Exhaust Gas Recirculation: Description and Operation

LINEAR EGR VALVE SYSTEM




Output messages are sent to the EGR system indicating the proper amount of exhaust gas recirculation necessary to lower combustion temperatures. This electronic metering of exhaust gas is ten times faster than a vacuum operated system and has improved diagnostic capabilities.

Solenoid Resistance:

Positioned at the top of the linear EGR assembly are five terminals:
^ "A" is the pulse width modulated negative signal from the PCM.
^ "E" is the positive voltage from the ignition.
^ "B," "C" and "D" are terminals from the PCM for the integral pintle position sensor.
- "B" is sensor ground.
- "C" is sensor output.
- "D" is +5 volts supply.

Electrical Components Of Linear EGR Valve:

The solenoid (bobbin and coil) assembly is energized by current which enters the valve through an electrical connector (terminal "E"), then flows through the solenoid assembly to the PCM creating an electromagnetic field. This field causes the armature assembly to be pulled upward, lifting the pintle a variable amount off the base.

The exhaust gas then flows from the cylinder head exhaust port (through the orifice) to the intake manifold. The height of the pintle is read by the pintle position sensor, and the control module closes the loop as desired position versus actual position read, changing the pulse width modulated command to the solenoid accordingly, until the actual pintle position equals the desired pintle position.

This results in improved flow accuracy. In most EGR designs, the flow is "Open Loop," in which the system has no feedback mechanism to monitor actual flow and then to correct it. The linear EGR valve is unique in that the control module continuously monitors pintle height and continuously corrects it in order to obtain accurate flow, making linear EGR a "Closed Loop" system. When the solenoid is de-energized (control module breaks the circuit), the pintle is sealed against the orifice, blocking exhaust flow to the intake manifold. When the solenoid is energized, engine vacuum acts to draw exhaust gases through the cylinder head passages, linear EUR valve, intake manifold and into each cylinder. Although the opening looks small, the EGR valve pintle is the flow limiter in the system.

The results of incorrect operation with too much EGR flow at idle, cruise, or cold operation, any of the following conditions could occur.
^ Engine stops after cold start.
^ Engine stops at idle after deceleration.
^ Vehicle surges during cruise.
^ Rough idle.

If the EGR valve should stay open all of the time , the engine would not idle. The results of incorrect operation with too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:
^ Spark knock (detonation).
^ Engine overheating.