Clutch mechanism for power driven hand tools

A clutch and safety overload for portable, power driven, hand tools is described. The clutch comprises a fixed half and a movable half which are urged into contact with each other more firmly as the load requirements increase. The load torque is fed back to the movable clutch half by a gear driven by the output spindle and which meshes with helical gearing carried by a jackshaft on which the movable clutch half is mounted. In one embodiment the overload safety is part of the clutch itself and involves a rotation of the movable clutch half in response to an overload condition, and against a spring force, which causes it to be displaced axially with respect to the jackshaft and out of engagement with the fixed clutch half. In a second embodiment, the overload safety comprises a mechanical linkage which disengages the clutch halves when the output stroke of the driven tool exceeds a predetermined amount.

FIELD OF THE INVENTION 
This invention relates to improvements in portable tools for cutting, 
pressing, or the like, which utilize a housing containing an electric 
motor, gear assembly, clutch, and drive for the tool, wherein the clutch 
comprises two clutch halves, one of which can be shifted with relation to 
the other against a spring force and can, at the beginning of the work 
stroke, be connected to the other clutch half by a control outside the 
housing. 
DESCRIPTION OF THE PRIOR ART 
An example of a prior art tool of this general type is set forth in German 
Pat. No. 929,343 and in the magazine "Industrieanzeiger, Essen" No. 29, 
Apr. 9, 1954, page 7. This tool is a portable shears, with a worm gear, 
whose worm wheel forms the clutch half which is firmly connected with the 
gear and which cooperates with a disk which acts as a movable clutch half 
and which can be connected from outside of the housing to the worm wheel, 
against a spring force. After the motor is running, the clutch can be 
engaged, so that the motor start-up difficulties can be overcome prior to 
the motor's full output being transmitted to the tool. The clutch can also 
be opened at any time, for example, during the desired working step or 
after the working step, without any time delay in transmitting the action 
to the tool. 
Of course, the output, which can be transmitted to the tool by the motor, 
depends on the coupling pressure with which the two clutch halves are 
urged against each other. Because the coupling force is applied from 
outside the housing and by hand, it is naturally limited. Even if the 
motor had an output greater than the transmissible output, the shears 
could be used only for doing the kind of work where the necessary work 
output is no greater than the transmissible output. In many cases, 
portable tools are required to yield a work output greater than that 
produced by a tool such as the above-described shears wherein the 
transmissible clutch output, which depends on the force applied by the 
operator, is limited. 
SUMMARY OF THE INVENTION 
The primary object of the present invention therefore is to improve the 
prior art portable tool of the kind described above so that its output 
will be independent of the activating force exerted by an operator. 
This problem is solved by utilizing a clutch wherein the two halves are 
urged against each other in proportion to the torque applied to the 
workpiece. A mechanical feedback mechanism is utilized to urge the two 
clutch halves together up to a predetermined limit at which point an 
overload clutch mechanism separates the two clutch halves. Such a clutch 
requires a considerably smaller operating force. To engage the clutch, it 
is merely necessary to overcome a spring force between the two clutch 
halves. 
An axially shiftable shaft, associated with the movable element of the 
clutch, carries outside helical gearing which is engaged by a rotating 
gear to generate an axial force on the shaft, thus pressing the two clutch 
halves together in relation to the transmitted torque. It is desirable to 
use helical gearing at about a 45.degree. angle to avoid binding of the 
gears. This helical gearing can, at the same time, be used in conjunction 
with an overload safety, as will be explained more fully below. 
The overload safety is preferably designed as a part of the operating 
clutch. One clutch half is positioned in an axially shiftable manner, on 
the axially shiftable shaft. A gear rim is attached to the shaft which, 
during engagement of the clutch, abuts against inside tooth gearing 
carried by the movable clutch half. The two sets of gear teeth are 
staggered with respect to each other and are normally retained in this 
condition by a spring attached between the shaft and the movable clutch 
half. When an overload occurs, the excess torque is transmitted to the 
axially shiftable shaft via its helical gearing. This will result in a 
rotation of the movable clutch half if the excess torque is sufficient to 
overcome the spring force. This rotation causes the two sets of gear teeth 
to mesh and the movable clutch half to shift axially with respect to the 
shaft and away from the fixed clutch half. As a result, the two clutch 
halves are separated without any need for manual clutch deactivation. Only 
when the tool is deactivated, is the overload safety reversed so that the 
two sets of gear teeth are staggered with respect to each other and the 
clutch can once again act as an operating clutch. 
In an alternative design of the overload safety, an end stop coupled to the 
movable clutch half is engaged at the end of the working stroke and is 
moved a short distance, whereby it disengages the clutch. In general, the 
end stop should be adjusted so that only one specific tool movement is 
possible, so that, for example, the blades of a cutting tool will move 
only a predetermined distance in order to avoid any damage to the 
workpiece or the tool. 
Both the operating clutch, with load-dependent switch-off, and the 
alternative design wherein the operating clutch is opened by the end stop, 
facilitate a very accurate and reproducible adjustment of the particular 
transmitted working force which controls the desired tool movement 
distance. Both of these embodiments can be housed in a space-saving manner 
in a portable tool housing and can utilize, for example, the housing and 
motor of a commercially available hand power drill.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The portable tool illustrated in FIGS. 1a and 1b is intended for performing 
pressing work, but the concept illustrated may be applied to other types 
of tools as well. Its basic structure consists of a motor housing 1 with 
the motor of a commercially available drilling machine whose power takeoff 
pinion 2 engages a gear wheel 3 of a reduction gear 4. The output of the 
reduction gear 4 comprises spindle 5 with outside screw thread and which 
is housed in a housing part 7 which is flanged on the motor housing 1 with 
screws 6. Spindle nut 8 is threaded internally and mounted on spindle 5. 
It is guided in housing part 7 in a nonrotating but longitudinally 
shiftable manner. The spindle nut 8 abuts against shoulder 9 of a sleeve 
10 which is likewise guided in housing part 7 in a nonrotating and 
longitudinally shiftable manner and which has an outside flange 11 between 
which and a shoulder 12 of housing part 7 there is arranged pressure 
spring 13, surrounding sleeve 10, within housing part 7. 
To the free end 14 of sleeve 10 there is connected, with a tension sleeve 
connection 15, a piston head 17 which is guided in a cylindrical housing 
segment 16 and which has two rollers 18 and 19 that protrude into slots in 
housing segment 16. When spindle 5 is actuated, spindle nut 8 moves 
longitudinally therealong in the direction of rollers 18 and 19, carrying 
with it sleeve 10, piston 17 and rollers 18 and 19. 
At the end of housing segment 16, there is a pressing tool 20 with two 
swingably positioned, double-arm pressing levers 21 (of which only one is 
illustrated) whose arms 22, protruding into the slots in housing segment 
16, are--upon activation of spindle 5--engaged and moved apart by rollers 
18 and 19, so that the pressing tools (not shown) located on the other 
arms 23 of pressing levers 21 will be pressed together. 
In the example illustrated in FIG. 1, the reduction gear 4 comprises a 
clutch with overload safety which is generally labeled 25. The gear wheel 
3, which meshes with the power takeoff pinion 2 of the motor has an 
interior conical surface 26 which forms one clutch half of clutch 25. 
Gear wheel 3 is positioned in a freely rotatable manner on a jackshaft 27 
which also carries the other clutch half 28. Jackshaft 27 is positioned in 
an axially movable manner in housing part 7 and carries helical gearing 29 
which engages a gear wheel 30 that is positioned in an axially immovable 
manner in housing part 7 and which, in turn, is firmly connected with 
spindle 5. 
On the side associated with gear wheel 3, the jackshaft 27 terminates in a 
pin 31 having abutment 32 which engages rod 33. In the embodiment 
illustrated, rod 33 is preferably a traction rod which ends in 
juxtaposition to motor switch 34 on motor housing 1, with an offset 35. 
Jackshaft 27 is supported on the housing at its left portion as viewed in 
FIG. 1b by a ball bearing 55. 
The activation of rod 33 by exerting traction on offset 35, closes motor 
switch 34 and the motor is activated. Simultaneously, jackshaft 27 with 
clutch half 28 is shifted sufficiently to the right as viewed in FIG. 
1b--against the action of spring 36 that is arranged between the two 
clutch halves 28 and 26 and via a ball bearing 56 on clutch half 28--that 
the clutch half 28 engages inside conical surface 26 of gear wheel 3 and 
thus closes the clutch, engaging reduction gear 4. In accordance with the 
clutch force, transmitted via rod 33, the motor output can now be 
transmitted via the reduction gear 4 to the spindle 5 and the tool 20. The 
clutch force thus available is set to be sufficient to shift piston head 
17 in the direction of pressing tool 20 so that rollers 18 and 19 engage 
arms 22 of pressing tool 20. 
To activate the pressing tools, a greater work output is required than that 
transmitted from the clutch 25 and this is obtained by the helical gearing 
29 of the jackshaft 27 which applies an axial force to jackshaft 27 via 
gear 30, increasing the coupling pressure of the clutch halves in keeping 
with the desired transmitted output. So long as the transmitted output is 
comparatively small, the clutch can again be opened by correspondingly 
deactivating the rod 33. In this way, using the axial shiftability between 
jackshaft 27 and gear wheel 3, it is possible to interrupt an initiated 
work process prior to the attainment of maximum driving force. Within 
certain limits, it is possible to achieve slipping of the clutch. This is 
advantageous, for example, in applying and lining up the tool. 
To insure that the force applied to the tool does not exceed a 
predetermined limit, clutch 25 contains an overload safety. For this 
purpose, there is attached to the jackshaft 27 a gear rim 37 (FIG. 2) and 
clutch half 28 carries associated inside gearing 38. Clutch half 28 is 
retained on jackshaft 27 by sleeve 39 that is attached thereto and that 
surrounds the gear rim 37. The sleeve 39, which is closed at one end, 
allows a certain amount of axial play between clutch half 28 and jackshaft 
27. The end stops which limit the axial movement of clutch half 28 are 
formed by the front side of the gear rim 37 and the end of sleeve 39. 
Clutch half 28 can be rotated with respect to jackshaft 27 within limits. 
For this purpose, sleeve 39 contains a recess which extends in the 
circumferential direction and through which there protrudes a pin 40, 
which is retained on jackshaft 27 and on whose end there is held a spring 
41 whose other end is fixed to clutch half 28. 
As can be seen in FIGS. 1 and 2, clutch 25 works as an operating clutch so 
long as gear rim 37 abuts against the front side of inside gearing 38 of 
clutch half 28, with the two sets of gear teeth staggered with respect to 
each other. If there is an overload, the axial force transmitted to 
jackshaft 27 by gear 30 via helical gearing 29 rotates clutch half 28 with 
respect to jackshaft 27 and the teeth of gear rim 37 mesh with the teeth 
of inside gearing 38. This also brings about a relative axial shift 
between clutch half 28 and jackshaft 27 which results in the opening of 
clutch 25. The press-on force at the cone of the clutch drops to zero and 
the loaded spindle is released as a result of return rotation. It should 
be apparent that the load-dependent switch-off can be adjusted by suitably 
dimensioning spring 41 which is connected between jackshaft 27 and clutch 
half 28. 
If clutch 25 is opened--either due to the response of the load-dependent 
switch-off or after termination of the work process when rod 33 is 
released--then sleeve 10 of the spindle is affected by pressure spring 13 
which is under tension during the working stroke. As a result of the 
pressure exerted by spring 13, sleeve 10 and spindle nut 8, are shifted in 
the direction of gear wheel 30 until the spindle nut 8 runs into stop 42. 
At the same time, gear wheel 30, jackshaft 27, and clutch half 28 are 
rotated in reverse to their initial positions. This action of spring 13 
becomes effective as soon as reduction gear 4 no longer provides any 
substantial output to spindle 5. 
In the example illustrated in FIGS. 3a and 3b the same reference numbers 
refer to the same parts. The tool illustrated is set up for the attachment 
of a cutting tool not illustrated in detail and for this purpose, housing 
part 7, has abutments 42 and 43 and, at end 14 of sleeve 10, an abutment 
44 which can be moved with sleeve 10. 
Clutch 25 is arranged on the same gear step of the reduction gear 4 as in 
the example according to FIG. 1. But in this case the overload safety is 
not part of the clutch. Clutch half 28 is firmly connected with jackshaft 
27 which is movably positioned in housing part 7. 
A fork 46, which is swingably positioned under the jackshaft 27 at 45, 
wraps around jackshaft 27 and, with a roller bearing 47, is supported on 
the one hand, on the reverse side of clutch half 28 and, on the other 
hand, on a shoulder 49 of jackshaft 27. Above jackshaft 27, the fork is 
flexibly held on a pin 50 which is positioned in an axially movable 
fashion in housing part 7. At the end 51 of pin 50, which faces toward 
motor housing 1 (not shown), there is engaged rod 33 which is guided out 
of the housing and which serves to activate clutch 25. As can be seen, 
force exerted on rod 33 toward the right in FIG. 3b causes fork 46 to 
swing around such that the two clutch halves are pressed against each 
other, against the action of spring 36 which is connected therebetween. A 
further increase in the clutch force is brought about, as described above, 
by the axial force which is introduced into jackshaft 27 via the helical 
gearing 29 and gear 30. 
In order to prevent overload and to limit the spindle movement distance, 
there is provided an end stop 61 for the stroke movement of spindle nut 8. 
This end stop 61 consists of a pot-like structural element which is 
arranged on the end of spindle 5 and whose casing 52 is disposed between 
hollow spindle 5 and sleeve 10 which surrounds spindle 5. The end stop 61 
is attached to rod 53 which is guided through hollow spindle 5 and hollow 
gear wheel 30 and is flexibly connected to fork 46 at 54. The rod 53 is 
supported on end stop 61 with a spring 57. The spring 57 is prestressed 
and prevents the accidental opening of the clutch. 
When spindle nut 8, during its forward movement, runs into end stop 61, it 
carries it and the connected rod 53 along for a short distance against the 
force of spring 57. Simultaneously fork 46 is swung around so that clutch 
25 is opened. This means that no further output is being transmitted from 
gear 4 and the tensioned spring 13, between sleeve 10 and housing 7 is 
released, returning the tool and the spindle to their initial positions. 
The next work operation can then be started by activating rod 33.