Center-of-car cushioning device with gas return

In a railway car having a frame and a slideable sill extending therethrough for interconnecting the couplings at the ends of the car, a cushioning assembly comprising, in combination, an outer cylinder, first and second annular end caps sealed to the ends of the cylinder, an inner metering cylinder extending between the end caps and spaced uniformly inwardly from the outer cylinder to define an annular reservoir therebetween, a piston slideable in the metering cylinder, a first piston rod extending from one side of the piston and having a sealed telescopic connection with the first annular end cap, a second piston rod in the form of a hollow thin-walled tube connected to the other side of the piston in alignment with the first piston rod, said second piston rod having a sealed telescopic connection with the second annular end cap, the wall of the tube forming the second piston rod being smoothly continuous and impervious so that the space within the second piston rod is isolated from the inner and outer cylinders in all positions of the piston, the first piston rod having a head at its outer end, the head and the first end cap presenting opposed abutting surfaces facing mutually inwardly to define an axial gap between them when the first piston rod is in its contracted state, stop members on the sill and the frame respectively normally positioned side by side in register with one another and both dimensioned to fill the gap between the abutting surfaces so that a shock to either one of the couplings resulting in endwise movement of the sill with respect to the frame in either direction causes the stop members to shift out of register with one another thereby to elongate the gap so as to tension and extend the first piston road, a pressurized mixture of hydraulic fluid and pressurized gas in the metering cylinder and reservoir, a set of metering orifices distributed along the length of the metering cylinder so that as the first piston rod is extended by the shock the mixture restrictedly flows through the metering orifices from a position in front of the piston through the reservoir to a position behind the piston thereby cushioning the shock, the second piston rod having a substantially greater diameter than the first piston rod so that the second piston rod presents a greater axially projected area to the pressurized mixture with the result that following the shock the pressurized mixture tends promptly to return the first piston rod to the retracted state in readiness for a subsequent shock.