Stepless VTEC

[manolis]

At www.pattakon.com a new Continuously Variable Valve Actuation system is presented, with working prototype photos, plots and animations (even stereoscopic ones).
Any engine, racing or normal, can be improved as the torque can be about constant from very low revs to the top allowable revs of the engine.

Comments? Objections?

[Hobson]

I think this thead will do better here than Trackdays.

[LandOfSnow]

BMW use this type of system in a even more advanced level on almost every current production engines (not sure about the 6-cyls). They call it valvetronic, these engines don't have the throttle butterflies at all. The throttle pedal directly changes the inlet valve lift. The torque still isn't constant though...

[manolis]

Originally posted by LandOfSnow
BMW use this type of system in a even more advanced level ....though...

The BMW’s valvetronic system comprises a basic variable valve lift mechanism and a lot of supporting systems.

The basic valvetronic mechanism, which actually achieves the continuously variable valve lift, is not “advanced”.
From one side it comprises a lot of constituents parts, a lot of interfering joints between cam lobe and valve stem, a lot of additional strong springs, a lot of reciprocating rollers, a lot of wear concentration points, a lot of inertia and friction limiting the revs limit and a lot of additional engine height.
From the other side when the basic valvetronic changes the valve lift (only the intake valve lift because it is not capable of controlling exhaust valves) it also changes the duration the valve is opened. For instance, if you need 1 mm valve lift, then you necessarily have 40 degrees valve opening duration. And if you need 180 degrees duration of valve opening, the only available valve lift is 8 mm. It also provides the valve opening not when the piston is near Top Dead Center but when the piston pass from the middle of its stroke, making absolutely necessary the cooperation with an efficient continuously VVT of wide angle.

In the low revs valvetronic cannot operate effectively with heavy load. Take for instance the case of 1000 rpm with full load. To fill the cylinder you need a very small valve lift – let say 1 mm – with valve duration of about 180 degrees. But the valvetronic can offer either 1 mm valve lift with 40 degrees valve opening, or 180 degrees with 8 mm valve opening. So the valvetronic has to compromise and finally to operate as a conventional valvetrain system, losing the benefits it claims it offers, that is extreme turbulence and swirl with perfect mixture homogeny.

As a confirmation, many journalists testing the 1.8 and 2.0 litter four cylinder valvetronic BMWs complained for lack of torque at very low revs.

But the system has also limitation at relatively high revs (due to inertia, friction and wear). The “deliberate” gradual fall of the torque at high revs obligates the driver to use the next gear in gearbox and return to the efficient (and safe for valvetronic) range of revs.

The case becomes strange:
On one hand, a VVA system seems theoretically the perfect tool to make an engine operate efficiently in a wider range of revs, compared to conventional.
On the other hand the BMW’s valvetronic VVA mechanism itself restricts the revs range of operation, at low lifts due to inherent design characteristics, at high revs due to its strength, its internal friction, its inertia loads and its excessive wear.

The supporting systems come to cure the weaknesses of basic valvetronic. A powerful CPU with strong software, a continuously VVT of wide angle (they call it double vanos), a high speed network, a number of electromotors and sensors, a drive by wire system and so on. Actually, the valvetronic mechanism alone, that is without the supporting systems, could not work even for a second, and it could never be installed on cheap and light engines.

So, even though BMW’s valvetronic is an absolute commercial success offering better economy, lower pollution and improved drivability than conventional and two step VVA systems (like Honda’s VTEC, Toyota’s VVTLi, Porsche’s Variocam Plus etc), it does have a lot of weaknesses, and its level is not so advanced when you examine it in depth.

If a continuously VVA system could combine the power output of Honda’s S2000 VTEC (120 PS per litter in normal production) with the economy, drivability, easy starting, low pollution etc of BMW’s valvetronic (if possible without additional supporting systems like VVT, CPU, network, drive by wire, electromotors etc) then it would be a very good system indeed.

Thank you.
Manolis Pattakos

[RWC]

Very well explained manolis!

[RWC]

The link is interesting.Kind of 'a cam following a cam' or like using a variable wedge (simplistically)
I don't know why some one don't just invent a camshaft with tapered cams and swiveling followers.Adjust the timing and lift by simply moving the camshaft along it's axis.