Maximum torque – as it becomes clear we need more to fill the cylinders. For this you need to open much earlier and is far too late to close intake valve, to keep the mixture inside and prevent its release back into the intake manifold. "Prom" is in turn closed with some advance Btdc to leave a little pressure in the cylinder. I think it's understandable.
So, now employs many similar systems, of which the most common Renault (VCP), BMW (VANOS/Double VANOS), KIA-Hyundai (CVVT), Toyota (VVT-i), Honda (VTC).
BUT these are not perfect, they can only shift the phase in one direction or the other, but can't really "narrow" or "expand" them. So now begin to appear more sophisticated system.
Honda (VTEC), Toyota (VVTL-i), Mitsubishi (MIVEC), Kia (CVVL)
To further adjust the valve lift was created even more advanced system, but the ancestor was a HONDA with its engine VTEC (Variable Valve Timing and Lift Electronic Control). The point is that in addition to changing phase, the system can no longer lift valve, thereby improving the filling of the cylinder or the exhaust. The HONDA is now used is the third generation of such motors, which absorbed both the VTC system (phase shifters) and VTEC (valve lift), and now it's called DOHC i-VTEC.
The system still more complex, it has advanced the camshafts which have Cams combined. Two ordinary edges, which push on the rocker arms in normal mode and average more advanced Cam (high profile), which is activated and presses the valve after say 5500 rpm. This design is available on each pair of valves and rocker arms.
How does VTEC? Up to about 5500 rpm the motor operates normally, using only the VTC system (i.e., turns the shifters). Average Cam as it is not closed with the other two at the edges, it just spins in the shuffle. And that's when the high rpm, the ECU gives the order to switch on the VTEC system starts to pumped oil and a special pin is pushed forward, it allows you to close all three "Cam" immediately starts to work with a high profile – now he presses a couple of valves, which is designed by the group. Thus, the valve is lowered much more that can further to fill the new cylinder with the working mixture and to divert a greater volume of "practicing".
It should be noted that VTEC is on the intake and exhaust shafts, it gives a real advantage and power gains at high rpm. An increase of about 5 – 7%, which is very good.
It should be noted, though HONDA was the first, now similar systems are used on many cars, such as Toyota (VVTL-i), Mitsubishi (MIVEC), Kia (CVVL). Sometimes, like in the Kia motors G4NA used lift valves with only one camshaft (here only on the intake).
BUT this design has its drawbacks, and the most important step is the inclusion in the work, meaning eat up to 5000 – 5500 and then feel (the fifth point) inclusion, sometimes as a jolt, then there are no smooth, as I would like!
A slow start up or Fiat (MultiAir), BMW (Valvetronic), Nissan (VVEL), Toyota (Valvematic)
Want smooth please, and then the first development was the company (drum roll) – FIAT. Who would have thought, they created the first MultiAir system, it is more complicated, but more accurate.
"Smooth operation" are used on the intake valves and the camshaft is generally not. It exists only on the exhaust part, but it has an impact on the intake (probably confused, but I'll try to explain).
The principle of operation. As I said, there is one shaft, and he guides and intake and exhaust valves. HOWEVER, if the "prom" he act mechanically (i.e., through banal Cams), but at the intake of the impact is transferred through a special electro-hydraulic system. Shaft (intake) is something like "jaws", which press on the valve itself, but on the pistons, and transmit those orders via a solenoid valve for operating hydraulic cylinders to open or close. Thus, it is possible to achieve the desired opening in a certain period of time and momentum. At low speeds, narrow phase, high – wide, and the valve extends to the desired height because here everything is controlled by hydraulics or electrical signals.
This allows you to make smooth on depending on engine speed. Now such developments there are also many manufacturers, such as BMW (Valvetronic), Nissan (VVEL), Toyota (Valvematic). But these systems are not perfect to the end, what is wrong? In fact here again there is the timing (which takes on about 5% power), there is a camshaft and the throttle, it takes a lot of energy, respectively, the efficiency of steals, I wish to give them up.
FreeValve
Failure completely from the shafts, throttle and timing drive (chain or belt) to make many manufacturers, but the first made it to the Swedes in the supercar Koenigsegg, which by the way develops as much as 1500 HP
How does this work? Instead shafts there are special electromagnetic actuators using pneumatic springs. The ECU controls each valve and is able to open and close it very quickly (100 times per second) and for any distance you want. It allows you to adjust phase at any given value! AND IT'S REALLY VERY COOL.
Tests showed that this motor is 30% more powerful and more efficient than their counterparts in the distribution system, and it is economical for the same 30%. Smoothness is up to par.
The downside is that this engine, noisy, a number of solenoid valves creates the clicking when opening, and it is growing with increasing momentum. Also the price of the unit is very high, but if you run a series of price may significantly fall.
What we covered the basic types of phase shifters and distribution systems without them. Who don't understand watch the video version, where I will try to tell you it's simple on the fingers.