The invention is directed to an electric motor, in particular for an electric tool, with driving means that can be connected to a voltage supply via switching means.
Electric tools are known. They have an electric motor whose drive shaft actuates a tool carrier, for example, a clamping element for receiving tools. Such known electric tools are, for example, drill machines, angle grinders, circular saws, and the like. To switch off these electric tools, they are cut off from the voltage supply, in particular via an on/off-switch. Because of the rotational energy stored in the rotating tool, this results in that the time to slow down to a full stop, or run-down times, can sometimes be very long. This can create dangerous situations for an inattentive user. Apart from the existing danger of injury, the tool cannot be put down without due attention until after a long pause when the tool comes to a stop.
In order to reduce run-down times in electric tools, it is known to provide them with a braking device. Apart from an electrodynamic brake in which the electric motor is switched from a motor operation to a generator operation after the electric tool is switched off, braking devices that act mechanically are also known. For this purpose, known electric tools have separate brake disks arranged on a drive shaft, a ring-shaped brake lining pressing against these brake disks when the electric motor is cut off from the voltage supply. This solution has the disadvantage that additional space must be provided in the electric tool for housing the brake disk and the brake lining.
A braking device for motors in which a brake pad integrated in a stator can be pressed against the stator by the force of a spring element is known from DE 2 401 846. A releasing force can be applied to the brake pad by means of a magnetic field.
A braking device for an electric motor in which active parts of the magnetic circuit of the stator form parts of the braking device and in which the later are embedded in the magnetic circuit of the stator field poles is known from DE 1 114 573 A.
Another braking device for electric motors in which mechanically acted braking devices are integrated in the stator is known from WO 97/09769.