Cruise Control Aggressiveness

[mondc95ba]

Hi All,

 

Is there any way of controlling the aggressiveness of cruise control. I have found that a heavier car in a higher gear tends to get on boost and ramp up to the desired speed quicker when already at the designated speed. (i.e Up a hill, on boost to maintain and then off boost as speed increase above set speed, repeating in a feedback loop)

When resuming cruise it tends to be steady and ramp up to speed at a fixed rate.

Is there any PID controlling variables that directly affects the at speed maintaining of speed, is there a torque variable I can limit.
 

[Roland@pcmtec]

Disclaimer: Tuning the cruise control system has the potential to create a dangerous situation. Ensure that any changes are tested in a safe environment.

Yes there is a PID controller which can be tuned for this.

Short answer:

Detune auF10835 Integral Gain

Detune auF10661 Proportional Gain

Reduce the maximum torque request auF11568

 

Long answer:

auF10835 is named incorrectly and is actually the integral gain where as auF10661 is the proportional gain. These parameters are only available in the workshop or 1 car workshop edition.

Note that this is actually a torque controller (the PID outputs a desired torque value). So it requires that your timing and torque tables are correct. You could also "tune" the cruise control by manipulating the torque values in the torque table. Most likely you are making more torque at lower loads than the car did from the factory, so when it commands say 50ftlb of torque it may actually be making 100ftlb of torque.

So two ways to fix it, fix your torque tables (time consuming and difficult without a dyno) or simply detune the loop and lower the gains.

If you want to datalog this you can datalog the following DMRs

MID90655 Torque Error (error term for the PID)

MID90666 Torque Request (setpoint - pre min/max limited and without frictional losses added)

MID90662 Torque Request (setpoint)

MID113140 Torque Actual (control variable - estimated)

MID90562 Current Integral Value

MID90592 Current Proportional Value

 

Some more variables of interest

auF10905 integral max (to prevent integral windup)

auF11568 maximum torque clip. You could try reducing this if you find the cruise control works fine, you just want to limit the max torque it can request. This might be the simplest fix.

 

auF10188 Max acceleration before zeroing out the integrator (you'll probably find this is being hit hence the oscillation)

There are also some fairly complicated quadratic models for how it determines the torque required for a given speed. These should remain accurate unless you have massively changed your CD (eg put a barra in a patrol) and I won't muddy the waters covering them as well. 

 

auF12551 Max acceleration rate vs a given speed. You could also try adjusting this to reduce the rate at which it ramps your speed from actual to the cruise control setpoint.

 

[mondc95ba]

Thanks Roland,

Appreciate the response. I have indeed changed my CD, by that I am guessing you mean car dynamics. It is a barra patrol.

Appears all of the parameters you have suggested changing are workshop edition parameters, I only have the professional extent of the licence. Sounds like auF10188 or auF12551 would be the ideal parameters to alter.

I currently have to operate the car with only 4 gears as the 5th gear has spun on the spline, removed the gear set and shift fork. So with the diff ratio I have at the moment, the car is cruising at 3k at 110km/h this is the problem area and demands the most torque for the speed. God knows how much fuel it consumes repeatedly accelerating also.

at 80km/h the feedback loop isn't as aggressive or I probably don't notice as much because it can't get into boost as easier.

Torque limiting with auF11568 to the torque figure achieved at 80km/h sounds like the way to go. Then it will flatline all the way upto 110km/h.

auF12551 sounds like an alternative to torque limiting but done similar to throttle restricting. Changing it to a more comfortable acceleration rate 4kph increment in 5 seconds i.e 0.8kph.s

 

Edited May 8, 2022 by mondc95ba