Alternative cranks

[Ripcrow]

Tinkering with a couple of crank design changes . Wondering if any of these designs offer any advantage over conventional cranks

 

[Ripcrow]

Tinkering with a couple of crank design changes . Wondering if any of these designs offer any advantage over conventional cranks

design 2 thoughts please

 

[Chiptosser]

Can you elaborate ? not real clear of what you are trying to convey.

 

[Ripcrow]

Instead of the big end being in a parralell line with the centre of the crank shaft if u off set it do u increase the twist force. If x length / throw = twist force then does having another point to exert force on crank increase power!try to explain again drawing are not good my etch a sketch dodgy. In the other picture the crank and big end are in a straight line but the length of the crank / throw is altered by having the crank arm connect on the opposite of the crank shaft to where the big end is( if big end is on right hand side and has a throw of 50 mm then if you increase the length of throw to 75 mm and have the connection on the opposite side does the increase length exert more force) this way stroke length is not altered but the length of arm exerting force is, I know clear as mud

 

[John Rus]

I'm not quite sure I understand it properly but if you want to increase torque you will be better off lengthening the crank throw rather than adding friction with other means.

John.

 

[Ripcrow]

My passion is efficient operation of engines. There is no increase in friction and I would like to achieve more power without increasing the capacity. With the off centre crank it gives 2 points of twist force being excerted on the shaft itself without altering capacity , with the other design all it does is allow for a long throw while actually not having one. Don't think this is a good idea but thought I would put it out there:hDe:

 

[Till]

Regarding power:

Let’s assume that the amount of obtainable energy in the combustion gasses, which is applied to the piston, is a fixed amount in total.

A mechanism is a like black box. All energies that go in must come out again somewhere.

If you install a “black box” in between piston and crank, the maximum amount energy obtainable from this black box is the amount of energy, which had gone into the box previously.
In this case, the losses “inside” the black box are zero (perfect!).

You can’t create additional energy by placing more lossy linkages in between piston and crank.
To increase output, you have to reduce losses (reduce friction).

But:
The length of the conrod influences the velocity plot of the incoming fresh gas. It’s the downward movement of the piston what creates the “suction” inside the cylinder. So if you do match the current flow section of the valves and the length of conrod, you can reduce pumping losses and gain extra power.

Is the second sketch something like this?
http://www.homemodelenginemachinist...design-ic-engine-20101/index4.html#post210944

 

[johnny1320]

How is this going to increase torque? where ever you place the rod end compared to the main jornal the center to center is still maintained.

 

[Ripcrow]

My thinking was that by moving the contact point with the crank u Change the centre point of the motion from the centre of the crank to the outer edge of the crank shaft,thinking that aswell as torque derived conventionally by the length of throw u also might gain from the additional twist of the offset ( if crank is 50 mm thick but force is applied at a point 25 mm above centre and by a arm of 100 mm long does it not mean that u get the result of 100 mm + 25 mm long throw without extra capacity needed in cylinders) capacity is unchanged because u adjust crank height to 25 mm above centre of crankshaft. No linkages needed apart from the standard big end , will mock one up tomorrow as etch a sketch is hard to follow

 

[charlesfitton]

(Are the pictures right side up in the Southern Hemisphere?)

 

[rhankey]

With your second diagram, all you have done is increase the effective throw slightly which will increase torque at the expense or RPM. Top dead center is in line with the hypotenuse of the triangle you have effectively created. In other words, TDC is not at 9 o'clock as you have drawn it, but at about 8 o'clock.

 

[crueby]

It does not matter where you connect the crank arm, it is only the distance from the center of the crank shaft to the center of the offset rod that matters. You could have the crank arm be a spiral, but it would not change things in function (aside from having more bending potential).

 

[mu38&Bg#]

Engine efficiency has been studied for well over 100 years. Concepts have been tried and proven. Any good engine design text will cover most of them. Direct injection and turbo is the latest and greatest in automobiles.

http://world.honda.com/powerproducts-technology/exlink/ This is probably the only engine out there that uses an unusual crank arrangement successfully. I think i read about it's efficiency at one time, but don't remember how it performed.

What sort of engines are you working on in regard to efficiency and what are you achieving now?

 

[Ripcrow]

Only new to modelling,my first engine was a simple air engine with variable valve timing,my crank was 20 mm throw and I found that it choked a lot of the time, my current project is a multicylinder sterling of my own design. I am a truck driver most of the time operating 15 ltr cummins engines,the Bugatti veyron produces 3000 hp but only transmits 1000 hp to the wheels,lots of power is lost due to heat in any engine.the basic design hasn't changed since the days of steam so I like to think of new ways to enhance the engines ability to harness power,modelling is my way of learning more about my interests