Patent Publication Number: US-2007119607-A1

Title: Power hand tool

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a hand tool and more particularly, to a power hand tool having a transmission position indicator (gearshift position indicator) that can be recognized clearly.  
      2. Description of the Related Art  
      Regular power hand tools are commonly provided with a multi-step speed changer (transmission) that is controllable to change the revolving speed of the output shaft subject to different working requirements.  
      The multi-step speed changer of a conventional power hand tool has an operating knob disposed at one side for operation by the user to change the gearshift position. The operating knob has marked thereon index signs, for example, H for high speed, M for standard speed and L for low speed, or a series of numerical signs such as 1, 2, 3, etc. for indicating the current gearshift position. However, one may work with a power hand tool in the night or under a dark environment. When working in the night or under a dark environment, the user may be unable to see the indication of the respective index sign well. If the user directly uses the power hand tool that is shifted to a wrong gearshift position (wrong revolving speed), a working mistake or accidental injury may occur.  
     SUMMARY OF THE INVENTION  
      The present invention has been accomplished under the circumstances in view. It is therefore an object of the present invention to provide a power hand tool, which enables the user to see the adjusted gearshift position clearly when in the dark.  
      To achieve this object of the present invention, the power hand tool comprises a housing having a through hole and a sighthole, a motor fixedly mounted inside the housing and having a power output end, a multi-step speed changer, and an indicator. The multi-step speed changer has a speed changing gear set coupled to the power output end of the motor, and a transmission mechanism coupled to the speed changing gear set and partially extending out of the through hole of the housing for operation by the user to selectively shift the speed changing gear set to one of a series of gearshift positions thereof. The transmission mechanism has a series of index signs corresponding to the gearshift positions, and the index signs are alternatively moved to the sighthole subject to the gearshift positions of the speed changing gear set. The indicator has a light emitting device mounted in the housing adjacent to the sighthole for illuminating one of the index signs of the transmission mechanism that is moved to the sighthole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a power hand tool according to a preferred embodiment of the present invention, wherein a part of the housing is removed for illustration purpose.  
       FIG. 2  is a side view of  FIG. 1 .  
       FIG. 3  is top view of the power hand tool according to the preferred embodiment of the present invention.  
       FIG. 4  is similar to  FIG. 3  but showing the gearshift position changed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIGS. 1-4 , a power hand tool in accordance with a preferred embodiment of the present invention is shown comprising a housing  10 , a motor  20 , a multi-step speed changer  30 , an indicator  40 , and a battery pack  50 .  
      The housing  10  has a through hole  11  and a sighthole  12  at one side, for example, the top side. Further, the housing  10  defines therein a plurality of receiving chambers.  
      The motor  20  is fixedly mounted inside the housing  10 , having a power output end for output of a rotary driving force to the outside.  
      The multi-step speed changer  30  comprises a speed changing gear set  31  and a transmission mechanism  32 . The speed changing gear set  31  is mounted inside the housing  10  and coupled to the power output end of the motor  20  for selectively changing the rotary driving force (constant revolving speed) to different revolving speeds (because this speed changing gear set is of the known art, no further detailed description in this regards is necessary). The transmission mechanism  32  comprises a gearshift control bar  321  and a transmission shaft  322 . The gearshift control bar  321  is axially slidably mounted inside the housing  10 , having an operating knob  323  disposed at one side thereof and extending through the through hole  11  to the outside of the housing  10  for operation by an external force (the user) to move the gearshift control bar  321  axially forwards or backwards. The gearshift control bar  321  has marked thereon index signs  324  (for example, H/M/L, or a series of numerical signs such as 1, 2, 3, etc.) corresponding to the gearshift positions provided by the speed changing gear set  31 . Through the sighthole  12 , one of the index signs  324  can be seen. The transmission shaft  322  has the two distal ends thereof respectively coupled to the speed changing gear set  31  and the gearshift control bar  321 . When operating the operating knob  323  to move the gearshift control bar  321 , the transmission shaft  322  is moved to change the gearshift position and at the same time the corresponding index sign  324  is moved into alignment with the sighthole  12 . Therefore, when operating the operating knob  323  to change the gearshift position (revolving speed), the user can see the corresponding index sign  324  through the sighthole  12 .  
      The indicator  40  comprises a light emitting device  41  and a light-transmissible covering  42 . The light emitting device  41  according to this embodiment is an LED (light emitting diode) mounted in the housing  10  near the sighthole  12 . The light-transmissible covering  42  according to this embodiment is a convex lens mounted in the sighthole  12  and adapted to magnify the image of the index sign  324  that is visible through the sighthole  12 .  
      The battery pack  50  is mounted inside the housing  10  and electrically coupled to the motor  20  and the light emitting device  41  of the indicator  40  to provide the motor  20  and the light emitting device  41  with the necessary working voltage, enabling the motor  20  to provide a rotary driving force and the light emitting device  41  to give off light.  
      The operation of the present invention is outlined hereinafter with reference to  FIGS. 3 and 4  again. When operating the operating knob  323  to shift the gearshift control bar  321  and to further drive the transmission shaft  322  to change the gearshift position, the corresponding index sign  324  is moved into alignment with the sighthole  12 , and at the same time the light emitted from the light emitting device  41  will stream on the index sign  324 , and therefore the user can see the corresponding index sign  324  through the light-transmissible covering  42 . By means of the illumination of the light emitting device  41  and the magnifying effect of the light-transmissible covering  42 , the user can see the corresponding index sign  324  clearly when working in the dark.