JP2563113B2 - Drive mode switching control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention is capable of switching the driving state of a vehicle between a two-wheel driving state and a four-wheel driving state, and in the four-wheel driving state, front wheels and rear wheels. The center differential that distributes and transmits power to the side can be switched between the locked state and the free state,
The present invention relates to a drive mode switching control device for a four-wheel drive vehicle capable of further freeing the idle wheel side in the two-wheel drive state.

<< Prior Art >> Conventionally, in addition to a 2/4 switching mechanism that switches the driving state of a vehicle from a two-wheel driving state to a four-wheel driving state, a transfer including a center differential switching mechanism that switches the center differential between a locked state and a free state. The device is known from "Power split device for vehicle" of JP-A-60-127232.

That is, the transfer device of this type will be described by taking the above-mentioned "vehicle power split device" as an example. As shown in FIG. 18, the output shaft b from the auxiliary transmission a is directly connected to the input member d of the center differential c. One of the output shafts e of the center differential c is formed hollow and is arranged coaxially with the output side b. A hub portion f is integrally formed at the shaft end portion of the output shaft e from the center differential c, and a hub portion g is integrally formed on the output shaft b from the auxiliary transmission a so as to face the hub portion f. Are formed.

A power take-off gear i of a chain transmission mechanism h for transmitting power to either the front wheel side or the rear wheel side is rotatably fitted to the output shaft e from the center differential c. A spline piece j is integrally formed with the center differential c so as to face a hub portion f provided on the output shaft e.

Then, this spline piece j and the above two hub parts
A coupling sleeve k slidably fitted to them is provided on the outer periphery of f and g. The coupling sleeve k is slidably moved in the axial direction, so that the power transmission state Can be switched between a two-wheel drive state and a four-wheel drive / center differential lock state or a four-wheel drive / center differential free state.

That is, the coupling sleeve k is connected to the two hub parts f and g.
When the two are engaged, the input member d of the center differential c and one output shaft e rotate integrally, and the rotation of the output shaft b of the auxiliary transmission a is transmitted to the other output shaft l of the center differential c. Is
At this time, the power take-off gear i of the chain transmission mechanism h
Does not rotate and is in a two-wheel drive state.

Further, when the coupling sleeve k is engaged with the three hub parts f and g and the spline piece j, the rotation of the output shaft b of the auxiliary transmission a also applies to the power take-off gear i of the chain transmission mechanism h. Power is transmitted, and at this time, the center differential c is locked and power is transmitted to the front wheel side and the rear wheel side. That is, a four-wheel drive / center differential lock state is set.

Further, the coupling sleeve k is connected to the hub portion f of one output shaft e of the center differential c and the power take-off gear i.
When the two transmission shafts e and l are engaged with each other, the rotation of the output shaft b of the auxiliary transmission a is transmitted to the input member d of the center differential c.
And the rotation of one of the output shafts e is transmitted to the power take-off gear i of the chain transmission mechanism h to be in the four-wheel drive / center differential free state. At this time, since the center differential c is in a free state, a torque corresponding to the load is distributed to the front and rear wheels.

Further, the transfer device as described above is provided so that the two-wheel drive state and the four-wheel drive state can be switched.
In the case of a two-wheel drive vehicle, the idle wheel side in the two-wheel drive state is free from the power transmission system such as the axle shaft by a freewheel device as disclosed in JP-A-56-135320. 2/4 of the above transfer
It is also known to stop the rotation of the power transmission system from the switching mechanism to the freewheel device, thereby improving the fuel economy of the two-wheel drive shaft.

By the way, in a four-wheel drive vehicle including the transfer device and the freewheel device as described above, when the drive state is switched from the two-wheel drive state to the four-wheel drive / center differential free state, the switching procedure is restricted. Occurs.

That is, by connecting the power transmission system from the drive mode switching mechanism (2/4 switching mechanism) whose rotation is stopped in the two-wheel drive state to the freewheel device to the engine side and the idle wheel side, In order to transmit the engine power to the idle wheels, first the drive mode switching mechanism of the transfer device is set to four-wheel drive / center differential lock state, the freewheel device is set to the lock state, and then the drive mode switching mechanism is set to four-wheel drive / Center differential free state is required.

In other words, if the drive mode switching mechanism is set to the four-wheel drive / center differential free state before the freewheel device is locked, the center differential outputs the load of one of the output shafts of the other output shaft that always transmits power. Since it is much lighter than the load, almost all of the power is distributed to the one output shaft side where the load is light. Then, almost no power is transmitted to the drive wheel on the other output shaft side, and the vehicle cannot maintain the traveling state. Further, in such a situation, it is impossible to lock the freewheel device because of the strength of the synchronization mechanism portion of the freewheel device.

On the other hand, if the freewheel device is locked before the drive mode switching mechanism is set to the four-wheel drive / center differential lock state, the front wheels and the rear wheels rotate at the same speed when the vehicle is traveling straight at a constant speed. Good when you are
When there is a difference in rotation speed between the front wheels and the rear wheels, such as when accompanied by cornering or acceleration / deceleration, the load applied to the synchronization mechanism section when the drive mode switching mechanism is activated becomes large. Operation becomes impossible from the viewpoint of strength.

Therefore, when these switching operations are electrically controlled, the switching of the center differential between the locked state and the free state and the switching between the two-wheel driving state and the four-wheel driving state respectively correspond. It is general that the changeover switch is operated by the changeover operation, but when the changeover switches are operated together to change over from the two-wheel drive state to the four-wheel drive / center differential free state, the above procedure is performed. Therefore, first, set the drive mode switching mechanism to 2
From wheel drive state to 4 wheel drive / center differential lock state,
Next, after the free wheel device is locked, the drive mode switching mechanism is shifted to the four-wheel drive / center differential free state.

On the contrary, when the switching operation from the four-wheel drive / center differential free state to the two-wheel drive state is performed, when the transmission of the driving force is interrupted, there is no problem in the strength of the synchronization mechanism portion. After switching the switching mechanism from the four-wheel drive / center differential free state to the two-wheel drive state by passing through the four-wheel drive / center differential lock state, the freewheel device is switched to the free state. The wheels are driven to reduce the load on the engine and improve fuel efficiency.

For this reason, in such a drive mode switching control device, a detection means for accurately knowing the actual switching movement position of the drive mode switching mechanism is indispensable. Conventionally, a position sensor is used as the switching movement position detecting means. Are used.

<< Problems to be Solved by the Invention >> By the way, in the conventional drive mode switching control device, it is impossible to switch the drive mode appropriately when the detecting means for the switching movement position fails.

That is, for example, if the drive mode detection means fails,
The switching position of the drive mode switching mechanism cannot be detected, and control by the switching control device cannot be executed. In this case, as a countermeasure against a failure, it is conceivable to fix the drive mode to one drive mode set at the switching stroke end (for example, two-wheel drive state), but if the drive mode at the time of failure is limited to one in this way, However, there is a possibility that the vehicle may not be suitable for the running state at that time.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a drive mode switching mechanism to a drive mode that is as suited as possible to the running state at that time when the drive mode detection means fails. An object of the present invention is to provide a drive mode switching control device for a four-wheel drive vehicle that can be switched and set.

<< Means for Solving the Problems >> In order to achieve the above-mentioned object, the present invention has a drive mode of a transfer device having a center differential including two-wheel drive, four-wheel drive / center differential lock, and four-wheel drive / center differential free. And a drive mode switching mechanism of a clutch gear type that passes through a four-wheel drive / center differential lock mode during switching between the two-wheel drive mode and the four-wheel drive / center differential free mode. Drive mode detection means for detecting the actual switching movement position of the switching mechanism, and switching of the idle wheel side in the two-wheel drive state between the free state and the locked state with respect to the power transmission system from the transfer device, four-wheel drive And a freewheel device for detecting the free state and the locked state of the freewheel device. Drive mode switching means based on output signals from the driver state detection means, an operation means operated by a driver to select the drive mode, and the operation means, the drive mode detection means, and the freewheel state detection means. When the operation of the mechanism and the freewheel device is controlled and the output signal from the drive mode detecting means is abnormal, the output signal from the freewheel state detecting means is given priority over the output signal from the operating means. A control means for switching the drive mode switching mechanism to a two-wheel drive state position or a four-wheel drive / center differential free state position according to the drive mode switching mechanism is provided.

<< Operation >> According to the present invention having the above configuration, when the output signal from the drive mode detection means is abnormal, the control means considers that the drive mode detection means has failed, and thereafter outputs the output signal from the operation means. Regardless of this, the operation of the drive mode switching mechanism is controlled as follows in accordance with the output signal from the free wheel state detecting means.

That is, if the freewheel state detecting means detects the locked state of the freewheel device, the drive mode switching mechanism is moved to the four-wheel drive / center differential free mode position to change the drive state of the vehicle to the four-wheel drive / center differential. Free it and keep it. On the other hand, if the freewheel state detecting means detects the free state of the freewheel device, the drive mode switching mechanism is moved to the two-wheel drive mode position to bring the vehicle into the two-wheel drive state and maintain the same. . At this time, since the two-wheel drive mode position and the four-wheel drive mode position are at both ends of the moving position of the drive mode switching mechanism, the drive mode switching mechanism can be reliably operated even if the drive mode detecting means is out of order. It can be positioned at a position as suitable as possible for the running state at the time.

«Examples» Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows a part-time four-wheel drive vehicle according to an embodiment of the present invention, 1 is a vehicle body of the vehicle, 2 is an engine mounted at a front end of the vehicle body 1 in a so-called vertical position, and 3 is an engine 2 of the vehicle. Is a manual transmission that shifts the output rotation of the vehicle, and a transfer device 9 is disposed behind the transmission 3, and the transfer device 9 includes front wheels 7, 7 and rear wheels that are idle wheels in the two-wheel drive mode. The wheels 8 and 8 are drive-coupled to each other via front and rear differential mechanisms 5 and 6 each including a Bevel gear mechanism.

The transfer device 9 has a transfer case 10 connected to a case 3a of the transmission 3 and an output shaft 3b of the transmission 3 is provided in the transfer case 10 as shown in FIG. Input shaft 11 arranged on the same axis
And a front wheel side output shaft arranged in parallel to the side of the input shaft 11.
An input shaft 11 and a rear wheel side output shaft 13 arranged on the same axis behind the input shaft 11 (to the right in the figure) are rotatably supported. At the front end portion of the input shaft 11, that is, the end portion on the transmission 3 side, a reduction mechanism 14 for reducing the rotation transmitted from the engine 2 to the wheels 7 and 8 is provided. This reduction mechanism 14
A sun gear 15 rotatably supported on the input shaft 11 and a plurality of pinions 16, 16 spline-coupled to the input shaft 11 at the rear of the sun gear 15 so as to rotate integrally therewith and mesh with the sun gear 15.
A pinion carrier 17 that carries ... And each pinion 16 described above.
A planetary gear mechanism having a ring gear 18 that meshes with the ring gear 18, and the ring gear 18 has a tooth portion 18 formed on its outer peripheral surface.
a is meshed with a tooth portion 10a formed on the inner surface of the transfer case 10, and is fixed to the transfer case 10 in a non-rotatable manner. On the other hand, on the outer periphery of the front end portion of the sun gear 15, the spline tooth portion 15a for the sun gear is provided on the pinion carrier 17
At the inner circumference of the front end of the
a are formed respectively. A cylindrical member 19 whose front end is spline-coupled to the output shaft 3b of the transmission 3 is integrally arranged around the front end portion of the input shaft 11, and the outer peripheral surface of the rear end portion of the cylindrical member 19 is used for the sun gear. A spline tooth portion 19a having the same diameter as the spline tooth portion 15a is formed, and a sleeve 20 having an inner peripheral spline tooth portion 20a capable of meshing with the sun gear spline tooth portion 15a at the rear end is slid on the spline tooth portion 19a. The sleeve 20 is movably and rotatably integrally spline-coupled, and a spline tooth portion 20b capable of meshing with the pinion carrier spline tooth portion 17a is formed on the outer peripheral surface of the rear end of the sleeve 20. Then, the sleeve 20 is slid on the cylindrical member 19 so that the outer peripheral spline tooth portion 20b becomes the pinion carrier spline tooth portion 17a or the inner peripheral spline tooth portion 2
0a is selectively meshed with the sun gear spline tooth portion 15a to control the operation of the speed reduction mechanism 14 to switch the power transmission ratio to the wheels 7 and 8 to a high speed state or a low speed state, and the sleeve 20 is illustrated. Is positioned at the front high speed position PH as shown by the solid line, and the outer peripheral spline tooth portion 20b
Is engaged with the tooth portion 17a for the pinion carrier, the output shaft 3b of the transmission 3 is directly connected to the transfer input shaft 11 via the pinion carrier 17 so as to rotate integrally therewith.
By transmitting the rotation of 3b to the input shaft 11 as it is without decelerating, the power transmission ratio is set to a high speed state, while the sleeve 20
Is positioned at the low speed position PL on the rear side as shown by the phantom line, and the inner peripheral spline tooth portion 20a is set to the tooth portion 15a for the sun gear.
, The transmission output shaft 3b is connected to the sun gear 15,
The H / L switching mechanism 21 is configured to reduce the power transmission ratio by transmitting the power to the transfer input shaft 11 via each pinion 16 and the pinion carrier 17 and decelerating the rotation thereof.

On the other hand, a planetary gear type center differential 22 is arranged at the rear end of the transfer input shaft 11. The sun gear 23 of the center differential 22 is rotatably supported on the input shaft 11, and the pinion carrier 25 carrying each pinion 24 is spline-coupled to the input shaft 11 on the rear side of the sun gear 23 in a rotationally integrated manner. It is connected to the wheel-side output shaft 13 so as to rotate together.

Further, a drive sprocket 27 is rotatably supported on the input shaft 11 on the front side of the center differential 22, and between the sprocket 27 and a driven sprocket 28 rotatably integrated on the front wheel side output shaft 12. A chain 29 is wound around, and the rotation of the input shaft 11 side is transmitted to the front wheel side output shaft 12 by the chain 29.

Further, the sun gear 23 and the ring gear 26 of the center differential 22 are respectively extended forward, and a clutch hub 30 having a spline tooth portion 30a on the outer peripheral surface is rotatably connected to the front end of the extended portion of the sun gear 23. On the other hand, ring gear 26
Of the clutch hub is rotatably supported on the outer periphery of the extension of the sun gear 23.
30 Spline tooth portion 30a having the same diameter as the outer spline tooth portion 30a
Are formed. The drive sprocket 27 is extended to the rear side, and the clutch hub is attached to the outer periphery of the extended portion.
30 Spline teeth 27a of the same diameter as spline teeth 30a on the outer circumference
Are formed. Further, a sleeve 31 is slidably spline-coupled to the spline tooth portions 30a, 26a, 27a of the clutch hub 30, the ring gear 26 of the center differential 22, and the drive sprocket 27 by the inner peripheral spline tooth portion 31a. Then, by sliding the sleeve 31 in the front-rear direction, the center differential 22 is switched to the free state or the locked state, and the drive state is switched to the two-wheel drive state or the four-wheel drive state, respectively. When the vehicle is positioned at the front end four-wheel drive / center differential free position P4F, the clutch hub 30 and the drive sprocket 27 are rotationally integrally connected to each other to bring about a four-wheel drive state, and the ring gear 26 and the sun gear 23 of the center differential 22 are connected. The center differential 22 is brought into a free state by disconnecting. When the vehicle is positioned at the front-rear intermediate four-wheel drive / center differential lock position P4L, the clutch hub 30 and the drive sprocket 27 are rotationally integrally connected to each other so as to be in a four-wheel drive state, and the ring gear of the center differential 22 is also arranged. 26 and the sun gear 23 are connected to bring the center differential 22 into a locked state. Further, as shown by the solid line in the figure, the sleeve 31 has a rear end two-wheel drive position P2.
When it is positioned at, the ring gear 26 of the center differential 22 and the sun gear 23 are connected to each other to lock the center differential 22, while the clutch hub 30 and the drive sprocket 27 are disconnected from each other to switch to the two-wheel drive state. A drive mode switching mechanism 32 is configured. Therefore, in this embodiment, the drive mode switching mechanism 32 constitutes the first switching mechanism and the second switching mechanism.

Further, as shown in FIG. 2, a shift rod 33 for controlling switching of the drive mode switching mechanism 32 is slidably supported on the transfer case 10, and the drive mode is mounted on the shift rod 33. Sleeve 31 of switching mechanism 32
Shift fork 34 that engages with and slides the sleeve 31
Has been fixed. A cam shaft 35, which is cam-coupled to the shift rod 33 and drives the rod 33 by rotation, is rotatably supported on the transfer case 10 on the side of the shift rod 33. It is drivingly connected to the attached electric motor 36, and the operation of the motor 36 controls the operation of the drive mode switching mechanism 32.
36 Rotate the sleeve 31 forward (left in the figure) by rotating it in one direction (CCW direction), and slide the sleeve 31 backward (right in the figure) by rotating it in the other direction (CW direction). It is configured to switch the free state, the locked state, and the two-wheel drive state or four-wheel drive state of the drive state.

In addition, as shown in FIG.
The mode 10 is provided with a mode detecting means 37 for detecting the actual switching movement position of the drive mode switching mechanism 32 based on the movement position of the shift rod 33. This mode detection means 37
In the illustrated example, three micro switches A, B, and C are provided, and when the drive mode switching mechanism 32 is in the two-wheel drive mode position P2, the switch A is turned on, and the four-wheel drive / center differential lock mode position P4L. Switch B is ON when
The switch C is turned on when the four-wheel drive / center differential free mode position P4F is set. Then, when the drive mode switching mechanism 32 is moved, if it is located between the two-wheel drive mode 2H and the four-wheel drive / center differential lock mode 4HL, both the switches A and B are turned on and the four-wheel drive is performed. Drive / Center differential lock mode 4HL
If it is located between the four-wheel drive / center differential free mode 4HF, the switches B and C are both turned on, and five positions can be detected. That is, the ON signals of the switches A, B, C output from the drive mode detecting means 32 are sequentially changed to AABBBCC as the drive mode switching mechanism moves.

An H / L shift rod 38 for switching control of the H / L switching mechanism 21 is slidably supported in the same direction as the input shaft 11 on the side of the transfer input shaft 11. The H / L shift rod 38 has three switching mode positions of a switching lever 62 in a transfer switching operation device 61, which will be described later, in order from the front side by sliding in the axial direction thereof, as shown in enlarged detail in FIG. In other words, 2 wheel drive / high speed mode position 2H (4 wheel drive / high speed / center differential free mode position 4HF), 4 wheel drive / high speed / center differential lock mode position 4HL and 4 wheel drive / low speed / center differential lock mode position 4LL respectively It is provided so that three positions can be taken. this
On the H / L shift rod 38, the sleeve of the above H / L switching mechanism 21
A fork 39 that engages with the sleeve 20 and slides the sleeve 20 is slidably supported by the boss portion 39a, and the boss portion 39a of the fork 39 is in sliding contact with a portion facing the inner surface of the transfer case 10. The surface 39b is formed. Further, a pin insertion hole 40 extending radially inward from the sliding contact surface 39b in the direction perpendicular to the axis is formed through the boss portion 39a of the fork 39, and a locking pin 41 is provided in the pin insertion hole 40. It is slidably inserted, and the tip of the locking pin 41 is provided on the outer peripheral surface of the H / L shift rod 38 so as to be engageable with an engaging groove 38a of a predetermined length formed so as to extend in the sliding direction. Has been. In addition, the boss portion 39 of the fork 39 is provided on the inner surface of the transfer case 10.
a A sliding contact plate 42, which is in sliding contact with the sliding contact surface 39b on the outer periphery, is fixed by bolts 43, 43.
A spring accommodating hole 44 is formed at a predetermined position in the spring accommodating hole 44, and a ball 45 capable of pressing the back surface of the locking pin 41 in the spring accommodating hole 44 and a spring 46 for urging the ball 45 toward the fork 39. When the pin insertion hole 40 of the boss 39a is aligned with the spring housing hole 44 by the movement of the fork 39, the locking pin 41 in the pin insertion hole 40 is fitted by the spring 46. The tip end portion is pressed and biased via the ball 45 so that the tip end portion thereof engages with the engagement groove 38a of the shift rod 38.

Further, the fork is attached to the outer periphery of the shift rod 38.
A ring-shaped connecting member 47 capable of axially pressing the boss portion 39a is movably and integrally coupled to a predetermined portion on the front side (left side in FIG. 5) of the boss portion 39a of the 39. The forward end position of the fork 39 is restricted by a restricting member 49 protruding from the sliding contact plate 42, and the H / L shift rod 38 is located at two front positions, that is, the two-wheel drive / high-speed mode position 2H and four-wheel drive. / High speed / Center differential lock mode When moving between 4HL positions, lock pin 41 with spring 46
Against the urging force of the shift rod 38, the push rod 38 is pushed out from the engaging groove 38a of the shift rod 38 to be immersed in the pin insertion hole 40, and the fork 39 stops moving even if the shift rod 38 slides, and the H / L switching mechanism 21
While prohibiting the switching operation of 2 mode positions 2H, 4
When the H / L shift rod 38 is slid from the HL to the rear end four-wheel drive / low speed / center diff lock mode position 4LL, the coupling member 47 integrated with the shift rod 38 causes the spring to move.
The locking pin 41 urged by 46 is slidable in the engaging groove 38a of the shift rod 38, and the fork 39 is moved to the shift rod 38.
The idle swing mechanism 50 is configured to move integrally with the H / L switching mechanism 21 to switch the H / L switching mechanism 21 to the low speed position PL. In FIG. 5, reference numeral 51 designates the ball 53 urged by the spring 52 and the engaging recess 3 on the outer periphery of the boss 39a of the fork 39.
It is a positioning mechanism that engages with 9c and 39d to position the stop position of the fork 39.

Further, as shown in FIG. 6, the connecting member 47 integrally connected to the H / L shift rod 38 has an engaging hole portion 47b.
The connecting portion 47a having the is formed integrally. The ball-shaped locking portion 54a of the tip end of the connecting arm 54 is fitted into and engaged with the engaging hole portion 47b of the connecting portion 47a.
Are fixed to the control rod 55, which is supported in parallel with the transfer case 10 on the side of the H / L shift rod 38, so as to move integrally therewith. Three engaging recesses 55a to 55c are provided on one side of the outer periphery of the rear end (right end in the figure) of the control rod 55.
Are formed at equal intervals in the axial direction, on the other hand, spring housing holes 56 are formed in the transfer case 10 facing the engaging recesses 55a to 55c of the control rod 55, and the spring housing holes 56 have the above-mentioned features. Each engaging recess 55a to 55c
A ball 57 engaged with the ball 57 and a spring 58 for urging the ball 57 in the engaging direction are fitted. The control rod is engaged by the engagement of the ball 57 with the engaging recesses 55a to 55c.
Position 55 at 3 positions corresponding to the above three drive modes: 2 wheel drive / high speed mode position 2H, 4 wheel drive / high speed / center differential lock mode position 4HL and 4 wheel drive / low speed / center differential lock mode position 4LL The positioning mechanism 59 is configured.

Further, one end of a push-pull type control cable 60 is connected to the front end of the control rod 55. The other end of the cable 60 is mechanically linked to a transfer switching operation device 61 for controlling the operation of the H / L switching mechanism 21 and the drive mode switching mechanism 32 as shown in FIG. The transfer switching operation device 61,
As shown in Fig. 7, a column operation mode switching lever
The switching lever 62 has a steering wheel 62.
64 is fixed to the upper end of a support shaft 63 that is rotatably arranged and supported substantially in parallel with the supporting steering shaft 65.
The other end of the cable 60 is connected to the tip of an arm member (not shown) fixed to the support shaft 63 so as to rotate together, and the support shaft 63 is rotated by the switching operation of the switching lever 62. It is designed to move the cable 60. Then, the switching lever 62 is rotated about its support shaft 63 to sequentially drive from the upper side in two wheel drive / high speed mode position 2H (four wheel drive / high speed / center differential free mode position 4HF) and four wheel drive. It is positioned at three switching positions: / high speed / center differential lock mode position 4HL and four-wheel drive / low speed / center differential lock mode position 4LL.

Further, near the upper end of the support shaft 63 of the switching lever 62,
The switching lever 62 has a low speed position of 4 wheel drive / low speed / center differential lock mode position 4LL and a high speed position of 4
Wheel drive / high speed / center differential lock mode position 4HL other than these switching positions, that is, 2 wheel drive / high speed mode position
A center diff changeover switch 66 is provided as a first switch means, which is changed over and operated according to the operation when the operation is changed over to 2H. That is, the center differential switch 66 is shown in FIGS.
As shown in the figure, it is composed of a switch main body 66a arranged in proximity to the support shaft 63, and a limit switch having an operating pin 66b biased and supported by the switch main body 66a so as to project toward the support shaft 63 side. The distal end portion of the operating pin 66b is arranged so as to be in sliding contact with the outer peripheral cam surface of a substantially columnar cam 67 that is pivotally attached to the support shaft 63. And
The cam 67 has a large-diameter portion 67a and a small-diameter portion 67b that is continuous with the large-diameter portion 67a in a two-step structure.
When 2 is in 2 wheel drive / high speed mode position 2H, cam 6
The large-diameter portion 67a of 7 pushes the operating pin 66b of the center differential switch 66 into the main body 66a to keep the switch 66 in the OFF state, while moving to the mode positions 4HL and 4LL other than the above two-wheel drive / high speed mode position 2H. At a certain time, the small diameter portion 67b causes the operating pin 66b of the changeover switch 66 to project from the inside of the main body 66a, so that the switch 66 is kept in the ON state.

Further, as shown in FIG. 7, the mode switching lever
A 2/4 switch 68 as a second switch means that is directly operated by the driver is attached to the 62. The 2/4 switch 68 is a momentary push switch that outputs a signal only while the driver is performing a push operation, as shown in enlarged detail in FIG. Therefore, for example, when a push operation is performed while the vehicle is in the two-wheel drive state, a command signal for switching from the two-wheel drive state to the four-wheel drive / center differential free state is output, and the vehicle is in the four-wheel drive / center differential free state. When a push operation is performed at any time, a command signal for switching from the four-wheel drive / center differential free state to the two-wheel drive state is alternately output.

In other words, the driving mode is the two-wheel drive / high-speed mode 2H, the four-wheel drive / high-speed / center differential free mode 4HF, the four-wheel drive / by the rotation operation of the changeover lever 62 and the push operation of the 2/4 changeover switch 68. High-speed / Center differential flock mode 4
HL and 4 wheel drive / low speed / center diff lock mode 4LL can be switched to each drive mode. At this time, when the switching lever 62 is positioned at the center 4 wheel drive / high speed / center diff lock mode position 4HL, the vehicle drive mode is set. Is switched to 4 wheel drive / high speed / center diff lock mode, and when the switching lever 62 is positioned at the lower 4 wheel drive / low speed / center diff lock mode position 4LL, the vehicle drive mode is changed to 4 wheel drive / low speed / center diff lock mode. On the other hand, when the changeover lever 62 is positioned in the upper two-wheel drive / high-speed mode 2H (four-wheel drive / high-speed / center differential free mode position 4HF), the 2/4 changeover switch 68 is operated in accordance with the changeover operation. Wheel drive mode or 4 wheel drive / high speed /
It is configured to switch to the center differential free mode.

Front and rear wheel output shafts of the transfer device 9
Reference numerals 12 and 13 are connected to the front and rear differential mechanisms 5 and 6 via propeller shafts (not shown), respectively. The front differential mechanism 5 includes a housing 69, an input shaft 70 supported by the housing 69 and connected to a front wheel side output shaft 12 of the transfer device 9, and a left and right side, as shown in FIG. It has axle shafts 71, 71 as output shafts connected to the front wheels 7, 7, respectively. For example, on the outer extension line of the right side (upper side in the figure) of the axle side 71, the axle shaft 71 and the right front wheel 7 are provided. A joint shaft 72 connecting the and is arranged concentrically. A small diameter portion 72a having a smaller diameter than the other portion is formed at a portion of the joint shaft 72 facing the axle shaft 71, while the outer end portion (right end portion) of the axle shaft 71 is larger than the other portions. A large diameter portion 71a having a large diameter is formed, and a fitting concave portion 71b into which the tip of the small diameter portion 72a of the joint shaft 72 is relatively rotatably fitted is provided on the end surface of the large diameter portion 71a. Also, the axle shaft 71
While a spline tooth portion 71c is formed on the outer circumference of the large diameter portion 71a of the joint shaft 72, a spline tooth portion 73a corresponding to the spline tooth portion 71c of the axle shaft 71 is provided on the outer circumference of the small diameter portion 72a of the joint shaft 72. The spline member 73 is fixed integrally with the rotation. Further, the outer peripheral spline tooth portion 73a of the spline member 73 and the spline tooth portion 7 of the axle shaft 71 are
A sleeve 74 is slidably connected to the spline portions 71b and 73a between the spline member 1b and the spline member 73 and the spline tooth portions 73a and 71b of the axle shaft 71 by the sliding of the sleeve 74. By switching to the meshed state, the differential mechanism 5 and the front wheels 7, 7 are connected so as to be able to transmit power, or the power transmission is cut off.

A fork 75 is movably integrated with the sleeve 74, and the fork 75 is fixed to one end (left end) of a shift rod 76 which is slidable in the same direction as the sliding direction of the sleeve 74 (horizontal direction). The other end (right end) of the shift rod 76 is connected to a diaphragm device 77 as an actuator. The diaphragm device 77 includes the shift rod 76.
And a first and second negative pressure chambers 79 and 80 defined by the diaphragm 78.
As shown in FIG. 2, each of the negative pressure chambers 7
The reference numerals 9, 80 are connected to an intake pipe (not shown) of the engine 2 via negative pressure passages 81, 82, respectively, and the intake negative pressure is introduced. Also, the negative pressure passages 81,8
2 is provided with a normally closed free solenoid valve 83 and a lock solenoid valve 84, respectively.The open / close control of these solenoid valves 83, 84 controls the connection and disconnection of the axle shaft 71 and the joint shaft 72. ,
When the free solenoid valve 83 is opened, the connection between the right axle shaft 71 connected to the front differential mechanism 5 and the joint shaft 72 connected to the right front wheel 7 is cut off, and the front wheels 7, 7 By rotating only the side gears and pinions (not shown) of the differential mechanism 5 when the (idle wheels) rotate, the rotation of the front wheels 7, 7 is prevented from being transmitted to the transfer device 9. Free state (unlocked state)
On the other hand, conversely, when the lock solenoid valve 84 is opened, the free wheel device 85 is configured such that the axle shaft 71 and the joint shaft 72 are rotationally integrally connected to each other to be in the locked state.

Further, in FIG. 3, reference numeral 86a denotes a freewheel lock detection switch for detecting that the freewheel device 85 is in the locked state based on the moving position of the shift rod 76, and 86a.
Similarly, b is a freewheel free detection switch for detecting that the freewheel device 85 is in a free state (unlocked state), and these both switches constitute a freewheel state detection means 87.
Although not shown, two freewheel lock detection switches 86a are provided.

Both solenoid valves 83, 8 for controlling the electric motor 36 for controlling the drive mode switching mechanism 32 and the freewheel device 85
The operation of 4 is controlled by a controller 88 having a built-in CPU as shown in FIG. Output signals from the three types of detection switches 37, 86, 87 and the center differential switch 66 and the 2/4 switch 68 of the transfer switching operation device 61 are input to the controller 88.

Further, the controller 88 is connected to a buzzer device 89 for notifying the driver of the switching of the drive modes by sounding, and a lighting display device 90 for displaying by lighting a lamp. The lighting display device 90 includes, for example, a four-wheel drive display lamp 91 (4WD lamp), a center differential display lamp 92 (C / D lamp), and a high / low speed display lamp 93 (H) of the speed reduction mechanism 14 arranged on the instrument panel. / L lamp) so that the four-wheel drive display lamp 91 lights up in the four-wheel drive mode and turns off in the two-wheel drive mode, and the center differential display lamp 92 lights up in the center differential lock mode. The high-low speed indicator lamp 93 is turned on in the low-speed mode and turned off in the high-speed mode.

The controller 88 constitutes the control means in the present invention. Hereinafter, the motor 36 and the solenoid valve will be described.
The operation control procedure for 83, 84, the buzzer device 89, and the lighting display device 90 will be described with reference to the flowcharts of FIGS. 11 to 16.

FIG. 11 shows the main routine. Immediately after the ignition switch is turned on, the initial setting is first performed in the step S0. That is, when the ignition switch is turned on, the output signal from the center differential switch 66, the output signal from the freewheel lock detection switch 86, and the output signal from the freewheel free detection switch 87 are read in step S1. Next, in step S2, it is determined whether or not the center differential switch 66 is in the ON state, and if this is YES, S21 to S25 described later will be described.
Shift from the two-wheel drive mode to the four-wheel drive / center differential lock mode switching subroutine shown in
After the vehicle drive state is set to the four-wheel drive / center differential lock state, the process proceeds to step S10.

On the other hand, if the determination in step S2 is NO, the next step
At S3, it is determined whether the freewheel device 85 is in the free state. Then, if this determination is YES, in the next step S4, the motor 36 is energized so as to rotate it in the CW direction (direction in which the sleeve 31 of the drive mode switching mechanism 32 is moved forward), and in the next step S5. The output signal from the mode detection switch 37 is read with and the sleeve 31 of the drive mode switching device 32 is moved to the two-wheel drive mode position in step S6.
Judgment is made as to whether or not it has been switched to P2, and this judgment is YES.
Steps S4 to S6 are repeated until the state becomes, the driving state of the vehicle is set to the two-wheel driving state 2H, and then the process proceeds to Step S10.

If the determination in step S3 is NO, step S7
To the motor 36 in the CCW direction (direction in which the sleeve 31 of the drive mode switching mechanism 32 is moved backward).
Then, in step S8, the output signal from the mode detection switch 37 is read, and in step S9, the sleeve 31 of the drive mode switching mechanism 32 is driven by four wheels.
It is determined whether or not the vehicle has been switched to the center differential free position P4F, and steps S7 to S9 are repeated until the determination is YES, and the vehicle drive state is changed to the four-wheel drive / center differential free state 4HF. Go to step S10.

In step S10, the four-wheel drive display lamp 91 (4WD lamp) and the center differential display lamp 9 of the lighting display device 90 are displayed.
The 2 (C / D lamp) and the high / low display lamp 93 (H / L lamp) are turned on as shown in Table 1 below to display the current drive mode to the driver.

When the initial setting is completed in this way, next, in step S11, the respective output signals of the center differential changeover switch 66 and the 2/4 changeover switch 68 are read out, and then in step S12, the operating state of both of these switches 66, 68 is changed to the present state. Table 2 below shows the destination drive modes for the other drive modes.
After deciding on the basis of step S13 to S37, the processing shifts to each switching subroutine shown in steps S13 to S37.

Each of the above subroutines will be described. FIG. 12 shows a flow of a switching subroutine when switching from the two-wheel drive mode 2H to the center differential free four-wheel drive / high speed mode 4HF. In this flow, first, in the first step S13, the buzzer device 89 sounds for 100 msec, for example, and in the next step S14, the four-wheel drive display lamp 91 in the lighting display device 90 blinks. This blinking is performed, for example, in a blinking form in which the ratio of the lighting time is larger than the extinguishing time, and the blinking form indicates to the driver that the two-wheel drive mode is being switched to the four-wheel drive mode.
After that, the process proceeds to step S15, the motor 36 is energized so as to rotate in the CCW direction (the direction in which the sleeve 31 of the drive mode switching mechanism 32 moves forward), and the drive mode switching mechanism is driven.
32 is switched from the rear two-wheel drive position P2 to the front-rear intermediate four-wheel drive / center differential lock position P4L, and the center differential 22 is locked. Thereafter, in step S16, the drive mode switching mechanism 32 is based on the output signal of the mode detection switch 37.
Is actually switched to the four-wheel drive center differential lock position P4L, and it is determined whether the drive mode is the four-wheel drive / high speed / center differential lock mode.
Steps S15 and S16 are repeated until S is reached. If the determination is YES, in step S17, an ON signal is output to the lock solenoid valve 84, and the freewheel device 85 is locked. Then, in step S18, based on the output signal of the freewheel lock detection switch 86,
It is determined whether or not the freewheel device 85 is actually in the locked state, and steps S17 and S18 are performed until this determination becomes YES.
repeat. Then, if the determination is YES, step S19
Then, the motor 36 is energized to rotate again in the CCW direction, and the drive mode switching mechanism 32 is switched from the four-wheel drive / center differential lock position P4L to the front four-wheel drive / center differential free position P4F. Free 22. Thereafter, in step S20, the drive mode switching mechanism 32 is actually switched to the four-wheel drive center differential free position P4F based on the output signal of the mode detection switch 37, and the drive mode is set to four-wheel drive / high speed / center. It is determined whether or not the differential free mode 4HF has been set, and steps S19 and S20 are repeated until this determination becomes YES, and when the determination becomes YES, the processing ends.

Fig. 13 shows 4-wheel drive mode 2H to center differential lock
The flow of the switching subroutine when switching to the wheel drive mode 4HL is shown. In this flow, first, in the first step S21, the four-wheel drive display lamp 91 and the center differential display lamp 92 in the lighting display device 90 are made to blink in the same manner as above, and thereafter, the same as steps S15 to S18 in the above-mentioned subroutine. Steps S22 to S25 are executed. That is, in step S22, the motor 36 is
Energize so as to rotate in the CW direction to lock the center differential 22, and then in step S23, the drive mode is set to 4-wheel drive / high speed / center differential lock mode 4HL based on the output signal of the mode detection switch 37. It is determined whether or not the result is YES, and steps S22 and S23 are repeated until this determination becomes YES. If the determination is YES, in step S24, an ON signal is output to the lock solenoid valve 84 to lock the freewheel device 85, and then in step S25, based on the output signal of the freewheel lock detection switch 86. It is determined whether or not the freewheel device 85 is actually in the locked state, and steps S24 and S25 are repeated until this determination becomes YES, while the control ends when the determination becomes YES.

In addition, Fig. 14 shows 4-wheel drive mode 4H with center differential lock.
The flow of the switching subroutine when switching from L to the center differential free four-wheel drive mode 4HF is shown. In this flow, first, in the first step S26, the center differential display lamp 92 is blinked, and then, in step S27, the motor 36 is energized so as to rotate in the CCW direction, and the drive mode switching mechanism 32 Is switched from the four-wheel drive / center differential lock position P4L to the front four-wheel drive / center differential free position P4F, and the center differential 22 is set in the free state. Then, in step S28, the drive mode is set to 4
Wheel drive / high speed / center differential free mode It is determined whether 4HF has been reached, and until this determination becomes YES, step S2
Repeat S7 and S28, and end when the judgment is YES.

Contrary to the above, FIG. 15 shows the flow of the switching subroutine when switching from the center differential free four-wheel drive mode 4HF to the center differential lock four-wheel drive mode 4HL. In this flow, in the first step S29, the center differential display lamp 92 is blinked, and in the next step S30, the motor 36 is rotated in the CW direction (direction in which the sleeve 31 of the drive mode switching mechanism 32 moves rearward). Thus, the drive mode switching mechanism 32 is switched from the four-wheel drive / center differential free position P4F to the rear four-wheel drive / center differential lock position P4L and the center differential 22 is locked. Then, in step S31, it is determined whether or not the drive mode is the four-wheel drive / high speed / center differential lock mode 4HL, and steps S30 and S31 are repeated until this determination becomes YES, and when the determination becomes YES, the process ends.

Also, Fig. 16 shows the center differential free four-wheel drive mode 4H.
The flow of the switching subroutine when switching from F to the two-wheel drive mode 2H is shown. In this flow, in the first step S32, the buzzer device 89 is sounded for, for example, 100 m seconds, and then in the next step S33, the four-wheel drive display lamp 91 at the lighting display position 90 is blinked. This blinking is performed in the flashing mode in which the ratio of the extinguishing time is larger than the lighting time, for example, from the two-wheel drive mode to the four-wheel drive mode. The driver is informed that switching is in progress. Then, in step S34, the motor 36 is energized so as to rotate in the CW direction, and the drive mode switching mechanism 32 is moved from the four-wheel drive / center differential free position P4F of the front wheels to the intermediate four.
It is moved toward the two-wheel drive position P2 at the rear end through the wheel drive / center differential lock position P4L.

Then, in step S35, the mode detection switch 3
Based on the output signal of 7, the drive mode switching mechanism 32 is actually switched to the two-wheel drive position P2, and it is determined whether or not the drive mode is the two-wheel drive / high speed mode 2H, and this determination is YES. Until the above, steps S34 to S35 are repeated. Then, if the determination is YES, an ON signal is output to the free solenoid valve 83 in step S36 to put the freewheel device 85 in a free state. After this step S37
At, it is determined whether or not the freewheel device 85 is actually in the free state based on the output signal of the freewheel lock detection switch 86, and steps S36 and S37 are repeated until this determination becomes YES. Then, when this determination is YES, the control ends.

By the way, the feature of the present invention is that when the mode detection means 37 fails, the controller 88 detects this,
Thereafter, the operation of the drive mode switching mechanism 32 is controlled according to the subroutine for failure of mode detecting means shown in FIG.

At this time, the controller 88 detects the failure of the mode detecting means 37 by the abnormality of the output signal output from the mode detecting means 37. That is, as described above, the output signal from the mode detecting means 37 is such that if the three switches A, B and C are normal, the ON output signals from them will always sequentially change with AABBBCC. Has become. Therefore, if the ON output signals of combinations other than these are not output or the ON output signals do not change in the above order, the controller 88 can detect that the mode detecting means 37 has a failure. When this failure is detected, the controller 88 immediately executes the following mode detection means failure subroutine regardless of the output signal from the switching operation device 61.

First, when control flows into this subroutine, in the first step S38, it is determined based on the output signal from the freewheel state detecting means 87 whether or not the freewheel device 85 is in the locked state.

Then, if this determination is YES, in the next step S39, the motor 36 is energized to rotate it in the CCW direction, and the mode switching mechanism 32 is set to the four-wheel drive / center differential free mode position P.
Move toward 4F. Then, in the next step S49, a limit switch provided in the motor 36 (this limit switch is turned ON when the load resistance of the motor 36 becomes excessive and its rotation is stopped.)
It is determined whether or not is turned on, and steps S39 and S40 are repeated until it is YES.

After this, if the determination in step S40 is YES, the timer is reset to T = 0 in the next step S41 to start measuring the time, and in the next step S42, the motor 3
After continuing to rotate 6 in the CCW direction, the next step S43 is performed again.
Check whether or not the above limit switch is turned on.

Then, if this determination is NO, that is, if the motor 36 starts to rotate again, the drive mode switching mechanism 32 has not been moved to the end of the moving position, so control is returned to the above step S39 and thereafter. Repeat steps S39 to S43.

Further, if the determination in step S43 is YES, that is, if the rotation of the motor 36 is stopped, it is determined in the next step S44 whether the measurement time T has exceeded a predetermined time, for example, 30 seconds. . And the judgment in this step S44 is N
If it is O, the control is returned to the step S42 and the step S42 is performed.
~ Repeat S44. On the other hand, the determination in step S44
If YES, that is, the motor 36 is energized but its rotation is stopped for a predetermined time (30 seconds)
When it reaches, it is determined that the drive mode switching mechanism 32 has been moved to the end of the moving position and is positioned at the four-wheel drive / center differential free mode position P4F, and the four-wheel drive display lamp 91 is made to blink in the next step S45. After that, keep this state.

Therefore, when the failure of the mode detection means 37 is detected by this, if the freewheel device 85 is in the locked state at that time, the drive mode switching mechanism 32 is forced to the four-wheel drive center differential free mode position. After being moved to P4F, the driving condition of the vehicle continues to be maintained in the four-wheel drive / center differential free condition, and at this time, the four-wheel drive indicator lamp 91 continues to blink to inform the driver that an abnormality has occurred. become.

On the other hand, if the determination in step S38 is NO, that is, if the freewheel device 85 is in the free state when the failure of the mode detection means 37 is detected, the control proceeds to step S46.
Then, the control which is substantially the same as the control in steps S39 to S44 is performed in steps S46 to S50. Note that the control in steps S46 to S50 is different from the control in steps 39 to S44 described above because the energization direction to the motor 36 in steps S46 and S48 is opposite, and the drive mode switching mechanism 32 is Is only switched to the two-wheel drive mode position P2, and a detailed description thereof will be omitted.

Then, when the determination in step S50 is YES, that is, the motor 36 is energized so as to be rotated in the CW direction, but its rotation is stopped for a predetermined time (30 seconds). Then, the controller 88 determines that the drive mode switching mechanism 32 has been moved to the end of the moving position and is positioned at the two-wheel drive position P2, and in the next step S52, the switching lever is switched based on the output signal from the center differential switching switch 66. It is determined whether the 62 is in the four-wheel drive / low speed / center differential lock mode position 4LL. If this is YES,
In the next step S53, the buzzer device 89 is sounded to warn the driver with a caution sound, and the process returns to step S53. If NO, the process returns to step S53, and thereafter the switching lever 62
A caution sound is emitted as soon as is switched to 4-wheel drive / low speed / center differential lock mode position 4LL. Note that the switching lever 62 generates the caution sound in this way.
Regardless of the switching position of the vehicle, if the vehicle is continuously maintained in the two-wheel drive state and the mode is mistakenly switched to the low speed mode, it is transmitted to the power transmission system on the rear wheel 8 side that is constantly driven. This is because the torque may become excessive and damage it.

Therefore, when the failure of the mode detecting means 37 is detected by this, if the free wheel device 85 is in the free state at that time, the drive mode switching mechanism 32 is forcibly moved to the two-wheel drive mode position P2. Then, the driving state of the vehicle continues to be maintained in the two-wheel driving state, and when the switching lever 62 is switched to the low speed mode at this time, the driver is informed by a caution sound.

When the drive mode switching mechanism 32 is forcibly switched to the two-wheel drive mode position P2 and the four-wheel drive / center differential free mode position P4F, the rotation of the motor 36 is stopped for a long time of 30 seconds or more. This is detected and confirmed in consideration of the case where the drive mode switching mechanism 32 is temporarily stopped during its movement due to some cause such as a temporary drop in the motor voltage. Is.

Further, as described above, the two freewheel lock detection switches 86a are provided, and the switching from the two-wheel drive state to the four-wheel drive state is not accepted unless the output signals from these switches are both in the ON state. In this way, the certainty of safety is enhanced.

<Effect> According to the present invention required above, when the drive mode detection means fails, the control means detects the output signal of the freewheel state detection means other than the output signal from the drive mode detection means. After that, the drive mode switching mechanism is forcibly switched to the two-wheel drive mode position or the four-wheel drive / center differential free mode position according to the free state or the locked state of the freewheel device regardless of the output signal from the operating means. Since it is operated to keep the driving state of the vehicle in the two-wheel driving state or the four-wheel driving / center differential free state, the driving mode switching mechanism can be appropriately switched even if the driving mode detecting means fails. You can

[Brief description of drawings]

1 to 17 show an embodiment of the present invention. FIG. 1 is a schematic side view of a four-wheel drive vehicle, FIG. 2 is a schematic view showing the entire configuration of a control device, and FIG. 3 is a freewheel. FIG. 4 is a cross-sectional view of the transfer device, FIG. 5 is a cross-sectional view of the idling mechanism, FIG. 6 is a cross-sectional view of the positioning mechanism of the control rod, and FIG. 7 is an arrangement of the transfer switching operation system. FIG. 8 is a front view showing a state, FIG. 8 is an enlarged view of a 2/4 selector switch mounting portion, FIG. 9 is a sectional view of a center differential switching detector, and FIG. 10 is a sectional view taken along line XX of FIG. Fig. 12 is a flow chart showing the main routine of the controller. Fig. 12 shows 4 from the two-wheel drive mode to the center differential free mode.
FIG. 13 is a flowchart showing a subroutine for switching to the wheel drive mode, FIG. 13 is a flowchart showing a subroutine for switching from the two-wheel drive mode to the center diff lock four-wheel drive mode, and FIG. 14 is the same as the center diff lock four-wheel drive mode. FIG. 15 is a flowchart showing a subroutine for switching to the center differential free mode, FIG. 15 is a flowchart showing a subroutine for switching from the center differential free four-wheel drive mode to the center differential lock mode, and FIG. 16 is a center differential free four-wheel drive. FIG. 17 is a flowchart showing a subroutine for switching from the mode to the two-wheel drive mode. FIG. 17 is a flowchart showing a subroutine when the mode detecting means fails,
FIG. 18 is a diagram showing a conventional transfer device. 2 …… Engine 7 …… Front wheel on idler side 8 …… Rear wheel on constant drive side 9 …… Transfer device 22 …… Center differential 32 …… Drive mode switching mechanism 36 …… Motor 37 …… Drive mode detection Means 61 …… Transfer switching operation device 85 …… Freewheel device 87 …… Freewheel state detecting means 88 …… Controller as control means

Claims (1)

(57) [Claims] 1. A drive mode of a transfer device having a center differential, switching between two-wheel drive, four-wheel drive / center differential lock, four-wheel drive / center differential free mode, two-wheel drive mode and four-wheel drive / center differential free mode. A clutch gear type drive mode switching mechanism that passes through a four-wheel drive / center differential lock mode during the switching between the drive mode and the drive mode detecting means for detecting the actual switching movement position of the drive mode switching mechanism; A freewheel device in which the idle wheel side in the wheel drive state is switched to a free state and a lock state with respect to the power transmission system from the transfer device and is brought into a locked state in the four-wheel drive state, and the freewheel device of the freewheel device A free wheel state detecting means for detecting a free state and a locked state, and the drive mode operated by a driver The operation of the drive mode switching mechanism and the freewheel device is controlled based on output signals from the operation means to be selected, the operation means, the drive mode detection means, and the freewheel state detection means, and the drive mode is selected. When the output signal from the detecting means is abnormal, the drive mode switching mechanism is set to the two-wheel drive mode position in accordance with the output signal from the free wheel state detecting means in preference to the output signal from the operating means. Or a drive mode switching control device for a four-wheel drive vehicle, comprising: a control means for switching the four-wheel drive / center differential free mode position.