Overload coupling or clutch

An overload clutch or coupling includes a hub section connected to one drive element and a housing connected to another drive element. Plungers are fitted in sockets in the housing such that the shank portions of the plungers project from one side of the housing and conical end faces project from the other side of the housing where they engage with plunger seats on the hub. The hub has pull pin sockets that receive spring-biased pull pins and apply a force to a pressure plate that acts on the projecting shank portions of the plungers to maintain them in the plunger seats. The plungers are displaced from the seats when the torque between the hub and housing exceeds the maximum torque to be transmitted by the coupling or clutch. The housing can slide along the plungers to accommodate floating movement between the driven and driving parts of the clutch or coupling. A keeper plate is attached to the hub to retain the housing against such floating axial movement when desired. A pinion gear carried by a clamp ring attached to the hub meshes with a hub gear for index positioning.

BACKGROUND OF THE INVENTION 
This invention relates to a coupling or clutch embodying a construction of 
parts to prevent an overload to the transmission of torque in a drive 
train. More particularly, the present invention relates to such a clutch 
or coupling of a detent-type wherein plungers are slideably supported in a 
housing part to engage with seats in a hub part under the force of 
spring-biased pull pins supported by the hub part to deliver a resilient 
force to the drive plungers via a pressure plate. When desired, axial 
floating between machine elements can be accommodated by sliding movement 
between the housing and hub of the clutch or coupling as well as a geared 
phase adjustment between the housing and hub. 
Various designs of a clutch or coupling used for an overload 
torque-limiting function are known in the art. In U.S. Pat. No. 3,924,421, 
for example, a cam plate is mounted on a driving member and a driven 
member is connected to a cam follower on a pivot lever. The follower 
engages with a seat in the cam under an applied force by a spring acting 
on the lever. The cam follower moves from the seat of the cam when an 
overload occurs whereby the driving member rotates relative to the driven 
member. The cam follower and cam are located in a lubricant-filled cavity 
formed in a housing which is supported by anti-friction bearings on the 
driven and driving members. 
In U.S. Pat. No. 3,282,387, there is disclosed a detent-type overload 
clutch having buttonhead plungers engaged with compression springs 
arranged so that the buttonhead portions of the plungers will move out of 
conical seats when an overload occurs. The conical seats are formed in a 
wear plate that abuts against one side of a driven member and coupled 
thereto by a key or dowel pin. The opposite side of the driven member is 
engaged by a flange. A detent support plate is connected to the flange by 
bolts. The detent support plate is connected to a driving member such as a 
motor. The force of the springs acting on the buttonhead plungers is 
applied by the flange to a broad surface area of the driven member. The 
frictional engagement between the flange and the driven member contributes 
to the torque-transmitting ability by the clutch. The maximum torque the 
clutch will transmit before disengagement takes place can be changed by 
changing the spring force and will vary with a change to the coefficient 
of friction between the flange and driven member due to temperature, 
humidity, deterioration of the friction surfaces and the like. Thus, 
erratic changes occur to the value of the maximum torque at which the 
clutch transmits before disengagement takes place. A detent clutch of this 
type cannot accommodate relative axial movement between the machine 
elements to which it is connected. When the possibility of axial movement 
is excluded by the design of the clutch, it must accommodate forces in an 
axial direction. These forces are applied in such a way to alter the 
spring pressure and adversely affect reliance on friction. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an overload coupling or 
clutch in which a spring force is self-contained within one part of the 
clutch or coupling to retain drive plungers carried by the other part of 
the clutch or coupling against seat surfaces carried by the first of the 
coupling or clutch parts until the transmission of a maximum torque is 
exceeded before disengagement takes place. 
It is a further object of the present invention to provide an improved 
overload clutch or coupling embodying a design wherein driven and driving 
parts are free to move due to an axially-directed thrust by a 
self-contained arrangement of spring-biased pull pins separate and apart 
from detent plungers. 
It is a still further object of the present invention to provide an 
overload clutch or coupling wherein driven and driving parts can float in 
an axial direction with respect to the rotational axis of the machine 
elements to which they are connected without upsetting or changing the 
maximum torque which the clutch transmits before disengagement takes 
place. 
It is another object of the present invention to provide an improved 
overload clutch or coupling embodying a construction of parts that permits 
the use of common or standard split, tapered bushings for attaching shafts 
to either or both of the driven and driving members as well as flange 
mounting to flat shoulder surfaces. 
It is a still further object of the present invention to provide an 
improved overload clutch or coupling wherein driven and driving parts may 
be used interchangeably whereby either part can be driven or driving. 
More particularly, according to the present invention there is provided an 
overload clutch or coupling comprising a housing having a plurality of 
plunger sockets generally parallel with and radially dispersed about a 
rotational axis about which said housing can rotate, a plurality of 
plungers each slideable lengthwise is one of said plunger sockets such 
that a conical end face on each plunger projects from one side of the 
housing while a shank portion of a plunger projects from the opposite side 
of the housing, hub means having a plurality of plunger seats each aligned 
to engage with the conical end face of one of the plungers, the hub means 
being rotatable about the rotational axis, a plunger plate for engaging 
the shank portions of the plungers projecting from the housing, the hub 
means further having a plurality of pull pin sockets distinct and apart 
from the plunger sockets, a plurality of spring-biased pull pins each 
supported by the hub means in one of the pull pin sockets to engage with 
the pressure plate for directing a torque-limiting force against the drive 
plungers to maintain the conical ends thereof engaged in the seats of the 
hub. 
When desired, the aforementioned hub means is designed to permit rotation 
of the hub with respect to the housing for indexing. For this purpose, the 
hub means includes a mounting hub, gear means on the mounting hub, a hub 
ring carrying the plunger seats for support by the mounting hub, and a 
pinion gear supported by the hub ring to mesh with the gear means for 
rotatably indexing the mounting hub relative to the hub ring. The hub 
means may include a mounting hub having a central bore with a divided side 
wall and fastening means for clamping the mounting hub onto a drive 
element. The housing and the hub means each preferably includes guide 
surfaces for relative floating movement therebetween along the rotational 
axis. Such floating movement can be prevented by the use of a retaining 
plate.

In FIGS. 1-3, there is illustrated an overload clutch wherein a housing 10 
has an annular construction to fit within a counterbore in a hub means 11. 
According to the present invention, either the housing or the hub means 
can be driven. For the purpose of the following description of the 
overload clutch, the housing 10 is considered the driven member and the 
hub means 11 is considered the driving member. The housing 10 has a 
tapered bore 12 to receive split, taperd bushings for attaching a drive 
shaft, not shown, thereto. In place of the tapered bore 12, other 
well-known forms of drive connections can be used without departing from 
the spirit of the present invention. The housing has a central rotational 
axis identified by the reference numeral 13 and a plurality of plunger 
sockets 14 in the form of parallel bored openings dispersed at different 
radii from axis 13, which is best shown in FIGS. 1 and 2, when single 
positioning is required or necessary. Otherwise, the bores can be at the 
same radii. It is preferred, although not essential, to provide an 
anti-friction bearing 15 between the outer edge of the housing 10 and the 
counterbore in the hub means 11. The bearing reduces detrimental effects 
due to friction for determining the maximum torque which the clutch is to 
transmit before disengagement occurs between the housing and the hub 
means. 
According to the present invention, plungers 16 are arranged for 
longitudinal sliding movement in the plunger sockets 14 such that conical 
end portions of the plungers engage in conical end faces or seats 17. The 
end faces are dispersed at same radii at sites corresponding to the 
plungers 16. The arrangement of parts is such that the conical end face of 
a plunger will engage only in one of the plunger seats. In the embodiment 
of the overload clutch shown in FIGS. 1-3, three plungers are used, 
although two plungers can be used or more than three can be used without 
departing from the spirit of the present invention. The plunger seats are 
formed in a flange section 18 which is joined to a hub section 19, both of 
which form part of the hub means 11. Pull pin sockets 21 are disposed 
concentrically about the rotational axis 13 at spaced-apart locations 
about the peripheral edge portion of the hub section 19. Six pull pin 
sockets are shown in FIG. 3. In each socket, there is a pull pin 22. A 
compression spring 23 surrounds a shank portion of a pull pin to impose a 
biasing force to an enlarged head portion 22A of the pull pin. The spring 
in each socket 21 seats against an end wall in the hub section. The pull 
pins have threaded end portions that engage with a pressure plate 24 such 
that the aggregate spring force transmitted by the pull pins is applied to 
shank portions of the plungers that project from the side of housing 10 
which is opposite the side of the housing from which the conical end faces 
of the plungers project. By this arrangement of parts, the force of the 
compression springs is self-contained within the hub means 11 without 
requiring a force path through the housing 10. In other words, the housing 
10 is not clamped to the hub means by application of the force of springs 
23. This eliminates a force factor necessary to overcome a thrust force, 
thus increasing the accuracy and dependability to the selection of a 
maximum torque which the coupling is to transmit. 
The plungers are physically separated from springs which force the plungers 
against seat surfaces. This assures that only the plungers ride on the 
seat surfaces. By providing that the housing fits within the counterbore 
in the hub means guided axial movement is achieved. The use of the 
antifriction bearing 15 minimizes radial friction and eliminates thrust 
friction. A drive output member 25 takes the form of a sprocket wheel 
affixed to the hub means by bolts 26. The hub means may be connected to a 
gear, dial plate or other drive elements by bolts or other forms of 
attachment. In FIGS. 1-3, a keeper plate 27 is shown to prevent relative 
axial sliding movement between the housing and the hub means. The keeper 
plate is attached to the hub means by bolts, not shown. The keeper plate 
can either be discarded or the central bore increased so that the housing 
can slide in the hub means for accommodating axial sliding movement within 
a limit established by the distance which the housing means can slide 
along the plungers between the pressure plate 24 and the flange section 
18. In the embodiment of the present invention shown in FIG. 4, the keeper 
plate is eliminated, whereby the housing 10 can float, i.e., move in a 
direction along the rotational axis toward or away from the hub flange 18. 
Such floating movement occurs without detriment to the operation of the 
overload clutch or coupling of the present invention since the hub merely 
slides along the plungers which are held in the plunger seats by the force 
of springs 23. This force is independent of the position of the housing. 
The embodiment of FIG. 4 further provides for the use of a hub 30 attached 
to the hub section by bolts 31. The hub 30 has a tapered bore 32 to 
receive split tapered bushings for attachment to a shaft or mounting to a 
flat shoulder surface. In FIG. 4, the housing 10, hub means 11, plungers 
16, pull pins 22 and pressure plate 24 have been identified with the same 
reference numerals used previously to identify these parts in FIGS. 1-3 
since their construction and relationship are the same. 
FIGS. 5 and 6 illustrate a further embodiment of the present invention 
wherein an overload coupling includes an arrangement of parts for 
adjusting the phase relation between the driven and driving members to 
which the coupling parts are connected. The same reference numerals are 
used to identify the same parts in the embodiment of FIGS. 1-3 and the 
embodiment of FIGS. 6 and 7. The flange section 18 and hub section 19 of 
the hub means 11 are mounted for rotation relative to a gear hub 33. The 
gear hub forms a mounting hub and has a tapered bore 34 for attachment to 
a shaft by the use of split tapered bushings. The hub gear has an outer 
shoulder surface 35 which seats against a journal surface 36 of hub flange 
18. Hub gear 33 has gear teeth 37 forming a spur gear that meshes with 
gear teeth of a pinion gear 38. The pinion gear is rotatably supported by 
a hub ring 39 attached to the hub section 19 by bolts 41. A squared end 
portion 38A of the pinion gear projects from the ring such that the pinion 
gear can be rotated by means of a suitable wrench whereby hub gear 33 
rotates relative to the ring. The shaft of a machine element to which the 
hub gear 33 is secured is rotatably indexed relative to the shaft of a 
machine element to which housing 10 is secured. After the desired angular 
relationship between hub gear 33 and housing 10 is established, the ring 
39 is clamped to the hub gear. For this purpose as shown in FIG. 5, the 
hub gear 33 is split by a radial saw cut in one wall section and a clamp 
bolt 43 is arranged to span the gap formed by the saw cut and extends into 
a tapped hole in the wall section of the ring. The bolt 43 is torqued to a 
desired extent to clamp the ring to the gear hub. The clamping action is 
such that the teeth of the pinion gear 38 are jammed against the teeth 37 
of the gear hub, thereby preventing relative rotation between these parts. 
To facilitate this clamping action, it is desirable to form a short radial 
saw cut 45 in a ring side wall section which is diametrically opposite the 
saw cut acted on by bolt 33. 
Although the invention has been shown in connection with certain specific 
embodiments, it will be readily apparent to those skilled in the art that 
various changes in form and arrangement of parts may be made to suit 
requirements without departing from the spirit and scope of the invention.