Patent ID: 7857908

Claim:
A dishwasher having a wash motor for pumping wash liquid and upper and lower spray arm for spraying the wash liquid pumped by the wash motor, the dishwasher comprising: a control unit for operating the wash motor to perform a lower wash cycle by the lower spray arm and an upper wash cycle by the upper spray arm, the control unit is configured to operate the wash motor at a preset first RPM (round per minute) and operate the wash motor at a second RPM for a predetermined duration during the upper wash cycle, wherein the first RPM is less than the second RPM, and the speed of the wash motor is repeatedly raised and lowered in a sporadic manner, or the wash motor is operated cyclically to raise its speed at regular intervals from a preset rpm during the upper wash cycle, and the wash motor is operated at a lower RPM during the lower wash cycle than the first and the second RPM.