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vrooom

Original Poster:

3,563 posts

153 months

[news] 
Friday 3rd December 2010 quote quote all

The car accerlates hard, until the wheels slips, the T/C unit cut off the spark ingtions.

But what about fuel? where they go? they are dumped into cylinder? or went down the return fuel line?

Will that cause adverse effect on fuel economy if it performed that way?

Ozzie Osmond

16,221 posts

132 months

[news] 
Friday 3rd December 2010 quote quote all
WASTE OF TIME!!!!!

pinchmeimdreamin

3,328 posts

104 months

[news] 
Friday 3rd December 2010 quote quote all
Have you had a beer ???

shovelheadrob

1,086 posts

57 months

[news] 
Friday 3rd December 2010 quote quote all
If you are accelerating hard enough to use the T/C, other than in the snow I don't think fuel economy is the main concern confused

Max_Torque

8,156 posts

103 months

[news] 
Friday 3rd December 2010 quote quote all
"modern" cars, i.e. those with traction control, use a "torque based" engine management system, it will only "cut" the sparks for the few firing events it takes for the slower "air side" torque control loop to cut back the throttle, then spark will be re-enstated. (depending on the torque reduction demand from the TCS, the ignition may not be completely cut, but just "retarded" to reduce torque.

Hence, only a couple of firing events worth of fuel are "lost" (maybe 50mg to 100mg total) and i don't think your gonna spot that!!
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Ozzie Osmond

16,221 posts

132 months

[news] 
Friday 3rd December 2010 quote quote all
Max_Torque said:
"modern" cars, i.e. those with traction control, use a "torque based" engine management system, it will only "cut" the sparks for the few firing events it takes for the slower "air side" torque control loop to cut back the throttle, then spark will be re-enstated. (depending on the torque reduction demand from the TCS, the ignition may not be completely cut, but just "retarded" to reduce torque.

Hence, only a couple of firing events worth of fuel are "lost" (maybe 50mg to 100mg total) and i don't think your gonna spot that!!
Nice summary.

The whole process is very closely related to torque management during gear shifts. Very relevant to modern auto transmissions and neatly explains why AMG Mercs, F 458 etc come with a standard transmission which is harder for an idiot driver to knacker...

trick3000tt

51 posts

100 months

[news] 
Saturday 4th December 2010 quote quote all
Just about every modern traction control uses fuel cut, not spark cut. Spark cut doesn't work very well at all on diesels, and pumping unburnt fuel straight through the engine and into a catalyst at 800deg on a petrol doesn't do much for its longevity. Older versions used to override the throttle but you cant get very accurate control using this method. Fuel economy actually improves when the t/c cuts in.

Ozzie Osmond

16,221 posts

132 months

[news] 
Saturday 4th December 2010 quote quote all
trick3000tt said:
Just about every modern traction control uses fuel cut, not spark cut.
But note also Max_Torque's comment on spark retardation for torque management.

Max_Torque

8,156 posts

103 months

[news] 
Saturday 4th December 2010 quote quote all
trick3000tt said:
Just about every modern traction control uses fuel cut, not spark cut. Spark cut doesn't work very well at all on diesels, and pumping unburnt fuel straight through the engine and into a catalyst at 800deg on a petrol doesn't do much for its longevity. Older versions used to override the throttle but you cant get very accurate control using this method. Fuel economy actually improves when the t/c cuts in.
Direct injected engines (be they compression or spark ignition) can use fuel cut as the "fast path" torque reduction response because they don't have to account for the fuel "puddle mass" in the intake system (being directly injected). On a conventional port injected engine fuel cut is just about impossible under current emissions regs as you cannot accurately control the cylinders AFR during the cut transitions, which tends to lead to excess exhaust emissions(usually large NOx feedgas spikes due to lean and partial burns). A full spark cut however means you just dump a small mass of completely unburnt fuel out of the exhaust port, where it is oxidised by the catalyst at low enough temp and pressure (compared in combustion temps/pressures) that the formation of NOx is eliminated. For the couple of firing events before the "slow path" airside controller catches up, the heat release from this exotherm is not enough to damage the catalyst substrate due to over temperature.

On the DI engine, fuel is injected directly into the combustion chamber, so no intake system puddle mass exists, so you can control fuel mass without lead/lag, and hence torque on an firing event by event basis without issues with missfiring or partial burns, effectively you have two "fast paths" using spark retard to ramp out torque, and then a full fuel cut once you get to the retard limit.

It is correct that fuel economy improves, but only compared to the non intervention case. reducing the engines torque means it uses less fuel, but during these interventions the engines efficiency IS reduced (Specific torque output falls) so you are using more fuel compared to just running at the lower torque value without TCS torque reduction.


It should also be noted that TCS also can increase engine torque if/when required, for example to prevent the rear wheels "underspeeding" if a low gear is selected too early, or the driver agressively backs out of the throttle (or decending a steep hill etc), In this case, the TCS will ask for a "torque up" event to maintian mean wheel speeds and hence equalise tyre slip ratios.

Bricol

117 posts

53 months

[news] 
Saturday 4th December 2010 quote quote all
Fit winter tyres.

Usually in the integrale I get about one week of commuting - main roads in on a morning, back roads on an evening. Fill up Monday morning, light comes on on the way in on Fridays.

This week, winter tyres fitted, same routes, covered in snow, and I still had half a tank Friday coming home . . .

So I reckon the winter tyres are worth a 50% saving in fuel.

Bri

tongue out
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