Exhaust Gas Recirculation: Description and Operation
EGR Valve Control Schematic:
PCM Wiring:
EGR Valve Assembly Sectional View:
DESCRIPTION
The Exhaust Gas Recirculation (EGR) valve regulates the amount of exhaust gas fed to the engine and is part of the Emission System. 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.
LOCATION
The EGR valve is located on the top LH side of engine.
Exhaust Gas Recirculation (EGR) Flow:
EGR System Components:
EXHAUST FLOW
Exhaust gases are routed to the engine through a corrugated semiflexible feed pipe (EGR valve pipe) which connects the crossover exhaust pipe to the crossover water pump housing.
In the crossover waterpump housing, exhaust gases are precisely metered by the PCM controlled EGR Valve, then cooled by engine coolant and finally routed to the front and rear cylinder heads. A potential drawback with EGR is that for certain driving schedules, deposits can accumulate when hot exhaust gases are cooled. The Northstar system uses the crossover waterpump housing as a cross-flow heat exchanger to cool exhaust gases in large easily cleaned passages to virtually eliminate any concern with deposit accumulation during the service life of the engine. This is done by having the cooling passage reduce EGR gasses below their deposit forming temperature prior to routing these gasses into cylinder distribution channels.
In each cylinder bank, exhaust gases travel under the intake manifold along an irregularly shaped sandwich passage made up of the aluminum alloy cylinder head and a non-metallic distribution plate. Engine vacuum acts to draw exhaust gases through outlets in the distribution plate where mixing with the incoming fuel/air charges for each cylinder occurs. Although the openings look small, the EGR valve pintle is the flow limiter in this system.
PCM CONTROL
The EGR Valve regulates the amount of exhaust gas fed to the engine. This mixture is dependent upon the height of the pintle above the orifice in the base of the valve. The EGR System 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 regulates the amount of exhaust gas fed to the engine. This device offers more precise EGR flow metering than a back pressure or digital type valve and superior emission control and driveability.
The PCM monitors the following sensors to control the linear EGR valve:
- Coolant Temperature (CT) Sensor
- Throttle Position (TP) Sensor
- Manifold Pressure (MAP)
- Manifold Air Temperature (MAT)
- Throttle Switch (ISC)
- RPM data
- Vehicle Speed Sensor (VSS)
CIRCUIT OPERATION
- Output messages are then sent to the EGR system indicating the proper amount of exhaust gas recirculation necessary to lower combustion temperatures.
- The solenoid assembly is energized by 12 volt current which enters the valve through an electrical connector, then flows through the solenoid assembly to the PCM and creates 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 exhaust manifold (through the orifice) to the cylinder distribution channels.
- 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 accuracy.