GB2472016A

GB2472016A - A gear train for contra-rotating propeller gas turbine engine

Info

Publication number: GB2472016A
Application number: GB0912619A
Authority: GB
Inventors: Ben John Eastment
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2009-07-21
Filing date: 2009-07-21
Publication date: 2011-01-26
Also published as: GB0912619D0

Abstract

A gear train, for contra-rotating propeller gas turbine engine, comprises a drive shaft 26 which extends within a static structure 28, such as a nacelle 21, and is supported by a bearing 30. The drive shaft 26 is coupled to a rear propeller 24 which has a hub 34 having bevel teeth that mesh with a plurality of bevel gears 38 mounted on members 36 that are mounted on, for example, the nacelle 21 via bearings 30. A front propeller 23 is fixed to a hub 42 that is rotatably mounted on the static structure via bearings 40 and has bevel teeth that mesh with the bevel gears 38. Thus, as the rear propeller 24 is driven the bevel gears 38 drives the front propeller 23 in an opposite direction. The front propeller 23 may be constrained either by further bevel gears 48 or by bearings. A speed probe or control mechanism can be simply mounted and control calculations are easily formulated. The propellers may be used in marine applications.

Description

GEAR TRAIN

The present invention relates to a gear train arrangement for contra-rotating propellers. It finds particular, although not exclusive, utility for a contra-rotating propeller gas turbine engine.

It is known to drive a pair of propellers from a single drive shaft at different speeds and / or directions, about a common axis, by the use of a differential, epicyclic gear arrangement. Drive, or torque, is output from the engine and is shared in predetermined proportions between the two propeller stages by predetermination of the gear ratios. For example, in a "pusher" configuration of engine used for propulsion of a vehicle such as an aircraft, where the propeller stages are axially behind the engine, the planet carrier may drive the front propeller stage whilst the annulus or ring gear drives the rear propeller stage. The two propellers therefore operate at independent speeds.

One disadvantage of this arrangement is that it is not simple to locate additional components, for example a pitch control mechanism or monitoring equipment, axially behind the epicyclic gear arrangement. This is because to pass signals and fluids from the engine to the components requires the signals or fluids to pass from the static engine frame of reference, through the front propeller stage rotating frame of reference and into the differently rotating rear frame of reference. Thus, slip rings and muff couplings must be provided at the interface between each pair of frames of reference, all of which are liable to be heavy, prone to leakage and increase the possible failure modes. Furthermore, any control calculations, for example to determine the amount of pitch alteration required for the rear propeller stage, must take account of the signal passage through the stationary and front frames of reference.

Alternatively, the additional components may be mounted in the rear rotating frame of reference and be controlled by components that are also in that frame of reference. However, it is understood by those skilled in the art that it is complex to formulate and implement control algorithms spanning multiple moving frames of reference.

The present invention seeks to provide a gear train that addresses the aforementioned problems.

Accordingly the present invention provides a gear train arrangement for contra-rotating propellers comprising: a first propeller drivable by a drive shaft; a static structure located coaxially with the drive shaft and radially outwardly thereof; a plurality of first gears mounted on the static structure and co-operating with the first gears; such that driving the first propeller in one direction causes the second propeller to rotate in the opposite direction through the co-operation with the first gears. This is advantageous because it is a simpler solution than the prior art and provides a comparatively large amount of rigid static structure to which other components can be mounted, for example mounting equipment or sensors.

The first propeller may include a bevel gear arrangement for co-operation with the first gears. The second propeller may include a bevel gear arrangement for co-operation with the first gears. This provides an elegant co-operation between each propeller and the first gears.

The gear train may further comprise a constraint arrangement for the second propeller. The constraint arrangement may be a plurality of second gears or a bearing. The second gears are preferred since they are more robust.

The gear train may further comprise a speed probe arranged to detect the speed of one of the first or second propellers. Only one speed probe is required since the first and second propellers rotate at known proportions of each other's speed.

The present invention also provides a contra-rotating propeller gas turbine engine comprising a gear train as described above. The engine may be arranged in a pusher configuration such that the first propeller comprises the rear propeller and the second propeller comprises the front propeller. Alternatively, the engine may be arranged in a puller configuration such that the first propeller comprises the front propeller and the second propeller comprises the rear propeller.

Alternatively the present invention provides a marine propeller comprising a gear train as described.

The present invention will be more fully described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of a gas turbine engine having contra-rotating propeller stages.

Figure 2 is a schematic sectional view of a gear train according to the present invention.

Figure 3 is a schematic transverse section, labelled III in Figure 2.

Figure 4 is a schematic rear view of an optional epicyclic gear arrangement for the rear propeller.

Referring to Figure 1, a twin-spooled, contra-rotating propeller gas turbine engine is generally indicated at 10 and has a principal rotational axis 9. The engine 10 comprises a core engine 11 having, in axial flow series, an air intake 12, an intermediate pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, an intermediate pressure turbine 18, a free power (or low-pressure) turbine 19 and a core exhaust nozzle 20. A nacelle 21 generally surrounds the core engine 11 and defines the intake 12 and nozzle 20 and a core exhaust duct 22. The engine 10 also comprises two contra-rotating propeller stages 23, 24 attached to and driven by the free power turbine 19 via shaft 26.

The gas turbine engine 10 works in a conventional manner so that air entering the intake 12 is accelerated and compressed by the intermediate pressure compressor 14 and directed into the high-pressure compressor 15 where further compression takes place. The compressed air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high-pressure, intermediate pressure and free power turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high-pressure, intermediate pressure and free power turbines 17, 18, 19 respectively drive the high and intermediate pressure compressors 15, 14 and the propellers 23, 24 by suitable interconnecting shafts. The propellers 23, 24 normally provide the majority of the propulsive thrust. In the embodiments herein described the propellers 23, 24 rotate in opposite senses so that one rotates clockwise and the other anti-clockwise around the engine's rotational axis 9.

An exemplary embodiment of the present invention is shown in Figure 2. The drive shaft 26 extends within static structure 28, which may be the nacelle 21 or another static component connected thereto, and is supported within the static structure 28 by means of a bearing 30. The drive shaft 26 extends beyond the static structure 28 and is coupled to the first, rear propeller stage 24.

Preferably the rear propeller 24 is mounted onto the drive shaft 26, but other coupling arrangements may be used instead. The propeller 24 comprises a plurality of blades 32 extending radially outwardly from a hub portion 34. The hub portion 34 may be a solid disc or in another, relatively rigid form.

Mounted to the static structure 28, and directed radially outwardly, is a plurality of members 36 upon each of which is rotatably mounted a first gear 38. In an exemplary embodiment shown in Figure 3, there are four first gears 38, each mounted on its own member 36, that are equi-angularly spaced around the static structure 28. The number of first gears 38 provided will depend upon the loads transmitted in a particular application of the gear train of the present invention.

The first gears 38 co-operate with the first, rear propeller 24 so that rotation of the first propeller 24 causes rotation of the first gears 38. Preferably there is a bevel gear arrangement provided on the front face of the rear propeller hub 34 so that the teeth of the first gears 38 interdigitate or intermesh with the bevel gear arrangement. Alternative methods of co-operation between the first gears 38 and the first, rear propeller 24 will be apparent to the skilled reader.

The second, front propeller 23 is rotatably mounted on the static structure 28 by means of a bearing 40 or similar, which axially locates the front propeller 23. The second, front propeller 23 also comprises a hub portion 42, generally a ring or annular disc, with a plurality of blades 32 extending radially outwardly therefrom. The hub portion 42 co-operates with the first gears 38 so that rotation of the first gears 38 causes rotation of the second, front propeller 23. The second, front propeller 23 may also have a bevel gear arrangement provided on its rear face that interdigitates or intermeshes with the teeth of the first gears 38. Alternative methods of co-operation between the first gears 38 and the second, front propeller 24 will be apparent to the skilled reader. The co-operation between the first gears 38 and the second propeller 23 may be the same or different as the co-operation between the first gears 38 and the first propeller 24.

Mounted to the static structure 28 in front of the second, front propeller 23 is a constraint arrangement 44 to prevent the front propeller 23 from moving axially towards the engine 10. In the illustrated, preferred embodiment the constraint arrangement 44 comprises plurality of radially upstanding members 46 each having a second gear 48 rotatably mounted thereon. There may be, for example, four second gears 48 which co-operate with the second, front propeller 23 in a similar or different manner to the co-operation of the first gears 38 with the first or second propellers 23, 24. Second gears 48 are preferred as a constraint arrangement 44 since they are simple and robust. In an alternative embodiment, the constraint arrangement 44 comprises a bearing.

Thus the gear train arrangement is driven by rotation of the drive shaft 26 which causes synchronous rotation of the first, rear propeller 24. The co-operation of the first gears 38 with the first propeller 24 drives these to rotate at 90° to the first propeller 24. The co-operation of the first gears 38 with the second propeller 23 drives the second propeller 23 to rotate at 90° to the first gears 38, in a plane parallel to the first propeller 24 but in the opposite sense. Hence, if the first propeller 24 rotates clockwise, the second propeller 23 rotates anti-clockwise. The first and second propellers 23, 24 rotate at a fixed speed differential, in opposite directions, with the speed dictated by the drive input to the first, rear propeller 24 by the drive shaft 26 from the engine 10.

This gear train arrangement results in the rotational speeds of the first, rear 24 and second, front 23 propellers being proportional to each other. Thus the gear train arrangement is a speed differential, rather than the

torque differential of the prior art. This has the

advantage that it is only necessary to measure the rotational speed of the first or the second propeller 23, 24 rather than of both propellers 23, 24. This reduces the number of components and therefore the weight, which is critical in aircraft applications.

The gear train arrangement of the present invention is advantageous because it is simple. This has benefits for manufacture and assembly, both in terms of time taken to assemble the arrangement and in build quality since there is less that can be done wrongly or poorly. There are also advantages for maintenance since it is relatively simple to remove the first, rear propeller 24 from the drive shaft 26 and thence access the second, front propeller 23 and other components. In prior arrangements it is highly complex to access the front components, adding time and cost to maintenance activity.

The gear train of the present invention provides substantially more static structure 28 than prior art arrangements. This can be used to mount the bearings 30, 40, to increase rigidity at the rear of the engine 10 and for location of sensors and actuation equipment. For example, actuation equipment for pitch change mechanisms for the first or second propeller blades 32 can be mounted on the static structure 28 which extends further rearward

than in prior art arrangements.

In a variant to the preferred embodiment of the gear train of the present invention, an epicyclic gearbox may be incorporated into the hub portion 34 of the first, rear propeller 24 as shown in Figure 4. In this case, the sun wheel of the epicyclic gearbox comprises the drive shaft 26. A plurality of planet gears 50 surround the sun wheel shaft 26 and rotate around it due to interdigitating teeth on the planets 50 and shaft 26. A ring gear 52 surrounds the planet gears 50 and rotates around it via interdigitating teeth. The ring gear 52 rotates more slowly than the drive shaft 26 due to the gearing ratio between the shaft 26, planet gears 50 and ring gear 52.

The location of the bevel gear arrangement 54 on the opposite face of the hub portion 34 is indicated by dotted lines in the figure. Thus the blades 32 are mounted onto the radially outer surface of the ring gear 52 and the first gears 38 co-operate with the bevel gear arrangement 54 that is coupled to or forms part of the ring gear 52.

This variant offers a more compact engine 10 since no external reduction gearbox is then necessary.

The present invention finds particular utility for small contra-rotating propeller engines, such as are used for unmanned aerial vehicles. However, the benefits can also be derived when used in larger engines. Although the gear train arrangement has been described with respect to a contra-rotating propeller gas turbine engine 10, particularly for aircraft applications, it can be applied with equal felicity in marine applications, such as podded contra-rotating propellers for large cruise liners.

Alternatively it may be used in wind and water turbine applications, on and off shore, where it is desirable to have simple arrangements that require minimal maintenance and are quick to work on when maintenance is required or scheduled.

Claims

Claims 1. A gear train arrangement for contra-rotating propellers comprising: * a first propeller drivable by a drive shaft; * a static structure located coaxially with the drive shaft and radially outwardly thereof; * a plurality of first gears mounted on the static structure and co-operating with the first propeller; * a second propeller mounted to rotate about the static structure, parallel to the first propeller and co-operating with the first gears; such that driving the first propeller in one direction causes the second propeller to rotate in the opposite direction through the co-operation with the first gears.
2. A gear train as claimed in claim 1 wherein the first propeller includes a bevel gear arrangement for co-operation with the first gears.
3. A gear train as claimed in claim 1 or 2 wherein the second propeller includes a bevel gear arrangement for co-operation with the first gears.
4. A gear train as claimed in any preceding claim further comprising a constraint arrangement for the second propeller.
5. A gear train as claimed in claim 4 wherein the constraint arrangement comprises a plurality of second gears.
6. A gear train as claimed in claim 4 wherein the constraint arrangement comprises a bearing.
7. A gear train as claimed in any preceding claim further comprising a speed probe arranged to detect the speed of one of the first or second propellers.
8. A contra-rotating propeller gas turbine engine comprising a gear train arrangement according to any preceding claim.
9. A contra-rotating propeller gas turbine engine as claimed in claim 8 wherein the engine is arranged in a pusher configuration such that the first propeller comprises the rear propeller arid the second propeller comprises the front propeller.
10. A contra-rotating propeller gas turbine engine as claimed in claim 8 wherein the engine is arranged in a puller configuration such that the first propeller comprises the front propeller and the second propeller comprises the rear propeller.
11. A marine propeller comprising a gear train arrangement as claimed in any of claims 1 to 7.
12. A gear train substantially as hereinbefore described with reference to the accompanying figures.