BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] 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
[0002] 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.
[0003] 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.
[0004] 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 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.
[0005] 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
[0006] 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.
[0007] 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
[0008]
FIG 1 is an exploded view of a power hand tool according to a preferred embodiment
of the present invention.
FIG 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.
FIG 3 is a schematic sectional view of the present invention showing the adjustment
device is at the second position.
FIG 4 is another schematic sectional view of the present invention showing the adjustment
device is at first position.
DETAILED DESCRIPTION OF THE INVENTION
[0009] 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.
[0010] 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.
[0011] The motor
20 is fixedly mounted inside the housing
10, having a motor shaft
21.
[0012] The battery pack
30 is detachably mounted to the housing
10, and adapted to provide the necessary working electricity to the motor
20.
[0013] The transmission gear set
40 is mounted inside the housing
10, comprising a 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.
[0014] The torque control mechanism
50 comprises an internal gear
51, a holder shell
52, an adjustment device
53, a plurality of springs
54, a plurality of steel balls
55, and a plurality of pins
56.
[0015] 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.
[0016] 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 shell
52 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.
[0017] 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 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.
[0018] The springs
54 are respectively mounted in the through holes
527 of the holder shell
52.
[0019] The steel balls
55 are respectively stopped between the springs
54 and the actuating end face
511 of the internal gear
51.
[0020] 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.
[0021] When the adjustment ring
531 is in the first position as shown in FIG 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 FIG 3, the steel balls
55 receive a second pressure from the springs
54. The second pressure is greater than the first pressure.
[0022] 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 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.
[0023] 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 element
63 in the third position.
[0024] 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.
[0025] Referring to FIG 4 and FIG 3 again, when the user rotated the front cap
14 to move the adjustment ring
531 to the aforesaid second position as shown in FIG 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.
[0026] 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 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.
[0027] 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.