Brakes – Internal-resistance motion retarder – Valve structure or location
Reexamination Certificate
1997-05-13
2001-08-21
Oberleitner, Robert J. (Department: 3613)
Brakes
Internal-resistance motion retarder
Valve structure or location
C188S282500
Reexamination Certificate
active
06276499
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a hydraulic shock absorber and more particularly to an improved, variable rate, hydraulic shock absorber.
There is a very popular type of hydraulic shock absorber wherein damping forces are obtained by positioning a piston in a sliding cylinder and to divide the cylinder into a pair of oppositely disposed fluid chambers. The piston is provided with two series of apertures each of which permits flow from one chamber to the other. By employing a plurality of stacked type plate valves on the opposite sides of the piston, the flow through the respective apertures can be controlled.
This type of device is quite effective, but as shown in the dotted line view of
FIG. 1
has a generally linear damping force characteristic with respect to displacement or piston speed. That is, as the speed of the piston increases, the damping force increases linearly as shown by the curve D. Although such devices are effective, they tend to require large suspension travels in order to achieve the desired ride characteristics.
There has been proposed, therefore, a type of damping arrangement as shown in FIG.
2
. This type of damping arrangement gives a speed to damping force characteristic as shown by the solid line curve C in FIG.
1
. During the original portion of the suspension travel, there is a relatively high damping force as indicated by the line C
1
. At a particular point P, which occurs at the piston speed Vo, the damping characteristic becomes less progressive in nature as seen by the curve C
2
. This provides very effective damping under small loads and still permits a soft ride without necessitating large suspension travel.
The type of construction employed to achieve the damping curve C in
FIG. 1
is obtained by the structure as shown in FIG.
2
. As seen in this figure, there is a piston rod
11
which is connected to one of the suspended elements in a manner which will be described in more detail later when the preferred embodiment is described. A piston
12
is connected in a suitable manner to the piston rod and is provided with a first series of apertures
13
that are spaced so that their axes lie on a circle set at a fixed distance from the axis of the piston rod
12
. The openings
13
permit flow from the chamber which exists above the piston
12
to a chamber
14
that is formed below it by an associated cylinder.
The flow through the apertures
13
is controlled by a stack plate type valve, indicated generally by the reference numeral
15
and which has a plurality of plate type valve elements
15
a
,
15
b
,
15
c
,
15
d
and
15
e
. These valve elements
15
a
through
15
e
are held on the piston rod by a retainer ring
16
in a manner known in the art. The structure as thus far described is like the conventional structure and would provide a damping force as shown by the curve D in FIG.
1
.
In order to provide the knee-type damping curve C of
FIG. 1
, a pre-load shim
17
is interposed between the plate type valve elements
15
a
and
15
b
. This shim
17
is selected of a desired thickness so as to deflect the valve plates
15
b
,
15
c
,
15
d
and
15
e
as shown in FIG.
2
. This, in effect, gives a pre-load that biases the valve plate
15
a
in its closed position.
A small bypass passage
18
is formed in the piston
12
and communicates the passages
13
with the chamber
14
bypassing the valve
15
. Thus, during initial upward movement of the piston
12
relative to the associated cylinder, the valve
15
will maintain in a closed position and the size of the orifice
18
will determine the shape of the damping curve C
1
. However, at the point P when the piston velocity reaches the velocity Vo, sufficient pressure will be generated so as to overcome the pre-load on the valve element
15
a
and it will open and the damping curve C
2
will then result.
As may be seen, the shim
17
in the conventional structure is disposed so that it is radially outwardly of the series of apertures
13
and hence the pressure or piston velocity at which the valve element
15
will open is fixed within a limited range. This is not desirable because it would be preferred to be able to obtain a damping curve that would have more adjustability so as to suit varying conditions.
It is, therefore, a principal object of this invention to provide an improved variable rate shock absorber of this type.
It is a further object of this invention to provide a shock absorber having a rate that may be varied in a greater range than the prior art type of constructions.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in a hydraulic shock absorber of the type having a cylinder forming a cylinder bore. A piston is slidably supported in the cylinder bore and divide the cylinder bore into a pair of opposite fluid chambers. A piston rod extends from the piston through one end of the cylinder for attachment to one element of a suspension system. The cylinder is connected to the other element of the suspension system so that when the two suspended elements move relative to each other, the piston will traverse the cylinder bore. First and second series of apertures are formed in the piston for permitting flow between the fluid chambers in opposite directions. First and second plate type valves are affixed to the piston in valving relationship to the respective series of apertures for controlling the pressure at which the apertures are opened and hence the damping force. Each series of plate type valves is comprised of a plurality of valve plates that are held in stacked relationship. At least one of these plate type valves includes a shim that is disposed between the valve plates for pre-loading the valve plates disposed between the shim and the piston. The shim is disposed so that it does not extend beyond the outer periphery of the apertures with which it is associated.
REFERENCES:
patent: 4485900 (1984-12-01), Kato et al.
patent: 4724937 (1988-02-01), Fannin et al.
patent: 4972929 (1990-11-01), Ivers et al.
patent: 5085300 (1992-02-01), Kato et al.
patent: 5706919 (1998-01-01), Kruckemeyer et al.
patent: 2103153 (1972-08-01), None
patent: 0632212 (1995-01-01), None
patent: 1367698 (1964-11-01), None
patent: 2106220 (1983-04-01), None
patent: 2157808 (1985-10-01), None
patent: 2226620 (1990-07-01), None
Beutler Ernest A.
Oberleitner Robert J.
Rodriguez Pamela J.
Yamaha Hatsudoki Kabushiki Kaisha
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