Intresting Engine

compression-official/

Hmm, my 2009 Honda Civic hybrid has variable intake valve timing, which seems to pretty much accomplish the same thing. They've been doing this for some time, probably dates back to at least 2006 on that model.

By reducing the charge drawn into the cylinders, it reduces the peak pressure, so that seems to be varying the compression, too. A pretty low-tech way to accomplish it, it doesn't make any chages to the lower end. This Infiniti scheme seems to add a LOT more complexity to the lower end. I wonder if this is some way to get around a Honda patent?

Jon

Or a Peugeot patent?

--jsw

I think you're misreading it, Jon. This engine is truly revolutionary. Varying valve timing as you describe just produces a pseudo-Atkinson cycle, used on today's hybrids:

What this new Nissan engine does is to actually change the compression ratio of the engine.

The nominal compression ratio of an ordinary engine (say, 10:1) is only achieved at full-throttle operation. At any other condition, the actual compression ratio is less, because less air-gas is let in. This is the chief reason that gasoline engines can't achieve the efficiency of diesels, which are always running at their nominal compression ratio.

If you can vary the compression ratio, you can approach the nominal ratio even at part-throttle operation. To achieve it, you actually have to increase the ratio *above* the nominal amount (say, to 14:1). When you do that, the part-throttle operation, which lets in less air-gas, causes the *actual* compression ratio, or effective compression ratio, to be returned to the optimum 10:1. (These values are just examples.)

You wind up with diesel-like efficiency. Then, the Atkinson cycle extracts more, by effectively extending the expansion stroke.

The Atikinson-cycle part of the operation is incidental to the variable compression ratio. It's the variable compression ratio that's the big deal. A true Atkinson cycle is quite efficient, but the pseudo Atkinson cycle of today's hybrids is less so.

I think you're misreading it, Jon. This engine is truly revolutionary. Varying valve timing as you describe just produces a pseudo-Atkinson cycle, used on today's hybrids:

What this new Nissan engine does is to actually change the compression ratio of the engine.

The nominal compression ratio of an ordinary engine (say, 10:1) is only achieved at full-throttle operation. At any other condition, the actual compression ratio is less, because less air-gas is let in. This is the chief reason that gasoline engines can't achieve the efficiency of diesels, which are always running at their nominal compression ratio.

If you can vary the compression ratio, you can approach the nominal ratio even at part-throttle operation. To achieve it, you actually have to increase the ratio *above* the nominal amount (say, to 14:1). When you do that, the part-throttle operation, which lets in less air-gas, causes the *actual* compression ratio, or effective compression ratio, to be returned to the optimum 10:1. (These values are just examples.)

You wind up with diesel-like efficiency. Then, the Atkinson cycle extracts more, by effectively extending the expansion stroke.

The Atikinson-cycle part of the operation is incidental to the variable compression ratio. It's the variable compression ratio that's the big deal. A true Atkinson cycle is quite efficient, but the pseudo Atkinson cycle of today's hybrids is less so.

Ed Huntress ===================================================================

Saab demonstrated a running variable compression supercharged 5 cylinder in

2000, see for example. Naturally GM killed it sometime after they acquired Saab, citing cost. This was an inline engine with the block split horizontally between crankshaft and cylinders, with a hinge down one side and a mechanism to lift the other side to control the compression.

----- Regards, Carl Ijames

Right.

Well, getting rid of pumping loss is a really good thing, so maybe this accomplishes the variable output without a throttle, at least under the driving range of operation (might still be needed for idle).

OK, that probably requires a degree in thermodynamics to understand.

Jon

I like the old-timey bizarre mechanical linkages used to acheive the weird motions folks used to really get excited over.

Cydrome Leader fired this volley in news:novt3m$7u2$ snipped-for-privacy@reader2.panix.com:

They're hardly "bizarr". I use such linkages on my machines to make explosive materials. Those 'bizarre' linkages are really a basic part of mechanics.

Look at some of the OLD (say, pre-1960s), purely-mechanical manuals on how to achieve various motions -- it's all in there!

Lloyd

Let me try the simple version and see if I can be clear: It is a thermodynamics issue. The higher the compression ratio, the greater is the Carnot efficiency of an engine. You don't need a thermodynamics background to get the idea of the Carnot cycle and efficiency. Wikipedia probably does it.

This is the main reason why diesels are so efficient: they always run at full, nominal compression. There is no throttle on the air. It's only the fuel that's varied as you advance from idle to full throttle.

On a spark-ignition engine, you keep the fuel/air mix as close to uniform as you can, and you vary the amount of the mix that gets into the cylinder, with the throttle. If you vary the fuel/air ratio by much (the ideal is 14.7 pounds of air for a pound of gasoline), the mixture won't ignite with a spark. So at full throttle, the engine will be running at a high compression ratio, the nominal ratio -- maybe 10:1 for example. At part throttle, the lesser amount of fuel/air mix produces a much lower effective compression ratio -- maybe 5:1 at some throttle settings. The Carnot efficiency goes to hell.

So you can see why having a variable compession ratio is such a big deal. Manufacturers have been trying to produce a variable compression ratio system that works well and that doesn't cost an arm and a leg, for close to a century.

The Atkinson cycle is something completely different, but it's another thermodynamics issue. I'll give it a try:

The true, original Atkinson cycle involved a short intake and compression stroke, and a long expansion stroke and exhaust stroke. A true Atkinson did it by means of a complex crank mechanism. The "pseudo Atkinsons," like the engines in today's hybrids, have the same-length stroke for all four parts of the cycle. But they open the intake valve late so the cylinder is less-filled. The expansion stroke, therefore, is *relatively* long for the amount of fuel being burned. You get more efficiency because the charge expands to a greater degree than normal. The nominal compression ratio is very high, but the *actual* compression is normal, because of the lesser cylinder-filling.

This Nissan engine combines both, but it's the compression ratio that's the big deal.

Tell me if this is as clear as mud.

Some of those are still around. This engine's crank is pretty wild. And some high-performance Stirlings use a rhombic-drive crank.

Engine efficiency increases with higher combustion ratio, limited by preignition and Knock.

Knock varies with combustion conditions and can be sensed with a microphone sharply tuned to the block's resonant frequency (thus filtering out other sounds) and controlled by backing off the spark advance until it nearly disappears. The old vacuum advance did this open-loop, advancing the spark further at light throttle when intake vacuum is high and releasing it back to the RPM-controlled centrifugal advance position when you floor the pedal. However this is the easy but not the best way.

SAAB's conceptually simple system moves the cylinder block up or down relative to the crankshaft and piston to vary the combustion chamber's size to maintain maximum allowable pressure and the best efficiency at any power demand.

Look at the positions of the orange eccentric shaft to the right of the connecting rod, and the red combustion chamber.

--jsw

It also turns out lots of those motions just aren't necessary. On another group there was chat about VHS tape recorders. Granted most machines now have some level of computer in them and mechanical timing stuff isn't needed anymore. The bottom line is cheap, not let's make elegant mechanisms anymore.

Back to VCRs, the original ones had like a half dozen motors. Recent ones, say made in the past 15-20 years were down to like 2 motors.

They designed all the complex mechanical nonsense out of the product. As it turns out, none of that complexity was really needed in the first place.

Cydrome Leader fired this volley in news:np04c9 $rtk$ snipped-for-privacy@reader2.panix.com:

But, "complexity" is not a part of an elegant mechanical design! Folks design stuff based on their "art" at the time. Elegance in mechanics peaked about 1930... It has gone down-hill ever since.

Lloyd

Here's a lovely tome into which one can get themself nicely lost:

1800 Mechanical Movements...

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

I have the four-volume set of "Ingenious mechanisms for designers and inventors". It's just FULL of good stuff, some (small amount) of which I've employed on my machines for the miltary.

Lloyd

I just saw one copy of the set on Amazon for $750, while individual volumes start at $0.54 used. They sound like fun. I recently picked up Practical Electronics for Inventors but haven't gotten to it yet. At the end of this month (I'm retiring earlier) I'll have more time to finish my hefty 'unread' bookshelf. Maybe even turn off Kindle Unlimited again for awhile...

The use of ancient mechanisms in new military machinery is wildly amusing to me. Physics doesn't change (much), and being able to use old inventor's mechanisms in new ways is a great idea. Kudos.

I've also been buying and using vintage machinery all my life because the old stuff is well designed and much cheaper than the new, while being perfectly good for my uses. Granted, a $12k sliding table saw makes a slightly better cut (0.1 RCH)than an old 10" cast iron jobber (followed me home from Gunner's) but it also costs $12k more and would take up over half my shop.

(Yeah, I know I got off-thread here with "vintage", but, just sayin'.)

I'm sure lost of this knowledge has been lost. For a long time now I've wondered how much effort it would take to design and built one of those giant mechanical calculators like banks used to have. Those things were absulutely insane in how complex they were and how many parts were crammed inside.

Even typewritters are works of art in how the actions feel nice in operation.

a $50 VCR is pretty amazing as well, when compared to an old one side by side. If you consider them black boxes, the new throw away ones do still work better. It's amazing how the the advancements in electronics rendered all the other mechanical parts useless.

You visit VintageMachinery.org..... lot of kindred spirits who use "vintage" machines...

Oh for a .pdf of the 1800 movements book...

This vintage 1909 engine stood the test of time. Love all cams and levers. Still fires up today.

Best Regards Tom.

More specifically the advance in cheap computing power obsoleted both mechanical control mechanisms and bulky discrete electronics such as in older televisions. When I was learning communications electronics in the Army in 1970 a phone line modem was the size of a 2-drawer file cabinet. Each circuit card held two discrete transistor NAND gates. The frequency shift modulator and demodulator were cleverly tuned transformer / filter circuits that the instructor didn't understand. They showed us evaluation samples of integrated circuit electronics but we learned to repair the 1960's gear that was in wide use.

In the early 80's I built a similar frequency-shift modem the size of a portable cassette recorder with parts from Radio Shack. The modem and recorder were the mass storage for my home-brew computer.

As soon as fast enough analog to digital converters became affordable, around 1990, a microcomputer could replace the remaining analog circuitry. That enabled the digital radios I prototyped at Mitre, and pocket-sized cell phones. The best A/Ds we could get back then were for the new Tektronix and HP digital oscilloscopes.

On the other hand, when I was working on the color ink jet printer in the mid 80's I halved the complexity of the electronics by a simple mechanical rearrangement of the print head geometry.

The Army had the technology for encrypted voice and data cell phones by 1970. The field-deployable electronics at the "cell tower" filled six interconnected trailer trucks plus a van for the microwave radio link, with a large Diesel generator on a trailer and at least two dozen men and a field kitchen to support it all. We would have been a tempting and easy target for Spetsnaz desantniki (paratroop commandos).

--jsw