POWER TOOL FOR TIGHTENING SCREW JOINTS AND RELEASE COUPLLING

1 . A power tool for tightening screw joints, comprising:

a rotation motor;

a device for initiating a braking torque to the motor when, in operation, a predetermined tightening condition has been reached;

an output shaft for connecting to a screw or nut engagement member; and

an intermediate torque transmission unit provided between the motor and the output shaft,

wherein the intermediate torque transmission unit includes a release coupling for interrupting torque transmission to the output shaft,

wherein the release coupling includes a first coupling part which is supported by a support shaft being rotationally connected to the motor and a second coupling part which is rotationally connected to the output shaft,

wherein the first coupling part is displaceable between a first position, where it is in engagement with the second coupling part for torque transmission to the output shaft, and at least a second position where it is out of engagement with the second coupling part and torque transmission to the output shaft is interrupted, and

wherein the first coupling part is guided in relation to the support shaft such that a relative rotational inertia movement of the first coupling part with respect to the support shaft caused by applying a braking torque to the motor causes the first coupling part to be displaced from the first position to said at least a second position.

2 . The tool according to claim 1 , wherein the rotation motor comprises an electrically driven motor.

3 . The tool according to claim 1 , wherein the device for initiating a braking torque to the motor comprises a circuit for initiating an electrical braking torque to the motor.

4 . The tool according to claim 1 , wherein the first coupling part is subjected to a force in the a direction of the first position by at least one of an elastic element, and an electric coil.

5 . The tool according to claim 1 , wherein the first coupling part is subjected to a force in a direction of the second position by an electric coil.

6 . The tool according to claim 1 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

7 . A release coupling device for a screw joint tightening power tool comprising:

a rotation motor;

a device for initiating a braking torque to the motor when, in operation, a predetermined tightening condition has been reached; and

an output shaft for connecting to a screw or nut engagement member,

wherein said release coupling is included in an intermediate torque transmission unit which is positioned between the motor and the output shaft,

wherein the release coupling is adapted to interrupt torque transmission to the output shaft, and

wherein the release coupling includes a first coupling part which is supported by a support shaft being rotationally connected to the motor and a second coupling part which is rotationally connected to the output shaft,

wherein the first coupling part is displaceable between a first position, where it is in engagement with the second coupling part for torque transmission to the output shaft, and at least a second position where it is out of engagement with the second coupling part and torque transmission to the output shaft is interrupted, and

wherein the first coupling part is guided in relation to the support shaft such that a relative rotational inertia movement of the first coupling part with respect to the support shaft caused by applying a braking torque to the motor causes the first coupling part to be displaced from the first position to said at least a second position.

8 . The coupling device according to claim 7 , wherein the first coupling part is subjected to a force in a direction of the first position by at least one of an elastic element, and an electric coil.

9 . The coupling device according to claim 7 , wherein the first coupling part is subjected to a force in a direction of the second position by the electric coil.

10 . The coupling device according to claim 7 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

11 . The tool according to claim 2 , wherein the device for initiating a braking torque to the motor comprises a circuit for initiating an electrical braking torque to the motor.

12 . The tool according to claim 2 , wherein the first coupling part is subjected to a force in a direction of the first position by at least one of an elastic element and an electric coil.

13 . The tool according to claim 3 , wherein the first coupling part is subjected to a force in a direction of the first position by at least one of an elastic element and an electric coil.

14 . The tool according to claim 2 , wherein the first coupling part is subjected to a force in a direction of the second position by an electric coil.

15 . The tool according to claim 3 , wherein the first coupling part is subjected to a force in a direction of the second position by an electric coil.

16 . The tool according to claim 2 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

17 . The tool according to claim 3 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

18 . The tool according to claim 4 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

19 . The coupling device according to claim 8 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.

20 . The coupling device according to claim 9 , wherein the first coupling part is guided by one of groups of a screw thread, a ball and groove, a pin and groove, and a cam and follower.