Proportioning Valve??

[Ryan Boysen]

Are there any teams out there that run without a bias bar or a proportioning valve? I could see some systems designed for the bias built in.. Your thoughts are appreciated.

[Ryan Boysen]

Are there any teams out there that run without a bias bar or a proportioning valve? I could see some systems designed for the bias built in.. Your thoughts are appreciated.

[Bill Kunst]

We ran without our first year, 2003? i think. despite our limited squad, we were able to design a near perfect balance into the brakes. You can do it, but you may need to make some variations in the pivots for the master cylinders to make the bias (different lever ratios for front and rear).

[drivetrainUW-Platt]

or you could use different sized masters instead of that double pivot pedal you guys ran that gave you different strokes

[jdstuff]

Ant particular reason why you don't want adjustable bias? Tilton bias bars are pretty light and simple enough to implement, considering we are already required to run a dual MC system. Just curious....

[drivetrainUW-Platt]

I volunteered to run the brake test last year and you would be suprised how hard it is for some teams to pass it! Not to rip on anyone but since they are well know, UTA went thru the bales probably 5 times before they passed...being able to change bias on the go is critical to getting the balance right for locking up tires.

[Ryan Boysen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jdstuff:
Ant particular reason why you don't want adjustable bias? Tilton bias bars are pretty light and simple enough to implement, considering we are already required to run a dual MC system. Just curious.... </div></BLOCKQUOTE>

Well, through investigation, we seemed to overkill on our sizes to begin with.. I don't think stopping will be an issue. We also went with a 1" tandem cylinder, as opposed to 2 smaller cylinders. But after calculating, it looks like after weight transfer, our rear needs about 80-90%.. which is almost worth leaving out the annoying flaring of lines.

Also, Our first year experience and time management as of thus far, really doesnt forsee any testing anyhow..

BUT, of course I think we may use it anyhow.

[Bill Kunst]

Not testing is exactly why you should have a bias bar, do not do a valve. The valve will only change initial pressure (think about how it works), not final pressure. Bias bar will actually change the balance of pressures.

[terra_dactile]

hi Ryan,
Correct me if i'm wrong but i'm pretty sure in the rules you need to have two seperate master cylinders, one for each line, so that if you have a leak, you dont lose all of your braking capacity.

Jude Berthault
ETS Formula SAE
Steering & brake System Leader

[Ryan Boysen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by terra_dactile:
hi Ryan,
Correct me if i'm wrong but i'm pretty sure in the rules you need to have two seperate master cylinders, one for each line, so that if you have a leak, you dont lose all of your braking capacity. </div></BLOCKQUOTE>

"It must have two independent hydraulic circuits such
that in the case of a leak or failure at any point in the system, effective braking
power is maintained on at least two wheels. Each hydraulic circuit must have its
own fluid reserve, either by the use of separate reservoirs or by the use of a
dammed, OEM-style reservoir."

We are using a tandem cylinder that is acting on both the front and rear, where if one line broke the other would still be actuated..

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looks like that if you can depict what it is showing..

Maybe im confused Bill, the proportioning valve is not going to work? we have it set up on only one half of the system.. not both.

[BStoney]

Ryan... better check with the rules committee on that one. that would not be fun to change at competition if in fact you needed two master cylinders. I interpret an independent hydraulic circuit to be one that has its own dedicated master cylinder. What you show in the "sketch" is truly only one circuit becuase they are sharing fluid, correct me if I am wrong. Also, if this master cylinder fails, you have no braking at all.

Not criticizing your design choice whatsoever, just simply wanted to make sure you don't get to Romeo and then can't compete because of your brakes..ya know?

My 0.02...

[Bill Kunst]

Ryan-
A proportioning valve is an adjustable restriction in a hydraulic system. What it does is drop the initial force to the calipers, but any amount of time on the pedal will see and effective increase in the pressure at the wheels where you don't need it. This is sort of the problem with compressed air systems that neck down and back up. When you run your impact, you lose effective cfm and psi, but the pressure eventually comes back to system pressure on that run after you stop running the impact. The proportioning valve will slow the reaction, not minimize the pressure, and this is why I do not like them. A balance bar, on the other hand, changes the lever ratio inbetween master cylinders and therefor changes the effective pressure through the lines. I hope that this helps you out.

[Ryan Boysen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BStoney:
Ryan... better check with the rules committee on that one. </div></BLOCKQUOTE>

Good point, I might want to look into that..

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> I interpret an independent hydraulic circuit to be one that has its own dedicated master cylinder. What you show in the "sketch" is truly only one circuit becuase they are sharing fluid, correct me if I am wrong. Also, if this master cylinder fails, you have no braking at all. </div></BLOCKQUOTE>

They actually do have their own resevoirs, and act independently.. so say you lost braking power in the first half.. the second half is still fully operational. This system is used in most OEM's. And believe it or not, I really haven't considered the MC failing at all.. hmm.. I guess the best thing to do is contact the rules commitee, Thanks for your input..

Bill, Thanks a lot for the info.. I think the way our system is set up, that a balance bar would be the best option.. unfortunate that we already purchased the proportioning valve.. Ill look things over and see it there is an adjustment I can make somewhere.

[Ryan Boysen]

to add.. I looked up our MC to sumbit to the rules committee and this is what I found..

A safety net for your brake system.
These Wilwood combination remote tandem master cylinders provide one of the safest ways to actuate 4-wheel or dual-caliper axle brake systems. These versatile, lightweight, and easily adapted master cylinders provide single-pushrod activation of two separate brake fluid circuits. By completely isolating the fluid reservoirs and circuits, the front and rear brakes are able to operate independently of each other and provide a safety net, should any one side of the system become inoperable. They're a great match for Wilwood's bolt-on disc brake kits, systems configured from OE components, and a variety of industrial applications.

[BStoney]

Ryan, sounds good...just didn't want you to get up there are be "up the creek"...

Now I understand what you are talking about...same as most OEM...

[Ryan Boysen]

Thanks B, I will post tomorrow about what the rules committee has to say, so then everyone will know.

[Dan B]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bill Kunst:
Ryan-
A proportioning valve is an adjustable restriction in a hydraulic system. What it does is drop the initial force to the calipers, but any amount of time on the pedal will see and effective increase in the pressure at the wheels where you don't need it. </div></BLOCKQUOTE>

Really?

http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml

[Bill Kunst]

Dan B,
I may be wrong, but some the companies in the past had passed needle valves as a proportioning valves. Anyway it goes, I will admit being wrong, but still reinforce that the balance bar is by far the better choice in this application. Now, in the case of a circle tracker, putting a valve into the front left may help with lockups entering a turn. Otherwise, it would be my advice, and from the looks of the article, to stay away from pro-valves in racing as the bias bar offers a finite adjustment for the boundary (extremes) that race cars operate at. Thanks for setting me straight,
Bill

P.S. The valve that I had seen in the past was a wilwood, and their current proportioning valve looks much different and bigger.

[Steve Yao]

Another:
Tilton's proportioning valve = not regulator (http://www.tiltonracing.com/pdfs/29.pdf)

[Wes]

Another advantage to the proportioning valve would be the ability to adjust brake bias on the fly. Not that a balance bar is difficult to adjust, but you can't exactly reach down and do it while you are driving.

[BeaverGuy]

It is just as easy to adjust a bias bar while driving as a proportioning valve. Tilton and Wilwood and probably many others make remote adjustment knobs for bias bars.

[drivetrainUW-Platt]

http://www.wilwood.com/Products/005-PedalAssemblies/004-RBBA/index.asp

[Ryan Boysen]

We actually mounted the proportioning valve right next to the seat, so while driving we can have instant difference, as opposed to stopping, getting out, wrenching.. ect..

Remote bias bar changes seem like more of a hassle.. Ours comes right along our rear line, that happens to go right by where we wanted it.

[NetKev92]

I don't imagine the judges getting upset about the single unit with dual masters. They're used on OEM automobiles that also require two seperate brake circuits. I think my Miata uses a single master for the fronts and a single for the rears. There is only one brake line to each corner, so I know that each corner is only connected to one of the two circuits. My old volvo 244 had two brake lines to each front corner. That allowed both circuits to operate a piston on the front and the rears were non-redundant.

It never hurts to ask though if there's any doubt in your mind.

[Bill Kunst]

Okay, good question for those that don't know this.

Why do the OEM's put their brakes in diagonal circuits? I know, do you...

[BeaverGuy]

Not all OEM's use the X distribution. It is most popular on front drive cars because it still allows for the proper braking force while meeting regulatory requirements. An II distirbution is preferred for vehicles with a rear bias.

[Bill Kunst]

Okay,
Not a whole lot of interest in this, or trying to spell out why they diagonal the lines now.

Simple, most cars get more than 60+% of the braking from the fronts. Losing that channel would be worst case (just after losing all braking). Followed by losing rears (&lt;40% of the braking). But if you lost one front and one rear you would be left with 50%. This makes for a better situation than losing the fronts, and looks to be necessary evil (meaning you would lose less if only the rears were lost) when you consider one more issue.

What are the effects on the vehicle's stability under braking when either the fronts or rears are lost? In a truck, losing the fronts means you aren't stopping. Losing the rears in most cars means that the vehicle might swap ends (doughnuts on the road). If you lost brakes on a diagonal, the vehicle would brake slightly yawed, but definitely would be more stable. Most vehicles would see somewhere around 20 or so degrees of yaw. The shorter the vehicle, the worse it would get.

Now, this is what I have heard from numerous mechanics on the reasoning behind the diagonal channels. When I heard this, it just made sense. If this is wrong, please let me know.

Bill Kunst

[kwancho]

Yeah, that stability part makes sense. But, if you lose the front brakes, you don't stop AND the car wants to swap ends. If you lose the rears, you decelerate slower, but you're stable..

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alex Kwan:
Yeah, that stability part makes sense. But, if you lose the front brakes, you don't stop AND the car wants to swap ends. If you lose the rears, you decelerate slower, but you're stable.. </div></BLOCKQUOTE>

When the brakes are locked, the wheels are sliding on the pavement and offer almost no resistance compared to the ones that are un-locked.

Thus, I'm positive that if your rear brakes lock, the car become REALLY sensitive to spinning. If your front brakes lock, you'll most likely lose your steering in a probably harmless understeer.

[kwancho]

Oh, uh, when you said lose the rears, I thought you meant lost rear braking.

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alex Kwan:
Oh, uh, when you said lose the rears, I thought you meant lost rear braking. </div></BLOCKQUOTE>

hmm, yeah. I basically repeated what you said. Sorry, I misread.

At least, we agree.

[Bill Kunst]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Didier Beaudoin:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alex Kwan:
Oh, uh, when you said lose the rears, I thought you meant lost rear braking. </div></BLOCKQUOTE>

hmm, yeah. I basically repeated what you said. Sorry, I misread.

At least, we agree. </div></BLOCKQUOTE>

Sorry about that, Got the ends all mixed up.
Bill