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SomptingGuy (Automotive) (OP)
2 Jul 10 5:00
Does anyone know what figure is quoted for the stroke (and therefore  displacement) of a VR engine (e.g. a VW 2.8l VR6)?  Is the stroke quoted as twice the crank throw or is it the measured stroke, taking into account the massive offset between the cylinder axis and crank centre-line.

- Steve

Tmoose (Mechanical)
2 Jul 10 6:08

http://sandbox.enjoybeing.net/pics/vw/3.2-vr6-block.jpg
Looks like the cylinders are angled to point ~ at the crank centerline, so 2X offset and measured stroke would be the same
SomptingGuy (Automotive) (OP)
2 Jul 10 6:11
Nope, there is something like a 12.5mm offset.  I was just wondering if the stroke (quoted as 90mm) takes that into account or not.

- Steve

BrianGar (Automotive)
2 Jul 10 9:35
Steve, the bore centreline 'V' angle is 15 degrees and they both(banks) lie equally above crank centreline(7.5 degrees off plumb). The stroke is indeed 90mm, the top of the pistons are machined at an angle(75 degrees in relation to skirt on the outer sides) so that they sit level with block face( At Tdc)
The crown moves 45mm from Tdc to Bdc.

The big pain with these is the fact that pistons need to be fitted with a special ring compressor as the rings meet the block deck at 75 degrees when inserting the piston to bore.
I made a turned tapered bush the size of bore and sliced at 75 degree's to aid fitting. Placed on deck the piston can be slid ito the tapered bush and into the cylinder without worry.

If you need further info on block structure let me know.

Brian.G  
ivymike (Mechanical)
2 Jul 10 9:38
The crown moves 45mm from Tdc to Bdc
that would be a stroke of 45mm?

So the actual stroke is 90mm... what is the radial dimension of the crank throw - the distance between the crankpin axis and the main bearing axis (was thinking about calculating it, but didn't get around to it)?

 
BrianGar (Automotive)
2 Jul 10 9:44
Sorry steve, mis type there, should read tdc to 90 degrees after tdc. What I mean is the crown moves the true amount of the crank stroke.
ivymike (Mechanical)
2 Jul 10 9:49
...but the crank is offset upward from the intersection of the bank planes, so there should be a slight difference between the piston stroke and (2x the crank throw), regardless of the angle at the top of the piston.
SomptingGuy (Automotive) (OP)
2 Jul 10 9:51
(An offset gives a stroke longer than 2x the crank throw)

- Steve

BrianGar (Automotive)
2 Jul 10 10:10
Give me a few hours to check this out guys, I have a vr6 short block in the workshop, I strongly remember the crown moving 90mm when measured. Perhaps the crank differs due to offset. I didn't mean to mis-inform above, but Im pretty certain the 'crown stroke' is 90mm.

Brian.
TrackRat (Automotive)
2 Jul 10 11:08
According to VW Ag engineering, the cylinders on the 15 degree VR6 2.8-3.2L are centered on the crank. The newer 10.6 degree VR6 3.2/3.6L DI engines the cylinders are offset from the crank centerline. On the 10.6 degree engines VW quotes "effective stroke" vs. true stroke for the 15 degree VR6 engines. I have no idea how offset the 10.6 degree cylinders are so I can help on that.
BrianGar (Automotive)
2 Jul 10 12:37
Had a fast look there, and SomptingGuy seems to be not too far off with his 12.5mm offset, The block is bare yet but I will throw in crank and a rod/piston pair later. From a quick look with some string and a vernier the bore centre lines look to be meeting well below crank centre, Ill go out on a limb and say that they are striking tangentially a circle of an approx diameter 25mm if you can imagine the main journal that size.
Another thing about the vr6 is that the big end journals are offset by 22 degrees. Hence the exhaust note, Id know one a mile away.
Helpful Member!(3)  TDIMeister (Automotive)
8 Jul 10 16:57
I believe TrackRat is correct in that the VR engines with 15° bank angle do not have cylinder offsets but the 10.6° ones in the 3.6 L, in order to clear the larger diameter pistons within the narrow bank-angle package, do.  I'll look into this.

I have a spreadsheet that can calculate the true stroke resolved to each °CA; however, what needs to also be known that's not always published is the piston-pin offset if there is any in order to get a correct calculation.
izzmus (Automotive)
8 Jul 10 20:56
Are the piston pins also offset?  Are the offset differentally?

Seems that it'd play hell with piston position bank to bank if they were not!

 
ivymike (Mechanical)
8 Jul 10 22:04
uh, why wouldn't you offset them all in the same direction and by the same amount, as is normally done?  (~0.5mm toward the thrust side if memory serves, but it's been a long time)

If the piston tops are asymmetric as described above, then the only real disadvantage of pin offset would be that it would necessitate different piston part numbers for the two banks (because the crown slope is thrustward on one bank and the opposite way on the other bank, but you'll offset the pins uniformly to thrust).
 
TDIMeister (Automotive)
9 Jul 10 9:23
OK, I checked out a VW SSP (Self-Study Programme) PDF that I have on the W-engine family, so this info can only apply authoritatively to that engine.  However, the W engines are basically 2 15° VR engines siamesed with a 72° major bank angle, so it stands to reason that things like cylinder offset that apply to each minor bank should also apply to the VR engines on which they're based.

http://bit.ly/aFxLBL

The above link to a page on the SSP document (there is no copyright mark, I checked) shows that the minor bank does indeed have a 12.5mm cylinder offset, but what is incredible is that the offset are on opposite sides of the crankshaft centerline (!!!), with the intersection point below said crankshaft centerline.  This means that the motions of the left-minor bank will be slightly different than the right-minor bank!!  This also means that the articulating angle of the connecting rods are different at given crank angles and, particularly close to TDC, in fact on opposite sides of the cylinder axis.

Given a 90.3mm stroke of the first-generation 2.8 VR6, 164mm con rod length, ±12.5mm cylinder offset and assumed zero piston-pin offset, maximum true stroke is 90.585mm.  On the right bank with positive cylinder offset (toward the anti-thrust side) the maximum stroke length occurs at 186° CA (referenced to TDC), and the pistons' closest approach to true TDC occurs at +3°CA (0.0016mm below true TDC).  On the left bank with negative cylinder offset, the same maximum stroke length of 90.585mm occurs at 174° CA and closest approach to true TDC occurs at -3°CA (also 0.0016mm below true TDC).

On another note, a slight piston pin offset (usually 0.5 to 2 percent of piston diameter) is introduced mainly for NVH purposes in order to smooth out the transition of the piston skirt position, which wants to stick to the anti-thrust side on the upward portion of the stroke and to the thrust side on the downward part.

Interesting stuff!
TDIMeister (Automotive)
9 Jul 10 9:25
Sorry, wrong page to the document uploaded and linked.  Here is the correct one:
http://bit.ly/are5NC
 
SomptingGuy (Automotive) (OP)
9 Jul 10 9:40
That fits with my understanding, I just didn't have any evidence.  Thanks.

- Steve

TDIMeister (Automotive)
9 Jul 10 10:20
A quick calculation on my spreadsheet illustrates the profiles of the VR6 as described in my previous post above:

Displacement: http://bit.ly/aDqcPv
Velocity: http://bit.ly/bRyAmY
Acceleration: http://bit.ly/91Ri58

The velocity and acceleration curves my be flipped from what some people are used to because I've employed the convention that a downward stroke displacement is negative.
TrackRat (Automotive)
9 Jul 10 14:51
An engine of beauty... all 1001 HP of it! <LOL>

They hand build these at the VW engine plant in Salzgitter, Germany. It's a very interesting factory and one people can and should tour if they get a chance.
vagman2 (Automotive)
9 Jul 10 15:02
Yeah,
I,ve been there. VW actually build a lot of diesel engines in that factory too. There is dedicated room for Bugatti engines. As I was told production target of Bugatti engines is 3 per week. They didn't let me inside the room, just watched eng. assembling through the glass.
These pics are from Cologne Auto Show last year though.
vagman2 (Automotive)
9 Jul 10 15:10
As I remember due to the VR shape the crank has to be assymetrical (not like R6's one) or sort of to obtain equal firing intervals. Guess have to find and read it again.
TDIMeister (Automotive)
14 Jul 10 9:28
A little update, Audi will introduce a new A8L with a 6.3L W12 engine to replace the outgoing 6.0L unit.  It will be basically 2 3.2L VR6 units siamesed together.  The 3.2L has a 10.6° minor bank angle instead of 15°.  Bore and stroke are 86.0/90.9 mm, respectively, for a displacement of 3168cc.  Cylinder offset is +/- 22mm (!!!) compared to 12.5mm of the predecessor.

What's crazy about this engine is that different pistons are required on the one minor bank side than the other, since all the direct gasoline injectors are on the same side of the head and the bowl-in-piston must have the same relationship to the injector position and in-cylinder charge motion.
TrackRat (Automotive)
14 Jul 10 11:03
Sounds like VW/Audi are getting way complicated on this W engine design. I must say that I am VERY surprised at Audi accepting this engine as VW and Audi compete like Ford and Chevy in my experience. I'll bet there are some very unhappy folks at Audi.
Axewielder (Aeronautics)
14 Jul 10 12:24
@ track rat, vw & Audi part of the VAG group and both use mostly the same parts across the range.
Ford, part of Ford Motor group, Chevy part of GM, two competing corps., im not quite seeing the comparison?
BTW big VAG fan and hoping to develop a twin charged 2.9 VR
TrackRat (Automotive)
14 Jul 10 12:46
Trust me... If you could see how VW and Audi engineering in Germany operate, they compete like Ford and Chevy. While competition can be good there is no love loss between these two auto devisions of VAG - in many cases... <LOL>

Audi redesigned their V-8 engine front end drive to shorten the engine so they would not be forced to use the VW W8 in an Audi. You will note that only the VW VR6 engine is used in any Audi models. The 4 cyl. and other engines are Audi designs, not VW and Audi is quick to tell you so.

I hope VW brings their twin-charger engine series to the U.S. The issue appears to be engine cost.
TDIMeister (Automotive)
14 Jul 10 14:35
Audi redesigned their V8 for more compact dimensions (mostly by moving the cam drive from a belt on the free-end to a chain on the flywheel-end) because the entire length of the engine hangs over the front axle in their drivetrain design.  Every mm of length saved aids in overhang, weight distribution, polar moment and pedestrian collision safety of the car.  Audi's V8 also long preceded the W8, dating back to the late 80s Audi V8 model.  I owned a car with a variant of that engine while in Germany, a 1994 S4 Avant 4.2 V8.

The Hybrid version of the VW Touareg/Audi Q7/Porsche Cayenne will all use use the 3.6 VR6 and not the any 90-degree V6 variant from Audi.

Yes, there's intense competition and even some conflict within the VW Group, like any inter-division rivalry within a large conglomerate, but it's not like GM/Ford.  But having just typed this, I must qualify that statement: I have personally worked in a project in a Tier-1 supplier where Ford and GM collaborated on a 6-speed transverse automatic transmission.  In development they were known by GM and Ford as X22F and 6F, respectively.  In production the X22F followed the more familiar convention and became the Hydra-Matic 6T70.  It was a pretty good collaboration.  I was in many a conference call with engineers and managers from both companies simultaneously.
TrackRat (Automotive)
14 Jul 10 15:12
My point was that the engineers at VW/Audi do not like to use the other division's engine designs. Audi engineers consider themselves "THE" auto engineers of Germany much to the chuckles of Porsche, BMW and M-B engineers. IMO they all have great engineers, but there is a definite mentality and some large egos involved at times. Some of the people just check their ego at the door and work harmoniously with their colleagues form all divisions without any issues.

When the dictate from Dr. Winterkorn or similar says you will use the 3.6L VR6 in the Q7 or the W8 in an Audi it is met with a lot of resistance.

Engineering groups at the same division are also very competitive. As an example the engine designers and development engineers at Ford U.S. 4-6-8 cyl. engines would not share ECU software strategies. They all insisted on their own unique ECU SW for personal more than professional reasons...

Anyway I'm sure there are unhappy campers at Audi when they are forced to use a VW engine design even though these engines tend to be good, reliable engines for the most part.

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