4 Valve Engines

4-VALVE ENGINES

Guided by

Mr. P. D. Sudersanan Asst prof, mech dept,

Dr. TTIT

INTRODUCTION• In automotive engineering, an engine is referred to as multi-valve

when each cylinder has more than two valves. Such designs have been around since at least 1912 and perhaps earlier.

• Most poppet valve, four-stroke internal combustion engines have at least two valves per cylinder (Diesel engines with one valve exist.) — One for intake of air and fuel, and another for exhaust of combustion products. Adding more valves improves the flow of intake and exhaust gases, potentially improving combustion efficiency, power, and performance.

• Many engines were made with two valves per cylinder, but, starting in the late 80s, a virtual explosion of multi-valve and DOHC engines came to market. As a result, even the most basic engines today usually contain four valves per cylinder, though the two valve configuration is still popular.

Types of Engines

• External combustion Engines

• Internal combustion Engines

Two stroke Engines

Four stroke Engines

Rotary Engines

Two stroke Engines• A two-stroke engine is an internal

combustion engine that completes the thermodynamic cycle in two movements of the piston compared to twice that number for a four-stroke engine

• This increased efficiency is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform simultaneously the intake and exhaust (or scavenging) functions

• In this way two-stroke engines often

provide strikingly high specific power

Four stroke Engines

• 4 stroke engines are typically much larger capacity than 2 stroke engines

• 4 stroke engines typically have valves at the top of the combustion chamber

• The simplest type has one intake and one exhaust valve • More complex engines have two of one and one of the other,

or two of each• The valves are opened and closed by a rotating camshaft at

the top of the engine• The camshaft is driven by either gear directly from the crank,

or more commonly by a timing belt

• During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring

• As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture

• At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward

• At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder

Rotary engines

• The Wankel rotary engine is a fascinating beast that features a very clever rearrangement of the four elements of the Otto cycle. It was developed by Felix Wankel in the 1950s

• In the Wankel, a triangular rotor incorporating a central ring gear is driven around a fixed pinion within an oblong chamber

WORKING OF WANKEL ENGINE

• The fuel/air mixture is drawn in the intake port during this phase of the rotation

• The mixture is compressed here

• The mixture burns here, driving the rotor around

• And the exhaust is expelled here

VALVES• All four-stroke internal combustion engines employ valves to

control the admittance of fuel and air into the combustion chamber

• In piston engines, the valves are grouped into 'inlet valves' which admit the entrance of fuel and air and 'outlet valves' which allow the exhaust gases to escape

• Each valve opens once per cycle and the ones that are subject to extreme accelerations are held closed by springs that are typically opened by rods running on a camshaft rotating with the engines' crankshaft

• Continuous combustion engines—as well as piston engines—usually have valves that open and close to admit the fuel and/or air at the startup and shutdown. Some valves feather to adjust the flow to control power or engine speed as well

Valve Classification

• Poppet valve

• Sleeve valve

• Rotary valve

POPPET VALVE• A poppet valve is a valve

consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide

• Poppet valves are used in most piston engines to open and close the intake and exhaust ports in the cylinder head

• The valve is usually a flat disk of metal with a long rod known as the valve system out one end

• The stem is used to push down on the valve and open it, with a spring generally used to close it when the stem is not being pushed on

Poppet valves in action in top of the cylinder

Sleeve valve

SLEEVE VALVE• The sleeve valve is a type of valve mechanism

for piston engines• A sleeve valve takes the form of one or more

machined sleeves. It fits between the piston and the cylinder wall in the cylinder of an internal combustion engine where it rotates and/or slides, ports (holes) in the side of the valve aligning with the cylinder's inlet and exhaust ports at the appropriate stages in the engine's cycle.

ROTARY VALVE

• A rotary valve is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes.

The common stopcock is the simplest form of rotary valve. Rotary valves have been applied in numerous applications, including:

• Changing the pitch of brass instruments • Controlling the steam and exhaust ports of steam

engines, most notably in the Corliss engine. • Periodically reversing the flow of air and fuel across

the open hearth furnace. • Loading sample on chromatography columns. • Certain types of 2-stroke gasoline engines.

MULTI-VALVE

• 3-valve engines

• 4-valve engines

• 5-valve engines

3-VALVE ENGINES

• The earliest mass production multi-valve engines were 3-valves because of its simple construction - it needs only a single camshaft to drive both intake valves and the exhaust valve of each cylinder.

• Today, there are still a few car cars using this cheap but inefficient design, such as Fiat Palio and Mercedes V6 and V8 engines.

4-valve engines

• A 4-Valve engine is designed for better performance than a regular 2-Valve engine

• More power: The 4-valve provides for a greater intake and exhaust area resulting in more power

• More Mileage: 4-valve not only enhances the performance but also returns a very good fuel economy

• More green: Comfortably meets BSIII regulations

What is the 4-valve engine?

• An engine that has valves that let the air-fuel mixture into the combustion chamber to be burned and then draw out the exhaust gas after the combustion. A conventional engine has one intake valve to let in the air-fuel mixture and one exhaust valve to let out the exhaust gases. But the 4-valve engine has two intake and two exhaust valves.

• A typical 2-valve engine has just 1/3 combustion chamber head area covered by the valves, but a 4-valve head increases that to more than 50%, hence smoother and quicker breathing.

• 4-valve design also benefits from a clean and effective combustion, because the spark plug can be placed in the middle.

• 4 valves are better to be driven by twin-cam, one for intake valves and one for exhaust valves.

• 4-valve type and its shape is designed with the minimum area necessary for the two intake and two exhaust valves.

• At the same time it is designed with a minimum intake and exhaust valve angles to realize an optimum combustion chamber shape.

MERITS:-

• The first merit of 4-valve design is that it allows the spark plug to be positioned in the center of the combustion chamber to provide more efficient flame spread and combustion. In other words, it enables highly efficient combustion.

• Also, the 4-valve design enables greater overall valve area than a 2-valve system for more efficient (per unit of area) intake and exhaust function. This is the second major merit.

COMPARISION OF 4-VALVES OVER 2-VALVES

• A conventional engine has one intake valve to let in the air-fuel mixture and one exhaust valve to let out the exhaust gases. But the 4-valve engine has two intake and two exhaust valves

• 4-valves is better than two because 4-valves give an engine steadier low-speed performance and a better acceleration feeling

• That’s why most race engines and high-performance engines have four valves.

For example, Yamaha’s YZR-M1 MotoGP race machine has four valves.

• The name of the game is velocity and turbulence/mixing of the intake charge at differing engine speeds. At low engine speeds, one intake valve gives increased velocity, hence better gas mixing and better cylinder filling. If you open a second intake valve at low engine speed, the velocity drops dramatically, leaving poor intake filling and a lean intake charge. The result is engine knock and less torque. On the other hand, at high RPM, breathing is the name of the game. The valves are open such a short length of time you need the maximum available intake area. Therefore 2 intake valves work better at high RPM. All of this is of course subject to the exhaust system design. A proper extractor exhaust can make a significant difference on a two valve system and a restrictive exhaust can nullify all the gains of a 4 valve system.

• When you have only 2 valves, the air/fuel mixture entering the cylinder can be tangential to the circle of the cylinder, giving a high degree of swirl, better air/fuel mixing and hence better performance at lower revs in an SI engine. At higher revs, enough turbulence is available to create good mixing, and so 4 valves are better, as they allow greater airflow

This technology is adopted on

•YZF R15 •PULSAR 135cc

5-valve engines

• It is arguable that whether 5 valves per cylinder helps raising engine efficiency

• 5-valve design doesn’t guarantee covering more head area than 4-valve

• All existing 5-valve engines have 3 intake valves and 2 exhaust valves per cylinder

• The Ferrari F355 makes use of this to enhance high-speed breathing but faster breathing also harms low-speed torque if no counter measure is taken. Therefore it is really more suitable to sports cars

• The advantage of 5-valve engine is still under question

VALVE TIMING DIAGRAM

Types of overhead camshaft

Single overhead camshaft (SOHC)

Double overhead camshafts (DOHC)

SINGLE OVERHEAD CAMSHAFT (SOHC)

• Single overhead camshaft (SOHC) is a design in which one camshaft is placed within the cylinder head

• The SOHC design has less reciprocating mass than a comparable pushrod design. This allows for higher engine speeds, which in turn will increase power output for a given torque

• The cam operates the valves directly or through a rocker arm, as opposed to overhead valve pushrod engines which have tappets, long pushrods, and rocker arms to transfer the movement of the lobes on the camshaft in the engine block to the valves in the cylinder head

• SOHC designs offen reduced complexity compared to pushrod designs when used for multi-valve heads in which each cylinder has more than two valves

DOUBLE OVERHEAD CAMSHAFT(DOHC)

• A double overhead camshaft valve train layout is characterized by two camshafts located within the cylinder head, one operating the inlet valves and one operating the exhaust valve

CONCLUSION 4-valve facilitate effective breathing and hence complete combustion of fuel

can be achieved

4-valve systems parallely provide complete escape of the productsof combustion due to which fresh air fuel mixture is completely accomidated

4-valve increases turbulance and hence uniform mixture of air fuel takes and hence complete combustion is achieved and pre ignition is avoided

4-valve require a complex DOHC mechanism which increases the production cost but in a long run it is compensated

By employing camless actuating mechanism, 4-valve technology can be adopted for small engine

Further improvement in 4-valve technology is in process so there is scope for improvement in technology as well as cost can be reduced

REFERENCES

• Automotive Engineering by R.P.Gupta

• Automotive Engineering by Kripal singh

• www.google.com

• www.wikipedia.com

• www.howstuffworks.com

• www.answers.com

THANK YOU