Patent Abstract:
A vibration damper piston includes a piston body with a bore from which first and second apertures respectively provide paths to first and second chambers of the vibration damper. A valve spool in the bore defines a pilot chamber and controls fluid flow between the first and second apertures. First and second springs bias the valve spool in opposing directions. A control orifice provides a continuous fluid path between the first chamber and the pilot chamber, and a variable orifice provides another fluid path between the second chamber and the pilot chamber. An actuator is operably connected to adjust the variable orifice in response to a control signal.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to apparatus, such as shock absorbers, for damping vibration in a motor vehicle, and more particularly to such apparatus having a dynamically adjustable damping characteristic. 
     2. Description of the Related Art 
     Hydraulic shock absorbers are commonly placed between the axles and the frame of a motor vehicle to reduce transmission of vibration from the wheels. Large trucks and off-road vehicles used in construction and agriculture incorporate similar vibration damping devices between the vehicle frame and the operator cab or between a seat and the vehicle body. The purpose of all these apparatus is to isolate the occupants from vibrations produced as the vehicle travels over the ground. 
     A typical prior hydraulic vibration damper comprised a cylinder divided by a damping piston into two working chambers filled with a fluid, such as oil. The cylinder was attached to either the axle or the frame of the vehicle and the piston was attached by a rod to the other vehicle component. Thus movement of the axle relative to the frame caused the piston to slide within the cylinder, thereby expanding one chamber and contracting the other chamber. Motion which retracted the piston rod into the cylinder is referred to as compression and motion in the opposite direction is called rebound. The damping piston had one or more fixed orifices through which the fluid flowed between the cylinder chambers. The orifices restricted the rate of that fluid flow, thereby limiting the rate of piston movement to dampen the vibration. Such prior apparatus provided a fixed damping characteristic for any given velocity. 
     Subsequently, adjustable vibration dampers were developed that included a bypass passage arranged between the two working chambers. An electrically operated proportional valve and a pressure-dependent valve were placed in series and activated during rebound and compression. The activation of the electrically operated valve was controlled in response to vibration of the vehicle detected by a sensor and opened the bypass passage by an amount that provided proportionally variable damping effect. The pressure-dependent valve opened only in response to pressure exceeding a defined level. 
     The bypass passage and its valves were mounted outside the vibration damper cylinder and increased the space required for that assembly. It is desirable to incorporate damping adjustment components into the cylinder and make a more compact assembly. 
     SUMMARY OF THE INVENTION 
     A vibration damper has a cylinder and a piston assembly with a rod extending out of the cylinder. The piston assembly includes a piston that is slideably received within the cylinder, thereby defining a first chamber and a second chamber each having fluid therein. 
     A novel piston comprises a piston body that has a bore, a first aperture extending between the bore and the first chamber, and a second aperture extending between the bore and the second chamber. A primary valve spool is moveably received within the bore, thereby defining a pilot chamber in the bore on one side of that spool. Movement of the primary valve spool into different positions in the bore controls fluid flow between the first and second aperture, and thus between the two chambers. In the preferred embodiment of the piston, the primary valve spool has a first position which allows fluid to flow between the first aperture and the second aperture, a second position which allows fluid to flow between the first aperture and the second aperture, and a third position that is between the first and second positions in which fluid flow between the first aperture and the second aperture is blocked. 
     A control orifice is provided through which fluid can flow continuously between the first chamber and the pilot chamber, and a variable orifice is provided through which fluid flows between the second chamber and the pilot chamber. An actuator, such as an electrical solenoid for example, is operably connected to vary the variable orifice in response to a control signal. 
     In one embodiment of the novel piston, the control orifice has a fixed size, and a fixed pilot orifice provides another flow path between the second chamber and the pilot chamber that is in parallel with the variable orifice. 
     Another aspect of the vibration damper piston is a unique combination of springs. A first spring provides resistance to motion of the primary valve spool in one direction, and a second spring provides resistance to motion of the primary valve spool in an opposing direction. In a preferred version of the piston, the first spring provides resistance to motion of the primary valve spool into the first position, but does not aid motion into the second position, and the second spring resists motion of the primary valve spool into the second position and aids motion into the first position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a hydraulic vibration damper that incorporates a novel piston assembly; 
         FIG. 2  is a longitudinal cross sectional view of the piston assembly in a de-energized state within a cylinder of the hydraulic vibration damper; 
         FIG. 3  is a side elevational view of the piston assembly; 
         FIG. 4  is a schematic diagram of a hydraulic circuit formed by components of the piston assembly; 
         FIG. 5  is a cross sectional view of the piston assembly during a compression phase if vibration damping; 
         FIG. 6  is a cross sectional view of the piston assembly during a rebound phase if vibration damping; and 
         FIG. 7  depicts an alternative version of a hydraulic vibration damper in which both a pilot orifice and a control orifices are variable. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference to  FIG. 1 , a mono-tube vibration damper  10  has first and second couplings  12  and  14 , which enable the device to be attached between two components of a vehicle to reduce transmission of vibrations from one component to the other. The first coupling  12  is at an end of a cylinder  16  and typically is attached to the wheel suspension of the vehicle. The second coupling  14  at one end of a piston assembly  18  typically is attached to the body of the vehicle. The piston assembly  18  has a tubular skirt  20  extending around the cylinder  16  in a manner that allows the piston assembly and the cylinder to move longitudinally with respect to each other. The particular vibration damper  10  has an external spring  22  between a flange  21  on the cylinder  16  and another flange  23  on the piston assembly  18 . However, the present invention can be employed with vibration dampers that do not have an external spring. Motion of the two vehicle components attached to couplings  12  and  14  produces compression of the vibration damper  10 , in which the two couplings come toward each other, and produces an opposite motion known as rebound. The present invention provides a novel piston for use with a variety of standard vibration dampers, thus the remainder of the vibration damper  10  has a conventional design. 
     With reference to  FIG. 2 , motion of the two vehicle components moves a piston  30  within the cylinder  16 , wherein the piston is attached to a piston rod  32 , both of which are parts of the piston assembly  18 . Specifically, the piston rod  32  is threaded onto a fitting  33  at one end of the piston  30  and extends through an opening (not shown) in the upper end of the cylinder  16  to the second coupling  14 . The piston  30  includes a piston body  34  with an annular, resilient seal  35  there around so as to be snuggly, yet slideably, received within the cylinder  16 . A compression chamber  24  and a rebound chamber  26  are defined within the cylinder  16  on opposite sides of the piston  30  and are filled with a fluid, such as oil. 
     The piston body  34  has a longitudinal bore  36  extending there through with one end of the bore opening into the compression chamber  24  and the other end of the bore being closed by a first pole piece  70  from which the piston rod fitting  33  projects. With addition reference to  FIG. 3 , several compression apertures  37  extend to the piston bore  36  from the compression chamber  24  and several rebound apertures  38  extend to that bore from the rebound chamber  26 . A pilot passage  39  from the rebound chamber  26  also opens into the piston bore  36 . 
     A spring assembly  40  is located in the open end of the piston body  34  at the compression chamber  24 . That spring assembly  40  comprises a first adjustor  42 , a second adjustor  46 , a retainer  47 , and a first spring  48 . The disk-shaped, first adjustor  42  is threaded into the open end of the piston body  34  and locked in place by a set screw  41 . The first adjustor  42  has a plurality of fluid flow apertures  43  extending there through and open into a spring chamber  44 . The second adjustor  46  is threaded into a central aperture in the first adjustor  42  and extends into the spring chamber  44 , terminating at an end with an outward extending flange  45 . The circular plate-shaped retainer  47  extends around the second adjustor  46  abutting the flange  45  and the first spring  48  is captivated between the retainer  47  and the interior surface of the first adjustor  42 . A preload force of the first spring  48  is varied by the amount that the second adjustor  46  is threaded into or out of the first adjustor  42 . 
     A valve assembly  49  is located in the piston body  34  and comprises a primary valve spool  50  slideably located within the piston bore  36 . The primary valve spool  50  is illustrated in the centered, closed position in which lands on the spool block fluid flow between the compression apertures  37  and the rebound apertures  38 . The primary valve spool  50  has a first metering notch  52  between a first land  51  and the end of the spool that faces the retainer  47 . As will be described, the first metering notch  52  provides a fluid path between the compression and rebound apertures  37  and  38  when the primary valve spool  50  moves upward in the orientation of the vibration damper  10  in  FIG. 2 . The primary valve spool  50  has a second metering notch  54  located between second and third lands  53  and  55  at the ends of the primary valve spool. The second metering notch  54  provides a path between the compression and rebound apertures  37  and  38  when the primary valve spool  50  moves in the downward direction. References herein to directional movement and relationships, such as up and down, or top and bottom, are with respect to the orientation of the components in the drawings, which may not be the orientation when the vibration damper  10  is attached to a vehicle. 
     A pilot chamber  56  is defined in the piston bore  36  on the remote side of the primary valve spool  50  from the first spring  48 . A flow passage  58  extends between the rebound chamber  26  and the pilot chamber  56  and a pilot orifice  60  restricts the flow of fluid through that flow passage. For example, the pilot orifice has a diameter of 1.55 mm. A control passage  62  extends between the compression chamber  24  and the pilot chamber  56  and has a control orifice  64  therein that restricts the flow of fluid there through. For example, the control orifice has a diameter of 2.50 mm. As will be described, controlling pressure within the pilot chamber  56  controls motion of the primary valve spool  50  and the stiffness of the vibration damper  10 . 
     The flow of fluid between the pilot chamber  56  and the rebound chamber  26  also is controlled by a pilot valve  61  that is operated by a solenoid actuator  66  located within the upper end section of the piston body  34 . Specifically, the solenoid actuator  66  comprises an electromagnetic coil  68  wound around a conventional bobbin. The first pole piece  70  of magnetic material extends downward into the electromagnetic coil  68  and is held against the coil by a retaining ring  72  that threads onto the upper end of the piston body  34 . The piston rod  32  threads onto the fitting  33  which projects outward from the first pole piece  70 . The first pole piece and the piston rod have apertures through which wires of a cable  74  extend to provide an electrical connection to the electromagnetic coil  68 . A non-magnetic solenoid tube  76  has a cylindrical portion which extends into the lower end of the electromagnetic coil  68  and has an outwardly extending flange that engages an inner shoulder of the bore  36  in the piston body  34 . A tubular, second pole piece  78  is securely pressed into the solenoid tube  76  within the electromagnetic coil  68  and projects downward therefrom in the piston bore  36  toward the primary valve spool  50 . The pilot passage  39  extends through the second pole piece  78  opening into a bore  86  in that pole piece. A second spring  80  biases the primary valve spool  50  away from the second pole piece  78 . The distance that the second pole piece  78  is pressed into the bore  36  of the piston body  34  determines the preload force of the second spring  80 . 
     The solenoid actuator  66  also includes an armature  82  of ferromagnetic material that slides up and down within the two pole pieces  70  and  78  under the influence of a magnetic field generated by the electromagnetic coil  68 . A tubular pilot spool  84  is secured to the lower end of the armature  82  and slides within a bore  86  in the second pole piece  78 . The pilot spool  84  has an exterior annular notch  88  which in different positions of the pilot spool provides a path for fluid to flow between the pilot passage  39  and the pilot chamber  56 . A third, or pilot, spring  90  biases the pilot spool  84  and the armature  82  with respect to the second pole piece  78  in an upward direction into the electromagnetic coil  68 . A set screw  91  threaded into the second pole piece  78  adjusts a pre-load force of the third spring  90 . 
       FIG. 3  shows the exterior of the piston  30  with the resilient seal  35  extending there around. The compression apertures  37  are located on the lower side of the sealing ring, whereas the rebound apertures  38  are located above the sealing ring. This view of the piston body  34  also illustrates the relative position of the pilot passage  39  and the pilot orifice  60 . 
     The components of the piston  30  define a hydraulic circuit that is depicted schematically in  FIG. 4 . Note that mono-tube type vibration damper  10  also has a free-floating, dividing piston  94  that separates the compression chamber  24  from a gas charge chamber  96 . During operation, the dividing piston  94  moves as the piston rod  32  moves in and out of the cylinder  16  and compensates for the volume of the piston rod to keep the compression and rebound chambers  24  and  26  full of oil at all times. 
     Upon installation on a vehicle, exertion of an external force either extends or contracts the vibration damper  10 , thereby causing the piston  30  to slide within the cylinder  16 . Depending upon the direction of the piston motion, pressure within either the compression or rebound chamber  24  or  26  increases, while pressure in the other chamber decreases. Fluid is transferred through the piston  30  in a controlled manner from the chamber with the higher pressure to the chamber with the lower pressure which dampens the piston motion. The rate at which the fluid flows determines the stiffness of the vibration dampening which is varied by adjusting the amount that the valve assembly  49  opens. 
     To understand the operation of the valve assembly  49 , it is beneficial to be familiar with how the internal chambers and passages communicate with the compression and rebound chambers  24  and  26 . First, realize that the pilot chamber  56  located between the primary valve spool  50  and the solenoid actuator  66  continuously communicates bidirectionally with the rebound chamber  26  through the flow passage  58  and the pilot orifice  60 . In addition, the compression chamber  24  also is in continuous bidirectional communication with the pilot chamber  56  via the control passage  62  and the control orifice  64 . In other words, there are no check valves in those passages  58  and  62 . Nevertheless, the pilot and control orifices  60  and  64  restrict the rate at which fluid flows through those passages between the compression and rebound chambers  24  and  26 . Looked at another way, the control orifice  64  is directly connected to both the compression chamber  24  and the pilot chamber  56 . The pilot orifice  60  is directly connected to both the rebound chamber  26  and the pilot chamber  56 . The term “directly connected” as used herein means that the associated components are connected together by a conduit without any intervening element, such as a valve, an orifice or other device, which restricts or controls the flow of fluid beyond the inherent restriction of any conduit. 
       FIG. 2  shows the valve assembly  49  in a state that occurs when the solenoid actuator  66  is de-energized and only static external forces are being applied to the vibration damper  10 . In this state, pressures in the compression and rebound chambers  24  and  26  are equal. With the solenoid actuator  66  de-energized, the third spring  90  pushes the pilot spool  84  and armature  82  upward into the illustrated closed position in which fluid flow through the pilot valve  61  between the pilot passage  39  and the pilot chamber  56  is blocked. At the same time, the second spring  80  pushes the primary valve spool  50  away from the second pole piece  78  and against the retainer  47  that is biased in the opposite direction by the first spring  48 . This places the primary valve spool  50  into a closed position in which the first land  51  and the second land  53  both engage the wall of the piston bore  36 , thereby blocking fluid flow between the compression apertures  37  and the rebound apertures  38  in the piston body  34 . As a result, the only path for fluid to flow through the piston  30  between the compression and rebound chambers  24  and  26  is via a path formed by the pilot orifice  60 , flow passage  58 , the pilot chamber  56 , the control passage  62 , and the control orifice  64 . The pilot orifice  60  significantly restricts that flow. Therefore, when the pilot valve  61  is closed, only the pilot orifice  60  defines the vibration response characteristic of the vibration damper  10 . 
     Now when vibration occurs, a pressure differential is created between the compression and rebound chambers  24  and  26 . Because the pilot spool  84  is closed, fluid can only flow between the compression and rebound chambers  24  and  26  through the relatively small pilot orifice  60 . When the vibration force has a direction that tends to retract the piston rod  32  into the cylinder  16 , the pressure in the compression chamber  24  become significantly greater than the pressure in the rebound chamber  26 . That greater pressure is communicated through the compression apertures  37  and acts on the surfaces of the first and second metering notches  52  and  54  in the primary valve spool  50 . Although that greater pressure tends to be communicated through the control passage  62  a pressure differential exists across the primary valve spool  50 , due to the control orifice  64  restricting flow into the pilot chamber  56 . 
     That pressure differential causes the primary valve spool  50  to move upward against the force of the second spring  80  as shown in  FIG. 5 . The primary valve spool  50  moves away from engagement with retainer  47  and the first spring  48  no longer acts on that primary valve spool. It should be understood that because the second adjustor  46  is threaded into the first adjustor  42 , the fixed gap between the flange  45  of the second adjustor  46  and the inner surface of the first adjustor  42  limits the expansion of the first spring  48 . Thus, the first spring  48  does not act on the primary valve spool  50  during the compression phase of the vibration damper operation. In that phase, however, the second spring  80  continues to act on the primary valve spool  50 . 
     As the primary valve spool  50  moves upward, the first land  51  moves off the wall of the piston bore  36  into the opening of the rebound apertures  38  which creates a path between the compression apertures  37  and the rebound apertures through the first metering notch  52 . This path allows the flow of fluid from the compression chamber  24  into the rebound chamber  26 , thereby accommodating retraction of the vibration damper  10 , i.e. downward motion of the piston  30 . Note that during the compression phase the second metering notch  54  does not open a flow path. The force of external spring  22  ( FIG. 1 ) limits the amount of retraction of the vibration damper  10 . 
     When the vibration force reverses direction tending to extend the piston rod  32  from the cylinder  16 , pressure within the rebound chamber  26  becomes greater than the pressure within the compression chamber  24 . The greater rebound chamber pressure drives the primary valve spool  50  downward toward the compression chamber  24  until that spool contacts the retainer  47  that is biased by the first spring  48 . This motion of the primary valve spool  50  initially closes the path between the compression and rebound apertures  37  and  38  that had been provided by the first metering notch  52  during the compression phase. Now, in the closed position illustrated in  FIG. 2 , the pilot orifice  60  again restricts the flow of fluid between the rebound and compression chambers  26  and  24 . 
     Shortly thereafter, pressure within the pilot chamber  56  becomes greater than the pressure within the compression chamber  24  due to the control orifice  64 . Thus a greater pressure acts on the primary valve spool surfaces in the pilot chamber  56  than the pressure from the compression chamber  24  acting on the lower spool surfaces. As a result of this pressure differential, the primary valve spool  50  moves downward as, depicted in  FIG. 6 . The force required for that downward motion now has to overcome the counteracting force of the first spring  48 . However, the net downward force from the pressure differential across the primary valve spool  50  is aided in the rebound phase by the force of the second spring  80 . Thus, the force of the second spring  80  affects motion of the primary valve spool  50  in both the rebound and compression phases, whereas the force of the first spring  48  only acts on the primary valve spool in the rebound phase 
     The primary valve spool  50  now moves into a position, depicted in  FIG. 6 , at which the second metering notch  54 , shown on the left side of the primary valve spool, provides a flow path between the rebound apertures  38  and the compression apertures  37 . Opening that path via the second metering notch  54  decreases the flow from the rebound chamber into the compression chamber  24  that is at a lower pressure. 
     The oscillation of the piston  30  due to the vibrations repeats this bidirectional motion of the primary valve spool  50 , thereby damping the vibrations. 
     As noted previously, when the solenoid actuator  66  is de-energized, the pilot valve  61  is in a closed state, thereby instilling a very stiff response characteristic to the vibration damper  10  due to the flow restriction of the pilot orifice  60 . That vibration response characteristic can be softened by opening the pilot valve  61  to create another flow path between the rebound chamber  26  and the pilot chamber  56 , bypassing the pilot orifice  60 . The pilot valve  61  is opened by applying an electric current to the solenoid actuator  66  thereby producing a magnetic field which moves the armature  82  and the attached pilot spool  84  downward. The magnitude of that electric current determines the amount that the pilot spool  84  moves and thus the size of the pilot passage thereby created. 
     Note that the second pole piece  78  has a relatively small first transverse aperture  98  extending there through and intersecting the pilot bore  86 . Farther away from the solenoid actuator  66 , a significantly larger second aperture  99  extends through the second pole piece  78  intersecting pilot bore  86 . Thus, when the solenoid actuator  66  is energized, the pilot spool  84  initially moves into a position at which the annular notch  88  there around communicates with both the pilot passage  39  and the first transverse aperture  98 . This forms a path for fluid to flow between those passages and therefore between the pilot chamber  56  and the rebound chamber  26 . This path is parallel path to the flow path provided by the pilot orifice  60  and provides a softer vibration response to the vibration damper  10 . 
     Increased activation of a solenoid actuator  66  moves the pilot spool  84  farther downward toward the primary valve spool  50  opening communication between the pilot passage  39  and both the transverse aperture  98  and  99 . This increases the fluid flow between the pilot chamber  56  and the rebound chamber  26 , which further softens the response characteristic of the vibration damper  10  for both rebound and compression. Therefore, the magnitude at which the solenoid actuator  66  is activated controls the distance that the pilot spool  84  moves, and varies the response characteristic of the vibration damper from a very stiff to a relatively soft response. 
     The fundamental concept of the embodiment depicted in  FIGS. 2-6  is that during vibrations, the pilot chamber  56  for controlling the primary valve spool  50  is maintained at an intermediate pressure to the pressures in the compression and rebound chambers  24  and  26 . This is accomplished by providing a fixed control orifice  64  between the compression chamber  24  and the pilot chamber  56  and by providing a variable orifice between the rebound chamber  26  and the pilot chamber. The variable orifice is formed by the pilot orifice  60  and the pilot valve  61 . Alternatively, the fundamental inventive concept can be implemented in an embodiment in which the fixed orifice is between the rebound chamber and the pilot chamber, and in which the variable orifice is between the compression chamber and the pilot chamber. As a further variation of the fundamental inventive concept, two variable orifices can be used to couple the pilot chamber to each of the compression and rebound chambers. 
     The preferred embodiment of the vibration damper piston utilizes a solenoid actuator responds to an electrical control signal by moving the pilot spool  84  to vary the flow path between the rebound chamber  26  and the pilot chamber  56 . Nevertheless, other types of actuators could be employed, such as one the responds to a hydraulic or a pneumatic control signal, for example. 
       FIG. 7  depicts an alternative version of a vibration damper  100  in which both the pilot and control orifices are variable. Many of the components are the same as in the first vibration damper  10  and have been assigned the same reference numerals. The primary difference is the pilot valve  102  that is a three-way valve thereby enabling the size of the pilot orifice between the rebound chamber  26  and the pilot chamber  56  to be varied and providing a variable control orifice between the compression chamber  24  and the pilot chamber  56 . As a consequence of providing that three-way pilot valve  102 , the fixed control orifice  60  that was present in the first vibration damper  10  has been eliminated. 
     The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.

Technology Classification (CPC): 5