Ducati - the one brand for best in class motorcycles has a special place in hearts among bike lovers and racers. Unlike when compared to other brands, Ducati bikes are always sportier and has superior distinct performance. This unique performance is due to a completely new approach and design of engine, its components and the framework of the motorcycle. I think that's the reason behind for its ultimate performance and also its cost against other superbikes. The Ducati is the only bike in market and in MotoGP championships to be equipped with a 4 cylinder V-twin type engine using a different valve train . The other competitors like Yamaha, Suzuki and Honda employ a 4 cylinder inline type engine in all their superbikes. Plus the Ducati's engines uses its own patented valve system called as desmodromic valve system which is responsible in part for its spectacular performance.
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| Ducati's desmodromic valve system |
In human heart, the valves of heart control the flow of blood and is responsible for the efficient pumping of blood all over the body. Likewise in an engine - the heart of every automobile has valves to control the flow of air/fuel and exhaust gases. If the valves fail the entire engine gets failed. Ducati's unique valve operating system powers up its engine to get unmatched performance. The conventional engine valves uses a cam lobe and valve spring mechanism for opening and closure of valves.
The conventional system uses a rocker arm with a push rod, and a timing chain,belt or direct drive through gears in case of OHC engines connected with camshaft to open and close the valves. During operation of engine the mechanisms mentioned above pushes the valve springs to open the valves. The closure of the valves are carried out by a valve spring which returns the valve back to its original position.
This valve mechanism is a conventional one where even the new variable valve timing technology (VVT-i) shares the same base with slight modification in varying the size of cam lobes dynamically.
The key difference of valve mechanism of Ducati from those of other conventional systems is the absence valve springs. Both the opening and closure of valves are controlled by camlobes and leverage system. The conventional valve systems are ideal under standard conditions and its possibility of failure is high if the engine is operating at more than 12k RPM's which is more than 100 cycles per second. In Ducati's desmodromic valve system the valve timings are perfectly maintained as both opening and closing of valves are directly controlled without any usage of valve springs.
Desmodromic valves have two cams and two actuators each for opening and closing without any return spring. The main benefit of the desmodromic system is the prevention of valve float at high rpm's. MotoGP bikes may have RPM's upto 18K.
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| Desmodromic poppet valve in Ducati engine |
In traditional sprung-valve actuation, as engine speed increases, the momentum of the valve will eventually overcome the spring's ability to close it completely before the piston reaches TDC (Top Dead Centre). This can lead to several problems. First, and most damaging, the piston collides with the valve and both are destroyed. Second, the valve does not completely return to its seat before combustion begins.
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| Ducati Desmosedici RR using desmodromic valve system |
This allows combustion gases to escape prematurely, leading to a reduction in cylinder pressure which causes a major decrease in engine performance. This can also overheat the valve, possibly warping it and leading to catastrophic failure. In sprung-valve engines the traditional remedy for valve float is to stiffen the springs. The desmodromic valve system resolves all the above issues.