SOLID MECHANICS TUTORIAL – FRICTION （固体力学教程-摩擦）.pdfVIP

SOLID MECHANICS TUTORIAL – FRICTION CLUTCHES This work covers elements of the syllabus for the Edexcel module 21722P HNC/D Mechanical Principles OUTCOME 3.2 On completion of this short tutorial you should be able to do the following. • Describe a conical and a flat plate clutch. • Describe a multiplate clutch. • Explain the constant wear theory. • Explain the constant pressure theory. • Solve problems involving power transmission with clutches. It is assumed that the student is already familiar with the following concepts. • Friction theory. • Angular motion. • Power transmission by a shaft. • Basic integral calculus. All these above may be found in the pre-requisite tutorials. © D.J.DUNN 1 FRICTION CLUTCHES 1. INTRODUCTION First lets revise the basics of dry friction. Consider a small block sliding over a surface. The force pressing the two surfaces together is R (the normal force). When the surfaces slip, the force F required to produce movement is equal and opposite of the friction force between the surfaces. F and R are related by Coulomb’s Law of Friction. F = µR where µ is the coefficient of friction. Figure 1 2. WEAR THEORY Research has shown that the wear between two rubbing surfaces depends upon the pressure between the surfaces and the speed at which they rub. There are two theories concerning the torque required to produce slip between the surfaces of a clutch. One theory assumes the pressure is even over the surface of contact in which case the wear is greater at the outside