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      03-21-2013, 08:26 PM   #100
drob23
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Quote:
Originally Posted by walile View Post
Also got some homework for you.

1. Please describe the system and explain why it is a feed forword control structure. List the input, output, and disturbance to the system.


2. If an active rear differential uses feed forward control structure, then does an active center differential also employ feed forward control? Why or why not?
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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