Editing Camshaft

{{Short description|Mechanical component that converts rotational motion to reciprocal motion}}
{{For|the fictional characters of the same name|Camshaft (Transformers)}}
[[Image:Nockenwelle ani.gif|thumb|A camshaft operating two valves]]

A '''camshaft''' is a [[Shaft (mechanical engineering)|shaft]] that contains a row of pointed [[Cam (mechanism)|cam]]s in order to convert [[rotation|rotational motion]] to [[reciprocating motion]]. Camshafts are used in [[piston engine]]s (to operate the intake and exhaust valves),<ref>{{Cite web|title=The 4 Strokes of an Engine|url=https://help.summitracing.com/app/answers/detail/a_id/5010/~/the-4-strokes-of-an-engine|access-date=2020-06-10|website=help.summitracing.com}}</ref><ref>{{Cite web|date=2000-12-13|title=How Camshafts Work|url=https://auto.howstuffworks.com/camshaft.htm|access-date=2020-06-10|website=HowStuffWorks|language=en}}</ref> mechanically controlled [[ignition system]]s and early [[Electronic speed control|electric motor speed controllers]].

Camshafts in piston engines are usually made from steel or cast iron, and the shape of the cams greatly affects the engine's characteristics.

==History==
[[Trip hammer]]s are one of the early uses of a form of cam to convert rotating motion, e.g. from a waterwheel, into the reciprocating motion of a hammer used in forging or to pound grain. Evidence for these exists back to the [[Han dynasty]] in China, and they were widespread by the medieval period.

Camshafts were first described by [[Ismail al-Jazari]] in 1206. Once the rotative version of the steam engine was developed in the late 18th century, the operation of the valve gear was usually by an [[Eccentric (mechanism)|eccentric]], which turned the rotation of the crankshaft into reciprocating motion of the valve gear, normally a [[slide valve]]. Camshafts more like those seen later in internal combustion engines were used in some steam engines, most commonly where high pressure steam (such as that generated from a [[Flash boiler|flash steam boiler]]), required the use of poppet valves, or piston valves. For examples see the [[Uniflow steam engine]], and the [[Gardner-Serpollet]] steam cars, which also included axially sliding the camshaft to achieve variable valve timing.

Among the first cars to utilize engines with single [[overhead camshaft]]s were the Maudslay, designed by Alexander Craig and introduced in 1902<ref>{{cite book |title=The New Encyclopedia of Motorcars 1885 to the Present |last= Georgano|first= G. N. |page=407 |year= 1982 |publisher= E. P. Dutton |location= New York|edition= Third|isbn= 0525932542|lccn= 81-71857|url= https://archive.org/details/newencyclopediao0000unse_v2r4/page/407}}</ref><ref>{{cite book |last1= Culshaw|first1= David|last2= Horrobin|first2= Peter|year= 2013 |title= The Complete Catalogue of British Cars 1895 – 1975 |location= Poundbury, Dorchester, UK|publisher= Veloce Publishing |page=210|isbn= 978-1-845845-83-4}}</ref><ref>{{cite journal|last=Boddy |first=William |url=https://www.motorsportmagazine.com/archive/article/january-1964/17/random-thoughts-about-ohc|title= Random Thoughts About O.H.C.|page=906 |journal=Motor Sport |date= January 1964 |access-date= 7 June 2020 |issue= 1|publisher= Teesdale Publishing |location= London, UK}}</ref> and the [[Marr (automobile)|Marr Auto Car]] designed by [[Michigan]] native [[Walter Lorenzo Marr]] in 1903.<ref name="Marr Auto Car Company">{{cite web|url=http://www.marrautocar.com/Marr_Auto_Car_Company/Welcome.html|title=Marr Auto Car Company |website=www.marrautocar.com |archive-url=https://web.archive.org/web/20140208183220/http://marrautocar.com/Marr_Auto_Car_Company/Welcome.html|archive-date=8 February 2014 |url-status=dead}}</ref><ref name=Kimes>{{cite book|last1=Kimes|first1=Beverly Rae|title=Walter L Marr: Buick's Amazing Engineer|year=2007|publisher=Racemaker Press|isbn=978-0976668343|page=40}}</ref>

== Piston engines ==
[[File:Cabeça de motor vista em corte cames.PNG|thumb|right|[[Overhead camshaft engine#Double overhead camshaft|DOHC]] cylinder head with intake camshaft lobe highlighted in blue]]

In [[piston engine]]s, the camshaft is used to operate the intake and exhaust [[poppet valve|valves]]. The camshaft consists of a cylindrical rod running the length of the [[cylinder bank]] with a number of [[Cam (mechanism)|cam]]s (discs with protruding ''cam lobes'') along its length, one for each valve. As the cam rotates, the lobe presses on the valve (or an intermediate mechanism), thus pushing it open. Typically, a ''valve spring'' is used to push the valve in the opposite direction, thus closing the valve once the cam rotates past the highest point of its lobe.<ref>{{Cite web|title=Lunati Cam Profile Terms|url=https://www.lunatipower.com/cam-profile-terms#:~:text=BASE%20CIRCLE:%20The%20%22base%20circle,valve%20lash%20settings%20are%20made.|access-date=2020-06-10|website=www.lunatipower.com}}</ref>

=== Construction ===
[[Image:Nockenwelle 2005.jpg|right|thumb|upright=0.5|Camshaft produced from [[semi-finished_casting_products#Billet|billet]] steel]]

Camshafts are made from metal and are usually solid, although hollow camshafts are sometimes used.<ref>{{cite web|title=What kind of camshaft – made of steel or cast iron?|url=https://www.camshaftkits.com/what-kind-of-camshaft-made-of-steel-or-cast-iron/|url-status=live|access-date=|website=www.camshaftkits.com|archive-url=https://web.archive.org/web/20200920054400/https://www.camshaftkits.com/what-kind-of-camshaft-made-of-steel-or-cast-iron/ |archive-date=2020-09-20 }}</ref> The materials used for a camshaft are usually either: 
* Cast iron: Commonly used in high volume production, chilled iron camshafts have good wear resistance since the chilling process hardens them. 
* Billet steel: For high-performance engines or camshafts produced in small quantities, steel [[Semi-finished_casting_products#Billet|billet]] is sometimes used. This is a much more time-consuming process, and is generally more expensive than other methods. The method of construction is usually either [[forging]], [[machining]], [[casting]] or [[hydroforming]].<ref>{{Cite web|date=2004-04-19|title=Custom Ground Cam - Affordable Custom Cam Grind - Circle Track|url=https://www.hotrod.com/articles/affordable-custom-cam-grind-tech/|access-date=2020-06-10|website=Hot Rod|language=en}}</ref><ref>{{Cite web|title=Custom-made billet camshafts: – Moore Good Ink|url=https://mooregoodink.com/quality-custom-made-billet-camshafts/|access-date=2020-06-10|language=en-US}}</ref><ref>{{cite web |title=Linamar Buying Mubea Camshaft Operations |url=https://www.forgingmagazine.com/forming/article/21922882/linamar-buying-mubea-camshaft-operations |website=www.forgingmagazine.com |access-date=7 June 2020}}</ref>

=== Location in engine ===
Many early internal combustion engines used a ''cam-in-block'' layout (such [[Flathead engine|flathead]], [[IOE engine|IOE]] or [[T-head engine|T-head]] layouts), whereby the camshaft is located within the engine block near the bottom of the engine. Early flathead engines locate the valves in the block and the cam acts directly on those valves.  In an overhead valve engine, which came later, the [[Tappet#Internal combustion engines|cam follower]] presses on a [[pushrod]] which transfers the motion to the top of the engine, where a rocker opens the intake/exhaust valve.<ref name="mechanicbase.com">{{Cite web|last=Sellén|first=Magnus|date=2019-07-24|title=DOHC Vs. SOHC - What's The Difference Between Them?|url=https://mechanicbase.com/engine/dohc-vs-sohc/|access-date=2020-06-10|website=Mechanic Base|language=en-US}}</ref> Although largely replaced by SOHC and DOHC layouts in modern automobile engines, the older overhead valve layout is still used in many industrial engines, due to its smaller size and lower cost.

As engine speeds increased through the 20th century, [[Overhead camshaft engine#Single overhead camshaft (SOHC)|single overhead camshaft]] (SOHC) engines— where the camshaft is located within the [[cylinder head]] near the top of the engine— became increasingly common, followed by [[Overhead camshaft engine#Double overhead camshaft|double overhead camshaft]] (DOHC) engines in more recent years. For OHC and DOHC engines, the camshaft operates the valve directly or via a short rocker arm.<ref name="mechanicbase.com"/>

The valvetrain layout is defined according to the number of camshafts per cylinder bank. Therefore, a V6 engine with a total of four camshafts - two camshafts per cylinder bank - is usually referred to as a ''double overhead camshaft'' engine (although colloquially they are sometimes referred to as "quad-cam" engines).<ref>{{cite web |title=What is Quad-cam engine? |url=http://carspector.com/dictionary/Q/quad-cam-engine/ |website=www.carspector.com |access-date=7 June 2020}}</ref>

=== Drive systems ===
{{main|Timing belt (camshaft)}}

Accurate control of the position and speed of the camshaft is critically important in allowing the engine to operate correctly. The camshaft is usually driven either directly, via a toothed rubber "timing belt"' or via a steel roller "timing chain". Gears have also occasionally been used to drive the camshaft.<ref>{{cite web |url=https://rrec.org.uk/Cars/Rolls-Royce_Motor_Car_Engines/The_V8_Engine_Birth_&_Beginnings.php |title=The V8: Birth and Beginnings |website=www.rrec.org.uk |archive-url=https://web.archive.org/web/20160315071015/http://www.rrec.org.uk/Cars/Rolls-Royce_Motor_Car_Engines/The_V8_Engine_Birth_%26_Beginnings.php |archive-date=15 March 2016 |url-status=dead |access-date=12 July 2020 }}</ref> In some designs the camshaft also drives the [[distributor]], [[Oil pump (internal combustion engine)|oil pump]], [[Fuel pump (engine)|fuel pump]] and occasionally the power steering pump.

Alternative drive systems used in the past include a vertical shaft with [[bevel gear]]s at each end (e.g. pre-World War I Peugeot and Mercedes Grand Prix Cars and the [[Kawasaki W800]] motorcycle) or a triple eccentric with connecting rods (e.g. the [[Leyland Eight]] car).

In a [[two-stroke engine]] that uses a camshaft, each valve is opened once for every rotation of the crankshaft; in these engines, the camshaft rotates at the same speed as the crankshaft. In a [[four-stroke engine]], the valves are opened only half as often, therefore the camshaft is geared to rotate at half the speed of the crankshaft.

=== Performance characteristics ===
{{main|Valve timing}}

==== Duration ====
The camshaft's duration determines how long the intake/exhaust valve is open for, therefore it is a key factor in the amount of power that an engine produces. A longer duration can increase [[Horsepower#Engine power test standards|power]] at high engine speeds (RPM), however this can come with the trade-off of less [[torque]] being produced at low RPM.<ref name="hotrod.com">{{cite web |title=Secrets Of Camshaft Power |url=https://www.hotrod.com/articles/ccrp-9812-secrets-of-camshaft-power/ |website=www.hotrod.com |access-date=18 July 2020 |language=en |date=1 December 1998}}</ref><ref>{{cite web |title=Camshaft RPM Range |url=https://help.summitracing.com/app/answers/detail/a_id/4704/~/camshaft-rpm-range |website=www.summitracing.com |access-date=18 July 2020}}</ref><ref name="jegs.com">{{cite web |title=Understanding Camshaft Fundamentals |url=https://www.jegs.com/tech-articles/camshaft-specification-basics.html |website=www.jegs.com |access-date=18 July 2020}}</ref>

The duration measurement for a camshaft is affected by the amount of lift that is chosen as the start and finish point of the measurement. A lift value of {{convert|0.050|in|mm|1|abbr=on}} is often used as a standard measurement procedure, since this is considered most representative of the lift range that defines the RPM range in which the engine produces peak power.<ref name="hotrod.com"/><ref name="jegs.com"/> The power and idle characteristics of a camshaft with the same duration rating that has been determined using different lift points (for example 0.006 or 0.002 inches) could be much different to a camshaft with a duration rated using lift points of 0.05 inches.

A secondary effect of increased duration can be increased ''overlap'', which determines the length of time that both the intake and exhaust valves are open. It is overlap which most affects idle quality, in as much as the "blow-through" of the intake charge immediately back out through the exhaust valve which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation.<ref name="hotrod.com"/><ref name="jegs.com"/> In general, increasing a camshaft's duration typically increases the overlap, unless the Lobe Separation Angle is increased to compensate.

A lay person can readily spot a long duration camshaft by observing the broad surface of the lobe where the cam pushes the valve open for a large number of degrees of crankshaft rotation.  This will be visibly greater than the more pointed camshaft lobe bump that is observed on lower duration camshafts.

==== Lift ====
The camshaft's lift determines the distance between the valve and the [[valve seat]] (i.e. how far open the valve is).<ref name="summitracing.com lift">{{cite web |title=Camshaft Lift |url=https://help.summitracing.com/app/answers/detail/a_id/4699/ |website=www.summitracing.com}}</ref> The farther the valve rises from its seat the more airflow can be provided, thus increasing the power produced. Higher valve lift can have the same effect of increasing peak power as increased duration, without the downsides caused by increased valve overlap. Most overhead valve engines have a rocker ratio of greater than one, therefore the distance that the valve opens (the ''valve lift'') is greater than the distance from the peak of the camshaft's lobe to the base circle (the ''camshaft lift'').<ref name="hotrod.com camshaft basics">{{cite web |title=Be The Camshaft Expert |url=https://www.hotrod.com/articles/0607phr-camshaft-basics/ |website=www.hotrod.com |access-date=18 July 2020 |language=en |date=14 June 2006}}</ref>

There are several factors which limit the maximum amount of lift possible for a given engine. Firstly, increasing lift brings the valves closer to the piston, so excessive lift could cause the valves to get struck and damaged by the piston.<ref name="jegs.com"/> Secondly, increased lift means a steeper camshaft profile is required, which increases the forces needed to open the valve.<ref name="summitracing.com lift"/> A related issue is ''valve float'' at high RPM, where the spring tension does not provide sufficient force to either keep the valve following the cam at its apex or prevent the valve from bouncing when it returns to the valve seat.<ref name="summitracing.com valve float">{{cite web |title=What is valve float? |url=https://help.summitracing.com/app/answers/detail/a_id/4765/kw/float |website=www.summitracing.com |access-date=18 July 2020}}</ref> This could be a result of a very steep rise of the lobe,<ref name="jegs.com"/> where the cam follower separates from the cam lobe (due to the valvetrain inertia being greater than the closing force of the valve spring), leaving the valve open for longer than intended. Valve float causes a loss of power at high RPM and in extreme situations can result in a bent valve if it gets struck by the piston.<ref name="hotrod.com camshaft basics"/><ref name="summitracing.com valve float"/>

==== Timing ====
The timing (phase angle) of the camshaft relative to the crankshaft can be adjusted to shift an engine's power band to a different RPM range. Advancing the camshaft (shifting it to ahead of the crankshaft timing) increases low RPM torque, while retarding the camshaft (shifting it to after the crankshaft) increases high RPM power.<ref name="compcams.com timing">{{cite web |title=COMP Cams Effect of Changes In Cam Timing and Lobe Separation Angle |url=https://www.compcams.com/cam-timing-lobe-separation-angle |website=www.compcams.com |access-date=19 July 2020}}</ref> The required changes are relatively small, often in the order of 5 degrees.{{citation needed|date=July 2020}}

Modern engines which have [[variable valve timing]] are often able to adjust the timing of the camshaft to suit the RPM of the engine at any given time. This avoids the above compromise required when choosing a fixed cam timing for use at both high and low RPM.

==== Lobe separation angle ====
The ''lobe separation angle'' (LSA, also called ''lobe centreline angle'') is the angle between the centreline of the intake lobes and the centreline of the exhaust lobes.<ref name="summitracing.com LSA">{{cite web |title=Camshaft Lobe Separation |url=https://help.summitracing.com/app/answers/detail/a_id/4702/ |website=www.summitracing.com |access-date=19 July 2020}}</ref> A higher LSA reduces overlap, which improves idle quality and intake vacuum,<ref name="compcams.com timing"/> however using a wider LSA to compensate for excessive duration can reduce power and torque outputs.<ref name="hotrod.com camshaft basics"/> In general, the optimal LSA for a given engine is related to the ratio of the cylinder volume to intake valve area.<ref name="hotrod.com camshaft basics"/>

==== Functionality ====
Camshafts are integral components of internal combustion engines, responsible for controlling the opening and closing of the engine's intake and exhaust valves. As the camshaft rotates, its lobes push against the valves, allowing the intake of air and fuel and the expulsion of exhaust gases. This synchronized process is crucial for optimizing engine performance, fuel efficiency, and emissions control. Without precisely engineered camshafts, the smooth and efficient operation of an engine would be compromised.<ref name="kelfordcams.com/vehicle-camshafts ">{{cite web |title=Vehicle Camshafts |url=https://kelfordcams.com/vehicle-camshafts|website=www.kelfordcams.com |access-date=4 January 2024}}</ref>

=== Alternatives ===
The most common methods of valve actuation involve camshafts and valve springs, however alternate systems have occasionally been used on internal combustion engines:
* [[Desmodromic valve]]s, where the valves are positively closed by a cam and leverage system rather than springs. This system has been used on various Ducati racing and road motorcycles since it was introduced on the 1956 [[Ducati singles#125 Desmo Ducati|Ducati 125 Desmo]] racing bike.
* [[Camless piston engine]], which use electromagnetic, hydraulic, or pneumatic actuators. First used in turbocharged Renault Formula 1 engines in the mid-1980s and slated for road car use in the [[Koenigsegg Gemera]].<ref>{{cite web |title=Koenigsegg Gemera - Technical specifications |url=https://www.koenigsegg.com/gemera/technical-specifications/ |website=www.koenigsegg.com |access-date=19 July 2020 |archive-date=3 March 2020 |archive-url=https://web.archive.org/web/20200303213619/https://www.koenigsegg.com/gemera/technical-specifications/ |url-status=dead }}</ref><ref>{{cite web| url=https://www.youtube.com/watch?v=Bch5B23_pu0 | archive-url=https://ghostarchive.org/varchive/youtube/20211118/Bch5B23_pu0| archive-date=2021-11-18 | url-status=live|website=www.youtube.com |title= The Future of the Internal Combustion Engine – Inside Koenigsegg |publisher= The Drive |access-date= 7 June 2020}}{{cbignore}}</ref>
* [[Wankel engine]], a rotary engine which uses neither pistons nor valves. Most notably used by Mazda from the 1967 [[Mazda Cosmo]] until the [[Mazda RX-8]] was discontinued in 2012.

== Electric motor speed controllers ==
Before the advent of [[solid state electronics]], ''camshaft controllers'' were used to control the speed of [[electric motor]]s.  A camshaft, driven by an electric motor or a [[pneumatic motor]], was used to operate [[contactor]]s in sequence.  By this means, [[resistor]]s or [[Tap (transformer)|tap changers]] were switched in or out of the circuit to vary the speed of the main motor.  This system was mainly used in electric train motors (i.e. [[electric multiple unit|EMUs]] and [[electric locomotives|locomotives]]).<ref>{{cite web|url=http://www.railway-technical.com/trains/rolling-stock-index-l/electric-locomotives.html|title=Electric Locomotives – The Railway Technical Website |website=www.railway-technical.com |access-date= 7 June 2020}}</ref>

==See also==
{{Commons category|Camshafts}}
* [[Crankshaft]]
* [[List of auto parts]]
* [[Sleeve valve]]

== References ==
{{reflist}}
[[zh-yue:凸輪軸]]
{{Automotive engine}}

{{Authority control}}

[[Category:Valvetrain]]
[[Category:Engine components]]
[[Category:13th-century inventions]]