Ball screw mechanism and electrically powered steering device utilizing the same

A ball screw mechanism which comprises:

• a ball screw shaft;
• a rotary nut having an internally threaded helical groove defined on an inner peripheral surface thereof in face-to-face relation with the ball screw mechanism, said rotary nut having at least one mounting hole defined therein;
• at least one bridge member accommodated within the mounting hole and having at least on groove defined therein and mounted in the rotary nut with the groove communicating neighboring convolutions of the internally threaded helical groove;
• and
• a separate fixing member mounted on the bridge member and including guide walls upstanding therefrom in a direction radially of the rotary nut along opposite side edges of the rotary nut with respect to a circumferential direction thereof, said guide walls being resiliently engaged with opposite inner side faces of the mounting hole defined in the rotary nut to thereby allow the bridge member to be fixedly retained within the mounting hole.

A ball screw mechanism which comprises:

• a ball screw shaft;
• a rotary nut having an internally threaded helical groove defined on an inner peripheral surface thereof in face-to-face relation with the ball screw mechanism, said rotary nut having at least one mounting hole defined therein, said mounting hole having opposite side faces formed with respective engagement steps defined therein;
• a plurality of balls rollingly accommodated in series within a ball rolling passage defined between the ball screw shaft and the internally threaded helical groove for transmitting a force from one of the rotary nut and the ball screw shaft to the other thereof;
• at least one bridge member accommodated within the mounting hole and having at least one groove defined therein and mounted in the rotary nut with the groove communicating neighboring convolutions of the internally threaded helical groove, said bridge member being formed with engagement grooves aligned and cooperable with the respective engagement steps;
• and
• a fixing member made up of a wire and engaged in part with the engagement steps and in part within the engagement grooves to thereby allow the bridge member to be fixedly retained within the mounting hole.