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© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Dynamic Simulation: Piston Assembly Example Objective  The objective of this module is to show how an example problem is solved using the Dynamic Simulation environment within Autodesk Inventor software.  This kinematic analysis problem involves imposing a rotational motion on the rotating assembly of a boxer style engine.  The Output Grapher is used to plot computed moments, displacements, velocities, and accelerations.  Friction in a prismatic joint is also illustrated.

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Components Pistons x 4 Connecting rods and piston pin bearing assemblies x 4 Crank Shaft Crankshaft Bearings x 3 Cylinder Liner x 4 Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 2

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Sub-assemblies  The connecting rod components and the piston components were modeled as sub-assemblies.  This will cause Inventor and Dynamic Simulation to treat them as rigid bodies with no relative motion between the sub-assembly parts. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 3 Connecting Rod Assembly Piston Assembly

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Ground Joints The cylinder liners and crankshaft bearings are fixed in the engine block and cannot move. They were positioned using the cylinder block and then grounded in Inventor. The ground is carried over into Dynamic Simulation. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 4

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Revolute Joint A mate is placed between the centerline of the crankshaft and the centerline of the crankshaft bearing. This constraint will be converted to a revolute joint in Dynamic Simulation. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 5

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Axial Crankshaft Constraint  A mate is placed between the two surfaces shown to position the crankshaft along the axis of the engine.  This constraint removes the translation DOF between the crankshaft and bearings.  A 2mm offset is required. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 6

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Revolute Joints Mates are placed between the centerlines of the piston bearings and the crankshaft journals. These will automatically be converted to revolute joints by Dynamic Simulation. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 7 Crankshaft Journals

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Axial Constraint  A mate is placed between the machined connecting rod surface and the face of the crankshaft journal.  This removes the translational DOF between the connecting rod assembly and the crankshaft.  This constraint is applied to each connecting rod assembly. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 8 Crankshaft journal face Machined connecting rod surface

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Revolute Joints In a manner similar to the other revolute joints, centerline mates are placed between the pistons and the connecting rod assemblies. This is called “Joint 1” in Module 3. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 9

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Assembly Constraints Prismatic Joints The final set of constraints is between the cylinder liners and the pistons. Centerline mates are again used. The centerline constraints will allow translational motion of the piston along the axis of the cylinder liner. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 10

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Completed Assembly The complete assembly is shown in the figure. The crankshaft can be rotated and all other parts move in accordance to the assembly constraints. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 11

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Dynamic Simulation Environment Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 12

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Dynamic Simulation Environment 4 Grounded Cylinder Liners 3 Grounded Crank Bearings (one bearing has two parts) Crankshaft 4 Piston Assemblies 4 Connecting Rod Assemblies Kinematic constraints are automatically generated by Dynamic Simulation from the assembly constraints. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 13

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Mobility  The mobility of the mechanism is checked using the Mechanism Status feature on the ribbon.  The mechanism has a mobility of one as expected.  The free DOF is the rotational DOF of the crankshaft. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 14

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Motion Groups The parts that can move are shown in a solid color. The parts that cannot move are shown in transparent mode. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 15

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Motion Constraint Right click on properties for Revolution Joint 1  A mobility of one requires that one motion constraint be specified.  A rotational velocity of 3600 deg/sec is applied to the crankshaft rotational degree of freedom.  This is equivalent to 600 rpm. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 16

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Input Motion As a check, the computed angular velocity is constant and is 3,600 deg/sec which agrees with the input angular velocity. Velocity Acceleration Position The angular position of the crank shaft should be a linear function of time with a slope of 3,600 deg/sec. The computed position is correct. The angular acceleration of the crank shaft should be zero since the velocity is a constant. The computed acceleration is correct. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 17

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Input Torque The computed torque that is required to impose a constant angular velocity of 3,600 deg/sec on the crankshaft is shown in the Output Grapher plot. Notice that the input torque is sinusoidal. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 18

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Input Torque  Positive values of the torque mean that energy is being put into the system so that the constant crankshaft angular velocity is maintained.  Negative values of the torque mean that energy is being taken out of the system so that the constant crankshaft angular velocity is maintained.  Since there is no friction in the system the net energy required to maintain a constant angular velocity of the crankshaft is zero.  The average torque is zero which indicates that the average input power is zero. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 19

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Friction Friction can be added by editing the properties of a joint. In this case we are adding a coefficient of friction of 0.2 to the translational degree of freedom of the prismatic joint between the piston and cylinder liner. Friction is added to all joints using this approach. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 20 The properties dialog box is obtained by right clicking on the joint.

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Input Torque with Friction The addition of a coefficient of friction of 0.2 increased the average torque from zero to 491 Nm. The input power required to overcome the friction in the system is Max = 6,267 Nm Min = -5,776 Nm Average = 491 Nm Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 21

© 2011 Autodesk Freely licensed for use by educational institutions. Reuse and changes require a note indicating that content has been modified from the original, and must attribute source content to Autodesk. www.autodesk.com/edcommunity Education Community Module Summary  This module provided an example of how to perform a dynamic simulation of a mechanism using Autodesk Inventor’s Dynamic Simulation environment.  This kinematic analysis problem involved imposing a rotational motion on the rotating assembly of a boxer style engine.  Correlations were made between the theory presented in previous modules and this example.  Although the mathematics is hidden from the user, the input information associated with joints and constraints can clearly be seen in the user interface. Section 4 – Dynamic Simulation Module 5 - Piston Assembly Example Page 22

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