Suspension arm for vehicle

When a load facing to the rear of a vehicle body acts on a knuckle mounting portion of an arm main body of a suspension arm, if the line of action of the load deviates vertically relative to the cross-sectional center of the arm main body, a moment that vertically deforms the arm main body occurs. However, since there are provided a first inclined projecting portion that is formed so as to bulge upward in an end part on a first vehicle body mounting portion side of a first bottom wall portion and has a height that gradually decreases in going from a first upper wall portion toward the second upper wall portion, and a second inclined projecting portion that is formed so as to bulge upward in an end part on the first vehicle body mounting portion side of a second bottom wall portion and has a height that gradually decreases in going from a third upper wall portion toward the second upper wall portion, it is possible to enhance the rigidity without increasing the weight of the arm main body, thus preventing deformation of the arm main body due to the load.

TECHNICAL FIELD

The present invention relates to a suspension arm for a vehicle in which an arm main body formed by press forming a metal plate includes a knuckle mounting portion on which a knuckle is mounted, a first vehicle body mounting portion that is provided inwardly of the knuckle mounting portion in a vehicle width direction and is mounted on a vehicle body, and a second vehicle body mounting portion that is provided toward a vehicle body rear side of the first vehicle body mounting portion and is mounted on the vehicle body.

Furthermore, the present invention relates to a suspension arm for a vehicle in which an arm main body formed by press forming a metal plate includes a knuckle mounting portion on which a knuckle is mounted and a vehicle body mounting portion mounted on a vehicle body, an outer face of the vehicle body mounting portion being fixed by welding to a weld part formed at an end edge of the arm main body.

Moreover, the present invention relates to a suspension arm for a vehicle that includes an arm main body formed by press forming a metal plate.

BACKGROUND ART

An arrangement in which an arm main body of a suspension arm formed by press forming a metal plate has a cross-sectional shape having an open lower face formed from an upper wall portion, a pair of side wall portions formed by downwardly bending opposite side edges of the upper wall portion, and a pair of lower wall portions formed by inwardly bending the lower edges of the side wall portions, a reinforcing rib downwardly recessed along opposite side edges of the upper wall portion is formed, and a raised part projecting upward between the two reinforcing ribs is formed is known from Patent Document 1 below.

Furthermore, an arrangement in which a hollow suspension arm is formed by superimposing and welding outer peripheral parts of a first plate-shaped member and second plate-shaped member formed by press forming a metal plate, and a pipe member for supporting a rubber bush joint is fixed by welding to an end part on the vehicle body side of the suspension arm is known from Patent Document 2 below.

Moreover, an arrangement in which an arm main body of a suspension arm formed by press forming a metal plate has a cross-sectional shape having an open lower face formed from an upper wall portion and a pair of side wall portions formed by downwardly bending opposite side edges of the upper wall portion, and rigidity is enhanced by forming a concavo-convex shape in which recesses and projections are continued in front and rear side wall portions is known from Patent Document 3 below.Patent Document 1: Japanese Patent Application Laid-open No. 9-123722Patent Document 2: Japanese Patent Application Laid-open No. 9-20115Patent Document 3: Japanese Patent Application Laid-open No. 2004-90750

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

The arrangement disclosed in Patent Document 1 above aims to enhance the twist rigidity of the arm main body by forming the reinforcing rib and the raised part in the upper wall portion of the arm main body so as to make the height of its shear center close to the height of a load-acting plane, but it is difficult to make the height of the shear center completely coincide with the height of the load-acting plane, and when a large load facing in the vehicle body fore-and-aft direction is inputted by the vehicle being suddenly braked or the wheel riding over a step, there is a possibility of the arm main body being deformed. In order to avoid this, the plate thickness of the arm main body might be increased, but by so doing the problem of the weight of the arm main body increasing occurs.

There is also known a suspension arm that is formed by press forming one sheet of metal plate in order to reduce the weight and cost, the suspension arm including a horizontally disposed upper wall portion and a pair of side wall portions formed by bending peripheral edges of the upper wall portion downwardly in the vertical direction at right angles.

When a pipe member for supporting a rubber bush joint is fixed by welding to an end part on the vehicle body side of such a suspension arm, the shape of the weld part is a rectangular ‘U’ shape having an open lower face formed from the upper wall portion and the pair of side wall portions. Therefore, when a load facing in the vehicle body fore-and-aft direction acts on the suspension arm by the vehicle being suddenly braked or the wheel riding over a step, although a sufficient strength is ensured for a welded place of the upper wall portion, which is in a direction parallel to the direction of the load, the strength of welded places of the side wall portions, which are at right angles to the direction of the load, becomes insufficient, and there is a possibility that the weld might detach, etc.

Moreover, when the wheel rides over a step on the road surface or when sudden braking is carried out, a large load is also applied to a mounting portion via which the arm main body of the suspension arm is mounted on a knuckle or a vehicle body, but a side wall portion having a sufficient height sometimes cannot be provided in the mounting portion of the arm main body because of the need for avoiding interference between the knuckle or vehicle body and the arm main body accompanying vertical movement of the suspension arm. In such a case, there is the problem that even by forming a concavo-convex shape described in Patent Document 1 above on a side wall portion having a low height a sufficient effect in enhancing the rigidity cannot be obtained. Furthermore, the concavo-convex shape is effective when a load is applied in a direction in which the side wall portion is twisted, but there is the problem that in a portion, such as the mounting portion via which the arm main body is mounted on a knuckle or vehicle body, in which a load in a bending direction is applied, a sufficient effect in enhancing the rigidity cannot be obtained.

Enhancing the rigidity of the arm main body by forming a so-called reverse flange by inwardly bending the lower end of the side wall portion could be considered, but it is difficult to fabricate a reverse flange in the mounting portion positioned at an end part of the arm main body, materials overlap or become excessive in the reverse flange portion, and stress is concentrated on this portion, thus instead causing a degradation in durability, which is a problem.

The present invention has been accomplished in light of the above-mentioned circumstances, and it is a first object thereof to enhance the rigidity of a suspension arm against a load in the vehicle body fore-and-aft direction inputted from the wheel side without causing an increase in weight.

Furthermore, it is a second object of the present invention to enhance the strength of a weld part when fixing by welding a vehicle body mounting portion to a suspension arm having a cross-sectional shape having an open lower face.

Moreover, it is a third object of the present invention to improve durability by enhancing rigidity in the vicinity of a knuckle mounting portion or a vehicle body mounting portion of a suspension arm.

Means for Solving the Problems

In order to attain the above first object, according to a first aspect of the present invention, there is proposed a suspension arm for a vehicle in which an arm main body formed by press forming a metal plate comprises a knuckle mounting portion on which a knuckle is mounted, a first vehicle body mounting portion that is provided inwardly of the knuckle mounting portion in a vehicle width direction and is mounted on a vehicle body, and a second vehicle body mounting portion that is provided toward a vehicle body rear side of the first vehicle body mounting portion and is mounted on the vehicle body, the suspension arm comprising: a first upper wall portion that extends substantially horizontally from the first vehicle body mounting portion to the second vehicle body mounting portion in a state in which the arm main body is mounted on the vehicle body; a second upper wall portion that extends substantially horizontally from the second vehicle body mounting portion to the knuckle mounting portion in a state in which the arm main body is mounted on the vehicle body; a third upper wall portion that extends substantially horizontally from the knuckle mounting portion to the first vehicle body mounting portion in a state in which the arm main body is mounted on the vehicle body; a first bottom wall portion that is at a position lower than the first and second upper wall portions and connects the first and second upper wall portions; a second bottom wall portion that is at a position lower than the second and third upper wall portions and connects the second and third upper wall portions, a first inclined projecting portion that is formed so as to bulge upward in an end part on the first vehicle body mounting portion side of the first bottom wall portion and has a height that gradually decreases in going from the first upper wall portion toward the second upper wall portion; and a second inclined projecting portion that is formed so as to bulge upward in an end part on the first vehicle body mounting portion side of the second bottom wall portion and has a height that gradually decreases in going from the third upper wall portion toward the second upper wall portion.

Further, according to a second aspect of the present invention, in addition to the first aspect, the first inclined projecting portion has a width that gradually decreases in going from the first upper wall portion toward the second upper wall portion.

Furthermore, according to a third aspect of the present invention, in addition to the first aspect, the second inclined projecting portion has a width that gradually decreases in going from the third upper wall portion toward the second upper wall portion.

Moreover, according to a fourth aspect of the present invention, in addition to the first aspect, the arm main body comprises a third bottom wall portion that is connected at substantially the same height to the first and second bottom wall portions at a position sandwiched between the first and second inclined projecting portions, and a through hole is formed in the third bottom wall portion.

Further, according to a fifth aspect of the present invention, in addition to the first aspect, an outer face of the vehicle body mounting portion is fixed by welding to a weld part formed at an end edge of the arm main body, the weld part of the arm main body comprises a first weld part that extends substantially horizontally in a state in which the arm main body is mounted on the vehicle body, and second and third weld parts that extend downwardly from opposite ends of the first weld part, a distance between lower ends of the second and third weld parts being set larger than a distance between upper ends thereof.

Furthermore, according to a sixth aspect of the present invention, in addition to the fifth aspect, the third weld part is bent in a direction in which the third weld part moves away from the second weld part while extending downwardly from a part that is connected to the first weld part.

Moreover, according to a seventh aspect of the present invention, in addition to the fifth aspect, the arm main body comprises the second vehicle body mounting portion to a rear of the vehicle body mounting portion as the first vehicle body mounting portion, a part sandwiched between the first and second vehicle body mounting portions of the arm main body comprises the upper wall portion and first and second side wall portions formed by downwardly bending opposite side edges of the upper wall portion, and the first side wall portion is bent in a direction in which its first vehicle body mounting portion side moves away from the second side wall portion and is continuous to the third weld part.

Further, according to an eighth aspect of the present invention, in addition to the seventh aspect, a downwardly recessed recess is formed in a part in which the upper wall portion and the first side wall portion are connected.

Furthermore, according to a ninth aspect of the present invention, in addition to the first aspect, the arm main body comprises the knuckle mounting portion on which the knuckle is mounted and the vehicle body mounting portion that is mounted on the vehicle body, and a concavo-convex portion is formed in a peripheral edge part of at least one of the knuckle mounting portion and the vehicle body mounting portion.

Moreover, according to a tenth aspect of the present invention, in addition to the ninth aspect, the concavo-convex portion has a substantially polygonal shape or a substantially circular shape.

Further, according to an eleventh aspect of the present invention, in addition the ninth aspect, the arm main body comprises the upper wall portion that extends in a substantially horizontal direction in a state in which the arm main body is mounted on the vehicle body, and a side wall portion that is formed by downwardly bending a peripheral edge of the upper wall portion, the height of the side wall portion is made smaller in the vicinity of at least one of the knuckle mounting portion and the vehicle body mounting portion in which the concavo-convex portion is formed than other parts, and the concavo-convex portion is formed on a border between the upper wall portion and the side wall portion.

Furthermore, according to a twelfth aspect of the present invention, in addition to the ninth aspect, the arm main body comprises the upper wall portion that extends in a substantially horizontal direction in a state in which the arm main body is mounted on the vehicle body, a side wall portion that is formed by downwardly bending a peripheral edge of the upper wall portion, and a lower wall portion that is formed by bending an end part that is not continuous to the upper wall portion in at least one part of the side wall portion, and the concavo-convex portion is formed at a position of a boundary between a part where the lower wall portion is provided and a part where the lower weld portion is not provided within the border between the upper wall portion and the side wall portion.

Moreover, in order to attain the above second object, according to a thirteenth aspect of the present invention, there is proposed a suspension arm for a vehicle in which an arm main body that is formed by press forming a metal plate comprises a knuckle mounting portion on which a knuckle is mounted and a vehicle body mounting portion that is mounted on a vehicle body, and an outer face of the vehicle body mounting portion is fixed by welding to a weld part formed at an end edge of the arm main body, wherein the weld part of the arm main body comprises a first weld part that extends substantially horizontally in a state in which the arm main body is mounted on the vehicle body, and second and third weld parts that extend downwardly from opposite ends of the first weld part, a distance between lower ends of the second and third weld parts being set larger than a distance between upper ends thereof.

Further, in order to attain the above third object, according to a fourteenth aspect of the present invention, there is proposed a suspension arm for a vehicle comprising an arm main body that is formed by press forming a metal plate, wherein the arm main body comprises a knuckle mounting portion on which a knuckle is mounted and a vehicle body mounting portion that is mounted on a vehicle body, and a concavo-convex portion is formed on a peripheral edge part of at least one of the knuckle mounting portion and the vehicle body mounting portion.

First and second vehicle body mounting portions17band17cof an embodiment correspond to the vehicle body mounting portion of the present invention, first and second upper wall portions17dand17eof the embodiment correspond to the upper wall portion of the present invention, first and second side wall portions17jand17kof the embodiment correspond to the side wall portion of the present invention, a recess17sof the embodiment corresponds to the concavo-convex portion of the present invention, and first to third weld parts w1to w3of the embodiment correspond to the weld part of the present invention.

Effects of the Invention

In accordance with the first aspect of the present invention, when, for example, a load facing toward the rear of the vehicle body acts on the knuckle mounting portion of the arm main body while the vehicle is being suddenly braked or the wheel is riding over a step, if the line of action of the load is vertically displaced relative to the cross-sectional center of the arm main body, a moment that vertically deforms the arm main body occurs, but since the first inclined projecting portion, which is formed in the end part on the first vehicle body mounting portion side of the first bottom wall portion so as to bulge upward and whose height gradually decreases in going from the first upper wall portion toward the second upper wall portion, and the second inclined projecting portion, which is formed in the end part on the first vehicle body mounting portion side of the second bottom wall portion so as to bulge upward and whose height gradually decreases in going from the third upper wall portion toward the second upper wall portion, are provided, it is possible to enhance the rigidity of the arm main body without increasing the weight and prevent deformation of the arm main body due to the load.

Furthermore, in accordance with the second aspect of the present invention, since the width of the first inclined projecting portion gradually decreases in going from the first upper wall portion toward the second upper wall portion, it is possible to prevent stress from concentrating at the border between the first inclined projecting portion and the first bottom wall portion.

Moreover, in accordance with the third aspect of the present invention, since the width of the second inclined projecting portion gradually decreases in going from the third upper wall portion toward the second upper wall portion, it is possible to prevent stress from concentrating at the border between the second inclined projecting portion and the second bottom wall portion.

Furthermore, in accordance with the fourth aspect of the present invention, since the third bottom wall portion connected to the first and second bottom wall portions at substantially the same height is provided at a position of the arm main body sandwiched between the first and second inclined projecting portions, and the through hole is formed in the third bottom wall portion, not only is it possible to enhance operability by utilizing the through hole as an insertion hole for a bolt, a nut, a tool, etc. when assembling the suspension arm on the vehicle body, but it is also possible to utilize the through hole as a drain hole for drainage or as a cutout hole for weight reduction.

Moreover, in accordance with the fifth or thirteenth aspect of the present invention, since the weld part at the end edge of the arm main body to which the outer face of the vehicle body mounting portion is welded is formed from the first weld part extending substantially horizontally and the second and third weld parts extending downwardly from opposite ends of the first weld part, when a load in the vehicle body fore-and-aft direction is inputted into the weld part, the strength of the first weld part, which is parallel to the direction of the load, is high, but the strength of the second and third weld parts, which are not parallel to the direction of the load, is low. In this arrangement, although the strength is the weakest when the second and third weld parts are at right angles relative to the direction of the load, setting the distance between the lower ends of the second and third weld parts larger than that between the upper ends thereof enables the direction of the second and third weld parts to be changed from being at right angles relative to the direction of the load to being more parallel, thus enhancing the strength thereof.

Furthermore, in accordance with the sixth aspect of the present invention, since the third weld part is curved in the direction in which it moves away from the second weld part while extending downwardly from the portion connected to the first weld part, making the direction of the lower part of the third weld part more parallel relative to the direction of the load and dispersing the load in the vehicle body fore-and-aft direction inputted to the weld part from the arm main body over a wider range of the first vehicle body mounting portion enables the durability of the weld part to be enhanced.

Moreover, in accordance with the seventh aspect of the present invention, since the arm main body includes the first vehicle body mounting portion on the front side and the second vehicle body mounting portion on the rear side, and among the upper wall portion and first and second side wall portions forming a portion sandwiched between the first and second vehicle body mounting portions, the first side wall portion bends in the direction in which the first vehicle body mounting portion side thereof moves away from the second side wall portion and is continuous to the third weld part, it is possible to disperse the load acting on the third weld part in the first side wall portion, thus enhancing the durability of the third weld part.

Furthermore, in accordance with the eighth aspect of the present invention, since the downwardly recessed recess is formed in the portion where the upper wall portion and the first side wall portion are connected, it is possible to enhance the rigidity of the portion of the arm main body sandwiched by the first and second vehicle body mounting portions by the reinforcing effect of the recess, thus further improving the durability of the suspension arm with respect to a load in the vehicle body fore-and-aft direction.

Moreover, in accordance with the ninth or fourteenth aspect of the present invention, since the arm main body of the suspension arm formed by press forming a metal plate has a concavo-convex portion formed in a peripheral edge part of the knuckle mounting portion, on which a knuckle is mounted, or the vehicle body mounting portion, which is mounted on the vehicle body, it is possible to enhance the rigidity of the knuckle mounting portion or vehicle body mounting portion by means of the concavo-convex portion, thus improving the durability toward the load input.

Furthermore, in accordance with the tenth aspect of the present invention, since the shape of the concavo-convex portion is substantially polygonal or substantially circular, regardless of the direction in which a load is inputted into the concavo-convex portion it is possible to ensure the rigidity in the vicinity of the concavo-convex portion.

Moreover, in accordance with the eleventh aspect of the present invention, the arm main body includes the upper wall portion and the side wall portion formed by downwardly bending the peripheral edge of the upper wall portion, and even when a sufficient height cannot be ensured for the side wall portion in order to avoid interference with another member in the vicinity of at least one of the knuckle mounting portion and the vehicle body mounting portion, since the concavo-convex portion is formed at the border between the upper wall portion and the side wall portion, it is possible to ensure the rigidity in the vicinity of the concavo-convex portion.

Furthermore, in accordance with the twelfth aspect of the present invention, the arm main body includes the upper wall portion, the side wall portion formed by downwardly bending the peripheral edge of the upper wall portion, and the lower wall portion formed by inwardly bending at least part of the side wall portion, and since the concavo-convex portion is formed at a position on the boundary, within the border between the upper wall portion and the side wall portion, between a portion where the lower wall portion is provided and a portion where it is not provided, it is possible to reinforce effectively by means of the concavo-convex portion a portion at which the lower wall portion stops and stress is easily concentrated.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

11Knuckle12Vehicle body17Arm main body17aKnuckle mounting portion17bFirst vehicle body mounting portion (vehicle body mounting portion)17cSecond vehicle body mounting portion (vehicle body mounting portion)17dFirst upper wall portion (upper wall portion)17eSecond upper wall portion (upper wall portion)17fThird upper wall portion17gFirst bottom wall portion17hSecond bottom wall portion17iThird bottom wall portion17jFirst side wall portion (side wall portion)17kSecond side wall portion (side wall portion)17nLower wall portion17oFirst inclined projecting portion17pSecond inclined projecting portion17qThrough hole17sRecess (concavo-convex portion)17uRecessA Distance between upper ends of second and third weld partsB Distance between lower ends of second and third weld partsw1First weld part (weld part)w2Second weld part (weld part)w3Third weld part (weld part)

BEST MODE FOR CARRYING OUT THE INVENTION

A mode for carrying out the present invention is explained below by reference to attached drawings.

First Embodiment

FIG. 1toFIG. 10show a mode for carrying out the present invention.

As shown inFIG. 1toFIG. 3, a strut type suspension system S that suspends a wheel W, which is a turning wheel, includes a suspension arm13that connects a vehicle body12and a knuckle11rotatably supporting the wheel W, and the vehicle body12and a bracket14provided on an upper part of the knuckle11are connected by a damper16that includes a suspension spring15on the outer periphery of an upper part.

An arm main body17of the suspension arm13, which has an arc-shaped curved shape overall, is formed by press forming a metal plate, and a knuckle mounting portion17aformed from a circular opening provided at the outer end in a vehicle width direction thereof is pivotably supported on a lower part of the knuckle11via a ball joint18. A first vehicle body mounting portion17bprovided inwardly of the knuckle mounting portion17aof the arm main body17in the vehicle width direction is formed from a pipe member having a circular cross-section welded to the arm main body17, and is elastically supported on the vehicle body12via a rubber bush joint19having an axis in the vehicle body fore-and-aft direction. A second vehicle body mounting portion17cprovided to the rear of the first vehicle body mounting portion17bof the arm main body17is formed from a circular opening, and is elastically supported on the vehicle body12via a rubber bush joint20provided thereon so as to have an axis in the vehicle body vertical direction.

The arm main body17is disposed substantially horizontally in a state in which the wheel W is not bumping or rebounding, and includes a first upper wall portion17d, a second upper wall portion17e, and a third upper wall portion17f, which rise high along the outer periphery of an upper face thereof. The first upper wall portion17dextends substantially horizontally from the first vehicle body mounting portion17bto the second vehicle body mounting portion17c, the second upper wall portion17eextends substantially horizontally from the second vehicle body mounting portion17cto the knuckle mounting portion17a, and the third upper wall portion17fextends substantially horizontally from the knuckle mounting portion17ato the first vehicle body mounting portion17b.

A portion surrounded by the first upper wall portion17d, the second upper wall portion17e, and the third upper wall portion17fforms a sunken flat face, a portion sandwiched between the first and second upper wall portions17dand17eis defined as a first bottom wall portion17g, a portion sandwiched between the second and third upper wall portions17eand17fis defined as a second bottom wall portion17h, and a portion sandwiched between the first bottom wall portion17gand the second bottom wall portion17hin the vicinity of the first vehicle body mounting portion17bis defined as a third bottom wall portion17i.

Outer edges of the first upper wall portion17d, the second upper wall portion17e, and the third upper wall portion17fare downwardly bent and are respectively defined as a first side wall portion17j, a second side wall portion17k, and a third side wall portion17m; the first side wall portion17jand the second side wall portion17kare continuous so as to surround the outer periphery of the second vehicle body mounting portion17c, but the second side wall portion17kand the third side wall portion17mare separated in the knuckle mounting portion17aarea, and the third side wall portion17mand the first side wall portion17jare separated in the first vehicle body mounting portion17barea. The lower edge of the second side wall portion17kis bent so as to go around a lower face side of the arm main body17and forms a lower wall portion17n.

As is clear fromFIG. 2,FIG. 7, andFIG. 9, at the boundary between the first bottom wall portion17gand the third bottom wall portion17i, a first inclined projecting portion17oextending from the inner edge of the first upper wall portion17dtoward the second upper wall portion17eis upwardly projectingly provided, and at the boundary between the second bottom wall portion17hand the third bottom wall portion17i, a second inclined projecting portion17pextending from the inner edge of the third upper wall portion17ftoward the second upper wall portion17eis upwardly projectingly provided. The first inclined projecting portion17ois formed into a triangular shape in which a part connected to the inner edge of the first upper wall portion17dis the highest and the widest and the height and width decrease therefrom toward the second upper wall portion17e. Similarly, the second inclined projecting portion17pis formed into a triangular shape in which a part connected to the inner edge of the third upper wall portion17fis the highest and the widest and the height and width decrease therefrom toward the second upper wall portion17e.

As is clear fromFIG. 5andFIG. 10, a part of the arm main body17that is welded to the pipe-shaped first vehicle body mounting portion17bis formed from a straight line-shaped first weld part w1to which an end part of the third upper wall portion17fis welded horizontally and in parallel to the axis of the first vehicle body mounting portion17b, an arc-shaped second weld part w2to which the third side wall portion17mformed by bending the outer edge of the third upper wall portion17fdownwardly at substantially right angles is welded along an outer peripheral face of the pipe-shaped first vehicle body mounting portion17b, and an arc-shaped third weld part w3to which the first side wall portion17jformed by bending the outer edge of the first upper wall portion17ddownwardly at an obtuse angle is welded along an outer peripheral face of the pipe-shaped first vehicle body mounting portion17b.

As is clear fromFIG. 2,FIG. 5, andFIG. 8, a circular through hole17qis formed in a central part of the third bottom wall portion17isandwiched between the first inclined projecting portion17oand the second inclined projecting portion17p, and a small diameter drain hole17ris formed in the second bottom wall portion17h, which is adjacent to the knuckle mounting portion17a. The through hole17qis utilized as a hole into which a bolt, a nut, a tool, etc. is inserted in order to enhance operability when assembling the suspension arm13onto the vehicle body, and at the same time functions also as a drain hole for draining water collected in the first to third bottom wall portions17g,17h, and17i. Furthermore, the drain hole17rfunctions, in cooperation with the through hole17q, as a drain hole for draining water collected in the first to third bottom wall portions17g,17h, and17i.

As is clear fromFIG. 2andFIG. 6, a plurality (5in the embodiment) of diamond-shaped recesses17sare formed in a portion around the second vehicle body mounting portion17cwhere the first upper wall portion17dand the second upper wall portion17eare connected, so as to surround approximately half of the periphery of the second vehicle body mounting portion17c. Among these recesses17s, one at an end is formed on a boundary between the second upper wall portion17eand the second side wall portion17k, the boundary corresponding to an end of the lower wall portion17nconnected to the second side wall portion17k(ref.FIG. 2andFIG. 3). The recesses17sare formed in a corner extending over the first and second upper wall portions17dand17eand the first and second side wall portions17jand17k, and the depth of the recesses17sis for example about half of the thickness of the arm main body17.

Furthermore, a plurality (3in the embodiment) of diamond-shaped recesses17t(seeFIG. 2) are formed in a corner on the second bottom wall portion17hside of the third upper wall portion17f, and a plurality (3in the embodiment) of diamond-shaped recesses17u(seeFIG. 2andFIG. 5) are formed in a corner on the first side wall17jside at the front end of the first upper wall portion17d.

The operation of the mode for carrying out the present invention having the above-mentioned arrangement is now explained.

When the vehicle brakes suddenly, the vehicle body attempts to move forward by virtue of inertia while leaving the wheel W on the road surface, and a load that attempts to make the knuckle mounting portion17amove to the rear side of the vehicle body relative to the first and second vehicle body mounting portions17band17cof the arm main body17of the suspension arm13therefore acts. Furthermore, when the wheel W rides over a step on the road surface, a load that attempts to move the knuckle mounting portion17ato the rear side of the vehicle body similarly acts.

In this process, if the line of action of the load deviates vertically from the cross-sectional center of the arm main body17, a moment that vertically deforms the arm main body17occurs, but it is difficult to make the cross-sectional center of the arm main body17coincide with the line of action of the load in the vertical direction. However, in accordance with the present embodiment, since the first inclined projecting portion17ois formed so as to bulge upward on the end part on the first vehicle body mounting portion17bside of the first bottom wall portion17gof the arm main body17, and the second inclined projecting portion17pis formed so as to bulge upward on the end part on the first vehicle body mounting portion17bside of the second bottom wall portion17hof the arm main body17, it is possible to enhance rigidity by means of these first and second inclined projecting portions17oand17pwithout increasing the weight of the arm main body17, thereby preventing deformation of the arm main body17by the load.

In particular, since the first inclined projecting portion17ois continuous to the first bottom wall portion17gwhile reducing in height and width in going from the first upper wall portion17dside toward the second upper wall portion17eside, and the second inclined projecting portion17pis continuous to the second bottom wall portion17hwhile reducing in height and width in going from the third upper wall portion17fside toward the second upper wall portion17eside, it is possible to prevent stress from concentrating at the border between the first and second inclined projecting portions17oand17pand the first and second bottom wall portions17gand17h. Moreover, since the third bottom wall portion17iconnected to the first and second bottom wall portions17gand17his provided at the position sandwiched between the first and second inclined projecting portions17oand17pof the arm main body17, and the through hole17qis formed in the third bottom wall portion17i, not only is it possible to enhance operability by utilizing the through hole17qas an insertion hole for a bolt, a nut, a tool, etc. when assembling the suspension arm13on the vehicle body12, but it is also possible to utilize the through hole17qas a drain hole for drainage or as a cutout hole for weight reduction.

Furthermore, since the plurality of diamond-shaped recesses17sare formed in the peripheral edge part of the second vehicle body mounting portion17cof the arm main body17, it is possible to enhance the rigidity of the second vehicle body mounting portion17cagainst a load inputted from any direction, thus improving durability. Since, among the plurality of recesses17s, one at an end is provided in the vicinity of the part where the lower wall portion17nstops and stress concentrates, it is possible to enhance effectively the rigidity of that part.

In particular, with regard to the second vehicle body mounting portion17c, which is supported on the vehicle body12by the rubber bush joint20in a vertically swingable manner, if the height of the first and second side wall portions17jand17ksurrounding the periphery thereof is high, there is a possibility that the first and second side wall portions17jand17kwill interfere with the vehicle body12, and the height of the first and second side wall portions17jand17kis therefore set lower for a part around the second vehicle body mounting portion17cthan other parts. As a result, the rigidity of the arm main body17becomes low in the vicinity of the second vehicle body mounting portion17c, but since the recesses17sare formed at the border between the first and second upper wall portions17dand17eand the first and second side wall portions17jand17kin that part, it is possible to enhance the rigidity in the vicinity of the second vehicle body mounting portion17cof the arm main body17.

Similarly, it is possible to enhance the rigidity between the knuckle mounting portion17aand the first vehicle body mounting portion17bof the arm main body17by means of the plurality of diamond-shaped recesses17tformed in the corner on the second bottom wall portion17hside of the third upper wall portion17fof the arm main body17, and it is also possible to enhance the rigidity in the vicinity of the first vehicle body mounting portion17bof the arm main body17by means of the plurality of diamond-shaped recesses17uformed in the corner on the first side wall portion17jside at the front end of the first upper wall portion17dof the arm main body17.

As shown inFIG. 5andFIG. 10, since the weld part at the end edge of the arm main body17, to which the outer face of the pipe-shaped first vehicle body mounting portion17bis welded, is formed from the substantially horizontally extending first weld part w1and the second and third weld parts w2and w3extending downwardly from the front and rear opposite ends of the first weld part w1, when a load facing to the rear of the vehicle body is inputted into the weld part, the strength of the first weld part w1, which is parallel to the direction of the load, is high, but the strength of the second and third weld parts w2and w3, which are not parallel to the direction of the load, is low. In this case, the strength of the second and third weld parts w2and w3is the weakest when they are at right angles relative to the direction of the load, but since the distance B between the lower ends of the second and third weld parts w2and w3is set larger than the distance A between the upper ends thereof, the direction of the second and third weld parts w2and w3changes from a right angle to being more parallel to the direction of the load, thus enhancing the strength.

In particular, since the third weld part w3is bent in the direction in which it moves away from the second weld part w2while extending downwardly from the part connected to the horizontally extending first weld part w1, the direction of the lower part of the third weld part w3is made closer to being parallel to the direction of the load, and the load in the vehicle body fore-and-aft direction inputted from the arm main body17into the weld part is dispersed over a wider range of the first vehicle body mounting portion17b, thereby enhancing the durability of the weld part. Moreover, among the first and second upper wall portions17dand17eand the first and second side wall portions17jand17kforming the portion sandwiched between the first and second vehicle body mounting portions17band17cof the arm main body17, since the first side wall portion17jis bent in the direction in which the first vehicle body mounting portion17bside thereof moves away from the second side wall portion17kand is continuous to the third weld part w3, it is possible to disperse the load applied to the third weld part w3toward the first side wall portion17j, thus enhancing the durability of the third weld part w3.

A mode for carrying out the present invention is explained in detail above, but the present invention may be modified in a variety of ways as long as the modifications do not depart from the spirit and scope thereof.

For example, in the embodiment the suspension arm13of the strut type suspension system S is illustrated, but the present invention may be applied to a suspension arm of any other type of suspension system.

Furthermore, in the embodiment the second weld part w2on the front side is formed downward at right angles relative to the first weld part w1on the upper side, and the third weld part w3on the rear side is formed obliquely downward to the rear relative to the first weld part w1on the upper side, but the second weld part w2on the front side may be formed obliquely downward to the front and the third weld part w3on the rear side may be formed downward at right angles; alternatively, the second weld part w2on the front side may be formed obliquely downward to the front and the third weld part w3on the rear side may be formed obliquely downward to the rear.

Moreover, in the embodiment the recesses17sare formed on the peripheral edge part of the second vehicle body mounting portion17c, but a recess may be formed on a peripheral edge part of the knuckle mounting portion17aor the first vehicle body mounting portion17b.

Furthermore, the same operational effects may be achieved by forming projections instead of the recesses17sof the embodiment, and the shape of the recesses17sis not limited to a diamond shape and may be various polygonal, circular, or elliptical shapes.