Background of the Invention Space frame architecture is increasingly being used in vehicle construction. A space frame is an assembly of individual frame components that are connected at joints to form a cage-like structure on which the other vehicle components are mounted, including the engine, the drive train, the suspension and the hang-on vehicle body parts. Tubular hydroforming potentially offers many advantages in space frame construction because it would enable manufacturers to increase frame stiffness, dimensional stability, fatigue life, and crashworthiness over nonhydroformed space frames while reducing frame mass and cost.

Hydroforming is a metal-forming process in which high pressure fluid is used to outwardly expand a tubular blank into conformity with surfaces of a die cavity of a die assembly to form an individual hydroformed member. Individual blanks can be hydroformed to have a wide range of longitudinal geometries and each hydroformed member can have a cross-sectional configuration that varies continuously along its length. Holes of various sizes and shapes can optionally be punched in the hydroformed member at selected locations along its length during or after the hydroforming process.

Prior art vehicle frames often included frame parts made by forming several structures by stamping and then welding these several individually stamped structures together. Vehicle manufactures can replace this type of frame part with a single hydroformed part, thereby reducing both the number of parts and the number of welds necessary to complete frame construction. Consequently, vehicle weight and assembly costs are reduced. Hydroformed parts also have higher strength, in part because of the plastic deformation of the wall of the blank during the hydroforming

process. More particularly, the outward expansion of the wall of the blank during hydroforming caused by the fluid pressure creates a work-hardening effect which uniformly hardens the metal material of the blank. This allows the manufacturer to replace several stamped frame parts with a single stiffer and lighter weight hydroformed part. Hydroforming also produces less waste metal material than stamping.

Thus, tubular hydroforming has many advantages over conventional stamping and welding. The number of frame parts can be reduced and the overall weight of the frame can be reduced through more efficient cross section design and through tailoring of the wall thickness along the length of each hydroformed part while at the same time achieving increased structural strength and frame stiffness. Tooling costs are lowered because fewer parts are required. Stacked tolerances (i. e., dimensional inaccuracies of the frame) are reduced because of the greater dimensional accuracy of each hydroformed part.

It is also advantageous in the automotive industry to be able to use existing equipment to manufacture space frame components. Because most vehicle body designs change each model year, however, it is usually necessary to change the configuration of the vehicle frame to realize a new vehicle body design and this can make frame component manufacturing equipment used for prior vehicle models obsolete.

A modular approach to space frame design can extend the useful life of space frame component manufacturing equipment because this approach allows portions of a space frame to be used for two or more models and yet allows the vehicle body design to be updated. A modular approach to space frame design would be particularly advantageous in space frame design that is constructed of hydroformed members because of the advantages offered by tubular hydroforming. It would thus be desirable in the automotive industry to have a hydroformed modular space frame that can provide easy assembly and allow the reuse of portions of the vehicle space frame among several vehicle models. It is also desirable to manufacture a space frame using as few parts as possible and to reduce stacked tolerances as much as possible.

Summary of the Invention An aspect of the present invention to meet the needs identified provides a vehicle space frame for constructing a pick-up truck type motor vehicle, comprising a body module and a front module. The body module includes a pair of laterally spaced, longitudinally extending main side rail structures and a pair of rearward-most upright structures each being connected to a respective main side rail structure and extending upwardly therefrom to form a pair of rearward-most pillars thereon. The body module further includes a pair of hydroformed upper longitudinal members each being defined by an outwardly deformed tubular metallic wall fixed in a predetermined irregular exterior surface configuration and each including a pillar- forming portion and a longitudinally extending portion. Each pillar-forming portion is connected to a respective main side rail structure and extends upwardly therefrom to form an A pillar and each longitudinally extending portion is connected at an opposite end portion thereof with an associated one of said rearward-most pillars, thereby defining a longitudinal length between the associated A-and rearward-most pillars. A plurality of connecting structures are included in the body module and are constructed and arranged to dispose the main side rail structures, the upper longitudinal members, and the pairs of pillars in laterally spaced fixed relation. The front module includes a pair of front lower side rail structures, a pair of front upper side rail structures and front connecting structure. The front connecting structure is constructed and arranged to connect the front lower side rail structures to one another in laterally spaced relation and the front upper side rail structures to one another in laterally spaced relation. The front module is rigidly fixed to the body module by rigidly interconnecting each front lower side rail structure with a respective main side rail structure and each front upper side rail structure to the pillar-forming portion of a respective hydroformed upper longitudinal member at a position spaced upwardly from the associated main side rail structure.

Brief Description of the Drawings FIG. 1 is a partially exploded perspective view of a space frame for a pickup- type vehicle constructed according to the principles of present invention; and

FIG. 2 is a schematic view of a hydroforming die assembly with a tubular blank therein.

Detailed Description of the Preferred Embodiment and Best Mode FIG. 1 shows a modular space frame 10 for a pickup truck-type vehicle. The space frame 10 includes a body module 20 and a front module 22. The body module 20 includes a pair of laterally spaced, longitudinally extending main side rail structures 14 and a pair of rearward-most upright structures 26. Each rearward-most upright structure 26 is connected to a respective main side rail structure 14 and extends upwardly therefrom to form a pair of rearward-most pillars on the main side rail structures 14.

The body module 20 also includes a pair of hydroformed tubular upper longitudinal members 30,32 each being defined by an outwardly deformed tubular metallic wall fixed in a predetermined irregular exterior surface configuration. The upper longitudinal members 30,32 are of mirror image construction, so only upper longitudinal member 30 will be discussed in detail, but the discussion applies equally to upper longitudinal member 32. Each upper longitudinal member 30 includes a pillar-forming portion 34 and an integral longitudinally extending portion 36. Each pillar-forming portion 34 is connected to a respective main side rail structure 14 at a joint 37 and extends upwardly therefrom to form a forward-most or"A"pillar thereon.

The longitudinally extending portion 36 of each upper longitudinal member 30 is integrally connected at one end with an associated pillar-forming portion 34 and is connected at an opposite end 38 thereof with an upper end of an associated rearward- most pillar 26 (to form an integral connection therewith as considered below). The longitudinally extending portion 36 of each hydroformed upper longitudinal member 30 thus defines a longitudinal length between the associated forward-most and rearward-most end pillars 26,34 on each side of the body module 20. The longitudinal length defined by the integral hydroformed structure minimizes the stacked tolerances between the forward-most and rearward-most pillars as taught and described in detail in commonly assigned United States Patent Number 6,092,865 and entitled HYDROFORMED SPACE FRAME AND METHOD OF

MANUFACTURING THE SAME. Each longitudinally extending portion 36 also provides a roof supporting structure or roof rail structure therebetween.

A plurality of laterally extending connecting structures, generally designated 40, are connected between the main side rail structures 14, between the upper longitudinal members 30,32, and between the rearward-most pillars 26. The plurality of connecting structures 40 are constructed and arranged to secure the main side rail structures 14, the upper longitudinal members 30,32, and the pairs of pillars 34,26 (i. e., the A pillars 34 and the rearward-most pillars 26) in laterally spaced, fixed relation.

Each upper longitudinal member 30 further includes a second hydroformed pillar-forming portion 50 extending integrally downwardly from the opposite end 38 of the longitudinally extending portion 36 thereof and forming a joint 52 with the associated main side rail structure 14 so that each upper longitudinal member 30 has a generally inverted U-shaped configuration. Each second pillar-forming portion 50 forms the rearward-most or"D"pillar 26 on each main side rail structure 14.

Each main side rail structure 14 extends rearwardly beyond the joint 52 with the second pillar-forming portion 50 of the associated upper longitudinal member 30, 32 so that the rearward-most portion of each main side rail structure 14 defines a lower side rail 54 of a bed portion of a pickup truck-type vehicle. The space frame 10 further includes a bed cross structure 58 extending laterally between the free ends of the bed forming lower portions 54 of the main side rail structures 14. A pair of bed upright structures 60 each extend upwardly from a respective free end of the bed cross structure 58. Each of a pair of longitudinally extending bed upper side rail structures 62 are connected between a respective bed upright structure 60 and an intermediate portion of the second pillar-forming portion 50 of the associated upper longitudinal member 30,32 (i. e., the associated D pillars).

The space frame 10 includes two pairs of intermediate upright structures 24 and 25. The pair members of each is pair 24,25 are connected between a respective main side rail structure 14 and the longitudinally extending portion 36 of an associated upper longitudinal member 30,32 thereby forming a pair of intermediate pillars of the body module 20. The pairs 24 and 25 constitute the B pillars and the C pillars, respectively, of the body module 20.

The B'and C pillars are preferably provided by a pair of tubular hydroformed U-shaped cross members 64,66. Each member 64,66 is defined by an outwardly deformed tubular metallic wall fixed in a predetermined irregular exterior surface configuration and each member 64,66 is mounted laterally between the main side rail structures 14 of the body module 20. Each U-shaped cross member 64,66 includes a cross portion 68,70, respectively, and a pair of leg portions 72,74, respectively, extending integrally from respective junctures 76,78 at opposite ends of the respective cross portion 68,70. Each leg portion 72,74 of each U-shaped cross member 64,66 is connected at a free end thereof to a respective main side rail structure 14 at respective joints 75,77 therewith and extends upwardly therefrom.

Each juncture 76,78 of each U-shaped member 64,66 is connected to the longitudinally extending portion 36 of the associated upper longitudinal member, 30, 32 at joints 23,27, respectively, so that the leg portions 72,74 of the first and second U-shaped cross members 64,66 thereby form the first and second pairs of longitudinally spaced corresponding, laterally spaced intermediate (B and C) pillars 24,25, as mentioned. Preferably, the joints 23,27 are formed by welding the junctures 76,78 in recesses formed in the upper longitudinal member 30 according the principles taught in US Patent no. 6,092,865, although the formation of a recess in either member is not necessary to form either joint 23,27. The members could be, for example, welded together without a recess. The cross portions 68,70 extend laterally between the longitudinally extending portions 36 of the upper longitudinal members 30,32 and between the pillars 24,25, thereby defining a lateral length between the pairs of corresponding intermediate pillars, 24,25. The cross portions 68,70 also provide part of the laterally extending connecting structure 40 of the body module 20 that is constructed and arranged to connect the intermediate pillars to one another in laterally spaced, fixed relation.

The front module 22 includes a pair of front lower side rail structures 18, a pair of front upper side rail structures 42 and front connecting structure, generally designated 44. The front connecting structure 44 is constructed and arranged to connect (i) the front lower side rail structures 18 to one another in laterally spaced fixed relation and (ii) the front upper side rail structures 42 to one another in laterally spaced fixed relation.

The front connecting structure 44 includes (1) a laterally extending forward upper cross structure 39 connected between the forward ends of the front upper side rail structures 42 at butt welded joints 41, thereby forming the bight portion and leg portions respectively of a front upper U-shaped structure, (2) a laterally extending forward lower cross structure 43 connected between the forward ends of the front lower side rail structures 18 at butt welded joints 45, thereby forming the bight portions and leg portions respectively of a front lower U-shaped structure, (3) a pair of laterally spaced, vertically extending connecting structures 47 each being connected generally between the bight portions 39,43 of the front upper U-shaped structure and the lower front U-shaped structure and (4) a laterally extending connecting structure 49 connected between the pair of leg portions (provided by the front lower side rail structures 18) of the front lower U-shaped structure.

The front module 22 is rigidly fixed to the body module 20 by rigidly interconnecting (1) each front lower side rail structure with a respective main side rail structure 14 (to form telescopically interengaged and welded joints therebetween that are not shown but which are indicated by a dashed line in FIG. 1) and (2) each front upper side rail structure 42 to a pillar-forming portion 34 of a respective hydroformed upper longitudinal member 30,32 at a position spaced upwardly from the associated main side rail structure 14 (at butt welded joints that are not shown but which are indicated by a dashed line in FIG. 1). The rearward end of each front upper side rail structure 42 is connected at a position spaced upwardly from the associated main side rail structure 14.

Preferably the main side rail structures 14 are provided by a pair of hydroformed tubular main side rail members 80,82 of mirror image construction.

Only side rail member 80 is considered in detail, but the discussion applies equally to member 82. The hydroformed side rail member 80 has an essentially straight forward portion 84, which transitions into an upwardly angled intermediate portion 86 which in turn transitions into an essentially straight rearward portion 88 (which provides the lower side rail 54 of the bed portion of the pickup truck bed).

The upper longitudinal member 30 is formed from a tubular metal blank that includes a butt weld connection 90. The structure and construction of the blank including the butt weld connection 90 and the subsequent hydroforming thereof is

considered in detail below. The end portion of the second pillar-forming portion 50 of the longitudinally extending portion 30 has an essentially rectangular cross section and extends below the hydroformed side rail member 80 through a notch 81 therein.

Preferably the upper longitudinal member 30 is welded into the notch 81 to form the joint 52. The end portion is provided with a cut out notch 92. A cross member 94 that is preferably of hydroformed construction and which forms a part of the laterally extending connecting structure 40 of the body module 20 is mounted in respective notches 92 in the upper longitudinal members 30,32 and is secured therein by welding or by other appropriate means.

Three laterally extending essentially straight cross members 96,98,100 (preferably formed by hydroforming) are mounted between the upper longitudinal members 30,32. Specifically, the pair of cross members 96,98 are rigidly fixed (preferably by welding) within hydroformed recesses 102,104, respectively, formed in the upper longitudinal members 30,32 to form joints 106,108, respectively. The cross member 100 is of generally tubular construction but is provided with flattened end portions that are disposed in overlying relation with the longitudinally extending portion 36 of each upper longitudinal member 30 and welded thereto to forming joints 110.

Preferably the bed cross structure 58 and bed upright structures 60 are provided by three separate essentially straight hydroformed tubular members 61,63, 65, respectively, that are butt welded together at joints 73. Preferably the hydroformed members 63,65 are butt welded to respective ends of the hydroformed member 61 that provides the cross structure 58. Similarly, each upper side rail structure 62 is preferably provided by an essentially straight hydroformed tubular member 67,69 that is connected to the space frame at joints 113,115 by butt welding.

Alternatively, the cross structure 58 and the pair of upright structures 60 at the rear of the bed portion of the space frame 10 can be provided by the leg portions and cross portion of an integral hydroformed U-shaped member (not shown) or by any other appropriate construction.

Preferably the front lower side rail structures 18 and the front upper side rail structures 42 are provided by individual hydroformed members 112,114,116,118, respectively. Similarly, the forward upper and lower cross structures 39,43 and the

cross structure 49 are preferably provided by hydroformed members 120,122,124, respectively (although any appropriate construction can be used). The hydroformed members 116,118,120 are preferably connected by welding at joints 41, the hydroformed members 112,114,122 are preferably connected by welding at joints 45 and the hydroformed members 112,114,124 are preferably connected by welding at joints 126. The vertically extending connecting structures 47 are preferably skeletonized sheet metal structures formed by stamping or by any other appropriate means and are secured between the cross members 120,122 by welding or by any other suitable means. The joints 37,75 are formed by welding the hydroformed members 30,72 in openings 113,115, respectively, in the main side rail structures 14.

Joint 77 can be formed by welding a notched portion 117 of the U-shaped member 74 to the upper and outer side surfaces of the main side rail structures 14.

The shape and the length of the upper and lower front side rail members and of the front connecting structure can be varied to provide a range of front module heights, front module widths (in the cross car direction) and front module lengths (and thus vehicle lengths). It can also be understood that when the front lower side rail structures are part of the body module (whether joined to the main side rail structures at a joint or integrally connected thereto), the body module will determine the vehicle length.

Hydroforming Method The preferred hydroforming process for forming each hydroformed member of space frame 10 described above can be understood from FIG. 2 Each hydroformed member is formed from a tubular blank 620 constructed of a suitable metal material and has a closed transverse cross section and open tubular ends. Each blank 620 may be constructed by any suitable method. For example, the transverse cross section of each blank 620 may be shaped by roll forming a continuous longitudinally extending strip of sheet metal in a roll forming operation and the transverse cross section subsequently closed by a seam welding operation. Thus, preferably, each of the hydroformed tubular members has only a single longitudinally extending seam weld that is formed in creating the original tubular blank. This is distinct from more conventional tubular frame members, which comprise two C-shaped or"clam-shell"

halves welded-to one-another in facing relation along two seams. The tubular blank is then cut to the length required to make a particular hydroformed member.

If required by the part geometry, it is within the scope of the invention to form a single tubular blank from two separately roll formed tubular blanks of different diameters which have been butt-welded to one another at a butt-welded connection.

That is, if the diameter of a single hydroformed member increases (or decreases) greatly along its longitudinal length, the tubular blank used to make that hydroformed member can be constructed by butt welding two blanks of different diameter. The diameters of the two ends to be butt-welded can be equalized either by using a reduction tool to reduce the diameter of one end of the larger diameter tubular blank or, alternately, by using a flaring or expansion tool to expand the diameter of an end portion of the smaller diameter blank, or a combination of both.

The result of either operation is to equalize the diameters of the two ends to be butt-welded together. The butt-welded connection is formed prior to the hydroforming operation, but the butt-welding operation can be performed either before or after any pre-bending operations (considered immediately below) are performed. An example of a hydroformed member having a butt weld connection is the upper longitudinal member 30 in the space frame 10 in FIG. 1 which includes a butt weld 90.

The blank may optionally be"pre-bent", that is, bent prior to being placed in a hydroforming die assembly, if the geometry of the part is complex or if there are to be any sharp bends in the finished member. For example, if there is to be a sharp bend (a bend of greater than 30°) in the hydroformed member, preferably the present invention bends the blank according the teachings of US Patent no. 6,065,502, entitled METHOD AND APPARATUS FOR WRINKLE-FREE HYDROFORMING OF ANGLED TUBULAR PARTS. The teachings of US Patent no. 6,065,502 can be used to avoid wrinkle formation during the bending operation, particularly on the concave portion of each bend in a hydroformed part. Examples of sharp bends in the individual hydroformed parts of the space frame 10 (FIG. 1) include the bend between each leg portion 72 and the cross portion 68 of the first U-shaped member 64.

It should be understood that the methodology of US Patent no. 6,065,502 would preferably not be used for parts that are bent at an angle of less than 30°.

Preferably, straight parts (such as cross member 94 in FIG. 1, for example) are hydroformed in accordance with the teachings of US Patent no. 5,979,201, ENTITLED HYDROFORMING DIE ASSEMBLY FOR PINCH-FREE TUBE FORMING. A blank may also be bent in a CNC bending machine prior to being placed in the die assembly. A suitable lubricant may be applied to the exterior of the blank prior to placing it in the die assembly.

With reference again to FIG. 2 the tubular blank 620 is then placed between the die halves 622,624 of the die assembly 626 and the assembly is closed. The tubular blank 620 is preferably immersed in a fluid bath so that it is filled with hydroforming fluid. A hydroforming ram assembly 628,630 is engaged with each end of the tubular blank 620 such that a ram member 636,638 of each assembly 628, 630 seals an end of a tubular blank 620. The ram members 636,638 include hydraulic intensifiers which can intensify the hydroforming fluid, thereby increasing the fluid pressure of the fluid within the blank 620 to irregularly outwardly deformed tubular metallic wall, generally designated 640, of the tubular blank 620 into conformity with the die surfaces 642 of the die cavity to thereby form a hydroformed member having an exterior surface that is fixed into a predetermined irregular configuration.

The ram members 636,638 push axially inwardly on opposite ends of the blank 620 to create metal flow within the blank during outward expansion. The fluid pressure and the axial pressure are independently controllable. Preferably, the ends of the tubular blank 620 are pushed axially inwardly during the hydroforming operation to maintain the wall thickness of the fully formed hydroformed member within a predetermined range of the wall thickness of the initial tubular blank 620. Preferably the ram members 636,638 cooperate to replenish or maintain the wall thickness of the outwardly expanding wall portions of the blank 620 so that the wall thickness of the resulting hydroformed member is within about +/-10% of the original wall thickness of the blank 620 (i. e., to compensate for wall thinning during diametric outward expansion of the tube).

The tubular blank 620 expands into conformity with the surfaces 642 defining the hydroforming die cavity so as to irregularly outwardly expand the metallic wall 640 of the blank 620 into conformity with the surfaces 620 of the die assembly 626 to

provide the metallic wall 640 with a shape corresponding to the desired shape for the member. The shape of each die cavity used to form each hydroformed member of each space frame 10,150,300,460 in accordance with the present invention is particularly adapted to the shape of the new and advantageous hydroformed tubular members contemplated herein.

If holes are to be formed in a hydroformed member, the holes may be formed whole the member is still in the die assembly during the hydroforming operation or may be formed after the hydroformed member is removed from the die assembly along with any other required further processing of the member. More particularly, holes may be formed during the hydroforming process in what is known in the art as a hydropiercing operation. A hydropiercing operation is disclosed in U. S. Patent No.

5,460,026 which is hereby incorporated by reference in its entirety into the present application. Alternatively, holes or notches may be cut in a hydroformed member after the hydroforming operation is completed. Recesses (such as recesses 102,104 in FIG. 1) can be formed in the walls hydroformed members during outward expansion of the metallic wall of the blank by using a net pad.

It can be appreciated that the transverse cross section of many of the hydroformed members varies along the length of the particular hydroformed member.

For example, the transverse cross sections of the leg portions 72 and the cross portion 68 of the tubular hydroformed cross member 64 vary long the longitudinal length thereof. The cross portion 68 has a relatively small, substantially rectangular cross- section and the leg portions 72 have relatively large substantially rectangular cross- section near the free ends thereof and an irregular transverse cross section in the middle portions thereof. It can be understood that altering the cross-sectional configuration of this tubular hydroformed member or of any other tubular hydroformed member disclosed herein can be accomplished without departing from the principles of the present invention.

Method of Forming a Space Frame It can thus be understood that a preferred method of forming a space frame 10 for a motor vehicle includes forming each of a pair of upper longitudinal members 30 in a hydroforming procedure, each procedure including providing an angularly shaped tubular blank 620 having a metallic wall 640, placing the blank 620 into a die

assembly 626 having die surfaces 642 defining a die cavity and providing pressurized fluid in an interior of the blank 620 to expand the wall 640 into conformity with the die surfaces 642, thereby forming a hydroformed member 30 defined by an irregularly outwardly deformed tubular metallic wall 640 fixed into a predetermined irregular exterior surface configuration and including a pillar-forming portion 34 and a longitudinally extending portion of 36. The method further includes providing components for a space frame comprising a body module 12 and a front module 22.

The body module components include a pair of main side rail structures 14 a pair of rearward-most upright structures 26 and a plurality of connecting structures 40. The front module components include a pair of front lower side rail structures, a pair of front upper side rail structures 42 and front connecting structure 44.

The method next requires assembling the modules so that in the body module the pillar-forming portion of each upper longitudinal member is connected to respective main side rail structure thereby forming a pair of A pillars, each rearward- most upright structure is connected between a respective main side rail structure and an end of the longitudinally extending portion of an associated upper longitudinal member to form a pair of rearward-most pillars (i. e., the D pillars), and the plurality of connecting structures are constructed and arranged to connect the main side rail structures and the upper longitudinal members in laterally spaced fixed relation; and so that in the front module, the front connecting structure connects the front upper side rail structures to one another in laterally spaced relation and the front lower side rail structures to one another in laterally spaced relation. The method next requires assembling the forward module to the body module to form a space frame by connecting the body module and the front module. The body module and front module are connected by connecting each main side rail structure with a respective front lower side rail structure and each front upper side rail structure to the pillar- forming portion of a respective upper longitudinal member at a position spaced upwardly from the associated main side rail structure.

Preferably the method further includes providing the body module with a pair of intermediate pillars and a cross structure connected therebetween by forming a cross member 64 in a hydroforming procedure.

The assembling procedure further includes assembling the space frame so that each of the leg portions of the U-shaped hydroformed cross member is connected between a respective main side rail structure and the longitudinally extending portion of the associated upper longitudinal member such that the leg portions form a pair of corresponding intermediate pillars which provide the B pillars of the space frame and the cross portion defines a lateral length between and provides a cross structure connected between the leg portions.

It should be pointed out that although various portions of the space frames 10 are referred to as"modular", this characterization is intended to be broadly construed and is not intended to limit the manner in which any of the space frames are constructed. It is preferred that the body module and front module of each space frame be assembled separately and then assembled together to form the respective space frames. It is contemplated to construct each space frame 10 in a variety of ways, however, and so it is to be understood that no limitations on the order in which the various hydroformed members and other structural members are joined together to form each space frame is to be implied by anything shown or stated in the present application.

Thus, while the invention has been disclosed and described with reference with a limited number of embodiments, it will be apparent that variations and modifications may be made thereto without departure from the scope of the invention.

Therefore, the following claims are intended to cover all such modifications, variations, and equivalents thereof in accordance with the principles and advantages noted herein.