Analysis of Rotational Vibration Mechanism of Camshaft at High Engine Speed in Engines with In-line Four-cylinder DOHC Configuration 2018-32-0072
Engines applied to super sports category motorcycles usually require high output and light weight. To achieve both of them, optimization of engine parts design, keeping durability in mind, is important. One such part is the cam chain. Particularly, in an in-line four-cylinder DOHC type engine, which is widely adopted to motorcycles in this category, when it runs at a high-speed revolution region, where the engine revolution speed is 10,000 rpm or higher, the rotation speed of the camshaft greatly fluctuates in the cycle of fourth-order per one revolution of the crank, and the cam chain tension increases. For this reason, it is particularly difficult to design. In this study, the mechanism of this phenomenon which are generated in the high-speed rotation region of the in-line four-cylinder DOHC engine, were analyzed by simulation. The analysis was conducted not only for the valve train but also for overall engine. As a result, it became clear that the vibration of the fourth order cycle and the increase of the cam chain tension arise from the resonance of the spring mass system, in which the cam chain works as a spring and the moment of inertia of the cam shaft acts as a mass. The resonance of the fourth order cycle was excited by the crank torque fluctuations of the second order cycle caused by the reciprocating motion of the piston, in addition to the cam torque fluctuations of the fourth order cycle.. A resonance with a different cycle of excitation force does not occur in a linear vibration system. However, this study revealed that the crank torque fluctuation of the second-order cycle also works as the excitation force of the resonance of the fourth-order cycle, due to the nonlinearity of the cam chain tension rigidity caused by the deformations of the chain guide.
Honda R&D Co., Ltd.
SAE/JSAE Small Engine Technology Conference