Section 2.2
MBE 900 Engines With EGR Systems
The MBE 900 is a four-stroke, high speed electronically-controlled diesel engine. Key emissions systems components include an EGR system that includes a gas-to-liquid cooler for hot EGR, a divided turbine housing turbocharger design, reed valves to prevent reverse gas flow, and a rotary valve that modulates EGR flow. See Figure "MBE 900 EGR System Components" .
Note: The four-cylinder engines, MBE 904 and 924, do not have a divided turbine housing.
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1. Exhaust Manifold |
6. EGR Delivery Pipe |
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2. EGR Rotary Valve |
7. EGR Cooler Coolant Supply |
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3. EGR Cooler |
8. EGR Exhaust Elbow |
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4. EGR Mixer |
9. Asymmetrical Turbocharger |
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5. Reed Valves |
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Figure 1. MBE 900 EGR System Components
The engine is equipped with full-flow oil filters, oil cooler, fuel filter(s), turbocharger, and an electronic engine control system that manages fuel delivery and EGR systems. Air is supplied by the turbocharger to the intake manifold and into the engine cylinders after passing through an air-to-air intercooler mounted in the vehicle ahead of the cooling system radiator. The intercooler cools the pressurized intake air charge coming from the turbocharger compressor before it is mixed with cooled recirculated exhaust gas and distributed to the intake ports by the intake manifold.
The MBE 900 engine utilizes electronically controlled fuel injection and cooled exhaust gas recirculation as the primary emission control technologies. The engine’s DDEC-ECU utilizes algorithms and several sensor inputs for management of the fuel injection and EGR systems. See Figure "MBE 900 EGR Sensor Locations (Right Side)" and Figure "MBE 900 EGR Sensor Locations (Left Side)" for sensor locations.
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1. Barometric Pressure Sensor (located underneath the DDEC-ECU) |
5. Camshaft Position Sensor |
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2. Engine Fuel Supply Temperature Sensor |
6. Crankshaft Position Sensor |
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3. Engine Coolant Temperature Sensor |
7. DDEC-ECU |
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4. Intake Manifold Pressure/Air Temperature Combination Sensor |
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Figure 2. MBE 900 EGR Sensor Locations (Right Side)
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1. Engine Oil Pressure Sensor |
3. Engine Oil Temperature Sensor |
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2. EGR Temperature Sensor |
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Figure 3. MBE 900 EGR Sensor Locations (Left Side)
The parameters sensed by the electronic control system are as follows:
- EGR Temperature after EGR Cooler
- Intake Manifold Pressure
- Intake Manifold Air Temperature
- Fuel Temperature
- Oil Temperature
- Oil Pressure
- Coolant Temperature
- Crankshaft Position
- Camshaft Position
- Accelerator Pedal Position
- Barometric Pressure
- Modulated EGR Valve Functionality
The controlled functions are as follows:
- Fuel injection duration
- Fuel Injection Timing — Beginning of Injection
- Modulated EGR Valve Position
- Idle Speed
The DDEC-ECU is one of two electronic controllers that make up the IES that is used in commercial vehicles with the MBE 900 engine. The separation of functions of each controller is such that the DDEC-VCU senses and controls the vehicle-influencing parameters such as cruise control, while the DDEC-ECU covers engine operating parameters as described above.
Section 2.2.1
TURBOCHARGER AND EXHAUST MANIFOLD
The turbocharger used on the MBE 906 and 926 engines features an asymmetrically split double-flow turbine housing. The exhaust manifold on these engines is designed so that exhaust flow from cylinders #1 through #3 is collected separately from exhaust gases for cylinders #4 through #6. The flow from each set of cylinders enters the turbine housing through separate inlets having different flow areas. The smaller inlet, receiving flow from cylinders #1 to #3, causes higher exhaust back pressure increasing the pressure differential driving EGR flow into the intake manifold. See Figure "EGR Exhaust Manifold for MBE 906 and 926 Engines" .
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1. EGR Outlet |
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Figure 4. EGR Exhaust Manifold for MBE 906 and 926 Engines
The turbocharger used on the MBE 904 and 924 engines has a single-flute turbine housing. The exhaust manifold on these engines is designed with one chamber for cylinders #1 through #4 and the EGR outlet is located on the end. See Figure "EGR Exhaust Manifold for MBE 904 and 924 Engines" .
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1. EGR Outlet |
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Figure 5. EGR Exhaust Manifold for MBE 904 and 924 Engines
Section 2.2.2
EXHAUST GAS RECIRCULATION SYSTEM
In general, the EGR rate of flow is modulated by the engine control system to optimize NOx and particulate levels in balance with the air fuel ratio using parameters from the various engine sensors.
The MBE 900 EGR system utilizes a combination of two EGR valves to control the exhaust gas flow. The first valve is a rotary plate valve located in the end cover of the EGR cooler. This valve is electro-magnetically actuated to control EGR flow. The actuator angle is determined by a DDEC-ECU-controlled PWM signal. See Figure "MBE 900 EGR Control Valve" .
Figure 6. MBE 900 EGR Control Valve
The second valve, not on the MBE 906, is a reed valve assembly downstream from the EGR cooler. See Figure "Reed Valves" . The reed valves ensure that while the EGR control valve is open, there is no reverse airflow from the intake system into the exhaust manifold. When the exhaust manifold pressure is higher than the intake manifold pressure, flow occurs. When the pressures are reversed, the reed valves prevent flow. Back flow could otherwise occur since the average intake manifold pressure is higher than the average exhaust manifold pressure. See Figure "MBE EGR System Operating Pressure Characteristics" .
Figure 7. Reed Valves
Figure 8. MBE EGR System Operating Pressure Characteristics
| MBE 900 and MBE 4000 EGR Technician's Manual - 7SE940 |
| Generated on 10-13-2008 |