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?

 

[JayMaechtlen]

Presumably a matter of cost.
Actually, there are two questions there -
1) aux cooling for existing brakes, possibly by total loss water spray, and
2) what about disk brakes, which are easier to cool?

Seems like you could do a total loss spray on the outside of the drums, and cool them pretty effectively. And/or you could add some forced ventilation to the existing drums (electric blower, thermally activated?)
I wonder if that (either of them, actually) could be a saleable aftermarket item?

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[IRstuff]

As always, cost is a major factor:

http://www.thetruckersreport.com/tr.../139262-why-do-american-trucks-still-use.html

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[140Airpower]

Yes, cost is a factor. And, if disks allowed a truck to descend a grade at 5mph more speed, maybe we wouldn't want that. but, the brake emergency problem is another matter. If a guy makes a mistake of coming down a particularly long grade at just a little too high a speed he can lose braking and die. It happens too often. An emergency stash of water could get him out of trouble. In fact, just having heat sensors at each brake is something that ought to be law.

 

[IRstuff]

Sure, and are you willing to pay double for all your vegetables? And that's assuming that a retrofit is even possible on all existing hardware. If every outdated trailer and trailer in the US and Mexico were replaced?

The bottom line is always the bottom line, and almost no one wants to pay THAT price, and they're willing to gamble. We developed a safety system for preventing a large portion of helicopter aerial collisions, and even with a relatively low cost, there was great reluctance, because outfitting the entire fleet would have cost ~$250 million, and that buys a lot of bullets and prevents losing bullet carrying capability.

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[140Airpower]

IRstuff, I don't know how much a big rig tractor and trailer cost, but I doubt that changing to disk brakes or a water emergency braking system will double the cost nor double the cost of the driver's compensation nor double the cost of growing, packing, stocking and selling the veggies. Hmm, did disk brakes double the cost of cars? I think it will add something to the cost and save some lives. How much are the lives worth? I'm just asking what are reasons not to do any of this and I expected to hear that costs are a reason. Is there any other, a technical downside that you can think of?

 

[140Airpower]

I should have researched this question before posting it. Here is a paper by Bendix. It is interesting at least for what it says about previous disk systems even considering that Bendix has a vested interest.

http://www.foundationbrakes.com/media/documents/airdiscbrakes/awhitepapercaseforairdiscbrakes.pdf

 

[patprimmer]

Maintenance costs and downtime. Disc pads do not live as long as linings.

No matter how much performance you build in it does not increase safety if the operator just uses the extra performance and leaves the same estimated margin. It saves time, but does not increase safety.

A total loss water system would require a lot of water at the cost of payload which means many operators would not use it when needed most.



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Pat
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[JackAction]

Logging trucks do have water-cooled brakes.

Here's one with the steam going downhill:

Here's the water spout:

Here's the 400 gallons water tank:

for more info: Link

 

[140Airpower]

Pat, good points. There are speed limits that are aggressively enforced on that dangerous stretch of I-5. An extra speed margin would result in more margin of safety. But in general what you say is true. Drivers tend to find out what the brakes will take and then use the margin, leaving none.
The idea of a water spray would not be for general use, but a desperation measure to slow a truck when it has lost brakes. Presumably, merely cooling the brakes enough restores function sufficient to slow the truck to a safe speed or stop it, and if the truck then descends within the recommended speed there is no problem. How much water would be required is a question, but I bet it's not a lot for a one time event IF the driver uses it as soon as he realizes the brakes are in trouble (assuming the brakes are just above operational temp). That's where sensors come in. The supply could be replenished at the next stop.

 

[IRstuff]

The reason for the cost increase is the extra overhead, maintenance/support costs. Since the original equipment, particularly for older trailers, is already depreciated, new equipment means new depreciation, in addition to the lost time for retrofitting. That all costs money.

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[140Airpower]

IRstuff, I think new mandates for braking performance from the NHTSA are going to force upgrading on existing truck and trailers, probably cheapest with improved drums. For new production, the NHTSA estimates less than $1500 to go disk all around on a tractor. There is pressure to get US and Canadian trucks in line with Europe which looks to be ahead on this. What additional maintenance costs will be born uniformly. I guess my question about disks is answered with it's gradually coming.

http://fleetowner.com/regulations/truck-stops-here-0201

JackAction, thanks for the photos. Logging trucks are special equipment on especially steep roads and I can see that they would be more likely to need extreme measures. For I-5 the argument would be is there enough of a need, but at least I see that it is being done on some trucks.

 

[JayMaechtlen]

comments on drum vs disk:

I expect that pad life is related to pad area - and lots of other factors, probably.
But I don't remember front drum brakes going as far as disks go now- I usually get 50-70k miles from front pads.
What did classic drums get? 20-40k miles?

Disk brakes can dissipate more heat than drums, but generally need some speed to pump air through them.
I took our Aerostar up a steep dirt road once - that was fine.
Coming back down, low gear wasn't low enough to control speed, the road was too steep and safe speed was maybe 15MPH.
The brakes faded badly, I barely got it stopped.
The disks weren't getting any airflow at 5-15mph, and overheated.

That's why I mentioned forced ventilation!

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[patprimmer]

I know what modern disk pads get. The point is what did classic disk pads get vs classic drum brake linings. In my experience when a similar car was offered with optional disk brakes, the disk brake option required more regular replacement. Maybe it was placebo or maybe small sample size or different demographics of the drivers

I agree the vents in the rotors rely on wheel speed to pump air so high speed light weight suits them better than low speed heavy weight.

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[140Airpower]

Jay, you are right that the biggest advantage of disk brakes, much better ventilation, is less effective at very slow speeds. So, you have to allow for that as you compensate for the grade. Otherwise, you cut your speed in half for a grade twice as steep. On unpaved roads it's harder to judge the grade. Jack mentioned 32%. That's horrendous.

 

[dgallup]

You are ignoring that nearly every diesel truck today is equipped with an engine brake that can absorb more power than it can put out a full "throttle". So as long as the trucker starts down the grade at a proper speed and in the correct gear, the engine can keep the speed under control without using the service brakes at all. That logging truck is obviously an exception.

Regarding maintenance costs, I have always found disk brakes much easier to work on than drums. Some designs like my motorcycle, the pads can be removed and changed by pulling one pin out, no need to remove the wheel. I've never seen a drum that can be serviced like that. Time is money in trucking so this could potentially save money.

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[140Airpower]

dgallup, I think you are only partly correct. First, the engine may not be able to control the truck's speed if the grade is TOO steep. The logging trucks are an example. Also, if the trailers brakes are not holding, engine braking could cause jackknifing. Second, the power of engine braking depends numerically on the gear ratio. So, at 60mph engine braking on a 6% grade should be hopelessly insufficient because of the gear ratio. The trucker has to downshift and he may not be able to get the gear he needs. Truckers have died trying everything to slow down. Runnaway trucks that have lost brakes may be doing 70mph or more and have no recourse except the escape turnouts that put the truck into a gravel trap. I've seen films of tests of traps. It's a hell of a ride, but a life saver. There are a couple of them on the Grapevine, one on the left side which I always thought was strange, but I guess if you can't hold the 35-45mph of the trucks in the right lane, you have to go left.

However, engine braking contributes. It could be all you need depending on grade, speed and gear.
Are you referring to "jake braking"? Is that is the most effective of several techniques? The speed limit for trucks on the grade is 35mph and at that speed, jake braking could probably hold the truck. But, I've seen trucks doing more than that.

http://www.crashforensics.com/tejonpass.cfm

 

[IRstuff]

"First, the engine may not be able to control the truck's speed if the grade is TOO steep. The logging trucks are an example. Also, if the trailers brakes are not holding, engine braking could cause jackknifing. "

That's not the case for I-5, though, since its grading was designed for even older trucks. And that's the reason why there's a brake check area prior to the downgrade. Invariably, the reason trucks have absymally poor maintenance, which is why changing the braking mechanism will most likely not help; the truckers will defer maintenance to the point of failure.

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[140Airpower]

IRstuff, that's true. The trucks I've seen with smoking brakes weren't going all that fast. It points possibly to brake problems due to maintenance.

 

[IRstuff]

It's not that different than on AirTalk, where the check engine light has been on for month,when caller calls,

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