Belt tensioner

A belt tensioner for an auxiliary-unit belt drive, which auxiliary-unit belt drive includes a generator having a generator housing, a generator shaft, and a generator pulley, around which a belt is wrapped, comprising:

• a first and second tensioning arms supported on the generator housing in pivotable in relation to each other and in relation to the generator and which enclose the generator shaft,
• a first and second tensioning rollers attached to the first and second tensioning arms respectively and configured to apply pre-tensioning force to the belt in a circulation direction thereof before and after the generator pulley, and
• a bow spring configured to produce the pre-tensioning force, wherein the bow spring is clamped between the tensioning arms in axial overlap with the tensioning rollers,
• wherein the tensioning arms restrict an arcuate spring space that accommodates the bow spring, and a wrap-around region of the generator pulley and is limited by two walls of a first tensioning arm, wherein the bow spring is clamped between a first wall of the two walls and a driver of the second tensioning arm, wherein the driver includes a protrusion that protrudes axially with respect to a circular-ring shaped end face of the second tensioning arm and protrudes into the arcuate spring space before a second wall of the two walls.