3412 Generator Set Engines Caterpillar

Electronic Control Module Power Circuit (Electronically Controlled Engines)

The electronically controlled engine uses a wide variety of electronic input devices. These components require an operating voltage. Also, these components could require a reference voltage.

The electronic control modules on these engines are not sensitive to the common external sources of noise. However, electro-mechanical buzzers can cause disruptions in the power supply. If electro-mechanical buzzers are used near the engine, the engine electronics should be powered directly from the battery system through a dedicated relay. The engine electronics should not be powered through a common power bus with other devices that are activated by the keyswitch.

The ordinary switch input circuits inside the Electronic Control Module (ECM) have a tolerance for resistance and a tolerance to shorts between wires. The tolerances are listed below.

• The Electronic Engine Control System will tolerate resistance in any ordinary switch up to 2.5 Ohms without malfunctioning.

• In any ordinary switch input, the Electronic Engine Control System will tolerate shorts between wires to 5000 Ohms without a malfunction.

The ECM draws a maximum of 6.5 Amperes at 24 volts from the electrical system under steady state conditions. While you are starting the engine, the ECM will draw a maximum of 9 Amperes. However, the Electronic Engine Control System will function with less than 24 volts. A minimum of 8 volts is required when the engine is cranked. A minimum of 24 volts is needed when the engine is running.

Power enters the ECM through the + battery wire. Power exits the ECM through the negative battery wire.

The Electronic Engine Control System is protected against power surges on the 24 Volt power supply. These power surges are due to alternator load dumps and due to jump starting with voltages up to 32 volts.

Engine Speed Input Circuit

Engine speed is sensed by an electronic engine speed sensor. This is similar to an electromagnetic pickup. The signal is generated by placing the sensor near a rotating component. However, the sensor requires an operating voltage. The sensor requires an operating voltage of 8.0 ± 0.4 Volts. This voltage is provided by the ECM.

The output of the engine speed sensor is a voltage pulse. The frequency is dependent on the speed of the engine. The frequency of the pulse is interpreted by the ECM as engine speed. When you crank the engine, the frequency of the signal is 10 to 50 Hz (Hertz). The frequency of the signal is approximately 120 Hz at low idle.

Fuel Rack Input Circuit

The engine fuel rack signal is obtained from an electronic linear position sensor. The sensor follows the movement of the rack assembly. This sensor requires an operating voltage of 8.0 ± 0.4 Volts. The sensor requires a reference voltage of 5.0 ± 0.25 Volts. These voltages are provided by the ECM.

The output of the rack position sensor is a voltage between 0.3 and 5.25 Volts. This voltage is dependent upon the position of the rack position sensor. The output voltage is interpreted by the ECM as the rack position.

Engine Coolant Temperature Circuit

The engine coolant temperature is obtained from an electronic sensor. The sensor is mounted on the engine. This sensor sends the data to the ECM through the engine wiring harness. The sensor requires an operating voltage of 8.0 ± 0.4 Volts. The sensor operates at a temperature range between 40 to 120°C (104 to 248°F).

At this range of input, the output of the coolant temperature sensor is good between 0.5 Volts and 4.5 Volts. This voltage is dependent upon the engine coolant temperature. The signal is interpreted by the ECM as the coolant temperature.

Input Circuit for the Inlet Air Pressure

The inlet air pressure sensor is located on the engine. Inlet air pressure is taken before the turbocharger and after the air cleaner. The inlet air pressure is routed to the sensor. The sensor requires a reference voltage of 5.0 ± 0.25 Volts.

The output of the inlet air pressure sensor is a DC voltage between 1.0 Volts and 5.0 Volts. This voltage is dependent upon the pressure that is felt by the inlet air pressure sensor. The signal is interpreted by the ECM as absolute inlet air pressure.

Boost Pressure Input Circuit

The boost pressure sensor is mounted in the air inlet manifold. The same operating voltages and the same reference voltages that are provided to the inlet air pressure sensor are also provided to this sensor.

The output of the boost pressure sensor is a DC voltage between 0.35 Volts and 4.6 Volts. This voltage is dependent upon the pressure that is felt by the boost pressure sensor. The signal is interpreted by the ECM as boost pressure (gauge).

Engine Oil Pressure Input Circuit

The engine oil pressure sensor is located in the engine oil lines. Engine oil pressure from the fuel injection pump is routed to this sensor. This sensor requires an operating voltage of 5 Volts.

The output of the oil pressure sensor is a DC voltage between 0.35 Volts and 4.6 Volts. This voltage is dependent upon engine oil pressure. The signal is interpreted by the ECM as oil pressure.

The engine oil pressure sensor is designed to measure oil pressure between 0 and 690 kPa (0 and 100 psi). Engine oil pressures that are greater than 690 kPa (100 psi) are read as 690 kPa (100 psi). This limited oil pressure reading range provides more accurate low oil pressure readings than a sensor that is capable of reading the maximum engine oil pressure. Low oil pressure readings are the most important oil pressure readings.

Input Circuit for the Throttle Control

The throttle position is obtained from an electronic sensor. An operating voltage of 24 Volts is provided to the sensor by the electrical system.

The output of the throttle position sensor is a constant frequency pulsed voltage of 0 to 5.25 Volts. The throttle position sensor regulates the pulse width of the signal that is generated. The frequency of the signal remains constant. The signal is interpreted by the ECM as the throttle position. The throttle position sensor's output pulse width is from 10 to 90%. The ECM interprets this signal. The ECM then generates a signal that represents the throttle position from 0 to 100%.

Shutoff Solenoid Output Circuit

The shutoff solenoid is an output component of the Electronic Engine Control System. This solenoid must be energized in order for the engine to run.

The output of the ECM to the shutoff solenoid is a pulsed voltage. This pulsed voltage can reach up to 6 Volts for about one half of a second after the power switch is turned ON for the purpose of pulling in the solenoid. This pulsed voltage can then drop off to approximately 1 Volt. This is adequate voltage to hold in the solenoid.

The Electronic Engine Control System is designed to continue operation of the engine with as many faults as possible. There are five conditions which will de-energize the shutoff solenoid. These conditions will shut down the engine. The five conditions are listed below:

• The loss of electrical power to the Electronic Control Module

• A worn shutoff solenoid

• An engine speed signal that is greater than 2500 RPM

• The loss of both engine speed signals

• A worn relay or switch in the engine overspeed switch box

Fuel Rack Output Circuit

Movement of the engine fuel rack is accomplished by the electronic engine control system with a rack solenoid. This rack solenoid is called a Brushless Torque Motor (BTM).

The movement of the rack solenoid (BTM) is proportional to the electrical current that flows through the solenoid. The ECM provides a pulsed voltage of 0.0 to 3.6 Volts to the rack solenoid (BTM).

The rack solenoid (BTM) moves the engine fuel rack through the movement of the governor servo spool valve and hydraulic pressure.

The electronic engine control system has a built-in operational test for the rack solenoid (BTM). This test is accomplished by using the following steps:

1. Remove the rack solenoid (BTM) from the housing.

2. Position the solenoid so that the arm of the solenoid is free to move.

3. Turn the power switch "ON".

The following results are the expected results.

• After five seconds, the solenoid arm will sweep to the full ON position.

• The solenoid arm will remain at the full ON position for a few seconds.

• The solenoid arm will then sweep back to the OFF position.

Sweep time will be about five seconds in both directions.

Output Circuit for the Check Engine Light

The data link harness provides information about the electronic engine control system to the check engine light. The light is ON when the power switch is ON and the engine is not running. This verifies that the lamp is working. The light should go out when the engine has been started and the correct engine oil pressure is reached. When the light does not go out shortly after starting the engine, this is an indication of either low oil pressure or an electronic system fault has been detected.

Electronic Speed Switch

Illustration 1	g00359852

The Overspeed Protection System is designed with controls that are built into a single unit. These controls monitor several functions at the same time. The following functions are monitored:

• Engine Overspeed

• Crank Termination

Engine Overspeed

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Personal injury or death can result from engine overspeed. If the engine overspeeds, it can cause injury or parts damage. Do Not operate the engine without the rack actuator solenoid (BTM) in place and with the fuel shutoff solenoid disabled.

This is an adjustable engine speed setting. This is normally set at 127% of rated speed. This setting prevents the engine from running at a speed that could cause damage.

An overspeed condition will cause the relay "SR1" to open. This will de-energize the shutoff solenoid. The de-energizing of the shutoff solenoid will cut the fuel to the engine. This will cause the engine to shut down.

Crank Termination

This is an adjustable engine speed setting that signals the starting motor that the engine is firing and cranking must be terminated. Once the speed setting is reached, a switch opens and the hour meter of the engine will start.

The Overspeed Protection System consists of the following components:

• Electronic Speed Switch (ESS)

• Relay "SR1"

• Terminal Block

Engine Electrical System

The engine electrical system has two circuits.

• The charging circuit

• The low amperage circuit

Some of the electrical system components are used in more than one circuit. The components are common in both circuits.

• Battery

• Disconnect switch

• Circuit breaker

• Ammeter

• Cables

• Wires from the battery

The charging circuit is in operation when the engine is running. An alternator makes electricity for the charging circuit. A voltage regulator in the circuit controls the electrical output. This electrical output will keep the battery at full charge.

The low amperage circuit is connected through the ammeter and the charging circuit is connected through the ammeter.

Charging System Components

Alternator

Illustration 2	g01247051
Typical example (1) Regulator (2) Roller bearing (3) Stator winding (4) Ball bearing (5) Rectifier bridge (6) Field winding (7) Rotor assembly (8) Fan

The alternator is driven by the crankshaft pulley through a belt that is a Poly-vee type. This alternator is a three-phase self-rectifying charging unit. The regulator is part of the alternator.

This alternator design has no need for slip rings or for brushes. The only part of this alternator that moves is the rotor assembly. All of the conductors that carry current are stationary. The following components are the conductors: the field winding, the stator windings, six rectifying diodes and the regulator circuit.

The rotor assembly has many magnetic poles. The magnetic poles are similar to fingers. An air space exists between each of the opposite poles. The poles have residual magnetism that produces a small amount of magnet-like lines of force (magnetic field). This magnetic field is produced between the poles. As the rotor assembly begins to turn between the field winding and the stator windings, a small amount of alternating current (AC) is produced in the stator windings. The alternating current is produced from the small magnetic lines of force that are created by the residual magnetism of the poles. The AC is changed into direct current (DC) when the current passes through the diodes of the rectifier bridge. Most of this current provides the battery charge and the supply for the low amperage circuit. The remainder of the current is sent to the field windings. The DC current flow through the field windings (wires around an iron core) increases the strength of the magnetic lines of force. These stronger magnetic lines of force increase the amount of AC that is produced in the stator windings. The increased speed of the rotor assembly also increases the current output of the alternator and the voltage output of the alternator.

Regulator Assembly

Illustration 3	g00360155
Typical example

The voltage regulator is a solid-state electronic switch. The voltage regulator senses the voltage of the system. The regulator then uses switches to control the current to the field windings. This controls the voltage output in order to meet the electrical demand of the system.

Starting System Components

Solenoid

A solenoid is an electromagnetic switch that performs two basic functions:

• The solenoid closes the high current starting motor circuit with a low current start switch circuit.

• The solenoid engages the starting motor pinion with the ring gear.

Illustration 4	g00292316
Typical solenoid schematic

The solenoid has windings (one set or two sets) around a hollow tube. A plunger with a spring load device is inside of the tube. The plunger can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is created. The magnetic field pulls the plunger forward in the tube. This moves the shift lever in order for the pinion drive gear to engage with the ring gear. The front end of the plunger then makes contact across the battery and across the motor terminals of the solenoid. The starting motor then begins to turn the flywheel of the engine.

When the start switch is opened, current no longer flows through the windings. The spring now returns the plunger to the original position. At the same time, the spring moves the pinion gear away from the flywheel.

When two sets of windings in the solenoid are used, the windings are called the hold-in winding and the pull-in winding. Both of the windings wind around the cylinder for an equal amount of times. The pull-in winding uses a wire with a larger diameter in order to produce a stronger magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in winding. The remainder of the current flows through the pull-in windings, to the motor terminal, and then to the ground. When the solenoid is fully activated, the current is shut off through the pull-in windings. Only the smaller hold-in windings are in operation for the extended period of time that is necessary for the engine to be started. The solenoid will now take a smaller amount of current from the battery. Heat that is created by the solenoid will be kept at an acceptable level.

Starting Motor

The starting motor rotates the engine flywheel at a rate that is fast enough to start the engine.

The starting motor has a solenoid (2). When the start switch is activated, the solenoid (2) will move the starter pinion (4) in order to engage the starter pinion (4) and the ring gear on the engine flywheel. The starter pinion (4) and the ring gear will engage before the circuit between the battery and the starting motor is closed by the electric contacts in the solenoid (2). When the circuit between the battery and the starting motor is complete, the starter pinion (4) will rotate the engine flywheel. A clutch provides protection for the starting motor so that the engine cannot turn the starting motor too fast. When the switch is released, the starter pinion (4) will move away from the ring gear.

Illustration 5	g01247102
Starting motor cross section (1) Field (2) Solenoid (3) Clutch (4) Starter pinion (5) Commutator (6) Brush assembly (7) Armature

Other Components

Circuit Breaker

The circuit breaker is a switch that opens the battery circuit if the current in the electrical system is higher than the rating of the circuit breaker. The metal disc (2) is activated by heat. If the current in the electrical system gets too high, the metal disc will get hot. This heat causes a distortion of the metal disc. A circuit breaker that is open can be reset when the metal disc becomes cooler. Push the reset button (1) in order to close the contact points and reset the circuit breaker.

Illustration 6	g01247131
Circuit breaker schematic (1) Reset button (2) Disc in open position (3) Contacts (4) Disc (5) Battery circuit terminals