Brake questions

[WALDOPIPE]

Hello:

Im designing the brake system for our car and i have some questions because i have found diferents values for the same thing like:

1. In the Rob Woods Modeling and Simulation of dynamic systems book pag 318 says that "the typical brakes components preassure are rated at 1000 psi; therefore, we will use about 600psi to include a safety factor", does somebody tell me where can i find the pressure at a caliper works? where can i find this value? I found in some paper that the pressure of a brake caliper is ussually 1200 to 3000 psi in critical moments. which value is rigth?

2.after some calculations im got that the brake dics diameter should be 5 or 6 inches comething like that, what are the pros or how much can affect me using a smaller or a bigger disc brake?

3. What kind of material dou you ussually manufactures all your brake parts, master cylinders, brake disc? does somebody use aluminium for the brake disc? plain alumminium or you make the aluminium a special treatment?

4. Does someone use a RESIDUAL PRESSURE VALVESin your brake system? what is the gain of using one of these?

Thank you all for your help and waiting for your response
Wishing you all tha best luck in your Fsae projects.
Grettings from Venezuela.

Oswaldo Leon
Formula SAE UCV Team Captain
www.fsaeucv.org (http://www.fsaeucv.org)

[WALDOPIPE]

Hello:

Im designing the brake system for our car and i have some questions because i have found diferents values for the same thing like:

1. In the Rob Woods Modeling and Simulation of dynamic systems book pag 318 says that "the typical brakes components preassure are rated at 1000 psi; therefore, we will use about 600psi to include a safety factor", does somebody tell me where can i find the pressure at a caliper works? where can i find this value? I found in some paper that the pressure of a brake caliper is ussually 1200 to 3000 psi in critical moments. which value is rigth?

2.after some calculations im got that the brake dics diameter should be 5 or 6 inches comething like that, what are the pros or how much can affect me using a smaller or a bigger disc brake?

3. What kind of material dou you ussually manufactures all your brake parts, master cylinders, brake disc? does somebody use aluminium for the brake disc? plain alumminium or you make the aluminium a special treatment?

4. Does someone use a RESIDUAL PRESSURE VALVESin your brake system? what is the gain of using one of these?

Thank you all for your help and waiting for your response
Wishing you all tha best luck in your Fsae projects.
Grettings from Venezuela.

Oswaldo Leon
Formula SAE UCV Team Captain
www.fsaeucv.org (http://www.fsaeucv.org)

[Brett Neale]

I would highly recommend finding a copy of Puhn's braking handbook. I believe most of your problems will be covered in there (our brake guy this year used it for all of his stuff).

4. I'm not sure if my description is correct... but anyways... An RCD valve is used in a braking system to keep some pressure in the lines, so the next time you stomp on the pedal there's enough pressure there to eliminate some of the cutoff travel in the pedal. I.e. the pedal has better feel with less vague feeling and less travel before the brake starts to bite.

[rjwoods77]

Waldopipe,

1:I think you are talking about Dr. Bob Woods not Rob Woods. I am sure he would like his credit. Allowable caliper pressure is often stated by people but it really depends on manufacturer. Most aftermarket automotive calipers are pressure tested to 2000-2500psi(ap,alcon,ssbc,stoptech,Performace friction) to test for leaks at the piston seals,bleeded screws and crossover pipes. It is possible for automotive style system to hit that high of pressure but unlikely due to a number of factors. The mosre pressure you supply to the caliper the more stress the caliper will be under. General rule would to keep the pressure relatively low 600-1000 as Dr. Woods stated. You must realize that the more pressure the brake system has the more deflection you will have in your brake lines, caliper, pedal box etc. Therefore the higher the brake pressure the more the system flexes the less responsive(tight) the system will feel. Also it will lead to higher stresses which in the long run might fatigue parts,seals to breakage. Motorcycle brakes will take much less pressure that an automotive brake as a general rule.

2: The larger the diameter the higher the breaking torque and the less line pressure required for a given stopping distance.

The larger the diameter the higher the moment of inertia of that disc has. For our size rotors it is rather negligable but worth talking about anyway. Also depends on factors such as annulus vs pad shape but there arent many pads to choose from that make this a viable topic once again.

The big one is the thermal analysis. Larger diamters will net you more disc volume that is what you need for better energy dissapation for equal disc thicknesses. You really need to start here to determine your brake requirements and then get to the hydraulic side of things. Its easy to bump up line pressure to compensate for bad calcs. Not so easy on the rotor side of things.

In general I would fit the largest diameter rotor you can in a given wheel and then tune the thickness to get where you need.

3:Aluminum is typical for M/C and calipers. Stainless steel is typical for caliper pistons. Rotors are all dependant upon what I talked about in #2 about thermal analysis. Your calc will tell you what you can get away with. AL-MMC is great to save weight on as long as you dont get higher han certain temps and you can source appropriate pad material. Do a search and you will see what most people are dealing with as that topic is way to long to talk about. I will however say that I have had good experience with MArtin Custom Brakes. They will laser cut and blanchard grind a rotor for you for 20 to 30 bucks each and they are made out of mild steel. The best material? No but they are readily available for cheap for being a custom job.

4: You only need to use residual pressure valves if your M/C fuild res. is BELOW the calipers. This included lines. If you have any part of you hydraulic system that allows the fluid to be higher that the M/C res then it will want to flow back. Head pressure of a fluid column from FLuid Dymanics class. Simple solution is to mount you M/C res. higher. It makes it easier to fill the M/C res if they arent all down in the bottom of the car anyway.

I will again promote with all my heart the Rudolph Limpert book. It really is the bible of braking.

http://www.amazon.com/Brake-Design-Safety-Second-R-198/...id=1189959811&sr=8-1 (http://www.amazon.com/Brake-Design-Safety-Second-R-198/dp/1560919159/ref=pd_bbs_sr_1/102-4494025-6636132?ie=UTF8&s=books&qid=1189959811&sr=8-1)

[WALDOPIPE]

Thank you very much for all your answers i really really apreciate it. Sorry Dr.Woods for my mistake.

Im trying to find wich is the best material to manufacture all the braking system. Somebody told me that the most dificult item to manufacture was the caliper because of all the leaks in the orings. Wich is your experiencie manufacturing this pieces.

I already have the Brake design and safety book that you recomend me, it was very difficult to obtain it because all the trouble that represent to bring it here to Venezuela.

Thanks again for all your anwers

[rjwoods77]

Problems shipping? Chavez vs. Bush sanctions? That book has an awesome example of how to do a repetative braking thermal analysis. The hard part about the caliper is the seal groove design. DO NOT USE ORINGS. Only cheap calipers have o rings. The problem with o-rings is that that roll/rotate when the piston goes back and forth. Alomost all hydraulic equipement is now using quad rings instead of o-rings as their main seal. A square section ring needs to be used as the main seal and a quad ring(4 lobed cros-section) can be used for the scraper/dust seal. This should help you understand the proper function of a square seal in a caliper.

http://delphi.com/pdf/techpapers/2002-01-0927.pdf

The only problem with seal leakage occurs from seal groove geometry that is bad or if you use shitty seals like o-rings. Most if not all of Wilwoods stuff is o-ring and thats why they make more money selling seal rebuild kits than they do with their calipers. Most of their stuff is junk anyway. There is a reason why ap/brembo/alcon stole all of their buisness in NASCAR. AS far as what is the proper material is all dependant on how you manufacture the items to begin with and what you are looking to do with it. It is sort of like asking "what is the best car?".

[WALDOPIPE]

You are totally right Mr Rob, here in Venezuela its not so easy to buy things outside in USA or anywhere, also you have to make a lot of paper in order to get the item that you has just bought. Also the custom agents are very but very slow in their work.

All of that makes that for us (Venezuelan Teams) bringing parts, books,materials from USA results very difficult but not impossible

Again thanks a lot for all your support and information. Im sure that i will ask again soon as long as my design get bigger.

[rjwoods77]

I am here for any questions you may have. I will give you this bit of advice. There is a lot of details in the design of a M/C and caliper that dont appear on the surface. If you arent doing this for a senior design project I would just buy the equipment. You can also contact me at my personal email if you want to send images and such. rjwoods77@yahoo.com I wish you and the team the best of luck. Seeing how you guys were consoling that girl after design showed alot about your team.

[The AFX Master]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Seeing how you guys were consoling that girl after design showed alot about your team. </div></BLOCKQUOTE>
That's another Venezuelan team Rob, and they did their own calipers since 05'. The girl was in charge of the brakes this year and a judge complained a FEA analysis showing "unacceptable deflections".. They were at least in design semifinals, but that guy did put them on 14th.
sad http://fsae.com/groupee_common/emoticons/icon_frown.gif