Patent Description:
Generally, a rear lower (or a rear lower member) of a vehicle forms a rear connection structure of a vehicle body frame so as to absorb an impact from a rear collision and safely protect the vehicle.

To this end, one side portion of the rear lower includes a plurality of reinforcing members protruding and bent forward/backward to increase rigidity, and a rear side member, a spring seat/sub-frame bracket, and a rear side panel are applied to the one side portion thereof so that the one side portion thereof is formed by integrating related parts including a bracket through a bonding process.

In particular, the rear lower also provides an engagement structure for a rear wheel suspension, thereby providing a support member welding structure on one side of the spring seat and a side surface of the rear lower using the plurality of reinforcing members.

However, since the rear lower is formed in a bonding structure of a plurality of parts using a rear lower panel and the plurality of reinforcing members, a complex structure and a weight increase may be caused and defects in a welded portion may occur.

For example, the rear lower is formed of about ten parts, and eight parts are applied as reinforcing members for rigidity. Paradoxically, since such a large number of reinforcing members increase a weight and a material cost and require a coupling structure between panels using welding, degradation in rigidity support force for a rear lower portion also occurs.

In particular, when the rear lower is mounted on the rear wheel suspension, an offset amount between a suspension mounting structure and parts of a side sill and/or a rear side member, which are major components of the vehicle body frame, is present, and the offset amount inevitably makes rigidity of the rear lower portion more vulnerable.

From e.g. <CIT> a component integration type rear lower according to the preamble of claim <NUM> and a vehicle body frame according to the preamble of claim <NUM> are known. Further, from <CIT>, <CIT> or <CIT>, vehicle body structures are known.

Exemplary embodiments of the present disclosure relate to a vehicle body frame. Particular embodiments relate to a vehicle body frame in which a rear lower to which a rear connection structure is applied is manufactured in a component integration type structure by die-casting so that the number of parts is extremely reduced and which is easily modified according to a design intent of a purpose built vehicle (PBV).

An embodiment of the present disclosure is directed to a vehicle body frame in which a weight reduction and a reduction in material cost are achieved due to a simplified structure such that an entire rear connection structure of the side sill and a rear side member is formed with a rear lower in a component integration type structure using die-casting without an application of a plurality of reinforcing materials and, in particular, rigidity of a coupled torsion beam axle (CTBA) is secured in a CTBA mounting structure using the rear lower, and a component integration type rear lower, which is easily modified according to a design intent of a purpose built vehicle (PBV) due to formability of the die-casting according to a size of the rear lower, is applied.

Other advantages of embodiments of the present disclosure can be understood by the following description and become apparent with reference to the embodiments of the present disclosure. Also, it is obvious to those skilled in the art to which the present disclosure pertains that the features and advantages of the present disclosure can be realized by the means as claimed and combinations thereof.

The present invention provides a component integration type rear lower with the features according to claim <NUM> and a vehicle body frame with the features according to claim <NUM>. Further preferred embodiments of the component integration type rear lower and the vehicle body frame are described in the respective dependent claims.

As an exemplary embodiment, the body frame may be made of aluminum and may be molded by die-casting so that the front-rear connection member, the bush mounting member, and the CTBA mounting member may be integrated.

As an exemplary embodiment, the front-rear connection member may include a center connector on which the side sill is placed from the top on an upper surface open space portion extending from the end portion of one side, and a rear connector which extends from the end portion of the other side to an open space and in which the rear side member is fitted in an upper surface of the open space.

As an exemplary embodiment, the rear connector may form an inner wall in a lateral direction with respect to an upper surface in which the rear side member is fitted so as to allow an end surface of the rear side member to be pressed against.

As an exemplary embodiment, the bush mounting member may include a bush mounting hole drilled in a center connector extending from the end portion of one side to form an upper surface open space so as to allow the side sill to be mounted from the top.

As an exemplary embodiment, the CTBA mounting member may include a trailing arm connector protruding from the end portion of one side to form a lateral open space so as to allow a partial portion of the CTBA to be fitted at a lateral portion, a spring seat protruding from a lower surface of the end portion of the other side to form a lower surface open space so as to allow an upper portion of the chassis spring to be fitted from the top, and a shock absorber connector forming a lateral open space at a side surface of the end portion of the other side so as to allow an upper portion of the shock absorber to be fitted in a lateral portion.

As an exemplary embodiment, a rear lower hole for a screw engagement with a bolt engaged with the partial portion of the CTBA may be drilled in the trailing arm connector.

As an exemplary embodiment, the side sill may be formed in an extruded material structure.

As an exemplary embodiment, the rear lower may be made of aluminum and may be molded by die-casting so that the front-rear connection member, the bush mounting member, and the CTBA mounting member may be integrated with the body frame.

As an exemplary embodiment, the front-rear connection member may fix the side sill and the rear side member using an engagement member.

As an exemplary embodiment, the engagement member and the side sill, and the engagement member and the rear side member are fixed by a flow drill screw (FDS) method.

As an exemplary embodiment, the front-rear connection member may include a center connector in which a partial portion of the side sill is placed from the top in an upper surface open space portion extending from the body frame in a connection section of the side sill, and a rear connector in which the body frame is extended to an open space so that a partial portion of the rear side member is fitted on an upper surface of the open space in a connection section of the rear side member.

As an exemplary embodiment, an end portion of the rear side member may be in close contact with an inner wall of the rear connector.

As an exemplary embodiment, a space of the side sill may be divided by partition ribs fixed to the center connector of the rear lower by the FDS method, and the center connector may extend from the end portion of one side to be formed as an upper surface open space so as to allow the side sill to be placed from the top.

As an exemplary embodiment, the rear side member may form an open rectangular cross-sectional structure or a closed rectangular cross-sectional structure.

As an exemplary embodiment, the bush mounting member may include a bush mounting hole fixed by a bush shaft in a state in which the bush is fitted in, and in the connection section of the side sill, the bush mounting hole may be formed by being drilled in the center connector extending from the body frame to the upper surface open space in which a partial portion of the side sill is placed from the top.

As an exemplary embodiment, the rear wheel suspension may include a CTBA, a chassis spring, and a shock absorber, and the CTBA mounting member may be engaged with one or more among the CTBA, the chassis spring, and the shock absorber.

As an exemplary embodiment, the CTBA mounting member may include a trailing arm connector protruding from a side surface of the body frame to form a lateral open space in which a trailing arm of the CTBA is fitted in a side portion in the connection section of the side sill, a spring seat protruding from a lower surface of the body frame to form a lower surface open space in which an upper portion of the chassis spring located in a spring seating portion of the CTBA is fitted from the top in the connection section of the rear side member, and a shock absorber connector recessed in a side surface of one side of the body frame to form a lateral open space in which an upper portion of the shock absorber is fitted in a side portion in the connection section of the rear side member.

As an exemplary embodiment, the trailing arm connector may form a rear lower hole which is screw-coupled to a bolt fixed to the trailing arm, and the spring seat may be formed in a cup-shaped structure which surrounds an outer diameter of a spring cup provided in the upper portion of the chassis spring.

As an exemplary embodiment, the side sill may include a left side sill and a right side sill, and a vehicle width including the battery space may be formed by as much as a separation distance between the left side sill and the right side sill.

As an exemplary embodiment, the left side sill and the right side sill may be connected by a center extruded material crossing the vehicle width.

Exemplary embodiments of the present disclosure will be described below in more detail with reference to the accompanying drawings, and these embodiments are examples of the present disclosure and the present disclosure is not limited to these embodiments.

Referring to <FIG>, the vehicle body frame <NUM> includes a side connection member <NUM> which is formed of a side sill <NUM> and a rear side member <NUM>. In this case, in the vehicle body frame <NUM>, a front side member (not shown) is connected in front of the side sill <NUM>.

Specifically, in the side connection member <NUM>, a rear lower <NUM> connects the side sill <NUM> to the rear side member <NUM>, and left/right side sills 30A and 30B are fixed using a center extruded material <NUM>.

For example, the rear lower <NUM> forms a front-rear connection member (or an entire rear connection structure) which connects the side sill <NUM> to the rear side member <NUM>.

Thus, the rear lower <NUM> is formed of a left rear lower and a right rear lower, the left rear lower connects the left side sill 30A of the side sill <NUM> to a left rear side member 40A of the rear side member <NUM>, and the right rear lower connects the right side sill 30B of the side sill <NUM> to a right rear side member 40B of the rear side member <NUM>.

In particular, each of the left rear lower and the right rear lower of the rear lower <NUM> is manufactured by a die-casting method using an aluminum material, and thus the rear lower <NUM> is characterized as a component integration type rear lower <NUM> which is formed of one part to which a separate reinforcing member is not applied.

For example, the side sill <NUM> is formed of the left side sill 30A and the right side sill 30B, and the left side sill 30A and the right side sill 30B are connected by the center extruded material <NUM>. In this case, the left side sill 30A and the right side sill 30B form left/right lower side surfaces in an intermediate section of the vehicle and are spaced apart from each other to form a battery space width Lb. The center extruded material <NUM> crosses the battery space width Lb to connect the left/right side sills 30A and 30B and is provided as two or more center extruded materials spaced apart from each other by an interval.

In particular, each of the left side sill 30A and the right side sill 30B may be formed in a structure of an extruded material such as the center extruded material <NUM> to have enhanced rigidity and enhanced durability. In this case, the extruded material is made of aluminum.

Thus, the side sill <NUM> forms a center frame of the vehicle body frame <NUM> with an integrated structure of the extruded material.

Therefore, an end portion of one side of the left side sill 30A of the side sill <NUM> is assembled with an engagement member <NUM> (see <FIG>) at the left rear lower of the rear lower <NUM>, and an end portion of one side of the right side sill 30B of the side sill <NUM> is assembled with the engagement member <NUM> (refer to <FIG>) at the right rear lower of the rear lower <NUM>.

For example, the rear side member <NUM> is formed of the left rear side member 40A and the right rear side member 40B, and the left rear side member 40A and the right rear side member 40B form left/right lower side surfaces in a rear section of the vehicle. In this case, end portions of one side of the left/right rear side members 40A and 40B are connected to a rear bumper back beam <NUM> which is a component of a rear bumper (not shown).

In particular, a cross section with a hollow inner space formed by welding two panels is formed at each of the left rear side member 40A and the right rear side member 40B. In this case, each of the left/right rear side members 40A and 40B is made of aluminum.

In addition, the rear side member <NUM> is formed in an open rectangular cross-sectional shape of "<IMG>" or a closed rectangular cross-sectional shape of "<IMG>" (see <FIG>) and is formed of the left rear side member 40A and the right rear side member 40B.

In particular, an end portion of one side of the left rear side member 40A of the rear side member <NUM> is assembled with the engagement member <NUM> (see <FIG>) at the left rear lower of the rear lower <NUM>, and an end portion of one side of the right rear side member 40B of the rear side member <NUM> is assembled with the engagement member <NUM> (refer to <FIG>) at the right rear lower of the rear lower <NUM>.

Meanwhile, referring to <FIG>, the rear lower <NUM> is formed of a gently curved body frame <NUM>, and the front-rear connection member, a bush mounting member (or a bush mounting structure), and a CTBA mounting member (or a CTBA mounting structure) are integrally formed on the body frame <NUM>, and thus the rear lower <NUM> is characterized as the component integration type rear lower <NUM>.

For example, the body frame <NUM> is formed of a left vertical body 21B and a right vertical body 21C which are vertical with respect to a horizontal body 21A to form an "H" cross-sectional structure, and one side and the other side of the body frame <NUM> form a height difference of a rear lower ground clearance H so that the body frame <NUM> is easily mounted on a chassis spring <NUM> and a shock absorber <NUM> of the rear wheel suspension. In this case, a position of the left vertical body 21B may be defined as a position toward an inner space of the vehicle, and a position of the right vertical body 21C may be defined as a position toward an outer space of the vehicle.

In particular, in the body frame <NUM>, an upper position b of the horizontal body 21A is located to be higher than a lower position B with respect to the left/right vertical bodies 21B and 21C, and a lower width A due to the left/right vertical bodies 21B and 21C is formed to be greater than an upper width a so that the "H" cross-sectional structure is formed in a trapezoidal shape.

For example, the front-rear connection member is integrally formed on the end portion of one side of the body frame <NUM> and includes a horizontally extended center connector <NUM>-<NUM> and a rear connector <NUM>-<NUM> which is integrally formed on an end portion of the other side of the body frame <NUM> to be extended horizontally.

For example, the bush mounting member includes a bush mounting hole <NUM> drilled in the center connector <NUM>-<NUM>. In this case, the bush mounting hole <NUM> is formed in a circular shape.

Specifically, the CTBA mounting member includes a trailing arm connector <NUM> formed to protrude horizontally from a side surface of the body frame <NUM> with an interval from the center connector <NUM>-<NUM> on one side of the body frame <NUM>, a spring seat <NUM> formed to protrude vertically from a lower surface of the body frame <NUM> with an interval from the rear connector <NUM>-<NUM> on the other side of the body frame <NUM>, and a shock absorber connector <NUM> formed as a space on a side surface of one side of the body frame <NUM> with an interval from the rear connector <NUM>-<NUM> on the other side of the body frame <NUM>.

For example, the trailing arm connector <NUM> is formed of left/right flanges protruding horizontally from the left/right vertical bodies 21B and 21C of the body frame <NUM> and surrounds portions of a trailing arm 200A of a CTBA <NUM> (see <FIG>), and the left/right flanges are drilled so as to form a female thread of a rear lower hole 25A for a screw engagement with a bolt 200B (see <FIG>).

For example, the spring seat <NUM> is formed by extending the left/right flanges protruding vertically from the left/right vertical bodies 21B and 21C of the body frame <NUM> in a cup shape (see <FIG>), and the cup shape surrounds and seats an end portion of the chassis spring <NUM> coupled to a spring cup 300A.

For example, the shock absorber connector <NUM> is formed in a structure in which the left vertical body 21B of the body frame <NUM> is pushed to and inserted into the horizontal body 21A in a portion in which the spring seat <NUM> is formed, thereby forming a side-open structure, and an upper portion of the shock absorber <NUM> (see <FIG>) is located in the side-open structure.

Meanwhile, <FIG> illustrate an example in which the rear wheel suspension is mounted on the side connection member <NUM> using the component integration type rear lower <NUM> in the vehicle body frame <NUM>.

Referring to <FIG>, the vehicle body frame <NUM> includes the side connection member <NUM> in which the rear lower <NUM> connects the side sill <NUM> to the rear side member <NUM>.

Specifically, the side connection member <NUM> fixes the side sill <NUM> and the rear side member <NUM> using the front-rear connection member of the rear lower <NUM>, fixes the bush <NUM> and the side sill <NUM> through a bush shaft 100A using the bush mounting member, and fixes the CTBA <NUM>, the chassis spring <NUM>, and the shock absorber <NUM>, which are components of the rear wheel suspension, using the CTBA mounting member.

In particular, since the rear lower <NUM> is manufactured by injection molding aluminum using a die-casting method (that is, a low pressure die-casting method), the rear lower <NUM> is easily adjusted with respect to rear lower specifications (i.e., a size and a length), and the easiness of changing the rear lower specifications satisfies a design characteristic of a purpose built vehicle (PBV) which requires a length change according to the purpose of the vehicle.

Referring to <FIG> and <FIG>, the front-rear connection member is implemented using the center connector <NUM>-<NUM> and the rear connector <NUM>-<NUM> which are formed on the body frame <NUM> of the rear lower <NUM>.

For example, the center connector <NUM>-<NUM> of the rear lower <NUM> faces upward and seats the side sill <NUM> in an open space of an upper surface extending from the end portion of one side of the rear lower <NUM>. Meanwhile, the rear connector <NUM>-<NUM> of the rear lower <NUM> extends from the end portion of the other side of the rear lower <NUM> to an open space in a " c" shape so that the rear side member <NUM> is fitted and seated in and fixed to an upper surface of the open space.

In addition, the center connector <NUM>-<NUM> and the side sill <NUM>, and the rear connector <NUM>-<NUM> and the rear side member <NUM>, are fixed using the engagement member <NUM>. In this case, a screw (or a bolt) is employed as the engagement member <NUM>, and the screw (or the bolt) is fixed to the side sill <NUM> and the rear side member <NUM> by a flow drill screw (FDS) method capable of unidirectional bonding of different materials.

For example, in the engagement member <NUM>, as shown in a section A-A and a section B-B at the center connector <NUM>-<NUM>, a plurality of screws (or bolts) pass through a surface contact portion, in which a wall surface of the center connector <NUM>-<NUM> is in contact with a wall surface of the side sill <NUM>, by the FDS method so that the center connector <NUM>-<NUM> and the side sill <NUM> are fixed. In this case, a space of the side sill <NUM> may be divided into a plurality of partition ribs <NUM> so that the side sill <NUM> has more enhanced rigidity and more enhanced durability.

For example, in the engagement member <NUM>, as shown in a cross section C-C at the rear connector <NUM>-<NUM>, a plurality of screws (or bolts) pass through a surface contact portion, in which a wall surface of the rear connector <NUM>-<NUM> is in contact with a wall surface of the rear side member <NUM>, by the FDS method so that the rear connector <NUM>-<NUM> and the rear side member <NUM> are fixed.

In particular, as shown in a cross section A-A in a state in which the side sill <NUM> is mounted on the top, an open structure of an upper surface of the center connector <NUM>-<NUM> is in close contact with the side wall of the center connector <NUM>-<NUM> to maximize support rigidity against an external force applied in a length direction (i.e., in a horizontal direction) of the rear lower <NUM>. In this case, the close contact means to have a welded portion in a surface contact state.

In addition, in the "⊂" shaped upper open space structure of the rear connector <NUM>-<NUM>, the rear side member <NUM> is fitted in an upper surface of the open space, and as shown in a cross section D-D in such an upper surface fitting state, an end portion Z of the rear side member <NUM> is in close contact with an inner wall of the rear connector <NUM>-<NUM> in an inner space of the rear connector <NUM>-<NUM>, thereby maximizing the support rigidity against the external force applied in the length direction (i.e., in the horizontal direction) of the rear lower <NUM>.

Referring to <FIG>, the bush mounting member is implemented by assembling the bush <NUM> with the center connector <NUM>-<NUM>, which is formed in the body frame <NUM> of the rear lower <NUM>, using the bush mounting hole <NUM>.

For example, the bush <NUM> is fitted in the bush mounting hole <NUM>, and the bush shaft 100A passes through a shaft hole of the bush <NUM> and crosses the partition rib <NUM> of the side sill <NUM> to be fixed by a bush cap (or a bush cap nut) connected to an end portion of the bush shaft 100A.

Therefore, as shown in a cross section E-E, a bush width Lc of the bush <NUM> is included in a side sill width (s/sill width) La of the side sill <NUM>, and an overlapping structure of the bush <NUM> and the side sill <NUM> may remove the bush width Lc from a vehicle width L formed by the left/right side sills 30A and 30B.

Thus, as shown in a cross section F-F, unlike the related art in which the bush width Lc and the s/sill width La of each of the left/right side sills are excluded in a utilization of a battery space width Lb from the vehicle width L formed of the left/right side sills 30A and 30B, in the vehicle body frame <NUM>, only the s/sill width La of each of the left/right side sills is excluded so that the battery space width Lb is expanded.

As a result, due to an increase in size of the battery space width Lb when compared with the related art, a high-voltage battery <NUM> mounted on the vehicle body frame <NUM> may increase battery capacity in the same condition when compared to the related art.

Referring to <FIG>, the CTBA mounting member is implemented by assembling the CTBA <NUM>, the chassis spring <NUM>, and the shock absorber <NUM> of the rear wheel suspension using the trailing arm connector <NUM>, the spring seat <NUM>, and the shock absorber connector <NUM> which are formed on the body frame <NUM> of the rear lower <NUM>.

For example, the CTBA <NUM> is formed in a substantially "<IMG>" shape of a spring seating portion 200C in left/right side surfaces of a straight-shaped axle body, and a trailing arm 200A formed in a bent portion of the spring seating portion 200C is fitted in a lateral open space formed in the trailing arm connector <NUM> of the rear lower <NUM>.

Then, as shown in a cross section G-G, the bolt 200B is fixed and screw-engaged with a pin hole of the trailing arm 200A through a rear lower hole 25A of the trailing arm connector <NUM> so that the CTBA <NUM> is assembled and integrated with the rear lower <NUM>.

For example, in a state in which a lower portion of the shock absorber <NUM> is engaged with a side surface of the CTBA <NUM>, an upper portion of the shock absorber <NUM> is seated in a lateral open space formed in the shock absorber connector <NUM> of the rear lower <NUM>.

Then, as shown in a cross section H-H, the upper portion of the shock absorber <NUM> is fixed by a mounting pin or the like in a state of being located in the space of the shock absorber connector <NUM> so that the chassis shock absorber <NUM> is assembled and integrated with the rear lower <NUM>.

For example, in a state in which a lower portion of the chassis spring <NUM> is seated in the spring seating portion 200C of the CTBA <NUM>, an upper portion of the chassis spring <NUM>, to which the spring cup 300A is coupled, is seated in a space formed in the spring seat <NUM> of the rear lower <NUM>.

Then, as shown in a cross section I-I, the upper portion of the chassis spring <NUM> is surrounded and seated in a cup-shaped structure of the spring seat <NUM> together with the spring cup 300A so that the chassis spring <NUM> is assembled and integrated with the rear lower <NUM>.

Referring to <FIG>, in a state in which the chassis spring <NUM> is located between the spring seating portion 200C of the CTBA <NUM> and the spring seat <NUM> of the rear lower <NUM>, the cup-shaped structure of the spring seat <NUM> swags to be coupled to an outer diameter of the spring cup 300A.

As described above, in the side connection member <NUM> applied to the vehicle body frame <NUM> according to the present embodiment, a connection section in which the side sill <NUM> constituting a frame of the intermediate section of the vehicle is connected to the rear side member <NUM> constituting a frame of the rear section of the vehicle is formed with the body frame <NUM> having a predetermined length at a height difference formed by the rear lower ground clearance H, and the rear lower <NUM>, in which the front-rear connection members (i.e., the center connector <NUM>-<NUM> and the rear connector <NUM>-<NUM>) fixing the side sill <NUM> and the rear side member <NUM> which form the battery space width Lb, the bush mounting members (i.e., the center connector <NUM>-<NUM> and the bush mounting hole <NUM>) engaged with the bush <NUM>, and the CTBA mounting members (i.e., the trailing arm connector <NUM>, the spring seat <NUM> and the shock absorber connector <NUM>) on which the rear wheel suspension is mounted are integrated with the body frame <NUM>, is included.

Therefore, the side connection member <NUM> is formed in a structure of a component integration type rear lower using die-casting so that, due to structure simplification, it is possible to reduce a weight and a material cost and secure rigidity of the CTBA <NUM>. In particular, due to moldability of the die-casting according to a size of the rear lower <NUM>, the rear lower <NUM> may be easily modified according to a design intent of a PBV.

A vehicle body frame to which a component integration type rear lower of embodiments of the present disclosure is applied implements the following actions and effects.

First, a rear lower is manufactured in a component integration type structure by die-casting and applied to a side sill and a rear side member of the vehicle body frame so that a weight reduction can be achieved due to structure simplification with respect to a rear connection structure.

Second, the component integration type rear lower is directly engaged with a coupled torsion beam axle (CTBA) and a chassis spring of a rear wheel suspension in an integrated CTBA mounting structure so that robustness of chassis mounting rigidity, which is a main path of driving noise due to transmission of a vibration caused by driving to a vehicle body, can be secured and thus driving noise reduction performance is improved.

Third, the component integration type rear lower locates a shock absorber of the rear wheel suspension inside a rear lower member in the integrated CTBA mounting structure so that a wider inner space can be secured by as much as a position movement of the shock absorber.

Fourth, the component integration type rear lower is capable of engaging a bush with a side sill in an integrated bush mounting structure so that a bush space formed between the side sills according to the related art can be removed and thus a space of a high voltage battery can be expanded when compared to the related art, thereby securing a larger battery capacity.

Fifth, the rear lower is manufactured in a component integration type structure by die-casting and applied to the rear connection structure of the vehicle body frame so that a number of reinforcing materials which are applied in the related art can be removed and thus a material cost and a mold cost according to a manufacturing of a single product can be reduced and an investment cost of a jig assembly and a weight according to a single product assembly can be reduced.

Claim 1:
A component integration type rear lower (<NUM>), comprising:
a body frame (<NUM>) having an end portion of a first side and an end portion of a second side and having a predetermined length;
a front-rear connection member (<NUM>-<NUM>, <NUM>-<NUM>) connecting a side sill (<NUM>) at the end portion of the first side and connecting a rear side member (<NUM>) at the end portion of the second side;
a bush mounting member coupling a bush (<NUM>) to the end portion of the first side; and
a coupled torsion beam axle (CTBA) mounting member (<NUM>, <NUM>, <NUM>) coupled to at least one of a CTBA (<NUM>), a chassis spring (<NUM>), or a shock absorber (<NUM>), the at least one of the CTBA (<NUM>), the chassis spring (<NUM>), or the shock absorber (<NUM>) being engaged with the end portion of the second side,
characterized by
the body frame (<NUM>) formed of a left vertical body (21B) and a right vertical body (21C) which are vertical with respect to a horizontal body (21A) to form an "H" cross-sectional structure, and
an upper position b of the horizontal body (21A) located to be higher than a lower position B with respect to the left and right vertical bodies (21B, 21C), and a lower width A due to the left and right vertical bodies (21B, 21C) formed to be greater than an upper width a so that the "H" cross-sectional structure is formed in a trapezoidal shape.