Output-mode switching device for electric tool

A switching device for an electric tool includes: an output shaft unit disposed in an outer casing, having an output shaft, a movable ratchet wheel mounted such that the movable ratchet wheel is movable axially along the output shaft and is non-rotatable therewith; a fixed ratchet unit having a fixed ratchet wheel sleeved around the output shaft and having ratchet teeth for meshing with ratchet teeth of the movable ratchet wheel; and a function switch unit having a switch ring mounted rotatably on the casing. Rotation of the switch ring about its axis results in rotation of pawls within the switch ring, thereby driving the pawls about its pivot points and meshing and/or non-meshing of the pawls with external ratchet teeth of the fixed ratchet wheel, thereby switching the output shaft among a continuous rotation, rotation in a single direction and simultaneously providing an axial impact during the rotation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Taiwanese patent application No. 105204526, filed on Mar. 31, 2016, which is incorporated herewith by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an electric tool, and more particularly to an output-mode switching device for an electric tool such that the switching device can switch among a continuous rotation, rotation in a single direction and rotation and simultaneously providing an axial impact during the rotation.

2. The Prior Arts

A conventional electric tool, like an electric drill, includes a motor, wherein its power is transmitted to an output shaft via a gear system. In order to tightening and/or loosening a screw or a nut smoothly, some electric tools are provided with impact function such that a fully tightened nut can be swiftly loosened and/or a loosely-mounted nut can be swiftly tightened relative to the object.

A conventional output-mode switching device for an electric tool is disclosed. The switching device can switch among a continuous rotation, rotation in a single direction and rotation and providing an axial impact during the rotation. However, it is noted that the structure is relatively complicated due to too many components, thereby incurring high manufacturing expense. In addition, when said switching device is applied in an electric tool, like rotating in a specific direction and simultaneously providing impact function along the axial direct, and in the event that an operating bit rotating in the specific direction is forced to rotate in a direction opposite to the specific direction, the motor and/or other components of the electric tool may be damaged. The reasons reside in that no stop means is provided to prevent the operating bit to rotate in the opposite direction of the specific direction.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide an output-mode switching device for an electric tool, which can eliminate the prior drawbacks, the complicated structure having too many components, thereby incurring high manufacturing expense. In the same time, when the switching device is applied in an electric tool, the operating bit can switch among a continuous rotation, rotation in a single direction and rotation and simultaneously providing an axial impact during the rotation. In the event that the operating bit rotating in the specific direction is forced to rotate in a direction opposite to the specific direction, the motor and/or other components of the electric tool are prevented from being damaged.

One distinct feature of the present invention resides in that an output shaft unit is disposed in an outer casing of an electric tool, which further includes a fixed ratchet unit, a torque unit and a function switch unit. The output shaft unit includes an output shaft and a movable ratchet wheel mounted in such a manner that the movable ratchet wheel is movable axially along the shaft and is non-rotatable with the shaft. The fixed ratchet unit includes a fixed ratchet wheel sleeved around the shaft and has ratchet teeth for meshing with movable ratchet teeth of the movable ratchet wheel. The function switch unit includes a switch ring mounted rotatably on the casing, wherein rotation of the switch ring about its axis results in rotation of pawls within the switch ring, thereby driving the pawls about its pivot points and meshing and/or non-meshing of the pawls with external ratchet teeth of the fixed ratchet wheel and switching the output shaft among a continuous rotation, rotation in a single direction and simultaneously providing an axial impact during the rotation.

An output-mode switching device for an electric tool includes: an outer casing, an output shaft unit, a fixed ratchet unit, a toque unit and a function switch unit. The outer casing defines an interior chamber. The output shaft unit is disposed in the interior chamber, includes an output shaft having a first shaft section and a movable ratchet wheel mounted on the first shaft section in such a manner that the movable ratchet wheel is movable axially along the output shaft and is non-rotatable with the output shaft. The movable ratchet wheel has a first end formed with circumferential ratchet teeth on its external surface thereof. The fixed ratchet unit includes a fixed ratchet wheel that is sleeved around the first shaft section and that has a second end formed with ratchet teeth for meshing with the ratchet teeth of the movable ratchet teeth and a restoration spring. The fixed ratchet wheel further has a plurality of external ratchet teeth formed on its outer surface. The restoration spring is being disposed between the movable ratchet wheel and the fixed ratchet wheel and has two opposite ends respectively abutting against the first end of the movable ratchet wheel and the second end of the fixed ratchet wheel. The toque unit includes a torque cover, an annular sleeve coupled with the torque cover, an annular cushion pad having a plurality of inner protrusions and a plurality of compression springs, the torque cover being mounted rotatably on the outer casing. The function switch unit includes a switch ring mounted rotatably on the outer casing behind the toque unit, a plurality of pawls and a plurality of torsion spring which are mounted pivotally within the switch ring so as to extend parallel with an axis of the switch ring such that rotation of the switch ring on the outer casing about its axis results in engagement of the inner protrusions of the annular cushion pad with the pawls, thereby driving the pawls about its pivot points and meshing and/or non-meshing of the pawls with the external ratchet teeth of the fixed ratchet wheel.

In the present embodiment, the output shaft is capable providing axial impact during rotating in a specific direction, the rotation of the output shaft in the specific direction provides high effective, since the output shaft is provided means from rotating in the direction opposite to the specific direction, thereby preventing damage done onto the motor or the other components. Each of The ratchet teeth formed on the second end and the external ratchet teeth formed on its outer surface of the fixed ratchet is asymmetric so is the ratchet teeth formed on the first end of the movable ratchet wheel for meshing and non-meshing with the ratchet teeth of the fixed ratchet wheel.

Preferably, each of the pawls has an abutment section for abutting against a respective one of the inner protrusions of the annular cushion pad, thereby driving the pawls during rotation of the annular cushion pad.

Preferably, the annular cushion pad has an inner wall surface from which the inner protrusions project radially and inwardly toward its axis thereof.

Compared with the prior output-mode switching device for an electric tool, the structure of the components of the present output-mode switching device is relatively simple, thereby lowering the manufacturing expense. In addition, since the output shaft is prevented from rotating in an opposite direction of a specific direction in which the output shaft is rotating, no damage can be done onto the motor and/or the other component of the switching device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to note that when referring a front end of an element, the other end opposite to the front end will be denoted as the second end. Every element will be described in the similar manner in order to better understanding of the present invention.

The present invention is to provide an output-mode switching device for an electric tool (like an electric drill) having an output shaft that can be switched among a continuous rotation, rotation in a single direction and rotation and simultaneously providing an axial impact during the rotation.

Referring toFIGS. 1-3, the output-mode switching device for an electric tool according to the present invention includes an output shaft unit1, a fixed ratchet unit2, an outer casing3defining an interior chamber, a toque unit4and a function switch unit5, wherein the output shaft unit1is disposed in the interior chamber of the outer casing3and includes an output shaft11, a first bearing unit112, a nut covering113and a movable ratchet wheel114. The output shaft11has several shaft sections with different diameters, a first shaft section111of polygonal cross-section extending towards the transmission structure, and a second shaft section opposite to the first shaft section111for clamping an operating bit, like a drill, in order to rotate the drill. The first bearing unit112is sleeved around the output shaft11at an appropriate position while the nut covering113and the movable ratchet wheel114are also sleeved around the output shaft11in such a manner that a polygonal hole1140in the movable ratchet wheel114engages the first shaft section111of the output shaft11so that the movable ratchet wheel114is movable axially along the output shaft11and is non-rotatable with the output shaft11. The movable ratchet wheel114has a first end provided with ratchet teeth1141circumferentially on its external surface thereof. In this embodiment, each ratchet teeth1141is asymmetric as best shown inFIG. 1B, having a small inclined side and a large inclined side at the other side such that during the rotation of the movable ratchet wheel114in the clockwise direction, the small inclined side of the ratchet teeth1141provides small resistance, thereby generating high effective output. In case the movable ratchet wheel114is rotated in the counterclockwise direction, the large inclined side of the ratchet teeth1141provides resistance, thereby preventing the movable ratchet wheel114from rotating in the counterclockwise direction.

The fixed ratchet unit2includes a fixed ratchet wheel21, two annular first cushion pads22, a restoration spring23, two annular cushion pads24, a bearing disk25and a first bearing unit26, wherein the fixed ratchet wheel21has a through hole210sleeved around the first shaft section111the output shaft11, a second end formed with ratchet teeth212. In this embodiment, each of the ratchet teeth212is asymmetric as best shown inFIG. 1A, having a small inclined side and a large inclined side at the other side for meshing with the ratchet teeth1141of the movable ratchet teeth114. The fixed ratchet wheel21further has a plurality of external ratchet teeth211formed on its outer surface. A compression spring serves as the restoration spring23is disposed between the movable ratchet wheel114and the fixed ratchet wheel21and having two opposite ends respectively abutting against the first end of the movable ratchet wheel114and the second end of the fixed ratchet wheel21.

After assembly, the first shaft section111of the output shaft11extends sequentially through the first bearing unit112, the nut covering113and the movable ratchet wheel114, and further through one first cushion pad22, the restoration spring23, another first cushion pads22, the through hole in the fixed ratchet wheel21, one second cushion pad24, the bearing disk25, another second cushion pad24and the second bearing unit26such that the two first cushion pads22respectively abut against the second end of the fixed ratchet wheel21and the first end of the movable ratchet wheel114while two opposite ends of the restoration spring23respectively abutting against the cushion pads22. The second cushion pads24respectively abut against the first end of the fixed ratchet wheel21and the second end of the second bearing unit26while the bearing disk25abuts against the second cushion pads24. The restoration spring23provides an axial compression force so as to space the movable ratchet wheel114and the fixed ratchet wheel21apart from each other on the output shaft11.

Note that the previously mentioned output shaft unit1and the fixed ratchet unit2are disposed within the interior chamber of the outer casing3such that all the elements mentioned above also located within the interior chamber.

The toque unit4includes a torque cover41, an annular sleeve411coupled with the torque cover41, an annular cushion pad412having a plurality of inner protrusions4121and a plurality of compression springs413, wherein the torque cover41has inner threads for rotatably fastened with outer threads of the outer casing3such that the torque cover41is rotable relative to the outer casing3. The annular cushion pad412is coupled to a first end of the annular sleeve411, after which the torque cover41, the annular sleeve411and the annular cushion pad412are coupled to the outer casing3so that the second ends of the compression springs413are mounted on the first end of the annular cushion pad412.

The function switch unit5includes a switch ring51mounted rotatably on the outer casing3behind the toque unit4, two pawls52which are mounted pivotally to screw holes5110in two mounting posts511of the switch ring51via two fastener screws53such that pivot axes of the pawls52extend parallel with an axis of the switch ring51. Each of two torsion springs54is sleeved around a respective mounting post511and has two opposite ends respectively abutting against the pawls and the switch ring51. It is to note that due to biasing action of the torsion spring54, the pawls52tend pivotally towards an axis of the switch ring51. Note that each of the pawls52has an abutment section522such that after assembly one end of each torsion spring54abuts against the abutment section522such that the engaging ends521of the pawls52abut against respective inner protrusions4121of the annular cushion pad412.

The toque unit4is used to adjust the torque of the output shaft11. When the torque cover41is rotated in a normal direction (clockwise direction) and/or in an opposite direction (counterclockwise direction) with respect to the outer casing3, the torque cover41is axially moved toward the first end and/or the second end. Movement of the torque cover41axially toward the first end results in pressing of the compression springs413, thereby driving the output shaft11in a high torque speed and movement of the torque cover41axially toward the second end releases pressing off the compression springs413, thereby driving the output shaft11in a low torque speed.

The function switch unit5is used to alter the modes of the output shaft11. There are marks provided on the outer surface of the switch ring51, as shown inFIG. 2, wherein the middle symbol “screw” refers to rotation of the output shaft11in a single direction, the right symbol “hammer” refers to rotation of the output shaft11and simultaneously providing impact force, the left symbol “drill” refers to continuous rotation of the output shaft11. Therefore, the operator can manually rotate the switch ring51to a desired position with respect to the outer casing3, and can achieve the desired output mode of the output shaft11.

The switching modes of the output shaft will be described in the following paragraphs.

As shown inFIG. 4, when the operator rotates the switch ring51in the clockwise direction so as to set the output mode of the output shaft11, the engaging ends521of the pawls52are engaged and driven by the inner protrusions4121of the annular cushion pad412such that the pawls52engage the ratchet teeth211formed on the external surface of the fixed ratchet wheel21. Since the fixed ratchet wheel21cannot rotate, rotation of the output shaft11simultaneously drives the movable ratchet wheel114. At this time due to reciprocal biasing of the restoration spring23, the ratchet teeth1141of the movable ratchet wheel114mesh and/or non-mesh with the ratchet teeth212formed on the end surface of the fixed ratchet wheel21. Thus, the output shaft11rotates and provides axial impacts reciprocally during the rotation, which means that the output shaft11is switched to the left side symbol of “drill”. It is to note that when the switch ring51is switched to the “drill” output mode, the fixed ratchet wheel21is prevented from rotating in the opposite direction due to its external ratchet teeth211engaging with the pawls52, thereby preventing damage done onto the motor due to overload.

Referring toFIG. 5, when the operator rotates the switch ring51relative to the casing30so as to adjust the output mode (“screw” mode), the engaging ends521of the pawls52are driven by the inner protrusions4121of the annular cushion pad412, thereby causing the engaging ends521of the pawls52do not fully engage the external ratchet teeth211of the fixed ratchet wheel21. Thus, when the transmission structure drives the output shaft11to rotate in the clockwise direction, since the restoration force of the spring23causes meshing between the ratchet teeth1141of the movable ratchet wheel114and the ratchet teeth212of the fixed ratchet wheel21, in which, rotation of the output shaft11in the clockwise direction simultaneously causes the movable and fixed ratchet wheels114,21to rotate in the same direction. Note that at this time, since the external ratchet teeth211of the fixed ratchet wheel21are prevented by the pawls52, the output shaft11is prevented from rotating in the counterclockwise direction, thereby causing rotation of the output shaft11in a single direction. In other words, the output shaft11functions as a screw driver.

Referring toFIG. 6, when the operator rotates the switch ring51relative to the casing30so as to adjust the output mode (“drill” mode), the engaging ends521of the pawls52are driven by the inner protrusions4121of the annular cushion pad412, thereby causing the engaging ends521of the pawls52do not engage the external ratchet teeth211of the fixed ratchet wheel21. Thus, when the transmission structure drives the output shaft11to rotate in the clockwise direction, since the restoration force of the spring23causes meshing between the ratchet teeth1141of the movable ratchet wheel114and the ratchet teeth212of the fixed ratchet wheel21, in which, rotation of the output shaft11in the clockwise direction simultaneously causes the movable and fixed ratchet wheels114,21rotate in the same direction. Note that at this time, since the external ratchet teeth211of the fixed ratchet wheel21are not prevented by the pawls52, the output shaft11is not prevented from rotating in the counterclockwise direction, thereby permitting rotation of the output shaft11in a single direction. In other words, the output shaft11functions as a drill.