Cylinder piston rod is guided through one end of the cylinder inwards
Cylinder piston device comprises a cylinder and a cylinder piston rod. The cylinder piston rod is guided through one end of the cylinder inwards and outwards of the cylinder. A damping body is provided for damping the axial movement of the cylinder piston rod with respect to the cylinder. This damping body is deflectable in response to change of direction of the axial movement. A deflection of the damping body results in change of the frictional resistance.
This invention relates to a cylinder piston device in which the movement of the cylinder piston rod with respect to the cylinder is frictionally damped. Such cylinder piston devices are used e.g. as gas springs provided for facilitating the lifting movement of a trunk lid in a motor-vehicle. They may be used, however, also as frictional dampers e.g. in washing machines. Moreover, they may be constructed as combined dampers which have both a frictional and a fluidic damping.
A cylinder piston device comprises a cylinder member having an axis and two ends and further comprising a cylinder piston rod member axially movable with respect to said cylinder member through at least one of the two ends. Frictional damping means are provided for damping the axial movement of the cylinder piston rod member with respect to the cylinder member. These frictional damping means comprise at least one elastic damping body, having a first portion and a second portion. The first portion is axially fixed to a first member of said cylinder member and said cylinder piston rod member, and the second portion is frictionally engageable with a substantially axially extending friction face of a second member of said cylinder member and said cylinder piston rod member. The elastic damping body is prestressed against said friction face. The elastic damping body exerts a damping force onto said cylinder piston rod member when being axially moved with respect to said cylinder member. This damping force is variable in response to a change of direction of the axial movement.
By the variation of the frictional force in response to the direction of axial movement the behaviour of the cylinder piston device can be adapted to various appliances in which the cylinder piston device is included. E. g., it is frequently necessary that in the damper of a washing machine, the damping action is dependent on the direction of axial movement. Particularly in gas springs used for lifting trunk lids or motor bonnets, different friction forces may be required for the lifting movement and the lowering movement.
According to a preferred embodiment, the second portion may be axially deflectable with respect to the first portion. Thus, axial deflection of said second portion occurs in response to axial movement of the cylinder piston rod member with respect to the cylinder member in a predetermined direction. By this axial deflection a change of the damping force occurs.
This preferred embodiment has the advantage of most simple construction and of minimum space requirements within the cylinder piston device.
The second portion of said elastic damping body may be deflectable between a rest position and a position of deflection. The rest position may be defined by a support element axially fixed with respect to the first member. Here, the second portion assumes the rest position in response to axial movement of the cylinder piston rod member in a first direction of movement with respect to the cylinder member and assumes the deflected position in response to axial movement of the cylinder piston rod member with respect to the cylinder member in a second direction of movement.
The geometry of the elastic damping body may be selected such that the elastic damping body provides an increased axial damping force in the rest position and a reduced axial damping force in the deflected position.
The elastic damping body may be made of various materials, such as synthetic plastic materials, natural and synthetic elastomeric materials. Preferably, the elastic damping bodies have an annular shape about the axis. The damping bodies may be made by usual manufacturing methods known in the art for shaping plastic and elastic materials. E. g., the elastic damping body may be produced by injection moulding.
The support element may have an annular supporting face substantially orthogonal with respect to the axis.
The second portion of the elastic damping body may have a friction face-engagement face engageable with the friction face, which friction face-engagement face is convex towards the friction face when viewed in a plane of section containing the axis. By selecting the radius of curvature of the friction face-engagement face, the degree of variation of the damping force in response to change of axial direction may be influenced.
The second portion of said annular elastic damping body may be provided with recesses opening towards the friction face. Such recesses may be used for providing an additional fluidic damping effect, when the cylinder piston rod is moved with respect to the cylinder member. This is particularly true, if the damping body is axially fixed on the cylinder piston rod as a piston member or as a part of a piston member.
The annular elastic damping body may have an annular recess about the axis in at least one end face thereof orthogonal with respect to the axis. This annular recess is preferably provided adjacent the second end portion. By such an annular recess the deflecting behaviour of the damping body may be varied.
If a high degree of deflection is desired, the annular elastic damping body may be provided with axial opposite annular recesses in both end faces thereof.
The first portion of the elastic body may be fixed to the cylinder member, and the second portion of said elastic body may thus be engageable with a friction face of the cylinder piston rod member. E. g., the elastic damping body may be located within the cylinder member adjacent one end of the cylinder member through which the cylinder piston rod member is guided. If a guiding and sealing unit is provided at this end, the elastic damping body may be located adjacent this guiding and sealing unit.
In an alternative embodiment, the elastic damping body is fixed with the first portion thereof with respect to the cylinder piston rod member, and the second portion of the elastic damping body is engageable with an internal friction face of the cylinder member. In particular, the elastic damping body may be fixed to an inner end portion of the cylinder piston rod member within the cylinder member.
The elastic damping body may be a part of a piston unit provided at the inner end of the cylinder piston rod member. As mentioned above, besides the frictional damping, there may be provided a fluidic damping. Such fluidic damping can be achieved in that a throttled passage extends between two working chambers provided on both sides of a piston unit. The throttled passage may be located within the damping body or within another component of a piston unit. It is also possible that the flow resistance of the throttled passage is responsive to the direction of relative movement of the cylinder piston rod member on the onehand, and the cylinder member on the other hand.
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