Axle case structure

Abstract

To improve torsional rigidity while suppressing weight increase.SOLUTION: An axle case structure 1 comprises an axle case body 2 which extends in a vehicle width direction of a vehicle. The axle case body has a hexagonal part 7 having a hollow hexagonal cross-sectional shape. The hexagonal part has an upper hexagonal part 10 and a lower hexagonal part 11 divided into upper and lower parts, the upper hexagonal part has a trapezoidal cross-sectional shape of which a lower bottom side is opened, and the lower hexagonal part has an inverted trapezoidal cross-sectional shape of which an upper bottom side is opened. The hexagonal part has a welding part 6R that fixes a butt part between the upper hexagonal part and the lower hexagonal part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an axle case structure applied to a vehicle. [Background technology]

[0002] For example, in a vehicle such as a trailer, an axle case is attached to leaf springs attached to the chassis. The axle case bears the main load in the vertical direction (vertical load). The cross-sectional shape of the axle case is generally a hollow rectangle, which has relatively high rigidity against vertical loads. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-298236 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, air springs have been increasingly used instead of leaf springs to prevent damage to cargo. In this case, left and right trailing arms are attached to the chassis so that they can rotate up and down, and left and right air springs are respectively provided between the chassis and the left and right trailing arms. Axle cases are then attached to the left and right trailing arms.

[0005] In this case, a relatively high torsional load is applied to the axle case when cornering, etc. In order to ensure sufficient rigidity (torsional rigidity) against this torsional load, it is possible to change the cross-sectional shape of the axle case to a hollow circle, which has relatively high rigidity against torsional loads.

[0006] However, if you try to ensure that a circular cross section has the same rigidity against vertical loads (vertical rigidity) as a rectangular cross section, the wall thickness will increase, which will increase the weight.

[0007] The present disclosure has been devised in light of the above circumstances, and its purpose is to provide an axle case structure that can increase torsional rigidity while suppressing weight increase. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, The axle case includes an axle case body extending in the vehicle width direction, The axle case body has a hexagonal portion having a hollow hexagonal cross-sectional shape, The hexagonal portion has an upper hexagonal portion and a lower hexagonal portion that are divided into upper and lower portions, The upper hexagonal portion has a trapezoidal cross-sectional shape with an open bottom side, The lower hexagonal portion has an inverted trapezoidal cross-sectional shape with an upper bottom side opened, The hexagonal portion has a weld portion that secures the butted portion of the upper hexagonal portion and the lower hexagonal portion. An axle case structure is provided.

[0009] Preferably, the butted portion is formed with a groove portion that opens radially outward of the axle case body, and a root surface portion that is adjacent to the radially inner side of the groove portion.

[0010] Preferably, the axle case structure includes spindles connected to both axial ends of the axle case body.

[0011] Preferably, the axle case structure forms a dead axle.

[0012] Preferably, the axle case structure includes an upper bracket for mounting a suspension, which is fixed to the upper hexagonal portion by welding, the upper bracket has an upper recess that is superimposed on the upper hexagonal portion, The upper recess has front and rear draft angles equal to the inclination angles of the front and rear slopes of the upper hexagonal portion relative to the direction of the reference vertical axis.

[0013] Preferably, the axle case structure includes a lower bracket for mounting a suspension, which is fixed to the lower hexagonal portion by welding, the lower bracket has a lower recess that is superimposed on the lower hexagonal portion, The lower recess has front and rear draft angles equal to the inclination angles of the front and rear slopes of the lower hexagonal portion relative to the direction of the reference vertical axis.

[0014] Preferably, the vehicle includes a trailing arm attached to a chassis so as to be rotatable in a vertical direction, and an air spring provided between the chassis and the trailing arm, The hex portion is attached to the trailing arm.

[0015] Preferably, the vehicle is a trailer. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to increase torsional rigidity while suppressing an increase in weight. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a left side view showing a portion of a vehicle to which the axle case structure of the present embodiment is applied. [Figure 2] FIG. 2 is a schematic perspective view showing an axle case structure. [Figure 3] FIG. 2 is a schematic exploded perspective view showing the axle case structure. [Figure 4] 1A and 1B show the axle case structure, in which FIG. 1A is a rear view and FIG. 1B is a perspective view showing the upper and lower brackets. [Figure 5] 3 is a cross-sectional view of the hexagonal portion taken along line VV of FIG. 2. [Figure 6]FIG. 4 is a cross-sectional view showing details of a welded portion. [Figure 7] FIG. 10 is a side view showing details of the mounting portion of the bracket. [Figure 8] 10 is a table comparing the axle case bodies of the conventional example and the present embodiment. [Figure 9] This shows the state of a conventional axle case body with a rectangular cross section when subjected to a torsional load. [Figure 10] 10 shows a state in which a hexagonal portion of the axle case body of this embodiment is subjected to a torsional load. [Figure 11] FIG. 10 is a side view showing details of a mounting portion when a suspension mounting bracket is mounted on a conventional axle case body having a rectangular cross section. [Figure 12] FIG. 10 is a rear view showing an axle case structure according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to the following embodiments.

[0019] Figure 1 shows a portion of a vehicle to which the axle case structure of this embodiment is applied. The front, rear, left, right, top, and bottom directions of the vehicle are as shown in the figure. For convenience, the directions of the axle case structure will be aligned with the directions of the vehicle.

[0020] The vehicle of this embodiment is a trailer towed by a tractor, and has a ladder frame as a chassis and left and right suspension devices 52 (only the left side is shown). The ladder frame has a pair of left and right side members 51 (only the left side is shown) and multiple cross members (not shown) that connect these side members 51. The left and right side members 51 and the suspension devices 52 are symmetrical, so the following description will mainly focus on the configuration of the left side only.

[0021] The suspension device 52 comprises a bracket 53 protruding from the underside of the side member 51, a trailing arm 54 rotatably attached to the bracket 53, and an air spring 55 provided between the side member 51 and the trailing arm 54.

[0022] The trailing arm 54 extends in the front-to-rear direction and includes an upper arm 56 and a lower arm 57 that are overlapped and integrated with each other. The front ends of the upper arm 56 and the lower arm 57 are attached to a rotating shaft 58 that is attached to the bracket 53 so as to be rotatable in the up-down direction as indicated by arrow a. The rotating shaft 58 extends in the left-to-right direction, and the trailing arm 54 is rotatable around the rotating shaft 58.

[0023] The axle case structure 1 of this embodiment is attached to the midpoint of the trailing arm 54 in the longitudinal direction (front-to-rear direction). The upper arm 56 extends rearward only as far as the axle case structure 1, but the lower arm 57 extends rearward to a position rearward of the axle case structure 1. The rear end of the upper arm 56 is positioned above the axle case structure 1. The lower arm 57 is bent downward in a crank shape just behind the axle case structure 1, with its rear end located behind the bent point.

[0024] The air spring 55 extends in the vertical direction and connects the rear end of the lower arm 57 to the side member 51 located above it. The air spring 55 is expandable and contractible in the vertical direction as indicated by arrow b.

[0025] The axle case structure 1 is attached to the trailing arm 54 by a pair of front and rear U-bolts 58. A spring seat 59 is sandwiched between the upper surface of the trailing arm 54 (i.e., the upper surface of the upper arm 56) and the U-bolt 58.

[0026] The suspension device 52 also includes a shock absorber 60. The shock absorber 60 is arranged at an angle so that it becomes higher as it goes forward. The front end of the shock absorber 60 is rotatably attached to a rotating shaft (not shown) that is attached to the bracket 53 and extends in the left-right direction. The rear end of the shock absorber 60 is rotatably attached to a rotating shaft 61 that is attached to the axle case structure 1 and extends in the left-right direction.

[0027] The above elements are also provided on the right side. Therefore, the vehicle is provided with left and right trailing arms 54 attached to left and right side members 51 so as to be able to rotate up and down, and left and right air springs 55 provided between the left and right side members 51 and the left and right trailing arms 54.

[0028] The axle case structure 1 of this embodiment forms a dead axle, which does not have the function of transmitting driving force to the rear wheels (not shown).In contrast, an axle that has the function of transmitting driving force to the wheels is called a drive axle.

[0029] Next, the axle case structure 1 of this embodiment will be described.

[0030] Fig. 2 is a schematic perspective view of the axle case structure 1, Fig. 3 is a schematic exploded perspective view of the axle case structure 1, and Fig. 4 is a rear view of the axle case structure 1. Of Figs. 2 to 4, only Fig. 4 shows a bracket, which will be described later. Also, Fig. 5 is a VV cross-sectional view of Fig. 2.

[0031] The axle case structure 1 includes an axle case main body 2 that extends in the vehicle width direction (left-right direction). The axle case main body 2 extends coaxially along a central axis (called the case axis) C that is parallel to the vehicle width direction (left-right direction). Unless otherwise specified, the axial, radial, and circumferential directions based on the case axis C will hereinafter be simply referred to as the axial, radial, and circumferential directions.

[0032] The axle case structure 1 also includes left and right spindles 3 connected to the left and right ends of the axle case main body 2 in the axial direction. Figure 3 shows the axle case main body 2 and spindles 3 separated. The spindle 3 is a short cylindrical member that extends in the vehicle width direction (left and right direction). A hub that supports the wheel is rotatably attached to the spindle 3, and part of the brake device is also attached to it. The spindle 3 is coaxially connected to the axle case main body 2 by welding.

[0033] The axle case body 2 is divided into two equal halves, top and bottom, at the height of the case axis C, and has an upper body 4, which is the upper divided piece, and a lower body 5, which is the lower divided piece. As shown in Figure 5, the upper body 4 and the lower body 5 are butted together and fixed by welding. The fixed parts by this welding are the welded parts, i.e., the front welded part 6F and the rear welded part 6R (collectively indicated by the reference symbol 6).

[0034] The axle case body 2 has a hollow hexagonal cross-sectional shape in the axial direction for the majority of its length, excluding both ends. This hollow hexagonal cross-sectional shape is the hexagonal section 7. The axle case body 2 also has, at both axial ends, a cylindrical section 8 that connects to the spindle 3, and a transition section 9 that connects the cylindrical section 8 and the hexagonal section 7, which are integrally and coaxially arranged.

[0035] The cylindrical portion 8 has a hollow circular cross-sectional shape, has the same outer shape as the spindle 3, and is butt-welded to the spindle 3. The transition portion 9 has a cross-sectional shape that gradually changes from a hollow circular shape to a hollow hexagonal shape between one end where it connects to the cylindrical portion 8 and the other end where it connects to the hexagonal portion 7.

[0036] The portions of the upper body 4 and the lower body 5 that make up the hexagonal portion 7 are the upper hexagonal portion 10 and the lower hexagonal portion 11. Therefore, the hexagonal portion 7 has upper and lower hexagonal portions 10 and 11 that are divided into upper and lower portions. Furthermore, the front weld portion 6F and the rear weld portion 6R exist over the entire length of the axle case body 2 and are also present in the hexagonal portion 7. Therefore, the hexagonal portion 7 has weld portions 6F, 6R that secure the butt joints of the upper hexagonal portion 10 and the lower hexagonal portion 11.

[0037] As shown in FIG. 5, the hexagonal portion 7 is hollow and has a substantially regular hexagonal cross-sectional shape. The hexagonal portion 7 has a cross-sectional shape that is symmetrical from top to bottom and from front to back. The upper hexagonal portion 10 has a trapezoidal cross-sectional shape with an open bottom side, and the lower hexagonal portion 11 has an inverted trapezoidal cross-sectional shape with an open bottom side. An inverted trapezoid is a shape obtained by turning a trapezoid upside down. The upper hexagonal portion 10 and the lower hexagonal portion 11 have cross-sectional shapes that are symmetrical from top to bottom.

[0038] The upper body 4 and the lower body 5, including the upper hexagonal portion 10 and the lower hexagonal portion 11, are formed by pressing a metal plate (specifically, a steel plate) having a thickness of t. The cross-sectional shape of the upper hexagonal portion 10 is a trapezoid that is symmetrical from front to back, and the cross-sectional shape of the lower hexagonal portion 11 is an inverted trapezoid that is symmetrical from front to back.

[0039] Here, an axis passing through the case axis C and parallel to the front-rear direction is defined as a reference front-rear axis C1, and an axis passing through the case axis C and parallel to the up-down direction is defined as a reference up-down axis C2.

[0040] The upper hexagonal portion 10 integrally comprises an upper surface portion 12 forming the upper base of the trapezoid, and front and rear sloped surfaces 13 and 14 formed at the front and rear ends of the upper surface portion 12. The upper surface portion 12 is parallel to the case axis C and the reference longitudinal axis C1. The front and rear sloped surfaces 13 and 14 are formed by bending the front and rear ends of the upper surface portion 12 downward by a predetermined angle θ1. In this embodiment, the angle θ1 is approximately 60°. The connection portions (bent portions) between the upper surface portion 12 and the front and rear sloped surfaces 13 and 14 are formed with a rounded cross section.

[0041] The lower hexagonal portion 11 integrally includes a lower surface portion 15 that forms the upper base of an inverted trapezoid, and a front slope portion 16 and a rear slope portion 17 that are connected to the front and rear ends of the lower surface portion 15. The lower surface portion 15 is parallel to the case axis C and the reference longitudinal axis C1. The front slope portion 16 and the rear slope portion 17 are formed by bending the front and rear ends of the lower surface portion 15 upward by a predetermined angle θ2. In this embodiment, the angle θ2 is equal to the angle θ1, approximately 60°. The connection portions (bent portions) between the lower surface portion 15 and the front slope portion 16 and the rear slope portion 17 are formed with a rounded cross section.

[0042] The lower ends of the front slope portion 13 and the rear slope portion 14 of the upper hexagonal portion 10 and the upper ends of the front slope portion 16 and the rear slope portion 17 of the lower hexagonal portion 11 are respectively butted against each other and welded at the front weld portion 6F and the rear weld portion 6R.

[0043] 6 shows the front welded portion 6F in detail. As shown in the figure, the lower end of the front sloped surface 13 of the upper hexagonal portion 10 and the upper end of the front sloped surface 16 of the lower hexagonal portion 11 are butted together to form a butt joint 19. This butt joint 19 is formed with a groove 20 that opens toward the radially outer side of the axle case body 2 (specifically, the front side), and a root surface 21 that is adjacent to the radially inner side of the groove 20 (specifically, the rear side).

[0044] The root surface portion 21 is a gap having a rectangular cross section formed by being sandwiched between a root face 22 of the upper front slope portion 13 and a root face 23 of the lower front slope portion 16, and has a predetermined root spacing U. The groove portion 20 is a gap having a V-shaped cross section formed by being sandwiched between a groove face 24 of the upper front slope portion 13 and a groove face 25 of the lower front slope portion 16, and has a predetermined included angle α. The included angle α is preferably 30° or more (15° on one side), and more preferably within the range of 45 to 60° (22.5 to 30° on one side).

[0045] Welding is performed from the radially outer side (specifically, from the front side) of the groove portion 20 and the root face portion 21. Reference symbol B in the drawing indicates a weld bead formed after welding.

[0046] The configuration of the front weld 6F is symmetrical vertically with respect to the reference longitudinal axis C1. The upper front inclined surface 13 and the lower front inclined surface 16 are inclined at predetermined angles θ3 and θ4 relative to the direction of the reference vertical axis C2 (which has been moved to the illustrated position for convenience) so that the upper and lower portions are more rearward. The angle θ3 is equal to 90°-θ1, and the angle θ4 is equal to 90°-θ2. In this embodiment, the angles θ3 and θ4 are both equal, approximately 30°.

[0047] The rear welded portion 6R has a configuration symmetrical to the front welded portion 6F in the front-rear direction, and therefore a description thereof will be omitted.

[0048] 1 and 4, the axle case structure 1 includes an upper bracket 31 for mounting a suspension that is fixed to the upper hexagonal portion 10 by welding, and a lower bracket 32 ​​for mounting a suspension that is fixed to the lower hexagonal portion 11 by welding. The welding is performed by fillet welding.

[0049] The upper bracket 31 and the lower bracket 32 ​​are both used to attach the axle case main body 2 to the suspension device 52. The left pair of upper bracket 31 and lower bracket 32 ​​are attached to the left end of the hexagonal portion 7. The right pair of upper bracket 31 and lower bracket 32 ​​are attached to the right end of the hexagonal portion 7. Since each pair of brackets 31, 32 are symmetrical, only the left side will be mainly described below.

[0050] 4(A) is a rear view showing the axle case structure 1, and FIG. 4(B) is a perspective view showing the upper bracket 31 and the lower bracket 32. As shown in FIG.

[0051] The upper bracket 31 and the lower bracket 32 ​​are formed by forging a metal material (specifically, steel). The upper bracket 31 and the lower bracket 32 ​​are configured to be roughly symmetrical from top to bottom, and as shown in FIG. 4, have a saddle-like shape that straddles the axle case main body 2. The upper bracket 31 and the lower bracket 32 ​​are disposed at the same position in the axial direction. Furthermore, as shown in FIG. 1, the upper bracket 31 and the lower bracket 32 ​​extend to positions forward and rearward of the axle case main body 2.

[0052] Here, to discuss only the upper bracket 31 in detail, the upper bracket 31 integrally has a planar seat portion 33 formed above the upper surface portion 12 of the upper hexagonal portion 10 and parallel to the upper surface portion 12, and a pair of front and rear legs 34 protruding downward from the seat portion 33.

[0053] As shown in FIG. 7 , an upper recess 35 is formed on the inside of the pair of legs 34 to be overlapped with or fitted onto the upper hexagonal portion 10. The upper recess 35 is a recess that is open at the bottom and closed at the top, and has a trapezoidal cross-sectional shape (cross-sectional shape perpendicular to the axial direction) that matches the outer shape of the upper hexagonal portion 10. The upper recess 35 has a bottom surface portion 36 that abuts against the top surface portion 12 of the upper hexagonal portion 10, a front side surface portion 37 that abuts against the front sloped surface portion 13 of the upper hexagonal portion 10, and a rear side surface portion 38 that abuts against the rear sloped surface portion 14 of the upper hexagonal portion 10. The connection portions between the bottom surface portion 36 and the front side surface portion 37 and the rear side surface portion 38 are formed in a rounded shape.

[0054] Here, since the upper bracket 31 is produced by forging, a draft angle needs to be formed in the upper bracket 31 so that it can be pulled out of the forging die. Generally, a draft angle of about 5 to 7 degrees is required. In the case of this embodiment, this draft angle is automatically created by the inclination of the front side surface portion 37 and the rear side surface portion 38.

[0055] That is, the front sloped surface 13 of the upper hexagonal portion 10 is inclined at an angle θ3 with respect to the direction of the reference vertical axis C2, and the front side surface 37 of the upper recess 35 is also inclined at the same angle θ3 with respect to the direction of the reference vertical axis C2. This allows the front side surface 37 to be in surface contact with the front sloped surface 13 without any gaps when the upper recess 35 is placed over the upper hexagonal portion 10.

[0056] Similarly, the rear inclined surface 14 of the upper hexagonal portion 10 is inclined at an angle θ5 (=θ3) with respect to the direction of the reference vertical axis C2, and the rear side surface 38 of the upper recess 35 is also inclined at the same angle θ5 with respect to the direction of the reference vertical axis C2. This allows the rear side surface 38 to be in surface contact with the rear inclined surface 14 without any gaps.

[0057] The front side surface portion 37 forms a front draft angle equal to the inclination angle θ3 of the front slope portion 13. The rear side surface portion 38 forms a rear draft angle equal to the inclination angle θ5 of the rear slope portion 14. Thus, the upper recess 35 has front and rear draft angles equal to the inclination angles θ3 and θ5 of the front slope portion 13 and the rear slope portion 14 of the upper hexagonal portion 10. These inclination angles θ3 and θ5 are sufficiently larger than a typical draft angle (approximately 5 to 7 degrees).

[0058] As described above, according to this embodiment, the necessary draft angle can be automatically formed simply by setting the front side surface portion 37 and the rear side surface portion 38 to the same inclination angles θ3 and θ5 as the front sloped surface portion 13 and the rear sloped surface portion 14. When they are overlapped, the front side surface portion 37 and the rear side surface portion 38 can be brought into surface contact with the front sloped surface portion 13 and the rear sloped surface portion 14, thereby achieving an ideal fit and ensuring high welding strength.

[0059] As shown in Figure 7, the front slope portion 13 and the underside of the front leg portion 34 are fillet welded at weld portion 39. Reference symbol B1 in the figure indicates the weld bead formed after welding. Similarly, the rear slope portion 14 and the underside of the rear leg portion 34 are fillet welded at weld portion 40. Reference symbol B2 in the figure indicates the weld bead formed after welding.

[0060] The upper bracket 31 and the upper hexagonal portion 10 may be welded to each other at other locations. For example, the left and right sides of the seat portion 33 may be welded to the upper hexagonal portion 10.

[0061] The lower bracket 32 ​​is symmetrical to the upper bracket 31 in the vertical direction, and therefore a detailed description thereof will be omitted. In the case of the lower bracket 32, a lower recess is formed that is superimposed on the lower hexagonal portion 11, and the lower recess has front and rear draft angles equal to the inclination angles θ4 and θ6 (see FIG. 5) of the front sloped portion 16 and the rear sloped portion 17 of the lower hexagonal portion 11.

[0062] The axle case structure 1 with the upper bracket 31 and the lower bracket 32 ​​attached in this manner is attached to the suspension device 52 in the following manner.

[0063] As shown in Figures 1 and 4, the axle case structure 1 is attached to the trailing arm 54 with a pair of front and rear U-bolts 58. At this time, the upper bracket 31 of the axle case structure 1 is placed on the lower surface of the lower arm 57. The spring seat 59 is placed on the upper surface of the upper arm 56.

[0064] The front and rear U-bolts 58 are positioned in a U-shape with an open bottom, and after straddling the spring seat 59, upper arm 56, and lower arm 57 from above, are inserted from above into insertion holes 45 (see FIG. 4(B)) provided at the four corners of the bearing surface portions 33 of the upper bracket 31 and the lower bracket 32. Nuts 62 are then tightened onto the lower ends of the front and rear U-bolts 58. This secures the spring seat 59, trailing arm 54, and axle case structure 1 together.

[0065] A pivot shaft 61 is attached to the front end of the lower bracket 32 ​​to rotatably support the rear end of the shock absorber 60 .

[0066] Next, the advantages of this embodiment will be described.

[0067] Figure 8 is a table comparing the axle case body of the conventional example and this embodiment. (A) is the case of the conventional axle case body with a hollow rectangular (specifically, square) cross-sectional shape. (B) is the case of the conventional axle case body with a hollow circular cross-sectional shape. (C) is the case of the axle case body of this embodiment with a hexagonal (specifically, regular hexagonal) cross-sectional shape. Each is intended for application to trailers with an allowable axle load of 10,0000 kg.

[0068] Both have the same cross-sectional height h of 140 mm and the same upper and lower rigidity (index) of 100. In the conventional examples (A) and (B), the axle case body is divided into upper and lower halves and welded together, just like the present embodiment (C).

[0069] Regarding the plate thickness t, it is 10.0 mm for the rectangular cross section (A), while it increases to 19.0 mm for the circular cross section (B), but only increases to 13.9 mm for the hexagonal cross section (C), which is less than the circular cross section (B).

[0070] Regarding the cross-sectional area (index), if the cross-sectional area for the rectangular cross-section (A) is set to 100, it increases to 146 for the circular cross-section (B), but only increases to 122 for the hexagonal cross-section (C), which is less than the increase in the circular cross-section (B).

[0071] On the other hand, with regard to the shear stress (index) for a constant torsional load, if the index for the rectangular cross section (A) is set to 100, it decreases to 76 for the circular cross section (B), but only to 88 for the hexagonal cross section (C), which is less than the decrease in the circular cross section (B).

[0072] In this way, when comparing circular and hexagonal cross sections with a rectangular cross section as the standard, the hexagonal cross section can suppress increases in plate thickness t and cross-sectional area compared to the circular cross section, thereby suppressing increases in weight. On the other hand, the hexagonal cross section can reduce shear stress more than the rectangular cross section, although not as much as the circular cross section, and can increase torsional rigidity more than the rectangular cross section.

[0073] Comparing the product weight per axis, changing from a rectangular cross section to a circular cross section increases the weight by 25 kg, whereas changing from a rectangular cross section to a hexagonal cross section increases the weight by only 12 kg.

[0074] Therefore, according to the axle case structure 1 of this embodiment, it is possible to increase the torsional rigidity while suppressing an increase in weight.

[0075] In particular, in the trailer of this embodiment, left and right trailing arms 54 are attached to the chassis (side members 51) so as to be rotatable in the vertical direction, and left and right air springs 55 are provided between the chassis and the left and right trailing arms 54, respectively. Then, the axle case structure 1 is attached to the left and right trailing arms 54.

[0076] In this case, when the vehicle is cornering, the difference in length between the left and right air springs 55 becomes relatively large, and the torsional load applied to the axle case structure 1 becomes higher than in a typical leaf spring suspension device. In this case, changing the cross-sectional shape of the axle case from rectangular to circular would result in a significant increase in weight. However, by adopting the axle case structure 1 of this embodiment, it is possible to increase torsional rigidity while suppressing this weight increase.

[0077] An air suspension type in which the air spring 55 is located only on one end of each of the left and right trailing arms 54, as in this embodiment, is called a two-bag type. In contrast, a type in which air springs are located on both ends instead of the left and right trailing arms is called a four-bag type. With a four-bag type, the torsional load on the axle case structure is not as strong as with a two-bag type. In other words, the axle case structure 1 of this embodiment is more suitable for a two-bag type, which is subject to stronger torsional loads than a four-bag type.

[0078] This embodiment also has the following advantage.

[0079] Figure 9 shows what happens when a conventional axle case body with a rectangular cross section is subjected to a torsional load. When this occurs, the axle case body experiences warping (warping or distortion) in which each side curves radially inward, as shown by the imaginary line a. This causes tensile stress b to act on the front and rear welds 101, tearing the root surface on the radially inner side from top to bottom, which can cause cracks to form on the root surface of the welds 101.

[0080] Meanwhile, Figure 10 shows the state of the hexagonal portion 7 of the axle case body 2 of this embodiment when subjected to a torsional load. At this time, warping occurs in the axle case body 2, with each side portion curving radially inward, as indicated by the imaginary line f. This causes compressive stress d to act on the radially inner root surface portions 21 of the front and rear welds 6F, 6R, pressing the upper and lower root faces 22, 23 (see Figure 6) against each other. This prevents cracks from occurring in the root surface portions 21 of the welds 6F, 6R.

[0081] On the other hand, a tensile stress e acts on the radially outer groove 20, tearing it apart vertically. However, because the inclined surfaces 13, 14, 16, and 17 are inclined relative to the reference vertical axis C2, as shown in Figure 6, the toe angle α1 of the weld bead B is larger than in the case of a rectangular cross section. This makes it possible to suppress crack generation due to the tensile stress e. The toe angle α1 is the angle between the toe (the edgemost part) of the weld bead B and the surface of the adjacent member.

[0082] This embodiment also has the following advantage.

[0083] 11 shows a state in which a suspension mounting bracket (specifically, an upper bracket) 102 is mounted on a conventional axle case body having a rectangular cross section. In this case, a recess 103 of the bracket 102 is provided with a typical draft angle θ7 of about 5 to 7 degrees.

[0084] However, because the front surface portion 104 and the rear surface portion 105 are not inclined relative to the direction of the reference vertical axis C2, gaps 106, 107 are formed between the bracket 102 and the front surface portion 104 or rear surface portion 105, and these gaps are at their maximum at the height of the lower end of the recess 103. Bridge-shaped weld beads 108, 109 are formed across these gaps 106, 107. This may reduce the weld strength.

[0085] One possible solution to this problem is to increase the size of the weld beads 108, 109, increasing their leg length a and throat thickness b. Another possible solution is to add a gap filling process by manual welding before the actual welding in the automatic welding process. However, both methods result in increased costs and weight.

[0086] 7, in this embodiment (the upper example is shown), the upper recess 35 of the upper bracket 31 has a draft angle equal to the inclination angles θ3 and θ5 of the front and rear slopes 13 and 14 of the upper hexagonal portion 10. This suppresses or prevents gaps from forming between the upper bracket 31 and the front and rear slopes 13 and 14, and prevents the weld bead B from becoming bridge-shaped, thereby forming a stable and sound weld bead B. This also ensures sufficient weld strength.

[0087] A minimum gap may be provided between the upper bracket 31 and the front sloped surface 13 and the rear sloped surface 14, which is favorable for overlapping and does not affect the welding strength. In this case, too, it is preferable that the inclination angles of the front side surface 37 and the front sloped surface 13 are equal, and it is also preferable that the inclination angles of the rear side surface 38 and the rear sloped surface 14 are equal.

[0088] The upper recess 35 must have a draft angle equal to or greater than a predetermined lower limit (for example, 5°). In view of this, it is preferable that the inclination angles θ3 and θ5 of the front and rear slopes 13 and 14 are equal to or greater than a predetermined lower limit.

[0089] [Variations] Next, a modified example of the present disclosure will be described. Note that parts that are the same as those in the basic embodiment are given the same reference numerals in the drawings and their explanations will be omitted. The following mainly describes the differences from the basic embodiment.

[0090] 12 is a rear view of an axle case structure 1 according to a modified example. This axle case structure 1 forms a drive axle that transmits driving force to the wheels, and in particular houses a differential device and left and right drive shafts inside. The axle case structure 1 is formed as a well-known banjo-type axle case.

[0091] The axle case structure 1 comprises an axle case main body 2 extending in the vehicle width direction (left-right direction) and left and right spindles 3 connected to both axial ends of the axle case main body 2. The axle case main body 2 is divided into two, top and bottom, with an upper body 4 as the upper divided piece and a lower body 5 as the lower divided piece. The upper body 4 and lower body 5 are butted together and fixed at a front weld 6F and a rear weld 6R (see Figure 5).

[0092] The axle case body 2 integrally comprises left and right cylindrical sections 8 located at both axial ends, left and right transition sections 9 located adjacent to the axial center of the cylindrical sections 8, left and right hexagonal sections 7 located adjacent to the axial center of the transition sections 9, and a gear case section 41 located adjacent to the axial center of the hexagonal sections 7. The gear case section 41 is provided in the axial center of the axle case body 2. The entire axle case body 2 is divided into an upper body 4 and a lower body 5, which are butt-welded to each other.

[0093] The gear case 41 houses the reduction / differential gear and part of the drive shaft. The gear case 41 integrally houses a ring 42 having a central axis C3 extending in the front-rear direction and open at the front and rear, and a tube 43 extending left and right from the ring 42. The front and rear openings of the ring 42 are closed by cover plates (not shown). The axially outer end of the tube 43, which connects to the hexagonal portion 7, has a hexagonal cross-sectional shape identical to that of the hexagonal portion 7.

[0094] Since the entire axle case body 2 is divided into upper and lower parts, the gear case portion 41 is also divided into upper and lower parts. The gear case portion 41 may be produced separately and connected to the hexagonal portion 7 by welding or the like.

[0095] The hexagonal portions 7 are located adjacent to the axial end portions, i.e., the left and right sides, of the gear case portion 41. As described above, the upper bracket 31 and the lower bracket 32 ​​for attachment to the suspension device 52 are attached to the hexagonal portions 7 by welding.

[0096] The effects of this modified example are the same as those of the basic embodiment. The axle case structure 1 of this modified example can also increase torsional rigidity while suppressing an increase in weight.

[0097] Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure are possible.

[0098] (1) For example, the cross-sectional shape of the hexagonal portion 7 does not have to be a regular hexagon, and may be asymmetrical front-to-back and / or top-to-bottom.

[0099] (2) The inclination angles (θ3 to θ6, etc.) of the inclined surfaces 13, 14, 16, and 17 of the hexagonal portion 7 relative to the reference vertical axis C2 may be partially or entirely the same or different.

[0100] (3) The suspension mounting brackets 31 and 32 are not essential, and one or both of them can be omitted. For example, both can be omitted, and the hexagonal part can be attached to the trailing arm with a spacer sandwiched between them and a U-bolt.

[0101] (4) The brackets 31 and 32 are not limited to forged products, but may be cast products, or may be press-molded products.

[0102] (5) The vehicle is not limited to a trailer and may be any type of vehicle. For example, the axle case structure of the present disclosure may be adopted for the rear axle of a truck. The type of suspension device may also be arbitrary.

[0103] The configurations of the above-described embodiments and variations can be combined in part or in whole unless there is a particular contradiction. The embodiments of the present disclosure are not limited to the above-described embodiments, and all variations, applications, and equivalents encompassed within the spirit of the present disclosure as defined by the claims are included in the present disclosure. Therefore, the present disclosure should not be interpreted as being limited, and can be applied to any other technology that falls within the spirit of the present disclosure. [Explanation of symbols]

[0104] 1 Axle case structure 2 Axle case body 3 spindles 6, 6F, 6R welded parts 7 Hexagonal part 10 Upper hexagonal part 11 Lower hexagonal part 19 Butt joint 20 Bevel 21 Root surface 31 Upper bracket 32 Lower bracket 35 Upper recess 51 Side member 54 Trailing arm 55 air spring

Claims

1. The vehicle has an axle case body extending in a vehicle width direction, The axle case body has a hexagonal portion having a hollow hexagonal cross-sectional shape, The hexagonal portion has an upper hexagonal portion and a lower hexagonal portion divided into upper and lower portions, The upper hexagonal portion has a trapezoidal cross-sectional shape with an open lower bottom side, The lower hexagonal portion has an inverted trapezoidal cross-sectional shape with an upper bottom side open, The hexagonal portion has a weld portion that fastens the butt portion of the upper hexagonal portion and the lower hexagonal portion. The axle case structure is characterized by:

2. The butted portion is formed with a groove portion that opens toward the radially outer side of the axle case body, and a root surface portion that is adjacent to the radially inner side of the groove portion. The axle case structure according to claim 1 .

3. The axle case body includes a spindle connected to both axial ends thereof. The axle case structure according to claim 1 .

4. Forming a dead axle The axle case structure according to claim 1 .

5. a suspension mounting upper bracket fixed to the upper hexagonal portion by welding; the upper bracket has an upper recess that is overlaid on the upper hexagonal portion; The upper recess has front and rear draft angles equal to the inclination angles of the front and rear slopes of the upper hexagonal portion relative to the direction of the reference vertical axis. The axle case structure according to claim 1 .

6. a lower bracket for mounting a suspension, the lower bracket being fixed to the lower hexagonal portion by welding; the lower bracket has a lower recess that mates with the lower hexagonal portion; The lower recess has front and rear draft angles equal to the inclination angles of the front and rear slopes of the lower hexagonal portion relative to the direction of the reference vertical axis. The axle case structure according to claim 1 .

7. The vehicle includes a trailing arm attached to a chassis so as to be rotatable in a vertical direction, and an air spring provided between the chassis and the trailing arm, The hexagonal portion is attached to the trailing arm. The axle case structure according to claim 1 .

8. The vehicle is a trailer. The axle case structure according to claim 1 .

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