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Variable compression?

NutmegCT

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Variable compression systems have been around for a long time. Recently, Nissan/Infiniti have introduced their "VC-Turbo" 2.0 four cylinder engine.

To me it seems pretty complex. As I've heard my doctor say, "The device worked perfectly until it failed."


I'm the least engineering savvy person in the world. Hey - I build things out of cardboard and aluminum foil. I admire engineering, but know nothing about details. This variable compression method seems to be a lot of metal flying around very fast, with constantly changing angles and forces.

What say you?
 

3798j

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I'm amazed by all of the approaches that manufacturers take in advancing the ICE. I'm hooked on YouTube's Jason Fenske's "Engineering Explained" series where he tries to give the explanations of how it all is supposed to work. Whether it's Honda's VTEC or BMW's VANOS dating back to the 1990's..or Mazda's Miller Cycle V6, it all surprises with the wild approaches. My current daily is a Toyota Tacoma that uses Toyota’s D4-S fuel injection system which offers both port and direct fuel injection. It also has a wide-band variable valve timing system that can run the engine both a fuel saving Atkinson Cycle or the Otto Cycle for more power when needed. When I started looking at it, I thought "who the heck thought this was possible?". While today's engine technology confuses me, I'm fascinated by it.
 

Alfred E. Neuman

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I think we're seeing the last generation or 2 of the IC engine. It just doesn't make sense to chase efficiency at the cost of every more complexity in the IC engine when an electric motor is both an order of magnitude simpler and more efficient to begin with. As soon as battery technology will let us get 500 miles per charge, it's game over. If Moore's law holds with battery improvements, we'll see that in under a decade.
Get behind a decent non-carbon electricity generation method like Thorium reactors and let's relegate burning stuff to go fast to the "having fun" category.
 

3798j

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^ Agree, and hard to argue otherwise....Though I sill have this fascination (since childhood) with the ICE.
 

Alfred E. Neuman

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^ Agree, and hard to argue otherwise....Though I sill have this fascination (since childhood) with the ICE.
Same here. I'd honestly like to see regulations push the mass market people movers in the EV direction, and loosen up laws on classics and low volume makers like Caterham, Morgan, and the like. The few thousand classics and modern holdovers don't hold a candle to the millions of rank and file commodity cars being sold every year.
 
OP
NutmegCT

NutmegCT

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Looks like my "what do you think of the VC engine?" has morphed into ICE thoughts.

Actually, I wanted to buy an electric vehicle myself, but after seeing the down side, decided on my four cylinder Altima.

Down side for me: environmental issues when manufacturing the batteries, battery power substantially reduced in winter (electric heat), high initial cost, lack of recharging stations, our 20 cent per kwh rates here in Connecticut, tax credits not useful for someone living on federal Social Security checks, etc.

Maybe in my next life?

Tom M.
PS - still haven't figured out why classic cars here at taxed so low, when so many owners seem to have a *lot* of resources. Any car over 20 years old is valued at $500 for property tax - regardless of the market value of the car. Hey, my house was built in 1826; would be nice for the property tax value to be limited to $500!
 

Alfred E. Neuman

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I'm honestly surprised the next step in IC efficiency isn't continuously variable valve timing. F1 has used pneumatically actuated valves for years so they can get them to operate at such high RPM without floating. Use that same technology or maybe simple electronic solenoids for the road to have an infinitely variable lift and duration for the valves based on exact engine load and rpm.
Not only would that improve efficiency, it would reduce the rotating mass of the engine by a good bit as well. Actually remove mechanical complexity in favor of simple actuators.
 
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NutmegCT

NutmegCT

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Alfred E. Neuman

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That's pretty much the way Mercedes does it. Cam sprocket is an actuator that can rotate the cam +/- 20 degrees or so advanced or retarded. No lift or duration adjustment on these cars (yet).

I'm waiting on completely eliminating camshafts and having valves operated individually by solenoids or the like.
 

PAUL161

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I have an old Case tractor that works that way. Low compression on start up advancing to a higher compression when running, works by fly weights on the timing gear. This tractor is 40+ years old, so the technology has been around for a while. This tractor also has a silent starter/generator and makes no noise when cranking, works very well. PJ

Oh yeah, it also has no water pump, circulates the coolant by convection, I've never seen it get hot enough to boil over.
 

DrEntropy

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Alfa did a VT cam setup in the early '90's, too.
 

3798j

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Alfa did a VT cam setup in the early '90's, too.
Says here (Wikipedia) they were the first automobile manufacturer to have VVT:

"Alfa Romeo was the first manufacturer to use a variable valve timing system in production cars (US Patent 4,231,330).[SUP][6][/SUP] The fuel injected models of the 1980 Alfa Romeo Spider 2000 had a mechanical VVT system. The system was engineered by Ing Giampaolo Garcea in the 1970s.[SUP][7][/SUP] All Alfa Romeo Spider models from 1983 onward used electronic VVT"
 

DrEntropy

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Yup. Didn't wanna be all: "neener-neener, Alfa did it frst!" or aught.
 

PAUL161

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But being an Alfa, it probably worked for about 236 miles...

Yeah, but just it's pretty looks make it all worthwhile! :applause: PJ
 

PC

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.... If Moore's law holds with battery improvements, ....
I doesn't. It never has. It never will.

It works for computing because computing is conceptual, not physical. Concepts have no mass, displace no volume, require no energy. They're limited only by physical implementation.

Batteries are pure physical implementation. They must exist in the real world, not the cyberspace. They have to contain/deliver energy. They must be made from real materials. They must be fabricated, handled, stored and disposed of. They're limited by chemistry. The relationships of chemistry and energy are very well understood.

That's why battery evolution is always incremental. A truly revolutionary new implementation may yield a geometric improvement in the short term. And there are certainly big improvements to be made. But the long term will always be incremental and in the end they're limited by physical reality.


.... F1 has used pneumatically actuated valves for years so they can get them to operate at such high RPM without floating. Use that same technology or maybe simple electronic solenoids for the road to have an infinitely variable lift and duration for the valves based on exact engine load and rpm.
Not only would that improve efficiency, it would reduce the rotating mass of the engine by a good bit as well. Actually remove mechanical complexity in favor of simple actuators.
Don't hold your breath on that. It'll likely happen some day. Not today. Not tomorrow. Nobody knows if it's years or decades away.

Fast, reliable electromechanical actuators have been a holy grail of engineering for more than a century. As with batteries, progress is incremental. Real world physical limitations continue to be a monster to overcome.

F1 valvetrains still use cams for actuation. The gas systems replace springs. Gas has far less mass than wire springs and never fatigues or breaks. It makes sense for engines where high revs and maximum power take precedence over cost and complexity.

Electromechanical actuation is a whole 'nother ballgame.
 

Alfred E. Neuman

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Mercedes doesn't use a Demodromic valve system that I know of. I know in the new 278 engine and maybe the 276 (V6 version of the 278 V8), they have a way to cut fuel and spark to certain cylinders and use an actuator to move the rocker off the cam so it runs as a 4 cylinder (I think) engine under low load cruising.
The only Desmodromic engine I can think of is Ducati. It's basically replacing the valve springs with a second rocker that lifts up on the valve stem to close the valve. The closing rocker follows a cam with the opposite profile of the opening cam. Lets them run really high RPM in an interference engine without worrying about valve float and bending expensive parts.
 
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