IIRC, Dynojet, initially anyways used rail car axles and added the drive drums to the wheels... I do believe they are inertial, though I'm sure you could add an eddy current brake to them to add some load... Last I heard, Roush was using eddy current dynos for their endurance testing and engine development, selling the generated power back to the utility!Originally Posted by acannell
Mike
"The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry
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Why not a balanced roller off the end of the engine, that rolls on another roller. Then usea large electric motor to create an "electric brake" or gear that down with viscous couplers.
The thing is you cant avoid having to dissipate 100% of engine power somehow even if its geared down. Even if I gear it down 100:1 and at 6000rpm the dyno load is only turning at 60rpm, the brake would still have to deal with whatever 300hp or 500hp the engine is putting out, the torque will just be that high.
But for a short dyno pull maybe it could work out. Maybe putting a bunch of disc brakes in series and engaging them simultaneously, theyd be able to dissipate all that energy for 10 seconds or so, especially if they are immersed in a liquid bath of some kind? I could get used disc brakes from the junkyard I would imagine? The amount of energy in a car going 80mph gets dissipated by just 4 brakes, mostly just 2, right? So what if I had 10 in series, all with liquid cooling? How bad can things get in 10 seconds at 500hp?
A 3500lb car at 80mph has about 1 million joules of energy.
Lets say that in an EMERGENCY stop, just 2 disc brakes can handle that without exploding or melting, with air cooling. Im not sure how long that stop would take, but probably alot less than 10 seconds. But lets say 10 seconds. So the brakes can handle 500,000J being dumped into each brake if done over 10 seconds.
So if we have a 500hp engine, and we assume it outputs 500hp continuously for 10 seconds (which it will not, but lets do worst case).
Thats about 400,000J per second. In ten seconds, 4 million J total, or 2million per brake. So 4 times the energy. So if we quadruple the number of brakes involved and involve a very good cooling system (liquid or air or whatever), and then take into consideration that the engine does not output 500hp continuously, I think we are in the ballpark.
google redneck dyno and have a laugh but it works
I was going to suggest having a turbine type viscous coupler, like a torque convertor. Then making multiple ones, and chambering them seperately, but in parallel. Then filling it with a thick fluid, like motor oil. Have their vanes designed to fan out when a higher engine load is required, I.E. like a windmill variating vanes dependent on windspeed. You could have this attached by some sort of clutch system, so the engine does not have to overcome the load immediately. Just random ideas.BTW me thinks you will have to figure out a highly inventive way to keep those brake discs cool. Dunking them in any fluid while operational is asking for poor performance, and dunking in cool liquid immediately after hard breaking is asking for embrittlement and a time bomb.
Water spray cooling for brakes isn't anything new...even for disc brakes. The PPG LeBaron pace cars had water spray cooling for the brakes. Also, look at the European semi-truck racing. They use water spray cooling for their brakes.
The thing is I don't think you can spray it directly on the friction surface. I think it has to be sprayed into the cooling vanes (I could be wrong here, so research is needed).
Seeing as there have been many cars that have been tuned on the street using the brake drag method, I don't see why this wouldn't work. You would just have to figure out how to measure the energy. Maybe mount the brake calipers on a pivoting fixture that when the brakes are applied it presses against a load cell and torque is calculated that way. As long as you can stall the acceleration of the engine, then you should be able to get a semi-accurate reading.
All logging trucks use water cooling for brakes here in Canada
If we spread the energy out over alot more disc brakes..like 10 brakes or something, maybe nothing beyond the normal brake venting would be needed. Or we could add forced mist jets right into the intake of each vented disc.
wwwwwaaaaaaahhh??? more info plez!Seeing as there have been many cars that have been tuned on the street using the brake drag method,
I would think the same way as any other dyno load..whether it be water, eddy, intertia...you put a load cell on whatever is preventing the rotation, in this case, the caliper that pinches the disc brake, and that gives you torque. Then with rpm you have power. Very accurate and just like the "real" dynos.I don't see why this wouldn't work. You would just have to figure out how to measure the energy. Maybe mount the brake calipers on a pivoting fixture that when the brakes are applied it presses against a load cell and torque is calculated that way. As long as you can stall the acceleration of the engine, then you should be able to get a semi-accurate reading.
Problem is 6000 rpm is like 400 mph on 205 50 R 15s..so most disc brakes are probably not designed for that speed, so some kind of gearing would be needed. I suppose you could just use a stock tranny or make some bad --- reduction gear. All it needs to do is survive and reduce like 5:1. Doesnt need to be small, light, or sound nice.
I think maybe one of the problems would be a non-linear load from brake fade or whatever other kind of behavior happens. So you would probably need enough disc brakes or a way of doing it so that the brake acts very linear or things are going to go wonky. Eddy current dynos are braking the disc with a magnetic field so theres no weird gas formation or getting hot and changing coefficients of friction..
This seems so weird that its hard to do on the cheap/simple. Theres got to be a way to pump energy into something for 10 seconds that keeps the load steady and controllable.
I guess you could put a huge roller under ground mounted wheel hubs and fill it with concrete, but not sure where the relationship between it exploding at high rpm and you being able to gear it down but still store enough energy in it at lower speed mates up. Im guessing its not in our favor.
Pull the gen head out of a big old diesel power backup system with a blown engine. Use that as your load. When the power blacks out power your neighborhood with your 8valve.
The water load idea sounds simple, or maybe you could even push air like the fan exercise bikes do. Would need something huge to drive air. Industrial compressor? The brakes sound like a bunch of trouble. I have an eddy current absorber if you want to check it out to see how its built. I think its pretty simple.
MinivanRider
Ken (5digits) has described a few times how he has done a few tunes on the highway using the brakes to put load on the engine and gears to get the rpm desired. Think brake boosting. Same idea. Of course you WILL wear out the brakes doing it this way, so use less expensive parts until you get the tune nailed down. The clutch will also have to be up to the task (or converter if you are using an auto).
If you are holding an engine at a constant rpm at a given throttle position, then the load is steady, so even if the brakes get hot and it takes more master cylinder pressure to hold the rpm steady things are golden. The power is being turned into heat and there isn't enough power to overcome the load.
Eddy current load generators can also have a change in load applied over a period of time due to the electrics heating up, which increases resistance and requires more power.
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