VVTI is a variable valve timing system developed by Toyota. If we translate this abbreviation from in English, then this system is responsible for the intelligent phase shift. Now on modern Japanese engines installed the second generation of mechanisms. And for the first time, VVTI began to be installed on cars since 1996. The system consists of a coupling and a special VVTI valve. The latter acts as a sensor.

Toyota VVTI valve device

The element consists of a body. The control solenoid is located in the outer part. He is responsible for the movement of the valve. The device also has O-rings and connector for connecting the sensor.

General principle of the system

The main control device in this valve timing system is the VVTI clutch. By default, the engine designers designed the valve opening phases to get good traction at low engine speeds. As the rpm increases, so does the oil pressure, due to which the VVTI valve opens. Toyota Camry and its 2.4 liter engine work on the same principle.

After this valve opens, the camshaft will rotate to a certain position relative to the pulley. The cams on the shaft are specially shaped and the intake valves will open slightly earlier as the element rotates. Accordingly, close later. This should most in the best way affect the power and torque of the engine high revs.

Detailed job description

The main control mechanism of the system (and this is the clutch) is mounted on the engine camshaft pulley. Its body is connected to the star or the rotor is connected directly to camshaft. Oil from is supplied from one or both sides to each petal of the rotor on the clutch, thereby causing the camshaft to turn. When the engine is not running, the system automatically sets the maximum delay angles. They correspond to the latest opening and closing intake valves. When the engine starts, the oil pressure is not strong enough to open the VVTI valve. To avoid any shocks in the system, the rotor is connected to the clutch housing with a pin, which, with an increase in lubrication pressure, will be squeezed out by the oil itself.

The operation of the system is controlled by a special valve. On a signal from the ECU, an electric magnet using a plunger will begin to move the spool, thereby passing oil in one direction or the other. When the motor is stopped, this spool moves due to the spring so as to set maximum angle delays. To turn the camshaft to a certain angle, the oil under high pressure through the spool is brought to one of the sides of the petals on the rotor. At the same time, a special cavity opens to drain. It is located on the other side of the petal. After the ECU understands that the camshaft is turned to desired angle, the pulley channels overlap and it will continue to be held in this position.

Typical symptoms of a VVTI system problem

So, the system must change the phases of operation. If there are any problems with it, then the car will not be able to function normally in one or more operating modes. There are several symptoms that can indicate malfunctions.

So, the car does not keep idle at the same level. This indicates that the VVTI valve is not working as it should. Also, the "braking" of the engine will tell about various problems in the system. Often, with problems with this phase change mechanism, it is not possible for the motor to operate at low speeds. Another problem with the valve can be indicated by error P1349. If on warm power unit high idle, the car does not drive at all.

Possible causes of valve failure

There are not so many main causes of valve malfunctions. There are two that are particularly common. So, the VVTI valve may fail due to the fact that there are breaks in the coil. IN this case the element will not be able to correctly respond to voltage transfers. Troubleshooting is easily done by checking the resistance measurement of the sensor coil winding.

The second reason why the VVTI (Toyota) valve does not work properly or does not work at all is sticking in the stem. The cause of such jamming may be the banal dirt that has accumulated in the channel over time. It is also possible that the sealing gum inside the valve is deformed. In this case, restoring the mechanism is very simple - just clean the dirt from there. This can be done by soaking or soaking the element in special liquids.

How to clean the valve?

Many malfunctions can be cured by cleaning the sensor. First you need to find the VVTI valve. Where this element is located can be seen in the photo below. It's circled in the picture.

Cleaning can be done with carburetor cleaners. To completely clean the system, remove the filter. This element is located under the valve - it is a plug in which there is a hole for the hexagon. The filter also needs to be cleaned with this liquid. After all the operations, it remains only to assemble everything in the reverse order, and then install it without resting against the valve itself.

How to check the VVTI valve?

Checking if the valve is working is very simple. To do this, a voltage of 12 V is applied to the sensor contacts. It must be remembered that it is impossible to keep the element energized for a long time, since it cannot work in such modes for so long. When voltage is applied, the rod will retract inward. And when the chain breaks, it will come back.

If the stem moves easily, then the valve is fully functional. It only needs to be washed, lubricated and can be operated. If it does not work as it should, then repair or replacement of the VVTI valve will help.

Self-repair valve

First, the generator control bar is dismantled. Then remove the fasteners of the hood latch. This will give access to the alternator axle bolt. Next, unscrew the bolt that holds the valve itself, and remove it. Then remove the filter. If the last element and the valve are dirty, then these parts are cleaned. Repair is a check and lubrication. You can also replace the sealing ring. More serious repairs are not possible. If a part doesn't work, it's easier and cheaper to replace it with a new one.

Self-replacement of the VVTI valve

Often cleaning and lubrication does not provide the desired result, and then the question arises complete replacement details. In addition, after the replacement, many car owners claim that the car began to work much better and fuel consumption decreased.

First, remove the generator control bar. Then remove the fasteners and gain access to the generator bolt. Open the bolt that holds desired valve. The old element can be pulled out and thrown away, and a new one is put in place of the old one. Then the bolt is tightened, and the car can be operated.

Conclusion

Modern cars are both good and bad at the same time. They are bad because not every operation related to repair and maintenance can be performed independently. But you can do the replacement of this valve with your own hands, and this is a big plus for the Japanese manufacturer.

Variable valve timing system (common international name Variable Valve Timing, VVT) is designed to regulate the parameters of the gas distribution mechanism, depending on the engine operating modes. The use of this system provides an increase in engine power and torque, fuel efficiency and a reduction in harmful emissions.

The adjustable parameters of the gas distribution mechanism include:

• moment of opening (closing) of valves;
• duration of valve opening;
• valve lift.

Together, these parameters make up the valve timing - the duration of the intake and exhaust strokes, expressed by the angle of rotation of the crankshaft relative to the "dead" points. The valve timing is determined by the shape of the camshaft lobe acting on the valve.

On different modes engine operation requires a different valve timing. So, at low engine speeds, the valve timing should have a minimum duration (“narrow” phases). At high speeds, on the contrary, the valve timing should be as wide as possible and at the same time ensure the overlap of the intake and exhaust strokes (natural exhaust gas recirculation).

The camshaft cam has a certain shape and cannot simultaneously provide narrow and wide valve timing. In practice, the cam shape is a compromise between high torque at low rpm and high power at high speeds crankshaft. This contradiction is exactly what the system for changing the valve timing resolves.

Depending on the adjustable parameters of the gas distribution mechanism, the following methods of variable valve timing are distinguished:

• rotation of the camshaft;
• the use of cams with different profiles;
• change in valve lift.

The most common are variable valve timing systems using camshaft rotation:

• VANOS (Double VANOS) from BMW;
• VVT-i(Dual VVT-i), Variable Valve Timing with intelligence from Toyota;
• VVT Volkswage Variable Valve Timing n;
• VTC, Variable Timing Control by Honda;
• CVVT, Continuous Variable Valve Timing from Hyundai, Kia, Volvo, General Motors;
• VCP, Variable Cam Phases by Renault.

The principle of operation of these systems is based on the rotation of the camshaft in the direction of rotation, which achieves an early opening of the valves compared to the initial position.

The design of the variable valve timing system of this type includes a hydraulically controlled clutch and a control system for this clutch.

hydraulic clutch(common name phase shifter) directly rotates the camshaft. The clutch consists of a rotor connected to the camshaft, and a housing, which is the camshaft drive pulley. There are cavities between the rotor and the housing, to which engine oil. Filling one or another cavity with oil ensures the rotation of the rotor relative to the housing and, accordingly, the rotation of the camshaft at a certain angle.

For the most part, a hydraulically controlled clutch is installed on the intake camshaft. To expand the control parameters in some designs, the couplings are installed on the intake and exhaust camshafts.

The control system provides automatic control of the operation of the hydraulically controlled clutch. Structurally, it includes input sensors, the electronic unit controls and actuators. The control system uses Hall sensors that evaluate the positions camshafts, as well as other sensors of the engine management system: crankshaft speed, coolant temperature, air flow meter. The engine control unit receives signals from sensors and generates control actions on executive device– electrohydraulic distributor. The distributor is solenoid valve and provides oil supply to the hydraulically controlled clutch and removal from it, depending on the engine operating modes.

The variable valve timing system provides for operation, as a rule, in the following modes:

• idling ( minimum crankshaft speed);
• maximum power;
• maximum torque.

Another type of variable valve timing system is based on the use of cams various shapes, which achieves a stepwise change in the duration of the opening and the height of the valves. Known such systems are:

• VTEC, Variable Valve Timing and Lift Electronic Control from Honda;
• VVTL-i, Variable Valve Timing and Lift with intelligence from Toyota;
• MIVEC, Mitsubishi Innovative Valve timing Electronic Control from Mitsubishi;
• Valvelift System from Audi.

These systems have basically the same design and operation, with the exception of the Valvelift System. For example, one of the most famous VTEC systems includes a set of cams different profile and control system.

The camshaft has two small and one large cam. Small cams through the corresponding rocker arms (rockers) are connected to a pair of intake valves. The large cam moves the free rocker.

The control system provides switching from one mode of operation to another by actuating the blocking mechanism. The locking mechanism is hydraulically driven. At low engine speeds (low load), the intake valves operate from small cams, while the valve timing is characterized by a short duration. When the engine speed reaches a certain value, the control system activates the locking mechanism. The rocker arms of the small and large cams are connected with a locking pin into one piece, while the force on the intake valves is transmitted from the large cam.

Other modification VTEC systems has three control modes, determined by the operation of one small cam (opening one intake valve, low engine speed), two small cams (opening two intake valves, medium speed), and a large cam (high speed).

Honda's modern variable valve timing system is the I-VTEC system, which combines the VTEC and VTC systems. This combination significantly expands the engine control parameters.

From a structural point of view, the most advanced version of the variable valve timing system is based on adjusting the valve lift height. This system allows you to abandon the throttle in most engine operating modes. The pioneer in this field is BMW company and her system Valvetronic. A similar principle is used in other systems:

• valvematic from Toyota;
• VEL, Variable Valve Event and Lift System by Nissan;
• MultiAir from Fiat;
• VTI, Variable Valve and Timing Injection from Peugeot.

In the Valvetronic system, changing the valve lift is provided by a complex kinematic scheme in which the traditional cam-rocker-valve connection is supplemented by an eccentric shaft and an intermediate lever. The eccentric shaft receives rotation from the electric motor through worm gear. The rotation of the eccentric shaft changes the position of the intermediate lever, which, in turn, sets a certain movement of the rocker and the corresponding movement of the valve. The change in valve lift is carried out continuously depending on the engine operating modes.

The Valvetronic system is installed only on the intake valves.

The Vvt-i valve is a variable valve timing system car engine internal combustion from the manufacturer Toyota.

This article contains answers to such fairly common questions:

• What is a Vvt-i valve?
• vvti device;
• What is the principle of operation of vvti?
• How to properly clean vvti?
• How to repair a valve?
• How is the replacement done?

Vvt-i device

The main mechanism is located in the camshaft pulley. The housing is connected together with a toothed pulley, and the rotor with a camshaft. Lubricating oil is delivered to the valve mechanism from either side of each petal rotor. Thus the valve and camshaft starts to rotate. At that moment, when the car engine is in a muffled state, the maximum angle of detention is set. This means that an angle is determined that corresponds to the most recent product of the opening and closing of the intake valves. Due to the fact that the rotor is connected to the housing by a locking pin immediately after start-up, when the pressure of the oil line is insufficient to effectively control the valve, no shocks can occur in the valve mechanism. After that, the locking pin opens with the help of the pressure that the oil exerts on it.

What is the principle actions Vvt-i? Vvt-i provides the ability to smoothly change the gas distribution phases, corresponding to all conditions for the functioning of an automobile engine. This function is ensured by rotating the inlet camshaft relative to the outlet valve shafts, along the angle of rotation of the crankshaft from forty to sixty degrees. As a result, there is a change in the moment of initial opening of the intake valve, as well as the amount of time when the exhaust valves are in the closed position, and the exhaust valves are open. The control of the presented type of valve is due to the signal that comes from the control unit. After a signal is received, an electronic magnet moves the main spool along the plunger, while passing oil in any direction.

At the moment when the car engine is not working, the spool moves with the help of a spring so that the maximum delay angle is located.

To produce a camshaft, oil under a certain pressure is moved to one side of the rotor with the help of a spool. At the same moment, a cavity opens on the other side of the petals to drain the oil. After the control unit determines the location of the camshaft, all the channels of the pulley are closed, thus, it is held in a fixed position. The operation of the mechanism of this valve is carried out by several conditions for the functioning of an automobile engine with different modes.

In total, there are seven modes of operation of an automobile engine, and here is a list of them:

1. Idling movement;
2. Movement at low load;
3. Movement with an average load;
4. High load travel and low level rotation speed;
5. High load travel and high level rotation speed;
6. Traveling with low coolant temperature;
7. During engine start and stop.

Self cleansing procedure a Vvt-i

Dysfunction is usually accompanied by many signs, so it is most logical to look at these signs first.

So, the main signs of a violation of normal functioning are as follows:

• The car abruptly stalls;
• The vehicle cannot maintain momentum;
• The brake pedal noticeably stiffens;
• Does not pull the brake pedal.

Now we can proceed to consider the process of purification of Vvti. We will carry out the purification of Vvti step by step.

So, the algorithm for cleaning Vvti:

1. Remove the plastic cover of the car engine;
2. We unscrew the bolts and nuts;
3. We remove the iron cover, the main task of which is to fix the generator of the machine;
4. We remove the connector from the Vvti;
5. We unscrew the bolt by ten. Don't be afraid, you won't be able to make a mistake, as there is only one of them.
6. We remove Vvti. Just in no case do not pull on the connector, because it fits snugly enough to it and a sealing ring is placed on it.
7. We clean Vvti with any cleaner that is designed to clean the carburetor;
8. To completely clean Vvti, remove the filter Vvti systems. The presented filter is located under the valve and has the form of a plug with a hole for the hexagon, but this item is optional.
9. Cleansing is complete, you just have to assemble everything in reverse order and tighten the belt without resting on Vvti.

Self Repair Vvt-i

Quite often, it becomes necessary to repair the valve, since simply cleaning it is not always effective.

So, first, let's look at the main signs of the need for repairs:

• The car engine does not hold idle;
• Brakes the engine;
• It is impossible to move the car at low speeds;
• No brake booster;
• Poor gear changes.

Let's look at the main causes of valve failure:

• The coil broke. In this case, the valve will not be able to respond correctly to the voltage transfer. Define this violation can be done by measuring the resistance of the winding.
• Seizes the stock. The cause of stem sticking can be the accumulation of dirt in the stem bore or deformation of the rubber that is located inside the stem. Dirt can be removed from the channels by soaking or soaking.

Valve repair algorithm:

1. We remove the regulating bar of the car generator;
2. We remove the fasteners of the lock of the hood of the car, thanks to this you can get access to the axial bolt of the generator;
3. We remove the valve. Just in no case do not pull on the connector, because it fits snugly enough to it and a sealing ring is placed on it.
4. We remove the filter of the Vvti system. The presented filter is located under the valve and has the form of a plug with a hole for the hexagon.
5. If the valve and filter are very dirty, then we clean them with special liquid to clean the carburetor;
6. We check the operability of the valve, using a short supply of twelve volts to the contacts. If you are satisfied with how it functions, then you can stop at this stage, if not, then follow these steps.
7. We put marks on the valve in order to prevent mistakes during re-installation;
8. Using a small screwdriver, disassemble the valve from two sides;
9. We take out the stock;

1. We wash and clean the valve;
2. If the valve ring is deformed, then replace it with a new one;
3. Roll up inside valve. This can be done with the help of a cloth, by pressing on the rod, to press the new sealing ring;
4. Change the oil that is in the coil;
5. We replace the ring, which is located on the outside;
6. Roll the outer side of the valve to press the outer ring;
7. The valve repair is completed and you just have to assemble everything in the reverse order.

Procedure self replacement valve Vvt-i

Often, cleaning and repairing the valve does not give much results, and then it becomes necessary to completely replace it. In addition, many motorists claim that after replacing the valve vehicle will work much better and fuel consumption will drop to about ten liters.

Therefore, the question arises: How should the valve be replaced correctly? We will replace the valve step by step.

So, the valve replacement algorithm:

1. Remove the car alternator control bar;
2. Remove the fasteners of the lock of the hood of the car, thanks to this you will be able to gain access to the axial bolt of the generator;
3. We unscrew the bolt that secures the valve;
4. We take out the old valve;
5. We install a new valve in place of the old one;
6. We twist the bolt securing the valve;
7. The valve replacement is complete and you just have to assemble everything in the reverse order.

Not really

The efficiency of an internal combustion engine often depends on the process of gas exchange, that is, filling air-fuel mixture and removal of exhaust gases. As we already know, the timing (gas distribution mechanism) is engaged in this, if you correctly and “finely” adjust it to certain speeds, you can achieve very good results in efficiency. Engineers have been struggling with this problem for a long time, it can be solved different ways, for example by acting on the valves themselves or by turning the camshafts ...

In order for the internal combustion engine valves to always work correctly and not be subject to wear, at first simply “pushers” appeared, then, but this turned out to be not enough, so manufacturers began to introduce so-called “phase shifters” on camshafts.

Why are phase shifters needed at all?

To understand what phase shifters are and why they are needed, read first useful information. The thing is that the engine does not work the same at different speeds. For idle and not high speeds, "narrow phases" are ideal, and for high - "wide".

narrow phases - If crankshaft rotates “slowly” (idling), the volume and speed of exhaust gases are also small. It is here that it is ideal to use "narrow" phases, as well as minimal "overlap" (the time of simultaneous opening of the intake and exhaust valves) - the new mixture is not pushed into an exhaust manifold, through open Exhaust valve, but also, accordingly, the exhaust gases (almost) do not pass into the intake. It's the perfect combination. If, however, “phasing” is made wider, precisely at low rotations of the crankshaft, then “working out” can mix with incoming new gases, thereby reducing its quality indicators, which will definitely reduce power (the motor will become unstable or even stall).

Wide phases - when the speed increases, the volume and speed of the pumped gases increase accordingly. Here it is already important to blow out the cylinders faster (from mining) and quickly drive the incoming mixture into them, the phases should be “wide”.

Of course, the usual camshaft leads the discoveries, namely its “cams” ​​(kind of eccentrics), it has two ends - one is as if sharp, it stands out, the other is simply made in a semicircle. If the end is sharp, then the maximum opening occurs, if it is rounded (on the other hand) - the maximum closure.

BUT regular camshafts have NO phase adjustment, that is, they cannot expand or make them narrower, yet engineers set average indicators - something between power and efficiency. If you fill up the shafts in one of the sides, then efficiency or economy engine will fall. “Narrow” phases will not allow the internal combustion engine to develop maximum power, but “wide” phases will not work normally at low speeds.

That would be regulated depending on the speed! This was invented - in fact, this is the phase control system, SIMPLY - PHASE SHIFTER.

Principle of operation

Now we will not go deep, our task is to understand how they work. Actually, a conventional camshaft at the end has a timing gear, which in turn is connected to.

The camshaft with a phase shifter at the end has a slightly different, modified design. Here are two "hydro" or electrically controlled clutches, which on the one hand are also engaged with the timing drive, and on the other hand with the shafts. Under the influence of hydraulics or electronics (there are special mechanisms), shifts can occur inside this clutch, so it can turn a little, thereby changing the opening or closing of the valves.

It should be noted that the phase shifter is not always installed on two camshafts at once, it happens that one is on the intake or exhaust, and on the second it’s just a regular gear.

As usual, the process is managed, which collects data from various ones, such as the position of the crankshaft, hall, engine speed, speed, etc.

Now I suggest that you consider the basic designs of such mechanisms (I think this will clear up your mind more).

VVT (Variable Valve Timing), KIA-Hyundai (CVVT), Toyota (VVT-i), Honda (VTC)

One of the first to suggest turning the crankshaft (relative to the initial position), Volkswagen, with his VVT system(many other manufacturers built their systems on its basis)

What does it include:

Phase shifters (hydraulic), mounted on the intake and exhaust shafts. They are connected to the engine lubrication system (actually, this oil is pumped into them).

If you disassemble the clutch, then inside there is a special sprocket of the outer case, which is fixedly connected to the rotor shaft. The housing and rotor can move relative to each other when pumping oil.

The mechanism is fixed in the head of the block, it has channels for supplying oil to both clutches, flows are controlled by two electro-hydraulic distributors. By the way, they are also fixed on the block head housing.

In addition to these distributors, there are many sensors in the system - crankshaft frequency, engine load, coolant temperature, position of the camshafts and crankshafts. When you need to turn to correct the phases (for example, high or low rpm), the ECU, reading the data, instructs the distributors to supply oil to the couplings, they open and the oil pressure begins to pump up the phase shifters (thus they turn in the right direction).

Idling - rotation occurs in such a way that the “inlet” camshaft provides a later opening and later closing of the valves, and the “exhaust” turns so that the valve closes much earlier before the piston approaches top dead center.

It turns out that the amount of the used mixture is reduced almost to a minimum, and it practically does not interfere with the intake stroke, this favorably affects the operation of the engine on idling, its stability and uniformity.

Medium and high rpm - here the task is to give out maximum power, so the "turning" occurs in such a way as to delay the opening of the exhaust valves. Thus, the gas pressure remains on the stroke stroke. Inlet, in turn, open after reaching the piston top dead points (TDC), and close after BDC. Thus, we kind of get dynamic effect"recharging" of the engine cylinders, which entails an increase in power.

Max Torque - as it becomes clear, we need to fill the cylinders as much as possible. To do this, you need to open much earlier and, accordingly, close the intake valves much later, save the mixture inside and prevent it from escaping back into the intake manifold. "Graduation", in turn, are closed with some lead to TDC in order to leave a slight pressure in the cylinder. I think this is understandable.

Thus, many similar systems are currently operating, of which the most common are Renault (VCP), BMW (VANOS / Double VANOS), KIA-Hyundai (CVVT), Toyota (VVT-i), Honda (VTC).

BUT these are not ideal either, they can only shift the phases in one direction or another, but they cannot really "narrow" or "expand" them. Therefore, more advanced systems are now beginning to appear.

Honda (VTEC), Toyota (VVTL-i), Mitsubishi (MIVEC), Kia (CVVL)

Even more advanced systems were created to further control the valve lift, but the ancestor was HONDA company, with own motor VTEC(Variable Valve Timing and Lift Electronic Control). The bottom line is that in addition to changing the phases, this system can raise the valves more, thereby improving the filling of the cylinders or the removal of exhaust gases. HONDA is now using the third generation of such motors, which have absorbed both VTC (phase shifters) and VTEC (valve lift) systems at once, and now it is called - DOHC i- VTEC .

The system is even more complex, it has advanced camshafts that have combined cams. Two conventional ones on the edges that press the rocker arms in normal mode and a middle, more extended cam (high profile) that turns on and presses the valves after, say, 5500 rpm. This design is available for each pair of valves and rocker arms.

How does it work VTEC? Up to about 5500 rpm, the motor operates normally, using only the VTC system (that is, it turns the phase shifters). The middle cam, as it were, is not closed with the other two at the edges, it simply rotates into an empty one. And when high speeds are reached, the ECU gives the order to turn on the VTEC system, oil starts to be pumped in and a special pin is pushed forward, this allows you to close all three "cams" at once, the most high profile- now it is he who presses a couple of valves for which the group is designed. Thus, the valve is lowered much more, which allows additional filling of the cylinders with new working mixture and allocate a larger amount of "working out".

It is worth noting that VTEC is on both the intake and exhaust shafts, this gives a real advantage and an increase in power at high speeds. An increase of about 5-7% is a very good indicator.

It is worth noting, although HONDA was the first, now similar systems are used on many cars, such as Toyota (VVTL-i), Mitsubishi (MIVEC), Kia (CVVL). Sometimes, as for example in the Kia G4NA engines, a valve lift is used on only one camshaft (here only on the intake).

BUT this design also has its drawbacks, and the most important is the stepwise inclusion in the work, that is, eat up to 5000 - 5500 and then you feel (the fifth point) the inclusion, sometimes as a push, that is, there is no smoothness, but I would like to!

Soft start or Fiat (MultiAir), BMW (Valvetronic), Nissan (VVEL), Toyota (Valvematic)

If you want smoothness, please, and here the first company in development was (drum roll) - FIAT. Who would have thought they were the first to create the MultiAir system, it is even more complex, but more accurate.

“Smooth operation” is applied here on the intake valves, and there is no camshaft here at all. It was preserved only on the exhaust part, but it also has an effect on the intake (probably confused, but I will try to explain).

Principle of operation. As I said, there is one shaft here, and it controls both the intake and exhaust valves. HOWEVER, if it affects the “exhaust” mechanically (that is, it is trite through the cams), then the inlet effect is transmitted through a special electro-hydraulic system. On the shaft (for intake) there is something like “cams” ​​that do not press the valves themselves, but the pistons, and they transmit orders through the solenoid valve to the working hydraulic cylinders to open or close. Thus, it is possible to achieve desired opening within a certain period of time and turnover. At low speeds, narrow phases, at 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 a smooth start depending on the engine speed. Now many manufacturers also have such developments, such as BMW (Valvetronic), Nissan (VVEL), Toyota (Valvematic). But these systems are not perfect to the end, what is wrong again? Actually, here again there is a timing drive (which takes about 5% of the power), there is a camshaft and throttle valve, this again takes a lot of energy, respectively, steals efficiency, if only they could be abandoned.

10.07.2006

Consider here the principle of operation VVT-i systems the second generation, which is now used on most Toyota engines.

The VVT-i system (Variable Valve Timing intelligent - variable valve timing) allows you to smoothly change the valve timing in accordance with engine operating conditions. This is achieved by turning the intake camshaft relative to the exhaust shaft in the range of 40-60 ° (by the angle of rotation of the crankshaft). As a result, the moment when the intake valves begin to open and the value of the "overlapping" time (that is, the time when the exhaust valve is not yet closed, and the intake valve is already open) change.

1. Construction

The VVT-i actuator is located in the camshaft pulley - the drive housing is connected to the sprocket or toothed pulley, rotor - with camshaft.
Oil is supplied from one side or the other of each of the petals of the rotor, causing it and the shaft itself to turn. If the engine is off, then the maximum delay angle is set (that is, the angle corresponding to the latest opening and closing of the intake valves). So that immediately after starting, when the pressure in the oil line is still insufficient for effective management VVT-i, there were no shocks in the mechanism, the rotor is connected to the body with a locking pin (then the pin is pressed out by oil pressure).

2. Operation

To turn the camshaft, pressurized oil is directed to one side of the rotor petals with the help of a spool, while the cavity on the other side of the petal opens to drain. After the control unit determines that the camshaft has taken the desired position, both channels to the pulley overlap and it is held in a fixed position.

Mode	№	Phases	Functions	Effect
Idling			The angle of rotation of the camshaft is set corresponding to the latest start of the opening of the intake valves (maximum delay angle). "Overlapping" of the valves is minimal, the reverse flow of gases to the inlet is minimal.	The engine idles more stable, fuel consumption is reduced
		Valve overlap is reduced to minimize backflow of gases to the intake.	Increased engine stability
		Valve overlap increases, while "pumping" losses are reduced and part of the exhaust gases enter the intake	Improving fuel economy, NOx emissions are reduced
High load, speed below average			Provides early closing of intake valves to improve cylinder filling	Increasing torque at low and medium speeds
		Provides late closing of intake valves for improved filling at high speeds	Increased maximum power
Low coolant temperature	-		Minimum overlap is set to prevent fuel wastage	Increased idle speed is stabilized, efficiency is improved
When starting and stopping	-		A minimum overlap is set to prevent exhaust gases from entering the intake	Improved engine starting

3. Variations

The above 4-blade rotor allows you to change the phases within 40 ° (as, for example, on engines of the ZZ and AZ series), but if you want to increase the angle of rotation (up to 60 ° for SZ), a 3-blade one is used or the working cavities are expanded.

The principle of operation and modes of operation of these mechanisms are absolutely similar, except that due to the extended range of adjustment, it becomes possible to completely eliminate valve overlap at idle, at low temperatures or at startup.