Editing Variable displacement

{{Short description|Combustion engine technology}}
'''Variable displacement''' is an [[automobile]] engine technology that allows the [[engine displacement]] to change, usually by deactivating [[Cylinder (engine)|cylinders]], for improved [[Fuel economy in automobiles|fuel economy]]. The technology is primarily used in large multi-cylinder engines. Many automobile manufacturers have adopted this technology as of 2005, although the concept has existed for some time prior to this.

==Theory of operation==
Cylinder deactivation is used to reduce the [[fuel consumption]] and [[Motor vehicle emissions|emissions]] of an [[internal combustion engine]] during light-load operation. In typical light-load driving the driver uses only around 30 percent of an engine’s maximum power. In these conditions, the [[throttle]] valve is nearly closed, and the engine needs to work to draw air. This causes an inefficiency known as pumping loss. Some large capacity engines need to be throttled so much at light load that the cylinder pressure at [[top dead centre]] is approximately half that of a small [[4-cylinder engine]]. Low cylinder pressure results in lower [[fuel efficiency]]. The use of cylinder deactivation at light load means there are fewer cylinders drawing air from the intake [[manifold]], which works to increase its fluid (air) pressure.  Operation without variable displacement is wasteful because fuel is continuously pumped into each cylinder and combusted even though maximum performance is not required. By shutting down half of an engine's cylinders, the amount of fuel being consumed is much less.  Between reducing the pumping losses, which increases pressure in each operating cylinder, and decreasing the amount of fuel being pumped into the cylinders, [[fuel consumption]] can be reduced by 8 to 25 percent in highway conditions.<ref name="reborn">{{cite web | url=http://autospeed.drive.com.au/cms/A_2618/article.html | archive-url= https://web.archive.org/web/20110728015843/http://autospeed.com.au/cms/article.html?&A=2618 | url-status=dead | archive-date=2011-07-28 | title=Cylinder Deactivation Reborn - Part 1, Autospeed, Issue 342, Michael Knowling |date=2005-08-03}}<br />
{{Cite web 
|date=2005-08-10
|title=Cylinder Deactivation Reborn - Part 2, Autospeed, Issue 343, Michael Knowling 
|url=http://www.autospeed.com.au/cms/A_2623/article.html
|archive-url=https://web.archive.org/web/20120331050613/http://www.autospeed.com.au/cms/A_2623/article.html
|url-status=dead
|archive-date=2012-03-31
|website=Autospeed AU}}</ref><ref name="greencar">{{cite web|url=http://www.greencar.com/articles/save-gas-cylinders-smart.php|archive-url=https://web.archive.org/web/20090703050625/http://www.greencar.com/articles/save-gas-cylinders-smart.php|url-status=dead|archive-date=2009-07-03|title=Save Gas: Cylinders get Smart|website= www.greencar.com|first=Bill|last=Siuru}}</ref>

Cylinder deactivation is achieved by keeping the intake and exhaust valves closed for a particular cylinder. By keeping the intake and exhaust valves closed, it creates an "air spring" in the [[combustion chamber]] – the trapped [[exhaust gases]] (kept from the previous charge burn) are compressed during the piston’s upstroke and push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gases have an equalising effect – overall, there is virtually no extra load on the engine. In the latest breed of cylinder deactivation systems, the [[engine management system]] is also used to cut fuel delivery to the disabled cylinders. The transition between normal engine operation and cylinder deactivation is also smoothed, using changes in [[ignition timing]], [[Cam (mechanism)|cam]] timing and throttle position (due to [[electronic throttle control]]). In most instances, cylinder deactivation is applied to relatively large displacement engines that are particularly inefficient at light load. In the case of a [[V12 engine|V12]], up to 6 cylinders can be disabled.<ref name="reborn" />

Two issues to overcome with all variable-displacement engines are unbalanced cooling and vibration.{{Citation needed|date=October 2013}}

==History==
The oldest engine technological predecessor for the variable-displacement engine is the [[hit and miss engine]], developed in the late 19th century. These single-cylinder [[stationary engine]]s had a [[centrifugal governor]] that cut the cylinder out of operation so long as the engine was operating above a set speed, typically by holding the exhaust valve open.

===Cadillac L62 V8-6-4===
[[File:81 Cadillac Sedan de Ville V864 (13923375327).jpg|thumb|Cadillac V8-6-4 emblem]]
First experiments with multiple-cylinder engines during [[World War II|WWII]],<ref name="cylinder">{{cite web|url=http://www.findarticles.com/p/articles/mi_m3012/is_1_185/ai_n9532648|title=FindArticles.com - CBSi|website=www.findarticles.com}}</ref> were re-attempted in 1981 on [[Cadillac]]'s ill-fated [[Cadillac V8 engine#V8-6-4|''L62'' "V8-6-4"]] engine. The technology was made a standard feature on all Cadillac models except [[Cadillac Seville|Seville]], which had the 350 diesel V-8 engine as a base engine. Cadillac, in conjunction with [[Eaton Corporation]], developed the innovative V-8-6-4 system which used the industry's first [[engine control unit]] to switch the engine from 8- to 6- to 4-cylinder operation depending on the amount of power needed.<ref name="cylinder"/> The original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. The cars had an elaborate diagnostics procedure, including showing engine trouble codes on the air conditioning display. However, the system was troublesome, misunderstood by customers, and a rash of unpredictable failures led to the technology being quickly retired.<ref name="cylinder"/>

===Alfa Romeo Alfetta CEM===
In 1981 [[Alfa Romeo]] developed in collaboration with the [[University of Genoa]] a semi-experimental variable displacement engine version of the [[Alfa Romeo Alfetta]], called Alfetta CEM (''Controllo Elettronico del Motore'', or Electronic Engine Management), and showed it at the [[Frankfurt Motor Show]].<ref name="lastampa CEM83" /> The {{convert|130|PS|kW bhp|0|abbr=on}} 2.0-litre modular engine featured [[fuel injection]] and [[Ignition system|ignition]] systems governed by an engine control unit, which could shut off two of four cylinders as needed in order to reduce fuel consumption. An initial batch of 10 examples were assigned to [[taxi]] drivers in Milan, to verify operation and performance in real-world situations.<ref name="lastampa CEM83">{{cite news |url=http://www.archiviolastampa.it/component/option,com_lastampa/task,search/mod,libera/action,viewer/Itemid,3/page,17/articleid,1026_01_1983_0088_0017_14332568/ |title=L'Alfa riduce i consumi "staccando" i cilindri |first=Vittorio |last=Sabadin |date=15 April 1983 |page=25 |newspaper=[[La Stampa]] |language=IT |access-date=6 March 2015}}</ref><ref name="lastampa CEM82">{{cite news |url=http://www.archiviolastampa.it/component/option,com_lastampa/task,search/mod,libera/action,viewer/Itemid,3/page,19/articleid,1039_01_1982_0094_0019_14861492/ |title=Alfa, il motore modulare per contenere i consumi |first=Michele |last=Fenu |date=7 May 1982 |page=19 |newspaper=[[La Stampa]] |language=IT |access-date=6 March 2015}}</ref> According to Alfa Romeo during these tests cylinder deactivation was found to reduce fuel consumption by 12% in comparison to a CEM fuel-injected engine without variable displacement, and almost by 25% in comparison to the regular production [[Carburettor|carburetted]] 2.0-litre.<ref name="lastampa CEM82" /> After the first trial, in 1983 a small series of 1000 examples was put on sale, offered to selected clients;<ref name="lastampa CEM83" /> 991 examples were produced. Despite this second experimental phase, the project had no further developments.

==={{anchor|Mitsubishi|MD}} Mitsubishi MD===
In 1982 [[Mitsubishi Motors|Mitsubishi]] developed its own variable displacement in the form of MD (Modulated Displacement) which proved that the technology, first used in Mitsubishi's 1.4 L [[Mitsubishi Orion engine|4G12]] [[Inline-four engine|straight-four]] engine, can function successfully.<ref>{{cite web|url=http://www.mitsubishi-motors.com/corporate/museum/history/1980/e/index.html |title="Mitsubishi Motors Web Museum", Mitsubishi Motors website |url-status=dead |archive-url=https://web.archive.org/web/20110716131014/http://www.mitsubishi-motors.com/corporate/museum/history/1980/e/index.html |archive-date=2011-07-16 }}</ref> Because Cadillac's system proved to be a failure and a four-cylinder engine was used, Mitsubishi hailed their own as a world first.<ref name="GDI">{{cite web|url=http://www.mitsubishi-motors.co.za/featuresites/mm_history/GDI.asp|title="Mitsubishi Motors History", Mitsubishi Motors South Africa website|access-date=2007-03-12|archive-url=https://web.archive.org/web/20070125232459/http://www.mitsubishi-motors.co.za/featuresites/mm_history/GDI.asp|archive-date=2007-01-25|url-status=dead}}</ref> The technology was later used in Mitsubishi's V6 engines.<ref name="mivec">[http://autospeed.drive.com.au/cms/A_2651/article.html "Mountain of MIVECs"] {{Webarchive|url=https://web.archive.org/web/20070505233011/http://autospeed.drive.com.au/cms/A_2651/article.html |date=2007-05-05 }}, Michael Knowling, ''AutoSpeed'', Issue 346, September 3, 2005</ref>

The system worked by disabling the valves on cylinders number 1 and 4 at speeds below {{convert|70|km/h|mph|1|abbr=on}}, at idling, and while decelerating. Fuel consumption figures were generally about 20 percent improved over the regular 4G12 engine.<ref name=sae362>{{cite journal | ref = oMD | last1 = Fukui | first1 = Toyoaki | first2 = Tatsuro | last2 = Nakagami | first3 = Hiroyasu | last3 = Endo | first4 = Takehiko | last4 = Katsumoto | first5 = Yoshiaki | last5 = Danno | title = Mitsubishi Orion-MD — A New Variable Displacement Engine | journal = SAE Transactions | volume = 92, section 3 | date = 1983 | pages = 362–370 | jstor = 44647614 }}</ref> Period sources, however, complained about the engine running very roughly while in two-cylinder mode, despite special engine mounts with hydraulic damping.<ref name=AC4459a>{{cite magazine | ref = JH1 | magazine = [[Autocar (magazine)|Autocar]] | title = Putting on the pressure | first = John | last = Hartley | publisher = IPC Business Press Ltd. | pages = 35–36 | date = 1982-06-05 | volume = 156 | number = 4459 }}</ref> Other efforts taken to minimize vibrations and harshness included a section of flexible exhaust pipe, not operating the system until the coolant temperature reached 70C, and a 70 percent heavier flywheel.<ref name=sae367>[[#oMD|Fukui ''et al'']], p.367</ref> Mitsubishi's effort remained short-lived, mainly because of a lack of response from car buyers.<ref name="higbee">{{cite news|last=Higbee|first= Arthur|date=20 November 1992|url=https://www.nytimes.com/1992/11/20/news/20iht-topi_17.html|title=Mitsubishi Engine Switches Cylinders|work= [[The New York Times]]|access-date=28 October 2013}}</ref>

In 1993, a year after Mitsubishi developed its own [[variable valve timing]] technology, the [[MIVEC]]-MD variant was introduced. The revived MD technology was now in its second generation with improved electronic engine controls enabling the switch from 4 to 2 cylinders to be made almost imperceptibly. In MD mode, the MIVEC engine utilizes only two of its four cylinders, which reduces significantly the energy wasted due to pumping losses. In addition, power loss due to engine friction is also reduced.<ref name="GDI"/> Depending on conditions, the MIVEC-MD system can reduce fuel consumption by 10–20 percent; although some of this gain is from the variable valve timing system, not from the variable-displacement feature.<ref name="mivec"/> Modulated Displacement was dropped around 1996.<ref name="mivec"/>

===Aftermarket systems===
A number of companies have developed aftermarket cylinder deactivation systems, with varying degrees of success. The 1979 EPA evaluation of the Automotive Cylinder Deactivation System (ACDS), which allowed eight-cylinder engines to be run on four cylinders, found that carbon monoxide and nitrogen oxide emissions were increased beyond the legal limits of the emission standards then in force.<ref name="acds">{{cite web|url=http://www.epa.gov/oms/consumer/devices/511817.pdf|title=Vehicles and Engines|first=US|last=((EPA, OAR, OTAQ))|website=www.epa.gov}}</ref> While fuel economy was increased, acceleration was seriously compromised, and the loss of engine vacuum led to a dangerous loss of braking assist when the system was in four-cylinder mode.<ref name="acds"/> In addition to these issues, while the company proposed a hydraulically controlled system that could be switched from within the car, the version they implemented had to be manually changed in the engine compartment using hand tools.<ref name="acds"/>

==Present==
There are currently two main types of cylinder deactivation mechanizations used today, depending on the type of the engine's valvetrain. The first is for [[Valvetrain#Pushrod|pushrod]] designs which uses solenoids to alter oil pressure delivered to lock pins in the lifters. With lock pin out of place, the lifters are collapsed and unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that remain closed when the cam pushes on the part in lost motion.

The second type is for overhead cam engines, and uses a pair of locked-together rocker arms that are employed for each valve. One rocker follows the cam profile, while the other actuates the valve. When a cylinder is deactivated, solenoid-controlled oil pressure releases a locking pin between the two rocker arms. While one arm still follows the camshaft, the unlocked arm remains motionless and doesn't move the valve.<ref name="type">[http://alternativefuels.about.com/od/researchdevelopment/a/cylinderdeact.htm "Cylinder Deactivation"], About.com, Christine & Scott Gable</ref> With computer control, fast cylinder deactivation and reactivation occur almost instantly.<ref name="greencar2">{{cite web|url=http://www.greencar.com:80/articles/variable-displacement-better-mpg.php|archive-url=https://web.archive.org/web/20120508210702/http://www.greencar.com/articles/variable-displacement-better-mpg.php|url-status=dead|archive-date=2012-05-08|title=Variable Displacement for Better MPG|website=www.greencar.com|first=Bill|last=Siuru|access-date=2009-11-30}}</ref>

Several automotive manufacturers have engines with cylinder deactivation in current production.

Daimler AG's ''[[Active Cylinder Control]]'' (ACC) variable displacement technology debuted in 2001 on the 5.8 L V12 in the CL600 and S600.

[[Mercedes-Benz]] developed their ''[[Multi-Displacement System]]'' [[V12 engine|V12]] in the late 1990s, which shuts off every other cylinder in the firing order. It was widely deployed on pushrod V8 engines starting with the 2004 [[DaimlerChrysler]] [[Chrysler Hemi engine#5.7 / 345|Hemi]].

Starting in 2003, [[Honda]] introduced ''[[Variable Cylinder Management]]'' on the [[Honda J engine|J family]] engines. Honda's system works by deactivating banks of cylinders, switching from 6 to 4 to 3 cylinders.

In 2005, [[General Motors Corporation|GM]] introduced their ''[[Active Fuel Management]]'' cylinder deactivation system (in the [[GM LS engine|Generation IV small-block]]) which, similar to Chrysler's MDS, switched off half of the cylinders. In 2018 GM introduced an improved system called ''Dynamic Fuel Management''<ref>{{Cite web|url=https://media.gm.com/content/media/us/en/chevrolet/home.detail.html/content/Pages/news/us/en/2018/may/0518--silverado-dfm.html|title=2019 Silverado Leads Industry With Dynamic Fuel Management|date=2018-05-18|website=media.gm.com|language=en|access-date=2019-02-26}}</ref> that shuts off any number of cylinders, in a variety of combinations, depending on immediate needs. The system is based on ''Dynamic Skip Fire,''<ref>{{Cite journal|last1=Tripathi|first1=Adya|last2=Shost|first2=Mark|last3=Switkes|first3=Joshua|last4=Wilcutts|first4=Mark|date=2013-04-08|title=Design and Benefits of Dynamic Skip Fire Strategies for Cylinder Deactivated Engines|url=https://www.sae.org/publications/technical-papers/content/2013-01-0359/|journal=SAE International Journal of Engines|language=en|volume=6|issue=1|pages=278–288|doi=10.4271/2013-01-0359|s2cid=110333295 |url-access=subscription}}</ref> a technology developed by California company Tula Technology<ref>{{Cite web|url=https://www.sae.org/news/2018/05/gm-2019-v8s-with-dfm-system|title=GM adopts advanced cylinder deactivation for 2019 Chevy Silverado V8s|website=www.sae.org|language=en|access-date=2019-02-26}}</ref> and the 6.2L engine incorporating it was named one of [[Ward's 10 Best Engines]] for 2019.

In 2012 [[Volkswagen]] introduced ''Active Cylinder Technology'' (ACT), the first manufacturer to do so in four-cylinder engines.<ref>{{cite web | url=http://www.volkswagen.co.uk/technology/petrol/active-cylinder-technology-act | title=Active Cylinder Technology (ACT) | access-date=2018-01-21 | archive-url=https://web.archive.org/web/20170621192104/http://www.volkswagen.co.uk/technology/petrol/active-cylinder-technology-act | archive-date=2017-06-21 | url-status=dead }}</ref>

In 2015 [[Alfa Romeo]] implemented cylinder bank deactivation in the Giulia and Stelvio Quadrifoglio [[Alfa Romeo 690T engine|V6 engine]], allowing it to operate as an inline-three under light loads.<ref name="AutoTecnica">{{Cite web |last=Daudo |first=Franco |date=March 23, 2019 |title=Alfa Romeo: la tecnica del V6 di Giulia e Stelvio Quadrifoglio |url=https://www.autotecnica.org/alfa-romeo-tecnica-v6-510-cv/ |website=Auto Tecnica |language=it}}</ref>

In November 2016 [[Ford Motor Company|Ford]] announced its compact three-cylinder [[Ford EcoBoost engine|Ecoboost]] engine with deactivation on one of the cylinders. This is the smallest engine so far to use deactivation, and will allow the benefits to be applied in small cars.<ref>{{Cite web|url=https://newatlas.com/ford-ecoboost-cylinder-deactivation/46700/|title=Three cylinders become two to improve EcoBoost engine efficiency|website=newatlas.com|date=30 November 2016|language=en|access-date=2017-10-25}}</ref>

In November 2017, [[Mazda]] announced standard cylinder deactivation in all 2018 [[Mazda CX-5|CX-5]] models, and availability on [[Mazda6]] models.<ref>{{cite web | url=http://www.motortrend.com/news/2018-mazda-cx-5-adds-cylinder-deactivation/ | title=2018 Mazda CX-5 Adds Cylinder Deactivation| work=MotorTrend| date=22 November 2017}}</ref><ref>{{cite web | url=https://insidemazda.mazdausa.com/the-mazda-way/technology/mazdas-new-cylinder-deactivation/ | title = Mazda's New Cylinder-Deactivation Offers Improved Fuel-Efficiency Without Sacrificing Driving Performance| date = 20 December 2017}}</ref>

As of the 2020 model year, about 15% of light-duty vehicles sold in the United States used cylinder deactivation, predominantly used by Mazda (64%), GM (44%), Honda (24%), and FCA (23%).<ref>{{Cite web|url=https://www.epa.gov/automotive-trends/highlights-automotive-trends-report|title = Highlights of the Automotive Trends Report|date = November 2021}}</ref>

==Related technologies==
[[Variable compression ratio]]. The best known such system was the experimental [[Saab Variable Compression engine]], which used a hinged block to move the pistons closer to or further from the head, thus changing the size of the combustion chambers. Other experimental systems include the Hefley engine, which uses a sliding crank race on an eccentric shaft,<ref name="hefley">{{cite web|url=http://www.hefleyengine.com|title=乐天娱乐_乐天国际娱乐平台注册㊣24小时在线服务*注册送彩金*》入口|website=www.hefleyengine.com}}</ref> and the Scalzo Piston Deactivation Engine, which uses a four-bar linkage, and has the distinction of being able to stop individual pistons entirely.<ref name="scalzo">{{cite web|url=http://www.scalzoautomotiveresearch.com/technology|title=The Piston Deactivation Engine|website=www.scalzoautomotiveresearch.com}}</ref> There are currently no production vehicles that use any of these designs.

Additionally, some engines such as Cadillac's [[Northstar engine series]] and Ford's [[Ford Modular engine|Modular]] and [[Ford Duratec engine|Duratec]] engines feature a fail-safe mode where if the engine overheats or loses coolant, the engine controller would cut fuel and spark to half of the cylinders.  With valve operation left unaltered, the noncombustive cylinders would air-cool the engine.<ref>{{cite web |last1=Allison |first1=Wesley |title=1997 Ford F-150 - Road Test |url=https://www.motortrend.com/reviews/1997-ford-f150-2 |website=Motor Trend |publisher=MotorTrend Group |access-date=28 May 2025}}</ref>

==Variable-displacement technologies==
* [[Bentley]] unveiled an updated [[Rolls-Royce – Bentley L Series V8 engine|L-Series]] engine in 2015 with variable displacement
* [[DaimlerChrysler]] [[Multi-Displacement System]] (MDS) was used in [[Chrysler Corporation|Chrysler]] models
* [[DaimlerChrysler]] [[Active Cylinder Control]] (ACC) was used in [[Mercedes-Benz]] models
* [[General Motors Corporation|General Motors]] [[Cadillac V8 engine#368 and V8-6-4|V8-6-4]] ([[Cadillac (automobile)|Cadillac]])
* [[General Motors Corporation|General Motors]] [[Cadillac Sixteen]] ([[Cadillac (automobile)|Cadillac]])
* [[General Motors Corporation|General Motors]] [[Active Fuel Management]]
* [[Honda]] [[Variable Cylinder Management]] (VCM)
* [[Mazda]] [[Skyactiv]]-G 2.5 engines manufactured from 2018 on feature cylinder deactivation.

==See also==
*[[Camless engine]]
*[[Saab Variable Compression engine]]
*[[Start-stop system]]

==References==
{{reflist}}

[[Category:Engine technology]]