Page 27 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes
Example: Multi-Point Fuel Injection (MPFI) System
An MPFI system is an automotive engine control system. A conceptual diagram of a car embedding
an MPFI system is shown in Fig.2.5. An MPFI is a real-time system that controls the rate of fuel
injection and allows the engine to operate at its optimal efficiency. In older models of cars, a
mechanical device called the carburettor was used to control the fuel injection rate to the engine.
It was the responsibility of the carburettor to vary the fuel injection rate depending on the
current speed of the vehicle and the desired acceleration. Careful experiments have suggested
that for optimal energy output, the required fuel injection rate is highly nonlinear with respect
to the vehicle speed and acceleration. Also, experimental results show that the precise fuel
injection through multiple points is more effective than single point injection. In MPFI engines,
the precise fuel injection rate at each injection point is determined by a computer. An MPFI
system injects fuel into individual cylinders resulting in better ‘power balance’ among the
cylinders as well as higher output from each one along with faster throttle response. The processor
primarily controls the ignition timing and the quantity of fuel to be injected. The latter is
achieved by controlling the duration for which the injector valve is open — popularly known as
pulse width. The actions of the processor are determined by the data gleaned from sensors
located all over the engine. These sensors constantly monitor the ambient temperature, the
engine coolant temperature, exhaust temperature, emission gas contents, engine rpm (speed),
vehicle road speed, crankshaft position, camshaft position, etc. An MPFI engine with even an 8-
bit computer does a much better job of determining an accurate fuel injection rate for given
values of speed and acceleration compared to a carburettor-based system. An MPFI system not
only makes a vehicle more fuel efficient, it also minimizes pollution by reducing partial
combustion.

Figure 2.5: A Real-Time System Embedded in an MPFI Car

Source: http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Embedded%20
systems/Pdf/Lesson-28.pdf

2.4.5 Telecommunication Applications

A few example uses of real-time systems in telecommunication applications are: cellular systems,
video conferencing, and cable modems.

Example: A Cellular System
Cellular systems have become a very popular means of mobile communication. A cellular
system usually maps a city into cells. In each cell, a base station monitors the mobile handsets
present in the cell. Besides, the base station performs several tasks such as locating a user,
sending and receiving control messages to a handset, keeping track of call details for billing
purposes, and hand-off of calls as the mobile moves. Call hand-off is required when a mobile
moves away from a base station. As a mobile moves away, its received signal strength (RSS)

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