Electric power steering apparatus

Patent metadata

Field	Value
Publication number	US-10427710-B2
Application number	US-201716320664-A
Country	US
Kind code	B2
Filing date	Aug 16, 2017
Priority date	Aug 24, 2016
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

An electric power steering apparatus of vector control system that calculates steering assist command values of dq axes based on at least a steering torque, calculates dq-axes current command values from the steering assist command values, converts the dq-axes current command values into 3-phase duty command values, driving-controls a 3-phase brushless motor by an inverter of a PWM control, and applies an assist torque to a steering system of a vehicle, wherein the electric power steering apparatus has plural dead time compensating functions of which efficiencies to respectively perform a dead time compensation of the inverter are different each other, and performs the dead time compensation by gradually shifting from one of the plural dead time compensating functions to an another dead time compensating function while mixing the plural dead time compensating functions.

First claim

The invention claimed is:

1. An electric power steering apparatus of a vector control system that calculates steering assist command values of dq-axes based on at least a steering torque, calculates dq-axes current command values from said steering assist command values, converts said dq-axes current command values into 3-phase duty command values, driving-controls a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle,
wherein said electric power steering apparatus has two dead time compensating functions A and B of which efficiencies to perform a dead time compensation of said inverter are different,
wherein said dead time compensating function A is a compensation function based on motor terminal voltages and has an effect in a low speed steering maneuver, and said dead time compensating function B is a compensation function based on a motor rotational angle and has an effect in a low speed steering maneuver and a middle speed steering maneuver, and
wherein said dead time compensation is performed by gradually switching from one of said dead time compensating functions A and B to other dead time compensating function while mixing said dead time compensating functions A and B.

2. The electric power steering apparatus according to claim 1 , wherein a ratio of mixing operation is linearly or nonlinearly changing based on a steering assist command value of a d-axis.

3. An electric power steering apparatus of a vector control system that calculates steering assist command values of dq-axes based on at least a steering torque, calculates dq-axes current command values from said steering assist command values, converts said dq-axes current command values into 3-phase duty command values, driving-controls a 3-phase brushless motor by an inverter of a pulse width modulation (PWM) control, and applies an assist torque to a steering system of a vehicle, comprising:
a dead time compensating section A that calculates first dq-axes compensation values relating to said dq-axes of said inverter based on 3-phase terminal voltages of said 3-phase brushless motor;
a dead time compensating section B that calculates second dq-axes compensation values relating to said dq-axes of said inverter based on a motor rotational angle; and
a compensation-value switching section that gradually and mutually switches while mixing said first dq-axes compensation values and said second dq-axes compensation values based on said steering assist command value of said q-axis, and outputs dq-axes dead time compensation values,
wherein a dead time compensation of said inverter is performed by a correction of said dq-axes current command values with said dq-axes dead time compensation values.

4. The electric power steering apparatus according to claim 3 , wherein said compensation-value switching section comprising:
a switch judging section to judge a compensation-value switch based on said steering assist command value of said q-axis;
a mixing-ratio calculating section to calculate a mixing-ratio R tA (%) of said first dq-axes compensation values and a mixing-ratio R tB (%) of said second dq-axes compensation values due to a compensation-value switch judgment flag from said switch judging section; and
a mixing section to input said first dq-axes compensation values and said second dq-axes compensation values, and to calculate said dq-axes dead time compensation values based on said mixing-ratio R tA (%) and said mixing-ratio R tB (%).

5. The electric power steering apparatus according to claim 4 , wherein said mixing section comprising:
a switch which inputs a count-up value and a count-down value and is switched due to said compensation-value switch judgment flag;
a count-value limiting section to limit, via an adding section, said count-up value or said count-down value from said switch and output said mixing-ratio R tB (%);
a holding unit which holds said mixing-ratio R tB (%) and adds to said adding section; and
a subtracting section to output said mixing-ratio R tA (%) by subtracting said mixing-ratio R tB (%) from a value of 100%.

6. The electric power steering apparatus according to claim 5 , wherein said count-up value and said count-down value are changeable.

7. The electric power steering apparatus according to claim 5 , wherein said mixing section comprising:
a first multiplying section which multiplies said first dq-axes compensation values with said mixing-ratio R tA (%);
a second multiplying section which multiplies said second dq-axes compensation values with said mixing-ratio R tB (%); and
an adding section to output said dq-axes dead time compensation values by adding a multiplied result of said first multiplying section and a multiplied result of said second multiplying section.

8. The electric power steering apparatus according to claim 5 , wherein said mixing-ratio R tA (%) and said mixing-ratio R tB (%) non-linearly vary and have a relation being R tA (%)+R tB (%)=100%.

9. The electric power steering apparatus according to claim 5 , wherein said correction is performed by an adding calculation of said dq-axes dead time compensation values and said dq-axes current command values.

10. The electric power steering apparatus according to claim 4 , wherein said mixing section comprising:
a first multiplying section which multiplies said first dq-axes compensation values with said mixing-ratio R tA (%);
a second multiplying section which multiplies said second dq-axes compensation values with said mixing-ratio R tB (%); and
an adding section to output said dq-axes dead time compensation values by adding a multiplied result of said first multiplying section and a multiplied result of said second multiplying section.

11. The electric power steering apparatus according to claim 4 , wherein said mixing-ratio R tA (%) and said mixing-ratio R tB (%) non-linearly vary and have a relation being R tA (%)+R tB (%)=100%.

12. The electric power steering apparatus according to claim 4 , wherein said correction is performed by an adding calculation of said dq-axes dead time compensation values and said dq-axes current command values.

Assignees

• Nsk Ltd

Inventors

• Takase Hiroaki
• MINAKI Ryo
• Sawada Hideki
• Sugawara Takayoshi

Classifications

• B62D5/046

  Controlling the motor · CPC title

• H02P21/06

  Rotor flux based control involving the use of rotor position or rotor speed sensors · CPC title

• H02M7/5395

  by pulse-width modulation · CPC title

• B62D6/00

  Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits (means for initiating a change in direction B62D1/00; steering valves B62D5/06; combined with means for inclining the vehicle body or wheels on bends B62D9/00) · CPC title

• H02P27/08 Primary

  with pulse width modulation · CPC title