Drive spring for a belt retractor, and belt retractor

A mainspring (10) for a belt retractor (24) comprising a strip-shaped spring body (12) extending substantially in S-shape in the relaxed state,

• wherein each of a first end (14) of the spring body (12) and a second end (16) of the spring body (12) has a helically wound portion (18, 20) of the spring body (12) and the second end (16) is opposed to the first end (14), and
• wherein a winding direction at the second end (16) is opposed to a winding direction at the first end (14),
• wherein
• a shape of the reciprocal (k) of the radius of curvature (r) of the spring body (12) has an inflection point (22) over a length (l) of the spring body (12).

A belt retractor (24) for a seat belt device of a vehicle, comprising

• a belt reel (26) rotatably supported about a central axis (26a) in a belt retractor housing (28), and
• a mainspring (10) for rotationally restoring the belt reel (26) to an idle position,
• wherein the mainspring (10) in its state mounted in the belt retractor (24) includes plural windings (30) which extend in a substantially helically nested manner, wherein an inner end (14i) of the mainspring (10) is connected to the belt reel (26) and an outer end (16a) of the mainspring (10) being opposed to the inner end (14i) is connected to the belt retractor housing (28),
• wherein
• the mainspring (10) is disposed substantially concentrically to the central axis (26a).