GB2107002A

GB2107002A - Journal bearing

Info

Publication number: GB2107002A
Application number: GB08129746A
Authority: GB
Inventors: Leonard Stanley Snell
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1981-10-02
Filing date: 1981-10-02
Publication date: 1983-04-20

Abstract

A journal bearing in the form of a ball race in which one race 12 is constrained against axial movement and one race 14 is movable axially to impose a small axial thrust load on the balls to prevent them skidding. The bearing is supported in fixed structure by means of a squeeze film and comprises a radially movable piston 16 which has a flange 17 that together with a flange 15 on the movable race 14 defines a chamber 22. Pressurised oil supplied to the squeeze film is fed to chamber 22 and acts on the movable race 14 to move it axially. <IMAGE>

Description

SPECIFICATION Journal bearing This invention relates to journal bearings.

Conventionally, journal bearings are made either as plain bearings or as roller bearings. In some applications it is impractical to use plain bearings because of the danger of the bearing seizing due to momentary lack of oil supply. In these applications the use of roller bearings overcomes the danger of the bearing seizing when the oil supply fails for a short period but under some high speed, high power applications, the rollers can skid and cause damage to the bearing.

Much effort has been expended in preventing rollers from skidding.

It is also well known to support bearings in squeeze films of oil to provide vibration damping.

Such a bearing is described in our British Patent 937515.

Generally, ball bearings are employed as thrust bearings and not journal bearings because of the axial constraint afforded by the balls, and such bearings would be unacceptable as journal bearings in high speed, high load applications.

There is a need to provide a journal bearing with rolling elements to enable the bearing to run for short periods without lubrication, whilst preventing the rolling elements skidding.

The invention as claimed enables ball bearings to be used as journal bearings in high speed, high load applications by enabling limited relative axial movement between the inner and outer races, and by utilizing the oil supply to the bearing to bias one of the races axially to impose a nip on the balls to prevent skidding of the balls.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawing which shows schematically a cross-sectional view of part of a journal bearing constructed in accordance with the present invention.

Referring to the drawing there is shown a journal bearing 10 which is mounted in fixed structure 11 of a gas turbine aero engine. The inner race 12 of the bearing is secured to a shaft 13. The outer race 14 is provided with a radially extending flange 1 5 and located around the outer race 14 is an intermediate member 16. The piston 1 6 a cylindrical member with a radially extending flange 17.

The piston 1 6 locates in a recess 1 8 in the fixed structure 11 and the recess forms a chamber into which oil is supplied. The piston 1 6 seals against end flange 19 of the fixed structure, and against a detachable plate 20 which is secured to the fixed structure 11, and effectively forms a seal at points A and B. A portion of the surface of the end plate 20 that faces the piston 1 6 is relieved so that oil supplied to the recess 18 forms a squeeze film in chamber 1 8 and acts on the end face 21 of the piston.

The flanges 1 5 and 17 are dimensioned so as to leave a radial gap between the outer race 14 and flange 17 between flange 1 5 and the piston member 1 6. A hole is provided in the piston 1 6 to allow oil from recess 1 8 to enter into a chamber 22 formed between the flanges 1 5 and 1 7.

Pressurised oil supplied to chamber 22, therefore, acts on the outer race 14 to urge it in an axial direction. This movement imposes an axial thrust load on the balls of the ball race thereby preventing the balls from skidding (shown by arrows T).

The pressurised oil admitted to the recess 1 8 that acts on end face 21 counterbalances the pressure exerted by the oil in chamber 22 on the flange 1 7. Thus the piston chamber 1 6 maintains a seal at points A and B but is free to move in radial directions. Oil supplied to chamber 22 leaks through the gaps between the piston 1 6 and flanges 1 5 and the gaps between the flange 1 7 and the outer race 14 to form a squeeze film.

If desired, pins or dogs (not shown) may be provided between the piston 1 6 and the fixed structure 11 or the plate 20 to prevent the piston 1 6 from rotating with the outer race.

The curved track in which the balls run in the inner and outer race 12 and 14 need not be of the close conformity type. Rather they can be of the form known as deep groove since the balls do not act as a thrust race other than in transmitting the lower anti-skid thrust.

In operation pressurised oil admitted to the recess 18 forms a squeeze film in the manner described in British Patent 937,515 and damps the vibration and orbital movement of the piston 16. A second minor squeeze film is also formed between the outer race 14 and the piston 1 6 as the oil leaks from the chamber 22. The vibration of shaft 13 is thus damped both squeeze films.

Although the above example shows the outer race 14 as the axially movable race it is to be understood that the inner race, may be movable and the outer race made axially immovable. In this case the intermediate member, i.e. piston 1 6 would be located between the inner race and fixed structure in the bore of the inner race and would locate in a recess in such fixed structure.

1. A journal bearing comprising a ball race running between first and second radially spaced races, the first race having a surface extending radially, against which a pressurised fluid can act to move the first race axially relative to the second race, an intermediate member having a radially extending surface which co-operates with the first race to define a pressurisable chamber, and means to admit pressurised fluid into the chamber to act on said radially extending surfaces thereby to move the first race axially relative to the second race and apply an axial thrust load on the balls sufficient to prevent them skidding.

2. A journal bearing according to Claim 1 wherein the intermediate member is located in a recess in relatively fixed structure and is movable radially in the recess, and means are provided for supplying pressurised fluid to the recess to form a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Journal bearing This invention relates to journal bearings. Conventionally, journal bearings are made either as plain bearings or as roller bearings. In some applications it is impractical to use plain bearings because of the danger of the bearing seizing due to momentary lack of oil supply. In these applications the use of roller bearings overcomes the danger of the bearing seizing when the oil supply fails for a short period but under some high speed, high power applications, the rollers can skid and cause damage to the bearing. Much effort has been expended in preventing rollers from skidding. It is also well known to support bearings in squeeze films of oil to provide vibration damping. Such a bearing is described in our British Patent 937515. Generally, ball bearings are employed as thrust bearings and not journal bearings because of the axial constraint afforded by the balls, and such bearings would be unacceptable as journal bearings in high speed, high load applications. There is a need to provide a journal bearing with rolling elements to enable the bearing to run for short periods without lubrication, whilst preventing the rolling elements skidding. The invention as claimed enables ball bearings to be used as journal bearings in high speed, high load applications by enabling limited relative axial movement between the inner and outer races, and by utilizing the oil supply to the bearing to bias one of the races axially to impose a nip on the balls to prevent skidding of the balls. An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawing which shows schematically a cross-sectional view of part of a journal bearing constructed in accordance with the present invention. Referring to the drawing there is shown a journal bearing 10 which is mounted in fixed structure 11 of a gas turbine aero engine. The inner race 12 of the bearing is secured to a shaft 13. The outer race 14 is provided with a radially extending flange 1 5 and located around the outer race 14 is an intermediate member 16. The piston 1 6 a cylindrical member with a radially extending flange 17. The piston 1 6 locates in a recess 1 8 in the fixed structure 11 and the recess forms a chamber into which oil is supplied. The piston 1 6 seals against end flange 19 of the fixed structure, and against a detachable plate 20 which is secured to the fixed structure 11, and effectively forms a seal at points A and B. A portion of the surface of the end plate 20 that faces the piston 1 6 is relieved so that oil supplied to the recess 18 forms a squeeze film in chamber 1 8 and acts on the end face 21 of the piston. The flanges 1 5 and 17 are dimensioned so as to leave a radial gap between the outer race 14 and flange 17 between flange 1 5 and the piston member 1 6. A hole is provided in the piston 1 6 to allow oil from recess 1 8 to enter into a chamber 22 formed between the flanges 1 5 and 1 7. Pressurised oil supplied to chamber 22, therefore, acts on the outer race 14 to urge it in an axial direction. This movement imposes an axial thrust load on the balls of the ball race thereby preventing the balls from skidding (shown by arrows T). The pressurised oil admitted to the recess 1 8 that acts on end face 21 counterbalances the pressure exerted by the oil in chamber 22 on the flange 1 7. Thus the piston chamber 1 6 maintains a seal at points A and B but is free to move in radial directions. Oil supplied to chamber 22 leaks through the gaps between the piston 1 6 and flanges 1 5 and the gaps between the flange 1 7 and the outer race 14 to form a squeeze film. If desired, pins or dogs (not shown) may be provided between the piston 1 6 and the fixed structure 11 or the plate 20 to prevent the piston 1 6 from rotating with the outer race. The curved track in which the balls run in the inner and outer race 12 and 14 need not be of the close conformity type. Rather they can be of the form known as deep groove since the balls do not act as a thrust race other than in transmitting the lower anti-skid thrust. In operation pressurised oil admitted to the recess 18 forms a squeeze film in the manner described in British Patent 937,515 and damps the vibration and orbital movement of the piston 16. A second minor squeeze film is also formed between the outer race 14 and the piston 1 6 as the oil leaks from the chamber 22. The vibration of shaft 13 is thus damped both squeeze films. Although the above example shows the outer race 14 as the axially movable race it is to be understood that the inner race, may be movable and the outer race made axially immovable. In this case the intermediate member, i.e. piston 1 6 would be located between the inner race and fixed structure in the bore of the inner race and would locate in a recess in such fixed structure. CLAIMS

2. A journal bearing according to Claim 1 wherein the intermediate member is located in a recess in relatively fixed structure and is movable radially in the recess, and means are provided for supplying pressurised fluid to the recess to form a squeeze film.

3. A journal bearing according to Claim 2 wherein the intermediate member is provided with an opening which admits pressurised fluid from the recess into the chambers defined between the first race and the intermediate member.

4. A journal bearing according to Claim 2 or Claim 3 wherein the intermediate member has radially extending surfaces which engage radially extending side edges of the recess to provide axial constraint of the intermediate member.

5. A journal bearing according to any one of the preceding claims wherein the first race is a radially outer race and the second race is a radially inner race.

6. A journal bearing substantially as hereindescribed with reference to the accompanying drawing.