Vehicle handling and control, Other Engineering

Your objective in this lab is to convince the assessor that you understand the basic concepts of how shock absorbers affect the ride and handling of a vehicle.  This will involve discussion of your understanding of the competing demands of ride quality and outright vehicle performance, and application of this knowledge to what you observe during this experiment.  Your report should be concise and informative.

Your report should be professional presented in a formal lab report layout, and include:

  • Cover Page
  • Abstract (summary of report findings)
  • Introduction
    • Objectives
    • Background theory, including:
      • How shock absorber works
      • How shock absorber dyno works
    • Methodology (doesn't need to be too involved, just basic info on what dyno and damper we used and what test data we collected, and the difference between PVP and CVP data)
  • Test results
  • Discussion
  • Conclusion

In your report, you should address the following (in no particular order):

  1. Discuss the need for different rates of damping at low and high speeds, and in compression and rebound
  2. Discuss the difference between "ride" and "handling", and identify whether they might correlate to low or high speed damping.
  3. Discuss how dampers contribute to vehicle control through the various stages of a typical cornering maneouevre
    1. Travelling down a straight
    2. Braking into a corner
    3. Turning into the corner
    4. Constant speed steady state mid corner
    5. Turning out of the corner
    6. Accelerating down the next straight
  4. Discuss the construction of a typical monotube shock absorber, and explain how different damping rates (compression and rebound, low and high speed) are achieved.  Don't forget to acknowledge any references you may use....
  5. Discuss the construction of a typical twin-tube damper, how it varies from a monotube damper, and what the relative advantages and disadvantages are of each design.   
  6. Discuss the importance of the high pressure gas chamber built into the damper tested in this experiment. With reference to your damper force vs. velocity plot, what effect does the chamber have on the performance of and damper and why?  Why do we need the gas chamber in the first place?
  7. Cavitation is a condition which must be avoided within a damper. Explain under what circumstances this may occur and how it can be avoided.
  8. Using your own knowledge, estimate and justify a typical range of shock speeds (in both Hz and mm/sec) in a typical Formula SAE vehicle that would represent
    1. Low speed damping
    2. High speed damping

To justify the above you may should consider the full range of suspension travel for a Formula SAE vehicle (25mm bump to 25mm droop = 50mm of travel total).  From this, estimate typical shaft speeds that the damper might see in body roll and over road bumps, etc.  Assume a wheel-to-damper motion ratio of 1:1 - i.e.1mm wheel travel = 1mm shock travel

  1. For the tested Penske twin-tube damper, plot resistance force against shaft speed for a reasonable range of speeds for this damper
    1. Speeds will be determined in the lab, in accordance with estimated shaft speeds encountered in a Formula SAE application
  2. On the plotted force vs velocity curves, identify any notable changes in damping coefficient that may represent a change from low speed to high speed damping regimes
  3. Calculate values for damping coefficients of this damper (low and high speed, rebound and compression).  Does the damper exhibit a noticeable "knee" in the damping curve, indicating transition from low to high speed damping?  Does the knee occur at a speed that agrees with your estimation of where low and high speed damping should be separated?
  4. Comment on whether these calculated damping values agree with the requirements you discussed in point 1 above.
  5. For the RMIT FSAE vehicle that these dampers were purchased for:
    1. Estimate the undamped sprung mass natural frequency of the front and rear suspension, (single DOF 1/8 car model)
    2. Using a reasonable value for the average damping of the tested shock absorber, calculate the critical damping ratio and damped sprung mass natural frequency of the front and rear suspension of this vehicle if fitted with this shock absorber
Posted Date: 3/6/2013 4:58:45 AM | Location : United States

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