A cylinder head sliced in half shows two overhead camshafts—one above each of the two valves. In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the A poppet valve is a Valve consisting of a hole usually round or oval and a tapered plug usually a disk shape on the end of a shaft also called a valve stem

Overhead camshaft, commonly abbreviated to OHC, valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters in a more direct manner compared to Overhead valves (OHV) and pushrods. A traditional reciprocating Internal combustion engine uses valves to control air and fuel flow into and out of the cylinders facilitating combustion The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the A combustion chamber is the part of an Engine in which Fuel is burned A poppet valve is a Valve consisting of a hole usually round or oval and a tapered plug usually a disk shape on the end of a shaft also called a valve stem An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft

Compared to OHV pushrod (or I-Head) systems with the same number of valves the reciprocating components of the OHC system are fewer and have a lower total mass. Though the system that drives the cams may become more complex, most engine manufacturers easily accept the added complexity in trade for better engine performance and greater design flexibility. Another performance advantage is gained as a result of the better optimized 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 crossection and length.

The OHC system can be driven using the same methods as an OHV system, which include using a rubber/kevlar toothed timing belt, chain, or in less common cases, gears. A timing belt, timing chain or cam belt is a part of an Internal combustion engine that controls the timing of the engine's valves. Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on Bicycles Motorcycles This is the page for mechanical Gears For other uses see Gear (disambiguation For the gear-like device used to drive a roller chain see Sprocket

Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. Variable valve timing, or VVT, is a generic term for an Automobile Piston engine technology In Automotive engineering, an engine is referred to as multi-valve (or multivalve) when each cylinder has more than two valves. OHC also inherently allows for greater engine speeds over comparable cam-in-block designs.

There are two overhead camshaft layouts:

• Single overhead camshaft - or SOHC
• Double overhead camshaft - or DOHC

Single overhead camshaft

A single overhead camshaft cylinder head from a 1987 Honda CRX Si. Year 1987 ( MCMLXXXVII) was a Common year starting on Thursday (link displays 1987 Gregorian calendar) () is a Multinational corporation, engine Manufacturer and engineering corporation headquartered in Japan. This article is about the first and second generation CR-Xs for the third generation version see Honda Civic del Sol.

Single overhead camshaft (SOHC) is a design in which one camshaft is placed within the cylinder head. In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the In an inline engine this means there is one camshaft in the head, while in a V engine or a horizontally-opposed engine (boxer; Flat engine) there are two camshafts: one per cylinder bank. A V engine is a common configuration for an Internal combustion engine. A flat engine is an Internal combustion engine with pistons that are all relatively horizontal

The SOHC design has less reciprocating mass than a comparable pushrod design. An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft This can allow for higher engine speeds, which in turn will increase power output for a given torque. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about The cam operates the valves directly or through a rocker arm, as opposed to overhead valve pushrod engines which have tappets, long pushrods, and rocker arms to transfer the movement of the lobes on the camshaft in the engine block to the valves in the cylinder head. Generally referred to within the Internal combustion engine of automotive marine motorcycle and reciprocating aviation engines the rocker arm is a reciprocating lever An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the

SOHC designs offer reduced complexity compared to pushrod designs when used for multi-valve heads in which each cylinder has more than two valves. An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft An example of a SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp (4 cylinder, 8 valve), a small early 1960s 2-door saloon car with a rear mounted alloy engine based on the Coventry Climax FWMA race engines. The Hillman Imp is a compact rear-engined saloon car that was manufactured under the Hillman Marque by the Rootes Group (later Chrysler The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 Coventry Climax was a British forklift truck, fire pump and speciality Engine manufacturer Exhaust and inlet manifolds were both on the same side of the engine block (thus not a crossflow cylinder head design). A crossflow cylinder head is a Cylinder head that features the intake and exhaust ports on opposite sides This did, however, offer excellent access to the spark plugs.

In the early 1980s Toyota and Volkswagen also used a directly actuated, SOHC parallel valve configuration with two valves for each cylinder. The 1980s was the decade spanning from January 1 1980 to December 31 1989. (pronounced) is a Multinational corporation headquartered in Japan, and is currently the world's largest Automaker. The Toyota system used hydraulic tappets while the Volkswagen system used bucket tappets with shims for valve lash adjustment. A tappet in Mechanical engineering is a projection which imparts a linear motion to some other component within an assembly A tappet in Mechanical engineering is a projection which imparts a linear motion to some other component within an assembly Of all valvetrain systems this is the least complex configuration possible.

Double overhead camshaft

Overhead view of Suzuki GS550 head showing dual camshafts and drive sprockets. From 1976 to 1987, Suzuki produced its GS line of Motorcycles These motorcycles had air-cooled in-line DOHC engines with two or four cylinders

A double overhead camshaft (also called DOHC, dual overhead cam, or twin cam (TC)) valve train layout is characterized by two camshafts being located within the cylinder head, one for inlet and one for exhaust valves. Typical automotive engines equipped with dual overhead camshafts can have from two to four camshafts in total, depending on the engine configuration. The term Twin Cam doesn't tell the exact location of camshafts, but it is mostly used to describe DOHC structure.

Double overhead camshafts are not required in order to have multiple inlet or exhaust valves, but are necessary for more than two valves that are directly actuated (though still usually via tappets). Not all DOHC engines are multivalve engines — DOHC was common in two valve per cylinder heads for decades before multivalve heads appeared. Today, however, DOHC is synonymous with multi-valve heads since almost all DOHC engines have between three and five valves per cylinder.

History

DOHC straight-8 in a 1933 Bugatti Type 59 Grand Prix racer

Among the early pioneers of DOHC were Isotta Fraschini's Giustino Cattaneo, Austro-Daimler's Ferdinand Porsche Stephen Tomczak (in the Prinz Heinrich), and W. O. Bentley (in 1919); Sunbeam built small numbers between 1921 and 1923. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the The term straight-8 is a colloquialism for an inline eight cylinder engine The Type 51 series succeeded the famous Type 35 as Bugatti 's premier racing car for the 1930s Grand Prix motor racing has its roots in organised automobile racing that began in France as far back as 1894 Isotta Fraschini represents two Italian manufacturing companies which produce respectively marine engines and luxury goods Austro-Daimler was an Austrian Automaker company from 1899 until 1934 Prof Dr Ing hc Ferdinand Porsche ( Walter Owen Bentley ( 16 September 1888 – 2 August 1971) often known as W Sunbeam was a Marque registered by John Marston Co Ltd of Wolverhampton, England, in 1888 ^[1] The first DOHC engines were two- or four-valve per cylinder designs from companies like Fiat (1912), Peugeot Grand Prix (1913, 4 valve), Alfa Romeo GP (1914, 4 valve) and 6C (1925), Maserati Tipo 26 (1926), Bugatti Type 51 (1931), and Audi. Fiat SpA (an Acronym for Fabbrica Italiana Automobili Torino (Italian Automobile Factory of Turin) is an Italian automobile manufacturer For the article about the bicycle manufacturer see Cycles Peugeot. Alfa Romeo Automobiles SpA is an Italian Automaker founded in 1910 ALFA 40/60 GP or GP was a fully working early racing car prototype made by the company now called Alfa Romeo. The Alfa Romeo 6C name was used on road race and sports cars made between 1925–1954 by Alfa Romeo Maserati is an Italian manufacturer of racing cars and Sports cars established on December 1, 1914, in Bologna. Bugatti was founded in Molsheim, France, as a manufacturer of high performance automobiles by Ettore Bugatti, an Italian The Type 51 series succeeded the famous Type 35 as Bugatti 's premier racing car for the 1930s AUDI AG, ( Xetra: NSU commonly known as Audi (aˈʊdi is a German Automobile manufacturer which produces Audi branded cars with headquarters Most Ferraris used two-valve DOHC engines as well. Ferrari SpA is an Italian Sports car manufacturer based in Maranello, Italy

When DOHC technology was introduced in mainstream vehicles, it was common for it to be heavily advertised. While used at first in limited production and sports cars, FIAT is credited as the first car company to use a belt-driven DOHC engine across their complete product line, in the mid-1960s. Fiat SpA (an Acronym for Fabbrica Italiana Automobili Torino (Italian Automobile Factory of Turin) is an Italian automobile manufacturer

See also

• Valvetrain
• Overhead valve
• Cam-in-block
• Camless

References

1. ^ Georgano, G. A traditional reciprocating Internal combustion engine uses valves to control air and fuel flow into and out of the cylinders facilitating combustion An overhead valve (OHV engine, also called pushrod engine or I-head engine is a type of Piston engine that places the Camshaft The cam-in-block Valvetrain layout of Piston engines is one where the Camshaft is placed within the Cylinder block, usually beside and slightly Most Piston engines today employ a Camshaft to operate Poppet valves This consists of a cylindrical rod running the length of the Cylinder bank with a number N. Cars: Early and Vintage, 1886-1930. (London: Grange-Universal, 1985).

External links

• OHV, SOHC, DOHC engine animated diagrams