| Author | Message | ||
| Robert J. Wies (Ncbob)
Rating: N/A |
On a day trip, today, to ATL I got into a discussion with a friend about the recent comments regarding the lack of 'aggressive' braking of MCI busses and we branched out into a chat about electromagnetic drive shaft braking retarders, which he told me that CA was ordering on all their state owned vehicles. This is a completely new area for me and I thought I might bounce it off some of the more learned among us. He explained that a disc, similar to what Audi used for their axle disc brakes, was attached to the drive shaft and spun inside an electromagnet, mounted to the chasis, to which current could be applied (either manually through a rheostat or coupled to the braking system) to create a magnetic field which would act as a retarder in addition to the on board brake system. I'm sure it's not a new or unique idea...just wondering if any of our sholars had toyed with the idea? NCbob | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Telma makes them. http://www.telma.com/en/index.php Basically as you say, rotating aluminum disk closely coupled to a variable electromagnet. As you increase current to the magnet, the aluminum disc starts to drag via eddy current that it generates (aluminum disk spinning inside a magnetic field is basically equivalent to a shorted-out generator, so it presents load to the driveshaft) The disc is made with lots of fins so as it gets hot while taking energy from your vehicle's driveshaft (slowing you down), it transfers that heat to the air. These things are very groovy. I'd LOVE to have one on my non-Jake-able bus. Only problem is they are not really popular in the USA yet so not many in junkyards, and they are big bucks to purchase new. Quite a lot of them in Europe where they are often doing neat things well ahead of us Americans... The same principle is used in Horton's two speed fan clutch drives. I have one on my Crown and also one on my Bluebird. On "low" the clutch is off and the magnets "eddy-current-couple" the drive to the fan just enough to have it spin at about 1/4 speed. When you need massive cooling the clutch engages everything at 1:1 Very nice systems, eddy-current drag designs... | ||
| John MC9 Rating: N/A |
Aren't they called "transmission retarders" and carry all sorts of headaches along? (Transmission heat, is the first major headache). Given the option, I'd do Jakes. | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Nope John, these are different. Transmission retarders use the tranny as the retarding mechanism, and all the heat generated by slowing you down is dissipated by the tranny and it's cooler. These are separate units that are bolted to the driveshaft independently from the tranny, and they do their job very well. Look at the website I provided above, and you'll see what they are all about. If I had a choice, I'd probably pick one over a jake, they are a lot simpler and can hold you back even more, and totally silent in doing so. | ||
| Mike (Busone)
Rating: N/A |
Just a couple of months ago my wife and I were behind a school bus and it had a sticker that said something like (Telma brake equipped.) I remember when going to school all the buses had these. Most of the drivers would use them more than the service brakes. | ||
| John MC9 Rating: N/A |
"Telma: Rotating parts called rotors are attached to the driveshaft. Separated by a narrow air gap, the stator is connected to the vehicle chassis. When electricity flows through the stator coils, electromagnetic fields with alternate polarities are created. As the rotors pass through these fields, eddy currents are generated which slow the rotors and thus slow the driveshaft. Any heat generated during braking is self-dissipated through the rotor vanes. " I dunno Gar, but it seems to me, that holding the entire bus back using the strength of the engine, versus holding the bus back via the transmission, is grossly out of sorts. With a transmission retarder, you're not only trying to hold the entire bus back, but the engine too. With the engine "jake" system, the engine is holding the transmission back, along with the rest of the bus. Systems defined | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
John, I think you have to look at it a different way. First off, these are NOT a transmission retarder. Transmission retarders are an entirely different beast, not really part of this discussion. A Telma is an entirely separate unit, as I said, that mounts a few feet behind the tranny, to the bus frame and to the driveshaft. The bus's transmission has nothing to do with it. Your link "systems defined" describes them very well under the heading "Electrical driveline retarders" When you activate the telma, it is going to be what holds the bus back, but it's not going to be "holding the engine back too".. in fact the engine will be helping because your foot will be off the gas, and the engine will be consuming a small amount of energy, helping the braking process. If you dig around on the Telma site, you will encounter some of the specs that these units are capable of producing... Go to "products and solutions", to "brochures" and and then download "the range", which is a PDF. Go in a few pages of the PDF and you'll find the retarding power of these things, which ranges from 350nm for the small ones (equivalvent to 258 ft pounds), to the largest one they make which will "eat" 3300nm of torque (equivalent to 2,400 foot pounds!!) That is WAY more braking power than any set of Jakes I've ever heard of, and more than most of us busnuts' engines can even produce, by a longshot. Basically these things are capable of producing braking power equivalent to or greater than the maximum horsepower that your engine can create. Jakes can't touch that!!! That's why they are so nifty... they have the capability to bring your bus down any grade, or if you want, almost to a screeching halt, with no wearable parts, no brake fade, no noise, and virtually total reliability. All the of the energy they consume when slowing you down gets turned into simple hot air, completely independant of the bus's engine, radiator, or transmission. And it's not due to friction, so nothing wears out or fades away. Reliable, mucho safe, and there when you need them...now that's something in my book!!! | ||
| SkipEagle20 Rating: N/A |
when an electric motor is shunt braked via electric brakeing it becomes a generator. maybe this principle could be applied and the power produced fed to the battery bank. | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Totally possible Skip... for an exciting preview of the near future, take a look at this one and poke around a bit: Allison Electric Drive PDF VERY interesting stuff is on the way!!! | ||
| t gojenola
Rating: |
I think you will find that on a rear-engine bus, this type of retarder must be attached to, and thus made a part of either the transmission or differential. This is because the driveshaft must be maintained in a stable alignment. On a long wheelbase unit, such as a schoolbus, the Telma retarder becomes a solid idler and bearing point in the middle of the long driveline. In this instance it might be OK. Anchorage's transit system had these installed in their old fleet of New Flyers (6V92/V730) back in the 80's and they were troublesome to say the least. By the time the coaches were surplused most had been removed or somehow disabled. The one I eventually aquired had one installed at the differential and it had been gutted. hth tg | ||
| John MC9 Rating: N/A |
Apples and grapes? Telma: Rotating parts called rotors are attached to the driveshaft. Separated by a narrow air gap, the stator is connected to the vehicle chassis. When electricity flows through the stator coils, electromagnetic fields with alternate polarities are created. As the rotors pass through these fields, eddy currents are generated which slow the rotors and thus slow the driveshaft. Any heat generated during braking is self-dissipated through the rotor vanes. What is an Electro Magnetic Retarder: Based on the Foucault theory, the eddy currents create in the circuitry of coil, pole and rotor a magnetic field which is used to decrease the rotation of the driveline without any friction or wear. The electro magnetic retarder is autonomous and driven by the driveline, which does not depend on engine performance and / or transmission gear. The electro magnetic retarder does not have any limitations due to the cooling capacity of the engine nor is an additional cooling circuit required. Voith Retarders: Voith Retarders are hydrodynamic brakes and feature a very simple structure: two impellers are facing another. The rotor and the stator. Between their chambers there is oil. The rotor is connected to the universal joint shaft of the vehicle, the stator to the stationary housing of the retarder. The rotor, driven by the universal joint shaft accelerates the oil, which is decelerated by the stator. This in turn decelerates the rotor and thereby brakes the vehicle. It appears they're all classified as "retarders", even though some are like the Allison and use fluid, and others use electro-magnetic devices (and where in the driveline they're placed). The advantage with the electro-magnetic ones, may be with the absence of need for elaborate cooling systems required for the fluid types.. The advantage of all the "retarder" types, over the Jake system, seems to be with is the ease of installation... I don't know about anyone else, but I feel like I've learned something today. | ||
| truthhunter@shaw.ca Rating: N/A |
Just filling in till MB has a chance to reply to J. MC 9 - and if the transmission should "fail" then were is your engine brake in the fail safe. Hope I did MB justice, (I'm trying) A odd ball Skidder made by Truckweld that I had way back had large Lockheed disk brakes mounted on the yokes of both differential (each with completely separate master cylinders)just to make sure one didn't loss critical braking on a step downgrade "pull of logs" [what are the chances someone would put transmission oil in both master cylinders to ensure a critical failure , well turned out 100%] Anyhow does anyone know the current draw on those Horton cooling fans clutches, might be the a good alternative to replacing the both sets of (missing) dampers on my MC 8 , living in the cold climate and all. Do they also have a "fan off mode" for initial warm-up with no current supplied? | ||
| John MC9 Rating: N/A |
(Oooh Noooo.... not Memmm Beeee!!!) Seriously, the retarders have their problems (maybe more so), just as the Jakes can have problems. Where's the "fail safe" with retarders if you lose electrical power? Egads.. It appears the retarders of any type are easier (less expensive) to install, than the Jake. If I'm wrong, let the fur fly.. I'm on the learning curve and my fur's been falling out anyway.. And.... the retarders seem to have a broader application list, than the Jake. The retarders can be swapped from a vehicle with a 2 banger vehicle to a 4 stroke, whereas the Jake cannot. Driving merits? Well.... one of those sites suggests that the retarder works well with the new ABS braking systems. That may be an advantage, since using a Jake on ice is suicide. I don't think I'd trust the retarder either (on ice), but I don't trust ABS brakes - period. I would wear my Reynolds Wrap hat, if need be.. Pros and cons... but they all have their place. Most articles suggest the Jakes are better at higher speed/rpm, and the retarders for lower speed/rpm.. We just know, that there's a Prevo guy with both.... (HAR) | ||
| truthhunter@shaw.ca Rating: N/A |
I prefer Alcan Wrap for my head pieces, the dull side is duller than Renyolds brand. But we all do-do it are way | ||
| Russ Barnes (Neoruss)
Rating: N/A |
Gee with one of these "electro-magnetic" retarders could I turn my 40,000 bus into a hybrid and get a tax credit from George? Interesting that these are all products from international companies. What do they know that we don't? | ||
| Marc Bourget Rating: N/A |
Russ said: "What do they know that we don't? " Could it be that fuel and maintenance prices are significant enough to warrant the extra expense for installation and maintenance??? | ||
| Craig (Ceieio)
Rating: N/A |
Russ - I think it has more to do with the roads. Lots of twisty turnies over there. Yes, there are some glorious open roads to be sure, but a lot more tight, twisty, up and down roads that make handling and braking a bigger deal (and more fun too! Well, in a car anyway. I have never taken a bus for a spin across the pond. It would probably put hair on your chest to be sure). :-) Craig - MC7 Oregon | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
My guess is it's because we have Allison and Jacobs over here, and they don't. Our two have themselves dug in pretty deeply within the industry, and our industry pretty much follows what they come up with, but not over there, where other ideas (which may well be better ones) have had a chance to prove themselves. Only then do we start to listen... | ||
| Max
Rating: N/A |
My Jumbocruiser 1977 Neoplan Car-o-tel has a Telma.Not new in Europa.In Tennessee the Garbage Truck's gettin Telma's.(Breaksavers)The Brakes last 10 times longer. | ||
| Tim Jones (Torquester)
Rating: N/A |
My opinions … but first…a little background: My conversion has a Caterpillar engine, Allison transmission, and Jacobs brake. I work as a technician on a fleet of school busses in the Rocky Mountain region. Most of the busses in the fleet where I work are equipped with some type of retarder. We have Allison MD3060R transmissions in some units (R stands for retarder). Some of these units utilize hand controls, some utilize foot controls, and all are electronically interfaced with the engine. I am not a real fan of these because I have been spoiled by the performance of the electromagnetic units. I feel like the braking performance is adequate but it is not as smoothly controllable as the electromagnetic units. They also introduce a tremendous amount of heat into the cooling system. We have one or two units with Jacobs style engine brakes. These do not impress me at all with their braking performance. The Jacobs engine brake on my bus is okay and I would not travel in the mountains without it but there is some loss of braking performance through the transmission and the braking horsepower still pales in comparison to the electromagnetic units. The balance of our fleet utilizes either the Thelma, or the Klam units. http://www.navarrainfo.com/klam/index.html These things are GREAT! You can actually drive these busses without using the service brakes for anything but holding the bus at a full stop on a hill. It is conceivable to me that a bus equipped with these could be driven its entire career without brake lining replacement. The newest Klam units are even equipped with a velocity set feature which acts as a downhill cruise control. This feature holds your speed during descents just like a cruise control but by using electromagnetic braking to hold you back. They are way cool and I love them. The applications for electromagnetic retarders on rear engine busses are limited in some applications by driveline length. Do not use any type of retarder in slippery conditions. I doubt that the money spent for any retarder could be recouped (through brake maintenance savings) in an RV application in flat land operation. In the hilly regions they are a necessity in my mind. Hth, Tq | ||
| Mark R. Obtinario (Cowlitzcoach)
Rating: N/A |
We operated two mini buses with Telma units in them. In the non-Telma equipped buses we were going through three sets of front pads, one set of rotors and calipers, and one set of rear brakes every 30K miles. In the Telma equipped buses we replaced one set of front pads and one set of calipers in 100K miles. Same size buses, same routes, same drivers. Would it be cost effective in an RV? It all depends upon the type of use and amount of use. Would I spe'c new buses with Telma retarders? You bet. Would I try to retrofit older buses with a Telma? It would depend upon how much longer I was going to keep the bus. Would I consider some sort of auxillary braking system on a bus? I think every heavy vehicle should have some sort of auxillary braking system so that the service brakes are never allowed to get hot, thereby keeping the service brakes in reserve for emergencies. What kind of auxillary braking system sort of depends upon lots of factors with cost of installation high on the list. Just for two cents worth. Mark O. | ||
| Stan Rating: N/A |
Thanks Tim and Mark. It is refreshing to get a post from someone with knowledge on the subject instead of people posting opinions that they read on another bulletin board. | ||
| John MC9 Rating: N/A |
And thank you Stan, for bringing that out. | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
How do electric retarders behave if they become overheated? It seems to me that the amount of energy taken off of the vehicle by any form of retarder or brakes is going to turn into heat if it cannot be stored. In that sense, it seems to me that an electric retarder will get just as hot as a driveline brake if it does the same amount of braking. In any case, the heat has to be conveyed to the air. The Jake seems to make a lot of sense because it does that directly, instead of heating something else up first. What do you guys think? In logging, there is a device called a Wichita brake that uses water as a storage medium for the heat. I would imagine if it overheated, it would just boil some water off to get rid of the heat. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
I'll let you know in a few weeks when I get mine running. There are two large"flywheels" on a Telma, one on each end, very heavy iron castings about 19" diameter, 2" thick, with major turbine shaped fan blades cast in that move a LOT of air when the thing's spinning. These "flywheels" are what the eddy currents are generated in, and they constantly cool themselves, probably a lot more than disc brake rotors because they are so massive and the fans are so big. What would happen if it actually overheated? They would work perfectly until Curie point of cast iron is reached, and then they would loose their magnetic properties and simply fade out. The Curie point is in the vicinity of 700-750 degrees C for iron, which is pretty whopping hot (1300 - 1400 degrees F !! ). My guess is that they never come close to getting that hot, as the hotter they get the faster heat transfers to the air that they are pumping. But I'll let you know, I'll be coming down the I-15 grade from Barstow, which is a few miles of constant 6%. I know how my Jakes work on that grade so it'll be a great comparison. I Still have that Telma for sale..... | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Thanks for the info, Gary, especially that part about the curie pont. Iron and water absorb a similar amount of energy per degree of temperature rise, volume for volume. But in most situations, you can heat iron up a lot more than water, short of a pressure vessel. I'l be watching for your posts. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska |
