Transmission and torque-limiting joint

A transmission and torque-limiting joint able to disengage the driven member from the driving member upon exceeding a maximum value of the transmitted torque and to allow re-engagement at a lesser value of the relative velocity, with cooperating recesses (5) and sliders (20); the sliders (20) are wedge-shaped so as to cooperate with pairs of shaped pads (10) urged towards one another by springs (12).

DESCRIPTION 
The subject of the invention is a coupling, that is to say a transmission 
and torque-limiting joint able to disengage the driven member from the 
driving member upon exceeding a maximum value of the transmitted torque 
and to allow re-engagement at a lesser value of the relative velocity, one 
of the two members being outer and the other inner. 
An objective of the invention is to produce the joint in such a way that 
the region around the axis of rotation is unencumbered and hence available 
for elements of the transmission. Another objective is to produce a joint 
which lends itself to many different applications, and which consists of 
several units which are identical but capable of varying performance. 
These and other objectives will become apparent from the text which 
follows. 
According to the invention, on the inner surface of the outer members 
receptive recesses are provided; in the inner member at least two 
tangential seats are provided, each extending orthogonally to a radial 
direction and lying parallel to a plane orthogonal to the axis of rotation 
of the joint; in correspondence with each of said tangential seats, a 
radial glide seat is formed extending between the periphery of said inner 
member and the tangential seat; in each of said tangential seats, two 
opposed pads can glide, elastically urged towards one another and having 
opposing surfaces with receptive symmetrical shapings; in each of said 
radial glide seats, a slider with a wedge-shaped inner profile can move, 
able to glide centripetally so as to penetrate between the two pads, thus 
parting them, when the elastic urgings acting on said pads are overcome; 
the slider exhibits a shaped outer profile able to cooperate with one or 
the other of said receptive recesses of the outer member. Said outer 
profiles of the wedge-shaped elements and said receptive recesses of said 
outer member are able to cooperate so as to transmit a torque between said 
two members, inner and outer, and to generate a centripetal thrust on the 
wedge-shaped element, which thrust increases with the increase in the 
transmitted torque, such as to cause the separation of the two pads with 
the aid of the wedge-shaped profile of the slider and of the centripetal 
movement of the slider such as to free the latter from the recess in which 
it was captive; the reverse movements with the aid of the elastic urgings 
on the pads being obtained after a reduction in the relative speed between 
said two members, driving and driven. 
The tangential seats of the inner member are separated from the axis of 
rotation of the members of the joint, leaving available the space around 
said axis of rotation. 
The sliders can extend plate-like so as to glide in glide seats with plane, 
parallel walls. Alternatively the sliders can be turned, with active 
chamfers and with anti-rotation keys or pins. 
According to an advantageous embodiment, the wedge-shaped profile of the 
sliders extends with two opposed intermediate surfaces having a dihedral 
of lesser aperture, two opposed end surfaces having a dihedral of greater 
aperture and defining the ridge of the wedge, and another two opposed 
surfaces also having a dihedral of greater aperture; correspondingly said 
opposing surfaces of the pads have shapings with one or two opposed 
intermediate regions defining one or two portions of a dihedral of the 
same aforesaid greater aperture, followed on opposite sides by regions 
defining one or two portions of dihedrals having the same abovementioned 
lesser aperture. 
In order to obtain effective behavior upon freeing and after freeing 
through excess torque transmitted between the two members of the joint 
there is provision that: the recesses of the inner surface of the outer 
member exhibit a first substantially radial flank, a bottom running 
substantially in correspondence with said inner surface, a second inclined 
flank, and a junction between said second inclined flank and said inner 
surface of the outer member; and that the shaped outer profile of the 
sliders exhibits correspondingly a first substantially radial flank, an 
end surface running substantially in correspondence with said inner 
surface of the outer member, a second inclined flank like that of the 
recesses and a junction between said end surface and said second flank 
having an orientation substantially corresponding to that of said junction 
of the recesses; and said two junctions are intended to come into mutual 
contact during the conditions of freeing and of independent rotation 
between said two members of the joint. 
The invention will be better understood by following the description and 
the attached drawing, which shows a practical non-limiting illustration of 
the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
According to what is illustrated in FIGS. 1 to 7, a joint or coupling is 
illustrated which comprises--in one and the same plane transverse to the 
axis of rotation X--X--three coupling units as shown in detail in FIGS. 1 
and 2 and which provides for the arrangement of the units in two 
transverse planes, so as to obtain an assembly with six units. Shown in 
FIG. 8 is a section similar to that of FIG. 5, but of an embodiment with 
just three units contained in one and the same single transverse plane. 
Indicated generically by 1 and 3 in FIGS. 1 to 7 are an outer member and an 
inner member of a joint or coupling, one of the two members driving and 
the other being driven. Considering in particular FIG. 5, the outer member 
1 is a forked element with a fork 1A of an articulated shaft (and in 
particular a cardan shaft) in which a skirt 1B is welded to the fork 1A 
and constitutes the part surrounding the inner member 3 and hence the part 
outside the member 3; this skirt 1B has, in particular, an inner surface 
1C which is circular cylindrical. Several receptive recesses 5, according 
to FIG. 6 three recesses, extend from said inner surface 1C of the outer 
member 1B, each recess exhibiting (see FIG. 4) a first flank 5A of 
substantially radial extent, a bottom 5B having an extent substantially 
corresponding with that of the inner surface 1C of the skirt 1B, a second 
flank 5C inclined with respect to a radial direction, and a junction 
surface 5E between the second flank 5C and said inner surface 1C of the 
skirt 1B of the outer member 1. 
The inner member 3 has a hub 3A and an axial appendage, with an axial hole 
7 which in the drawing is a through-hole and which has a stretch with 
longitudinal grooved profiles to allow rapid engagement or disengagement 
with a grooved shaft, and with ball-type or other equivalent retaining 
means which are known per se in the art. The hub 3A has three projections 
3B which are delimited by portions of cylindrical surfaces substantially 
corresponding to those of the inner surface 1C of the skirt 1B forming 
part of the outer member. In each of these projections at least one 
tangential seat 9 is made which in practice can be a cylindrical seat with 
its axis lying in a transverse plane with respect to the axis X--X of 
rotation of the joint formed by the two members 1 and 3; in FIG. 5 there 
are two seats 9, whereas in FIG. 8 there is a single seat 9. The seat 9 
extends as a blind hole and is for the most part of circular section. Each 
seat 9 glidingly accommodates two pads 10, which are opposite one another 
with respect to a radial plane passing through the axis X--X. The opposite 
faces 10A of the two pads 10 accommodated in one and the same seat 9 
exhibit receptive shapings which consist of two opposing intermediate 
regions 10B defining portions of a dihedral of relatively sharp aperture 
and which are followed--on opposite sides of the intermediate regions 
10B--by outer regions 10C and regions 10E further in and defining, with 
the corresponding regions of the opposing pad, two dihedrals of mutually 
identical aperture and of lesser aperture as compared with the aperture of 
the dihedral formed by the intermediate regions 10B of the two opposing 
pads 10. From the face opposite the shaped one 10A, the pads 10 exhibit a 
wide seat 10F able to accommodate changeable and/or multiple springs 12 
for determining an elastic exertion on the respective pads 10 towards the 
opposite pad, that is to say an exertion which tends to bring together the 
two shaped surfaces 10A, 10B, 10C, 10E of each of the pads. The springs 12 
of one of the pads 10 react on the closed bottom of the seat 9 and the 
springs 12 of the other of the pads 10 react on a bearing 14 introduced 
into the seat 10 and held therein by a plug means 16 or the like, to allow 
the fitting of the components accommodated in the seat 9. 
Each of the projections 3B of the inner member 3A exhibits a radial glide 
seat 18 (FIGS. 1 and 2) which is defined by two plane walls lying in 
geometrical planes orthogonal to the axis of the corresponding seat(s) 9 
formed in the relevant projection 3B. The radial glide seat 18 can be 
recessed using suitable tools and the seat 18 interferes with the 
corresponding seat(s) 9. A plate-like slider 20 which is shaped with an 
inner profile generically indicated by 20A can glide in a radial direction 
in each radial glide seat 18. This inner profile exhibits (seen in 
particular in FIG. 4) two opposite intermediate surfaces 20B with a 
dihedral of lesser aperture, two opposite end surfaces 20C with a dihedral 
of greater aperture and defining the ridge of the wedge, and another two 
opposite surfaces 20E with a dihedral of greater aperture identical to 
that of the dihedral of the surfaces 20C; the inclinations of the surfaces 
with dihedral 20B correspond substantially with those of the surfaces 10E 
and the inclinations of the surfaces with dihedral 20C and 20E correspond 
substantially with those of the surfaces 10E and 10C of the pads 10. Each 
slider 20 exhibits an outer profile shaped correspondingly with that of 
the recesses 5 and in particular the outer shaping exhibits a first 
substantially radial flank 20F which corresponds with the first flank 5A 
of the recess 5, an end surface 20G which extends substantially in a 
manner corresponding to the extent of the bottom 5B and of the surface 1C, 
a second flank 20H inclined substantially like the second flank 5C of the 
recess 5, as well as a junction surface 20L which extends between said end 
surface 20G and said second flank 20H and which has an orientation 
substantially corresponding to that of said junction 5E of the recesses 5. 
It is noted that each seat 18 in the embodiment of FIGS. 1 to 6 extends in 
the projection 3B in which it is made in order to interfere with two 
flanking tangential seats 9, since the seats 9 are six in total, i.e. two 
for each of the three projections 3B of the inner hub 3, 3A. In the 
embodiment of FIG. 8 the inner hub 3A is narrower and only one trio of 
seats 9 is provided, one for each of the projections 3B. 
In either of the versions indicated above there is provision for the hub 3A 
of the inner member 3 to be held by a discoidal cover 22 (FIGS. 5 and 8) 
applied to the end of the cavity defined by the skirt 1B. Suitable 
leaktight linings such as 24 and 26 will be provided in order to ensure 
lubrication inside the cavity defined by the skirt 1B, for the operability 
of the components of the above-described joint and the operation of which 
is explained hereinbelow; the supply of lubricant will be ensured by 
suitable lubricators such as 28. 
Irrespective of the embodiment, it should be observed that the central part 
of the hub of the inner member 3 remains available as space which can be 
used for the mechanics of the joint, such as the through seat 7 with 
mating grooved profiles, or the like which may be required for the 
application to which a torque-limiting joint according to the invention is 
applicable. 
In the torque transmission position, the various elements of the joint or 
coupling are arranged as shown in FIGS. 1 and 6. The two pads 10 are 
adjacent, with the surfaces 10A in contact or almost in contact with each 
other, with the aid of the elastic exertion imposed by the springs 12. The 
sliders 20 are moved in the centrifugal direction, i.e. in the direction 
of the arrow FY of FIG. 1 and become housed in a corresponding recess 5. 
Therefore the flanks 20F and 20H come substantially into contact with the 
flanks 5A and 5C, the end surface 20G ends up opposite the bottom 5B and 
the wedge surfaces 20C correspond with the opposing intermediate surfaces 
10B of the adjacent pads 10. Transmission occurs through the thrust 
between the flanks 5C and 20H, from the driving member to the driven 
member which can either be the inner or outer one. When the resisting 
torque, which is overcome by the torque transmitted as stated above, 
exceeds a certain value, a thrust is determined between the inclined 
surfaces 20H and 5C, through which a thrust in the centripetal direction 
(i.e. in the direction opposite to the arrow FY) is determined on the 
sliders 20, and the wedge consisting of the surfaces 20C of the end 20A of 
each slider 20 tends to urge the two pads 10 in a direction such as to 
part them against the action of the respective antagonist springs 12. When 
the resisting torque reaches a predetermined limit, i.e. when the driving 
torque exceeds a certain limit, the thrust in the direction opposite to 
the arrow FY, i.e. the centripetal thrust on the sliders 20, is such that 
it overcomes the elastic reaction of the springs 12 causing the pads 10 to 
separate until each unit among those described by the position of FIG. 1 
is made to reach the position of FIG. 2, in which the slider 20 has 
penetrated with a centripetal movement causing the parting of the pads 10 
and the bearing of the wedge surfaces 20E against the wedge surfaces 10B, 
as is clearly visible in FIG. 2; under these conditions the end surfaces 
20G of the sliders 20 are in alignment with the inner surface 1C of the 
skirt 1B of the outer member and the angular mating between the two 
members 1 and 3 ceases and hence it is possible to obtain relative angular 
gliding between the two members, as shown by the offset between the 
sliders 20 and the recess 5 which is illustrated in FIG. 2. Thereby the 
freeing of the two members of the joint or coupling is obtained, as well 
as a relative and relatively very fast rotation, whereby the sliders 20 do 
not tend to penetrate again into the recesses 5 which come into 
correspondence with the aforesaid sliders, until such time as this 
relative angular movement diminishes in speed; the tendency for the 
sliders 20 to penetrate into the recesses 5 is determined by the 
centrifugal components, i.e. those in the direction of the arrows FY, 
which the pads 10 exert on the sliders 20 through the effect of the 
elastic thrust of the springs 12 across the contacting surfaces 10E and 
20B which define dihedrals of relatively limited aperture. With a high 
relative speed between the two members 1 and 3, when a slider 20 passes in 
front of a recess 5 there is at most a slight impact between the surface 
of the junction 20L and the surface of the junction 5E and hence the 
slider (see FIG. 15) does not have time to penetrate into the recess 5 and 
continues its movement and passes over the aforesaid recess 5; this takes 
place until such time as the relative tangential speed between the two 
members 1 and 3, i.e. between the projections 3B and the inner surface 1C 
of the skirt 1B, diminishes to the point where the centrifugal thrust in 
the direction of the arrow fy on the sliders 20 is sufficient to cause the 
sliders 20 to penetrate again into the recesses 5, so as to return from 
the position of FIG. 2 to the position of FIG. 1; this diminution in the 
relative speed can also be such as to reach the condition of rest or 
anyway of near-equality between the speed of the two members. Particularly 
noteworthy operation of the torque-limiting coupling is thereby obtained, 
aimed at the dynamical requirements sought or desired of these 
contrivances. 
By varying the number of units like those illustrated in FIGS. 1 and 2--for 
example two or three or four or multiples of two or of three or of four, 
for example four, six, eight--it is possible to obtain a wide range of 
different dynamical effects. Further possibilities of variations within 
the scope of the same morphology of the driving and driven members of the 
joint can be obtained by modifying the characteristics of the elastic 
thrusts of the springs 12, by substituting one spring by another, 
respectively adding or removing coaxial helical springs to or from the 
seats 10F of the pads 10. Variations in the characteristics of a joint can 
also be obtained by varying the inclination of the flanks 5C and 20H 
respectively by varying the inclinations of the surfaces 10E, 10B, 10C and 
the surfaces 20C, 20B, 20E, to obtain a variation in the radial components 
acting on the sliders 20 in the positions shown in FIGS. 1 and 2 
respectively. 
Comparing FIGS. 5 and 8 it is noted that with the same types of components 
it is possible to obtain two different joints, with three units and with 
six units respectively, arranged in two planes transverse to the axis X--X 
of the joint or coupling. 
In FIGS. 1 to 8 an application is envisaged in combination with a cardan 
articulation of a transmission shaft for example for telescopic 
transmissions which are customary in the art of agricultural machinery or 
the like. Applications may be varied; in FIGS. 9 et seq. a few of the 
possible versions are illustrated. In FIGS. 9 and 10 the combination of a 
joint with three or six units like those shown in FIGS. 1 and 2 is 
envisaged, for a toothed sprocket wheel or alternatively for a toothed 
gear wheel. In FIG. 11 the application of a contrivance like that of FIGS. 
9 and 10 at the input or at the output of a transmission gearbox, 
illustrated generically, is shown. In FIGS. 12 and 13 the application of a 
joint or coupling according to the invention to a conical ring gear in a 
box for an angle transmission is shown. In FIG. 14 an embodiment is shown 
in which four units are arranged complanate, i.e. with the axes of the 
tangential seats of the four seats lying in the same plane orthogonal to 
the axis of rotation of the cone; this arrangement can be doubled by 
arranging another four units in another transverse plane. 
It is to be understood that the drawing shows merely an illustration given 
solely by way of practical demonstration of the invention, it being 
possible for this invention to vary in form and in arrangement without 
however departing from the scope of the concept underlying the aforesaid 
invention. 
The possible presence of reference numerals in the attached claims has the 
purpose of facilitating the reading of the claims with reference to the 
description and to the drawing, and does not limit the scope of the 
protection represented by the claims.