TRACTION CONTROL SYSTEMS
Historically, it was always supposed that you could never have
enough of a good thing. One immediately thinks of the Bible (one
does, doesn't one?) and Proverbs chapter 9, verse 9 - "Give
instruction to a wise man, and he will be yet wiser".
There comes a stage in motorcycle development when huge power
becomes too much power, and bikes go from being challenging to
being unrideable. Power corrupts; absolute power corrupts
absolutely. Maybe Kenny Roberts had this in mind when he asked
that a set of 500 barrels be fitted to his TZ700; with less power
to corrupt the handling, he lopped several seconds off his
laptimes. It's no use having the power if you can't use it. We in
the FB office, insecure inadequates as we are, constantly
emphasize that size doesn't matter, it's not what you've got it's
what you do with it, it's not the meat it's the motion, etc etc.
Engines have the same problems, and traction control is a way of
stopping them shooting off prematurely, so to speak.
It seems a little strange to be writing an analysis of a system
which has not yet been used on racing bikes, and has only ever
been seen overtly in the two-wheeled world on the Honda Pan
European (of which more later), but we'll certainly be seeing
more of it in the future and FB is first on the case.
TCS is not new; I have worked on TCS on cars, and have driven
cars so equipped. I am also working on a system for a bike team,
no names, no pack drill. There is talk of Aprilia testing a
system, but I don't know anything about it and can only speculate
as to what it might be, not what it is. Of course, if I were
writing Muck, Crap, and Nonsense I would speculate a load of
half-baked tosh and call it a scoop.
The concept of traction control is easy; when the rear wheel
spins, have an automatic system for reducing the power to it
until it gets its grip back. The rider or driver can therefore
smack the machine on to 100% throttle as soon as he's by the apex
of a corner in the sure knowledge that he won't be spat off. It
sounds too good to be true, and it probably is.
After extensive research, the first instance of the use of
traction control that I can find was on diesel-electric
locomotives. In the old days, the steam locos had all of their
driving wheels linked together, and drivers became highly skilled
at operating the regulator for best acceleration without wheel
slippage. When diesel-electrics took over, this became much more
difficult; there were electric motors on each axle, and some
could be slipping madly while others were gripping well. The
driver couldn't tell as all he could hear was the diesel engine,
which was governed to run at constant speed.
There is a story of a train driver sitting happily in a long
uphill tunnel (a real one, not a Freudian dream) in the north-
east with 60mph showing on his speedo, who was actually doing the
railway equivalent of a burnout, but couldn't tell because it was
so dark. He shat himself when a track worker standing by the
line tapped on the cab side window and shouted "Sloo doon, marra,
ya graindin' hules in worr reels!".
In coalmining areas (younger readers may not be familiar with
these, and should ask an adult) a train was used to transport
coal from the pit to the power station. The sophistication of the
process was such that the train never actually stopped; at each
end of the journey was a circular track called a "merry-go-round"
where the wagons were loaded or unloaded automatically as the
train went by at a steady 1 1/2 to 2mph. The train was entirely
under computer control and the driver could step down for a tea-
break.
The problem was that the speed had to be maintained absolutely
constant, or else the wagon loading/unloading process would be
wrecked. This could not be achieved by running the electric
motors in the wheels at constant speed or constant power because
the powdered coal meant that there was very little grip and the
drag of the wheels could go up and down suddenly as the wheel
flanges graunched on the curved rails.
The cure? A traction control system. By running speed sensors on
both driven and undriven wheels to detect slippage, power could
be diverted from those wheels which were spinning to those which
had good grip or were dragging their flanges, all of the while
referencing the actual speed back to the 1.5-2mph safe limits. In
addition, axles which were spinning madly had their brakes
applied automatically as well as having their power taken away,
pioneering two methods of traction control which were taken up
by the automotive industry later.
The price of this technology was an outrageous L3/4m, and this
was in 1970, the days when for 10 shillings you could go to the
cinema, have a couple of pints of Scruttock's Dirigible
Grumblebelly, 10 Players Gaspin Full Strength, a good blow job,
and still have change for a bag of chips and a pickled egg on the
way home. By heck, them were the days (I was six at the time).
A computer which weighs and costs as much as a First Division
footballer is not a big deal on a freight locomotive, but the
automotive industry was not overly interested until the 1980s,
when computers ceased to be kinky and were actually becoming
quite erotic. (Definition: "Erotic" is something sensual and
beautiful which you can do with a single feather. "Kinky" is when
you have to use the whole chicken).
In the 1980s, a crude traction control system appeared (though it
was kept secret at the time) on the cars of the Toleman-Hart
turbo F1 team, which were underfinanced but brilliantly
engineered. With not much less than 1,000bhp available from a
1500cc four-cylinder engine, the cars of this era were something
of a handful, to say the least. Brian Hart and Zytek (who made
the electronic engine control unit) came up with a way of
monitoring the front and rear wheel speeds, and opening the turbo
wastegate to dump excess power if too much slippage was detected.
By today's standards, this was a very slow and crude way of doing
the job, but it worked.
Although initially only intended for use at the starting line,
during a rain-soaked 1984 Monaco GP it allowed Ayrton Senna (then
nothing more than a prospect for future greatness) to haul in and
catch the race leader, the then near-invincible Alain Prost in
his McLaren-TAG/Porsche, just as the Clerk of the Course (Alain's
old mate Jacky Ickx) decided to stop the race due to the
"dangerous conditions". According to the rules, the result was
declared as the order on the previous lap, thus scandalously
robbing Senna of his first GP win.
Other F1 teams did not leap to follow Toleman's lead, possibly
because they didn't twig what Harty was up to, but also because
they knew that new regulations for normally-aspirated engines
were coming shortly, and it was supposed that traction control
would then not be necessary. In fact, the 3500cc normally
aspirated engines were only a season or two old when power
outputs were again over 700bhp and ways had to be found of
reducing the power when there was excessive tyre slippage.
Of course, it's easy enough to say "reduce the power when there
is excess slip" but how do you reduce the power, and by how much?
How much slip is too much? Is there a "correct" amount of slip?
In the car world, it is accepted that the tyres will run at
relatively large slip angles for best grip. (The slip angle is
the angle between where the tyre is pointing, and where it's
actually going. There needn't be any sliding at small slip
angles, because the tyre sidewalls will squidge around to
accommodate the difference).
If the car's well set up, the driver ought to be able to hold it
in a slight four-wheel drift (ie optimum slip angle on all four
tyres) out of most corners, certainly the medium-speed ones. The
difference between 'ard drivers and big girls' blouses comes down
to the ability to drift a car into a bend as well as out of it,
to keep on optimum slip angle for longer, and bottle. Don't be
too quick to dismiss four wheel racers as posing pooftahs (even
though a fair proportion of them are); it's a different world
entirely when you're experiencing more than 3g sideforce - bikes
hardly ever get above 0.7g.
The great thing about cars is that even quite a junior driver can
overcook things a lot, and still expect to gather it all up
again. He might not be fast, but he'll be spectacular and fairly
safe. The novice bike racer, by contrast, only has to go over the
edge a little bit and he'll be finding sand in his snot for the
next week, because bikes, especially those on slicks, operate at
very small slip angles. This is bad news for TCS because the
difference between being right on the edge and having just let go
may well be too ill-defined for a computer to spot. If it chimes
in too early, too late or too frantically, we're looking at a
high-side.
Because of the cars' wide tolerance of slip angles, methods of
power modulation can be fairly crude without making the car
uncontrollable; the bike designer is not allowed such freedom.
Five ways of reducing tractive effort have been tried with
varying degrees of success on cars; using the brakes, cutting the
sparks, retarding the spark timing, cutting the fuel, and using
the throttle.
The simplest, and probably most effective, way of reducing power
momentarily is by switching the sparks off. It's easy for an
engine management system to understand, you can knock it off and
then back on again extremely quickly (one rev of the engine will
last 0.006 seconds) and you can make it progressive by cutting
one, two, or more cylinders. It makes a distinctive d-d-d-d-d
sound, like being on the rev-limiter, and makes you think you can
really feel the tyres nailing themselves down. To floor the
throttle in Mallory hairpin in the pouring rain knowing that you
are on your way to the Devil's Elbow with the last possible ounce
of grip is quite an experience.
There are disadvantages, not all of which are applicable to
bikes. For a start, the jerky action can cause the differential
to get tied up in knots (but bikes don't have diffs, of course)
and there is also a question mark over what it will do for engine
and transmission reliability. Cosworth flatly refused to let
Benetton F1 cut sparks out, on engine longevity grounds. Frankly,
if I were Luciano Benetton I would have stopped photographing
dead AIDS cases, rolled up the sleeves of my baggy green sweater,
said "I pay-a da bills, I cut-a da sparks", and made them an
offer they couldn't refuse.
Retarding the ignition, either on all or just a few of the
cylinders, is a kinder option which also has the advantage of
being very difficult to detect, so some people might speculate
that this is a good way of having traction control when the rules
don't allow it; but I couldn't possibly comment. Certainly, there
are grumblings around the Indycar field that some teams are up to
this trick, and the F1 crowd are watching each other like hawks
(and bickering every now and then) now that "driver aids" are
supposedly banned. This is the system used by the Pan Euro; its
ECU will wind up to 40 degrees off the ignition advance if
wheelspin is detected.
The alternative of turning the fuel off is just as easy and quick
as snuffing the sparks (if you're running electronic fuel
injection, of course) because your ECU can turn individual
injectors on and off at will - and you won't be dropping raw fuel
into the hot exhaust pipe to pop and bang.
The super-smooth way of knocking off power is by having the ECU
take over the throttle control from the driver, so the throttle
itself is operated by a servomotor or hydraulic ram, with the
driver's right foot providing a sensor input for the ECU, which
it will check along with the revs, wheel speeds, g-force, etc,
etc, before it decides how far open the throttle should be.
Speaking as one who knows what it is like to take his foot off a
throttle pedal on the way into a corner, only to find it jammed
wide open (I used to be 6' 2" you know) I'm not exactly thrilled
by this sort of thing.
Well, it's progress, as they say, and I suppose I'll just get
used to it; after all, it's fly-by-wire which stops the Airbus
from falling out of the sky. Ahem. Allegedly. I did actually
design a fly-by-wire throttle for a racing car once; it was
causing me so many sleepless nights as I agonised over the
implications of it malfunctioning that I came up with the idea of
having two separate throttle slides, one above the other. One for
the driver, one for the ECU. That way, the driver could always
shut off totally, even if the ECU didn't want to.
These days, no-one in F1 takes any notice of such niceties; on