Patent Publication Number: US-6989503-B2

Title: Power tool trigger assembly

Description:
The present invention relates to a trigger assembly for an electric power tool. 
   BACKGROUND OF THE INVENTION 
   The speed of electric power tools is often controlled by means of a pull-trigger, which is used to switch on and off the motor as well as to adjust the motor speed/torque. The pull-trigger invariably incorporates an electrical switch for control, which is either a mechanical switch or a solid-state switch. 
   The invention seeks to provide an improved trigger controller. 
   SUMMARY OF THE INVENTION 
   According to the invention, there is provided a trigger assembly for an electric power tool, comprising a switch for electrical connection to said power tool for controlling its operation, and a trigger coupled with the switch for operating the switch. The trigger has upper and lower ends and is pivotable about its upper end between an outer position in which the switch is open and an inner position in which the switch is closed. Also included is a locking member provided adjacent the lower end of the trigger for locking the trigger in the outer position. The locking member is movable from a locking position locking the trigger in the outer position to an unlocking position releasing the trigger. 
   Preferably, the locking member is provided inside the lower trigger end. 
   Preferably, the locking member is carried by the lower trigger end. 
   It is preferred that the trigger assembly includes a spring provided inside the lower trigger end and resiliently biasing the locking member into the locking position. 
   It is further preferred that the trigger assembly further includes a release member accessible on the outside of the trigger and in engagement with the locking member to enable manual movement of the locking member to the unlocking position against the action of the spring. 
   Further more preferably, the release member is connected to the locking member by a rod on which the spring is disposed and co-acts between the locking member and the trigger. 
   Further more preferably, the release member comprises a knob slidably supported on the trigger. 
   In a preferred embodiment, the trigger assembly includes a fixture for abutment by the locking member in the locking position to thereby lock the trigger in the outer position, the locking member being manually movable to the unlocking position to avoid the fixture. 
   More preferably, the fixture comprises a part of a casing of the switch. 
   More preferably, the fixture comprises a projection substantially aligned with the locking member when the locking member is in the locking position. 
   For convenience of operation, the trigger assembly includes a separate releasable locking member provided adjacent the upper end of the trigger for locking the trigger in the inner position. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of an embodiment of a trigger assembly embodying the invention, for operating an electric power tool; 
       FIG. 2  is a partially broken away and exploded perspective view of the trigger assembly of  FIG. 1 ; 
       FIG. 3  is a schematic circuit diagram of the trigger assembly of  FIG. 1 ; 
       FIGS. 4A to 4E  are successive side views of the trigger assembly of  FIG. 2 , showing its operation in sequence; and 
       FIGS. 5A ,  5 B and  5 C are cross-sectional top end views of the trigger assembly of  FIGS. 4A ,  4 D and  4 E, respectively. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
   Referring to the drawings, there is shown a trigger assembly  10  embodying the invention for controlling the operation of an electric power tool such as a hand drill that includes an electric motor. The trigger assembly  10  comprises a switch unit  100  and a trigger unit  200  located generally in front of and above the switch unit  100  for operating the same. 
   The switch unit  100  has an oblong vertical plastic casing  110  and includes a pair of internal switches  120  that are in use connected in series with the power tool motor, on opposite sides thereof, for turning on and off the motor. Alternatively, only one of the switches  120  may be used for the motor, with the other switch  120  for an auxiliary electronic/electrical device such as a battery or level meter. 
   The two switches  120  are operated by an elongate common actuator  122  to close and open in tandem. The actuator  122  is resiliently biassed downwards by an internal coil spring  121  such that both switches  120  are normally-open. The switch casing  110  is embraced, on its front side, by a plastic chassis  112  which slidably receives and supports the actuator  122  for relative upward and downward movement to operate the switches  120 . 
   The chassis  112  and actuator  122  extend upwardly to their respective upper ends  114  and  124 , where they are coupled with the trigger unit  200 . Whilst the chassis end  114  turns to the front, the actuator end  124  is crooked to the rear. The chassis  112  includes a fixed projection  116  that sticks out to the front. 
   The trigger unit  200  has a shell-like plastic trigger  210  which is hinged at its upper end  212  to the upper end  114  of the chassis  112  for pivotal movement relative to the switch unit  100 . The trigger end  212  has opposed walls reinforced by inner metal plates  213  including a pair of rear lugs that are connected to the actuator upper end  124  by a metal hinge pin  211 . 
   By this hinged connection, the trigger  210  is pivotable inwardly, from an outer or OFF position ( FIG. 4A  or  4 B) to an inner or ON position ( FIG. 4C ,  4 D or  4 E) thereof, upon pressing by the index, middle and ring fingers of a user&#39;s hand pulling the trigger  210  to thereby slide the actuator  122  upwards, counteracting the spring  121 , and in turn close both switches  120 . Under the action of the spring  121 , the trigger  210  normally stays in the outer position, slopping outwardly. 
   The trigger unit  200  incorporates a locking device  300  for locking the trigger  210  in the OFF position, for safety reasons to prevent accidental depression or pulling of the trigger  210 . The locking device  300  is provided and concealed inside a lower end  214  of the trigger  210 , being supported and carried thereby. It is formed by a locking member  310 , a connected vertical rod  320  upstanding therefrom, a compression coil spring  330  disposed on the rod  320 , and a sliding knob  340  in engagement with the locking member  310  via the rod  320 . 
   The sliding knob  340  has a horizontal stem  342  inserted through a vertical front slot into the trigger  210 , where the stem  342  has an end hole through which the rod  320  is threaded downwardly for connection therewith. The rod  320  is retained with the knob stem  342  by an upper rod end  322  that is expanded, with a C-clip  324  fitted on the rod  320  immediately underneath the stem  342 . The rod  320  is loosely supported at its end  322  below the knob stem  342  by a fork  216  through opposed prongs thereof, that fork  216  being an internal fixed part of the trigger  210 . 
   The spring  330  co-acts between the fork  216  and the locking member  310  to thereby resiliently bias the locking member  310  downwards into a locking position ( FIG. 4A ) adjacent the projection  116  on the switch casing  110 . In this position, the locking member  310  is aligned with and abuts the projection  116  or is blocked or obstructed, whereby the trigger  210  is locked in the OFF position and the electric drill cannot be switched on unintentionally. 
   The knob  340  is located about halfway up the front outer surface of the trigger  210 , at a position that can conveniently be accessed or manipulated by the index finger of the user&#39;s hand operating the trigger  210 , for momentarily sliding the knob  340  upwards against the action of the spring  330  to an unlocking position ( FIG. 4B ). In this position, the locking member  310  is displaced upwardly from and thus avoids the projection  116 , whereby the trigger  210  is released and can be then pressed to the ON position ( FIG. 4C ) for switching on the drill. 
   The trigger unit  200  further includes a separate locking device  400  for locking the trigger  210  in the ON position, which is provided at the upper end  212  of the trigger  210 . The locking device  400  comprises a spring-loaded locking pin  410  with press knob  420 , which extends laterally from left to right through the trigger end  212  and in particular its left wall and metal plate  213  and the chassis end  114  ( FIG. 5A ), falling short of the right wall and metal plate  213 . The locking pin  410  is located by the chassis end  114 , relative to which the trigger end walls and plates  213  are pivotable as the trigger  210  is pulled and released. 
   When the trigger  210  is pulled back, there will be aligned a hole on the right metal plate  213 , whereupon the locking pin  410  can be pressed further inward by the knob  420  to have its widened flat end  412  engage with this hole. Then the trigger  210  is locked in the ON position ( FIG. 5B ). The trigger  210  can be released for self return to the OFF position by momentarily pulling it slightly further back ( FIG. 5C ), whereupon the widened flat end  412  is released and the locking pin  410  springs back. As the locking device  400  is of the type not uncommonly known, it will not be described in greater detail herein. 
   It is envisaged that the release knob  340  may take any other suitable form such as a press button that protrudes downwardly from the lower end  214  of the trigger  210 , in which case the button can conveniently be pressed by the small or ring finger of the user&#39;s hand operating the trigger  210 . 
   The subject invention is especially, but not exclusively, applicable to trigger mechanisms of the type concerned, i.e. those designed for pulling by three fingers instead of the index finger alone, as the lock-off device is inevitably subject to a relatively larger trigger pulling force. By locating the lock-off device at or near the free end of the trigger in the broad sense, the force or torque it needs to withstand is minimized. 
   The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiments may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.