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. 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. Cheap and simple, continuous VVT improves torque delivery across the whole rev range. Lack of variable lift and variable valve opening duration, thus less top end power than cam-changing VVT. Most car makers, such as:. F rom the picture, it is easy to understand its operation.
The end of camshaft incorporates a gear thread. The thread is coupled by a cap which can move towards and away from the camshaft. Because the gear thread is not in parallel to the axis of camshaft, phase angle will shift forward if the cap is pushed towards the camshaft. Similarly, pulling the cap away from the camshaft results in shifting the phase angle backward.
Whether push or pull is determined by the hydraulic pressure. There are 2 chambers right beside the cap and they are filled with liquid these chambers are colored green and yellow respectively in the picture A thin piston separates these 2 chambers, the former attaches rigidly to the cap.
Liquid enter the chambers via electromagnetic valves which controls the hydraulic pressure acting on which chambers. For instance, if the engine management system signals the valve at the green chamber open, then hydraulic pressure acts on the thin piston and push the latter, accompany with the cap, towards the camshaft, thus shift the phase angle forward.
Continuous variation in timing is easily implemented by positioning the cap at a suitable distance according to engine speed. Macro illustration of the phasing actuator. However, the word " Integillent " emphasis the clever control program.
Not only varies timing according to engine speed, it also consider other conditions such as acceleration, going up hill or down hill. C ombining cam-changing VVT and cam-phasing VVT could satisfy the requirement of both top-end power and flexibility throughout the whole rev range, but it is inevitably more complex. At the time of writing, only Toyota and Porsche have such designs.
However, I believe in the future more and more sports cars will adopt this kind of VVT. Its powerful functions include:. Like VVT- i , the variable valve timing is implemented by shifting the phase angle of the whole camshaft forward or reverse by means of a hydraulic actuator attached to the end of the camshaft.
The timing is calculated by the engine management system with engine speed, acceleration, going up hill or down hill etc. It also has 2 cam lobes acting on that rocker arm follower, the lobes have different profile - one with longer valve-opening duration profile for high speed , another with shorter valve-opening duration profile for low speed.
At low speed, the slow cam actuates the rocker arm follower via a roller bearing to reduce friction. The high speed cam does not have any effect to the rocker follower because there is sufficient spacing underneath its hydraulic tappet. When speed has increased to the threshold point, the sliding pin is pushed by hydraulic pressure to fill the spacing.
The high speed cam becomes effective. Note that the fast cam provides a longer valve-opening duration while the sliding pin adds valve lift. However, VVTL- i offers variable lift, which lifts its high speed power output a lot.
Therefore it is undoubtedly the best VVT today. However, it is also more complex and probably more expensive to build. Continuous VVT improves torque delivery across the whole rev range; Variable lift and duration lift high rev power.
More complex and expensive. Toyota Celica GT-S. Variocam Plus uses hydraulic phasing actuator and variable tappets. Variocam of the Carrera. However, I found their mechanisms virtually share nothing. To sum up what those advantages are, below are the top four pros of a variable valve timing engine.
When you step on the gas pedal to accelerate the vehicle, your engine will be capable of a higher RPM which generally translates to more power to a point. Variable valve timing has a lot to do with making this happen.
That roaring sound you hear when you step on the gas pedal is the variable valve timing system hard at work to keep your engine running strong. Engine efficiency has a lot to do with the timing of the exhaust valve and intake valve. If these valves can be managed and timed properly from the variable valve timing technology, then the engine will be able to produce the same power without needing so much fuel.
This means fewer trips to the gas station and more money saved on fuel costs. Any time your engine provides a better fuel economy, you will see reduced carbon emissions too. Variable valve timing technology does not get enough credit for its eco-friendly nature. If you live in a state which has required emissions testing, then this technology will increase your chances of helping you pass the test.
If you continue to maintain an efficient and high performing engine, then you can expect to get a great number of years out of it. A lot of people will wait until their engines go bad before they decide to replace their vehicle. If you have variable valve timing in your engine, then it will help keep it strong for as long as possible. Of course, there are other factors involved in keeping an engine healthy too. Make sure you regularly get oil changes and use the right kind of fuel.
Even if there were, the answer would likely change in a year or two as technology advances. For example, traditional piston engines often are required to sacrifice low-end torque for high-end power or vice versa. A VVT engine more easily accommodates both of these preferred performance conditions.
As with traditional piston engines, VVT engines use cams on a camshaft to drive the flow of air into the intake and exhaust valves. The timing of this valve lift directly affects how much air is taken in during each engine cycle. At times when the engine requires more air flow for example high speeds or acceleration , a traditional piston engine often does not allow enough air to flow during each cycle, resulting in lower output performance.
Conversely, a traditional piston engine that has been designed to feature longer exhaust and intake cycles will result in reduced fuel efficiency at slower speeds. There are several proprietary VVT engine technologies that work slightly differently to prolong exhaust and intake cycles at high speeds and reduce cycles at slow speeds.
The three major solutions to varying the valve timing of an engine are as follows:.
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