jniemeier Posted: Sep 25 2005, 06:51 PM

Someone asked about schools. I have no special advice about that. Find a school that has a solid Mechanical Engineering program. Most state universities do. Specialization comes in your masters program, should you go that route, and most people advise going to a different school for your masters anyway. Getting a degree is to teach you to think, and what get's you in a company's door. Actual useful knowledge starts when you get to work. That said, it's a good idea to pay attention when they teach IC Engines by Obert. (See above) I took it from a German, ex-VW engine guy whom we were legitimately afraid of.

Electric Valve Trains: Now there's a subject we could all debate for weeks. Basic benefit: Changing the duration of the lift event on the fly. Think of the motion of today's cam and spring driven valves. Cam design programs calculate four derivatives: (you paid attention in math class, right?) displacement, velocity, acceleration, and jerk. Even the jerk has to be smooth, if that makes sense. There's a whole lot more to it than lift and duration. Ok, fine. Chances of replicating this motion with an electrical solenoid? Zero. But do we need this gradual start - fast lift - gradual stop type motion? Well, if you want to keep from fracturing valve stems, you sure need to gradually close the valve. The solenoid guys call this "soft landing", and I understand there are patents for that via reversing the current at just the right moment. How do you know when the right moment is? You now need a valve position sensor. And it better be a darn fast one considering how fast the valve is moving much less the extremely nasty environment (see earlier posts). If you can do the soft landing, how much juice will it take to run the solenoids? Last I read, a couple research firms said they could do it with 1.5 kilowatts for a 16v four cylinder. Not terrible, but still too much, and I don't think it's been demonstrated either, although EMVT cars have certainly been driven around. (I'm sorry I don't know right off how much power it takes to drive a 4 cylinder's cam- but keep in mind that when the follower is on the back side of the profile, the spring is returning energy to the system not consuming it.) After we figure out lift profile, soft landing, position feedback, and power consumption, we still must face reliability of elec connections, packaging it to fit, noise (very important), lubrication, cost of the solenoids, cost of the control electronics, packaging of the control electronics, manufacturability and of course durability. It's a huge challenge, but what's new? There are a lot of bright guys in research companies who thought they could do it. Notice I've switched to past tense. I think full electric valve train is a pretty cold trail. One caveat though: HCCI combustion (Homogeneous Charge Compression Ignition) could be a huge efficiency improvement, but may require VT control like electric valves. If you want to know about HCCI, you'll have to look it up. I can't explain it very well. Think of controlling a gas engine like a diesel. Extremely tough, although I think this one will ultimately succede.

The fully variable valvetrain that's in production of course is BMW's Valvetronic. It changes lift and duration at the same time. We designed a system that did this also, but we could never get it cheap enough to sell it. I guess BMW has a different view of the value equation for new technologies. Interesting question: how much valve lift does it take to idle a 4 cyl engine? 0.3mm or even a bit less. That's amazing. And you can do it at 500 rpm or so, which saves a bunch of fuel. Turns out cars spend a lot of time idling.

There are a bunch of systems that change lift in two and even three steps. Most famous is Honda's VTEC. They have at least 6 variations of it in production, including on the new 3 liter V6 that does high and low lift and cylinder deac in the same engine. That is fantastic, and no doubt comes close to the benefit of Valvetronic for a lot less money. The Mitsubishi MIVEC system can do three steps and has been around for a while. Porsche have a two step system on the Turbo which is made by INA of Germany. Then of course there's cam phasing. That's old news, and on most cars these days.

The system that I've just read that IS going to enter production is Fiat's Electro Hydraulic VT. They sometimes call it UniAir. Electric solenoids open a high pressure oil circuit which has an actuator to open the valve. This sounds like a good idea, but the hydraulic fluid was always a challenge. The viscosity change due to temperature was a killer. Evidently FIAT have solved that problem. They will use it on a diesel (lower redline) starting next year or so. UniAir can do variable duration and lift by basically truncating the lift profile when it's had enough by dumping the oil through a relief valve. Should be great if it works. I actually met Dr Petronio, the father of UniAir once. (I was selling, but he wasn't buying!) He had been working on it for years at that time, and you could just tell that by-God he was not going to give up. Sometimes, even in a corporation the size of FIAT-GM Powertrain (they've since split up) it boils down to one very tenacious guy. In fact, I think it almost always does. That's interesting, eh?

Oh, and don't bother trying to dream up other "gates" or types of valves besides poppet valves, like the spherical rotating ones you read about. Talk about patents- in valve types, everything has been tried before. Nothing will seal combustion pressure like an inward opening poppet valve. No matter what system creates the opening and closing motion, today's poppet valves will always be used in piston engines. And don't even get me started on ported two strokes.

Pop quiz: How does a Ferrari valve get a larger lift profile than the what's ground into their cam?

Now, if I write any more you guys are going to have to start passing the hat. I'm going to bed.
Jim N.
'73 2.0 with a nicely lashed, single return spring, pushrod and rocker arm mechanical valve train that I can fix and adjust in my garage.