Amish Elegance
Schadenfreude
- Joined
- May 1, 2006
- Messages
- 3,465
Tacos anyone??
Don't you dare... There is some damn good controls information being spilled here, I plan on learning from it.
It sounds like you two are saying the same thing, just using different terminology. Lol.
tapatalking from droidx
At points I agree.
Ok... Never having messed with EFI Live, but growing up in a business that breathes PID controls I actually have a rudimentary understanding of what you two are fighting about. I am not an engineer (Preface) welcome corrections to understanding.
The way I see these ECM's working as they relate to the tables: The following are known's: Pumps ability to create pressure as it relates to volume. Injectors ability to deplete said pressure based upon volume with given commanded duty cycles. (This is before we muck with it) I know there are many other tables that factor in to this, but these are the only two we are talking about.
As far as the ECM is concerned, you put your foot in it. Injector duration is controlled independently of pressure commands (for purposes of this conversation). As the throttle demands dictate, the ECM reads the pressure table and sends a duty cycle to the FCA. The feedback for this function comes from the rail PRESSURE sensor. If this action is within the permitted hysteresis (I know that term is mostly used in temperature control), no derivative function is necessary. The PID controller is always varying FCA position to match the changing values in the pressure table. At steady state, the integral function assists to stabilize.
OK... PID just has to do with the Rate and Accuracy of which the ECM varies the FCA position trying to hit the pressure value on the table. Sometimes it can (commanded is equal to actual), sometimes it cant (Commanded not equal to actual)
This speaks to the comment about the set-point being aggressively above attainable pressures. The further the feedback value from the rail pressure sensor is away from the pressure on the table, the more drastic the ECM's response will be. Setting a value of 36K will snap the FCA to 100%. At this point you are not even trying to measure.
One exception... the pressure limit value. PID controls have operational bandwidths that can be set to confine them. Regardless of commanded values. Think of it as a limit function. You all say its 23k and change, seems like a good thing given the previously viewed tables.
But my understanding of PID controls, and the degree of their reaction being based upon the degree of deviation from command, commanding a set-point that much higher than the limit would produce a very unstable environment. The ECM would ramp the FCA duty cycle wildly as it approached the upper limit value. That value would kick in, drastically reduce the duty cycle, however the second it fell below the proportional value of the cutoff, you are still VERY far away from setpoint, prompting a harsh reaction by the ECM upon the FCA to correct this sending pressure readings oscillating further degrees from commanded.
As the FCA is also an actuator, is its function also encoded and PID controlled? That is to say, are its movements in response to commanded duty cycle from the ECM measured and functioning perhaps on a PID loop of their own as it relates to movement?
I marvel at some of JSP's other posts. The measurements taken from his fuel system were then CALCULATED into table values for tunes for his standalone. Maybe everybody does this, I just remember him being more open than most.
I digress. Control Engineers fascinate me and infuriate me as I work with them. But I admire them when their voodoo works. I've tried to learn from the ones around here as much as I can. How am I doing?
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