Control device for four-wheel drive vehicle

Abstract

To provide a control device for four-wheel-drive vehicle capable of suppressing occurrence of large shock even if an ignition switch is switched from ON state to OFF state in a state in which torsion is caused on a driving system.SOLUTION: A control device 100 includes: a torsion determination part 102 that determines the generation of torsion in a driving system; and a first clutch control part 104 that controls the degree of engagement of the first clutch to be transmitted via a clutch 46 for front-wheel drive. The control device 100, in the case that torsion in the driving system is generated when an ignition switch is switched from ON state to OFF state, performs engagement degree reducing control that gradually or continuously decreases engagement pressure of the clutch 46 for front-wheel drive.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] As a result of extensive research, the inventors have found that 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 an auxiliary drive wheel, a large shock can occur when the ignition switch is switched from the on state to the off state. More specifically, in a four-wheel drive vehicle such as the one described above, when so-called tight corner braking occurs or when a torsion is generated in the drive system consisting of the propeller shaft, drive shafts, etc., such as after sudden braking, the first clutch is suddenly released when the ignition switch is switched from the on state to the off state, which can suddenly release the torsion in the drive system and cause a large shock.

[0005] Therefore, the present invention aims to provide a control device for a four-wheel drive vehicle that can suppress the occurrence of large shocks even when the ignition switch is switched from the on state to the off state when a twist occurs in the drive system, such as when so-called tight corner braking occurs or after sudden braking. [Means for solving the problem]

[0006] (1) The control device for a four-wheel drive vehicle of the present invention is used in a four-wheel drive vehicle that is equipped with 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 an auxiliary drive wheel, and is switchable between 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. The control device has a torsion determination unit that determines the occurrence of torsion in the drive system, and a first clutch control unit that controls the degree of engagement of the first clutch, and is characterized in that when an ignition switch equipped in the four-wheel drive vehicle is switched from an on state to an off state, the first clutch control unit performs engagement reduction control to gradually or continuously reduce the degree of engagement of the first clutch, provided that the torsion determination unit determines that torsion has occurred in the drive system.

[0007] The control device for a four-wheel drive vehicle of the present invention is configured to perform control (engagement reduction control) to gradually or continuously reduce the degree of engagement of the first clutch when an ignition switch is switched from an on state to an off state, on the condition that it is determined that torsion has occurred in the driveline. As a result, the control device for a four-wheel drive vehicle of the present invention can gradually release the first clutch when the ignition switch is switched to the off state while torsion has occurred in the driveline. Therefore, the control device for a four-wheel drive vehicle of the present invention can suppress the occurrence of shock caused by a sudden release of torsion in the driveline, even if the ignition switch is turned off while torsion has occurred in the driveline.

[0008] (2) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the engagement reduction control reduces the engagement degree of the first clutch through multiple steps, including: a first step of reducing the engagement degree of the first clutch to a sweep start engagement degree that is lower than the engagement degree before the ignition switch is switched from the on state to the off state when the ignition switch is switched from the on state to the off state; and a second step of reducing the engagement degree of the first clutch over time from the sweep start engagement degree after the first step.

[0009] The control device for a four-wheel drive vehicle of the present invention can, when an ignition switch is switched from an on state to an off state while torsion is occurring in the drivetrain, first reduce the degree of engagement of the first clutch to a sweep start engagement degree in a first step, and then reduce the degree of engagement of the first clutch from the sweep start engagement degree over time in a second step. By performing engagement reduction control in this manner, the control device for a four-wheel drive vehicle of the present invention can gradually reduce the degree of engagement of the first clutch while minimizing the time required to release the first clutch, and suppress the occurrence of a large shock associated with a sudden release of torsion in the drivetrain.

[0010] (3) In the control device for a four-wheel drive vehicle of the present invention, the engagement degree reduction control preferably terminates the second step on the condition that the torsion in the drive system is eliminated in the second step, and then performs a third step of releasing the first clutch.

[0011] The control device for a four-wheel drive vehicle of the present invention terminates the second step on the condition that the torsion in the driveline is eliminated in the second step, and performs control to disengage the first clutch in the third step. In this way, the control device for a four-wheel drive vehicle of the present invention can disengage the first clutch after the torsion in the driveline is eliminated, thereby suppressing the occurrence of a large shock due to disengagement of the first clutch. Furthermore, by transitioning from the second step to the third step as described above, the time required to disengage the first clutch can be shortened compared to when the second step is continued and the degree of engagement of the first clutch is reduced until the first clutch is released (disengaged).

[0012] (4) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the torsion determination unit is capable of determining the magnitude of torsion in the drive system using the steering angle as part or all of an index, and the engagement degree reduction control is performed based on the magnitude of torsion in the drive system determined by the torsion determination unit.

[0013] By being configured as described above, the control device for a four-wheel drive vehicle of the present invention can perform engagement reduction control to minimize the shock that occurs when switching from four-wheel drive to two-wheel drive, taking into account the torsion of the drive system that occurs depending on the magnitude of the steering angle.

[0014] (5) The control device for a four-wheel drive vehicle of the present invention may be characterized in that the first clutch is a wet multi-plate clutch whose degree of engagement can be adjusted according to the magnitude of oil pressure, and the first clutch control unit controls the magnitude of the degree of engagement of the first clutch according to the magnitude of oil pressure acting on the first clutch.

[0015] By being configured as described above, the control device for a four-wheel drive vehicle of the present invention can minimize the shock that occurs when switching from four-wheel drive to two-wheel drive when torsion occurs in the drive system, even if a wet multi-plate clutch is used as the first clutch. [Effects of the Invention]

[0016] According to the present invention, a control device for a four-wheel drive vehicle can be provided that can suppress the occurrence of large shocks even when switching from four-wheel drive to two-wheel drive when so-called tight corner braking occurs or when a twist occurs in the drive system, such as after sudden braking. [Brief explanation of the drawings]

[0017] [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 control flow executed by the control device when the vehicle shown in FIG. 1 switches from a four-wheel drive state to a two-wheel drive state. [Figure 3] 4 is a timing chart showing changes in the degree of engagement of the first clutch when the vehicle shown in FIG. 1 switches from a four-wheel drive state to a two-wheel drive state. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 either the front-wheel drive clutch 46 or the dog clutch 94 is disconnected (disengaged), the power transmission path to the front wheels 14L, 14R is cut off, and 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.

[0032] 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 includes a torsion determination unit 102, a first clutch control unit 104 (first clutch control unit), and a second clutch control unit 106.

[0033] The torsion determination unit 102 is configured to determine whether torsion has occurred in the drivetrain of the vehicle 10. The torsion determination unit 102 acquires information such as steering angle, vehicle speed, lateral acceleration, 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. based on detection signals from sensors provided in the vehicle 10, and can use this information as part or all of the indicators to determine whether torsion has occurred in the drivetrain of the vehicle 10.

[0034] Specifically, considering that twisting occurs in the driveline due to tight corner braking, the occurrence of twisting in the driveline of the vehicle 10 can be determined by combining one or more pieces of information, such as steering angle, vehicle speed, lateral acceleration, and yaw rate. Also, considering that twisting occurs due to sudden deceleration, the occurrence of twisting in the driveline of the vehicle 10 can be determined by combining one or more pieces of information, such as pressure supplied to the brake booster (master cylinder pressure), brake pressure, tire rotation speed, rate of change of tire rotation speed, and deceleration. In this embodiment, considering that twisting occurs in the driveline due to tight corner braking under conditions of low vehicle speed and large steering angle, the twisting determination unit 102 determines that twisting has occurred in the driveline of the vehicle 10 when the vehicle speed is equal to or less than a predetermined speed and the steering angle is equal to or greater than a predetermined magnitude.

[0035] 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 degree of engagement based on the engagement pressure of the front-wheel drive clutch 46. 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 torque transmitted to the front propeller shaft 24 by controlling the magnitude of hydraulic pressure acting on the front-wheel drive clutch 46.

[0036] 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.

[0037] Here, the above-described control device 100 is characterized by the control performed when the ignition switch of the vehicle 10 is switched from the on state to the off state. The control performed when the ignition switch of the vehicle 10 is switched from the on state to the off state will be described in detail below in accordance with the flowchart of Fig. 2 and with reference to the timing chart of Fig. 3.

[0038] (Step 1) In step 1, the control device 100 checks whether the ignition switch of the vehicle 10 has been switched from the on state to the off state. If it is confirmed that the ignition switch has been switched to the off state, the control flow proceeds to step 2.

[0039] (Step 2) In step 2, the control device 100 determines whether or not a torsion has occurred in the driveline of the vehicle 10 using the torsion determination unit 102. If no torsion has occurred, the control flow proceeds to step 3. On the other hand, if a torsion has occurred, the control flow proceeds to step 4.

[0040] (Step 3) When the control flow proceeds to step 3, the control device 100 disengages the front-wheel drive clutch 46. Thereafter, the control device 100 proceeds to step 4.

[0041] (Step 4) In step 4, the control device 100 performs processing to switch the dog clutch 94 to a disengaged state under control of the second clutch control unit 106. Thereafter, the control device 100 advances the control flow to step 5.

[0042] (Step 5) When the control flow proceeds to step 5, the control device 100 is shut down, thereby completing the series of controls according to the control flow in FIG.

[0043] (Step 6) On the other hand, if the torsion determination unit 102 determines in step 2 that torsion has occurred in the drivetrain of the vehicle 10, then in step 6 and subsequent steps of the control flow, control is performed to gradually or continuously reduce the degree of engagement of the front-wheel drive clutch 46 (degree of engagement reduction control). In this embodiment, in step 6, as a first step of the degree of engagement reduction control, control is performed to reduce the degree of engagement (engagement pressure) of the front-wheel drive clutch 46 to a predetermined sweep start degree of engagement (sweep start engagement pressure). Here, as shown in FIG. 3 , the sweep start degree of engagement is set to a degree of engagement that is lower than the degree of engagement of the front-wheel drive clutch 46 before the ignition switch of the vehicle 10 is switched from the on state to the off state. When the degree of engagement of the front-wheel drive clutch 46 is reduced to the sweep start degree of engagement, the control flow proceeds to step 7.

[0044] (Step 7) In step 7, as a second step of the engagement degree reduction control, control is performed to reduce (gradually decrease) the engagement degree of the front-wheel drive clutch 46 over time from the sweep start engagement degree. This causes the engagement degree of the front-wheel drive clutch 46 to gradually decrease. When the control to reduce the engagement degree of the front-wheel drive clutch 46 is started in step 7, the control flow proceeds to step 8.

[0045] (Step 8) When the control flow proceeds to step 8, the control device 100 checks whether the torsion in the driveline of the vehicle 10 has been resolved, based on the output signal from the torsion determination unit 102. If the torsion in the driveline of the vehicle 10 has not been resolved, the control flow returns to step 7, and control to reduce the engagement degree of the front-wheel drive clutch 46 continues. On the other hand, if it is confirmed that the torsion in the driveline of the vehicle 10 has been resolved, the control flow proceeds sequentially to steps 3 to 5 described above, and after the front-wheel drive clutch 46 and the dog clutch 94 are disengaged, the control device 100 is shut down. That is, the control device 100 disengages the front-wheel drive clutch 46 in step 3, then disengages the dog clutch 94 in step 4, and then shuts down. This completes the series of controls related to the control flow in FIG. 2.

[0046] As described above, the control device 100 mounted on the vehicle 10 has the following characteristic configurations (a) to (e). Therefore, the control device 100 can achieve the following effects in the vehicle 10.

[0047] (a) As described above, the control device 100 of this embodiment is equipped with a front-wheel drive clutch 46 (first clutch) that selectively disconnects or connects 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 disconnects or connects the power transmission path between the front propeller shaft 24 and the front wheels 14L, 14R (auxiliary drive wheels), and is used in a vehicle 10 that can switch between a two-wheel drive state in which driving force is transmitted from the driving force source 12 to the left and right main drive wheels by disengaging at least one of the front-wheel drive clutch 46 and the mesh clutch 94, and a four-wheel drive state in which driving force is also transmitted from the driving force source 12 to the left and right front wheels 14L, 14R by engaging the front-wheel drive clutch 46 and the mesh clutch 94, respectively. The control device 100 also includes a torsion determination unit 102 that determines whether torsion has occurred in the drivetrain, and a first clutch control unit 104 that controls the degree of engagement of the front-wheel drive clutch 46. In the control device 100 of this embodiment, when an ignition switch provided in the vehicle 10 is switched from an ON state to an OFF state, the first clutch control unit 104 performs engagement reduction control to gradually or continuously reduce the degree of engagement of the front-wheel drive clutch 46, provided that the torsion determination unit 102 determines that torsion has occurred in the drivetrain. This allows the control device 100 to gradually release the front-wheel drive clutch 46 when the ignition switch is switched to an OFF state while torsion has occurred in the drivetrain. Therefore, the control device 100 of this embodiment can suppress shock caused by a sudden release of torsion in the drivetrain, even if the ignition switch is switched to an OFF state while torsion has occurred in the drivetrain.

[0048] (b) Furthermore, as described above, when the ignition switch is switched from the on state to the off state while torsion is occurring in the drivetrain, the control device 100 can first reduce the degree of engagement of the front-wheel drive clutch 46 to the sweep start engagement degree in a first step, and then reduce the degree of engagement of the front-wheel drive clutch 46 over time from the sweep start engagement degree in a second step. This allows the control device 100 to gradually reduce the degree of engagement of the front-wheel drive clutch 46 while minimizing the time required to release the front-wheel drive clutch 46, thereby preventing large shocks from occurring due to the sudden release of torsion in the drivetrain.

[0049] In this embodiment, when the engagement degree of the front wheel drive clutch 46 is reduced by the engagement degree reduction control, the engagement degree of the front wheel drive clutch 46 is first reduced to the sweep start engagement degree in the first step (corresponding to step 6), and then the engagement degree of the front wheel drive clutch 46 is reduced over time in the second step (corresponding to step 7). However, the present invention is not limited to this.

[0050] Specifically, the control device 100 may not include a first step of reducing the engagement degree of the front-wheel drive clutch 46 to the sweep start engagement degree, but may instead control the front-wheel drive clutch 46 to reduce its engagement degree at a predetermined rate over time, as in the second step of this embodiment, from when the ignition switch is switched from the on state to the off state. Furthermore, the control device 100 may vary the rate of reduction in the engagement degree per unit time, rather than reducing the engagement degree of the front-wheel drive clutch 46 at a substantially constant rate over time in the second step as in this embodiment. Furthermore, the control device 100 may reduce the engagement degree of the front-wheel drive clutch 46 in a stepwise (stage-like) manner, rather than continuously reducing the engagement degree of the front-wheel drive clutch 46 in the second step (corresponding to step 7) as in this embodiment.

[0051] (c) The control device 100 of this embodiment is configured to end the second step (corresponding to step 7) of the engagement degree reduction control on the condition that the torsion in the drive system is eliminated (corresponding to step 8) while the engagement degree of the front-wheel drive clutch 46 is being reduced in the second step, and to perform a third step (corresponding to step 3) of disengaging the front-wheel drive clutch 46. This enables the control device 100 to minimize the time required for the front-wheel drive clutch 46 to be disengaged, while suppressing the occurrence of a large shock due to the disengagement of the front-wheel drive clutch 46.

[0052] In this embodiment, the gradual reduction in the degree of engagement of the front-wheel drive clutch 46 is stopped and the front-wheel drive clutch 46 is released on the condition that the torsion in the drive system is eliminated while the degree of engagement of the front-wheel drive clutch 46 is being gradually reduced in step 7, but the present invention is not limited to this. For example, the control device 100 may not perform control corresponding to the third step, but may continue the step (second step) of gradually reducing the degree of engagement of the front-wheel drive clutch 46 until the front-wheel drive clutch 46 is released (disengaged state).

[0053] (d) In the control device 100 of this embodiment, the torsion determination unit 102 can determine the magnitude of torsion in the driveline using the steering angle as part or all of an index, and engagement degree reduction control is performed based on the magnitude of torsion in the driveline determined by the torsion determination unit 102. This allows the control device 100 to perform engagement degree reduction control in consideration of the torsion in the driveline that occurs depending on the magnitude of the steering angle, so as to minimize the shock that occurs after the ignition switch is switched from the on state to the off state.

[0054] The torsion determination unit 102 may determine the magnitude of torsion in the drivetrain using only the steering angle as an index, or may determine the magnitude of torsion using other indexes in addition to or instead of the steering angle. Specifically, as described above, the torsion determination unit 102 can acquire information such as the steering angle, vehicle speed, lateral acceleration, 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. based on detection signals from sensors provided in the vehicle 10, and use this information as part or all of the indexes to determine the occurrence of torsion in the drivetrain of the vehicle 10.

[0055] (e) In the control device 100 of this embodiment, the front-wheel drive clutch 46 is a wet multi-plate clutch whose degree of engagement can be adjusted according to the magnitude of hydraulic pressure, and the first clutch control unit 104 controls the magnitude of the degree of engagement of the front-wheel drive clutch 46 according to the magnitude of the hydraulic pressure (engagement pressure) acting on the front-wheel drive clutch 46. As a result, even when a wet multi-plate clutch is used as the front-wheel drive clutch 46, the control device 100 can minimize the shock that occurs when the ignition switch is switched from the on state to the off state while torsion is occurring in the drive system.

[0056] 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.

[0057] 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]

[0058] 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]

[0059] 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: Twist judgment 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 control device for a four-wheel drive vehicle used in a four-wheel drive vehicle that can be switched between a torsion determination unit that determines whether torsion has occurred in the drivetrain; a first clutch control unit that controls the degree of engagement of the first clutch; and When an ignition switch provided in the four-wheel drive vehicle is switched from an on state to an off state, the first clutch control unit releases the first clutch on the condition that the torsion determination unit determines that no torsion has occurred in the drivetrain, and performs engagement degree reduction control to gradually or continuously reduce the engagement degree of the first clutch on the condition that the torsion determination unit determines that torsion has occurred in the drivetrain, the torsion determination unit is capable of determining the magnitude of torsion of the drivetrain, The first clutch control unit performs the engagement degree reduction control on the condition that the magnitude of torsion in the drive system determined by the torsion determination unit is equal to or greater than a certain value.

2. The engagement degree reduction control a first step of reducing, when the ignition switch is switched from an on state to an off state, a degree of engagement of the first clutch to a sweep start degree of engagement that is lower than a degree of engagement before the ignition switch is switched from an on state to an off state; a second step of decreasing the engagement degree of the first clutch from the sweep start engagement degree over time after the first step; 2. The control device for a four-wheel drive vehicle according to claim 1, wherein the degree of engagement of the first clutch is reduced through a plurality of steps including:

3. 3. The control device for a four-wheel drive vehicle according to claim 2, wherein the engagement degree reduction control terminates the second step on the condition that the torsion in the drive system is eliminated in the second step, and performs a third step of disengaging the first clutch.

Images