Go to Ultimatecarpage.com

Go Back   Ultimatecarpage.com forums > Automotive forums > Technical forums


Reply
 
Thread Tools Display Modes
  #1  
Old 06-10-2004, 04:45 PM
KnifeEdge_2K1's Avatar
KnifeEdge_2K1 KnifeEdge_2K1 is offline
Enthusiast
 
Join Date: Feb 2004
Posts: 2,266
3 cylinder engines

how do 3 cylinder engines work? i know atleast some 3 cylinder engines use the same intake, compression, combustion, exhaust cycle as most regular petrol engines. at any given time in an inline or boxer engine each piston will be in one of the four cycles, no 2 pistons will be in the same cycle, this is so that the piston undergoing combustion can power the rest of the cylinders and the car itself, in a 3 cylinder the only method i can think of making it work is to let teh rotational enertia do the work which would theoretically push the idle speeds higher, does this make any sense?
Reply With Quote
  #2  
Old 06-10-2004, 05:26 PM
Matra et Alpine's Avatar
Matra et Alpine Matra et Alpine is offline
Super Moderator
 
Join Date: Dec 2003
Posts: 27,781
nr Edinburgh, Whisky-soaked Scotland
Quote:
Originally Posted by KnifeEdge_2K1
how do 3 cylinder engines work? i know atleast some 3 cylinder engines use the same intake, compression, combustion, exhaust cycle as most regular petrol engines. at any given time in an inline or boxer engine each piston will be in one of the four cycles, no 2 pistons will be in the same cycle, this is so that the piston undergoing combustion can power the rest of the cylinders and the car itself, in a 3 cylinder the only method i can think of making it work is to let teh rotational enertia do the work which would theoretically push the idle speeds higher, does this make any sense?
You're right with the rotational inertia.
The more cylinders the more overlap the bang cycle has and the smoother the engine is.
Some of thsi can be taken out by increasing the mass of the crank with offset weights and increasing the flywheel. Unfortunately the increased mass makes for slower acceleration of rpm AND REDUCTION in top end revs as the higher mving mass becomes more unstable.
This smooths out the engine at lowe engine speeds, reduce the weight and the engine becomes temperamental and hard to keep at a low idle ( lightened BDAs and Climax's being some of the worst/lumpiest )

All engines run the Otto cycle in each piston.
What an engine designer CAN play with is the timing of each cylinders cycle by position the big end on the crank relative to erach other.
Some triples actually run like a twin with 2 cylinders firing together, others spread them evenly. BUT a triple is hard to keep balanced and counter-rotatiing balancing shafts are needed to keep things revving smoothly at high speeds. Few bikes still run triples and some of the japanese micro-cars of the 80s used 600cc triples - basically their bike engines !!
This timing can be cltered by the engine designer. In cars it has become pretty much standard and no vairation beyond the accepted norm for I, H and V configurations.
Bikes, however, are playing with this at the peak end of the sport. MotoGp bikes are run with 4s running as twins, opposing 3 and 2s in 5s and 4v1 has been suggested as having been tried by Honda. These make BIG differences in bikes due to their low weight and alter dramatically the way the bike can use the tyre. It seems this isn't tried in cars, probably because the extra weight and larger tyre contact makes it irrelevant.
__________________
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'
Reply With Quote
  #3  
Old 06-10-2004, 05:46 PM
foto_choppa's Avatar
foto_choppa foto_choppa is offline
Enthusiast
 
Join Date: May 2004
Posts: 1,368
Location: gone, unless my rep dont come back!
great topic

wow i never realy thought about that, i honestly have no idea, great topic
__________________
have fun with all my attached pictures guys!
Reply With Quote
  #4  
Old 06-10-2004, 07:44 PM
KnifeEdge_2K1's Avatar
KnifeEdge_2K1 KnifeEdge_2K1 is offline
Enthusiast
 
Join Date: Feb 2004
Posts: 2,266
wow matra thankx, that cleared up alot, i kinda lost u at the end of the post but i think i got the gist of it
Reply With Quote
  #5  
Old 06-11-2004, 03:22 AM
Matra et Alpine's Avatar
Matra et Alpine Matra et Alpine is offline
Super Moderator
 
Join Date: Dec 2003
Posts: 27,781
nr Edinburgh, Whisky-soaked Scotland
Quote:
Originally Posted by KnifeEdge_2K1
wow matra thankx, that cleared up alot, i kinda lost u at the end of the post but i think i got the gist of it
yeah, it rally needs a drawing

I'll try - 4 is easy ....

Firing order can be 1-2-3-4 or 1&3-2&4 so the first config gets one ignition and power pulse each revolution. The second gets one ignition every 2 revolutions but each power pulse is now twice as large. That assumes 180deg crank as the norm on a car. This is done to use the power pulse from one piston to be at the optimal timing for the other piston in compression. If this isn't done it becomes very hard to keep and engine inbalance as the compression piston has to then find the energy from some stored place - the crank or the flywheel.

In the Honda 5 it is secret what they are actually doing but those who've seen a crank have put forward a few suggestions....

One options would be 1-2-3-4-5, this could be achieved with a crank with 34degree offset. Like the 90deg-4 crank this is likely to be VERY unbalanced, need a large flyweehl and contra-rotatin balance shafts. What si THOUGHT they do is with a 180deg crank they fire 1&2&3-4&5, so get the 1 ignition per 2 revs and power pulses 2 and 3 times the single. They have been known to have tried the 'big bang' equivalent and had 4 sylinders and 1 working. In the bike world this has also been used on some tracks by Ducati with their twin firing BOTH at the same time. Bikes seem to be able to use tyres ( in a way I've never heard explained ) to 'smooth' out these pulses and to get better traction.

Engine design and timing is a real engineering challenge when you start playing with the cycle overlaps and timing. A search on the Hon RC211V engine and the Ducati V4 will likely bring up more details for those interested in what CAN be done
__________________
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'
Reply With Quote
  #6  
Old 06-12-2004, 06:49 AM
SilverArrowZ's Avatar
SilverArrowZ SilverArrowZ is offline
Rookie
 
Join Date: May 2004
Posts: 282
Location: Kuching, Sarawak, Malaysia
talk about 3 cylinder engine, 3 out of 10 cars at where i live is running on them and girls like them as they are small and cute.

Well, matra is really the encyclopedia here and i do not know much about how they work. All i know is that they idle at about 1200rpm, slightly higher than nomral I4 and V6 (no you won't be able to find V8 here).

These cars i refered to is actually local made, but all are made based on Daihatsu's chasis, mira, move... you get the idea.

the lowest displacement engine i got here at malaysia would be 660cc. Single cam 12 valve(4 per cylinder) and only gives out 31hp@6400rpm and yes you need an engine checkup after you bring 4 adult up a hill. best thing is you can get 50mile per gallon out of these "toys"
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
if you could take any 10 cars and put any 10 engines and race them... Batmobile_Turbo Car comparison 12 06-13-2004 09:13 PM
Engines 101 for Slick Matra et Alpine General Automotive 61 05-07-2004 05:25 PM
BMW Engines Jonny Flash General Automotive 3 05-01-2004 10:22 AM
DKM vs. KKM rotary engines Airthrow Technical forums 3 03-23-2004 10:33 PM
BMW to turbocharge the engines? bum-man General Automotive 0 03-22-2004 07:30 PM



All times are GMT -7. The time now is 12:29 AM.

 

1998 - 2019 Ultimatecarpage.com