How Does Vvti Work?

[funkyg]

In normal engines the valves are opened/closed via cam belt aren't they? (I have very basic engine knowledge)

How then does the vvti engine change the valve timing? Surely the timing will always have the same ratio to the engine speed?

Mike.

[funkyg]

After a web search I have found the answer to my question.

http://www.billzilla.org/vvtvtec.htm

Details here for those who are interested, it compares the Toyota VVTI with the Honda VTEC.

Interesting, if a little confusing!

Mike.

[Mackers]

thats lick don't work :(

[PeaJay]

thats lick don't work :(

←

Worked ok here!

though it says the 1ZZ-FE engine is a VVTL-i engine.

whereas I thought it was a VVT-i engine (as claimed in the Avensis bumph)

still, what ever flavour of VVT it is, it works ok

(not had any oil usage problems here) :D

[ronnyboy696]

Does anybody want a reply to this question?#

VVT-i stands for variable valve timing intelligent.

if you are driving hard, OCV will adjust valves to open to overlap slightly to allow more air/fuel mixture in, making more power.

opposite for miss daisy driving. valves wont overlap. so less air/fuel mixture. less power. equals better emissions, better fuel economy

[raywong]

great website, i was always wondering wot revs would the vvti kicks in, becos i know that at around 5500-6000 the vtec would kick in, but i am not sure when vvti would start.

Ray :)

[funkyg]

great website, i was always wondering wot revs would the vvti kicks in, becos i know that at around 5500-6000 the vtec would kick in, but i am not sure when vvti would start.

Ray :)

←

Can't you feel it? Mine kicks in around 3000 rpm, and you can really feel the difference.

Mike.

[funkyg]

Does anybody want a reply to this question?#

VVT-i stands for variable valve timing intelligent.

if you are driving hard, OCV will adjust valves to open to overlap slightly to allow more air/fuel mixture in, making more power.

opposite for miss daisy driving. valves wont overlap. so less air/fuel mixture. less power. equals better emissions, better fuel economy

←

I knew what it was and what it did, I just didn't know HOW it did it.

Mike

[Black Knight]

Actually the description used in that is a little off (although the principle is right)

It's not a piston (as most people think about it) but 2 meshing rotors one inside the other. The inner is connected to the cam, the outer to the chain. Apply oil pressure (controlled by the oil valve) and you shift the inner rotor relative to the outer and hey presto VVT :)

[Steve84]

Hi sorry its a late post but this may help shed some light onto the advantage of vvti., Doesn't mention that most vvt-i's use a lot of oil (save that for another day) but i guess they only focus on the advantages

I find my corolla realy pulls her finger out at around 3500rpm up to 6000rpm so i guess this is where the vvt-i comes to life.

VVT-i (Variable Valve Timing with intelligence)

Toyota' s award-winning Variable Valve Timing with intelligence

(VVT-i) technology utilises a sophisticated computer to vary the air intake valve timing according to driving conditions and engine load.

By adjusting the overlap time between the exhaust valve closing and intake valve opening, the engine characteristics can be changed to provide instant engine torque across the entire rev range. This gives the best of both worlds: Powerful acceleration and superior fuel economy. In addition, more complete fuel burn at a higher combustion temperatures leads to fewer emissions.

VVt-i info taken from www.toyota.co.uk

[fastbob72]

Actually you don't feel a noticeable kick with the vvti as it's progressive whereas the early vtec utilised two cam profiles and switched from the mild economic profile to the wilder profile at a certain point in the rev range,pretty high 5000+ I understand and it's that switch from sedate to performance profiles that gives it such a kick..... you could almost liken it to the old twin choke carbs (mechanical type obv) which for the majority of day to day driving used the primary choke but when you buried the throttle the secondary choke kicked in too as the butterflys were linked as the prim reached about 3/4 open it started opening it's pal too with them both reaching WO at the same time.

For those of you who remember Capris, Cortinas, Escorts or even XR2s with twin choke webers will remember the kick, well vtec had that similar on/off feel too.

vvti however the cam profile remains the same but it's relationship to the crankshaft is variable by around +/- 30° so when there's no variation cam timing is normal,but it can advance smoothly so that the inlet opens sooner or retards so it opens late. It doesn't change the cam profile but varies the degree of valve overlap according to what the ECU signals. The ECU takes it cue from various parameters depending on the signal. from the various sensors. This is where the 'intelligence' comes in to it, it's progressively variable depending on the engines load,speed,temp,vehicle speed etc, etc.

It also can increase overlap to allow spent gases into the cylinders in a sense like with EGR but it reduces the pumping losses at the same time.

A lot of folk tend to underrate vvti in comparison to the vtec because of the Honda's on/off nature making the increase in power feel more apparent whereas the progressive nature of the vvti which doesn't have that noticeable kick but more a smoother, steady delivery of power which makes the Honda seem like the better system. performance wise but I don't believe that's true. The Toyota does pick up her heels and fly the higher you rev the more she flys but again it's a smooth increase........ it feels analogue whereas the vtec feels digital, if you know what i mean lol

[dufunk]

Honda always tried to have the same characteristics with there engines, Toyota have tried a lot of different things with variable valve timing and have actually made quite a few enhancements not to say they have taken it to the next level over Honda but they have experimented a lot and the use of it with electric power is ahead of any other manufacture. You look at the single beams vvti and dual vvti beams 3sge both were terrific engines and you power, torque and good fuel economy right across the rev range Honda's lacked this allow they made there type r's as light as possible to cope. Yes we have the Lift on the 2zz and 4age but again they were more useable engines than some vtec's maybe not as aggressive in the lift but good torque and go across the rev range. 2GRFSE engine is the same dual vvti great progressive power and torque were as the J series Honda's had nothing down low.