טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDvorjetski Meiri
SubjectDesign of Unidirectional Clutch
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Itzhak Porat


Abstract

The subject of this research issue is the ratchet & pawl type unidirectional clutch. This clutch rectifies mechanical vibrations in a way that the pulling of the driven shaft is being made by a pawl swiveled to the drive shaft.

An original analytical model was first developed for this type of clutch. The model proposes that the mechanism changes its number of degrees of freedom throughout its movement. The mechanism has four different kinematic stages, which differ in the number of their degrees of freedom. The dominating kinematic constraints at each specific stage were developed as well as the conditions for switching/transferring from one stage to another. A comprehensive algorithm for the whole transfer operation is proposed.

The dynamic equations, which describe every stage of the mechanism’s movement, were developed. The dynamic model of the mechanism includes a pawl and a ratchet with mass, a column friction model between the pawl and the ratchet, gravity and a load moment on the ratchet. The dynamic equations were written using the Newton-Euler method. In this method the internal contact forces are easily taken care of.

A computer program was written that solves the differential equations and runs the transfer algorithm.

A systematic examination was performed of parameters that have been found as dominant or have some other of interest. Prior to the parametric investigation other results were examined: time utilization by mechanism - at each stage, the use of teeth - a per teeth examination, periodicity by tooth map, the evolution of internal forces. The following parameters were investigated for their influence on the mechanism: number of teeth in the ratchet, drive shaft frequency, drive shaft amplitude, load moment on ratchet and teeth height in the ratchet.