Introduction

NOTE: For Specifications with illustrations, make reference to SPECIFICATIONS for G342C NATURAL GAS ENGINE ATTACHMENTS, Form No. SENR2368. If the Specifications in Form SENR2368 are not the same as in the Systems Operation and the Testing and Adjusting, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

Woodward PSG Governors

SCHEMATIC OF LATEST PSG GOVERNOR
1. Return spring. 2. Output shaft. 3. Output shaft lever. 4. Strut assembly. 5. Speeder spring. 6. Power piston. 7. Flyweights. 8. Needle valve. 9. Thrust bearing. 10. Pilot valve compensating land. 11. Buffer piston. 12. Pilot valve. 13. Pilot valve bushing. 14. Control ports. A. Chamber. B. Chamber.

Introduction

The Woodward PSG (Pressure compensated Simple Governor) can operate as an isochronous or a speed droop type governor. It uses engine lubrication oil, increased to a pressure of 175 psi (1200 kPa) by a gear type pump inside the governor, to give hydra/mechanical speed control.

Pilot Valve Operation

The fuel injection pump camshaft drives a governor drive unit. This unit turns pilot valve bushing (13) clockwise as seen from the drive unit end of the governor. The pilot valve bushing is connected to a spring driven ballhead. Flyweights (7) are fastened to the ballhead by pivot pins. The centrifugal force caused by the rotation of the pilot valve bushing causes the flyweights to pivot out. This action of the flyweights changes the centrifugal force to axial force against speeder spring (5). There is a thrust bearing (9) between the toes of the flyweights and the seat for the speeder spring. Pilot valve (12) is fastened to the seat for the speeder spring. Movement of the pilot valve is controlled by the action of the flyweights against the force of the speeder spring.

The engine is at the governed (desired) rpm when the axial force of the flyweights is the same as the force of compression in the speeder spring. The flyweights will be in the position shown. Control ports (14) will be closed by the pilot valve.

Fuel Increase

When the force of compression in the speeder spring increases (operator increases desired rpm) or the axial force of the flyweights decreases (load on the engine increases) the pilot valve will move in the direction of the drive unit. This opens control ports (14). Pressure oil flows through a passage in the base to chamber (B). The increased pressure in chamber (B) causes power piston (6) to move. The power piston pushes strut assembly (4), that is connected to output shaft lever (3). The action of the output shaft lever causes clockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL ON direction.

PSG GOVERNOR INSTALLED
2. Output shaft. 15. Fuel control linkage.

As the power piston moves in the direction of return spring (1) the volume of chamber (A) increases. The pressure in chamber (A) decreases. This pulls the oil from the chamber inside the power piston, above buffer piston (11) into chamber (A). As the oil moves out from above buffer piston (11) to fill chamber (A) the buffer piston moves up in the bore of the power piston. Chambers (A and B) are connected respectively to the chambers above and below the pilot valve compensating land (10). The pressure difference felt by the pilot valve compensating land adds to the axial force of the flyweights to move the pilot valve up and close the control ports. When the flow of pressure oil to chamber (B) stops so does the movement of the fuel control linkage.

Fuel Decrease

When the force of compression in the speeder spring decreases (operator decreases desired rpm) or the axial force of the flyweights increases (load on the engine decreases) the pilot valve will move in the direction of speeder spring (5). This opens control ports (14). Oil from chamber (B) and pressure oil from the pump will dump through the end of the pilot valve bushing. The decreased pressure in chamber (B) will let the power piston move in the direction of the drive unit. Return spring (1) pushes against strut assembly (4). This moves output shaft lever (3). The action of the output shaft lever causes counterclockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL OFF direction.

EARLIER PSG GOVERNOR
6. Power piston. 8. Needle valve. 10. Pilot valve compensating land. 11. Buffer piston. 14. Control ports. A. Chamber. B. Chamber.

As power piston (6) moves in the direction of the drive unit the volume of chamber (A) decreases. This pushes the oil in chamber (A) into the chamber above buffer piston (11). As the oil from chamber (A) flows into the power piston it moves the buffer piston down in the bore of the power piston. The pressure at chamber (A) is more than the pressure at chamber (B). Chambers (A and B) are connected respectively to chambers above and below the pilot valve compensating land (10). The pressure difference felt by the pilot valve compensating land adds to the force of the speeder spring to move the pilot valve down and close the control ports. When the flow of oil from chamber (B) stops so does the movement of the fuel control linkage.

Hunting

There is a moment between the time the fuel control linkage stops its movement and the time the engine actually stops its increases or decrease of rpm. During this moment there is a change in two forces on the pilot valve, the pressure difference at the pilot valve compensating land and the axial force of the flyweights.

The axial force of the flyweights changes until the engine stops its increase or decrease of rpm. The pressure difference at the pilot valve compensating land changes until the buffer piston returns to its original position. A needle valve (8) in a passage between space (A) and (B) controls the rate at which the pressure difference changes. The pressure difference makes compensation for the axial force of the flyweights until the engine stops it increase or decrease of rpm. If the force on the pilot valve compensating land plus the axial force of the flyweights is not equal to the force of the speeder spring the pilot valve will move. This movement is known as hunting (movement of the pilot valve that is not the result of a change in load or desired rpm of the engine).

The governor will hunt each time the engine actually stops its increase or decrease of rpm at any other rpm than that desired. The governor will hunt more after a rapid or large change of load or desired rpm than after a gradual or small change.

PSG GOVERNOR
8. Needle valve.

NOTE: The Woodward PSG Governor is removed from the engine to show the needle valve (8). When the governor is installed on the engine, the needle valve (8) is between the governor and the cylinder block.

Speed Adjustment

The earliest PSG governors use a screw (1). When the screw is turned clockwise it pushes the link assembly (2) down. This causes an increase in the force of speeder spring (3) and pilot valve (4) will move down. See PILOT VALVE OPERATION. The engine will increase speed until it gets to the desired rpm. When the screw is turned counterclockwise the link assembly moves up. This causes a decrease in the force of the speeder spring and the pilot valve will move up. The engine will decrease speed until it gets to the desired rpm.

Later PSG governors use a clutch assembly (6) driven by a 110V AC/DC or 24V DC reversible synchronizing motor (5) to move link assembly (7) up or down. The clutch assembly protects the motor if the adjustment is run against the stops. The motor is controlled by a switch that is remotely mounted. The clutch assembly can be turned manually if necessary.

EARLIEST PSG GOVERNOR
1. Screw. 2. Link assembly. 3. Speeder spring. 4. Pilot valve.

LATER PSG GOVERNOR
5. Synchronizing motor. 6. Clutch assembly. 7. Link assembly.

Speed Droop

EARLIER PSG GOVERNOR
1. Bracket. 2. Pivot pin. 3. Output shafts.

Speed droop is the difference between no load rpm and full load rpm. This difference in rpm divided by the full load rpm and multiplied by 100 is the percent of speed droop.

The speed droop of the PSG governor can be adjusted. The governor is isochronous when it is adjusted so that the no load and full load rpm is the same. Speed droop permits load division between two or more engines that drive generators connected in parallel or generators connected to a single shaft.

Speed droop adjustment on PSG governors is made by movement of pivot pin (2). When the pivot pin is put in alignment with the output shafts, movement of the output shaft lever will not change the force of the speeder spring. When the force of the speeder spring is kept constant the desired rpm will be kept constant. See PILOT VALVE OPERATION. When the pivot pin is moved out of alignment with the output shafts, movement of the output shaft lever will change the force of the speeder spring proportional to the load on the engine. When the force of the speeder spring is changed the desired rpm of the engine will change.

On earlier PSG governors the cover must be removed to adjust the speed droop. Later models have an adjustment lever outside the governor connected to pivot pin (2) by link (4).

LATER PSG GOVERNOR
2. Pivot pin. 4. Link.

Shutoff And Alarm System Components

Oil Pressure Switch

Micro Switch Type

The oil pressure switch is used to give protection to the engine from damage because of low oil pressure. When oil pressure lowers to the pressure specifications of the switch, the switch closes and activates the fuel shutoff solenoid.

On automatic start/stop installations, this switch closes to remove the starting system from the circuit when the engine is running with normal oil pressure.

The switch for oil pressure can be connected in a warning system for indication of low oil pressure with a light or horn.

As pressure of the oil in bellows (6) becomes higher, arm (4) is moved against the force of spring (3). When projection (10) of arm (4) makes contact with arm (9), pressure in the bellows moves both arms. This also moves button (8) of the micro switch to activate the micro switch.

OIL PRESSURE SWITCH (Micro Switch Type)
1. Locknut. 2. Adjustment screw. 3. Spring. 4. Arm. 5. Spring. 6. Bellows. 7. Latch plate. 8. Button for micro switch. 9. Arm. 10. Projection of arm.

Some of these switches have a "Set For Start" button. When the button is pushed in, the micro switch is in the START position. This is done because latch plate (7) holds arm (9) against button (8) of the micro switch and the switch operates as if the oil pressure was normal. When the engine is started, pressure oil flows into bellows (6). The bellows move arm (4) into contact with latch plate (7). The latch plate releases the "Set For Start" button and spring (5) moves it to the RUN position. This puts the switch in a ready to operate condition.

Earlier Type Switch

Early type switches for oil pressure have a control knob (1). The knob must be turned (reset) every time the engine is stopped. Turn the knob counterclockwise to the OFF position before the engine is started. The knob will move to the RUN position when the oil pressure is normal.

OIL PRESSURE SWITCH (Earlier Type)
1. Control knob.

Pressure Switch

These type pressure switches are used for several purposes and are available with different specifications. They are used in the oil system and in the fuel system. One use of the switch is to open the circuit between the battery and the fuel shutoff solenoid after the oil pressure is below the pressure specifications of the switch. It also closes when the engine starts.

PRESSURE SWITCH

Another use of the switch is to close and activate the battery charging circuit when the pressure is above the pressure specification of the switch. It also disconnects the circuit when the engine is stopped.

Some switches of this type have three terminal connections. They are used to do two operations with one switch. They open one circuit and close another with the single switch.

Water Temperature Contactor Switch

The contactor switch for water temperature is installed in the water manifold. No adjustment to the temperature range of the contactor can be made. The element feels the temperature of the coolant and then operates the micro switch in the contactor when the coolant temperature is too high, the element must be in contact with the coolant to operate correctly. If the cause for the engine being too hot is because of low coolant level or no coolant, the contactor switch will not operate.

The contactor switch is connected to the fuel shutoff solenoid to stop the engine. The switch can also be connected to an alarm system. When the temperature of the coolant lowers to the operating range, the contactor switch opens automatically.

WATER TEMPERATURE CONTACTOR SWITCH

Circuit Breaker

The circuit breaker gives protection to an electrical circuit. Circuit breakers are rated as to how much current they will permit to flow. If the current in a circuit gets too high it will cause heat in disc (3). Heat will cause distortion of the disc and contacts (2) will open. No current will flow in the circuit.

An open circuit breaker will close (reset) automatically when it becomes cooler.

CIRCUIT BREAKER SCHEMATIC
1. Disc in open position. 2. Contacts. 3. Disc. 4. Circuit terminals.

Mechanical Overspeed Switch

The overspeed switch is installed on the tachometer drive shaft on the fuel injection pump. The switch activates when the engine speed is equal to the overspeed setting. When the overspeed switch has activated, the contacts do not automatically return to their normal positions. The reset button (1) must be pushed by the operator to make switch contacts return to their normal positions. The usual setting for the overspeed switch is 18% higher than the rated speed of the engine.

MECHANICAL OVERSPEED SWITCH
1. Button.

Some overspeed switches also have underspeed contacts. These contacts close at approximately 600 rpm as the engine speed increases. The underspeed setting is not adjustable.

Power Take-Off Clutches

POWER TAKE-OFF CLUTCH (Typical Illustration)
1. Ring. 2. Driven discs. 3. Link assemblies. 4. Lever. 5. Key. 6. Collar assembly. 7. Nut. 8. Yoke assembly. 9. Hub. 10. Plates. 11. Output shaft.

Power take-off clutches (PTO's) are used to send power from the engine to accessory components. For example, a PTO can be used to drive an air compressor or a water pump.

The PTO is driven by a ring (1) that has spline teeth around the inside diameter. The ring can be connected to the front or rear of the engine crankshaft by an adapter.

NOTE: On some PTO's located at the rear of the engine, ring (1) is a part of the flywheel.

The spline teeth on the ring engage with the spline teeth on the outside diameter of driven discs (2). When lever (4) is moved to the ENGAGED position, yoke assembly (8) moves collar assembly (6) in the direction of the engine. The collar assembly is connected to four link assemblies (3). The action of the link assemblies will hold the faces of driven discs (2), drive plates (10) and hub (9) tight together. Friction between these faces permits the flow of torque from ring (1), through driven discs (2), to plates (10) and hub (9). Spline teeth on the inside diameter of the plates drive the hub. The hub is held in position on the output shaft (11) by a taper, nut (7) and key (5).

NOTE: A PTO can have from one to three driven discs (2) with a respective number of plates.

When lever (4) is moved to the NOT ENGAGED position, yoke assembly (8) moves collar assembly (6) to the left. The movement of the collar assembly will release link assemblies (3). With the link assemblies released there will not be enough friction between the faces of the clutch assembly to permit a flow of torque.