Announcement

Collapse
No announcement yet.

Speed Density operation

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Speed Density operation

    I was doing some reading on how the average speed density ECU works trying to relate it to PRJ's modifications. From what i understand so far is that this is speed density with alpha-N blending during closed loop and part throttle driving. i know the MAP sensor is obviously important because i forgot to hook the map line up to my ECU and the car idled/ran like complete crap without it lol.

    This is where i learned a lot about speed density and the alpha-N blending.
    http://support.moates.net/theory-speed-density/

    what i think is the MAP sensor is replacing the MAF input in the code meaning that most of the values aside from the VE table itself and the IAT correction are reused for SD. im just curious about how the SD works because i think if i can understand it better the concept can be applied to other motronics as well. i'd like to turbo my V8 after i swap it on its stock ECU and use the SD code in the original ECU with a few hardware modifications to use an external MAP sensor like a GM 3BAR fed to the same analog input. hopefully im going in the right direction.
    "The really good drivers got the bugs on the side windows." Walter Röhrl

  • #2
    Later motronic using the MAF sensor first and later they switch to MAP, I see the advantages when you have an MAF sensor but I also see the disadvantages in regard to leakages etc pp.

    Megasquirt speed density explanation is quite good, may this helps: http://www.megamanual.com/v22manual/mfuel.htm

    Comment


    • #3
      All speed density algorhitms is pretty same (use pressure, VE table, common formula for convert flow to mass), because there is no way to make it differently. But one thing is completely different - intake air temperature process. Its headache if we discuss engines, and double headache if turbo-engines. Temperature for conversion formula must consider coolant and air in several engine states, use only intake air temperature will lead to an undesirable result. In addition, in some modes of engine operation, indirect air mass calculation will always work incorrectly, so it will be necessary to make calculations by throttle and RPM (Alpha-N), or use constanlty WBO like in modern cars

      Comment


      • #4
        Yes. Ideal or real gas law or something different. Heat soak issues with bad placed IAT sensors etc pp.

        I like also the idea to use two map sensors. Before and after throttle body. :-)

        Comment


        • #5
          Heat soak issues with bad placed IAT sensors etc pp.
          There need because of transition effect of air, it heats up from cylinder head, valves, intake system e.t.c. and this is more related to coolant than intake temperature. Like load not fully related to RPM, but in throttle position too.

          Comment


          • #6
            Yes you need some strategies for hot start etc. when you use which sensor and when you ignore the sensor.

            As I mentioned newer Motronic use MAF sensor and switch later to MAP, maxed out MAF sensor for example.

            Comment


            • #7
              My code is explained in the wiki.

              I convert MAP to LOAD first, because otherwise if you have maps in the ECU that are RPM x MAP every time you change the VE you need to remap everything.
              If you have RPM x LOAD you only need to fix the VE map and everything else falls in place.
              http://tuner.ee - http://www.facebook.com/tuner.ee

              Comment


              • #8
                i think i noticed this in the motor chip binary, it looks like you simply removed the original MAF input and replaced it with the MAP input instead. im my mind that would place the MAP signal right in the middle of the load calculation part just like the MAF was. i know its more complicated than that over all but thats how it sums up to me.
                "The really good drivers got the bugs on the side windows." Walter Röhrl

                Comment


                • #9
                  Originally posted by vwnut8392 View Post
                  i think i noticed this in the motor chip binary, it looks like you simply removed the original MAF input and replaced it with the MAP input instead. im my mind that would place the MAP signal right in the middle of the load calculation part just like the MAF was. i know its more complicated than that over all but thats how it sums up to me.
                  That's not how it works at all. Original is simply MAF off a counter / rpm * lin = load.
                  If you look into the code you will see that the entire maf lin and load calc function is missing.
                  http://tuner.ee - http://www.facebook.com/tuner.ee

                  Comment


                  • #10
                    I havnt gone in depth into how it works honesly in the code, i just know it works and it works well plus its easier to tune it than with a MAF. correct me if im wrong but you essentially replaced the x3 MAF tables with the VE table as the basis for open loop/in boost fueling? like once above the lambda load threshold the main contributor is the VE table?
                    "The really good drivers got the bugs on the side windows." Walter Röhrl

                    Comment


                    • #11
                      Lambda has nothing to do with it. VE is pressure to load conversion.
                      http://tuner.ee - http://www.facebook.com/tuner.ee

                      Comment


                      • #12
                        Originally posted by prj View Post
                        Lambda has nothing to do with it. VE is pressure to load conversion.
                        but the VE table is the basis for all of the fueling right? once the load limit map is exceeded the ECU stops using closed loop meaning the lambda table is not used anymore, it instead follows the VE table only in open loop till the load value goes below the what the load limit table has specified. what your saying is that the lambda table has nothing to do with the operation of the engine at all anymore and there is no closed loop operation? im trying to understand how the maps function with each other during engine operation.
                        "The really good drivers got the bugs on the side windows." Walter Röhrl

                        Comment


                        • #13
                          Originally posted by vwnut8392 View Post

                          ...once the load limit map is exceeded the ECU stops using closed loop meaning the lambda table is not used anymore, ....
                          Not correct... ECU always use "lambda table" if you mean 0x8E13 Fuel enrichment map. Lambda control is just an adjuster of incorrect setting/tuning and/or change of environment ( not correct IAT correction maps for example) for which Rasp wrote above. He wants perfect settings. If we have perfect settings and there is no deviation from them i.e. stable environment, lambda control will be more or less useless.

                          Dmitri wrote that the VE table has nothing to do with lambda load threshold and Fuel enrichment map directly. The value from the VE map is one of the parameters for load calculation + Fuel enrichment map + IAT correction maps + Wall Film enrichment maps + Lambda correction value/s + warmup enrichment maps + etc. and etc. calculated on the basis of Injector constant. Then your question "but the VE table is the basis for all of the fueling right?" have the answer!
                          look for ram_46 and will find how it's added and then load recalculated by this VE map values then look for ram_7B and will find how load is recalculated by value from the SD IAT map.
                          Last edited by d_anev; 2 April 2018, 12:20.

                          Comment


                          • #14
                            Originally posted by vwnut8392 View Post
                            im trying to understand how the maps function with each other during engine operation.
                            You should start with basics and not overcomplicate things once again.

                            First: Fuel injection is always a good estimate based on calculations (air mass, target lambda, injector characteristics, temperatures, etc). In closed loop operation ECU reads feedback from the lambda probe. If lambda feedback and target lambda are different, ECU applies corrections based on the difference. In this ECU there are no different fueling algorithms for open or closed loop operation. You should know this by a look into your book.

                            Second. Speed density is only a new way to measure load. Original ECU uses MAF for this. Once the load has been calculated, not a single function cares how and where the load was measured.

                            Comment

                            Working...
                            X