VVAFreeRollerComparedToExisting
You can hardly find articles (on the web, in
magazines etc) where the writer doesn't praise the engines of Honda S2000 and
Honda Civic TypeR (above left) as the best ever: economic, environment
friendly, extraordinary powerful and at the same time driver friendly.
What makes the difference is simply their two
modes of operation (or of breathing), one for high revs and another for medium
to low revs. To achieve the two step operation they use, per pair of valves,
three cam lobes, three rocker arms, three rollers, some locking pins and
hydraulic control. The rocker arms are made with extreme construction accuracy,
and every time the lift is changed the system ought to pass through a "critical
condition": it is the moment the rockers ARE and ARE NOT engaged (the "critical
condition" is also met in Toyota's GTS/VVTLi, in Porsche's VarioCamPlus etc :
every time the lift is changed some pins or wedges and their holders are
"punished" and have to endure the abuse).
Throw away the two side cam lobes (get rid of
them or just keep them idle).
Throw away one of the two "side" rollers and
use the other one as the "free" roller cam follower.
Throw away the locking pins.
Throw away the hydraulic control system, or
short circuit it.
Rotate properly the central rocker and weld
(glue/paste/union) the three rocker arms to form a single one having a single
roller (or substitute the three rocker arms with a single piece light alloy
one).
Insert the "free" roller between the wild cam
lobe and the roller on the rocker arm.
Insert a "slowly moving" almost idle control
shaft, on which rolls the pin of the "free" roller.
And forget "critical conditions" and extreme
accuracies, because now the transition from one mode of operation to another
occurs smoothly / progressively / softly, by just rotating the control shaft
easily, as your foot presses the gas pedal (no pins and holders, no ON-OFF
operation).
The 2D animation above
explains things (mouse click on the picture to download the file, and then open
it):
The mechanism at the left side
of the animation is the existing one, the state of the art, while the mechanism
at the right side is the new one. For simplicity it is shown, in the mechanism
at left, only one of the side rocker arms. When the animation is running on the
screen, press Space Bar key on keyboard to get the next available mode. Use the
, . / keys of keyboard to proceed step by step.
The mechanism at left has
just two modes of operation: 11.0 mm or 7.7 mm valve lift. When the wild cam
lobe activates the valves, their stroke is 11.0 mm and when the mild cam lobes
activate the valves their stroke is 7.7 mm and their duration shorter. The
mechanism at the right side has infinite (limitless) modes, of which only four
are shown, for 12.3, 7.5, 4.0 and 1.6 mm valve lift. At low revs and partial
loads (i.e. at short valve lifts) the actual overlap of the mechanism at the
right side is many times smaller than the overlap of the original engine,
therefore it is as wrong as it gets that the new mechanism does not control
overlap as well. On the contrary, the new mechanism is a very effective
Variable Valve Timing (or "actual overlap control") system: starting with
strong overlap and cam lobes of long duration and of high lift, the dramatic
reduction of the valve lift at medium, low and extremely low revs drastically
and effectively reduces, or roughly eliminates, the actual overlap. All it takes,
to change the valve lift, is to rotate the control shaft by pressing the gas
pedal with your foot. The operation is continuous (and not ON-OFF). The intake
manifold and its throttle valve can be eliminated as the intake valves can play
the role of the throttle valve too.
In the 3D animation the
control shaft is sliced to expose the parts of the mechanism beneath. The one
piece is in its normal place and the other one is shown at the right side of
the window. The "free" roller cam follower rolls on the cam lobe periphery and
on the rocker arm roller periphery and not on the control shaft. Only the pin
of the "free" roller rolls along a cylindrical surface cut on the control shaft
and shown in the right side. The other two cylindrical surfaces (or slices) on
the control shaft are there to make space for the motion of the free roller and
of the cam lobe.
The control shaft is well
oversized and heavier than necessary only to emphasize that there is plenty of
space for its installation into any engine already in the road.
The pin of the roller of the
rocker arm can be held on the rocker arm even without complete "rings", like
the fork in the animation "VVAFreeRollerRockerFork", as the direction of the
load is limited.
If necessary, practice
proves unnecessary so far, a spring from the body of the rocker arm to the pin
of the free roller can provide the necessary restoring force at low or zero
valve lift, in order to keep the free roller in touch to the cam lobe.
The result?
Infinite modes of operation with valve lifts
varying from about 0.2 mm (for idling) to more than 12.0 mm (compared to
just 11.0 mm or 7.7 mm of the original
engine), excellent control of the actual overlap and ability of using any
combination of exhaust and intake valve lifts (i.e. 12.0 mm exhaust with 1.0 mm
intake, but also 0.7 mm exhaust and 1.0 mm intake etc).
And what is so important from the
drivers/neighbors/citizens point of view?
Significantly less fuel consumption and
pollution at idling, at low revs and at partial loads: it is the town traffic
itself.
Less consumption and pollution at all revs
and loads.
Smoother idling at lower revs and easier
starting at all conditions.
Capability for higher revs as concerns the
limitations imposed by the valve train system, due to the lower inertia of the
quickly moving parts.
Longer time intervals between valve train
adjustments, because most of the time the valve train system operates almost
without loads. It is obvious that at partial lifts the stress in the valve
train is incomparably smaller as opposed to the conventional or the two step
mechanisms.
More power output, because the peak torque of
the original engine can now be sustained beyond the red line revs, without any
spoiling of the drivability at medium and low revs or at lighter loads: on the
contrary at low to very low revs the engine becomes very torquie.
Freedom to choose throttless operation.
Freedom to use cheap "throttle bodies"
(without throttles inside, i.e. "throttless throttle bodies", as the throttling
is now the job of the intake valves, which have continuously variable lift,
from zero) in the place of the existing intake manifold.
By selecting just two valve lifts or control
shaft angles, from the limitless available, the engine with the new VVA is
reduced to the state of the art VVA engines, that is it can operate similarly
to the existing engines with the only two modes of operation, like Honda S2000,
Honda Civic TypeR, Toyota VVTLi/GTS, Porsche Variocam Plus etc. The rest
infinite modes are there to prove the superiority of the new system and to
improve spherically the behavior of the engine at all revs and every load,
offering the option to choose the best - from infinite available - mode of
breathing for the specific operational conditions.
Two step compared to continuously variable
breathing systems: it is like having a shoe-shop offering just two sizes of
shoes, one for children and one for adults. If the customer is lucky OK, if
not... The example seems extreme, but deeply looked it is a good one. Of course
two step systems are better than conventional (only one size of shoes), but
when all demands can be satisfied, why to compromise in just two lifts?
The reason for going from two or three step systems to continuously variable
valve lift systems is exactly the same reason for going from conventional to
two or three step systems: to improve the internal combustion engine. Above
everything else to increase the intake air velocity, because the flame
propagation is proportional to the air velocity. And as there is no substitute
for a faster combustion, there is no substitute for the fast air motion during
combustion. All the rest are details. Just look around to see the struggle to
make the incoming air a little faster.
To summarize:
Starting with a Honda S2000 or a Honda Civic
TypeR or a Toyota Celica GTS/VVTLi engine :
·
the existing rocker arms are modified or replaced (the final ones are
simpler, lighter and stronger),
·
two control shafts are rotatably mounted along cylinder head beside
camshafts,
·
the EFI unit is reprogrammed,
and this is all. The original camshafts
remain in their original bearings with their mild cam lobes inactive, the timing
chain is the original at its original position, the external dimensions of the
engine stay as they were, and so on.
Once again: fewer, lighter and simpler quick
moving parts, easy control, continuous operation without "critical conditions"
are only some of the benefits the new system can offer to the state of the art
engines.
And as regards the reliability, suffices it
to notice an obvious thing: since the new system will spend most of its life at
partial loads and at medium to low revs (as all road engines do) it will last
much longer than the rest parts of the internal combustion engine. As you can
see, for the new system medium to low revs and partial loads (i.e. short valve
lifts) mean operation practically without loads, and hence without wear or
fatigue of the parts involved (i.e. reliable operation and longer time
intervals between tuning/adjustments).
VVAFreeRollerFlatWallStereo
Here there is an immovable
wall (the rectangle parallel to the valve axis). There is a valve roller on top
of the valves. There is also a "free" roller cam follower. The free roller
rolls on the cam lobe as the cam rotates. The "free" roller rolls also on the
valve roller. The pin of the free roller rolls on a cylindrical surface of the
control shaft. The control shaft is rotatable about the axis of the "free"
roller when the later is at "rest" position, i.e. in contact to the basic
circle of the cam lobe. The valves are free from thrust loads (just like in the
case of bucket lifters). The mechanism is lighter and stronger and of lower
friction. All working surfaces are rolling to each other and no one is sliding.
In case the radius of the
cylindrical surface of the control shaft along which rolls the pin of the
"free" roller equals to the sum of the radiuses of the valve roller, of the
free roller and of the free roller pin, the system can offer zero valve lift
too.
In case the free roller is
removed and the camshaft acts immediately on the valve roller, a "constant"
lift system results that can replace the conventional "bucket lifters" system,
providing less inertia and less friction. It is the arrangement without control
shaft, in the last image showing "various arrangements".
VVAFreeRoller&BucketLifters
Here a "free"
roller cam follower rolls on the cam lobe, on the upper surface of the bucket
lifters, and along a flat surface of the control shaft. As the control shaft
rotates, the valve lifts change from zero to a maximum. The system can work
even if the triple roller shown is substituted with a single low diameter pin
as shown in the "VVAFreePinFlatControl" animation above.
VVAFreeRoller&Rocker
The mechanisms
shown can easily be applied in engines with rocker arms / hydraulic valve
clearance adjusters (very common arrangement lately).
Modifying the
rocker arm, the original roller can be moved lower in order to make space for
the insertion of the free roller without the need of displacing the camshaft.
There is the
option to remove the rocker arm roller and replace it with a fork/holder of the
free roller, as shown in the next animation.
There is also the
option to flatten the upper part of the rocker arm and use just one roller and
a flat surface on control shaft.
In case of
mechanical lash adjuster, a coaxial to the adjuster spring can keep the
lash of the mechanism only in the swivel joint.
VVAFreeRollersRockersUniCam
In case of engines with single camshaft and
rocker arms, free rollers can be inserted between the rollers of the rocker
arms and the cam lobes. The two control shafts can combine any valve lift in
intake to any valve lift in exhaust. The system remains very short and simple.
There is the option to use a unique cam lobe to control all cylinder valves.
VVAFreeRollers&Rockers&UniCam&CommonControl
In case of engines with rocker arms, single camshaft
and double pivot shafts, free rollers can be inserted between the rollers of
the rocker arms and the cam lobes. In this case, a unique control shaft can
control the intake and the exhaust valve lifts. The system remains very short
and simple.
The Forums and the
alternatives
The VVA system was published in more than 250
Internet Forums relative to engines, cars, motorcycles, racing, technology and
ecology. The typical comment was : but the small "push rods" seem weak.
Actually the small "push rods" are too strong and too light and their benefits
are proved in practice. Nevertheless it is now published another version of the
VVA system with rollers as the means for keeping the distance of specific axes
constant. In the arrangements below the "control shaft" is red.
In some cases there were mentioned the
hydraulic and the electromagnet alternative systems as a better solution. The
main advantage of the hydraulic and electromagnet systems is their theoretical
ability to control all the parameters, i.e. the duration and the lift and the
timing. Theoretically they seem superior. But in practice there are still many
problems to be answered. Let alone their power consumption.
The new VVA, in comparison, appears simple
and carry all the experience of the camshaft based systems. Its energy
consumption is not just beyond competitors, but literally speaking it is
several times less than their best. It consumes very small amounts of power
(friction) at short and very short valve lifts, i.e. where the normal engine
spends almost all its life. It also provides infinite modes of operation and
effective control of the overlap, without the need of additional timing system.
"But the hydraulic / electromagnet systems
will offer absolute control", some people insist.
The case reminds someone found in the desert,
thirsty to death, who refuses to drink the water offered to him because it is
neither mineral nor of his favor brand. To evaluate cam-less systems, they have
first to get in practice.
For the moment the new VVA
seems the best solution as it combines:
the economy, the low
pollution and the easy handling of BMW's valvetronic (which, on the other hand,
is not applicable to exhaust valves, cannot efficiently handle the condition of
low revs with full load, and cannot achieve high power concentration as it is
unable to operate reliably at high revs),
with the high (or even
higher) power concentration of Honda's S2000,
without the "critical
conditions" of Honda's VTEC,
without the height, the
stress and the wear concentration points of BMW's valvetronic,
with simple mechanical or
electromechanical control,
with low height, weight and
friction,
with reliable operation,
and, above all, with the ability
to be installed on new and old engines easily and at low cost.
In any case, the world must
be grateful to BMW for valvetronic and to Honda for VTEC, because these two
companies, among automakers, do improve for a step the "internal combustion
engine". BMW claims - with valvetronic - a 10 to 15% fuel economy and pollution
reduction, combined to improved drivability, and nobody doubts. And with S2000,
Honda proves it is possible to get (milk) from an engine 120 PS per liter and
at the same time good behavior at medium and low revs.
The new system does combine
and improve the benefits of both schools, being at the same time simpler and
cheaper.
On the other hand, the hybrid cars are based
exclusively on the weakness of the car engines to have acceptable efficientcy
at specific conditions (of revs and loads) frequently met in town traffic. But
if the efficiency of the reciprocating engines becomes acceptably good along
all the spectrum of loads and revs, then the hybrid car's position weakens.
Just a system to stop and restart (turn off and on) the engine when the car
waits in traffic lights, combined to the VVA system and to a long ratios
gearbox (the plenty of torque from extremely low revs, due to the VVA,
overcomes the long ratios), is all it takes.
The response
Long ago there were sent personal messages to
the heads and stuff of the "Mechanical Engineering" and "Internal Combustion
Engines" sections of many famous (and other not so famous) Universities, asking
their comments and especially their objections regarding the new system. There
are no replies yet. Not a single one! Not even a reply like "hello there, we
received a message from you". It may be their standard policy, but they ought
to be ashamed for it: it is one of their unwritten duties, it is also the most
challenging part of their job.
The people
Some people are focused on the seconds, and
the tenths of a second, their car need for accelerating to some speed.
Some others are focused on the reliable
operation of their car, on the easiness of starting at extreme temperatures, on
the quiet operation, on the torquie character of their engine that leave them
relaxed at driving, on the safety offered by increased power and torque.
Some others are focused on the technology
inside their engines.
But everybody (including Earth) will be
happier if for the same kilometers it is burnt less fuel and they are produced
less poisons.
A car technology magazine wrote, a few months
ago, that this system has been measured cutting polluting gases, especially
carbon monoxide, forty times, from 1.8% to 0.05% in volume, and although the
writer is a mechanical engineer and the magazine of high quality and
reliability, nobody asked to take the car to verify the claim, neither
Greenpeace, nor environmentalists of any kind, nor mayors, nor citizens,
neither lung doctors nor lung patients… It seems that air pollution is not a
problem any longer!
Millions of cars can be improved in performance,
in fuel economy, in easiness of use and in clean exhaust at a cost which soon
will be returned to the owner as less money for fuel.
Normally equipped machine shops can apply the
modification mentioned.
And the automakers have the option to decide
whether the system will be installed in their cars from the factory, or later.
We wait for your comments and objections.
Thank you