Power wrench torque transmission mechanism

A torque transmission mechanism to be used in a power wrench includes a body driven by a motor, having a central bore to rotatably support therein a toothed end of an output shaft. The toothed end of the shaft has a pair of diametrically opposite teeth, each defined by two circumferentially opposite contact faces that extend along radii of the output shaft. The body has a radial notch communicating the bore with a coupling member pivotally received therein. The coupling member has two opposite wings alternately movable into the bore with the rotation thereof to selectively engage one of the teeth for driving the shaft. A centrifugal clutch is provided between the body and the motor to control the movement of the wings. The control comprises two pins movable between an engagement position where the pins engage the coupling member and prevents the wings of the coupling member from moving into the bore and a disengagement position where the pins disengage from the coupling member and the coupling member is allowed to rotate freely. The pins have circumferential grooves to be loosely received within open slots provided on the clutch, while maintaining the pins thereon, to accommodate sideways force applied thereto so as to increase the service life thereof.

FIELD OF THE INVENTION 
The present invention relates generally to a power wrench which is capable 
of applying torque impulse to loose/tighten the wheel stub in an 
intermittent fashion and in particular to a torque transmission mechanism 
for the power wrench. 
BACKGROUND OF THE INVENTION 
Power wrenches for loosening/tightening stud nuts or bolt by applying 
intermittent torque thereto are known. Examples are U.S. Pat. Nos. 
4,727,780, 4,920,831, 4,947,939, 5,035,161 and 5,412,546, Japanese patent 
publication No. 7-42617 and Japanese utility model No. 3017657, Chinese 
patent Nos. 24796 and 213255, Canadian patent Nos. 1,245,482 and 
2,030,473, Australian patent No. 589089 and Taiwanese patent Nos. 34467 
and 62327. All these patents are related to power wrenches comprising a 
hollow body coupled to a motor to be driven thereby, a coupling member 
having two opposite wings pivoted to the body and rotatable relative 
thereto to have either one of the wings swing into the body, an output 
shaft having a toothed end rotatably and substantially co-axially received 
within the body to be engaged by the wings of the coupling member so as to 
drive the output shaft to transmit torque to a tool, such as a socket, 
secured to an opposite end of the shaft and a clutch to control the 
engagement between the wings and the toothed end of the output shaft so as 
to generate an intermittent torque output at the output shaft. 
Among these known patents, U.S. Pat. No. 5,412,546 is a particularly good 
design. The design of this U.S. patent, however, still has some drawbacks 
in the torque transmission mechanism thereof and can be further improved. 
It is therefore desirable to provide a power wrench, based on the teaching 
of U.S. Pat. No. 5,412,546 with further improvement to overcome the 
drawbacks of the prior patent. 
SUMMARY OF THE INVENTION 
The principal object of the invention is to provide a power wrench torque 
transmission mechanism comprising improvements over the known device of 
U.S. Pat. No. 5,412,546 by providing the output shaft with a double-faced 
tooth configuration so as to improve the working efficiency of the teeth 
of the output shaft, as compared to single-faced configuration teeth 
adapted in the '546 patent. 
It is another object of the present invention to provide a torque 
transmission mechanism wherein the control pins that are driven by the 
centrifugal clutch to control the torque impulse output of the output 
shaft are loosely connected to the centrifugal clutch so as to accommodate 
sideways force applied thereto and thus increase the service life thereof 
as compared to the completely fixed control pins adapted in the prior art. 
In accordance with the present invention, there is provided a power wrench 
torque transmission mechanism, comprising a body driven by a motor and 
having a central bore to rotatably support therein a toothed end of an 
output shaft. The toothed end of the shaft has a pair of diametrically 
opposite teeth, each defined by two circumferentially opposite contact 
faces that extend along radii of the output shaft. The body has a radial 
notch communicating the bore with a coupling member pivotally received 
therein. The coupling member has two opposite wings alternately movable 
into the bore with the rotation thereof to selectively engage one of the 
teeth for driving the shaft. A centrifugal clutch is provided between the 
body and the motor to control the movement of the wings. The control 
comprises two pins movable between an engagement position where the pins 
engage the coupling member and prevents the wings of the coupling member 
from moving into the bore and a disengagement position where the pins 
disengage from the coupling member and the coupling member is allowed to 
rotate freely. The pins have circumferential grooves to be loosely 
received within open slots provided on the clutch, while maintaining the 
pins thereon, to accommodate sideways force applied thereto so as to 
increase the service life thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings and in particular FIG. 1, wherein a power 
wrench torque transmission mechanism constructed in accordance with the 
present invention is shown, the power wrench torque transmission mechanism 
of the present invention, which will be abbreviated "the mechanism" 
hereinafter, is generally housed in a housing (not shown) to be driven by 
a motor (not shown) which is also housed within the housing under the 
control of a user-actuateable switch (not shown). The mechanism comprises 
a hollow cylindrical main body 1, having a central bore 10 with an open 
end 14 and a closed end 15 connected together by a cylindrical 
circumferential side wall 16. A projection 151, preferably cylindrical, is 
co-axially or concentrically mounted to the closed end 15 of the main body 
1 with a central hole 152 extending therethrough to receive and fix to a 
spindle of the motor (not shown) so as to be rotatable with the motor 
spindle for transmitting torque/rotation from the motor to the main body 
1. 
The main body 1 comprises a radial notch 11 formed on the side wall 16 and 
in communication with the central bore 10 to loosely receive therein a 
coupling member 2 of complemental shape and size. A pivot pin 4 extends 
through holes 12 formed on the main body 14 at axially opposite edges of 
the notch 11 and a hole 20 formed on the coupling member 2 to freely 
rotatably support the coupling member 2 within the notch 11. The hole 20 
is formed on a central portion of the coupling member 2 with two opposite 
wings 23 and 24 extending laterally from the central portion of the 
coupling member 2 where the hole 20 is located. 
Preferably, each of the wings 23 and 24 has a remote end edge 22 which 
points into the central bore 10. The free rotation of the coupling member 
2 about the pivot pin 4 allows the end edge 22 of either one of the wings 
23 and 24 to move from a neutral position where the coupling member 2 is 
substantially flush with the side wall 16 of the main body 1 and thus the 
end edges 22 are located substantially symmetrical with respect to the 
main body 1 so as to form a continue cylindrical surface with the 
cylindrical side wall 16 of the main body 1 toward a working position 
where the end edge 22 of one of the wings 23 and 24 is moved into the 
central bore 10. 
The coupling member 2 also has an inclined side surface 21 formed on one 
side thereof facing the closed end 15 of the main body 1 and extending 
from the end edge 22 of one of the wings 23 and 24 to the edge 22 of the 
other wing. 
The open end 14 of the main body 1 receives an output shaft 3 to extend 
into the central bore 10 of the main body 1 so that an expanded end 31 of 
the output shaft 3 is rotatably supported within the central bore 10 of 
the hollow cylindrical main body 1 and substantially registered with the 
notch 11 and the coupling member 2. The output shaft 3 has an opposite, 
driving tip end 32 extending out of the wrench housing and adapted to 
engage and drive a tool, such as a socket. 
The expanded end 31 of the output shaft 3 comprises a pair of teeth 310, 
preferably diametrically opposite to each other and each comprising a 
double-faced configuration that comprises two circumferentially opposite 
contact faces 311 substantially extending along radii of the output shaft 
3. The teeth 310 are shaped and sized so as to be rotatable within the 
central bore 10 of the main body 1 when the coupling member 2 is in the 
neutral position, but engageable by the end edge 22 of one of the wings 23 
and 24 of the coupling member 2 by the contact engagement between one of 
the faces 311 and the end edge 22 when the coupling member 2 is rotated 
relative to the main body 1 to the working position where the one of the 
end edges 22 is moved deeply into the central bore 10. 
The double-faced configuration of the teeth 310 of the output shaft 3 
provides the advantage that once the end edges 22 of the coupling member 2 
miss one of the teeth 310, they may hit the contact face 311 of the other 
tooth 310 so that the working efficiency of the power wrench may be 
increased as compared to the conventional design wherein the teeth have 
only one contact face. 
A centrifugal clutch 5 is mounted to the projection 151 of the closed end 
15 of the main body 1. As best seen in FIGS. 2 and 3, the centrifugal 
clutch 5 comprises a disk-like member 54 having a first surface facing the 
closed end 15 of the main body 1 on which at least a control pin 6 is 
fixed to point toward the closed end 15 of the main body 1. It is 
preferable to have two such control pins 6 fixed on the disk 54 as 
illustrated in the specific embodiment shown in the drawings. 
The disk 54 also has a second surface facing away from the closed end 15 of 
the main body 1 on which a cylinder 540 is formed to be movably or 
slidably fit over the projection 151 of the main body 1. 
To mount the control pins 6, the disk 54 has formed thereon an open slot 
541 of a given width for each of the control pins 6. Each of the control 
pins 6 has formed on an end thereof a circumferential groove 61, see FIG. 
1, which has an outer diameter substantially corresponding to the width of 
the open slot 541 to be loosely and thus movably receivable therein with 
an opposite free end of the control pin 6 pointing toward the closed end 
15 of the main body 1. Preferably, a pre-determined clearance is provided 
between the circumferential groove 61 of each of the control pins 6 and 
the width of the respective open slot 541 of the disk 54. This allows the 
control pins 6 to accommodate sideways forces applied thereto during the 
operation of the wrench so as to elongate the service life thereof. 
The closed end 15 of the main body 1 has holes 13 formed thereon and 
corresponding in position to the control pins 6 so that when the disk 54 
of the clutch 5 is movably fit over the projection 151, the control pins 6 
are received within the holes 13 to be movable, by the movement of the 
disk 54 relative to the projection 151, between an engaging position where 
the free ends of the control pins 6 extend out of the holes 13 and enter 
the notch 11 to be located closely under and in contact engagement with 
the inclined side surface 21 of the coupling member 2 and thus prevent the 
coupling member 2 from rotation relative to the main body 1 and maintain 
the coupling member 2 at the neutral position thereof, as shown in FIGS. 4 
and 6, and a disengaging position where the control pins 6 are withdrawn 
into the holes 13 and disengage from the inclined side surface 21 of the 
coupling member 2 and thus forming no constraint to the rotation of the 
coupling member 2, as shown in FIGS. 5 and 7. 
Preferably, the free ends of the control pins 6 are tapered to facilitate 
their movement into contact engagement with the inclined side surface 21 
of the coupling member 2 and helping forcing the wings 23 and 24 to move 
from the working position back to the neutral position by the camming 
engagement therebetween. 
The centrifugal clutch 5 further comprises a base plate 55 fixed to the 
projection 151 of the main body 1 with two movable members 51 movably 
attached thereto. Each of the movable members B1 is rotatably supported on 
the base plate 55 with a pair of helical springs 52 are arranged between 
the two movable members 51 to bias the movable members 51 toward each 
other. Each of the movable members 51 also has an end in contact 
engagement with the disk 54 so that when the movable members 51 are 
rotated relative to the base plate 55 away from each other, the disk 54 is 
allowed to move relative to the projection 151 of the main body 1 and thus 
moving the control pins 6 to disengage from the coupling member 2. 
Each of the movable members 51 has a weight 53 fixed thereon which when 
rotated in a high speed generates a force to move the movable members 51 
against the helical spring 52 with the centrifugal force acting thereupon. 
In operation, since the centrifugal clutch 5 is fixed to the projection 151 
of the main body 1, the rotational speed of the main body 1 generates a 
centrifugal force acting upon the weights 53 of the centrifugal clutch 5 
to rotate the movable members 51 relative to the base plate 55 against the 
biasing force of the helical springs 52. Under this situation, the disk 54 
is allowed to move relative to the cylindrical projection 151 of the main 
body 1 to disengage the control pins 6 from the coupling member 2 (the 
disengaging position) and thus allowing the coupling member 2 to rotate 
relative to the main body 1, making one of the wings 23 and 24 move into 
the central bore 10 to hit and impact one of the teeth 310 of the output 
shaft 3 so as to transmit a torque impulse or rotation to the tool fixed 
to the driving tip end 32 of the output shaft 3 for performing 
loosening/tightening operation. 
On the other hand, once the driving tip end 32 is engaged with a nut or 
bolt, the rotation of the output shaft 3 is stopped by the reaction torque 
from the nut or bolt to be loosened/tightened. Under this situation, the 
biasing force of the helical springs 52 becomes greater than the 
centrifugal force provided by the rotation of the weights 53 so as to 
force the disk 54 and the control pins 6 to move toward the main body 1 
and thus the control pins 6 enter into the notch 11 toward the engaging 
position, forcing the coupling member 2 back to the neutral position 
thereof. The rotation of the output shaft 3 then resumes due to the 
disengagement of the coupling member 2 from the teeth 310 of the output 
shaft 3. The repeated high speed and low speed cycle of the output shaft 3 
will continue until the nut or bolt is tightened or loosened. 
It is apparent that although the invention has been described in connection 
with the preferred embodiment, it is contemplated that those skilled in 
the art may make changes to the preferred embodiment without departing 
from the scope of the invention as defined in the appended claims.