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#1
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traction control algorithms
Hi,
I'm trying to gather some information about traction control systems, in particular ABS and ESC. I'm mainly interested in what the inputs are to those systems, and what algorithms the controllers use. I understand they work by applying brake torque to chosen wheels. I'm making a simple car simulation using Pacejka's model and want to simulate those systems and see how they work. So I'm not really interested in the engineering side. I'm sure there are papers or websites that talk about this, any links would be very welcome. Thanks! Michal |
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#2
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traction control algorithms
> I'm trying to gather some information about traction control systems,
> in particular ABS and ESC. Traction control usually cut's fuel to cylinders in a cyclical pattern, and in some street cars it may just retard the spark. Stability control uses individual wheel braking. |
#3
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traction control algorithms
On Dec 12, 5:36*pm, "rcgldr" > wrote:
> > I'm trying to gather some information about traction control systems, > > in particular ABS and ESC. > > Traction control usually cut's fuel to cylinders in a cyclical pattern, > and in some street cars it may just retard the spark. Stability control > uses individual wheel braking. You are right. Replace traction control with stability control everywhere in my post. |
#4
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traction control algorithms
On Dec 12, 4:40*pm, Michal Brzozowski >
wrote: > Hi, > > I'm trying to gather some information about traction control systems, > in particular ABS and ESC. I'm mainly interested in what the inputs > are to those systems, and what algorithms the controllers use. I > understand they work by applying brake torque to chosen wheels. Another question. Does anyone have Pacejka data for one tire model on 2 different sufraces? Like on dry and wet asphalt. Or any idea how to modify the parameters of one tire to change the surface to more slippery. Thanks |
#5
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traction control algorithms
rcgldr wrote:
> Traction control usually cut's fuel to cylinders in a cyclical pattern, > and in some street cars it may just retard the spark. Stability control > uses individual wheel braking. My old car was an Oldsmobile Alero and it had traction control (ETS) and the manual said it used individual pressure on the wheels for traction control which is the opposite of what you are saying. |
#6
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traction control algorithms
>> Traction control usually cut's fuel to cylinders in a cyclical pattern,
>> and in some street cars it may just retard the spark. Stability control >> uses individual wheel braking. > My old car was an Oldsmobile Alero and it had traction control (ETS) and > the manual said it used individual pressure on the wheels for traction > control which is the opposite of what you are saying. Note the qualifier 'usually' regarding cutting engine power for traction control. In the case of race cars, the rules dictate that traction control is done via the engine, usually via the ECU. In the Indy Racing League, the drivers can dynamically adjust the traction control on board. Only a few race series, like the Dutch Supercar Challenge, allow stability control (DSC allows any assists, and just classifies cars based on power to weight ratios). http://en.wikipedia.org/wiki/Electro...bility_control http://en.wikipedia.org/wiki/Traction_control http://www.f1technical.net/articles/7 |
#7
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traction control algorithms
Michal Brzozowski wrote:
> I'm trying to gather some information about traction control systems, > in particular ABS and ESC. I'm mainly interested in what the inputs > are to those systems, and what algorithms the controllers use. I > understand they work by applying brake torque to chosen wheels. Racer uses: traction_control { ; Allowed front/rear wheel speed ratio (1.1=10% difference allowed) max_velocity_ratio=1.1 ; When to turn TC off min_velocity_ratio=1.0 min_velocity=0 } abs { ; Anti-lock braking system ; Allowed front/rear wheel speed ratio max_velocity_ratio=1.1 ; When to turn TC off min_velocity_ratio=1.0 min_velocity=0.1 ; Braking factor when ABS is applied braking_factor=1.0 } Where a velocity ratio (left vs right wheel) is detected. These days cars have so many sensors that engineers can use multiple inputs to devise more intelligent controllers (mostly flowing around the car on the CAN bus). > I'm making a simple car simulation using Pacejka's model and want to > simulate those systems and see how they work. So I'm not really > interested in the engineering side. Well, the engineering side is often a good way to start thinking about implementations. ;-) Cheers, Ruud |
#8
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traction control algorithms
Michal Brzozowski wrote:
> On Dec 12, 4:40 pm, Michal Brzozowski > > wrote: >> Hi, > Another question. Does anyone have Pacejka data for one tire model on > 2 different sufraces? Like on dry and wet asphalt. Or any idea how to > modify the parameters of one tire to change the surface to more > slippery. Reduce D. For MF5.x Pacejka, you have the PDX and PDY variables. From a piece of MF5.2 source: Cx=pcx1*lcx; mux=(pdx1+pdx2*dfz)*(1.0f-pdx3*gamma_x*gamma_x)*lmux; // Different in Pac2006 Ex=(pex1+pex2*dfz+pex3*dfz*dfz)*(1.0f-pex4*sign_kx)*lex; // Limiter on Ex (eq 23) if(Ex>1.0f)Ex=1.0f; Dx=mux*Fzn; // *zheta[1]; Kx=Fzn*(pkx1+pkx2*dfz)*expf(pkx3*dfz)*lkx; // K=BCD (=stiffness) Anything that reduces Dx also reduces grip. Pacejka targets more to tweak the lambda values, lmux for example, to do your friction tweaking (set it to 0.8 for example for wet). The nice thing about lambda values is that you don't quickly miss effects in other parts, such as combined slip etc. For older Pacejka versions also look to decrease D (a2/b2). Note that wet tires are quite ok these days, so don't go changing D to half of what it was. Cheers, Ruud |
#9
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traction control algorithms
On Dec 15, 11:56*pm, Ruud van Gaal > wrote:
> Michal Brzozowski wrote: > > I'm trying to gather some information about traction control systems, > > in particular ABS and ESC. I'm mainly interested in what the inputs > > are to those systems, and what algorithms the controllers use. I > > understand they work by applying brake torque to chosen wheels. > > Racer uses: [snip] > > Where a velocity ratio (left vs right wheel) is detected. These days > cars have so many sensors that engineers can use multiple inputs to > devise more intelligent controllers (mostly flowing around the car on > the CAN bus). Thanks Ruud! I'm interested in how racer handles the increase in slip in both ABS and traction control. * Do you completely turn off the brakes/throttle when you detect loss of grip, or set it to a smaller value, like 0.3 of the original torque? * What are the frequencies that you increase/decrease the torque with? Wikipedia says that real life ABS do it up to 20Hz. I've gotten best results with 50Hz for ABS, and much smaller, like 5Hz for traction control. I'm wondering if this has any real life meaning or if it's just a side effect of slip ratio oscillations at small speeds and the like. |
#10
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traction control algorithms
Michal Brzozowski wrote:
> On Dec 15, 11:56 pm, Ruud van Gaal > wrote: >> Michal Brzozowski wrote: >>> I'm trying to gather some information about traction control systems, >>> in particular ABS and ESC. .... > I'm interested in how racer handles the increase in slip in both ABS > and traction control. > > * Do you completely turn off the brakes/throttle when you detect loss > of grip, or set it to a smaller value, like 0.3 of the original > torque? For ABS & TC, I turn off brakes & throttle completely. It seems that for some cars, TC is achieved by skipping ignition for a few steps. I'm sure ABS in real life is more complicated, with parts that are actually breakable, but setting brakes to 0 seems ok. > * What are the frequencies that you increase/decrease the torque with? > Wikipedia says that real life ABS do it up to 20Hz. I really has ABS & TC done in the innerloop, at 1000Hz thus. Probably the resulting turning on/off of brakes / throttle is much lower, since the wheel velocity ratio is looked at all the time, and these don't change that quickly. I've never done any testing to the resulting frequencies. I hope to get a Fanatec wheel where driving the brake pedal actuator might invoke the need for a better ABS implementation (slower?). Cheers, Ruud |
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