Pitch change arrangement for a variable pitch turbo-fan

Claim 2

1 A pitch change assembly for a variable pitch fan of a turbofan gas turbine engine comprising a plurality of fan blades circumferentially arranged and rotatably mounted on a fan rotor, a control ring arranged coaxially with and rotatably mounted on the fan rotor, each fan blade being connected to the control ring by a lever such that relative rotation between the control ring and the fan rotor varies the pitch of the fan blades, a plurality of circumferentially arranged hydraulic rams mounted on the fan rotor and arranged to be supplied with hydraulic fluid, each hydraulic ram comprising a piston, a shaft and a cylinder, the piston and shaft being arranged to move within the cylinder, each shaft being connected to the control ring by a bell crank such that movement of the pistons and shafts causes relative rotation between the control ring and the fan rotor, each hydraulic ram being arranged so that the pistons and shafts move radially such that the centrifugal force of the pistons and shafts is applied to the bell cranks so that a counter turning moment is applied to the control ring to oppose the centrifugal turning moment of the fan blades.

Claim 3

2 A pitch change assembly as claimed in claim 1 in which the total centrifugal force of the pistons and shafts is arranged to provide a counter turning moment on the control ring which is greater than the total centrifugal turning moment of the fan blades such that the fan blades turn to course setting if the supply of hydraulic fluid fails.

Claim 4

3 A pitch change assembly as claimed in claim 1 or 30 claim 2 in which each of the bell cranks has a lever connected to the control ring, the fan.blade lever length being twice the length of the bell crank lever, connected to the control ring.

Claim 5

4 A pitch change assembly substantially as hereinbefore described with reference to and as shown in the accompanying figures.

Claim 6

4 A pitch change assembly substantially as hereinbefore described with reference to and as shown in the accompanying figures.

Claim 7

1 1 12 A turbofan gas turbine engine comprising a core engine and a fan assembly, the core engine comprising in flow series compressor means, combustor means and turbine means, the fan assembly being positioned upstream of the core engine, tile fan assembly comprising a plurality of fan blades circumferentially arranged and rotatably mounted on a fan rotor, a control ring arranged coaxially with and rotatably mounted on the fan rotor, each fan blade being connected to the control ring by a lever such that relative rotation between the control ring and the fan rotor varies the pitch of the fan blades, a plurality of circumferentially arranged hydraulic rams mounted on the fan rotor and arranged to be supplied with hydraulic fluid, each hydraulic ram comprising a piston, a shaft and a cylinder, the piston and shaft being arranged to move within the cylinder, each shaft being connected to the control ring by a bell crank such that movement of the pistons and shafts causes relative rotation between the control ring and the fan rotor, each hydraulic ram being arranged so that the pistons and shafts move radially such that the centrifugal force of the pistons and shafts is applied to the bell cranks so that a counter turning moment is applied to the control ring to oppose the centrifugal turning moment of the fan blades.

Claim 8

1 1 12 A turbofan gas turbine engine comprising a core engine and a fan assembly, the core engine comprising in flow series compressor means, combustor means and turbine means, the fan assembly being positioned upstream of the core engine, tile fan assembly comprising a plurality of fan blades circumferentially arranged and rotatably mounted on a fan rotor, a control ring arranged coaxially with and rotatably mounted on the fan rotor, each fan blade being connected to the control ring by a lever such that relative rotation between the control ring and the fan rotor varies the pitch of the fan blades, a plurality of circumferentially arranged hydraulic rams mounted on the fan rotor and arranged to be supplied with hydraulic fluid, each hydraulic ram comprising a piston, a shaft and a cylinder, the piston and shaft being arranged to move within the cylinder, each shaft being connected to the control ring by a bell crank such that movement of the pistons and shafts causes relative rotation between the control ring and the fan rotor, each hydraulic ram being arranged so that the pistons and shafts move radially such that the centrifugal force of the pistons and shafts is applied to the bell cranks so that a counter turning moment is applied to the control ring to oppose the centrifugal turning moment of the fan blades.

Claim 9

6 A turbofan gas turbine engine as claimed in claim 5 in which the total centrifugal force of the pistons and shafts is arranged to provide a counter turning moment on the control ring which is greater than the total centrifugal turning movement of the fan blades such that the fan blades turn to course setting if the supply of hydraulic fluid fails.

Claim 10

7 A turbofan gas turbine engine as claimed in claim 5 or 6 in which each of the bell crank has a lever connected to the control ring, the fan blade lever is twice the length of the bell crank lever connected to the control ring. A

Claim 11

8 A turbofan gas turbine engine as claimed in claim 5, claim 6 or claim 7 in which the fan assembly is driven by the turbine means via gear means.

Claim 12

9 A turbofan gas turbine engine as claimed in claim 8 in which the gear means comprises a sun gear secured to and driven by shaft means, a plurality of spur gears meshing with and driven by the sun gear and an annulus gear meshing with and driven by the spur gears, the annulus gear being arranged to drive the fan assembly, the spur gears being rotatably mounted in a carrier.

Claim 13

A turbofan gas turbine engine as claimed in claim 9 in which the carrier is secured to a static structure.

Claim 14

11 A turbofan gas turbine engine as claimed in any of claims 5 to 10 in which an intake means extends axially through the fan assembly to supply air to the core engine, the intake means being formed At its radial extremity at least partially by the fan rotor.

Claim 15

12 A turbofan-gas turbine engine as claimed in claim 11 in which the intake means is annular.

Claim 16

13 A turbofan gas turbine engine as claimed in claim 11 or 12 in which a plurality of struts extend radially across the intake means, a first and a second pipe extends through each strut to supply hydraulic fluid to and return hydraulic fluid from the hydraulic rams.

Claim 17

14 A turbofan gas turbine engine as claimed in any of claims 5 to 13 in which a muf f structure allows the transfer of hydraulic fluid between a static structure and the fan assembly, the muff structure comprising an outer member, a liner member coaxial with and secured within the outer member and an inner member coaxial with and positioned within the liner member, the outer member being secured to the static structure, the inner member being secured to and rotating with the fan assembly, the outer member and the liner member defining therebetween two axially spaced annular manifolds, the liner member and the inner member defining therebetween two axially spaced annular manifolds arranged in the same axial L 4 position as the annular manifolds between the outer and the liner member, the liner member having to interconnect member ports between the annular manifolds formed the outer member and the liner member and the annular manifolds formed between the liner member and the and the inner member, the outer member having ports to connect the annular manifolds formed between the outer member and the liner member with the supply of hydraulic fluid, the inner member having ports to connect the annular manifolds formed between the liner member and the inner member with the hydraulic rams. gas turbine substantially as hereinbefore reference to and as shown in the A turbofan described with accompanying drawings. Published 1988 at The Patent OMce, State House. 6671 High 1-101born, London WCIR 4TP Fimher copies may be obtained from The Patent OMce. Sales Branch. St Mary Cray, Orp3ngton, Kent BR5 3RD Printed by Multaplex techniques Itd. St Mary Cray, Kent Con. 1/87.