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traction control algorithms



 
 
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  #1  
Old December 12th 09, 04:40 PM posted to rec.autos.simulators
Michal Brzozowski
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Posts: 4
Default 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  
Old December 12th 09, 05:36 PM posted to rec.autos.simulators
rcgldr[_2_]
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Posts: 42
Default 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  
Old December 12th 09, 05:40 PM posted to rec.autos.simulators
Michal Brzozowski
external usenet poster
 
Posts: 4
Default 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  
Old December 13th 09, 05:54 PM posted to rec.autos.simulators
Michal Brzozowski
external usenet poster
 
Posts: 4
Default 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  
Old December 14th 09, 06:40 PM posted to rec.autos.simulators
Cronos
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Posts: 10
Default 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  
Old December 14th 09, 09:42 PM posted to rec.autos.simulators
rcgldr[_2_]
external usenet poster
 
Posts: 42
Default 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  
Old December 15th 09, 11:56 PM posted to rec.autos.simulators
Ruud van Gaal
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Posts: 16
Default 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  
Old December 16th 09, 12:01 AM posted to rec.autos.simulators
Ruud van Gaal
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Posts: 16
Default 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  
Old December 16th 09, 08:20 PM posted to rec.autos.simulators
Michal Brzozowski
external usenet poster
 
Posts: 4
Default 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  
Old December 21st 09, 12:22 PM posted to rec.autos.simulators
Ruud van Gaal
external usenet poster
 
Posts: 16
Default 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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