Modeling Mechanical Systems using Virtual Test Bed

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Modeling Mechanical Systems using Virtual Test Bed

• Department of Mechanical Engineering
• Advanced Actuators Research Group
• Thomas Brewer
• Daniel Sloope
• Dr. David Rocheleau

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Mechanical Modeling in VTB

• VTB can be used to model mechanical systems.
  Equivalent electro-mechanical systemsboth linear
  and rotationalcan be described using VTBs
  across and through variables.

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Internal Combustion Engine (ICE) Valve Train
Modeling using VTB

• A new camless engine is being design in
  conjunction with AARG, Siemens, and Honda.
• A model was built to show valve train component
  position, velocity, and acceleration.
• Below are schematics of the valve train and the
  model in VTB.

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Cam Model

• A Cam Profile Model had to be created for the
  input for the Valve Train Model. The profile
  needed a lift of 10 mm and a duration of 270º.
• A Fourier Series Approximation was written and
  plotted in MathCAD and the first and second
  derivative were graphed. Below are the MathCAD
  plots for input position, velocity, and
  acceleration.

• Since the valve train components are nearly
  rigid, the outputs of the model should look very
  similar to these graphs.

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Model Outputs

• Again, the components of the valve train are
  nearly rigid therefore, the model depends
  greatly upon the rocker arm lever ratio.
• In this model the ratio is 3 to 2.
• Below are the VTB model results.

Input Position
Input Velocity
Input Acceleration
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Work to date

• The cam model produced the right lift and
  duration period.
• The valve train model produced predicted results.
  The position, velocity and acceleration of the
  valve were two-thirds that of the input (since
  the lever ratio was 3 to 2).

Additional work

• Model each valve train component of a Honda GX31
  engine in ProEngineer.
• Use ProMechanica to compute the moment of inertia
  of each component.
• Calculate accurate spring and damping
  coefficients.
• Verify the models results against the GX31
  running at different speeds.

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Passive and Active Automotive Suspension
Modelingusing VTB

• Importance
• Comfort
• Handling
• Widely Varied Suspension Types and Vehicle
  Properties
• Varied Constants and Dynamics
• VTB allows easy modeling of many suspension types
  with many different vehicles.

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Vehicle Dynamics
Movement around Center of Gravity
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Suspension Components
Suspension
Tire
Acts as a Spring-Mass-Damper
Springs and Dampers Most Common Suspension Type
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Quarter Car Suspension

• Quarter Car models one-fourth of a automobile
  suspension.
• Only Captures Vertical Movement.

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Half Car Suspension

• Incorporates Two Quarter Car models connected
  with a Beam.
• Allows modeling of pitch as well as body position.

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Full Car Suspension

• Advantages
• Captures all of the motions of a real vehicle
• Pitch and Roll can be evaluated simultaneously
  with vertical compliance
• Disadvantages
• Existing Full-Car Models are expensive
• New Models are difficult to develop

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Passive Suspension Model

• Full Car Model using Springs and Dampers.
• Traditional automotive suspension system.

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Fully Active Linear Motor,California Linear
Devices

• Can be incorporated into a vehicle suspension
  system.
• Low Time Constant 15 ms
• Simple Control
• Increased current Increased force
• Reasonable Max Force 1125 lbs

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Active Suspension VTB Model

• Utilizes mechanical actuators in place of Springs
  and Dampers.
• Control System developed by E.M. ElBeheiry.
• Improves both comfort of ride and vehicle
  handling.

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Results
Active Suspension
Passive Suspension
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Future Work

• Model verification vs. Physical system
• Measure response of actual vehicle
• Compare with models predicted response

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Acknowledgements

• Dr. Eugene Solodovnik, Research Associate, USC
  Electrical Engineering.
• Dr. Sarah Baxter, Associate Professor, USC
  Mechanical Engineering.
• Eric Vilar, Ph.D. Candidate, USC Electrical
  Engineering.