Abstract:
A hydraulic strut system that damps vehicle vibration and includes a compressible fluid, a strut, and a valve plate. The strut includes three concentric tubes defining an inner cavity, an intermediary cavity, and an outer reservoir cavity, the inner cavity and intermediary cavity being fluidly coupled, wherein the inner cavity receives a piston that divides the inner cavity into a first volume and a second volume, the piston having an aperture that allows one way flow from the first volume to the second volume. The valve plate is removably coupled to the strut, and includes a first fluid path that allows one-way fluid flow from the intermediary cavity to the reservoir cavity, the first fluid path including a damping valve that damps fluid flowing therethrough; and a second fluid path that allows one-way fluid flow from the reservoir cavity to the inner cavity, the second fluid path further including a replenishment valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 13/176,720, filed 5 Jul. 2011, which claims the benefit of U.S. Provisional Application Nos. 61/361,493 filed 5 Jul. 2010 and 61/423,573 filed 15 Dec. 2010, all of which are both incorporated in their entirety by this reference. This application is related to U.S. Pat. Nos. 6,811,167 and 6,988,599, which are both incorporated in their entirety by this reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to the damper field, and more specifically to an improved suspension strut in the vehicle suspension field. 
     BACKGROUND 
     There are a variety of dampers in automotive suspensions, including a mono-tube type strut, a twin-tube type strut, and a triple-tube type strut. Within each variation, there are variations with valve arrangement and fluid management. The triple-tube type strut construction includes tube and valve arrangement that allows for fluid flow within the strut that is generally in a single direction for both the compression and rebound direction of the suspension strut, whereas both mono-tube and twin-tube type struts require fluid to flow in different directions for the compression and rebound directions. This single-direction property of the triple-tube type strut allows for damping control of the fluid flow within the triple-tube type strut to be localized to one general area within the strut for both compression and rebound directions. As a result, conventional semi-active or continuously variable damping control systems typically utilize the triple-tube type strut and a single active solenoid valve to control damping force for both the compression and rebound directions of the strut. 
     Conventional triple-tube type strut dampers include many internal parts that function to tune the dampening properties of the strut and are, for this reason, quite complex. Additionally, the damping mechanisms that are utilized in such triple-tube type struts may leak, decreasing the efficiency of the damper, or may be relatively expensive. As shown in  FIG. 1  (prior art), the active valve  10  in typical triple-tube type strut dampers is often mounted perpendicular to the long axis of the damper tube  12  and substantially adjacent to the base valve  14  that allows replenishment flow to the inner cavity  16  during the rebound stroke of the strut. This may allow such triple-tube type strut dampers to increase the range of travel of the suspension strut given a total strut height. However, this arrangement requires a fastening mechanism that does not benefit from the compressive forces from tube assembly and/or the vehicle. In semi-active or continuously variable damping control systems that utilize compressible fluids where the pressure within the suspension strut may increase to substantially high levels, the fastening mechanism used to mount the active valve perpendicularly to the axis of the damper tube may become substantially costly to withstand such high pressures. Because of complexity of typical triple-tube type strut dampers, cost is relatively high and adoption of such semi-active or continuously variable damping control systems in the field is substantially impaired. 
     Thus, there is a need in the vehicle suspension field to create an improved suspension strut. This invention provides such strut. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic representation of a semi-active suspension strut of the prior art. 
         FIGS. 2A and 2B  are schematic representations of the suspension strut of the preferred embodiments with the displacement rod and cavity piston displaced away from the valve plate and with the displacement rod and cavity piston displaced toward the valve plate, respectively. 
         FIGS. 3A ,  3 B, and  3 C are schematic representations of the valve plate with a passive damper valve in an orthogonal view, taken along Line A-A in  FIG. 3A  with the damping flow path, and taken along Line B-B in  FIG. 3A  with the replenishment flow path, respectively. 
         FIG. 4  is a schematic representation of flow during the compression stroke. 
         FIGS. 5A and 5B  are schematic representations of flow during the rebound stroke of the outflow from the pressure chamber and the rebound flow into the interior cavity, respectively. 
         FIGS. 6A and 6B  are schematic representations of the valve plate with a variation of an actuatable damper valve with decreased damping force and increased damping force, respectively. 
         FIGS. 7A ,  7 B, and  7 C are a schematic representation of the valve plate with a first, second, and third variation of a regenerative damper valve, respectively. 
         FIG. 8  is a schematic representation of the regenerative suspension strut system embodiment. 
         FIGS. 9A and 9B  are schematic representations of flow during the compression stroke for a first and a second embodiment of the regenerative suspension strut system embodiment, respectively. 
         FIGS. 10A and 10B  are schematic representations of flow during the rebound stroke of the outflow from the pressure chamber and the rebound flow into the interior cavity, respectively, for the regenerative suspension strut system embodiment. 
         FIGS. 11A and 11B  are schematic representations of the valve plate with a passive damper valve in an orthogonal view, taken along Line A-A in  FIG. 3A  with the damping flow path, and taken along Line B-B in  FIG. 3A  with the replenishment flow path, respectively. 
         FIGS. 12 and 13  are schematic representations of alternative flow paths of the regenerative suspension strut system of the preferred embodiments. 
         FIG. 14  is a graphical representation of the operating regions of the suspension strut and the energy that may be recovered using the regenerative suspension strut system of the preferred embodiments. 
         FIGS. 15 and 16  are schematic representations of variations of the regenerative suspension system strut with a second compliant volume and a reservoir, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments of the invention is not intended to limit the invention to these preferred embodiments, but rather to enable any person skilled in the art to make and use this invention. 
     As shown in  FIGS. 2 and 3 , the suspension strut  100  of the preferred embodiments is preferably used with a vehicle having a wheel contacting a surface under the vehicle, such as the road, and preferably functions to suspend the wheel from the vehicle while allowing compression movement of the wheel toward the vehicle and rebound movement of the wheel toward the surface. The suspension strut  100  preferably includes a compressible fluid  102 ; a hydraulic tube  110  including an inner tube  130  that defines an inner cavity  132  that contains a portion of the compressible fluid  102 , a secondary tube  140  that substantially envelopes the inner tube  130  and cooperates with the inner tube  130  to define an intermediary cavity  142  that contains another portion of the compressible fluid  102  and that accepts fluid flow from the inner cavity  132  through an inner flow path, and a housing tube  150  that substantially envelops the secondary tube  140  and cooperates with the secondary tube  140  to define a reservoir cavity  152  that contains another portion of the compressible fluid  102 ; a displacement rod  120 ; a cavity piston  122  coupled to the displacement rod  120  and extending into the hydraulic tube, thereby separating the inner cavity into a first volume  134  and a second volume  136 , and that includes an aperture  124  that allows flow of fluid from the first volume  134  to the second volume  136  during the compression movement of the wheel; and a valve plate  160  coupled to the end of the hydraulic tube  110  opposite the displacement rod no that defines a first fluid path  162  from the intermediary cavity  142  to the reservoir cavity  152  (also referred to as “damping flow” path) and a second fluid path from the reservoir cavity  152  to the first volume  134  (also referred to as “replenishment flow” path), and includes a damper valve  166  that substantially affects the flow of fluid through the first fluid path  162 . The valve plate  160  may also include an inlet/outlet valve  172  or a regeneration valve  170  that allows for additional fluid to enter the hydraulic strut  110  and/or extraneous fluid to exit the hydraulic strut  110  (for example, to increase or decrease, respectively, the suspending force provided by the suspension strut  100 ). The flow of fluid into and/or out of the hydraulic strut through the regeneration valve  170  and/or inlet/outlet valve  172  may be actively driven by one or more pumps, such as the digital displacement pump or motor as described in U.S. Pat. No. 5,259,738 entitled “Fluid Working Machine” and issued on 9 Nov. 1993, which is incorporated in its entirety by this reference, but may alternatively be any other suitable type of hydraulic pump. 
     In the preferred embodiments, the hydraulic tube  110  is coupled to the body of the vehicle and the displacement rod  120  is coupled to the wheel of the vehicle, which decreases the unsprung weight of the vehicle and may be beneficial in the dynamics of the vehicle. The hydraulic tube  110  and the displacement rod  120  preferably cooperate to translate forces felt by the wheel into a force substantially along the long axis of the suspension strut no. The hydraulic tube no preferably includes a vehicle interface  114  (shown in  FIG. 2 ). Similarly, the displacement rod preferably includes a wheel interface  126 . The vehicle interface  114  and the wheel interface  126  are preferably non-permanent attachment interfaces, for example, an eye that allows for a bolt to couple to the body of the vehicle or the wheel, screw holes to receive coupling screws, clips, Velcro, or any other suitable removable attachment mechanism. However the vehicle  114  and wheel interface  126  may alternatively be a substantially permanent attachment interface, for example, a welding joint. However, any other suitable interface type and arrangement of the suspension strut  100  relative to the vehicle may be used. 
     The suspension strut  100  of the preferred embodiments allows the base valve as seen in typical struts to also function to dampen the fluid flow within the strut, and functions to combine the dampening mechanism (the damper valve  166 ) and the base valve into the valve plate  160 . This provides a substantially more compact and relatively simple construction as compared to the prior art (shown in  FIG. 1 ). When desired, a valve plate  160  of any particular valve plate is preferably replaceable with another valve plate  160 . For example, if a first valve plate  160  malfunctions, a second valve plate  160  may be swapped in to replace the first valve plate  160  to restore function of the suspension strut  100 . Similarly, because most of the fluid control is contained within the valve plate  160 , the fluid flow within the strut may be adjusted by using different types of valve plates  160  without any substantial change to other components of the suspension strut  100 . For example, a first valve plate  160  with a first set of fluid flow control and characteristics may be replaced with a second valve plate  160  with a second set of fluid flow control and characteristics relatively easily. Additionally, by placing most of the fluid control within a removable valve plate  160 , the suspension strut  100  may be easily updated with alternative valve plates  160  that provide additional and/or other functions as the application of the strut  100  changes and/or as valve plate  160  designs change. For example, a first valve plate  160  with a passively actuated damper valve  166  may be swapped with a second valve plate  160  with an active damper valve  166 , changing the strut  100  from a passive suspension strut to a semi-active suspension strut. This feature may substantially increase the versatility and adaptability of the suspension strut  100  by allowing the same suspension strut  100  to be repeatedly used even as applications (or even conditions) may change. 
     The compressible fluid  102  the preferred embodiments functions to supply the suspending spring force hydraulic suspension strut. The compressible fluid  102  is preferably a silicone fluid that compresses about 1.5% volume at 2,000 psi, about 3% volume at 5,000 psi, and about 6% volume at 10,000 psi. Above 2,000 psi, the compressible fluid has a larger compressibility than conventional hydraulic oil. The compressible fluid, however, may alternatively be any suitable fluid, with or without a silicon component that provides a larger compressibility above 2,000 psi than conventional hydraulic oil. 
     The hydraulic tube  110  the preferred embodiments functions to contain compressible fluid  102  to provide damping force as the displacement rod  120  and the cavity piston  122  is displaced towards (compression stroke) and away from (rebound stroke) the valve plate  160  as the wheel of the vehicle experiences irregularities in the road, for example, as the vehicle turns or encounters bumps. The hydraulic tube  110  is preferably of a triple-tube construction that allows for substantially single-directional flow within the hydraulic tube  110  during both compression and rebound strokes, as shown in  FIG. 4  and  FIG. 5 , respectively. As shown in  FIG. 4 , during the compression stroke, the displacement rod  120  and cavity piston  122  are displaced toward the valve plate  160 . Thus, fluid  102  flows from the first volume  134  of the internal cavity to the second volume  136  through the aperture  124  of the cavity piston  122 . Because of the displacement rod  120  that is coupled to the cavity piston  122  and occupies a portion of the volume of the second volume  136 , a portion of the fluid  102  is displaced into the intermediary cavity  142  from the internal cavity  132  through an inner flow path. The inner flow path fluidly couples the intermediary cavity  142  to the internal cavity  132  near or below the lowest stroke point of the cavity piston  122 , and is preferably a valve in a second valve plate, but may alternately be an aperture through the inner tube wall, connection tubing or any other fluid connection. From the intermediary cavity  142 , the fluid flows through the first fluid path  162  of the valve plate  160  to the reservoir cavity  152 . As the fluid  102  flows through the first fluid path  162 , the fluid  102  flows through damper valve  166 , which provides a damping force to the fluid  102  and, subsequently, to the suspension strut  100 . As shown in  FIG. 5A , during the rebound stroke, the displacement rod  120  and cavity piston  122  are displaced away from the valve plate  160 . The aperture  124  preferably includes an aperture valve that is preferably a one-direction valve, fluid flow from the first volume  134  into the second volume  136  is permitted and flow from the second volume  136  into the first volume  134  is prevented. Thus, as the second volume  136  is decreased during the rebound stroke, fluid  102  is displaced from the second volume  136  into the intermediary cavity  142  (as fluid flow into the first volume  134  is prevented by the aperture valve), and follows a path substantially identical to the one described above for the compression stroke. Concurrently, the volume of the first volume  134  increases as the displacement rod  120  and cavity piston  122  are displaced away from the valve plate  160 . To prevent aeration, fluid  102  is directed into the first volume  134  to replenish the fluid contained in the internal cavity  132 , as shown in  FIG. 5B , and fluid  102  from the reservoir cavity  152  is directed through the second fluid path  164  of the valve plate  160  into the internal cavity  132 . The valve plate  160  preferably includes a replenishment valve coupled to the second fluid path  164  that is preferably a one directional valve that opens when the pressure in the first volume is decreased as a result of the rebound stroke. Both the aperture valve and the replenishment valve preferably do not increase the pressure of the fluid flowing through, and preferably allow both sides of the valve to become substantially equal pressure when the valve is opened. For example, the aperture valve and the replenishment valve may each be a check valve that allows substantially unhindered flow in one direction and prevents flow in an opposite direction. The aperture valve and the replenishment valve may alternatively be a butterfly valve, a ball valve, a diaphragm valve, a needle valve, or any other valve, and may be either passive or active. However, the aperture valve and replenishment valve may be of any other suitable type and arrangement. 
     The housing tube  150 , secondary tube  140 , and internal tube  130  are preferably steel tubes that withstand the pressure provided by the compressible fluid during either a compression or rebound stroke. In the suspension strut  100  of the preferred embodiments, the fluid control is mostly contained within the valve plate  160 . This substantially decouples fluid control from the housing, secondary, and internal tubes and allows for the housing, secondary, and internal tubes to be optimized as pressure vessels that better withstand the pressures that may be present in a compressible fluid strut system. Because each vehicle (or “application”) may require different characteristics from the suspension strut  100 , the geometry of each of the housing, secondary, and internal tubes, may be tailored to each application. The housing, secondary, and internal tubes of any suitable geometry preferably include a valve plate interface that interfaces with the valve plate  160 . The valve plate interface preferably allows for the valve plate  160  to couple to any suitable geometry of the housing, secondary, and internal tubes. The valve plate interface may include a first end that is customized for a specific geometry of housing, secondary, and internal tubes and a second end that is adapted to the geometry of the valve plate  160 . Alternatively, the valve plate interface may be formed into the housing, secondary, and internal tubes. For example, the housing, secondary, and internal tubes may each be a desired geometry for a substantial portion of the hydraulic tube no and taper into diameters that accommodate for a valve plate  160 . However, the valve plate interface may be any other suitable arrangement. 
     As described above, the valve plate  160  functions to provide most of the fluid control within the suspension strut  100 . The valve plate  160  preferably defines a first fluid path  162  from the intermediary cavity  142  to the reservoir cavity  152  (also referred to as “damping flow” path) and a second fluid path from the reservoir cavity  152  to the first portion of the inner cavity  132  (also referred to as “replenishment flow” path), and includes a damper valve  166  that substantially affects the flow of fluid through the first fluid path  162 . The valve plate  160  is preferably mounted to the end of the hydraulic tube  110  opposite of the displacement rod, as shown in  FIGS. 2 and 3 , but may alternatively be arranged in any other suitable location. As shown in  FIGS. 2A ,  2 B, and  3 A, the valve plate  160  is preferably clamped onto the housing, secondary, and inner tubes using a cap  180 . The cap  180  may include a plurality of holes that receive bolts that function to apply pressure onto the cap  180  to clamp the valve plate  160  onto the tubes  150 ,  140 , and  130 . However, the valve plate  160  may be assembled to the hydraulic tube no using any other suitable mechanism or arrangement. The valve plate  160  may also include a sealant, such as o-rings, that substantially seal the interface between the valve plate  160  and the housing, secondary, and inner tubes to substantially prevent fluid leakage. 
     As shown in  FIG. 3B , the valve plate  160  defines a first fluid path  162  between the intermediary cavity  142  and the reservoir cavity  152 . A damper valve  166  is coupled to the first fluid path  162  to substantially affect the flow of fluid  102  through the first fluid path  162 , providing the damping force on the fluid  102  and, subsequently, the suspension strut  100 . The damper valve  166  is preferably a passive valve in a first variation, a manually actuated valve in a second variation, an active valve in a third variation, or a regenerative valve in a fourth variation. 
     In the first variation, the damper valve  166  is a passive valve. The passive damper valve  166  is preferably a one directional valve that allows fluid flow when the pressure difference between a first side (side closest to the intermediary cavity  142 ) and the second side (side closet to the reservoir cavity  152 ) is at a certain level. The damper valve  166  of the preferred embodiments is preferably a disc valve (or shim stack) where fluid deflects the disc valve in one direction when a certain pressure differential is reached between either side of the disc valve, opening the valve for fluid flow, and where the disc valve prevents fluid flow in the opposite direction. Disc valves, which are generally robust, reliable, and consistent, are often used in a damper valve. Because typical semi-active or continuously variable damping control systems require active damper valves, however, disc valves (which are generally passive damper valves) are typically not used in triple-tube type strut architectures. Further, because of the fluid flow paths in such systems, it is difficult-to-impossible to apply a disc valve within a conventional semi-active or continuously variable damping control systems that utilize the triple-tube type strut. The valve plate  160  of the preferred embodiments, however, allows for a disc valve to be used in a triple-tube type strut architecture by, as shown in  FIG. 3B , defining a first fluid path  162  that directs fluid flow in a flow direction suitable for a disc valve from the intermediary cavity  142  and directs flow from the disc valve to the reservoir cavity  152 . Additionally, as will be described later, the same disc valve may be converted into a manually actuated or active arrangement. However, the damper valve  166  of the first variation may be any other suitable type of passive damper valve, such as a check valve, a ball valve, check valve, or needle valve. 
     In the second variation, the damper valve  166  is a manually actuated valve. As an example, a technician may use the manually actuated valve damper valve  166  to adjust the damping characteristics of the suspension strut  100 . The manually actuated damper valve  166  may be a bi-state valve that allows for a high damping force state and a low damping force state, but may alternatively be variable with a plurality of degrees of damping forces. As mentioned above, the disc valve exhibits damping properties that are desirable in a damper valve. Thus, the damper valve  166  of the second variation preferably includes a disc valve and an actuator  167 , as shown in  FIGS. 6A and 6B . The actuator  167  of the second variation of the damper valve  166  is preferably a manual actuator. The actuator  167  preferably includes a piston  169  that is arranged over the disc valve that functions to provide an adjustable pressure onto the disc valve to adjust the damping force provided by the disc valve. More specifically, because fluid flow must deflect the disc valve in order to flow through the valve, by applying a pressure onto the disc valve through the piston  169 , the force necessary to deflect the disc valve increases, increasing the damping force on the fluid  102  flowing through the disc valve. In a first version of the actuator  167  of the manually actuated damper valve  166 , the actuator  167  may include a screw coupled to the piston  169  that is accessible by a user. To adjust the damping force provided by the disc valve, a user may tighten the screw to push the piston  169  towards disc valve. In a second version of the manually actuated damper valve  166 , the valve plate  160  may function to define a third fluid path  165  that directs fluid  102  from the intermediary cavity  142  to the reservoir cavity  152 , as shown in  FIGS. 6A and 6B . The third fluid path  165  preferably passes over the top of the piston  169 , applying a fluid pressure across the top of the piston  169 . Because damping force is preferably applied to the fluid  102  that flows from the intermediary cavity  142  to the reservoir cavity  152 , a portion of the already existing flow between the intermediary cavity  142  and the reservoir cavity  152  may be relatively easily directed across the piston  169  when a damping force is desired. The actuator  167  of this variation preferably includes a fluid flow valve  163  that is manually actuated, for example, a needle valve, which is coupled to the third fluid path  165  downstream of the piston  169 . By adjusting the rate of fluid flow through the third fluid path  165 , the pressure provided by the fluid  102  onto the piston  169  may be adjusted. As shown in  FIG. 6B , when the fluid valve  163  is closed, fluid flows into the third fluid path  165 , but cannot flow into the reservoir cavity  152 , resulting in increased fluid  102  pressure onto the piston  169 , and subsequently, increased damping force provided by the damper valve  166 . As shown in  FIG. 6A , when the fluid valve  163  is open and fluid flows through the third fluid path  165  into the reservoir cavity  152 , the pressure applied by the piston  169  is low, as the pressures in the first  134  and third  165  flow paths are substantially equivalent. However, the manually actuated damper valve  166  may be of any other suitable arrangement. 
     In the third variation, the damper valve  166  is an active valve, allowing the suspension strut  100  to function as a semi-active suspension strut. The active damper valve  166  may be a bi-state valve that allows for a high damping force state and a low damping force state, but may alternatively be variable with a plurality of degrees of damping forces. The active valve variation of the damper valve  166  is preferably used to provide substantially instantaneous adjustments of the damping force provided by the suspension strut  100 , preferably during use in a vehicle while the vehicle is in motion, for an example, if a bump in the road is detected or if the vehicle makes a sudden turn. As mentioned above, the suspension strut  100  may also be used with an active control suspension system, which may function to actively change the suspending force provided by the suspension strut  100  by increasing or decreasing the amount of fluid  102  contained within the suspension strut  100 . Vehicle dynamics may be controlled on more than one level by combining a semi-active suspension strut  100  with an active control suspension system, providing a vehicle that can substantially quickly adapt to a vast variety of driving conditions. The active damper valve  166  is substantially similar to the manual damper valve  166  as described above. The active damper valve  166  preferably also includes a disc valve and an actuator  167 , as shown in  FIGS. 6A and 6B . The actuator  167  of the third variation of the damper valve  166  is preferably an active actuator that may be electronically actuated, for example, by a processor or remotely by a user. The active actuator  167  preferably also includes a piston  169  that is arranged over the disc valve that functions to provide an adjustable pressure onto the disc valve to adjust the damping force provided by the disc valve. A first variation of the actuator  167  of the active damper valve  166  is substantially similar to the first variation of the actuator  167  of the manually actuated damper valve  166 . The actuator  167  of the active damper valve  166  of the first variation includes a motor that is coupled to a screw that functions to raise or lower the piston  169  away from or towards the disc valve, adjusting the damping force provided by the disc valve. A second variation of the actuator  167  of the active damper valve  166  is substantially similar to the second variation of the actuator  167  of the manually actuated damper valve  166 . The valve plate  160  functions to define a third fluid path  165  that directs fluid  102  from the intermediary cavity  142  to the reservoir cavity  152  to provide pressure across the top of the piston  169 , thus adjusting the pressure provided by the piston onto the disc valve and adjusting the damping force provided by the disc valve. The actuator  167  of the active damper valve  166  of the second variation includes a fluid flow valve  163  that is active, for example, a pilot valve that is actuated by a solenoid or any other suitable type of actuated fluid valve, coupled to the third fluid flow path  165  downstream of the piston  169 . The fluid flow valve  163  functions provide control of the fluid flow through the third fluid path  165  substantially identical to the manual fluid flow valve  163 . In a third variation, the stiffness of the damper valve may be electronically controlled by using materials that exhibit different strain properties with the application of heat or electricity, or by using electromagnets. However, the active damper valve  166  may be of any other suitable arrangement. 
     In the fourth variation, the damper valve  166  is a regenerative valve, as shown in  FIG. 7 . In this variation, the damper valve  166  may be either passive or active. As fluid flow is damped, a significant amount of energy is dissipated. In conventional dampers, the energy is dissipated as heat and substantially wasted. The damper valve  166  of the fourth variation, however, provides a method and means to harness the energy, in particular, to convert the energy into electrical energy. In a first example, shown in  FIG. 7A , the damper valve  166  may include an impeller that is coupled to a motor. As fluid flows past the impeller, the impeller is caused to spin, and the energy used to spin the impeller is used to generate electricity in the generator. The fluid  102  is damped as a result because of the work used to spin the impeller. In the passive version of the damper valve  166  of the fourth variation, the work required to spin the impeller is substantially constant at all times. In the active version of the damper  166  of the fourth variation, increasing the electrical generation required from the generator may increase the work required to spin the impeller, increasing the damping of the fluid  102  (examples shown in  FIGS. 7B and 7C ). However, any other variation of a damper valve  166  that is regenerative may be used. 
     As described above, the first, second, and third variations (and potentially the fourth variation) all preferably utilize a similar construction that includes a disc valve. Because of this feature, it is conceivable that the same housing for the valve plate  160  may be used with different variations of the damper valve  166 , allowing a valve plate  160  that was outfitted with a passive damper valve  166  to be upgraded to an active damper valve  166  with the same housing for the valve plate  160 . 
     The valve plate  160  preferably includes one of the above variations of damper valve  166 , but may alternatively include any number or suitable combinations of the above variations. For example, the regenerative damper valve  166  of the fourth variation may be combined with the passive damper valve  166  of the first variation. More specifically, the valve plate  160  of this variation may also include both an impeller/generator assembly and a disc valve that cooperate to provide two fluid flow paths in situations with substantially high volume of fluid flow that a regenerative valve alone may not be able to accommodate. Additionally, because the regenerative valve includes a substantial number of moving parts, the regenerative valve may fail and prevent fluid from flowing through. By allowing a second path for fluid flow, the suspension strut  100  may continue to function. However, the valve plate  160  may be any other suitable variation. As mentioned above, the suspension strut  100  of the preferred embodiments preferably allows for different valve plates  160  to be used with the same hydraulic tube body, meaning a suspension strut  100  that originally used a valve plate  160  with a damper valve  166  of the first variation may be exchanged with a valve plate  160  with a damper valve  166  of the second, third, or fourth variation, allowing the suspension strut  100  to function differently without substantial changes to any other component of the suspension strut  100 . 
     As shown in  FIG. 8 , the suspension strut system  100  may additionally include a regenerative valve and a pump, fluidly coupled to the first fluid path  162 , to form a regenerative suspension strut  101 . Much like the fourth variation of the damper valve, the regenerative suspension strut  101  functions to regenerate energy from fluid flow within the strut, and is preferably also operable in non-regenerative modes. 
     The regenerative suspension system  101  may additionally include a third flow path  165  (“regenerative fluid path” or “pump path”), to which the regenerative valve and pump are coupled, wherein the third flow path fluidly couples the intermediary cavity to the reservoir cavity through the valve plate, preferably in parallel with the first flow path  162   134 , more preferably sharing an inlet and an outlet with the first flow path  162 . The regenerative suspension strut system  101  preferably operates in a first mode that provides a damping force substantially internally within the suspension strut  100  by directing the displaced compressible fluid  102  to a damper valve  166  and a second mode that provides a damping force substantially external to the suspension strut  100  by directing the flow of compressible fluid  102  into the pump  190  to drive the pump  190  and recover energy. In the second mode, the force required to drive the pump  190  provides the damping force. The regenerative suspension strut system  101  may include a third mode where the damping force is provided both through the damper valve  166  and by directing flow of compressible fluid into the pump  190  and/or a fourth mode where the pump  190  pumps fluid  102  back into the suspension strut  100 . The damper valve  166  and the regeneration valve  170  may be thought of as operating in parallel such that fluid flow from the strut  100  may flow to either valve depending on the state of the valve. Alternatively, the damper valve  166  and the regeneration valve  170  may be the same physical valve with multiple modes to function to direct fluid into the pump  190 , to dampen fluid  102 , and/or to both direct fluid into the pump  170  and to dampen the fluid  102 . Similarly, to maintain operation of suspension strut  100  when the processor and/or the electronics of the damper valve  166  and/or the regeneration valve  170  fail, the damper valve  166  is preferably of the type of valve where the failure mode still provides substantial damping force (for example, for a damper valve  166  that is a shim stack valve that increases damping force with increasing stiffness, the shim stack preferably fails in a semi-stiff orientation) to the suspension strut  100 . However, any other suitable arrangement of the damper valve  166  and the regeneration valve  170  may be used. 
     The flow pattern of the regenerative suspension strut  101  during the compression stroke is preferably substantially similar to that described above. As shown in  FIG. 9 , during the compression stroke, the displacement rod  120  and cavity piston  122  are displaced toward the valve plate  160 . Thus, fluid  102  flows from the first volume  134  of the internal cavity to the second volume  136  through the aperture  124  of the cavity piston  122 . Because of the displacement rod  120  that occupies a portion of the volume of the second volume  136  and is coupled to the cavity piston  122 , the volume available for the displaced compressible fluid  102  to occupy is less in the second volume  136  than in the first volume  134 , and the pressure of the fluid within the second volume  136  increases. A portion of the fluid  102  may be displaced into the intermediary cavity  142  from the internal cavity  132  and, from the intermediary cavity  142 , the fluid flows through the first and/or third fluid path  162  of the valve plate  160 . In the first mode, the compressible fluid  102  is then directed to the damper valve  166  to apply a damping force on the compressible fluid  102  (shown in  FIG. 8 ). In the second mode, the fluid  102  is directed through the regeneration valve  170  to the pump  190  to drive the pump  190  and to recover energy. Alternately and/or additionally, in the third mode, the fluid  102  is directed to both the damper valve  166  and the regeneration valve  170  (shown in  FIGS. 9 and 11A ). However, any other suitable arrangement of the flow during the compression stroke may be used. 
     Likewise, the flow pattern of the rebound stroke is substantially similar to that described above. As shown in  FIG. 10A , during the rebound stroke, the displacement rod  120  and cavity piston  122  are displaced away from the valve plate  160 . The aperture  124  preferably includes an aperture valve that is preferably a one-direction valve that only allows fluid flow from the first volume  134  into the second volume  136  and not from the second volume  136  to the first volume  134 . Thus, the fluid pressure within the second volume  136  is again increased and follows a path substantially identical to the one described above for the compression stroke, potentially further driving the pump  190  to recover energy during the rebound stroke. Fluid  102  is directed into the first volume  134  from a compliant volume  191  (as shown in  FIG. 8 ) to prevent aeration within the first volume  134  as the suspension strut  100  extends, as shown in  FIG. 10B . This compliant volume  191  may be the reservoir cavity  152 , such that fluid  102  from the reservoir cavity  152  is directed through the second fluid path  164  of the valve plate  160  into the internal cavity  132 , as shown in  FIG. 11B . The valve plate  160  preferably includes a replenishment valve coupled to the second fluid path  164  that is preferably a one-directional valve that opens when the pressure in the first volume is decreased as a result of the rebound stroke. 
     As shown in  FIGS. 8 ,  12  and  13 , the regenerative suspension strut system  101  may function to direct the compressible fluid  102  to only the damper valve  166  (the first mode), only the regeneration valve  170  (the second mode), or to both the damper valve  166  and the regeneration valve  170  (the third mode). The regenerative suspension strut system  101  may include a processor that determines the mode depending on the use scenario, the user preferences, and/or any other suitable factor. In a first example, directing fluid through the regeneration valve  170  and into the pump  160  to drive the pump may provide a substantially slower damping response than directing fluid into the damper valve  166 . In this first example, when the processor detects a maneuver of the vehicle that requires a faster suspension response, for example, during a fast turn or a substantial bump in the road, the processor may select to operate in the first mode. In a second example, a user may select to operate in the first mode because of the increased responsiveness of the suspension system. For example, the user may plan on driving quickly on mountain roads that include a substantial number of turns. In a third example, the user may know that the road ahead contains a substantial amount of irregularities, for example, an unpaved road. Because of the high number of irregularities, the instances in which energy may be recovered from the suspension system may be high and the user may select the second mode. In a fourth example, the user may select a “fuel economy” mode, which instructs the processor to put a preference on utilizing the second mode. In this example, the user does not instruct a particular mode to operate in, but instructs the processor to prioritize one mode over another and allows the processor to determine the appropriate mode based on the driving scenario. In a fifth example, the processor may select to operate in the fourth mode for increased flexibility where flow is directed to both the damper valve  166  and the regeneration valve  170 . In this example, the processor may function to determine the percentage of fluid that is directed to the damper valve  166  and to the regeneration valve  170 . For example, the amount of damping force that is provided by the pump  190  may be an amount that is determined by the characteristic of the pump  190  (such as the initial starting pressure necessary). If an increased damping force is necessary, the processor may determine to route more fluid to the damper valve  166 . Similarly, the because the damper valve  166  and the pump  160  may be thought of as providing damping force in parallel to the suspension system, the processor may determine a desired amount of damping force and evaluate a percentage flow combination between the damper valve  166  and pump  160  to achieve the desired damping force. In a sixth example, the processor may detect that the pump  190  is malfunctioning and may determine to direct all fluid flow into the damper valve  166 . However, any other suitable selection of the operation modes of the regenerative suspension strut system  101  may be used. 
     As described above, the pressure in the compressible fluid  102  used to drive the pump  190 . However, energy is used to direct fluid  102  back into the first volume  134  to replenish the volume in the first volume  134  during the rebound stroke. To improve the fuel economy of the vehicle, the pressure at which fluid  102  is directed back into the first volume  134  is preferably substantially less than the pressure of the fluid  102  used to drive the pump  190 , which results in a net positive energy recovery in the regenerative suspension strut system  101 . The rate and/or pressure at which the fluid  102  is directed back into the first volume  134  during the rebound stroke is preferably actively controlled to increase energy efficiency. Similarly, the rate and/or pressure at which the fluid  102  is displaced from the second volume  126  is preferably also actively controlled to balance with the pressure of fluid injected into the first volume  124 . In typical suspension strut systems, the rebound stroke is passive and is substantially dependent on the type of road irregularity, for example, the shape of the bump on the road. In other words, energy that could have been captured from the compression of the suspension due to the bump in the road is used in the uncontrolled retraction of the suspension after the bump. By substantially controlling the rebound stroke through controlling the rate and/or pressure at which fluid  102  is injected into the first volume  134  and/or through controlling the rate and/or pressure at which fluid  102  is displaced from the second volume  136 , energy recovery in the regenerative suspension strut system  101  may be substantially improved over a typical suspension system. This control may be obtained by controlling the fluid flow rate with the pump  190 , wherein the pump  190  controls fluid flow into the first volume  134  indirectly by controlling the fluid ingress into the reservoir cavity. Alternately, the pump  190  may be directly coupled to the first volume  134 , wherein the valve plate further includes a fourth flow path coupling the pump outlet to the first volume  134  and a second replenishment valve, disposed within the fourth flow path, that allows one-way fluid flow from the pump to the first volume  134 . 
     The pump  190  and damper valve  166  may also function to provide a retractive force on the regenerative suspension strut  101   100 . Typical suspension struts are configured to provide a force to suspend the vehicle, or, in other words, a force to extend the strut, and compresses only when there is an external force such as a bump or a turn, and typically do not provide a force to compress the strut, or a retractive force. An active suspension utilizing a single acting cylinder actuator may change the height of the strut, but cannot provide a retractive force unless the strut is fully extended. By facilitating control over the compressible fluid flow to/from the second volume  136 , the regenerative suspension strut system  101  is able to provide such a retractive force. As shown in  FIGS. 9 and 10 , fluid flow from the first volume  134  to the second volume  136  results in an increased pressure within the second volume  136 , which is relieved when the fluid  102  is forced through the damper valve  166  and/or pump  190  and damped. However, if an imbalance between the flow rate out through the damper valve  166  and/or the pump  190  and flow rate into the second volume  136  is present, the pressure within the volume of fluid contained within the second volume  136  cannot be relieved, and a force to push the cavity piston  122  back towards the valve plate  160  is present, providing a retractive force. Varying the amount of fluid that is bled through the damper valve  166  and/or directed to pump  190  may control this retractive force. This may be particularly useful if a particular position of the strut that is shorter than the fully extended is desired. An additional retractive force may be achieved by driving the pump  190  to pump fluid into the second volume  136 , as shown by the dashed line  4   a  in  FIG. 14 . Alternatively, if the pump  190  is driven to pump fluid  102  out of the second volume  136 , the retractive force may be decreased to substantially zero and/or a force to extend the suspension strut  100  may result. This pull force may be used to relatively quickly restore the height of the triple tube strut  100  or for any other suitable use. However, any other suitable method to produce a retractive force in the suspension strut  100  may be used. 
     As shown in  FIG. 14 , the regenerative suspension strut system  101  of the preferred embodiments functions to recover a substantial amount of energy used to operate the triple tube strut  100 . The X-axis of  FIG. 14  represents displacement frequency seen in the suspension strut  100 , for example, from irregularities in the road while the Y-axis represents the force that the suspension strut provides on the vehicle, in other words, the suspending force. Curve  1  represents the equilibrium position of the triple tube strut  100 , which changes depending the weight of the vehicle, the payload of the vehicle, or any other suitable parameter. Curve  2  represents the force preferably provided by the regenerative suspension strut system  101  to the vehicle (for example, through a suspension strut  100  of the triple tube strut construction), in other words, the operating region of the suspension strut  100 , and Curve  4  represents the retractive force provided by the suspension strut  100 , as described above. The shaded region  3  describes the operating region of the suspension strut from which energy may be recovered, in particular, the energy from irregularities on the road. Portion  3 A represents the region of irregularities that require suspension response speeds that may be provided by the pump  190  while Portion  3 B (cross-hatched) represents the region of irregularities that require a faster response, for example, when the damper valve  166  is used to provide the damping force. In typical driving scenarios, a majority of the irregularities encountered may require suspension response speeds that may be provided by the pump  190 . As a result, a substantial portion of the energy from road irregularities may be recovered. The substantially direct linkage between the suspension strut  100  and the pump  190  also decreases the amount of parasitic energy losses within the regenerative suspension strut system  101 , which increases the efficiency at which energy may be recovered. 
     As shown in  FIG. 15 , the regenerative suspension strut system  101  of the preferred embodiments may also include a second compliant volume  192  that is preferably isolated from the system when fluid  102  is actively directed to the pump  190  and may be connected when fluid  102  is not directed to the pump  190 . The second compliant volume  192  receives fluid  102  from damper valve  166  to alleviate the pressure of the fluid  102  that would otherwise be used to drive the pump  190 . In particular, the suspension strut  100  may be operated at higher pressures when fluid is actively directed to the pump  190  because increased pressure in the fluid  102  is substantially quickly alleviated through the pump  190 . However, when fluid is not actively directed to the pump  190 , the pressure within the triple tube strut  100  may be too high for passive operation (e.g., the strut  100  may be too stiff) and fluid may then be directed to the second compliant volume  192  to decrease the pressure within the suspension strut  100 . This embodiment preferably utilizes the third variation of the damper valve  166  (such as that shown in  FIG. 7B ), but may alternately utilize any variation of the damper valve  166  as described above. However, any other suitable arrangement of the fluid flow to allow both internal damping through the damper valve  166  and external damping through the pump  190  may be used. 
     As described above, the pump  190  may function to direct fluid back into the suspension strut  100  to replenish flow within the suspension strut  100 . Alternatively, the regenerative suspension strut system  101  may include a reservoir  194 , as shown in  FIG. 16 , from which the suspension strut  100  may draw fluid  102  to replenish the fluid  102  within the suspension strut  100 . In this variation, the suspension strut  100  may function substantially similarly to a pump that pumps fluid  102  at substantially high pressures during the compression stroke into the pump  190  to drive the pump  190  and recover energy, and to draw fluid from the reservoir  194  at a substantially lower pressure during the rebound stroke. During the compression stroke, the pump  190  functions to dampen fluid flow to provide a damping force and during the rebound stroke, the reservoir  190  provides fluid at a lower pressure than the fluid used to drive the pump  190  to recover energy, satisfying the pressure relationships for energy recovery as described above. In this variation, the regeneration valve  170  preferably directs fluid  102  during the compression stroke from the suspension strut  100  into the pump  190  and preferably directs fluid  102  from the reservoir  194  into the suspension strut  100  from the reservoir  194 . This variation of the regenerative suspension strut system  101  is preferably otherwise substantially similar to the variations as described above. 
     As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.