Abstract:
An air spring having a relatively low and a relatively high spring height includes a retainer, a base housing, an elastomeric sleeve secured to the retainer at a first end and secured to the base housing at a lower end to form a chamber, the elastomeric sleeve expanding from a relatively collapsed configuration at the low air spring height into an expanded configuration at the high air spring height. A confined bladder is disposed within the chamber, the bladder being inflatable to displace a variable portion of an expanded volume within the sleeve chamber at the high air spring height. The spring rate of the air spring is adjusted by an adjustment to the volume of air displaced by the inflated bladder within the sleeve chamber and by overpressurizing the bladder relative to the air spring sleeve, whereby the air spring is adapted to provide a relatively low spring rate at the lower height and a relatively high spring rate at the higher height.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to air springs and, in particular, to a height and spring rate adjustable air spring. 
     BACKGROUND OF THE INVENTION 
     Air springs are in common use for motor vehicles and various machines and other equipment. The springs are designed to support a suspension load such as a vehicle. The springs are often combined with a separate shock absorber device in the suspension that functions to dampen oscillations. Air springs typically consist 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 by which the air spring is mounted. The end members move inward toward each other and also away as the motion of the suspension requires. 
     It is desired in certain applications to provide an air spring for an automotive suspension system designed to operate at two or more suspension ride heights. Such a spring typically will have a fabric reinforced rubber sleeve that forms a rolling lobe that rolls on a piston(s) at either one or both ends of the spring. The piston(s) can either be cylindrical or have conical tapers that will either increase the spring rate with a positive taper or decrease the spring rate with a negative taper. A multiple ride height air spring will have the lobe rolling over different portions of the piston(s) at each height, and these different piston portions can have specific conical tapers to influence the spring rate at that ride height. 
     With a multi-ride height suspension, it is often desirable, such as in off-road SUV vehicles, to have a higher suspension spring rate at the taller or higher suspension ride height(s) to improve vehicle stability, safety, and ride comfort, when driving over uneven surfaces. In order to move the air spring from a shorter height to a taller height, it is typical to add a large amount of internal air volume to the air spring. This additional internal air volume, however, greatly reduces the spring rate of the air spring well beyond the capability of design tools such as piston tapering or other air spring shaping to correct. The reduction in air spring rate attendant the taller height mode of operation thus n&#39;s counter to the desired objective of a higher spring rate at higher heights in order to achieve the aforementioned off-road performance objectives. 
     The industry, accordingly, is in need for a multi-height air spring that includes means for efficiently, predictably, and reliably functioning at multiple heights. The desired air spring, moreover, must function at multiple heights and provide means for creating a higher spring rate at the higher heights and a lower spring rate at the lower heights. The optimum air spring ideally should achieve these objectives in a design that is cost-effective to manufacture, assembly, deploy, and maintain. 
     SUMMARY OF THE INVENTION 
     An air spring having a relatively low and a relatively high spring height is disclosed to include a retainer, a base housing, an elastomeric sleeve secured to the retainer at a first end and secured to the base housing at a lower end to form a chamber, the elastomeric sleeve expanding from a relatively collapsed configuration at the low air spring height into an expanded configuration at the high air spring height. A confined bladder is disposed within the chamber, the bladder being inflatable to displace a variable portion of an expanded volume within the sleeve chamber at the high air spring height. The spring rate of the air spring is adjusted by an adjustment to the volume of air displaced by the inflated bladder within the sleeve chamber and by over-pressurizing the bladder relative to the air spring pressure, whereby the air spring functions to provide a relatively low spring rate at the lower height(s) and a relatively high spring rate at the higher height(s). 
    
    
     
       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 transverse section view through a first embodiment of an air spring configured pursuant to the invention and shown in the collapsed condition; 
         FIG. 2  is a transverse section view thereof shown in the expanded or inflated second height condition; 
         FIG. 3  is a transverse section view through a second alternate embodiment of an air spring configured pursuant to the invention and shown in the collapsed condition; and 
         FIG. 4  is a transverse section view through the air spring of  FIG. 3  shown in the expanded or inflated second height condition. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates the inventive air spring  10 . The air spring  10  has four main components: the upper retainer  12 , the piston  14 , the elastomeric sleeve  16 , and the internal bladder  18 . The elastomeric sleeve  16  is secured at first end  20  to the upper retainer  12  and to the piston  14  at the opposing end  22 , forming a chamber  24 . 
     The elastomeric sleeve  16  is preferably comprised of at least 3 plies: an outer elastomeric ply, at least one reinforcing ply formed of elastomeric embedded reinforcing cords, and an inner elastomeric ply. In the illustrated sleeve  16 , upper end  20  of the sleeve  16  is secured onto the upper retainer  12  by means of a clamping ring  26  in a conventional manner, similar to that disclosed in U.S. Pat. No. 5,005,808. Alternatively, the upper sleeve end  20  may have an inextensible bead about which the upper retainer  12  is crimped for securing the sleeve end  20 , similar to those disclosed in U.S. Pat. No. 5,535,994 or 5,580,033. Similarly, the lower sleeve end  22  is secured to the piston  14  at the clamping region  28  of the piston by means of a clamping ring  30 . Alternatively the ends of the sleeve may be secured to the upper retainer  12  or piston  14  by any other attachment methods that are commonly known in the air spring or hose industries. 
     When the air spring  10  is in use, the upper retainer  12  and the piston  14  move axially toward and away from each other, and the sleeve  16  travels up and down the sides of the piston; however, the sides of the piston  14  may flare out or flare in as needed to tune the suspension performance. The piston  14  has an internal chamber  32  and an axial bore  33  extending therethrough. The bore  33  is defined by cylindrical walls  34  extending from a lower piston wall  36  to an upper piston wall  38 . 
     The bladder  18  resides within the sleeve  16  as shown in  FIGS. 1-4 , and an upper bladder retainer  40  provided to which an upper bladder end  42  is attached by clamping ring  44  or any other suitable means. A lower bladder end  46  similarly to sleeve  16  attaches to the piston  14  by means of claiming ring  48  or other suitable means. The bladder is fabricated similar to the sleeve  16  in the ply construction of preference described above. The upper and lower ends of the bladder  18  are connected in sealed fashion to the retainer  40  and piston  14  so as to define an internal chamber  50 . 
     An air inlet  52  extends through the upper sleeve retainer  12  and provides the access means by which to inflate and deflate sleeve chamber  24 . Similarly, the axial bore  33  extending through piston  14  communicates with the chamber  50  of the bladder  18  and provides the access means by which to inflate and deflate the bladder  18 . It should be noted that air inlet  52  and piston bore  33  are functionally independent so as to allow the sleeve and bladder to be inflated to differing pressures as will be described below. 
     The sleeve  16  and bladder  18  are variable volume chambers and may be selectively inflated from the deflated condition shown in  FIG. 1  into the inflated configuration shown in FIG.  2 . The bladder  18  is folded into a bellows configuration in the deflated state shown in FIG.  1 . In the bellows configuration, the bladder  18  includes multiple bellows folds  53  as shown. 
       FIGS. 4 and 5  show another embodiment of the present invention. In  FIGS. 4 and 5  an air spring has an upwardly open piston housing  56  defined by opposite sidewalls  58 ,  60  and a lower wall  62 . A shock absorber  64  is mounted through the center of the spring, a configuration common in vehicular suspension design. The shock absorber includes a cylinder  66  positioned within housing  56  and a reciprocating rod  68  secured at an upper end  70  to the upper retainer  12 . A cylindrical mounting bracket  72  is affixed at an upper end along radially extending outer edge flanges  74  to an underside of upper retainer  12 . An air inlet  76  extends through the upper retainer and flange  74  to communicate with inner chamber  50 . The upper end  42  of the bladder  18  is attached to outer ends of flange  74  by means of clamping ring  44 . The lower end  46  is attached to a lower end of the bracket  72  by means of clamping ring  48 . Other attachment means known to those skilled in the art may be employed if so desired. 
       FIG. 3  shows the alternative embodiment in the “low suspension”, deflated condition. Bladder  18  is substantially deflated and hangs along the outer sides of bracket  72 . In the shown condition, the rod  68  to shock absorber  64  is retracted within cylinder  66  and the upper retainer  12  is in the “down” position.  FIG. 4  shows the alternative embodiment in the “high suspension”, inflated condition. The bladder  18  is inflated within the sleeve  16  by air admitted under pressure through inlet  76 . Likewise, the sleeve  16  is inflated by air admitted under pressure through inlet  52 . As shown, bladder  18  is in a non-contacting relationship with the outer sleeve  16  in each condition represented by  FIGS. 1-4 , inclusive. 
     The subject air spring can be controlled to operate at two different suspension heights represented in the preferred embodiment by  FIGS. 1 and 2 , and in the alternative embodiment by  FIGS. 3 and 4 . The air spring specifically provides a lower spring rate at the lower suspension ride height and a higher spring rate at the higher suspension ride height. When an air spring is conventionally designed with sufficient air volume to provide a low spring rate at a low spring height, that same spring will have a much larger air volume when it is extended to a higher ride height. This larger air volume will cause the spring rate to be softer, which is undesirable in a vehicle riding at an extended suspension height. The purpose of the bladder  18  is to confine the additional air volume that is a result of extending an air spring, such that the spring rate will not be softened by the added volume. 
     It will be appreciated from  FIGS. 1-4  that the subject invention employs a sleeve and retainer system that is designed for an automotive suspension system, and specifically designed to operate at multiple suspension ride heights. For the purpose of explaining the operation of the invention, two of such heights are designated as “high” and “low”. The air spring sleeve forms a rolling lobe that rolls on a piston at either one or both ends of the spring. The piston(s) can either be cylindrical or have conical tapers that will either increase the spring rate with a positive taper or decrease the spring rate with a negative taper. 
     A multi-ride height air spring will have the sleeve lobe rolling over different portions of the piston(s) at each ride height, and these different piston portions can have specific conical tapers to influence the spring rate at that ride height. 
     With a multi-ride height suspension, it is often desirable to have a higher suspension spring rate at the taller suspension ride heights, to improve vehicle stability, safety, and ride comfort when driving over uneven surfaces, such as off-road. As air springs move from the shorter height to the taller height, however, as explained above, the larger amount of internal air volume reduces the spring rate of the air spring beyond the capability of design tools such as piston tapering or other air spring shaping to correct. From the following equation, it will be understood that the spring air volume is a dominant variable: 
       K   =         N   *     P   abs     *     AE   2       V     +       P   g     *     (       ⅆ           ⁢   AE     /     ⅆ           ⁢   X       )             
 
Where:
         K=spring rate   N=polytropic gas constant 1.41 for air   P abs =absolute gas pressure at midpoint of stroke   V=gas volume at midpoint of stroke   P g =gas gauge pressure at midpoint of stroke   X=total air spring stroke around the midpoint   AE=Effective Area of the air spring at the midpoint of stroke (load/air pressure=effective area)   dAE/dX=change in effective area divided by stroke (an effect of piston or spring tapering)       

     The bladder  18  serves to capture the additional internal air volume created when the air spring extends to the taller ride height of  FIGS. 2 and 4  from the lower heights of  FIGS. 1 and 3 . This captured air within bladder  18  makes the air unavailable for softening the spring rate of the air spring. The bladder  18  is mounted inside the air spring sleeve  16  and will operate at either 0 psig or at a pressure significantly (10 to 50 psi) higher than the pressure in the suspension air spring sleeve  16 . The air pressure within the bladder is independently controllable from the air pressure placed within the sleeve  16 . At the lower ride height, the inner bladder is collapsed by the high air pressure in the surrounding suspension air spring sleeve, and the bladder occupies a minimal volume inside the air spring. The air spring including sleeve  16  is designed pursuant to conventional principles to have adequate size and shape to support the suspension load and provide the desired spring rate at this ride height. 
     When the suspension control system (not shown) drives the suspension to a higher ride height, high pressure air (preferably 10 to 50 psi higher than the pressure in the suspension air spring sleeve) is introduced into the internal bladder. The psi values set forth herein are preferably but the invention is not intended to be limited thereto. The bladder expands and eventually reaches its maximum length, diameter, and design volume as determined by the fabric reinforcement with which it is built. As the bladder is expanding, it increases the air pressure in the surrounding air spring by compression, and this forces air within the spring to achieve the required load support air pressure at the extended ride height. Once the desired taller ride height is reached, the control system may have to either vent or add some air to the air spring sleeve to achieve the required load support air pressure at the extended ride height. 
     It will be noted from  FIGS. 1-4  that the inner bladder is not tall enough when fully inflated to contact both ends of the air spring, and therefore does not directly act as a spring in the suspension. Since the inner bladder is deliberately “overpressurized” relative to the air pressure in the suspension air spring sleeve, its air volume means virtually unchanged during the cyclic air spring movements, and accompanying air spring cyclic volume/pressure changes. Therefore, the inner bladder volume does not contribute to softening of the spring rate of the suspension air spring. Without the spring rate softening effect from the additional air volume in the inner bladder, other air spring design tools such as piston or spring tapering can be used to effectively increase the spring rate of the suspension at the extended air spring ride height. 
     It will further be noted that the two embodiments of the invention shown in  FIGS. 1-2  and  3 - 4  are not the only alternative embodiments possible. Also, the pressure ranges given above are intended to be representative and not restrictive of the scope of the invention. In  FIGS. 1 and 2 , the bladder is a sleeve that is molded with a bellows shape such that it can fold into a compact shape when compressed by deflation. In  FIGS. 3 and 4 , the air spring is modified to incorporate the shock absorber mounted through the center of the spring. In this embodiment, the bladder is a rolling lobe sleeve that is molded such that it lengthens and contracts in diameter when deflated. 
     From the foregoing, it will be apparent that the subject invention accomplishes the needs of the industry for a multi-height air spring that includes means for efficiently, predictably, and reliably functioning at multiple heights. The subject air spring, moreover, functions at multiple heights and provides means for creating a higher spring rate at the higher heights and a lower spring rate at the lower heights. The subject air spring optimizes and meets criteria that required tradeoffs in the prior art. A present air spring, moreover, is achieved in a design that is cost-effective to manufacture, assembly, deploy, and maintain. The invention is particularly useful for off-road capable SUV suspensions by providing a comfortable ride at a low ride height for good fuel economy and good vehicle stability while driving on streets and highways. When desired, the invention allows the use of an extended ride height with stiffer spring rates for off-road driving with good vehicle clearance and good vehicle stability on uneven surfaces. 
     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.