Tool head structure of power screwdriver

A tool head structure of power screwdriver, including an engaging clutch device for indirectly controlling the rotation of a driven member. The clutch device includes weight blocks which are subject to centrifugal force and thrown outward so as to indirectly press the leaf springs to further press the brake blocks. The brake blocks extend into an inner annular section of the rotary seat to drivingly engage with the driven member in the rotary seat. Therefore, when the rotary seat is coupled with a motor, at low rotational speed, simply the rotary seat is rotated. However, when the rotary seat reaches a certain high rotational speed, the weight blocks are subject to centrifugal force to indirectly press the brake blocks to drivingly engage with the driven member, whereby the driven member is rotated to tighten or untighten the screw.

BACKGROUND OF THE INVENTION 
The present invention relates to a tool head structure of power 
screwdriver, which includes less parts and can be easily manufactured and 
assembled. The tool head structure can be durably used with better driving 
effect and can be easily carried. The tool head structure is applicable to 
power tools such as power screwdriver for tightening and untightening car 
tire screws. 
Power tools are widely used in various fields to facilitate operation and 
save time and labor. For example, a power socket wrench is used to 
untighten and tighten the screws (nuts) of a car tire to facilitate 
detacment and installation of the car tire. In the power socket wrench, 
the socket is driven by a motor via a driving mechanism so as to easily 
tighten and untighten the screws or nuts. 
FIG. 10 shows a clutch and driving mechanism of a conventional power 
screwdriver, including a base 10, a driving member 20, a driven member 30, 
a pivot shaft 40, a clutch 50 and two pin members 60. The base 10 is 
formed with a central hole 100. The wall of the base 10 is formed with a 
notch 101 communicating with the central hole 100. The clutch 50 is 
disposed with a front panel 51 for connecting the clutch 50 with one end 
of the base 10. An output shaft of a motor is coupled with the clutch for 
driving the base to rotate. The driving member 20 is formed as an arch 
block and pivotally connected with upper portion of the notch 101 via the 
pivot shaft 40. The driving member 20 is freely swingable about the pivot 
shaft 40 in the notch 101. The front end of the driven member 30 is formed 
with tooth blocks 301. The rear end of the driven member 30 is disposed 
with a square connector for connecting with the socket. The tooth blocks 
301 are positioned into the central hole 100 of the base 10. Each pin 
member 60 is formed with an annular groove 601. The front panel 51 of the 
clutch 50 is formed with two slots 501. The pin members 60 are fitted into 
the slots 501 at the annular grooves 601 and extended into the through 
holes 102 of the base. In normal state, the pin members 60 are locked at 
lower end of the driving member 20. After the clutch 30 is rotated at high 
speed, the pin members 60 are backward retracted into the through holes 
102 of the base 10. During swinging, two ends of the driving member 20 
collide the driven member 30 in the central hole so as to rotate the 
driven member 30 and indirectly drive the socket. 
According to the above arrangement, when the driving member 20 collides the 
tooth blocks 301 of the driven member 30, the driving member 20 will 
suffer a reaction force which forms a shear force exerted onto the pivot 
shaft 40. This may lead to damage of the pivot shaft. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a tool head 
structure of power screwdriver, which includes less parts and can be 
easily manufactured and assembled. The tool head structure can be durably 
used with very high driving effect. 
According to the above object, the tool head structure of power screwdriver 
of the present invention includes an engaging clutch device, a driven 
member and a housing enclosing the clutch device and the driven member. 
The clutch device serves to indirectly control the rotation of a driven 
member. One end of the driven member is disposed with an engaging block. 
The driven member is filled in an inner annular section of the rotary 
seat. Two brake blocks are pressed by springs and leaf springs and 
forcedly installed in slide ways of upper end of the inner annular section 
of the rotary seat via weight blocks in cooperation with the springs. When 
the rotary seat is coupled with a motor of the power tool, at low 
rotational speed, simply the rotary seat is rotated. However, when the 
rotary seat reaches a certain high rotational speed, the weight blocks are 
subject to centrifugal force to indirectly press the leaf springs and the 
brake blocks to make the brake blocks extend into the inner annular 
section of the rotary seat and drivingly engage with the driven member. 
Therefore, the driven member is rotated to tighten or untighten the screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Please refer to FIG. 1. The tool head 1 of the present invention includes a 
housing 1, an engaging clutch device 2 and a driven member 3. The clutch 
device 2 includes a rotary seat 21, brake blocks 22, brake block springs 
23, leaf springs 24, weight blocks 25 and extension spring 26. 
Referring to FIGS. 2 and 3, the rotary seat 21 is formed with an inner 
annular section 211 and two slide ways 212 passing through the inner 
annular section 211. As shown in FIG. 3, two sides of the slide way are 
disposed with engaging boards 2121 disposed with the brake block springs 
23. One end of the rotary seat is disposed with an extending rotary shaft 
213. At a certain length of the rotary shaft is disposed laterally 
extending locating arms 214, 215. The end of the rotary shaft is formed 
with a stepped section 216. Pin members 217, 218 are disposed on the 
rotary shaft near the slide ways 212. 
The brake block 22 has a profile corresponding to that of the slide way 
212. The brake block 22 is formed with a slope block body 221. Two sides 
of the slope block body 221 are formed with projecting blocks 222 for 
pressing the brake block springs 23. 
The leaf spring 24 is an arched plate disposed with a hook section 241 and 
a pin hole 242. 
Referring to FIG. 3-1, the weight block 25 includes an upper half block 254 
and a lower half block 255 which are respectively formed with 
corresponding cavities 2541, 2551. The cavity 2541 of the upper half block 
254 is communicated with a narrowed through hole 2542. The wall of the 
cavity 2551 of the lower half block 255 is formed with a thread section 
2552. After placing a spring 256 into the cavity, a bolt 257 is passed 
through the through hole 2542 to screw with the thread section 2552 so as 
to mate the upper and lower half blocks. In addition, the two half blocks 
are formed with locating sockets 258 in which a locating pin 259 is 
positioned. An upper end of the upper half block 254 is formed with a pin 
hole 251. Two sides of lower end of the lower half block 254 are disposed 
with two engaging bosses 252. A pin member 253 is passed through the 
locating arm 214 and the pin holes 251 so as to swingably locate the 
weight block 25 on the locating arms 214, 215. Two ends of the extension 
spring 26 are hooked on the engaging bosses 252 of the weight blocks 25 on 
two sides of the rotary seat 21, whereby in normal state, the two weight 
blocks are adjacent to each other. 
When assembled, the projecting block 222 of the brake block 22 presses the 
spring 23 into the slide way 212. The spring 23 cooperates with the 
engaging boards 2121 on two sides of the slide way to support and 
resiliently lift the brake block 22. The leaf spring 24 is pivotally 
connected with the rotary shaft 213 via the pin members 217, 218 and the 
pin hole 242. The weight block 25 is pivotally connected with the locating 
arms 214, 215 via the pin member 253 and hooked with the spring 26 so as 
to form the clutch device 2 of the present invention. 
Please refer to FIGS. 4 to 6, wherein FIG. 4 shows that the clutch device 2 
is not rotated in a normal state. The two brake blocks 22 are lifted by 
the spring 23 into the slide ways 212. At this time, the rotary shaft 213 
is coupled with the motor. At a low rotational speed, the rotary seat 21 
will self-rotate without engaging with the driven member 3. As shown in 
FIG. 5, when the rotary seat 21 is rotated to a higher speed, due to 
centrifugal force, the weight blocks 25 are synchronously respectively 
thrown outward. Therefore, the long end of the body thereof expectedly 
presses the leaf spring 24 to indirectly depress the brake block 22 to 
extend into the inner annular section 211 of the rotary seat 21.Referring 
to FIG. 6, the brake blocks 22 are formed with slope blocks 221 opposite 
to each other (as shown in FIGS. 8 and 9). 
Referring to FIGS. 1 and 3, the rotary shaft 31 is disposed at the center 
of the driven member 3. The end of the rotary shaft is disposed with a 
stepped section 311. A bearing 32 is fitted on the stepped section 311 and 
filled into the hole of the inner annular section 211 of the rotary seat 
21. In addition, a large bearing 33 is fitted on the other end of the 
driven member 3. The driven member 3 is fitted with a collar 34 and 
installed in the housing 1. One end face of the driven member 3 proximal 
to the brake block 22 is disposed with an arch engaging block 312. 
Referring to FIGS. 8 and 9, after the weight block 25 is pressed downward 
due to high speed rotation of the rotary seat 21, the slope block 221 at 
the center of the brake block 22 will extend into the inner annular 
section 211. At this time, the slope block 221 will collide the engaging 
block 312 of the driven member 3. By means of the design of the slope 
block 221, the brake block 22 will instantaneously retract. After the 
engaging block 312 slides into the space between the two brake blocks 22 
along the slope block 221, the rotary seat 21 is drivingly engaged with 
the driven member 3 to provide the torque for tightening or untightening a 
screw. 
The driving engagement between the rotary seat 21 and the driven member 3 
is achieved in such a manner that the slope blocks 221 of the brake blocks 
22 are oppositely arranged with different rotary directions. Therefore, 
when the driven member 3 is driven clockwisely (as shown in FIG. 8), the 
engaging block 312 of the brake block 3 will slide over the slope block 
221a and is engaged with the back engaging section a of the slope block 
221 as shown in FIG. 8 to achieve the driving engagement. Reversely, as 
shown in FIG. 9, in the case of counterclockwise rotation, after the 
engaging block 312 of the driven member 3 slides over the slope block 221, 
the engaging block 312 will engage with the back engaging section b of the 
slope block 221a to achieve the driving engagement so as to buffer the 
collision force of the brake block 22 onto the engaging block 312 of the 
driven member 3. 
Referring to FIGS. 3-1, 4 and 5, under high speed rotation of the rotary 
seat 21, the weight blocks 25 in the brake blocks 22 will suffer 
centrifugal force and be thrown away to compress the leaf springs 24. 
Thereafter, via the leaf springs 24, the force is transmitted to press the 
brake block 22, making the slope block 221 descend to collide the engaging 
block 312 of the driven member 3. At this time, a reaction force is 
exerted onto the brake block 22. The weight block 25 is designed to have 
separate upper and lower half blocks 254, 255 so that under high speed 
rotation of the rotary seat 21, by means of the centrifugal depression 
force of the locating arms 214, 215, a trend of compression of the weight 
blocks 25 is indirectly absorbed by the springs 255 in the weight blocks 
25. Therefore, the leaf springs 24 are prevented from being compressed and 
bent and deformed so as to prolong the using life. 
Referring to FIG. 7, the tool head 1 of the present invention is coupled 
with a lock ring 4 and a main body 5. The end of the tool head is disposed 
with resilient latch claws 6 for connecting the tool head with the main 
body 5 enclosing a motor to form an electric power tool. 
It should be noted that the above description and accompanying drawings are 
only used to illustrate some embodiments of the present invention, not 
intended to limit the scope thereof Any modification of the embodiments 
should fall within the scope of the present invention.