SHAFT SEAL

Abstract: A shaft seal wherein at least one contact surface (7) of a fixed structural part (5), e.g. a bearing housing, cooperates with at least one contact surface (6) of a unit (2) rotating together with the shaft (1), whereby a pressure medium is arranged to be supplied between said surface (6,7) for keeping the surfaces spaced apart. The unit (2) rotating together with the shaft (1) is fitted to the shaft in such a manner that a certain obliquity and movement of the shaft in axial direction relative to said unit is permitted, and that a force is caused to act upon on said unit, which force strives to displace the unit towards the contact surface (7) of the fixed structural part (5) and is counteracted by said pressure medium.

Description: Technical field The present invention refers to a shaft wherein at least one contact surface of a fixed structural part, e.g. a bearing housing, cooperates with at least one contact surface of a unit rotating together with the shaft, whereby a pressure medium is arranged to be supplied between said surfaces for keeping the surfaces spaced apart. Background of the invention Shaft seals are earlier known (see e.g. FR-A-2 385 013), which consists of two discs one of which is fixed to the shaft and the other one being fixed to the bearing housing. By means of a pressure medium - gas or liquid - which is introduced in the slit between the discs, is created a film, which on one hand eliminates friction between the discs and on the other hand provides the sealing. If the pressure medium during operation should cease and the film between the discs thus should disappear, then the seal would break down if no particular steps have been taken for preventing this. Another drawback is that such a seal has a very low ability of absorbing any shaft obliquities. Purpose and most essential features of the invention The purpose of the present invention is to provide a shaft seal of the type mentioned in the introduction, which has an uncomplicated design and provides an efficient and friction free seal, and which furthermore can take up shaft obliquities. This has been achieved in that the unit rotating together with the shaft is fitted to the shaft in such a manner that a certain obliquity and movement of the shaft in axial direction relative to said unit is permitted, and that a force is caused to act upon on said unit, which force strives to displace the unit towards the contact surface of the fixed structural part and is counteracted by said pressure medium, whereby, if the supply of pressure medium should cease during operation, the unit will be displaced on the shaft towards the contact surface of the fixed structural part, thereby closing the slot between the contact surfaces and causing a relative rotation between the unit and the shaft. Description of the drawing The invention hereinafter will be further described with reference to the accompanying drawing, which shows a section through a shaft having fitted thereto a shaft seal according to one embodiment of the invention. Description of the invention In the drawing 1 designates a shaft carrying a disc 2, which by means of a rubber ring 3 is held at and sealed off against the shaft 1. The disc 2 thus will rotate together with the shaft 1. A groove 4 is provided in the disc 2 below the rubber ring 3, in which groove can be collected fragments torn off from the rubber ring 3. In front of the rotating disc 2 is provided a fixed disc 5, e. g. a portion of the bearing housing through which the shaft 1 extends. The rotating disc 2 and the fixed disc 5 have opposed contact surfaces 6 and 7 resp., which by means of a pressure medium, gas or liquid, are kept apart. The pressure medium is supplied via a duct 8 in the fixed disc 5 to the space between the surfaces 6 and 7. Between the fixed disc 5 and the rotating disc 2 is arranged to act a closing force. In the embodiment shown this force is constituted by a magnetic force, in that the fixed disc 5 is equipped with magnets 9 and the rotating disc 2 is made of a magnetic material. The closing force can also be effected in another manner, e g by means of spring force acting upon the rotating disc 2. The closing force shall be so big that, at loss of the pressure medium, the rotating disc 2 is displaced to engagement with the fixed disc 5 and closes the slot therebetween. The pressure medium is supplied to the space between the surfaces 6 and 7 via the duct 8 and provides a gas or liquid film therebetween, which film keeps the discs 2 and 5 separated. As the rotating disc 2 is fitted to the shaft 1 only by means of a sealing ring 3 a certain obliquity of the shaft 1 is permitted relative to the disc 2, and also a certain movement of the shaft 1 in the longitudinal direction caused by thermal expansion. If the supply of pressure medium should cease during operation then the rotating disc 2 would be displaced on the shaft 1 towards the fixed disc 5, as mentioned above, thereby closing the slot between them. The shaft hereby will slip in the sealing ring 3 and a seal breakdown is prevented.

Claims: 1. A shaft seal wherein at least one contact suface (7) of a fixed structural part (5), such as a bearing housing, cooperates with at least one contact surface (6) of a unit (2) rotating together with the shaft (1), whereby a pressure medium is arranged to be supplied between said surfaces (6, 7) for providing the sealing and for keeping the surfaces spaced apart to eliminate friction, characterized in that the unit (2) rotating together with the shaft (1) is connected to the shaft (1) by means of a flexible element (3) in such a manner that a certain obliquity and movement of the shaft in axial direction relative to said unit is permitted, and that a means is provided exerting a force to act upon said unit (2), which force strives to displace the unit towards the contact surface (7) of the fixed structural part (5) and is counteracted by said pressure medium, whereby, upon loss of pressure, said unit (2) will be displaced on the shaft (1) towards the fixed structural part (5), thereby closing the slot between the contact surfaces (6, 7) and causing a relative rotation between said unit (2) and the shaft (1). 2. A shaft seal as claimed in claim 1, wherein the flexible element (3) is an elastic sealing ring (3). 3. A shaft seal as claimed in claim 1 or 2, wherein said force is effected by means of a magnetic force. 4. A shaft seal as claimed in claim 1 or 2, wherein said force is effected by means of spring force.

Inventors: LIND, BJOERN, Lind, Björn
Applicants: SKF NOVA AB
Application year: 1988
Main classification: F16J15
IPC codes: F16J15