The Function of The Valve
The role of the valve is specifically responsible for the input of air into the engine and the exhaust gas after combustion. From the engine structure, divided into intake valve (intake valve) and exhaust valve (exhaust valve). The role of the intake valve is to suck air into the engine, mixed with fuel combustion; the role of the exhaust valve is to exhaust the exhaust gas after combustion and heat dissipation.
Valve, Gench Engine Valve, is an important part of the engine. The role of the valve is specifically responsible for the input of air into the engine and the discharge of exhaust gases after combustion.
From the engine structure, divided into intake valve (intake valve) and exhaust valve (exhaust valve). The role of the intake valve is to suck air into the engine, and fuel mixing combustion; the role of the exhaust valve is to exhaust the combustion exhaust gas and heat dissipation.
The material of the valve is usually divided into 40Cr, 4Cr9Si2, 4Cr10Si2Mo, 21-4N and 23-8N etc. 5Cr8Si2, 4Cr9Si3, 21-2N, 21-12N, 23-8N, XB etc. have been used in large quantities on some introduced models. High-temperature nickel-based alloys are also beginning to be used on the exhaust valves of high-load diesel engines.
Classified from the finished structure of the valve, usually divided into the whole valve, bimetal butt-weld valve and hollow sodium-filled valve, etc..
Additional processes are usually top weld piece, top overlay, taper overlay, surface nitriding treatment, surface chrome plating treatment, etc.
Working Conditions of The Valve
Valve and valve seat is one of the key components affecting the reliability and safety of the engine, mainly used to start and close the engine work process of the intake and exhaust tract, control the fuel mixture or air into and exhaust gas discharge. Valve and valve seat work in a very harsh environment, in addition to high-temperature gas corrosion, but also to withstand the impact of the burst of pressure in the cylinder, the main failure mode is wear.
Forms of Valve Failure
The valve and valve seat wear loss usually has four types, namely contact fatigue wear, high-temperature corrosion wear, abrasive wear and high-temperature creep, and the wear loss process follows the general mechanical parts wear law, creep and corrosion media at high temperatures play an accelerating role in the process.
Valve and valve seat at the same time there are some abnormal wear factors, such as: the combustion chamber air contains a lot of dust; too much carbon in the combustion chamber; combustion chamber water into the valve and valve seat rust, etc.. Engine valve and valve seat wear loss effect makes the intake and exhaust tract is not closed, resulting in engine leakage, cylinder pressure is reduced, the power drops, fuel consumption increases, in serious cases will also lead to engine exhaust black smoke, air filter fugitive air, starting difficulties, etc..
Composition of The Valve
Valve is composed of valve head and rod. Valve head temperature is very high (intake valve 570 ~ 670K, exhaust valve 1050 ~ 1200K), and also subject to the pressure of the gas, valve spring force and transmission components inertia force, its lubrication, cooling conditions are poor, requiring the valve must have a certain strength, stiffness, heat and wear resistance. Intake valves are generally alloy steel (chrome steel, nickel-chromium steel), exhaust valves using heat-resistant alloy (silicon chrome steel). Sometimes in order to save heat-resistant alloy, the exhaust valve head with heat-resistant alloy, and the rod with chrome steel, and then the two welded together.
The shape of the valve head is flat top, spherical top and flared top, etc. Flat top is generally used. Flat top valve head structure is simple, easy to manufacture, small heat absorption area, small mass, intake and exhaust valves can be used. Spherical top valve is suitable for exhaust valve, its strength is high, 5i7654 exhaust resistance is small, exhaust gas elimination effect is good, but its heat area is large, mass and inertia is large, processing is complicated. The flared type has a certain streamline shape and can reduce the intake resistance, but its head has a large heat area and is only suitable for intake valves.
Valve cone angle is the angle of the valve sealing surface, generally 45 °, some are 30 ° (CA1091 sex car 6102 type engine). 30 ° of the valve is considered the same lift, valve taper is small, the valve through the end surface is large, the intake resistance is small, but due to the taper of the valve head edge is thin, rigidity is small, poor sealing and thermal conductivity, generally used for the intake valve. The thickness of the valve edge is generally 1 ~ 3mm, to prevent the work and valve seat impact and damage or burned by high temperature. In order to reduce the intake resistance, improve the efficiency of the cylinder intake, most of the engine intake valve than the exhaust door is large. Used intake valve and exhaust door color is also different.
The valve stem is cylindrical, in the valve guide for reciprocating movement,such as kubota engine rebuild cost its surface must be heat-treated and polished. The shape of the valve stem end depends on the form of valve spring fixing, the common structure is two halves of the locking plate to fix the spring seat, the end of the valve stem has a ring groove to install the locking plate, some are fixed with a locking pin, the end of which has a hole for the installation of the locking pin.
Status of The Valve
In order to improve the intake and exhaust efficiency, now more than the use of multi-valve technology, common is each cylinder arrangement with four valves (there are also single-cylinder 3 or 5 valve design, the same principle, such as the Audi A6 engine), 4 cylinders is a total of 16 valves, we often see on the car data “16V” on the engine a total of 16 valves. This multi-valve structure is easy to form a compact combustion chamber, the injector arrangement in the center, so that the oil and gas mixture can be more rapid, more uniform combustion, the weight of the valve and the opening of the valve is properly reduced, so that the valve opening or closing speed faster.