Drive-By-Wire Throttle Body Characteristics

Are you using an off the shelf controller, or homemade?

https://www.youtube.com/watch?v=YJu-hR4h_KA

http://www.talkingelectronics.com/EMR-2/SimplePWMThrottle.pdf

Here's the controller:http://www.amazon.com/gp/product/B00HU031D6?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

I don't think this controller you listed will work for this application, at least not without modification....but you'll need somebody else to sort that out....I would just get one that is designed for this purpose...

http://www.autodiagnosticsandpublishing.com/etc_electrothrottle_electronic_throttle_tester.html

Yes, I've been thinking...the motor and gears are going to have some stiction/friction that is going to interfere with precise tracking (unlike a servo or stepper, the motor is a simple brushed DC motor that works against a spring that is trying to close the butterfly). The throttle body has a sensor that reports the butterfly position to the ECM, which is also reading the position of the accelerator pedal. I'm guessing that the ECM imposes some signal onto the PWM to overcome the mechanical problems and make the butterfly match the position of the pedal. I'm combing the net and will report anything I find.

I suspect that you're assuming that all PWM controllers are interchangeable, but they're not. In addition to the duty cycle, there's things like the output voltage/current, the actual pulse width/height, and the shape/timing/frequency of the pulses, all of which will have an impact on how the motor responds and the throttle moves.

Here's an explanation that seems to imply some PID functionality in the ECM:

http://www.cvel.clemson.edu/auto/systems/throttle_control_demo.html

The driver in the demo is just a basic square wave of 12 volts, but there is a reversing switch in the circuit. That puzzles me; there must be more to this than I assumed.

I'm going to look for pics of the guts of the throttle body.

Hello SSCpal that throttle body can have programing in the computer for opening rate as well as a timing protocol to pull timing out for detonation depending on which computer you are using. This may be some of your issues trying to fight for control of the throttle body opening rate and rpm that may be programed/installed in the computer.That is if you are controlling max rpm, if not it as well may try to interfere with the operation of said throttle body. Also if the TPS switch is bad it can also cause issues with the programing and operations of the throttle body us a DVOM and check the sweep of the TPS and make sure that it has the right characteristics you were trying to get.

Probably not, the throttle body is a "dumb" device, basically a reversible DC motor that gets all its intelligence and commands from the ECM. Since SSCpal is trying to bypass the ECM and move the plate directly with his own electronics, there's nothing in the throttle body that would subvert his commands. He just has to provide the right level and type of signal to make it respond properly.

One other thing I forgot about, check for stray electronic scatter that may drive your unshielded controller just a little nuts. Sometimes it is the simple things that bite us in the backside.

One other item I just thought about is your computer equipped with traction control. It might also have something to say how the throttle opens and stays open or flutters depending on wheel speed and g-force. Just to keep the tires from spinning and loosing traction.This item is especially true of Corvette and Camaro computers. You will have to install a switch to turn off that feature if in fact it is the problem.

Yes, the ECM has very sophisticated PID functionality, but in this case it's only used for ECC (Error Correction Control) of the internals of the control loop, not its intended response. For this type of control we want the position of the throttle plate to track exactly the position of the gas pedal; i.e., proportional control, not the integral (cumulative) or derivative (rate of change) of the pedal position.
The Clemson link has some useful information about the nature of the signal to the throttle body. They used a unipolar 12VDC, 1.6A pulse at 1kHz to move the motor, which is considerably different than the 13kHz repetition rate from your controller. The reversing relay that they used to change the polarity of the pulse is probably implemented in the ECM's driver by using bipolar switching in the output circuitry.

Hi Lockduke. I'm not using an ECM or other sophisticated controller, just a generic PWM generator. I'm been looking at patents and the real controllers appear to have PID functions in a feedback loop from the throttle body, as well as other processing. Since the throttle bodies are very simple (just a small DC motor with a plastic gear train working against a spring to turn the butterfly) and subject to the usual mechanical infirmaries, it makes sense that it will take more moxie than a plain PWM to achieve precision. All I've found so far are block diagrams, but I'm going to keep looking for schematics and detail explanations.

FYI, my goal was to build a stand-alone ETC for my hot rod. It may be harder than I anticipated. But the learning is fun.

You might check with John Mahovich who makes throttle bodies. for a whole host of vehicles for the racing industries he has been a real big help in our 4.6 twin turbo set up for a lot of the hard parts like timing chains and repairs for weak points on the 4.6. He is the brains behind Accu Fab machine. They make throttle bodies and other trinkets for those of us who think jewlery has oil and gas attached to it

Yeah, AccuFab makes expensive manual throttle bodies. I'm finding some videos of guys controlling electronic throttle bodies with Arduinos. And Arduinos can do PID. Guess I'm gonna take the plunge and get smart on them. I prefer working in analog, but the future is digital.

..or maybe not. I've found lots of simple analog circuits to do PID control. Anyone have any experience with that approach?

I still have only a basic idea of what is actually going on between the throttle body and a typical ECM. There is some PID in there, but what else might be needed I don't know. I need to start with basic PID theory and see if it is enough to do the job.

No point in dissecting a typical ECM; they are full of microprocessors and all the smarts are in the software.

Could you use something as simple as a multi-position switch with a high number of contacts with given voltages like a variac ?

No, two problems: 1) the mechanical inconsistencies. The motor and gears are not precision parts, and they will wear over time, so some control loop to keep the butterfly matching the foot pedal is needed. And 2) DC motors prefer their rated voltage; dropping it can make a hot and cranky motor. That's why we do PWM on them.

I think I'm going to build an analog PID controller (lotsa simple circuits on the net) to drive the PWM generator. I found a 1994 patent 5,333,584 that breaks out these functions in a block diagram of an ECM. So I'm getting closer to what is needed to make this work.

Nice over view here....

http://www.aa1car.com/library/throttle-by-wire.htm

http://home.cogeco.ca/~rpaisley4/Throttles.html

http://www.autospeed.com/cms/article.html?&title=The-Programmable-Management-Leap&A=2074

I am coming into the new world of electronic controlled race systems kicking and screaming all the way. Oh yeah I just hired a 3 year old genius to do our electronics my great grandson he can find thing on my new phone I did not know existed or how to get them on the screen, he is more qualified to tune this car than I.