EGR Valve: Description and Operation

EGR Valve Flow:

EGR Valve Assembly Sectional View:

DESCRIPTION
The Exhaust Gas Recirculation (EGR) valve regulates the amount of exhaust gas fed to the engine. The PCM controls the EGR valve by sending a Pulse Width Modulated (PWM) signal to the bobbin and coil subassembly contained within the EGR valve. The PCM monitors various sensors to control the amount of EGR flow.

The EGR Valve is unique in that the PCM continuously monitors pintle height and continuously corrects it in order to obtain accuracy. When the solenoid is de-energized (PCM breaks the circuit), the pintle is sealed against the orifice, blocking exhaust flow to the cylinder distribution channels.

OPERATION
The PCM commands the EGR valve to open a specific amount by varying the PWM signal to the linear EGR valve. The EGR contains a sensor that relates the actual valve position back to the PCM. Similar to Throttle Position sensor reading, the EGR pintle position is expressed as being 0% at closed position and 100% at the fully open position. In this way, the PCM is constantly comparing commanded EGR position versus actual EGR position. This results in improved flow accuracy. The amount of exhaust gas mixture is dependent upon the height of the pintle above the orifice in the base of the valve.

Construction
The EGR Valve is comprised of the following subassemblies shown in Figure:

^ Bobbin and Coil (Solenoid) Assembly.
^ Armature Assembly.
^ Base.

The bobbin and coil (solenoid) assembly consists of one solenoid that is encapsulated to maximize reliability, seal coils from the environment, and prevent movement of the coils and terminal. Inside the solenoid (bobbin and coil) assembly is an armature assembly, consisting of a pintle and valve assembly, two seals, retaining washers, a seal spring, an armature spring, and a bearing. The valve pintle shaft is sealed from the exhaust chamber by a bearing. In addition, an armature shield, held in place by a compression spring, deflects exhaust gas from the shaft and the armature. The base adapter and base plate make up the base assembly.

The PCM controlled EGR Valve offers more precise EGR flow metering than a back pressure or digital type valve and superior emission control and driveability.