Modified crank

[Ripcrow]

Does anyone know of a way to distort a cranks circular motion into a oscillating motion.I am thinking that if we decrease the up and down motion and increase the side motion we could increase torque and decrease cylinder volume

 

[enfieldbullet]

i think i know what you are saying, but please elaborate.

i don't think its possible to have such flexibility in a normal design. it would probably take complications that would decrease the efficiency beyond the possible gain.

if you have something more concrete please send a drawing.

 

[Hopper]

Yamaha gets a similar effect, to an extent, by not mounting its cylinders dead above the crankshaft centre, but mounts the cylinders forward a small amount so that when piston is at TDC, the rod is not pushing straight downwards in line with crankpin and crankshaft.

As for an elliptical crank throw, never seen it done. Usually fitting longer or shorter connecting rods is the way of varying the associated angles to gain more or less torque on a given stroke.

 

[Ripcrow]

Thanks for your replys I never thought off offsetting the cylinder.Do you think that if you ran a egg shape mounted on the crank that mounted a circular big end with a bearing race would that increase torque or would we lose our gains by increased friction

 

[lohring]

Below are a couple of pictures of a patented design that increases the dwell at bottom dead center. The principle could be used for a lot of variations in travel versus rotation.

Lohring Miller

View attachment Basic_shape-1.doc

View attachment Basic_Diagram-1.doc

 

[ShedBoy]

Yamaha gets a similar effect, to an extent, by not mounting its cylinders dead above the crankshaft centre, but mounts the cylinders forward a small amount so that when piston is at TDC, the rod is not pushing straight downwards in line with crankpin and crankshaft.

As for an elliptical crank throw, never seen it done. Usually fitting longer or shorter connecting rods is the way of varying the associated angles to gain more or less torque on a given stroke.

This explains Desaxe Engine fairly well. ETW wrote an interesting article on it but I can't find it, used in some of his designs.

Brock

 

[lennardhme]

Easily done with a scotch yoke or one of its variations - better for slower rpm's & slightly less efficient.

 

[Ripcrow]

Thanks for the info I am new to model engineering and have started building an engine of my own design no drawings ,only a lathe and welder.my real interest is in engine effiency and my engine is based on a sterling principle. My machining ability leave a lot to be desired and I am very impressed by the quality of work and knowledge displayed here.

 

[Noitoen]

In the Toyota Prius's engine, the centre line of the cylinder is not the same as the crank shaft. By using this, the linear speed of the piston is different going up and down. Similar to the effect you have on a shaper where the forward motion is slower than the backward. How it gains in efficiency, I don´t know.