# Patent

## Title
Attachment arrangement for a composite leaf spring which accommodates longitudinal movement through shear displacement

## Abstract

A suspension system includes a composite leaf spring attachment system having a bracket, a mount and a shear damper mounted therebetween. The mount is rectilinear in cross-section to receive a rearward leaf spring segment of the composite leaf spring. During flexing of the leaf spring, the rearward leaf spring segment of the leaf spring slides within the mount. The shear damper in combination with sliding of the leaf spring through the mount accommodates this longitudinal lengthen during flexing. Also, due to the width of the of the leaf spring segment the shear damper may alternatively be utilized alone to accommodate the flexing of the leaf spring as the significant width of the composite leaf spring provides a large mounting platform for a significantly large shear damper heretofore unavailable with relatively thin conventional steel leaf springs.

## Background
BACKGROUND OF THE INVENTION
The present invention relates to a leaf spring suspension and, more particularly, to an attachment arrangement for mounting the leaf spring to a vehicle mainframe to accommodate longitudinal movement of the leaf spring during flexing thereof through shear movement of a damper.
Various conventional vehicle suspensions include a leaf spring fabricated from a series of superimposed steel leaves. Steel leaf springs may be disadvantageous because they are relatively heavy, noisy, and subject to corrosion.
More recently, fiber reinforced resin composite materials have been utilized as a substitute for steel leaf springs. In some leaf springs of this type, a curved central section of the spring is molded from longitudinally extending fibrous material impregnated with a thermosetting resin. Separate metal end sections are attached through mechanical connectors to the ends of the curved central section. Another form of fiber reinforced resin composite leaf spring includes continuous strands of fibrous material impregnated with a thermosetting resin, which are wound around spaced bushings or pins in a loop configuration. After winding, the wound structure is placed in a mold with the parallel runs of the loop being brought together in flatwise contiguous relation while the resin is subsequently cured to provide an integral structure.
Each leaf spring is located adjacent a longitudinal vehicle frame rail underneath the body of a truck or trailer chassis. Although providing many benefits including light weight and great strength, attachment of fiber reinforced resin composite leaf springs to the vehicle frame rails may pose various difficulties.
One difficulty includes the preference for avoiding mounting arrangements that require locating apertures through the composite leaf spring. Penetration of the composite leaf spring severs the fibrous materials and correspondingly reduces the physical characteristics of the spring. Conversely, elimination or minimization of apertures further decreases the mounting versatility for particular vehicle designs as specific metal end sections are utilized for frame rail mounting. That is, each leaf spring must be specifically tailored to a specific vehicle which may decrease the versatility of each leaf spring.
Other mounting arrangements include rather complicated brackets to avoid locating apertures through the leaf spring. Disadvantageously, the bracket arrangement may be relatively heavy in weight, which may offset some of the weight advantage inherent to composite materials.
Furthermore, conventional mounting arrangements commonly provide a metal to composite interface. These dissimilar material interfaces are wear points which may weaken the composite material and reduce the life of the suspension.
Accordingly, it is desirable to provide an uncomplicated composite leaf spring attachment arrangement that accommodates various suspension members, does not require through apertures, avoids dissimilar material wear points, and is light in weight.
SUMMARY OF THE INVENTION
The suspension system according to the present invention includes a composite leaf spring attachment system which includes a bracket, a mount and a shear damper mounted therebetween. The bracket is attached to the longitudinal vehicle frame.
The mount is rectilinear in cross-section to receive a rearward leaf spring segment of the composite leaf spring. During flexing of the leaf spring, the rearward leaf spring segment of the leaf spring slides within the mount.
The shear damper further accommodates flexing of the leaf spring. As the leaf spring flexes, the shear damper moves in shear in a direction substantially parallel to the longitudinal length of the leaf spring. The shear damper in combination with sliding of the leaf spring through the mount accommodates this longitudinal movement during flexing.
The rearward leaf spring segment is relatively wide in comparison to comparative conventional steel leaf springs. Due to the width of the of the rearward leaf spring segment the shear damper may alternatively be utilized alone to accommodate the flexing of the leaf spring. That is, the significant width of the composite leaf spring provides a large mounting platform for a significantly large shear damper heretofore unavailable with relatively thin conventional steel leaf springs.
Another rear leaf spring attachment system includes a mount formed integrally with the leaf spring through a molding process which overmolds a complimentary material directly to the leaf spring at a desired position.
The present invention therefore provides an uncomplicated composite leaf spring attachment arrangement which accommodates various suspension members, does not require through apertures, avoids dissimilar material wear points, and is light in weight.



BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
FIG. 1 is a general perspective view of a suspension system for use with the present invention;
FIG. 2A is a general side perspective view of a composite leaf spring;
FIG. 2B is a general top perspective view of a composite leaf spring;
FIG. 2C is a sectional view of the composite leaf spring taken along line 2C—2C in FIG. 2A;
FIG. 2D is a sectional view of the composite leaf spring taken along line 2D—2D in FIG. 2A;
FIG. 3 is an exploded view of an axle beam attachment system for use with a composite leaf spring;
FIG. 4 is a side partial section view of a composite leaf spring suspension system according to the present invention;
FIG. 5 is a front view of a composite leaf spring suspension system according to the present invention;
FIG. 6 is an expanded view of an axle beam attachment system;
FIG. 7 is an expanded view of a front attachment system for use with a composite leaf spring;
FIG. 8 is an expanded view of another integral front attachment system integral to a composite leaf spring designed according to the present invention;
FIG. 9 is an expanded view of a rear attachment system for use with a composite leaf spring; and
FIG. 10 is an expanded view of another rear attachment system integral to a composite leaf spring designed according to the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a general perspective view of a steerable air spring suspension system 10. Although a steerable air spring suspension is disclosed in the illustrated embodiment, it should be understood that other suspensions will benefit from the present invention. The present invention is particularly applicable to relatively heavy commercial vehicles.
The system 10 generally includes a primary structural support such as an axle beam 14. The axle beam 14 is preferably a single hollow square beam located transverse to a vehicle longitudinal axis 15. A pair of steerable hub assemblies 16 are pivotally supported by the axle beam 14. A king pin 18 or similar member pivotally attaches the steerable hub assembly 16 to the axle beam 14 in a known manner. The steerable hub assemblies 16 are articulatable through a steering gear assembly (not shown) and are linked together by a linkage 20.
To dampen movement of the axle beam 14, a flexible member such as a composite leaf spring 22 is attached to longitudinal mainframes 24 which extend parallel to the vehicle longitudinal axis 15. The composite leaf springs 22 are attached to the mainframes 24 through a front leaf spring attachment system 26 and a rear leaf spring attachment system 28. An axle beam attachment system 30 attaches the axle beam 14 to each composite leaf spring 22 intermediate the attachment systems 26, 28.
Each composite leaf spring 22 is preferably manufactured of a fiber reinforced resin composite material according to a manufacturing process such as that provided by Liteflex LLC of Englewood, Ohio. Generally, continuous strands of fibrous material impregnated with a thermosetting resin are wound around spaced bushings or pins in a loop configuration. After winding, the wound structure is placed in a mold with the parallel runs of the loop being brought together in flatwise-contiguous relation. The resin is then subsequently cured to provide an integral oval structure which is separated and trimmed to provide two separate leaf springs. It should be understood that various manufacturing methods for the fiber reinforced resin composite material leaf spring will benefit from the present invention.
The axle beam attachment system 30 attaches the leaf spring 22 to the axle beam 14 through U-bolts 32 which sandwich the leaf spring between an upper clamp plate 34 and a lower clamp plate 36. The U-bolts 32 pass over the clamp plates 34, 36 around the axle beam 14 and are retained below the axle beam 14 with a fastener plate 37 and fasteners 38. The fastener plate 37 preferably straddles the open end of the U-bolts 32 to retain the axle beam 14. The axle beam attachment system 30 location in combination with the leaf spring shape defines the characteristics of the suspension system.
Other suspension components such as an air bag 40 and a shock 42 are mounted between each leaf spring 22 and longitudinal mainframe 24. It should be understood that other suspension component positions and mounts independent of the axle beam attachment system 30 will also benefit from the present invention.
A stop 44 mounted to the upper surface of the upper clamp plate 34 preferably contacts a main beam stop 46 to prevent over flexing of the leaf spring 22. That is, stops 44, 46 limit the compression of the leaf spring 22 to avoid the potential for over flexing and possible damage therefrom.
Referring to FIGS. 2A, 2B, 2C and 2D, the leaf spring 22 includes a mounting segment 48 which engages the axle beam attachment system 30 (FIG. 1) to provide an infinitely adjustable mounting location for infinite positioning of the axle beam 14 location setbacks to accommodate a multiple of vehicles. That is, the axle beam 14 may be located anywhere along the mounting segment 48 to provide a desired axle beam 14 setback.
The mounting segment 48 provides a tapered width (FIG. 2B) combined with an expanding depth. That is, within the mounting segment 48, the width is consistently decreasing as the depth is consistently increasing. Any position along the longitudinal length of the mounting segment 48 thereby provides a unique cross-sectional shape (49; FIG. 2C) taken parallel to the axle beam 14. That is, any longitudinal position provides a unique combination of leaf spring width and leaf spring depth as illustrated by the different cross-sectional shapes illustrated in FIGS. 2C and 2D. Preferably, a cross-section parallel to the axle beam 14 taken anywhere along the mounting segment 48 will provide a constant area of the cross-sectional shape 49.
Referring to FIG. 3, an interior cavity 50 of the upper clamp plate 34 and an interior cavity 51 of the lower clamp plate 36 defines the position of the axle beam attachment system 30 along the mounting segment 48. The interior cavity 50, 51 are each a generally U-shaped to correspond with the desired position along the mounting segment 48. The base of each interior cavities 50, 51 is angled relative to the interface between the plates 34, 36. That is, each interior cavity 50, 51 includes a tapered width and angled surface which corresponds to the leaf spring 22 width and depth for a predetermined mounting segment 48 longitudinal location (FIG. 4).
The upper clamp plate 34 and the lower clamp plate 36 can only be assembled to the leaf spring at a single predefined longitudinal location within the mounting segment 48. That is, the interior cavities 50, 51 provide a shape equivalent to the leaf spring 22 at the predetermined location for interlocking the axle beam attachment system 30 with the leaf spring 22 at that predetermined location. As any longitudinal segment within the mounting segment 48 provides a singular cross-sectional shape, interior cavities 50, 51 defined for that shape will only properly fit at that predetermined location. The term “interlocking” as used herein defines the manner in which the axle beam attachment system will not slide along the leaf spring once assembled thereto due to the interface therebetween.
Preferably, the upper clamp plate 34 and the lower clamp plate 36 include matching apertures 54 for receipt of fasteners 56 such as bolts. The upper clamp plate 34 and the lower clamp plate 36 sandwich the leaf spring 22 within the interior cavity 50, 51. Once bolted together, the upper clamp plate 34 and the lower clamp plate 36 are interlocked onto the leaf spring 22 at the longitudinal position defined by the interior cavity 50, 51. That is, a leaf spring receipt cavity 52 (FIG. 5) defined by a combination of interior cavities 50, 51 is unique to the leaf spring segment at the desired the axle beam attachment system 30 position to provide an interlocking interface therebetween.
The clamp plates 34, 36 may alternatively be overmolded upon the leaf spring 22 at the predefined axle beam attachment system 30 position. The individual clamp plates 34, 36 are thereby replaced by a single component 53 (FIG. 6) formed upon the leaf spring 22 through a molding process which overmolds a complimentary material directly to the leaf spring 22 at the desired position. Even if the overmolded material does not directly adhere to the leaf spring the unique cross-sectional shape of the leaf spring along the mounting segment 48 still achieves the interlocking interface.
Referring to FIG. 7, the front leaf spring attachment system 26 is illustrated. The forward leaf spring segment 56 of the leaf spring 22 preferably defines an arcuate segment 58. The arcuate segment 58 is essentially a hook or bend of at least approximately ninety degrees to a main longitudinal segment 60 (FIG. 4) of the leaf spring 22. The forward segment is relatively thicker in depth due to the additional flexure stress at this attachment location.
The front leaf spring attachment system 26 includes a bracket 62 mounted to the longitudinal mainframes 24, a retaining pin 64 and a bumper 66. The bracket 62 is generally C-shaped (FIG. 1) such that the opening thereof receives the forward leaf spring segment 56 of the leaf spring 22. The bracket 62 is attached to the longitudinal mainframes 24 in any known manner such as through fasteners or welding.
The retaining pin 64 preferably includes a shank 68 surrounded by a resilient tube 70 such as rubber or the like. The shank 68 is preferably a bolt which threads through the bracket 62 across the opening thereof.
The bumper 66 is located adjacent a rear wall 63 of the bracket 62 opposite the retaining pin 64. The bumper includes an arcuate face 72 to engage the arcuate segment 58 and a serpentine face 74 opposite the arcuate face 72. The serpentine face 74 engages a corresponding bracket serpentine 76 such that flexing of the leaf spring 22 will not displace the bumper 66. It should be understood that various bumper shapes will benefit from the present invention.
The arcuate segment 58 at least partially surrounds the retaining pin 64. Preferably, an inner radius portion 73 of the arcuate segment 58 engages the retaining pin 64 while an outer radius 75 of the arcuate segment 58 engages the bumper 66. The forward leaf spring segment 56 of the leaf spring 22 is thereby securely, yet resiliently, retained within the front leaf spring attachment system 28 without penetrating fasteners.
Referring to FIG. 8, another leaf spring 22′ is illustrated. A tubular member 76 manufactured of a resilient material is molded directly into the inner radius portion 73′ of the leaf spring 22′. A molding process molds the tubular member 76 directly to the leaf spring 22′ thereby simplifying the retaining pin to a single fastener, such as a bolt, which is passed through the tubular member 76 to mount the leaf spring 22′.
Referring to FIG. 9, the rear leaf spring attachment system 28 is illustrated. The rear leaf spring attachment system 28 includes a rear bracket 78, a mount 80 and a shear damper 82 mounted therebetween. The bracket 78 is attached to the longitudinal mainframes 24 in any known manner such as through fasteners or welding.
The mount 80 is preferably rectilinear in cross-section (FIG. 4) to receive a rearward leaf spring segment 84 of the leaf spring 22. That is, the mount 80 is preferably a rectangular tube to receive the rearward leaf spring segment 84. The rearward leaf spring segment 84 is mounted within a resilient bumper 86 or the like such that direct contact between the leaf spring 22 and the mount 80 is avoided. During flexing of the leaf spring 22, the rearward leaf spring segment 84 of the leaf spring 22 slides within the mount 80 and resilient bumper 86.
The shear damper 82 further accommodates flexing of the leaf spring 22. As the leaf spring flexes, the shear damper 82 moves in shear in a direction substantially parallel to the longitudinal lengthening of the leaf spring 22. That is, as the front leaf spring attachment system 26 effectively fixes longitudinal movement of the leaf spring 22, the rear leaf spring attachment system 28 needs to move in a longitudinal manner to accommodate the longitudinal lengthen of the leaf spring 22 as the leaf spring flexes toward a flatter arcuate geometry. The shear damper 82 in combination with sliding of the leaf spring 22 through the mount 80 accommodates this longitudinal lengthen during flexing.
Referring to FIG. 10, another rear leaf spring attachment system 28′ is illustrated. The rear leaf spring attachment system 28′ includes a rear bracket 78′, a mount 80′ and a shear damper 82′ mounted therebetween. The mount 80′ is formed integrally with the leaf spring 22′ through a molding process which overmolds a complimentary material directly to the leaf spring 22′ at the desired position.
The shear damper 82′ alone accommodates the flexing of the leaf spring 22′. It should be further understood that the shear damper 82′ may be included in the overmolding process such that a single integral rear leaf spring attachment system 28′ is formed as part of the leaf spring 22′. The another rear leaf spring attachment system 28′ need only be attached to the longitudinal mainframes 24 during assembly of the suspension system 10.
The rearward leaf spring segment 84 is relatively wide in comparison to comparative conventional steel leaf springs. Due to the width of the of the rearward leaf spring segment 84 the shear damper 82 may be successfully utilized alone to accommodate the flexing of the leaf spring 22. That is, the shear damper 82 can accommodate the flexing of the leaf spring 22 because the significant width of the leaf spring 22 provides a large mounting platform for a significantly large shear damper 82 heretofore unavailable with relatively thin conventional steel leaf springs.
The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A suspension system comprising:
a composite leaf spring comprising a forward leaf spring segment defining an arcuate segment, a rearward leaf spring segment, and a mounting segment intermediate said forward leaf spring segment and said rearward leaf spring segment; and
a rear attachment system comprising a shear damper mounted to said rearward leaf spring segment;
a mount overmolded to said rearward leaf spring segment, said shear damper mounted directly to said mount.

2. A suspension system comprising:
a composite leaf spring comprising a forward leaf spring segment defining an arcuate segment, a rearward leaf spring segment, and a mounting segment intermediate said forward leaf spring segment and said rearward leaf spring segment; and
a rear attachment system comprising a shear damper mounted to said rearward leaf spring segment; and
a substantially rectilinear mount to receive said rearward leaf spring segment, said rearward leaf spring segment substantially free to longitudinally slide within said substantially rectilinear mount.

3. A method of mounting a composite leaf spring to a rear attachment system mounted to a vehicle mainframe comprising the steps of:
(1) forming a rearward leaf spring segment as an end of a composite leaf spring;
(2) attaching a shear damper between the rearward leaf spring segment and the vehicle mainframe such that the rearward leaf spring segment is longitudinally movable parallel to the vehicle mainframe as the shear damper moves in shear and fixing the shear damper to the vehicle mainframe and a mount overmolded to the rearward leaf spring segment.

4. A method of mounting a composite leaf spring to a rear attachment system mounted to a vehicle mainframe comprising the steps of:
(1) forming a rearward leaf spring segment as an end of a composite leaf spring;
(2) slidably retaining the rearward leaf spring segment within a mount; and
(3) attaching a shear damper between the mount and the vehicle mainframe such that the rearward leaf spring segment is longitudinally movable parallel to the vehicle mainframe as the shear damper moves in shear and the rearward leaf spring segment slides within the mount.