Porsche patents a variable-compression-ratio engine to boost power and fuel efficiency


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Porsche has received a patent on a new form of the variable-compression-ratio engine. This would be especially useful with turbocharged engines that today run at lower compression ratios, to avoid over-stressing the engine when the turbocharger is forcing more air into the combustion chambers. The patent was sought by Porsche’s huge consulting arm along with Porsche client Hilite International, suggesting the engine technology might be offered to other automakers if and when it’s made commercially viable.
Why variable compression ratio matters

Today’s gasoline-engine cars compress the outside air to about a tenth its original volume, a 10:1 ratio, inside each cylinder. Compress it more and you get detonation – also called knock or ping – before the spark plug ignites the air-fuel mixture at or near top dead center, when the piston is at the top of its travel.
Technology has raised compression ratios to 11:1 or 12:1 and as high as 13:1 in Mazda SkyActiv cars. Premium-grade gasoline allows for higher compression ratios than regular. Knock sensors can adjust ignition timing to avoid detonation. Still, design engineers have to back off on the base compression ratio when there’s a turbocharger involved, which affects efficiency at low rpm, which reduces mpg in the vehicle and its desirability to the buyer. It also makes the car feel like a pig when your first tromp on the throttle (turbo lag). Enter the variable-compression-ratio engine and Porsche’s new technology.
How Porsche does it: adjustable length connecting rods

Porsche and Hilite conceived a way to adjust the apparent length of the connecting rods, the metal arms that connect to the crankshaft and drive the pistons up and down. A solenoid allows small oil-pressure-driven rods and an eccentric adjuster to raise or lower the bearing supporting the piston. The patent diagram appears to show a high and low position currently, not a variable height.
The car starts off with the piston in the high position. When the turbo begins injecting pressurized air, the piston drops to the low position. That reduces the compression ratio momentarily, allowing for more turbocharger boost and more power. The Porsche-Hilite design appears to be comparatively simple, at least compared to other variable-compression-ratio efforts that date back a century.
Development still needed

From patent to engine in production could be several years. Even a relatively simple design needs to be tested for durability and quirks that might show up outside the lab. Still, engines of the last 25 years have become increasingly more complex without any falloff in basic reliability. Hilite International makes components used in variable valve timing controls (VVT) that run reliably despite their complexity.
Since Porsche is a consulting group as well as an automaker, and in some years in the past made more money off consulting, this is likely to be a technology with the possibility of being adopted throughout the industry on small engines — just as Mitsubishi’s balancer shafts are now common on almost every four-cylinder engine. These designs also show that the gasoline internal combustion engine will continue to be the dominant powerplant in passenger cars.

 

Interesting concept, I wonder how long it will take to go into racing engines. Which is usually the first step.

 

Add this with Delphi's variable valve timing and variable cam lobes and you have several engines all wrapped up in one! Mild to wild all digitally controlled, one engine. KEWL

 

It will never go into racing engines, unless it's done as a publicity stunt. First, and the part that most people don't understand, is that racing engines typically can be designed for a very narrow operating band. You don't need variable CR on a racing engine. Street cars have to be much more flexible, operating over a very wide performance range. Combine this with emissions and CAFE requirements and that's why the street car needs the technology.

Of course, the fact that this has to be about the heaviest connecting rod ever built doesn't bode well for a racing application. It does have one Porsche attribute, however. It also has to be about the most expensive con rod ever built...

 

Crap like this is exactly why I like old, simple cars.

I spent 2 days last week replacing a plastic coolant housing on the backside of the head of my 1.8 turbo Audi daily driver.

$12 part, $600 installed at the dealer. I bit. Halfway thru I would have paid $1000 for anybody to take the damn thing away and finish it.

Remove plugs, injectors, cut of lots of single-use clamps on various vacuum lines...Hope you remember where it all goes back to later

I like German cars. I used to like working on them, and have owned a bunch of Porsches over the years.

The current crop of Porsches depreciate like lead balloons because of the time-bomb factor of engine rebuilds costing about what the cars sell for...

 

All cars seem to be much harder to work on now, Pop round to your Citroen Dealer for a replacement headlamp bulb? Thank you sir, 4 hours labor to remove the bumper to gain access.
Some cars have been a pig to do certain jobs back in the day, replace the clutch on a Rover 200o or MGB, remove complete engine and gearbox first. Replace the battery on a Triump Stag, easy after removing the alternator, radiator and power steering pump.
But routine maintenance was mostly straightforward, I always found older American cars easy to work on simply because there was plenty of room to get to whatever needed attention. I know some cars needed the wheels off to facilitate removing the spark plugs, but as part of a routine service that wasn't normally a problem.

The adjustable con rod is an interesting concept, but it will need lots of development before it finds its way into passenger car I think. Like Joe said, weight is going to be a major stumbling block to overcome.

Roger.

 

C'mon, Joe. It won't be that heavy when Porsche builds it out of forged titanium...

... which brings us to your second point...

- Eric

 

Heavy AND complicated. Sure seems like they could've done something simpler with a movable plug in the dome of the combustion chamber, operated either mechanically or with a solenoid. But maybe that would block optimum port routing or coolant flow.

 

^ Yes. Just like my E36 BMW -- $650 to replace a rear wheel bearing; $50 for the bearing, $600 for the dealer to put it in for you. It's nothing complicated, but a major PITA that's un-doable unless you can fabricate special tools.

As it turns out, right now I'm in the middle of one of those jobs that I'd gladly pay someone to finish for me. Aargh.

Personally, I hate cars that have computerized their electronics to the point that there isn't an ignition key, or a radio button any more... just a flat panel display that you have to use to interface any aspect of the car that the user is permitted to control. I don't want a car like that. This means that I'm stuck fixing up older cars.

I think this whole Porsche concept is nothing more than an example of the type of Rube Goldberg engineering that is required in order to comply with ridiculous government mandates.

 

We can't deny that modern computer control of engines is one of the reasons that you can have a 707 HP Hemi that still meets current emissions requirements. That doesn't mean that I want one, however.

I refuse to own a car with a touch screen, for example. I've driven enough rental cars with one and I don't want one for my personal use. Most of the computer controlled crap in modern cars isn't necessary, it's there because it can be. For example, new cars apparently have a "feature" in the stereo that limits the volume of the sound system at startup. I'll go in and change this when I get a rental car, but the max setting usually still isn't as loud as I want it...

Another example is newer Chevy trucks. I drove one belonging to a friend once and apparently there's a "feature" that angles the outside mirrors differently when in reverse. WTF??? I'm trying to back up a horse trailer, not parallel park against a curb!

On the other hand, with the right support equipment (my OTC Genysis), I can diagnose and tune my 1999 Chevy Crewcab Dually from the driver's seat without even getting my hands dirty, so there are some advantages to electronics. For example, instead of having to pull plug wires one at a time to find the misfire, I simply read the misfire table from the computer. It told me that the no. 2 cylinder was the problem. Replaced that plug wire and problem fixed.

 

The Germans are great for taking something simple and complicating it

 

Older IS better! Nothin beats climbing into a engine bay and sitting on the inners to change plugs n such. Now I have to dig a mile of plastic off the engine to even find it. I know its in there somewhere cuz I can hear it, just cant see it!...lol

 

They can't hold a candle to the French. Citroen CX.

Roger.

 

Now come on the Saab folks had a good market for complexity. The biggest issue for Euro and Asian cars is trying to stuff 10#'s of crap in a 5# container.

 

I think the idea that older is better is simplistic and wrong. Same with newer is better. Like was said above, today's engines have different requirements than yesterday's. Our car requirements for our classics are: run well, don't overheat or burn oil, sound good, have power, and last a good long while. New cars have all that, plus emissions, economy, and needing to run on continually crappier fuel.

A simpler engine can handle simpler requirements, while a more complex set of requirements requires a more complex engine. If we could have a modern block and heads, with better engineering, but still keep all the simplicity of no or low emissions, low economy, and the guaranteed availability of zinc oils and premium gas, we'd all say it's the best of all worlds and take it. So, older is not better*, but SIMPLER always is. *Except when older stuff used better materials.

Now, to the con rod at hand. I think it is overly complicated. I would tried something with putting the crank journals on an oil pressure advance system like VVT cams have. If it were achievable, you could advance the crank journal via an eccentric cam either out or in. In would be low comp, and out would be higher comp and a longer stroke by a bit.

 

One of my favorite cars

 

If Ambrose Beirce had lived in modern times his definition of Citroen might have been;

Citroen (n, adv.). A complicated way of achieving not very much.



Roger.

 

Funny


I've never owned a CX, but it was a car I coveted when I was a kid in Spain. From people who have owned them, the oleopneumatic suspension is very durable and easy to maintain if you know what you are doing. If not...

 

Until the Hydropneumatic displacer diaphragm goes porous. Replace the displacer, it can't be serviced. Price £230 each in 1989, maybe $500 at contemporary exchange rates. Now, just try finding one.
It's fair to say they have a great smooth ride over poor road surfaces, but no better than comparably priced cars on good ones.
An old neighbor had a Citroen BX with the same suspension, One day he stopped for a rest during a long journey, when he pulled away he didn't wait for the suspension to pump up, nor did he see a stump protruding a couple of inches just in front of his car.
It tore off the oil pan and ripped the engine from its mountings. The car was written off due to the damage.

Roger.

 

Saab had proposed a variable compression ratio on their turbo cars in the 80's. The head was pivoted on one side and then tilted it on the other. They later scrapped the idea due to mechanical issues.

 

I live in Connecticut. Is there another type of road surface?

 

I remember that now, but apparently it was GM, during their brief ownership of Saab, who killed it:



There was also the MCE-5 engine from France that promised variable CR using a rocker in the middle of the connecting rod back in 2009.

 

Actually, you are overstating it just a bit; all that is required is to remove the P.S. pump bolts and move it out of the way:

 

I stand corrected, maybe changing the alternator was a complicated involved job. I haven't worked on one in years.

Roger.

 

I was surpised to see the car mentioned at all in this space, but a search of the the term Stag shows you have posted about it (and not at all glowingly)a few times over the years...guess you've had some unpleasant experiences with them.

 

The Triumph Stag was a fine example of what was wrong with the British motor industry when it was current.
Although I think it was a fine looking car, underneath the skin was an underdeveloped engine, with one bank of cylinder head bolts at 45 degrees to perpendicular and a few other peculiarities, all very sloppily assembled by a bolshie workforce supervised by awesomely incompetent management.
Unsurprisingly, they were prone to head gasket problems, not helped by the blocks not being cleaned properly after casting, or indeed not machined properly either, which led to radiators getting plugged after a few hundred miles.
Why British Leyland didn't write off this engine, (a 3 liter sohc lump) and fit the Rover 3500 (erstwhile Buick 215) which had it's shortcomings largely sorted by then beats me.
I never owned one, however I knew several who did, to a man they were fed up with their money pit cars when they were relatively new.
However the ones that are left are very desirable and command high prices at collecter car auctions these days. It's probably fair to say the ones that are left have all their inherent design faults addressed by now.
Perhaps it could be compared to the Chevrolet Corvair or Pontiac Fiero as a car that should have been so much better, but failed to deliver it's early promise.

Roger.

 

Back in the 80's, we dropped a Buick V6 and added rack and pinion steering to a Triumph Stag. Talk about 10#'s of sh(stuff) in a 5# bag. It did wake that car up though.

 

Actually the Stag came with rack and pinion steering from the factory.

As for the engine, I won't argue with anything Roger said. The ones left with their original engines have been (mostly) sorted. My parents owned one in the mid-late 70s, and it did overheat, and it did get a Buick 215 from a '62 or '63 Special. But with today's modern antifreezes (level checked regularly and flushed every 2 years, use of demineralized water in a 50/50 mix), and the addition of supplemental electric cooling fans, my original-engined car does not run hot in the least. The Stag is unquestionably much better suited for life as a pampered collector car than a daily diver. Of course, so many other cars built in the 70s in, oh let's say...the U.S. were problem free and an absolute joy to own!

 

Hmmm the car was in boxes at the shop, I assumed it was added because I had to fab brackets for it. May be because of the Buick V6. They are a beautiful body style.