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For similarly-named engines with two pistons per cylinder, see opposed-piston engine
Animation of a boxer engine Benz Contramotor, the first commercial flat-engine design, ca.
A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, whereby each cylinder has two pistons sharing a central combustion chamber.
The most common configuration of flat engines is the boxer engine configuration, in which the pistons of each opposed pair of cylinders move inwards and outwards at the same time. The other configuration is effectively a V engine with a 180-degree angle between the cylinder banks: in this configuration each pair of cylinders shares a single crankpin, so that as one piston moves inward, the other moves outward.
The first flat engine (Benz Contramotor) was built in by Karl Benz. Flat engines have been used in aviation, motorcycle and automobile applications. They are now less common in cars than straight engines (for engines with fewer than six cylinders) and V engines (for engines with six or more cylinders). Flat engines are more common in aircraft, where straight engines are a rarity and V engines have almost vanished except in historical aircraft. They have even replaced radial engines in many smaller installations.
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Difference between two flat 6 cylinder engines: 180° V on the left, boxer on the rightThe advantages of flat engines are a short length, low centre of mass and suitability for air cooling (due to the well-exposed, large-surface-area cylinders and cylinder heads, and their short length).
Compared with the more common straight engines, flat engines have better primary balance (resulting in less vibration);[1] however, the disadvantages are increased width and the need to have two cylinder heads. Compared with V engines &#; the most common layout for engines with six cylinders or more &#; flat engines again have a lower centre of mass, and, for six-cylinders, better primary balance; the disadvantage is again their being wider.[2]
The most common usages of flat engines are:
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BMW R68 flat-twin boxer engineMost flat engines use a "boxer" configuration, where each pair of opposing pistons move inwards and outwards at the same time, somewhat like boxing competitors punching their gloves together before a fight.[3] Boxer engines have low vibration, being they are the only common configuration that has no unbalanced forces, regardless of the number of pairs of cylinders. Boxer engines therefore do not require either a balance shaft[4] or counterweights on the crankshaft to balance the weight of the reciprocating parts. However, a rocking couple is present, since each cylinder is slightly offset from the other member of its pair due to the distance between the crankpins along the crankshaft.[3]
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An alternative configuration for flat engines is as a 180-degree V engine, which has been used on most twelve-cylinder flat engines. In this configuration, each pair of pistons shares a crankpin, this being simpler than the boxer configuration, where each piston has its own separate crankpin.
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Twin-boxer of Johann Puch, Patent AT () World War II-era Riedel starter motorIn , the Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine. Amongst the first commercially-produced aircraft to use a flat engine was the Santos-Dumont Demoiselle range of aeroplanes, which was powered by boxer-twin engines.[citation needed]
Several boxer-four engines have been produced specifically for light aircraft. A number of manufacturers produced boxer-six aircraft engines during the s and s.[citation needed]
During World War II, a boxer-twin engine called the "Riedel starter" was used as a starter motor/mechanical APU for the early German jet engines, such as the Junkers Jumo 004 and BMW 003. Designed by Norbert Riedel, these engines have a very oversquare stroke ratio of 2:1 so that they could fit within the intake diverter, directly forward of the turbine compressor.[citation needed]
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Flat engines offer several advantages for motorcycles including a low centre of mass, low vibration, suitability for shaft drive, and equal cooling of the cylinders (for air-cooled engines).[5][6] The most common design of flat engine for motorcycles is the boxer-twin, beginning with the Fée flat-twin engine, manufactured by the Light Motors Company, which was the first production motorcycle engine.[7] BMW Motorrad have a long history of boxer-twin motorcycles, beginning in with the BMW R32[5]
Several motorcycles have been produced with flat-four engines, such as the &#; Zündapp K800 and the &#; Honda Gold Wing. In , the Honda Gold Wing engine was upsized to a flat-six design.[8]
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When used in cars, advantages of flat engines are a low centre of mass (which improves the handling of the car),[4] short length, low vibration and suitability for air cooling (due to the well exposed, large surface area, cylinder heads and short length). However the larger width of flat engines (compared with the more common inline and V layouts) is a drawback, particularly when the engine is located between the steered wheels.[citation needed]
Flat engines were used by various automobile manufacturers &#; mostly with a boxer-four design &#; up until the late s. Since then, only Porsche and Subaru have remained as significant manufacturers of flat engines.[citation needed]
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Due to the short length of flat engines, locating a flat engine outside of the car's wheelbase results in minimal overhang.[10] Therefore, many cars with flat engines have used a rear-engine, rear-wheel-drive layout. Examples include the flat-twin BMW 600 (&#;) and BMW 700 (&#;); the flat-four Tatra 97 (&#;), Volkswagen Beetle (&#;) and Porsche 356 (&#;); and the flat-six Chevrolet Corvair (&#;), Porsche 911 (-present), and Tucker 48 (&#;).
The opposite layout, front-engine front-wheel drive, was also common for cars with flat engines. Examples include the Citroën 2CV (&#;), Panhard Dyna X (&#;), Lancia Flavia (&#;), Citroën GS (&#;), Alfa Romeo Alfasud (&#;) and Subaru Leone (&#;).
Subaru have been producing cars with a front-engine, four-wheel-drive layout powered by flat engines (mostly boxer-four engines) since . Examples include the Subaru Leone (&#;), Subaru Legacy (-present) and Subaru Impreza (&#;present). The front half-shafts come out of a front differential that is part of the gearbox. A rear driveshaft connects the gearbox to the rear half-shafts.
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The traditional front-engine, rear-wheel-drive layout is relatively uncommon for cars with flat engines, however some examples include the Toyota 86 / Subaru BRZ (&#;present), Jowett Javelin (&#;), Glas Isar (&#;) and the Tatra 11 (&#;).
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The first flat engine was produced in by German engineer Karl Benz.[5][11] Called the kontra engine, it was a boxer-twin design. Early uses of flat engines in cars include the Lanchester 8 hp Phaeton boxer-twin, the Wilson-Pilcher boxer-four,[12] the Wilson-Pilcher 18/24 HP boxer-six and the Ford Model A, the Ford Model C and the Ford Model F.[13]
In , the Volkswagen Beetle (then called the "KdF-Wagen") was released with a rear-mounted flat-four engine. This Volkswagen air-cooled engine was produced for many years and also used in the Volkswagen Type 2 (Transporter, Kombi or Microbus), the Volkswagen Karmann Ghia sports car and the Volkswagen Type 3 compact car. A water-cooled version, known as the Wasserboxer, was introduced in and eventually replaced the air-cooled versions.
The majority of sports cars throughout Porsche's history are powered by flat engines, beginning with its first car; the - Porsche 356 used an air-cooled boxer-four engine. Also using boxer-four engines were the - Porsche 914, the - Porsche 912 and the -present Porsche Boxster/Cayman (982). The Porsche 911 has exclusively used boxer-six engines from its introduction in until the present. In , the Porsche 911 switched from being air-cooled to water-cooled.
Porsche flat-eight engines were used in various racing cars throughout the s, such as the Porsche 804 Formula One car and the - Porsche 908 sports car. A flat-twelve engine was also produced by Porsche for the - Porsche 917 sports car.
Chevrolet used a horizontally opposed air-cooled 6 cylinder engine in its Corvair line during its entire production run from to in various applications and power ratings, including one of the first uses of a turbocharger in a mass-produced automobile.
The Subaru EA engine was introduced in and began Subaru's line of boxer-four engines that remain in production to this day.[14] Most of Subaru's models are powered by a boxer-four engine in either naturally aspirated or turbocharged form. A print ad for the Subaru GL coupe referred to the engine as "quadrozontal".[15] The company also produced boxer-six engines from to and &#;.[16] In , the Subaru EE engine became the world's first passenger car diesel boxer engine. This engine is a turbocharged boxer-four with common rail fuel injection.[4][17][18][19]
Ferrari used flat-twelve engines for various Formula One cars in the s. A road car flat-twelve engine (using a 180-degree V12 configuration) was used for the - Ferrari Berlinetta Boxer, - Ferrari Testarossa and their derivatives.[20]
Toyota uses the designation Toyota 4U-GSE for the boxer-four engine in the Toyota-badged versions of the Toyota 86 / Subaru BRZ twins, although the engine is actually designed and built by Subaru as the Subaru FA20 engine.[3]
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Just like two boxing athletes competing in a match, the boxer engine works similarly. The horizontally positioned pistons inside the engine create a better balance with their side-to-side motion as compared to V-shaped engines. Thus, this engine does not need counterweights for balance and creates less vibration with a fluid motion.
It leads to decreased wear and tear, not to forget the transmission positioned directly behind the engine and provides support to its unique symmetry. Many car manufacturers utilize boxer engine also known as horizontally-opposed engine to provide their vehicles with added acceleration, speed, and complete balance.
As we all know, a boxer engine is one of the most common types of flat engine. It is also known as an opposed engine. A boxer engine is an internal combustion engine. To be more specific, it has opposing cylinders on each side of a central rotating crankshaft.
With the cylinders setting like this, we can expect the opposing pistons to move outward and inward at the same time. To make it easier to understand, it is just like a boxer cycling his arm between left and right punches.
Not everyone is a fan of history, we get that. However, having a bit of knowledge about this amazing car component is quite useful. The Boxer Engine was invented by Karl Benz in , and Mercedes-Benz surely claims the credit for this.
After 2 years, the &#;contra/kontra&#; engine, also known as the two-cylinder flat engine, was developed and debuted. This was a huge invention at the time. The design was applied to almost every single vehicle: Race cars, normal cars, even commercial automobiles.
The best of the best engines have their share of advantages and disadvantages. There are certain advantages of a boxer engine that make it stand out from other car engines.
Owing to its pistons working together to create the perfect balance, there will not be another smoother engine system inside a car than this. Of course, when it comes to automobile performance, car owners want it to be as smooth as possible. This means there would not be any issues related to vibration from the engine, along with adding to the boxer engine reliability in the longer run. In order to do that, this comes down to balancing the weight of the car as well as the engine.
For this reason, a boxer engine helps spread out and balance the weight much more effectively than a normal engine due to its wide and flat design. Last but not least, car drivers can improve their handling precision with a boxer engine.
The perfect balance combined with the size of the boxer engine leads to less load on the crankshaft. Thus, it provides a significant boost in power to the rotational inertia of the car, which offers extreme power without any issues.
Since the movement of the engine will balance each other out, the boxer engine also vibrates much less than other types of engine. The design of the boxer engine helps maintain low weight. Along with that, drivers don&#;t need to install parts to reduce vibration.
The horizontally-opposed engine, owing to its unique design gathers a low center of gravity in the car. It offers the driver better handling of the vehicle allowing sports car lovers to race on the track without much understeer.
One of the most important benefits of a boxer engine is that it has a low center of gravity. There are many car owners who want their automobiles to be as low to the ground as possible, and this boxer engine is definitely their cup of tea. It raises stability as well as improves agility. Not to mention, car owners can also increase lateral quickness with this engine.
Last but certainly not least, the boxer engines are designed to sheer off due to the fact that it is flat and can be positioned really low.
The boxer engine is different regarding performance, and structure as compared to other types of car engines. However, at times some boxer engine disadvantages that a car owner might face include:
On one hand, the boxer engines provide an unmatched performance to a sports car. However, the wide configuration makes it a bit hard to work on these mechanically. Besides, the obstruction of airflow they create in the engine area might even lead to their failure at high speeds. The car owner might need an expert with relevant industry knowledge about car engines.
The boxer engines are one complex example of automobile engineering, as the two-cylinder heads and valves require much maintenance. The owner of the vehicle with this kind of engine needs to take care of the engine to keep it running smoothly. The slightest neglect in the upkeep of boxer engines can lead to a considerable drop in their performance. It is one of the boxer engine problems, which is resolved by taking care of the engine on time.
The offset position of the engine can lead to some rocking with the connection to the connection rod or crankshaft. However, it all depends on how well is the horizontally opposed engine maintained by the car owner.
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Watch more to know how the engine boxer works:
Thus, a boxer engine might help the sports car enthusiast win the race. However, the performance of the engine will depend purely on how well-maintained it is. Those looking to experience both power and performance in their cars should have a boxer engine installed in it.
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