Abstract:
A power transfer unit is comprised of: a casing having a first side and a second side; a first shaft being rotatably supported by a first bearing sitting on the first side and a second bearing sitting on the second side, penetrating the casing from a coupling portion to the second side, and combining with the transmission to receive torque; a second shaft being rotatably supported by a third bearing sitting on the first side and a fourth bearing sitting on the second side and gearing with the first shaft to rotate in parallel with the first shaft, the second shaft comprising a bevel gear; and a third shaft being rotatably supported by the casing and gearing with the bevel gear, wherein the first bearing is disposed closer to the coupling portion than the bevel gear is.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation Application of, and as such claims priority to, PCT International Application No. PCT/JP2014/060274 (filed Apr. 9, 2014), the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In a front-wheel-drive vehicle, an engine installed in a front of the vehicle body generates torque and a differential receives and distributes the torque to right and left front-wheels. In a case of a four-wheel-drive vehicle, generally in combination with a transmission including the differential, a power transfer unit (PTU) for extracting and transmitting part of the torque to rear-wheels is used. 
         [0003]    The PTU has to change axial direction from an output shaft of the transmission to a propeller shaft and also has to absorb an offset between these shafts. Design thereof must bear a severe restriction as locations of these shafts are determined in advance. Further, the fact that the PTU is required to be installed in a relatively small space among other devices such as an engine and a transmission is also a requirement that limits the design. 
         [0004]    Japanese Patent Application Laid-open No. 2008-208947 discloses a related art. 
       SUMMARY 
       [0005]    The disclosure herein relates to a power transmission device in an automobile, and in particular to a power transfer unit for an automobile for distributing torque from one set of axles to another set of axles particularly in a four-wheel-drive vehicle. 
         [0006]    Respective shafts in the PTU, an input shaft in particular, must be often elongated in a lengthwise direction to meet the aforementioned design requirements. To support such long shafts without eccentric motion or precessional motion is often difficult. Eccentric motion or precessional motion affects other members combined with the shaft in question or imposes a non-negligible load on oil seals for example, or, in severer cases, causes the device to vibrate. 
         [0007]    The device described below has devised in light of the aforementioned problems. According to an aspect, a power transfer unit for extracting torque from a transmission of an automobile is comprised of: a casing having a first side having a coupling portion for combining with the transmission and a second side opposed to the first side; a first shaft being rotatably supported by a first bearing sitting on the first side of the casing and a second bearing sitting on the second side of the casing, penetrating the casing from the coupling portion to the second side, and combining with the transmission to receive the torque; a second shaft being rotatably supported by a third bearing sitting on the first side of the casing and a fourth bearing sitting on the second side of the casing and gearing with the first shaft to rotate in parallel with the first shaft, the second shaft comprising a bevel gear; and a third shaft being rotatably supported by the casing and extending in a direction distinct from the first shaft and the second shaft, the third shaft comprising an internal end including a pinion gear in mesh with the bevel gear and an external end led out of the casing, wherein the first bearing is disposed closer to the coupling portion than the bevel gear is. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a sectional plan view of an example power transfer unit, which is taken from a section running along axes of respective shafts. 
           [0009]      FIG. 2  is a side view of the power transfer unit viewed from a side opposed to a transmission. 
           [0010]      FIG. 3  is a side view of the power transfer unit viewed from a side on the transmission. 
       
    
    
     DESCRIPTION 
       [0011]    Examples will be described hereinafter with reference to  FIGS. 1 through 3 . 
         [0012]    Throughout the following description and the appended claims, a direction where first and second shafts run is defined as a lateral direction and a direction perpendicular thereto is defined as a longitudinal direction. Further, when the casing  11  is illustrated in a plan view, a series of wall sections thereof at one extremity in the lateral direction is defined as a first side and a series of wall sections at another extremity is defined as a second side. 
         [0013]    In the meantime, presently illustrated relations of the right and the left, and the top and the bottom, are but one example. Modifications where the right and the left are reversed or upside down are of course possible. 
         [0014]    Referring to  FIG. 1 , a power transfer unit (PTU) according to the present example can be used in an application for taking out part of torque from a transmission of a vehicle and transmitting it to a propeller shaft directed in a direction distinct from a shaft of the transmission. 
         [0015]    The PTU  1  is comprised substantially the whole of a casing  11  housing. The casing  11  has a coupling portion  13  at the first side projecting leftward, which is combined with the transmission and fixed by means of a coupling flange  14  shown in  FIG. 3 . The propeller shaft is combined with a shaft  7  led downward out of the casing  11 . 
         [0016]    The PTU  1  is comprised of a first shaft  3 , a second shaft  5 , a third shaft  7 , gears  37 , 55 , 57 , 73  for drivingly coupling them, and bearings  33 , 35 , 51 , 53 , 71  for supporting them. Any of them can be housed in the casing  11 . The first shaft  3  is combined with the transmission to receive the torque, the second shaft  5  gearing therewith to rotate in parallel therewith mediates the torque transmission, the bevel gear  57  and the pinion gear  73  change direction of rotation, and the PTU  1  then outputs the torque through the third shaft  7  to the propeller shaft. 
         [0017]    Referring to  FIGS. 2 and 3 , these shafts  3 ,  5  and  7  do not lie in the same plane but mutually have offsets in height. The sum of these offsets absorbs a relatively large offset between the transmission and the propeller shaft. Conversely, it may be difficult to absorb the large offset without these three shafts. 
         [0018]    Referring again to  FIG. 1 , the casing  11  is so constructed as to be dividable into a first part  11   a  including the first side and a second part  11   b  including the second side. Each of the first part  11   a  and the second part  11   b  may be further dividable but is preferably formed in a unitary body. Being formed in a unitary body is beneficial for convenience of assembly and also for strength and stiffness. 
         [0019]    The casing  11  is comprised of an opening  15  opened at the coupling portion  13  and an opening  17  opened at the second side, and the first shaft  3  penetrates the casing  11  from the opening  15  to the opening  17 . The first shaft  3  is, at an end projecting from the opening  15 , comprised of a coupling means such as splines  31 , thereby being drivingly combined with the transmission. 
         [0020]    The first shaft  3  may be tubular in its lengthwise direction. While the transmission has a differential installed therein for output, its output shaft  9  is led out through the first shaft  3  rightward. The output shaft  9  is, for example, coupled with the axle. 
         [0021]    The first shaft  3  is rotatably supported by a pair of bearings  33 , 35  at least. These bearings can be ball bearings, for example, but bearings of any other type may be instead used. 
         [0022]    To seat the first bearing  33 , the first part  11   a  of the casing  11  is, on the internal face and at the first side, comprised of a first race  21 . The first race  21  fits on the entire circumference of the first bearing  33 . To seat the second bearing  35 , the second part  11   b  of the casing  11  is, on the internal face and at the second side, comprised of a second race  27 . The second race  27  also fits on the entire circumference of the second bearing  35 . 
         [0023]    Around an entrance of the opening  13  and between its internal face and the first shaft  3 , an oil seal  81  is interposed. The oil seal  81  is configured not only to seal the oil therein but also to prevent oil inflow from the exterior, thereby preventing both leakage and mixture of oil. Similarly, around an entrance of the opening  15  and between its internal face and the first shaft  3 , an oil seal  83  is interposed. As will be understood from the above description, the first race  21  and the oil seal  81  inherently get close to each other and the second face  27  and the oil seal  83  inherently get close to each other. 
         [0024]    The first shaft  3  is comprised of the first gear  37  for gearing with the second shaft  5 . The first gear  37  may be formed in a unitary body with the first shaft  3  if possible but may be formed in a separate body as shown in the drawing. In a case of the first gear  37  being a separate body, spline coupling may be used for coupling it with the first shaft  3 , but welding or any other means may be instead used. To set the first gear  37  in place, the first shaft  3  may have a step  39 . As a side face of the first gear  37  gets in contact with the step  39 , it falls into place. Or, the part in question may be welded or any other means may be applied thereto. 
         [0025]    The second shaft  5  runs in parallel with the first shaft  3  and its total length is generally housed in the casing  11 . The second shaft  5  is also rotatably supported by a pair of bearings  51 , 53 , at least. To bear thrust reaction force from the bevel gear  57 , these bearings  51 , 53  can be taper roller bearings, for example, but any other type may be instead used. 
         [0026]    To seat the third bearing  51 , the first part  11   a  of the casing  11  is, on the internal face and at the first side, comprised of a third race  23 . The third race  23  fits on the entire circumference of the third bearing  51 . To seat the fourth bearing  53 , the second part  11   b  of the casing  11  is, on the internal face and at the second side, comprised of a fourth race  29 . The fourth race  29  also fits on the entire circumference of the fourth bearing  53 . 
         [0027]    The first race  21  and the third race  23  may have no offset in the lateral direction as shown in the drawing but may have some offset. Similarly the second race  27  and the fourth race  29  may have no offset in the lateral direction as shown in the drawing but may have some offset. 
         [0028]    The second shaft  5  is comprised of the second gear  55  for gearing with the first shaft  3 . The second gear  55  may be formed in a unitary body with the second shaft  5  as shown in the drawing but may be formed in a separate body. 
         [0029]    The second shaft  5  is further comprised of the bevel gear  57 . The bevel gear  57  is a so-called hypoid gear and may be formed in a unitary body with the second shaft  5  if possible. The bevel gear  57  is, however, normally formed in a separate body and is coupled with the second shaft  5  by means of splines, for example. The bevel gear  57  is disposed between the gear set  37 ,  55  and the bearings  33 ,  51 . To set the bevel gear in place, the second shaft  5  may have a step  61  and a bolt  59  may be used for the purpose of fixation and regulation of the position. 
         [0030]    The bevel gear  57  may fit in the third bearing  51  and be directly supported thereby. As the third bearing  51  directly bears the reaction force received by the bevel gear  57 , the bevel gear  57  is prevented from making eccentric motion or precessional motion and accordingly the second shaft  5  is prevented from making eccentric motion or precessional motion. 
         [0031]    The third shaft  7  is, at its internal end, comprised of the pinion gear  73 . Corresponding to the bevel gear  57 , the pinion gear  73  is also a hypoid gear. The third shaft  7  is further, at the external end, comprised of a flange  75 , for example, for combining with the propeller shaft. Any combination means can be used in place of the flange  75 . 
         [0032]    The third shaft  7  may be formed in a unitary body but may be formed from two or more members, which are mutually axially movable so as to regulate relative positions. In the example illustrated in the drawing, for instance, it is constituted of a part including the pinion gear  73  and a part including the flange  75 , which are mutually combined by means of splines. It is thereby capable of transmitting torque from the pinion gear  73  to the flange  75 , and the pinion gear  73  is capable of regulating its axial position relative to the flange  73 . It may be comprised of a nut  77  in order to regulate pressure to the bevel gear  57 . More specifically, the present example has an advantage to allow regulation of tooth contact of the pinion gear  73  onto the bevel gear  57 . 
         [0033]    The casing  11  is comprised of an opening  25  for receiving the third shaft  7 . The third shaft  7  is, along with a tubular portion  71  housing the unit bearing  78 , for example, inserted into the opening  25 . The internal end of the third shaft  7  is within the casing  11  and makes the pinion gear  73  move from the second side to the bevel gear  57  to engage with the bevel gear  57 . In order to regulate the axial position, a shim  74  is interposed between the casing  11  and the tubular portion  71  and tightening the bolt  76  gives pressure to the unit bearing  78 . 
         [0034]    The external end of the third shaft  7  is led out of the casing  11  and is combined with the propeller shaft via the flange  75 . Around an external end of the tubular portion  71 , and between the tubular portion  71  and the third shaft  7 , an oil seal  72  is interposed. This prevents both leakage and mixture of oil as with the other oil seals. 
         [0035]    As will be understood from the above explanation, the first race  21  and the third race  23  are included in the first part  11   a,  and the second race  27  and the fourth race  29  are included in the second part  11   b.  When separating the second part  11   b  from the first part  11   a,  the first race  21  and the third race  23  are exposed in the deepest part within the first part  11   a.  The first shaft  3  and the second shaft  5 , along with the bearings and the gears accompanying them, can be readily fit in the exposed races  21  and  23 , and mutual gearing can be simultaneously established. When the second part  11   b  is combined with the first part  11   a  so as to cover these parts, the bearings  35 ,  53  are simultaneously fit in the second race  27  and the fourth race  29 . Assembly of these components is thereby finished. After finishing the assembly, the third shaft  7  is inserted therein and then tooth contact between the pinion gear  73  and the bevel gear  57  can be regulated. More specifically, the present example prominently facilitates assembly of the PTU  1 . 
         [0036]    As will be readily understood as well, the first bearing  33  comes close to the coupling portion  13 , the opening  15 , and the oil seal  81  of the casing  11 ; and the second bearing  35  comes close to the opening  17  and the oil seal  83 . Therefore, if the first shaft  3  makes an eccentric motion or precessional motion, an influence on the oil seals or components combined therewith would be small. Further the pair of bearings  33 ,  35  staying away from each other supports the first shaft  3 , the eccentric motion or the precessional motion per se hardly occurs. 
         [0037]    As the second shaft  5  is also supported at both ends, the eccentric motion or the precessional motion hardly occurs. Further, as the bevel gear  57  that receives the thrust reaction force is supported directly by the bearing  51 , the source of the eccentric motion or the precessional motion is done away with per se. 
         [0038]    Further, as any of the bearings has its entire circumference supported by each race, off-center force will not act on any of the bearings and the races, thereby ensuring firm support for the shafts. As the first race  21  and the third race  23  constitute a unitary body and the second race and the fourth race constitute a unitary body, the whole structure has a high stiffness and also a high strength. Therefore each shaft is more firmly supported. 
         [0039]    Further, as the bearing  33  is disposed further leftward as compared with the bevel gear  57 , interference therebetween is avoided and the bevel gear  57  is not required to deviate upward in order to avoid the bevel gear  57 . Further it is also not required to make the diameter of the bearing  33  larger in order to prevent the eccentric motion or the precessional motion. The casing  11  can be therefore reduced in size in the longitudinal direction and thus a region  12  shown in  FIGS. 1 and 3 , enclosed by dotted chain lines, can be cut off. As described already, the PTU has a restriction on installation, by which the PTU must be installed in a space among other devices. While this reduction in size might appear relatively minor, this significantly improves freedom of design. 
         [0040]    Although certain examples have been described above, modifications and variations of the examples described above will occur to those skilled in the art, in light of the above teachings.