Drive-by-wire for dual carbs/throttle bodies???, would you run them?? Options

[Mueller]

A lot of newer cars do not have the traditional cable that goes from the gas pedal to the throttle body...instead the pedal has a potentiometer*, this in wired to the ECU which tells the throttle body how much to open, just because you have your foot buried to the floor, the throttle body might only be open 50% since the ECU is dictating what is going on.

Now a drive-by-wire throttle body could be wired directly to the pot. on the gas pedal to be 1:1 at all times......with a setup like this on dual carbs or individual throttle bodies, no need to worry about thermal expansion of motor and how that effects the linkage.


* (similar to a variable resitor which varies the voltage output depending on foot placement)

[tat2dphreak]

I think it would be a good thing... wouldn't this also mean 1 less thing to not unhook when you pull the engine? what are you thinking in terms of design?

[alpha434]

Why not just install a bigger computer too? And green brakes? And maybe a satelite navigation system? And don't forget electric adjustable seats.

Haha.

Depends on how accureat the system is. I've thought about it once before. One of those things that would be best used on a new buildup.

[URY914]

I don't think it would be allowed in most race groups. As a safety issue they like cables and return springs.

But you a street car it'd be cool.

[r_towle]

Sure would be a nice way to have hide away linkage on a beetle...

I like that clean look.

I would say go for the weber market first...that has a larger installed base...
I have a dual weber 40mm you could use as a test mule till summer...then the kid comes back...

I think in the engine bay it would be fine...I would be very concerned putting sensitive electronics on the floor or either a beetle or a 914 considering the black hole effect that the floorboard area has in both cars...


Rich

[fiid]

I'd be interested in how the actuation is actually done - I would think that there would be a return spring and perhaps a solenoid to pull the throttle open with some kind of pwm coming from the ECU.

Anyways - I'd mess with it... sounds cool. I'd make sure it's REALLY stable before going anywhere with it though.

[Porcharu]

QUOTE (fiid @ Feb 28 2006, 02:33 PM)

I'd be interested in how the actuation is actually done - I would think that there would be a return spring and perhaps a solenoid to pull the throttle open with some kind of pwm coming from the ECU. Anyways - I'd mess with it... sounds cool. I'd make sure it's REALLY stable before going anywhere with it though.

On my 2005 Suby engine it is a stepper motor - at least if feels like one. My truck uses on also, they must have spent a ton of time getting the feel just right - I had no idea it was drive by wire - of course it's an electronically controlled diesel so all you are changing is the injector pulse width anyway.

I am not using it on my Suby conversion - just a plain ol' 65mm throttle body. (IMG:http://www.914world.com/bbs2/html/emoticons/driving.gif)

[tat2dphreak]

I'm thinking it could be done much like a wah-wah/volume pedal... same principal... a big pedal actuates a much smaller "volume knob" (aka potentiometer) using a gear possibly... I'm sure we could figure something out... take a part a cry baby and that would be a start (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[jd74914]

QUOTE (tat2dphreak @ Feb 28 2006, 05:47 PM)

I'm thinking it could be done much like a wah-wah/volume pedal... same principal... a big pedal actuates a much smaller "volume knob" (aka potentiometer) using a gear possibly... I'm sure we could figure something out... take a part a cry baby and that would be a start (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

That sounds like a good way to do it as long as the petal is 100% steady and bloted down.

[lapuwali]

QUOTE (fiid @ Feb 28 2006, 02:33 PM)

I'd be interested in how the actuation is actually done - I would think that there would be a return spring and perhaps a solenoid to pull the throttle open with some kind of pwm coming from the ECU. Anyways - I'd mess with it... sounds cool. I'd make sure it's REALLY stable before going anywhere with it though.

Just open the bonnet on your wife's Legacy. Soob's have had throttle by wire for awhile now. My wife's Forester has it, too.

Pretty easy to do traction control this way, too.

Despite my pro-EFI stance, I'm strangely against drive-by-wire. I also don't like traction control, stability control, ABS, or any of that. And yes, I just read the GRM article on the subject.

[grantsfo]

QUOTE (URY914 @ Feb 28 2006, 01:54 PM)

I don't think it would be allowed in most race groups. As a safety issue they like cables and return springs. But you a street car it'd be cool.

I'm curious what do race groups do about Boxsters and 996 series cars that use drive by wire?

[JWest]

Having been involved in testing some of the most advanced control-by-wire systems on the planet, I would say that this should not be attempted by someone who does not have a firm understanding of control systems and FMET. Amazingly strange things can happen in suprisingly simple systems. (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)

The liability is too great (not just life and limb, but even just an expensive engine).

Note that I am not typically a nay-sayer to people's ideas.

[Mueller]

QUOTE (James Adams @ Feb 28 2006, 04:21 PM)

Having been involved in testing some of the most advanced control-by-wire systems on the planet, I would say that this should not be attempted by someone who does not have a firm understanding of control systems and FMET. Amazingly strange things can happen in suprisingly simple systems. (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif) The liability is too great (not just life and limb, but even just an expensive engine). Note that I am not typically a nay-sayer to people's ideas.

for some reason I have a fear that the kid down the street with the remote controlled car could be having an ill effect on the throttle in my car (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

[jsteele22]

Yeah I've been thinking about that one as well. If the issue is merely coupling throttle bodies on opposite sides of a boxer engine, one way to approach it would be to run a conventinoal cable to side A of the engine, and have side B driven by a stepper or servo motor to exactly copy the position of side A.

Getting a stepper or servo motor to hold the throttle open the correct amount is a piece of cake from an engineering point of view; the problem is making it accomplish this in the harsh environment of an engine bay and never failing. But even there, for a single person futzing around with their own car, I don't think that's such a big issue if they are careful. In Megasquirt, for example, you could add some kind of shutdown to be activated if RPM exceeds some threshold while the clutch is pressed. Only one digital input to add (clutch position) and a couple of lines of code. Still, if I had something like this set up, I'd consider the vehicle "experimental" and not drive it in traffic, long distance, etc. until I was _really_ sure about it.


So Mike, are you back to thinking about your ITB project ?

[MecGen]

Hey Guys

Throttle by wire is a proven system used since the mid 90s.
Real drive by wire is coming, Throttle, Brakes, and Steering. On the gas pedal, you have 3 potentiometers, each to check the other, fail safe.
Problems associated with a wired throttle is the cost of the actuator, I bet even used its a good penny, and of course Programming, programming, programming. These are some VERY complex code, I looked at a Ford 7.3 flash and fell on my head. The system is so intertwined with other systems that it would be a nightmare to reverse the code, and I don't know if the MS could handle it.
It sure could make swaps a little easier (IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif)

+Karma
Later

(IMG:http://www.914world.com/bbs2/html/emoticons/beer.gif)

[Mueller]

QUOTE (jsteele22 @ Feb 28 2006, 04:28 PM)

So Mike, are you back to thinking about your ITB project ?

yep...ordered some special aluminum brazing rod with special flux (not to be confused with the stuff sold at the car shows and flea market)

[Andyrew]

Hey mikey.. can you design me a writing instrument.. that is NOT a pencil and NOT a pen? (dont give me no feather either)

I just gotta be different!! (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

sorry....

cool idea.. Dont think that heat expansion is that big of a deal... throw some heat wrap on the cable cover... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Mueller]

QUOTE (Andyrew @ Feb 28 2006, 04:39 PM)

Hey mikey.. can you design me a writing instrument.. that is NOT a pencil and NOT a pen? (dont give me no feather either) I just gotta be different!! (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) sorry.... cool idea.. Dont think that heat expansion is that big of a deal... throw some heat wrap on the cable cover... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

need a different writing instrument??
not sure about you, but I can write my name in the snow (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

[jsteele22]

QUOTE (lapuwali @ Feb 28 2006, 04:09 PM)

QUOTE (fiid @ Feb 28 2006, 02:33 PM) I'd be interested in how the actuation is actually done - I would think that there would be a return spring and perhaps a solenoid to pull the throttle open with some kind of pwm coming from the ECU. Anyways - I'd mess with it... sounds cool.  I'd make sure it's REALLY stable before going anywhere with it though. Just open the bonnet on your wife's Legacy. Soob's have had throttle by wire for awhile now. My wife's Forester has it, too. Pretty easy to do traction control this way, too. Despite my pro-EFI stance, I'm strangely against drive-by-wire. I also don't like traction control, stability control, ABS, or any of that. And yes, I just read the GRM article on the subject.

What was the GRM article ?

About the actuation, the easiest would be a servo motor. The most familiar example is probably the servos in a model airplane/boat/etc, but servo motors can also be quite large. You send them a a PWM signal and they rotate to the corresponding position. PWM stands for Pulse Width Modulation. You sen a signal which is either low (0 volts) or high (5V, say) and the width of the plse determines the position. PWM signals are very easy to generate, and very immune to noise. For this example, the input is the variable resistor driven by the pedal. The feedback is the variable resistor on the throttle body (the TPS). These signals are scaled (if neccesary), compared, and if say the TPS isn't opened enough, the output signal is increased. The output would be a voltage which is then converted to a pulse width. That's the basic idea. As with any negative-feedback control system you have to tune a few parameters to get acceptably fast response without running the risk of oscillations, overshoot, etc.

Less simple than a servo is a stepper motor. These are very common (take a look at Jameco.com) and popular with hobbyists : google it and you can learn a whole bunch. Basically the big advantage, and the big disadvantage, is that its all digital. The motor has several (usually 4 or 6) wires, and if you run current in one wire and out another, the motor will take one "step". Then you stop that, pick another pair of wires and run some current through, and it takes another step. And so on. A single step is typically 1.8 or 3.6 degrees and can be in either direction depending on the direction of the current. You can even be tricky and make it go half a step by driving two pairs of wire at the same time. So the whole problem comes down to choosing which pair of wires to drive and when, and for how long. All the kind of thing that microcontrollers are great at doing. The meager digital outputs of the microcontroller usually go to a chip called an "H-bridge" that can put out enough current to drive the motor. One possible disadvantage to stepper motors is that you don't know directly the position of the motor. But if you start from a known position (say, by trying to close the throttle plate by 360 degrees, so it is guaranteed to be closed) you can then count steps in each direction to know where you are. So in principle, you don't need any other kind of position sensor. But for a robust (safe) system, it's prolly a good idea. Even though its more work, having the system be all digital has its advantages. Any parameters that need to be tuned can be modified in software, rather than relying on physical components like resistors, which can change their value with variations in temperature, age, and grime. And you can email your parameters to someone across the country to try.

[bondo]

Electric cars use this setup all the time, as they pretty much have to. They make somewhat hardened "pot boxes" that are set up for a linkage, and they even make fully self contained pedals with the pot inside.

Most have a redundant microswitch that can be set up to cut off main power if the pedal is all the way up as a safety feature. Perhaps you could wire this up to a backup system that would cut the fuel pump power if it sensed low vacuum (open throttle) at the same time as sensing your foot off the pedal (microswitch).