Cum functioneza ASC+T pe un BMW E36?

[lucianemil]

Vreau sa stiu daca are cineva un BMW E36 cu ASC+T. Sunt curios pentru ca eu am unul si vreau sa stiu cum se comporta pe zapada noraoi etc in comparatie cu DSC-ul. Am condus multe BMW-uri cu DSC I si II si III iar raspunsul este ca DSC este un ESP cu alt nume. Despre prima generatie ASC veau sa stiu mai multe!

[Myx]

Vreau sa stiu daca are cineva un BMW E36 cu ASC+T. Sunt curios pentru ca eu am unul si vreau sa stiu cum se comporta pe zapada noraoi etc in comparatie cu DSC-ul. Am condus multe BMW-uri cu DSC I si II si III iar raspunsul este ca DSC este un ESP cu alt nume. Despre prima generatie ASC veau sa stiu mai multe!

 

diferenta e mare ....in sensul ca ASC e mult mai slab ..doar taie gazul ..te trezesti brusc cu masina lesinata fara putere ....DSC e net superior ...la mine saltul a fost invers ASc si apoi DSC .......

[lucianemil]

diferenta e mare ....in sensul ca ASC e mult mai slab ..doar taie gazul ..te trezesti brusc cu masina lesinata fara putere ....DSC e net superior ...la mine saltul a fost invers ASc si apoi DSC .......

 

 

uite ce zice un american??

 

Brian Brown here gives us a run through on a very difficult and important subject, traction control. Hopefully this will help you understant this subject better. Automatic Stability Control plus Traction (ASC + T) is BMW's electronic traction control system. It was optional on the '96 318ti and then became standard for the '97 model year. A limited slip differential was available in '95 and '96, but couldn't be ordered in combination with ASC + T on the 318ti (I think only the M3 was available with both).

 

ASC + T is integrated into the Antilock Braking System (ABS). To a large extent ASC + T functions like ABS in reverse.

 

As with all of their control firmware, BMW is very secretive about the details of the specific control algorithms that this system uses. I don't like this, but I really can't blame them for trying to protect some of their trade secrets.

 

The description I can give comes from information I have read about about braking and traction control systems in general, as well as some information that BMW publishes. Also, there are a number of things that I have noticed by experimenting with this system and comparing it to other cars that reveal addition clues to what's going on.

 

I'm going to do this in two posts. For the first post, I'm going to go over the ABS system. It's necessary to understand ABS in order to examine ASC + T.

 

Like most materials, the rubber on a tire has the greatest friction (traction) on pavement when it isn't sliding. Remember that when the tire is rolling, the contact patch on the ground is stationary. When a tire is skidding, the contact patch is sliding. To achieve maximum braking (or acceleration or cornering) force, it's necessary to keep the contact patch from sliding.

 

Now that I've just stated that, I need to make a slight revision. Due to a number of force interactions when the tire rubber and tread flexes, the maximum traction force occurs when there is ten to twenty percent slippage. This turns out to be really useful. If there was no slippage at all before loss of traction, it would be almost impossible for the system to predict impending loss until after it actually occurred. (Learning a 'feel' for this slippage is an extremely useful skill for the driver too, but that's another subject). By adjusting (reducing) the braking force at a wheel that's about to lock up, maximum traction can be maintained.

 

There is a toothed ring that spins at each wheel next to a magnetic hall-effect sensor. As the wheel turns, the sensor sends out a pulse to the ABS controller as each tooth passes by it. By measuring the frequency of the pulses coming in, the controller can determine how fast the wheel is turning. Note that it can't tell which direction the wheel is turning, the pulses are the same either way. It assumes the wheel is rolling forward. By comparing the speed difference of each wheel, it can detect when one or more wheel(s) are slowing down faster than the car, indicating an impending loss of traction. The ABS controller then commands the ABS hydraulic unit to release the pressure on that wheel's brake. It then reapplies brake pressure as soon as it senses that the wheel has sped back up. This happens rapidly over and over (about 8 times a second) so that there is a perceived pulsing or buzzing sensation. By adjusting the braking this way, this wheel's tire is held right at it's maximum traction limit.

 

On 318ti's without ASC + T, the ABS is a three channel system. That means that the ABS hydraulic unit has a separate control valve for each front wheel, and a third control valve that is shared by both back wheels. Because of that, when one rear wheel starts to lose traction, braking has to be reduced to both rear wheels.

 

The ABS control firmware takes into account not just the difference in speed between each wheel, but also a maximum deceleration rate (in case the system misses and a wheel does actually lock up), as well as compensation for cornering (the outside wheels in a corner need to spin faster than the inside wheels. So it checks to see if the difference between the inside and outside at the front is similar to the difference between the inside and outside at the rear.) Another important compensation that ABS performs is for "split-mu" surfaces. An example of this is when the two wheels on one side of the car are on the road (lots of traction), and the wheels on the other side are off the road (less traction). If the system just adjusted to each wheel's maximum braking force (which is what some less-advanced ABS systems do), the tires on the side of the car on the pavement would apply a force that would make the car tend to spin out. The split-mu detection algorithm will reduce the over-all braking force just enough to prevent this from happening.

 

ABS has three significant advantages: It reduces the need for driver skill during panic situations. It can separately control braking thresholds. Most important: it allows the driver to steer while braking at the limit. Let's discuss this last one a little more. A tire for all practical purposes has a fixed amount of traction in any direction (accelerating, braking, cornering). When steering and braking at the same time, this traction has to be shared between the two functions. When braking in a straight line, all of a tires traction can be used for braking. When cornering at the limit, the tire has no available traction for braking. Between these two extremes, the traction can be shared. ABS automatically adjusts the brakes for the traction that's left over after the cornering force.

 

ABS has a couple of disadvantages: in deep snow or gravel it's actually better for the wheel's to lock up. On completely glare ice, locked wheels will often stop a car faster because even though the sliding friction is less than non-sliding friction, it is applied 100% of the time rather than only the part of the time when the brakes are pulsed on. Also, ABS changes the technique necessary for trying to bring a car that is already spinning out to a stop. Rather than just putting in both the brake and the clutch, it's also necessary to steer.

 

The real problems with ABS are due to driver error. One issue is driver over-confidence. ABS doesn't make the car stop on a dime. The slipperier the surface, the longer the car needs to stop. It is still necessary for the driver to accurately determine what a safe stopping distance is for the present conditions and to drive accordingly. The other issue is driver confusion. Recent studies are finding that many drivers are unfamiliar with ABS. They may back off the pedal when they feel the pulsing, or they may actually try the old method of pumping the brake pedal. Both will radically increase stopping distances. With ABS, the proper emergency technique is simply to plant your foot on the brake pedal hard, and leave it there until the car comes to a stop. Another oversight that many people who are somewhat familiar with ABS make it that you can still steer while your foot is hard on the brakes. To revise what I just said: In an emergency stop, apply the brake hard and hold it there, while trying to steer *around* any obstacles you may be approaching.

 

I think that it's a really good idea to practice with the ABS brakes. Pick locations that are away from others, preferably off of roads with traffic. Try slamming on the brakes as hard as you can and hold it until the car comes to a complete stop. Do this on dry, wet, and snowy surfaces. Find a place with plenty of run-off room and try some hard cornering while braking, again on dry, wet, and snowy. Try braking hard and doing lane changes to avoid imaginary obstacles that are in front of you. Please be careful when you try this and make sure that you have plenty of room and that you won't be catching others by surprise.

 

Just like antilock brakes (ABS), BMWs Automatic Stability Control + Traction (ASC + T) system utilizes the concept of using electronic control to enable the tires to be loaded up to their maximum level of adhesion.

 

There are some differences about what ASC + T has to deal with compared to ABS. ABS has to control the braking force at all four wheels. ASC + T has to control the power delivery of the engine, and the way the rear differential distributes torque between the two back wheels. The overall objective is quite similar, to enable each rear wheel to be powered to the limit of its adhesion, and to stabilize the car from spinning out when power is over-applied.

 

The car's first traction problem comes from the differential.

 

The differential is a gear unit that couples the rear wheels to the single driveshaft coming from the transmission. It has to transmit power from the transmission, while allowing the rear wheels to spin at different speeds. The wheels need to turn at different speeds because when the car goes around a corner, the outside wheels have a longer path to travel than the inner ones do. If both back wheels were directly coupled to each other (forcing them to both turn at the same speed), then they would 'fight' any effort of the driver steering around a corner.

 

Think of a bulldozer with a caterpillar tread on each side. This machine doesn't have a steering wheel. The driver steers it by controlling the speed of each tread. To go in a straight line, both tracks go at the same speed. To turn, one tread goes faster than the other (maybe even in the opposite direction).

 

A car, on the other hand, relies on wheels that can be pointed with a steering wheel as the main method of steering control, not variations in driveline power/speed distribution. The driveline needs to just go along with whatever wheel speed differences occur from the car being steered. (The new Honda Prelude type SH is probably the first car to attempt to distribute power in a way to activate steering, but it's a new exception).

 

A conventional differential is a set of gears that couples twisting forces of three devices (in a car's case, the transmission and two wheels). Torque must be distributed to all three. Under normal conditions, both wheels are coupled together through the ground. In this situation, torque can be transmitted from the transmission to both wheels.

 

If the coupling of the two wheels through the ground is disrupted (as when a wheel is spinning), then the differential can't usefully distribute the torque. All of the power is being applied to the spinning wheel, and not to the wheel that still has traction.

 

There have been a number of different differential designs to counter this problem, with varying degrees of effectiveness, complexity, cost, and side-effects. Collectively these are referred to as Limited Slip Differentials. I'm not going to get into these right now, but they are a very interesting topic for discussion.

 

An electronic traction control system can help prevent a wheel from spinning by applying that wheel's brake. This not only maximizes the traction at that wheel, but more importantly it enables the differential to apply power to the other wheel, which probably has more traction.

 

The car's second traction problem is when the torque from the engine exceeds the total traction available at both wheels. An electronic traction control system can deal with this problem by reducing the engine output.

 

On 318ti's with traction control, the ASC + T is integrated with the ABS functions. There is a single electronic control unit (with more processing power than an ABS-only unit), and the same four spinning toothed rings with magnetic pickups to determine individual wheel speeds.

 

The hydraulic control unit has four channels. The ABS-only unit has three channels, only one for both rear wheels. Separate rear channels are required for individual control of rear wheel spin. (This could also mean that the ASC + T system has even better braking performance).

 

The ASC + T control unit has a high-speed (CAN) data link to the main engine control unit, and has control of a throttle actuator motor. This allows it to reduce engine power.

 

There is a dashboard switch that allows the ASC + T to be disabled (but the ABS functions remain active).

 

The ASC + T system determines that a wheel is spinning by comparing the rear wheels' speed to the front. Also, there is probably a maximum wheel acceleration threshold built into the system.

 

The ASC + T system intervenes in two stages: When it detects one rear wheel near the threshold of adhesion, it starts to rapid pulse the brake to that wheel (just like ABS). When the second rear wheel nears the limit of adhesion, engine power is reduced.

 

The first stage (single wheel braking) actually improves vehicle performance. The second stage (engine reduction) doesn't improve performance available, but it adjusts output so that all that is available is fully utilized.

 

The dashboard ASC + T light only flashes when the system enters the second stage, and is reducing engine power. It doesn't flash when the system is only braking a wheel about to slip. This can be demonstrated most easily in the snow. By using the dashboard button to turn ASC + T on and off, it becomes immediately apparent that it is assisting traction even when the light doesn't come on.

 

The first stage can apply braking power in two levels. From 0 to 25MPH, a high level of braking force is pulsed to a wheel about to slip. >From 25MPH to 62MPH, a reduced level of braking force is used (this is both to reduce brake heating, as well as to smooth out operation). Above 62MPH the brakes aren't applied, and the first stage is inactive.

[Myx]

LOL..nu stiu daca va sta cineva sa citeasca tot ce ai pus ...Eu ti-am spus o comparatie clara :) oricum e bine ca are si ASc o redresezi mai usor dar uneori prin faptul ca pierzi puterea brusc nu stiu cat e de util

[florin83]

Vreau sa stiu daca are cineva un BMW E36 cu ASC+T. Sunt curios pentru ca eu am unul si vreau sa stiu cum se comporta pe zapada noraoi etc in comparatie cu DSC-ul. Am condus multe BMW-uri cu DSC I si II si III iar raspunsul este ca DSC este un ESP cu alt nume. Despre prima generatie ASC veau sa stiu mai multe!

 

diferenta e mare ....in sensul ca ASC e mult mai slab ..doar taie gazul ..te trezesti brusc cu masina lesinata fara putere ....DSC e net superior ...la mine saltul a fost invers ASc si apoi DSC .......

 

Nu taie doar gazul.. din contra,gazul il taie in ultima instanta. Intai franeaza rotile spate (doar spate) si daca exagerezi taie gazul.

Am mers cu ceva masini cu DSC si in linie dreapta eu n-am vazut nici o diferenta. In curbe situatia se schimba.. DSC-ul isi arata superioritatea..

[ovy318i]

e slab ASC,eu m-am jucat un pic cu masina si derapeaza lateral destul de repede,pe zapada,intervine cam tarziu,pe asfalt ud sau praf e destul de ok,dar ma asteptam sa-mi taie gazul sau sa-mi blocheze roata inainte de a incepe masina sa derapeze lateral si eu am incercat la viteze mici ,pana in 40-50 km/ora.

[florin83]

la viteze d-astea am incercat si eu.

Pe zapada, acceleratia la podea.. tras stanga-dreapta brusc de volan. Pleaca de spate f.putin, cativa zeci de cm.. Am mers si cu masini cu DSC si sincer nu am vazut diferenta in conditiile scrise mai sus.

[Myx]

e slab ASC,eu m-am jucat un pic cu masina si derapeaza lateral destul de repede,pe zapada,intervine cam tarziu,pe asfalt ud sau praf e destul de ok,dar ma asteptam sa-mi taie gazul sau sa-mi blocheze roata inainte de a incepe masina sa derapeze lateral si eu am incercat la viteze mici ,pana in 40-50 km/ora.

 

 

Poate asa ca stii ca nu te poti baza pe el ...nu prea tragi de masina ...Cu DSC ai tendinta sa impingi masina la limita tocmai pt ca stii ca poate .. sistemele astea elecronice te incurajeaza sa calci mai mult pedala ...sa intri mai tare in curba etc ...Nu toti conducem rational mereu ...Ne mai apuca nebunia :)

Edited December 29, 2008 by myxage

[Sorin Enache]

Si eu am asc si pot sa zic ca zilele astea de cand a inceput poleiul noaptea prin buc imi licare intr-una la plecari de pe loc sau in curbe cand accelerez sa fac un drift ... si vreau sa zic ca eu unul am fost impresionat...adica pur si simplu nu imediat ci cu o mica eroare de 1 m maxim te pune pe trasa normala... eu am model din 95 si a fost model individual.

[florin83]

Si eu am asc si pot sa zic ca zilele astea de cand a inceput poleiul noaptea prin buc imi licare intr-una la plecari de pe loc sau in curbe cand accelerez sa fac un drift ... si vreau sa zic ca eu unul am fost impresionat...adica pur si simplu nu imediat ci cu o mica eroare de 1 m maxim te pune pe trasa normala... eu am model din 95 si a fost model individual.

 

1m e mult.. nu se duce atat. Poate jumatate de metru..

[Sorin Enache]

Si eu am asc si pot sa zic ca zilele astea de cand a inceput poleiul noaptea prin buc imi licare intr-una la plecari de pe loc sau in curbe cand accelerez sa fac un drift ... si vreau sa zic ca eu unul am fost impresionat...adica pur si simplu nu imediat ci cu o mica eroare de 1 m maxim te pune pe trasa normala... eu am model din 95 si a fost model individual.

 

1m e mult.. nu se duce atat. Poate jumatate de metru..

 

 

Cam asa am zis cu bataie...acum depinde si cat de mult o calc in curba :) nu normal...dar se duce f putin... ii multumesc lui fratimi-o ca m-a ajutat sa o iau pentru ca de 1 luna de zile de cand am luat-o tot ma uit pe net dupa modele asemenea si nu am mai vazut una cu atatea dotari... si nici inainte de asta nu am vazut decat 2 una neagra si una rosie...aia rosie era cu cutie automata si aia neagra era ffffffff joasa... cu jante din alea imense pe spate...dar DAR nu avea ASC....adica cel putin butonul dintre incalziri nu exista...

[roco123]

Si eu am asc si pot sa zic ca zilele astea de cand a inceput poleiul noaptea prin buc imi licare intr-una la plecari de pe loc sau in curbe cand accelerez sa fac un drift ... si vreau sa zic ca eu unul am fost impresionat...adica pur si simplu nu imediat ci cu o mica eroare de 1 m maxim te pune pe trasa normala... eu am model din 95 si a fost model individual.

 

1m e mult.. nu se duce atat. Poate jumatate de metru..

 

 

Cam asa am zis cu bataie...acum depinde si cat de mult o calc in curba :) nu normal...dar se duce f putin... ii multumesc lui fratimi-o ca m-a ajutat sa o iau pentru ca de 1 luna de zile de cand am luat-o tot ma uit pe net dupa modele asemenea si nu am mai vazut una cu atatea dotari... si nici inainte de asta nu am vazut decat 2 una neagra si una rosie...aia rosie era cu cutie automata si aia neagra era ffffffff joasa... cu jante din alea imense pe spate...dar DAR nu avea ASC....adica cel putin butonul dintre incalziri nu exista...

Mai sunt masini cu dotari ca a ta si peste chiar, desi la ta ii lipsesc foarte putine.

Din cate vad, cruise control, scaune electrice, Harman Kardon, trapa.....chiar numai asta vad ca iti lipseste, trapa oricum e in plus daca ai clima...

Eu la e36 nu am ASC si e destul de nasol :)

DSC e beton la e46, te face sa impingi la limita masina, mai ales cand accelerezi pe gheata si nu fuge spatele deloc :)

[Bobo1987]

Tovarasi,nu ati vrea sa mearga masina singura?! :) Eu unul nu am simtit atat de tare diferenta intre ASC si DSC...Intr-adevar,este o diferenta,insa nu pe cat o exagerati voi... :) Cred ca o pot observa doar cei cu f.multi km facuti pe un BMW cu ASC+T si pe unul cu DSC.Unora le place sa faca din tantar armasar... :) Sper ca nu am deranjat pe nimeni,dar asta e parerea mea :) ...

[Sorin Enache]

@ roco123 scaune electrice da... desi nu am vazut pe nici un model de pe net ..in perioada de cautare care a durat aprox 1 luna... trapa da...dar toate cele care aveau trapa nu aveai climatronic digital sau computer de bord, cruise control...la manuale tot asa nu am vazut nici una in perioada de cautare...deci ce pot sa zic... arata-mi 1 cu toate dotarile astea si eu sunt multumit....

 

Tinand cont ca a mea e model individual ...ceea ce spune multe...

 

Merci

[roco123]

@ roco123 scaune electrice da... desi nu am vazut pe nici un model de pe net ..in perioada de cautare care a durat aprox 1 luna... trapa da...dar toate cele care aveau trapa nu aveai climatronic digital sau computer de bord, cruise control...la manuale tot asa nu am vazut nici una in perioada de cautare...deci ce pot sa zic... arata-mi 1 cu toate dotarile astea si eu sunt multumit....

 

Tinand cont ca a mea e model individual ...ceea ce spune multe...

 

Merci

E normal sa fii multumit, sunt foarte putine pisici ca a ta, cu asa dotari.

Eu am zis restu dotarilor, care ar face un full full.

Pielea e frumoasa tare, dar iarna parca te asezi pe ciment pana isi va face efectul incalzirea in scaune.

Si in plus la e36 nu ai incalzire si-n sezut, ingheti la propriu :)

[Sorin Enache]

@ roco123 scaune electrice da... desi nu am vazut pe nici un model de pe net ..in perioada de cautare care a durat aprox 1 luna... trapa da...dar toate cele care aveau trapa nu aveai climatronic digital sau computer de bord, cruise control...la manuale tot asa nu am vazut nici una in perioada de cautare...deci ce pot sa zic... arata-mi 1 cu toate dotarile astea si eu sunt multumit....

 

Tinand cont ca a mea e model individual ...ceea ce spune multe...

 

Merci

E normal sa fii multumit, sunt foarte putine pisici ca a ta, cu asa dotari.

Eu am zis restu dotarilor, care ar face un full full.

Pielea e frumoasa tare, dar iarna parca te asezi pe ciment pana isi va face efectul incalzirea in scaune.

Si in plus la e36 nu ai incalzire si-n sezut, ingheti la propriu :)

 

 

Ba are incalzire in sezut sa sti... la scaunu din dreapta e ... la mine crek nu mai functioneaza, adica pe scaunul soferului...prbb s-o fi dus vun fir..

[Ciupanezu]

Tovarasi,nu ati vrea sa mearga masina singura?! :) Eu unul nu am simtit atat de tare diferenta intre ASC si DSC...Intr-adevar,este o diferenta,insa nu pe cat o exagerati voi... :) Cred ca o pot observa doar cei cu f.multi km facuti pe un BMW cu ASC+T si pe unul cu DSC.Unora le place sa faca din tantar armasar... :) Sper ca nu am deranjat pe nimeni,dar asta e parerea mea :) ...

 

Diferenta este imensa daca stai sa te gandesti ca DSC-ul functioneaza si in curbe, adica exact acolo unde este mai usor sa faci accident.

[dinu.negrean]

Probabil Bobo1987 nu conduce foarte sportiv sau nu are foarte multa experienta. Diferenta e mare de tot intre cele doua sisteme

[Bobo1987]

Probabil Bobo1987 nu conduce foarte sportiv sau nu are foarte multa experienta. Diferenta e mare de tot intre cele doua sisteme

Sa stii ca nu conduc foarte sportiv,insa asta e parerea mea:ca este o difernta intre ASC+T si DSC , insa nu atat de mare pe cat o exagereaza alti colegi de forum... :) Sunt de acord cu ce a spus Ciupanezul si aici zic eu ca este si diferenta:ca DSC-ul actioneaza si in curbe si iti da un plus de confort mai ales iarna...

[florin83]

pai si ASC-ul actioneaza in curbe, dar doar pe rotile din spate.. :)

[Ciupanezu]

AcĂžioneazĂŁ cam inutil ĂŽn curbe.

[florin83]

adica? :)

 

Tu ai DSC sau ASC?

[Ciupanezu]

DSC.

 

Am condus maÂşini cu ASC Âşi am observat cĂŁ nu te ajutĂŁ sĂŁ restabileÂşti traiectoria maÂşinii, doar ĂŽĂži taie puterea Âşi opreÂşte patinarea roĂžilor.

[florin83]

Intradevar, nu e ca DSC, dar sa zici ca e inutil e cam aiurea..

Crezi ca degeaba l-au pus cei de la BMW pe atatea modele?

[Ciupanezu]

Am spus cĂŁ e inutil ĂŽn curbe nu ĂŽn general. :)

 

L-au pus pe atâtea modele pentru cã asta exista la acel moment.

 

Poate cã "inutil" e un cuvânt cam dur...