Auto Tech: GM's Two-Mode hybrid

"a lot of heat generated in the power inverter module" ??! If
that's true, they're doing something wrong.
.
The 2-mode seems to have taken the basic, simple 2-motors-plus-
engine lashup we derive so much enjoyment from and turned it
into a monster -- three planetaries instead of one, three or
four physical clutches, hydraulics ... basically lobotomizing
the hybrid driveline right back into the stone age. I'm still
trying to understand this nightmare, but haven't found any really
good info on it and certainly nothing that tells me why it's
any better than the Prius' single-planetary system.
.
_H*

 

Hobbit, I agree with you on the heat. Heat is lost energy. Sometimes, though, heat is just the cost of doing business. For some systems, a byproduct of heat is inevitable.

"The 6.0-litre Generation IV small block V8 engine.." Since when was 6.0L a "small" block???

"This engine features Active Fuel Management, which deactivates four of the engine's cylinders during light load operation to save fuel." I've always liked that concept since Honda introduced it on their V6's. I wonder why every engine doesn't implement this technology.

"this engine also keeps the intake valve open a little longer than a normal engine, allowing a reverse flow into the intake manifold. This reduces the effective compression ratio, allowing the expansion ratio to increase while retaining normal combustion pressures. Efficiency is gained because the high expansion ratio delivers a longer power stroke and reduces the heat wasted in the exhaust."
I had to read this about five times before I fully understood how this is a benefit. Interesting concept, if the empirical data supports it. I just hope there's enough heat in the Carnot cycle to offset the loss due to adiabatic conditions. The only reason that I am concerned is because usually more efficient engines have higher compression ratios. Porsche's 3.0L six uses 11.3:1. PRIUS uses 13.0:1. High compression ratio harnesses more power from the fuel (or allows you to use less fuel and get the same power as a lower compression ratio). I wish GM the best of luck with their "lower compression ratio, higher expansion ratio." Go get 'em boys!

Yes, I understand what your technology is saying. I get it. You release some of the intake back into the manifold; having less power per stroke during times of "constant velocity on flat terrain." Maybe if you didn't have a 6,000 pound vehicle, requiring the torque of a 6.0L "small block," you would be able to use a smaller engine with a higher compression ratio. Instead, you have to vary the compression ratio because during times of towing a 6000 pound vehicle up a steep grade, you will need to retain the higher compression ratio PLUS 6.0L at full bore. Oh yeah, I get it. Especially at $4.25 per gallon (the new high here in So.Cal)

 

Because it's cheaper to lobby/buy Congress & the Pres. and fight CAFE than to hire a couple engineers to design it into their products.

 

"this engine also keeps the intake valve open a little longer than a normal engine, allowing a reverse flow into the intake manifold. This reduces the effective compression ratio, allowing the expansion ratio to increase while retaining normal combustion pressures. Efficiency is gained because the high expansion ratio delivers a longer power stroke and reduces the heat wasted in the exhaust."

I believe the Pruis does this. It's what is refer to as an Atkinsonized engine.

 

Smells to me like GM has a bad case of "Not Invented Here" syndrome.

 

Yeah, I really don't get it. In most mechanical/electrical problems simplicity = efficiency. Not always of course, but more often than not.

Toyota took the Camry 4 cyl, added a hybrid and it went faster, about 1/2 way between the 4 cyl and V6, while improving fuel consumption by 26% over the 4cyl and 35% over the V6, or about 30% based on its performance.

Toyota added a hybrid to the V6 Highlander 4WD, improved fuel consumption by better than 27% and it got faster.

Ford added a hybrid to the 4 cyl Escape and improved fuel consumption by almost 32% while performance stayed constant.

GM puts a 2-mode on the Tahoe, has to grow the engine to 6L, improves fuel consumption by 24% (RWD, <20% 4WD), but its slower than the normal 5.3L.

Still seems like simpler may still be better to me.

Rob