ENGINE GOVERNOR
It is located on engine right side at power take off end. Its main work is to keep engine RPM stable as per throttle notch position irrespective of load and road. It also work the following
1. Controls fuel oil supply
2. Co-ordinate between main generator and diesel engine HP.
4. Helps in engine starting and stopping
Three types of governor are used in Diesel locomotive.
1. Electro Hydraulic Governor (EH)
2. Wood Ward Governor (WW)
3. Microprocessor Control Based Governor (MCBG)
Pilot valve assembly Speed coil
Stabilizing coil Slave piston no. 1
Slave piston no. 2 Clutch coil
Arm A Arm B
Reference spring main shaft
Output shaft Oil sump
Pressure relief valve Strainer
Fuel limit cam Load control rheostat
Stabilizing potentiometer two spy glass
Working system
Outside the governor body other then above equipment governor pump is provided in expresser room at engine right side. The governor pump is driven by FPM. Governor sump is filled with 3.79 liter oil. When pump starts working, it sucks oil from governor sump and builds 135 psi pressure and sends to governor hydraulic system.
Fuel rake control shaft is connected to governor output shaft (which is out side of governor body) through linkage pin. Fuel rake of 16 cylinders is controlled by output shaft. Arm B is connected to output shaft in side the governor. Main shaft is connected to arm A inside of governor body. Clutch coil is provided in between arm A and arm B. Minimum 50V is required to energize the clutch coil, this supply is given by battery/AG. Original position of arm A is full fuel position and arm B is no fuel position when engine is shut down.
Speed pilot valve controls oil supply in governor hydraulic system, two forces works on this valve, reference spring which pulls pilot valve upwards and stabilizing coil/speed coil which push the valve downwards. When pilot valve lifted up, 135psi pressure oil goes to bottom of slave piston No.1. When balance current is 475 mA in speed coil, speed pilot valve balanced and flow of oil to slave piston no.1 is stopped.
While engine starting - When FPB kept ON governor pump starts and stabilizing coil energize hence oil will go on the top of slave piston no.1 and pressed it downward due to which main shaft rotate clock wise, arm A will go on arm B and LCR change its position from 1 o’ Clock to 4 o’ Clock and SP from 3 O’ Clock to 6 O’ Clock.
Clutch coil energize when engine start button is pressed, arm A and B will magnetically locks and stabilizing coil de-energize, pilot valve lifted up and oil goes to bottom of slave piston no.1. Main shaft rotate anti clockwise hence arm A, arm B and out put shaft moves toward full fuel position. Governor linkage pressed downwards and fuel racks opened. Fuel is injected in the cylinder, fuel combustion starts.
As fuel combustion starts in cylinder, main crank shaft speed increase, out put current of Tacho generator goes to speed coil. When speed coil gets 475 milliamps current, reference spring brings speed pilot valve in balanced position. This position occurs when main crank shaft rpm is 400, fuel rack stable and due to fixed fuel oil supply engine achieved idle speed.
Increasing/decreasing of engine speed - when throttle notches opened, engine speed relay (ESR) picks up according to notch position and add resistance in series of speed coil. Current in speed coil decreases below 475mA, reference spring pulls the pilot valve upwards. More oil will go in the bottom of slave piston no.1. Main shaft rotate anti clockwise and arm A, arm B and out put shaft travel towards full fuel position, Engine racks opens further hence fuel supply in the cylinder is increased.
Tacho generator out put increased due to increasing in engine speed as per notch and 475mA current goes to speed coil even though resistance were added and fuel rack stabled. When throttle notch decreases engine speed also decreases and reverse action takes place as per notch position.
To stop the engine - When stop button or MUSD pressed, stabilizing coil energize and pilot valve goes downward, governor oil goes on top of slave piston no.1 and press piston downwards hence main shaft rotate clockwise and arm A and arm B both comes on no fuel position. Engine shut down due to no fuel supply.
Engine shut down through safety device – Whenever any one of MFPB-1, 2, MB-1, 2, FPB circuit breakers trips or OPS, SAR, LWS safety device operated that time clutch coil de energized, arm A & arm B separated. Arm B comes to no Fuel position and engine stopped due to no fuel supply.
Working of LCR - It protect the engine from bough down. When train is running with excess load on up gradient with full notch, main generator demands increases and same time engine rpm decreases. In this situation balanced current decreases in speed coil due to decreasing speed of Tacho generator. More oil goes in the bottom of slave piston no.1, maximum fuel rack (29.5mm) opened after that main shaft rotates more in anti clockwise hence LCR comes in active zone (11 - 8 O’ Clock) which decreases main generator excitation and main generator demands reduced hence load on engine decreases, engine rpm maintain as per notch and engine safe guard from bough down.
Duties towards EH governor –
1. Check oil level in governor sump
2. Tightness of empanel plug
3. There should not any leakage in governor hydraulic system
4. Governor linkage pin should be fitted properly
5. Check the position of LCR and SP
WOOD WARD GOVERNOR
Main parts of WW governor
Drive shaft Pump
Fly weight Main rotating bush
Speeder spring Main pilot valve plunger
Buffer piston Speed setting valve plunger
Power piston rotating bushing
Speed setting piston Triangular plate
Oil sump A, B, C, D solenoid
Air sensing device vain servo motor
Load control potentiometer shut down plunger assembly
Tail rod over riding solenoids
Glass tube Empanel plug
Description - Its sump capacity is 2.5 litters. A glass tube is provided to check the oil level. Governor pump is fitted inside the governor body. It maintains the oil pressure at 100psi in the system. The pump and rotating bushing get drive by right side camshaft. Fuel rake control shaft is connected to power piston through linkage and all 16 cylinder fuel rake is controlled by control shaft. Engine fuel rake opens when power piston lifts up.
Speed setting valve plunger is provided in governor speeder section, it controlled by triangular plate. A, B, C, D solenoids valve are fitted on triangular plate, according to notches these solenoids valves are picked up and press triangular plate and speed setting valve plunger downward it is called increment. Opening of fuel rakes are proportionate to increment and engine speed increases.
During the engine starting – When engine starts governor pump also starts working hence rotating bushing starts rotating with the help of drive shaft and oil passage open for buffer piston. Oil pressure is increased between buffer piston and power piston hence power piston lifts up and due to lifting of power piston fuel rakes opened, fuel supply starts in engine cylinder.
Fly weights are connected to main rotating bushing, they are balanced when engine RPM stable on idle (400 rpm) through compensating beam. Passage of oil to buffer piston stopped, power piston stable and idle rpm is maintained.
Increasing/Decreasing of engine speed – According to throttle notches A, B, C, D solenoids picks up sequentially and pressed the triangular plate, Speed setting valve plunger comes downward and pressure mounted on speed setting piston results in compression in speeder spring, fly weights bend inside hence main pilot valve plunger goes downward. Oil passage open for buffer piston and power piston lifts up, fuel rake opening increased and engine rpm increased. Fly weight comes in balanced position, again engine speed stabled as per notch position and fuel rakes also stabled. When throttle notch decreases, reverse procedure starts and due to less fuel supply engine speed decreases.
To stop the engine – When stop button/MUSD pressed or LWS operated D valve energies. Due to D valve energizing alone minus two (-2) increment comes and rotating bushing pressed. Oil on speed piston and speeder spring goes to sump and fly weight goes away from balance position, hence oil from buffer piston also goes in to sump and fuel rack comes on no fuel position and engine shut down.
Low lube oil shut down plunger - In WW governor OPS fitted inside the governor, when ever due to any reason lube oil pressure drops to 1.1kg/cm2 shut down plunger operates due to which oil on speed piston and speeder spring goes to sump through shut down plunger assembly and fly weight goes away from balance position and oil from buffer piston also goes to sump, fuel rack comes on no fuel position and engine will shut down.
Duties towards WW governor -
1. Check oil level in glass tube.
2. Check tightness of empanel plug
3. Check linkage pin
4. Resetting of shut down plunger
5. Check oil leakage on governor body
6. Check connection of booster air and lube oil pipe.
Difference between EH and WW governor-
Micro control based governor ((MCBG)
It is provided on some locomotives, its working is
1. To maintain engine speed as per throttle notches.
2. Matching the horse power of engine and main generator.
3. To control the fuel rack in proportionate to booster air pressure.
4. Shut down the engine due to low lube oil pressure.
5. Reduce the excitation during the wheel slip
Description –This governor has two units’ viz. control and actuator Both the units are connected through cable
Control unit – It is provided in loco pilot cab, it has important electronic circuits and display unit. It has following module/ cards.
1. Control card
2. Input card
3. Load and clutch card
4. Motor control card-2 no.
5. Display control card
6. Power supply module
Display screen – It is provided on control unit and it shows following data/position
1. Notch position
2. Engine speed
3. Fuel rack opening position
4. Booster air pressure
5. Lube oil pressure
6. Fuel oil pressure
7. LCP position
It also displays the defect messages. This unit has reset button, acknowledge button, booster air pressure measuring bypass switch, OSTA testing switch.
Control unit When defect comes in loco, relevant messages display and buzzer start sound if it is normal defect buzzer will stop and message will clear automatically after some time. If it is major defect in engine, message will not clear automatically, it require to press acknowledge button to clear the message, these types of messages are –
1. OSTA tripped
2. Low lube oil
3. Tacho generator failed
4. Over current in fuel rack drive motor
5. Fuel rack drive motor failed
6. Lube oil pressure sensor defective
7. Fuel oil rack position sensor defective A
Actuator unit – It is located at engine right side power take off end; it has stator motor, gear box and clutch, spring to control fuel rack; fuel rack position and pressure sensor. It is connected through cable to control unit.
Working- The input card fitted in control unit senses engine cranking or status of Loco / Engine and give signals to control cards accordingly.
Engine Starting- The input card send signals to Load and Clutch control card, Motor control card at the time of engine starting.
Electromagnetic clutch fitted in actuator unit will operated by Load and Clutch control card due to which stepper motor connects with Rack and pinion. The rack and pinion is connected with fuel linkage.
Motor control card supplies current to stepper motor and the motor opens engine fuel rack due to which engine will start.
Engine Speed Control – On opening throttle, the input card sense signals and send it to control card. The control card gives signals to motor card accordingly it increases current level of stepper motor due to which fuel rack opens further and engine speed will increase.
Input card gets signals of engine speed continuously from Tacho generator, accordingly current of stepper motor controlled by control card and Motor control due to which engine speed will maintain.
