Unless you’re directly involved with engine design, it’s hard to keep up with all of the creative methods engineers have used to integrate variable valve actuation into a standard internal combustion engine. In this day of computer controls, you would think mechanical methods would be losing ground, but I received a note from Danny Williams about the Williams Helical Camshaft and it’s pretty neat.
The helical camshaft has a cam lobe design that changes duration as the cam is twisted. It goes from relatively short duration to almost as long as you like. They made a replacement for a 250cc Suzuki camshaft to demonstrate how it works and it seems to do the job.
The precision of computer control and electronic actuation of each valve without even using a cam strikes me as the high tech future instead of using mechanical means where a cam is involved, but a mechanical method might work better in smaller or less expensive engines or it might be better in all sorts of engines. Like I said, unless you do this sort of thing every day, sorting through the pros and cons of each system is difficult.
There is a lot of material on the Williams website going into great detail plus a number of videos. For those who prefer to see a solution machined in metal instead of designed on a computer, the helical cam is worth a look. Check it out.
Link: Williams Helical Camshaft
Link: Wikipedia – variable valve timing
Oldyeller8 says
Back in 1984 my race mentor/mechanic/endurance race team manager told me of a cam design he had come up with and wanted to run it by me. So think on it. Rubber Cam lobes…
Increased lift and duration with increased RPM.
A little ahead of his time I think!
Mike says
I love this technology. After spending 2 years working on VVT and phasing, this looks very interesting. I have issues though with the ultimate usable duration. I understand this design is capable of essentially infinite duration, however what use is that? The best scenario is to have valve lift coincident with the piston moving downward (negating mass flow), and closing as the piston changes direction (again negating mass flow). Obviously you cannot negate mass flow, so the duration will be longer, however where is the limit? When I was working on VVT, the holy grail (for maximum HP) was to accelerate the valve as quickly as possible to maximum port flow, hold at that position for as long as possible, then close the valve as quickly as possible. There are obviously physical limits in the valve train that limit this ability, however that would be the best for max HP. How is minimum lift accomplished? The advantage of the BMW system (or electro-mechanical) is to vary air flow into the engine via valve lift, hence ultimate open duration. This system simply deals with duration.
I like the idea though.
Mike says
The BMW system (or electro-mechanical) eliminates the need for throttle plates, hence no intake tract vacuum, but couple that with direct injection, could be the best case. This Williams system still have standard intake tract, but with variable duration. Interesting…
Ian says
Infinite lift duration I can think of being useful for easier starting at least:
Open the valves, spin the starter motor to get some momentum in the flywheel, then snap then pump in precisely the right amount of fuel for per-cylinder firing and snap into proper valve timing again.
Lower power requirements as it’s not have to compress while it’s spinning up so, maybe, smaller battery, lighter starter-motor. Every little helps.
todd says
Pretty cool. There was a guy that lived a few blocks from me (Bob Walters, Logicam, Dial in Cams) that made centrifugal advance cams and variable ratio rockers for VWs in his garage. I have a special cam and lifter set he made for me in my bug -20 years ago-. It would be interesting to see if I can bother him to come out of retirement and come up with a tiny motorcycle version…
I think non-cam based valve actuation allow nearly infinite control of valve opening, duration, and overlap that you can’t (easily) get with a cam shaft. the idea is to develop it so far that you eventually won’t need a throttle.
-todd
Paulinator says
Pretty cool? That’s really cool!
Opening the exhaust valve is a major event. By the time you add the complexity of electro / pneumatic / mechanical magic to remove the bump-stick, why don’t you keep going and remove the crankshaft, too? Run a free piston engine that is optimized at a specific rpm for your electric drive….Or embrace this purely mechanical technology until the next viable major leap is taken.
rich peabody says
I grew up trying to get VaryCams (sp) to work….a rubber cushion on the cam sprocket…bent a bunch of valves once…..made the car significantly slower once….but I still like the idea!
I know that Chrysler had a running V-10 Viper engine at the time they were introduced that had solenoids as valve actuators…and could be controlled by the on-board computer….Chrysler sought to have electricity (and computers) control everything mechanical…
Neat stuff! Thanks!
David/cigarrz says
Nice! Interesting technical post Kneeslider, love the brain gymnastics, enjoying their website.
Robert Jamieson says
Bearing in mind that this development is fairly “low tech†in its approach (i.e. does not rely on state of the art computerised, camshaft-less valve actuating systems that the major automotive manufacturers are apparently developing for their next generation models), what would be the likely market(s) for this camshaft ?
Would it be possibly a way for developing nation manufacturers to obtain more performance (both output, and fuel economy) from their necessarily simpler designs of motors ?
Or maybe, seen as an after-market sales opportunity for camshaft developers in, say, the United States ?
Danny Williams says
I thank everybody for their interesting comments.
Mike – the cam doesn’t exactly have infinite duration – but it does have theoretically 720 degrees which is much the same effectively – the valve would never really close at 720 degrees duration.
You are also right about excessive amounts of duration. For outright performance purposes maybe 60 degrees of extra duration is all that could be used.
For throttle-free engine load control possibly more than 60 degrees could be used but the Suzuki engine under test idled at 45 extra degrees of late inlet valve closing. There is a video of this on the website. The somewhat spectactular 40% of improvement in idle fuel consumption is also genuine. Possibly partly because engines like the GSX 250 (two cylinder/twin cam) are notably not very fuel efficient at idle. An injected multi-cylinder car (or bike) engine would probably not show the same gains in idle fuel saving but there probably would be a very useful saving. Note that the fuel saving and high RPM power gains can both be in the same engine with the appropriate controls.
Mike also – there is no reason that the helical cam could not be used as the “driver” in a BMW-Valvetronic type of valve gear layout – this would give an even more ridiculous range of lift/duration combinations but most would have little relevance to four-stroke cycle theory.
Bart says
Danny – Thanks for sharing this here. It is an intriguing design.
The “extra” degrees are employed at the intake valve closing event, right?
So when you say you have added 45 extra degrees of late closing for idle control, that puts you out somewhere around 85 deg ABDC, is that right?
If so, does that mean the inlet port “double pumps”, is the charge being sent back up the inlet port at such a high late closure event? (because port velocities/charge momentum is so low at low revs/loads)
In my experience engine building, less duration and an early closure of the intake valve would be the way to get idle speed/part load control.
What am I missing here, curious mind wants to know!
jim says
Good compromise between ultra-expensive, computer-controlled camless systems and complex VVT systems. It certainly can provide performance gains — the VVT system on the Toyota 2.7-liter four in my Tacoma makes it run like it has a good six under the hood.
The purely mechanical approach has its attraction, especially for retrofiting in older engines and third-world markets, but I think the future in valve actuation is in solenoids or hydraulic systems as in F-1. The Holy Grail is instantaneous opening and closing with infinitely variable duration and lift for all operating conditions — and mechanical camshafts will never be able to deliver that, no matter how tricky.
todd says
Bart, the assumptions is that the degrees are measured at the crankshaft, not the cam.
-todd
Mike says
Bart makes a good point about double pumping. Is this system going to create an ultra-rich mixture, creating emissions issues as presented with the CV Carbs installed? Obviously if this was incorporated with a direct injection system, I can see some interesting economy and HP gains.
Bart says
todd – I have same assumption as you, talk’in crankshaft degrees here.
mike – my baseline assumption is that a typical high perf motor like Danny used here will have intake closure around 40 deg ABDC. Adding 45 deg to that gets 85 deg ABDC. It could work because the double pumping would be at low manifold vacuum (there wouldn’t be much work being done by an idling piston to shove air out a big open hole) and then at valve closure there would be only minimal compression done, just enough to meet idling load. I think its just a motorhead communication gap here.
Also, I think the motor he used has fuel injection, but I’m not sure; I don’t keep up with all the motocross stuff. You’re right if it were carbed, it might double pump fuel with a carb at such long durations. But timed fuel injection can beat that problem down.
OMMAG says
The big advantage of the mechanical solution (helical cut cam) is that it is simple.
Simple ….. the first rule of engineering design … KISS.
Williams follows the rule … I predict success.
Bob Nedoma says
When it breaks down, can I fix it myself (and/or) can I afford to get it fixed, that’s what matters, as far as [this one] invention is concerned. There is enough of throw away stuff out there already.
Danny Williams says
Bart – THe Wiki article below has some graphs at the end of it which were measured directly off the cam in the photos and videos – so you can see for yourself what +45 degrees would be.
http://en.wikipedia.org/wiki/Helical_camshaft
The engine as tested was (apart from the cam) exactly as Mr. Suzuki made it. I had originally thought (before it ran) that I would need big-volume plenum chambers etc. to stop the backflow caused by the LIVC upsetting the carbs. Despite many hours of running I have no idea why there is no sign of backflow. Even at +85 degrees nothing is obvious. At +85 (zero on the compression gauge) the engine turns over on the starter as freely as if the sparkplugs were not fitted – so it could be handy for starting a high CR engine (a diesel maybe?)- as somebody commented.
Speaking of diesels – modified long-duration cams can’t be used in diesels because they then won’t have enough cylinder pressure to ignite the fuel for starting or at low RPM. Using this cam would allow the use of longer duration cams in diesels – just how much this would help power output remains to be seen.
The measurements are in crankshaft degrees.