Engine Design Philosophy

Site Subscriber Joined: 07 Oct 2004 Posts: 2281

Right, this has been puzzling me for a while. I'm sure I've mentioned it before but a mate o' mine gets around in a 2.3 V5 Mark 4 VW Golf.

Reading about the engine on Wikipedia, it says that the V5 engine (or VR5 I should say) is derived it's earlier VR6 engine used in the Mark 3 and is the first 5-cylinder Vee to be used in a car.

Question is - why would you go to the hassle of removing a cylinder? I can see a number of problems with this before you even start:

A) Cost, any newly designed engine regardless of whether it's derived from an existing engine, is going to cost money. It is inherent when you consider that this adaptation of the engine will require new top and bottom end castings, not to mention the adaptations to the cam and crankshafts that will have to be made.

B) On a V-engine that has odd numbers of cylinders, surely there's going to be issues with imbalance in the crankshaft and the rest of the drivetrain, it certainly can't be a very refined unit. Furthermore all these problems will necessitate further spending on...

C) Designing a properly balanced cranktrain, uprated engine mounts and completely new management to run it.

D) The benefits.... what exactly are they? Surely it can't be a space saving measure since you'll have a 3-cylinder bank that's full length anyway? You'll lose power and space in the engine can't have been a problem for the Mark 4 since there's the 4Motion and R32 variants which use a V6 lump. It's not like it even fills a niche either, if you can't afford the 4M or the R32 you've still got the 1.8T-engined Golfs.

Basically, I can't see what the point is. It's pointless extravagance on the part of a big car manufacturer unless someone would care to enlighten me onto a suitable good reason as to why VW might have designed a V5 engine!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

less space main reason and a quirky design feature to gather interest.

Also the more cylinders you have for a certyain capacity things go better except fuel economy.

eg, 2 litre 4 pot or a 2 litre 5 pot, the 5 pot will make more power

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

also audi and volvo have used straight 5's for a long time, especially audi

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

my dad's fiat marea has the 2.4 version of the VAG straight 5. Sounds cool!

On the balancing point, straight 4s can only ever be crap in terms of secondary balance anyway. That's why Lancia and Mitsubishi etc. have employed counter rotating balanacer shafts in the past.

I'd be interested to know the firing order etc of the 5 cylinder engines though.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

1-3-5-4-2 generally fires every 144 degrees opposed to the 4 pots every 180.

Balancer shafts have been used on many cars for a long long time.

straight 6's and derivitives of that i.e, V12, w 24's etc are perfectly balanced.

only 4 pots to be primary and secondary balanced are flat fours

Site Subscriber Joined: 07 Oct 2004 Posts: 2281

Now that's funny because I thought inline 4-cylinder engines would have been better balanced than any V-engine purely down to the fact that the cylinders are inline and you don't have pistons moving at angles to one another to compensate for?

Also, if a 4-cylinder is poorly balanced, is a derivative like a V8 less, equally, or more refined?

I find engine configurations quite interesting, spent a few hours tonight just looking at various configurations, loads more designs other than the straight, vee and flat configurations I thought there were.

I think the radial design is quite clever:

[IMG:280:233:f3339d7b5c]http://upload.wikimedia.org/wikipedia/commons/a/ab/Radial_engine.gif[/img:f3339d7b5c]

I'm also intrigued by X-engine configurations (like flat engine configuration but uses two horizontally opposed V-engines in preference to the conventional two horizontally opposed inline engines)

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

V12's are fine becuase they are generally around 60 degrees and its again the fact its 2 straight sixes sharing a crank.

V8's vary, all depends on firing order and if its got a flat plane crank etc.

You not seen the rotary engine? Its a radial engine, the prop is bolted to the engine and the crank is bolted to the plane, the whiole engine and prop spin.

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

In the model aircraft world there are a few 'wacky' designs too..

migrating combustion chamber engine

http://www.ericksonmotors.com/mccsim.htm

rotating cylinder valve engine, the piston actually reciprocates along the axis of rotation, obviously only ever a single cylinder setup.

http://www.hobbycentre.com.au/RCVENG07.html

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

this page has an animation of a rotary engine going

http://www.century-of-flight.net/new%20site/frames/rotary%20engines_frame.htm

Retroholic Joined: 23 Dec 2005 Posts: 3315

bunch of wankels Laughing

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

erm no engine discussed so far in this thread is a wankel engine

Retroholic Joined: 23 Dec 2005 Posts: 3315

rotarys are wankels

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

radial rotary engine... not a wankel rotary

Retroholic Joined: 23 Dec 2005 Posts: 3315

whats the difference?? wankels are a sweet design just no1 wants to play with them!

Level 9 User Joined: 03 Jul 2006 Posts: 412

I was looking at an engine the other day in a museum near me which had a 'wobble plate'. It was basically 10 or 12 cylinders arranged in a circle all pointing upwards. they fired in turn (1,2,3,4...10) and were connected to a circular plate. as the pistons worked their way around the edge of this plate they would make it wobble! this was converted into rotary motion for a crankshaft.

Quite efficient if ir remember correctly

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

yeah ive seen cgi animations of that, very odd

Retroholic Joined: 23 Dec 2005 Posts: 3315

[img:491:491:4769716b8d]http://img154.imageshack.us/img154/9798/wankeldz8.gif[/img:4769716b8d]

i found this here http://www.keveney.com/Wankel.html

love the design

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

again no one has mentioned anything about wankels apart from you BB

Retroholic Joined: 23 Dec 2005 Posts: 3315

yea i no but there the best

Site Subscriber Joined: 07 Oct 2004 Posts: 2281

bbracer16valver";p="108500 wrote:

whats the difference?? wankels are a sweet design just no1 wants to play with them!

Only Mazda use them in the RX-8 at the minute.

Despite their relative simplicity and use of less parts by comparison to a conventional piston engine, there's a number of issues with a Wankel, the main one is to do with poor internal sealing due to the expansion/contraction properties of the metal housings.

They also do not completely combust the fuel which leads to emission problems. Mazda solved this by enriching the fuel/air mixture which favours complete combustion but at the expense of fuel economy.

There are also additional stresses placed on a Wankel rotary due to the combustion always taking place in the same part of the engine without the cooling effect of the intake charge that you get on a piston engine. The result is one side of the rotary becoming superheated while the other is supercooled (probably not the best terms to use but you get my drift)

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

rotaries are nowhere near as good as conventional reciprocating piston engines.

Theres no torque power bands poor.

Sure they are nice to drive and the issues are blown way out of proportion, but they are not that great, I have worked on abnd rebuilt a good few in my time.