Brakes – Internal-resistance motion retarder – Resistance alters relative to direction of thrust member
Reexamination Certificate
1999-04-23
2001-03-20
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Resistance alters relative to direction of thrust member
C188S282100, C188S282800, C188S287000, C188S304000, C188S318000, C188S319200
Reexamination Certificate
active
06202807
ABSTRACT:
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'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.
REFERENCES:
patent: 2917303 (1959-12-01), Vierling
patent: 4139182 (1979-02-01), Nagase et al.
patent: 4591031 (1986-05-01), Kirst
patent: 5361706 (1994-11-01), Kunczynski
patent: 5388711 (1995-02-01), Hodges
Graham Matthew C.
Nikolai Mersereau & Dietz, P.A.
Williams Thomas A.
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