Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Reexamination Certificate
1998-01-14
2001-04-10
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
C188S284000, C188S316000, C267S127000
Reexamination Certificate
active
06213261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a hydropneumatic spring, which is preferably arranged between a vehicle body and a wheel guiding part in a motor vehicle, having a fluid-filled cylinder which is entered by an outwardly sealed piston rod connected to a piston which divides the cylinder into first and second working chambers, the first working chamber of the cylinder being in hydraulic connection with a first spring energy store via a valve device for altering the force-deflection progressivity characteristic of the spring (rate of change in the spring force as the spring is deflected), the second working chamber of the cylinder being in hydraulic connection with a second spring energy store, and a bypass connecting the first working chamber to the second working chamber when the hydropneumatic spring is in a mid deflection range.
2. Description of the Related Art
A prior art hydropneumatic spring having two spring energy stores is known from European reference EP 0 634 298 A1. In a spring cylinder, a piston rod is guided over a large portion in an axially movable manner and is sealed outwardly and with respect to a working chamber. The piston rod has a stop plate but does not have a piston. The portion of the piston rod with the stop plate enters the working chamber which is hydraulically connected to a spring energy store via a valve device. When the piston rod is in the mid-spring deflection range, an annular groove provided on the piston rod is connected to the working chamber via a bypass arranged in the piston rod, while a second spring energy store, between the seals, opens out into the piston rod guide. In the mid spring deflection range, the hydraulic connection between the two spring energy stores takes place via the annular groove and the bypass. Therefore, the force-deflection progressivity characteristic of the spring (rate of change of the spring force as a function of the amount of deflection) is consequently less or flatter in the mid spring deflection range. The complex structural design of this prior art spring cylinder entails high costs for the components and high costs for their assembly. In particular, in the spring range in which the second spring energy store is shut off from the annular groove, the pressure of the spring energy store has the effect of exerting a transverse force on the piston rod, which brings about an undesired increase in the frictional force during the axial movement of the piston rod.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a hydropneumatic spring which has a structurally simple, deflection-dependent alteration of the force-deflection progressivity characteristic of the spring, high functional reliability with low friction and low costs in production and assembly.
This object is achieved according to the invention by a piston cylinder unit having a cylinder and a piston connected at an end of a piston rod dividing the cylinder into a first working chamber on the piston rod side of the piston and a second working chamber on the other side of the piston with a bypass being arranged between the first and second working chambers having at least one channel which extends in the axial direction and can be controlled by the outside surface of a piston solidly connected to the piston rod such that the first working chamber and the second working chamber are connected by the bypass when the piston is within a mid-deflection position range. A first spring energy store is in constant operative connection with the first working chamber on the piston rod side and a second spring energy store is in constant operative connection with the second working chamber, via a valve device in each case. The trouble-free connection of the first and second spring energy stores to the first and second working chambers and the deflection-dependently controllable bypass between the first and second working chambers make it possible in a simple way to provide a hydropneumatic spring whose overall spring deflection is subdivided into a plurality of spring deflection ranges with different spring force-deflection rates or progressivities in each of the ranges. The mid spring deflection range, in which the first and second working chambers and consequently the first and second spring energy stores are hydraulically connected to one another by the bypass, has a flat force-deflection progressivity characteristic. The adjoining spring deflection ranges have much steeper force-deflection progressivity characteristic. High functional reliability, in comparison with the prior art reference EP 0 634 298 A1, with low friction of the mutually movable components is obtained, since the piston supported on the inside wall of the cylinder forms the second guide for the piston rod and no radial forces are exerted on the piston rod by the spring energy stores in any spring deflection range.
In one embodiment, according to the invention, the first spring energy store communicates via a valve device and a connection arranged in the cylinder, directly into the first working chamber on the piston rod side, while the second spring energy store is hydraulically connected via the valve device, via a further connection in the cylinder, to the second working chamber remote from the piston rod. The connections of the first and second energy stores are in this case preferably arranged on the cylinder such that they are not covered by the piston. In addition, a pulling stop may, for example, be provided on the piston rod to prevent the piston from reaching the position of the known connection parts may which even protrude slightly into the respective working chamber. Special machining of the inside surface of the cylinder after fitting the connections to the first and second spring energy stores is consequently no longer required.
In another embodiment, as the invention shows, the second spring energy store is hydraulically connected to the second working chamber remote from the cylinder via the valve device and a longitudinal channel arranged in the piston rod. The longitudinal channel is preferably formed by a tubular piston rod. The first spring energy store opens out via the valve device into the first working chamber of the cylinder on the piston rod side as described in the first embodiment. In this way, particularly when the hydropneumatic spring is fitted with an upward extending piston rod, a connection of the second spring energy store is required to take up only the slight movements of the connection joint and may be of a corresponding simple configuration.
This also applies to a further embodiment which is formed by the second spring energy store communicating via the valve device and a connection in the cylinder into the second working chamber while the first spring energy store is hydraulically connected to the first working chamber on the piston rod side via the valve device and a longitudinal bore which is arranged in the piston rod and in which a transverse opening is located proximate the piston between the longitudinal bore and the first working chamber.
In a further embodiment, a very simple and low-cost configuration for the bypass is created by a channel which runs in the longitudinal direction of the cylinder designed such that it is open toward the piston over its entire length and has a varying cross section along the axial direction. This channel may, according to the invention, be formed by a plurality of grooves made in the cylinder. The channel may also have a plurality of longitudinal grooves provided with different lengths, which are arranged in the same position or different positions within the length of the cylinder tube.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustra
Cohen & Pontani, Lieberman & Pavane
Graham Matthew C.
Mannesmann Sachs AG
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