Diesel engine braking idea

Exhaust brakes are available for diesels to help get down long steep grades safely without cooking the brakes. They work by choking off the exhaust flow, turning the engine into a compressor. But they are expensive and trouble prone.

Gas engines have decent engine braking, just by closing the throttle valve, cutting off the air flow into the engine, turning it into a vacuum pump.

So how about installing a big throttle valve on the turbo inlet, or on the intake manifold inlet for use as an engine brake? Is there any reason that wouldn't work?

One possible problem is putting the butterfly before the turbo, puts the turbo in a vacuum and sucks oil into the intake past the seals.

R.

BTW, the "Jake brake" is a Cummins invention, invented by the man himself.

That's a good point, and also I don't know if the intercooler could take the vacuum without collapsing. So the valve would have to be on the inlet of the intake manifold. Any other thoughts? I would think that it has been tried, but maybe not?

If you did it after the turbo and slammed it shut then the pressure between the turbo and throttle plate would spike through the roof, maybe make the turbo try to spin backwards or blow off the hose clamps, especially since the exhaust pressure also drop seriously fast I think the turbo gas engines with a blow through set up have a pressure relief system.

Jake brakes work by opening the exhaust valve sooner in the compression cycle and reducing the amount of energy transferred to the crankshaft. I am not sure how introducing a throttle blade into the intake tract would work although I get your line of reasoning.

We ran jakes on dozens of trucks for decades and never had any issues other than breaking wiring connectors when working around the heads. I think they are very reliable at least in a heavy duty application. At least on a Cummins. Not to sure about those crappy Detroit's and Cat's.

The modern stuff just uses the variable geometry turbo to provide engine braking, it works pretty well. I think all of the current model year 3/4 and 1 ton trucks have a turbo-based exhaust brake, which is not trouble prone like the older external hardware.

All also have intake throttles but don't use them for engine braking purposes because you'd then also need a compressor side bypass valve, which diesels don't have.

I would think the huge difference in the gas/diesel compression ratios would limit the gas engine's effectiveness as a brake.

I think they actually work by opening the ex valve just after TDC on the power stroke so the compression does not push the crank down right after it slowed it via compression on the compression stroke. Thats why they are so noisy.

The exhaust brake on my 2002 CTD was a butterfly in the exhaust after the turbo. I had to clean it once and the little shuttle valve that controlled it stuck once and crippled the engine (no power at all) I loved the sound of it in action and it was very effective when pulling and stopping the 8,000# travel trailer we had. There was no exhaust valve lifting on that engine.