a new and improved occupant compartment for a sled to create safety in a modern fleet of vehicles
Nearly every single vehicle (99%) from 2020 onward is equipped with an AEB (Automatic Emergency Braking) system to protect passengers by detecting obstacles and stopping the car automatically [1]. This technology is helpful, however, not all AEB systems are created equal. This becomes an occupant safety problem due to the volume of AEB-equipped vehicles in the modern fleet and the change in body positioning during evasive manuevers such as braking. During my time at Children’s Hospital of Philadelphia, my goal was to redesign the occupant compartment of a laboratory testing sled designed to recreate real-world scenarios to provide safety recommendations for vehicle companies.
Duration
June 2023 - August 2023
Children’s Hospital of Philadelpha - Center for Injury Research and Prevention
Dr. Vaentina Graci & Madeline Griffith, MS
[1] Graci, V., Maltenfort, M., Schneider, M., Griffith, M., Seacrist, T., & Arbogast, K. B. (2021). Quantitative characterization of AEB pulses across the modern fleet. Traffic Injury Prevention, 22(sup1), S62–S67. https://doi.org/10.1080/15389588.2021.1961227
Skills
Injury Biomechanics
Fusion 360
Designing for constraints
Hands-On Building
Interdisciplinary Team Skills
Challenge:
GOAL: improve an occupant compartment for a novel testing apparatus
My challenge was to create an improved occupant compartment by giving it a lower center of mass (COM), a more reliable camera mounting system, decreasing the overall weight while maintaining stability, and ensuring reliability and repeatabililty through the design.
The Process
Outcome:
DELIVERABLE: a fully-CAD’ed out model adhering to the design constraints
From my work over the summer, I achieved an improved occupant compartment with a lower center of mass, increased stability through seat blocks, a more generalizable seat, a new base, and a lighter overall design.
I began the project through a mass literature review to understand the scope of AEB and what exactly I was solving for. From there, I went into the specifics of the occupant compartment, iterating with each SLED Lab meeting, to finally deliver a final design.
The Sled.
There are a lot of sleds out there to test occupant kinematics. The issue with them is that they’re extremely expensive and take up a ton of space — for a small garage shop in Philadelphia, PA, you might see that there’s a problem here. This sled is fascinating because it uses physics to recreate a forward feel for the occupant while using rotation. Check out the video below to see it in action!
The SLED Lab at CHOP
As a member of this team for the summer, I joined a team of incredible individuals who cared deeply about the space of injury biomechanics and making things better for people. Keeping people at the center of what we did was a core value of Children’s Hospital of Philadelphia.
On this team, I didn’t work with solely engineers, though. From people with injury sciences backgrounds to child psychologists, I interacted with a variety of people. During one of my presentations, someone in my cohort asked me, “What’s CAD?” This interdisciplinary team only confirmed my love for working with people of different backgrounds.
Some Physics!
The spinning sled definitely looks scary, but the physics is anything but. Using the rotational kinematics of the arm and the 180 degree rotation of the compartment itself, a forward resultant force is created when the two line up. This mimics the effect of different AEB pulses on a human test subject!
A little bit more science…
I promise not to get too boring with the diagrams and graphs, but this one is interesting! On the left is pulse, or the acceleration profile of a vehicle. There are a few different parts to this curve, but the important thing is the ramp time. When this part of the graph is short, the decrease in acceleration changes in a shorter amount of time, which in turn, translates to a higher occupant jerk.
So what exactly does this mean? More jerk means that there’s a more abrupt motion of the occupant, making them an out-of-position vehicle passenger in the case of an accident. And with every car manufacturer having a different pulse profile for their automatic emergency braking, this occupant safety problem lies in passengers not being protected by the car safety mechanisms in the case of an AEB scenario!
(Told you this wouldn’t be boring.)
Conducting a mass literature review confimed the why of the design. Not only did I gain an understanding of biomechanics and vehicles, but I was able to tie it to my passion in designing for human variability. I read journals on how certain populations are more likely to be injured or killed in car crashes becuase of their size or gender; acommodation doesn’t just mean discomfort, it can mean something far more dire than that. This research phase helped me understand why this research needed to be done to create better vehicle safety for all occupants.
Demolition time!
This design had a lot going on. Not only was it very heavy to be whipped around at such significant accelerations, but the seat itself was an issue. Due to both the outdated and specific natures of the seat, it could only be used as testing for front-seat conditions. Additionally, the car seat was very signature “Toyota” (the project sponsor), so it wasn’t as universal as it should be for this type of experiment. This was a consideration that was added into the mix after the deconstruction phase occurred.
The Original Design
Don’t underestimate the power of brute force and a heat gun.
We found a seat that met my goal of a more generalizable seat, but there was an issue: it was far too heavy to use. With the presence of a sliding mechanism underneath, that added about 30 pounds of solid metal to the seat. However, I wanted to improve the existing seat as a part of this project. So with a hammer, a heat gun, and some pent-up frustration, we were able to get the bottom carriage off of the seat while maintaining its integrity.
With the bottom now exposed, there was another issue: how do we mount the seat to the new frame? This problem was solved with the creation of seat blocks. A different set was created for both the front and the back to securely mount the seat, ensuring security and stability.
Seat block for the front (left) and for the back (right)
Designing the seat blocks
The design proposal
After several weeks of the program commenced with weekly lab meetings, the idea for the design was set. It would feature a lower center of mass through not only the lighter seat, but would lower the occupant’s feet down more, creating a natural feel when they sat in the seat to create the most relaxed positioning possible. The more generalizable seat was an improvement, as was the sketch of a new camera mounting system using PVC pipes to get a better angle of head and neck kinematics. The measurements were firmed up at this point, and the CAD work begun.
A closer look: CAD
Computer-Aided Design is a fantastic tool to help design real-world things in the quickly iterative environment of a computer. Before this program begun, CAD was a bit of an overwhelming concept to me since I wasn’t familiar with it. However, this internship gave me the opportunity to learn in a fast-paced environment. Fusion 360 and I went from strangers to best friends in the final weeks of the program as I got to designing. Failing became less scary over time as I grew in my iteration skills and learned to fearlessly ask for help.
The Final Design.
The final product successfully met the design requirements and was an improved version of the existing compartment. Future work includes the mounting of a PVC camera cage I designed to be used around the sled in order to capture better video of key body kinematics for each trial.
Acknowledgements!
Huge thank you to Dr. Valentina Graci and to Madeline Griffith who introduced me to the world of injury biomechanics and became mentors to me. Thanks to everyone else in the CHOP cohort, especially to my wonderful friends I made in the program, especially Madeline McCreary & Melissa Rosahl.