I am new to this forum, but I landed quite a few times on it in some researches on google. I am freelance motorsport engineer currently working at WRT (Belgian GT3 team) as a data-performance engineer.
Recently, I have been trying to better understand the LSD principle and especially the Salisbury differential, as it is the type that we have on our Audi R8 LMS's. I think I have captured most of the working principle, but there is something I can't get my head around, or at least it seems that I am the only one understanding it this way.
So my point of doubt is the action of the differential under heavy braking. What I usually understand from any article is that the differential is on the coast ramp when the car is decelerating, then on the preload (if any) off throttle around the apex and finally on the power ramp on throttle. Now I don't really agree with the coast side thing. To me, you get on the coast ramp only if your engine is effectively braking your wheels, so off the brakes and off throttle (or at very little throttle, not enough to overcome the inner friction). To me, under braking it has to be on the power ramp as well, since the deceleration off the wheels is higher than the natural deceleration of the engine itself, so the brakes are also dissipating the energy stored in the flywheel and hence it is the same case as when the power is delivering torque, because the wheels are trying to slow down the engine in both cases.
If I am right, it means that the coast ramp is a lot less important than the power ramp because it is only active for a very short amount of time in a usual cornering manoeuvre, and it might even never be the case, if the rolling resistance of the wheels is very high (high toe in/out, highly preloaded caliper springs,...) so that the engine back torque is not capable to reach the same magnitude.
Does that sound logical or am I completely off ? Now there's also the fact that the braking torque is so high compared to what the engine delivers, that the differential is locked for sure until the brakes are already well released, to maybe it barely crosses the power ramp before switching to the coast side.
Thanks in advance for your replies !
Last edited by JH_WRT on Thu May 25, 2017 12:19 pm, edited 1 time in total.