OT: Big rig trucks: why air brakes and not electric brakes

[john.k]

if you read the Atlas Copco book,you will see compressed air was used for power in Paris for a considerable period.....and when electric light was invented ,air powered DC generators were installed....AC also relates ,that by adding pulses to the system ,clocks could be run off compressed air to an exact time .There were air powered lifts,machines,lights ,and may other ingenious uses.....The first big compressors used water pistons to beat the massive heat of compression.

 

[Robert R]

This question and answer blog dated 2011is a description of how to operate both freight and passenger car air brakes There is also some discussion of trains that have been equipped with electrically controlled air brakes. The information will come in handy should you need to stop a runaway train.

The authors are retired train engineers and current train museum engineers.

Freight vs Passenger Braking - Trains Magazine - Trains News Wire, Railroad News, Railroad Industry News, Web Cams, and Forms

The answer by Paul North in the blog describes the use of electronic/ pneumatic brakes:

The current (since fall 2007) trials of Electronically-Controlled Pneumatic brakes ("ECP") by BNSF, NS, and UP are a major step forward to address the problems that you identify. See the FRA's PowerPoint-type briefing presentation on ECP brakes of August 2006 at: http://www.fra.dot.gov/downloads/safety/ecp_overview3a.pdf Some interesting approaches, statistics, and information are in there - such as Quebec Cartier has been running its iron ore trains with them since 1997 ! For lots of practical reasons - as identified in the FRA presentation - the implementation just needs to be gradual, starting with certain "closed" or "captive" high-mileage traffic, and broadening out from there.

 

[DDoug]

U.S ones also do regen braking but you have less electric trains than Ruanda

Uhm....."regen" and put into a 4 megawatt toaster....Please doo try to keep up sir....

 

[john.k]

There was a crash some years ago in California caused in part by drivers not knowing that application of the loco air brakes shut off the electrodynamic braking.The reason being that application of both braking would cause flat spotting of loco wheels....The other reason for the crash was poor maintenance,some of the dynamic braking units being inoperative.

 

[Tci_]

Although no authority on air brakes I have driven trucks since the early 80's. I believe the quandary about air brakes is more about overall safety across a vast network. As mentioned earlier, trucks and most trailers have at least one set of spring brakes we call Maxi's that apply braking force when there is no air. These are only as good as the rest of the brake system. Meaning the cam's and shoes and drums all have to be in working condition for optimal spring brake operation. these are basically a parking brake. The actual braking once the system is charged is applied through the pedal. If you have a problem like a line leak you can easily hear it and find it and repair it. If you have that same leak in many/most instances it is well within the systems ability to produce so you actually still have full working brakes even though you have a leak. A leak will not cause a spark and following electrical fire either. Brakes get very hot on a big rig and sometimes even catch on fire. If you completely loose your air either through some mechanical failure, which is very rare, or more commonly through pumping your brakes too much then the spring brakes will come on and maybe you will stop. The weight involved with semi's means that even perfectly working brakes will only do so much. This is why you see run-away truck ramps out here in the high country where the hills are steep. There are whole secondary braking systems in most trucks these days including transmission retarders and engine brakes that help to bolster the air brakes and in some cases do all the braking on light grades. The potential for failed electrical brakes and the mess it would be to try and trade trailers across the whole country make electrical a no-go. Air brakes are relatively cheap as well which may be the final deciding factor of all.

 

[john.k]

Many years ago in England the anti truck lobby were very strong ,and truck air brakes had to be three separate systems on all wheels ,including the front....all the air chambers had triple diaphragms in them ,to be failsafe.Made everything very expensive...and spring brakes were rejected ,and the Westinghouse parking brake setup had a roller locked outer pushrod .....the park brake could only be relesed by applying compressed air.,unlike a spring brake where a puller screw could be inserted,and used to release the brake.....Killed the export market for English trucks ,which at one time was very strong.

 

[Dieseldoc]

In my experience in another life, I can’t recall a Conductor ever using his valve for the purpose of assisting the engineer to control the train. Not saying that it’s hasn’t occurred. However at the time radio com could be spotty and if a Conductor could not make contact with the motors, and “felt” need, he would make an first application, watch the cab gauge and see if there was a change. Drawdown would cause the automatic valve on the motors to start “singing”, replenishing air in the brake pipe, (a signaling method), of which the engineer would see and hear, causing a response, in reducing even further the train line pressure to complete a stop or make communication with the Conductor for instructions.

 

[thermite]

Many years ago in England the anti truck lobby were very strong ,and truck air brakes had to be three separate systems on all wheels ,including the front....all the air chambers had triple diaphragms in them ,to be failsafe.Made everything very expensive...and spring brakes were rejected ,and the Westinghouse parking brake setup had a roller locked outer pushrod .....the park brake could only be relesed by applying compressed air.,unlike a spring brake where a puller screw could be inserted,and used to release the brake.....Killed the export market for English trucks ,which at one time was very strong.

Not disputing the brakes lore, but "very strong" as to allowing English lorries to escape Blighty at all might well have justified naval bombardment of the ports by the intended victims!

 

[idacal]

they have been putting these in some government trucks fire, ambulance, that do a lot of in town driving. but the power consumption is high, price is high, and its added weight. some locales in europe allow a weight credit so they are much more popular. looks like an off road fire hazard in the western us. Welcome To TELMA USA

 

[dsergison]

You have to push pretty hard but ...

View attachment 281110

Seems very dubous.

Seems you would have to get the hubs glowing hot to loosen the spokes enough to matter to the stability.
At which point you would catch fire.

 

[EmGo]

Seems very dubous.

Seems you would have to get the hubs glowing hot to loosen the spokes enough to matter to the stability.
At which point you would catch fire.

You want Mert's number ?

btw, brake disks do glow red hot, you can see them at night. Drums see as much energy but they can't cool well and the expanding drum moves away from the shoes so they don't work as well ... but yes, they do get hot. Very hot.

 

[moonlight machine]

You want Mert's number ?

btw, brake disks do glow red hot, you can see them at night. Drums see as much energy but they can't cool well and the expanding drum moves away from the shoes so they don't work as well ... but yes, they do get hot. Very hot.

Not much chance he knows who Mert is!

 

[m16ty]

Numbers Greg....Show me a solenoid coil (or other actuator) that packs that much power in the same size as a maxi brake canister.

This is one limiting factor I see. Even if you could get some sort of electric solenoid or actuator to hold the spring back, I would think it would take a massive current draw, and would have to be pulling that current the whole time the brakes are released.

I think the main reason air brakes are still the norm is to not try to fix what isn't broken. Air brakes have been around a long time, are proven, and work.

Also, truck systems that also control the trailer are hard to make changes to. For instance, there has been a desire to change truck voltage to 24v, and 24v does work better for starting these big diesel engines and the big electrical requirements of trucks. The problem is, nobody has a 24v trailer. Lots of operations pull different trailers all the time, so the truck can't really remain married to the same trailer. In other words, if you buy a 24v truck, nobody has a trailer you can pull. So you buy an electric brake truck, and even if you get an electric brake trailer to go with it, you can't pull anybody else's trailer if needed. This really limits your usefulness. It all comes back to "if it ain't broke, don't fix it".

 

[john.k]

Electric brakes on larger axles were mostly for military use.....simple reason was that tanks and tractors didnt have air systems,consequently conventional trucks towing heavy guns had an electric brake controll ....the only one Ive personally owned is the NM Mack ,and they had a big cylindrical brake controll (rheostst?) mounted on the dash..."Warner Electric Brake"..They also had a 700ci gasoline engine ,and were thirsty.

 

[john.k]

Electric brakes on heavy vehicle axles didnt need a lot of power,because they were generally of a servo type....A smaller inner drum was braked by the electrics ,this inner drum could rotate and apply the shoes of the main wheel brake.....Years ago ,lots of big trucks had hydraulic brakes ,as they were a lot lighter that air brake setups ,and if used with a vacuum booster ,didnt need a compressor on the engine either....Spring brakes generally killed hydraulic brakes on big trucks ,because a simple system could be failsafe.