Note: Descriptions are shown in the official language in which they were submitted.
CA 02573330 2007-01-08
POWER HAND TOOL
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power hand tools and more particularly, to a
power hand tool having a torque control mechanism and an impact mechanism.
2. Description of the Related Art
A conventional power impact wrench is known comprising a motor, a
transmission gear set, and an impact mechanism. The transmission gear set
reduces the
revolving speed of the rotary driving force of the motor to a predetermined
level for
output. The impact mechanism is adapted to produce an impact against the
output shaft
of the power hand tool intermittently and rapidly in same direction of
rotation when the
output shaft of the power hand tool encountered a resisting force that
surpasses the
output torque, for enabling the output shaft to overcome the resisting force
and to keep
working.
There is known an electric screwdriver, which comprises a motor, a
transmission gear set, and a torque control mechanism. The transmission gear
set
reduces the revolving speed of the rotary driving force of the motor to a
predetermined
level for output. The torque control mechanism is adapted to set the maximum
output
torque of the electric screwdriver, preventing damage to the workpiece.
The aforesaid impact mechanism and torque control mechanism are designed
to fit two reversed requirements. Normally, these two mechanisms do not
coexist in a
power hand tool. However, these two mechanisms may be required in a certain
condition. For example, when a user uses an electric wrench to dismount a tire
from a
vehicle, the electric wrench needs an impact function to overcome the
dismounting
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obstacle, which may be produced due to rust on the screw bolts at the tire or
other
reasons; in order to prevent damage to the screw bolts at the tire due to an
excessive
high torque when mounting the tire, it is necessary to have a torque setting
function in
the power hand tool. However, when arranging these two mechanisms in a power
hand
tool, the functioning of the torque setting mechanism may be damaged when
starting
the impact mechanism, and the impact mechanism fail to function when started
the
torque setting mechanism.
Therefore, it is desirable to provide a power hand tool having a torque
control mechanism and an impact mechanism, which eliminates the aforesaid
problem.
SUMMARY OF THE INVENTION
The present invention has been accomplished under the circumstances in
view. It is therefore one object of the present invention to provide a power
hand tool
having a torque control mechanism and an impact mechanism, which allows
switching
of the impact mechanism between the working position and the non-working
position.
To achieve this object of the present invention, the power hand tool
comprises a housing that accommodates a motor, a transmission gear set, a
torque
control mechanism, and an impact mechanism therein. The torque control
mechanism
has an adjustment device that is movable between a first position and a second
position
inside the housing by a rotation action to set the output torque of the power
hand tool.
The output torque of the power hand tool is at the minimum condition and the
adjustment device stops the impact mechanism from working to prevent
destruction to
the torque setting of the power hand tool when the adjustment device is in the
second
position.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1 is an exploded view of a power hand tool according to a preferred
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embodiment of the present invention.
FICi. 2 is another exploded view in an enlarge scale of a part of the power
hand tool according to the preferred embodiment of the present invention.
FIC~ 3 is a schematic sectional view of the present invention showing the
adjustment device is at the second position.
FICx 4 is another schematic sectional view of the present invention showing
the adjustment device is at first position.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1-3, a power hand tool 1 in accordance with the present
invention is shown comprised of a housing 10, a motor 20, a battery pack 30, a
transmission gear set 40, a torque control mechanisms 50, and an impact
mechanism
60.
The housing 10 is comprised of a left half shall 11, a right half shell 12, a
front shell 13, and a front cap 14. The left half shell 11 and the right half
shell 12 are
abutted against each other. The front shell 13 is fastened to the front side
of the abutted
left half shell 11 and right half shell 12. The front cap 14 has a rear
coupling flange 141
pivotally coupled to the inside wall of the front shell 13 in front of the
left half shell 11
and the right half shell 12 for allowing rotary motion of the front cap 14
relative to the
front shell 13, and a plurality of locating blocks 142 equiangularly spaced
around the
inside wall.
The motor 20 is fixedly mounted inside the housing 10, having a motor shaft
21.
The battery pack 30 is detachably mounted to the housing 10, and adapted to
provide the necessary working electricity to the motor 20.
The transmission gear set 40 is mounted inside the housing 10, comprising a
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first sun gear 41 fixedly mounted on the motor shaft 21 of the motor 20, a
first planet
carrier 42, a second sun gear 421 provided at the center of the first planet
carrier 42, a
first planet gear set 43 rotatably supported on the first planet carrier 42
and meshed
with the first sun gear 41, a second planet carrier 44, a third sun gear 441
provided at
the center of the second planet carrier 44, a second planet gear set 45
rotatably
supported on the second planet carrier 44 and meshed with the second sun gear
421, a
third planet carrier 46, an output shaft 461 fixedly provided at the center of
the third
planet carrier 46, a third planet gear set 47 rotatably supported on the third
planet
carrier 46 and meshed with the third sun gear 441, a first internally toothed
ring 48
meshed with the first planet gear set 43, a second internally toothed ring 49
selectively
meshed with the second planet gear set 45 or the first planet carrier 42, and
a barrel
491 affixed to the inside of the housing 10 to house the aforesaid parts of
the
transmission gear set 40. The transmission gear set 40 reduces the speed of
the rotary
driving force from the motor 20 for output through the output shaft 461.
Further,
shifting the position of the second internally toothed ring 49 changes the
revolving
speed of the output shaft 461. Because this transmission gear set 40 is a
known design
commonly used in conventional power hand tools, no further detailed
description in
this regard is necessary.
The torque control mechanism 50 comprises an internal gear 51, a holder
she1152, an adjustment device 53, a plurality of springs 54, a plurality of
steel balls 55,
and a plurality of pins 56.
The internal gear 51 is meshed with the third planet gear set 47 inside the
housing 10, having an actuating end face 511 and a plurality of protruding
portions 512
respectively extending from the actuating end face 511 and spaced from one
another at
an equal angle.
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The holder shell 52 comprises a shell body 521 and a round shank 524. The
shell body 521 has a first end face 522 and a second end face 523. The round
shank
524 extends perpendicularly from the second end face 523 of the shell body
521,
having an outer thread 525 around the periphery and two longitudinal sliding
grooves
526 at two sides. The shell body 521 has a plurality of through holes 527 cut
through
the first end face 522 and the second end face 523. The holder shel152 defines
an axial
hole 528 extending through the center of the shell body 521 and the center of
the round
shank 524. The holder shell 52 is fixedly mounted inside the housing 10
adjacent to
one side relative to the internal gear 51 with the first end face 522 facing
the actuating
end face 511 of the internal gear 51.
The adjustment device 53 is comprised of an adjustment ring 531, a needle
bearing 532, and a ring member 533. The adjustment ring 531 has a first end
face 5311,
a second end face 5312 opposite to the first end face 5311, an inside wall
5313, an
outside wall 5314, an inner thread 5315 extending around the inside wall 5313
and
corresponding to the outer thread 525 of the round shank 524 of the holder
shell 52,
and a plurality of locating grooves 5316 spaced around the outside wall 5314
and
adapted to receive the locating blocks 142 of the front cap 14. The inner
thread 5315 of
the adjustment ring 531 is meshed with the outer thread 525 of the round shank
524 of
the holder shell 52, keeping the locating grooves 5316 respectively coupled to
the
locating blocks 142. Therefore, rotating the front cap 14 causes the
adjustment ring 531
to move along the round shank 524 of the holder shell 52 between a first
position and a
second position. The ring member 533 has two protruded positioning portions
5331 at
the inner wall thereof. The ring member 533 is sleeved onto the round shank
524 of the
holder shell 52 such that the two protruded positioning portions 5331 are
respectively
coupled to the longitudinal sliding grooves 526 of the holder shell 52 and the
ring
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member 533 is located between the second end face 523 of the holder shell 52
and the
first end face 5311 of the adjustment ring 531. The needle bearing 532 is
attached to
the second end face 5312 of the adjustment ring 531.
The springs 54 are respectively mounted in the through holes 527 of the
holder shell 52.
The steel balls 55 are respectively stopped between the springs 54 and the
actuating end face 511 of the internal gear 51.
The pins 56 are respectively inserted into the through holes 527 of the holder
shell 52 and stopped between the springs 54 and the ring member 533 against
the first
end face 5311 of the adjustment ring 531.
When the adjustment ring 531 is in the first position as shown in FICx 4, the
steel balls 55 receive a first pressure from the springs 54. When the
adjustment ring
531 is in the second position as shown in FICz 3, the steel balls 55 receive a
second
pressure from the springs 54. The second pressure is greater than the first
pressure.
When the internal gear 51 is locked and prohibited from rotary motion, the
transmission gear set 40 reduces the revolving speed of the rotary driving
force from
the motor 20 for output through the output shaft 461. When the internal gear
51 is
unlocked and allowed to rotate and when the output shaft 461 receives a
resisting force,
the internal gear 51 will be rotated, causing the transmission gear set 40 to
run idle.
When wishing to cause rotation of the internal gear 51, it is necessary to
have the
protruding portions 512 at the actuating end face 511 of the internal gear 51
overcome
the pressure from the steel balls 55. Therefore, when the pressure from the
steel balls
55 at the actuating end face 511 of the internal gear 51 is relatively
increased, the
internal gear 51 must receive a relatively greater rotary driving force to
overcome the
pressure from the steel balls 511, i.e., the output shaft 461 must receive a
relatively
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greater resisting force to have the internal gear 51 be rotated, and this
resisting force is
the relatively maximum torque outputted from the output shaft 461 at that
condition.
Therefore, when the adjustment ring 531 is in the second position, the
pressure from
the steel balls 55 against the actuating end face 511 of the internal gear 51
reaches the
maximum, and this pressure is the maximum torque that the output shaft 461 can
output. When the adjustment ring 531 is in the first position, the pressure
from the steel
balls 55 at the actuating end face 511 becomes the least, and this pressure is
the
smallest output torque of the output shaft 461.
The impact mechanism 60 comprises a final output shaft 61, a transmission
shaft 62, an impact element 63, and a spring member 64. The output shat 61 of
the
impact mechanism 60 is rotatably mounted in the front cap 14 and partially
extended
out of the front cap 14, having a coupling portion 611 at one end. The
transmission
shaft 62 is coupled to the output shaft 461 of the second planet carrier 46 of
the
transmission gear set 40 for synchronous rotation with the output shaft 461.
The impact
element 63 is sleeved onto the transmission shaft 62 and axially movable along
the
transmission shaft 62 between two positions, namely, the third position and
the fourth
position. The impact element has a coupling portion 631. When the impact
element 63
is in the third position, the coupling portion 631 of the impact element 63 is
kept
coupled to the coupling portion 611 of the final output shaft 61 of the impact
mechanism 60, allowing rotation of the final output shaft 61 with the
transmission
shaft 62 and the output shaft 461 of the second planet carrier 46 of the
transmission
gear set 40. When the impact element 63 is in the fourth position, the
coupling portion
631 of the impact element 63 is disengaged from the coupling portion 611 of
the final
output shaft 61 of the impact mechanism 60. The spring member 64 is supported
between the transmission shaft 62 and the impact element 63 to hold the impact
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element 63 in the third position.
Further, when the adjustment ring 531 is in the aforesaid first position, the
second end face 5312 is pressed on the needle bearing 532 against the impact
element
63 to hold the impact element 63 in the aforesaid third position, prohibiting
movement
of the impact element 63 to the aforesaid fourth position.
Referring to FIG 4 and FIC'z 3 again, when the user rotated the front cap 14
to move the adjustment ring 531 to the aforesaid second position as shown in
FIC~ 3,
the output torque of the output shaft 461 of the transmission gear set 40
reaches the
maximum. When the final output shaft 61 receives a resisting force at this
time, the
impact element 63 is forced to move from the aforesaid third position to the
aforesaid
fourth position and then disengaged from the final output shaft 61. At the
time the
impact element 63 disengages from the final output shaft 61, the spring member
64
immediately pushes the impact element 63 back to the third position to force
the
coupling portion 631 of the impact element 63 into engagement with the
coupling
portion 611 of the final output shaft 61, thereby achieving the designed
impact effect.
This impact effect won't stop till the resisting force received by the final
output shaft
61 is reduced.
When the user rotated the front cap 14 to move the adjustment ring 531 to
the aforesaid first position, the output torque of the output shaft 461 of the
transmission
gear set 40 reaches the minimum, and the adjustment ring 531 is stopped at the
needle
bearing 532 against the impact element 63 to hold the impact element 63 in the
aforesaid third position. When the final output shaft 61 receives a resisting
force at this
time, the adjustment ring 53 prohibits the impact element 63 from moving to
the fourth
position, and therefore the impact mechanism 60 cannot produce an impact
effect at
this time. If the resisting force received by the final output shaft 61
surpasses the
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torque outputted from the output shaft 461 of the transmission gear set 40 at
this time,
the internal gear 51 will be rotated to interrupt transmission of force from
the motor 20
to the output shaft 461 of the transmission gear set 40. Therefore, the power
hand tool
1 can only output the set torque, preventing the production of a transient
high torque
due to the effect of the impact mechanism 60, thereby preventing damage to the
workpiece.
Although a particular embodiment of the invention has been described in
detail for purposes of illustration, various modifications and enhancements
may be
made without departing from the spirit and scope of the invention.
Accordingly, the
invention is not to be limited except as by the appended claims.
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