| 摘要 |
<p>The running speed of the fan 24 is continuously and proportionally changed responsive to the temperature of the cooling water either alone or in conjunction with the external atmospheric conditions, e.g. atmospheric temperature and relative humidity, to control the cooling capacity of the cooling apparatus. The control system consists of a main fan motor 29, an electronic adjustment circuit responsive to the cooling water temperature and external conditions and a power transmission means consisting of a variable pitch diameter belt speed changing means 62, 63, 64 and, preferably, a constant pitch belt reduction device 91, 92, 93, whereby the speed changing ratio of the belt speed changing means is continuously and proportionally varied depending upon the control signals from the adjustment circuit. The ratio variation is effected by displacing one cheek 62b of pulley 62 by means of a screw 70 which engages a nut 72 and is rotated in one direction or the other by means of a reversible electric motor which is controlled by the control signals. The adjustment circuit may have a soft-start control circuit which ensures that the speed changing means 62, 63, 64 is at its greatest reduction ratio when the motor 29 is started. <IMAGE></p> |
