Autoliv - Realistic Knee Airbag Linear Impact Fixture

Team: Ryan Kendall, Ezra Kennedy, Derek Lee, and Cam Slade

Sponsor: Autoliv

Project Description

Autoliv uses linear impact testing as a cheaper and faster means of testing airbags.

  • The current linear impact test doesn’t reflect reality as well as some of the other more complicated tests, such as the sled test. The goal is to define a new set of kneeforms that are as easy to use in testing, but better reflect the reality of legs in a car crash.

Requirements/Constraints:

  • The kneeforms must be able to be set up by one technician.
  • They must represent the size and mass of an AM50 Dummy.
  • They must hold up to repeated use.
  • They must attach and work with Autoliv’s existing testing setup.

Design Description

The design consists of four main subassemblies.

  • The hinge pivots the kneeforms to allow for a more realistic range of motion.
  • The breakaway prevents rotation upon initial acceleration.
  • The shock absorbers and hard stops soften the impact.
  • And the Ratchet arm keeps the knees from swinging around after impact.
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Performance Review

Analyses performed:

  • Ball Bearing Cycles
  • Finite Element Analysis on Supporting Plates
  • Maximum and Desired Angle of Rotation
  • Knee Sizing
  • Mass
  • Shock Absorber
  • Lower Leg Kinematics during Impact.

These Analyses determined that the desired angle of rotation, kneeform size, and correct mass of the kneeforms would be a viable option in a system that held up to repeated tests and better reflected the lower legs in a car crash.

Conclusion

  • The design met all the necessary constraints. The one requirement that it struggles with is the deviation from the sled test. There is a significant spike in the acceleration data when the kneeforms hit the hardstops that is not present in the sled data. Changes have been made to the design to hopefully fix that, but the changes have not yet been tested.
  • There were several lessons learned:
    • The difficulty of designing systems around large impulses. This negated several of our possible designs.
    • The importance of timely communication with ourselves and our sponsor.

Recommended future work:

  • There needs to be more research done into the shock absorbers. Where hydraulic systems add more resistance at high speeds, their exact reaction to hitting the airbag is unknown here.
  • We went too hard and then too soft on the hardstops, a nice in-between rubber is needed.