Straight-three engine

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A straight-three engine, also known as inline-three engine, or a triple, is an internal combustion engine with three cylinders arranged in a straight line or plane, side by side.

Most inline-three engines employ a crank angle of 120°, and are thus rotationally balanced; however, since the three cylinders are offset from each other, the firing of the end cylinders induces a rocking motion from end to end, since there is no opposing cylinder moving in the opposite direction as in a rotationally balanced straight-six. The use of a balance shaft in an antiphase to that vibration produces a smoothly running engine.

An exception to the 120° crankshaft can be found in some of the inline-three engines made by motorcycle manufacturer Laverda. In these engines (sometimes referred to as 180° triples), the outer pistons rise and fall together like a 360° straight-two engine. The inner cylinder is offset 180° from the outer cylinders. In these engines, cylinder #1 fires 180°. Later, cylinder #2 fires, and then 180° later cylinder #3 fires. There is no power stroke on the final 180° of rotation.

Automobile use

The smallest inline-three engine was the 543 cc Suzuki F5A, which was used in the 1982 Cervo. Smart currently produces a diminutive 799 cc inline-three diesel engine, the smallest automotive diesel engine in production^{[citation needed]}. Most inline-three engines fall below 1.2 litres, with a 1,198 cc Volkswagen Group unit seen as the largest petrol unit. A 1.8 litre (1779 cc) diesel engine was produced by VM Motori to the 1984 Alfa Romeo 33 1.8 TD, the largest inline-three produced for automotive use.

Basic versions of the Suzuki Swift/Forsa and related Geo/Chevy Metro used an inline-three.

Some Daihatsu cars use inline-three engines. The Charade and the Mira/Cuore used (or are still fitted with) this engine type. Three-cylinder 1.0 litre diesel and turbo diesel engines were also offered in Daihatsu Charades.

The Volkswagen Group was known for using three cylinder petrol and diesel engines in the Audi A2, Volkswagen Polo, Seat Ibiza and Škoda Fabia. The engines in these cars ranged from 1.2 petrols with 4v per cylinder that delivered 60bhp to 1.4 diesels that delivered 90bhp and had turbo's with variable vane geometry and delivered outstanding economy, this particular engine was used solely in the Audi A2. The most innovative 3 cylinder engine the Volkswagen Group released was the 1.2 litre diesel, it was one of the first aluminium diesel engines and at the time of release it was the lightest and most economic engine in production. It won many awards and was used in the AudiA2 3l and the Volkswagen Lupo 3l

Subaru also used a inline-three in the Subaru Justy and the export version of the Subaru Sambar, called the Subaru Sumo, using their Subaru EF engine.

Mitsubishi has also made extensive use of three cylinder engines.

In the 1950s and 1960s, the Saab 93, Saab 95, Saab 96, and certain DKW automobiles were powered by inline-three-cylinder, two-stroke engines.

The first-generation Honda Insight (2000-2006) used a 1.0 litre inline-three engine in conjunction with an electric motor in its hybrid system.

Toyota, Peugeot and Citroen are using a common inline-three-cylinder engine in models of Aygo, 107 and C1 respectively.

Currently, the only new three-cylinder car available in North America is the Smart fortwo.

Motorcycle use

four-stroke

The four-stroke inline-three is used by Aprilia, Laverda, Triumph, Yamaha, BMW, Benelli, Petronas, MV Agusta and the BSA.

The Triumph Rocket III has a 2,294 cc inline-three engine. It is currently the largest engine in a motorcycle being made by a major manufacturer.

two-stroke

Between 1972 and 1977, Suzuki made the inline-three-cylinder water-cooled 750cc GT750 and the aircooled GT550 and GT380.

Between 1969 and 1978, Kawasaki made inline-three-cylinder H1 models in 250cc, 350cc, 400cc, 500cc and 750cc, all air-cooled.

References

• http://www.laverdamania.com/millegb.htm^{[dead link]}
• http://www.autozine.org/technical_school/engine/smooth1.htm