EGR Valve: Description and Operation

Exhaust Gas Flow:

DESCRIPTION
The linear Exhaust Gas Recirculation (EGR) valve is operated exclusively by control module command. The control module monitors various engine parameters:
^ Throttle Position (TP) sensor.
^ Manifold Absolute Pressure (MAP).
^ Engine Coolant Temperature (ECT) sensor.
^ Pintle position sensor.

OPERATION
Output messages are then 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 vacuum-operated models and offers improved diagnostic capabilities as well.

Positioned at the top of the Linear EGR assembly are 5 terminals:
1. A is the pulse width modulated negative signal from the Powertrain Control Module (PCM).
2. E is the positive from the ignition.
3. 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.

The solenoid (bobbin and coil) assembly is energized by 12 volt current which enters the valve through an electrical connector (terminal E), then flows through the solenoid assembly to the PCM and creates and 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 exhaust manifold (through the orifice) to the intake manifold. The height of the pintle is read by the pintle position sensor, and the PCM closes the loop on 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 correct it.

The Linear EGR valve is unique in that the PCM 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 (PCM breaks the circuit), the pintle is seated against the orifice, blocking exhaust flow to the intake manifold.