Functionality of EGR Components
The following subsections detail the functions of specific EGR components.
DDEC V Electronic Control Unit
The Electronic Control Unit (ECU) provides overall engine management, self-diagnostic checks, and monitors other system components. System diagnostic checks are made at ignition-on and continue throughout all engine-operating modes.
A DDEC equipped engine is built with an electronically controlled fuel injection system which eliminates control racks or mechanical linkages requiring periodic adjust. Fuel economy and vehicle performance are also improved during cold starting and the increased initial idle speed allows for fast engine warm-up.
Horsepower, torque, idle, and engine speed are managed by the ECU. Such functionality eliminates the need for a mechanical governor. Mechanical governors are equipped with springs that require adjustments for idle and high-speed control.
The Accelerator Pedal Assembly (AP) eliminates the need for any throttle linkage eliminating throttle delay.
The DDEC V ECU has two 68-pin Tyco connectors; one for the engine and the other for the vehicle. There are two data links on the Vehicle Interface Harness (VIH). One link is based on SAE J1708 and the second is SAE J1939. The engine harness, is Controller Area Network (CAN) based and will be used for proprietary communications such as multi-ECU applications and DDC factory programming. See Figure "Series 60 DDEC V EGR Engine Harness" for the Engine Harness and see Figure "DDEC V Vehicle Interface Harness" for the Vehicle Interface Harness.
Turbocharger Compressor Inlet Temperature Sensor
The Turbocharger Compressor Inlet Temperature Sensor (TCI) sensor is installed by the OEM within piping between the air filter and the turbocharger inlet. The TCI sensor along with other DDEC sensors are monitored by the ECU as a means of fuel management during normal operation.
The TCI sensor is supplied a 5-volt signal from the ECU and returns a voltage signal to the ECU relative to turbocharger compressor air inlet temperature. As return voltage decreases the air inlet temperature voltage increases. The TCI operating values during normal engine operation are 0.10-5.0 V.
The venturi tube with a port at each end is located in the EGR delivery pipe which is connected to the EGR cooler outlet. The Venturi tube ports are connected to the Delta P Sensor to monitor the pressure differential across the venturi as EGR exhaust gases flow through the EGR delivery pipe to the charge air mixer. DDEC V uses this information along with temperature and density of the exhaust gases to determine precise EGR Mass Flow Rate.
Figure 1. Venturi Tube
The primary purpose of the EGR cooler, see Figure "EGR Cooler" , is to cool the engine exhaust gases prior to entering the intake manifold. Exhaust gas cooling is accomplished by the flow of exhaust gases through the EGR cooler tubes. The EGR cooler core then transfers the heat removed from the exhaust gases to the engine coolant. The cooled exhaust gases are then mixed with incoming air from the charge air cooler before being sent to the intake manifold.
Figure 2. EGR Cooler
Charge Air Mixer
The charge air mixer, see Figure "Charge Air Mixer" , combines exhaust gases into the fresh air supply flowing from the charge air cooler. Once the air has passed the charge air mixer, the intake manifold diffuses the EGR exhaust gases evenly to each cylinder. DDEC sensors are mounted in the intake manifold to monitor the air temperature and boost pressure.
Figure 3. Charge Air Mixer
Charge Air Cooler
The Charge Air Cooler (CAC), see Figure "Charge Air Cooler" , is mounted in front of the cooling system radiator and is connected to the turbocharger and intake manifold which permits a more dense charge of air to be delivered to the engine. The compressed air leaving the turbocharger is directed through the CAC before it flows into the CAC to be mixed with EGR exhaust gases before entering the intake manifold. Cooling is accomplished by incoming air flowing past the tubes and fins of the CAC. The compressed intake charge air flowing through the CAC core transfers the heat to the tubes and fins where it is dissipated to the outside air.
Figure 4. Charge Air Cooler
Variable Nozzle Turbocharger
Variable nozzle turbocharger (VNT), see Figure "VNT Actuator" , uses an actuator to regulate and control turbine vanes. There is no wastegate with this system. The VNT actuator is mounted on a bracket attached to the turbocharger and receives air pressure from engine-mounted VPOD. The VNT actuator connects via a rod to the pin joint of the turbine external arm. Rotation of the external arm simultaneously rotates several pivoting nozzle vanes positioned inside the turbine housing at the outer periphery of the turbine wheel. This adjusts turbocharger speed, boost and EGR flow in accordance with DDEC engine management control.
Note: VNT actuator is spring loaded. If air pressure is lost the actuator will open the VNT vanes resulting in low/no boost.
Figure 5. VNT Actuator
Variable Pressure Output Device
There is one VPOD which controls the VNT. See Figure "EGR Valve and VNT Control System" . The location of the VPOD is application dependent.
Two system components are required for proper operation of the EGR valve and the VNT control system.
- 12V or 24V Power Supply
- DDEC V ECU: PWM#3 (E1) EGR and PWM#4 (E4) VNT
Note: VNT is fully open at 7% and closed at 90%
Figure 6. EGR Valve and VNT Control System
Hydraulically Actuated EGR Valve
The EGR valve is hydraulically actuated using engine oil and eliminates the need for an EGR VPOD. The butterfly valve design is still used to control the exhaust gas flow through the EGR cooler. The ECU continuously monitors all engine operation modes and performs self diagnostic checks for engine RPM, engine load, altitude, incoming air temperature, and uses this information to determine the EGR valve position. The ECU changes the EGR valve position via a PWM to the solenoid in the actuator. See Figure "Hydraulic Actuator with Solenoid" .
Note: When installing a new hydraulic actuator or EGR valve, manually closing the valve during installation will make the first start up easier. Once the engine has started and oil pressure through the actuator has equalized, operation will be normal.
The EGR valve operating values are 0-12 V or 0-24 V depending on vehicle electrical system.
Figure 7. Hydraulic Actuator with Solenoid
EGR Temperature Sensor
The ECU uses the EGR Temperature Sensor to monitor exhaust gas temperatures in the EGR delivery pipe and uses exhaust temperature and delta pressure across the venturi tube to determine rate of EGR flow. The temperature sensor is supplied a 5-volt reference signal from the ECU and returns a voltage signal to the ECU relative to exhaust gas temperatures in the EGR delivery pipe. The sensor return voltage decreases as exhaust gas temperature increases (sensor operating values are 0.10-5.0 V). See Figure "EGR Tempertaure Sensor" to view the sensor with connector.
Figure 8. EGR Tempertaure Sensor
Delta P Sensor
The Delta P Sensor monitors the pressure differential across the venturi (in the EGR delivery pipe at the EGR cooler outlet) and uses the delta pressure and exhaust temperature to determine the rate of EGR flow. See Figure "Delta P Sensor" . The sensor is supplied a 5-volt reference signal from the ECU and returns a voltage signal to ECU relative to pressure difference across the Venturi tube. Return sensor voltage increases as pressure differential increases during engine operation (operating values are 0.23-4.77 V).
1. Thermostat Housing
2. Delta P Sensor
Figure 9. Delta P Sensor
Intake Manifold Pressure Sensor
The Intake Manifold Pressure Sensor (IMP Sensor), see Figure "Turbocharger Boost Sensor" , is used to monitor air pressure in the intake manifold. The DDEC V ECU uses this air pressure data for fuel management during engine acceleration. The IMP Sensor sensor is supplied a 5-volt reference signal by ECU and returns a voltage signal to the ECU relative to turbo boost pressure. Return voltage increases as boost pressure increases. Operating values are 0.10-5.0 V during normal engine operation.
Figure 10. Turbocharger Boost Sensor
|Series 60 EGR Technician's Manual - 7SE60|
|Generated on 10-13-2008|