Positional variable orifice pin for hydraulic pressure control in a draft gear

A draft gear assembly for absorbing buff and draft shocks encountered in railroad rolling stock, said draft gear assembly comprising:

• (a) a housing having a closed end and an open end opposing said closed end, said housing further having a rear portion adjacent said closed end and a front portion adjacent said open end, said rear portion having a bottom wall and said front portion being in open communication with said rear portion;
• (b) a compressible cushioning element centrally disposed within said rear portion with one end thereof abutting at least a portion of an inner surface of said bottom wall of said housing, said compressible cushioning element extending longitudinally from said one end and includes a hydraulic cylinder and at least one cylinder spring disposed intermediate said cylinder and said bottom wall, said hydraulic cylinder including:
• (i) a cylinder housing,
• (ii) a piston having a piston head and an axial bore of a first predetermined diameter having a rear wall and an open end, an axial counterbore abutting said axial bore at said open end, an axial cylinder guide of a second predetermined diameter concentric with said axial bore, said axial cylinder guide abutting said axial bore at said rear wall end, said axial cylinder guide having a second cavity bored perpendicular to said cylinder guide for connecting it with an outside of said piston, said second cavity for further relieving a pressure in said axial cylinder guide, said piston slideably disposed within said cylinder housing to establish a high pressure chamber and a low pressure chamber,
• (iii) a flexible boot having one end fastened to said piston and having a second end fastened to a cap and boot adapter of said cylinder,
• (iv) a rubber gasket mounted within said cap and boot adapter for sealing a space between said cap and boot adapter and said cylinder to prevent leakage,
• (v) at least one fluid passage disposed within said piston for establishing a communication between said high pressure chamber and said low pressure chamber;
• said at least one fluid passage having a flow restricting orifice disposed at one end adjacent said axial counterbore of said piston, said flow restricting orifices exposed to said high pressure chamber,
• (vi) an expansion ring and a piston ring mounted within an annular groove formed within said piston head,
• (vii) a first cavity coplanar with said annular groove of said piston head,
• (viii) a pin disposed within said first cavity, said pin extending through said piston head, said pin having ends adjacent said expansion ring,
• (ix) a metering pin slideably disposed within said piston, said metering pin including an inner surface and an outer surface, a stem element attached to said inner surface and movable within said axial bore and said axial cylinder guide, said stem element having a working end of a predetermined length and a first predetermined diameter and a step portion of a second predetermined diameter disposed adjacent said working end, at least one aperture disposed within said metering pin for equalizing fluid pressure between said high pressure chamber and said low pressure chamber of said piston, said metering pin at least partially closing said flow restricting orifice when said metering pin is in its fully released position,
• (x) a restricted bore extending from a surface of said piston head to said at least one fluid passage for insuring a rapid return of said variable orifice metering pin to its full release position,
• (xi) a compression coil spring of a predetermined spring rate disposed within said axial bore of said piston having one end oriented towards said rear wall of said axial bore and having another end abutting said inner surface of said metering pin, said compression coil spring biasing said metering pin against said pin disposed within said first cavity, and
• (xii) a positional variable metering means disposed within said piston and operable in a first position for increasing a reaction fluid pressure in said low pressure chamber of said hydraulic cylinder causing an increased shock absorbing capacity of said draft gear assembly during operational buff conditions, said positional variable metering means operable in a second position for lowering said reaction fluid pressure in said low pressure chamber of said hydraulic cylinder for compliance with requirements of a drop hammer test;
• (c) a positioning means on said inner surface of said closed end of said housing for maintaining said one end of said hydraulic compressible cushioning element centrally positioned in said rear portion of said housing during compression and extension of said hydraulic compressible cushioning element;
• (d) a seat means having at least a portion of one surface thereof abutting the opposite end of said hydraulic compressible cushioning element and mounted to move longitudinally within said housing for assisting in releasing said draft gear assembly after an application of a force on said draft gear and during a release of a such force on said draft gear assembly;
• (e) a friction cushioning means positioned at least partially within said front portion of said housing for absorbing energy during a compression of said draft gear assembly, said friction cushioning means including:
• (i) a pair of laterally spaced outer stationary plates having an outer surface and an opposed inner friction surface, said outer surface engaging said housing, said pair of outer stationary plates having a Brinell hardness of between about 429 and 495 throughout,
• (ii) a pair of laterally spaced movable plates of substantially uniform thickness and having an outer friction surface and an inner friction surface and at least one substantially flat edge intermediate said outer and inner friction surfaces, said one edge engaging said seat means, at least a portion of said outer friction surface movably and frictionally engaging said inner friction surface of said outer stationary plate,
• (iii) a pair of laterally spaced tapered plates having an outer and an inner friction surface, said outer friction surface movably and frictionally engaging at least a portion of said inner friction surface of said movable plate,
• (iv) a pair of laterally spaced wedge shoes having at least a portion of an outer friction surface movably and frictionally engaging at least a portion of an inner friction surface of said tapered plate and at least a portion of one edge engaging said seat means, said pair of wedge shoes having a predetermined tapered portion which is tapered upwardly and outwardly from a plane intersecting a longitudinal center line of said draft gear assembly at an angle of about 53 degrees on an opposed edge thereof, and
• (v) a center wedge having a pair of matching tapered portions at an angle of about 53 degrees for engaging said tapered portion of said wedge shoe to initiate frictional engagement of said friction cushioning means and thereby absorb energy;
• and
• (f) a spring release means engaging and longitudinally extending between said seat means and said center wedge for continuously urging said friction cushioning means outwardly from said compressible cushioning means to release said friction cushioning element when an applied force compressing said draft gear is removed.