CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is the U.S. National Stage of International Patent Application No. PCT/EP2019/025465, filed Dec. 20, 2019, which claims the benefit of European Patent Application No. 18214666.2, filed Dec. 20, 2018, which are each incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a portable power chiseling tool, for example a hammer drill or an electric chisel.

WO 2008/071489 A1 describes a portable power chiseling tool. The portable power tool has a pneumatic striking mechanism, which is driven by an electric motor. A reduction gear unit adapts the speed of the electric motor to the striking rate of the striking mechanism. The reduction gear unit has a first stage and a second stage. The second stage is designed as part of an eccentric gearwheel to enable this to be integrated into the portable power tool in view of spatial restrictions.

GB 1 210 006 describes a portable power chiseling tool, the transmission of which is exposed to high loads. The loading results from the reaction forces of the striking mechanism and also when a drill bit is blocked. In this case, the teeth of the transmission stages can break. The transmission is of correspondingly robust design.

DISCLOSURE OF THE INVENTION

A portable power chiseling tool has a tool holder for holding a tool on a working axis, an electric motor and a striking mechanism. The striking mechanism has an exciter piston coupled to the motor, a striker guided on the working axis, and a pneumatic chamber which is closed by the exciter piston and the striker and is provided for coupling a movement of the striker to the exciter piston. The speed of the electric motor corresponds to at least 20 times a striking rate of the striking mechanism. The speed of the electric motor is greater than 80,000 revolutions per minute. The ratio of the mass of the electric motor (8) to the rated power of the electric motor is less than 0.2 g/W.

The advantages of a lightweight high-speed electric motor are balanced out inter alia by the necessity of an additional stage for speed reduction and the increased sensitivity thereof. According to the invention, it has been recognized that, starting from the currently customary speeds of 25,000 rpm, no positive effect is to be expected if the speed is doubled to 50,000 rpm. The disadvantages of the additional transmission stage predominate. However, in this way it has been recognized that there is a positive effect from high speeds above 80,000 rpm.

