Dual tube lower frame midrail structure

A lower frame midrail structure for an automotive vehicle is formed from a pair of tubular members manufactured through a hydroforming process. The two tubular members are welded together in a longitudinally extending portion to provide support for the mounting structure of a bumper assembly. The joinder of the two tubular members creates a lower frame midrail cross-section that has a generally vertical internal web to strengthen and stiffen the midrail structure. The two tubular members laterally diverge from one another in a divergent zone in which the laterally spaced tubular members provide a stable interior and exterior support for a shock tower support member to be welded to the top of the tubular members. The hydroforming process can form openings in the sidewalls of the tubular members to permit passage of cross frame members to enhance the welding of the cross frame members to the midrail structure.

FIELD OF THE INVENTION

This invention relates to a lower frame midrails for an automotive vehicle and, more particularly, to a midrail assembly formed from a pair of side-by-side tubular members, which provide an enhanced support for the shock tower support member.

BACKGROUND OF THE INVENTION

Lower frame midrails in an automotive vehicle support the central part of an automotive chassis and provide a cantilevered support for the rear bumper assembly. Conventionally, the rear bumper assembly would include a transverse bumper beam, lower frame rails and appropriate attachment brackets for connecting the bumper beam to the lower frame rails and the lower frame rails to the midrails. The rear shock tower support members are mounted on top of the midrails, conventionally in a cantilevered manner off of a single fabricated rail structure.

The structure of a lower frame midrail can vary significantly from manufacturer to manufacturer. As can be seen in U.S. Patent Publication No. 2004/0080188, filed by Masanori Igarashi, et al and published on Apr. 29, 2004, the longitudinal frame rails are connected by a cross frame member with legs that straddle the shock absorber column. A bracket is placed over the leg to mount and support the shock absorber. In U.S. Pat. No. 4,708,391, issued to Mitusou Nakano on Nov. 24, 1987, the longitudinal frame rails are reinforced by a member that is located adjacent both longitudinal sides of the shock absorber spring.

U.S. Pat. No. 5,411,311, issued to Roger Shimmell, et al on May 2, 1995, and assigned to Ford Motor Company, the front shock absorber towers are braced with a transverse member between the towers and members located between the cowl and the shock absorber towers. U.S. Pat. No. 5,988,734, issued to Stephen Longo, et al on Nov. 23, 1999, teaches a conventional bumper mounting configuration wherein the vehicle frame is reinforced by a central tunnel and reinforcing pads between the tunnel and the rails. Akira Nomura, in U.S. Pat. No. 6,773,057, issued on Aug. 10, 2004, teaches that the front shock strut tower can be supported on an apron, which is reinforced by members that extend between the longitudinally extending tubular members.

It would be desirable to provide lower frame midrails for use in conjunction with a bumper and lower frame rail structure of an automobile that are particularly adaptable to manufacturing through hydroforming processes and which can be utilized to provide a stable support for the rear shock tower.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome the aforementioned disadvantages of the known prior art by providing a lower frame midrail structure that is formed from a pair of tubular members.

It is a feature of this invention that the lower frame midrail structure can be formed through hydroforming processes to enhance manufacturing efficiencies.

It is an advantage of this invention that the geometrical configuration of the lower frame midrails can be sized to correspond to a bumper beam that integrally incorporates the bumper beam and lower frame mounting rails.

It is still another advantage of this invention that the two tubular members of the lower frame midrails can be welded together at a longitudinally extend portion for mounting with the bumper support structure.

It is still another feature of this invention that the lower frame midrails can be separated in a divergent portion to provide interior and exterior support for a shock tower support member.

It is a further advantage of this invention that the shock tower support stamping can have support on laterally spaced frame members to provide a stable support for the rear shock tower.

It is another object of this invention to provide a dual tube lower frame midrail structure that is durable in construction, inexpensive of manufacture, facile in assemblage, and simple and effective in use.

These and other objects, features and advantages are accomplished according to the instant invention by providing a lower frame midrail structure for an automotive vehicle that is formed from a pair of tubular members manufactured through a hydroforming process. The two tubular members are welded together in a longitudinally extending portion to provide support for the mounting structure of a bumper assembly. The joinder of the two tubular members creates a lower frame midrail cross-section that has a generally vertical internal web to strengthen and stiffen the midrail structure. The two tubular members laterally diverge from one another in a divergent zone in which the laterally spaced tubular members provide a stable interior and exterior support for a shock tower support member to be welded to the top of the tubular members. The hydroforming process can form openings in the sidewalls of the tubular members to permit passage of cross frame members to enhance the welding of the cross frame members to the midrail structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 1 and 2, a bumper and lower frame rail, including a shock tower support, forming a part of the rear end of an automobile frame and incorporating the principles of the instant invention, can best be seen. The frame10of the automobile is preferably formed from hydroformed tubular members. Such tubular members can be spot-welded and/or MIG-welded to form an integral frame assembly for the rear end of a vehicle.

Hydroforming is a process by which a standard tubular stock member is placed into a form shaped to correspond to the particular member to be formed and to correspond to the particular section required for the frame design. A liquid is then introduced into the interior of the tubular stock and pressurized until the tubular stock expands to assume the shape defined by the configured form. The expanded and re-shaped tubular stock now has a substantially different shape. By forming cutouts and other access openings into the re-shaped tubular member, spot-welding electrodes can gain access to opposing adjacent sides to create a weld bond between juxtaposed members. In this manner, a frame, as an example, for an automobile can be created using in large part hydroformed tubular members. One skilled in the art will readily recognize that some MIG-welding will be required in areas where access holes are detrimental to the integrity of the frame structure. Preferably, such MIG-welding processes are performed at a sub-assembly or at a supplier level.

In the automotive rear end frame10depicted in the drawings, the bumper15is formed from welded hydroformed members. Similarly, the lower frame rails20, which connect to the bumper15and project forwardly therefrom, are formed from tubular hydroformed members. The shock tower support member25is preferably a stamping that is formed into a specific shape and mounted on the lower frame rails20, as is described in greater detail below.

The lower frame rail20is formed from two hydroformed tubular members21,22that have corresponding first longitudinally extending portions23that are welded together at the rearwardmost end of the members21,22preferably by MIG-welding along the generally horizontal seam between the members21,22. As is best seen inFIGS. 1 and 5, the lower frame rail structure20would then have an internal vertical web24formed from the adjacent sidewalls of the two tubular members21,22, oriented as an exterior member21and an interior member22. The internal web24substantially increases the strength and stiffness of the lower frame rail20, compared to a conventional tubular member.

The longitudinally extending portions23are positioned for connection to the bumper15, as will be described in greater detail below. Forwardly of the longitudinally extending portions23, the two tubular members21,22diverge to define a divergent portion28to provide a lateral spacing between the two members21,22. At this point of divergence, the shock tower support25is affixed, preferably by welding, to the top of the two tubular members21,22. The tubular members21,22converge into a second longitudinally extending portion29forward of said divergent portion28.

Unlike conventional shock tower stampings, the shock tower support member25is adequately supported both inboard and outboard on the laterally spaced members21,22to provide a stable foundation for the shock tower (not shown). The shock tower support stamping25transfers road loads directly to the frame10and also provides sectional stability for any rear impact loads that might be encountered. This design results in a stiffer, stronger, yet lighter joint than is known in the prior art.

To facilitate the use of spot welding techniques, the tubular members21,22can be formed with appropriate access openings (not shown) in the sidewalks for passage of a welding electrode. Similarly, cross frame members30can be welded between the opposing sides of the lower frame rails20to span the lateral distance across the vehicle frame10. The cross frame members30can be inserted into appropriate openings27in the sidewalls of the tubular members21,22to permit the passage of the cross frame members30internally into the interior tubular member22to enable the cross frame members30to be welded directly to the interior tubular member22.

Preferably, as is best seen inFIG. 6, at least one of the cross frame members30adjacent the shock tower support25will pass through appropriate openings27in the interior tubular member22to engage the exterior tubular member21to permit welding between both members21,22and the cross frame member30. Such fabrication will add cross-vehicle stiffness to the frame10, as well as provide a robust joint at the shock tower support25. Preferably, the interior and exterior tubular members21,22converge so that the lower frame rail20will extend forwardly with a central vertical web24, as is shown with respect to the rearward longitudinally extending portions23.

The bumper15can also be constructed from two hydroformed members16,17, with the upper tubular member16being located on top of the lower tubular member17. Preferably both tubular bumper members16,17are shaped substantially identically with a rearwardly positioned bight portion18and opposing mounting legs19. The two tubular members16,17can be MIG-welded along the generally horizontally extending seam therebetween to form a dual-celled bumper15. Formation of the tubular members through the hydroforming process permits the introduction of deformation triggers39, i.e. fold points to direct the deformation of the bumper in a prescribed manner when encountering an impact load.

This bumper15not only has the transversely oriented bight portion18forming the laterally extending rear bumper beam12, but the integrally formed longitudinally extending mounting legs19provide the function of mounting the bumper beam12to the lower frame rails20. A curved transition portion13preferably separates the transverse bight portion18from the longitudinal mounting legs19. In conventional bumper design, the bumper beam, mounting rails, and attachment brackets are separate parts that are assembled to form the bumper structure. The formation of the bumper15according to the principles of the instant invention substantially reduces the number of parts required. With the two tubular members16,17being welded together in a vertical orientation, the resultant structure has a horizontally oriented internal web14that enhances strength and stiffness for the bumper structure15.

One of ordinary skill in the art will readily realize that the bumper15could also be formed through a roll-forming process in which the upper and lower cells of the bumper beam15would be separated by a horizontally oriented internal web14. While the formation of the tubular members16,17through the hydroforming process enables the tubular members16,17to have triggers39formed therein during the formation process, the crash triggers39would have to be formed in the bumper by a separate processing step if the bumper15were manufactured through the roll-forming process.

Referring particularly toFIGS. 3-5, the forward ends of the mounting legs19are formed to mate with the dual tube lower frame rails20. Each tubular member16,17is formed with a reduced-sized terminal end35that can fit between the interior and exterior sidewalls of the lower frame rails20, whereas the remainder of the mounting legs19are formed to correspond geometrically with the longitudinally extending portions23of the lower frame rails20. As a result, the insertion of the reduced-sized terminal end35into the rearward ends of the lower frame rails20results in a generally uniformly shaped frame10with the overall width and depth of the bumper structure15being substantially equal to the overall width and depth of the lower frame rails20.

To accommodate the interference between the horizontal internal web14of the mounting legs19and the vertical internal web24of the longitudinally extending portions23of the lower frame rails20, the reduced-size terminal end35is formed with a slot37into the top and bottom walls of both of the upper and lower tubular members16,17. When the reduced-size ends35of the mounting legs19are inserted into the lower frame rails20, the vertical internal web24slides into the aligned slots37.