Audi Q7 2017 Manual page 16

Function
When J234 instructs the safety belt to deploy, the propel-
lant charge (1) ignites and there is a sudden rise of pres-
sure inside the guide tube/pressure chamber (3). The pres-
sure moves the piston (2) and the "Snake" (5) downward.
After the "Snake" (5) has moved out of the guide tube, it
contacts the gear (7) which is firmly connected to the
retractor shaft (6). The teeth of the gear mesh with the
"Snake" due to the material characteristics and geometry of
the components. The "Snake" is pushed further down and
causes the gear together with the retractor shaft to rotate.
12
Pyrotechnic pro-
pellant charge (1)
Piston (2)
Guide tube/pres-
sure chamber (3)
"Snake" (5)
637_101
"Snake" (5)
Gear (7)
Retractor shaft (6)
637_102