Page 381 - Understanding Automotive Electronics

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11 FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS

5. Self-diagnosis for fail-safe operation
6. Back-up MPU
7. Crankshaft angular position measurement for ignition timing
8. Direct mass air flow sensor
Although these technological changes have improved the performance and
reliability of the electronically controlled engine, the fundamental control
strategy for fuel metering has not changed. The fuel metering strategy has been
and will probably continue to be (at least for the short term) to provide a
stoichiometric mixture to the engine. This strategy will remain intact as long as
a three-way catalytic converter is used to reduce undesirable tailpipe exhaust gas
emissions. However, within the constraint of stoichiometric mixture control
strategy, there will be some technological improvements in engine control.
These improvements will occur in mechanical and electrical components as
well as in software that is optimized for performance and efficiency.
In the area of mechanical components, research is being done in the area
of variable parameter intake structures. New mechanisms and
electromechanical actuators are being developed that will permit
1. Induction systems with variable geometry
2. Variable valve timing
3. Variable nozzle turbochargers
4. Throttle actuators
The performance and efficiency of any engine are markedly influenced by the
intake system. The intake system configuration directly affects the volumetric
efficiency of the engine, which is a measure of engine performance as an air
pump. The design of an intake system in the past has involved many
compromises and trade-offs that were made to enable high volumetric
efficiency over the entire engine operating range. Variable geometry is achieved
through the use of new electromechanical mechanisms or actuators that can
change the shape and dimensions of intake system components.
One such system is illustrated in Figure 11.1 for an experimental V-6
engine. This system has two separate intake systems, each of which has a
throttle valve. In a traditional engine, the intake manifold is tuned to achieve
maximum torque at a particular RPM. The system of Figure 11.1, which is
known as a variable impedance aspiration system (VIAS), has two separate
intake pipes leading from a plenum chamber to the cylinder banks, with a
butterfly valve connecting the two sides. By suitable opening and closing of this
valve, the effective dimensions of the intake pipes are changed, thereby tuning
the intake. Figure 11.1b shows the relative torque output for an open and
closed valve. Note the improved torque at low RPM.
An important aspect of volumetric efficiency is the valve timing (see Chapter
1). Valve timing and valve lift profile are designed with many constraints to ensure
the best possible volumetric efficiency over a wide range of engine operations. In

368 UNDERSTANDING AUTOMOTIVE ELECTRONICS