Brakes – Internal-resistance motion retarder – Resistance alters relative to direction of thrust member
Reexamination Certificate
1996-10-22
2001-06-19
Butler, Douglas C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Resistance alters relative to direction of thrust member
C188S322150, C188S282600, C188S322220
Reexamination Certificate
active
06247563
ABSTRACT:
The invention relates to the pistons of hydraulic dampers, especially those of the pressurized monotube type.
A hydraulic damper includes a piston which can slide inside a tube in order to divide the internal space thereof into two chambers filled with fluid. A through passage is provided within the piston in order to place the two chambers in communication, and interacts with a valve system governing the opening of the passage as a function of the flow of fluid which depends on whether the damper is in a phase of extension or one of compression.
A suspension system can usually be characterized on the basis of a curve giving the force exerted on the damper as a function of the rate of travel of the piston inside it. At the present time, the classical curves deviate, both in the phase of extension and in the phase of compression, from the theoretical damping straight line to follow a progression which is substantially linear but with a rapid deflection on entering the compression phase to end up with a relative stabilization of the force irrespective of the value of the speed.
Now, especially for some types of vehicle, it has been observed that better comfort would require the application of forces which are lower than those which result from the classical damping laws, particularly at high speeds, typically above 0.5 m/s.
The invention aims to provide a solution to this problem, particularly for dampers the piston of which is equipped with a floating valve which is well known to those skilled in the art, in which the same passage paths are used for the flow of fluid in both directions, whereas in other types of hydraulic damper separate flow paths are provided for the compression phase and for the extension phase.
The invention therefore proposes a piston with valve for a hydraulic damper tube, comprising a piston body having a fluid passage interacting with a floating valve element for controlling in both directions the amount of fluid flowing through the passage. According to a general characteristic of the invention, the floating valve element includes a spring washer, the deflection of which in the free state is between approximately 0.1 times and approximately 2 times the thickness of the said washer.
In other words, whereas in conventional pistons with valves the floating valve includes a washer which, as far as manufacturing tolerances allow, is flat, the invention on the other hand envisages forming this floating valve from a spring washer which has a pre-determined deflection in the free state in the context of the present invention, “deflection in the free state” is understood to be the deflection of the washer when it is not mounted on the piston.
The use of such a spring washer makes it possible to obtain a damping law which has one or two points of inflection in the phase of compression and/or of extension.
In other words, such a low lies within the classical damping laws and, especially in the extension phase, has a substantially flat region. The invention therefore makes it possible to reduce the force exerted on the damper at high speeds, and this improves the ride comfort for certain types of vehicles, while at the same time making it possible not to reduce the force excessively at moderate speeds (typically between 0.1 m/s and 0.5 m/s).
It has been observed that a spring washer cone height of less than 0.1 times the thickness does not substantially alter the damping law, whereas at more than twice the thickness there is a risk of the spring washer becoming inverted and thus leading to a malfunction of the floating valve.
A deflection approximately equal to the thickness of this washer has given satisfactory results, in particular good endurance behaviour.
The spring washer may also be preloaded, that is to say that its deflection when mounted on the piston is less than its deflection in the free state. This preload can be obtained by arranging at least one annular shimming plate of chosen thickness between the piston body and a central annular plate supporting an upper annular plate protruding slightly beyond the central plate and against the free edge of which the said spring washer bears.
Another subject of the invention is a spring washer for the floating valve of a hydraulic damper, as defined earlier.
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Charleux Eric
De Carbon Roland Bourcier
Butler Douglas C.
Smith Gambrell & Russell
Societe Francaise Des Amortisseurs de Carbon
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