Re: A simuv2 backport of the clutch/gear-change inertia fix

[email protected] wrote:
> On Wed, 09 Jan 2008 21:19:42 +0100, Christos Dimitrakakis 
> <[email protected]> wrote:
> 
>> (rather than having the engine break simply proportional to the 
>> maximum engine torque at each rpm, it is a linear function of the 
>> torque produced at maximum power - this means that there is always 
>> some engine break, and it is always higher at higher revs).
> 
> 
> Hi,
> 
> maybe this is just a first order approximation but isn't the engine 
> breaking more a function of engine capacity, compression ratio and 
> number of cylinders ? Although these factors will affect the max torque 
> it does not mean the torque is what determines the engine breaking.
> 

Well, it is not easy to determine this.  The idea for the model is to 
say that there is a 'engine brake' parameter for each engine, which we 
can call F.  Now, in this model, F just tells you how much of the 
produced power is wasted at maximum output power. (So F is the converse 
of efficiency at maximum power)  I think that for most engines it's 
fixed at 30%.

  > I guess this fix is an improvement on the old model but may be somewhat

This fix just fixes a bug in the old model (where in some cases you had 
no engine braking at all, and where fuel was magically generated in your 
tank).

> off target in that it is not related to the engine parameters that do 
> determine the engine breaking.

It is not clear how to determine braking from the engine parameters, 
which is why we have 'engine brake' parameter F.  From what you say, I 
think that if F is set correctly according to each engine, the model 
type (a constant + linear factor for braking) is adequate and the only 
question is how to determine F.


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