Posted on 05/07/2005 11:10:29 PM PDT by spetznaz
Hm, guess I'm on deck. Ever consider running an automotive ping list, spetz?
To understand the W12, you have to go back a little bit in engine history. For the purposes of this discussion, we're going to assume that all these engines will be used in a longitudinal or "north-south" configuration where the crankshaft is aligned with the car's long axis.
Traditionally, there have been two successful form factors for reciprocating piston engines used in cars; first, there is the inline, where all of the cylinders are aligned in a row or line. So called "straight sixes" and "straight eights" as well as the common four cylinder commuter car engine are of this format. (A special case of the inline engine is the "slant-six", where an inline six is tilted onto its side a number of degrees in order to make it take up less room vertically. More on this later.) The other type is the "Vee" type where the cylinder bank is split into two banks placed at angles to each other, creating the angle between them that gives the form factor it's name.
Most V-type engines have a 45, 60, 90, or 180 (called a "flat" or "boxer" engine) degree separation between the two cylinder banks. In other words, the angle between theoretical lines drawn straight down the piston connecting rods on each bank would be a certain number of degrees. The most popular and most successful V6's of late have been 60 degree V6s, where each cylinder is offset 30 degrees from vertical. As a comparison for you dinosaurs still dealing with inefficient creaky old American V8s, the vast majority of those are 90 degree V8s - where the cylinders are at right angles to each other.
Why a V-configuration engine, you may ask? Well, if you make the cylinders short enough, you can interleave the cylinders in such a way that you can have a V8 engine that has a short overall length, on par with an inline four. You can also get a low hoodline by using a high angle V engine - it takes up less space vertically. However, by doing so, you make a number of trades - you reduce the number of main bearings you have in the engine (an inline eight has nine main bearings, a V8 has four) which increases the stress on the remaining bearings, a vee engine produces more stress than an inline does on bearings because unless it's a "boxer" vee you never have balanced power pulses, and you now have a very wide engine which may not fit in a smaller car. You will also have a vibration issue because of the uneven power pulses that needs to be dampened somehow, and you'll have a lot of wasted space under the arms of the vee that you can't put things in (unless you want to annoy your customers and mechanics by installing accessories that can't be serviced from the top).
An inline six or eight is stronger and will live far longer than a vee-type of the same size and number of cylinder, but is much longer and taller; this leads to their own packaging problems. You can lay an inline down at an angle on its side (the "slant" engines to reduce the hoodline, but again that means that you have to make the car wider to accomodate the engine. However, the smoothest running engines in the world are inlines or siamesed inline engines with an even number of cylinders greater than four (V12s, V16s).
So, if you're looking at a six cylinder car from a design standpoint, you *want* to have an inline six, but you may not be able to deal with the packaging issue. The corporate 60 degree V6 looks awfully tempting, but you'll have to shoehorn it into the engine bay because it is so wide, leading to servicing issues. (Look at a 300ZX or 350Z's engine bay for an example - the engine is shoehorned in between the strut towers, and there's minimal room.) So what to do? Most makers just accept that the engine bay is going to be short on room if they're going to meet today's styling, efficiency, and other packaging constraints. VW did something different.
Continued in the next post.
Minor correction to that last - a V8 has five main bearings.
What VW did is to build a relatively short stroke V6 that had a 15 degree angle. This made the engine much narrower than a traditional 60 degree V6, yet it allowed them to keep the length shorter than an inline six while reducing internal stresses, vibration to near I6 levels. It also, incidentally, let them put medium displacement six cylinder engines in cars that normally would have had to make do with a large displacement (and buzzy) four cylinder. A cutaway picture of the beast can be seen at http://heckteck.de/vr6.jpg - it's a very clever job of engineering. What does this have to do with the W12?
Most V12's are essentially two inline sixes running off a common crankshaft ("siamesed"). Since the VR6 is sort of a hybrid between an inline six and a V6 and leans more towards the inline side, VW decided to see what happened if they siamesed two VR6's together. What they got was the W12, which turns out to be a very good engine indeed - it's a lot shorter than it is wide, which makes for interesting packaging options. VW has further adapted this technique to create a W8 and a W16; the W8 has already been used in the Passat, which wouldn't be able to accomodate anything larger than a conventional V6 under normal circumstances.
The W12 is 72 degrees between the two VR6 modules that comprise each bank. It's 512mm long, 710mm tall, 715mm wide, and weighs just 239kg. Compare that to a "traditional" BMW V12 which is about the same height and width but twice the length and you can see the advantages. It also uses quite a bit of higher technologies - variable valve timing, exotic metallurgy, lots more.
There are disadvantages to this idea, though. The casting and machining is more difficult to successfully achieve than, say, the BMW or Mercedes V12s (with a corresponding relative increase in production price somewhat mitigated by the fact that it's just two VR6's) and the valvetrain can be a problem to design (getting four cams into that space can get ugly). In addtion, special attention has to be paid to the lubrication system design to ensure that weird things do not happen - and you have to be very particular about what kind of oil goes into the beast.
Any questions? :)
"What happens if I don't like Rolls-Royces?"
"When the revolution comes you'll have no choice."
So we can get the Chinese knock off for $1000 and as a side benfit, it comes with a McDonald's Happy Meal coupon?
Plus, a big plus....radiation and bullet proof?
the total length is EIGHT FEET MORE THAN IT'S WHEELBASE!
It aint no minicooper...
,,, it seems they can copy everything except democracy.
Yeah, and a Granada looks like a Mercedes...
Hideous and hideouser.
And they're probably both made of that famously soft Chinese steel.
With wheels by Tonka.
Mind-Numbed Robot: I think post 41 and 42 should answer all your queries on the W12.
wait til they get involved in copying the unpopular sex acts!
,,, LOL!!!
Roger that!
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