JP2024126394A - Four-wheel drive vehicle - Google Patents

Abstract

To provide a four-wheel-drive vehicle configured to suppress generation of abnormal noise and vibration when switching a four-wheel-drive state to a two-wheel-drive state.SOLUTION: A four-wheel-drive vehicle 1 can switch between a four-wheel-drive state in which a front motor 23 drives a left-front wheel 13 and a right-front wheel 14 and a rear motor 21 drives a left-rear wheel 11 and a right-rear wheel 12 and a two-wheel-drive state in which clutch devices 6L and 6R of a front-wheel-side driving force transmitting system 4 that transmits driving force to the left-front wheel 13 and the right-front wheel 14 are brought into release states and the rear motor 21 drives the left-rear wheel 11 and the right-rear wheel 12. When the four-wheel-drive state is switched to the two-wheel-drive state, a control device 20 controls the clutch devices 6L and 6R in a fastening state and in the release state, while reducing driving force generated by the front motor 23 down to vibration-suppression torque that can suppress vibration of the front-wheel-side driving force transmitting system 4.SELECTED DRAWING: Figure 1

Description

The present invention relates to a four-wheel drive vehicle in which one of the front and rear wheels is driven by a main drive source and the other is driven by a secondary drive source.

Conventionally, some four-wheel drive vehicles are configured so that one of the front and rear wheels is driven by a main drive source and the other is driven by a secondary drive source. The four-wheel drive vehicle described in Patent Document 1 includes a motor generator as the secondary drive source, a speed reduction mechanism that reduces the rotation of the motor generator, and a differential gear that distributes the torque amplified by the speed reduction mechanism to the left and right wheels, and a switching device composed of a dog clutch or the like is disposed between the differential gear and the drive shaft. When traveling at high speeds, a control device switches the switching device from a transmission state in which torque is transmitted to a blocking state in which torque transmission is blocked so that the rotation speed of the motor generator does not exceed the limit, resulting in a two-wheel drive state.

JP 2020-192922 A (see paragraphs [0030]-[0032])

In a four-wheel drive vehicle configured as described above, when the switching device is switched from the transmission state to the disconnection state, the torsion in the drive force transmission shaft, such as the drive shaft, may be suddenly released, causing abnormal noise and vibration.

The present invention aims to provide a four-wheel drive vehicle that can suppress the generation of abnormal noise and vibration when switching from four-wheel drive to two-wheel drive.

In order to achieve the above object, the present invention provides a four-wheel drive vehicle that includes a pair of left and right main drive wheels, a pair of left and right auxiliary drive wheels, a main drive source that drives the pair of left and right main drive wheels, an auxiliary drive source that drives the pair of left and right auxiliary drive wheels, a differential device to which the driving force of the auxiliary drive source is input, a pair of left and right clutch devices that are respectively arranged between the differential device and the pair of left and right auxiliary drive wheels, and a control device that controls the auxiliary drive source and the pair of left and right clutch devices, and that can switch between a four-wheel drive state in which the pair of left and right auxiliary drive wheels are driven by the auxiliary drive source and the pair of left and right main drive wheels are driven by the main drive source, and a two-wheel drive state in which the pair of left and right clutch devices are in a released state and the pair of left and right main drive wheels are driven by the main drive source, and the control device controls the pair of left and right clutch devices from an engaged state to a released state when switching from the four-wheel drive state to the two-wheel drive state, with the driving force generated by the auxiliary drive wheels reduced to a vibration suppression torque that can suppress vibration in the driving force transmission system that transmits the driving force to the pair of left and right auxiliary drive wheels.

The four-wheel drive vehicle of the present invention makes it possible to suppress the generation of abnormal noise and vibrations when switching from four-wheel drive to two-wheel drive.

1 is a schematic diagram showing an example of the general configuration of a four-wheel drive vehicle according to an embodiment of the present invention; FIG. 2 is a cross-sectional view showing an example of the configuration of a front differential device and a right-side clutch device together with a part of a drive shaft. 5 is a flowchart showing a specific example of a control method executed by the control device when switching from a four-wheel drive state to a two-wheel drive state.

[Embodiment]
An embodiment of the present invention will be described with reference to Figures 1 to 3. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

Figure 1 is a schematic diagram showing an example of the general configuration of a four-wheel drive vehicle 1 relating to an embodiment of the present invention. The four-wheel drive vehicle 1 includes a pair of left and right main drive wheels, a left rear wheel 11 and a right rear wheel 12, a pair of left and right auxiliary drive wheels, a rear motor 21 that is a main drive source that drives the left rear wheel 11 and the right rear wheel 12, a rear inverter 22 that supplies motor current to the rear motor 21, a front motor 23 that is an auxiliary drive source that drives the left front wheel 13 and the right front wheel 14, a front inverter 24 that supplies motor current to the front motor 23, a high-voltage battery 25 connected to the rear inverter 22 and the front inverter 24, a control device 20 that controls the rear motor 21 and the front motor 23, a rear wheel side drive force transmission system 3 that transmits the drive force of the rear motor 21 to the left rear wheel 11 and the right rear wheel 12, and a front wheel side drive force transmission system 4 that transmits the drive force of the front motor 23 to the left front wheel 13 and the right front wheel 14.

The rear inverter 22 switches the DC current supplied from the high-power battery 25 in response to a PWM signal output from the control device 20, and supplies it to the front motor 23 as a motor current. Similarly, the front inverter 24 switches the DC current supplied from the high-power battery 25 in response to a PWM signal output from the control device 20, and supplies it to the front motor 23 as a motor current. The control device 20 can also regeneratively brake the rear motor 21 or the front motor 23 to supply regenerative current from the rear inverter 22 or the front inverter 24 to the high-power battery 25.

The left rear wheel 11 and the right rear wheel 12, and the left front wheel 13 and the right front wheel 14 have wheels 111, 121, 131, 141, and tires 112, 122, 132, 142 mounted on the wheels 111, 121, 131, 141, respectively. The wheels 111, 121, 131, 141 are attached to hub units 113, 123, 133, 143, respectively. Wheel speed sensors 114, 124, 134, 144 that detect the rotational speed of each wheel are attached to the hub units 113, 123, 133, 143, respectively. The control device 20 can obtain information on the rotational speed of the left rear wheel 11 and the right rear wheel 12, and the left front wheel 13 and the right front wheel 14 via an in-vehicle network such as a Control Area Network (CAN).

The rear wheel side driving force transmission system 3 includes a reduction mechanism 31 that reduces the output rotation of the rear motor 21, a rear differential device 32, a left drive shaft 33L arranged between the rear differential device 32 and the hub unit 113 of the left rear wheel 11, and a right drive shaft 33R arranged between the rear differential device 32 and the hub unit 123 of the right rear wheel 12. The rear differential device 32 distributes the driving force of the rear motor 21 amplified by the reduction mechanism 31 to the left rear wheel 11 and the right rear wheel 12 via the drive shafts 33L and 33R. The drive shafts 33L and 33R each have a pair of constant velocity joints 331 and 332, and an intermediate shaft 333 arranged between the constant velocity joints 331 and 332.

The front wheel side driving force transmission system 4 includes a speed reducing mechanism 41 that reduces the output rotation of the front motor 23, a front differential device 5, a left clutch device 6L and a drive shaft 7L between the front differential device 5 and the hub unit 133 of the left front wheel 13, and a right clutch device 6R and a drive shaft 7R between the front differential device 5 and the hub unit 143 of the right front wheel 14. In this embodiment, the left clutch device 6L is disposed between the front differential device 5 and the drive shaft 7L, and the right clutch device 6R is disposed between the front differential device 5 and the drive shaft 7R. The front differential device 5 corresponds to the differential device of the present invention.

The reduction mechanism 41 has an output gear 411 fixed to the output rotating shaft 231 of the front motor 23, and a reduction gear 412 arranged between the output gear 411 and the front differential device 5. The reduction gear 412 has a large diameter gear portion 412a meshed with the output gear 411, a small diameter gear portion 412b that is smaller in diameter than the large diameter gear portion 412a, and a shaft portion 412c that connects the large diameter gear portion 412a and the small diameter gear portion 412b so that they cannot rotate relative to each other.

The drive shafts 7L, 7R each have a pair of constant velocity joints 71, 72 and an intermediate shaft 73 disposed between the pair of constant velocity joints 71, 72. Of the pair of constant velocity joints 71, 72, the constant velocity joint 71 on the front differential device 5 side is a sliding type constant velocity universal joint that allows axial displacement along the rotation axis of the front differential device 5 and tilting relative to this axial direction, while the other constant velocity joint 72 is a fixed type constant velocity universal joint that only allows tilting relative to the axial direction of the intermediate shaft 73.

The clutch devices 6L, 6R are controlled by the control device 20 and are switched between an engaged state and a released state. When the left clutch device 6L is in an engaged state, driving force is transmitted from the front differential device 5 to the left front wheel 13 via the drive shaft 7L, and when the left clutch device 6L is in a released state, the transmission of driving force to the left front wheel 13 is cut off. When the right clutch device 6R is in an engaged state, driving force is transmitted from the front differential device 5 to the right front wheel 14 via the drive shaft 7R, and when the right clutch device 6R is in a released state, the transmission of driving force to the right front wheel 14 is cut off.

The control device 20 controls the rear motor 21, the front motor 23, and the clutch devices 6L, 6R to switch between a four-wheel drive state in which the pair of left and right auxiliary drive wheels, the left front wheel 13 and the right front wheel 14, are driven by the front motor 23 and the pair of left and right main drive wheels, the left rear wheel 11 and the right rear wheel 12, are driven by the rear motor 21, and a two-wheel drive state in which the pair of left and right clutch devices 6L, 6R are released and the left rear wheel 11 and the right rear wheel 12 are driven by the rear motor 21.

Figure 2 is a cross-sectional view showing an example of the configuration of the front differential device 5 and the right clutch device 6R together with a portion of the drive shaft 7R. The left clutch device 6L is configured in the same way as the right clutch device 6R.

The constant velocity joint 71 is a tripod joint having an outer joint member 711, an inner joint member 712, and multiple rollers 713. The outer joint member 711 has a cylindrical cup portion 711a with a bottom and a shaft-shaped stem portion 711b, and a spline fitting portion 711c is provided at the tip of the stem portion 711b. The inner joint member 712 has three leg shafts 712a, and a roller 713 is arranged on the outer periphery of each leg shaft 712a. Figure 2 shows one of the multiple leg shafts 712a and rollers 713. An intermediate shaft 73 is fitted into the center of the inner joint member 712 so that it cannot rotate relative to the center.

The front differential device 5 is an LSD (Limited Slip Differential) with a differential limiting function that suppresses differential rotation between the left front wheel 13 and the right front wheel 14, and includes a differential case 51, a ring gear 52 fixed to the differential case 51, left and right side gears 53, 54, a plurality of first pinion gears 55 meshing with the left side gear 53, a plurality of second pinion gears 56 meshing with the right side gear 54, side washers 57, 58 arranged between the side gears 53, 54 and the differential case 51, and a center washer 59 arranged between the side gears 53, 54. The first pinion gear 55, the second pinion gear 56, and the side gears 53, 54 each have helical teeth formed thereon. The differential case 51 is housed in the differential carrier 81 and is rotatably supported relative to the differential carrier 81 by a pair of bearings 91, 92. As an example, the bearings 91, 92 are tapered roller bearings in which multiple partially conical rolling elements (rollers) are arranged between the inner and outer rings.

2, one of the multiple first pinion gears 55 is shown below the side gears 53, 54, and one of the multiple second pinion gears 56 is shown above the side gears 53, 54. The first pinion gear 55 and the second pinion gear 56 are housed in a retaining hole 510 formed in the differential case 51 and mesh with each other to form a pinion gear set. The differential case 51 has multiple retaining holes 510 formed at equal intervals in the circumferential direction, and each of the multiple retaining holes 510 houses a set of the first pinion gear 55 and the second pinion gear 56. When the left front wheel 13 and the right front wheel 14 rotate at different speeds in the four-wheel drive state, the first pinion gear 55 and the second pinion gear 56 rotate about their respective central axes within the retaining hole 510 while revolving together with the differential case 51.

When the first pinion gear 55 and the second pinion gear 56 rotate within the retaining hole 510, a frictional force is generated between the inner surface 510a of the retaining hole 510 and the tooth tip surface 55a of the first pinion gear 55 and the tooth tip surface 56a of the second pinion gear 56. This frictional force becomes a differential limiting force that suppresses the differential rotation of the left front wheel 13 and the right front wheel 14. In addition, the frictional force generated by the side gears 53, 54 being pressed against the side washers 57, 58 or the center washer 59 by the axial thrust force generated in the side gears 53, 54 due to the meshing of the first pinion gear 55 and the second pinion gear 56 with the side gears 53, 54 also becomes a differential limiting force that suppresses the differential rotation of the left front wheel 13 and the right front wheel 14.

When the left front wheel 13 and the right front wheel 14 rotate differentially due to this differential limiting force, a driving force according to the TBR (Torque Bias Ratio) of the front differential device 5 is transmitted from the left front wheel 13 to the right front wheel 14, or from the right front wheel 14 to the left front wheel 13. Here, TBR is a value obtained by dividing the magnitude of the torque output from the high-torque side gear of the side gears 53, 54 by the magnitude of the torque output from the low-torque side gear when the side gears 53, 54 are rotating differentially. Hereinafter, the torque transmitted between the left front wheel 13 side and the right front wheel 14 side via the front differential device 5 due to this differential limiting force is referred to as TBR-compatible torque.

The differential case 51 has a first case member 511 and a second case member 512, which are joined together by a number of bolts 513. The bolts 513 are inserted through bolt holes 511a, 512a formed in the first case member 511 and the second case member 512, and are screwed into threaded holes 52a formed in the ring gear 52.

The ring gear 52 is meshed with the small diameter gear portion 412b of the reduction gear 412, and the driving force of the front motor 23 amplified by the reduction mechanism 41 is input from the ring gear 52 to the front differential device 5. The front differential device 5 distributes and outputs the input driving force of the front motor 23 from the side gears 53, 54 to the left rear wheel 11 and the right rear wheel 12.

A clutch case 82 that houses a part of the clutch device 6R is fixed to the differential carrier 81 by a number of bolts 83. The clutch case 82 has an insertion hole 820 through which the stem portion 711b of the outer joint member 711 of the constant velocity joint 71 is inserted. A seal member 90 is attached to the insertion hole 820 to prevent foreign matter from entering the inside of the clutch case 82, and the seal member 90 is in elastic contact with the stem portion 711b.

The clutch device 6R has a first clutch member 61 and a second clutch member 62, a sleeve 63 which is a cylindrical meshing member arranged on the outer periphery of the first clutch member 61 and the second clutch member 62, a shift fork 64 which engages with the sleeve 63 and moves back and forth, a guide pin 65 which guides the movement of the shift fork 64, an actuator 66 which operates by a current supplied from the control device 20, and a position sensor 67 for detecting the operating state of the actuator 66.

In FIG. 2, the rotation axis O of the side gears 53, 54 of the front differential device 5 and the first and second clutch members 61, 62 is indicated by a dashed line. Hereinafter, the direction parallel to the rotation axis O is referred to as the axial direction. A plurality of internal teeth 63a are formed on the inner peripheral surface of the sleeve 63, with tooth traces extending in the axial direction.

The first clutch member 61 has a splined engagement portion 611 that engages with the side gear 54 so as not to rotate relative to the side gear 54, a disk-shaped meshing portion 612 on which a number of external teeth 612a are formed that mesh with a number of internal teeth 63a of the sleeve 63, a cylindrical shaft portion 613 provided between the meshing portion 612 and the splined engagement portion 611, and a cylindrical boss portion 614 that protrudes from the meshing portion 612 toward the constant velocity joint 71 side of the drive shaft 7R. The shaft portion 613 is rotatably supported by a bearing 93 relative to the differential carrier 81.

The second clutch member 62 has a cylindrical meshing portion 621 with multiple external teeth 621a that mesh with multiple internal teeth 63a of the sleeve 63, a fitting portion 622 with a fitting hole 622a into which the spline fitting portion 711c of the outer coupling member 711 of the constant velocity joint 71 is fitted so as not to rotate relative to the sleeve 63, and an intermediate portion 623 between the meshing portion 621 and the fitting portion 622. The boss portion 614 of the first clutch member 61 is disposed inside the meshing portion 621, and a bearing 94 is disposed between the meshing portion 621 and the boss portion 614. The fitting portion 622 and the intermediate portion 623 are rotatably supported by bearings 95 and 96 with respect to the clutch case 82. As an example, the bearings 93 to 96 are ball bearings in which multiple spherical rolling elements (balls) are disposed between the inner and outer rings.

The meshing portion 612 of the first clutch member 61 and the meshing portion 621 of the second clutch member 62 are aligned in the axial direction, and the number of teeth and pitch circle diameter of the multiple external teeth 612a, 621a are the same. The sleeve 63 is movable in the axial direction between a release position where it meshes only with the meshing portion 621 of the second clutch member 62, and a fastened position where it meshes with the meshing portion 612 of the first clutch member 61 and the meshing portion 621 of the second clutch member 62.

The position of the sleeve 63 is detected by a position sensor 67. The position sensor 67 is, for example, a proximity switch, and in the example shown in FIG. 2, the position sensor 67 is attached to the clutch case 82 so that the detection signal of the position sensor 67 is in the ON state when the sleeve 63 is in the fastened position. However, the position sensor 67 may be attached so that the detection signal is in the ON state when the sleeve 63 is in the released position, or two position sensors 67 may be attached so that the detection signals are in the ON state when the sleeve 63 is in the released position and when it is in the fastened position. The detection signal of the position sensor 67 is output to the control device 20.

Figure 2 shows a released state where the sleeve 63 is in the released position above the first clutch member 61 and the second clutch member 62, and a fastened state where the sleeve 63 is in the fastened position below the first clutch member 61 and the second clutch member 62. In the released state, the first clutch member 61 and the second clutch member 62 can rotate relative to each other. In the fastened state, the first clutch member 61 and the second clutch member 62 are connected by the sleeve 63 so that they cannot rotate relative to each other, and a driving force is transmitted between the first clutch member 61 and the second clutch member 62.

The sleeve 63 has an annular engagement groove 630 into which the shift fork 64 engages. A through hole 640 is formed in the shift fork 64, and a guide pin 65 is inserted through the through hole 640. The guide pin 65 extends in the axial direction, with one end held by the differential carrier 81 and the other end held by the clutch case 82. The shift fork 64 moves in the axial direction along the guide pin 65 together with the sleeve 63 due to the moving force applied by the actuator 66.

The actuator 66 has a motor 661 to which current is supplied from the control device 20, a linear motion mechanism 662 that converts the rotational motion of the motor 661 into linear motion in the axial direction, and a rod 663 that protrudes in the axial direction from the linear motion mechanism 662. The shift fork 64 is fixed to the tip of the rod 663, and a moving force is applied to the shift fork 64 by the linear motion of the rod 663. The linear motion mechanism 662 is accommodated in an accommodation hole 821 formed in the clutch case 82. A cylindrical bush 84 is arranged between the inner surface of the accommodation hole 821 and the linear motion mechanism 662.

When the clutch device 6R is engaged and the differential case 51 of the front differential device 5 rotates due to the driving force of the front motor 23, the first clutch member 61 and the second clutch member 62 rotate together with the side gear 54, and the driving force is transmitted to the right front wheel 14 via the clutch device 6R and the drive shaft 7R. At this time, a rotational resistance torque is generated by the rolling elements in the bearings 91 to 96 rolling between the inner and outer wheels, and a rotational resistance torque is also generated by the stem portion 711b of the constant velocity joint 71 sliding against the seal member 90. In other words, a torque of a magnitude equal to the output torque output from the side gear 54 of the front differential device 5 minus these rotational resistance torques is transmitted to the drive shaft 7R. The same is true for the left drive shaft 7L.

When the four-wheel drive vehicle 1 is traveling in four-wheel drive mode, the torque transmitted to the left front wheel 13 and the right front wheel 14 causes torsion in the intermediate shaft 73 of the drive shaft 7L or the drive shaft 7R. When switching from four-wheel drive to two-wheel drive, if the clutch devices 6L, 6R are released while torsion is occurring in the intermediate shaft 73 of the drive shafts 7L, 7R, the torsion in the intermediate shaft 73 is suddenly released, which may cause abnormal noise and vibration and cause discomfort to the driver, etc.

For this reason, in this embodiment, when switching from four-wheel drive to two-wheel drive, the control device 20 controls the clutch devices 6L, 6R from an engaged state to a released state while reducing the driving force generated by the front motor 23 to a vibration suppression torque capable of suppressing vibrations in the front wheel side driving force transmission system 4. The vibration suppression torque is a torque smaller than the driving force generated by the front motor 23 in the four-wheel drive state. Next, with reference to FIG. 3, a method for controlling the four-wheel drive vehicle 1 when switching from the four-wheel drive state to the two-wheel drive state will be described in detail.

Figure 3 is a flowchart showing a specific example of a control method executed by the control device 20 when switching from a four-wheel drive state to a two-wheel drive state. In this flowchart, the control device 20 first determines whether the rotational speed difference, which is the difference between the rotational speed of the left front wheel 13 and the rotational speed of the right front wheel 14, is equal to or greater than a threshold value (step S1). This threshold value may be a fixed value or a variable value that changes depending on the vehicle speed.

If the result of the judgment in step S1 is positive (Yes), the control device 20 determines the rotation direction and rotation speed of the first pinion gear 55 and the second pinion gear 56 in the retaining hole 510 of the differential case 51 based on the rotation speeds of the left front wheel 13 and the right front wheel 14 (step S2), and calculates the TBR corresponding torque based on the results obtained in step S2 (step S3).

Next, the control device 20 calculates the rotational resistance torque of the front wheel drive force transmission system 4 based on the rotational speeds of the left front wheel 13 and the right front wheel 14 (step S4). Specifically, the control device 20 calculates the rotational resistance torque of the differential case 51 of the front differential device 5, the first clutch member 61 and the second clutch member 62 of the clutch devices 6L, 6R, and the constant velocity joints 71 of the drive shafts 7L, 7R.

Next, the control device 20 determines which of the left front wheel 13 and the right front wheel 14 is the wheel that rotates at a higher speed (step S5). After that, the control device 20 sets a torque command value, which is a target value of the driving force generated by the front motor 23, based on the calculation result of step S3, the calculation result of step S4, and the judgment result of step S5 (step S6). This torque command value is the magnitude of the vibration suppression torque that can suppress the vibration of the front wheel side driving force transmission system 4, and specifically, it is a value at which the transmission torque of either the left or right intermediate shaft 73 that transmits torque to the wheel that rotates at a higher speed, that is, the wheel of the left front wheel 13 or the right front wheel 14, which has a higher rotation speed, is substantially 0 Nm. In this way, in this embodiment, the torque command value is set based on the calculation result of step S3, so that the driving force generated by the front motor 23 is controlled taking into account the TBR corresponding torque.

Next, the control device 20 controls the front motor 23 so that the magnitude of the driving force generated by the front motor 23 becomes the torque command value set in step S6 (step S7), and when the magnitude of the driving force generated by the front motor 23 substantially matches the torque command value (step S8: Yes), the control device 20 controls the clutch device 6L, 6R that transmits the driving force to the wheel rotating at a higher speed to be in a released state (step S9). Specifically, a current is supplied to the motor 661 of the actuator 66, and the sleeve 63 is moved from the fastened position toward the released position.

Then, the control device 20 determines whether the movement of the sleeve 63 to the release position has been completed (step S10). This determination can be made based on the detection signal of the position sensor 67. Hereinafter, of the clutch devices 6L, 6R, one of the clutch devices that transmits driving force to the wheel on the high-speed rotation side is referred to as the high-speed rotation side clutch device, and the other clutch device is referred to as the low-speed rotation side clutch device.

When the movement of the sleeve 63 of the high-speed rotation clutch device to the release position is completed (step S10: Yes), the control device 20 synchronizes the rotation of the differential case 51 with the rotation of the wheel on the low-speed rotation side, which is the left front wheel 13 or the right front wheel 14, which has a slower rotation speed, by controlling the speed of the front motor 23 (step S11). In other words, the rotation speed of the front motor 23 is controlled to a speed corresponding to the rotation speed of the wheel to which the driving force is transmitted by the low-speed rotation clutch device. Specifically, the rotation speed obtained by multiplying the reduction ratio between the output rotating shaft 231 of the front motor 23 and the differential case 51 by the reduction mechanism 41 is set as the speed specification value and the front motor 23 is controlled. Note that the magnitude of the driving force generated by the front motor 23 at this time is smaller than the torque command value set in step S6 because the high-speed rotation clutch device is in the release state.

Next, the control device 20 determines whether the rotation of the differential case 51 is synchronized with the rotation of the wheel on the lower rotation speed side (step S12), and when these rotations are synchronized, i.e., when the rotation speed of the front motor 23 matches the speed specification value set in step S11 (step S12: Yes), it controls the clutch device on the lower rotation speed side to be released (step S13).

Then, the control device 20 determines whether the movement of the sleeve 63 to the release position has been completed (step S14), and when the movement to the release position has been completed (step S14: Yes), the control device 20 decelerates the front motor 23 (step S15). This deceleration is performed, for example, by regenerative braking of the front motor 23. The control device 20 decelerates the front motor 23 until the rotation of the front motor 23 stops, and when the rotation of the front motor 23 stops (step S16: Yes), the control device 20 ends the processing of the flowchart shown in FIG. 3.

On the other hand, if the result of the judgment in step S1 is negative (No), the control device 20 calculates the rotational resistance torque of the front wheel side driving force transmission system 4 in the same manner as in step S4 (step S17), sets a torque command value for the front motor 23 based on the calculated rotational resistance torque so that the transmission torque of the intermediate shaft 73 is substantially 0 Nm (step S18), and controls the front motor 23 so that the magnitude of the driving force generated by the front motor 23 becomes the torque command value set in step S18 (step S19).

Then, when the driving force generated by the front motor 23 substantially matches the torque command value (step S20: Yes), the control device 20 simultaneously moves the sleeves 63 of the clutch devices 6L, 6R toward the release position, and controls the clutch devices 6L, 6R to be both in the released state (step S21). After that, the control device 20 determines whether the movement of the sleeves 63 of the clutch devices 6L, 6R to the release position is complete (step S22), and when the movement to the release position is complete (step S22: Yes), the control device 20 stops the rotation of the front motor 23 by controlling steps S15 and S16.

In the flowchart shown in FIG. 3, when the result of the determination in step S1 of whether the rotation speed difference between the left front wheel 13 and the right front wheel 14 is equal to or greater than a threshold is affirmative (Yes), a determination is made in step S5 as to which of the left front wheel 13 and the right front wheel 14 is the wheel rotating at a higher speed. However, this is not limiting, and a determination as to which wheel is rotating at a higher speed may also be made in step S1. In addition, when the front differential device 5 does not have a differential limiting function and the TBR is close to 1 (for example, when the TBR is 1.2 or less), it is not necessary to take the TBR torque into consideration.

(Effects of the embodiment)
According to the embodiment described above, when switching from the four-wheel drive state to the two-wheel drive state, the clutch devices 6L, 6R are controlled from the engaged state to the released state while the driving force generated by the front motor 23 is reduced, so that it is possible to suppress the generation of abnormal noise and vibration caused by the sudden release of the torsion of the intermediate shaft 73 of the drive shafts 7L, 7R when the clutch devices 6L, 6R are released. In addition, when the rotation speed difference between the left front wheel 13 and the right front wheel 14 is equal to or greater than a threshold value, the high-speed rotation side clutch device is released before the low-speed rotation side clutch device, so that it is possible to smoothly switch from the four-wheel drive state to the two-wheel drive state without greatly increasing or decreasing the rotation speed of the front motor 23. Furthermore, in this embodiment, the driving force generated by the front motor 23 is controlled in consideration of the TBR corresponding torque, so that it is possible to appropriately suppress the generation of abnormal noise and vibration when switching from the four-wheel drive state to the two-wheel drive state even when the front differential device 5 has a differential limiting function.

(Additional Note)
The present invention has been described above based on the embodiment, but the invention according to the claims is not limited to this embodiment. It should be noted that not all of the combinations of features described in the embodiment are essential to the means for solving the problems of the invention. The present invention can be modified as appropriate by omitting some configurations or adding or replacing configurations without departing from the spirit of the invention. Furthermore, the present invention can be modified as follows, for example.

In the above embodiment, the clutch devices 6L, 6R are disposed between the front differential device 5 and the drive shafts 7L, 7R, respectively. However, instead of this arrangement, clutch devices capable of interrupting the transmission of driving force may be disposed between the drive shafts 7L, 7R and the hub units 133, 143 of the left front wheel 13 and the right front wheel 14, respectively. In this case, the connection between the hub wheels that rotate integrally with the wheels 131, 141 in the hub units 133, 143 and the constant velocity joint 72 is interrupted by an engaging member such as the sleeve 63 in the above embodiment.

In the above embodiment, the clutch devices 6L, 6R are described as being mesh clutches, but this is not limiting, and for example, a friction-type multi-plate clutch may be used. Furthermore, in the above embodiment, the left and right front wheels are described as being auxiliary drive wheels, and the left and right rear wheels are described as being main drive wheels, but the left and right front wheels may be described as being main drive wheels, and the left and right rear wheels as being auxiliary drive wheels.

1...4-wheel drive vehicle 11...Left rear wheel (main drive wheel)
12...Right rear wheel (main drive wheel) 13...Left front wheel (secondary drive wheel)
14...Right front wheel (auxiliary drive wheel) 20...Control device 21...Rear motor (main drive source) 23...Front motor (auxiliary drive source)
4... Front wheel drive force transmission system 5... Front differential device
6L, 6R...Clutch device 7L, 7R...Drive shaft

Claims (5)

a pair of left and right main drive wheels, a pair of left and right auxiliary drive wheels, a main drive source that rotationally drives the pair of left and right main drive wheels, an auxiliary drive source that rotationally drives the pair of left and right auxiliary drive wheels, a differential device to which driving force of the auxiliary drive source is input, a pair of left and right clutch devices that are respectively disposed between the differential device and the pair of left and right auxiliary drive wheels, and a control device that controls the auxiliary drive source and the pair of left and right clutch devices, wherein the four-wheel drive vehicle is switchable between a four-wheel drive state in which the pair of left and right auxiliary drive wheels are driven by the auxiliary drive source and the pair of left and right main drive wheels are driven by the main drive source, and a two-wheel drive state in which the pair of left and right clutch devices are released and the pair of left and right main drive wheels are driven by the main drive source,
When switching from the four-wheel drive state to the two-wheel drive state, the control device controls the pair of left and right clutch devices from an engaged state to a released state in a state in which the driving force generated by the auxiliary drive source is reduced to a vibration suppression torque capable of suppressing vibration of a driving force transmission system that transmits the driving force to the pair of left and right auxiliary drive wheels.
Four-wheel drive vehicle. When switching from the four-wheel drive state to the two-wheel drive state, the control device calculates a rotational resistance torque of the driving force transmission system, and controls the driving force generated by the auxiliary driving source based on the calculated rotational resistance torque to release one of the pair of left and right clutch devices, and then releases the other clutch device.
2. A four-wheel drive vehicle according to claim 1. When switching from the four-wheel drive state to the two-wheel drive state, the control device controls the driving force generated by the auxiliary drive source in consideration of the torque transmitted between the pair of left and right auxiliary drive wheels via the differential device, and brings one of the clutch devices into a disengaged state.
3. A four-wheel drive vehicle according to claim 2. When the other clutch device is in a released state, the control device controls the rotation speed of the auxiliary drive source to a speed corresponding to the rotation speed of the auxiliary drive wheel to which the driving force is transmitted by the other clutch device, of the pair of left and right auxiliary drive wheels.
4. A four-wheel drive vehicle according to claim 2 or 3. When switching from the four-wheel drive state to the two-wheel drive state, the control device determines which of the pair of left and right auxiliary drive wheels is the auxiliary drive wheel on the high-speed rotation side, and controls one of the clutch devices that transmits driving force to the auxiliary drive wheel on the high-speed rotation side as the one of the clutch devices.
4. A four-wheel drive vehicle according to claim 3.

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