Fluid reaction surfaces (i.e. – impellers) – Ambient fluid or exhaust gas directed through hub – fairing...
Reexamination Certificate
1999-06-08
2001-04-03
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Ambient fluid or exhaust gas directed through hub, fairing...
C416S234000, C416S24400R
Reexamination Certificate
active
06210110
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to outboard and stern drive engines, and more particularly, to apparatus for preventing gases (e.g., exhaust, air) from flowing into a propeller blade.
Through-propeller exhaust type engines include an exhaust casing extending from a power head, and a lower unit secured to the exhaust casing. The lower unit includes a gear case which supports a propeller shaft, and a propeller is engaged to the shaft. The propeller includes an outer hub through which exhaust gases are discharged.
During operation, a region of low pressure is developed rearwardly of the propeller. A thin low pressure boundary layer around the hub can also develop. The low pressure condition rearwardly of the hub has a tendency to join with the low pressure boundary layer, and exhaust gas migrates forwardly along the propeller hub between the blades and along the rear, or low pressure, face of the propeller blades, thereby causing conditions of “cavitation” or “ventilation”. Such conditions prevent the propeller blade from biting into the water and result in an efficiency loss. In addition, excessively low pressure in the region rearwardly of the propeller hub results in a drag on the forward movement of the engine through the water.
Known propeller structures for preventing ventilation include diverging flare rings and converging rings at the rear end of the propeller hub. The rings affect the flow of water over the hub and prevent migration of the exhaust gases along the hub. For example, with an aluminum propeller, and after die cast operations, the ring is formed by welding, swaging, or attaching a full-circle ring to the hub.
With such rings, and even during minor underwater impacts, the rings can be damaged and even lost. That is, the rings can be separated from the propeller hub and then sink to the bottom of the river, lake, or ocean. Damage and loss of such rings can result in customer dissatisfaction.
In addition, and with some ring configurations, slots are formed in the ring during fabrication. Formation of the slots in the ring results in high stress areas adjacent the slots, i.e., at the edges of the slots. Such high stress areas, i.e., the edges, are susceptible to cracking and breaking off. Such cracked or broken off edges are not aesthetically acceptable and can result in customer complaints.
BRIEF SUMMARY OF THE INVENTION
The present invention, in one aspect, is a propeller including a flare having a sinusoidal, or tulip, shape at a trailing edge of the propeller. The sinusoidal flare shape of the propeller trailing edge has less stress concentration than the stress concentration associated with at least some known flare rings. Specifically, stress is reduced in the sinusoidal flare shape due to smooth trailing surface and the uneven edge of the flare. As a result, potential for cracking the trailing edge of the flair is reduced. In addition, the flare has greater strength as compared to at least some known flare rings in that stresses are more evenly distributed along the tulip shaped trailing edge. The reduced stress concentration also enables expanding the flare more than is possible with some known flare rings.
REFERENCES:
patent: 5114313 (1992-05-01), Vorus
patent: 5158433 (1992-10-01), Cleary
patent: 5527195 (1996-06-01), Neisen
Look Edward K.
McDowell Liam
Outboard Marine Corporation
Teasdale LLP Armstrong
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