differential gear

Abstract

A differential gear of the present disclosure is mounted on a vehicle, and includes a pair of side gears, at least two pinions that are engaged with the pair of side gears, respectively, and a differential case that houses the pair of side gears and the at least two pinions, and supplies or discharges lubricating oil to or from the inside via an opening. The differential case includes at least two bearing surfaces that are formed on an inner peripheral surface of the differential case in a manner to support the pinions, a weir portion that extends in a direction along a rotation direction of the differential case and connects the adjacent bearing surfaces between the adjacent bearing surfaces, and an oil accumulation portion that is formed on the inner peripheral surface by the weir portion in a manner to be located on a side opposite to the opening in an axial direction of the side gears. Thus, it is possible to well suppress a shortage of the lubricating oil with respect to a sliding portion and to make the differential gear compact.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a differential gear mounted on a vehicle. BACKGROUND

[0002] In the past, as such a differential gear, a differential gear including a pair of pinions, a pair of side gears meshing with the pair of pinions, and a differential case housing the pair of pinions and the pair of side gears, in which the differential case has a pinion shaft hole through which a pinion shaft supporting the pinion is inserted and a drive shaft hole through which a drive shaft to which the side gears are fixed is inserted (for example, refer to Patent Literature 1) has been known. In the differential case of the differential gear, a single oil hole for supplying working oil as lubricating oil into the differential case is formed at a position radially outward of a side gasket disposed between the side gears and the differential case. Also, an oil outflow restricting member is disposed inside the differential case, extends to a portion radially inward of an outer periphery of the side gasket, and causes oil to accumulate in a portion radially inward of the oil hole inside the differential case. Thus, the working oil can be smoothly supplied from the oil hole to the inside of the differential case, and the working oil can be supplied to the side gasket regardless of the rotation state of the differential case.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Patent No. 6390786 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, at the time of start of the vehicle and the like, since the working oil starts to be sucked by the oil pump, the oil level in the differential case decreases. Therefore, even if the oil outflow restricting member is disposed inside the differential case as in the above-described conventional differential gear, there is a possibility that the lubricating oil in the differential case is insufficient to properly lubricate and cool the sliding portions.

[0008] Therefore, the main object of the present disclosure is to compactly suppress the lubricating oil of the sliding portions from being insufficient.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The differential gear of the present disclosure includes a pair of side gears, at least two pinions that mesh with the pair of side gears, respectively, and a differential case that houses the pair of side gears and the at least two pinions and supplies or discharges lubricating oil to or from the inside via an opening portion. In the differential gear mounted on a vehicle, the differential case includes at least two bearing surfaces formed on an inner peripheral surface of the differential case so as to support the pinions, a weir portion that extends in a direction along a rotation direction of the differential case and connects the adjacent bearing surfaces between the adjacent bearing surfaces, and an oil accumulation portion that is formed on the inner peripheral surface by the weir portion so as to be located on a side opposite to the opening portion with respect to the weir portion in an axial direction of the differential case.

[0011] The differential gear of the present disclosure mounted on a vehicle includes a pair of side gears, at least two pinions that mesh with the pair of side gears, respectively, and a differential case that houses the pair of side gears and the at least two pinions and supplies or discharges lubricating oil to or from the inside via an opening portion. And, the differential case includes at least two bearing surfaces formed on an inner peripheral surface of the differential case so as to support the pinions, a weir portion that extends in a direction along a rotation direction of the differential case and connects the adjacent bearing surfaces between the adjacent bearing surfaces, and an oil accumulation portion that is formed on the inner peripheral surface by the weir portion so as to be located on a side opposite to the opening portion with respect to the weir portion in an axial direction of the differential case. Thereby, when the oil level in the differential case is lowered, the lubricating oil can be secured in the oil accumulation portion, and the lubricating oil in the oil accumulation portion is made to spread over a sliding portion between the pinions and the bearing surfaces and the like by the rotation of the differential case. As a result, the shortage of the lubricating oil with respect to the sliding portion can be well suppressed and the increase in the surface pressure at the sliding portion can be coped with, so that the differential gear can be compactified. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a cross-sectional view showing the differential gear of the present disclosure.

[0013] Figure 2 is a side view showing a case main body of the differential case that constitutes the differential gear of the present disclosure.

[0014] Figure 3 is a partial cross-sectional view showing the case main body of the differential case that constitutes the differential gear of the present disclosure.

[0015] Figure 4 is a main part enlarged perspective view showing the case main body of the differential case that constitutes the differential gear of the present disclosure. DETAILED DESCRIPTION

[0016] Next, a mode for carrying out the invention of the present disclosure is described with reference to the drawings.

[0017] Figure 1 is a schematic configuration view of a differential gear 1 of the present disclosure. The differential gear 1 shown in this drawing is mounted on, for example, a front-wheel drive vehicle, and transmits power from a transmission (not shown) to left and right drive wheels (omitted from the drawing). As shown in the drawing, the differential gear 1 includes a pair (two) of side gears 2 fixed to corresponding drive shafts (not shown), a pair (two) of pinions 3 meshing with the pair of side gears 2 at right angles, a pinion shaft 4 supporting the pair of pinions 3, a differential case 5 accommodating the pair of side gears 2 and the pair of pinions 3, and a differential ring gear 6 fixed (coupled) to the differential case 5. Figure 1

[0018] Each of the side gears 2 and the pinions 3 is a straight bevel gear. A side gasket 7 is arranged between each of the side gears 2 and the differential case 5, and a pinion gasket 8 is arranged between each of the pinions 3 and the differential case 5. The differential case 5 is rotatably supported coaxially with the drive shafts via bearings BR by a transmission case (not shown). In the present embodiment, the differential gear 1 is arranged in a differential chamber divided into a working oil reservoir chamber formed in a lower portion of the transmission case.

[0019] The differential case 5 of the differential gear 1 includes a case main body 50 rotatably supporting one side of the side gears 2 and a cover 59 rotatably supporting the other side of the side gears 2. In the present embodiment, the case main body 50 and the cover 59 are each a metal cast product. A plurality of bolt holes are formed in the flange portions of the outer peripheral portions of the case main body 50 and the cover 59, respectively. The case main body 50 and the cover 59 are coupled (fixed) to each other via a plurality of bolts 9 engaged with the corresponding bolt holes of the case main body 50 and the cover 59, and are coupled (fixed) to the differential ring gear 6 via the plurality of bolts 9.

[0020] Figure 2 Figure 3 As shown in the drawing, a plurality of (two in the present embodiment) opening portions (window portions) 51 for supplying and discharging working oil as lubricating oil are formed at intervals in the rotational direction of the differential case 5 mainly on the case main body 50 of the differential case 5. In running of a vehicle including the differential gear 1, working oil accumulated in the differential chamber is supplied to the inside of the differential case 5 from the opening portions 51 by stirring of the differential ring gear 6, or working oil dripping from a supply pipe or the like not shown is supplied to the inside of the differential case 5 from the opening portions 51. In the present embodiment, the opening area of each of the opening portions 51 is, for example, at least a degree that the pinions 3 do not substantially pass through, and is not used for assembly of the pinions 3 and the like with respect to the differential case 5. In this way, by reducing the opening area of each of the opening portions 51, the torsional rigidity of the torque transmission portion of the differential case 5 can be further improved. ​​​

[0021] In addition, as shown in Figure 3 and Figure 4 In the inner peripheral surface of the housing main body 50 of the differential case 5, a plurality of (two in the present embodiment) support surfaces 52 that respectively support (receive) the corresponding pinions 3 are formed. Each support surface 52 is formed in a concave spherical surface shape by cutting processing, and a pinion gasket 8 is disposed between each support surface 52 and the back surface of the corresponding pinion 3. Also, in the inner peripheral surface of the housing main body 50, a plurality of (two in the present embodiment) weir portions (rib portions) 53a and a ring-shaped weir portion (rib portion) 53b are formed by casting.

[0022] The plurality of weir portions (first weir portions) 53a each protrude toward the axial center (radially inner side) of the housing main body 50 in the vicinity of the central portion in the axial direction of the side gear 2 (differential case 5), and extend in the direction along the rotation direction of the differential case 5 (side gear 2) between adjacent support surfaces 52 along the plurality of opening portions 51. In addition, the ring-shaped weir portion (second weir portion) 53b protrudes toward the axial center (radially inner side) of the housing main body 50 at the end portion on the side of the cover 59 (differential ring gear 6) of the housing main body 50, that is, on the side opposite the opening portion 51 in the axial direction of the side gear 2, and extends in the direction along the rotation direction of the differential case 5. Also, the weir portion 53b is spaced apart and opposed to the plurality of weir portions 53a in the axial direction of the side gear 2. Thus, on the housing main body 50 (differential case 5), a plurality of (two in the present embodiment) oil reservoirs 53 that extend in the direction along the rotation direction of the differential case 5 between adjacent support surfaces 52 are divided and formed by the plurality of weir portions 53a on the side of the opening portion 51 and the ring-shaped weir portion 53b on the side of the differential ring gear 6. That is, each oil reservoir 53 is located on the side opposite the opening portion 51 in the axial direction of the side gear 2 (differential case 5) than the differential ring gear 6, and is formed in the inner peripheral surface so as to be recessed toward the outer peripheral surface side of the housing main body 50 (differential case 5) with respect to the support surface 52. In addition, each oil reservoir 53 is formed in the housing main body 50 in a manner in which the weir portion 53b, the oil reservoir 53, the weir portion 53a, and the opening portion 51 are arranged in this order from the side of the differential ring gear 6.

[0023] As shown in Figure 3 and Figure 4 One oil introduction port 54 is formed on each support surface 52. The oil introduction port 54 of each support surface 52 is located on the front side in the rotation direction of the side gear 2 (drive shaft) of the vehicle when advancing including the differential gear 1, that is, on the side of the differential ring gear 6 in the axial direction of the side gear 2 (differential case 5) than the opening portion 51. Figure 3The oil guide inlet 54 is formed in the differential case 5 so as to communicate with the corresponding oil storage portion 53, and at least partially overlaps the pinion gear gasket 8 when viewed in the axial direction of the pinion gear 3. In addition, each oil guide inlet 54 is formed on the side opposite the side of the differential ring gear 6 in such a manner as to approach the center of the corresponding bearing surface 52 in the axial direction of the differential case 5.

[0024] In addition, a guide portion 55 for guiding the working oil in the oil storage portion 53 toward the corresponding oil guide inlet 54 is formed by casting on each oil storage portion 53 (inner peripheral surface of the case main body 50) of the differential case 5. Each guide portion 55 is a protruding portion that protrudes from the bottom surface of the oil storage portion 53 toward the axial center (radially inner side) of the case main body 50, so that the oil storage portion 53 gradually narrows in the axial direction of the side gear 2 (differential case 5) as it moves away from the differential ring gear 6 in the axial direction of the differential case 5 and approaches the oil guide inlet 54. In the present embodiment, each oil guide inlet 54 is formed so as to extend linearly toward the axial center of the pinion shaft 4 in the direction of rotation of the differential case 5, but is not limited thereto. That is, each oil guide inlet 54 can be inclined with respect to the direction of rotation of the differential case 5, can be formed offset in the axial direction of the side gear 2 (drive shaft) with respect to the axial center of the pinion shaft 4, or can be formed so that the oil guide inlet 54 extends in a curved (bent) manner.

[0025] In the differential gear 1 configured as described above, working oil as lubricating oil is supplied to the inside of the differential case 5 via the opening portion 51 during vehicle travel, and a portion of the working oil supplied to the differential case 5 is stored in the oil storage portion 53 located below when the vehicle is stopped. Thus, at the time of vehicle start, even if the oil level in the differential chamber and the differential case 5 is lowered due to the oil pump drawing the working oil in the working oil storage chamber in the transmission case, it is possible to ensure working oil as lubricating oil in the oil storage portion 53 of the differential case 5.

[0026] Therefore, even if the working oil is stirred up by the differential gear ring 6 at the time of vehicle start or is insufficiently supplied into the differential case 5 by the supply pipe, the working oil in the oil accumulation portion 53 can be made to spread to the sliding portions between each side gear 2 and the differential case 5, between each pinion 3 and the supporting surface 52, and the like by the rotation of the differential case 5. As a result, the shortage of lubricating oil with respect to the sliding portions can be well suppressed, and the increase in surface pressure at the sliding portions can be dealt with, so that, for example, each side gear 2 can be made small in diameter to make the differential gear 1 compact. That is, in the differential gear 1, even if the surface area of the sliding portions at the periphery of the side gears 2, the pinions 3, and the like is reduced due to the compactness, a sufficient amount of working oil (lubricating oil) can be ensured in the differential case 5 during the operation of the differential gear 1, that is, during vehicle travel, so that the increase in surface pressure at the sliding portions can be well dealt with. Furthermore, the weir portions 53a, 53b for dividing the oil accumulation portion 53 on the case main body 50 also function as rib portions, so that the strength of the differential case 5, and further the differential gear 1, can be further improved.

[0027] In addition, the oil guide inlet 54 is formed on each supporting surface 52 of the differential case 5, the oil guide inlet 54 communicates with the corresponding oil accumulation portion 53 on the front side in the rotation direction of the differential case 5 (side gear 2) at the time of vehicle advancement, and the oil guide inlet 54 at least partially overlaps the pinion washer 8 as viewed in the axial direction of the pinion 3. That is, the oil guide inlet 54 is formed only on the front side in the rotation direction of the differential case 5 at the time of vehicle advancement with respect to the supporting surface 52, and is not formed on the rear side of the supporting surface 52 on which the rear side portion of the pinion washer 8 is pressed. Thereby, compared to the case where the oil guide inlet 54 is formed on the rear side of the supporting surface 52, the increase in surface pressure acting on the supporting surface 52 can be suppressed, so that even when the rear side portion of the pinion washer 8 in the rotation direction of the differential case 5 is pressed on the supporting surface 52 and the surface pressure increases as the vehicle advances while accelerating, the durability of the supporting surface 52 can be well ensured. Therefore, by forming the oil guide inlet 54 only on the front side in the rotation direction of the differential case 5 of each supporting surface 52, the durability of the differential case 5 (case main body 50) can be well ensured, and a sufficient amount of working oil (lubricating oil) can be supplied between the pinion washer 8 and the supporting surface 52 to well lubricate and cool the supporting surface 52 and the pinion washer 8 pressed on the supporting surface 52. In addition, as shown in FIG. 6, since the oil guide inlet 54 is occluded in a manner not to communicate with the pinion shaft hole into which the pinion shaft 4 is inserted, the working oil guided to the oil guide inlet 54 can be caused to overflow from the oil guide inlet 54 to be efficiently supplied between the supporting surface 52 and the pinion washer 8. Also, since no notch for the oil guide inlet 54 is formed on the pinion shaft hole, the decrease in strength of the pinion shaft hole can be suppressed. Figure 3

[0028] ​Further, in the differential gear 1, the differential gear ring 6 is fixed to the differential case 5, and each oil accumulation portion 53 is formed closer to the differential gear ring 6 than the opening portion 51 in the axial direction of the differential case 5. That is, since the outer diameter of the differential case 5 is largest on the differential gear ring 6 side, by forming each oil accumulation portion 53 on the differential case 5 closer to the differential gear ring 6 using the weir portions 53a, 53b, the volume of each oil accumulation portion 53 can be sufficiently ensured.

[0029] Further, the case main body 50 of the differential case 5 includes a guide portion 55 that causes the corresponding oil accumulation portion 53 to gradually narrow in the axial direction of the side gear 2 as it moves away from the differential gear ring 6, thereby guiding the working oil within the oil accumulation portion 53 to the oil guide inlet 54 on the side opposite the differential gear ring 6. Further, each oil guide inlet 54 is formed in the differential case 5 closer to the center of the corresponding bearing surface 52 in the axial direction of the differential case 5. Thereby, the working oil within the oil accumulation portion 53 can be smoothly guided into the oil guide inlet 54 by rotation of the differential case 5, and supplied from the oil guide inlet 54 to the pinion gear 3, the pinion gear spacer 8, and the periphery of the bearing surface 52 as lubricating oil. Further, by biasing each oil guide inlet 54 from the center of the oil accumulation portion 53 in the axial direction of the differential case 5 toward the center of the bearing surface 52 in the axial direction, the working oil can be efficiently supplied to each bearing surface 52, and the area of the opening portion 51 can be sufficiently ensured, and the differential case 5 can be made more compact compared to when the oil guide inlet 54 is closer to the center of the oil accumulation portion 53.

[0030] As described above, the differential gear 1 according to the present disclosure is mounted on a vehicle, and includes a pair of side gears 2, two pinion gears 3 that mesh with the pair of side gears 2, and a differential case 5 that houses the pair of side gears 2 and the two pinion gears 3, and supplies lubricating oil to the inside or discharges working oil as lubricating oil from the inside via an opening portion 51. Further, the differential case 5 includes two bearing surfaces 52 formed on the inner peripheral surface of the differential case 5 so as to support the pinion gears 3, weir portions 53a that extend in a direction along the rotation direction of the differential case 5 and connect adjacent bearing surfaces 52 between the adjacent bearing surfaces 52, and oil accumulation portions 53 formed on the inner peripheral surface by the weir portions 53a on the side of the side gears 2 opposite the opening portion 51 in the axial direction.

[0031] Thereby, the lack of lubricating oil with respect to the sliding portions at the portions between the side gears 2 and the differential case 5, between the pinion gears 3 and the bearing surfaces 52, and the like can be well suppressed, and thus the increase in surface pressure in the sliding can be dealt with. As a result, the differential gear 1 can be made more compact.

[0032] In addition, an oil introduction port can be additionally provided on each of the support surfaces 52 of the housing main body 50, the oil introduction port communicating with the oil accumulation portion 53 on the rear side in the rotation direction of the differential housing 5 at the time of vehicle forward travel and coinciding with the pinion gear gasket 8 when viewed in the axial direction of the pinion gear 3, and the oil introduction port can be formed only on the rear side in the rotation direction of the differential housing 5. Further, the differential gear 1 can include three or more pinion gears 3 and support surfaces 52.

[0033] [SUMMARY OF EMBODIMENTS]

[0034] As described thus far, the differential gear according to an embodiment of the present disclosure includes a pair of side gears (2), at least two pinion gears (3) each meshing with the pair of side gears (2), and a differential housing (5) that houses the pair of side gears (2) and the at least two pinion gears (3) and supplies or discharges lubricating oil to or from the inside via an opening portion (51). In the differential gear (1) mounted on a vehicle, the differential housing (5) includes at least two support surfaces (52) formed on an inner peripheral surface of the differential housing (5) so as to support the pinion gears (3), a weir portion (53a) extending in a direction along a rotation direction of the differential housing (5) and connecting adjacent support surfaces (52) between the adjacent support surfaces (52), and an oil accumulation portion (53) formed by the weir portion (53a) on the inner peripheral surface so as to be located on a side opposite to the opening portion (51) in an axial direction of the differential housing (5) with respect to the weir portion (53a).

[0035] Such a differential gear is mounted on a vehicle and includes a pair of side gears, at least two pinion gears each meshing with the pair of side gears, and a differential housing that houses the pair of side gears and the at least two pinion gears and supplies or discharges lubricating oil to or from the inside via an opening portion. Also, the differential housing includes at least two support surfaces formed on an inner peripheral surface of the differential housing so as to support the pinion gears, a weir portion extending in a direction along a rotation direction of the differential housing and connecting adjacent support surfaces between the adjacent support surfaces, and an oil accumulation portion formed by the weir portion on the inner peripheral surface so as to be located on a side opposite to the opening portion in an axial direction of the differential housing with respect to the weir portion. Thus, when the oil level in the differential housing decreases, lubricating oil can be ensured in the oil accumulation portion, and the lubricating oil in the oil accumulation portion is caused to spread to sliding portions such as between the pinion gears and the support surfaces by rotation of the differential housing. As a result, it is possible to well suppress a shortage of lubricating oil with respect to the sliding portions and to cope with an increase in surface pressure of the sliding portions, and thus it is possible to make the differential gear compact.

[0036] In addition, a pinion gasket (8) can be provided between the back surface of each of the pinions (3) and the support surface (52), an oil introduction port (54) can be formed in each of the support surfaces (52), the oil introduction port (54) communicates with the oil reservoir (53) on the front side in the rotation direction of the differential case (5) when the vehicle is advancing, and at least partially overlaps the pinion gasket (8) when viewed in the axial direction of the pinion (3).

[0037] Thus, when the vehicle is accelerating and advancing, even if the rear side portion of the pinion gasket in the rotation direction of the differential case is pressed against the support surface and the surface pressure increases, the durability of the support surface can be ensured. Therefore, by forming the oil introduction port on the front side of each of the support surfaces in the rotation direction of the differential case, the durability of the differential case can be ensured, and a sufficient amount of working oil (lubricating oil) can be supplied between the pinion gasket and the support surface to lubricate and cool the support surface and the pinion gasket pressed against the support surface.

[0038] Further, a ring gear 6 can be fixed to the differential case 5, and the oil reservoir 53 can be formed in the differential case 5 in the order of the oil reservoir 53, the weir 53a, and the opening 51 from the ring gear 6 side in the axial direction.

[0039] Thus, the volume of the oil reservoir can be sufficiently ensured.

[0040] In addition, the weir can include a first weir 53a provided on the opening 51 side of the oil reservoir 53, and a second weir 53b provided on the ring gear 6 side of the oil reservoir 53.

[0041] Further, the differential case (5) can include a guide portion (55) that narrows the oil reservoir (53) gradually away from the ring gear (6) in the axial direction, thereby guiding the lubricating oil in the oil reservoir (53) to the oil introduction port (54) on the side opposite the ring gear (6), and the oil introduction port (54) can be formed in the support surface (52) so as to approach the center of the support surface (52) in the axial direction.

[0042] Thus, the working oil in the oil accumulation portion can be smoothly introduced into the oil introduction port by rotation of the differential case, and the working oil as lubricating oil can be supplied from the oil introduction port to the periphery of the pinion gear, the pinion gear gasket, and the bearing surface. In addition, by biasing each oil introduction port from the center of the oil accumulation portion in the axial direction of the differential case to the side opposite the side of the ring gear in the axial direction, and by forming the oil introduction port on the bearing surface in a manner to approach the center of the bearing surface in the axial direction, the working oil can be efficiently supplied to each bearing surface, and the area of the opening portion can be sufficiently ensured, and the differential case can be compact compared to the case in which the oil introduction port approaches the center of the oil accumulation portion.

[0043] Moreover, the invention of the present disclosure is not limited by any of the above-described embodiments, and various modifications can be made within the scope of the present disclosure, as is self-evident. Furthermore, the above-described embodiments are merely one specific example of the invention described in the summary of the invention, and do not limit the elements of the invention described in the summary of the invention.

[0044] Industrial applicability

[0045] The invention of the present disclosure can be utilized in the manufacturing industry of differential gears and the like.

Claims

1. A differential gear for mounting on a vehicle, comprising: a pair of side gears; at least two pinions that mesh with the pair of side gears, respectively; a differential case that houses the pair of side gears and the at least two pinions and supplies or discharges lubricating oil to or from the inside via an opening portion, wherein the differential case includes: at least two bearing surfaces that are formed on an inner peripheral surface of the differential case in a manner to support the pinions; a weir portion that extends in a direction along a rotation direction of the differential case and connects adjacent bearing surfaces between the adjacent bearing surfaces; an oil accumulation portion that is formed by the weir portion on the inner peripheral surface in a manner to be located on a side opposite to the opening portion in an axial direction of the differential case; and a guide portion; a pinion gasket is disposed between a back surface of each of the pinions and the bearing surface, an oil introduction port is formed on each of the bearing surfaces, the oil introduction port being in communication with the oil accumulation portion on a front side in the rotation direction of the differential case when the vehicle is moving forward and at least partially overlapping the pinion gasket when viewed in an axial direction of the pinion, a ring gear is fixed to the differential case, the guide portion causes the oil accumulation portion to gradually narrow in the axial direction as it moves away from the ring gear and guides the lubricating oil in the oil accumulation portion to the oil introduction port on a side opposite to the ring gear side, the oil introduction port is formed on the bearing surface in a manner to approach a center of the bearing surface in the axial direction.

2. The differential gear according to claim 1, wherein the oil accumulation portion is formed in a manner to be arranged in the order of the oil accumulation portion, the weir portion, and the opening portion from the ring gear side in the axial direction.

3. The differential gear according to claim 2, wherein the weir portion includes: a first weir portion that is disposed on the opening portion side of the oil accumulation portion; and a second weir portion that is disposed on the ring gear side of the oil accumulation portion.

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