EP3371042A1

EP3371042A1 - Hub for bicycles

Info

Publication number: EP3371042A1
Application number: EP16816740.1A
Authority: EP
Inventors: Antonello Briosi
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-11-05
Filing date: 2016-11-04
Publication date: 2018-09-12
Also published as: ITUB20155121A1; WO2017077487A1

Abstract

The hub (1) for bicycles comprises: at least one rotation shaft (2) installable on a frame of a bicycle, on which a group of bearings (4) is mounted which are able to allow the rotation of the shaft (2) around an axis (5) of rotation; at least one first pedal crank (6) and one second pedal crank (7), associated with the shaft (2) for setting the bicycle in motion; with the pedal cranks (6, 7) which comprise: - an inner reticular structure (34); an outer casing (35) enveloping at least partially the inner structure (34) and made of a composite material of carbon fiber.

Description

HUB FOR BICYCLES

Technical Field

This invention relates to a hub for bicycles, particularly to a front hub.

Background Art

The known front hubs have a tube, i.e. a tubular body, at the extremities of which are mounted the pedal cranks for the setting in motion of the vehicle. On the tube, one or more sprocket wheels are also keyed forming part of the vehicle transmission system.

The latter is usually composed of a group of front sprocket wheels, associated with the pedal cranks, and a group of rear sprocket wheels, integral with the rear wheel.

The two groups are connected by means of a chain which, operated by the rotation of the front sprocket wheels, drags the rear sprocket wheels in motion, and therefore the rear wheel of the vehicle.

The tube is installed on the bicycle frame by means of one or more bearings that may be of various types such as, e.g., ball bearings, sliding bearings, etc..

In any case, the bearings allow the tube itself to rotate around a fixed axis with respect to the bicycle frame.

This manner, by pushing on the pedal cranks it is possible to set the tube in rotation, and therefore the sprocket wheels.

The known front hubs have several drawbacks.

A first drawback is linked to the pedal cranks.

These, in fact, must combine characteristics of both resistance, to cope with stresses of the flexural and torsional type which act on them during pedaling, and of lightness, in order to perform nimble and fast pedaling without compromising the run and burdening on the frame to a minimum extent.

Pedal cranks are known made of a solid material, very durable, but heavy. Pedal cranks are also known with a lightened, partially hollow structure, lightweight but little resistant.

Another drawback is linked to the installation, assembly and adjustment of the hub and of the elements associated with it.

The installation, assembly and adjustment operations of the various elements are, in fact, very complex and difficult to achieve without the intervention of specialized technicians.

Just think of the setting in position of the pedal cranks, which is not always immediate and requires accuracy both as regards the search for the correct position, and as regards the final fastening, which must ensure stability and holding in order to avoid problems to the user during pedaling.

This implies both a lot of time spent in the above operations and the onset of management and maintenance costs linked to the intervention of the specialized technician.

Another drawback concerns the structural stability of the hub and of the elements associated with it.

The stability and holding of the pedals have already been mentioned previously, but also the stability and holding of the other elements is often the cause of malfunctions.

The holding and stability of the bearings, e.g., is very important both for the proper functioning of the transmission system, and for the prevention of any structural damage to the hub and to the transmission system that would arise in the case where those bearings were loose and movable relative to one another. A third drawback of known hubs is linked to the fact that, to obviate the drawbacks described above, front hubs are often used, with elements associated with them, specifically designed according to the model of bicycle on which they are to be installed.

This results in poor flexibility of use of the hub so designed, that is, it can hardly be installed on different bicycles from that for which it was designed. This implies an increase in production costs, since for every model of bicycle a specific hub should be conceived, designed and realized.

Description of the Invention

The main aim of this invention is to provide a lightweight hub for bicycles and, at the same time, resistant to the stresses acting on the pedal cranks during pedaling.

Within this aim, one object of this invention is to provide a hub for bicycles which is easy and fast to install and adjust. One object of this invention is to provide a hub for bicycles that allows ensuring the stability and holding of the various elements associated therewith.

A further object of this invention is to provide a hub for bicycles usable in a flexible manner on different models of bicycles.

Another object of this invention is to provide a hub for bicycles which allows overcoming the mentioned drawbacks of the prior art within the ambit of a simple, rational, easy, effective to use and affordable solution.

The above mentioned objects are achieved by this hub for bicycles having the characteristics of claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become better evident from the description of a preferred, but not exclusive, embodiment of a hub for bicycles, illustrated by way of an indicative, but non-limiting, example in the accompanying drawings, wherein:

Figures 1 and 2 are axonometric views of the hub according to the invention;

Figure 3 is a sectional view of the hub according to the invention;

Figure 4 is a sectional view of a detail of the hub according to the invention;

Figures 5 and 6 are axonometric views of details of the hub according to the invention;

Figure 7 is an axonometric exploded view of the hub according to the invention. Embodiments of the Invention

With particular reference to such figures, reference number 1 globally indicates a hub for bicycles, particularly a front hub.

The hub 1 comprises at least one rotation shaft 2 installable on a frame of a bicycle, for simplicity not shown in the figures.

The shaft 2 e.g. is composed of a tube, as illustrated in the figures.

The tube 2 is fitted in a tubular casing 3 forming part of the bicycle frame.

On the tube 2 is mounted a group of bearings 4 adapted to allow the rotation of the tube itself around an axis 5 of rotation.

The bearings 4 are positioned between the inner surface of the tubular casing 3 and the outer surface of the tube 2 and are of the type of ball bearings.

The hub 1 also comprises a first pedal crank 6 and a second pedal crank 7 useful for the setting the bicycle in motion.

According to the invention, the pedal cranks 6, 7 comprise an inner reticular structure 34.

In particular, the inner structure 34 comprises two running elements 36 and a plurality of diagonal elements 37 bound to one another and to the running elements 36 so as to define triangular cavities 38 in the inner structure itself. The inner structure 34, in fact, is a reticular structure made with a single row of running elements 36 and diagonal elements 37 coplanar to one another and defining a reticular structure.

The reticular structure extends between two side boards 39a, 39b arranged in the proximity of the extremities of the pedal cranks 6, 7.

This structural conformation makes the pedal cranks 6, 7 resistant to flexural efforts despite a certain amount of lightness due to the cavities.

In this embodiment, the triangular cavities 38, with the exception of the end cavities, i.e. of the cavities arranged in the proximity of the side boards 39a, 39b, are of the type of isosceles triangles.

The triangular cavities 38, therefore, have substantially equal inclination angles so as to allow the even distribution of the efforts induced by the flexural stresses to which the pedal crank 6 or the pedal crank 7 is subjected.

Advantageously, the inner structure 34 is made of "Ergal", an aluminum alloy 7075 having high mechanical resistance.

The use of other types of alloys cannot however be ruled out to be used in place of Ergal.

Furthermore, still according to the invention, the pedal cranks 6, 7 comprise an outer casing 35 enveloping at least partially the inner structure 34.

The outer casing 35, in fact, envelops the inner structure 34 such as a stocking, covering it.

In this embodiment, the casing 35 entirely covers the inner structure 34, from the side board 39a to the side board 39b.

This solution allows the pedal cranks 6, 7 to withstand the efforts induced by the torsional stresses.

This way, the resistance to the flexural stresses due to the inner structure 34 are integrated with further resistant component, actually increasing the overall resistance of the pedal cranks 6, 7.

Advantageously, the casing 35 is made of a composite material of carbon fiber. This way, in addition to ensuring high mechanical resistance, resulting from the intrinsic properties of the material, top lightness is also ensured.

A pedal crank having the inner structure 34 and the outer casing 35 previously described, thus, has greater resistance to torsional and flexural efforts with respect to a pedal crank made of a solid structure and having the same weight. In other words, the resistance being equal, the pedal cranks 6, 7 illustrated in the figures are much lighter than a similar pedal crank made of a solid structure. In this embodiment, the pedal cranks 6, 7 have positioning seats 8 shaped so as to be associated with the extremities of the tube 2 to achieve a pack assembly of the pedal cranks themselves with the tubular casing 3 and with a sprocket wheel 9 forming part of the bicycle transmission system.

Alternative solutions cannot be ruled out in which, for example, instead of a single sprocket wheel 9 there are several sprocket wheels arranged in a spool. Similarly, different solutions cannot be ruled out in which the tubular casing 3 is shaped differently, e.g. with enlarged extremities with respect to the central part, or in which there are several bearings arranged differently, or in which the bearings are of a different type to the ball ones (e.g. sliding bearings, cylindrical roller bearings or tapered roller bearings).

Advantageously, the tube 2 is made of a composite material of carbon fiber, but other materials cannot be ruled out.

This way it is possible to make a very lightweight tube 2 and, at the same time, highly resistant to the stresses to which it is subjected during normal use.

As illustrated in the figures, the tube 2 has a first end portion 10 comprising at least a first positioning element 11, adapted to facilitate, precisely, the positioning of a first pedal crank 6.

The tube 2 also has a second end portion 12, opposite to the first end portion 10 and having at least a second positioning element 13, adapted to facilitate the positioning of a second pedal crank 7.

In this embodiment, the tube 2 is tubular with the first end portion 10 which has two first positioning elements 11 and with the second end portion 12 which has five second positioning elements 13.

In particular, the positioning elements 11, 13 are extensions of the tube 2, that is, they follow the shape of the tube 2 forming a toothing which forms a crown on the relative end portion 10, 12 with which they are associated.

As regards the first end portion 10, the first positioning elements 11 are formed at diametrically opposite positions.

The first positioning elements 11 are adapted to couple to respective cavities formed on the first pedal crank 6 at the respective positioning seat 8 and so as to allow the correct angular positioning of the same.

Different solutions cannot be ruled out, in which for example the first positioning elements 11 are arranged on different positions to those illustrated, provided that the same fulfill the function to correctly position the first pedal crank 6.

The solution cannot also be ruled out in which the first positioning elements 11 are in a number different to two.

Conveniently, the first end portion 10 has an inner flared surface 14 in the shape of a cone narrowing from the inside to the outside of the tube 2.

As illustrated in Figure 4, in the proximity of the first end portion 10, the inner section of the tube 2 narrows from the inside of the tube itself towards the outside.

Conveniently, the hub 1 comprises a first positioning system 15, 18 at least partly fitted in the tube 2 and adapted to lock the first pedal crank 6 in a predefined position.

In particular, the first system 15, 18 comprises a coupling element 15 with a through hole 17 and having an outer surface 16 substantially flared, adapted to be coupled to the inner surface 14 of the first end portion 10 so as to define a cone-on-cone coupling.

In this embodiment, the coupling element 15 is of the type of a pin insertable within the tube 2 from the second end portion 12.

The pin 15 is of a size such as to make a cone-on-cone coupling with the inner flared surface of the first end portion 10 of the tube. The pin 15 is also made of a solid body, that is, has a continuous outer edge and fully engaged on the inner surface 14.

Alternative solutions cannot be ruled out in which, for example, the pin 15 is star-shaped, that is, with a toothed edge adapted to be coupled to the aforementioned inner surface.

The solution cannot also be ruled out in which in place of the through hole 17 there is a hole with blind bottom.

The first system 15, 18 also comprises a first locking element 18 having a first insertion body 19 engageable in the through hole 17 of the coupling element 15 and a first locking head 20 associated with the first insertion body 19 and adapted to abut against the first pedal crank 6.

The first insertion body 19, in fact, is inserted into the through hole 17 through a positioning seat 8 formed on the first pedal crank 6.

The first locking head 20 abuts against the first pedal crank 6 thus preventing the first locking element 18 to move forward inside the tube 2.

In particular, the through hole 17 is internally threaded and the first insertion body 19 is externally threaded so as to form with the hole itself a screw-nut screw coupling.

The screwing of the first locking element 18 allows the locking in position of the first pedal crank 6, a compressive force being exerted on it by the locking head 20 which brings the pedal crank itself closer to the first end portion 10.

Such screwing, moreover, expands the pin 15 which in turn expands the tube 2 thus increasing the frictional forces on the surfaces in contact.

This way "shrink- fit friction" is obtained, i.e. a fixing of the various parts thanks to the increase in the aforementioned friction forces.

The first insertion body 19, moreover, comprises a threaded connecting seat 21, formed at the opposite position to the first locking head 20 and adapted to interact with a second positioning system 22, 23.

Advantageously, in fact, the hub 1 comprises a second positioning system 22, 23, at least partly inserted inside the tube 2, adapted to lock the second pedal crank 7 in a predefined angular position.

The second positioning system 22, 23 is associable with the first positioning system 15, 18 for the arrangement of the second pedal crank 7 in a longitudinal position adjustable along the axis of rotation, which coincides with the axis of the tube 2.

In particular, the second positioning system 22, 23 comprises a second locking element 22 prismatically insertable in the second end portion 12 so as to define a prismatic coupling with the second pedal crank 7 for locking the latter in the aforementioned predefined angular position.

The second positioning system also comprises a connecting element 23 inserted in the tube 2 and associated with the connecting seat 21.

In this embodiment, the second end portion 12 of the tube 2 is inserted inside the positioning seat 8 of the second pedal crank 7 with the second positioning elements 13 which protrude at least partially from the pedal crank itself.

The second locking element 22 has a second insertion body 24 and a second locking head 25.

The second insertion body 24, similar to the first insertion body 19, is inserted to measure into the tube 2 through the second positioning seat 8.

The second locking head 25 is adapted to abut against the second pedal crank 7. Advantageously, the second locking head 25 comprises positioning tabs 26, equal in number to the number of the positioning elements 13, and which extend in a radial manner on the lying plane of the head itself.

The positioning tabs 26 define a toothed profile which, when the head is in abutment against the pedal crank, is coupled to the positioning elements 13. In particular, the second positioning elements 13 position themselves in the spaces left between one tab and the other, thus ensuring the prismatic coupling between the second locking element 22 and the second pedal crank 7.

The presence of the positioning tabs 26, in fact, prevents any mutual rotation between the second locking element 22 and the tube 2 and, therefore, between the second pedal crank 7 and the tube 2, thus fixing the angular position thereof. Advantageously, on the second pedal crank 7, in the proximity of the positioning seat 8, at least one locator element 27 is formed adapted to facilitate the identification of the correct angular position of the pedal crank itself.

In this embodiment, the locator element 27, aligned with a preselected second positioning element 13a, univocally identifies the angular position of the second pedal crank 7.

The geometric arrangement of the locator element 27 and of the first and second positioning elements 11, 13 is such that, once the angular position of the first pedal crank 6 is defined, the position is also defined of the second positioning element 13 and, therefore, through the locator element 27, also the angular position of the second pedal crank 7.

Different solutions cannot however be ruled out in which, for example, the locator element 27 is formed in a different position, or is shaped differently, provided that it allows positioning the two pedal cranks 6, 7 rotated by 180° relative to one another.

The presence cannot also be ruled out of a plurality of locator elements 27.

In any case, the second locking element 22 has a recessed seat 28 communicating with a recessed channel 29 crossed by the connecting element 23.

In this embodiment, the recessed seat 28 is substantially cylindrical.

The connecting element 23 is of the type of a threaded screw adapted to form a screw-nut screw coupling with the connecting seat 21.

As illustrated in the figures, the threaded screw 23 has a threaded elongated body 23 a and a cylindrical head 23b.

The elongated body 23a crosses longitudinally the second locking element 22 and the tube 2 and is screwed onto the connecting seat 21 of the first locking element 18.

The cylindrical head 23b, on the contrary, takes a recessed position on the second locking element 22, in particular in the recessed seat 28.

The conformation of the cylindrical head 23b and of the recessed seat 28 allows the connecting element 23 to rotate also with the cylindrical head 23b positioned in the recess, there being no prismatic coupling between the two.

This allows screwing the elongated screw 23 more or less tightly and, therefore, adjusting both the longitudinal position of the second pedal crank 7, and the compressive force adapted to retain in a pack the elements positioned between the two pedal cranks. The adjustment of the longitudinal position of the second pedal crank 7 implies the adjustment of the distance between the pedal cranks themselves.

This distance is called "q-factor" and is variable depending on the type of bicycle.

Advantageously, between the tube 2 and the pedal cranks 6, 7 are inserted interposition elements 40 adapted to ensure the contact between the elements interposed between the two pedal cranks when the distance between the two (q- factor) is greater than the length of the tube itself.

This way it is possible to adapt the hub 1 to different types of bicycles having different "q-factors" by simply replacing the interposition elements 40 with others of suitable dimensions.

Still according to the invention, the hub 1 comprises locking means 30 of the second pedal crank 7 in the aforementioned longitudinal position.

In particular, the locking means 30 comprise a pair of gripping elements 31 formed on the pedal crank and enveloping the tube 2.

As illustrated in Figure 6, the gripping elements 31 are extensions of the second pedal crank 7 that, in the proximity of the positioning seat 8, envelop the positioning seat 8 itself.

The gripping elements 31 are associated with a tightening element for simplicity not shown in the figures, adapted to mutually approach the gripping elements themselves so as to grip the second end portion 12 housed in the positioning seat and, therefore, to allow the fixing of the longitudinal position of the second pedal crank 7 and the aforementioned shrink-fit friction.

In particular, each gripping element 31 comprises a median pin 32 having a passage 33 intended to let the tightening element pass through.

The passages 33 of each median pin 32 are substantially aligned to allow the insertion of the tightening element.

The tightening element can be of the type of an Allen screw, but alternative solutions cannot be ruled out.

The operation of this invention is as follows.

The first positioning system 15, 18 allows the mounting of the first pedal crank 6 on the tube 2. The first end portion of the tube 2 is associated with the positioning seat 8 of the first pedal crank 6 through the insertion of the positioning elements 11, 13 in the seat itself.

The first pedal crank 6, this way, is positioned in a predefined angular position. The locking of the first pedal crank 6 in such a position is achieved through the cone-on-cone coupling of the coupling element 15 and through the screwing of the first locking element 18 in the coupling element itself.

The forces exerted by such screwing, together with the cone-on-cone coupling, lock the pedal crank in the predefined angular position.

The second positioning system 22, 23, on the other hand, allows the mounting of the second pedal crank 7 on the second end portion 12 of the tube 2.

The angular position of the second pedal crank with respect to the axis 5 of the tube 2 is determined by the alignment of the second positioning element 13a with the locator element 27.

The locking of the second pedal crank 7 in the aforementioned angular position is made by means of the insertion of the second locking element 22.

The particular shape of the second insertion body 24 and, especially, of the second locking head 25, ensures the prismatic coupling between the pedal crank itself and the tube 2, thus preventing relative rotations between the two.

The connecting element 23, on the other hand, allows the adjustment of the longitudinal position of the second pedal crank 7, in addition to ensuring the holding of the hub 1 and of the other elements associated with it in a pack.

The elongated body 23a, in fact, being screwed to the connecting seat 21 of the first locking element 18, transmits a longitudinal force along the elongated body itself which tends to bring the second pedal crank 7 closer to the first pedal crank 6.

The coupling between the second locking head 25 and the positioning seat 8 of the second pedal crank 7 allows the connecting element to rotate and, therefore, to be screwed or unscrewed for the adjustment of the longitudinal position of the pedal crank itself.

The second pedal crank 7, therefore, is subjected to a force which brings it closer to the first pedal crank 6. This way, the elements interposed between the two pedal cranks (tubular casing 3, bearings 4, sprocket wheel 9) are compressed and, consequently, their stability is facilitated.

The longitudinal position of the second pedal crank 7 is fixed through the locking means 30.

In particular, by screwing the tightening element, the gripping elements 31 are approached to each other thus creating a gripping effect of the elements themselves on the tube 2.

This manner the second pedal crank is retained in the longitudinal position determined with the screwing of the connecting element 23.

It has in practice been found that the described invention achieves the intended objects and the fact is particularly stressed that the devised hub is resistant to the stresses acting on the pedal cranks during pedaling.

The pedal cranks described above, in fact, optimize the ratio between resistance and lightness thanks to the combination of the inner reticular structure, which is light and flexural resistant at the same time, and the carbon fiber casing, which is light and also torsion resistant.

The hub devised is also quick and easy to install and adjust.

The various components of the hub, in fact, are easy and user-friendly to assemble.

The adjustment of the positions of the pedal cranks, in particular, is particularly simple.

The first and the second positioning system, in fact, comprise components and elements particularly easy to assemble.

In the first positioning system, for example, the coupling element is inserted in an user- friendly manner in the tube, as well as the first locking element is easily inserted into the positioning seat.

The devised hub also ensures high stability and high holding of the various elements associated therewith, both thanks to the effect of the shrink- fit friction, and to the screwing of the various elements, in particular of the second connecting element.

The action of the second connecting element, in fact, facilitates the holding of the pack assembly of the pedal cranks and of the components interposed between them.

The through hole of the coupling element facilitates such action, thus increasing the surface area available for the screw-nut screw coupling between the threaded element and the connecting element.

The devised hub for bicycles, finally, can be used with flexibility on different models of bicycles, since it does not have any particular characteristics of a bicycle model rather than another, but has characteristics adaptable to any model, in particular thanks to the possibility of the longitudinal adjustment of the second pedal crank.

The hub described, in fact, does not have a fixed "q-factor" but allows an adjustment of such a parameter thanks to the longitudinal positioning of the second pedal crank and thanks to the use of interposition elements.

Claims

1) Hub (1) for bicycles comprising:

at least one rotation shaft (2) installable on a frame of a bicycle, on which a group of bearings (4) is mounted which are able to allow the rotation of said shaft (2) around an axis (5) of rotation;

at least one first pedal crank (6) and one second pedal crank (7), associated with said shaft (2) for setting said bicycle in motion;

characterized in that said pedal cranks (6, 7) comprise:

an inner reticular structure (34);

- an outer casing (35) enveloping at least partially said inner structure (34) and made of a composite material of carbon fiber.

2) Hub (1) according to claim 1, characterized in that said inner structure (34) comprises two running elements (36) and a plurality of diagonal elements (37) bound to one another and to said running elements (36) to define triangular cavities (38) in said inner structure (34).

3) Hub (1) according to one or more of the preceding claims, characterized in that at least one of said triangular cavities (38) is of the type of an isosceles triangle.

4) Hub (1) according to one or more of the preceding claims, characterized in that said inner structure (34) is made of Ergal.

5) Hub (1) according to one or more of the preceding claims, characterized in that said shaft (2) comprises at least one tube (2) and said hub (1) comprises: a first positioning system (15, 18) at least partly inserted inside said tube (2) and able to lock said first pedal crank (6) in a predefined position;

- a second positioning system (22, 23) at least partly inserted inside said tube (2), able to lock said second pedal crank (7) in a predefined angular position, and associable with said first system (15, 18) for the arrangement of said second pedal crank (7) in a longitudinal position adjustable along said axis (5); and

- locking means (30) of said second pedal crank (7) in said longitudinal position.

6) Hub (1) according to one or more of the preceding claims, characterized in that said tube (2) is made of a composite material of carbon fiber.

7) Hub (1) according to one or more of the preceding claims, characterized in that said tube (2) has a first end portion (10) comprising at least a first positioning element (11), able to facilitate the positioning of said first pedal crank (6), and a second end portion (12), opposite to said first end portion (10) and having at least a second positioning element (13), able to facilitate the positioning of said second pedal crank (7).

8) Hub (1) according to one or more of the preceding claims, characterized in that said first end portion (10) has an inner flared surface (14) in the shape of a cone narrowing from the inside to the outside of said tube (2).

9) Hub (1) according to one or more of the preceding claims, characterized in that said first positioning system (15, 18) comprises:

a coupling element (15) with a through hole (17) and having an outer surface (16) substantially flared, able to be coupled to said inner surface (14) of said first end portion (10) to define a cone-on-cone coupling.

a first locking element (18) having a first insertion body (19) engageable in said through hole (17) and a first locking head (20) associated with said insertion body (19) and able to abut against said first pedal crank (6).

10) Hub (1) according to one or more of the preceding claims, characterized in that said through hole (17) is internally threaded and said first insertion body

(19) is externally threaded to form with said hole (17) a screw-nut screw coupling.

11) Hub (1) according to one or more of the preceding claims, characterized in that said insertion body (19) comprises a threaded connecting seat (21) formed in the opposite position to said first locking head (20).

12) Hub (1) according to one or more of the preceding claims, characterized in that said second positioning system (22, 23) comprises:

a second locking element (22) prismatically insertable in said second end portion (12) to define a prismatic coupling with said second pedal crank (7) for locking the latter in said predefined angular position;

a connecting element (23) inserted in said tube (2) and associated with said connecting seat (21). 13) Hub (1) according to one or more of the preceding claims, characterized in that said connecting element (23) is of the type of a threaded screw able to form with said connecting seat (21) a screw-nut screw coupling.

14) Hub (1) according to one or more of the preceding claims, characterized in that said locking means (30) comprise a pair of gripping elements (31) formed on said second pedal crank (7), enveloping said tube (2) and associated with a tightening element which is able to approach said gripping elements (31) to one another.