Rotational angle detection apparatus and power steering apparatus

A power steering apparatus comprising:

• a steering mechanism including an input shaft rotatable according to a rotation of a steering wheel and an output shaft connected to the input shaft via a torsion bar, the steering mechanism being configured to transmit a steering operation performed on the steering wheel to a turning target wheel;
• a housing rotatably holding the input shaft and the output shaft;
• a magnetic member provided at the output shaft and configured in such a manner that an N pole and an S pole are disposed adjacent to each other around the rotational axis;
• a detection member provided so as to face the magnetic member and made from a magnetic material;
• a holding member fixed to the input shaft and including a first holding member and a second holding member each made from a thermoplastic resin material, the holding member being configured to hold the detection member so as to prevent a contact between the detection member and the second member by the first holding member and the second holding member fixedly welded to each other with the detection member sandwiched between the first holding member and the second holding member;
• a recessed portion provided on one side of the first holding member that faces the second holding member, and formed so as to be opened to a second holding member-side, the recessed portion including a bottom portion;
• a wall portion provided along an opening edge of the recessed portion and formed in such a manner that a distance between the wall portion and the second holding member falls below a distance between the bottom portion and the second holding member, and the wall portion does not abut against the second holding member;
• a protruding portion facing the recessed portion and provided at the second holding member so as to protrude toward a recessed portion-side, the protruding portion being configured to allow the first holding member and the second holding member to be welded to each other by being melted with a distal end portion thereof in abutment with the bottom portion;
• and
• a magnetic sensor configured to detect an angle of a relative rotation between the input shaft and the output shaft by detecting a change in a magnetic field in the detection member that changes due to a relative rotation between the magnetic member and the detection member that is caused along with the relative rotation between the first member and the second member;
• an electric motor configured to supply a steering assist force to the steering mechanism;
• and
• a motor control circuit configured to calculate an instruction signal directed to the electric motor based on a torque generated between the input shaft and the output shaft that is acquired from a signal output from the magnetic sensor, and output the instruction signal to the electric motor.

A fixation structure comprising:

• a holding target member made from a metallic material;
• a holding member made from thermoplastic resin and including a first holding member and a second holding member, the holding member being configured to hold the holding target member by the first holding member and the second holding member fixedly welded to each other with the holding target member sandwiched between the first holding member and the second holding member;
• a recessed portion provided on one side of the first holding member that faces the second holding member and formed so as to be opened to a second holding member-side, the recessed portion including a bottom portion;
• a wall portion provided along an opening edge of the recessed portion and formed in such a manner that a distance between the wall portion and the second holding member falls below a distance between the bottom portion and the second holding member, and the wall portion does not abut against the second holding member;
• and
• a protruding portion facing the recessed portion and provided at the second holding member so as to protrude toward a recessed portion-side, the protruding portion being configured to allow the first holding member and the second holding member to be welded to each other by being melted with a distal end portion thereof in abutment with the bottom portion,
• wherein the second holding member is provided in such a manner that the distance between the bottom portion and the second holding member is set so as to allow the protruding portion or a part of the bottom portion which is melted when the first holding member and the second holding member are fixedly welded to each other to be grown as a burr, and the burr to abut against the second holding member.