The present invention relates to a new shaft-hub coupling joint with automatic clearance recovery. The invention is aimed at transmitting a torque between shaft and hub, regardless of its direction and the intensity variations, without respective movements due to the clearance between the same components .

As it is known and strictly in brief, the field of the invention is the one pertaining to the shaft- hub coupling means, for example used for rotary actuator valves. This kind of means (keys, tongues, etc..) are devices able to transmit the rotating movement of a rotating shaft to the hub which is splined thereto. Normally, the mounting tolerances between shaft-tongue-hub allows the complete removal of clearances only increasing remarkably the production and assembly costs, and this is a remarkable disadvantage, in particular for quarter turn actuator valves where the actuator position has to be controlled and known exactly. In order to remove these clearances, the working tolerances of shafts, hubs and keys are to be extremely considered. Moreover, it is needed a forced assembly, with the problems deriving therefrom. Even with fine workings and forced couplings, the - removal of clearances is not guaranteed over time since the elastic deformations due to the forcing action are generally minor or equal to the surface deformations/settlings of the seats and tongue. In such components, the connection of the servomotor with the valve has a shaft provided with a tongue, which has to transmit a very high torque. This kind of joint, for its own working and assembling features, has clearances when coupled.

At the state of the art, there are known solutions to said problem, as for example in the German patent n° DE 4017671 where the clearance between the armature and the shaft is avoided by means of a wedge acting against an edge of the slit provided on the thrust disk which connects the joint and a plane surface of the shaft. Another example is represented by the United States patent n° US 3742264 where 'the rotor is connected to the driving shaft by means of a wedge. The coupling comprises a spring, a wedge with square cross section having a central hole and a threaded end. The threaded end is fixed to the rotor and the wedge is inserted in a corresponding opening of the driving shaft. The rotation pushes the spring elements outward against the inner wall of the driving shaft and allows the rotor assembly to be rigidly fixed to the shaft. Yet, the previous solutions do not solve the above stated problem completely and efficiently, and moreover they cannot be adapted to all the configurations of the shaft available on the market .

Therefore there is the need to overcome the above stated problem minimizing the clearance between the same components, without worsening the working tolerances of the shaft-hub seats and of the same coupling means.

This aim is achieved with the joint object of the present invention, which, by using some prismatic elements, which are suitably dimensioned and positioned on the hub, is adapted to the configurations of the seats thus recovering the whole clearance.

An embodiment' of the present invention is provided with a clearance recovery means comprising a plurality of prismatic elements to be inserted inside a spline in the hub. In this way, the unique portion of the joint modified is the seat of the same hub. The clearance automatic recovery means is in fact accommodated inside this seat. Said clearance recovery means, for its configuration, is insensitive to the combination of "tolerances" of the seats. Moreover, said system can be applied on shafts provided with standard splines for transmission keys.

These and other advantages will be described in detail, with reference to the appended drawings, in which :

Figure 1 is a 3D view of the assembled joint;

Figure 2 is an exploded view of the joint according to the invention;

Figure 3 is a section of the joint showing the scheme of the forces acting on the joint;

Figure 4 is an exploded view of the joint, according to the invention, representing the prismatic elements constituting the clearance automatic recovery means and the forces mutually exchanged by the same;

Figure 5 is an example of the dimensioning of the clearance automatic recovery means and of the hub seat ;

Figure 6 is a scheme relating to the angular dimensioning of the prismatic elements.

Referring to figures 1 and 2, an embodiment of the present invention, the coupling joint comprises a shaft 1 provided with a standard seat 10 for standardized coupling means as for example keys or tongues, a hub 4 provided with at least a spline 2 and a clearance recovery means 11, in turn comprising a plurality of prismatic elements 6, 7, 8.

As it is shown in the exploded view of figure 2, the prismatic elements 6, 7, 8 of the clearance recovery means 11 are assembled in sequence in the spline 2 and are pre-loaded by an integral cover 3, for example by means of a coupling screwed to the hub 4. In figure 3 it is possible to follow the torque transmission between shaft and hub. In fact, the shaft transmits a force by means of the vertical wall 13 of its seat 10 to the prismatic element 7. So, by means of following exchanges of forces between the prismatic elements, the element 6 transmits the force to the hub 4 by means of the vertical wall 9 of its spline 2.

After the assembly, as it is shown in figures 1 and

3, the clearance between the various components, shaft seat - prismatic elements - hub seat, is equal to zero. In fact, as it is shown in figure 4, inside the seat provided on the shaft 10 the first prismatic elements are inserted: two prismatic elements 7 and one pyramidal element 8. The element

8 sets its major base on the base 12 of the seat

10, while the two elements 7 rest along the oblique sides of the element 8, but their bases remain lifted. So, they do not rest on the base 12 of the seat 10 since the sum of their bases and the base of the element 8 is greater than the maximum width of the seat 10 (a>al, see figure 5) . In the following, the two prismatic elements 6 are set on 7. The two outer vertical walls 14 of the two prismatic elements 6 lean on the vertical walls 9 of the spline of the hub 2. Finally, all the elements thus positioned are closed by the cover 3 which, in the inner portion, is provided with a grove 5. On this groove 5, the sum of the bases of 6, 7, and 8 is greater the maximum width of the groove 5 (b>bl, see figure 5), so the upper end of the element 7 does not rest on the groove 5.

Since the various elements are independent with respect to each other, their movement during the closing step is casual, but the final result at the end of the operation is always equal.

In figure 5, there are highlighted two assembly sequences of the clearance recovery means, according to the assembly tolerances.

According to a first assembly sequence, the two elements 6 slide on the elements 7 and contact the vertical walls 9, thus centering themselves. The cover closing guarantees that the elements 6, which cannot expand themselves, go down and cause the elements 7 to slide on 8. The two vertical walls 13 of the elements 7 expand and so press on the vertical walls 15 of the seat of the shaft 10 and the whole will be blocked. It is not important that the element 8 is not centered, the system is independent and moves autonomously to find balance. The element 8 can be shifted to the side but the two elements 7 bring it in balance position again. According to another possible assembly sequence, the elements 7 and the element 8 are moved first to the balance position inside the seat 10. Then, the elements 6 are moved on the 7 to remove the clearance on the hub.

The inventive clearance automatic recovery means achieves its aim thanks to an extremely exactly calculated force distribution.

Analytical considerations in fact demonstrate that considering a ^' generic prismatic element with an angle of 10° between its bases and applying a generic force of 10ON, the same can be decomposed in two forces, a parallel one and a perpendicular one to the inclined plane (table 1, figure 6a) . A different angle (>10) does not compromise the function of the clearance recovery but stresses cover and screws according to the torque transmitted. The force perpendicular to the inclined plane is the force which presses on the surface and interacts with the coefficient of friction, while the parallel force is the one which tends to cause the elements constituting the clearance recovery means 11 go out from their seat. The friction force, i.e. the force opposing to the movement, is calculated multiplying the perpendicular force by the coefficient of friction. If the friction force is greater than the parallel force, the clearance recovery means 11 remains in balance and does not move. If such balance is inverted, it is provided a thrust going out from the seat of the clearance recovery means. Assuming that the coefficient of sliding friction is 0,2 for steel on steel, in such a case it is possible to vary the angle up to over 11° before a balance inversion occurs. So, maintaining the characteristic ^* angle of the generic prismatic element equal to 10° (figure 6b), said prismatic elements 6, 7, 8 do not tend to go out from their own seat, which is a movement also prevented by the outer cover 3.

Also increasing the initial force arbitrarily, however the proportion between the forces is always equal, with the consequent balance maintained by the prismatic elements between each other and with their own seat. By these data it is deduced that the pre-load thrust on the cover 3 does not depend on the transmitted torque (in the example provided it generates a force of 100N) but only by the preload of the cover screws.

Table 1

So, by acting on the pre-load of the screws (possibly also interposing a spring element between screw head and cover) , it is sure that the clearances are removed over time. Also in case of "settling" of the seat-tongue surfaces, the preload of the prism 6, 7, 8 is maintained by the elasticity of the assembly cover 3, screw and spring elements. Therefore, the spring deformation of the assembly screws-cover (and possible spring elements) allows to recover clearances due to a possible micro-deformation of the seats-prisms.