Propulsion unit for boats

Abstract

An outboard propulsion unit (1) for a bbooaatt ccoommpprriisseess a mounting support (2) for connection to a boat, a motor (3) removably connected to a plate (4), which in turn is removably connected to a hollow housing (5) that is pivotally mounted to the support (2) so as to be rotatable around a vertical rotation axis (6), thereby rotating the plate (4) and the motor (3) together; a drive shaft (7) extending within the hollow housing (5) and operatively connected to said motor (3), a gearbox (9) connected to a bottom end of the housing (5) and configured to transmit motion from the drive shaft (7) to a pair of coaxial shafts, comprising an inner shaft (10) and an outer shaft (11), which are rotatable in opposite directions; a first propeller (13) constrained to said inner shaft (10), and a second propeller (14) constrained to said outer shaft (11), wherein said motor (3) is an electric motor.

Description

[0001] “PROPULSION UNIT FORBOATS”

[0002] * * *

[0003] TECHNICAL FIEED

[0004] The present invention relates to a propulsion unit for boats comprising a pair of contra-rotating propellers for moving a boat in water.

[0005] In particular, the propulsion unit is of the outboard type, meaning that it is intended to be installed outside a hull of a boat.

[0006] PRIOR ART

[0007] Marine propulsion units can generally be classified as inboard or outboard depending on the position of the propulsion unit itself with respect to the hull of the boat.

[0008] In general, an inboard propulsion unit provides for the positioning of an engine and its transmission inside the hull and the presence of a drive shaft to which a propeller is connected, wherein said shaft extends through the bottom of the hull.

[0009] In an outboard propulsion unit, on the other hand, the engine, transmission, and propeller are generally positioned outside the hull, by means of a rotating connection that allows the propulsion unit itself to rotate around a vertical or substantially vertical axis. In this way, the propellers can be rotated around said axis to allow the boat to maneuver.

[0010] Furthermore, marine propulsion units can be classified into two types, depending on the positioning of the at least one propeller with respect to the boat.

[0011] In particular, propulsion units of the pushing or pulling type are distinguished.

[0012] A pushing propulsion unit comprises at least one propeller oriented towards the stern of the boat, so as to generate a propulsive force that pushes the boat through the water.

[0013] A pulling propulsion unit, instead, uses one or more propellers oriented forward, towards the bow of the boat, to produce a propulsive force that pulls the boat through the water.

[0014] With reference to the type of inboard pulling propulsion units, the use of two contra-rotating propellers on the same shaft is known, that is to say, comprising two propellers rotating in opposite directions to pull the boat through the water. The two propellers are mounted on concentric shafts housed rotatably, with opposite rotation directions, inside a housing designed for underwater use.

[0015] The housing is orientable around a vertical or substantially vertical rotation axis. The rotation axis substantially corresponds to a drive shaft that connects an internal combustion engine to a transmission, which is in turn operatively connected to the concentric shafts.

[0016] The rotation of the housing around the rotation axis varies the direction of the thrust of the propellers in water, thus acting as a rudder and allowing the boat to be steered.

[0017] Such a solution comprising a pair of contra-rotating propellers has the advantage of ensuring better grip in the water, allowing improved performance and maneuverability of a boat.

[0018] Furthermore, the use of two propellers allows the torque from the internal combustion engine to be distributed, enabling a reduction in the size of the gears necessary to transmit motion between the drive shaft and the concentric shafts and therefore of the underwater housing, with the resulting advantages from a fluid dynamic standpoint.

[0019] On the other hand, being an inboard solution, it is necessary to provide a passage for the drive shaft through the hull of the boat.

[0020] Moreover, such a solution is not very flexible from a design point of view because it requires the design of a specific space onboard the boat (hold or engine room), thus preventing easy use and adaptation of the solution to different boats.

[0021] Furthermore, the maintenance of such a solution is complex, requiring the hauling of the boat to access the housing containing the coaxial shafts and the gears for transmitting motion between the drive shaft, connected to the internal combustion engine, and the coaxial shafts themselves.

[0022] Unlike inboard units, an outboard propulsion unit is easier to install on board a boat.

[0023] To install an outboard propulsion unit, a support structure is provided at the transom, that is to say, the rear end area of the stern that ends with a more or less flat portion and connects the two sides of the boat.

[0024] The outboard propulsion unit is then connected to said structure so that it can rotate around a vertical or substantially vertical axis. In the field, there is a need for an outboard propulsion unit with contra-rotating propellers capable of ensuring high performance and maneuverability, within a solution optimized in terms of efficiency and output.

[0025] In addition, there is a need for an outboard propulsion unit with a reduced environmental impact compared to traditional solutions.

[0026] OBJECTS OF THE INVENTION

[0027] The object of the present invention is to improve the performance of an outboard propulsion unit with contra-rotating propellers compared to traditional solutions.

[0028] A further object of the present invention is to reduce the environmental impact of an outboard propulsion unit compared to traditional solutions.

[0029] Another object of the present invention is to optimize the dimensions of the portions of an outboard propulsion unit with contra-rotating propellers that, during use, are immersed, in order to enhance hydrodynamic performance.

[0030] A further object of the present invention is to allow adjustment of the installation geometry of an outboard propulsion unit with contra-rotating propellers to the portion of the boat's transom, to adapt it to specific navigation conditions, within a solution that is practical, flexible, and efficient to use.

[0031] These and other objects are achieved by an outboard propulsion unit according to claim 1. The dependent claims specify further advantages of the outboard propulsion unit according to the invention.

[0032] The advantages offered by the outboard propulsion unit according to the invention are evident.

[0033] Indeed, the outboard propulsion unit according to the invention comprises a support for connection to a stern portion of a boat, a motor removably connected to a plate in turn removably connected to a hollow housing at an upper end thereof, wherein the hollow housing is pivoted to the support so as to be able to rotate around a vertical rotation axis, dragging the plate and the motor in rotation. The outboard propulsion unit further comprises a drive shaft extending inside the hollow housing along the rotation axis and operatively connected to the motor, a gearbox connected to a lower end of the hollow housing and configured to transmit motion from the drive shaft to a pair of coaxial shafts, wherein the pair of coaxial shafts comprises an inner shaft and an outer shaft rotatable in opposite directions to one another, both extending along a propulsion direction transverse to the rotation axis, a first propeller constrained to the inner shaft and a second propeller constrained to the outer shaft, downstream of the first propeller along the propulsion direction, wherein the motor is of the electric type.

[0034] Compared to traditional solutions, such a propulsion unit with contra-rotating propellers makes it possible to achieve high performance while maintaining an overall compact solution.

[0035] By reducing the dimensions of the portions that, during use, are submerged, the fluid dynamic resistance is reduced, improving energy efficiency and the maneuverability of the boat.

[0036] Moreover, the use of an electric motor significantly reduces the environmental impact of such a propulsion unit compared to traditional solutions.

[0037] DESCRIPTION OF THE FIGURES

[0038] The present invention will now be described, by way of illustration but not limitation, according to its preferred embodiments, with particular reference to the Figures of the attached drawings, in which:

[0039] Figure 1 shows a top perspective view of an outboard propulsion unit according to the invention;

[0040] Figure 2 shows a bottom perspective detail view of certain components of an outboard propulsion unit according to the invention;

[0041] Figure 3 shows a lateral sectional view of an outboard propulsion unit according to the invention;

[0042] Figure 4 shows an enlarged detail view of a component of an outboard propulsion unit according to the invention;

[0043] Figure 5 shows a detailed lateral sectional view of certain components of an outboard propulsion unit according to the invention;

[0044] Figure 6 shows a rear perspective view of certain components of a propulsion unit according to the invention.

[0045] DESCRIPTION OF THE INVENTION

[0046] With reference to the embodiment shown in the attached Figures, an outboard propulsion unit — hereinafter also referred to simply as propulsion unit — for brevity, according to the invention is indicated overall with reference numeral 1.

[0047] A boat comprising such a propulsion unit 1, although not illustrated in the attached Figures, also falls within the scope of the present invention.

[0048] In the following description and in the attached Figures, explicit reference will be made to a pulling-type propulsion unit 1, that is to say, in which the propellers are oriented towards the bow and exert a pulling action on the boat to which the propulsion unit 1 is connectable.

[0049] It is understood that an alternative embodiment is possible, not illustrated, in which the propulsion unit 1 is of the pushing type, i.e., in which the propellers are oriented towards the stern and, therefore, configured to exert a pushing action to cause the advancement of the boat.

[0050] With reference to the schematic view illustrated in the attached Figure 1 and to the sectional view shown in Figure 3, the propulsion unit 1 comprises a support 2 for connecting the propulsion unit 1 itself to a stem portion of a boat.

[0051] It is noted that the support 2 is shown by way of example.

[0052] In fact, the support 2 may take on a configuration overall different from that shown in the Figures, for example depending on the shape of the stern of the boat to which the propulsion unit 1 is intended to be connected, while still falling within the same inventive concept of the invention.

[0053] The propulsion unit 1 comprises a motor 3, removably connected to a plate 4, which in turn is removably connected to a hollow housing 5.

[0054] The plate 4 acts as a support and interface for connecting the motor 3 to the hollow housing 5.

[0055] In particular, the plate 4 is connected to an upper end of the hollow housing 5.

[0056] By way of example but not limitation, the plate 4 has a through opening or a seat that can be engaged by an upper end portion of the hollow housing 5, and transverse through seats configured to face corresponding transverse through seats defined at the upper end portion of the hollow housing 5 and engageable by respective screws or pins so as to mutually fasten the plate and the hollow housing 5.

[0057] The hollow housing 5, in turn, is pivoted to the support 2 so as to be rotatable around a vertical rotation axis 6, dragging in rotation the plate 4 and the motor 3.

[0058] The propulsion unit 1 further comprises a drive shaft 7 that extends inside the hollow housing 5.

[0059] The drive shaft 7 is operatively connected to the motor 3 and extends aligned with the rotation axis 6 to transfer motion from an upper portion of the propulsion unit 1 towards a lower portion thereof, where a pair of propellers is positioned, as described in more detail below.

[0060] In accordance with the embodiment illustrated in the attached Figures, and with particular reference to the sectional view in Figure 3, the drive shaft 7 is connected to a power take-off of the motor 3 via a coupling 8.

[0061] The coupling 8 is of the elastic type and is configured to absorb vibrations and shocks transmitted during operation of the motor 3. Furthermore, the use of an elastic coupling allows for the compensation of any misalignments between the drive shaft 7 and the power take-off of the motor 3.

[0062] According to a preferred embodiment, the coupling 8 is a star coupling, although it is understood that alternative types of elastic couplings capable of performing a similar function to that of a star coupling are also possible.

[0063] The operation of a star coupling is considered to be within the reach of a person skilled in the art and, therefore, will not be described further.

[0064] The propulsion unit 1 comprises a gearbox, indicated overall with reference numeral 9, connected to a lower end of the hollow housing 5.

[0065] The gearbox 9 comprises bevel gears inside it, configured to transmit motion from the drive shaft 7 to a pair of coaxial shafts, each of which is operatively connected to a respective propeller.

[0066] In particular, the pair of coaxial shafts comprises an inner shaft 10 and an outer shaft 11, rotatable in opposite directions to one another and both extending along a propulsion direction 12 transverse with respect to the rotation axis 6.

[0067] Both the inner shaft 10 and the outer shaft 11 are rotatable around the same propulsion axis, which is oriented parallel to the propulsion direction 12.

[0068] The inner shaft 10 is solid and extends through the outer shaft 11, which is hollow.

[0069] The propulsion unit 1 comprises a pair of propellers, each connected to a respective shaft, in succession along the propulsion direction 12, to be rotated in opposite directions relative to each other.

[0070] In particular, the propulsion unit 1 comprises a first propeller 13 connectable to the inner shaft 10 and a second propeller 14 connectable to the outer shaft 11, in proximity to the first propeller 13. In the attached Figures, a first propeller 13 and a second propeller 14 are shown, each comprising three blades, although alternative embodiments are possible comprising a different number of blades or blades with a different configuration than that illustrated.

[0071] The inner shaft 10 has an engagement portion 15 along which the first propeller 13 is mounted. The engagement portion 15 is positioned outside the gearbox 9, facing the bow of a boat to which the propulsion unit 1 can be connected (see sectional view in Figure 5).

[0072] The engagement portion 15 is configured to engage a central through cavity of the first propeller 13 in order to mutually secure the first propeller 13 and the inner shaft 10 and to prevent relative rotation around a propulsion axis corresponding to the propulsion direction 12.

[0073] The first propeller 13 is held in axial position along the inner shaft 10 by means of a locking nut 16, which can be screwed along a threaded portion 17 provided on the inner shaft 10. In particular, the threaded portion 17 is provided near the engagement portion 15.

[0074] The second propeller 14 is fitted onto the outer shaft 11, in proximity to a bow-end portion of the outer shaft 11 itself.

[0075] Similarly to what is described for the first propeller 13, the second propeller 14 defines a corresponding central through seat, engageable by the outer shaft 11 to connect the second propeller 14 and the outer shaft 11 and prevent their relative rotation.

[0076] The propulsion unit 1 comprises a retaining ring 18, for example a Seeger ring or, more generally, an elastic ring, engageable in a corresponding radial seat defined along the outer shaft 11 near the bow end, in order to axially secure the second propeller 14 and the outer shaft 11 itself (see Figure 5).

[0077] The gearbox 9 comprises inside it bevel gears adapted to transfer the motion from the drive shaft 7 to the inner shaft 10 and the outer shaft 11.

[0078] The gearbox 9 also functions as a support element for bearings adapted to rotatably support the drive shaft 7, the inner shaft 10, and the outer shaft 11, as will be further described.

[0079] The gearbox 9 houses inside it a driving gear 19, connected to a bottom end of the drive shaft 7, which engages, on opposite sides, a first driven gear 20 and a second driven gear 21.

[0080] The first driven gear 20 is connected to the inner shaft 10, while the second driven gear 21 is connected to the outer shaft 11. The first driven gear 20 and the second driven gear 21 are opposed to each other (see Figure 5).

[0081] Preferably, the driving gear 19, the first driven gear 20, and the second driven gear 21 are configured as bevel gears having a transmission ratio of 1:1.

[0082] The first driven gear 20 and the second driven gear 21 are coaxial to each other and rotatable around the propulsion axis.

[0083] The driving gear 19, instead, is rotatable around the rotation axis 6.

[0084] The rotation of the driving gear 19 causes opposite-direction rotation of the first driven gear 20 and the second driven gear 21.

[0085] Due to the transmission ratio, the torque transmitted by the driving gear 19 is evenly distributed between the first driven gear 20 and the second driven gear 21, allowing the use of smaller gears compared to those used in traditional solutions with the same total power to be transmitted.

[0086] The gearbox 9 comprises a hollow central body 22, of substantially cylindrical shape, a stern cover 23, and a bow cover 24 removably connected to each other.

[0087] Preferably, the stern cover 23 and the bow cover 24 are connected to opposite ends of the hollow central body 22, respectively at a stem side and a bow side.

[0088] Preferably, the stern cover 23 and the bow cover 24 are screwed to the hollow central body 22. For this purpose, the stem cover 23 and the bow cover 24 each have externally threaded portions adapted to engage respective portions defined on opposite sides of the hollow central body 22, which in turn have corresponding internal threaded portions.

[0089] The bow cover 24 defines a through opening 25 for the passage of the inner shaft 10 and the outer shaft 11.

[0090] The propulsion unit 1 comprises at least one sealing element 26 interposed between the outer shaft 11 and the through opening 25, for example a sealing ring, to ensure hydraulic sealing and to prevent water ingress into the gearbox 9.

[0091] The stern cover 23, on the other hand, is closed.

[0092] According to a preferred embodiment, the stern cover 23 has a handling portion 27 shaped to protrude outwardly from the stern cover 23 itself and to serve as a handling point for screwing or unscrewing the stern cover 23 relative to the hollow central body 22.

[0093] According to the embodiment shown in the attached Figures, the hollow central body 22 defines a flared through opening 28 in proximity to the installation position of the driving gear 19 in the hollow central body 22 (see, for example, Figure 2).

[0094] The flared through opening 28 allows the housing of the driving gear 19 inside the hollow central body 22, at an upper portion thereof.

[0095] In fact, the hollow central body 22 has a cylindrical or substantially cylindrical shape. The driving gear 19 has an outer diameter greater than the available cross -section of the hollow central body 22 at its upper portion.

[0096] The flared through opening 28 allows the passage of respective portions of the driving gear 19 that protrude outside of the upper portion of the hollow central body 22.

[0097] The flared through opening 28 has a converging configuration, from the upper portion of the hollow central body 22 towards a central portion thereof, to facilitate the assembly of the driving gear 19 inside the gearbox 9.

[0098] During assembly of the driving gear 19, after inserting the driving gear 19 into the hollow central body 22, thanks to the flared shape of the through opening 28, it is possible to access a lower portion of the driving gear 19 to lift it and bring it near the upper portion of the hollow central body 22, where the bottom end of the drive shaft 7 is located.

[0099] The propulsion unit 1 comprises closure elements for both openings defined in the hollow central body 22 by the flared through opening 28, not illustrated in the attached Figures, which can be sealingly secured to the hollow central body 22 itself.

[0100] According to an alternative embodiment, not shown in the attached Figures, the hollow central body 22 lacks the flared through opening 28 and has an upper portion configured in such away as to allow the installation of the driving gear 19 inside the hollow central body 22 without interference with it.

[0101] According to the embodiment shown in the attached Figures, the propulsion unit 1 comprises a connection element 29 for connecting the gearbox 9 and the hollow housing 5.

[0102] The connection element 29 has a top portion 30 configured to engage a bottom end of the hollow housing 5, thereby being firmly connected to it.

[0103] Optionally, the top portion 30 and the hollow housing 5 are mutually fixed by adhesive bonding.

[0104] The connection element 29 then has a connection portion 31, opposite to the top portion 30 and configured for removable connection with the gearbox 9. In particular, the connection portion 31 is configured to be flat or substantially flat so as to abut against at least one appendage 32 protruding from a top part of the gearbox 9, to which it can be connected via a removable connection, for example using screws, bolts, or similar means.

[0105] According to this embodiment, the connection element 29 is an insert engagable within the hollow housing 5 to allow connection between the latter and the gearbox 9.

[0106] Byway of example, the hollow housing 5 may be made of composite material, such as carbon fiber. In this case, the connection element 29 functions as an insert to enable, as mentioned, the reciprocal connection between the hollow housing 5 and the gearbox 9, as well as to ensure a uniform distribution of stress at the bottom portion of the hollow housing 5, in order to prevent potential damage (caused by possible localized overstressing).

[0107] According to this embodiment, the propulsion unit 1 may include an additional insert 29' engaged at the top end of the hollow housing 5 (see Figure 3), to perform functions analogous to those previously described for the connection element 29.

[0108] In particular, the gearbox 9 has a pair of appendages 32 extending from opposite sides of the gearbox 9 and spaced apart from one another, which support a central sleeve 33 through which the drive shaft 7 passes (see Figure 4).

[0109] It is understood that an alternative embodiment is also possible, not illustrated in the accompanying Figures, wherein the hollow housing 5 directly incorporates a connection element and is therefore directly connected to the gearbox 9.

[0110] The central sleeve 33 included in the gearbox 9 serves as a support for a rolling bearing 34, which is mounted on the drive shaft 7.

[0111] According to a preferred embodiment, the rolling bearing 34 is an angular contact bearing (see Figure 5).

[0112] The hollow central body 22, as configured, provides high structural strength while still allowing access openings for internal operations, for example by removing the stern cover 23 or the bow cover 24, to perform maintenance activities.

[0113] The propulsion unit 1 includes a first support bearing 35, for supporting an aft end of the inner shaft 10, allowing its rotation around the propulsion axis parallel to the propulsion direction 12.

[0114] Preferably, the first support bearing 35 is a tapered roller bearing.

[0115] The first support bearing 35 is housed within the gearbox 9, positioned along the propulsion direction 12 between the first driven gear 20 and the stem cover 23.

[0116] Specifically, the first support bearing 35 is internally engaged by one end of the inner shaft 10 and externally engages a bearing seat defined in the stem cover 23 (see Figure 5).

[0117] The propulsion unit 1 further includes a second support bearing 36, for supporting a portion of the outer shaft 11, enabling its rotation around the propulsion axis (propulsion direction 12).

[0118] The second support bearing 36 is positioned within the gearbox 9, along the propulsion direction 12, between the second driven gear 21 and the bow cover 24.

[0119] Specifically, the second support bearing 36 is internally engaged by a portion of the outer shaft 11 and externally engages a corresponding seat formed in the bow cover 24.

[0120] The propulsion unit 1 comprises a thrust bearing 37 interposed between the outer shaft 11 and the inner shaft 10.

[0121] The thrust bearing 37 is housed inside the gearbox 9.

[0122] It supports the outer shaft 11 relative to the inner shaft 10 and permits relative rotation between them.

[0123] Additionally, the thrust bearing 37 acts as a stop element designed to support axial loads between the outer shaft 11 and the inner shaft 10, i.e., loads that may develop along the propulsion direction 12.

[0124] According to a preferred embodiment, the thmst bearing 37 is a plain bearing, for example a bushing.

[0125] Specifically, in this embodiment, the thmst bearing 37 comprises a hollow stem 38 and an enlarged portion 39, wherein the enlarged portion 39 extends radially outward from the hollow stem 38.

[0126] More precisely, the enlarged portion 39 extends from one end of the hollow stem 38.

[0127] The hollow stem 38 is internally engaged by the inner shaft 10 and externally engages an end portion of the outer shaft 11.

[0128] The enlarged portion 39 is interposed along the propulsion direction 12 between the inner shaft 10 and the outer shaft 11.

[0129] In particular, the enlarged portion 39 abuts at the stern side against a shoulder formed along the inner shaft 10, and at the bow side against the end of the outer shaft 11.

[0130] The thmst bearing 37, thus configured, provides effective rotatable support of the outer shaft 11 relative to the inner shaft 10, even in the presence of axial thrusts that may develop between them due to stresses transmitted by the first propeller 13 and / or second propeller 14 during their rotation in water.

[0131] The propulsion unit 1 further includes an additional support bearing 40, interposed between the inner shaft 10 and the outer shaft 11, positioned diametrically opposite to the thrust bearing 37.

[0132] More specifically, the additional support bearing 40 is positioned along the propulsion direction 12, near the bow end of the outer shaft 11.

[0133] This additional support bearing 40 is configured to rotatably support the outer shaft 11 relative to the inner shaft 10.

[0134] By way of non-limiting example, the additional support bearing 40 is configured as a needle bearing.

[0135] The propulsion unit 1 includes a shell 41 designed to house the gearbox 9 within it, thereby forming a sealed enclosure.

[0136] In the attached Figure 1, the shell 41 is shown schematically with a dashed line to better illustrate the gearbox 9 contained within; it has been omitted in the remaining figures.

[0137] The shell 41 has a hydrodynamic shape, to reduce drag and enhance maneuverability of the propulsion unit 1.

[0138] According to one embodiment, the shell 41 comprises two portions that can be sealingly joined to form an enclosure around the gearbox 9.

[0139] As mentioned, the propulsion unit 1 includes a support 2 for connection to an aft portion of a boat.

[0140] Preferably, the support 2 comprises a mounting plate 42 to which at least one bracket is connected, configured to enable a pivoting connection between the hollow housing 5 and the support 2.

[0141] With reference to the embodiment shown in the attached Figures, the propulsion unit 1 includes a top bracket 43 and a bottom bracket 44, both connected to the mounting plate 42 in a spaced-apart arrangement.

[0142] The top bracket 43 and the bottom bracket 44 are aligned and parallel to one another.

[0143] The top bracket 43 is configured to function as a load-bearing support for the weight of the engine 3. The bottom bracket 44, instead, acts as a stabilizing element, countering torques generated by the first propeller 13 and second propeller 14 with respect to the support 2.

[0144] The top bracket 43 defines a first through opening 45, and likewise, the bottom bracket 44 defines a second through opening 46 (see, for example, Figure 6).

[0145] The first through opening 45 and the second through opening 46 are aligned along the rotation axis 6 and define respective passages for the hollow housing 5.

[0146] It is noted that the propulsion unit 1 includes respective bushings, positioned between the top bracket 43 and the hollow housing 5, as well as between the bottom bracket 44 and the hollow housing 5, to enable relative rotation of the hollow housing 5 with respect to the support 2 around the rotation axis 6, and to reduce stresses acting on the hollow housing 5 at its connection points to the support 2.

[0147] In particular, the propulsion unit 1 includes a top bushing 47, engaged in the first through opening 45 of the top bracket 43, and a bottom bushing 48, engaged in the second through opening 46 of the bottom bracket 44.

[0148] The propulsion unit 1 further includes an adjustment device, by which the relative position of the plate 4 with respect to the support 2 can be changed along the rotation axis 6, for example to raise the plate 4 relative to the support 2.

[0149] By raising the position of the plate 4 relative to the support 2, the position of the first propeller 13 and the second propeller 14 is likewise raised with respect to the support 2.

[0150] In accordance with the embodiment illustrated in the attached Figures, the top bushing 47 acts as an adjustment device.

[0151] To this end, the top bushing 47 includes a head portion 49 that protrudes outward from the top bushing 47 and defines a thickness interposed between the plate 4 and the top bracket 43.

[0152] In particular, the head portion 49 has a bottom surface configured to abut against the top bracket 43 and a top surface, opposite the bottom surface, configured to abut against the plate 4.

[0153] The thickness of the head portion 49 defines the separation distance between the plate 4 and the top bracket 43 and, therefore, the height at which the first propeller 13 and second propeller 14 are positioned relative to the support 2.

[0154] The term “height” here refers to the relative position of the first propeller 13, the second propeller 14 (as well as the motor 3 and the plate 4) with respect to the support 2 along the rotation axis 6.

[0155] Alternatively or in combination with the top bushing 47, it is possible to employ one or more additional bushings (not illustrated in the attached Figures) to be positioned between the top bushing 47 and the plate 4 in order to further raise the latter relative to the support 2.

[0156] The ability to adjust the height of the first propeller 13 and the second propeller 14 allows the thrust they exert to be optimized based on operating conditions, such as the presence or absence of wave motion.

[0157] According to an alternative embodiment of the propulsion unit 1, not shown in the attached Figures, the fixing plate 42 includes a single bracket for rotatable connection around the rotation axis 6 between the hollow housing 5 and the support 2.

[0158] In this embodiment, the bracket extends along the rotation axis 6 to a greater length than that of the top bracket 43 and the bottom bracket 44 shown in the attached Figures.

[0159] The single bracket must be able to securely support the hollow housing 5, the motor 3, the plate 4, and the components operatively connected thereto, and also ensure high resistance to bending and the moments generated by the forces from the first propeller 13 and the second propeller 14 during operation of the propulsion unit 1.

[0160] The hollow housing 5 externally features an engagement portion 50, which is cylindrical or substantially cylindrical in shape, and a maneuvering portion 51, located below the engagement portion 50, with an airfoil or similar profile.

[0161] The engagement portion 50, thus configured, can slide relative to the top bracket 43 and the bottom bracket 44 along the rotation axis 6 to raise or lower the hollow housing 5 with respect to the support 2.

[0162] The maneuvering portion 51 instead functions as a rudder to allow the vessel to which the propulsion unit 1 is connected to be steered.

[0163] According to an alternative embodiment not illustrated in the attached Figures, the adjustment device includes a system for varying the relative distance between the plate 4 and the top bracket 43, configured as an adjustable piston.

[0164] In a further alternative embodiment, not illustrated in the attached Figures, the adjustment device includes a motorized pinion operatively connected to at least one of the top bracket 43 or the bottom bracket 44, wherein the pinion engages with a rack secured to the plate 4 and extending along a direction parallel to the rotation axis 6.

[0165] The motorized pinion is operatively connected to an electric motor that can be selectively actuated to cause the pinion to rotate, thus enabling selective lifting or lowering of the rack and, accordingly, of the plate 4.

[0166] The propulsion unit 1 according to the invention is also configured to adjust the preload of the gears within the gear housing 9.

[0167] According to the embodiment shown in the attached Figures, the preload between the bevel gears housed in the gear housing 9 is adjusted based on the screwing of the stern cover 23 to the hollow central body 22.

[0168] To allow for adjustment of the screwing degree of the stem cover 23 to the hollow central body 22, the stem cover 23 includes a toothed peripheral portion 52 along which multiple seats are defined, each selectively engageable by a locking screw 53 which, in turn, is connectable to a respective threaded seat 54 formed in the hollow central body 22 (see Figures 2 and 3) .

[0169] The toothed peripheral portion 52 is formed near a section of the stem cover 23 that, in use, abuts or faces the hollow central body 22 when the stern cover 23 is connected thereto.

[0170] In practice, the locking screw 53 allows the cover 23 to be locked in position, preventing any relative rotation between it and the hollow central body 22.

[0171] To increase or decrease the preload between the driving gear 19, the first driven gear 20, and the second driven gear 21, it is sufficient to respectively screw in or unscrew the stem cover 23 with respect to the hollow central body 22.

[0172] The extent of the rotation used to screw or unscrew the stem cover 23 determines the variation in the preload force.

[0173] The hollow central body 22 also features an additional threaded seat 55, located at a bow portion of the hollow central body 22, opposite the stern portion where threaded seat 54 is located.

[0174] According to the embodiment shown in the attached Figures, and in particular Figure 3, the hollow central body 22 has a symmetrical configuration with respect to a vertical symmetry plane that passes through the rotation axis 6 and is parallel to one of the stern or bow ends, to which the stem cover 23 or the bow cover 24, respectively, is attached.

[0175] This symmetrical configuration allows the stern cover 23 to be used to adjust the bevel gear preload even if the threaded seat 54 becomes damaged, without requiring the replacement of the entire hollow central body 22. In such a case, it is sufficient to disassemble the hollow central body 22 and rotate it 180° around the rotation axis 6 so that the alternative threaded seat 55 can be used instead of threaded seat 54.

[0176] Based on the foregoing, it is clear that the propulsion unit 1 according to the invention is capable of achieving its intended purposes.

[0177] The propulsion unit 1, in fact, includes an electric motor 3 operatively connected to a first propeller 13 and a second propeller 14 that rotate in opposite directions.

[0178] The use of an electric motor 3 overcomes the drawbacks of traditional solutions using internal combustion engines, offering not only reduced environmental impact but also greater structural simplicity.

[0179] The motor 3 includes an interface for connection to electric power supply components, not shown in the attached Figures, which are installable onboard the vessel to which the propulsion unit 1 is connectable.

[0180] Furthermore, the use of a gear housing 9 containing various bearings, including a thrust bearing 37 positioned between the inner shaft 10 and the outer shaft 11, increases the efficiency and performance of such a traction-type outboard propulsion unit 1.

[0181] The presence of the thrust bearing 37 ensures optimal relative rotation between the inner shaft 10, operatively connected to the first propeller 13, and the outer shaft 11, operatively connected to the second propeller 14, even under thrust loads acting along the propulsion direction 12.

[0182] The use of such a thrust bearing 37 improves stability during the relative rotation of the inner shaft 10 and outer shaft 11, enabling high rotational speeds.

[0183] Additionally, the ability to vary the distance between the first propeller 13 and the second propeller 14 with respect to the support 2 along the rotation axis 6 allows the geometry of the propulsion unit 1 to be modified.

[0184] In particular, the first propeller 13 and second propeller 14 can be brought closer to the water surface depending on operating conditions, such as the presence or absence of wave motion.

[0185] In the latter condition, the first propeller 13 and second propeller 14 can be raised toward the free water surface to optimize the performance of the propulsion unit 1.

[0186] The above describes several embodiments and suggested variations of the present invention, but it should be understood that those skilled in the art may make modifications and changes without thereby departing from the scope of protection, as defined by the appended claims.

Claims

CLAIMS1. Outboard propulsion unit (1) for a boat, comprising: a mounting support (2) for connecting said propulsion unit (1) to a stem portion of a boat; a motor (3) removably connected to a plate (4), which in turn is removably connected to a hollow housing (5) at a top end thereof, wherein said hollow housing (5) is pivotally mounted to said support (2) so as to rotate around a vertical rotation axis (6), thereby causing said plate (4) and said motor (3) to rotate together; a drive shaft (7) extending inside said hollow housing (5) along said rotation axis (6) and operatively connected to said motor (3); a gearbox (9) connected to a bottom end of said hollow housing (5) and configured to transmit motion from said drive shaft (7) to a pair of coaxial shafts, wherein said pair of coaxial shafts comprises an inner shaft (10) and an outer shaft (11), rotatable in opposite directions to each other, both extending along a propulsion direction (12) transverse to said rotation axis (6); a first propeller (13) constrained to said inner shaft (10); a second propeller (14) constrained to said outer shaft (11), at said first propeller (13) along said propulsion direction (12); wherein said motor (3) is an electric motor.

2. Outboard propulsion unit (1) according to claim 1, wherein said first propeller (13) and said second propeller (14) are both oriented toward the bow relative to said outboard propulsion unit (1) and exert a pull-type thrust action.

3. Outboard propulsion unit (1) according to claim 1 or 2, wherein said gearbox (9) comprises a thrust bearing (37) interposed between said inner shaft (10) and said outer shaft (11), wherein said thrust bearing (37) allows relative rotation between said inner shaft (10) and said outer shaft (11) and defines a stop element to support thrust loads between said inner shaft (10) and said outer shaft (11) along said propulsion direction (12).

4. Outboard propulsion unit (1) according to claim 3, wherein said thrust bearing (37) comprises a hollow stem (38) and an enlarged portion (39) protruding outward from said hollow stem (38), wherein said enlarged portion (39) extends at one end of said hollow stem (38) and is interposed and retained along said propulsion direction (12) between an end of said outer shaft (11) and a shoulder of said inner shaft (10), wherein said end of said outershaft (11) and said shoulder of said inner shaft (10) are both housed within said gearbox (9)-5. Outboard propulsion unit (1) according to any of the preceding claims, wherein said gearbox (9) comprises a hollow central body (22), substantially cylindrical in shape, a stem cover (23), and a bow cover (24), each threadably connected to opposite sides of said hollow central body (22).

6. Outboard propulsion unit (1) according to claim 5, wherein said hollow central body (22) defines a flared through opening (28) at a top portion of said hollow central body (22), wherein a drive gear (19) is installed, connected to a bottom end of said drive shaft (7).

7. Outboard propulsion unit (1) according to any of the preceding claims, comprising a connecting element (29) for joining said gearbox (9) to a bottom end of said hollow housing (5), wherein said connecting element (29) has a top portion (30) configured to engage and connect to said bottom end of said hollow housing (5), and an attachment portion (31), opposite said top portion (30), configured for removable connection to said gearbox (9).

8. Outboard propulsion unit (1) according to any of the preceding claims, comprising a shell (41) for sealingly housing said gearbox (9), said shell (41) being hydrodynamically shaped to reduce drag in water.

9. Outboard propulsion unit (1) according to any of the preceding claims, wherein said support (2) comprises a mounting plate (42) to which a top bracket (43) is connected, said top bracket (43) being pivotally engaged by said hollow housing (5) to rotate around said rotation axis (6), wherein said top bracket (43) defines a first through opening (45).

10. Outboard propulsion unit (1) according to claim 9, comprising a top bushing (47) engaging said first through opening (45) and interposed between said top bracket (43) and said plate (4) of said motor (3) along said rotation axis (6), wherein said top bushing (47) comprises a head portion (49) protruding outward from said top bushing (47) and defining a separating thickness between said plate (4) and said top bracket (43).

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