Cruise control ethrottle table

[UnknownMiscreant]

Hi,

I'm currently playing around with cruise control on a Mini R53 running a MiniLinkX ECU (1.6L supercharged)

While trying to tune the cruise PID I ran into problems with getting it smooth across a range of speeds due to dramatic differences in engine torque at lower RPM. The controller needs to be much more aggressive to maintain smooth operation at town speeds (50km/h) than at highway speeds of 100km/h.

I have created a second e-throttle table to use to add some aggression to the throttle curve at low RPM, but directly copying the existing APS vs RPM table (predictably) didn't change the throttle plate behavior.

Is there a variable I should use to setup a cruise control e-throttle target table other than APS? I can't see anything that looks likely. I saw someone suggesting doing something similar in a G4+ thread but no info about whether it worked.

The e-throttle controller is setup and about as good as I think it'll get. Step change isn't perfect, but I can't get it going much faster without introducing oscillation. The brake and clutch switches are setup and working. The cruise buttons are being passed in over CAN from some electronics I designed to translate the PWM output from steering wheel buttons.

I've attached the map and a zipped PC log. Cruise is used for 15seconds at 2:40. I stopped using it after that as I wanted to keep the throttle steady state to try refine the fuel map. Can do some screenshots of relevant parts if you let me know what variables you want to see.

Thanks in advance

current - Copy.pclx

PC Datalog - 2022-08-15 4;02;23 pm.7z

[Adamw]

One problem I see is you have idle control kicking in and out during cruise so that's pulling a lot of timing out.  Set up the speed lockout should solve that.  

Secondly, Im not very familiar with the mini engine, but the ignition advance seems very low at low load cruise speeds, has the ignition been tuned to MBT?  For example in our subaru at 2000RPM 40kpa I have 39deg advance, yours has 28.

So those changes may help some, but I think you will struggle to achieve great cruise control at 1500RPM in anything except a big lazy V8.  

 

 

1 hour ago, UnknownMiscreant said:

Is there a variable I should use to setup a cruise control e-throttle target table other than APS? I can't see anything that looks likely. I saw someone suggesting doing something similar in a G4+ thread but no info about whether it worked.

Im not sure off the top of my head how much effect the E-throttle target has on cruise control as Ive never really needed to think about it, I assume the PID loop controls the throttle plate set point directly, but there must also be some blend that goes on in the background between driver commanded and ECU commanded under some conditions as it is a smooth transition if you give it some pedal when cruise is active.  My suspicion is if pedal is sitting at zero then the E-throttle target table probably has no effect.  You could try adding say 5% to the e-throttle target when cruise is active to see if it has any influence.  

If the target table does actually have an influence then you could set up a math channel "Cruise set speed - driving wheel speed" to generate a cruise speed error value, then put this on the axis of your throttle target.  

 

[UnknownMiscreant]

Thanks Adam, much appreciated.

54 minutes ago, Adamw said:

One problem I see is you have idle control kicking in and out during cruise so that's pulling a lot of timing out.  Set up the speed lockout should solve that. 

I will try it. I didn't set that up as its primarily a road car so I wanted to make sure it would keep a decent idle while rolling out of gear.

58 minutes ago, Adamw said:

Secondly, Im not very familiar with the mini engine, but the ignition advance seems very low at low load cruise speeds, has the ignition been tuned to MBT?  For example in our subaru at 2000RPM 40kpa I have 39deg advance, yours has 28.

No it hasn't. The map is a pile of garbage. I got it done remotely as local dynos were booked out when I first got the ECU (yes I should have waited.) I've had to fix quite a few basic things on it myself... best one was a vac leak the guy blamed on intercooler boots but turned out to be dashpot.... I'm going to take it up to SAS after I get the last of the mods done to it and get it tuned properly.

1 hour ago, Adamw said:

So those changes may help some, but I think you will struggle to achieve great cruise control at 1500RPM in anything except a big lazy V8.  

I did manage to get it working really well if I tuned the controller for it (just sucked at 100km/h). It easily cruises around town at 1500rpm (granted CHC is pretty flat). But yes I get your point a boosted 4pot isn't exactly a torque monster lol

1 hour ago, Adamw said:

Im not sure off the top of my head how much effect the E-throttle target has on cruise control as Ive never really needed to think about it, I assume the PID loop controls the throttle plate set point directly,

In my so far limited testing it seemed inconsistent. I initially had tables 1 and 3 identical, and then while driving I edited table 3 to what it was in the attached map - it seemed to change how the cruise behaved as I edited values. Noticed the crosshairs never moved from 0 though. I did a store before powering down.

When I drove the car again later that day the cruise felt worse again. I haven't tested it enough to definitively say whether the its a bug in the ECU software but it certainly seems suspicious. Is this something you'd be able to have a play with on a simulator to verify? It seems like rather a corner case.

I also have a logfile from when I played around with e throttle table 3 but even compressed its too large to upload into this thread - only have 3MB left apparently.

[Vaughan]

15 hours ago, Adamw said:

Im not sure off the top of my head how much effect the E-throttle target has on cruise control as Ive never really needed to think about it, I assume the PID loop controls the throttle plate set point directly, but there must also be some blend that goes on in the background between driver commanded and ECU commanded under some conditions as it is a smooth transition if you give it some pedal when cruise is active.  My suspicion is if pedal is sitting at zero then the E-throttle target table probably has no effect.  You could try adding say 5% to the e-throttle target when cruise is active to see if it has any influence.  

Uses the larger of the cruise and the combined E-Throttle Target Tables/ISC/Torque etc

I have noticed when playing with my MR2 (big 3.5l v6) that it tends to surge a little at 100kph but I haven't spent a whole lot of time tuning it's cruise control

[UnknownMiscreant]

5 hours ago, Vaughan said:

Uses the larger of the cruise and the combined E-Throttle Target Tables/ISC/Torque etc

I have noticed when playing with my MR2 (big 3.5l v6) that it tends to surge a little at 100kph but I haven't spent a whole lot of time tuning it's cruise control

Thanks, that explains the behavior I was seeing perfectly. Bumping up the ethrottle target table base smoothed things out a bit by lowering the dips on the TPS oscillations.

Are there any other potentially hacky things I could do to try to alter the aggressiveness based on RPM? Only thing I can think of is putting the Ethrottle target on the y axis of a target table, but I think all that'll do is earn me a Darwin Award!

[Adamw]

Before you waste too much time on it I would first get it tuned so its torque output is more optimised and has a better relationship to throttle.  In your log the throttle is moving between about 6% and 26% just to maintain 50kmh.  You should have a huge increase in torque between 6% and 25% throttle, so something seems very wrong there (the idle ign def wouldnt have been doing you any favors).  A typical torque to throttle relationship curve shown below, the torque numbers arent relevant but the exponential curve is always there with a butterfly throttle.  Looking at logs from our subaru at 50kmh cruise the throttle is between about 8-15%, ~1900RPM (not sure if 4th or 5th gear).  At 105kmh it is much the same, around 10-16% ~3600RPM (suspect 5th gear). 

 

This is just a random log I had on my PC, 3mins of west auckland motorway driving so it is certainly not flat road.  The largest error in speed vs set speed after the 8:40 mark where I bumped the set speed up is 0.6kmh across the whole 3mins.  You could get speed control even better than this but fuel economy takes a hit with the throttle working harder. This log was from some early testing before we changed the way the feedfoward is applied at the initiation of cruise which is why you see the spike in proportional and a small speed error at the start of the cruise then a large integral for the rest (throttle used to initially drop as you lifted off the pedal).  Initiation is now much nicer than this and no integral wind up.     

[UnknownMiscreant]

21 minutes ago, Adamw said:

Before you waste too much time on it I would first get it tuned so its torque output is more optimised and has a better relationship to throttle.  In your log ..........

I think you're right. I'll get it tuned on a dyno and then waste time sorting this out. The ignition table looks scarily similar to the R53 base map you guys provide.

The enable and resume already behaves very similar to OE cruise. Sort out the torque curve and it'll help with everything else.

Thanks for you help - much appreciated. I've lurked on here and the FB group for a while and your input is always valuable.

[Stevo79]

Hi,

Just wondering if you managed to get the Mini OEM Cruise Control to work with the Link G4x properly at all? If you did, what sort of interface did you use?

 

 

 

 

 

 

[UnknownMiscreant]

9 hours ago, Stevo79 said:

Hi,

Just wondering if you managed to get the Mini OEM Cruise Control to work with the Link G4x properly at all? If you did, what sort of interface did you use?

I've replied to your DM.

Figured I'd do it there as I'm not sure what the rules on here are about selling stuff.

[Thomas Barnes]

I used the Link 4 way Key pad, My cruise works amazing. Even on a turbo converted engine with less torque low down.

[UnknownMiscreant]

Good to know you managed to get it working well on a turbo swap.

I only built an interface as I wanted to stick with the OE buttons, it also doubled as a simple way of getting exterior lights onto a CAN frame for a custom tach project. I wasn't feeling like tapping the BCU wiring lol

[RandomChap]

On 1/2/2023 at 3:57 PM, Thomas Barnes said:

I used the Link 4 way Key pad, My cruise works amazing. Even on a turbo converted engine with less torque low down.

Can it be done if the MINI didn't have a cruise already?

[Adamw]

The easiest option is probably a CAN keypad as Thomas did.  

[RandomChap]

Ah, ok, that's a good idea. It was more so if the MINI needed the OEM cruise wiring in the car already or the Link supersedes that and I can just use the ECU to control it and add it to a non-cruise car, that's the dream 

[Adamw]

The minimum requirements for cruise control to work are; electronic throttle, a driving wheel speed input, a brake pedal switch and the cruise switches.  Your car has all of those in stock form except the switches, so you just need to add something that can act as the switches and you will be able to have cruise control. 

The factory mini cruise switch is a bit of an odd one that used a K-line communication to talk to the factory ecu which we currently dont support, but any CAN bus, analog or digital type switch can be used.