FIELD OF THE INVENTION

The present invention concerns a device for damping of a piston being connected to a piston rod and being moveable to and fro inside a cylinder housing of a cylinder, including a damping recess being associated with the piston and a damping protrusion for co-operation with the damping recess and for attachment to a first cylinder end wall of the cylinder housing, wherein the damping protrusion, with a aid of a first sealing device, is arranged to establish a damping chamber in co-operation with a contact portion inside the damping recess for damping the movement of the piston inside the cylinder housing in the region of a first position of the piston. The invention also concerns a hydraulic cylinder and a shock absorber including such a device as well as a use of such a device .

BACKGROUND OF THE INVENTION

Devices for damping are previously known in the form of arrangements for end position damping in hydraulic cylinders with a moveable piston inside a cylinder room. In an end position of the piston close to a cylinder end wall, a damping chamber is arranged to be established in that a damping protrusion on the one element (the piston or the cylinder end wall) will enter a damping recess in the other element.

Hereby a damping chamber is established which contains a certain amount of hydraulic liquid. During the final movement of the piston in the direction of an end position with

established damping chamber, at least a part of this liquid will now be forced to pass some form of restriction.

Hereby the kinetic energy of the piston and possible associated components will be absorbed by the hydraulic liquid and be transformed to heat in the liquid and adjacent

elements. The restriction can be comprised of the very slot between the damping protrusion and the damping recess, a throttle arranged in a particularly arranged throttle channel or a combination thereof.

For end position damping in both directions, arrangements are known which comprise damping recesses and damping

protrusions associated with both cylinder end walls of the hydraulic cylinder. On the piston rod side it is here arranged such that a damping protrusion is arranged surrounding the piston rod and that a corresponding damping recess is arranged adjacent to the piston rod opening of the cylinder end wall in question. Such a solution requires increased axial dimensions in order to give room for the damping devices.

AIM AND MOST IMPORTANT FEATURES OF THE INVENTION

The aim of the present invention is to provide a further developed device for damping allowing effective damping at the same time as possibility of a compact construction.

This aims are achieved in respect of a device of the kind indicated above in: - that the damping protrusion is

constructed to extend axially in an inside portion of the length of the cylinder housing with a proximal end to be attached to the first cylinder end wall and with a distal, free end in a region inside the hydraulic cylinder opposite to the first cylinder end wall, - that the damping recess is constructed to extend through the piston and into the piston rod and is arranged to receive the damping protrusion in said first position, and - that the damping protrusion in the area of its free end is provided with a second sealing device in order to establish a damping chamber in co-operation with said contact portion also in a second position of the piston. Hereby is achieved that the device can be produced axially very compact, since the components belonging to the damping arrangements as a whole are positional inside the hollow piston and the hollow piston rod of a hydraulic device such as a hydraulic cylinder or a shock absorber.

Hereby no elements have to extend axially from the piston or the cylinder end walls, elements that would unavoidably result in increased axial length of a hydraulic cylinder or a shock absorber wherein they would be inserted.

This is a great advantage since maintained stroke length of a hydraulic device such as a hydraulic cylinder or a shock absorber can be achieved with axially reduced dimensions.

Reversed, an increased stroke length of a hydraulic device such a hydraulic cylinder or a shock absorber can be achieved using the same axial dimensions as in a conventional hydraulic device such as a hydraulic cylinder or a shock absorber.

When, in a preferred aspect of the invention, each sealing device includes a conical portion that is widening in the direction of the respective adjacent end of the damping protrusion, whereupon a flexible sealing ring having conical inside is axially moveable, it is achieved that the damping will be self regulating. Self regulation is based on the fact that the damping protrusion is provided with a conical portion which is widening in the direction of an adjacent cylinder end wall and thus is diminishing inwards, towards the centre of the cylinder, and whereupon a flexible damping ring with a conical inside is axially moveably arranged.

Depending on the speed of the piston when the damping chamber is established, the damping ring will be pressed more or less upwards on the conical portion and consequently will expand more or less radially. Hereby a damping slot between the periphery of the damping ring and the inside of the damping recess will vary depending on the pressure difference between the sides of the damping ring, which results in that the damping will be dependent on the speed of the piston. The higher the speed of the piston, the greater the resulting damping will become.

It should be understood that damping properties can be adapted to the prevailing conditions of the application in question by dimensioning the lengths, diameters, cone angles of the parts involved as well as the hardness and the flexible properties of the sealing rings.

When the damping recess is a bore in the piston rod, manufacture is simplified and an economical and technically advantageous construction is ensured.

Suitably the contact portion is in the form of a portion having reduced inner diameter compared to the remaining parts of the damping recess. It is preferred that the contact portion is comprised of an inner portion of a sleeve inserted inside the damping recess.

It is possible to construct the first and the second sealing devices to have different characteristics in order to obtain different damping properties for the movements in the two movement directions of the piston. This can be suitable if for example different forces are expected in the different directions .

The inventive device is advantageously arranged in a hydraulic cylinder which exhibits inlet/outlet for hydraulic liquid, and which is normally arranged to perform work in connection with a linear movement controlled by supply of said hydraulic liquid. The device is then applied firstly to provide end position damping of the piston movement in the both directions. The first direction of the piston is then a first end position and the second position of the piston is then a second end position. The inventive device is advantageously also applied in respect of a shock absorber, which contains a hydraulic liquid and is normally arranged to damp a movement between two machine parts controlled by the limitation of flow of said hydraulic liquid. The device is then applicable in order to provide extra damping in different length positions or end positions of the piston.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be explained in more detail by way of embodiments and with reference to the drawing, whereon:

Figs. 1 and 2 show axial sections through a hydraulic cylinder according to the invention with arrangements for end position damping in both directions in a first and in a second position of the piston.

DESCRIPTION OF EMBODIMENT

Figs. 1 and 2 illustrate a preferred variant of an inventive hydraulic cylinder 1 with a piston 3 being end position damped in both direction, being connected to a piston rod 4 and being moveable to and fro inside a cylinder housing 2. A first cylinder end wall indicated with 5 exhibits a feed channel 7 for hydraulic liquid. A second cylinder end wall is indicated with 6. From the first cylinder 1 end wall 5 extends a damping protrusion 9 in principle in form of a central rod, which extends from a proximal end 10 through essentially the entire axial length of the hydraulic cylinder to a distal free end 11.

In the shown example, the damping protrusion is a unit including a central screw, which co-operates with a screw hole in the first cylinder end wall. Onto the screw there are arranged components having bores corresponding to the screw, components forming distance portions as well as parts of the sealing devices.

The piston is as conventional provided with usual seals for the co-operation with the cylinder housing.

A damping recess 8 is arranged inside the piston and the piston rod. Altogether, a hollow inside these components form a recess, comprising said damping recess 8, arranged to receive the damping protrusion in a first end position of the piston, which is shown in Fig. 1.

In the region of its proximal end 10, the damping protrusion 9 exhibits a first sealing device 12 for cooperation with a contact portion 17 in the form of a portion such as a sleeve with reduced inner diameter compared to the remaining portion of the damping recess, in order to establish a damping chamber in the region of a first end position of the piston 3. This position is shown in Fig. 1.

Also in the area of its free end 11, the damping

protrusion 9 exhibit a second sealing device 15 for cooperation with said contact portion 17, in order to establish a damping chamber also in a region of a second end position of the piston 3, opposite to the first cylinder end wall 5. This position is shown in Fig. 2.

Each sealing device 12, 15 includes a conical portion 14 and 16, respectively, that is widening in the direction of the respective adjacent end 10, 11 of the damping recess 9. Onto these portions there is a respective flexible sealing ring 13 and 18, having a conical inside, axially moveable. The damping will hereby be self regulating for reasons explained above.

The invention can be modified within the scoop of the following claims. It is for example possible to construct both damping devices with different characteristics in order to obtain different damping properties for the movements in the two movement directions of the piston. The hydraulic cylinder can be constructed differently from what is shown on the drawings, as can the construction of the piston and the piston rod as well as of the contact

portion. The damping protrusion can be made differently and be fastened to the first cylinder end wall with alternative means from what is shown. It is further possible to adapt the length of the parts of the damping protrusion in order to ensure that damping is obtained at desired positions of the piston.

The invention has been described in the above embodiments to the background of a hydraulic cylinder, but it is equally applicable in respect of a shock absorber.

An inventive shock absorber includes a hydraulic liquid, and is normally arranged to damp a movement between two

machine parts controlled by the limitation of flow of said hydraulic liquid. The device according to the invention is hereby applicable in order to provide extra damping in

different length positions or end positions of the piston. The piston can in this case exhibit normal sealing devices vis-avis the cylinder housing and the first and second sealing devices can be arranged for damping in other positions than end positions in order to adapt the shock absorber to

requirements of the applications in question.