Locking device for output shaft of electric tools

Information

  • Patent Grant
  • 6454020
  • Patent Number
    6,454,020
  • Date Filed
    Tuesday, January 29, 2002
    22 years ago
  • Date Issued
    Tuesday, September 24, 2002
    22 years ago
Abstract
A locking device for output shaft of electric tools includes a plurality of brake pads arranged as a circle in a passage in a casing and the brake pads can be limited by a driving disk to co-rotate with a cam mounted on an output shaft. When the output shaft is rotated manually, the brake pads are pushed by the cam and contact the inside of the passage so as to secure the output shaft to output a torque. The driving disk has a hole wherein two hill portions extend from two opposite sides of the hole. The output shaft extends through the hole. A cover plate is mounted to the driving disk and has an aperture whose two opposite sides are located alignment with the two opposite sides of the hole in the driving disk. The driving disk has pawls on a surface thereof and limit the brake pads not to contact the inside of the passage.
Description




FIELD OF THE INVENTION




The present invention relates to a locking device for securing the output shaft of an electric tool when the shaft is used manually with electric power.




BACKGROUND OF THE INVENTION




A conventional electric tool is generally driven by electric power which can be a rechargeable pack or a power supply coming from the wall. An active gear connected to the driving shaft of motor is engaged with a gear set which is then engaged with a passive gear connected to the output shaft. When the electric power is out, the user may use the output shaft manually and the passive gear is used as an active gear to drive the driving shaft of the motor. This causes the drill spins together with the operation and cannot output a torque to unscrew a screw or bolt. Some manufacturers develop a locking device for secure the output shaft during manual operation so that the output shaft can output a torque. The locking device includes several brake pads each having a longitudinal protrusion and a radial protrusion. These brake pads are supposed to contact an inside of a casing in which the output shaft is located. A cam is mounted to the output shaft and rotated with the output shaft. A driving disk is connected to the gear set and includes several fan-shaped bosses which are respectively located between the brake pads. When the driving disk is rotated, the bosses shift the longitudinal protrusions to release the brake status of the brake pads so that the output shaft, the cam and the brake pads are co-rotated. When the driving disk stops, and the output shaft is rotated in opposite direction, the cam pushes the brake pads to contact the inside of the casing to secure the output shaft. However, the longitudinal protrusions of the brake pads could separate from the driving disk when-the driving disk reduces its speed. The brake pads will impact the inside of the casing and generate noise.




SUMMARY OF THE INVENTION




In accordance with one aspect of the present invention, there is provided a locking device for output shaft of electric tools and the device includes a casing having a passage through which a shaft extends. The shaft has a polygonal distal end on which a cam is mounted. The cam has a plurality of protrusions and recesses are defined between the protrusions. A plurality of brake pads each have two blocks and are located in the passage of the casing. A driving disk has a plurality of pawls on a first surface thereof and a width of each of the pawls is less than a distance between two blocks of each of the brake pads. A hole is defined through the driving disk and the distal end of the output shaft is engaged with the hole of the driving disk. Two opposite sides of the hole of the driving disk have a hill portion at an intermediate portion thereof. A plurality of concavities are defined in a second surface of the driving disk and each of which receives a spring a ball therein. A cover plate is mounted to the second surface of the driving disk and a plurality of holes are defined through the cover plate. The number of the holes in the cover plate are two times of the number of the concavities in the driving disk. The balls are engaged with half number of the holes. The cover plate has an aperture and two opposite sides of the aperture are in alignment with two opposite sides of the hole in the driving disk.




The primary object of the present invention is to provide a locking device wherein the swing of the brake pads are limited when the rotation of speed of the driving disk is reduced so that the brake pads will not impact the inside of the passage of the casing.




The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is an exploded view to show the locking device of the present invention;





FIG. 2

is an exploded view to show the driving disk and a cover plate of the locking device of the present invention;





FIG. 3

is an exploded view to show another embodiment of the driving disk and a cover plate of the locking device of the present invention;





FIG. 4

is a cross sectional view to show the locking device of the present invention;





FIG. 5

is a cross sectional view seen from the cutting line A—A;





FIG. 6

is a plan view to show the locking device when the shaft is driven counter clockwise by the driving disk, and





FIG. 7

is a plan view to show the locking device when the shaft is driven clockwise by the driving disk.











DETAILED DESCRIPTION OF THE INVENTION




Referring to

FIGS. 1

to


4


, the locking device for an electric tool of the present invention comprises a casing


1


which is connected to a barrel of the tool which is not shown, and a passage


11


is defined through the casing


1


. A knurl surface


110


is defined in an inside of the passage


11


. An output shaft


2


with a bearing is received in the passage


11


and includes a distal end


21


which includes two surfaces defined in two sides thereof. A cam


5


has a hole


51


in which the distal end


21


is engaged and the cam


5


includes protrusions


52


and recesses


53


defined between the protrusions


52


. Five brake pads


3


are arranged as a circle and received in the passage


11


. Each of the brake pad


5


has two blocks


32


on two ends thereof and a knurl surface


33


is defined in an outside of each of the brake pads


3


. The brake pads


3


are respectively located in the recesses


53


of the cam


5


of the output shaft


2


.




A driving disk


4


for driving the output shaft


2


includes a hole


42


through which the distal end


21


of the shaft


2


extends. Two opposite sides of the hole


42


each have a hill portion


421


on the intermediate portion thereof so that two fan-shaped spaces


422


are defined at two sides of the hill portion


421


. A raised portion


41


extends from a first surface of the driving disk


4


and a plurality of pawls


411


extend from the raised portion


41


. The width of each of the pawls


411


is less than the distance between two blocks


31


of each of the brake pads


3


. A plurality of rods


43


extend from a second surface of the driving disk


4


and pinions (not shown) are respectively mounted on the rods


43


so that the driving disk


4


can be rotated by a gear set (not shown). A plurality of concavities


44


are defined in the second surface of the driving disk


4


and each concavity


44


has a spring


6


a ball


7


received therein. A cover plate


8


is mounted to the second surface of the driving disk


4


and a plurality of holes


81


are defined through the cover plate


8


. The number of the holes


81


is two times of the number of the concavities


44


. The balls


7


are urged by the corresponding springs


6


and engaged with the holes


81


so that the cover plate


8


cannot rotated relative to the driving disk


4


. The cover plate


8


has an aperture


82


and two opposite sides


821


of the aperture


82


are located in alignment with the two parallel sides of two fan-shaped spaces


422


on different sides as shown in FIG.


6


. The two respective sides of other two fan-shaped spaces


422


of the hole


42


are not located in alignment with the other two sides of the aperture


82


.




As shown in

FIG. 2

, a plurality of recesses


46


are defined in the second surface of the driving disk


4


and each recess


46


communicates with a notch


47


located adjacent to the recess


46


. A plurality of flanges


83


extending from the cover plate


8


and may insert through the notches


47


when connecting the cover plate


8


to the driving disk


4


, and the flanges


83


are then slid into the recesses


46


. This allows the cover plate


8


to be rotatable relative the driving disk


4


but will not disengaged from the driving disk


4


.





FIG. 3

shows the other way that the driving disk


4


is engaged with the cover plate


8


. A pressing plate


9


having a circular hole


91


is matched with the cover plate


8


. The driving disk


4


has stubs


45


which extend through holes in the cover plate


8


and then are pressed to be flat to press on a periphery of the pressing plate


9


and secure the cover plate


8


and the pressing plate


9


to the driving disk


4


.




The pawls


411


are arranged between the two blocks


31


of the brake pads


3


and the angle that the distal end


21


of the output shaft


2


can swing in the two fan-shaped spaces


422


is larger than the angle that the pawls


411


swing between the two blocks


31


, such that the two ends of the pawls


411


contact the blocks


31


when the driving disk


4


is rotated clockwise or counter clockwise.




The motor of the tool drives the gear set which drives the driving disk


4


The pawls


411


contact the blocks


31


on one end of the brake pads


3


and restrain the swing of the brake pads


3


. Therefore, the outer surface of the brake pads


3


will not contact the inside of the passage


11


so that the output shaft


2


, the cam


5


and the brake pads


5


can be rotated by the driving disk


4


.




When no electric power is supplied, an torque is applied to the output shaft


2


, the distal end


21


drives the cam


5


and the protrusions


52


push protrusion on the inner surface


32


of the brake pads


3


and the knurl surface


33


of the brake pads


3


contact the knurl surface


110


in the passage


11


so as to secure the output shaft


2


which is not driven by the driving disk


4


. Therefore the output shaft


2


can be operated manually to output a torque.




In order to avoid the impact between the brake pads


3


and the inside of the passage


11


when the speed of the driving disk


4


is reduced to cause the distal end


21


of the output shaft


2


to swing within the fan-shaped spaces


422


and the brake pads


3


to swing due to initial movement, the cover plate


8


provides a correction function. The aperture


82


of the cover plate


8


is completely matched with the distal end


21


of the output shaft


2


so that the distal end


21


of the output shaft


2


does not have any room to move in the fan-shaped spaces


422


during the rotation of the output shaft


2


. When the speed of the driving disk


4


is reduced, the output shaft


2


does not move in the fan-shaped spaces


422


and the brake pads


3


stop swinging so that the no noise is generated and the output shaft


2


is rotated smoothly without the interruption of the brake pads


3


.





FIG. 6

shows that when the driving disk


4


rotates counter clockwise, the balls


7


are engaged with the holes


81


on the left side of the cover plate


8


. The two sides of the distal end


21


contact the two sides of the two fan-shaped spaces


422


on opposite sides, so that the output shaft


2


can be rotated counter clockwise by the driving disk


4


. When the output shaft


2


is to be rotated clockwise, the user holds the knob (not shown) on the driving disk


4


and rotates the driving disk


4


clockwise till the balls


7


are engaged with the holes


81


on the right side as shown in FIG.


7


. The driving disk


4


can be rotated and drives the output shaft


2


clockwise without any noise.




While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.



Claims
  • 1. A locking device for output shaft of electric tools, comprising:a casing having a passage; a shaft rotatably received in the passage and having a polygonal distal end; a cam mounted to the output shaft and co-rotated with the output shaft, the cam having a plurality of protrusions and recesses defined between the protrusions; a plurality of brake pads each having two blocks and a protrusion extending from an inner surface of each of the brake pads, the brake pads located in the passage of the casing; a driving disk having a plurality of pawls on a first surface thereof and a width of each of the pawls being less than a distance between two blocks of each of the brake pads, a hole defined through the driving disk and the distal end of the output shaft engaged with the hole of the driving disk, two opposite sides of the hole of the driving disk each having a hill portion at an intermediate portion thereof, a plurality of concavities defined in a second surface of the driving disk and each of which receives a spring a ball therein, and a cover plate mounted to the second surface of the driving disk and a plurality of holes defined through the cover plate, the number of the holes in the cover plate being two times of the number of the concavities in the driving disk, the balls engaged with half number of the holes, the cover plate having an aperture and two opposite sides of the aperture being in alignment with two opposite sides of the hole in the driving disk.
  • 2. The device as claimed in claim 1, wherein the second surface of the driving disk has a plurality of recesses and each recess communicating with a notch located adjacent to the recess, the cover plate having a plurality of flanges which are inserted into the notches and slid into the recesses to connect the cover plate to the driving disk.
  • 3. The device as claimed in claim 1, wherein the second surface of the driving disk has a plurality of stubs which extend through the cover plate and are pressed to be flat to secure the cover plate to the driving disk.
US Referenced Citations (7)
Number Name Date Kind
4076449 Theis, Jr. et al. Feb 1978 A
4947939 Hung Aug 1990 A
5887666 Chen et al. Mar 1999 A
5915484 Hsieh Jun 1999 A
6209658 Yoon Apr 2001 B1
6230819 Chen May 2001 B1
6311787 Berry et al. Nov 2001 B1