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					MECH 375 Machine Design


         Steam Engine Project
  • Department Discussions / Brainstorming Of
    The Steam Engine Development Program
      – Using The Interface Check List To Start The
        Abstraction Phase Of Design

  • Kinematics Analysis Of Piston Engines

  • Thermodynamics Of Piston Expander
    Engines
 MECH 375 Machine Design

         Development Using
       The Interface Check List
• Basic Sketch                   • Allocate Tolerances
• Develop Math Model             • Assembly Process
   – Describe System Physics
   – Preliminary Structural
                                 • Component Selection
     Requirements                • Modeling Flow Chart
   – Preliminary Design Intent
                                   / Model Parts
   – Structural Analysis
• Identify Interfaces
                                 • Final Tolerance
                                   Check At Each
                                   Interface
 MECH 375 Machine Design


                      Design Intent
• What is Design intent for a crank and slider?
• Turn translation energy exerted by steam on piston into
  rotation energy / motion on the crankshaft.

        Crank Shaft            Clearance
MECH 375 Machine Design

Basic Crank And Slider Design
                          Side View


                                               Bore




  ½ Stroke                            Stroke
MECH 375 Machine Design


Basic Crank And Slider Design
                          Top View
                                     Clearance
  Crank Shaft
 MECH 375 Machine Design


                Basic Sketch Of Motor
• No porting                                 Rear bearing

• No mounting harware
     Crank shaft     Forward bearing               Connecting rod

Crank support

                                              Cylinder Block



Rear crank                                                      Cylinder head
case




                                       Side View               Piston pin
MECH 375 Machine Design


        Basic Sketch Of Motor
• How Do We Describe The Physics Of Operation?
• How Much Power Will It Make With R&D’s Steam
  Source?




                                      Inlet Port

                                      Exhaust
                                      Port



                          Side View
MECH 375 Machine Design



    Requirements For Engines
• The Engines Must Use Standard Bearings
  – McMaster Car
• Piston Clearance Volume Between 2-5% Of
  Max Cylinder Volume
  – Piston Area x Stroke = Max Cylinder Volume
  – Clearance Volume = .02 x Max Cylinder Volume
• Other Tolerances To Be Discussed In
  Department Meetings
MECH 375 Machine Design

 Basic Piston Expander Design
                          Rear View


                                      Bore




  ½ Stroke

  Basic Kinematics
  Linkage
MECH 375 Machine Design

     Piston Engine Kinematics
                          Rod length l


  ½ Stroke r       θ            φ



                           x
MECH 375 Machine Design

           Power Transmission
             FBD Of Piston
                  Fp



  F Side



              φ

                       F Rod
MECH 375 Machine Design



     Shaft Torque From Piston
                              F perp
                                       F Rod

                                  φ
                          θ

                    φ         θ

                                               F Rod

                                                       Fpiston


                                   F Side

                                                          F perp
MECH 375 Machine Design

How Do We Evaluate Cylinder
 Pressure To Obtain Power?
• Thermodynamics Portion Of The Analysis
• Need To Make Some Basic Simplifying
  Assumptions:
  – Consider The Cylinder The Control Volume
  – First Pass Assume No Heat Transfer
      • Adiabatic – No Heat Transfer
      • Reversible Process - Isentropic
      • Simple Valve Operation
MECH 375 Machine Design



     Thermodynamic Analysis
• Assuming A Closed Adiabatic System:
  – Ideal Gas Behavior
  – Simple Valve Operation
MECH 375 Machine Design

    Engine Thermodynamics
What’s Happening In The Cylinder?
           2       3              1 Intake Opens
                                  2 Top Dead Center
                                  3 Intake Closes
Cylinder                          3-4 Adiabatic Expansion
Pressure
                                  4 Exhaust Opens
                                  5 Bottom Dead Center
                                  6 Exhaust Closes
           1                          4
               6
                                          5

                       Cylinder
                       Volume
MECH 375 Machine Design



                   Next Steps
• Utilize The Kinematics and Thermodynamics
  To Complete Simulation Provided On Web Site
• Simulation Will Evaluate:
  – Output Torque
  – Component Loading
  – Cylinder Pressures and Temperatures
• Utilize Component Loading In Stress Analysis
  Of Various Parts
MECH 375 Machine Design



             Simulation Inputs
• The R&D Department Has Refined The
  Steam Generator To Produce 500 psi
  Steam At 400 ºF.
• Utilize These Inputs For Your Engine
  Performance Predictions
• Vary Valve Port Timing To Try To
  Optimize Output Power / Efficiency.
MECH 375 Machine Design

      Interfaces Of The Motor
• What Is The Design Intent Of The Interfaces?
• What Information Will The Simulation Provide
  Regarding Interfaces?
• What Information Regarding Component
  Loading?


                                      Inlet Port

                                      Exhaust
                                      Port



                          Side View
MECH 375 Machine Design

    To Establish Fits, Evaluate
    Requirements For Engines
• The Engine Must Be Capable Of 5,000
  RPM and 10Hp
  – Indicates Requirements For Bearings
  – Indicates Loose Running Clearance Needed
    For Slider Due To High RPM’s
  – Indicates High Level Of Positional / Location
    Accuracy Needed In Mating Parts
MECH 375 Machine Design



      Motor Assembly Process
• Two Sub-Assemblies Are Put Together
  Prior To Final Assembly
  – Forward Crank Support Sub-Assembly
  – Piston And Rod Sub-Assembly
• All Sub-Assemblies Will Require Separate
  Sub-Assembly Drawings
• This Will Drive The Family Tree
MECH 375 Machine Design



   Assemblies / Family Tree’s
• Assemblies And Sub Assemblies Should
  Reflect The Assembly Process
• The Lower Level Parts Should Reflect The
  Assembly They Are Used On
• The Family Tree Is A Graphical
  Representation Of The Parts Used In The
  Assembly And How They Are Assembled
MECH 375 Machine Design

     Requirements For Engines:
           Engine Parts
1.   Crank Shaft          8. Forward Bearing
2.   Connecting Rod       9. Rear Bearing
3.   Piston               10. Cylinder Head
4.   Piston Pin           11. Cylinder Head
5.   Cylinder Block           Gasket
6.   Crank Support        12. Screw Size 1
7.   Rear Crank Case      13. Screw Size 2
MECH 375 Machine Design


                  Family Tree
 MECH 375 Machine Design

         Design Documentation
• Each Designer Will Develop An Engineering Notebook
• The Notebook Will At Minimum Contain:
   – System Requirements
       • Functional Requirements
       • System Simulation And Power Predictions
   – Assembly Section
       • Sketches
       • Interface Check List
       • Tolerance Analysis Of Each Interface
   – Separate Section For Each Part
       • Detailed Sketches
       • Tolerance Allocations
       • Structural Analysis
MECH 375 Machine Design



           Parts Development
• Utilize The Simulation For General Sizing
  Of Components Using The Materials
  Specified In The Interface Work Sheet.
• Flow Charts Of The Parts Are A MUST!
• Flow Charts Should Be Developed With
  An Eye Toward Assembly And Future
  Modifications.