ENGINEERING TRIPOS PART IIA - 2012/2013

Module 3C8 - Machine Design

AIMS

This module is concerned with the design of machines in which the efficient and reliable transmission of mechanical power is a key requirement. The field of application is very wide. The course will focus on two applications: road vehicles and bicycles. Specific areas of study are:

1. Power matching
   To understand how components are combined to make up a mechanical power transmission system, with particular reference to setting the operating point to achieve a desired performance. To apply the principles of power matching to hybrid drives.
2. Mechanics of contacts
   To analyse the contact stresses and kinematical behaviour of solid contacts and to understand the design of rolling element bearings.
3. Gears
   To understand the design of involute gears and to appreciate the stress limits and practical problems of gears. To analyse the behaviour of multiple drives and planetary gears.
4. Rolling element bearings
   To introduce methods for specifying the type and arrangement of rolling element bearings to meet a specified duty.

LECTURE SYLLABUS

1. Power matching (3L) Dr D.J. Cole
   
   • Introduction and applications: automotive transmission, bicycle transmission
   • Sources and loads; devices and their characteristics
   • Power matching using a simple gear ratio
   • Hybrid drives
2. Mechanics of contacts (4L) Prof. J.A. Williams
   
   • Hertzian point contacts
   • Stresses and stiffness
   • Hertzian line contacts
   • Applications in bearings and CVTs
3. Gears (6L) Dr D.J. Cole
   
   • Geometry and kinematics
   • Failure, root bending and contact fatigue
   • Design and applications
   • Multiple drives and planetary gears
   • Design calculations for planetary gears
4. Traction drives (1L) Dr D.J. Cole
   
   • Traction drives (CVTs)
5. Rolling element bearings (2L) Dr D.J. Cole
   
   • Bearing types; life equation
   • Shaft and bearing arrangements

OBJECTIVES

As specific objectives, by the end of the course students should be able to:

1. Power matching
   • Understand how power transmission components are used as part of a system, including hybrid drives.
   • Determine the operating point and calculate the optimum speed ratio for specified conditions.
2. Mechanics of contacts
   
   • Calculate the strength limitations of solid contacts.
   • Analyse the kinematical behaviour of contacts, especially in rotating machinery.
   • Understand and analyse the performance of friction drives.
3. Gears
   
   • Be familiar with the geometry and kinematics of involute wheels and racks.
   • Understand the criterion for tooth bending failure and be able to derive the Hertz pressure at tooth contacts.
   • Use power and torque calculations to analyse epicyclic gears and gear drives.
4. Rolling element bearings
   
   • Select a rolling element bearing for a specific duty.

COURSEWORK

Laboratory experiment on power matching a human to a bicycle. The lab can be written up as a Full Technical Report.

Information on Examples Papers

REFERENCES

Please see the Booklist for Part IIA Courses for references for this module.