MBE 900 & MBE 4000 EGR

Section 2.1 MBE 4000 Engines With EGR Systems

Section 2.1
MBE 4000 Engines With EGR Systems

The MBE 4000 is a four-stroke, high speed electronically controlled diesel engine. The cylinder block contains a camshaft that actuates two intake valves and two exhaust valves per cylinder, and pressurizes the fuel injection system electronic unit pumps.‪

The engine is equipped with full-flow oil filter, 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 4000 utilizes electronically controlled fuel injection and cooled exhaust gas recirculation as the primary emission control technologies. The engine’s DDEC Engine Control Unit (DDEC-ECU) utilizes algorithms and several sensor inputs for management of the fuel injection and EGR systems. See Figure "MBE 4000 EGR Sensor Locations (Left Side)" and Figure "MBE 4000 EGR Sensor Locations (Right Side)" for sensor locations.‪

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 1. Engine Fuel Supply Temperature Sensor‪

 5. Engine Coolant Temperature Sensor‪

 2. Intake Manifold Pressure/Air Temperature Combination Sensor‪

 6. Barometric Pressure Sensor (located underneath the DDEC-ECU)‪

 3. Camshaft Position Sensor‪

 7. DDEC-ECU‪

 4. Crankshaft Position Sensor‪

 ‪

Figure 1. MBE 4000 EGR Sensor Locations (Left Side)

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 1. EGR Temperature Sensor‪

 2. Engine Oil Pressure and Engine Oil Temperature Combination Sensor‪

Figure 2. MBE 4000 EGR Sensor Locations (Right Side)

The parameters sensed by the DDEC-ECU are as follows:‪

  • Turbocharger Speed
  • EGR Temperature after EGR-Cooler
  • Charge Air Supply Temperature
  • Intake Manifold Pressure
  • Intake Manifold Air Temperature
  • Fuel Temperature
  • Oil Temperature
  • Oil Pressure
  • Coolant Temperature
  • Crankshaft Position
  • Camshaft Position
  • Barometric Pressure
  • Modulated EGR Valve Functionality

The controlled functions are as follows:‪

  • Fuel Injection Duration
  • Fuel Injection Timing — Beginning Of Injection (BOI)
  • Modulated EGR Valve Position (downstream from EGR Cooler)
  • EGR Shutoff Valve Position (Upstream of EGR Cooler)
  • Idle Speed Boost Pressure (with Actuation of Optional Engine Brake)

The DDEC-ECU is one of two electronic controllers that make up the “Integrated Electronic System” (IES) that is used in commercial vehicles with the MBE 4000 engine. The separation of functions of each controller is such that the DDEC Vehicle Control Unit (DDEC-VCU) senses and controls the vehicle-influencing parameters such as cruise control, while the DDEC-ECU covers engine operating parameters as described above. The DDEC-ECU is positioned on the left side of the engine and is cooled by means of fuel.‪

The various sensed parameters and control logic programmed into the DDEC-ECU determines which mode of engine operation will apply. These running engine-operating modes include: ‪

  • Engine Speed Controlled Mode (Including Idle Mode)
  • Torque Controlled Mode
  • Emergency Mode

The MBE 4000 engines for NAFTA On-Highway 2004 applications use a liquid-cooled EGR system. Exhaust from the front three cylinders is routed through the EGR system.‪

Section 2.1.1
TURBOCHARGER AND EXHAUST MANIFOLD

The turbocharger used on the MBE 4000 engine features an asymmetrically split double-flow turbine housing. The exhaust flow of cylinders No. 1 through 3 is collected in a manifold separate from cylinders No. 4 through 6, with the flow from each manifold entering the turbine housing through separate inlets having different flow areas. The smaller inlet causes higher exhaust back pressure providing the required level of pressure to drive EGR. The turbocharger design must accommodate operations at elevated compressor wheel speeds because of the need to flow EGR. See Figure "Cross Section of MBE 4000 Exhaust Manifold with EGR " .‪

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Figure 3. Cross Section of MBE 4000 Exhaust Manifold with EGR

Due to the compressor characteristics, it is not possible to use EGR at low engine speeds.‪

Section 2.1.2
EXHAUST GAS RECIRCULATION SYSTEM

In general, the engine control system modulates the EGR rate of flow using parameters from the various engine sensors to an optimize NOx and particulate levels in balance with the air fuel ratio. ‪

The EGR system utilizes a combination of three EGR valves to control the exhaust gas flow. See Figure "MBE 4000 EGR System Components" . First there is an EGR shutoff valve on the hot side of the EGR cooler. Secondly, there are reed valves mounted at the outlet of the EGR cooler. The third valve is an electromagnetically actuated EGR control valve located downstream from the reed valves. The system controls EGR flow during steady state and transient modes. EGR control is optimized for maximum NOx control with consideration for particulate emission levels. ‪

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 1. Asymmetrical Turbocharger‪

 6. EGR Delivery Pipe‪

 2. EGR Hot Pipe‪

 7. EGR Control Valve‪

 3. EGR Shutoff Valve‪

 8. Reed Valves‪

 4. EGR Cooler‪

 9. EGR Cooler Coolant Return‪

 5. EGR Mixer‪

10. Exhaust Manifold‪

Figure 4. MBE 4000 EGR System Components

The EGR shutoff valve, located before the EGR cooler, closes the EGR system during the engine braking mode to prevent EGR cooler damage from high exhaust pressures. See Figure "MBE 4000 EGR Shutoff Valve" .‪

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Figure 5. MBE 4000 EGR Shutoff Valve

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. See Figure "Reed Valves" . 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" . ‪

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Figure 6. Reed Valves

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Figure 7. MBE EGR System Operating Pressure Characteristics

The EGR control valve meters the exhaust flow into the EGR mixer. The DDEC-ECU controls the actuator position to determine the amount of valve opening. See Figure "MBE 4000 EGR Control Valve" .‪

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Figure 8. MBE 4000 EGR Control Valve


MBE 900 and MBE 4000 EGR Technician's Manual - 7SE940
Generated on 10-13-2008

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