Abstract:
An air spring wherein the spring constant of the air spring can be readily tuned to achieve a desired ride performance is disclosed. The air spring has a cylindrical elastomeric sleeve, bead plates, and support rings. The sleeve is secured at each end to a bead plate. The support rings are secured to the bead beads, extending radially outward from the bead plates. The support rings have an inner shoulder, an outer shoulder, and a tracking surface extending between the shoulders. When the air spring is at design height, the sleeve contacts only the inner shoulders of the support rings. By limiting the initial contact of the sleeve with ring and determining where this contact occurs, the movement of the sleeve during jounce can be modified, altering the effective area rate of change.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to an air spring. More specifically, the air spring is a piston-less air spring designed to achieve a desired spring constant. 
     BACKGROUND OF THE INVENTION 
     Air springs have been used for motor vehicles and various machines and other equipment for a number of years. The springs are designed to support a suspension load such as a vehicle. The air spring usually consists of a flexible elastomeric reinforced sleeve that extends between a pair of end members. The sleeve is attached to end members to form a pressurized chamber therein. The end members mount the air spring on spaced components or parts of the vehicle or equipment on which the air spring is to be mounted. The internal pressurized gas, usually air, absorbs most of the motion impressed upon or experienced by one of the spaced end members. 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. The design height of the air spring is a nominal position of the spring when the spring is in neither jounce or rebound. 
     There have been two basic designs of air springs: a rolling lobe air spring, as seen in U.S. Pat. Nos. 3,043,582 and 5,954,316, and a bellows type air spring, as seen in U.S. Pat. Nos. 2,999,681 and 3,084,952. In a rolling lobe type air spring, the airsleeve is a single circular shaped sleeve secured at both ends. During jounce, the airsleeve rolls down the sides of a piston support. In a bellows type air spring, the multiple meniscus shaped portions of the air sleeve extend out radially as the spring is in jounce. 
     For every air spring, the spring rate is an indicator of the characteristics of the air spring. The spring rate k may be determined by the following known equation: 
     
       
         k=((n*Pa*(Ae) 2 )/V)+(Pg*(dAe/dx)) 
       
     
     where 
     n=gas constant, typically 1.38, 
     Pa=absolute pressure, 
     Ae=effective area, 
     V=internal volume, 
     Pg=gage pressure, 
     x=height of air spring, 
     dAe/dx=Effective Area Rate of Change. 
     The effective area Ae, is determined by: 
     
       
         Ae=Fs/Pg 
       
     
     where 
     Fs=spring force. 
     For a given application, there is a specified operating pressure and target load, so the effective area for the spring is fixed. 
     In most applications, it is desired that the spring constant k be relatively small. In other applications, it may be desired that the spring constant be variable depending upon the operating conditions of the vehicle. For example, when encountering uneven road surfaces, if only one axle at a time responds to the uneven surface, then it is desired to have a lower spring constant. However, if multiple axles are simultaneously responding to the uneven surface, it is desired to have a higher spring constant. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an air spring wherein the spring constant of the air spring can be readily tuned to achieve a desired ride performance. Specifically, the inventive air spring has a cylindrical elastomeric sleeve, bead plates, and support rings. The sleeve is secured at each end to a bead plate. The support rings are secured to the bead beads, extending radially outward from the bead plates. The support rings have an inner shoulder, an outer shoulder, and a tracking surface extending between the shoulders. When the air spring is at design height, the sleeve contacts only the inner shoulders of the support rings. 
     By limiting the initial contact of the sleeve with the ring and determining where this contact occurs, the movement of the sleeve during jounce can be modified, altering the effective area rate of change. 
     In another aspect of the invention, the air spring and the rings may also be defined by the relationship of the sleeve hinge point and the relative location of the ring inner shoulders. Each sleeve end has a hinge point about which the sleeve moves during operation of the air spring. The hinge point at each sleeve end is axially outward from the adjacent support ring inner shoulder relative to the axial cross sectional line AL located at the maximum diameter of the sleeve when the air spring is at design height. 
     In another aspect of the invention, the air spring and rings may also be defined by the relationship of the maximum diameters of the sleeve and the rings at design height. At design height, the diameter of the support rings at the outer shoulder is greater than the maximum diameter of the sleeve. 
     The support rings may have a variety of configurations. The support ring may have a solid structure or may have a trough type configuration for reduced weight. The rings may be formed out of metals or thermoplastics or thermoresins. The rings may have a plurality of corrugated ribs to provide strength to the ring. The ring may have either an extending toe or an extending tab for fitment with the related bead rings. The ring may have any radially outwardly extending tab to assist the air spring in balance when the air spring is mounted. When the rings are employed with an air spring, the top and the bottom rings may have identical or differing configurations depending upon the desired air spring performance characteristics. 
    
    
     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 is a cross-sectional view of an air spring in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of an air spring in jounce, and showing the airspring at design height and in full rebound; and 
     FIGS. 3,  4 ,  5 ,  6 , and  6 A are alternative embodiments of the support ring. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the present invention, it was desired to form an air spring with a larger than conventional spring rate k. In accordance with the equation for determining the spring rate k for a determined application, the only variables which may be manipulated to increase the spring constant k are the internal volume V, which may be decreased to increase the spring constant, and the effective area rate of change dAe/dx, which may be increased to increase the spring constant. The inventor of the present invention found that decreasing the internal volume of the air spring was an ineffective solution due to an increased weight of volume minimizers and jounce height interference problems such minimizers created. The inventor found that the effective area rate of change can be manipulated to produce an air spring with a relatively large spring constant k. 
     The present invention is a rolling lobe type air spring designed to provide a relatively large spring constant. By way of example, and not limiting the different features of the present invention, FIG. 1 is a cross sectional view of an air spring  10  at design height in accordance with the present invention. 
     The air spring  10  has a rolling lobe cylindrical elastomeric airsleeve  12 . The airsleeve  12  is typically constructed from at least one layer of rubberized reinforcing cord  14 . The airsleeve  12  is secured at one end to the upper bead plate  16  and at the second end to a lower bead plate  18 , forming a pressurized chamber  20 . The ends of the airsleeve  12  are crimped about the circumferential edges of the bead plates  16 ,  18 . Alternatively, at the ends of the airsleeve  12  may be secured by a crimping ring and crimping retainer plate, which are conventional in the art. The crimping of the ends of the airsleeve  12  creates a hinge point  22  about which the airsleeve  12  flexes when the air spring  10  is in rebound and jounce. The air spring  10  may also be provided with conventional elements such as an internal bumper  24  and air valves  26 , see FIG.  2 . 
     For reinforcement of the airsleeve  12 , at least one layer of reinforcement  14  may be provided within the sleeve  12 . The reinforcement layer  14  is formed of conventional cords such as polyester, nylon, aramid, glass, or steel; the chosen reinforcement material is determined by the forces to which the air spring  10  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 sleeve  12  is not girdled as with a bellows type air spring, so that the sleeve  12  may move in the manner to be discussed below. 
     Mounted about the upper and the lower bead plates  16 ,  18  are support rings  28 . The support rings  28  are circular and extend about the full circumference of the bead plates  16 ,  18 . The rings  28  have a contact surface. The contact surface is defined by an inner sidewall  30 , an inner shoulder  32 , a tracking surface  34 , an outer shoulder  36 , and an outer sidewall  38 . Each shoulder  32 ,  36  is located where the direction plane of the surface changes. The tracking surface  34  extends between the inner shoulder  32  and the outer shoulder  36  and has a width Wt. 
     The tracking surface width Wt is such that the tracking surface  34  extends radially at least to the maximum width Ds of the airsleeve  12 . The overall diameter Dr of the bead ring  28  is at least equal to or greater than the maximum diameter Ds of the airsleeve  12  when the air spring  10  is at the design height. Additionally, at design height, the axial distance Wr between the tracking surfaces of the opposing rings  28 , as measured at the outer shoulders  36 , is at least equal to the tracking surface width Wt. 
     The height of at least the inner sidewall  30 , as measured from the base of the ring  28  to the inner shoulder  32 , is such that the hinge point  22  of the airsleeve  12  is axially outward from the inner shoulder  32  relative to the axial cross sectional line AL located at the maximum diameter Ds of the mounted airsleeve  12 . Because of the relative position of the ring inner shoulder  32  and the sleeve hinge point  22 , when the air spring  10  is at design height, as seen in FIG. 1, the airsleeve  12  contacts only the inner shoulder  32  of the support ring  28  and does not lie upon the tracking surface  34 . 
     FIG. 2 illustrates the air spring  10 ′ in jounce position. For comparison, it also shows the air spring  10  at design height and the air spring  10 ″ at full rebound position. 
     When the air spring  10 ′ is compressed, as the airsleeve  12  is already contacting the support ring  28 , the airsleeve  12  increases contact with the tracking surface  34 , see FIG. 2, and the effective maximum diameter of the sleeve  12  rapidly increases. The ratio of the ring diameter Dr to the design height maximum sleeve diameter Ds, and the ratio of the design height ring separation distance Wr to the tracking surface width Wt are optimized so that as jounce begins, the sleeve  12  is rapidly pushed radially outward. Thus, as the sleeve diameter increases, the effective area of the spring  10  rapidly changes. The change in effective area is greater than the change in the spring height. Thus, the effective area rate of change increases, increasing the value of the spring constant k. By crafting the contour of the tracking surface  34 , the rate of change in effective area can be “tuned” to meet any desired performance characteristics, and other exemplary contours are shown in FIGS. 3-6. Preferably, the ratio Dr/Ds is at least 1.0, and the ratio Wr/Wt is not greater than 2.0. 
     As compression of the airspring  10  continues, the effective area rate of change stabilizes. However, by that time this point is reached by the air spring  10 ′, the volume of the airsleeve  12  is sufficiently reduced that the spring rate k remains high. 
     At close to full jounce, when the air spring  10 ′ is at its most compressed position, the airsleeve  12  begins to contact the outer shoulder  36  and the sleeve  12  begins to roll down the outer sidewalls  38 . As the sleeve  12  begins to roll down the sidewalls  38 , the rate of increase of the internal pressure of the air spring  10 ′ is reduced. At this point the ratio of the ring diameter Dr to the jounce height maximum sleeve diameter is less than 1.0, and preferably less than 0.98. 
     The ring  28  may have a variety of configurations and may be formed from different materials, so long as the ring  28  has a contact surface with an inner shoulder, tracking surface, and outer shoulder upon which the airsleeve  12  travels during jounce. 
     The rings  28  of FIG. 1 have an open trough configuration. The rings have a radially inner extending flange  40  for mounting the rings  28  onto the bead plates  16 ,  18 . The rings  28  of FIG. 2 have a solid construction with a contact surface substantially similar to the rings  28  of FIG.  1 . The rings  28  have a small radially inner lip  42  so that the rings  28  rest on the outer surfaces of the bead plates  16 ,  18  when mounted. 
     The contact surface of the ring  28  of FIG. 3 has a multiple contour configuration. This ring  28  is also illustrated as solid, but may be formed as an open trough, similar to the ring of FIG. 1 to reduce the weight of the ring  28 . The radially innermost point of the ring  28  is a small lip  42  for retention on the bead plates  16 ,  18 . 
     The ring  28  of FIG. 4 is formed by two stamped metal pieces  44 ,  46 . The piece  44  forming the contact surface is similar to the ring  28  of FIG.  1 . The second piece  46  is secured to the open trough of the first piece  44  to result in a more structurally stable ring  28 . 
     The ring  28  of FIG. 5 is formed of conventional thermoplastic or thermoset materials of the type used to manufacture airspring pistons. To obtain the necessary structural stability needed, the ring  28  is formed as a series of accordion ribs  48 . The outer surface of the ring  28  approximates the contact surface of the other exemplary rings  28  and enables the airsleeve  10  to move in the desired manner. 
     FIGS. 6 and 6A illustrate another variation of the stamped metal ring  28 . The ring  28  has both a radially inner extending flange  40  and a radially outer extending flange  50 . The outer extending flange  50  may be continuous about the outer circumference of the ring  28 , or the width of the flange  50  may vary. When the air spring  10  is to be mounted on a narrow surface such as a beam  52 , the edges of the air spring  10  overhang the beam  52 . To provide additional reinforcement, the flange width is increased to a maximum width at two opposite locations that then contact the beam  52  when the air spring  10  is mounted. 
     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.