Manual hoist with overload preventer

A manual hoist with overload preventer wherein rotation in the winding direction under overload is automatically arrested; however, when an overload develops after hoisting or pinching of a load, unwinding is possible. The apparatus includes an operation ring, and a friction ring and a drive ring both being capable of engaging the operation ring. When the driving ring is turned in the winding direction, the operation ring remains engaged with both the friction ring and the drive ring, enabling the relative rotation of the drive ring and the friction ring. When the drive ring is turned in the unwinding direction, the drive ring and the friction ring are rotated as a unit through the operation ring.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a manual hoisting apparatus of the lever type or 
chain block type. More particularly, this invention relates to a manual 
hoisting apparatus such that the rotation in the hoisting or winding 
direction is automatically precluded under overload and that even when the 
apparatus is overloaded by an external force acting after hoisting or 
pinching of a load, the rotation of a drive ring is positively transmitted 
to a drive shaft to lower or release the load. 
2. Description of the Prior Art 
The conventional manual hoisting apparatus includes the one proposed by the 
present applicant and disclosed in Japanese Unexamined Patent Publication 
No. 60-202093. 
The apparatus described in the above patent literature comprises a load 
sheeve rotatably supported by side plates constituting the body of the 
hoisting device and drive shaft rotatably mounted on said load sheave. 
This drive shaft is extending beyond the side plates supporting the load 
sheave. The portion of said drive shaft which extends from one of said 
plates is formed with a thread. Screwed onto this thread is a shaft 
driving member, to which a force exerting member is further threaded. 
Secured to the other projecting end of said drive shaft is a drive pinion 
which is arranged to drive the load sheave via a reduction gear train. The 
shaft driving member mentioned above has a boss extending towards said 
force exerting member. Rotatably mounted on said boss is a ratchet wheel 
which is flanked by friction disks. The ratchet wheel is engaged with an 
anti-reversal ratchet pawl in such a manner that it is rotatable only in 
the winding or hoisting direction. It should be understood that reference 
to the winding or hoisting direction refers to the direction in which any 
member rotates when sheave 3 is rotating in a winding or hoisting 
operation; conversely, reference to the unwinding direction of movement 
means the direction that any member rotates when the sheave 3 is unwinding 
for lowering its load. 
Further, the above force exerting member carries a manual chain sprocket 
which is pressed by a conical friction ring at a predetermined pressure. 
Thrown on said chain sprocket wheel is a manipulating chain and the load 
sheave is turned in the hoisting direction or the lowering direction via 
said sprocket wheel. 
In the above conventional hoisting apparatus, if one attempts to hoist up a 
load under overload conditions, the torque applied to the ratchet wheel 
through said sprocket wheel, force exerting member and friction disk upon 
pulling of the chain is exceeded by the force pressing the force exerting 
member against the shaft driving member via said drive shaft owing to the 
overload, with the result that said sprocket wheel idles on the conical 
friction ring. Therefore, the hoisting of the overload in excess of the 
rating is automatically arrested. 
To lower the suspended load, the sprocket wheel is turned in the unwinding 
direction to reduce the pressing force acting on the friction disk and to 
thereby rotate the drive shaft in the unwinding direction. 
In the above arrangement, however, in the situation where the hoisting 
apparatus is used for pinching the truck load and the operation is carried 
out within the rating, the load sheave may be subjected to an unexpected 
overload owing to the vibrations of the truck or a sudden displacement of 
the truck load or owing to an external force that may act on the suspended 
load. In such an event, the force applied by the load sheave to rotate the 
drive shaft causes the force exerting member to be pressed hard against 
the friction disk. 
Therefore, even if the sprocket wheel is turned in the unwinding direction 
to drive the load sheave in the unwinding or loosening direction, the 
torque exerted by said friction disk to arrest rotation of the force 
exerting member exceeds the torque applied to said sprocket wheel, with 
the result that the sprocket wheel idles with respect to the conical 
friction ring, thus preventing the unwinding (loosening) rotation of the 
load sheave. Therefore, once such a situation develops, it is 
time-consuming and troublesome for the operator to take the load off. 
BRIEF SUMMARY OF THE INVENTION 
It is a primary object of this invention to provide a novel manual hoisting 
apparatus of the lever type or chain block type which is free of the above 
disadvantages of the prior art apparatus. 
It is another object of this invention to provide a manual hoisting 
apparatus such that the drive wheel such as the sprocket wheel idles to 
automatically stop hoisting of a load. 
It is a still another object of this invention to provide a manual hoisting 
apparatus such that even when it is overloaded by an unexpected external 
force acting after hoisting or pinching of a load, the rotation of the 
drive wheel can be transmitted to the drive shaft via the operation wheel, 
thus permitting an unwinding operation. 
The manual hoisting apparatus according to this invention comprises a load 
sheave, a drive shaft mounted on said load sheave, a shaft driving member 
secured to said drive shaft, an anti-reversal ring rotatable only in one 
direction is rotatably mounted on said drive shaft, a force exerting 
member threaded onto said drive shaft and adapted to press said 
anti-reversal ring firmly against said shaft driving member on rotation in 
the winding direction, a friction ring disposed on the opposite side of 
said force exerting member with respect to said shaft driving member and 
adapted to move in the axial direction relative to said force exerting 
member but be unable to turn in a circumferential direction, a drive ring 
interposed between said force exerting member and friction ring, a biasing 
means interposed between said friction ring and force exerting member and 
adapted to press said drive ring at a predetermined pressure, an operation 
ring disposed rotatably with respect to said drive shaft, said operation 
ring having an engaging means, said friction ring having an engaging means 
which is engageable with said engaging means of said operation ring, said 
drive ring having an engaging means engageable with the engaging means of 
said operation ring, and when said drive ring is turned on the winding 
direction with said engaging means remaining engaged with the engaging 
means of said friction ring and the engaging means of said drive ring, 
said drive ring and friction ring are relatively rotatable whereas when 
said drive ring is turned in the unwinding direction, said drive ring and 
friction ring are rotatable as a unit through said engaging means. 
The other objects and features of this invention will become apparent from 
the following detailed description made with reference to the accompanying 
drawings and from the new matter pointed out in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a load sheave 3 is rotatably supported through 
bearings 4, 4 in the center between side plates 1 and 2 disposed in 
parallel with a predetermined spacing. This load sheave 3 is centrally 
provided with a shaft hole 3a through which a drive shaft 5 is a 
extending. 
Both ends of said drive shaft 5 project outwards beyond the load sheave 3 
and the outer circumference of one projecting end of said drive shaft 5 is 
formed with a thread 5a, a spline 5b and a reduced-diameter thread 5c in 
the order of progressively reducing diameter from the near to the far side 
with respect to said side plate 2. The thread 5a mentioned above is a 
thread having a large pitch. 
Though not shown in the drawings, the other projecting end of said drive 
shaft 5 is connected to a pinion gear with which said load sheave 3 is 
associated for driving through a reduction gear train. 
Threaded on the thread 5a of said drive shaft 5 are a shaft driving member 
6 and a force exerting member 7 in the order mentioned from the near to 
the far side with respect to said side plate 2. 
The shaft driving member 6 has been threaded on said thead 5a as far as it 
goes. The shaft driving member 6 is formed with a boss 6a projecting 
towards said outwardly located force exerting member 7 and a disk portion 
6b around said boss 6a. This boss 6a supports a pair of friction members 8 
and 9 and an anti-reversal ring in the form of a ratchet wheel 10 
interposed therebetween. 
The said ratchet wheel 10 constitutes an anti-reversion wheel capable of 
turning only in one direction. The ratchet wheel 10 and the friction 
members 8, 9 disposed on both sides thereof are pressed against the disk 
portion 6b of the shaft driving member 6 by the force exerting member 7 
juxtaposed with said shaft driving member 6. 
Indicated at 11 is a ratchet pawl pivotally supported by said side plate 2 
which engages said ratchet wheel 10 to permit selective rotation of the 
wheel 10 in the winding direction of the load sheave 3. 
The force exerting member 7 is formed with a first large-diameter boss 7a 
and a second small-diameter boss 7b on the opposite side with respect to 
said shaft driving member 6. As shown in FIG. 8, the first boss 7a is 
circumferentially formed with a plurality of recesses 7c at equal 
intervals. The second boss 7b is formed with a thread 7d. 
Each of the recesses 7c . . . of said force exerting member 7 is engaged by 
one of projections 12b . . . of the conical friction ring 12, with the 
projection 12b projecting inwardly from a through hole 12a of said conical 
friction ring 12. The recesses 7c . . . of said force exerting member and 
the projections 12b are capable of relative movement in the axial 
direction only and are locked against movement in the circumferential 
direction [FIGS. 4 and 5]. 
As shown in FIG. 8, the diameter of the conical friction ring 12 increases 
with an increasing distance from the force exerting member 7 and the 
increased-diameter end of the conical friction ring is formed with a 
cavity 12c. 
A disk spring 13 is set on the second boss 7b of the force exerting member 
is installed within said cavity 12c, with the outer periphery of said disk 
spring 13 abutting the bottom of said cavity 12c. The dish spring 13 is 
secured in position by a nut 15 which is screwed onto a thread 7d of said 
second boss 7b through a washer 14 contacting the inner periphery of said 
dish spring 13. 
At the forward end (the reduced-diameter end) of said conical friction ring 
12, there is interposed a drive gear 16 formed as a drive ring with a 
conical inner surface defining a through hole 16c. The aforementioned dish 
spring 13 presses the lateral surface of the drive gear 16 through said 
conical friction ring 12 towards the force exerting member 7 at a 
predetermined force. 
The pressing force exerted by said dish spring 13 can be adjusted with said 
nut 15. Thus, the washer 14 is held against rotation in a groove 7e formed 
in the second boss 7b of the force exerting member (FIG. 8) and the 
peripheral projections of said washer 14 are bent to engage the plurality 
of recesses. 
The large-diameter end of said conical friction ring 12 is formed with not 
less than one ring-engaging cutout 12d. The cutout 12d is such that both 
sides thereof in the circumferential direction are at substantially right 
angles with the end edge of the ring and reaches into the bore of the 
drive gear 16. 
In contrast, said drive gear 16 is formed with a trapezoidal cutout 16a in 
the position corresponding to the cutout 12d of the conical friction ring 
12. As shown in FIG. 8, this cutout 16a is formed in such a manner that 
its forward side in the winding direction is at substantially right angles 
with the end edge of the ring and the rear side thereof is constituted by 
an inclined wall 16b defining a space expanding towards the end edge. 
Facing the conical friction ring 12 and drive gear 16 is an operation ring 
17 which is provided with engaging means in the form of a projection 17a 
adapted to fit into said cutouts 12d and 16a. 
It is understood that the geometric relation of the projection 17a of said 
operation ring with the cutout 12d of said friction ring and the cutout 
16a of said drive gear may be reversed. 
The operation ring 17 is centrally formed with a circular cavity 17b and a 
through cavity 17c of reduced diameter. This through cavity 17c accepts a 
spring retainer 18 engaged by the spline 5b of said drive shaft 5 and the 
operation ring 17 is free to turn on the outer periphery of said spring 
retainer 18. 
Indicated at 19 is a nut threaded onto the reduced-diameter thread 5c of 
said drive shaft 5. This nut 19 serves to prevent disengagement of said 
spring retainer 18 from the drive shaft 5. 
The aforementioned spring retainer 18 is increased in outer diameter 
towards its outer end and fits into the inner circumferential surface of 
the cavity 17b of said operation ring 17 to form a closed annular space 20 
between it and said operation ring 17. The operation ring 17 engaged with 
the spring retainer 18 is pressed towards the drive gear 16 by a spring 21 
loaded in said annular space 20. 
Disposed as surrounding the drive gear 16 on the circumference of said 
force exerting member 7 and operation ring 17 is an operating lever 22 
which is freely rotatable about the drive shaft 5. 
Indicated at 23 is a switching pawl housed in the operating lever 22. In 
response to the switching operation of a handle 25 secured to a shaft 24 
projecting out from the operating lever 22, this switching pawl 23 effects 
the engagement and disengagement with the drive gear 16 in the winding and 
unwinding directions. 
Thus, FIGS. 1 and 2 show the disengaged state of the switching pawl 23. As 
the handle 25 is turned clockwise from the position indicated by solid 
lines in FIG. 2 to the position indicated by two dot-broken lines in FIG. 
2, the switching pawl 23 is engaged with the drive gear 16 to rotate the 
drive gear 16 in the winding direction as shown in FIG. 3. On the other 
hand, as the handle 25 is turned counterclockwise from the position 
indicated by solid lines to the position indicated by two dots-broken 
lines in FIG. 2, the switching pawl 23 is engaged with the drive gear 16 
in such a manner that the drive gear 16 is rotated in the unwinding 
direction. 
The reference numeral 26 represents a biasing member built into the 
operating lever 22. This biasing member 26 is constantly pressed against 
the switching pawl 23 by a spring 27, whereby the switching pawl 23 turned 
by the handle 25 to a given position is retained in that position. The 
functions and effects of the embodiment are explained below. 
(A) Winding operation within the rated load range. 
The switching pawl 23 is engaged with the drive gear 16 to rotate the gear 
16 in the winding direction and, then, the operating lever 22 is turned in 
reciprocation. Then, within the rated load range, the conical friction 
ring 12 is frictional association with said drive gear 16 revolves 
together with the drive gear as a unit and, further, rotates the drive 
shaft 5 in the winding direction (clockwise direction) through the force 
exerting member 7 in spline connection therewith by the projection and 
recesses 12b, 7c . . . , so that via the gear train not shown, the load 
sheave 3 is turned in the same direction as the drive shaft 5 to wind up 
the load within the rated range. 
(B) Winding operation under overload conditions. 
When the load acting on the load sheave 3 is an overload, an attempt to 
wind up the load by reciprocation of the operating lever 22 results in 
slippage between them as the torque required for driving the drive gear 16 
is larger than the frictional force acting between the conical friction 
ring 12 and drive gear 16. 
Moreover, when the drive gear 16 is rotated by the operating lever 22 in 
the winding direction, the operation ring 17 engaged with the cutout 12d 
of the conical friction ring 12 and the cutout 16a of the drive gear 16 is 
pushed out to the position contacting the lateral surface of the drive 
gear 16 against the biasing force of the spring 21 as its projection 17a 
slides on the inclined side 16b of the cutout 16a (to the right in FIG. 
1), with the result that it is released from the engagement with the drive 
gear 16 as shown in FIG. 7. 
Therefore, even if the operating lever 22 is reciprocated under an 
overload, the drive gear 16 released from the engagement with the 
operation ring 17 does idling with respect to the conical friction ring 12 
to automatically prevent damage to the apparatus due to hoisting of an 
overload. 
(C) Unwinding operation. 
On the other hand, when the switching pawl 23 is switched to the unwinding 
direction and the operating lever 22 reciprocated, the drive gear 16 
engaged by the switching pawl 23 is rotated in the unwinding direction 
(counterclockwise direction). 
When the load on the load sheave is less than the rating, there occurs no 
slippage between the drive gear 16 and the conical friction ring 12 so 
that the rotation of the direction of loosening the force exerting ring 7 
may take place. 
Further, if the load becomes excessive so as to overload the load sheave 
side, this overload causes rotation of the drive shaft and, accordingly, 
the shaft driving member 6, with the result that the drive gear slides on 
the conical friction ring 12. 
Then, the projection 17a of said operation ring 17 engages the 
perpendicular face 16d of the cutout 16a of the drive gear 16 which lies 
in the winding direction. And as the drive gear 16 is thereby rotated in 
the unwinding direction, the operation ring 17 is also rotated in the same 
direction (FIG. 6). 
When the operation ring 17 is out of engagement with the drive gear 16 as 
shown in FIG. 7, the rotation of the drive gear 16 and the consequent 
shift of the cutout 16a to the position facing the projection 17a causes 
the operation ring 17 kept pressed by the spring 21 to move towards the 
drive gear 16. As a result, the projection 17a of the operation ring 17 
engages the cutout 16a of the drive gear 16 as shown in FIG. 6 and 
thereafter, the operation ring 17 is rotated in the same direction as the 
drive gear 16. 
Since the projection 17a of said operation ring 17 has been engaged by the 
cutout 12d of the conical friction ring 12, the rotation of the operation 
ring 17 in association with the drive gear 16 as a unit causes the 
operation ring 17 to drive the conical friction ring 12 engaged by the 
projection 17a in the unwinding direction. 
Therefore, the force exerting member 7 spline-coupled to the conical 
friction ring 12 is shifted away from the friction member 9, thus ceasing 
to press the friction member 9. 
The shaft driving member 6 thus relieved of the frictional engagement with 
the ratchet wheel 10 is turned along with the drive shaft 5 by the load 
acting on the load sheave 3 in the direction of lowering the load 
(unwinding direction). 
The drive shaft 5 is rotated until the force exerting member 7 has pressed 
the friction member 9 again and the load is moved in the unwinding 
direction during the intervening period. 
Therefore, even if the machine is overloaded as an accidental force acts on 
the suspended load which, as such, is within the rated load range, or by a 
rolling vibration of the truck in the situation where the machine is used 
in the loading of the truck, one may turn the drive gear 16 in the 
unwinding direction with the operating lever 22 to shift the suspended 
load downwards or loosen the overload acting on the load sheeve 3. 
It will be apparent from the above description that the present invention 
provides a very useful manual hoist offering the following advantages. 
(1) In hoisting an overload, the drive gear is released from the operation 
ring to idle and thereby automatically stop lifting the load. 
(2) Even if the machine is overloaded by an external force after hoisting 
or tightening of the load, the rotation of the drive gear can be 
transmitted to the drive shaft via the operation ring so as to effect 
unloading. 
Thus, as the drive ring is turned in the unwinding direction by 
reciprocating the operating lever, for instance, the operation ring is 
engaged with the drive gear to turn the force exerting member away from 
the friction member, with the result that the load sheave is easily 
rotated in the unwinding or load loosening direction. 
The above explanation pertains to the embodiment wherein the drive ring is 
a drive gear but the drive ring may be a manual sprocket wheel. 
The embodiment specifically described in the foregoing detailed description 
is only intended to illustrate this invention and many changes and 
modifications may be made by those skilled in the art without departing 
from the spirit and scope of this invention which is only delimited by the 
appended claims.