Outboard Motor Midsection comprised of a Constant-Profile, Airfoil-Shaped Extrusion

Abstract

A structural tube within a marine propulsion system directly provides steering functionality from its interaction with the water and houses hardware used to transmit power from the engine to the propeller shaft. Said invention comprises a long, hollow, tube of constant cross section, the exterior profile of which takes the shape of an airfoil.

Claims

1. A device within a watercraft propulsion system comprising a tube with an airfoil shaped exterior profile of constant cross section, which contains at least one hollow cavity, which is manufactured using an extrusion process, and in its application contains power transmission hardware routed through its cross section.

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Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a view of the invented midsection in isolation.

[0015] FIG. 2 is a view of the cross section of the invented midsection detailing the internal features.

[0016] FIG. 3 shows the invented midsection as part of an outboard motor assembly in one potential configuration.

[0017] FIG. 4 shows the invented midsection within an outboard motor assembly attached to a boat, demonstrating the extension of the midsection below the boat bottom to provide steering functionality.

[0018] FIG. 5 shows the invented midsection held by a tooling fixture for a welding process, demonstrating the type of sleeve type tooling that can be utilized in post processing operations to accommodate multiple extrusion lengths

DETAILED DESCRIPTION

[0019] The basic form of the invented midsection is detailed in FIGS. 1, 2, 3. Starting with FIG. 1, the invented midsection is seen in isolation. In this view, the general proportions of the invented midsection are evident, and the airfoil profile of the exterior is visible. The end of the extrusion is exposed, showing some of the interior features of the cross section.

[0020] In FIG. 2, a detailed view of the extrusion cross section is provided. The airfoil shaped exterior profile 201 defines the outermost wall of the extrusion. In addition to providing the steering functionality discussed earlier, the exterior wall creates the bulk of the flexural rigidity afforded by the extrusion. The cross section also includes several fully enclosed circular holes 202 which serve as alignment features for manufacturing fixtures. These holes also have the potential to be tapped with machine screw threads if necessary to accommodate screws in an outboard motor assembly. The positioning of the holes is application dependent and can be arranged to satisfy particular design requirements. Webbing features 203 provide mechanical support to said holes. The webbing features also provide crush resistance to the exterior of the tube, offer a modest amount of flexural rigidity, and isolate the cavities within the interior of the cross section from each other. The cavities provide spaces to route hardware related to the associated outboard motor assembly. By isolating the cavities from each other, various mutually exclusive environments can be maintained. For example, one cavity could be flooded with lubrication while another remained dry, allowing for components to be installed requiring each condition.

[0021] The first advantage of the invented midsection, as discussed extensively in the summary, is the ability to use extrusion manufacturing processes instead of casting. This change is facilitated by the invented device's uniform cross section, which is a prerequisite to using extrusion processes. By switching the process from casting to extrusion, many benefits are realized, including a reduction in cost, an increase in production speed, better mechanical properties, and reduced post processing effort. Because conventional midsections have a variable cross section, they are inherently unable to utilize extrusion processes, unlike the present design.

[0022] Of the many materials from which the invented midsection could be extruded, the most practical would be a member of the 6000 series aluminum alloys. These alloys are strong, lightweight, corrosion resistant, and easy to extrude. The particular alloy within this series, as well as the particular temperature and machine configuration, would be selected based on application specific design requirements such as strength, ease of extrusion, and cost. A wide range of process parameters is anticipated to be suitable while still producing an acceptable end result. The extrusion of 6000 series aluminum alloys is a commodity process which is performed by many vendors across the globe, and is universal enough that consistent results can be expected from any properly equipped manufacturer.

[0023] FIG. 3 shows the invented midsection in the context of a potential outboard motor configuration. The invented midsection 301 is seen interposed between a rotary power source 304 and a lower unit 303, which houses the propeller shaft. Item 302 is a shroud, which is identified only to differentiate it from the midsection 301 since they have a similar appearance. The most important function of FIG. 3 is to demonstrate how the lower unit 303 can be simplified after the invented midsection 301 is implemented. As described earlier in the disclosure, the addition of steering functionality onto the midsection allows steering structures such as skegs to be removed from the lower unit. This greatly reduces the size and complexity of the geometry on the lower unit. The lower unit 303 in FIG. 3 shows the potential simplicity and compact size of this component once steering functionality is removed.

[0024] FIG. 4 shows the invented midsection 401 as part of an outboard motor assembly, which is mounted onto the transom of a skiff. As can be seen, the midsection extends below the bottom of the boat into the free stream of water. When configured as shown the midsection receives ample water flow past it, and functions as the outboard motor's steering mechanism as introduced earlier.

[0025] This steering functionality is the most valuable benefit afforded by the invented midsection. As mentioned in the summary, this functionality is achieved by shaping the midsection exterior as an airfoil and by extending the midsection all the way into the free stream of water below the boat. The airfoil shape minimizes drag forces, and provides large lateral steering forces when the midsection is pivoted in the water stream.

[0026] The characteristic function of airfoil shapes in their application is to minimize force in the direction opposite of travel, and to controllably produce force in the perpendicular direction. This functionality occurs when moving through a fluid. For the invented midsection, the use of the airfoil shape is somewhat unusual; traditionally, airfoils are oriented such that the deliberately produced forces point in the skyward direction in order to counteract gravity. In this application the deliberately produced forces are pointed in the starboard and port directions relative to the powered watercraft, in order to steer the vessel.

[0027] The practical advantage of having steering functionality on the midsection is the ability to eliminate this functionality from the lower unit. By removing steering structures from the lower unit, the part becomes much smaller and simpler, as seen in the suggested lower unit design from FIG. 3, item 303. The geometric simplicity of the non-steerable lower unit enables superior manufacturing methods to be used when making it. The feasible methods include die-casting, plastic injection molding, and CNC milling, to name a few, all of which produce results superior to the casting processes typically required to produce steerable lower units. As mentioned before, the addition of steering functionality onto the midsection does not add any complexity to its manufacturing process; extrusion is still feasible.

[0028] It is necessary to note that the term airfoil in the entirety of this disclosure and in the subsequent claims is defined as a shape which resembles a teardrop 201 that produces the dynamic forces as described in paragraph [0027] when moving through a fluid. The words foil and hydrofoil were considered as alternatives to the term airfoil since airfoil has several possible connotations. The word foil was forgone because of its many possible meanings and lack of universal understanding as a shape with the described dynamic properties. Hydrofoil was forgone because of the word's generally understood meaning as a specific wing-like device to lift a ship's hull out of the water.

[0029] FIG. 5 shows the invented midsection 501 fixed against a structural plate 503 during a welding process in the creation of a potential outboard motor assembly. The figure highlights a sleeve type tooling 502 that can be utilized during post-processing and assembly steps to fixture the midsection as required. This particular style of sleeve type tooling is length independent, meaning that multiple extrusion lengths can easily be accommodated by a single fixture at each processing step.

[0030] This ability to use length insensitive fixturing affords the last main advantage of the invented midsection, the ability to easily manufacture multiple length permutations of the same midsection cross section. As described in the invention background section, the complex cross section of conventional midsections makes it difficult to manufacture multiple lengths. In order to do so, unique molds designs are necessary for each length during the casting operation. Subsequent to the casting process, unique fixtures are required for each length during the post processing steps. In the case of the invented midsection, the manufacture of multiple length permutations is extremely easy. During the initial extrusion operation, the creation of different length midsections is trivialthey are simply cut to the desired lengths from the single large extrusion produced by the extruder. Subsequent to the initial formation, fixturing of the various lengths during the post processing and assembly steps can easily be accomplished through the use of sleeve type tooling, as described in the previous paragraph. Only a single tooling assembly of this sleeve type is required at each processing station to handle all the length permutations being manufactured.