Gear Shift Fork Stiffness Optimisation 2011-01-2235

This paper presents a simulation of the stiffness of the shift fork of a manual transmission using contact pattern analysis and optistrut. All the subsystem (i.e. synchronizer and the shift system component) are constrained to optimize the shift fork stiffness. A-5-speed manual transmission is used as an example to illustrate the simulation, co-relation and validation of the optimization of the gear shift fork stiffness. The shift system was modeled in the software to collate the synchronization force, shift system gap etc with the constraint on the shift fork. It is constrained by the synchronizer sleeve and the fork mounting on the gear shift rail. The synchronizer force is then applied on the gear shift fork pads which are translated to the synchronizer sleeve. It has a number of pads which come into contact at different occasion of the synchronization because of the varying stiffness of the fork. The contact is distributed to optimize the deflection of the fork in the synchronizer for abuse load. The synchronization force is distributed over the pads which are in contact during the synchronization phase. The fork tends to deflect with the synchronizer sleeve during synchronization thus acting as a damper and storing energy. In the free flight zone the energy is released thus providing a positive drop (The derivative function of the detent ramp profile should turn negative) and reducing the double bump i.e. (the force generated when the synchronizer sleeve hits the clutch body ring) during synchronization. It also reduces the fork pre- loading (the gear shift fork is always positively in contact with the synchronizer sleeve after the synchronization has taken place) as the fork is retrieved after synchronization from the sleeve contact. The gear shift lever vibration and gear rattle is also reduces as the shift fork contact from the gear shift sleeve is relieved. Thus the contact analysis and optistrut of the shift fork ensures that the gear shift fork is optimized for stiffness and stress thus aiding in synchronization.