Abstract:
A device operable to distribute driving forces to left and right wheels of a vehicle, includes: a differential mechanism, a driving-force adjuster and a differential limiter. The differential mechanism is operable to distribute a driving force from a drive source of the vehicle to the left and right wheels as distributed driving forces, while allowing a rotation difference between the left and right wheels. The driving-force adjuster is operable to adjust each of the distributed driving forces. The differential limiter is operable to limit rotation difference between the left and right wheels by applying a limiting torque to the differential mechanism.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a driving-force laterally-distributing device and, more particularly, to a technique for distributing a driving force from a driving force source such as an engine properly to left and right wheels in accordance with the running state of a vehicle. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, there has been developed a device for controlling a yawing moment to act on a vehicle, by generating a driving force difference between left and right wheels at a turning time of a vehicle, thereby to improve the turning performance of the vehicle. 
         [0005]    For example, Japanese Patent No. 2,738,225 discloses a driving-force laterally-distributing device provided with a driving force transmission control mechanism for distributing the driving forces of the left and right wheels by transmitting the driving force of an engine from an input unit, while allowing the rotation difference between the left and right wheels, through a differential mechanism to transmit the driving force to the axles of the left and right wheels and by shifting the driving force of one of the axles of the left and right wheels to the driving force of the other. 
         [0006]    According to the technique disclosed in Japanese Patent No. 2,738,225, however, the driving force difference is established between the left and right wheels by shifting the driving force to either the left or right wheel, but cannot be limited. 
         [0007]    Therefore, there arise a problem that the slip of the left and right drive wheels at the straight running time of the vehicle cannot be suppressed. 
         [0008]    If the slip of the left and right drive wheels at the straight running time of the vehicle is suppressed by the technique of Japanese Patent No. 2,738,225, for example, the driving force shifts to either the left or right wheel, thereby to cause a problem that the vehicle turns. 
       SUMMARY 
       [0009]    According to one aspect of the invention, there is provided a device operable to distribute driving forces to left and right wheels of a vehicle, the device including: a differential mechanism, operable to distribute a driving force from a drive source of the vehicle to the left and right wheels as distributed driving forces, while allowing a rotation difference between the left and right wheels; a driving-force adjuster, operable to adjust each of the distributed driving forces; and a differential limiter, operable to limit rotation difference between the left and right wheels by applying a limiting torque to the differential mechanism. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiment may be described in detail with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  is an entire constitution diagram of a vehicle having a driving-force lateral-distributing device according to the invention; 
           [0012]      FIG. 2  is a sectional view of the driving-force laterally-distributing device according to the invention; 
           [0013]      FIG. 3  is a constitution diagram schematically showing the driving-force laterally-distributing device according to the invention; 
           [0014]      FIG. 4  is a perspective view of a left partition portion in the driving-force laterally-distributing device according to the invention; 
           [0015]      FIG. 5  is a constitution diagram schematically showing a driving-force laterally-distributing device according to a first modification; 
           [0016]      FIG. 6  is a constitution diagram schematically showing a driving-force laterally-distributing device according to a second modification; 
           [0017]      FIG. 7  is a constitution diagram schematically showing a driving-force laterally-distributing device according to a third modification; 
           [0018]      FIG. 8  is a constitution diagram schematically showing a driving-force laterally-distributing device according to a fourth modification; and 
           [0019]      FIG. 9  is a constitution diagram schematically showing a driving-force laterally-distributing device according to a fifth modification. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Exemplary embodiments of the present invention are described in the following with reference to the accompanying drawings. 
         [0021]    Reference is made to  FIG. 1  to  FIG. 4 , of which:  FIG. 1  is an entire constitution diagram of a vehicle having a driving-force lateral-distributing device according to the invention;  FIG. 2  is a sectional view of the driving-force laterally-distributing device according to the invention;  FIG. 3  is a constitution diagram schematically showing the driving-force laterally-distributing device according to the invention; and  FIG. 4  is a perspective view of a left partition portion. 
         [0022]    As shown in  FIG. 1 , a vehicle  1  is a four-wheel drive vehicle constituted to comprise: an engine  2  mounted as a drive source on a body front portion; a transmission  4  connected to one side of the engine  2 ; a center diff  6  connected to the transmission  4  for distributing the driving force to a front-wheel side and a rear-wheel side; a front diff  16  for distributing the driving force distributed to the front-wheel side by the center diff  6 , to the individual axles  12  and  14  of a left front wheel  8  and a right front wheel  10 ; a propeller shaft  18  for transmitting the driving force distributed to the rear-wheel side by the center diff  6 , to the rear-wheel side; and a driving-force laterally-distributing device  28  connected to one end of the propeller shaft  18  for distributing the driving force to the individual axles  24  and  26  (the left- and right-wheel axles) of a left rear wheel  20  and a right rear wheel  22  in accordance with the running state of the vehicle  1 . 
         [0023]    The engine  2 , the transmission  4 , the center diff  6  and the front diff  16  thus far described are well known in the art, and the driving-force laterally-distributing device  28  according to the invention is described in detail in the following. 
         [0024]    The driving-force laterally-distributing device  28  is constituted by housing, in a body case  30 : an input unit  32  forming one end side of the propeller shaft  18 ; a differential mechanism unit  34  (a differential unit) connected to the input unit  32  and arranged on the left rear-wheel axle  24  and the right rear-wheel axle  26 ; a driving-force laterally-adjusting mechanism unit  36  (a driving-force laterally-adjusting unit) arranged on the right rear-wheel axle  26 ; and a differential limiting mechanism unit  38  (a differential limiting unit) arranged on the left rear-wheel axle  24 . 
         [0025]    The body case  30  is constituted to include: an input case unit  40  for housing the input unit  32 ; a central wall portion  42  connected to the input case unit  40  and partitioning the differential mechanism unit  34  and the driving-force laterally-adjusting mechanism unit  36 ; a right-side wall portion  46  for housing the driving-force laterally-adjusting mechanism unit  36  together with the central wall portion  42  while interposing a right partition portion  44 ; a left partition portion  48  for housing the differential mechanism unit  34  together with the central wall portion  42  and partitioning the differential mechanism unit  34  and the differential limiting mechanism unit  38 ; and a left-side wall portion  50  for housing the differential limiting mechanism unit  38  together with the left partition portion  48 . 
         [0026]    The right-side wall portion  46 , the left partition portion  48  and the left-side wall portion  50  are generally formed into such cup shapes as are individually opened toward the central wall portion  42  and as have holes capable of passing the axles  24 ,  26  and so on of the left and right wheels  20  and  22  therethrough. 
         [0027]    Moreover, the central wall portion  42  and the right partition portion  44  are also formed to have such holes in their central portions as can pass the axles  24 ,  26  and so on therethrough. In the individual holes of those individual wall portions  42 ,  44 ,  46 ,  48  and  50 , moreover, the individual axle members such as the left rear-wheel axle  24  and the right rear-wheel axle  26  are rotatably born through bearings or the like. 
         [0028]    Especially in the central wall portion  42 , oil seal members  42   a  and  42   b  are arranged in the hole portions so that they partition the side of the differential mechanism unit  34  and the side of the driving-force laterally-adjusting mechanism unit  36  liquid-tight. 
         [0029]    In the body case  30 , moreover, oils of different kinds are reserved in such one area on the side of the differential mechanism unit  34  partitioned liquid-tight that the input unit  32 , the differential mechanism unit  34  and the differential limiting mechanism unit  38  are housed, and in the other area on the side of the driving-force laterally-adjusting mechanism unit  36 . 
         [0030]    As shown in  FIG. 4 , moreover, the left partition portion  48  has a plurality of plate-shaped rib portions  48   a  formed radially on its inner circumference in the axial direction (as will be simply called the “axle direction”) of the axles  24  and  26  of the left and right rear wheels  20  and  22  and in the radial directions, i.e., radially of the axles  24  and  26 . Here, the rib portions  48   a  are so spaced at a predetermined distance from the differential mechanism unit  34  that they are positioned to have no direct interference with the differential mechanism unit  34 . 
         [0031]    The specific constitutions of the individual units housed in the body case  30  are described in the following. 
         [0032]    The input unit  32  is equipped at its leading end with a drive gear  32   a , which meshes with the crown gear  52  of the differential mechanism unit  34 . 
         [0033]    In the differential mechanism unit  34 , a generally cylindrical diff case  54  is connected to the left-side face of the crown gear  52 . 
         [0034]    Moreover, the diff case  54  has the so-called double pinion type planetary gear mechanism. Specifically, a ring gear  54   a  is formed on the inner circumference of the diff case  54 , and a sun gear  56  is splined to one end portion of the right rear-wheel axle  26 . Between the ring gear  54   a  and the sun gear  56 , there are arranged a pair of planetary pinions  58   a  and  58   b , which mesh with the ring gear  54   a  on one side and with the sun gear  56  on the other side. Here in  FIGS. 2 and 3 , the planetary pinions  58   a  and  58   b  are individually shown by one, but totally three sets of paired planetary pinions  58   a  and  58   b  are arranged between the ring gear  54   a  and the sun gear  56 . 
         [0035]    Moreover, the left-end portions of the shafts of the individual planetary pinions  58   a  and  58   b  are borne in a left-side planetary carrier  60   a  splined to one end portion of the left rear-wheel axle  24 . On the other hand, the right-end portions of the shafts of the individual planetary pinions  58   a  and  58   b  are borne on a right-side planetary carrier  60   b , which is splined to the left-end portion of an input intermediate shaft  62  rotatably fitted on the right rear-wheel axle  26 . 
         [0036]    Specifically in the differential mechanism unit  34 , the rotational driving force from the engine  2  is transmitted through the propeller shaft  18  from the input unit  32  to the crown gear  52  so that the diff case  54  rotates together with the crown gear  52 . Moreover, the ring gear  54   a  on the inner circumference of the diff case  54  rotates so that the planetary pinions  58   a  and  58   b  revolve, while rotating on their axes, around the sun gear  56 . As a result, the rotational driving forces are transmitted individually through the left-side planetary carrier  60   a  to the left rear-wheel axle  24 , through the right-side planetary carrier  60   b  to the input intermediate shaft  62  of the driving-force laterally-adjusting mechanism unit  36 , and through the sun gear  56  to the right rear-wheel axle  26 . 
         [0037]    In the driving-force laterally-adjusting mechanism unit  36 , there are arranged: the input intermediate shaft  62  which is rotatably fitted on the outer circumference of the right rear-wheel axle  26  so that it rotates synchronously with the right-side planetary carrier  60   b ; an accelerating intermediate shaft  64  which is arranged on the right side of the input intermediate shaft  62  and rotatably fitted on the outer circumference of the right rear-wheel axle  26 ; and a decelerating intermediate shaft  66  which is rotatably fitted on the outer circumference of the accelerating intermediate shaft  64 . 
         [0038]    Moreover, at the right-end portion of the input intermediate shaft  62 , the left-end portion of the accelerating intermediate shaft  64  and the left-end portion of the decelerating intermediate shaft  66 , respectively, there are formed an input counter gear portion  62   a , an accelerating counter gear portion  64   a  and a decelerating counter gear portion  66   a . These individual counter gear portions  62   a ,  64   a  and  66   a  are arrayed in the axle direction, and their tooth numbers are set such that the accelerating counter gear portion  64   a  is less but the decelerating counter gear portion  66   a  is more than the input counter gear portion  62   a.    
         [0039]    Moreover, accelerating/decelerating gears  68  are arranged on the outer circumference sides of the aforementioned individual counter gear portions  62   a ,  64   a  and  66   a . Here, only one accelerating/decelerating gear  68  is shown in  FIGS. 2 and 3 , but totally three sets of accelerating/decelerating gears  68  are arranged on the outer circumference sides of the individual counter gear portions  62   a ,  64   a  and  66   a.    
         [0040]    The accelerating/decelerating gear  68  has a center shaft  70  supported at the end portion of the body case  30  by the central wall portion  42  and the right partition portion  44 . On the outer circumference of the center shaft  70 , moreover, there are integrally and rotatably formed: an input gear portion  72  for meshing with the input counter gear portion  62   a , an accelerating gear portion  74  for meshing with the accelerating counter gear portion  64   a ; and a decelerating gear portion  76  for meshing with the decelerating counter gear portion  66   a . The tooth numbers of those individual gear portions  72 ,  74  and  76  are set such that the accelerating gear portion  74  is more but the decelerating gear portion  76  is less than the input gear portion  72 . 
         [0041]    In short, the rotational driving force, as transmitted to the input intermediate shaft  62 , is transmitted from the input counter gear portion  62   a  through the input gear portion  72  to the accelerating/decelerating gear  68 . Moreover, the rotating speed, as transmitted from the accelerating gear portion  74  of the accelerating/decelerating gear  68  through the accelerating counter gear portion  64   a , of the accelerating intermediate shaft  64  is accelerated, by the aforementioned tooth number relation, i.e., by the relation of the gear ratio, to a rotating speed higher than that of the input intermediate shaft  62 . On the other hand, the rotating speed, as transmitted from the decelerating gear portion  76  through the decelerating counter gear portion  66   a , of the decelerating intermediate shaft  66  is decelerated to a rotating speed lower than that of the input intermediate shaft  62 . 
         [0042]    Moreover, an accelerating clutch portion  78  and a decelerating clutch portion  80  of multi-disc type friction clutches are formed at the right-side end portions of the accelerating intermediate shaft  64  and the decelerating intermediate shaft  66 . 
         [0043]    Specifically, an accelerating-side disc supporting member  82  is splined to the right-side end portion of the accelerating intermediate shaft  64 , and a plurality of accelerating-side inner discs  84  are splined, while keeping a predetermined spacing inbetween, to the outer circumference of the accelerating-side disc supporting member  82 . On the other hand, a decelerating-side disc supporting member  86  is so splined to the right-side end portion of the decelerating intermediate shaft  66  as is located on the left side of the accelerating-side disc supporting member  82 , and a plurality of decelerating-side inner discs  88  are splined, while keeping a predetermined spacing inbetween, to the outer circumference of the decelerating-side disc supporting member  86 . 
         [0044]    Moreover, outer discs  90  are individually arranged between the individual accelerating-side inner discs  84  and between the individual decelerating-side inner discs  88 . 
         [0045]    Moreover, a cylindrical clutch housing  92  is disposed to cover the individual discs  84 ,  88  and  90  and the individual disc supporting members  82  and  86 , and the outer circumferences of the outer discs  90  are splined to the inner circumference of the clutch housing  92 . 
         [0046]    In the clutch housing  92 , there is formed a partition plate  92   a  which partitions the individual discs  84  and  90  on the accelerating side and the individual discs  88  and  90  on the decelerating side. In the two left- and right-side faces of the clutch housing  92 , moreover, there are formed a plurality of through holes  92   b  and  92   c , which are juxtaposed in the circumferential direction. Pistons  94   a  and  96   a  are so inserted into the through holes  92   b  and  92   c  as can slide in the axial directions. 
         [0047]    The pistons  94   a  and  96   a  are the portions of hydraulic piston mechanisms  94  and  96 , which are positioned on the two left and right sides of the clutch housing  92  and which are disposed in the right-side wall portion  46  and the right partition portion  44  of the body case  30 , respectively. The hydraulic piston mechanisms  94  and  96  form part of an electronically controlled oil pressure generating device, which is operationally controlled by the not-shown ECU mounted on the vehicle  1 . 
         [0048]    Moreover, the clutch housing  92  is splined at its right-side end portion to the right rear-wheel axle  26 . 
         [0049]    In short, the accelerating clutch portion  78  is constituted to include the clutch housing  92 , the hydraulic piston mechanism  94  disposed in the right-side wall portion  46 , the accelerating-side disc supporting member  82 , and the inner disc  84  and the outer disc  90  on the accelerating side. The decelerating clutch portion  80  is constituted to include the clutch housing  92 , the hydraulic piston mechanism  96  disposed in the right partition portion  44 , the decelerating-side disc supporting member  86 , and the inner disc  88  and the outer disc  90  on the decelerating side. 
         [0050]    When the individual discs  84  and  90  on the accelerating side are pushed by the piston  94   a  on the accelerating side, for example, the driving force is transmitted between the accelerating intermediate shaft  64  and the right rear-wheel axle  26 . When the individual discs  88  and  90  on the decelerating side are pushed by the piston  96   a  on the decelerating side, the driving force is transmitted between the decelerating intermediate shaft  66  and the right rear-wheel axle  26 . Here, the individual disks  84 ,  88  and  90 , as disposed in the accelerating clutch portion  78  and the decelerating clutch portion  80 , are basically used in a slip state, i.e., in a half-clutch state. 
         [0051]    On the other hand, the differential limiting mechanism unit  38  is the so-called differential limiting clutch made of a multi-disc friction clutch. 
         [0052]    Specifically, a differential limiting clutch disc supporting member  100  is splined to the left-side end portion of the diff case  54  of the differential limiting mechanism unit  34 , and a plurality of differential limiting clutch inner discs  102  are splined, while keeping a predetermined spacing inbetween, to the outer circumference of the differential limiting clutch disc supporting member  100 . 
         [0053]    Moreover, a differential limiting clutch outer disc  104  is arranged between the individual differential limiting clutch inner discs  102 . 
         [0054]    Moreover, a cylindrical differential limiting clutch housing  106  is disposed to cover those individual discs  102  and  104 , and the differential limiting clutch outer disc  104  is splined to the inner circumference of the differential limiting clutch housing  106 . 
         [0055]    The differential limiting clutch housing  106  abuts rotatably at its right-side face against the left partition portion  48  of the body case  30  through a thrust bearing  108 . 
         [0056]    Moreover, the differential limiting clutch housing  106  is constituted to include two parts, i.e., a clutch case  106   a  and a clutch flange  106   b , which are splined to each other. Therefore, the frictional clutch disc can be assembled in the differential limiting clutch housing  106 . 
         [0057]    In the left-side face of the differential limiting clutch housing  106 , on the other hand, a plurality of through holes  106   c  are so formed as are arrayed in the circumferential direction. Pistons  110   a  are so individually fitted in the through holes  106   c  as can slide in the axial directions. 
         [0058]    The pistons  110   a  form part of a differential limiting clutch hydraulic piston mechanism  110 , which is positioned on the left side of the differential limiting clutch housing  106  and disposed in the left-side wall portion  50  of the body case  30 . The differential limiting clutch hydraulic piston mechanism  110  also forms part of the electronic control oil pressure generating device, which is operationally controlled like the hydraulic piston mechanism  94  and  96  of the accelerating clutch portion  78  and the decelerating clutch portion  80  by the ECU of the vehicle  1 . 
         [0059]    Moreover, the left-side end portion of the differential limiting clutch housing  106  is splined to the left rear-wheel axle  24 . 
         [0060]    Thus, the differential limiting mechanism unit  38  is constituted to include the differential limiting clutch disc supporting member  100 , the differential limiting clutch housing  106 , the differential limiting clutch hydraulic piston mechanism  110 , the differential limiting clutch inner disk  102  and the differential limiting clutch outer disk  104 . 
         [0061]    Moreover, the individual discs  102  and  104  are pushed and engaged by the pistons  110   a , for example, so that the rotations transmitted from the diff case  54  are transmitted, as they are, through the differential limiting clutch housing  106  to the left rear-wheel axle  24 . Here, the differential limiting clutch inner disc  102  and the differential limiting clutch outer disc  104  are made of such steel discs as can be brought into complete engagement (or can be directly coupled). 
         [0062]    The operations of the driving-force laterally-distributing device thus constituted are described in the following. 
         [0063]    In this driving-force laterally-distributing device  28 , the rotational driving force from the engine  2  is transmitted from the drive gear  32   a  of the input unit  32  to the crown gear  52  of the differential mechanism unit  34 . 
         [0064]    In this differential mechanism unit  34 , moreover, when the diff case  54  rotates, and the planetary pinions  58   a  and  58   b  rotate and revolve through the ring gear  54   a  so that the rotational driving force is transmitted through the left-side planetary carrier  60   a  to the left rear-wheel axle  24  and through the sun gear  56  to the right rear-wheel axle  26 . 
         [0065]    By these actions of the differential mechanism unit  34 , the rotating speed difference between the axles  24  and  26  is allowed by the behaviors of the planetary pinions  58   a  and  58   b , so that the rotational driving force inputted is equivalently transmitted to the axles  24  and  26  of the left and right wheels  20  and  22 . 
         [0066]    On the other hand, the rotations of the right-side planetary carrier  60   b  are transmitted through the input intermediate shaft  62  to the driving-force laterally-adjusting mechanism unit  36 . 
         [0067]    In the driving-force laterally-adjusting mechanism unit  36 , the rotating speed inputted from the input intermediate shaft  62  is so transmitted through the accelerating/decelerating gears  68  that it is accelerated for the accelerating intermediate shaft  64  and decelerated for the decelerating intermediate shaft  66 . 
         [0068]    On the other hand, the right rear-wheel axle  26  rotates through the sun gear  56  of the differential mechanism unit  34  so that the clutch housing  92  of the driving-force laterally-adjusting mechanism unit  36  also rotates. 
         [0069]    In accordance with the control of the ECU, moreover, the pistons  94   a  and  96   a  of the hydraulic piston mechanisms  94  and  96  on either the accelerating side or the decelerating side push the corresponding individual disks  84 ,  88  and  90  so that the driving force is transmitted at the accelerating clutch portion  78  or the decelerating clutch portion  80  between the accelerating intermediate shaft  64  or the decelerating intermediate shaft  66  and the right rear-wheel axle  26 . 
         [0070]    Specifically in the accelerating clutch portion  78 , the rotating speed of the accelerating inner disc  84  on the side of the accelerating intermediate shaft  64  is higher than the rotating speed of the outer disc  90  on the side of the right rear-wheel axle  26 . If the individual discs  84  and  90  are made in this state to engage with each other, therefore, the rotational driving force on the side of the accelerating intermediate shaft  64  shifts to the side of the right rear-wheel axle  26  in accordance with the principle that the driving force is transmitted from the higher side to the lower side of the rotating speed. As a result, the driving force of the right rear-wheel axle  26  increases, but the rotational driving force of the left rear-wheel axle  24 , as transmitted from the accelerating intermediate shaft  64  through the accelerating/decelerating gear  68 , the input intermediate shaft  62  and the differential mechanism unit  34 , decreases. 
         [0071]    In case the decelerating clutch unit  80  is engaged, on the contrary, the rotational driving force of the right rear-wheel axle  26  decreases, but the rotational driving force of the left rear-wheel axle  24  increases. 
         [0072]    When the accelerating clutch portion  78  and the decelerating clutch portion  80  are individually out of engagement, the rotational driving force is transmitted to the axles  24  and  26  of the left and right wheels  20  and  22  exclusively by the operations of the differential mechanism unit  34 . 
         [0073]    On the other hand, the rotational driving force of the diff case  54  of the differential mechanism unit  34  is transmitted through the differential limiting clutch disc supporting member  100  of the differential limiting mechanism unit  38  to the differential limiting clutch inner disc  102 . 
         [0074]    In accordance with the control of the ECU, moreover, the pistons  110   a  of the differential limiting clutch hydraulic piston mechanism  110  push and engage the friction clutches  102  and  104  of the individual differential limiting clutches. The engagement limits the differential, as has been allowed in the differential mechanism unit  34 , between the diff case  54  and the left rear-wheel axle  24 . 
         [0075]    In short, the rotational driving force from the input unit  32  is transmitted directly to the left rear-wheel axle  24 . 
         [0076]    Moreover, the differential mechanism unit  34  limits the differential of the diff case  54  from the left-side planetary carrier  60   a  connected to the left rear-wheel axle  24 , that is, the planetary gears  58   a  and  58   b  and the sun gear  56 . As a result, the limitation is also made on the differential of the right rear-wheel axle  26  through the sun gear  56 , that is, on the differential of the axles  24  and  26  of the left and right rear wheels  20  and  22 . 
         [0077]    On the basis of the operations thus far described, the ECU controls not only the accelerating clutch portion  78  and the decelerating clutch portion  80  of the driving-force laterally-adjusting mechanism unit  36  but also the differential limiting clutches of the differential limiting unit  38  in accordance with the running state of the vehicle  1 , thereby to distribute the proper driving force to the left and right rear wheels  20  and  22 . 
         [0078]    At a turning time of the vehicle  1 , for example, the driving force difference suitable for the turn can be established in the left and right rear wheels  20  and  22  by the aforementioned driving-force laterally-adjusting mechanism, thereby to improve the turning performance and the traction performance. 
         [0079]    At the straight running time of the vehicle  1 , on the other hand, the slips of the left and right rear wheels  20  and  22  can be suppressed by the aforementioned differential limiting mechanism, thereby to improve the traction performance. 
         [0080]    Thus, the running stability not only at the turning time but also at the straight running time can be improved to perform the driving force distribution more properly according to the running state. 
         [0081]    In the driving-force laterally-distributing device  28 , moreover, the individual units  32 ,  34 ,  36  and  38  are housed in the body case  30 , and the oil is shared among the input unit  32 , the differential mechanism unit  34  and the differential limiting mechanism unit  38 . As a result, the driving-force laterally-distributing device  28  can be made to have the compact and simple constitution, thereby to suppress the complexity of the structure and the layout and the rise in the cost. 
         [0082]    Moreover, the differential limiting mechanism unit  38  is arranged on the left side of the differential mechanism unit  34 , that is, on the side opposite to the driving-force laterally-adjusting mechanism unit  36 , so that its space can be sufficiently retained. 
         [0083]    Moreover, the rib portions  48   a  are formed at the left partition portion  48  defining the differential mechanism unit  34  and the differential limiting unit  38 , so that they can support the differential limiting mechanism unit  38  and the body case  30  themselves sufficiently. Moreover, the rib portions  48   a  are formed radially of the axle direction so that they can suppress the agitation of the oil, as might otherwise be caused by the rotations of the diff case  54  of the differential mechanism unit  34 . At the same time, the excessive temperature rise of the oil or the body case  30  can be suppressed by the heat dissipation through the rib portions  48   a , thereby to keep the actions of the differential mechanism unit  34 , the differential limiting mechanism unit  38  and so on satisfactory. 
         [0084]    On the other hand, the right-side face of the differential limiting clutch housing  106  of the differential limiting mechanism unit  38  abuts against the left partition portion  48  having those rib portions  48   a  through the thrust bearing  108 . When the individual disks  102  and  104  are pushed by the pistons  110   a  of the differential limiting mechanism unit  38 , the pushing force can be dispersed to the left partition portion  48 , so that the elastic deformation of the differential limiting mechanism unit  38  can be suppressed to improve the responsiveness of the differential limitation and the durability satisfactorily. 
         [0085]    Thus, the driving-force laterally-distributing device according to the invention is enabled, by the simple constitution, to perform the driving force distribution more properly according to the running state. 
         [0086]    The description on the mode of embodiment of the driving-force laterally-distributing device according to the invention is thus far finished. However, the mode of embodiment should not be limited to the aforementioned one. 
         [0087]    For example, the aforementioned mode of embodiment may also be modified into driving-force laterally-distributing devices having constitutions, as shown in  FIG. 5  to  FIG. 9 . 
         [0088]    Specifically, a driving-force laterally-distributing device  200 , as shown in  FIG. 5 , according to a first modification is constituted to have a differential mechanism unit  202  equipped with a diff case  204  having the so-called bevel gear, in place of the diff case  54  which is disposed in the differential mechanism unit  34  of the aforementioned mode of embodiment and which has the planetary gear mechanism. 
         [0089]    A driving-force laterally-distributing device  300 , as shown in  FIG. 6 , according to a second modification is constituted to divide the driving-force laterally-adjusting mechanism unit  36  of the aforementioned embodiment so laterally that a right driving-force adjusting unit  304  for distributing the driving force from the left rear wheel to the right rear wheel is arranged on the right side of a differential mechanism unit  302  and that a left driving-force adjusting unit  308  for distributing the driving force from the right rear wheel to the left rear wheel is arranged on the left side of a differential limiting unit  306 . 
         [0090]    A driving-force laterally-distributing device  400 , as shown in  FIG. 7 , according to a third modification is constituted to have a driving-force laterally-adjusting mechanism unit  402  equipped with an accelerating gear  404  having two gear portions, in place of the accelerating/decelerating gear  68  which is disposed in the driving-force laterally-adjusting mechanism unit  36  of the aforementioned mode of embodiment and composed of the three gear portions. 
         [0091]    A driving-force laterally-distributing device  500 , as shown in  FIG. 8 , according to a fourth modification is constituted to have a driving-force laterally-adjusting mechanism unit  502  equipped with a brake  504  for shifting the driving force from the left axle to the right axle and a brake  506  for shifting the driving force from the right axle to the left axle, in place of the accelerating clutch portion  78  and the decelerating clutch portion  80 , which are disposed in the driving-force laterally-adjusting mechanism unit  36  of the aforementioned mode of embodiment. 
         [0092]    A driving-force laterally-distributing device  600 , as shown in  FIG. 9 , according to a fifth modification is constituted to divide the driving-force adjusting unit into a right driving force adjusting unit  602  and a left driving force adjusting unit  604 , as in the aforementioned second modification, so that the individual driving force adjusting units are equipped with a brake  606  for shifting the driving force from the left axle to the right axle and a brake  608  for shifting the driving force from the right axle to the left axle, in place of the clutches of the aforementioned fourth modification. 
         [0093]    Here, the functions of the differential mechanism unit, the driving force adjusting unit and the differential limiting mechanism unit in those individual modifications are substantially identical to those of the differential mechanism unit  34 , the driving force adjusting unit  36  and the differential limiting mechanism unit  38 . 
         [0094]    In the aforementioned mode of embodiment, for example, the driving-force laterally-distributing device  28  is disposed on the rear-wheel side of the four-wheel drive vehicle. However, the invention should not be limited thereto but can be so modified in addition to those modifications that the device is disposed on the front-wheel side of the four-wheel drive or on the front-wheel drive car or the rear-wheel drive car. 
         [0095]    In the aforementioned mode of embodiment, moreover, the vehicle  1  employs the engine  2  as the drive source, which should not be limited thereto but may be a motor or the like. 
         [0096]    In the aforementioned mode of embodiment, moreover, the driving-force laterally-distributing device  28  is equipped with the driving-force laterally-adjusting mechanism unit  36  on the right side and the differential limiting mechanism unit  38  on the left side with respect to the differential mechanism unit  34 . However, the constitution may also be modified by reversing the arrangement laterally.