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TheBrian

Subaru is developing turbo hybrid for 2007

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I found this article, which says Subaru is developing an EJ20 turbo + hybrid, which they hope to put in a Legacy in 2007. It would compete against the likes of the Accord hybrid. They expect to beat the Accord hybrid by a few MPG.

 

The engine uses the Miller cycle, where forced induction over-fills the combustion chamber, but the intake valves are left open during the beginning of the compression stroke, to allow good fuel-air mixture. The torquey electric motor makes up for the lack of low-end torque on the part of the turbo Miller-cycle engine.

 

It's a pretty interesting article, and it's cool that Subaru is doing yet another thing a totally unusual way. I'm impressed with how quickly they expect to get this technology to market. If they do pull off the numbers they're talking about in 2007, they might just get the attention and brand recognition they crave.

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Cool, i told my mom that she should get rid of that volvo for a Subie, she said " only if its a hybrid" i think we're in business now :grin:

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The Miller-cycle is interesting because it introduces the term "expansion ratio" as separate from the compression ratio.

 

Normally it is the increased expansion ratio (on the power stroke) that is the primary reason for the increased operating efficiency as a result of increasing the what would normally be refered to as the "compression ratio".

 

The miller cycle engines run static C.R.'s of around 13:1, but lowers the effective C.R. (compression pressure) to conventional levels by way of hanging the intake valves open longer to allow a partial reversion discharge. However the expansion ratio remains 13:1.

 

Not sure if that made sense. :confused:

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You can also get a Miller cycle engine in a Mazda Millenia, but I'm not sure of the years. It uses a supercharger though instead of a turbocharger (Miller cycle requires use of forced induction, and when the piston is coming back up with the intake valve still open, the pressure of the incoming air charge will press against the charge in the cylinder, so less air comes back out than one might expect. I suppose that with the use of a turbocharger, they probably use some sort of variable valve timing on the intake cam to advance the cam timing at idle and off boost, otherwise you'd lose quite a chunk of your charge.

 

There is a good article on Wikipedia and on howstuffworks.com on the Miller cycle.

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Yeah, "reversion discharge" isn't completely accuarate. Delaying the start of the actual compression until the piston has traversed part of the way up the "compression" stroke (by way of delaying intake valve closing) would be a better way of putting it.

 

Good point about the variable valve-timing. It'd be neccessary to close the intakes earlier at low rpm/ high-load conditions to preserve usable torque and turbo spool-up.

 

I think I originally learned of the miller cyle through Wikipedia. I had a difficult time understanding their description at first, but it's pretty simple once you see the big machine.

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