Chrispy_ wrote:Interesting comments from Synthetel2 about gas pedals being closer to binary than linear; I don't think I've ever owned a car with an electronic throttle, so that kind of figures - where just 10% throttle = 90% peak torque at that engine speed.
Pancake wrote:Interesting comment but complete crap. The throttle exists to make fuel-to-air ratio combustible in petrol engines, which is in a fairly narrow range compared to diesels. My car has an electronic throttle and I know it quite well as I pull it apart and service it with love and care and sweet tenderness... Anyway, throttles are most definitely not "binary" in how they work. The clever little computer in my car modulates the throttle (in conjunction with mass air flow sensor) to give the perfect blend of air and fuel to keep each cylinder (multipoint EFI) burning happily at the required torque output at current RPM as demanded by my right foot. It's a beautiful thing.
You're both thinking I said things I didn't actually say.
10% accelerator doesn't map to 90% anything unless you're at extremely low RPM (probably below idle), have an extremely large throttle body per the engine's displacement, or are abusing a TBW amp that makes it look to the ECU like you're pressing the accelerator further than you are (yeah, those exist). If an engine somehow did naturally end up with characteristics like that in conditions closer to cruise, it would be very obnoxious to drive, and the manufacturer would have put some kind of non-linearity the other direction into the system to compensate.
I never said TBWs were binary. It's a curve, it's just that most of the curve tends to be compressed into an early part of the accelerator's travel. Airflow and fuelling have to be matched, and neither is perfectly responsive, but fuelling can be changed much much quicker and more precisely than airflow, so in practice ECUs tend to control airflow on the basis of accelerator position (or any other source for an abstract power demand, maybe to smooth out shifting or something) and then adjust fuelling to match however much air is actually flowing. (GDIs have potential to throw a lot of wrenches in this model. AFRs may tweak based on accelerator position rather than something further down the chain if the goal is responsiveness. DFCO exists and is another big exception.)
Waco wrote:I still prefer throttle cables to electronic throttles. One more thing to break, one more thing to introduce lag, etc. I don't mind the system on my C5, but I really wish it were simpler.
captaintrav wrote:I never thought of but the TBW system probably is why my Durango seems pretty nonchalant when you mash the gas from a dead stop, cause the power once you hit about 30mph seems a lot more so. I always chalked it up to the revs needing to get up, but I bet it has more to do with the programming TBW than the engine's torque curve. Probably saves the AWD system from being too abused.
notfred wrote:My 03 Subaru had a TBW and on that the throttle opening wasn't noticeably different but the throttle closing was very slow - that helps with emissions but sucks when you are going for a quick gear change.
TBWs should have no inherent reason to be that laggy, but somehow not one of them I've ever driven feels as crisp as a decent mechanical system. Chrysler(/Dodge/Jeep) in particular seems to have major issues with this.
Slow-acting DFCO (deceleration fuel cutoff) isn't inherently tied to TBWs, but they seem to have arisen about the same time. Dammit ECUs, when I let off the gas I don't want you continuing to burn fuel for an extra second! As if they think I'm unsure I actually want the engine braking I asked for.
Chrispy_ wrote:Can't help but feel that modern pedal feel could be improved immensely if they just used an eccentric cam on the throttle cable to make engine torque slightly closer to linear in relation to the pedal travel.
Auto-transmission '97 Legacy Outbacks (EJ25D) use a dual-cam system that achieves this effect (probably many others do too, but that's the one I've seen it on).