Four-wheel drive switching control device

Abstract

To provide a 4WD switching control device capable of switching from 2WD to 4WD, even when excessive slippage occurs in a drive wheel.SOLUTION: A 4WD switching control device (90) is mounted in a vehicle (1) which is capable of switching between two-wheel drive and four-wheel drive and comprises a transfer (4) capable of controlling distribution of drive force between drive wheels and driven wheels and a coupling (70) capable of controlling transmission of the drive force that the transfer distributes to the driven wheels. The 4WD switching control device has a control section (90) which controls the transfer and the coupling. When the control section determines that slippage occurs in the drive wheel when switching to the four-wheel drive, the control section first controls the transfer to initiate the distribution of drive force to the driven wheels, and then controls the coupling to initiate transmitting the drive force to the driven wheels.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a 4WD shift control device, and more particularly to a 4WD shift control device that can switch from two-wheel drive to four-wheel drive even when excessive slip occurs in the drive wheels. [Background technology]

[0002] Conventionally, there are known vehicles such as automobiles that can switch the drive mode of the drive wheels from two-wheel drive (2WD) to four-wheel drive (4WD) depending on the road surface conditions while traveling, as disclosed in Patent Document 1, for example. When traveling on normal roads with good grip, this conventional vehicle ensures fuel efficiency by running in 2WD. When traveling on slippery roads such as snowy roads, this vehicle ensures off-road performance by switching the drive mode from 2WD to 4WD. Here, when switching from 2WD to 4WD, for example, if the vehicle is a FR (front engine, rear drive) type, the friction clutch on the front wheel side is first engaged to enable the driving force distributed from the transfer via the front propeller shaft to be transmitted to the front wheels. Then, in this state, when the rotation of the front propeller shaft synchronizes with the rotation of the rear propeller shaft that drives the rear wheels, which are the main drive wheels, in the transfer, the mesh clutch is engaged to connect the front propeller shaft to the power transmission path. As a result, in the vehicle, the driving force is distributed from the transfer to the rear propeller shaft and the front propeller shaft. In an FR type vehicle, the drive mode of the drive wheels is switched from 2WD to 4WD by this procedure and the vehicle is driven.

[0003] Incidentally, in a conventional vehicle, when driving on a snowy road as described above, the drive mode is switched to 4WD. However, at that time, if the drive wheels come into contact with the frozen road surface and slip excessively, and the rotation difference between the drive wheels and the non-drive wheels becomes large, the vehicle may not be able to switch to 4WD. In detail, for example, in the case of a FR type vehicle, if the rear wheels, which are the main drive wheels, slip excessively during 2WD driving, the rear propeller shaft, which transmits the drive force to the slipping rear wheels, will rotate at a high speed. In this state, if the friction clutch on the front wheel side is engaged to switch to 4WD, the front propeller shaft connected to the front wheels, which are non-drive wheels due to the engagement, will rotate at a lower speed than the rear propeller shaft, and a large rotation difference will occur between the propeller shafts. Due to this rotation difference, the rotation between the propeller shafts in the transfer is not synchronized, and the dog clutch cannot be engaged. As a result, in the conventional vehicle, in the above case, the drive mode cannot be switched from 2WD to 4WD and the vehicle cannot be driven. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Patent Application Publication No. WO2015 / 129695 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is devised to solve the above-mentioned problems, and aims to provide a 4WD switching control device that can switch from two-wheel drive to four-wheel drive even when excessive slip occurs in the drive wheels. [Means for solving the problem]

[0006] The 4WD switching control device of the present invention is a 4WD switching control device provided on a vehicle capable of switching between two-wheel drive and four-wheel drive, which has a transfer capable of controlling the distribution of driving force to driven wheels and non-driven wheels, and a coupling capable of controlling the transmission of the driving force distributed from the transfer to the non-driven wheels, and has a control unit that controls the transfer and the coupling, and is characterized in that when the control unit determines that slip is occurring in the driven wheels when switching to four-wheel drive, it controls the transfer to start distributing the driving force to the non-driven wheels, and then controls the coupling to start transmitting the driving force to the non-driven wheels. Effect of the Invention

[0007] According to the 4WD shift control device of the present invention, it is possible to provide a 4WD shift control device that can switch from two-wheel drive to four-wheel drive even when excessive slip occurs in the drive wheels. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an FR vehicle to which a 4WD switching control device according to one embodiment of the present invention is applied. [Diagram 2] FIG. 4 is a diagram for explaining switching of drive modes (conventional control). [Diagram 3] FIG. 2 is a diagram for explaining switching of drive modes when a drive wheel slips (conventional control). [Figure 4] 4A and 4B are diagrams for explaining switching of drive modes when a drive wheel slips (drive wheel slip response control). [Diagram 5] 4 is a flowchart of a process for determining whether or not to execute drive wheel slip response control (FR vehicle). [Figure 6] 1 is a schematic configuration diagram of a FF vehicle to which a 4WD switching control device according to one embodiment of the present invention is applied. [Figure 7] 4 is a flowchart of a process for determining whether or not to execute drive wheel slip response control (FF vehicle). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a FR (front engine, rear drive) vehicle to which a 4WD switching control device according to an embodiment of the present invention is applied. As shown in FIG. 1, the vehicle 1 is a FR type four-wheel drive (4WD) vehicle based on two-wheel drive (2WD) by rear wheels 82, 83. This vehicle 1 employs a standby 4WD that can automatically switch the drive mode from 2WD to 4WD depending on the road surface condition on which the vehicle 1 is traveling. During 2WD traveling, the vehicle 1 performs two-wheel drive by transmitting the driving force of the engine 2 from the transfer device 4 to the rear wheels 82, 83, which are the main drive wheels. During 4WD traveling, the vehicle 1 performs four-wheel drive by further transmitting a part of the driving force of the engine 2 from the transfer device 4 to the front wheels 80, 81. That is, in the vehicle 1, the driving force output from the engine 2 is input to the input shaft 11 of the transfer device 4 via the transmission 3, and is distributed inside the transfer device 4 to the rear wheels 82, 83 side and the front wheels 80, 81 side according to the drive mode.

[0010] The driving force distributed to the rear wheels 82, 83 is output from a rear output shaft (not shown) of the transfer device 4 and input to the rear differential 5 via the rear propeller shaft 12 connected to the rear output shaft. The driving force is then equally distributed to the left and right in the rear differential 5 and transmitted to the left and right rear wheels 82, 83 via the rear axle shafts 15, 16. Meanwhile, the driving force distributed to the front wheels 80, 81 is transmitted from the drive sprocket 4A of the transfer device 4 to the driven sprocket 13 via the transfer chain 4B. A front propeller shaft 14 is extended from the driven sprocket 13 to the front wheel side, and its tip is connected to the front differential 6. Therefore, the driving force transmitted to the driven sprocket 13 is input to the front differential 6 via the front propeller shaft 14, is equally distributed to the left and right in the front differential 6, and transmitted to the left and right front wheels 80, 81 via the front axle shafts 17, 18.

[0011] Of the front axle shafts 17, 18, the front axle shaft 18 connected to the right front wheel 81 is provided with a coupling 70 between the front differential 6 and the front wheel 81. This coupling 70 allows the vehicle 1 to electronically control the driving force distributed to the front wheels, and also reduces power loss in 2WD mode. The front differential 6 is composed of a ring gear, a differential case, side gears, a differential pinion, etc. (none of which are shown). A ring gear that meshes with a pinion gear (not shown) at the tip of the front propeller shaft 14 is fixed to the differential case so as to be rotatable together with the front propeller shaft 14. A differential pinion shaft (not shown) is held in the hollow part of the differential case in a direction perpendicular to the rotation axis of the differential case, and a pair of differential pinions are rotatably supported on both ends of the differential pinion shaft in a direction facing each other. A pair of side gears arranged on the left and right sides of the hollow part of the differential case with the differential pinion shaft as a boundary mesh with these differential pinions. One end of the front axle shafts 17, 18 inserted into the differential case, that is, the end not connected to the front wheels 80, 81, is connected to each of these side gears so as to be rotatable together with the front axle shafts 17, 18. The rear differential 5 is also configured in the same manner as the front differential 6. The operations of the rear differential 5 and the front differential 6 are well known and therefore will not be described here.

[0012] The coupling 70 is configured to separate the front axle shaft 18 into two at the midpoint, provide clutches 72, 73 at the ends of each of the clutches, and engage and disengage the clutches 72, 73 by an actuator 71. The clutches 72, 73 are engaged and disengaged by arbitrarily adjusting the position of the actuator 71 according to an instruction from an electronic control unit (ECU: Electronic Control Unit) 90 that performs overall control of the vehicle 1. For example, in 4WD mode, the ECU 90 adjusts the position of the actuator 71 according to the instruction so that the clutches 72, 73 are engaged, thereby connecting the right front wheel 81 and the front differential 6 via the front axle shaft 18. Therefore, in 4WD mode, the driving force input from the front propeller shaft 14 to the front differential 6 is equally distributed to the left and right in the front differential 6, and is transmitted to the front wheels 80, 81 via the front axle shafts 17, 18. On the other hand, in 2WD, the ECU 90 adjusts the position of the actuator 71 in response to the instruction to release the clutch, thereby releasing the engagement of the clutches 72, 73 by the actuator 71 and disconnecting the right front wheel 81 from the front differential 6. This causes the side gear of the front differential 6 connected to the left front wheel 80 to spin freely, and in 2WD, the front drive system from the front differential 6 to the drive sprocket 4A of the transfer device 4 no longer rotates, thereby reducing power loss. The ECU 90 is mainly composed of a microcomputer, and executes a program read from a storage device (not shown), and performs overall control of the vehicle 1 by detecting the state of the vehicle based on output signals from various sensors arranged in the vehicle 1. The ECU 90 corresponds to the "control unit" of the present invention. In addition, sensors arranged in the vehicle 1 include, in particular, wheel speed sensors that detect the rotation speed of each wheel, and rotation speed sensors that detect the rotation speeds of the rear propeller shaft 12 and the front propeller shaft 14 in the transfer device 4 (none of which are shown).

[0013] Here, the switching of the drive mode will be described with reference to FIG. 2. In the vehicle 1, the switching of the drive mode from 2WD to 4WD is performed in the following procedure. When the ECU 90 switches the drive mode of the drive wheels from 2WD to 4WD, it first adjusts the position of the actuator 71 provided in the coupling 70 to engage the clutches 72, 73 of the coupling 70, which are disengaged in 2WD. By engaging the clutches 72, 73, the rotation of the front wheels 80, 81 is transmitted to the front propeller shaft 14 via the front differential 6, and the propeller shaft 14 starts to rotate (FIG. 2(1)→(2)). Next, the ECU 90 detects the rotation speed of the front propeller shaft 14 and the rotation speed of the rear propeller shaft 12 of the transfer device 4, which drives the rear wheels 82, 83, using a sensor (FIG. 2(2)). Then, when the rotation of the front propeller shaft 14 is synchronized with the rotation of the rear propeller shaft 12, the ECU 90 engages a dog clutch (not shown) provided in the transfer device 4. By engaging this dog clutch, the front propeller shaft 14 is connected to the power transmission path of the transfer device 4, which had been disconnected until then, and distribution of driving force to the front wheels 80, 81 begins, and the vehicle 1 begins to run in 4WD (FIG. 2 (2) → (3)). Note that in this specification, this switching according to the conventional procedure will be referred to as "conventional control."

[0014] However, as described above, when the rear wheels, which are the driving wheels, slip excessively during 2WD driving, and the difference in rotation between the rear wheels, which are the non-driving wheels, becomes large, there are cases in which it is not possible to switch to 4WD. Explaining with reference to FIG. 3, when the rear wheels, which are the driving wheels, slip during 2WD driving, the driving mode is switched to 4WD in a state in which the rotation speed of the rear wheels is higher than the rotation speed of the front wheels, which are the non-driving wheels (FIG. 3(1)). When the clutch of the coupling is engaged in this state, the rotation of the front wheels is transmitted to the front propeller shaft via the front differential by the engagement of the clutch, and the propeller shaft starts to rotate, but the rotation speed is lower than that of the rear propeller shaft. In other words, in this case, since the dog clutch of the transfer device is in a released state, the rotation speed of the front propeller shaft rotated by the front wheels (non-driving wheels) is lower than that of the rear propeller shaft that rotates the slipping rear wheels (driving wheels) (FIG. 3(1)→(2)). Therefore, in vehicle 1, although the vehicle waits for the timing when the rotation of the front propeller shaft will synchronize with the rotation of the rear propeller shaft, the two propeller shafts do not synchronize. As a result, in vehicle 1, the dog clutch of the transfer device remains in the released state and is not engaged, so the drive mode cannot be switched from 2WD to 4WD (Figure 3 (3)).

[0015] In order to deal with this problem, the vehicle 1 of this embodiment is devised as follows so that the vehicle can be switched from 2WD to 4WD even when excessive slip occurs in the drive wheels. In this specification, this devise is called "drive wheel slip response control." The drive wheel slip response control will be described below with reference to FIG. 4. In the vehicle 1, when the rear wheels 82, 83, which are the driving wheels, slip during 2WD driving, the drive mode is switched to 4WD in a state in which the rotation speed of the rear wheels is higher than the rotation speed of the front wheels 80, 81, which are the non-driving wheels (FIG. 4(1)). In order to switch the drive mode from 2WD to 4WD in this state, the ECU 90 first engages the dog clutch provided in the transfer device 4 to connect the front propeller shaft 14 to the power transmission path that drives the rear propeller shaft 12. In this case, the front propeller shaft 14 is not rotating, and there is a rotation difference between the front propeller shaft 14 and the rear propeller shaft 12 that drives the rear wheels 82, 83, but the clutches 72, 73 of the coupling 70 are in a released state. Therefore, in this case, the front propeller shaft 14 is separated from the front wheel side, so that the front propeller shaft 14 can be connected to the power transmission path in the transfer device 4 (FIG. 4(1)→(2)). This connection increases the rotation speed of the front propeller shaft 14 to the rotation speed of the rear propeller shaft 12 (FIG. 4(2)). Then, the ECU 90 adjusts the position of the actuator 71 provided on the coupling 70 to engage the clutches 72, 73 that were in a released state. Engaging the clutches 72, 73 connects the front propeller shaft 14 to the non-driven front wheels 80, 81 that are rotating behind the front wheels via the front differential 6, thereby establishing a power transmission path on the front wheel side (FIG. 4(3)). As a result, driving force is distributed and transmitted from the transfer device 4 to the front wheels 80, 81 through the front propeller shaft 14, and the vehicle 1 begins to run in 4WD mode.

[0016] The above-mentioned drive wheel slip response control is executed when the drive wheels (rear wheels 82, 83 in the vehicle 1 of this embodiment) are slipping excessively, and therefore the execution of this control is determined by the processing of the flowchart shown in Fig. 5. The processing of the flowchart in Fig. 5 executed by the ECU 90 will be described below. In step S1, the ECU 90 determines whether or not a condition for switching the drive mode of the vehicle 1 from 2WD to 4WD is met. This condition is met, for example, when the ECU 90 detects that the vehicle 1 is traveling on a slippery road such as a snowy road based on an output signal from a sensor (such as a wheel speed sensor). This condition is also met when the driver switches the drive mode of the drive wheels to 4WD by operating a rotary-type drive mode changeover switch (both not shown) arranged on the instrument panel inside the vehicle cabin. If the condition is not met, the ECU 90 returns to step S1 and repeats the above process (NO side). On the other hand, if the condition is met, the ECU 90 proceeds to step S2 (YES side). In step S2, the ECU 90 judges whether the rotation speed of the rear wheels is higher than that of the front wheels based on the output signal of the wheel speed sensor. In this judgment, it is preferable to compare the average rotation speeds of the rear wheels 82, 83 and the front wheels 80, 81. If the rotation speed of the rear wheels is higher than that of the front wheels, the ECU 90 can determine that the rear wheels are slipping, so it proceeds to S3 and executes drive wheel slip response control (YES side), and if not, it proceeds to step S4 and executes conventional control (NO side).

[0017] Note that instead of the processing of step S2 described above, the processing of step S2' enclosed by a dashed line on the right side of Fig. 5 may be executed. In this case, in step S2', the ECU 90 determines whether the rotation speed of the rear wheels is higher than the rotation speed of the front wheels + "α" based on the output signal of the wheel speed sensor. Since the amount of slip (rotation speed) of the rear wheels has a width (tolerance range) that is permissible depending on the drive system of the vehicle, this permissible range is set as the dead band "α". Note that the dead band "α" is a value from 0 to n, and when the dead band "α" is set to 0 (zero), the same determination processing as the above step S2 is performed.

[0018] Next, another embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 6 is a schematic diagram of a FF (front engine, front drive) vehicle to which a 4WD switching control device according to an embodiment of the present invention is applied. As shown in FIG. 6, a vehicle 101 according to another embodiment is a FF type four-wheel drive (4WD) vehicle based on two-wheel drive (2WD) by front wheels 180, 181. The vehicle 101 employs a standby 4WD that can automatically switch the drive mode from 2WD to 4WD depending on the road surface condition on which the vehicle is traveling. During 2WD driving, the vehicle 101 performs two-wheel drive by transmitting the driving force of the engine 102 only to the front wheels 180, 181, which are the main driving wheels, by disengaging a dog clutch (not shown) provided in the transfer device 104. On the other hand, during 4WD driving, the vehicle 101 performs four-wheel drive by transmitting a part of the driving force of the engine 102 from the transfer device 104 to the rear wheels 182, 183 via the rear propeller shaft 112 by engaging the dog clutch. That is, in the vehicle 101, the driving force output from the engine 102 is input to the transfer device 104 via the transmission 103. Then, inside the transfer device 104, the input driving force is distributed to the front wheels 180, 181 side and the rear wheels 182, 183 side according to the drive mode.

[0019] The main difference between the vehicle 101 of the second embodiment and the vehicle 1 of the first embodiment is the drive system. That is, in the vehicle 101, the transmission 3 and the front differential 6 of the vehicle 1 are integrated to form a transaxle type transmission 103. In addition, in the transfer device 104 of the vehicle 101, the front propeller shaft 14 and the members and mechanisms for transmitting the driving force thereto in the transfer device 4 of the vehicle 1 are omitted, and the driving force is transmitted to the rear wheels via the rear propeller shaft 112 in 4WD. In addition, in the vehicle 101, the coupling (170) separates the rear axle shaft 116 into two in the middle, and the ends of the two shafts are provided with clutches 172, 173, respectively, and the clutches 172, 173 are connected and disconnected by an actuator 171. Apart from these points, the vehicle 101 of the second embodiment and the vehicle 1 of the first embodiment have the same configuration, so that the description thereof will be omitted.

[0020] In the vehicle 101, the drive mode is switched from 2WD to 4WD in the following procedure. When the ECU 190 switches the drive mode of the drive wheels from 2WD to 4WD, it first adjusts the position of the actuator 171 provided in the coupling 170 to engage the clutches 172, 173 of the coupling 170, which are disengaged in 2WD. The ECU 190 corresponds to the "control unit" of the present invention. By engaging the clutches 172, 173, the rotation of the rear wheels 182, 183, which are non-driven wheels, is transmitted to the rear propeller shaft 112 via the rear differential 105, and the rear propeller shaft 112 starts to rotate. Next, the ECU 190 detects the rotation speed of the drive shaft side member of the dog clutch, which is in a disengaged state and is provided in the transfer device 104 that transmits the driving force to the front wheels 180, 181, which are driven wheels, and the rotation speed of the rear propeller shaft 112, using a sensor (not shown). The sensor is provided in transfer device 104. When the rotation of the rear propeller shaft 112 is synchronized with the rotation of the drive shaft side member (driving force input side), ECU 190 engages the mesh clutch of transfer device 104. By engaging this mesh clutch, rear propeller shaft 112 is connected to the power transmission path of transfer device 104 that was previously disconnected, and distribution of driving force to rear wheels 182, 183 begins, and vehicle 101 starts running in 4WD. In this specification, this switching according to the conventional procedure is referred to as "conventional control."

[0021] As mentioned above, when driving in 2WD mode, if the driven front wheels slip excessively and the difference in rotation between them and the non-driven rear wheels becomes too great, it may not be possible to switch to 4WD. In order to deal with this problem, the vehicle 101 of this embodiment is devised as follows so that the vehicle can be switched from 2WD to 4WD even when excessive slip occurs in the drive wheels. In this specification, this devise is called "drive wheel slip response control." This drive wheel slip response control will be described below. In the vehicle 101, when the front wheels 180, 181, which are the driving wheels, slip during 2WD driving, the driving mode is switched to 4WD in a state in which the rotation speed of the front wheels is higher than the rotation speed of the rear wheels 182, 183, which are the non-driving wheels. In order to switch the driving mode from 2WD to 4WD in this state, the ECU 190 first engages the dog clutch provided in the transfer device 104 to connect the rear propeller shaft 112 to the power transmission path that drives the front wheels 180, 181. In this case, the rear propeller shaft 112 is not rotating, and there is a rotation difference between the rear propeller shaft 112 and the drive shaft side member of the dog clutch, which is in a released state of the transfer device 104 and rotates together with the driving of the front wheels 180, 181. However, since the clutches 172, 173 of the coupling 170 are in a released state and the rear propeller shaft 112 is in a separated state from the rear wheel side, the rear propeller shaft 112 can be connected to the power transmission path in the transfer device 104. In this way, by engaging the dog clutch of the transfer device 104 to connect the rear propeller shaft 112 to the power transmission path, the rotation speed of the rear propeller shaft 112 is increased to the rotation speed of the drive system driving the front wheels 180, 181. Then, the ECU 190 adjusts the position of the actuator 171 provided on the coupling 170 to engage the clutches 172, 173 that are in a released state. By engaging the clutches 172, 173, the rear propeller shaft 112 and the rear wheels 182, 183 that are non-driven wheels and rotated by the rear differential 105 are connected, and a power transmission path on the rear wheel side is established. As a result, the driving force is distributed and transmitted from the transfer device 104 to the rear wheels 182, 183 side through the rear propeller shaft 112, and the vehicle 101 runs in 4WD mode.

[0022] The above-mentioned drive wheel slip response control is executed when the drive wheels (front wheels 180, 181 in the vehicle 101 of this embodiment) slip excessively, and therefore the execution of this control is determined by the process of the flowchart shown in Fig. 7. The process of the flowchart in Fig. 7 executed by the ECU 190 will be described below. In step S101, the ECU 190 determines whether or not a condition for switching the drive mode of the vehicle 101 from 2WD to 4WD is satisfied. This condition is satisfied, for example, when the ECU 190 detects that the vehicle 101 is traveling on a slippery road such as a snowy road based on an output signal of a sensor (such as a wheel speed sensor). This condition is also satisfied when the driver switches the drive mode of the drive wheels to 4WD by operating a rotary type drive mode changeover switch (both not shown) arranged on the instrument panel inside the vehicle cabin. If the condition is not satisfied, the ECU 190 returns to step S101 and repeats the above process (NO side). On the other hand, if the condition is satisfied, the ECU 190 proceeds to step S102 (YES side). In step S102, the ECU 190 judges whether the rotation speed of the front wheels is higher than the rotation speed of the rear wheels based on the output signal of the wheel speed sensor. In this judgment, it is preferable to take the average of the rotation speeds of the front wheels 180, 181 and the rear wheels 182, 183 and compare them. If the rotation speed of the front wheels is higher than the rotation speed of the rear wheels, the ECU 190 can determine that the front wheels are slipping, so the process proceeds to S103 and executes drive wheel slip response control (YES side). On the other hand, if this is not the case, the ECU 190 proceeds to step S104 and executes conventional control (NO side).

[0023] Note that instead of the processing of step S102 described above, the processing of step S102' surrounded by a dashed line on the right side of Fig. 7 may be executed. In this case, in step S102', ECU 190 determines whether the rotation speed of the front wheels is higher than the rotation speed of the rear wheels + "α" based on the output signal of the wheel speed sensor. Since the slip amount (rotation speed) of the front wheels has a width (tolerance range) that is allowable by the drive system of the vehicle, this tolerance range is set as the dead band "α". Note that the dead band "α" is a numerical value from 0 to n, and when the dead band "α" is set to 0 (zero), the same determination processing as the above step S102 is performed.

[0024] As described above, the 4WD shift control device according to the present invention makes it possible to switch from 2-wheel drive to 4-wheel drive even when excessive slip occurs in the drive wheels. [Explanation of symbols]

[0025] 1,101 vehicles 4,104 Transfer device 70,170 Coupling 80,81 Front wheels (FR vehicles) 82,83 rear wheels (FR vehicle) 180,181 Front wheels (FF vehicles) 182,183 rear wheels (FF vehicles) 90,190 ECU (control unit)

Claims

1. A transfer capable of controlling distribution of driving force to driving wheels and non-driving wheels; a coupling capable of controlling the transmission of the driving force distributed from the transfer to the non-driven wheels; A 4WD switching control device provided in a vehicle capable of switching between two-wheel drive and four-wheel drive, a control unit for controlling the transfer and the coupling, When the control unit determines that slippage occurs in the drive wheels when switching to the four-wheel drive, the control unit controls the transfer to start distributing the drive force to the non-drive wheels, and then controls the coupling to start transmitting the drive force to the non-drive wheels. 4WD switching control device.

2. a wheel speed sensor for detecting the rotation speed of each of the drive wheels and the non-drive wheels; The control unit determines that slip is occurring in the drive wheels when a rotation speed of the drive wheels is higher than a rotation speed of the non-drive wheels based on information from the wheel speed sensor.

2. The 4WD switching control device according to claim 1 .

3. The control unit determines whether or not the vehicle is slipping by taking into account the rotation speed of the non-driven wheels and a dead zone width.

3. The 4WD switching control device according to claim 2.

4. 4. The 4WD switching control device according to claim 1, wherein the vehicle is a FR type vehicle, and the driving wheels are rear wheels.

5. 4. The 4WD switching control device according to claim 1, wherein the vehicle is a FF type vehicle, and the driving wheels are front wheels.

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