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| Illustration 1 | g00281790 |
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7W-2743 Electronic Speed Switch ("ESS") (1) 75% Verify button (2) Reset button (3) LED overspeed light (4) Seal screw plug for adjusting the overspeed (5) Seal screw plug for adjusting the crank terminate speed (6) Seal screw plug for adjusting the oil step pressure speed setting | |
The electronic speed switch (ESS) is a single unit that contains controls which monitor four functions at the same time:
- Engine overspeed
- Crank termination
- Oil step latch
- Engine oil step pressure
Two different electronic speed switches are used. The switches are only different in the location of the mounting holes. The "ESS" is mounted in the junction box.
Engine overspeed is an adjustable engine speed setting. The normal setting is 118% of rated speed. The setting prevents the engine from running at a speed that could cause damage to the engine. An engine speed that is greater than the engine speed setting will close a switch which shuts off the fuel to the engine. If the optional air inlet shutoff is provided, the switch will also shut off the inlet air.
Crank termination is an adjustable engine speed setting that signals the starter motor that the engine is firing and the cranking must be terminated. A switch will open in order to stop the current flow to the starter motor circuit when the engine speed setting is reached. The starter motor pinion gear will then disengage from the engine flywheel ring gear.
Oil Step Latch (3500 Series Engines)
The setting of the oil step latch is not adjustable. After (ESS-17) on the terminal strip of the junction box is energized, the contacts of the oil pressure step switch are held in the closed position. The oil pressure step switch will remain closed until 2 seconds after the engine has completely stopped. This action will prevent the shutoff from resetting below the oil step speed setting.
Engine Oil Step Pressure (3500 Series Engines)
Engine oil step pressure is an adjustable engine speed setting that gives protection from engine failure which is caused by too little oil pressure for a specified speed range. In order to maintain oil pressure protection throughout the complete speed range of operation, two different oil pressure switches are used. Switch (OPS1) has a low pressure rating and switch (OPS2) has a high pressure rating. The engine oil pressure switches are mounted in the engine oil manifold that is located on the rear side of the junction box.
The following conditions are for the operation of the oil step latch:
- An engine that uses an oil step latch must maintain an oil pressure that is greater than the rating of the low oil pressure switch (OPS1) when the engine runs below the oil step pressure speed setting.
- An engine that uses an oil step latch must maintain an oil pressure that is greater than the rating of the high oil pressure switch (OPS2) when the engine runs above the oil step pressure speed setting.
If one of the two conditions for the engine oil pressure are not correct, the low oil pressure alarm switch (LOPAS1) or (LOPAS2) will energize an alarm. (OPS1) or (OPS2) also energizes the slave relay (SR1). This process de-energizes the fuel solenoid which shuts off the fuel flow to the engine.
The engine oil pressure switches and the alarm switches are mounted in the engine oil manifold that is located on the rear side of the junction box. The slave relay is mounted in the junction box.
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| Illustration 2 | g00281827 |
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Generation of the Magnetic Pickup Signal (1) Clearance dimension (2) Magnetic pickup (3) Wires to connector (4) Locknut (5) Flywheel housing (6) Flywheel ring gear | |
The magnetic pickup is a permanent magnet generator with a single pole. Wire coils surround a permanent magnet pole piece. When the teeth of flywheel ring gear (6) rotate through the magnetic lines of force that are around the magnetic pickup pole (2), an AC voltage is generated. A positive voltage is generated when each tooth rotates by the pole piece. When the space between the teeth rotates by the pole piece, a negative voltage is generated. Engine speed is measured by the frequency of these signals.
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| Illustration 3 | g00293065 |
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(2) Magnetic pickup sensor that is mounted in the flywheel housing. | |
The magnetic pickup is mounted through the flywheel housing (5).
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| Illustration 4 | g00281830 |
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Engine oil pressure switch | |
The engine oil pressure switch uses a spring loaded piston in order to activate an internal microswitch that is set for a specific pressure rating. This microswitch is very accurate over the operating temperature range. The microswitch also has a high electrical contact rating which improves reliability.
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| Illustration 5 | g00293068 |
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(1) Oil pressure switch (OPS1)
(2) Low oil pressure alarm switch (LOPAS1) | |
The engine oil pressure switches and the alarm switches are mounted on the engine oil manifold that is located on the rear side of the junction box.
3200 Series, 3300 Series, and 3400 Series Engines
The low engine oil pressure switch is an optional part.
Low oil pressure causes the low oil pressure alarm switch (LOPAS1) to energize an alarm. The oil pressure switch (OPS1) energizes the slave relay (SR1) which then deactivates the fuel solenoid (FS). This process shuts off fuel flow to the engine.
The operation of the oil pressure switches are described in the "Engine Oil Step Pressure (3500 Series Engines)" section of this manual.
Water Temperature Contactor Switch (WTS)
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| Illustration 6 | g00281831 |
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Water temperature contactor switch | |
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| Illustration 7 | g00293066 |
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(1) Water temperature contactor switch that is mounted in the cylinder block. | |
The water temperature contactor switch is mounted into the coolant system. The switch is wired to the protection circuit. The switch contains an element that detects the temperature of the coolant. The switch must be in contact with the coolant. When the engine coolant temperature becomes too high, the switch closes. Closure of the switch activates an alarm. Closure of the switch also shuts off the fuel flow to the engine.
The slave relays are a standard type. When the slave relay is energized, contacts open across one circuit and contacts close across another circuit. The slave relays control the power to three components:
- Air shutoff solenoid (if equipped)
- Fuel solenoid
- 2-301A Electric Governor Control (if equipped)
Slave relays are mounted in the junction box.
The optional starting aid switch is located on the front of the junction box door. The switch is a spring return switch that must be held in the ON position. When the SAS is in the ON position, the valve of the starting aid solenoid (SASV) energizes. A specific amount of ether is then injected into a holding chamber. When the SAS is released, the SASV releases the ether into the engine.
The starting aid switch can be deactivated in two ways:
- The contact of the crank termination relay on the electronic speed switch (ESS) will open at a preset engine speed. This will stop the current to the circuit of the SAS.
- The engine temperature becomes high enough to open the start aid temperature switch ("SATS").
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The engine must be cranking before using the start aid switch. Damage to the engine is possible if ether is released to the engine but not exhausted or burned by the engine when cranking. |
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| Illustration 8 | g00281837 |
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Circuit breaker (1) Reset button (2) Disc in open position (3) Contacts (4) Disc in closed position (5) Battery circuit terminals | |
A circuit breaker is a switch that opens the circuit if the current in the electrical system is higher than the rating of the circuit breaker.
A metal disc that is controlled with heat and a contact (3) will complete the circuit through the circuit breaker. If the current in the electrical system is too high, the metal disc becomes too hot. The heat causes a distortion of the metal disc which opens the contacts (2). Open contacts break the circuit. A circuit breaker that is open can be reset after the circuit breaker cools. Push the reset button (1) in order to close the contacts (4) and reset the circuit breaker.
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Find and correct the problem that causes the circuit breaker to open. Correcting the problem before running the engine will help prevent damage to the circuit components caused by too much current. |
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| Illustration 9 | g00281839 |
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Air shutoff (Typical example) (1) Air transfer pipe (2) Valve assembly (3) Shutoff shaft (4) Governor control shaft (5) Air shutoff solenoid (6) O-ring seal (7) Diode assembly | |
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| Illustration 10 | g00293067 |
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(5) Air shutoff solenoid that is mounted in the air intake pipe. | |
The air shutoff solenoid (5) is located in the air inlet system on the top of the engine. When the air shutoff solenoid ("ASOS") is energized, the inlet air to the engine is mechanically shut off. The ASOS can be energized in the following two ways:
- The ASOS is energized by the overspeed switch (OS).
- The ASOS is energized by the emergency stop switch (ES).
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| Illustration 11 | g00281970 |
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Fuel solenoid (Typical example) (1) Diode assembly (2) Spring (3) Governor drive (4) Fuel solenoid (5) Shaft | |
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| Illustration 12 | g00293070 |
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(4) Fuel solenoid (FS) that is mounted on the governor. | |
The fuel solenoid (FS) (4) is located on the governor or on the fuel injection pump of the engine. When the FS is energized, the spring (2) and the shaft (5) will cause the fuel rack to move directly or the fuel rack will move through the governor drive to the FUEL ON position. The FS must remain energized or the fuel flow will be stopped to the engine.
2301A Electric Governor Control
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| Illustration 13 | g00293071 |
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(1) 2301A Electric Governor Speed Control | |
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| Illustration 14 | g00293069 |
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Electric governor actuator (EGA) (2) and fuel solenoid (FS) (3). The components are mounted on the top of the engine. | |
The 2301A Electric Governor Control system consists of the following components:
- 2301A Control
- Actuator (EGA)
- Magnetic pickup (MPU)
The 2301A Electric Governor Control system provides precision engine speed control. The 2301A Control constantly monitors the engine rpm. The control makes the necessary corrections to the engine fuel setting through an actuator that is connected to the fuel system.
The engine rpm is measured by the magnetic pickup ("MU"). The magnetic pickup makes an AC voltage that is sent to the 2301A Control. The 2301A Control then sends a DC voltage signal to the actuator in order to adjust the fuel flow.
The actuator changes the electrical signal from the 2301A Control to a mechanical output. The mechanical output of the actuator causes the linkage from the actuator to move the fuel rack. This will increase the flow of fuel to the engine or this will decrease the flow of fuel to the engine. If the engine speed is more than the speed setting, the 2301A Control will decrease the voltage output which causes the actuator to move the linkage in order to decrease the fuel flow to the engine.
Battery Discharge By The Electric Protection System
When the engine is not running there are two components in the electric protection system which continue to draw small amounts of current from the battery:
- Electronic speed switch
- Alternator which charges the battery
An electric protection system that has only one of these components can remain shut down for several months without discharging the battery. An electric protection system can remain idle for a minimum of one month without discharging the battery. Cold weather decreases the efficiency of the battery. This increases the discharge of the battery. In most applications, the engine is started weekly or a battery charger is used to keep the battery at full charge. Therefore, few starting problems occur.
The suggestions that follow can be used to prevent battery discharge when the engine is not used for extended time periods. Rental fleets are an example of not operating engines for extended time periods.
If the engine will not be operated for several weeks and if the engine will not be connected to a battery charger, disconnect the battery cable from the negative post (-) of the battery.
A 7N-0718 Battery Disconnect Switch can be installed in order to reduce the discharge of the battery when the engine is not frequently operated for extended periods of time. The switch should be installed between the negative terminal (-) of the battery and the negative terminal (-) of the starting motor. Fabricate a bracket in order to mount the switch. Install the bracket close to the battery or close to the starter motor. The switch can be mounted inside the power distribution box on generator set engines. In all applications, the Battery Disconnect Switch must be mounted within 30° of vertical.