Desmodromic variable timing explained

Ducati has unveiled its ‘Ducati Testastretta DVT’ system – desmodromic valve timing which will be fitted to the upcoming new addition of the Multistrada adventure bike, complete with Euro 4 compliance.

Ducati claims it’s the first motorcycle engine with variable timing of both the intake and exhaust camshafts, overcoming “an engineering gap in current production motorcycle engines”. The company says it optimises engine performance throughout the rev range and in any operating condition, to guarantee the highest power, smooth delivery, muscular torque at low rpm and reduced fuel consumption.

The Ducati Testastretta DVT engine is 1198cc and produces a claimed 160hp at 9500rpm, and 136Nm at 7500rpm. The torque hits 80Nm at 3500 rpm, and it remains consistently over 10 Nm between 5750-9500rpm. The current non-DVT Multistrada is good for 150hp and 124.5Nm.

DVT is equipped with a dual spark system that uses two spark plugs per cylinder head, providing a twin flame-front that ensures complete combustion across a very short period of time. Each spark plug is managed independently, to optimise efficiency throughout the rev range and in all conditions of use. An anti-knock sensor ensures safe engine operation even while using lower octane fuel or in situations potentially detrimental to combustion efficiency, e.g. at high altitude. In order to achieve a smoother cycle-to-cycle engine operation, Ducati has used a secondary air system similar to that developed for extremely high-performance engines.

DVT does not affect the valve clearance adjustment schedule

HOW DOES DVT WORK?
When a new engine is designed, one of the most critical parameters to determine its 'character' is the amount of intake and exhaust valve overlap. The overlap angle is defined as the interval of crankshaft rotation, expressed in degrees, during which both the intake and exhaust valves are open at the same time. This overlap occurs between the end of the exhaust stroke and the start of the intake stroke and is normally a single value that does not change. However, the Testastretta DVT is not limited by a fixed valve overlap angle.

Instead, the DVT’s overlap angles can change, thanks to a valve timing adjuster fitted to the end of each of the two camshafts per cylinder head. The DVT system consists of an external housing, rigidly connected to the cam belt pulley, and an internal mechanism which is connected to the camshaft and can independently rotate inside the housing. This rotation of the internal mechanism, either in advance or in delay with respect to the housing, is precisely controlled by varying the oil pressure in special chambers of the mechanism. The oil pressure is adjusted by dedicated valves and the timing of each cam is dynamically controlled by a sensor located in the cam covers.

The DVT engine uses the unique valve train that made the Bologna-based Italian manufacturer a world-famous name. Thanks to this unique system, the intake and exhaust valves are closed mechanically and with the same level of accuracy as they are opened. The term Desmodromic derives from the Greek words “desmos=link” and “dromos=stroke, travel”; in mechanical engineering terms, it refers to mechanisms designed to actuate valves both in the opening direction and in the closing direction.

Ducati claims DVT leads to an average eight per cent reduction in fuel consumption compared to the previous non-variable configuration.

The new Multistrada will be unveiled at the 2014 EICMA motorcycle show, which starts in Milan on November 4.