Thermorheological Dampers

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.