Abstract:
The disclosed invention is directed toward an improved airspring bumper ( 20 ) and an airspring ( 10 ) comprising the improved bumper ( 20 ). The bumper ( 20 ) is defined by a dual reinforcing structure comprising concentric sets of ribs ( 50, 58 ) for absorbing and distributing loads generated from contact between the bumper ( 20 ) and an opposing retainer ( 16 ). The bumper ( 20 ) is secured to one of the airspring retainers ( 18 ) by a compression fit between the retainer ( 18 ) and the bumper ( 20 ) or by a central barbed post ( 36 ).

Description:
FIELD OF THE INVENTION 
     The disclosed invention relates to air springs. In particular, the invention is directed towards an improved internal bumper for an air spring and a method of mounting the improved bumper. 
     BACKGROUND OF THE INVENTION 
     Air springs have been used for motor vehicles and various machines and other equipment for a number of years. Air springs provide cushioning between movable parts, primarily to absorb shock loads imparted thereon. The air spring usually consists of a flexible elastomeric reinforced sleeve that extends between a pair of end members. The sleeve is attached to the end members to form a pressured chamber therein. Depending on the specific air spring construction, there may be one or more pistons located within the flexible sleeve. The air spring is mounted on spaced components or parts of the vehicle or equipment. 
     The internal pressurized fluid, generally air, absorbs most of the shock impressed upon or experienced by one of the spaced end members by which the air spring is mounted. The end members move inwards and towards each other and also away and outwards from each other upon absorbing the imparted shock. 
     To prevent the end members from contacting each other during inward movement, many air springs have internal bumpers mounted on one of the end members. The bumper extends axially into the interior of the pressurized chamber. The bumper absorbs shock when the air spring experiences severe shocks and deflections and prevents a total collapse or deflection of the air spring in the event of an air spring failure. 
     Known internal bumpers include the solid elastomeric bumpers disclosed in U.S. Pat. Nos. 4,506,910 and 4,787,606. The bumpers are mounted on either end member of the air spring. The bumpers are attached to the end member by means of a post having an enlarged end over which the solid rubber bumper is mounted. When the bumper is made from solid rubber, hydraulic loading of the rubber occurs when the bumper is subjected to repetitive high forces, and this loading is transferred to the metal retainer. 
     U.S. Pat. No. 5,201,500 discloses a thermoplastic, non-solid bumper. The bumper is secured to a post by circumferentially arranged flexible fingers. While this bumper eliminates the issue of hydraulic loading of a solid rubber bumper, the disclosed bumper is subject to the fingers breaking off due to excessive or repetitive shock absorption The disclosed bumper is also more complex and costly to manufacture because of the flexible fingers. 
     The present invention is directed toward an improved bumper for an air spring that overcomes the limitations of the above mentioned prior art bumpers. 
     SUMMARY OF THE INVENTION 
     The disclosed invention is directed toward an improved airspring bumper and an airspring comprising the improved bumper. The airspring is comprised of a flexible sleeve secured at opposing ends by retainers. The bumper is secured to one of the retainers so that the outer surface of the bumper can contact the opposing retainer. The inventive bumper is defined by a dual reinforcing structure comprising concentric sets of ribs for absorbing and distributing loads generated from contact between the bumper and an opposing retainer. 
     The inventive bumper may have the further aspect of each set of reinforcing ribs being defined by radially extending supporting ribs. 
     The inventive bumper may have the further aspect of the reinforcing ribs being defined by each set of ribs being enclosed by a reinforcing ring. 
     Another aspect of the inventive bumper includes the sets of reinforcing ribs of the bumper having different axial heights. Furthermore, when the ribs are defined by different heights, the radially innermost set of ribs may extend into a well formed in the central portion of the retainer on which the bumper is mounted. 
     In a further aspect of the airspring, the bumper is secured to the retainer by means of compression fit between the bumper and the retainer. 
     In anther aspect of the airspring, the bumper is secured to the retainer by means of a barbed post that is secured to the retainer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described by way of example and with reference to the accompanying drawings in which: 
     FIG. 1 illustrates a cross-sectional view of an airspring with the inventive bumper; 
     FIG. 2 illustrates a cross-sectional view of the inventive bumper; and 
     FIG. 3 illustrates another cross-sectional view of the inventive bumper 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an air spring  10 . The air spring  10  is the type conventionally referred to as a “rolling lobe” airspring, comprising an airsleeve  12 , piston  14 , an upper retainer  16 , a lower retainer  18 , and a bumper  20 . For reinforcement of the sleeve  12 , at least one layer of reinforcement  22  may be provided within the sleeve  12 . The reinforcement layer  22  is formed of conventional cords such as polyester, nylons aramid, glass, or steel; the chosen reinforcement material is determined by the forces to which the air spring will be subject upon use. The length and diameter of the sleeve  12 , and thus the overall size of the air spring  10 , varies depending upon the end use of the air spring  10 . 
     The upper end of the sleeve  12  is secured to the upper retainer  16 , while the lower retainer  18  and the piston  14  secure the lower end of the sleeve  12 , forming a pressurized chamber  24 . The upper retainer  16  has a combination stud  26  permitting the fluid to flow into the pressurized chamber  24 . The preferred fluid introduced into the chamber  24  is air. The upper retainer  16  may also be provided with a mounting stud  28 . The upper end of the sleeve  12  is illustrated as being attached to the upper retainer  16  by means of an interlocking construction between the upper retainer  16  and an internal bead  30  located at the upper end of the airsleeve  12 . The sleeve  12  may also be attached to the upper retainer  16  by other known conventional methods, such as snapping the sleeve onto the retainer or the use of a bead retaining ring located outward of the sleeve as illustrated in U.S. Pat. No. 5,535,994. 
     As noted above, the lower end of the sleeve  12  is secured between the lower retainer  16  and the piston  14 . The lower end of the sleeve has a bead  32  to assist in securing the sleeve  12 . The beads  30 ,  32  of the air sleeve  12  may be steel cable wires, as well as other known conventional air spring bead construction materials. 
     The lower retainer  18  is a solid metal ring, with a central opening  34 . The retainer  18  is secured to the piston  14  by means of an extending post  36  and a locking nut  38 . The post  36  passes through a central opening  40  in the piston  14 . The opposing end of the post  36 , distant from the locking nut  38 , has a series of concentric barbs  42 . About halfway between the two ends of the post  36  is a formed plate washer  44 . Prior to assembling the airspring, the post  36  is welded into the retainer  18  with the formed plate washer  44  flush against the retainer  18 . The bumper  20  is then pushed onto the post  36  and secured by means of the compression fit between the bumper  20  and the post  36 ; the barbs assist in maintaining the bumper  20  on the post  36  by restraining movement of the bumper  20 . Then, upon assembling the air spring, the post  36  is inserted into the central opening  40  of the piston  14  and the locking nut  38  is secured to the post  36  to secure the retainer  18  to the piston  14 . 
     The bumper  20  is more clearly illustrated in FIGS. 2 and 3. The bumper  20  has a flat or slightly curved top surface  46  and a bottom surface  48  that rests against the lower retainer  18 . The bumper  20  has an dual reinforcing structure comprising concentric sets of ribs and rings. The outer ring portion  50  of the bumper  20  has an outer ring wall  52  and a plurality of radially extending ribs  54 , see FIG.  3 . The ribs  54  are spaced about the circumference of the outer ring portion  50 , defining spaces  56  between the ribs  54 . The ribs  54  have a depth equal to the full depth of the outer ring portion  50 . 
     The inner ring portion  58  has elements similar to the outer ring portion  50 . An inner ring wall  60  defines the inner ring portion  58 , and a plurality of radially extending ribs  62  define a plurality of spaces  64 . The ribs  62  are spaced about the central point  66  of the bumper, the radially inner edge  68  of the ribs  62  being spaced from each other by width W. The radially innermost edges  70  of the bottom  68  of the ribs  62  are undercut to accommodate the formed plate washer  44 . 
     The inner rib spacing width W is approximately equal or just less than the maximum diameter of the barbs  42 . If the width W is greater than the diameter of the barbs  42  than the desired compression fit between the bumper  20  and the post  36  is not obtained. If the width W is significantly less than the maximum diameter of the barbs  42  than extreme force is required to mount the bumper  20 . Additionally, the outer diameter D of the inner ring portion  58  of the bumper  20  is approximately equal to the inside diameter of the central well  72  of the lower retainer  18 , to assist in the compression fit of the bumper  20 . 
     The overall height H of the bumper  20 , as measured from the top surface  46  to the bottom edge  48 , may vary depending upon the ultimate end use of the airspring  10  and the desired spring rate of the bumper  20 . The height H is a component of the height H B  and the height H T . The height H T  is height of the outer ring portion  50 ; the height H B  is the height of the remaining, lower portion of the bumper  20 . The height H B  is dependent upon the depth of the central well  72  of the lower retainer  18 , so that when the bottom  48  of the bumper  20  contacts the base of the well  72 , the inner edge  74  of the outer ring portion  20  contacts the lower retainer  18 . When it is desired to vary the height of the bumper  20 , either the height H T  can be increased or decreased, or the height H B  and the depth of the central well  72  can be correspondingly varied; or both heights may be varied with the understanding that the variance of the height H T  will have a greater impact on the spring rate of the bumper and the variance of the height H B  will have a greater impact on the total weight of the airspring  10 . For ease of manufacturing, when it is desired to vary the height H of the bumper, only the height H T  is varied Varying only the height H T  allows the bumper to still provide the needed structural support for the shocks to which the bumper is to be subjected as the length of the structural ribs  56 ,  62  also vary with the height H T . 
     The bumper  20  is formed from a thermoplastic or thermoset material capable of withstanding repeated impact forces and capable of transmitting forces. The tensile strength of the material should be within the range of 28,000 to 45,000 psi, have a flex strength in the range of 40,000 to 60,000 psi, and notched izod strength of 2.0 to 12.0 ft-lb/in. Materials that meet these required characteristics include, but are not limited to, fiberglass reinforced nylon, long fiber reinforced thermoplastic, commercially available under trade name CELSTRAN, and short fiber reinforced thermoplastic, commercially available under trade name ZYTEL. The preferred material is polyurethane with a 60% load of long glass fiber, the fibers have a length of about  11  mm. 
     The present inventive bumper  20 , in comparison to conventional solid rubber or solid plastic bumpers, distributes the load more evenly, thereby eliminating any hydraulic loading of the metal retainer  18 . Thus the bumper  20  can be subjected to a large amount of impact force without damaging the retainer  18 . 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.