New vehicle dynamics reference

[Austin]

Thought you guys would be interested.

There is a new vehicle dynamics reference out, it covers all the basics but then also goes into the more detailed topics such as stability and aero taking a slightly different approach. It also covers things such as temperature modelling in tires, inerters and the effects of the diff. (Ive found it hard to find good references for this stuff)

The first 55 pages are free to look at and all the details can be found at:

http://www.ebook.com/ebooks/Al...f_the_Race_Car/16469 (http://www.ebook.com/ebooks/All/The_Dynamics_of_the_Race_Car/16469)

Happy reading

[Austin]

Thought you guys would be interested.

There is a new vehicle dynamics reference out, it covers all the basics but then also goes into the more detailed topics such as stability and aero taking a slightly different approach. It also covers things such as temperature modelling in tires, inerters and the effects of the diff. (Ive found it hard to find good references for this stuff)

The first 55 pages are free to look at and all the details can be found at:

http://www.ebook.com/ebooks/Al...f_the_Race_Car/16469 (http://www.ebook.com/ebooks/All/The_Dynamics_of_the_Race_Car/16469)

Happy reading

[murpia]

Interesting stuff.

Based on Austin's description of 'detailed topics such as stability and aero taking a slightly different approach. It also covers things such as temperature modelling in tires...' I had a private bet with myself before clicking the link that the author was Danny Nowlan.

His Racecar Engineering articles are pretty bold in presenting a great deal of maths for a 'popular' magazine. Aside from Milliken he's the only author I have found to take a stability approach to vehicle dynamics and he adds a transient tyre temperature model to that. Very powerful.

Regards, Ian

[Hector]

Austin, have you actually read this book? I've spent a lot of time searching for the effects of the differential on vehicle dynamics but have found very little so far. Milliken RCD had a short blurb as have several other texts and technical papers (mostly published by FSAE teams) but I've found very little on how to model the effects. What kind of detail are we talking here? Even though I'm now an FSAE alum I spent four years doing drivetrain and trying to model the effects of differentials and the question still bugs me.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I've found very little on how to model the effects. What kind of detail are we talking here? Even though I'm now an FSAE alum I spent four years doing drivetrain and trying to model the effects of differentials and the question still bugs me. </div></BLOCKQUOTE>

Where exactly are you stuck in your analysis?

[BillCobb]

Modeling the 'differential' is actually quite straightforward. Having the properties of the differential is where the problems start, especially when you have high end (=high cost) manufacturers who have claims about their product's characteristsics, but those claims are unsupported by test results or characterizing functions. You need a lab test sequence (i.e. dyno closed loop control) to smoke out the truth. Effects on the steering axle are more pronounced with a differential, hence the penalty to FWD and AWD. If friction is a strong player, you need a great friction model in your math.

I'd worry more about about steering effort science than differential effects, and, as for the importance of tire temperature effects in FSAE, that belongs in the comedy section. I'd guess that 50% of the cars in the autocross are driver limited and 30% are motor/driveline restricted, not chassis and/or tire limited.

Those fractions seem to apply to ALL racing forms IMHO (even horse racing, in my past experience)...

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">as for the importance of tire temperature effects in FSAE, that belongs in the comedy section. I'd guess that 50% of the cars in the autocross are driver limited and 30% are motor/driveline restricted, not chassis and/or tire limited. </div></BLOCKQUOTE>

+1.

Not to mention... however hot your tires wind up running, you're pretty much gonna be stuck with that.

[Austin]

Hector, I havent had a chance to read the book all the way through yet, but have read quite a few of the sections including the Diff part. The diff section does actually go into a bit of detail.

It goes through how to determine the correct locking ratio for the diff to ensure that maximum tractive force is obtained at the drive wheels and how to determine if your diff is over locked or under locked and how that relates to the traction ellipse of the driving wheels. Finally it discusses the effect of the diff on the stability index of the car.

As far as evaluating the diff it is one of the better references I have come across.

In terms of gathering accurate data for a diff I agree with BillCobb, friction will just make trying to model the internal effect a nightmare.

I must also agree with the fact that drivers are a huge limiting factor in FSAE and tire temperature effects are probably never going to be considered in the formula, but I guess the book is aimed at motorsport in general and not just FSAE.

It would however be interesting to see what kind of heat cycle the tire go's through during the course of the lap, yes they heat up and you are stuck with that but that's not to say that is a completely uncontrollable effect, you can alter the amount of energy dumped into the tire by adjusting various suspension parameters. I wounder how great the tire temperature effect is on FSAE tires, I suppose if they drop off quickly when they get too hot it may be better to run a slightly softer setup to ensure they never get there. Although I must admit I spent most of my time in FSAE trying to get heat into the bloody things.