Editing Variable displacement (section)

==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"/>