Parallel twin
Parallel twin refers to a two-cylinder in - line engine .
Definitions
Two-cylinder in-line engines exist in different heat engines of the group of reciprocating engines . Petrol engines are predominantly found , less often diesel engines of the parallel twin design. They are manufactured in different designs:
- Synchronous rotation: Both pistons are at the same time in the upper (TDC) and lower (BDC) dead center . In this way, four-stroke engines achieve an even ignition interval, but there is also no need to balance the inertia forces.
- Counter-rotation: mainly found in two-stroke engines . If one piston is in TDC, then the other is in BDC. The first order inertia forces of the opposing pistons thus cancel each other out; the second-order inertial forces, however, are identical to those in the same direction.
- Neither in the same direction nor in opposite directions - crank pin offset between 0 and 180 °, e.g. B. 90 °.
The actually English term "parallel twin" is used with two meanings; there is no binding or standardized definition. One meaning exclusively describes the synchronous runner like this. Terms such as “180-degree twin” (derived from the stroke offset) or “row twin” can be found for the counter-runner.
The other meaning does not limit the designation in such a way and designates all in-line two-cylinder units as parallel twin. In the Anglo-Saxon region, especially Great Britain , the term is used largely independently of the stroke offset, also to differentiate it from the two-cylinder boxer ("flat twin") or two-cylinder V-engine ("V-twin"). In-line two-cylinders are also referred to as “straight-two”, “straight-twin” or “inline-twin”, with “straight” and “inline” being general terms for in-line engines. The term “true straight twin”, which in the German translation probably means “real in-line two-cylinder”, and much more often the term “360 degree parallel twin”, which means “in-line two-cylinder with 360” in German, is seldom found there Degree of crank pin misalignment "or" parallel synchronous twin "means. The fact that the best-known English two-cylinder in-line engines were designed as synchronous motors for motorcycles favors the more exclusive meaning of the term "parallel twin" as a synonym for synchronous motors, especially in the motorcyclist scene , while in Great Britain when using the The term "parallel twin" always includes the crankshaft offset to differentiate between parallel and counter-rotating.
Co-running
The co-rotating in the simplest case with two crankshafts store and a single wide bend to be built. An example of this is the Opti-Twin designed by Richard Küchen or the Fiat Nuova 500 . English motorcycle engines of this type from the 1930s to 1970s usually have a large flywheel in the center of the crankshaft and therefore two independent crankshaft throws on the left and right of the flywheel. The crankshaft can either be manufactured in one piece (Royal Enfield) or screwed together from several components (older Triumph, Norton). With this type of construction, the crankshaft is subjected to very high loads; its strength and tendency to oscillate limit the power and maximum speed of such engines. That is why modern designs always have two individual crankings and a third or fourth bearing point in the middle. Examples are the Kawasaki W 650 (3 bearings) and the Yamaha XS 650 or Triumph Bonneville T100 (4 bearings). BMW and Rotax developed a synchronous rotor for the F 800 with a third connecting rod on its own crank pin offset by 180 ° to the others between the cylinders. It acts on a balance weight via a swinging lever. The crankshaft of the F 800 engine has four bearings. The Norton company implemented such a concept for the successor model of the Norton Commando as early as the 1970s . The prototype of this motorcycle is owned by one of Norton's successor companies and was restored in 2008. The Italian motorcycle brand Laverda also used the parallel twin in the SF models.
With a synchronous parallel twin without balancer shafts , only the rotating masses (connecting rod base and crank pin) can be completely balanced. The oscillating compensate (upper piston and connecting rod) masses vibrationsvermeidend by counterweights on the crankshaft generates a vibration in the horizontal direction. For this reason, synchronous rotors are usually designed with balancing factors of around 80 percent, which means that a residual vibration remains in the vertical direction, which usually does not interfere with the motorcycle, and generates a lower vibration in the horizontal direction than with full mass balance. The exception here is the Norton Commando motor with a balance factor of around 50 percent, which generates few horizontal vibrations, the strong vertical vibrations of which are compensated for by the motor's rubber mounts. A complete mass balance in all factors can only be compensated with additional design effort (compensating connecting rod and / or shaft as in the Fiat Twin Air twin cylinder engine built from 2010 ). The balance shafts do not have to rotate in opposite directions as with Lanchester balancing , but in the same direction, then the crankshaft with its counterweights balances one half of the vertical oscillation, the balance shafts the other half and the horizontal oscillations cancel each other out. Instead, the engines in small cars were suspended in particularly soft rubber mounts.
In addition, the air in the crankcase has to be compressed, which costs energy, and engines with one cylinder have the same problem. The advantage of the four-stroke engine is the even power delivery, because the ignition interval between the two cylinders is symmetrical at 360 degrees. In the simplest case, two spark plugs can be controlled with one ignition coil .
Counter-runner
The counter-runner always has two crank pins; the pistons run up and down alternately. The counter-rotation of the pistons balances the first-order inertia forces, but the cylinder spacing creates a tilting moment. Typical examples of counter-rotating engines are all two-stroke parallel twins and almost all two-cylinder four-stroke engines made by Honda and Yamaha in the 1960s to 1980s. In connection with a vibration-reducing balance shaft, this type came u. a. also used in the Honda CBF 500 produced between 2004 and 2007 . Also MZ used this type in the models 1000 S / SF / ST . The offset of the crankshaft by 180 degrees enables a center bearing, but counter-rotating engines were also built without center bearings in the past.
The ignition interval of four-stroke counter-rotating engines is asymmetrical; 180 degrees after one cylinder fires the next, then one and a half revolutions of the crankshaft (360 + 180 = 540 degrees) pass before the first cylinder fires again. As the pistons move in exactly the opposite direction, the volume of the crankcase always remains the same, the air in it is only moved from the space in the cylinder below the piston moving downwards into the space below the other piston, which wastes less energy than compressing it the air. The counter-rotor thus saves a little energy compared to the synchronous rotor. Since the two-stroke principle fires with every revolution of the crankshaft, the ignition interval in the two-stroke counter-rotor is symmetrical. The best-known example of such an engine is the Trabant . Examples of four-stroke counter-rotations are, for example, two-cylinder diesel engines from Deutz in tractors from the 1950s and 60s.
In a counter-rotating parallel twin, the oscillating (only in the first order) and rotating masses of the cylinders balance each other out. As a result, the motor theoretically runs with less vibration than a synchronous rotor. Due to the counter-rotating movement of the masses, depending on the position of the crank pins, a tilting and swiveling movement is generated which is perceived as a vibration.
Two-cylinder in-line engine with crank pin offset
There are also two-cylinder in-line engines with crankpins offset between 0 and 180 °. Thanks to the now no longer unusual offset of 90 °, the ignition interval (four-stroke: 270 ° / 450 °) of a two-cylinder V-engine with a 90 ° cylinder angle and its sound is achieved. However, you also get concentricity problems at low speeds, but these can be kept within acceptable limits by adjusting the flywheel mass and balance shaft. Examples of motorcycle engines include the Yamaha models MT-07 , TDM and TRX , the Honda CRF1000L Africa Twin , the Norton Commando 961 and the Triumph Scrambler ; the engine developed by Honda for the NC series is also constructed in this way. Another example is the engine of the BMW C 650 Sport and GT scooters .
The engine of the Husqvarna Nuda 900 , which was built from 2012 to 2013 , had a crank pin offset of 45 ° and therefore an ignition offset of 315 ° / 405 °, which corresponds to that of a V2 engine with a 45 ° cylinder angle.
See also
Individual evidence
- ↑ Helmut Heusler, MO 3/2007: Technical article Ideal 1000 cm³ motorcycle engine Part 2, pages 62 to 67.
- ↑ Helmut Heusler, MO 4/2007: Technical article Ideal 1000 cm³ motorcycle engine Part 3, pages 85 to 91.
- ↑ motorline.cc author Thilo Kozik describes the synchronous motor of the Triumph Thruxton as a "classic parallel twin "
- ^ RM Clarke, Royal Enfield Big Twins, Brooklands Books, ISBN 185520665X , p. 28
- ↑ Ian Falloon, Triumph Motorcycles, Motorbooks, ISBN 978-0-7603-4545-0 , pictures p. 13 and 17 - the screw connection of the middle swing weight can be clearly seen
- ↑ MOTORRAD compares the engine of the Husqvarna Nuda 900 with that of the BMW F 800 R.