A straight-three engine, also known as an inline-triple, or inline-three (abbreviated I3 or L3), is a reciprocating piston internal combustion engine with three cylinders arranged in a straight line or plane, side by side.
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|
Four-stroke straight-three motorcycle engines have been produced for both road and racing purposes by Aprilia, Laverda, Triumph, Yamaha, BMW, Benelli, Petronas, MV Agusta, and BSA.
When BMW first moved to watercooled engines they first released the K100 I4 closely followed by the K75 with a 3 in line engine. the K75 was very popular due to the lower weight and the good torque range provided by the 3 cylinder engine.
The Triumph Rocket III, has a 2,294 cc (140.0 cu in) straight-three engine and the company has produced a number of other transversely mounted straight-three engines, such as the water-cooled T509 Speed Triple, which was also the company's first fuel injected machine; and 1,050 cc Speed Triple.
Current production motorcycles with triple engines:
- MV Agusta F3 675, F3 800, Brutale 675, Brutale 800, Rivale 800, Stradale 800
- Triumph Daytona 675, Street Triple, Speed Triple, Rocket III, Tiger (800, Sport 1050, Explorer 1200), Trophy, Sprint
- Yamaha MT-09/FZ-09, Yamaha XSR900, Yamaha Tracer 900
- Benelli: TNT899, TNT 1130 R, TNT 1130 K, TNT 1130 K Amazonas
Following a comparative study at Osaka University's Faculty of Engineering, between in-line and L-shaped motors, Kawasaki Motors decided to develop a range of high performance, two stroke straight-three engines. Between 1969 and 1978, the company produced air-cooled inline, triple engines with capacities of 250 cc, 350 cc, 400 cc, 500 cc, and 750 cc, and the H1-R 500cc and H2-R or KR750 750 cc racing models in both air-cooled and water-cooled forms.
Inline three-cylinder engines are not limited to propelling motor vehicles. They may also be used in general industrial applications. An example is the Fairbanks-Morse 32E14 slow-speed diesel engine which is shown coupled to a water pump.
Inline three engines are common in diesel engined tractors, as well as other agricultural machinery. Nearly all manufacturers of diesel tractors have had models with three-cylinder engines. Perhaps the best known example of any kind of three-cylinder diesel engine is the Perkins AD3.152 that was used in Massey Ferguson 35 tractors, as well as in Fordson Dexta and several other tractors. This engine was also used for marine and stationary applications. Other manufacturers include Nuffield (BMC), Bolinder-Munktell/Volvo BM, International Harvester, John Deere, Deutz-Fahr, Kubota, Ford and many others.
|Wikimedia Commons has media related to Straight-3 engines.|
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V4 replaces straight three
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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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