Engine valve control: camshaft or electronic control

[harrylu]

I just watched a video by Koenigsegg engineers and came across this question. Why is camshaft the primary control of the engine valves? Using electronic controlled actuators would certainly benefit the engine in aspect of performance, but might increase the cost of production as well. People now implementing variable valve timing systems but why not just use actuators? Anybody know any cars running on camless engine?

 

[jack action]

People have been working on this for a long time:

in '97: http://www.thefreelibrary.com/Aura+Systems+Receives+Follow-on+Contract+from+Yamaha+Motor+Corp.+to...-a019262778

in '01: http://www.grandprix.com/ft/ftpw012.html

in '09: http://www.popularmechanics.com/cars/news/4261289

 

[Ranger Mike]

excellent Jack...

 

[harrylu]

People have been working on this for a long time:

in '97: http://www.thefreelibrary.com/Aura+Systems+Receives+Follow-on+Contract+from+Yamaha+Motor+Corp.+to...-a019262778

in '01: http://www.grandprix.com/ft/ftpw012.html

in '09: http://www.popularmechanics.com/cars/news/4261289

Thanks for the info! What I was really wondering is why no companies use this in production engines? I do have some thoughts in mind, such as: the camshaft is more reliable, it's cheaper to produce and maintain. But it's just not enough to convince myself. Is there any other reasons?

 

[jack action]

But it's just not enough to convince myself. Is there any other reasons?

From http://www.grandprix.com/ft/ftpw012.html:

On a "paper engine" that represented a 3l, V12, optimizing valve timing and lift for all RPM between 6,000-19,000 showed benefits below 8,000rpm, but little difference above that figure.

Mario Illien, Ilmor-Mercedes, has gone on the record against LVA on the basis that the power consumption would be too great. The need to accelerate each of the 40, 40gm (1.4oz) valves and associated hardware at around 4000g requires an actuator force of 1600N (360lbf). He also stated that valve to piston clearances are around 0.2mm (0.008 in) and so the precision needed in controlling the valve position would be problematical. Also, the heavy electromagnetic coils and magnets would be above the CofG of the engine and so raise it overall.

So, little benefit versus questionable feasibility means LVA is most unlikely.

From http://www.popularmechanics.com/cars/news/4261289:

In this design, automotive supplier Valeo replaces the intake camshaft of a twin-cam engine with electro-magnetic valve actuators, instead of the more pricey and complex approach of replacing both camshafts with these cam actuators. The intake-only approach offers improvement in fuel economy between 16 and 19 percent--very close to the results with two sets of actuators. The improvement comes from infinitely variable valve lift and timing--without requiring a 42-volt system. This is still a comparatively expensive step, but it offers a big improvement and could be cost-effective down the road.

 

[psycho rich]

The springs must rob a lot of horsepower ,it's hard to turn over a motor by hand (spark plugs removed).

 

[jack action]

The springs must rob a lot of horsepower ,it's hard to turn over a motor by hand (spark plugs removed).

Actually no, springs don't take power away. What ever is needed to compress them is given back when they go to their original length. A spring is a mechanical device that stores energy, it doesn't consume it.

The force you are fighting when turning an engine by hand is the friction between the mating parts (piston-cylinder, bearings, etc.).

 

[Doug Huffman]

With the plugs removed, my Caracci 52 Hp F-Vee engine was easily turned by hand.

 

[psycho rich]

How much of the heat generated is from burning fuel / friction?

 

[jack action]

How much of the heat generated is from burning fuel / friction?

Based on this definition of friction MEP, around 10% of the energy is used to fight friction at idle, 20-25% at maximum power and up to 33% for an engine like the ones found in top fuel dragsters.

For a 2-stroke engine, it should be at least 7% less because there are no camshaft or accessories to turn (oil pump, water pump, etc.).

 

[OldEngr63]

There is a fundamental difficulty in using electromagnetic actuation for engine valves. A fairly large force is required to open the valve against the valve spring (the spring is required to seal the valve against the seat when the actuator is not energized), and this requires a relatively large solenoidal force. That means high current through a large inductance, but the large inductance resists changes in current through it. Valve actuation times are very short, so the change in current must be very quick, hard to do with large inductance.

For comparison, consider a rail gun. There, it a very large current is required with a quick rise also, but they go to extremes to keep the circuit reactance very nearly zero (a few milliohms at most). This is very hard to do in a production item like a solenoidal actuator for an engine valve.

Some might suggest the use of something like a piezoelectric instead of a solenoid. That would give you a much quicker rise, but the stroke is very, very small. You can use a linkage to multiple the stroke, but at the expense of a loss in force. To compensate for the force loss, you can ask for more piezoforce, but that means more current (and heat) in the piezoelectric.

There ain't no free lunch!