Axle case tube weld structure

Abstract

To provide a tube welding part structure for an axle case, in which the welding quality of a welding part at a butting part of an axle housing and a tube is optimized in accordance with a place in a peripheral direction.SOLUTION: A tube welding part structure for an axle case 1 is formed such that a tube 3 for supporting a wheel is made to butt against both ends of an axle housing 2 for housing an axle in a vehicle width direction; a cylindrical backing 4 is disposed inside the butting parts of the tube 3 and the axle housing 2; and the axle housing 2 and the tube 3 are welded so as to be melted into the backing 4. Projected parts 4x for defining a gap G of the butting parts when the axle housing 2 and the tube 3 are made to butt against each other are formed in the front and rear parts of the outer peripheral surface of the backing 4 in a vehicle body longitudinal direction. Recesses 4y for obtaining a penetration depth V1 when the axle housing 2 and the tube 3 are welded are formed in the upper and lower parts of the outer peripheral surface of the backing 4.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a tube welding part structure of an axle case, in which tubes for supporting wheels are attached to both ends in the vehicle width direction of an axle housing that houses an axle, a cylindrical backing is arranged inside the butting part, and the axle housing and the tubes are welded so as to melt into the backing.

Background Art

[0002] Fig. 1(a) shows an exploded view of an axle case 1, and Fig. 1(b) shows an assembled view of the axle case 1. As shown in the drawings, as the axle case 1, tubes 3 for supporting wheels are butted against both ends in the vehicle width direction of an axle housing 2 that houses an axle, and a cylindrical backing 4 is arranged inside the butting part between the tube 3 and the axle housing 2, and the axle housing 2 and the tube 3 are welded so as to melt into the backing 4 (see Figs. 4 and 5 of Patent Document 1). B in Fig. 1(b) is a welding bead.

[0003] Specifically, as shown in Figs. 1(a) and 1(b), the axle housing 2 is formed by welding an upper side plate 2a and a lower side plate 2b that are formed into a U-shaped cross section by press working, and four triangular plates 2c are welded to a central opening portion. A ring 5 for attaching a carrier that supports a differential mechanism is welded to the opening at the front of the vehicle body of the axle housing 2, and a cover 6 is welded to the opening at the rear of the vehicle body of the axle housing 2.

[0004] Also, as shown in Fig. 2(a) which is a view of Fig. 1(b) seen from the opposite direction, spring sheets 8 for attaching a suspension device are welded to the angular portions 7 in the left and right cross sections in the vehicle width direction of the axle housing 2, and ring-shaped brake flanges 10 for attaching a brake device are inserted and welded to the circular portions 9 in the left and right cross sections in the vehicle width direction of the axle housing 2. Tubes 3 for supporting wheels are butted against both ends in the vehicle width direction of the axle housing 2.

[0005] As shown in Figure 2(b), a cross-sectional view of portion b in Figure 2(a), a cylindrical backing 4 (see Figure 1(a)) is placed inside the abutting joint between the tube 3 and the circular cross-sectional portion 9 of the axle housing 2, and the axle housing 2 and the tube 3 are welded so as to penetrate the backing 4 (100% complete penetration welding). The axle housing 2 and the tube 3 are welded together around the entire circumference, and B is the weld bead. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Utility Model Publication No. 4-91501 [Patent Document 2] Japanese Patent Publication No. 2001-334396 [Patent Document 3] Japanese Patent Publication No. 2009-291834 [Patent Document 4] Japanese Patent Publication No. 2011-136350 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, when the axle case 1 shown in Figures 1 and 2 above is mounted on a large truck or the like and driven, various input modes from the road surface can cause high stress at the weld between the tube 3 and the axle housing 2, which can lead to fatigue cracks and subsequent oil leaks, posing a challenge during the development and evaluation phase of the axle case 1. In particular, the impact of vertical bending input on the axle case 1 is significant, and the welding quality at the vertical position of the weld between the tube 3 and the axle housing 2 (weld bead B) is crucial.

[0008] To elaborate on this point, as shown in Figure 2(a), the axle case 1 deforms downwards as shown by the dashed line L, due to the downward application of the vehicle weight W to the spring seat 8 and the upward application of the road surface reaction force R to the tube 3 via the wheel. In the downwardly deformed axle case 1, compressive stress is generated at the top and tensile stress at the bottom. Therefore, it is important to improve the welding quality of the weld joint (weld bead B) between the axle housing 2 and the tube 3 by increasing the penetration depth at the upper part which is subjected to compression and the lower part where tension occurs. However, as shown in Figure 2(b), even if the penetration rate of the weld joint between the axle housing 2 and the tube 3 is 100% using backing 4, cracks may occur at the joint J1 between the axle housing 2 and backing 4 and at the joint J2 between the tube 3 and backing 4 in durability tests simulating deterioration due to aging, and further quality improvement is expected.

[0009] On the other hand, in the axle case 1, which is deformed downwards due to the vehicle weight W and road surface reaction force R as shown by the dashed line L in Figure 2(a), the front and rear portions of the weld joint (weld bead B) between the axle housing 2 and the tube 3 are near the neutral axis in the longitudinal direction of the vehicle body, and almost no tension or compression is applied to the front and rear portions of the tube weld joint (weld bead B) in the longitudinal direction of the vehicle body. Therefore, in the front and rear portions of the tube weld joint in the longitudinal direction of the vehicle body, it is desirable to improve the welding quality by maintaining the root spacing G (spacing between the axle housing 2 and the tube 3) of the weld joint at a predetermined interval, rather than increasing the penetration depth to increase the welding strength.

[0010] While welding structures using backing are generally known for applications other than axle cases, such as those described in Patent Documents 2, 3, and 4, these methods do not address the tube welds of axle cases. Therefore, they do not take into account the stress state of the axle case, which is bent and deformed downwards due to the weight of the vehicle and road surface reaction forces, and thus have not led to an improvement in welding quality.

[0011] The object of the present invention, conceived in consideration of the above circumstances, is to provide an axle case tube weld structure in which the welding quality of the weld at the axle housing and tube butt joint is optimized according to the circumferential location, in an axle case tube weld structure that deforms downward convexly due to the weight of the vehicle and road surface reaction force. [Means for solving the problem]

[0012] According to the tube welded joint structure for axle cases of the present invention, which was devised to achieve the above objective, a tube supporting the wheel is abutted against both ends in the vehicle width direction of the axle housing that houses the axle, a cylindrical backing is placed inside the abutting portion between the tube and the axle housing, and the axle housing and the tube are welded so as to melt into the backing, the front and rear portions in the longitudinal direction of the vehicle body on the outer surface of the backing only Furthermore, a protrusion is formed to determine the gap between the axle housing and the tube when they are joined together, and the upper and lower outer surfaces of the backing only The provided axle case tube weld structure is characterized in that a recess is formed to increase the penetration depth when welding the axle housing and the tube.

[0013] In the tube welded joint structure of the axle case according to the present invention, the convex portion consists of a flange-shaped convex portion, and the recess consists of a groove-shaped recess, the height of the flange-shaped convex portion gradually decreases as it moves circumferentially away from the front or rear of the backing in the longitudinal direction of the vehicle body until it becomes flush with the outer surface of the backing, and the depth of the groove-shaped recess gradually becomes shallower as it moves circumferentially away from the upper or lower of the backing until it becomes flush with the outer surface of the backing, and the flange-shaped convex portion and the groove-shaped recess may be connected at the portion where they are flush with the outer surface of the backing.

[0014] In the tube welded joint structure of the axle case according to the present invention, the maximum height of the flange-shaped protrusion may be 1 / 3 or less of the backing plate thickness, and the maximum depth of the groove-shaped recess may be 1 / 3 or less of the backing plate thickness.

[0015] In the tube welded joint structure of the axle case according to the present invention, the cylindrical body constituting the backing has a cut-out portion in which a part of the circumferential direction is cut off, and may be able to contract radially at the interval of the cut-out portion. [Effects of the Invention]

[0016] The tube welded joint structure for the axle case according to the present invention can provide the following effects. (1) When welding the axle housing and the tube together, the recesses formed on the upper and lower parts of the outer surface of the cylindrical backing positioned inside the axle joint allow for increased penetration depth at the upper and lower parts of the axle joint, and the protrusions formed on the front and rear parts of the outer surface of the backing in the longitudinal direction of the vehicle body allow for maintaining a predetermined distance between the front and rear of the axle joint (root spacing). (2) Thus, when the axle case deforms downward due to the weight of the vehicle and road surface reaction force, the penetration depth at the weld between the axle housing and the tube can be increased at the upper part where compression occurs and at the lower part where tension occurs, and the root spacing at the front and rear parts near the neutral axis can be maintained at a predetermined interval, and the welding quality of the weld at the butt joint between the axle housing and the tube can be optimized according to the location in the circumferential direction. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1(a) is an exploded perspective view of the axle case, and Figure 1(b) is an assembled view of the axle case. [Figure 2] Figure 2(a) is a perspective view showing how the axle case deforms downwards due to the weight of the vehicle and road surface reaction force, and Figure 2(b) is a cross-sectional view of part b of Figure 2(a) showing a conventional example. [Figure 3]It is an explanatory view of the tube welding part structure of the axle case according to an embodiment of the present invention. FIG. 3(a) is a cross-sectional view (a cross-sectional view taken along line III-III in FIG. 2(a)) in which a cylindrical backing arranged inside the butting part of the axle housing and the tube is cut in a ring shape. FIG. 3(b) is a cross-sectional view taken along line b-b in FIG. 3(a), and FIG. 3(c) is a cross-sectional view taken along line c-c in FIG. 3(a). [Figure 4] It is a perspective view of the backing shown in FIG. 3(a) according to the present embodiment.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in such embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to omit redundant explanations, and elements not directly related to the present invention are not shown.

[0019] (Overview of the Tube Welding Part of the Axle Case 1) As shown in FIGS. 1(a), 1(b), and 2(a), the tube welding part of the axle case 1 according to an embodiment of the present invention has tubes 3 that support wheels butted against both ends in the vehicle width direction of an axle housing 2 that houses an axle. Inside the butting part of the tube 3 and the axle housing 2, a cylindrical backing 4 is arranged, and an axle case 1 in which the axle housing 2 and the tube 3 are welded (B is a weld bead) over the entire circumference in the circumferential direction so as to melt into the backing 4 is assumed. Since the configuration of this axle case 1 is basically the same as the axle case 1 described above using FIGS. 1(a), 1(b), and 2(a), the same reference numerals are given to the same components and the description is omitted, and the characteristic parts of the present invention will be described below.

[0020] Figure 3 shows an explanatory diagram of the tube weld structure of the axle case 1 according to one embodiment of the present invention. Figure 3(a) is a cross-sectional view (section taken along line III-III in Figure 2(a)) of a cylindrical backing 4 arranged inside the butt joint between the axle housing 2 and the tube 3, Figure 3(b) is a cross-sectional view taken along line bb in Figure 3(a), and Figure 3(c) is a cross-sectional view taken along line cc in Figure 3(a). As shown, the front and rear portions of the outer circumferential surface of the cylindrical backing 4 in the longitudinal direction of the vehicle body only When the axle housing 2 and the tube 3 are brought together, a protrusion 4x is formed to determine the distance (root distance G) between the axle housings (2) and the tubes (3), and the upper and lower outer surfaces of the backing 4 only When welding the axle housing 2 and the tube 3, a recess 4y is formed to increase the penetration depth.

[0021] (Convex part 4x, concave part 4y) Figure 4 shows a perspective view of the backing 4 according to this embodiment shown in Figure 3(a). As shown, the convex portion 4x consists of a flange-shaped convex portion, and the concave portion 4y consists of a groove-shaped concave portion. The height of the flange-shaped convex portion 4x gradually decreases as it moves circumferentially away from the front or rear of the backing 4 in the longitudinal direction of the vehicle body, and eventually becomes flush with the outer circumferential surface of the backing 4. The depth of the groove-shaped concave portion 4y gradually decreases as it moves circumferentially away from the top or bottom of the backing 4, and eventually becomes flush with the outer circumferential surface of the backing 4. The flange-shaped convex portion 4x and the groove-shaped concave portion 4y are connected at the portion that is flush with the outer circumferential surface of the backing 4.

[0022] As shown in Figure 3(a), the range of the upper flange-shaped recess 4y is 90 degrees from left to right (45 degrees to the uppermost vertical part of the cylindrical backing 4), the range of the lower flange-shaped recess 4y is 90 degrees from left to right (45 degrees to the lowermost part of the backing 4), the range of the front groove-shaped recess 4x is 90 degrees from up to down (45 degrees to the frontmost part of the backing 4 in the longitudinal direction of the vehicle body), and the range of the rear groove-shaped recess 4x is 90 degrees from up to down (45 degrees to the rearmost part of the backing 4). However, each range is not limited to 90 degrees.

[0023] As shown in Figure 3(a), the groove-shaped recess 4y at the top of the backing 4 has its maximum depth at the top in the vertical direction, and the groove depth gradually decreases as it descends from the top to the left and right, reaching zero depth (flush with the outer surface of the backing 4) at a 45-degree position, where it connects to the zero-height portion of the flange-shaped protrusion 4x. Similarly, the groove-shaped recess 4y at the bottom of the backing 4 has its maximum depth at the bottom in the vertical direction, and the groove depth gradually decreases as it rises from the bottom to the left and right, reaching zero depth (flush with the outer surface of the backing) at a 45-degree position, where it connects to the zero-height portion of the flange-shaped protrusion 4x.

[0024] As shown in Figure 3(a), the flange-shaped protrusion 4x at the front of the backing 4 has its maximum height at the very front in the longitudinal direction of the vehicle body, and its height gradually decreases as it moves vertically from the front, becoming zero height (flush with the outer surface of the backing) at a 45-degree position, where it connects to the zero-depth portion of the groove-shaped recess 4y. Similarly, the flange-shaped protrusion 4x at the rear of the backing 4 has its maximum height at the very rear in the longitudinal direction of the vehicle body, and its height gradually decreases as it moves vertically from the rear, becoming zero height (flush with the outer surface of the backing) at a 45-degree position, where it connects to the zero-depth portion of the groove-shaped recess 4y.

[0025] As shown in Figure 3(b), which is a cross-sectional view along line bb in Figure 3(a), the maximum height H of the flange-shaped protrusion 4x is less than or equal to 1 / 3 of the plate thickness T of the backing 4. Also, as shown in Figure 3(c), which is a cross-sectional view along line cc in Figure 3(a), the maximum depth of the groove-shaped recess 4y is less than or equal to 1 / 3 of the plate thickness T of the backing 4. Furthermore, the end faces of the axle housing 2 and the tube 3 have inclined surfaces 11 and vertical surfaces 12, respectively, and the vertical surfaces 12 are positioned opposite each other at a predetermined interval (root spacing G) to form a weld groove. The maximum height H of the flange-shaped protrusion 4x is set to be lower than the vertical surfaces 12.

[0026] (Cut and missing portion 4z) As shown in Figure 4, the cylindrical body constituting the backing 4, which has a flange-shaped protrusion 4x and a groove-shaped recess 4y, has a cut-out portion 4z in which a part of the circumferential direction is cut off, and is able to contract radially within the gap X of the cut-out portion 4z. When the cylindrical body constituting the backing 4 is mounted on the inner surface of the axle housing 2 or the inner surface of the tube 3, it is properly fitted by being contracted radially within the range of the gap X of the cut-out portion 4z.

[0027] (Effects / Actions) The tube welded joint structure of the axle case 1 according to this embodiment can exhibit the following functions and effects.

[0028] As shown in Figure 3(a), the recesses 4y (groove-shaped recesses) formed on the upper and lower parts of the outer circumferential surface of the backing 4 allow for increased penetration depth V1 and penetration width V2 when welding the axle housing 2 and the tube 3, as shown in Figure 3(c), thereby improving welding quality. Specifically, as shown by the dashed line L in Figure 2(a), the axle case is bent downwards due to the vehicle weight W and the road surface reaction force R, causing compression at the top and tension at the bottom of the weld joint (weld bead B) between the axle housing 2 and the tube 3. By increasing the penetration depth V1 and penetration width V2 of the weld joint (weld bead B) between the axle housing 2 and the tube 3 in these upper and lower parts using the recesses 4y, the amount of penetration can be increased, improving the welding strength in the upper and lower parts.

[0029] Also, as shown in Fig. 3(a), convex portions 4x (flange-like convex portions) formed at the front and rear in the vehicle body longitudinal direction on the outer peripheral surface of the backing 4 can hold the interval G (root interval) of the butting portion at a predetermined interval when the axle housing 2 and the tube 3 are joined together as shown in Fig. 3(b), thus improving the welding quality. Specifically, as shown by the virtual line L in Fig. 2(a), when the axle case 1 is bent downward and convex by the vehicle weight W and the road surface reaction force R, the front and rear portions in the vehicle body longitudinal direction of the welded portion (weld bead B) between the axle housing 2 and the two tubes 3 are near the neutral axis, so almost no tensile or compressive force is applied. In these front and rear portions, since the root interval G of the welded portion (weld bead B) (the interval between the axle housing 2 and the tube 3) can be held at a predetermined interval by the convex portions 4x, the welding quality is improved.

[0030] In the front and rear portions shown in Fig. 3(a) and Fig. 3(b) where the convex portions 4x are formed, the penetration depth V3 and the penetration width V4 during welding are smaller than the penetration depth V1 and the penetration width V2 of the upper and lower portions where the concave portions 4y are formed (V3 < V1, V4 < V2). Since it is near the neutral axis described above and almost no tensile or compressive force occurs, rather than increasing the penetration depth V3 and the penetration width V4 to increase the penetration amount and enhance the welding strength, the merit of improving the welding quality by holding the root interval G of the welded portion at a predetermined interval by the convex portions 4x is greater.

[0031] That is, as shown in Fig. 3(a), Fig. 3(b), and Fig. 3(c), the welded portion (weld bead B) between the axle housing 2 and the tube 3 has a small stress near the neutral axis when the axle case 1 is bent downward and convex by the vehicle weight W and the road surface reaction force R. The root intervals G of the welded portions at the front and rear are ensured to be an appropriate predetermined value by the convex portions 4x provided at the front and rear of the backing 4, and the penetration depth and the penetration width (penetration amount) at the upper and lower portions where the stress is large are increased by the concave portions 4y provided at the upper and lower portions of the backing 4. Therefore, the welding quality of the welded portion at the butting portion between the axle housing 2 and the tube 3 can be optimized according to the circumferential location, and the welding strength of the entire circumference in the circumferential direction is improved.

[0032] In this way, when the axle case 1 is bent and deformed downwards due to the vehicle weight W and road surface reaction force R, the welding root spacing G at the front and rear, where the stress on the weld bead B is small and close to the neutral axis, can be maintained at an appropriate predetermined value by the protrusions 4x provided at the front and rear of the backing 4. The penetration depth V1 and penetration width V2 (penetration amount) at the upper and lower parts, where the stress on the weld bead B is large, can be increased by the recesses 4y provided at the upper and lower parts of the backing 4 (V1>V3, V2>V4). As a result, the occurrence of cracks due to deterioration over time at the joint J1 between the axle housing 2 and the backing 4, and at the joint J2 between the tube 3 and the backing 4, can be suppressed, and oil leakage from the axle case 1 due to cracks can be prevented.

[0033] (Regarding the flange-shaped protrusion 4x and groove-shaped recess 4y) As shown in Figures 3(a) and 4, in the tube weld structure of the axle case 1 according to this embodiment, the convex portion 4x consists of a flange-shaped convex portion, and the concave portion 4y consists of a groove-shaped concave portion. The height of the flange-shaped convex portion 4x changes gradually, and the depth of the groove-shaped concave portion 4y changes gradually, and these are connected. Therefore, when welding the axle housing 2 and the tube 3, the circumferential penetration depth changes smoothly and gradually, thus avoiding stress concentration.

[0034] Furthermore, as shown in Figure 3(a), the flange-shaped projection 4x protrudes from the outer surface of the backing 4 over a range of 180 degrees in the circumferential direction, 90 degrees on each side. Therefore, when the axle housing 2 and the tube 3 are brought together and the flange-shaped projection 4x is sandwiched between them, the flange-shaped projection 4x can be supported over a wide area, suppressing wobbling between the two, and allowing them to be properly welded in the circumferential direction while maintaining a predetermined root gap G.

[0035] (Regarding the height H of the flange-shaped protrusion 4x and the depth D of the groove-shaped recess 4y) As shown in Figures 3(a) and 3(b), the height (maximum height) H of the flange-shaped protrusion 4x is less than or equal to 1 / 3 of the plate thickness T of the backing 4 (H ≤ (T / 3)). Therefore, the amount of penetration during welding is not excessively hindered by the flange-shaped protrusion 4x, and a penetration depth V3 and penetration width V4 that can achieve the required strength can be secured. As shown in Figure 3(b), the maximum height H of the flange-shaped protrusion 4x is lower than the height of the vertical surface portion 12 of the weld groove. Therefore, compared to the case where the maximum height H of the flange-shaped protrusion 4x is higher than the height of the vertical surface portion 12, it does not hinder penetration during welding.

[0036] Furthermore, as shown in Figures 3(a) and 3(c), since the depth (maximum depth) D of the groove-shaped recess 4y is less than or equal to 1 / 3 of the plate thickness T of the backing 4 (D ≤ (T / 3)), even if the penetration depth V1 and penetration width V2 increase due to the groove-shaped recess 4y, the weld will not penetrate through the backing 4. In other words, as shown in Figure 3(b), when welding conditions are maintained that ensure a penetration depth V3 and penetration width V4 that can exhibit a predetermined strength in the parts where the flange-shaped protrusion 4x exists (front and rear), the welds at the butt joint between the axle housing 2 and the tube 3 are welded in the circumferential direction, the upper and lower welds will not penetrate through the backing 4 due to the groove-shaped recess 4y shown in Figure 3(c).

[0037] (Regarding the cut-off / missing portion 4z) As shown in Figure 4, the cylindrical body constituting the backing 4, which has a flange-shaped protrusion 4x and a groove-shaped recess 4y, has a cut-out portion 4z in which a part of the circumferential direction is cut off, and is able to contract radially within the gap X of the cut-out portion 4z. When the cylindrical body constituting the backing 4 is mounted on the inner surface of the axle housing 2 or the inner surface of the tube 3, it is properly fitted by being contracted radially within the range of the gap X of the cut-out portion 4z.

[0038] The cylindrical body constituting the backing 4 is inserted into the inner surface of the axle housing 2 or the inner surface of the tube 3 while appropriately contracted at the gap X, and is then pressed against the inner surface of the axle housing 2 or the inner surface of the tube 3 by releasing the contraction and restoring to its original diameter. In this case, as shown in Figure 1(a), the manufacturing tolerances of the inner surface of the axle housing 2, which consists of the upper side plate 2a and the lower side plate 2b, etc., and the manufacturing tolerances of the inner surface of the tube 3 can be absorbed by the backing 4 appropriately contracting radially at the gap G of the cut-out portion 4z.

[0039] Preferred embodiments of the present invention have been described above with reference to the attached drawings. However, it goes without saying that the present invention is not limited to the embodiments described above, and that various modifications or alterations within the scope of the claims also fall within the technical scope of the present invention. [Industrial applicability]

[0040] This invention can be used in a tube weld structure for an axle case, in which a tube is butted against an axle housing, a cylindrical backing is placed inside the butt joint, and the axle housing and the tube are welded together so that they fuse with the backing. [Explanation of symbols]

[0041] 1 Axle case 2 Axle Housing 3 tubes 4 Backing 4x protrusions (flange-shaped protrusions) 4y recess (groove-like recess) 4z Cutting and missing section B. Welded area (weld bead) G. Spacing of butt joints (weld root spacing) V1 Penetration depth H Maximum height of flange-shaped projection D Maximum depth of groove-like recess X Missing interval

Claims

1. An axle case tube weld structure in which axle housings an axle, and tubes supporting the wheels are abutted against both ends in the vehicle width direction of the axle housing, a cylindrical backing is placed inside the abutting portion between the tubes and the axle housing, and the axle housing and the tubes are welded together so as to fuse with the backing, On the outer surface of the backing, protrusions are formed only on the front and rear portions in the longitudinal direction of the vehicle body, for determining the distance between the axle housing and the tube when they are joined together. The axle case tube weld structure is characterized in that recesses are formed only on the upper and lower parts of the outer circumferential surface of the backing to increase the penetration depth when welding the axle housing and the tube.

2. The aforementioned protrusion consists of a flange-shaped protrusion, The recess consists of a groove-shaped recess, The height of the flange-shaped protrusion gradually decreases as it moves circumferentially away from the front or rear of the backing in the longitudinal direction of the vehicle body, until it becomes flush with the outer surface of the backing. The depth of the groove-like recess gradually decreases as it moves away from the upper or lower part of the backing in the circumferential direction, until it becomes flush with the outer circumferential surface of the backing. The tube welded portion structure of an axle case according to claim 1, characterized in that the flange-shaped protrusion and the groove-shaped recess are connected at a portion that is flush with the outer circumferential surface of the backing.

3. The maximum height of the flange-shaped projection is 1 / 3 or less of the thickness of the backing plate. The tube welded joint structure for an axle case according to claim 2, characterized in that the maximum depth of the groove-shaped recess is 1 / 3 or less of the thickness of the backing plate.

4. The tube welded joint structure for an axle case according to any one of claims 1 to 3, characterized in that the cylindrical body constituting the backing has a cut-off portion in which a part of the circumferential direction is cut off, and is contractible radially at the interval of the cut-off portion.

Images