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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.

Engine oil combined with SPZn instead of ZnDTP shows excellent total base number (TBN) retention in oxidation and NOx gas bubbling tests. The wear resistance of engine oil combined with SPZn was similar to oil combined with ZnDTP in a four-ball test. Prototype engine oils with 1.0 wt% of sulfated ash and 0.04wt%-0.09wt% of SPZn-derived phosphorus were prepared and a JASO valve train wear test was performed on them. The wear resistance of engine oil including SPZn with P = 0.09 wt% was greater than that of engine oil including ZnDTP. This result shows the possibility of reduce the phosphorus in engine oil by using SPZn.

Since the intake and exhaust valve timings that provide the best fuel economy, idle stability, or highest power change according to the engine operating zone, a variable valve timing system is very beneficial. Also, roller followers, which reduce mechanical friction loss of a valve train mainly at low engine speed, are commonly used to improve fuel economy in urban driving conditions. This paper presents a newly developed 4-valve variable-valve-timing mechanism with roller followers. Different intake- and exhaust-valve timings and lifts are selected independently, depending upon whether engine speed is low or high. Durability tests of running at maximum engine speed and switching between low- and high-speed cams were conducted and good test results were obtained.