I was reading in the latest Autocar that both Mercedes-Benz and BMW are developing 3-cylinder petrol engines for the base models in some of their ranges - in M-B's case, even possibly the C-Class. The next BMW 1-series is being designed to cope with the particular vibration characteristics of 3-cylinder engines. These engines, which would be turbocharged, would provide similar power to equivalent 4-cylinders but with better economy because of lower frictional losses, even though they need a balancer shaft.
VW seem to have dropped their 1.4 TDI 3-cylinder diesel in the new Polo in favour of a new 1.6 TDI 4-cylinder.
{Typo in header corrected}
Edited by Dynamic Dave on 27/07/2009 at 22:22
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If they run a pair of mutually contra rotating balance shafts running at twice crank speed, they might be OK. from a balance point of view, but they would still struggle to give smoothness at very low engine speed because of the longer firing interval.
It will be interesting to see what MB and BMW come up with to overcome the firing interval problem - hopefully, it will be something smarter than a very heavy flywheel.
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Isn't it the case that the roughness of a 3-cylinder engine is caused by an inevitable inbalance in the reciprocating masses - since 2 pistons will be going up while one is going down and vice versa and also because the firing order has to be linear - i.e. 1,2,3 or 3,2,1. I thought that regarding actual power impulses at the flywheel they are smoother than a four, although with fewer impulses per cycle.
Edited by Sofa Spud on 27/07/2009 at 14:32
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>>since 2 pistons will be going up while one is going down and vice versa
In the sense of reciprocating force balance, no. As the cylinders are phased at 120 degree crank intervals these forces cancel. (The maths is remarkably similar to how the 3 voltages in a three phase electrical power supply always add up to a constant value at any instant)
What is unbalanced is secondary pitching moments. This means, twice per revolution, the crank nose will dip while the flywheel end will rise.
This pitching moment arises because the piston motion is not symmetric in a front / rear sense.
If you connect a 3 cylinder engine, to another one, appropriately out of phase, this pitching moment cancels, and you get the perfect balance of the straight 6.
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And don't forget Ford are going to produce 3 cylinder engines as well in the next Focus (1.0L 109Bhp)
We could be in for some interesting times shortly ........
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Fiat was developing a side-by-side twin with turbocharging. I am still looking forward to it.
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Not Ford's first 3-cylinder. Ford Dexta tractor(1960's) had a three cylinder diesel-tho' it was basically a modified Perkins.
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Not Ford's first 3-cylinder. Ford Dexta tractor(1960's) had a three cylinder diesel-tho' it was basically a modified Perkins.
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I know these well from my teenage years on the farm, in fact this engine was so common, it was used in the later Ford 2000's and 3000's which were very numerous indeed in the 70s and 80's.
I also think the famous and popular Massey 135's were a 3 cylinder disel too, and I never remember thinking for a second that they had a balance and vibration problem in those days !
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I also think the famous and popular Massey 135's were a 3 cylinder disel too
Yes,and IIRC they were the very devil to start on a cold morning!
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If they run a pair of mutually contra rotating balance shafts running at twice crank speed they might be OK. from a balance point of view but they would still struggle to give smoothness at very low engine speed because of the longer firing interval.
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Thats the arrangement for a 4 cyl engine. A 3 cylinder engine requires a single balance shaft running at same speed as crankshaft.
Drive a VAG 1.2 3 cylinder HTP engine and you will be amazed at how smooth it is and how much torque is available at little above idle speed.
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>>Thats the arrangement for a 4 cyl engine. A 3 cylinder engine requires a single balance shaft running at same speed as crankshaft.
There are both primary and secondary moments - to solve the problem completely, you need 3 balance shafts, and some balance weights adding to the crank itself (or subtracting depending upon how you look at it!)
One balance shaft running at a crank speed, but, in the opposite direction to the crank, and the two shafts mutually counter rotating running at twice crank speed.
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The Skoda Fabia 1.2 3 cylinder I drove for a while was a delight to drive. Quiet, smooth and economical but a bit noisy at Mway speeds due to the gearing.
If it had been fitted with a turbo it would have been a little cracker!
I've no doubt 3 pot engines could be improved further by the likes of BMW & Mercedes.
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I guess we can't blame manufacturers for responding to the challenge of lower CO2 emissions / lower (or zero) VED. Their market research will tell them this is what customers want to buy. Better economy and lower emissions grabs the headlines, a bit of vibration does not.
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they will use clever electronics to balance these things out. Probably by varying the detonation process time, or even throwing in some out of phase "bang" parts of the cycle
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A perky three cyl like the Daihatsu unit in my Charade is very suited to small characterful cars, especially if it was turbocharged.
Interesting times ahead for sure, more technical advances than F1!
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I suppose at low rpm, they will be using the crank motor/alternator like in the current 1 series.
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The VAG 1.2 Diesel was fine in the A2 (drove a 75hp version and preferred it the her 1.2 petrol - some have shipped it to 120-130 HP).
The 1.0 Corsa is underpowered (Son had '52 reg that I drove twice) but also a reasonable town car, not really noisy at all and achieved 50 mpg..
MB and BMW late to the game?
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And, of course, not forgetting that most Peugeot 107 / Citroen C1 / Toyota Aygos have 3-cylinder engines too - as do Smarts.
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Thats rahter like saying the turkey is looking forward to christmas,
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I seem to remember many years ago on Tomorrow's World an experimental three cylinder horizontal radial engine fitted in to a Fiesta type vehicle, when they started it up it sounded like a bag of spanners. Of course we were probably told at the time all engines would be like this in ten years time.
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they also said CDs would never become unplayable.......
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Peugeot 107 / Citroen C1 / Toyota Aygos have 3-cylinder engines too ...
As also did the Suzuki Swift 1-litre from the mid-80s (daughter had one). Not a bad engine once the auto-choke heating system was unblocked.
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An update on this is that this week's Autocar has a feature about the radical rethink of the BMW 3 series for the next model. It's reported that the base petrol and diesel models will have 3-cylinder engines in place of 4-cylinder ones, and that the new engines will effectively be be based on half of the relevant 6-cylinder engine. (aren't their fours two-thirds of their sixes?).
Edited by Sofa Spud on 07/08/2009 at 22:38
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Quote:....."""It will be interesting to see what MB and BMW come up with to overcome the firing interval problem - hopefully, it will be something smarter than a very heavy flywheel."""
A triple-mass flywheel???? :)
Edited by Sofa Spud on 07/08/2009 at 22:42
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I was just watching an episode of Classic Gear on Tv and they featured the Ferrari 355 Spider. Its naturally aspirated engine developed 100bhp per litre due to a copious sprinkling of valves per cylinder.
If BMW produced a 3 pot 1.2 and let it breathe it could be quite a performer.
Presumably there must be a maximum amount of power which can be obtained from any given litre of capacity.
Anyone know what that limit is?
Calling Number Cruncher, come in Number Cruncher...over.
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3 cylinder engines on Beemers!!??
This green, cuddly hug-a-tree nonsense has gone far enough! Never! What next? Front Wheel Drive? (Chance would be a fine thing)
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3 cylinder engines on Beemers!!?? This green cuddly hug-a-tree nonsense has gone far enough! Never! What next?
I think it's still the case that they don't sell vehicles with even the 4cyl engine in the US - nothing less than 6 for the American market.
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The fundamental limit is given by the aerodynamics of the inlet port.
Once all of the airflow through the inlet port reaches the speed of sound, the maximum mass flow rate of the port is reached. Once you've reached the speed where you can't get any more air mass injested, that's the limit for that engine.
There is a measure of engne performance which removes the effect of size - it's called brake mean effective pressure. Comparing engines BMEP figures allows the state of tune of an engine to be assessed with getting bogged down in tiresome discussions about torque and power.
As a starter, see;
www.epi-eng.com/piston_engine_technology/bmep_perf...m
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About 320 bhp per litre for a NA engine - the racing Honda RC 116 50 cc twin of 1966:) 16bhp at 21,500 rpm, 4 valves per cylinder. Should give the 1.2 engine a bit of pep - 384 bhp I make it. So long as you're prepared to rebuild the engine after 500 km or so.
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The Skoda Fabia 1.2 3 cylinder I drove for a while was a delight to drive. Quiet smooth and economical but a bit noisy at Mway speeds due to the gearing.
Hmmm...in our SEAT Ibiza it's horrible at low speeds - it's juddery and noisy and feels like the engine isn't fastened in properly. Been looked at several times but it's the same for 5 years and never got worse so can't be anything incorrectly (or not) fitted. It does go a lot better on flowing A roads when given its head though
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first time I drove a 3 pot Vx Corsa, I thought it had a plug out... awful tickover, rough at pulling away... just like a 4 running on 3....
... now a Suzuki 3 pot.... (Cappuccino) great little thing... smooth as... nice pick up... loved it!
Edited by smokie on 09/08/2009 at 08:25
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...feels like the engine isn't fastened in properly...
I had a couple of the old shape Ibizas.
Both suffered from this, particularly in second.
The gearlever would move quite bit when you went from power on to over-run.
For once, the phrase: 'They're all like that, sir,' might be true.
Anyway, BP, I know how much you like the Ibiza, really. :)
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No-one seems to have described the experience of the 1.0L 3 cylinder in the Yaris, which is apparently the same engine as the Aygo/C1. I had one on loan, and it felt more powerful than the Jazz 1.2, presumably because of the gearing and higher revs. I didn't have it long enough to assess fuel consumption, but it felt pretty good on motorways and small roads, and admirably smooth.
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The 1.1 3 cyl engine in younger daughter's Mitsubishi Colt was a revelation after the SEAT (VAG) 3 cyl - you really would be pushed to know it wasn't a 4cyl engine and some road-testers have said the 1.1 3 cyl is nicer than Mitsubishi's 1.3 4cyl.
Pity the gearchange is so awful!
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and some road-testers have said the 1.1 3 cyl is nicer than Mitsubishi's 1.3 4cyl.
I'd read that, but the 1.1 CZ1 I test drove at the local Mitsu dealer was awful, whereas the 1.3 CZ2 seemed pretty good, and we bought one.
However I liked the 3 cyl 1.0 old model Corsa I drove a few years ago.
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The gearlever would move quite bit when you went from power on to over-run.
Ours certainly does that, in a most dramatic manner.
It's wierd really - it's mainly sound. It sound's very juddery and sort of rorty but if you can look through that it actually feels OK. At one visit the dealer said it was front disc brake shields vibrating (which it isn't). A neighbour has a 1.2 Polo and that doesn't make the same sound at all.
Anyway BP I know how much you like the Ibiza really. :)
It's not a bad car but the fact that it's broken down 4 times now with the same fault is completely unacceptable these days. The dealers are too thin on the ground now too - in one rip-off moment ours has ruined the ownership experience and any other dealer would be more than an hour away.
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