Less common than straight-four engines, straight-three engines have nonetheless been used in various motorcycles, cars and agricultural machinery.
A crankshaft angle of 120 degrees is typically used by straight-three engines, 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).
Usage in cars
Amongst 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 introduced of Saab's 750 cc (46 cu in) two-stroke engine, which was also used in the Saab 95 and Saab 96 until 1980. 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 straight-three versions of the Ford EcoBoost engine - a turbocharged 1.0-litre petrol engine - was introduced in the 2012 Ford Focus. It uses of 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 balancer shafts. In 2016, cylinder deactivation was added, claimed to be a world first for three-cylinder engines.
|1977-1993||Daihatsu C-series||Petrol||Used in the Diahatsu Charade and Diahatsu Mira/Cuore|
|1983-2001||Suzuki G10||Petrol||Debuted in the Suzuki Cultus/Swift|
|1986-1995||VM Motori R392||Diesel||Turbocharged, used in the Alfa Romeo 33|
|1987-present||Mitsubishi 3G8||Petrol||Debuted in the Mitsubishi Minica|
|1991-2008||Daewoo S-TEC||Petrol||Used in the Daewoo Tico and Daewoo Matiz|
|1996-2002||GM X10XE||Petrol||Debuted in the Opel Corsa|
|1998-2007||Mercedes-Benz M160||Petrol||Turbocharged, used by Smart|
|1998-2005||Volkswagen R3 PD TDI 3L||Diesel||Turbocharged, used in the Volkswagen Lupo and Audi A2|
|1999-2014||Mercedes-Benz OM660||Diesel||Turbocharged, used by Smart|
|1999-2005||VN Motori R 315||Diesel||Turbocharged, debuted in the Hyundai Accent|
|2000-2006||Honda ECA1||Petrol||Used by the Honda Insight hybrid car|
|2003-present||Mitsubishi 3A9||Petrol||Debuted in the Mitsubishi Mirage|
|2004-2011||Hyundai U engine||Diesel||Turbocharged, debuted in the Kia Picanto|
|2004-present||Volkswagen R3 (EA111)||Petrol||Debuted in the Volkswagen Fox|
|2004-2009||Mercedes-Benz OM639||Diesel||Turbocharged, used by the Smart Forfour and Mitsubishi Colt|
|2004-present||Toyota 1KR-FE||Petrol||Debuted in the Toyota Aygo|
|2010-present||Nissan HR||Petrol||Some versions supercharged, debuted in the Nissan Micra|
|2011-2017||Fiat XSDE||Diesel||Debuted in the India-market Chevrolet Beat|
|2012-present||BMW B37||Diesel||Turbocharged, debuted in the Mini (F56)|
|2012-present||Renault TCe||Petrol||Turbocharged, debuted in the Renault Clio IV|
|2013-present||BMW B38||Petrol||Turbocharged, debuted in the BMW i8|
|2013-present||GM small gasoline engine||Petrol||Turbocharged, debuted in the Opel Adam|
|2014-present||PSA Group PureTech||Petrol||Turbocharged, debuted in the Peugeot 308|
Usage in motorcycles
From 1985-1995, the BMW K75 was produced with a straight-three engine (based on the straight-four engine from the BMW K100). The British company Triumph has produced several models with transversely-mounted straight-three engines, such as the 1994-present Triumph Speed Triple and the 2004-present Triumph Rocket III.
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. Most versions were air-cooled, however several were water-cooled. 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.
An example of an agricultral application is the Fairbanks-Morse 32E14 low-speed diesel engine, which is shown in the picture to the right coupled to a water pump.
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.
|Wikimedia Commons has media related to Straight-3 engines.|
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V4 replaces straight three
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The 1071cc, inline, triple-cylinder configuration produces 803 pounds of thrust and pushes the boat to about 55 mph.
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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...
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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.
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Motivation comes from a 3-cylinder, 650cc petrol engine that kicks out a mere 51bhp (52PS/38kW) and 60Nm (44lb-ft) of torque.
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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.
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