Ring gear unit structure

Abstract

The present invention provides a ring gear unit for use in differential gears that can improve strength or durability within a limited size range. [Solution] The ring gear unit has an annular portion 3 on which external teeth are formed, with a disc portion 4 inside the annular portion 3, and two leg portions 5 are formed on the outer circumference of the disc portion 4 at two locations symmetrically with respect to the center of the annular portion 3, projecting in the axial direction of the annular portion 3, and mounting holes 15 for fitting a pinion shaft are formed in the leg portions 5, wherein spherical recesses 14 are formed on the opposing surfaces 6 of the leg portions 5, and the sides of the leg portions 5 that sandwich the recesses 14 have a cross-sectional shape of a convex arc R portion 11, and the width of the leg portion 5, which is the distance between the boundary lines 12 on the opposing surfaces 6 of the R portion 11, is wider than the width of the recesses 14.

Description

Technical Field

[0001] The present invention relates to a ring gear unit in a differential device, and more particularly to a ring gear unit in which a ring gear is integrated with a connecting piece or a protruding piece for integrating the ring gear with a differential case.

Background Art

[0002] An example of this type of ring gear is described in Patent Document 1. In the ring gear described in Patent Document 1, a protruding portion called a "boss portion" that extends in the axial direction is formed on the inner peripheral side of an annular portion provided with teeth on the outer peripheral portion. The boss portion is a pair of arcuate cross-sectional portions provided at symmetric positions around the central axis of the annular portion, and the boss portion is brought into close contact with the outer surface of the differential case (referred to as the "diff case") so as to hold the diff case and integrated with the diff case. Further, a mounting hole for fitting a pinion shaft is formed in the boss portion. The boss portion is formed by making a through hole in the central portion of a disk-shaped material, cutting the left and right portions on both sides centered on the through hole into a substantially rectangular shape, and bending them in the plate thickness direction. Thereafter, the outer peripheral portion of the disk-shaped material is formed into a rim shape having a predetermined width in the axial direction. Further, the bent portion is formed into a predetermined shape such as an arcuate cross section to form the boss portion. In the shape described in Patent Document 1, the width of the leg portion measured in the circumferential direction to which torque is applied is substantially constant from the root to the tip. Further, since the root portion is a boundary portion bent from the disk portion of the above-described material, it rises almost at a right angle to the disk portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The ring gear described in Patent Document 1 transmits torque to the pinion shaft via a boss portion. The boss portion is formed to protrude axially from the annular plate portion, and the pinion shaft is fitted into a mounting hole formed in the boss portion. Therefore, bending stress or shear stress tends to concentrate at the base of the boss portion. As a result, in the configuration described in Patent Document 1, the stress concentration at the base of the boss portion may reduce strength or durability, and to avoid this, it may be necessary to enlarge the boss portion or the ring gear itself.

[0005] This invention was made in view of the above-mentioned technical problems, and aims to provide a ring gear unit for use in differential gears that can improve strength or durability within a limited size range. [Means for solving the problem]

[0006] To achieve the above objective, this invention provides a ring gear unit structure having a disc portion inside an annular portion on which external teeth are formed, with two leg portions formed on the outer circumference of the disc portion at two locations symmetrically with respect to the center of the annular portion, projecting in the axial direction of the annular portion, and mounting holes for fitting a pinion shaft into the leg portions, wherein spherical recesses are formed on the opposing surfaces of the leg portions, the sides of the leg portions flanking the recesses are R portions with a convex arc cross-sectional shape, and the width of the leg portion, which is the distance between the boundary lines of the R portions on the opposing surfaces, is wider than the width of the recesses.

[0007] In this invention, the width of the leg portion may gradually increase from the tip portion of the leg portion towards the base portion on the disc portion side.

[0008] Furthermore, in this invention, the radius of curvature of the R portion may gradually decrease from the root portion toward the disk portion. [Effects of the Invention]

[0009] In this invention, since a mounting hole for fitting the pinion shaft is formed in the leg, bending stress or shear stress is applied to the base of the leg. However, since the width of the leg is wider than the width of the spherical recess, the edge of the recess is contained within the opposing surface and is separated from both sides of the leg. In other words, the edge is a place where the cross-sectional shape changes abruptly and stress tends to concentrate there, but since the edge is separated from both sides of the leg, the stress concentration points that occur when forming a spherical recess can be eliminated, which is advantageous for improving strength or durability.

[0010] In particular, by gradually widening the width of the legs towards the base, it becomes possible to further improve the strength or durability of the legs.

[0011] Furthermore, by gradually reducing the radius of curvature of the R-shaped sections on both sides of the leg towards the disc section at the base, the change in shape from the leg to the disc section becomes smoother, eliminating or mitigating stress concentration and improving strength or durability. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view showing an example of a rough material in an embodiment of this invention. [Figure 2] This is a perspective view showing an example of an intermediate product that has been machined from the rough material. [Modes for carrying out the invention]

[0013] Next, embodiments of this invention will be described with reference to the attached drawings. It should be noted that the embodiments described below are merely examples of how to implement this invention and do not limit it.

[0014] The ring gear unit according to this invention is a gear component that integrates a ring gear and a leg portion for connecting it to the differential case in a differential gear. A rough shape is produced by hot forging, and the product is manufactured by performing metal processing such as machining on the rough shape. Figure 1 shows the rough shape 1, and Figure 2 shows the intermediate product 2 after machining. Note that the gear (external teeth) is omitted in Figure 2.

[0015] In Figure 1, the symbol "3" represents the annular portion, which is formed to a predetermined width and thickness, and has gears (external teeth) formed on its outer circumferential surface to form a ring gear. The inner circumference of the annular portion 3 is a disc portion 4, and a pair of legs 5 are formed from this disc portion 4 in the axial direction of the annular portion 3. The legs 5 are plate-like portions formed on the outermost part of the disc portion 4, and are opposite each other with the center of the disc portion 4 in between. The inner surfaces of each are opposing surfaces 6, and the opposite back surface 7 is arc-shaped, following the outer edge of the disc portion 4 or the inner surface of the annular portion 3.

[0016] In the rough material 1, the disc portion 4 is closed and is divided into two equal parts by a diametrical line passing through its center, with the leg portions 5 formed in each half of the region. That is, the base is a semicircular portion enclosed by an arc 8 with a diameter slightly smaller than the outer diameter of the disc portion 4 and a line 9 adjacent to the diametrical line dividing the disc portion 4 in two, and each leg portion 5 is formed rising from this base portion. The part of the base of the leg portion 5 that intersects with the disc portion 4 is rounded to form a smooth curved surface, and the back surface 7 of the leg portion 5 rises almost vertically from the disc portion 4 via this rounded, smooth concave curved surface. In contrast, the base portion on the opposing surface 6 side is a curved surface 10 that is smoothly recessed toward the line 9. This curved surface 10 extends to about 1 / 2 to 1 / 3 of the height of the leg portion 5 from the disc portion 4, and the opposing surface 6 above the curved surface 10 is flat in the rough material 1. Therefore, each leg portion 5 has a shape in which the base portion widens towards the outer edge of the disc portion 4.

[0017] The left and right sides of each leg 5 have rounded edges (R-shaped) (R-shaped) sections

[0018] The rough material 1 described above is subjected to machining to produce the intermediate product 2, which is schematically shown in Figure 2. A multi-stage hole 13 of different diameters is formed in the center of the disc portion 4. This hole 13 is for inserting a shaft (not shown) and fitting a bearing to support that shaft, or for housing a side gear (not shown) and fitting a bearing to support that side gear.

[0019] On the opposing surfaces 6 of each leg portion 5 described above, a spherical recess 14 is formed, extending from the outermost edge of the hole portion 13 through the curved surface portion 10 to the flat portion. This recess 14 is a curved portion that follows the back surface of a pinion gear (not shown) or the back surface of a bearing material for the pinion gear, and may be made to be in close contact with the outer surface of a differential case (not shown). The width of this recess 14 is smaller than the width of the leg portion 5 described above. The width of the recess 14 is the largest distance measured in the diametrical direction of the disc portion 4 among the edges 14a that define the recess 14 on the opposing surface 6 of the leg portion 5. Therefore, the portion of the edge 14a defining the recess 14 is located inside the boundary line 12 on the opposing surface 6 of the leg portion 5 described above. In other words, R portions 11 are formed on both sides of the leg portion 5 that sandwich the recess 14, and the portion of the edge 14a defining the recess 14 is not located within the R portions 11 that are provided on the leg portion 5 to avoid stress concentration. This improves the strength and durability of the leg portion 5. A mounting hole 15 for fitting a pinion shaft (not shown) is formed in the center of the recess 14. In Figure 2, the reference numeral "16" indicates a pin hole, and a pin inserted here stops the rotation of the pinion shaft.

[0020] The differential gear device using the ring gear unit described above may be similar to the device described in Patent Document 1, for example, in which a pair of pinion gears are positioned between a pair of left and right side gears, and these side gears and pinion gears are rotatably housed inside a differential case. The legs 5 described above are placed along the outer circumference of the differential case, thereby integrating the two by embracing the differential case with the ring gear unit. The pair of pinion gears are rotatably fitted and held on a pinion shaft perpendicular to the rotational axis of the side gears, and both ends of the pinion shaft are fitted into mounting holes 15 formed in the legs 5 and rotated by pins inserted into pin holes 16.

[0021] Torque transmission to the differential gear device configured as described above is performed via the gear formed in the annular portion 3, that is, the ring gear. When the ring gear rotates, the leg portion 5 integral with it rotates about the central axis of the ring gear. Therefore, the pinion shaft fitted in its mounting hole 15 rotates about an axis orthogonal to this, and the pinion gear fitted in this revolves about the rotational center axis of the side gear. As a result, torque is transmitted to the left and right side gears meshing with the pinion gear, causing the side gears to rotate. In that case, when the pinion gear rotates about the pinion shaft, the left and right side gears rotate differentially. Therefore, since torque is transmitted from the ring gear via the leg portion 5 to the pinion shaft, that is, the differential gear device, a bending load or a shear load directed in the circumferential direction of the disk portion 4 is applied to the leg portion 5. In the above-described ring gear unit according to this invention, since the width of the root portion of the leg portion 5 is wider than the width of the portion where the mounting hole 15 is formed, the rigidity or strength against the above-described bending and shearing is increased. Further, since the portion of the edge 14a partitioning the spherical concave portion 14 is set inside the R portion 11 provided to avoid stress concentration in the leg portion 5, the portion of the edge 14a does not become a factor of stress concentration. As a result, the strength or durability of the leg portion 5 or the ring gear unit is improved.

[0022] Note that the present invention is not limited to the structure shown in the above-described embodiment, and can be appropriately modified and implemented within the scope of the object of the present invention. For example, the shape of the leg portion may be a shape other than the shape shown in FIG. 1 or FIG. 2.

Explanation of Reference Numerals

[0023] 1 Rough stock 2 Intermediate product 3 Annular portion 4 Disk portion 5 Leg portion 6 Opposing surface 7 Rear surface 8 Arc 9 Straight line 10 Curved surface portion 11 R section 12 Boundaries 13 Hole 14 recess 14a Edge 15 mounting holes 16 pin holes

Claims

1. The structure of a ring gear unit having a disc portion inside an annular portion on which external teeth are formed, and having legs formed on the outer circumference of the disc portion at two locations symmetrically with respect to the center of the annular portion, projecting in the axial direction of the annular portion, and having mounting holes formed in the legs for fitting a pinion shaft, A spherical recess is formed on the opposing surfaces of the aforementioned legs. The portions on both sides of the leg portion flanking the recess have a curved shape with a convex arc in cross-section. The width of the leg portion, which is the distance between the boundary lines on the opposing surfaces of the R portion, is wider than the width of the recess. A ring gear unit structure characterized by the following.

2. The structure of the ring gear unit according to claim 1, The width of the leg portion gradually widens from the tip of the leg portion towards the base on the disc portion side. A ring gear unit structure characterized by the following.

3. The structure of the ring gear unit according to claim 2, The radius of curvature of the R portion gradually decreases from the base portion toward the disk portion. A ring gear unit structure characterized by the following.

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