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The word poppet shares etymology with "puppet": it is from the Middle English popet ("youth" or "doll"), from Middle French poupette, which is a diminutive of poupée.The use of the word poppet to describe a valve comes from the same word applied to marionettes, which, like the poppet valve, move bodily in response to remote motion transmitted linearly.
This is true however, only for models until the year 2006, after which the engine's design was modified to erase this flaw. It is notorious that the problem still arises on the new models, but it can be dealt with by a proper tuning of the poppet valve's backlash every 6,000 kilometres (3,730 mi).
The poppet valve's previous problems with sealing and wear had been remedied by the use of better materials and the inertia problems with the use of large valves were reduced by using several smaller valves instead, giving increased flow area and reduced mass, and the exhaust valve hot spot by Sodium-cooled valves. Up to that point, the single ...
Valve float is an adverse condition which can occur at high engine speeds [1] when the poppet valves in an internal combustion engine valvetrain do not properly follow the closure phase of the cam lobe profile. This reduces engine efficiency and performance.
A crossflow T-head sidevalve engine The usual L-head arrangement Pop-up pistons may be used to increase compression ratio Flathead with Ricardo's turbulent head. A flathead engine, also known as a sidevalve engine [1] [2] or valve-in-block engine, is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as in an overhead valve ...
Most modern engines use poppet valves, although sleeve valves, slide valves and rotary valves have also been used at times. Poppet valves are typically opened by the camshaft lobe or rocker arm, and closed by a coiled spring called a valve spring. Valve float occurs when the valve spring is unable to control the inertia of the valvetrain at ...
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.
Rotary valves are potentially highly suitable for high-revving engines, such as those used in racing sportscars and F1 racing cars, on which traditional poppet valves with springs can fail due to valve float and spring resonance and where the desmodromic valve gear is too heavy, large in size and too complex to time and design properly. Rotary ...