JP2009046005A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of limiting the power of an assist motor without using a boosting means. <P>SOLUTION: An ECU 40 sets a d-shaft voltage limit value Vd* and a q-shaft voltage limit value Vq* by limiting a d-shaft voltage command value Vd*<SB>0</SB>and a q-shaft voltage command value Vq*<SB>0</SB>set by proportional integral control according to the deviation of a d-shaft current command value Id* and a d-shaft actual current value Id and the deviation of a q-shaft current command value Iq* and a q-shaft actual current value Iq to be reduced based on the consumption power W of the assist motor 30 and a power limit value W<SB>LIM</SB>, when the consumption power W is larger than a power limit value W<SB>LIM</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that limits power of an assist motor that assists steering.

  2. Description of the Related Art Conventionally, as an electric power steering apparatus that limits power of an assist motor that assists steering, for example, a control apparatus for an electric power steering apparatus shown in Patent Document 1 is known. This electric power steering apparatus is provided with a step-up / step-down circuit as a boosting means for boosting the input voltage, and generates a steering assist force by boosting the input voltage to a target boost voltage set according to the steering state. The power of the assist motor is limited.

Specifically, for example, when the motor torque command value set by the steering torque, the vehicle speed, or the like is large, the power of the assist motor is limited so that the target boost voltage is set small, thereby generating heat from the inductor, each switch, etc. Suppressed.
JP 2003-267235 A

  By the way, for example, in a hybrid vehicle that uses an engine and a drive motor as a drive system, a high voltage (for example, 46V) limited in power by an on-board DC-DC converter is directly supplied to an assist motor that assists steering. Has been. In this case, if the power limiting function of the DC-DC converter malfunctions, it becomes impossible to limit the power of the assist motor. In this case, if the electric power steering apparatus itself does not have a power limiting function such as a booster, the DC-DC converter may be overloaded when the assist motor is in an overload state, for example. is there.

  Even if the electric power steering apparatus has a boosting means, even if the boosting means malfunctions or the electric power steering apparatus does not have the boosting means itself, Such power limitation of the assist motor cannot be performed. In this case, the assist motor rotates at a high speed, for example, when the steering wheel is turned to the maximum steered state where the steered wheels cannot be turned any more during sudden steering. In a steering situation where the steered wheel suddenly stops when it is running, the assist motor's power limitation cannot limit the speed of the assist motor. There arises a problem that it acts as a strong torsion torque on a steering system such as an intermediate shaft or a universal joint arranged between the two. This problem is not limited to a hybrid vehicle, but also applies to an electric power steering apparatus that uses a 12V battery as a power source.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus capable of limiting the power of an assist motor without using a boosting unit. is there.

In order to achieve the above object, the electric power steering apparatus according to claim 1 described in the claims can assist the steering of the steering system (23, 24, 24a, 25) by the steering wheel (21) of the vehicle. An assist motor (30) for outputting an assist force, motor current value detection means (47) for detecting motor current values (Id, Iq) supplied to the assist motor, and a current command value ( Current command value setting means (40) for setting Id *, Iq *) and voltage command values (Vd * ₀ , Vq * ₀ ) by proportional-integral control according to the deviation between the current command value and the motor current value. When the power consumption (W) of the assist motor is larger than a predetermined power limit value (W _LIM ), based on the power consumption and the predetermined power limit value The voltage Limiting means (40) for limiting the command value to decrease and setting voltage limit values (Vd *, Vq *), and a motor for controlling the assist motor based on the voltage limit value limited by the limiting means And a control means (40).

  According to the first aspect of the present invention, the voltage command value set by the proportional-integral control according to the deviation between the current command value and the motor current value is calculated when the power consumption of the assist motor is larger than the predetermined power limit value. The voltage limit value is set by limiting to decrease based on a predetermined power limit value.

  Thereby, when the power consumption of the assist motor is larger than a predetermined power limit value, for example, when the assist motor is in an overload state or when the steering wheel suddenly stops during high-speed rotation of the assist motor, The assist motor is driven and controlled based on the voltage limit value limited so as to decrease the voltage command value.

For this reason, even when the power limiting function of the DC-DC converter malfunctions or when the boosting means malfunctions, or even when the boosting means itself is not provided, it decreases as described above. By controlling the drive of the assist motor based on the voltage limit value thus limited, the power of the assist motor can be limited. By this power limitation, for example, the rotation speed of the assist motor is appropriately limited.
Therefore, it is possible to limit the power of the assist motor without using a booster.

  In the invention of claim 2, the predetermined power limit value acts on the steering system by a sudden stop of a steering system such as an intermediate shaft or a universal joint rotating at a predetermined rotational speed by the assist force of the assist motor. This is a power value corresponding to the predetermined rotational speed when the rotational force such as the assist torque or the rotational inertial force is an allowable value.

  For this reason, in a steering situation in which the steering system rotates beyond the predetermined rotational speed, the assist motor is power limited based on the voltage limit value limited to decrease as described above. As a result, the steering system does not rotate beyond the predetermined rotation speed, so that even if the steering wheel suddenly stops during high-speed rotation of the assist motor as in the end contact state, the steering system allowable value Rotational force exceeding the above does not act on the steering system.

  According to a third aspect of the present invention, the limiting means sets the voltage limit value to be equal to the voltage command value when the power consumption is equal to or less than the predetermined power limit value. This is because when the power consumption of the assist motor is less than or equal to the predetermined power limit value, it is not necessary to limit the power of the assist motor. Thereby, unnecessary voltage limiting processing can be eliminated.

  According to a fourth aspect of the present invention, the limiting means multiplies the voltage command value by the predetermined power limit value and divides the voltage command value by the power consumption of the assist motor, whereby the predetermined power limit value and the power consumption of the assist motor are calculated. In accordance with the ratio, the voltage command value is set by limiting the voltage command value to decrease.

  As a result, the voltage limit value is limited in consideration of the ratio between the predetermined power limit value and the power consumption of the assist motor. Therefore, the power consumption of the assist motor controlled based on the limited voltage limit value is set to the predetermined power limit value. Thus, the power limit value of the assist motor can be appropriately limited.

  According to a fifth aspect of the present invention, the predetermined power limit value is set according to a voltage value input from a power source. As a result, even if the value of the voltage input from the power source is reduced due to deterioration of the power source or the like, the predetermined power limit value is reduced to limit the power of the assist motor. Avoidance and engine stall avoidance can be done.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the configuration of the electric power steering apparatus according to the present embodiment will be described based on FIGS. 1 (A) and 1 (B).
FIG. 1A is a configuration diagram showing an example of the overall configuration of the electric power steering apparatus 20 according to the first embodiment of the present invention. The electric power steering apparatus 20 mainly includes a steering wheel 21, a steering shaft 22, an intermediate shaft 23, an intermediate shaft 24, a pinion input shaft 25, a torque sensor 26, a speed reducer 27, a rack and pinion 28, and a rod 29. , Assist motor 30, motor rotation angle sensor 31, ECU 40, and the like.

  As shown in FIG. 1A, one end side of a steering shaft 22 is connected to the steering wheel 21, and the input side of a torque sensor 26 is connected to the other end side of the steering shaft 22. Further, one end side of the intermediate shaft 23 is connected to the output side of the torque sensor 26. The torque sensor 26 includes a torsion bar (not shown) and two resolvers attached to both ends of the torsion bar so as to sandwich the torsion bar. The input / output receives one end of the torsion bar and outputs the other end. By detecting the twist amount of the torsion bar between the two resolvers, the steering torque T and the steering angle θs by the steering wheel 21 can be detected.

  A reduction gear 27 is coupled to the intermediate shaft 23 connected to the output side of the torque sensor 26, and assist force output from the assist motor 30 is transmitted to the intermediate shaft 23 via the reduction gear 27. Configured to get.

  That is, although not shown in the drawing, the speed reducer 27 as a power transmission mechanism is configured such that the motor gear attached to the output shaft of the assist motor 30 and the speed reduction gear of the speed reducer 27 can mesh with each other. When the output shaft of the assist motor 30 rotates, the reduction gear of the speed reducer 27 rotates at a predetermined reduction ratio, so that the driving force (assist force) by the assist motor 30 can be transmitted to the intermediate shaft 23.

  A motor rotation angle sensor 31 capable of detecting the rotation angle (motor rotation angle θm) of the assist motor 30 is attached to the assist motor 30, and corresponds to the motor rotation angle θm detected by the motor rotation angle sensor 31. It is comprised so that the signal to perform can be output to ECU40.

  Between the other end side of the intermediate shaft 23 and one end side of the pinion input shaft 25, an intermediate shaft 24 is arranged via a universal joint 24a or the like, respectively. It plays a role of transmitting the rotation of the shaft 23 as the rotation of the pinion input shaft 25.

On the other end side of the pinion input shaft 25, a pinion gear that can be engaged with a rack groove of a rack shaft (not shown) constituting the rack and pinion 28 is formed.
In the rack and pinion 28, the rotational movement of the pinion input shaft 25 can be converted into a linear movement of the rack shaft, and rods 29 are connected to both ends of the rack shaft. Steering wheels FR and FL are connected via a knuckle (not shown). Thus, when the pinion input shaft 25 rotates, the actual steering angle of the steered wheels FR, FL can be changed via the rack and pinion 28, the rod 29, etc., so that the rotation amount and the rotation direction of the pinion input shaft 25 can be changed. The steered wheels FR and FL can be steered.

  Next, the electrical configuration of the ECU 40 that controls the driving of the assist motor 30 will be described with reference to FIG. As shown in FIG. 1B, the ECU 40 is mainly configured by an MPU 60, an interface I / F 42, a motor drive circuit 50, and the like. The interface I / F 42 and the motor are connected to the MPU 60 through an input / output bus. A drive circuit 50 and the like are connected. Reference numeral 47 shown in FIG. 1B is a current sensor 47 that can detect a motor current value i that actually flows through the assist motor 30. Sensor information regarding the motor current value i detected by the current sensor 47 is as follows. The motor current value signal can be input to the MPU 60 via the interface I / F 42.

  The MPU 60 includes, for example, a microcomputer, a semiconductor memory device (ROM, RAM, EEPROM, etc.) and the like, and has a function of executing basic assist motor control of the electric power steering device 20 by a predetermined computer program. Is. That is, the MPU 60 performs vector control of the assist motor 30 based on the motor rotation angle θm detected by the motor rotation angle sensor 31.

  The interface I / F 42 has a function of inputting various sensor signals input from the torque sensor 26, the motor rotation angle sensor 31, or the current sensor 47 to the predetermined port of the MPU 60 through an A / D converter or the like. It is what you have.

  The motor drive circuit 50 has a function of converting electric power supplied from the DC power supply Batt into controllable three-phase AC power (see FIG. 2), and includes a PWM circuit and a switching circuit.

  Accordingly, in the ECU 40 shown in FIG. 2, a signal corresponding to the steering torque T of the torque sensor 26 or a signal corresponding to the motor rotation angle of the motor rotation angle sensor 31 or the current sensor 47 is obtained by PI control (proportional integral control) described later. Since the assist motor 30 can generate assist torque suitable for the steering state based on the three-phase actual current values Iu, Iv, and Iw, the electric power steering apparatus 20 allows the steering wheel 21 to steer the driver. Assistance is possible.

  Next, the calculation process of the PI control system for the assist motor 30 by the ECU 40 will be described with reference to FIG. This calculation process is performed by, for example, a timer interrupt process executed by the MPU 60 of the ECU 40 at predetermined intervals (for example, 0.2 mSec (milliseconds)).

  As shown in FIG. 2, the signal corresponding to the steering torque T input from the torque sensor 26 to the MPU 60 is input to the phase compensator 61 after the noise component is removed by a filter circuit (not shown). The phase compensator 61 performs a process of advancing the phase in order to increase the responsiveness to the output of the torque sensor 26, and then outputs a phase-compensated torque signal to the assist controller 62.

  The assist controller 62 assists the steering force based on the detected torque based on the torque signal input from the phase compensator 61. Therefore, the current value for the secondary magnetic flux generated by the assist motor 30, that is, the field current value (d-axis (Current command value Id *) and a current value corresponding to the assist torque, that is, a torque command current value (q-axis current command value Iq *) is set. For example, the d-axis current command value Id * is set by field weakening control, and the q-axis current command value Iq * is set by a predetermined map or arithmetic expression based on the detected torque. The d-axis current command value Id * and the q-axis current command value Iq * set in this way are output to the addition unit located in the preceding stage of the PI control units 63 and 64, respectively.

  In the addition unit positioned in front of the PI control units 63 and 64, a d-axis current command value Id * and a q-axis current command value Iq * output from the assist control unit 62, and a three-phase two-phase conversion unit 68 described later. Addition processing for obtaining a deviation between the d-axis actual current value Id and the q-axis actual current value Iq of the motor drive circuit 50 to be fed back is performed. As a result, the deviation between the d-axis current command value Id * and the d-axis actual current value Id and the deviation between the q-axis current command value Iq * and the q-axis actual current value Iq are respectively calculated, and the PI control units 63 and 64 are respectively calculated. Is output.

In the PI control units 63 and 64, proportional-integral control is performed. That is, the PI control unit 63 performs proportional-integral calculation based on the deviation between the d-axis current command value Id * output from the previous addition unit and the d-axis actual current value Id, and a predetermined proportional sensitivity and integral gain. Then, a process of outputting the d-axis voltage command value Vd * ₀ to the voltage limiter 65 is performed as an integral value correction operation until the target value is reached. That is, the PI control unit 63 performs feedback calculation processing together with the addition unit.

Similarly, the PI control unit 64 performs proportional-integral calculation based on the deviation between the q-axis current command value Iq * and the q-axis actual current value Iq, and a predetermined proportional sensitivity and integral gain, until the target value is reached. As an integral value correction operation, a process of outputting the q-axis voltage command value Vq * ₀ to the voltage limiter 65 is performed.

In the voltage limiting unit 65, the d-axis actual current value Id and the q-axis actual current value Iq input from the three-phase / two-phase conversion unit 68 and the d-axis voltage command value Vd * ₀ input from the PI control units 63 and 64 and based on the q-axis voltage command value Vq * _0, the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ was limited to reduce the d-axis voltage limit value Vd * and q-axis voltage limit By setting the value Vq *, the power limiting process of the assist motor 30 is performed. The d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * thus set are output to the two-phase / three-phase converter 66. This power limiting process will be described in detail with reference to the flowchart shown in FIG.

  The two-phase / three-phase conversion unit 66 performs dq reverse conversion (three-phase conversion) on the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * input from the voltage limiter 65, and the voltage command value of each phase Processing for calculating Vu *, Vv *, Vw * is performed. The voltage command values reversely converted by the two-phase / three-phase conversion unit 66 are output to the PWM conversion unit 67 as a U-phase voltage command value Vu *, a V-phase voltage command value Vv *, and a W-phase voltage command value Vw *. The PWM converter 67 performs a process of converting the voltage command values Vu *, Vv *, Vw * of each phase into PWM command values PWMu *, PWMv *, PWMw * for each phase.

  In the motor drive circuit 50, on the basis of the PWM signals PWMu *, PWMv *, and PWMw * of each phase output from the PWM converter 67, switching circuits (not shown) are turned on / off for each of the U phase, V phase, and W phase. As a result, the motor drive circuit 50 converts the DC power supplied from the DC power supply Batt into three-phase AC power and supplies the drive power to the assist motor 30, which is suitable for the steering state detected by the torque sensor 26. Assist torque is generated in the assist motor 30.

  At this time, when the power limiting process in the voltage limiting unit 65 described later is performed, the duty ratio of each PWM signal is small according to the limiting degree of the d-axis voltage limiting value Vd * and the q-axis voltage limiting value Vq *. The driving power supplied to the assist motor 30 is reduced. Thereby, the power limiting process equivalent to the power limiting function of the booster circuit or the like can be performed. By this power limitation, for example, the rotation speed of the assist motor 30 is appropriately limited.

  The output current output from the motor drive circuit 50 is detected by the current sensor 47 for each phase, and each of the three phases 2 is obtained as a U-phase actual current value Iu, a V-phase actual current value Iv, and a W-phase actual current value Iw. It is output to the phase conversion unit 68.

  The motor rotation angle calculation unit 69 performs a process of calculating the motor rotation angle θm based on a signal corresponding to the motor rotation angle input from the motor rotation angle sensor 31. The motor rotation angle θm thus calculated is output to the three-phase / two-phase converter 68.

  The three-phase / two-phase conversion unit 68 performs dq conversion (two-phase conversion) on the actual current values Iu, Iv, and Iw of the respective phases (three phases) input from the current sensor 47 to obtain the d-axis actual current value Id. And processing for calculating the q-axis actual current value Iq. The three-phase / two-phase conversion unit 68 also receives the motor rotation angle θm from the motor rotation angle calculation unit 69. The output current value of the motor drive circuit 50 converted by the three-phase / two-phase conversion unit 68 is the addition unit located in the preceding stage of the aforementioned PI control units 63 and 64 as the d-axis actual current value Id and the q-axis actual current value Iq. Each is fed back. Thereby, as described above, the feedback calculation processing by the PI control units 63 and 64 becomes possible. The d-axis actual current value Id and the q-axis actual current value Iq are also output to the voltage limiting unit 65.

  By performing such vector control of the assist motor 30 by the MPU 60, the electric power steering apparatus 20 can be controlled. Here, the flow of the power limiting process of the assist motor 30 in the voltage limiting unit 65 described above will be described in detail with reference to the flowchart shown in FIG. FIG. 3 is a flowchart showing the flow of the power limiting process of the assist motor 30.

First, in step S101, the d-axis voltage command value Vd * ₀ and q-axis voltage command value Vq * ₀ output from the PI control units 63 and 64 and the d-axis actual current value output from the three-phase two-phase conversion unit 68 are displayed. When Id and q-axis actual current value Iq are acquired, in step S103, power consumption W is calculated by the following equation (1).
W = Vd * ₀ * Id + Vq * ₀ * Iq (1)

Next, in step S105, it is determined whether or not the power consumption W is greater than the power limit value _WLIM . The power limit value _WLIM is an assist torque that acts on the steering system due to a sudden stop of the steering system such as the intermediate shaft 24 and the universal joint 24a that are rotating at a predetermined rotational speed by the assist force of the assist motor 30. And a power value corresponding to the predetermined rotational speed when the rotational force such as the rotational inertial force is an allowable value, and is set to 500 W, for example.

If the power consumption W is equal to or less than the power limit value W _LIM (No in S105), it is determined that it is not necessary to limit the power of the assist motor 30, and in step S107, the d-axis voltage limit value Vd is determined. * = Vd * ₀ , q-axis voltage limit value Vq * = Vq * ₀ .

On the other hand, if the power consumption W is greater than the power limit value _WLIM (Yes in S105), it is determined that it is necessary to limit the power of the assist motor 30, and a voltage limiting process is performed in step S109. In this process, the d-axis voltage limit values Vd * and q that are limited to decrease the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ based on the following formulas (2) and (3). A shaft voltage limit value Vq * is set.
Vd * = Vd * ₀ × W _LIM / W (2)
Vq * = Vq * ₀ × W _LIM / W (3)

Here, voltage limiting processing of the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ based on the above formulas (2) and (3) will be described with reference to FIG. FIG. 4 is an explanatory diagram showing the relationship between the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ and the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq *.

When the power consumption W calculated by the above equation (1) is larger than the power limit value _WLIM , the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ are shown in a wavy circular arc in FIG. together located on the power consumption W shown Te located outside the power limit value W _LIM shown by the solid line arcuate (see point P ₁ in FIG. 4).

When the voltage is limited so that the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ are decreased based on the above formulas (2) and (3), as can be seen from FIG. 4, the d-axis voltage limit value Vd * and q-axis voltage limit Vq * are that the voltage limit to be located at a point P ₂ on the power limit value W _LIM indicating the power consumption W shown in wavy arc by a solid line-shaped arc Become.

  When the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * are set in step S107 or step S109 described above, the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * are set in step S111. It is output to the two-phase / three-phase converter 66.

As described above, in the electric power steering apparatus 20 according to the present embodiment, the ECU 40 determines the deviation between the d-axis current command value Id * and the d-axis actual current value Id and the q-axis current command values Iq * and q. The d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ set by proportional-integral control according to the deviation from the actual shaft current value Iq, the power consumption W of the assist motor 30 is the power limit value W _LIM If larger, the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * are set by limiting the power consumption W and the power limit value W _LIM so as to decrease.

Thereby, when the power consumption W of the assist motor 30 is larger than the power limit value _WLIM , for example, when the assist motor 30 is in an overload state or when the assist motor 30 rotates at high speed, the steered wheels FR and FL are steered. In the case of a sudden stop, the assist motor is based on the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * that are limited to decrease the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * _0. 30 is driven and controlled.

For this reason, for example, when the power limiting function of the DC-DC converter that supplies a high voltage to the assist motor 30 in the hybrid vehicle malfunctions or the boosting means of the electric power steering device 20 malfunctions. In this case, the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq, which are limited to decrease as described above, even when the electric power steering apparatus 20 does not include the boosting unit itself. By controlling the driving of the assist motor 30 based on *, the power of the assist motor 30 can be limited. By this power limitation, for example, the rotation speed of the assist motor 30 is appropriately limited.
Therefore, it is possible to limit the power of the assist motor 30 without using a booster.

Further, in the electric power steering apparatus 20 according to the present embodiment, the power limit value _WLIM is determined by the intermediate shaft 24, the universal joint 24a, and the like that are rotating at a predetermined rotational speed by the assist force of the assist motor 30. This is a power value corresponding to the predetermined rotational speed when the rotational force such as the assist torque or the rotational inertia force acting on the steering system due to the sudden stop of the steering system is an allowable value.

  For this reason, in a steering situation where the steering system rotates beyond the predetermined rotational speed, it is based on the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * that are limited to decrease as described above. Thus, the power of the assist motor 30 is limited. As a result, the steering system does not rotate beyond the predetermined number of rotations, so that the steering wheel FR, FL can be steered even when the steering wheels FR, FL suddenly stop during high-speed rotation of the assist motor 30 as in the end contact state. A rotational force that exceeds the allowable value of the system does not act on the steering system.

Furthermore, in the electric power steering apparatus 20 according to the present embodiment, ECU 40, if the power consumption W is equal to or less than the power limit value W _LIM, the d-axis voltage limit value Vd * and q-axis voltage limit value Vq * It is set to be equal to the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ . This is because when the power consumption W of the assist motor 30 is equal to or less than the power limit value W _LIM , it is not necessary to limit the power of the assist motor 30. Thereby, unnecessary voltage limiting processing can be eliminated.

Furthermore, in the electric power steering apparatus 20 according to the present embodiment, the ECU 40 multiplies the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ by the power limit value _WLIM and consumes power. By dividing by W, the d-axis voltage command value Vd * ₀ and the q-axis voltage command value Vq * ₀ are limited so as to decrease in accordance with the ratio of the power limit value _WLIM to the power consumption W. An axis voltage limit value Vd * and a q-axis voltage limit value Vq * are set.

As a result, the d-axis voltage limit value Vd * and the q-axis voltage limit value Vq * are limited in consideration of the ratio between the power limit value _WLIM and the power consumption W, so the limited d-axis voltage limit value Vd * The power consumption W of the assist motor 30 controlled based on the q-axis voltage limit value Vq becomes substantially equal to the power limit value _WLIM, and the power limit of the assist motor 30 can be appropriately performed.

In addition, this invention is not limited to the said embodiment, You may actualize as follows, and even in that case, an effect | action and effect equivalent to the said embodiment are acquired.
(1) As described above, the power limit value W _LIM is not limited to 500 W, for example, but is set according to the ECU input voltage value Vb that is the value of the voltage input to the ECU 40 from the DC power supply Batt. May be. At this time, power limit value _WLIM increases as ECU input voltage value Vb increases based on the ECU input voltage value-power limit value map shown in FIG. 5, and ECU input voltage value Vb exceeds a predetermined threshold value. And may be set to be constant.
As a result, even when the ECU input voltage value Vb is lowered due to deterioration of the DC power supply Batt or the like, the power limit value _WLIM is lowered and the power of the assist motor 30 is limited, thereby avoiding element damage due to an increase in the drawn current. And engine stalls can be avoided.

(2) The voltage limiting unit 65 is not limited to the power limiting process for the assist motor 30 based on the flowchart shown in FIG. 3, but the power limiting process for the assist motor 30 is performed based on the flowchart shown in FIG. May be. FIG. 6 is a flowchart showing a flow of a modified example of the power limiting process of the assist motor 30.

Specifically, as shown in FIG. 6, when the absolute value of the steering angle θs detected by the torque sensor 26 is less than the predetermined angle threshold θs ₁ in step S200, the determination of No is repeated. When the absolute value of the steering angle θs becomes equal to or greater than the predetermined angle threshold value θs ₁ (Yes in S200), the process from step S101, that is, the above-described power limiting process is performed. Here, θs ₁ is the steering angle immediately before the end contact state is reached. For example, if the steering angle θs in the end contact state is ± 360 °, θs ₁ is set to 350 °.

  For this reason, when steering is performed immediately before the end contact state, the assist motor 30 is limited so that the rotation speed of the assist motor 30 is reliably reduced by the power limiting process of the assist motor 30. Thereby, the rotational inertia force acting on the steering system such as the intermediate shaft 24 and the universal joint 24a in the end contact state can be surely reduced.

(3) In the above embodiment, as shown in FIG. 1, a so-called column-type electric power steering apparatus capable of transmitting the assist force output from the assist motor 30 to the pinion input shaft 25 via the speed reducer 27. However, the present invention is not limited to this example. For example, the rack and pinion 28 includes an assist motor and a speed reducer, and the assist force output from the assist motor is transmitted via the speed reducer. Therefore, the present invention may be applied to a so-called rack type electric power steering apparatus that can transmit to the rack mechanism.
Further, a so-called rack parallel type electric power steering device in which the rack shaft and the assist motor are arranged in parallel, a so-called pinion type electric power steering device in which the assist motor is arranged in the pinion portion having the pinion input shaft 25, Or you may apply to what is called a dual pinion type electric power steering device.

FIG. 1A is a block diagram showing an example of the overall configuration of an electric power steering apparatus according to an embodiment of the present invention, and FIG. 1B is a circuit block diagram showing a configuration example of an ECU and the like. It is a functional block diagram regarding the PI control system of the assist motor according to the present embodiment. It is a flowchart which shows the flow of the electric power limitation process of an assist motor. It is explanatory drawing which shows the relationship between d-axis voltage command value and q-axis voltage command value, d-axis voltage limit value, and q-axis voltage limit value. It is explanatory drawing which shows an example of ECU input voltage value-power limiting value map. It is a flowchart which shows the flow of the modification of the electric power limiting process of an assist motor.

Explanation of symbols

20 ... Electric power steering device 23 ... Intermediate shaft (steering system)
24 ... Intermediate shaft (steering system)
24a ... Universal joint (steering system)
25 ... Pinion input shaft (steering system)
30 ... assist motor 40 ... ECU (current command value setting means, voltage command value setting means, limiting means, motor control means)
47 ... Current sensor (motor current value detection means)
Batt ... DC power supply
Id ... d-axis actual current value Id * ... d-axis current command value Iq ... q-axis actual current value Iq * ... q-axis current command value Vb ... ECU input voltage value Vd * ... d-axis voltage limit value Vd * ₀ ... d-axis Voltage command value Vq * ... q-axis voltage limit value Vq * ₀ ... q-axis voltage command value W ... Power consumption W _LIM ... Power limit value

Claims (5)

An assist motor that outputs an assist force capable of assisting steering of the steering system by the steering wheel of the vehicle;
Motor current value detection means for detecting a motor current value supplied to the assist motor;
Current command value setting means for setting a current command value according to the steering situation;
Voltage command value setting means for setting a voltage command value by proportional-integral control according to a deviation between the current command value and the motor current value;
Limiting means for setting a voltage limit value by limiting the voltage command value to decrease based on the power consumption and the predetermined power limit value when the power consumption of the assist motor is greater than a predetermined power limit value When,
Motor control means for controlling the assist motor based on the voltage limit value restricted by the restriction means;
An electric power steering apparatus comprising:   The predetermined power limit value is a value when the rotational force acting on the steering system due to a sudden stop of the steering system rotating at a predetermined rotational speed by the assist force of the assist motor is an allowable value. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus has an electric power value corresponding to a predetermined rotational speed.   3. The electricity according to claim 1, wherein the limiting unit sets the voltage limit value to be equal to the voltage command value when the power consumption is equal to or less than the predetermined power limit value. Power steering device.   The limiting means sets the voltage limit value by limiting the voltage command value to be decreased by multiplying the voltage command value by the predetermined power limit value and dividing by the power consumption. The electric power steering apparatus according to claim 1 or 2, characterized in that   The electric power steering apparatus according to any one of claims 1 to 4, wherein the predetermined power limit value is set according to a voltage value input from a power source.

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