'Radial' Crankshaft?

Probably yes.
Surly the question should be.
Is there a better way of burning fuel which gives rotary motiion directly rather than linear?
Or maybe you just need to invent the 'Linear Wheel'?
Del

Were you thinking about an 'axial' crankshaft like a ball point pen mechanism? This would give you absolute control over the relative speed of various parts of the strokes.

Of course you'd need to couple two crank shafts in parallel to utilise four cylinders etc. And you'd need another coupled parallel shaft to "get the transmission power" out of the engine block.

I think the disadvantages would outweigh the advantages, but, it would be nice to see a working model.

This question has so many unclear aspects to it I don't know where to start. Well first off the choice of which approach in any engineering design is "best" will always be a collection of known and unknown conditions that will change with each application. In this case it seems that the OP is applying this question of linear to rotary motion in the case of an internal combustion engine producing the linear motion of a piston into the rotary motion of the flywheel. However, if one does just a simple comparison of other rotary to linear systems and vice versa that happens in an automobile, a quick observation will show that the steering wheel assembly translates rotary motion to linear motion with the use of a Pitman arm and recirculating ball bearings or a rack and pinion mechanism.

Now getting back to the implied condition of use in an engine. There are engines that do not burn fuel in a linear motion, turbines and the narrow niche market Wankel rotary engine. So this begs the question, what advantage (if any) does one find from the lever arm varying geometry of a crankshaft, connecting rod and piston when it is used in the ubiquitous internal combustion engine? I don't know myself, but I suspect that pressure levels timing generated from the explosive burning of fuel and piston motion translates to a relatively smooth torque from the short sharp shocks one normally associates with a confined space explosion.

I seem to recall that the Wankel gets better milage the faster it goes.

There ARE ways to achieve what you are looking for- Reduced friction and improved power transfer.

You just have to sit down and address all of the issues "built-in" to the current design.

Such an engine will be hitting the market relatively soon. The prototype is about 6 months away, but the design is already finished. Resolution requires throwing out the current "play book" and deciding to build the engine in a totally different fashion by such actions as-

Eliminating the "cast" crankshaft in favor of an assembled model that will allow better bearings to be used

Eliminating the "cast" engine block and "movable connecting rods with bearings" that transfer much less power to the crank than is produced at the piston due to the inherent significant losses that occur when you re-direct a linear load to an axial action

Eliminating "internal combustion" to generate the pressure on the pistons which also requires much higher engine weight for enough metal to resist those explosions that produce the pressure

Eliminating a single-action power transfer (from a positive pressure applied to the piston for about 180 degrees of the engine's rotation)

Eliminating metal rings to contain the pressure (mostly) but also require oil-based lubrication

Eliminating having the lubricant being introduced by splashing through a pool of oil- adding energy loss due to the friction losses and the impact of the crank into the face of the oil pool

You get the idea. WE have been using the "standard" internal engine design for a lot of years because- even though it was not very good or very efficient, it generally worked and most people did not take the time to try to figure out another way to get power delivered to the transmission or whatever end-use.

"Such an engine will be hitting the market relatively soon. The prototype is about 6 months away, but the design is already finished."

Please keep us posted, I'm quite sure we'll all be very interested. Nevertheless, however suggestive of various fundamental paradigm shifts your description may be, it obviously still implies a "radial crankshaft".

I'm not sure what you are asking either...whether it relates to engines, or just energy conversion. As it relates to IC engines, which are a form of heat engine, the limits are well defined by the Carnot cycle. As it relates to energy conversion, that is a straightforward efficiency ratio of input energy to output energy. (the difference being converted to heat via friction or other 'losses'.) unlike the carnot cycle, this can approach 100%.

cheers

Chris

All of these "new" improvements have been around for decades and are found in many extant high performance (ergo high efficiency) power plants. Speed of production and therefore cost is what has limited the wider proliferation of these techniques. Modern automated production processes will eventually make these enhancements ubiquitous.

...like splash lubrication in IC engines disappeared in the 1950's with the universal adoption of pressurized lubrication. Splash lube still hung around in old designs still being produced for cost reasons only.

See the RANKIN Model motor - quite interesting and very efficient rotary movement

Still didn't succeed in mass production (or there are dome trials...)

I looked around, found nothing except a reference to a steam engine. Did you meant that?

Yup, we still seem stuck with the radial crank, which, adopted from the spinning wheel, suited Watt's constant pressure engine perfectly. Otto's first I.C. 'explosive' engines (gas) relied on a linear rack & pinion. The 'compressive' characteristics of the radial crank enabled Diesel to ignite coal-dust.

There are a couple of 'linear flight' alternatives, including the elgant 'rhombic drive' split-crank/twin shaft arrangement deployed in Sterling engines (UK sub-marines), and the 'scotch yoke' vertically sliding plate incorporating a horizontal slot (opposed 90deg to objective travel), with which the crank-pin engages. Both configurations are intrinsically 'radial' cranks with extended residence at TDC & BDC.

Wankel's lovely thing gets under the point, it 'lifts' the crank, rather like rolling a stone instead of jumping down on it. Commercially, thermal stress, friction and fuel consumption of the 'rotary' combined crankcase/combustion chamber is still a challenge.

Best wishes, James GvG

You have answered your own question (in the piston ICE context) with;

"The 'compressive' characteristics of the radial crank"

Lack of this in other piston linkages costs more power and yields less torque from characteristic expansion pressure gradients.

2¢

What are the 'other' piston linkages (which lack the compressive characteristic of the radial crank), and yeald less torque?

Linear flight and reduced 'dwell' seems a reasonable design objective.

Jam

I'm not sure why you would think 'reduced dwell' is a good thing. Assuming by 'dwell' you mean the ±15⁰ at top and bottom dead center, where piston speed is more or less zero. If so, have a look at the 'flame front' rates at the top and also at the residual pressure and exhaust outflow time around the bottom.

If you also look at the universal gas laws, for the compression forces verses the mechanical advantage of a crank, you may see why the 'lineal' - such as rack and pinion - even when 'opposed' - don't quite suit the piston ICE velocities/pressures/forces.

Of course it's easier to see the 'geometry' looking at a single cylinder 'over-square' ICE, but having done so, look at the 'under-square' state of the art in such as F1.

The only real alternate is 'continuous combustion', such as a turbine, where no 'componentry reversal' occurs. Wankel's have inertial 'flopping'. Swash plates have piston/con-rod reversal, and so on.

But, in a 'stop-go' world of traffic, a turbine has its own set of 'dwell' limitations.

Perhaps what you could look at is a tiny gas turbine/Lithium-ion electric hybrid.

Assuming price is no problem.

Hi 34.5.

Sure you'd agree, residual pressure at BDC is waste. Most of what was created (during the c.15deg you mention) went in heat, and ('sine') friction.

I still don't know what other piston linkages (lacking compressive force) you refer to tho, any such arrangement would be useful (since compressive action not needed in constant pressure engines), and I'm not sure why a 'lineal' arrangement 'dont quite suit' the percussive 'velocities/pressures/forces', not sure in what respect you mean.

When Otto converted to radial crank (for benefit of compression you mention) he had to massively re-inforce cylinder, con-rod, crank/pins and piston -and introduce 'evaporative' water-cooling.

An alternative crank with reduced TDC residence and linear flight would run cooler, more quietly with less friction and fuel consumed. There is no advantage to the 'dwell' (hence v.short stroke/high RPM race engines) beyond more fully burning the massive amount of calorific 'bang' we squeeze in. If we put less fuel, used more efficiently even if not fully burned, there would be less un-burnt fuel emitted.

When you count the RPM of an FI engine it's not hard to imagine an awful lot going on per nanosecond, yet some ICs work at 60 RPM, yet the combustion rate is (essentially) the same. If 'extended dwell' were vital to the efficient workings of an explosive engine, the fractionally short residence of an F1 piston would not be achievable.

In other words, if 10,000 rpm for piston combustion were the 'ceiling', a crank arrangement producing half the 'dwell' will run at 5,000 RPM? Perhaps much of the RPM/power relationship is about reducing the unproductive, fuel burning dwell-time.

Also, sideways 'sine' friction (of radially mounted piston) slows the motor, the harder you push the more friction generated, often the first cause of major repairs. The radial action is almost illogical; imagine leaning a walking-stick against the wall and banging the top downwards with a rock to effect sideways motion of the bottom/tip (away from angle of lean, which at TDC is zero). You would need a stout, low modulus stick. hard pavement and massive hammer to make it move. If you lift the tip instead...

I really really like all the answers and suggestions on this topic.

V.best, James

'I'm sure there must be a better way'. (Uni Anon)

There are things to be done around BTC that take time. Piston movement is largely unnecessary and lateral forces are virtually zero.

"not sure in what respect you mean"; I suspect you have not gone and really looked at the relationships and factors I outlined.

"An alternative crank with reduced TDC residence"; would have proportionally higher inertial reversal losses (and no doubt more junk to make it happen).

"There is no advantage to the 'dwell'"; Then why is spark timing 10's of degrees BTDC? (see flame front propagation and 'peak pressure' development)

Piston speed sets the limit - long stoke is the enemy of rpm. Rpm is the friend of power per kg. Kg is friend of economy in transport. "Mass flow" determines power. An F1 could run on the smell of an oily rag if the computer is programed to do so.

"If you lift the tip instead..."; or oil it.

You may like 'all the suggestions' but I would like not having to explain it multiple times because you haven't bothered to research it, then had a good think about it. Particularly in terms of forces, vectors and time

Hi... a piston is what holds the rings like compression and oil rings and on the bottom the rod hooks on the crank with 2 bearings.as the crank turns the piston goes up and down in the cylinder to give you compression.

Regards,

Xing

it's probably the worst of the worst design for an internal engine. auto companies are reluctant to change engine designs because of the billions of dollars they must spend on re-tooling.