JP3379373B2 - Frame structure for ultra low floor bus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frame structure for an ultra-low-floor bus, and more particularly, to ensure that an in-vehicle passage leading to a rear entrance / exit of rear wheels is close to a lateral space area of an engine mounted at a rear portion of a vehicle body. The present invention relates to a frame structure for a constructed ultra-low floor bus.

[0002]

2. Description of the Related Art Conventionally, most car bodies for buses have a structure in which an outer wall of a body on the floor and an underfloor structure are separately manufactured and are integrally connected to each other. As a body for this bus, some of the ones that use a ladder-type frame that is continuous in the front and rear of the body as an underfloor structure are also adopted, but in recent years, a solid auxiliary frame has been individually manufactured for each input section of concentrated load. In addition, a frameless stress skin structure (also referred to as a frameless structure or a monocoque structure) in which a plurality of these auxiliary frames arranged in the vehicle front-rear direction are integrally coupled to the outer wall of the body on the floor to ensure the overall strength ) Is often used.

The auxiliary frame used in this frameless structure receives a front and rear road surface reaction force applied to the vehicle body and input loads from the engine and the power transmission system, etc., and receives the input loads from the body on the floor having a function as a side rail. By transmitting it to the outer wall, the input load can be dispersed and supported by the entire vehicle body. By the way, in order to improve the efficiency of getting in and out of a route bus, etc., we have installed an entrance / exit in the rear of the rear wheels and have lowered the entrance / exit in recent years to make the floor of the passenger compartment flattering after the entrance / exit. There is a so-called ultra-low floor that has improved For example, as shown in FIG.
The engine 101 and the power transmission system 102 are disposed on the rear end side of the vehicle body, and the driving force from the power transmission system is transmitted to the rear wheels 104 via the rear axle 103.

In the case of a bus having a frameless structure, the rear auxiliary frame 105 has a pair of side rails 10.
5 and a plurality of outriggers 107 that connect them to each other.
The rear wheel shaft 103 is connected via the. Here, the engine 101 and the power transmission system 102 are the rear auxiliary frame 105.
Will be installed on the
In the case of the bus), the accommodation area (engine room) R of the engine 101 and the power transmission system 102 is arranged so as to project above the floor.

[0005]

However, when such an ultra-low floor bus 100 is adopted in a route bus having a rear entrance / exit 106 behind the rear wheels, a passage for passengers following the rear entrance / exit 106 is secured. The space area for the interference with the engine room R of the engine and the power transmission system narrows the width N of the passenger passage. Therefore, in this case, the engine 101 and the power transmission system 102 in the rear auxiliary frame 105
It is considered that the portion 105 'on which the vehicle is mounted is biased in the vehicle width direction Y with respect to the vehicle body center line L to secure a passage for passengers having a sufficient width, but if such an offset structure is simply adopted. The part 105 'on which the engine or the like is mounted is likely to be twisted and deformed with respect to the part 105 "in front of the part 105'.

An object of the present invention is to ensure a passenger passage of a sufficient width in a lateral area of an accommodation area of an engine and a power transmission system without lowering rigidity strength, and to promote improvement of getting on / off property. It is to provide a frame structure for a low floor bus.

[0007]

In order to achieve the above-mentioned object, the invention of claim 1 is provided with a pair of side rails arranged in parallel with each other at a predetermined interval in the vehicle width direction. In a frame structure for an ultra-low floor bus formed so as to have a front part that receives a road surface reaction force from a rear wheel via a spring receiving means of an air suspension, and a rear part on which an engine and its power transmission system are mounted. A bent portion that connects the front portion and the rear portion to each other, and that biases the rear portion with respect to the front portion by a predetermined amount in the vehicle width direction with respect to the vehicle body center line,
The spring receiving means located on the rear side of the rear wheel is joined to the spring receiving member protruding toward the vehicle width direction outer side on the outer walls of the side rails of the front portion and the bent portion and the periphery of the spring receiving member. And a frame-shaped bracket, and a passenger passage is formed in a space area opposite to the bias side of the engine and its power transmission system mounted on the rear portion.

Therefore, by displacing the rear portion with respect to the front portion, spring receiving means is provided at the connecting position of the front portion and the bent portion where the torsional stress is most likely to be concentrated, and this spring receiving means is The spring receiving means is formed by a spring receiving member projecting outwardly in the vehicle width direction with respect to each side rail outer wall of the front portion and the bent portion, and a frame-shaped bracket joined to the peripheral edge of the spring receiving member. However, it not only constitutes the spring suspension means of the air suspension, but also can strengthen the torsional rigidity at the connecting position of the front part and the bent part where the torsional stress is most likely to concentrate, and the engine and its power transmission system are mounted. The rear portion of the passenger compartment can be biased, and a passenger passage can be formed in a space area opposite to the biased side.

According to a second aspect of the invention, in the frame structure for an ultra-low floor bus according to the first aspect, there is provided an outrigger integrally connecting the pair of side rails, and spring receiving means located on the rear side of the rear wheel, The front and bent side rail outer walls and the outer wall of the outrigger are formed of a spring receiving member protruding outward in the vehicle width direction and a frame-shaped bracket joined to the periphery of the spring receiving member. It is characterized by

Therefore, the spring receiving means is joined to the outer walls of the side rails of the front portion and the bent portion and the outer wall of the outrigger so as to project toward the outer side in the vehicle width direction and the peripheral edge of the spring receiving member. Since it was formed with a frame-shaped bracket that
The outrigger can more reliably promote the enhancement of the torsional rigidity at the connecting position of the front portion and the bent portion by the spring receiving means.

[0011]

1 shows a frame structure for an ultra-low floor bus to which the present invention is applied. This ultra-low floor bus frame structure is adopted as a rear frame member 3 that supports the rear wheels 2 of a route bus 1 as shown in FIG. The route bus 1 adopts a frameless structure, in which an outer wall of the body on the floor and a plurality of underfloor structures are integrally connected to each other to secure rigidity and strength. In particular, the underfloor structure of this route bus 1 includes a rear frame member 3 and
The front frame member 5 supports the front wheel 4, and the intermediate frame member m interposed between the front and rear frame member portions 5 and 3.

As shown in FIG. 1, the rear frame member 3
Is a pair of left and right side rails 6 and 7 arranged side by side in the vehicle width direction Y at intervals A, and a plurality of outriggers 12 and 1 extending in the vehicle width direction that integrally couple these side rail pairs.
3, 14, 15 and a cross member (not shown). The pair of side rails 6 and 7 are front portions 601 and 70 that receive the road surface reaction force from the rear wheels 2 via the air suspension 8.
1, an engine 9 and a clutch 10 connected to the engine 9,
A rear portion 602 for mounting a power transmission system such as the mission 11
702 and bent portions 603 and 703 that connect the front portion and the rear portion to each other.

Here, the bent portions 603 and 703 are the front portions 60.
1, 701 to the rear part 602, 702 the vehicle body center line L
It is configured to be biased to the right side (the upper side in FIG. 1) in the vehicle width direction Y by a predetermined amount δ while being parallel to (the center line in plan view). Here, the front part 6 of the side rail pair 6, 7
01 and 701 are provided with the rear wheel 2 through the air suspension 8.
Is attached, and the first outrigger 12 is attached to the front end of the same part.
Are integrally connected.

The first outrigger 12 is assembled in a partition shape by a prismatic frame and a steel plate provided between the frames, and a pair of left and right front parts 601 and 701 are provided on the rear wall surface 17 side.
Are joined. In the center of the first outrigger 12, the floor surface F is located in the area sandwiched between the left and right front parts 601 and 701.
The first cross member 23 forming the Furthermore,
At the joint between the first outrigger 12 and the front portions 601, 701, and at the position outside the front portions 601, 701 in the vehicle width direction Y, the spring receiving means 18, at the front portion of the air suspension 8,
19 are integrally joined.

The left and right spring receiving means 18 and 19 are provided in the front portion 6.
01, 701 and the spring receiving members 181, 191 made of sheet metal, which are joined to the respective outer side walls of the first outriggers 12 orthogonal to the 01, 701 and project outward in the vehicle width direction Y, and the spring receiving members 181, 191. The frame-shaped brackets 182 and 192 are joined to the outer peripheral edges of the free ends, and the gussets b that join the respective end portions of the frame-shaped brackets to the front portions 601 and 701. The joining means may be welding, rivets, bolting, bonding or the like. As shown in FIGS. 1 and 3,
The left and right spring receiving means fixes the upper end portion of the air spring S to the lower surface of each spring receiving member 181, 191. Note that the symbol d
Indicates a bead-shaped reinforcing member that strengthens the rigidity of each spring receiving member 181, 191.

Each frame-shaped bracket 18 of the left and right spring receiving means
2,192 has a relatively large vertical width (vertical width),
As a result, sufficient rigidity and strength are ensured for receiving the vertical road surface reaction force transmitted from the air spring S, and the front portion 60 is provided.
It is formed so that rigidity can be enhanced as a part of the front end portion of 1,701. The configurations of the left and right spring receiving means 18, 19 will be further described.

The left and right frame-shaped brackets 182, 192 have the same height position in the vertical direction as the upper surfaces of the front parts 601, 701, and their outer ends are joined to the first outriggers 12. Further, the spring receiving members 181, 191 are the frame-shaped brackets 18
It is arranged at a position lower in the vertical direction than 2, 192, and is joined to the lower portions of the frame-shaped brackets 182, 192.
A step plate Z is provided on the upper surfaces of the spring receiving members 181, 191.
(See FIG. 8) are integrally joined, thereby forming a step that can be used by a passenger seated in a seat (not shown) on the tire house H.

As shown in FIG. 1, the left and right frame-shaped brackets 1
The support members 21 of the shock absorber 20 are attached to the portions where the outer ends of the first and second outriggers 82 and 192 are joined. The support member 21 is formed as a vertically long bracket having a U-shaped cross section toward the rear, and the upper end of the shock absorber 20 is bolted to a lid-shaped piece at the upper end thereof. By arranging the shock absorber in the vicinity of the air spring and on the outer side in the vehicle width direction, the effect of the shock absorber is sufficiently exerted against twisting and vertical vibration of the vehicle body.

Left and right bent portions 603 on the rear side of the rear wheel 2.
A second outrigger 13 extending in the vehicle width direction Y is provided on the 703.
Are crossed together. The second outrigger 13 is assembled in a partition wall shape by a prismatic frame and a steel plate provided between the frames, and the left and right side portions thereof are the left and right bent portions 603.
703, a central projecting frame 22 is provided in the central right area, a passenger passage E (see FIG. 1) is secured in the central left area, and a floor support frame 29 is provided below the floor support frame. Is joined to the left bent portion 603.

Here, the floor support frame 29 has a structure in which a pair of square pipes are vertically arranged side by side with a predetermined interval, and one end of each is joined to the central projecting frame 22 and the other end is a left bent portion 603.
To be joined to. Floor support frame 29 and left bent portion 603
An upper gusset 30 forming a floor surface F is joined to the upper surface of the above, and a lower gusset (not shown) is also joined to the lower surface. Here, the left and right ends of the upper gusset 30 and the lower gusset (not shown) are also joined to the passage wall member 28 and the lower portion on the left side of the second outrigger 13, which will be described later, thereby strengthening the rigidity of the lower portion of the floor surface F.

The second outrigger 13 and the left and right front parts 60
Spring receiving means 24, 25 at the rear portion of the air suspension 8 are integrally joined in the vicinity of the connecting position of the left and right bent portions 603, 703. The left bent portion 603 is connected to the left front portion 601 via the front vertical column 26 while maintaining a vertical step. Here, in particular, the left turn portion 603
(The frame on the side of the entrance J in FIG. 2) was kicked down to lower the floor surface F downward. That is,
As shown in FIG. 6, the left front portion 601 has a rear end portion formed as a front vertical column 26, and a front end of the left bent portion 603 is joined to a lower portion of the front vertical column 26 to form an upper portion of the front vertical column 26. The reverse bent portion 601 ′ that is bent in the opposite direction in plan view is joined.

The rear end of the reverse bent portion 601 'is further bent and formed as a lateral bent portion 601 "outside the vehicle width direction Y. Here, the reverse bent portion 601' and the lateral bent portion 601". Respectively, the outer vertical wall members h are integrally joined to each other continuously to the lower part, and these reverse bent portions 601 ′, side bent portions 601 ″, and the outer vertical wall members h are the left outer wall of the second outrigger 13. It is to be noted that, in the lower part of the outer vertical wall member h, the square pipes 31 forming part of the second outrigger 13 are vertically arranged side by side through a predetermined space, and Square pipe 31
The upper gusset 30 and the left bent portion 60 are located in the center of the vehicle body.
Joined to 3. Further, the lower corner pipe 31 has a lower gusset and a left bent portion 603, which are not shown in the figure, on the center side of the vehicle body.
Is also joined to the floor surface F, which also strengthens the rigidity of the floor surface F.

Left bent portion 6 joined to the lower part of the front vertical column 26
The rear end of 03 is joined to the lower end of the rear vertical column 27 that forms the front end of the left rear portion 603, and the left bent portion 603 is formed at the front end of the rear vertical column 27.
The inner passage wall member 28 is joined to the upper portion of the. The upper gusset 30 serving as the floor is joined to the upper surface of the left bent portion 603. The front end of the inner passage wall member 28 has a central projecting frame 2
2 is joined to the support member 221 extending in the vertical direction. Thus, here, the front vertical column 26, the reverse bending part 601 ', the side bending part 601 ", and the outer vertical wall member h form the outer wall of the passenger passage E, and the rear vertical column 27 and the inner passage. The wall member 28 forms the inner side wall of the passenger passage E, and the upper gusset 30 forms the floor surface F, thereby ensuring the passenger passage E continuing to the rear entrance J of the route bus 1. There is.

Here, the left and right spring receiving means 24, 25
Are sheet metal spring receiving members 241 and 251 projecting outward from the side rail outer walls in the vehicle width direction Y, and a frame-shaped bracket 24 joined to the outer peripheral edge of each spring receiving member.
2, 252. Spring receiving members 241, 25
1 is a front part 601, 701, a left reverse bent part 601 ', 60
1 ″, the right bent portion 703, and the second outrigger 13 are joined together and project outwardly in the vehicle width direction. Further, the frame-shaped bracket 242 is provided on the outer circumference of the free ends of the spring receiving members 241 and 251. , 252 are joined together.
The front ends of 42 and 252 are vertical frames 2 on the front 601 side.
6, or the front portion 701, and reinforcing gussets g are joined to the respective upper end surfaces. Frame bracket 24
The rear end portions of the 2, 252 are joined to the left and right outer side walls of the second outrigger 13.

As shown in FIG. 1 and FIG. 3, the rear left and right spring receiving means 24, 25 bring the upper ends of the air springs S into contact with the lower surfaces of the spring receiving members 241, 251 as well as four bolt holes (not shown). The air spring S is bolted using. Note that reference numeral d indicates a reinforcing frame that strengthens the rigidity of the spring receiving members 241 and 251. Left and right spring receiving means 24,
Each of the frame-shaped brackets 242 and 252 of 25 has a relatively large vertical width (vertical width), thereby ensuring a sufficient rigidity and strength to receive the vertical road surface reaction force transmitted from the air spring S. Parts 601, 701 and bent part 60
As a part of each of 3,703, it is configured so that rigidity can be enhanced.

The structure of the rear spring receiving means 24, 25 will be further described.

The left frame-shaped bracket 242 has the same height position in the vertical direction as the upper surface of the front portion 601, and the outer end is joined to the second outrigger 13. In addition, the spring receiving member 2
41 is arranged at a position lower in the vertical direction than the frame-shaped bracket 242, and is joined to the lower portion of the frame-shaped bracket 242. Next, the right spring receiving means 25 will be described. The right frame-shaped bracket 252 has the same height position in the vertical direction as the upper surface of the front portion 701, and the outer end is joined to the second outrigger 13. Further, the spring receiving member 251 is arranged at a lower position in the vertical direction than the frame-shaped bracket 252, and is joined to the lower portion of the frame-shaped bracket 252.

As shown in FIG. 1, the left and right frame-shaped brackets 2
The support members 32 of the shock absorber 20 are attached to the portions where the outer ends of the second outer triggers 42 and 252 and the second outrigger 13 are joined. The support member 32 has a U-shaped cross section toward the rear wheel side and is formed as a vertically elongated bracket, and the upper end of the shock absorber 20 is bolted to the lid-shaped piece at the upper end thereof. Front part 6 mentioned above
Left and right spring receiving means 1 arranged on the front side of 01,701
8, 19 and left and right spring receiving means 2 provided on the rear side
4, 25 are configured to receive a road surface reaction force from the rear wheel 2 via the air suspension 8 as shown in FIGS. 3 to 5.

Here, the air suspension 8 is the rear wheel 2
The rear axle 40 that pivotally supports the rear axle 40, a pair of suspension arms 41 that are integrally connected to the left and right of the rear axle 40 and are long in the front-rear direction, and spring receivers 411 that are formed at the front and rear ends of the left and right suspension arms 41. A combined air spring S, a shock absorber 20 whose lower end is pin-connected to the outer end of each spring receiver 411 in the vehicle width direction Y, and a spherical joint 42 are formed in a V shape as a whole and a central front wall of the rear axle 40. The lower radius rod 43 connected through the rear axle 40, the speed reducers 44 arranged at the left and right ends of the rear axle 40, and the upper radius rod connected to the upper ends of the left and right speed reducers 44 through horizontal pins (not shown) and extending forward. And 45.

Here, in FIG. 3, the upper end of each air spring S has front and rear, left and right spring receiving means 18, 19, 24,
It is bolted to the lower wall of 25. The tips of the left and right upper radius rods 45 are bolted to the upper joints of the first outriggers 12 via the lateral pins and the joints 46, and the left and right tips of the lower radius rods 43 are attached to the first outriggers 12 via the lateral pins and the joints 47. It is bolted to the lower joint. With these upper and lower radius rods,
The rear axle 40 and the rear wheel 2 are vertically movably coupled to the vehicle body. Further, the left and right rear axle arms 41 and the air springs S buffer the vertical vibration, and the shock absorbers 20 absorb the vertical vibration. ing.

The left and right reduction gears 44 here are for reducing the rotational force received by the rear axle 40 via the differential 48 and transmitting it to the rear wheels 2 at the upper position. The outer diameter shape of the storage part of the differential 48 of 40 is made small, and thereby the floor surface F can be lowered. As shown in FIGS. 1 and 6, the left rear portion 602 has a front end joined to the rear vertical column 27, and the outrigger 15 is joined to the rear end via a bracket 33. As shown in FIGS. 1 and 7, the right rear portion 702 has a front end joined to the right bent portion 703, and the bumper 15 is joined to the rear end via a bracket 33.

The left and right rear parts 602 and 702 are located at the central positions thereof, and the third outrigger 14 and the second cross member 35 are provided.
Are integrally connected by the third cross member 36 at the rear position. Third outrigger 1
4 is formed by assembling a plurality of square pipes into a long frame shape,
When viewed from the front-rear direction of the vehicle, it is formed into a substantially trapezoidal shape, and each member is made to be a part of a main member when the engine room is formed.

At the center of the lower portion of the third outrigger 14, engine support brackets 35 at the left and right ends of the second cross member 35 are provided.
1 are integrally connected, and this also enhances the rigidity. Here, the power transmission system such as the engine 9, the clutch 10 and the transmission 11 is mounted on the left and right rear parts 602 and 702 via the second and third cross members 35 and 36. In this case, the center line L1 of the power transmission system is arranged on the right side of the vehicle body center line L in the vehicle width direction Y by a predetermined amount δ.

Therefore, the passenger passage E having a sufficient width M can be formed in the lateral region of the engine room R opposite to the biased side, and the efficiency of getting on and off can be promoted. Moreover, here, due to the offset structure, the right front portion 701 where the torsional stress is most likely to be concentrated
The spring receiving means 25 on the right side is arranged at the connecting position of the bent portion 703 on the right side and the bent portion 703 on the right side.
The spring receiving member 251 is joined to each outer side wall of the bent portion 703 and protrudes outward in the vehicle width direction Y, and the frame-shaped bracket 252 is joined to the peripheral edge of the spring receiving member. Therefore, the spring receiving member 251 and the frame-shaped bracket 252 having a large vertical width can sufficiently enhance the joint rigidity between the front portion and the bent portion, and in particular, the torsional rigidity can be surely enhanced, and the ultra-low offset structure can be achieved. The durability of the floor bus frame can be improved.

[0035]

According to the first aspect of the present invention, the spring receiving means is provided at the connecting position of the front portion and the bent portion where the torsional stress is most likely to be concentrated, and the spring receiving means is formed into the spring receiving member and the frame shape. Since it is formed with the bracket, this spring receiving means not only constitutes the spring receiving means of the air suspension, but it is possible to strengthen the torsional rigidity of the connecting position of the front part and the bent part where the torsional stress is most likely to concentrate, Moreover, the rear portion on which the engine and its power transmission system are mounted is biased, and the passenger passage is formed in the space area opposite to the bias side. For this reason,
The torsional rigidity of the connecting position between the front part and the bent part can be reliably strengthened, the durability of the vehicle body can be improved, and the passengers with a sufficient width on the side of the accommodating area of the engine and its power transmission system. The width of the passage can be secured, and the efficiency of getting on and off can be promoted.

According to a second aspect of the invention, in the frame structure for an ultra-low floor bus according to the first aspect, in particular, the spring receiving member is formed by joining the spring receiving means to the outer walls of the front portion, the bent portion and the outrigger. Since it is formed of the frame-shaped bracket and the frame-shaped bracket, the outrigger here can more reliably promote the strengthening of the torsional rigidity at the connecting position of the front portion and the bent portion by the spring receiving means. Therefore, the torsional rigidity at the connecting position of the front portion and the bent portion can be more reliably strengthened.

[Brief description of drawings]

FIG. 1 is a plan view of an ultra-low floor bus frame structure as one embodiment of the present invention.

FIG. 2 is a side view of a route bus including the frame structure for ultra-low floor buses shown in FIG.

FIG. 3 is a plan view of an air suspension of a route bus including the frame structure for the ultra-low floor bus of FIG.

4 is a perspective view of an air suspension of a route bus equipped with the frame structure for the ultra-low floor bus of FIG. 1. FIG.

FIG. 5 is a rear view of a rear axle of a route bus including the frame structure for the ultra-low floor bus of FIG.

FIG. 6 is a side view of a left side frame used in the frame structure for an ultra-low floor bus shown in FIG.

7 is a side view of a right side frame used in the frame structure for an ultra-low floor bus in FIG.

8 is a cutaway exploded perspective view of a floor of a bus including the frame structure for ultra-low floor buses of FIG.

FIG. 9 is a schematic cutaway plan view of a conventional frame structure for an ultra-low floor bus.

[Explanation of symbols]

1 route bus 2 rear wheels 3 Rear frame member 4 front wheels 5 Front frame member 6 side rails 7 Side rail 8 air suspension 12 Outrigger 13 Outrigger 14 Outrigger 18 Spring receiving means 19 Spring receiving means 24 Spring receiving means 25 Spring receiving means 251 Spring receiving member 252 Frame bracket 601 front 701 front 602 rear 702 rear 603 Bent section 703 Bent section δ predetermined amount E Passage for passengers L body center line S air spring Y vehicle width direction

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuya Hashimoto No. 1 Enjo-cho Dojo, Toyama Prefecture, inside Mitsubishi Motor Corporation Bus Manufacturing Co., Ltd. (72) Inventor Masahiko Nakanishi No. 1 Enchu-cho, Enjo-gun, Toyama Prefecture Motor Vehicle Bus Manufacturing Co., Ltd. (56) References JP-A-8-142911 (JP, A) JP-A-8-310439 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B62D 31/02 B62D 21/11 B62D 25/20

Claims (2)

(57) [Claims] 1. A pair of side rails arranged in parallel with each other in the vehicle width direction at predetermined intervals, wherein the pair of side rails receives a road surface reaction force from a rear wheel via a spring receiving means of an air suspension. In an ultra-low-floor bus frame structure formed so as to have a front portion and a rear portion on which an engine and its power transmission system are mounted, a front portion and a rear portion are connected to each other, and a rear portion is connected to the front portion. A spring receiving means located at the rear side of the rear wheel is provided on each side rail outer wall of the front portion and the bending portion in the vehicle width direction. It is formed of a spring bearing member protruding outward and a frame-shaped bracket joined to the periphery of the spring bearing member, and is opposite to the bias side of the engine and its power transmission system mounted on the rear portion. Forming passenger passages in the space A frame structure for ultra-low floor buses characterized by being made. 2. The frame structure for an ultra-low floor bus according to claim 1, further comprising an outrigger integrally connecting the pair of side rails, the spring receiving means located on the rear side of the rear wheel, the front portion and the folding portion. It is characterized in that it is formed by a spring receiving member projecting outwardly in the vehicle width direction on each side rail outer wall of the curved portion and an outer side wall of the outrigger, and a frame-shaped bracket joined to the periphery of the spring receiving member. Frame structure for ultra-low floor buses.