Abstract:
A monotube shock absorber which is capable of high compression damping forces while operating at low pressure for reduced friction is disclosed. The monotube shock absorber includes a pressure tube, a piston assembly, a piston rod, a fixed valve assembly and a floating piston. A variety of methods for securing the fixed valve assembly to the pressure tube are disclosed including use of single piece pressure tubes and pressure tube assemblies. In addition, a method for assembling the monotube shock absorber including an oil filling technique is described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/865,781 (filed on Aug. 14, 2013), the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a low pressure, high compression, damping monotube shock absorber. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    Shock absorbers are used in conjunction with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the automobile. 
         [0005]    The most common type of shock absorbers for automobiles are the dashpot type in which a piston is located within a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber. Because the piston, through valving, has the ability to limit the flow of damping fluid between the upper and lower working chambers within the pressure tube when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and a reserve tube which is positioned around the pressure tube. A base valve is located between the lower working chamber and the fluid reservoir to also produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile during stroking of the shock absorber. 
         [0006]    A conventional monotube shock absorber typically includes highly pressurized hydraulic fluid because its ability to dampen vibrations is limited by the initial static pressure of the hydraulic fluid. Having to maintain a high initial static pressure is undesirable for a number of reasons. A monotube shock absorber configured to operate at a lower pressure, thus reducing friction at the seals, would therefore be desirable. A monotube shock absorber that does not experience excessive noise caused by cavitation would also be desirable. Furthermore, methods and devices for securing a fixed valve assembly within a tube of a monotube shock absorber would be desirable. 
       SUMMARY 
       [0007]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0008]    The present disclosure is directed to a monotube shock absorber that can operate at low pressure and still provide high compression damping. 
         [0009]    The present teachings provide for a monotube shock absorber including a pressure tube, a fixed valve assembly, a piston rod, a piston assembly and a floating piston. The pressure tube includes a first end and a second end. The floating piston is slidably mounted in the pressure tube and it defines a gas chamber between the floating piston and the first end. The fixed valve assembly is fixedly mounted within the pressure tube to define a compensation chamber between the fixed valve assembly and the floating piston. The fixed valve assembly is configured to permit passage of hydraulic fluid therethrough. The piston assembly is slidably seated within the pressure tube to define a rebound chamber between the piston assembly and the second end, and to define a compression chamber between the piston assembly and the fixed valve assembly. The piston assembly is attached to the piston rod configured to move the piston assembly towards the fixed valve assembly during a compression stroke and away from the fixed valve assembly during an extension stroke. The piston assembly includes piston valve assemblies configured to permit hydraulic fluid to pass therethrough. During the compression stroke, the piston assembly forces hydraulic fluid out of the compression chamber and into the compensation chamber through the fixed valve assembly generating an increase in pressure in the compression chamber. Simultaneously, hydraulic fluid is forced out of the compression chamber and into the rebound chamber through one of the piston valve assemblies generating a decrease in pressure in the rebound chamber. The pressure drop across the fixed valve assembly and the pressure drop across the piston valve assembly both contribute to generating compression damping force. During the extension stroke, the piston assembly forces hydraulic fluid out of the rebound chamber and into the compression chamber through another one of the piston valve assemblies to generate an increase in pressure in the rebound chamber. Simultaneously, hydraulic fluid is drawn from the compensation chamber into the compression chamber through the fixed valve assembly thereby decreasing pressure in the compression chamber. The compression chamber pressure decrease is made small by reducing the restriction to flow through the fixed valve assembly during the extension stroke, the pressure drop across the piston valve assembly primarily generates extension damping force. 
         [0010]    The present teachings also provide for a monotube shock absorber including a pressure tube assembly, an adaptor or adaptor assembly, a fixed valve assembly, a piston rod, a piston assembly and a floating piston. The pressure tube assembly includes a first tube having a first end and a second tube separate and spaced apart from the first tube and having a second end. The adaptor or adaptor assembly is configured to connect the first tube and the second tube of the tube assembly together. The floating piston is slidably mounted in the pressure tube and it defines a gas chamber between the floating piston and the first end of the first tube. The fixed valve assembly is coupled to the adaptor or adaptor assembly to mount the fixed valve assembly in the pressure tube assembly, and define a compensation chamber between the fixed valve assembly and the floating piston. The fixed valve assembly is configured to permit passage of hydraulic fluid therethrough. The piston assembly is slidably seated within the second tube to define a rebound chamber between the piston assembly and the second end of the second tube, and to define a compression chamber between the piston assembly and the fixed valve assembly. The piston assembly is attached to the piston rod configured to move the piston assembly towards the fixed valve assembly during a compression stroke, and away from the fixed valve assembly during an extension stroke. The piston assembly includes piston valve assemblies configured to permit hydraulic fluid to pass therethrough. 
         [0011]    The present teachings further provide for a method for assembling a monotube shock absorber. The method includes: inserting a floating piston and a fixed valve assembly in a pressure tube such that the floating piston abuts or nearly abuts the fixed valve assembly in the pressure tube, and such that the floating piston is between the fixed valve assembly and a first end of the pressure tube to define a gas chamber between the floating piston and the first end; rigidly affixing the fixed valve assembly to the pressure tube; adding a first amount of a hydraulic fluid into the pressure tube from a second end of the pressure tube that is opposite to the first end such that the hydraulic fluid covers a side of the valve assembly that is opposite to the floating piston; advancing a plunger into the pressure tube from the second end to push less than an entirety of the hydraulic fluid through the fixed valve assembly and into contact with the floating piston to push the floating piston to a first distance away from the fixed valve assembly thereby defining a compensation chamber between the fixed valve assembly and the floating piston filled with the hydraulic fluid; adding a second amount of the hydraulic fluid into the pressure tube from the second end; inserting a rod guide assembly into the pressure tube from the second end with both a piston rod and a piston assembly coupled to the piston rod in cooperation with the rod guide assembly. As the rod guide assembly is inserted the hydraulic fluid passes through a piston valve assembly of the piston assembly to occupy a gap between the piston assembly and the rod guide assembly and the hydraulic fluid is further pushed through the valve assembly into the compensation chamber to move the floating piston to a second distance away from the valve assembly and further towards the first end; and charging the gas chamber through an opening in the pressure tube at the gas chamber. The piston assembly defines a compression chamber between the piston assembly and the fixed valve assembly, and defines a rebound chamber between the piston assembly and the rod guide assembly. 
         [0012]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0013]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0014]      FIG. 1  is a schematic representation of a typical automobile which incorporates the monotube shock absorbers in accordance with the present disclosure; 
           [0015]      FIG. 2  is a cross-sectional view of a monotube shock absorber according to the present teachings; 
           [0016]      FIG. 3  is a cross-sectional view of the detail of area  3  in  FIG. 2 ; 
           [0017]      FIG. 4  is a cross-sectional view of a fixed valve assembly of the monotube shock absorber of  FIG. 2  secured within a tube of the monotube shock absorber with a plurality of crimps; 
           [0018]      FIG. 5  is a planar top view of the fixed valve assembly of  FIG. 2  secured within the tube with a plurality of crimps; 
           [0019]      FIG. 6  is a cross-sectional view of a fixed valve assembly secured within the tube with a 360° crimp; 
           [0020]      FIG. 7  is a top view of the fixed valve assembly of  FIG. 6  secured with the 360° crimp; 
           [0021]      FIG. 8  is a cross-sectional view of a fixed valve assembly secured within the tube with a weld between the tube and the fixed valve assembly; 
           [0022]      FIG. 9  is a cross-sectional view of a fixed valve assembly secured within the tube with a generally U-shaped collar welded to the tube and crimped onto the fixed valve assembly; 
           [0023]      FIG. 10  is a cross-sectional view of a fixed valve assembly mounted with an L-shaped collar welded to the tube, the fixed valve assembly coupled to the L-shaped collar with a press-fit; 
           [0024]      FIG. 11  is a cross-sectional view of a fixed valve assembly mounted between two tube portions of the tube with a weld between a flange of the fixed valve assembly and both the first and second tube portions on opposite sides of the flange; 
           [0025]      FIG. 12  is a cross-sectional view of a fixed valve assembly welded to the tube; 
           [0026]      FIG. 13  is a cross-sectional view of a fixed valve assembly welded to the second tube at an interface between the first and second tubes; 
           [0027]      FIG. 14  is a cross-sectional view of a fixed valve assembly secured at a stepped transition portion of a single piece tube with a weld; 
           [0028]      FIG. 15  is a cross-sectional view of a fixed valve assembly secured to a single piece multi-diameter tube with a weld; 
           [0029]      FIG. 16  is a cross-sectional view of a fixed valve assembly secured at an interface between first and second tubes of a tube assembly secured together with a weld, the fixed valve assembly is secured between the first tube and the second tube; 
           [0030]      FIG. 17  is a cross-sectional view of a fixed valve assembly secured between first and second tubes of a tube assembly with an adaptor assembly threadably coupled to each of the first and the second tubes and a retention ring threadably coupled to the adaptor assembly; 
           [0031]      FIG. 18  is a cross-sectional view of a fixed valve assembly between first and second tubes of a tube assembly with an adaptor assembly threadably coupled to the first tube and adhesively coupled to the second tube, as well as with a retention ring threadably coupled to the adaptor assembly; 
           [0032]      FIG. 19  is a cross-sectional view of a fixed valve assembly mounted between first and second tubes with a first adaptor adhesively coupled to the first tube and with a second adaptor adhesively coupled to the second tube, the first and second adaptors are threadably coupled together; 
           [0033]      FIG. 20A  illustrates insertion of a fixed valve assembly and a floating piston in a tube of a monotube shock absorber according to a method of the present teachings; 
           [0034]      FIG. 20B  illustrates securing the fixed valve assembly in the tube; 
           [0035]      FIG. 20C  illustrates addition of a first portion of hydraulic fluid within the tube; 
           [0036]      FIG. 20D  illustrates pushing hydraulic fluid through the fixed valve assembly to move the floating piston away from the fixed valve assembly; 
           [0037]      FIG. 20E  illustrates addition of a second portion of hydraulic fluid within the tube; 
           [0038]      FIG. 20F  illustrates positioning of a rod guide at an end of the tube; and 
           [0039]      FIG. 20G  illustrates insertion of the rod guide within the tube and charging the tube with gas. 
       
    
    
       [0040]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0041]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0042]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0043]    Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views; there is shown in  FIG. 1  a vehicle incorporating a suspension system incorporating the shock absorbers in accordance with the present invention and which is designated generally by the reference numeral  10 . Vehicle  10  includes a rear suspension  12 , a front suspension  14  and a body  16 . Rear suspension  12  has a transversely extending rear axle assembly (not shown) adapted to operatively support a pair of rear wheels  18  of vehicle  10 . The rear axle assembly is operatively connected to body  16  by means of a pair of monotube shock absorbers  20  and a pair of helical coil springs  22 . Similarly, front suspension  14  includes a transversely extending front axle assembly (not shown) to operatively support a pair of front wheels  24  of vehicle  10 . The front axle assembly is operatively connected to body  16  by means of a second pair of monotube shock absorbers  26  and by a pair of helical coil springs  28 . Monotube shock absorbers  20  and  26  serve to dampen the relative motion of the unsprung mass (i.e., front and rear suspensions  12  and  14 , respectively) and the sprung mass (i.e., body  16 ) of vehicle  10 . While vehicle  10  has been depicted as a passenger car having front and rear axle assemblies, monotube shock absorbers  20  and  26  may be used with other types of vehicles or in other types of applications such as vehicles incorporating independent front and/or independent rear suspension systems. Further, the term “shock absorber” as used herein is meant to refer to dampers in general and thus will include MacPherson struts. 
         [0044]    Referring now to  FIG. 2 , monotube shock absorber  20  is shown in greater detail. While  FIG. 2  illustrates only monotube shock absorber  20 , it is to be understood that monotube shock absorber  26  also includes the features described below for monotube shock absorber  20 . Monotube shock absorber  26  only differs from monotube shock absorber  20  in the manner in which it is adapted to be connected to the sprung and unsprung masses of vehicle  10 . Monotube shock absorber  20  comprises a pressure tube  30 , a piston assembly  32 , a piston rod  34 , a fixed valve assembly  36  and a floating piston  38 . 
         [0045]    Pressure tube  30  has a first end  40  and a second end  42 . Extending between first and second ends  38  and  40  is an outer wall and an inner wall of pressure tube  30 . The outer wall is opposite to the inner wall. 
         [0046]    At first end  40  is a first mount  44 . First mount  44  can be any suitable mounting device or structure for securing monotube shock absorber  20  to any suitable portion of a vehicle&#39;s suspension. For example, first mount  44  can be coupled to any suitable portion of the vehicle&#39;s sprung mass or unsprung mass. 
         [0047]    At second end  42  is a rod guide assembly  46 . Rod guide assembly  46  is secured within pressure tube  30  at second end  42  in any suitable manner. For example, rod guide assembly  46  can define a recess which is sized, shaped, and positioned to cooperate with a coupling flange extending from the inner wall of pressure tube  30 . Any suitable number of recesses and coupling flanges can be included about rod guide assembly  46  and the inner wall of pressure tube  30  respectively. The coupling flanges can be formed in any suitable manner, such as by crimping. 
         [0048]    Rod guide assembly  46  further includes a tube seal, which can be any suitable seal to prevent passage of hydraulic fluid between rod guide assembly  46  and the inner wall of pressure tube  30 . The tube seal can be any suitable type of seal, such as an O-ring seal. Rod guide assembly  46  further includes a rod seal extending about a bore defined by rod guide assembly  46 . The bore extends through rod guide assembly  46  to accommodate piston rod  34 . The rod seal can be any suitable seal configured to prevent passage of hydraulic fluid between the bore defined by rod guide assembly  46  and piston rod  34  so that hydraulic fluid is unable to escape out from within pressure tube  30 . 
         [0049]    At an end of piston rod  34  is a second mount  48 . Second mount  48  can be any suitable mounting device or structure configured to mount monotube shock absorber  20  to a vehicle. For example, the second mount  48  can be configured to couple with an unsprung or sprung mass of a vehicle. 
         [0050]    Piston assembly  32  is mounted to piston rod  34 , and is slidably movable within pressure tube  30  during compression strokes and extension strokes of piston rod  34 . During a compression stroke, piston assembly  32  is moved towards first end  40  and away from second end  42 . During the extension stroke, the piston assembly  32  is moved away from first end  40  and towards second end  42 . 
         [0051]    Piston assembly  32  generally includes extension valving  52  and compression valving  54 . The extension and compression valving  52  and  54  can be any suitable type of valving configured to selectively permit or restrict passage of hydraulic fluid therethrough at a predetermined rate during compression and extension of the piston rod  34 . 
         [0052]    Floating piston  38  generally includes a first end  72  and a second end  74 , which is opposite to first end  72 . Extending about a peripheral sidewall of floating piston  38  between first end  72  and second end  74  is a seal  76 . Seal  76  can be any suitable seal, such as an O-ring, suitable to prevent passage of hydraulic fluid between floating piston  70  and pressure tube  30 . Seal  76  thus sealingly mates with the inner wall of pressure tube  30 . Floating piston  38  is seated within pressure tube  30  between piston assembly  32  and first end  40  of pressure tube  30 . Floating piston  38  is configured to slide within pressure tube  30  towards and away from first end  40 . 
         [0053]    Fixed valve assembly  36  is fixedly mounted to pressure tube  30  between piston assembly  32  and floating piston  38 . Between floating piston  38  and first end  40  of pressure tube  30  is defined a gas chamber  80 . Gas chamber  80  can include air or any suitable gas ( 350  of  FIG. 200 ), such as nitrogen. Between fixed valve assembly  36  and floating piston  38  is defined a compensation chamber  82 . Between the piston assembly  32  and fixed valve assembly  36  is defined a compression chamber  84 . Between piston assembly  32  and second end  42  is defined a rebound chamber  86 . Compensation chamber  82 , compression chamber  84 , and rebound chamber  86  can include any suitable hydraulic fluid ( 300  of  FIG. 20C ), such as oil. 
         [0054]    Fixed valve assembly  36  is fixed to pressure tube  30  between piston assembly  32  and gas chamber  80  forming the three chambers filled with oil, rebound chamber  86 , compression chamber  84  and compensation chamber  82 . Rebound chamber  86  is between rod guide assembly  46  and piston assembly  32 . Compression chamber  84  is between piston assembly  32  and gas chamber  80 . Compensation chamber  82  is between fixed valve assembly  36  and floating piston  38  and gas chamber  80  is between floating piston  38  and the first end  40 . 
         [0055]    During compression of monotube shock absorber  20 , fluid is forced from compression chamber  84  to compensation chamber  82  through fixed valve assembly  36  generating an increase in pressure in compression chamber  84 . Simultaneously, fluid is forced from compression chamber  84  to rebound chamber  86  through compression valving  54  of piston assembly  32  thus generating a decrease in pressure in rebound chamber  86 . The pressure drop across fixed valve assembly  36  and the pressure drop across piston assembly  32  contribute to generating compression damping force. Due to the rise in pressure in compression chamber  84  during the compression stroke, compression damping force is not limited by the initial static pressure which is the case with a prior art monotube shock absorber. The initial static pressure can be kept low to reduce friction from the seal. 
         [0056]    During an extension stroke of monotube shock absorber  20 , fluid is forced from rebound chamber  86  to compression chamber  84  through extension valving  52  of piston assembly  32  thus generating an increase in pressure in rebound chamber  86 . Simultaneously, fluid is drawn from compensation chamber  82  to compression chamber  84  through fixed valve assembly  36  thus generating a decrease in pressure in compression chamber  84 . The pressure decrease in compression chamber  84  is made small by reducing the restriction to flow through fixed valve assembly  36  for an extension stroke. The pressure drop across piston assembly  32  primarily generates damping force during an extension stork. 
         [0057]    With continued reference to  FIGS. 2 and 3  and additional reference to  FIGS. 4 and 5 , fixed valve assembly  36  will now be described in detail. The fixed valve assembly  36  generally includes a valve body  102  having a first side  104  and a second side  106 , which is opposite to first side  104 . 
         [0058]    Between first and second sides  104  and  106  is an outer surface of the valve body  102 . 
         [0059]    Valve body  102  defines extension valving  110  and compression valving  112 . Extension and compression valving  110  and  112  can be any suitable valving to selectively permit passage of hydraulic fluid therethrough at desired rates and in desired directions. For example and as illustrated in  FIG. 5 , extension and compression valving  110  and  112  can each include a plurality of orifice holes defined within, and extending through, the valve body  102 . Any suitable number of orifice holes can be included with extension valving  110  and compression valving  112 , and the orifice holes can be arranged in any suitable manner. For example, the orifice holes of extension valving  110  can be arranged spaced apart in a generally circular arrangement about a center of valve body  102 . Compression valving  112  can similarly include a plurality of spaced apart orifice holes arranged about an axial center of valve body  102 , but arranged closer to the axial center than extension valving  110 . 
         [0060]    The orifice holes can have any suitable diameter to regulate flow of hydraulic fluid therethrough. Each plurality of orifice holes can include valve discs or plates to selectively permit passage of hydraulic fluid therethrough, and/or any suitable device or configuration suitable for regulating passage of hydraulic fluid therethrough. For example, a check valve  114  biased by a valve spring  116  can be included to regulate passage of hydraulic fluid through extension valving  110 . A check valve  118  biased by a valve spring  120  can be included to regulate passage of hydraulic fluid through compression valving  112 . Check valves  114  and  118 , and valve springs  116  and  120 , can be coupled to valve body  102  in any suitable manner, such as with a fastener  122 . 
         [0061]    The fixed valve assembly  36  can be fixedly secured within pressure tube  30  between the piston assembly  32  and floating piston  38  in any suitable manner. For example and as illustrated in  FIGS. 3 ,  4  and  5 , pressure tube  30  can be provided with a plurality of crimps or protrusions  130 , such as in the form of crimps extending into a valve body recess  132  formed in valve body  102 . Crimps  130  may form tube recesses at the outer wall of pressure tube  30 . Fixed valve assembly  36  can be secured with any suitable number of crimps  130 , such as eight. To prevent passage of hydraulic fluid between the outer surface of valve body  102  and the inner wall of pressure tube  30 , valve body  102  can include any suitable seal, such as an O-ring  140 . 
         [0062]      FIGS. 3 ,  4 , and  5  illustrate one exemplary configuration for securing fixed valve assembly  36  within pressure tube  30 . Any other suitable device, method, or configuration can be used to secure fixed valve assembly  36  within pressure tube  30 . For example,  FIGS. 6-19  illustrate additional fixed valve assemblies  36 B- 36 N fixed to pressure tube  30  in a variety of different ways. Fixed valve assemblies  36 B- 36 N are generally similar to fixed valve assembly  36 , and thus like features are illustrated with like reference numerals. With respect to the like features, the description of the features set forth above and the discussion of fixed valve assembly  36  also applies to fixed valve assemblies  36 B- 36 N. Features of any of the fixed valve assemblies  36 - 36 N can be included in any of the other fixed valve assemblies  36 - 36 N. 
         [0063]    With initial reference to  FIGS. 6 and 7 , fixed valve assembly  36 B is illustrated as secured to pressure tube  30  with a rolled crimp  150 . Rolled crimp  150  can extend 360° around valve body  102 , or any suitable distance about valve body  102 . If rolled crimp  150  extends 360° about valve body  102 , O-ring  140  may not be necessary because rolled crimp  150  will typically be sufficient to restrict flow of hydraulic fluid between valve body  102  and the inner wall of pressure tube  30 . Other than being secured with rolled crimp  150 , fixed valve assembly  36 B is substantially similar to fixed valve assembly  36 , and like features are illustrated with the same reference numbers. 
         [0064]    With reference to  FIG. 8 , valve body  102  of fixed valve assembly  36 C includes a metal injection molded body, which is generally in contrast to, for example, valve body  102  of fixed valve assembly  36 , which can be made of sintered iron or powder metal. Because valve body  102  of fixed valve assembly  36 C is a metal injection molded valve body, valve body  102  of fixed valve assembly  36 C can be welded directly to the inner wall of pressure tube  30 , such as with a laser weld, a seam weld or any other welding operation. While valve body  102  of fixed valve assembly  36 C is described as a metal injection molded valve body, valve body  102  of fixed valve assembly  36 C can be manufactured as a screw machined part or manufactured by any means known in the art. 
         [0065]    With reference to  FIG. 9 , fixed valve assembly  36 D is fixably secured within pressure tube  30  with a collar  160 . Collar  160  is made of any suitable material, such as stamped metal. Collar  160  is crimped around valve body  102  such that collar  160  extends from first side  104  to second side  106  around the outer surface of valve body  102 . Collar  160  thus generally has a U-shaped cross-section as illustrated in  FIG. 9 . Collar  160  is welded to the inner wall of pressure tube  30  in any suitable manner, such as with a laser weld, a seam weld or any other welding operation. Valve body  102  can be made of a material that may not necessarily be suitable for welding directly to pressure tube  30 , such as sintered iron or powder metal or may be made of any other material such as plastic, metal or any other suitable material. 
         [0066]    With reference to  FIG. 10 , fixed valve assembly  36 E is secured to pressure tube  30  with a collar  170 . Collar  170  can be made of any material suitable for being directly welded to the inner wall of pressure tube  30 . Thus valve body  102  can be made of a material that is generally not suitable for welding directly to pressure tube  30 , such as sintered iron or powder metal or may be made of any other material such as plastic, metal or any other suitable material. Collar  170  can be stamped of any suitable material and crimped around first side  104  of valve body  102  in order to provide collar  170  with a generally L-shaped cross-section in which collar  170  extends from first side  104  to and along the outer surface of valve body  102 . Valve body  102  can be secured to collar  170  in any suitable manner, such as with a press-fit. Collar  170  can be secured to the inner wall of pressure tube  30  with a suitable weld, such as a laser weld, a seam weld or any other welding operation. 
         [0067]    With reference to  FIG. 11 , fixed valve assembly  36 F includes a flange  180  extending from the outer surface of valve body  102 . Flange  180  can be a continuous annular flange, or can be a plurality of spaced apart flanges. As illustrated in  FIG. 11 , pressure tube  30  need not be a continuous tube extending between first end  40  and second end  42 , but may rather be a pressure tube assembly  30 ′ which includes two or more separate tubes, such as a first tube  200  and a second tube  202 . First tube  200  includes first end  40  and extends to fixed valve assembly  36 F. Second tube  202  includes second end  42  and extends to fixed valve assembly  36 F. Fixed valve assembly  36 F is arranged such that flange  180  is between first and second tubes  200  and  202 . First tube  200  is secured to a first side of flange  180 , and second tube  202  is secured to a second side of flange  180 . First and second tubes  200  and  202  are secured to flange  180  in any suitable manner, such as with a weld or any other means illustrated in this disclosure or by any means known in the art. Any suitable weld can be used, such as a seam weld, a laser weld or any other welding operation. 
         [0068]    With reference to  FIG. 12 , fixed valve assembly  36 G includes a collar  190 , which can be cold-headed, forged or manufactured by any means known in the art. Collar  190  is crimped and bent around the outer surface of valve body  102  such that collar  190  extends from first side  104  to a flange  192  proximate to second side  106 . Collar  190  extends around flange  192  in order to help couple collar  190  to valve body  102 . Flange  192  is optional, and thus collar  190  may extend entirely to second side  106 . Collar  190  may be secured to the inner wall of pressure tube  30  in any suitable manner, such as with a weld. Any suitable weld can be used, such as a seam weld, a laser weld or any other welding operation. In order to accommodate collar  190 , pressure tube  30  can be provided with a larger inner diameter. 
         [0069]    With reference to  FIG. 13 , fixed valve assembly  36 H can be secured generally at an interface between first tube  200  and second tube  202  of pressure tube assembly  30 ′. First tube  200  can be provided with a larger diameter than second tube  202  and can be secured to second tube  202  with any suitable weld, such as a seam, laser weld or any other known welding operation between the inner wall of first tube  200  and the outer wall of second tube  202 . Valve body  102  can be made of any suitable material configured to permit valve body  102  to be welded to second tube  202 , such as with a laser weld or any other welding operation. For example, valve body  102  can be a metal injection molded valve body or manufactured by any means known in the art. Although  FIG. 13  illustrates pressure tube assembly  30 ′ as including separate first and second tubes  200  and  202 , pressure tube assembly  30 ′ can be replaced with a unitary pressure tube  30  as illustrated in  FIG. 14 . 
         [0070]      FIG. 14  illustrates fixed valve assembly  36 I secured at a transition portion  204  of pressure tube  30 . Pressure tube  30  is unitary and generally flares outward at transition portion  204  such that the diameter of pressure tube  30  at a first portion is greater than at a second portion. Fixed valve assembly  36 I is secured to pressure tube  30  at transition portion  204  in any suitable manner, such as with a laser weld or any other welding operation. The configurations of  FIGS. 13 and 14  are advantageous for a plurality of reasons, such as because they permit optimized axial packaging by reducing the full compressed length of monotube shock absorber  20  while still maintaining the volume of chambers  80  and  82 , and minimize valve body material. 
         [0071]    With reference to  FIG. 15 , fixed valve assembly  36 J includes flange  180 . Pressure tube assembly  30 ′ is split into first tube  200  and second tube  202 . Pressure tube assembly  30 ′ includes a tapered portion  206 , which is part of first tube  200 . Between tapered portion  206  and first end  40 , pressure tube assembly  30 ′ has a larger diameter as compared to the portion of pressure tube assembly  30 ′ between tapered portion  206  and second end  42 . Pressure tube assembly  30 ′ is split into first and second tubes  200  and  202  in the smaller diameter area proximate to tapered portion  206 . The first and second tubes  200  and  202  are secured together with flange  180  therebetween in any suitable manner, such as with a suitable weld  210 . Any suitable weld can be used, such as a seam weld, a butt weld or any other welding operation. Pressure tube assembly  30 ′ is thus provided with an expanded gas chamber  80  and an expanded compression chamber  82  between fixed valve assembly  36 J and second end  42 . Expanded chambers  80  and  82  reduce dead length of monotube shock absorber  20  and optimizes stroke for a given axial length while still maintaining the volume of chambers  80  and  82 . 
         [0072]    With reference to  FIG. 16 , fixed valve assembly  36 K is secured within pressure tube assembly  30 ′ where first tube  200  and second tube  202  of pressure tube assembly  30 ′ are coupled together. First and second tubes  200  and  202  can be secured together in any suitable manner, such as with a weld  222 . Weld  222  can be any suitable weld, such as a seam weld or any other welding operation formed where first and second tubes  200  and  202  overlap. First and second tubes  200  and  202  overlap such that the inner wall of first tube  200  abuts the outer wall of second tube  202 . First tube  200  includes a plurality of flanges or tabs  220  formed in any suitable manner, such as by staking or by any other means known in the art. A flange  224  of fixed valve assembly  36 K is seated between flanges/tabs  220  in second tube  202  in order to secure fixed valve assembly  36 K at the interface between first and second tubes  200  and  202 . First tube  200  has a larger diameter than second tube  202  in order to provide expanded chambers  80  and  82  as discussed above. 
         [0073]    With reference to  FIG. 17 , fixed valve assembly  36 L is fixed within pressure tube assembly  30 ′ with an adaptor assembly  230 . Adaptor assembly  230  generally includes an adaptor  232  and a retention ring  234 . Adaptor  232  includes a first flange  236 , and a second flange  238 . First flange  236  and second flange  238  extend from opposite sides of adaptor  232 . First flange  236  includes first threads  240  and second threads  242 . First threads  240  and second threads  242  are on opposite sides of first flange  236 . Second flange  238  includes third threads  244  on an inner surface thereof. Adaptor  232  includes an inner protrusion or retention member  246 . One or more retention members  246  can be included, and configured to abut flange  192  of valve body  102 . 
         [0074]    First threads  240  are configured to cooperate with internal threads  248  at the inner wall of pressure tube assembly  30 ′ in order to secure adaptor  232  to first tube  200  of pressure tube assembly  30 ′. Third threads  244  are configured to cooperate with external threads  250  at the outer wall of pressure tube assembly  30 ′ in order to secure adaptor  232  to second tube  202  of pressure tube assembly  30 ′. Retention ring  234  is generally an annular ring threadingly received by adaptor  232  and seated against first side  104  of valve body  102 . Retention ring  234  generally abuts first side  104  of valve body  102  in order to retain valve body  102  against inner protrusion or retention member  246 , and couple fixed valve assembly  36 L to adaptor assembly  230 . With reference to  FIG. 18 , fixed valve assembly  36 M is affixed in pressure tube assembly  30 ′ with adaptor assembly  230 , but with second flange  238  affixed to the outer wall of pressure tube assembly  30 ′ with an adhesive  260 . Any suitable adhesive can be used. While threading and adhesives have been illustrated as attachment methods for adaptor  232  and retention ring  234 , other methods including brazing, welding or any other attachment method known in the art can be utilized. 
         [0075]    With reference to  FIG. 19 , fixed valve assembly  36 N can be affixed within pressure tube assembly  30 ′ with an adaptor assembly  270 . Adaptor assembly  270  generally includes a first adaptor  272  and a second adaptor  274 . First adaptor  272  generally includes a first flange  276  and a second flange  278 . Between first and second flanges  276  and  278  is a first retention member  280 , which can extend generally perpendicular with respect to first and second flanges  276  and  278  towards an axial center of pressure tube assembly  30 ′. First retention member  280  can be a ring, or one or more flanges. Second adaptor  274  generally includes a first flange  282  and a second flange  284 . Second flange  284  defines a second retention member or flange  286  configured to abut and cooperate with flange  192  of valve body  102 . First flange  282  further includes a seal  288 , which can be any suitable seal, such as an O-ring. Second flange  284  further includes threads  290  on an outer surface thereof, which are configured to cooperate with threads  292  on an inner surface of second flange  278 . 
         [0076]    First adaptor  272  is arranged such that first retention member  280  is seated on an end of first tube  200  facing second tube  202 . First adaptor  272  is secured to first tube  200  in any suitable manner, such as with an adhesive connection  294  between the outer wall of first tube  200  of pressure tube assembly  30 ′ and first flange  276 . Second adaptor  274  is secured to the outer wall of second tube  202  of pressure tube assembly  30 ′ in any suitable manner, such as with an adhesive connection  296  between second flange  284  and the outer wall of second tube  202 . 
         [0077]    Second adaptor  274  is arranged such that second retention member  286  extends inward towards an axial center of pressure tube assembly  30 ′ and such that second adaptor  274  is seated against an end of second tube  202  of pressure tube assembly  30 ′ opposite to, and facing, first tube  200  of pressure tube assembly  30 ′. With valve body  102  seated against second adaptor  274  such that flange  192  of valve body  102  abuts second retention member  286  of second adaptor  274 , first and second adaptors  272  and  274  are coupled together through cooperation between threads  290  of first adaptor  272  and threads  292  of second adaptor  274 . Upon coupling first and second adaptors  272  and  274  together, first retention member  280  will abut first side  104  of valve body  102  in order to retain fixed valve assembly  36 N in cooperation with adaptor assembly  270 . In place of first retention members  280  can be retention ring  234 , as illustrated in  FIGS. 17 and 18  for example. While threading and adhesives have been illustrated as attachment methods for adaptor assembly  270 , other methods including brazing, welding or any other attachment method known in the art can be utilized. 
         [0078]    Operation of monotube shock absorber  20  will now be described. During a compression stroke of piston rod  34 , hydraulic fluid, such as oil, is forced from compression chamber  84  into compensation chamber  82  through compression valving  112  of any of fixed valve assemblies  36 - 36 N described herein. 
         [0079]    Forcing hydraulic fluid into compensation chamber  82  from compression chamber  84  generates an increase in pressure in compression chamber  84 . Simultaneously, hydraulic fluid is forced from compression chamber  84  into rebound chamber  86  through compression valving  54  of piston assembly  32 . Forcing hydraulic fluid from compression chamber  84  into rebound chamber  86  generates a decrease in pressure in rebound chamber  86 . 
         [0080]    A pressure drop across fixed valve assembly  36 - 36 N (pressure in compression chamber  84  minus pressure in compensation chamber  82 ) and a pressure drop across piston assembly  32  (pressure of compression chamber  84  minus pressure of rebound chamber  86 ) both contribute to generating compression damping force of monotube shock absorber  20 . Due to the rise in pressure of compression chamber  84  during compression, compression damping force is not limited by initial static pressure of compression chamber  84 , which is in contrast to conventional monotube shock absorbers in which compression damping force is limited to the initial static pressure of the shock absorber. Thus, the initial static pressure of compression chamber  84  of monotube shock absorber  20  can be kept low in order to reduce seal friction. 
         [0081]    During extension of piston rod  34 , hydraulic fluid is forced from rebound chamber  86  into compression chamber  84  through extension valving  52  of piston assembly  32 , thus increasing pressure within rebound chamber  86 . Simultaneously, hydraulic fluid is drawn from compensation chamber  82  into compression chamber  84  through extension valving  110  of fixed valve assembly  36 - 36 N, thus decreasing pressure in compression chamber  84 . The decrease in pressure of compression chamber  84  is made small by reducing the restriction on hydraulic fluid flow passing through extension valving  110  of fixed valve assembly  36 - 36 N. The pressure drop across piston assembly  32  thus primarily generates extension damping force. 
         [0082]    With reference to  FIGS. 20A-20G , a method for assembling monotube shock absorber  20  including fixed valve assembly  36  will now be described. The method of  FIGS. 20A-20G  also applies to the fixed valve assemblies  36 B- 36 N described herein, as well as to any other suitable fixed valve assembly, the only substantial difference being how the other fixed valve assemblies are secured within pressure tube  30  and/or pressure tube assembly  30 ′. 
         [0083]    With initial reference to  FIG. 20A , floating piston  38  and the fixed valve assembly  36  are inserted into pressure tube  30  from second end  42  and slid within pressure tube  30  towards first end  40 . Floating piston  38  and fixed valve assembly  36  can be inserted using any suitable device, such as a pusher that allows air to escape out from within pressure tube  30  past the pusher. After fixed valve assembly  36  is inserted to a desired depth, fixed valve assembly  36  is secured in position by crimping pressure tube  30  ( FIG. 20B ) at a specified location of pressure tube  30  using any suitable crimping device to form crimps  130 , as illustrated in  FIGS. 2 and 3  for example. While  FIG. 20B  illustrates a crimping operation, any other method of attachment of the fixed valve assembly described herein or known in the art can be utilized. 
         [0084]    With reference to  FIG. 20C , after fixed valve assembly  36  is secured within pressure tube  30 , pressure tube  30  is partially filled with hydraulic fluid  300 , such as with a first amount  300 A of hydraulic fluid  300 . Hydraulic fluid  300  is located against fixed valve assembly  36  on a side thereof opposite to floating piston  38 . 
         [0085]    With reference to  FIG. 20D , a suitable plunger, such as plunger  302 , is used to push an amount of hydraulic fluid  300  through fixed valve assembly  36 . Plunger  302  can be pushed with any suitable device. Plunger  302  includes an O-ring seal  306  and a check valve  308 . O-ring  306  mates with the inner wall of pressure tube  30  to provide a seal therewith, which prevents hydraulic fluid  300  from passing between the plunger  302  and the inner wall of pressure tube  30 . 
         [0086]    Plunger  302  is initially seated within pressure tube  30  with check valve  308  open such that air can pass through check valve  308 . Once plunger  302  reaches hydraulic fluid  300 , check valve  308  is closed to permit plunger  302  to push hydraulic fluid  300  further within pressure tube  30 . Using plunger  302 , hydraulic fluid  300  is pushed through fixed valve assembly  36 , and specifically through compression valving  112  thereof. Hydraulic fluid  300  contacts floating piston  38  and pushes floating piston  38  towards first end  40 . Hydraulic fluid  300  fills compensation chamber  82  between floating piston  38  and fixed valve assembly  36 . After plunger  302  is pushed to a desired distance, check valve  308  is opened and plunger  302  is removed. Opening check valve  308  allows air to pass through plunger  302 , and prevents creation of a suction force, which may draw hydraulic fluid  300  back through fixed valve assembly  36 . After plunger  302  is withdrawn from within pressure tube  30 , additional hydraulic fluid  300  is added, such as a second amount  300 B of hydraulic fluid  300 . Together first and second amounts  300 A and  300 B of hydraulic fluid  300  provide the total amount of hydraulic fluid  300  for monotube shock absorber  20 . 
         [0087]    With reference to  FIG. 20F , rod guide assembly  46  with piston rod  34  and piston assembly  32  coupled thereto is inserted into pressure tube  30  from second end  42  of pressure tube  30 . Rod guide assembly  46  is inserted into pressure tube  30  with piston assembly  32  spaced apart from rod guide assembly  46  to define a gap between piston assembly  32  and rod guide assembly  46 . When rod guide assembly  46  is inserted to a depth within pressure tube  30  such that the tube seal is at second end  42  of pressure tube  30 , hydraulic fluid  300  will make initial contact with rod guide assembly  46 . Piston assembly  32  is at a controlled position with respect to rod guide assembly  46  based on the amount of hydraulic fluid  300 A from the first fill and the stroke of the plunger  302  such that when the rod guide assembly  46  is inserted, the level of hydraulic fluid  300  will rise to meet the bottom of the rod guide assembly  46  at the same time the tube seal on the rod guide assembly  46  meets pressure tube  30 . 
         [0088]    With reference to  FIG. 200 , as rod guide assembly  46  is pushed entirely into pressure tube  30 , rod guide assembly  46  pushes hydraulic fluid  300  further through fixed valve assembly  36  to move floating piston  38  closer to first end  40 . After rod guide assembly  46  has been inserted into pressure tube  30 , piston rod  34  is fully extended and gas chamber  80  is charged with a pressurized gas, such as nitrogen, air or any other suitable gas through a suitable opening to gas chamber  80 . After the rod guide assembly  46  has been inserted, the upper end of pressure tube  30  is closed by spin closing, crimping, welding, circlip or any other means known in the art. Then the gas chamber  80  is charged through the suitable opening and the first mount  44  is attached by welding, crimping or other means known in the art. 
         [0089]    The present teachings provide numerous advantages over conventional monotube shock absorbers. For example, the present teachings provide for a fast response and resistance to fade often seen with conventional monotube shock absorbers due to physical separation of the hydraulic fluid and the gas, but do not experience the compression damping force limitation of conventional monotube shock absorbers. The monotube shock absorber  20  according to the present teachings can operate at lower pressure than conventional monotube shock absorbers, thus reducing friction at the seals thereof. The present teachings can further provide independent bleed tuning within the hydraulic valves, with compression bleed being controlled by fixed valve assembly  36 - 36 N and rebound bleed being controlled by piston assembly  32 . Due to the pressure increase in the compression chamber during compression, monotube shock absorber  20  according to the present teachings are not limited in the amount of compression damping that can be generated based on the charge of gas therein. 
         [0090]    While floating piston  38  has been described as the means for separating the gas from the hydraulic oil, other methods such as diaphragms, bladders, bags, closed cell foams or other means known in the art can be utilized. Also, floating piston  38  can be replaced by a baffle as disclosed in co-pending application Ser. No. ______ filed the same day as the present application and entitled “Low Pressure High Compression Damping Monotube Shock Absorber Having A Baffle”, the entire disclosure of which is incorporated herein by reference. 
         [0091]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
         [0092]    Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0093]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0094]    When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0095]    Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
         [0096]    Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.