This article needs additional citations for verification .(December 2009) |
The mean piston speed is the average speed of the piston in a reciprocating engine. It is a function of stroke and RPM. There is a factor of 2 in the equation to account for one stroke to occur in 1/2 of a crank revolution (or alternatively: two strokes per one crank revolution) and a '60' to convert seconds from minutes in the RPM term.
For example, a piston in an automobile engine which has a stroke of 90 mm will have a mean speed at 3000 rpm of 2 * (90 / 1000) * 3000 / 60 = 9 m/s.
The 5.2-liter V10 that debuted in the 2009 Audi R8 has the highest mean piston speed for any production car (26.9 m/s) thanks to its 92.8 mm stroke and 8700-rpm redline. [1]
The mean of any function refers to the average value. In the case of mean piston speed, taken in a narrow mathematical sense, it is zero because half of the time the piston is moving up and half of the time the piston is moving down; this is not useful. The way the term is usually used is to describe the distance traveled by the piston per unit of time, taking distance positive in both up and down senses. It is related to the rate that friction work is done on the cylinder walls, and thus the rate that heat is generated there. This is sort of a non-puzzle. It represents a specification to be designed to rather than as a result of design and the mean piston velocity is a function of the revolutions per minute, that is, the piston at a specific rpm is going to be the same at the peak of the graph as it is at the trough, that is at 286.071 degrees on the crankshaft if the rpm is held consistent. At 0 and 180 degrees, the piston velocity is zero. Piston velocity is a test of the strength of the piston and connecting rod subassembly. The alloy used to make the piston itself is what determines the maximum velocity that the piston can reach before friction coefficients, heat levels and reciprocating stress overcome the maximum levels that the piston can sustain before it begins to fail structurally. As the alloy tends to be fairly consistent across most manufacturers, the maximum velocity of the piston at a given rpm is determined by the length of the stroke, that is, the radius of the journal of the crankshaft. The most common engine types in production are built to square, or below square. That is, a square engine has the same diameter of cylinder bore as the total length of the stroke from 0 to 180 degrees, whereas in an undersquare engine, the total length of the stroke is greater than the diameter of the bore. The opposite, oversquare, is mostly used in higher performance engines where the torque curve approaches the peak of the maximum piston velocity. Generally in this type of engine, the volume of the cylinder can be artificially enhanced with turbochargers or superchargers, increasing the amount of fuel/air available for combustion. An example is found in Formula 1 racing engines, where the cylinder diameter is substantially greater than the length of the stroke, resulting in higher available rpm but necessitating greater requirements of the strengths of connecting rods and pistons and higher temperature tolerances for bearings. The cylinder diameter in these engines are fairly small (under 45 mm) and the stroke is less than that, depending on the torque curve and maximum available rpm as designed by the builder. Peak torque is reached at higher rpm and is spread over a wider range of rpm. The specifications of these are known factors and can be designed to. Torque is a function of the length of the stroke, the shorter the stroke, the less available torque at lower rpm, but the piston velocity can be taken to much greater speeds, meaning higher engine rpm. These types of engines are much more delicate and require a much higher level of precision in the moving parts than square or undersquare engines. Up until the early 1960s, the focus by designers was on torque rather than piston velocity, probably due to material considerations and machining technologies. As materials have improved, engine rpm has increased.
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines, mechanically controlled ignition systems and early electric motor speed controllers.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
As used in mechanical engineering, the term tractive force can either refer to the total traction a vehicle exerts on a surface, or the amount of the total traction that is parallel to the direction of motion.
A W8 engine is an eight-cylinder piston engine with four banks of two cylinders each, arranged in a W configuration.
The Austin Motor Company A-series is a British small straight-4 automobile engine. Launched in 1951 with the Austin A30, production lasted until 2000 in the Mini. It used a cast-iron block and cylinder head, and a steel crankshaft with three main bearings. The camshaft ran in the cylinder block, driven by a single-row chain for most applications, and with tappets sliding in the block, accessible through pressed steel side covers for most applications, and with overhead valves operated through rockers. The cylinder blocks are not interchangeable between versions intended for conventional end-on mounted gearboxes and the 'in-sump' transaxle used on British Motor Corporation/British Leyland front wheel drive models such as the Mini. The cylinder head for the overhead-valve version of the A-series engine was designed by Harry Weslake – a cylinder head specialist famed for his involvement in SS (Jaguar) engines and several Formula One-title winning engines. Although a "clean sheet" design, the A-series owed much to established Austin engine design practise, resembling in general design and overall appearance a scaled-down version of the 1200cc overhead-valve engine first seen in the Austin A40 Devon which would form the basis of the later B-series engine.
Alfa Romeo Twin Spark (TS) technology was used for the first time in the Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars (GTA, TZ) to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.
The Scotch Yoke is a reciprocating motion mechanism, converting the linear motion of a slider into rotational motion, or vice versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The location of the piston versus time is simple harmonic motion, i.e., a sine wave having constant amplitude and constant frequency, given a constant rotational speed.
Engine balance refers to how the forces are balanced within an internal combustion engine or steam engine. The most commonly used terms are primary balance and secondary balance. First-order balance and second-order balance are also used. Unbalanced forces within the engine can lead to vibrations.
In a reciprocating piston engine, the stroke ratio, defined by either bore/stroke ratio or stroke/bore ratio, is a term to describe the ratio between cylinder bore diameter and piston stroke length. This can be used for either an internal combustion engine, where the fuel is burned within the cylinders of the engine, or external combustion engine, such as a steam engine, where the combustion of the fuel takes place outside the working cylinders of the engine.
The Volkswagen G60 and G40 were inline-four cylinder automobile petrol engines, which uses a specific method of forced induction by way of a scroll-type supercharger. The G60 engine was formerly manufactured by the German automaker Volkswagen Group, and was installed in a limited number of their 'hot hatch' cars from their Volkswagen Passenger Cars marque from August 1988 to July 1993.
In a piston engine, the bore is the diameter of each cylinder.
The Pratt & Whitney R-1860 Hornet B was a relatively uncommon aircraft engine. It was a development of Pratt & Whitney's earlier R-1690 Hornet and was basically similar, but enlarged in capacity from 1,690 to 1,860 cubic inches (30.5 L). Cylinder bore was increased by 1/8" and the crankshaft stroke by 3/8". Both engines were air-cooled radial engines, with a single row of nine cylinders.
Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.
The Michel engine was an unusual form of opposed-piston engine. It was unique in that its cylinders, instead of being open-ended cylinders containing two pistons, were instead joined in a Y-shape and had three pistons working within them.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
The Volkswagen-Audi V8 engine family is a series of mechanically similar, gasoline-powered and diesel-powered, V-8, internal combustion piston engines, developed and produced by the Volkswagen Group, in partnership with Audi, since 1988. They have been used in various Volkswagen Group models, and by numerous Volkswagen-owned companies. The first spark-ignition gasoline V-8 engine configuration was used in the 1988 Audi V8 model; and the first compression-ignition diesel V8 engine configuration was used in the 1999 Audi A8 3.3 TDI Quattro. The V8 gasoline and diesel engines have been used in most Audi, Volkswagen, Porsche, Bentley, and Lamborghini models ever since. The larger-displacement diesel V8 engine configuration has also been used in various Scania commercial vehicles; such as in trucks, buses, and marine (boat) applications.