Tech: Ducati’s DVT explained
Variable valve timing will aid grunt
Ducati’s new Diavel 1260, which we showcased last week, will inherit the firm’s DVT variable valve timing system designed to allow a motor to work at its optimum at both high and low engine speeds.
Why you need it
The dream of every bike manufacturer is to produce a motor that’ll respond well from tickover, drive strongly though the middle of its rev range and then perform properly with a searing top end. However, the laws of physics means that normally only two out of three are possible.
One of the most important things that determine a bike’s 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. Having some valve overlap has advantages, as the delayed closing of the exhaust valve encourages the final remnants of gas to exit the exhaust port. There’s also the advantage of the opening of the intake valve before top dead centre which lets a fresh charge enter, which can help force the exhaust gas to flow out of the exhaust port and replacing it with an additional charge for the following cycle. The more overlap a bike has the more efficient it is at higher rpm. But a long overlap means it’s worse at low rpm as the combustion process is less efficient, and the emissions poorer. But VVT has the potential to stop this and also improves smoothness at low rpm.
How it works
A valve timing adjuster is 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 cambelt pulley and an internal mechanism which is connected to the camshaft and can independently rotate inside the housing. The rotation of the internal mechanism is controlled by varying the oil pressure in special chambers. The oil pressure is adjusted by dedicated valves and the timing of each cam is controlled by a sensor located in the cam covers. This sensor is fed info from the ECU related to gear position, engine speed, load and rpm for the optimum overlap in every riding position. It means the engine’s overlap can constantly vary according to demands. It gives a huge range of adjustment. The 1198 Testastretta V-twin superbike has 41 degrees of valve overlap, while the detuned version of that motor, which is still used in this year’s Diavel, gives 11 degrees, to help with flexibility and midrange. But the Testastretta DVT is not limited by a fixed valve overlap angle. It allows bigger angles of overlap than the 1198 at high rpm for optimum power while at the same time smaller angles than the current Diavel for emissions and low-speed performance. The best of both worlds.