Fluid reaction surfaces (i.e. – impellers) – Combined or convertible – Hub lubrication or seal
Reexamination Certificate
1999-12-20
2001-08-28
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Combined or convertible
Hub lubrication or seal
C415S009000, C137S068110
Reexamination Certificate
active
06280142
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 bearing race
16
′ which is in fluid communication with the hub cavity. The cover
16
′ 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 housing
26
′. The pressure relief device requires a housing
28
′ which is attached to the hub housing
26
′.
Therefore, there exists a need for a pressure relief device that provides relief for a rapid increase in 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 both ends. 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. A first o-ring is located on the first portion adjacent the stepped portion.
The pressure relief device also includes a pressure relief insert. The pressure relief insert includes a cylindrical portion that is adapted in size and shape to fit within the first housing. A first end of the cylindrical portion is solid and has a plurality of fracture tabs protruding radially therefrom. The first end of the pressure relief insert also includes a channel with a second o-ring disposed therein.
A plurality of resilient fingers extend axially from a second end of the cylindrical portion. The resilient fingers are arranged along a circumferential edge of the second end. The resilient fingers include a stepped portion distally located from the second end of the cylindrical portion. The distance from the stepped portion to the fracture tabs is equal to the length of the outer wall of the housing such that when the pressure relief insert is inserted into the housing the fracture tabs will rest on the first end of the housing and the stepped portion of the resilient fingers rest on the second end of the housing thus locking the pressure relief insert within the housing. The second o-ring located on the cylindrical portion of the pressure relief insert forms a seal between the pressure relief insert and the housing.
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 is formed 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 first 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 pressure tabs are designed to fracture at a desired pressure. The fracture occurs at the intersection of the fracture tab and cylindrical portion of the pressure relief insert allowing the pressure relief insert to be forced out of the housing by the cavity pressure. The seal between the pressure relief insert and the housing will be broken when the pressure relief insert has traveled a sufficient distance such that the second o-ring is no longer compressed.
REFERENCES:
patent: 3377957 (1968-04-01), Bilton
patent: 4365643 (1982-12-01), Masclet et al.
patent: 4487104 (1949-11-01), Cooper
patent: 5632505 (1997-05-01), Saccone et al.
patent: 803506 (1951-04-01), None
patent: 1318057 (1973-05-01), None
patent: 1469573 (1977-04-01), None
patent: WO-00/66428-A1 (2000-11-01), None
Carvalho Paul A.
Pruden Robert W.
Look Edward K.
Nguyen Ninh
United Technologies Corporation
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