GB2570656A

GB2570656A - Coolant system

Info

Publication number: GB2570656A
Application number: GB1801570.1A
Authority: GB
Inventors: Bloor Andrew
Original assignee: Safran Electrical and Power SAS
Current assignee: Safran Electrical and Power SAS
Priority date: 2018-01-31
Filing date: 2018-01-31
Publication date: 2019-08-07
Anticipated expiration: 2038-01-31
Also published as: WO2019149563A1; GB201801570D0; GB2570656B

Abstract

A coolant system 400 for electrical generator 440 in aircraft engine, comprising a turbine 435 driven by a propulsion system fluid (e.g. lubricating and/or cooling fluid of an engine gearbox) circulating in a propulsion system fluid circuit 415 of the aircraft engine. Turbine rotation is transferred to a pump 430. The pump drives a coolant fluid (e.g. oil) around a coolant fluid circuit 410, cooling an electrical generator 440. Advantageously, the segregated independent cooling circuit 410 is separate from the propulsion system fluid circuit 415, reducing possibility of contamination the propulsion system fluid in case of a failure. Preferably, a mechanical or magnetic gearbox 455 creates a speed differential between the turbine and pump. The turbine and pump may comprise permanent magnets and/or electromagnets for causing the magnetic field of a rotating turbine to cause the magnetic means of the pump to rotate, removing the need for fluid seals between them. An auxiliary back-up electrical generator 452 may be coupled to the turbine to generate electricity, which may be stored in a battery or capacitor 495 and used to power the pump 430. A switch 465 or a clutch (265, figure 2) may selectively couple the pump to the turbine.

Description

The invention relates to coolant systems. In particular, the invention relates to coolant systems with total oil segregation, for use in aircraft engines.

Background to the Invention

Electrical generators have both an operating temperature range (within which they can operate) and an optimum temperature range (within which they operate most efficiently). In use, electrical generators create heat due to inefficiencies in generation. Electrical generators are typically cooled by a circulating fluid to ensure a) that they are kept within the operating temperature range, and b) that they are preferably kept in their optimum temperature range.

Aircraft propulsion systems typically comprise an engine which may be connected to an electrical generator. In such systems, the electrical generator may be driven by a gearbox output of the engine to generate the electricity needed to power the aircraft's electrical consumption.

Generally, aircraft engine electrical generators are cooled using an oil filled system by circulating oil being driven by a mechanical pump. To reduce the number of system components, some modern aircraft engines use a single oil system to cool multiple parts of the aircraft engine, such as both the gearbox and the generator being cooled from a single cooling circuit using s shared fluid flow. However, failure of this single oil system will lead to multiple parts ofthe aircraft engine overheating, which can lead to a failure ofthe engine as a whole. Further, failure in one engine area, such as the generator, might cause knock-on effects in another system by contaminants being distributed by the shared fluid flow.

To improve redundancy, in some aircraft engines the electrical generator may have its own self-contained coolant system, complete with its own coolant path, mechanical pump, gearbox and connection to a drive shaft. However, in restricted space environments having multiple redundant coolant systems is often challenging. The reason this is challenging is that, in aircraft applications, the electrical generators are typically under the highest load during idling of the aircraft before take-off. At this time, all of the aircraft's systems will be operating, and the aircraft's entertainment and galley systems may be starting up. During idling, the aircraft's engines will be turning at their lowest speeds (as no thrust is required), hence the drive to the coolant pumps will be at its lowest speed. Additionally, with generators running at lowest speed, currents will be highest and so heat generated due to resistance in them will also be high. To cope with these requirements, prior art coolant systems have been designed to provide sufficient fluid flow at idling speeds to cope with maximum generator output. Thus high cooling capacity coolant systems are required to keep the electrical generators from overheating at idle speeds with high demand. Once at cruise speeds, such coolant systems either overcool the electrical generators, which can move them out of their optimum operating temperature and reduce their efficiency, or otherwise coolant is diverted via a bypass which means energy being used to drive this excess flow via the pump is wasted.

Not only are such redundant coolant systems inefficient, they also bring space and weight penalties to the resultant aircraft engine. There therefore exists a need for an improved coolant system.

Summary of the Invention

According to a first aspect of the invention, there is provided a coolant system for an electrical generator of an aircraft propulsion system, comprising: a turbine configured to be driven in rotation by a propulsion system fluid circulating in a first propulsion system fluid circuit, so as to generate rotational motion; a coolant fluid circuit with a coolant fluid therein for cooling an electrical generator; and a pump, arranged to drive the coolant fluid around the coolant circuit, wherein the rotational motion of the turbine is transferred to the pump, causing the pump to drive the coolant fluid around the coolant fluid circuit.

An advantage of the first aspect of the invention is that it provides an independent coolant system which does not require direct fluid communication with the circulating propulsion system fluid, thereby reducing the possibility of contaminating the propulsion system fluid in the case of a failure.

According to a second aspect of the invention, there is provided an aircraft propulsion system comprising a coolant system in accordance with the first aspect of the invention.

An advantage of the second aspect of the invention is that it provides an aircraft propulsion system with an independently cooled electrical generator which reduces the chance of a failure of the prime mover of the aircraft propulsion system. The aircraft propulsion system of the second aspect of the invention may also be relatively lighter, smaller and/or more efficient than prior art propulsion systems.

According to a third aspect of the invention, there is provided an aircraft comprising an aircraft propulsion system, the aircraft propulsion system comprising a coolant system in accordance with the first aspect of the invention.

An advantage of the third aspect of the invention is that it provides an aircraft with a propulsion system that has an independently cooled electrical generator which reduces the chance of a failure of the prime mover of the aircraft propulsion system. The aircraft may also be relatively lighter, smaller and/or more efficient. This enables the aircraft to be lighter and hence more fuel efficient. Additionally, the aircraft may carry more fuel for a given aircraft weight, thereby extending the range of the aircraft through both efficiency gains and an extended fuel capacity. Moreover, a reduction in aircraft weight may allow a higher take-off weight for a given size of aircraft propulsion system.

Further features of the invention are defined in the appended dependent claims.

Brief Description of the Drawings

By way of example only, the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a coolant system in accordance with the prior art;

Figure 2 shows invention;	a	coolant	system	in	accordance	with	an	embodiment	of	the
Figure 3 shows invention; and	a	coolant	system	in	accordance	with	an	embodiment	of	the
Figure 4 shows	a	coolant	system	in	accordance	with	an	embodiment	of	the
invention.

Detailed Description of Preferred Embodiments

Figure 1 illustrates a coolant system 100 which is known in the prior art for use in aircraft propulsion systems. The coolant system 100 comprises a coolant circuit 110. The coolant circuit 110 contains a coolant fluid (not shown) which can be circulated around the coolant circuit 110. In this illustrated example, the coolant can be oil, which can be circulated to and from an oil sump 120, although any suitable coolant can be used.

The coolant system 100 also comprises a pump 130 arranged within the coolant circuit 110. The pump is configured to circulate the coolant flow around the coolant circuit 110.

The coolant system 100 also comprises an electrical generator 140, which is the object to be cooled. The electrical generator 140 is arranged in or near the coolant circuit 110, such that excess heat can be transferred from the electrical generator to the coolant fluid.

The electrical generator 140 is mechanically coupled to the pump 130, preferably through a reduction gear 150. The electrical generator 140 causes the pump 130 to operate and circulate the coolant fluid in the coolant circuit 110. The reduction gear 150 enables the high output speed of the electrical generator to be reduced to a more suitable input speed for the pump 130. Using the generator 140 to drive its own coolant does reduce the efficiency of the generator. However, this has been taken to be an acceptable compromise in the prior art.

The coolant system 100 also comprises a heat exchanger 160. The heat exchanger 160 allows the coolant fluid to exchange excess heat. In an aircraft engine, the heat exchanger 160 is typically an oil to air heat exchanger, which is located at or near an air interface surface of the aircraft engine. The heat exchanger 160 increases the efficiency of the coolant system 100, thereby enabling a smaller pump 130 and/or smaller coolant circuit 110. Other heat exchangers, such as oil-air, oil-fuelor oil-oil heat exchangers can be employed.

The coolant system 100 also comprises a pressure relief valve 170. The pressure relief valve 170 allows excess pressure, which can be caused by changing operational environments, to be vented from the system.

The coolant system 100 may also comprises a filter 180, a bypass 190 and a further pressure relief valve 195. The filter 180 allows unwanted particulates to be removed from the coolant fluid. The bypass 190 permits the coolant to be circulated when the filter 180 becomes totally blocked by debris. The pressure relief 195 enables some of the coolant fluid to be removed from circulating in the coolant circuit 110 when all of the available coolant fluid flow is not required.

The prior art coolant system 100 described above is typical of a mechanically driven oil pump which draws mechanical power from the generator input shaft, preferably via a set of reduction gears. The oil is drawn from the sump 120 through the pump 130, heat exchanger 160 and filter 180 to then lubricate and cool the active components of the electrical generator 150. The speed of the pump 130 and therefore the oil flow rate, is dictated by the speed of the output of the generator. This gives a low oil flow rate at a low generator speed and a high oil flow rate at a high generator speed.

It is a feature inherent in the design of a variable frequency electrical generator that its efficiency increases with its speed. When operating at high load and low speed conditions the most heat is developed, due to the high currents requires to generate the necessary power. At high speed, even at high load, much less heat is developed. The coolant system 100 must be sized according to the needs of the electrical generator 150 during low speed/high load operation. A large coolant system 100 is required to ensure sufficient cooling during low speed/high load operation. This means that at high speeds, considerable power is lost driving the pump 130 since most of the coolant fluid flow may be diverted by the by-pass 190 to not pass near or through the electrical generator 140, effectively wasting a significant amount of the input power during a large proportion of the operating cycle of the generator.

Figure 2 illustrates a coolant system 200 in accordance with a first embodiment of the invention. The coolant system 200 comprises a coolant circuit 210. The coolant circuit 210 contains a coolant fluid (not shown) which can be circulated around the coolant circuit 210 to cool a generator 240. In this illustrated example, the coolant fluid is oil, which can be circulated to and from an oil sump 220.

The coolant system 200 also comprises a pump 230 arranged within the coolant circuit 210. The pump 230 is configured to circulate the coolant fluid around the coolant circuit 210.

The coolant system 200 may also comprise, or at least be in thermal communication with, an electrical generator 240, which is the object to be cooled. The coolant circuit 210 is arranged in proximity to, or through a part of, the electrical generator 240, such that excess heat can be transferred from the electrical generator 240 to the coolant fluid.

The coolant system 200 also comprises a heat exchanger 260. The heat exchanger 260 allows excess heat in the coolant circuit 210 to be removed. In an aircraft engine, the heat exchanger 260 is typically an oil to air heat exchanger, which is located at or near an air interface surface of the aircraft engine. The heat exchanger 260 increases the efficiency of the coolant system 200, thereby enabling a smaller pump 230 and/or smaller coolant circuit 210.

The coolant system 200 also comprises a pressure relief valve 270. The pressure relief valve 270 allows excess pressure, which can be caused by changing operational environments, to be vented from the system.

The coolant system 200 also comprises a filter 280, a bypass 290 and a further pressure relief valve 295. The filter 280 allows unwanted particulates to be removed from the coolant fluid. The bypass 290 permits the coolant to be circulated when the filter 180 becomes totally blocked by debris. The pressure relief 295 enables some of the coolant fluid to be removed from circulating in the coolant circuit 210 when all of the available coolant fluid flow is not required.

Aircraft propulsion systems as described herein typically include an aircraft engine and a generator configured to generate power for electrical systems of the aircraft from a mechanical, typically rotational, output of the aircraft engine. The coolant system 200 also comprises a turbine 235. The turbine 235 is arranged within a propulsion system fluid circuit 215, such that circulation of a propulsion system fluid within the first propulsion system fluid circuit 215 causes the turbine to rotate. This rotational force can be harnessed to drive the pump 230, and thereby drive the coolant fluid in the coolant fluid circuit 210. The propulsion system fluid and its fluid circuit in all embodiments described herein may be a lubricating and/or cooling fluid, such as oil, comprised in the aircraft engine or a related part of the system such as a gearbox, for example. The propulsion system fluid circuit may therefore be an engine fluid circuit, or a gearbox fluid circuit, or some other fluid circuit of the propulsion system, distinct from the generator coolant circuit 210.

One advantage of this arrangement is that the two fluid circuits 210, 215 are independent, in that they do not share a common fluid. Failure of the coolant fluid circuit (by for example a fluid leak or a fluid contamination) 210 will have no effect on the propulsion system fluid circuit 215. Similarly, contamination of the coolant fluid by any other failure within the generator will not affect the first propulsion system fluid.

A further advantage of this arrangement is that generator 240 is not required to drive the coolant fluid in the coolant circuit 210, as is the case in the prior art. This reduction of demand on the generator 240 leads to the generator 240 being more efficient, since power for driving fluid in the coolant circuit can pass more directly from the engine to the coolant circuit, without being subject to conversion losses associated with passing via the input shaft of the generator.

To drive the pump 230, the turbine 235 may be directly mechanically linked to the pump 230. Any suitable mechanical link known in the art may be used, such as a drive shaft, with or without reduction gears. With a direct mechanical link, fluid seals (not shown) are required to ensure separation of fluid between the coolant and first propulsion system fluid circuits 210, 215.

The coolant system 200 may also comprise a speed converter device 255. The speed converter device 255 is arranged between the turbine 235 and the pump 230. The speed converter device is configured to receive a rotational input torque from the turbine 235 and to output rotational torque to the pump 230. The speed converter device is arranged to cause a rotational speed differential between the input rotational force it receives from the turbine 235 and the rotational force it outputs to the pump 230. In this manner, the speed of the pump 230 (and hence the fluid flow in the coolant circuit 210) can be adjusted to be greater than, or less than, the fluid flow in the propulsion system fluid circuit 215. The speed differential can therefore be selected as a suitable speed differential depending upon the operating conditions of the generator or the engine to which it is connected. Operating conditions which may influence the speed differential may include the engine rotational speed, electrical load on the generator, or both, among others.

Where the pump 230 and the turbine 235 are mechanically linked, the speed converter device may be a gearbox or any other mechanical speed conversion device. The speed conversion device is preferably configurable to provide a plurality of different speed differentials, which are selectable.

The coolant system 200 may further comprise a pump decoupling device 265. The pump decoupling device 265 is arranged between the turbine 235 and the pump 230. The pump decoupling device 265 is configured to decouple the rotation of the turbine 265 from the pump 230. In this exemplary embodiment, the pump decoupling device 265 may be a solenoid, mechanical relay or clutch capable of decoupling the mechanical link between the turbine 235, the pump 230 and/or the speed converter device 255. Alternatively, the pump decoupling device 265 may form part of a speed converter device, and be arranged to stop or limit torque transfer across the speed converter device 255.

The coolant system 200 may further comprise sensing means 275. The sensing means 275 is arranged to monitor the movement and/or output of the pump 230. Monitoring movement and/or output (or the lack thereof) enables the electrical generator 240 to be controlled to reduce or stop its output to avoid overheating in the event of a failure in the coolant system 200. The sensing means 275 may use any suitable sensor to achieve this monitoring, such as an optical movement sensor, an electrical current and/or voltage sensor, or a magnetic sensor (to sense movement of one or more magnetic fields).

The coolant system 200 may further comprise an auxiliary motor drive 285. The auxiliary motor drive is operably coupled to the pump 230. The auxiliary motor drive 285 is configured to cause the pump to drive the coolant fluid around the coolant fluid circuit 210. The auxiliary motor drive 285 may be used instead of, or in addition to, the drive provided through the turbine/pump coupling. The auxiliary motor drive 285 provides a back-up method of driving the pump 230 in the event of a failure of the turbine 235 or a failure in the first propulsion system fluid circuit 215.

The auxiliary motor drive 285 may be an electric motor configured to drive the pump 230, a mechanical motor configured to drive the pump 230, a mechanical drive shaft configured to drive the pump 230, an electromagnetic winding configured to drive the pump 230, or any other suitable means for driving a pump known in the art.

In some environments, the risk of failure of the fluid seals required to isolate the coolant fluid circuit and first propulsion system fluid circuits 210, 215 may be unacceptable. Figure 3 shows an alternative arrangement of the present invention which addresses this risk.

As with coolant system 200, coolant system 300 comprises one or more of a coolant fluid circuit 310 suitable for cooling an electrical generator 340 and an oil sump 320. The coolant system 300 may also comprise, or be in thermal communication with an electrical generator 340, which is the object to be cooled. The coolant system 300 may also comprise one or more of a heat exchanger 360, a pressure relief valve 370, a filter 380, a bypass 390 and a further pressure relief valve 395.

The coolant system 300 also comprises a turbine 335. The turbine 335 is arranged within a propulsion system fluid circuit 315, such that circulation of a propulsion system fluid within the propulsion system fluid circuit 315 causes the turbine to rotate. This rotational force can be harnessed to drive the pump 330, and thereby drive the coolant fluid in the coolant fluid circuit 310. In this exemplary embodiment, the turbine 335 comprises one or more magnetic means (not shown). The magnetic means may be permanent magnets or electromagnets. The magnetic means cause the turbine 335 to produce a rotating magnetic field when the turbine 335 is being rotated by propulsion system fluid flowing in the propulsion system fluid circuit 315.

The coolant system 300 also comprises a pump 330 arranged within the coolant fluid circuit 310. The pump 330 is configured to circulate the coolant fluid around the coolant fluid circuit 310. In this exemplary embodiment, the pump 330 also comprises one or more magnetic means. The magnetic means may be permanent magnets or electromagnets. The magnetic means are arranged such that the rotating magnetic field of the turbine 335 causes the magnetic means of the pump 330 to rotate, thereby enabling the pump 330 to drive the coolant fluid through the coolant fluid circuit 310.

The use of a magnetically coupled turbine 335 and pump 330 removes the need for fluid seals in the coolant and first propulsion system fluid circuits, and hence removes the risk associated with failure of such seals. As with the previous exemplary embodiment, an advantage of this arrangement is that the two fluid circuits 310, 315 are independent, in that they do not share a common fluid. Failure of the coolant fluid circuit 310 (by for example a fluid leak or a fluid contamination) will have no effect on the first propulsion system fluid circuit 315.

A further advantage of this arrangement is that generator 340 is not required to directly drive the coolant fluid in the coolant fluid circuit 310, differently to the case in the prior art. This reduction of demand on the electrical generator 340 leads to the electrical generator 340 operating more efficiently, since power for driving fluid in the coolant circuit can pass more directly from the engine to the coolant circuit, without being subject to conversion losses associated with passing via the input shaft ofthe generator.

The coolant system 300 may also comprise a speed converter device 355. The speed converter device 355 is arranged between the turbine 335 and the pump 330. The speed converter device 355 is configured to receive input rotational torque from the turbine 335 and to output rotational torque to the pump 330. In this exemplary embodiment, the speed converter device 355 may be a magnetic gearbox, which is coupled to both the turbine 335 and the pump 330.

The speed converter device 355 is arranged to cause a rotational speed differential between the input rotational force it receives from the turbine 335 and the rotational force it outputs to the pump 330. In this manner, the speed ofthe pump 330 (and hence the coolant fluid flow in the coolant fluid circuit 310) can be adjusted to be greater than, or less than, the propulsion system fluid flow in the propulsion system fluid circuit 315. The rotational speed differential may be selectable depending upon operating parameters of the engine and/or generator, as discussed in relation to Figure 2.

The coolant system 300 may further comprise a pump decoupling device 365. The pump decoupling device 365 is arranged between the turbine 335 and the pump 330. The pump decoupling device 365 is configured to decouple the rotation ofthe turbine 365 from the pump 330. In this exemplary embodiment, the pump decoupling device 365 may be a solenoid or mechanical relay capable of decoupling the magnetic fields of the turbine 335, the pump 330 and/or the speed converter device 355. Alternatively, the pump decoupling device may form part of a speed converter device, and be arranged to stop or limit torque transfer across the speed converter device 365.

The coolant system 300 may further comprise sensing means 375. The sensing means 375 is arranged to monitor the movement and/or output of the pump 330. Monitoring movement and/or output (or the lack thereof) enables the electrical generator 340 to be controlled to reduce or stop its output to avoid overheating in the event of a failure in the coolant system 300. The sensing means 375 may use any suitable sensor to achieve this monitoring, such as an optical movement sensor, an electrical current and/or voltage sensor, or a magnetic sensor (to sense movement of one or more magnetic fields).

The coolant system 300 may further comprise an auxiliary motor drive 385. The auxiliary motor drive is operably coupled to the pump 330. The auxiliary motor drive 385 is configured to cause the pump to drive the coolant fluid around the coolant fluid circuit 310. The auxiliary motor drive 385 may be used instead of, or in addition to, the drive provided through the turbine/pump coupling. The auxiliary motor drive 385 provides a back-up method of driving the pump 330 in the event of a failure of the turbine 335 or a failure associated with the propulsion system fluid circuit 315.

The auxiliary motor drive 385 may comprise an electric motor configured to drive the pump 330, a mechanical motor configured to drive the pump 330, a mechanical drive shaft configured to drive the pump 330, an electromagnetic winding configured to drive the pump 330, or any other suitable means for driving a pump known in the art.

Figure 4 shows an alternative embodiment of the present invention which also overcomes the risk of failure of the fluid seals. As with coolant system 200, coolant system 400 comprises one or more of a coolant fluid circuit 410 suitable for cooling an electrical generator 440 and an oil sump 420. The coolant system 400 may also comprise an electrical generator 440, which is the object to be cooled. The coolant system 400 may also comprise one or more of a heat exchanger 460, a pressure relief valve 470, a filter 480, a bypass 490 and a further pressure relief valve 495.

The coolant system 400 also comprises a turbine 435. The turbine 435 is arranged within a first propulsion system fluid circuit 415, such that circulation of a propulsion system fluid within the first propulsion system fluid circuit 415 causes the turbine to rotate. This rotational force can be harnessed to drive the pump 430, and thereby drive the coolant fluid in the coolant fluid circuit 410. In this exemplary embodiment, the turbine 435 comprises one or more magnetic means (not shown). The magnetic means may be permanent magnets or electromagnets. The magnetic means cause the turbine 435 to produce a rotating magnetic field when the turbine 435 is being rotated by propulsion system fluid flowing in the propulsion system fluid circuit 415.

The coolant system 400 also comprises an auxiliary electrical generator 452. The auxiliary electrical generator 452 is rotationally coupled to the turbine 435. The rotating magnetic field generated by rotation of the turbine 435 causes the auxiliary electrical generator to generate electrical power.

The coolant system 400 also comprises a pump 430 arranged within the coolant fluid circuit 410. The pump 430 is configured to circulate the coolant fluid around the coolant fluid circuit 410. In this exemplary embodiment, the pump 430 may also comprises one or more magnetic means. The magnetic means may be permanent magnets or electromagnets. The magnetic means can be arranged such that an external rotating magnetic field can cause the magnetic means of the pump 430 to rotate, thereby enabling the pump 430 to drive the coolant fluid around the coolant fluid circuit 410.

The auxiliary electrical generator 452 is coupled to the pump 430. The electricity generated by the auxiliary electrical generator 452 may be used to directly drive the pump 430 through an electrical coupling. Alternatively, the generated electricity may be used to drive a stator coil (not shown) which causes magnetic means forming part of the pump (not shown) to drive the pump 430. This embodiment thus provides a method of electrically coupling the two isolated fluid circuits 410, 415.

The coolant system 400 may further comprise electrical storage means 495. The electrical storage means can be used to store excess generated electricity, smooth the supply of electricity and/or supply stored electricity when required.

The electrical storage means may be any device suitable for storing electrical energy, such as a battery or a capacitor.

The coolant system 400 may further comprise a pump decoupling device 465. The pump decoupling device 465 is arranged between the turbine 435 and the pump 430. The pump decoupling device 465 is configured to decouple the rotation of the turbine 465 from the pump 430. In this exemplary embodiment, the pump decoupling device 465 may be a switch or relay which breaks the electrical coupling between the pump 430 and the turbine 435.

The coolant system 400 may further comprise sensing means 475. The sensing means 475 is arranged to monitor the movement and/or output of the pump 430. Monitoring movement and/or output (or the lack thereof) enables the electrical generator 440 to be controlled to reduce or stop its output to avoid overheating in the event of a failure in the coolant system 400. The sensing means 475 may use any suitable sensor to achieve this monitoring, such as an optical movement sensor, an electrical current and/or voltage sensor, or a magnetic sensor (to sense movement of one or more magnetic fields).

The coolant system 400 may further comprise an auxiliary motor drive 485. The auxiliary motor drive is operably coupled to the pump 430. The auxiliary motor drive 485 is configured to cause the pump to drive the coolant fluid around the coolant fluid circuit 410. The auxiliary motor drive 485 may be used instead of, or in addition to, the drive provided through the turbine/pump coupling. The auxiliary motor drive 485 provides a back-up method of driving the pump 430 in the event of a failure of the turbine 435 or the propulsion system fluid circuit 415.

The auxiliary motor drive 485 may be an electric motor configured to drive the pump 430, a mechanical motor configured to drive the pump 430, a mechanical drive shaft configured to drive the pump 430, an electromagnetic winding configured to drive the pump 430, or any other suitable means for driving a pump known in the art.

The use of an electrically coupled turbine 435 and pump 430 removes the need for rotational fluid seals between the coolant and first propulsion system fluid circuits, and hence removes the risk of failure of such seals causing contamination of one fluid circuit the other fluid circuit. As with the previous exemplary embodiments, an advantage of this arrangement is that the two fluid circuits 410, 415 are independent, in that they do not share a common fluid. The risk of failure of the coolant fluid circuit 410 (by for example a fluid leak or a fluid contamination) having an effect on the first propulsion system fluid circuit 415 is therefore greatly reduced.

A further advantage of this arrangement is that generator 440 is not required to drive the coolant fluid in the coolant fluid circuit 410. This reduction of demand on the electrical generator 440 leads to the electrical generator 440 being more efficient, since power for driving fluid in the coolant circuit can pass more directly from the engine to the coolant circuit, without being subject to conversion losses associated with passing via the input shaft of the generator.

The coolant system 400 may also comprise a speed converter device 455. The speed converter device 455 is arranged between the turbine 435 and the pump 430. The speed converter device 455 is configured to change the rotational speed differential between the turbine 435 and the pump 430. In this exemplary embodiment, the speed converter device 455 may be any device capable of adjusting the electrical output of the auxiliary electrical generator 452. In this manner, the speed of the pump 430 (and hence the coolant fluid flow in the coolant fluid circuit 410) can be adjusted to be greater than, or less than, the first propulsion system fluid flow in the first propulsion system fluid circuit 415. The speed differential can therefore be selected as a suitable speed differential depending upon the operating conditions of the generator or the engine to which it is connected. Operating conditions which may influence the speed differential may include the engine rotational speed, electrical load on the generator, or both, among others.

Features of the present invention are defined in the appended claims. Whilst particular combinations of features have been presented in the claims, it will be appreciated that other combinations, such as those provided above, may be used.

The above example describe one way of implementing the present invention. It will be appreciated that modifications of the features of the above examples are possible within the scope of the independent claims.

Claims

1. A coolant system for an electrical generator of an aircraft propulsion system, comprising:

a turbine configured to be driven in rotation by a propulsion system fluid circulating in a first propulsion system fluid circuit so as to generate rotational motion;

a coolant fluid circuit with a coolant fluid therein for cooling an electrical generator; and a pump, arranged to drive the coolant fluid around the coolant circuit, wherein energy from the rotational motion of the turbine is transferred to the pump, causing the pump to drive the coolant fluid around the coolant fluid circuit using energy obtained from the propulsion system fluid flowing in the first propulsion system fluid circuit.

2. The coolant system of claim 1, further comprising:

a speed converter device, arranged between the turbine and the pump, wherein the speed converter device is configured to cause a rotational speed differential between the turbine and the pump.

3. The coolant system of claim 2, wherein the speed converter device comprises a magnetic gearbox.

4. The coolant system of claim 3, wherein the turbine comprises a first magnetic means, the first magnetic means configured to magnetically couple to the magnetic gearbox.

5. The coolant system of claim 4, wherein the pump comprises a second magnetic means, the second magnetic means configured to magnetically couple to the magnetic gearbox.

6. The coolant system of claim 5, wherein the first magnetic means comprises a permanent magnet, and/or the second magnetic means comprises a permanent magnet.

7. The coolant system of claim 2, wherein the speed converter device comprises a mechanical gearbox.

8. The coolant system of claim 1, further comprising:

an auxiliary electrical generator, the auxiliary electrical generator being mechanically coupled to the turbine and electrically coupled to the pump, wherein the rotational motion of the turbine causes the auxiliary electrical generator to generate electricity, and wherein the pump is powered by the generated electricity.

9. The coolant system of claim 8, further comprising:

electrical storage means, the electrical storage means being electrically coupled to the auxiliary electrical generator and the pump, wherein the electrical storage means is configured to store generated electricity and to supply stored electricity to the pump.

10. The coolant system of any preceding claim, further comprising:

a pump decoupling device, the pump decoupling device arranged to decouple the pump from the turbine.

11. The coolant system of any preceding claim, further comprising a sensing unit, operably coupled to the pump, wherein the sensing unit is arranged to monitor an output of the pump.

12. The coolant system of any preceding claim, further comprising:

an auxiliary motor drive, operably coupled to the pump, the auxiliary motor drive configured to cause the pump to drive the coolant fluid around the coolant fluid circuit.

13. The coolant system of claim 12, wherein the auxiliary motor drive comprises a stator winding operably coupled to the pump.

14. The coolant system of any preceding claim, further comprising:

a first propulsion system fluid pump, arranged to drive the propulsion system fluid around the first propulsion system fluid circuit.

15. The coolant system of claim 14, wherein the first propulsion system fluid pump is comprised in an aircraft propulsion system auxiliary gearbox.

16. The coolant system of any preceding claim, further comprising:

a heat exchanger, arranged in the coolant fluid circuit, configured to cool the coolant fluid as it passes through the heat exchanger.

17. An aircraft propulsion system comprising a coolant system in accordance with 5 any of claims 1 to 16.

18. An aircraft comprising an aircraft propulsion system, the aircraft propulsion system comprising a coolant system in accordance with any of claims 1 to 16.