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Thermorheological Dampers

Use Peltier elements to modulate oil viscosity in damper valves
  [vote for,

The average car rides around suspended above the wheels with springs. To prevent even the slightest perturbation sending the car bouncing around, hydraulic dampers are usually fitted. There are lots of variations, but for the most part, movement of the wheel relative to the main body of the car forces oil through small holes.

The oil is viscous and resists movement in a manner proportional to velocity. To adjust how much damping force, or resistance to force, you can either change the viscosity of the oil or the size of the holes. You can do clever things with valves and so on to change bump and rebound damping independently but essentially, once you set up your dampers they're staying like that, and you will likely never have absolutely perfect damping for any given conditions.

One solution to this, is magnetorheological damping <link> found on a select few cars. This uses iron particles suspended in the fluid with a some form of proprietary detergent. This behaves in a conventional manner in the absence of a magnetic field. However, by putting an electromagnetic coil around the valve area and energizing it the iron particles align in the damping oil and you get a fairly profound increase in viscosity.

Now you have two damping rates, energized and resting. you can even get clever and quickly switch the field on and off to operate a pulse-width modulation type effect and get an approximation of damping between on and off. Sadly there are disadvantages with the system. Firstly, it's banned in many forms of motorsport*, it's expensive, there's probably not a lot of choice in magnetoreheological fluids, who knows how long they last and er... they'll likely turn out to be abrasive or horrifically toxic or something.

So, my solution. The holes through which the oil flows will be temperature controlled. Temperature is a well understood way of modulating viscosity. We're going to use little tiny Peltier elements to heat/cool the very small volumes of oil passing through the small holes. Standard shock "pistons"** have quite large holes, but then there's often stacks of spring washers to restrict that and get variable rates. Instead, we optimize oil viscosity and hole size down as far as possible to reduce the amount of thermal work needed. Now we can rapidly heat and or cool the oil in transit and modulate its viscosity up and down without all that nasty iron. A clever part would be to mount Peltier elements in such a way that they are able to pump heat into or out of the shock oil as a whole. Often, off road racing shocks have a heat problem.

*which is absolutely fine for all the OTHER teams ** annoyinly, the holes are stationary and the oil moves in many cases.

bs0u0155, Mar 12 2018

Magnetorheological Dampers https://en.wikipedi...orheological_damper
[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.
8th of 7, Mar 12 2018

       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?
MaxwellBuchanan, Mar 12 2018

       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.
8th of 7, Mar 12 2018

       //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 ratio.   

       *I wonder how much of the list price on a Ferrari is insurance against being sued...
bs0u0155, Mar 13 2018

       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.
wjt, Mar 16 2018

       // cat's whiskers //   

       If you want to experiment, we have several sacks of those that we keep as trophies. You're welcome to a few kilos.
8th of 7, Mar 16 2018

       I saw something in a magazine (quite likely Popular Science or Popular Mechanics) a while ago (probably around ten years) about a prototype car (I think by Mercedes–Benz) that used lidar to scan the road ahead and proactively adjust its suspension damping. They did a demo of it where they balanced a glass of water on the back seat and drove along a pothole test track without spilling any.   

       Why not just adjust the valves rather than trying to heat/cool the liquid, which will be slow and will not have much effect on viscosity, according to my intuition?
notexactly, Mar 25 2018

       I found a simple way that allows a brim-full glass of gin to remain unspilled after a three-mile drive over bumpy roads. Just drink the fucker first.
MaxwellBuchanan, Mar 25 2018


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