A Comprehensive Method for Piston Secondary Dynamics and Piston-Bore Contact 2007-01-1249
Low vibration and noise level in internal combustion engines has become an essential part of the design process. It is well known that the piston assembly can be a major source of engine mechanical friction and cold start noise, if not designed properly. The piston secondary motion and piston-bore contact pattern are critical in piston design because they affect the skirt-to-bore impact force and therefore, how the piston impact excitation energy is damped, transmitted and eventually radiated from the engine structure as noise. An analytical method is presented in this paper for simulating piston secondary dynamics and piston-bore contact for an asymmetric half piston model. The method includes several important physical attributes such as bore distortion effects due to mechanical and thermal deformation, inertia loading, piston barrelity and ovality, piston flexibility and skirt-to-bore clearance. The method accounts for piston kinematics, rigid-body dynamics and flexibility. A time integration algorithm is used based on a modified Newmark-Beta method for nonlinear systems. A contact algorithm using a complementarity method, determines the contact characteristics between the flexible piston and a rigid liner during the engine cycle. Results show the effect of piston design parameters on piston secondary motion and the resulting impact forces, and friction.