Page 341 - Understanding Automotive Electronics

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9 AUTOMOTIVE INSTRUMENTATION

TRIP INFORMATION COMPUTER

The trip information One of the most popular electronic instruments for automobiles is the
computer analyzes fuel trip information system. This system has a number of interesting functions and
flow, vehicle speed, and can display many useful pieces of information, including the following:
fuel tank quantities, and 1. Present fuel economy
then calculates informa- 2. Average fuel economy
tion such as miles to
empty, average fuel 3. Average speed
economy, and estimated 4. Present vehicle location (relative to total trip distance)
arrival time. 5. Total elapsed trip time
6. Fuel remaining
7. Miles to empty fuel tank
8. Estimated time of arrival
9. Time of day
10. Engine RPM
11. Engine temperature
12. Average fuel cost per mile

Additional functions can be performed, which no doubt will be part of future
developments. However, we will discuss a representative system having features
that are common to most available systems.
A block diagram of this system is shown in Figure 9.27. Not shown
in the block diagram are MUX, DEMUX, and A/D converter components,
which are normally part of a computer-based instrument. This system can
be implemented as a set of special functions of the main automotive
instrumentation system, or it can be a stand-alone system employing its
own computer.
The vehicle inputs to this system come from the three sensors that
measure the following variables:
1. Quantity of fuel remaining in the tank
2. Instantaneous fuel flow rate
3. Vehicle speed

Other inputs that are obtained by the computer from other parts of the
control system are
1. Odometer mileage
2. Time (from clock in the computer)
The driver enters inputs to the system through the keyboard. At the
beginning of a trip, the driver initializes the system and enters the total trip
distance and fuel cost. At any time during the trip, the driver can use the
keyboard to ask for information to be displayed.

328 UNDERSTANDING AUTOMOTIVE ELECTRONICS