Engine valve
The valve is a part of the gas distribution mechanism. Valve mechanism (valve drive mechanism) is an integral part of the gas distribution mechanism (Timing).
Timing is nizhneklapannym and verkhnekapannym. Modern power units everywhere have the upper arrangement of valves.
The valve implements a direct supply to the cylinders of a certain portion of the fuel-air mixture or only air, and also produces exhaust gases. Four-stroke internal combustion engine requires at least two valves per cylinder for normal operation.
There are two types of valves, which depends on their direct function:
- inlet valve;
- exhaust valve;
Today, plate-type valves are installed on modern motors, having a rod. The valve device includes a so-called valve plate. The most common design of the internal combustion engine received valves, which are located in the cylinder head (GBC). That place, where the valve is in contact with the cylinder head, called the valve seat. ICE valve seat steel or cast iron, pressed into the cylinder head.
The highest quality filling of the engine cylinder with fuel-air mixture or air requires, so that the diameter of the inlet valve plate is larger, than the exhaust valve. Inlet and outlet valves have some differences for this reason. The inlet valve often gets a larger plate diameter. This is done for that, to improve the filling of the cylinders with fuel-air mixture or air only.
As for the exhaust valve, increasing the diameter of his plate is also a necessity. This is necessary for better cleaning of the cylinders from combustion products. Note, that the size of the inlet and outlet valves is limited by the size of the combustion chamber itself, which is made in the cylinder head. Qualitative filling of cylinders and cleaning are realized not by increase in diameter of a plate of one valve, and by installing more valves per cylinder.
ICE valves in the process of motor operation experience severe mechanical and thermal loads. For this reason, they are made of special heat-resistant and wear-resistant metal alloys. The edge of the valve plate can be reinforced, sometimes the plate itself is reinforced by ceramic spraying. As for the rod, then an all-metal rod is provided for the intake valve. The exhaust valve has a hollow rod, additionally receives sodium filling to improve the cooling of the valve plate.
Increased attention is paid to the issue of cooling the exhaust valves, especially for productive power units. Exhaust valves are subjected to a much higher thermal load. As already mentioned, valves in such engines have an empty rod, which is filled with sodium inside. This solution is an effective way of cooling. The specified sodium at an exit of the engine on working temperature melts inside a hollow core of the valve., and then flows in molten form. This transfers excess heat from the heated valve plate to its rod.
The location of the valve plate to the unit is called the chamfer. To ensure that the chamfer does not suffer from the accumulation of soot, and even heat distribution was implemented, solutions for rotation are used in the design of the valve mechanism (turning) valve during engine operation.
The modern device of the most widespread engine provides the scheme with four valves, which means the presence of two inlet and two outlet valves for each individual cylinder. At the time of opening (the valve lowers) the inlet valve forms an annular passage. Through this passage between the valve plate and the valve seat, the fuel-air mixture or only air enters the cylinder.. The efficiency of filling the cylinder will depend on the cross-sectional area, which further affects the performance of the piston during operation.
Two-valve can also meet, three-valve and five-valve circuits of the timing device. In the first case, only one inlet and one outlet valve per cylinder is used. For three-valve circuits is characterized by the presence of two inlet and one outlet valve. A five-valve circuit means, standing three inlet and two outlet valves. The number of valves per cylinder depends on the total size of the combustion chamber of a particular engine, implementation of the valve actuator, degree of forcing of the motor, as well as a number of other factors.
The opening of the valve is realized by pressing the valve rod. The valve actuator is responsible for opening. This drive transmits the force from the camshaft (camshaft). Modern engines use two basic valve drive schemes: the drive by means of hydraulic pushers of the valve and realization of the drive by means of roller levers.
Closing the valve during the operation of the internal combustion engine is carried out using a special spring of a certain stiffness. The stiffness of such a spring must be limited, so as not to create large shock loads on the valve seats. The force of the spring forces the valve plate to tightly close the inlet or outlet channel. The valve spring is attached to the rod by means of a plate of the valve spring and crackers. During engine operation, especially under load, resonant oscillations may occur on the valves. To eliminate this nuance, two valve springs with multidirectional turns can be installed at once.
The stiffness of such springs is less compared to solutions, which were obtained with only one spring. The use of two springs implies that, that they are wound in different directions. This is to prevent the valve from jamming as a result of a single spring breaking. Thus, the engineers eliminated the risk of the coils of one valve spring getting between the coils of another. To reduce friction, the valve mechanism structurally has the above-mentioned rollers (roller lever), which are on the pushers and levers of the valve actuator.
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