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| Traction Control http://gemellocattivo.com/forum/viewtopic.php?f=19&t=290 |
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| Author: | mk e [ Thu Dec 15, 2016 12:08 pm ] |
| Post subject: | Re: Traction Control |
I took a look in the motec manual and it appears all they do when TC is armed is look at the current speed, allowed slip, and gear then clculate what engine rpm that is and set the rev limiter to that rpm. Done. No tuning anything. There is somehting to be said for simple I suppose 
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| Author: | mk e [ Thu Dec 15, 2016 1:27 pm ] |
| Post subject: | Re: Traction Control |
Here's my thought.....I like using the throttle but don't like the idea of needing to tune a PID So my thought is to take an approach similar to the motec which progressively kills spark but progressivley remove throttle. So really they have a window of slip with 0% spark cut at one end and 100% spark cut at the other of the window and they interpolate in the middle I would assume. A very simple proportional control and they don't care that they ever get to target, just stay between the limits. With the throttle that would just become an interpolation between driver requested throttle and closed.....so it can only be closing the throttle. This a little simpler in that they need to know what gear the car is in to calculate the rpm but with this system that wouldn't matter. |
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| Author: | apalrd [ Thu Dec 15, 2016 2:13 pm ] |
| Post subject: | Re: Traction Control |
You could use an over-rev controller similar to idle control in principle (except lowering max TPS instead of raising min TPS). Then you could tune the controller by setting a rev limit, going WOT, seeing how it reacts, going back to idle, ... with no load or rolling load but without breaking traction. This would always control to the rev limit directly, which is calculated from the target slip, so the target slip should be held perfectly. |
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| Author: | mk e [ Thu Dec 15, 2016 3:29 pm ] |
| Post subject: | Re: Traction Control |
I think it's going to react differently in each gear, depending on lateral acceleration and available traction (wet/dry/cold) and rpm (available torque).....righterent rate of change/responce so differnent PID factrors. That is what I'd expect anyway I think? I'm also pretty uncomfortable with the ECU opening the throttle when the engine at power and vehicle at speed......I'm leaning toward the way less perfect motec like method where the function can only close the throttle or release control back to the user. hmmmm....making sure the user knows TC is active also seems important as does how exactly the system disengages. |
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| Author: | mk e [ Fri Dec 16, 2016 10:15 am ] |
| Post subject: | Re: Traction Control |
I wrote something yesterday that seems to work to calculate a throttle posiotn based on slip using the high slip throttle = 0 low slip throttle = 100% of user request I don't know how well it will work in practice...ignition kill is very fast and responsive and my fear it the throttle isn't. The code is the same really except 1 line to do throttle or ignition control so I guess I'll finish the work to have TC engage (right now Icalulate it but don't use anywhere) A soft rev limiter could be done the same way. EL has a setup to vary spark or fuel cut probabiliy to for soft limits but the documentation is a bit weak on how to implement it so I haven't .....but again it could really be the same code base whether throttle, spark or fuel. Looking at the TC engage in motec they want in gear vehicle moving Check that the setting are valid Pretty simple really........ |
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| Author: | apalrd [ Fri Dec 16, 2016 12:19 pm ] |
| Post subject: | Re: Traction Control |
I think a rpm-holding PID should be able to rev limit well in all conditions. Possibly using a soft-spark retard feature to help it along if it overshoots too much. The over-rev control can still provide a throttle limit instead of a direct throttle command. You could even have it latch the current command when slip is detected so it doesn't have to bring the limit down suddenly. |
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| Author: | mk e [ Fri Dec 16, 2016 1:49 pm ] |
| Post subject: | Re: Traction Control |
I probably don't have a choice. Iput the simple code in for the rev limiter and it oscillates pretty bad in the simulator, much worse than a hard fule or spark cut do. The way I calculated the throttle posiiotn is to multiple the driver comand by a factor that is clamped 0-1.....so the most it can ever be is what the driver is asking for. I'll add a PID to control the fractor, still clamped 0-1. |
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| Author: | mk e [ Fri Dec 16, 2016 4:04 pm ] |
| Post subject: | Re: Traction Control |
I got something kind of working for rev but you have to come up pretty slowly to stop from hitting the hard limiter several times before the PID gets control so it's more a suppliment then an actual control and I'm not so sure it added value. Now it could very well be my simulator is not deceling as fast as it should and this think is working better than the sim is saying......it certainly would prevent you from hitting the hard limiter at the end of a straight and unsettlying the chassis just before the corner. I don't know...... |
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| Author: | apalrd [ Fri Dec 16, 2016 5:14 pm ] |
| Post subject: | Re: Traction Control |
I would play with it in EL but my main computer is a Mac. How does the simulation handle the throttle and airflow into the engine? With a 'normal' plenum intake, you could add a 'quick fill' throttle target adder which sets the throttle over-open or over-closed to reach target MAP more quickly, but that shouldn't be a problem with ITBs. |
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| Author: | mk e [ Fri Dec 16, 2016 7:18 pm ] |
| Post subject: | Re: Traction Control |
apalrd wrote: I would play with it in EL but my main computer is a Mac. is that even allowed for anyone calling himself an engineer?  apalrd wrote: How does the simulation handle the throttle and airflow into the engine? With a 'normal' plenum intake, you could add a 'quick fill' throttle target adder which sets the throttle over-open or over-closed to reach target MAP more quickly, but that shouldn't be a problem with ITBs. It a power generated minus power used. The power used is friction and pumping losses which are based on the BMEP formula... times 2 because it didn't seen enough...so it's a bit of a guess. The flow is based on TPS and available flow area, and some tables to convert to MAF and then MAF to MAP...which feeds the pumping losses. Right now the throttle stay open until it hits the limit (as you want on a performance setup) but then simply can't react quickly enough to close it so it hits the hard stop and bounces the throttle closed in 4-6 bounces. I may do something to prime the PID so when it hit the soft limit it slams the throttle shut. It works with a less violent input, but WOT in neutral with a powerful engine....it bounce a bit playing catch up. |
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