JP7526124B2 - Transmission - Google Patents

Description

The present invention relates to a transmission device, in particular a transmission device that includes a planetary gear mechanism including a planetary gear and a carrier that supports the planetary gear, and a differential device including a differential case body that receives rotational force from the carrier, in which the outer peripheral ends of the differential case body and the carrier are connected to each other via a welded joint.

In this invention and this specification, the "circumferential direction" refers to the circumferential direction of an imaginary circle whose center line is the rotation axis (the first axis in this embodiment) of the carrier and the differential case body.

The above-mentioned transmission device has been known for some time (see, for example, Patent Document 1 below). In the outer peripheral wall portions of the differential case body and carrier of this type of transmission device, high-rigidity wall portions and low-rigidity wall portions are distributed at different positions in the circumferential direction. For example, in the outer peripheral wall portion of the differential case body, this distribution relates to the fact that multiple pinion gear shaft supports and multiple window holes are arranged alternately in the circumferential direction, while in the outer peripheral wall portion of the carrier, it relates to the fact that multiple pillar portions of the carrier are arranged in parallel with gaps in between in the circumferential direction.

JP 2017-116092 A

However, in the transmission device of Patent Document 1, the part to be welded and the abutment part for axial positioning are located at the same position on the opposing surfaces of the carrier and the differential case body. However, if, instead of this structure, the abutment part is located at a position different from the part to be welded, the following concerns may arise depending on the positional relationship between the abutment part and the high-rigidity wall part.

In other words, after the outer peripheral ends of the differential case body and the carrier are welded together, the welded portion undergoes thermal contraction and shrinks and deforms in the axial direction of the differential case. In the above case, if the abutting portion is located in a position corresponding to the high-rigidity wall portion of the differential case body and/or carrier, the abutting portion, which is firmly supported by the high-rigidity wall portion, exerts a strong bracing effect against the above-mentioned shrinkage deformation of the welded portion, causing no small amount of residual stress in the welded portion, which may cause delayed fracture.

The present invention was proposed in light of the above, and aims to provide a transmission device that can solve the above-mentioned residual stress problem even if abutment parts for axial positioning are located at a location separate from the welded part between the opposing surfaces of the carrier and the differential case body.

To achieve the above object, the present invention provides a transmission device that includes a planetary gear mechanism including a planetary gear and a carrier that supports the planetary gear, and a differential device including a differential case body that receives a rotational force from the carrier, and in which the outer peripheral ends of the differential case body and the carrier are connected to each other via a welded portion, the first feature of the present invention is that at least one of the differential case body and the carrier has an outer peripheral wall portion that has a high rigidity wall portion and a low rigidity wall portion that is less rigid than the high rigidity wall portion at different positions in the circumferential direction, and between the opposing surfaces of the differential case body and the carrier, an abutment portion for axial positioning that abuts the opposing surfaces against each other at a location other than the welded portion is provided at a circumferential position at least excluding the circumferential position of the high rigidity wall portion.

In addition to the first feature, the present invention has a second feature in that the carrier includes an end wall portion that rotatably supports the planetary gears, and a plurality of pillar portions that are each located between adjacent planetary gears in the circumferential direction and are integrally connected to the end wall portion, and the abutment portion is provided at a circumferential position that excludes at least the circumferential position of the pillar portions.

In addition to the first or second feature, the present invention has a third feature in that the carrier includes an end wall portion that rotatably supports the planetary gears, and a plurality of pillar portions that are each located between adjacent planetary gears in the circumferential direction and are integrally connected to the end wall portion, the outer peripheral wall portion of the differential case body includes a plurality of pinion gear shaft supports that support pinion gears of a differential gear mechanism provided within the differential case body, and the pinion gear shaft supports at least partially overlap the pillar portions when viewed in a projection plane perpendicular to the rotation axis of the differential case body.

In addition to any one of the first to third features, the present invention has a fourth feature in that a plurality of the abutment portions are disposed at intervals in the circumferential direction between the opposing surfaces, and the circumferential range of the non-abutment area sandwiched between the abutment portions adjacent in the circumferential direction is wider in the circumferential direction than the high-rigidity wall portion located in a position corresponding to the non-abutment area.

In addition to the third feature, the fifth feature of the present invention is that the outer peripheral wall of the differential case body has holes that open to the outer peripheral surface of the outer peripheral wall between the pinion gear shaft supports that are adjacent in the circumferential direction.

According to the first feature, in a transmission device in which the outer peripheral ends of the differential case body and the carrier are connected to each other via a welded portion, at least one of the differential case body and the carrier has at least an outer peripheral wall portion having a high rigidity wall portion and a low rigidity wall portion at different positions in the circumferential direction, and between the opposing surfaces of the differential case body and the carrier, an abutment portion for axial positioning that abuts the opposing surfaces at a position other than the welded portion is provided at a circumferential position excluding at least the circumferential position of the high rigidity wall portion. As a result, even if the welded portion is thermally contracted and deformed in the axial direction after welding, there is no concern that the abutment portion will exert a strong bracing effect against the above-mentioned shrinkage deformation, so that the residual stress of the welded portion can be effectively reduced and the occurrence of delayed fracture can be effectively prevented. In addition, since the abutment portion can effectively exert an axial positioning function at the portion corresponding to the low rigidity wall portion, the carrier and the differential case body can be accurately positioned to each other during welding.

According to the second feature, the abutment portion is provided at a circumferential position that excludes at least the circumferential position of the column portion of the carrier, so that the abutment portion can be positioned at a circumferential position of the carrier that avoids the high-rigidity wall portion associated with the column portion, and residual stress in the welded portion can be effectively reduced.

According to the third feature, the pinion gear shaft support included in the outer peripheral wall of the differential case body overlaps at least partially with the column of the carrier when viewed in a projection plane perpendicular to the rotation axis of the differential case body. This allows the abutment portion to be positioned in a circumferential position that avoids both high-rigidity wall portions even if the phases of the pinion gear shaft support, i.e., the high-rigidity wall portion of the differential case body, and the high-rigidity wall portion related to the column of the carrier are aligned or approximately aligned. This makes it possible to more effectively reduce residual stress in the weld.

According to the fourth feature, a plurality of abutting portions are arranged at intervals in the circumferential direction between the opposing surfaces of the differential case body and the carrier, and the circumferential range of the non-abutting area sandwiched between adjacent abutting portions in the circumferential direction is wider in the circumferential direction than the high-rigidity wall portion located at a position corresponding to the non-abutting area. This allows the non-abutting area between the opposing surfaces to be expanded beyond the circumferential width of the high-rigidity wall portion, and the circumferential width of the abutting portion can be reduced to the minimum necessary, thereby more effectively reducing residual stress in the welded portion.

According to the fifth feature, the outer peripheral wall of the differential case body has holes that open onto its outer peripheral surface between adjacent pinion gear shaft supports in the circumferential direction, and the wall portion around the holes is a low-rigidity wall portion. The abutment portion is disposed on this low-rigidity wall portion, so that the residual stress in the welded portion can be effectively reduced.

FIG. 1 is an overall vertical sectional view and an enlarged sectional view of a main portion of a transmission device according to a first embodiment of the present invention. FIG. 2 is an overall cross-sectional view (cross-sectional view taken along line 2-2 in FIG. 1) of the differential device, with the side gears and side gear washers omitted. Figure 3 is a side view of the first side wall 20s of the differential case as seen from the carrier side (view along the arrow line 3-3 in Figure 1), where Figure 3(A) is a diagram omitting the washer for the side gear, and Figure 3(B) is a diagram showing the same washer in solid lines. FIG. 4 is a side view of the differential case body as seen from the carrier side (as viewed from the arrows along line 4-4 in FIG. 1). Figure 5 is a side view (view taken along line 5-5 in Figure 1) of the first end wall portion 31 of the carrier (i.e., the second side wall 20s' of the differential case) as seen from the differential case main body side, where Figure 5(A) is a view omitting the washer for the side gear (corresponding to Figure 3(A)), and Figure 5(B) is a view showing the same washer in solid lines (corresponding to Figure 3(B)). FIG. 6 is a cross-sectional view of a main portion of the reducer (cross-sectional view taken along line 6-6 in FIG. 1). FIG. 7 is an exploded side view for explaining the relative configuration of opposing surfaces of a differential case body and a carrier before welding. FIG. 8 is a side view of the carrier end wall portion (i.e., the second side wall 20s' of the differential case) according to the second embodiment as viewed from the differential case main body side, and corresponds to FIG. 5(B).

First, the first embodiment will be described with reference to Figures 1 to 7.

In FIG. 1, a transmission device A mounted on a vehicle, such as an automobile, includes a transmission case 10 fixedly supported at a suitable position on the vehicle body, and a single transmission unit U housed and supported within the transmission case 10.

The transmission unit U is a unit that combines a reducer R, which is made of a planetary gear mechanism that reduces the power from a power source (not shown, for example, an electric motor mounted on a vehicle), and a differential device D that distributes and transmits the output of the reducer R to the first and second output shafts 51, 52 while allowing differential rotation, and the carrier C of the reducer R and the differential device D rotate integrally around the first axis X1. The first and second output shafts 51, 52 rotate the left and right drive wheels in tandem via an interlocking mechanism (not shown).

Next, a specific example of the differential device D will be described mainly with reference to Figures 1 and 2. The differential device D includes a differential case 2 that receives rotational force from the reduction gear R, and a differential gear mechanism 21 that is housed in a mechanism room inside the differential case 2. In particular, the differential device D of this embodiment has a flattened differential case structure in which the first and second side walls 20s, 20s' of the differential case 2 are formed into thin disk shapes along an imaginary plane perpendicular to the rotation axis (first axis X1).

The differential gear mechanism 21 includes a plurality of pinion shafts 22 (four in this embodiment) whose both ends are fitted and fixed to the differential case 2 and disposed on a second axis X2 perpendicular to the first axis X1, a plurality of pinion gears 23 each rotatably supported on the pinion shafts 22, and a pair of side gears 24 that mesh with each pinion gear 23 and are rotatable around the first axis X1. The four pinion shafts 22 (and therefore the pinion gears 23) are disposed at equal intervals around the circumferential direction of the differential case 2, i.e., with a phase difference of 90 degrees.

The pinion gear 23 and the side gear 24 are bevel gears, but the type of gear is not limited to bevel gears. The pair of side gears 24 function as output gears for the differential gear mechanism 21, and the inner ends of the first and second output shafts 51 and 52 are spline-fitted to the inner peripheral surfaces of cylindrical bosses 24b provided in the center of both side gears 24.

The pair of side gears 24 each have a boss portion 24b, a thin, disk-shaped thin-walled intermediate portion 24m that extends radially outward from the outer periphery center of the boss portion 24b along the imaginary plane, and a gear portion 24g that is integrally connected to the tip of the thin-walled intermediate portion 24m.

The back surface of the gear portion 24g (i.e., the surface that contacts the side gear washer Ws described below) is formed as a circular plane parallel to the imaginary plane, and protrudes axially outward beyond the outer surface of the thin-walled middle portion 24m. Therefore, a circular, flat dead space that is unique to the flat differential case structure is formed on the outer surface of the thin-walled middle portion 24m.

In the embodiment, for convenience of explanation, the left side gear 24 in FIG. 1 is called the first side gear, and the right side gear 24 is called the second side gear. In addition, of the two side walls of the differential case 2, the left side wall in FIG. 1 is called the first side wall 20s, and the right side wall is called the second side wall 20s'.

The differential case 2 comprises a differential case body 20 formed in a roughly cup-like shape with one open end, and a closing wall serving as a second side wall 20s' that is connected to the differential case body 20 and closes the open end. In this embodiment, the closing wall is formed by the first end wall portion 31 of the carrier C. That is, the first end wall portion 31 is part of the carrier C (end wall portion), but also functions as part of the differential case 2 (second side wall 20s').

When the differential D is used alone (i.e., separate from the reduction gear R), the blocking wall becomes the second side wall 20s' that is dedicated to the differential case.

The differential case body 20 comprises a case body main part 20M and a cylindrical trunk part 20D that is fitted and fixed (e.g., welded) to the outer peripheral end of the case body main part 20M. The case body main part 20M includes a cylindrical bearing boss part 20b and a thin, disk-shaped first side wall 20s that is integrally connected to the inner end of the bearing boss part 20b and extends radially outward along the imaginary plane.

The portion of the inner surface of the first side wall 20s that corresponds to the gear portion 24g of the first side gear 24 constitutes a planar side gear support surface 20sf1 that is parallel to the imaginary plane. That is, the side gear support surface 20sf1 abuts and supports the back surface of the gear portion 24g of the first side gear 24 in a rotatable and slidable manner via the annular side gear washer Ws.

As is clear from FIG. 3B, a number of anti-rotation projections Wst that protrude radially inward are integrally provided at intervals in the circumferential direction on the inner periphery of the side gear washer Ws. The number of anti-rotation projections Wst is not limited to the embodiment, and there must be at least one.

As can be seen from Figs. 1 and 3, the inner surface of the first side wall 20s has an annular step 20so formed on the inner periphery thereof by recessing one step axially outward, an annular protrusion t adjacent to the radial outer end of the annular step 20so and projecting axially inward beyond the side gear support surface 20sf1, and multiple oil grooves 2g extending radially from the inner surface and crossing the side gear support surface 20sf1. The outer end of the boss 24b of the first side gear 24 is rotatably received in the annular step 20so.

The protrusion t is disposed at a position facing the outer surface of the thin-walled middle portion 24m of the first side gear 24, which is set back axially inward from the back surface of the gear portion 24g (i.e., at a position that protrudes into the dead space). Therefore, by utilizing the dead space, the protrusion t can be effortlessly protruded from the inner surface of the first side wall 20s without widening the differential case 2 in the axial direction, which is advantageous in flattening the differential case 2 in the axial direction.

As can be seen in FIG. 3(A), the inner ends of the multiple oil grooves 2g are engaged with the annular protrusion t so as to cross the protrusion t in the radial direction, and the engaged portions form engagement recesses to that are recessed from the convex surface of the protrusion t. As can be seen in FIG. 1 and FIG. 3(B), the anti-rotation protrusions Wst protruding from the inner periphery of the side gear washer Ws engage with at least some of the engagement recesses to in a manner that prevents relative rotation, thereby preventing the washer Ws from rotating relative to the differential case 2.

In the embodiment, the oil groove 2g is formed so that it crosses the protrusion t, and the engagement recess to is formed at its inner end at the same time as the groove 2g is formed, which makes it easier to mold the engagement recess to. However, in another embodiment, the engagement recess to may be formed in the protrusion t at a position different from the oil groove 2g (i.e., separately and independently from the formation of the oil groove 2g). Also, the engagement recess to does not necessarily have to cross the protrusion t.

The engagement recess to provided on the protrusion t and the anti-rotation protrusion Wst provided on the inner periphery of the washer Ws constitute an uneven engagement portion that engages with each other to prevent the washer Ws from rotating on the differential case main body 20. That is, one of the uneven engagement portions is the engagement recess to, and the other is the protrusion Wst.

The outer peripheral surface of the bearing boss portion 20b is supported on the inner peripheral surface of the transmission case 10 via a bearing 26 so as to be rotatable about the first axis X1. The inner peripheral surface of the bearing boss portion 20b is provided with a spiral groove 20bg as necessary, and the spiral groove 20bg can exert a screw pump action to feed lubricating oil outside the differential case 2 into the differential case 2 as the bearing boss portion 20b and the first output shaft 51 rotate relative to each other. Furthermore, a guide protrusion is provided on the outer end surface of the bearing boss portion 20b as necessary to guide the oil flowing inside the transmission case 10 to the spiral groove 20bg.

Next, an example of the trunk 20D of the differential case main body 20 will be described. The trunk 20D includes a cylindrical outer peripheral wall 20c, an annular inner peripheral wall 20a surrounding the boss 24b of the side gear 24, and an intermediate wall 20m arranged to bypass the pinion gear 23 and integrally connect the outer peripheral wall 20c and the inner peripheral wall 20a. The outer peripheral wall 20c has a plurality of first openings O1 (four in this embodiment) arranged at 90 degree intervals in the circumferential direction, communicating the inside and outside of the outer peripheral wall 20c, and the intermediate wall 20m faces the radially inner side of the first openings O1. A plurality of second openings O2 capable of accommodating the pinion gears 24 are defined between the outer peripheral wall 20c and the inner peripheral wall 20a.

The wall portion of the outer peripheral wall portion 20c that is sandwiched in the circumferential direction between the first openings O1, O1 that are adjacent in the circumferential direction functions as the pinion gear shaft support portion 20cp, and a first support hole h1 that fits and supports the outer end portion of the pinion shaft 22 is formed in the center of the wall portion. The inner peripheral wall portion 20a also has a plurality of second support holes h2 that fit and support the inner end portion of the pinion shaft 22, and the wall portion around the second support hole h2 also functions as the pinion gear shaft support portion.

The outer end of the pinion shaft 22 is fixed to the body 20D by a retaining pin 28 (see FIG. 1) that crosses the outer end and is inserted into a horizontal hole in the outer peripheral wall 20c. The retaining pin 28 is securely retained in the differential case 2 by engaging with a carrier C that is welded to the differential case body 20. Note that the fixing means for the pinion shaft 22 is not limited to the embodiment, and other fixing means (e.g., rivets, bolts, retaining rings, etc.) can be used.

Furthermore, the fastening means between the case body main part 20M and the torso part 20D may be other fastening means (e.g., bolt fastening, rivet, etc.) instead of welding, or the case body main part 20M and the torso part 20D may be formed integrally.

Next, we will explain the support structure of the second side gear 24 by the first end wall portion 31 (i.e., the second side wall 20s') of the carrier C.

The first end wall portion 31 is formed in a disk shape along the imaginary plane, and its outer surface 31f on the second side gear 24 side (i.e., corresponding to the inner surface of the second side wall 20s') has a planar side gear support surface 20sf2 parallel to the imaginary plane. The side gear support surface 20sf2 abuts and supports the back surface of the gear portion 24g of the second side gear 24 via the side gear washer Ws in a rotatable and slidable manner.

Furthermore, the outer surface 31f of the first end wall portion 31 has an annular projection t located on its inner periphery and projecting axially inward beyond the side gear support surface 20sf2, and multiple oil grooves 2g' extending radially from the outer surface 31f and across the side gear support surface 20sf2. In particular, the projection t is positioned opposite the outer surface of the thin-walled intermediate portion 24m of the second side gear 24 (i.e., projecting into the dead space).

As can be seen in FIG. 5(A), the inner ends of the multiple oil grooves 2g' are embedded in a portion of the annular projection t (i.e., up to the middle of the radial width of the projection t), and the embedded portion forms an engagement recess to that is recessed from the convex surface of the projection t. As can be seen in FIG. 5(B), anti-rotation protrusions Wst protruding radially inward from the inner periphery of the side gear washer Ws engage with at least a portion of the engagement recess to in a manner that prevents relative rotation, thereby preventing the washer Ws from rotating relative to the carrier C, which also serves as the second side wall 20s'.

Then, on the second side wall 20s' side, the engagement recess to and the anti-rotation protrusion Wst protruding from the inner periphery of the washer Ws form an uneven engagement portion that engages with each other to prevent the washer Ws from rotating.

In addition, a spiral groove 31g is provided on the inner peripheral surface of the first end wall portion 31 as necessary, and the spiral groove 31g can exert a screw pump action to supply lubricating oil in the reducer R into the differential case 2 as the first end wall portion 31 and the second output shaft 52 rotate relative to each other.

The protrusions t to be provided on the first and second side walls 20s, 20s' may be provided on the inner periphery of the inner surface of the side wall 20s' (i.e., the inner periphery or its vicinity) like the protrusion t on the second side wall 20s' side, or may be provided in the middle part near the inner periphery of the side wall 20s like the protrusion t on the first side wall 20s side.

Furthermore, the protrusions t may be formed continuously in a circular ring shape centered on the first axis X1, as in the case of the protrusions t on the second side wall 20s' side, or may be arranged in an arc shape along the circumferential direction, as in the case of the protrusions t on the first side wall 20s side. Alternatively, they may be formed in any shape that does not extend in the circumferential direction.

Next, an example of the reducer R will be described with reference mainly to Figures 1 and 6. The reducer R has a sun gear 41, which is the input side of the reducer R, a ring gear 42, which is arranged concentrically with the gear portion 41g of the sun gear 41 and is non-rotatably fitted and fixed to the inner circumference of the transmission case 10, a plurality of planetary gears P (four in the illustrated example) that mesh with the sun gear 41 and the ring gear 42, and a carrier C that rotatably supports the plurality of planetary gears P.

The sun gear 41 is configured by forming a gear portion 41g on the outer periphery of the tip of a cylindrical shaft-shaped sun gear body 41m. The sun gear body 41m is rotatably supported on the transmission case 10 via a bearing (not shown), and a second output shaft 52 passes loosely vertically through the sun gear body 41m. The outer end (not shown) of the sun gear body 41m is interlocked and connected to the output side of a power source (not shown, for example, an electric motor) via an interlocking mechanism (not shown), and rotational power can be input from the power source.

The carrier C has first and second end wall portions 31, 32, each formed in a disk shape and spaced apart from each other in the axial direction, and four pillar portions 33 that extend in a direction along the first axis X1 and are arranged at equal intervals in the circumferential direction (i.e., with a phase difference of 90 degrees) to integrally connect the end wall portions 31, 32. Each pillar portion 33 is formed in a sector-shaped cross section, as can be seen in FIG. 6.

Four planetary gears P are arranged in the spaces defined between adjacent pillars 33 in the circumferential direction, and the planetary gears P are supported at both ends by the first and second end wall portions 31 and 32 via pivots 34 so as to be freely rotatable.

If necessary, the carrier C may be rotatably supported on the transmission case 10 via bearings. Also, in FIG. 5, reference numeral 31h denotes a support hole provided in the first end wall portion 31 for fitting and supporting (e.g., press-fitting) the pivot 34, which coincides with the position of the pivot 34 when the reducer R is in an assembled state. Also, in the illustrated example, the pivot 34 is shown as a separate part from the gear body portion of the planetary gear P, but the pivot 34 may be configured integrally with the gear body portion of the planetary gear P, in which case the pivot 34 is rotatably supported on the first and second end wall portions 31 and 32 via bearings.

The outer peripheral ends of the body 20D of the differential case body 20 and the carrier C of the reducer R are integrally joined together via a welded portion w, and an example of this welded structure will be described below with reference mainly to Figures 1, 4, 5, and 7.

Between the opposing surfaces of the first end wall portion 31 of the carrier C and the trunk portion 20D of the differential case body 20, there is provided a spigot fitting portion I located at the outer peripheral end for radially positioning the carrier C and the differential case body 20M, and a plurality of abutment portions T arranged adjacent to the radial inside of the spigot fitting portion I for axially positioning the carrier C and the differential case body 20M.

The spigot fitting portion I is composed of an annular protrusion 20Di provided by protruding one step from one of the opposing surfaces of the outer peripheral ends of the first end wall portion 31 and the body portion 20D (in this embodiment, the outer surface of the body portion 20D), and an annular recess 31i provided by receding one step from the other (in this embodiment, the outer surface 31f of the first end wall portion 31). The concentric engagement of the annular protrusion 20Di and the annular recess 31i determines the radial positioning of the carrier C and the differential case body 20. Then, the opposing surfaces of the first end wall portion 31 and the body portion 20D are welded (for example, laser welded) from the radially outer side radially outside the engagement surface of the annular protrusion 20Di and the annular recess 31i in the concentrically fitted state, and the carrier C and the differential case body 20 are joined via the weld w.

Before welding, the surfaces to be welded of the first end wall portion 31 and the body portion 20D are opposed and close to each other to an extent that does not interfere with the butting of the butt portion T (i.e., axial positioning) or the welding operation.

In addition, in the region adjacent to the radial inner end of the spigot fitting portion I and extending in an annular shape, the opposing faces F1, F2 between the first end wall portion 31 and the body portion 20D are formed in the same annular plane parallel to the imaginary plane, with the first opposing face F1 on either side (in the embodiment, the side face portion of the outer surface 31f of the first end wall portion 31 adjacent to the radial inner side of the spigot fitting portion I).

In contrast, the second opposing surface F2 (in the embodiment, the end surface portion of the outer end surface of the outer peripheral wall portion 20c adjacent to the radially inner side of the spigot fitting portion I) on the other side of the opposing surfaces F1, F2 has a plurality of abutting convex surfaces F2t spaced apart in the circumferential direction and in close contact with the first opposing surface F1, and a plurality of concave surfaces F2h each sandwiched between adjacent abutting convex surfaces F2t in the circumferential direction. Each concave surface F2h is recessed more than the abutting convex surface F2t, so it does not come into contact with the first opposing surface F1, i.e., it defines an axial gap between the first opposing surface F1.

Thus, on the radially inner side of the spigot fitting portion I (and therefore the welded portion w), the opposing surfaces F1, F2 of the first end wall portion 31 and the body portion 20D are abutted against the first opposing surface F1 by only the abutting convex surface F2t of the second opposing surface F2, and the axial positioning of the differential case body 20 and the carrier C is determined by the abutting portion T (i.e., the contact portion between the first opposing surface F1 and the abutting convex surface F2t). In other words, the first and second opposing surfaces F1, F2 do not abut against each other over their entire circumference, but only at a number of abutting portions T that are spaced apart in the circumferential direction.

The circumferential position of the concave surface F2h (and therefore the non-butting area between the first and second opposing surfaces F1, F2) is set to a range that is the same as or slightly wider than the circumferential range of the high-rigidity wall portions H, H' in the outer peripheral wall portions of the differential case body 20 and the carrier C (first end wall portion 31), as is clear from FIG. 7. In other words, the circumferential position of the butting portion T is set to a range that is the same as or slightly narrower than the circumferential range of the low-rigidity wall portions L, L' in the differential case body 20 and the carrier C (first end wall portion 31).

The above-mentioned convex abutment surface F2t and concave surface F2h may be provided on the second opposing surface F2 instead of or in addition to the structure in which they are provided on the first opposing surface F1.

In the embodiment, in each outer peripheral wall of the differential case body 20 and the carrier C, as shown in FIG. 7, the high-rigidity wall portions H, H' and the low-rigidity wall portions L, L' are distributed at different positions in the circumferential direction. For example, in the case of the differential case body 20, the wall portion (i.e., the pinion gear shaft support portion 20cp) that supports the multiple pinion shafts 22 of the outer peripheral wall portion 20c of the trunk portion 20D is thick and sturdy to firmly support the pinion shafts 22, and is the high-rigidity wall portion H. On the other hand, the wall portion sandwiched between the adjacent pinion gear shaft support portions 20cp in the circumferential direction has a window hole (i.e., the first opening O1) or a hollow portion that opens on the outer peripheral surface of the wall portion, and is the low-rigidity wall portion L that has lower rigidity than the pinion gear shaft support portion 20cp, i.e., the high-rigidity wall portion H.

In contrast, the first end wall portion 31 of the carrier C has multiple pillars 33 extending integrally from it, and the wall portions corresponding to each pillar 33 are sufficiently reinforced by the pillars 33 to form high-rigidity wall portions H', but the wall portions corresponding to the spaces between adjacent pillars 33 in the circumferential direction are not sufficiently reinforced by the pillars 33, and therefore become low-rigidity wall portions L', which have lower rigidity than the wall portions corresponding to the pillars 33, i.e., high-rigidity wall portions H'.

In addition, in the embodiment, as is clear from Figures 2, 6, and 7, the multiple pinion gear shaft support portions 20cp of the outer peripheral wall portion 20c of the differential case main body 20 and the multiple pillar portions 33 of the carrier C are arranged to overlap partially (most of them in the illustrated example) when viewed in a projection plane perpendicular to the first axis X1. In other words, the pinion gear shaft support portions 20cp that form the high rigidity wall portion H of the differential case main body 20 and the wall portions corresponding to the pillar portions 33 of the first end wall portion 31 that form the high rigidity wall portion H' of the carrier C are arranged to be in phase with each other or approximately in phase with each other, but in the embodiment, the abutment portion T is arranged at a circumferential position that avoids both of the high rigidity wall portions H, H'.

In addition, in this embodiment, the circumferential range of the non-abutment area (i.e., the area of the concave surface F2h) sandwiched between the abutment portions T adjacent in the circumferential direction is set to be wider in the circumferential direction than the high-rigidity wall portions H, H' of the outer peripheral wall portions of the differential case main body 20 and the first end wall portion 31 that are located in a position corresponding to the non-abutment area.

Next, the operation of the above embodiment will be explained.

In the transmission device A, when the sun gear 41 is rotated by an electric motor (not shown), the sun gear 41 and the ring gear 42 mesh with each planetary gear P, and the rotational driving force of the sun gear 41 is transmitted to the carrier C while being decelerated. The rotational driving force transmitted to the differential case body 20 fixed to the carrier C is then distributed by the differential gear mechanism 21 in the differential case body 20 while allowing differential rotation to the first and second output shafts 51, 52, and is further transmitted from the first and second output shafts 51, 52 to the left and right drive wheels.

In this embodiment, between the opposing surfaces of the differential case body 20 and the first end wall portion 31 of the carrier C, a plurality of abutment portions T for axial positioning are arranged at a location other than the welded portion w (i.e., between the first and second opposing surfaces F1, F2 located at a location adjacent to the radial inner end of the spigot fitting portion I) as described above. Moreover, the positions of these abutment portions T are set at circumferential positions excluding at least the circumferential positions of the high-rigidity wall portions H, H' of each outer peripheral wall portion of the differential case body 20 and the carrier C (first end wall portion 31) (in other words, circumferential positions corresponding to at least a portion of the low-rigidity wall portions L, L').

As a result, even if the welded portion w thermally shrinks and deforms in the axial direction after welding, there is no need to worry about the butt portion T exerting a strong bracing effect against the above-mentioned shrinkage deformation, so the residual stress of the welded portion w can be effectively reduced and delayed fracture can be effectively prevented. In addition, the butt portion T can effectively exert an axial positioning function in the areas corresponding to the low-rigidity wall portions L, L', so the carrier C and the differential case main body 20 can be accurately positioned relative to each other during welding.

In addition, the abutment portion T is disposed at a circumferential position that excludes at least the circumferential position of the wall portion of the first end wall portion 31 that corresponds to the column portion 33 (i.e., the high-rigidity wall portion H'), so that the abutment portion T can be disposed at a circumferential position of the carrier C that avoids the high-rigidity wall portion H' associated with the column portion 33, and the residual stress of the welded portion w can be effectively reduced.

The pinion gear shaft support 20cp provided on the outer peripheral wall 20c of the differential case main body 20 overlaps at least a portion (most of the pinion gear shaft support 20cp in the illustrated example) with the column 33 of the carrier C when viewed in a projection plane perpendicular to the first axis X1. The pinion gear shaft support 20cp, i.e., the high-rigidity wall H of the differential case main body 20, and the high-rigidity wall H' of the carrier C related to the column 33 are in phase or substantially in phase with each other. In this embodiment, the abutment portion T can be positioned at a circumferential position that avoids both high-rigidity wall portions H, H', so that the residual stress of the welded portion w can be reduced more effectively.

Furthermore, as is clear from FIG. 7, the abutment portions T of the embodiment are arranged at intervals in the circumferential direction between the first and second opposing surfaces F1, F2, and the circumferential range of the non-abutment area (i.e., the area of the concave surface F2h) located between the circumferentially adjacent abutment portions T is wider in the circumferential direction than the high-rigidity wall portions H, H' located in a position corresponding to the non-abutment area. This allows the non-abutment area to be expanded beyond the circumferential width of the high-rigidity wall portions H, H', and the circumferential width of the abutment portion T can be reduced to the minimum necessary, making it possible to more effectively reduce the residual stress in the welded portion w.

The outer peripheral wall portion 20c of the differential case main body 20 has a hole, i.e., a first opening O1, that opens into its outer peripheral surface, and the portion surrounding the first opening O1 forms a low-rigidity wall portion L. This allows the abutment portion T to be placed at the corresponding portion of this low-rigidity wall portion L, thereby effectively reducing the residual stress of the welded portion w.

In the differential device D of the embodiment, the side walls 20s, 20s' on at least one side (both sides in the illustrated example) of the differential case 2 and the back surface of the corresponding side gear 24 are in slidable contact with the washer Ws in between, and a concave-convex engagement portion (i.e., the engagement recess to of the protrusion t and the protruding piece Wst of the washer Ws) is provided between the protrusion t on the inner surface of the side walls 20s, 20s' and the inner periphery of the washer Ws to prevent the washer Ws from rotating on the differential case 2. This allows the washer Ws to be prevented from rotating on the differential case 2 with a simple anti-rotation structure including the protrusion t of the side walls 20s, 20s'. This anti-rotation effect means that the only countermeasures required to prevent the washer Ws from seizing are those that are caused by the sliding of the side gear 24 against the washer Ws, and as will be described later, this has the advantage of being able to efficiently apply countermeasures to specific areas.

In addition, the protrusion t that protrudes inward in the axial direction can increase the rigidity of the side walls 20s, 20s' by making a portion of the side walls 20s, 20s' axially thicker and acting as a reinforcing rib. However, even if an engaging recess t is provided in a portion of such protrusion t (reinforcing rib), the resulting decrease in rigidity of the side walls 20s, 20s' can be minimized.

Furthermore, the above-mentioned protrusions t are arranged on the inner periphery of the inner surface of the side walls 20s, 20s' or in the middle part near the inner periphery end, and extend or are arranged in the circumferential direction, so that the protrusions t can reinforce the periphery of the inner periphery end of the side walls 20s, 20s' over a wide circumferential range. In addition, the protrusions t are located coaxially with the first axis X1 and concentrically hold the washer Ws surrounding the protrusions t, so that the washer Ws and the side gear 24 are arranged coaxially, and the washer Ws and the side gear 24 can slide without eccentricity in the radial direction. This makes it possible to prevent the surface pressure of the sliding surface between the washer Ws and the side gear 24 from increasing locally.

As described above, the differential device D of this embodiment has a differential case structure that is flat in the axial direction, so the side gears 24 can be made larger in diameter without increasing the axial size of the differential case 2. This larger diameter ensures a large sliding area for the side gear washers Ws.

In addition, in the flat differential case structure of the embodiment, the washer Ws is prevented from rotating on the side walls 20s, 20s' by the rotation prevention structure, which makes it possible to pinpoint and efficiently prevent seizure caused by the sliding of the side gear 24 against the washer Ws, and increases the design freedom for seizure prevention. For example, if multiple oil grooves 2g, 2g' recessed into the inner surfaces of the side walls 20s, 20s' are arranged close to both sides of each pinion gear 23 in the circumferential direction as in the embodiment, the flowing oil in the oil grooves 2g, 2g' can effectively cool the washer Ws, especially the area near the pinion gear 23 where the surface pressure is high.

Furthermore, in the flat differential case structure of the embodiment, the special provision of the protrusions t that protrude axially from the inner surfaces of the side walls 20s, 20s' (i.e., the reinforcing rib effect) increases the rigidity of the flat side walls 20s, 20s', i.e., effectively suppresses bending deformation of the side walls 20s, 20s' (and therefore the side gear support surfaces 20sf1, 20sf2). This makes it possible to ensure a sufficient sliding area between the washers Ws on the side gear support surfaces 20sf1, 20sf2 and the back surface of the side gear 24.

In this way, in the flat differential case structure of the embodiment, a special anti-rotation means for the washer Ws is provided, and part of the anti-rotation means (the protrusion t on the inner surface of the side walls 20s, 20s') is used to increase the rigidity (suppress deformation) of the side walls 20s, 20s', thereby ensuring a sufficient sliding area between the washer Ws and the side gear 24, and improving cooling near the pinion gear 23, which is subject to high surface pressure.

Figure 8 also shows the second embodiment. In the first embodiment, the anti-rotation projection t protruding from the inner surface of the first and second side walls 20s, 20s' of the differential case 2 is a circular ring of a constant width in the radial direction, whereas in the second embodiment, a part of the outer periphery of the circular ring-shaped anti-rotation projection t' protruding from the inner surface of the first and second side walls 20s, 20s' is cut out straight to form a two-sided shape (i.e., a pair of parallel flat portions tf'). In accordance with the two-sided shape, the corresponding portion of the inner periphery of the side gear washer Ws (i.e., the protruding piece portion Wst') is also formed in a similar two-sided shape.

The washer Ws is prevented from rotating relative to the differential case 2 by the projection Wst', i.e. the two-sided width portion of the inner peripheral surface of the washer Ws, and the projection t', whose outer peripheral shape is a two-sided width shape, engaging with each other in a concave-convex manner. In addition, in FIG. 8, only the outer surface 31f of the first end wall portion 31 of the carrier C, which also serves as the second side wall 20s' of the differential case 2, and the washer Ws are illustrated, but the inner surface of the first side wall 20s and the washer Ws are also of the same shape.

The other configurations of the second embodiment are basically the same as those of the first embodiment, so each component of the second embodiment is given the same reference numeral as the corresponding component of the first embodiment, and further explanation is omitted. Thus, the second embodiment can also achieve basically the same effects as the first embodiment.

Although not shown, as a modification of the second embodiment, the outer periphery of the anti-rotation projection t' protruding from the inner surface of the first and second side walls 20s, 20s' may be changed to a polygonal shape (e.g., triangular, rectangular, hexagonal, etc.) instead of a two-sided shape. In this case, the corresponding portion of the inner periphery of the side gear washer Ws is also formed into a similar polygonal shape to correspond to the above polygonal shape. Then, the polygonal portion of the inner periphery of the washer Ws and the projection t' on the inner surface of the side walls 20s, 20s', which has a polygonal outer periphery, engage with each other in a concave-convex manner so as not to rotate relative to each other, thereby reliably preventing the washer Ws from rotating relative to the differential case 2.

Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and various design changes are possible without departing from the gist of the invention.

For example, in the above embodiment, an electric motor is exemplified as a power source that applies a rotational driving force to the input part (sun gear 41) of the transmission device A, but instead of or in addition to the electric motor, an on-board engine may be used as a power source.

In the above embodiment, the transmission device A is implemented in a vehicle (e.g., an automobile) transmission device, and the differential device D in the transmission device A distributes and provides rotational driving force to the left and right driving wheels of the vehicle. However, in the present invention, the differential device D may be used as a center differential to distribute and provide rotational driving force to the front and rear driving wheels of the vehicle. Alternatively, the transmission device A of the present invention may be implemented as a transmission device that combines a reduction gear R and a differential device D in various mechanical devices other than vehicles.

In the above embodiment, the end wall portion 31 of the carrier C also serves as the second side wall 20s' of the differential case 2, and the end wall portion 31 is welded to the differential case body 20. However, instead of such a connection structure, a connection structure in which the second side wall of the differential case 2 also serves as the end wall portion of the carrier C and the second side wall is welded to the column portion of the carrier C can also be implemented. Alternatively, a connection structure in which the end wall portion 31 of the carrier C and the second side wall 20s' of the differential case body 20 are constructed separately and are welded together can also be implemented.

In the above embodiment, the opposing surfaces of the carrier C and the differential case body 20 are welded continuously around the entire circumference, but the opposing surfaces may be welded only partially around the circumference.

In the above embodiment, the differential case 2 has a flat differential case structure in which the first and second side walls 20s, 20s' are thin disk-shaped along the imaginary plane, but the first and second side walls 20s, 20s' may be tapered slightly inclined relative to the imaginary plane. Alternatively, the first and second side walls 20s, 20s' may be curved in a dome shape.

In the above embodiment, the high-rigidity wall portions H, H' of the outer peripheral wall portions of the differential case main body 20 and the carrier C are aligned in the circumferential direction, but an embodiment in which the high-rigidity wall portions H, H' are offset in the circumferential direction is also possible. In this case, the abutment portion T is disposed at a circumferential position that excludes at least the circumferential positions of the high-rigidity wall portions H, H'.

In the above embodiment, the washer Ws for the side gear is prevented from rotating by engaging the inner surfaces of the first and second side walls 20s, 20s' of the differential case 2 with each other in a concave-convex manner, but such anti-rotation means for the washer Ws may be omitted.

A . . . Transmission device C . . Carrier D . . Differential device F1, F2 . . . First and second opposing surfaces as opposing surfaces H, H' . . . High rigidity wall portion L, L' . . . Low rigidity wall portion O1 . . . First opening P as hole . . . Planetary gear R . . . Speed reducer T constituting the planetary gear mechanism . . . Abutment portion X1 . . . First axis w as the rotation axis of the differential case main body . . . Welded portion 20 . . . Differential case main body 20c . . . Outer peripheral wall portion 20cp of the differential case main body . . . Pinion gear support portion 21 . . . Differential gear mechanism 23 as a differential mechanism . . . Pinion gear 24 . . . Side gears 31, 32 . . . First and second end wall portions 33 as end wall portions . . . Pillar portion

Claims (5)

A transmission device comprising: a planetary gear mechanism (R) including a planetary gear (P) and a carrier (C) supporting the planetary gear (P); and a differential device (D) including a differential case body (20) receiving a rotational force from the carrier (C), in which outer peripheral ends of the differential case body (20) and the carrier (C) are connected to each other via a welded portion (w),
At least one of the differential case body (20) and the carrier (C) has at least an outer peripheral wall portion having a high-rigidity wall portion (H, H') and a low-rigidity wall portion (L, L') having a lower rigidity than the high-rigidity wall portion (H, H') at different positions in the circumferential direction,
Between the opposing surfaces of the differential case body (20) and the carrier (C), abutment portions (T) for axial positioning, which butt the opposing surfaces (F1, F2) against each other at a location other than the welded portion (w), are provided at a circumferential position excluding at least the circumferential position of the high-rigidity wall portions (H, H'). A transmission device characterized in that The carrier (C) includes end wall portions (31, 32) that rotatably support the plurality of planetary gears (P), and a plurality of pillar portions (33) that are respectively located between adjacent planetary gears (P) in the circumferential direction and are integrally connected to the end wall portions (31, 32),
The transmission device according to claim 1, characterized in that the abutting portion (T) is provided at a circumferential position excluding at least a circumferential position of the pillar portion (33). The carrier (C) includes end wall portions (31, 32) that rotatably support the plurality of planetary gears (P), and a plurality of pillar portions (33) that are respectively located between adjacent planetary gears (P) in the circumferential direction and are integrally connected to the end wall portions (31, 32),
The outer peripheral wall portion (20c) of the differential case body (20) includes a plurality of pinion gear shaft supporting portions (20cp) that support pinion gears (23) of a differential gear mechanism (21) provided in the differential case body (20),
The transmission device according to claim 1 or 2, characterized in that the pinion gear shaft support portion (20cp) at least partially overlaps with the column portion (33) when viewed in a projection plane perpendicular to the rotation axis (X1) of the differential case main body (20). A plurality of the abutting portions (T) are disposed between the opposing surfaces at intervals in the circumferential direction,
A transmission device according to any one of claims 1 to 3, characterized in that the circumferential range of the non-abutment area sandwiched between the abutment portions (T) adjacent to each other in the circumferential direction is wider in the circumferential direction than the high rigidity wall portions (H, H') located in a position corresponding to the non-abutment area. The transmission device according to claim 3, characterized in that the outer peripheral wall portion (20c) of the differential case main body (20) has holes (O1) that open to the outer peripheral surface of the outer peripheral wall portion (20c) between the pinion gear shaft support portions (20cp) adjacent in the circumferential direction.