Electric motor drive circuit for electric power steering systems for vehicles

An electric drive circuit for controlling an electric motor used in an electric power steering system for vehicles, said electric drive circuit comprising:

• a bridge circuit comprising first input terminal, second input terminal, first output terminal, second output terminal, first FET, connected between said first input terminal and said first output terminal, second FET connected between said first input terminal and said second output terminal, third FET connected between said second put terminal and said second output terminal, fourth FET connected between said second input terminal and said first output terminal, and electric power connected between said first and second input terminals;
• said electric motor being connected between said first and second output terminals;
• control means for supplying a first control signal via a first line to said first FET to drive the same, a second control signal via a second line to said second FET to drive the same, a third control signal via a third line to said third FET to drive the same, and a fourth control signal via a fourth line to said foruth FET to drive the same;
• and
• said first and third control signals being generated concurrently with each other to drive said electric motor in a first direction, said second and fourth control signals being generated concurrently with each other to drive said electric motor in a second direction, and said first and third control signals and said second and fourth control signals being generated independently of each other;
• said power steering system further comprises an input shaft operatively connected to a steering wheel, an output shaft operatively connected to a steered wheel to which said electric motor operatively supplies auxiliary torque, torque detecting means for detecting steering torque acting on said input shaft, and steering velocity detecting means for detecting steering velocity of the input shaft;
• and
• said control means generates said first, second, third and fourth control signals dependent upon detection signals from said torque detecting means and said steering speed detecting means.