GB2109482A - Bearing overheat indicating apparatus - Google Patents

Abstract

A bearing overheat indicating apparatus comprises a pin of meltable material 27 which secures weight 25 to arm 28 within a rotating portion of a shaft 19 adjacent, and supported by the bearing, and upon bearing overheat occurring the meltable material 27 melts causing displacement of the weight 25 which causes an out of balance of the shaft which is detected by a vibration detector. in an alternative apparatus a tube 30 secured to the shaft, contains, at an enlarged portion 31, a relatively dense liquid e.g. mercury which is retained by plugs of meltable material, or a meltable solid. <IMAGE>

Description

SPECIFICATION Bearing overheat indicating apparatus This invention relates to apparatus for indicating when a bearing is in an overheated condition and is more particularly suitable for use on a main shaft bearing included in a gas turbine engine.

It will be appreciated that gas turbine engine main shaft bearings must be capable of running at high speeds under high load conditions for long periods. However in the event of failure of the bearing lubricating system, the bearing is subjected to a very rapid increase in temperature due to the frictional effects imposed upon it. This will result in both the rolling elements and bearing races wearing extremely rapidly which if the condition is allowed to persist will ultimately result in total destruction of the bearing.

Obviously in the case of a gas turbine engine used for aircraft propulsion a bearing failure can give rise to a situation in which rapidly rotating engine components are not contained within the engine casing, and the uncontained engine debris may therefore cause damage to adjacent aircraft structure.

As will be appreciated by those skilled in the art most present gas turbine engines are equipped with devices which monitor the level of vibration within the engine. Such vibration monitoring devices are primarily intended to indicate relatively large increases in vibration such as for example in the event of a compressor, or turbine "blade off" occurring.

An object of the present invention is to utilise the vibration indicating devices to indicate when a bearing is in an overheat condition. So avoiding wiring internal to the rotors and slip rings etc.

According to the present invention a bearing overheat indicating apparatus comprises at least one portion of meltable material which is situated within a rotating portion of the bearing race or adjacent shaft, which meltable material melts upon bearing overheat occurring and causes an out of balance of the bearing, which out of balance is detected by a vibration detector.

Preferably the meltable material consists of a low melting point metal, which melts upon an overheat occurring and flows within the bearing race or adjacent shaft portion to cause an out of balance therein.

Alternatively the low melting point material forms a pin or stop which serves to secure a weight which is displaced upon the overheat occurring to cause an out of balance condition.

Preferably the weight is pivotably mounted within the shaft and secured by the low melting point metal in a condition where the bearing is balanced under normal operating conditions.

Alternatively the low melting point material forms as a plug or stopper which melts upon an overheat occurring and allows a supply of relatively dense liquid to be displaced to cause an out of balance situation.

Preferably the dense liquid comprises mercury.

Furthermore such bearing overheat detection apparatus are particularly suitable for use on at least one bearing supporting a gas turbine engine main shaft.

For better understanding of the invention embodiments thereof will be more particularly described by way of example only and with reference to the accompanying drawings in which Figure 1 shown a diagrammatic side view of a gas turbine engine including a main bearing incorporating an embodiment of the present invention.

Figure 2 shows an enlarged view of a main engine bearing showing an embodiment of the invention in greater detail.

Figure 3 shows a view on arrow 3 of the embodiment shown at figure 2.

Figure 4 shows details of a further embodiment of the present invention.

Referring to the drawings a gas turbine engine shown generally at 10 comprises in flow series a low pressure compressor 12, a high pressure compressor 13, combustion equipment 14, a high pressure turbine 15, and a low pressure turbine 1 6 the engine terminating in an exhaust nozzle 1 7.

The high and low pressure compressors and turbines are each supported by high and low pressure main engine shafts 18 and 19, these shafts being rotatably mounted within pairs of rolling element bearings 20 and 21.

A bearing overheat detector made in accordance with an embodiment of the present invention is applied to the most upstream bearing supporting the low pressure shafi 1 9. However such a device could equally well be applied to any particular bearing, or in fact all the bearings if it is considered beneficial to provide such protection.

Figure 2 of the drawings shows an enlarged cross-sectional view of the bearing 21 which supports the upstream end of the low pressure shaft 1 9 and also shows an embodiment of the present invention. The arrangement consists of a radiaily inner bearing race 22 supported upon low pressure shaft 19, and a radially outer bearing race 23 which is supported from fixed structure not shown in the drawings; a plurality of rolling element bearings one of which is shown at 24 being interposed between the two bearing races 22 and 23.

Arranged within the low pressure shaft 1 9 is a pivotably mounted weight 25, as can be seen more clearly from figure 3 of the drawings the pivotably mounted weight 25 is rotatably mounted at pivot points 26 and is prevented from moving rotationally during normal operating conditions by means of a pin 27 which is made from a low melting point material. It will be appreciated that under normal operating conditions it is arranged such that the weight 25 of the structure 28 to which it is pivotably attached are arranged to balance each other out such that substantiaily no out of balance force is imposed upon the bearing and adjacent structure.

If however an overheat occurs in the vicinity of the bearing; the low melting point pin 27 will melt and allow the weight to be displaced by reason of the direction of rotation of the shaft 19 such that the weight will assume the position shown in broken lines at figure 3. Such movement of the weight 25 will thus cause an out of balance force which will manifest itself as a vibration of relatively large magnitude which will be picked up by the engine vibration indicators. The vibration indicator may then provide an indication to the pilot or flight engineer of an engine malfunction of alternatively may provide a signal to the engine control system such that the engine may be automatically shut down.

It is not proposed in this specification to describe the engine vibration monitoring system in detail as these are well known devices which are provided upon all large modern gas turbine engines. Such devices usually comprise a spring loaded mass, the movement of which either changes the capacitance of a capacitor or acts upon a piezo electric crystal to provide the necessary signal.

Figure 4 shows an alternative embodiment of the present invention. In this case a hollow tube 30 is arranged within the shaft 1 9. The enlarged portion of the tube 31 may be filled with a relatively dense liquid such as for example mercury which is retained within the portion 31 of the tube by means of axially extending plugs 32a and 32b which are made from a low melting point material. The weight of the mercury 31 is balanced out in normal operating conditions by the provision of material 33 secured to the wall of the shaft 1 9 to act as a balance weight.

If a bearing overheat condition occurs the axially extending plugs 31 and 32 melt and allow the mercury to go round the tube 30 to a location adjacent the balance weight 33 thus causing an out of balance condition which can readily be detected by the engine vibration detector system.

It will be appreciated that the dense liquid provided at 30 could actually consist entirely of a low melting point solid. However this may cause difficulties in not hot melting quickly enough to avoid damage to the bearing.

Alternatively the cavity 30 could be filled with lead or some other very low melting point metal and the axially extending plugs 32a and 32b may be made from aluminium based alloy. Thus the lead will melt and become liquid before the plugs 31 and 32 melt, such that the device will respond rapidly when the plugs do in fact melt.

Furthermore it will be appreciated that whilst the particularly described embodiments of the present invention have been diiected to a bearing overheat detector suitable for use on an aircraft gas turbine engine. The invention is not restricted to such an application. Such a bearing overheat detector could equally well be used on a variety of machines including rolling element bearings, which are subjected to high loading or speeds etc.

Claims (8)

1. A bearing overheat indicating apparatus comprises at least one portion of meltable material which is situated within a rotating portion of the bearing race or adjacent shaft, which meltable material melts upon bearing overheat occurring and causes an out of balance of the bearing, which out of balance is detected by a vibration detector.

2. A bearing overheat indicating apparatus as claimed in claim 1 in which the meltable material consists of a low melting point metal which metal melts upon an overheat occurring and flows within the bearing race or adjacent shaft portion to cause an out of balance therein.

3. A bearing overheat indicating apparatus as claimed in claim 1 in which the low melting point material forms a pin or step which serves to secure a weight which is displaced upon the overheat occurring to cause an out of balance condition.

4. A bearing overheat indicating apparatus as claimed in claim 3 in which a weight is pivotably mounted within the shaft and secured by the low melting point pin in a condition where the bearing is balanced under normal operating conditions.

5. A bearing overheat detector as claimed in claim 1 in which the low melting point metal forms a plug or stopper which melts upon an overheat occurring and allows a supply of relatively dense liquid to be displaced to cause an out of balance situation.

6. A bearing overheat detector as claimed in claim 5 in which the relatively dense liquid comprises mercury.

7. A bearing overheat indicating apparatus as claimed in any preceding claim suitable for use on at least one bearing supporting a gas turbine engine main shaft.

8. A bearing overheat indicating apparatus as claimed in any preceeding claim, substantially as hereinbefore described by way of example only and with reference to the accompanying drawings.