Abstract:
A transmission mechanism includes a first gear unit having an axially-movable ring gear and a second gear unit having an axially-movable fixing ring. The fixing ring includes first and second protrusions on two sides, respectively. When the ring gear moves, the first inner teeth and the outer teeth of the second planet gear disk are engaged with each other or disengaged from each other. When the fixing ring moves, the first protrusions and the first positioning ridges are engaged with each other or disengaged from each other, or the second protrusions and the second positioning ridges are engaged with each other or disengaged from each other. By the different combinations of the statuses due to movement of the ring gear and the fixing ring, the input speed from the motor gear is transferred into four different speeds which is output from an output shaft.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a transmission mechanism for a power tool, and more particularly, to a transmission mechanism capable of providing four different torques and speeds. 
     2. The Prior Arts 
     Conventional power tools, such as a power drill, generally include a transmission mechanism for outputting power from a motor to an output shaft. Some of the transmission mechanisms can provide various speeds and therefore the speed of the output shaft is adjustable. However, most of the speed-adjustable transmission mechanisms provide only three speeds or less and the power tools capable of providing four speeds usually have complicated transmission mechanisms and higher manufacturing cost. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a four-speed transmission mechanism for a power tool with simple structure and reduced manufacturing cost. 
     The characteristic of the present invention is that a transmission mechanism comprises two gear units. By engagement of the two gear units, four different output speeds and torques can be output. 
     In order to achieve the objective, a transmission mechanism according to the present invention includes a first gear unit and a second gear unit. The first gear unit includes a first planet gear disk, a plurality of first planet gears, a ring gear having first inner teeth, a second planet gear disk having outer teeth and a first pinion, and a plurality of second planet gears. The first planet gears are connected to the first planet gear disk and engaged with the first inner teeth of the ring gear. The second planet gears are connected to the second planet gear disk and engaged with the first pinion. The ring gear is axially movable to engage the first inner teeth with the outer teeth of the second planet gear disk, or to disengage the first inner teeth from the outer teeth of the second planet gear disk. The first planet gear disk is connected with an output shaft. The second gear unit includes a third planet gear disk having a plurality of second positioning ridges, a fixing ring having a plurality of first protrusions and a plurality of second protrusions, an inner gear having a plurality of first positioning ridges and second inner teeth, and a plurality of third planet gears having a second pinion. The third planet gears are connected to the third planet gear disk and the second pinions are engaged with the second inner teeth of the inner gear. The third planet gears are engaged with a motor gear. The fixing ring is axially movable to engage the first protrusions with the first positioning ridges, or to engage the second protrusions with the second positioning ridges. 
     When the ring gear is moved to engage the first inner teeth with the outer teeth of the second planet gear disk and the fixing ring is moved to engage the first protrusions with the first positioning ridges, an input speed from the motor gear is transferred into a first speed (high speed) which is output from the output shaft. 
     When the ring gear is moved to engage the first inner teeth with the outer teeth of the second planet gear disk and the fixing ring is moved to engage the second protrusions with the second positioning ridges, an input speed from the motor gear is transferred into a second speed (mediate-high speed) which is output from the output shaft. 
     When the ring gear is moved to disengage the first inner teeth from the outer teeth of the second planet gear disk and the fixing ring is moved to engage the first protrusions with the first positioning ridges, an input speed from the motor gear is transferred into a third speed (mediate-low) which is output from the output shaft. 
     When the ring gear is moved to disengage the first inner teeth from the outer teeth of the second planet gear disk and the fixing ring is moved to engage the second protrusions with the second positioning ridges, an input speed from the motor gear is transferred into a fourth speed (low speed) which is output from the output shaft. 
     Preferably, the ring gear includes a first groove defined in an outer periphery thereof and a first rod is engaged with the first groove to control axial movement of the ring gear. 
     Preferably, the fixing ring includes a second groove defined in an outer periphery thereof and a second rod is engaged with the second groove to control axial movement of the fixing ring. 
     Preferably, the first and second protrusions are disposed on two opposite sides of the fixing ring and extend axially toward two opposite directions. The first positioning ridges are located on an outer periphery of the inner gear and the second protrusions are located on an outer periphery of the third planet gear disk. 
    
    
     
       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 an exploded view to show a transmission mechanism according to an embodiment of the present invention; 
         FIG. 2  is a perspective view, partially removed, to show the transmission mechanism of the present invention, wherein the output speed is switched to high; 
         FIG. 3  is a perspective view, partially removed, to show the transmission mechanism of the present invention, wherein the output speed is switched to mediate-high; 
         FIG. 4  is a perspective view, partially removed, to show the transmission mechanism of the present invention, wherein the output speed is switched to mediate-low; and 
         FIG. 5  is a perspective view, partially removed, to show the transmission mechanism of the present invention, wherein the output speed is switched to low. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a transmission mechanism according to an embodiment of the present invention is disclosed and all of the parts have a first end and a second end which is located opposite to the first end. The first end is the direction that the output shaft of the power tool directs, and the second end is the direction that the motor gear is located. 
     Referring to  FIGS. 1 to 5 , especially to  FIG. 1 , the transmission mechanism comprises a first gear unit  1  and a second gear unit  2 . The first gear unit  1  includes a first planet gear disk  12 , a plurality of first planet gears  13 , a ring gear  14  having a plurality of first inner teeth  142 , a second planet gear disk  15  having a plurality of outer teeth  151  and a first pinion  152 , and a plurality of second planet gears  27 . The first planet gear disk  12  has a plurality of shafts  122  extending axially from the first end thereof, and a plurality of first planet gear shafts  121  axially extend from the second end of the first planet gear disk  12 . Each of the first planet gear shafts  121  has one of the first planet gears  13  connected thereto, and each shaft  122  extends through a roller  17 . An action member  16  is connected to the first end of the first planet gear disk  12  so that each roller  17  is located in a central hole  160  of the action member  16 . Then, the first planet gear disk  12 , the action member  16 , the rollers  17  and a bearing  19  are connected in a front case  11  from the second end of the front case  11 . An inner periphery of the front case  11  has a plurality of inner ribs  111  extending therefrom. The second end has an output shaft  18  which includes a polygonal shaft  181  which extends into the front case  11  from the first end of the front case  11 . The output shaft  18  is cooperated with the bearing  19  and the polygonal shaft  181  extends through a polygonal hole  120  of the first planet gear disk  12 . When the first planet gear disk  12  rotates, the first planet gear disk  12  cooperates with the rollers  17  and the action member  16  to drive the polygonal shaft  181  of the output shaft  18  to rotate. The action between the first planet gear disk  12 , the rollers  17 , the action member  16  and the output shaft  18  belongs to the prior art, and therefore the detail is not described here. 
     The ring gear  14  is a ring-shaped member and includes a first groove  141  defined in an outer periphery thereof and a plurality of outer ribs  144  extend axially from the ring gear  14 . The first inner teeth  142  are defined in the inner periphery of the ring gear  14 . The ring gear  14  is connected to the second end of the first planet gear disk  12  so that the first planet gears  13  are engaged with the first inner teeth  142 . A C-shaped first rod  143  has two ends thereof engaged with the first groove  141  and the first rod  143  is connected to a rear case  21 . When a user operates the first rod  143 , the ring gear  14  is shifted axially and the outer ribs  144  are engaged with the inner ribs  111 . 
     The second planet gear disk  15  has the outer teeth  151  and the first pinion  152  is connected to the first end of the second planet gear disk  15 . The second end of the second planet gear disk  15  has a plurality of second planet shafts  153  connected thereto and each second planet shaft  153  is connected with one of the second planet gears  27 . The second planet gear disk  15  is installed in the inside of the ring gear  14  and the first pinion  152  is engaged with the first planet gears  13 . The user operates the first rod  143  to control the movement of the ring gear  14  to make the first inner teeth  142  of the ring gear  14  be engaged with or disengaged from the outer teeth  151  of the second planet gear disk  15 . 
     The second gear unit  2  includes a third planet gear disk  23 , a fixing ring  24 , a plurality of third planet gears  25  and an inner gear  26 . The third planet gear disk  23  has a plurality of second positioning ridges  231  disposed on an outer periphery thereof. The third planet gear disk  23  has a plurality of third planet gear shafts  232  extending axially from the first end thereof and each third planet gear shaft  232  is connected with one of the third planet gears  25 . Each of the third planet gears  25  has a second pinion  251  co-axially connected to the first end thereof. 
     The fixing ring  24  is a ring-shaped member and includes a second groove  243  defined in an outer periphery thereof. The fixing ring  24  includes a plurality of first protrusions  241  extending axially from the first end thereof and a plurality of second protrusions  242  extending axially from the second end thereof. The inner gear  26  has a plurality of first positioning ridges  263  extending axially from the outside thereof and a third grove  261  defined in the outer periphery thereof. Second inner teeth  262  are defined in the inside of the inner gear  26 . The third planet gear disk  23  connected with the third planet gears  25  are installed in the rear case  21 . A C-shaped second rod  244  has two ends thereof engaged with the second groove  243  and the second rod  244  is connected with the rear case  21 . The inner gear  26  is also installed in the rear case  21  and at least one pin  264  extends through a wall of the rear case  21  and is inserted into the third groove  261  to restrict the inner gear  26 . Thus, the inner gear  26  can rotate in the rear case  21  and can not move axially. The front case  11  and the rear case  21  connect to form a complete case so as to accommodate the first and second gear units  1 ,  2 . The motor gear  22  is connected to a motor (not shown) and extends into the rear case  21  from the second end of the rear case  21  to be engaged with the third planet gears  25 . The second pinions  251  are engaged with the second inner teeth  262 . The user can operate the second rod  244  to axially move the fixing ring  24  to engage the first protrusions  241  with the first positioning ridges  263 , or engage the second protrusions  242  with the second positioning ridges  231 . 
     As shown in  FIG. 2 , when the user operates the first rod  143 , the ring gear  14  is shifted axially toward the second end so that the first inner teeth  142  are engaged with the outer teeth  151  of the second planet gear disk  15 . The second rod  244  is also operated to move the fixing ring  24  toward the first end so that the first protrusions  241  are engaged with the first positioning ridges  263  of the inner gear  26 . At this state, the inner gear  26  cannot rotate. When the motor gear  22  rotates in the forward direction, the second planet gears  27  are rotated in the reverse direction and the second planet gear disk  15  rotates in the forward direction. Because the ring gear  14  is engaged with the first planet gears  13  and the second planet gear disk  15 , the ring gear  14 , the second planet gear disk  15  and the first planet gear disk  12  rotate simultaneously. Therefore, the input speed from the motor gear  22  is transferred into a first speed (high) which is output from the output shaft  18 . 
     As shown in  FIG. 3 , when the user operates the first rod  143 , the ring gear  14  is shifted axially toward the second end so that the first inner teeth  142  are engaged with the outer teeth  151  of the second planet gear disk  15 . The second rod  244  is also operated to move the fixing ring  24  toward the second end so that the second protrusions  242  are engaged with the second positioning ridges  231  of the third planet gear disk  23 . At this state, the third planet gear disk  23  cannot rotate. When the motor gear  22  rotates in the forward direction, the second planet gears  27  are rotated in the reverse direction and the inner gear  26  rotates in the reverse direction so that the second planet gear disk  15  rotates in the forward direction and reduces its speed. Because the ring gear  14  is engaged with the first planet gears  13  and the second planet gear disk  15 , the ring gear  14 , the second planet gear disk  15  and the first planet gear disk  12  rotate simultaneously. Therefore, the input speed from the motor gear  22  is transferred into a second speed (mediate-high) which is output from the output shaft  18 . 
     As shown in  FIG. 4 , when the user operates the first rod  143 , the ring gear  14  is shifted axially toward the first end so that the first inner teeth  142  of the ring gear  14  are disengaged from the outer teeth  151  of the second planet gear disk  15  and the outer ribs  144  of the ring gear  14  are engaged with the inner ribs  111  of the front case  11 . The second rod  244  is also operated to move the fixing ring  24  toward the first end so that the first protrusions  241  of the fixing ring  24  are engaged with the first positioning ridges  263  of the inner gear  26 . At this state, the inner gear  26  cannot rotate. When the motor gear  22  rotates in the forward direction, the second planet gears  27  are rotated in the reverse direction and the second planet gear disk  15  rotates in the forward direction. Because the ring gear  14  is engaged with front case  11 , the ring gear  14  cannot rotate. The first pinion  152  of the second planet gear disk  15  drives the first planet gears  13  to rotate in the reverse direction. The first planet gear disk  12  reduces its speed and rotates in the forward direction so that the input speed from the motor gear  22  is transferred into a third speed (mediate-low) which is output from the output shaft  18 . 
     As shown in  FIG. 5 , when the user operates the first rod  143 , the ring gear  14  is shifted axially toward the first end so that the first inner teeth  142  of the ring gear  14  are disengaged from the outer teeth  151  of the second planet gear disk  15  and the outer ribs  144  of the ring gear  14  are engaged with the inner ribs  111  of the front case  11 . The second rod  244  is also operated to move the fixing ring  24  toward the second end so that the second protrusions  242  of the fixing ring  24  are engaged with the second positioning ridges  231  of third planet gear disk  23 . At this state, the third planet gear disk  23  cannot rotate. When the motor gear  22  rotates in the forward direction, the second planet gears  27  and the inner gear  26  are rotated in the reverse direction. Therefore, the second planet gear disk  15  reduces its speed and rotates in the forward direction. Because the ring gear  14  is engaged with front case  11 , the ring gear  14  cannot rotate. The first pinion  152  of the second planet gear disk  15  drives the first planet gears  13  to rotate in the reverse direction. The first planet gear disk  12  is reduced its speed and rotates in the forward direction so that the input speed from the motor gear  22  is transferred into a fourth speed (low) which is output from the output shaft  18 . 
     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.