Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Patent
1998-05-01
2000-05-02
Knight, Anthony
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
277560, F16J 1532
Patent
active
060562927
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a shaft seal, particularly a seal for the shaft of a hydraulic steering valve, having a sealing ring zone surrounding the shaft and, located on the shaft side of the sealing ring zone, at least one sealing edge which contacts the shaft to form a seal in the region of an annular sealing surface defining a radial plane which lies essentially at right angles to the longitudinal center axis of the shaft, wherein the sealing edge, of which there is at least one, has a contour such that it intersects the annular sealing surface several times. The invention furthermore relates to a method for manufacturing such a shaft seal.
DESCRIPTION OF RELATED ART
Generic shaft seals of the described type are known per se. One of the preferred applications for such seals is in hydraulic steering valves. Hydraulic steering valves, such as rotary disk valves, are known per se. An input shaft and an output shaft that is connected with the input shaft by means of a torsionally elastic element, typically a torque rod, are arranged in a housing. The output shaft engages with the rack of a steering gear via a pinion. Normally, a valve sleeve surrounding the input shaft is connected with the output shaft. Hydraulic fluid is supplied to the corresponding steering ducts through steering bores via connections disposed on the side the housing.
In this type of power-assisted steering valves, shaft seals of the aforementioned type are used. Such seals typically comprise an outer sealing ring zone which is made in such a way that the shaft seal can be fixed relative to the shaft in its housing or to another component. Typically, the sealing ring zone is made of an elastic material with an annular embedding for reinforcement which can also be an elastic element. Normally, at least one sealing edge, which forms a single component together with the elastic material, is disposed on the sealing ring zone pointing toward the shaft. In practice, this sealing edge forms a ring surrounding the shaft, which is usually very small in axial direction, i.e., it takes the form of a ridge. There is typically no drag flow in the direction of the sealing edge, and thus the seal surface, as a function of the system. The seal surface is an imaginary annular surface along the outer contour of a shaft along which the sealing edge contacts the shaft to form a seal. In the absence of drag flow, this may result in inadequate lubrication of the seal surface, particularly in fast rotating shafts. This significantly increases mechanical and thermal stress which is due, among other things, to the fact that there is no fluid exchange in the seal surface or the seal gap. Normally, the sealing edge lies in a plane perpendicular to the shaft axis. Here, lubrication depends on complicated flow processes due to the interaction between microscopic roughnesses and the viscoelastic seal material. To improve lubrication in rotating shafts under unfavorable lubricant flow conditions, it has previously been proposed to arrange an O-ring at an angle to the shaft axis. The use of an O-ring lying at an angle to the shaft axis produces additional friction and also does not permit tolerances, that is, no eccentricity compensation is possible. In fast turning shafts, the seals float and lubrication occurs as a result of what is known as hydrodynamic friction. However, this does not occur with slow moving shafts, for example, those used in power-assisted steering systems.
Characteristic for the steering valve application is the lack of lubrication between the shaft and the seal which occurs because of the slow speeds and the lack of drag flow in the contact area of shaft and seal. This can create undesirably high friction and result in stick slip phenomena including noise.
DE 22 64 042 A1 discloses a shaft seal for fast moving shafts. This seal is made in such a way that the sinusoidal seal edge is formed when the seal portion made of elastic material is manufactured. Since the sealing edge sinusoidally migrates in axial direction and s
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Fortschritte in der Dichtungstechnik, In: Kugellager-Zeitschrift, 242, S. 27-31.
Knight Anthony
TRW Fahrwerksysteme GmbH & Co. KG
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