Desmodromic valve

A desmodromic valve is a reciprocating engine poppet valve that is positively closed by a cam and leverage system, rather than by a more conventional spring. The valves in a typical four-stroke engine allow the air/fuel mixture into the cylinder at the beginning of the cycle and exhaust gases to be expelled at the end of the cycle. In a conventional four-stroke engine valves are opened by a cam and closed by return spring. An engine using desmodromic valves has two cams and two actuators, each for positive opening and closing without a return spring. Desmodromic poppet valve in Ducati engine. Etymology The word comes from the Greek words desmos (δεσμός, translated as "bond" or "knot") and dromos (δρόμος, "track" or "way"). This denotes the major characteristic of the valves being continuously "bound" to the camshaft. Idea The common valve spring system is satisfactory for traditional mass-produced engines that do not rev highly and are of a design that requires low maintenance. At the period of initial desmodromic development, valve springs were a major limitation on engine performance because they would break from metal fatigue. Vacuum melt processes developed in the 1950s helped remove impurities in the steel used to make valve springs, although after sustained operation above 8000 RPM often springs would still fail.The desmodromic system was devised to remedy this problem. Furthermore, as maximum RPM increases, higher spring force is required to prevent valve float, leading to increased cam drag and higher wear on the parts at all speeds, problems addressed by the desmodromic mechanism. Design and history Desmodromic poppet valve example. Fully controlled valve movement was conceived during the earliest days of engine development, but devising a system that worked reliably and was not overly complex took a long time. Desmodromic valve systems are first mentioned in patents in 1896 by Gustav Mees. Austin's marine engine of 1910 produced 300 bhp and was installed in a speedboat called "Irene I"; its all-aluminium, twin-overhead-valve engine had twin magnetos, twin carburetors and desmodromic valves. The 1914 Grand Prix Delage and Nagant (see Pomeroy "Grand Prix Car") used a desmodromic valve system (quite unlike the present day Ducatisystem). Azzariti, a short lived Italian manufacturer from 1933 to 1934, produced 173 cc and 348 cc twin-cylinder engines, some of which had desmodromic valve gear, with the valve being closed by a separate camshaft. The Mercedes-Benz W196 Formula One racing car of 1954-1955, and the Mercedes-Benz 300SLR sports racing car of 1955 both had desmodromic valve actuation. In 1956, Fabio Taglioni, a Ducati engineer, developed a desmodromic valve system for the Ducati 125 Grand Prix, creating the Ducati 125 Desmo. He was quoted to say: The specific purpose of the...

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Distributor

A distributor is an enclosed rotating shaft used in spark-ignition internal combustion engines that have mechanically-timed ignition. The distributor's main function is to route secondary, or high voltage, current from the ignition coil to the spark plugs in the correct firing order, and for the correct amount of time. Except in magneto systems, the distributor also houses a mechanical or inductive breaker switch to open and close the ignition coil's primary circuit. The first reliable battery operated ignition was developed by Dayton Engineering Laboratories Co. (Delco) and introduced in the 1910 Cadillac. This ignition was developed by Charles Kettering and was considered a wonder in its day. Atwater Kent invented his Unisparker ignition system about this time in competition with the Delco system. By the end of the 20th century mechanical ignitions were disappearing from automotive applications in favor of inductive or capacitive electronic ignitions fully controlled engine control units (ECU), rather than directly timed to the engine's crankshaft speed. Typical distributor with distributor cap. Also visible are mounting/drive shaft (bottom), vacuum advance unit (right) and capacitor (centre). Car ignition system. Upper right is Distributor. Description A distributor consists of a rotating arm or rotor inside the distributor cap, on top of the distributor shaft, but insulated from it and the body of the vehicle (ground). The distributor shaft is driven by a gear on the camshaft on most overhead valve engines, and attached directly to a camshaft on most overhead cam engines. (The distributor shaft may also drive the oil pump.) The metal part of the rotor contacts the high voltage cable from the ignition coil via a spring-loaded carbon brush on the underside of the distributor cap. The metal part of the rotor arm passes close to (but does not touch) the output contacts which connect via high tension leads to the spark plug of each cylinder. As the rotor spins within the distributor, electric current is able to jump the small gaps created between the rotor arm and the contacts due to the high voltage created by the ignition coil. The distributor shaft has a cam that operates the contact breaker (also called points). Opening the points causes a high inductionvoltage in the system's ignition coil. The distributor also houses the centrifugal advance unit: a set of hinged weights attached to the distributor shaft, that cause the breaker points mounting plate to slightly rotate and advance the spark timing with higher engine revolutions per minute (rpm). In addition, the distributor has a vacuum advance unit that advances the timing even further as a function of the vacuum in the inlet manifold. Usually there is also a capacitorattached to the distributor. The capacitor is connected parallel to the breaker points, to suppress sparking to prevent excessive wear of the points. Around the 1970s the primary breaker points were largely replaced with a Hall effect sensor or optical...

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Ignition magneto

An ignition magneto, or high tension magneto, is a magneto that provides current for the ignition system of a spark-ignition engine, such as a petrol engine. It produces pulses of high voltage for the spark plugs. The older term tension means voltage. The use of ignition magnetos is now confined mainly to engines where there is no other available electrical supply, for example in lawnmowers and chainsaws. It is also widely used in aviation piston engines even though an electrical supply is usually available. In this case the magneto's self-powered operation is considered to offer increased reliability; in theory the magneto should continue operation as long as the engine is turning. Bosch magneto circuit, 1911 Simple low-tension magneto, for a single-cylinder engine Armature of a high-tension magneto Section through a high-tension magneto, with distributor History Firing the gap of a spark plug, particularly in the combustion chamber of a high-compression engine, requires a greater voltage (or higher tension) than can be achieved by a simple magneto. The high-tension magneto combines an alternating current magneto generator and a transformer. A high current at low voltage is generated by the magneto, then transformed to a high voltage (even though this is now a far smaller current) by the transformer. The first person to develop the idea of a high-tension magneto was Andre Boudeville, but his design omitted a condenser (capacitor); Frederick Richard Simms in partnership with Robert Bosch were the first to develop a practical high-tension magneto. Magneto ignition was introduced on the 1899 Daimler Phönix. This was followed by Benz, Mors, Turcat-Mery, and Nesseldorf, and soon was used on most cars up until about 1918 in both low voltage (voltage for secondary coils to fire the spark plugs) and high voltage magnetos (to fire the spark plug directly, similar to coil ignitions, introduced by Bosch in 1903). Operation In the type known as a shuttle magneto, the engine rotates a coil of wire between the poles of a magnet. In the inductor magneto, the magnet is rotated and the coil remains stationary. As the magnet moves with respect to the coil, the magnetic flux linkage of the coil changes. This induces an EMF in the coil, which in turn causes a current to flow. One or more times per revolution, just as the magnet pole moves away from the coil and the magnetic flux begins to decrease, a cam opens the contact breaker and interrupts the current. This causes the electromagnetic field in the primary coil to collapse rapidly. As the field collapses rapidly there is a large voltage induced (as described by Faraday's Law) across the primary coil. As the points begin to open, point spacing is initially such that the voltage across the primary coil would arc across the points. A capacitor is placed across the points which absorbs the energy stored...

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Cylinder bank

Internal combustion piston engines (those with more than one cylinder) are usually arranged so that the cylinders are in lines parallel to the crankshaft. Where they are in a single line, this is referred to as an inline or straight engine. Where engines have a large number of cylinders, the cylinders are commonly arranged in two lines, placed at an angle to each other as a V engine. Each line is referred to as a cylinder bank. The angle between cylinder banks is described as the bank angle. Napier Lion W or broad arrowlayout with three banks A Zvezda M503 radial engine with inline banks Number of cylinders Engines with six cylinders are equally common as either straight or vee engines. With more cylinders than this, the vee configuration is more common. Fewer cylinders are more usually arranged as an inline engine. There are exceptions to this: straight-8 engines were found on some pre-war luxury cars with the bonnet length to house them. A few V4 engines have also been produced, usually where an extra-compact engine was required, including some outboard motors with a vertical crankshaft. Although twin-cylinder engines are now rare for cars, they are still commonly used for motorcycles and the vee-twin and inline twin are both widely used. Advantages of multi-bank engines An obvious advantage to a multi-bank engine is that it can be shorter in length. This allows a torsionally stiffer construction for both the crankshaft and crankcase. The most important advantage though is less obvious: a multi-plane engine can be arranged to have better balance and less vibration. This depends on the layout of the crankshaft more than the cylinder banks alone: the planes on which the pistons are arranged, thus their timing and vibration, depend on both the cylinder bank and the crankshaft angles. Unusual arrangements The W or broad arrow arrangement uses three cylinder banks, usually a W-12 with three banks of four cylinders. Narrow-angle vee engines, such as the Lancia V4 and the Volkswagen VR6, have such a narrow bank angle that their cylinders are combined into a single cylinder block. These are still described as vee engines, although they may be described as having either two (as for other engines) or (more commonly in these cases) one cylinder bank. Radial engines In a radial engine, cylinders are arranged radially in a circle. Simple radials use one row (i.e. one circle) of cylinders. Larger radials use two rows, or even four. Most radials are air-cooled with separate cylinders and so there are no banks as such. Most radials also have odd numbers of cylinders in each row and stagger these between successive rows, for...

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Fuel pump

A fuel pump is a frequently (but not always) 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 or under high pressure to the fuel injection system. Often, carbureted engines use low pressure mechanical pumps that are mounted outside the fuel tank, whereas fuel injected engines often use electric fuel pumps that are mounted inside the fuel tank (and some fuel injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine). Fuel pressure needs to be within certain specifications for the engine to run correctly. If the fuel pressure is too high, the engine will run rough and rich, not combusting all of the fuel being pumped making the engine inefficient and a pollutant. If the pressure is too low, the engine may run lean, misfire, or stall.   A high-pressure fuel pump on a Yanmar 2GM20 marine diesel engine Mechanical pump Mechanical fuel pump, fitted to cylinder head Prior to the widespread adoption of electronic fuel injection, most carbureted automobile engines used mechanical fuel pumps to transfer fuel from the fuel tank into the fuel bowls of the carburetor. The two most widely used fuel feed pumps are diaphragm and plunger-type mechanical pumps. Diaphragm pumps are a type of positive displacement pump. Diaphragm pumps contain a pump chamber whose volume is increased or decreased by the flexing of a flexible diaphragm, similar to the action of a piston pump. A check valve is located at both the inlet and outlet ports of the pump chamber to force the fuel to flow in one direction only. Specific designs vary, but in the most common configuration, these pumps are typically bolted onto the engine block or head, and the engine's camshaft has an extra eccentric lobe that operates a lever on the pump, either directly or via a pushrod, by pulling the diaphragm to bottom dead center. In doing so, the volume inside the pump chamber increased, causing pressure to decrease.This allows fuel to be pushed into the pump from the tank (caused by atmospheric pressure acting on the fuel in the tank). The return motion of the diaphragm to top dead center is accomplished by a diaphragm spring, during which the fuel in the pump chamber is squeezed through the outlet port and into the carburetor. The pressure at which the fuel is...

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Carburetor

A carburetor (American English) or carburettor (British English; see spelling differences) is a device that mixes air and fuel for internal combustion engines in the proper ratio for combustion. It is sometimes colloquially shortened to carb in the UK and North America or carby in Australia. To carburate or carburet (and thus carburation or carburetion, respectively) means to mix the air and fuel or to equip (an engine) with a carburetor for that purpose. Carburetors have largely been supplanted in the automotive and, to a lesser extent, aviation industries by fuel injection. They are still common on small engines for lawn mowers, rototillers and other equipment.   Bendix-Technico (Stromberg) 1-barrel downdraft carburetor model BXUV-3, with nomenclature Etymology The word carburetor comes from the French carbure meaning "carbide". Carburer means to combine with carbon (compare also carburizing). In fuel chemistry, the term has the more specific meaning of increasing the carbon (and therefore energy) content of a fluid by mixing it with a volatile hydrocarbon. History and development The first carburetor was invented by Samuel Morey in 1826. Later, Enrico Bernardi developed another carburetor at the University of Padua in 1882, for his Motrice Pia, the first petrol combustion engine (one cylinder, 121.6 cc) prototyped on 5 August 1882. A carburetor was among the early patents by Karl Benz (1888) as he developed internal combustion engines and their components. Early carburetors were of the surface type, in which air is combined with fuel by passing over the surface of gasoline. In 1885, Wilhelm Maybach and Gottlieb Daimler developed a float carburetor based on the atomizer nozzle. The Daimler-Maybach carburetor was copied extensively, leading to patent lawsuits. British courts rejected the Daimler company's claim of priority in favor of Edward Butler's 1884 spray carburetor used on his Petrol Cycle. Hungarian engineers János Csonka and Donát Bánki patented a carburetor for a stationary engine in 1893. Frederick William Lanchester of Birmingham, England, experimented with the wick carburetor in cars. In 1896, Frederick and his brother built the first gasoline-driven car in England, a single cylinder 5 hp (3.7 kW) internal combustion engine with chain drive. Unhappy with the car's performance and power, they re-designed the engine the following year using two horizontally-opposed cylinders and a newly designed wick carburetor. Carburetors were the common method of fuel delivery for most US-made gasoline engines until the late 1980s, when fuel injection became the preferred method. This change was dictated by the requirements of catalytic converters and not due to an inherent inefficiency of carburation. A catalytic converter requires that there be more precise control over the fuel / air mixture in order to control the amount of oxygen remaining in the exhaust gases. In the U.S. market, the last cars using carburetors were: 1990 (General public) : Oldsmobile Custom Cruiser, Buick Estate Wagon, Cadillac Brougham, Honda Prelude (Base Model), Subaru Justy 1991 (Police) : Ford Crown Victoria Police Interceptor with the 5.8 L (351 cu in) V8 engine. 1991 (SUV) : Jeep Grand...

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Fuel filter

A fuel filter is a filter in the fuel line that screens out dirt and rust particles from the fuel, normally made into cartridges containing a filter paper. They are found in most internal combustion engines. Fuel filters serve a vital function in today's modern, tight-tolerance engine fuel systems. Unfiltered fuel may contain several kinds of contamination, for example paint chips and dirt that has been knocked into the tank while filling, or rust caused by moisture in a steel tank. If these substances are not removed before the fuel enters the system, they will cause rapid wear and failure of the fuel pump and injectors, due to the abrasive action of the particles on the high-precision components used in modern injection systems. Fuel filters also improve performance, as the fewer contaminants present in the fuel, the more efficiently it can be burnt. A fuel filter on a pickup truck, showing its mounting location on the firewall. A fuel filter on a Yanmar 2GM20marine diesel engine. Fuel filters need to be maintained at regular intervals. This is usually a case of simply disconnecting the filter from the fuel line and replacing it with a new one, although some specially designed filters can be cleaned and reused many times. If a filter is not replaced regularly it may become clogged with contaminants and cause a restriction in the fuel flow, causing an appreciable drop in engine performance as the engine struggles to draw enough fuel to continue running normally. Some filters, especially found on diesel engines, are of a bowl-like design which collect water in the bottom (as water is more densethan diesel). The water can then be drained off by opening a valve in the bottom of the bowl and letting it run out, until the bowl contains only diesel. Many fuel filters contain a water sensor to signal to the engine control unit or directly to the driver (lamp on dashboard) if the water reach the warning level. It is especially undesirable for water in fuel to be drawn into a diesel engine fuel system, as the system relies on the diesel for lubrication of the moving parts, and if water gets into a moving part which requires constant lubrication (for example an injector valve), it will quickly cause overheating and unnecessary wear. This type of filter may also include a sensor, which will alert the operator when the filter needs to be drained. In proximity of the diesel fuel filter there might be a fuel heater to avoid the forming of paraffin wax (in case of low temperatures) inside the filtrating element which can stop the fuel flow to the engine.

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