Re: [Translating resource] A Japanese Stirling engine course
Posted: Wed Mar 29, 2023 9:52 pm
Lesson 5 - 2 100Watt experimental Stirling engine: part C
This part talks about solving an issue of unbalanced power output from compression and expansion piston.
An adequate mechanical part with high precision can make drastic changes on the performance a machine.
This part starts from 14:12 to 22:53
https://youtu.be/9Risg8ItEjo?t=854
Though we completely assembled this engine, it failed in the test run.
First problem is in the crank system.
Here(left crank was linked to the compression piston and right crank was linked to the expansion piston).
Usually the power output from the expansion piston is stronger and unbalance between two cranks happened.
In order to solve this problem, a timing belt was used to link these two cranks and the shaft of flywheel.
Timing belt is depicted by dotted line in right half of this drawing.
(Picture stated at 14:58)
(Picture title: Timing belt method of fist design)
That shaft on top of two cranks is the shaft for power output.
Each crank had about half of their circumference connected to the belt.
Only a third of circumference of the power shaft was connected to the belt.
This made the situation quite difficult because the unbalanced power from cranks created unstable tension to the belt.
The belt were eventually tore by pulses of force.
We changed many types of belts and all of them failed.
We then started finding a mechanism which can endure such unbalanced torque while stably delivering the output.
It troubled us a lot and we finally found our solution.
(Picture started at 16:44)
(Picture title: 3 balanced cranks(triangular cranks) )
This mechanism was found in a book called <<Shinhen Kikai no moto / Fundamentals of machinery>>
This book was written in 1978.
Though this is an old book, the basic mechanism for linkages and other machinery are included in this book.
This book is very important to me.
(At 17:50 Took one copy of that book fro the shelf behind him )
This is my copy of that book.
This mechanism is depicted in the drawing on the left.
1,2,3 are rotating shafts and 4,5,6 forms up a triangular crank.
This crank system allows the three shafts(1,2,3) rotate at the same speed.
We were excited by this discovery and started trying to make this mechanism.
Sadly, we were not skilled enough to make it by ourselves.
We made our prototype, but the length of cranks are not precise enough.
This prototype crank generated pretty bad performance.
In the end we had to order this part from professional machine shops for precision better than 0.01mm.
This is the triangle crank we've been discussing.
(Picture started at 19:38)
(Picture title: Three parallel crank and coupling rods)
The shaft marked as "1" is for expansion side, "3" for compression, and "2" for flywheel.
We did try and error on this mechanism several times and eventually succeeded with that ordered part.
This is the final version of that compact Stirling engine.
(Picture started at 20:30)
(Picture title: Structure of 100W class small Stirling engine)
Its width is 304 mm and height is 462mm.
On the bottom part the triangular crank is installed.
The performance of this part was very impressive, high precision really makes the difference.
Above the crank there are two cylinder liners which cover the piston shaft.
The bottom of each cylinder liner is sealed by a o-ring and one slid bearing is used there to regulate the movement of piston shaft.
A cooler device covers the cold end of compression side.
It was made from copper pipes.
As for the heater on expansion side, we tried to use the original heater from previous build.
It was a block casing with holes and heating wires were inserted in that.
But since this build was too compact, there was no room for this part.
We had no choice but to use 1kW cable heaters.
The heater was wrapped on the hot side for two to three layers.
Since there are buffer pressure applied on this model, we decided to use a larger fly wheel.
This part talks about solving an issue of unbalanced power output from compression and expansion piston.
An adequate mechanical part with high precision can make drastic changes on the performance a machine.
This part starts from 14:12 to 22:53
https://youtu.be/9Risg8ItEjo?t=854
Though we completely assembled this engine, it failed in the test run.
First problem is in the crank system.
Here(left crank was linked to the compression piston and right crank was linked to the expansion piston).
Usually the power output from the expansion piston is stronger and unbalance between two cranks happened.
In order to solve this problem, a timing belt was used to link these two cranks and the shaft of flywheel.
Timing belt is depicted by dotted line in right half of this drawing.
(Picture stated at 14:58)
(Picture title: Timing belt method of fist design)
That shaft on top of two cranks is the shaft for power output.
Each crank had about half of their circumference connected to the belt.
Only a third of circumference of the power shaft was connected to the belt.
This made the situation quite difficult because the unbalanced power from cranks created unstable tension to the belt.
The belt were eventually tore by pulses of force.
We changed many types of belts and all of them failed.
We then started finding a mechanism which can endure such unbalanced torque while stably delivering the output.
It troubled us a lot and we finally found our solution.
(Picture started at 16:44)
(Picture title: 3 balanced cranks(triangular cranks) )
This mechanism was found in a book called <<Shinhen Kikai no moto / Fundamentals of machinery>>
This book was written in 1978.
Though this is an old book, the basic mechanism for linkages and other machinery are included in this book.
This book is very important to me.
(At 17:50 Took one copy of that book fro the shelf behind him )
This is my copy of that book.
This mechanism is depicted in the drawing on the left.
1,2,3 are rotating shafts and 4,5,6 forms up a triangular crank.
This crank system allows the three shafts(1,2,3) rotate at the same speed.
We were excited by this discovery and started trying to make this mechanism.
Sadly, we were not skilled enough to make it by ourselves.
We made our prototype, but the length of cranks are not precise enough.
This prototype crank generated pretty bad performance.
In the end we had to order this part from professional machine shops for precision better than 0.01mm.
This is the triangle crank we've been discussing.
(Picture started at 19:38)
(Picture title: Three parallel crank and coupling rods)
The shaft marked as "1" is for expansion side, "3" for compression, and "2" for flywheel.
We did try and error on this mechanism several times and eventually succeeded with that ordered part.
This is the final version of that compact Stirling engine.
(Picture started at 20:30)
(Picture title: Structure of 100W class small Stirling engine)
Its width is 304 mm and height is 462mm.
On the bottom part the triangular crank is installed.
The performance of this part was very impressive, high precision really makes the difference.
Above the crank there are two cylinder liners which cover the piston shaft.
The bottom of each cylinder liner is sealed by a o-ring and one slid bearing is used there to regulate the movement of piston shaft.
A cooler device covers the cold end of compression side.
It was made from copper pipes.
As for the heater on expansion side, we tried to use the original heater from previous build.
It was a block casing with holes and heating wires were inserted in that.
But since this build was too compact, there was no room for this part.
We had no choice but to use 1kW cable heaters.
The heater was wrapped on the hot side for two to three layers.
Since there are buffer pressure applied on this model, we decided to use a larger fly wheel.