TECHNICAL FIELD

This invention relates to variable diameter rotors for aircraft and more particularly to a simplified drive system for effecting retraction and extension of variable diameter rotor blades.

BACKGROUND

A tilt rotor aircraft is one which typically has a pair of pods supported on aircraft wings for supporting a pair of rotors, the pods being movable between a vertical position when the rotors serve as helicopter rotors for vertical take- offs and landings, and a horizontal position when the rotors serve as propellers for forward flight.

Generally, a large rotor diameter is advantageous for operating the aircraft in the helicopter mode to provide low disk loading which results in efficient operation, low noise levels and diminished downwash velocities.

On the other hand, a relatively small diameter is advantageous in the propeller mode to reduce tip speed and blade area for improved propulsion efficiency, minimized blade aero-elastic properties and to simplify ground handling.

Various mechanisms are known for providing the means for extending and retracting variable diameter rotor blades. For

example, in U.S. Patent No. 3,768,923, a jackscrew and nut arrangement is used to produce telescopic motion between inner and outer blade portions. (see Fig. 1) Two coaxial shafts 1 and 2 are connected to upper and lower beveled gears 3 and 4 to form part of a differential unit which includes pinion gears 5 and 6 which are connected to the jackscrew shafts 7 and 8 in each blade. The coaxially shafts rotate with the rotor drive shaft 9 during constant diameter operation.

However, each shaft has a brake 10 and 11 such that when the brake is applied, the selected shaft and rotor rotate at different speeds. Depending on which shaft undergoes braking, this speed differential drives the respective bevel gear and jackscrews for rotation, with rotation in different directions depending on which brake is applied to which coaxial shaft. Thus, application of the brake to one shaft will drive the jackscrew to either extend or retract the rotor blade.

While such an assembly is acceptable in some circumstances, such as with articulated or hingeless rotor hubs, it is quite complex and difficult to incorporate into a gimbelled rotor hub which requires shaft flexibility.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a drive system for a variable diameter rotor which is simple in design yet adaptable to gimbelled rotor hubs. It is a further object to provide a drive system for a variable diameter rotor which utilizes a single shaft extending through the rotor drive shaft.

It is a further object to provide a variable diameter rotor drive system which is lightweight.

These and other objects of the present invention are achieved by providing a drive system for a variable diameter rotor having one or more variable diameter blades supported by a hub, the drive system comprising a coaxial shaft disposed within a rotor drive shaft, the rotor drive shaft connected to the hub for corotation therewith, retraction and extension means in the hub for effecting retraction or extension of a rotor blade, and, gear means for selectively varying the speed of the coaxial shaft relative to the rotor drive shaft such that the coaxial shaft rotates at either a higher or lower speed relative to the rotor drive shaft. Such means may comprise brake means associated with the coaxial shaft to slow the shaft and a gear set engaged with the shaft such that engaging the gear set increases the relative rotational speed of the coaxial shaft within the rotor drive shaft.

In one embodiment of the invention, rotor power is used to cause the coaxial shaft to rotate at a higher rotational speed which may be used for either retraction or extension of the rotor blades. Preferably the gear set and brake are located in association with the lower portion of the rotor drive shaft. Utilizing a single coaxial shaft, drive system complexity and weight are reduced, simplifying the hub for accommodation of a gimbelled rotor head utilizing a universal joint. Thus, a low weight efficient drive system is provided.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Fig. 1 is a prior art double coaxial shaft drive system.

Fig. 2 is a cross-sectional view of one embodiment of the hub usable with the drive system of the invention. Fig. 3 is a cross-sectional view of an alternative embodiment of the hub of Fig. 2.

Fig. 4 is a cross-sectional view of an embodiment of the drive system of the invention.

Fig. 5 is a cross-sectional view of an alternative embodiment of the drive system of the invention.

Fig. 6 is another alternative embodiment of the invention.

Fig. 7 is another alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 2, a gimbelled hub system 1 for a variable diameter rotor is shown. The hub system has a rotor drive shaft 2 which communicates through gimbelled bearings 3 to a hub 4. One or more jackscrews 5 extend from the hub 4 with the jackscrews supported by bearings 6 in the hub. Each jackscrew has a threaded portion 7 which engages a nut or other stationary portion of a movable blade section, not shown. Typically, the jackscrew and blade section are threadably engaged such that rotation of the jackscrew will cause translation of the movable blade section. Such a system is described in U.S. Patent No. 3,884,594, the disclosure of which is hereby incorporated by reference.

A bevel gear 8 is attached to a stub shaft 9 which is supported at one end by bearings 10 in the hub, and at the other end is attached to a universal joint 11 mounted on a yoke 12 of a coaxial shaft 13. The bevel gear 8 is engaged to bevel pinion 14 attached to the jackscrews 5. Corotation of the shafts 2 and 13 at the same speed results in no movement between the bevel gear 8 and bevel pinions 14. When the shaft 13 moves slower than the drive shaft 2, the stub shaft 9 slows and the bevel gear 8 inside the hub slows and the pinion 14 is then caused to roll around the bevel gear, turning the jackscrew 5 to adjust blade diameter. When the coaxial shaft 13 moves faster than the drive shaft 2, this drives the bevel gear 8 in the hub to cause the bevel pinions to turn in the opposite direction turning the jackscrews 5 in the opposite direction. The choice of gear teeth and jackscrew thread taper determine which direction of rotation extends or retracts the blades. For illustrative purposes, the gear drive system will be described such that the slower speed will retract the blade and the faster speed will extend the blade. It will be understood that the opposite configuration could easily be accommodated with the present invention.

Fig. 3 shows an alternative embodiment of the hub, with the stub shaft 9a in an upper rather than lower orientation which allows for compactness of the hub components. Preferably, a gear drive system is provided in association with a lower end of the shaft 13 for driving the shaft. Referring to Fig. 4, the drive shaft 2 has a lower end 20 supported for rotation by bearings 21 within a transmission

housing 22. The drive shaft has a drive gear 23 engaged to an engine shaft 24 for driving to rotor blades. A locking clutch or brake 25 is used to lock the shaft 13 and the drive shaft 2 for corotation during constant blade diameter operation. The brake 25 acts on an outwardly extending disk 26 to lock the two shafts together in conventional fashion. Such disk brakes are well known in the field. The brake action is typically initiated on pilot command possibly using a solenoid control switch. A bearing 27 rotatably supports the shaft 13 to allow a variation in rotational speed to occur between the two shafts.

The drive shaft 2 has a lower end which forms a differential housing 28. Within the housing are located a pair of bevel pinions 29 supported by pins 30 and bearings 31. An upper bevel gear 32 which is fixed to the shaft 13 is engaged with the bevel pinions. A lower bevel gear 33 is also engaged with the bevel pinions. The lower bevel gear is fixed to a stub shaft 34, supported rotatably relative to the housing 28 by bearings 35. The stub shaft has a disk 36 which is engagable by brake 37. The shaft 13 also has a lower disk 38 engagable by a brake 39. Both brakes 37 and 39 are supported on the transmission housing 22.

For purposes of illustration the brake 37 is an extension brake, causing extension of the blades when actuated, and the brake 39 is a retraction brake, causing retraction of the blades when actuated. However, depending on the choice of bevel gear ratios, this operational convention could be reversed.

In operation, the brake 25 is engaged to maintain a desired constant blade diameter. Should extension be desired, the brake 25 is disengaged and the blade extension brake 37 applied. This slows the stub shaft 34 which causes the bevel gear 33 to drive the pinions 29 to turn the shaft 13 at a speed higher than the rotor drive shaft speed. This is accomplished by utilizing proper pinion gear ratios which cause a multiplication of the rotor speed. The increased shaft speed drives the upper bevel gear pinions to rotate the jackscrews and extend the blades. When the desired extension is achieved, the brake 37 is disengaged and the brake 25 reengaged.

To retract the blades, the brake 25 is disengaged but the retraction brake 39 is applied which slows the shaft 13 relative to the rotor drive shaft. This causes the bevel gear pinions in the hub to drive the jackscrew in the opposite direction to reduce the rotor diameter. When the retraction is complete, the brake 39 is disengaged and the brake 25 reengaged. The brakes and clutches are operated in conventional fashion, for example, through a solenoid mechanism. The choice of bevel gear and pinion ratios may be for example as would provide an increase in RPM with brake application such that the shaft 13 rotates at about +/- 260 RPM relative to the rotor drive shaft speed depending on whether the retraction (- ) or extension (+) brake is engaged. Of course, other speeds can easily be accommodated.

Alternatively, the gear drive system may utilize a parallel shaft, rather than a coaxial stub shaft. Referring to Fig. 5, an alternative embodiment of the invention is shown. The shaft 2 has a locking brake 40 and disk 41 as before for locking the shafts 2 and 13 together for corotation during constant blade diameter operation. The rotor drive shaft 2 has a first spur gear 42 fixed at a midportion thereof and the coaxial shaft 13 has a second spur gear 43 fixed at an end 44 thereof. The location of the corotation brake is considered a matter of design choice. The first spur gear 42 engages a sleeve shaft 45 through a mating spur gear 46. The shaft 45 has a disk 47 at a lower end thereof. The sleeve shaft is fitted over a parallel shaft 48 which is rotatably supported by bearings 49 and 50. The bearings are seated on transmission housing portions 51 and 52. The parallel shaft 48 has a lower spur gear 53 engaged with the second spur gear 43 on the coaxial shaft 13. The parallel shaft also includes a brake 54 for operation with the disk 47 of the sleeve shaft 45. A brake 55 supported on transmission housing portion 56 is disposed adjacent a disk 57 extending from the shaft 13. In operation, the brake 40 is engaged during constant diameter operation, with the brakes 54 and 55 disengaged. At this time, the parallel shaft 48 rotates freely, as does the sleeve shaft 45. To effect a retraction, as before, the brake 40 is disengaged and the brake 55 applied, slowing the shaft 13 relative to the rotor drive shaft 2 to effect rotation of the jackscrews in the rotor hub, described previously. When the

desired retraction is complete, the brake 55 is disengaged and the brake 40 reengaged.

To effect an extension, the brake 40 is disengaged and the brake 54 is applied. This locks the parallel shaft 48 to the sleeve shaft 45, thus driving the parallel shaft 48 through gears 42 and 46 using rotor power. The gears 46 and 53 are chosen to yield a gear ratio which produces a multiple of the rotor shaft speed to cause the gear 53 to drive the shaft 13 at a speed higher than the rotor drive speed the effect rotation of the rotor hub in the opposite direction. When the desired extension is complete, the brake 54 is disengaged and the brake 40 reengaged.

With either embodiment, a single coaxial shaft is utilized for communicating with the jackscrews in the rotor hub, thus simplifying the hub and allowing accommodation of a universal joint for use in gimbelled rotors. Also, locating the controls and gearing in association with the lower portion of the rotor drive shaft, in the transmission housing, simplifies maintenance and accessibility to the drive system components. Lubrication is also simplified.

In another embodiment of the invention, shown in Fig. 6, a retraction brake 60 is associated with a disk 61 on the parallel shaft 48a rather than on the shaft 13. Thus, applying the brake 60 slows the parallel shaft which acts through the gear 53a to slow the shaft 13. This simplifies construction of the shaft 13 and unifies construction of the drive system.

In yet another embodiment of the invention, shown in Fig. 7, an upper shaft section 62 is substituted for the sleeve shaft 45. The upper shaft section has a bore 63 sized to accept an end 64 of a lower shaft section 65 therein. The lower shaft end 64 is freely rotatable within the bore. The upper shaft section 62 has a sour gear 46a and a disk 47a. The lower shaft has a brake 54a and a spur gear 53a. Thus, this embodiment operates in accordance with the embodiment of Fig. 5. As described previously, the choice of gear set ratios may be chosen to accommodate various rates of retraction or extension. For example, a pair of spur gears, representing gears 42 and 45, may be chosen to have a 7:5 ratio to yield a parallel shaft speed of about 370 RPM. A gear set ratio of 5:7, representing gears 43 and 53, would then yield a shaft speed of about 514 RPM or + 254 RPM relative to the drive shaft speed. Of course, any reasonable speed can be attained.

Using the drive system of the invention, variable diameter rotors are adaptable to gimbelled rotors increasing their utilization. However, any variable diameter rotor can benefit by the increased efficiency, simplified lower gear design of the invention and the invention is not limited to use in gimbelled rotors.

While preferred embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes or modifications could be made without varying from the scope of the present invention.