Abstract:
A speed controlling hydraulic dampener comprises a tubular housing defining a closed cylindrical chamber for containing a hydraulic fluid. The chamber containing two separate pistons and piston rods that extend through sealed openings in the ends of the housing. The second piston is spring-biased. First and second orifices are provided in the wall of the housing which are connected by a tubular passageway. A special seal arrangement cooperates with the first piston rod and with the wall of the housing defining the cylindrical chamber. This seal includes a third orifice extending longitudinally therethrough and cooperating with this orifice is a flow-controlling needle valve that can be used to adjust the rate of flow of hydraulic fluid from a first portion of the chamber through the first orifice, the tubular passageway and the second orifice to a zone between the first and second pistons.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to devices for controlling the rate at which a movable object is allowed to move relative to a fixed object, and more particularly to an improved design for a hydraulic dampener that is positionable between the movable object and the fixed object. 
     II. Discussion of the Prior Art 
     A variety of hydraulic dampening devices have been used in the past to limit the speed with which an object acted upon by an applied force will move relative to a fixed body. For example, in U.S. Pat. No. 5,297,912, assigned to applicant, there is described a ladder rack assembly that is adapted to be mounted to the roof of a van or other type vehicle for transporting ladders on the rack. A four-bar linkage assembly that is adapted to be actuated by the rotation of an elongated handle allows the ladders to be transported from a first position on and parallel to the top of the vehicle to a second position along side the vehicle where they can be readily removed from the rack and carried away by a workman. As the weight of the ladder is brought over center on the rack, gravity suddenly, takes over which would cause the ladder on the rack to drop suddenly were it not for the inclusion of hydraulic dampeners to slow down the movement of the ladders relative to the stationary vehicle. 
     Hydraulic dampeners of the type described are also often found on machine tools, such as a vertical/horizontal band saws. In this application, a hydraulic dampener can be used to control the rate at which the assembly carrying the orbiting saw blade will move through the workpiece as cutting takes place. 
     To achieve smooth and effective control, it is imperative that the speed controlling hydraulic damper not leak hydraulic fluid because when that hydraulic fluid is replaced by a compressible medium (air) erratic movement takes place. Rather than a smooth unidirectional descent, the movable object may bounce or oscillate. Ultimately, seal failure can lead to an uncontrolled descent, a situation to be avoided. 
     To avoid loss of hydraulic fluid and attendant air entry into the cylinder of the hydraulic dampener, it is required that there be an effective seal between the piston rod and the cylinder at the point where the cylinder rod exits the cylinder. 
     In prior art speed controlling hydraulic dampeners, as the piston rod is being drawn out from the cylinder, a vacuum is created because the volume in the cylinder formerly occupied by the piston rod is reduced. This, too, results in the introduction of air and a spongy performance when the piston is again driven back into the cylinder. 
     It is accordingly a principal object of the present invention to provide an improved speed controlling hydraulic dampener for controlling the movement of a fixed object relative to a stationary object. 
     Another object of the present invention is to provide a speed controlling hydraulic dampener having improved sealing structures for precluding the entry of air into the cylinder during actuations thereof. 
     Another object of the invention is to provide a speed controlling hydraulic dampener having means for compensating for the reduction in volume of hydraulic fluid in the cylinder as the cylinder rod is being drawn out from the cylinder to prevent the formation of a vacuum within the cylinder. 
     SUMMARY OF THE INVENTION 
     These and other objects and advantages of the invention are achieved by providing a hydraulic dampener that comprises a housing having first and second end caps defining a closed cylindrical chamber for containing a hydraulic fluid therein. A first piston rod extends through a bore formed in the first end cap and secured to the first piston rod is a first, main piston. A second piston rod extends through a bore formed in the second end cap and the second piston rod also supports a second, auxiliary piston that is disposed proximate one end thereof. A biasing means which may comprise a helical compression spring cooperates with the second end cap and second piston for biasing the second piston toward the first end cap. First and second longitudinally spaced orifices are formed in the wall of the housing defining the cylindrical chamber where the first is between a high pressure seal and an intermediate pressure seal on the first end cap and the second orifice is located in the zone between the first and second pistons. A tubular, hydraulic fluid conducting passageway extends between the first and second orifices. A means is provided for adjusting the rate of flow of hydraulic fluid through the first orifice and the tubular passageway into the zone between the main piston and the auxiliary piston when the first piston rod is moved in direction to reduce the spacing between the first piston and the first end cap. Finally, a one-way valve cooperates with the first piston for permitting return flow of hydraulic fluid from the zone between the main and auxiliary pistons into the space in the cylinder between the first piston and the first end cap when the first piston rod is moved in a direction to increase the spacing between the first piston and the first end cap. 
     A further feature of the improved speed controlling hydraulic dampener of the present invention resides in the structure whereby the rate of flow of hydraulic fluid through the passageway is made adjustable. A piston rod seal member forming a part of the first end cap is operatively disposed between the wall of the housing and the first piston rod for blocking flow of hydraulic fluid past the first end cap. The first end cap has an orifice formed therein that is fluid communication with the housing&#39;s first orifice, thereby reducing the high pressure generated between the piston and first end cap by the force pulling the piston rod outward down to the bias pressure created by the spring biased auxiliary piston acting on the hydraulic fluid in the zone between the two pistons. An adjustment screw extending through the first end cap cooperates with the orifice in the end cap for adjustably occluding hydraulic fluid flow therethrough into the first orifice and the passageway. The end cap seal members comprise a seal lantern including an annular groove that is formed in a peripheral surface thereof that aligns with the first orifice in the housing wall and a high pressure seal is supported by the seal lantern on one side of the annular groove with an intermediate pressure seal supported by the seal lantern on an opposite side of the annular groove. In this fashion, the pressure drop across the intermediate pressure seal as the piston rod is being forced into the cylinder is greatly reduced, minimizing the ability of ambient pressure air to enter the system and for hydraulic fluid to leak past the seal. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The constructional and operational features of the present invention will now be explained with the aid of the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
     FIG. 1 is a longitudinal cross-sectional view of the speed controlling hydraulic dampener configured in accordance with the present invention; 
     FIG. 2 is an enlarged partial view showing the main piston rod seal and speed controlling structure of the preferred embodiment of FIG. 1; and 
     FIG. 3 is an enlarged partial section view of a left end portion of the preferred embodiment illustrated in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the device and associated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import. 
     Referring first to FIG. 1, there is indicated generally by numeral  10  a speed controlling hydraulic dampener constructed in accordance with the present invention. It is seen to include a cast aluminum housing  12  having a first end cap assembly  14  affixed to the right end of the housing  12  by four bolts, as at  16 . Likewise, an end cap  18  is affixed to the left end of the housing  12  by bolts, as at  20 . The housing  12  with its first and second end caps  14  and  18  define a closed cylindrical chamber  22  for containing a hydraulic fluid  24  therein. 
     The end cap  14  includes a cylindrical bore  26  and extending through this bore into the chamber  22  is a first piston rod  28  having a first piston  30  affixed to the end portion thereof. The piston rod  28  further includes a concentric bore  32  containing a compression spring  34  that normally urges a ball valve member  36  against a valve seat member  38  (FIG. 3) held in place by a bolt  40 . 
     Extending through the second end cap  18  is a second, tubular piston rod  42  that has a second piston  44  secured to the rightmost end thereof. A compression spring  46  of a relatively high spring constant surrounds the piston rod  42  and cooperates with the second end cap  18  and the second piston  30  to normally urge the second piston  30  to the right when viewed in the drawings. A Zerk-type fitting  47  is affixed to the left end of the tubular piston rod  42 , allowing injection of hydraulic fluid into the cylinder on an as-needed basis. 
     Integrally formed with the housing  12  is a tubular, hydraulic fluid conducting passageway  48  that extends between and fluidly couples a first orifice  50  (FIG. 2) to a second orifice  52  (FIG.  3 ). The first orifice  50  is located proximate the first end cap assembly  14  while the second orifice  52  is aligned with a zone  54  between the main piston  30  and the auxiliary piston  44 . 
     Considering next the seals incorporated into the speed controlling hydraulic dampener, each of the pistons  30  and  44  includes an elastomeric cup seal retained in annular grooves formed in the periphery of the pistons. The first or main piston  30  includes a cup seal  56  while the second piston  44  includes a cup seal  58 . The cup seals  56  and  58  function to prevent passage of hydraulic fluid in the interface between the cylindrical wall  22  and the respective pistons. 
     Forming a part of the end cap assembly  14  at the right end of the housing is a mechanism for adjusting the rate of flow of hydraulic fluid through the first orifice  50  and the tubular passageway  48  into the zone  54 , via orifice  52 , when the piston rod  28  is pulled outwardly from the housing  12 . It comprises a piston rod seal assembly, indicated generally by numeral  60 , that includes a seal lantern  62  having an annular groove  64  formed in the periphery thereof where the groove  64  positionally aligns with the first orifice  50  when the end cap  14  is secured in place. Additional annular grooves  66  and  68  are formed in the periphery of the seal lantern  62  on opposed sides of the peripheral groove  64  and fitted into the grooves  66  and  68  are high and intermediate pressure O-rings  70  and  72 , respectively, which serve to seal against the inner wall of the chamber  22 . The high and intermediate pressure O-rings  70  and  72  serve to preclude flow of hydraulic fluid along the interface between the seal lantern  62  and the wall  22 . 
     The seal lantern  62  includes a cylindrical bore for receiving the piston rod  28  therethrough and extending inwardly of the lantern from the bore are annular grooves  74  and  76  into which are fitted high and intermediate pressure annular cup seals  78  and  80 , respectively. 
     The end cap assembly  14  includes yet a further cup seal member  82  that cooperates with the piston rod  28  as a wiper to prevent ingress of foreign objects, such as dust or other debris. A further intermediate pressure O-ring seal  84  is provided at the interface between the lantern  62  and the end cap assembly  14 . 
     With continued reference to FIG. 2, it can be seen that the seal lantern  62  includes a longitudinal bore or orifice  86  that extends to and joins with the peripheral groove  62  which is aligned with the orifice  50 . Threaded into a threaded bore  88  in the end cap assembly  14  is an adjustment screw  90  having a tapered tip  92  cooperating with the bore  86  as a needle valve. When the adjustment screw  90  is rotated clockwise, the conical tip  92  can be made to completely occlude flow of hydraulic fluid through the orifice or bore  86 . When the screw is then backed-off from this position, the rate of flow of hydraulic fluid through the orifice  86 , the orifice  50  and the fluid conducting passageway  48  as the piston  30  is moved to the right within the cylindrical chamber  22  can be adjusted. 
     OPERATION 
     Having described the constructional features of the speed controlling hydraulic dampener, consideration will next be given to its mode of operation. 
     The hydraulic dampener  10  will typically be connected between a fixed or stationary object, such as a frame or the like, and an object that is movable with respect to that frame. This is typically accomplished by passing a pin (not shown) through the aligned apertures  94  and through an aperture in the frame member inserted into the slot  96 . Likewise, the movably member will have an apertured ear (not shown) inserted between the legs of a clevis or coupling  98  and with a pin (not shown) passing through the aligned apertures  100 . 
     With the device as shown in FIG. 1, i.e., with the main piston rod  28  fully inserted into the chamber  22  and with a hydraulic fluid, such as hydraulic oil, filling the space between the first or main piston  30  and the seal assembly  60 , as well as the zone  54  between the auxiliary low pressure piston  44  and the main high pressure piston  30  and with the passageway  48  also filled with oil, an equilibrium condition prevails with the coil spring  46  pushing the piston  44  against the oil in the zone  54 . 
     Now, as the piston rod  28  is pulled outwardly of the cylinder through the bore  26  in the end plate assembly  14 , the ball valve  36  will be seated and the oil  24  will be forced through the orifice  86 , and via the annular groove  64  formed in the lantern  62 , out the orifice  50  and into the passageway  48 . The oil circulates through the passageway and through the orifice  52  into the zone  54  to increase the pressure therein and move the spring-loaded piston  44  to the left against the force of the spring  46 . 
     Because the piston rod  28  is being pulled out from the chamber  22 , there would be a decrease in pressure forcing oil through orifice  86  were it not for the auxiliary piston applying a force to the main piston through the volume of oil in the zone  54 . The spring-loaded piston  44  moves to the right approximately {fraction (1/10)} th  the distance of movement of the piston  30 , given that the cross-sectional area of the piston rod  28  is about {fraction (1/10)} th  of the cross-sectional area of the cylindrical bore  22 . The rate of flow of oil from the main chamber between piston  30  and end cap  14  to the zone  54 , via the passageway  48 , is dependent upon the setting of the speed adjustment screw  90 . 
     Now, after the piston rod  28  is fully extended and a force is applied to the clevis  98  to drive the piston rod  28  back into the cylinder, as the piston  30  moves to the left, the pressure on the ball valve  36  overcomes the force of the coil spring  34 , displacing the ball valve from its seat and permitting the flow of hydraulic fluid from the zone  54  through the now-open ball valve  36  and back into the main chamber defined between the piston  30  and the end cap  14 . The reduction in oil in the zone  54  reduces the pressure on the piston  44  allowing the spring  46  to move that piston to the right. 
     The passageway  48  connecting the orifice  52  to the annular groove  64 , via orifice  50 , serves to maintain the pressure within the groove at an intermediate pressure of the oil in the zone  54  relative to the higher pressure in the main chamber and ambient pressure. By providing high pressure seal elements  70  and  78  and intermediate pressure seal elements  72  and  80  disposed on opposite sides of the annular groove  64 , leakage of oil along the interface between the seal lantern  62 , the cylindrical wall of the housing and the piston rod is eliminated. As such, entry of ambient pressure air into the chamber is also eliminated. Thus, the speed controlling hydraulic dampener of the present invention does not become spongy with prolonged use, but continues to provide a smooth transition of the movable object secured to the clevis  98  with respect to a fixed object or frame connected to the tail piece  97  at a rate that can be set by the adjustment screw  90 . 
     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.