Electric Protective System

Introduction

The electric protective system is designed to activate an alarm or shut the engine off if there is a problem or a failure in any of four different engine systems. The engine systems monitored are: engine overspeed, starter motor crank terminate, engine oil pressure and engine coolant temperature.

The electric protective system consists of the basic components that follow: magnetic pickup, electronic speed switch, water temperature contactor switch, two time delay relays and two slave relays. This system monitors the engine from starting through rated speed.

Component Description

Magnetic Pickup (MPU) - The magnetic pickup is a single pole, permanent magnet generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of force around the pickup, an AC voltage is made. A positive voltage is made when each tooth goes by the pole piece. Each time the space between the teeth goes by the pole piece, a negative voltage is made. Engine speed is then determined by the frequency of these signals.

Electronic Speed Switch (ESS) - The 4W2218 Electronic Speed Switch can easily be identified by its black color (the earlier speed switch was yellow). This speed switch has controls (in a single unit) to monitor three of the basic functions. These three functions are:

Engine Overspeed - An adjustable engine speed setting (normally 118% of rated speed) that gives protection to the engine from damage if the engine runs too fast. This condition will cause a switch to close that shuts off both the inlet air and the fuel to the engine.

Crank Terminate (Starter Motors) - An adjustable engine speed setting that gives protection to the starter motor from damage by overspeed. This condition will cause a switch to open that stops current flow to starter motor circuit, and the starter motor pinion gear will then disengage from engine flywheel ring gear.

Engine Step Oil Pressure - An adjustable engine speed setting that gives protection to the engine from a failure caused by not enough oil pressure. To maintain desired protection through the complete speed range of engine operation, two different oil pressure switches are used [280 kPa (40 psi), 140 kPa (20 psi)]. Once the step oil pressure speed setting is made, an engine that runs above this speed setting must maintain an oil pressure that is more than 280 kPa (40 psi). An engine that runs at a speed below this speed setting must maintain an oil pressure that is more than 140 kPa (20 psi). If either condition is not correct, a switch will close to activate an alarm or cause the fuel to be shut off to the engine.

Water Temperature Contactor Switch - This contactor switch is a separate unit (mounted in the regulator housing) that is wired into the shutdown circuit. It has an element that feels the temperature of the coolant (it must be in contact with the coolant). When the engine coolant temperature becomes too high, the switch closes to activate an alarm or cause the fuel to be shut off to the engine.

Time Delay Relays - These relays are special ON/OFF switches with two controls that will either make the relay activate immediately, or after a 9 second delay. One of the time delay relays is used to arm the shutdown system, and the other time delay relay controls the oil pressure circuits for the two oil pressure switches. Both time delay relays have a 70 second OFF delay to be sure of complete engine shutdown.

Slave Relays - These are standard type relays that, when energized, have contacts that open across one circuit and close across another circuit. When activated, one of the relays will activate an alarm or cause the fuel to be shut off, and the other relay will cause the inlet air to be shut off.

Component Locations On Engine

WATER TEMPERATURE CONTACTOR SWITCH
1. Regulator housing. 2. Contactor switch.

LOCATION FOR MAGNETIC PICKUP (Later Engines)
1. Plug (one of three available locations on top of flywheel housing).

JUNCTION BOX OPENED
1. Terminal strips. 2. Electronic speed switch (ESS). 3. Slave relays. 4. Time delay relays. 5. Oil pressure switches. 6. Circuit breakers.

AIR SHUTOFF SOLENOID
1. Air shutoff housing. 2. Air shutoff solenoid. 3. Aftercooler housing.

JUNCTION BOX CLOSED
1. Junction box. 2. Fuel shutoff switch. 3. Circuit breakers. 4. Magnetic pickup. 5. Electric governor actuator (EGA).

LEFT SIDE OF ENGINE
1. Enclosure group.

Individual Circuit Description

The information that follows show the current flow through the wiring schematic. As switches are opened or closed, either automatically or manually, the current flow of the individual circuit affected is shown schematically.

Also included (on each facing page) is a story that explains all the components involved for this particular condition, and why the current will take the path shown.

Engine Stopped (Fig. 1)

With the engine stopped, power is always available across terminals 3 and 4 of time delay relays (TD1 and TD2) and across terminals 5 and 6 of electronic speed switch (ESS). At this time all switches are in their normally open or normally closed positions.

Engine Stopped

Fig. 1

Manual Start

Electric Starter Motors (Fig. 2)

When the start pushbutton (PB) or remote start switch (RSS) is pushed, current will flow through starter motor magnetic switches (SMMS1 and SMMS2). With magnetic switches energized, contacts (SMMS1 and SMMS2) close and pinion solenoids (PS1 and PS2) are energized. This causes contacts (PS1 and PS2) to close, and starter motors (SM1 and SM2) will now crank the engine. When engine starts to run and the rpm increases to the speed of the crank terminate (CT) speed setting, the ESS(CT) switch will automatically open across terminals ESS-11 and ESS-12 to stop current flow to the start pushbutton.

Air Starter Motor (Current Flow Not Shown in Fig. 2)

If engine has an air starter motor, current will flow through DC operated air start solenoid valve (ASSV) when start pushbutton (PB or RSS) is pushed. The ASSV will open the air supply to the air starter motor, which will now crank the engine. When the engine starts to run and the rpm increases to the speed of the crank terminate (CT) speed setting, ESS(CT) switch will automatically open across terminals ESS-11 and ESS-12 to stop current flow to ASSV pushbutton. This will move the valve to shut off the air supply to the air starter motor.

Starting Engine With Electric Starter Motors

Fig. 2

Engine Starts To Run: No Faults

When the engine starts to run, the speed will increase to the speed setting of the ESS crank terminate function, and the ESS(CT) switch across terminals ESS-11 and ESS-12 will open. The current flow is now stopped to the start pushbutton for the starter motor(s) as shown in Fig. 3.

When the ESS(CT) switch (line 10) opens across terminals ESS-11 and ESS-12, ESS(CT) switch (line 32) will close across terminals ESS-11 and ESS-10. This closed switch will give current flow to Control 1 (terminal 1) of time delay relay (TD1), and will immediately close switch (TD1) across terminals TD1-6 and TD1-7 (line 25). The complete protection system is now armed to activate an alarm or cause engine shutdown if there is a fault in any of the three engine systems now being monitored.

ENGINE STARTS TO RUN: NO FAULTS

Fig. 3

Engine Runs At Rated Speed: No Faults

With no existing problems and engine running at rated speed, or at some speed above the oil step speed setting, the circuit will look like Fig. 4. The oil pressure step switch (OPSS) at line 36 is now closed, but oil pressure switch (OPS2) is now open, so there is still no current flow to TD2. The engine will continue to run with these conditions.

OPS2 will not open until there is at least 280 kPa (40 psi) oil pressure available, and after opening, will not close again until the oil pressure has dropped below 240 kPa (35 psi). The ESS(OPSS) switch is not activated to open until engine speed is the same as, or above, the step oil pressure speed setting. After it is activated, the ESS(OPSS) switch has a 9 second delay before it closes. This makes sure that oil pressure has time to increase enough to open OPS2, or system would constantly activate engine shutdown.

ENGINE RUNS AT RATED SPEED: NO FAULTS

Fig. 4

Engine Shutdown Due to Fault: Loss Of Engine Oil Pressure (At Engine Speeds Above Oil Step Speed Setting)

The circuit of Fig. 5 shows the current flow if there is a fault in the high pressure side of the oil pressure circuit. When engine oil pressure drops below 240 kPa (35 psi), oil pressure switch (OPS2) will close. Since the engine is running at a speed above the step oil pressure setting, ESS(OPSS) switch is already closed and the circuit is now completed to Control 1 (terminal 1) of time delay relay (TD2). There is no time delay at Control 1, so TD2 relay contacts (line 20) will close immediately across terminals TD2-6 and TD2-7. This makes a complete circuit from the battery through TD1 contacts (line 25) to activate oil pressure indicator (OPI) and to energize slave relay (SR1).

When SR1 is energized, contacts across terminals SR1-1 and SR1-2 open and contacts across terminals SR1-1 and SR1-3 close. The circuit is now completed to energize fuel shut-off solenoid (FSOS), and the fuel is shut off to the engine.

ENGINE SHUTDOWN DUE TO FAULT: LOSS OF ENGINE OIL PRESSURE (AT ENGINE SPEEDS ABOVE OIL STEP SPEED SETTING)

Fig. 5

Engine Running Below Oil Step Speed Setting: No Faults (Or Just Accelerating Through Step Speed)

If engine continues to run below the step oil pressure speed setting, oil pressure step switch (OPSS) will remain open and will not complete the circuit to shutdown as shown in Fig. 6. Since oil pressure has increased enough to run at this speed (OPS1 switch is open), the engine can safely run at this speed and will not be shut down.

If the engine is accelerating through oil step speed setting, the circuit could still look as shown in Fig. 6. When engine speed is the same as (or goes above) the oil step speed setting engine oil pressure must increase to 280 kPa (40 psi) to open oil pressure switch (OPS2) within the 0 second time delay of the oil pressure step switch ESS(OPSS). The OPSS switch will close after 9 seconds and, if OPS2 is still closed, engine will shut down as shown in Fig. 5. If OPS2 has opened before OPSS has closed, engine will continue to run as shown in Fig. 4.

Engine Running Below Oil Step Speed Setting: No Faults (Or Just Accelerating Through Step Speed)

Fig. 6

Engine Shutdown Due To Fault: Low Oil Pressure (At Engine Speed Below Oil Step Speed Setting)

As engine is started and begins to run, crank terminate switch ESS(CT) opens across terminals ESS-11 and ESS-12 and closes across terminals ESS-11 and ESS-10. This immediately arms the system when current is sent to Control 1 (terminal 1) of time delay relay (TD1), which closes TD1 relay contacts (line 25) across terminals TD1-6 and TD1-7.

At the same time that TD1 is armed, there is current flow to Control 2 (terminal 2) of time delay relay (TD2) if oil pressure switch (OPS1) has not yet opened. The engine oil pressure has 9 seconds (from the time that TD1 is armed) to increase to the 140 kPa (20 psi) necessary to open OPS1. If OPS1 does not open, TD2 contacts will close across terminals TD2-6 and TD2-7 and slave relay (SR1) will be energized. SR1 relay contacts (line 42) will now open across terminals SR1-1 and SR1-2, and SR1 relay contacts (line 40) will close across terminals SR1-1 and SR1-3. The fuel shut-off solenoid (FSOS) is now energized, and will shut the fuel off to the engine.

If the engine had been running (with no faults) at a speed less than the oil step setting, and then lost engine oil pressure, the protection system would cause engine shutdown in the same way as shown in Fig. 7. OPS1 would close when oil pressure decreased to 105 kPa (15 psi), and 9 seconds later the engine would shut down.

Engine Shutdown Due To Fault: Low Oil Pressure (At Engine Speeds Below Oil Step Speed Setting)

Fig. 7

Engine Shutdown Due To Fault: Coolant Overheating

The current flow of the circuit shown in Fig. 8 is for an engine running at a speed above the oil step setting with coolant temperture hot enough [98°C (208°F)] to close water temperature contactor switch (WTS). When WTS closes, this completes the circuit through slave relay (SR1) and through water temperature indicator (WTI). When slave relay (SR1) is energized, the contacts across terminals SR1-1 and SR1-3 will close. Now the fuel shut-off solenoid (FSOS) is energized to shut the fuel off to the engine.

After 70 seconds (when TD1 contacts open), the engine can be started again, but it will immediately be shutdown. The engine will not continue to run until coolant temperature cools down enough to open switch WTS.

NOTE: Engine shutdown caused by coolant overheating will also be the same if the engine is running at a speed below the oil step setting.

Engine Shutdown Due To Fault: Coolant Overheating

Fig. 8

Engine Shutdown Due To Fault: Engine Overspeed

When engine speed increases above the overspeed setting (118% of rated speed) of the electronic speed switch (ESS), the overspeed switch ESS(OSS) will close across terminals ESS-7 and ESS-8 (line 23). This completes the circuit from the battery through overspeed indicator (OSI) and also through both slave relays (SR1 and SR2) as shown in Fig. 9.

Both slave relays (SR1 and SR2) are now energized at the same time. SR2 contacts will close across terminals SR2-1 and SR2-3 to activate air shut-off solenoid (ASOS). ASOS will now shut the inlet air off to the engine. At the same time, SR1 contacts open across terminals SR1-1 and SR1-2 (Line 42) and close across terminals SR1-1 and SR1-3 (line 40). The fuel shut-off solenoid (FSOS) is now activated, and will shut the fuel off to the engine.

A reset button on the ESS must be pushed to open the overspeed switch ESS(OSS), and the air shut-off lever (at top of air inlet housing) must be manually reset before the engine will run.

Engine Shutdown Due To Fault: Engine Overspeed

Fig. 9

Shutdown System With 2301 Electric Governor Control: No Faults

When the 2301 Electric Governor Control (EGC) is used, all systems of the electronic speed switch (ESS) are activated the same way as shown with a 3161, UG8D or a UG8L governor. The only difference in the circuit is that the fuel shut-off solenoid (FSOS) at line 40 is not used, and a jumper between terminal 26 and 27 is not used.

With the circuit shown in Fig. 10, current normally flows through electric governor actuator (EGA). When a fault in the system causes current to energize slave relay (SR1), the contacts open across terminals SR1-1 and SR1-2 (line 42) and close across terminals SR1-1 and SR1-3 (line 40).

When SR1 contacts open across terminals SR1-1 and SR1-2, the current can no longer flow through the EGA. The mechanical spring load in the EGA system will now move the fuel control rod to shut the fuel off to the engine.

NOTE: Except for the differences shown above, all fault circuits for the ESS system are the same for the EGC as those shown in Fig. 5 through Fig. 9 for the 3161 and UG8 governors.

Shutdown System With 2301 Electric Governor Control: No Faults (Circuit Shown at Rated Speed)

Fig. 10