Ducati Testastretta DVT (Desmodromic Variable Timing)
DUCATI has announced what it says is the first ever motorcycle engine with variable timing of both the intake and exhaust camshafts.
Named the Testastretta DVT (Desmodromic Variable Timing), Ducati say that this new Desmodromic engine will "lead the way for a whole new generation of such engines" and that "the innovative new design overcomes an engineering gap in current production motorcycle engines and underlines Ducati's strength in developing ground-breaking engine and motorcycle technologies".
The variable timing system is able to continuously adjust valve timing by acting independently on both the intake and exhaust camshafts. The system is said to optimise engine performance throughout the rev range, in any operating condition, to guarantee the highest power, smooth delivery, reduced fuel consumption and "muscular torque at low rpm".
With full Euro 4 compliance, Ducati say that DVT "sets a new standard in the combination of power, delivery and usability of motorcycle engines". With a bore of 106 mm, 67.9 mm stroke and the 1,198 cm³, the engine is said to be good for maximum power of 160 hp at 9,500 rpm and maximum torque of 136 Nm at 7,500 rpm
With "Desmodromic distribution", Dual Spark (DS) ignition and anti-knock sensor, this new generation of Euro 4 compliant engineering "independently adjusts both the timing of the camshaft controlling the intake valves, and the timing of the camshaft controlling the exhaust valves, optimising high rpm performance for maximum power, while, at medium and low rpm, it ensures smooth operation, fluid power delivery and high torque. "This means that the vehicle's engine will adapt its characteristics according to rpm values, while always ensuring compliance with exhaust emission standards and keeping fuel consumption low".
Ducati go on to say that "when any new engine is designed, one of the most critical parameters to determining 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 Ducati Testastretta DVT’s overlap angles can change, thanks to the introduction of the DVT (Desmodromic Variable Timing) system - 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 regard 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".
Ducati say that the 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".
This system is used in all Ducati models, and has been extremely successful in World
Superbike MotoGP motorcycles. Ducati say that "in the development of the DVT, the Desmodromic valve train represents a major advantage over a traditional spring based timing system - the actuation of the valves at low engine speed requires less force, not having to compress the valve springs, which allowed us to limit the size of each cam phaser with obvious benefits in terms of lightweight construction and compactness for a perfect engine integration".
Despite the increase in power Ducati say that the DVT system "has a positive impact on fuel efficiency, with an average 8% reduction in fuel consumption compared to the previous non-variable configuration". Ducati has repositioned the fuel injectors to target their spray directly onto the rear of the hot intake valve, instead of the colder surface of the intake port wall. The resulting enhanced fuel vaporisation is said to improve combustion efficiency and ensure a smoother delivery.
In order to achieve a smoother cycle-to-cycle engine operation, Ducati say they have used a secondary air system, similar to that developed for extremely high-performance engines. This optimises combustion without increasing emissions, by completing the oxidisation of unburnt hydrocarbons to reduce HC and CO levels.
Ducati say that the DVT system does not affect the valve clearance adjustment schedule, and, in fact, only requires major services at the same 30,000 km intervals as their existing designs
www.ducati.com
