h a l f b a k e r y
Renovating the wheel
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The average car rides around suspended above
wheels with springs. To prevent even the
perturbation sending the car bouncing around,
dampers are usually fitted. There are lots of
but for the most part, movement of the wheel
the main body
of the car forces oil through
The oil is viscous and resists movement in a
proportional to velocity. To adjust how much
force, or resistance to force, you can either
viscosity of the oil or the size of the holes. You
clever things with valves and so on to change
rebound damping independently but essentially,
set up your dampers they're staying like that,
likely never have absolutely perfect damping for
One solution to this, is magnetorheological
found on a select few cars. This uses iron
suspended in the fluid with a some form of
detergent. This behaves in a conventional
manner in the
absence of a magnetic field. However, by putting
electromagnetic coil around the valve area and
it the iron particles align in the damping oil and
fairly profound increase in viscosity.
Now you have two damping rates, energized and
you can even get clever and quickly switch the
off to operate a pulse-width modulation type
get an approximation of damping between on
Sadly there are disadvantages with the system.
banned in many forms of motorsport*, it's
there's probably not a lot of choice in
fluids, who knows how long they last and er...
turn out to be abrasive or horrifically toxic or
So, my solution. The holes through which the oil
be temperature controlled. Temperature is a well
understood way of modulating viscosity. We're
little tiny Peltier elements to heat/cool the very
volumes of oil passing through the small holes.
shock "pistons"** have quite large holes, but
often stacks of spring washers to restrict that
variable rates. Instead, we optimize oil viscosity
size down as far as possible to reduce the
thermal work needed. Now we can rapidly heat
the oil in transit and modulate its viscosity up
without all that nasty iron. A clever part would
mount Peltier elements in such a way that they
pump heat into or out of the shock oil as a
off road racing shocks have a heat problem.
*which is absolutely fine for all the OTHER
** annoyinly, the holes are stationary and the oil
[bs0u0155, Mar 12 2018]
||// The average car rides around with suspended above the wheels with springs. //
||You probably want to be taking a bit more water with it, mate.
||Quite frankly, you're rambling a bit. It's not big, and it's not clever, and it would in theory be embarrassing for your friends, if - that is - you had any, which of course you don't. For obvious reasons.
||Hang on a mo, [bs]. Are you changing the damping on the
timescale of individual bumps (milliseconds) or in response
to general road conditions (seconds)?
||Also, why isn't it simpler to have the holey part consist of
two nested holey sleeves, and just rotate one sleeve
relative to the other to change the available hole size?
||Just don't buy him any more, [MB]. Keep him talking while we call him a taxi.
||Don't mention it to anyone else, he's going to be very embarrassed when he finally wakes up tomorrow.
||//Hang on a mo, [bs]. Are you changing the damping on
the timescale of individual bumps (milliseconds) or in
response to general road conditions (seconds)?//
||The control is the key to how well it's going to work. I
imagine that the implementation used by Ferrari is going
to be more sophisticated than, say, Holden. At a basic
level, you can use throttle position or brake sensor to
change the relative damping at either end to counter the
squat/heave forces induced by acceleration or braking.
Then maybe you could feed in steering angle and speed to
firm up compression damping on the outside front and
soften compression/increase rebound on the inside. For a
gold star you can blend it all together have the outside
front softening the inside rear etc. and hope it doesn't
glitch in a litigious way*.
||If you were being even more sophisticated, you might use
the front wheel as a bump sensor for the rear. You might
sense impact and set the car up for emergency braking.
You'd even have some control over ride height at speed,
you could use the constant small bumps to compress the
suspension and really firm up the rebound damping so you
reach a lower equilibrium... oooooh!
||That gives me an idea, place the Peltier between a
compression and a rebound hole, and rather than all
damping you can much more simply use it to fine tune the
||*I wonder how much of the list price on a Ferrari is
insurance against being sued...
||Some sort of sensor, maybe the cat's whiskers, could give road terrain therefore give time for complex processing for shocks. It would add another dimension to all wheel vectoring.
||If you want to experiment, we have several sacks of those that we keep as trophies. You're welcome to a few kilos.