Page 103 - Automotive Engineering

CH AP TER 4 .1 Digital engine control systems

4.1.9.1 Engine crank (start) 7. Secondary air to catalytic converter.
8. Fuel economy controlled.
The following list is a summary of the engine operations 9. Emissions controlled.
in the engine crank (starting) mode. Here, the primary
control concern is reliable engine start.
4.1.9.4 Closed-loop control
1. Engine RPM at cranking speed.
2. Engine coolant at low temperature. For the closest control of emissions and fuel economy
3. Air/fuel ratio low. under various driving conditions, the electronic engine
control system is in a closed loop. Fuel economy and
4. Spark retarded.
emissions are controlled very tightly. The following is
5. EGR off. a summary of the engine operations during this period:
6. Secondary air to exhaust manifold. 1. Engine RPM at command of driver.
7. Fuel economy not closely controlled. 2. Engine temperature in normal range (above warm-up
8. Emissions not closely controlled. threshold).
3. Average air/fuel ratio controlled to 14.7, 0.05.
4.1.9.2 Engine warm-up 4. EGO sensor’s temperature above minimum thresh-
old detected by a sensor output voltage indicating
While the engine is warming up, the engine temperature a rich mixture of air and fuel for a minimum amount
is rising to its normal operating value. Here, the primary of time.
control concern is rapid and smooth engine warm-up. A 5. System returns to open loop if EGO sensor cools
summary of the engine operations during this period below minimum threshold or fails to indicate rich
follows: mixture for given length of time.
1. Engine RPM above cranking speed at command of 6. EGR controlled.
driver.
7. Secondary air to catalytic converter.
2. Engine CT rises to minimum threshold.
8. Fuel economy tightly controlled.
3. Air/fuel ratio low.
9. Emissions tightly controlled.
4. Spark timing set by controller.
5. EGR off. 4.1.9.5 Hard acceleration
6. Secondary air to exhaust manifold.
When the engine must be accelerated quickly or if the
7. Fuel economy not closely controlled. engine is under heavy load, it is in a special mode. Now,
8. Emissions not closely controlled. the engine controller is primarily concerned with pro-
viding maximum performance. Here is a summary of the
operations under these conditions:
4.1.9.3 Open-loop control 1. Driver asking for sharp increase in RPM or in engine
power, demanding maximum torque.
The following list summarizes the engine operations
when the engine is being controlled with an open-loop 2. Engine temperature in normal range.
system. This is before the EGO sensor has reached the 3. Air/fuel ratio rich mixture.
correct temperature for closed-loop operation. Fuel 4. EGO not in loop.
economy and emissions are closely controlled.
5. EGR off.
1. Engine RPM at command of driver.
6. Secondary air to intake.
2. Engine temperature above warm-up threshold.
7. Relatively poor fuel economy.
3. Air/fuel ratio controlled by an open-loop system to
8. Relatively poor emissions control.
14.7.
4. EGO sensor temperature less than minimum
threshold. 4.1.9.6 Deceleration and idle
5. Spark timing set by controller. Slowing down, stopping, and idling are combined in an-
6. EGR controlled. other special mode. The engine controller is primarily

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