Seat Belt Adjuster

This has probably happened to all of us. We are driving, or more likely, riding, in a car and the brakes are put on. Perhaps we were reaching for a cup in the cup holder or rummaging through the glove box. Suddenly, we are pulled tight against the back of the seat. What on earth just happened? Is the seat belt attacking us? Well, though it may feel like the seat belt has suddenly grew tentacles and is trying to force you straight through the back of your bucket seat, the truth is that the seat belt is actually trying to save your life. You just became another victim of the seat belt adjuster.

Seat belt adjusters have one job, and that job is to save your life if you are driving or riding and get into an accident. These seat belt adjusters used to come standard on most new cars, though they have rather fallen out of favor since the advent of the air bag. But what are seat belt adjusters, how do they work, and why does it feel like my seat belt is trying to strangle me?

Seat belt adjusters are simply a locking mechanism or inertia reel that will tighten when the seat belt is pulled forward very quickly due to the driver slamming on the car's brakes or the momentum caused by an accident. If you have ever been the unwary victim of the seat belt adjuster, you will notice that the seat belt adjuster does not work its magic when you pull the seat belt forward slowly (as if leaning down to pick something up off the floorboard), no, the seat belt adjuster only constricts to save the passenger if the seal belt is pulled forward rapidly. No matter if you were just simply eager to grab something from the glove box or if you were getting in a major accident, the seat belt adjuster does not make a fine distinction (it is just a principal of physics after all, what can you expect?), instead it pulls you tight in order to save your life.

So how do these seat belt adjusters work? Well, when the brakes are applied or you move forward quickly, the seat belt adjuster is implemented with a centrifugal (circular force) clutch. If the seat belt reel spins quickly, as it would in an accident, the centrifugal clutch engages. But that's just in some seat belt adjusters. In others, the seat belt is secured by a weighted object, such as a pendulum or ball bearing. They lock the reel in the event of an accident and ensure that you are properly secured in your place.

There are several types of inertial reel seatbelt adjusters. The No Locking Retractor (aka NLR) is commonly used in recoiling lap belts, while the Emergency Locking Retractor – Vehicle Sensitive (ELR V) consists of a locking mechanism that is activated in an emergency due to deceleration or the rollover of the auto. (That's what it means by "vehicle sensitive.") Further, the ELR VW stands for "Emergency Locking Retractor – Vehicle and Webbing Sensitive." This is the smartest seat belt adjuster of all, allowing the driver or passenger free movement within the confines of the seat belt. This is the seat belt type that automatically adjusts to the shape and size of the wearer and its locking mechanism is only activated in the event of deceleration, roll over, a quick acceleration of the seat belt strap (i.e. learning forward quickly as if getting something from the dashboard or in the event of getting rear ended).

While most seat belt locking mechanisms have fallen out of favor due to the advent and technological advancement of the air bag, they were successful in saving people’s lives in accidents for years and, though they could sometimes be inconvenient, should be lauded for that simple fact.