Inflatable Seatbelts:
The Forefront of
Backseat Safety

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Safety engineers at Ford have good reason to feel a bit puffed up. More than 10 years in the making, their recent development of the world's first inflatable rear seatbelt is turning heads as a key safety feature of the redesigned 2011 Ford Explorer.

An engineering team led by Srini Sundararajan, safety technical leader for Ford Research and Advanced Engineering, was behind the innovation, which combines the functionality of a conventional seatbelt with some of the features of a frontseat airbag. Driving their work was a passion to prove that something thought to be impossible was within their grasp.

The key to the inflatable seatbelt is a tubular airbag folded like an accordion and stored within the belt. That design adds more than safety, it makes the seatbelt more cushioned, more comfortable and, Ford hopes, more likely to be used than conventional rear belts.

Today, only 61% of rear-seat passengers in the U.S. are buckling up, according to the National Highway Traffic Safety Administration.

Within 40 ms after a crash, the inflatable bag breaks through the belt fabric as it fills with air, expanding sideways across the occupant's torso and shoulder. The inflated belt helps distribute crash force energy across five times more of the occupant's torso than a traditional belt.

The new Ford Explorer will feature the inflatable seatbelts.

Sundararajan says the decade-long R&D process focused on a few especially challenging engineering issues. "It's a very simple and logical system, but it required extensive trial and error and testing over several years to prove out the technology and ensure precise, reliable performance in a crash situation," says the 21-year Ford veteran.

The belt's thicker, tubular design required engineers to get creative when developing features such as the belt-retracting system, the buckle, and the mechanism for delivering inflation gas.

The seatbelt latch is the conduit through which gas enters the airbag. Photo courtesy of Wayne Cunningham/CNET.

Unlike most conventional airbags, Ford's design uses cold-compressed gas for inflation instead of a heat-generating chemical reaction. Gas flows through the novel buckle from a cylinder housed below the seat. Because the device doesn't need to fill a spatial gap between the belt and the occupant, the inflatable belt is able to fill more slowly and at lower pressure than traditional airbags.

"It took a great deal of trial and error, but we created a new buckle that incorporated a gas-delivery tube with a locking mechanism for the belt tongue and latch," he says. "These challenges were addressed by the team through several brainstorming sessions, quick and simple tests, and CAD models to estimate part location and fit."

Over time, Ford plans to offer the technology in all its vehicles globally, although there are challenges in adapting the design for cars other than SUVs.

"The current system uses two retractors for the belts, which results in a packaging challenge in a vehicle environment," Sundararajan says. "In the future, we hope this technology can be achieved through a single retractor. Additionally, it would be quite challenging to design a new version that uses a more traditional buckle, tongue, and/or fewer parts. For non-SUV-type vehicles, this technology may have to be modified slightly to fit the package space available in the vehicle."

Michael MacRae is an independent writer.

It’s a very simple and logical system but it required extensive trial and error and testing over several years to prove out the technology and ensure precise reliable performance in a crash situation. Srini Sundararajan, safety technical leader, Ford Research and Advanced Engineering

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