Lower structure of vehicle

Abstract

A lower structure of a vehicle (50) disclosed herein comprises: a first cross member (1) that couples, in the vehicle width direction, a pair of left and right side-frames (8) each extending in the front-rear direction of the vehicle (50); a second cross member (2) that couples the side-frames (8) in the vehicle width direction and that is disposed adjacent to the first cross member (1) and apart therefrom in the vehicle front-rear direction; a propeller shaft (6) that is supported on the upper surface of the first cross member (1); and a bracket (3) that couples the first cross member (1) and the second cross member (2) in the vehicle front-rear direction in the vicinity of a support part of the propeller shaft (6) on the first cross member (1).

Description

Vehicle undercarriage

[0001] This case relates to a vehicle undercarriage that includes a cross member that supports a propeller shaft.

[0002] In vehicles in which a drive source is located away from the drive wheels, a drive force is transmitted using a propeller shaft. In this type of vehicle, the drive source and a transmission are attached to one end of the propeller shaft, and a differential device is attached to the other end of the propeller shaft. Furthermore, when the propeller shaft has a structure in which two shafts (a front propeller shaft and a rear propeller shaft) are connected to the front and rear, the vicinity of these connection points must be supported by the vehicle body. Regarding such a support structure for a propeller shaft, for example, Patent Document 1 describes a structure in which a semicircular notch is provided in the lower part of a cross member and the propeller shaft is supported inside the notch.

[0003] Patent Publication No. 2021-037784

[0004] Conventional propeller shaft support structures have the problem that it is difficult to improve the vibration and noise characteristics of a vehicle. For example, in the technology described in Patent Document 1, the cross member that supports the middle portion of the propeller shaft is likely to vibrate together with the propeller shaft, and good noise vibration harshness (NVH) performance may not be achieved.

[0005] One of the objects of the present invention, which was devised in light of the above-mentioned problems, is to provide a vehicle undercarriage that can improve the vibration and noise characteristics of a vehicle with a simple configuration. However, in addition to this object, another object of the present invention is to achieve effects derived from the respective configurations shown in the "Description of Embodiments" below, which are effects that cannot be obtained with conventional technologies.

[0006] The disclosed vehicle undercarriage can be realized as the following disclosed embodiments (application examples), which solve at least part of the above-mentioned problems. Each of the embodiments from embodiment 2 onwards is an embodiment that can be selected as an additional element, and each of the embodiments can be omitted. None of the embodiments from embodiment 2 onwards discloses an embodiment or configuration that is essential to the present invention.

[0007] Aspect 1. The disclosed vehicle undercarriage includes a first cross member connecting a pair of left and right side frames extending in the fore-and-aft direction of the vehicle in the vehicle width direction, a second cross member connecting the side frames in the vehicle width direction and positioned adjacent to the first cross member with a gap in the fore-and-aft direction of the vehicle, a propeller shaft supported on an upper surface of the first cross member, and a bracket connecting the first cross member and the second cross member in the vehicle fore-and-aft direction near a support portion of the first cross member for the propeller shaft.

[0008] Aspect 2. In relation to the aspects including Aspect 1 above, it is preferable that the first cross member is located above the second cross member, extends in the vehicle width direction, and has a recessed portion formed in a curved shape recessed downward in the center of the vehicle width direction, the support portion is provided in the recessed portion, and the bracket is connected to the recessed portion.

[0009] Aspect 3. In the aspects including Aspect 1 above, it is preferable that the second cross member be formed to have higher rigidity than the first cross member. Aspect 4. In the aspects including Aspect 1 above, it is preferable that the bracket be fastened to the upper surface of the first cross member and welded to the upper surface of the second cross member.

[0010] Aspect 5. With regard to aspects including Aspect 1 above, it is preferable that the bracket has an upper surface portion that is fixed to the upper surface of the first cross member and extends approximately horizontally in the fore-and-aft direction of the vehicle, and side surfaces that extend approximately vertically downward from each of the left and right end edges of the upper surface portion at the end of the bracket facing the second cross member and are fixed to the upper surface of the second cross member, and that the upper surface of the second cross member fixed to the bracket is located at a lower position than the upper surface of the first cross member fixed to the bracket.

[0011] Aspect 6. In the aspects including Aspect 5 above, it is preferable that the side portion extends below the upper surface of the second cross member and is fixed to the surface of the second cross member facing the first cross member. Aspect 7. In the aspects including Aspect 6 above, it is preferable that the side portion is formed in a triangular shape in a side view.

[0012] Aspect 8. With regard to the aspects including Aspect 5 above, it is preferable that the upper surface portion has fastening holes for fastening the bracket to the first cross member, and that the positions of the fastening holes in the vehicle longitudinal direction are set to be substantially the same as the positions of the ends of the side surfaces of the bracket on the first cross member side.

[0013] According to the disclosed vehicle undercarriage, by connecting the first cross member and the second cross member in the fore-and-aft direction of the vehicle with a bracket near the support portion of the propeller shaft, the rigidity of the first cross member to which the support portion is fixed can be increased, thereby suppressing noise and vibration associated with rotation of the propeller shaft. Furthermore, the resonance frequency of the first cross member can be increased. Therefore, the vibration and noise characteristics of the vehicle can be improved with a simple configuration.

[0014] 1 is an exploded perspective view showing the undercarriage of a vehicle; FIG. 2 is a top view showing the main parts of the undercarriage of a vehicle; (A) is a rear view of a first cross member, and (B) is a cross-sectional view of the first cross member shown together with the surrounding structure; (A) is a rear view of a second cross member, and (B) is a cross-sectional view of the second cross member shown together with the surrounding structure; FIG. 3 is a perspective view showing an enlarged main part of the undercarriage of a vehicle; and FIG. 4 is a six-view diagram of a bracket. (A) is an enlarged perspective view of a main part of the undercarriage of a vehicle, and (B) is a perspective view for explaining a modified example thereof.

[0015] The disclosed vehicle understructure is an understructure including a cross member supporting a vehicle propeller shaft, and is applied to a vehicle having a propeller shaft. This understructure is applicable to, for example, a frame vehicle or a monocoque vehicle. The propeller shaft is a propulsion shaft for transmitting rotational driving force generated by the vehicle's drive source to the drive wheels. The propeller shaft is provided under the vehicle near the center in the vehicle width direction, extending in the fore-and-aft direction. The propeller shaft is used, for example, in a vehicle in which an engine or motor is installed in an engine compartment at the front of the vehicle, to transmit rotational driving force to the rear wheels.

[0016] Regarding the definitions of directions in the embodiments, the front-rear direction (vehicle length direction) is defined based on the forward / reverse direction of the vehicle, and the left-right direction (vehicle width direction) is defined based on the front-rear direction. The up-down direction is defined based on the state in which the vehicle is stopped on a flat road surface. Regarding the inward / outward directions of the vehicle, the direction from the outside of the vehicle toward the passenger compartment in the vehicle width direction is defined as the inward direction, and the direction from the passenger compartment toward the outside of the vehicle is defined as the outward direction. To the right of the vehicle's median plane (the vertical plane dividing the vehicle into left and right halves), the right direction is the outward direction, and the left direction is the inward direction. To the left of the vehicle's median plane, the left direction is the outward direction, and the right direction is the inward direction.

[0017] 1 is an exploded perspective view showing the undercarriage of a vehicle 50 according to an embodiment. The vehicle 50 is a frame vehicle having a structure in which a body 51 is mounted on a frame 52. Vibration-damping mounts (not shown) are interposed between the body 51 and the frame 52. Structurally separating the body 51 from the frame 52 makes it easy to employ a frame 52 with high rigidity against bending and torsional deformation, thereby improving the off-road performance and durability of the vehicle 50. Specific examples of frame vehicles include SUVs (Sport Utility Vehicles), off-road vehicles, buses, trucks, etc.

[0018] The frame 52 is fitted with a drive source (e.g., an engine, a motor, etc.) of the vehicle 50 and a propeller shaft 6. The propeller shaft 6 has a structure in which a front propeller shaft 61 and a rear propeller shaft 62 are connected in the front and rear directions. The front end of the front propeller shaft 61 is connected to a transmission 5 for, for example, changing the speed of the rotational driving force generated by the drive source. The rear end of the rear propeller shaft 62 is connected to a rear differential device 7 for, for example, distributing the driving force to the left and right rear wheels. The rear end of the front propeller shaft 61 in the fore-and-aft direction (or the front end of the rear propeller shaft 62) is rotatably supported relative to the frame 52 via a bearing 4. The bearing 4 functions as a support that supports the front propeller shaft 61 relative to the frame 52.

[0019] The frame 52 is formed by bridging multiple cross frames between a pair of side frames 8. The side frames 8 extend in the fore-and-aft direction (vehicle length direction) and are also called side rails or side members. The pair of side frames 8 are arranged approximately symmetrically (plane symmetrically) with a gap in the vehicle width direction. The fore-and-aft central portions of the side frames 8 are formed in a shape that is lower than the front and rear portions. The fore-and-aft central portions of the side frames 8 are arranged approximately horizontally, for example, below the underside of the body 51 (vehicle interior floor). Furthermore, the front and rear portions of the side frames 8 are arranged approximately horizontally so as to pass above the rotation centers of the wheels (drive shafts, etc.).

[0020] The cross frame is a frame that extends in the vehicle width direction and connects a pair of side frames 8 in the vehicle width direction. The cross frames are provided at multiple positions spaced apart in the front-to-rear direction. The frame 52 consisting of the side frames 8 and the cross frames is also called a ladder frame because of its ladder-like appearance. At the front and rear of the side frames 8, cross frames are disposed in positions where, for example, the rotation center of the wheels and the structure around the suspension are reinforced. In addition, for example, two cross frames are disposed in the center of the side frames 8 in the front-to-rear direction for reinforcement. In this embodiment, the rear cross frame of the two cross frames is referred to as the first cross member 1, and the front cross frame is referred to as the second cross member 2.

[0021] The first cross member 1 and the second cross member 2 are each provided to connect a pair of left and right side frames 8 extending in the longitudinal direction of the vehicle 50 in the vehicle width direction. The first cross member 1 is provided to secure on-board devices mounted below the body 51 and to support a front propeller shaft 61 on its upper surface. The front propeller shaft 61 is supported on the upper surface of the first cross member 1. In this embodiment, a tank 53 (described later) is fixed in a suspended state below the first cross member 1. The front propeller shaft 61 is also supported on the upper surface of the first cross member 1 via a bearing 4. The bearing 4 is fixed to the center of the first cross member 1 in the vehicle width direction. However, the bearing 4 can be omitted. The front propeller shaft 61 can be supported directly (or indirectly via a known sliding member) on the upper surface of the first cross member 1.

[0022] The second cross member 2 is provided to further reinforce the longitudinal center portion of the side frame 8 that is reinforced by the first cross member 1. The second cross member 2 is disposed adjacent to and spaced apart from the first cross member 1 in the longitudinal direction. In this embodiment, the second cross member 2 is disposed in front of the first cross member 1 in a position that does not interfere with the tank 53 that is fixed by hanging below the first cross member 1.

[0023] The bearing 4 is fixed to the transverse center of the upper surface of the first cross member 1. The first cross member 1 is shaped to support the bearing 4 from below. The first cross member 1 and the second cross member 2 are connected to each other via a bracket 3. The bracket 3 is arranged to connect the transverse center of the first cross member 1 and the second cross member 2 in the fore-and-aft direction near the bearing 4 (e.g., just in front of or just behind). In other words, the bracket 3 connects the first cross member 1 and the second cross member 2 in the fore-and-aft direction near a support portion of the first cross member 1 for the propeller shaft 6. The bracket 3 is preferably positioned so as to overlap the propeller shaft 6 in a top view. This efficiently suppresses vibrations of the bearing 4 and the first cross member 1 that occur as the propeller shaft 6 rotates.

[0024] Figure 2 is a top view showing the surrounding structure of the first cross member 1 and the second cross member 2. In Figure 2, the first cross member 1 and the second cross member 2 are arranged parallel to each other, with the second cross member 2 being arranged in front of the first cross member 1. The first cross member 1 in Figure 2 is formed with a wider member width (front-to-rear dimension in top view) than the second cross member 2. The dashed lines in Figure 2 represent the outlines of the propeller shaft 6, the tank 53, and the exhaust system 54 in top view. The propeller shaft 6 is arranged near the center of the vehicle in the width direction.

[0025] Various on-board devices are disposed below the hill portion 12 of the first cross member 1. The on-board devices include a tank 53 and an exhaust system 54. The tank 53 is disposed on one side of the vehicle width (e.g., to the left of the propeller shaft 6 and below one of the pair of hill portions 12), and the exhaust system 54 is disposed on the other side of the vehicle width (e.g., to the right of the propeller shaft 6 and below the other of the pair of hill portions 12). The tank 53 includes, for example, a fuel tank, various additive tanks, an engine oil tank, a refrigerant tank, and a washer fluid tank. The exhaust system 54 includes, for example, an exhaust pipe, an exhaust purification catalyst device, a muffler device, and the like. The bearing 4 is mounted on the outer periphery of the propeller shaft 6. The bracket 3 is disposed in front of the bearing 4.

[0026] 3A is a rear view of the first cross member 1, and FIG. 3B is a longitudinal cross-sectional view of the first cross member 1 together with the surrounding structure. The first cross member 1 is formed in a roughly M-shaped seagull shape when viewed from the front and rear. The seagull shape refers to a shape similar to the shape of a seagull flying with its wings spread when viewed from the front (or rear), such as a shape resembling the graph of a quartic function with two maxima and one minimum.

[0027] The first cross member 1 is divided into three regions based on its position in the vehicle width direction, and a recessed portion 11 and a pair of hills 12 are defined based on this classification. The recessed portion 11 is located in the center of the vehicle width direction, and the bearing 4 is fixed to its upper surface 17. The recessed portion 11 is formed in a downwardly recessed (curved) shape in the center of the vehicle width direction below the bearing 4 so as not to interfere with the front propeller shaft 61 and the bearing 4. The recessed portion 11 is positioned so that at least its upper surface 17 (preferably the entire recessed portion 11) is located above the second cross member 2. A support portion for supporting the propeller shaft 6 is provided in the recessed portion 11, and the bracket 3 is connected to the recessed portion 11. In this embodiment, a support bracket 13 for fixing the bearing 4 is fixed to the upper surface 17 of the recessed portion 11. The front propeller shaft 61 is supported by the recessed portion 11.

[0028] The hill portions 12 are a pair of portions located on the left and right sides of the recessed portion 11, and are portions connected to the side frames 8. The hill portions 12 are formed in a mountain shape that protrudes upward. The highest point of the hill portions 12 is called the peak portion 14. The peak portion 14 is provided at a position close to the center of the hill portions 12 in the vehicle width direction. The peak portion 14 is located more inward in the vehicle width direction than floor side members 56, which will be described later. Various on-board devices (e.g., a tank 53, an exhaust system device 54, etc.) are disposed below the hill portions 12.

[0029] The height dimension of the first cross member 1 is set to be relatively small at the recessed portion 11. The height dimension of the hill portion 12 at a position close to the recessed portion 11 is also set to be relatively small, similar to the height dimension of the recessed portion 11. On the other hand, the height dimension of the hill portion 12 at a position far from the recessed portion 11 is set to be relatively large, and is greatest at the joint portion with the side frame 8.

[0030] The upper surface of the hill portion 12 is formed in an upwardly curved shape so as to smoothly connect to the inner surface of the side frame 8 in both front and rear views. The lower surface of the hill portion 12 is formed in a downwardly curved shape so as to smoothly connect to the lower surface of the side frame 8 in both front and rear views. By making the height dimensions of the left and right ends of the first cross member 1 relatively larger than that of the center portion, the attachment state of the first cross member 1 to the side frame 8 becomes more stable.

[0031] The first cross member 1 is formed into a cylindrical shape with a closed cross section by joining an upper member 15 and a lower member 16. The shape of the upper member 15 is, for example, a curved flat plate in the recessed portion 11, and in the hill portion 12, for example, a shape in which the central portion in the longitudinal direction rises as it approaches the side frame 8 (a hat-like shape with an open bottom). On the other hand, the shape of the lower member 16 is, for example, a shape in which the central portion in the longitudinal direction is depressed over the entire cross section in the vehicle width direction (a hat-like shape with an open top). Both longitudinal edges of the upper member 15 are joined to both longitudinal edges of the lower member 16. This forms the closed cross-sectional shape of the first cross member 1. However, the specific structure of the first cross member 1 is not limited to this.

[0032] As shown in Figure 3(B) , a floor panel 55 that forms the underside of the body 51 is located above the first cross member 1. A pair of left and right floor side members 56 are fixed to the underside of the floor panel 55. The floor side members 56 are members that reinforce the floor panel 55 and extend in the front-to-rear direction. The floor side members 56 are located outward in the vehicle width direction from the crest 14 of the hill portion 12 in front and rear views.

[0033] This makes it less likely that the first cross member 1 will interfere with the floor side member 56 compared to when the floor side member 56 is positioned directly above the peak 14. Similarly, the wiring 58 and piping 59 routed below the floor panel 55 are also positioned further outward in the vehicle width direction than the peak 14 of the hill 12 in the front and rear views. This makes it easier to ensure sufficient space for routing the wiring 58 and piping 59.

[0034] A tunnel portion 57 formed in a tunnel-like bulge is provided in the portion of floor panel 55 above propeller shaft 6. This makes it less likely that propeller shaft 6 will interfere with floor panel 55 compared to a case where tunnel portion 57 is not provided. Furthermore, the greater the upward bulge of tunnel portion 57, the easier it is to set the height (vertical position) of recess 11 relatively high, making it easier to ensure a sufficient distance between propeller shaft 6 and the road surface.

[0035] The upper surface of the tank 53 is formed in a shape that follows the shape of the underside of the first cross member 1, and is positioned directly below the first cross member 1. For example, a metal belt (not shown) is wound around the underside of the tank 53. Both ends of the metal belt are attached to the first cross member 1. In this way, the tank 53 is suspended and fixed to the first cross member 1. The exhaust system device 54 is also disposed below the hill portion 12 so as to ensure a predetermined distance from the lower member 16. Because the hill portion 12 is formed in a mountain-like shape that protrudes upward, it is easy to set the height of the exhaust system device 54 relatively high, making it easier to ensure a sufficient distance between the exhaust system device 54 and the road surface.

[0036] 4A is a rear view of the second cross member 2, and FIG. 4B is a longitudinal cross section of the second cross member 2 along with the surrounding structure. The second cross member 2 is formed to have higher rigidity than the first cross member 1. For example, the second cross member 2 is formed to have a shape with a larger overall height dimension (thickness in the vertical direction) compared to the first cross member 1. In other words, the height dimension H of the first cross member 1 at the portion where they are located at the same position in the vehicle width direction is １ and the height dimension H of the second cross member 2 ２ When compared with １ >H ２ Each height dimension H １ , H ２ Alternatively, the second cross member 2 is formed using a plate material that is thicker than the first cross member 1. That is, the plate thickness W of the first cross member 1 is set. １ and the plate thickness W of the second cross member 2 ２ When comparing with W ２ >W １ Each plate thickness W １ , W ２ is set.

[0037] The second cross member 2 is divided into three sections based on its position in the vehicle width direction, and a horizontal section 21 and a pair of sloped sections 22 are defined based on this classification. The horizontal section 21 is a section located in the center of the vehicle width direction and is a horizontally arranged, linear section. The horizontal section 21 has a larger vehicle width dimension than the recessed section 11 of the first cross member 1 and extends outward in the vehicle width direction beyond the crests 14 of the left and right hill sections 12. The sloped sections 22 are a pair of sections located on each of the left and right sides of the horizontal section 21 and are connected to the side frames 8. The sloped sections 22 are formed in an upward gradient from both left and right ends of the horizontal section 21 toward the side frames 8.

[0038] The height dimension of the second cross member 2 is set to be approximately constant at the horizontal portion 21. The height dimension of the sloped portion 22 at a position close to the horizontal portion 21 is also set to be approximately the same as that of the horizontal portion 21. On the other hand, the height dimension of the sloped portion 22 at a position far from the horizontal portion 21 is set to be relatively large, and is maximum at the joint with the side frame 8.

[0039] The upper surfaces of the sloped portions 22 are formed in an upwardly curved shape so as to smoothly connect to the inner surfaces of the side frames 8 in front and rear views. The lower surfaces of the sloped portions 22 are formed in a shape so as to smoothly connect to the lower surfaces of the side frames 8 in front and rear views. By making the height dimensions of the left and right ends of the second cross member 2 relatively larger than that of the center portion, the attachment state of the second cross member 2 to the side frames 8 becomes more stable.

[0040] The second cross member 2 is formed into a cylindrical shape with a closed cross section by joining an upper member 23 and a lower member 24. The upper member 23 is, for example, U-shaped with an open bottom, and the lower member 24 is, for example, U-shaped with an open top. The second cross member 2 is joined, for example, by fitting one of the upper member 23 and the lower member 24 inside the other. This forms the closed cross section structure of the second cross member 2. As shown in FIG. 5 , the second cross member 2 of this embodiment is formed into a rectangular cylindrical shape having an upper surface 25, a rear surface 26, a lower surface 27, and a front surface 28. However, the specific structure of the second cross member 2 is not limited to this.

[0041] 4(B), the height of the lower surface 27 of the second cross member 2 is set to be aligned with the height of the lower surface of the tank 53. In addition, the height of the upper surface 25 of the second cross member 2 is set to be lower than the exhaust system device 54 and to ensure a predetermined gap with respect to the exhaust system device 54. The height of the upper surface 25 of the second cross member 2 is preferably set to be slightly lower than the lowest point on the upper surface 17 of the recessed portion 11.

[0042] 5 is an enlarged perspective view showing the connection portion between the first cross member 1 and the second cross member 2 via the bracket 3. The figure shows a state in which the propeller shaft 6 and bearing 4 have been removed. The center portion of the first cross member 1 in the vehicle width direction is connected to the center portion of the second cross member 2 in the vehicle width direction via the bracket 3. The front end portion of the bracket 3 is welded and fixed to the top surface 25 of the second cross member 2, and preferably to the top surface 25 and the rear surface 26 of the second cross member 2. Meanwhile, the rear end portion of the bracket 3 is fastened and fixed with fasteners (e.g., bolts, nuts, rivets, etc.) in surface contact with the top surface 17 of the first cross member 1.

[0043] FIG. 6 is a six-view diagram of the bracket 3. The bracket 3 has an upper surface portion 31, a right side surface portion 32, and a left side surface portion 33. The upper surface portion 31 is a planar portion disposed substantially horizontally. The overall shape of the upper surface portion 31 is, for example, substantially rectangular when viewed from above. The upper surface portion 31 shown in FIG. 6 has a substantially rectangular front side (toward the second cross member 2) and a flared rear side (toward the first cross member 1). The rear end of the upper surface portion 31 is provided with an upper surface extension portion 34 that bulges further rearward (toward the first cross member 1), and fastening holes 35 through which fasteners are inserted.

[0044] The right side surface portion 32 is a planar portion extending downward from the right edge of the top surface portion 31, and the left side surface portion 33 is a planar portion extending downward from the left edge of the top surface portion 31. The right side surface portion 32 and the left side surface portion 33 are arranged approximately perpendicular to the top surface portion 31. The right side surface portion 32 and the left side surface portion 33 shown in FIG. 6 are formed flat on the front side (toward the second cross member 2) and curved on the rear side (toward the first cross member 1). When the bracket 3 is fixed to the second cross member 2, the right side surface portion 32 and the left side surface portion 33 extend downward below the top surface 25 of the second cross member 2.

[0045] The overall shape of the right side surface portion 32 and the left side surface portion 33 is, for example, a substantially triangular shape in side view. The right side surface portion 32 and the left side surface portion 33 shown in Figure 6 are shaped like a triangle with the front side (the second cross member 2 side) forming the base and the rear side (the first cross member 1 side) forming the apex. The front-to-rear positions of the rear ends (apexes) of the right side surface portion 32 and the left side surface portion 33 (the first cross member 1 side) are set so that they are substantially the same as the front-to-rear positions of the fastening holes 35. In other words, the positional relationship between the right side surface portion 32 and the left side surface portion 33 is set so that the dashed dotted lines corresponding to the positions of the rear ends of the right side surface portion 32 and the left side surface portion 33 pass through the inside of the fastening holes 35 in the six-sided view shown in Figure 6.

[0046] The front side (second cross member 2 side) of the right side surface 32 is provided with a horizontal edge 36 that abuts the upper surface 25 of the second cross member 2, and a vertical edge 37 that abuts the rear surface 26 of the second cross member 2. Similarly, the front side (second cross member 2 side) of the left side surface 33 is provided with a horizontal edge 38 that abuts the upper surface 25 of the second cross member 2, and a vertical edge 39 that abuts the rear surface 26 of the second cross member 2. The horizontal edge 36, 38 are welded to the upper surface 25, and the vertical edge 37, 39 are welded to the rear surface 26.

[0047] 7(A) is a perspective view showing the fixing locations of the second cross member 2 and the bracket 3. The upper surface portion 31 of the bracket 3, which is fixed to the upper surface 17 of the first cross member 1, is located at a higher position than the upper surface 25 of the second cross member 2. In other words, the upper surface 25 of the second cross member 2, which is fixed to the bracket 3, is located at a lower position than the upper surface 17 of the first cross member 1, which is fixed to the bracket 3. As a result, on the front side of the bracket 3 (the second cross member 2 side), a cylindrical closed cross-sectional structure is formed surrounded by four sides: the upper surface portion 31, the right side surface portion 32, the left side surface portion 33, and the upper surface 25.

[0048] Furthermore, when the horizontal end edges 36, 38 are brought into contact with the top surface 25 of the second cross member 2, an inside corner is formed between the right side surface 32 and the left side surface 33 and the top surface 25. By fillet welding these inside corners, the bracket 3 is firmly fixed to the top surface 25 of the second cross member 2. Furthermore, when the vertical end edges 37, 39 are brought into contact with the rear surface 26 of the second cross member 2, an inside corner is formed between the right side surface 32 and the left side surface 33 and the rear surface 26. By fillet welding these inside corners, the bracket 3 is firmly fixed to the rear surface 26 of the second cross member 2.

[0049] Figure 7(B) is a perspective view showing a modified example of the structure shown in Figure 7(A). Horizontal flange portions 41 are formed on the horizontal end edges 36, 38 of this bracket 3, and vertical flange portions 42 are formed on the vertical end edges 37, 39. The horizontal flange portions 41 are planar portions extending substantially horizontally from the horizontal end edges 36, 38 toward the outside in the vehicle width direction, while the vertical flange portions 42 are planar portions extending substantially perpendicularly from the vertical end edges 37, 39 toward the outside in the vehicle width direction. The horizontal flange portions 41 are lap-welded in surface contact with the upper surface 25 of the second cross member 2, thereby firmly fixing the bracket 3 to the upper surface 25 of the second cross member 2. The vertical flange portions 42 are lap-welded in surface contact with the rear surface 26 of the second cross member 2, thereby firmly fixing the bracket 3 to the rear surface 26 of the second cross member 2.

[0050] [2. Actions and Effects] (1) The undercarriage structure of the vehicle 50 described above comprises a first cross member 1, a second cross member 2, a propeller shaft 6, and a bracket 3. The first cross member 1 connects a pair of left and right side frames 8 extending in the fore-and-aft direction of the vehicle 50 in the vehicle width direction. The second cross member 2 connects the side frames 8 in the vehicle width direction and is disposed adjacent to the first cross member 1 with a gap therebetween in the fore-and-aft direction of the vehicle 50. The propeller shaft 6 is supported on the upper surface of the first cross member 1. The bracket 3 connects the first cross member 1 and the second cross member 2 in the fore-and-aft direction of the vehicle 50 near a support portion of the first cross member 1 for the propeller shaft 6.

[0051] In this way, by connecting the first cross member 1 and the second cross member 2 in the fore-and-aft direction with the bracket 3 near the support portion of the propeller shaft 6, the rigidity of the first cross member 1 to which the support portion is fixed can be increased, thereby suppressing noise and vibration associated with rotation of the propeller shaft 6. In addition, the resonance frequencies of the first cross member 1 in the up-down and fore-and-aft bending modes can be increased. Therefore, the vibration and noise characteristics of the vehicle 50 can be improved with a simple configuration.

[0052] (2) The first cross member 1 is located above the second cross member 2, extends in the vehicle width direction, and has a recess 11 formed in a curved downward shape in the center of the vehicle width direction. A support portion for the propeller shaft 6 is provided in the recess 11, and the bracket 3 is connected to this recess 11. This configuration increases the rigidity of the fixing points between the bracket 3 and the second cross member 2, thereby improving the vibration and noise characteristics of the vehicle 50.

[0053] (3) The second cross member 2 is formed to have higher rigidity than the first cross member 1. For example, the height dimension of the second cross member 2 is set to be larger overall compared to the first cross member 1. This allows the vibration of the first cross member 1 to be efficiently suppressed by the highly rigid second cross member 2. Therefore, the vibration and noise characteristics of the vehicle 50 can be improved with a simple configuration.

[0054] (4) The bracket 3 is fastened to the upper surface 17 of the recess 11 of the first cross member 1 and welded to the upper surface 25 of the second cross member 2. In this way, by increasing the rigidity of the fixing points between the bracket 3 and the second cross member 2, the vibration of the first cross member 1 can be efficiently suppressed by the second cross member 2, thereby improving the vibration and noise characteristics of the vehicle 50.

[0055] (5) The bracket 3 has a top surface 31 and side surfaces (right side surface 32 and left side surface 33). The top surface 31 is fixed to the top surface 17 of the recess 11 of the first cross member 1 and extends in the fore-and-aft direction and approximately horizontally. The right side surface 32 and left side surface 33 extend approximately vertically downward from the left and right end edges of the top surface 31 at the end of the bracket 3 on the second cross member 2 side and are fixed to the top surface 25 of the second cross member 2.

[0056] Additionally, the top surface 25 of the second cross member 2 is located at a position lower than the top surface 17 of the recess 11 of the first cross member 1 that is fixed to the bracket 3. This allows a cylindrical closed cross-sectional structure to be formed on the front side of the bracket 3 (the second cross member 2 side) that is surrounded by four sides: the top surface 31, the right side surface 32, the left side surface 33, and the top surface 25. This therefore increases the rigidity of the fixing points between the bracket 3 and the second cross member 2, thereby improving the vibration and noise characteristics of the vehicle 50.

[0057] (6) The right side surface 32 and the left side surface 33 of the bracket 3 extend downward below the upper surface 25 of the second cross member 2 and are fixed to the surface (rear surface 26) of the second cross member 2 facing the first cross member 1. In other words, the bracket 3 is fixed to the upper surface 25 and the rear surface 26 of the second cross member 2. This further increases the rigidity of the fixing points between the bracket 3 and the second cross member 2, thereby improving the vibration and noise characteristics of the vehicle 50.

[0058] (7) As shown in Figure 6, the right side surface 32 and the left side surface 33 of the bracket 3 are formed in a triangular shape in a side view. This simple configuration increases the rigidity of the right side surface 32 and the left side surface 33 while reducing the weight of the bracket 3. Furthermore, even if the upper surface 17 of the recessed portion 11 of the first cross member 1 vibrates in the up-down, left-right, or front-rear directions, these vibrations can be efficiently suppressed, thereby improving the vibration and noise characteristics of the vehicle 50.

[0059] (8) The upper surface portion 31 has fastening holes 35 for fastening the bracket 3 to the first cross member 1. The longitudinal positions of the fastening holes 35 are set to be substantially the same as the positions of the ends of the right side surface portion 32 and the left side surface portion 33 of the bracket 3 that are on the first cross member 1 side. This increases the rigidity of the bracket 3 compared to when the ends of the right side surface portion 32 and the left side surface portion 33 that are on the first cross member 1 side are positioned further forward, thereby improving the vibration and noise characteristics of the vehicle 50.

[0060] (9) As shown in Figures 3(A) and 3(B), the underside of the first cross member 1 is formed so as to be connected to the underside of the side frame 8 in a front view at the joint between the hill portion 12 and the side frame 8. This increases the unity and rigidity between the first cross member 1 and the side frame 8, further improving the vibration damping effect and vibration noise characteristics.

[0061] (10) Furthermore, as shown in Figures 3(A) and 3(B), the upper surface of the first cross member 1 is formed in a shape that smoothly connects to the inner surface of the side frame 8 when viewed from the front. This increases the unity between the first cross member 1 and the side frame 8, making them more rigid, and further improving the vibration damping effect and vibration and noise characteristics.

[0062] [3. Other] The above-described embodiments are merely illustrative and are not intended to exclude various modifications or applications of techniques not explicitly described in the present embodiments. Each configuration of the present embodiments can be modified in various ways without departing from the spirit of the present embodiments. Furthermore, each configuration of the present embodiments can be selected or combined as needed.

[0063] While the above embodiment illustrates a substructure applied to a frame vehicle having a structure in which a body 51 is mounted on a frame 52, this substructure can also be applied to a monocoque vehicle. Furthermore, while the above embodiment illustrates a substructure for a vehicle 50 in which the second cross member 2 is disposed adjacent to the front of the first cross member 1, the second cross member 2 may be disposed adjacent to the rear of the first cross member 1. Furthermore, the propeller shaft 6 does not have to have a structure in which two shafts 61, 62 are connected in the front and rear. By at least disposing the second cross member 2 adjacent to the first cross member 1 with a gap in the front-to-rear direction and connecting the first cross member 1 and the second cross member 2 with the bracket 3, the same operational effects as those of the above embodiment can be achieved.

[0064] The present invention is applicable to the vehicle undercarriage and frame manufacturing industry, and also to the vehicle manufacturing industry to which such undercarriage or frame is applied.

[0065] REFERENCE SIGNS LIST 1 First cross member 2 Second cross member 3 Bracket 4 Bearing (support portion for propeller shaft 6) 5 Transmission 6 Propeller shaft 7 Rear differential device 8 Side frame 11 Depressed portion 12 Hill portion 13 Support fitting 14 Summit portion 15 Upper member 16 Lower member 17 Upper surface 21 Horizontal portion 22 Sloping portion 23 Upper member 24 Lower member 25 Upper surface 26 Rear surface 27 Lower surface 28 Front surface 31 Upper surface portion 32 Right side surface portion (side surface portion) 33 Left side surface portion (side surface portion) 34 Upper surface extension portion 35 Fastening hole 36 Horizontal edge 37 Vertical edge 38 Horizontal edge 39 Vertical edge 50 Vehicle 51 Body 52 Frame 53 Tank 54 Exhaust system device 55 Floor panel 56 Floor side member 57 Tunnel section 58 Wiring material 59 Piping material 61 Front propeller shaft 62 Rear propeller shaft

Claims

1. A vehicle undercarriage comprising: a first cross member connecting a pair of left and right side frames extending in the longitudinal direction of the vehicle in the vehicle width direction; a second cross member connecting the side frames in the vehicle width direction and positioned adjacent to the first cross member with a gap in the longitudinal direction of the vehicle; a propeller shaft supported on the upper surface of the first cross member; and a bracket connecting the first cross member and the second cross member in the longitudinal direction of the vehicle near a support portion of the first cross member for the propeller shaft.

2. The vehicle undercarriage structure according to claim 1, wherein the first cross member is located above the second cross member, extends in the vehicle width direction, and has a recessed portion formed in a curved shape recessed downward in the center of the vehicle width direction, the support portion is provided in the recessed portion, and the bracket is connected to the recessed portion.

3. A vehicle undercarriage structure according to claim 1 or 2, characterized in that the second cross member is formed to have higher rigidity than the first cross member.

4. A vehicle undercarriage structure as set forth in claim 1 or 2, characterized in that the bracket is fastened to the upper surface of the first cross member and welded to the upper surface of the second cross member.

5. A vehicle undercarriage structure as described in claim 1 or 2, characterized in that the bracket has an upper surface portion fixed to the upper surface of the first cross member and extending approximately horizontally in the fore-and-aft direction of the vehicle, and side portions extending approximately vertically downward from each of the left and right end edges of the upper surface portion at the end of the bracket facing the second cross member and fixed to the upper surface of the second cross member, and the upper surface of the second cross member fixed to the bracket is positioned lower than the upper surface of the first cross member fixed to the bracket.

6. A vehicle undercarriage structure as set forth in claim 5, characterized in that the side portion extends below the upper surface of the second cross member and is fixed to the surface of the second cross member facing the first cross member.

7. The vehicle undercarriage structure according to claim 6, wherein the side portion is formed in a triangular shape when viewed from the side.

8. A vehicle undercarriage structure as described in claim 5, characterized in that the upper surface portion has fastening holes for fastening the bracket to the first cross member, and the position of the fastening holes in the vehicle fore-and-aft direction is set to be approximately the same as the position of the end of the side portion of the bracket on the first cross member side.

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