Straight-three engine

A straight-three engine (also called an inline-triple or inline-three)[1][2][3][4][5][6][7] is a three-cylinder piston engine where cylinders are arranged in a line along a common crankshaft.

Engine block of an Elsbett straight-three diesel engine

Less common than straight-four engines, straight-three engines have nonetheless been used in various motorcycles, cars and agricultural machinery.

Design
four stroke Straight-three engine with firing order 1-3-2

A crankshaft angle of 120 degrees is typically used by straight-three engines,[8] since this results in an evenly spaced firing interval. Another benefit of this configuration is perfect primary balance and secondary balance, however an end-to-end rocking couple is induced because there is no symmetry in the piston velocities about the middle piston. A balance shaft is sometimes used to reduce the vibrations caused by the rocking couple.

Other crankshaft angles have been used occasionally. The 1976–1981 Laverda 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 2020 Triumph 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).[9][10]

Usage in cars
Circa-1960 Saab two-stroke engine
2010 Suzuki K10B engine

Among the first cars to use a straight-three engine is the 1953–1955 DKW F91, powered by a 900 cc (55 cu in) two-stroke engine. The 1956–1960 Saab 93 saw the introduction of Saab's 750 cc (46 cu in) 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 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.

The Subaru EF engine is a 4-stroke petrol engine which was introduced in 1984 and used in the Justy[6] 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.[11] 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.[12] In 2016, cylinder deactivation was added, claimed to be a world first for three-cylinder engines.[13]

Other car engines
YearsNameFuelNotes
1977–1993Daihatsu C-seriesPetrolUsed in the Daihatsu Charade and Daihatsu Mira/Cuore[14]
1983–2001Suzuki G10PetrolDebuted in the Suzuki Cultus/Swift[6][15]
1986–1995VM Motori R392DieselTurbocharged, used in the Alfa Romeo 33
1987–presentMitsubishi 3G8PetrolDebuted in the Mitsubishi Minica
1991–2008Daewoo S-TECPetrolUsed in the Daewoo Tico and Daewoo Matiz
1996–2002GM X10XEPetrolDebuted in the Opel Corsa
1998–2007Mercedes-Benz M160PetrolTurbocharged, used by Smart
1998–2005Volkswagen R3 PD TDI 3LDieselTurbocharged, used in the Volkswagen Lupo and Audi A2[16]
1999–2014Mercedes-Benz OM660DieselTurbocharged, used by Smart
1999–2005VM Motori R 315DieselTurbocharged, debuted in the Hyundai Accent
2000–2006Honda ECA1PetrolUsed by the Honda Insight hybrid car
2003–presentMitsubishi 3A9PetrolDebuted in the Mitsubishi Mirage[17]
2004–2011Hyundai U engineDieselTurbocharged, debuted in the Kia Picanto
2004–presentVolkswagen R3 (EA111)PetrolDebuted in the Volkswagen Fox[18]
2004–2009Mercedes-Benz OM639DieselTurbocharged, used by the Smart Forfour and Mitsubishi Colt[19][20]
2004–presentToyota 1KR-FEPetrolDebuted in the Toyota Aygo
2010–presentNissan HRPetrolSome versions supercharged, debuted in the Nissan Micra[21]
2011–2017Fiat XSDEDieselDebuted in the India-market Chevrolet Beat[22]
2012–present Ford EcoBoost Petrol Some versions turbocharged, debuted in the Ford Focus (3rd generation)
2012–presentBMW B37DieselTurbocharged, debuted in the Mini (F56)
2012–presentRenault TCePetrolTurbocharged, debuted in the Renault Clio IV
2013–presentBMW B38PetrolTurbocharged, debuted in the BMW i8
2013–presentGM small gasoline enginePetrolTurbocharged, debuted in the Opel Adam[23][24]
2014–presentPSA Group PureTechPetrolTurbocharged, debuted in the Peugeot 308
2018–presentGM E-TurboPetrolTurbocharged; debuted in the Chevrolet Orlando
2020–presentToyota G16EPetrolTurbocharged, debuted in the Toyota GR Yaris.

Usage in motorcycles
1969–1975 Kawasaki H1 Mach III
2004–present Triumph Rocket III engine
See also: 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.[25]

Four-stroke

Four-stroke straight-three engines have been used in road bikes and racing bikes by several companies.[26][27][28]

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[29], 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.[30]

In 2019, the Moto2 class in the MotoGP World Championship switched to using Triumph 765 cc (46.7 cu in) triple engines.[31]

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.[32][33] Most versions were air-cooled, however several were water-cooled.[34] 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.[34]

Other uses

Agriculture
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 75 bhp (56 kW).[35]

See also
Wikimedia Commons has media related to Straight-3 engines.

References
  1. Robson, Graham (August 15, 2010). "The car and the team". Saab 96 & V4. Rally Giants. Veloce Publishing. p. 27. ISBN 978-1-84584-256-7. V4 replaces straight three
  2. Let's Ride: Sonny Barger's Guide to Motorcycling. Sonny Barger, Darwin Holmstrom. HarperCollins, 8 Jun 2010
  3. Superbikes: The World's Top Performance Machines. Alan Dowds. Tangerine Press, 2004
  4. Cycle world, Volume 44. CBS Publications, 2005
  5. Gorant, Jim (December 1997). Oldham, Joe (ed.). "Jet Ski Saviors". Popular Mechanics. New York, NY USA: Hearst. 174 (12): 54–57. ISSN 0032-4558. Retrieved 2012-07-02. The 1071cc, inline, triple-cylinder configuration produces 803 pounds of thrust and pushes the boat to about 55 mph.
  6. Dinkel, John, ed. (July 1988). "Comparison Road Test: 3x3". Road & Track. Newport Beach, CA USA: Diamandis Communications. 39 (11): 66–74. ISSN 0035-7189. 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...
  7. Mayersohn, Norman; Zino, Ken (March 1988). Oldham, Joe (ed.). "Car of the Future Part 3 of a Series – Power for Tomorrow". Popular Mechanics. New York, NY USA: Hearst. 165 (3): 53–57. ISSN 0032-4558. Retrieved 2012-07-02. Under a more sophisticated modular engine plan, a basic 3-liter V6 could be split into an inline Three, chopped into a V4 or melded into a V12.
  8. "Here's The Problem With Three-Cylinder Engines". Car Throttle. Retrieved 2019-12-03.
  9. "TIGER 900 ENGINE & CAPABILITY". Triumph Motorcycles UK. Retrieved 10 February 2020.
  10. Cameron, Kevin. "Triumph's New T-Plane Firing Order Explained". Cycleworld. Retrieved 10 February 2020.
  11. "Smallest Ford Engine Ever! Three-Cylinder EcoBoost (and Two New Transmissions)". Retrieved 2017-04-03.
  12. "Ford's 3-cyl. EcoBoost Delivers the Goods". 2014-05-15. Retrieved 2017-04-03.
  13. "Ford To Offer Fuel-Saving Cylinder Deactivation Tech FOR 1.0 Litre EcoBoost; Global First For A 3-Cylinder Engine". 2016-11-29. Retrieved 2017-04-03.
  14. Logan (September 23, 2011). "New car: 2012 Daihatsu Mira e:S". Motor Mania. Retrieved 2012-07-03. Motivation comes from a 3-cylinder, 650cc petrol engine that kicks out a mere 51bhp (52PS/38kW) and 60Nm (44lb-ft) of torque.
  15. Daniel Zevedei. "Suzuki Swift 1.0 GL - 5-doors, hatchback". Auto-types.com. Retrieved 2014-06-20.
  16. "Audi A2 1.2 TDI: the three-litre car from Audi". AUDI AG - press release (Press release). AudiWorld.com. 1999-11-28. Retrieved 2009-08-22.
  17. Jackson, Paul (February 1, 2008). "Chapter 6: The Next Generation". The Little Book of Smart. Veloce Publishing. pp. 94–95. ISBN 978-1-84584-148-5. 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.
  18. "New VW Fox in depth". Volkswagen AG. WorldCarFans.com. 2005-04-04. Retrieved 2009-08-18.
  19. Daniel Zevedei. "Mitsubishi Colt 1.1 Inform - 5-doors, hatchback". Auto-types.com. Retrieved 2014-06-20.
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  21. "HR12DDR Engine | NISSAN | TECHNOLOGICAL DEVELOPMENT ACTIVITIES". Nissan-global.com. Retrieved 2014-06-20.
  22. "LAUNCHED! Chevrolet Beat diesel starts at Rs 4.29 lakh". WWW.bsmotoring.com. BS Motoring. July 25, 2011.
  23. "New All-Aluminum 3-Cylinder Turbo Sets Refinement Benchmark". Media.opel.com. 2013-08-07. Retrieved 2014-06-20.
  24. "Opel presents new 1.0 ECOTEC Direct Injection Turbo engine at Aachen Colloquium". Media.gm.com. 2013-10-08. Retrieved 2014-06-20.
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  35. “Pilot” magazine February 1986 page 32
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