RE: 4 Stroke Redesigned
Discussion
Would the engine work in the horizontal?
The idea of a boxer engine is the crank is in the middle, and and so the engine is in balance as the flywheel will be in the middle also.
But if the main crank was off-set then would it still work? I suppose you could use a clever transfer box??
The idea of a boxer engine is the crank is in the middle, and and so the engine is in balance as the flywheel will be in the middle also.
But if the main crank was off-set then would it still work? I suppose you could use a clever transfer box??
atom290 said:
Would the engine work in the horizontal?
The idea of a boxer engine is the crank is in the middle, and and so the engine is in balance as the flywheel will be in the middle also.
But if the main crank was off-set then would it still work? I suppose you could use a clever transfer box??
You're right - it wouldn't be a boxer engine, it would just have near horizontal cylinder bores like a boxer, but without opposing cylinders on the other side of the crank. Mea culpa...
The troubles I see with it are to due with the odd shape of the combustion chamber, and the way the 'valve' piston rings would be exposed in the port while the piston is down.
It's a neat idea, but not really a major change from typical valves.
Why not use a desmodromic cam to lift valves out of the way, as opposed to a rods/pistons? Essentially the same thing, but with the benefits of valve stem sealing and a more optimized combustion chamber.
Gary
It's a neat idea, but not really a major change from typical valves.
Why not use a desmodromic cam to lift valves out of the way, as opposed to a rods/pistons? Essentially the same thing, but with the benefits of valve stem sealing and a more optimized combustion chamber.
Gary
chuntington101 said:
you could swap the top crank for pneumatic cylinders. then you could run wahtever timing you wanted.
hope the development continues as i like some of the ideas used!
thanks Chris.
PS. i have seen some HUGE opposing piston engines at the train musseum in York. they had mounted in a triangle formation from what i remember. it was a monter!
Yes, that was the English Electric Delta.
cdp said:
you could swap the top crank for pneumatic cylinders. then you could run wahtever timing you wanted.
hope the development continues as i like some of the ideas used!
thanks Chris.
PS. i have seen some HUGE opposing piston engines at the train musseum in York. they had mounted in a triangle formation from what i remember. it was a monter!
Yes, that was the English Electric Delta.
No, it was the Napier Deltic
Whichever dick wrote the new4stroke website has done it in flash, the pillock. I presume we're looking at an engine with a smaller piston where the head would normally be, covering and uncovering ports? If so, it's a pretty ancient idea for four-strokes, not to mention its honourable history in the two-stroke world. The advantages over poppet valves would be larger port area and faster opening and closing; also since the valve piston is driven in both directions, rather than relying on spring return, the valve gear is probably capable of higher revs. Generally nobody thinks it's worth the hassle though.
A lot of people seem to think that the valve piston rings would wear as they keep passing the intake/exhaust ports. I'm not so sure they would as that's exactly what the piston rings do in a two stroke engine, often with a number of ports spread around the bore. I reckon dynamic balance and vibration would be more of a problem. There's an awful lot of metal changing direction very quickly.
danmangt40 said:
this is sooooo rehashed. there's a reason we're still using spring arrangements. In general, the only reason for mechanical replacement would only be to eliminate valve float, and this one would have entirely too much inertia to even worry the top end of conventional high revvers.
Not sure about this - the OHC (i.e. crank) would be rotating at half main crankshaft speed. If the bottom end is capable of high revs, there should be no reason why you can't make a top end with smaller pistons capable of half as much. Bear in mind that you don't have the issue of valve/seat impact because there is no longer a seat.
gilbertd said:
A lot of people seem to think that the valve piston rings would wear as they keep passing the intake/exhaust ports. I'm not so sure they would as that's exactly what the piston rings do in a two stroke engine, often with a number of ports spread around the bore. I reckon dynamic balance and vibration would be more of a problem. There's an awful lot of metal changing direction very quickly.
Yes but they're called oil burners for a reason
gary_tholl said:
The troubles I see with it are to due with the odd shape of the combustion chamber, and the way the 'valve' piston rings would be exposed in the port while the piston is down.
It's a neat idea, but not really a major change from typical valves.
Why not use a desmodromic cam to lift valves out of the way, as opposed to a rods/pistons? Essentially the same thing, but with the benefits of valve stem sealing and a more optimized combustion chamber.
Gary
I imagine the chamber could be shaped how you want, even hemi shaped depending on where you TDC the pistons, the advantage of this method being the size and speed of the charge also it doesn't have a valve stem to flow around. I think it's a winner apart from emmissions, it'll burn oil like a 2 stroke x number of cylinders
>> Edited by apache on Monday 21st February 17:29
francisb said:
- relative inlet and exhaust 'piston' timing cannot be varied as they run from the same overhead crank.
thats enough to kill the idea stone dead as a way of moving forward no ?
also can imagine very high wear around where the 'valve' piston rings clear the ports.
exactly - would need to be 'hard' seals more like the ones on a wankle rotory engine (Mazda has moved the ports so this problem doesn't exist anymore) plus if you compare the weight of the 'valve train' compared to the main piston/crank the force of the combustion will put accelerate them more quickly and open the exhaust valve and wasting power.
strikes me as being pretty inefficient.
It's an interesting idea, I wouldn't say it's all that elegant though. All these sorts of things are worth trying, but I have a feeling that this one will remain in the realm of the "homebuilt".
I think the thing that always strikes me with the opposed piston approach is that it's not that easy to find somewhere for a sparkplug.
You always end up going down the road of the deltic. 2 stroke opposed piston diesel. Not to say that the idea is bad. You always get a far better power to weight ratio with a two stroke, and when setup like the deltic, it's pretty smooth, with all the dynamic inertia balancing out.
Aside from that I always liked aircooled 2 strokes anyway. I think it's the smell.
I think the thing that always strikes me with the opposed piston approach is that it's not that easy to find somewhere for a sparkplug.
You always end up going down the road of the deltic. 2 stroke opposed piston diesel. Not to say that the idea is bad. You always get a far better power to weight ratio with a two stroke, and when setup like the deltic, it's pretty smooth, with all the dynamic inertia balancing out.
Aside from that I always liked aircooled 2 strokes anyway. I think it's the smell.
bar_steward said:
exactly - would need to be 'hard' seals more like the ones on a wankle rotory engine (Mazda has moved the ports so this problem doesn't exist anymore) plus if you compare the weight of the 'valve train' compared to the main piston/crank the force of the combustion will put accelerate them more quickly and open the exhaust valve and wasting power.
Funny - I hadn't even looked at it that way, but his design will actually produce power through the little 'valve pistons' aswell.
As you put it "open the exhaust valve and wasting power" - the power won't be wasted, rather it'll be put into the 'valve crank' to drive the 'valve pistons', and will even feed power through to the main crank if the output exceeds the power required to turn the 'valve crank'. Will require a beefy old timing connection between the two cranks then - probably geared.
Looking at the diagram I can see a couple of other concerns, although these may be soluble:-
1) Oil leaking into/around the intake and exhaust ports - depending on the location of the piston rings (i.e. unless he re-locates them!), there would appear to be overlap, so that on full compression oil could escape behind the piston rings...how did Mazda solve this, and can it apply to cyliners???
2) Given that both intake and exhaust are open for a noticeable overlap (plus the drawing showing metal between them interfering with clean flow), can we be sure that all, or substantially all, exhaust gases will be vented...if not, aren't we losing efficiency?
Agreed with the comments about weight...and therefore CoG compromise, and the increased difficulty in VVT / VTEC style operations.
OK, criticism over...nice to see some alternative thinking, can it be made to work effectively???
1) Oil leaking into/around the intake and exhaust ports - depending on the location of the piston rings (i.e. unless he re-locates them!), there would appear to be overlap, so that on full compression oil could escape behind the piston rings...how did Mazda solve this, and can it apply to cyliners???
2) Given that both intake and exhaust are open for a noticeable overlap (plus the drawing showing metal between them interfering with clean flow), can we be sure that all, or substantially all, exhaust gases will be vented...if not, aren't we losing efficiency?
Agreed with the comments about weight...and therefore CoG compromise, and the increased difficulty in VVT / VTEC style operations.
OK, criticism over...nice to see some alternative thinking, can it be made to work effectively???
Looks interesting doesn't it
I could see the engines revving quite well, if they can balance out all the forces, get the sealing right. I can see the drawback in that the space needed betwwen the cylinders would be bigger perhaps, as you would need space between cylinders to fit the OHC crank bearings and counter weights etc. That would mean slighty longer engines, at a guess. It's an intersting idea, having variable cubic capacity design.
I quite like the idea of the REVETEC engine. Which is a boxer type engine.
www.revetec.com/website/
The two cams rotate and raise the piston with a scissor-like action to the bearings. Once at the top of the stroke the air/fuel mixture is fired. The expanded gas then forces the bearings down the ramps of the cams spreading them apart ending the stroke. The point of maximum mechanical advantage or transfer is around 10deg ATDC (the piston moving approximately 5% of its travel) making the most of the high cylinder pressure. Hence the design is raising the efficiency of the bottom end of an engine from 64 percent to a huge 89.6 percent.
This compares to a conventional engine that reaches maximum mechanical advantage around 60deg ATDC. (after the piston has moved through 40% of its travel, losing valuable cylinder pressure). The effective cranking distance is determined by the length from the point of bearing contact to the centre of the output shaft (NOT the stroke). A conventional engine's turning distance is half of the piston stroke. The piston acceleration throughout the stroke is controlled by the cam “grind” which can be altered to give acceleration to suit a certain fuel and/or torque application. This also allows different port timing on opposite strokes, increasing efficiency on 2-Stroke engines.
The piston assembly slides rigidly through the block eliminating piston to cylinder-bore contact. This reduces wear and lubrication requirements. This also reduces piston shock to a negligible amount making ceramic technology suitable. One module which comprises of a minimum of five moving components, produces six power strokes per revolution. Increasing the number of lobes on each cam to five produces ten power strokes without increasing the number of components.
Besides the interesting advantages highlighted, the Revetec also has the following advantages as well:
Output shaft can be run in either direction if multilobed cams with symmetrical lobes are employed. Hence you can run the engine backwards !! No reverse gear thenAlso all rotational forces are counteracted via the counter rotating cam – eliminates the need for a heavy flywheel.Little or no bore contact/piston side thrust, which reduces wear on cylinder bore. Also, by the looks of things, the 'block' is modular, although the sump/heads are not. A bit like the japenese rotary engines. So you could have a 'four rotor' REVETEC engine and 'add' a couple of 'rotors' and end up with a 'Six rotor' or in this case, a six cylinder flat boxer engine Finaly, being a boxer type design, it has a low CG, unlike the 'tall' over head crank engine.
This seems much better funded/marketed, with what seems a fair bit of car manufacturer interest...okay, so it looks like it could be fitted to a Proton, but Proton own Lotus and a new Lotus fitted with this engine would be quite interesting indeed.
I look forward to hearing about more progress about both these engines.
Regards
John S
>> Edited by John_S4x4 on Monday 21st February 22:15
I could see the engines revving quite well, if they can balance out all the forces, get the sealing right. I can see the drawback in that the space needed betwwen the cylinders would be bigger perhaps, as you would need space between cylinders to fit the OHC crank bearings and counter weights etc. That would mean slighty longer engines, at a guess. It's an intersting idea, having variable cubic capacity design.
I quite like the idea of the REVETEC engine. Which is a boxer type engine.
www.revetec.com/website/
The two cams rotate and raise the piston with a scissor-like action to the bearings. Once at the top of the stroke the air/fuel mixture is fired. The expanded gas then forces the bearings down the ramps of the cams spreading them apart ending the stroke. The point of maximum mechanical advantage or transfer is around 10deg ATDC (the piston moving approximately 5% of its travel) making the most of the high cylinder pressure. Hence the design is raising the efficiency of the bottom end of an engine from 64 percent to a huge 89.6 percent.
This compares to a conventional engine that reaches maximum mechanical advantage around 60deg ATDC. (after the piston has moved through 40% of its travel, losing valuable cylinder pressure). The effective cranking distance is determined by the length from the point of bearing contact to the centre of the output shaft (NOT the stroke). A conventional engine's turning distance is half of the piston stroke. The piston acceleration throughout the stroke is controlled by the cam “grind” which can be altered to give acceleration to suit a certain fuel and/or torque application. This also allows different port timing on opposite strokes, increasing efficiency on 2-Stroke engines.
The piston assembly slides rigidly through the block eliminating piston to cylinder-bore contact. This reduces wear and lubrication requirements. This also reduces piston shock to a negligible amount making ceramic technology suitable. One module which comprises of a minimum of five moving components, produces six power strokes per revolution. Increasing the number of lobes on each cam to five produces ten power strokes without increasing the number of components.
Besides the interesting advantages highlighted, the Revetec also has the following advantages as well:
Output shaft can be run in either direction if multilobed cams with symmetrical lobes are employed. Hence you can run the engine backwards !! No reverse gear then
Also all rotational forces are counteracted via the counter rotating cam – eliminates the need for a heavy flywheel.Little or no bore contact/piston side thrust, which reduces wear on cylinder bore. Also, by the looks of things, the 'block' is modular, although the sump/heads are not. A bit like the japenese rotary engines. So you could have a 'four rotor' REVETEC engine and 'add' a couple of 'rotors' and end up with a 'Six rotor' or in this case, a six cylinder flat boxer engine Finaly, being a boxer type design, it has a low CG, unlike the 'tall' over head crank engine. This seems much better funded/marketed, with what seems a fair bit of car manufacturer interest...okay, so it looks like it could be fitted to a Proton, but Proton own Lotus and a new Lotus fitted with this engine would be quite interesting indeed.
I look forward to hearing about more progress about both these engines.
Regards
John S
>> Edited by John_S4x4 on Monday 21st February 22:15
Now *that* really is an elegant design.
I like that alot. I can see a problem though. What happens when the bearings wear out?
If you have a pair of taper roller bearings, I'd imagine it compromises the ammount if space along the axis of the "crank". If you use a parallel roller bearing, there is the tendancy for the outer shell to become oval.
I suppose what I'm trying to say is that I'm a little concerned that the outer shell of the bearing isn't contained in a bulk of material, which is usually where the strength of a bearing comes from.
It's definately a good idea though. It's a bit like a scotch crank.
I like that alot. I can see a problem though. What happens when the bearings wear out?
If you have a pair of taper roller bearings, I'd imagine it compromises the ammount if space along the axis of the "crank". If you use a parallel roller bearing, there is the tendancy for the outer shell to become oval.
I suppose what I'm trying to say is that I'm a little concerned that the outer shell of the bearing isn't contained in a bulk of material, which is usually where the strength of a bearing comes from.
It's definately a good idea though. It's a bit like a scotch crank.
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