DEVICE FOR PREVENTING A SHAFT ROTATION

FIELD OF THE INVENTION

The present invention relates to a device for preventing or stopping rotation of a shaft coupled to a motor, i.e. of a shaft that transfers a torque between two or more members connected thereto, when the motor is not operating and/or substantially is not transmitting torques to the shaft.

In other words, the device according to the present invention is suitable to exert mechanical braking actions, i.e. resisting forces and/or torques, capable of preventing or stopping the rotational motion of the shaft on which the device acts when the motor is not operating.

In particular, the device according to the present invention can be fitted to the motor of a watercraft, in such a manner as to prevent and/or stop rotation of a transmission shaft to which a motor and a propeller are coupled.

PRIOR ART

When the motor is switched off and no longer transmits torque to the propeller through the shaft to which the two members are coupled, the propeller is free to move due to the inertia and due to the flow of fluid that strikes it, thus continuing its rotational motion. This effect is particularly felt in sailing boats equipped with a motor for auxiliary propulsion activated during manoeuvres or in the case of need, coupled to a propeller through a transmission of hydraulic type.

In fact, when the motor is switched off and the watercraft proceeds using sailing (wind) propulsion, the motor does not transmit any torque to the propeller, which therefore continues its rotational motion due to inertia and to the flow of the current that strikes it during forward motion of the watercraft. In the case in which the transmission of motion from the motor to the propeller is of hydraulic type, or in the case in which an endothermic motor activates at least one pump of a hydraulic circuit responsible for rotation of the motor shaft of the propeller, when the motor is stopped and is no longer operating, this hydraulic transmission is not able to develop resisting actions capable of preventing, or at least of reducing, rotation of the shaft, which is therefore substantially free to rotate.

It must also be noted that propellers of the variable pitch type are currently used, with the possibility of automatically arranging the blades in a “feathered” position when there is no driving torque, i.e. in the position in which the blades offer the least fluid dynamic resistance possible when the motor is not operating. This position, which is obtained through controlled rotation of the blades about their axis, can only be reached if the motor shaft not moving and therefore if the rotational motion of the propeller is stopped.

The fact that the propeller continues its rotational motion even after the motor has been switched off, due to inertia and to the flow of fluid that strikes it, prevents the blades from reaching the feathered position which, as stated, requires the propeller to be stopped.

For this reason, the propeller continues its rotational motion causing problems of noise, resistance to motion and consequent mechanical wear during sailing, until the watercraft stops moving or the motor is switched on again.

In particular, the fact that the propeller continues to turn in an undesirable manner, besides causing increased resistance to the forward motion of the watercraft, can also cause damage to the propeller itself, to the transmission, and to the motor, given that this undesirable rotation increases the number of working hours that must be taken into account correctly for maintenance operations and for changing parts subject to wear.

To deal with this problem, and to stop motion of the shaft, and therefore allow the blades of the propeller to reach the “feathered” position, it is necessary to try to stop the rotational motion of the shaft, for example by acting directly thereon through clamps, or similar tools available on board.

Naturally, these operations are very difficult to carry out, and in fact often the shaft is not easily accessible, for example due to the limited spaces in which it is installed, and are also very dangerous for the safety of the person who attempts to stop the rotational motion of the shaft.

Other solutions have been proposed for preventing shaft rotation through devices capable of blocking its rotation when the motor to which it is coupled is not operating.

For example, the document U.S. Pat. No. 4,464,127 describes a device to immobilize a transmission shaft comprising two portions that are activated hydraulically to come into contact with the outer surface of the shaft causing locking thereof by friction contact. More in detail, the two portions are actuated by means of hydraulic cylinders connected to a power supply circuit that causes movement of the two portions in a position of contact with the shaft. In this manner, the friction generated between the two portions, and in particular by the friction means with which these portions are equipped, with the outer surface of the shaft, causes locking of this latter because of friction generated by contact between the surfaces.

The device described above has some disadvantages mainly due to the presence of the hydraulic actuation. In fact, the device for immobilizing a motion transmission shaft described above requires to be connected to a suitable hydraulic distribution circuit, which causes a certain difficulty for installation and above all costly maintenance, also due to the noteworthy dimensions of this device.

Moreover, as a system of hydraulic type is present, the device is not very reliable. Given that locking of the shaft is closely related to the pressure of the fluid that drives the hydraulic cylinders, any loss of load of the fluid inside this circuit, for example in the case of breakage or malfunction, means that it is not possible to reach the pressure required to generate sufficient friction to cause locking of the shaft.

The object of the present invention is to overcome the problems of the prior art and to provide a device for preventing rotation of a motion transmission shaft, and consequently to cause stopping thereof, when the motor constrained thereto is not operating, which is simple to produce and which can be easily installed on and removed from the shaft, for example when wishing to carry out maintenance operations.

Moreover, a further object of the present invention is to provide a device for preventing rotation of a motor shaft of small dimensions, in such a manner that it can be easily installed on and adapted to different watercraft, and in particular to sailing craft, and which simultaneously offers high reliability in the locking of the shaft.

Furthermore, an object of the present invention is to provide a device for preventing rotation when the motor is not operating, which can be used in sailing boats equipped with hydraulic transmission between motor and propeller, which allows locking of the shaft and therefore stops undesirable shaft rotation in order to reach the “feathered” position of the blades.

Not least, an object of the present invention is to provide a device for preventing shaft rotation of “automatic” type, i.e. which does not require external controls and/or actuation by a user.

SUMMARY OF THE INVENTION

These and other objects are achieved by means of a device for preventing and/or stopping the rotation of a motion transmission shaft connected kinematically to at least one motor according to claim 1, of the type comprising at least a first element fixed with respect to the motion transmission shaft, and at least a moving element, and means to constrain said at least one moving element to the transmission shaft jointly in such a manner as to rotate integrally with the shaft and in such a manner as to move between a position of friction contact with said at least one fixed element, to allow stopping of the shaft, and a position of disengagement from said fixed element, to allow release of the shaft. Advantageously, the device provides that said means to constrain said at least one moving element to the shaft comprise at least one link for movement of said at least one moving element along a direction having at least a radial component with respect to the shaft.

According to a possible embodiment of the present invention, the moving elements are free to move between the position of friction contact with the fixed element, to stop the shaft, toward the position of disengagement therefrom in which the shaft is free to rotate, and vice versa.

In this manner, when a predefined threshold angular velocity of the shaft is exceeded, this causes movement of the moving elements to the position of disengagement from the fixed element, while when the rotation speed decreases, the moving elements return, under the effect of their weight, to the position of friction contact with the fixed element.

The friction contact between the moving element and the fixed element preferably takes place by means of the contact of inclined surfaces produced in a mating (correspondent) manner on the moving element and on the fixed element.

Moreover, according to a possible embodiment, the means to constrain said at least one moving element to the shaft also comprise at least one contrast member to counter in a controlled manner the movement of said at least one moving element, at least along this direction having at least a radial component, toward the aforesaid position of disengagement from said at least one fixed element.

This solution, as will be apparent to those skilled in the art, allows the moving element of the device to be caused to move with respect to the transmission shaft along this radial direction by the centrifugal force acting on the same moving element—when the shaft is made to rotate—even if this motion is countered in a controlled manner, i.e. only for certain rotation values of the motor shaft, by the contrast member, which can preferably be constituted by one or more springs.

In this manner, the moving element can reach the aforesaid position of disengagement from the corresponding fixed element, starting from its position of friction contact with this latter, only when it is able to overcome the resistance to radial translation thereof exerted by the contrast member (for example a spring), i.e. only when the motor shaft has reached an angular velocity at which the centrifugal force, to which the moving element is subjected, exceeds the aforesaid countering radial force exerted by the spring.

In practice, as shall be apparent also from the description below, the constraining means described above and claimed allow temporary movement of said at least one moving element in the position of disengagement from the fixed element, only when a predefined angular velocity of the motion transmission shaft is exceeded.

It is clear that the device according to the present invention acts automatically without the need to control movement of the moving element from the position of friction contact with the fixed element in order to stop the shaft, to the position of disengagement from this fixed element to release the shaft, and vice versa.

This means that, when a driving force produced by a motor connected to this transmission shaft no longer acts thereon, the decrease, due to friction, of the rotation speed of this transmission shaft causes a corresponding decrease of the centrifugal face and consequently causes operation of the contrast member, which counters radial movement of the moving element and return of this latter toward the position of friction contact with the corresponding fixed element, so as to brake rotation of the transmission shaft.

It must be noted that the aforesaid moving elements can be constrained directly or indirectly to the shaft, provided that they are rotatable integrally therewith and at the same time movable, at least radially, with respect to said shaft.

In the case in which, according to a preferred embodiment of the present invention, the contrast member also acts as return member of said at least one moving element toward its position of friction contact with the related fixed element, and for example this member is constituted by at least one return spring, or other equivalent elastic element, when the centrifugal force acting on the moving element decreases, this return spring causes the moving element to promptly take its position of friction contact with the fixed element, so as to brake and rapidly stop rotation of the motion transmission shaft.

According to some preferred embodiments of the present invention, the constraint (link) for movement of said at least one moving element along a direction having at least a radial component with respect to the transmission shaft can be a link of the sliding type, to allow translation of the moving element with respect to the shaft along this direction having at least a radial component, or can be a pivot link, in which the pivot axis is orthogonal to the rotation axis of the transmission shaft. Preferably, the device according to the present invention allows prevention of shaft rotation in sailing craft when the motor is not operating and is not transmitting torques to the propeller. In fact, the device has been designed so that the return force exerted by the suitable contrast members with which it is equipped, and in particular springs, allows the moving elements to be retained in a position of contact with the fixed element and consequently locking of the shaft when the engine is not operating and the propeller continues its rotational motion due to inertia and to the flow of fluids that strikes it.

BRIEF DESCRIPTION OF THE FIGURES

These and other advantages of the present invention will be more apparent from the following description and from the drawings, attached by way of non-limiting example, wherein:

FIG. 1 shows, in a partially sectional view according to a plane passing through the rotation axis of the shaft, a possible embodiment of the device for preventing shaft rotation according to the present invention;

FIG. 1A shows a schematic view according to a plane perpendicular to the rotation axis of the shaft of a possible embodiment of the moving elements of the device;

FIGS. 1B and 1C show according to a plane perpendicular to the rotation axis of the shaft a further possible embodiment of the moving elements of the device respectively in the position disengaged from the shaft and in the position to stop the shaft.

FIG. 2 shows, in a partially sectional view according to a plane passing through the rotation axis of the shaft, a further possible embodiment of the device for preventing shaft rotation according to the present invention;

FIG. 3 shows, in a partially sectional view according to a plane passing through the rotation axis of the shaft, a further possible embodiment of the device for preventing shaft rotation according to the present invention equipped with means for regulation of the contrast member,

FIG. 4 shows, in a partially sectional view according to a plane passing through the rotation axis of the shaft, a further possible embodiment of the device for preventing shaft rotation according to the present invention equipped with guides of the moving elements passing through the device;

FIG. 5 is a sectional view according to a plane perpendicular to the rotation axis of the shaft of the device according to FIG. 4;

FIG. 6 shows in detail the member to counter movement of the moving element used in the device according to FIGS. 4 and 5.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

With reference in general to the accompanying figures, some preferred embodiments of the device 1 for preventing and/or stopping rotation of a motion transmission shaft according to the present invention will be described. In the accompanying figures, the same numerical reference will be assigned to those components of the device 1 that exercise, albeit with dissimilar forms, an identical function.

As can be seen in the figures, the device 1 of the present invention is mounted on a motion transmission shaft 10 in order to exert resisting actions which prevent and/or stop rotation thereof when the motor to which the shaft 10 is connected is not operating.

Naturally, the shaft 10 can be any type among those known in the art, and is adapted to transfer torque from a motor, not shown in the accompanying figures, to one or more further members constrained to the shaft, and vice versa.

In particular, as already stated, the device according to the present invention can prevent or stop rotation of a shaft 10 of a watercraft, adapted to transmit torque between a motor and a propeller, and vice versa, above all in the case in which a transmission of hydraulic type is present between motor and propeller, and the propeller is of the variable pitch type, capable of adopting a “feathered” position when there is no driving torque, i.e. capable of adopted a configuration such as to offer the least possible fluid dynamic resistance, when no torque is transmitted to this propeller.

Generally, the device 1 according to the present invention comprises at least one fixed element 2 which is constrained to one or more points of the structure inside which the motor shaft 10 is mounted in a rotatable manner. This fixed element 2 can be configured in such a manner as to constitute the external part of the device 1 and can house therein all the other components, so as to produce a compact and easily installable and removable device.

Naturally, an external casing, not shown in the accompanying figures, can be provided to protect the device according to the present invention.

In the case in which the device 1 is installed on a watercraft, the fixed element 2 can preferably be constrained to the hull of the watercraft or to parts of the related propulsion that do not rotate together with the motion transmission shaft 10; for this purpose, as shown, for example, in the embodiment of FIGS. 2, 3 and 4, a rod 50 secured to a fixed part with respect to the shaft is constrained to the fixed element 2 for preventing rotation thereof.

The device 1 according to the invention also comprises one or more moving elements 5, constrained directly or indirectly to the shaft 10 through specific constraining means 3, 20, 21, 22, 30, in such a manner as to rotate integrally therewith and at the same time be able to move between a position of friction contact with at least part of the aforesaid fixed element 2, for preventing or stopping rotation of this shaft 10, and a position of disengagement from said fixed element 2, to allow release of the shaft 10. Advantageously, according to the present invention, these constraining means comprise a specific link 3, 20, 21, 22 to allow the moving elements 5 to move along a direction having at least a radial component with respect to the rotation axis A of the shaft 10.

As will be apparent to those skilled in the art, when the moving elements 5 are in contact with the fixed element 2, the friction generated between the surfaces allows prevention of rotation of the shaft 10 to which the moving elements are constrained, while when these moving elements 5 are not in contact with the fixed element 2, and are therefore in the position to release the shaft 10, this latter is free to rotate as the device 1 does not exert any resisting actions thereon.

The friction contact between the moving element 5 and the fixed element 2 preferably takes place by means of contact of inclined surfaces 6, 6′, produced in a correspondent manner on the moving element 5 and on the fixed element 2.

As shown in the accompanying figures, the inclined surfaces 6, 6′ of the moving element 5 and of the fixed element 2 have a “wedge” configuration, in such a manner as to cause friction contact therebetween to cause stopping of the shaft 10. Therefore, the moving elements 5 act like the blocks of a brake.

More in detail, movement from the position of friction contact of the moving elements 5 with the corresponding fixed element 2, due to the links 3, 20, 21, 22 of said constraining means, which in fact allows these moving elements 5 to move along a direction having at least a radial component with respect to the shaft 10, takes place due to the centrifugal force Fc produced by rotation of this shaft 10 on which the moving elements 5 are constrained, which in fact rotate integrally therewith.

In fact, for a given value of centrifugal force Fc, during rotation of the shaft 10 the moving elements 5 tend to move away from the position of friction contact with the fixed element 2 of the device 1, in which stopping of the shaft 10 is caused, moving toward the position of disengagement from the fixed element 2, in which the moving elements 5 are not in contact therewith, and therefore the shaft 10 is able to rotate freely.

According to an embodiment of the present invention, the moving elements 5 are free to move between the position of friction contact with the fixed element 2, to stop the shaft 10, toward the position of disengagement therefrom in which the shaft is free to rotate, and vice versa.

In this manner, after exceeding a predefined threshold angular velocity of the shaft 10, movement of the moving elements 5 in the position of disengagement from the fixed element 2 is caused, while when the rotation speed decreases the moving elements 5 return, under the effect of their weight, to their position of friction contact with the fixed element 2.

It is clear that, in the embodiment described above, in which the moving elements 5 can move freely, the weight of these moving elements 5 must be suitably dimensioned during the design phase, so that for a desired number of revolutions of the shaft 10 and of the corresponding action of the centrifugal force generated, they are made to move away from the position of friction contact with the fixed element 2 for release of the shaft. At the same time, it must be taken into account that the weight of the moving element 5 must be such as to generate a braking force of an intensity such as to cause the shaft to stop following friction contact with the fixed element 2.

In particular, in the case in which stopping of the shaft is caused through friction contact of the inclined surfaces 6, 6′ of the moving element 5 and of the fixed element 2, the braking force generated following contact is equal to the weight of the moving element multiplied by the friction coefficient of the contact surfaces and divided by the sine of the angle of inclination of the inclined surfaces in contact, according to a relation well known in mechanics.

Preferably, the angle of inclination of the surfaces 6, 6′ is comprised in the interval between 0.5° and 2°, and even more preferably this angle is less than on degree.

According to an alternative embodiment, movement of the moving elements (5) is suitably regulated and controlled, and the constraining means 3, 20, 21, 22 of the device comprise at least one contrast member 30, having the purpose of obstructing, in a controlled manner, i.e. only when predefined load conditions occur, movement of the moving elements 5, at least along said radial component thereof, toward their position of disengagement from the related fixed element 2.

In particular, according to the present invention, this contrast member 30 is configured to allow temporary movement of the moving elements 5 in the position of disengagement from the fixed element 2, only after exceeding a predefined angular velocity of this shaft 10.

It must be noted that while in the embodiments illustrated in the accompanying figures the device is equipped with at least one contrast member 30, this element may be omitted, as described above, in such a manner that the movement of the moving elements 5 between the stop position and the position disengaged therefrom, and its return to the stop position (because of friction contact with the fixed element 2) as a result of the weight of the moving elements 5 themselves, remains free.

The contrast member 30 of the device 1 is such as to counter, at least for certain values thereof, the centrifugal force Fc which, during rotation of the shaft 10, tends to move the moving elements 5 away from the position of friction contact with the fixed element 2 of the device 1, in which the shaft 10 is locked, toward the position of disengagement from this fixed element, in which the moving elements 5 are not in contact with the fixed element 2, and therefore the shaft 10 is able to rotate freely.

According to a preferred aspect of the present invention, said member to contrast (counter) movement, at least along the related radial component, of the moving elements 5 toward their position of disengagement from the corresponding fixed element 2, can be constituted by one or more springs 30, or other similar elastic means, which also have the function of returning the moving elements 5 toward their position of friction contact with the fixed element 2.

A similar contrast member 30 is therefore configured to allow temporary movement of the moving elements 5 to the position of disengagement from the fixed element 2 only after exceeding a predefined threshold angular velocity of the shaft 10 (i.e. when the centrifugal force Fc reaches greater intensity with respect to the return force exerted on the moving elements 5 by these members 30), and to return these moving elements 5 to their position of friction contact with the fixed element 2, when the angular velocity of the shaft 10 drops below the aforesaid threshold value.

In the case in which springs 30 are used as contrast member, a suitable choice of the elastic constant of these springs 30, together with the choice of any preload conditions and of the masses of the moving elements 5, allows these moving elements 5 to move toward their position of disengagement from the related fixed element 2, toward which they are retained by the springs 30, overcoming the related elastic force, only when the centrifugal force Fc acting thereon exceeds a threshold value defined during the design phase, i.e. only when the angular velocity of the shaft 10 exceeds a certain predefined value.

In this manner, when the shaft 10 is rotating at low speed, for example because the related motor has been switched off, the elastic force exerted by the spring 30 tends to counter movement of the moving elements 5, preventing them from abandoning the position of contact with the fixed element 2 due to the centrifugal force caused by rotation.

However, when the rotation speed of the shaft 10 is sufficiently high, the centrifugal force generated will reach an intensity such as to overcome the elastic force exerted by the spring 30 on the moving elements 5 and consequently will allow these latter to disengage from the related fixed element 2, thus leaving the shaft 10 free to rotate.

It must be noted that, although in the preferred embodiments of the present invention illustrated here, this contrast member 30 has the form of cylindrical helical spring, or springs, any other type of spring, and/or any other means known in the art capable of countering, in a temporary or controlled manner, movement of the moving elements 5 toward their position of disengagement from the fixed element 2, such as fluid dampers, or suitable elastically deformable elements, can be used alternatively, without departing from the scope of protection requested here.

It must also be noted that the term “controlled contrast members” is intended as any contrast member that is configured and calibrated to counter movement of the moving elements 5 as a function of the force acting on these moving elements 5, without permanently preventing movement thereof, but only obstructing this movement. For example, this controlled contrast member can perform the function of preventing motion of the moving elements 5 only until a certain driving force (in this case constituted by the centrifugal force) acting on the moving elements 5 is reached, beyond which the contrast member is not longer able to immobilize these elements. According to a possible embodiment, the device is equipped with means 40 for regulation of the contrast members 30, which are capable of determining any modifications of the return force exerted thereby. In this manner, it is possible to modify the threshold angular velocity of the shaft 10 at which the contrast members 30 allow temporary movement of the moving elements 5 to the position of disengagement from the fixed element 2 and at the same time to return these moving elements 5 to their position of friction contact with the fixed element 2 when the angular velocity of the shaft 10 drops below said threshold value.

More in detail, in the embodiment illustrated in FIG. 3, in which the contrast members employed are springs 30, said regulation means 40 comprise a screw 41, operable from the outside, which allows modification of the preload of the spring 30 by means of controlled compression thereof depending on whether the screw 41 is screwed or unscrewed. As a result, the related elastic force exerted by the spring 30 is modified causing variation of the conditions for which the moving elements 5 can move toward their position of disengagement from the related fixed element 2, toward which they are retained by the springs 30. In fact, it is apparent that for a different value of elastic force (force countering movement of the moving elements) exerted by the springs, the intensity of the centrifugal force Fc acting thereon necessary to allow movement thereof will vary, thus causing a modification of the threshold value of the angular velocity of the shaft 10 which allows actuation of the device according to the present invention.

It must also be noted that the device according to the present invention can be produced in two or more parts, preferably two mutually separable half-parts, in such a manner as to be easily constrained on the shaft whose rotation is to be controlled. More in detail, in the case of installation of the device on a watercraft, locking of the device formed by the two mutually separable half-parts that are subsequently constrained through means known for this use, such as a plurality of screws (see for example FIGS. 1 and 3), is considerably simplified as it is not necessary to remove the propeller shaft from the watercraft.

It must also be noted that, in order to make the device safer, according to another possible embodiment, the parts of which it is composed are mutually constrained by means of a system of interlocks, preferably with cooperating parts arranged at 90° from one another, which are thus locked to one another. This method of constraint prevents the parts of which the device is composed, subject to rotation and therefore to centrifugal force, from becoming dangerously loose, or even separating.

As will be described in more detail with reference to the embodiment illustrated in FIGS. 4 and 5, the guides 22 of the moving elements 5 passing through the body of the device cooperate in retaining in assembled position the parts of the device which are coupled to one another with this system of interlocks.

With reference now to the embodiment of the device 1 according to the invention illustrated in FIGS. 1 and 1A, this comprises a plurality of moving elements 5, or blocks, which are constrained in such a manner as to rotate integrally with the shaft 10, by means of interposing of a frame 3, integral with the shaft 10, and of guides, or pins 20, projecting integrally from the frame 3 in radial direction with respect to the shaft 10, and configured to act as a link of the sliding type for each of the moving elements 5.

More in detail, the frame 3 is substantially annular in shape and has a central portion, in the form of a sleeve, having an internal diameter such as to allow fitting thereof on the shaft 10, and a peripheral portion, also annular, which extends in a manner coaxial to the shaft 10, and which acts as support for the guides 20 of the blocks 5.

The frame 3 can be secured to the shaft 10 according to known means, such as by interference fit of parts or using constraining means such as screws, pins, bolts and the like, just as the guides 20 can also be secured to the frame 3 by known means (such as interlocking, or screwing of threaded parts, etc.).

In the embodiment illustrated in FIG. 1, the device 1 is equipped with two moving elements, or blocks, 5, each of which is substantially in the shape of an annular sector, when viewed on a plane perpendicular to the rotation axis of the shaft 10 (see FIG. 1A). The blocks 5 have dimensions substantially equal to half of an annular sector. However, other embodiments are possible, for example in which the device is equipped with four moving elements, or blocks, 5, each having dimensions substantially equal to a quarter of annular sector.

FIGS. 1B and 1C show a further possible embodiment of the moving elements 5, illustrated schematically respectively in position of disengagement from the shaft and in the position to stop the shaft.

In the same manner as illustrated in FIG. 1A, FIGS. 1B and 1C show two moving elements 5, each having a shape substantially equal to a half of annular sector, viewed in a plane perpendicular to the rotation axis of the shaft 10, and which are equipped with at least one raised surface portion 5.1.

More in detail, the moving element 5 is provided on the lateral surface thereof with a raised portion 5.1 with respect to the other portions 5.2. of its lateral surface. As will be more apparent below, the raised surface portion 5.1, which is preferably produced in the central portion of its half of annular sector shape, is destined to come into friction contact with the fixed element 2 to cause locking of the shaft. Moreover, the Applicant has verified that the presence of a portion 5.1, even if only slightly raised (one or a few millimetres of thickness) with respect to the other portions 5.2 of the surface, greatly facilitates movement of the moving element from the position to stop the shaft to the position of disengagement therefrom, and vice versa, without heat and rotational motion being in any manner able to obstruct this movement of the moving element required for correct operation of the device.

The blocks 5 are constrained to the frame 3 in such a manner that as a whole, when viewed in a plane perpendicular to the axis of the shaft 10, they substantially define a circular ring around the shaft 10.

It must be noted that although in the embodiments illustrated the blocks 5 have this annular sector shape, other embodiments of the moving elements 5 can be used without departing from the scope of protection of the present invention.

As stated, each moving element 5 is constrained to the frame 3, and in particular to the annular peripheral portion thereof, by means of a pair of guides, or pins 20, or similar means, projecting from the frame 3 toward the shaft 10, along a radial direction with respect to this shaft 10.

While specific reference has been made to guides 20 arranged radially with respect to the shaft 10, other embodiments are possible, in which the guides 20 lie in a plane passing through the rotation axis A of the shaft 10, but are not directed radially with respect thereto, although allowing translation of the blocks 5 along a direction with a radial component with respect to the axis A, or, the guides 22 lie in a plane parallel to a plane passing through the rotation axis A of the shaft 10 and are preferably perpendicular to this shaft 10 (consequently leaving the blocks 5 free to translate along a direction with a radial component), as in the embodiment illustrated in FIGS. 4 and 5. These guides 20 are configured to act as link of the sliding type in relation to the blocks 5, i.e. to constrain the blocks 5 to the frame 3, and therefore to the shaft 10, in such a manner as to allow radial movement thereof with respect to the rotation axis A of the shaft 10—movement caused by the centrifugal force, as already described—and at the same time make these blocks 5 rotate integrally with the frame 3 and therefore with this shaft 10.

In other words, in the embodiment of this invention illustrated herein in FIG. 1, the two moving elements, or blocks, 5, are constrained in a translatable manner on the frame 3, integral with the shaft 10, in such a manner as to be free to move along a radial direction and at the same time be constrained to rotate integrally with this shaft 10.

In the embodiment illustrated in FIG. 1, the device 1 also comprises a fixed element 2 which, as stated, can be constrained, for example, to parts of a watercraft or of a propulsion fixed with respect to the shaft 10, and which comprises a portion destined to come into friction contact with the moving elements, or blocks, 5.

This friction contact with the fixed element 2 by the blocks 5 is generated, according to the embodiment described here, by means of inclined portions 6 produced on the lateral surface of each moving element 5, which are configured to come into contact with corresponding inclined surfaces 6′ arranged on the fixed element 2.

As already stated, the friction generated by the contact of the inclined portions 6 and 6′, respectively of the moving elements 5 and of the fixed element 2, and therefore the braking force exerted by the device 1 on the shaft 10, will depend on the inclination of the surfaces 6 and 6′ chosen during the design phase, and on the materials of which they are composed.

This portion 6′ of the fixed element 2 is configured to intercept the blocks 5 during their radial movement, only in a position that these blocks 5 reach when they are not stressed by the centrifugal force Fc to which they are subjected due to rotation of the shaft 10.

In this manner, due to the guides 20, the blocks 5 can translate in a radial direction between a position of disengagement from the fixed element 2 (upward in FIG. 1) and a position of friction contact with this fixed element 2 (downward in FIG. 1), as a function of the rotation speed reached by the shaft 10.

Moreover, as can be seen in FIG. 1, each moving element, or block, 5, is also connected along a radial direction with a cylindrical helical spring 30, for example acting in extension or in compression, which constitutes part of the corresponding controlled contrast members of the radial movement of the blocks 5 toward their position of disengagement from the fixed element 2. These cylindrical helical springs 30 also act as means for the return of these blocks 5 toward said position of disengagement from the fixed element 2.

The elastic force exerted by each spring 30 is calibrated in such a manner as to cause each moving element 5 to remain in the position of friction contact with the fixed element 2, at least until the centrifugal force Fc acting on the blocks 5, generated by rotation of the shaft 10, is insufficient to overcome the return force of these springs 30. When the centrifugal force Fc acting on the blocks 5 is sufficiently intense to overcome the return force of the springs 30, this centrifugal force Fc causes the blocks to move radially along the guides 20, toward said position of disengagement from the fixed element 2.

It must be noted that, during the design phase of the device 1, the mass of the moving elements 5, their distance from the rotation axis A of the shaft and the characteristics of the spring 30 are determined; therefore it is basically possible to establish the rotation speed of the shaft 10 at which the device 1, after installation on the shaft 10, will start to function, allowing temporary movement of the moving elements 5 from the position of friction contact with the fixed element 2 to the position of disengagement in which the shaft 10 is free to rotate. Moreover, as shown in FIG. 3, according to a possible embodiment, the elastic force exerted by each spring 30 can be modified manually by the user acting on suitable regulation means 40, which comprise a screw 41 adapted to modify the extension of this spring 30, modifying the preload thereof.

As already stated, the device according to the present invention illustrated in FIG. 1 can also function without contrast members, and in particular without the spring 30, in such a manner that movement of the blocks 5 from the position of friction contact with the fixed element 2, and in its return to this position when the centrifugal force decreases (linked to the number of revolutions of the shaft 10) as a result of the weight of the block 5, remains free.

With reference now to the embodiment of the present invention illustrated in FIG. 2, the device 1 illustrated provides that the moving elements 5 are constrained to a frame 3 integral with the shaft 10, in such a manner as to be able to rotate, at least partially, about a hinge 21, constrained to this frame 3.

This frame 3, in the same manner as the one described in relation to FIG. 1, has a substantially annular extension and is fitted on the shaft 10 by means known in the art. The hinge 21, constituted for example by a metal pin secured to the frame 3 and coupled in rotation to a moving element 5, has a rotation axis which is substantially orthogonal to the rotation axis A of the shaft 10, in such a manner that the rotational motion R of each moving element 5 about this hinge 21 has a component along a radial direction with respect to this shaft 10, so that the centrifugal force acting on the moving elements during rotation of the shaft 10 causes rotation of the moving elements 5 about the related hinges 21.

The device 1 is completed by a fixed element 2, suitably constrained, for example, to the hull of a watercraft, and configured to temporarily engage with friction with the moving elements 5, and with the suitable return means of these elements.

According to this embodiment, each moving element 5 is configured in such a manner as to comprise a part 5A of small dimensions equipped with at least one inclined surface 6, adapted to come into contact with at least one corresponding inclined surface 6′ of the fixed element 2, and a part 5B of larger dimensions. As the part 5B is of larger dimensions with respect to the part 5A, the centrifugal force Fc generated during rotation of the shaft will act prevalently thereon, causing rotation of the moving element about the point of constraint 21.

Also in the case of the device 1 of FIG. 2, a spring 30, or similar elastic contrast and return means, acting on each moving element 5, allows the part 5A of each moving element 5 to be retained in the position of friction contact with the fixed element 2, until the centrifugal force acting on this moving element is eliminated or remains below a predefined threshold.

It must be observed that, also in the embodiment of the device 1 of FIG. 2, the springs 30 are configured to act radially on the moving elements, or blocks, 5, so that their line of action on these blocks 5 is a straight line arranged radially with respect to the shaft 10.

Therefore, in the same manner as the device illustrated in FIG. 1, when rotation of the shaft 10 is such that the centrifugal force generated is of lesser intensity than the elastic return force of the spring 30, the moving elements 5 are retained in the position of friction contact with the fixed element 2, thus causing the shaft to stop.

Instead, when rotation of the shaft 10 reaches a value that allows the corresponding centrifugal force Fc generated on the moving elements 5 to overcome the intensity the elastic return force of the spring 30, the moving elements 5 which would tend to move radially toward the periphery of the device, due to the point of constraint 21, of hinge type, with the frame 3 are subjected to rotation thereabout in the direction indicated in FIG. 2 by the arrow R.

This rotation of the moving elements 5 causes compression of the spring 30, through the part 5B thereof, and consequently temporary movement of the part 5A from the position of friction contact with the fixed element 2, toward the related position of disengagement, in which the shaft 10 is free to rotate as the device does not exert resisting forces thereon.

It must be noted that, just as for the embodiment illustrated in FIG. 1, the term “temporary movement” from the position of contact has been used in the present description to indicated that in the moment in which rotation of the shaft 10 generates a centrifugal force Fc of lesser intensity than that of the return force exerted by the springs 30, the moving elements 5 are returned to the position of contact with the fixed element 2.

Also in this embodiment, the at least one contrast member 30 of the device can be omitted, in such a manner that movement of the moving elements 5 remains free.

With reference now to the embodiment of the present invention illustrated in FIGS. 4 and 5, this comprises two moving elements 5, or blocks, which are constrained in such a manner as to be rotatable integrally with the shaft 10, through interposing of a frame 3, integral with the shaft 10, and of guides 22 configured to act as a link of the sliding type for each of the moving elements 5.

More in detail, the device comprises four guides 22, arranged in pairs laterally with respect to the shaft 10, and directed perpendicular to the rotation axis A of the shaft 10 and preferably lying in a plane parallel to a plane passing through this rotation axis A of the shaft 10.

As is visible in particular in FIG. 5, the guides 22 pass inside the device in such a manner as to act as a sliding link in relation to the two moving elements 5, guiding movement thereof between the position to stop the shaft and the position of disengagement therefrom, and vice versa.

In fact, the guides 22 are configured to act as link of the sliding type in relation to the blocks 5, i.e. to constrain the blocks 5 to the frame 3, and consequently to the shaft 10, in such a manner as to allow radial movement thereof with respect to the rotation axis A of the shaft 10, movement caused by centrifugal force, and at the same time make these blocks 5 rotate integrally with the frame 3 and therefore with this shaft 10.

As already stated, the parts of the device can be mutually coupled by means of an interlocking constraint, and the guides 22 passing inside the body of the device cooperate in maintaining the parts in assembled position. The applicant has verified that this method of interlocking constraint allows the total weight of the device to be limited, at the same time obtaining high reliability in the coupling of the parts by means of the action of the guides 22 which, as stated, cooperate in retaining the parts in assembled position, also providing rigidity to the device as a whole, preventing the centrifugal force to which it is subjected from causing loosening or even separation of the parts of which it is constituted.

In the same manner as the other embodiments described previously with reference to FIGS. 1 and 2, the frame 3 is substantially annular in shape and has a central portion, in the form of a sleeve, having an internal diameter such as to allow fitting thereof on the shaft 10, and a peripheral portion, also annular, which extends coaxially to the shaft 10, and acts as a support for the guides 22 which can be secured to the device, and in particular to the frame 3, by known means (such as interlocking, or screwing of threaded parts, etc.).

The device 1 is equipped with two moving elements, or blocks, 5, each of which has substantially the shape of an annular sector and having dimensions equal to half of an annular sector, when viewed on a plane perpendicular to the rotation axis of the shaft 10.

In particular, in the embodiment illustrated in FIGS. 4 and 5, the moving elements 5 according to FIGS. 1B and 1C are preferably used, i.e. equipped with at least one portion of raised lateral surface 5.1.

Moreover, the device 1 also comprises a fixed element 2 which, as stated, can be constrained, for example, to parts of a watercraft or of a propulsion fixed with respect to the shaft 10, and which comprise a portion destined to come into friction contact with the moving elements, or blocks, 5.

This friction contact with the fixed element 2 by the blocks 5 is generated, in the same manner as described with reference to the embodiment of FIG. 1, by means of inclined portions 6 produced on the lateral surface of each moving element 5, which are configured to come into contact with corresponding inclined surfaces 6′ arranged on the fixed element 2.

As already stated, the friction generated by the contact of the inclined portions 6 and 6′, respectively of the moving elements 5 and of the fixed element 2, and consequently the braking force exerted by the device 1 on the shaft 10, will depend on the inclination of the surfaces 6 and 6′ chosen in the design phase, and on the materials of which they are composed.

As will be apparent at this point of the description, due to the guides 22, the blocks 5 can translate in a direction with a radial component between a position of disengagement from the fixed element 2 (upward in FIGS. 5 and 6) and a position of friction contact, with this fixed element 2 (downward in FIGS. 5 and 6), as a function of the rotation speed of the shaft 10.

Moreover, as can be seen in FIG. 5 and more in detail in FIG. 6, and in the same manner as the embodiment of FIG. 1, each moving element, or block, 5, is also connected to a spring 30, for example acting in extension or in compression, which constitutes part of the corresponding controlled contrast members of radial movement of the blocks 5 toward their position of disengagement from the fixed element 2. These cylindrical helical springs 30 also act as return means of these blocks 5 toward said position of disengagement from the fixed element 2.

Also in this embodiment, the elastic force exerted by each spring 30 is calibrated in such a manner as to cause each moving element 5 to remain in the position of friction contact with the fixed element 2, at least until the centrifugal force Fc acting on the blocks 5, generated by rotation of the shaft 10, is insufficient to overcome the return force of these springs 30. When the centrifugal force Fc acting on the blocks 5 is sufficiently intense to overcome the return force of the springs 30, the blocks 5 are caused to move radially by this centrifugal force Fc along the guides 22, toward the aforesaid position of disengagement from the fixed element 2.

Also in this embodiment, the contrast members, and in particular the springs 30, can be omitted in such a manner that movement of the moving elements 5 remains free.

Moreover, as can be seen in the detailed view of FIG. 6, and as already described in relation to FIG. 3, according to a possible embodiment, the elastic force exerted by each spring 30 can be modified manually by the user acting on suitable regulation means 40, which comprise a screw 41 adapted to modify the extension of this spring 30, modifying the preload thereof.

Moreover, as can be seen in FIGS. 5 and 6, the device comprises a spring guiding rod 31, adapted to prevent the spring 30, during compression or elastic return thereof to the non-deformed condition, from being subject to modifications in shape, mainly caused by the rotational motion to which the device, and consequently the spring 30, is subjected due to rotation of the shaft 10. Naturally, the spring-guiding rod can also be employed in the other embodiments of the device described previously with reference to FIGS. 1, 2 and 3.

Operation of the device 1 illustrated here, with reference to the three embodiments described above respectively with reference to the FIGS. 1, 2 and 4, is as follows.

After having defined, during the design phase, the values of the masses of the moving elements 5 and the elastic force that the springs 30 must exert to counter movement of these moving elements 5, as a function of the angular velocity reached by the shaft 10 during operation thereof, the device 1 is assembled in such a manner that the fixed element 2 is firmly integral with a fixed part with respect to the shaft 10, that the frame 3 is fitted on this latter and that the moving elements, or blocks, 5 are constrained to the frame 3 by the guides 20 (FIG. 1), by the pins 21 (FIG. 2) or by the guides 22 (FIGS. 4 and 5), with the same connection as the return springs, or contrast members, 30, also secured to the frame 3 and constrained to the blocks 5, in such a manner as to return them to a position of friction contact with said fixed element 2.

When the shaft 10, connected to a motor, is stopped, the return springs 30 retain the blocks 5 in friction contact with the fixed element 2, so that the shaft 10 cannot rotate even in the case of external stresses.

During the motor start-up transient, for low angular velocities of the shaft 10, even if the links 20, 21, 22 of the blocks 5 to the frame 3 would allow these blocks 5, stressed by the centrifugal force, to move from said position of friction contact with the fixed element 2, the dimensions of the blocks 5 and of the springs 30 are such that these latter efficiently counter the initial limited centrifugal force to which the blocks 5 are subjected.

When the rotation speed of the shaft 10 increases, and consequently the centrifugal force Fc acting on the blocks 5 increases, these will start to move according to a direction, having in any case a radial component, defined by the type of link 20, 21, 22 (of the sliding or pivot (hinge) type), when the centrifugal force Fc to which they are subjected exceeds the elastic return force of the springs 30.

In other words, the blocks 5, stressed radially by the centrifugal force Fc and free to move at least in this radial direction due to the links 20, 21, 22, will start to move away from their position of friction contact with the fixed element 2, disengaging therefrom, when the centrifugal force Fc, proportional to the angular velocity of the shaft 10, is sufficiently intense to overcome the elastic return force of the related springs 30.

When the motor coupled to the motion transmission shaft 10 is switched off, or in any case the torque transmitted to this shaft 10 is drastically decreased, if the rotation speed of the shaft 10, and consequently the centrifugal force Fc acting on the blocks 5, becomes less than the elastic return force of the spring 30, for example when the shaft 10 rotates through inertia, these springs 30 return the blocks 5 to their position of friction contact with the fixed element 2 of the device 1, thereby causing the shaft 10 to stop immediately.

Although having made specific reference to the embodiments in which the device is equipped with contrast members 30 of the movement of the moving elements 5, as will be apparent to those skilled in the art, operation of the device without these contrast members 30, wherein the moving elements 5 can move freely, is the same as described above.

In particular, from the condition of stopping of the shaft 10 when the centrifugal force increases due to the increase in the number of revolutions, the braking force exerted by the friction contact between the moving elements 5 and the fixed element will decrease until being cancelled, causing movement of the moving elements 5 toward the position of disengagement from the shaft 10, in which this latter is free to rotate. When the centrifugal force decreases, for example in the case of stopping the motor connected to the shaft 10, the moving elements 5 will tend to return to the position to stop the shaft in the position of friction contact with the fixed element 2 under the effect of their weight.

As stated, the device 1 according to the present invention can advantageously be applied to the motion transmission shaft of a sailing craft, preferably equipped with a variable pitch propeller capable of adopting a “feathered” position when there is no driving torque, to promptly stop rotation of the motion transmission shaft of the propeller when the motor is not operating and does not transmit torques to the propeller.

In fact, the device 1 according to the present invention allows the rotational motion of the shaft to be stopped when the motor is switched off and without this device 1 the propeller, and consequently the shaft 10, would continue to rotate due to the inertia and to the flow of fluid caused by movement of the watercraft, thereby preventing automatic arrangement of the blades in their “feathered” position.

The device 1 is designed in such a manner that the return force exerted by the contrast member (for example the springs 30) allows the moving elements 5 to be retained in position of contact with the fixed element 2, and consequently locking of the shaft 10, when the engine is not operating and the propeller continues its rotational motion due to inertia and to the flow of fluids that strikes it.

In this manner, it is possible to promptly stop the shaft 10 when no driving forces are acting thereon, in such a manner that the propeller can be arranged automatically in the position in which the blades are in “feathered” configuration and offer the least resistance to fluid.

Naturally, the force exerted by the return members 30 is such as to allow movement of the moving elements 5 to the position of disengagement, releasing the shaft 10, when the engine is activated, thereby allowing normal operation of the propeller.

DEVICE FOR PREVENTING A SHAFT ROTATION

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