Patent Application
20090200717
The invention relates to vehicle suspension systems, and more particularly, to a plastic piston for an air spring configured for off-set mounting.
Pneumatic springs, commonly referred to as air springs, have been used in conjunction with motor vehicles for a number of years to provide cushioning between movable parts of the vehicle primarily to absorb shock loads impressed on the vehicle axles by the wheels striking an object in the road, such as a bump, depression, or other obstruction. One basic design of pneumatic springs is referred to as a rolling lobe air spring, examples of which are illustrated in U.S. Pat. Nos. 3,043,582; 5,535,994; and 6,460836.
Rolling lobe air springs typically include a flexible elastomeric reinforced sleeve that extends between a pair of end members. The sleeve is attached to the end members to form a pressurized chamber therebetween and the end members mount the air spring on spaced components or parts of the vehicle or other equipment for which shock absorption is desired. The internal pressurized gas, usually air, absorbs most of the motion impressed upon one of the spaced end members due to road shocks experienced by the vehicle. The end members move inwards and towards each other when the spring is in jounce and away and outwards from each other when the spring is in rebound. One of the end members is referred to as a retainer plate and sealingly couples to the sleeve. The retainer plate is used to mount the air spring to one part of the vehicle (e.g., vehicle body). The other end member may include an air spring piston. The piston provides both a means for mounting the air spring to another part of the vehicle (e.g., vehicle axle) and a surface for the rolling lobe sleeve to travel upon when the air spring is subjected to compression forces.
A number of air spring designs exist. By way of example, some air springs are designed to have center mounting. Center-mounted air springs are configured to mount to the vehicle such that the center point of the mounting is along the centerline of the air spring. The piston in center-mounted air springs has typically been formed from metal so as to withstand the forces acting thereon during jouncing. More recently, however, pistons for center-mounted air springs have been formed from hard thermoplastic materials. Plastic pistons are thought to provide certain advantages over metal pistons, including improved corrosion resistance, lower cost, lower weight, and other advantages.
In some applications, it may desirable to have off-set mounting at one or both of the end members of the air spring. Off-set mounting provides coupling to the vehicle such that the center point of the mounting is spaced from the centerline of the air spring. The off-set mounting subjects the air spring to altered and potentially increased loading, which must be accounted for in the overall design of the air spring. Accordingly, the piston for off-set mounted air springs is typically formed from metal so as to accommodate the increased loading.
In a manner analogous to center-mount air springs, recent attempts have been made to form the piston of off-set mounted air springs from plastics, and thus gain the benefits as outlined above. However, such attempts have proven problematic. In this regard, heretofore pistons formed primarily of plastic have failed to adequately accommodate the increased loading due to off-set mounting. Accordingly, in such off-set mounted designs, the plastic pistons have been supplemented with a metal (e.g., steel) backing plate that increases the structural integrity of the piston so as to accommodate the increased loading. The addition of the metal backing plate, however, destroys or significantly reduces the benefits gained by forming the piston from plastic.
Accordingly, there is a need for an improved air spring having a piston substantially formed of plastic and adapted for off-set mounting with a vehicle.
An embodiment of the invention that addresses these and other drawbacks provides an air spring piston having an outer wall with a first end and a second end. In one embodiment, an end wall may substantially close the first end and the second end may be open. The outer wall defines an inner cavity of the piston having a centerline. The air spring piston further includes a support structure disposed in the inner cavity for providing structural support to the piston. The support structure includes a plurality of ribs projecting from the outer wall, such as in a generally radial direction relative to the centerline, and at least one strut. The strut includes a first end coupled to the outer wall at a first location and a second end coupled to the outer wall at a second location spaced from the first location such that the strut does not intersect the centerline of the inner cavity.
In one embodiment, the support structure includes a central hub disposed about the centerline of the inner cavity and at least one of the ribs extends from the outer wall to the central hub. Additionally, the support structure may include two such struts, which in one embodiment may be parallel to each other. The at least one strut may include a thickened portion intermediate the two ends of the strut, which in one embodiment may be hollow along at least a portion thereof. Moreover, the support structure may include at least one support tab having a first end coupled to the outer wall and a second end coupled to the at least one strut, such as along the thickened portion thereof. The piston may further include at least one mounting boss adapted to receive a fastener for securing the piston to a support. In one embodiment, the at least one mounting boss is coupled to the outer wall and disposed in the inner cavity. In such an embodiment, the at least one strut may couple to the outer wall through the mounting boss.
In another embodiment of the invention, an air spring piston includes an outer wall having a first end and a second end and defines an inner cavity of the piston having a centerline. The air spring piston further includes at least one mounting boss adapted to receive a fastener for providing off-set mounting of the piston to a support, such as to a component of a vehicle. The at least one mounting boss has a geometric center that is spaced from the centerline of the inner cavity. The at least one mounting boss may be coupled to the outer wall and disposed in the inner cavity. In this embodiment, substantially the entire piston may be formed from a plastic. This embodiment may further include a support structure having a plurality of ribs projecting from the outer wall and at least one strut having a first end coupled to the outer wall at a first location and a second end coupled to the outer wall at a second location spaced from the first location such that the at least one strut does not intersect the centerline of the inner cavity. Additionally, the one strut may couple to the outer wall through the at least one mounting boss.
In yet another embodiment, an air spring for a vehicle having first and second components includes a first retainer plate adapted to be coupled to the first component of the vehicle. An elastomeric sleeve has a first end and a second end, wherein the first end is sealingly coupled to the first retainer plate. The air spring further includes a piston having a first end sealingly coupled to the second end of the sleeve and a second end adapted to be coupled to the second component of the vehicle. The piston includes an outer wall having a first end and a second end and defines an inner cavity of the piston having a centerline. The air spring piston further includes at least one mounting boss adapted to receive a fastener for providing off-set mounting of the piston to the second component of the vehicle. The at least one mounting boss has a geometric center that is spaced from the centerline of the inner cavity. Substantially the entire piston may be formed from a plastic.
These and other objects, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description taken in conjunction with the accompanying drawings.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.
With reference to
The first retainer plate 12 may include interlocking structure for coupling the first retainer plate 12 to the first end 20 of sleeve 14 in a sealed manner. By way of example, first retainer plate 12 may include a base surface 25 and a downwardly turned U-shaped flange 26 along a periphery thereof that receives the first end 20 of sleeve 14 therein. First retainer plate 12 may further include at least one fastener for coupling the first retainer plate 12 to the first component of the vehicle 19. The fastener may include threaded studs 28, 30 or other such fasteners as recognized by those of ordinary skill in the art capable of securely fastening the first retainer plate 12 to the first component of the vehicle 19. The first retainer plate 12 may further include a port for introducing fluid into the pressurized chamber 24. In one embodiment, stud 30 may additionally operate as such a port. As is conventional, the first retainer plate 12 may be formed of metal.
The elastomeric sleeve 14 bounds at least a portion of the pressurized chamber 24 and allows compression and expansion thereof during loading of the air spring 10. The sleeve 14 may include at least one reinforcement layer 32 for providing some strength to the sleeve 14, but yet permitting the sleeve 14 to flex during use of air spring 10. The reinforcement layer 32 may be formed of cords such as conventional polyester, nylon, aramid, steel, or other suitable materials known to those of ordinary skill in the art. The chosen reinforcement material is application specific and determined by the forces to which the air spring 10 will be subjected upon use. Moreover, the length of sleeve 14 varies depending on the specific application and may be readily determined by those of ordinary skill in the art.
As noted above, the first end 20 of sleeve 14 is sealingly coupled to the flange 26 of first retainer plate 12. To this end, the first end 20 of sleeve 14 may include an internal bead 34, which is captivated within the flange 26 of first retainer plate 12, to strengthen the attachment therebetween. The bead 34 may be formed from steel cable wires or other conventional air spring bead construction materials. Although a flange/bead coupling is described herein, the sleeve 14 may be coupled to the first retainer plate 12 by other known conventional techniques, such as snapping the sleeve 14 onto the first retainer plate 12 or the use of a bead retaining ring located outward of the sleeve 14, as is illustrated in U.S. Pat. No. 5,535,994. As illustrated in
As noted above, the piston 18 is configured to mount to a second component of the vehicle 21 and provide a surface on which sleeve 14 rolls during compression of the air spring 10. The piston 18 may be generally cylindrically shaped and have a first end 36 adapted to be coupled to the second retaining plate 16 and the second end 22 of sleeve 14, a second end 38 adapted to be coupled to the vehicle, and an outer wall 40 that extends between the first and second ends 36, 38 and defines an inner cavity 42. Although the piston 18 is described as being cylindrical, the invention is not so limited as other shapes (e.g., square, rectangular, etc.) are contemplated to be within the scope of the invention. As illustrated in
In one embodiment, the first end 36 is generally a closed end defined by an end wall 44 that is configured to facilitate coupling of the second retainer plate 16 and second end 22 of sleeve 14 thereto. To this end, the end wall 44 is generally bowl shaped having a substantially flat base surface 46 and a sloping side surface 48 extending between the base surface 46 and the outer wall 40. The second retainer plate 16 has a shape complementary to the shape of end wall 44 and mates therewith to captivate the second end 22 of sleeve 14. Accordingly, the second retainer plate 16 includes a substantially flat base 50 and a flange 52 extending about base 50 and angled relative thereto. The second retainer plate 16 may be formed of metal as is generally known in the art.
As illustrated in
While air spring 10 is described as including second retainer plate 16 for coupling sleeve 14 to piston 16, those of ordinary skill in the art will recognize that the second retainer plate 16 is optional and the elastomeric sleeve 14 may be secured to piston 18 without such a retainer plate. In this regard, various snap-on designs may be used to secure the sleeve 14 to the piston 18, as is generally known in the art. Moreover, although the first end 36 of piston 18 is described as being essentially closed by end wall 44, the invention is not so limited as at least a portion of the first end 36 may be open (e.g., air volume piston). Accordingly, the invention is not limited to the exemplary embodiment shown in the figures.
As illustrated in
For off-set mounting, the geometric center of the mounting structure is not aligned with or coaxial with a centerline 70 of air spring 10 (
In another aspect of the invention, the piston 18 is substantially formed from a polymer or plastic, such as thermoplastic materials. As used herein, substantially formed from a plastic means that in the piston's operational state (i.e., capable of accommodating the forces on the air spring during operation) the piston 18 is 70% or higher by weight of plastic, and may be as high as over 90% by weight of plastic. More particularly, in various embodiments, the piston 18 may be formed from polyamide, polypropylene, or other suitable plastic resins or materials. The plastic material may be reinforced with various fillers, such as fiberglass or other solid filler materials as recognized by those of ordinary skill in the art. In one exemplary embodiment, the piston 18 is formed from polyamide with 30% fiberglass loading. Those of ordinary skill in the art will recognize other plastic materials, reinforced or non-reinforced, which may be used to form the piston 18 in accordance with the invention. Forming the piston 18 from plastic, as opposed to the more common metal, provides improved corrosion resistance, lower cost, lower weight, and other advantages. The plastic piston 18 may be formed by well-known processes, such as an injection molding process.
Unlike conventional off-set mounted air springs with plastic pistons, piston 18 is configured to withstand the increased forces due to the off-set mounting, but without the use of any metal backing plate to provide enhanced structural support. Accordingly, the benefits of using plastic in the piston construction will not be destroyed or significantly diminished in the inventive design. To provide for the increased loading due to off-set mounting without a backing plate, piston 18 includes an internal support structure, generally shown at 72, that provides the structural integrity to piston 18 to accommodate the increased loads due to the off-set mounting. The internal support structure 72 may be formed from plastic and is typically formed from the same material as outer wall 40 and end wall 44. Moreover, the internal support structure 72 may be integrally formed with the outer wall 40 and end wall 44, such as in a molding process. In other words, the piston 18 may be a unitary, integrally formed structure. The invention, however, is not so limited.
As shown in
In further reference to
In addition to the support structure described above, internal support structure 72 further includes at least one, and preferably two or more, struts 78 (two shown) that enhance the structural integrity of piston 18 so as to accommodate the increased loading due to off-set mounting. Each strut 78 has a first end 104 coupled to the inner surface 82 of the end wall 44 and a second end 106 extending therefrom and toward the second end 38 of the piston 18. In this exemplary embodiment, the struts 78 extend substantially the full length of the piston 18. Alternatively, the struts 78 may extend for only a portion of the length of the piston 18 (not shown).
In one aspect, the struts 78 extend between two spaced locations of outer wall 40. More particularly, each strut 78 has a first side edge 108 coupled to the inner surface 66 of the outer wall 40 at a first location and a second side edge 110 coupled to the inner surface 66 of the outer wall 40 at a second location spaced from the first location such that the strut 78 does not extend through the centerline 70 of the air spring 10 (e.g, struts 78 are chords to outer wall 40). As shown in
The struts 78 may have a substantially constant thickness, which may, for example, be generally thicker than the ribs 76 (not shown), although not so limited. Alternatively, and as shown in
The internal support structure 72 may further include one or more support tabs 118 (one shown for each strut 78) extending from the inner surface 66 of the outer wall 40 to the strut 78, such as at the thickened portion 112 of the strut 78. Each support tab 118 includes a platform portion 120 adjacent the outer wall 40 and a web portion 122 that extends from the platform portion 120 to the thickened portion 112 of the strut 78. The support tabs 118 have a first end 124 coupled to the inner surface 82 of the end wall 44 and a second end 126 extending therefrom and toward the second end 38 of the piston 18. In this exemplary embodiment, the support tabs 118 may extend substantially the full length of the piston 18. Alternatively, the support tabs 118 may extend for only a portion of the length of the piston 18.
The configuration of the internal support structure 72 provides the structural support to piston 18 that allows the piston to be formed substantially of plastic and used for off-set mounting to a vehicle, without the use of any metal backing plate. Accordingly, the advantages of plastic pistons, as realized in center-mounted air spring designs, may now be achieved for off-set mounted air spring designs.
While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, while the description of air spring 10 focused on the primary structural elements of the air spring, other well-known features may be incorporated into air spring 10. By way of example, and as shown in
Thus, the various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user.
