The present invention is related to vehicle chassis. More specifically, the invention is related to a snowmobile chassis constructed with the use of effective load sharing joints and reinforcing structure.
A vehicle chassis includes a vehicle's structural elements. These elements may be attached to an underlying frame. In vehicles with unitized or “unibody” construction, the chassis may essentially comprise the frame and include everything but the cosmetic body panels of the vehicle.
Vehicle chassis elements are frequently constructed of relatively thin sheets of metal. Chassis elements must be constructed to endure significant mechanical loads while being lightweight and non-bulky to allow for flexibility in vehicle construction.
In one embodiment, the invention includes a system for constructing a vehicle. This system may include a first sheet of material, a second sheet of material, a reinforcing third sheet of material, and a self piercing rivet. The reinforcing third sheet of material may be of a different composition than at least one of the first sheet of material or second sheet of material. The self piercing rivet may attach the first sheet of material and the second sheet of material to the third sheet of material to form a joint that allows load sharing or structural reinforcement of at least one of the first sheet of material or the second sheet of material by the third sheet of material.
In another embodiment the invention includes a snowmobile that includes a chassis made of at least two sheets of chassis material, an engine supported by the chassis, at least one ski supported by the chassis, a steering column operatively connected to the at least one ski for steering the snowmobile and an endless track supported by the chassis and being operatively connected to the engine. This embodiment may further include a third sheet of material of a different composition than at least one of the sheets of chassis material. A self piercing rivet may attach the at least two sheets of chassis material to the third sheet of material.
Yet another embodiment of the invention may include a snowmobile chassis made of first and second sheets of chassis material being formed of aluminum. This embodiment may further include a third sheet of chassis material being formed to reinforce the first and second chassis sheets and of a material other than aluminum. A self-piercing rivet may join together the first, second, and third sheets of material to allow load sharing and structural reinforcement of the first and second sheets of chassis material.
Another embodiment of the invention may include a snowmobile that includes a suspension element, a chassis with at least two layers of overlapping chassis material, a mount for attaching the suspension element to the chassis, and a self piercing rivet that attaches the mount to the chassis and fastens together the at least two layers of chassis material.
Another embodiment of the invention may include a snowmobile chassis that includes at least one layer of chassis material. The embodiment also has a heat exchanger or other chassis element constructed of at least three layers of material and a self piercing rivet that attaches the heat exchanger or other chassis element to the chassis by fastening the cooler to the at least one layer of chassis material.
Another embodiment of the invention includes a system for attaching a tube to a chassis. This embodiment includes a tube that has opposing sides with a hollow passage between the sides. A portion of the tube may be compressed so that the sides of the tube are adjacent to each other. This embodiment also includes a chassis comprising at least one sheet of material and a self piercing rivet that attaches the sheet of material to the tube at the optionally compressed portion of the tube by fastening the adjacent sides of the tube to the sheet of material.
In another embodiment of the invention, a method of constructing a snowmobile chassis includes fabricating a chassis element, fabricating a second chassis element, positioning a first layer of chassis material formed of aluminum, layering three sheets of chassis material, two of the sheets being formed of aluminum, one of the sheets being configured to reinforce the two aluminum sheets and of a material other than aluminum, and riveting the three sheets together via a self-piercing rivet to form a joint, the joint allowing load sharing and structural reinforcement of the two aluminum sheets of chassis material.
The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Several forms of the invention have been shown and described, and other forms will now be apparent to those skilled in art. It will be understood that embodiments shown in drawings and described above are merely for illustrative purposes, and are not intended to limit scope of the invention as defined in the claims which follow.
In the construction of vehicle chassis, it can be useful to employ structural elements formed of relatively thin sheets of material. These elements may, for example, be a beam-like structure that is subjected to any one of, or a combination of, torsional, tensile, compressive or bending loads. Chassis elements may be fabricated by stamping or otherwise cutting the element from a sheet of stock material. Elements may also be fabricated by bending or forming a sheet of material to a desired shape. The chassis may also be fabricated by welding, riveting, bolting, or otherwise fastening constituent chassis elements together to form the desired structure.
Various construction techniques exist to build such an element that is strong enough to withstand the forces acting on it when used in a vehicle chassis. A box section, where the sheet of material is formed into a beam with a box-shaped cross-sectional frame structure can be formed to strengthen the element. I-section and C-sections, which look like these respective letters in cross-section, are other structures that may be used to create stronger chassis elements from sheets of material. However, these structures may require additional material, increasing vehicle weight and expense, and may take up valuable space that could otherwise be used for other vehicle components.
One construction technique to strengthen load bearing elements constructed of one or more sheets of material without necessarily creating bulky structures is to attach a layer of reinforcing material to the base sheet or sheets of material to increase its cross-sectional thickness and load bearing capability. Prior art means of attaching these reinforcing layers such as welding, for example, can dramatically reduce the materials' strength through heat damage. It is believed, for example, that the aluminum alloy commonly referred to as Aluminum 5052-H34 has a yield strength reduction of approximately 54% from 31,200 psi to 13,000 psi in the heat affected zone after welding. It should be noted that these heat impacts are localized near any welded seams, which may be the area intended to be strengthened.
In one embodiment of the invention, a reinforcing material is attached to a chassis formed of two or more layers of base material using one or more self piercing rivets. This construction method has the advantage of having minimal impact on the strength of the underlying and reinforcing sheet or sheets of material as compared to welding.
Attaching a reinforcing layer using a self piercing rivet may also be superior to using traditional fasteners that require predrilled holes. Holes formed in the sheets of material for these fasteners are slightly larger than the fasteners themselves, creating “play” between the fastened sheet of metal and the fastener.
Further fasteners that require predrilled holes, particularly traditional rivets but also many threaded fasteners, may be more likely to fail under shear stresses. Shear stress is stress transverse to the length of the fastener that may be applied when two or more sheets of material joined by the fastener are subjected to forces oriented parallel to the surfaces of the sheets of material. Shear stress can be more easily envisioned as a force that is attempting to cut the fastener transversely.
The self piercing rivet may also have higher shear strength than many conventional rivets that require predrilled holes. Also, conventional fasteners that require predrilled holes, whether rivets or threaded fasteners, may have problems with the holes expanding creating “play” or “slop” in the joint. This problem increases as more layers of material are joined because the holes for the fasteners must be typically larger to allow for alignment of the holes through each of the several layers of material. Additionally, vibration or movement between the layers of material may cause the holes to widen as the material contacts the fastener(s). By using self piercing rivets, alone or in conjunction with other fastening techniques, the inventor has overcome limitations in prior art chassis manufacturing.
A snowmobile 10 in accordance with an embodiment of the present invention is shown in
In the exemplary snowmobile shown in FIG. I the steerable skis 54 may be attached to a front suspension system 62 that includes an A-arm or wish-bone, henceforth referred to as an A-arm 64 component. The A-arm 64 is pivotally mounted on an A-arm mount 66 that is affixed to the front portion of the chassis 22. The A-arm 64 can be generally referred to as a suspension element. A suspension element can be any structural element that connects the frame or chassis to the components of the vehicle that contact the ground during operation. Suspension elements are typically movable relative to the chassis or frame and may be connected to a shock absorber assembly that may contain a form of spring and/or a shock or other damping element that controls the rate and quality of this movement. A suspension system other than the A-arm suspension system, such as a trailing arm or strut-type suspension system, may be used without departing from the scope of the invention.
The vehicle chassis 20 has a longitudinal axis that runs from the front portion 22 of the chassis to the rear portion 24 of the chassis essentially along a line that bisects the chassis.
A chassis cross-member 92 configured in this example as a U-channel is oriented generally transverse to the main chassis 20. The load or force applied along arrow A is skew or at an angle not perpendicular to the chassis 20. The joint formed by the three-layer self piercing rivets 80 of this embodiment of the invention transmit this force to the transverse chassis cross member 92. The self piercing rivets 80 help form a joint that is strong enough to redirect the angled force to the chassis cross member 92, which is a stronger member due to its U-shaped configuration, among other factors. This joint can easily be constructed with the use of self piercing rivets which have the advantages described above, among others.
Arrow A indicates a load or force applied to the lower rear A-arm mount 66 in a direction generally parallel to the lower rear A-arm 64 (shown in
This application of the self piercing rivet takes advantage of the self piercing rivet's ability to carry a significant load in shear. The force oriented along the arrow A exerts a shear force generally transverse to the self piercing rivets 80. These fasteners can withstand this load and effectively transfer it to the reinforcing layer (not shown) and the chassis 20 through the cross member chassis element 92.
The use of self piercing rivets may also reduce or eliminate the need for fasteners that require predrilled holes in the chassis 20 and/or the reinforcing material 70. This may reduce production time and costs. Also, these fasteners frequently can become loose as the tolerance or gap between the fastener and the hole through which the fastener is placed expands over time.
The heat exchanger 26 or similar element that is attached to the chassis 20 by the self piercing rivet 80 may provide structural integrity to the chassis in a manner similar to the other reinforcing and load sharing joints described herein. In other words, in addition to providing a superior mounting of the heat exchanger 26 to the chassis 20, the self piercing rivet 80 and systems and methods of the invention may use elements mounted to the chassis to reinforce the chassis.
While exemplary embodiments of this invention and methods of practicing the same have been illustrated and described, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.