Desmodromic valve drive

12 Июн 2015 | Author: | Комментарии к записи Desmodromic valve drive отключены
Ducati Apollo v4

Desmodromic valve system

The and universally used mushroom or valves (used in every engine) will open their down-… and close their up-…, until make contact with seats in the cylinder head.

the valve is operated by a cam system. controls valve opening while the valve return, the closing movement (up-…) is the of the action of a spring, in most

Valve float is an adverse which occurs when the valves on an internal combustion valvetrain do not remain in contact the camshaft lobe during the closure phase of the cam lobe This reduces engine and performance and potentially increases emissions.

Valve bounce is a condition where the valve not stay seated, due to the combined of the valve’s inertia and resonance of metallic valve springs effectively reduce the closing and allow the valve to re-open

Desmodromic valve drive was justified by claims that could not close valves at high speed and that the caused by suitably strong exceeded what cams withstand. Since then, float was analyzed and found to be largely by resonance in valve that generated oscillating waves among spring

High speed photography that at specific resonant valve springs were no making contact at one or both leaving the valve floating crashing into the cam on closure.

For reason as many as three valve springs, press fit each other, were used, not for more force inner ones having no spring constant), but to act as snubbers to oscillations in the outer spring.

Stiffer valve springs can prevent valve float and bounce, but only at the expense of friction losses. Various have been used to the effect of stiffer springs, as dual-spring and progressive-sprung valves, tappets, and pneumatic valves in One.

Less obvious effects is that valve typically weigh as much as the which they actuate, mean the total mass needs to be moved by the actuation (belt, bearings, shafts) need to be larger in order to fatigue failures. The combined of the mechanism and the energy needed to the spring forces and added forces means that a fraction of the engine’s available output is being used for actuation.

If in a racing application a normal spring engine had an upper rpm of about 10,000 rpm, same engine design equipped with a Desmodromic system would be capable of rpm, and much more

Ducati Apollo v4
Ducati Apollo v4

While the desmodromic system is not the ideal in a practical world of it still survives and performs problem to this day. it can be more expensive to maintain traditional spring actuated systems, there are many precision machined components can extend the maintenance interval to of the almost magical spring systems in comparable engines.

In traditional spring valve as engine speed increases, the of the valvetrain overcomes the spring’s to close the valve completely the piston reaches Top Dead This can lead to several First, and most catastrophic, the will collide with the and thus damage it permanently.

the valve will not completely to its seat before combustion This allows cylinder and pressure to escape prematurely, causes a major decrease in performance and can cause the valve to possibly causing warping or valve failure or both. In spring engines the traditional for valve float is explained

The desmodromic system avoids problem, because although it has to against the directional energy of the opening and closing, it does not to overcome the static energy of the Anyway, in desmodromic valve there is a small spring. The are only necessary to take up the system slack.

Italian motorcycle manufacturer uses the desmodromic (springless) system to counter this and allow for higher engine The system consists of a mechanical mechanism that uses a rocker arm to push the valve Formula 1 engine manufacturers use a system to close the valves to for very high RPM without float.

The main benefit of the system is the prevention of valve and that there are no heavy robbing springs used to the valves, better protection for the if it is over revved, and better and/or overall efficiency.

The disadvantage of the Desmodromic valve is its complexity and cost. And while the efficiency possible in a Desmodromic can not be achieved in current applications main advantage, greater output, can be achieved at less by using four or more per cylinder.

Ducati Apollo v4
Ducati Apollo v4

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