Systems Operations

Usage:

Electronic Locomotive Control System

The Electronic Locomotive Control System consists of:

1. Main Electronic Control Box.

2. Standard Personality Module.

3. Engine Speed Sensor.

4. Rack Position Sensor.

5. Rack Actuator (the particular type depends on the engine type).

6. Optional Voltage Sensor (Customer Supplied).

7. Optional Current Sensor (Customer Supplied).

8. Optional Derate Module.

9. Optional Personality Module with Optional Software.

10. Optional Mounting Group Assembly (a prewired assembly containing items 1 & 8).

11. Optional Water Temperature Sensor and Temperature Interface Module.

The various functions performed by the locomotive control system are fully defined by the active software package.

The main control box contains resident software that performs the basic tasks of engine speed governing and engine power control. The control loops defined by this software use data in the standard personality module for their various parameter settings. This is the most basic system configuration and uses items 1 through 5. The engine load is controlled by modulating the generator's excitation current. This can be done in one of two ways: either by directly driving the exciter from the control, or by using a low current voltage drive circuit which interfaces with certain types of locomotive generator excitation systems.

The next available level of complexity includes the addition of either item 6 and/or item 7. Item 6 is a D.C. signal proportional to the generator output voltage, and item 7 is a D.C. signal proportional to the generator output current. The hardware that generates these signals can be supplied by the customer, or Caterpillar's locomotive application group. When these items are included, the main generator can be protected from damage by voltage and current limiting control loops in the resident software.

If items 6 and 7 are both included, the customer can also specify direct closed loop control of the power to the traction motors over all (or part) of the throttle range.

The next available level of complexity includes the addition of item 8 (derate module), which also requires the addition of item 9 (optional personality module). The derate module provides five additional D.C. analog inputs to the system. The resident software cannot access this derate module, therefore optional software is required that resides in the optional personality module.

This derate module and the optional personality module provide the Electronic Locomotive Control System with a high degree of flexibility for use on a wide variety of locomotive types, including those fitted with dynamic brakes and a wheelslip or wheel-creep control system.

Item 10 is a optional mounting group assembly that contains the Main Electronic Control Box and the Optional Derate Module. These items are prewired to two Railroad Industry Standard Terminal Strips. Because it is prewired, Caterpillar recommend, that where possible, this mounting group assembly be specified for all applications requiring the Derate Module.

The sensor and module in item 11 are used to linearly derate the engine power as a function of water temperature. This feature protects the engine during operation in high ambient temperatures.

Basic System With Voltage And Current Sense

Typical Optional System With Derate Module

Electronic Locomotive Control Box

Electronic Locomotive Control Box (With Personality Module Removed)
(1) J2 Connector. (2) J1 Connector.

The various functions performed by the locomotive control system are fully defined by the active software package. There are two types of software packages: resident, and optional. The main difference between them lies in their degrees of customization.

Functions With Resident Software

The resident software in the electronic locomotive control box contains various control loops that govern engine speed, control engine power and generator power, and limit generator voltage and current. The resident software uses data in the standard personality module for parameter settings which are unique to a particular combination of engine, generator and locomotive. These parameters include items such as notch code, engine speed, rack settings, ramp rates, voltage limits, current limits, etc. The engine speed and rack settings would normally be chosen to minimize the specific fuel consumption of the engine.

The customer-supplied, optional, voltage-sense and current-sense signals allow the generator to be protected against overvoltage and overcurrent conditions. They also provide the customer with the option of specifying closed loop traction power control. At low throttle levels this feature can provide precise control of traction power which is more important at low throttle settings than specific fuel consumption.

The resident software does not contain any wheelslip detection strategy; it does contain wheelslip response strategy that ramps the generator excitation in response to a digital input from an external wheelslip detection system on the locomotive.

Functions With Optional Software

When an optional personality module is fitted, the input and output signal functions and the operation of the control are defined in the optional software. An optional software package can be designed to perform any function within the limitations of the hardware. A library of optional software packages is available for existing applications. After the software package for each new application is fully developed, it is added to this library.

Personality Module

There is more than one personality module available, the choice of personality module will depend on the software and/or hardware requirements of the particular application.

Standard Personality Module

The standard personality module contains all the customized settings for the resident software in the main control box. It also contains the calibrate mode switch (used to calibrate the rack position sensor) and adjustments for low idle and the wheelslip response ramp rates.

Optional Personality Module

The optional personality module contains the same calibrate switch and adjustments as the standard module. It also contains a larger memory capacity to accommodate customized software that can be executed instead of the resident software.

Engine Speed Sensor

The engine speed sensor provides a digital voltage signal which represents engine speed to the Electronic Locomotive Control Box. The location of the sensor depends on the engine type; it is normally mounted on the flywheel housing adjacent to the ring-gear teeth. The sensing element magnetically detects the gear teeth as they pass by and generates a corresponding A.C. voltage. Electronics inside the sensor convert the A.C. voltage into a digital voltage signal.

Rack Position Sensor

The rack position sensor measures the fuel rack position and sends a digitally coded signal to the main control box. The sensor assembly includes a linear potentiometer and an active electronic module that digitally encodes the potentiometer signal. The details of the potentiometer mounting differ from engine type to engine type. There are two types of mounting designs; one for 3412 Engines and one that is common for 3500 and 3600 Engines.

3500 Rack Position Sensor Installation

3600 Rack Position Sensor Installation

Rack Actuator

The Electronic Locomotive Control Box is designed to drive a Woodward Rack Actuator. Woodward make a wide range of electro-hydraulic actuators that share a common electrical interface and can all be driven by the Electronic Locomotive Control Box. The particular actuator for a particular application depends on the type of engine used in that application. Typically, the following actuators are used on the following engines:

3412 ... EG3P

3500 ... EG10P

3600 ... EG29P

In each case the actuator is mechanically connected to the engine's rack linkage and it positions the rack as a function of the drive current from the Electronic Locomotive Control Box. The relationship between rack position and drive current is very close to linear.

EG-3P Actuator

The EG-3P Actuator is an engine driven device that hydraulically changes an electrical input to a mechanical output (terminal shaft rotation) that controls the engine fuel rack or carburetor.

The EG-3P Actuators is used with the Electronic Locomotive Control Box. The actuator's terminal (output) shaft position is directly proportional to the input signal to the actuator. The actuator normally goes to minimum fuel position if the electric signal is stopped.

The output signal of the electric control box is a level of voltage that determines the actuator terminal shaft position required to maintain a particular load on the engine. The voltage is always the same polarity. This type of control unit requires an actuator in which the output shaft takes a position proportional to the voltage of the input signal.

The main element of the actuator is an electrohydraulic transformer which controls oil flow to and from the power piston through the action of a polarized solenoid. The position of the actuator shaft is proportional to the input current to the solenoid coil controlling the hydraulic pilot valve plunger.

Operation of the actuator is as follows:

The drive shaft rotates between 1200 and 3000 rpm. It can rotate in one direction only. The direction of rotation is determined by the placement of plugs in the oil passages in the actuator base and case. A relief valve is incorporated within the actuator to maintain the operating oil pressure at approximately 2400 kPa (350 psi) above supply pressure.

Engine lubrication oil from an internal sump in the engine enters the suction side of the oil pump. The pump gears carry the oil to the pressure side of the pump, first to fill the oil passages and then to increase the hydraulic pressure. When the pressure becomes great enough to overcome the relief valve spring force and push the relief valve plunger down to uncover the bypass hole, the oil goes back through the inlet side of the pump.

The movement of two opposing pistons turns the actuator terminal shaft. The engine fuel linkage is fastened to the terminal shaft. Pressure oil from the pump is supplied directly to the bottom of the loading piston. Pressure in this hydraulic circuit always moves the terminal shaft in the "decrease fuel" direction.

Since the linkage that connects the loading piston to the terminal shaft is shorter than the linkage that connects power piston to the terminal shaft, the loading piston cannot move up unless the power piston moves down. The power piston moves down only when the oil blocked under it can go to sump.

The flow of oil to and from the power piston is controlled by the pilot valve plunger. With the pilot valve plunger "centered", no oil flows to or from the power piston. The pilot valve plunger is "centered" when its control land exactly covers the control port in the pilot valve bushing.

The greater of two forces moves the pilot valve plunger up or down. When the forces are equal, the plunger does not move.

The pilot valve plunger is connected to a permanent magnet that is spring-suspended in the field of a two-coil solenoid. The output signal from the electric control box is directed to the solenoid coils and produces a force, proportional to current in the coils, which moves the magnet - and pilot valve plunger - down.

A spring force moves the pilot valve plunger and magnet up. The centering spring is positioned on top of the case in which the solenoid coils are located. It puts a constant upward force on the pilot valve plunger. The restoring spring puts a downward force on the pilot valve plunger. The downward force from the restoring spring depends upon the position of the restoring lever. The restoring lever moves up to decrease the restoring spring force as the terminal shaft turns in the "increase fuel" direction. The resultant force from the combined output of the centering spring and restoring spring is a force that moves the pilot valve plunger in the "up" direction. This combined force increases as the terminal shaft moves in the "increase fuel" direction.

Schematic Of EG-3P Actuator (Without Needle Valve Adjustment)

With the unit running on-speed under steady-state conditions, the combined spring force and the force from the solenoid coils are equal but opposite.

When the unit is running on-speed under steady-state conditions, the pilot valve plunger is "centered". A decrease in voltage input to the solenoid coils (due to a decrease in speed setting or a decrease in load) decreases the force and will lower the pilot valve plunger. However, the unchanged spring force is now greater and lifts the plunger above center. As oil moves from under the power piston, the terminal shaft turns in the "decrease fuel" direction. When the terminal shaft has turned far enough for the new fuel requirement, the increase in restoring spring force will equal the decrease in downward force from the solenoid coils, and the pilot valve plunger will be "centered" again by equal but opposite forces that push on it.

When the voltage signal input to the solenoid coils increases (due to an increase in load or an increase in speed setting), similar but opposite conditions will take place. The now greater downward force from the solenoid coils will move the pilot valve plunger down. The power piston and restoring lever will be moved up, decreasing the downward force of the restoring spring. When the terminal shaft turns far enough for the new fuel requirement, the decrease in restoring spring force now equals the increase in downward force from the solenoid coils, and the pilot valve plunger will be centered again by the equal but opposite forces that push on it.

EG-10P Actuator

EG-10P Actuator
(1) EG-10P Actuator.

The EG-10P Actuator is an engine driven device that hydraulically changes an electrical input to a mechanical output (terminal shaft rotation) that controls the engine fuel rack.

This actuator is used with the Electric Locomotive Control Box. The Electric Locomotive Control Box sends a voltage input signal to the solenoid coils of the actuator. The position of the actuator terminal (output) shaft is directly proportional to this input signal to the actuator. When the voltage signal to the actuator is stopped, the terminal shaft of the actuator will move to a position to shut the fuel off to the engine.

The direction of rotation for the correct oil flow is determined at the factory by placement of plugs in specific oil passages in the actuator base and case. There is a relief valve in the actuator to maintain operating oil pressure at a minimum of 1723 kPa (250 psi). Some older units operate at 2750 kPa (400 psi).

NOTE: The only adjustment that can be made to the EG-10P Actuator is the external needle valve. See subject Needle Valve.

To better understand the complete operation of the actuator, a separate explanation of each system follows. These systems are: Oil Pump, Mechanical, Electrical, Hydraulic and Feedback (Mechanical & Hydraulic Buffer).

Schematic Of EG-10P Actuator

Oil Pump System

Engine lubrication oil is supplied (from the engine sump) through inside passages to the suction sides of the three gear actuator oil pump. The pump gears push the oil to the pressure side of the pump to fill the system and increase the hydraulic pressure. When the pressure becomes great enough to overcome the force of the relief valve spring, the relief valve plunger is pushed down to uncover the bypass opening. This bypass oil now goes back to the inlet side of the pump.

Basic Mechanical System

The power piston is connected to the actuator terminal (output) shaft. The engine fuel rack linkage is also connected to the terminal shaft. When there is an increase or decrease in engine load, the movement of the power piston will turn the terminal shaft. The linkage will now move the fuel racks to the new fuel setting to maintain the correct engine speed at the new load condition.

Basic Electrical System

An engine speed sensor is installed in the flywheel housing of the engine to make an AC voltage signal. The frequency of this AC signal is controlled by the speed of the gear teeth that pass through the magnetic field of the pickup. This engine speed frequency signal is sent to the Electric Locomotive Control Box. The Electric Locomotive Control Box makes a comparison between this input signal for actual engine speed and the desired engine speed that the control box has been set to maintain. If the actual engine speed and the speed setting are not the same, the Control Box will send a corrected DC voltage signal to the solenoid coils of the actuator. The actuator will now adjust to a new fuel setting to make the engine speed the same as the speed setting.

The pilot valve plunger is connected to a permanent magnet that is spring-suspended in the field of a two-coil solenoid. The output signal from the Control Box is applied to the solenoid coils to make a magnetic force which is proportional to the current in the coils. This force always tries to move the magnet and pilot valve plunger in the down (increase fuel) direction. The centering spring (at top of plunger) force always tries to move the magnet and pilot valve plunger in the up (decrease fuel) direction.

When the unit runs on-speed at steady-state conditions, these two forces are equal but in opposite directions. The pilot valve plunger at this time will be "centered" (the control land covers the control port).

If there is a decrease in the engine speed setting at the Control Box, or an increase in engine speed (because of a decrease in the engine load), the input voltage to the actuator solenoid coils will be decreased. The magnetic force of the solenoid coils also will now be decreased. Since the force of the centering spring is now greater than the force of the coils, the pilot valve plunger will move above the "centered" position. This allows oil under the power piston to drain to sump, and the down movement of the power piston will cause rotation of terminal shaft in the decrease fuel direction.

If there is an increase in the engine speed setting at the Control Box, or a decrease in engine speed (because of an increase in engine load), the input voltage to the actuator solenoid coils will be increased. The magnetic force of the solenoid coils also will now be increased. Now the force of the coils will be greater than the force of the centering spring, and the pilot valve plunger will move down to allow pressure oil under the power piston.

Since the surface area (that oil pressure works against) of the power piston is larger at the bottom than at the top, the piston will move up. The rotation of the terminal shaft will now be in the increase fuel direction.

Basic Hydraulic System

The power piston is the part of the actuator that does all of the work. Under normal conditions, the oil pressures at both the top and bottom of the piston are balanced, and the piston remains stationary at the "centered" position. The pilot valve plunger controls the flow of oil to and from the power piston. The control land at the bottom of the pilot valve plunger is just large enough to completely cover the control port in the pilot valve bushing when the plunger is exactly "centered."

If the signal from the Electronic Locomotive Control Box makes the pilot valve plunger move up, the oil under the power piston can drain past the control land to sump. The higher oil pressure at the top of the piston will now move the piston down until the control land of the plunger will again close the control port. This piston movement will also move the terminal shaft (in the decrease fuel direction), since they are connected together.

If the signal from the Electronic Locomotive Control Box makes the pilot valve plunger (and control land) move down, pump oil pressure can now pass through the control port to the bottom of the piston. Even though the pump oil pressure in the circuit above the piston is the same as the circuit below the piston, the piston will move up. This is due to a larger surface area available to the oil pressure at the bottom of the piston than the surface area at the top of the piston. The movement of the piston will now turn the terminal shaft in the increase fuel direction.

Feedback Systems

A high degree of stability is necessary to maintain a constant output from the generator set. The stability of a system controlled by the Electronic Locomotive Control Box is increased with the use of a temporary actuator feedback signal that biases (makes a correction to) the Control Box command signal to the pilot valve plunger. Since the Control Box makes an adjustment rapidly to a change in engine load, the actuator can make the engine go into a "hunt" condition (temporary increase and decrease in engine speed) if the corrections are too sensitive. The purpose of the feedback system is to prevent over-correction to the load change.

The EG-10P Actuator is different because two feedback systems are used, one mechanical and one hydraulic. Under normal conditions, the mechanical system will correctly control the actuator. However, during cold engine start-up conditions, the addition of the hydraulic buffer system eliminates erratic (variable) speed problems caused by the cold engine oil. The result of the two systems is constant speed control at all times. The explanation for the operation of each feedback system is as follows:

Mechanical Feedback System

The temporary feedback signal is accomplished in this system by the addition of linkage and a restoring spring arrangement that applies a secondary force to the centering spring.

Decreased Engine Load

With this condition, the voltage signal to the solenoid coils is decreased and the centering spring force will raise the pilot valve plunger to release oil under the power piston to sump. The power piston will now move down to turn terminal shaft in the decrease fuel direction. The mechanical linkage of the feedback lever is also connected to the terminal shaft and will move down. The restoring lever will also move down to put the restoring spring in compression. The restoring spring force is opposite the upward force of the centering spring. The resultant force (from the restoring lever and restoring spring) will now help the solenoid move the pilot valve plunger back down to the "centered" position before it would have been moved down by just the voltage signal change to the solenoid itself. Therefore, the actuator acts to position the terminal shaft in the new decreased fuel position without allowing an underspeed condition.

Increased Engine Load

This condition will increase the voltage signal to the solenoid coils, and the pilot valve plunger will move down because the magnetic force is greater than the centering spring force. The control land will now let pressure oil to the bottom of the power piston, and the power piston will move up. The terminal shaft will turn in the increase fuel direction and, at the same time, move the feedback lever and the restoring lever up. Now there is less compression on the restoring spring.

The resultant centering spring force (upward) is now stronger than the magnetic force of the solenoid coils, and the pilot valve plunger will move up to the "centered" position before it would have been moved up by just the voltage signal change to the solenoid itself. Therefore, the actuator has moved the terminal shaft in the increased fuel position without allowing an overspeed condition.

Hydraulic Buffer Feedback System

The temporary feedback signal in this system uses a pressure differential that is applied across the compensation land of the pilot valve plunger. This pressure differential is accomplished by the buffer system.

Decreased Engine Load

With the pilot valve "centered", no oil flows to or from the power piston. If there is a decrease in load (causing an increase in engine speed), the solenoid coils will get a voltage signal to lift the pilot valve plunger. The oil under the power piston will now be released to go to sump. Pump pressure oil on the right side of the buffer piston will now force the buffer piston to the left. This displacement of oil in the power cylinder oil pressure circuit will move the power piston down and cause rotation of the terminal shaft in the decrease fuel direction.

The movement of the buffer piston to the left also decreases the compression of the buffer spring on the right side, and increases the compression of the buffer spring on the left side. The increase of the left buffer spring force (caused by resistance to this movement) results in a small decrease in oil pressure on the left side of the buffer piston and on the bottom surface of the pilot valve plunger compensation land. This pressure difference on the two sides of the compensation land makes a force (greater at the top) to push the pilot valve plunger back down to the "centered" position.

When the terminal shaft has turned far enough to satisfy the new fuel requirement, the force of the pressure difference on the compensation land will have again "centered" the pilot valve plunger (even though the engine speed is not yet completely back to normal). The movement of the power piston, and the terminal shaft, is now stopped.

The continued decrease of engine speed to its steady-state setting results in a continued increase in downward force to the pilot valve plunger as the Electronic Control signal (to the solenoid coils) increases to its on-speed value. At the same time, the pressure difference on each side of the buffer piston (and at top and bottom of the compensation land) is being released by the flow of oil through the needle valve orifice. This controlled discharge allows the buffer piston to return slowly to its normal, "centered" position. The increase in the solenoid voltage signal to its on-speed value, and the controlled reduction of the pressure difference on the two sides of the compensation land occur exactly at the same rate (while the pilot valve plunger remains "centered") until the engine is again at the on-speed condition at the decreased load.

Increased Engine Load

When the engine load is increased, engine speed will decrease. The Electronic Locomotive Control Box will now send a stronger signal (more voltage) to the solenoid coils, and the pilot valve plunger will move down. The control land has now opened the control port to allow pump pressure oil to the bottom of the power piston. Even though the pressure on each side of the power piston is approximately the same at this time, the pressure against the larger surface area at the bottom of the piston makes a larger force and the power piston will move up. This upward piston movement will cause terminal shaft rotation in the increase fuel direction, and the engine speed will begin to increase.

When the power piston moves up, the displacement of the oil above the power piston will move the buffer piston to the right. This movement will cause a pressure increase on the bottom surface of the compensation land. The pilot valve plunger will now move up to close the control port of the pilot valve bushing before engine speed returns to normal. Any movement of the power piston, and the terminal shaft, is now stopped.

As the engine starts its return to normal speed, the controlled discharge of the oil pressure difference through the needle valve orifice is at the same rate that the voltage signal is decreased to the solenoid coils. The engine now returns to its steady-state condition, with the terminal shaft already set at the new fuel position that is required for the increase in engine load.

Needle Valve

The needle valve orifice is adjustable to permit a variable time rate that a pressure differential acts on the compensation land of the pilot valve plunger. This permits limited control of the EG-10P actuator to be calibrated (set) to the response characteristics of the engine. Normally the settings can be made in the range of 1/2 to 1 1/2turns open to get the desired characteristics.

EGB-29P Actuator

The EGB-29P Actuator is an engine driven device that hydraulically changes an electrical input to a mechanical output (terminal shaft rotation) that controls the engine fuel rack or carburetor. The EGB-29P has an integral mechanical ballhead governor that allows the engine to operate even if the electrical governor fails.

The EGB-29P Actuator consists of three distinct sections: (1) an electric actuator section; (2) a mechanical governor section; (3) a hydraulic amplifier section which amplifies the force output of the other two sections through a power cylinder which provides the hydraulic power needed to position the output shaft. The amplifier section also provides a source of pressure oil for that section and for the power cylinder.

The three sections are interconnected through the loading piston. The loading piston position determines the actuator output shaft position. Either the electrical or mechanical governor section can control the position of the loading piston.

Schematic Of EGB-29P Actuator

The separate explanation of each of the three sections follows.

Hydraulic Amplifier Section

The EGB-29P Actuator contains two separate hydraulic circuits. Each circuit utilizes the oil of a common sump contained within the actuator. The relay oil pump provides pressure oil required by the amplifier section. The actuator drive shaft, driven at a speed proportionate to engine speed, rotates the pump drive gear and rotating bushing. Oil from sump is transported from the supply side to the pressure side around the outside of the two gears. The meshing gears then have little space between the teeth to move oil from the pressure side back to the supply side of the pump.

Pressure oil forces the accumulator pistons up, opposing the downward force of the accumulator springs. When the pistons move up sufficiently, one piston uncovers a bypass hole through which excess oil is returned to sump. The accumulator provides a reservoir of pressure oil and also a relief valve to limit maximum pressure in the hydraulic circuit.

The arrangement of the four check valves on the suction and discharge side of the oil pump permits the actuator drive shaft to rotate in either direction without any changes to the governor. Were the pump gears to rotate in directions opposite those shown the open check valves would close and the closed check valves would open.

The relay servo piston is connected to the actuator terminal (output) shaft. The terminal shaft position establishes the fuel rack or carburetor opening. The relay servo piston position establishes the terminal shaft position and the terminal lever and linkage position.

The relay valve plunger in the rotating bushing controls the flow of oil to and from the underside of the relay servo piston. If the plunger is in a centered position, the control land exactly covers the control port in the rotating bushing. No oil flows to, or from, the piston. Pressure oil continually urges the piston down in the direction to decrease engine fuel. However, the piston cannot move down to decrease fuel unless the oil trapped between the underside of the piston and the relay valve plunger control land can escape to sump. This trapped oil can escape only if the relay valve plunger is raised. If the relay valve plunger is lowered, pressure oil is directed to the underside of the piston as well as to the upper side of the piston. Because the pressure acts upon a greater area on the lower side of the piston, the resulting force is in the direction to push the piston up and increase fuel.

Loading piston and attached output nut position, as set by either the electrical actuator or mechanical governor section, controls the movement of the relay valve plunger. If the actuator is directed to decrease fuel the loading piston will move down.

This downward movement of the piston and nut pushes the left end of the intermediate lever down. As the right end of the intermediate lever moves up, the left end of the relay beam is raised (the beam pivots about the screw in the end of the relay terminal lever). The relay valve plunger is thus lifted above center and the servo piston rotates the terminal shaft in the decrease fuel direction.

As the relay terminal lever rotates in the decrease fuel direction the screw in the left end of the lever is raised. This permits the oil pressure on the dashpot land to push the relay plunger down, pivoting the relay beam about the bearing in the right end of the intermediate lever. (The dashpot land is, in effect, a "differential piston" with the area on the upper side of the land greater than the area on the lower side. With pressure oil on both sides of the piston it will move in the downward direction.) As the relay valve plunger reaches a centered position, flow of oil from under the relay servo piston stops, thereby stopping the terminal shaft.

If the loading piston and output nut moves up, oil pressure on the upper side of the dashpot land now pushes the relay plunger down. At the same time, the right end of the intermediate lever is pushed down keeping the left end of the lever in contact with the output nut.

With the relay valve plunger below center, pressure oil flows to the lower side of the servo piston and pushes the piston up. The terminal shaft rotates in the increase fuel direction. As the relay terminal lever rotates, the screw in the end of the lever pushes the right end of the relay beam down. The relay beam pivots about the roller bearing in the right end of the intermediate lever, lifting the relay valve plunger back to a centered position and stopping further movement of the terminal shaft.

Electric Actuator Section

During the normal mode of operation the electric actuator will be controlling and the mechanical governor power piston will be at the top of its stroke.

Pressure oil for the electrical and mechanical governor sections is provided by the sub-governor oil pump. The pump relief valve plunger, acting against the relief valve spring, maintains the oil pressure required in these sections. Because the oil volume used is relatively small, no accumulator is required. The sub-governor oil pump operates the same way as the relay oil pump.

The electric actuator pilot valve plunger controls the flow of oil to and from its power piston. The pilot valve plunger is connected to a magnet which is spring-suspended in the field of a two-coil polarized solenoid. An output signal from the Electronic Locomotive Control Box is applied to the polarized coil and produces a force, proportionate to the current in the coil, which tends to drive the magnet and pilot valve plunger down. A combination of the restoring spring and centering spring force tends always to raise the magnet and center the pilot valve plunger. When the actuator is running under steady-state conditions, these opposing forces are equal and the pilot valve plunger is in a centered position (the control land of the plunger exactly covers the control port in the pilot valve bushing). This occurs only when the plunger position is exactly proportional to the amount of electric signal. With the pilot valve plunger centered, no oil flows to or from the power piston.

If the signal from the Electronic Locomotive Control Box decreases (due to an increase in engine speed or a decrease in unit speed setting), an unbalanced force results. The combination of the restoring spring and centering spring force, now relatively greater, raises the pilot valve plunger. Oil under the electric actuator power piston is thus connected to sump. The oil pressure constantly applied to the upper side of the loading piston now forces the pistons down as the floating lever pivots about its connection to the mechanical governor power piston. The loading piston causes the amplifier section to rotate the terminal shaft in the "decrease" direction.

As the electric governor power piston moves down, it lowers the left end of the first restoring lever. The clamping plate, attached to the first restoring lever, pushes down on the second restoring lever. The loading on the restoring spring is increased and applies pressure to lower the pilot valve plunger. The loading piston and electric actuator power piston move down until the increase in restoring spring force is sufficient to offset the increased force in an upward direction resulting from the decrease in the electric signal. When the pilot valve plunger is pushed back to its centered position, movement of the power piston, loading piston and terminal shaft stop.

The position of the actuator shaft is always proportional to the electric input signal to the actuator. If the electric input signal increases, the pilot valve plunger will be lowered, pressure oil will flow to the underside of the power piston and push the piston up; the loading piston will be raised, rotating the terminal shaft in the "increase" direction. At the same time, the upward movement of the power piston, acting through the restoring levers, decreases the restoring spring force so the pilot valve plunger will recenter to stop movement of the terminal shaft.

Mechanical Governor Section

The mechanical governor controls the engine during starting. It also functions as a backup governor if there is a loss of signal from the Electronic Locomotive Control Box or if the Electronic Locomotive Control Box or electric actuator section should fail in such a way to call for maximum fuel. The mechanical governor pilot valve plunger controls the flow of oil to its power piston. If the plunger is centered, no oil flows through the pilot valve and the piston is stationary. The greater of two opposing forces moves the pilot valve plunger. The speeder spring force tends to push it down; the centrifugal force developed by the rotating flyweights is translated into an upward force which attempts to raise the plunger. There is one speed at which the centrifugal force of the flyweights is equal and opposite to the speeder spring force. At this speed the pilot valve is centered.

With the speed setting of the mechanical governor set slightly higher than the electric actuator, the centrifugal force of the rotating flyweights is not sufficient to lift the pilot valve plunger to its centered position. Therefore, with the electric actuator controlling, pressure oil is continually directed to the underside of the mechanical governor power piston to hold it up against its stop. With the actuator running on-speed with the mechanical governor controlling, the pilot valve plunger is centered. (This can only occur if the electrical actuator calls for a speed higher than the speed setting of the mechanical governor.) If a load is added to the engine and governor speeds decrease the pilot valve plunger is lowered by the speeder spring force which is greater than the lessened centrifugal force of the flyweights.

Pressure oil flows to the buffer piston and moves it toward the power piston.

The oil displaced by the buffer piston forces the power piston upward, the loading piston is raised and the terminal shaft rotated in the direction to provide the fuel needs for the new load.

The movement of the buffer piston toward the power piston partially relieves the compression of the left buffer spring and increases the compression of the right buffer spring. The force of the right buffer spring, tending to resist this movement, causes a slightly higher oil pressure on the left side of the buffer piston than on the right. The pressure on the left of the buffer piston is transmitted to the underside of the compensation land of the pilot valve plunger. The difference of pressure produces a force which acts to push the pilot valve plunger back to its centered position.

When the terminal shaft has been rotated far enough to satisfy the new fuel requirement, the force of the pressure differential on the compensation land plus the centrifugal force of the rotating flyweights will have recentered the pilot valve plunger. Even though engine speed is not yet completely back to normal, servo piston and terminal shaft movement is stopped. The continued increase of speed to normal results in continued increase in centrifugal force developed by the rotating flyweights. This increase of speed to normal does not cause the flyweights to lift the pilot valve plunger above center because the leakage of oil through the needle valve orifice equalizes the pressure above and below the compensation land at a rate proportional to the return of the engine speed to normal.

With equalization of pressure through the needle valve, the buffer springs return the buffer piston to its normal, central, position.

Were the engine load to decrease, the resultant increase in governor speed would cause the flyweights to move outward and raise the pilot valve plunger. With the pilot valve plunger raised, the area to the left of the buffer piston would be connected to sump. The loading piston, continually being urged downward by oil pressure from the sub-governor pump, would move down and force the power piston down. The movement would reduce the fuel to meet the new requirement. Again, differential pressure across the compensation land would assist in recentering the pilot valve plunger, and close the pilot valve ports while speed decreases to normal.

The speed at which the mechanical governor controls the engine is determined by the loading or compression of the speeder spring which opposes the centrifugal force of the flyweights.

Speed Droop

Speed droop is used in mechanical governors to automatically divide and balance load between engines driving the same shaft or paralleled in an electrical system. (Speed droop is defined as the decrease in governor speed as its output connection to the engine fuel linkage moves in an increase direction. How far the governor speed decreases for a given stroke, determines the amount of droop.)

Speed droop is incorporated in the EGB-29P Mechanical Governor through linkage which varies the loading on the speeder spring as a function of the power piston position. The change in speeder spring force for a given movement of the power piston is determined by the power piston droop setting and speeder spring scale. If the pivot pin connecting the speed droop floating lever to the speed adjusting lever linkage is on the same centerline as the speed droop lever pivot arm, there is no change in speeder spring forces as the power piston moves and the mechanical governor responds as an isochronous (constant speed) control. The further the adjustable pin is moved away from the pivot arm centerline, the greater is the change in compression of the speeder spring for a given power piston movement.

With the actuator operating under control of the electric actuator section, the speed droop feature is, in effect, inoperative. This is because during such operation the mechanical governor power piston remains in the same position for all engine loads. Thus, the speed droop linkage does not alter the speeder spring compression when the electric governor section of the actuator is controlling.

Shutdown Solenoid (Energize To Run)

The shutdown solenoid is mounted internally within the actuator column. It is connected through tubing and internal passages, to the upper side of the dashpot land on the relay valve plunger in the hydraulic amplifier section of the actuator section of the actuator. When the solenoid is de-energized, oil pressure on the upper side of the dashpot is dumped. This allows the oil pressure acting on the under side of the dashpot land to raise the relay valve plunger which, in turn, dumps the trapped oil under the power piston. The oil pressure acting on the top of the power piston the forces the piston to move to the minimum fuel position.

Shutdown Solenoid (Energize To Shut-Off)

The shutdown solenoid is mounted internally within the actuator column. It is connected through tubing and internal passages, to the upper side of the dashpot land on the relay valve plunger in the hydraulic amplifier section of the actuator section of the actuator. When the solenoid is energized, oil pressure on the upper side of the dashpot is dumped. This allows the oil pressure acting on the under side of the dashpot land to raise the relay valve plunger which, in turn, dumps the trapped oil under the power piston. The oil pressure acting on the top of the power piston the forces the piston to move to the minimum fuel position.

Derate Module

The derate module provides the main governor with 5 optional analog input signals. These can be used by customized software in the optional personality module for a variety of signal functions eg:

* Analog wheelslip signal.

* Dynamic brake lever signal.

* Water temperature signal.

* Analog throttle signal (for non locomotive applications).

* Pressure sensor (to monitor barometric pressure)

The input signal range is 0 to 50 volt DC full scale, except for the pressure sensor which is 0 to 14 volt DC full scale.

Other derate modules will be developed for applications requiring different full scale voltages.

Mounting Group

Mounting Group
(1) Electronic Control Box. (2) Personality Module (not part of the mounting group). (3) J2 Connector. (4) J1 Connector. (5) Protection Diodes. (6) Terminal Strips. (7) Derate Module

On any Loco II installation that requires a derate module, it is recommended that the mounting group assembly be used. This provides the customer with a prewired assembly containing the following items:

Main Electronic Control BoxProtection DiodesDerate ModuleRailroad Industry Standard Terminal Strips

The terminal strips are typical of the type used in locomotives manufactured in North America.

SD40-2/SD45-2 Installation

See the SD40-2 and SD45-2 Installation Guide (section 5) for more details of this type of installation.

Temperature Sensor And Temperature Interface Module

Water Temperature Sensor

Temperature Interface Module

Typical Wiring Diagrams

The following diagrams show typical wiring information for installing the governor on a variety of locomotives.

It should be noted that the Main Electronic Control Box has three connections for battery power, these need to be protected against transients by external diodes as shown. Caterpillar Part No. 7C2668 is an encapsulated package containing four diodes that are suitable for this purpose. When using the mounting group, these diodes are not necessary since they are included in the prewired mounting group assembly.

Typical Locomotive Wiring Diagram Using The Mounting Group And Optional Software