JP6481857B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that generates a steering assist force (assist force) by an electric motor.

  In Patent Document 1 below, there is an electric power steering (EPS) that includes a main power source and an auxiliary power source including a capacitor, and supplies power to the motor drive circuit from the auxiliary power source when the main power source fails. It is disclosed.

JP 2014-108767 A

  In the invention described in Patent Document 1, when the power supply is switched from the main power supply to the auxiliary power supply capacitor and the steering operation is continued, the charge accumulated in the capacitor is discharged. The voltage (capacitor voltage) gradually decreases. For this reason, there is a possibility that the assist will be cut off at the moment when the capacitor voltage falls below the minimum voltage at which EPS operation is possible, and so-called handle removal may occur.

  Therefore, it can be considered that the assist force is gradually reduced in proportion to the capacitor voltage. However, as shown in FIG. 8, the capacitor voltage fluctuates according to the change in the capacitor current during steering. FIG. 8 shows an example of changes in the capacitor current and the capacitor voltage when the stationary steering is repeatedly performed in a state where the power source is switched from the main power source to the capacitor in the conventional example described in Patent Document 1. . For this reason, when the assist force is reduced in accordance with the change in the capacitor voltage, there is a problem that the assist force fluctuates and the steering feeling is not good.

  An object of the present invention is to provide an electric power steering apparatus capable of gradually reducing assist force in accordance with a decrease in voltage between terminals of an auxiliary power source and improving steering feeling when a main power source is abnormal. It is.

  According to the first aspect of the present invention, an electric power steering apparatus comprising a main power source (31) and an auxiliary power source (44), and supplying electric power from the auxiliary power source to a drive circuit (52) of the electric motor when the main power source is abnormal. 1) current detection means (46) for detecting the output current of the auxiliary power supply, voltage detection means (47) for detecting the voltage across the terminals of the auxiliary power supply, and the current detection means when the main power supply is abnormal Conversion means (71) for converting the voltage between the terminals detected by the voltage detection means into a reference voltage in which voltage fluctuation due to a change in the output current of the auxiliary power source is reduced based on the output current detected by The electric power steering apparatus includes target current value correcting means (62) for correcting the target current value of the electric motor based on the reference voltage obtained by the converting means. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

  In this configuration, the assist control can be continued by the auxiliary power source when the main power source is abnormal. In addition, when the main power supply is abnormal, the target current value can be reduced and corrected in accordance with the decrease in the inter-terminal voltage of the auxiliary power supply. As a result, the assist force can be gradually reduced in accordance with the decrease in the inter-terminal voltage of the auxiliary power supply. As a result, the driver can be given a sign that the assist has been cut off, so that the occurrence of so-called steering wheel removal can be suppressed when the assist is cut off. In addition, the continuation time of assist control when the main power supply is abnormal can be extended.

  In this configuration, the target current value is not corrected based on the voltage between the terminals of the auxiliary power supply itself, but is the voltage between the terminals of the auxiliary power supply after the voltage fluctuation due to the change in the output current of the auxiliary power supply is reduced. The target current value is corrected based on the reference voltage. As a result, the target current value can be smoothly reduced in accordance with the decrease in the inter-terminal voltage of the auxiliary power supply, so that the steering feeling when the main power supply is abnormal can be improved.

According to a second aspect of the present invention, when the output current detected by the current detection means is Ic, the terminal voltage detected by the voltage detection means is Vc, and the resistance of the electric motor is Rm, the conversion means Is an electric power steering apparatus according to claim 1, configured to convert the inter-terminal voltage Vc into a reference voltage Vco based on the following equation (a).
Vco = Vc + Ic · Rm (a)
According to a third aspect of the present invention, there is provided a target torque value for setting a target current value of the electric motor using a steering torque acquisition means (12) for acquiring a steering torque and a steering torque acquired by the steering torque acquisition means. The target current value correcting means includes a setting means (61), and is configured to correct the target current value set by the target current value setting means based on the reference voltage obtained by the converting means. The electric power steering apparatus according to claim 1 or 2.

  According to a fourth aspect of the present invention, the target current value correcting means is set by a correction gain setting means (71) for setting a correction gain based on a reference voltage obtained by the converting means, and the target current value setting means. The electric power steering apparatus according to claim 3, further comprising means (72) for correcting the target current value by multiplying the target current value to be set by the correction gain set by the correction gain setting means. .

  A fifth aspect of the present invention is the electric power steering apparatus according to any one of the first to fourth aspects, wherein the auxiliary power source is a capacitor.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing an electrical configuration of the electric power steering apparatus of FIG. FIG. 3 is a flowchart showing a procedure of main power supply abnormality monitoring processing performed by the power supply control ECU. FIG. 4 is a block diagram showing an electrical configuration of a motor control circuit in the EPS ECU. FIG. 5 is a graph showing a setting example of the target current value Im ^{* with} respect to the detected steering torque T. FIG. 6 is a flowchart showing the procedure of the correction gain calculation process when the main power supply is abnormal, which is executed by the correction gain calculation unit when the main power supply is abnormal. FIG. 7 is a graph showing an example of setting the correction gain with respect to the reference voltage. FIG. 8 is a waveform diagram showing an example of changes in the capacitor current and the capacitor voltage when the stationary power steering is repeatedly performed in a state where the power source is switched from the main power source to the capacitor in the conventional example described in Patent Document 1. is there.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
An electric power steering device (EPS) 1 includes a steering wheel 2 as a steering member for steering a vehicle, and a steering mechanism that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2. 4 and a steering assist mechanism 5 for assisting the driver's steering. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable.
A torque sensor 11 is disposed in the vicinity of the torsion bar 10. The torque sensor 11 detects the steering torque T applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9. In this embodiment, the steering torque T detected by the torque sensor 11 is detected, for example, as a torque for steering in the right direction as a positive value and a torque for steering in the left direction as a negative value. It is assumed that the magnitude of the steering torque increases as the absolute value thereof is detected.

  The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13 (the lower end in FIG. 1).

  The rack shaft 14 extends linearly along the left-right direction of the automobile. A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 18 for assisting steering and a speed reduction mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20.

The worm shaft 20 is rotationally driven by the electric motor 18. Further, the worm wheel 21 is connected to the steering shaft 6 so as to be integrally rotatable. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven and the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 20 by the electric motor 18.

  The vehicle is provided with a vehicle speed sensor 24 for detecting the vehicle speed V. The steering torque T detected by the torque sensor 11, the vehicle speed V detected by the vehicle speed sensor 24, and the like are input to an EPS ECU (ECU: Electronic Control Unit) 12. The EPS ECU 12 performs so-called assist control by controlling the electric motor 18 based on these inputs and the like.

Electric power is supplied to the motor drive circuit 52 (see FIG. 2) in the EPS ECU 12 by one or both of the main power supply 31 and the auxiliary power supply device 32. The auxiliary power supply device 32 is controlled by the power supply control ECU 33. The EPS ECU 12 and the power supply control ECU 33 are connected via a communication line.
FIG. 2 is a circuit diagram showing an electrical configuration of the electric power steering apparatus 1.

  The EPS ECU 12 includes a motor control circuit 51 composed of a microcomputer, and a motor drive circuit (inverter circuit) 52 that is controlled by the motor control circuit 51 and supplies electric power to the electric motor 18. The output signal from the current sensor 53 for detecting the motor current flowing through the electric motor 18 is input to the EPS ECU 12. Details of the motor control circuit 51 will be described later.

The auxiliary power device 32 is connected to the main power source 31 in series. The auxiliary power supply device 32 includes a relay 41, a charging circuit 42, a discharging circuit 43, a capacitor 44 as an auxiliary power supply, current sensors 45 and 46, and a voltage sensor 47.
The relay 41 is disposed between the positive terminal of the main power supply 31 and the charging circuit 42. A connection point between the relay 41 and the charging circuit 42 is indicated by P1. The charging circuit 42 is a circuit for charging the capacitor 44. The charging circuit 42 includes a pair of switching elements 42A and 42B connected in series, and a booster coil 42C connected between the connection point P3 and the connection point P1 of these switching elements 42A and 42B. The switching elements 42A and 42B are n-channel MOSFETs.

  The source of the upper switching element 42A is connected to the drain of the lower switching element 42B. The drain of the switching element 42A on the upper stage side is connected to the output terminal (connection point P2) of the capacitor 44. The source of the lower switching element 42B is grounded. The connection point P1 is connected to the input terminal (connection point P5) of the capacitor 44. By alternately turning on the pair of switching elements 42A and 42B, the output voltage (battery voltage VB) at the connection point P1 can be boosted and applied to the output terminal of the capacitor 44, so that the capacitor 44 can be charged.

  The discharge circuit 43 is connected to the charging circuit 42 in series. The discharge circuit 43 includes a pair of switching elements 43A and 43B connected in series. The switching elements 43A and 43B are n-channel MOSFETs. The source of the upper switching element 43A is connected to the drain of the lower switching element 43B. The drain of the switching element 43A on the upper stage side is connected to the output terminal (connection point P2) of the capacitor 44. The source of the lower switching element 43B is connected to the input terminal (connection point P5) of the capacitor 44. A connection point P4 between the pair of switching elements 43A and 43B is connected to a motor drive circuit 52 in the EPS ECU 12.

  When the lower switching element 43B is on and the upper switching element 43A is off, power is supplied from the main power supply 31 to the motor drive circuit 52. When the lower switching element 43B is off and the upper switching element 43A is on, discharging from the capacitor 44 to the motor drive circuit 52 is possible. As a result, electric power is supplied to the motor drive circuit 52 by both the main power supply 31 and the capacitor 44. When the lower switching element 43B and the upper switching element 43A are alternately turned on, the voltage VD applied to the motor drive circuit 52 can be changed according to the ratio of the on time of both.

  The current sensor 45 detects the output current (battery current IB) of the main power supply 31. The current sensor 46 detects the output current (capacitor current Ic) of the capacitor 44. The voltage sensor 47 detects a voltage between terminals of the capacitor 44 (capacitor voltage Vc). The detection values of the current sensors 45 and 46 and the detection value of the voltage sensor 47 are input to the power supply control ECU 33. The input voltage VD of the motor drive circuit 52 is detected by the voltage sensor 48. The detection value of the voltage sensor 48 is input to the power supply control ECU 33. The power control ECU 33 receives an ignition state detection signal (not shown) indicating the state of the ignition key.

The power supply control ECU 33 performs on / off control of the relay 41 based on the ignition state detection signal. The power supply control ECU 33 performs on / off control of the four switching elements 42A, 42B, 43A, and 43B in the auxiliary power supply device 32 based on detection values of the current sensors 45 and 46, the voltage sensors 47 and 48, and the like.
The power supply control ECU 33 has a function of monitoring whether or not a main power supply abnormality has occurred. The main power supply abnormality means a state in which an appropriate voltage is not applied from the main power supply 31 to the motor drive circuit 52 due to a failure of the main power supply 31, a failure of the relay 41, or the like.

  When the main power supply abnormality is not detected (hereinafter referred to as “normal control”), the power supply control ECU 33 controls the four switching elements 42A, 42B, 43A, and 43B based on the main power supply power PS. To do. The main power supply power PS is the actual power of the main power supply 31 consumed by the EPS ECU 12 through the assist control, and is calculated based on, for example, the detection value (battery current IB) of the current sensor 45.

  Specifically, when the main power supply power PS is less than a predetermined charge / discharge threshold KE, the power supply control ECU 33, for example, turns on the lower switching element 43B in the discharge circuit 43 to turn on the upper stage side. The switching element 43A is set to OFF. Further, the power supply control ECU 33 alternately turns on the pair of switching elements 42A and 42B in the charging circuit 42 as necessary. As a control method for alternately turning on the switching elements 42A and 42B in the charging circuit 42 when the main power supply power PS is less than the charge / discharge threshold KE, a method disclosed in Japanese Patent Application Laid-Open No. 2014-150672 is used. May be. As a result, power is supplied to the motor drive circuit 52 only by the main power supply 31, and the capacitor 44 is charged as necessary.

  When the main power supply power PS is equal to or greater than a predetermined charge / discharge threshold value KE, the power supply control ECU 33 turns off the pair of switching elements 42A and 42B in the charging circuit 42. Further, for example, the power control ECU 33 sets the upper switching element 43A in the discharge circuit 43 to ON and sets the lower switching element 43B to OFF. As a result, electric power is supplied to the motor drive circuit 52 by both the main power supply 31 and the capacitor 44. In this case, the power supply control ECU 33 may alternately turn on the pair of switching elements 43A and 43B in the discharge circuit 43. As a control method for alternately turning on the switching elements 43A and 43B in the discharge circuit 43 when the main power supply power PS is equal to or higher than the charge / discharge threshold KE, a method disclosed in Japanese Patent Application Laid-Open No. 2014-91343 is used. May be.

FIG. 3 is a flowchart showing a procedure of main power supply abnormality monitoring processing by the power supply control ECU 33.
The power supply control ECU 33 determines whether or not the input voltage VD of the motor drive circuit 52 is equal to or lower than a predetermined value A (A> 0) (step S1). The input voltage VD is detected by the voltage sensor 48. When the input voltage VD is larger than the predetermined value A (step S1: NO), the power supply control ECU 33 returns to step S1.

  When it is determined in step S1 that the input voltage VD is equal to or less than the predetermined value A (step S1: YES), the power supply control ECU 33 is in a state where the input voltage VD is equal to or less than the predetermined value A for a predetermined time or more. It is determined whether or not it has been continued (step S2). When the state where the input voltage VD is equal to or less than the predetermined value A does not continue for the predetermined time or longer (step S2: NO), the power supply control ECU 33 returns to step S1.

  When it is determined in step S2 that the state where the input voltage VD is equal to or less than the predetermined value A continues for a predetermined time or longer (step S2: YES), the power supply control ECU 33 determines that a main power supply abnormality has occurred. In this case, the power supply control ECU 33 notifies the motor control circuit 51 in the EPS ECU 12 that a main power supply abnormality has occurred (step S3), and a power supply for switching the power supply from the main power supply 31 to the capacitor 44. Switching processing is performed (step S4). Specifically, the power supply control ECU 33 turns off the upper switching element 42A in the charging circuit 42, turns on the lower switching element 42B, and turns on the upper switching element 43A in the discharge circuit 43. The lower switching element 43B is turned off. As a result, the electric charge accumulated in the capacitor 44 is discharged to the motor drive circuit 52 and the electric motor 18. Therefore, even when the main power supply is abnormal, the EPS ECU 12 can continue the assist control. However, when the capacitor voltage Vc falls below the minimum EPS operable voltage VL (for example, 9 [V]) by the EPS ECU 12, the assist control is stopped.

FIG. 4 is a block diagram showing the configuration of the motor control circuit 51 in the EPS ECU 12.
The motor control circuit 51 includes a CPU and a memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a target current value setting unit 61, a target current value correction unit 62, a current deviation calculation unit 63, a PI control unit 64, a PWM control unit 65, and a current detection unit 66. It is.

The target current value setting unit 61 sets the target current value Im ^* based on the steering torque T detected by the torque sensor 11 and the vehicle speed V detected by the vehicle speed sensor 24. A setting example of the target current value Im ^{* with} respect to the detected steering torque T is shown in FIG. For the detected steering torque T, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The target current value Im ^* is a positive value when a steering assist force for rightward steering is to be generated from the electric motor 18, and a steering assist force for leftward steering is to be generated from the electric motor 18. Sometimes it is negative.

The target current value Im ^* is positive with respect to a positive value of the detected steering torque T, and is negative with respect to a negative value of the detected steering torque T. When the detected steering torque T is a minute value in the range (torque dead zone) of -T1 to T1 (for example, T1 = 0.4 N · m), the target current value Im ^* is set to zero. When the detected steering torque T is a value outside the range of -T1 to T1, the target current value Im ^* is set such that the absolute value of the target current value Im ^* increases as the absolute value of the detected steering torque T increases. ing. Further, the target current value Im ^* is set such that the absolute value thereof decreases as the vehicle speed V detected by the vehicle speed sensor 24 increases. As a result, a large steering assist force can be generated during low-speed traveling, and the steering assist force can be reduced during high-speed traveling.

In this embodiment, the target current value correction unit 62 gradually decreases the target current value Im ^* set by the target current value setting unit 61 according to the decrease in the capacitor voltage Vc when the main power supply is abnormal. During normal control, the target current value correction unit 62 outputs the target current value Im ^* set by the target current value setting unit 61 as it is. Details of the configuration and operation of the target current value correction unit 62 will be described later. The target current value Im ^* output from the target current value correcting unit 62 is given to the current deviation calculating unit 63.

The current detection unit 66 detects the motor current (actual current value) Im based on the output signal of the current sensor 53. The current deviation calculation unit 63 calculates a deviation (current deviation ΔIm = Im ^* −Im) between the target current value Im ^* output from the target current value correction unit 62 and the actual current value Im detected by the current detection unit 66. To do.
The PI control unit 64 performs a PI calculation on the current deviation ΔIm calculated by the current deviation calculation unit 63 to generate a drive command value for guiding the current Im flowing through the electric motor 18 to the target current value Im ^* . The PWM control unit 65 generates a PWM control signal having a duty ratio corresponding to the drive command value and supplies the PWM control signal to the motor drive circuit 52. As a result, electric power corresponding to the drive command value is supplied to the electric motor 18.

The current deviation calculation unit 63 and the PI control unit 64 constitute a current feedback control unit. By the action of the current feedback control means, the motor current Im flowing through the electric motor 18 is controlled so as to approach the target current value Im ^* .
The configuration and operation of the target current value correction unit 62 will be described in detail. The target current value correction unit 62 includes a correction gain calculation unit 71 and a correction gain multiplication unit 72. The correction gain calculator 71 calculates the correction gain G based on the capacitor current Ic and the capacitor voltage Vc when the main power supply is abnormal. The correction gain calculator 71 sets the correction gain G to 1 during normal control. When the main power supply abnormality occurs, the power control ECU 33 notifies the motor control circuit 51 to that effect, so that the correction gain calculation unit 71 can recognize that the main power supply abnormality has occurred.

Correction gain multiplication unit 72, the correction gain G is calculated by the correction gain calculation unit 71, by multiplying the set target current value Im ^* by the target current value setting unit 61 corrects the target current value Im ^* .
FIG. 6 is a flowchart showing the procedure of the correction gain calculation process when the main power supply is abnormal, which is executed by the correction gain calculation unit 71 when the main power supply is abnormal.

  The correction gain calculator 71 acquires the capacitor voltage Vc and the capacitor current Ic via the power supply control ECU 33 (step S11). Then, the correction gain calculator 71 converts the capacitor voltage Vc into a reference voltage Vco in which voltage fluctuation due to a change in capacitor current is reduced (steps S12 and S13). The voltage fluctuation component of the capacitor voltage Vc is considered to be a voltage drop due to the resistance of the electric motor 18 (resistance between motor terminals). Therefore, the correction gain calculation unit 71 first calculates the correction voltage Vcmp corresponding to the voltage fluctuation component of the capacitor voltage Vc based on the following equation (1) (step S12).

Vcmp = Ic × Rm (1)
In the formula (1), Rm is the resistance of the electric motor 18.
Then, as shown in the following equation (2), the correction gain calculation unit 71 calculates the reference voltage Vco with reduced voltage fluctuation by adding the correction voltage Vcmp to the capacitor voltage Vc (step S13).

Vco = Vc + Vcmp (2)
Thereafter, the correction gain calculator 71 sets the correction gain G based on the reference voltage Vco (step S14). An example of setting the correction gain G with respect to the reference voltage Vco is shown in FIG. The correction gain G is set so as to decrease as the reference voltage Vco decreases. FIG. 7 shows an example in which the maximum value of the capacitor voltage Vc is 14.5 [V] and the minimum EPS operable voltage VL is 9 [V]. Specifically, in a range where the reference voltage Vco is less than Vco1 [V] and a range larger than Vco2 (> Vco1) [V], the rate of change of the correction gain G with respect to the reference voltage Vco is set to be small. For example, Vco1 is about 11 [V], and Vco2 is about 12.5 [V], for example. On the other hand, when the reference voltage Vco is in the range of Vco1 [V] to Vco2 [V], the rate of change of the correction gain G with respect to the reference voltage Vco is set large. The correction gain G set by the correction gain calculator 71 is given to the correction gain multiplier 72.

Thereafter, the correction gain calculation unit 71 determines whether or not the reference voltage Vco is equal to or lower than the minimum voltage VL at which EPS operation is possible (step S15). When the reference voltage Vco is greater than the minimum EPS operable voltage VL (step S15: NO), the correction gain calculation unit 71 returns to step S11.
If it is determined in step S15 that the reference voltage Vco is equal to or lower than the minimum EPS operable voltage VL (step S15: YES), the correction gain calculation unit 71 ends the correction gain calculation process when the main power supply is abnormal. .

In the embodiment, the assist control can be continued by the capacitor (auxiliary power source) 44 when the main power source is abnormal. In addition, when the main power supply is abnormal, the correction gain G for reducing and correcting the target current value Im ^* can be gradually decreased in accordance with the decrease in the capacitor voltage Vc. As a result, the assist force can be gradually reduced as the capacitor voltage Vc decreases. As a result, the driver can be given a sign that the assist has been cut off, so that the occurrence of so-called steering wheel removal can be suppressed when the assist is cut off. In addition, the continuation time of assist control when the main power supply is abnormal can be extended. In other words, the capacitance of the capacitor 44 can be reduced.

In this embodiment, when the main power supply is abnormal, the correction gain G is not set based on the capacitor voltage Vc itself, but is a reference that is the capacitor voltage Vc after the voltage fluctuation due to the change in the capacitor current is reduced. It is set based on the voltage Vco. Thereby, the correction gain G can be smoothly reduced according to the decrease in the capacitor voltage Vc. Therefore, the target current value Im ^* can be smoothly reduced according to the decrease in the capacitor voltage Vc, so that the steering feeling when the main power supply is abnormal can be improved.

In the embodiment described above, the target current value is corrected by correcting the target current value Im ^* set by the target current value setting unit 61 by the target current value correcting unit 62 when the main power supply is abnormal. However, the target current value may be corrected by changing the map used in the target current value setting unit 61 based on the reference voltage Vco. Specifically, a plurality of maps (maps of target current values with respect to steering torque) corresponding to a plurality of reference voltages Vco are created and stored in advance. Further, a map selection unit is provided that calculates the reference voltage Vco from the capacitor voltage Vc and selects a map corresponding to the calculated reference voltage Vco when the main power supply is abnormal. The target current value setting unit 61 sets a target current value using the map selected by the map selection unit when the main power supply is abnormal. In this case, the target current value correction unit 62 in FIG. 4 is not necessary.

In the embodiment described above, the auxiliary power source is constituted by a capacitor, but the auxiliary power source may be an auxiliary power source other than the capacitor.
In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 12 ... ECU for EPS, 31 ... Main power supply, 32 ... Auxiliary power supply apparatus, 33 ... Power supply control ECU, 44 ... Capacitor, 46 ... Current sensor, 47 ... Voltage sensor, 52 ... Motor drive circuit , 61 ... target current value setting unit, 62 ... target current value correction unit, 71 ... correction gain calculation unit, 72 ... correction gain multiplication unit

Claims (5)

An electric power steering device comprising a main power source and an auxiliary power source, and supplying power from the auxiliary power source to a drive circuit of an electric motor when the main power source is abnormal,
Current detecting means for detecting an output current of the auxiliary power source;
Voltage detecting means for detecting a voltage between terminals of the auxiliary power source;
Based on the output current detected by the current detection means when the main power supply is abnormal, the voltage between the terminals detected by the voltage detection means is converted to a reference voltage in which voltage fluctuation due to the output current change of the auxiliary power supply is reduced. Conversion means to
An electric power steering apparatus comprising: target current value correcting means for correcting a target current value of the electric motor based on a reference voltage obtained by the converting means. When the output current detected by the current detection means is Ic, the terminal voltage detected by the voltage detection means is Vc, and the resistance of the electric motor is Rm, the conversion means is expressed by the following equation (a). The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to convert the inter-terminal voltage Vc into a reference voltage Vco based on the base voltage Vc.
Vco = Vc + Ic · Rm (a) Steering torque acquisition means for acquiring steering torque;
A target current value setting means for setting a target current value of the electric motor using the steering torque acquired by the steering torque acquisition means;
The target current value correcting unit is configured to correct a target current value set by the target current value setting unit based on a reference voltage obtained by the converting unit. The electric power steering apparatus as described. The target current value correcting means includes
Correction gain setting means for setting a correction gain based on the reference voltage obtained by the conversion means;
The electric motor according to claim 3, further comprising: means for correcting the target current value by multiplying the target current value set by the target current value setting means by the correction gain set by the correction gain setting means. Power steering device.   The electric power steering apparatus according to any one of claims 1 to 4, wherein the auxiliary power source includes a capacitor.

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