Cylinder head

Last updated
K20 head.jpg
Side view of a DOHC cylinder head (with the valves and camshafts installed)
Cylinderhead.JPG
Underside of a OHV cylinder head (with the valves installed)

In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders [1] and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern overhead valve and overhead camshaft engines, the cylinder head is a more complicated block often containing inlet and exhaust passages, coolant passages, valves, camshafts, spark plugs and fuel injectors. Most straight engines have a single cylinder head shared by all of the cylinders and most V engines have two cylinder heads (one per bank of cylinders).

Contents

Design

A summary of engine designs is shown below, in chronological order for automobile usage.

Valve and camshaft configurations
TypeCamshaft
location
Intake valves
location
Exhaust valves
location
Sidevalve
(flathead)
BlockBlockBlock
Inlet over exhaust
(IOE)
BlockHeadBlock
Overhead valve
(OHV)
BlockHeadHead
Overhead camshaft
(OHC)
HeadHeadHead

Sidevalve engines

In a flathead (sidevalve) engine, all of the valvetrain components are contained within the block, therefore the head is usually a simple sheet of metal bolted to the top of the engine block. Sidevalve engines were once universal in automobiles but are now largely obsolete in automobiles, aside from small engines such as lawnmowers, weed trimmers and chainsaws.

A later development called the intake over exhaust (IOE) engine, which combined elements of the sidevalve and overhead valve designs. Used extensively in American motorcycles in the early 1900s, the IOE engine remained in production in limited numbers until the 1990s. IOE engines are more efficient than sidevalve engines, but also more complex, larger and more expensive to manufacture.

Overhead valve & overhead camshaft engines

In an overhead valve (OHV) or overhead camshaft (OHC) engine, a cylinder head consists of several passages (called ports); some of which form the path for intake gasses from the intake manifold to the combustion chamber, and the others are for exhaust gases to travel from combustion chamber to the exhaust manifold. The cylinder head also contains the valves and the spark plugs.

Specifically in an OHV engine, a single camshaft is located within the engine block and uses pushrods and rocker arms to actuate valves. OHV engines are typically more compact than equivalent DOHC engines, however they have largely been replaced by DOHC designs, except in some American V8 engines.

In an overhead camshaft OHC design, the cylinder head contains the valves, spark plugs and inlet/exhaust tracts (as per an OHV engine), but the camshaft is now located in the cylinder head instead of the engine block. [2] The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and still also utilizing rocker arms (but without any pushrods), or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing 'bucket' tappets. OHC engines with a single camshaft per cylinder bank were widely used in automobiles in the 1960s to 1990s, with most designs using a rocker arm to actuate the valves on the opposite side of the engine to the camshaft. OHC engines with dual camshafts per cylinder bank (DOHC engines) have become widespread in modern automobile engines since the 1990s. DOHC engines allow optimum positioning of the valves for a crossflow cylinder head and direct actuation of valves (i.e. without rockers). They therefore generally allow for higher-RPM operations, however they are typically larger in size (especially width) than equivalent OHV or SOHC engines.

For water-cooled OHV and OHC engines, the cylinder head also contains passages for the engine's coolant fluid, which is used to transfer heat away from the cylinder head.

Number of cylinder heads in an engine

Most modern engines with a "straight" (inline) layout today use a single cylinder head that serves all the cylinders. Engines with a "V" layout or "flat" layout typically use two cylinder heads (one for each cylinder bank), however a small number of 'narrow-angle' V engines (such as the Volkswagen VR5 and VR6 engines use a single cylinder head spanning the two banks. Most radial engines have one head for each cylinder, although this is usually of the monobloc form wherein the head is made as an integral part of the cylinder. This is also common for motorcycles, and such head/cylinder components are referred to as barrels.

Some engines, particularly medium- and large-capacity diesel engines built for industrial, marine, power generation, and heavy traction purposes (large trucks, locomotives, heavy equipment, etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.

See also

Related Research Articles

<span class="mw-page-title-main">Poppet valve</span> Type of valve

A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into or out of an engine, but with many other applications.

<span class="mw-page-title-main">Camshaft</span> Mechanical component that converts rotational motion to reciprocal motion

A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines, mechanically controlled ignition systems and early electric motor speed controllers.

<span class="mw-page-title-main">Hemispherical combustion chamber</span> Combustion chamber with a domed cylinder head

A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head notionally in the approximate shape of a hemisphere. An engine featuring this type of hemispherical chamber is known as a hemi engine.

<span class="mw-page-title-main">Crossflow cylinder head</span>

A crossflow cylinder head is a cylinder head that features the intake and exhaust ports on opposite sides. The gases can be thought to flow across the head. This is in contrast to reverse-flow cylinder head designs that have the ports on the same side.

<span class="mw-page-title-main">VTEC</span> Automobile variable valve timing technology

VTEC is a system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low RPM. The VTEC system uses two camshaft profiles and hydraulically selects between profiles. It was invented by Honda engineer Ikuo Kajitani. It is distinctly different from standard VVT systems which change only the valve timings and do not change the camshaft profile or valve lift in any way.

<span class="mw-page-title-main">Overhead camshaft engine</span> Valvetrain configuration

An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block.

<span class="mw-page-title-main">Overhead valve engine</span> Type of piston engine valvetrain design

An overhead valve (OHV) engine, sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead engines, where the valves were located below the combustion chamber in the engine block.

<span class="mw-page-title-main">Ford Sidevalve engine</span> Reciprocating internal combustion engine

The Ford Sidevalve is a side valve from the British arm of the Ford Motor Company, often also referred to as the "English Sidevalve". The engine had its origins in the 1930s Ford Model Y, and was made in two sizes, 933 cc (56.9 cu in) or "8 HP", and 1,172 cc (71.5 cu in) or "10 HP". The early engines did not have a water pump as standard, instead relying on thermosiphon cooling as the Model T engine had. A water pump was added in 1953 for the 100E models when the engine was re-engineered to the point that few specifications are identical between the early and the later series. The Sidevalve engine was used in many smaller Fords as well as farm vehicles, commercial vehicles and a marine version in boats. Production of the engine was stopped in 1962. Windscreen wipers were often driven by the vacuum generated in the inlet manifold.

<span class="mw-page-title-main">Multi-valve</span> Type of car engine

In automotive engineering a multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.

<span class="mw-page-title-main">Ford flathead V8 engine</span> Reciprocating internal combustion engine

The Ford flathead V8 is a V8 engine with a flat cylinder head designed by the Ford Motor Company and built by Ford and various licensees. During the engine's first decade of production, when overhead-valve engines were used by only a small minority of makes, it was usually known simply as the Ford V‑8, and the first car model in which it was installed, the Model 18, was often called simply the "Ford V-8", after its new engine. Although the V8 configuration was not new when the Ford V8 was introduced in 1932, the latter was a market first in the respect that it made an 8-cylinder affordable and a V engine affordable to the emerging mass market consumer for the first time. It was the first independently designed and built V8 engine produced by Ford for mass production, and it ranks as one of the company's most important developments. A fascination with ever-more-powerful engines was perhaps the most salient aspect of the American car and truck market for a half century, from 1923 until 1973. The engine was intended to be used for big passenger cars and trucks; it was installed in such until 1953, making the engine's 21-year production run for the U.S. consumer market longer than the 19-year run of the Ford Model T engine for that market. The engine was on Ward's list of the 10 best engines of the 20th century. It was a staple of hot rodders in the 1950s, and it remains famous in the classic car hobbies even today, despite the huge variety of other popular V8s that followed.

<span class="mw-page-title-main">Flathead engine</span> A type of four-stroke engine

A flathead engine, also known as a sidevalve engine or valve-in-block engine, is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine.

<span class="mw-page-title-main">BMC C-Series engine</span> Reciprocating internal combustion engine

The BMC C-Series is a straight-6 automobile engine produced from 1954 to 1971. Unlike the Austin-designed A-Series and B-Series engines, it came from the Morris Engines drawing office in Coventry and therefore differed significantly in its layout and design from the two other designs which were closely related. This was due to the C-Series being in essence an enlarged overhead valve development of the earlier 2.2 L Straight-6 overhead camshaft engine used in the post-war Morris Six MS and Wolseley 6/80 from 1948 until 1954, which itself also formed the basis of a related 1.5 L 4-cylinder engine for the Morris Oxford MO in side-valve form and the Wolseley 4/50 in overhead camshaft form. Displacement was 2.6 to 2.9 L with an undersquare stroke of 88.9 mm (3.50 in), bored out to increase capacity.

<span class="mw-page-title-main">Tappet</span> Internal combustion engine part

A tappet is a valve train component which converts rotating motion into linear motion in activating a valve. It is most commonly found in internal combustion engines, which converts the rotating motion of the camshaft into linear motion of intake and exhaust valves, either directly or indirectly.

<span class="mw-page-title-main">Valvetrain</span> Mechanical system in an internal combustion engine

A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

Designed by Aurelio Lampredi, the Fiat SOHC engine first appeared in the front-wheel drive (FWD) Fiat 128 of 1969. The in-line four-cylinder engine comprised an iron block with an aluminium cylinder-head containing a single overhead camshaft operating directly on both the inlet and exhaust valves in a reverse-flow cylinder-head configuration. The camshaft was driven by a belt rather than chain. The engine remained in production until about 2010 and grew in capacity over the years from 1100 cc to an eventual 1900 cc. The Fiat 130 2.9 L (2,866 cc) V6 engine, also appearing in 1969, although having crossflow cylinder head, is directly related to the 128 SOHC engine, but with a 1.20 upscale in bore and stroke. It was gradually replaced by the Pratola Serra engine series starting from 1995, although it was also converted to use a multivalve DOHC head, giving birth to the Torque engine, used until 2005.

A hydraulic tappet, also known as a hydraulic valve lifter or hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. Conventional solid valve lifters require regular adjusting to maintain a small clearance between the valve and its rocker or cam follower. This space prevents the parts from binding as they expand with the engine's heat, but can also lead to noisy operation and increased wear as the parts rattle against one another until they reach operating temperature. The hydraulic lifter was designed to compensate for this small tolerance, allowing the valve train to operate with zero clearance—leading to quieter operation, longer engine life, and eliminating the need for periodic adjustment of valve clearance.

<span class="mw-page-title-main">IOE engine</span> Type of combustion engines

The intake/inlet over exhaust, or "IOE" engine, known in the US as F-head, is a four-stroke internal combustion engine whose valvetrain comprises OHV inlet valves within the cylinder head and exhaust side-valves within the engine block.

<span class="mw-page-title-main">T-head engine</span> Type of early internal combustion engine

A T-head engine is an early type of internal combustion engine that became obsolete after World War I. It is a sidevalve engine distinguished from the more common L-head by its valve placement. In T-head engines, the intake valves are located on one side of the engine block and the exhaust valves on the other. When viewed from the end of the crankshaft, especially in a cutaway view, the cylinder and combustion chamber resemble a 'T', leading to the name "T-head". In contrast, an L-head engine has all valves on the same side.

References

  1. Wright, G. (2015). Fundamentals of Medium/Heavy Duty Diesel Engines. Jones & Bartlett Learning. p. 310. ISBN   978-1-284-06705-7 . Retrieved 2020-11-07.
  2. "FORD DuraTec Engine 3D Simulation(18) - Dailymotion Video". www.dailymotion.com. 27 August 2009. Retrieved 27 March 2022.