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# Epicyclic Crankshaft

Single, V-twin, V-4, in-line 4? Change the effective configuration as you go.
 (+2, -2) [vote for, against]

Imagine an ordinary four cylinder in-line, four stroke engine with five main bearings. (This system wouldn’t be limited to such a configuration, but let’s take this as a simple initial case.)

Each throw of the crankshaft is replaced by a pair of identical epicyclic gearboxes, one each side of the conrod. The big end bearing is attached (eccentrically) to the planet cages on each side of the conrod. The crankshaft itself is replaced by five short shafts in each main bearing. Each end of each shaft (apart from the end bearings) is splined into the sun wheel of a gearbox.

The annuli are fixed (in relation to the cylinder block), so that power is transferred to the “crankshaft” as usual. The velocity of the crankshaft in relation to the four stroke cycle will, of course, be determined by the ratio of the gears in the gearbox

Now if you rotate the annuli of a pair of gearboxes through a small arc, you can change the TDC of that piston relative to the other pistons in the engine. Thus you could change a four cylinder engine to become, in effect, a single cylinder engine with all the power strokes occurring at the same time, or a twin, with even (BMW) or uneven (Harley et al) power strokes.

Valve timings could be varied by a similar linked system on the camshaft or possibly pneumatically or electro-magnetically. Injection and ignition timing would be fully electronic. Tuning the exhaust might pose some problems.

Now you have a car with the low down grunt for pulling away from the lights and high end smooth cruising.

 — Gordon Comstock, Mar 07 2007

Epicyclic Gear http://en.wikipedia...lic_gear_ratios.png
Sorry, I’m no good at drawings. What I’m proposing is that the big end is attached to the green planet cage, eccentrically – say at the same place as one of the planets. The yellow sun replaces the crank/output shaft and the pink annulus (ooh err Missus) is fixed. Now as the conrod pushes the planet cage round, the sun will turn (in a ratio determined by the relative sizes of the sun and annulus. If now the annulus is rotated (say with a worm gear on external teeth on the annulus) the TDC of the piston is advanced or retarded. [Gordon Comstock, Mar 08 2007]

Epicyclic gears for those not flash-averse http://www.mekanizm...m/transmission.html
Press the Kuiper button to fix the annulus and you will see the motion of the planets in relation to the sun. [Gordon Comstock, Mar 08 2007]

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or it coul be called 'How to add a whole mess of parts to a nice simple 4 cly engine'
 — the dog's breakfast, Mar 07 2007

I can see high-end custom bike applications: how about hinged cylinders? Just because you can...
 — Ned_Ludd, Mar 07 2007

 What is the point of making an engine run erratically that would otherwise run relatively smoothly?

Would someone (that completely understands this idea) please create an image of this idea and make a link to it.
 — BJS, Mar 07 2007

This is why the PTO requires drawings.
 — ldischler, Mar 07 2007

 BJS - //What is the point of making an engine run erratically that would otherwise run relatively smoothly?//

For the same reason that trials bikes are big singles and racing bikes of similar capacity are multi-cylinder. With this you could have the best of both worlds.
 — Gordon Comstock, Mar 08 2007

It's an interesting idea but.... //with all the power strokes occurring at the same time//..... wouldn't this cause a massive amount of vibration and strain on the common shafts?
 — xenzag, Mar 08 2007

trial bikes are great and so are racing bikes but single cyl in trial is to keep weight down,powerand torque per cc is less, but that is not primary concern. multi cyl racers put out much more power and torque for same displaced volume because of number of firings per revolution and less restrictions on gas flows. so they have more weight with the more cylinders but the increase in power more than makes up for it.
 — the dog's breakfast, Mar 08 2007

Dont you think the reciprocating engine has enough moving parts... More moving parts = more mechanical resistance requiring more power to overcome that resistance not to mention the need for more oil pressure and more oil filtration capacity... Why not just spend some money developing the rotary engine instead? (Rolls Royce built a diesel rotary unit once)
 — Brickcarco, Mar 08 2007

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