Development of a Motorcycle Engine with a Three-dimensional Cam for Continuous Variable Valve Lift and Timing Mechanism

From the viewpoint of protection of the global environment, reduction of CO₂ emissions are high-priority issues for vehicles, along with the demand for increased power performance. One of the more popular technological developments that can help to resolve such incompatible characteristics is the variable valve lift mechanism. Among them, the three-dimensional cam for continuous variable valve lift and timing mechanism has been developed as a technology applicable to motorcycles, because of its small, compact layout and capability of running under high speed engine conditions. The 3-D cam is provided with numerous cam profiles set in an orderly manner and forming a three dimensional map and at points making contact with a spherical roller tappet. An accelerator actuator slides the cam along the camshaft to continuously vary the power output from idling to maximum. Besides the above advantages, the 3-Dcam engine has the following positive characteristics: (1) By simply moving the position of the 3-D cam on the camshaft, the valve timing as well as the valve lift and event are changed simultaneously, thus removing the need of any Variable Valve Timing system. (2) It is possible to obtain the most suitable cam profile, including the cam ramp design, for each valve lift. To make the intake and exhaust valves simultaneously variable contributes to obtaining the optimum valve lifts and timings under all running conditions. (3) The lightweight inertia and the high stiffness of the valve trains can allow running under high speed engine conditions more than 10000rpm. (4) By adopting roller tappets any mechanical loss of valve trains is reduced in comparison with a conventional engine.