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Desmodromic valve AI simulator
(@Desmodromic valve_simulator)
Hub AI
Desmodromic valve AI simulator
(@Desmodromic valve_simulator)
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 spent gases at the end of the cycle. In a conventional four-stroke engine, valves are opened by a cam and closed by return spring. A desmodromic valve has two cams and two actuators, for positive opening and closing without a return spring.
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.
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. In the 1950s new vacuum melt processes helped to remove impurities from the metal in valve springs, increasing their life and efficiency greatly. However, many springs would still fail at sustained operation above 8000 RPM. The desmodromic system was devised to remedy this problem by completely removing the need for a spring. Furthermore, as maximum RPM increases, higher spring force is required to prevent valve float, leading to larger springs (with increased spring mass, and thus greater inertia), cam drag (as the valve springs require energy to compress, robbing the engine of power), and higher wear on the parts at all speeds, problems addressed by the desmodromic mechanism.
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.[citation needed] 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 carburettors 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 Ducati system).
In 1925, Spanish engineer Wifredo Ricart obtained patent FR590149 for a similar valve drive mechanism.
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.
A later version of the Daimler-Benz inverted V12, like the 601 and 603X, the type that were used in the Messerschmitt Bf 109 (1930s), had desmodromic valves.
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 spent gases at the end of the cycle. In a conventional four-stroke engine, valves are opened by a cam and closed by return spring. A desmodromic valve has two cams and two actuators, for positive opening and closing without a return spring.
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.
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. In the 1950s new vacuum melt processes helped to remove impurities from the metal in valve springs, increasing their life and efficiency greatly. However, many springs would still fail at sustained operation above 8000 RPM. The desmodromic system was devised to remedy this problem by completely removing the need for a spring. Furthermore, as maximum RPM increases, higher spring force is required to prevent valve float, leading to larger springs (with increased spring mass, and thus greater inertia), cam drag (as the valve springs require energy to compress, robbing the engine of power), and higher wear on the parts at all speeds, problems addressed by the desmodromic mechanism.
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.[citation needed] 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 carburettors 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 Ducati system).
In 1925, Spanish engineer Wifredo Ricart obtained patent FR590149 for a similar valve drive mechanism.
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.
A later version of the Daimler-Benz inverted V12, like the 601 and 603X, the type that were used in the Messerschmitt Bf 109 (1930s), had desmodromic valves.
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