Depressurization Device for the Bearing Lubricating Chambers of a Turbomachine

1. Field of the Invention

The invention relates to turbomachines, such as aircraft turbojet engines, in which the bearings are permanently lubricated by liquid lubricant feed circuits during operation. Such a circuit normally includes a liquid lubricant reservoir, and a pump for delivering the lubricant to a nozzle situated in the immediate vicinity of each of the bearings. The bearings are mounted in lubrication chambers which are closed by seals and from the, bottom of which a duct leads for the recovery of an emulsion consisting of the liquid lubricant mixed with air. Incorporated in this duct is a recovery pump which delivers the above-mentioned emulsion to a liquid lubricant/air separator after first having been cooled in a suitable cooling device. From the separator the cooled liquid is returned to the reservoir, while the air is evacuated directly to the outside through an exhaust port.

The lubrication chambers surrounding the bearings in a turbomachine are located in areas which are at an excess pressure relative to the internal pressure of these chambers under normal operational conditions of the turbomachine, the excess pressure usually being provided by the compressor of the turbomachine. This arrangement normally prevents any escape of liquid lubricant to the outside of the lubrication chambers.

However, when the operating speed of the turbomachine is below its idling rate, the pressure normally prevailing outside the lubrication chambers may come close to the pressure prevailing inside the chambers, and may even fall below this pressure. Such conditions may particularly occur when there is a considerable fall in the rotational speed for whatever reason, when the machine cuts out and rotates only in self-rotation, when attempts at restarting the machine are made from stop, and when the machine operates without ignition.

Such a reduction in the pressure which normally prevails outside the lubrication chambers of the bearings in a turbomachine causes leakage of lubricant towards the outside of the lubrication chambers. This leakage results in a pollution of the turbomachine and of its immediate environment, which can be seen from the outside. On an aircraft, such leakage results in depletion of the necessarily reduced reserve of lubricant liquid, which can put at risk the engines and, consequently, the aircraft.

2. Summary of the Prior Art

To solve this problem, it is known to fit the lubrication system of a turbomachine with a device for depressurizing the lubrication chambers of the bearings, such as described in FR-A-2 536 120. This device establishes a communication between each chamber and the outside, and maintains in these chambers a pressure equal to the outside pressure increased only by the pressure drop due to the flowing of the air-lubricant emulsion in the device. This device normally comprises a duct, termed a venting duct, connected to each chamber, at least one air-lubricant separator which is usually that of the turbomachine, and an exhaust duct extending from the separator.

However, the device remains ineffective at the low speeds of the turbomachine mentioned earlier, as the compressor no longer provides excess pressure around the lubrication chambers;.

It is an object of the invention therefore to provide an improved depressurization device which permits the lubrication chambers which surround each of the bearings in a turbomachine to be further depressurized in certain conditions, so as to eliminate all risks of a leak of the lubricating liquid by ensuring that, under all operational conditions, the pressure ill the lubrication chambers is always lower than that prevailing outside the said chambers.

According to the invention this object is achieved by equipping the depressurization device of the lubrication chambers with auxiliary pumping means and connecting an external pressure source, preferably the compressor of one or more other turbomachines, to the auxiliary pumping means for operating said pumping means when required, the device including means for controlling the auxiliary pumping means.

In such a device the control means is actuated when a monitoring system of the turbomachine detects that its rotational Speed falls below the normal idling speed. The auxiliary pumping means is then automatically actuated, the effect of which is to lower the pressure in the lubrication chambers sufficiently to prevent any risk of the lubricating liquid leaking out of the chambers.

In a preferred embodiment of the invention the auxiliary pumping means is constituted by a jet nozzle disposed in the exhaust duct of an air/lubricant separator serving the depressurization device, the nozzle being supplied with pressurized air from the external pressure source through a normally closed valve which constitutes the control means.

In another embodiment of the invention the auxiliary pumping means is constituted by a jet nozzle placed in each venting duct, all of the jet nozzles being supplied by pressurized air from the external pressure source through one or more normally closed valves which constitute the control means.

In the case where the turbomachine fitted with the depressurization device of the invention is used on a twin-engine aircraft, the source of external pressure for the device may be constituted by the compressor of the second turbomachine.

The depressurization device of the second turbomachine then preferably comprises a second jet nozzle disposed in the exhaust duct of the air/lubricant separator of the second turbomachine, this second jet nozzle being supplied by pressurized air from the compressor of the first turbomachine through a normally closed second valve.

It is possible to replace the jet nozzles by pumps comprising a blower driven by a turbine supplied with compressed air, but this solution is more costly. It may be noted also that the turbomachines, on grounds of weight and cost, are preferably each equipped with only one air/lubricant separator, which is mechanically driven, but the invention is applicable in the same way to depressurization devices comprising an air/lubricant separator specific to the device.

Preferably the compressors of the first and second turbomachines are connected to the respective jet nozzles by ducts including a common section, and a non-return valve is disposed in each duct between the respective compressor and the common section.

The improved device in accordance with the invention bas the advantage of being light, which is especially important for aircraft. The device is simple and may be made without moving parts other than the valves and closure means for the ducts. The device is consequently reliable and inexpensive.

Further features and advantages of the invention will become apparent from the following description of two preferred embodiments of the invention, given by way of example, with reference to the attached drawings. FIG. 1 shows diagrammatically two turboshaft engines of multiple-engine aircraft, each having associated therewith a depressurization device in accordance with one embodiment of the invention.

FIG. 2 is a diagram showing in greater detail a lubricant supply and return circuit for the bearings of one or other of the turboshaft engines, together with the part of the depressurization device which is associated with this circuit.

FIG. 3 shows diagrammatically two of the engines of a multi-engine aircraft, each having associated therewith a depressurization device in accordance with an alternative embodiment of the invention.

In FIG. 1 the references 10a and 10b indicate in a general manner two turbojet engines of a multi-engine aircraft. The rotating parts of each of these engines 10a and 10b are supported by bearings, the nature and the number of which depend on the type of engines involved. Three of these bearings are shown in each of the engines, being indicated by 12a in the engine 10a and by 12b in the engine 10b.

The lubrication of the bearings 12a, 12b in the engines 10a, 10b is ensured by two lubricating liquid feed circuits 24a, 24b. One of these two circuits is shown diagrammatically in FIG. 2, but since they are identical it will be understood that the other is constructed in a similar manner.

For the sake of convenience, only one bearing 12a, 12b has been represented in FIG. 2, but it will be understood that in practice the circuit 24a, 24b will feed lubricating liquid to all the bearings of the corresponding turbojet engine 10a, 10b. In addition, although the bearing 12a, 12b shown in FIG. 2 is a ball bearing, it will be understood that other types of bearings may equally be involved.

As indicated in FIG. 2, the bearing 12a, 12b is interposed between a rotatable part, constituted here by a shaft 14a, 14b, and a non-rotatable part 16a, 16b. 0n both sides of the bearing 12a, 12b this non-rotatable part 16a, 16b supports a rotary seal 18a, 18b. A lubrication chamber 20a, 20b is thus defined in a substantially fluid-tight manner around the bearing 12a, 12b. The lubrication chamber 20a, 20b is situated in an area 22a, 22b of the turbojet engine which is normally over-pressurized relative to atmospheric pressure, the over-pressure being produced by the compressor of the engine.

Under normal operating conditions of the turbojet engine the arrangement which has just been described ensures that the lubricating liquid, such as oil, introduced into the lubrication chamber 20a, 20b by the feed circuit 24a 24b remains confined in this chamber as a consequence of the pressure difference which prevails between the area 22a, 22b and the lubrication chamber 20a, 20b.

The feed circuit 24a, 24b includes a tank 26a, 26b filled with lubricating liquid 28. A duct 30a, 30b for the delivery of lubricating liquid connects the tank 26a, 26b to a nozzle 32a, 32b situated in each of the lubrication chambers 20a, 20b surrounding the bearings 12a, 12b of the turbojet engine 10a, 10b. The nozzles 32a, 32b are directed towards the bearings 12a, 12b so as to spray the latter continuously with lubricating liquid 28 when the engine is operating. For this purpose, the lubricating liquid delivery duct 30a, 30b includes a lubricating liquid injection pump 34a, 34b.

The lubricating liquid injected under pressure into each of the lubrication chambers 20a, 20b falls back under gravity to the slanting bottom of the chamber, from where it is recovered as a lubricating liquid/air emulsion by means of a duct 36a, 36b fitted with a lubricating liquid recovery pump 38a, 38b. The pump 38a, 38b delivers the emulsion to a separator 40a, 40b for separating the lubricating liquid and the air. Between the pump 38a, 38b and the separator 40a, 40b, the duct 36a, 36b passes through a cooling exchanger 42a, 42b which lowers the temperature of the lubricating liquid by heat exchange with the aircraft fuel.

The lubricating liquid/air separator 40a, 40b is a centrifugal device of known construction, comprising fins or cellular masses which rotate to cause separation of the air from the lubricating liquid under centrifugal action. The lubricating liquid is recovered from the bottom of the separator 40a, 40b by a duct 44a, 44b which returns the liquid to the tank 26a, 26b. The air escapes from the separator 40a, 40b along a central exhaust duct 46a, 46b. If for any reason, the speed of either of the turbojet engines 10a, 10b falls below idling speed, the excess pressure usually prevailing in the zone 22a, 22b surrounding each of the lubrication chambers 20a, 20b can for a while drop below the pressure prevailing inside the chambers. In this event lubricating liquid can leak from the chambers 20a, 20b and cause internal pollution of the turbojet engine. In some cases, lubricating liquid may also find its way into the flow path of the air for the internal operation of the aircraft. Furthermore, a substantial leak can seriously deplete the reserve of lubricating liquid and thus put the engine and the aircraft in danger. To eliminate this risk it is usual to provide the lubrication circuit 24a and 24b of each of the turbojet engines 10a and 10b with a device permitting the depressurization of the lubrication chambers 20a, 20b.

The depressurization device comprises a venting duct 48a, 48b for establishing communication of the lubrication chamber 20a, 20b surrounding each of the bearings of the respective engine with free air. The duct 48a, 48b opens into the upper part of each lubrication chamber 20a, 20b and connects the lubrication chamber to a separator 40a, 40b which separates lubricating liquid and air and which has an air exhaust 46a, 46b. Generally speaking, and for obvious economic reasons, the same air/lubricant separator 40a, 40b and exhaust duct 46a, 46b will be used for the depressurization device and for the lubricant recovery circuit involving the ducts 36a, 36b and 44a, 44b.

The venting ducts 48a, 48b connect each lubrication chamber 20a, 20b to the common separator 40a, 40b of the engine 10a, 10b, and enable the pressure prevailing in each of the lubrication chambers 20a, 20b to be maintained at a level close to atmospheric pressure.

In order that the pressure prevailing in the lubrication chambers 20a, 20b may be lowered still further when, under particular operating conditions of one or other of the turbojet engines 10a and 10b, the pressure in the zone 22a, 22b falls to a value close to atmospheric pressure, in accordance with the invention the depressurization device is provided with an auxiliary pump, preferably situated downstream of the lubricating liquid/air separator 40a, 40b in the exhaust duct 46a, 46b of the separator.

In the embodiment represented in FIGS. 1 and 2 this auxiliary pump is constituted by a jet nozzle 49a, 49b comprising a convergent-divergent unit 50a, 50b placed in the duct 46a, 46b, and a nozzle 51a, 51b opening in the vicinity of the part of smallest section in the convergent-divergent unit and directed downstream. The nozzles 51a, 51b of each of the jet nozzles 49a, 49b is connected to a pressurized air supply duct 52, 52b (FIG. 1), and in operation the jet issuing therefrom draws with it to the outside the air exiting from the separator 40a, 40b along the duct 46a, 46b. Each of the ducts 52a and 52b includes a valve 54a, 54b which is normally closed to render the jet nozzle 49a, 49b inoperative, i.e. when the respective engine is operating in a manner which does not bring about risk of leakage of lubricating liquid to the outside of the lubrication chambers 20a, 20b.

In the embodiment illustrated in FIG. 1, the end of the duct 52a remote from the jet nozzle 49a opens into the compressor 56b of the turbojet engine 10b, and the end of the duct 52b remote from the jet nozzle 49b opens into the compressor 56a of the turbojet engine 10a. A portion of each duct 52a, 52b between the compressors 56a and 56b and the valves 54a and 54b is formed by a common section 52, and a non-return valve 58a is located in the part of the duct 52a between the compressor 56b and the common section 52, and a non-return valve 58b is located in the part of the duct 52b between the compressor 56a and the common section 52.

In operation, the valve 54a or 54b is opened automatically under the control of a suitable circuit 60 when the data supplied to this circuit by sensors provided in the turbojet engine 10a or 10b reveal that the operating speed of the latter is inadequate to ensure that the lubricating liquid will be confined inside the lubrication chambers 20a, 20b which surround each of the bearings of the engine. Opening the valve 54a immediately establishes communication between the air compressor 56b of the turbojet engine 10b and the injection nozzle of the jet nozzle 49a. A pumping effect is then immediately imposed on the air situated in the lubrication chambers 20a surrounding the bearings 12a of the engine 10a, which creates a partial vacuum in these chambers and hence prevents any risk of lubricating liquid leaking from the chambers.

The operation of the depressurization device which is associated with the turbojet engine 10b is identical to that of the device associated with the turbojet engine 10a . It is controlled by the opening of the valve 54b, and results in the creation of a partial vacuum in the lubrication chambers 20b which surrounds the bearings 12b of the engine 10b.

FIG. 3 shows a second embodiment of the invention which can be applied to an assembly of two or more turboshaft engines. For the sake of clarity, only two engines 10a and 10b are shown, but the following description applies similarly to a greater number of engines.

Each turboshaft engine is set up and connected in the same way as the others, and hence the embodiment will be described only in relation to the engine 10a. The compressor of the engine 10a is connected to a common duct 52 by a duct 53a fitted with a non-return valve 58a which permits the flow of air only in a direction towards the compressor-common duct 52. Connected on the enclosures surrounding the bearings of the engine 10a are the venting ducts 48a which lead to free air via an oil separator 40a. The cleansed air issuing from the separator 40a is conducted to the inlet of a jet nozzle 49a which is arranged to be supplied with pressurized air by a duct 55a connected at its other end to the common duct 52. The duct 55a includes a closure means 54a which is normally closed and is automatically controlled by a suitable circuit 60 fitted to the aircraft.

Other turboshaft engines 10 may be arranged and connected in the same way to the common duct 52 under control from the circuit 60, as shown for the engines 10a and 10b.

In operation the common duct 52 is supplied with pressurized air by the compressors of the turbomachines 10, 10a, 10b which are connected to it, but there is normally no air flow in the common duct 52 because all the closure means 54a, 54b etc. are normally closed. If one of the engines, for example the engine 10a, falls below its idling speed, this is detected by the circuit 60 of the aircraft which then opens the closure means 54a. Pressurized air from the duct 52 is thus delivered to the jet nozzle 49a through the duct 55a, thus causing a lowering of pressure in the jet nozzle 49a which is transmitted to the enclosures surrounding the bearings of the engine 10a through the oil separator 40a and the duct 48a.

The embodiments which have just been described with reference to FIGS. 1 to 3 apply solely to multi-engined aircraft. In the more generation case of the prevention of leakage of lubricating liquid from the lubrication chambers which surround the bearings of a turbomachine of any type, it is possible to connect the nozzle of the jet nozzle placed in the venting duct to an external source of compressed air.

It will be noted that the implementation of auxiliary pumping means 49a, 49b in the depressurization device of the bearing chambers 12a, 12b in accordance with the invention is advantageous on account of the fact that the presence of the venting ducts 48a, 48b permits the drop in pressure produced by the pumping means 49a, 49b to be transmitted to the said chambers 20a, 20b.

Placement of the pumping means 49a, 49b in the lubricant recovery duct 36a, 36b would not be effective, as the recovery pumps 38a, 38b are usually of the positive displacement type, for example geared pumps, and would oppose the transmission of the pressure fall between the chambers 12a, 12b and the outside. Moreover, whatever their type, the recovery pumps 38a, 38b generate substantial pressure variations which could not be compensated by the pumping means 49a, 49b of the invention.