Variable pitch fan for gas turbine engine

• US 3,922,852 A
• Filed: 10/17/1973
• Issued: 12/02/1975
• Est. Priority Date: 10/17/1973
• Status: Expired due to Term

• Current Assignee: Stephen Drabek
• Original Assignee: Stephen Drabek
• Inventors: Drabek, Stephen
• Primary Examiner(s): Husar, C. J.
• Assistant Examiner(s): Garrett, Robert E.
• Application Number:
  US05/407,222
• Time in Patent Office: 776 Days
• Field of Search: 60/226R,262 415/130 416/162,164-168,153,154
• US Class Current: 60/226.1
• CPC Class Codes: F01D 7/00 Rotors with blades adjustable in operation; Control thereof for reversing F01D1/30
• CPC Class Codes: F05D 2220/36 specially adapted for the fan of turbofan engines
• CPC Class Codes: F05D 2260/74 by turning around an axis perpendicular the rotor centre line
• CPC Class Codes: F05D 2260/76 the adjusting mechanism using auxiliary power sources
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft

Abstract

A variable pitch fan together with actuation apparatus are provided for a gas turbine engine of the bypass type. The actuation apparatus includes at least one linear actuator which remains in fixed connection relative to the engine static structure and interconnects to a helical cam means on board the fan rotor through a preloaded thrust bearing. The linear movement of the actuator is converted into angular movement by the helical cam means whereby the angular movement can be applied to all the fan blades to simultaneously vary their pitch.

Claims

1. A variable pitch fan and actuation apparatus for a gas turbine engine of the bypass type having a bypass duct and a fan drive shaft, a static frame structure, a fan frame structure mounted in driven engagement with the fan drive shaft for rotation about the static frame structure, a plurality of circumferentially spaced apart variable pitch fan blades extending into the bypass duct and fixedly attached to the fan frame structure for rotation therewith, linear actuator means fixedly connected to the static frame structure, angular actuator means fixedly connected to the fan frame structure for rotating the fan blades in unison about their respective center axes to thereby vary the pitch of the fan blades, means for interconnecting the linear actuator means and the angular actuator means so as to permit relative rotation therebetween, and helical cam means for converting linear movement of the linear actuator means into angular movement of the angular actuator means to thereby permit the pitch of the fan blades to be varied by linear movement of the linear actuator means in accordance with differing engine operating requirements, limit stop means connected to the linear actuator means for restricting the linear movement of the linear actuator means to predefined travel distances in order to provide limit stops beyond which the pitch of the fan blades cannot be varied, inactivating means for inactivating the limit stop means so that the pitch of the fan blades may be fully varied.

2. The variable pitch fan and actuation apparatus of claim 1 further including reduction gear means connected between the fan drive shaft and the fan frame structure for reducing the rotational speed of the fan frame structure relative to the fan drive shaft.

3. The variable pitch fan and actuation apparatus of claim 1 wherein the linear actuator means includes an actuator piston drive rod and the interconnecting means comprises a preloaded thrust bearing having an inner bearing ring fixedly attached to the piston drive rod and an outer bearing ring fixedly attached to the helical cam means.

4. The variable pitch fan and actuation apparatus of claim 3 wherein the helical cam means comprises a three parr spline assembly having an intermediate tubular portion projecting forwardly in a sleevelike manner from fixed connection to the inner bearing ring together with a plurality of helical teeth on its inner surface which engage the spaces between helical teeth provided around the outer surface of an inner tubular portion, means for restraining the inner tubular portion from translation relative to the fan axis and further including a plurality of circumferentially spaced apart straight teeth or splines around the forward end of the outer cylindrical surface of the intermediate tubular portion in engagement with a plurality of circumferentially spaced apart straight teeth or splines formed on the inner cylindrical surface of an outer tubular portion and means for restraining the outer tubular portion from translation relative to the fan axis whereby linear movement of the linear actuator means converts to angular and translational movement of the intermediate tubular portion which simultaneously converts to angular movement of the outer tubular portion.

5. The variable pitch fan and actuation apparatus of claim 4 wherein the angular actuator means includes a unison bevel gear extending radially outward from connection to the outer tubular portiOn and having a plurality of circumferentially spaced apart teeth formed around the outer rim thereof which engage teeth extending from a plurality of circumferentially spaced apart sector gears each one of which is integrally connected to a respective root portion from a variable pitch fan blade.

6. The variable pitch fan and actuation apparatus of claim 5 wherein the inherent turning moments incurred by the variable pitch fan blades due to the high centrifugal forces operating thereon are countered by opposite turning moments induced by the individual sector gears which have an extended radius so as to provide one portion of a dynamic turning moment balance counterweight with the other portion provided by an integral extension from the blade root wherein the mass of the sector gear and integral extension are spaced apart along an axis normal to the chord of the attached blade so as to provide a dynamic turning moment approximately equal to the inherent dynamic turning moment of the blade.

7. The variable pitch fan and actuation apparatus of claim 5 wherein the root portion of each variable pitch fan blade is attached at its inner radial end to a circumferential flange which engages a plurality of circumferentially spaced apart anti-friction bearings and the rotating frame structure provides a reinforced cylindrical support section which includes a plurality of circumferentially spaced apart radial bores therethrough, each one of which receives a root portion from a variable pitch fan blade and each radial bore includes an overlapping circumferential flange portion aligned in substantially opposing relation to a corresponding circumferential flange from a blade root so as to maintain the anti-friction bearings therebetween thereby maintaining each blade for rotation about its center axis.

8. The variable pitch fan and actuation apparatus of claim 5 wherein the axial loading between the outer rim of the unison bevel gear and the individually spaced apart sector gears is accommodated by a dry lubricated thrust bearing sandwiched between the forward face of the unison bevel gear and the rotating frame structure.

9. The variable pitch fan and actuation apparatus of claim 4 wherein the limit stop means comprises an extension fixedly connected to the actuator piston drive rod, said extension including a cam track therein and the inactivation means comprises a second actuator which is maintained in fixed connection relative to the static frame structure and includes a retractable pin extending therefrom into engagement with the cam track such that during all phases of flight the pin may be actuated into engagement within the cam track to provide stop limits beyond which the pitch of the fan blades 12 cannot be varied and that when the pin is retracted from the cam track the fan blades may be extended into a position correlating with reverse fan pitch.

10. The variable pitch fan and actuation apparatus of claim 4 wherein the gas turbine engine includes a compressor section, a combustion section and a turbine section arranged in serial flow relation downstream of the variable pitch fan and the fan drive shaft extends upstream of the turbine section drivably engaging the fan through a tubular shaft extension, the aft end of which is in splined connection to the forward end of the drive shaft and the outer surface of which is in splined connection to the inner surface of the inner tubular portion.

11. The variable pitch fan and actuation apparatus of claim 2 wherein the reduction gear means comprises an inner spur gear connected for rotation with the fan drive shaft and having a plurality of outwardly extending teeth engaged by the outside teeth of a plurality of circumferentially spaced apart planet gears which are rotatably retained relative to the stationary frame structure wherein the teeth of the planetary gears engage inwardly extending teeth from an outer ring gear which is fixedly connected to the rotating frame structure thereby effecting an overall reduction in thE rotational speed of the fan in relation to the fan drive shaft.