V6 engine

A V6 engine is a V engine with six cylinders mounted on the crankshaft in two banks of three cylinders, usually set at either a 60 or 90 degree angle to each other. The V6 is one of the most compact engine configurations, usually ranging from 2.0 L to 4.3 L displacement (however, much larger examples have been produced for use in trucks), shorter than the inline 4 and more compact than the V8 engine. Because of its short length, the V6 fits well in the widely used transverse engine front-wheel drive layout. A V6, 24-valve, DOHC engine Applications The V6 is commercially successful in mid-size cars in the modern age because it is less expensive to build and is smoother in large sizes than the inline 4, which develops increasingly serious vibration problems in larger engines. The wider 90° V6 will fit in an engine compartment designed for a V8, providing a low-cost alternative to the V8 in an expensive car, while the narrower 60° V6 will fit in most engine compartments designed for an I4, proving a more powerful and smoother alternative engine to the four. Buyers of luxury and/or performance cars might prefer an inline 6, which has better smoothness or a flat 6 which has a lower centre of gravity. Recent forced induction V6 engines have delivered horsepower and torque output comparable to contemporary larger displacement, naturally aspirated V8 engines, while reducing fuel consumption and emissions, such as the Volkswagen Group's 3.0 TFSI which is supercharged and directly injected, and Ford Motor Company's turbocharged and directly injected EcoBoost V6, both of which have been compared to Volkswagen's 4.2 V8 engine. Modern V6 engines commonly range in displacement from 2.0 to 4.3 L (120 to 260 cu in), though larger and smaller examples have been produced, such as the 1991 Mazda MX3,and the Rover KV6 engine. In Europe, where petrol is much more expensive than in the USA, V6 diesels have proved a more popular option. The American-designed Chrysler 300C has a 3-litre Mercedes V6 engine, which vastly outsells the petrol-engined car. History Some of the first V6-powered automobiles were built in 1905 by Marmon. This firm became something of a V-engine specialist; beginning with V2 engines, then V4s, V6s, V8s, and, in the 1930s, a V16 engine. Marmon was one of the few automakers of the world to offer a V16-powered automobile. From 1908 to 1913 the Deutz Gasmotoren Fabrik produced gasoline-electric train sets (Hybrid) which used a V6 as generator engine. In 1918 Leo Goosen designed a V6-powered car for Buick Chief Engineer Walter L. Marr. Only one prototype Buick V6 car was built in 1918; it was long used by the Marr family. Lancia V6 The first series-production V6 was introduced by Lancia in 1950 with the Lancia Aurelia model. Lancia sought a smoother...

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Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part. Computer animation of a camshaft operating valves History The camshaft was first described in Turkey (Diyarbakır) by Al-Jazari in 1206. He employed it as part of his automata, water-raising machines, and water clocks such as the castle clock. The camshaft later appeared in European mechanisms from the 14th century. Among the first cars to utilize engines with single overhead camshafts were the Maudslay designed by Alexander Craig and introduced in 1902 and the Marr Auto Car designed by Michigan native Walter Lorenzo Marr in 1903. Uses In internal combustion engines with pistons, the camshaft is used to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes protruding from it, one for each valve. The cam lobes force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate. Automotive Materials Camshafts can be made out of several types of material. These include: Chilled iron castings: Commonly used in high volume production, chilled iron camshafts have good wear resistance since the chilling process hardens them. Other elements are added to the iron before casting to make the material more suitable for its application. Billet Steel: When a high quality camshaft or low volume production is required, engine builders and camshaft manufacturers choose steel billet. This is a much more time consuming process, and is generally more expensive than other methods. However, the finished product is far superior. CNC lathes, CNC milling machines, and CNC camshaft grinders will be used during production. Different types of steel bar can be used, one example being EN40b. When manufacturing a camshaft from EN40b, the camshaft will also be heat treated via gas nitriding, which changes the micro-structure of the material. It gives a surface hardness of 55-60 HRC. These types of camshafts can be used in high-performance engines. Timing A steel billet racing camshaft with noticeably broad lobes (very long duration) The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of the air/fuel mixture intake and exhaust gases, they must be opened and closed at the appropriate time during the stroke of the piston. For this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain. Direct drive using gears is unusual because of the cost. The frequently reversing torque caused by the slope of the cams tends to cause gear rattle which for an all-metal gear train requires further expense...

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Variable valve timing

In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems. Two-stroke engines use a power valve system to get similar results to VVT. Cylinder head of Honda K20Z3. This engine uses continuously variable timing for the inlet valves Background theory The valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the combustion chamber. The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing can be the same for all engine speeds and conditions, therefore compromises are necessary. An engine equipped with a variable valve timing actuation system is freed from this constraint, allowing performance to be improved over the engine operating range. Piston engines normally use valves which are driven by camshafts. The cams open (lift) the valves for a certain amount of time (duration) during each intake and exhaust cycle. The timing of the valve opening and closing, relative to the position of the crankshaft, is important. The camshaft is driven by the crankshaft through timing belts, gears or chains. An engine requires large amounts of air when operating at high speeds. However, the intake valves may close before enough air has entered each combustion chamber, reducing performance. On the other hand, if the camshaft keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. Opening the intake valve while the exhaust valve is still open may cause unburnt fuel to exit the engine, leading to lower engine performance and increased emissions. Continuous versus discrete Early variable valve timing systems used discrete (stepped) adjustment. For example, one timing would be used below 3500 rpm and another used above 3500 rpm. More advanced "continuous variable valve timing" systems offer continuous (infinite) adjustment of the valve timing. Therefore, the timing can be optimized to suit all engine speeds and conditions. Cam phasing versus variable duration The simplest form of VVT is cam-phasing, whereby the phase angle of the camshaft is rotated forwards or backwards relative to the crankshaft. Thus the valves open and close earlier or later; however, the camshaft lift and duration cannot be altered...

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Timing belt (camshaft)

A timing belt, timing chain or cambelt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes. In an interference engine the timing belt or chain is also critical to preventing the piston from striking the valves. A timing belt is usually a toothed belt -- a drive belt with teeth on the inside surface. A timing chain is a roller chain. Most modern production automobile engines use a timing belt or chain to synchronize crankshaft and camshaft rotation; some engines instead use gears to directly drive the camshafts. The use of a timing belt or chain instead of direct gear drive enables engine designers to place the camshaft(s) further from the crankshaft, and in engines with multiple camshafts a timing belt or chain also enables the camshafts to be placed further from each other. Timing chains were common on production automobiles through the 1970s and 1980s, when timing belts became the norm, but timing chains have seen a resurgence in recent years. Timing chains are generally more durable than timing belts – though neither is as durable as direct gear drive – however, timing belts are lighter, less expensive, and operate more quietly. Timing belt Timing covers, lower pulley, accessory belts removed, exposing timing belt on a Nissan RB30E Engine Engine applications Replacing a timing belt on a car In the internal combustion engine application the timing belt or chain connects the crankshaft to the camshaft(s), which in turn control the opening and closing of the engine's valves. A four-stroke engine requires that the valves open and close once every other revolution of the crankshaft. The timing belt does this. It has teeth to turn the camshaft(s) synchronised with the crankshaft, and is specifically designed for a particular engine. In some engine designs the timing belt may also be used to drive other engine components such as the water pump and oil pump. Types Gear or chain systems are also used to connect the crankshaft to the camshaft at the correct timing. However, gears and shafts constrain the relative location of the crankshaft and camshafts. Even where the crankshaft and camshaft(s) are very close together, as in pushrod engines, most engine designers use a short chain drive rather than a direct gear drive. This is because gear drives suffer from frequent torque reversal as the cam profiles "kick back" against the drive from the crank, leading to excessive noise and wear. Fibre or nylon covered gears, with more resilience, are often used instead of steel gears where direct drive is...

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Overhead camshaft

Overhead camshaft, commonly abbreviated to OHC, is a valvetrain configuration which places the camshaft of an internal combustion engine of the reciprocating type within the cylinder heads ("above" the pistons and combustion chambers) and drives the valvesor lifters in a more direct manner compared with overhead valves (OHV) and pushrods. A cylinder head sectioned to expose its valvetrain shows the cam-shaped lobes of two overhead camshafts, one above each of the two tappets located atop hollow-sectioned valves Overview Compared with OHV pushrod systems with the same number of valves, the reciprocating components of the OHC system are fewer and have a lower overall mass. Though the system that drives the camshafts may be more complex, most engine manufacturers accept that added complexity as a trade-off for better engine performance and greater design flexibility. The fundamental reason for the OHC valvetrain is that it offers an increase in the engine's ability to exchange induction and exhaust gases. (This exchange is sometimes known as "engine breathing". ) Another performance advantage is gained as a result of the better optimised port configurations made possible with overhead camshaft designs. With no intrusive pushrods, the overhead camshaft cylinder head design can use straighter ports of more advantageous cross-section and length. The OHC design allows for higher engine speeds than comparable cam-in-block designs, as a result of having lower valvetrain mass. The higher engine speeds thus allowed increases power output for a given torque output. Disadvantages of the OHC design include the complexity of the camshaft drive, the need to re-time the drive system each time the cylinder head is removed, and the accessibility of tappet adjustment if necessary. In earlier OHC systems, including inter-war Morrises and Wolseleys, oil leaks in the lubrication systems were also an issue. Single overhead camshaft A Honda D16A3 series single overhead camshaft cylinder head from a 1987 Honda CRX Si. Single overhead camshaft (SOHC) is a design in which one camshaft is placed within the cylinder head. In an inline engine, this means there is one camshaft in the head, whilst in an engine with more than one cylinder head, such as a V engine or a horizontally-opposed engine (boxer; flat engine) – there are two camshafts, one per cylinder bank. In the SOHC design, the camshaft operates the valves directly, traditionally via a bucket tappet; or via an intermediary rocker arm. SOHC cylinder heads are generally less expensive to manufacture than double overhead camshaft (DOHC) cylinder heads. Timing belt replacement can be easier since there are fewer camshaft drive sprockets that need to be aligned during the replacement procedure. SOHC designs offer reduced complexity compared with overhead valve designs when used for multivalve cylinder heads, in which each cylinder has more than two valves. An example of an SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp (four cylinder, eight valve), a small,...

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Six-stroke engine

The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-strokeengines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes. In the single-piston designs, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to drive an additional power and exhaust stroke of the piston in the same cylinder in an attempt to improve fuel-efficiency and/or assist with engine cooling. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. These designs use either steam or air as the working fluid for the additional power stroke. The designs in which the six strokes are determined by the interactions between two pistons are more diverse. The pistons may be opposed in a single cylinder or may reside in separate cylinders. Usually one cylinder makes two strokes while the other makes four strokes giving six piston movements per cycle. The second piston may be used to replace the valve mechanism of a conventional engine, which may reduce mechanical complexity and enable an increased compression ratio by eliminating hotspots that would otherwise limit compression. The second piston may also be used to increase the expansion ratio, decoupling it from the compression ratio. Increasing the expansion ratio in this way can increase thermodynamic efficiency in a similar manner to the Miller or Atkinson cycle. Engine types Single-piston designs These designs use a single piston per cylinder, like a conventional two- or four-stroke engine. A secondary, non-detonating fluid is injected into the chamber, and the leftover heat from combustion causes it to expand for a second power stroke followed by a second exhaust stroke. Griffin six-stroke engine The Kerr engine at the Anson Engine Museum In 1883, the Bath-based engineer Samuel Griffin was an established maker of steam and gas engines. He wished to produce an internal combustion engine, but without paying the licensing costs of the Otto patents. His solution was to develop a "patent slide valve" and a single-acting six-stroke engine using it. By 1886, Scottish steam locomotive maker Dick, Kerr & Co. saw a future in large oil engines and licensed the Griffin patents. These were double-acting, tandem engines and sold under the name "Kilmarnock". A major market for the Griffin engine was in electricity generation, where they developed a reputation for happily running light for long periods, then suddenly being able to take...

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Split-single

The split-single (Doppelkolbenmotor to its German and Austrian manufacturers), is a variant on the two-stroke engine with two cylinders sharing a single combustion chamber. 'Valveless' engine of 1919, showing the operating cycle Post WWII arrangement, carburettor to the front under the exhaust (neither visible). Transfer port visible at back. One connecting rod 'piggy-backed' on another. Principle of operation Animation The split-single system sends the intake fuel-air mixture up one bore to the combustion chamber, sweeping the exhaust gases down the other bore and out of the exposed exhaust port. The rationale of the split-single two-stroke is that, compared to a standard two-stroke single, it can give better exhaust scavenging while minimising the loss of unburnt fresh fuel/air charge through the exhaust port. As a consequence, a split-single engine can deliver better economy, and may run better at small throttle openings. A disadvantage of the split-single is that, for only a marginal improvement over a standard two-stroke single, the "Twingle" has a heavier and costlier engine. Since a manufacturer could produce a standard twin-cylinder two-stroke at an equivalent cost to a Twingle, it was perhaps inevitable that the latter should become extinct. There have been "single" (i.e. twin-bore) and "twin" (i.e. four-bore) models. Unusually for a motorcycle engine, some Twingles have the carburettor mounted on the front of the engine, beneath the exhaust. History In the 60-year history of this arrangement there were two important variants, earlier versions have a single, Y-shaped or V-shaped connecting rod and these look much like a regular single-cylinder two-stroke engine with a single exhaust, a single carburettor in the usual place behind the cylinders and a single sparkplug. Racing versions of this design can be mistaken for a regular twin-cylinder, since they had two exhausts or two carburettors but these are actually connected to a single bore in an engine with a single combustion chamber. Some models, including those in mass-production, used two spark-plugs igniting one combustion chamber. After World War II, more sophisticated internal mechanisms improved mechanical reliability and led to the carburetor being placed in front of the barrel, tucked under and to the side of the exhaust. This is the arrangement which was used on the Puch 250 SGS and sold in the United States by Sears from the 1950s through the early 1970s under their own Allstate brand, with the engine being referred to in Sears literature as the Twingle. Lucas (invented 1905) The first split-single engine was the Lucas, built in the UK in 1905. It used 2 separate crankshafts connected by gears to drive 2 separate pistons, so that the engine had perfect primary balance. Garelli (invented 1912) In 1912 Italian engineer Adalberto Garelli...

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