GB1582209A - Apparatus for sealing the bearing chamber of a turbo machine shaft - Google Patents

Description

(54) APPARATUS FOR SEALING THE BEARING CHAMBER OF A TURBO MACHINE SHAFT (71) We, MOTOREN- UND TURBINEN- UNION MUNCHEN GmbH, a joint stock company organised under the laws of Germany, of Postfach 50 06 40, 8000 Munchen 50, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a turbomachine having apparatus sealing a bearing chamber of the shaft of the turbomachine, especially a gas turbine engine, having a single-stage compressor or a multi-stage compressor with relatively great stage compression ratio, the compressors being axial and/or radial compressors.It is known to maintain a seal against the turbomachine shaft or another component rotating fixed to that shaft, by passing a stream of sealing fluid, such as air, steam or gas through a contact free seal, e.g. a labyrinth seal, in opposition to leakage flow.

Seal systems which operate in this way are commonly designed so that air or steam or gas is introduced into the bearing chamber via a restrictor body in the form of a labyrinth thereby avoiding the leakage of oil. Air (or steam or gas) unavoidably entering the oil compartment, automatically causes heat to be transferred thereto, an effect of the temperature and material characteristics of the sealing air (or steam or gas) itself, and may result in thermal stressing of the bearing and associated corresponding heating-up of the lubricating oil. Furthermore, sealing air (or steam or gas) entering the bearing chamber may cause foaming of the lubricating oil and other associated problems.

Finally, the problems connected with heat dissipation from the bearing chamber and the recooling of the lubricating oil cannot be neglected.

In some configurations of turbomachines, it is inevitable that a bearing chamber has to be sealed against the highest pressure encountered in the entire machine system.

In the case of a multi-stage machine, where there are no space restrictions in designing a seal for bearing chambers, the problems encountered are not so serious. In this case, however, it is necessary to provide sealing air (or steam or gas) from a middle stage of the machine with a temperature and pressure which are both lower than the highest temperature and the highest pressure in the system. The leakage flow led off through the vent line is either discharged or, as the case may be, re-fed to the machine cycle at a suitable point.

With a single-stage machine (e.g., radial compressor), however, the temperature and pressure of the sealing air cannot be lower at the tapping point than at the machine end.

Sealing of the bearing chamber can therefore only be accomplished by means of a single labyrinth. The same usually applies to multistage machines with larger stage compression ratios (e.g., axial radial compressors). A single labyrinth has also been used where, insufficient space is available for the use of a triple labyrinth.

In the above examples, the sealing medium is, of necessity, air (or gas or steam) at the highest pressure and at the highest temperature encountered in the system, thus giving rise to all the attendant disadvantages for the bearing and the lubricating system (heating-up of the oil compartment, oil foaming, oil defoaming, oil-air separation, oil cooling, bearing temperatures, overall temperature level in the lubricating system, oil quantities). As the pressure ratio across the labyrinth is automatically high, correspondingly great quantities of sealing medium enter the oil compartment.

An object of this intention is to enable satisfactory sealing, especially in cases where only confined space is available for installation, with minimum thermal stressing of the bearings and the lubricating system.

According to the present invention we propose a turbomachine having apparatus sealing a bearing chamber of the turbomachine shaft comprising a dual labyrinth seal system including a first labyrinth seal system including a first labyrinth seal interposed between a supply of high pressure sealing medium and a second chamber surrounding the bearing chamber, and a second labyrinth seal between the said second chamber and the bearing chamber, the seal being maintained by high pressure sealing medium flowing in turn, through the first and second labyrinth seals into the bearing chamber, in opposition to leakage flow.

Preferably a venting system is provided including a vent line for leading some of the sealing medium in the second chamber to a suitable point in the working cycle of the turbomachine, the remainder of the sealing medium flowing into the bearing chamber through the said second labyrinth seal. The pressure upstream of the first labyrinth seal, normally the highest pressure in the entire system, is reduced by it. After passing the first labyrinth seal, most of the sealing air (or steam or gas) is bled off and returned to the machine cycle at a suitable point; the pressure of the remaining air being further reduced in flowing through the second labyrinth seal into the bearing chamber and sealing it thereby.

By means of the vent between the first and second labyrinth seal, the pressure obtaining at this point can be adjusted so that it is only slightly higher than the pressure in the oil compartment or bearing chamber. The pressure ratio across the second labyrinth is therefore low. Consequently the sealing air (gas or steam) flow into the oil compartment is correspondingly small.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which is a schematic longitudinal cross section on the centre line gas-turbine engine.

The gas turbine engine shown in the figure comprises a compressor 1, combustion chamber 2 and gas generator turbine 3 which form the gas generator and mechanically independent free power turbine 4 downstream of gas generator turbine 3.

In the drawing, a bearing chamber 6 directly associated with the bearing 5 has labyrinth seals 10 and 11 and is surrounded by a second chamber 7 having labyrinth seals 8, 9 through which passes a stream of sealing gas. The initially high pressure of the sealing gas outside of the second chamber 7 is reduced as the stream passes through the labyrinth seal 8 or 9 and before entering the labyrinth seals 10, 11 most of the gas is being led off from the second chamber 7 via a vent line 12 and returned to the working cycle upstream of power turbine 4. The remaining smaller volume of the sealing air flows through the labyrinth seals 10, 11 to provide sealing of the bearing chamber 6, and the pressure is further reduced.

A practical example of this invention can be based on the assumption that only about 1/3 of the total tapped sealing gas flow is required for the sealing of the bearing chamber.

Expediently, the cross-sectional areas for that portion of the sealing gas flow entering the second chamber 7 (arrows G) can furthermore be selected so that, in conjunction with the venting system mentioned, the pressure obtaining in the second chamber 7 is only slightly higher than in the bearing chamber 6.

Instead of, for instance, to a single-stage axial compressor this invention would preferably be applicable to multi-stage compressors with relatively large stage pressure ratios, whereby the compressors may be of the axial and/or radial type.

WHAT WE CLAIM IS: 1. A turbomachine having apparatus sealing a bearing chamber of the turbomachine shaft comprising a dual labyrinth seal system including a first labyrinth seal interposed between a supply of high pressure sealing medium and a second chamber surrounding the bearing chamber, and a second labyrinth seal between the said second chamber and the bearing chamber, the seal being maintained by high pressure sealing medium flowing in turn, through the first and second labyrinth seals into the bearing chamber, in opposition to leakage flow.

2. A turbomachine according to claim 1 and comprising a venting system including a vent line leading some of the sealing medium in the second chamber to a suitable point in the working cycle of the turbo-machine, the remainder of the sealing medium flowing into the bearing chamber through the said second labyrinth seal.

3. A turbomachine according to claim 2 wherein the cross-sectional area of the sealing medium flow path at inlet to the second chamber is such that, in conjunction with the venting system the presence in the second chamber is only slightly higher than in the bearing chamber.

4. A turbomachine according to claim 2 which is a gas turbine engine and has compressor means comprising a single stage or multi stage compressor, a combustion chamber, a gas generator turbine, and a mechanically independent free power turbine driven by gases from the gas generator turbine, the said turbomachine shaft interconnecting the compressor means and the gas generator turbine.

5. A turbomachine according to claim 4 wherein the vent line leads from the second chamber to a point immediately upstream of the said free power turbine, the sealing medium being air compressed by the said compressor means.

6. A turbomachine having apparatus sealing a bearing chamber of the turbomachine shaft, constructed and arranged substantially as herein before described with reference to and as illustrated in the accompanying drawing.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. suitable point in the working cycle of the turbomachine, the remainder of the sealing medium flowing into the bearing chamber through the said second labyrinth seal. The pressure upstream of the first labyrinth seal, normally the highest pressure in the entire system, is reduced by it. After passing the first labyrinth seal, most of the sealing air (or steam or gas) is bled off and returned to the machine cycle at a suitable point; the pressure of the remaining air being further reduced in flowing through the second labyrinth seal into the bearing chamber and sealing it thereby. By means of the vent between the first and second labyrinth seal, the pressure obtaining at this point can be adjusted so that it is only slightly higher than the pressure in the oil compartment or bearing chamber. The pressure ratio across the second labyrinth is therefore low. Consequently the sealing air (gas or steam) flow into the oil compartment is correspondingly small. One embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which is a schematic longitudinal cross section on the centre line gas-turbine engine. The gas turbine engine shown in the figure comprises a compressor 1, combustion chamber 2 and gas generator turbine 3 which form the gas generator and mechanically independent free power turbine 4 downstream of gas generator turbine 3. In the drawing, a bearing chamber 6 directly associated with the bearing 5 has labyrinth seals 10 and 11 and is surrounded by a second chamber 7 having labyrinth seals 8, 9 through which passes a stream of sealing gas. The initially high pressure of the sealing gas outside of the second chamber 7 is reduced as the stream passes through the labyrinth seal 8 or 9 and before entering the labyrinth seals 10, 11 most of the gas is being led off from the second chamber 7 via a vent line 12 and returned to the working cycle upstream of power turbine 4. The remaining smaller volume of the sealing air flows through the labyrinth seals 10, 11 to provide sealing of the bearing chamber 6, and the pressure is further reduced. A practical example of this invention can be based on the assumption that only about 1/3 of the total tapped sealing gas flow is required for the sealing of the bearing chamber. Expediently, the cross-sectional areas for that portion of the sealing gas flow entering the second chamber 7 (arrows G) can furthermore be selected so that, in conjunction with the venting system mentioned, the pressure obtaining in the second chamber 7 is only slightly higher than in the bearing chamber 6. Instead of, for instance, to a single-stage axial compressor this invention would preferably be applicable to multi-stage compressors with relatively large stage pressure ratios, whereby the compressors may be of the axial and/or radial type. WHAT WE CLAIM IS:

1. A turbomachine having apparatus sealing a bearing chamber of the turbomachine shaft comprising a dual labyrinth seal system including a first labyrinth seal interposed between a supply of high pressure sealing medium and a second chamber surrounding the bearing chamber, and a second labyrinth seal between the said second chamber and the bearing chamber, the seal being maintained by high pressure sealing medium flowing in turn, through the first and second labyrinth seals into the bearing chamber, in opposition to leakage flow.

2. A turbomachine according to claim 1 and comprising a venting system including a vent line leading some of the sealing medium in the second chamber to a suitable point in the working cycle of the turbo-machine, the remainder of the sealing medium flowing into the bearing chamber through the said second labyrinth seal.

3. A turbomachine according to claim 2 wherein the cross-sectional area of the sealing medium flow path at inlet to the second chamber is such that, in conjunction with the venting system the presence in the second chamber is only slightly higher than in the bearing chamber.

4. A turbomachine according to claim 2 which is a gas turbine engine and has compressor means comprising a single stage or multi stage compressor, a combustion chamber, a gas generator turbine, and a mechanically independent free power turbine driven by gases from the gas generator turbine, the said turbomachine shaft interconnecting the compressor means and the gas generator turbine.

5. A turbomachine according to claim 4 wherein the vent line leads from the second chamber to a point immediately upstream of the said free power turbine, the sealing medium being air compressed by the said compressor means.

6. A turbomachine having apparatus sealing a bearing chamber of the turbomachine shaft, constructed and arranged substantially as herein before described with reference to and as illustrated in the accompanying drawing.