Continuously Variable Transmission (CVT)

NVECS = Intelligent & Innovative Vehicle Electronic Control System
CVT = Continuously Variable Transmission
CVT continuously controls the O-pulley diameter and changes the gear change ratio.
CVT makes for optimal tuning between the smaller pulley piston, discharge rate reducing oil pump, and the direct control torque converter by which an efficient engine output transfer and a smooth ride are realized. Based on accelerator travel information from actual drivers under actual driving conditions, the optimal efficiency point between the engine and the CVT was obtained and a supple and smooth driving feel is obtained under numerous conditions while also achieving low fuel consumption.

all in 1 here ab0ut VVT...

http://www.autozine.org/technical_school/engine/vvt_2.htm

crower
put the info here la
don use link
thanks

1) Cam-Changing VVT
Honda pioneered road car-used VVT in the late 80s by launching its famous VTEC system (Valve Timing Electronic Control). First appeared in Civic, CRX and NS-X, then became standard in most models.

You can see it as 2 sets of cams having different shapes to enable different timing and lift. One set operates during normal speed, say, below 4,500 rpm. Another substitutes at higher speed. Obviously, such layout does not allow continuous change of timing, therefore the engine performs modestly below 4,500 rpm but above that it will suddenly transform into a wild animal.

This system does improve peak power - it can raise red line to nearly 8,000 rpm (even 9,000 rpm in S2000), just like an engine with racing camshafts, and increase top end power by as much as 30 hp for a 1.6-litre engine !! However, to exploit such power gain, you need to keep the engine boiling at above the threshold rpm, therefore frequent gear change is required. As low-speed torque gains too little (remember, the cams of a normal engine usually serves across 0-6,000 rpm, while the "slow cams" of VTEC engine still need to serve across 0-4,500 rpm), drivability won't be too impressive. In short, cam-changing system is best suited to sports cars.

Honda has already improved its 2-stage VTEC into 3 stages for some models. Of course, the more stage it has, the more refined it becomes. It still offers less broad spread of torque as other continuously variable systems. However, cam-changing system remains to be the most powerful VVT, since no other system can vary the Lift of valve as it does.

Advantage: Powerful at top end
Disadvantage: 2 or 3 stages only, non-continuous; no much improvement to torque; complex
Who use it ? Honda VTEC, Mitsubishi MIVEC, Nissan Neo VVL.

Honda's 3-stage VTEC

Honda's latest 3-stage VTEC has been applied in Civic sohc engine in Japan. The mechanism has 3 cams with different timing and lift profile. Note that their dimensions are also different - the middle cam (fast timing, high lift), as shown in the above diagram, is the largest; the right hand side cam (slow timing, medium lift) is medium sized ; the left hand side cam (slow timing, low lift) is the smallest.

This mechanism operate like this :

Stage 1 ( low speed ) : the 3 pieces of rocker arms moves independently. Therefore the left rocker arm, which actuates the left inlet valve, is driven by the low-lift left cam. The right rocker arm, which actuates the right inlet valve, is driven by the medium-lift right cam. Both cams' timing is relatively slow compare with the middle cam, which actuates no valve now.

Stage 2 ( medium speed ) : hydraulic pressure (painted orange in the picture) connects the left and right rocker arms together, leaving the middle rocker arm and cam to run on their own. Since the right cam is larger than the left cam, those connected rocker arms are actually driven by the right cam. As a result, both inlet valves obtain slow timing but medium lift.

Stage 3 ( high speed ) : hydraulic pressure connects all 3 rocker arms together. Since the middle cam is the largest, both inlet valves are actually driven by that fast cam. Therefore, fast timing and high lift are obtained in both valves.

yo bro crower thanks for ur info

Nissan Neo VVL
Very similar to Honda's system, but the right and left cams are with the same profile. At low speed, both rocker arms are driven independently by those slow-timing, low-lift right and left cams. At high speed, 3 rocker arms are connected together such that they are driven by the fast-timing, high-lift middle cam.

You might think it must be a 2-stage system. No, it is not. Since Nissan Neo VVL duplicates the same mechanism in the exhaust camshaft, 3 stages could be obtained in the following way:

Stage 1 (low speed) : both intake and exhaust valves are in slow configuration.
Stage 2 (medium speed) : fast intake configuration + slow exhaust configuration.
Stage 3 (high speed) : both intake and exhaust valves are in fast configuration.

Cam-Phasing VVT
Cam-phasing VVT is the simplest, cheapest and most commonly used mechanism at this moment. However, its performance gain is also the least, very fair indeed.

Basically, it varies the valve timing by shifting the phase angle of camshafts. For example, at high speed, the inlet camshaft will be rotated in advance by 30° so to enable earlier intake. This movement is controlled by engine management system according to need, and actuated by hydraulic valve gears.


Note that cam-phasing VVT cannot vary the duration of valve opening. It just allows earlier or later valve opening. Earlier open results in earlier close, of course. It also cannot vary the valve lift, unlike cam-changing VVT. However, cam-phasing VVT is the simplest and cheapest form of VVT because each camshaft needs only one hydraulic phasing actuator, unlike other systems that employ individual mechanism for every cylinder.

Continuous or Discrete

Simpler cam-phasing VVT has just 2 or 3 fixed shift angle settings to choose from, such as either 0° or 30°. Better system has continuous variable shifting, say, any arbitary value between 0° and 30°, depends on rpm. Obviously this provide the most suitable valve timing at any speed, thus greatly enhance engine flexiblility. Moreover, the transition is so smooth that hardly noticeable.

Intake and Exhaust

Some design, such as BMW's Double Vanos system, has cam-phasing VVT at both intake and exhaust camshafts, this enable more overlapping, hence higher efficiency. This explain why BMW M3 3.2 (100hp/litre) is more efficient than its predecessor, M3 3.0 (95hp/litre) whose VVT is bounded at the inlet valves.

In the E46 3-series, the Double Vanos shift the intake camshaft within a maximum range of 40° .The exhaust camshaft is 25°.


Advantage: Cheap and simple, continuous VVT improves torque delivery across the whole rev range.
Disadvantage: Lack of variable lift and variable valve opening duration, thus less top end power than cam-changing VVT.
* Who use it ? Most car makers, such as: Audi 2.0-litre - continous inlet
* Audi 3.0 V6 - continous inlet, 2-stage exhaust
* Audi V8 - inlet, 2-stage discrete
* BMW Double Vanos - inlet and exhaust, continuous
* Ferrari 360 Modena - exhaust, 2-stage discrete
* Fiat (Alfa) SUPER FIRE - inlet, 2-stage discrete
* Ford Puma 1.7 Zetec SE - inlet, 2-stage discrete
* Ford Falcon XR6's VCT - inlet, 2-stage discrete
* Jaguar AJ-V6 and updated AJ-V8 - inlet, continuous
* Lamborghini Diablo V12 since SV - inlet, 2-stage discrete
* Mazda MX-5's S-VT - continous inlet
* Mercedes V6 and V8 - inlet, 2-stage ?
* Nissan QR four-pot and V8 - continuous inlet
* Nissan VQ V6 - inlet, continuous ?
* Nissan VQ V6 since Skyline V35 - inlet, electromagnetic
* Porsche Variocam - inlet, 3-stage discrete
* PSA / Renault 3.0 V6 - inlet, 2-stage
* Renault 2.0-litre - inlet, 2-stage discrete
* Subaru AVCS - inlet, 2-stage ?
* Toyota VVT-i - continuous, mostly inlet but some also exhaust
* Volvo 4 / 5 / 6-cylinder modular engines - inlet, continuous
* Volkswagen VR6 - inlet, continuous ?
* Volkswagen (Audi) W8 and W12 - continuous inlet, 2-stage exhaust

g0t byk lg l0r...
that y i use link...

lagik lagik
use link lazy to read la
got pic bout how these works?

hmm.... yea.... have pic show better de.. i m the 1 who lazy 2 read all this...keke

more knowledge i get now..
thanks,....

wow.. u read all huh???... i no read... lazy... keke