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Camshaft design

F

florin.ics

New member
I try to design a combustion engine, it`s a simpel 4-line cylinder, i designed it from my head since i have no plans or such things. I want to syncronize the camshaft to open the valves and i kind of have no idea about this. I know i have to syncronize the link from crankshaft to camshaft. I don`t know how to make the gears and i`m not quite sure if i made cams like they should be. Maybe someone can help me. I`ll put a printscreen so you can see how it looks like. I will upload a pic so you can see.

2cntx1u.jpg
 
florin.ics,


This is quite easy actually, you just need to create a gear mate between the timing gear on the crank and the gear on the cam shaft (or gears in the DOHC case). This mate is created by selecting the circumference of the gears (which can be either modeled as gears, or simple circles). Also, you need to create a cam mate between the cam lobe and each valve. This is created by selecting the circumference of the cam lobe and the flat surface at the end of each valve stem.


The crank gear should be half the diameter of the cam gear for a 4-stroke, and your intake/exhaust came lobes need to be out of phase - right now it looks like both valves for each cylinder open at the same time. This won't work.


Hope this helps,


Jim
http://www.linkedin.com/in/shawengineering
Edited by: jimshaw
 
Hi jim. Actually i know how to set make those mates, what i asked is how to syncronize cams so they open and close valves in right engine timing. But i figured out. I set cams 1,4 and 2,3 180 degrees one from others and also cams 2,3 90 degrees from 1,4. Also the rotation of camshaft must be 2 times slower than the rotation of crankshaft. Now i`m trying to make the spring that make the valve close to extend and compress while valves are opening. And also the transmision belt that send the move from crankshaft to camshafts, even if i set the gear ratio, i want to make it more reallistic.
 
florin,


ah, I see. The firing order should be 1-3-4-2, so align your cam lobes accordingly. Also, and it depends how accurate you want to get with this model, but the intake and exhaust cam lobes have different profiles, and there should be an overlap (when both valves are open). Here's a link to a neat diagram on the latter: http://www.answers.com/topic/valve-overlap.


For the valve spring, you'll need to do top-down design, are you familiar with this method?


For the timing belt, do you want to show the teeth rotate through the gear teeth? If so, you'll need to use top-down design as well.


Jim
http://www.linkedin.com/in/shawengineering
 
Ok i will try to syncronize them after that order, since i didn't use any dimension and all were random i`m not sure if i can still make that very accurate.

About top-down design i don't know that feature, i'm still at the beginning of 3d cad work. Yes i want the teeths move with the belt also. I can use a drive chain also, doesn`t specially need to be a belt.

Thank you for the links also.
 
Florin,


The moving spring is quite easy, but the trick is you cannot use the standard "helix" curve to create your spring. This is because the height paramter in the helix tool cannot be linked to other parts - and linking the geometry of one part to the location of other parts within an assembly is the whole point of top-down design.


To accomplish this I created a "sweep withtwist along path". I used a simple surface feature to create the spiral, then swept a solid circle through it to create the spring, then I deleted the surface. Here's the surface feature (pay attention to the green profile and the pink trajectory). It has 3600* of twist (ten revolutions):


View attachment 5893


And here is the animation: 2010-12-31_141844_valve_spring.zip


Let me know if you need more detail on the technique.


Jim
http://www.linkedin.com/in/shawengineering
 
I`ve made the spring, but what i don`t know is how can i use it for other valves as well, without having to design it for each valve since i can`t use a concentric mate with the valve. Also mirror or pattern won`t work because they will take the movement from the first spring.
 
Florin,


For top-down design, I typically create a new empty part and fix it at the origin. As a result, there is no way to pattern/mirror this part, as there are no assembly mates used to place the part, and no symmetry within the engine to take advantage of.


That being said, however, you can probable just create a subassembly of 4 springs for each cylinder, and then reuse that sub-assembly for each cylinder...


Jim
http://www.linkedin.com/in/shawengineering
 
Florin,


I've tried to create a belt which would have teeth that rotate with the engine, but I cannot get it to work. My approach was to drive the teeth location from the angle of rotation of the crankshaft but there are two problems in doing that:


1. SW is not recalculating the equations at each time step. As a result, it is not updating the geometry with the new tooth location. It updates in the model, but not in the animation.


2. The angle is cyclical, so once it rotates past 360*, it starts over. This will make the animation innacurate, and the only way to make it "appear real" is to fake it, or take advantage of some situation (like only rotating it 359* during the animation).


You'll need to upgrade to a more capable animation software to get what you want. Or you could coneduct a transientFEA analysis with Rigid Body Dynamics, contact elements, and nonlinear material properties, but that would be like swatting a fly with a bazooka.


Jim
http://www.linkedin.com/in/shawengineering
 
Jim,

Thanks for your time, how about a simple belt without teeths, can i use that so i will have a realistic animation?
 
Florin,


No worries. I really wanted to try and get it to work, but the more advanced the geometry gets, the harder it would be. If SW had a trajpar function (like ProE) I think we could have gotten it.


For a regular belt, you should be able to just draw a simple extrusion. Using top-down design (i.e. locking an empty part at the origin, right-click edit, then use the geometry of the pulleys to create the geometry for the belt) you should be able to create it quite easily. However, when it comes time to animate, it will just look like a solid part.


Like in this vid:2011-01-06_115607_belt.zip


Jim
http://www.linkedin.com/in/shawengineering
Edited by: jimshaw
 
Yes, i did that with belt feature, but what i want is that belt moves along with the gears, if that is possible somehow, not just be static.
 
florin,


No. How do you know it's moving unless you see geometry travel along the belt path, like teeth. If the belt is completely smooth, then you wouldn't be able to tell if it's moving or not. Unfortunately, I can't figure out how to make Solidworks move the belt along it's path. I think you're going to need a dedicated animation software.


Jim
http://www.linkedin.com/in/shawengineering
 
Well, it`s because of the material used, to make it appear more realistic, when i render the animation the belt can be seen as static.
 
Hi Jim, yes i got the spring to compress finally, i made a sepparate spring for each pair of valves, because pattern would only compress all like the main pattern.
 
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