the front-wheel drive clutch 46 in accordance with the drive mode set by the drive mode setting unit 102. As described above, in this embodiment, the front-wheel drive clutch 46 is a wet-type multi-plate clutch whose degree of engagement (engagement pressure) can be adjusted by controlling the magnitude of hydraulic pressure. Therefore, the first clutch control unit 104 controls the magnitude of the transmission torque to the front propeller shaft 24 by controlling the magnitude of hydraulic pressure acting on the front-wheel drive clutch 46.

[0046] The second clutch control unit 106 controls the operation of the dog clutch 94 to control torque transmission from the front-wheel drive clutch 46 to the front-wheel differential gear unit 28. The second clutch control unit 106 controls the operation of the dog clutch 94 in accordance with the drive mode set by the drive mode setting unit 102. As described above, the dog clutch 94 can be engaged by applying pressure (negative pressure). Therefore, the second clutch control unit 106 can switch the dog clutch 94 between an engaged state and a disengaged state by controlling the magnitude of the pressure acting on the dog clutch 94.

[0047] Here, the above-described control device 100 is characterized by the control that is performed when the drive mode selection switch 140 does not operate normally. The control that is performed when the drive mode selection switch 140 does not operate normally will be described in detail below in accordance with the flowchart in Fig. 2 and with reference to the timing chart in Fig. 3.

[0048] (Step 1) In step 1, the control device 100 checks whether the drive mode selection switch 140 of the vehicle 10 is in an abnormal state due to a malfunction, poor communication, etc. If it is determined that the drive mode selection switch 140 is in an abnormal state, the control flow proceeds to step 2.

[0049] (Step 2) In step 2, the control device 100 checks whether the drive mode of the vehicle 10 was two-wheel drive fixed mode before an abnormality in the drive mode selection switch 14 was confirmed in step 1. If the drive mode was two-wheel drive fixed mode, the control flow proceeds to step 3. On the other hand, if the drive mode was other than two-wheel drive fixed mode, i.e., four-wheel drive fixed mode or variable drive system mode, the control flow proceeds to step 4.

[0050] (Step 3) When the control flow proceeds to step 3, the drive mode setting unit 102 of the control device 100 changes the drive mode from the previous two-wheel drive fixed mode to the variable drive system mode. As a result, the control device 100 controls the vehicle 10 to operate in the variable drive system mode regardless of the state of the drive mode selection switch 140 (see FIG. 3(a)). Specifically, the control device 100 engages the dog clutch 94 under control of the second clutch control unit 106. Furthermore, the control device 100 engages the front-wheel drive clutch 46 at a predetermined standby engagement degree S in preparation for the occurrence of slippage under control of the first clutch control unit 104. As a result, when slippage occurs in the rear wheels 16L, 16R, which are the main drive wheels, the front-wheel drive clutch 46 is fully engaged, thereby enabling the drive state of the vehicle 10 to be switched to four-wheel drive.

[0051] (Step 4) On the other hand, when the control flow proceeds from step 2 to step 4 described above, the drive mode setting unit 102 of the control device 100 maintains the drive mode in the state it was in before the abnormality occurred in the drive mode selection switch 140. That is, if the drive mode before the abnormality occurred in the drive mode selection switch 140 was the variable drive system mode, the drive mode is maintained as the variable drive system mode (see FIG. 3(b)). Also, if the drive mode before the abnormality occurred in the drive mode selection switch 140 was the fixed four-wheel drive mode, the drive mode is maintained as the fixed four-wheel drive mode (see FIG. 3(c)).

[0052] The control device 100 mounted on the vehicle 10 described above has the following characteristic configurations (a) to (c), and therefore can achieve characteristic effects that cannot be achieved with conventional technologies, as described below.

[0053] (a) The control device 100 of this embodiment includes a front-wheel drive clutch 46 (first clutch) that selectively connects or disconnects the power transmission path between the driving force source 12 and the front propeller shaft 24 (power transmission member), and a mesh clutch 94 (second clutch) that selectively connects or disconnects the power transmission path between the front propeller shaft 24 and the front wheels 14L, 14R (auxiliary drive wheels). The control device 100 has two wheel drive fixed modes in which the driving force is transmitted from the driving force source 12 to the left and right main drive wheels by respectively releasing the front-wheel drive clutch 46 and the mesh clutch 94. The control device 100 is used in a vehicle 10 that can be driven in a drive mode selected from a plurality of drive modes, including a fixed four-wheel drive mode in which drive force is transmitted from the drive force source 12 to the left and right front wheels 14L, 14R by engaging the front-wheel drive clutch 46, and a variable drive system mode in which drive control is performed to increase the distribution of drive force transmitted to the front wheels 14L, 14R relative to the drive force transmitted to the rear wheels 16L, 16R by changing the degree of engagement of the front-wheel drive clutch 46 while engaging the dog clutch 94 when a predetermined condition is satisfied, and that is equipped with a drive mode selection switch 140 that accepts the selection of the drive mode. The control device 100 has a drive mode setting unit 102 that sets the drive mode of the vehicle 10 based on a signal output from the drive mode selection switch 140, and clutch control units (first clutch control unit 104 and second clutch control unit 106) that control the operation of the front-wheel drive clutch 46 and the dog clutch 94 in accordance with the drive mode set by the drive mode setting unit 102. When the vehicle 10 is being driven in two-wheel drive fixed mode, the control device 100 is configured so that the drive mode setting unit 102 performs a drive mode change process to change the drive mode from two-wheel drive fixed mode to variable drive system mode, with malfunction of the drive mode selection switch 140 being some or all of the initiation conditions.

[0054] As described in (a) above, the control device 100 is configured to perform a drive mode change process in which the drive mode setting unit 102 switches the drive mode from the fixed two-wheel drive mode to the variable drive system mode on the condition that a switch malfunction occurs when the drive mode is in the two-wheel drive state. Therefore, the control device 100 of this embodiment can control the operation of the vehicle 10 so that the vehicle can travel in an appropriate drive state depending on the situation when a drive mode switching switch malfunctions when the drive mode is in the two-wheel drive state. Specifically, when a drive mode switching switch malfunctions when the drive mode is in the two-wheel drive state, the control device 100 can switch to the four-wheel drive state when a situation arises in which switching to the four-wheel drive state is desirable, such as when slippage occurs, or can switch to the two-wheel drive state when the four-wheel drive state is not necessary or when tight corner braking occurs.

[0055] (b) In the control device 100 of the present embodiment described above, when the vehicle 10 is being driven in the variable drive system mode, the drive mode setting unit 102 maintains the drive mode in the variable drive system mode, provided that a malfunction of the drive mode selection switch 140 occurs.

[0056] Because the control device 100 of this embodiment is configured in this manner, it can maintain the drive mode in the variable drive system mode even after a malfunction of the drive mode selection switch 140 occurs, making it possible to drive in an appropriate drive state depending on the situation.

[0057] (c) In the control device 100 of the present embodiment described above, when the vehicle 10 is being driven in the fixed four-wheel drive mode, the drive mode setting unit 102 maintains the drive mode in the fixed four-wheel drive mode, provided that a malfunction of the drive mode selection switch 140 occurs.

[0058] Because the control device 100 of this embodiment is configured in this manner, it is possible to prevent the drive mode from being unexpectedly changed to a fixed two-wheel drive mode or a variable drive system mode after a malfunction of the drive mode selection switch 140, and to prevent the vehicle from switching to a two-wheel drive state against the user's intention.

[0059] In this embodiment, the control device 100 has been illustrated as having the features (a) to (c) above, but the present invention is not limited to this. For example, it is possible for the control device 100 not to have the configurations (b) and (c) above, or to have other configurations. Specifically, it is possible for the control device 100 to have the configurations shown in the following first to third modified examples. Each modified example will be described below. In the following description, detailed description of configurations common to the above-described embodiment will be omitted, and the same configurations will be described using the same reference numerals.

[0060] <First Modification> In the above-described control device 100, when the vehicle 10 is being driven in the two-wheel drive fixed mode, the drive mode setting unit 102 performs a process (drive mode change process) to change the drive mode from the two-wheel drive fixed mode to the variable drive system mode, with the malfunction of the drive mode selection switch 140 being the starting condition. However, it is possible to add one or more other conditions as the starting condition for performing the drive mode change process.

[0061] Specifically, in the control device 100 of the first variant, the start condition for the drive mode change process is that, when the vehicle 10 is being driven in two-wheel drive fixed mode, the drive mode selection switch 140 malfunctions and one of the following conditions (α) to (γ) is satisfied, and then the drive mode setting unit 102 performs the drive mode change process. (α) Tire slippage is occurring. (β) Driving on a low μ road. (γ) The outside temperature is below a specified temperature. According to this modification, the following effect (d) can be obtained.

[0062] (d) The control device 100 of this modified example performs the drive mode change process using the drive mode setting unit 102 satisfying at least one of the above (α) to (γ) as one of the start conditions. Therefore, in the control device 100 of this modified example, even if a malfunction occurs in the drive mode selector switch 140, the drive mode change process is not performed until a situation arises in which four-wheel drive mode should be selected, as in the above (α) to (γ).

[0063] With the above-described configuration, even if a malfunction occurs in the drive mode selector switch 140, the vehicle can be driven in the two-wheel drive fixed mode as intended by the user until the situation requires the four-wheel drive state, allowing the user to drive the vehicle 10 without any discomfort. Furthermore, with the above-described configuration, once the situation requires the four-wheel drive state, the vehicle can be appropriately switched to the four-wheel drive state and driven when the situation requires the four-wheel drive state.

[0064] In this modified example, an example is shown in which the satisfaction of any of the following conditions (α) to (γ) is added as a condition for starting the drive mode change process, but the present invention is not limited to this, and conditions other than (α) to (γ) may be added, or any of (α) to (γ) may be deleted from the conditions.

[0065] <Second Modification> The control device 100 described above performs a process (drive mode change process) to change the drive mode from two-wheel drive fixed mode to variable drive system mode when the drive mode selection switch 140 malfunctions while the vehicle 10 is driven in two-wheel drive fixed mode, but one or more other conditions can be added as a start condition for performing the drive mode change process. For example, as shown in Figure 4(a), a control device 200 of a second modified example includes a stability determination unit 208 in addition to the drive mode setting unit 102, first clutch control unit 104, and second clutch control unit 106 described above, and the determination result of the stability determination unit 208 is taken into account as a start condition for performing the drive mode change process.

[0066] The stability determination unit 208 determines the stability of the vehicle 10. The stability determination unit 108 can determine the stability of the vehicle 10 based on one or more indicators. In this modification, the stability determination unit 208 uses the following conditions (A) to (C) as indicators for determining the stability of the vehicle 10, and determines that the vehicle 10 is in a stable state when any one of the conditions is satisfied. (A) Vehicle 10 is stopped. (B) The gravitational acceleration acting on the vehicle 10 in the longitudinal and lateral directions is within a predetermined range. (C) The yaw rate sensor value is within a specified range.

[0067] In this modified example, the control device 200 sets as a start condition for performing the drive mode change process when the vehicle 10 is being driven in two-wheel drive fixed mode, the drive mode selection switch 140 malfunctions, and the stability determination unit 208 determines that the vehicle 10 is in a stable state. Therefore, even if the drive mode selection switch 140 malfunctions when the vehicle 10 is being driven in two-wheel drive fixed mode, the control device 200 waits without performing the drive mode change process for changing the drive mode from two-wheel drive fixed mode to the drive system variable mode until the stability determination unit 208 determines that the vehicle 10 is in a stable state.

[0068] The control device 200 of the second modified example has the following characteristic configurations (e) and (f), and therefore can achieve the following characteristic effects that cannot be achieved by conventional techniques.

[0069] (e) The control device 200 of the second modified example described above has a stability determination unit 208 that determines the stability of the vehicle 10, and performs drive mode change processing with the drive mode setting unit 102 determining that the vehicle is in a stable state as one of the start conditions.

[0070] The control device 200 of the second modified example performs the drive mode change process with the stability of the vehicle 10 being ensured as a start condition, and therefore can perform the drive mode change process when the stability of the vehicle 10 is high, in preparation for situations where four-wheel drive driving is required. Note that, unlike the control device 100 exemplified in the above embodiment, this modified example shows an example in which the stability of the vehicle 10 is added as a start condition for starting the drive mode change process, but the present invention is not limited to this, and other conditions may also be added as start conditions for the drive mode change process.

[0071] (f) Furthermore, in the control device 200 of the second modified example, the stability determination unit 208 determines that the running state is stable using at least one of the above conditions (A) to (C) as the determination criterion.

[0072] The control device 200 of the second modified example can perform the drive mode change process when the vehicle 10 is in a stable state, such as when the vehicle 10 is stopped, when the gravitational acceleration acting on the vehicle 10 is within a predetermined value, or when the yaw rate sensor value is within a predetermined range. In this modified example, the stability determination unit 208 uses the above-described (A) to (C) as examples of indicators for determining the stability of the vehicle 10. However, the present invention is not limited to these examples, and other determination conditions may also be taken into consideration when making the determination. In addition, in this modified example, the vehicle 10 is determined to be in a stable state if at least one of the above conditions (A) to (C) is satisfied. However, the present invention is not limited to these examples, and the vehicle 10 may not be determined to be in a stable state unless, for example, two or more of the conditions (A) to (C) or other conditions are satisfied.

[0073] <Third Modification> The control device 100 described above performs the drive mode change process using a malfunction of the drive mode selection switch 140 when the vehicle 10 is being driven in two-wheel drive fixed mode as a starting condition, and changes the drive mode from the two-wheel drive fixed mode to the variable drive system mode. However, the drive mode may also be changed when a malfunction of the drive mode selection switch 140 occurs when the vehicle 10 is being driven in four-wheel drive fixed mode. Based on this knowledge, the control device 300 of the third modified example changes the drive mode from the four-wheel drive fixed mode to the variable drive system mode when a malfunction of the drive mode selection switch occurs and the vehicle enters a state that is estimated to be a tight corner braking state when the four-wheel drive vehicle is being driven in four-wheel drive fixed mode.

[0074] 4(b), the control device 300 of the third modified example includes a vehicle state estimation unit 308 that can estimate whether the vehicle 10 is in a tight corner braking state. The vehicle state estimation unit 308 may have any configuration as long as it can estimate whether the vehicle is in a tight corner braking state, but for example, it can estimate whether the vehicle is in a tight corner braking state based on the occurrence of torsion in the drive train of the vehicle 10.

[0075] More specifically, the vehicle state estimation unit 308 can acquire information such as steering angle, vehicle speed, lateral acceleration, yaw rate, etc. based on detection signals from sensors provided in the vehicle 10, and use this information as part or all of the indicators to determine the occurrence of torsion in the drivetrain of the vehicle 10, and estimate whether or not the vehicle is in a tight corner braking state based on the result. Specifically, the vehicle state estimation unit 308 can estimate that the vehicle 10 is in a tight corner braking state when the vehicle speed is equal to or lower than a predetermined speed and the steering angle is equal to or greater than a predetermined size, taking into consideration that torsion in the drivetrain occurs due to tight corner braking under conditions where the vehicle speed is low and the steering angle is large.

[0076] The control device 300 of the third modified example has the following characteristic configuration (g), and therefore can achieve the following characteristic effects that cannot be achieved by conventional techniques.

[0077] (g) In the control device 300 of the present embodiment described above, when the vehicle 10 is being driven in the fixed four-wheel drive mode, the drive mode setting unit 102 changes the drive mode from the fixed four-wheel drive mode to the variable drive system mode if the drive mode selection switch 140 malfunctions and the vehicle enters a state that is estimated to be a tight corner braking state.

[0078] By configuring the control device 300 of this modified example as described above, if the drive mode selection switch 140 malfunctions while the vehicle is being driven in fixed four-wheel drive mode, and a state that is assumed to be a tight corner braking state occurs, the control device 300 can control the operation of the vehicle 10 so that the tight corner braking state is eliminated and the vehicle can continue driving by changing to variable drive mode.

[0079] The configurations described in the above embodiment and the first to third modified examples are merely examples of the present invention, and the configuration of each component can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, a wet multi-plate clutch is used as the front-wheel drive clutch 46 (first clutch) that selectively connects or disconnects the power transmission path between the driving power source 12 and the front propeller shaft 24 (power transmission member), but the present invention is not limited to this. For example, the front-wheel drive clutch 46 can be various clutches whose engagement degree can be controlled, such as an electrically controlled clutch or a clutch whose engagement degree can be adjusted by magnetic force. Furthermore, in this embodiment, a dog clutch 94 is used as the second clutch that selectively connects or disconnects the power transmission path between the front propeller shaft 24 and the front wheels 14L, 14R (auxiliary drive wheels), but the present invention is not limited to this. The second clutch can be any suitable clutch, such as a wet multi-plate clutch, an electrically controlled clutch, or a clutch whose engagement degree can be adjusted by magnetic force.

[0080] The present invention is not limited to the above-described embodiments and variations thereof, and other embodiments may be possible within the scope of the claims. The components of the above-described embodiments may be arbitrarily selected and combined. Furthermore, any component of the embodiments may be arbitrarily combined with any component described in the Summary of the Invention or any component embodying any component described in the Summary of the Invention. The present invention intends to obtain rights to these as well through amendments to this application or divisional applications, etc. [Industrial Applicability]

[0081] The present invention can be suitably used in control devices for four-wheel drive vehicles in general, which are equipped with a first clutch that selectively disconnects or connects the power transmission path between a driving force source and a power transmission member, and a second clutch that selectively disconnects or connects the power transmission path between the power transmission member and an auxiliary drive wheel. [Explanation of symbols]

[0082] 10: Vehicle (four-wheel drive vehicle) 12: Driving force source 14L, 14R: Front wheels (auxiliary drive wheels) 16L, 16R: Rear wheels (main drive wheels) 18: Power transmission device 24: Front propeller shaft (power transmission member) 46: Front wheel drive clutch (first clutch) 94: Dog clutch (second clutch) 100: Control device 102: Driving condition detection unit 104: First clutch control unit (clutch control unit) 106: Second clutch control unit (clutch control unit) 108: Stability judgment section 200: Control device 208: Stability judgment section 300: Control device 308: Vehicle state estimation unit

Claims

1. a first clutch that selectively connects or disconnects a power transmission path between the driving power source and the power transmission member; a second clutch that selectively connects or disconnects a power transmission path between the power transmission member and the auxiliary drive wheels, a two-wheel drive fixed mode in which driving force is transmitted from the driving force source to the left and right main drive wheels by disengaging at least one of the first clutch and the second clutch; a four-wheel drive fixed mode in which the first clutch and the second clutch are engaged to transmit driving force from the driving force source to the left and right auxiliary drive wheels; a variable drive system mode in which, while engaging the second clutch, when a predetermined condition is satisfied, the degree of engagement of the first clutch is changed to perform drive control to increase the distribution of the driving force transmitted to the auxiliary drive wheels relative to the driving force transmitted to the main drive wheels; and and can be driven in a driving mode selected from a plurality of driving modes including A control device for a four-wheel drive vehicle used in a four-wheel drive vehicle equipped with a drive mode selection switch that accepts selection of the drive mode, a drive mode setting unit that sets a drive mode of the four-wheel drive vehicle based on a signal output from the drive mode selection switch; a clutch control unit that controls the operation of the first clutch and the second clutch in accordance with the drive mode set by the drive mode setting unit; and the drive mode setting unit performs a drive mode change process to change the drive mode from the two-wheel drive fixed mode to the drive system variable mode, with the occurrence of an operational malfunction of the drive mode selection switch as a partial or complete start condition when the four-wheel drive vehicle is being driven in the two-wheel drive fixed mode; a drive mode setting unit that maintains the drive mode in the four-wheel drive fixed mode when the drive mode selection switch malfunctions while the four-wheel drive vehicle is being driven in the four-wheel drive fixed mode.

2. a stability determination unit that determines the stability of the four-wheel drive vehicle; 2. The control device for a four-wheel drive vehicle according to claim 1, wherein the drive mode setting unit performs the drive mode change process when the stability determination unit determines that the vehicle is in a stable state as one of the start conditions.

3. 3. The control device for a four-wheel drive vehicle according to claim 1, wherein the drive mode setting unit performs the drive mode change process using as one of the start conditions at least one of the following conditions being satisfied: (α) tire slippage has occurred; (β) the vehicle is traveling on a low μ road; and (γ) the outside air temperature is equal to or lower than a predetermined temperature.

4. 4. The control device for a four-wheel drive vehicle according to claim 1, wherein the drive mode setting unit maintains the drive mode in the variable drive system mode on the condition that a malfunction of the drive mode selection switch occurs when the four-wheel drive vehicle is being driven in the variable drive system mode.

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