A straight-three engine (also called an inline-triple or inline-three) [1] [2] [3] is a three-cylinder piston engine where cylinders are arranged in a line along a common crankshaft.
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, [4] 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). [5] [6]
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, although this was predated by the 3 cylinder 15hp Rolls Royce produced in 1905 and a number of other cars of this era also used 3 cylinder engines. 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 [3] 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. [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 the Daihatsu Charade and Daihatsu Mira/Cuore [10] |
| 1983–2001 | Suzuki G10 | Petrol | Debuted in the Suzuki Cultus/Swift [3] [11] |
| 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 [12] |
| 1999–2014 | Mercedes-Benz OM660 | Diesel | Turbocharged, used by Smart |
| 1999–2005 | VM 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 [13] |
| 2004–2011 | Hyundai U engine | Diesel | Turbocharged, debuted in the Kia Picanto |
| 2004–present | Volkswagen R3 (EA111) | Petrol | Debuted in the Volkswagen Fox [14] |
| 2004–2009 | Mercedes-Benz OM639 | Diesel | Turbocharged, used by the Smart Forfour and Mitsubishi Colt [15] [16] |
| 2004–present | Toyota 1KR-FE | Petrol | Debuted in the Toyota Aygo |
| 2010–present | Nissan HR | Petrol | Some versions supercharged, debuted in the Nissan Micra [17] |
| 2011–2017 | Fiat XSDE | Diesel | Debuted in the India-market Chevrolet Beat [18] |
| 2012–present | Ford EcoBoost | Petrol | Some versions turbocharged, debuted in the Ford Focus (3rd generation) |
| 2012–present | BMW B37 | Diesel | Turbocharged, debuted in the Mini (F56) |
| 2012–present | Renault TCe | Petrol | Naturally aspirated and Turbocharged, debuted in the Renault Clio IV [ broken anchor ] |
| 2013–present | BMW B38 | Petrol | Turbocharged, debuted in the BMW i8 |
| 2013–present | GM small gasoline engine | Petrol | Turbocharged, debuted in the Opel Adam [19] [20] |
| 2014–present | PSA Group PureTech | Petrol | Naturally aspirated and Turbocharged, debuted in the Peugeot 308 |
| 2018–present | GM E-Turbo | Petrol | Turbocharged; debuted in the Chevrolet Orlando |
| 2020–present | Toyota G16E | Petrol | Turbocharged, debuted in the Toyota GR Yaris. |
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, 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, [25] 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. [26]
In 2019, the Moto2 class in the MotoGP 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.
The Kawasaki 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 1972–1980 Suzuki GT series engines were used for both road bike and racing bikes, and were available in both air-cooled and water-cooled versions. [30]
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.
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). [31]
A V6 engine is a six-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration.
A V4 engine is a four-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration.
A straight-twin engine, also known as an inline-twin, vertical-twin, or parallel-twin, is a two-cylinder piston engine whose cylinders are arranged in a line along a common crankshaft.
A straight-four engine is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft.
The straight-six engine is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine balance, resulting in fewer vibrations than other designs of six or fewer cylinders.
The straight-five engine is a piston engine with five cylinders mounted in a straight line along the crankshaft.
A U engine is a piston engine made up of two separate straight engines placed side-by-side and coupled to a shared output shaft. When viewed from the front, the engine block resembles the letter "U".
The Triumph slant-four is an inline four-cylinder petrol car engine developed by the Triumph Motor Company. It first appeared in 1968 in the Saab 99. The first Triumph model to use the engine did not appear until 1972. With an original capacity of 1.7 L, displacement grew over time to 2.0 L. Triumph production ended in 1981.
A multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing, and with more smaller valves may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.
The Triumph Triples are a family of modern DOHC inline three-cylinder motorcycle engines made from 1990 onwards by the Triumph Motorcycle Company at their Hinckley, Leicestershire factory. The inspiration for the later triples was the pushrod Triumph Trident, produced from 1968 to 1974 at the Triumph factory at Meriden Works.
A transverse engine is an engine mounted in a vehicle so that the engine's crankshaft axis is perpendicular to the direction of travel. Many modern front-wheel drive vehicles use this engine mounting configuration. Most rear-wheel drive vehicles use a longitudinal engine configuration, where the engine's crankshaft axis is parallel with the direction of travel, except for some rear-mid engine vehicles, which use a transverse engine and transaxle mounted in the rear instead of the front. Despite typically being used in light vehicles, it is not restricted to such designs and has also been used on armoured fighting vehicles to save interior space.
A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.
The Saab two-stroke was a two-stroke cycle, inline, two cylinder, and later three cylinder engine manufactured by Swedish automotive manufacturer Saab that was based on a design by German manufacturer DKW.
A single-cylinder engine, sometimes called a thumper, is a piston engine with one cylinder. This engine is often used for motorcycles, motor scooters, motorized bicycles, go-karts, all-terrain vehicles, radio-controlled vehicles, power tools and garden machinery. Single-cylinder engines are made both as 4-strokes and 2-strokes.
The Kawasaki triples were a range of 250 to 750 cc motorcycles made by Kawasaki from 1968 to 1980. The engines were air-cooled, three-cylinder, piston-controlled inlet port two-strokes with two exhaust pipes exiting on the right side of the bike, and one on the left. It was the first production street motorcycle with capacitor discharge ignition (CDI). Right from the first triple model, the 1968 Mach III H1 500 cc, it was a sales success that gained a reputation for almost unmatched acceleration as well as an air of danger for inexperienced riders trying to cope with the bike's increased power to weight ratio over any previously available stock motorcycles.
A big bang engine has an unconventional firing order designed so that some of the power strokes occur simultaneously or in close succession. This is achieved by changing the ignition timing, changing or re-timing the camshaft, and sometimes in combination with a change in crankpin angle. The goal is to change the power delivery characteristics of the engine. A regular firing multi-cylinder engine fires at approximately even intervals, giving a smooth-running engine. Because a big-bang engine has uneven power delivery, they tend to run rougher and generate more vibration than an even-firing engine.
The Standard wet liner inline-four engine was an inline four cylinder petrol engine produced by the Standard Motor Company. Originally developed concurrently for passenger car use and for the Ferguson TE20 tractor, it was widely used for Standard passenger cars of the 1950s, most notably the Vanguard. Later it was successfully used in Standard's popular early generation Triumph TR series sports cars.
The Standard SC engine is a cast-iron overhead valve straight-four engine designed and initially produced by Standard Triumph. Over its production life displacement grew from an initial size of just over 800 cc to nearly 1500 cc. Introduced in the Standard Eight in 1953, it would eventually be used in a wide range of vehicles from Standard, Triumph, and MG.
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.