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My questions about camshaft design

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

RE: My questions about camshaft design

why don't you just get a student license of commercial software like ValDyn?
 

RE: My questions about camshaft design

(OP)
1º - I was suppose to be taking a BSc in automotive engineering turns out the school hasn't tougth me nothing automotive yet (second year) so i better learn things by myself.

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

There are often subtle differences between pure academic (i.e. student) licenses and those granted for FSAE use.

- Steve

RE: My questions about camshaft design

How long have you got!? Taking on this type of project does not normally fall under the remit of a 'student project' - I don't mean you can't do it, but you'll probably find that you won't have the time or resources to do it right.

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.profblairandassociates.com/GPB_4stHEAD_ValveTrainAnalysis_theory.html

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

http://books.google.com/books?id=2RQkAAAAMAAJ&;source=gbs_ViewAPI&pgis=1

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

(OP)
facty, i understand the complexety of the analysis. my next step is to study MDOF systems, after that i'll be able to calculate oil film tickness and bucket stress. about valve lift, im using two B-splines with 10 points each (one for opening other for closing) first and last 3 points on each curve set lash, ramp velocity, max lift and negative aceleration at the center, the other 4 points are moved to manipulate the displacement curve, i can replicate the acceleration and velocity profiles of the designs in prof Blair's articles with same KLD values. I migth need to add one more point to control max jerk as that is a bit high. i can also translate the valve lift profile to the physical form of the cam lobe.
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

The coding of the MDOF is quite a challenge if you hope to model bounce, separation and clash within your simulation. I'd suggest using a Runge-Kutta approach to solving your MDOF system. Start with a simple system - no bounce, separation or clash - get this working with a robust solver and then deal with the more complicated scenario.

RE: My questions about camshaft design

Pedro, here's an FSAE paper that describes an FSAE project to redesign the camshaft to improve performance - might be of some interest:

www.sae.org/technical/papers/2008-32-0073

RE: My questions about camshaft design

(OP)
hi, thanks again facty, i've founded that paper a while ago, i haven't bougth it yet because we are going to turbocharge the engine.

RE: My questions about camshaft design

PedroCG,

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

Larry

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

(OP)
larry, i think theres no rules about head porting but there's rules about outside services, it must be a student project... i would consider partnering after i see the results of what im doing, i live in Portugal so i dot know how many people are developing (in a serious way) camshafts.

RE: My questions about camshaft design

Pat,

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

Larry

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

Thanks Pat, FSAE allows outside services in some cases as long as the vendor is signed up with SAE and FSAE and offers that service to all teams and not just one individual.  The actual request has to go through FSAE via the SAE web site though. Also, for a clarification on the Unigraphics Porting post the other day, there is a certain amount of information that would need to be exchanged that is usually covered by a NDA agreement and could not be posted openly.  What I did explain though is that any information regarding Unigraphics and CNC Porting (to a point) would be openly posted so that everyone would benefit from the information.  Hopefully that clears that one up as well.  I did discuss that one with the "Boss Man" if you know who I mean.

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

FSAE have their own forums elsewhere and they are fairly active.  I don't know if they are moderated, but they do seem clear of overt advertising.  Maybe it's because there's no money to be had?

- Steve

RE: My questions about camshaft design

I must admit that I have a bit of a soft spot for the guys involved in FSAE, although I havent had much to do with it.

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

(OP)
Ok, one more question, what kind of data does a grinding machine needs? i have expressed the shape of the cam in cartesian coordinates about the center of the base circle

RE: My questions about camshaft design

Pedro, that would depend on the type of machine you are using.  If it is a manual machine, it typically uses what is called a master lobe that is mounted on the end of the grinder to machine the actual lobe on the camshaft.  This master lobe is several times larger than the actual lobe but I do not remember the actual ratio.  If it is a CNC grinder, it uses the same data as any other type of CNC machine.

Larry

RE: My questions about camshaft design

There are several different file formats that are recognised by the most common standard types of cam grinding machines:  .des, .opn, .cls, .s96, .p and .r files

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

The first thing I would do is determine what company was going to manufacture my camshaft.  Once that decision is made you can contact them, tell them who you are and the nature of your project.  Then you let them tell you the file format required to produce a camshaft on their machine.  I have seen Berco and Storm Vulcan machines that originally used a master lobe converted to cnc machines so do not assume anything here.  If at all possible, ask to speak to the person who does the camshaft design work as he will most likely be able to answer most of your questions.  One thing you will have to expect is that you will probably run into some proprietary issues along the way.  One possibility is they might want you to send your general design information to them and they might format it so that it is compatible with their machines.

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

(OP)
i see. thanks again guys, btw i can see now why most of the teams from Portugal dont toy with the engine alot...

RE: My questions about camshaft design

If you know machine work you could mill the master on a standard milling machine, with the proper attachments of course. In the past I've done a non engine cam on such machines, and could have done what you are talking about. It would take some major time and no mistakes.  

RE: My questions about camshaft design

Pedro,

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

Pedro,

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

(OP)
we have tougth of that before, buy a used set of camshafts and have them reground, the new profile will probably be "smaller".

RE: My questions about camshaft design

When's your deadline PedroCG?

- Steve

RE: My questions about camshaft design

Pedro, what do you mean when you say the new profile will be smaller?  If you are thinking that the newly reground used cores will be physically smaller from a dimension standpoint, that is true but most likely more of the material will be removed from the base circle.  If you are thinking that the lobe characteristics will be smaller from a performance standpoint, that is false.  Regrinding camshafts is a common occurance even when you start out with a new core.  This is where the experience of the tech support guys at the cam company can be of service to you.  Most likely you will be able to get at least one good regrind out of a set of cast cores for your engine.

RE: My questions about camshaft design

(OP)
SomptingGuy, the objective is to race the car in 2011 so having everything ready for testing and training in the beginnings of 2010 would be nice.

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

I hate to be practical but why are you attempting to design a cam? Presumably the engine is from a motorcycle - you must be able to find a suitable grind available off-the-shelf which is almost certainly going to be better than anything you can do yourself (or anybody can probably do themselves). If you want to be different, build a system like that shown in the "Helical camshaft" thread.    
 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

The FSAE engine is usually a 600cc motorcycle engine taken from one of the sportsbikes - as you say. BUT the engine has a single 20mm restrictor in its intake ducting. You'll find that there are no "off-the-shelf" parts designed for this purpose, and anyway, this is a university design project were the students are being prepared for a possible carreer in engine design with a racing team/company etc so it is essential that they are exposed to the practices involved in this design process. Understanding unsteady gas dynamics and their effect on engine tuning is key to this process. Then being able to design a cam to provide the optimum valve lift events for the tuned engine with the dynamic constraints imposed by the mechanical valvetrain is the ultimate learning goal for the students. It will let them appreciate why the cams "on the shelf" are designed the way they are.

RE: My questions about camshaft design

Thank you for your answer Facty. I did more-or-less realise that the students were probably expected to build their own gear rather than buy it and this was why PedroCG was designing his own profile. The students may learn a lot but the chances of actually designing a really useful profile are (I think) very slim. I didn't know about the 20mm restrictor. I honestly don't know how the restrictor would affect the type of cam profile needed. It would be interesting to know what other people have done. Given enough time/money I think my approach would be basically trial-and-error using existing profiles from other bikes or even cars.  

RE: My questions about camshaft design

The students are being introduced to engineering science and analytical design techniques so that, as graduate professional engineers, they don't have to practise "trial and error", but instead will have the necessary skills and understanding to "optimise" a design problem and save time and resources at the testing and development stage.

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

Facty - I understand what you are on about - FSAE cars etc. are student training exercices - not necessarily the best way to do things. If a professional engineer was given the job by his employer to come up with a cam to suit Pedro's needs I think his first move would not be to sit down and design one from scratch. He would first look for an existing suitable profile - if nothing was available (and there always is something) he (or she) would then think about designing one. You yourself rightly advised Pedro on 11 March that designing his own cam was an enormous job and it was not wise to attempt such a thing. I think a lot of FSAE design in general is a bit unnecessaryly complicated - but once again you can justify pretty much anything on the grounds of student training. By unnecessary I mean F1 style carbon fibre chassis and spindly suspension arms, inboard bellcrank layouts, excessive electronics etc. I think it would be very interesting after the FSAE competition is run and won for the best FSAE cars then to face a competition against cars built by professional racing teams and amateur (home-built) cars. I have a feeling the student/academic cars would not win - even against the home-builts - but I could be wrong. Maybe there should be a separate racing class for FSAE cars - they are occasionally seen in hillclimbs etc.  Possibly my overall point could be that students should not be trained to immediately go for the most complex and academic solution to a problem - simple and effective should be considered as well.         

RE: My questions about camshaft design

BigVlad,

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

(OP)
well facty just answered the question for me... i just want to add that if one is to be called an engineer one must be an engineer and not just some guy that spend 3 or more years in the university, thats what i think.

RE: My questions about camshaft design

(OP)
i forgot one thing, i think the helical camshaft would be very unpratical if not impossible for this aplication, its a direct acting (bucket) system so the contact path is probably to wide.

RE: My questions about camshaft design

It has been related to me that Keith Duckworth had a saying.  The only people who write about Jerk are Jerks.

Not saying it is right or wrong, just saying.

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