The invention relates to a manually supported power wrench comprising a housing with a rotation motor, a power transmission and an output shaft, wherein the power transmission includes a flywheel reaction torque absorber. In particular, the invention concerns a power wrench of the above type wherein the housing is provided with a handle for operator control of the wrench.

The basic idea behind a power wrench of the above type is to protect the operator from uncomfortable reaction forces by having the flywheel absorb part of the reaction torque transferred to the housing during tightening of screw joints and/or having kinetic energy of the flywheel boost the output torque at the end of the tightening process. The flywheel may also be arranged to boost the output speed during an initial phase of a tightening process. In order to achieve any of these objects the flywheel may be accelerated to relatively high speed levels. This means that if the flywheel bearings or anything else would break down or accidentally cause mechanical contact between the flywheel and the housing during operation of the wrench the relatively high kinetic energy of the flywheel would be transferred to the housing, which would result in the operator being exposed to a rather violent and hazardous reaction force.

It is an object of the invention to provide a power wrench of the above described type that includes a means for protecting the operator from any hazardous forces in case of a breakdown of any part of the wrench that would cause a sudden interconnection between the flywheel and the housing, whereby the kinetic energy of the flywheel is prevented from reaching and harming the operator.

Further objects and advances of the invention will appear from the following specification and claims. Preferred embodiments of the invention are described below with reference to the accompanying drawings.

In the drawings

Fig. 1 shows a side view partly in section of a power wrench according to one embodiment of the invention.

Fig. 2 shows a similar view of an alternative embodiment of the invention .

Fig. 3 shows on a larger scale fraction III of the power wrench in Fig. 2 illustrating the cylindrical wall of the housing provided with a friction lining.

The power wrench shown in Fig. 1 comprises a housing with a handle 11 for operator control of the wrench. The housing is divided into two parts, namely a rear part 10a and a forward part 10b. The wrench includes a rotation motor with an output spindle 12, a power

transmission, and an output shaft 15 for connection to a screw joint to be tightened. The power transmission comprises a drive spindle 16 connected to the output spindle 12 of the motor, a planetary gearing and a flywheel 20. The planetary gearing comprises a sun gear 18 that is connected to a drive spindle 16 that in turn is connected to the output spindled 12. The sun gear 18 is arranged to drive a couple of planet wheels 19 that are interconnected by means of a planet carrier 21, which is formed as one piece member with the output shaft 15. A surrounding gear rim 22 of the planetary gearing is connected to the flywheel 20 via a disc shaped connection portion 23. The flywheel 20 is rotatively supported relative to the forward housing part 10b by means of two bearings 24.

As mentioned above, the housing comprises a rear half 10a which is formed with the handle 11 and which supports the motor, and a forward part 10b containing the power transmission 14. In a first embodiment of the invention the rear half 10a and the forward part 10b are interconnected via a release coupling 30. The release coupling 30 is arranged to prevent the operator from being exposed to hazardous forces. The release coupling 30 is arranged to prevent rotation between the two housing parts 10a, 10b during normal operation of the wrench, but to allow relative rotation between the two housing parts 10a, 10b in an emergency case, i.e. in case of a dead stop of the flywheel 20 relative to the forward housing part 10b. The release point of the coupling 30 may be adjusted and set by means of the clamp nut 28. The forward housing part 10b has a rear axially extending ring shaped flange 25 which is rotatively supported on a radial flange 26 on the rear housing part 10a and axially locked relative thereto by a clamp nut 28 threaded onto the axial flange 25. On both sides of the radial flange 26 there are provided two friction rings 29 which are clamped into frictional contact with the radial flange 26 by the clamp nut 28. This arrangement forms a friction type release coupling 30 between the two housing parts 10a and 10b and has the purpose of preventing accidental hazardous forces emanating from the kinetic energy of the flywheel 20 to reach the rear housing part 10a and thereby the operator via the handle 11.

Such accidental sudden mechanical interconnection between the flywheel 20 and the forward housing part 10b may be caused by a brake down of the bearing with an abrupt stop of the flywheel 20 as a result. Since the operation order of the power transmission 14 including the flywheel 20 as well as the control of the motor during a screw joint tightening process may be arranged in different ways and is not the object of the invention it is not described in further detail in this specification. However, the basic idea of the flywheel arrangement is to obtain a reaction torgue absorption during a tightening processes to thereby protect the operator from uncomfortable and tiresome reaction forces. This means that the flywheel 20 may attain rather high speed at some instances which means that it contains a high kinetic energy. If, during a high speed seguence of the flywheel 20 something occurs such that the latter is suddenly mechanically interconnected to the housing, for instance a breakdown of the bearings 24, the high kinetic energy of the flywheel 20 would be abruptly transferred to the housing and to the operator via the handle 11.

In Fig. 2 there is illustrated an alternative embodiment of the invention wherein the forward and rear housing parts 10a and 10b are rigidly interconnected, but instead a release coupling 44 is provided between the flywheel supporting bearings 24 and the flywheel 20 itself. This means that if a breakdown should occur in the bearings 24 resulting in a dead stop of the flywheel 20 the friction coupling forming the release coupling 44 would prevent a sudden transfer of kinetic energy from the flywheel 20 to the housing 10a, 10b. Instead, the flywheel 20 would still be allowed to rotate with respect to the housing in the release coupling, although at a higher friction than provided by the supporting bearings 24. In an alternative embodiment a release coupling is instead provided between the flywheel supporting bearings 24 and the housings 10a, 10b. Further, in this embodiment a low friction lining 40 may be provided the on inner wall of the forward housing part 10b. See Fig. 3. As an alternative a low friction lining may be provided on the outer surface of the flywheel 20. Together the low friction lining 40 at the periphery of the flywheel 20 and the release coupling 44 between the bearings 24 and the flywheel 20 will prevent the operator from being exposed to any violent and hazardous forces.

It is to be noted that the invention is not limited to the above described examples but could be freely varied within the scope of the claims. For instance, the friction type release couplings may have alternative designs and may even be replaced by other types of couplings with the same protective characteristics to protect the operator from dangerous forces in case of malfunction of the power wrench. Between the two housing halves 10a and 10b the friction ring arrangement could be replaced by any kind of cam mechanism or even a breakpin dimensioned to withstand reaction forces developed during normal wrench operation but to be sheared off and break the connection between the housing halves in case of a sudden flywheel stop.