Suspension subframe structure

Provided is a suspension subframe structure that can activate a load path using an extension frame in an impact while avoiding increase in vehicle weight and also enables a suspension subframe to disengage from a vehicle body when an impact load is too large to be absorbed by the extension frame alone. The suspension subframe structure of the present invention includes a suspension subframe 110 that supports a suspension member 60 for a front wheel. The suspension subframe 110 includes: a body 111 that transmits an impact load input from a vehicle front side toward a vehicle rear side; a fixed portion 124 disposed near the body 111 and fixed to a vehicle body; and a connection portion 121 connecting the fixed portion 124 to the body 111. The connection portion 121 is provided with fragile portions 121f, 122g having a lower strength against a load in a vehicle front-rear direction than the body 111 and the fixed portion 124.

TECHNICAL FIELD

The present invention relates to a suspension subframe structure and to a vehicle-body structure of a vehicle, such as an automobile.

BACKGROUND ART

A known vehicle-body front structure includes a pair of right and left front side frames extending in a front-rear direction of a vehicle and constituting a front portion of a vehicle body and includes a suspension subframe (hereinafter, also simply referred to as a “subframe”) disposed below the front side frames for supporting right and left suspension links for front wheels.

A subframe of a vehicle-body front structure disclosed in Patent Literature 1 is formed of a U-shape opening rearward in plan view that is comprised of right and left side portions disposed below front side frames and a front side portion connecting front ends of the right and left side portions in a vehicle width direction. The subframe is fixed to the front side frames at respective rear ends of the right and left side portions. The subframe is mounted with tower members that stand upright from respective front ends of the right and left side portions and are connected to respective bottom faces of the front side frames. The tower members are mounted with a pair of extension frames that extend frontward from an intermediate position, in an up-down direction, of the tower members.

In the structure disclosed in Patent Literature 1, an impact load from the vehicle front side is distributed over a main load path where the load is directly input to the front side frames and a load path where the load is input to the front side frames via the extension frames and the tower members. As such, the structure can distribute the impact load by providing the load path that goes through the extension frames.

The above extension frame can function as a shock absorbing member that absorbs an impact load from the vehicle front side by deforming under the load. The tower member functions as a load receiving portion that receives the impact load input via the extension frame in order to ensure the impact load absorption by the extension frame.

In the vehicle-body front structure disclosed in Patent Literature 1, the extension frame is connected to an intermediate portion of the tower member. Therefore, it is necessary to make the tower member rigid in order to restrain its bending deformation under an impact load input from the vehicle front side and thus ensure sufficient shock absorbing function of the extension frame. However, making the tower member rigid often leads to increase in the vehicle weight, so that there is room for improvement in decreasing the vehicle weight.

Thus, it may be possible that the tower members are removed and instead a load path is created that runs from the extension frames through the right and left side portions of the subframe to the front side frames via the respective rear ends of the right and left side portions of the subframe. In this case, rear ends of the extension frames may be directly connected to respective front ends of the right and left side portions of the subframe that have a high rigidity in the front-rear direction. This enables the subframe to function as a load receiving portion that receives the impact load input to the extension frames from the vehicle front side, thus facilitating shock absorption by the extension frames.

Meanwhile, using the subframe, which has a high rigidity against a load in the front-rear direction, as the load path as described above may cause deformation of a vehicle cabin due to the impact load that has not been fully absorbed by the extension frames being transmitted to the vehicle cabin via the subframe. Also, deformation of the front side frames may be inhibited in the region in the vehicle front-rear direction where the high-rigidity subframe is located, which may in turn inhibit the shock absorbing function of the front side frames and thus result in deformation of the vehicle cabin.

To solve these problems, a mounting structure may be adopted that can facilitate disengagement of the subframe from the vehicle body in response to input of a large load that cannot be fully absorbed by deformation of the extension frames. For example, for vehicles mounted with a transversely mounted powertrain that rolls so as to fall rearward in response to input of an impact load from the vehicle front side, a mounting structure may be adopted that allows the subframe to disengage downward from its mounted position on the vehicle body by utilizing the rolling motion of the powertrain.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, besides the above rolling motion, the powertrain can make various motions in response to input of an impact load from the vehicle front side depending on how the powertrain is installed, such as sliding motion toward the vehicle rear side. Hence, depending on how the powertrain is installed, the above-described mounting structure utilizing the rolling motion of the powertrain may not be adopted, and in such cases a new measure is required to facilitate the disengagement of the subframe from the vehicle body.

Hence, an object of the present invention is to provide an entirely new suspension subframe structure that can effectively restrain deformation of the vehicle cabin while creating a load path that goes through the suspension subframe, in the event of an impact load being input from the vehicle front side.

Solution to Problem

The present invention to achieve the above object is a suspension subframe structure including: a suspension subframe that supports a suspension member for a front wheel, characterized in that the suspension subframe includes: a body that transmits an impact load input from a vehicle front side toward a vehicle rear side; a fixed portion disposed near the body and fixed to a vehicle body; and a connection portion connecting the fixed portion to the body, and the connection portion is provided with a fragile portion having a lower strength against a load in a vehicle front-rear direction than the body and the fixed portion.

According to this invention, when an impact load is input to the suspension subframe from the vehicle front side, breakage is facilitated at the fragile portion between the body and the fixed portion. This facilitates displacement of the body relative to the fixed portion, which in turn facilitates substantial disengagement of the suspension subframe from the vehicle body. This restrains a large impact load from the vehicle front side from being transmitted to the vehicle cabin via the suspension subframe and also restrains the suspension subframe from inhibiting deformation of the vehicle body, such as the front side frame, in the region in the vehicle front-rear direction where the suspension subframe is located. Hence, the present invention can effectively restrain deformation of the vehicle cabin by breaking the load path going through the suspension subframe when an input load is relatively large, while distributing the input load by using that load path when the load is relatively small.

The above breakage in the fragile portion can occur under an input load in the vehicle front-rear direction. This means that the above disengagement of the suspension subframe from the vehicle body does not require an input load in the up-down direction from the powertrain. Hence, the present invention can effectively restrain deformation of the vehicle cabin as described above, regardless of how the powertrain is installed.

In the present invention, preferably, an extension frame extending from a front end of the body toward the vehicle front side is connected with the suspension subframe.

According to this invention, when an impact load is input to the extension frame from the vehicle front side, the body of the suspension subframe connected to the rear end of the extension frame functions as a load receiving portion, which ensures effective shock absorption by deformation of the extension frame.

If the suspension subframe remains fixed to the vehicle body in the event of input of a load greater than or equal to a load that can be absorbed by the extension frame (hereinafter also referred to as an “impact load greater than or equal to a predetermined load”), a residual impact load would be transmitted to the vehicle cabin via the body of the suspension subframe.

According to the present invention, on the contrary, the suspension subframe is broken at the fragile portion and thus substantially disengages from the vehicle body, which can effectively restrain the impact load that fails to be absorbed by the extension frame from being transmitted to the vehicle cabin.

In the present invention, preferably, the fixed portion is disposed laterally to the body.

According to this invention, the fixed portion is disposed beside the body, which realizes a compact structure of the suspension subframe in the up-down direction. Hence, the present invention can effectively restrain deformation of the vehicle cabin as described above while improving layout flexibility in the up-down direction.

In the present embodiment, preferably, the body has a closed cross-section continuous in the vehicle front-rear direction, the fixed portion is a sleeve member into which a bolt for fastening to the vehicle body is inserted, and the connection portion is a plate member joined to an end face of the sleeve member with the bolt.

According to the present invention, the connection portion is composed of a plate member that has a lower strength than the body, which has a closed cross-section continuous in the vehicle front-rear direction, and the fixed portion, which is composed of a sleeve member, and thus the present invention can effectively facilitate breakage of the connection portion. Hence, as described above, the present invention can effectively restrain deformation of the vehicle cabin as the invention allows for breakage of the load path going through the suspension subframe when an input load is relatively large, while distributing the input load by using that load path when the load is relatively small.

In the present embodiment, preferably, a reinforcement member is mounted at a portion of the connection portion located between the fixed portion and the body, and the fragile portion is provided at a portion of the connection portion located closer to the fixed portion relative to the reinforcement member.

According to the present invention, the connection portion is mounted with the reinforcement member. This facilitates, in response to input of an impact load from the vehicle front side, breakage of the fragile portion at a portion of the connection portion located closer to the fixed portion relative to the reinforcement member, while assuring favorable mounting strength for the suspension subframe in normal conditions.

Additionally, since the reinforcement member is disposed between the body and the fixed portion, interference between the fixed portion and the reinforcement member can be readily avoided when the body is displaced toward the vehicle rear side relative to the fixed portion in response to input of an impact load from the vehicle front side. Hence, the present invention can realize effective breakage of the fragile portion that utilizes the displacement of the body relative to the fixed portion.

In the present embodiment, preferably, the fragile portion is provided with a breakage facilitating portion that facilitates breakage to allow the fixed portion to be displaced toward the vehicle front side relative to the body when a load is input to the body from the vehicle front side.

According to this invention, when an impact load is input to the body of the suspension subframe from the vehicle front side, the breakage facilitating portion provided to the fragile portion facilitates breakage to allow the fixed portion to be displaced toward the vehicle front side relative to the body, thus enabling the suspension subframe to disengage from the vehicle body so as to slide toward the vehicle rear side.

Advantageous Effect of Invention

The suspension subframe structure of the present embodiment can effectively restrain deformation of the vehicle cabin while creating a load path that goes through the suspension subframe, in the event of an impact load being input from the vehicle front side.

DESCRIPTION OF EMBODIMENT

A detailed description will now be given of a suspension subframe structure according to an embodiment of the present invention.

Referring toFIGS.1to3, a description will be given of a front vehicle-body structure1including the suspension subframe structure of the present embodiment.

As shown inFIGS.1and2, the front vehicle-body structure1includes a pair of right and left front side frames20,20extending in a vehicle front-rear direction, a dash cross30disposed along a front face of a dash panel (not shown) and connecting the front side frames20,20, and a suspension subframe structure100disposed below the front side frames20,20.

The vehicle of the present embodiment uses a front-engine rear-wheel drive (FR) system.

A powertrain4including a longitudinally mounted engine41and a transmission42connected to a rear side of the engine41is disposed in an engine room E between the front side frames20,20(seeFIG.3).

Each of the front side frames20,20includes a front linear portion21extending frontward from the dash cross30substantially horizontally, an inclined portion22extending rearward from a rear end of the front linear portion21obliquely downwardly, and a rear linear portion23extending further rearward from a lower end of the inclined portion22substantially horizontally.

The front linear portion21of each of the front side frames20,20is composed of an inner panel24positioned on a vehicle-width-direction inner side and an outer panel25positioned on a vehicle-width-direction outer side; these panels24,25are joined to each other in the vehicle width direction. The inner panel24has a cross-section of a hat-shaped profile that opens toward the vehicle-width-direction outer side, and the outer panel25has a cross-section of a hat-shaped profile that opens toward the vehicle-width-direction inner side. These panels24,25extend in the vehicle front-rear direction. The outer panel25and the inner panel24are joined to each other at their upper and lower edge portions. This gives the front linear portion21itself a closed cross-section that is continuous in the vehicle front-rear direction.

The inclined portion22of each of the front side frames20,20has a cross-section of a hat-shaped profile that opens upward. The inclined portion22is disposed such that its rear portion is lowered along the shape of the dash panel31, and an upper edge portion of the inclined portion22is joined to the dash panel31. This results in a closed cross-section continuous in the vehicle front-rear direction being formed between the inclined portion22and the dash panel31(seeFIG.8).

The rear linear portions23,23of the front side frames20,20are connected at their rear ends to a front end of a floor frame (not shown) extended in the vehicle front-rear direction. A floor panel (not shown) is joined onto the rear linear portions23,23and the floor frame, and a front end edge of the floor panel is connected to the dash panel. The rear linear portions23,23and the floor frame each have a cross-section of a hat-shaped profile that opens upward, thus forming a closed cross-section continuous in the vehicle front-rear direction between the floor panel and each of the rear linear portions23,23and the floor frame.

A main crash can53is connected to a front end of each of the front side frames20,20via a set plate51and a mounting plate52. The main crash can53is formed of a cylindrical body or the like that absorbs an impact load from the vehicle front side. A bumper reinforcement54extending in the vehicle width direction is attached to front ends of the pair of right and left main crash cans53,53.

Referring toFIG.3in addition toFIGS.1and2, the above suspension subframe structure100will be described. The suspension subframe structure100includes: a pair of right and left suspension subframes110,110that are disposed below the front side frames20,20and respectively support lower arms60,60as suspension members for front wheels; a pair of right and left extension frames130,130that are joined to front ends of the respective suspension subframes110,110and extend toward the vehicle front side; and first to third cross members140,150,160that each connect the right and left frames110,110,130,130.

Sub crash cans55,55extend frontward from front ends of the respective extension frames130,130. A sub bumper reinforcement58extending in the vehicle width direction is provided in front of the sub crash cans55,55. The right and left sub crash cans55,55are connected to each other via the sub bumper reinforcement58.

Each of the lower arms60,60supported by the respective suspension subframes110,110includes a front arm portion61that extends substantially parallel to the vehicle width direction and a rear arm portion62that extends substantially horizontally from a vehicle-width-direction intermediate portion of the front arm portion61toward the vehicle-width-direction inner side and toward the rear side. The lower arm60is, as a whole, formed substantially in an L-shape in plan view.

The lower arm60is formed, in its inner portion in the vehicle width direction, with a front connecting portion61aand a rear connecting portion62a. The front connecting portion61ais connected to a relatively front portion of the suspension subframe110, and the rear connecting portion62ais connected to a relatively rear portion of the suspension subframe110. The front connecting portion61ais provided at a vehicle-width-direction inner side end of the front arm portion61, and the rear connecting portion62ais provided at a rear end of the rear arm portion62.

The front connecting portion61aof the front arm portion61is supported by a front bracket63mounted across a front end of the suspension subframe110and a rear end of the extension frame130such that the front connecting portion61acan pivot about an axis extending in the vehicle front-rear direction. The rear connecting portion62aof the rear arm portion62is supported by a rear bracket64mounted on the suspension subframe110such that the rear connecting portion62acan pivot about an axis extending in the vehicle front-rear direction.

As shown inFIGS.4and5, the suspension subframe110includes a body111supporting the lower arm60. The rear end of the extension frame130is connected to a front end112of the body111of the suspension subframe110. A rear end113of the body111is fixed to the front side frame20via a rear vehicle body mounting portion X3(described later).

The body111of the suspension subframe110is an elongated portion disposed to extend in the vehicle front-rear direction. The body111is composed of an upper member114having a cross-section of a squared U-shape that opens downward and a lower member115having a cross-section of a squared U-shape that opens upward. A lower edge portion of the upper member114and an upper edge portion of the lower member115are joined to each other by, for example, welding. Between the upper member114and the lower member115, the body111forms a closed cross-section continuous in the vehicle front-rear direction.

Specifically, the upper member114includes a top face114a, and an outer side face114band an inner side face114cin the vehicle width direction. The lower member115includes a bottom face115a, and an outer side face115band an inner side face115cin the vehicle width direction. The outer side faces114b,115band the inner side faces114c,115cof the upper member114and the lower member115are respectively joined to each other, thereby forming a closed cross-section continuous in the vehicle front-rear direction (seeFIG.5(d)).

The front end112of the body111of the suspension subframe110is formed with an opening116(seeFIG.5(a)) that is delimited by the upper member114and the lower member115.

As shown inFIGS.5(a) and5(c), similarly to the body111of the suspension subframe110, the extension frame130is composed of an upper member131on the upper side and having a cross-section of a squared U-shape that opens downward and a lower member132on the lower side and having a cross-section of a squared U-shape that opens upward; this gives the extension frame130itself a closed cross-section that is continuous in the vehicle front-rear direction.

Specifically, the upper member131includes a top face131a, and an outer side face131band an inner side face131cin the vehicle width direction. The lower member132includes a bottom face132a, and an outer side face132band an inner side face132cin the vehicle width direction. The outer side faces131b,132band the inner side faces131c,132cof the upper member131and the lower member132are respectively joined to each other, thereby forming a closed cross-section continuous in the vehicle front-rear direction (seeFIG.5(c)).

A rear end133of the extension frame130has a smaller outer diameter than that of a portion of the extension frame130located frontward of the rear end133.

The frames110,130are connected to each other by the rear end133of the extension frame130being inserted into the opening116(seeFIG.5(a)) of the front end112of the body111of the suspension subframe110. The frames110,130are joined to each other by, for example, welding at a connection portion80between the frames110,130. This makes the extension frame130and the suspension subframe110integrally continuous in the vehicle front-rear direction (seeFIG.5(a)).

In the present embodiment, the extension frame130is given a lower rigidity against an input load in the vehicle front-rear direction than that of the suspension subframe110. This allows the extension frame130and the suspension subframe110, which are continuous in the vehicle front-rear direction, to perform different functions. Specifically, this allows the suspension subframe110, which is located on the rear side and has a relatively high rigidity, to serve as a load receiving portion and allows the extension frame130, which is located on the front side and has a relatively low rigidity, to perform a load absorbing function.

Now a description will be given of the first to third cross members140,150,160disposed between the right and left suspension subframes110,110and extension frames130,130of the suspension subframe structure100, with reference toFIG.3.

The frame-like first cross member140is attached to front ends134,134of the pair of right and left extension frames130,130. The first cross member140extends substantially linearly so as to connect the front ends134,134of the extension frames130,130in the vehicle width direction.

The connection portion80between the right suspension subframe110and the right extension frame130and a connection portion between the left suspension subframe110and the left extension frame130are connected to each other via the second cross member150.

The second cross member150includes: a front side portion151that extends in the vehicle width direction between the right and left extension frames130,130so as to connect these frames130,130; right and left side portions152,152that extend toward the vehicle rear side respectively from right and left ends of the front side portion151; and a reinforcement frame153that is disposed between the right and left side portions152,152. The reinforcement frame153includes a transverse frame portion154that extends in the vehicle width direction between rear ends of the right and left side portions152,152so as to connect these rear ends and a longitudinal frame portion155that extends in the vehicle front-rear direction between the transverse frame portion154and the front side portion151so as to connect these portions154,151.

As shown inFIG.5(b), the front side portion151is composed of a front side portion upper member156that extends in the vehicle width direction and has a cross-section of a squared U-shape opening downward and a plate-like lower member159that closes an open end of the front side portion upper member156. The lower member159has a wider width in the vehicle front-rear direction than that of the front side portion upper member156and protrudes rearward relative to the front side portion upper member156. The lower member159is disposed over a region in the vehicle front-rear direction that spans the extension frame130and the suspension subframe110.

The front side portion upper member156includes a top face156a, a front face156b, and a rear face156c. The front side portion upper member156is disposed on a top face159aof the lower member159with the front face156bdisposed along a front end159bof the lower member159. Lower ends of the front face156band the rear face156care joined to the top face of the lower member159, thereby forming a closed cross-section continuous in the vehicle width direction between the front side portion upper member156and the lower member159.

As shown inFIG.5(c), the top face156aof the front side portion upper member156is joined, at its respective edge portions156d,156din the vehicle width direction, to the top faces131a,131aof the extension frames130,130.

As shown inFIGS.5(c) and5(d), respective ends159c,159cof the lower member159in the vehicle width direction are joined to the bottom faces132a,132aof the extension frames130,130and the bottom faces115a,115aof the bodies111,111of the suspension subframes110,110.

As shown inFIG.5(d), the right and left side portions152,152are composed of the aforementioned lower member159and respective right and left side upper members157,157that are integral and continuous with the aforementioned front side portion upper member156. The right and left side upper members157,157are disposed to extend in the vehicle front-rear direction and are continuous with the front side portion upper member156at their front ends. Thus, the front side portion upper member156and the right and left side upper members157,157as a whole form a U-shape in plan view that opens toward the vehicle rear side (seeFIG.3).

An inner edge portion157bof each of the right and left side upper members157,157is located lower than its outer edge portion157ain the vehicle width direction. Each of the right and left side upper members157,157includes an inclined portion157cthat gradually lowers as it goes from the outer edge portion157ato the inner edge portion157b.

The inner edge portions157b,157bof the respective right and left side upper members157,157are joined to the top face159aof the lower member159, and the outer edge portions157a,157aare respectively joined to the top faces114a,114aof the bodies111,111of the suspension subframes110,110.

Thus, a closed cross-section continuous in the vehicle front-rear direction is formed by each of the right and left side upper members157,157, the lower member159, and the inner side faces114c,115cof each of the bodies111,111of the suspension subframes110,110.

As shown inFIG.3, each of the right and left side portions152,152of the second cross member150has a width that gradually increases toward the vehicle front side in plan view. Thus, reinforcement portions151A,151A having an arc contour are formed at respective corners between the front side portion151and the right and left side portions152,152. This increases the rigidity of the lower arm60of the suspension device against a lateral force, restraining deformation of the suspension subframe110and the extension frame130toward the vehicle-width-direction inner side.

As described above, the second cross member150includes the substantially T-shaped reinforcement frame153, which is formed by the transverse frame portion154connecting the rear ends of the right and left side portions152,152of the second cross member150and the longitudinal frame portion155connecting intermediate portions of the transverse frame portion154and the front side portion151.

As shown inFIG.5(b), the transverse frame portion154has a cross-section of a squared U-shape that extends in the vehicle width direction and opens downward. Meanwhile, the longitudinal frame portion155has a cross-section of a squared U-shape that extends in the vehicle front-rear direction and opens downward.

The transverse frame portion154includes a top face154a, a front face154bon the vehicle front side, and a rear face154con the vehicle rear side. The rear face154cis disposed along a rear end159dof the lower member159. The front face154band the rear face154cof the transverse frame portion154are joined to the top face of the lower member159. This results in a closed cross-section that is continuous in the vehicle width direction between the transverse frame portion154and the lower member159. Side portions154d,154eof the transverse frame portion154are respectively joined to the inclined portions157c,157cof the right and left side portions152,152(seeFIGS.3and4).

The longitudinal frame portion155includes a top face155a, and side faces155b,155bin the vehicle width direction. Lower ends of the side faces155b,155bin the vehicle width direction are joined to the lower member159. This results in a closed cross-section that is continuous in the vehicle front-rear direction between the longitudinal frame portion155and the lower member159. A front end155cof the longitudinal frame portion155is joined to the rear face156cof the front side portion151.

Now a detailed description will be given of a joining area Z of the second cross member150at which the second cross member150is joined to the extension frame130and the suspension subframe110, with reference toFIG.4.

As described above, the outer edge portions156d,156dof the front side portion upper member156and the outer edge portions157a,157aof the right and left side upper members157,157of the second cross member150are respectively joined to the top faces131a,131aof the rear ends133,133of the extension frames130,130and the top faces114a,114aof the front ends112,112of the suspension subframes110,110.

The ends159c,159cof the lower member159are joined to the bottom faces132a,132aof the rear ends133,133of the extension frames130,130and the bottom faces115a,115aof the front ends112,112of the suspension subframes110,110.

This results in the second cross member150being joined to the extension frame130and the suspension subframe110such that the second cross member150lies across the connection portion80between the extension frame130and the suspension subframe110and holds the frames130,110from the vehicle-width-direction inner side. This restrains breakage, in the up-down direction and toward the vehicle-width-direction inner side in particular, of the connection portion80between the frames110,130.

Also, as shown in the bottom view ofFIG.6, the lower arm60of the suspension device is supported via the front bracket63by portions on the outer side faces132b,131bsides in the vehicle width direction of the rear end133of the extension frame130and portions on the outer side faces114b,115bsides in the vehicle width direction of the front end112of the suspension subframe110, as described above. The front bracket63is joined to the bottom faces of the frames110,130at a portion denoted by W so as to be continuous with these bottom faces. In other words, the front bracket63is joined to a portion of the bottom face132aof the extension frame130near the outer side faces132b,131bin the vehicle width direction of the rear end133and joined to a portion of the bottom face115aof the suspension subframe110near the outer side faces114b,115bin the vehicle width direction of the front end112.

Thus, the connection portion80between the extension frame130and the suspension subframe110is reinforced, on its vehicle-width-direction inner side, by the corresponding one of the right and left side portions152,152of the second cross member150and is reinforced, on its vehicle-width-direction outer side, by the front bracket63. This more effectively restrains breakage deformation of the connection portion80between the frames130,110. Note that reinforcement of the vehicle-width-direction outer side of the connection portion80between the frames130,110is achieved by the front bracket63, without the need for any additional component.

As shown inFIG.4, a vehicle-width-direction outer side end of the second cross member150is joined to the extension frame130and the suspension subframe110so as to extend across the frames130,110. That is, a joining area Z of the second cross member150at which the second cross member150is joined to the extension frame130and the suspension subframe110includes an extension frame-side joining area81at which the second cross member150is joined to the extension frame130and a suspension subframe-side joining area82at which the second cross member150is joined to the suspension subframe110.

At the joining area Z, a vehicle front-rear direction dimension of the extension frame-side joining area81is shorter than that of the suspension subframe-side joining area82.

As such, the extension frame-side joining area81is made not longer than needed, which prevents the second cross member150from inhibiting deformation of the extension frame130in response to input of an impact load from the vehicle front side. This enables the extension frame130to exercise a good shock absorbing function.

Meanwhile, making the suspension subframe-side joining area82relatively long helps increase the strength and rigidity of the suspension subframe110against a load in the vehicle front-rear direction. This enables the suspension subframes110,110to exercise a good function as a load receiving portion in response to input of an impact load from the vehicle front side, which in turn enables the extension frames130,130to exercise a good shock absorbing function.

As shown inFIG.3, the third cross member160is connected to the rear ends113,113of the suspension subframes110,110so as to connect the rear ends113,113in the vehicle width direction. The third cross member160is a plate member extending in the vehicle width direction and fixed to the rear ends113,113of the suspension subframes110,110from below with multiple bolts161. . .161or the like.

Additionally, as shown inFIG.2, the above suspension subframe structure100is provided, on its right and left sides, with three sets of front vehicle body mounting portions X1, X1, intermediate vehicle body mounting portions X2, X2, and rear vehicle body mounting portions X3, X3as mounting portions for the front side frames20,20. Below a description will be given of each mounting portion.

Each front vehicle body mounting portion X1is composed of a connection member71mounted on the front end134of the extension frame130. Specifically, the connection member71is connected at its lower portion72to the extension frame130and is formed of a tower shape rising upward from this connecting portion.

Additionally, the connection member71is formed of a hollow box shape, and its top face73on the vehicle-width-direction outer side is mounted on the bottom face25aof the outer panel25of the front side frame20via a mount bush74. The connection member71is mounted on the bottom face25aof the outer panel25with a fastening member75(seeFIG.3).

The sub crash can55is connected to an upright wall-like front face76of the connection member71via a mounting plate57.

The intermediate vehicle body mounting portion X2is composed of a powertrain mount bracket (hereinafter, also simply referred to as a “mount bracket”)90. The mount bracket90accommodates an engine mount (not shown) for elastically supporting the powertrain4(seeFIG.3). The mount bracket90is fixed to the body111of the suspension subframe110. In the present embodiment, the mount bracket90is integrally formed by casting such as aluminum die casting. However, materials for the mount bracket90are not limited to aluminum.

The mount bracket90is provided with a hollow accommodation portion91including an accommodation space that opens upward. The accommodation portion91is of a cylindrical shape, for example. The accommodation portion91accommodates a mount support structure (not shown) connected to a powertrain-side bracket provided on the powertrain4side.

The mount bracket90is provided with multiple fastening portions92,93,94for fastening to the suspension subframe structure100. The multiple fastening portions92,93,94consist of a front fastening portion92provided at a front edge portion of the mount bracket90, a rear fastening portion93provided at a rear edge portion of the mount bracket90, and an intermediate fastening portion94provided between the front fastening portion92and the rear fastening portion93in the vehicle front-rear direction.

Specifically, these fastening portions92,93,94are respectively composed of multiple flange portions92a,93a,94athat extend outward from a lower end of an outer peripheral portion91aof the accommodation portion91of the mount bracket90. These flange portions92a,93a,94aare formed with bolt insertion holes (not shown), and the mount bracket90is fastened to the suspension subframe structure100with bolts inserted into these bolt insertion holes.

Meanwhile, the suspension subframe110is formed with bolt fastening holes111a,111b(seeFIG.4) for mounting the mount bracket90that are located at positions corresponding to the above bolt insertion holes of the front fastening portion92and the rear fastening portion93of the mount bracket90, respectively.

Each of the right and left side portions152,152of the second cross member150is formed with a bolt fastening hole152afor mounting the mount bracket90that is located at a position corresponding to the bolt insertion hole of the intermediate fastening portion94. At the substantially same position as the transverse frame portion154in the vehicle front-rear direction, the intermediate fastening portion94is fastened to a portion of the corresponding side portion152near the rear end thereof. This restrains displacement of the mount bracket90that causes it to fall toward vehicle-width-direction inner side (so-called inward falling).

The bolts92c,93c,94c(seeFIG.3) inserted into the bolt insertion holes of the mount bracket90, the bolt fastening holes111a,111bof the suspension subframe110, and the bolt fastening hole152aof the right and left side portions152(seeFIG.4) are screwed into weld nuts (not shown) provided on the bottom face115aof the suspension subframe110and the bottom face159of the side portion152. The mount bracket90is thus fastened to the suspension subframe110.

The mount bracket90is formed with a protruding portion95that extends upward toward the vehicle-width-direction outer side from a vehicle-width-direction outer edge of an upper wall portion91bof the accommodation portion91. The protruding portion95is provided, at its outer end95ain the vehicle width direction, with a pillar portion95bthat projects upward. The pillar portion95bis mounted on the bottom face25aof the outer panel25with a bolt95cat a rear portion of the front linear portion21of the front side frame20, thus forming the intermediate vehicle body mounting portion X2. The intermediate vehicle body mounting portion X2is rigidly joined to the front side frame20without any intervening damping element, such as a rubber bush.

As shown inFIGS.7and8, the rear vehicle body mounting portion X3is provided at a lateral side in the vehicle width direction of the rear end113of the body111of the suspension subframe110.

The rear vehicle body mounting portion X3includes an upper plate member121as an upper connection portion disposed on the upper side, a lower plate member122as a lower connection portion disposed on the lower side, and a reinforcement member123disposed between the upper plate member121and the lower plate member122.

The upper plate member121and the lower plate member122are disposed substantially perpendicularly to the vehicle up-down direction and in parallel with each other. The upper plate member121and the lower plate member122respectively include: side edge portions121a,122aextending parallel to the outer side faces114b,115bin the vehicle width direction of the suspension subframe110; front edge portions121b,122bextending obliquely such that their rear portions protrude more outwardly in the vehicle width direction; and rear edge portions121c,122cconnecting respective rear ends of the side edge portions121a,122aand respective rear ends of the front edge portions121b,122b. The upper plate member121and the lower plate member122as a whole are of a substantially triangular shape in plan view.

The rear edge portion121cof the upper plate member121is provided with an upper joined portion121dthat extends from the rear edge portion121cto the vehicle lower side. The rear edge portion122cof the lower plate member122is provided with a lower joined portion122dthat extends from the rear edge portion122ctoward the vehicle upper side. The upper joined portion121dand the lower joined portion122dare overlapped and welded to each other, whereby the upper plate member121and the lower plate member122are joined together.

The side edge portion121aof the upper plate member121and the side edge portion122aof the lower plate member122are respectively joined to the top face114aand the bottom face115aat the rear portion of the body111of the suspension subframe110. Thus, the rear vehicle body mounting portion X3is joined to the body111of the suspension subframe110.

The upper plate member121and the lower plate member122of the rear vehicle body mounting portion X3are respectively provided with bolt insertion holes121e,122efor fastening the suspension subframe110to the front side frame20. The bolt insertion holes121e,122eare spaced to the vehicle-width-direction outer side from the body111of the suspension subframe110.

The reinforcement member123connects the upper plate member121and the lower plate member122. The reinforcement member123includes a front portion123aextending parallel to the front edge portions121b,122bof the upper and lower plate members121,122in plan view and a rear portion123bextending from a rear end of the front portion123ato the vehicle rear side. The reinforcement member123generally has a V-shape in plan view comprised of the front portion123aand the rear portion123b. As shown inFIGS.7and8, the rear portion123bof the reinforcement member123is provided between the body111of the suspension subframe110and the bolt insertion holes121e,122eof the upper and lower plate members121,122.

An upper end123cand a lower end123dof the reinforcement member123are respectively joined to the upper plate member121and the lower plate member122, and the front end123eis joined to the side faces114b,115bof the body111of the suspension subframe110.

The lower end of the rear portion123bof the reinforcement member123is provided with a tongue piece portion123fthat extends from the lower end toward the vehicle-width-direction inner side, and the rear portion123bis joined at the tongue piece portion123fto the top face of the lower plate member122. The lower plate member122is provided with a work opening122f(seeFIG.7) at its position corresponding to the tongue piece portion123f, and the work opening122fallows the tongue piece portion123fto be passed therethrough and joined to the lower plate member122from below.

A sleeve member124as a spacer is disposed between the upper plate member121and the lower plate member122at a position corresponding to the bolt insertion holes121e,122eof these plate members121,122. The sleeve member124is a fixed position fixed to the front side frame20with a bolt125.

The sleeve member124is disposed near a lateral side of the body111such that an axis of the sleeve member124is perpendicular to the upper plate member121and the lower plate member122. A hole124aof the sleeve member124is aligned with the bolt insertion hole121eof the upper plate member121and the bolt insertion hole122eof the lower plate member122. A rear edge portion of the rear portion123bof the above-described reinforcement member is joined to an outer peripheral surface124bof the sleeve member124by, for example, welding. Thus, the sleeve member124is positioned with respect to the upper plate member121and the lower plate member122via the reinforcement member123.

Meanwhile, as shown inFIG.8, a bracket26for fixing the rear vehicle body mounting portion X3is joined to a rear end of the inclined portion22of the front side frame20. The bracket26has a cross-section of a squared U-shape that opens upward, and includes a bottom face26aand side faces26b,26b.

The bracket26is located below the front side frame20, and the side faces26b,26bof the bracket26are joined to the respective side faces22b,22bin the vehicle width direction of the inclined portion22of the front side frame20.

The bottom face26aof the bracket26is provided with a bolt hole26cat a position corresponding to the bolt insertion holes121e,122eof the rear vehicle body mounting portion X3, and a pipe-shaped weld nut26eis joined to a top side26dof the bottom face26a.

At the rear vehicle body mounting portion X3, a bolt125is inserted from below into the bolt insertion hole122eof the lower plate member122, the hole124aof the sleeve member124, the bolt insertion hole121eof the upper plate member121, and a bolt hole26cof the bracket26, and thus a distal end of the bolt125is screwed into the weld nut26e, whereby the suspension subframe110is fastened and fixed to the underside of the front side frame20.

As a result of this fastening, the sleeve member124is fixed at its upper end face to the upper plate member121and fixed at its lower end face to the lower plate member122. Hence, the sleeve member124is connected to the body111via the upper plate member and the lower plate member122.

A hole22ais provided in an underside of the rear end of the inclined portion22of the front side frame20at a position corresponding to the above weld nut26e. Inserting a distal end of the weld nut26einto the hole22aprevents the bolt125from falling.

Now a description will be given of a behavior of the suspension subframe structure100according to the present embodiment in response to input of an impact load from the front side of the vehicle body including the suspension subframe structure100.

An impact load input to the bumper reinforcement54from the vehicle front side is transmitted to the vehicle rear side via the main crash cans53,53and the front side frames20,20.

Also, an impact load input to the sub bumper reinforcement58from the vehicle front side is transmitted to the front side frames20,20via the sub crash cans55,55, the extension frames130,130, the bodies111,111of the suspension subframes110,110, and the rear vehicle body mounting portions X3, X3.

As such, in the present embodiment, the load can be distributed over the two load paths to be transmitted to the vehicle rear side.

Also, when a relatively large impact load is input to the bumper reinforcement54and the sub bumper reinforcement58from the vehicle front side, the main crash cans53,53and the sub crash cans55,55crush to absorb the impact. A residual impact load that has not been absorbed by the crush deformation of the crash cans53,53,55,55is input to the front ends of the front side frames20,20and the extension frames130,130and transmitted to the vehicle rear side through the above two load paths.

When a larger impact load is input from the vehicle front side, the front side frames20,20and the extension frames130,130deform to absorb the impact load. At this time, the suspension subframes110,110effectively function as the load receiving portion by virtue of the closed cross-section structure described above, which enhances the shock absorbing function of the extension frames130,130.

At this time, in the intermediate vehicle body mounting portions X2, X2, the bolts95c,95care displaced in the vehicle up-down direction due to deformation of the front side frames20,20and the extension frames130,130, which allows the suspension subframes110,110to disengage from the front side frames20,20relatively easily.

Since the intermediate vehicle body mounting portions X2, X2are rigidly joined without any intervening damping element, such as a rubber bush, the impact load from the vehicle front side is input to the connection portions without being absorbed by a rubber bush and the like. In the present embodiment, the mount bracket90constituting each of the intermediate vehicle body mounting portions X2, X2is made of aluminum and thus has a relatively low strength, so that the mount bracket90is easily broken under the impact load from the vehicle front side. This allows the suspension subframes110,110to disengage from the front side frames20,20relatively easily.

In the front vehicle body mounting portions X1, X1, the front side frames20,20are connected to the extension frames130,130each via the mount bush74, and thus their connection is not easy to release as compared to the intermediate vehicle body mounting portions X2, X2. Nonetheless, as the extension frames130,130have the load absorbing function unlike the suspension subframes110,110, the extension frames130,130do not hinder the deformation of the front side frames20,20.

Additionally, when a large impact load (impact load greater than or equal to a predetermined load) that cannot be absorbed by the deformation of the extension frames130,130is input to the suspension subframes110,110, the suspension subframes110,110, which are the high-rigidity portions, do not deform greatly and can start retracting together with the powertrain4.

At this time, in the rear vehicle body mounting portions X3, X3, the upper plate members121,121and the lower plate members122,122of the suspension subframes110,110are to retract together with the bodies111,111.

Meanwhile, the lower ends of the inclined portions22,22of the front side frames20,20mounted with the rear vehicle body mounting portions X3, X3are configured to experience less deformation, for they constitute vehicle body portions near the front end of the vehicle cabin. Hence, the bolts125,125used for fastening of the rear vehicle body mounting portions X3, X3are made hard to drop. This facilitates keeping the sleeve members124,124fixed to the front side frames20,20with the bolts125,125.

Thus, when the impact load is input to the body111of the suspension subframe110from the vehicle front side via the extension frame130, the sleeve member124and the bolt125are to be displaced toward the vehicle front side, as shown by the arrow F inFIG.7, relative to the upper plate member121and the lower plate member122retracting together with the body111.

Here, in the suspension subframe110, the upper plate member121and the lower plate member122, via which the sleeve member124is connected to the body111, have a lower strength against a load in the vehicle front-rear direction than that of the body111and the sleeve member124.

In particular, as shown inFIG.7, portions of the upper plate member121and the lower plate member122in the vehicle width direction that are located closer to the sleeve member124relative to the reinforcement member123are not reinforced by the reinforcement member123, thus defining fragile portions121f,122gwith a lower strength.

Additionally, in the fragile portions121f,122gof the upper plate member121and the lower plate member122, the bolt insertion holes121e,122ehaving the bolt125inserted therethrough can function as breakage facilitating portions that facilitate breakage of the upper plate member121and the lower plate member122by the bolt125, as shown inFIG.8.

Hence, when the sleeve member124and the bolt125are to be displaced toward the vehicle front side relative to the upper plate member121and the lower plate member122as described above (see the arrow F inFIG.7), interference of the bolt125with front edges of the bolt insertion holes121e,122eof the fragile portions121f,122gbrings about breakage of the upper plate member121and the lower plate member122that permits such relative displacement. This facilitates breakage such that the bolt125breaks into portions of the fragile portions121f,122gthat are located frontward of the bolt insertion holes121e,122e.

As the suspension subframe110breaks in the fragile portions121f,122gbetween the body111and the sleeve member124in this manner, the rear vehicle body fastening portion X3of the suspension subframe110essentially disengages from the front side frame20.

This allows the extension frames130,130and suspension subframes110,110, which do not have the function of absorbing the impact load any more, to disengage from the vehicle body. This in turn effectively restrains deformation of the inside of the vehicle cabin that might otherwise be caused by retraction of the suspension subframes110,110.

Since each of the reinforcement members123,123is located between the corresponding one of the bodies111,111of the suspension subframes110,110and the corresponding one of the sleeve members124,124, interference between the sleeve members124,124and the reinforcement members123,123can be readily avoided when the bolts125,125and the sleeve members124,124are displaced relatively toward the vehicle front side.

While the suspension subframe structure including the extension frames has been described in the above embodiment, the present invention is applicable to a suspension subframe structure that does not include extension frames.

INDUSTRIAL APPLICABILITY

As described above, the present invention can activate the load paths using the extension frames in an impact while avoiding increase in vehicle weight and also enables the suspension subframes to disengage from the vehicle body when an impact load is too large to be absorbed by the extension frames alone; as such, the present invention may be suitably used in the field of vehicle body manufacturing.

REFERENCE SIGNS LIST