ITRE20120070A1 - FORK FOR CARDAN JOINT - Google Patents

Description

DESCRIPTION

â € œFORK FOR CARDAN JOINTâ €

The present invention generally relates to cardan shafts, for example cardan shafts which are used in the agricultural sector to connect the power take-off of a tractor to the power take-off of an agricultural implement pulled by the tractor itself, or carried or semi-carried by the tractor. tractor. More particularly, the present invention relates to the forks with which the cardan joints of the cardan shaft are engaged to the respective power take-offs.

As is known, a cardan shaft generally comprises two cardan joints, of which a first cardan joint is suitable for being coupled to the tractor power take-off, and a second cardan joint is suitable for being coupled to the power take-off of the tractor. implement, which are mutually connected by a shaft, which can be inextensible or telescopic, in order to accommodate the variations in distance between the power take-offs that may occur during maneuvers or due to the roughness of the ground.

Going into more detail, each cardan joint conventionally comprises a cross to which two forks are articulated, of which a first fork is directly fixed to the telescopic shaft and a second fork is adapted to be engaged on the relative power take-off.

To allow this engagement, the second fork comprises a connection hub, which is centrally crossed by a slotted axial cavity adapted to substantially accommodate the power take-off.

The second fork is also equipped with a locking system, by means of which it is possible to axially lock the power take-off in the axial cavity of the connection hub.

A typical locking system generally comprises a latch, for example a cylindrical body, which is slidably received in a respective seat formed in the hub of the fork. Inside this seat, the bolt can slide between a locked position, in which it partially occupies the axial cavity of the fork hub, and an unlocked position, in which it leaves the axial cavity completely free. The bolt is also normally provided with a stem or button which protrudes outside the receiving seat, and with a spring which is inserted on said button and is able to push the bolt towards the locking position.

To engage the universal joint on the power take-off, a user must first press the button to move the bolt to the unlocked position against the action of the spring, then he must insert the hub of the fork on the power take-off and slide it on it, until reaching a position in which the power take-off has a circumferential groove.

When this circumferential groove is substantially coplanar to the bolt, the bolt automatically snaps into the locking position pushed by the spring, partially occupying the groove and therefore axially binding the fork hub to the PTO in a bilateral way.

To disengage the universal joint from the power take-off, the user must press the locking system button again against the action of the spring, in order to return the bolt to the unlocked position, and then remove the hub of the fork from the socket. of strength.

From the above it is clear that these engagement and disengagement operations can be rather difficult, slow and uncomfortable, especially in consideration of the fact that the power take-offs are positioned at relatively low heights (both tractor side and implement side), that the forks are normally enclosed by rigid protections, and that the cardan shafts have a rather high weight.

An object of the present invention is therefore to provide a fork for a cardan joint which can be engaged on the relative power take-off in a simpler, more comfortable and quicker way than in the known art.

Another object of the present invention is to achieve the aforementioned objective within a simple, rational and rather low-cost solution.

These and other objects are achieved by the characteristics of the invention reported in independent claim 1. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

In particular, an embodiment of the present invention makes available a fork for a cardan joint, comprising a connection hub provided with an axial cavity suitable for receiving a power take-off, a bolt having an axis orthogonal to the axis of the cavity and slidingly coupled to the connection hub, so as to be able to slide along its axis between a locking position, in which the bolt partially occupies the axial cavity of the connecting hub, and an unlocking position, in which the bolt leaves the axial cavity of the hub clear connecting means, elastic action means adapted to push the bolt into the locking position, and means for moving the bolt into the release position in contrast with said elastic action means. The fork also comprises a pin having an axis orthogonal to both the axes of the bolt and the cavity of the connection hub, which is slidingly coupled to the connection hub, so as to be able to slide along its axis between an advanced position, in which has a protruding cantilevered end inside the axial cavity of the connection hub, and a rear position, in which said end leaves the axial cavity of the connection hub free, elastic action means able to push the pin into an advanced position, and a locking body integral with the pin and located outside the axial cavity of the connection hub which, when the pin is in the forward position, is able to lock the bolt in the unlocked position and, when the pin is in the rear position, it allows the bolt to move to the locked position.

Thanks to this solution, the bolt remains locked in the unlocked position whenever the fork connection hub is removed from the power take-off, so that each subsequent engagement phase no longer requires the user to manually operate the bolt, but only that the fork connection hub is slid onto the power take-off. In fact, the simple relative sliding of the power take-off in the connection hub will also produce the displacement of the pin towards the rear position and therefore will free the bolt, which can snap into the circumferential groove of the power take-off according to the conventional methods described above. .

According to an aspect of the invention, the means for moving the bolt into the release position can comprise a rod having an axis parallel to the bolt axis, which has an end fixed to the bolt and an opposite free end protruding from a wall of the hub. connection.

In this context, the means suitable for pushing the bolt into the locking position can comprise a spring interposed between said wall of the connecting hub and an abutment element placed at the free end of the bolt stem.

These expedients have the advantage of providing a mechanically rather simple and versatile solution for moving the bolt into the unlocked position.

An embodiment of the invention can in fact provide that the bolt rod can be operated by means of a direct manual intervention by a user, as occurs with a traditional button.

Other embodiments, on the other hand, may provide that the fork also comprises an unlocking device adapted to act on the stem to move the bolt into the unlocked position.

The presence of this additional unlocking device can slightly complicate the mechanism but advantageously allows to dislocate, that is to bring away from the fork, the parts on which the user must act manually to move the bolt into the unlock position, for example it allows to bring them to a more comfortable position to reach.

In this regard, an aspect of the invention provides that said unlocking device may comprise a rocker arm articulated to the connection hub according to a rotation axis orthogonal to the bolt axis, actuation means for rotating the rocker arm in a predetermined unlocking direction. , and means for connecting the rocker arm with the stem, which are adapted to transform a rotary movement of the rocker arm in said unlocking direction into an axial movement of the bolt from the locked position to the unlocked position.

In particular, the means for actuating the rocker can comprise a cable having an end fixed to the rocker and an opposite end equipped with a hooking element, for example with an eyelet adapted to be harpooned with a hook, in order to pull the cable.

The connecting means between the rocker arm and the stem can comprise at least one bracket associated with the outside of the connection hub so as to be guided to slide in the direction of the bolt axis, said bracket being articulated to the rocker arm and being equipped with at least one wall designed to be in contact with the free end of the stem.

These expedients have the advantage of providing a rather simple mechanically solution that allows the bolt to be operated remotely, without having to directly access the rod and without necessarily having to remove the rigid protections that cover the cardan joint.

According to a different aspect of the invention, the fork can also comprise an invitation shank adapted to receive the power take-off, which is coaxially and slidably inserted inside the axial cavity of the connection hub, so as to be able to slide between an extracted position and a retracted position, and elastic action means adapted to push the guide tang towards the extracted position.

This invitation tang basically has the function of providing a reference for aligning the hub of the fork with the power take-off, when the protection that covers the universal joint is very long, to the point that the fork is completely covered and hidden from view.

In particular, the invitation shank can be provided with an element protruding radially towards the inside, which is able to fit together smoothly in one of the grooves of the power take-off.

This protruding element has the advantage of being able to correctly orient the connection hub of the fork with respect to the power take-off.

Finally, other embodiments of the present invention make available a cardan joint comprising the fork described above, as well as a cardan shaft comprising said cardan joint.

Further characteristics and advantages of the invention will become evident by reading the following description provided by way of non-limiting example, with the aid of the figures illustrated in the attached tables.

Figure 1 is a perspective view of a cardan shaft.

Figure 2 is the perspective view of figure 1, in which the cardan shaft is shown without the protections.

Figure 3 is a perspective view showing a PTO shaft fork in engagement position with a respective power take-off.

Figure 4 is the section IV-IV of figure 3.

Figure 5 is the V-V section of figure 4.

Figure 6 is the section VI-VI of figure 4.

Figure 7 is the view of Figure 4 shown in a first phase of the engagement operation on the power take-off.

Figure 8 is the section VIII-VIII of figure 7.

Figure 9 is the view of figure 4 shown in a second phase of the engagement operation on the power take-off.

Figure 10 is the X-X section of figure 9.

Figure 11 is a perspective view of a cardan joint for a cardan shaft according to an alternative embodiment of the invention, and shown with the protection hood.

Figure 12 is a top view of the gimbal of figure 11, shown without the protection hood.

Figure 13 is the section XIII-XIII of figure 12.

Figure 14 is a perspective view of a universal joint for a cardan shaft according to another alternative embodiment of the invention, and shown without the protective hood.

Figure 15 is a top view of the cardan joint of figure 14. Figure 16 is the section XVI-XVI of figure 15.

Figure 17 is the section XVII-XVII of figure 16.

Figure 18 is the perspective view of Figure 14, in which the cardan joint is shown separated from the power take-off and in which the protective hood is shown in cut-away.

Figures 1 and 2 show a cardan shaft 10, which is designed to connect the power take-off of a tractor to the power take-off of an implement pulled by the tractor itself, or carried or semi-carried by the tractor.

The tractor PTO and the implement PTO are structurally similar. As illustrated in Figure 7, each power take-off 11 essentially consists of a splined shaft, which has a chamfer 12 at its end and a circumferential groove 13 in an intermediate position.

As illustrated in Figure 2, the cardan shaft 10 comprises a telescopic shaft 20 at the ends of which two cardan joints are fixed, of which a first cardan joint 30 is generally adapted to be connected to the power take-off of the tractor, and a second cardan joint 40 is generally adapted to be connected with the power take-off of the implement. In other embodiments, the shaft 20 could be rigid and inextensible.

Each cardan joint 30 and 40 comprises a cross member 50 and two forks articulated to said cross member 50, of which a fork 60 adapted to be fixed to the end of the telescopic shaft 20 and a fork 70 adapted to be engaged on the power take-off.

More in detail, the crosspiece 50 comprises a central body 51 from which two pairs of coaxial and opposed pins 52 protrude. The axes of each pair of pins 52 are coplanar with each other and angularly offset by ninety degrees.

Both forks 60 and 70 comprise a connection hub 80 from which two opposing brackets 81 are derived, which are substantially symmetrical with respect to a plane containing the axis of the connection hub 80. Each bracket 81 has an eyelet 82, whose axis is perpendicular to the axis of the connection hub 80 and coincides with the axis of the eyelet 82 of the opposite bracket 81. The eyelets 82 of each bracket 81 are articulated to a respective pair of opposite pins 52 of the crosspiece 50.

As illustrated in Figure 1, an outer covering sleeve, globally indicated with 90, is rotatably coupled to the forks 60, which is able to remain stationary with respect to the rotation of the cardan shaft 10, so as to protect the users from accidental contact with moving parts. In particular, the covering sleeve 90 comprises a tube 91 which coaxially surrounds and covers a portion of the telescopic shaft 20, and a coaxial cup or hood 92 which surrounds and at least partially covers the cardan joint 30 and 40.

As illustrated in Figures 7 and 8, the connecting hub 80 of each fork 70 has an internally grooved axial cavity 71, which is adapted to fit coaxially and to size on the power take-off 11. In other words, the axial cavity 71 has a cross section substantially coinciding with the cross section of the power take-off 11, that is, having a profile comprising an alternation of protruding ribs 72 and grooves 73, which are adapted to slidingly couple respectively with the grooves and with the protruding ribs of the power take-off force The connection hub 80 is also provided with a device for axially locking the power take-off 11 in the axial cavity 71. The locking device comprises a bolt 100, preferably cylindrical in shape, whose central axis X is orthogonal to the Y axis of the axial cavity 71, and is substantially tangent to a circumscribed circumference to the transverse section le of the axial cavity 71 itself. Said bolt 100 is coaxially and slidingly received in a cylindrical seat 105, which is formed in an eccentric lateral portion 87 of the connection hub 80. Said cylindrical seat 105 is open at one end, it passes through one of the grooves 73 of the cavity axial 71, and is closed at the opposite end by a back wall 110.

The bolt 100 is provided with a coaxial stem 115, protruding overhanging, which is slidably inserted to size inside a through hole obtained in the bottom wall 110. The free end of the stem 115 protrudes from the opposite side of the bottom wall 110 and carries an enlarged head 120. A compression spring 125 is inserted on the protruding portion of the stem 115, which is interposed and axially blocked between the enlarged head 120 and the bottom wall 110. In this way, the compression spring 125 constantly pushes the bolt 100 towards a position of complete insertion in the relative cylindrical seat 105, in which it abuts against the bottom wall 110, as illustrated in figures 5 and 6.

Thanks to the arrangement of the cylindrical seat 105, when the bolt 100 is in this position of complete insertion, a portion of its lateral surface partially occupies the axial cavity 71 of the connecting hub 80, transversely occluding one of the grooves 73. In particular, in this position of maximum insertion, the minimum distance between the lateral surface of the bolt 100 and the Y axis of the seat 71 is substantially equal to the radius of the cross section of the power take-off 11, at the bottom of the circumferential groove 13.

Starting from this position of maximum insertion, the bolt 100 can be pushed in the opposite direction to the action of the compression spring 125, making it slide in the cylindrical seat 105 until it reaches a position in which it leaves the axial cavity 71 of the hub completely free. connection 80, as shown in figure 8.

As can be seen in Figure 7, the locking device further comprises a small piston 130, whose Z axis is orthogonal both to the X axis of the bolt 100 and to the Y axis of the cavity 71 of the connecting hub 80. The piston 130 Ã It is positioned on the connection hub 80 next to the bolt 100, between the eccentric portion 87 in which the cylindrical seat 105 is defined and the end from which the brackets 81 protrude. The piston 130 comprises a pin 135, which is slidably and coaxially inserted in a radial through hole which is obtained in the side wall of the connection hub 80, in correspondence with the groove 73 which is occluded by the bolt 100. The pin 135 projects coaxially and cantilevered from a plate 140, which remains positioned outside the connection hub 80. Said plate 140 is coaxially inserted in a cylindrical seat 145, in which it can slide in the direction of the Z axis, which is defined by a bushing 150 welded on the external surface of the connection hub 80, close to the eccentric portion 87 in which the cylindrical seat 105 is formed. In other embodiments, the bushing 150 can be made directly in the molding of the fork 70, i.e. in a single body with the latter. In particular, said eccentric portion 87 has a lateral opening which is closed by the bush 150, so that the cylindrical seat 145 of the plate 140 partially intersects and therefore communicates with the cylindrical seat 105 of the bolt 100. The bush 150 is closed at the bottom by the side wall of the connection hub 80 and above by a top wall. Inside the bush 150 there is also received a compression spring 155, which is interposed between the top wall and the plate 140, so as to constantly push the piston 130 towards the advanced position illustrated in figure 7.

When the piston 130 is in this advanced position, the plate 140 is in contact with the side wall of the connection hub 80 and partially occupies the cylindrical seat 105 which receives the bolt 100. In this way, the lateral surface of the plate 140 It is adapted to stay in contact with the rear end of the bolt 100 which is in the unlocked position, in such a way as to prevent it from moving back towards the locked position. At the same time, the pin 135 protrudes radially inside the axial cavity 71 of the connection hub 80, for a length generally less than the radial dimension of the chamfer 12 which is obtained at the end of the power take-off 11.

Starting from this advanced position, the piston 130 can be moved against the spring 155 towards the retracted position which is illustrated in figure 9. In this retracted position, the pin 135 is completely retracted into the radial hole, while the plate 140 is received in the bushing 150 in a position such as to leave the cylindrical seat 105 of the bolt 100 free, which is therefore free to slide towards the locking position pushed by the spring 125.

In the light of what has been described, the operation of the locking device provides that the bolt 100 is initially in the release position, constrained by the plate 140 of the piston 130 which is in an advanced position (as illustrated in Figures 7 and 8). In this way, the power take-off 11 can be freely inserted into the axial cavity 71 of the connection hub 80, until the chamfer 12 comes into contact with the protruding portion of the pin 135. Continuing with the insertion, the chamfer 12 acts as a cam which transforms the relative axial movement of the power take-off 11 into an axial movement of the pin 135, pushing the entire piston 130 towards the rear position (as illustrated in Figure 9). When the piston 130 reaches the retracted position, the plate 140 releases the constraint of the bolt 100, which is however prevented from moving towards the locking position by the rib of the power take-off 11 which occupies the relative internal groove 73 of the connection hub 80 (as shown in figure 10). The insertion of the power take-off 11 is then continued until the circumferential groove 13 is substantially coplanar with the cylindrical seat 105 of the bolt 100 (as illustrated in Figure 4). In this position, the rib of the power take-off 11 is interrupted, so that the bolt 100 moves with a snap into the locking position pushed by the spring 125. Once this position has been reached, the bolt 100 is transversely engaged in the circumferential groove 13, locking axially the power take-off 11 to the connecting hub 80 bilaterally.

To release the power take-off 11, a user simply has to press the enlarged head 120 of the rod 115 in contrast with the spring 125, until the bolt 100 is in the release position, and then withdraw the power take-off 11 back from the cavity. axial 71 of the connection hub 80. In this way, as soon as the power take-off 11 moves back beyond the pin 135, the piston 130 snaps back into its forward position, pushed by the spring 155, constraining the bolt 100 in the unlocked position, ready to be coupled to another power take-off as described above.

Figure 11 illustrates a variant of the locking system, which allows the user to bring the bolt 100 to the unlocked position without having to access the rod 115 and without having to disassemble the cap 92 of the covering sleeve 90.

In practice, this variant differs from what has been previously described in that it comprises an unlocking device 200 adapted to act on the stem 115 to move the bolt 100 into the unlocked position.

In particular, said release device 200 comprises a bracket or U-bolt 205, which is slidingly coupled to the outside of the eccentric portion 87 of the connection hub 80, so as to be able to slide in a direction parallel to the X axis of the bolt 100. Said stand 205 has in particular a flat wall and two opposite end walls bent at right angles, of which one wall is placed in contact with the free end of the bolt 100 while the other wall is placed in contact with the enlarged head 120 of the stem 115 (see figure 13).

The flat wall of the U-bolt 205 is kept pressed on the eccentric portion 87 of the connection hub 80 by a plate 210, which comprises a portion superimposed on the flat portion of the U-bolt 205 and a portion projecting laterally. The protruding portion is articulated to the connection hub 80, so as to be able to rotate around an articulation axis perpendicular to the X axis of the bolt 100. The superimposed portion, on the other hand, has a slot 215 which defines a fork in which it is received a cylinder 220, which is fixed to the flat wall of the U-bolt 205, so as to be able to transform a rotation of the plate 210 into a rectilinear movement of the U-bolt 205 and vice versa.

The device also comprises a cable 225, for example a rather rigid steel cable, which has an end fixed to the plate 210 by means of a screw placed in an eccentric position with respect to the articulation axis, and a second free end which is fixed a hooking eyelet 230.

As shown in Figure 11, said cable 225 is contained in the hood 92 of the covering sleeve 90, and extends from the plate 210 towards the telescopic shaft 20, so as to bring the hooking eyelet 230 in correspondence with a through hole 235 obtained at the bottom of the cap 92.

In this way, the plate 210 substantially behaves like a rocker arm which can be rotated around its own articulation axis by means of the cable 225, causing a translation of the U-bolt 205 and vice versa.

With this locking device, the engagement phase of the power take-off 11 takes place according to the same methods described for the first embodiment, with the only difference that, when the bolt 100 moves to the locked position, it causes a contextual translation of the U-bolt 205 and therefore a rotation of the plate 210 in a determined locking direction.

To disengage the power take-off 11, a user must rotate the protection 90, until the hooking eye 230 faces the hole 235 of the protection hood 92. At this point, the hooking eye 230 can be grasped by means of a hook tool 240, in such a way as to pull the cable 225 and thus make the plate 210 rotate in an unlocking direction opposite to the previous locking direction. In this way, the rotation of the plate 210 causes a translation of the U-bolt 205 and therefore of the rod 115 and of the bolt 100 towards the release position. Once this position has been reached, the user can remove the power take-off 11 exactly as described above.

Figure 14 illustrates another variant of the fork 70, which makes it easier to engage the power take-off 11 in the connection hub 80, in the event that the protective hood 92 (see figure 18) has an extension such as to completely cover the fork 70 itself.

In practice, this variant provides that an invitation shank 300 is associated with the fork 70, adapted to coaxially receive the power take-off 11. In the example illustrated, said invitation shank 300 comprises a ring 305 having an internal diameter slightly greater than the external diameter of the power take-off 11. The invitation shank 300 further comprises a plurality of guide rods 310, which are fixed cantilevered on the same side of the ring 305, so as to be arranged parallel and circumferentially distributed around the axis of the latter. last. Each of these guide rods 310 is slidably received in a respective channel 315 which extends parallel to the direction of the Y axis of the connecting hub 80, and is formed on the bottom of a groove 73 of the axial cavity 71, so as to do not interfere with the engagement of the power take-off 11.

Thanks to this structure, the guide shank 300 is coaxial with the cavity 71 of the connection hub 80 and is able to slide with respect to the latter between an extracted position, in which the ring 305 protrudes outside the cap. protection 92, and a retracted position, in which the ring 305 is in proximity to the connection hub 80.

In particular, the invitation shank 300 is constantly pushed towards the extracted position (shown in figure 18) by a compression spring 320, which externally wraps the guide rods 310 and is interposed between the ring 305 and the hub. connection 80.

To prevent the guide shank 300 from slipping out of the connection hub 80, a threaded dowel 325 is provided (see figures 16 and 17), which is screwed into a radial hole of the connection hub 80, so to protrude inside a channel 315 which receives a guide rod 310. This guide rod 310 has a slot or recess 330, which is adapted to slidingly receive the protruding portion of the threaded dowel 325 and has a limited extension, in such a way that said protruding portion of the grain 325 does not allow the complete extraction of the guide shank 300.

Finally, the guide tang 300 comprises a pin 335, which protrudes from the inner surface of the ring 305 radially inwards. Said pin 335 is axially aligned with one of the grooves 73 of the internal cavity 71 of the connection hub 80, and has such dimensions as to be able to slide in one of the grooves of the power take-off 11.

Thanks to this solution, before the engagement of the power take-off 11, the invitation shank 300 is in the extracted position, pushed by the spring 320 and blocked by the threaded dowel 325, as shown in figure 18. To engage the power take-off 11 , the ring 305 of the invitation tang 300 is inserted on the power take-off 11. In this way, the pin 335 is slidably received in one of the grooves of the power take-off 11, correctly orienting the cavity 71 of the connection hub 80 with respect to the power take-off 11 itself. Continuing with the insertion, the ring 305 slides on the power take-off 11 until the pin 335 reaches the end of the groove in which it is inserted, after which the guide shank 300 is forced to slide axially with respect to the connection hub 80, towards its retracted position, remaining integral with the power take-off 11. This insertion continues until the connection hub 80 slides onto the power take-off 11 and reaches the position in which the locking device comes into operation .

In this regard, it should be noted that the locking device illustrated in Figures 14 to 18 conforms to the second version described above, and operates in the same way. However, it is not excluded that, in other embodiments, the locking system may conform to the first version described above.

Naturally, a person skilled in the art could make numerous modifications of a technical applicative nature to everything that has been described, without thereby departing from the scope of the invention as claimed below.

Claims (11)

CLAIMS 1. A fork (70) for universal joint (30), comprising a connection hub (80) provided with an axial cavity (71) suitable for receiving a power take-off (11), a bolt (100) having axis (X ) orthogonal to the (Y) axis of the cavity (71) and slidingly coupled to the connection hub (80), so as to be able to slide along its own axis (X) between a locking position, in which the bolt (100) occupies partially the axial cavity (71) of the connection hub (80), and an unlock position, in which the bolt (100) leaves the axial cavity (71) of the connection hub (80) free, elastic action means (125 ) adapted to push the bolt (100) into the locking position, and means (115) to move the bolt (100) into the unlocking position in contrast with said elastic action means (125), characterized in that it comprises a pin ( 135) having axis (Z) orthogonal to both axes (X, Y) of the bolt (100) and of the cavity (71) d and the connection hub (80), which is slidingly coupled to the connection hub (80), so as to be able to slide along its axis (Z) between an advanced position, in which it has a protruding cantilevered end to the inside the axial cavity (71) of the connection hub (80), and a rear position, in which said end leaves the axial cavity (71) of the connection hub free, elastic action means (155) able to push the pin ( 135) in the forward position, and a locking body (140) integral with the pin (135) and located outside the axial cavity (71) of the connection hub (80) which, when the pin (135) is in position forward, it is able to lock the bolt (100) in the unlocked position and, when the pin (135) is in the rear position, it is able to allow the bolt (100) to move to the locked position. A fork (70) according to claim 1, wherein the means for moving the bolt (100) into the unlocked position comprise a stem (115) having an axis parallel to the axis (X) of the bolt (100), which it has an end fixed to the bolt (100) and an opposite free end protruding from a wall (110) of the connection hub (80). A fork (70) according to claim 2, in which the elastic action means adapted to push the bolt (100) into the locking position comprise a spring (125) interposed between said wall (110) of the connection hub (80 ) and an abutment element (120) placed at the free end of the stem (115). A fork (70) according to claim 2, comprising an unlocking device (200) adapted to act on the stem (115) to move the bolt (100) into the unlocked position. A fork (70) according to claim 4, wherein said release device (200) comprises a rocker arm (210) articulated to the connection hub (80) according to an axis of rotation orthogonal to the axis of the bolt (100), actuation means (225) for rotating the rocker arm (210) in a predetermined unlocking direction, and means for connecting (205) the rocker arm with the stem (115), which are adapted to transform a rotary movement of the rocker arm (210 ) in said unlocking direction in an axial movement of the bolt (100) from the locking position to the unlocking position. A fork (70) according to claim 4, wherein said actuation means comprise a cable (225) having one end fixed to the rocker arm (210) and an opposite end equipped with a hooking element (230). A fork (70) according to claim 4, wherein said connecting means comprises a bracket (205) associated with the outside of the connecting hub (80) so as to be guided to slide in the direction of the axis of the latch ( 100), said bracket (205) being articulated to the rocker arm (210) and being provided with at least one wall able to stay in contact with the free end of the stem (115). 8. A fork (70) according to claim 1, comprising an invitation shank (300) adapted to receive the power take-off (11), which is coaxially and slidingly inserted inside the axial cavity (71) of the hub connection (80), so as to be able to slide between an extracted position and a retracted position, and means with elastic action (320) adapted to push the guide shank (300) towards the extracted position. 9. A fork (70) according to claim 8, wherein said lead shank (300) is provided with an element (335) projecting radially inwards, which is adapted to slide together in one of the grooves of the power take-off (11). A cardan joint (30) comprising a fork (70) according to any one of the preceding claims. A cardan shaft (10) comprising at least one cardan joint (30) according to claim 10.