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View Full Version : Lotus Engineering's Fully Variable Valve Train



78Z
11-10-2003, 11:59 PM
http://www.baileycar.com/AVT_html.html

lawguy
11-11-2003, 01:19 PM
The camless- infinitely variable valve system is a bit of a "Holy Grail" for engine designers. Just think of it. With the right system, not only can you get impressive power and economy gains through better control of combustion over the entire RPM range, but gains can be had through the elimination of throttle butterflies and controlling airflow with the valves alone.

Also, the starter motor can be eliminated and the engine can be shut down at stop lights to save gas (without an electric motor to fill gaps like the Prius).

Super 7
11-11-2003, 02:31 PM
It will be here someday, I'm sure.

I saw photo's of a BMW with electromagnetic valve actuation a few years ago. It could only run at low RPM as I recall.

I wonder they don't use air like the F1 motors do to close valves. Not positive enough?

MattP
11-12-2003, 04:31 AM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Super 7:
It will be here someday, I'm sure.

I saw photo's of a BMW with electromagnetic valve actuation a few years ago. It could only run at low RPM as I recall.

I wonder they don't use air like the F1 motors do to close valves. Not positive enough?<hr></blockquote>

I noticed that they said Electro-hydrolic. I know that Hydrolic fluid has less compressability than air, maybe they felt that it would give closer control of the system. Plus the system could be pressurized and they just by servo operating a piston or even with a stepper motor. where I would think the air would require some sort of compressor.

MattP

PC
11-12-2003, 02:27 PM
I like that quote in the article "it is just control of an actuator." The elusive element has always been coming up with a controllable actuator that could do the job, run at real engine speeds, survive in the engine environment and function for a useful period of time. Until now there have been systems that ran but never had all of the attributes at the same time. Once you have all of those you still have to figure out how to build them at a reasonable price. A daunting task indeed.

At $5k to $7k for each valve they obviously have along way to go. What it didn't mention was how fast they can rev or how long they last. It also doesn't mention what kind of outboard support equipment the R&D systems require, power supplies, hydraulic pumps, etc. It will be very interesting to see where it goes.

I've only read one description of F1 pneumatic valves and that was on some guy's website so I can't vouch for how accurate it was. It said that the systems were relatively conventional in that they used air as a replacement for mechanical springs rather than as controlled actuators. That makes sense, air makes a nearly ideal spring in that it has near zero mass and doesn't fatigue or break. Your rev limit is higher and doesn't degrade over time as with metal coil springs. You do see guys pulling into the pits to top off their air though.

Whether you actuate with mechanical, hydraulic pneumatic or electric mechanisms it will take energy to move the valves. One way or another some form of crank derived drive, hydraulic pump, compressor or generator will be needed.


PC.
graemlins/hammer.gif

lawguy
11-14-2003, 12:57 PM
I think that it will always come back to some electrical component, no matter whether hydraulic or whatever. In the next several years, you will start to see 42 volt systems which will help. I predict that once the 42 volt systems come online, there will only be one engine-driven accessory- the alternator. Everything else, from power steering, to A/C to whatever, will be electrical.

Roger
11-14-2003, 07:05 PM
Liquids like hydraulic fluids have zero compressibility - this makes them ideal for controlled valve opening. Air for closing is o.k - it does compress but as such acts pretty much like a spring.
F1 cars must have camshafts I think - and they must be steel. I need ot look up the regs but I tihnk that's so.

PC
11-14-2003, 08:39 PM
Yes, actuating a valve with air is slowed by the delay of the actuator building enough pressure to move the valve mass. The problem with liquids is that they have significant mass and viscosity, two properties that are problematic for high-speed operation. As with all engineering, it's a balancing act.

As I understand it the air in F1 engines is used more as a spring rather than actuator. Cams open the valves against the force of the air springs and the valves are then closed by the air springs. This works just like a coil spring because air is compressible, a near perfect spring. The added benefits of air are that it has low mass and does not fatigue.

In a coil spring valvetrain revs are limited by the springs' ability to keep acting as springs. At some speed they will not be able to move fast enough and with enough force to close the valve due to their own mass and internal friction. The valves "float" rather than close. Due to fatigue that speed declines during use. Race engines will often lose top end revs over the course of a single race. In a motor with tight piston to valve spacing they can crash.

Air springs are not subject to fatigue but do suffer from seal friction and leakage. Again, it's a balancing act.

Mercedes and Ducati have had success with mechanical valve actuators that did not rely on springs. Their Desmodromic engines use rockers to close the valves. Desmo velvetrains do have the drawback of higher mass than spring systems. These of course have fixed, not variable lift or timing.

If anybody out there has a definitive description of how today's F1 motors really do work I'd love to hear it.


PC.

MattP
11-17-2003, 12:40 AM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by PC:

If anybody out there has a definitive description of how today's F1 motors really do work I'd love to hear it.


PC.<hr></blockquote>

Fast.

Just couldn't resist. images/icons/tongue.gif

MattP