Fully Variable Desmodromic VVA, "race winner" and "fuel ecconomy winner".
The first DVVA prototype (it has two "camshafts").
In the DVVA of the above animation, there is only one "camshaft" (actually a shaft with eccentric pins) for the opening AND the closing of all valves (intake and exhaust).
Left image: the "Lost Motion Control Shafts"/magenta (actually grooves/slots along which the yoke roller and its pin roll, being in simultaneous abutment to both sides/walls) are at angles providing short duration and negative overlap.
Middle image: the Lost Motion Control Shafts are at angles providing long duration, while the Constant Duration Control Shafts (they displace the pin of the big end of the red rods) are at angles providing medium valve lift. The angular overlap is long while the actual overlap is medium.
Right image: the Lost Motion Control Shafts are at angles providing long duration, while the Constant Duration Control Shafts are at angles providing high valve lift. The angular overlap is long. The actual overlap is extreme.
The Lost Motion Control Shaft and the Constant Duration Control Shaft modify the action coming from the eccentric pin into a controllable valve lift profile.
There is neither need of valve springs nor of any other restoring spring. This, in turn, allows significantly shorter, stronger and lighter valves, lower height of the cylinder head and shorter length of the timing belt/chain.
All rods of the linkage are rid of bending loads.
The absence of valve springs leads to less friction and wear.
The valve lift profile is defined by the groove's profile and by the geometry of the linkage.
Locking the pin of the big end of the red rod, the system degrades to a desmodromic Lost Motion VVA.
Locking the groove (magenta), the system degrades to a desmodromic Constant Duration VVA.
Locking both, the groove (magenta) and the big end of the red rod, the system degrades to a "single mode" Desmodromic Valve Train". Comparing the state of the art Desmodromic Valve Train (current winner of the motoGP) with the "single mode" DVVA, the latter:
is rid of "complementary" long periphery restoring camlobes,
is rid of quick moving parts loaded in bending,
is rid of sliding friction,
has shorter and lighter valves due to the arrangement of the valve guides and due to the absence of side loads on the valve stems,
so it is capable for higher revs and more power.
The DVVA can approach the available valve lift profiles of any existing valve train (conventional, VVA or Desmodromic). So, there is no reason for not being (the DVVA) more fuel efficient and for not providing top power.
Rid of valve springs, rid of unnecessary loads (like the restoring force from the valve springs at medium and low revs), rid of heavy quick moving parts, rid of sliding friction etc, the reliable rev limit of the engine is no longer set by the valve train but by the underneath mechanism (crankshaft, connecting rods, pistons and block).
Comparing the DVVA with the FVVA
At left is a FVVA or Fully Variable Valve Actuation
mechanism. It needs valve springs to restore the valves at their rest position,
it also needs restoring springs for some parts of the FVVA mechanism.
At
right is a Desmodromic (from the Greek words "desmos", meaning "tie", and
"dromos", meaning "road"/"track"/"path") Fully Variable Valve Actuation
system or DVVA. The DVVA needs neither valve springs, nor other kind of restoring
springs. The DVVA is as Desmodromic as Ducati's valve train systems for normal and
racing moto engines. And, at the same time, the DVVA is infinite times more variable than the state of the art Variable Valve Actuation systems, like BMW's valvetronic, Nissan's VVEL, Honda's A-VTEC etc (see Pattakon's FVVA
system).
To learn more and 'play' with DVVA's
capabilities, download and run the program 'DVVA1.exe' (95 KB) by clicking on the
image: The 'DVVA1.exe' shows animated a Desmodromic Fully
Variable Valve Actuation mechanism, and computes and presents graphically the
valve lift profile according the desirable / selected angles of the two control
shafts.
Locking at an angle the control shaft that holds the roller, the system "degrades" down to a Desmodromic Constant Duration VVA (suitable for applications where the simplified direct control and the instant response are mandatory, like in motoGP). Locking at an angle the other control shaft, the system "degrades" down to a Desmodromic Lost Motion VVA. Locking both control shafts, the system degrades to a Desmodromic valve train.
Without springs of any kind and without camshafts, the DVVA
can operate reliably at extreme revs for racing use, like motoGP and Formula1,
and at the same time the DVVA, compared to the state of the art VVAs and to the
conventional valve train systems, increases fuel economy and reduces pollution,
being more driver friendly and pleasant.
