Page 794 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Automotive instrumentation and telematics C HAPTER 23.1

communication is achieved by the sending gateway (i.e., include a standard display having speed and fuel quantity
subsystem) transmitting messages over the network and the capability of displaying warning messages to the
(e.g., wire interconnect). Each message has a specific driver.
format (protocol) that includes a message identifier. The Another benefit of the EFIS-type display is the capa-
identifier defines the content of the message, its priority, bility of displaying diagnostic information to a service
and is unique within the network. In addition to the data technician. The service technicians can select a display
and identifier, each message includes error-checking bits mode that presents fault codes from any vehicle sub-
as well as beginning and end of file. system whenever the car is taken for repairs or during
The CAN communication system has great flexibility, routine maintenance operations.
permitting new subsystems to be added to an existing Of particular importance is the capability of digital
system without modification, provided the new additions instrumentation to identify intermittent faults. The in-
are all receivers. Each gateway (subsystem) can be strumentation computer can store fault codes with
upgraded with new hardware and software at any time a time stamp that gives the time of occurrence to indicate
with equipment that was not available at the time the car to a service technician that a particular component or
left the manufacturing plant or even when it left the subsystem is experiencing intermittent failures. Such
dealer. Essentially, the CAN concept with its open failures are extremely difficult to diagnose because they
standards frees the development of new telematics ap- are often not present when the car is brought in for ser-
plications from the somewhat lengthy development cycle vice. In this mode of operation the instrumentation
of a typical automobile model. Furthermore, it offers the computer along with its software reconfigurable display
potential for the aftermarket addition of new subsystems. is serving a role somewhat analogous to a flight data
recorder on an aircraft.

23.1.13 The glass cockpit
23.1.14 Trip information computer
The development of a cost-effective solid-state equiva-
lent of the CRT can have enormous application in auto- One of the most popular electronic instruments for
motive instrumentation. It can yield a completely automobiles is the trip information system. This system
reconfigurable display system similar to the multifunc- has a number of interesting functions and can display many
tion display used in some modern transport aircraft. Such useful pieces of information, including the following:
displays are termed a glass cockpit in aircraft parlance. It
is also known as an electronic flight information system 1. Present fuel economy
(EFIS). 2. Average fuel economy
A single CRT acting as a display for a digital 3. Average speed
instrumentation system has the capability of displaying
any of several choices of data readout, including 4. Present vehicle location (relative to total trip
distance)
1. Navigation data
5. Total elapsed trip time
2. Subsystem status parameters
6. Fuel remaining
3. Attitude (artificial horizon)
7. Miles to empty fuel tank
4. Air data (airspeed, altitude, etc.)
8. Estimated time of arrival
It can also be used for diagnosis of problems with various 9. Time of day
aircraft subsystems. In this case it can present a pictorial
diagram of any aircraft subsystem (hydraulic system or 10. Engine RPM
electrical system) so that the flight crew does not have to 11. Engine temperature
resort to hunting through a manual for the aircraft to
diagnose a problem with a subsystem. 12. Average fuel cost per mile
One of the benefits of an automotive glass cockpit is Additional functions can be performed, which no doubt
its great flexibility. Any message in any format can be will be part of future developments. However, we will
displayed. In fact, the format can be chosen by the driver discuss a representative system having features that are
via a set of switches or by a keypad arrangement. The common to most available systems.
driver selects a particular display format from a number A block diagram of this system is shown in Fig. 23.1-27.
of choices and the display will be reconfigured to his Not shown in the block diagram are MUX, DEMUX,
choice by software, that is, by the program stored in the and A/D converter components, which are normally
instrumentation computer. A likely default choice would part of a computer-based instrument. This system can

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