Screwdriver with adjustable device to limit transmitted torque
A screwing tool with a device to adjust transmitted torque comprises a handle to introduce a torque to the device, which is borne in the hollow of the handle and a drive shaft as an output element of the torque. On the drive shaft inside the handle, two separate couplings are assembled, having between them a compression spring exerting a spring force against the two couplings. Each coupling comprises a first and a second socket engaging each other by gearings at their opposing faces. The maximum torque at which the torque transmission will be interrupted can be adjusted by an adjustment element wherein the distance between the couplings can be changed, thereby resulting in a change of the tension of the spring exerting a load on the couplings. The teeth of the gearings slide and the sockets rotate relatively to each other and interrupt the torque-transmission if a pre-adjusted torque is exceeded.
1. A screwing tool with an adjustable device to limit transmitted torque, said device comprising a handle with an axially extending hollow in which a mechanism is arranged to interrupt the transmission of torque from the handle to a drive shaft if a pre-adjusted torque value is exceeded, said mechanism comprising a drive shaft on which two couplings are assembled, each coupling comprising a first and second socket which are engaging each other by a gearing at their opposing side faces, both first sockets are engaging with an inner gearing with a gearing on the circumferential surface of the drive shaft and are moveable in a longitudinal direction, both second sockets are rotatively coupled and in mesh with the handle by means of a gearing, and a compression spring arranged with pre-tension between the two couplings, said hollow in the handle being shut by a cap.
2. A screwing tool as defined in claim 1 wherein the first sockets are borne and radially supported with their cylindrical surface by the cylindrical hollow in the handle which encloses the sockets at least at a part of their longitudinal extension.
3. A screwing tool as defined in claim 1 wherein the second sockets have an axial boring in which the drive shaft is borne rotatably.
4. The screwing tool as defined in claim 1 wherein the second socket of the front coupling is rotatively coupled with the handle by a gearing at its front side.
5. The screwing tool as defined in claim 1 wherein the second socket of the rear coupling is borne moveably in a longitudinal, axial direction along the drive shaft, said second socket having a geared circumferential surface with which it is engaging in a gearing which is molded into this part of the hollow of the handle.
6. The screwing tool as defined in claim 1 wherein the rear end face of the second socked of the rear coupling is shaped as a spiralic pitched surface.
7. The screwing tool as defined in claim 1 wherein an adjustment element is arranged behind the second socket of the rear coupling, at this adjustment element the face opposite to the second socket of the rear coupling is also shaped as a spiralic pitched surface with which it contacts the spiralic surface of the second socket of the rear coupling, said adjustment element at the rear face has a fine gearing.
8. The screwing tool as defined in claim 1 wherein an adjustment disc is arranged between the adjustment element and the cap of the handle, said adjustment disc at its face opposite to the adjustment element also has a fine gearing engaging with the gearing of the adjustment element, both parts are pressed together by the force exerted by the compression spring.
9. The screwing tool as defined in claim 8 wherein the adjustment element has a pin with which it penetrates the adjustment disc and the cap of the handle and is borne in these parts, the pin has a recess at its end provided for to insert a key to turn the adjustment element.
10. The screwing tool as defined in claim 8 wherein the graduation of the gearing at the adjustment disc are so chosen that within a given range of torque values intermediate torque values can be adjusted in equal steps.
11. The screwing tool as defined in claim 10 wherein the surface of the pin and the surface of the cap around the pin are marked with scale marks and the position of the markings relative to each other indicate the pre-tension of the spring respectively the adjusted maximum torque which will be transmitted.
12. The screwing tool as defined in claim 1 wherein the gearing of the first and second sockets has a substantially triangular tooth-profile wherein the angle of the teeth-flanks relative to the axis of the sockets is larger in a screw fastening direction than in a screw loosening direction, the screw fastening direction being opposite to the screw loosening direction.
13. The screwing tool as defined in claim 1 wherein the angle a of the teeth-flanks relative to the axis of the sockets in a screw fastening direction is larger if the device is designed for a range of lower torques than if the device is designed for a range of higher torques.
14. The screwing tool as defined in claim 13 wherein the angle of the teeth-flanks relative to the axis of the sockets is 0° in a screw loosening direction.
15. The screwing tool as defined in claim 14 wherein the profile of the teeth is shaped wave-like and the teeth are rounded or flattened at their ridge.
16. The screwing tool as defined in claim 1 wherein the gearing at the drive shaft, in the boring of the first sockets, at the circumferential surface of the second socket of the rear coupling and in the hollow of the handle have a substantially rectangular tooth-profile.
17. The screwing tool as defined in claim 1 wherein the handle and the cap are connected by thread.
18. The screwing tool as defined in claim 1 wherein the drive shaft, the first and second sockets of the couplings, the adjustment element, the adjustment-disc, the compression spring, the handle and the cap are arranged such that there is no axial load exerted onto the drive shaft.
19. The screwing tool as defined in claim 1 wherein the axial force exerted by the compression spring is lead in one direction through the first and second socket, the adjustment element and the adjustment disc into the cap of the handle, in the other direction through the first and second socket into the front part of the handle.
20. The screwing tool as defined in claim 1 wherein the drive shaft, the first and second sockets, the adjustment element, the adjustment disc, the handle and the cap are made of plastic.
21. The screwing tool as defined in claim 20 wherein one of the parts with a surface sliding against a surface of another part is made of Polyamide (PA) and the other part is made of Polyoxymethylene (POM) where as at least at one part of the basic material is compounded with a sliding improving additive.
22. The screwing tool as defined in claim 20 wherein the plastic materials used have a heat-resistance up to 220° C.
23. The screwing tool as defined in claim 1 wherein at least one of the drive shaft, the first and second sockets, the adjustment element, the adjustment disc, the handle, and the cap is made of metal.
24. The screwing tool as defined in claim 1 wherein a core-handle made of metal has an outer cross-section contour which is non-circular and an ergonomically shaped handle-sleeve made of plastic material is removably assembled on the metal handle.
25. The screwing tool as defined in claim 1 wherein the shank of a screwdriver-blade or a holder for screwdriver-inserts (bits) is inserted exchangeably in the driver shaft and held its position by a clamping device connected with the driver shaft.