Straight-twin engine

Parallel twin refers to a two-cylinder inline engine.


Two-cylinder in-line engines exist at different heat engines the group of piston engines. Mostly are two-stroke engines and four-stroke engines, rare diesel engines parallel twin - construction encountered. They are manufactured in different designs:

The term " parallel twin " with two meanings is used, a binding or standard definition does not exist. The meaning refers solely to the co-rotating way. For the counter-rotating terms, please refer to such as " 180 -degree Twin" (derived from the stroke offset ), or "Series Twin".

However, the other meaning is not limited to such a designation and includes all two-cylinder in a parallel -Twin. In Anglo-Saxon countries, especially the United Kingdom, the term is also used regardless of the stroke offset, even as a demarcation line two-cylinder boxer ( "flat twin" ) or V- twin-cylinder ( "V -twin "). Two-cylinder in but there are also referred to as "Straight -two", "Straight twin" or " inline twin", where " straight" and "inline" general terms for in-line engines. For the co-rotating one rarely finds there the term " True straight twin", which in the German translation probably means most likely "real two-cylinder in " considerably more common, the term " 360 degree parallel twin", which in German " Parallel Twin with 360 degree firing interval "or " parallel co-rotating twin " bedeuztet. The fact that the great British twin-cylinder in-line engines were designed as a direct- runner for motorcycles, favored on the continent, the more exclusive meaning of " parallel twin " as a synonym for the DC- runner, particularly in the motorcyclists scene, while in the UK using the the term is " parallel twin" always called the crank throw to distinguish direct and counter-rotating with.

Co-rotating twin-cylinder in-line engine

The DC Runners can be built in the simplest case of two crankshaft bearings and a single wide angle bend. one example of this is designed by Richard kitchens Opti -Twin or the Fiat Nuova 500 English motorcycle engines of this type from the 1930s to 1970s have usually in the middle of the crankshaft, a large flywheel and therefore two independent crank throws left and right of the flywheel. Here, the crankshaft either in one piece ( Triumph ) or several components screwed together (Norton ) are. In this design, the crankshaft is very highly stressed, their strength and tendency to oscillate limit performance and maximum speed of such motors. Therefore, modern designs have always two individual bends and a third or fourth bearing in the middle. Examples include the Kawasaki W650 (3 locations) and the Yamaha XS 650 ( four locations) called. BMW and Rotax developed for the F 800 a DC- runner who has a Ausgleichspleuel on its own, to the other by 180 ° crank pin offset between the cylinders. The crankshaft of the F - 800 engine is mounted in quadruplicate. Already in the 70s the company Norton realized such a concept for the successor to the Norton Commando. The prototype of this bike is owned by one of the successor companies of Norton and has been restored in 2008. The Italian motorcycle brand Laverda sat in the SF models also give a parallel twin.

In a co-rotating parallel twin - either the rotating ( connecting rod and crank pin ) or oscillating ( piston and connecting rod upper ), the compositions are vibrationsvermeidend balanced, but never both simultaneously. If the oscillating masses completely offset by counterweights on the crankshaft, these produce a strong vibration in the horizontal direction when the balancing mass is 90 degrees to the oscillation plane. Therefore, co-rotating parallel twin are usually constructed with impact factors in the area of 80 percent, by the residual vibration remains in the vertical direction, which does not interfere with the motorcycle in the rule, and a lower vibration generated in the horizontal direction than in fully balanced. An exception is the engine of the Norton Commando with a balance factor of around 50 percent, which generates little horizontal vibrations, the strong vertical vibrations are compensated by the rubber mounting the engine. A complete in all factors mass balance can only be compensated with additional design effort ( balance shafts or Ausgleichspleuel ). In the small car they were instead suspended in particularly soft rubber bearings. Occasionally, the rotating masses were more than compensated to reduce the cost of a lateral movement of the pounding of the engine. In addition, the air in the crankcase must be pressed together what energy costs, the same problem also engines of a cylinder. Advantage in the four-stroke engine is the uniform distribution of force, because the firing interval of the two cylinders with 360 degree symmetrical. In the simplest case can be driven with a twin coil two spark plugs.

Counter-rotating twin-cylinder in-line engine

The counter- runner always has two crank pins; the pistons run alternately up and down. The counter-rotation of the piston causes a vibration compensation, but remains due to the cylinder spacing a tilting moment. Typical examples of counter-rotating engines are all two-stroke parallel twins and almost all two-cylinder four-stroke engines from Honda and Yamaha in the 1960s to 1980s. In conjunction with a vibration -reducing balancer shaft, this type concluded inter alia in the produced between 2004 and 2007 Honda CBF 500 for use. Today, among other things used in the models, this type MZ 1000 S / SF / ST. The offset of the crankshaft 180 degrees allows a center bearing, but also counter-rotating engines were built earlier without central warehouse.

The firing interval of four clocking counter rotating engines is asymmetric; already 180 degrees after a cylinder fires the next, then go by one and a half revolutions of the crankshaft ( 360 180 = 540 degrees) before the first cylinder fires again. As the pistons move exactly in opposite directions, the volume of the crankcase is always the same, the air therein is only moved out of the space in the cylinder below the piston moving down into the space below each other's piston, which wastes less energy than compressing the air. Thus, the counter-rotating saving some energy compared to direct runners. As is ignited at the two-stroke principle at each crankshaft revolution, the firing interval of the two-stroke counterparts armature is symmetrical. The best-known example of such an engine is the Trabant. Examples of four-stroke counterpart runners include two-cylinder diesel engines from Deutz tractors in the 1950s and 60s.

In a counter-rotating parallel twin, the oscillating and rotating masses of the same cylinder are mutually exclusive. This allows the motor runs theoretically less vibration than a direct runners. The opposing motion of the masses, but tilt and pan movement is generated depending on the position of the crank pin, which is perceived as a vibration.

Two-cylinder inline engine with a special stroke offset

There are also in-line two-cylinder, the crank pins are offset by 90 °. This achieves the firing interval ( four-stroke: 270 ° / 450 ° ) of a two -cylinder V- engine with 90 ° cylinder angle, and therefore its unmistakable sound. However, one thus gets the concentricity problems at low speeds. As an example, the Yamaha TDM, Yamaha TRX, the Norton Commando 961 and the Triumph Scrambler be mentioned, also developed for the new NC - Series Honda engine is designed to. Ducati and Moto Guzzi set today only the V - a motor.