Throttle opening vs gas pedal position in drive-by-wire systems

[briank]

In drive-by-wire throttle does the gas pedal position correspond directly with the actual throttle opening? I drive an automatic Scion xB 2nd gen, and one of my objectives when accelerating in 4th (overdrive) is to just push the gas pedal enough to keep the torque convertor in lock-up/ and to not downshift. It would be interesting to know if the manufacturer has set the throttle opening and fuel duty cycle map to continue to slightly increase even if the gas pedal is at the same position. The reason I suspect this is happening is that the instant mpg stays at an almost constant value as I accelerate from about 40 to 55 mph. If the throttle opening remained constant one would expect the instant mpg to increase by 37.5% as 37.5% more distance is covered at 55 mph compared to at 40 mph with the same gas pedal depression amount.

As an aside, I'm thinking of rigging up a resistance spring under the accelerator pedal at the point where the trans TC stops remaining locked. Right now I find that if the instant mpg goes under about 18 or 19 mpg, I am pushing the pedal too much and it go out of lock-up or downshift if I'm around below 42 mph.

[gone-ot]

...short answer: No.

...reason: your foot depresses a resistor that sends a differing voltage to the ECM, and the ECM then tells the fuel injector(s) to squirt more/less fuel into the engine; there's no one-to-one correlation, in fact, reprogramming the ECM can actually change the throttle-response (how much/fast you have to press the throttle).

[redpoint5]

Great question Brian. I have been wondering the same thing myself. Holding a constant throttle position in my TSX appears to show a constant instant MPG even though my speed is increasing.

I do know the ECM can override the throttle input you are giving. When it last snowed, I tried to get up my driveway with traction control turned off but I was too generous with the throttle and had too much wheel spin. Turning traction control on, I put the hammer down to the floor and the car very slowly accelerated, and I built up just enough momentum to get the car in the garage.

Computers doing the thinking takes all the fun out of driving, but at least it gets your car in the garage.

[mwebb]

there is a lot happening in drive by wire systems

early DBW in a 2002 jetta selected from Measured value blocks ,related PIDs are graphed while sweeping accel pedal slowly open and closed , key on engine off .

some accel pedal sensor position values start high and switch low and some are reversed , same with throttle plate position sensors and
there is redundancy

change in rate of speed of the accel pedal movement has a larger effect on throttle plate movement than most can imagine

the accelerator pedal input
is the input from driver to ECM ,
the ECM then opens or closes the throttle based on how it weighs that input along with all the other inputs it is receiving at the time

[briank]

I was always aware that angular velocity (and perhaps angular acceleration) of the gas pedal depression had an effect similar to pushing the accelerator a greater distance. It seems even the angular velocity is taken into account by the transmission. This is why I have to ease the accelerator forward slowly. Maybe I have to put in a one way damper as well. (Probably not for safety reasons)

I think every drive-by-wire car could easily be fitted with an economy mode button whereby only larger accelerator displacements tell the ECU to increase EFI duty cycle/downshift (linear relationship). A normal and sports mode could then take into account angular velocity. If only I could get at the software that controls this. It would be nice if manufacturers had a "hidden" feature to set such modes. (like holding down odometer button, while pressing the gas pedal 10 times while key is ACC position) I think a car with such a hidden feature would get a "cult" following among the eco crowd. I've driven a few cars with an eco mode which controls the transmission shift points.