lesson 29　CONTROL SYSTEMS 轮机英语课件.ppt

LESSON 29 CONTROL SYSTEMS (DIESEL ENGINE BRIDGE CONTROL SYSTEM) II Fig. 9 shows the basic requirements for starting and control of a direct reversing slow speed diesel engine. The basic control loop for diesel engine is of closed loop form with a two or, three-term controller, possibly with a load limiting device and alarm, controlling the engine speed. Desired value signals for engine rpm are transmitted from the bridge control position or engine room remote control position and and compared with the measured value signal from a propeller shaft speed sensor, the difference between these two signals being the rpm deviation from the required. This error signal is then used by the controller to adjust the fuel racks to return the engine speed to that required. Electronic, electro-pneumatic, electro-hydraulic and pneumatic systems may be used for signal transmission and fuel rack operation. The direction of rotation required is achieved by moving a lever in a horizontal slot, movement to either extreme operating the valves controlling the servo-motor which positions the cam shaft for the correct air start and fuel valve timing for the required direction of rotation. The lever is then moved in a vertical slot, the initial movement actuating(操纵、驱动) the starting sequence on air and and when a pre-set rpm has been reached (30 r/min for example) the air is tripped(切断) and fuel applied. Subsequent(后续的) movement of the lever operates a servo-mechanism which adjusts the speed setting lever on the engine and which is in turn connected to the governor. The starting sequence is monitored by the interlock and check circuits shown, and a programmer(程序控制器). This allows the maximum acceleration to commensurate with(与…相应) safe operational requirements of the engine whilst manoeuvring but prevents engine overloading. It also programmes the increase in power when moving from Full Ahead to Full Away, guarding against excessive power demands and propeller cavitation(空洞、气蚀) a