Water Cooled Disk Brakes for Big Rigs 3

[140Airpower]

It's an obvious idea. Coming down off the Ridge Route (AKA The Grapevine) portion of I-5, on the north end's over 3000 foot descent I've seen trucks with brakes smoking or actually on fire. I've asked myself why don't they use disk brakes? Also, if you've seen European truck tractor races, you've seen the steam from the water cooling of the brakes. As an emergency expedient, water would save a truck in trouble. Why not?

 

[MintJulep]

Heat input is proportional to speed squared.

Cooling - treating the disk vanes as a fan - is proportional to speed, more or less.

So if the cooling is sized correctly for high speed, high energy stops then you should be ahead of the game at slow speeds.

At any rate, considering that there is a substantial population of trucks with the tractor's front brakes disconnected because drivers still think that they get better braking performance that way I don't think there is much of a market for disks.

 

[dgallup]

Jake Brake is one trademarked name for an engine retarder designed by the Jacobs Engineering company. Nearly every engine manufacture has more or less the same thing. These brakes can absorb considerably more power than the engine puts out so if the engine can haul it up the hill the engine can slow it going down the hill providing the driver starts the descent slow enough and in the correct gear. I don't think jack knifing would be any concern unless on a low traction surface.

If the driver lets the speed build up too much there is nothing but the escape road that is going to save him.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[rmw]

Over the road truckers get paid to haul payload, not water so any extra weight that displaces revenue producing payload is a deal killer. Off road truckers like loggers don't have to worry about gross weight, so the added weight of water, tanks, etc., is justified in increased productivity. Same would hold true with race trucks.

In my experience with truck brakes years ago (haven't messed with them since I was on a SAE Brake Div, retarder sub-committee about 20 years ago, so my info may be old) was that disc brakes would save the rig, but destroy themselves. In other words, in an abusive braking situation, you could get safey down the hill, but the discs would be completely gone, requiring replacement at the bottom. At least the driver would be alive to perform the replacement, but it would mess up his schedule.

Drum brakes, on the other hand just get hot and expand away from the ability of the pads to maintain contact with them, thereby releasing the rig to crash after a very fast ride, but after the crash, when the drums cooled off, the brakes on the (now) wrecked vehicle would work just fine.

Any driver who is smoking his brakes on the Grapevine is (A) smoking something himself, or (B) from back east somewhere. I did get a motor home's brakes a little too hot on the Grapevine once and was in for a ride I'll never forget. The worst part was that my family was on board.

There are all kinds of retarders on the market to help with productivity on downhill runs ranging from engine brakes already mentined (although I believe someone has been reading too much sales literature based on testing we did during my stint on the committee) but all of them add some weight, and weight is king in OTR trucking. The lightest of course is the engine brake.

I once demonstrated an electromagnetic retarder on an 18 wheeler (trailer axle mounted) that was 4 times more powerful than the engine brakes of the time and when the operator applied the first step of the four step retarder actuator and snidely turned and sneered at me 'see it is about the same as the engine brake' to which I replied, "yes, but you have 3 more positions, all the while grabbing the retarder control handle and moving it through the second, third to the fourth position. If only I'd had a camera to capture the look on his face as he commenced to grabbing gears to match his rapidly declining speed.

rmw

 

[140Airpower]

rmw, Very interesting information. I never heard of an electromagnetic retarder.
Some truckers do push the margin. You see some outpacing others by 10 or 15mph. However, how fast they can safely go depends on their load. Although I've never seen a runaway truck, I always can smell their brakes on the Grapevine grade and usually there is at least one with brakes smoking by the time they reach the bottom.
I wouldn't assume a trucker in trouble must necessarily be on something or dumb. All that has to happen is he gets a wrong weight for his load or he makes an insufficient compensation for it or he underestimates the grade. Your own experience with your RV shows it's easy to make a mistake.
The water idea was for a one-time emergency use, not continuous. How much do you think would be needed to save overheated brakes and slow the rig to a safe speed or stop it? How about for a motor home?

In Malibu there is a truck killing road called Kanan-Dume (Doom) Road. Coming out of the Santa Monica Mountains down to PCH is a long downgrade that I think truckers tend to underestimate. They are banned from being on the road in the first place, but they sometimes take it anyway. Every few years there is another, usually fatal, incident.

 

[IRstuff]

I do I-5 pretty regularly, about 5 times a year, but I've rarely seen smoking brakes, but I could just be concentrating on getting to where I'm going. It could also be that the holiday truck traffic is different. But, no doubt trucks are going faster than they're supposed to be on the downgrades, which presumably they compensate for by driving SLOOOOOWLY on the flats.

"The water idea was for a one-time emergency use, not continuous." but the water has to be carried continuously.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[patprimmer]

I fully support what rmw says. Truckers do not like giving up payload at all.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[crerus75]

140Airpower,
You've probably heard of/seen the retarders but haven't realized it-- they are commonly used as the retarder on eddy current chassis dynos. Frenelsa and Telma are the two brands that come to mind, though there are others.

 

[140Airpower]

IRstuff, yes it would be a constant weight penalty, but the amount would only be for a one-time use, enough to cool the brakes so that effectiveness is restored to slow a truck from say 50 or 60mph to about 30mph by normal braking action. A system would have to be mandated, not voluntary and I suppose the industry would fight it. It's a speculative idea.
Disk brakes alone, if universal, would allow a higher safe speed. Truckers should welcome that. But, adopting higher speeds on grades would use up the safety margin that disks provide as pointed out before. In any case it appears disks will eventually become the standard here as they are in Europe.

The CHP says the escape ramps get used 30-35 times a year. Truck traffic is up to 22,000 per day. I think most truckers in trouble simply ride it out. They can probably negotiate the car traffic up to about 70-75mph. I've seen only a few flipped over trucks off the shoulder at the bottom of the grade and those were not necessarily runaways.

crersu75, I looked up he retarders, thanks.

 

[rmw]

Bottom line: water cooling brakes is solving a symptom of the problem, not the problem. Except as noted later, if a trucker is smoking his brakes, he is going too fast for the conditons, part of which is determined by the amount of retardation he/she has on board in the form of compression brakes, exhaust brakes, electromagnetic, hydraulic, etc., etc. I've seen drivers with engine brakes (compression brakes) smoke their brakes too when they overran the ability of the engine brakes to hold them back. Cold brakes will stop anything. Keeping the brakes from overheating is a requirement of professional driving (and staying alive.)

Now things happen, like missing a gear on a downhill where one would have to use more brakes than normal to bring the rig back under control. But the average driver who is smoking those brakes you are seeing is just a dunce and needs to be doing something else. Sorry - it is a hard saying, but look at the 99% of drivers that arean't smoking brakes on the same hill.

The exception I mentioned earlier is where the smoke isn't the brakes, but grease from a leaking wheel seal burning off when the brakes get hot. The brakes overall may be hot, but not too hot to control the vehicle, but hot enough to torch off any greast built up by grease leaking through a seal onto a brake drum.

Now Crerus, Frenelsa & Telma.... That takes me back several lifetimes. 140 AP, google Klam, Zelu, and the word "ralentizadores" if you want to read any more about electromagnetics.

rmw

 

[140Airpower]

rmw, you said "the average driver who is smoking those brakes you are seeing is just a dunce and needs to be doing something else. Sorry - it is a hard saying, but look at the 99% of drivers that arean't smoking brakes on the same hill".

I certainly agree that it is the driver's professional obligation to not overrun his brakes, but mistakes happen to the best and IIRC much more than 1% of the trucks on the grade had smoking brakes and I could always smell somebody's brakes. However, most of my experience was in the '90s when I did about 120 trips to the Bay Area. I take that route only a few times a year nowadays and only to the Frazier Pk turnoff. The difference in that is that I'm not in a lane to watch the fastest trucks nor do I go all the way down.

Now it occurs to me that in my memory most smoking brakes I've seen were on the trailers, not the tractor and I think that makes a difference. Anyway, I did run across a quote by a trucker who also noted he always sees someones brakes smoking. Like I said, some guys run 10-15mph faster than the other trucks and that may or may not be ok.

 

[140Airpower]

About truckers: Although I think more than 1% of trucks on the Grapevine get to the bottom with overheated brakes, the vast majority, probably over 95%, do not. Like I said, overheating your brakes is not necessarily a sign of incompetence. A safe speed depends on your load and even a smart guy can make a mistake estimating what he can do. Experience is everything. What makes Kanann-Dume Rd so bad is that the grade is 8% and truckers have no experience on that road. A load safe for 35mph on the Grapevine has to be taken down Kanan-Dume at 25mph. If the trucker does 30 he'll likely be in trouble.

 

[JackAction]

Is there really a problem? I don't know if you're always talking about the same road in all your posts, but you've said earlier:

The CHP says the escape ramps get used 30-35 times a year. Truck traffic is up to 22,000 per day.

That means that 99,999595 % of the trucks don't have any problems going down that hill. At least nothing too serious. Furthermore, those escape ramps did the job: stop the (very few) runaway trucks. And if we're talking about modifying the brake system of all trucks & trailers across North America, even the ones that don't go on these kinds of roads, the number of decimals needed for this number will become ridiculously high.

In my honest opinion, that should answer the question in your original post:

Why not?

Otherwise, if we really want to eliminate all possible accidents due to deficient brakes, we could also ask: Why not put a parachute in the back of every trailer in case of emergency, just like the ones used by dragster?

Even then, I'm sure there will still be a parachute that won't open at one time or another when needed.

 

[rmw]

Ah, 140AP, you now get to learn another truism about the trucking world. A fairly significant number of trucks (meaning truck/trailer rigs) on the road are owner operators who own their own tractor and lease it to a company who provides the trailer - a company owned trailer.

Guess whose brakes get abused with that combination. There is even a term for it (or at least was 25 years ago when that scene was part of my world) amoung owner operators: "Company jake brake" which meant that they would reach over and pull the trailer brake handle to ensure that they do the lions share of the braking while sparing the use of their own tractor's brakes.

Secondly, company trailers get bounced around and often spend large periods of time out and about before they make it into a terminal where maintenance is performed on them, so encountering a company trailer with brakes in all states of disrepair isn't uncommon at all which means that when they are used, some brakes on the trailer are doing all the work while others less well adjusted are less heavily loaded. That is even true of company trailers behind company tractors.

So, not suprising at all to read that you see more trailer brakes smoking.

rmw

 

[140Airpower]

Jack, we've discussed MANY techniques to control the speed of trucks on grades. If there was no problem, no special techniques would be needed. None are needed for cars. If ANY single technique was completely satisfactory there would be no need for any others. Just because 99.99+ percent of trucks don't use the ramps does not at all mean that that percentage have NO problems. The truth is that trucks are and always have been severely underbraked for long grades on today's roads and there is no fail-safe. Otherwise escape roads would not be necessary. It's an area for innovation. If you are not interested, ok.

 

[140Airpower]

rmw, I kind of started to have suspicions about that.

 

[rmw]

140AP,

Thre is no need for innovation. There is a laundry list of equipment that will aid trucks get downhill or even do all the hold back required. The unfortunate thing as Pat P states above is that truckers are not willing to sacrifice payload - or that is to say that - anything that they perceive would reduce payload (because some of what they do replaces payload but they accept it as normal and I'll name a couple below.)

For now the comment is about the need to innovate or not. The retardation system that will do all the holdback adds about 1500 lbs to the rig's tare weight and the industry won't have it. For the weight of the water that you proposed adding, they can have the finest retarders on the market. Heavier retarders are fairly well accepted in the offroad community where they don't have to worry about state or federal weight laws.

I know first hand of a situation where a trailer axle retarder user was smoothing off of I-8 eastbound out of San Diego on a serious downgrade - 8% which is maximum allowed on the Interstate system - at night at about the automobile speed limit of 70 mph (and knowing him, I bet he was crowding that by a few mph) and due to a total malfunction of the electrical system associated with his 12/24V starting system, when a certain circuit breaker opened up, he lost every bit of his electrical system, lights, engine controls, everything including his electric retarder. Well, the saying is that cold brakes will stop anything and he proved it that night. He stated that he wouldn't have been able to stop like that twice in a row, but he did get it stopped and to the side of the road whereupon the circuit breaker cooled off, remade and his electrics returned. I know about it because he came straight to me and made me figure it out and come up with a fix, which I did. I don't remember all the details now of what we modified, but if I studied a 12/24V starting system for a few minutes I'd remember.

He had a 1693 Cat engine which was adapted from a motor grader engine and there were no engine brakes for that model. He typically ran downhills so fast with that trailer axle retarder that he had to put a sign on the back of his trailer warning other truckers not to attempt to follow him off down grades. The trailer axle manufacturer showed a photo of his trailer rear doors at major truck shows and truckers stopped by with regularity and told stories of trying to follow him and getting into big trouble. His CB handle was 'Sarge' and the stories about that old man were rampant in those days.

He was different in that he was willing to make the payload sacrifice and understood that the increase in productivity (he ran a reefer between Texas and California, chickens westbound, produce eastbound for a grocery chain) plus the peace of mind made up the difference.

And now for the perceptions.

The American trucking industry, and I include Canada and most of Central and South America is in love with the twin screw tractor while Europe figured out decades ago that they couldn't afford all that extra dead weight for no more benefit that it produces. So there is 1500 lb. right there.

Trailers knows as "taughtliners" or "curtain sides" add about 1100 lbs to the weight of a trailer but those who think that faster unloading from the sides is worth that weight penalty gladly pay the price for payload reduction.

Electric starters - I knew of a bulk hauler and tanker outfit in Utah some years back that did the math and realized that air starters (and associated equipment) were lighter than electric starters and associated equipment so their fleet was equipped with air starters. It was interesting one bitter cold winter day I was at their shop to see one of their rigs out against the fence with an electrical cord and an air line strung out to the rig to try to get it started (electricity because the battery was dead and the engine kill switch was electric and needed power to allow the rig to start).

So it is all a matter of perception. They accept what they perceive they need regardless of the weight it adds and reject what they perceive that adds weight if their granddaddy didn't do it that way.

Where the electromagnetics really became popular was in France and Spain in the '60's - '70's when the national governments gave an automatic overweight allowance for the weight of any retarder on board. Why not go for the best which was also the heaviest. I am not so sure those laws still apply since I have been away from it so long.

I don't know where all the work we did on the Retarder Sub Committee for the SAE is today, but there is quite a bit published on the topic if you can find it, but the bottom line conclusion was that until and unless governments got on board and gave an overweight allowance for safety equipment it wasn't going to happen. IN the case of our country as you know, that involves getting 50 states to all get together on something. Hearding cats would be easier.

And then of course, there is the old fashioned way that was done before Clessie Cummins invented what Jacobs Chuck Co would market as the "Jake Brake" and that is to select a gear low enough to ride all the way down the hill without any or precious little use of brakes and just go slow. The Grapevine is a long way to gear low and go slow especially when the "large cars" are streaking by you in the fast lane, but many a trucker has done just that so that he would live to see another day.

I have personally driven many a load of skiiers in large motor coaches down some of the nastiest slopes Colorado has to offer with nothing but gears, but when there are up to 46 people sitting behind you whose lives at stake you find out that it can be done. We didn't go fast, but noone objected and we all lived for me to be able to write this.

rmw

 

[140Airpower]

rmw, A wonderful post! There ain't nothing like the observations and wisdom of an old hand who's smart enough to have understood and benefited from his experience.

 

[140Airpower]

rmw, We live in a technological society. Innovation is the source and product of technology.
When you find a variety of solutions to a problem it's a sign that probably none of them work well enough or have merits that obviously outweigh their drawbacks. I think THE solution to heavy truck braking on grades has either not been found -or exists but has not been mandated.

Note that friction brakes alone could do the job under all conditions of speed and grade given ENOUGH dissipation. The rate of energy dissipation to hold a constant speed on a grade is only double at 70mph what it is at 35mph. That energy is basically just the gravitational potential energy difference between two altitudes. This energy does not disappear. It has to be dissipated. The rate of dissipation required is proportional to the rate of vertical descent. All the various techniques transfer this energy to the air. Jake-braking pumps air to high temperatures and pressures and releases it without getting any return energy in the expansion. Electromagnetic brakes have a lot of airflow and fins to pump energy to the atmosphere identically to friction brakes. These techniques add dissipation to what the friction brakes provide -no "better" than an additional or better set of friction brakes could do.
Here "better" has to do with space, weight, cost, etc.
For example, at the Telma website they have a video with Jay Leno that shows their $10,000 driveline unit. Coincidentally, its heatsinks look like large brake disks. These heatsinks limit how much braking this unit can provide because, unless the unit can charge a battery pack, the energy from braking has to go to the atmosphere through these heatsinks. Now these heatsinks could be replaced by two cheap same-sized disk brakes and dissipate the same or probably much more energy (because they can operate at a much higher temperature). So, additional and better friction braking is a possible solution that exists but has not been mandated. Of course it may not be the BEST solution and maybe should not be mandated.

 

[rmw]

So get you a patent, a financial backer (unless you are already really rich) and get out there and convince the marketplace or if you have even more money, the lawmakers.

rmw

 

[140Airpower]

rmw, Just throwing ideas out there. That one has already been rejected, as evidenced by current practice. But I do believe truck safety is more limited by vested interests and politics than by technology. The bare economics reminds me of the calculations that gave us the Pinto gas tanks.