Abstract:
The present invention provides the art with a shock absorber which is capable of compensating for the differing thermal expansion between two materials. The shock absorber in its various embodiments includes a free floating pressure tube that is able to expand or contract axially without breaking a seal, a hybrid piston rod with a shaft of one material that compensates for differing thermal expansions and a cap of another material that absorbs axial forces, a unique rod guide assembly with a biasing member that compensates for differing thermal expansions, and a unique cylinder end assembly with a biasing member made from springs, a rubber block, or pressurized gas.

Description:
FIELD OF THE INVENTION 
     Hydraulic dampers, such as shock absorbers, are used in connection with motor vehicle suspension systems to absorb unwanted vibrations which occur during the operation of the motor vehicle. The unwanted vibrations are dampened by shock absorbers which are generally connected between the sprung portion (i.e., the vehicle body) and the unsprung portion (i.e., the suspension) of the motor vehicle. A piston assembly is located within the compression chamber of the shock absorber and is usually connected to the body of the motor vehicle through a piston rod. The piston assembly includes a valving arrangement that is able to limit the flow of damping fluid within the compression chamber when the shock absorber is compressed or extended. As such, the shock absorber is able to generate a damping force which “smooths” or “dampens” the vibrations transmitted between the suspension and the vehicle body. 
     A prior art thermal expansion compensating twin tube shock absorber  100  is shown in  FIG. 1 . Shock absorber  100  comprises an elongated pressure tube  102  provided for defining a hydraulic fluid containing compression chamber  104  and an elongated reserve tube  106  provided for defining a hydraulic fluid containing reservoir  108 . 
     Disposed within compression chamber  104  is a reciprocal piston assembly  110  that is secured to one end of an axially extending piston rod  112 . Piston rod  112  is supported and guided for movement within pressure tube  102  by means of a combination seal and rod guide assembly  114  located at the upper end of pressure tube  102  and having a centrally extending bore  116  through which piston rod  112  is reciprocally movable. Disposed within bore  116  between rod guide assembly  114  and piston rod  112  is a bushing  118  which is used to facilitate movement of piston rod  112  with respect to rod guide assembly  114 . 
     A compliant cylinder end assembly, generally designated at  120 , is located at the lower end of pressure tube  102 . The compliant cylinder end assembly  120  includes a base valve assembly  122  that functions to control the flow of hydraulic fluid between compression chamber  104  and fluid reservoir  108  as well as biasing member  124  that compensates for the differing axial thermal expansion between the various components of shock absorber  100 . Fluid reservoir  108  is defined as the space between the outer peripheral surface of pressure tube  102  and the inner peripheral surface of reserve tube  106 . 
     The upper and lower ends of shock absorber  100  are adapted for assembly into a motor vehicle. Piston rod  112  is shown having a threaded portion  126  for securing the upper end of shock absorber  100  to the motor vehicle while reserve tube  106  is shown incorporating a flange  128  having a pair of mounting holes  130  for securing the lower end of shock absorber  100  to the motor vehicle (McPherson strut configuration). While shock absorber  100  is shown in a McPherson strut configuration having threaded portion  126  and flange  128  for securing it between the sprung and unsprung portions of the motor vehicle, it is to be understood that this is merely exemplary in nature and is only intended to illustrate one type of system for securing shock absorber  100  to the motor vehicle. As will be appreciated by those skilled in the art, upon reciprocal movement of piston rod  112  and piston assembly  110 , hydraulic fluid with compression chamber  104  will be transferred between an upper portion  132  and a lower portion  134  of compression chamber  104  as well as between compression chamber  104  and fluid reservoir  108  through valve assembly  122  for damping relative movement between the sprung portion and the unsprung portion of the motor vehicle. 
     This quick exchange of hydraulic fluid through valve assembly  122  and piston assembly  110  as well as the friction between piston assembly  110  and pressure tube  102  and the friction between piston rod  112  and rode guide  114  generates heat which is undesirable during prolonged operating conditions. 
     In addition to absorbing the heat generated while providing the damping function for the motor vehicle, shock absorber  100  is also required to operate over a broad range of temperatures ranging from severe cold temperatures of the winter months to the extremely hot temperatures of the summer months. Prior art shock absorbers are manufactured using steel for pressure tube  102  and reserve tube  106 . While steel has been proven to be an acceptable material for these components, tubes manufactured from aluminum offer the advantages of weight savings as well as improved heat dissipation. If the typical pressure tube  102  were manufactured from steel while reservoir tube  106  were manufactured from aluminum, the difference in their relative axial thermal expansion rates may present problems for the shock absorber when operating over the necessary temperature extremes. Specifically, structural failure may occur under extreme cold temperatures or loss of pressure tube preload and sealing may occur under extreme hot temperatures. 
     Accordingly, continued development of shock absorbers with aluminum tubes includes the further development of methods to compensate for differing thermal expansion between aluminum and steel as well as the differing thermal expansion between any other two materials. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a shock absorber which is capable of compensating for the differing thermal expansion between two materials and thus eliminating the possibility of structural failure due to extreme cold temperatures as well as the possibility of pressure tube preload loss and sealing failure under extreme hot temperatures. 
     In one embodiment of the present invention, the shock absorber includes a free floating pressure tube that is capable of compensating for differing thermal expansion by freely moving between the rod guide assembly and the valve assembly. 
     In another embodiment of the present invention, a unique piston rod is provided that includes an aluminum rod that eliminates the difference in thermal expansions. The rod has a steel cap that absorbs compression forces. 
     In another embodiment of the present invention, a unique compensating rod guide assembly is provided that includes a thermal compensation element capable of compensating for the differing thermal expansion between the pressure tube and the reserve tube. 
     In still another embodiment of the present invention, a unique compensating cylinder end assembly is provided that includes a thermal compensation element, and the means for securing the element to the valve assembly. This compensating element is either a spring, an elastomeric block, or gas pressure. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
         FIG. 1  is a longitudinal cross-sectional view through a prior art thermal expansion compensating shock absorber; 
         FIG. 2  is a longitudinal cross-sectional view of a shock absorber incorporating a floating pressure tube; 
         FIG. 3  is a side view of a unique aluminum piston rod with a steel cap; 
         FIG. 4  is an enlarged side view of a threaded steel cap; 
         FIG. 5  is an enlarged side view of a bonded steel cap; 
         FIG. 6  is an enlarged cross-sectional view of a compensating rod guide assembly with Belleville springs; 
         FIG. 7  is an enlarged cross-sectional view of a compensating rod guide assembly with a bearing bush retainer; 
         FIG. 8  is an enlarged cross-sectional view of an alternate compensating rod guide assembly with a bearing bush retainer; 
         FIG. 9  is an enlarged cross-sectional view of a compensating rod guide assembly with a retainer; 
         FIG. 10  is an enlarged cross-sectional view of a compensating cylinder end assembly with Belleville springs; 
         FIG. 11  is an enlarged cross-sectional view of the compensating cylinder end assembly of  FIG. 10  illustrating a circle-clip and retainer support for the compensating member; 
         FIG. 12  is an enlarged cross-sectional view of the compensating cylinder end assembly of  FIG. 10  illustrating a spring retainer for the compensating member; 
         FIG. 13  is an enlarged cross-sectional view of the compensating cylinder end assembly of  FIG. 10  illustrating a double ring retainer for a compensating member; 
         FIG. 14  is an enlarged cross-sectional view of an alternate compensating cylinder end assembly having a two piece end assembly that sandwiches the compensating member; 
         FIG. 15  is an enlarged cross-sectional view of an alternate compensating cylinder end assembly illustrating the pressure tube and compensating member disposed within the valve assembly; 
         FIG. 16  is an enlarged cross-sectional view of a compensating cylinder end assembly with Belleville springs at the base; 
         FIG. 17  is an enlarged cross-sectional view of a compensating cylinder end assembly with an elastomeric block at the base; 
         FIG. 18  is an enlarged cross-sectional view of a compensating cylinder end assembly with gas pressure at the base; and 
         FIG. 19  is an enlarged cross-sectional view of an alternate compensating cylinder end assembly with gas pressure at the base. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Continued reference is made generally to  FIG. 1  and specifically to the components of shock absorber  100  throughout the subsequent description. It is to be understood that the construction of shock absorber  100  is merely exemplary in nature and is only intended to illustrate one type of hydraulic damping apparatus within which the compensating elements of the present invention can be utilized. 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIG. 2  a unique compensating shock absorber  200  having a floating pressure tube  202  and a base valve assembly  222 . Rod guide assembly  114  and base valve assembly  222  are mechanically secured to reserve tube  106 . As the relative length of reserve tube  106  changes due to thermal conditions, the relative distance between rod guide assembly  114  and base valve assembly  222  changes. In the prior art, pressure tube  102  is fixed at one end to one portion of rod guide assembly  114  and at the other end to base valve assembly  122 , such that changes in the length of pressure tube  102  due to thermal conditions were compensated for using a multi-piece valve assembly  122 . In this embodiment of the present invention, a floating pressure tube  202  replaces pressure tube  102  of the prior art in order to compensate for the different thermal expansions of reserve tube  106  and floating pressure tube  202 . Floating pressure tube  202  is sealed to rod guide assembly  114  and base valve assembly  222  using O-rings  204 . Floating pressure tube  202  is able to move freely between rod guide assembly  114  and base valve assembly  222  as the relative length of reserve tube  106  changes. Thus, both a standard valve guide assembly and a standard base valve assembly can be easily modified to accept floating pressure tube  202 . 
     In another embodiment of prior art shock absorber  100 , a hybrid piston rod  312  replaces the prior art piston rod  112  as shown in  FIGS. 3–5 . Typically the prior art piston rod  112  is made from steel while rod guide assembly  114  is made from aluminum. Under extreme thermal conditions the seal between piston rod  112  and rod guide  114  can be broken by the different thermal expansion of the two materials. Hybrid piston rod  312  includes an aluminum piston shaft  314  and a steel piston post  316 . As shown in  FIG. 4 , piston post  316  includes an internal bore  318  which slidingly receives the end of piston shaft  314 . A circle-clip  320  retains the assembly of piston post  316  and piston shaft  316 . As shown in an alternative embodiment in  FIG. 4 , piston post  316  has an open threaded bore  322  for receiving a threaded end of piston shaft  314 . Piston post  316  may be threaded on to piston shaft  314 . Alternatively, as seen in  FIG. 5 , a modified steel piston post  330  with a flat end  332  may be adhesively secured to the end of piston shaft  314 . In operation, aluminum piston shaft  314  expands and contracts at the same rate as aluminum rod guide assembly  114  and thus prevents a break in the seal between the two. Steel piston post  316 , or alternately modified steel piston post  320 , absorbs the axial force on piston rod  312  when shock absorber  100  is in compression. 
     In still another embodiment of prior art shock absorber  100 , various compensating piston rod guide assemblies are shown in  FIGS. 6–9 . The compensating piston rod guide assembly  414 , as shown in  FIG. 6 , supports and guides the movement of piston rod  112  and also compensates for the different thermal expansion of pressure tube  102  and reserve tube  106 . Compensating piston rod guide assembly  414  includes bore  116  and bushing  118 , as well as a plurality, an even number in the preferred embodiment, of Belleville springs  424  disposed between rod guide  414  and pressure tube  102 . The difference in thermal expansion between steel pressure tube  102  and aluminum reserve tube  106  is compensated for by the increase or decrease in the compensation of Belleville springs  424 . 
     On the left side of  FIG. 7 , an alternate compensating piston rod guide  414 ′ is shown. Alternate piston rod guide  414 ′ includes a bearing bush retainer  450  disposed between Belleville springs  424  and rod guide  414 ′. Bearing bush retainer  450  seals rod guide  414 ′ and pressure tube  102  and retains bushing  118 , and is further designed to support Belleville springs  424 . The thermal expansion of pressure tube  102  is directly compensated for by Belleville springs  424 . On the right side of  FIG. 7 , piston rod guide  414 ′ is shown with bearing bush retainer  450  being replaced by compensation retainer  450 ′. Compensation retainer  450 ′ functions the same as bearing bush retainer  450  in that it retains bushing  118  and it is designed to support Belleville springs  424 . The thermal expansion is directly compensated for by Belleville springs  424 . 
     In another embodiment, a compensating piston rod guide  414 ″ is shown on the left side of  FIG. 8 , wherein bearing bush retainer  452  is disposed between the pressure tube  102  and Belleville springs  424 . Bearing bush retainer  452  is similar to bearing bush retainer  450  in that it seals rod guide  414 ″ and pressure tube  102  and it supports Belleville springs  424 . The difference between bearing bush retainer  452  and  450  is that Belleville springs  424  are disposed between rod guide  414 ″ and bearing bush  452  instead of between bearing bush retainer  450  and pressure tube  102  as shown in  FIG. 7 . The thermal expansion is directly compensated for by Belleville springs  424 . On the right side of  FIG. 8 , piston rod guide  414 ″ is shown with bearing bush retainer  452  being replaced by compensation retainer  452 ′. Compensation retainer  450 ′ functions the same as bearing bush retainer  452 ′ in that it retains bushing  118  and it is designed to support Belleville springs  424  with Belleville springs  424  being disposed between rod guide  414 ″ and bush retainer  452 ′. The thermal expansion is directly compensated for by Belleville springs  424 . 
     In still another embodiment, a compensating piston rod guide  414 ′″ is shown in  FIG. 9 , wherein bearing bush retainer  452  has been replaced by a compensation spring support  460 . Spring support  460  acts to support Belleville springs  424  but it does not retain bushing  118 . Belleville springs  424  are disposed between rod guide  414 ′″ and spring support  460 . The thermal expansion is directly compensated for by Belleville springs  424 . 
     In yet further embodiments of prior art shock absorber  100 , various compensating cylinder end assemblies are shown in  FIGS. 10–19 . In  FIG. 10 , a compensating cylinder end assembly, generally designated as  520 , is located at the lower end of pressure tube  102  and functions to control the flow of hydraulic fluid between compression chamber  104  and fluid reservoir  108 . Compensating end assembly  520  further acts to compensate for the differing axial thermal expansion between the various components of shock absorber  100 . 
     In  FIG. 10 , compensating cylinder end assembly  520  includes a base valve assembly  522  and a plurality, an even number in the preferred embodiment, of Belleville springs  524  disposed between pressure tube  102  and base valve assembly  522 . The difference in thermal expansion between the steel pressure tube  102  and the aluminum reserve tube  106  is compensated for by the increase or decrease in the compression of Belleville springs  524 . This embodiment differs from the prior art shown in  FIG. 1  by eliminating the need for the multi-piece base valve assembly  122  shown in  FIG. 1 . 
     Various methods for securing Belleville springs  524  to an end assembly are shown in  FIGS. 11–14 . In  FIG. 11 , the compensating cylinder end assembly  520 ′ includes a reaction ring  550 . Reaction ring  550  is retained to the outside of pressure tube  102  by a circle-clip  552 . Belleville springs  524  are disposed between ring  550  and compression valve assembly  522 . 
     In  FIG. 12 , a compensating cylinder end assembly  520 ″ includes an S-shaped spring retainer  560 . Spring retainer  560  is positioned between the bottom of pressure tube  102  and the top of Belleville springs  524 , and acts to retain Belleville springs  524  between spring retainer  560  and valve assembly  522 . 
     In  FIG. 13 , the compensating cylinder end assembly  520 ′″ includes a first retaining ring  570  and a second retaining ring  572 . First retaining ring  570  is positioned such that it is in contact with the bottom of pressure tube  102 . Second retaining ring  572  is secured to valve assembly  522 . Belleville springs  524  are disposed between first retaining ring  570  and second retaining ring  572 . 
     In  FIG. 14 , an alternate compensating cylinder end base valve assembly is designated at  620 . Compensating end base valve assembly  620  is divided into two portions, an upper portion  650  and a lower portion  652 , and includes a plurality of Belleville springs  624  disposed between the two portions  650  and  652 . Upper portion  650  is connected to pressure tube  102  and lower portion  652  is connected to or abuts reserve tube  106 . Upper portion  650  fits within lower portion  652  and is sealed by an O-ring  654 . Belleville springs  624  are disposed between the two portions  650 ,  652  and act to compensate for the different thermal expansion of pressure tube  102  and reserve tube  106  by moving upper portion  650  and lower portion  652  towards or away from each other. 
     In  FIG. 15 , an alternate compensating cylinder end assembly is designated at  720 . Cylinder end assembly  720  includes a base valve assembly  722  having a cylindrical wall  750  and a plurality of Belleville springs  724 . Cylindrical wall  750  is connected to and surrounds a base valve assembly  722  and further extends towards the opposite end of shock absorber  100 . Pressure tube  102  slides within cylindrical wall  750 , and is sealed by an O-ring  752 . Belleville springs  724  are disposed between pressure tube  102  and valve assembly  722  within cylindrical wall  750 . 
     In another embodiment of shock absorber  100 , compensating cylinder end assembly  820  is shown in  FIG. 16 . Compensating end assembly  820  includes a base valve assembly  822 , a plurality of Belleville springs  824 , a base plate  850 , an O-ring  852 , and a bottom retainer  854 . Base plate  850  is capable of moving axially and is sealed to reserve tube  106  by O-ring  852 . Bottom retainer  854  is fixed to reserve tube  106  using a retaining ring  856  and provides a flat, stable bottom for cylinder end assembly  820 . Belleville springs  824 , an even number in the preferred embodiment, are disposed between base plate  850  and bottom retainer  854 . Belleville springs  824  act to compensate for the different thermal expansion of the various components of shock absorber  100  through base plate  850  and bottom retainer  854 . In an alternate cylinder end assembly  820 ′, as shown in  FIG. 17 , Belleville springs  824  are replaced with an elastomeric block  860 . Elastomeric block  860  is disposed between base plate  850  and bottom retainer  854  and compensates for the different thermal expansion of pressure tube  102  and reserve tube  106  by expanding or compressing as necessary. 
     In compressing cylinder end assembly  920 , which includes a base valve assembly  922  as shown in  FIG. 18 , pressurized gas  950 , for example compressed air, is disposed between a base plate  952  and a bottom retainer  954 . Bottom retainer  954  is sealed to reserve tube  106  by a weld  956  or other means known in the art such that the gas  950  remains pressurized. Pressurized gas  950  compensates for the different thermal expansion of pressure tube  102  and reserve tube  106  by expanding or compressing as necessary, and also reduces the weight of the shock absorber. In alternate cylinder end assembly  920 ′ as shown in  FIG. 19 , bottom retainer  954  has been removed. Pressurized gas  950  is disposed between base plate  952  and reserve tube  106  and compensates directly for the different thermal expansion of the pressure tube  102  and the reserve tube  106 . 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.