Patent Publication Number: US-RE46112-E

Title: Dual lobe airspring

Description:
This application claims priority from U.S. Provisional application serial No. 60/139,056 filed Jun. 11, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to compressible fluid type spring devices for vehicle suspensions. More specifically, the invention relates to airsprings of the type with a flexible type rubber sleeve having rolling lobes. 
     Airsprings having a sleeve for forming a closed chamber to receive a pressurized fluid are well known. Usually, the airspring sleeve includes a corded fabric or a nylon cord to strengthen the sleeve and retain the sleeve shape. 
     Rolling lobe type airsprings are well known in the art and are made with a sleeve having a chamber portion connected to a closure memeber member and an inverted rolling lobe portion connection to a piston that partially reciprocates in the chamber portion of the sleeve. The general formula for calculating a spring rate of such an airspring is well known and documented such as in U.S. Pat. No. 4,629,170. 
     An airspring is a load support member that utilizes the compressible characteristics of air for a spring effect. One method of changing the spring rate of an airspring is to change the effective area that is acted on by the internal pressure of the spring. This is done by altering the external shape of the piston which laterally supports part of the rolling lobe portion of the sleeve. Theoretically, there is no change in effective area or spring rate if the piston is straight sided or cylindrical. However, a reduced effective area is achieved by a frustoconical shaped piston that reduces size as it enters the chamber portion; and an increase in spring rate is achieved by a frustoconically shaped piston whose size increases as it enters the chamber portion. 
     In use, rolling lobe airsprings typically encounter angular displacements or torque which result in ride harshness. The ride harshness is pronounced at low amplitude undulation of the vehicle. Rolling lobe airsprings having one piston and one rolling lobe can only compensate for very small angular displacements. Also, rolling lobe airsprings having two substantially cylindrical pistons and two rolling lobes, due to the increased amount of piston travel, can only compensate for very small angular displacements. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an airspring and method are provided. The airspring has a construction that can accommodate large angular displacement of the vehicle suspension. The airspring construction can also be used to vary the spring rate associated with a piston entering and exiting an air chamber. An airspring is provided which has a sleeve having two rolling lobes and two pistons. 
     The first rolling lobe is connected at an end of the first rolling lobe to a first piston. The second rolling lobe is connected at an end of the second rolling lobe to a second piston. Each of the first and second pistons includes a rolling surface that in conjunction with the first and second rolling lobes defines an effective area for each of the first and second pistons. The minimum effective area of the second piston is less than the minimum effective area of the first piston and the maximum effective area of the second piston is greater than the maximum effective area of the first piston. 
     In a preferred embodiment of the invention, the first piston is substantially frustoconical cylindrical and the second piston is substantially frustoconcical. In an alternate embodiment, the geometric shape that determines the effective area need not be symmetrical about any axis and may describe any contour as required by a user. 
     An object of the invention is to provide an airspring design that includes two pistons and two rolling lobes with one of the pistons performing a majority of the longitudinal displacement. 
     An advantage of the invention is that large angular displacements of the vehicle suspension can be accommodated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an axial cross section of a prior art airspring of the rolling lobe type. 
         FIG. 2  is an axial cross section of the present invention. 
         FIG. 3  is an axial cross section of the present invention at the end of the rebound stroke. 
         FIG. 4  is an axial cross section of the present invention at the end of the compression stroke. 
         FIG. 5  is a perspective cross-sectional view of the present invention. 
         FIG. 6  is a perspective cross-sectional view of the present invention at the end of a rebound stroke. 
         FIG. 7  perspective cross-sectional view of the present invention at the end of a compression stroke. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an airspring, indicated generally at  10 , of a prior art construction. The airspring  10  includes a sleeve  12  having a chamber portion A-B and a rolling lobe portion B-C. The chamber portion A-B is connected at an end  18  to a closure member  20  by use of a mounting member  22 . The rolling lobe portion B-C is connected at an end  24  to a piston  26  by use of a mounting member  28 . In use, the piston  26  and the rolling lobe portion B-C moves into the chamber portion A-B. The closure member  20  however, is fixed with respect to the chamber portion A-B. Since the closure member  20  is fixed with respect to the chamber portion A-B, angular displacements of an unsprung portion (not shown) of a vehicle are not readily accommodated by the airspring  10 . 
     An airspring, indicated generally at  10 , is illustrated in  FIG. 2 . The airspring  10  is mounted to an unsprung portion (not shown) of a vehicle and a sprung portion (not shown) of a vehicle. 
     FIG. 3 illustrates an example embodiment wherein the first piston 18 of the airspring 10 is coupled to a second portion 36 of a vehicle chassis, and the second piston 28 of the airspring 10 is coupled to a first portion 34 of the vehicle chassis. In the example of FIG. 3, the first piston 18 is fixed to the second portion 36 and the second piston 28 is fixed to the first portion 34 of the vehicle chassis. However, there could be another component (not shown) located between the first piston 18 and the second portion 36 of the vehicle chassis. There could also be another component (not shown) located between the second piston 28 and the first portion 34 of the vehicle chassis. For example, another frame or suspension component could be disposed between the first piston 18 and the second portion 36 of the vehicle chassis or between the second piston 28 and the first portion 34 of the vehicle chassis. The additional component could also be used to couple the first piston 18 to the second portion 36 of the vehicle chassis, or to couple the second piston 28 to the first portion 34 of the vehicle chassis. 
     The airspring  10  includes a sleeve  16  typically formed from a resilient material and embedded with a fibrous member of any suitable type such as made with synthetic fibers of nylon, rayon, polyester, fiberglass and aramid or natural fibers such as cotton. The sleeve  16  includes a closed chamber portion A-B for receiving pressurized air or fluid. 
     The chamber portion A-B interconnects a first rolling lobe A-C and a second rolling lobe B-D. Throughout this disclosure, the letters A-B are used to designate a chamber portion, the letters A-C are used to designate a first rolling lobe and the letters B-D are used to designate a second rolling lobe in order to facilitate an easy comparison of such portions in the various examples. 
     First rolling lobe A-C is connected at one end  24  to a first piston  18  by the use of a mounting member  20 . The first piston  18  includes a rolling surface  22  which in conjunction with the first rolling lobe A-C defines an effective area which is acted on by the pressurized air in the closed chamber A-B. 
     Second rolling lobe B-D is connected at one end  26  to a second piston  28  by the use of a mounting member  30 . The second piston  28  includes a rolling surface  32  which in conjunction with the second rolling lobe B-D defines an effective area which is acted on by the pressurized air in the closed chamber A-B. 
     In the preferred embodiment,  FIGS. 2-4 , the rolling surface  32  and the second rolling lobe B-D define a maximum effective area range which is greater than the maximum effective area range defined by the rolling surface  22  and the first rolling lobe A-C, and a minimum effective area that is less than the minimum effective area defined by the rolling surface  22  and the first rolling lobe A-C. The rolling surface 22 of the first piston  18  is substantially cylindrical and the rolling surface  32  of second piston  28  is substantially frustoconical, as shown in FIGS. 2-4. Surface  22  of first piston  18  may also be frustoconical as shown in  FIG. 2 . In use, the first piston  18  reciprocates longitudinally in and out of the chamber portion A-B. The second piston  28  is substantially static along the longitudinal axis. 
       FIG. 3  illustrates the airspring  10  in the maximum extended position, also known in the art as the rebound position. In the rebound position, the first piston  18  has partially reciprocated longitudinally out of the chamber portion A-B. The first rolling lobe A-C has traveled along the rolling surface  22 . The rolling surface  32 , due to angular displacement of the unsprung portion (not shown) of a vehicle, may contact the second rolling lobe B-D along only a portion of the second piston  28  circumference. 
       FIG. 4  illustrates the airspring  10  in the maximum compressed position. In the compressed position, the first piston  18  has reciprocated into the chamber portion A-B. The first rolling lobe A-C has traveled along the rolling surface  22 . The rolling surface  32 , due to angular displacement of the unsprung portion (not shown) of a vehicle, contacts the second rolling lobe B-D along all of the second piston  28  circumference. In addition, a portion of the second piston  28  has partially reciprocated into the chamber portion A-B. Since the rolling surface  32  and the second rolling lobe B-D define an maximum effective area which is greater than an effective area defined by the rolling surface  22  and the first rolling lobe A-C, the second piston  28  reciprocates into the chamber portion A-B less than the first portion piston  18 . The angular displacement of the central axis of the second piston  28  as compared to a central axis of the first piston  18  is in the range of α=0° to 35°. One skilled in the art will appreciate that a movement of the first piston relative to the second piston is not necessarily coaxial nor is it necessarily constrained to any particular path or paths. By way of example, in certain operating situations, movement of the second piston will describe a path in two dimensions or in three dimensions relative to the first piston. In others, relative movement of each piston will be linear, but will not necessarily describe co-axial paths. In yet others, movement of the first piston and the second piston will each describe a path in three dimensions. 
     The behavior of the airspring is a function of the ratio of the effective area of the first piston, A e1 , and the effective area of the second piston, A e2 . The effective area for each piston is found by the following equation:
 
A e =90 /4[(D 1 +D 2 )/2] 2 (0.9)
 
where D 1  is the diameter of the lobe at the piston and D 2  is the diameter of the piston at the tangent point of contact of the lobe on the piston surface. This equation may be adapted to accommodate a rolling surface, for example rolling surface  22  or  32 , having a complex shape, meaning, the equation describing rolling surface  22  or  32  can be a first, second, third or greater order equation. The effective area equation then becomes:
 
A e =π/4[(D 1 (x)+D 2 (x))/2] 2 (0.9)
 
where D 1 (x) and D 2 (x) are functions which are unique to each end and piston of the airspring. In particular, D 2 (x) is the first, second, third or greater order surface of revolution equation describing the shape of the piston rolling surface  22  or  32 . D 1 (x) may also describe a cylindrical, conical, ellipsoidal or other geometric shape depending on the form of the sleeve  16  at the particular end. Therefore, the size of the effective area of each piston can be variable along an axis depending on the shape of the piston rolling surface and of the sleeve. The movement of the airspring can then be predicted based upon the following relationships:
 
A e1 &gt;A e2    (1)
 
A e1 =A e2    (2)
 
A e1 &lt;A e2    (3)
 
For equation (1), the lobe will roll on the rolling surface of piston  2  at a rate determined by the shape of the piston  2  effective area, until the effective areas of both pistons  1  &amp;  2  are equal as described in equation (2). For equation (2), neither lobe will roll on either piston rolling surface. For equation (3), the lobe will roll on the rolling surface of piston  1  at a rate determined by the shape of the piston  1  effective area, until the effective areas of both pistons  1  &amp;  2  are equal as described in equation (2). Therefore, the airspring will operate properly so long as at least one point in the range of the size of the variable effective area of the first piston is equal to at least one point in the range of the size of the variable effective area of the second piston. The equal point values may be adjusted to determine the travel of each piston relative to the other, or relative to another fixed point remote from the airspring, such as a vehicle chassis.
 
       FIG. 5  is a perspective cross-sectional view of the present invention. 
       FIG. 6  is a perspective cross-sectional view of the present invention at the end of a rebound stroke. The rotation/translation of second piston  28  is shown having angle α with reference to the y axis, although movement relative to the x and z axes is also possible. Second piston  28  is generally fixed to a frame (not shown). The inventive air spring can operate as a ball joint, accommodating rotational and translational movement imposed by the frame in any direction, which movements are symbolically represented in one position by the angle α. The first piston  18 , while fixed to a moveable frame, may also rotate/translate in any of three dimensions in concert with the second piston  28  according to the movement of the frame. The frame in this description may comprise a suspension component of an automobile or truck chassis, or any other form of device using a system having interconnected components that require controlled relative movements. It is this unique ability to accommodate a wide variety of movements that allows the inventive air spring perform as a ball joint as well as an energy absorbing device. Of course, one of the pistons may be fixed to a frame while the other rotates/translates as shown in this  FIG. 6 . 
       FIG. 7  is a perspective cross-sectional view of the present invention at the end of a compression stroke. The rotation/translation of second piston  28  is shown having angle β with reference to the x, y, and z axes. Angle β on the compression stroke need not be equivalent to angle α of the rebound stroke in  FIG. 6 . The angle may vary on each end of the stroke based upon the design needs of a user. 
     The foregoing detailed description is used for purpose of illustration only and is not intended to limit the scope of the invention which is to be determined from the appended claims.