Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Reexamination Certificate
1999-09-10
2001-06-12
Schwartz, Christopher P. (Department: 3613)
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
Reexamination Certificate
active
06244397
ABSTRACT:
The present invention relates to a double-acting shock absorber according to the preamble of claim
1
.
Shock absorbers of this kind are generally known in the prior art and are used for damping all kinds of vibrating, oscillating and impact movements. The interplay of forces during the inwards and outwards strokes is not symmetrical in such cases, since the first chamber contains the piston rod, with the result that the surface area of liquid which acts on that side of the piston is less than the effective surface area of the second chamber. In order to avoid this drawback, it has been proposed in the prior art to lengthen the piston rod, so that it always extends completely through the cylinder. This has the drawback that it is necessary to provide further sealing means at the location of that part of the piston rod which projects out of the cylinder but has no further function. Moreover, with a design of this nature it is no longer possible to arrange fastening means, such as eyelets, on the axis of the stroke movement. Fastening means of this kind then have to be arranged on the side. Consequently, on the one hand more space is required, and on the other hand the transmission of forces is less effective, due to the fact that a moment is generated. For this reason, in many applications the drawback of the unequal effective surface area on opposite sides of the piston is accepted, or else the fastening means is displaced so far into the axis that the emerging piston rod meets no longer any obstruction.
However, in the art shock absorbers are increasingly being used for damping movements of very low amplitude, i.e. movements of an amplitude which is significantly less than 1 cm, being in the order of magnitude of millimetres. A very rigid shock absorber is needed in such cases if optimum shock absorption is to be achieved. Since the shock absorber is dimensioned on the basis of the minimum damping which it has to carry out, i.e. that with the smallest piston surface area, i.e. where the piston rod is situated, this situation means that the shock absorber has to be oversized, for the shock absorber has to be calculated on the basis of the highest load occurring, which is generated by that surface of the piston which lies on the opposite side. This design of increased weight runs counter to the desire to provide more lightweight structures, and is no longer acceptable in certain applications.
From U.S. Pat. No. 2,057,893 A a shock absorber is known in which some compensation is realized by providing a third chamber having a changeing volume. The volume of this third chamber increases as the piston rod moves further into the first chamber and the third chamber is in communication with the second chamber. Because this is a gas filled shock absorber a further compensation is obtained by the gas inside the absorber.
The object of the present invention is to avoid the drawback described above and to provide a double-acting shock absorber which saves space, can be of optimum design for both the inwards and outwards stroke with regard to the strength thereof, and in which moreover it is possible to attach the fastening means at any desired location. Furthermore full compensation of the volume of the piston rod is aimed.
This object is achieved in a double-acting shock absorber as described above with the characterising features of claim
1
. The presence of a third chamber provides compensation for the presence of the piston rod. This means that in the event of equal loading during the inwards and outwards stroke, equal forces are generated inside the shock absorber. This is important in particular for shock absorbers which execute a short stroke and therefore have to be particularly (oil)rigid.
The volume of the third chamber, and more particularly the change thereof, is always essentially equal to the change in volume in the first chamber caused by the inward or outward movement of the piston rod. This means that the total volume of the first and second chambers remains constant despite the inward or outward movement of the piston rod, owing to the change in volume of the third chamber. Volume compensation of this nature can be achieved particularly easily if the third chamber is also delimited by the first and second parts, i.e. its “length” also changes when the first and second parts move with respect to one another. By then selecting the surface area to be equal to the surface area of the piston rod, it is possible to provide complete compensation for the volume of the piston rod.
According to an advantageous embodiment of the invention, the cylinder is externally provided with a plunger, and the second part is provided with a cylindrical circumferential part, which is designed to interact with the plunger and is provided, in the region of a free end, with further sealing means, in order to delimit the third chamber therebetween.
In such a case, the exterior of the cylinder, i.e. of the first part, can function as a plunger rod for the plunger, with the circumferential part of the second part being provided with suitable sealing means. The above-described plunger and the conventional sealing means for the conventional piston rod can form a unit. Moreover, expansion-compensation means for the shock-absorber liquid may be arranged therein. This is because this liquid will expand slightly when heated, a fact which is noticeable particularly in the case of relatively rigid shock absorbers and has to be compensated for.
The actual shock absorber itself, i.e. the piston-cylinder assembly, may be designed in any manner which is known from the prior art. This relates in particular to the design of the passages for the oil, which may be provided with valves which are optionally externally actuable. Electrical adjustment is possible, and it is also possible to provide a volume of gas in order to assist the functioning of the liquid.
It is stated above that the shock absorber according to the invention can be used on any structure according to the prior art where it is necessary to provide damping between two moving parts. In particular, this shock absorber can be used as a vibration or rotation absorber for wheel sets, and more particularly wheel sets which are used in railways.
REFERENCES:
patent: 1727121 (1929-09-01), Haines
patent: 2057893 (1936-10-01), Gross
patent: 2533226 (1950-12-01), Davis et al.
patent: 2649936 (1953-08-01), Crabtree
patent: 2728419 (1955-12-01), Crabtree
patent: 5924528 (1999-07-01), Vermolen
patent: 509363 (1952-03-01), None
patent: 3934386 (1991-04-01), None
patent: 3932287 (1991-04-01), None
patent: 0220370 (1987-05-01), None
patent: 0607545 (1994-07-01), None
patent: 2132313 (1984-07-01), None
Bachman & LaPointe P.C.
Bartz C. T.
Koni B.V.
Schwartz Christopher P.
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