Motor-driven power steering apparatus

• US 6,727,669 B2
• Filed: 09/17/2002
• Issued: 04/27/2004
• Est. Priority Date: 09/18/2001
• Status: Active Grant

• Current Assignee: Toyoda Koki Kabushiki Kaisha
• Original Assignee: Toyoda Koki Kabushiki Kaisha
• Inventors: Sakai, Atsuo, Ito, Kazuhiko, Suzuki, Hiroshi
• Primary Examiner(s): Masih, Karen
• Application Number:
  US10/244,557
• Publication Number:
  US 20030071587A1
• Time in Patent Office: 588 Days
• Field of Search: 318/139, 318/254, 318/439, 318/138, 318/599, 318/812, 318/811, 180/446
• US Class Current: 318/139
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input

Abstract

A motor-driven power steering apparatus includes a motor for generating assisting force to be imparted to a steering mechanism, a control signal generation section for generating a motor control signal on the basis of at least steering torque applied to a steering wheel, a motor drive unit for driving the motor in accordance with the motor control signal, and a step-up circuit provided between a battery to the motor drive unit. The step-up circuit includes a step-up coil whose one end is connected to the battery, a first switching element connected between the other end of the step-up coil and the ground, a second switching element connected between the other end of the step-up coil and an output terminal, and a capacitor connected between the output terminal and the ground and smoothing output voltage appearing at the output terminal. The apparatus further includes a step-up circuit control unit which detects the output voltage and controls the first and second switching elements on the basis of difference between a target output voltage and the detected output voltage. During power generation periods, at least the first switching element is turned on and off in order to increase the output voltage supplied to the motor through step-up operation. During regeneration periods, at least the second switching element is turned on and off.

Claims

1. A motor-driven power steering apparatus for a vehicle, comprising:

a steering mechanism for steering the vehicle in accordance with operation of a steering wheel;

a motor mechanically coupled to the steering mechanism and generating assisting force to be imparted to the steering mechanism;

control signal generation means for generating a motor control signal on the basis of at least steering torque applied to the steering wheel;

motor drive means for driving the motor in accordance with the motor control signal;

a step-up circuit provided in a current supply circuit extending from a battery to the motor drive means, the step-up circuit including a step-up coil whose one end is connected to the battery for reception of battery voltage, a first switching element connected between the other end of the step-up coil and the ground, a second switching element connected between the other end of the step-up coil and an output terminal, and a capacitor connected between the output terminal and the ground and smoothing output voltage which is produced by means of the step-up coil and appears at the output terminal; and

step-up circuit control means for detecting the output voltage and controlling the first and second switching elements on the basis of difference between a target output voltage and the detected output voltage in such a manner that during power generation periods, at least the first switching element is turned on and off in order to increase the output voltage supplied to the motor through step-up operation, and during regeneration periods, at least the second switching element is turned on and off.

2. A motor-driven power steering apparatus according to claim 1, wherein the first and second switching elements are each constituted by a field effect transistor.

3. A motor-driven power steering apparatus according to claim 1, wherein the step-up circuit control means turns the first and second switching elements on and off alternately on the basis of the difference between the target output voltage and the detected output voltage in such a manner that during power generation periods, the output voltage supplied to the motor is increased through step-up operation, and during regeneration periods, regenerative current output from the motor flows to the battery.

4. A motor-driven power steering apparatus according to claim 2, wherein the step-up circuit control means turns the first and second switching elements on and off alternately on the basis of the difference between the target output voltage and the detected output voltage in such a manner that during power generation periods, the output voltage supplied to the motor is increased through step-up operation, and during regeneration periods, regenerative current output from the motor flows to the battery.

5. A motor-driven power steering apparatus according to claim 1, further comprising:

steering state judgment means for determining, on the basis of the difference between the target output voltage and the detected output voltage, whether the motor is in a power generation state or in a regeneration state, wherein

the step-up circuit control means turns at least one of the first and second switching elements on and off on the basis of the state of the motor determined by the steering state judgment means.

6. A motor-driven power steering apparatus according to claim 2, further comprising:

steering state judgment means for determining, on the basis of the difference between the target output voltage and the detected output voltage, whether the motor is in a power generation state or in a regeneration state, wherein

the step-up circuit control means turns at least one of the first and second switching elements on and off on the basis of the state of the motor determined by the steering state judgment means.

7. A motor-driven power steering apparatus according to claim 5, wherein the step-up circuit control means turns only the first switching element on and off when the steering state judgment means determines that the motor is in a power generation state, and turns the first and second switching elements on and off alternately when the steering state judgment means determines that the motor is in a regeneration state.

8. A motor-driven power steering apparatus according to claim 5, wherein the step-up circuit control means turns only the first switching element on and off when the steering state judgment means determines that the motor is in a power generation state, and turns only the second switching element on and off when the steering state judgment means determines that the motor is in a regeneration state.

9. A motor-driven power steering apparatus according to claim 5, wherein the step-up circuit control means turns the first and second switching elements on and off alternately when the steering state judgment means determines that the motor is in a power generation state, and turns only the second switching element on and off when the steering state judgment means determines that the motor is in a regeneration state.

10. A motor-driven power steering apparatus according to claim 6, further comprising a bootstrap circuit including a bootstrap capacitor and connected to a line extending between the battery and the drain of the first switching element, the bootstrap circuit being connected to a gate of the second switching element as a drive power source for the second switching element in order to apply electrical potential of the bootstrap capacitor to the gate of the second switching element, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns the first and second switching elements on and off alternately;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means turns the second switching element on and off and turns the first switching element on and off at a predetermined duty ratio in alternating periods of constant intervals.

11. A motor-driven power steering apparatus according to claim 6, further comprising a bootstrap circuit including a bootstrap capacitor and connected to a line extending between the battery and the drain of the first switching element, the bootstrap circuit being connected to a gate of the second switching element as a drive power source for the second switching element in order to apply electrical potential of the bootstrap capacitor to the gate of the second switching element, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns the first and second switching elements on and off alternately;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means performs PWM control in order to turn only the second switching element on and off at a duty ratio and restricts the duty ratio so as not to exceed a predetermined duty ratio.

12. A motor-driven power steering apparatus according to claim 6, further comprising load state judgment means for determining a load status of the motor, wherein

the step-up circuit control means turns at least one of the first and second switching elements on and off on the basis of the steering state as detected by the steering state judgment means and the load state of the motor as determined by the load state judgment means.

13. A motor-driven power steering apparatus according to claim 12, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns only the first switching element on and off and maintains the second switching element off continuously if the load state judgment means determines that the motor is in a light load state, and turns the first and second switching elements on and off alternately if the load state judgment means determines that the motor is in a heavy load state;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means turns only the second switching element on and off.

14. A motor-driven power steering apparatus according to claim 12, further comprising a bootstrap circuit including a bootstrap capacitor and connected to a line extending between the battery and the drain of the first switching element, the bootstrap circuit being connected a gate of the second switching element as a drive power source for the second switching element in order to apply electrical potential of the bootstrap capacitor to the gate of the second switching element, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns only the first switching element on and off and maintains the second switching element off continuously if the load state judgment means determines that the motor is in a light load state, and turns the first and second switching elements on and off alternately if the load state judgment means determines that the motor is in a heavy load state;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means turns the second switching element on and off and turns the first switching element on and off at a fixed duty ratio in alternating periods of constant intervals.

15. A motor-driven power steering apparatus according to claim 12, further comprising a bootstrap circuit including a bootstrap capacitor and connected to a line extending between the battery and the drain of the first switching element, the bootstrap circuit being connected a gate of the second switching element as a drive power source for the second switching element in order to apply electrical potential of the bootstrap capacitor to the gate of the second switching element, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns only the first switching element on and off and maintains the second switching element off continuously if the load state judgment means determines that the motor is in a light load state, and turns the first and second switching elements on and off alternately if the load state judgment means determines that the motor is in a heavy load state;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means performs PWM control in order to turn only the second switching element on and off at a duty ratio and restricts the duty ratio so as not to exceed a predetermined duty ratio.

16. A motor-driven power steering apparatus according to claim 6, further comprising a bootstrap circuit including a bootstrap capacitor and connected to the drain of the second switching element, the bootstrap circuit being connected a gate of the second switching element as a drive power source for the second switching element in order to apply electrical potential of the bootstrap capacitor to the gate of the second switching element, wherein when the steering state judgment means determines that the motor is in a power generation state, the step-up circuit control means turns the first and second switching elements on and off alternately;

and when the steering state judgment means determines that the motor is in a regeneration state, the step-up circuit control means turns only the second switching element on and off.

17. A motor-driven power steering apparatus according to claim 1, wherein the step-up circuit control means includes:

target output voltage setting means for setting a target output voltage of the step-up circuit;

control computation means for performing at least computation for proportional control on the basis of the difference between the target output voltage and the detected output voltage and for outputting a computed value; and

PWM computation means for performing PWM computation on the basis of the computed value so as to determine a duty ratio, wherein

the first and second switching elements are turned on and off in accordance with the determined duty ratio; and

the target output voltage setting means changes the target output voltage in accordance with an operation state parameter indicative of an operation state of the vehicle or the motor.

18. A motor-driven power steering apparatus according to claim 1, wherein the step-up circuit control means includes:

target output voltage setting means for setting a target output voltage of the step-up circuit;

control computation means for performing at least computation for proportional control on the basis of the difference between the target output voltage and the detected output voltage and for outputting a computed value; and

PWM computation means for performing PWM computation on the basis of the computed value so as to determine a duty ratio, wherein

the first and second switching elements are turned on and off in accordance with the determined duty ratio; and

the step-up circuit control means restricts the duty ratio so as not to exceed a predetermined duty ratio.

19. A motor-driven power steering apparatus according to claim 1, further comprising:

status parameter detection means for detecting a parameter indicative of states of the step-up circuit; and

judgment means for comparing the parameter detected by the status parameter detection means with a judgment value and judging whether or not the step-up circuit is normal, wherein

the step-up circuit control means stops step-up control for the step-up circuit when the judgment means judges that the step-up circuit is not normal.

20. A motor-driven power steering apparatus according to claim 19, further comprising:

first open-close means connected to a battery-voltage supply section of the step-up circuit and turned on and off by the step-up circuit control means; and

second open-close means for controlling supply of electrical power to the motor, wherein

when the judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means turns the first and second open-close means off.

21. A motor-driven power steering apparatus according to claim 19, wherein when the judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means maintains the first switching element off continuously and maintains the second switching element on continuously.

22. A motor-driven power steering apparatus according to claim 2, further comprising:

first open-close means connected to a battery-voltage supply section of the step-up circuit and turned on and off by the step-up circuit control means; and

a circuit which includes a first resistor connected to a connection point between the drain of the first switching element and the battery-voltage supply section and which receives an ignition voltage when an ignition switch is turned on, wherein the step-up circuit control means includes;

first element control means, operated when the ignition switch is turned on, for turning at least the first switching element on or off before the first open-close means is turned on;

drain voltage detection means for detecting drain voltage of the first or second switching element; and

first failure judgment means for comparing the drain voltage with a first failure judgment value and determining whether the step-up circuit suffers a failure.

23. A motor-driven power steering apparatus according to claim 22, further comprising:

second open-close means for controlling supply of electrical power to the motor, wherein

when the first failure judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means turns the first and second open-close means off.

24. A motor-driven power steering apparatus according to claim 22, further comprising:

second open-close means for controlling supply of electrical power to the motor, wherein

when the first failure judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means turns the first and second open-close means on, maintains the first switching element off continuously, and maintains the second switching element on continuously.

25. A motor-driven power steering apparatus according to claim 2, further comprising:

first open-close means connected to a battery-voltage supply section of the step-up circuit and turned on and off by the step-up circuit control means;

a circuit which includes a second resistor connected to the drain of the second switching element and which receives an ignition voltage when an ignition switch is turned on, wherein the step-up circuit control means includes;

second element control means, operated when the ignition switch is turned on, for turning the first and second switching elements on simultaneously, turning the first and second switching elements off simultaneously, or turning the first switching element off and the second switching element on, before the first open-close means is turned on;

drain voltage detection means for detecting drain voltage of at least the first switching element; and

second failure judgment means for comparing the drain voltage with a second failure judgment value and determining whether the step-up circuit suffers a failure.

26. A motor-driven power steering apparatus according to claim 25, further comprising:

second open-close means for controlling supply of electrical power to the motor, wherein

when the second failure judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means turns the first and second open-close means off.

27. A motor-driven power steering apparatus according to claim 25, further comprising:

second open-close means for controlling supply of electrical power to the motor, wherein

when the second failure judgment means judges that the step-up circuit suffers a failure, the step-up circuit control means turns the first and second open-close means on, maintains the first switching element off continuously, and maintains the second switching element on continuously.