Presentation on theme: "LESSON 29 CONTROL SYSTEMS (DIESEL ENGINE BRIDGE CONTROL SYSTEM) II."— Presentation transcript:
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 ) and critical speed slipping.
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).
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.
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.
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 ).
When both bridge and engine room pointers are on this segment, the bridge has control of the engine,
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.
Local manual control facilities also must be provided.
Bridge instrumentation will vary according to the desires of the ship owner and manufacturer,
but is required to include rpm indicator, direction of rotation indicator and starting air pressure,
whilst for u nattended m achinery s pace vessels, an emergency stop control system independent of the bridge control system is required.
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.
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.
In some cases facilities may be provided for emergency overriding oil pressure shutdown.
If this facility is used, adequate warning must be given to the engine room staff.
READING MATERIAL A. CONTROL OF PROPULSION MACHINERY FROM THE NAVIGATING ( 航行、驾驶 ) BRIDGE
1. Under all sailing conditions, including manoeuvring, the speed, direction of thrust and, if applicable,
the pitch of the propeller shall be fully controllable from the navigating bridge.
a) Such remote control shall be performed by a single control device for each independent propeller,
with automatic performance of all associated services, including, where necessary, means of preventing overload of the propulsion machinery.
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.
2. Propulsion machinery order from the navigating bridge shall be indicated in the main machinery control room or at the propulsion machinery control position.
3. Remote control of the propulsion machinery shall be possible only from one locating at a time.
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.
The system shall include means to prevent the propelling thrust from altering significantly when transferring control from one location to another.
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.
5. The design of the remote automatic control system shall be such that in case of its failure an alarm will be given.
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.
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
b) propeller speed and pitch position in the case of controllable pitch propeller.
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.
An alarm shall be provided to indicate low starting air pressure set at a level which still permits starting operations of the propulsion machinery.
B. BRIDGE CONTROL SYSTEMS (U. M. S.)
Bridge control of propulsion plant and propulsion control systems centralized in a control room are now normal provision.
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.
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.
Their Type SBC7 bridge console and control console panels are shown on Fig. 10 and 11, these being indicative( 指示的 ) of the instrumentation involved.
In addition to the parts listed a non-reply telegraph( 非应答式车钟 ) receiver or telegraph indicator panel is mounted adjacent to the engine emergency manoeuvering controls.
C. ALARM SYSTEM
An alarm system shall be provided indicating any fault requiring attention and shall:
1. be capable of sounding an audible alarm in the main machinery control room or at the propulsion machinery control position,
and indicate visually each separate alarm function at a suitable position
2. have a connection to the engineers' rooms and to each of the engineers cabins through a selector switch, to ensure connection to at least one of those cabins.
Administrations may permit equivalent arrangements
3. activate an audible and visual alarm on the navigating bridge for any situation which requires action by or attention of the officer on watch;
4. as far as is practicable, be designed on the fail-to-safety principle; and
5. activate the engineers’ alarm if an alarm function has not received attention locally at limited time.
The alarm system shall be continuously powered and shall have an automatic change-over to a stand-by power supply in case of loss of normal power supply.
D. AUTOMATION ON SHIPS
Typical example of automation on ships are fire detection and extinguishing systems; emergency lighting systems;
automatic start of standby pumps supplying lubricating oil and fuel oil to the propulsion machinery; and automatic speed reduction or stopping of propulsion machinery when faults are detected.
Further improvements can be achieved in an integrated control system by incorporating digital data processing equipment--that is, a computer.
This remarkable machine can provide rapid and accurate supervision, analysis, recording and display of the conditions it is monitoring.
In so doing, it serves as an extremely valuable aid to human judgement.
But in some control systems the computer is arranged to make the necessary decision and take the necessary action without human intervention. This is called direct digital control.
Integrated bridge-engine room control systems are now available that combine the functions of engine room monitoring and control, collision avoidance, docking and manoervering, navigation, and cargo handling.
These systems include one or several computers for facilitating data inquisition, processing, logging and display, and for exerting some degree of direct digital control over the machinery.
E. REMOTE CONTROL AND AUTOMATION OF LARGE ARINE DIESEL ENGINES
The simplest way to achieve remote control of large marine diesel engines is by providing a separate manoeuvring stand beside, or in front of, the engine.
Mostly, this stand has been developed into a large desk or console, comprising all the instruments needed for manoeuvring and serving the main and auxiliary engines, together with all the measuring instruments.
Further automation requires remote control from any place in the engine room or a special control room and, in many cases, from the bridge.
Today automation is being developed with the purpose of relieving the operators, and especially the men on the bridge, from paying any attention to levers, hand-wheels, instruments, etc.
However, in most cases a manoeuvring stand at the engine is still left for direct operation of the engine in case of emergency.
There are three remote control arrangements in general use, (a) from engine control room to engine; (b) from bridge to engine; (c) from both bridge and engine control room to engine.
The remote control is pneumatic up to 3O meters and electro-pneumatic beyond this distance.
Here is given one of the remote control types applied to large marine diesel engine. It is built on pneumatic elements with a relatively simple electronic control for fine speed adjustment.
The system provides automatic control of the main engine from the bridge and manual control from the control room in the engine room.
The pneumatic system is most reliable; and the electronic system is simple and easily maintained.
The electronic system contains only three insert type units;
one is a power unit containing a transformer and a rectifier to give 24 V dc and 115 and 200 V ac;
the second is a programme unit for various fine speed adjustments; and the third is an electronic control for the electric step motor.
Even if all electronics should fail, bridge control with the pneumatic system is possible.
When the officer on the bridge moves a selector switch on the bridge console to Bridge Control, the Bridge Control on the control room telegraph lights up and an alarm sounds on the telegraph until acknowledged.
There are also two buttons marked Fine Setting up and Fine Setting down on the bridge console.
When the ship is manoeuvred out of port and it is required to increase the ship speed from Full Ahead to service speed, the officer on watch has only to depress the Automatic Acceleration Up button for the speed to be automatically and gradually increased to the required speed within a period of about 30 minutes--but again, this period is adjustable.
To stop this gradual acceleration the program button Automatic Acceleration off must be depressed.
The same system applies in reverse when the speed must be gradually returned--for example, when entering a port.
The following indications are provided on the bridge console: (1) tachometer, (2) starting air pressure, (3) control air pressure, (4)control lamps for: (5) bridge control,
(6) control room control, (7) manual control on engine, (8) transfer of order, (9) speed correction and (10) critical speed range.
Also fitted in the bridge console are an emergency stop button and control lamp and an emergency run button and control lamp.
There are also alarms which sound when the engine is overloaded, tripped, or fails to start, and when the starting air pressure or control air pressure is too low, or when the electric power fails.
As the manual telegraph is also used for the engine control, the Stand by and Finished with Engine orders are carried out by using separate buttons.