Electric power steering apparatus

An electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said first current command value, comprising:

• a first converting section to convert said first current command value to a first rack axial force;
• a rack position converting section to convert a rotational angle of said motor to a judgment rack position;
• a rack end approach judging section to judge that a steering approaches to a rack end based on said judgment rack position and to output a rack displacement and a switching signal;
• a viscoelastic model following control section to generate a second rack axial force including a viscoelastic model as a reference model based on said first rack axial force, said rack displacement and said switching signal;
• and
• a second converting section to convert said second rack axial force to a second current command value;
• wherein said viscoelastic model following control section comprising:
• a feed-forward control section to feed-forward control based on said rack displacement and to output a third rack axial force;
• a feed-back control section to feed-back control based on said rack displacement and said first rack axial force and to output a fourth rack axial force;
• a first switching section to switch-ON/OFF an output of said third rack axial force by said switching signal;
• a second switching section to switch-ON/OFF an output of said fourth rack axial force by said switching signal;
• and
• an adding section to output said second rack axial force by adding outputs of said first and second switching sections;
• wherein said assist-control is performed by adding said second current command value to said first current command value so as to suppress a rack end hitting.

An electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said first current command value, comprising:

• a first converting section to convert said first current command value to a first rack axial force;
• a rack position converting section to convert a rotational angle of said motor to a judgment rack position;
• a rack end approach judging section to judge that a steering approaches to a rack end based on said judgment rack position and to output a rack displacement and a switching signal;
• a viscoelastic model following control section to generate a second rack axial force including a viscoelastic model as a reference model based on said first rack axial force, said rack displacement and said switching signal;
• and
• a second converting section to convert said second rack axial force to a second current command value;
• wherein said viscoelastic model following control section comprising:
• a feed-back control section to feed-back control based on said rack displacement and said first rack axial force and to output a second rack axial force, and
• a switching section to switch-ON/OFF an output of said second rack axial force by said switching signal,
• wherein control parameters of said feed-back control section are changed based on said rack displacement or a target rack displacement,
• wherein said assist-control is performed by adding said second current command value to said first current command value so as to suppress a rack end hitting.

An electric power steering apparatus that calculates a current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said current command value, comprising:

• a configuration of a model following control comprising a feed-back control section including a viscoelastic model as a reference model within a predetermined angle (x0)at front of a rack end;
• wherein said feed-back control section comprises a feed-back element to calculate a target rack displacement based on an input-side rack axial force (f), and a control element section to output an output-side rack axial force (ff) based on a positional deviation between said target rack displacement and a rack displacement (x);
• wherein said electric power steering apparatus further comprising:
• a correcting section to change parameters of at least one-side of said feed-back control section and said control element section and set corrected parameters;
• an axial force calculating section to calculate a rack axial force (f4) based on said steering torque and said current command value;
• a limiter to limit a maximum value of said rack axial force (f4) with a limiting value and to output said input-side rack axial force (f);
• and
• a steering state judging section to judge a steering state;
• wherein said parameters of said feed-forward control section are changed or switched in accordance with said rack displacement (x) and a judgment result of said steering state judging section.