Power hand tool

Abstract

A power hand tool includes a housing, a motor mounted inside the housing, a transmission member coupled to the motor, a driven member, which has grooves on one side thereof facing the transmission member, a plurality of steel balls respectively mounted in the grooves of the driven member, a plurality of spring members respectively mounted in the transmission member and stopped at the steel balls for enabling the driven member to be rotated by the transmission member upon operation of the motor, and a tool bit adaptor fastened to the driven member. When the driven member receives a heavy reaction force through the tool bit adaptor, the steel balls can be disengaged from the grooves, thereby causing disconnection of the transmission member from the driven member so that the power hand tool runs idle to prevent

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to power hand tools and more specifically, to a power hand tool, which can prevent damage to the internal transmission mechanism thereof and/or the fastener driven by the power hand tool upon receiving a reaction overload.

2. Description of the Related Art

A conventional power hand tool mainly comprises a housing and a motor mounted inside the housing. A bit adaptor is connected to an output shaft of the motor for holding a bit, for example a screwdriver bit. When pressed the starting button of the power hand tool to start the motor, the output shaft is driven to rotate the bit adaptor and the screwdriver bit held in the bit adaptor, thereby driving the screw engaged with the screwdriver bit into a workpiece, for example, a circuit board.

However, if the user does not release the starting button immediately after the screw has been fully driven into the workpiece, the output shaft will keep rotating the bit adaptor and the screwdriver bit against the screw at the workpiece. At this time, the screw or workpiece or the internal transmission mechanism of the power hand tool may be damaged due to an overload. In order to prevent this problem, the user must keep adjusting the force pressed on the starting button so as to adjust the output torque of the power handle tool. Therefore, the use of this kind of power hand tool is inconvenient.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances in view. It is therefore one objective of the present invention to provide a power hand tool, which can prevent damage to the internal transmission mechanism, the workpiece or the fastener upon an overload.

To achieve this objective of the present invention, the power hand tool comprises a housing having an accommodation chamber therein, a motor mounted in the accommodation chamber, a transmission member mounted in the accommodation chamber and coupled to the motor for rotation by the motor, a driven member mounted in the accommodation chamber and provided with at least one groove on one side thereof facing the transmission member, at least one steel ball mounted in the at least one groove of the driven member, and at least one spring member mounted in the transmission member and stopped at the steel ball, thereby enabling the driven member to be rotated by the transmission member upon operation of the motor.

When the power hand tool receives a reaction overload, the steel ball is forced to disengage from the groove, thereby causing disconnection of the transmission member from the driven wheel such that the transmission member runs idle. Therefore, the power hand tool runs idle when receives an overload, preventing damage to the internal transmission mechanism thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a power hand tool according to a preferred embodiment of the present invention.

FIG. 2 is a sectional view of the power hand tool according to the preferred embodiment of the present invention, showing that the steel balls are engaged in the grooves of the driven member.

FIG. 3 is similar to FIG. 2, but showing that the driven member is rotated with an angle and the steel balls are forced to disengage from the grooves of the driven member.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, a power hand tool 10 in accordance with a preferred embodiment of the present invention comprises a housing 20, a motor 30, a transmission member 40, a driven member 50, a plurality of steel balls 60, a plurality of spring members 70, and a tool bit adaptor 80.

The housing 20 is formed of two cover shells 22 abutted together, defining therein an accommodation chamber 24. Further, a starting button (not shown) is provided at the housing 20.

The motor 30 is mounted in the accommodation chamber 24 of the housing 20 and electrically coupled to the starting button at the housing 20. The motor 30 has an output shaft 32 and a pinion 34 fixedly mounted on the output shaft 32.

The transmission member 40 is mounted in the accommodation chamber 24 of the housing 20 and has a transmission gear 42 meshed with the pinion 34. The transmission gear 42 has a center axle hole 422 through the front and back sides thereof, and a plurality of through holes 424 equiangularly spaced around the center axle hole 422. The transmission member 40 further comprises a cover plate 44 attached to one side of the transmission gear 42. The cover plate 44 has a through hole 442 corresponding to the center axle hole 422 of the transmission gear 42.

The driven member 50 is mounted in the accommodation chamber 24 of the housing 20 and has a driven wheel 52 and a driving shaft 54. The driven wheel 52 has a center through hole 522 corresponding to the center axle hole 422 of the transmission gear 42, and a plurality of arched grooves 53 formed on one side facing the transmission gear 42 and equiangularly spaced around the center through hole 522. The arched groove 53 has a front end 532 and a rear end 534. The center through hole 522 of the driven wheel 52 is a polygonal through hole. The driving shaft 54 has a front end 542, a rear end 544, and a shoulder 546 between the front end 542 and the rear end 544. The shoulder 546 has a polygonal cross section fitting the polygonal through hole 522 of the driven wheel 52. The rear end 544 of the driving shaft 54 is inserted in proper order through the center through hole 522 of the driven wheel 52, the center axle hole 422 of the transmission gear 42 and the through hole 442 of the cover plate 44, and then a retainer 56 is fastened to the rear end 544 of the driving shaft 54 to secure the driving shaft 54 to the transmission member 40. Further, a cushion ring 58 is mounted on the driving shaft 54 and sandwiched between the cover plate 44 and the retainer 56.

The steel balls 60 are respectively mounted in the front end 532 of each of the arched grooves 53 of the driven wheel 52 and partially projecting in the spring holes 424 of the transmission gear 42.

The spring members 70 are respectively mounted in the spring holes 424 of the transmission gear 42 and stopped between the steel balls 60 and the cover plate 44. The spring members 70 impart a pressure to the steel balls 40 against the inside wall of each arched groove 53 of the driven wheel 52, thereby allowing synchronous rotation of the driven wheel 52 and the driving shaft 54 with the transmission gear 42.

The tool bit adaptor 80 is fastened to the front end 542 of the driving shaft 54 to hold, for example, a screwdriver bit for synchronous rotation with the driving shaft 54 to drive a screw (not shown) engaged with the tool bit adaptor into or out of the workpiece.

Referring to FIG. 3, when the user keeps the starting button of the power hand tool 10 pressed and started the motor 30, the motor 30 drives the transmission member 40 and the driven member 50 to rotate, causing synchronous rotation of the tool bit adaptor 80 and the attached screwdriver bit, thereby driving the attached screw into the workpiece. If the user does not release the starting button of the power hand tool 10 after the screw has been fully driven into the workpiece, the tool bit adaptor 80 may receive a heavy reaction load. At this time, a thrust force from the driven wheel 52 against the steel balls 60 may surpass the spring force imparted by the spring members 70 to the steel balls 60, thereby causing the steel balls 60 to be forced by the driven wheel 52 into the inside of the spring holes 424 and the driven wheel 52 will be rotated relative to the transmission gear 42, such that the transmission member 40 is separated from the driven wheel 52 to run idle. When the transmission member 40 runs idle, no more torque will be transmitted to the screw through the driven member 50 and the tool bit adaptor 80, thereby preventing the possible damage to the screw, workpiece or the transmission mechanism of the power tool.

As indicated above, the power hand tool 10 of the present invention utilizes the spring members 70, the steel balls 60 and the arched grooves 53 to have the transmission member 40 be disconnected from the driven wheel 52 when the tool bit adaptor 80 receives an excessive reaction force, preventing damage to the parts of the power hand tool 10.

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.

Claims

1. A power hand tool comprising:

a housing having an accommodation chamber therein;

a motor mounted in said accommodation chamber;

a transmission member mounted in said accommodation chamber and coupled to and rotatable by said motor;

a driven member mounted in said accommodation chamber, said driven member having at least one groove at one side thereof facing said transmission member;

at least one steel ball mounted in said at least one groove of said driven member; and

at least one spring member mounted in said transmission member and stopped at said at least one steel ball to force the steel ball to stop against a wall of said at least one groove of said driven member, thereby enabling said driven member to be rotated by said transmission member.

2. The power hand tool as claimed in claim 1, further comprising a tool bit adaptor fastened to and rotatable by said driven member.

3. The power hand tool as claimed in claim 1, wherein said transmission member comprises a transmission gear having at least one spring hole and a cover plate attached to said transmission gear; wherein said at least one spring member is mounted in said at least one spring hole with two distal ends thereof stopped against said at least one steel ball and said cover plate.

4. The power hand tool as claimed in claim 3, wherein said driven member comprises a driven wheel having said at least one groove, a driving shaft having an end fastened to said tool bit adaptor and the other end inserted through said driven wheel, said transmission gear and said cover plate and coupled with a retainer.

5. The power hand tool as claimed in claim 4, further comprising a cushion ring mounted onto said driving shaft and sandwiched between said cover plate and said retainer.

6. The power hand tool as claimed in claim 4, wherein the driven wheel has a plurality of arched said grooves equiangularly spaced around a center thereof.