BIANCHI, Massimiliano (C/O Max Prop S.r.L. 1, Milano, 20156, IT)
| CLAIMS 1. A variable pitch propeller of the type comprising at least one blade pivoted rotatably to a cylindrical propeller casing (3), a propeller hub assembly (10, 11) coupled to a propulsor and positioned coaxially inside said propeller casing (3), a kinematic mechanism for adjusting the rotary motion of said at least one blade about its axis of pivoting to said propeller casing (3) as a function of the relative motion of said propeller hub assembly (10, 11) with respect to said cylindrical propeller casing (3), means (12, 15, 30, 31, 8) for coupling in rotation said propeller hub assembly (10, 11) to said propeller casing (3), comprising at least one elastic element (8) interposed between said hub assembly (10, 11) and said propeller casing (3), said coupling means having at least one inoperative position in which motion is not transmitted from said hub assembly (10, 11) to said propeller casing (3), characterized in that in said inoperative position of said coupling means (12, 15, 30, 31, 8), between said hub assembly (10, 11) and said propeller casing (3) at least a first angular space (a) is present for counter-clockwise rotation of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa, and at least a second angular space (β) is present for clockwise rotation of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa. 2. The propeller according to claim 1, characterized in that said coupling means (12,. 15, 30, 31, 8) comprise at least one driving tooth (15) externally integral with said hub assembly (10, 11) and a relative abutment (12) projecting internally from said propeller casing (3). 3. The propeller according to claim 2, characterized in that said at least one elastic element (8) is interposed between said at least a first tooth (15) and said relative abutment (12), in at least said inoperative position of said coupling means. 4. The propeller according to claim 2 or 3, characterized in that it comprises at least a first stop (30) and at least a second stop (31) for said elastic element (8), integral respectively with said propeller casing (3) and with said hub assembly (10, 11). 5. The propeller according to claim 4, characterized in that said at least one first stop (30) arid said at least one first driving tooth (15) substantially define a single bearing surface for a first end of said at least one elastic element (8) when said coupling means are in said inoperative position. 6. The propeller according to claim 4 or 5, characterized in that said at least one second stop (31) and said abutment (12) substantially define a single bearing surface for a second end of said at least one elastic element (8) when said coupling means are in said inoperative position. 7. The propeller according to claim 4, 5 or 6, characterized in that said at least one first stop (30) and said at least one second stop (31) engage temporarily with the respective ends of said at least one elastic element (8) during clockwise rotation of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa, starting from said inoperative position, said at least one driving tooth (15) and said relative abutment (12) not being simultaneously engaged with the ends of said at least one elastic element (8). 8. The propeller according to any one of claims 4 to 7, characterized ih that said at least one driving tooth (15) and said relative abutment (12) are temporarily engaged with the ends of said at least one elastic element (8) during counterclockwise rotation of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa, starting from said inoperative position, said first stop (30) and said second stop (31) not being simultaneously engaged with the ends of said at least one elastic element (8). 9. The propeller according to any one of the preceding claims, characterized in that said at least one elastic element (8) is stressed in compression and/or extension with respect to its unstressed condition during rotation in clockwise direction or in counter-clockwise direction of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa. 10. The propeller according to any one of the preceding claims, wherein said at least one elastic element (8) is positioned within said first angular space (a) for counter-clockwise rotation of said hub assembly (10, 11) with respect to said propeller casing (3), or vice versa. 11. The propeller according to any one of the preceding claims, characterized in that said at least one elastic element (8) is a metal leaf spring of the flexing type. 12. The propeller according to any one of the preceding claims, characterized in that said first angular space (a) extends for an angle comprised between A and B and in that said second angular space (β) extends for an angle comprised between C and D, when said coupling means are in said inoperative position. 13. The propeller according to any one of the preceding claims, characterized in that said propeller hub assembly comprises at least one intermediate element (11) interposed between the propeller hub (10) and said cylindrical propeller body (3), said first and second angular rotation space (α, β) being defined between said intermediate element (11) and said cylindrical propeller casing (3). 14. The propeller according to claim 13, wherein said at least one intermediate element (11) is provided with a first (20) and with a second (21) contact surface with said propeller hub (1) mutually spaced apart by an angular space (ε) for rotation of said hub (10) with respect to said intermediate element (11). |
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FIELD OF THE INVENTION
The present invention relates to a propeller, preferably for marine use, of the variable pitch type, i.e. capable of automatically modifying the fluid dynamic pitch of the blades during operation to ensure high performance in different conditions of use. In more detail, the present invention relates to a nautical propeller with automatic pitch variation capable of efficiently absorbing accidental impacts to which the propeller may be subjected during use in forward drive and in reverse drive.
PRIOR ART
The market currently offers propellers in which the fluid dynamic pitch variation of the blades takes place automatically, by activating the propeller itself. Generally, these propellers comprise a cylindrical propeller casing, on which the propeller blades are pivoted according to a direction transverse to the axis of the propeller casing, or more generally perpendicular to the forward axis of the propeller, and a drive shaft, coupled coaxially to the propeller casing.
The propeller is also provided with means for transmitting rotary motion from the shaft to the propeller casing, and with a kinematic mechanism for regulating the rotary motion of each blade about its axis of pivoting to the propeller casing, preferably adapted to transform the rotary motion of the drive shaft into a rotary motion of each blade about its own pivot axis.
In order to allow operation of the aforesaid kinematic mechanism to transform rotation of the drive shaft into rotation of the blades, the motion transmission means allow the shaft to rotate idly with respect to the propeller casing at least for a predefined angular range. Idle rotation of the drive shaft in this angular range, with respect to the propeller casing, causes, due to the aforesaid kinematic mechanism for regulation/transformation, relative rotation of the blades with respect to the propeller casing, with consequent variation in their angle of incidence with respect to the fluid and therefore of the fluid dynamic pitch.
A propeller of this type is described in the document WO 2008/075187, by Max Prop S.r.l., in which relative rotation of the drive shaft with respect to the propeller casing is regulated by an elastic element interposed therebetween, which allows continuous pitch adjustment during operation in forward drive.
In particular, the elastic element allows the blades to be positioned to the optimal pitch during operation, balancing the forces acting on the propeller, mainly the drive torque generated by the propulsor and the drag torque, until reaching a balanced position. Moreover, the elastic element interposed between the drive shaft and the cylindrical casing of the propeller allows absorption of impacts to which the blades, or more in general the propeller, may be subjected during navigation in forward drive. In fact, as previously stated, the elastic element regulates rotation of the drive shaft with respect to the cylindrical casing of the propeller, and vice versa, in a given angular range and acts as a shock absorber in the event of accidental impacts that may occur during navigation in forward drive.
However, the propeller may also be subjected to accidental impacts during reverse drive, for example while performing manoeuvres.
In this regard, some prior art propellers are also capable of providing protection against impacts during navigation in reverse drive by means of a specific device, separate from the device that allows variation of the fluid dynamic pitch of the blades, by means of a further elastic element.
This type of propeller is generally provided with two elastic elements. The first elastic element allows automatic pitch variation during forward drive, in relation to the torque that opposes rotation of the propeller, by means of the angular displacement, controlled by the elastic element, of the propeller casing with respect to the hub which determines rotation of each blade about its axis, as described above with reference to the document WO 2008/075187 by Max Prop S.r .
The second elastic element is instead interposed between the propeller hub and the drive shaft and provides protection against impacts during forward drive and during reverse drive, allowing partial idle rotation of the hub about the drive shaft by means of elastic deformation of the elastic element interposed therebetween.
Therefore, propellers currently available allow automatic pitch variation to be obtained during use in forward drive and absorption of accidental impacts both in forward motion in forward drive and in that in reverse drive, through the use of distinct devices, and in particular distinct elastic elements, each of which is destined to perform a specific function.
These propellers suffer from some drawbacks; in fact, being provided with distinct devices, each comprising a different elastic element destined to perform a specific function, their dimensions are not very compact and they are also very complex and costly to produce.
An object of the present invention is to provide a variable pitch propeller with automatic pitch adjustment during forward drive which can also be used for navigation in reverse drive.
Another object of the present invention is to provide a propeller that does not have the limitations and drawbacks of prior art described above and which allows automatic pitch adjustment during use in forward drive and, at the same time, allows absorption of accidental impacts to which the propeller, or its blades, may be subjected during motion in both directions of drive, both forward and reverse.
SUMMARY OF THE INVENTION
These and other objects are achieved by the variable pitch propeller according to the first independent claim and the subsequent dependent claims.
The variable pitch propeller, according to the present invention, comprises at least one blade pivoted rotatably to a cylindrical casing of the propeller, a propeller hub assembly coupled to a propulsor and positioned coaxially inside the propeller casing, a kinematic mechanism for adjusting the rotary motion of said at least one blade about its axis of pivoting to the propeller casing as a function of the relative motion of the propeller hub assembly with respect to its cylindrical casing, and means for coupling in rotation the propeller hub assembly to the propeller casing, comprising at least one elastic element interposed between the hub assembly and the propeller casing.
These coupling means have at least one inoperative position, i.e. a position in which motion is not transmitted from the hub assembly to the propeller casing, in which, between the hub assembly and the propeller casing, at least a first angular space is present for counter-clockwise rotation of said hub assembly with respect to the propeller casing, or vice versa, and at least a second angular space is present for clockwise rotation of the hub assembly with respect to the propeller casing, or vice versa.
The presence of a first and of a second angular space for rotation of the hub assembly with respect to the cylindrical propeller casing, or vice versa, respectively according to a counter-clockwise and clockwise direction of rotation, by means of a single elastic element, allows simultaneous adjustment of the fluid dynamic pitch of the blades in forward drive and absorption of any accidental impacts both during navigation in forward drive and navigation in reverse drive.
The coupling means also comprise at least a first driving tooth, which is externally integral with the hub assembly and a relative abutment which projects internally from the propeller casing. According to a preferred embodiment, the propeller is provided with a single driving tooth externally integral with the hub assembly and with a relative abutment projecting internally from the cylindrical propeller casing. The elastic element is preferably housed in the angular space for counter-clockwise rotation of the hub assembly with respect to the cylindrical propeller casing between the driving tooth and the relative abutment, in a manner such as to adjust the relative rotation between the hub assembly and the cylindrical casing when the propulsor imparts rotation according to both directions of rotation, clockwise and counterclockwise.
In fact, when the propulsor is activated in counter-clockwise direction, which is preferably used for navigation in forward drive, the hub assembly rotates with respect to the cylindrical propeller casing, overcoming the resistance offered by the elastic element, which is compressed between the driving tooth and the relative abutment.
This relative rotation of the hub assembly with respect to the cylindrical propeller casing causes rotation of the blades with respect to the cylindrical propeller casing towards an angle of incidence, and therefore an optimal fluid dynamic pitch for a given operating condition.
In fact, the elastic element allows balancing of the forces acting on the propeller, and in particular the drive torque generated by the propulsor and the drag torque caused by friction and by resistance of the fluid. Advantageously, the same elastic element also allows absorption of any impacts to which the propeller may be subjected during operation, providing a shock absorption transient within the first angular space for rotation of the hub assembly with respect to the propeller casing, or vice versa.
When the drive shaft is driven in rotation by the propulsor in clockwise rotation direction, preferably used for navigation in reverse drive, the presence of the second angular space for clockwise rotation of the hub assembly with respect to the propeller casing, or vice versa, also allows absorption of impacts during navigation in reverse drive through the same elastic element, which is subjected to an action of traction or of compression. Moreover, it must be noted that the presence of the second angular space for clockwise rotation of the hub assembly with respect to the propeller casing, or vice versa, and of the elastic element interposed therebetween, could also allow continuous variation of the fluid dynamic pitch of the blades to be obtained during reverse drive.
According to a possible embodiment of the propeller according to the present invention, the ends of the elastic element, for example a torsion (or flexing) spring, are constrained respectively to the hub assembly and to the cylindrical propeller casing, and therefore during reverse drive the spring is subjected to an action of traction (extension) due to counter-clockwise rotation of the hub assembly with respect to the cylindrical propeller casing, or vice versa.
According to a preferred embodiment, the propeller according to the present invention allows absorption of the impacts during navigation in reverse drive through compression of the elastic element, preferably a torsion (or flexing) spring, interposed in a position resting between the hub and the cylindrical propeller casing. In fact, according to a preferred embodiment, the means for coupling in rotation of the propeller also comprise a first stop and at least a second stop for the elastic element, which are integral respectively with the propeller casing and with the hub assembly. Preferably, the propeller is provided with a first and with a second stop. In the inoperative position of the propeller the first stop and the driving tooth substantially define a single bearing surface for the first end of the elastic element, while the second stop and the abutment substantially define a single bearing surface for the second end of the elastic element. Possible impacts to which the blade or blades of the propeller, or the propeller itself, may be subjected during navigation in reverse drive are absorbed through the elastic element which provides a shock absorption transient during relative rotation of the hub assembly with respect to the cylindrical propeller casing in counter-clockwise direction. In particular, this shock absorption transient is obtained by means of compression of the elastic element between the second and the first stop, during clockwise angular displacement of the driving tooth from the inoperative position until reaching the position in contact with the abutment projecting from the cylindrical propeller casing which acts as limit stop.
In fact, during clockwise rotation of the hub assembly with respect to the propeller casing, or vice versa, the first and the second stop engage temporarily with the respective ends of the elastic element, while the driving tooth and the relative abutment are not simultaneously engaged with the ends of the elastic element.
According to this embodiment, when the propeller is used for navigation in forward drive and the hub assembly rotates counter-clockwise with respect to the propeller casing, or vice versa, the driving tooth and relative abutment engage temporarily with the ends of the elastic element causing compression thereof, while the first and the second stop are not simultaneously engaged with the ends of the elastic element. In this manner, it is possible through the same elastic element, and without the need for further devices that would make the propeller too complex, heavy and costly, to absorb any impacts both during motion in forward drive and in reverse drive, besides allowing automatic adjustment of the fluid dynamic pitch during forward drive to ensure optimal performance in all conditions of use.
BRIEF DESCRIPTION OF THE DRAWINGS.
Further characteristics and advantages of the present invention will be more apparent from the following description, provided by way of example with reference to the accompanying drawings, wherein:
• Fig. 1 is a sectional view according to a plane perpendicular to the hub assembly, of a possible embodiment of the propeller according to the present invention in inoperative position;
• Fig. 2 is a sectional view according to a plane perpendicular to the hub assembly, of a further possible embodiment of the propeller according to the present invention in inoperative position;
• Figs 3 A - 3D show four possible embodiments of the elastic element usable with the propeller according to the embodiment of Fig. 1.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION
Figs. 1 and 2 show sectional views of two possible embodiments of the variable pitch propeller according to the present invention, preferably for marine use, capable of absorbing accidental impacts to which it can be subjected during use both in forward drive and in reverse drive.
The propeller according to present invention comprises a hollow cylindrical casing 3 and a hub assembly 10, 11 of the propeller coupled to a propulsor, not shown in the figures.
The propulsor is constrained according to know methods to the hub assembly 10, 11, or this latter can consist of an end of the drive shaft, not shown in the accompanying figures.
The hub assembly 10, 11 of the propeller is coupled coaxially to the cylindrical casing 3 in a manner such as to allow, as will be better described hereinafter, the transmission of rotary motion from the drive shaft to the cylindrical casing.
The propeller blades, again not shown in the figures, are pivoted to the cylindrical propeller casing in a manner such as to rotate about their axis of pivoting; in other words, the blades can rotate along an axis orthogonal with respect to the axis defined by the hub assembly 10, 11 of the propeller, which coincides with the drive direction of the propeller during forward and reverse motion.
The propeller according to the present invention also comprises a kinematic mechanism for adjusting the rotary motion of each of the blades about its axis of pivoting to the propeller casing as a function of the relative motion of the hub assembly with respect to the cylindrical propeller casing.
In more detail, the kinematic mechanism determines rotation of the blades about their pivot axis, thereby varying the angle of incidence with respect to the fluid (and therefore the fluid dynamic pitch) when the drive shaft, and therefore the hub assembly 10, 11, rotates in relation to the cylindrical propeller casing 3 by a non-null rotation angle, or vice versa.
The kinematic mechanism for adjusting the rotary motion, not represented in the accompanying figures, is, for example, of the type comprising a truncated-cone shaped gear pinion, integral with the root of each blade, i.e. at the end of the blade housed inside the propeller casing.
The hub assembly of the propeller is provided with a gear wheel integral with a central truncated-cone shaped pinion, which permanently meshes the pinions of the respective blades, so that rotation of the central pinion with respect to the cylindrical propeller casing causes corresponding rotation of the blades about the respective axes of pivoting to the propeller casing, or vice versa.
This rotation of each blade about its axis causes variation of the relative angle of incidence and therefore of the fluid dynamic pitch of the propeller.
Consequently, relative rotation of the hub assembly 10,11 with respect to the cylindrical propeller casing 3 causes rotation of the blades, according to an angle that is naturally a function of the relative angle of rotation between the hub assembly and the cylindrical propeller casing.
The kinematic mechanism described above can naturally be replaced with equivalent means that, by means of relative rotation between the drive shaft, and therefore the hub assembly 10, 11, and the cylindrical propeller casing 3, allow variation of the fluid dynamic pitch, transforming the rotation motion imparted by the propulsor in rotation of the blades about their axis of pivoting, and vice versa.
As can be seen in the accompanying figures, the propeller according to the present invention comprises means 12, 15, 30, 31 and 8 for coupling in rotation the hub assembly 10, 11 to the cylindrical propeller casing 3 when the propulsor operates in rotation the hub assembly in both directions of rotation, clockwise and counterclockwise. The means 12, 15, 30, 31 and 8 for coupling in rotation the hub assembly 10, 11 to the cylindrical propeller casing 3 comprise an elastic element 8 that is interposed between the cylindrical propeller casing 3 and the hub assembly 10, 11. As will be better described hereinafter, the elastic element 8 allows automatic adjustment of the fluid dynamic pitch during use of the propeller in forward drive as it allows adaptation of the relative rotation between the hub assembly 10, 11 and the cylindrical casing 3 in the different conditions of use, balancing the forces acting on the propeller, and in particular the drive torque delivered by the propulsor and the drag torque caused by the fluid dynamic forces that act on the propeller blades. Moreover, the elastic element 8 allows absorption of the impacts to which the propeller may be subjected during use in both directions of drive, forward and reverse. In Figs. 1 and 2, the means 12, 15, 30, 31 and 8 for coupling in rotation the propeller according to the present invention are represented in inoperative position, which correspond to the position in which no motion is transmitted by the hub assembly 10, 11 to the cylindrical propeller casing 3, or vice versa.
In the inoperative position of the means 12, 15, 30, 31 and 8 for coupling in rotation of the hub assembly 10, 11 to the cylindrical propeller casing 3, a first angular space a is present for counter-clockwise rotation of the hub assembly with respect to the cylindrical propeller casing, or vice versa, and a second angular space β is present for clockwise rotation of the hub assembly with respect to the cylindrical propeller casing, or vice versa.
Preferably, counter-clockwise rotation of the drive shaft is used for navigation in forward drive, while clockwise rotation is used for navigation in reverse drive. However, the system operates equally by producing the profiles in a mirror image manner with respect to the embodiments shown in the figures. In this case, clockwise rotation of the drive shaft would be used for navigation in forward drive, while counter-clockwise rotation would be used for navigation in reverse drive.
The presence of a first and of a second angular space a and β for rotation of the hub assembly 10, 11 with respect to the cylindrical propeller casing 3, or vice versa, respectively according to counter-clockwise and clockwise direction of rotation, through a single elastic element 8 allows simultaneous adjustment of the fluid dynamic pitch of the blades in forward drive and absorption of any accidental impacts both during navigation in forward drive and navigation in reverse drive. As shown in Figs. 1 and 2, the means 12, 15, 30, 31 and 8 for coupling of the propeller according to the present invention comprise a first driving tooth, or portion, 15 which is externally integral with the hub assembly 10, 11 and a relative abutment 12 which projects internally from the propeller casing 3.
In the inoperative position of the propeller, shown in Figs. 1 and 2, the elastic element 8 is interposed between the driving tooth 15 and the relative abutment 12 in a manner such as to regulate the relative rotation between the hub assembly and the cylindrical casing, or vice versa, when the propulsor imparts rotation according to both directions of rotation, clockwise and counter-clockwise.
According to a preferred embodiment, the elastic element 8 is interposed in the angular space a for counter-clockwise rotation of the hub assembly 10, 11 with respect to the cylindrical casing 3, between the driving tooth 15 and the relative abutment 12.
In this manner, when the propulsor is activated in counter-clockwise direction, which as stated is preferably used for navigation in forward drive, the hub assembly 10, 1 1 rotates with respect to the cylindrical propeller casing 3, overcoming the resistance offered by the elastic element 8, which is subjected to a action of compression between the driving tooth 15 and the relative abutment 12.
In other words, during navigation in forward drive the elastic element 8 opposes rotation in counter-clockwise direction of the hub assembly 10, 11 with respect to the cylindrical propeller casing 3, and vice versa.
This relative rotation of the hub assembly 10, 1 1 with respect to the cylindrical propeller casing 3, adjusted by the elastic element 8, causes rotation of the blades with respect to the cylindrical propeller casing towards an angle of incidence, and therefore an optimal fluid dynamic pitch for a given operating condition. The elastic element 8, opposing the relative rotation of the hub assembly 10, 11 with respect to the cylindrical propeller casing 3 makes the relative angular displacement of the hub assembly 10, 1 1 with respect to the cylindrical propeller casing 3 variable as a function of the forces acting on the elastic element 8, and therefore as a function of the drive torque of the propulsor and of the drag torque which, through the blades, is transmitted to the cylindrical propeller casing 3.
The elastic element 8 allows balancing of the forces acting on the propeller, and in particular the drive torque generated by the propulsor and the drag torque caused by friction and by the resistance of the fluid. In other words, the propeller according to the present invention allows automatic and continuous variation of the fluid dynamic pitch of the blades when the propulsor drives in rotation the hub assembly in counterclockwise direction, preferably used for forward motion of the boat, ensuring a high performance during use.
It must be noted that the same elastic element 8 also allows absorption of any impacts to which the propeller, or its blades, may be subjected during operation in forward drive, adjusting the relative rotation of the hub assembly and of the cylindrical propeller casing in the first angular space a.
As stated above, the presence of a second angular space β for clockwise rotation of the hub assembly 10, 11 with respect to the propeller casing 3, or vice versa, allows absorption of impacts through the elastic element 8 also during reverse drive motion. According to the present invention, absorption of impacts during reverse drive motion can take place by subjecting the elastic element 8 to an action of traction or of compression. In the embodiment shown in Fig. 2, absorption of impacts in reverse drive is obtained by subjecting to traction the elastic element 8, which can for example consist of a metal torsion (or flexing) leaf spring.
In more detail, the ends of the spring 8 are constrained according to known means respectively to the driving tooth 15 and to the relative abutment 12 at the surfaces identified with the references A and B. In this manner, when the hub assembly rotates in clockwise direction, and the driving tooth 15 moves from the inoperative position in the angular space β (comprised between the references C and D) toward the abutment 12, the spring is subjected to an action of traction, or extension, which allows any impacts to be absorbed. In other words, the second angular space β, which extends for an angle comprised between the references C and D, forms a shock absorbing transient during rotation in counter-clockwise direction of the hub assembly 10, 11 with respect to the cylindrical propeller casing 3, or vice versa. As described above, when the propeller is used for navigation in forward drive, the spring 8 is subjected to compression between the driving tooth 15 and the relative abutment 12, following rotation in counter-clockwise direction of the hub assembly 11 with respect to the cylindrical propeller casing, or vice versa, allowing automatic adjustment of the pitch of the blades and absorption of impacts. Fig. 1 shows a preferred embodiment of the propeller according to the present invention, in which the elastic element 8 is subjected to an action of compression both when the propulsor is operated in a counter-clockwise direction, preferably used for navigation in forward drive, and when the propulsor is operated in clockwise direction, preferably used for navigation in reverse drive.
According to this embodiment, the elastic element preferably consists of a torsion (or flexing) spring whose ends are not constrained to the hub assembly or to the cylindrical propeller casing, but which is interposed resting therebetween.
In fact, as can be seen in Fig. 1, the spring is inserted in the angular space a comprised between the references A and B and is interposed between the hub assembly 10, 1 1 and the cylindrical propeller casing 3 with the ends thereof resting on the surfaces identified by the references A and B.
In detail, the means for coupling in rotation the hub assembly 10, 1 1 to the propeller casing 3 besides being provided with a driving tooth 15 and with the relative abutment 12 described previously, also comprise a first stop 30 and a second stop 31 for the spring, which are integral respectively with the propeller casing 3 and with the hub assembly 10, 11.
As shown in Fig. 1, in the inoperative position of the propeller, the first stop 30 and the driving tooth 15 substantially define a single bearing surface, identified by the reference A, for the first end of the spring 8, while the second stop 31 and the abutment 12 substantially define a single bearing surface, identified by the reference B, for the second end of the spring.
In the inoperative position of the propeller shown in Fig. 1 , the ends of the spring are in the position engaged with the bearing surfaces, respectively consisting, as stated, of the driving tooth 15 and of the first stop 30, and of the abutment 12 together with the second stop 31.
In fact, as can be seen in the sectional view of Fig. 1, when the propeller is in inoperative condition, the driving tooth 15 and the first stop 30 are in a mutually opposed position in the space between the hub assembly 10, 1 1 and the cylindrical propeller casing 3. This space, in the sectional view according to a plane perpendicular to the hub assembly of Fig. 1, is represented by a circular crown. Likewise, the abutment 12 and the second stop 31 are in a mutually opposed position between the hub assembly 10, 1 1 and the cylindrical propeller casing 3.
As shown in the sectional view of Fig. 1, the driving tooth 15 is produced in a manner such that it projects from the hub assembly for almost two thirds of the space between the hub assembly and the cylindrical propeller casing. In other words, in the sectional view of Fig. 1, the driving tooth 15 substantially occupies two thirds of the gear wheel between the hub assembly 10, 1 1 and the cylindrical propeller casing 3. On the contrary, the first stop 30 projects from the cylindrical propeller casing in an opposed position with respect to the driving tooth 15, in a manner such as to occupy substantially one third of the space between the hub assembly 10, 11 and the cylindrical propeller casing 3. Naturally, the driving tooth 15 and the first stop 30 are not in mutual contact to avoid problems of friction that would have negative effects on correct operation of the propeller and in particular on the relative rotation between the hub assembly and the cylindrical casing.
As shown in Fig. 1, this particular configuration, and the ratio between the dimensions illustrated above for the driving tooth 15 and the first stop 30, is also valid for the abutment 12 and the second stop 31.
Any impacts to which the blade or blades of the propeller, or the propeller itself, may be subjected during navigation in reverse drive are absorbed through the spring 8, which provides a shock absorbing transient during rotation in clockwise direction of the hub assembly with respect to the cylindrical propeller casing, and vice versa, in the angular space β comprised between the references C and D.
In particular, this shock absorbing transient is obtained through compression of the spring 8 between the second 31 and the first 30 stop, during clockwise angular movement of the driving tooth 15 from the inoperative position until reaching the position of contact with the projecting abutment 12 of the cylindrical propeller casing 3 which acts as limit stop.
In fact, during rotation in clockwise direction of the hub assembly 10, 1 1 with respect to the cylindrical propeller casing 3, or vice versa, the first 30 and the second 31 stop are in the position temporarily engaged with the respective ends of the spring 8, while the driving tooth 15 and the relative abutment 12 are not simultaneously engaged with the ends of the spring.
Displacement in clockwise direction of the driving tooth 15 in the angular space β (comprised between the references C and D) causes compression of the spring 8 between the first 30 and the second 31 stop, providing a shock absorbing transient during navigation in reverse drive.
It must be noted that the term position temporarily engaged was used to indicate that starting from the inoperative position of the propeller, following a rotation in clockwise direction of the hub assembly with respect to the cylindrical casing, or vice versa, the ends of the spring are resting against the first and second stop until the propeller is returned to the inoperative position, or the direction of rotation is inverted. Instead, when the hub assembly rotates in counter-clockwise direction with respect to the propeller casing, or vice versa, the ends of the spring are in the position engaged with the driving tooth 15 and the relative abutment 12 until the propeller is returned to the inoperative position, or the direction of rotation is inverted.
In fact, according to the embodiment of the propeller according to the present invention described above, when the propeller is used for navigation in forward drive and the hub assembly 10, 11 rotates in counter-clockwise direction with respect to the cylindrical propeller casing 3, or vice versa, the driving tooth 15 and the relative abutment 12 are in the position temporarily engaged with the ends of the spring causing compression thereof, while the first and the second stop are not simultaneously engaged with the ends of the elastic element. In this manner it is possible, through the elastic element and without the need for further devices that would make the propeller too complex, heavy and costly, to absorb any impacts both during forward drive and reverse drive, as well as allowing automatic adjustment of the fluid dynamic pitch during forward drive in order to ensure optimal performance in all conditions of use.
Figs. 3A - 3D show some possible embodiments of elastic elements that can be used in the embodiment of the propeller described above with reference to Fig. 1, in which the spring is subjected to an action of compression both during absorption of impacts and during adjustment of the fluid dynamic pitch of the blades in forward drive and during absorption of impacts in reverse drive. In particular, Figs. 3A and 3B show two possible embodiments of a leaf spring provided with a plurality of notches and appropriately bent to form an elastic bushing.
In Fig. 3A the notches with which the elastic element is provided extend longitudinally, i.e. along a direction parallel to the propeller axis, while in Fig. 3B the notches extend radially along directions that converge towards the centre of the propeller.
Figs. 3C and 3D show two particular embodiments of the notches of the elastic elements. In Fig. 3C the notches have a continuous profile that can be obtained through known machining processes, such as electric discharge machining, laser jet cutting, water jet cutting, etc.. Instead, the elastic element shown in Fig. 3D has notches provided with a stepped, and non-continuous profile, obtained by machining with machine tools using, for example, milling cutters with decreasing depths.
With reference to Figs. 1 and 2, it must be noted that the hub assembly of the propeller according to the present invention can consist of an intermediate element 11 interposed between the hub 10 and the cylindrical casing 3 of the propeller. In more detail, the intermediate element 11 is interposed in the circumferential space between the hub 10 and the cylindrical casing 3 of the propeller, and partially occupies this circumferential space.
In this case, the first and the second angular space a and β are defined between the intermediate element 11 and the cylindrical propeller casing 3. Moreover, the driving tooth 15 and the second stop 31 are produced projecting on the intermediate element 1 1.
Moreover, as can be seen in Figs. 1 and 2, the intermediate element is provided with a first 20 and with a second 21 contact surface with the hub 10 (or directly with the drive shaft), mutually spaced apart by an angular space for relative rotation of the hub 10 with respect to the intermediate element 1 1, indicated in the figures with the reference ε.
The first surface 20 is destined for contact with the hub when the propulsor imparts rotation in counter-clockwise direction, generally used for navigation in forward drive. On the contrary, when the direction of rotation of the propulsor is reversed, according to the clockwise direction, generally used for navigation in reverse drive, the hub 10 reaches the position of contact with the second surface 21 of the intermediate element 11.
Relative rotation equal to the angle ε of the hub 10 with respect to the intermediate element 11, i.e. the angle of rotation of the hub 10 necessary to reach the position of contact with the second surface 21 of the intermediate element 11, allows the fluid dynamic pitch of the blades to be varied, taking them to a value suitable for navigation in reverse drive. Therefore, the propeller according to the present invention allows automatic variation of the pitch of the blades when the hub rotates in counter-clockwise direction, while when the hub rotates in clockwise direction the blades reach a predetermined fluid dynamic pitch, suitable for navigation in reverse drive.