JP5224032B2 - Steering control device - Google Patents

Description

  The present invention relates to a steering control device for driving and controlling an AC motor for assisting steering of a vehicle.

Conventionally, as this type of steering control device, an assist torque command value to be output to an AC motor is determined as a q-axis current command value of the vector control method, and d of the vector control method is used to perform field weakening control of the AC motor. What determines an axial current command value is known. Here, in the vector control method, the field flux direction of the AC motor is referred to as the d-axis, and the direction orthogonal to the field flux direction is referred to as the q-axis. Therefore, the d-axis current directed in the d-axis direction does not directly contribute to the output torque of the AC motor, and only the q-axis current directed in the q-axis direction directly contributes to the output torque of the AC motor. The field weakening control is performed only when the rotational speed of the AC motor exceeds a predetermined reference rotational speed and the back electromotive force becomes a problem. That is, the d-axis current flows only when the steering wheel is sharply operated and the rotational speed of the AC motor exceeds a predetermined reference rotational speed (see, for example, Patent Document 1).
JP 2007-153273 A (paragraphs [0026], [0031], FIGS. 1 and 2)

  By the way, in the vector control method, in order to convert the q-axis current and the d-axis current into the phase current of the AC motor, information on the electrical angle of the AC motor is required. However, there are cases where the actual electrical angle of the AC motor and the electrical angle detected by the rotational position sensor do not exactly match due to the detection error of the rotational position sensor provided in the AC motor. FIG. 6 shows a qd coordinate system for the true electrical angle of the AC motor, and a q′-d ′ coordinate system when the rotational position sensor makes a false detection with an error angle α shifted from the true electrical angle. It is shown. Here, the d-axis current command value Id * ′ is determined to be a predetermined value “Id * ′ 1” based on the electrical angle erroneously detected by the rotational position sensor, and the q-axis current command value Iq * ′ is set to “0”. If determined, the current is supplied to the AC motor in accordance with the q-axis current command value Iq * 1 obtained by projecting the d-axis current command value Id * ′ onto the q-axis of the qd coordinate system. Will be energized. That is, if the rotational position sensor is not erroneously detected, a q-axis current that should not be energized is energized to the AC motor, and assist torque resulting from the d-axis current command value Id * 'is output. In the conventional steering control device, when the predetermined condition is satisfied, only the q-axis current is limited and the current limitation is not performed on the d-axis current. Therefore, only the q-axis current is limited. In this case, the influence of the d-axis current command value Id * ′ on the assist torque is increased, and the steering feeling may be uncomfortable.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a steering control device capable of preventing the uncomfortable feeling of steering feeling when the current is limited.

  In order to achieve the above object, the steering control device (40) according to the invention of claim 1 includes a motor drive current (Iu, Iv, Iw) to an AC motor (19) for assisting steering of the vehicle (10). Is determined as the q-axis current command value (Iq *), and the inverter torque (43) is generated from the output of the battery (92), and the assist torque command value to be output to the AC motor (19) according to the operation status. A current command value determining unit (50) for determining a d-axis current command value (Id *) for performing field-weakening control while suppressing back electromotive force of the AC motor (19) and a current command value determining unit (50) are determined. The q-axis current limiting unit (83) includes a q-axis current limiting unit (83) that limits the q-axis current command value (Iq *) when a predetermined condition is satisfied. Q-axis current command value (Iq ). If it is limited, having characterized in that with a d-axis current command value at the same rate as the restriction (d-axis current limiting unit (84 to limit the Id *)).

  According to a second aspect of the present invention, in the steering control device (40) according to the first aspect, the battery output voltage detecting means (81) for detecting the output voltage (Vb) of the battery (92) and the output of the battery (92). Maximum allowable power determining means (MAP2) for determining the maximum allowable power (W *) that can be supplied to the AC motor (19) according to the voltage (Vb), and the maximum allowable power determined by the maximum allowable power determining means (MAP2) When power is W *, q-axis current command value is Iq *, d-axis current command value is Id *, q-axis voltage command value is Vq *, and d-axis voltage command value is Vd *, W When the relationship of * <Iq * · Vq * + Id * · Vd * is established, the limiting coefficient γ obtained by γ = W * / (Iq * · Vq * + Id * · Vd *) Multiplying the current command value (Iq *, Id *) of the shaft, these q-axis and d-axis And a command value limiter (82) for limiting the current command value (Iq *, Id *).

[Invention of Claim 1]
According to the configuration of the first aspect, even if the q-axis current resulting from the d-axis current command value is actually energized to the AC motor due to the detection error of the electrical angle of the AC motor, the predetermined condition is satisfied and the q-axis is satisfied. When the current command value is restricted, the d-axis current command value is also restricted in conjunction with the restriction of the q-axis current command value, so that the q-axis current resulting from the d-axis current command value is also restricted. Thereby, the influence of the q-axis current resulting from the d-axis current command value with respect to the assist torque can be suppressed, and the uncomfortable feeling of steering feeling can be prevented.

[Invention of claim 2]
According to the configuration of claim 2, the maximum allowable power W * determined according to the output voltage of the battery, the q-axis current command value Iq *, the d-axis current command value Id *, and the q-axis voltage command value Vq *. When the relationship between the d-axis voltage command value and Vd * is W * <Iq * · Vq * + Id * · Vd *, γ = W * / (Iq * · Vq * + Id * · Vd *) is multiplied by the q-axis and d-axis current command values to limit the q-axis and d-axis flow command values. Thereby, the electric power which can be supplied from a battery can be effectively utilized for an AC motor.

[First Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a vehicle 10 equipped with an electric power steering device 11. The electric power steering device 11 includes a steered wheel shaft 13 extending in the left-right direction of the vehicle 10, and the steered wheel shaft 13 is inserted into a cylindrical housing 15 fixed to the vehicle body 10H. . Moreover, the both ends of the shaft 13 between steered wheels are connected with each steered wheel 12 and 12 via the tie rods 14 and 14, and when the shaft 13 between steered wheels moves straight, the steered wheels 12 and 12 will steer. ing.

  The electric power steering apparatus 11 includes an AC motor 19 (hereinafter simply referred to as “motor 19”) as a drive source. The motor 19 is, for example, a three-phase AC motor having a hollow cylindrical structure, which is fixed in the cylindrical housing 15, and the steered wheel shaft 13 passes through the center of the motor 19. Then, the ball nut 22 fixed to the inner surface of the cylindrical rotor 21 in the motor 19 and the ball screw portion 23 formed on the outer surface of the inter-steering wheel shaft 13 are screwed together, and when the rotor 21 rotates, the ball screw portion 23 is Move directly. The motor 19 is provided with a rotational position sensor 25 for detecting the rotational position θ2 of the rotor 21. The U, V, W phase windings in the motor 19 are, for example, star-connected. Then, a motor drive current from an inverter circuit 43 to be described later flows, for example, from any one of U, V, W phase windings to the remaining two phase windings, or U, V , W flow from any two phase windings to the remaining one phase winding.

  A rack 24 is formed on one end side of the inter-steering wheel shaft 13, and a pinion 18 provided at a lower end portion of the steering shaft 16 is engaged with the rack 24. A handle 17 is attached to an upper end portion of the steering shaft 16, and a torque sensor 27 and a steering angle sensor 26 are attached to an intermediate portion of the steering shaft 16. Then, the steering angle sensor 26 detects the steering angle θ1 of the handle 17, and the torque sensor 27 detects the load torque Tf. Further, a vehicle speed sensor 28 for detecting the vehicle speed V from the rotational speed is provided in the vicinity of the steered wheel 12.

  In order to drive and control the motor 19, a steering control device 40 according to the present invention is mounted on the vehicle 10. As shown in FIG. 2, the steering control device 40 includes an inverter circuit 43 and a signal processing circuit 44. Further, the steering control device 40 is activated by being connected to the battery 92 by turning on the ignition switch 94.

  The inverter circuit 43 is a three-phase bridge circuit including U, V, and W phase circuits 43U, 43V, and 43W between a positive electrode and a negative electrode (GND) of the battery 92. The U-phase circuit 43U is provided with an upper-stage switch UH and a lower-stage switch UL connected in series, and a motor drive is connected to a U-phase output line 19U extending from a common connection point of both the switches UH and UL. A U-phase winding of the motor 19 is connected via a current sensor Su (for example, a shunt resistor) for detecting the current Iu. Similarly, the V-phase circuit 43V includes an upper-stage switch VH and a lower-stage switch VL, and the V-phase winding of the motor 19 is connected to the V-phase output line 19V via the current sensor Sv. At the same time, the W-phase circuit 43W includes an upper-stage switch WH and a lower-stage switch WL, and the W-phase winding of the motor 19 is connected to the W-phase output line 19W via the current sensor Sw. Further, the switch groups UH, UL, VH,... Are composed of, for example, N-channel MOSFETs, and the gate terminals of these MOSFETs are connected to the signal processing circuit 44.

  The signal processing circuit 44 includes a CPU 45, a storage unit 46, an A / D converter 47, an input interface 48 and an output interface 49. The CPU 45 receives the detection signals of the vehicle speed sensor 28, the steering angle sensor 26, and the rotational position sensor 25 through the input interface 48, and the torque sensor 27, current sensors Su, Sv, Sw through the A / D converter 47. , And a detection signal of a voltage sensor 81 described later is taken in. The CPU 45 outputs an on / off control signal to the switch groups UH, UL, VH,... Of the inverter circuit 43 via the output interface 49 to control the inverter circuit 43.

  Here, the motor drive currents Iu, Iv, Iw flow through the respective phase windings of the motor 19 from the upper stage side of the inverter circuit 43 and then flow to the lower stage side of the inverter circuit 43. Specifically, the switch group UH, UL, VH,... Of the inverter circuit 43 is such that any one of the upper switches UH, VH, WH is turned on and the lower switches UL, VL, WL are turned on. There are a pattern in which any two of them are turned on and a pattern in which any two of the upper switches UH, VH, WH are turned on and any one of the lower switches UL, VL, WL is turned on. As an example, the broken line arrow in the inverter circuit 43 in FIG. 2 indicates that, for example, only the V-phase switch VH is on on the upper side of the inverter circuit 43 and only the U-phase and W-phase switches UL and WL are on on the lower side. In this case, the motor drive current is shown. In this case, the motor drive current Iv flows into the V-phase winding of the motor 19 from the upper stage side of the inverter circuit 43 through the current sensor Sv, and the motor drive current Iv is divided into the U and W-phase windings of the motor 19 to The drive currents Iu and Iw are obtained. Among them, the motor drive current Iu flows into the lower stage side of the inverter circuit 43 through the current sensor Su, and the motor drive current Iw flows into the lower stage side of the inverter circuit 43 through the current sensor Sw. Then, the CPU 45 switches the on / off pattern of each switch group UH, UL, VH,... According to the rotational position of the rotor 21 detected by the rotational position sensor 25, so that the motor drive currents Iu, Iv, Iw are changed. The three-phase alternating currents that are 120 degrees out of phase with each other are passed through the motor 19.

  In the steering control device 40, the CPU 45 executes a motor control program (not shown) stored in the storage unit 46, whereby the control system shown in the block diagram of FIG. 3 is configured. In the figure, reference numeral 50 denotes a current command value determination unit, which is used to determine the current command values for the motor drive currents Iu, Iv, Iw as q-axis current command value Iq * and d-axis current command value in the vector control method. Output as Id *.

  Here, since only the q-axis current of the q-axis current and the d-axis current directly contributes to the output torque of the motor 19, the current command value determination unit 50 assists the motor 19 to output the q-axis current command value Iq *. It is determined as a torque command value. On the other hand, since the d-axis current can reduce the counter electromotive force of the motor 19 as will be described in detail later, the current command value determination unit 50 determines that the rotational speed (rotational speed) of the motor 19 is a predetermined reference rotational speed. In such a case, field weakening control is performed by applying a d-axis current. Hereinafter, the process for determining the q-axis current command value Iq * and the process for determining the d-axis current command value Id * will be described separately.

  The q-axis current command value Iq * is determined as follows. That is, the current command value determining unit 50 is based on the load torque Tf detected by the torque sensor 27 and the torque-current command value map (not shown) stored in the storage unit 46 (see FIG. 2). An assist current command value (= Ix) corresponding to Tf is determined. Further, the steering angle θ1 detected by the steering angle sensor 26 is differentiated with respect to time to obtain a steering angular velocity, and based on the steering angular velocity and a steering angular velocity-current command value map (not shown) stored in the storage unit 46, A damper current command value (= Iy) corresponding to the steering angular velocity is determined. Further, the gain (= G1) is determined from the vehicle speed V detected by the vehicle speed sensor 28 and the vehicle speed-gain map (not shown) stored in the storage unit 46. The q-axis current command value Iq * (= G1 · (Ix−Iy)) is determined by multiplying the value obtained by subtracting the damper current command value from the assist current command value.

  The torque-current command value map is set such that, for example, the assist current command value increases as the load torque Tf increases. As a result, the increase in the load torque Tf can be reduced by the assist torque of the motor 19 according to the assist current command value, and the driver can feel the stable steering reaction force regardless of the friction coefficient of the road surface. The operation can be performed.

  The steering angular velocity-current command value map is set so that the damper current command value increases as the steering angular velocity increases. Since this damper current command value is subtracted from the assist current command value, when the steering operation is performed steeply, the steering resistance increases, and a damper effect is produced.

  Further, the vehicle speed-gain map is set so that the gain decreases as the vehicle speed V increases. As a result, the assist torque of the motor 19 decreases as the vehicle speed V increases, and sudden steering at high speed is restricted, while the vehicle 10 can be turned significantly by light steering at low speed.

  The d-axis current command value Id * is determined as follows. That is, the current command value determination unit 50 obtains the rotational speed N (rotational speed) per unit time of the motor 19 by differentiating the rotational position of the motor 19 detected by the rotational position sensor 25 with respect to time. Then, the d-axis current command value Id * is determined based on the rotation speed N and the rotation speed-d-axis current command value map MAP1 (see FIG. 4A) stored in the storage unit 46. Here, in the rotational speed-d-axis current command value map MAP1, the d-axis current command value Id * is “0” while the rotational speed N of the motor 19 reaches 0 to a predetermined reference rotational speed N1, When the number N becomes equal to or higher than the reference rotational speed N1, the value of the d-axis current command value Id * with respect to the rotational speed N is set so as to satisfy the relationship of the following formula (4). And when d-axis current satisfy | fills the relationship of following formula (4), since a counter electromotive force is canceled, the fall of the assist torque by the back electromotive force or the fall of a rotation speed can be prevented. That is, field weakening control can be performed.

Specifically, in the vector control method, the following known voltage-current equations (1) and (2) are established among the q-axis current Iq, the q-axis voltage Vq, the d-axis current Id, and the d-axis voltage Vd. .
Vd = (Ra + p · Lq) · Id−ω · Lq · Iq (1)
Vq = ω · Ld · Id + (Ra + p · Lq) · Iq + ω · Ke (2)

Ke: Counter electromotive voltage constant Ld: Self-inductance of d-axis armature winding Lq: Self-inductance of q-axis armature winding Ra: Armature winding resistance p: Differential operator ω: Motor rotation speed (number of rotations)

  Here, “ω · Ke” in the third term in the above formula (2) is a counter electromotive voltage. Moreover, the said Formula (2) can be deform | transformed like the following formula | equation (3) ("A" in Formula (3) is a constant).

  Vq = A · Iq + ω (Ld · Id + Ke) (3)

  As is clear from this equation (3), in order to cancel the back electromotive voltage, a d-axis current satisfying the relationship of the following equation (4) may be supplied to the motor 19.

  Id = −Ke / Ld (4)

  Accordingly, the rotational speed-d-axis current command value map MAP1 (see FIG. 4A) satisfies the relationship of the above formula (4) when the rotational speed N of the motor 19 becomes equal to or higher than the reference rotational speed N1. In addition, the value of the d-axis current command value Id * with respect to the rotation speed N is set.

  Based on the q-axis current command value Iq * and the d-axis current command value Id * determined as described above, three-phase AC motor drive currents Iu, Iv, and Iw are generated as follows. That is, as shown in FIG. 3, the q-axis current command value Iq * determined by the current command value determination unit 50 is multiplied by the q-axis current limit coefficient G10, and the q-axis current detection value Iqf fed back as described later. At the same time, it is taken into the PI controller 51q for the q axis. Here, both the q-axis current limiting coefficient G10 and the d-axis current limiting coefficient G11 described below are normally “1”.

  Similarly, the d-axis current command value Id * determined by the current command value determination unit 50 is multiplied by the d-axis current limit coefficient G11, and the d-axis PI control is performed together with the d-axis current detection value Idf fed back as described later. Into the container 51d. The q-axis and d-axis PI controllers 51q and 51d respectively perform PI control to calculate q-axis and d-axis voltage command values Vq * and Vd *. Then, a 2-3 phase converter (dq reverse converter) 52 performs a dq reverse conversion on the q-axis and d-axis voltage command values Vq * and Vd * to provide a current command value for three-phase AC. Vu *, Vv *, Vw * are calculated.

  Based on the current command values Vu *, Vv *, and Vw *, three-phase AC motor drive currents Iu, Iv, and Iw are generated, and the PWM control unit 53 performs PWM control on the motor drive currents Iu, Iv, and Iw. . Specifically, the PWM control unit 53 turns on and off the switches UH, UL, VH,... From the intersection of the current command values Vu *, Vv *, Vw * and a predetermined triangular wave (not shown). PWM command values PWMu, PWMv, PWMw are generated and applied to the switches UH, UL, VH,. As a result, three-phase AC motor drive currents Iu, Iv, and Iw are output from the inverter circuit 43 to the motor 19.

  Further, the current sensors Su, Sv, Sw obtain current detection values Iuf, Ivf, Iwf for the three-phase AC motor drive currents Iu, Iv, Iw, and send them to the 3-2-2 phase converter (dq converter) 54. take in. The current detection values Iuf, Ivf, and Iwf are dq converted into a q-axis current detection value Iqf and a d-axis current detection value Idf by a 3-2 phase converter (dq converter) 54. The q-axis current detection value Iqf is fed back to the q-axis PI controller 51q, and the d-axis current detection value Idf is fed back to the d-axis PI controller 51d.

  The rotational position θ2 of the rotor 21 detected by the rotational position sensor 25 of the motor 19 is converted into the electrical angle θrm by the electrical angle converter 58, and then the 3-2 phase converter 54 and the 2-3 phase converter. 52 for dq conversion and dq reverse conversion.

  In the steering control device 40 of the present embodiment, for example, in order to limit the assist torque output by the motor 19 when the steering wheel 17 is turned to the limit and the end state is reached, the q-axis current limiting coefficient G10 described above is used. The value is changed from a normal value “1” to a predetermined value (eg, 0.5). This is because if the steering wheel 12 is in the end contact state and the steered wheels 12 do not steer, if the motor 19 outputs an assist torque, the assist torque may cause deformation of mechanical structural parts of the steering system. It is. Therefore, when the end contact detection unit 85 provided in the steering control device 40 detects the end contact of the steering wheel 17, the q-axis current limiting unit 83 sets the value of the q-axis current limit coefficient G10 to a predetermined value (less than 1) ( For example, the q-axis current command value Iq * is limited to 0.5).

  In addition, the end contact detection part 85 can determine with "it is an end contact state" on condition that all the following 3 end contact determination requirements of (1)-(3) are satisfy | filled, for example. (1) The amount of change in the q-axis current detection value Iqf is greater than a preset threshold, (2) the load torque Tf is greater than a preset threshold, and (3) the steering angular velocity is preset. Greater than the threshold value.

  In the present embodiment, the d-axis current limiting unit 84 limits the d-axis current command value Id * in conjunction with the limitation of the q-axis current command value Iq * by the q-axis current limiting unit 83. . Specifically, the d-axis current limiting unit 84 changes the value of the d-axis current limiting coefficient G11 to the same value as the q-axis current limiting coefficient G10.

  In the present embodiment, when the remaining amount of the battery 92 decreases, the command value limiter 82 limits the q-axis and d-axis current command values Iq * and Id *. Specifically, the command value limiter 82 acquires the output voltage of the battery 92 detected by the voltage sensor 81, and the maximum allowable power that can be supplied to the motor 19 is shown in the battery voltage-motor allowable power map MAP2 shown in FIG. (Corresponding to “maximum allowable power determining means” of the present invention). The battery voltage-motor allowable power map MAP2 indicates that when the output voltage Vb of the battery 92 is equal to or higher than the first reference voltage Vb1, the motor allowable power W * becomes the maximum power W1 of the motor 19 itself. Is set.

  Further, when the output voltage Vb of the battery 92 becomes smaller than the first reference voltage Vb1, the motor allowable power W * gradually decreases in proportion to the decrease of the output voltage Vb of the battery 92, and the output of the battery 92 When the voltage Vb becomes smaller than the second reference voltage Vb2, the motor allowable power W * is set to “0”.

  Then, the command value limiter 82 includes the following among the maximum allowable power W *, the q-axis current command value Iq *, the d-axis current command value Id *, the q-axis voltage command value Vq *, and the d-axis voltage command value Vd *. It is determined whether or not the relationship of the formula (5) is established, and if it is established, the limiting coefficient γ is calculated from the following formula (6). Then, the values of the q-axis current limiting coefficient G10 and the d-axis current limiting coefficient G11 are changed to the limiting coefficient γ, thereby limiting the power consumption of the motor 19.

W * <Iq * · Vq * + Id * · Vd * (5)
γ = W * / (Iq * · Vq * + Id * · Vd *) (6)

  The description related to the configuration of the present embodiment has been described above, and the function and effect of the present embodiment will be described next. When the ignition switch 94 of the vehicle 10 is turned on, the steering control device 40 operates by receiving electric power from the battery 92. When the steering wheel 17 is steered, the motor 19 outputs an assist torque to assist the steering. At this time, the steering control device 40 takes in the detection results of the steering angle sensor 26, the torque sensor 27, and the vehicle speed sensor 28 as information relating to the driving situation, and based on these detection results, a q-axis current command as a command value of the assist torque. The value Iq * is determined. Then, three-phase AC motor drive currents Iu, Iv, and Iw corresponding to the q-axis current command value Iq * are generated by the inverter circuit 43, and the motor 19 is energized to output assist torque.

  As described above, the q-axis current command value Iq * is changed according to the operation state, but the d-axis current command value Id * is normally set to “0”. When the handle 17 is sharply turned, the d-axis current command value Id * becomes a value other than “0”. Specifically, when the handle 17 is sharply turned, the rotation speed of the motor 19 for outputting the assist torque following the steering wheel 17 increases. When the motor 19 exceeds the reference rotational speed N1, the assist torque begins to decrease rapidly due to the influence of the counter electromotive force (see the broken line in FIG. 4B). Therefore, in the present embodiment, when the rotational speed of the motor 19 exceeds the reference rotational speed N1, the d-axis current command value Id is based on the rotational speed-d-axis current command value map MAP1 shown in FIG. Set field * to a value other than “0” to perform field weakening control. Thereby, the counter electromotive force of the motor 19 is suppressed, and the reduction of the assist torque can be mitigated.

  Now, when the handle 17 is cut to the limit and is in the abutting state, the q-axis current limiter 83 limits the q-axis current command value Iq * in order to suppress the assist torque and protect the mechanical parts of the steering system. Then, the d-axis current limiter 84 limits the d-axis current command value Id * in conjunction with the q-axis current limiter 83. That is, when the q-axis current command value Iq * is limited while the field weakening control is performed and the predetermined condition is satisfied, the d-axis current command value Id is linked to the limitation of the q-axis current command value Iq *. * Also restricted. Therefore, even if the q-axis current resulting from the d-axis current command value Id * is actually energized to the motor 19 due to the electrical angle detection error of the motor 19, the predetermined condition is satisfied and the q-axis current command value is limited. When this is done, the q-axis current resulting from the d-axis current command value is also limited. As a result, the influence of the q-axis current due to the d-axis current command value Id * with respect to the assist torque can be suppressed, and the uncomfortable feeling of steering feeling can be prevented.

  By the way, when the remaining capacity of the battery 92 decreases, the steering control device 40 suppresses the maximum allowable power that can be supplied from the battery 92 to the motor 19, and suppresses the capacity decrease rate of the battery 92. Therefore, the command value limiter 82 of the steering control device 40 determines the maximum allowable power W * according to the output voltage Vb of the battery 92. The maximum allowable power W *, the q-axis current command value Iq *, the d-axis current command value Id *, the q-axis voltage command value Vq *, and the d-axis voltage command value Vd * are expressed by the following formula ( 7), the command value limiter 82 multiplies the q-axis and d-axis current command values Iq * and Id * by the limit coefficient γ determined by the following equation (8) to give these current commands. The values Iq * and Id * are limited. As a result, the electric power that can be supplied by the battery 92 can be effectively utilized for the motor 19 while suppressing the capacity reduction rate of the battery 92.

W * <Iq * · Vq * + Id * · Vd * (7)
γ = W * / (Iq * · Vq * + Id * · Vd *) (8)

  As described above, according to the steering control device 40 of the present embodiment, it is possible to prevent an uncomfortable feeling of steering feeling and to effectively use the electric power that can be supplied by the battery 92 for the motor 19.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) The motor 19 driven and controlled by the steering control device 40 according to the first embodiment is connected to the inter-steering wheel shaft 13 between the steered wheels 12 and 12 via a ball screw mechanism. The present invention may be applied to a steering control device that drives and controls a connected motor.

  (2) The q-axis current limiting unit according to the present invention may limit the q-axis current command value Iq * when at least one of a plurality of conditions is satisfied. For example, in the first embodiment, the q-axis current limiting unit 83 sets the q-axis current command when the handle 17 is brought into a contact state or the inverter circuit 43 exceeds the reference temperature. It may be configured to limit the value Iq *.

  (3) Other than the above example, the q-axis current command value Iq * is limited, for example, when the current is limited by fail-safe when an abnormality occurs, or when the road surface μ is small such as an icing road surface Therefore, there is a case where the assist force necessary for steering the handle 17 is “0” or an extremely small value.

The conceptual diagram of the vehicle which concerns on one Embodiment of this invention. Circuit diagram of steering control device Steering control device block diagram (A) Conceptual diagram of rotation speed-d-axis current command value map, (B) Graph showing the relationship between the maximum value of the assist torque and the rotation speed Conceptual diagram of battery voltage-motor allowable power map Conceptual diagram showing the case where the rotational position sensor erroneously detects the electrical angle of the AC motor

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle 11 Electric power steering apparatus 17 Handle 19 Motor (AC motor)
DESCRIPTION OF SYMBOLS 25 Rotational position sensor 40 Steering control apparatus 43 Inverter circuit 44 Signal processing circuit 50 Current command value determination part 81 Voltage sensor 82 Axis current limiting part 83 q-axis current limiting part 84 d-axis current limiting part 92 Battery Id * d-axis current command value Iq * q-axis current command value Iu, Iv, Iw Motor drive current MAP2 Motor allowable power map (maximum allowable power determining means)
W * Motor allowable power γ Limit factor

Claims (2)

An inverter circuit that generates a motor drive current to an AC motor for assisting steering of the vehicle from the output of the battery;
A command value for assist torque to be output to the AC motor is determined as a q-axis current command value according to an operating condition, and a d-axis current command value for performing field-weakening control while suppressing back electromotive force of the AC motor is determined. A current command value determination unit for
In a steering control device comprising a q-axis current limiting unit that limits the q-axis current command value determined by the current command value determination unit when a predetermined condition is satisfied,
A steering control comprising a d-axis current limiting unit that limits the d-axis current command value at the same rate as the limit when the q-axis current command value is limited by the q-axis current limiting unit. apparatus. Battery output voltage detecting means for detecting the output voltage of the battery;
Maximum allowable power determining means for determining the maximum allowable power that can be supplied to the AC motor according to the output voltage of the battery;
The maximum allowable power determined by the maximum allowable power determining means is W *, the q-axis current command value is Iq *, the d-axis current command value is Id *, the q-axis voltage command value is Vq *, d When the shaft voltage command value is Vd *,
W * <Iq * · Vq * + Id * · Vd *
When the relationship is established,
γ = W * / (Iq * · Vq * + Id * · Vd *)
And a command value limiter for multiplying the q-axis and d-axis current command values by the limit coefficient γ determined in (1) and (2) to limit the q-axis and d-axis current command values. The steering control device according to 1.

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