Straight-three engine

{{Short description|Type of engine}} [[File:Elsbett-3cyl-open.jpg|thumb|Engine block of an Elsbett straight-three diesel engine]] A '''straight-three engine''' (also called an '''inline-triple''' or '''inline-three''')<ref name="Saab96nV4Robson">{{cite book |last = Robson |first = Graham |title = Saab 96 & V4 |series = Rally Giants |date = August 15, 2010 |publisher = Veloce Publishing |isbn = 978-1-84584-256-7 |page = 27 |chapter = The car and the team |quote = V4 replaces straight three}}</ref><ref>{{cite journal |last1 = Gorant |first1 = Jim |editor-last = Oldham |editor-first = Joe |date=December 1997 |title = Jet Ski Saviors |journal = Popular Mechanics |volume = 174 |issue = 12 | pages = 54–57 |location = New York, NY USA |publisher = Hearst |issn = 0032-4558 |access-date = 2012-07-02 |url = https://books.google.com/books?id=MGYEAAAAMBAJ&q=Inline+Triple+Popular+Mechanics |quote = The 1071cc, inline, triple-cylinder configuration produces 803 pounds of thrust and pushes the boat to about 55 mph.}}</ref><ref name="RnT3x3July93">{{cite journal |editor-last = Dinkel |editor-first = John |date=July 1988 |title = Comparison Road Test: 3x3 |journal = Road & Track |volume = 39 |issue = 11 |pages = 66–74 |location = Newport Beach, CA USA |publisher = Diamandis Communications |issn = 0035-7189 |quote = Its engine is still the same 993-cc sohc inline-3, producing 48 bhp at 5100 5100 rpm and 57 lb-ft torque at 3200...}}</ref> is a three-cylinder piston engine where cylinders are arranged in a line along a common crankshaft.

Historically less common than straight-four engines, straight-three engines have been used in small and mid-sized vehicles, motorcycles, and agricultural machinery. Their use has increased since the 2020s as part of a broader industry trend toward smaller, turbocharged engines to meet fuel economy and emissions requirements. By the mid-2020s, they accounted for a small but growing share of new vehicles, after being rare prior to 2020.

Compared to straight-four engines, straight-three engines are typically lighter and have fewer moving parts, which can improve efficiency, but have limitations in performance and are prone to vibration, which have largely been overcome by advances in engine and vehicle design.

== Design == [[File:Reihenmotor Drei Zylinder.gif|thumb|Four-stroke straight-three engine with firing order 1-3-2]] Compared with straight-four engines, which always have a cylinder on its power stroke, straight-three engines have intervals in which no cylinder is on its power stroke. As a result, individual combustion events must be stronger to achieve comparable output.<ref name=":0" />

A 120-degree crankshaft is typically used in straight-three engines,<ref>{{Cite web|url=https://www.carthrottle.com/post/heres-the-problem-with-three-cylinder-engines/|title=Here's The Problem With Three-Cylinder Engines|website=Car Throttle|language=en|access-date=2019-12-03}}</ref> producing evenly spaced firing intervals. This configuration provides perfect primary and secondary balance in the reciprocating-plane, but primary and secondary rotating-plane imbalances are present. This manifests as an end-to-end rocking couple due to asymmetry in piston motion about the center cylinder, resulting in pronounced low-frequency vibrations that can be difficult to isolate. These can be mitigated through measures such as balance shafts and engine mounts designed to limit their transmission to the vehicle structure.<ref name=":0" />

Other crankshaft configurations have also been used. The 1976–1981 Laverda Jota motorcycle used a 180-degree crankshaft, in which the outer pistons move together while the inner piston is offset by 180 degrees, resulting in evenly spaced power strokes followed by a longer interval without one. The 2020 Triumph Tiger 900 uses a "T-plane" crankshaft with throws at 90-degree intervals, with cylinders 1 and 3 separated by 180 degrees.<ref>{{cite web |title=TIGER 900 ENGINE & CAPABILITY |url=https://www.triumphmotorcycles.co.uk/motorcycles/adventure/tiger-900/engine-and-capability |website=Triumph Motorcycles UK |access-date=10 February 2020}}</ref><ref>{{cite web |last1=Cameron |first1=Kevin |title=Triumph's New T-Plane Firing Order Explained |url=https://www.cycleworld.com/story/bikes/triumphs-new-t-plane-firing-order-explained/ |website=Cycleworld |access-date=10 February 2020}}</ref>

Straight-three engines can offer improved fuel efficiency due to their smaller size, lower mass, and reduced internal friction from having fewer moving parts. For a given displacement, each cylinder is also larger than in a straight-four engine, allowing larger valves and improved airflow.<ref name=":0" />

== Usage in cars == [[File:Tuned-SAAB-twostroke.jpg|thumb|Circa-1960 Saab two-stroke engine]] [[File:Suzuki K10B.JPG|thumb|2010 Suzuki K10B engine]] One of the first 3 cylinder cars include the 3 cylinder 15hp Rolls Royce produced in 1905 . The 1956–1960 Saab 93 saw the introduction of Saab's {{convert|750|cc|cuin|0|abbr=on}} two-stroke engine, which was also used in the Saab 95, Saab 96 and Saab Sonett until 1968 after which it was replaced by the Ford Taunus V4 engine.

The Wartburg cars (manufactured in East Germany) and FSO Syrena (manufactured in Poland) also used straight-three engines.

The 1967 Suzuki Fronte 360 uses a {{convert|256|cc|0|abbr=on}} two-stroke engine. In 1980, Suzuki began production of a {{convert|543|cc|0|abbr=on}} four-stroke engine, which was introduced in the Alto and Fronte models.

The Subaru EF engine is a 4-stroke petrol engine which was introduced in 1984 and used in the Justy<ref name="RnT3x3July93" /> and the Sumo (the export version of the Sambar).

The straight-three versions of the Ford EcoBoost engine – a turbocharged 1.0-litre petrol engine – was introduced in the 2012 Ford Focus.<ref>{{cite web |url=https://social.ford.com/en_US/story/sustainability/green/smallest-ford-engine-ever-three-cylinder-ecoboost-and-two-new-transmissions.html |title=Smallest Ford Engine Ever! Three-Cylinder EcoBoost (and Two New Transmissions) |access-date=2017-04-03}}</ref> It uses an unbalanced flywheel to shift the inherent three-cylinder imbalance to the horizontal plane where it is more easily managed by engine mounts, and so remove the need to use balance shafts.<ref>{{cite web|url=http://wardsauto.com/technology/ford-s-3-cyl-ecoboost-delivers-goods |title=Ford's 3-cyl. EcoBoost Delivers the Goods |date=2014-05-15 |access-date=2017-04-03}}</ref> In 2016, cylinder deactivation was added, claimed to be a world first for three-cylinder engines.<ref>{{cite web|url=https://media.ford.com/content/fordmedia/feu/en/news/2016/11/29/ford-to-offer-fuel-saving-cylinder-deactivation-tech-for-1-0-lit.html |title=Ford To Offer Fuel-Saving Cylinder Deactivation Tech FOR 1.0 Litre EcoBoost; Global First For A 3-Cylinder Engine |date=2016-11-29 |access-date=2017-04-03}}</ref>

Historically, straight-three engines have been less popular than straight-four engines in small and mid-sized vehicles. However, their use increased in the 2020s as part of a broader industry trend toward smaller, turbocharged engines to meet fuel economy and emissions requirements.<ref name=":0">{{Cite web |last=Valdes-Dapena |first=Peter |date=2023-04-15 |title=How little engines are taking over American cars in a big way |url=https://www.cnn.com/2023/04/15/business/american-cars-three-cylinder-engines |access-date=2026-03-25 |website=CNN |language=en}}</ref> In the United States, three-cylinder engines grew from less than 1% of new vehicles before 2020 to about 5% by the 2025 model year, roughly matching the share of eight-cylinder gasoline engines, while four-cylinder engines remained dominant at 60% of the market in 2025.<ref>{{Cite web |last= |first= |date=February 2026 |title=Automotive Trends Report |url=https://www.epa.gov/automotive-trends/download-automotive-trends-report |access-date=2026-03-25 |website=United States Environmental Protection Agency |language=en}}</ref>

{| class="wikitable" |+ Notable straight-three engines |- ! Years !! Name !! Fuel!! Notes !Ref. |- | 1977–1993 || Daihatsu C-series || Petrol || |<ref>{{cite web | url = http://motormania.eu.com/MM/2011/09/23/car-2012-daihatsu-mira-es/ | title = New car: 2012 Daihatsu Mira e:S | author = Logan | date = September 23, 2011 | work = Motor Mania | access-date = 2012-07-03 | quote = Motivation comes from a 3-cylinder, 650cc petrol engine that kicks out a mere 51bhp (52PS/38kW) and 60Nm (44lb-ft) of torque.}}</ref> |- | 1983–2001 || Suzuki G10 || Petrol || |<ref name="RnT3x3July93" /><ref>{{cite web|author=Daniel Zevedei |url=http://www.auto-types.com/suzuki-swift-10-gl-5-doors-hatchback-5-speed-manual-63979.html |title=Suzuki Swift 1.0 GL - 5-doors, hatchback |publisher=Auto-types.com |access-date=2014-06-20}}</ref> |- | 1986–1995 || VM Motori R series|| Diesel || Turbocharged | |- | 1987–present || Mitsubishi 3G8 || Petrol || | |- |1988–present |Honda E0 series |Petrol |Some versions turbocharged | |- | 1991–2008 || Daewoo S-TEC || Petrol || | |- | 1996–2002 || GM X10XE || Petrol || | |- | 1998–2007 || Mercedes-Benz M160 || Petrol || Turbocharged | |- | 1998–2005 || Volkswagen R3 PD TDI 3L || Diesel || Turbocharged |<ref>{{cite press release|title=Audi A2 1.2 TDI: the three-litre car from Audi|url=http://www.audiworld.com/news/99/a2_2/content.shtml|date=1999-11-28|work=AUDI AG - press release|publisher=AudiWorld.com|access-date=2009-08-22}}</ref> |- | 1999–2014 || Mercedes-Benz OM660 || Diesel || Turbocharged | |- | 1999–2005 || VM Motori R 315 || Diesel || Turbocharged | |- | 2000–2006 || Honda ECA1 || Petrol || Mated to IMA hybrid system | |- |2003–present |Honda P series |Petrol |Some versions turbocharged | |- | 2003–present || Mitsubishi 3A9 || Petrol || |<ref name="LittleSmartBook">{{cite book| last = Jackson| first = Paul| title = The Little Book of Smart| date = February 1, 2008| publisher = Veloce Publishing| isbn = 978-1-84584-148-5| pages = 94–95| chapter = Chapter 6: The Next Generation| quote = There were plenty of changes under the skin, too, with the original smart-built turbocharged engine being replaced (on petrol-engined versions) by a Mitsubishi design – still with three cylinders but now a larger (999cc) capacity.}}</ref> |- | 2004–2011 || Hyundai U engine || Diesel || Turbocharged | |- | 2004–present || Volkswagen R3 (EA111) || Petrol || |<ref>{{cite web|title=New VW Fox in depth|url=http://www.worldcarfans.com/10504049256/6|work=Volkswagen AG|publisher=WorldCarFans.com|date=2005-04-04|access-date=2009-08-18}}</ref> |- | 2004–2009 || Mercedes-Benz OM639 || Diesel || Turbocharged |<ref>{{cite web|author=Daniel Zevedei |url=http://www.auto-types.com/mitsubishi-colt-11-inform-5-doors-hatchback-5-speed-manual-40988.html |title=Mitsubishi Colt 1.1 Inform - 5-doors, hatchback |publisher=Auto-types.com |access-date=2014-06-20}}</ref><ref>{{Cite web|title=Om639 Engine - Diesel Engine - Turbocharger|url=https://www.scribd.com/document/356042267/Om639-Engine|access-date=2020-08-24|website=Scribd|language=en}}</ref> |- | 2004–present || Toyota 1KR-FE || Petrol || | |- | 2010–present || Nissan HR || Petrol || Some versions supercharged |<ref>{{cite web|url=http://www.nissan-global.com/EN/TECHNOLOGY/OVERVIEW/hr12ddr.html |title=HR12DDR Engine | NISSAN | TECHNOLOGICAL DEVELOPMENT ACTIVITIES |publisher=Nissan-global.com |access-date=2014-06-20}}</ref> |- | 2011–2017 || Fiat XSDE || Diesel || |<ref>{{cite journal|url=http://www.bsmotoring.com/news/launched-chevrolet-beat-diesel-starts-at-rs-429-lakh/3813/1|title=LAUNCHED! Chevrolet Beat diesel starts at Rs 4.29 lakh|website=WWW.bsmotoring.com|publisher=BS Motoring|date=July 25, 2011}}</ref> |- | 2012–present || BMW B37 || Diesel || Turbocharged | |- | 2012–present | Ford EcoBoost | Petrol | Some versions turbocharged | |- |2012–present |Honda S series |Petrol |Some versions turbocharged | |- | 2012–present || Renault TCe || Petrol ||Some versions turbocharged | |- | 2013–present || BMW B38 || Petrol || Turbocharged | |- | 2013–present || GM small gasoline engine || Petrol || Turbocharged |<ref>{{cite web|url=http://media.opel.com/content/media/intl/en/opel/news.detail.html/content/Pages/news/intl/en/2013/opel/08-07-newall-aluminium-3-zylinder-turbo.html |title=New All-Aluminum 3-Cylinder Turbo Sets Refinement Benchmark |publisher=Media.opel.com |date=2013-08-07 |access-date=2014-06-20}}</ref><ref>{{cite web|url=http://media.gm.com/media/intl/en/opel/news.detail.html/content/Pages/news/intl/en/2013/opel/10-08-opel-sidi-turbo-aachen.html |title=Opel presents new 1.0 ECOTEC Direct Injection Turbo engine at Aachen Colloquium |publisher=Media.gm.com |date=2013-10-08 |access-date=2014-06-20}}</ref> |- | 2014–present || PSA Group PureTech || Petrol ||Some versions turbocharged | |- |2016–present |Fiat Global Small Engine |Petrol |Some versions turbocharged | |- | 2018–present || GM E-Turbo || Petrol || Turbocharged | |- | 2018–present || Ingenium AJ150 || Petrol || Turbocharged | |- | 2020–present || Toyota G16E|| Petrol || Turbocharged | |- | 2020–present || Koenigsegg TFG || Petrol || Turbocharged | |}

{{See also|List_of_motorcycles_by_type_of_engine#Straight_three {{!}} List of motorcycles by type of engine}}

The advantages of a straight-three engine for motorcycles are that it has a shorter length than an inline-four engine and produces less vibration than a straight-twin engine.<ref>How Your Motorcycle Works: Your Guide to the Components & Systems of Modern Motorcycles. Peter Henshaw Veloce Publishing Ltd, 15 Sep 2012</ref>{{page needed|date=November 2020}}

===Four-stroke=== Four-stroke straight-three engines have been used in road bikes and racing bikes by several companies.<ref name=ride>365 Motorcycles You Must Ride. Dain Gingerelli, Charles Everitt, James Manning Michels. MBI Publishing Company, 10 Jan 2011</ref>{{page needed|date=November 2020}}<ref>The Motorcycle Book, Alan Seeley. MotorBooks International, 2 May 2004</ref>{{page needed|date=November 2020}}<ref>Human Hurricane, Wilson, Steve. Walneck's Classic Cycle Trader, April 2005</ref>{{page needed|date=November 2020}}

From 1985–1995, the BMW K75 was produced with a straight-three engine (based on the straight-four engine from the BMW K100).

British company Triumph is particularly renowned for a transversely-mounted straight-three engine. Variants have been used in their Speed Triple,<ref>Cycle world, Volume 44 CBS Publications, 2005. "inline triple"</ref> Trident, Sprint, and Tiger series. In addition Triumph makes the Rocket III model, various variants of which have held the record for motorcycle with the largest engine displacement.<ref>Triumph Motorcycles: Twins & Triples. Timothy Remus. MotorBooks International, 10 Oct 1997</ref>

In 2019, the Moto2 class in the MotoGP World Championship switched to using Triumph 765 cc (46.7 cu in) triple engines.<ref name="Telegraph 2019">[https://www.telegraph.co.uk/cars/features/triumph-enters-grand-prix-racing-moto2-engine-supplier/ Triumph enters Grand Prix racing as Moto2 engine supplier] ''The Telegraph'', 18 December 2018. Retrieved 15 December 2019.</ref>

===Two-stroke=== Two-stroke designs are less common in straight-three engines than four-stroke designs, however several were produced by Japanese manufacturers in the late 1960s through to 1980s.

The Kawasaki triple engine was produced from 1968 to 1980 and was used in various road bikes and racing bikes.<ref>The Kawasaki Triples Bible: All Road Models 1968–1980, Plus H1r and H2r Racers in Profile. Alastair Walker, Veloce Publishing Ltd, 15 Jan 2011. P.18</ref><ref>365 Motorcycles You Must Ride. Dain Gingerelli, Charles Everitt, James Manning Michels. MBI Publishing Company, 10 Jan 2011. P.188</ref> Most versions were air-cooled, however several were water-cooled.<ref name="walker">Japanese Production Racing Motorcycles. Mick Walker. Redline Books, Sep 2004</ref> Similarly, the 1972–1980 Suzuki GT series engines were used for both road bike and racing bikes, and were available in both air-cooled and water-cooled versions.<ref name="walker" /> {{clear right}}

== Other uses == === Agriculture === [[File:FairbanksMorse-EngPump-JSPark-Aug2008.jpg|thumb|1940s Fairbanks-Morse straight-three diesel engine]]

An example of an agricultural application is the ''Fairbanks-Morse 32E14'' low-speed diesel engine.

The straight-three layout is common for diesel tractor engines, such as the ''Perkins AD3.152''. This engine was used in the Massey Ferguson 35 and Fordson Dextra tractors, as well as for marine and stationary applications.

=== Aviation === The Hewland AE75 is a 750 cc two-stroke aircraft engine that was produced in the mid-1980s. It was an inverted three-cylinder design with liquid-cooling that produced {{convert|75|bhp|abbr=on}}.<ref>“Pilot” magazine February 1986 page 32</ref> {{clear right}}

== See also == {{commons category|Straight-3 engines}} * Straight engine * V3 engine {{clear right}}

== References == {{reflist|30em}}

{{DEFAULTSORT:Straight-03}} 3 Category:Straight-three engines