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03-25-2014 05:56 PM

So I have done some research on measuring volume but I haven't found anything that seems like it would make this project anywhere close to easy.

I send pistons out to be made by WIseco/CP/JE etc and they can all take my design and lop off the top at the required height to get the volume required but I would much rather be able to do this myself and I am hoping quickly and easily.

For anyone who isn't familiar with piston design, this is a little tricky because there is the negative volume of the valve reliefs.

This is based off the compression height. A flat piston would have zero dome or dish.

Negative relief into the piston is dish and positive volume above the compression height is dome.

In order to get the actual dome or dish you need to take the volume of material sticking above the compression height and subtract the volume of any material removed below the compression height.

http://members.rennlist.com/v1uhoh/compress_image002.gif

What is the fastest easiest way to do this?

8 REPLIES

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03-25-2014 06:36 PM

I'm on my iPad and far from my computer to illustrate this. But try making a "dummy" cylinder the same diameter of the piston. Then find its volume and position it's bottom at the same elevation as the lowest point of the Piston surface. Then use Boolean subtract to remove material form this dummy cylinder and use the remaining volume to subtract from the original volume.

I'll play with this in the Morning and send a picture.

Bob

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03-25-2014 06:53 PM - edited 03-25-2014 07:19 PM

Hi there,

There shouldn't be anything stopping you from doing the 'lopping off" yourself, just cut the bottom of the part away, then run the ** Physical Properties** command on the

Your not wanting the volume of the combustion chamber right?....just the piston dome.

Sean CresswellDesign ManagerStreetscape LimitedSolid Edge ST10 [MP0] Classic [x2 seats]Windows 10

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03-25-2014 07:05 PM

Bob I am trying to imagine how to do this in a way that will factor for both positive and negative volume without adding other volume from any piston included below the compression height. I will play with it a little bit. An example will be greatly appreciated. I could upload a piston model if it would help.

Sean

The problem is that the valve reliefs go below the compression height.

If I lop the piston off at the compression height (the flat at the top of the piston) then I will also lop off some of the valve relief.

I could do something like reverse the 'lop' then use surfacing to create a container that represents the remaining volume of each valve relief then subtract that combined number from the volume of everything sticking above the compression height but this seems overly convoluted.

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03-25-2014 07:36 PM

I think I figured out a decent solution and I think it pretty much uses a combination of both of your suggestions.

I made the dummy shape, then I overlapped them enough in the assembly to make a complete negative. After that I cut the depth of both down to the flange edge (compression height in this case).

At that point I had the positive volume in the piston and the negative volume in the negative. Subtract one from the other and it should be the piston dome.

Don't mind my funny looking piston. I threw it together as fast as possible to test this out.

If anyone sees any flaws in my logic or knows of a better way I would love to hear it.

I would find this to be acceptably fast and easy though.

Now on to test it on my production part.

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03-25-2014 09:06 PM

Glad you got a workable solution.....pretty sure that example would only work in assembly, as they have edge contact between "volumes", so would encounter the kernel limitation "Zero-thickness [non-manifold] body".

Sean CresswellDesign ManagerStreetscape LimitedSolid Edge ST10 [MP0] Classic [x2 seats]Windows 10

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03-25-2014 11:31 PM

I did the measurement in the model as the assembly adds both volumes as opposed to supbtracting one as I need. I wasn't able to do an extruded cut down to zero however I was able to make a new sketch then cut out the entire piston aside from the islands of material above that plane without complaint from SE.

It appears to have worked out well as far as I can tell.

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03-26-2014 08:57 AM

Using SE since V12, 2002

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03-26-2014 12:51 PM

I am assuming you are trying to get a number you can use to adjust your calculation for compression ratio and that sort of thing. Take a look at this, I created a volume which represents an arbitrary cylinder minus the volume of the net dome using multi body subtract. Then you simply subtract that volume (algebraically) from the volume of the cylinder to get the total dome. I put both into the assembly so I could use the property manager to get the volumes but you could always calculate the cylinder volume with a calculator. I get a dome of 2197mm^3. Look in the variable table of the assembly.

Using SE since V12, 2002

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