Improvements in or relating to gas bearings

Abstract

A gas bearing system has at least one gas bearing (30, 32, 34) with a moving part and a static part and which can be operated in both aero-dynamic and aero-static modes. The system has a source (36) of pressurised gas fluidly connected with the bearing and a control system (134) for regulating the supply of pressurised gas to the bearing in dependence on the rotational speed of the moving part. The system has particular application in a turbocharger (1) where a flow of pressurised gas from the source is introduced into the bearing at the start-up and slow down phases of operation of the turbocharger, the flow being stopped, or reduced, when the turbocharger has reached normal operating speeds.

1 . A gas bearing system comprising at least one gas bearing having a moving part and a static part, the parts having opposed surfaces separated by a gap, the at least one bearing being configured to generate a layer of pressurised gas in the gap due to gas-dynamic effects in response to relative movement between the moving and static parts, the system also comprising a source of pressurised gas fluidly connected with the at least one bearing to deliver pressurised gas into the gap, and a control system for regulating the supply of pressurised gas to the at least one gas bearing in dependence on the rotational speed of the moving part, wherein the at least one bearing comprises at least one journal bearing in which the static part comprises a tubular sleeve and the moving part comprises a journal surface of a shaft located within the sleeve, the sleeve having a plurality of restrictors fluidly connected with the source of pressurised gas for admitting pressurised gas from the source into the gap between the journal and the sleeve, a plurality of grooves being spaced circumferentially about the journal surface opposite the restrictors for dynamically generating a layer of pressurised gas in the gap. 
     
     
         2 . A gas bearing system as claimed in  claim 1 , wherein the control system is configured such that, in use, pressurised gas from the source is supplied to the bearing at all times whilst the moving part is rotating, the flow of the pressurised gas being lower at higher rotational speeds of the moving part than at lower rotational speeds. 
     
     
         3 . A gas bearing system as claimed in  claim 1 , wherein the control system is configured such that, in use, pressurised gas from the source is supplied to the bearing at a higher rate when the moving part rotates at speeds below a first threshold speed than when the moving part rotates at speeds at or above the first threshold speed. 
     
     
         4 . A gas bearing system as claimed in  claim 1 , wherein the control system is configured such that, in use, pressurised gas is supplied to the bearing only when the moving part rotates at a speed below a first threshold rotational speed. 
     
     
         5 . (canceled) 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         12 . A gas bearing system as claimed in  claim 1 , wherein, the grooves each having a leading edge, a trailing edge, and a bottom surface. 
     
     
         13 . A gas bearing system as claimed in  claim 12 , wherein the grooves are arranged in two rows spaced apart in an axial direction of the shaft by a central land portion, each groove having an inner edge proximal to the land portion and an outer edge distal from the land portion, the inner edge being offset circumferentially behind the outer edge relative to the intended direction of rotation of the journal surface, the restrictors being circumferentially spaced about the sleeve opposite the land portion. 
     
     
         14 . (canceled) 
     
     
         15 . (canceled) 
     
     
         16 . A gas bearing system as claimed in  claim 12 , wherein the bottom surface of at least one of the grooves is curved so that the depth of the groove varies in a direction between its leading edge and its trailing edge. 
     
     
         17 . A gas bearing system as claimed in  claim 16 , wherein the bottom surface curves from the trailing edge towards the leading edge such that the groove is deeper at the leading edge than the trailing edge. 
     
     
         18 . A gas bearing system as claimed in  claim 16 , wherein the bottom surface curves from the leading edge towards the trailing edge such that the groove is deeper at the trailing edge than the leading edge. 
     
     
         19 . A gas bearing system as claimed in  claim 16 , wherein the bottom surface has a generally u-shaped concave curve, being deeper in a central region between the leading and trailing edges than at the leading and trailing edges. 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . (canceled) 
     
     
         24 . (canceled) 
     
     
         25 . (canceled) 
     
     
         26 . A hybrid static/dynamic gas bearing comprising a static part and a moving part, the static and moving parts having opposed surfaces with a gap in-between, wherein the bearing is a journal bearing, the static part comprising a tubular sleeve and the moving part comprising a journal surface of a shaft located within the sleeve, the sleeve having a plurality of restrictors for introducing a pressurised gas into the gap between the journal and the sleeve, a plurality of grooves being spaced circumferentially about the journal surface opposite the restrictors for dynamically generating a layer of pressurised gas in the gap in response to relative movement of the journal surface and the sleeve. 
     
     
         27 . A hybrid static/dynamic gas bearing as claimed in  claim 26 , wherein each of said grooves has groove having a leading edge, a trailing edge and a bottom surface which is curved to vary the depth of the groove between the leading edge and the trailing edge. 
     
     
         28 . A hybrid static/dynamic gas bearing as claimed in  claim 27 , wherein the bottom surface curves from the trailing edge towards the leading edge such that the groove is deeper at the leading edge than the trailing edge. 
     
     
         29 . A hybrid static/dynamic gas bearing as claimed in  claim 27 , wherein the bottom surface curves from the leading edge towards the trailing edge such that the groove is deeper at the trailing edge than the leading edge. 
     
     
         30 . A hybrid static/dynamic gas bearing as claimed in  claim 27 , wherein the bottom surface is generally u-shaped being deeper in a central region between the leading and trailing edges than at the leading and trailing edges. 
     
     
         31 . (canceled) 
     
     
         32 . (canceled) 
     
     
         33 . A hybrid static/dynamic gas bearing as claimed in  claim 26 , wherein the grooves are arranged in two rows spaced apart in an axial direction of the shaft by a central land portion of the journal surface, each groove having an inner edge proximal to the land portion and an outer edge distal from the land portion, the inner edge being offset circumferentially behind the outer edge relative to the intended direction of rotation of the journal surface and wherein the restrictors are circumferentially spaced about the sleeve opposite the land portion. 
     
     
         34 . (canceled) 
     
     
         35 . (canceled) 
     
     
         36 . (canceled) 
     
     
         37 . (canceled) 
     
     
         38 . (canceled) 
     
     
         39 . A hybrid static/dynamic gas journal bearing comprising a tubular sleeve having a cylindrical surface and a journal surface of a shaft rotationally supported within the cylindrical surface of the sleeve, the sleeve having a plurality of restrictors for introducing a pressurised gas into a gap between the journal surface and the cylindrical surface of the sleeve, a plurality of grooves being spaced circumferentially about the journal surface for dynamically generating a layer of pressurised gas in the gap in response to relative movement of the journal surface and the sleeve, wherein the grooves are arranged in two rows spaced apart in an axial direction of the shaft by a central land portion and configured in a herring bone pattern so as to draw air into the bearing towards the central land in response to rotation of the journal within the sleeve in an intended direction of rotation, the restrictors being circumferentially spaced about the sleeve opposite the land portion of the journal surface.