Monoshocks and modal isolation...

Running on from yesterday's slightly cryptic post about modal isolation and the joy of being able to get exactly the right amount of damping in particular modes (getting the right amount of spring stiffness is usually easy). I thought I'd better elaborate. The picture above is from a Force hillclimb chassis (you can tell it's a hillclimber by the absence of just about everything in the search for stuff-all weight) and is about the best photograph I could find of a monoshock suspension. You can see that the two pushrods operate a single bellcrank. When both pushrods are displaced upwards, the crank rotates and moves the coilover unit in bump. When there is differential movement, the crank displaces along its 'axle' against the action of stacks of Belleville washers.

The design shown has two major design issues. There's very little roll movement possible and that movement is undamped. This isn't an issue in a wing-equipped car because you actually want very little roll else your expensive carbon fibre is going to be none-to-gently abrading itself on the tarmac. The absence of damping is an issue. At the end of the day these cars are going to be driven by amateur racers (gifted or not) and it's worth trading a few tenths of a second for driver confidence in the car. A car vibrating around in roll does not normally give a driver confidence.

So, how can we get around these two problems. Firstly we can replace the Belleville stack with normal helical coil springs. With more movement we can get more roll at less loading. With more lateral movement comes more side loading of the coilover unit which is bad, but this is easily curable by using a wider yoke rather than a clevis connect the coilover to the bellcrank. The only way to introduce damping is to fit a damper unit for the lateral movement. I'm thinking of having a Y-shaped bellcrank with a secondary inner arm. This inner arm would be static relative to the rotation of the bellcrank and move linearly with the roll movement. You can then fit a damper to the inner arm, connect it to the body and hey presto, properly damped, modally isolated suspension. and with little weight penalty over conventional two coilovers plus anti-roll bar.

The only other thing I'm considering is to put all this gubbins on the floor of the chassis and operate it by pullrods rather than push rods. A saving in centre of gravity height. In fact the only downside I can see is that corner weighting will be slightly harder as you'll have to preload one side of the roll springs relative to the other to transfer the weight. You do however get very easy ride height adjustment.

So I have a mental picture of how it'll all go together (I don't do visuals except in CAD becuase I'm quite possibly the World's worst sketch artist. I've got to sketch up a couple of dampers and some linear shaft bearings (well I say sketch, when I really mean drag them off of 3dContentCentral - thank you OnDrive) and then I can do a concept model for your general delectation.