Valve
Auto Terms,  Car device,  Engine unit

Engine valve. Purpose, device, design

In order for a four-stroke internal combustion engine of any car to work, its device includes many different parts and mechanisms that are synchronized with each other. Among such mechanisms is the timing. Its function is to ensure the timely operation of the valve timing. What it is is described in detail here.

In short, the gas distribution mechanism opens the intake / exhaust valve at the right time to ensure the timing of the process when performing a particular stroke in the cylinder. In some case, it is required that both holes are closed, in the other, one or even both are open.

Engine valve. Purpose, device, design

Let's take a closer look at one detail that allows you to stabilize this process. This is a valve. What is the peculiarity of its design, and also how does it work?

What is an engine valve

A valve is a metal part installed in the cylinder head. It is part of the gas distribution mechanism and is driven by a camshaft.

Depending on the modification of the car, the engine will have a lower or upper timing. The first option is still found in some old modifications of power units. Most manufacturers have long since switched to the second type of gas distribution mechanisms.

Engine valve. Purpose, device, design

The reason for this is that such a motor is easier to tune and repair. To adjust the valves, it is enough to remove the valve cover and it is not necessary to dismantle the entire unit.

Purpose and features of the device

The valve is a spring-loaded element. At rest, it tightly closes the hole. When the camshaft turns, the cam located on it pushes the valve down, lowering it. This opens the hole. The camshaft arrangement is described in detail in another review.

Each detail plays its own function, which is structurally impossible to perform for a similar element located nearby. There are at least two valves per cylinder. In more expensive models, there are four of them. In most cases, these elements are in pairs, and they open different groups of holes: some are inlet and others are outlet.

Engine valve. Purpose, device, design

Intake valves are responsible for the intake of a fresh portion of the air-fuel mixture into the cylinder, and in engines with direct injection (a type of fuel injection system, it is described here) - the volume of fresh air. This process occurs at the moment when the piston completes the intake stroke (from top dead center, after removing the exhaust, it moves downward).

The exhaust valves have the same opening principle, only they have a different function. They open a hole for the removal of combustion products into the exhaust manifold.

Engine valve design

The parts in question are included in the valve group of the gas distribution mechanism. Together with other details, they provide a timely change in valve timing.

Consider the design features of valves and related parts, on which their effective operation depends.

Valves

The valves are in the form of a rod, on one side of which there is a head or poppet element, and on the other, a heel or end. The flat part is designed for tight sealing of openings in the cylinder head. A smooth transition is made between the cymbal and the rod, not a step. This allows the valve to be streamlined so that it does not create resistance to the fluid movement.

In the same motor, the intake and exhaust valves will be slightly different. So, the first types of parts will have a wider plate than the second. The reason for this is the high temperature and high pressure when the combustion products are removed through the gas outlet.

Engine valve. Purpose, device, design

To make the parts cheaper, the valves are in two parts. They differ in composition. These two parts are joined by welding. The working chamfer of the outlet valve disc is also a separate element. It is deposited from another type of metal, which has heat-resistant properties, as well as resistance to mechanical stress. In addition to these properties, the end face of the exhaust valves is less susceptible to rust formation. True, this part in many valves is made of a material identical to the metal from which the plate is made.

The heads of the inlet elements are usually flat. This design has the required rigidity and ease of execution. Uprated engines can be fitted with concave disc valves. This design is slightly lighter than the standard counterpart, thereby reducing the inertia force.

As for the exhaust counterparts, the shape of their head will be either flat or convex. The second option is more efficient, as it provides better removal of gases from the combustion chamber due to its streamlined design. Plus the convex plate is more durable compared to the flat counterpart. On the other hand, such an element is heavier, because of which its inertia suffers. These types of parts will require stiffer springs.

Engine valve. Purpose, device, design

Also, the stem design of this type of valves is slightly different from the intake parts. To provide better heat dissipation from the element, the bar is thicker. This increases the resistance to strong heating of the part. However, this solution has a disadvantage - it creates a greater resistance to the removed gases. Despite this, manufacturers still use this design, because the exhaust gas is emitted under strong pressure.

Today there is an innovative development of forced-cooled valves. This modification has a hollow core. Liquid sodium is pumped into its cavity. This substance evaporates when heated strongly (located near the head). As a result of this process, the gas absorbs heat from the metal walls. As it rises upward, the gas cools and condenses. The liquid flows down to the base, where the process is repeated.

In order for the valves to ensure the tightness of the interface, a chamfer is selected in the seat and on the disc. It is also done with a bevel to eliminate the step. When installing the valves on the motor, they are rubbed against the head.

Engine valve. Purpose, device, design

The tightness of the seat-to-head connection is affected by the corrosion formed on the shoulder, and the outlet parts often suffer from carbon deposits. To extend valve life, some engines are equipped with an additional mechanism that turns the valve slightly when the outlet is closed. This removes the resulting carbon deposits.

Sometimes it happens that the valve shank breaks. This will cause the part to fall into the cylinder and damage the motor. For failure, it is enough for the crankshaft to make a couple of inertial revolutions. To prevent this situation, auto valve manufacturers can equip the part with a retaining ring.

A little about the features of the valve heel. This part is subjected to frictional force as it is affected by the camshaft cam. For the valve to open, the cam must push it down with enough force to compress the spring. This unit must receive enough lubrication, and so that it does not wear out quickly, it is hardened. Some motor designers use special caps to prevent wear of the rod, which are made of materials that are resistant to such loads.

Engine valve. Purpose, device, design

To prevent the valve from getting stuck in the sleeve during heating, the part of the stem near the cymbal is slightly thinner than the part near the heel. To fix the valve spring, two grooves are made at the end of the valves (in some cases, one), into which the crackers of the support are inserted (a fixed plate where the spring rests).

Valve springs

The spring affects the efficiency of the valve. It is needed so that the head and seat provide a tight connection, and the working medium does not penetrate through the formed fistula. If this part is very stiff, the camshaft cam or heel of the valve stem will quickly wear out. On the other hand, a weak spring will not be able to ensure a tight fit between the two elements.

Since this element works under conditions of rapidly changing loads, it can break. Powertrain manufacturers use different types of springs to help prevent quick breakdowns. In some timing, double types are installed. This modification reduces the load on an individual element, thereby increasing its working life.

Engine valve. Purpose, device, design

In this design, the springs will have a different direction of the turns. This prevents particles of the broken part from getting between the turns of the other. Spring steel is used to make these elements. After the product is formed, it is tempered.

At the edges, each spring is ground so that the entire bearing part is in contact with the valve head and the upper plate attached to the cylinder head. To prevent the part from being oxidized, it is coated with a layer of cadmium and galvanized.

In addition to the classic timing valves, a pneumatic valve can be used in sports vehicles. In fact, this is the same element, only it is set in motion by a special pneumatic mechanism. Thanks to this, such an accuracy of operation is achieved that the motor is capable of developing incredible revolutions - up to 20 thousand.

Engine valve. Purpose, device, design

Such a development appeared back in the 1980s. It contributes to clearer opening / closing of the holes, which no spring can provide. This actuator is powered by compressed gas in a reservoir above the valve. When the cam hits the valve, the impact force is approximately 10 bar. The valve opens, and when the camshaft weakens the impact on its heel, the compressed gas quickly returns the part to its place. To prevent pressure drop due to possible leaks, the system is equipped with an additional compressor, the reservoir of which is at a pressure of about 200 bar.

Engine valve. Purpose, device, design
James Ellison, PBM Aprilia, CRT Test Jerez Feb 2012

This system is used in motorcycles of the MotoGP class. This transport with one liter of engine volume is capable of developing 20-21 thousand crankshaft revolutions. One model with a similar mechanism is one of the Aprilia motorcycle models. Its power was an incredible 240 hp. True, this is too much for a two-wheeled vehicle.

Valve guides

The role of this part in the operation of the valve is to ensure that it moves in a straight line. The sleeve also helps to cool the rod. This part needs constant lubrication. Otherwise, the rod will be subjected to constant thermal stress and the sleeve will quickly wear out.

The material that can be used to make such bushings must be heat resistant, withstand constant friction, well remove heat from the adjacent part, and withstand high temperatures. Such requirements can be met by pearlite gray cast iron, aluminum bronze, ceramic with chrome or chrome-nickel. All of these materials have a porous structure, thereby helping to retain oil on their surface.

Engine valve. Purpose, device, design

The bushing for the exhaust valve will have slightly more clearance between the stem than the inlet equivalent. The reason for this is the greater thermal expansion of the waste gas removal valve.

Valve seats

This is the contact portion of the cylinder head bore near each cylinder and valve disc. Since this part of the head faces mechanical and thermal stresses, it must have good resistance to high heat and frequent impacts (when the car is driving fast, the camshaft rpm is so high that the valves literally fall into the seat).

If the cylinder block and its head are made of aluminum alloy, the valve seats will necessarily be made of steel. Cast iron already copes well with such loads, so the saddle in this modification is made in the head itself.

Engine valve. Purpose, device, design

Plug-in saddles are also available. They are made from alloyed cast iron or heat-resistant steel. So that the chamfer of the element does not wear out so much, it is performed by layering heat-resistant metal.

The insert seat is fixed in the head bore in different ways. In some cases, it is pressed in, and a groove is made in the upper part of the element, which is filled with the metal of the head body during installation. This creates the integrity of the assembly from different metals.

The steel seat is attached by flaring the top in the head body. There are cylindrical and conical saddles. In the first case, they are mounted to the stop, and the second have a small end gap.

Number of valves in the engine

A standard 4-stroke combustion engine has one camshaft and two valves per cylinder. In this design, one part is responsible for the injection of a mixture of air or just air (if the fuel system has direct injection), and the other is responsible for the removal of exhaust gases into the exhaust manifold.

More efficient operation in the engine modification, in which there are four valves per cylinder - two for each phase. Thanks to this design, a better filling of the chamber with a new portion of VTS or air is provided, as well as accelerated removal of exhaust gases and ventilation of the cylinder cavity. Cars began to be equipped with such motors starting in the 70s of the last century, although the development of such units began in the first half of the 1910s.

Engine valve. Purpose, device, design

To date, to improve the operation of power units, there is an engine development in which there are five valves. Two for the outlet, and three for the inlet. An example of such units are the models of the Volkswagen-Audi concern. Although the principle of operation of the timing belt in such a motor is identical to the classical options, the design of this mechanism is complicated, which is why innovative development is expensive.

A similar unconventional approach is also being taken by the automaker Mercedes-Benz. Some engines from this automaker are equipped with three valves per cylinder (2 intake, 1 exhaust). Additionally, two spark plugs are installed in each chamber of the pot.

Engine valve. Purpose, device, design

The manufacturer determines the number of valves by the size of the chamber into which fuel and air enters. To improve its filling, it is necessary to ensure a better inflow of the fresh portion of BTC. To do this, you can increase the diameter of the hole, and with it the size of the plate. However, this modernization has its own limits. But it is quite possible to install an additional intake valve, so automakers are developing just such cylinder head modifications. Since the intake speed is more important than the exhaust (the exhaust is removed under the pressure of the piston), with an odd number of valves, there will always be more intake elements.

What valves are made of

Since the valves operate under conditions of maximum temperature and mechanical stress, they are made of metal that is resistant to such factors. Most of all heats up, and also encounters mechanical stress, the place of contact between the seat and the valve disc. At high engine speeds, the valves quickly sink into the seats, creating a shock at the edges of the part. Also, in the process of combustion of a mixture of air and fuel, the thin edges of the plate are subjected to sharp heating.

Engine valve. Purpose, device, design

In addition to the valve disc, the valve sleeves are also stressed. The negative factors that lead to wear on these elements are insufficient lubrication and constant friction during fast valve movement.

For these reasons, the following requirements are imposed on valves:

  1. They must seal the inlet / outlet;
  2. With strong heating, the edges of the plate should not deform from impacts on the saddle;
  3. Must be well streamlined so that no resistance is created to the incoming or outgoing medium;
  4. The part shouldn't be heavy;
  5. The metal must be tough and durable;
  6. Should not undergo strong oxidation (when the car rarely drives, the edges of the heads should not rust).

The part that opened the hole in diesel engines heats up to 700 degrees, and in gasoline counterparts - up to 900 above zero. The situation is complicated by the fact that with such strong heating, the open valve does not cool. The outlet valve can be made of any high alloy steel that can withstand high heat. As already mentioned, one valve is made from two different types of metal. The head is made of high temperature alloys and the stem is made of carbon steel.

As for the intake elements, they are cooled by contact with the seat. Nevertheless, their temperature is also high - about 300 degrees, so it is not allowed that the part deforms when heated.

Engine valve. Purpose, device, design

Chromium is often included in the raw material for valves, which increases its thermal stability. In the process of combustion of gasoline, gas or diesel fuel, some substances are released that can aggressively affect metal parts (for example, lead oxide). Nickel, manganese and nitrogen compounds may be included in the valve head material to prevent adverse reaction.

And finally. It's not a secret for anyone that in any engine, over time, the valves burn out. Here is a short video about the reasons for this:

REASONS WHICH THE VALVES IN THE CAR ENGINE BURN OUT 95% of drivers DIDN'T KNOW IT

Questions and answers:

What do valves in an engine do? As they open, the intake valves allow fresh air (or air / fuel mixture) to flow into the cylinder. Open exhaust valves lead exhaust gases to the exhaust manifold.

How to understand that the valves are burnt out? A key feature of burned-out valves is the triple movement of the motor regardless of rpm. At the same time, the engine power is decently reduced, and the fuel consumption increases.

Which parts open and close the valves? The valve stem is connected to the camshaft cams. In many modern engines, hydraulic lifters are also installed between these parts.

2 comment

  • Husseyn

    salami. manim masini Vaz 21099 . Let me say one lapel from each month. quickly burns. what could be the reason for this

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