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{{short description|Component of a cylinder of an internal combustion engine}}
{{multiple image
{{one source|date=November 2020}}
| align = right
[[Image:Cylinderhead.JPG|thumb|A 302/5.0L [[Ford Windsor engine|Ford Windsor V8]] cylinder head]]
| direction = vertical
[[File:Cylinder head of a Caterpillar engine.jpg|alt=Cylinder head of a Caterpillar engine|thumb|Cylinder head of a Caterpillar engine]]
| width = 300
In an [[internal combustion engine]], the '''cylinder head''' (often informally abbreviated to just '''head''') sits above the [[cylinder (engine)|cylinder]]s on top of the [[cylinder block]].<ref name="Wright 2015 p. 310">{{cite book | last=Wright | first=G. | title=Fundamentals of Medium/Heavy Duty Diesel Engines | publisher=Jones & Bartlett Learning | year=2015 | isbn=978-1-284-06705-7 | url=https://books.google.com/books?id=s5_OCwAAQBAJ&pg=PA310 | access-date=2020-11-07 | page=310}}</ref> It closes in the top of the cylinder, forming the [[combustion chamber]]. This joint is sealed by a [[head gasket]]. In most engines, the head also provides space for the passages that feed [[Atmosphere of Earth|air]] and [[fuel]] to the cylinder, and that allow the [[Exhaust gas|exhaust]] to escape. The head can also be a place to mount the [[poppet valve|valves]], [[Spark plug|spark plugs]], and [[Fuel injection|fuel injectors]].▼
| image1 = K20 head.jpg
| caption1 = Side view of a [[Dual overhead camshaft|DOHC]] cylinder head (with the valves and camshafts installed)
| image2 = Cylinderhead.JPG
| caption2 = Underside of a [[Overhead valve engine|OHV]] cylinder head (with the valves installed)
}}
 
▲In ana [[internalReciprocating combustionengine|piston engine]], the '''cylinder head''' (often informally abbreviated to just '''head''') sits above the [[cylinder (engine)|cylindercylinders]]s on top of the [[cylinder block]].,<ref name="Wright 2015 p. 310">{{cite book | last=Wright | first=G. | title=Fundamentals of Medium/Heavy Duty Diesel Engines | publisher=Jones & Bartlett Learning | year=2015 | isbn=978-1-284-06705-7 | url=https://books.google.com/books?id=s5_OCwAAQBAJ&pg=PA310 | access-date=2020-11-07 | page=310}}</ref> It closes informing the toproof of the cylinder, forming the [[combustion chamber]]. This joint is sealed by aIn [[headsidevalve gasketengine]]. In most engines,s the head alsois providesa spacesimple forplate theof passagesmetal thatcontaining feedthe [[Atmosphere ofspark Earth|airplug]]s and possibly [[fuelAir-cooled engine|heat dissipation fins]]. toIn themore cylinder,modern and[[overhead thatvalve allowengine|overhead thevalve]] and [[Exhaustoverhead gascamshaft engine|exhaustoverhead camshaft]] toengines, escape. Thethe head canis alsoa bemore acomplicated placemetal toblock that also mountcontains the inlet and exhaust passages, and often [[poppetRadiator valve(engine cooling)|valvescoolant passages]], [[Spark plug|spark plugsValvetrain]] components, and [[FuelFuel_injection#Direct injection systems|fuel injectors]].
 
=== Number of cylinder heads in an engine ===▼
A piston engine typically has one cylinder head per [[Engine_configuration#Multiple_cylinder_banks|bank of cylinders]].
 
Most modern engines with a [[straight engine|"straight" (inline) layout]] today use a single cylinder head that serves all the cylinders.
 
Engines with a [[V engine|"V" layout]] or [[flat engine|"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 engine|VR5]] and [[VR6 engine|VR6]] engines) use a single cylinder head spanning the two banks.
 
Most [[radial engine]]s have one head for each cylinder, although this is usually of the [[monobloc engine#Cylinder head|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 engine]]s built for industrial, marine, power generation, and heavy traction purposes (large [[truck]]strucks, [[locomotive]]s, [[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. ▼
 
== Design ==
{{refimprove|section|date=March 2022}}
 
A summary of engine designs is shown below, in chronological order for automobile usage.
==Engine/valvetrain configurations==
 
{| class="wikitable" style="text-align:left"
|+ Valve and camshaft configurations
|-
! TypeEngine type <br/> (in chronological order)!! [[Camshaft]] <br/> location !! Intake [[Poppet_valve#Usage_in_internal_combustion_engines|valves]] <br/> location !! Exhaust [[Poppet_valve#Usage_in_internal_combustion_engines|valves]] <br/> location
|-
| '''[[Sidevalve engine|Sidevalve]]<br/>(flathead)''' || Block || Block || Block
|-
| '''[[IOE engine|Inlet over exhaust]]<br/> (IOE)''' || Block || Head || Block
Line 24 ⟶ 42:
 
=== Sidevalve engines ===
In a [[flathead engine|flathead]] (''sidevalve'') engine, all of the [[valvetrain]] components are [[cam-in-block|contained within the block]], therefore the head is usually a simple sheetplate of metal bolted to the top of the [[engine block]]. Sidevalve engines were once universal in automobiles but are now largely obsolete in automobiles, asidefound fromalmost exclusively in small engines such as lawnmowers, weed trimmers and chainsaws.
 
===Intake over exhaust (IOE) engines===
A later development called the [[IOE engine|intakeIntake overOver exhaustExhaust]] (IOE) engine, whichengines 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 valveengines (OHV & overhead camshaft engines OHC)===
In an [[overhead valve engine|overhead valve]] (OHV) or [[overhead camshaft engine|overhead camshaft]] (OHC) engine, athe cylinder head consists ofcontains several airflow passages (called ''ports''); some ofintake whichports formdeliver the path forfuel+air intake gassescharge from the [[intake manifold]] to the [[combustion chamber]], and theexhaust othersports areroute forcombustion exhaustwaste gases toout travel fromthe combustion chamber to the [[exhaust manifold]]. The cylinder[[poppet valve|Valves]] open and close the ports, with the intakes offset fore-and-aft from the exhausts. The head also contains the [[poppetspark valve|valvesplug]]s, and theon [[sparkInternal plugcombustion engine cooling#Liquid cooling|water-cooled]]s. engines, the coolant passages.
 
==== Overhead valve (OHV) engines ====
Specifically in an OHV engine, a single [[camshaft]] is located within the [[engine block]] and uses [[pushrod]]s and [[rocker arm]]s 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.▼
A single [[camshaft]] located in the engine block uses [[pushrod]]s and [[rocker arm]]s to actuate all the valves.
 
▲Specifically in an OHV engine, a single [[camshaft]] is located within the [[engine block]] and uses [[pushrod]]s and [[rocker arm]]s to actuate valves. OHV engines are typically more compact than equivalent DOHCOHC engines, howeverand fewer parts mean cheaper production, but they have largely been replaced by DOHCOHC designs, except in some American V8 engines.
In an [[overhead camshaft engine|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. 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' [[Tappet#Overhead cam engines|tappets]]. OHC engines with a [[Single overhead camshaft|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 overhead camshaft|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.
 
====Overhead camshaft (OHC) engines ====
For [[Internal combustion engine cooling# Liquid cooling|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.
An [[Overhead camshaft engine|overhead camshaft]] (OHC) engine locates the camshaft(s) in the cylinder head above the combustion chamber. Eliminating pushrods lessens valvetrain inertia and provides space for optimized port designs, both providing increased power potential.
 
In a [[Overhead camshaft engine#Single_overhead_camshaft_(SOHC)|single overhead camshaft]] (SOHC) engine, the camshaft may be seated centrally between valve rows, or directly above a single row of valves (replacing rocker arm actuation with [[Tappet#Overhead cam engines|tappets]]). SOHC engines were widely from the 1960s to 1990s. (eliminating pushrods but still utilizing rocker arms)
▲=== Number of cylinder heads in an engine ===
The number of cylinder heads in an engine is a function of the [[engine configuration]]. Almost all [[straight engine|inline (straight) engines]] today use a single cylinder head that serves all the cylinders. A [[V engine|V (or Vee)]] engine has two cylinder heads, one for each [[cylinder bank]] of the 'V'. For a few compact 'narrow-angle' V engines, such as the [[Volkswagen Group|Volkswagen]] [[VR6 engine|VR6]], the angle between the cylinder banks is so narrow that it uses a single head spanning the two banks. A [[flat engine]] (basically a V engine, where the angle between the cylinder banks is now 180°) has two heads. Most [[radial engine]]s have one head for each cylinder, although this is usually of the [[monobloc engine#Cylinder head|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''.
 
[[Overhead camshaft engine#Double_overhead_camshaft_(DOHC)|Double overhead camshaft]] (DOHC) engines seat a camshaft directly above each row of offset valves (intakes inboard, exhausts outboard).<ref>{{cite web |title=FORD DuraTec Engine 3D Simulation(18) - Dailymotion Video |url=https://www.dailymotion.com/video/xaafuy_ford-duratec-engine-3d-simulation-1_tech |website=www.dailymotion.com |access-date=27 March 2022 |language=en |date=27 August 2009}}</ref> DOHC designs allow optimal [[crossflow cylinder head|crossflow]] positioning of valves to provide higher-[[RPM]] operation. They are typically larger in size (especially width) than equivalent OHV or SOHC engines. Even though more components raise production costs, DOHC engines seen widespread use in automobile engines since the 1990s.
▲Some engines, particularly medium- and large-capacity [[diesel engine]]s built for industrial, marine, power generation, and heavy traction purposes (large [[truck]]s, [[locomotive]]s, [[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.
 
The design of the cylinder head is key to the performance and efficiency of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the [[volumetric efficiency]] and [[compression ratio]] of the engine.<ref>{{cite web |last1=Mr.johnson |first1=https://latesttechn.com/engine |title=[2] |url=https://www.sciencedirect.com/topics/engineering/cylinder-heads}}</ref>
 
==Gallery==
<gallery mode="packed" heights="200px" perrow="3" style="text-align:left">
<gallery>
Image:DOHC-Zylinderkopf-Schnitt.jpg |A[[Double cylinderoverhead camshaft|DOHC]] head- sliced in half showing the intake and exhaust valves, intake and exhaust ports, coolant passages, cams, tappets and valvecutaway springs.view
Image:Head D15A3.JPG|A [[overhead camshaft#Single overhead camshaft|single overhead camshaft]] (SOHC) cylinder head from a [[Honda|SOHC]] [[Honda D engine#D15A3|Honda D15A3]]. engine
Image:Malossi 70cc Morini cylinder head.jpg|[[Flathead engine|Flathead]] head for a [[Moto Morini]] scooter (bottom top piece on left, top piece on right)
Image:K20 head.jpg|A [[overhead camshaft#Double overhead camshaft|double overhead camshaft]] (DOHC) cylinder head from a Honda [[Honda K engine#K20Z3|K20Z3]].
Image:Suzuki-GS550-DOHC.jpg|[[Double overhead camshaft|DOHC]] head for an air-cooled [[Suzuki GS series|Suzuki GS550]] engine
Image:Malossi 70cc Morini cylinder head.jpg|The bottom (left) and top (right) of a Malossi cylinder head for single-cylinder, [[two-stroke]] scooters. Hole in the middle for the spark plug, four holes for the cylinder bolt posts.
Image:SuzukiCylinder-GS550-DOHChead.jpg|[[Overhead view of an [[air-cooledvalve engine|air-cooledOHV]] cylinder head fromfor a [[Suzuki]]GMC [[Suzuki(General GSMotors seriesdivision)|GS550GMC]] showingvan dual(view camshaftsof underside, drivewith sprocketsvalves and coolingexhaust fins.manifold also visible)
Image:Cylinder-head.jpg|The cylinder head from a [[GMC (General Motors division)|GMC]] [[van]]. The [[poppet valve|valves]] and part of the [[exhaust manifold]] are visible.
</gallery>
 
== See also ==
* {{Commons category-inline | 1=Cylinder heads}}▼
* [[Crossflow cylinder head]]
* [[Reverse-flow cylinder head]]
* [[Head gasket]]
* [[Junk head]]
* [[Monobloc head]]
* [[Flathead engine]]
* [[T-head engine]]
 
==References==
{{reflist}}
 
==External links==
{{Portal|Cars}}
▲* {{Commons category-inline | 1=Cylinder heads}}
* [http://www.dailymotion.com/video/xaafuy_ford-duratec-engine-3d-simulation-1_tech Assembly of Ford Duratec Engine 3D simulation]—video showing construction and operation of a four-cylinder internal combustion engine.
 
{{Internal combustion engine}}
{{Aircraft piston engine components}}
 
[[Category:Cylinder head| ]]
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