Talk:Helical camshaft

Notes

The following notes are to further explain and enlarge upon various contentious statements that were made in the article "Helical camshaft" and awarded a "citation needed".
Note 1. There were originally two statements here but the gist of the two was much the same - that there had never been a genuine practical and useful variable duration camshaft (with the six listed desirable properties). This is certainly something of a sweeping statement and you would very likely never find a well-known writer, engineer (or whatever) making such a statement, and I never have found such a statement. However I believe it to be fundamentally true. The following arguments are mainly of the type "if they do exist, where are they?" Certainly it is self-evident that there are not many variable duration systems (of the continuous, full lift etc. type) commercially available. There are basically only two possible candidates: - the Rover/MGF VVC and the Ferrari tapered 3D lobe system. Despite various claims on the internet I am not sure that the Ferrari type was ever commercially available. The local Ferrari dealer tells me (a bit of OR here) that he has been working on Ferrari engines for 32 years and has never seen or heard of such a system. The Rover type certainly was available and may be the only true variable duration arrangement ever commercially available. Even though the Rover was very clever (an example of real lateral thinking) and had most of the six listed properties, it had a fatal and insoluble flaw. The flaw was that each valve (or each pair of valves in a four-valve type) in an engine needed its own individual eccentric drive and its own controller. This means eight sets (if both intake and exhaust cams are variable) for a four cylinder engine ( plus four sets of coaxial shafts, chain drives at both ends of the engine etc.) The duration range for the Rover VVC is usually given as about 70 degrees - good but probably not enough for LIVC. Presumably the duration upper limit would be restricted by the amount of eccentricity the cam drive could handle. The final verdict on the Rover VVC must be that it is a very good attempt but it is not ever going to be really successful. Turning now to the Ferrari system. (Actually I only call it the "Ferrari system" for convenience - I have seen essentially similar ideas in the USPTO dating back to the 1940s and there are also quite recent patents in the USPTO with the same idea - 7341032 being a good example). The Ferrari variable duration system amounts to having an elongated cam lobe with different duration profiles at either end - there being a continuous gradation of profile (and duration) between the two extremes. Unfortunately there is a fundamental problem with the concept. The flanks of lobe are no longer parallel with the axis of rotation of the camshaft. In the past (and present for that matter) this problem has been attacked in various ways - one of the most popular being to use a ball-ended follower. In a geometrical sense this works but in practice the surface stress from the resulting point contact means that it is impractical. The other main method is to use a flat-faced but pivoting follower. I am not totally sure but I suspect that this doesn't quite work geometrically. It is slightly difficult to define exactly why it is not a workable idea but the fact that Ferrari apparently never used it would imply that it has fundamental problems. I also think that the duration range would be somewhat limited. Any attempt to produce a really wide duration range would increase the sloping flank problems. At the risk of sounding like an advertising copywriter again, these are not problems that affect the helical cam. Increasing the duration has no effect on how the follower "sees" the lobe surface and, given that there is available space, any duration is possible. There is plenty of information available on the internet about the Rover VVC (by Googling those words). There is less about the Ferrari system on the net but there is a good reference to it in John Lumley's well-known book "Engines- An Introduction" (Cambridge University Press) on pages 63-64. I was not going to write about the BMW Valvetronic as it is not a "full-lift" duration change system (full-valve lift being one of my criteria). Even though the Valvetronic does produce genuine duration change it is better described as a variable lift system. It is in very wide use so I think it has to be written about. When valve lift is directly proportional to valve opening duration (as is with the Valvetronic) at very short duration/low lift settings (something like 0.5mm at idle) the effect on gas flow into the engine is very similar to a variable-lift only system. With the variable lift layout, the duration is unchanged but at very low valve lifts (say, less than 0.5mm) there is effectively no gas flow anyhow towards the beginning and ending of the valve opening period. This shortens the effective duration. It is interesting to note that BMW in their official publicity material tend to refer to the Valvetronic as a variable lift system and don't mention duration much at all. (As an aside here, one of the official-looking BMW websites, "BMW World - Technology", claims that "The Valvetronic engine needs no timing belt or chain." It does of course, and there is an illustration right next to the quoted words clearly showing the chain). The point being that publicity material references are not always of much use. According to BMW the Valvetronic has a very good service record and causes few maintenance problems (despite its apparently Rube Goldberg-esque design). However my personal opinion is that it actually produces little advantage over "conventional" cam arrangements. BMW claim about 10% improvement in fuel economy but I suspect that this is mainly "spin". As I wrote in the main article (if it hasn't been deleted) the Valvetronic's lift at idle is probably too low to produce genuine EIVC effects. The claims of better throttle response etc. are also debatable. It is purely speculation on my part but I suspect that the Valvetronic was BMW's response to the Honda VTEC - a matter of prestige. As several other manufacturers have done, they would have been better off with a licenced VTEC or a VTEC copy. That pretty much concludes the case for commercially available variable duration systems. Only one real contender (the Rover VVC), one possible contender (Ferrari) and one widely used non-starter (Valvetronic).
The next major category is types that never looked like making it into production. This is even trickier than possible commercially available types. You cannot be really sure that a "Wondercam" has not been produced somewhere but has never seen the light of day. Rather than boringly go through all the various proposed schemes to be found in the USPTO files (and the general classifications have about 2000 relevant patents - but these are mainly made up of probably 10 or so basic principles) and point out their flaws etc. it is probably best to attack the problem indirectly. This is returning to the "where are they" approach. If Honda knew of a "Wondercam" why did they choose the stepped VTEC system for production? Honda certainly have patents showing continuous duration range types. Did they know of better systems but chose VTEC just to be ornery? The logical answer has to be that they didn't know of anything better. The same applies to other manufacturers that are using VTEC-type systems (such as Nissan, Porsche and a few others I think). Clearly these companies also didn't know of anything better. Why did Rover develop their unbelieveably complex VVC? Likewise BMW and Ferrari. THe answer has to be that no-one knew of anything better - there is no "Wondercam" and never has been. In Lumley's book the only continuously variable duration system he discusses is the Ferrari which he describes as a "genuine variable valve timing system" (page 63). Without trying to put words into his mouth presumably he considers the Ferrari to be the best of the continuously variable types - better than others he knows of. Also on page 63 he writes of what he refers to as "what may be the ultimate in valve gear" - the Lotus "camless" system - again the implication is that he knows of nothing better, mechanical or otherwise. This pretty much concludes the case for the defence - no all-encompassing reference to prove the point but a lot of indirect material which I think is fairly conclusive.
Having said all the above the surprising thing is that after so many years (and so much effort etc. etc.) there does appear to be a canditate for the title of "Wondercam" - the helical cam. I have been interested in engines and basically all things mechanical for maybe 50 years (I started young). It has always puzzled me a little that there was apparently no useable variable duration system as it didn't appear to be against any of the laws of mechanics, physics or nature in general. I had more-or-less come to assume that it was a similar situation to a mechanical infinitely variable ratio gear arrangement - not theoretically impossible but unlikely to ever happen. Then suddenly, out of the blue, up pops the helical camshaft. Maybe with manufacturing and possible fragility problems but nevertheless an apparently workable "Wondercam". Having had an interest in the subject for so long I felt somewhat compelled to write the main article and this subsequent long explanatory note. One of the main points I was trying to make in the main article was that the appearance of the helical cam was a one-in-a-million (billion?) event. I would be very interested to read any comments that anyone would like to make - especially regarding possible contenders (past or present) for the title of "Wondercam".

Note 2. This note is in response to the call for more explanation and discussion about the "dubious" statement "it appears to employ a previously unknown principle in its essential helical movement". The meaning intended here is not to imply that helical mechanisms are unique - they are, of course, quite common. The intended meaning was that within this general group of variable duration camshafts of the "combined profile" type there was no known camshaft apart from the helical camshaft that used a helical movement in a similar manner. With the "combined profile" camshaft typically two adjacent cam lobes (with a small angular region of constant radius on their "noses") are aligned for minimum duration or progressively misaligned to increase the duration - a single follower covering both lobes. The resultant movement of the follower is thus that of the combined profile (hence the name for the general group) of the two lobes. Without known exception the relative movement of the lobes is strictly one of pure rotation about the axis of the camshaft with no movement along the length of the camshaft's axis. In a sense the motion is two-dimensional only. The fundamental problem with this layout is that the maximum duration range is restricted by the necessarily limited small constant radius area on the lobe's nose (see 1527456 for the general idea. Note that it is impractical to use as much constant nose radius as that shown in the patent). There is apparently no known method to get around this problem. The helical camshaft is different in that the relative movement of the two lobes is not purely rotational but has an element of lengthwise movement, thus making the overall motion helical. In a sense the movement becomes three-dimensional rather than two-dimensional. Even though a small area of constant radius is still needed on the minimum duration profile, there is no geometrical restriction on the amount of duration possible (just some practical ones, like lack of space for lengthwise movement). There is no other known camshaft of the "combined profile" type that uses a helical movement of its modifying elements to change the duration.
The problem then is to produce evidence for this claim. There seems to me to be a slight contradiction here with logic. To prove something exists, one produces references, articles, photos, drawings etc. or ultimately the object itself is produced. In contrast NOT being able to produce any of these things does not prove that something does not exist, just that there is a likelyhood that it doesn't exist. All I can produce in the way of evidence is that I have never seen, heard or read of a device similar to the helical camshaft. And neither has anyone else I have asked. I have seen copies of the USPTO patent search which turned up several examples of helical mechanism being used to produce various variable timing effects but nothing like the helical camshaft. There was only one patent cited (from the 1920s, if I remember correctly) that used the helical movement in even a vaguely relevant way but this was on the base circle. I would have to say that the inventor's use of a helical movement was "accidental". All this is not to say that something like the helical camshaft design does not exist in the files of some foreign patent office or even just "exists" somewhere else. So the case for the helical movement being totally unique is not proven definitely, but the implication is strongly in favour of it being unique. Certainly the evidence is strong enough for me to make the "dubious" sweeping statement. As with Note 1 I would be very interested if any reader does have relevant information. Clivedog (talk) 03:31, 27 December 2008 (UTC)

Cleanup

Some very good info here and pics, but I think this needs quite a bit of clean up work and maybe some rewriting to condense it a bit. Also, some parts feel like they've been pulled from an advertisement and should be removed.

Plagerism?

It appears almost the whole, if not the whole thing has been copied from http://www.helicalcamshaft.com/. I don't known if that website is GFDL compatible though. I have an odd feeling one of the editors is the own though, and can clear this up. Wizard191 (talk) 16:57, 1 December 2008 (UTC)

Sorry about the problems. This is my (Clivedog) first attempt at Wikipedia writing and I have found it extremely tricky - to put it mildly. I understand only a fraction of the various rules etc. relating to Wiki matters. I certainly do have copyright permission to use the material in the website. I was originally writing a totally new article but then I saw that it was heading in much the same direction as the material on the website. I decided then to basically rewrite the website article but make it more neutral and leave out anything that appeared to be promotional material etc. I thought it was a bit over-long myself. You (Wizard) appear to have a distinctly engineering background (or interest in engineering) so perhaps you can suggest where changes can be made or do a bit of editing yourself. Is there a form or whatever I should fill in about the copyright matter? —Preceding unsigned comment added by Clivedog (talk • contribs)

Not a problem, please see your talk page for a continuation of the discussion. Wizard191 (talk) 04:13, 2 December 2008 (UTC)

Advertisement/POV

My recommendation for this article is to decrease the amount of point of view comments (POV). It reads like a advertisement because it makes the helical camshaft out to be the best cam ever invented and nothing even comes close. While this may be true, its an extreme POV and would require a LOT of references to back it up. As such, the POV needs to be neutralized. Spend more time talking about what it does, how it works, applications and future, than how it is better than any other VAA (camless or mechanical). There's nothing wrong with noting its advantages, as long as the disadvantages are laid out too. Create a "Advantages and disadvantages" section to do so. Wizard191 (talk) 02:44, 12 December 2008 (UTC)

From this link I see that this article is linked to Internal combustion engine, Grand Prix motorcycle racing, Poppet valve, Camshaft, VTEC, Variable valve timing, Overhead camshaft, Overhead valve, Homogeneous charge compression ignition, Motorcycle engine, Camless, Valvetrain, Cam-in-block, Pneumatic valve springs and Variable valve actuation. I'd be very surprised if this article is really relevant to most of those. TomRawlinson (talk) 20:24, 13 December 2008 (UTC).

You are right, most of those links are probably unnecessary. Wizard191 (talk) 20:32, 13 December 2008 (UTC)

My guess is that this design is so non-notable that it should not be linked from any of the major articles above. Perhaps leave at Pneumatic valve springs and Variable valve actuation only. TomRawlinson (talk) 20:41, 13 December 2008 (UTC)

Agreed. Wizard191 (talk) 20:53, 13 December 2008 (UTC)

I've left it at Variable valve timing, Homogeneous charge compression ignition, Camless, Pneumatic valve springs and Variable valve actuation. If this gets me in a shit-load of trouble I'll expect you to back me up! TomRawlinson (talk) 21:20, 13 December 2008 (UTC)

Haha, you won't "get in trouble". The worst thing that can happen is someone reverts it. But in either case I'll back you up. Wizard191 (talk) 21:51, 13 December 2008 (UTC)

I just wanted to drop a line on this talk page noting that this is a fascinating mechanical concept I hadn't been exposed to. It'd be great to see some more references and perhaps external links if there are any. 69.193.11.2 (talk) 21:37, 27 January 2012 (UTC)

Try Googling "helical camshaft" - the company's website is first in the list of "hits". The website is quite interesting (if you are interested in the more radical aspects of VVT). The whole thing is a little long-winded but has some interesting video segments as well. I think it is probably the most comprehensive description of the HC system available publicly. There is some more interesting material on the Wiki article "talk" page as well (- in case you didn't see it). Clivedog (talk) 07:39, 1 January 2013 (UTC)