Path: utzoo!utgpu!attcan!uunet!convex!killer!mit-eddie!mit-amt!mit-caf!fritz
From: fritz@mit-caf.MIT.EDU (Frederick Herrmann)
Newsgroups: sci.electronics
Subject: Re: ??: computer-controlled engines
Message-ID: <1202@mit-caf.MIT.EDU>
Date: 4 Aug 88 02:50:54 GMT
References: <7200006@silver>
Reply-To: fritz@mit-caf.UUCP (Frederick Herrmann)
Organization: Microsystems Technology Laboratories, MIT
Lines: 42

In article <7200006@silver> commgrp@silver.bacs.indiana.edu writes:
>I've heard the following rumors about digital engine-control 
>computers:

>4.  Radio-frequency interference can jam the computer, causing various 
>effects like engine stop or full throttle.  This definitely happens 
>with radio transmitters mounted in the car; there was a long 
>discussion of it on rec.ham-radio last year.  Manufacturer's 
>recommendation: Don't install any 2-way radios. What happens when you 
>are next to a semi with a 100-watt CB "linear" amplifier??

In '86 I was a summer student at the GM proving grounds in Milford MI,
working with the electromagnetic compatibility (EMC) group.
(Disclaimer: I didn't speak for GM then, and I don't now).  GM does a
lot of testing to try and make sure problems like this don't occur.

Radio-frequency tests are performed by parking vehicles in large
anechoic chambers and zapping them at various frequencies, amplitudes,
and antenna configurations; and tests for mobile transmitters are
performed outdoors in a specially constructed shed with no metal
parts.

Tests are also performed with 60 Hz magnetic fields, as might be
encountered around power lines, and with electrostatic discharge
simulators to make sure you don't fry the stereo when you scoot your
fanny across the upholstery.  The worst case for ESD is when you get
out of the vehicle, and then reach back inside to flip a switch.
Charge in conserved, so when the capacitance goes down the voltage
goes up (Q=CV).

It should be noted that the engine control unit is also a source of
EMC trouble.  Digital designers go for more computing power and faster
clocks, but those fast rise times have significant high frequency
components that can cause problems for other electronic parts.

While I was there, GM was interested in using more component-level
bench tests, since they are easier to perform than whole-vehicle tests
in anechoic chambers, but I don't know how actively they are pursuing
that idea.

Frederick Herrmann
fritz@caf.mit.edu