Shock absorber

Details Shock absorber Shock absorber

1998-11-06

2001-03-13

Oberleitner, Robert J. (Department: 3613)

Brakes

Internal-resistance motion retarder

Resistance alters relative to direction of thrust member

C188S322130, C188S322150, C188S282800, C267S256000, C104S026200

Reexamination Certificate

active

06199671

ABSTRACT:

BACKGROUND OF THE INVENTION
THIS invention relates to a shock absorber, and in particular to a shock absorber for use as a wagon retarder of the type in which movement of a wagon wheel along the rail is regarded by the retarder acting against a peripheral flange of the wheel.
In the applicant's corresponding U.S. Pat. No. 5,730,260, which is incorporated herein by reference in its entirety, a rail retarder-type shock absorber is disclosed which includes a cylinder defining a cavity between a pair of end walls. A piston rod extends axially through one of the end walls, and a piston is mounted on the piston rod between the end walls so as to divide the cavity into first and second working chambers containing a damping fluid. A first array of passages extends through the piston and communicates between the first and second chambers, and a sprung valve assembly is provided for obturating the first array of passages in the event of the velocity of the piston rod relative to the cylinder exceeding a predetermined value. A second array of passages communicates between the working chambers and provides a fluid flow path when the first array of passages is blocked by the sprung valve assembly. Restricted exhaust orifices communicate with the second array of passages for limiting the flow of fluid through the second array of passages so as to control the movement of the piston rod. The dimensions of the exhaust orifices are determined in accordance with the desired force-displacement profile of the shock absorber.
In a preferred embodiment, a so-called “relaxable orifice” version of the shock absorber is provided in the form of a moveable orifice plate which is spring biased against the rearmost face of the piston to define the restricted exhaust orifices and to allow them to open in response to an increase in pressure.
Whilst this shock absorber has been found to operate effectively, a number of manufacturing steps are associated with the formation of the first and second arrays of passages, as well as the formation and adjustment of the restricted exhaust orifices.
In addition, in the “relaxable orifice” version, it has been proved difficult to release sufficient fluid as the orifice plate opens to ensure that the counter-force exerted by the retarder is insufficient to cause bounce and possible derailment in the case of lighter rolling stock moving at relatively high speeds.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a shock absorber comprising:
a) a cylinder defining a cavity between first and second end walls;
b) a piston rod extending axially through one of the end walls;
c) a piston assembly carried on the piston rod and mounted to slide axially within the cylinder so as, to divide the cavity into first and second working chambers arranged to contain damping fluid;
d) first passage means extending through the piston assembly and communicating between the first and second working chambers;
e) first valve means for at least partly closing the first passage means in the event of the axial velocity of the piston relative to the cylinder in a first axial direction exceeding a predetermined value, and
f) at least one permanently open restricted orifice being defined in the first valve means and communicating between the first and second working chambers via the first passage means on closure of the first valve means,
the restricted orifice being restricted relative to the first passage means so as to limit the flow of damping fluid between the first and second working chambers and to set up a pressure differential therebetween to apply a predetermined damping force, with the dimensions of the restricted orifice being determined in accordance with the desired force-displacement profile of the shock absorber.
Preferably, the valve means includes a valve plate and biasing means for biasing the valve plate into an open position, with the restricted orifice means extending through the valve plate and communicating directly with the first passage means when the valve plate is closed.
Preferably, the first valve means is located operatively upstream of the first passage means within the first working chamber.
The restricted orifice means typically has a diameter of 0-3 mm, and preferably of around 2 mm.
In one form of the invention, the shock absorber includes second passage means communicating between the first and second working chambers, second valve means for at least partly obturating the second passage means, and second biasing means for biasing the second valve means into a closed position, the second valve means being arranged to open in response to a predetermined pressure differential existing between the first and second working chambers.
Typically, the second valve means includes a second valve plate defining a pressure accumulator well portion which is responsive to pressure exerted by fluid via the second passage means, the second valve plate being arranged to open in response to a predetermined pressure differential existing between the first and second working chambers.
Advantageously, the first passage means comprises a plurality of equi-spaced cylindrical first passages extending axially through the piston assembly, the at least one permanently open restricted orifice comprises a plurality of corresponding equi-spaced cylindrical restricted orifices extending axially through the first valve means, and alignment means are provided for aligning the first passages with the restricted orifices.
According to a further aspect of the invention there is provided a shock absorber comprising:
a) a cylinder defining a cavity between first and second end walls;
b) a piston rod extending axially through one of the end walls;
c) a piston assembly carried on the piston rod and mounted to slide axially within the cylinder so as to divide the cavity into first and second working chambers arranged to contain damping fluid;
d) first passage means extending through the piston assembly and communicating between the first and second working chambers;
e) second passage means extending through the piston assembly and communicating in use between the first and second working chambers;
f) first valve means for at least partly closing the first passage means in the event of the axial velocity of the piston relative to the cylinder in a first axial direction exceeding a predetermined value; and
g) second valve means for at least partly obturating the second passage means,
the second valve means including a valve plate defining a pressure accumulator well which is responsive to pressure exerted by fluid via the second passage means, and biasing means for biasing the valve plate into a closed position, the second valve means being arranged to open in response to a predetermined pressure differential existing between the first and second working chambers.
Advantageously, at least one restricted orifice is defined in the first valve means and communicates between the first and second working chambers via the first passage means on closure of the first valve means, the restricted orifice being restricted relative to the first passage means so as to limit the flow of damping fluid between the first and second working chambers and set up a pressure differential therebetween to apply a damping force.
The second valve means may be in the form of a true valve, in that it is capable of completely obturating the second passage means.
Alternatively, the second valve means may alternatively be in the form of an orifice plate which only partly obturates the second passage means so as to define a permanently open restricted exhaust orifice.
Typically, the pressure accumulator well includes an annular stepped recess, and the piston assembly includes an operatively rearmost face having a complementally stepped projection which locates within the recess in a sliding fit.
The invention extends to a rail retarder including a shock absorber of the type described, as well as to a piston assembly comprising integers a) to f) above.


REFERENCES:
patent: 483529 (1892-10-01), B

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