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Old 01-12-2017, 12:11 PM   #11
lohring
 
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Thanks. For some reason I didn't realize that the seals were in the outer case. However, everything I said about an accurate and smooth surface is still true. It just needs to be on the inner element. It may be easier to get this finish and the seals may wear in well enough against say a cast iron inner element for a demonstration prototype. Production engines would need a better solution for long life. I'm looking forward to seeing your prototype. This could be a very promising design.

Lohring Miller


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Old 01-12-2017, 09:56 PM   #12
Buchanan
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EDM cutting leaves a porous hardened surface, if you propose to use an alloy steel this hardened surface will crack when bent. Do you have a miraculous post bend finishing process that will remove the cracks and produce the smooth non abrasive surface required for a long lasting oil and pressure seal?


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Old 01-13-2017, 02:15 PM   #13
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Hello Buchanan

You write:
“EDM cutting leaves a porous hardened surface, if you propose to use an alloy steel this hardened surface will crack when bent. Do you have a miraculous post bend finishing process that will remove the cracks and produce the smooth non abrasive surface required for a long lasting oil and pressure seal?”


The porous hardened surface is a good characteristic (it keeps lubricant etc).

There are some “miraculous” multi-axis wire EDM machines by which you can cut accurately an already bent sheet of metal, and so you bypass the problem mentioned.

Such EDM machines cut accurately bevel gears etc.

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Old 01-13-2017, 02:15 PM   #14
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Hello Lohring

Talking for the seals of the Wankel, LiquidPiston and PatWankel, here are some interesting, I hope, details:

With their different arrangement of the seals, LiquidPiston creates new “sealing” problems (not existing in the Wankel engine).

According the following drawing (from the patent of LiquidPiston):



there is an immovable “peak” seal, 825, which abuts on the cylindrical working surface 202R of the inner body,

there is also a side seal, 801, in a groove of the inner body, which follows the motion of the inner body.


A LiquidPiston side seal, as the seals of the conventional Wankel, undergoes a substantially variable (in direction and in amplitude) acceleration around the seal and around the cycle.

Here is the inertia force an apex seal of a conventional Wankel applies to the epitrochoidal casing :



(at some angles the inertia vectors outwards, at some other angles it vectors inwards),



and here is the acceleration required in order a point at the top edge (the outmost edge) of the side seal of a LiquidPiston engine to follow the motion imposed by the spinning / orbiting rotor:



and here it is shown, for comparison, the acceleration required in order a point at the innermost edge of the side seal of a LiquidPiston engine to follow the motion imposed by the spinning / orbiting rotor:



The following drawing helps in understanding the previous plots (the red circles show the path the outmost edge of the side seal follows, the cyan circles show the path the innermost edge of the side seal follows) :



R1 is the "crank-arm" of the eccentric shaft, R2 is the distance of the specific point of the seal from the center of the rotor.


The gaps between the apex-seals /corner-seals / side-seals of the Wankel engine are gaps between bodies moving together (they are all inside grooves / holes of the rotor).


In the LiquidPiston, the side seal moves together with the inner body (the rotor), while the rest seals are stationary.
Any clearance of the synchronizing gear-wheels,
and any clearance in the bearings supporting the rotor (the bearing by which the rotor is rotatably mounted on the eccentric shaft and the bearings by which the eccentric shaft is rotatably mounted on the immovable casing),
and any “play” of the side seal inside its groove,
and any flexing of the eccentric shaft (or power shaft) due to inertia and/or combustion loads,
all are added to the required gap between the side seal and the “button seal”.
Note: around each chamber there are four such gaps.

The result is even more gas leakage than in the conventional Wankel.


Now think how the seals are arranged and are working in the PatWankel.

In the PatWankel with the working surface on the inner body, all the seals are inside grooves made on the outer body and perform a pure rotation (during a cycle, the inertia force remains constant in direction and constant in amplitude). Etc.


By the way, without an eccentric shaft, there is no flexing of the eccentric shaft.
Without inertia loads on the bearings, the clearance between the inner and the outer bodies is smaller.
Without eccentric shaft, no balance webs are required.

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Manolis Pattakos
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Old 01-23-2017, 09:21 AM   #15
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Hello all.

Here are the specifications of the XMv3 of LiquidPiston:



According the famous MIT university, the DARPA and the more than famous Shikorsky company, it is a promising engine design.


Here are a few calculations based on the above specifications and on the way the XMv3 operates.

They are required two only rotations of the eccentric shaft in order a combustion to take place in each working chamber (of the three existing). This means 1.5 combustion per eccentric shaft rotation.

In comparison, in a Wankel they are required three eccentric shaft rotations in order a combustion to take place in each working chamber (of the three existing). This means one only combustion per eccentric shaft rotation.

More combustions per shaft rotation sounds great.

However there is a significant side effect:
In the Liquid Piston the synchronizing gearing is heavily loaded by the combustion pressure.
Depending on the angle of the eccentric shaft, the teeth of the two gearwheels take a good percentage of the force acting on the “rotor” due to the high pressure gas.

In comparison the synchronizing gearing of a Wankel runs unloaded for as long as the engine runs at constant rpm.


At 10,000rpm the power output of the XMv3 is 3PS.

According the previous, 10,000rpm means 5,000combustions per working chamber of the XMv3.

Unless I am wrong, this is equivalent to a 70cc 4-stroke reciprocating piston engine operating at 10,000rpm (because it also burns 5,000 times per minute the mixture contained in a chamber of 70cc).

A good 4-stroke makes more than 100mN of torque per lit (1,000cc) of displacement (even at the peak power revs).
This way, a torque of 7mN from a 4-stroke 70cc reciprocating piston engine is reasonable.

7mN at 10,000rpm means a power output of 14*7mN*10= 10PS.

This is more than 300% of what the XMv3 makes.

Do I miss something?

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Manolis Pattakos
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Old 01-24-2017, 05:46 AM   #16
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Hello all.

Here is the inner body of an unconventional rotary engine and the way to cut it in a lathe:



(instructions in how to see it stereoscopically at http://www.pattakon.com/pattakonStereoscopy.htm )


At operation it would be like:




It comprises two only parts, each spinning at constant speed about its own fixed axis (which means perfect balancing without any balance webs).
The eccentric shaft of the Wankel RX8 and of the LiquidPiston rotary engines is eliminated.
The power / torque is delivered by a shaft / extension of the inner body:



There are two combustions per shaft rotation (i.e. as much as in a Wankel with two rotors).

The big difference is in the sealing.

More about how this engine (PatWankel) operates are at http://www.pattakon.com/pattakonPatWankel.htm


Regarding the machining of the working surface shown in the first animation:

On the chock of a lathe it is secured eccentrically a shaft.
The red gearwheel is secured immovable on the lath bed.
The body with its gearwheel (white) is rotatably mounted on the shaft.
As the chock rotates, the body to be machined performs a combined motion (it spins about the shaft and it orbits together with the shaft).
Given the shape of the seals to be used (the simplest form? the circular), the cutting tool has to follow a specific “path” (like half circle, for instance) in order to create / form the working surface on the part (the working surface is whereon the seals will abut and slide during operation; the seals are mounted in grooves made on the outer body).

In case of seals having simple form, even a conventional (not CNC) lathe can be used.

Similarly for the honing / polishing.


Thoughts?

Objections?

Thanks
Manolis Pattakos
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Old 01-24-2017, 01:20 PM   #17
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That will work with both cutting tools and a grinder mounted like common ball cutters. The next problem is machining the seal slots in the outer body. To follow the inner body their location and contour needs to be fairly accurate, but the width needs to be very accurate. I can envision an end mill on a cnc mill cutting the groove in each half. I don't believe you can depend on springs to make up any inaccuracies. Also, the seal seems to transition from riding on the spherical surface to the flat surface on the ends of the inner element. That will be tough to seal with a one piece ring. Perhaps you would do better with a multi piece seal. I can envision a 1/2 circle segment for the outer section combined with circular arc face seal segments near the hub. They could be connected by a cylindrical piece like the Wankel apex seals.

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Old 01-24-2017, 04:34 PM   #18
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Hello Lohring

You write:
“That will work with both cutting tools and a grinder mounted like common ball cutters. The next problem is machining the seal slots in the outer body. To follow the inner body their location and contour needs to be fairly accurate, but the width needs to be very accurate. I can envision an end mill on a cnc mill cutting the groove in each half. I don't believe you can depend on springs to make up any inaccuracies.”

I was thinking of the manufacturing of the grooves exactly as you write it.


You also write:
“Also, the seal seems to transition from riding on the spherical surface to the flat surface on the ends of the inner element. That will be tough to seal with a one piece ring. Perhaps you would do better with a multi piece seal. I can envision a 1/2 circle segment for the outer section combined with circular arc face seal segments near the hub. They could be connected by a cylindrical piece like the Wankel apex seals.”

As shown in the ASME papers (previous posts), one of the big problems of the Wankel rotary is the excessive gas leakage through the gaps between the several parts comprising the Sealing Grid.

This is what the PatWankel tries to do. To apply the efficient sealing of the reciprocating piston engines to the rotary engines.


At http://www.pattakon.com/pattakonPatWankel.htm web page it has been added another version of sealing for “gerotor” rotary engines (Wankel, Colley, LiquidPiston etc), as follows:

A common characteristic of the prior art rotary engines is that some of the seals, and some of the seal grooves, are shared between neighbour working chambers.

In comparison to a reciprocating piston engine, a Wankel rotary engine uses two apex seals per working chamber, with the one apex seal (and its groove) shared with the leading working chamber, and with the other apex seal (and its groove) shared with the trailing working chamber. In this version, each combustion chamber utilizes not only its own seals, but also its own grooves for seals.



The apex seal "plays" inside its groove on the rotor, bouncing between the two flanks of its groove.
For instance, the "leading" apex seal of a chamber, when the exhaust starts in the leading chamber, leaves the "trailing flank" and moves towards the leading flank of its groove, allowing a significant leakage towards the exhaust. At the end of its "stroke" it slaps the "leading flank" of its groove.



There are similar problems in the Reverse_Wankel / LiquidPiston rotary engine: each "peak seal" with its groove is shared between two neighbouring working chambers.



A "peak seal" cannot help bounching between, and slapping on, the two flanks of its groove.

In the following design, each seal relates exlussively with one only combustion chamber:



The converging of the grooves enables the two different seals at the specific apex of the rotor to abut closer to the geometrically correct point on the epitrochoid working surface (on one hand, this reduces the required motion of the seals inside their grooves in order to remain permanently in contact with the working surface on the casing, on the other hand, this reduces the "dead" volume, i.e. the volume between neighbouring apex seals).

With the following design each peak seal of a Reverse_Wankel / LiquidPiston engine relates with the combustion in one only working chamber.



Among the advantages of the PatWankel_iGR design is the independence of the sealing of neighbouring chambers, also the elimination of the leakage towards the leading and trailing chambers: each seal seats onto the right side of its groove and uses the pressure in its own chamber to tightly abut on the working surface during the high pressure period of the cycle, i.e. as in the reciprocating piston engines.

Significant advantage is also that only the one face of each seal relates with high temperature gas; its other face abuts on the cool "bottom" of its groove; this way, the thermal load on the seal reduces substantially (the number of combustions it participates is half of those of a conventional apex seal), the mechanical stress of the seal is reduced substantially (there is neither bouncing of the seal among the flanks of the groove, nor slapping of the seal on the flanks of the groove when the one of the neighbouring chambers fires), the cooling of the seal is improved, etc.
All these improve the long-term reliability of the engine.

Here is a modified Wankel according the previous:



Here is a PatWankel wherein the working surface is on the outer body (not shown). The inner body (actually the rotor) is sliced, with the one seal in place and the other two seals disassembled:



Here ia another PatWankel wherein the working surface (whereon the seals abut and slide) is the external surface of the inner body:



There are a few new animations explaining the previous.


Thoughts?

Objections?

Thanks
Manolis Pattakos
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Old 02-04-2017, 06:50 AM   #19
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Hello all.

Some animations and text have been recently added to the http://www.pattakon.com/pattakonPatWankel.htm web page:


In the following PatWankel, wherein each seal and each groove serve one only working chamber, the working surface (whereon the seals abut and slide) is the external surface of the inner body:



Here is the inner body alone, with the three seals on it:



In the following drawing the two, of the three, seals have been removed.



The working chamber at left is at its TDC with its seal surrounding it and sealing it.
The inner body is like a "piston" pushed deaply into the working chamber (an unconventional piston that needs neither a connecting rod, nor a crankshaft).

At operation the "piston" (i.e. the inner body), remaining permanently in contact with the seal, is pushed outwards from the chamber and the volume increases, then the "piston" is pushed inwards and the volume decreases, and so on:



Every point of the inner periphery of the seal remains permanently in contact with the external surface of the inner body.

And if, instead of keeping the outer body (and the seals with it) immovable, the outer body is spinning at constant speed about a fixed axis (and the inner body with the working surface is also spinning at constant speed about another fixed axis), the elimination of the eccentric shaft comes with many other advantages:






Regarding the Wankel rotary engine:

Here is one of the worst problems the engineers of NSU and Mazda experienced several decades ago:



Confused?

No it is not the speed bumps on the roads.

It is the “speed bump” on the apex “road”, i.e. on the casing:





Look at the “speed bump” at the lower and at the top side of the casing.

Look at the “reverse” centrifugal force an apex seal experiences each time it passes from the area between the two spark plugs (or from the anti-diametrically from the spark plugs are).

Have you ever passed over a “speed bump” with, say, 50mph (80Km/h)?
Did the car take off the road?

Imagine an apex seal taking-off the casing (at the “speed bump” area) and landing later, several degrees of eccentric shaft rotation, on the casing, bouncing a few times . If an RX-8 is forced to over-rev (say, braking abruptly with the engine) it cannot avoid such a problem.
The Wankel RX-8 requires strong springs under the apex seals, otherwise each apex seal will take off the epitrochoid twice per revolution around the casing.

Think the difference in the PatWankel wherein the inner body rotates at constant seed about a fixed axis and the outer body rotates at constant speed about is own fixed axis, which means constant magnitude of the centrifugal acceleration.

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Manolis Pattakos
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Old 02-04-2017, 02:55 PM   #20
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I think you are on the right track, but making the seal "rings" with enough precision will be challenging. I still think the problem area will be where the spherical outer surface transitions to the flat end of the inner body. I would be tempted to try to make an engine if I thought I knew how to make the one piece ring. I own an OS Wankel. It ran very well in model airplanes, but the expectations of fuel economy and engine life are much lower than in full size applications.

Lohring Miller


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