Patent Publication Number: US-11022208-B2

Title: Drive-force transmitting apparatus for vehicle

Description:
This application claims priority from Japanese Patent Application No. 2019-109915 filed on Jun. 12, 2019, the disclosure of which is herein incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a drive-force transmitting apparatus for a vehicle, particularly, to techniques for solving insufficiency of oil supply. 
     BACKGROUND OF THE INVENTION 
     JP-2017-47732 A discloses a drive-force transmitting apparatus in which an oil supply hole  41   a  is provided in a bearing support portion  41  of a case  11 , such that an oil is to be supplied through the oil supply hole  41   a  to, for example, a bearing  31  that is to be lubricated. Further, this Japanese Patent Application Publication teaches that the case  11  is provided with an oil guide portion  7  for guiding the oil to the oil supply hole  41   a.    
     SUMMARY OF THE INVENTION 
     By the way, in an arrangement in which the oil guide portion is provided to define a path configured to guide the oil to flow toward the oil supply hole from a diagonally upper side of the oil supply hole, when a flow velocity of the oil flowing along the path is increased, the oil is likely to flow to a position deviated from the oil supply hole, whereby an amount or rate of flow of the oil introduced into the oil supply hole could be smaller than a required amount or rate, so that there is a risk of lubrication insufficiency. 
     The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a drive-force transmitting apparatus for a vehicle, wherein the apparatus is capable of introducing a required amount of oil into the oil supply hole even when the flow velocity of the oil flowing along the oil guide portion is high. 
     The above object is achieved according to the following aspects of the present invention. 
     According to a first aspect of the invention, there is provided a drive-force transmitting apparatus for a vehicle, which comprises: a casing provided with an oil supply hole through which an oil is to be supplied to a lubrication-required element, wherein the casing is provided with a first guide portion and a second guide portion, wherein the first guide portion defines a first path that is configured to guide the oil to flow from a diagonally upper side of the oil supply hole, toward the oil supply hole, and wherein the second guide portion defines a second path that is configured to divide or separate the oil flowing along the first path, into a part of the oil and another part of the oil in an intermediate portion of the first path and to cause the part of the oil to join with the another part the oil in a position located right above the oil supply hole. For example, the first guide portion is constituted by at least a first rib which extends from an inside wall surface of the casing, while the second guide portion is constituted by at least a separating rib which extends from the inside wall surface of the casing, wherein the first rib is located on an upper side of the oil supply hole and on one of opposite sides, in a horizontal direction of the drive-force transmitting apparatus, of the oil supply hole, wherein the first rib has a guide surface which faces generally toward the other of the opposite sides of the oil supply hole and which is inclined toward the other of the opposite sides of the oil supply hole in a downward direction of the drive-force transmitting apparatus, such that the oil is to be guided to flow along the guide surface from the diagonally upper side of the oil supply hole toward the oil supply hole, and wherein the separating rib is adjacent to the first rib in the horizontal direction and is located on the upper side of the oil supply hole, the separating rib having an upper end surface that intersects with the guide surface of the first rib in a position corresponding to the intermediate portion of the first path in which the oil flowing along the first path is to be separated into the part of the oil and the another part of the oil. Further, for example, the upper end surface of the separating rib is inclined upwardly in a direction which is parallel to the horizontal direction and which is away from the guide surface of the first rib. Still further, for example, the mechanical oil pump is configured to pump out the oil stored in an oil storage that is constituted by a lower portion within the casing, wherein the drive-force transmitting apparatus further comprises a rotary member that is at least partially immersed in the oil stored in the oil storage, and wherein the lubrication-required element is a bearing by which the rotary member is rotatably supported. 
     According to a second aspect of the invention, the drive-force transmitting apparatus according to the first aspect of the invention further comprises: a rotary member that is to be rotated together with drive wheels of the vehicle; and a mechanical oil pump that is to be driven by the rotary member to discharge the oil that is to be guided to flow from the diagonally upper side of the oil supply hole toward the oil supply hole. 
     According to a third aspect of the invention, in the drive-force transmitting apparatus according to the first or second aspect of the invention, the lubrication-required element is a bearing fitted in an inner peripheral portion of a cylindrical tubular member that is provided with the oil supply hole. 
     In the drive-force transmitting apparatus according to the first aspect of the invention, the oil flowing along the first path is separated, by the second guide portion defining the second path, into the part of the oil and the another part of the oil in the intermediate portion of the first path whereby a flow velocity of the oil is reduced. Further, the part of the oil flowing along the second path and the another part of the oil flowing the first path are caused to join with each other in the position located right above the oil supply hole, so that the two parts of the oil are caused to collide with each other, whereby each of directions of flows of the two parts of the oil is changed to a direction toward the oil supply hole. Thus, the oil into which the two parts of the oil have been integrated is introduced into the oil supply hole. Owing to this arrangement, even when the flow velocity is high, it is possible to reduce the oil flowing to a position deviated from the oil supply hole, thereby making it possible to restrain an amount of the oil introduced into the oil supply hole, from being smaller than a required amount. 
     In the drive-force transmitting apparatus according to the second aspect of the invention, the mechanical oil pump is to be driven by the rotary member that is to be rotated together with the drive wheels of the vehicle, and the oil discharged from the mechanical oil pump is supplied toward the oil supply hole from the diagonally upper side of the oil supply hole, so that the flow velocity of the oil discharged from the oil pump is increased in proportion with increase of a running speed of the vehicle. However, owing to provision of the second guide portion, the oil can be introduced efficiently into the oil supply hole even when the flow velocity of the oil discharged from the oil pump is increased. 
     In the drive-force transmitting apparatus according to the third aspect of the invention, the oil flowing into the oil supply hole is supplied to the bearing fitted in the inner peripheral portion of the cylindrical tubular member, whereby the bearing can be effectively lubricated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view schematically showing, by way of example, construction of a hybrid vehicle to which the present invention is applied; 
         FIG. 2  is a view of an axle case shown in  FIG. 1 , as seen from a side of a gear room; 
         FIG. 3  is a view showing, in enlargement, an oil supply hole and its periphery shown in  FIG. 2 ; 
         FIG. 4  is a view conceptually showing flows of an oil when the oil is discharged from a pipe toward a partition wall; and 
         FIG. 5  is a view conceptually showing flows of the oil which is moved downward through a clearance between a step and a rib that are shown also in  FIG. 4 , and which s eventually moved into the oil supply hole. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the accompanying drawings. The figures of the drawings are simplified or deformed as needed, and each portion is not necessarily precisely depicted in terms of dimension ratio, shape, etc. 
     Embodiment 
       FIG. 1  is a view schematically showing, by way of example, construction of a hybrid vehicle  8  to which the present invention is applied. The vehicle  8  includes an engine  12 , right and left drive wheels  14   r ,  14   l  (hereinafter simply referred to as “drive wheels  14 ” unless they are to be distinguished from each other) and a drive-force transmitting apparatus  10 . The drive-force transmitting apparatus  10  is to be used advantageously in a hybrid vehicle of FF (front engine/front drive) system. The drive-force transmitting apparatus  10  is a drive-force transmitting apparatus of hybrid type, which is to be disposed between the engine  12  and drive wheels  14  of the vehicle  8 , so as to transmit a drive force outputted from the engine  12  as a drive-force source and a drive force outputted from a second electric motor MG 2  as another drive-force source, to the right and left drive wheels  14   r ,  14   l , via, for example, a differential device  20  and right and left axles  22   r ,  22   l  (hereinafter simply referred to as “axles  22 ” unless they are to be distinguished from each other). 
     As shown in  FIG. 1 , the drive-force transmitting apparatus  10  includes the above-described differential device  20 , the above-described axles  22 , an input shaft  23 , a planetary gear device  24 , an output gear  26 , a counter gear  28 , a differential drive gear  30 , a counter shaft  32 , a drive-force transmitting shaft  34 , a reduction gear  36 , a first electric motor MG 1  and the above-described second electric motor MG 2 . The input shaft  23  is disposed to be rotatable about a first axis CL 1 . The planetary gear device  24 , first electric motor MG 1  and output gear  26  are disposed to be coaxial with the input shaft  23  and are located radially outside the input shaft  23 . The drive-force transmitting shaft  34  is disposed to be rotatable about a second axis CL 2 . The second electric motor MG 2  is disposed to be coaxial with the drive-force transmitting shaft  34  so as to be rotatable about the second axis CL 2 . The reduction gear  36  is disposed on the drive-force transmitting shaft  34 . The counter shaft  32  is disposed to be rotatable about a third axis CL 3 . The counter gear  28  and differential drive gear  30  are disposed on the counter shaft  32 . The differential device  20  and the axles  22  are disposed to be rotatable about a fourth axis CL 4 . All of these rotary members are disposed within a casing  40  as a non-rotary member. The drive-force transmitting apparatus  10  further includes a parking lock mechanism  37  configured to stop rotation of the output gear  26 . It is noted that all of the first through fourth axes CL 1 -CL 4  are rotary axes that are parallel to a width direction of the vehicle  8 . 
     Each of the first and second electric motors MG 1 , MG 2  may be an electric motor having a function of a motor operable to convert an electric energy into a mechanical drive force and/or a function of a generator operable to convert a mechanical drive force into an electric energy, and preferably, is a motor generator having both of the functions so as to be operated as a selected one of the motor and the generator. In the present embodiment, the first electric motor MG 1  has a function of an electric generator operable to receive a reaction force from the engine  12 , and a function of an electric motor operable to start the engine  12  while the engine  12  is at rest. Meanwhile, the second electric motor MG 2  has a function of an electric motor functioning as a vehicle drive power source to generate a vehicle driving force, and a function of an electric generator operable to perform a regenerative operation for converting a reverse driving force received from the drive wheels  14 , into an electric energy. It is noted that the term “drive force” used in the present specification is synonymous with a drive torque or a drive power. 
     The input shaft  23  is connected to the engine  12  through members such as a crank shaft  12   a  and a damper (not shown), in a drive-force transmittable manner. The input shaft  23  is held, through members such as a bearing  18 , by the casing  40  as the non-rotary member, such that the input shaft  23  is rotatable about the first axis CL 1 . 
     The planetary gear device  24 , which is disposed to be coaxial with the first axis CL 1 , is a single-pinion type planetary gear device (differential mechanism) that includes a sun gear S, a carrier CA and a ring gear R. The planetary gear device  24  serves as a drive-force distributing mechanism configured to distribute the drive force of the engine  12  to the first electric motor MG 1  and the output gear  26 . The sun gear S of the planetary gear device  24  is connected to the first electric motor MG 1  in a drive-force transmittable manner. The carrier CA of the planetary gear device  24  is connected to the engine  12  through the input shaft  23  and the crank shaft  12   a  in a drive-force transmittable manner. The ring gear R of the planetary gear device  24  is connected to the output gear  26  in a drive-force transmittable manner. It is noted that the ring gear R and the output gear  26  are formed integrally with each other, namely, are constituted by a compound gear. 
     The first electric motor MG 1  is disposed in a position adjacent to the planetary gear device  24 , with a partition wall  56  (that is a part of the casing  40 ) being located between the first electric motor MG 1  and the planetary gear device  24  in a direction of the first axis CL 1 . The first electric motor MG 1  includes an annular-shaped stator  42  that is unrotatably fixed to the causing  40 , an annular-shaped rotor  44  disposed on an inner peripheral side of the stator  42 , and a rotor shaft  46  connected to an inner periphery of the rotor  44 . The stator  42  is provided with a stator coil  48  wound thereon. The rotor shaft  46  is held at its axially opposite end portions by the casing  40  through a pair of bearings  47   a ,  47   b , such that the rotor shaft  46  is rotatable about the first axis CL 1 . 
     The output gear  26  is connected to the ring gear R of the planetary gear device  24 , and meshes with the counter gear  28  that is disposed on the counter shaft  32 . 
     The second electric motor MG 2  and the reduction gear  36  are disposed to be rotatable about the second axis CL 2 , with the partition wall  56  being located between the second electric motor MG 2  and the reduction gear  36  in a direction of the second axis CL 2 . 
     The second electric motor MG 2  includes an annular-shaped stator  50  that is unrotatably fixed to the causing  40 , an annular-shaped rotor  52  disposed on an inner peripheral side of the stator  50 , and a rotor shaft  54  connected to an inner periphery of the rotor  52 . The stator  50  is provided with a stator coil  55  wound thereon. The rotor shaft  54  is held at its axially opposite end portions by the casing  40  through a pair of bearings  57   a ,  57   b , such that the rotor shaft  54  is rotatable about the second axis CL 2 . 
     The reduction gear  36  is formed integrally with the drive-force transmitting shaft  34 , and meshes with the counter gear  28  disposed on the counter shaft  32 . The number of teeth of the reduction gear  36  is smaller than the number of teeth of the counter gear  28 . Thus, rotation of the second electric motor MG 2  is transmitted to the counter shaft  32  through the reduction gear  36  and the counter gear  28 , such that a rotational speed of the counter shaft  32  is made lower than a rotational speed of the second electric motor MG 2 . The drive-force transmitting shaft  34  is held at its axially opposite end portions by the casing  40  through a pair of bearings  59   a ,  59   b , such that the drive-force transmitting shaft  34  is rotatable about the second axis CL 2 . 
     The counter shaft  32  is held at its axially opposite end portions by the casing  40  through a pair of bearings  61   a ,  61   b , such that the counter shaft  32  is rotatable about the third axis CL 3 . 
     The counter gear  28  and the differential drive gear  30  are disposed on the counter shaft  32 , unrotatably relative to the counter shaft  32  that is to be rotated about the third axis CL 3 . The counter gear  28  meshes with the output gear  26  and the reduction gear  36  so that the drive force outputted from the engine  12  and/or the drive force outputted from the second electric motor MG 2  are to be transmitted. The differential drive gear  30  meshes with a differential ring gear  38  of the differential device  20 . Thus, when the drive force drive force outputted from the engine  12  and/or the drive force outputted from the second electric motor MG 2  are transmitted to the counter gear  28  through the output gear  26  and/or the reduction gear  36 , the drive force or forces are transmitted to the differential device  20  through the counter shaft  32  and the differential drive gear  30 . 
     The differential device  20  and the pair of axles  22   r ,  22   l  are disposed to be rotatable about the fourth axis CL 4 . The differential ring gear  38  of the differential device  20  meshes with the differential drive gear  30  so that the drive force outputted from the engine  12  and/or the drive force outputted from the second electric motor MG 2  are to be inputted to the differential device  20  through the differential ring gear  38 . 
     The differential device  20  is constituted by a well-known differential mechanism, and is configured to transmit the drive force to the right and left axles  22   r ,  22   l  while allowing rotation of each of the axles  22   r ,  22   l  relative to the other of the axles  22   r ,  22   l . It is noted that detailed description of the differential device  20 , which is a known device, is not provided. The differential device  20  is held, at its opposite end portions that are opposite to each other in a direction of the fourth axis CL 4 , by the casing  40  through a pair of bearings  62   a ,  62   b , such that the differential device  20  is rotatable about the fourth axis CL 4 . 
     The differential ring gear  38  of the differential device  20  meshes with a pump driving gear  64  that is provided to rotate or drive a differential-interlocking oil pump P 1 . The differential-interlocking oil pump P 1  is a mechanical oil pump that is connected to the differential ring gear  38  of the differential device  20  through the pump driving gear  64  in a drive-force transmittable manner. When the differential ring gear  38  of the differential device  20  is rotated, the differential-interlocking oil pump P 1  is mechanically rotated or driven together with rotation of the differential ring gear  38 . That is, the differential ring gear  38  serves as a rotary drive source of the differential-interlocking oil pump P 1 . It is noted that the differential ring gear  38  and the differential-interlocking oil pump P 1  correspond to “rotary member (that is to be rotated together with drive wheels)” and “mechanical oil pump”, respectively, which are recited in the appended claims. 
     An oil is stored in an oil storage that is constituted by a lower portion within the casing  40 . When the differential-interlocking oil pump P 1  is rotated or driven, the oil stored in the oil storage is pumped out and is discharged from an outlet port (not shown) of the oil pump P 1 . The outlet port of the oil pump P 1  is connected to a pipe  66  (see  FIG. 4 ), so that the oil discharged from the outlet port of the oil pump P 1  is pumped or delivered through the pipe  66 . 
     The drive-force transmitting apparatus  10  includes, in addition to the differential-interlocking oil pump P 1 , another mechanical pump in the form of an engine-interlocking oil pump P 2  that is be rotated or driven by the engine  12 . The oil pump P 2  is disposed on one of opposite end portions of the input shaft  23  which is remote from the engine  12  in an axial direction of the input shaft  23 . The engine-interlocking oil pump P 2  includes a drive gear (not shown) that is disposed on the above-described one of the opposite end portions of the input shaft  23 , so that the engine-interlocking oil pump P 2  is rotated or driven together with rotation of the engine  12 . Therefore, with the engine  12  being rotated, the engine-interlocking oil pump P 2  is driven whereby the oil is discharged from the engine-interlocking oil pump P 2 . 
     In the drive-force transmitting apparatus  10  constructed as described above, the drive force of the engine  12  is transmitted to the right and left drive wheels  14   r ,  14   l  through the planetary gear device  24 , output gear  26 , counter gear  28 , counter shaft  32 , differential drive gear  30 , differential device  20  and axles  22   r ,  22   l  in this order of description. Further, the drive force of the second electric motor MG 2  is transmitted to the right and left drive wheels  14   r ,  14   l  through the rotor shaft  54 , drive-force transmitting shaft  34 , reduction gear  36 , counter gear  28 , counter shaft  32 , differential drive gear  30 , differential device  20  and axles  22   r ,  22   l  in this order of description. It is noted that the term “drive force” used in the present specification is synonymous with a drive torque or a drive power. 
     The casing  40  is constituted by a housing  40   a , an axle case  40   b  and a case cover  40   c  that are fixed to one another. The axle case  40   b  opens in its opposite ends that are opposite to each other in the direction of the first axis CL 1 . The axle case  40   b  is fixedly connected at one of the openings to the housing  40   a  through screw bolts, such that the one of the openings is enclosed by the housing  40   a . The axle case  40   b  is fixedly connected at the other of the openings to the case cover  40   c  through screw bolts, such that the other of the openings is enclosed by the case cover  40   c.    
     The axle case  40   b  is provided with the partition wall  56  that extends in a direction perpendicular to the first axis CL 1 . By the partition wall  56 , an interior of the casing  40  is sectioned into a gear room  58  and a motor room  60 , such that various gears or devices such as the planetary gear device  24 , output gear  26 , counter gear  28 , reduction gear  36  and differential device  20  are disposed within the gear room  58  and such that the first and second electric motors MG 1 , MG 2  are disposed within the motor room  60 . 
     Hereinafter, there will be described lubrication of the bearing  62   a  that is disposed in the gear room  58  to rotatably support the differential device  20 . It is noted that the bearing  62   a  corresponds to “lubrication-required element” that is recited in the appended claims. 
       FIG. 2  is a view of the axle case  40   b  as seen from a side of the gear room  58 . In the drawing sheet of  FIG. 2 , its leftward direction corresponds to a rear-side direction of the vehicle  8 , while a rightward direction corresponds to a front-side direction of the vehicle  8 . Further, in drawing sheet of  FIG. 2 , its upward direction corresponds to an upward direction perpendicular to a flat horizontal road surface in an apparatus installed state that is defined as a state in which the drive-force transmitting apparatus  10  is installed on the vehicle  8  and the vehicle  8  is on the flat horizontal road surface. The first through fourth axes CL 1 -CL 4  shown in  FIG. 1  correspond to respective rotational axes shown in  FIG. 1 . 
     In the casing  40 , the oil stored in the oil storage that is constituted by the lower portion within the casing  40  is scooped up by the differential ring gear  38  (not shown in  FIG. 2 ) that is at least partially immersed in the oil stored in the oil storage, whereby the oil is supplied to various gears and various bearings that are disposed within the gear room  58 . It is noted that a vertical direction and a horizontal direction in the drawing sheet of  FIG. 2  corresponds to a vertical direction and a horizontal direction of the drive-force transmitting apparatus  10 , respectively, and that a lower portion of the casing  40  constitutes a bottom wall  40   d  of the casing  40  which defines the above-described oil storage. 
     Further, the axle case  40   b  is provided with a bearing support portion  72  which has a tubular cylindrical shape and which protrudes from a wall surface  56   a  of the partition wall  56  in a direction perpendicular to the wall surface  56   a . The bearing support portion  72  has an oil supply hole  70  which opens in its outer circumferential surface and which passes through its circumferential wall, such that the oil is to be supplied through the oil supply hole  70  to the bearing  62   a  that supports the differential device  20 . Since the oil supply hole  70  is held in communication with the bearing  62   a , the bearing  62   a  can be lubricated by the oil that is introduced into the oil supply hole  70 . It is noted that the bearing  62   a  is fitted in an inner peripheral portion of the bearing support portion  72  (see  FIG. 5 ), so that the oil scooped up by the differential ring gear  38  is unlikely to easily reach the bearing  62   a . Therefore, the bearing  62   a  is to be lubricated by the oil flowing into the oil supply hole  70 . It is noted that the wall surface  56   a  of the partition wall  56  and the bearing support portion  72  correspond to “inside wall surface” and “cylindrical tubular member” that are recited in the appended claims. 
     The oil supply hole  70  is configured to receive therein the oil discharged from the differential-interlocking oil pump P 1  through the pipe  66 .  FIG. 3  is a view showing, in enlargement, the oil supply hole  70  and its periphery shown in  FIG. 2 . 
     In  FIG. 3 , a hatched part indicates an oil collision portion  68  with which the oil discharged from the pipe  66  is caused to collide. The oil collision portion  68  is a part of the wall surface  56   a  of the partition wall  56 , and is located on a diagonally upper side (left upper side) of the oil supply hole  70 . The pipe  66  has a distal end portion which is located in a position opposed to the oil collision portion  68 , and which is substantially perpendicular to the wall surface  56   a  of the partition wall  56 . Therefore, the oil discharged from the distal end portion of the pipe  66  is directed toward the wall surface  56   a  of the partition wall  56 . The oil discharged from the distal end portion of the pipe  66  is caused to collide with the oil collision portion  68  of the wall surface  56   a  of the partition wall  56 , and is then moved toward the oil supply hole  70  after having being caused to collide with the oil collision portion  68 . It is noted that the oil discharged from the pipe  66  is not supplied directly to the oil supply hole  70  because there is a space limitation that does not allow the pipe  66  to extend down to the oil supply hole  70 . 
     The oil collision portion  68  is located above the oil supply hole  70 , so that the oil caused to collide with the oil collision portion  68  is moved downwardly toward the oil supply hole  70 . The axle case  40   b  is provided with first and second ribs  78 ,  79  that extend from the wall surface  56   a  of the partition wall  56  in a perpendicular direction that is perpendicular to the wall surface  56   a , i.e., in a direction in which the distal end portion of the pipe  66  is distant from the wall surface  56   a , such that the oil caused to collide with the oil collision portion  68  that is located on the diagonally upper side of the oil supply hole  70 , can be efficiently guided to the oil supply hole  70  by the first and second ribs  78 ,  79 . The first and second ribs  78 ,  79  are located on a lower side of the oil collision portion  68 , and are arranged in a V shape as seen in the perpendicular direction. The first and second ribs  78 ,  79  are formed integrally with the axle case  40   b  in a casting process. The first rib  78  is located on an upper side of the oil supply hole  70  and on one of opposite sides, in the horizontal direction of the drive-force transmitting apparatus  10 , of the oil supply hole  70 . 
     The first and second ribs  78 ,  79  are spaced apart from each other by a spacing distance that is increased in the upward direction of the drive-force transmitting apparatus  10 , so as to cooperate with each other to receive the oil caused to collide with the oil collision portion  68  and to be dropped downwardly. The spacing distance between the first and second ribs  78 ,  79  is reduced in a downward direction of the drive-force transmitting apparatus  10 , and the oil supply hole  70  is located in a position adjacent to lower ends of the first and second ribs  78 ,  79 . That is, the oil supply hole  70  is located in the positioned between the lower ends of respective first and second ribs  78 ,  79 . Thus, the oil caused to collide with the oil collision portion  68  is caused to flow along wall surfaces  78   a ,  79   a  of the respective first and second ribs  78 ,  79 , and is guided by the wall surfaces  78   a ,  79   a  as guide surfaces, to the oil supply hole  70 . The wall surface  78   a  of the first rib  78  faces generally toward the other of the above-described opposite sides of the oil supply hole  70 , and is inclined toward the other of the opposite sides of the oil supply hole  70  in the downward direction, such that the oil is to be guided to flow along the wall surface  78   a  from the diagonally upper side of the oil supply hole  70  toward the oil supply hole  70 . 
     By the way, the differential-interlocking oil pump P 1  is driven by the differential ring gear  38  that is rotated together with the drive wheels  14 , so that an amount or rate of the oil discharged from the oil pump P 1  is increased with increase of a running speed V of the vehicle  8 . Therefore, the oil in the pipe  66  is pressurized to a degree that is increased in proportional with the running speed V, and a flow velocity of the oil discharged from the pipe  66  is increased with increase of the pressurized degree of the oil in the pipe  66 . When the flow velocity of the oil discharged from the pipe  66  is considerably increased, the oil flowing along the wall surface  78   a  of the first rib  78  could pass over the oil supply hole  70 , so that there is a risk that an amount or rate of the oil introduced into the oil supply hole  70  could be smaller than a required amount or rate. 
     However, in the present embodiment, the oil collision portion  68  is surrounded by wall surfaces that are defined in the axle case  40   b , for thereby reducing the flow velocity of the oil caused to collide with the oil collision portion  68 . Specifically, the wall surface  56   a  is provided with a step  80  that extends perpendicularly to the partition wall  56  to surround the oil collision portion  68 . Further, the wall surface  56   a  is provided with a block rib  82  that is located below the oil collision portion  68 . The block rib  82  also extends perpendicularly to the partition wall  56  to surround the oil collision portion  68 , so as to block flows of the oil splashing from the oil collision portion  68 . The block rib  82  is formed integrally with the axle case  40   b  in a casting process. 
     The block rib  82  extends from the wall surface  56   a  of the partition wall  56  in the perpendicular direction. Further, as shown in  FIG. 3  that is a view as seen in the perpendicular direction, the block rib  82 , which cooperates with the step  80  to surround the oil collision portion  68 , is inclined downwardly in the rear-side direction of the vehicle  8  that corresponds to the leftward direction in the drawing sheet of  FIG. 3 . The block rib  82  has a height substantially the same as a height of the step  80 , wherein the height corresponds to a distance from the wall surface  56   a  of the partition wall  56  in the perpendicular direction. Thus, the oil collision portion  68  is surrounded by a wall surface  80   a  defined by the step  80  and a wall surface  82   a  of the block rib  82 . It is noted that a gap or clearance  84  is provided in a position which is located below the oil collision portion  68  and which is located between the block rib  82  and the step  80 , such that the oil caused to collide with the oil collision portion  68  is guided downwardly toward the oil supply hole  70 . 
     The oil discharged from the pipe  66 , is caused to collide with the oil collision portion  68 , and then to splash to fly in various directions. However, the oil splashing to fly in the various directions is caused to collide with the wall surface  80   a  of the step  80  and the wall surface  82   a  of the block rib  82  that surround the oil collision portion  68 . With the collision of the oil within a space around the oil collision portion  68 , the flow velocity of the oil is reduced. Further, the oil caused to splash downwardly is caused to collide with the block rib  82 , so as to be temporarily blocked within the space around the oil collision portion  68 , whereby the collision of the oil is repeated within the space, so that the flow velocity of the oil is effectively reduced. 
       FIG. 4  is a view conceptually showing flows of the oil when the oil is discharged from the pipe  66  toward the oil collision portion  68  of the partition wall  56 , wherein arrows represent directions of the respective flows of the oil. It is noted that the view of  FIG. 4  is for the purpose of conceptually showing the flows of the oil, and that shapes and configurations shown in  FIG. 4  do not precisely coincide with those shown in  FIG. 3 . 
     As shown in  FIG. 4 , the pipe  66  is arranged to extend in the above-described perpendicular direction toward the wall surface  56   a  of the partition wall  56  of the axle case  40   b , so that the oil discharged from the distal end portion of the pipe  66  is directed to the oil collision portion  68  of the wall surface  56   a  of the partition wall  56 . The oil caused to collide with the oil collision portion  68  splashes and flies in various directions surrounding the oil collision portion  68 , as indicated by arrows in  FIG. 4 . Since the oil collision portion  68  is surrounded by the wall surface  80   a  of the step  80  and the wall surface  82   a  of the block rib  82 , the splashing oil is temporarily blocked within the space surrounded by these surfaces  80   a ,  82   a , and is caused to collide with these surfaces  80   a ,  82   a , whereby the flow velocity of the oil is reduced. The oil whose flow velocity is reduced is moved downwardly through the clearance  84  that is defined between the step  80  and the block rib  82 . 
     The block rib  82  has a shape and a size and is disposed in a position, wherein the shape, size and position are predetermined through experimentation or determined by an appropriate design theory, such that the oil flows down through the clearance  84  at a flow velocity that enables the oil to be introduced into the oil supply hole  70  without the oil passing over the oil supply hole  70 . For example, where the shape, size and position of the block rib  82  are adjusted in a manner that widens the space which is around the oil collision portion  68  and which surrounded by cooperation of the step  80  and the block rib  82 , it is possible to reduce the flow velocity of the oil discharged through the clearance  84 . Thus, by taking account of this, the shape, size and position of the block rib  82  are adjusted such that the flow velocity of the oil discharged through the clearance  84  becomes an appropriate speed value. 
     Referring back to  FIG. 3 , the oil whose flow velocity is reduced within the above-describe space around the oil collision portion  68 , is moved downwardly through the clearance  84  defined between the step  80  and the block rib  82 , and then is moved further downwardly from a diagonally upper side (from an upper left side as seen in the drawing sheet) of the oil supply hole  70  along the wall surface  78   a  of the first rib  78 . The oil moved downwardly along the wall surface  78   a  of the first rib  78  is guide by the first rib  78  to be introduced into the oil supply hole  70  that is located in the position adjacent to the lower end of the first rib  78 . 
     In this instance, if the flow velocity of at least a part of the oil is not reduced to a speed value low enough in the space around the oil collision portion  68 , the at least the part of the oil could flow in directions deviated from a direction toward the oil supply hole  70  so that there is a risk that the at least the part of the oil would pass over the oil supply hole  70 . In the present embodiment, for the purpose of reducing the oil passing over the oil supply hole  70 , the axle case  40   b  is provided with a separating rib  86  that is configured to divide or separate the oil flowing along the first rib  78 , into a part of the oil and another part of the oil in an intermediate portion of the first rib  78  and to cause the part of the oil to join with the another apart of the oil in a position located right above the oil supply hole  70 , so as to guide the oil into the oil supply hole  70 . The separating rib  86  is adjacent to the first rib  78  in the horizontal direction and is located on the upper side of the oil supply hole  70 , and is as well as the first and second ribs  78 ,  79  is formed integrally with the axle case  40   b  in a casting process. 
     The separating rib  86  is a generally cuboid-shaped rib that protrudes from the wall surface  56   a  of the partition wall  56  in the above-described perpendicular direction such that the separating rib  86  has a side surface which is elongated in the vertical direction and which is in contact with the wall surface  78   a  of the first rib  78 . The separating rib  86  has a height smaller than a height of the first rib  78 , wherein the height corresponds to a distance from the wall surface  56   a  of the partition wall  56  in the perpendicular direction. The separating rib  86  has an upper end surface  86   a  that intersects with the wall surface  78   a  of the first rib  78  in a position corresponding to the intermediate portion of the first path L 1  in which the oil flowing along the first path L 1  is to be separated into the part of the oil and the another part of the oil. The upper end surface  86   a  of the separating rib  86  is inclined upwardly in the rightward direction as seen in the drawing sheet of  FIG. 3 , i.e., in a direction which is parallel to the horizontal direction and which is away from the wall surface  78   a  of the first rib  78 . Owing to provision of the separating rib  86 , the oil flowing downwardly along the wall surface  78   a  of the first rib  78  is caused to collide with an upper end surface  86   a  of the separating rib  86  whereby the flow velocity of the oil is reduced. Further, the oil flowing downwardly along the first rib  78  is separated into a part of the oil and another part of the oil, such that the part of the oil flows downwardly along a second surface  86   c  of the separating rib  86 . The second surface  86   c  is another side surface opposite to the above-described side surface that is in contact with the wall surface  78   a  of the first rib  78 . Further, the above-described part of the oil is caused to join with the above-described another part of the oil in the position located right above the oil supply hole  70 . A direction of flow of the above-described part of the oil and a direction of the above-describe another part of the oil are changed when the two parts of the oil join with each other, and the mutually joined two parts of the oil are introduced into the oil supply hole  70 . 
       FIG. 5  is a view conceptually showing the flows of the oil which is moved downwardly through the clearance  84  between the step  80  and the block rib  82  that are shown also in  FIG. 4 , and which is eventually introduced into the oil supply hole  70 . It is noted that the view of  FIG. 5  is a perspective view showing shapes and configurations shown in  FIG. 3 , in a simplified manner, and that the shown shapes and configurations do not precisely coincide with those shown in  FIG. 3 . 
     The oil, which has been caused to collide with the oil collision portion  68  located above the oil supply hole  70 , is caused to collide also with the wall surface  80   a  of the step  80  and the wall surface  82   a  of the block rib  82  in a repeated manner. Then, after the flow velocity of the oil has been reduced as a result of the repeated collision of the oil, the oil is moved downwardly through the clearance  84  defined between the step  80  and the block rib  82 , as shown in  FIG. 5 . After having been moved downwardly of the clearance  84 , the oil is moved toward the first rib  78 . When reaching an upper portion of the wall surface  78   a  of the first rib  78 , the oil is moved from a diagonally upper side of the oil supply hole  70  along the wall surface  78   a  of the first rib  78  and is then caused to collide with the upper end surface  86   a  of the separating rib  86 . With the oil being caused to collide also with the upper end surface  86   a , the flow velocity of the oil is further reduced. 
     As shown in  FIG. 5 , the upper end surface  86   a  of the separating rib  86  is inclined upwardly in a direction away from the first rib  79  toward the second rib  79 . Further, the separating rib  86  has a first surface  86   b  and the above-described second surface  86   c . The first surface  86   b  is parallel to the wall surface  56   a  of the partition wall  56 . The second surface  86   c  is opposed to the wall surface  79   a  of the second rib  79 , and is opposite to the above-described side surface that is in contact with the wall surface  78   a  of the first rib  78 . Owing to provision of the separating rib  86 , the oil moved along the wall surface  78   a  of the first rib  78  is separated into two parts that are to flow along two paths consisting of first and second paths L 1 , L 2 . Specifically, the first path L 1  is configured to guide the oil to flow downwardly from the diagonally upper side of the oil supply hole  70 , along the wall surface  78   a  of the first rib  78 , toward the oil supply hole  70 . The second path L 2  is configured to separate the oil flowing along the first path L 1 , into the above-described part of the oil and the above-described another part of the oil, in the intermediate portion of the first path L 1  (in which the oil is caused to collide with the upper end surface  86   a  of the separating rib  86 ), and to guide the above-described part of the oil to flow downwardly along the second surface  86   c  toward the oil supply hole  70 . 
     In  FIG. 5 , arrows represented by solid lines indicate flows of the oil guided by the first path L 1 . The first path L 1  is configured to guide the oil to flow downwardly from the diagonally upper side of the oil supply hole  70 , along the wall surface  78   a  of the first rib  78 , and is configured, after the oil is caused to collide with the upper end surface  86   a  of the separating rib  86 , to guide the above-described another part of the oil toward the first surface  86   b  of the separating rib  86  such that the another part of the oil flows downwardly along the first surface  86   b  toward the oil supply hole  70 . The first path L 1  is constituted mainly by the first rib  78 . It is noted that the first rib  78  corresponds to “first guide portion (that defines a first path)” recited in the appended claims. 
     Further, in  FIG. 5 , arrows represented by broken lines indicate flows of the oil guided by the second path L 2 . The second path L 2  is configured, after the oil is caused to collide with the upper end surface  86   a  of the separating rib  86 , to guide the above-described part of the oil toward the second surface  86   c  of the separating rib  86  such that the part of the oil is moved up along the upper end surface  86   a  and then flows downwardly along the second surface  86   c  toward the oil supply hole  70 . The second path L 2  is constituted by the separating rib  86 . It is noted that the second rib  86  corresponds to “second guide portion (that defines a second path)” recited in the appended claims. 
     When the flow velocity of the oil is low upon its collision with the upper end surface  86   a  of the separating rib  86 , the oil is moved toward the first surface  86   b , without being moved up over the upper end surface  86   a  toward the second surface  86   c . That is, when the flow velocity of the oil is low, the oil is introduced into the oil supply hole  70  via the first path L 1 . 
     On the other hand, when the flow velocity of the oil flowing along the first path L 1  becomes high, the oil could arrive in a position deviated from the oil supply hole  70 . Specifically, as indicated by solid arrows in  FIG. 5 , the flow of the oil could be offset onto right side (as seen in the drawing sheet) of the oil supply hole  70 , so that the oil is likely to pass over the oil supply hole  70  without the oil flowing into the oil supply hole  70 . However, in the present embodiment, when the flow velocity of the oil is high, a part of the oil caused to collide with the upper end surface  86   a  is moved up over the upper end surface  86   a  and is then guided to the oil supply hole  70  via the second surface  86   c , namely, is moved along the second path L 2  that may referred also to as “bypass path” bypassing a part of the first path L 1 . Thus, when the flow velocity becomes high, the oil is flow along the first and second paths L 1 , L 2 . 
     Then, as shown in  FIG. 5 , the part of the oil flowing along the second path L 2  is caused to join with the another part of the oil flowing along the first path L 1  in the position right above the oil supply hole  70 , whereby a direction of the flow of another part of the oil along the first path L 1  is changed and eventually the oil is guided into the oil supply hole  70 . 
     Thus, when the flow velocity of the oil is high, the flow of the oil is divided into the flow along the first path L 1  and the flow along the second path L 2 , and then the flow along the first path L 1  and the flow along the second path L 2  are caused to join with each other and collide with each other in the position right above the oil supply hole  70 , whereby each of the direction of the flow along the first path L 1  and the direction of the flow along the second path L 2  is changed to a direction toward the oil supply hole  70 , so that the oil is introduced into the oil supply hole  70 . Therefore, with the oil discharged from the pipe  66  efficiently flowing into the oil supply hole  70 , a sufficient amount of the oil is supplied to the bearing  62   a  rotatably supporting the differential device  20  whereby insufficiency of lubrication of the bearing  62   a  is resolved. 
     The separating rib  86  has a shape and a size and is disposed in a position, wherein the shape, size and position are predetermined through experimentation or determined by an appropriate design theory, such that, when the flow velocity of the oil becomes high, the flowing oil is separated, on the upper end surface  86   a , into the part of the oil that is to flow along the second path L 2  and the another part of the oil that is to flow along the first path L 1 , and the part of the oil flowing along the second path L 2  and the another part of the oil flowing along the first path L 1  are caused to join with each other in the position right above the oil supply hole  70 , and are introduced into the oil supply hole  70 . For example, an increase of an area of the upper end surface  86   a  of the separating rib  86  facilitates the reduction of the flow velocity of the oil. Further, the flow amount or rate of the part of the oil flowing along the second path L 2  can be adjusted by adjusting a degree of inclination of the upper end surface  86   a . The direction of the flow of the part of the oil along the second path L 2  can be adjusted as needed by adjusting, for example, a shape of the second surface  86   c  of the separating rib  86 . Thus, the part of the oil flowing along the second path L 2  and the another part of the oil flowing along the first path L 1  can be caused to join with each other in the position right above the oil supply hole  70 , and can be introduced into the oil supply hole  70 . 
     As described above, in the present embodiment, the oil flowing along the first path L 1  is separated, by the separating rib  86  defining the second path L 2 , into the part of the oil and the another part of the oil in the intermediate portion of the first path L 1  whereby the flow velocity of the oil is reduced. Further, the part of the oil flowing along the second path L 2  and the another part of the oil flowing the first path L 1  are caused to join with each other in the position located right above the oil supply hole  70 , so that the two parts of the oil are caused to collide with each other, whereby each of directions of flows of the two parts of the oil is changed to a direction toward the oil supply hole  70 . Thus, the oil into which the two parts of the oil have been integrated is introduced into the oil supply hole  70 . Owing to this arrangement, even when the flow velocity is high, it is possible to reduce the oil flowing to a position deviated from the oil supply hole  70 , thereby making it possible to restrain an amount of the oil introduced into the oil supply hole  70 , from being smaller than a required amount. 
     In the present embodiment, the differential-interlocking oil pump P 1  is to be driven by the rotary member in the form of the differential ring gear  38 , and the oil discharged from the differential-interlocking oil pump P 1  is supplied toward the oil supply hole  70  from the diagonally upper side of the oil supply hole  70 , so that the flow velocity of the oil discharged from the differential-interlocking oil pump P 1  is increased in proportion with increase of the running speed of the vehicle  8 . However, owing to provision of the separating rib  86 , the oil can be introduced efficiently into the oil supply hole  70  even when the flow velocity of the oil discharged from the differential-interlocking oil pump P 1  is increased. 
     While the preferred embodiment of this invention has been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied. 
     For example, in the above-described embodiment, the drive-force transmitting apparatus  10  is a drive-force transmitting apparatus of FF type in which the various gears and rotary shafts are disposed on the four axes CL 1 -CL 4 . However, the construction of the drive-force transmitting apparatus according to the present invention is not limited to the detail in the above-described embodiment. The present invention is applicable to any drive-force transmitting apparatus for a vehicle, as long as the drive-force transmitting apparatus has a construction in which the oil discharged from the pipe  66  is moved from the diagonally upper side of the oil supply hole so as to be introduced into the oil supply hole. 
     In the above-described embodiment, the differential-interlocking oil pump P 1  is to be driven by rotation of the differential ring gear  38  of the differential device  20 . However, this detail is not essential. For example, the differential-interlocking oil pump P 1  may be driven by the counter gear  28  or any other rotary member that is to be rotated together with the drive wheels  14 . Further, the mechanical oil pump, which is recited in the appended claims, does not have to be driven necessarily by rotation of a rotary member that is to be rotated together with the drive wheels  14 , but may be constituted by the engine-interlocking oil pump P 2  in place of the differential-interlocking oil pump P 1 , for example, such that the oil discharged from the engine-interlocking oil pump P 2  is delivered by the pipe  66  and is discharged from the pipe  66 . That is, the mechanical oil pump, which is recited in the appended claims, may be constituted by any mechanical oil pump that could be rotated at a high rotational speed depending on a running state of the vehicle. 
     It is to be understood that the embodiment described above is given for illustrative purpose only, and that the present invention may be embodied with various modifications and improvements which may occur to those skilled in the art. 
     NOMENCLATURE OF ELEMENTS 
     
         
           10 : vehicle drive-force transmitting apparatus 
           14 : drive wheels 
           38 : differential ring gear (rotary member to be rotated together with drive wheels) 
           40 : casing 
           40   b : axle case 
           62   a : bearing (lubrication-required element) 
           70 : oil supply hole 
           72 : bearing support portion (cylindrical tubular member) 
           78 : first rib (first guide portion) 
           86 : separating rib (second guide portion) 
         L 1 : first path 
         L 2 : second path 
         P 1 : differential-interlocking oil pump (mechanical oil pump)