Brakes – Internal-resistance motion retarder – Resistance alters relative to direction of thrust member
Reexamination Certificate
2000-03-27
2001-08-21
Butler, Douglas C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Resistance alters relative to direction of thrust member
C188S322150, C188S322220, C188S317000, C188S280000
Reexamination Certificate
active
06276498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a piston for a piston/cylinder assembly in which a working piston fastened to a piston rod is arranged in a working cylinder filled with damping medium, wherein the piston is axially displaceable in the working cylinder and has damping valves for both the tension and compression directions of movement, each damping valve having a group of passage ducts which open on an outlet side at a control edge covered by valve disks.
2. Description of the Related Art
Pistons for hydraulic vibration dampers are already known, for example, from German Utility Model 19 41 188. In these known pistons, a piston body is fastened to a piston rod and has a group of passage ducts for each of the tension and compression directions of movement. Each group of passage ducts runs obliquely relative to the piston rod axis and opens on the outlet side into an annular groove forming a control edge and covered by valve disks. A problem with these prior art devices is that the obliquely running passage ducts cannot be produced together with the piston body because, for example, during sintering, the machining tools cannot be brought parallel to the piston rod axis. For this reason, the passage ducts must be produced in a further manufacturing operation such as, for example, by drilling or by a machining operation such as cutting if the cross sections are not a circular shape.
Other pistons for hydraulic telescopic vibration dampers are known, for example, from German reference DE-C 38 24 420 in which the inner radius of the inflow-side passage ducts is, starting from the piston rod axis, approximately as large as the outer radius of the outflow-side passage ducts. By virtue of this geometry, the passage ducts may be produced by noncutting machining operation, since, in each case, a part of the machining tool can penetrate axially in the direction of the piston rod axis from one end face of the piston body.
All damping systems are required to provide increasing degrees of comfort in vehicles. Comfort is influenced essentially by damping and friction. These comfort requirements, in combination with the required body damping, lead to precisely defined damping characteristic curves which are typically decreasing characteristic curves that have a compression/tension ratio in the lower speed range that does not correspond to the compression/tension ratio occurring at higher speeds. That is to say, the compression damping value at a first damping speed is higher than its corresponding value at a second damping speed and the tension damping value lower at the first damping speed than its corresponding value at the second damping speed. This relationaship has an adverse effect on comfort. To generate decreasing characteristic curves, relatively soft spring leaves or helical springs are highly prestressed so that they have high piston gradients. A problem with this solution is that the assemblies become rougher and therefore also louder. This roughness results primarily from the contact of the first spring leaf with the piston surface which occur at the higher speeds, higher forces and higher accelerations during opening and closing associated with highly prestressed springs.
For example, in known level-regulating systems such as disclosed in European Patent EP 0.867.317 Al there are no corresponding solutions, since these devices have large piston pin diameters along with relatively small piston diameters. The result of this configuration is that the area between the piston rod and the piston diameter comprises a small pressure-loaded surface and therefore requires high prestressing gradients to generate decreasing characteristic curves.
SUMMARY OF THE INVENTION
The object of the invention is to provide a piston-cylinder arrangement having tension damping valves and compression damping valves for independently setting the damping characteristics of the compression stage and the tension stage of the piston-cylinder arrangement, including the damping characteristics at low piston speeds, and having valve disks of the tension damping valves and compression damping valves that comprise relatively large pressure-loaded surfaces for generating decreasing damping force characteristic curves.
The object of the present invention may be achieved in that the passage ducts for the compression valve and the tension valve run axially parallel over at least part of their length so that the inlet and outlet regions of each of the passage ducts are arranged axially one behind the other and in that on each axial side of the working piston one group of passage ducts emerge on the end face and the other group of passage ducts emerges radially outward.
When the diameters of the valve disks are as large as possible in this configuration, large pressure-loaded surfaces are created which respond relatively easily and may be used to achieve decreasing damping force characteristic curves.
In a further embodiment, the compression and tension damping valves comprise spring disks.
According to an essential feature of the present invention, the working piston includes at least two parts.
In an embodiment which is simple to manufacture, a part of a wall of at least one group of passage ducts is formed by the outer circumference of the piston rod.
In another embodiment having a simple design, part of the length of the passage ducts is used for both for the tension stage and for the compression stage of movement.
To ensure automated mounting, according to an essential feature of the present invention, the piston rod has a pin onto which the individual parts of the working piston and of the damping valves may be slipped axially one behind the other and fixed thereon.
According to a further embodiment, the working piston may be designed in two parts in which one of the two parts has elements necessary for compression damping and the other part has the elements necessary for tension damping.
According to a further essential feature, there is provision for the working piston to be designed in two parts in which one of the two parts is arranged for guiding and sealing the piston relative to the working cylinder.
A further embodiment comprises valves disks of at least one of the compression damping valve and the tension damping valve having a constant passageway.
The working piston may also be designed with two valve bodies in which a first of the two valve bodies comprises a nonreturn valve.
To achieve high damping forces during a sudden outward deflection of the vehicle wheel, for example when the vehicle wheel falls into a pothole, the passage ducts of the tension damping valve may comprise a cross section which additionally throttles the damping medium at high piston speeds.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
REFERENCES:
patent: 4624347 (1986-11-01), Mourray
patent: 4821852 (1989-04-01), Yokoya
patent: 3824420 (1990-02-01), None
patent: 19914557 (2000-11-01), None
Butler Douglas C.
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
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