Propeller pitch lock system
View Patent ↗A variable pitch propulsor system with a propeller pitchlock system which utilizes a follower style pitchlock ballscrew screw which tracks the actuator axial stroke. The pitchlock system transfers the propeller yoke loads, from the ballscrew ballnut to the pitchlock nut allowing the propeller to pitchlock; utilizes the same screw thread lead angle for normal ballscrew back driving operation as well as pitch locking capabilities; provides a single ballscrew which is capable of both being back driven by the ballnut and structurally adequate for reacting the blade loads resulting from any flight condition; and minimizes the requirement of additional rotation and torque transferring interfaces between the ballscrew and pitchlock nut.
1. A pitchlock system comprising:
a ballscrew screw mounted along an axis of rotation, said ballscrew screw having an external screw ball track groove;
a pitchlock nut mounted about said ballscrew screw, said pitchlock nut including an internal pitchlock nut thread;
a ballscrew ballnut mounted about said ballscrew screw and axially adjacent said pitchlock nut, said ballscrew ballnut having an internal ballnut track groove; and
a ballscrew ballnut spring which biases said ballscrew ballnut toward said pitchlock nut, said ballscrew ballnut spring collapsible such that said ballscrew screw is movable between an operational position and a pitchlock position, said internal pitchlock nut thread lockable with said external screw ball track groove in said pitchlock position.
2. The pitchlock system as recited in claim 1 , wherein said internal ballnut track groove and said external screw ball track groove have a common helix angle.
3. The pitchlock system as recited in claim 2 , further comprising a multiple of ball bearings mounted within said internal ballnut track groove and said external screw ball track groove.
4. The pitchlock system as recited in claim 1 , wherein said pitchlock nut thread includes a toroidal profile, said pitchlock nut thread defines a clearance with said external screw ball track groove in said operation position.
5. The pitchlock system as recited in claim 4 , wherein said pitchlock nut thread includes a lead angle configured which prevents said ballscrew screw from back driving said pitchlock nut in said pitchlock position.
6. The pitchlock system as recited in claim 4 , wherein said pitchlock nut thread includes an ACME thread.
7. The pitchlock system as recited in claim 4 , wherein said pitchlock nut thread includes a screw thread profile which contacts only the flanks of the external screw ball track groove in said pitchlock position.
8. The pitchlock system as recited in claim 1 , further comprising a timing keyway between said pitchlock nut and said ballscrew ball nut to prevent rotation of said pitchlock nut and align said internal pitchlock nut thread and said internal ballnut track groove.
9. The pitchlock system as recited in claim 1 , wherein said ballscrew screw includes a flange engageable with a axially fixed surface to react a full actuator fine pitch hydraulic pressure output and a resultant blade load in response to said pitchlock position.
10. The pitchlock system as recited in claim 1 , further comprising a pitchlock piston having a pitchlock load tube, said ballscrew screw mounted for rotation about said pitchlock load tube through a ballscrew bearing support assembly.
11. The pitchlock system as recited in claim 10 , further comprising a pitchlock transfer tube mounted within said pitchlock load tube to communicate a pitchlock pressure to said pitchlock piston.
12. A propulsor system comprising:
a yoke assembly mounted along an axis of rotation, said yoke assembly defining a yoke bore;
a ballscrew screw mounted along said axis of rotation and at least partially within said yoke bore, said ballscrew screw having an external screw ball track groove;
a pitchlock nut mounted to said yoke bore and about said ballscrew screw, said pitchlock nut having an internal pitchlock nut thread;
a ballscrew ballnut mounted for axial movement along said axis of rotation within said yoke bore axially adjacent said pitchlock nut and about said ballscrew screw, said ballscrew ballnut having an internal ballnut track groove; and
a ballscrew ballnut spring within said yoke bore to axially bias said ballscrew ballnut toward said pitchlock nut, said ballscrew ballnut spring collapsible such that said ballscrew screw is movable between an operational position and a pitchlock position, said internal pitchlock nut thread lockable with said external screw ball track groove in said pitchlock position.
13. The system as recited in claim 12 , wherein said yoke assembly includes an actuator piston between a fine pitch chamber and a coarse pitch chamber, a multiple of blade assemblies mounted to said yoke assembly.
14. The system as recited in claim 13 , wherein said ballscrew screw includes a flange engageable with a axially fixed surface of said coarse pitch chamber to react a full actuator fine pitch hydraulic pressure output and a resultant aerodynamic blade load in response to said pitchlock position.
15. The system as recited in claim 14 , further comprising a pitchlock piston adjacent said axially fixed surface opposite said flange, said pitchlock piston in contact with a pitchlock load tube which extends through said axially fixed surface, said ballscrew screw mounted for rotation about said pitchlock load tube through a ballscrew screw support assembly.
16. The pitchlock system as recited in claim 15 , further comprising a pitchlock transfer tube mounted within said pitchlock load tube to communicate a pitchlock pressure to said pitchlock piston, said pitchlock pressure in opposition to a coarse pitch pressure within said coarse pitch chamber.
17. A method of pitchlocking a propulsor system comprising the steps of:
(1) axially biasing a ballscrew ballnut toward a pitchlock nut located axially adjacent said ballscrew ballnut, the ballscrew ballnut and pitchlock nut rotationally fixed relative a ballscrew screw mounted for backdriving therein;
(2) overcoming the biasing of said step (1) in response to a pitchlock condition; and
(3) axially shifting the ballscrew screw such that an external ball track groove of the ballscrew screw engages with a set of internal pitchlock nut threads and the ballscrew screw is prevented from backdriving within the pitchlock nut.
18. A method as recited in claim 17 , wherein said step (2) further comprises:
changing a contact angle between a set of ball bearings between the ballscrew ballnut and the ballscrew screw.
19. A method as recited in claim 17 , wherein said step (2) further comprises:
axially loading the ballscrew ballnut in a fine pitch direction until the axially load overcomes the biasing.
20. A method as recited in claim 17 , wherein said step (3) further comprises the steps of:
(a) axially shifting the ballscrew screw in response to a reduction of coarse pitch pressure below a predetermined blade load; and
(b) closing a pitchlock gap between the ballscrew screw and contact surface such that the ballscrew screw contacts the contact surface such that the ballscrew is prevented from rotating.