G3406 and G3412 Generator Set Engines Caterpillar


Ignition System - Electronic Ignition System (EIS)

Usage:

G3412 GNA
The EIS includes these components: EIS control module, engine speed/timing sensor, manifold air pressure sensor, detonation sensors, ignition transformers, spark plugs and wiring harnesses. The EIS control module is wired to an engine mounted junction box. The junction box provides an interface for communication between the operator and the EIS control module. The operator can use the Caterpillar Electronic Technician (Cat ET) or the Digital Diagnostic Tool (DDT) for the communication.

Illustration 1 demonstrates the relationship between the parts of the system.




Illustration 1g00942307

Schematic of the electronic ignition system and related components

(1) Engine mounted junction box

(2) Engine speed/timing sensor

(3) Manifold air pressure sensor

(4) Detonation sensor

(5) EIS control module

(6) Cat ET

(7) DDT

(8) Ignition transformer

(9) Spark plug

EIS control module (5) is mounted on the engine. The EIS control module must be programmed for the installation in order to properly control the ignition. Cat ET (6) or DDT (7) are used to program the EIS control module. The DDT can be connected to junction box (1) .

Note: For information on the programmable parameters, refer to Systems Operation, "Electronic Control System Parameters".

Two switches have an effect on the ignition system: the engine control switch and the switch for fuel selection.

When the engine control switch is switched to the manual start position, the EIS control module begins operating the ignition system.

If the switch for fuel selection is in the natural gas position, the EIS control module will use the desired timing that is programmed. If the switch for fuel selection is in the propane position, the EIS control module retards the timing by ten degrees.

The EIS control module uses engine speed/timing sensor (2), manifold air pressure sensor (3), and detonation sensors (4) to monitor engine operation.

Information from the EIS control module is sent to engine mounted junction box (2). If a problem with the electronic ignition system is detected, a diagnostic code is generated. The diagnostic code can be monitored withCat ET or with the DDT.

The EIS control module has several internal components that perform different functions. The components and the functions are listed in Table 1.

Table 1
Internal Components and Functions of the EIS Control Module    
Component     Function    
Ignition control     Receive input from these components:
Engine control switch
Switch for fuel selection
Cat ET
DDT    
Provide information on engine status and diagnostics to electronic service tools.
Provide desired timing and voltage to the ignition transformers' control.
Receive input from the interpreters and the filter.
Ignition transformers' control     Receive input from the ignition control.    
Provide voltage to the transformers.
Provide input to the interpreter of diagnostics for the transformers.
Interpreter of diagnostics for the transformers     Receive input from the ignition transformers' control.    
Provide input to the ignition control.
Interpreter for the signal from the engine speed/timing sensor     Receive input from the engine speed/timing sensor.    
Provide input to the ignition control.
Interpreter for the signal from the manifold air pressure sensor     Receive input from the manifold air pressure sensor.    
Provide input to the ignition control.
Filter for the detonation sensors     Receive input from the detonation sensors.    
Provide input to the ignition control.

The relationships of the EIS control module, the sensors, and the transformers are described below.

Engine Speed/Timing Sensor

The engine speed/timing sensor provides information about engine speed and the position of the crankshaft to the EIS control module.




Illustration 2g00818359

(1) Engine speed/timing sensor

A timing wheel is mounted in front of the governor drive. Engine speed/timing sensor (1) is installed in the cover. A magnetic pickup is located in the plastic sliphead of the sensor. The EIS control module supplies approximately 13 VDC to the sensor. As the teeth of the timing wheel rotate past the sliphead of the sensor, the sensor generates a signal that matches the pattern of the teeth. The signal is sent to an interpreter for the EIS control module.




Illustration 3g00807464

Engine speed/timing sensor and timing wheel

The timing wheel has a special tooth pattern that indicates the position of the camshaft and the direction of rotation. The timing wheel has 24 slots in the outer diameter. Twenty-one of the slots are narrow. Three of the slots are about 2.5 times wider than the rest of the slots. When the engine rotates in the normal direction, the slots pass the engine speed/timing sensor in the following order:

  • 1 wide slot

  • 3 narrow slots

  • 2 wide slots

  • 18 narrow slots

The number one cylinder is at the top center position when the edge of the first narrow slot passes the center of the sliphead. All 24 teeth pass the sliphead during one revolution of the camshaft or two revolutions of the crankshaft.

With information from the engine speed/timing sensor, the EIS control module is able to calculate the positions of the pistons in the cylinders. According to the ignition timing that is selected, the EIS control module sends voltage pulses to the transformers for firing of the spark plugs.

The engine speed/timing sensor also monitors engine speed. If a speed sensitive timing map is selected, the EIS control module adjusts the ignition timing according to the engine rpm.

The EIS control module will shut down the engine if problems with the engine speed/timing sensor's electrical circuit are detected. The corresponding diagnostic code is generated.

Manifold Air Pressure Sensor




Illustration 4g00818361

Manifold air pressure sensor

The EIS control module supplies approximately 13 VDC to the manifold air pressure sensor. The sensor monitors the absolute inlet manifold air pressure. The sensor sends a signal to the EIS control module. The EIS control module has an interpreter that uses the signal to calculate the engine load. If a timing map that is sensitive to load is selected, the EIS control module adjusts the ignition timing according to the calculated load.

The EIS control module will generate a diagnostic code if problems with the manifold air pressure sensor's electrical circuit are detected.

Detonation Sensors

Two different types of detonation sensors are available. One type is a sensor assembly. The other type consists of two parts: buffer module and accelerometer.




Illustration 5g00942676

Sensor assembly

The sensor assembly is attached to wiring and to a connector for the engine harness.




Illustration 6g00818378

Two-piece detonation sensor

(1) Buffer module

(2) Accelerometer

Accelerometer (2) provides electrical signals to buffer module (1). The buffer provides a signal with an offset of approximately 6 VDC to a filter in the EIS control module.

A detonation sensor is located on the upper cylinder block on each side of the engine. Each sensor monitors one bank of cylinders. The EIS control module supplies approximately 13 VDC to the sensors.

The detonation sensors provide an electrical signal of the mechanical engine vibrations to the EIS control module. The frequency of the signal corresponds to the mechanical frequency of the vibrations. The amplitude of the signal is proportional to the intensity of the vibrations.

The EIS control module monitors the signals in order to determine the presence and the severity of detonation. The EIS control module retards the timing in order to limit detonation levels.

The retardation of timing is the first level of protection against detonation. The EIS control module can retard timing by as few as 0.1 degrees before top center for light detonation levels. The timing can be retarded up to 9 degrees before top center for severe detonation.

As the detonation level decreases, the EIS control module will begin to advance the timing out of the detonation retarded timing. The advance is proportional to the level of detonation. The rate is faster for lighter detonation.

Engine shutdown is the second level of protection against detonation. If retardation of the timing is unsuccessful and the detonation continues at severe levels, the EIS control module will signal for an engine shutdown.

Protection from detonation is enabled under the following conditions:

  • The inlet manifold air pressure reaches an absolute pressure of 110 kPa (16 psi).

  • If a diagnostic code is generated for the manifold air pressure sensor, protection from detonation is enabled regardless of the inlet manifold air pressure.

Protection from detonation is disabled under the following conditions:

  • The inlet manifold air pressure reaches an absolute pressure of less than 110 kPa (16 psi).

  • The engine speed is less than 500 rpm.

The EIS control module will generate a diagnostic code if a problem with the electrical circuit for the detonation sensors is detected.

Ignition Transformers




Illustration 7g00735979

(1) Ignition transformer

(2) Spark plug

(3) Valve cover

(4) MS connector

(5) EIS control module

Each cylinder has an ignition transformer that is located under the valve cover. Each transformer has a primary circuit and a secondary circuit.

To initiate combustion in a cylinder, the EIS control module sends a pulse of approximately 190 volts to the primary coil of the ignition transformer. The transformer increases the voltage to a range between 8000 and 32,000 volts. The high voltage creates a spark across the spark plug electrode.

The transformers are grounded through the valve covers. Use caution when a valve cover is removed.

------ WARNING! ------

Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring.

Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers.

----------------------

Always disconnect the ignition harness from the transformer when a valve cover is removed.

The ignition harness is routed outside the engine to an MS connector on the valve cover base. Another wiring harness connects to the transformers inside the valve cover.

The EIS control module monitors the ignition system. The EIS control module will generate a diagnostic code if problems with the electrical circuit are detected.

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