Dual strut transmission housing structure for marine propulsion systems

Abstract

Provided herein is a marine propulsion device including a prime mover having a drive shaft, a cowling surrounding the prime mover, and first and second struts secured to the cowling, each of the struts having a forward portion, an internal belt space, and an aft portion. The marine propulsion device further includes a lower unit coupled to a distal end of the strut, a sprocket rotatably disposed within the lower unit, a shaft rotatably coupled to the sprocket, and a belt rotatably connecting the drive shaft to the sprocket, whereby a first portion of the belt is disposed within the internal belt space of the first strut and a second portion of the belt is disposed within the internal belt space of the second strut. The marine propulsion device further includes a thermal circuit (with a heat transfer fluid) extending from the cowling through each strut and into the lower unit.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 031,979, filed May 29, 2020, the entire contents of which are incorporated herein by reference.

[0002] Field of the Disclosure The present disclosure relates to marine propulsion systems, and more particularly to a housing structure for transmitting power between a prime mover and a propeller shaft. [Background technology]

[0003] Marine propulsion engines have historically been categorized into three general types: inboard marine propulsion systems, outboard marine propulsion systems, and sterndrive or inboard-outboard marine propulsion systems.

[0004] An inboard propulsion system includes a prime mover, which uses an energy source to convert the energy into rotational motion for one or more shafts, and a transmission that transmits the rotational force to a propeller shaft that protrudes from the bottom of the boat. A propeller is attached to the end of the submerged shaft and generates thrust, which is directed by a rudder, usually located aft of the propeller. An outboard motor generally includes a powerhead with a prime mover, lower unit, or gearcase that houses the propeller and shaft, and a midsection that provides a physical connection between the powerhead and lower unit while allowing the transmission to transfer power from the prime mover to the propeller shaft. The entire outboard motor is mounted on the boat's transom and can be removed. A sterndrive system, also known as an inboard-outboard system, houses the prime mover inside the boat. The prime mover shaft is connected to an outdrive transmission that transmits power to the lower unit or gearcase.

[0005] Sterndrive and outboard marine propulsion systems traditionally use one set of right-angle bevel gears to transfer rotational power from the prime mover to the propeller. In the case of combustion engines, an additional gear set is used to allow for counter-rotation.

[0006] A variety of power transmission methods are known from the prior art, including belt or chain transmissions. Synchronous belts have become robust and durable, enabling their use in higher power marine engine transmissions. Implementing such existing belt technology presents challenges in physical housing arrangement and mechanical assembly. The frontal area and hydrodynamic shape of the underwater portion of a marine propulsion system significantly impacts system drag and efficiency. Adapting belt drive technology with traditional physical structures designed to accommodate rotating shafts and gears presents obstacles to an overall efficient design. The embodiments of the present disclosure are intended to address the above-mentioned challenges and others.

[0007] overview The objects and advantages of the disclosed subject matter will be set forth in and apparent from the following description, and will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as the appended drawings.

[0008] To achieve these and other advantages and in accordance with the objectives of the disclosed subject matter, the disclosed subject matter, as embodied and broadly described, includes a marine propulsion device including: a first strut extending from a proximal end to a distal end; and a second strut extending from a proximal end to a distal end, each of the first strut and the second strut having a forward portion, an internal belt space, and an aft portion, the first strut being aligned with the second strut and the first strut being spaced apart from the second strut; a lower unit coupled to the distal ends of the first strut and the second strut, the lower unit having a nose portion, a middle portion, and a tail portion; a sprocket rotatably disposed within the lower unit; and a sprocket rotatably coupled to the sprocket. a shaft concentric with the sprocket, the shaft having a front side extending in front of the sprocket and a rear side extending behind the sprocket; a belt rotatably connecting the drive shaft to the sprocket, a first portion of the belt being disposed within the internal belt space of the first strut and a second portion of the belt being disposed within the internal belt space of the second strut; and a thermal circuit extending from the cowling, through each of the first and second struts, and into the lower unit, the thermal circuit having a heat transfer fluid configured to flow through the thermal circuit.

[0009] In some embodiments, the first strut and the second strut have complementary shapes.

[0010] In some embodiments, the spacing between the first and second struts is uniform over the length of the first and second struts.

[0011] In some embodiments, a thermal circuit is disposed within the anterior portion of each of the first and second struts.

[0012] In some embodiments, the thermal circuit is bidirectional through each of the first and second struts.

[0013] In some embodiments, the thermal circuit further extends through an intermediate portion of the lower unit.

[0014] In some embodiments, the thermal circuit further extends through a tail portion of the lower unit.

[0015] In some embodiments, a plate is disposed at the proximal ends of the first and second struts, the plate being substantially perpendicular to the first and second struts.

[0016] In some embodiments, a propeller is coupled to the rear of the shaft.

[0017] In some embodiments, the lower unit includes a nosecone and a tail fairing.

[0018] In some embodiments, the sprocket is located within the middle portion of the lower unit.

[0019] In some embodiments, the first strut and the second strut are substantially linear.

[0020] In some embodiments, the first strut and the second strut each have a wing shape, with the leading edge of the wing shape corresponding to the leading portion of the first strut and the second strut, and the trailing edge of the wing shape corresponding to the trailing portion of the first strut and the second strut.

[0021] In some embodiments, at least one strut includes a removable trailing edge portion.

[0022] In some embodiments, one or more skegs may extend from the lower unit.

[0023] In some embodiments, at least one strut and the lower unit are formed as separate components.

[0024] In some embodiments, the thermal circuit forms a closed fluid path.

[0025] In some embodiments, the distal end of at least one strut is disposed in the middle portion of the lower unit.

[0026] In some embodiments, the inner belt space and the coolant circuit are separate passages.

[0027] According to another aspect of the present disclosure, a marine propulsion device includes a first strut extending from a proximal end to a distal end and a second strut extending from the proximal end to a distal end, each of the first strut and the second strut having a forward portion, an internal belt space, and an aft portion, the first strut being aligned with the second strut and the first strut being spaced apart from the second strut; and a lower unit coupled to the distal ends of the first strut and the second strut, the lower unit having a nose portion, a middle portion, and a tail portion. A marine propulsion device is provided that includes a lower unit, a sprocket rotatably disposed within the lower unit, a shaft rotatably coupled to and concentric with the sprocket, the shaft having a front side extending forward of the sprocket and a rear side extending rearward of the sprocket, and a belt rotatably connecting the drive shaft to the sprocket, a first portion of the belt being disposed within an internal belt space of a first strut and a second portion of the belt being disposed within an internal belt space of a second strut. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is an isometric view of an outboard motor according to an embodiment of the present disclosure. [Figure 2]FIG. 2 is a block diagram illustrating component level interactions between the overall propulsion system and the dual-strut lower unit, according to an embodiment of the present disclosure. [Figure 3] 1A is a partial side view of a dual strut and lower unit bullet-shaped structure, showing generally below line 1-1 shown in FIG. 1, in accordance with an embodiment of the present disclosure. FIG. [Figure 4] 1. FIG. 2 is a partial front view showing generally below line 1-1 shown in FIG. 1, in accordance with an embodiment of the present disclosure. [Figure 5] 3. FIG. 4 is a cross-sectional side view showing generally below line 3-1 shown in FIG. 3, in accordance with an embodiment of the present disclosure. [Figure 6] 3. FIG. 4 is a cross-sectional top view showing generally below line 3-1 shown in FIG. 3, in accordance with an embodiment of the present disclosure. [Figure 7] 3. FIG. 4 is a cross-sectional front view showing generally below line 3-1 shown in FIG. 3, in accordance with an embodiment of the present disclosure. [Figure 8] 1 is a schematic diagram illustrating an outboard motor transmission system according to an embodiment of the present disclosure; [Figure 9] 1 is a schematic diagram illustrating a belt drive transmission system according to an embodiment of the present disclosure. [Figure 10A] 1A-1C are computational fluid dynamics visualizations of a dual strut and a single strut, according to embodiments of the present disclosure; [Figure 10B] 1A-1C are computational fluid dynamics visualizations of a dual strut and a single strut, according to embodiments of the present disclosure; [Figure 11] 10 is a graphical representation showing initial computational fluid dynamics drag results for a dual strut (left) compared to a single strut (right), according to an embodiment of the present disclosure.

[0029] Detailed Description An outboard motor powertrain generally includes a prime mover, such as a combustion engine or electric motor, a vertical drive shaft, bevel gears, a clutch, and a propeller shaft (to which a propeller is attached). The bevel gear is a gear between two intersecting shafts, and the gear teeth are conical. The bevel gear provides higher efficiency than any other gear and can allow for gear reduction between the intersecting shafts. A clutch is used to allow the prime mover to move in a single direction, but also allows the propeller shaft to rotate in both clockwise and counterclockwise directions. In various embodiments, the outboard motor can use a dog clutch to shift between forward, neutral, and reverse. The dog clutch requires the engagement and disengagement of a shift gear, which causes rapid wear on the gear teeth. To minimize this wear, the entire assembly can be submerged in oil or a lubricant, which can be harmful to the environment and difficult to dispose of. Heat dissipation from major components, including, but not limited to, the prime mover, gears, and bearings, may be incorporated into this type of outboard motor for reliable operation. The outboard motor may draw fluid (e.g., seawater) from a body of fluid (e.g., the sea). Within this body of fluid, the outboard motor operates by circulating the fluid around the system to cool the components. However, this external fluid intake introduces contaminants, including, but not limited to, salt, sand, and / or mud, which can accelerate wear and corrosion processes. In some embodiments, the prime mover may be housed in the lower unit below the waterline. This configuration offers advantages due to simplicity, but limits heat transfer capabilities. In various embodiments, alternative means of power transmission include, for example, chain drive systems and belt drive systems instead of a vertical drive shaft and bevel gears. In various embodiments, synchronous belts may be sturdy and durable, allowing for potential use in higher-power marine engine transmissions.In various embodiments, implementing such belt or chain technology presents challenges in physical housing arrangement and mechanical assembly, as the frontal area and hydrodynamic shape of the underwater portion of a marine propulsion system significantly impacts the drag and efficiency of the system.

[0030] Therefore, there is a need for a marine propulsion system that is optimized for belt-drive and chain-drive prime movers while reducing drag (e.g., improving hydrodynamic qualities) and improving heat dissipation. Embodiments of the present disclosure are intended to address the above-mentioned challenges and others.

[0031] In various embodiments, a sterndrive or outboard marine propulsion system includes a prime mover that transmits power to a driven shaft via a synchronous belt, an anti-ventilation plate, a lower unit housing, one or more skegs extending from the bottom of the lower unit housing, and a set of struts (e.g., two struts) connecting the lower unit housing to attachment points on the anti-ventilation plate and the cowling (and / or frame structure within the cowling). In various embodiments, the sets of struts can be substantially aligned (e.g., parallel) with one another. In various embodiments, each strut can include one or more (e.g., multiple) removably attachable and modular trailing edge portions. In various embodiments, the removably attachable trailing edge portions can allow for fine tuning of hydrodynamic characteristics.

[0032] In various embodiments, the attachment points connect the midsection to the lower unit and prime mover in outboard marine propulsion system embodiments, or to the lower unit and outdrive in sterndrive marine propulsion systems. In various embodiments, certain system variables allow for lower drag, higher performance, and efficient adaptation of belt drive technology. In various embodiments, marine propulsion system components may be modular, interchangeable, and / or configured with integrated cooling passages. In various embodiments, incorporating heat dissipation features into a multi-strut (e.g., dual-strut) structure can provide increased surface area with multiple struts, thereby optimizing heat transfer capabilities. In various embodiments, multiple struts (e.g., two struts) increase the surface area of ​​the struts in contact with the water, thereby improving heat transfer (e.g., conduction) with the water (similar to fin heat transfer).

[0033] In various embodiments, the frontal area and hydrodynamic shape of the underwater portion of a marine propulsion system can affect the resistance and efficiency of the system. Reducing drag in a marine propulsion system directly improves the net efficiency of the system. In various embodiments, a set of struts may be underwater in use, and the set of struts may have any suitable hydrodynamic shape to reduce and / or optimize drag. For example, each strut may include an airfoil shape, with the leading edge of the airfoil corresponding to the front side of the strut.

[0034] In operation, the belt generally has a tight side and a slack side. In various embodiments, the belt may be insulated (i.e., sealed) from the body of surrounding water in which the prime mover operates. In various embodiments, both sides of the belt may be supported to provide tension to the belt. In various embodiments, tensioning the belt can reduce (e.g., prevent) contamination from the surrounding water. In various embodiments, the marine propulsion system may include, among other things, a continuous loop transmission. For example, the prime mover may be mechanically (e.g., rotationally) connected to a propeller via a belt or chain.

[0035] In various embodiments, the struts may be positioned a predetermined distance from one another to allow fluid flow between the struts. For example, in a dual-strut arrangement, the struts may be positioned between about 2 inches and about 24 inches from one another. In various embodiments, the struts may be positioned between about 1.5 inches and about 6 inches from one another. In various embodiments, for larger applications (e.g., yachts, tugboats, etc.), the struts may be positioned several feet apart. In various embodiments, the struts may be positioned up to about 12 feet apart. In various embodiments, the strut spacing may depend on one or more performance factors, such as, for example, (1) the hydrodynamic interaction between the struts and / or (2) the hydrodynamic drag of the lower unit. In various embodiments, wider struts may result in less fluid interaction (interference) between multiple struts. In various embodiments, wider struts may improve certain performance factors. In various embodiments, the size (e.g., drag area) of the lower unit can be minimized, thereby minimizing drag. In various embodiments, the size of the lower unit can be minimized by providing a small frontal area of ​​the lower unit. In various embodiments, the size of the lower unit can be proportional to the size of the struts. For example, for wider struts, a larger lower unit can be provided. In various embodiments, the struts do not have to be parallel to one another. For example, the struts can be non-linear or arranged at an angle (e.g., a "V" shape) relative to the horizon (sea level).

[0036] In various embodiments, each strut may include a vertical strut cross-sectional profile that minimizes water drag. In various embodiments, the cross-sectional profile may reduce (e.g., minimize) the drag area while allowing sufficient space to accommodate a continuous loop (e.g., a belt or chain). In various embodiments, each strut may include an airfoil shape. In various embodiments, any strut (e.g., some or all) may have a substantially uniform shape along its length. In various embodiments, any strut (e.g., some or all) may have a shape that varies along its respective length. For example, the struts may taper from a wider airfoil (with a higher drag area) to a thinner airfoil (with a lower drag area) from the leading edge to the trailing edge, or may taper in the opposite direction. In various embodiments, any strut (e.g., some or all struts) may have a substantially uniform width along the length of the strut (in the direction of flow). For example, an airfoil shape may have a substantially similar (e.g., equal) chord length and / or camber line along the entire length of the strut. In various embodiments, any strut (e.g., some or all struts) may have a width that varies along the length of the strut (in the direction of flow). For example, an airfoil shape may have a chord length and / or camber line that varies along the entire length of the strut. The struts may have mirror image shapes that are symmetrical about a central axis that passes through the strut. Alternatively, each strut may be formed with a unique shape / contour relative to adjacent struts.

[0037] In various embodiments, each strut may include separate spaces configured to accommodate each side of the continuous loop (i.e., a slack side and a tight side). In various embodiments, the separate spaces within any one or all of the vertical struts may be configured to move fluid (e.g., a heat transfer fluid) throughout the outboard motor.

[0038] In various embodiments, one or more struts may include a dividing line, which allows the strut to be divided into two or more sections. In various embodiments, the dividing line allows easy access so that a continuous loop (e.g., a chain or belt) can be installed or removed during or after manufacture (e.g., for repair). The dividing line may extend along the entire length of the strut (e.g., between the nose cone and the anti-ventilation plate).

[0039] FIG. 1 shows an isometric view of an outboard-type marine propulsion system 100. In various embodiments, the marine propulsion system 100 (e.g., an outboard motor) may include a powerhead section, a prime mover cowling, a belt drive, an anti-ventilation plate, a dual-strut transmission housing, a lower unit with a propeller, and a skeg. In various embodiments, the outboard-type marine propulsion system 100 includes a mount 101 configured to removably couple the transom of the boat to an outboard motor mid-section 102 via a transom mounting pad 103. In various embodiments, the outboard motor can be steered by various means, including, but not limited to, cables, pulleys, hydraulic actuators, and / or electromechanical actuators. These means are attached to a steering bracket 104 and rotate the outboard motor about the axis of a steering tube 105. In various embodiments, the angle of the outboard motor, and therefore the propulsion angle, can also be controlled about an inclined axis 106. In various embodiments, the prime mover components, whether electrically powered or liquid fuel powered, are located below the upper cowling 107. In various embodiments, the side of the cowling 107 facing the transom of the vessel may include a face plate 108. In various embodiments, the drive shaft of the prime mover is connected to a propeller shaft 109 via a synchronous drive belt (not shown). In various embodiments, the synchronous drive belt itself drives a propeller 110, which generates momentum to propel the vessel to which the marine propulsion system 100 is attached. In other embodiments, the propeller may be replaced with an impeller, waterjet, or other propulsion device. In this embodiment, the propeller tail cone 111 and tail fairing 112 match the geometric contours of the propeller to minimize turbulence losses and maximize efficiency. In other embodiments, the shapes of the propeller tail cone 111 and tail fairing 112 may be tailored to accommodate different propellers.A sprocket (located within the lower unit) is concentrically mounted on the propeller shaft 109 and housed within the lower unit 114. In various embodiments, the lower unit 114 may include a nosecone 115 at its forward portion. One or more struts 116 provide an open passageway for the belt, thereby transmitting power from a sprocket mounted to the prime mover below the upper cowling 107 to a sprocket on the propeller shaft 109. The separate strut 116 bodies allow the belt to operate without additional rolling components, enabling the highest possible efficiency. The one or more struts 116 are spaced apart so that the belt does not need to be guided around obstacles or profiles, as is required in the prior art. The strut bodies have hydrodynamic strut leading edges 117 and strut trailing edges 118 that reduce drag and maximize laminar flow to the propeller 110. The struts 116 are connected to an anti-ventilation plate 120, which is secured to a middle section bottom collar 121, which is itself secured to the bottom of the middle section. According to various embodiments, a middle section top collar 122 can provide an interface between the middle section 102 and the upper cowling 107. In various embodiments, one or more skegs 124 are disposed on the underside of the lower unit. In various embodiments where two or more skegs are provided, each skeg may be equiangularly positioned around the lower unit 114 and may be located upstream of the propeller.

[0040] FIG. 2 shows a block diagram 200 depicting component-level interactions between the overall propulsion system and the dual-strut lower unit. The component blocks are generally located onboard or outboard and are mechanically or electrically connected as indicated by the legend. In various embodiments, an operator controls the system via a control helm, which uses onboard communication signals to connect to the energy storage system and an additional communication cable to connect to the outboard power electronics. Communication protocols can be used, including, but not limited to, serial, CAN bus, SPI, analog, and digital. In various embodiments, the energy storage system is connected to the power electronics block via a DC bus. In various embodiments, the DC bus can range from 12 V to over 900 V. In various embodiments, the power electronics block generally contains all power stages and control components required to use DC voltage to drive the prime mover. In various embodiments, based on signals from the control helm, the power electronics can draw energy from the energy storage system via the DC bus and control the prime mover. In various embodiments, the prime mover may be an electric motor with phase power and a feedback signal. In various embodiments, the prime mover is mechanically coupled to a synchronous belt via a drive shaft. In various embodiments, the belt rotates a driven shaft located within the lower unit, thereby powering the propeller.

[0041] FIG. 3 shows a partial side view of the dual-strut and lower unit bullet-shaped structure, generally below line 1-1 shown in FIG. 1 . Line 1-1, in some embodiments, is the waterline of the outboard motor during operation. During operation, all components below the waterline 1-1 are submerged and contribute to the hydrodynamic drag of the system. As described in the background art, sterndrive and outboard motor marine propulsion systems can use a single-strut housing connecting the gearcase to the powerhead. Additionally, nearly all combustion-powered outboard motors use a shaft and bevel gear system to transmit power from the combustion or electric powerhead to the propeller. These types of lower units require mechanical mechanisms for shifting from forward to neutral and from neutral to reverse. This type of power transmission requires consistent maintenance for gear lubrication, wears rapidly due to shifting at non-zero rotational speeds, and can cause a 15% efficiency loss. The bevel gears also generate significant noise.

[0042] Recent advances in materials technology have enabled the development of more robust synchronous belt drives, which have the potential for increased efficiency, reduced noise, reduced maintenance, and lower costs. The present disclosure enables the use of synchronous belts in marine propulsion systems with a multi-strut body arrangement, where each side of the belt runs through a different strut. Additionally, the present disclosure provides a method for using electronic reversal from an electric prime mover, thereby eliminating the need for complex mechanical switching means.

[0043] In various embodiments, a multiple-strut design minimizes fluid flow disturbance to the propeller during maneuver. In various embodiments, a multiple-strut (e.g., dual-strut) design increases the overall system rigidity while reducing the drag-causing frontal area (i.e., drag area). In various embodiments, the interface between the strut 116 and the anti-ventilation plate 120 is integrally formed. In various embodiments, the interface between the strut 116 and the anti-ventilation plate 120 is mechanically secured (e.g., with bolts and nuts). In various embodiments, the bottom of the strut may be integrally formed with the lower unit 114. In various embodiments, the lower unit 114 may be bullet-shaped (bullet + cartridge). In various embodiments, the first portion (e.g., tight side) and second portion (e.g., slack side) of the synchronous belt 130 are protected from water and / or external fluids within the air spaces within the first and second struts 116. Thus, the belt 130 extends (vertically during operation) through the first strut 116 into the lower unit 114, where it engages with and drives the propeller 110 (forward / reverse), and extends upward through the second strut 116 and back into the cowling 107.

[0044] In various embodiments, drag can be reduced by hydrodynamic shaping applied to the leading edge 117 and trailing edge 118 of the struts 116. In various embodiments, convexity on the sides of the struts 116 between the leading edge 117 and trailing edge 118 reduces form drag and wave formation. In various embodiments, the convexity profile need not be symmetrical between struts and could be varied for different applications (i.e., not all struts need have the same shape). In various embodiments, the struts 116 can be the inverse of each other (e.g., a first strut can be the inverse of a second strut). In various embodiments, the sides of the struts 116 can be substantially parallel and of equal length. In various embodiments, the struts can be non-parallel. In various embodiments, the spacing between the struts can increase or decrease over the height of the struts.

[0045] In various embodiments, the sides of the struts 116 may not have recesses. In various embodiments, the leading edge 117 may be integrally formed with the strut 116. In various embodiments, the leading edge 117 may be manufactured separately and removably secured to the strut 116. In various embodiments, the trailing edge 118 may be integrally formed with the strut 116. In various embodiments, the trailing edge 118 may be manufactured separately and removably secured to the strut 116, for example, via strut attachment points (e.g., by screws, bolts, etc.). In various embodiments, the leading edge 117 and / or the trailing edge 118 may be modular and replaceable to optimize performance. Additionally or alternatively, the struts may include access panels to allow for belt repair and inspection. The access panels may be spaced apart from the leading / trailing edges and may be located within a generally flat section of the strut.

[0046] In various embodiments, the struts may include active control of the leading and / or trailing edge surface profile during operation. For example, electronic control (e.g., real-time or manual) can change the camber or chord length of the airfoil profile. In another example, electronic control (e.g., real-time or manual) can change the width (e.g., drag area) of the airfoil profile so that a continuous loop (e.g., a belt) has enough room to operate in airspace.

[0047] Further reducing hydrodynamic drag and increasing propulsion efficiency occurs throughout the structure's geometry. In various embodiments, the incoming fluid flow first interacts with the nosecone 115. In various embodiments, the geometry of the nosecone 115 may be geometrically designed to provide a smooth transition from the nosecone 115 through the nosecone / lower unit interface to the lower unit 114. In various embodiments, the nosecone 115 is removable and replaceable. In various embodiments, the nosecone 115 may include any suitable shape. For example, the nosecone 115 may include a round, bullet-like shape. In various embodiments, the middle portion 113 of the lower unit 114 may have a substantially cylindrical shape (e.g., a cartridge shape). In another example, the nosecone 115 may be substantially conical with a more pointed tip. In various embodiments, as fluid flow passes through the lower unit 114, the tail fairing 112 can minimize loss-causing boundary layer separation across the tail fairing / lower unit interface because boundary layer separation causes turbulence and therefore increases pressure drag on the propulsion system 100. In various embodiments, the tail fairing 112 is shaped so that the tail fairing / propeller hub interface hydrodynamically mates with the propeller hub to optimize flow into the propeller. Thus, the struts 116, lower unit 114, nosecone 115, and tail fairing 112 can be configured in a visually seamless design with no abrupt changes in size / shape / diameter, and the assembly of these components forms a continuous exterior surface to minimize drag.

[0048] In various embodiments, the tail fairing may be a frusto-conical shape that tapers from a larger diameter at the mid-section 113 to a smaller diameter at the propeller 110. In various embodiments, as the propeller 110 rotates and creates areas of high and low pressure, flow is directed over the propeller tail cone 111, which can reduce turbulence and further minimize drag on the propulsion system 100. In a typical combustion-based marine engine, the engine exhaust is directed generally downward through a single component and outward through the center of the propeller. The present disclosure eliminates this type of exhaust and allows for a more efficient overall hydrodynamic approach.

[0049] In various embodiments, one or more skegs 124 may be attached to the middle portion 113 of the lower unit 114. In various embodiments, the middle portion 113 may include one or more skeg attachment points configured to allow for the attachment of one or more skegs 124. In various embodiments, the skeg 124 may have a generally fin-like shape. In various embodiments, the skeg 124 may have a constant thickness along its length. In various embodiments, the skeg 124 may have a depth that varies along its length. For example, the skeg 124 may taper from a first, larger depth d1 to a second, smaller depth d2. In various embodiments, one side of the skeg 124 may be vertical while the other side may be tapered. In various embodiments, both sides of the skeg 124 may be tapered. In various embodiments, the skeg 124 may have a curved or airfoil shape, similar to the struts 116. In various embodiments, the skeg 124 is removable and replaceable at the skeg / lower unit interface. In various embodiments, the skeg 124 may be integrally formed at the skeg / lower unit interface. In various embodiments, the skeg 124 contributes to stability and hydrodynamic flow interactions by having a trailing edge that minimizes turbulence in the flow entering the propeller 110. In various embodiments, the lowermost edge of the skeg 124 may be lower than the blades of the propeller 110, providing protection for the propeller 110 from physical object strikes. Additionally or alternatively, the position of the skeg 124 may be adjustable upstream / downstream relative to the lower unit 114.

[0050] FIG. 4 is a partial front view, showing generally below line 1-1 in FIG. 1. As shown in FIG. 4, prime mover 128 is rotationally coupled to belt 130 via a drive shaft (not shown). As the prime mover rotates, either left side 130a of belt 130 or right side 130b of belt 130 can transmit rotational force to and from the propeller. In the illustrated example in which belt 130 is rotating counterclockwise (from the perspective of prime mover 128), left side 130a of belt 130 is the slack side, and right side 130b of belt 130 is the tight (i.e., tensioned) side. In various embodiments, the width of the gap between two struts 116 (as measured by the distance between the inner edges of each strut) can be varied to allow the passage of fluid (e.g., seawater) and to accommodate larger or smaller overall component dimensions while maintaining right side 130b of belt 130 and left side 130a of belt 130 parallel to one another. In various embodiments, the distance d between the inner edges of the struts 116 gap can be varied based on ideal performance metrics, for example, to reduce frontal (drag) area. In various embodiments, the distance d between the outer edges outer can be varied to accommodate, for example, a thicker pitched belt. In various embodiments, the strut / lower unit interface can have a graduated hydrodynamic shape to minimize flow disturbances as water moves through the strut 116 toward the propeller 110. In various embodiments, the propeller 110 can be positioned in front of the strut 116. In various embodiments, an anti-ventilation plate 120 can be connected to the top (i.e., proximal end) of the strut 116 to prevent the propeller from ingesting air from the surface. The anti-ventilation plate can be generally referred to as a "cavitation plate." The upper end of the strut 116 can be directly connected to the cowling 107. Additionally or alternatively, the upper end of the strut 116 can be connected to a mounting plate / frame that houses the cowling 107.

[0051] FIG. 5 shows a partial side view, partially cut away, showing generally below line 3-1 in FIG. 3. In various embodiments, the sprocket 126 is concentrically secured to the propeller shaft 119, which exits the lower unit bullet through the tail fairing 112. In various embodiments, the interior of the lower unit 114 is protected from seawater by seals at all edges and interfaces, including a set of shaft seals. In various embodiments, both leading edges 117 of the struts 116 include coolant passages 117a to allow the passage of coolant. In various embodiments, coolant enters each strut through a coolant port and then flows through the coolant passages 117a, which remove heat from the coolant by conduction. The present disclosure thus provides a closed-circuit fluid cooling system, where the coolant circulation path is maintained within the struts 116, the nosecone 115, and the anti-ventilation plate 120. Therefore, the coolant system need not rely on ambient water intake during operation. In various embodiments, one or more coolant passages 117a in each strut allow coolant to flow into the nosecone volume 115a, which acts as an underwater heat-blocking reservoir. In various embodiments, the nosecone volume 115a includes one or more nosecone turbulators 115b (e.g., undulating structures / walls / strips) configured to increase turbulence of the heat-transfer fluid, thereby increasing heat-blocking capability. Optionally, the coolant passages 117a may extend throughout the anti-ventilation plate 120.

[0052] In various embodiments, coolant can flow in both directions through the struts 116 and into the thermal circuit 140 via the coolant passages 117a. In various embodiments, the coolant passages 117a can include tubes, hoses, pipes, and / or other fluid transport methods. In various embodiments, the thermal circuit can include heat-generating components, including, but not limited to, electronic controls, pumps, and / or power electronics and prime movers. In various embodiments, a set of coolant port seals ensures that the heat transfer fluid is not contaminated. In various embodiments, additional space can be provided in the trailing edge 118, the belt-receiving space 131, the tail fairing 112, and / or the lower unit 114 that can be used for additional coolant passages. In various embodiments, the longitudinal width of the belt-receiving space 131 can be varied to accommodate different size belts. In various embodiments, the trailing edge 118 may be mechanically secured by a set of trailing edge fasteners 118a configured for anchoring within an anchor panel 118b (e.g., a T-block). In various embodiments, this attachment method allows the trailing edge 118 to be separated from the strut 116 for installation and removal of the belt 130. In various embodiments, the belt-receiving space 131 may be optimized so that the size of the space (e.g., the width of the space) is minimized. In various embodiments, from a hydrodynamic perspective, the less space there is, the better (e.g., less drag area). In various embodiments, the belt-receiving space 131 may be approximately 1 / 8 inch on each side of the belt 130. In various embodiments, the sprocket gap 125 may have a 1 / 8 inch gap as well. In various embodiments, the sprocket gap 125 may be smaller than the space between the belt 130 and the inside of the belt-receiving space 131 because the belt can only move a small amount around the sprocket 126 .In various embodiments, the belt-receiving space 131 may have a spacing (e.g., width) of between about 0.01 inches and about 0.25 inches on each side of the belt. For example, with 0.25 inches of spacing on each side of the belt 130, the total width of the belt-receiving space 131 is 0.25 inches + 0.25 inches + the belt thickness (in inches). In various embodiments, the belt-receiving space 131 may include a spacing (e.g., width) of between about 0.01 inches and about 6 inches on each side of the belt. In various embodiments, this spacing may correspond to the system size. In various embodiments, the spacing (e.g., width) may be about 12 inches on each side of the belt.

[0053] FIG. 6 is a partial cross-sectional, partial top view generally below line 3-1 shown in FIG. 3. In various embodiments, the nosecone 115 has an outer contour that maintains attached flow with the surrounding body of fluid (e.g., reducing / preventing boundary layer separation). According to various embodiments, the nosecone 115 is conical. According to various embodiments, the nosecone 115 may be blunt or rounded at the tip. In various embodiments, the contour may be modified to accommodate different operating conditions. In various embodiments, the lower unit 114 may be cylindrical and connected to both struts. In various embodiments, the trailing edge 118 may be connected to the strut 116 by fasteners anchored in a T-block 118b, which is itself held in place by the walls of the dual strut body. In various embodiments, the leading edge 117 may include a coolant passage 117a having a circular diameter. In various embodiments, the coolant passages 117 a may have a substantially constant diameter throughout the thermal circuit 140 .

[0054] FIG. 7 illustrates a partial cross-sectional, partial front view generally below line 3-1 shown in FIG. 3. As shown in FIG. 7, the lower unit 114 and struts 116 include belt-receiving spaces through which the belt 130 can pass. In various embodiments, the struts 116 include inner and outer strut walls. In various embodiments, the inner and outer strut walls may be formed from any suitable material and may be integrally formed with the remainder of the strut body, although this is not required. In various embodiments, the thickness of the strut walls may be selected based on the application, which may increase rigidity or reduce drag. In various embodiments, within the lower unit 114, a belt-driven sprocket 126 is concentric with the propeller shaft 119. In various embodiments, a keyway 127 is used to transfer torque between the sprocket 126 and the propeller shaft 119. In various embodiments, splines may be used, or the sprocket 126 and the propeller shaft 119 may be integrally formed. In various embodiments, an air-filled sprocket gap 125 exists within the lower unit 114 to accommodate the thickness of the belt 130. In various embodiments, a dual-strut configuration allows the belt 130 to rotate about the sprocket 126 without physically contacting another portion of the lower unit 114. In various embodiments, this contactless operation allows for lubrication-free operation compared to other engines that require the belt or transmission components to operate in an oil-filled bath. The belt 130 may wrap around the sprocket 126, engaging each face for approximately 180 degrees of the sprocket's rotation. The sprocket 126 may include raised teeth, as shown, to increase frictional engagement with the belt and generate more torque.

[0055] FIG. 8 is a schematic diagram of a conventional outboard motor transmission system. In various embodiments, the outboard motor transmission system utilizes a prime mover 807 with a vertically extending drive shaft 808. In various embodiments, power is transferred from the vertical drive shaft and the horizontal propeller shaft using gears. In various embodiments, a pinion gear 809 is used in conjunction with crown gears 811 and 813 to transfer rotational speed to the driven shaft. In many embodiments, a clutch is used with a sliding collar 812 that can engage the crown gear in either a clockwise or counterclockwise direction. In various embodiments, this mechanism allows the propeller shaft rotation direction to be changed while maintaining the prime mover drive direction.

[0056] Figure 9 shows a schematic diagram of a belt drive transmission system. In various embodiments, Figure 9 is a schematic diagram of a specific embodiment for an alternative means of power transmission between a prime mover 901 and a lower driven shaft 905. In various embodiments, the prime mover may utilize a horizontally extending drive shaft 903, support a sprocket or gear 902, and drive a lower sprocket or gear 906 via a continuous loop 904.

[0057] In various embodiments, any strut may include a nonlinear shape. In various embodiments, to accommodate a nonlinear shape, the belt may remain substantially linear, but the width of the belt-receiving space 131 (the space between the belt and the inner wall of the strut space) may vary. In various embodiments, the strut may include a pulley (e.g., a roller pulley) configured to form a curve for the belt 130 to follow. In various embodiments, a low-friction pad may be positioned at any suitable location within the belt-receiving space 131. In various embodiments, any combination of the above three methods may work together to achieve a nonlinear strut shape. In various embodiments, the leading edge of the strut may include a non-uniform contour (when viewed from top to bottom).

[0058] The various components disclosed herein (e.g., struts, nose cones, fairings, skegs) may be formed from a variety of materials, including metals (e.g., aluminum, steel, titanium, etc.), rigid polymers and plastics, wood, etc. In various embodiments, the various components may include composite materials (e.g., carbon fiber, fiberglass, etc.). In various embodiments, the various components may include rubber. In various embodiments, the various components may include thermoplastics. In various embodiments, the various components may include any suitable metal-based alloy. In various embodiments, the various components may include materials with high thermal conductivity and high corrosion resistance. In various embodiments, the various components may include one or more coatings (anodizing, powder coating, chemical vapor deposition, paint, etc.). In various embodiments, the various components may be formed from two or more materials (i.e., the nose cone may be primarily aluminum with a rubber-based tip).

[0059] Figures 10A-10B show computational fluid dynamics visualizations of the disclosed dual strut (top) and a conventional single strut (bottom). In various embodiments, this half-body analysis was used to understand the hypothetical fluid dynamic effects and impact of the dual strut compared to a single strut. The plots shown in Figures 10A-10B show laminar flow as evidenced by the primarily uniform shading of the fluid flow values ​​(the dark portion of the plot in Figure 10B is above the waterline).

[0060] Figure 11 shows a graphical representation of the initial computational fluid dynamics drag results for the disclosed dual strut (left) (approximately 37,500 Newtons over 150 iterations) compared to a conventional single strut (right) (approximately 45,500 Newtons over 150 iterations). The simulations demonstrated the hydrodynamic advantages of the dual strut compared to the single strut.

[0061] The descriptions of various embodiments of the present disclosure are provided for illustrative purposes and are not intended to be exhaustive or limiting of the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terms used in this specification are selected to most clearly explain the principles of the embodiments, practical applications of technologies found in the market, or technical improvements, or to enable other skilled in the art to understand the embodiments disclosed herein.

Claims

1. 1. A marine propulsion device comprising: a first strut extending from a proximal end to a distal end and a second strut extending from a proximal end to a distal end, each of the first strut and the second strut having a front portion, an internal belt space, and a rear portion, the first strut being aligned with the second strut and the first strut being spaced apart from the second strut; a lower unit coupled to the distal ends of the first strut and the second strut, the lower unit having a nose portion, a middle portion, and a tail portion; a sprocket rotatably disposed within the lower unit; a shaft rotatably coupled to and concentric with the sprocket, the shaft having a front side extending in front of the sprocket and a rear side extending behind the sprocket; a belt rotatably connecting a drive shaft to the sprocket, a first portion of the belt being disposed within the internal belt space of the first strut and a second portion of the belt being disposed within the internal belt space of the second strut; and a thermal circuit extending from a cowling through each of the first strut and the second strut into the lower unit, the thermal circuit having a heat transfer fluid configured to flow through the thermal circuit, the thermal circuit being bidirectional through each of the first strut and the second strut; A marine propulsion device having:

2. 2. The marine propulsion device of claim 1, wherein the first strut and the second strut have complementary shapes.

3. 2. The marine propulsion device of claim 1, wherein the spacing between the first strut and the second strut is uniform over the length of the first strut and the second strut.

4. 2. The marine propulsion device of claim 1, wherein the thermal circuit is disposed within the forward portion of each of the first strut and the second strut.

5. 2. A marine propulsion device in accordance with claim 1, wherein said thermal circuit further extends through said intermediate portion of said lower unit.

6. 2. A marine propulsion device in accordance with claim 1, wherein said thermal circuit further extends through said tail portion of said lower unit.

7. 2. A marine propulsion device according to claim 1, further comprising a plate disposed at the proximal ends of the first and second struts, the plate being perpendicular to the first and second struts.

8. 10. The marine propulsion device of claim 1, further comprising a propeller coupled to said rear side of said shaft.

9. 10. The marine propulsion device of claim 1, wherein said lower unit includes a nosecone and a tail fairing.

10. 2. The marine propulsion device of claim 1, wherein the sprocket is disposed within the intermediate portion of the lower unit.

11. 2. The marine propulsion device of claim 1, wherein said first strut and said second strut are linear.

12. 2. The marine propulsion device of claim 1, wherein the first strut and the second strut each have an airfoil shape, a leading edge of the airfoil shape corresponding to the forward portion of the first strut and the second strut, and a trailing edge of the airfoil shape corresponding to the aft portion of the first strut and the second strut.

13. 10. The marine propulsion device of claim 1, wherein at least one strut includes a removable trailing edge portion.

14. 10. A marine propulsion device in accordance with claim 1, further comprising one or more skegs extending from said lower unit.

15. 2. A marine propulsion device in accordance with claim 1, wherein at least one strut and said lower unit are formed as separate components.

16. 2. A marine propulsion device in accordance with claim 1, wherein said thermal circuit defines a closed fluid path.

17. 2. The marine propulsion device of claim 1, wherein the distal end of at least one strut is disposed in the intermediate portion of the lower unit.

18. 1. A marine propulsion device comprising: a first strut extending from a proximal end to a distal end and a second strut extending from a proximal end to a distal end, each of the first strut and the second strut having a front portion, an internal belt space, and a rear portion, the first strut being aligned with the second strut and the first strut being spaced apart from the second strut; a lower unit coupled to the distal ends of the first strut and the second strut, the lower unit having a nose portion, a middle portion, and a tail portion; a sprocket rotatably disposed within the lower unit; a shaft rotatably coupled to and concentric with the sprocket, the shaft having a front side extending in front of the sprocket and a rear side extending behind the sprocket; a belt rotatably connecting a drive shaft to the sprocket, a first portion of the belt being disposed within the internal belt space of the first strut and a second portion of the belt being disposed within the internal belt space of the second strut; and and a thermal circuit extending through each of the first strut and the second strut, through an anti-ventilation plate, and into the lower unit, the thermal circuit having a heat transfer fluid configured to flow therethrough, the internal belt space and the thermal circuit being separate passageways.

Images