Some might like this info about braking:

http://www.delphi.com/pdf/tech...3.PDF

 

There's three kinds of numbers:

The first kind is like dollars...or lap times.

The second are the kind with too many decimal points.

And the third are Dimensionless Coefficients.

Scott, who thinks dimensionless coefficients are scary...they remind me of the idea-less thoughts that crowd my brain...

 

That looks like just the kind of article I dread running into when I buy a "Racecar Engineering" magazine. I can read and understand a good bit of what is in the magazine and then bump into the article with all the freakin math and funky graphs goes straight over my head.

Barry H.

 

.... and I dont need 10 pages of math and funky graphs to tell me the **** dont work when you overheat it

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">Some might like this info about braking:

http://www.delphi.com/pdf/tech...3.PDF</TD></TR></TABLE>

theres really no information to be had from this paper other than the obvious. the point of the paper was just that they created a good computer model to predict brake fluid temperature and could then change parameters to design around.

shrug.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">There's three kinds of numbers:

The first kind is like dollars...or lap times.

The second are the kind with too many decimal points.

And the third are Dimensionless Coefficients.

Scott, who thinks dimensionless coefficients are scary...they remind me of the idea-less thoughts that crowd my brain...</TD></TR></TABLE>

oh c'mon dimensionless coefficients are fun!

Good ol Buckingham Pi...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">

theres really no information to be had from this paper other than the obvious.</TD></TR></TABLE>

Some guys are just so hard to please!! I tought there was a thing or two to learn.

In particular, speaking of the obvious, I discussed brake cooling with Andy Lin when I bought my first set of pads from him a few years ago. He said more than once to just cool the caliper, while I was asking him for a source of brake ducts to cool the centre of the rotor, as that is the source of all the nasty heat, but he kept saying to just direct air at the caliper. So even guys in the brake business might use some of the info from that paper, to learn the obvious. The charts of heating and cooling are particularly nice, as is the section of the brake system showing the color map of temperature. And I never knew your brake fluid could start to boil ten minutes after you park the car.

 

We got to see some neat graphs that tell you,
(1) Bleed your brake fluid often to keep the %water at zero.
(2) Aluminum brake pistons / calipers transmit the heat WAY faster to your brake fluid so don't use em.

 

Good article. I had to make a similar simulation for a Heat Transfer class, minus the transient stuff.

The heat soaking of the caliper and fluid long after the car parks is interesting.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 577HondaPrelude &raquo;</TD></TR><TR><TD CLASS="quote">We got to see some neat graphs that tell you,
(1) Bleed your brake fluid often to keep the %water at zero.
(2) Aluminum brake pistons / calipers transmit the heat WAY faster to your brake fluid so don't use em.</TD></TR></TABLE>

He didn't really model the cooling of the components as well. One could argue that the steel and Al calipers reached the same steady state temp after a short cool down period, and it'll actually be much easier to cool the Al caliper down with spot cooling(such as a duct).


I wouldn't just cool the caliper of a car, although it does help to have some air dumping over it. The rotor is where the heat is generated, and where you'd like to cool so as to keep the lining of your pads touching the rotor as cool as possible.

 

Wow lots of math, still think my article had more relevent information. Although its an interesting read, thanks for the link. Anyway i thought you had to pay for all the SAE papers, how do you get the pdf versions?

 

These types of analyses are approximate due to the required oversimplification of the physical processes involved. The actual solution to these partial differential equations can not be found exactly. As a result, this paper's author had to simplify his analysis to obtain the results. For example, the actual convective heat transfer coefficient computation is very complex and the author of this paper just used an "effective heat transfer coefficient", which may be in error up to 30%. Other simplifications include using semi-infinite slab approximations for the transient cases. In effect, they are order of magnitude estimates and as such, the biggest benefit is not in the actual temperatures obtained, but rather, the temperature trends for the different materials used in the calipers and brake pads.




Modified by Johnny Mac at 2:38 AM 9/2/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Johnny Mac &raquo;</TD></TR><TR><TD CLASS="quote"> Other simplifications include using semi-infinite slab approximations for the transient cases</TD></TR></TABLE>

Ah ha!

Transient response! Who knew?

RJ - who is going to work on maximizing his brake fluid temperature's transient response! I will win for sure now!

 

You know we can do infintly more complex analisys of these problems, but we can measure more than we can control, and fully understand even less. So really for most of us i think that paper pretty much gives us as much as we need.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ohjolt2 &raquo;</TD></TR><TR><TD CLASS="quote">You know we can do infintly more complex analisys of these problems, but we can measure more than we can control, and fully understand even less. So really for most of us i think that paper pretty much gives us as much as we need.</TD></TR></TABLE>

How would you go about doing a more complex analysis?

 

I copied and pasted some of the places where they used a fudge factor or a generalization, their are more but you get the idea. It could be more complex, NASA would have spent 5 million dollars on it. The point i was making was general, that all issues concerning cars and other systems can be made very complex, but the law of diminishing returns has to come into play some where. On our cars we have only so many variables we can change, modeling other variables and modeling to a degree of acuracy that requires so much effort seems to be pointless. Now if we were all F1 engineers then we could afford and it would be usefull to get *** deep into the math. I think its allways good to read papers and articles of a technical nature, even thought we cant change some of the things they may discuss because its still insightfull to understand why certain things happen. I guess i am trying to say that their is a balence here, and that article pretty much told me all i need to know about brake fulid boiling after i turn my car off.
Note the copy and past lost the equations as they dont convert to ascii well.

A simple linear relation between the tire
slip and tire-road adhesion can be used as a good
approximation for the mild to moderate braking on a dry
road though they exhibit a highly nonlinear relation over
the complete range of tire slip.

Since reliable contact conductance data for many engineering
materials are not readily available including
brake friction pairs, the proper value for the thermal
model was selected based on the measured temperature
data. Good results were obtained with the contact conductance
of 10,000-30,000 which agrees well
to the measured conductance values of common engineering
materials [12].

It was assumed that the heat is uniformly distributed
on the disk swept area and pad contact surfaces.
It should be noted that the localized contacts under some
braking conditions [13,14] may result in much higher
maximum temperatures on the disk and pad surfaces
than are calculated under the uniform heating assumption.

COOLING CONSIDERATION – The air flow around the
brake components is highly complex due to the complicated
body shapes and the rotating wheels in an air
crossflow. Though the convection heat transfer coefficients
of brake components can be measured in the wind
tunnel, it is difficult to apply the results to the actual vehicle
brake cooling due to the stationary ground surface
and stationary wheels in typical test conditions [15]. On
the other hand, progress in the computing capacity and
numerical techniques has produced realistic predictions
of the air flow around the brake components and the corresponding
heat transfer coefficients [16,17]. Though
these results can be used in the thermal analysis of the
particular vehicle and brake system, the numerical process
is still expensive and hence the results are not
readily available for many vehicles in production or under
development.

 

uh, you guys dont seem to get that the point of the article is not to talk about varying factors involved in making a better performing brake system, its just to show that they made a computer model, and gave two examples to prove the numerical analysis and empirical data match up reasonably well. yah, the point is to design a better system in the end or get more understanding, but its not part of THIS article.

you can get this point by reading the abstract, intro and conclusion which is all plain english. the first thing i always do before i waste my time going thru the many pointless research papers out there.

if you guys really want some kind of brake system analysis, why dont you dig up one of the other papers/articles it refers to in the biblio.

ohjolt, you seem to like to discuss about theory and find others to talk about it at no end. i see no point in discussing and even arguing when it only further proves theory, and not practice.