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From: Tony Tremlett on 5 Feb 2010 09:38
"Marvin " <textme@-remove.this-inbox.com> wrote in message <g7vcam$cl6$1(a)fred.mathworks.com>...
> Hello!
>
> As part of a university project I am trying to obtain the
> forces generated by a tyre of a car using a Magic
> Formula/Pacejka tyre model in Simulink. For this, I modelled
> the driveline that starts at the input shaft of the
> differential and ends at the tyres. The model includes
> damping, stiffness and inertia data for the driveline
> components. The torque received by the differential&#8217;s input
> shaft is provided by a look-up table (torque in Nm vs.
> rotational engine speed in 1/s). A state-space block is fed
> with this input torque as well as the torque generated by
> the tyres as a result of the Magic Formula tyre model
> evaluation. The outputs of the state-space block that are of
> interest to me are the two rotational speeds of the tyres
> (in 1/s). These are then used to calculate the slip of the
> tyre. The two obtained slip quantities are then used in
> conjunction with the vertical load on the tyres in the Magic
> Formula evaluation to obtain tyre forces. As has been said
> before, the tyre forces are an input for the state-space
> block and thus get multiplied by the tyre radius.
> Furthermore is the output of the Magic Formula block (the
> two tyre forces) being used to calculate vehicle speed on a
> simple force equals mass times acceleration basis. The
> obtained vehicle speed can then be converted back to
> rotational engine speed and thus is used as the input for
> the torque look-up table. Gear changes do not occur, i.e.
> the vehicle is driven in first gear all the time.
>
> The model works without producing any errors but the results
> I obtain seem to be wrong. First of all the velocity of the
> &#8220;car&#8221; should always increase as the model does not include
> any resistances or losses. The vehicle speed vs. time plot
> however shows several dips in the curve, i.e. a negative
> slope of the curve shortly followed by a positive slope.
> This pattern is basically repeating until it reaches some
> form of equilibrium. Similar patterns can be seen for the
> rotational speed of the wheel, the tyre forces generated as
> well as the slip quantities. All of them seem to &#8220;oscillate&#8221;
> and then at some point reach equilibrium, like a 1-DOF
> system. Apart from the oscillating bit, the magnitude of
> slip as well as the rotational speed is way too large. They
> are however closely related, so solving one bit might solve
> the other. On the other side, the magnitudes of the tyre
> forces and the vehicle speed seem reasonable.
>
> I put the .m file, the Simulink model as well as some
> pictures of the results on the following website:
>
> http://www-student.lboro.ac.uk/~ttmr2
>
> Can anyone explain the oscillating bit? I can absolutely not
> figure out where that is supposed to come from. Hopefully
> finding the cause of the oscillations will also clarify why
> the wheel rotational speed and slip quantities are that large.
>
> Any help much appreciated. If you are planning to download
> the Matlab and Simulink file you have to add a .m and .mdl
> as file extension to the file names in the &#8220;save as&#8221; dialog
> respectively.
>
> Marvin


Hi,

I'm trying to do something similar, but build up a model which will also predict limited slip differential characteristics, and their influence on the two wheel speeds...

I am fairly new to simulink and have started to build a fairly basic model, but it would be good to see how this existing model has been built up - does anyone know where I can view this model or one similar? The link to l'boro uni needs updating....

Any help would be much appreciated,

Tony
(Cranfield Uni)
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