Vvt i how it works. Timing systems VVT-i from Toyota Corporation

Variable valve timing systems revolutionized engines internal combustion, and they became popular thanks to Japanese models 90s. But how do the most famous systems differ from each other in operation?

Internal combustion engines have not been as efficient as possible since their inception. The average efficiency of such motors is 33 percent - all the rest of the energy created by the combustion air-fuel mixture is wasted. Therefore, any way to make the internal combustion engine more energy efficient was in demand, and the variable valve timing system has become one of the most successful solutions.

The system changes the valve timing (the moment at which each valve opens and closes during the operating cycle), their duration (the moment when the valve is open) and lift (how much the valve can open).

As you know, an intake valve in an engine sends a fuel / air mixture into the cylinder, which is then compressed, burned, and pushed into the opening exhaust valve. These valves are driven by tappets that are controlled by the camshaft using a set of cams for the perfect closing to opening ratio.

Unfortunately, conventional camshafts are made in such a way that only valve opening can be controlled. This is the problem, as valves must open and close differently at different engine speeds for maximum efficiency.

For example, on high speed When the engine is running, the intake valve must be opened a little earlier due to the fact that the piston moves so quickly that it does not allow enough air to get inside. If the valve is opened a little earlier, then it will enter the cylinder more air, which will increase the combustion efficiency.

Therefore, instead of a compromise between camshafts for high and low revs, a variable valve timing system appeared, recognized as one of the most effective in this area. Various companies we have interpreted this technology in different ways, so let's take a look at the most popular ones.

Vanos (or Variable Nockenwellensteuerung) is BMW's attempt to create a variable valve timing system, and it was first used on the M50 engine installed on the 5-series in the 90s of the last century. It also uses the principle of delaying or advancing the interaction of the timing mechanisms, but using a gear train inside the camshaft pulley, which moves together or against the camshaft, changing the phases of operation. This process is controlled electronic unit control that uses oil pressure to move the gear train forward or backward.

As with the rest of the systems, gear moves forward to open the valves a little earlier, increasing the amount of air entering the cylinders and increasing the engine's power output. In fact, BMW first introduced a single Vanos that only worked on the intake camshaft in certain modes at different engine speeds. German company later developed a system with two Vanos, which is considered more advanced, since it affects both camshafts, and also regulates the position of the throttle valve. Double Vanos was created for the S50B32, which was installed on the BMW M3 in the back of the E36,.

Now almost everyone has large manufacturer has its own name for the valve timing system - Rover has VVC, Nissan has VVL, and Ford has developed VCT. And this is not surprising, considering that this is one of the most successful finds for internal combustion engines. Thanks to her, manufacturers were able to both reduce consumption and increase the power of their motors.

But with the advent of pneumatic valve control, these systems will retire. However, now is just their time.

VVTi Toyota what is it and how does it work? VVT-i - so called the designers of the auto concern Toyota system valve timing control, which have come up with their own system for increasing the efficiency of internal combustion engines.

This does not mean that only Toyota has such mechanisms, but we will consider this principle using its example.

Let's start with decryption.

The abbreviation VVT-i sounds in the original language as Variable Valve Timing intelligent, which we translate as intelligent variable valve timing.

For the first time on the market, this technology is presented by Toyota ten years ago, in 1996. All auto concerns and brands have similar systems, which speaks of their benefits. They are called, however, all differently, confusing ordinary motorists.

What has VVT-i brought to the motor industry? First of all, an increase in power, uniform throughout the entire rev range. Motors have become more economical and therefore more efficient.

The valve timing control or the control of the moment of raising and lowering the valves occurs by turning on desired angle.

How it is implemented technically, we will consider further.

Vvti toyota what is it or how does VVT-i gas distribution work?

Toyota VVT-i system what it is and what it is for, we understood. Time to delve into her insides.

The main elements of this engineering masterpiece:

VVT-i clutch;
solenoid valve(OCV - Oil Control Valve);
Control block.

The algorithm for the operation of this whole structure is simple. The clutch, which is a pulley with cavities inside and a rotor fixed to the camshaft, is filled with oil under pressure.

There are several cavities, and the VVT-i valve (OCV) is responsible for this filling, acting on the commands of the control unit.

Under the pressure of oil, the rotor, together with the shaft, can turn through a certain angle, and the shaft, in turn, determines when the valves rise and fall.

In the start position, the position of the intake camshaft provides maximum thrust for low revs motor.

As the speed rises, the system turns the camshaft so that the valves open earlier and close later - this helps to increase the output at high rpm.

As you can see, the VVT-i technology, the principle of operation of which was considered, is quite simple, but, nevertheless, effective.

Development of VVT-i technology: what else have the Japanese come up with?

There are other varieties of this technology. So, for example, Dual VVT-i controls the operation of not only the intake camshaft, but also the exhaust.

This made it possible to achieve even higher engine parameters. Further development of the idea was named VVT-iE.

Here, Toyota engineers completely abandoned the hydraulic method of controlling the camshaft position, which had a number of drawbacks, because to turn the shaft, it was necessary for the oil pressure to rise to a certain level.

It was possible to eliminate this drawback thanks to the electric motors - now they turn the shafts. So that's it.

Thank you for your attention, now you yourself can answer the question "VVT-i Toyota what is it and how does it work" to anyone.

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The split gear, which allows you to adjust the valve opening / closing phases, was previously considered an accessory only sports cars... In many modern engines the variable valve timing system is used routinely and works not only for the benefit of increasing power, but also to reduce fuel consumption and emissions harmful substances v environment... Consider how Variable Valve Timing (the international name for this type of system) works, as well as some of the features of the VVT device on BMW cars, Toyota, Honda.

Fixed phases

It is customary to refer to the valve timing as the opening and closing moments of the intake and exhaust valves, expressed in degrees of rotation. crankshaft regarding BDC and TDC. In graphical terms, the period of opening and closing is usually shown with a diagram.

If we are talking about phases, then changes can be made:

the moment the intake and exhaust valves begin to open;
the duration of being in the open state;
lift height (the amount by which the valve is lowered).

The vast majority of engines have fixed valve timing. This means that the parameters described above are determined only by the shape of the cam. camshaft... The disadvantage of such a constructive solution is that the shape of the cams calculated by the designers for the engine will be optimal only in a narrow range of revolutions. Civilian engines are designed in such a way that the valve timing corresponds to normal vehicle operating conditions. After all, if you make an engine that will drive very well “from the bottom”, then at above average rpm the torque, as well as the peak power, will be too low. It is this problem that the variable valve timing system solves.

How VVT works

The essence of the VVT system is to adjust the valve opening phases in real time, focusing on the engine operating mode. Depending on the design features each of the systems, this is implemented in several ways:

by turning the camshaft relative to the camshaft gear;
the inclusion of cams at certain speeds, the shape of which is suitable for power modes;
by changing the valve lift.

The most widespread are systems in which the phases are adjusted by changing the angular position of the camshaft relative to the gear. Despite the fact that in work different systems a similar principle is laid, many auto concerns use individual designations.

Renault – Variable Cam Phases (VCP).
BMW - VANOS. Like most automakers, initially only the intake camshaft was equipped with such a system. The system, in which fluid couplings for changing the valve timing are installed on the exhaust camshaft, is called Double VANOS.
Toyota - Variable Valve Timing with intelligence (VVT-i). As is the case with BMW, the presence of a system on the intake and exhaust camshafts is referred to as Dual VVT.
Honda - Variable Timing Control (VTC).
Volkswagen in this case acted more conservatively and chose an international name - Variable Valve Timing (VVT).
Hyundai, Kia, Volvo, GM - Continuous Variable Valve Timing (CVVT).

How phases affect engine performance

At low revs, the maximum filling of the cylinders will provide a late opening exhaust valve and early intake closure. In this case, the valve overlap (the position in which the exhaust and intake valves are simultaneously open) is minimal, so the possibility of pushing out the remaining in the cylinder is excluded. exhaust gases back to the inlet. It is because of the wide-phase ("riding") camshafts on forced motors often have to be installed increased revs idle move.

At high revs, to get the most out of the engine, the phases should be as wide as possible, since the pistons will pump much more air per unit of time. In this case, the overlapping of the valves will have a positive effect on the purging of the cylinders (the exit of the remaining exhaust gases) and the subsequent filling.

That is why the installation of a system that allows you to adjust the valve timing, and in some systems, the valve lift, to the engine operating mode, makes the engine more flexible, more powerful, more economical and at the same time more environmentally friendly.

Device, principle of operation of VVT

The phase shifter is responsible for the angular displacement of the camshaft, which is a fluid coupling, the operation of which is controlled by the engine ECU.

Structurally, the phase shifter consists of a rotor, which is connected to a camshaft, and a housing, the outer part of which is a camshaft gear. There are cavities between the housing of the hydraulic clutch and the rotor, the filling of which with oil leads to the movement of the rotor, and, consequently, the displacement of the camshaft relative to the gear. In the cavity, oil is supplied through special channels. The amount of oil entering through the channels is controlled by an electro-hydraulic distributor. The distributor is a conventional solenoid valve that is controlled by the ECU via a PWM signal. It is the PWM signal that makes it possible to smoothly change the valve timing.

The control system, in the form of an engine ECU, uses the signals of the following sensors:

DPKV (the crankshaft speed is calculated);
DPRV;
DPDZ;
DMRV;
DTOZH.

Systems with different cam shapes

Due to the more complex design, the system for changing the valve timing by acting on the rocker arms of the cams of different shapes has become less widespread. As in the case of Variable Valve Timing, carmakers use different designations to refer to systems that are similar in principle of operation.

Honda - Variable Valve Timing and Lift Electronic Control (VTEC). If both VTEC and VVT are used on the engine, then such a system is abbreviated as i-VTEC.
BMW - Valvelift System.
Audi - Valvelift System.
Toyota - Variable Valve Timing and Lift with intelligence from Toyota (VVTL-i).
Mitsubishi - Mitsubishi Innovative Valve timing Electronic Control (MIVEC).

Principle of operation

Honda's VTEC system is perhaps one of the most famous, but other systems work in a similar way.

As you can see from the diagram, in the low speed mode, the force on the valves through the rocker arms is transmitted by the run-in of the two outer cams. In this case, the middle rocker moves "idle". When switching to the mode high revs the oil pressure extends the locking rod (locking mechanism), which converts the 3 rocker arms into a single mechanism. The increase in valve travel is achieved due to the fact that the camshaft cam with the largest profile corresponds to the middle rocker arm.

A variation of the VTEC system is a design in which different rocker arms and cams correspond to the modes: low, medium and high revolutions. At low rpm, only one valve opens with a smaller cam, at medium rpm, two smaller cams open 2 valves, and at high rpm, the largest cam opens both valves.

The extreme round of development

A stepwise change in the duration of opening and the valve lift height allows not only to change the valve timing, but also to almost completely remove the function of regulating the engine load from the throttle valve. This is primarily about the Valvetronic system from BMW. It was BMW specialists who first achieved such results. Now similar developments have: Toyota (Valvematic), Nissan (VVEL), Fiat (MultiAir), Peugeot (VTI).

Open to a small angle throttle creates a significant opposition to the movement of air currents. As a result, part of the received from combustion air-fuel mixture energy is spent on overcoming pumping losses, which negatively affects the power and economics of the car.

In the Valvetronic system, the amount of air entering the cylinders is controlled by the degree of lift and the duration of the valve opening. This was realized by introducing an eccentric shaft and an intermediate lever into the design. The lever is connected by a worm gear with a servo drive, which is controlled by the ECU. Changes in the position of the intermediate lever shifts the impact of the rocker arm towards more or less opening of the valves. The principle of operation is shown in more detail in the video.

The split gear, which allows you to adjust the opening / closing phases of the valves, was previously considered an accessory only to sports cars. In many modern engines, the variable valve timing system is used routinely and works not only to increase power, but also to reduce fuel consumption and emissions of harmful substances into the environment. Let's consider how Variable Valve Timing (the international name for this type of systems) works, as well as some features of the VVT device on BMW, Toyota, Honda cars.

Fixed phases

It is customary to call the timing of the opening and closing moments of the intake and exhaust valves, expressed in degrees of rotation of the crankshaft relative to BDC and TDC, by the valve timing. In graphical terms, the period of opening and closing is usually shown with a diagram.

If we are talking about phases, then changes can be made:

the moment the intake and exhaust valves begin to open;
the duration of being in the open state;
lift height (the amount by which the valve is lowered).

The vast majority of engines have fixed valve timing. This means that the parameters described above are determined only by the shape of the camshaft cam. The disadvantage of such a constructive solution is that the shape of the cams calculated by the designers for the engine will be optimal only in a narrow range of revolutions. Civilian engines are designed in such a way that the valve timing corresponds to normal vehicle operating conditions. After all, if you make an engine that will drive very well “from the bottom”, then at above average rpm the torque, as well as the peak power, will be too low. It is this problem that the variable valve timing system solves.

How VVT works

The essence of the VVT system is to adjust the valve opening phases in real time, focusing on the engine operating mode. Depending on the design features of each of the systems, this is implemented in several ways:

by turning the camshaft relative to the camshaft gear;
the inclusion of cams at certain speeds, the shape of which is suitable for power modes;
by changing the valve lift.

The most widespread are systems in which the phases are adjusted by changing the angular position of the camshaft relative to the gear. Despite the fact that a similar principle is laid in the operation of different systems, many auto concerns use individual designations.

Renault – Variable Cam Phases (VCP).
BMW - VANOS. Like most automakers, initially only the intake camshaft was equipped with such a system. The system, in which fluid couplings for changing the valve timing are installed on the exhaust camshaft, is called Double VANOS.
Toyota - Variable Valve Timing with intelligence (VVT-i). As is the case with BMW, the presence of a system on the intake and exhaust camshafts is referred to as Dual VVT.
Honda - Variable Timing Control (VTC).
Volkswagen in this case acted more conservatively and chose an international name - Variable Valve Timing (VVT).
Hyundai, Kia, Volvo, GM - Continuous Variable Valve Timing (CVVT).

How phases affect engine performance

At low revs, maximum cylinder filling will ensure late opening of the exhaust valve and early closing of the intake valve. In this case, valve overlap (the position in which the exhaust and intake valves are simultaneously open) is minimized, so that the remaining exhaust gases in the cylinder cannot be pushed back into the intake. It is because of the wide-phase ("top") camshafts on forced motors that it is often necessary to set increased idle speed.

Device, principle of operation of VVT

The phase shifter is responsible for the angular displacement of the camshaft, which is a fluid coupling, the operation of which is controlled by the engine ECU.

The control system, in the form of an engine ECU, uses the signals of the following sensors:

DPKV (the crankshaft speed is calculated);
DPRV;
DPDZ;
DMRV;
DTOZH.

Systems with different cam shapes

Honda - Variable Valve Timing and Lift Electronic Control (VTEC). If both VTEC and VVT are used on the engine, then such a system is abbreviated as i-VTEC.
BMW - Valvelift System.
Audi - Valvelift System.
Toyota - Variable Valve Timing and Lift with intelligence from Toyota (VVTL-i).
Mitsubishi - Mitsubishi Innovative Valve timing Electronic Control (MIVEC).

Principle of operation

Honda's VTEC system is perhaps one of the most famous, but other systems work in a similar way.

As you can see from the diagram, in the low speed mode, the force on the valves through the rocker arms is transmitted by the run-in of the two outer cams. In this case, the middle rocker moves "idle". When switching to high speed mode, the oil pressure extends the locking rod (locking mechanism), which turns the 3 rocker arms into a single mechanism. The increase in valve travel is achieved due to the fact that the middle rocker arm corresponds to the camshaft cam with the largest profile.

The extreme round of development

The throttle valve open to a small angle creates significant resistance to the movement of air currents. As a result, part of the energy obtained from the combustion of the air-fuel mixture is spent on overcoming pumping losses, which negatively affects the power and economics of the car.

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

The device of the VVTI system valve of Toyota cars

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

General principle of the system

The main control device in this variable valve timing system is the VVTI clutch. By default, the engine designers designed the valve opening phases so as to obtain good traction at low engine speeds. As the speed rises, the oil pressure also increases, 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 have a special shape, and during the rotation of the element, the intake valves will open a little earlier. Accordingly, close later. This should have the best effect on the power and torque of the engine at high revs.

Detailed job description

The main control mechanism of the system (and this is the clutch) is installed on the engine camshaft pulley. Its body is connected to a star or the rotor is connected directly to the camshaft. Oil is supplied from one or both sides to each rotor petal on the clutch, thereby causing the camshaft to turn. When the engine is not running, the system automatically sets the maximum dwell angles. They correspond to the latest opening and closing of the 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 by a pin, which will be squeezed out by the oil itself when the lubricant pressure rises.

The system is controlled by a special valve. On a signal from the ECU, an electric magnet with the help of a plunger will begin to move the spool, thereby passing oil in one direction or the other. When the motor is at a standstill, this spool is moved by a spring to expose maximum angle delays. To turn the camshaft at a certain angle, oil under high pressure by means of a spool it 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 realizes that the camshaft is rotated to the desired angle, the pulley channels overlap and it will be further held in this position.

Typical Symptoms of VVTI System Problems

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

So, the car does not hold idle speed on the same level. This indicates that the VVTI valve is not working as expected. Also, the "braking" of the engine will tell about various malfunctions in the system. Often, with problems with this phase change mechanism, it is not possible for the motor to operate at low speeds. P1349 code may also indicate problems with the valve. If on a warm power unit high idle speed, the car does not drive at all.

Possible causes of valve failure

There are not so many main reasons for valve malfunctions. There are two that are especially common. So, the VVTI valve can 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 transmissions. Fault diagnosis is easily carried out by checking the resistance measurement of the coil winding of the sensor.

The second reason why the VVTI valve (Toyota) does not work properly or does not work at all is a sticking in the stem. The reason for such seizures may be commonplace 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, it is very easy to restore the mechanism - it is enough to clean the dirt from there. This can be done by soaking or soaking the element in special fluids.

How do I clean the valve?

Many faults can be repaired 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 is circled in the picture.

Cleaning can be done with carburetor cleaning fluids. To completely clean the system, the filter is also removed. This element is located under the valve - it is a plug with a hole for a hexagon. The filter must also be cleaned with this liquid. After all the operations, it remains only to collect everything in reverse order, and then install without resting on the valve itself.

How to check the VVTI valve?

It is very easy to check if the valve is working. 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. At the moment of energization, the stem will be pulled inward. And when the circuit breaks, he will come back.

If the stem moves easily, the valve is fully functional. It only needs to be rinsed, 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 of the valve

First, dismantle the generator control bar. Then remove the bonnet lock fasteners. This will give access to the generator axle bolt. Next, unscrew the bolt that holds the valve itself and remove it. Then remove the filter. If the last element and valve are dirty, then these parts are cleaned. Repairs are inspection and lubrication. You can also replace the O-ring. More serious renovation is not possible. If a part doesn't work, it is 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, many car owners, after the replacement, claim that the car began to work much better and fuel consumption has decreased.

To begin with, remove the regulating bar of the generator. Then remove the fasteners and gain access to the generator bolt. Cut off the bolt that holds desired valve... The old element can be pulled out and discarded, and a new one is put in place of the old one. Then the bolt is tightened and the vehicle can be operated.

Conclusion

Modern cars are both good and bad at the same time. They are bad in that 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.