Rockville

It seems every week we get a new device and its acronym. An average person can remember between three to five items so instead of long winded names we get the first letters of each moniker. I once tried to list them all and it was over one page and required smaller and smaller fonts to accomplish. The little "i" in VVT-i stands for intelligence. This means that there are situational commands built into the ECU (Electronic Control Unit) software that mimic decisions that a person might make if they were available but way faster! What is involved with variable valve timing with intelligence is a device on the front end of the camshaft that can advance or retard the camshaft position for a range of about 45 degrees. The floating adjustment can make the timing optimal for acceleration, fuel consumption and reduced emissions. Once the driver puts their foot into the Gas pedal the VVT-i changes the cam(s) position(s) and allows for increased air/fuel mixture in the combustion chamber which creates more power on demand. The Lexus VVT-i is actuated hydraulically and performs its functions from 1,000 RPM's (revolutions per minute) all the way to redline. Previous systems would function only at the upper RPM ranges and were mechanically introduced and not variable like the Lexus system. The first VVT-i was introduced in the GS400 in 1998. We now have it in all models. The 3rd Gen GS and new 2nd Gen IS motors have started a new trend. Dual VVT-i. Now the exhaust camshafts have the same actuators on the front end. This can create more exotic effects on demand. The intake/exhaust cams are linked by small timing chains yet they can change their positions independently so there can actually be quite an overlap duration if desired. Yamaha helped engineer the new high pressure direct injectors that along with VVT-i give new possibilities of power, reduced emissions and dramatically better fuel efficiencies so you can have your cake and eat it too.

My office buddy and I were discussing the new 4.6 Liter V8 that will share all of the new technologies above in a larger format. We grew up on Cubic Inches. We calculated the new LS 460 engine to be about 283 C.I's. That was the size of the typical Chevy small block which later grew into the 327. Anyway there used to be a fuel injected 283 that produced 283 horsepower which was quite an acheivement back then. Now we see the same size Lexus engine developing 380 Horsepower! At the same time in a fuel efficient MPG ( mid 20's) and Ultra Low Emissions Vehicle (ULEV)! 1967 was the first year of emission controls and collectors covet the older muscle cars for their power and sound. Sunoco 260 was 44.9 cents in those days but everything else has inflated since in cost too. We are entering a new and improved Muscle era with DVVT-i leading the way....

Rock

Bichon

This one doesn't pass the sanity test on several levels.

First, why would Lexus program their ECU to permanantly learn the driving style at a time when the owners manual advises to avoid sudden acceleration? Surely the engineers know that the driving style the car sees during break in is not representative of what it will see later in life.

Second, the whole point of dynamic adaptation in the car's electronic controllers is to adapt to changing conditions. For example, if the car gets a tank of 87 octane gas, the ECU will detect it fairly quickly and pull timing. After that tank has burned and the car once again has premium, it will gradually re-adapt and timing will advance. Again, the whole point of having the ECU learn is to adapt to changing conditions, including fuel quality, temperature, state of tune, driving style, etc.

NjDude

I may be comparing apples with oranges, but I was told the same thing when I bought my VR6 Jetta 5 years ago.

Bichon

In the case of your VW, I know it isn't true. I've spoken to a number of VW/tAudi tuners who have told me that pulling the battery cable erases all dynamic ECU adaptation. I've also graphed enough acceleration runs with VW-Tool and VAG-COM to see that even without pulling the battery cable, the Bosch ECU adapts rather quickly to changes in operating parameters. (By operating parameters I mean switching to race gas, tweaking engine parameters with Revo Teknik's Lemmiwinks, etc.)

SteVTEC

There is a preset map in the engine that determins VVT-i cam advance or retard angle, and it's based primarily on engine speed and load demands (torque output). VVT-i was actually first used on the 2JZ-GE engine and deployed in the Supra and probably a few other cars at the time in 1995-1996 or so.

Toyota published an SAE paper on VVT-i in 1996 and the timing advance/retard map looks like this.



At idle the cam is fully retarded (late opening) for idle stability.

Medium speeds, medium loads: the cam timing is fully advanced. This creates overlap with the exhaust valve opening and an internal EGR effect that reduces fuel consumption, emissions, and also pumping losses.

WOT: The cam starts out fully advanced at low RPM. You want earlier intake valve closure to prevent intake charge reversion where part of your intake charge bounces back out of the cylinder and into the ports. This reduces volumetric efficiency and peak torque. As RPM increases, the intake timing is retarded. Volumetric efficiency favors later IVO/IVC angles relative to crank as the RPMs increase since there is less time for cylinder filling at high rpm. You want maximum vaccum pressure in the cylinders by the time the intake valves open to draw air in as quickly as possible.

If you are actually resetting the ECU and feel something different after that, what may be happening is that you're resetting the long and short term fuel trim settings. "some" cars not all do have adaptive control units for electronic throttle control or transmission shift logic that "may" change after resetting, but I really don't think VVT-i maps are going to change via ECU resetting. These are preset.

Hanlce

Please correct me if Im wrong,.I was under the impression that vvti also help your engine to save gas by shutting off unneeded cylinders while xriving in high speeds. Like v8 engine uses only 4 cylinders, and 3 cylinders in case onf a v6.?

LexBob2

What you are referring to is cylinder deactivation.

tex2670

Revival of a 12 year old thread. New record?

plex

iTrader: (11)

Not true vvti doesn't shut off cylinders.

Sulu

Cylinder deactivation requires the ability to shut off the intake and exhaust valves (and the fuel injection) to the cylinder(s) that are shut off.

So, while cylinder deactivation requires a computer-controlled variable valve-timing (VVT) system (like VVT-i) to shut off the valves, having a system like VVT-i does not necessarily mean that the car has cylinder deactivation.

Aron9000

VVT-i is Toyota's version of Honda's VTEC. Switches cam profiles/lobes at a certain RPM from a more "conservative" lobe that gives better low end torque and fuel economy to one that gives higher rpm breathing/power. I thought this was kind of an old thread, been driving our family's old 2000 Avalon the past few days while my Lexus is in the shop. That car has the 1MZ-FE, the first Toyota V6 with VVT-i(has VVT-i on the engine cover). I must say that car isn't really quick by modern standards, but the engine/transmission is one sweetheart silky smooth combo. Its super quiet, super smooth, shifts are crisp but never felt. Put your foot down, it shifts down a gear or two right on command, even at interstate speeds of 60, 70, 80, 90mph, that thing moves and its always whisper quiet. Read the wikipedia article about that year Avalon, it has a .28 coefficent of drag, pretty damn impressive for a tall, sort of boxy traditional sedan.