SEAT BELT PRETENSIONER

An apparatus (10) for tensioning belt webbing (14) around an occupant of a vehicle to restrain movement of the occupant includes a rotary trochoidal motor (40). The motor (40) includes a housing (44) having a wall with an inner surface (46) defining a chamber (48). A rotor (42) is rotatable in the chamber and has fluid engagement surfaces (50, 52, 54). An output shaft (66) is supported for rotation relative to the housing (44). A fluid source (80) is actuatable to supply fluid under pressure into the chamber (48) and against the fluid engagement surfaces (50, 52, 54) of the rotor (42) to rotate the rotor in a first direction of rotation in the chamber to thereby rotate the output shaft (66). A belt webbing engagement member (22) is engageable with the belt webbing (14) to tension the belt webbing. The output shaft (66) is interconnected with the belt webbing engagement member (22) to transmit force from the rotating output shaft to the belt webbing engagement member to tension the belt webbing (14).