Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Reexamination Certificate
1998-07-28
2001-05-29
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
C267S226000
Reexamination Certificate
active
06237733
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to railcar cushioning devices, in particular to a railcar cushioning device which is responsive from a neutral position to both buff and draft forces.
BACKGROUND ART
Railcars experience a great deal of shock during coupling operations and other train action which can damage cargo on the railcars and the railcars themselves. To absorb the high forces experienced by railcars during these operations, cushioning devices have been employed between the frame of the railcar and its coupler.
The shock experienced by railcars results from both buff and draft forces applied to the coupler of the railcar. The term “buff” is used to describe the movement experienced by a coupler when it is moved towards its associated railcar. These buff forces are usually experienced during coupling operations between the railcars. “Draft” describes the outward movement of the coupler away from its associated railcar in response to pulling forces acting on the coupler.
These cushioning devices are usually hydraulic piston and cylinder arrangements which absorb both buff and draft forces. The cylinders are filled with a hydraulic fluid which is forced through ports in the cylinder wall in response to the impact force applied to the piston. Characteristic of these cushioning devices, however, is the low level of impedance they provide in response to very low buff and draft forces. This response to very low buff and draft forces creates the undesirable effect of “slack” between the railcars.
There is a need therefore for a cushioning device for a railcar that operates at a very high impedance when subjected to low level forces to thereby reduce the effect of slack between the railcars while still providing an effective cushion for absorbing high levels of shock between the railcars.
In addition, related art shock absorbers, when not undergoing shock, will restore the piston and shock absorber to an extended position. The restoration occurs due to gas pressure in the cylinder pushing the piston to the extended position. If a draft shock occurs while the piston is in the full extended position, the shock absorber will not be able to accommodate the draft shock because the railcar pocket stops mechanically prohibit further extension movement.
SUMMARY OF THE INVENTION
The cushioning device of this invention has a neutral position for the piston. In the neutral position, the piston is located at an intermediate position, spaced between the buff and draft ends of the cylinder. If a buff shock occurs while in the neutral position, the piston and cylinder move relative to each other, with the piston moving towards the buff end to absorb the shock. Liquid in the cylinder passes through ports into the reservoir during this movement. Preferably, pressure relief valves will be located in at least some of the ports for requiring a minimum pressure before movement of the piston can occur. If a draft movement occurs, the piston will move toward the draft end of the cylinder, also absorbing shock.
To provide the neutral position, a spring is employed within the cylinder. The spring allows free restoration of the piston until the piston reaches the neutral position. Upon reaching the neutral position, any continued movement of the piston towards the draft end of the cylinder must further compress the spring. The spring force is selected to be greater than the force being exerted by gas pressure on the piston during restoration. Therefore, the spring force stops the piston at the neutral position. If a draft shock occurs while the piston is in the neutral position, the piston will further compress the spring.
In the preferred embodiment, a spring is mounted inside the cylinder. The cylinder has a buff end and a draft end and contains a fluid comprising liquid and gas for absorbing shock due to buff and draft movement. A piston carried inside of the cylinder is urged toward the draft end of the cylinder. Either the piston or the cylinder is adapted to be secured to a coupling for coupling to adjacent railcars. The internal positioning spring is provided for stopping further restoring movement of the piston toward the draft end of the cylinder at a selected neutral position spaced from the draft end of the cylinder. However, the spring allows the piston to move from the neutral position toward the draft end of the cylinder if a draft shock occurs of sufficient magnitude while the piston is in the neutral position.
REFERENCES:
patent: 3111201 (1963-11-01), Bliven
patent: 3211442 (1965-10-01), Auner
patent: 3722639 (1973-03-01), Keijzer et al.
patent: 3860098 (1975-01-01), Porter et al.
patent: 3958673 (1976-05-01), Allinquant et al.
patent: 4960188 (1990-10-01), Wossner
patent: 5265710 (1993-11-01), Gabas et al.
patent: 5325942 (1994-07-01), Groves et al.
patent: 5501438 (1996-03-01), Handke et al.
patent: 5570763 (1996-11-01), Parejo
patent: 5642823 (1997-07-01), Kalina et al.
Article from Railway Age; Jul. 1998.
Bomgardner Charles T.
Hodges Richard N.
Kalina Harry B.
Bradley James E.
Felsman, Bradley, Vaden, Gunter & Dillon L.L.P.
FM Industries, Inc.
Graham Matthew C.
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