Patent Publication Number: US-2022227227-A1

Title: Transfer device of vehicle

Description:
TECHNICAL FIELD 
     The present disclosure relates to a transfer device of a vehicle, particularly, a transfer device applied to a four-wheel-drive vehicle. 
     BACKGROUND OF THE DISCLOSURE 
     As four-wheel-drive (4WD) vehicles, so-called FR (front-engine rear-wheel-drive) based 4WD vehicles in which a drive source (e.g., an engine) supplies a driving force not only to rear wheels but also to front wheels are known. In such an FR-based 4WD vehicle, the drive source and a transmission are disposed at a front part of a vehicle body so that their axes extend in a front-and-rear direction of the vehicle body, and the driving force transmitted from the transmission is sent to the rear wheels (main drive wheels) through a rear-wheel output shaft extending rearwardly via a rear-wheel propeller shaft and a rear-wheel differential gear. In addition, a transfer device which extracts a driving force to be transmitted to the front wheels (auxiliary drive wheels) is provided on the rear-wheel output shaft, and the driving force extracted to a front-wheel output shaft of the transfer device is transmitted to the front wheels via a front-wheel propeller shaft extending forwardly and a front-wheel differential gear. 
     As such a transfer device, it is known that the transfer device is provided, on the rear-wheel output shaft, with a coupling which extracts the driving force for the front wheels, and the driving force extracted by the coupling is transmitted to the front-wheel output shaft via a chain-type or a gear-type powertrain mechanism. 
     In the 4WD vehicle with the transfer device, generally, each of the front-wheel propeller shaft and the rear-wheel propeller shaft is coupled to the front-wheel output shaft or the rear-wheel output shaft via a universal joint provided to an end part of the propeller shaft on the transfer device side. 
     When the front-wheel propeller shaft is coupled to the front-wheel output shaft which is disposed in parallel with the rear-wheel output shaft, a joint part provided to a component member of the universal joint of the front-wheel propeller shaft may be spline-engaged with the front-wheel output shaft, and a bolt member may be used to retain the front-wheel propeller shaft. 
     For example, JP6624177B2 discloses a transfer device in which a joint part of a front-wheel propeller shaft is spline-engaged with a front-wheel output shaft, and a bolt member is inserted from an end part of the front-wheel output shaft on the opposite side from the front-wheel propeller shaft toward the joint part to be threadedly engaged, and thereby, the front-wheel propeller shaft being retained. 
     Further, in the transfer device disclosed in JP6624177B2, in order to improve assemblability of the front-wheel propeller shaft with respect to the front-wheel output shaft, the front-wheel propeller shaft is attached to the front-wheel output shaft by making a spline-engagement part between the front-wheel output shaft and the joint part of the front-wheel propeller shaft be a non-press fitting, and inserting the bolt member into a sleeve member, which is fitted into the front-wheel output shaft, to be threadedly engaged with the joint part. Accordingly, since the front-wheel propeller shaft is attached to the front-wheel output shaft in the state where the bolt member is integrally assembled to the joint part, it is suppressed that the bolt member is loosened with respect to the joint part due to a relative rotation caused by backlash in a rotational direction at the spline-engagement part between the front-wheel output shaft and the joint part. 
     On the other hand, due to the backlash at the non-press fitted spline-engagement part between the joint part and the front-wheel output shaft as an auxiliary-drive-wheel output shaft, the joint part may be moved with respect to the front-wheel output shaft and cause vibration. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is made in view of the above situations, and one purpose thereof is to provide a transfer device of a vehicle, capable of reducing vibration of a joint part of a propeller shaft to an output shaft for auxiliary drive wheels, and suppressing loosening of a bolt member threadedly engaged with the joint part. 
     According to one aspect of the present disclosure, a transfer device of a vehicle is provided, which includes a main-drive-wheel output shaft coupled to an output shaft of a transmission and extending to one side in a front-and-rear direction of the vehicle, an auxiliary-drive-wheel output shaft disposed in parallel with the main-drive-wheel output shaft, and a powertrain mechanism configured to transmit a driving force extracted from the main-drive-wheel output shaft to the auxiliary-drive-wheel output shaft. The auxiliary-drive-wheel output shaft is connected to a propeller shaft extending to the other side in the vehicle front-and-rear direction and having a universal joint at an end part thereof on an auxiliary-drive-wheel output shaft side. An end part of the auxiliary-drive-wheel output shaft on a propeller shaft side is formed in a hollow shape and includes a fitting part configured to be spline-engaged with a joint part provided to a component member of the universal joint of the propeller shaft, and the spline-engagement between the fitting part of the auxiliary-drive-wheel output shaft and the joint part of the propeller shaft is a non-press fitting. The joint part is provided, at an end part thereof on the one side, with a centering part extending to the one side and having an outer diameter smaller than an outer diameter of the joint part. The centering part is provided, at an end part thereof on the one side, with a bolt hole extending to the other side. The auxiliary-drive-wheel output shaft is provided, on the one side of the fitting part, with a flange part extending to radially inward of the auxiliary-drive-wheel output shaft and having a centering hole corresponding to the centering part. A spacer is disposed on the one side of the flange part, and a bolt member is disposed on the one side of the spacer to be inserted into the spacer from the one side toward the bolt hole of the centering part and attached to the bolt hole. The centering part is inserted into the centering hole so that the joint part is centered on the auxiliary-drive-wheel output shaft. The flange part is sandwiched between the spacer and the joint part, and the bolt member is attached to the bolt hole so that the propeller shaft is assembled to the auxiliary-drive-wheel output shaft. 
     According to this configuration, since the joint part of the propeller shaft is centered on the auxiliary-drive-wheel output shaft by the centering part, the vibration of the joint part of the propeller shaft with respect to the auxiliary-drive-wheel output shaft can be reduced. Moreover, by the flange part of the auxiliary-drive-wheel output shaft being sandwiched between the spacer and the joint part, and the bolt member being attached to the bolt hole provided to the centering part of the joint part while being inserted into the spacer from the one side in the vehicle front-and-rear direction, the bolt member is suppressed from being loosened with respect to the bolt hole due to a relative rotation caused by backlash in a rotational direction between the fitting part of the auxiliary-drive-wheel output shaft and the joint part which are splined-engaged with each other. 
     A length of the flange part in the vehicle front-and-rear direction may be shorter than a distance between the end part of the joint part on the one side and an end part of the spacer on the other side in the vehicle front-and-rear direction. 
     According to this configuration, a gap is made between the flange part of the auxiliary-drive-wheel output shaft and the spacer and/or between the flange part and the joint part of the propeller shaft. Moreover, since the spline-engagement between the fitting part of the auxiliary-drive-wheel output shaft and the joint part is a non-press fitting, the joint part rotates relative to the auxiliary-drive-wheel output shaft. In this state, because of the gap, it is difficult for a force in the rotational direction to loosen the bolt member by acting on a seat of the bolt member attached to the bolt hole. Therefore, the loosening of the bolt member can be prevented. 
     The joint part may be provided, at the end part thereof on the one side, with an intermediate shaft part extending to the one side between the joint part and the centering part and having an outer diameter smaller than the outer diameter of the joint part and larger than the outer diameter of the centering part. 
     According to this configuration, since the joint part of the propeller shaft is provided with the intermediate shaft part, the length between the end part of the joint part at the one side and the end part of the centering part at the one side becomes longer. Accordingly, the vibration of the joint part is further suppressed, and assemblability upon the spline-engagement of the fitting part of the auxiliary-drive-wheel output shaft with the joint part of the propeller shaft is improved. 
     A length of the flange part in the vehicle front-and-rear direction may be shorter than a distance between an end part of the intermediate shaft part on the one side and an end part of the spacer on the other side in the vehicle front-and-rear direction. 
     According to this configuration, the gap is made between the flange part of the auxiliary-drive-wheel output shaft and the spacer and/or between the flange part and the intermediate shaft part of the propeller shaft. Because of this gap, when the joint part of the propeller shaft rotates relative to the auxiliary-drive-wheel output shaft, it is difficult for a force in the rotational direction to loosen the bolt member by acting on the seat of the bolt member attached to the bolt hole. Therefore, the loosening of the bolt member can be prevented. 
     The auxiliary-drive-wheel output shaft may be provided with a spacer holding part extending to the one side from the flange part and having a spacer insertion hole into which the spacer is inserted. A first seal member may be provided at the other side of the fitting part of the auxiliary-drive-wheel output shaft so as to seal between the auxiliary-drive-wheel output shaft and the joint part, and a second seal member may be provided to an outer circumferential surface of the spacer so as to seal between the spacer holding part and the spacer. 
     According to this configuration, since the fitting part of the auxiliary-drive-wheel output shaft, the joint part of the propeller shaft, and the centering part of the joint part inserted into the centering hole of the flange part of the auxiliary-drive-wheel output shaft are located between the first and second seal members in the vehicle front-and-rear direction, it can be avoided that foreign matter enters from outside and is caught between the fitting part and the joint part, and between the centering hole and the centering part. Therefore, the vibration of the joint part of the propeller shaft with respect to the auxiliary-drive-wheel output shaft can further certainly be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a powertrain mechanism of a four-wheel-drive vehicle on which a transfer device of the vehicle according to one embodiment of the present disclosure is mounted. 
         FIG. 2  is a cross-sectional view illustrating an output shaft for auxiliary drive wheels of the transfer device illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, one embodiment of the present disclosure is described with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram illustrating a powertrain mechanism of a four-wheel-drive vehicle on which a transfer device according to this embodiment of the present disclosure is mounted. As illustrated in  FIG. 1 , the four-wheel-drive (4WD) vehicle  1  on which the transfer device according to this embodiment is mounted, is a front-engine rear-wheel-drive (FR) based 4WD vehicle, and an engine  2  as a drive source and a transmission  3  are disposed at a front part of a vehicle body so that their axes extend in a front-and-rear direction of the vehicle body. 
     On the rear side of the transmission  3 , a transfer device  10  is provided to transmit a driving force sent from the engine  2  through the transmission  3 , to rear wheels (main drive wheels) via a rear-wheel propeller shaft extending to the vehicle-body rear side and a rear-wheel differential gear, as well as to extract a driving force to be transmitted to front wheels (auxiliary drive wheels). 
     The transfer device  10  includes a rear-wheel output shaft  11  (main-drive-wheel output shaft) coupled to an output shaft  3   a  of the transmission  3  and extending rearwardly (one side in the vehicle front-and-rear direction), a front-wheel output shaft  12  (auxiliary-drive-wheel output shaft) disposed in parallel with the rear-wheel output shaft  11 , and a powertrain mechanism  13  which transmits the driving force extracted from the rear-wheel output shaft  11  to the front-wheel output shaft  12 . 
     The transfer device  10  also includes a coupling  16  provided on the rear-wheel output shaft  11  and coupled to the rear-wheel output shaft  11  to extract the driving force for the front wheels from the driving force transmitted to the rear-wheel output shaft  11 . For example, an electromagnetic-type coupling is used as the coupling  16 . 
     The powertrain mechanism  13  is a gear type, and includes a drive gear  14  which is provided on the front side of the coupling  16  on the rear-wheel output shaft  11  so as to be coupled to the coupling  16 , and a driven gear  15  which is provided on the front-wheel output shaft  12  and coupled thereto to mesh with the drive gear  14 . The powertrain mechanism  13  transmits the front-wheel driving force, which is extracted from the rear-wheel output shaft  11  by the coupling  16 , to the front-wheel output shaft  12 . 
     A front-wheel propeller shaft  30  extending forwardly is coupled to a front end part of the front-wheel output shaft  12 . The front-wheel propeller shaft  30  has a universal joint  31  at its rear end part, and is coupled to the front-wheel output shaft  12  via the universal joint  31 . 
     The front-wheel propeller shaft  30  also includes a universal joint  32  at its front end part, and is coupled to an input shaft  41  of a front-wheel differential gear  40  via the universal joint  32 . The input shaft  41  of the front-wheel differential gear  40  is coupled to an axle  42  which is coupled to each of the left and right front wheels. 
     Accordingly, the front-wheel driving force extracted from the rear-wheel output shaft  11  by the coupling  16  is transmitted to the front-wheel output shaft  12  via the powertrain mechanism  13 , and then transmitted from the front-wheel output shaft  12  to the front wheels via the front-wheel propeller shaft  30  and the front-wheel differential gear  40 . 
     In the 4WD vehicle  1 , the coupling  16  extracts the front-wheel driving force while changing a front/rear torque distribution ratio of the front wheels to the rear wheels within a range from 0:100 to 50:50. Note that operation of the coupling  16  is controlled by a control unit (not illustrated). 
     The transfer device  10  also includes a damper  17  on the rear-wheel output shaft  11  between the coupling  16  and the drive gear  14 . The damper  17  lowers a resonance frequency at which the front-wheel side drive system (from the coupling  16  to the front wheels via the drive gear  14 , the driven gear  15 , the front-wheel output shaft  12 , the front-wheel propeller shaft  30 , and the front-wheel differential gear  40 ) resonates with a torque vibration of the engine  2 , to be below a practical range of the engine  2 . 
     Next, the transfer device  10  is described in more detail with reference to  FIG. 2 . 
       FIG. 2  is a cross-sectional view illustrating the front-wheel output shaft  12  of the transfer device  10  illustrated in  FIG. 1 . As illustrated in  FIG. 2 , the transfer device  10  is provided with a transfer case  51 , and the transfer case  51  includes a first case member  52  and a second case member  53  disposed in this order from forward. The first case member  52  and the second case member  53  are fastened to each other using a fastening bolt (screw)  54 . 
     As illustrated in  FIG. 1 , each of the rear-wheel output shaft  11  coupled to the output shaft  3   a  of the transmission  3 , and the front-wheel output shaft  12  disposed in parallel with the rear-wheel output shaft  11  is rotatably supported inside the transfer case  51 . 
     The powertrain mechanism  13  is disposed inside the transfer case  51  between a vertical wall part  52   a  of the first case member  52  and a vertical wall part  53   a  of the second case member  53 , and the drive gear  14  is disposed on the rear-wheel output shaft  11  and the driven gear  15  is disposed on the front-wheel output shaft  12 . 
     As illustrated in the drawing, the driven gear  15  is provided with a rear extending part  15   a  extending radially inwardly and rearwardly, and the radial inward of the rear extending part  15   a  is coupled to the front-wheel output shaft  12  to be formed integrally with the front-wheel output shaft  12 . 
     The driven gear  15  is rotatably supported by the transfer case  51  via a bearing  57  disposed between an inner circumferential surface of the driven gear  15  and the transfer case  51 , and a bearing  58  disposed between the rear side of the front-wheel output shaft  12  and the transfer case  51 . 
     The front-wheel output shaft  12  is formed in a hollow shape, and extends in the front-and-rear direction of the rear extending part  15   a  provided to the driven gear  15 . The vehicle-body front side of the front-wheel output shaft  12  is coupled to the front-wheel propeller shaft  30  (hereinafter, referred to as the “propeller shaft  30 ”) via the universal joint  31 . 
     The universal joint  31  is provided with, as component members, an outer joint member  33  provided at the transfer device  10  side, an inner joint member  35  coupled to a shaft member  34  of the propeller shaft  30 , a ball  36  interposed between the outer joint member  33  and the inner joint member  35  to transmit motive force therebetween, and a cage  37  disposed between an inner circumferential surface of the outer joint member  33  and an outer circumferential surface of the inner joint member  35  to hold the ball  36 . Accordingly, the universal joint  31  can transmit the motive force between the outer joint member  33  and the shaft member  34 . 
     The universal joint  31  further includes a cover member  38  provided to cover a movable range of the shaft member  34 , and a boot  39  provided to cover between the shaft member  34  and the cover member  38 . The cover member  38  is provided to extend substantially cylindrically to the front side from the outer joint member  33 . The boot  39  is made of elastic material, such as rubber, and provided so as to seal between an outer circumferential surface of the shaft member  34  and an inner circumferential surface of the cover member  38 . 
     The outer joint member  33  of the universal joint  31  is provided with a joint part  61  extending rearwardly. The joint part  61  is formed in a substantially cylindrical shape, and is formed, on its outer circumferential surface, with a spline part  61   b  extending in an axial direction of the joint part  61 . 
     An inner circumferential surface of a front end part of the front-wheel output shaft  12  is provided with a fitting part  12   a  which is spline-engaged with the joint part  61  of the propeller shaft  30 . The fitting part  12   a  is formed with a spline part  12   b  extending in an axial direction of the front-wheel output shaft  12 . The spline part  61   b  of the joint part  61  of the propeller shaft  30  is fitted into the spline part  12   b  of the fitting part  12   a  of the front-wheel output shaft  12  so that the fitting part  12   a  of the front-wheel output shaft  12  is spline-engaged with the joint part  61  of the propeller shaft  30 . 
     In the spline part  12   b  formed in the front end part of the front-wheel output shaft  12 , tooth parts and groove parts are formed in parallel with the axis of the front-wheel output shaft  12 . Further, in the spline part  61   b  formed in the joint part  61  of the propeller shaft  30 , tooth parts and groove parts are formed in parallel with the axis of the joint part  61 , and thereby, the spline-engagement between the fitting part  12   a  of the front-wheel output shaft  12  and the joint part  61  of the propeller shaft  30  is a non-press fitting. 
     The joint part  61  of the propeller shaft  30  is provided with an intermediate shaft part  62  extending rearwardly. The intermediate shaft part  62  is formed in a substantially cylindrical shape with an outer diameter smaller than that of the joint part  61 . 
     The intermediate shaft part  62  of the propeller shaft  30  is provided with a centering part  63  extending rearwardly. The centering part  63  is formed in a substantially cylindrical shape with an outer diameter smaller than that of the intermediate shaft part  62 . Further, the joint part  61 , the intermediate shaft part  62 , and the centering part  63  are provided so as to be coaxial with each other. 
     The centering part  63  is formed, at its rear end part, with a bolt hole  64  extending forwardly through the centering part  63  and the intermediate shaft part  62 . 
     Further, the front-wheel output shaft  12  is formed, on the rear side of the fitting part  12   a,  with a flange part  121  extending radially inwardly from an inner circumferential surface of the front-wheel output shaft  12 . 
     The flange part  121  extends radially inwardly from the inner circumferential surface of the front-wheel output shaft  12 , thus having a centering hole  122  corresponding to the centering part  63 . This centering hole  122  is formed in a circular shape and configured so that an axis of the centering hole  122  is in agreement with the axis of the front-wheel output shaft  12 , an inner diameter of the centering hole  122  is larger than the outer diameter of the centering part  63 , and a length of the centering hole  122  in the front-and-rear direction is shorter than that of the centering part  63 . For example, the length of the centering hole  122  in the front-and-rear direction is set to 5.8 mm, and that of the centering part  63  is set to 6.2 mm. For example, the difference between the lengths of the centering part  63  and the centering hole  122  is set within a range from 0.1 mm to 1 mm. 
     On the rear side of the flange part  121 , a substantially cylindrical spacer  70  is disposed so as to extend rearwardly. The front-wheel output shaft  12  is provided, on the rear side of the flange part  121 , with a spacer holding part  123  extending rearwardly to hold the spacer  70 . The spacer holding part  123  has a spacer insertion hole  124  which extends rearwardly, and the spacer  70  is inserted therein. This spacer insertion hole  124  is configured so that an inner diameter of the spacer insertion hole  124  is larger than the inner diameter of the centering hole  122  and an outer diameter of the spacer  70 . 
     On the rear side of the spacer  70 , a bolt member  20  is disposed, which is inserted from the rear side of the spacer  70  into the bolt hole  64  of the centering part  63  to be attached to the bolt hole  64 . The transfer case  51  is formed with an insertion hole  53   b  corresponding to a rear end part of the front-wheel output shaft  12 , and the spacer  70  and the bolt member  20  can be inserted therein. 
     The bolt member  20  has a hexagonal head part  21 , and a screw part  22  extending forwardly from the head part  21 . 
     In the transfer device  10 , upon assembling of the propeller shaft  30  to the front-wheel output shaft  12 , the centering part  63  provided to the joint part  61  is inserted into the centering hole  122  of the flange part  121  of the front-wheel output shaft  12  while the rear side of the spline part  61   b  of the joint part  61  is fitted into the front side of the spline part  12   b  of the front-wheel output shaft  12 , and thus, the joint part  61  is centered on the front-wheel output shaft  12 . In this state, the spacer  70  is inserted into the spacer insertion hole  124  from the rear end part of the front-wheel output shaft  12 , and the bolt member  20  is inserted into the spacer  70  toward the bolt hole  64  of the centering part  63  from the rear end part of the front-wheel output shaft  12 . As a result, the joint part  61  of the propeller shaft  30  is attached to the fitting part  12   a  of the front-wheel output shaft  12 . 
     When the bolt member  20  is attached to the bolt hole  64 , the spacer  70  located between the head part  21  of the bolt member  20  and the centering part  63  of the joint part  61  contacts the centering part  63 . Here, the length of the centering part  63  in the front-and-rear direction is equal to a distance in the front-and-rear direction between a rear end part of the intermediate shaft part  62  of the joint part  61 , and a front end part of the spacer  70 . Therefore, since the distance between the rear end part of the intermediate shaft part  62  and the front end part of the spacer  70  is longer than the length of the centering hole  122  of the flange part  121  (i.e., the length of the flange part  121 ) in the front-and-rear direction, the flange part  121  is sandwiched between the spacer  70  and the intermediate shaft part  62  while having a gap between the flange part  121  and the spacer  70  and/or between the flange part  121  and the intermediate shaft part  62 . This gap allows that the bolt member  20  is fastened to generate a given axial force while pushing a rear end surface of the centering part  63  without pushing the flange part  121  in a state where the flange part  121  is sandwiched between the intermediate shaft part  62  and the head part  21  of the bolt member  20  via the spacer  70 . 
     The transfer device  10  is also provided with a plurality of seal members which prevent lubricant inside the transfer case  51  from leaking outside. As illustrated in  FIG. 2 , a seal member  71  is provided between the first case member  52  and the front side of the front-wheel output shaft  12 , and a seal member  72  is provided between the second case member  53  and the rear side of the front-wheel output shaft  12 . Moreover, grease is supplied between the fitting part  12   a  of the front-wheel output shaft  12  and the joint part  61  of the propeller shaft  30 , a seal member  73  is provided between the joint part  61  and the front side of the fitting part  12   a,  and a seal member  74  is provided between the spacer holding part  123  and the spacer  70 . 
     Although in this embodiment the intermediate shaft part  62  is provided between the joint part  61  and the centering part  63  of the propeller shaft  30 , a centering part extending rearwardly may be provided to the joint part of the propeller shaft. In this case, a distance from the front end part of the front-wheel output shaft to a front end part of the flange part in the front-and-rear direction is desirable to be slightly shorter than the length of the joint part in the front-and-rear direction. 
     As described above, in the transfer device  10  according to this embodiment, the fitting part  12   a  formed in the end part of the front-wheel output shaft  12  on the propeller shaft side is spline-engaged with the joint part  61  provided to the universal joint  31  of the propeller shaft  30 , and the centering part  63  provided to the joint part  61  is inserted into the centering hole  122  of the flange part  121  of the front-wheel output shaft  12 , thereby the joint part  61  being centered on the front-wheel output shaft  12 . Then, the spacer  70  is inserted into the spacer insertion hole  124  from the rear end part of the front-wheel output shaft  12 , and the bolt member  20  is inserted into the spacer  70  toward the bolt hole  64  of the centering part  63  from the rear end part of the front-wheel output shaft  12  to be fastened to the bolt hole  64 , thereby the joint part  61  of the propeller shaft  30  being attached to the fitting part  12   a  formed at the front side of the front-wheel output shaft  12 . 
     According to this, since the joint part  61  of the propeller shaft  30  is centered on the front-wheel output shaft  12  by the centering part  63 , the vibration of the joint part  61  of the propeller shaft  30  with respect to the front-wheel output shaft  12  can be reduced. Moreover, by the flange part  121  of the front-wheel output shaft  12  being sandwiched between the spacer  70  and the joint part  61 , and the bolt member  20  being attached to the bolt hole  64  provided to the centering part  63  of the joint part  61  while being inserted into the spacer  70  from the rear side, it is suppressed that the bolt member  20  is loosened with respect to the bolt hole  64  due to a relative rotation caused by backlash in the rotational direction between the fitting part  12   a  of the front-wheel output shaft  12  and the joint part  61  which are splined-engaged with each other. 
     Further, since the joint part  61  of the propeller shaft  30  is provided with the intermediate shaft part  62 , the length between the rear end part of the joint part  61  and the rear end part of the centering part  63  becomes longer. According to this, the vibration of the joint part  61  is further suppressed, and assemblability upon the spline-engagement of the fitting part  12   a  of the front-wheel output shaft  12  with the joint part  61  of the propeller shaft  30  is improved. 
     Further, the gap is made between the flange part  121  of the front-wheel output shaft  12  and the spacer  70  and/or between the flange part  121  and the intermediate shaft part  62  of the propeller shaft  30 . Because of this gap, when the joint part  61  of the propeller shaft  30  rotates relative to the front-wheel output shaft  12 , a force in a rotational direction to loosen the bolt member  20  is difficult to be acted on a seat of the bolt member  20  attached to the bolt hole  64 . Therefore, the loosening of the bolt member  20  can be prevented. 
     Further, since the fitting part  12   a  of the front-wheel output shaft  12 , the joint part  61  of the propeller shaft  30 , and the centering part  63  of the joint part  61  inserted into the centering hole  122  of the flange part  121  of the front-wheel output shaft  12  are located between the seal members  73  and  74  in the front-and-rear direction, it can be avoided that foreign matters enter from outside and are caught between the fitting part  12   a  and the joint part  61 , and between the centering hole  122  and the centering part  63 . Therefore, the vibration of the joint part  61  of the propeller shaft  30  with respect to the front-wheel output shaft  12  can certainly be reduced. 
     The present disclosure is not limited by the illustrated embodiment, but various improvements and changes in design are possible without departing from the spirit of the present disclosure. 
     As described above, according to the present disclosure, in the transfer device mounted on the 4WD vehicle, the vibration of the joint part of the propeller shaft with respect to the output shaft for the auxiliary drive wheels is reduced, as well as the coming off of the propeller shaft being suppressed, and thereby, the present disclosure may suitably be used in a field of manufacturing this type of vehicles. 
     It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof, are therefore intended to be embraced by the claims. 
     DESCRIPTION OF REFERENCE CHARACTERS 
       1  Four-wheel-drive Vehicle 
       3  Transmission 
       3   a  Output Shaft of Transmission 
       10  Transfer Device 
       11  Rear-wheel Output Shaft (Main-drive-wheel Output Shaft) 
       12  Front-wheel Output Shaft (Auxiliary-drive-wheel Output Shaft) 
       12   a  Fitting Part 
       13  Powertrain Mechanism 
       20  Bolt Member 
       30  Propeller Shaft 
       31  Universal Joint 
       61  Joint Part 
       63  Centering Part 
       64  Bolt Hole 
       70  Spacer 
       121  Flange Part 
       122  Centering Hole