Patent Application
20110171027
This application relates to a propeller pitch change mechanism wherein torque compensation is provided from a drive input.
Propeller pitch change mechanisms are known, and are utilized in a propeller assembly which carries a plurality of blades. The assembly is driven to rotate, and carries the blades for rotation. However, the pitch angle of the blades can be adjusted to provide an adjustable thrust from the rotation of the assembly.
A pitch change mechanism typically has included a gear train which causes the blade to rotate within a hub that carries the blade. There are challenges in the prior art in that there are forces on the blades which tend to force the blades toward a flat position wherein the provided thrust is minimized.
There is a total twisting moment (“TTM”) on each blade which is the algebraic sum of a centrifugal twisting moment, an aerodynamic twisting moment, and friction which always resists the direction of motion.
The prior art systems have been required to overcome all of these forces. This TTM is large, and causes parasitic loss of energy when the pitch change mechanism must drive the blade, and overcome the forces.
A propeller assembly has a plurality of propeller blades, and a pitch change mechanism including at least one motor. A drive input drives the plurality of propeller blades to rotate about a central drive axis. The pitch change mechanism is operable upon driving of the motor to move the propeller blades relative to the drive input. The drive input includes a drive input gear transmission to change a pitch angle of the blades when the blades are moved relative to the drive input by the pitch change mechanism. Further, a method of operating a propeller assembly to change a pitch angle is disclosed and claimed.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Propeller assembly 20 is illustrated in
As can be seen in
As mentioned above, in the prior art, the pitch change mechanism has typically caused each blade to rotate relative to the arm bores 24. The known pitch change mechanisms have also been required to overcome a good deal of force from the total twisting moment, as described above.
As shown in
Ball bearings 36 support the hub 22 and a support shaft 40 on the shaft 32 at one end. Other ball bearings 38 support a compensation shaft 67 at an opposed end of the shaft 32.
As shown, the shaft 32 extends to an end 58 beyond a gear 62, and then back outwardly of the gear 62 to a gear tooth portion 66. Portion 66 is driven to rotate with the shaft 32, and drives the gear 62. Gear 62 is mounted for rotation within a plate 167, which is part of the hub 22.
The gear 62 drives gear teeth 64 on the compensation shaft 67. Compensation shaft 67 includes a bevel gear tooth section 68 which engages with a bevel gear 56 at an end 52 of each propeller blade 26.
Ball bearings 54 secure each arm bore 24 and hub 22 to rotate with a blade 26. Generally, a ball bearing necklace is received between grooves and shanks in the arm bores and the blades to secure the blades within the arm bores.
When it is desired to change the pitch angle, the control C controls the motor or motors 48 to drive the gears 46 and 44 to engage and drive gear teeth 42 on the support shaft 40. This causes the hub 22 to pivot or rotate about the axis Y relative to shaft 32.
When the motor 48 drives the gear 46 to rotate the hub 22, the hub and the propeller blades 26 all rotate, causing the hub 22 and hence the propeller blades 26 to rotate relative to the shaft 32. When this occurs, the bevel gear 68 resists the relative movement of the bevel gears 56 from the plurality of propeller blades 26. Instead, the bevel gears 56, and hence the propeller blades 26 are caused to rotate about the axis X and change the pitch angle. Stated another way, the motor 48 and its gear train could be termed an active pitch change mechanism, which in turn causes a passive pitch change mechanism, including gears 66, 62, 64, 68, 56 to actually change the pitch angle for each of the propeller blades 26.
Thus, the compensation side of the drive of the blade 26 can be designed to address the total twisting moment such that the motor 48 must only overcome a much smaller force when seeking to change the pitch angle of the blade 26.
Since the torque from the drive input or prop shaft 28 is utilized to compensate for the bulk of the total twisting moment, the motor 48 and its gear train need overcome the much smaller frictional forces resisting movement of the hub 22. As such, the disclosed invention allows for a much smaller package of actuation structure, and further provides much more efficient operation in that it eliminates a good deal of parasitic loss.
While
The motor(s) 48 may be hydraulic or electric.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
