Engine Control Using Torque Estimation

N

NateDogg

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Sparked form other discussions and my knowledge of torque, here is a introduction of what I have learned on this matter.


In-cylinder pressure and engine torque have been reconized as fundamental preformance variables in internal comustion engines for a time now. Conventionally, the in-cylinder pressure has been directly measured using in-cylinder pressure transducers in a lab enviroment. Then, the indicated torque has been calculated from the measured in-cylinder pressure based on the engine geometry while the net engine torque has been obtained considering the torque losses. however, such direst measurements using conventional pressure sensors inside engine cylinders are not only very expensive but nit reliable for production engines. For this reason, the real world applications based on these fundamental performance variables in commercially produced cars have not been established yet. therefore, instead of employing the expensive yet not reliable approach, this research study investigates different approaches of obtaining and using such performance variables by estimating the net cylinder torque resulting from each combustion event while utilizing pre-existing sensors and essily accessible engine state variables, such as the instantaneous angular position and velocity of the crankshaft. This approach will enhance the on-board and real time estimations of engine state variables such as instantaneous torque in each individual cylinder and bring out many possible event-based applications for misfire detection and general purpose condition monitoring.

Ok with that said, The crankshaft of an engine is exposed to complex forces and torque exitations created by the cobustion process from each cylinder. These torque excitations cause the engine crankshaft to rotate at a certain angular velocity. And, the resulting angular speed of engine crankshaft to rotate at a certain angular velocity. And, the resulting angular speed of engine crankshaft consists of a slowly varying mean component and a quickly varying fluctuating componet around the mean value, caused by the combustion events in each cylinder. Outcome of the torque estimation approaches strongly relied on the ability to correlate the characteristics of the crankshaft angular position, speed, and its fluctuations to the characteristics of actual cylinder torque. Over the past years, this torque estimation problem has been investigated by numerous researches explicitly or implicitly, inverting an engine dynamic model of various complexities. Those researches have developed and validated the dynamic models describing the cylinder torque to the crankshaft angular velocity dynamics in internal comustion engines.

Kinda a mouth full, but I find it interesting.

more to come...in fact...a lot more :)
 
Cool, but the torque measured at the flywheel is a result of mean in-cylinder pressure converted to mechanical force across all cylinders. Right?
 
Originally posted by Windsor377@Mar 3 2003, 10:22 PM
Cool, but the torque measured at the flywheel is a result of mean in-cylinder pressure converted to mechanical force across all cylinders. Right?
Actually, is usally measured from cylinder #1 with a 720degree rotation of the crankshaft. But could easily be converted to all cylinders.


There are two seperate approaches to estimate the indicated torque based on the crankshaft speed fluctuations. The first approach consists of estimating the in-cylinder combustion pressure then calculating the indicated torque based on the estimated pressure and the engine geometry. The other approach consists of directly estimating the indicated torque from the crankshaft speed fluctation measurement.

As said before, in any case of estimation approaches, the model funtion mainly consists of three primary variables: the crankshaft dynamics, position, speed, and acceleration. From the previous studies on other engines, a function related to the crankshaft angular position should be includeed instead of crank angle itself in the basis function because the angular position is clearly cyclic with a period of 4 pie, therefore it introduces a diccontinuity as every engine cycle. Since the mathematical foundation of the stochastic technique are continuous, this discontinuity will lead to undesirable mathematical errors. Therefore, after looking at various continuous funtions representing the crankshaft positions, it was concluded that a function is mathematically related to the crankshaft position but more closly related to the behaviors of in-cylinder pressure or indicated torque whould be more accurate....
 
[/I]ok, sorry about the spelling and wording errors, was in a hurry. On I go....

Since, the compression and expansion strokes, not including the combustion flash, can be considered as polytropic, the in-cylinder pressure roughly follows pV = constant. Since the volume of a cylinder for a given engine can be obtained through the geometry and crank angle, a position function F1 can be considered to be directly proportional to V during the compressionand expansion strokes, and constant elsewhere in order to represent the position of the crankshaft. Such function has a high level of correlation with the measured in-cylinder pressure or with the measured indicated torque since it effectively represents the motored pressure or motored torque information. For the crankshaft speed signal, it was also obvious from the previous studies that the only relevant signal is the crankshaft velocity signal fluctuating around its mean value. Therefore, the general correlation function for estimating the in-line cylinder pressure or indicated torque can be written as afunction of the position function F1 angular speed fluctuation O, and angular acceleration A

Estimated Value = F(F1,0,A)
 
Originally posted by NateDogg+Mar 4 2003, 10:24 AM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (NateDogg @ Mar 4 2003, 10:24 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--Windsor377@Mar 3 2003, 10:22 PM
Cool, but the torque measured at the flywheel is a result of mean in-cylinder pressure converted to mechanical force across all cylinders.&nbsp; Right?
Actually, is usally measured from cylinder #1 with a 720degree rotation of the crankshaft. But could easily be converted to all cylinders.

[/b][/quote]
Kinda late so I con't get into too much here (plus I owe you another spreadsheet!!!). Just a little semantical hair splitting here. We said the same thing here...just different words. And the flywheel reading needs to take all cylinders into account.

Got a quick question. Do you have any constants for estimating or factoring deflection for a given combination?...and what damper do you all prefer?

...keep it coming!!!
 
No, I can't find any either. Thats all that I can understand from that article, everything beyond that goes over my head. None the less it is intresting.
 
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