Quote:
Originally Posted by drob23
Thanks professor!
Here you go
1) It is a feed forward control system because it does not need to track reference signals. The system is not unstable to begin with, thus it can be appropriately tuned open loop.
driver input y_1 = [SWA; throttle] sensor y_2 = [vel; yawRate]
measurement y = [y_1; y_2]
input u = [torque R/L]
disturbance d = n/a
It's actually an open-loop controller because there really is no disturbance. Mitsu is the only company I'm aware of that tries to track a reference yaw rate, so it can be done closed loop. It takes some kind of nonlinear combination of the ABS, active center diff and rear active diff.
2) The center diff uses a combination of feed forward and feedback control. The feed forward component functions similar to sports rear diff, when you mash the gas (torque goes rear) or turn the wheels (torque goes rear), torque will be appropriated as needed.
On the other hand, the most worrisome disturbance it rejects is the loss of tractive force. This is not know a priori, there is no knowledge of when the road will be slick, this can only be calculated by the vehicles stability control system which employs a Kalman Filter to estimate wheel slip through ABS sensors. The center diff receives this information via CAN.
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First of all, I sincerely apologize to everyone for
I have to be honest, I went out for a Tim Hortons coffee and comeback impressed. Makes me wonder if it's the same person. Just want to point out that
- There is at least one active rear differential implementation that track reference signals but the control algorithm is very tightly coupled with the entire AWD system and it's not Mitsubishi. I think we can agree that you can have both feed forward and feed forward + feedback design.
If Audi Sport Differential is a simple feed forward system, to be honest I am surprised. At this day and age, it seems a bit primitive. But then again, it doesn't have active center diff to dance with. Might as well KISS.
- I philosophically disagree with the Porsche implementation.
Braking system IMHO should be used for reducing vehicle speed or ESP applications, not to help it go faster! Even though I do acknowledge some advantages of that design. Namely the cost and weight saving.
- We certainly have a fundamental philosophical disagreement on system design.
To me, a Torsen or crown gear based system is both primitive and inferior. Sure it's the feed-forward control design that you love so much. But what it really is saying is that
hey all the behaviors of the system is programmed mechanically into the design and is passive in its nature.
As you pointed out yourself that ideally you want less power to the front wheels during corning. Well, can the Audi system proactively shift more power to the rear as steering input is detected? NO!
The GTR ATTESA E-TS is an incredible system, certainly did not archive such incredible performance using a simple feed-forward design.