My questions about camshaft design
My questions about camshaft design
(OP)
Hi, the past month or so i've been diving in this subject, i've read some Race Engine Technology articles by prof Blair and Associates and whats available trough google books of Norton's "Camshaft Design and Manufacturing".
My objective is to develop an accurate enough software to predict valve train dynamics for a direct acting (bucket) system. The software will be used to project a cam for a FSAE car.
I'll use this thread to get some help in some questions.
The first thing i looked at was those 3 arc cams then polynomials and then splines. Splines prove to be the best, all polynomials will work but some will be more troublesome than others to "fine tune".
So my first question is: whats the problem with infinite jerk? 3 arc cams have infine jerk at the inflection points, they also have less area under the displacement for higher acceleration values and those are clear disavantages, but the jerk part i dont understand since its not related directly to force it will not cause loss of contact. i guess
My objective is to develop an accurate enough software to predict valve train dynamics for a direct acting (bucket) system. The software will be used to project a cam for a FSAE car.
I'll use this thread to get some help in some questions.
The first thing i looked at was those 3 arc cams then polynomials and then splines. Splines prove to be the best, all polynomials will work but some will be more troublesome than others to "fine tune".
So my first question is: whats the problem with infinite jerk? 3 arc cams have infine jerk at the inflection points, they also have less area under the displacement for higher acceleration values and those are clear disavantages, but the jerk part i dont understand since its not related directly to force it will not cause loss of contact. i guess





RE: My questions about camshaft design
RE: My questions about camshaft design
2º - Student license doesn't mean free, at least thats the case for 4stHEAD and solidworks.
3º - I have this theory about learning, when someone teaches you something you... learn, when you understand something by yourself you get smarter.
sorry if this "sounded" bitter, but i'm realy disapointed with school.
RE: My questions about camshaft design
- Steve
RE: My questions about camshaft design
The commercial softwares you've mentioned (Valdyne, 4stHEAD etc) that tackle valvetrain dynamic analysis cost significant money because many hours and hundreds of thousands of lines of code have been used to perfect them - not to mention time spent on validating the algorithms used with special test rigs or actual engine testing!
Look at the complexity of the mathematical model required to attempt a dynamic analysis on a bucket valvetrain:
www
The analysis must include bounce and separation between all the parts and also clash between the coils in the spring - this is not easy to accomplish mathematically. What you will also find is that in attempting to do this there is very little published information on the damping coefficients used - and it is these that can greatly influence the ensuing solution.
The main input to such an analysis is the valve lift profile - again, as you have mentioned, this is no easy topic to tackle. The commercial softwares use combinations of curves, splines and smoothing techniques that take many thousands of lines of code to perfect - a project in itself!
To answer your question re jerk - think of jerk like an impact - if your jerk is high then you may as well be hitting your valvetrain with a sledge hammer.
Finally, you might find that if you contact the Sales guys supplying these commercial softwares that they have "freebie" policies for FSAE teams!
RE: My questions about camshaft design
I believe Acceleration and jerk translate into extra load on the valve train. If the "contact stress" on the cam follower exceeds some nominal value (depends on materials) then wear and fatigue become problems.
Non smooth acceleration or pulses can provoke resonant frequencies. If the resonance is spring surge then spring reliability is directly compromised and valve bounce can appear. That's no fun.
RE: My questions about camshaft design
damping coeficients will be dificult to find but... one thing at its time.
for now im satysfied with the jerk explanation, its hard to look at it separately from acceleration, i guess water inside a bottle is a good example, with high jerk the water goes crazy inside the bottle.
Tmoose, resonace will allways be a problem, theres so many harmonics that its hard to avoid them, one just shoots for a range of frequencys where the harmonics are low.
thanks for the replys.
RE: My questions about camshaft design
RE: My questions about camshaft design
www.sae.org/technical/papers/2008-32-0073
RE: My questions about camshaft design
RE: My questions about camshaft design
Have you considered partnering with one of the camshaft developers at one of the more reputable camshaft companies? If you are interested in going that direction, I would be willing to make the necessary introductions and I can assure you this guy is as smart as anyone in the country that is developing camshafts. One thing though, he does not use commercial code and if I told you the code he uses for his development, you would probably fall out of your chair.
Another thing, what are your rules/limitations as far as cylinder heads? Is CNC Porting allowed? If so, and you have someone on your team sharp enough to develop the port designs, I would be willing to donate my time and my machine time as well since that is my business.
Larry
RE: My questions about camshaft design
Have you read the site rules and guidelines. You have promised to break the rules in your 2 recent posts and you are VERY borderline in this post. To avoid red flags, I suggest you read, comprehend and abide by the rules.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: My questions about camshaft design
RE: My questions about camshaft design
While it was not my intention to do so, I see what you are talking about and I wish to thank you for bringing this to my attention and keeping me honest. This will not happen again as I will be more careful regarding any post of mine.. I truly did not think that volunteering a service was a violation though for someone such as a student.
Larry
RE: My questions about camshaft design
That is why I posted advice rather than just red flagging it.
In my fairly long experience here, judging by posts that stay vs those that disappear, if you do post e-mail addys it will get red flagged. You can post links to a URL which then contains contact details if you do so in response to a request, but not as blatant self promotion. Student posts are also banned, especially ones that appear to be homework assignments, but the definition of student is fuzzy (some are working engineers and part time students for instance) but FSAE is generally not red flagged, or at least they tend to not disappear.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: My questions about camshaft design
I am more than willing to share what knowledge I have (to a point) that will benefit others. I have been doing this type of work too long for others not to benefit in some way, shape, form or fashion from what little I can share.
Larry
RE: My questions about camshaft design
- Steve
RE: My questions about camshaft design
I wonder whether there would be any merit setting up an FSAE Forum under the Automotive Engineers part of this site? At least everything would be out in the open then?
MS
RE: My questions about camshaft design
- Steve
RE: My questions about camshaft design
RE: My questions about camshaft design
Larry
RE: My questions about camshaft design
As LarryCoyle pointed out, there is also the possibility of creating a 'master cam'. The machines that do this are: Berco, Storm Vulcan and Van Norman.
If you are going to write code to produce cam profiles and their corresponding manufacturing data, I would also suggest that you include in your program the facility to output the manufactured cam profile in exactly the same format as would be recorded by a cam profile measuring machine on the manufactured camshaft. You can then check that the manufactured profile is as intended!
RE: My questions about camshaft design
You need to understand Pedro that you are pretty much doing a one-off camshaft design. This means that you need to make sure you are working with a manufacturer that currently offers something for the engine type you are working with. That will ensure that they have blank cores in stock or readily available. The last thing you want to do is to have to work with what is called a "round lobe" core as this drives the expense up considerably.
RE: My questions about camshaft design
RE: My questions about camshaft design
RE: My questions about camshaft design
You will see in the SAE paper I mentioned earlier that they were able to use the existing stock cams and get them reground. A reputable cam grinding shop will be able to regrind existing cams for about 200 pounds (at today's exchange rates that's equal to about 201 Euro!!!).
The fact most of the 600cc engines used in FSAE have a separate cam for exhaust and intake means you can set timings to whatever you like. As a FSAE university you will be able to get any of the 1D performance simulation codes for free to analyse your engine intake (including restrictor) ducting, exhaust ducting and valve lift events, and optimise them for peak performance. If the optimised valve lift profiles fall within the envelope of the stock cams then you are in business - regrind!
RE: My questions about camshaft design
facty has a great idea that I totally forgot about. Since I am sure there are certain parameters that you have to remain within, this would probably provide you a very cost effective option. You could probably talk to one of the current cam manufacturers that offer grinds for your engine and ask if they offer regrinds. If so, there is a very good chance they have something very close to what you need. It would involve a few phone calls or emails and it should be worth that.
Good catch facty... As many years as I worked for a cam company, I can't believe this went right over my head.
Larry
RE: My questions about camshaft design
RE: My questions about camshaft design
- Steve
RE: My questions about camshaft design
RE: My questions about camshaft design
larrylcoyle, i believe the new profile will have less duration and since the original one must be agressive ish... but i may be wrong we haven't done any simulation on that area yet, mostly chassis and suspension for now.
the project is 8 years old on that school, many people have passed and last year the car was finaly put together, now some things need to be "re-engineerd"... what should be an advantadge (time) proved to be a disavantadge in this case.
RE: My questions about camshaft design
About 3 posts down on this Packard site is A recollection by one of the principals of HO Racing, a respected Pontiac specialist outfit in the 70s.
http://ww
RE: My questions about camshaft design
You don't need to worry too much about cast cores etc. - motorbike cams are fairly small and a blank can be fairly easily and cheaply machined from 4140 (or similar) and nitrided after grinding.
Rothbart's book "Cam Design Handbook" could be useful.
RE: My questions about camshaft design
RE: My questions about camshaft design
RE: My questions about camshaft design
Earlier on this thread I posted a link to an SAE paper where the students successfully designed valve lift profiles for the exhaust and intake, and consequently cams, that produced a significant increase in performance of their engine - so it is indeed possible. What you'll find is that this type of successful project will probably be supervised by a member of faculty with experience in engine design!
RE: My questions about camshaft design
RE: My questions about camshaft design
If you think any serious racing team, whether it be from F1, Inycar, NASCAR, LeMans Series, MotoGP, Superbikes, MX1...., I could go on ad infinitum, design their "engines off the shelf" then you are seriously wrong - they do it in-house and then get a reputable Cam Manufacturer/Grinder to make it. Yes, home-builders or back-yard-specialists utilise exiting parts, so I have no argument there.
I advised Pedro NOT to sit down and develop his own "cam design software" from scratch!! - there are several very good software applications out there (used by the aforementioned race teams) that already do this and which FSAE teams can get for free or at a great discound due to their academic status!
If a professional engineer at an engine design company was asked to design a cam to suit a specific purpose then I doubt he/she would be satisfied with what was "out-there". Engine design, and specifically optimising performance, is all about understanding the unsteady gas dynamics dynamics as far as pure engineering is concerned. The job of the engineer/designer is to produce the most optimised design before the inevitable testing and development phase. If the engineer has the understanding and tools/applications then a great deal of resource and therefore expense can be saved as there will be less 'suck-it-and-see' testing required.
Most of the great advances in engine performance over the last thirty years has come from a better understanding of the engineering science underlying the engine - the unsteady gas dynamics and the combustion.
Don't get me wrong, experienced engine builders and testers play a massive role in engine design through application of this experience and "know-how", but the real advances come from a better "understanding" of the fundamentals.
You are totally right in sayin that engineering students should not be trained to go for the most complex analyses, but they surely need to be aware of all the possibilities if they are to become successful professional engineers.
RE: My questions about camshaft design
RE: My questions about camshaft design
RE: My questions about camshaft design
Not saying it is right or wrong, just saying.