Influence of the hydraulic fluid pipe on the dynamic stability of a shift gearbox

Abstract

AbstractShift gearboxes are used in vehicle drive trains in order to transmit the driving torque of the motor and to shift between different transmission ratios. Because of the occurrence of sliding friction forces and ‐torques during the shifting period, unwanted vibrations can arise. Several mechanisms which lead to a destabilization of the stationary state in shift gearboxes are conceivable: variable friction coefficient [1], wobbling clutch disc [2], or vibrations because of coupled DoFs due to the helical gearing [3].The latter effect results in translational oscillations in axial and radial direction of the clutch disc. It was observed that damping forces influence the boundary of the region of stability in the parameter space ‐ though it is not entirely clear where such forces originate from. For this reason, in this work the effect of the fluid of the hydraulic actuation of the clutch system is analyzed. The fluid pipe is situated in the center of the gear unit input shaft and forces the fluid to oscillate when the system becomes unstable. In return, the fluid implies shear stress and pressure on the adjacent mechanical parts (shaft, pressure plates). The analysis of the stationary state of the coupled system reveals a clear effect of fluid properties on the stability: both the mass density and the kinematic viscosity are able to change the location of the border between stable and instable regions in the parameter space. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)