Environmental Engineering Reference
In-Depth Information
its headers and trailer information, does the requisite processing and passes the
data packet onto layer 3 etc. up to layer 7. As a result of all this processing
the original ACAD drawing sent by computer A arrives at the application running
on computer B.
The point of this example was to illustrate that the FTP server on the Micro-
systems workstation running the Solaris operating system is not required to even
know that the Dell Hyper-Threading PC at node B is running Microsoft Windows
2000 Professional. The file is transferred flawlessly. This same need for flawless
and fault tolerant communications is present in the automobile networks, but the
consequence of a 'lost' data packet is far more serious when the data packet was
sent from the vehicle system controller to the hybrid M/G to command generating
mode at torque level
T
x
to slew the engine speed down while simultaneously having
commanded the engine electronic throttle control to reduce airflow and com-
manding an upshift to the automatic transmission during vehicle acceleration.
Communications architecture in the future automobile will be an open system
so that any supplier can build modules that connect to the published network
standard and its function will execute flawlessly. Vehicle powertrain controls today
follow the OSEK operating system (Offene Systeme und deren Schnittstellen fur
die Elektronik im Kraftfahrzeug). Engine controllers have progressed from 8-bit
cores having 128 kB of ROM, through 16 bit 256 kB engines, onto today's 32-bit
chips supported by 512 kB to 1 MB of ROM.
4.6.1 Communication protocol: CAN
During most of the early years of electronic engine control and for hybrid propul-
sion technologies, some form of CAN communications between the various sub-
systems has been in use. Early SAE standards categorized in-vehicle networks
according to data handling speed. Setting a standard based on data handling speed
in effect determined the types of devices that could be served and the types of data
communication protocols that could be applied. Early hybrid propulsion commu-
nications architectures relied on class B and some provision was made for class C,
CAN, where very fast data exchange was necessary, such as in the powertrain
controller. Class A is a low speed protocol used primarily for in-vehicle body
electrical functions such as power seat and power window controls. Protocol's on
class A networks include local interconnect network (LIN) and TTP/A.
Class B networks are designed for data sharing between devices in the hope of
minimizing if not eliminating redundant sensors - for example, instrumentation,
speed control functions, emissions systems and others. Class B network protocols
include ISO 9141-2 and SAE J1850.
CAN class C network protocol was developed for real time control applica-
tions, hence the reference to powertrain control functions. Also included in class C
protocol is vehicle dynamics control. Protocols listed under class C are CAN and
J1039.
The various in-vehicle network classes are described in Table 4.23 along with
typical in-vehicle applications served.
