Patent Application
20050183777
1. Field of the Invention
The invention pertains to a damping valve for a vibration damper, including a valve body having a flow channel through which a working medium can flow from one side to the other side of the valve body, the channel having an inlet and an outlet, at least one of the inlet and outlet having a cross-section which is larger than the cross-section of the channel.
2. Description of the Related Art
A working medium flowing through a valve is subjected to a flow resistance which is determined by, among other things, the geometry of a flow channel. Unfavorable flow conditions in a flow channel can generate noise, which it may not be possible to tolerate in certain practical applications. The flow channels of damping valves are therefore provided with special shapes. U.S. Pat. No. 6,401,755 describes a damping valve for a vibration damper, where the damping valve has a funnel-shaped inlet to and/or outlet from the flow channel. The funnel shape occupies a comparatively large amount of space, which is often not available in the case of a damping valve for a vibration damper, because otherwise the walls in the area of the damping valve would become too thin. The damping valve in U.S. Pat. No. 6,401,755 consists of a sintered body, which can be made even into complicated shapes with comparatively little effort.
U.S. Pat. No. 6,018,868 and DE 198 46 460 A1 describe a piston which is made as a precision-stamped part. Stamping necessarily leads to the formation of radii at the transitions to the flow channels around the elevated valve seating surfaces; these radii are highly dependent on manufacturing tolerances. As a result, noise can be produced, and the lifting behavior of the valve disk can be imprecise. The attempt has been made to correct these defects by lightly regrinding the valve seating surfaces, but this manufacturing operation is expensive and requires a subsequent burr-removal step. The burrs on the pistons are removed mechanically by a vibratory grinding process. The pistons are place in a vibrating container together with abrasive bodies and a grinding fluid and kept in constant motion. The burrs are thus knocked off. This process, however, is not especially advantageous with respect to the valve seating surfaces, the surface quality of which can be impaired.
As an alternative to grinding, a pressing of the valve seating surfaces is conceivable, but if the tolerances are unfavorable, undefined geometries can be present in the flow path leading from the flow channels to the valve seating surfaces.
The task of the present invention is to improve the flow channel inside the valve body in such a way that the generation of noise is minimized.
According to the invention, the inlet and/or the outlet has a flow deflection profile in which a vortex flow is produced, the flow filaments of which form a fluid cushion for the working medium.
The fluid cushion acts almost as a bearing for the flow and ensures a nomturbulent or at least low-turbulence flow, so that flow noise at the valve is minimized.
In a further advantageous elaboration, the flow deflection profile is designed as a stepped profile. A stepped profile can also be produced with high precision in valve bodies made by stamping.
The transition between the length of the step and its height can also be rounded to help achieve the desired vortex flow.
Experiments have shown that a stepped profile in which the ratio of the height of the step to its width is in the range of 1:1 to 1:6 produces especially favorable flow conditions.
Alternatively, the flow deflection profile can be formed by a vortex chamber, which is formed in the wall of the flow channel.
To give the flow an effective twist inside the flow chamber, the floor of the flow chamber is rounded in the flow direction.
The flow channels themselves can be produced with satisfactory precision. It is difficult, however, to produce the transition from the flow channel to the seating surface for the valve disk. For this reason, the outlet is designed to merge into the seating surface for the valve disk, and the flow deflection profile is provided upstream of the seating surface. The worst noise is produced at the valve seating surface, because an undefined flow can cause the valve disk to rise abruptly under certain conditions.
In another advantageous embodiment, a processing allowance for the stamping operation at the valve seating surface is included in the distance which determines the height of the step, i.e., the difference between the level of the forward edge and that of the rear edge of the flow deflection profile. Instead of a grinding operation to produce a defined valve seating surface, a much lower-cost stamping operation can thus be performed, which does not require any finishing work on the valve seating surface.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
The single-tube vibration damper 1 consists essentially of a pressure tube 3, in which a valve body in the form of a piston 5 is mounted on a piston rod 7 with freedom of axial movement. At the outlet end of the piston rod 7, a piston rod guide 9 closes off a damping medium-filled working space 11, which is separated by a separating piston 13 from a gas space 15, which has a bottom piece 17 with an eye 19 at the end.
When the piston rod moves, damping medium is displaced through damping valves 21 in the piston 5, which are formed by valve disks 23. A piston ring 25, which extends around the circumference of the piston 5, prevents the medium from flowing around the sides of the piston.
The flow deflection profile 33a can be considered a microprofile in comparison with the size of the outlet 32a and the cross section of the flow channel 31a. Thus, for example, the length 39 of the step in the variant according to
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 008 648.6 | Feb 2004 | DE | national |
