Abstract:
A power tool includes a variable speed device which can be set in an auto mode or a manual mode. The power tool does not need the user to set the speed when it is operated at the auto mode. The power tool is reset to be the high-speed mode when it is activated. The speed is reduced along with the working load so as to output high torque, maintain the best working efficiency and protect the power tool under the operative status. The power tool can be set to the manual mode so as to work in a single type of function.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a power tool, and more particularly, to a power tool with a variable speed device which allows the user to change the speeds by manual way or by automatic way. 
         [0003]    2. The Prior Arts 
         [0004]    The conventional power tool, such as a power drill, usually could be operated in variable speeds. However, before the operation, the users have to manually set up the speeds of the power tools that are suitable for the works. If the users do not have sufficient experience, they do not know how to choose a suitable speed for the work. The power tool in not worked in a proper speed and therefore the work cannot be done properly. Sometimes, the power tools are damaged due to improper operation. 
       SUMMARY OF THE INVENTION 
       [0005]    A primary objective of the present invention is to provide a power tool having a variable speed device that can be set at a manual mode or an auto mode to complete different tasks and overcomes the shortcomings of the conventional variable speed devices. The shortcomings of the conventional variable speed devices include that the inexperienced users are unable to set up proper speeds and the power tools would be damaged under improper working speeds. 
         [0006]    The characteristics of the power tool having a variable speed device according to the present invention is that operating speeds can be set at a manual mode or an auto mode. When setting up the power tool under the auto mode, the user does not need to set up the speed of operation and the power tool can be reset to the high-speed status when the power tool is activated. The speed of operation is automatically reduced to increase the output torque when the load increases. Thus, the power tool according to the present invention can be in the best working efficiency. Moreover, the power tool is protected from damaged and the damages due to working under improper speeds are avoided. Furthermore, the power tool can be set at the manual mode which sets the variable speed device at a fixed speed so as to repeatedly operate the power tool by the single function. 
         [0007]    A power tool having a variable speed device according to the present invention includes an output unit having an output shaft. A tubular member has an interior space and a plurality of slots is defined axially in the inner periphery thereof The tubular member is connected to the output unit. A variable speed gear set is located in the tubular member and has an output end, a first inner gear, a second inner gear and a disk located from the first end to the second end of the variable speed gear set. The output end is connected to the output shaft. The first inner gear has a plurality of first protrusions on the second end thereof and the second inner gear has a plurality of second protrusions on the outside thereof The disk has a plurality of third protrusions on the second end thereof A locking member is connected to the outside of the tubular member and movable axially relative to the tubular member. The locking member has a plurality of pressing pins which extend toward the first end and the second end of the locking member. The locking member further has a plurality of hooks extending toward the second end thereof and the hooks are engaged with the slots. The pressing pins each has a first end thereof connected with a spring which has the first end thereof contacting with the output unit. A speed switch ring is connected to the second end of the tubular member and has a plurality of inclined surfaces on the first end thereof A plurality of fourth protrusions and a plurality of toothed portions are located on the second end of the speed switch ring. The second ends of the pressing pins of the locking member are in contact with the inclined surfaces. A function switch ring is connected to the second end of the speed switch ring. A movable inner gear is connected to the speed switch ring and the function switch ring. An annular groove is defined in the outside of the movable inner gear which has a plurality of inner teeth defined in the inner periphery thereof A plurality of fifth protrusions is located on the first end of the movable inner gear and a plurality of sixth protrusions is located on the second end of the movable inner gear. A wire is movably located in the annular groove of the movable inner gear. An inner gear is connected to the inner periphery of the movable inner gear and the inner gear has outer toothed portion defined in the outside thereof and inner toothed portion defined in the inner periphery thereof A transmission disk has a transmission gear on the first end thereof and a plurality of planet gears is located on the second end thereof The planet gears are connected to the inner periphery of the movable inner gear and engaged with the inner teeth of the movable inner gear and the outer toothed portion of the inner gear. The transmission gear is engaged with the variable speed gear set. An end cap is connected to the second end of the movable inner gear and has a plurality of protrusions on the outer periphery thereof An inclined groove is defined in the outside of the end cap and the wire is movably engaged with the inclined groove. A plurality of gears is pivotably connected to the end cap and protrudes beyond the inner periphery of the end cap. The gears are engaged with the inner teeth of the movable inner gear and the outer toothed portion of the inner gear. When the end cap is rotated in a first direction or a second direction manually, the wire is moved toward the first end or the second end thereof so as to control the engagement between the sixth protrusions of the movable inner gear and the seventh protrusions of the end cap. An auto switch is located in the tubular member and connected with the wire so as to control the wire to move toward the first end or the second end, and control movement of the hooks of the locking member to engage with the first protrusions, the second protrusions or the third protrusions of the variable speed gear set according to working load. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      FIG. 1  is a perspective view showing a power tool having a variable speed device in accordance with the present invention; 
           [0010]      FIG. 2  is a partially exploded view showing the power tool in  FIG. 1  of the present invention; 
           [0011]      FIG. 3  is an exploded view showing the variable speed device according to the present invention; 
           [0012]      FIGS. 4A and 4B  are two different perspective views showing a speed switch ring of the variable speed device according to the present invention; 
           [0013]      FIGS. 5A and 5B  are two different perspective views showing an end cap of the variable speed device according to the present invention; 
           [0014]      FIGS. 6A and 6B  are two different perspective views showing a function switch ring of the variable speed device according to the present invention; 
           [0015]      FIG. 7  is a perspective view showing the switch device of the variable speed device according to the present invention; 
           [0016]      FIG. 8  shows that the variable speed device according to the present invention outputs low speed and high torque in an auto mode; 
           [0017]      FIG. 9  shows that a locking member moves toward a second end when the working load increases gradually and the variable speed device is in auto mode; 
           [0018]      FIG. 10  shows that hooks of the locking member are engaged with second protrusions of a second inner gear so that the second inner gear cannot rotate, while the variable speed device is in auto mode; 
           [0019]      FIG. 11  shows that sixth protrusions of a movable inner gear are engaged with seventh protrusions of the end cap, so that the movable inner gear and the inner gear are fixed and cannot rotate, while the variable speed device is in a manual mode; 
           [0020]      FIG. 12  shows that fifth protrusions of the movable inner gear are engaged with fourth protrusions of the speed switch ring, and the movable inner gear drives the speed switch ring to rotate simultaneously, while the variable speed device is in auto mode; and 
           [0021]      FIG. 13  shows that switch gears of the auto switch are engaged with the toothed portions of the speed switch ring. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    With reference to the drawings and in particular to  FIGS. 1 and 2 , a power tool comprises a casing  5  in which a variable speed device  10 , a motor  2  and a switch device  3  are received. A battery pack  4  is connected to the lower end of the casing  5  so as to provide power to the motor  2 . The switch device  3  comprises a trigger  31  which has a hole  311  so as to control the activation of the motor  2 . A driving shaft  21  of the motor  2  is connected to a motor gear  22  which is engaged with a gear system of the variable speed device  10 . The variable speed device  10  comprises a speed switch ring  106  to control the output speed of an output shaft  1011 . The variable speed device  10  has a function switch ring  107  for switching the operation modes of the power tool between an auto mode and a manual mode. 
         [0023]    The power tool according to the present invention has a first end and a second end. The first end means the end that is close to the tool bit and the second end is the end opposite to the first end. Thus, in the specification, the first and second ends are defined as mentioned above. 
         [0024]    As shown in  FIG. 3 , the variable speed device  10  according to an embodiment of the present invention comprises an output unit  100 , a variable speed gear set  102 , a tubular member  103 , a locking member  104 , a speed switch ring  106 , a transmission disk  110 , an inner gear  108 , a function switch ring  107 , a wire  111 , a movable inner gear  112  and an end cap  113 . The output unit  100  includes a top casing  101  which has two bearings  1013  and the output shaft  1011  is cooperated with the bearings  1013 . The first end of the output shaft  1011  is assembled with the tools, such as a screw-driving bit or a drilling head, and the second end of the output shaft  1011  has a polygonal shaft  1012 . The first end of the output shaft  1011  extends out of the first end of the top casing  101 . 
         [0025]    As shown in  FIG. 3 , the tubular member  103  has an interior space and a plurality of slots  1031  defined axially in the outer periphery thereof The tubular member  103  has a lug located on the outside of the first end and a first hole  1032  and a second hole  1033  are defined through the lug. Bolts are used to extend through the first and second holes  1032 ,  1033  to fix the first end of the tubular member  103  to the second end of the top casing  101  so as to connect the tubular member  103  with the output unit  100 . 
         [0026]    As shown in  FIG. 3 , the variable speed gear set  102  is located in the interior space of the tubular member  103 . The variable speed gear set  102  according to the preferred embodiment has an output end  1021 , a first inner gear  1022 , a second inner gear  1023  and a disk  1024  disposed from the first end to the second end thereof The output end  1021  has a polygonal hole  10211  corresponding to the polygonal shaft  1012  of the output shaft  1011 . Thus, after the polygonal shaft  1012  of the output shaft  1011  is engaged with the polygonal hole  10211  of the variable speed gear set  102 , the output end  1021  is able to simultaneously rotate the output shaft  1011 . The first inner gear  1022  has a plurality of first protrusions  10221  disposed on the second end thereof and the second inner gear  1023  has a plurality of second protrusions  10231  disposed on the outside thereof The disk  1024  has a plurality of third protrusions  10241  disposed on the second end thereof The output end  1021 , the first inner gear  1022 , the second inner gear  1023  and the disk  1024  form a gear assembly which is known and will not described in detail. 
         [0027]    As shown in  FIG. 3 , the locking member  104  according the preferred embodiment is shaped in a ring. An inner diameter of the locking member  104  is slightly larger than an outer diameter of the tubular member  103  so that the locking member  104  is connected to the outside of the tubular member  103  and movable axially relative to the tubular member  103 . The locking member  104  has a plurality of holes along the periphery thereof and each hole is connected with a pressing pin  1042  whose two ends respectively extend toward the first end and the second end of the locking member  104 . The first end of each pressing pin  1042  is cooperated with a spring  105  and the second end of each pressing pin  1042  has a hook  1041  extending toward the second end thereof When the locking member  104  is mounted to the tubular member  103 , the hooks  1041  are movably engaged with the slots  1031  of the tubular member  103 , and the springs  105  each has its first end contacting with the second end of the top casing  101  so that the locking member  104  is capable of moving axially relative to the tubular member  103 , but cannot rotate relative to the tubular member  103 . 
         [0028]    The speed switch ring  106  according to the preferred embodiment is movably mounted to the outside of the tubular member  103 . As shown in  FIG. 4A , the speed switch ring  106  includes a plurality of inclined surfaces  1062  disposed on the first end thereof and the inclined surfaces  1062  are located corresponding to the pressing pins  1042  of the locking member  104 . As shown in  FIG. 4B , a plurality of fourth protrusions  1063  are located on the second end of the speed switch ring  106  and a plurality of toothed portions  1064  are located on a part of the outer periphery of the second end of the speed switch ring  106 . The speed switch ring  106  has at least one speed plate  1061  at the outside thereof When the speed switch ring  106  is mounted to the tubular member  103 , the second ends of the pressing pins  1042  of the locking member  104  are respectively in contact with the inclined surfaces  1062 . When the speed switch ring  106  rotates in the first direction, the inclined surfaces  1062  push the pressing pins  1042  of the locking member  104  and move the locking member  104  toward the first end. When the speed switch ring  106  rotates in the second direction, the inclined surfaces  1062  are cooperated with the elastic forces of the springs  105  to drive the locking member  104  toward the second end. 
         [0029]    As shown in  FIGS. 6A and 6B , the function switch ring  107  according to the preferred embodiment has a function plate  1071  disposed on the outside thereof and a groove  1072  is defined axially in the inner periphery of the function switch ring  107  and located corresponding to the function plate  1071 . The function plate  1071  is connected to the second end of the speed switch ring  106 . 
         [0030]    As shown in  FIG. 3 , the movable inner gear  112  according the preferred embodiment has an annular groove  1124  defined in the outside thereof. The movable inner gear  112  has a plurality of fifth protrusions  1122  on the first end thereof and a plurality of sixth protrusions  1123  on the second end thereof. A plurality of inner teeth  1121  are defined in the inner periphery of the movable inner gear  112 . According to the preferred embodiment, the C-shaped wire  111  is a metallic wire and bent to include a transverse section  1110  and an upright section  1111 . The C-shaped wire  111  is engaged with the annular groove  1124  of the movable inner gear  112  and the transverse section  1110  is engaged with the groove  1072  of the function switch ring  107 . Thus, the movable inner gear  112  is received in the function switch ring  107 . When the function switch ring  107  is rotated, the wire  111  is movable in the annular groove  1124 . After the movable inner gear  112  and the wire  111  are connected to the function switch ring  107 , the function switch ring  107  is connected to the second end of the speed switch ring  106 . Then the connected speed switch ring  106  and the function switch ring  107  are connected to the transmission disk  110 . The transmission disk  110  has a transmission gear  1101  disposed on the first end thereof and a plurality of pins  1102  are connected to the second end of the transmission disk  110 . A plurality of planet gears  109  are mounted to the pins  1102 , respectively. The transmission gear  1101  is engaged with the gears in the variable speed gear set  102  from the second end of the variable speed gear set  102 . The inner gear  108  is then connected to the transmission disk  110 . The inner gear  108  includes a plurality of inner toothed portions  1081  defined in the inner periphery thereof and a plurality of outer toothed portions  1082  defined in the outside thereof When the inner gear  108  is connected to the transmission disk  110 , the inner toothed portions  1081  are engaged with the planet gears  109  and the outer toothed portions  1082  are engaged with the inner teeth  1121  of the movable inner gear  112 . 
         [0031]    As shown in  FIGS. 3 ,  5 A and  5 B, the end cap  113  is connected to the second end of the movable inner gear  112  and separates the planet gears  109  and the movable inner gear  108  by the washer  119  at the inside of the end cap  113  so that the planet gears  109  and the movable inner gear  108  are not overly scrub the inside of the end cap  113 . The end cap  113  has a plurality of seventh protrusions  1133  on the outer periphery thereof and an inclined groove  1134  is defined in the outside of the end cap  113 . The upright section  1111  of the wire  111  is movably engaged with the inclined groove  1134 . A plurality of recesses  1131  are defined in the wall of the end cap  113  and each recess  1131  has an axial hole  1132  defined in a vertical face thereof A plurality of pins  115  extend through gears  114  and are pivotably connected to the axial holes  1132  so that the gear  114  extends beyond the inner diameter of the end cap  113 . Therefore, the gears  114  are engaged with the inner teeth  1121  of the movable inner gear  112  and the outer toothed portion  1082  of the inner gear  108 . The end cap  113  has a wall extending from the lower end thereof and the wall has a third hole  1135  and a fourth hole  1136 . 
         [0032]    As shown in  FIG. 3 , an auto switch  116  according to the preferred embodiment includes a connection member  1161 , a block  1162  having inner teeth  11621  and a hole  11622 , a worm rod  1164 , a lever  1163 , a first pin  117 , a second pin  118  and a switch gear  1165 . The connection member  1161  has two extensions on two opposite ends thereof and each extension has a hole  11612 . Four notches  11611  are respectively located at the four corners of the connection member  1161  so that the two notches  11611  on two sides of the connection member  1161  are located on a straight line. A curved plate  11613  extends downward from the lower end of the connection member  1161 . The lever  1163  is a metallic rod which is bent to form a hook  11631 . The lever  1163  is connected to the connection member  1161  and restricted by the notches  11611  of the connection member  1161 . The worm rod  1164  is threadedly engaged with the inner teeth  11621  of the block  1162 . The worm rod  1164  has a rotation rod  11641  at an end thereof The rotation rod  11641  extends through the keyway  11651  of the switch gear  1165 . The switch gear  1165  is engaged with the toothed portion  1064  of the speed switch ring  106  as shown in  FIG. 13 . The first pin  117  extends through the worm rod  1164  and the switch gear  1165 , and the two ends of the first pin  117  respectively extend through the first hole  1032  of the tubular member  103  and the third hole  1135  of the end cap  113 . The second pin  118  extends through the hole  11622  of the block  1162  and the hole  11612  of the connection member  1161 . The two ends of the second pin  118  respectively extend through the second hole  1033  of the tubular member  103  and the fourth hole  1136  of the end cap  113 . The curved plate  11613  of the connection member  1161  is engaged with the hole  311  of the trigger  31 . When the trigger  31  is pulled to move the connection member  1161 , the lever  1163  and the block  1162  simultaneously, the worm rod  1164  and the switch gear  1165  are simultaneously rotated to rotate the speed switch ring  106 . The parts of the auto switch  116  are assembled as shown in  FIG. 7 . 
         [0033]    The operation modes of the power tool according to the present invention could be an auto mode or a manual mode. The following descriptions are regarding to the auto mode. As shown in  FIG. 12 , when the power tool is operated under the auto mode, the user switches the function plate  1071  of the function switch ring  107  toward the first direction to rotate the function switch ring  107  and the wire  111  is simultaneously rotated with the function switch ring  107 . The upright section  1111  of the wire  111  is guided by the inclined groove  1134  of the end cap  113  to move toward the first end and drives the movable inner gear  112  toward the first end. The fifth protrusions  1122  on the first end of the movable inner gear  112  are engaged with the fourth protrusion  1063  on the second end of the speed switch ring  106 . Therefore, when the movable inner gear  112  is driven to rotate, the speed switch ring  106  is simultaneously rotated with the movable inner gear  112 . 
         [0034]    As shown in  FIG. 7 , when the user presses the trigger  31  on the auto switch  116 , the trigger  31  drives the connection member  1161  to move. The lever  1163  connected to the connection member  1161  would pull the block  1162  to move. The inner teeth  11621  of the block  1162  drive the worm rod  1164  to rotate. Thus, the switch gear  1165  is driven to rotate and the switch gear  1165  rotates the speed switch ring  106 . The inclined surfaces  1062  on the first end of the speed switch ring  106  move the locking member  104  toward the first end, and the locking member  104  moved with the trigger  31  until the trigger  31  finishes the designated travel thereof. The hooks  1041  of the locking member  104  are engaged with the first protrusions  10221  of the first inner gear  1022  so that the movable inner gear  112  cannot rotate. The variable speed gear set  102  is in the status of high speed and low torque. When the working load gradually increases, the reaction force applied to the inner gear  108  increases. When the reaction force is larger than the elastic force of the springs  105 , the inner gear  108  rotates reversely and the outer toothed portions  1082  drive the gear  114  to rotate. Then, the inner gear  108  and the speed switch ring  106  are driven to rotate. Because the inclined surfaces  1062  restrict the movement, the elastic force from the springs  105  pushes the locking member  104  toward the second end as shown in  FIG. 9 . The hooks  1041  of the locking member  104  switches from the engagement with the first protrusions  10221  of the first inner gear  1022  to the engagement with the second protrusions  10231  of the second inner gear  1023 . Therefore, the second inner gear  1023  cannot rotate. The variable speed gear set  102  is in the status of mediate speed and mediate torque to overcome the working load of the output shaft as shown in  FIG. 10 . When the working load continuously increases, the power tool proceeds the aforementioned steps and the hooks  1041  of the locking member  104  are switched to be engaged with the third protrusions  10241  of the transmission disk  1024  to make the variable speed gear set  102  be in the status of low speed and high torque to finish the tasks as shown in  FIG. 8 . 
         [0035]    The following descriptions are regarding to the manual mode. As shown in  FIG. 11 , when the user sets the power tool according to the present invention to be operated in the manual mode, the user shifts the function plate  1071  of the function switch ring  107  toward the second direction to rotate the function switch ring  107  which drives the wire  111  toward the second direction. The upright section  1111  of the wire  111  is guided by the inclined groove  1134  of the end cap  113  to move toward the second end. The movable inner gear  112  is moved toward the second end and the sixth protrusions  1123  on the second end of the movable inner gear  112  are engaged with the seventh protrusions  1133  of the end cap  113  so as to restrict the movable inner gear  112  from rotating. The gear  114  is fixed and cannot rotate. The inner gear  108  that is engaged with the gear  114  is also not able to rotate. Under this status, even if the working load increases, the movable inner gear  112  cannot be rotated so that the variable speed device cannot auto change the speed and this is the manual mode. When the speed needs to be changed, the user needs to manually shift the speed plate  1061  of the speed switch ring  106  to change the speed. 
         [0036]    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.