| 摘要 |
For their pump drive dishwashers are usually equipped for reasons of cost only with an unregulated asynchronous motor which however is temperamental in terms of the sealing requirements involved, and a simple controller operating circuit (13) for executing the functional program because a rotary speed-controllable drive could not comply with the price limit which is preset by the market. However rotary speed control would be highly desirable in terms of the level of efficiency, energy demand and the generation of noise. In order to embody a dishwasher with a pump drive which involves a low level of wear and which is controllable in respect of its rotary speed without a substantial increase in cost, the use of a dc motor (11) with field windings (19) which can be alternately supplied with current by way of sensor-controlled switching sections (34) is an optimum. In that case a commutator (18) which is responsive to the polarity of the multi-pole permanent-magnetic rotor (17) which is supported in the form of a wet rotor member in the air gap predetermines which of the field windings (19) is to be actuated at the time. Hum phenomena by virtue of the residual ripple of the dc field voltage can be compensated by superimposition of pulse width modulation, in opposite relationship to the variation in amplitude. Such compensation is unnecessary however if pure rotary speed regulation is not effected by way of the controller (14), but infraposed current regulation is afforded for operation at a constant torque at the predetermined rotary speed. This additional circuit (20) for actuation of the field windings (19) is advantageously fitted directly to the motor (11) and in turn actuates it substantially by way of the previous interfaces from the operating circuit (13) which has remained practically unchanged.
|
