Differential housing with reduced voltage concentration and differential device

Abstract

Differential housing (2) comprising: - a body (21) having a differential chamber (21a) in which a differential gear mechanism is arranged; - a pair of extensions (22) between which the body (21) is arranged and which extend away from the body (21) along the central axis (Ax) passing through the center of the differential chamber (21a), each of the pair of extensions (22) being rotatably supported by a corresponding bearing (5) of a pair of bearings (5); and - an annular flange (23) arranged axially from a center of the body (21) on one side of the body (21) between the extensions (22), the one side of the body (21) being a gear side, and wherein the annular flange (23) is widened outwards in the outer diameter direction and is concentrically welded to a ring gear (3) on the gear side.which has a toothed surface, wherein the outer diameter direction is an outward radial direction centered on the central axis (Ax),- wherein the flange (23) has a bearing surface (23a) and a rounded base (23b) arranged axially along the central axis (Ax) on the gear side, wherein the bearing surface (23a) is in contact with a surface of the ring gear (3) arranged on a side opposite the toothed surface, the toothed surface facing the gear side and wherein the rounded base (23b) is continuously connected to the bearing surface (23a), and- wherein the body (21) has a rounded area in a region between the flange (23) and one of the extensions (22) arranged on the gear side, wherein the rounded area distributes stresses,which are generated at the rounded base (23b) by a gear reaction force originating from the ring gear (3).

Description

BACKGROUND The present invention relates to a differential housing and a differential device. In particular, the invention relates to a technique that is useful for reducing a stress concentration generated by a gear reaction force on the differential housing. A differential device used in a motor vehicle is equipped with a differential housing containing a differential gear. In a typical mounting design, the differential gear is attached to a ring gear (or a "locking driven gear") by means of a bolt. In recent years, however, a fastening design has been used that employs a welded connection instead of bolted fastenings to meet the requirements for weight reduction and high vehicle mileage. Reference is made, for example, to the unexamined Japanese patent applications JP 2010-91046A and JP 2011-117540A. DE 102 38 236 A1 relates to a transverse differential for a motor vehicle with two welds. JP 2005-282 817 A and JP 2011-12 759 A each teach a differential gear for a vehicle. SHORT DESCRIPTION Simply replacing a bolted fastening with a welded fastening for a differential housing and ring gear mounting structure can lead to an excessive concentration of stress in one area of ​​the differential housing, namely at a rounded base of a flange welded to the ring gear. The object of the present invention is to suppress stress generated on a rounded base of a flange to which a bevel gear is welded in a suitable manner. The problem is solved by a device according to claim 1. Further developments of the device are the subject of the dependent claims. According to one aspect, the present invention provides a differential housing comprising a differential chamber in which a differential gear mechanism is provided. The differential housing has the following: two supported parts, which are supported such that the differential housing is rotatable about the central axis of the differential chamber; and an annular flange, which is provided between the two supported parts and projects in the outer diameter direction and is concentrically welded to a ring gear. The outer diameter direction is an outward-pointing radial direction centered around the central axis of the differential chamber. The flange has a bearing surface or contact surface and a rounded base, which are arranged axially on one side of the differential housing that runs along the central axis of the differential chamber. The bearing surface is in contact with a surface of the ring gear located on the opposite side from a toothed face of the ring gear. The rounded base is continuously coupled to the bearing surface. A rounded area for distributing stress generated at the rounded base by a gear reaction force originating from the ring gear is provided in a region between the flange and one of the supported parts located on one side. According to another aspect, the rounded area can have a first and a second rounded area, which are individually provided in the region between the flange and the extension of the extension arranged on the gear side. According to another aspect, the rounded area on an outer circumference of the differential housing can be provided centered around the central axis over the entire circumference. According to another aspect, the present invention provides a differential device comprising: a differential housing according to one of the aspects described above; a ring gear; and two bearings, each supporting a corresponding part of the two supported parts. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show: Fig. 1 a top view of a differential device according to an embodiment of the invention; Fig. 2 a sectional view of the differential device along a line II-II of Fig. 1; and Fig. 3 a sectional view of a differential device according to the prior art. DETAILED DESCRIPTION In the following, some exemplary embodiments of the invention are described in detail with reference to the accompanying drawings. Before describing the embodiments of the invention, a differential device according to the prior art is explained with reference to Fig. 3. A differential device used in a motor vehicle is equipped with a differential housing in which a differential gear is located. In a typical mounting configuration, as illustrated in Fig. 3, the differential gear is attached to a ring gear (or a "locking driven gear") by means of a screw. Simply replacing a bolted fastening with a welded fastening for a differential housing and ring gear assembly can lead to an excessive concentration of stresses in one area of ​​the differential housing, namely on a rounded base of a flange welded to the ring gear, considering the two factors mentioned below. One of the factors is that, in the case of a welded connection, the point of application of a gear reaction force acting from the ring gear onto the flange is shifted towards the outer diameter side of the flange compared to a bolted connection. This results in an increased distance from the rounded base of the flange to the point of application of L1 to L2, as shown in Fig. 3. This can lead to an increase in the moment load applied when the gear reaction force acts on the rounded base. Another factor is that, to suppress tilting of the ring gear towards the flange due to thermal contraction after welding, the flange thickness, as shown by the dashed line in Fig. 3, must be sufficiently reduced, for example, compared to bolted fastenings. This can lead to a reduction in the flange's strength against the gear reaction force and an increase in the stress load that is consequently generated at the rounded base. The increase in stress at the rounded base, which is due to the two factors described above, can be addressed by increasing the dimensions of the rounded base itself or by replacing a material of the differential housing with a high-strength material. However, increasing the size of the rounded base can have disadvantages, such as an increase in the weight of the differential housing and a reduced length for mounting the ring gear, while using a high-strength material can lead to higher costs. For this reason, a technique is desired that allows suitable suppression of the stress load generated at the rounded base without dependence on the measures described above. Fig. 1 shows a top view of a differential device 1 according to an embodiment. Fig. 2 shows a sectional view of the differential device 1 along line II-II of Fig. 1. The differential device 1 according to the embodiment can have a shape that is essentially rotationally symmetrical about the central axis Ax described below as the axis of symmetry; accordingly, Fig. 2 shows only one half of the differential device 1 on one side of the central axis Ax. With reference to Fig. 1 and Fig. 2, the differential device 1 can be a differential used for a motor vehicle, which has a differential housing 2 which, without limitation, can be made of cast iron. The differential housing 2 can have a hollow housing body 21 with a differential chamber 21a. The differential chamber 21a can contain a bevel gear type differential gear mechanism (not shown) in which a pair of lateral gears and a pair of pinions mesh with each other. The housing body 21 can have two substantially cylindrical extensions 22 and 22' extending along the substantially horizontal central axis Ax, which passes through the center of the differential chamber 21a, with the extensions extending from respective innermost diameter regions located on both sides of the housing body 21. The extensions 22 and 22' can each have an outer periphery supported by a corresponding bearing 5, which can be a tapered roller bearing, allowing the differential housing to rotate about the central axis Ax. The extensions 22 and 22 can each have a cylindrical inner area in conjunction with the differential chamber 21a, through which a drive shaft (not shown), which is coupled to the corresponding lateral gears inside the differential chamber 21a, can be inserted through the cylindrical inner area. The housing body 21 can have two bearing openings 21b and 21b (of which only one is shown in Fig. 1 and Fig. 2) as well as two lubricant inlets not shown, both of which are formed in the center in one direction along the central axis Ax (hereinafter referred to as the ‘axial direction’). The two bearing openings 21b and 21b can support respective shafts of the pinions (not shown) inside the differential chamber 21a and can be formed orthogonally to the central axis Ax in one direction, allowing the interior and exterior of the housing body 21 to be connected. The two lubricant inlets can serve to introduce a lubricant from the outside into the differential chamber 21a and can be designed orthogonal in one direction to both the central axis Ax and the direction along the two bearing openings 21b and 21b. The housing body 21 can have a flange 23 and a mating area 24 on one side axially from the center (on the right side in Figs. 1 and 2; this side is hereinafter referred to as the “gear side”). The flange 23 can have an annular plate shape. A bevel gear 3 or a “final driven gear” is attached to the flange 23 and can be fitted onto the mating area 24. The flange 23 is designed such that it extends outwards from the housing body 21 in the outer diameter direction (i.e., extending outwards in a radial direction centered around the central axis Ax) and has a surface on the gear side that serves as a gear bearing surface 23a. The gear bearing surface 23a can be arranged essentially orthogonally to the central axis Ax. A rounded base 23b with a predetermined radius is continuously coupled to the gear bearing surface 23a on the inner diameter side of the gear bearing surface 23a. The fitting area 24 can be located on the gear side of the flange 23 and be continuously coupled to the gear bearing surface 23a of the flange 23. In particular, the fitting area 24 can have an outer circumference 24a that is cylindrical around the central axis Ax and is continuously coupled to the gear bearing surface 23a via the rounded base 23b of the flange 23. The ring gear 3 has a toothed surface and can have a stepped section 31 located on the opposite side of the toothed surface and having an outer diameter that essentially corresponds to the outer diameter of the flange 23. The ring gear 3 can be arranged on the housing body 21 such that an inner circumference of the ring gear 3 fits onto the outer circumference 24a of the mating area 24, so that the toothed surface faces the gear side and an end face of the stepped section 31 is in contact with the gear bearing surface 23a. The end face of the step area 31 and the gear support surface 23a of the flange 23, which are in contact with each other, can be welded together over the entire circumference to a predetermined welding depth starting from the outer circumferential side, so that the ring gear 3 is attached concentrically to the differential housing 2. The housing body 21 has two rounded areas 21r, i.e. a first rounded area 21r1 and a second rounded area 21r2, which are formed on an outer circumference of the housing body 21 that is closer to the gear side than the flange 23. The first rounded area 21r1 can be formed around its entire circumference, centered about the central axis Ax, on a portion of the housing body 21 located at a base of the fitting area 24 on the gear side of the fitting area 24. The second rounded area 21r2 can be formed around its entire circumference, centered about the central axis Ax, on a portion of the housing body 21 located closer to the gear side and the inner diameter side of the housing body 21 than the first rounded area 21r1, and to which the second rounded area 21r2 is coupled with the extension 22 on the gear side. In other words, the two rounded areas 21r can be individually formed in a region of the differential housing 2 between the flange 23 and the extension 22 on the gear side. The two rounded areas 21r reduce stresses generated at the rounded base 23b by gear reaction forces acting on the flange 23 from the ring gear 3. In the differential housing 2, the gear reaction force, which contains a load component acting axially on the side opposite the gear side (hereinafter referred to as the "housing body side"), can be applied to the flange 23, with the extensions 22 clamped by their respective bearings 5, resulting in a concentration of stress due to the gear reaction force at the rounded base 23b of the flange 23. To address this problem, the differential housing 2 in the exemplary embodiment has two rounded areas 21r in the region between the flange 23 and the extension 22 on the gear side. It should be noted that this region is smooth in existing housings. By forming the two rounded areas 21r in this region, the stress attributable to the gear reaction force can be concentrated on the two rounded areas 21r. Consequently, the stress generated at the rounded base 23b, which is closer to the point of application of the gear reaction force than the two rounded areas 21r of the flange 23, is distributed, thus suppressing the formation of excessive stress that exceeds the strength of the differential housing 2. It should be mentioned that such factors as the number, positions and sizes of the rounded areas 21r are not subject to any special restrictions as long as the rounded base 23b of the flange 23 and parts of the differential housing 2 including the actual rounded areas 21r are within a permissible strength range. For example, one, three, or more rounded areas 21r may be provided. One, three, or more such rounded areas 21r may also be provided, for example, on an inner periphery of the differential housing 2 (or on an inner periphery of the housing body 21). According to the preceding embodiment, one or more rounded areas 21r, which distribute the stresses arising at the rounded base 23b, are provided in the region of the differential housing 2 between the flange 23 and the extension 22. The rounded base 23b is continuously coupled to the gear bearing surface 23a of the flange 23. The flange 23 is welded to the ring gear 3, and the extension 22 is located on the gear side corresponding to the side on which the gear bearing surface 23a is provided. Mit dieser Konfiguration wird die Spannung, die zwischen dem Flansch 23 und der Verlängerung 22 auf der Zahnradseite als Ergebnis der in Richtung auf die Gehäusekörperseite auf den Flansch 23 wirkenden Zahnradreaktionskraft bei abgestützten Verlängerungen 22, dh beim Einspannen derselben mittels ihrer jeweiligen Lager 5, generiert wird, durch den neu vorgesehenen einen oder mehreren abgerundeten Bereich 21r verteilt. Dies ermöglicht eine Minderung der Konzentration der Spannung an der abgerundeten Basis 23b des Flansches 23. Thus, it is possible to suppress the stress load generated at the rounded base 23b of the flange 23 in a suitable manner without, for example, increasing the dimensions of the rounded base 23b or using a high-strength material. Alternatively, two rounded areas 21r can be provided separately in the region from the flange 23 to the extension 22 on the gear side. This allows the stress generated between the flange 23 and the extension 22 on the gear side to be distributed across the rounded areas 21r. In this way it is possible to suppress the stresses generated at the rounded base 23b of the flange 23 in a more suitable manner. Reference symbol list 1 Differential device 2 Differential housing 3 Ring gear 5 Bearing 21 Housing body 21a Differential chamber 21b Bearing openings 21r Rounded area 21r1 First rounded area 21r2 Second rounded area 22 Extensions 23 Flange 23a Bearing surface 23b Rounded base 24 Fit area 24a Outer circumference 31 Step area Ax Center axis L1 Distance L2 Distance

Claims

Differential housing (2) comprising: - a body (21) having a differential chamber (21a) in which a differential gear mechanism is arranged; - a pair of extensions (22) between which the body (21) is arranged and which extend away from the body (21) along the central axis (Ax) passing through the center of the differential chamber (21a), each of the pair of extensions (22) being rotatably supported by a corresponding bearing (5) of a pair of bearings (5); and - an annular flange (23) arranged axially from a center of the body (21) on one side of the body (21) between the extensions (22), the one side of the body (21) being a gear side, and wherein the annular flange (23) is widened outwards in the outer diameter direction and is concentrically welded to a ring gear (3) on the gear side.which has a toothed surface, wherein the outer diameter direction is an outward radial direction centered on the central axis (Ax),- wherein the flange (23) has a bearing surface (23a) and a rounded base (23b) arranged axially along the central axis (Ax) on the gear side, wherein the bearing surface (23a) is in contact with a surface of the ring gear (3) arranged on a side opposite the toothed surface, the toothed surface facing the gear side and wherein the rounded base (23b) is continuously connected to the bearing surface (23a), and- wherein the body (21) has a rounded area in a region between the flange (23) and one of the extensions (22) arranged on the gear side, wherein the rounded area distributes stresses,which are generated at the rounded base (23b) by a gear reaction force originating from the ring gear (3). Differential housing (2) according to claim 1, wherein the rounded area has a first and a second rounded area (21r, 21r1, 21r2) which are individually provided in the region between the flange (23) and the extension (22) of the extension arranged on the gear side. Differential housing (2) according to claim 1 or 2, wherein the rounded area is provided on an outer circumference of the differential housing (2) centered around the axis (Ax) over the entire circumference. Differential device comprising: - a differential housing (2) according to any one of claims 1 to 3; - a ring gear (3); and - two bearings (5) each supporting a corresponding part of the two extensions (22).

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