The camshaft is an apparatus often used in piston engines to operate poppet valves. A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert 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 It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. Piston engines are typically arranged with their pistons in rows moving inside individual cylinders A cam is a projecting part of a rotating Wheel or shaft that strikes a Lever at one or more points on its circular path The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.
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History
The first known cam and camshaft were invented in Iraq (Mesopotamia), described by Al-Jazari in 1206. For a topic outline on this subject see List of basic Iraq topics. Mesopotamia (from the Greek meaning "land between the rivers" is an area geographically located between the Tigris and Euphrates rivers largely corresponding Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī ( 1136 - 1206) (أَبُو اَلْعِزِ بْنُ إسْماعِيلِ بْنُ الرِّزاز الجزري [1] The cam and camshaft later appeared in European mechanisms from at least the 14th century,[2] or possibly earlier. [3]
Timing
The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear Since the valves control the flow of 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. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear 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 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 In some designs the camshaft also drives the distributor and the oil and fuel pumps. A distributor is a device in the Ignition system of an Internal combustion engine that routes High voltage from the Ignition coil to the A lubricant (sometimes referred to as a "Lube" is a substance (often a liquid introduced between two moving surfaces to reduce the Friction between them improving "Fuel pump" should not be confused with Fuel dispenser, a device that dispenses fuel into an automobile Also on early fuel injection systems, cams on the camshaft would operate the fuel injectors. Fuel injection is a system for mixing fuel with air in an Internal combustion engine.
In a two-stroke engine that uses a camshaft, each valve is opened once for each rotation of the crankshaft; in these engines, the camshaft rotates at the same rate as the crankshaft. The two-stroke Internal combustion engine differs from the more common Four-stroke engine by completing the same four processes (intake compression combustion exhaust In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft. Today Internal combustion engines in cars, Trucks motorcycles aircraft construction machinery and many others most commonly use a four-stroke cycle.
Duration
Duration can often be confusing because manufacturers may select any lift point to advertise a camshaft's duration and sometimes will manipulate these numbers. The power and idle characteristics of a camshaft rated at . 006" will be much different than one rated the same at . 002". Whenever duration is quoted, be sure to note the lift at which it is given.
Many performance engine builders have learned to gauge a race profile's aggressiveness by looking at the duration at . 020", . 050" and . 200". The . 020" number determines how responsive the motor will be and how much low end torque the motor will make. 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 . 050" number is used to estimate where peak power will occur, and the . 200" number gives an estimate of the power potential.
In general, duration determines how many crankshaft degrees a camshaft maintains more than a given tappet lift. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear A tappet in Mechanical engineering is a projection which imparts a linear motion to some other component within an assembly
Camshaft position
Depending on the location of the camshaft, the cams operate the valves either directly or through a linkage of pushrods and rockers. Direct operation involves a simpler mechanism and leads to fewer failures, but requires the camshaft to be positioned at the top of the cylinders. In the past when engines were not as reliable as today this was seen as too much bother, but in modern gasoline engines the overhead cam system, where the camshaft is on top of the cylinder head, is quite common. 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 Some engines use two camshafts each for the intake and exhaust valves; such an arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine may have four camshafts. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the A V engine is a common configuration for an Internal combustion engine.
Maintenance
The rockers or cam followers sometimes incorporate a mechanism to adjust and set the valve play through manual adjustment, but most modern auto engines have hydraulic lifters, eliminating the need to adjust the valve lash at regular intervals as the valvetrain wears, and in particular the valves and valve seats in the combustion chamber. Engineering tolerance is the permissible limit of variation in a physical Dimension, a measured value or Physical property of a A hydraulic lifter, also known as a hydraulic Tappet or a hydraulic Lash adjuster is a device for maintaining zero valve clearance in an internal The valve seat in an internal combustion gasoline or Diesel engine is the surface against which an Intake or an exhaust A combustion chamber is the part of an Engine in which Fuel is burned
Sliding friction between the surface of the cam and the cam follower which rides upon it is considerable. In order to reduce wear at this point, the cam and follower are both surface hardened, and modern lubricant motor oils contain additives specifically to reduce sliding friction. Case hardening or surface hardening is the process of hardening the surface of a metal often a low Carbon steel, by infusing elements into the material's A lubricant (sometimes referred to as a "Lube" is a substance (often a liquid introduced between two moving surfaces to reduce the Friction between them improving Motor oil, or engine oil, is an Oil used for lubrication of various Internal combustion engines While the main function is to lubricate Moving The lobes of the camshaft are usually slightly tapered, causing the cam followers or valve lifters to rotate slightly with each depression, and helping to distribute wear on the parts. The surfaces of the cam and follower are designed to "wear in" together, and therefore when either is replaced, the other should be as well to prevent excessive rapid wear. In some engines, the flat contact surfaces are replaced with rollers, which eliminate the sliding friction and wear but adds mass to the valvetrain.
Alternatives
In addition to mechanical friction, considerable force is required to overcome the valve springs used to close the engine's valves. This can amount to an estimated 25% of an engine's total output at idle, reducing overall efficiency. Two approaches have been tried to reclaim this "wasted" energy but have proven difficult to implement:
- Springless valves, like the desmodromic system employed today by Ducati
- Camless valvetrains using solenoids or magnetic systems have long been investigated by BMW and Fiat, and are currently being prototyped by Valeo and Ricardo
See also
Gallery
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Components of a typical, four stroke cycle, DOHC piston engine. In general mechanical terms the word desmodromic is used to refer to mechanisms that have different controls for their actuation in different directions Ducati Motor Holding SpA ( Borsa Italiana: DMH is an Italian Motorcycle manufacturer located in Bologna Italy. 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 A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which ( BMW) (Bavarian Motor Works is an independent German automobile manufacturer founded in 1916 Fiat SpA (an Acronym for Fabbrica Italiana Automobili Torino (Italian Automobile Factory of Turin) is an Italian automobile manufacturer Valeo is a French automotive components manufacturer History The Société Anonyme Française du Ferodo was founded in 1923 in Saint-Ouen a suburb of Paris The sleeve valve is a type of Valve mechanism for Piston engines distinct from the more common Poppet valve. Cylinder head porting refers to the process of modifying the intake and exhaust ports of an Internal combustion engine to improve the quality and quantity of the gas flow The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear Today Internal combustion engines in cars, Trucks motorcycles aircraft construction machinery and many others most commonly use a four-stroke cycle. (E) Exhaust camshaft, (I) Intake camshaft, (S) Spark plug, (V) Valves, (P) Piston, (R) Connecting rod, (C) Crankshaft, (W) Water jacket for coolant flow. A spark plug (also very rarely nowadays in British English: a sparking plug) is an electrical device that fits into the Cylinder 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 A piston is a component of Reciprocating engines Pumps and Gas compressors It is located in a cylinder and is made gas-tight by Piston In a reciprocating Piston engine, the connecting rod or conrod connects the Piston to the crank or Crankshaft. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear |
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Double overhead cams control the opening and closing of a cylinder's valves. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the |
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Valve timing gears on a Ford Taunus V4 engine — the small gear is on the crankshaft, the larger gear is on the camshaft. 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 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 The Taunus V4 was a V4 Piston engine with one Balance shaft, introduced by Ford Motor Company in Germany The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear The gear ratio causes the camshaft to run at half the RPM of the crankshaft. The gear ratio is the relationship between the number of teeth on two Gears that are meshed or two Sprockets connected with a common Roller chain, or the |
Footnotes
- ^ Georges Ifrah (2001). The Universal History of Computing: From the Abacus to the Quatum Computer, p. 171, Trans. E. F. Harding, John Wiley & Sons, Inc. (See [1])
- ^ A. Lehr (1981), De Geschiedenis van het Astronomisch Kunstuurwerk, p. 227, Den Haag. (See [2])
- ^ http://emp.byui.edu/DavisR/202/202C16.html retrieved June 21, 2007
Dictionary
camshaft
-noun
- A shaft fitted with cams; especially one in a piston engine that activates the valves.
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