MIT2_72s09_lec18

MIT2_72s09_lec18 - MIT OpenCourseWare http://ocw.mit.edu...

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.72 Elements of Mechanical Design Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . 2.72 Elements of Mechanical Design Lecture 1 8 : Friction-based elements Reading and plans Reading: 14.1 14.7 16.2, 16.6, 16.9 Today: Friction-based elements Martin Culpepper, All rights reserved 2 Friction-based machine elements Purpose: Bring two bodies to same relative speed Friction forces do the work Force/Torque and Mass/Inertia are in play Used in many types of ubiquitous machines Drum brakes Disk brakes Clutches etc Martin Culpepper, All rights reserved 3 Clutches www.tech.plymouth.ac.uk/sme/desnotes/clutlabe.jpg Courtesy of David Grieve. Used with permission. Martin Culpepper, All rights reserved 4 Drum brakes Images removed due to copyright restrictions. Please see http://www.carbibles.com/images/drum-double.jpg http://peugeot.mainspot.net/glossary/14_drum_brake_assembly.jpg Can you imagine how much fun it is to put this together What would be problematic? Martin Culpepper, All rights reserved 5 Disk brakes Images courtesy of phaty on flickr and Wikimedia Commons, http://commons.wikimedia.org What are the holes for? Martin Culpepper, All rights reserved 6 Perspective on heat, back of the envelope Assume you need to stop a 2 ton truck: 65 to 0 mph; how much energy must be dissipated as heat/sound? Assuming that this happens so fast that the steel components of the brake absorb the heat (assume little energy goes into sound/vibration) before it is taken away by convection or conduction what max magnitude of T are we looking at? (e.g. worst case) Really need modeling software to do this properly but rough analysis is enlightening Martin Culpepper, All rights reserved 7 Types of actuation Pneumatic/hydraulic (e.g. pistons) High force (hydraulic) Inexpensive (pneumatic) Maintenance (hardware/leaks & fluid)...
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MIT2_72s09_lec18 - MIT OpenCourseWare http://ocw.mit.edu...

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