Control device for four-wheel drive vehicle

Abstract

To provide a control device for four-wheel drive vehicle capable of exhibiting excellent slip responsiveness without giving discomfort to a user in a four-wheel-drive vehicle adopting a control system that detects occurrence of a slip and increases distribution of driving force to an auxiliary driving wheel.SOLUTION: A control device 100 includes: a traveling state comprehending part 102 for comprehending a traveling state of a vehicle 10; and a first clutch control part 104 that controls the degree of engagement of a first clutch to be transmitted via a clutch 46 for front-wheel drive. The control device 100, under the condition that drive control by a standby control system is performed, can perform control so as to stand by for occurrence of a slip in the state of having the clutch 46 for front-wheel drive engaged at a prescribed standby engagement degree S. The control device 100 gradually or continuously changes the standby engagement degree S in accordance with the state of occurrence of driving force in the vehicle 10.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 temporarily driven by a prime mover, 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 and the first axle. This control system includes a first clutch that disconnectably connects the propeller shaft and the sub-shaft, a second clutch that disconnectably connects the sub-shaft and 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 configuring this control system, Patent Document 1 aims to enable rapid switching between 2WD mode and AWD 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] The inventors have studied potential problems associated with a control system that detects slippage and increases the distribution of driving force to the auxiliary drive wheels in a four-wheel drive vehicle equipped with a first clutch that selectively connects or disconnects a power transmission path between a drive power 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 the auxiliary drive wheels. As a result, they have discovered that, in order to suppress vehicle slippage using such a control system, it is effective to engage the first clutch in advance at a predetermined engagement level (hereinafter also referred to as a "standby engagement level"), assuming a response delay of the first clutch. For example, if the first clutch is hydraulically operated, they have discovered that it is effective to apply a predetermined hydraulic pressure (hereinafter also referred to as a "standby pressure") to the first clutch in advance. This shortens the time required from the detection of slippage until driving force is distributed to the auxiliary drive wheels via the first clutch, thereby suppressing the amount of vehicle slippage.

[0005] On the other hand, it was discovered that if the standby engagement degree (standby pressure) of the first clutch is set high in order to minimize the response delay of the first clutch, so-called tight corner braking will occur when the vehicle is turning, which may cause discomfort to the user.

[0006] Combining these findings, the inventors have come to the conclusion that when a control method is adopted in a four-wheel drive vehicle such as that described above that detects the occurrence of slip and increases the distribution of driving force to the auxiliary drive wheels, it may be possible to improve slip responsiveness without causing discomfort to the user by optimizing the standby engagement degree according to the situation, rather than increasing the standby engagement degree uniformly.

[0007] Therefore, the present invention aims to provide a control device for a four-wheel drive vehicle that employs a control method that detects the occurrence of slippage and increases the distribution of driving force to the auxiliary drive wheels, and that is capable of exhibiting excellent slip response while minimizing the discomfort felt by the user. [Means for solving the problem]

[0008] (1) A control device for a four-wheel drive vehicle of the present invention includes a first clutch that selectively disconnects or connects a power transmission path between a driving force source and a power transmission member, and a second clutch that selectively disconnects or connects a power transmission path between the power transmission member and auxiliary drive wheels, and provides a two-wheel drive state in which driving force is transmitted from the driving force source to left and right main drive wheels by disengaging at least one of the first clutch and the second clutch, and a four-wheel drive state 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, under the condition that occurrence of slip in the four-wheel drive vehicle is detected while the second clutch is engaged. and a variable drive distribution state in which drive control is performed using a standby control method that increases the distribution of drive force transmitted to the auxiliary drive wheels relative to the drive force transmitted to the main drive wheels by changing the degree of engagement of the first clutch. The control device for a four-wheel drive vehicle is used in a four-wheel drive vehicle that can switch drive states between a variable drive distribution state in which drive control is performed using a standby control method that increases the distribution of drive force transmitted to the auxiliary drive wheels relative to the drive force transmitted to the main drive wheels by changing the degree of engagement of the first clutch, and is characterized in that, provided that drive control using the standby control method is being performed, the control device can control the first clutch to wait in a state where it is engaged at a predetermined standby engagement degree in preparation for the occurrence of slippage, and changes the standby engagement degree in a stepwise or continuous manner depending on the propulsive force generation status in the four-wheel drive vehicle.

[0009] The control device for a four-wheel drive vehicle of the present invention, when engaging the first clutch at a predetermined standby engagement degree in preparation for the occurrence of slip, changes the standby engagement degree in a stepwise or continuous manner depending on the propulsive force generation status of the four-wheel drive vehicle, provided that drive control using the standby control method is being performed. As a result, the control device for a four-wheel drive vehicle of the present invention can appropriately control the engagement degree of the first clutch so as to switch to the four-wheel drive state with good responsiveness when slip occurs and minimize the amount of slip, while minimizing the discomfort felt by the user when tight corner braking occurs.

[0010] (2) The control device for a four-wheel drive vehicle of the present invention is preferably characterized in that the accelerator opening in the four-wheel drive vehicle is used as part or all of an indicator of the propulsive force generation status in the four-wheel drive vehicle, and the standby engagement degree is increased as the accelerator opening becomes larger, at least within a predetermined range of accelerator opening.

[0011] Because the control device for a four-wheel drive vehicle of the present invention is configured as described above, the standby engagement degree is set higher the greater the accelerator opening, thereby minimizing the occurrence of slippage. Furthermore, when the control device for a four-wheel drive vehicle of the present invention is configured as described above, the braking force due to tight corner braking increases the greater the accelerator opening, but the driving force also increases when the accelerator opening is large. Therefore, the control device for a four-wheel drive vehicle of the present invention can minimize the discomfort felt by the user due to the generation of braking force due to tight corner braking.

[0012] (3) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the standby engagement degree is changed in a stepwise or continuous manner using at least one of the accelerator opening, throttle opening, fuel cut state, torque generated in the driving force source, and input torque to the transfer case as part or all of an indicator of the propulsive force generation status in the four-wheel drive vehicle.

[0013] The state of propulsive force generation in a four-wheel drive vehicle can be accurately grasped by using one or more pieces of information selected from the above-mentioned accelerator opening, throttle opening, fuel cut status, torque generated in the drive power source, and input torque to the transfer case as indicators. The control device for a four-wheel drive vehicle of the present invention performs control to change the standby engagement degree by utilizing this information. Therefore, the control device for a four-wheel drive vehicle of the present invention can appropriately control the engagement degree of the first clutch so as to switch to the four-wheel drive state responsively when slippage occurs and minimize the amount of slippage, while enabling cornering without the user feeling the occurrence of tight corner braking.

[0014] (4) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the standby engagement degree is changed in a stepwise or continuous manner depending on the occurrence of tight corner braking in the four-wheel drive vehicle.

[0015] With this configuration, the control device for a four-wheel drive vehicle of the present invention can adjust the standby engagement degree taking into account the occurrence of tight corner braking. As a result, the control device for a four-wheel drive vehicle of the present invention can appropriately control the engagement degree of the first clutch so as to switch to the four-wheel drive state responsively when slip occurs and minimize the amount of slip, while further reducing the sense of discomfort felt by the user when tight corner braking occurs.

[0016] (5) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the degree of standby engagement is changed in a stepwise or continuous manner using at least one of the steering angle and lateral acceleration in the four-wheel drive vehicle as part or all of an indicator of the occurrence of tight corner braking in the four-wheel drive vehicle.

[0017] By configuring the control device for a four-wheel drive vehicle of the present invention in this way, it is possible to optimize the degree of standby engagement in accordance with the steering angle and lateral acceleration, which are indicators of tight corner braking. [Effects of the Invention]

[0018] According to the present invention, a control device for a four-wheel drive vehicle that employs a control method for detecting the occurrence of slip and increasing the distribution of driving force to the auxiliary drive wheels can be provided that is capable of exhibiting excellent slip responsiveness while minimizing the discomfort felt by the user in a four-wheel drive vehicle. [Brief explanation of the drawings]

[0019] [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 a method for controlling a front-wheel drive clutch when drive control is performed by a standby control method in the vehicle shown in FIG. [Figure 3] 4 is a timing chart showing changes in the standby engagement degree of the front-wheel drive clutch when the vehicle shown in FIG. 1 performs drive control using a standby control system. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The vehicle 10 is equipped with a selector switch 140 for switching the drive state. The selector switch 140 can be set to any one of three drive states: "2WD," "4WD LOCK," and "4WD AUTO." When the selector switch 140 is set to "2WD," one or both of the front-wheel drive clutch 46 and the dog clutch 94 are disengaged. This puts the vehicle 10 in a state where it drives in two-wheel drive mode. When the selector switch 140 is set to "4WD LOCK," the dog clutch 94 is engaged and the front-wheel drive clutch 46 is fully engaged. This puts the vehicle 10 in a state where it drives in four-wheel drive mode.

[0035] Furthermore, when the selector switch 140 is set to "4WD AUTO," the system is placed in a state (drive distribution variable state) in which drive control is performed using a standby control method that increases the distribution of drive force transmitted to the front wheels 14L, 14R, which are auxiliary drive wheels, relative to the drive force transmitted to the rear wheels 16L, 16R, which are primary drive wheels, by changing the degree of engagement of the front-wheel drive clutch 46 while engaging the dog clutch 94, provided that slippage is detected in the vehicle 10. In other words, when the selector switch 140 is set to "4WD AUTO," the dog clutch 94 is placed in an engaged state, and the system is placed in a standby state in which the front-wheel drive clutch 46 is engaged at a predetermined standby engagement degree S in preparation for the occurrence of slippage. When the changeover 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 to four-wheel drive by fully engaging the front-wheel drive clutch 46 while the mesh clutch 94 is maintained in an engaged state.

[0036] 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, for example, a microcomputer equipped with a CPU, RAM, ROM, an input / output interface, etc. The control device 100 includes a driving state detection unit 102, a first clutch control unit 104 (first clutch control unit), and a second clutch control unit 106.

[0037] The running state grasping unit 102 grasps the running state of the vehicle 10. The running state grasping unit 102 can grasp the state of generation of propulsive force in the vehicle 10 based on information output from sensors and the like provided in the vehicle 10. Specifically, the running state grasping unit 102 can grasp the state of generation of propulsive force in the vehicle 10 using at least one of the accelerator opening, throttle opening, fuel cut state, torque generated in the driving force source 12, and input torque to the transfer 22 of the vehicle 10 as part or all of the indexes. In this embodiment, the running state grasping unit 102 acquires information related to the accelerator opening A from the vehicle 10 side and can grasp the state of generation of propulsive force in the vehicle 10. Furthermore, the running state grasping unit 102 can grasp whether the vehicle 10 is slipping based on the presence or absence of slippage in the rear wheels 16L, 16R, which are the main drive wheels.

[0038] 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. As described above, in this embodiment, the front-wheel drive clutch 46 is a wet 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 torque transmitted to the front propeller shaft 24 by controlling the magnitude of hydraulic pressure acting on the front-wheel drive clutch 46.

[0039] The second clutch control unit 106 controls the operation of the dog clutch 94 to control the torque transmission from the front-wheel drive clutch 46 to the front-wheel differential gear unit 28. 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.

[0040] Here, the above-described control device 100 is characterized by a method of controlling the front-wheel drive clutch 46 when the selector switch 140 is set to "4WD AUTO" and drive control is performed using the above-described standby control method. Below, the control method of the front-wheel drive clutch 46 when drive control is performed using the standby control method for the vehicle 10 will be described in detail in accordance with the flowchart in Figure 2 and with reference to the timing chart in Figure 3.

[0041] (Step 1) In step 1, the control device 100 checks whether the vehicle 10 is in a state where drive control is performed using the standby control method by checking whether the selector switch 140 is set to "4WD AUTO." If it is confirmed that the vehicle 10 is set to "4WD AUTO," the control flow proceeds to step 2 to optimize the standby engagement degree S of the front-wheel drive clutch 46.

[0042] (Step 2) In step 2, the control device 100 engages the dog clutch 94 under the control of the second clutch control unit 106. As a result, when the dog clutch 94 is engaged, the control flow proceeds to step 3.

[0043] (Step 3) In step 3, the control device 100 determines whether or not slippage has occurred in the vehicle 10 using the running state determination unit 102. If it is confirmed that slippage has not occurred, the control flow proceeds to step 4. On the other hand, if slippage has occurred, the control flow proceeds to step 8.

[0044] (Step 4) In step 4, the control device 100 acquires information related to the accelerator opening degree A from the vehicle 10 side in the traveling state grasping unit 102 in order to grasp the propulsive force generation state in the vehicle 10. Thereafter, the control device 100 advances the control flow to step 4.

[0045] (Step 5) In step 5, the control device 100 checks whether the accelerator of the vehicle 10 is open. If the accelerator opening degree A is zero, that is, the accelerator is off, the control flow proceeds to step 5, and if the accelerator is open, the control flow proceeds to step 6.

[0046] (Step 6) When the control flow proceeds from step 5 to step 6, the first clutch control unit 104 of the control device 100 controls the operation of the front-wheel drive clutch 46 so that the front-wheel drive clutch 46 is engaged at the minimum standby engagement degree Smin in preparation for the occurrence of slippage of the vehicle 10. In this embodiment, the front-wheel drive clutch 46 is hydraulically driven, and therefore a hydraulic pressure (minimum standby pressure Pmin) required to engage the front-wheel drive clutch 46 at the minimum standby engagement degree Smin is applied to the front-wheel drive clutch 46 (see FIG. 3).

[0047] Here, the minimum standby engagement degree Smin is an engagement degree that is defined as the minimum value of the engagement degree of the front wheel drive clutch 46 when the vehicle 10 is driven and controlled using the standby control method, and the engagement degree of the front wheel drive clutch 46 is maintained at the minimum standby engagement degree Smin while the accelerator opening degree A is zero.

[0048] (Step 7) On the other hand, when the control flow proceeds from step 5 to step 7, the first clutch control unit 104 performs control to adjust the engagement degree of the front-wheel drive clutch 46 so that the front-wheel drive clutch 46 is engaged at an optimal standby engagement degree S in accordance with the accelerator opening degree A in the vehicle 10. In this embodiment, the standby engagement degree S is set to be the minimum standby engagement degree Smin plus an additional engagement degree Spls that is proportional to the accelerator opening degree A.

[0049] Specifically, the additional engagement degree Spls is derived as a value obtained by multiplying a predetermined constant k by the accelerator opening degree A (Spls = k × A), and the standby engagement degree S is derived as the sum of the additional engagement degree Spls and the minimum standby engagement degree Smin (S = Spls + Smin). In other words, the standby engagement degree S is derived from S = k × A + Smin. In step 7, operation control (hydraulic control in this embodiment) of the front-wheel drive clutch 46 is performed so that the front-wheel drive clutch 46 is engaged at the standby engagement degree S derived in this manner (see FIG. 3).

[0050] (Step 8) When the control flow proceeds from step 3 to step 8 described above, the control device 100 puts the vehicle 10 into a four-wheel drive state. Specifically, the control device 100 increases the engagement degree of the front-wheel drive clutch 46 from the standby engagement degree S, so that the front-wheel drive clutch 46 is fully engaged. This puts the vehicle 10 into a state where it can be driven in four-wheel drive mode.

[0051] The control device 100 mounted on the vehicle 10 described above has the following characteristic configurations (a) and (b), and is therefore able to achieve characteristic effects. Furthermore, the control device 100 can also achieve characteristic effects that could not be achieved by conventional techniques by adopting the following configurations (c) to (e).

[0052] (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 dog 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). By releasing at least one of the front-wheel drive clutch 46 and the dog clutch 94, the control device 100 can select two-wheel drive mode in which driving force is transmitted from the driving force source 12 to the left and right rear wheels 16L, 16R (main drive wheels), and a front-wheel drive mode in which driving force is transmitted to the left and right rear wheels 16L, 16R (main drive wheels). The control device 100 is used in a vehicle 10 capable of switching between a four-wheel drive state in which drive force is transmitted from the drive power source 12 to the left and right front wheels 14L, 14R by engaging the drive clutch 46 and the dog clutch 94, respectively, and a variable drive distribution state in which drive control using a standby control method is performed in which the degree of engagement of the front-wheel drive clutch 46 is changed 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 while the dog clutch 94 is engaged, provided that slippage is detected in the vehicle 10. Furthermore, the control device 100 is capable of controlling the front-wheel drive clutch 46 to wait in a state where it is engaged at a predetermined standby engagement degree S in preparation for slippage, provided that drive control using the standby control method is being performed. The control device 100 is configured to change the standby engagement degree S depending on the propulsive force generation status of the vehicle 10. Therefore, the control device 100 can appropriately control the degree of engagement of the front-wheel drive clutch 46 so as to minimize the discomfort felt by the user when tight corner braking occurs, while responsively switching to four-wheel drive mode when slippage occurs and minimizing the amount of slippage.

[0053] Note that, although the control device 100 of the present embodiment continuously increases the standby engagement degree S in proportion to the magnitude of the propulsive force in accordance with the generation status of the propulsive force in the vehicle 10, the present invention is not limited to this. For example, the control device 100 may control the standby engagement degree S to increase in stages as the propulsive force increases in accordance with the magnitude of the propulsive force of the vehicle 10. Also, in the present embodiment, an example has been shown in which the control device 100 controls the standby engagement degree S to increase in proportion to the magnitude of the propulsive force in the vehicle 10, but the present invention is not limited to this. Specifically, the magnitude of the propulsive force and the magnitude of the standby engagement degree S do not necessarily need to be proportional, and the magnitude of the propulsive force and the magnitude of the standby engagement degree S may be specified based on a predetermined mathematical formula, table, or the like.

[0054] (b) In the control device 100 of this embodiment, the accelerator opening degree A of the vehicle 10 is used as an index of the state of propulsive force generation in the vehicle 10, and the standby engagement degree S is set based on the accelerator opening degree A. Furthermore, the control device 100 is configured to increase the standby engagement degree S the greater the accelerator opening degree A. In this way, the control device 100 can set the standby engagement degree S to an optimal value according to the accelerator opening degree A, minimizing the occurrence of slippage while minimizing any discomfort felt by the user due to the generation of braking force during tight corner braking.

[0055] Note that the control device 100 of this embodiment increases the standby engagement degree S as the accelerator opening degree A increases, and although an example has been shown in which the standby engagement degree S is set in this manner regardless of the magnitude of the accelerator opening degree A, the present invention is not limited to this. For example, the control device 100 may control the standby engagement degree S by setting it higher the greater the accelerator opening degree A, provided that the accelerator opening degree A is within a predetermined range, but may not perform such control when the accelerator opening degree A is outside the predetermined range. More specifically, while the accelerator opening degree A is equal to or less than a predetermined value, the standby engagement degree S may be set higher the greater the accelerator opening degree A, and when the accelerator opening degree A becomes higher than the predetermined value, the standby engagement degree S may not be changed from when the accelerator opening degree A was the predetermined value. That is, the control device 100 may set an upper limit to the magnitude of the standby engagement degree S, and set the standby engagement degree S higher as the accelerator opening degree A increases up to that upper limit, and when the standby engagement degree S has reached the upper limit, the standby engagement degree S may not be set higher than the upper limit even if the accelerator opening degree A increases further. With this configuration, it is possible to prevent the standby engagement degree S from becoming higher than necessary.

[0056] (c) The control device 100 of this embodiment changes the standby engagement degree S in a stepwise or continuous manner using the accelerator depression degree A in the vehicle 10 as an indicator of the state of thrust generation in the vehicle 10. However, the state of thrust generation in the vehicle 10 can be determined by using one or more pieces of information as an indicator instead of or in addition to the accelerator depression degree A. For example, the control device 100 can use at least one of the throttle opening, the fuel cut status, the torque generated in the driving force source 12, and the input torque to the transfer 22, in addition to the accelerator depression degree A, as part or all of an indicator for determining the state of thrust generation in the vehicle 10, and change the standby engagement degree S in a stepwise or continuous manner based on this indicator. This makes it possible to accurately determine the state of thrust generation in the vehicle 10 and to determine it from multiple angles, thereby increasing the possibility of setting the standby engagement degree S to an appropriate value to control the front-wheel drive clutch 46.

[0057] (d) The control device 100 of this embodiment may be configured to change the standby engagement degree S in a stepwise or continuous manner depending on the state of tight corner braking occurring in the vehicle 10.

[0058] With this configuration, the control device 100 can adjust the standby engagement degree S taking into account the occurrence of tight corner braking. As a result, the control device 100 of this embodiment can appropriately control the engagement degree of the front wheel drive clutch 46 so as to switch to four-wheel drive mode with good responsiveness when slippage occurs and minimize the amount of slippage, while further reducing the sense of discomfort felt by the user when tight corner braking occurs.

[0059] (e) Furthermore, the control device 100 of this embodiment may be configured to change the standby engagement degree S in a stepwise or continuous manner using at least one of the steering angle and lateral acceleration of the vehicle 10 as part or all of the indicators of the occurrence of tight corner braking in the vehicle 10.

[0060] By configuring the control device 100 in this manner, it is possible to optimize the standby degree of engagement S in accordance with the steering angle and lateral acceleration, which are indicators of tight corner braking.

[0061] In order to grasp the occurrence of tight corner braking, in addition to the steering angle and lateral acceleration, information obtained from the vehicle 10 such as yaw rate, pressure supplied to the brake booster (master cylinder pressure), brake pressure, tire rotation speed, rate of change of tire rotation speed, deceleration, etc., as well as detection signals from sensors provided on the vehicle 10, can be used as part or all of the indicators.By utilizing this information as well, the control device 100 can optimize the standby engagement degree S according to the steering angle and lateral acceleration, which are indicators of tight corner braking.

[0062] 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 force 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 any of 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). However, the present invention is not limited to this. Any appropriate clutch can be used as the second clutch, such as a wet multi-plate clutch, an electrically controlled clutch, or a clutch whose engagement degree can be adjusted by magnetic force.

[0063] 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]

[0064] 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]

[0065] 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

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 state 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 state 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 distribution state in which drive control is performed using a standby control method in which the degree of engagement of the first clutch is changed while the second clutch is engaged, on the condition that occurrence of slippage in the four-wheel drive vehicle is detected, thereby increasing the distribution of drive force transmitted to the auxiliary drive wheels relative to the drive force transmitted to the main drive wheels; A control device for a four-wheel drive vehicle used in a four-wheel drive vehicle capable of switching a drive state, On the condition that drive control by the standby control method is being performed, control can be performed to wait in a state in which the first clutch is engaged at a predetermined standby engagement degree in preparation for the occurrence of slippage, A control device for a four-wheel drive vehicle, characterized in that while the accelerator opening of the four-wheel drive vehicle is zero, the standby engagement degree is maintained at a minimum standby engagement degree, and the standby engagement degree is changed in a stepwise or continuous manner depending on the propulsive force generation status in the four-wheel drive vehicle.

2. an accelerator opening degree in the four-wheel drive vehicle is used as a part or all of an indicator of a propulsive force generation state in the four-wheel drive vehicle; 2. The control device for a four-wheel drive vehicle according to claim 1, wherein the standby engagement degree is increased as the accelerator opening degree increases, at least within a predetermined range of accelerator opening degree.

3. an accelerator opening degree in the four-wheel drive vehicle is used as a part or all of an indicator of a propulsive force generation state in the four-wheel drive vehicle; 3. The control device for a four-wheel drive vehicle according to claim 1, wherein the standby engagement degree is kept constant when the accelerator opening degree is equal to or greater than a predetermined value.

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