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LESSON 29

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.

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LESSON 29

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  1. LESSON 29 • CONTROL SYSTEMS • (DIESEL ENGINE BRIDGE CONTROL SYSTEM) II

  2. Fig. 9 shows the basic requirements for starting and control of a direct reversing slow speed diesel engine.

  3. 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.

  4. Desired valuesignals for engine rpm are transmitted from the bridge control position or engine room remote control position and

  5. and compared with the measuredvaluesignalfrom a propeller shaft speed sensor, the difference between these two signals being the rpm deviation from the required.

  6. This error signal is then used by the controller to adjust the fuelracks to return the engine speed to that required.

  7. Electronic, electro-pneumatic, electro-hydraulic and pneumatic systems may be used for signal transmission and fuel rack operation.

  8. The direction of rotation required is achieved by moving a lever in a horizontal slot,

  9. 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.

  10. The lever is then moved in a vertical slot, the initial movement actuating(操纵、驱动) the starting sequence on air and

  11. and when a pre-set rpm has been reached (30 r/min for example) the air is tripped(切断) and fuel applied.

  12. 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.

  13. The starting sequence is monitored by the interlock and check circuits shown, and a programmer(程序控制器).

  14. This allows the maximum acceleration to commensurate with(与…相应) safe operational requirements of the engine whilst manoeuvring but prevents engine overloading.

  15. 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) and critical speed slipping.

  16. For crash manoeuvres(应急操作) the lever is moved from one extreme to the other, the sequence of events is then controlled to braking, starting and reaching full speed (ahead or astern).

  17. Delays may be fitted to prevent braking air being applied until the engine speed has dropped to a pre-determined r/min to prevent excessive use of starting air and cavitation.

  18. An alarm may be fitted to warn if starting air is applied to the engine for longer than, for example, 15 seconds. Crash manoeuvre signals may cut-out the governor.

  19. Bridge/Engine room control transfer may be carried out by the bridge-engine room telegraph(传令钟) with a special bridge control segment(控制部分).

  20. When both bridge and engine room pointers are on this segment, the bridge has control of the engine,

  21. but if the pointer on either telegraph is moved from this position, the engine room has control, and manoeuvring may be carried out using the engine room/bridge telegraph.

  22. Local manual control facilities also must be provided.

  23. Bridge instrumentation will vary according to the desires of the ship owner and manufacturer,

  24. but is required to include rpm indicator, direction of rotation indicator and starting air pressure,

  25. whilst for unattended machinery space vessels, an emergency stop control system independent of the bridge control system is required.

  26. Also the bridge watchkeeper must be made aware of any machinery fault, that the fault is being attended to and that it has been rectified.

  27. There should be two means of communication between the bridge and main control station in the machinery space, one to be independent of the main electrical power supply.

  28. In some cases facilities may be provided for emergency overriding oil pressure shutdown.

  29. If this facility is used, adequate warning must be given to the engine room staff.

  30. READING MATERIAL • A. CONTROL OF PROPULSION MACHINERY FROM THE NAVIGATING (航行、驾驶) BRIDGE

  31. 1. Under all sailing conditions, including manoeuvring, the speed, direction of thrust and, if applicable,

  32. the pitch of the propeller shall be fully controllable from the navigating bridge.

  33. a) Such remote control shall be performed by a single control device for each independent propeller,

  34. with automatic performance of all associated services, including, where necessary, means of preventing overload of the propulsion machinery.

  35. b) The main propulsion machinery shall be provided with an emergency stopping device on the navigating bridge which shall be independent of the navigating bridge control system.

  36. 2. Propulsion machinery order from the navigating bridge shall be indicated in the main machinery control room or at the propulsion machinery control position.

  37. 3. Remote control of the propulsion machinery shall be possible only from one locating at a time.

  38. The transfer of control between the navigating bridge and machinery spaces shall be possible only in the main machinery space or in the main machinery control room.

  39. The system shall include means to prevent the propelling thrust from altering significantly when transferring control from one location to another.

  40. 4. It shall be possible for all machinery essential for the safe operation of the ship to be controlled from a local position, even in the case of failure in any part of the automatic or remote control system.

  41. 5. The design of the remote automatic control system shall be such that in case of its failure an alarm will be given.

  42. Unless the Administration considers it impracticable, the present speed and direction of thrust of the propeller shall be maintained until local control is in operation.

  43. 6. Indicators shall be fitted on the navigating bridge for: • a) propeller speed and direction of rotation in the case of fixed pitch propeller; or

  44. b) propeller speed and pitch position in the case of controllable pitch propeller.

  45. 7. The number of consecutive(连续的，连贯的) automatic attempts which fail to produce a start shall be limited to safeguard sufficient starting air pressure.

  46. An alarm shall be provided to indicate low starting air pressure set at a level which still permits starting operations of the propulsion machinery.

  47. B. BRIDGE CONTROL SYSTEMS (U. M. S.)

  48. Bridge control of propulsion plant and propulsion control systems centralized in a control room are now normal provision.

  49. Systems provided vary to some extent to suit the particular engine requirements of the major designs, e.g. Burmeister & Wain or Doxford or MAN etc.

  50. As a typical example, the standard design for Sulzer RND engine provides engine control from the wheelhouse telegraph with fully automatic direction selection, starting, speed control and safety devices.

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