Trigger switch

A trigger switch for hand-held electric power tools in which an actuating arm for actuating a switch mechanism is pivotally supported in a case by way of a pivot shaft pivotally supported by a pair of parallel lateral walls defining the case, and a trigger member having a front end and a pair of lateral flanges is pivotally supported by the case in a coaxial relationship with the pivot shaft by way of the lateral flanges. By securely coupling an extension of the pivot shaft with one of the flanges, the switch mechanism internally accommodated in the case can be actuated by operating the trigger member. Since the switch mechanism is internally accommodated in the case, a considerable saving of space can be accomplished. Since the coupling between the pivot shaft and the trigger member can be accomplished by the extension of the pivot shaft passed through the case by way of a round opening provided in the case, sealing of the switch mechanism can be easily accomplished.

TECHNICAL FIELD 
The present invention relates to a trigger switch for hand-held electric 
power tools. 
BACKGROUND OF THE INVENTION 
Conventionally, a trigger switch for hand-held electric power tools, as 
illustrated in FIG. 4, consisted of a switch unit having a push-button 
member 4 projecting out of a case 3, and a trigger member 1 pivotally 
supported by the case 3 by means of a pivot shaft 2 and adapted to bear 
upon the push-button member 4 when it is actuated or, in other words, 
pulled by a finger. According to this structure, since the push-button 
member 4 projects out of the case 3, and the trigger member 1 acts upon 
the free end of the push-button member 4, it has been difficult to achieve 
a compact design of the trigger switch. Also, the need for a push-button 
switch means a high cost not only for the component parts themselves but 
also for assembling them. Furthermore, since the push-button member moves 
into and out of the case, it has been difficult to achieve a satisfactory 
sealing of the switch mechanism which is coupled to the push-button 
member. Additionally, the use of such a push-button mechanism requires a 
relatively large force to be applied to the trigger member for its 
operation. 
BRIEF SUMMARY OF THE INVENTION 
In view of such problems of the prior art, a primary object of the present 
invention is to provide a trigger switch for hand-held electric power 
tools which is compact in size. 
A second object of the present invention is to provide a trigger switch 
which requires a relatively small force for its operation. 
A third object of the present invention is to provide a trigger switch 
which permits sealing of its switch mechanism to be easily accomplished. 
A fourth object of the present invention is to provided a trigger switch 
which is economical to manufacture. 
According to the present invention, these and other objects can be 
accomplished by providing a trigger switch, comprising: a case 
accommodating a switch mechanism therein and having a pair of parallel 
lateral walls; a pivot shaft extending across the lateral walls and 
pivotally supported by the lateral walls; an actuating arm integrally 
attached to the pivot shaft and adapted to actuate the switching mechanism 
when the pivot shaft is rotated around its central axial line along with 
the actuating arm; and a trigger member having a front end, and a pair of 
flanges extending from either side of the front end in mutually parallel 
relationship and pivotally supported by the casing around a pivot axis 
coaxial with the pivot shaft; one end of the pivot shaft extending 
laterally from one of the lateral walls of the case and integrally coupled 
with one of the flanges of the trigger member. 
Thus, since the switch mechanism is incorporated in the case, a compact 
design is made possible. Since the coupling between the pivot shaft and 
the trigger member can be accomplished by an extension of the pivot shaft 
which may include a part having a round cross section rotatably received 
in a round opening of a wall portion of the case, sealing of the interior 
of the case can be accomplished in a simple manner as compared with a 
conventional trigger switch using a push-button member moving into and out 
of the case. 
The integral coupling between one of the flanges and the extension of the 
pivot shaft may be accomplished by fitting a part of the extension having 
a non-circular cross section into an opening having a complementary shape 
provided in one of the flanges. If the other end of the pivot shaft is 
simply received in a cavity defined in the inner side of the associated 
one of the parallel walls, an even more favorable sealing result can be 
obtained as opposed to the case in which the two ends of the pivot shaft 
are both rotatably received in openings completely passed through the 
lateral walls of the case.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
FIG. 1 shows an embodiment of the trigger switch according to the present 
invention, and FIG. 2 is a front view showing its external appearance. 
A case 11 made of synthetic resin accommodates therein an operation arm 13 
which is securely attached to a pivot shaft 12 rotatably supported by two 
lateral walls of the case 11 and is adapted to be actuated by a trigger 
member 32 pivotally supported by the case 11 in a coaxial relationship 
with the pivot shaft 12 as described hereinafter. The case 11 may consist 
of a part of the grip of a hand-held electric power tool, or may be 
adapted to be mounted inside such a grip. A first terminal piece 14 is 
fixed to a part of the case 11 near the pivot shaft end of the operation 
arm 13, and an engagement piece 16 integrally extends from the first 
terminal piece 14 into a cavity 15 defined in the operation arm 13. 
A free end of this engagement piece 16 pivotally supports a base end of a 
movable piece 17 by way of a metallic receiving member 18. A moveable 
spring 19 is interposed between a front edge of an opening 17a provided 
substantially in a middle part of the moveable piece 17 and the engagement 
piece 16 in a curved fashion, with the convex surface of the moveable 
spring 19 facing the front part (the upper part as seen in FIG. 1) of the 
case 11 so that the base end of the moveable piece 17 may be engaged by 
the metallic receiving member 18. A moveable contact 20 is fixedly 
attached to a free end of the moveable piece 17. 
This support structure is similar to that of a normal micro switch. It is 
possible to use switch mechanisms of other kinds without departing from 
the spirit of the present invention as long as they may be conveniently 
accommodated within the case 11. 
Opposite to the moveable contact 20 is located a fixed contact 23 which is 
fixedly secured to a free end of a fixed piece 22 integrally extending 
from a second terminal 21. Numerals 24 and 25 denote screw holes for 
securing lead wire ends to the terminals 14 and 21, respectively, numeral 
26 denotes a switch mounting hole for securing the switch in the grip of a 
hand-held electric power tool, and numeral 27 denotes an intermediate 
terminal. 
The pivot shaft 12 includes an extension on one side of the operation arm 
13 which consists of a first part 28 having a circular cross section and 
second part 29 extending from the free end of the first part and provided 
with a non-circular cross section by being cut along its two sides in a 
parallel fashion. The first part 28 having a circular cross section is 
rotatably fitted into a round hole 31 of a cover 30 closing a front 
opening of the case 11 so as to define a complete case as shown in FIG. 3, 
and the second part 29 having a rectangular cross section is securely 
fitted into a rectangular hole 34 formed in one of a pair of lateral 
flanges 33 of the trigger member 32 which straddle across an assembly 
consisting of the case 11 and the cover 30 so as to be rotatable 
integrally therewith. The other of the two flanges 35 of the trigger 
member 32 is provided with a round hole 36 which is coaxial with and 
conformal to the other round hole 31, and a hollow pin 37 having a 
circular cross section and projecting from the other side of the case 11 
coaxially with the pivot shaft 12 is rotatably received in this round hole 
36 of one of the flanges of the trigger member 32. Another small round pin 
38 projecting from the other side of the operation arm 13 as a second 
extension of the pivot shaft 12 is rotatably received in a small round 
hole 39 formed in the inner side of the hollow pin 37 of the case 11. 
As shown in FIG. 1, a compression coil spring 42 is interposed between a 
boss 40 projecting from the inner side of the front end of the trigger 
member 32 and a cavity 41 formed in the front end of the case 11 so as to 
urge the trigger member 32 away from the front face of the case 11 around 
the pivot shaft 12. 
Now, the mode of operation of this trigger switch is described in the 
following. 
Referring to FIG. 1, when the trigger member 32 is depressed against the 
force of the spring 42 by a finger, the operation arm 13 rotates in the 
same direction (in clockwise direction in FIG. 1) by way of the 
rectangular second part 29 of the pivot shaft extension, and a front edge 
15a of the cavity 15 presses upon the moveable piece 17. Once the moveable 
piece 17 goes over a certain critical point, the direction of the urging 
force of the moveable spring 19 acting upon the moveable piece 17 is 
reversed, and the moveable contact 20 comes into contact with the fixed 
contact 21 under the spring force of the moveable spring 19 with the 
result that an electric signal is obtained from the first terminal piece 
14 and the second terminal piece 21. When the pressure upon the trigger 
member 32 is removed, the trigger member 32 is restored to its original 
position by the restoring force of the spring 42 along with the operation 
arm 13 so that the moveable piece 17 returns to its original position 
under the restoring force of the movable spring 19, and the moveable 
contact 20 is removed away from the fixed contact 23. 
The integral coupling between the trigger member 32 and the operation arm 
13 in the case 11 is accomplished by fitting the rectangular second part 
29 into the rectangular hole 34 on the one hand and fitting a round first 
part 28 into the round hole 31 of the case 11 on the other hand, with the 
small pin 38 of the pivot shaft 12 being engaged with the trigger member 
32 indirectly by way of the hollow pin 37 of the case 11, as shown in FIG. 
3. According to this structure, since no part of the pivot shaft 12 is 
completely and directly passed through the other round hole 39 of the case 
11 or other part of the corresponding flange of the trigger member 32, a 
favorable sealing can be accomplished. 
Obviously, the engagement between the trigger member 32 and the operation 
arm 13 may be accomplished by non-circular parts thereof, such as a 
rectangular part 29 and a rectangular hole 34. Also, it is possible to 
provide a pair of round shafts projecting from either side of the 
operation arm 13, pass them through round holes provided in the case 11 
and the cover 30, and crimp, press fit or otherwise secure their free ends 
in the holes of the trigger member 32. Screws and other securing means may 
also be used. 
Further, as a switch mechanism for use in the case 11, a throw-type switch 
which directly acts upon an elastic moveable piece may also be used 
instead of the snap action mechanism used in the illustrated embodiment. 
Thus, according to the trigger switch of the present embodiment, since it 
comprises a trigger member pivotally supported by a case at its one end 
and urged rotatably away from the case, an operation arm received in the 
case so as to be integrally rotatable with the trigger member by way of a 
pivot shaft, a moveable piece which is displaced by the rotation of the 
operation arm, a moveable contact attached to a free end of the moveable 
piece, and a fixed contact mounted on the case opposite to the moveable 
contact, the integral coupling between the pivot shaft of the operation 
arm and the trigger member is simplified, and, owing to the fact that the 
entire switch mechanism along with the actuating arm coupled to the 
trigger member by way of a pivot shaft is located within the case, both 
compact design and light operating load can be accomplished at the same 
time. Further, since there is no slide member projection out of the case, 
a favorable sealing effect can be accomplished, and a cost reduction can 
be easily accomplished through simplification of sealing requirements. 
Although the present invention has been shown and described with respect to 
detailed embodiment, it should be understood by those skilled in the art 
that various changes and omission in form and detail may be made therein 
without departing from the spirit or scope of this invention.