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Old 08-04-2010, 09:22 PM   #1 (permalink)
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Digital Gas Pedal

if one were to rethink the gas pedal, and use an algorithm to determine the throttle position based on rpm and load, what inputs would you use to calculate the optimum throttle position at each rpm and load situation?

The goal would be to accelerate at optimum brake specific fuel consumption. The driving method would differ from the current gas pedal/throttle method. Instead of holding the gas pedal at the optimum depth to achieve a certain speed, the pedal would be on or off. The driver would accelerate to a certain speed, and then release the pedal, coasting down to a slower speed, then depressing the pedal to accelerate again.

When the gas pedal is depressed, a microprocessor would measure the rpm and load, and using a math function, would determine the ideal throttle position.

A shutdown / starter system could be incorporated to allow the motor to be shut down completely during the pedal off / coast phase. This could be a manually operated bump start or a controlled electric starter. If manually operated in highest gear, the operator could coordinate releasing the clutch and depressing the gas pedal. An electric start would only be required if the vehicle speed were too low to bump start.

It may be simpler for the operator to actuate the digital gas pedal only in highest gear, and at other times, the classic gas pedal function could be used. A switch could be used to allow the operator to control whether the gas pedal function, selecting either classic or digital.

Inputs:
ODBC LOD Engine Load
ODBC RPM
Is transmission in highest gear? Yes/No
Vehicle speed

Outputs:
ODBC TPS Throttle Position
or a voltage output to represent a typical drive by wire throttle control voltage

Algorithm:
Basic Engine Operating Line, modified to show ODBC LOD vs. RPM
Is transmission in highest gear? If yes, operate digital gas pedal, if no, classic gas pedal
If vehicle speed is below 5mph, use electric start upon gas pedal actuation


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Does this seem to be based on solid theory?

It does not sound particularly difficult to construct.

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Old 08-04-2010, 09:39 PM   #2 (permalink)
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Well my 2004 Pickup is fly- by-wire just like alot of new cars, I assume they do this already. (I can feel myself getting flamed already!)

Last edited by daring4; 08-04-2010 at 09:55 PM..
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Old 08-05-2010, 06:46 AM   #3 (permalink)
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I have a drive by wire accelerator and I suspect that it is nothing more than a potentiometer on the pedal end, which means that the throttle is controlled by the changing voltage drop on the throttle end. By tapping into the connector at the pedal, I think an arduino or other processor could simulate voltage levels to control the throttle by using pulse width management.
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Old 08-05-2010, 07:06 AM   #4 (permalink)
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I'm pretty sure OEMs are doing this to some point already. I'm not sure to what point though. It also helps in this case to have a CVT transmission.
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Old 08-05-2010, 08:49 AM   #5 (permalink)
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FYI, any car with a cruise control is "fly by wire" when in cruise, though the default actuator speed might be annoying in traffic.
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Old 08-05-2010, 04:12 PM   #6 (permalink)
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The digital gas pedal mod would be different than cruise control, it would be set up to give a pulse of power and acceleration exactly at the most efficient throttle position for the given engine load, then as the maximum desired speed is reached, releasing the digital gas pedal would turn the engine off to coast as the pedal was released.

This mod would only be useful in situations where you could EOC.

You might be able to use it in normal traffic. For example on 55 mph country roads, you could do a 50mph-60mph EOC pattern. You would piss off the tailgaters but most traffic could continue at about 55mph.

It would require some operator skill in depressing the digital gas pedal at the same time as engaging the clutch. However we already do this when bump starting.

I do not intend to build this, because it would require many hours on a test track before I would trust my self created controller on the public roads.
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Old 08-05-2010, 10:56 PM   #7 (permalink)
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My 2010 Ford Ranger still uses a mechanical throttle cable to the gas pedal. Obviously, not all new vehicles have fly-by-wire gas pedals. FYI.
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Old 08-09-2010, 07:54 PM   #8 (permalink)
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I didn't see a post where someone said "all" new vehicles had fly-by-wire gas pedals...
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Old 08-09-2010, 09:17 PM   #9 (permalink)
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I could see a momentary switch on the wheel or shifter that "locks in" best bsfc, once that is determined (using existing cruise control actuators and safties possibly).

Then you can just clutch/shift like normal and hold the button once you are re-engaged until it is time to shift (see indicator light thread). Could also work on an automatic for most efficient accel.

It needs to be bulletproof for general consumption, but I'm sure a wary hobbiest could pull it off.

My TDI doesn't really need one though, the most efficient curve is basically the torque curve, you just have to wang it open and shift at the right time, and stop accelerating at the right time.

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Last edited by dcb; 08-09-2010 at 10:28 PM.. Reason: where's the bumblebee!?!
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