Patent Publication Number: US-2009229397-A1

Title: Protection Device For Speed Shifting Mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a protection device for preventing unintentionally shift to a speed shifting mechanism of a power tool. 
     2. The Prior Arts 
     A conventional power tool such as a power screw driver generally includes a motor which provides power to drive an output shaft on which a bit is connected. In order to provide proper speed for different tasks, a gear reduction unit is used to regulate the high revolutions of the motor and connected to the output shaft. Generally, the conventional power tools includes high speed, constant speed and low speed operation modes for different requirements of the tasks and a switch is located on outside of the power tool so that the user can shift the switch to choose desired gear. 
     Besides, there is a button to control the power and when the user pushes the button, the motor is activated and provides power to the tool, and if the button is not pushed, the tool is not activated. Nevertheless, the switch for shifting gears of the conventional power tools do not have such protection button so that when the motor is activated, the switch is not protected so that the switch might be shifted unintentionally. The speed of the output shaft is then suddenly changed during operation and this may cause damage to the objects or even the users. 
     The present invention provides a protection device which locks the switch so that even when the switch is touched unintentionally, the gear does not change so as to protect the tool, the object and the user. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a protection device which improves the shortcoming of the conventional power tool whose switch for shifting gears cannot be locked and may be unintentionally shifted to damage the objects. 
     The protection device includes a tube rotatably mounted to a case of a power tool and a shifter of the protection device is connected to the tube which is rotated when the shifter is shifted. A control member includes a positioning plate from which a protrusion extends and the protrusion is engaged with one of positioning notches defined in the tube so as to lock the tube to prevent the tube from rotation when the switcher is unintentionally touched. 
     The protection device of the presenting invention includes a case with a gear reduction unit received therein and a slot is defined through the case. A tube is rotatably mounted to the case and includes a plurality of positioning notches. A guide groove is defined through the tube. A button mechanism comprises an activation rod, a shifter and a button, in which the activation rod is connected to the gear reduction unit via the slot, and the shifter is engaged with the guide groove and connected to the activation rod. The button is secured on the shifter. A control member comprises a positioning plate which has a protrusion and the protrusion is engaged with one of the positioning notches to lock the tube. When the protrusion is disengaged from the positioning notch, the tube can be rotated for shifting the shifter. 
     According to the present invention, the button mechanism is well protected and the purpose for preventing unintentional shifting is achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which: 
         FIG. 1  is a partial cross sectional view to show a power tool with a protection device in accordance with the present invention; 
         FIG. 2A  is a perspective view to show a button of the protection device in accordance with the present invention; 
         FIG. 2B  shows a shifter of the protection device in accordance with the present invention; 
         FIG. 2C  shows a guide groove of a tube of the protection device in accordance with the present invention; 
         FIG. 2D  shows an activation rod of the protection device in accordance with the present invention, and 
         FIG. 3  shows positioning notches in the tube and a control member includes a positioning plate with a protrusion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings and in particular to  FIGS. 1 and 2A , a protection device for a speed shifting mechanism in accordance with the present invention comprises a case  1  with a gear reduction unit  4  received therein and the gear reduction unit  4  includes a planet gear system and multiple types of gears. A motor gear  6  is driven by a motor (not shown) and the gear reduction unit  4  changes the speed from the motor and the speed is then transferred to the output shaft  7 . 
     The gear reduction unit  4  is connected to a button mechanism  3  as shown in  FIG. 2D  and the button mechanism  3  includes an activation rod  33  whose two ends are inserted into the two slots  11  defined through the case  1  and connected to the gear reduction unit  4 . A tube  2  as shown in  FIG. 2C  is rotatably mounted to the case  1  and a guide groove  21  is defined through the tube  2 . A plurality of positioning notches  22 A,  22 B and  22 C are defined on a periphery of the tube  2 . If the power tool includes three gears which are high speed, constant speed and low speed, there are three positioning notches  22 A,  22 B and  22 C for the three gears as shown in  FIG. 3 . A shifter  32  is engaged with the guide groove  21  and is connected with the activation rod  33  as shown in  FIG. 2B  and a button  31  is connected to the shifter  32  as shown in  FIG. 2A . 
       FIG. 3  shows that a control member  5  is connected to the power tool so as to control the activation of the motor. The control member  5  comprises a positioning plate  51  which has a protrusion  511 . The protrusion  511  is engaged with one of the positioning notches  22 A,  22 B and  22 C to lock the tube  2 . 
     When the control member  5  is not yet pushed, the motor is not activated, the protrusion  511  on the positioning plate  51  is not engaged with any of the positioning notches  22 A,  22 B and  22 C, and the tube  2  is freely rotatable, the user can shift the button  31  to move the shifter  32  and the activation rod  33  to shift the gears. The shifter  32  is engaged with the guide groove  21  so that when the shifter  32  is moved, the tube  2  is rotated along with the movement of the shifter  32 . When the power tool is set to high speed, the protrusion  511  is engaged with the positioning notch  22 A. When the power tool is set to constant speed, the protrusion  511  is engaged with the positioning notch  22 B. When the power tool is set to low speed, the protrusion  511  is engaged with the positioning notch  22 C. When the user pushes the control member  5  to activate the motor, the protrusion  511  is engaged with one of the positioning notches  22 A,  22 B or  22 C to lock the tube  2 . In other words, tube  2  cannot be rotated even if the button  31  is unintentionally pushed so that the gear reduction unit  4  in the case  1  is protected. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.