How does Air Suspension work ?

Thanks for the link, describes the layout well will read more later..

P.S.

You might want to look at the flow diagram as it looks to me as though all the sensors and springs are on the left !!!!!

Rich

Yep.

I don't think the volume of an air spring changes that much for a given height, they aren't just a simple bag. They are more toroidal with the lower connection to a curved cone that is inside the center of the toroid. Take a look at the big air springs under some trucks when the truck is empty to see this.

Each bag is controlled separately and continuously (with a DII even after the car is switched off to some extent). The control is very slugged so bumps and humps don't get air being released or pumped in. The control is for average ride height over a minute or so. Increase the load (say load six bags of cement into the back) and the bags will compress the ride height drop and the ECU fires the pump (if engine on) to increase the pressure and restore the height.

Take out the cement, the springs expand with the lightened load, ride height increases, ECU opens exhaust valve(s) to lower the pressure and thus height. A DII will do this several times as you off load the back end.

If you raise or lower the pressure without changing the load you can adjust the height of the vehicle. On the DII the "off road" switch lifts the back end a couple of inches from normal and you can get an optional key fob that will allow you to lower the back a couple of inches below normal.

Pressure, temperature, and volume are related. It's basic physics (though the temperature has to be measured on an absolute scale, with zero at about -273.16 Celsius). Part of the reason for the more complicated bag shape is to get the total volume big enough, compared to the changes arising from wheel/axle movement. Get too small a total volume, and things get hot too quickly. But the details of that are not quite so basic physics.

I'd hazard a guess that the shape of the air springs is related allowing flexibility without the "rubber" (let's not start that one again!) splitting. I also can't see the variables above being of great concern - the system (allowing for hysteresis) is far more simple - the sensor says the corner is lower than the target so more air is added until it isn't - and air is let out if over height.

Richard

On or around Sun, 31 Dec 2006 09:09:40 +0000 (GMT), snipped-for-privacy@zhochaka.org.uk ("David G. Bell") enlightened us thusly:

yeah, but for a given ride height unless the bag itself expands and contracts (which I assume it does to a small extent) then the pressure is the thing that varies most. Presumably, adding air raises the temperature, and this increases the pressure as well. Contrariwise, venting air from it should lower the temperature.

when it's actually working, due to bumps in the road, then compressing it will reduce the volume and thus increase the pressure and temperature, while decompressing will decrease the volume and reduce the pressure and temperature, so on the average I'd not expect it to heat up much.

This is true but the volume and temp are not changing a great deal in an air spring. As the ride height is being maintained at the same level the distance between top and bottom plates is, in the longer term, constant. Therefore the spring has the same shape and thus volume.

The temp will probably rise from ambient under the repeated compression/expansion bumps/humps but I'd expect it to become fairly stable after a while, unless road conditions change (more or less bumps/humps).

This just leaves the pressure to be adjusted to affect the ride height.