Astraight-three engine (also called aninline-triple orinline-three)[1][2][3] is a three-cylinderpiston engine where cylinders are arranged in a line along a common crankshaft.
Less common thanstraight-four engine, straight-three engines have nonetheless been used in various motorcycles, cars and agricultural machinery.
Acrankshaft angle of 120 degrees is typically used by straight-three engines,[4] since this results in an evenly spacedfiring interval. Another benefit of this configuration is perfectprimary balance andsecondary balance, however an end-to-endrocking couple is induced because there is no symmetry in the piston velocities about the middle piston. Abalance shaft is sometimes used to reduce the vibrations caused by the rocking couple.
Other crankshaft angles have been used occasionally. The 1976–1981Laverda Jota motorcycle used a 180 degree crankshaft, where the outer pistons rise and fall together and inner cylinder is offset from them by 180 degrees. This results in three power strokes evenly-spaced at 180 degrees each, and then no power strokes during the final 180 degrees of crankshaft rotation. The 2020Triumph Tiger 900 motorcycle uses a "T-Plane" crankshaft where the crankshaft throws are at 90 intervals, such that the throws for cylinders 1 and 3 are separated by 180 degrees (therefore the three throws together forming a "T" shape when viewed from the end).[5][6]
One of the first 3 cylinder cars include the 3 cylinder 15hp Rolls Royce produced in 1905 . The 1956–1960Saab 93 saw the introduction of Saab's 750 cc (46 cu in) two-stroke engine, which was also used in theSaab 95,Saab 96 andSaab Sonett until 1968 after which it was replaced by theFord Taunus V4 engine.
TheWartburg cars (manufactured in East Germany) andFSO Syrena (manufactured in Poland) also used straight-three engines.
The 1967Suzuki Fronte 360 uses a 256 cc (16 cu in) two-stroke engine. In 1980, Suzuki began production of a 543 cc (33 cu in) four-stroke engine, which was introduced in the Alto and Fronte models.
TheSubaru EF engine is a 4-stroke petrol engine which was introduced in 1984 and used in theJusty[3] and theSumo (the export version of the Sambar).
The straight-three versions of theFord EcoBoost engine – a turbocharged 1.0-litre petrol engine – was introduced in the 2012 Ford Focus.[7] 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.[8] In 2016,cylinder deactivation was added, claimed to be a world first for three-cylinder engines.[9]
| Years | Name | Fuel | Notes |
|---|---|---|---|
| 1977–1993 | Daihatsu C-series | Petrol | Used in theDaihatsu Charade andDaihatsu Mira/Cuore[10] |
| 1983–2001 | Suzuki G10 | Petrol | Debuted in theSuzuki Cultus/Swift[3][11] |
| 1986–1995 | VM Motori R392 | Diesel | Turbocharged, used in theAlfa Romeo 33 |
| 1987–present | Mitsubishi 3G8 | Petrol | Debuted in theMitsubishi Minica |
| 1991–1992 | Elsbett ELKO 3.82.92t | Diesel | Small-scale production engine for biodiesel conversions |
| 1991–2008 | Daewoo S-TEC | Petrol | Used in theDaewoo Tico andDaewoo Matiz |
| 1996–2002 | GM X10XE | Petrol | Debuted in theOpel Corsa |
| 1998–2007 | Mercedes-Benz M160 | Petrol | Turbocharged, used bySmart |
| 1998–2005 | Volkswagen R3 PD TDI 3L | Diesel | Turbocharged, used in theVolkswagen Lupo andAudi A2[12] |
| 1999–2014 | Mercedes-Benz OM660 | Diesel | Turbocharged, used bySmart |
| 1999–2005 | VM Motori R 315 | Diesel | Turbocharged, debuted in theHyundai Accent |
| 2000–2006 | Honda ECA1 | Petrol | Used by theHonda Insight hybrid car |
| 2003–present | Mitsubishi 3A9 | Petrol | Debuted in theMitsubishi Mirage[13] |
| 2004–2011 | Hyundai U engine | Diesel | Turbocharged, debuted in theKia Picanto |
| 2004–present | Volkswagen R3 (EA111) | Petrol | Debuted in theVolkswagen Fox[14] |
| 2004–2009 | Mercedes-Benz OM639 | Diesel | Turbocharged, used by theSmart Forfour andMitsubishi Colt[15][16] |
| 2004–present | Toyota 1KR-FE | Petrol | Debuted in theToyota Aygo |
| 2010–present | Nissan HR | Petrol | Some versions supercharged, debuted in theNissan Micra[17] |
| 2011–2017 | Fiat XSDE | Diesel | Debuted in the India-marketChevrolet Beat[18] |
| 2012–present | FordEcoBoost | Petrol | Some versions turbocharged, debuted in theFord Focus (3rd generation) |
| 2012–present | BMW B37 | Diesel | Turbocharged, debuted in theMini (F56) |
| 2012–present | Renault TCe | Petrol | Naturally aspirated and Turbocharged, debuted in theRenault Clio IV[broken anchor] |
| 2013–present | BMW B38 | Petrol | Turbocharged, debuted in theBMW i8 |
| 2013–present | GM small gasoline engine | Petrol | Turbocharged, debuted in theOpel Adam[19][20] |
| 2014–present | PSA Group PureTech | Petrol | Naturally aspirated and Turbocharged, debuted in thePeugeot 308 |
| 2018–present | GM E-Turbo | Petrol | Turbocharged; debuted in theChevrolet Orlando |
| 2018–present | Ingenium AJ150 | Petrol | Turbocharged mild hybrid and plug-in hybrid; debuted in theRange Rover Evoque andLand Rover Discovery |
| 2020–present | ToyotaG16E | Petrol | Turbocharged, debuted in theToyota GR Yaris |
| 2020-present | KoenigseggTFG engine | Petrol | Turbocharged, Freevalve engine debuted inKoenigsegg Gemera. |
| 2016-present | FCAFiat Global Small Engine "FireFly" | Petrol | Naturally aspirated and Turbocharged, debuted in the Brazilian version of the 2017Fiat Uno#Fiat Novo Uno (2010–2021) |
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.[21][page needed]
Four-stroke straight-three engines have been used in road bikes and racing bikes by several companies.[22][page needed][23][page needed][24][page needed]
From 1985–1995, theBMW K75 was produced with a straight-three engine (based on the straight-four engine from the BMW K100).
British companyTriumph is particularly renowned for a transversely-mounted straight-three engine. Variants have been used in theirSpeed Triple,[25]Trident,Sprint, andTiger series.In addition Triumph makes theRocket III model, various variants of which have held the record for motorcycle with the largest engine displacement.[26]
In2019, the Moto2 class in theMotoGP World Championship switched to using Triumph 765 cc (46.7 cu in) triple engines.[27]
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.
TheKawasaki triple engine was produced from 1968 to 1980 and was used in various road bikes and racing bikes.[28][29] Most versions were air-cooled, however several were water-cooled.[30] Similarly, the 1972–1980Suzuki GT series engines were used for both road bike and racing bikes, and were available in both air-cooled and water-cooled versions.[30]
An example of an agricultural application is theFairbanks-Morse 32E14 low-speed diesel engine.
The straight-three layout is common for dieseltractor engines, such as thePerkins AD3.152. This engine was used in theMassey Ferguson 35 andFordson Dextra tractors, as well as for marine and stationary applications.
TheHewland 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 75 bhp (56 kW).[31]
V4 replaces straight three
The 1071cc, inline, triple-cylinder configuration produces 803 pounds of thrust and pushes the boat to about 55 mph.
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...
Motivation comes from a 3-cylinder, 650cc petrol engine that kicks out a mere 51bhp (52PS/38kW) and 60Nm (44lb-ft) of torque.
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.