Bosch Power Tools 1375-01, 1375AK manual Robust Technology for LONG-TERM HEAVY-DUTY USE, Fan

ROBUST TECHNOLOGY FOR LONG-TERM HEAVY-DUTY USE.

A real concept:	The operating
High-frequency Tools	frequency determines
	the performance

Ahigh-frequency motor is a three-phase current motor with a short-circuit rotor. Its stator and rotor consist of a laminated sheet-metal bundle. If the stator winding of the motor is connected to the three-phase current supply, a magnetic field is created (rotary field), which runs through the motor due the arrangement of the winding and which is dependent on number of pole pairs and the frequency.

Fan

How a good idea was consistently further developed: The designation ’high-frequency tools’ came to be known through the market launch of the tools and was given to those powerful high-frequency tools with asynchronous motors, operated with three-phase current at an increased frequency of 200 or 300 Hz. In a physical sense, there is no real connection between these tools and genuine high-frequency technology, but they still came to be known under this name.

In hand tools, rotary current at increased frequency of 200 or

300 Hz combines high electrical performance with minimal motor weight. As the frequency of the rotary current increases, there is a proportional increase in motor speed and thus in the perfor- mance of asynchronic motors. This is limited by the maximum admissible circumference velocity (operating rotational speed) of the tools. An optimum perfor- mance/weight ratio is achieved by high-frequency tools operating at a frequency of 200 to 300 Hz

(Fig. 1). Large differences bet- ween motor rotational speed and operating rotational speed require larger gears. This means that weight savings from the rotary current drive are negated by the increased weight from the stepdown gearing. High-frequency installations using exclusively grinders should be operated at 300 Hz. Using rotary current at increased frequency optimally fulfils the demand for light yet high-performance hand tools.

Stator

Rotor

Housing

Weight (kg)

Total weight

Gear weight

Motor weight

0 100 200 300 400 500

Frequency (Hz)

Fig. 1 The graph shows the dependence of motor and gearing weight on frequency at constant motor performance and rated rotational speed. 300 Hz yields an optimum performance/weight ratio.

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