It comes to mind while reading another thread that valve timing with a cam and rockers is a bit old fashioned. I mean it would be no sweat to have ECU controller actuators electronically control both the timing and lift of the valvetrain.

Is there a car with such a system? It would seem to me you could tune a lot better.

 

I believe the new high end BMWs will all be equipped with that.

It would be very cool, wouldn't it? Having the perfect valve lifting timing for every RPM range?

 

An Electro-Magenetic Valvetrain is something of a holy grail in the Formula 1 racing community. But thus far no one has developed a system that works any better than the current cam based ones. The word is that both Honda and Renault may have EMV systems working this season.

Many have said that there is no real advantage in EMV as the cam shaft does a lot of work very quickly and with very few moving parts. An EMV system will have a Whole Lot of new parts (and more parts to break). Just think of all the servos and wires and such that will be required at each valve.

EMV does have advantages though, electrically you would be able to open and close any valve at any time. Pretty neat stuff, but I have no idea if there is any real advantage in that.

The rumor is that neither Honda's new system nor Renault's is totally electrically operated and neither will be camless. I can't imagine that this technology will filter down to the street any time soon, even if it did I wouldn't want to be the first on my block with an EMV car.

[Edited by Mikey on 04-12-2001 at 11:32 PM]

 

What's also interesting is Saab's Variable Compression technology - a lot more power from a smaller displacement.

Details http://www.saab.com/home/GLOBAL/en/index.xml

 

The automakers have spent a fortune working towards electromechanical valves. As it became clear over twenty years ago that cheap microprocessors would be available, infinitely adjustable valves were a target.

It is just a hell of a lot harder to rapidly control the openings to a chamber that has huge pressure swings and rapid movement of gasses than was anticipated.

It has worked in a lab but it is slow to refine and mass produce economically compared to the existing technology that has evolved for over 100 years.

 

I've seen some videos of a Ford Explorer with a V6 that has electro-magnetic solenoids to actuate the valves. As I understood it, the biggest problems now are the size of the solenoids that are needed create really big EM fields and they are also very loud and the EM field doesn't collapse quickly enough to allow the actuators to work at higher rpms.

I thought the F1 motors used pneumatic actuators on the valves?

 

I also thought they had been using pneumatic valve actuation for some time now in F1, but I could be wrong. I heard the real problem with EMV was that they couldn't figure out a way to keep the solenoids used to actuate the valves from overheating.

My understanding is that the vario-cam technology or whatever they call it on the Toyotas is like VTEC with a clutchpack of some sort at the cam gear. Just one more thing to break.

 

There is a company here in the states which already has such systems running on road vehicles in a prototype stage. They recently drove a semi truck (tractor only) to the top of Pikes Peak equiped with such a valvetrain.

There are still a number of limitations as follows:

1. Operating speed - it is still difficult to get the solenoids used to operate quickly enough to meet the needs of modern, high rpm engines. Hence the first test on a diesel, which probably doesn't see more than 3500-4000 rpm. This is a problem that can certainly be solved with time.

2. Power requirements - existing 14v auto systems just can't provide the necesary current to make these things work. It takes a lot of energy to move a 80-100 gram valve up and down 12-13 mm at 60-70 Hz (think about how much energy it takes to drive a large subwoofer to those excursions)

3. Durability - how long will these solenoids last? A car that averages 3000 rpm at an average of 40 mph for 100,000 miles will see a total of nearly half a billion cycles on the solenoid in a 200 degree F environment. Again, this can be overcome with time and development, but I don't know if I'd want to own the first example :-).

Part of the operating speed problem can be accomplished by using a traditional valve return system (spring or pneumatic as in F1). This limits your energy output to only the opening cycle. It does not necessarily cut your output in half though, as the prototype systems now working have a rest position that is half open - IOW, it takes energy to fully open or close the valve. This setup may also improve lifetime since the system may have more off time.

The big piece of the enrgy puzzle will be the new 42v car electrical systems coming on line in the near future.

On the BMW front, they introduced a prototype infinitely variable lift system a couple years ago that they said would eventually make it to production. It uses a separate cam to vary the rocker ratio of the cam. Thus, it still has to work off of a basic cam, but hte variable rocker allows you to change duration and lift, within reason. The hope was to be able to throttle the engine using only the valves (light throttle = small valve openings), although I think thta will be pretty tough. It would elimintae a lot of pumping losses though by getting rid of the throtte body.

UL

 

Formula One cars do use a pneumatic valve return system. It replaces the valve springs but not the rest of the system. All current F1 cars still have a cam.

Pneumatic systems are ok for F1, but will probably never make it to average road cars. The gas lost during use needs to be replenished by a pressurized tank and refilled on occasion, not very user friendly.

 

Actually, Ducati, an Italian motorcycle manufacturer, has long used "desmodromic" valve actuation. This direct/captive valve actuation opens and closes the valve with precision - no springs to float...