Engine Speed Control PDF

c G c c e c c G c c c c c c c CHAPTER c Engine Speed Control c G 6 Introduction G The engines covered in this program are equipped with a Woodwar...

c G c c e c c G c c c c c c c CHAPTER c Engine Speed Control c G 6 Introduction G The engines covered in this program are equipped with a Woodward PGR c deals only governor as shown in Figure 8.1 which: c With conventional regulates the amount of fuel delivered to the engine engine cylinders by the fuel injectors. G control. G EMDEC is assists in controlling main generator output by regulating covered in a main generator excitation through the load regulator. separate G training By balancing generator load with a set engine speed, the governor maintains a G Program. constant kilowatt output by the engine/generator combination for each throttle position. c Speed selection is accomplished through the actuation of combinations of electric c solenoids within the governor; fuel control through the governors internal hydraulic system, hence the term electro - hydraulic. G c The governor senses engine RPM and adjusts the position of the layshaft, which in turn regulates fuel injector output to maintain engine RPM at the operator selected G level. G The Woodward governor is a complex precision device; it will be covered in depth in a subsequent course however, this chapter will briefly cover some of the b significant points. G c ITS LocomotiveTraining Series - Student Text 8-1 a G  3 The governor has three main systems: 3 u) speed sensing 3 speed control 3 load regulation 3 It also has a completely self contained 3 hydraulic system with reservoir, pump, and accumulators to lubricate the internal parts and 3 operate various parts of the governor, 3 The governor has protective devices which 3 will shut the engine down should there be a loss of pressure in the engines' lube oil system or a 3 11. EL9ctfidReceptacle failure of the engines cooling system. 12. Ecgine Oil Pressure Connection 13. nme m!ayk u m u $ t o r 19 14. RebaknCng Servo Oil Filter 15. VentPM 16. OilDrainCock Figure 8-1 Woodward Electro-Hydraulic Governor 3 17. T e n i d Shaft control kJ) Speed Sensing and Fuel Control kll 3' The basic operation of the Woodward governor is illustrated in Figure 8.2. Shutdown Rod 3 Fuel Limit Lock Nut Bushing Locknut Fuel Limit Nut Shutdown Bushing 3 0.79 mm (1/32") Gap At Idle Speed Setting Piston 22293 Figure 8.2 Basic Operation 8-2 ElectroMotive Model 567,645 & 710 Series Diesel Engines G c c c c The governor drive shaft is driven from the accessory gear train through an angle L drive unit and provides the energy to drive the governors components and sense and respond to changes in engine speed. This drive shaft turns the enclosed hydraulic gear c pump, the flyweight assembly and the rotating bushing which encloses the pilot valve. As the governor rotates, oil is pumped into accumulators to provide a working supply of G oil under pressure for the governor. c; The flyweights are mounted on pivots and held inwards by the pressure of the c, speeder spring on their fingers. These fingers are also connected to the top of the pilot valve that controls the flow of oil to and from the power piston. c( c As the engine is started, the centrifugal force of the flyweights is insufficient to overcome the pressure of the speeder spring. The pilot valve is held down and allows oil c to flow from the accumulators, through the rotating bushing, and through the buffer piston to the underside of the power piston. c Oil pressure under the power piston builds up and overcomes spring pressure to c move the piston upwards. Fuel injection rates are controlled by the power piston, 6 which through the layshaft and racks, controls the fuel injectors. Raising the power piston moves the layshafts, which in turn move the injector racks inwards to a higher c fuel position. c As more fuel is delivered to the engine and speed increases, centrifugal force on c the flyweights causes them to move outwards, raising the pilot valve plunger and shutting off the supply of oil to the underside of the power piston. This action maintains c fuel delivery, and engine speed, at a set level. c Should engine speed increase beyond desired, the weights move outwards further, raising the pilot valve plunger. This opens ports to allow oil to drain back from the CJ underside of the power piston. c The power piston moves down, cutting back the amount of fuel delivered to the c engine. dr Engine RPM stabilizes in the "balance" position, controlled by the action of the flyweights and speeder spring pressure. (2 L G c cr. Ci c CSI G c c ITS LocomotiveTraining Series - Student Text 8-3 I r,  Speed Control In the last section we saw how the governor maintains engine speed in the "balance" position. Now we will look at how the governor responds to changes in the throttle position by means of the speed setting system (Figure 8.3) Speed setting of the governor is accomplished by energizing different combinations of the four electric solenoids (A,B,C,D). The A, B, and C solenoids have plungers that bear on a triangular plate, attached to a fulcrum point on a lever. Each of these three solenoids is positioned at a different distance from the fulcrum point of the plate. By energizing different solenoids (or combinations of solenoids) the plate is depressed to different levels. r.. Pressure Oil $5Trapped Oil Intermittent Oil Iintermediate Oil Figure 8.3 Speed Control The lever is attached to the top of the speed control pilot valve on one end; and through linkages to the top of the speed setting piston on the other end. The D solenoid is attached to another rotating bushing which surrounds the speed setting pilot valve. When the throttle is moved to a higher position, calling for more engine speed, one solenoid (or a combination of solenoids) are energized. Energizing the solenoids causes the triangular plate to be depressed. Through the plate and lever, the speed setting pilot valve is depressed, allowing oil to flow to the top of the speed setting piston. 8-4 Electro-Motive Model 567.645 & 710 Series Diesel Engines tl i 0 3 a !3 9 3 4 3 3 3 9 0 3 (7 3 0 a 3 3 3 3 3 3 3 3 3 3 3 9 Q ”) 3 9 3 r> 3  G, 3 Load Regulation The next part of the governor to be covered is the load regulation system (Figure 8.4). This system controls the excitation of the main generator, and balanced with engine RPM, the power output. This section provides a brief description of the operation as system will be dealt with in detail in later courses. The system uses linkages and a load regulator pilot valve to control oil flow to and from the load regular vane motor. Figure 8.4 Load Regulation The vane motor operates a resistor that controls the current used for main generator excitation, and therefore output. (on microprocessor controlled locomotives, the load regulator sends a reference signal to the computer to control loading). 8-6 Electro-MotiveModel 567,645 & 710 Series Diesel Engines c c c G c; If the horsepower demand is less than or greater than the engine is adjusted to c develop for a given RPM, then this system will increase or decrease generator excitation (and therefore output) to meet the changed demand. c If the horsepower demand is less than rated, oil is directed to one side of the vane L motor to increase resistance in the main generator field circuit, and cut back G horsepower developed. At the same time, the governor responds by cutting back fuel delivery to maintain a constant engine RPM. c If the horsepower demand is more than is proper for a set engine speed, again the c load regulator system will limit the main generator output and engine fuel delivery to c maintain a maximum rated output. c In addition to basic load regulation, the system also compensates for engine performance variations caused by barometric pressure changes. c Should barometric pressure (or airbox pressure) reduce, the load regulator system c is affected by the change in pressure. The lower the air box pressure, the sooner the load c regulator will limit main generator excitation. c Another component of this system is the overriding solenoid (ORS),which when energized by other systems, such as wheel slip, will act to reduce excitation. c c Protective Devices CJ The low lube shutdown system protects the engine in case of a failure of the G mechanical support systems. c The shutdown system can be activated by: c 1. "True" low lubricating oil pressure; c G 2. "False" low lube pressure caused by a failure of i e cooline svstem ant v , detected by either of the low cooling water portion of the E.P.D. or hot oil c detector; G 3. "False" low lube pressure caused by the E.P.D. sensing a positive crankcase pressure (crankcase is normally under a slight vacuum); G c 4. "False" low lube pressure caused by manual engagement of the system connected to a lube oil line from the engine on one side and speed setting c oil pressure on the other side. ~ c; C c G c c ITS Locomotive Training Series -Student Text 8-7 I 0  3 3 3 Oil F8ilura Oiaphrrgm \ 3 3 3 u es 3 3 u cus 3 ts 3 3 Figure 8.5 Low Lube Oil Shut Down 6J 3 Should oil pressure in the line drop below the speed setting oil pressure, the system will take action to shut down the engine. 3 When the engine is at idle, there is a mechanism that builds in a delay of 50 to w 60 seconds. This delay is to allow oil pressure to build up when starting the engine. 3 The delay is reduced in steps to the third throttle position. In the fourth position and higher there is no time delay in the shut down system. 3 To shut the engine down, the system bleeds the speed setting oil from the top 3 of the speed setting piston. 3 The governor reacts by moving the layshaft and racks to the no fuel position, 3 shutting down the engine. kd A switch is tripped setting off an alarm in the operators cabin, and a plunger 13 protrudes from the side of the governor exposing a red band. The engine cannot be restarted until this plunger is reset.. L. The hot oil detector and engine protective device both simulate a loss of oil d pressure by bleeding oil pressure off of the line to the governor. u 1 3 ;L, G) 8-8 Eiectro-Motive Model 567,645 & 710 Series Diesel Engines LI c c c Governor Maintenance c Governor oil should be changed at regularly scheduled intervals. Always maintain c governor oil level to the top mark in the governor oil level gauge. A large percentage of c governor problems are caused by dirty oil. Always use clean oil and a clean container when topping up or refilling the governor. Dirt and other impurities can be introduced c with governor oil or can form when oil breaks down or forms sludge. Dirt or sludge can cause the valves, pistons, or plungers inside the governor to stick or seize in their bores C causing erratic operation and poor response. c. In some instances where it is not possible to remove the governor to disassemble c and clean it, governor performance may be restored by flushing the governor with fuel oil or kerosene. Solvents should not be used to flush a governor, as they can damage sea,, c and gaskets. c Governor Flushing c c Open the drain cock and drain the governor oil. c; Refill the governor with clean fuel oil and restart the engine. c Using the injector control lever, vary the engine speed from approximately 400 to 500 RPM for about five minutes, then stop the engine and drain the fuel oil c from the governor. c Repeat the process until the fuel oil drained appears clean, then fill the gover- G nor with clean governor oil. c Restart the engine and repeat the above process, then drain the oil to remove c any trapped kerosene. c Fill the governor with clean oil. Adjust the compensation needle valve using the following procedure. c G Compensation Adjustment c The compensating mechanism prevents the engine from "hunting" or racing by c arresting the movement of the power piston after it has travelled a sufficient amount to give the desired speed. c Compensation adjustment is the only adjMsDent that is recommended-to be done G with the governor on the engine. All other governor adjustments should be done on a c calibrated test stand by specially trained personnel. c Adjustment of the compensation mechanism is required when an engine is being started for the first time, after installation of a new or reconditioned governor, or after a G governor has been drained and cleaned and new oil added. G e c - ITS Locomotive Training Series Student Text 8-9 3 0  This adjustment purges the governor oil system of trapped air. Adjust the compensation as follows: Ensure that the governor oil level is between the lines on the sight glass. Start the engine and operate at idle speed. Open the compensating needle valve by turning counterclockwise several turns. Loosen the vent plug several turns, but do not remove it. The engine will hunt and surge, and air will bleed from the system at the vent plug. When onlv oil flows from the vent plug, slowly close the compensating needle valie until the hunting stops or slows. Tighten the vent plug to prevent oil leakage, and add oil to the governor if necessary. Allow the engine to reach normal operating temperature, then open the compensating needle valve and allow the governor to hunt. Close the needle valve until the hunting stops. Test the governor by changing speeds with the injector control lever observing the governor recovery. If the governor returns to a steady speed, the adjustment is satisfactory. If hunting resumes, close the compensating needle valve slightly then test again. This compensating needle valve should be kept open as far as possible to prevent sluggishness and still maintain even governor operation. After compensation is set, it should not require another adjustment. 17. Temhul Shalt canmi Figure 8.6 8-10 Electro-Motive Model 567.645 & 710 Series Diesel Engines c :. c G c Governor Qualification c Many governors are needlessly changed out because of the lack of proper trouble- G shooting procedures. Governor problems usually show up as engine speed variations G such as hunting, surging or jiggle, but an engine showing signs of engine speed varia- tion does not necessarily have a governor problem. Before changing a suspected gover- c nor, verify that the speed variation is not caused by one of the following conditions: G Check the linkage between the governor and the fuel racks for binding or c excessive backlash. c Disconnect each injector from the injector control shaft by removing the pin from the adjusting link, then operate the injector rack in and out checking for c binding or tight spots. Make sure all injectors are the proper type for the application. G c Check engine operation to be sure that all cylinders are firing properly. G Check for bubbles in the return fuel sightglass. If evident, verify that the fuel system is functioning properly, using the checks in the fuel system trouble- c shooting section of this text. c Check the setting of the governor compensation needle valve. c Ensure that the load on the engine is not fluctuating and causing the engine c RPM to respond to these changes. Items to check include the load regulator wiper arm to make sure the vane motor is not causing the load regulator to e hunt, excitation circuit causing overexcitation of the main generator and ma1 c function of protective device such as current overload relays. c With the engine at maximum speed and full load, check the quadrant on the governor. If the rack dimension is shorter than the limit on the governor G identification plate, the engine is either overloaded or lacking fuel. c Check speed setting circuits for correct voltage levels and proper e sequencing. G Check the governor drive for any evidence of misalignment, roughness, or c excessive backlash. c Flush governor following the procedure outlined in this chapter. G _ L -. Only after these checks are made and no other reason can be found for tht.'$pk?ed fluctuations, should a governor be changed. G G G ci G c ITS LocomotiveTraining Series -Student Text 8-11 g 0 c c G /c G c c G c c c c c c c c c c c c c U c c c c G G c c d c 0