Coupling

A coupling includes at least one thin-walled sleeve which forms an axially extending defining wall of a substantially annular chamber. The chamber is arranged to be supplied with a pressure medium to elastically deform said sleeve in a radial direction into clamping engagement with a surface on an element which is to be connected to the coupling, the shape and dimension of said surface substantially corresponding to the shape and dimension of a surface on the sleeve remote from said chamber. The chamber has extending therefrom a channel arrangement which is arranged to cooperate with coupling-release means which can be activated by relative movement between said surfaces, or by a given torsional deformation thereof, to a state in which pressure medium can flow through said channel arrangement from said chamber to relieve the chamber of pressure acting therein.

The present invention relates to a coupling of the kind which includes at 
least one thin-walled sleeve which forms an axially extending defining 
wall of a substantially annular chamber, the chamber being arranged to be 
supplied with a pressure medium for substantially elastically deforming 
said sleeve in a radial direction into clamping engagement with a surface 
on an element which is to be connected to the coupling, the shape and 
dimension of said surface substantially corresponding to the shape and 
dimension of a surface on the sleeve remote from said chamber. 
Couplings of this kind are previously known from, for example, the Swiss 
Pat. No. 408 552 and the French Pat. No. 1 092 416. 
The object of the present invention is to provide a novel and useful 
coupling of the above kind, which is provided with a safety device which 
requires but a relatively small space and by which the elements connected 
together by said coupling are disengaged one from each other when said 
elements are subjected to an overload. 
To this end it is proposed in accordance with the invention that in a 
coupling of the aforedescribed kind the chamber has extending therefrom a 
channel arrangement which is arranged to cooperate with coupling-release 
means which can be activated by relative movement between said surfaces, 
or by a given torsional deformation thereof, to a state in which pressure 
medium can flow through said channel arrangement from said chamber, to 
relieve the chamber of pressure acting therein. In this way, there is 
obtained a very reliable free-coupling function with the use of but a few, 
inexpensive additional components. 
When the chamber is relatively narrow in its radial direction, at least one 
of the axially extending defining walls of the chamber has arranged in the 
surface thereof facing the interior of the chamber, said grooves 
facilitating the flow of said pressure medium to said channel arrangement 
upon activation of said coupling-release means. 
In this way it is ensured that pressure medium will flow more rapidly from 
the chamber through the channel arrangement than would otherwise be the 
case. 
In the event of an overload on the coupling, with the subsequent activation 
of the coupling-release means, there may still be some frictional heat 
developed by continued relative rotation between said surfaces. To prevent 
damgage to the element and/or the coupling as a result of said frictional 
heat, the pressure medium may be one which has friction reducing 
properties and the channel arrangement may be arranged to open out between 
said surfaces. Alternatively or in addition thereto, at least one 
lubricant pocket filled with a suitable lubricant may be arranged in the 
region between the chamber wall and said surface on said element. 
In one form of the coupling-release means, said means includes a shear pipe 
which communicates with said chamber and which upon relative movement 
between said surfaces will shear, to permit said pressure medium to flow 
from said chamber, thereby relieving the pressure on said elastically 
deformable sleeve. 
Alternatively, the coupling-release means may include a valve which is 
arranged to be opened upon said relative movement between the surfaces or 
upon said given torsional deformation thereof, to permit pressure medium 
to flow from said chamber. 
In accordance with an advantageous embodiment, the coupling-release means 
comprises a further chamber located adjacent said surfaces and arranged to 
contain a medium which will expand when heated by frictional heat 
developed upon relative movement between said surfaces; a plunger acted 
upon by said expandible medium; a closure valve arranged in said channel 
arrangement; and a double-armed lever, each of the ends of which acts on a 
respective one of said plunger and said closure valve. In this embodiment 
the expandible medium which may be a gas, is heated by the frictional heat 
developed by said relative rotation and expands, to displace the plunger 
cooperating with said further chamber. Displacement of the plunger causes 
the lever to pivot and the valve to be opened. 
Activation of the coupling-release means may be effected by activating 
means fixedly connected either to said element or to the coupling itself. 
It will be understood that in the case of the abovementioned embodiments 
when the coupling-release means is activated, the pressure-medium flowing 
from the chamber will pass out of the coupling, and it will be necessary 
to re-fill the chamber before re-coupling the element. To avoid this, the 
channel arrangement may conveniently be a closed channel arrangement which 
communicates with a further chamber having a movable defining wall. The 
further chamber is filled with said pressure medium and the movable wall 
thereof is prevented from moving in the absence of an overload by a 
pivotable lever arrangement having a first lever arm which bears at one 
end against said wall and which acts at its other end on said element via 
a mono-stable second lever arm. When there is no relative movement between 
said surfaces, the mono-stable lever arm is unable to pivot, and hence the 
first lever arm will exert pressure on the movable wall, preventing the 
same from moving. Upon relative movement between said surfaces, however, 
the mono-stable lever arm will be caused to pivot, causing the pressure to 
be relieved on said first lever arm and hence also on said wall, whereupon 
the wall is able to move under the pressure of said pressure medium, to 
enlarge said further chamber, allowing pressure medium to flow from the 
first mentioned chamber thereinto. 
To enable the pressure medium to be re-pressurized when re-setting the 
coupling-release means, the movable wall of the further chamber is 
suitably formed by an externally threaded block which is in meshing 
arrangement with an internally screw-threaded sleeve, which sleeve is 
displaceable together with said block and one end of which abuts said 
lever arrangement. Thus, all that need be done is to unscrew the block 
somewhat in the sleeve, such that the first and second levers can be 
readily reset, whereafter the block is again screwed into the sleeve to 
pressurize the pressure medium.

Those elements in the Figures which coincide or substantially coincide with 
one another have been identified by the same references. 
In FIG. 1 the reference 10 identifies generally a coupling which is 
connected to an element 11, which in the illustrated embodiment has the 
form of a shaft. The coupling comprises an inner part 12 in the form of a 
sleeve and an outer part 13 which surrounds part 12 and which has a flange 
14 on which there can be firmly mounted a further element (not shown) 
which shall be connected to the shaft 11 by means of the coupling 10. The 
parts 12, 13 are tightly connected together at the ends thereof, for 
example, by welding, the space between the connecting locations forming an 
annular chamber 15 which can be connected to a source of pressure medium 
17 via a radial inlet 16. The pressure medium 17, which preferably 
comprises an oil of low viscosity, is compressed in the inlet 16 and the 
chamber 15 by means of a plunger 18 which seals against the walls of the 
inlet 16 and which is fixedly mounted on the inner end of a screw 20 which 
is screwed into a threaded bore 19 in the flange 14. When the pressure 
medium is thus compressed, the sleeve 12 is deformed radially inwardly in 
a manner such that the coupling 10 is positively clamped against the 
surface 21 on the shaft 11 facing the sleeve 12. 
When the coupling 10 is overloaded it will rotate relative to the shaft 11, 
and to prevent the shaft and the coupling being damaged as a result of 
exaggerated friction between the shaft surface 21 and the inside surface 
22 of the sleeve 12, the chamber 15 is provided with a channel arrangement 
or outlet 23 in which there is mounted a member 24 which normally closes 
the outlet but which can be activated to a state in which the outlet is 
caused to be opened and the pressure in the chamber 15 relieved as a 
result of relative movement between the surface 21 and the inside surface 
22 of the sleeve 12. This member 24 is shown to comprise a screw which has 
a hole passing axially therethrough and which is screwed into an outer 
part of the outlet 23. The inner end of the screw 24 sealingly abuts the 
walls of the outlet 23 and carries at its outer end an outwardly 
projecting shear pipe 25 which is closed at its outer end. The pipe 25 is 
accommodated in an axial opening in a collar 26 fixedly connected to the 
shaft 11, said pipe 25 being sheared by relative rotation between the 
shaft 11 and the coupling 10 in a manner such as to allow pressure medium 
to depart from the chamber 15 via the outlet 23 and the bore of said screw 
24. As indicated at 27, the chamber 15 may be provided on its inside with 
axially extending grooves for facilitating and accelerating the flow of 
pressure medium in a direction towards the outlet 23. Further, as 
indicated at 28, pockets for lubricant can be arranged in the region 
between the surface 21 and the sleeve 12 for preventing exaggerated 
friction between the shaft and the coupling when the safety device of said 
coupling is released upon overloading. If the shear pipe 25 is extended 
and the collar 26 arranged at a considerable distance from the coupling 
10, the coupling-release means will also become activated when the shaft 
11 is subjected to a given torsional deformation. 
In the embodiment illustrated in FIG. 2, the inlet 16 is shown connected to 
the pressure-medium chamber 15 via an obliquely positioned passage 29, 
while the outlet 23 extends radially and forms a flared chamber, the 
radially inner end of which is defined by the shaft surface 21, from which 
chamber the pressure medium can pass out between the surfaces 21, 22 when 
the coupling-release means is released. The member 24 of the FIG. 2 
embodiment comprises a valve plug which is sealingly displaceable in said 
outlet. The valve plug is held in the illustrated, sealing position by 
means of a ball 30 which is located between the shaft surface 21 and the 
radially inner end of the valve plug 24. With rotation of the shaft 11 
relative to the coupling 10 as a result of overloading, the ball 30 will 
roll in the peripheral direction of the shaft 11 to a position in which it 
leaves the inner surface of the valve plug 24, such that the valve body 
brings the chamber 15 into communication, via the channel arrangement 29, 
16, 31 and 32, with the radially outer portion of the flared chamber 23, 
so that the pressure in the chamber 15 is relieved. 
In the embodiment illustrated in FIG. 3, the inlet 16 is shown to be 
connected to the outlet 23. Similar to the FIG. 1 embodiment, the member 
24 has a shear pipe 25 arranged in its outer end, said end being of 
conical configuration. The shear pipe rests in a conically shaped shear 
rod 33 which is rigidly connected to a further flange 34 forming part of 
the coupling and being arranged at a considerable distance from the flange 
14. When the coupling is subjected to a given torque, with subsequent 
torsion of the coupling 10 and the shaft 11, which shaft is tubular in the 
illustrated embodiment, the shear pipe will shear as a result of the 
relative movement between the flanges 14 and 34, so that pressure medium 
can depart from the chamber 15 through the channel arrangement formed by 
inlet 16, outlet 23 and the bore of the member 24. Subsequent to the 
coupling being relieved of the pressure therein, said coupling 10 can 
freely rotate on the hollow shaft 11, which shaft can be keyed, for 
example, to an engine shaft. 
In the FIG. 4 embodiment there is arranged in the sleeve 12 a further 
chamber 40 in the form of a channel or pocket which contains an expandible 
substance, such as a gas, liquid or a metal rod having a coefficient of 
linear expansion which is greater than that of the material from which the 
coupling is made. Said substance acts on a plunger 41, which in turn acts 
on one end of a double-arm lever 42. Lever 42 is pivotally mounted on a 
pivot 43, and the other end of the lever acts on a further plunger 44 
which bears against a spring-loaded valve member 45 of a check valve. A 
channel arrangement 46 connects the chamber 15 to a pressure medium inlet 
47. The arrangement is such that when the coupling is overloaded, the heat 
generated by the friction between the surfaces 21, 22 upon relative 
rotation therebetween causes the substance in the chamber 40 to expand, 
whereupon the plunger 41 will be displaced in a manner to pivot the lever 
42 in a clock-wise direction. As it pivots, the lever pushes against 
plunger 44, to move the valve member 45 off its seating, thereby allowing 
the pressurized medium in chamber 15 to flow therefrom, out through inlet 
47 via the channel arrangement 46. 
In the embodiment illustrated in FIGS. 5 and 6 the coupling has a pressure 
medium chamber 15, which is radially defined by two thin-walled sleeves 
12, 13 which are elastically separable to clamp a tube portion 50 against 
the shaft 11 and at the same time to secure an annular member 51 to the 
outer sleeve 13 of the coupling 10. The coupling includes a part-circular 
flange portion 14 such as to exhibit a recess 52 accommodating a lever 
arrangement comprising a double-arm lever 53 pivotally mounted at 54 and a 
lever arm 55 pivoted on one end of lever 53. The lever arm 55 is biassed 
by spring means 56 to a position in which it extends radially towards and 
in engagement with the shaft 11. 
The chamber 15 communicates via a channel arrangement 57 with a further 
chamber 58 having a movable defining wall means. Said wall means comprises 
an internally screw-threaded sleeve 59 which is slidably arranged in the 
flange portion 14 and an externally screw-threaded block 60 in meshing 
engagement with the sleeve 59. As shown, the other end of the lever 53 
bears against one end of the sleeve 59. In the illustrated position of the 
lever arrangement the lever 53 is, because of the position of lever arm 55 
relative to the shaft 11, unable to pivot in a counter-clockwise direction 
to enlargen the chamber 58 by movement of the wall means 59, 60 as a 
result of the pressure of the medium acting thereupon. In the case of 
overloading, however, relative rotation between the shaft 11 and the 
coupling 10 will cause the lever arm 55 to pivot against the action of the 
spring means 56, thereby freeing the lever 53. The pressurized medium 
acting on the movable wall means 59, 60 will then cause the sleeve 59 to 
move axially in a manner to enlargen the further chamber 58, thereby 
lowering the pressure in the chamber 58 so as to relinguish the clamping 
forces on the members 50 and 51. It will be understood that the spring 
means 56 constantly strive to reset the lever arrangement to the 
illustrated position, but are unable to do so because the pressure medium 
resists against axial movement of the wall means 59, 60 inwardly. The 
lever arrangement is reset by unscrewing the block 60 so as to enlargen 
the chamber 58 still further, to an extent such that the force exerted by 
the spring means 56 is able to overcome the pressure exerted by said 
medium. Subsequent to the resetting of the lever arrangement, the block 60 
is screwed into the sleeve 59 to presurize said medium, thereby again 
bringing the coupling into clamping engagement with the members 50 and 51. 
The invention is not restricted to the aforedescribed and illustrated 
embodiments, but can be modified within the scope of the following claims. 
Thus, the chamber 15 can be defined radially outwardly instead of radially 
inwardly as illustrated, by a thin axially extending defining wall when 
the coupling is to be mounted in a bore surrounding said coupling.