The EGR is turned off for low engine speeds and high loads. Otherwise, over the broad range of normal operation, the EGR control map values are set at mid-range. The EGR control valve has a practical adjustable range from 5% (closed position) to 85% (position of maximal flow area).
The EGR will operate until conditions are encountered that result in unacceptable operating characteristics. If coolant temperature, barometric pressure, engine speed, and percent torque are below certain limits, the EGR will be disabled. Excessively high charge air temperature will disable the EGR to prevent engine damage.
The following limits apply to the EGR control valve logic:
- When Engine Coolant Temperature (ECT) is below 18 °C (64 °F), independent of speed and load, the EGR is disabled.
- When ECT is below 60 °C (140 °F) at low loads, the EGR is disabled to avoid buildup of condensed exhaust products (such as hydrocarbons and soot) in the EGR cooler and other downstream components.
- When torque is less than 5% of available, the EGR is disabled to avoid diverting exhaust gases when needed for engine braking.
- When Intake Air Temperatures (IAT) is greater than or equal to 100 °C (212 °F), EGR is disabled.
Note: The engine diagnostics use an IAT greater than or equal to 100 °C (212 °F) as an indication of an EGR cooler failure.
- At engine speeds lower than 1150 rpm, the EGR is turned off.
- During starting, the EGR is turned off for better startability.
- When the air mass flow is insufficient for the speed and load, the EGR is turned off to control smoke.
- At light loads, the EGR is turned off.
- The EGR is turned off at about 1740 m (5708 ft).
Note: The DDEC Engine Control Unit uses barometric pressure to estimate altitude. The average barometric pressure for an altitude of 1740 m (5708 ft) is 82.0 kPa (24.2 in. Hg).
- If the EGR temperature sensor fails, the EGR is shut off.
- If the self-diagnostics indicate a malfunction of the EGR control valve, the EGR is shut off.
|MBE 900 and MBE 4000 EGR Technician's Manual - 7SE940|
|Generated on 10-13-2008|