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Author Topic: Braking systems  (Read 3937 times)
rv_safetyman
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« Reply #15 on: April 13, 2007, 07:35:30 AM »

Ross, I am sure you weighed your bus after you got it done.  However, I would bet at least a dollar that your MCI 9 weighs a bunch more than 28K. 

I am out of town and don't have my files with me, but I think my empty weight (Eagle 10) was over 22K.  Almost everyone I have talked to with a 40 foot bus is well in excess of 34K - many over 40K!!  I had mine weighed at an FMCA event and I was 36.5K.

I made a simple one with an air cylinder hooked brake pedal and plumbed to the bogey relay valve.  That makes the braking proportional to the bus brakes.  It takes a minute or two to hook it up, which is the advantage of the M&G.  I have all the parts to make a breakaway except that I can't find a small pressure cylinder.

The M&G is a great system.  In addition they are BUS folks and attend each of the Converted Coach pre-rallies to the FMCA events.

I looked at an installation in Perry and saw that they have a really nice pressure tank.  However, it did not appear that the tank had a one way valve.  I sure it must, but it was not obvious.

It just makes good sense to have the extra braking.

Jim
« Last Edit: April 13, 2007, 07:44:43 AM by rv_safetyman » Logged

Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
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edroelle
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« Reply #16 on: April 13, 2007, 09:14:07 AM »

The M&G appears to be a nice system in that you don't have to add/remove the cylinder at the brake pedal.

I am probably too picky as an engineer.  I went to the FMCA seminar where many of the supplemental brake system suppliers discussed their products in a forum.  I was not convinced to purchase a system.  Let me tell you why, if you desire a lengthy discription.

As background, I have a very good understanding of the brakes and brake systems since I was a brake engineer for GM for many years.

My concern is the lack of CORRECT proportional braking.  Pulling air from a bus brake does give somewhat a proportional brake.  But, is it the same between an MCI, Prevost, Eagle, and GM.   In other words, for a given deceleration, is the activation air pressure to the bus (and thus the towed vehicle) the same between manufacturers?  Is it the same between disc and drum?  Does the supplemental brake system supplier provide different systems for all these combination?  I don't think so.

The supplemental brake system suppliers with the cylinder attached to the brake pedal, do not account for the different towed vehicle brake system designs either.  If you are braking the bus at say 5 ft/sec-sec, you want to declerate the car at the same, or lesser a rate (so you do not burn up the car brakes by trying to stop the bus, BUT want the towed vehicle brakes to do something).  Various vehicles decelerate at different rates for a given brake pedal force based on master cylinder size, base brake sizing, etc. - especially in no power (no vacuum) condition.

In summary, is a supplemental brake system better than nothing, at stopping better?  Probably.  Is the system good enough to spend $700+?  A better design needs to emerge.

Ed Roelle
Flint, MI
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Len Silva
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« Reply #17 on: April 13, 2007, 09:37:07 AM »

One of my concerns about these braking systems is that they tie in directly to the bus's rear brake line.  It seems to me that if you had a break-away or just a hose failure in the line to the toad that it would compromise the bus brakes.

I haven't looked yet myself but with all the various relay and protection valves available, there should be a way to protect the air supply if the toad line fails.

Len
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rv_safetyman
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« Reply #18 on: April 13, 2007, 01:58:09 PM »

Ed, I agree with all of your comments.  However, like most everything, the solution is a compromise.  You are much more experienced than I, but when I played with peddle pressure on various cars, they all seemed to be in a reasonable range (with the vacuum applied).  What I could not evaluate was the pressure required when the system was not assisted. 
 
The assumption (you know the definition of assumption Grin) I made was that the OEMs balanced all of the variables you mentioned so that the pedal pressure for various vehicles came out in a similar range.  I suspect that they (you) gave a lot of thought to both assisted and failed assist conditions.  It seems to me that the system must be designed so that the required pedal pressure would fall within the somewhat limited range of human capability.  What the heck is that idiot trying to say Huh  Simply stated, I think that the pedal pressure to activate the system would not vary a lot between vehicles. 

If that assumption is not too far off, then the "generic" systems probably are designed to provide a reasonable force within that range.

As many of us have said in this thread, any system is better than no system.

Len, I gave a lot of  thought to the issue you brought up.  First of all, recall that the brakes on each axle have relay valves where the supply line is rather large.  I ran a rather small line from the relay valve on the bogey axle.  What that means is that a broken line would only affect one axle (the bogey axle affects the braking less than the drive axle which has bigger brakes) and with the small line, I think that you would get some braking even with the broken line. 

A person could get real clever and put a relay valve in the toad system and supply it with air from one of the tanks with a pressure cut off valve that would shut down the toad brake system if the air pressure in that tank dropped below the cut off value (usually 50 PSI).

When all is said and done, we are being legislated into having some sort of system, so this discussion may be academic.

Jim

 
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Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
Tony LEE
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« Reply #19 on: April 13, 2007, 02:49:55 PM »

I would have thought that any modification to the original airbrake system - ie extending it to the toad without (or even with) relay/isolation valves -- would require an engineers certification.

Having a small bore line to the toad brake will mean a longer time to apply the brake -- and that doesn't matter, but without a quick exhaust valve in circuit, will take longer to release as well and this could increase brake and tyre wear and result in jerking on the linkage.

As far as getting the exact set up so as to neither underbrake or overbrake the toad, this would require an adaptive controller set up to adjust the braking so as to maintain zero force in the towing linkage (which is what an over-ride brake tries to do in a crude way). Possible but hardly practical which is why our systems would normally be set up to underbrake as the lesser of two evils.
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Hi yo silver
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« Reply #20 on: April 14, 2007, 08:07:51 PM »

Perhaps what is needed on board the toad is a device similar to the EOTD or End of Train Device that the railroads use.  It is an air brake application device that is initiated by way of radio telemetry.  When an emergency brake application is made on the head end of a train, the radio signal transmitted to the EOTD prompts it to apply the brakes to the rear of the train almost simultaneously, by way of a 12-24 vdc solenoid.  The advantage in the case of a long train is that all the controlling air pressure doesn't have to be exhausted from one port at the head end of the train, rather it is exhausted at the rear of the train as well, shortening the response time for the braking system.  Those of you who are familiar with railroad braking systems know there are some fundamental differences in those systems and the brake system on a bus, but the principal of operation would be the same.  The device could be set at a threshold to respond only in case of a hard braking application.  Hey, this will be a whole new invention, won't it?  YOU HEARD IT HERE FIRST!  Whaddoya think?   
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« Reply #21 on: April 14, 2007, 08:43:50 PM »

If surge brakes make you dizzy...

These people have the gadget that works with your electric brake controller..

http://www.carlisleinternetsales.com/

I don't have anything to do with the company or product, Just know they work in horsetrailer and boat trailer applications.

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Len Silva
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« Reply #22 on: April 15, 2007, 10:23:23 AM »

All right. I don't know if this is re-inventing the wheel or thinking outside the box, but here goes.

I don't want the tow car brakes applied at all under normal driving conditions, only when I REALLY NEED all the braking I can get.

So, how about a PR-2 adjustable protection valve followed by a QR-1 Quick release valve.  The PR-2 could be set at 40-50 lbs so no air is supplied to the car unless in a hard stop.

Additionally, how about an electric vacuum pump and battery supply from the coach so that the power brakes AND the anti-lock features of the toad are utilized?

It seems to me that it would be very difficult to truly set up the toad brakes to be proportional.  I know that I've seen a lot of travel trailers where the tires are smoking even under a normal traffic stop because they are so hard to set up properly.

FWIW,

Len
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JackConrad
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« Reply #23 on: April 15, 2007, 10:31:08 AM »

Len,
   I installed a brake application pressure gauge on our MC-8.  I was watching it yesterday on the way home from a bluegrass festival. Easy "brakes applies for gentle slow down" was about 10-15 PSI.  firm "OK, need to come to full stop at the stop sign" was about 25-30 PSI. It takes an "OH hell, that light just turned red" application to get to 45-50 PSI.  Jack
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Len Silva
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« Reply #24 on: April 15, 2007, 10:32:49 AM »

Jack,

I was just guessing at the pressures, what do you think of the concept?

Len
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« Reply #25 on: July 10, 2007, 03:31:50 PM »

Based on Ed's comments I wrote to M&G with these questions and here is the question/reply:

Does your air brake system allow for calibration?  If the toad has too much pressure it will to stop the bus and overheat the toad brakes.
 Do you have some kind of check valve when tapping the coach service air?  I trying to prevent a major air leak if the toad air line fails.

"Our system is vehicle specific and designed for the towed vehicle. It will not over apply the brakes. There is no need for a check valve. We use a 1/4" OD air line, if line has a leak, the brakes on coach will not be affected. The compressor on coach will put in more air than is lost."

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buswarrior
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« Reply #26 on: July 10, 2007, 08:25:33 PM »

A 1/4 inch line rupture will more than defeat the air compressor in our coaches!!!! Amazing what some folks will actually put into print in order to sell their product. Thanks for the research Hobie!

The tractor trailer folks plumbing has some solutions in the way of valving that will automatically protect the tow vehicle's air system.

Tapping into the service brake air system in an older single circuit brake system (pre 1975) is really doing a dance with the devil, without some form of protection, should there be a line failure or break away of the toad.

The authorities are not going to ignore RV's forever. I think it might be best to get oneself some form of supplemental braking for the toad. You don't want a vacation trip interupted by some jurisdiction telling you to park at the side of the road until you make good on it. And no doubt some whopper of a fine will follow....!

Len, I like the way you think!

happy coaching!
buswarrior
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