Patent ID: 12234906

EXPLANATION OF REFERENCE NUMERALS

C . . . differential case, Ci . . . inner surface of differential case, Cb1, Cb2. . . bearing boss parts as boss parts, D . . . differential device, Gp . . . pinion gear lubricating oil groove, Gpi . . . opened part of pinion gear lubricating oil groove, P1, P2. . . first and second pinion gear support surfaces as pinion gear support surfaces, S1, S2. . . first and second side gear support surfaces as side gear support surfaces, X1, X2. . . first and second axial lines,15,16. . . helical grooves as oil introduction channels,18. . . window,19. . . support base,22. . . pinion gear,23. . . side gear,30. . . clearance as oil introduction channel,40. . . diameter-enlarged inner surface part,40o. . . inner surface bottom part,41. . . first diameter-enlarged inner surface part as inner diameter changing part,50. . . main guide weir as oil introduction part,52. . . second weir as enclosure,54,541,542. . . auxiliary weir

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention is described based on the accompanying drawings.

First, reference is made toFIGS.1to4to describe a first embodiment. InFIG.1, a transmission case10of a vehicle (for example, an automobile) houses a differential device D configured to divide and transmit a power from a not shown power source (for example, an engine installed in a vehicle, a motor, and the like) to output shafts11,12that are paired as left and right output shafts. The differential device D comprises a differential case C rotatable about a first axial line X1, and a differential mechanism20to be built in the differential case C. The left and right output shafts11,12, respectively, are interlocked with and coupled to left and right drive wheels (not shown).

In the present specification and the present invention, the term “axial direction” means a direction along the first axial line X1. Furthermore, the term “radial direction” means a direction along a radius of a circle about the first axial line X1.

The differential case C is divided into and comprises a first half case body C1having a substantially bowl shape and a second half case body C2having a lid shape to close an open end of the first half case body C1. The first half and second half case bodies C1, C2, respectively, include a flange part Cf1and a flange part Cf2provided continuously to outer peripheries of the first half and second half case bodies C1, C2. These flange parts Cf1, Cf2are laid over and detachably coupled to an inner circumferential flange part Rb of a ring gear R with two or more bolts36. The first half and second half case bodies C1, C2have respective facing surfaces provided with concave and convex engagement portions37to be coaxially engaged with each other.

The ring gear R includes gear teeth Ra to be engaged with, for example, a drive gear9, which acts as an output part of a transmission device connected to a power source. This results in transmission of a rotation driving force from the power source to the differential case C via the ring gear R. The ring gear R may be a helical gear or a spur gear.

There is defined, between the first half and second half case bodies C1, C2, an internal space17configured to function as a mechanism chamber to house the differential mechanism20therein. In particular, the first half case body C1is provided with, in its body part, windows18in pairs that allow communication between an inside and an outside of the differential case C and are formed so as to face each other across the first axial line X1. These windows18can not only function as inlet and outlet ports for oil, but also function as working windows to allow a cutting tool, a jig, a finger, or the like to be put in or taken out when an inner surface Ci of the differential case C is machined or the differential mechanism20is assembled to the differential case C.

The first half case body C1includes an axially-outer part provided with, as a part integral therewith, a first bearing boss Cb1. The second half case body C2includes an axially-outer part provided with, as a part integral therewith, a second bearing boss Cb2. The first and second bearing bosses Cb1, Cb2are oriented in opposite directions and have cylindrical shapes extending coaxially. The first and second bearing bosses Cb1, Cb2each are one example of the boss part. The first and second bearing bosses Cb1, Cb2are supported, on outer peripheries thereof, by the transmission case10via a bearing13and a bearing14, respectively, in a freely rotatable manner about the first axial line X1.

Each of the first and second bearing bosses Cb1, Cb2has an inner circumferential surface fitted with and supporting a corresponding one of the left and right output shafts11,12via a hollow shaft part23jof each side gear23to be described later such that the corresponding one of the left and right output shafts11,12is freely rotatable. Moreover, the first and second bearing bosses Cb1, Cb2, respectively, are provided with one or more lines (two lines in the embodiment) of helical grooves15,16(see,FIG.1) for drawing lubricating oil therein. The helical groove15of the first bearing boss Cb1and the helical groove16of the second bearing boss Cb2have helical directions opposite to each other.

During the automobile making a turn, as the differential mechanism20rotates at different speeds, the first and second bearing bosses Cb1, Cb2and the respective hollow shaft parts23jof the side gears23on the left and right sides rotate with respect to each other. In response to this, the helical grooves15,16, each of which is one example of the oil introduction channel, can exhibit a pumping action to deliver the lubricating oil from the outside of the differential case C to the inner surface Ci of the differential case C (particularly, side gear support surfaces S1, S2to be described later). At respective outer ends, the first and second bearing bosses Cb1, Cb2, respectively, are provided with guide protrusions g1, g2configured to enable guiding of the lubricating oil that scatters and flows down around the differential case C of the transmission case10to upstream ends of the helical grooves15,16.

The differential mechanism20comprises: a pinion shaft21arranged in a center part of the differential case C along a second axial line X2orthogonal to the first axial line X1and supported by the differential case C; pinion gears22in pairs fitted to and supported by the pinion shaft21in a freely rotatable manner; and the side gears23,23in pairs to mesh with the respective pinion gears22and supported by the differential case C in a freely rotatable manner about the first axial line X1.

The pinion shaft21in the present embodiment has both ends fitted in pinion shaft support holes25provided in the body part of the first half case body C1. Moreover, the pinion shaft21is fixed to the differential case C with a fixing pin24that is inserted in the body part. The way to fix the pinion shaft21is not limited to the present embodiment, and various fixing ways (for example, clamping, screwing, and the like) may be employed.

The side gears23,23in pairs function as output gears of the differential mechanism20. These side gears23,23have respective inner circumferential parts, which are in spline engagement with leading ends of the output shafts11,12in pairs.

Each side gear23includes: a side gear main body23mincluding teeth and having a large diameter; and a hollow shaft part23jprotruding at a center in a back side of the side gear main body23mas a piece integral with the side gear main body23m. The back side of one side gear23is supported in a rotatable and slidable manner, via a side gear washer Ws, by a first side gear support surface S1of an inner surface Ci1of the first half case body C1. The first side gear support surface S1is continuous to an inner end of the first bearing boss Cb1. The back side of the other side gear23is supported in a rotatable and slidable manner, via the side gear washer Ws, by a second side gear support surface S2of an inner surface Ci2of the second half case body C2. The second side gear support surface S2is continuous to an inner end of the second bearing boss Cb2.

Each of the first and second side gear support surfaces S1, S2in the present embodiment is formed in an annular planar surface orthogonal to the first axial line X1. Alternatively, each side gear support surface may be formed in a part of a tapered or spherical surface (see, a third embodiment inFIGS.7,8) in place of the annular planar surface. Furthermore, each of the first and second side gear support surfaces S1, S2is provided with side gear lubricating oil grooves Gs in pairs such that the side gear lubricating oil grooves Gs cross a corresponding one of the side gear support surfaces S1, S2. The side gear lubricating oil grooves Gs communicate with downstream ends of the respective helical grooves15,16. It should be noted that the side gear washer Ws may be omitted. In this case, the respective back sides of the side gears23are directly supported by the first and second side gear support surfaces S1, S2in a rotatable and slidable manner.

The inner surface Ci of the differential case C includes a diameter-enlarged inner surface part40that couples the side gear support surfaces S1, S2in pairs to each other and has a diameter enlarged relative to each of the side gear support surfaces S1, S2. The diameter-enlarged inner surface part40includes a first diameter-enlarged inner surface part41and a second diameter-enlarged inner surface part42. The first diameter-enlarged inner surface part41corresponds to an outer peripheral area in the inner surface Ci1of the first half case body C1, is relatively wider in the axial direction, and has an annular shape. The second diameter-enlarged inner surface part42corresponds to an outer peripheral area in the inner surface Ci2of the second half case body C2, is relatively narrower in the axial direction, and has an annular shape.

The first diameter-enlarged inner surface part41includes a steeply-enlarged inner surface part41aand a gently-enlarged inner surface part41b. The steeply-enlarged inner surface part41ahas a diameter steeply increasing from an outer peripheral end of the first side gear support surface S1toward the second side gear support surface S2(that is, an enlarging rate of its inner diameter is high). The gently-enlarged inner surface part41bhas a diameter gently increasing from the steeply-enlarged inner surface part41atoward the open end of the first half case body C1(that is, an enlarging rate of its inner diameter is low). The first diameter-enlarged inner surface part41is one example of the inner diameter changing part of the present invention (particularly, the fourth feature) having a diameter enlarged, in an axial range from the first side gear support surface S1on one side of the differential case C in the axial direction to at least opened parts Gpi of pinion gear lubricating oil grooves Gp to be described later (in the embodiment, to the open end of the first half case body C1), toward the other side of the differential case C in the axial direction.

The second diameter-enlarged inner surface part42is formed by only a steeply-enlarged inner surface part that has a diameter steeply enlarged from an outer peripheral end of the second side gear support surface S2toward an open end of the second half case body C2(that is, an enlarging rate of its inner diameter is high). It should be noted that each of the second diameter-enlarged inner surface part42and the steeply-enlarged inner surface part41amay be a part of a spherical surface or a sloped surface.

With respect to the above-described diameter-enlarged form of the first and second diameter-enlarged inner surface parts41,42, the first and second diameter-enlarged inner surface parts41,42each have an annular recessed surface configuration with the deepest part (that is, most recessed in a radially outward direction), in the diameter-enlarged inner surface part40, at a joining part between the first and second diameter-enlarged inner surface parts41,42and its peripheral part. The recessed surface configuration is a part of an inner surface bottom part40o. In the inner surface bottom part40o, oil introduced on the diameter-enlarged inner surface part40through the side gear support surfaces S1, S2flows along the first and second diameter-enlarged inner surface parts41,42and is accumulated due to an action of a centrifugal force as the differential case C rotates. In the embodiment, as is clear fromFIGS.2,3, the inner surface bottom part40ois formed like a shallow depression.

The pinion gears22have respective spherical back sides supported by support bases19in pairs that are provided to the diameter-enlarged inner surface part40(more specifically, the first diameter-enlarged inner surface part41) of the inner surface Ci of the differential case C in a manner to protrude concentrically to the pinion shaft21and face each other. Specifically, respective top surfaces of both the support bases19, which face each other, are formed into concave surfaces having spherical shapes, and form a first pinion gear support surface P1and a second pinion gear support surface P2as the pinion gear support surfaces to support the pinion gears. The respective back sides of the pinion gears22abut and are supported by the pinion gear support surfaces P1, P2via pinion gear washers Wp in a rotatable and slidable manner. The pinion gear washers Wp may be omitted. In this case, the respective back sides of the pinion gears22are directly supported by the first and second pinion gear support surfaces P1, P2in a rotatable and slidable manner.

As viewed in a projection plane (see,FIG.2) orthogonal to the second axial line X2, each of the first and second pinion gear support surfaces Pt, P2is provided with a line of a pinion gear lubricating oil groove Gp linearly and orthogonally extending to the axial line X1. Both ends of each pinion gear lubricating oil groove Gp function as the opened parts Gp that are directly open to an outer circumferential surface of a corresponding one of the support bases19. As is clear fromFIG.3, the opened parts Op are open to the inner surface bottom part40oof the diameter-enlarged inner surface part40.

The inner surface Ci of the differential case C may not be provided with the support bases19described above, and a part of the inner surface Ci can be pinion gear support surfaces. In this case, by providing the inner surface Ci of the differential case C, in the vicinity of outer circumferences of the pinion gear support surfaces, with parts slightly recessed from the pinion gear support surfaces, the ends of the pinion gear lubricating oil grooves Gp are open to the inner surface Ci of the differential case C in the outer circumferences of the pinion gear support surfaces P1, P2through resulting slight recesses.

Furthermore, the pinion gear lubricating oil grooves Gp of the first and second pinion gear support surfaces P1, P2are arranged at positions axially symmetrical to the first axial line X1as viewed in the projection plane (see, FIG.2) orthogonal to the second axial line X2. Although the first and second pinion gear support surfaces P1, P2in the embodiment are illustrated as spherical recessed surfaces by way of example, each pinion gear support surface may be a tapered surface or a planar surface orthogonal to the second axial line X2.

In the inner surface Ci of the differential case C, there is provided main guide weirs50protruding therefrom. The main guide weirs50are configured to guide at least some of oil to the pinion gear support surfaces P1, P2such that the at least some of the oil deviates from a flow direction from the first and second side gear support surfaces S1, S2to the windows18along the inner surface Ci and flows around the window18. The main guide weirs50each are a part of the oil guiding part of the present invention. In the present embodiment, the main guide weirs50are formed so as to (i) enclose entire circumferences of the respective windows18and extend in a circumferential direction of the windows18and (ii) protrude radially inward of the first diameter-enlarged inner surface part41of the inner surface Ci (that is, toward the first axial line X1).

Each of the main guide weirs50particularly in the first embodiment includes a first weir51, a second weir52, and third weirs53in pairs. The first weir51is situated between, in the axial direction, the first side gear support surface S1in the first half case body C1and a circumferential rim of a corresponding one of the windows18, and extends in the circumferential direction of the corresponding one window18. The second weir52is situated between, in the axial direction, the second side gear support surface S2in the second half case body C2and the circumferential rim of the corresponding one window18, and extends in the circumferential direction of the corresponding one window18. The third weirs53in pairs are situated between, in a circumferential direction of the differential case C, the pinion gear support surfaces P1, P2and the circumferential rim of the corresponding one window18, and extend in the circumferential direction of the corresponding one window18.

The third weirs53couple one end of the first weir51in the circumferential direction and one end of the second weir52in the circumferential direction to each other; and couple the other end of the first weir51in the circumferential direction and the other end of the second weir52in the circumferential direction to each other. Respective coupling portions of the third weirs53to the first and second weirs51,52are arcuately formed so as to follow a curve of the circumferential rim of the corresponding one window18. In the first diameter-enlarged inner surface part41of the differential case C, the second weir52is located between the inner surface bottom part40odescribed above and the windows18, and formed to protrude radially inward of the inner surface bottom part40o(that is, toward the first axial line X1).

Next, a description is given to an operation effect of the first embodiment. During traveling of an automobile into which the differential device D of the present embodiment is assembled, a rotation driving force from the power source is transmitted from the ring gear R to the differential case C. Then, the rotation driving force is divided and transmitted to the left and right output shafts11,12via the differential mechanism20of the differential device D with the differential mechanism20being allowed to rotate at different speeds. In this case, the differential mechanism20does not rotate at different speeds during the automobile travelling straight. Specifically, the first and second bearing bosses Cb1, Cb2of the differential case C and the left and right side gears23(that is, the output shafts11,12) rotate forwardly, not rotate relative to each other, respectively.

In contrast, during the automobile making a turn, the first and second bearing bosses Cb1, Cb2and the left and right side gears23rotate relative to each other, respectively, as the differential mechanism20rotates at different speeds due to differences in turning radius of left and right drive wheels. As a result of this relative rotation, the helical grooves15,16can exhibit the pumping action. Thus, the oil introduced from the outside of the differential case C (particularly, near an outer end of each of the bearing bosses Cb1, Cb2) into the helical grooves15,16with the guide protrusions g1, g2flows to the side gear support surfaces S1, S2inside the differential case C through the helical grooves15,16. Specifically, the oil flows into the side gear lubricating oil grooves Gs to thereby lubricate the side gear support surfaces S1, S2. The oil that has lubricated the first and second side gear support surfaces S1, S2is radially released, due to the action of the centrifugal force generated by rotation of the differential case C, from any position on outer ends of the first and second side gear support surfaces S1, S2, and flows along the first and second diameter-enlarged inner surface parts41,42.

The oil that has been released from the side gear support surfaces S1, S2flows along the diameter-enlarged inner surface part40(specifically, the first and second diameter-enlarged inner surface parts41,42) of the differential case C substantially in the axial direction, and in the end, the oil released is gathered in the inner surface bottom part40o, which is a radially outermost part of the diameter-enlarged inner surface part40. Since the opened parts Gpi of the pinion gear lubricating oil grooves Gp face the inner surface bottom part40o, the oil accumulated in the inner surface bottom part40ois sufficiently supplied to the pinion gear lubricating oil grooves Gp, to thereby efficiently lubricate the pinion gear support surfaces P1, P2.

Particularly, in the embodiment, since the oil is introduced from the helical grooves15,16as the oil introduction channels into the differential case C through the side gear support surfaces S1, S2, there is a greater ratio of the oil flowing from the side gear support surfaces S1, S2to the diameter-enlarged inner surface part40in the axial direction (toward the windows18). In this regard, the inner surface Ci of the differential case C is specially provided with the main guide weirs50so as to guide at least some of the oil such that the at least some of the oil deviates from a flow direction from the side gear support surfaces S1, S2to the windows18along the diameter-enlarged inner surface part40(specifically the first and second diameter-enlarged inner surface parts41,42) of the inner surface Ci of the differential case C, and flows around the windows18. Thus, particularly the first and second weirs51,52of each main guide weir50, situated between the side gear support surfaces S1, S2and the corresponding one window18, can guide the oil flowing in the axial direction from the side gear support surfaces S1, S2through the diameter-enlarged inner surface part40so as to gather the same to the inner surface bottom part40oin a manner to flow the oil around the windows18. This can suppress outflow of the oil through the windows18. Accordingly, the oil that has lubricated the first and second side gear support surfaces S1, S2can be reused for lubrication of other parts to be lubricated in the differential case C, thereby improving lubrication efficiency of parts in the differential case C.

The respective pinion gear support surfaces P1, P2provided to the inner surface Ci of the differential case C in the embodiment are provided with the pinion gear lubricating oil grooves Gp, which are open to the inner surface Ci of the differential case C in the outer circumferences of the pinion gear support surfaces P1, P2. Thus, as discussed above, the oil guided with the main guide weirs50so as to flow around the windows18can be effectively supplied to the pinion gear lubricating oil grooves Gp, and the pinion gear support surfaces P1, P2can be efficiently lubricated.

Particularly, the third weirs53of each main guide weir50, situated between the pinion gear support surfaces P1, P2and the corresponding one window18, do not interrupt a flow of the oil from the first side gear support surface S1on the one side of the differential case C in the axial direction to the second side gear support surface S2on the other side of the differential case C in the axial direction around the corresponding one window18. Moreover, for the oil flowing from the pinion gear support surfaces P1, P2to the corresponding one window18in the circumferential direction, the third weirs53function to prevent outflow of the oil through the corresponding one window18.

The side gear support surfaces S1, S2in the embodiment are formed into the annular planar surfaces orthogonal to the first axial line X1. The inner surface Ci of the differential case C couples the side gear support surfaces S1, S2in pairs to each other, and comprises the diameter-enlarged inner surface part40having a diameter enlarged relative to each of the side gear support surfaces S1, S2. The diameter-enlarged inner surface part40includes the inner surface bottom part40oto which the oil flowing along the diameter-enlarged inner surface part40is gathered due to the centrifugal force. Consequently, the oil introduced from the helical grooves15,16through the side gear support surfaces S1, S2flows along the diameter-enlarged inner surface part40under the centrifugal force and is easily accumulated in the inner surface bottom part40o, which is situated in a radially outer side of the diameter-enlarged inner surface part40. Since the side gear support surfaces S1, S2, in particular, are annular planar surfaces and extend radially outward, an area having an enlarged diameter (that is, deeper radially outward) can be widely obtained in the inner surface Ci of the differential case C in the axial direction as compared to a case where the side gear support surfaces S1, S2themselves each have a structure in which the diameter is gradually enlarged from an inner circumferential end to an outer circumferential end thereof (for example, a differential case structure in which the side gear support surfaces S1, S2each are formed into a spherical shape or tapered shape). A large amount of the oil can be stored in the inner surface bottom part40o, which is recessed most in the area having an enlarged diameter.

Moreover, between the inner surface bottom part40oand the windows18, the inner surface Ci of the differential case C is provided with the main guide weirs50(more specifically, the second weirs52) that protrude toward the first axial line X1(that is, radially inward) with respect to the inner surface bottom part40o. The pinion gear lubricating oil grooves Gp are open to the inner surface bottom part40o. Thus, a large amount of the oil accumulated in the inner surface bottom part40ocan be sufficiently supplied to the pinion gear lubricating oil grooves Op, thereby efficiently lubricating the pinion gear support surfaces P1, P2.

FIGS.5and6illustrate a second embodiment of the present invention. The main guide weirs50in the first embodiment are illustrated as continuously extending weirs so as to enclose the entire circumferences of the windows18. In the second embodiment, each main guide weir50includes, in a part thereof (part corresponding to the third weirs53in the first embodiment), a non-continuous area.

Specifically, in the second embodiment, auxiliary weirs54are provided to the first diameter-enlarged inner surface part41in a protruding manner in place of the third weir53in the first embodiment. Each auxiliary weir54extends from a part of an outer circumference of a corresponding one of the support bases19, closer to the second side gear support surface S2with respect to the opened parts Gpi of the pinion gear lubricating oil groove Gp in the axial direction, to the corresponding one window18and is smoothly continuous to the first weir51. Both ends of the second weir52are continuous to the outer circumference of the support base19.

Furthermore, in the second embodiment, each of the pinion gear support surfaces P1, P2is provided with two lines of pinion gear lubricating oil grooves Gp parallel to each other across the second axial line X2.

As described above, the first diameter-enlarged inner surface part41in the inner surface Ci of the differential case C constitutes the inner diameter changing part of the present invention (particularly, the fourth feature) that has a diameter enlarged, in the axial range from the one side of the differential case C in the axial direction (in the embodiment, the first side gear support surface S1) to at least the opened parts Gpi (in the embodiment, the open end of the first half case body C1), toward the other side of the differential case C in the axial direction. The auxiliary weirs54function to capture some of the oil flowing on the first diameter-enlarged inner surface part41as the inner diameter changing part from the first side gear support surface S1to the second side gear support surface S2, to thereby guide the same to the opened parts Gpi.

The oil introduced into the differential case C from the helical groove15through the corresponding first side gear support surface S1flows along the first diameter-enlarged inner surface part41(the inner diameter changing part) toward the second side gear support surface S2under the centrifugal force resulting from rotation of the differential case C. In the second embodiment, the auxiliary weirs54capture some of the oil to thereby guide the same to the opened parts Gpi. In this case, each auxiliary weir54extends from the part of the outer circumference of the corresponding one support base19, closer to the second side gear support surface S2with respect to the opened parts Gpi in the axial direction, toward the corresponding one window18. Thus, even in the case of a flow path of a direction in which the oil flowing toward the second side gear support surface S2along the first diameter-enlarged inner surface part41(the inner diameter changing part) does not directly flow into the opened parts Gpi, the oil flowing between the opened parts Gpi and the windows18can be captured by the auxiliary weirs54. The oil captured by the auxiliary weirs54tends to flow from positions captured toward the second side gear support surface S2along the first diameter-enlarged inner surface part41(the inner diameter changing part). Thus, by extending the auxiliary weirs54toward the first side gear support surface S1(in other words, an upstream side in a direction in which the oil flows along the first diameter-enlarged inner surface part41) in the axial direction, the oil captured by the auxiliary weirs54can be efficiently introduced to the opened parts Gpi located closer to the second side gear support surface S2(in other words, a downstream side in the direction in which the oil flows along the first diameter-enlarged inner surface part41) along the auxiliary weirs54. As described above, the oil captured by the auxiliary weirs54can be efficiently guided to the opened parts Gpi and sufficiently supplied to the pinion gear lubricating oil grooves Gp. Accordingly, the pinion gear support surfaces P1, P2can be efficiently lubricated. It should be noted that, in the second embodiment, the respective auxiliary weirs54are continuous to the first weirs51and thus, the oil captured by the first weirs51can be also guided to the opened parts Gpi. Accordingly, the oil can be effectively supplied to the pinion gear lubricating oil grooves Gp.

Other configurations in the second embodiment are basically the same as those in the first embodiment. Thus, constituent elements in the second embodiment are labelled with the same reference numerals used for the corresponding constituent elements in the first embodiment, and detailed description of configurations of these constituent elements will be omitted. The second embodiment can also achieve operation effects that are basically the same as those of the first embodiment due to the main guide weirs50(particularly, the first and second weirs51,52).

Furthermore,FIGS.7,8illustrate a third embodiment of the present invention. In the first and second embodiments, the differential case C is divided into and comprises the first half and second half case bodies C1, C2, whereas in the third embodiment, the differential case C is formed into a seamless, integral case including an inner surface Ci having a spherical shape. The differential case C includes a body part provided with large windows18in pairs through which the side gears23and the pinion gears22are assembled into the differential case C. Still further, an outer circumferential part of the differential case C is integrally provided with a flange part Cf to fix the ring gear R thereto such that the flange part Cf and the one sides of the windows18are aligned in a direction along the first axial line X1.

Furthermore, each of the left and right side gears23integrally includes, in the center in the back side of the side gear main body23mincluding the gear teeth, a boss part23bhaving a short length in place of the hollow shaft part23jhaving a long length as in the first and second embodiments. The inner surface Ci of the differential case C comprises: annular recesses31,32, the side gear support surfaces S1, S2; and the pinion gear support surfaces P1, P2. The annular recesses31,32, respectively, are continuous to inner circumferential inner ends of the first and second bearing bosses Cb1, Cb2and receive the boss parts23b. The side gear support surfaces S1, S2have annular and spherical shapes, are continuous to outer circumferential ends of the annular recesses31,32, and support respective spherical back sides of the side gears23directly or via the side gear washers Ws such that the side gears23can rotate and slide on the side gear support surfaces S1, S2. The pinion gear support surfaces P1, P2have annular and spherical shapes, are continuous to inner open ends of the pinion shaft support holes25, and support respective spherical back sides of the pinion gears22directly or via the pinion gear washers such that the pinion gears22can rotate and slide on the pinion gear support surfaces P1, P2.

Still further, the inner circumferential surfaces of the first and second bearing bosses Cb1, Cb2, respectively, are directly fitted with the output shafts11,12, with clearances30defined in a size large enough to allow the lubricating oil to flow therein. Each clearance30is a part of an oil introduction channel that can introduce the lubricating oil from the outside of the differential case C to the first and second side gear support surfaces S1, S2(particularly, the side gear lubricating oil grooves Gs). It should be noted that outer ends of the first and second bearing bosses Cb1, Cb2in the third embodiment may be provided with guide protrusions g1, g2(illustration omitted), respectively, for introducing the lubricating oil as in the first embodiment. Furthermore, in place of the clearances30described above, the inner circumferential surfaces of the first and second bearing bosses Cb1, Cb2may be provided with oil introduction channels, that is, the helical grooves15,16, respectively, as in the first embodiment.

As described above, in the third embodiment as well, the inner surface Ci of the differential case C is provided with the pinion gear lubricating oil grooves Gp and the side gear lubricating oil grooves Gs. In particular, the pinion gear lubricating oil grooves Gp extend in parallel to the first axial line X1, unlike in the first and second embodiments, as viewed in a projection plane orthogonal to the second axial line X2(see,FIG.7). The pinion gear lubricating oil grooves Gp and the side gear lubricating oil grooves Gs are formed into grooves arranged along a circular arc about a specific axial line X3that passes through a spherical center Cx of the inner surface Ci of the differential case and the windows18.

The main guide weirs50are provided in a protruding manner in the inner surface Ci of the differential case C as the oil guiding part so as to guide at least some of oil to the pinion gear support surfaces P1, P2such that the at least some of the oil deviates from a flow direction from the first and second side gear support surfaces S1, S2to the windows18along the inner surface Ci of the differential case C and flows around the windows18.

The main guide weirs50in the third embodiment are formed on weir-forming platforms60in pairs. Each of the weir-forming platforms60protrudes radially inward of the inner surface Ci of the differential case C, that is, toward the first axial line X1, and is interposed between each of the pinion gear support surfaces P1, P2and a corresponding one of the windows18. Each weir-forming platform60extends, adjacent to the corresponding one window18, so as to substantially follow the first axial line X1, and has both ends reaching in the vicinity of the first and second side gear support surfaces S1, S2.

On an outer periphery of each weir-forming platform60, there is provided a step face between the weir-forming platform60and the inner surface Ci. The step face includes a first step face61, a second step face62, and a third step face63. Particularly, the first step face61having a circular arc shape along an outer circumference of the first side gear support surface S1functions as a first weir to guide at least some of oil, flowing out from the outer circumference of the first side gear support surface S1, toward the pinion gear support surfaces P1, P2in a manner to flow the at least some of the oil around the windows18. The second step face62having a circular arc shape along an outer circumference of the second side gear support surface S2functions as a second weir to guide at least some of oil, flowing out from the outer circumference of the second side gear support surface82, toward the pinion gear support surfaces P1, P2in a manner to flow the at least some of the oil around the window18. The third step face63extending in an elongated manner in a circular arch shape between each of the pinion gear support surfaces P1, P2and the corresponding one window18functions as a third weir to suppress outflow of the oil, flowing between each of the pinion gear support surfaces P1, P2and the corresponding one window18, through the window18.

The outer periphery of the weir-forming platform60, particularly the first to third step faces61to63described above can guide at least some of oil to the pinion gear support surfaces P1, P2such that the at least some of the oil deviates from a flow direction from the side gear support surfaces S1, S2to the window18along the inner surface Ci of the differential case C and flows around the window18. Thus, such a configuration can contribute to suppression of outflow of the oil through the windows18. Accordingly, in the third embodiment, the first to third step faces61to63of the weir-forming platform60, which function as the first to third weirs described above, constitute each of the main guide weir50.

In the third embodiment, in the inner surface Ci of the differential case C, respective areas forming top faces of the weir-forming platforms60, respective areas forming rotating and sliding surfaces of the side gear support surfaces S1, S2with respect to the side gears23, and respective areas forming rotating and sliding surfaces of the pinion gear support surfaces P1, P2with respect to the pinion gears22are machine-worked surfaces formed in the same spherical surface. Areas different from those mentioned, that is, areas in the inner surface Ci surrounded by the weir-forming platforms60, the pinion gear support surfaces P1, P2, and the side gear support surfaces S1, S2, the pinion gear lubricating oil grooves Gp, and the side gear lubricating oil grooves Gs are unworked surfaces positioned lower (that is, toward a radially outer side) than the above-described machine-worked surfaces. When the differential case C is molded, for example, cast-molded, the unworked surfaces are as-cast surfaces left without being subsequently worked after casting. InFIG.8, the unworked surfaces are indicated by stippling.

Machining of the inner surface Ci of the differential case C is performed by, for example, using a cutting tool for machining (for example, a bite for turning a tool) to be moved into a molded material of the differential case through the window18along the specific axial line X3, with the material of the differential case being rotated about the specific axial line X3.

This method for machining in the third embodiment is applicable to the inner surface Ci of the first half case body Cb1in the first and second embodiments as well. In this case, in the inner surface Ci1of the first half case body Cb1in the first and second embodiments, the respective areas forming the top surfaces of the main guide weirs50and the respective areas forming rotating and sliding surfaces of the pinion gear support surfaces P1, P2with respect to the pinion gears22are worked surfaces formed in the same spherical surface. Moreover, the respective areas forming the rotating and sliding surfaces of the side gear support surfaces S1, S2with respect to the side gears23are planar worked surfaces. Areas different from the aforementioned, that is, areas of the inner surface Ci surrounded by the main guide weirs50, the pinion gear support surfaces P1, P2, and the side gear support surfaces S1, S2, and the pinion gear lubricating oil grooves Gp and the side gear lubricating oil grooves Gs are unworked surfaces that are positioned lower (that is, toward a radially outer side) than the above-described worked surfaces.

Other configurations in the third embodiment are basically the same as those in the first embodiment. Thus, constituent elements in the third embodiment are labelled with the same reference numerals used for the corresponding constituent elements in the first embodiment, and detailed description of configurations of these constituent elements will be omitted. The third embodiment can also achieve operation effects that are basically the same as those of the first embodiment.

Furthermore,FIGS.9A,9B,9Cillustrate a modified example of the auxiliary weir54illustrated in the second embodiment by way of example, as a schematic view seen radially from the center of the differential case C.

Specifically, in a first modified example illustrated inFIG.9A, an auxiliary weir541extends from a part of the circumference of the support base19, closer to the second side gear support surface S2with respect to the opened part Gpi of the pinion gear lubricating oil groove Gp in the axial direction, toward the window18in the circumferential direction (that is, a direction along the rotating direction) of the differential case C. Moreover, the auxiliary weir541has its extended end bent in the axial direction toward the first side gear support surface S1into an L-shape, to thereby include a projection541a. There is a gap55between the projection541aand the main guide weir50. In the first modified example, between the opened part Gpi of the pinion gear lubricating oil groove Gp and the window18(in other words, a position displaced from the opened part Gpi in the circumferential direction described above), the auxiliary weir541acan effectively capture the oil flowing in the axial direction with respect to first side gear support surface S1, to thereby effectively guide the same to the opened part Gpi. Accordingly, lubrication performance can be improved for the pinion gear support surfaces P1, P2.

In a second modified example illustrated inFIG.9B, from a part of the outer circumference of the support base19, closer to the second side gear support surface S2with respect to the opened part Gpi of the pinion gear lubricating oil groove Gp in the axial direction, an auxiliary weir542extends in the above-described circumferential direction of the differential case C toward the window18in a manner to slightly tilt toward the first side gear support surface S1. Moreover, the auxiliary weir542has its extended end connected to the main guide weir50. In the second modified example, a part of the main guide weir50(the first weir51) extends in a manner to be continuous to the auxiliary weir542, to thereby function as an auxiliary weir. Thus, the first weir can effectively capture the oil flowing from the first side gear support surface S1toward the window18in the axial direction, to thereby effectively guide the same to the opened part Gpi. Accordingly, the lubrication performance can be improved for the pinion gear support surfaces P1, P2.

In a third modified example illustrated inFIG.9C, another auxiliary weir543is added to the second modified example ofFIG.9B. The auxiliary weir543extends toward the first side gear support surface S1in the axial direction from the circumference of the support base19at a position opposite to the auxiliary weir542across the opened part Gpi. In the third modified example, the auxiliary weir543extending in the axial direction effectively captures the oil flowing along the auxiliary weir542but merely passing through the opened part Gpi without being introduced therein and/or the oil flowing in the circumferential direction at a position slightly distanced from the auxiliary weir542in the axial direction, to thereby introduce the same to the opened part Gpi. Accordingly, the lubrication performance can be improved for the pinion gear support surfaces P1, P2.

Although the embodiments and their modified examples of the present invention have been described hereinabove, the present invention is not limited to the embodiments and modified examples, and the design of the invention can be variously changed within a scope not departing from the spirit of the invention.

For example, the embodiments described above show that the differential device D is implemented in a differential device for an automobile. Alternatively, in the present invention, the differential device D may be implemented in vehicles different from automobiles and/or various mechanical devices different from vehicles.

The above-described embodiments show, by way of example as schematically illustrated inFIG.4A, the main guide weir50protruding from the inner surface Ci of the differential case C radially inwardly (toward the first axial line X1) as the oil guiding part to guide the oil such that the oil deviates from a flow direction from the side gear support surfaces S1, S2to the window along the inner surface of the differential case and flows around the window. Alternatively, at least a part of the oil guiding part may include, as illustrated inFIG.4B, an inner wall of a groove, adjacent to the window18, provided in the inner surface Ci of the differential case C. In this case, some of the oil flowing toward the window18flows around and is accumulated in the inner wall of the groove adjacent to the window18, so that there is an increased amount of oil kept in the inner surface Ci of the differential case C. Accordingly, outflow of the oil through the window18can be suppressed. Alternatively, as illustrated inFIG.4C, a part of the oil guiding part may be served as the protrusion50athat protrudes opposite to the window18and is integrally continuous to the weir50provided in a protruding manner to the inner surface Ci of the differential case C. In this case, an improved effect of damming up the oil flowing toward the window18is exhibited.

The above-described embodiments show, as an example of the oil introduction channel to introduce the oil from outside the differential case C to the side gear support surfaces S1, S2, (i) the helical grooves15,16, respectively, (first and second embodiments) that are provided in the inner circumferential surfaces of the first and second bearing bosses Cb1, Cb2of the differential case C and that can exhibit a pumping action, and/or (ii) the clearance30(third embodiment) provided to fitting parts between the bearing bosses Cb1, Cb2and the output shafts11,12. However, the oil introduction channel is not limited to the embodiments, and may be, for example, a straight line groove provided in the inner circumferential surface of each of the bearing bosses Cb1, Cb2.

The above-described embodiments show that both sides in the axial direction of the differential case C are provided with the bearing bosses Cb1, Cb2as boss parts in a continuous manner, and both the bearing bosses Cb1, Cb2are provided with the oil introduction channels (the helical grooves15,16or the clearance30). Alternatively, in the present invention, one introduction channel may be provided to only a bearing boss on one side of the differential case C in the axial direction. Alternatively, one bearing boss may be provided as a boss part in a continuous manner to a side part of the differential case C on one side of the differential case C in the axial direction, and the one bearing boss may be provided with an oil introduction channel.

In the above-described embodiments, the height of the main guide weir50and/or the auxiliary weirs54,541to543(that is, the height of protrusion from the inner surface Ci of the differential case C toward a radially inner side (toward the first axial line X1)) may be substantially the same or partly different (difference in height) in the whole longitudinal range. If the latter is the case, a weir corresponding to a part of the differential case C to receive the most intense centrifugal force during rotation of the differential case C may be particularly set to be high.

The main guide weir50as the oil guiding part may not necessarily be arranged in all the areas in the inner surface Ci of the differential case C when there are multiple areas between the pinion gear support surfaces P1, P2and the windows18and multiple areas between the side gear support surfaces S1, S2and the windows18. For example, when one oil introduction channel (helical groove15,16, or the clearance30) is provided to only the bearing boss Cb1on one side in the axial direction of the differential case C or the bearing boss Cb2on the other side in the axial direction, the main guide weir50(particularly, the first and second weirs51,52) may be provided only between the first side gear support surface S1or the second side gear support surface S2, on the same side as the oil introduction channel, and the window18. Alternatively, the main guide weir50(particularly, the third weir53) may be provided only between the first pinion gear support surface P1or the second pinion gear support surface P2, in a rear side in the rotating direction of the differential case C about the window18during the automobile traveling forwards, and the window18.

Furthermore, the main guide weir50(particularly, the first and second weirs51,52) situated in a range between the side gear support surfaces S1, S2and the circumferential rim of the corresponding one window18in the axial direction does not necessarily covers the entire circumferential rim of the corresponding one window18in the circumferential direction in the aforementioned range. For example, as in the first and second weirs61,62in the third embodiment (see,FIGS.7and8), partly covering the above-described circumferential rim in the circumferential direction can suppress outflow of the oil through the corresponding one window18to some extent.

Still further, the main guide weir50and the auxiliary weirs54,541to543may be continuous to each other as in the second embodiment (see,FIGS.5,6) and the second and third modified examples of the second embodiment (see, FIGS. B, C) or may be separated with the gap55interposed as in the first modified example (see,FIG.9A).

In the first and third embodiments, the first weirs51,61and the second weirs52,62in the main guide weir50are continuous weirs. Alternatively, the first weirs51,61and the second weirs52,62may be separated.

The first and second embodiments describe the diameter-enlarged inner surface part40of the differential case C as a part including (i) the first diameter-enlarged inner surface part41including the steeply-enlarged inner surface part41aand the gently-enlarged inner surface part41band (ii) the second diameter-enlarged inner surface part42consisting of the steeply-enlarged inner surface part alone. Moreover, the recessed surface configuration including the joining part between the steeply-enlarged inner surface part41aand the second diameter-enlarged inner surface part42and its peripheral part is provided as the inner surface bottom part40oto gather the oil. In the present invention (particularly, the first to third features), the diameter enlarged configuration of the diameter-enlarged inner surface part40of the differential case C is not limited to the first and second embodiments.

For example, an area(s) of the gently enlarged inner surface part41band/or the steeply-enlarged inner surface part41amay be formed in a cylindrical surface (that is, having a constant inner diameter in the whole axial range). Alternatively, only the area of the second diameter-enlarged inner surface part42may be formed in the cylindrical surface. In these cases, the cylindrical surface is the inner surface recessed part40o. Alternatively, at least a partial area of the gently-enlarged inner surface part41bmay be formed in a recessed surface having the largest diameter in its axial center and having a V-shape in a lateral section, while the areas of the steeply-enlarged inner surface part41aand the second diameter-enlarged inner surface part42are formed in the cylindrical surface. In this case, a depression in the V-shaped recessed surface is the inner surface recessed part40o. Alternatively, the diameter-enlarged inner surface part40may have an inner diameter gradually increasing (i) from one end of the diameter-enlarged inner surface part40in the axial direction toward a center part or a specific intermediate part displaced from the center part and (ii) from the other end in the axial direction toward the center part or the specific intermediate part, to thereby be formed in a recessed surface having the largest diameter in the center part in the axial direction or the specific intermediate part and having a V-shape in a lateral section. In this case, a depression of the V-shape recessed surface is inner surface recessed part40o.