The invention relates to a tilting pad journal bearing for supporting a rotatable shaft.

Tilting pad journal bearings are widely used for supporting rotating shafts in high speed rotary machines, in order to minimise effects of shaft vibrations, and uneven shaft loading.

Traditionally such bearings have used hard metallic pivots, pivotal inserts or spring pivots for mounting bearing pads in the bearing housing (for example, U.S. Patent 4039228 discloses a tilting pad journal bearing having hard pivotal inserts) .

Disadvantages exist with both of the above methods of pad mounting, since a hard pivot tends to amplify shaft vibrations through the bearing housing and into the supporting structure, and spring pivots provide unsatisfactory bearing conformability. Additionally high stresses can occur due to point loading at the pivot point which reduces the life of the bearing, and increases the possibility of bearing failure due to fatigue.

According to the present invention there is provided a tilting pad journal bearing for supporting a shaft, which bearing comprises:

(a) an annular housing locatable around said shaft;

(b) a plurality of movable bearing members, each having an arcuate inner bearing surface and an opposed arcuate outer surface, said members being disposed around said housing such that in use said inner bearing surfaces make bearing contact with said shaft, or a component attached thereto, movement restricting means being provided integral with or attached to said housing and arranged to restrict the circumferential movement of said bearing members relative to said housing; and

(c) a plurality of inwardly projecting pivot members located in said housing, each being disposed contiguous with a respective bearing member, and;

(i) having a concave pivot surface portion arranged to complementarily abut said outer arcuate surface of said bearing member such that each bearing member is pivotable about a respective pivot surface portion; and or, (ii) comprising a polymer material.

The provision of concave pivot surface portions and the use of a polymer material for the pivot members alleviates the abovementioned disadvantages of known bearings.

It is preferred that each of said pivot members is in the form of an elongate member, having its longitudinal axis substantially parallel to said shaft. It is further preferred that the pivot members are of substantially circular cross- section. Preferably the pivot members are of an engineering polymer material, such as a polytheretherketone (PEEK) or the like.

It is preferred that the movement restricting means comprises a plurality of stop members (preferably elongate pins) fixable in the housing adjacent the opposed ends of each bearing member, the longitudinal axis of each of the pins preferably being arranged substantially parallel to the shaft.

Preferably the bearing members are of a ceramic material, or at least provided with a ceramics bearing surface.

Preferably bearing contact is made with a component attached to the shaft, which component is preferably an annular sleeve having an interference fit with the shaft. Advantageously the component is of a ceramic material, or at least provided with a bearing contacting surface of a ceramic material.

It is preferred that the bearing members are regularly spaced around the housing. Advantageously at least four, and more preferably six, bearing members are provided around the housing.

In use, the bearing according to the invention may be air or gas lubricated, or hydrodyna ically lubricated with a suitable lubricant, which lubricant may be water, oil or the like.

The invention will be further described in a particular embodiment, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a sectional end view through a shaft supported by a bearing according to the invention;

Figure 2 is a sectional view along X-X of the bearing shown in Figure 1.

Referring to Figures 1 and 2, a collar 1 is mounted on a rotatable shaft 2 by means of an interference fit. A ceramic sleeve 3 is interference fitted around the collar and axially held by means of a securing sleeve 4 fixed to the collar by means of a screw 5.

Six ceramic bearing pads 6 are arranged in a regularly spaced relationship around an annular housing 7, being located in a U-shaped channel in the housing so as to prevent movement of the pads 6 in the axial direction of the shaft. The pads 6 are mounted on respective cylindrical polymeric pivots 8 located in the housing 7 so as to partially project into the U-shaped channel and support the pads 6. The pivots 8 each have a concave surface portion 10 in the region of contact with the pads 6; the concave surface portion 10 abuts and conforms to the arcuate outer surface of respective bearing pads 6. Location stop pins 9 are mounted in the housing 7 so as to traverse the channel section intermediate the ends of adjacent pads 6, in order to prevent circumferential movement of the pads 6 induced by rotation of the shaft 2.

In operation, the shaft 2 rotates in unison with the collar 1, ceramic sleeve 3 and securing sleeve 4. The outer surface of the ceramic sleeve forms a moving bearing surface with which the bearing pads 6 are in bearing contact. The bearing pads 6, are pivotable on their respective polymer pivots in order to compensate for any radial movement of, or out of balance forces in the rotating shaft. The use of a polymer pivot such as polyetheretherketone (PEEK) , and also the provision of the concave surface portion 10, provides high conformability and damping properties, and improved overall bearing characteristics especially in terms of vibration isolation, reducing vibration transmitted through the bearing to a supporting structure.

The bearing is hydrodynamically lubricated, contained in a sealed unit in a conventional manner.