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12th May 2011, 22:27 | #61 | |
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| Re: ECM changed, now what? Quote:
hard deposits like soot, tar and gum, the nozzle and needle behave differently. here's by how much: i talk about a 2 litre engine. the values i quote are not standard but a comparable to an engine of this size. you may apply a multiplication factor based on engine size. hence for the 1.3 litre FIAT engine, the values may be 60% of what i write. i dont know for sure. this is just for reference. at low idle, the injection pressures can be as low as 250 to 500 bar and the needle is also lifted for a small time. the time for which the injector remains open during this time is about 400 to 750 us (microseconds) and the injection quantity can vary from 3 mg to 10 mg. at the end of something like 2 lakh km on the engine, this quantity may reduce by as much as 80% so instead of 5mg, it is sending something like 1mg only. a correction is necessary and is incorporated over the life of the injector in the form of "Zero Fuel Calibration" so i will leave the injector open for something like 900us as compared to the 400 when new. the percentage variation in injection quantity is a function of rail pressure and the relative time for which the injector remains open and is pretty much inversely proportional to both. think of this analogous to your common house water tap. we want to fill a bucket of water. the there are three variables: 1. percentage of tap opening 2. time for which the tap remains open 3. the location of water reservoir / tank. the higher this is, the faster the water will fill. people staying in a tall building with an overhead tank will know this. the residents at the ground floor have water coming out with most force. the ones staying on top floor suffer from low pressures. point 1 is the injector lift. point 2 is injector lift duration (in microseconds; a derived unit can be crank angles) and point 3 is rail/injection pressure. simple hold on... it gets better form here! mind you, the injection does not happen instantaneously so there is a finite time lag which begins from the ECU sending the signal to the injector opening initiation. say this is 100 us. the injection pressure build up is also not instantaneous. say it is 50 us its called ramp up time. similar 150 us during ramp down as well. thats 300 us of nothing. this value changes over the opeating range so what i am saying is, the percentage of drift will change over the rev-range and thru the torque map; coming as low as 20% worst case to 80% as discussed. the drift will be detected by one of the learnings incorporated in the ECU. the ECU knows that for a certain engine operating condition, an 'x' amount of fuel needs to go in. it will also know, that if this amount of fuel doesnt go it, the driver will depress the accelerator pedal further. so there's a mismatch. this is one of the ways to figure it out. every engine also has a friction map. meaning, the amount of energy lost to friction is available in a table form across the rev range and over time. this amount of energy after a lot of processing sublimates into amount of fuel. so this finds its way into the drift calibration. i could go on because the ECU has thousands of such maps and corrections. the higher the emission and durability targets, the complex this gets! good food for thought eh? and imagine getting paid for this!! thats what gave me the jollies Last edited by Eddy : 13th May 2011 at 20:03. Reason: removed extra smiley | |
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12th May 2011, 22:34 | #62 | |
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| Re: ECM changed, now what? Quote:
the other often comes with a vacuum pump fitted to it with a woodruff key. the missing tooth by iteslf will not tell the TDC is occuring at that time. there is a fixed relation of the missing tooth and the TDC. say 75 degrees BTDC. but what you cant figure out is that whether the TDC is arriving at the end of compression or at the end of exhaust. you can waste spark, but not diesel by firing every time TDC comes. for this, the cam phase sensor is used. for one TDC, both the valves will be closed and for the other, the exhaust valve will be open. you can realistically have the lobes and pump mounting any which way. both are possbile. | |
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12th May 2011, 22:58 | #63 | ||
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| Re: ECM changed, now what? Quote:
Thats true... consider a 4-cyl inline, at a certain given point, two cyls will be at TDC and two will be at BDC... to identify the cyl which is in the power stroke, u need an additional cam sensor... by simple math, a missing tooth can only tell u a specific position (of course within tolerance) in a 360 deg cycle. To detect the position in a 720 deg cycle, you will need an additional position sensor... hence the cam sensor Quote:
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12th May 2011, 23:45 | #64 | ||
BHPian | Re: ECM changed, now what? Quote:
6 degree which will be effectively 3 degree for one complete cycle(4 strokes) Quote:
The cam sensor is the one which points to the TDC. it generates two triggers per every cylinder. one indicates pilot and other indicates main. | ||
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12th May 2011, 23:52 | #65 | |
Senior - BHPian Join Date: Dec 2010 Location: Ghaziabad/Hyderabad/Mysore
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| Re: ECM changed, now what? Quote:
What I'm thinking is:
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12th May 2011, 23:56 | #66 |
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| Re: ECM changed, now what? |
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13th May 2011, 00:19 | #67 | |
BHPian | Re: ECM changed, now what? Quote:
2. ECU do recommend the user via SVS lamps(service vehicle soon). drifts are applicable for turbo, air mass, intake manifold pressure, pressure control valves etc.. 3. could not understand what you meant. 4. ALL diesel CRDIs are drive by wire and only MPFI with electric throttle flap is drive by wire. yes its 60 teeth minus two. few OEMs deviate from this. | |
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13th May 2011, 01:20 | #68 | |
Senior - BHPian Join Date: Dec 2010 Location: Ghaziabad/Hyderabad/Mysore
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| Re: ECM changed, now what? Quote:
What I meant was - control system can be open loop or closed loop. Open loop is faster and simpler but has accuracy limitations - in some cases these can be corrected by periodic calibration (like the case for injectors). closed loop is slower but more accurate (e.g. measure O2 levels via lambda sensors and use that information for fuel injection) - in a way drift due to aging/temperature change etc. is corrected for in real time. so I was wondering whether the engine is being controlled via a full fledged closed loop control system that also calibrates all of its parameters from time to time. I could figure at least this one out By the way, is there any modern text on engine control - I have a copy of Heywood's book but nothing modern, and I guess the techniques you guys are mentioning were not possible when Heywood wrote his book. My level (a reference for you when you suggest a text): I have good enough knowledge of sensors physics, control systems behaviour analysis and design, and electronics and have been teaching students Physics and Maths for years. Last edited by vina : 13th May 2011 at 01:23. | |
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13th May 2011, 13:38 | #69 | ||||
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| Re: ECM changed, now what? Quote:
Quote:
Quote:
With the internal relationships of the engine components 'cast in iron' so to say, why wouldn't we be able to keep track of what is the current position of each of the components from one signal? (Assumption: engine rotates in only one direction all the time ; ignore back-fire in petrol engines?) The missing teeth only confirm that the signal is 'plausible', and give a certain positional reference. Beyond the first recognizable reference during starting crank, wouldn't everything appear (to the ECU) as a set of repeating events strung out over time? The only time variance would be RPM dependent. Most of the timing relationships actually start with data written in configuration (ROM). This is done on paper first, looking at the design of the engine, and then configuring on the test bed. How else would the control guys adapt the same ECU for 4/5/6 cyl engines? If not, one would have to write software all over again for every new engine, and incur - instead of incremental cost - one complete s/w dev cycle cost every time. For example, to know whether the engine has started firing during the start-up cranking, one looks for the (angular) acceleration of the crankshaft for each cylinder cycle. Using a conventional encoder is one (rather costly due to cost of the encoder) method. The cheaper (and low cost) method is to look at the changing time relationship of the pulse leading and trailing edges of the pulse train coming from the tone-wheel sensor. A set of continuous 'successes' signifies engine can be switched to normal mode of operation (idling). Quote:
And, if someone manages to write a tome on modern engine control, he / she would be violating a lot of NDAs. IP, baba, do you want to bankrupt the companies or what? Last edited by tsk1979 : 13th May 2011 at 17:36. | ||||
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13th May 2011, 14:11 | #70 | ||
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| Re: ECM changed, now what? Quote:
The 3 deg (or is it 6?) uncertainty in determining TDC is something I'm finding astonishing. Is 60 ppr as standard as 48/ 96 for ABS? For 2 missing tooth, are these non symmetrically placed. (If so, obviates need for the second quadrature channel) Any progress on decoding the injector code? Quote:
If one were to model the injector, what would the model be? And as it ages, would the model remain valid, with just a change of parameters, or would we have to change the model. Further questions (if any) after Star's reply. Regards Sutripta | ||
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13th May 2011, 14:57 | #71 | |
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| Re: ECM changed, now what? Quote:
Regards Sutripta | |
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13th May 2011, 17:02 | #72 | |||
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| Re: ECM changed, now what?
Oh, they most certainly do. Both the principle and the (lowercase) practice. Quote:
Quote:
Quote:
Sir, what I meant was any encoder, whether absolute or incremental, would be pointless since it will add to the cost of controls without giving overriding benefits. The difference is you are expecting mandatory presence of an encoder for knowing c/s angle (c/s angle domain reference), whereas I as a programmer am not (time domain reference). Last edited by DerAlte : 13th May 2011 at 17:07. | |||
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13th May 2011, 17:12 | #73 |
Team-BHP Support | Re: ECM changed, now what? The Safari diesel engine has 2 sensors related to timing 1. Crank Angle sensor 2. Cam sensor On the early 3.0s, when either of them died, the engine would not start, leading to many stranded owners on the highway. Tata fixed it with a more robust model in later iterations. Therefore the 2.2 has never had the dreaded "Cam sensor/Crank angle sensor failure issue". I suspect, the ECU programming would not be time driven. It would be more of "interrupt driven" with timekeeping purpose just as a "failure checker". For example, if you interrupts are coming at the wrong time, you could put the engine into shutdown or limp home mode. |
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13th May 2011, 18:23 | #74 |
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| Re: ECM changed, now what? Oh shoot!!! <running away to find a buyer for the 3.0l DICOR> You are right, @tsk, the programming IS interrupt (incl. non-interrupt Event / soft interrupts) driven. The allusion to time hear is not about clock-driven real time, it is relationship with the edges arriving from the c/s and cam sensors. The edges arrive at RPM dependent times relative to the previous one - and interrupts are raised by the module that is monitoring the edges. The main software just keeps count of how many edges passed to figure out where the c/s is (angularly). The edge-monitoring module also figures out things like edge or pulse not arrived on time (comparing with short term history, since there are no sudden changes expected one pulse to the next) and makes the other modules handle exceptions as applicable. Not allowing the engine to start on failure of either sensor is rather drastic. It is possible to allow engine start and limited operation (limp-home; pollution standards can wait) under such circumstances. This is one example of difference in techniques between one injection system vendor and another. |
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13th May 2011, 19:40 | #75 | |||
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| Re: ECM changed, now what? Quote:
IS there only 1 pilot injection? I heard the famous Quadrajet / MJD / DDiS has 4 injections per cylinder? And thats why the combustion is better than market and it is able to meet BS ?? norms Quote:
Sir, What IFF the encoder fails, I've seen many encoders fail over time in a different environment and we have accidents [not in a car of course] Plus they are bloody expensive and very sensitive to dirt!! I doubt any automobile manufacturer uses them!! Quote:
Ok - Now that we have great minds here - let me start with my silly questions : 1. How do the Remap guys tweak the values? What values are tweaked? 2. How does piggy back ECU affect the vehicle - I want to understand the disadvantages. 3. Can we erase the ECM - Chances? Last edited by headers : 13th May 2011 at 19:42. | |||
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