Fluid reaction surfaces (i.e. – impellers) – With control means responsive to non-cyclic condition... – Pressure or altitude responsive
Reexamination Certificate
1999-05-05
2001-06-05
Ryznic, John E. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With control means responsive to non-cyclic condition...
Pressure or altitude responsive
C416S156000, C137S068230
Reexamination Certificate
active
06241473
ABSTRACT:
TECHNICAL FIELD
This invention is directed to a pressure relief device for the cavity of a propeller hub, and more particularly to a pressure relief device that serves as ball hole loading cover in a propeller hub and is designed to relieve the hub internal pressure at a predetermined value.
BACKGROUND ART
Typical propulsion systems in modern aircraft comprise a propeller, propeller blades mounted in arm bores extending from the propeller hub and a pitch change actuator for changing the pitch of the propeller blades.
The propeller blade is mounted in the arm bore for movement therein. Blade retention bearings are located circumferentially within the arm bore such to facilitate pitch change of the propeller blade. The hub is sealed and contains a specified volume of oil to lubricate the blade retention bearings. The minimum oil volume is chosen to minimize weight and ensure the arm bores are completely filled and oil distributes evenly within the cavity when acted on by centrifugal force.
The pitch change actuation device uses high pressure hydraulic fluid applied to piston located within the pitch change actuator to change blade pitch. A leak in the pitch change actuator could cause the hub to become pressurized causing high loads on the propeller components. Pitch change actuation systems are designed to place the blade in a feather position to minimize drag upon loss of hydraulic pressure. Therefore it is more desirable to vent the hub cavity and lose pitch change capability than to pressurize the hub.
There are several prior art methods for limiting hub cavity pressure. Some systems vent the hub cavity back to a sump in the control system. If the cavity is a closed system, a pressure relief device is employed to vent the system overboard. This device can be a valve, or a component designed to fail at a predetermined pressure.
FIGS. 1 and 2
illustrate prior art relief valves designed to open at a predetermined pressure. Pressure relief valves add expense and increase system weight because a mounting interface must be provided for the valve. Relief valves are also typically low flow devices, and therefore provide minimal over pressure protection in the event that there is a high flow rate leak into the hub cavity.
FIG. 1
illustrates a pressure relief device
10
′ wherein the cover
12
′ is designed to fracture releasing the spherical seal
14
′ to vent the hub cavity. The spherical seal
14
′ is located in a cavity
16
′ which is in fluid communication with the hub cavity. The cover
12
′ is mounted to an external surface
18
′ of the hub
20
′. This device requires external mounting hardware and exhibits wide tolerances in activation pressure due to its configuration and dimensional tolerances.
FIG. 2
illustrates a second pressure relief device
22
′ positioned in a passage
24
′ located within the hub
26
′. The pressure relief device requires a housing
28
′ which is attached to the hub
26
′.
Therefore, there exists a need for a pressure relief device that provides relief for a rapid increase of oil pressure in the hub, due to high flow rate leakage into the hub, while minimizing weight and the need for external mounting bosses and hardware.
DISCLOSURE OF THE INVENTION
The primary object of the present invention is to provide a pressure relief device which is actuated a predictable pressure for a hub cavity. Another object of the present invention is to provide a pressure relief device that mounts in the ball loading hole of a bearing race, requiring no external mounting features.
The pressure relief device according to the subject invention includes a housing adapted in size and shape to fit in a ball loading hole of a propeller hub. The housing is cylindrical in shape and is open at a first end and closed at a second end. The outer wall of the housing includes a first portion having a first circumference located at a first end and a second portion located at a second end having a second circumference. The second circumference is greater than the first circumference, creating a stepped portion at the intersection of the first and second circumferences. An o-ring is located on the first portion adjacent the stepped portion.
The second end comprises a thin walled diaphragm which forms the closure at the second end. The diaphragm is designed to rupture at a predetermined pressure. In a further embodiment of the subject invention the diaphragm includes a notch or other feature to ensure activation at lower and more predictable hub pressure.
The second end also includes a pull tab to facilitate installation and removal of the pressure relief device. The pull tab is oriented relative the notch such that the forces exerted through the pull tab on the diaphragm, during installation or removal are minimized.
The wall of the ball loading hole has a third circumference located at an external opening, and a fourth circumference, located a distance from the external opening. The third circumference is greater than the fourth circumference forming a complementary step at the intersection of the third and fourth circumferences. Located just inside the ball loading hole is a channel adapted in size and shape to receive a snap ring.
The pressure relief device is inserted into the ball loading hole such that the first end of the pressure relief insert is exposed to the pressure in the hub cavity. When inserted, the o-ring forms a seal between the outer wall of the housing and the wall of the ball loading hole. The complementary step of the ball loading hole and the step of the outer wall of the housing cooperate to limit travel of the pressure relief device toward the hub cavity when the pressure within the hub cavity is less than the external pressure. The snap ring retains the pressure relief device within the ball loading hole when high pressure is present in the hub cavity.
The thin walled diaphragm is designed to rupture at a desired pressure to vent the pressure within the hub cavity. When present the diaphragm ruptures at the notch located on a surface of the thin walled diaphragm.
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Corley Thomas G.
Pruden Robert W.
Soule Matthew C.
Ryznic John E.
United Technologies Corporation
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