EMD turbocharged

[doug u]

Many years ago I read an article that when EMD turbocharged the engine it is not a pure turbo. The turbo (compressor) linked to mechanical drive like a supercharger , then at high RPM (run 7 or 8) the mechanical drive drops out then it is exhaust driven (turbocharged). Is this possible , I have never heard of such a system that can function this way. It would be a good setup because of no turbo lag in this kind of system. Is the artical actually true or not.

[GDRMCo]

Yes, it's a mechanical turbo, it's run by a direct mechanical system like a supercharger until a certain RPM then the mechanical link is disconnected via clutch and runs like a normal turbocharger.

[creepycrank]

I just want to add that its a overrunning type clutch as in a bicycle where your are peddling along at a constant speed but the bicycle speeds up when going down hill. On an EMD turbo there is a planetary speed up gear drive that drive the turbo at about 16,000 rpm but with the increase in volume of exhaust gases it will speed up to about 20,000 rpm at full engine load. You see this on load sharing generators as they speed match first them pick up the load, 

The EMD turbo set up is unique to their design. Other 2 stroke engines such as Fairbanks Morse, Detroit Diesel and the Cleveland Diesel 495 all are 2 stage in that they have have a mechanically driven blower and a free spinning turbo around that. The BIG Wartsila engines get started using electric motor blowers that cut out as the load picks up and the turbo speeds up. 

[doug u]

This turbo design only a EMD design. The overrunning cluch could be in and out at any speed. Did this design help reduce the smoke due to turbo lag on most turbo? This setup couldn't work on a car, could it, cars have a noticeable turbo lag. Supercharging would place the engine under boost all the time (not good). If GM could have made this design work on a car it would remove the turbo lag and not have constant boost at higher speed like a supercharger. Although turbos in a car run up to 100000 RPM and down sizing the design would be difficult at best. But I feel that such a design in a car would fun to drive. Cross application of this design would be a challenge for GM. When I read this , I was thinking cars.

[creepycrank]

We are focused on the clutch feature but their is also a speed increaser gear drive requirement also. In EMD's case its about 18 to 1. Extracting energy from the exhaust can be a problem with the very high speed for a turbine. On turbo compound engines such as the Curtis Wright R3350 engine they had a crankshaft driven supercharger as well as turbines gear to the crankshaft. Detroit Diesel has a truck engine in production now that is supposed to be turbo compound but I don't know the details on the connection but its worth a 10% increase in power. Several years ago ABB had a turbine system that operated in the exhaust from a ship's main engine that was used to drive a generator for the ships hotel power and no connection to the crankshaft but ships run for days without any of the needles moving

For car engines and truck diesel I think they use variable nozzles to pick up turbo speed faster.

[rvos1979]

Creepycrank:

The new Detroit Diesel DD series engines have a regular turbocharger, additionally, another turbo compressor wheel is driven off the crankshaft via step up gearing, like the EMD turbo, minus the overrunning clutch.  Supposed to be good for about another 50lb-ft of torque.........

I am currently driving a 2013 ISX Cummins, has a variable vane turbo on it, is interesting sometimes, like during regeneration the turbo will spool itself up, have had 20 pounds of boost at 900 rpm just running around a parking lot........