A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.^[1]

History

An early cam was built into Hellenistic Hellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BC to about 146 BC ; note, however that Koine Greek language and Hellenistic philosophy and religion are also indisputably elements of the Roman era until Late Antiquity. It was immediately preceded by the Classical Greece period, and immediately water-driven automata An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation from the 3rd century BC.^[2] The camshaft was later described in Iraq Iraq , officially the Republic of Iraq (Arabic: جمهورية العراق (help·info) Jumhūrīyat Al-Irāq, Kurdish: كؤماری عێراق‎, Komara Îraqê) is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert (Mesopotamia Mesopotamia is a toponym for the area of the Tigris-Euphrates river system, largely corresponding to modern-day Iraq, as well as some parts of northeastern Syria, southeastern Turkey, and southwestern Iran) by Al-Jazari Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī (Arabic: أَبُو اَلْعِزِ بْنُ إسْماعِيلِ بْنُ الرِّزاز الجزري‎) was a prominent Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden in 1206. He employed it as part of his automata, water-raising machines, and water clocks A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel where the amount is then measured such as the castle clock A castle clock is a visually complicated clock originally appearing near the top of a castle and later a church tower. The original inventor was Al-Jazari, who described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. Some consider it to be an early example of a programmable analog computer.^[3] The cam and camshaft later appeared in European mechanisms from at least the 14th century,^[4] or possibly earlier.^[5]

Uses

In internal combustion engines with pistons A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the, the camshaft is used to operate poppet valves 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. The shaft guides the plug portion by sliding through a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it. It then consists of a cylindrical rod running the length of the cylinder bank Internal combustion piston engines are typically arranged with their pistons in rows, or 'planes', moving inside individual cylinders. This allows the engine block to be built from a single piece of machined metal. Engines sometimes have more than one row of pistons, each with their own block, referred to as cylinder banks with a number of oblong lobes protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism as they rotate.

Automotive

Material

Camshafts can be made out of several different types of material. These include:

Chilled iron castings: this is a good choice for high volume production. A chilled iron camshaft has a resistance against wear because the camshaft lobes have been chilled, generally making them harder. When making chilled iron castings, 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 is required, engine builders and camshaft manufacturers choose to make the camshaft from steel billet. This method is also used for low volume production. This is a much more time consuming process, and is generally more expensive than other methods. However the finished product is far superior. When making the camshaft, CNC Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via handwheels or levers, or mechanically automated via cams alone. The first NC machines were built in the 1940s and '50s, based on existing tools that were modified with lathes A metal lathe or metalworking lathe is a large class of lathes designed for precisely machining relatively hard materials. They were originally designed to machine metals; however, with the advent of plastics and other materials, and with their inherent versatility, they are used in a wide range of applications, and a broad range of materials. In, CNC milling machines A milling machine is a machine tool used to machine solid materials. Milling machines exist in two basic forms: horizontal and vertical, which terms refer to the orientation of the cutting tool spindle. Unlike a drill press, in which the workpiece is held stationary and the drill is moved vertically to penetrate the material, milling also involves and CNC camshaft grinders will be used. 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 Heat treatment is a method used to alter the physical, and sometimes chemical properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired via gas nitriding, which changes the micro-structure of the material. It gives a surface hardness of 55-60 HRC The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, which are denoted by a single letter, that use different loads or. These types of camshafts can be used in high-performance engines.

Timing

The relationship between the rotation of the camshaft and the rotation of the crankshaft The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to is of critical importance. 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 The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to either directly, via a gear A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, magnitude, and mechanism, or indirectly via a belt or chain called a timing belt A timing belt, or cam belt , is a part of an internal combustion engine that controls the timing of the engine's valves. Some engines, like the flat-4 Volkswagen air cooled engine, and the straight-6 Toyota F engine use timing gears. Timing belts replace the older style timing chains that were in common usage until the 1970's and 1980's (although or timing chain Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery. It is a simple, reliable, and efficient means of power transmission. In some designs the camshaft also drives the distributor A distributor is a device in the ignition system of an internal combustion engine that routes high voltage from the ignition coil to the spark plugs in the correct firing order. The first reliable battery operated ignition was developed by Dayton Engineering Laboratories Co. and introduced in the 1910 Cadillac. This ignition was developed by and the oil and fuel pumps A fuel pump is a frequently essential component on a car or other internal combustion engined device. Many engines (older motorcycle engines in particular) do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank through a line or hose to the engine. But in non-gravity feed designs, fuel has to be pumped from the. Some General Motors vehicles also have the power steering pump driven by the camshaft. Also on early fuel injection Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s systems, cams on the camshaft would operate the fuel injectors.

In a two-stroke engine A two-stroke engine is an internal combustion engine that completes the thermodynamic cycle in two movements of the piston compared to twice that number for a four-stroke engine. This increased efficiency is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform simultaneously the intake and 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. In a four-stroke engine Today, internal combustion engines in cars, trucks, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion , and exhaust strokes that occur during two crankshaft rotations per working cycle of the gasoline engine and diesel engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.

The timing of the camshaft can be advanced to produce better low end torque or it can be retarded to produce better high end torque.

Duration

Duration is the number of crankshaft degrees of engine rotation during which the valve is off the seat. As a generality, greater duration results in more horsepower. The RPM at which peak horsepower occurs is typically increased as duration increases at the expense of lower rpm efficiency (torque).^{[citation needed]}

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".

Many performance engine builders 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 Torque, also called moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist the motor will make. The .050" number is used to estimate where peak power will occur, and the .200" number gives an estimate of the power potential.

A secondary effect of increase duration is increasing overlap, which is the number of crankshaft degrees during which both intake and exhaust valves are off their seats. It is overlap which most affects idle quality, inasmuch as the "blow-through" of the intake charge which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In reality, increasing a camshaft's duration typically increases the overlap event, unless one spreads lobe centers between intake and exhaust valve lobe profiles.

Lift

The camshaft "lift" is the resultant net rise of the valve from its seat. The further the valve rises from its seat the more airflow can be realised, which is generally more beneficial. Greater lift has some limitations. Firstly, the lift is limited by the increased proximity of the valve head to the piston crown and secondly greater effort is required to move the valve's springs to higher state of compression. Increased lift can also be limited by lobe clearance in the cylinder head construction, so higher lobes may not necessarily clear the framework of the cylinder head casing. Higher valve lift can have the same effect as increased duration where valve overlap is less desirable.

Higher lift allows accurate timing of airflow; although even by allowing a larger volume of air to pass in the relatively larger opening, the brevity of the typical duration with a higher lift cam results in less airflow than with a cam with lower lift but more duration, all else being equal. On forced induction motors this higher lift could yield better results than longer duration, particularly on the intake side. Notably though, higher lift has more potential problems than increased duration, in particular as valve train rpm rises which can result in more inefficient running or loss or torque.

Cams that have too high a resultant valve lift, and at high rpm, can result in what is called "valve bounce", where the valve spring tension is insufficient to keep the valve following the cam at its apex. This could also be as a result of a very steep rise of the lobe and short duration, where the valve is effectively shot off the end of the cam rather than have the valve follow the cams’ profile. This is typically what happens on a motor over rev. This is an occasion where the engine rpm exceeds the engine maximum design speed. The valve train is typically the limiting factor in determining the maximum rpm the engine can maintain either for a prolonged period or temporarily. Sometimes an over rev can cause engine failure where the valve stems become bent as a result of colliding with the piston crowns.

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 In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It consists of a platform containing part of the combustion chamber (usually, though not always), and the location of the poppet valves and spark plugs. In a flathead engine, the mechanical parts of the valve train are all contained within, is quite common.

Number of camshafts

While today some cheaper engines rely on a single camshaft per cylinder bank, which is known as a single overhead camshaft (SOHC), most modern engine designs (the overhead-valve or OHV An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine), and uses pushrods or rods to actuate rocker arms above the engine being largely obsoleted from passenger vehicles), are driven by a two camshafts per cylinder bank arrangement (one camshaft for the intake valves and another for the exhaust valves); such camshaft arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft. The Vee configuration generally reduces the overall engine length, height and weight compared to, which has two separate cylinder banks, may have four camshafts (colloquially known as a quad-cam engine^[6]).

More unusual is the modern W engine The W engine is a specific type of reciprocating / piston internal combustion engine configuration. The cylinder banks resemble the letter W, in the same way a V engine resembles the letter V. There have been three entirely different implementations of this concept: one with three banks of cylinders, one with four banks, and one with two banks of (also known as a 'VV' engine to distinguish itself from the pre-war In real estate the term refers to buildings from the 1930s in the Functionalist or Art Deco styles W engines) that has four cylinder banks arranged in a "W" pattern with two pairs narrowly arranged with a 15 degree separation. Even when there are four cylinder banks (that would normally require a total of eight individual camshafts), the narrow-angle design allows the use of just four camshafts in total. For the Bugatti Veyron The Bugatti Veyron EB 16.4 is the most recent version of a mid-engined full-sized grand tourer developed by the German car-manufacturer Volkswagen and produced by the Volkswagen-brand Bugatti Automobiles SAS at their headquarters in Château St. Jean in Molsheim , and whose production and development is often credited to Ferdinand Karl Piech. It, which has a 16 cylinder W engine configuration, all the four camshafts are driving a total of 64 valves 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. The shaft guides the plug portion by sliding through a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it.

The overhead camshaft design adds more valvetrain components that ultimately incur in more complexity and higher manufacturing costs, but this is easily offset by many advantages over the older OHV design: multi-valve design In automotive engineering, an engine is referred to as multi-valve when each cylinder has more than two valves. Such designs have been around since at least 1912 (Peugeot) and perhaps earlier, higher RPM Revolutions per minute is a unit of frequency of rotation: the number of full rotations completed in one minute around a fixed axis. It is used as a measure of rotational speed of a mechanical component limit and design freedom to better place valves, ignition (Spark-ignition engine The term spark-ignition engine normally refers to internal combustion engines, specifically petrol engines, where the initiation of the combustion process of the air-fuel mixture is ignited within the combustion chamber by a spark from a spark plug. The term contrasts with diesel-fueled compression-ignition engines, where the heat generated from) and intake/exhaust ports.

Maintenance

The rockers or cam followers A cam follower, also known as a track follower, is a specialized type of roller or needle bearing designed to follow cams. Cam followers come in a vast array of different configurations, however the most defining characteristic is how the cam follower mounts to its mating part; stud style cam followers use a stud while the yoke style has a hole sometimes incorporate a mechanism to adjust and set the valve play Dimensions, properties, or conditions may vary within certain practical limits without significantly affecting functioning of equipment or a process. Tolerances are specified to allow reasonable leeway for imperfections and inherent variability without compromising performance through manual adjustment, but most modern auto engines have hydraulic lifters 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 combustion engine. The conventional means of adjusting valve actuation always requires a small clearance to be left between the valve and its rocker or cam follower to allow for thermal expansion and, eliminating the need to adjust the valve lash at regular intervals as the valvetrain wears, and in particular the valves and valve seats The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve in the combustion chamber The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston on a crankshaft or a turbine disc in a gas turbine. The energy can also be used to produce thrust when.

Sliding friction Friction is not a fundamental force, as it is derived from electromagnetic force between charged particles, including electrons, protons, atoms, and molecules, and so cannot be calculated from first principles, but instead must be found empirically. When contacting surfaces move relative to each other, the friction between the two surfaces 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 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 surface, forming a thin layer of a harder alloy. Case hardening is usually done after the part in question has been formed into its final shape, but can also be done to increase the hardening, and modern lubricant motor oils Motor oil, or engine oil, is an oil used for lubrication of various internal combustion engines. While the main function is to lubricate moving parts, motor oil also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts. Dieter Klamann's text provides extensive technical detail about motor oils contain additives specifically to reduce sliding friction. 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. Some approaches to reclaiming this "wasted" energy include:

• Springless valves, like the desmodromic Desmodromic valves are those which are positively closed by a cam and leverage system, rather than relying on the more conventional valve springs. The term desmodromic is derived from two Greek roots, desmos and dromos (course, track) system employed today by Ducati Ducati Motor Holding S.p.A. is a motorcycle manufacturer in Bologna, Italy. Ducati has achieved prominence in the motorcycle industry, success in motorcycle racing, and is known for its marriage of style with performance
• Camless Most four-stroke piston engines today employ one or more camshafts to operate poppet valves. The lobes on the camshafts operate cam followers which in turn open the poppet valves. A camless uses electromagnetic, hydraulic, or pneumatic actuators to open the poppet valves instead. Actuators can be used to both open and close the valves, or an valvetrains using solenoids A solenoid[nb 1] is a three-dimensional coil wound into a tightly packed helix. In physics, the term solenoid refers to a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as or magnetic systems have long been investigated by BMW and Fiat, and are currently being prototyped by Valeo and Ricardo
• The Wankel engine, a rotary engine which uses neither pistons nor valves, best known for being used by Mazda in the RX-7 and RX-8 sports cars.

Gallery

See also

• Sleeve valve
• Crankshaft

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