Abstract:
The air spring is comprised of a flexible airsleeve, a retainer, and a main piston. The airsleeve is secured at one end by the retainer and at the opposing end by the main piston. A hollow restraining piston extends from the retainer and into the main piston. The restraining piston acts as a lateral stabilizer, over extension restraint and height control. The hollow region in the restraining piston communicates through at least one passage with an air chamber formed between the airsleeve and the outer surfaces of the restraining piston and the main piston. Fluid is admitted to or exhausted from the air spring through a valve which functions relative to the displacement of the restraining piston and the main piston.

Description:
FIELD OF THE INVENTION 
     The present invention is directed toward an air spring. More specifically, the present invention is directed towards an air spring that combines functions of separate components of a suspension system of a vehicle into a single unit. 
     BACKGROUND OF THE INVENTION 
     When a vehicle is in motion, the road disturbances encounter by the vehicle input kinetic energy into the passenger cabin of the vehicle and that energy must be dissipated for the comfort of the passenger and any cargo being carried by that vehicle. To dissipate the energy, it is known in the art to employ the use of either shock absorbers or air springs. 
     U.S. Pat. No. 4,844,428 discloses an air spring assembly wherein the air spring assembly can be adjusted to obtain an optimum spring constant. The air spring is comprised of a shock absorber and a reversible electric motor to vary the spring constant of the air spring. While the disclosed air spring combines many functions, the entire air spring is cumbersome and complex. 
     U.S. Pat. No. 4,786,035 discloses an air spring with an internal restraint. The air spring is provided with an elongated flexible strap that extends between the end members of the air spring. While this provides the air spring with a means of limited restraint, there is no means for limiting the radial movement of the air spring. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards an air spring that combines functions formerly provided by separate components into a single unit. The air spring combines at least two of the following functions: axial spring, lateral stabilizer, jounce bumper, damper, over extension restraint and height control. 
     The air spring of the present invention is comprised of a flexible airsleeve, a retainer, and a main piston. The airsleeve is secured at one end by the retainer and at the opposing end by the main piston. A hollow restraining piston extends from the retainer and into the main piston. The restraining piston acts as a lateral stabilizer, over extension restraint and height control. 
     In another aspect of the inventive air spring, the hollow region in the restraining piston communicates through at least one passage with an air chamber formed between the airsleeve and the outer surfaces of the restraining piston and the main piston. 
     In another aspect of the invention, the air spring is further comprised of a valve. The valve selectively admits or exhausts a fluid from the air spring as a function of the relative displacement of the restraining piston and the main piston. 
     In another aspect of the air spring, the restraining piston grips an upper portion of the valve to selectively admit or exhaust the fluid. The valve admits fluid into the air spring when the air spring is at a jounce position and the valve exhausts fluid when the air spring is at a rebound position. 
     In another aspect of the air spring, a pressure chamber is formed between the restraining piston and the main piston. The pressure chamber communicates through at least one passage with the hollow region of the restraining piston. At least one of the passages between the pressure chamber and the hollow interior of the restraining piston being a check valve. 
    
    
     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 the inventive air spring 
     FIG. 2 is a cross-sectional view of the air spring when in a compressed state; and 
     FIGS. 3A-3C are various embodiments of the guide means. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     By way of example, and not limiting the different features of the present invention, FIG. 1 illustrates an air spring  10  in accordance with the present invention. The air spring  10  has a cylindrical airsleeve  12 . The airsleeve  12  is typically constructed from at least one layer of rubberized reinforcing cord. The airsleeve  12  is secured at one end to the upper retainer  14  and at the second end to a main piston  18 . The airsleeve  12  is secured at both ends by securing rings  16 , a conventional technique in the art. Alternatively, at least the upper end of the airsleeve  12  may be secured by an internal bead and crimping retainer plate, which are conventional and known to those skilled in the art. The airsleeve  12  is illustrated as a rolling lobe type construction, but a bellows type construction with a plurality of lobes may be employed as the airsleeve  12 . The airsleeve  12  encloses a volume  20 . 
     The upper retainer  14  has a central aperture  22 , in which a restraining piston  24  is secured. To maintain an airtight seal between the upper retainer  14  and the restraining piston  24 , an o-ring  26  may be inserted into a groove  28  located within the aperture  22 . The restraining piston  24  extends through a central aperture  30  into the main piston  18 . Similar to the upper end of the restraining piston  24 , an airtight seal may be obtained with an o-ring  32  in a groove located within the aperture  30 . 
     A radially extending flange  34  defines the lower end of the restraining piston  24 . The flange  34  may also be provided with an o-ring similar in construction to those previously disclosed. As seen in FIG. 1, the majority of the restraining piston  24  has a diameter approximately equivalent to the aperture  30  of the main piston  18 . The outermost diameter of the radially extending flange  34  is approximately equivalent to the interior diameter of the main piston  18 . Due to these diameter relationships, three interrelated air chambers are created within volume  20 . 
     The first chamber  38  is within the restraining piston  24 , and can include the volume within the main piston  18  when the air spring  10  is in a rebound position, as illustrated in FIG.  1 . The second chamber  40  is between the outer surface of the restraining piston  24  and the interior of the main piston, see FIG.  2 . The third chamber  42  is a toroidal area between the airsleeve  12  and the exterior of the restraining piston  24  and the main piston  18 . The volume of the first, second, and third chambers  38 ,  40 ,  42  is variable, as will be discussed further below. 
     The enclosed volume  20 , and the first, second, and third chambers  38 ,  40 ,  42 , are pressurized with compressed fluid, preferably air, through the inlet port  44  at the base  46  of the main piston  18 . Adjacent to the inlet port  44  in the main piston base  46  is an exhaust port  48 . Between the ports  44 ,  48  and the first chamber  38  is a flat disk  50  functioning as a valve. The disk  50  has an offset hole  52  and is free to rotate about its center. Centrally attached to the disk  50  is a rigid twisted ribbon  54  that engages a guide means  56  on the interior side of the restraining piston  24 . The illustrated ribbon  54  is twisted so that each edge  58  travels through a ninetydegree arc. The arc through which the ribbon  54  travels may be greater or less than ninety degrees depending upon the twist characteristics of the ribbon  54 . This characteristic will vary with the dimensions of the air spring  10 . 
     The guide means  56  may be constructed in a plurality of ways, as seen in FIGS. 3A-3C. As illustrated in FIG. 3A, the guide means  56  may be a pair of extending projections  59  that grip almost the full width of the central portion of the ribbon  54 . Alternatively, the extending projections  60  may be provided with a slot  62  for engaging the ribbon edges  58 , see FIG.  3 B. The guide means  56  may also be a continuous circular element  64 , see FIG.  3 C. The circular guide  64  has two radially opposing slots  64  into which the ribbon edges  58  are inserted. Whatever means is used to grip the ribbon  54 , the guide means  56  should have a curvature that compensates for the curvature of the ribbon  54 , allowing the guide means, and thus the restraining piston  24 , to travel freely along the length of the ribbon  54 . 
     Because of the twist of the ribbon  54 , and the rigid mounting of the ribbon  54  in the rotatable disk  50 , as the restraining piston  24 , and the attached guide means  56 , moves from an expanded position to a compressed position, the ribbon  54 , and thus, the disk  50 , is rotated. The rotation of the ribbon  54  and the disk  50  results in three operating positions of the disk  50 . 
     When the air spring  10  is at its rebound height, i.e. its maximum height, as seen in FIG. 1, the disk  50  is rotated so that the offset hole  52  and the exhaust port  44  are aligned, permitting compressed fluid out of the first chamber  38 . At this position, the first chamber  38  is at its maximum volume, as it includes the volume within the interior of the main piston  18 . Fluid enters and exits the third chamber  42  through a passageway  68  located in the restraining piston. The second chamber  40  has a zero volume. 
     As the air spring  10  is being compressed, the disk  50  is rotated wherein the offset hole  52  is not aligned with either port  44 ,  48 , preventing any air from entering or escaping from the air spring  10 . However, in this position, the second chamber volume begins to increase as fluid flows through an orifice restriction  70 . Concurrently, the volume of the first and third chambers  38 ,  42  begin to decrease. 
     When the air spring  10  is in the jounce position, i.e. its minimum height, the offset hole  52  is aligned with the inlet port  44 , permitting the supply of compressed fluid to enter the enclosed volume  20 , see FIG.  2 . When the air spring  10  is in this position, the second chamber, which acts as a rebound pressure chamber, is at its maximum volume. To further control the pressure within the second chamber, a check valve  72  may be installed. Between the restraining piston  24  and the end of the main piston  18  is a rubber bumper  74  to absorb excessive jounce loading. Conversely, for severe rebound conditions, a rebound bumper  76  is provided between the restraining piston  24  and the open end of the main piston  18 . 
     To achieve a desired ride quality, check valves or flow controls may be inserted into the inlet or exhaust ports  44 ,  48 . The exhaust port  48  may be vented directly to the atmosphere, or it may be vented into a reservoir that also supplies the inlet port. 
     It should be noted that when the suspension of the vehicle upon which the air spring  10  is mounted is dropped, the air spring  10  is placed in a service mode, wherein all of the fluid within the air spring  10  is vented. When the air spring is restored to the jounce position, the fluid is restored to the air spring  10  is restored and the air spring  10  is ready to function. 
     The interconnecting relationship between the restraining piston  24  and the main piston  18  provides lateral restraint to the air spring  10 , thus eliminating the need to supply an external lateral restraint means to the air spring  10 . This construction also combines within the air spring  10  a damper, jounce bumper, rebound restraint and height control means. 
     While the illustrated air spring  10  is not shown with any mounting means to secure the air spring  10  in its intended application, those of skill in the art would readily appreciate that the mounting configuration of the air spring  10  is determined by the end requirements and the system into which the air spring  10  is being 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 would be within the fully intended scope of the invention as defined by the following appended claims.