Valvetrain

Valvetrain

A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.

Valvetrain is an all-encompassing term used to describe the mechanisms and parts which control the operation of the valves.

Layout

Valvetrain: The valvetrain consists of valves, rocker arms, pushrods, lifters, and the cam shaft. Valvetrain opening/closing & duration controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close/duration is controlled by the camshaft which is synchronized to the crankshaft by a chain or belt.

Valvetrains are built in several configurations, each of which varies slightly in layout but still performs the task of opening and closes the valves at the time necessary for proper operation of the engine. These layouts are differentiated by the location of the camshaft within the engine:

; Overhead camshaft: The camshaft (or camshafts, depending on the design employed) is located above the valves within the cylinder head, and operates either indirectly or directly on the valves.

; Cam-in-block: The camshaft is located within the engine block, and operates directly on the valves, or indirectly via pushrods and rocker arms. Because they often require pushrods they are often called "pushrod" engines.

; Camless: This layout uses no camshafts at all. Technologies such as solenoids are used to individually actuate the valves.

Parts

As stated above, the valvetrain is the mechanical system responsible for operation of the valves. Valves are usually of the poppet type, although many others have been developed such as sleeve, slide and rotary valves.

Poppet valves typically require small coil springs, appropriately named valve springs, to keep them closed when not actuated by the camshaft. They are attached to the valve stem ends, seating within spring retainers. Other mechanisms can be used in place of valve springs to keep the valves closed: Formula 1 engines employ pneumatic cylinder heads in which pneumatic pressure closes the valves, while motorcycle manufacturer Ducati uses desmodromic mechanisms to manually close the valves.

Depending on the design used, the valves are actuated directly by a rocker arm, finger or bucket tappet. Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact, while cam-in-block engines use rocker arms. Rocker arms are actuated by a pushrod, and pivot on a shaft or individual ball studs in order to actuate the valves.

Pushrods are long, slender metal rods seated within the engine block. At the bottom ends the pushrods are fitted with lifters, either solid or hydraulic, upon which the camshaft, located within the cylinder block, makes contact. The camshaft pushes on the lifter, which pushes on the pushrod, which pushes on the rocker arm, which rotates and pushes down on the valve.

Camshafts must actuate the valves at the appropriate time in the combustion cycle. In order to accomplish this the camshaft is linked to and kept in synchronisation with the crankshaft (the main shaft upon which the pistons act) through the use of a metal chain, rubber belt or geartrain. Because these mechanisms are essential to the proper timing of valve actuation they are named timing chains, timing belts and timing gears, respectively.

ee also

* Cam-in-block
* Overhead camshaft
* Camless

External links

* [http://www.samarins.com/glossary/dohc.html Animation (OHV, OHC and DOHC)]


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • valvetrain — noun The collective mechanisms and parts that control the operation of the valves in an internal combustion engine …   Wiktionary

  • valvetrain — [1] The various parts making up the valve and its operating mechanism which causes the valves to open and close. [2] The system of valves that lets the fuel charges in and let the exhaust gases out …   Dictionary of automotive terms

  • Honda D engine — D16Y4 Engine D16Z6 Engine Lightly Customized …   Wikipedia

  • Subaru EA engine — Infobox Automobile engine name = Subaru EA 81 aka = manufacturer = Fuji Heavy Industries type = Flat 4 bore = 3.622 in (92 mm) stroke = 2.638 in (67 mm) displacement = 108.7 in³ (1781 cm³) length = diameter = width = height = weight = 171 lb (78… …   Wikipedia

  • Honda J engine — Infobox Automobile engine name=Honda J engine manufacturer=Honda Motor Manufacturing production=1996 ndash; class=SOHC 60° V6 predecessor=Honda C engine similar=Chrysler SOHC V6 Ford Cyclone GM HFV6 Nissan VQ Toyota GRThe J series was Honda s… …   Wikipedia

  • Overhead camshaft — A cylinder head sliced in Fifths shows two overhead camshafts one above each of the two valves. Overhead cam (OHC) valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves… …   Wikipedia

  • Overhead valve — OHV redirects here. OHV may also refer to Off highway vehicle. Components of a pushrod valve actuation system …   Wikipedia

  • Volkswagen air cooled engine — Infobox Automobile engine name = E motor aka = manufacturer = Volkswagen type = Flat 4 bore = 75 mm stroke = 64 mm displacement = Auto cc|1131 length = diameter = width = height = weight = block = head = Aluminum valvetrain = OHV supercharger =… …   Wikipedia

  • Mazda FE-DOHC engine — Mazda FE DOHC Manufacturer Mazda Also called FE DE, FE ZE and FE3 Production Hiroshima, Japan Hofu, Japan Predecessor Mazda FE Successor Mazda FS, Mazda L e …   Wikipedia

  • Toyota Type A engine — The Type A engine was a straight 6 engine produced from 1935 through 1947 by Toyota.The Type B was a technically more advanced version of Type A.The Type C was a straight 4 engine derived from the Type A.Many parts were interchangeable between… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”