Abstract:
A piston actuator assembly having includes a piston liner slidably disposed within a housing. A piston is slidably disposed within the piston liner and partially slidably disposed in the valve body. A plurality of pressurized fluid passages communicate with the piston actuator assembly and provide a first flow of hydraulic fluid and a second flow of hydraulic fluid. A plurality of seals maintains separate fluid pressure chambers selectively pressurized to achieve a plurality of actuator positions. A plurality of exhaust passages communicate with the piston actuator assembly providing pressure relief to allow for predictive movement of the piston and piston liner.

Description:
FIELD 
       [0001]    The present invention relates generally to linear hydraulic actuators for a transmission, and more particularly to a linear hydraulic actuator for a transmission having a moveable sleeve and piston that move independently relative to one another in order to provide an actuator capable of obtaining three positions. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    Typical automatic and dual clutch transmissions employ a hydraulic control system operable to perform various functions within the transmission. Examples of these functions include controlling torque transmitting devices, cooling, lubrication, and the actuation of valve assemblies and components. The torque-transmitting devices may include a series of synchronizers operable to selectively connect, for example, a gear to a driveshaft. These synchronizers may be operated mechanically through a hydraulically operated piston actuator assembly. 
         [0004]    A piston actuator assembly is controlled by pressurized hydraulic fluid to effect a position change in the mechanical device connected to the actuator. One type of piston actuator assembly found in dual clutch transmissions having synchronizer assemblies includes a piston actuator assembly operable to mechanically move a shift fork in the synchronizer assembly in order to position a synchronizer between a neutral, or unengaged position, and at least one engaged position. In the neutral position, the synchronizer is not engaged with a gear. In the first engaged position, the synchronizer is engaged with a first gear. In the second engaged position, the synchronizer is engaged with a second gear. 
         [0005]    While these piston actuators are useful for their intended purpose, there is a constant desire to reduce the complexity of the control algorithm which returns the pistons or valves back to a neutral location and to improve the packaging efficiency of the actuator while maintaining robust and reliable operation. Accordingly, there is room in the art for an improved hydraulic piston actuator assembly having a compact package for a confined space application, improved assembly efficiency and a simpler control algorithm. 
       SUMMARY 
       [0006]    A piston actuator assembly is provided including a housing, a piston, a piston liner, a seal assembly, a first hydraulic fluid chamber and a second hydraulic fluid chamber. The piston actuator assembly is capable of moving an actuator between and to three positions. A neutral position is quickly achieved by applying equal pressures on both sides of a piston of the piston actuator assembly. 
         [0007]    In one aspect of the present invention, the housing has a bore, a first and a second apply passage and a first and a second exhaust passage. The bore has an inner surface, an open end and a closed end. The piston actuator assembly further includes a piston slidably disposed in the bore of the housing. The piston has a head portion and a connecting rod portion. The head portion has a first and a second apply surface area and the connecting rod portion extends through the open end of the bore of the housing. The piston liner is slidably disposed in the bore of the housing between the housing and the head portion of the piston. The piston liner has a bore, a first and a second end, an inner and an outer surface and a liner apply surface area. The seal assembly is disposed in the open end of the housing bore, wherein the seal assembly has a sealing surface through which the connecting rod portion of the piston is sealingly supported. The first hydraulic fluid chamber is defined by at least the inner surface of the bore of the housing and the first apply surface area of the head portion of the piston, wherein the first apply passage communicates with the first hydraulic fluid chamber. The second hydraulic fluid chamber is defined by at least the inner surface of the bore of the housing, the liner apply surface area of the piston liner, the second apply surface area of the head portion of the piston and the sealing surface of the seal assembly. The second apply passage communicates with the second hydraulic fluid chamber. The hydraulic passages are selectively pressurized to move the head of the piston into at least three positions. A first position is defined by the head of the piston adjacent the closed end of the bore of the housing. A second position is defined by the head of the piston adjacent the seal assembly. A third position is defined by the head of the piston disposed approximately midway between the closed end of the bore of the housing and the seal assembly. 
         [0008]    In another aspect of the present invention, the seal assembly further includes a first and a second seal, wherein the first seal has an inner cavity and the second seal is disposed in the inner cavity of the first seal. 
         [0009]    In yet another aspect of the present invention, the seal assembly further includes a center bore and an annular channel, wherein the annular channel is in communication with the center bore and the first exhaust passage of the housing. 
         [0010]    In yet another aspect of the present invention, the piston actuator assembly further includes an annular channel defined by the inner surface of the bore of the housing and the outer surface of the piston liner, wherein the annular channel is in communication with the second exhaust passage of the housing. 
         [0011]    In yet another aspect of the present invention, the seal assembly further includes a first and a second connecting rod seal and a bushing, wherein the first and second connecting rod seal and bushing are disposed on the inner diameter of the cylinder of the seal assembly. 
         [0012]    In yet another aspect of the present invention, the piston further includes a center bore and a piston pin wherein the center bore of the piston has an open end at the second apply surface area of the head portion of the piston. The piston liner further includes a center guide wherein the center guide has a pair of slots and is attached to the second end of the piston liner and extends into the center bore of the head portion of the piston. The piston pin is disposed in the head portion of the piston and passes through the pair of slots of the center guide slidably securing the piston to the center guide of the piston liner. 
         [0013]    In yet another aspect of the present invention, the bore of the housing further includes a bore liner having a first end and an outer surface. The first end of the bore liner is in contact with the seal surface of the seal assembly and the outer surface of the bore liner is in contact with the inner surface of the housing bore. 
         [0014]    In yet another aspect of the present invention, the piston liner further includes a first and a second seal groove and a first and a second ring seal. The first seal groove is disposed in the outer surface of the piston liner proximate to the first end, the second seal groove is disposed in the outer surface of the piston liner proximate to the second end, the first ring seal is disposed in the first seal groove and the second ring seal is disposed in the second seal groove. 
         [0015]    In yet another aspect of the present invention, the piston liner further includes a retainer groove and a ring retainer, wherein the retainer groove is disposed on the inner surface of the piston liner proximate to the first end and the ring retainer is disposed in the groove. 
         [0016]    In yet another aspect of the present invention, the piston liner further includes an exhaust fluid passage disposed between the first and the second seal groove connecting the inner surface and the outer surface of the piston liner. 
         [0017]    In yet another aspect of the present invention, the piston liner further includes a rim, a retainer groove and a ring retainer. The rim is disposed on the inner surface of the piston liner proximate to the first end and the retainer groove is disposed on the inner surface of the piston liner proximate to the second end and the ring retainer is disposed in the retainer groove. 
         [0018]    In yet another aspect of the present invention, the piston liner further includes a retainer groove and a ring retainer. The retainer groove is disposed on the inner surface of the piston liner proximate to the second end and the ring retainer is disposed in the retainer groove. 
         [0019]    In yet another aspect of the present invention, the piston head further includes an outer surface, a seal groove and a ring seal. The seal groove is disposed on the outer surface and the ring seal is disposed in the seal groove. 
         [0020]    Further objects, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
     
    
     
       DRAWINGS 
         [0021]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way; 
           [0022]      FIG. 1A  is a cross-section of a piston actuator assembly in accordance with an embodiment of the present invention with the piston and piston liner in a neutral position; 
           [0023]      FIG. 1B  is a cross-section of the piston actuator assembly with the piston and piston liner in a first position; 
           [0024]      FIG. 1C  is a cross-section of the piston actuator assembly with the piston and piston liner in a second position; 
           [0025]      FIG. 2A  is a cross-section of a piston actuator assembly in accordance with an embodiment of the present invention with the piston and piston liner in a neutral position; 
           [0026]      FIG. 2B  is a cross-section of the piston actuator assembly with the piston and piston liner in a first position; 
           [0027]      FIG. 2C  is a cross-section of the piston actuator assembly with the piston and piston liner in a second position; 
           [0028]      FIG. 3A  is a cross-section of a piston actuator assembly in accordance with an embodiment of the present invention with the piston and piston liner in a neutral position; 
           [0029]      FIG. 3B  is a cross-section of the piston actuator assembly with the piston and piston liner in a first position; and 
           [0030]      FIG. 3C  is a cross-section of the piston actuator assembly with the piston and piston liner in a second position. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0032]    Referring to the drawings, wherein like reference numbers refer to like components, in  FIG. 1A  a cross-section of an embodiment of a piston actuator assembly  10  according to the principles of the present invention is shown and will now be described. The piston actuator assembly  10  includes a housing  20 , a piston liner  22 , a piston  24 , and a seal assembly  26 . 
         [0033]    The housing  20  defines a bore  28  having a first portion  30  and a second portion  32 . The first portion  30  is proximate an open end  28 A of the bore  28  and has an inner surface  30 A. A bore liner  36  is disposed in the bore  28  proximate the first portion  30 . The bore liner  36  has an inner surface  36 A and an outer surface  36 B. The outer surface  36 B is in contact with the inner surface  30 A of the first portion  30  of the bore  28  and includes a seal groove  36 C. A ring seal  36 D is disposed in the seal groove  36 C and is compressed between the bore liner  36  and the first portion  30  of the bore  28 . The second portion  32  of the bore  28  is proximate a closed end  28 B of the bore  28  and has an inner diameter that is larger than the inner diameter of the inner surface  36 A of the bore liner  36 . The difference in the diameters between the bore liner  36  and the second portion  32  of the bore  28  forms a step  38  at the interface of the bore liner  36  and the second portion  32  of the bore  28  of the housing  20 . 
         [0034]    The piston liner  22  is slidably disposed between the bore liner  36  and the piston assembly  24  and is configured to coordinate movement with the piston assembly  24 , as will be described in greater detail below. The piston liner  22  is generally annular and includes an outer surface  40 , an inner surface  42 , a first end  22 A and a second end  22 B opposite the first end  22 A. The outer surface  40  includes a first portion  40 A and a second portion  40 B. The second portion  40 B has an outer diameter greater than an outer diameter of the first portion  40 A. The second portion  40 B is sealingly engaged with the inner surface  32  of the housing  20 . In the example provided, a seal ring  40 C is located within a seal groove  40 D formed in the second portion  40 B of the outer surface  40 . However, it should be appreciated that other methods and mechanisms for sealing the piston liner  22  to the housing  20  may be employed without departing from the scope of the present invention. The outer surface  40  further includes a radially extending step portion  46  located between the first and second portions  40 A,  40 B. The step portion  46  acts as a stop for the piston liner  22  against the step  38  of the bore liner  28 . The inner surface  42  of the piston liner  22  defines a bore  22 C. The bore  22 C extends through the piston liner  22  and communicates with a first opening  48 A located in the first end  22 A and with a second opening  48 B located in the second end  22 B. The outer and inner surfaces  40 ,  42  of the piston liner at least partially coordinate to define a liner apply surface  47 . The liner apply surface  47  is a surface of the piston liner  22  proximate the second end  22 B on which a pressurized hydraulic fluid acts causing the piston liner  22  to move within the bore  36  of the housing  20 . 
         [0035]    The piston liner  22  further includes a piston guide  54  fixed to the second end  22 B of the piston liner  22 . The piston guide  54  extends through the bore  22 C of the piston liner  22  and into the opening  48 A. The piston guide  54  includes a pair of slots  54 A on opposite sides of the piston guide  54 . 
         [0036]    The piston liner  22  slides linearly within the bore  28  of the housing  20 . The step  38  of the bore liner  36  confines the linear movement of the piston liner  22  in a first direction A and the second end  28 B of the bore  28  confines the linear movement of the piston liner  22  in a second direction B. 
         [0037]    The step  46  of the piston liner  22  coordinates with the step  38  of the bore liner  36  to from an annular channel  55  between the bore  28  of the housing  20 , the bore liner  36  and the piston liner  22 . Pressurized hydraulic fluid that passes by the ring seal  40 C of the piston liner  22  collects in the annular channel  55 . The annular channel  55  communicates with a first exhaust passage  56  of the housing  20  to prevent an accumulation of pressurized hydraulic fluid from affecting the predictive movement of the piston liner  22 . 
         [0038]    The piston  24  is slidably disposed in the bore  28  of the housing  20  and is configured to coordinate with the piston liner  22 , as will be described in greater detail below. The piston  24  includes a piston head  57  secured to an elongated connecting rod  58 . The piston head  57  includes an inner surface  60 , an outer surface  62 , a first end  24 A and a second end  24 B opposite the first end  24 A. The outer surface  62  includes a first portion  62 A proximate the first end  24 A of the piston  24  and a second portion  62 B proximate the second end  24 B of the piston  24 . The first portion  62 A has an outer diameter larger than an outer diameter of the second portion  62 B. The first portion  62 A is sealingly engaged with the inner surface  36 D of the bore liner  36  and the second portion  62 B is sealingly engaged to the inner surface  42  of the piston liner  22 . For example, a seal ring  63 A is located within a seal groove  63 B formed in the first portion  62 A of the outer surface  62  and a seal ring  63 C is located within a seal groove  63 D formed in the second portion  62 B of the outer surface  62 . However, it should be appreciated that other methods and mechanisms for sealing the piston  24  to the bore liner  36  and the piston liner  22  may be employed without departing from the scope of the present invention. 
         [0039]    The piston  24  further includes a first piston apply surface  64 A and a second piston apply surface  64 B. The first and second piston apply surfaces  64 A,  64 B are the surfaces of the piston  24  on which the hydraulic fluid acts to cause the piston  24  to move within the piston liner  22  and bore  28  of the housing  20 . The first piston apply surface  64 A is the exposed surface of the first end  24 A of the piston head  57 . The second piston apply surface  64 B is the exposed surface of the second end  24 B of the piston head  57 . 
         [0040]    The connecting rod  58  includes a first portion  58 A and a second portion  58 B. More specifically, the first portion  58 A of the connecting rod  58  has an end  58 C and is fixedly disposed in a center bore  66  formed by the inner surface  60  of the piston head  57 . The second portion  58 B of the connecting rod  58  includes an end portion  58 D that extends through the first end  30  of the bore  28  of the housing  20 . A groove  68  is formed in an end portion  58 D of the second portion  58 B to allow for connection to, for example, a shift fork (not shown) or other operable mechanism. However, it should be appreciated that other methods and mechanisms for connecting the connecting rod  58  to another operable mechanism may be employed without departing from the scope of the present invention. The connecting rod  58  further includes a center bore  70  extending from the end  58 C of the first portion  58 A into the connecting rod  58 . The center bore  70  has an opening  70 A in the end  58 C through which the piston guide  54  extends. The piston  24  further includes a piston pin bore  72  disposed perpendicularly to the center bore  70  of the connecting rod  58 . More specifically, the piston pin bore  72  passes through the second portion  62 B of the piston head  57  and the first portion  58 A of the connecting rod  58 . A piston pin  74  is fixedly disposed in the pin bore  72 , passing through the center bore  70  of the connecting rod  58  and the slots  54 A of the piston guide  54 . The piston pin  74  coordinates with the piston guide  54  and slots  54 A to confine relative movement between the piston  24  and the piston liner  22  to the length of the piston guide slots  54 A. However, it should be appreciated that other methods and mechanisms of confining relative movement between the piston liner  22  and the piston  24  may be employed without departing from the scope of the present invention. 
         [0041]    The seal assembly  26  is disposed in the first end  28 A of the bore  28  of the housing  20  and is retained by a seal retainer  75  fixed to the housing  20  by a fastener  75 A. The seal assembly  26  has an inner surface  26 A and an outer surface  26 B. The inner surface  26 A forms a bore  26 C through which the connecting rod  58  of the piston  24  passes. The outer surface  26 B is sealingly engaged with the inner surface  30 A of the bore  30  of the housing  20 . Also, the inner surface  26 A is sealingly engaged with and provides support to the connecting rod  58 . In the example provided, a first ring seal  76 A and a second ring seal  76 B are located, respectively, in a first seal groove  78 A and a second seal groove  78 B. The ring seals  76 A,  76 B are compressed between the outer surface  26 B of the seal assembly  26  and the bore  28  of the housing  20  providing a high pressure hydraulic seal. Furthermore, a first seal  80 A, a second seal  80 B, and a bearing  82  are located on the inner surface  26 A. The seals  80 A,  80 B provide a dynamic high pressure seal between the inner surface  26 A of the seal assembly  26  and the connecting rod  58  while the bearing  82  provides radial support to the connecting rod  58 . However, it should be appreciated that other methods and mechanisms for sealing the sealing assembly  26  to the bore  30  and supporting and sealing the connecting rod  58  may be employed without departing from the scope of the present invention. 
         [0042]    The seal assembly  26  includes a first seal carrier  84  and a second seal carrier  86 . The first seal carrier  84  has an inner surface  84 A that forms an internal cavity  84 B in which is disposed the second seal carrier  86 . The second seal carrier  86  is sealingly engaged with the inner surface  84 A of the first seal carrier  84 . Furthermore, the second seal carrier  86  has an outer surface  86 A that coordinates with the inner surface  84 A of the first seal carrier  84  to form an annular channel  88 . The annular channel  88  collects hydraulic fluid that passes by the first seal  80 A. The annular channel  88  is in communication with an exhaust fluid passage  90  in the first seal carrier  84 . The exhaust fluid passage  90  in the first seal carrier  84  is in communication with a second exhaust fluid passage  92  of the housing  20 . The seal assembly  26  contemplated provides maximum flexibility and interchangeability, however it should be appreciated that other methods and mechanisms of sealing the bore  28  may be employed without departing from the scope of the present invention. 
         [0043]    The piston actuator assembly  10  further includes a first hydraulic pressure chamber  100  and a second hydraulic pressure chamber  102 . The hydraulic pressure chambers  100 ,  102  are generally formed by the coordination of the surfaces of the bore  28  of the housing  20 , bore liner  36 , piston liner  22 , piston  24  and seal assembly  26 . For example, the first hydraulic pressure chamber  100  is defined by a surface  26 D of the seal assembly  26 , the inner surface  36 A of the bore liner  36  and the first piston apply surface  64 A. The first hydraulic pressure chamber  100  communicates with a first hydraulic apply passage  104  of the housing  20  through a fluid passage  106  of the bore liner  36 . Selectively pressurized fluid is introduced to the first hydraulic apply passage  104  and therefore into the first hydraulic pressure chamber  100 . 
         [0044]    The second hydraulic pressure chamber  102  is defined by at least the inner surface  30 A of the bore  28  of the housing  20 , the liner apply surface  44  and the second piston apply surface  64 B. The second hydraulic pressure chamber  102  communicates with the second hydraulic fluid passage  106  of the housing  20 . Selectively pressurized fluid is introduced to the second hydraulic fluid passage  106  and therefore into the second hydraulic pressure chamber  102 . 
         [0045]    Referring to  FIGS. 1A ,  1 B and  1 C, the operation of the piston actuator assembly  10  will now be described.  FIG. 1A  illustrates a cross-section of the piston actuator assembly  10  in a neutral position. The neutral position corresponds to the operation of disengaging a gear from the synchronizer or a drive shaft. The neutral position is typically achieved by partially pressurizing the first pressure cavity  100  and the second pressure cavity  102  to approximately equal pressures. The hydraulic fluid contacts the surfaces of the first pressure cavity  100  thus implementing a resulting pressure on the first piston apply surface  64 A of the first pressure cavity  100 . Furthermore, the hydraulic fluid contacts the surfaces of the second pressure cavity  102  thus implementing a resulting pressure on the second piston apply surface  64 B and the liner apply surface  47  of the second pressure cavity  100 . The resultant force on the second piston and liner apply surfaces  47 ,  64 B overcome the resultant force on the first piston apply surface  64 A and the hydraulic fluid moves the piston  24  and piston liner  22  until the step  46  of the piston liner  22  contact the step  38  of the bore liner  36 . At this point the resultant force generated by the hydraulic fluid acting on the second piston apply surface  64 B alone is not enough to overcome the apply force acting on the first piston apply surface  64 A so the piston  24  and piston liner stops moving in the defined neutral position. Accordingly, in the neutral position, the piston  24  is positioned such that the second end  24 B of the piston contacts the piston liner  22  proximate the second end  22 B and the radial step  55  of the piston liner  22  contacts the radial step  28  of the bore liner  36 . 
         [0046]      FIG. 1B  illustrates a cross-section of the piston actuator assembly  10  placed in a first position. The first position corresponds to the operation of engaging a first gear to the synchronizer or a drive shaft. The first position is achieved by pressurizing the first pressure cavity  100  and depressurizing the second pressure cavity  102 . The hydraulic fluid contacts the surfaces of the first pressure cavity  100  thus implementing a resulting pressure on the first piston apply surface  64 A of the first pressure cavity  100 . Furthermore, the hydraulic fluid is allowed to drain with or without pressure assistance from the second pressure cavity  102 . The resultant force on the first apply surface  64 A due to the hydraulic fluid moves the piston  24  in the B direction. Accordingly, in the first position, the piston  24  is positioned such that the second end  24 B of the piston contacts the piston liner  22  proximate the second end  22 B and the second end  22 B of the piston liner  22  is positioned proximate the closed end  28 B of the bore  28 . 
         [0047]      FIG. 1C  illustrates a cross-section of an embodiment of the piston actuator assembly  10  placed in a second position. The second position corresponds to the operation of engaging a second gear to a synchronizer or a drive shaft. If the piston actuator assembly  10  is moving from the first position, the first gear is disengaged and the second gear is engaged after the piston  24  passes through the neutral position. The second position is achieved by depressurizing the first pressure cavity  100  and pressurizing the second pressure cavity  102 . The hydraulic fluid contacts the surfaces of the second pressure cavity  102  thus implementing a resulting pressure on the second piston apply surface  64 B and the liner apply surface  47  of the second pressure cavity  102 . Furthermore, the hydraulic fluid is allowed to drain with or without pressure assistance from the first pressure cavity  100 . The resultant force on the apply surfaces  47 ,  64 B due to the hydraulic fluid moves the piston  24  and piston liner  22  in the A direction. Accordingly, in the second position, the piston  24  and the piston liner  22  are positioned such that the first end  24 A of the piston is positioned proximate a surface  26 D of the seal assembly  26  and the radial step  55  of the piston liner  22  contacts the radial step  38  of the bore liner  36  and maintains position of the piston liner  22 . 
         [0048]    Referring now to  FIG. 2A  a cross-section of a second embodiment of a piston actuator assembly  110  is shown and will now be described. The piston actuator assembly  110  includes a housing  120 , a piston liner  122 , a piston  124 , and a seal assembly  126 . The housing  120  includes an inner surface  120 A that defines a bore  128 . The inner surface  120 A has a first portion  130 , a second portion  132 , and a third portion  134 . The first portion  130  is proximate an open end  128 A of the bore  128  and has an inner surface  130 A. The second portion  132  is proximate a closed end  128 B of the bore  128 . The third portion  134  is disposed between the first and second portions  130 ,  132  and has an inner diameter that is smaller than the inner diameter of the first portion  130  and larger than the inner diameter of the second portion  132 . The inner surface  120 A of the housing  120  further includes a first radially extending step portion  138 A and a second radially extending step portion  138 B. The first step portion  138 A is formed at the interface of the first portion  130  and the third portion  134 . The second step portion  138 B is formed at the interface of the second portion  132  and the third portion  134 . 
         [0049]    The piston liner  122  is slidably disposed between the inner surface  120 A of the housing  120  and the piston assembly  124  and is configured to coordinate movement with the piston assembly  124 , as will be described in greater detail below. The piston liner  122  is generally annular and includes an outer surface  140 , an inner surface  142 , a first end  122 A and a second end  122 B opposite the first end  122 A. The outer surface  140  includes a first portion  140 A, a second portion  140 B and a third portion  140 C. The first portion  140 A is disposed proximate to the first end  122 A of the piston liner  122  and has an outer diameter larger than the second portion  140 B. The second portion  140 B is disposed proximate the second end  122 B of the piston liner  122 . The third portion  140 C is disposed between the first portion  140 A and the second portion  140 B and has an outer diameter smaller than the outer diameter of the first portion  140 A and larger than the outer diameter of the second portion  140 B. The first portion  140 A and third portion  140 C are sealingly engaged with the first portion  130  and the third portion  134 , respectively, of the inner surface  132  of the housing  120 . In the example provided, a first seal ring  141 A is located in a first seal groove  141 B formed in the first portion  140 A of the outer surface  140 . Also, a second seal ring  141 C is located in a second seal groove  141 D formed in the third portion  140 C of the outer surface  140 . However, it should be appreciated that other methods and mechanisms for sealing the piston liner  122  to the housing  120  may be employed without departing from the scope of the present invention. 
         [0050]    The outer surface  140  further includes a first radially extending step portion  146 A and a second radially extending step portion  146 B. The first step portion  146 A is located between the first portion  140 A and the third portion  140 C. The second step portion  146 B is located between the second portion  140 B and the third portion  140 C. The first step portion  146 A coordinates with the first step portion  138 A of the inner surface  120 A of the housing  120  to form a first annular channel  150  between the bore  128  and the piston liner  122 . Pressurized hydraulic fluid that passes by the ring seal  140 D of the piston liner  122  collects in the first annular channel  150 . The first annular channel  150  communicates with a first exhaust passage  152  of the housing  120  to prevent an accumulation of pressurized hydraulic fluid from affecting the predictive movement of the piston liner  122 . The second step portion  146 B acts as a stop for the piston liner  122  against the second step portion  138 B of the inner surface  120 A of the housing  120 . 
         [0051]    The inner surface  142  of the piston liner  122  defines a bore  122 C. The bore  122 C extends through the piston liner  122  and communicates with a first opening  148 A located in the first end  122 A and with a second opening  148 B located in the second end  122 B. The inner surface  142  has a first portion  142 A located proximate the first end  122 A of the piston liner  122  and a second portion  142 B located proximate the second end  122 B. The first portion  142 A of the inner surface  142  of the piston liner  122  has a larger inner diameter than the second portion  142 B. The inner surface  142  of the piston liner  122  further includes a radially extending step portion  142 C that is formed at the interface of the first portion  142 A and the second portion  142 B of the inner surface  142  of the piston liner  122 . The first portion  142 A of the inner surface further includes a retainer ring  143  disposed in a groove  143 A which limits travel of the piston  124  relative to the piston liner  122 . However, it should be appreciated that other methods and mechanisms of limiting relative movement of the piston  124  within the piston liner  122  may be employed without departing from the scope of the present invention. 
         [0052]    The piston liner  122  further includes a first liner apply surface  144 A and a second liner apply surface  144 B. The first liner apply surface  144 A is a surface of the piston liner  122  proximate the first end  122 A on which a pressurized hydraulic fluid acts causing the piston liner  122  to move within the bore  128  of the housing. The second liner apply surface  144 B is a surface of the piston liner  122  proximate the second end  122 B on which a pressurized hydraulic fluid acts causing the piston liner  122  to move within the bore  128  of the housing. 
         [0053]    The piston  124  is slidably disposed in the bore  128  of the housing  120  and is configured to coordinate with the piston liner  122 , as will be described in greater detail below. The piston  124  includes a head portion  156  and an elongated connecting rod portion  158 . The head portion  156  includes an outer surface  162 , a first end  124 A and a second end  124 B opposite the first end  124 A. The outer surface  162  includes a first portion  162 A proximate the first end  124 A and a second portion  162 B proximate the second end  124 B. The first portion  162 A has an outer diameter larger than an outer diameter of the second portion  162 B. The first portion  162 A and the second portion  162 B are sealingly engaged with the first portion  142 A and the second portion  142 B, respectively, of the inner surface  142  of the piston liner  122 . In the example provided, a seal ring  164 A is located within a seal groove  166 A formed in the first portion  162 A of the outer surface  162  of the head portion  156 . Also, a seal ring  164 B is located within a seal groove  166 B formed in the second portion  162 B of the outer surface  162  of the head portion  156 . 
         [0054]    The outer surface  162  of the head portion  156  further includes a radially extending step portion  162 C formed at the interface of the first portion  162 A and the second portion  162 B of the outer surface. The step portion  162 C of the head portion  154  of the piston  124  coordinates with the step portion  142 C of the inner surface  142  of the piston liner  122  to act as a stop preventing further movement of the piston  124  in the B direction relative to the piston liner  122 . Also, the step portion  162 C of the outer surface  162  of the head portion  154  coordinates with the step portion  142 C of the inner surface  142  of the piston liner  122  to form a second annular channel  163  between the piston  124  and the piston loner  122 . Pressurized hydraulic fluid that passes by the ring seals  164 A,  164 B of the head portion  154  of the piston  124  collects in the second annular channel  163 . The second annular channel  163  communicates with an exhaust passage  122 C of the piston liner  122 , the first annular channel  150  and the first exhaust passage  152  of the housing  120  to prevent an accumulation of pressurized hydraulic fluid from affecting the predictive movement of the piston  124 . Furthermore, the first end  124 A of the head portion  154  of the piston  124  coordinates with the retainer ring  143  of the piston liner  122  to act as a stop preventing further movement of the piston  124  in the A direction relative to the piston liner  122 . 
         [0055]    The piston  124  further includes a first piston apply surface  164 A and a second piston apply surface  164 B. The first and second piston apply surfaces  164 A,  164 B are the surfaces of the piston  124  on which the hydraulic fluid acts to cause the piston  124  to move within the piston liner  122  and bore  128  of the housing  120 . The first piston apply surface  164 A is the exposed surface of the first end  124 A of the head portion  156 . The second piston apply surface  164 B is the exposed surface of the second end  124 B of the head portion  156 . 
         [0056]    The connecting rod portion  158  includes a first portion  158 A and a second portion  158 B. More specifically, the first portion  158 A of the connecting rod portion  158  has an end  158 C fixedly attached to the first end  124 A of the head portion  156 . The second portion  158 B extends through the open end  130  of the bore  128  of the housing  20 . A groove  168  is formed in the second portion  158 B to allow for connection to, for example, a shift fork (not shown) or other operable mechanism. However, it should be appreciated that other methods and mechanisms of connection may be employed without departing from the scope of the present invention. 
         [0057]    The seal assembly  126  is disposed in the first end  128 A of the bore  128  of the housing  120  and is retained by a plate  175  held in place by a ring retainer  175 A disposed in a groove  175 B formed in the housing  120  proximate the open end  128 A. The seal assembly  126  has an inner surface  126 A and an outer surface  126 B. The inner surface  126 A forms a bore  126 C through which the connecting rod  158  of the piston  124  passes. The outer surface  126 B is sealingly engaged with the inner surface  130 A of the bore  130  of the housing  120 . Also, the inner surface  126 A is sealingly engaged to the connecting rod portion  158 . In the example provided, a first ring seal  176 A and a second ring seal  176 B are located, respectively, in a first seal groove  178 A and a second seal groove  178 B. The ring seals  176 A,  176 B are compressed between the outer surface  126 B of the seal assembly  126  and the bore  128  of the housing  120  providing a high pressure hydraulic seal. Furthermore, a first seal  180 A, a second seal  180 B, and a bearing  182  are located on the inner surface  126 A. The seals  180 A,  180 B provide a dynamic high pressure seal between the inner surface  126 A of the seal assembly  126  and the connecting rod portion  158  while the bearing  182  provides radial support to the connecting rod portion  158 . However, it should be appreciated that other methods and mechanisms for sealing the sealing assembly  126  to the bore  130  and the connecting rod portion  158  may be employed without departing from the scope of the present invention. 
         [0058]    The seal assembly  126  includes a first seal carrier  184  and a second seal carrier  186 . The first seal carrier  184  has an inner surface  184 A that forms an internal cavity  184 B in which is disposed the second seal carrier  186 . The second seal carrier  186  is sealingly engaged with the inner surface  184 A of the first seal carrier  184 . Furthermore, the second seal carrier  186  has an outer surface  186 A that coordinates with the inner surface  184 A of the first seal carrier  184  to form an annular channel  188 . The annular channel  188  collects hydraulic fluid that passes by the first seal  180 A. The annular channel  188  is in communication with an exhaust fluid passage  190  in the first seal carrier  184 . The exhaust fluid passage  190  in the first seal carrier is in communication with a second exhaust fluid passage  192  of the housing  120 . 
         [0059]    The piston actuator assembly further includes a first hydraulic pressure chamber  200  and a second hydraulic pressure chamber  202 . The hydraulic pressure chambers  200 ,  202  are formed by the coordination of the surfaces of the bore  128  of the housing  20 , piston liner  122 , piston  124  and seal assembly  126 . For example, the first hydraulic pressure chamber  200  is defined by at least the inner surface  120 A of the bore  128 , a surface  126 D of the seal assembly  126 , the first liner apply surface  144 A and the first piston apply surface  164 A. The first hydraulic pressure chamber  200  communicates with a first hydraulic apply passage  204  of the housing  120 . Selectively pressurized fluid is introduced to the first hydraulic apply passage  204  and therefore into the first hydraulic pressure chamber  200 . 
         [0060]    The second hydraulic pressure chamber  202  is defined by at least the inner surface  120 A of the bore  128 , the second liner apply surface  144 B and the second piston apply surface  164 B. The second hydraulic pressure chamber  202  communicates with the second hydraulic fluid passage  206  of the housing  120 . Selectively pressurized fluid is introduced to the second hydraulic fluid passage  206  and therefore into the second hydraulic pressure chamber  202 . 
         [0061]    Referring to  FIGS. 2A ,  2 B and  2 C, the operation of the piston actuator assembly  110  will now be described.  FIG. 2A  illustrates a cross-section of the piston actuator assembly  110  in a neutral position. The neutral position corresponds to the operation of disengaging a gear from the synchronizer or a drive shaft. The neutral position is achieved by partially pressurizing the first pressure cavity  200  and the second pressure cavity  202 . The hydraulic fluid contacts the surfaces of the first pressure cavity  200  thus implementing a resulting pressure on the first piston apply surface  164 A and the first liner apply surface  144 A of the first pressure cavity  200 . Furthermore, the hydraulic fluid contacts the surfaces of the second pressure cavity  202  thus implementing a resulting pressure on the second piston apply surface  164 B and the second liner apply surface  144 B of the second pressure cavity  200 . The resultant force on the second piston and second liner apply surfaces  144 B  164 B overcome the resultant forces on the first piston and second liner apply surfaces  144 A,  164 A and the hydraulic fluid moves the piston  124  and piston liner  122  until the first end  122 A of the piston liner  122  contacts a surface  126 D of the seal assembly. The resultant force generated by the hydraulic fluid acting on the second apply surface  164 B is not enough to overcome the force acting on the first apply liner apply surface  164 A. The piston liner  122  stops moving in the defined neutral position. Accordingly, in the neutral position, the piston  124  is positioned such that the radial step  162 A of the piston  124  contacts the radial step  142 C of the inner surface  142  of the piston liner  122  and the first end  122 A of the piston liner  122  contacts a surface  126 D of the seal assembly. 
         [0062]      FIG. 2B  illustrates a cross-section of the piston actuator assembly  110  placed in a first position. The first position corresponds to the operation of engaging a first gear to the synchronizer or a drive shaft. The first position is achieved by pressurizing the first pressure cavity  200  and depressurizing the second pressure cavity  202 . The hydraulic fluid contacts the surfaces of the first pressure cavity  200  thus implementing a resulting pressure on the first piston apply surface  164 A and the first liner apply surface  144 A of the first pressure cavity  200 . Furthermore, the hydraulic fluid is allowed to drain from the second pressure cavity  202 . The resultant force on the first apply surfaces  144 A,  164 A due to the hydraulic fluid moves the piston  124  in the B direction. Accordingly, in the first position, the piston  124  is positioned such that the radial step  162 A of the piston contacts the radial step  142 C of the inner surface  142  of the piston liner  122  and the second end  122 B of the piston liner  122  is proximate the closed end  128 B of the bore  128 . 
         [0063]      FIG. 2C  illustrates a cross-section of an embodiment of the piston actuator assembly  110  placed in a second position. The second position corresponds to the operation of disengaging a gear from the synchronizer or a drive shaft. If actuated from the first position, the first gear is disengaged and then the second gear is engaged after passing through the neutral position. The second position is achieved by depressurizing the first pressure cavity  200  and pressurizing the second pressure cavity  202 . The hydraulic fluid contacts the surfaces of the second pressure cavity  202  thus implementing a resulting pressure on the second piston apply surface  164 B and the second liner apply surface  144 B of the second pressure cavity  202 . Furthermore, the hydraulic fluid is allowed to drain from the first pressure cavity  200 .The resultant force on the second apply surfaces  144 B,  164 B due to the hydraulic fluid moves the piston  124  and piston liner  122  in the A direction. Accordingly, in the second position, the piston  124  and the piston liner  122  are positioned such that the first end  124 A of the piston is proximate the retainer ring  143  of the inner surface  142  of the piston liner  122  and the first end  122 A of the piston liner  122  contacts the surface  126 D of the seal assembly  126 . 
         [0064]    Referring now to  FIG. 3A  a cross-section of another embodiment of a piston actuator assembly  210  is shown and will now be described. The piston actuator assembly  210  includes a housing  220 , a piston liner  222 , a piston  224 , and a seal assembly  226 . The housing  220  includes an inner surface  220 A that defines a bore  228 . The inner surface  220 A has a first portion  230  and a second portion  232 . The first portion  230  is proximate an open end  228 A of the bore  228  and has an inner surface  230 A. The second portion  232  is proximate a closed end  228 B of the bore  228 . The first portion  230  has an inner diameter that is larger than the inner diameter of the second portion  232 . The inner surface  220 A of the housing  220  further includes a radially extending step portion  238 . The step portion  238  is formed at the interface of the first portion  230  and the third portion  234 . 
         [0065]    The piston liner  222  is slidably disposed between the inner surface  220 A of the housing  220  and the piston assembly  224  and is configured to coordinate movement with the piston assembly  224 , as will be described in greater detail below. The piston liner  222  is generally annular and includes an outer surface  240 , an inner surface  242 , a first end  222 A and a second end  222 B opposite the first end  222 A. The outer surface  240  includes a first portion  240 A and a second portion  240 B. The first portion  240 A is disposed proximate to the first end  222 A of the piston liner  222  and has an outer diameter larger than the second portion  240 B. The second portion  240 B is disposed proximate the second end  222 B of the piston liner  222 . The first portion  240 A has an outer diameter larger than the outer diameter of the second portion  240 B. The first portion  240 A is sealingly engaged with the first portion  230  of the inner surface  232  of the housing  220 . The second portion  240 B is sealingly engaged with the second portion  232  of the inner surface of the housing  220 . In the example provided, a first seal ring  241 A is located in a first seal groove  241 B formed in the first portion  240 A of the outer surface  240 . Also, a second seal ring  241 C is located in a second seal groove  241 D formed in the third portion  240 C of the outer surface  240 . However, it should be appreciated that other methods and mechanisms for sealing the piston liner  222  to the housing  220  may be employed without departing from the scope of the present invention. 
         [0066]    The outer surface  240  further includes a radially extending step portion  246  located at the interface of the first portion  240 A and the third portion  240 C. The step portion  246  coordinates with the step portion  238  of the inner surface  220 A of the housing  220  to form an annular channel  250  between the bore  228  and the piston liner  222 . Pressurized hydraulic fluid that passes by the ring seals  241 A,  241 C of the piston liner  222  collects in the annular channel  250 . The annular channel  250  communicates with a first exhaust passage  252  of the housing  220  to prevent an accumulation of pressurized hydraulic fluid from affecting the predictive movement of the piston liner  222 . 
         [0067]    The inner surface  242  of the piston liner  222  defines a bore  222 C. The bore  222 C extends through the piston liner  222  and communicates with a first opening  248 A located in the first end  222 A and with a second opening  248 B located in the second end  222 B. The inner surface  242  has a first portion  242 A located proximate the first end  222 A of the piston liner  222  and a second portion  242 B located proximate the second end  222 B. The first portion  242 A of the inner surface  242  of the piston liner  222  has a smaller inner diameter than the second portion  242 B. The second portion  242 B of the inner surface  242  further includes a retainer ring  243 A disposed in a groove  243 B. 
         [0068]    The piston liner  222  further includes a first liner apply surface  244 A and a second liner apply surface  244 B. The first liner apply surface  244 A is a surface of the piston liner  222  proximate the first end  222 A on which a pressurized hydraulic fluid acts thereby causing the piston liner  222  to move within the bore  228  of the housing  220 . The second liner apply surface  244 B is a surface of the piston liner  222  proximate the second end  222 B on which a pressurized hydraulic fluid acts thereby causing the piston liner  222  to move within the bore  228  of the housing  220 . 
         [0069]    The piston  224  is slidably disposed in the bore  228  of the housing  220  and is configured to coordinate with the piston liner  222 , as will be described in greater detail below. The piston  224  includes a head portion  256  and an elongated connecting rod portion  258 . The head portion  256  includes an outer surface  262 , a first end  224 A and a second end  224 B opposite the first end  224 A. The outer surface  262  is sealingly engaged with the second portion  242 B of the inner surface  242  of the piston liner  222 . In the example provided, a seal ring  264 A is located within a seal groove  266 A formed in the outer surface  262  of the head portion  256 . However, it should be appreciated that other methods and mechanisms for sealing the piston  224  to the piston liner  222  may be employed without departing from the scope of the present invention. 
         [0070]    The head portion  254  of the piston  224  coordinates with the first portion  242 A of the inner surface  242  of the piston liner  222  to act as a stop preventing further movement of the piston  224  in the A direction relative to the piston liner  222 . Also, the head portion  254  coordinates with the retainer ring  243 A of the piston liner  222  to act as a stop preventing further movement of the piston  224  in the B direction relative to the piston liner  222 . 
         [0071]    The piston further includes a first piston apply surface  264 A and a second piston apply surface  264 B. The first and second piston apply surfaces  264 A,  264 B are the surfaces of the piston  224  on which the hydraulic fluid acts to cause the piston  224  to move within the piston liner  222  and bore  228  of the housing  220 . The first piston apply surface  264 A is the exposed surface of the first end  224 A of the head portion  256 . The second piston apply surface  264 B is the exposed surface of the second end  224 B of the head portion  256 . 
         [0072]    The connecting rod portion  258  includes a first portion  258 A and a second portion  258 B. More specifically, the first portion  258 A of the connecting rod portion  258  has an end  258 C fixedly attached to the first end  224 A of the head portion  256 . The second portion  258 B extends through the open end  230  of the bore  228  of the housing  20 . A groove  268  is formed in the second portion  258 B to allow for connection to, for example, a shift fork (not shown) or other operable mechanism. 
         [0073]    The seal assembly  226  is disposed in the first end  228 A of the bore  228  of the housing  220  and is retained by a plate  275  held in place by a ring retainer  275 A disposed in a groove  275 B formed in the housing  220  proximate the open end  220 A. The seal assembly  226  has an inner surface  226 A and an outer surface  226 B. The inner surface  226 A forms a bore  226 C through which the connecting rod  258  of the piston  224  passes. The outer surface  226 B is sealingly engaged with the inner surface  230 A of the bore  230  of the housing  220 . Also, the inner surface  226 A is sealingly engaged with the connecting rod portion  258 . In the example provided, a first ring seal  276 A and a second ring seal  276 B are located, respectively, in a first seal groove  278 A and a second seal groove  278 B. The ring seals  276 A,  276 B are compressed between the outer surface  226 B of the seal assembly  226  and the bore  228  of the housing  220  providing a high pressure hydraulic seal. Furthermore, a first seal  280 A, a second seal  280 B, and a bearing  282  are located on the inner surface  226 A. The seals  280 A,  280 B provide a dynamic high pressure seal between the inner surface  226 A of the seal assembly  226  and the connecting rod portion  258  while the bearing  282  provides radial support to the connecting rod portion  258 . However, it should be appreciated that other methods and mechanisms for sealing the sealing assembly  226  to the bore  230  and sealing and supporting the connecting rod portion  258  may be employed without departing from the scope of the present invention. 
         [0074]    The seal assembly  226  includes a first seal carrier  284  and a second seal carrier  286 . The first seal carrier  284  has an inner surface  284 A that forms an internal cavity  284 B in which is disposed the second seal carrier  286 . The second seal carrier  286  is sealingly engaged with the inner surface  284 A of the first seal carrier  284 . Furthermore, the second seal carrier  286  has an outer surface  286 A that coordinates with the inner surface  284 A of the first seal carrier  284  to form an annular channel  288 . The annular channel  288  collects hydraulic fluid that passes by the first seal  280 A. The annular channel  288  is in communication with an exhaust fluid passage  290  in the first seal carrier  284 . The exhaust fluid passage  290  in the first seal carrier is in communication with a second exhaust fluid passage  292  of the housing  220 . 
         [0075]    The piston actuator assembly  210  further includes a first hydraulic pressure chamber  300  and a second hydraulic pressure chamber  302 . The hydraulic pressure chambers  300 ,  302  are formed generally by the coordination of the surfaces of the bore  228  of the housing  220 , piston liner  222 , piston  224  and seal assembly  226 . For example, the first hydraulic pressure chamber  300  is defined by at least the inner surface  220 A of the bore  228 , a surface  226 D of the seal assembly  226 , the first liner apply surface  244 A and the first piston apply surface  264 A. The first hydraulic pressure chamber  300  communicates with a first hydraulic apply passage  304  of the housing  220 . Selectively pressurized fluid is introduced to the first hydraulic apply passage  304  and therefore into the first hydraulic pressure chamber  300 . 
         [0076]    The second hydraulic pressure chamber  302  is defined by at least the inner surface  220 A of the bore  228 , the second liner apply surface  244 B and the second piston apply surface  264 B. The second hydraulic pressure chamber  302  communicates with the second hydraulic fluid passage  308  of the housing  220 . Selectively pressurized fluid is introduced to the second hydraulic fluid passage  308  and therefore into the second hydraulic pressure chamber  302 . 
         [0077]    Referring to  FIGS. 3A ,  3 B and  3 C, the operation of the piston actuator assembly  210  will now be described.  FIG. 3A  illustrates the piston actuator assembly  210  in a neutral position. The neutral position corresponds to the operation of disengaging a gear from the synchronizer or a drive shaft. The neutral position is achieved by partially pressurizing the first pressure cavity  300  and the second pressure cavity  302  to approximately equal pressures. The hydraulic fluid contacts the surfaces of the first pressure cavity  300  thus implementing a resulting pressure on the first piston apply surface  264 A and the first liner apply surface  244 A of the first pressure cavity  300 . Furthermore, the hydraulic fluid contacts the surfaces of the second pressure cavity  302  thus implementing a resulting pressure on the second piston apply surface  264 B and the second liner apply surface  244 B of the second pressure cavity  300 . The resultant force on the first piston and first liner apply surfaces  244 A,  264 A overcome the resultant force acting on the second piston and second liner apply surfaces  244 B,  264 B. The hydraulic fluid moves the piston  224  and piston liner  222  until the first end  224 A of the piston contacts the first portion  242 A of the inner surface  242  of the piston liner  222  and the second end  222 B of the piston liner  222  contacts the closed end  228 B of the bore  228 . At this point the resultant force generated by the hydraulic fluid acting on the first piston apply surface  264 A is less than the force acting on the second piston apply surface  264 B. The piston  224  and piston liner  222  stops moving in the defined neutral position. Accordingly, in the neutral position, the piston  224  is positioned such that the first end  224 A of the piston contacts the first portion  242 A of the inner surface  242  of the piston liner  222  and the second end  222 B of the piston liner  222  contacts the closed end  228 B of the bore  228 . 
         [0078]      FIG. 3B  illustrates a cross-section of the piston actuator assembly  210  placed in a first position. The first position corresponds to the operation of engaging a first gear to the synchronizer or a drive shaft. The first position is achieved by pressurizing the first pressure cavity  300  and depressurizing the second pressure cavity  302 . The hydraulic fluid contacts the surfaces of the first pressure cavity  300  thus implementing a resulting pressure on the first piston apply surface  264 A and the first liner apply surface  244 A of the first pressure cavity  300 . Furthermore, the hydraulic fluid is allowed to drain from the second pressure cavity  302 . The resultant force on the first apply surfaces  264 A,  244 A due to the hydraulic fluid moves the piston  224  in the B direction. Accordingly, in the first position, for example, the piston  224  is positioned such that the second end  224 B of the head portion  256  of the piston  224  contacts the ring retainer  243 A of the inner surface  242  of the piston liner  222  and the second end  222 B of the piston liner  222  is proximate the closed end  228 B of the bore  228 . However, it should be appreciated that the piston  224  may not contact the ring retainer  243 A in the first position without departing from the scope of the present invention. 
         [0079]      FIG. 3C  illustrates a cross-section of an embodiment of the piston actuator assembly  210  placed in a second position. The second position corresponds to the operation of engaging a second gear from the synchronizer or a drive shaft. If actuated from the first position, the first gear will be disengaged and then the second gear will be engaged after passing through neutral. The second position is achieved by depressurizing the first pressure cavity  300  and pressurizing the second pressure cavity  302 . The hydraulic fluid contacts the surfaces of the second pressure cavity  302  thus implementing a resulting pressure on the second piston apply surface  264 B and the second liner apply surface  244 B of the second pressure cavity  302 . Furthermore, the hydraulic fluid is allowed to drain from the first pressure cavity  300 . The resultant force on the second apply surfaces  264 B,  244 B due to the hydraulic fluid moves the piston  224  and piston liner  222  in the A direction. Accordingly, in the second position, for example, the piston  224  and the piston liner  222  are positioned such that the first end  224 A of the piston contacts the first portion  242 A of the inner surface  242  of the piston liner  222  and the first end  222 A of the piston liner  222  is proximate a surface  226 D of the seal assembly  226 . However, it should be appreciated that the first end  224 A of the piston may not contact the first portion  242 A of the inner surface  242  of the piston liner  222  without departing from the scope of the present invention. 
         [0080]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.