When I pull on seatbelts really quickly they lock into place, and I know that’s supposed to stop you from getting hurt in a car accident, but I just don’t get how the stopping mechanism works.
In: Engineering
It is possible to make the mechanisms a few different ways. But the most common ones have a few weights on the spinning axle. Normally these weights are close to the center of the axle due to a few small springs. However when the axle moves fast the weights gets forced out through the centrifugal effect. As the weight move out they catch some catches on the housing of the unit and therefore locking the entire mechanism from spinning. This way you are able to slowly let the seatbelt out when you are getting into the car and when you move around in the seat. However in the event of a collision the seatbelts will move too fast and lock in place.
There are usually 2 locking mechanism and 1-2 tensioning mechanism.
Locking
1. as you described, it is a centrifugal locking.
When pull out speed exceeds a specific, law regulated, limit some teeth get pushed outwards against some springs by centrifugal force – below the limit the springs are stronger and teeth cannot move outwards.
2. A force controlled locking.
When any force during driving (acceleration, braking, curves, accident) exceeds 0.3g of force the seatbelt becomes locked.
This is what you experience for once during mentioned driving situations, but also on steep hills in a parked car.
Tensioning
1. spring loaded or explosive charge tensioning the belt in case of an accident. Triggered by some sensors.
2. Pre tensioning to avoid unwanted and dangerous passenger movent caused by a loose belt. This is triggered by dangerous driving situations or reaching some g force.
This do only some newer cars have.
You always want your belt to be fastened and not loose. Remove your jacket as it will cause the belt to be longer than needed or at least put the jacket completely over the belts (open jacket needed).
Latest Answers