Electrical torque screwdriver

An electrical torque screwdriver includes a handle, a shaft, a torque limiter, and an electrical switch. The shaft is disposed on the handle and rotatable but not movable linearly. The torque limiter includes a driving tooth, a slipping block, a pawl, and at least one restoring element. The driving tooth is disposed on the shaft. The slipping block is disposed on the handle. The slipping block is displaceable linearly but not rotatable. The pawl is disposed on the slipping block and engaged with the driving tooth. The restoring element is pivotally disposed on the handle and has a restoring force, wherein one end of the restoring element resists against the slipping block for pushing the pawl to be engaged with the driving tooth. The electrical switch is disposed on the handle for optionally resisting against the other end of the restoring element to stop the restoring element.

RELATED APPLICATIONS

The application claims priority to Taiwan Application Serial Number 100119593, filed Jun. 3, 2011, which is herein incorporated by reference.

BACKGROUND

1. Field of Invention

The present invention relates to a screwdriver. More particularly, the present invention relates to an electrical torque screwdriver.

2. Description of Related Art

In general, if a user applies a force on a screwdriver, the applied force will be completely transmitted to a workpiece. Therefore, when the applied force is greater than what the workpiece can take, the workpiece will be damaged. Thus, some people apply the technique of torque wrench on the screwdriver for allowing the screwdriver to loose the workpiece, thereby avoiding damaging the workpiece when the workpiece receives too much force from the user. However, such a screwdriver will not be able to perform jobs requiring larger torque.

SUMMARY

Therefore, an aspect of the present invention is to provide an electrical torque screwdriver. When the applied force is greater than what the workpiece can take, the electrical torque screwdriver will slip from the workpiece to avoid damaging the workpiece. In addition, the electrical torque screwdriver can be switched to a screwdriver for general use.

According to an embodiment of the present invention, the electrical torque screwdriver includes a handle, a shaft, a torque limiter and electrical switch. The shaft is disposed on the handle, wherein the shaft is rotatable but not movable linearly. The torque limiter includes a driving tooth, a slipping block, a pawl and at least one restoring element. The driving tooth is disposed on the shaft. The slipping block is disposed on the handle, wherein the slipping block is displaceable linearly but not rotatable. The pawl is disposed on the slipping block and engaged with the driving tooth. The restoring element which is pivotally disposed on the handle and has a restoring force, wherein one end of the restoring element resists against the slipping block for pushing the pawl to be engaged with the driving tooth. The electrical switch is disposed on the handle for optionally resisting against the other end of the restoring element to stop the restoring element.

When an excessive force is applied through the handle to the torque limiter, the torque limiter will be loosened to prevent the shaft from damaging the workpiece. If the electrical switch resists against the restoring element, the torque limiter will not be loosened; and can be used as a general-use screwdriver for performing jobs requiring greater torque.

DETAILED DESCRIPTION

FIG. 1is a schematic three-dimensional view of an electrical torque screwdriver according to one embodiment of the present invention.FIG. 2is a schematic exploded view of the electrical torque screwdriver shown inFIG. 1. As shown inFIG. 1andFIG. 2, the electrical torque screwdriver includes a handle100, a shaft200, a torque limiter300and electrical switch400. The shaft200is disposed on the handle100, wherein the shaft200is rotatable but not movable linearly. The torque limiter300includes a driving tooth310, a slipping block320, a pawl330and at least one restoring element340. The driving tooth310is disposed on the shaft200. The slipping block320is disposed on the handle100, wherein the slipping block320is displaceable linearly but not rotatable. The pawl330is disposed on the slipping block320and engaged with the driving tooth310. The restoring element340is pivotally disposed on the handle100and has a restoring force, wherein one end of the restoring element340resists against the slipping block320for pushing the pawl330to be engaged with the driving tooth310. The electrical switch400is disposed on the handle100for optionally resisting against the other end of the restoring element340to stop the restoring element340.

FIG. 3is a schematic partial cross-sectional view of the driving tooth310engaged with a pawl330shown inFIG. 1. When a user rotates the handle100, the shaft200will be driven through the slipping block320, the pawl330and the driving tooth310. Therefore, if a screwdriver head or a socket is mounted on the shaft200, the screwdriver can be used for loosening or tightening screws or nuts.

FIG. 4is a schematic partial cross-sectional view of the driving tooth310escaping from the pawl330shown inFIG. 3. When the applied force is large enough to compress a spring350for pushing the restoring element340to rotate, the pawl330and the slipping block320will be displaced linearly, so that the pawl330will escape from driving tooth310. At this time, the slipping block320will push the restoring element340to rotate. Accordingly, the shaft200and the handle100will rotate oppositely, and thus the applied force cannot be transmitted to the shaft200.

FIG. 5is a schematic partial cross-sectional view of the electrical switch400resisting against a restoring element340shown inFIG. 3. When the user switches the electrical switch400to make the electrical switch400resist against the restoring element340, the slipping block320will not be displaced linearly, so that the pawl330cannot escape from driving tooth310. Hence, when the user applies a force on the handle100, the applied force can be completely transmitted to the shaft200as general use of a screwdriver.

Referring toFIG. 2, a technique that the shaft200disposed on the handle100is rotatable but not movable linearly, is that a ring groove110is disposed on the handle100, and a circular disk210is disposed on the shaft200, wherein the circular disk210is accommodated in the ring groove110. Therefore, the circular disk210can rotate around in the ring groove110but not move linearly to achieve the technique that the shaft200is rotatable but not movable linearly.

A technique that the slipping block320disposed on the handle100is displaceable linearly but not rotatable, is that a rectangle sliding block321is disposed on the slipping block320, and a sliding track120is disposed on the handle100, wherein the sliding block321is accommodated in the sliding track120. Therefore, the sliding block321can displace linearly but not rotate around to achieve the technique that the slipping block320is displaceable linearly but not rotatable.

A technique that the restoring element340has a restoring force means that an elastic element is disposed in the handle100. In other words, two ends of the elastic element are respectively connected to the restoring element340and the handle100. When the restoring element340is forced to rotate, the elastic element will be compressed to save the force. When the applied force of the restoring element340is released, the restoring element340will be rotated in place by the restoring force of the elastic element. However, the technique of the restoring force, such as how to set up and connect to the elastic element etc, is a well known technology and thus is not described again. On the embodiment, the spring350is an example of the elastic element350, and the spring350is also an example for its two ends respectively to resist against the handle100and the restoring element340.

The electrical switch400means that the device is controlled by current. In other words, the electrical switch400will be driven to resist against the restoring element340when the current is inputted to the electrical switch400. However, there is also a possibility that, the electrical switch400will be driven to leave from the restoring element340when the current is inputted to the electrical switch400. As described above, the driven technique is designed in accordance with user or designer requirements. The embodiment is an example that the electrical switch400is driven to resist against the restoring element340when the current is inputted to the electrical switch400. The most common electrical switch400is a solenoid valve. In the embodiment, a solenoid valve is an example of the electrical switch400. However, the electrical switch400is a well known device and thus is not described herein again.

In the embodiment, the electrical switch400is a solenoid valve. When the electrical switch400is stretched to resist against the restoring element340, the pawl330cannot escape from driving tooth310and can be operated as a general-use screwdriver. When the electrical switch400is withdrawn back, the slipping block320can be displaced linearly, and thus the pawl330can escape from driving tooth310and can be operated as a general-use torque screwdriver. Since solenoid valve is a popular product presented in the market, the material cost can be reduced greatly.

The handle100includes a frame130, and the restoring element340is pivotally disposed on the frame130, and the sliding track120is also disposed on the frame130. The design and production difficulties can be simplified if the restoring element340and the slipping block320are combined on the frame130.

The number of the restoring elements340is two, and the two restoring elements340are coaxial and pivotally disposed on the handle100. Using the two restoring elements340to resist against the slipping block320can improve the stability of linear displacement of the slipping block320.

Referring toFIG. 3, the restoring element340includes a stopping part341, a restoring driving part342, a first axis343and a second axis344. The stopping part341resists against the slipping block320. The first axis343passing through a central pivot point of the restoring element340and the handle100is parallel to a displacement direction of the slipping block320. The second axis344passing through the central pivot point of the restoring element340and the handle100is parallel to a restoring direction. A first distance L1vertical to the first axis343is the shortest distance formed between the stopping part341and the first axis343, and a second distance L2vertical to the second axis344is the shortest distance formed between the restoring driving part342and the second axis344. Under a condition of the driving tooth310engaged with the pawl330, the first distance L1is smaller than the second distance L2.

Therefore, if the torque (the applied force by the slipping block320×the first distance L1) made by the slipping block320for rotating the restoring element340is the same as the torque (the restoring force by the spring350×the first distance L2) made by the spring350for rotating the restoring element340, the applied force by the slipping block320has to be greater than the restoring force by the spring350. In other words, when the user applies a force to compress the spring350for pushing the restoring element340to rotate, since the first distance L1is smaller than the second distance L2, the spring350with a smaller spring constant (k=F/x, k is a spring constant; F is an applied force; x is a stretched or compressed distance) can be used for providing the user with a greater resistance. Since the price of the spring350with a smaller spring constant is relatively low, the overall manufacturing cost can be reduced.

The restoring driving part342indicates a position connected to the elastic element. In the embodiment, the restoring driving part342is the place resisted against by the spring350.

The restoring direction is a direction of a restoring force applied on the restoring element340by the elastic element. In the embodiment, the restoring direction is the direction of the spring350resisting against the restoring element340.