JP2006262668A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device in which torque ripple is not generated in an electric motor even when the electric motor is controlled in a state where a torque ripple component is included in a feedback system.
The torque ripple inherent to the motor 8 generated by the number of rotor poles and the stator configuration in the motor 8 is measured, and the angle calculation means 24 is converted into a map corresponding to the rotation angle of the motor 8 detected by the resolver 23. To store. The angle calculation means 24 reads a torque ripple component from the map based on the rotation angle detected by the resolver 23 during operation, and transmits this torque ripple component to the target current correction means 32. The target current correction unit 32 corrects the target current by subtracting the torque ripple component from the target current to generate a corrected target current. Further, the target current correcting means 32 supplies this corrected target current as a reference signal to the feedback Q-axis PI control means 27 and the like.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering device that applies power of an electric motor to a steering device of an automobile.

  The electric power steering device generates, for example, an auxiliary torque corresponding to the steering torque with an electric motor, and transmits the auxiliary torque to a steering system to reduce the steering torque. That is, an auxiliary torque corresponding to the magnitude of the steering torque is generated by the control of the control device, and this auxiliary torque is transmitted to the steering system to reduce the steering force of the steering wheel. As described above, various techniques for realizing an electric power steering device by controlling an electric motor have been reported (for example, see Patent Document 1).

  A technique for assisting steering torque by generating auxiliary torque using a three-phase brushless motor is also known. According to this technology, an arbitrary two-phase current is detected from a three-phase current of a three-phase brushless motor, and a d-axis current (field current) and a q-axis current (torque) based on the rotation angle signal of the three-phase brushless motor. The shaft current is fed back by dq conversion (3-phase 2-axis conversion). Then, the feedback d-axis current and q-axis current are individually controlled and compared with the command current, respectively, and d-axis PI control and q-axis PI control are performed, respectively, and dq reverse conversion (two-axis three-phase conversion) is performed. It is converted into a three-phase PWM signal to control the duty of the three-phase brushless motor. By using such a dq conversion method, vector control of a three-phase brushless motor can be performed by detecting an arbitrary two-phase current among the three-phase currents, so that the control system is greatly simplified (for example, , See Patent Document 2).

Further, a technique of an electric power steering device is disclosed in which the torque ripple generated in the electric motor is removed so that the steering wheel does not vibrate, and the steering feeling during running is improved. According to this technique, the torque ripple component superimposed on the torque signal of the electric motor is extracted and analyzed, and the offset correction of the detected current is performed according to the torque ripple component. As a result, the current ripple corresponding to the torque ripple component is canceled from the detected current, and as a result, the electric motor can be controlled with high accuracy by the detected current not including the torque ripple component. Accordingly, no torque ripple is generated in the auxiliary torque generated by the electric motor, and thus the steering torque can be assisted smoothly (see, for example, Patent Document 3).
JP 2000-279000 A (see paragraph numbers 0010 to 0023, FIGS. 1 to 5) Japanese Patent Laying-Open No. 2004-40883 (see paragraph numbers 0027 to 0038, FIG. 2) JP 2004-359178 A (see paragraph numbers 0029 to 0036, FIG. 1 and FIG. 2)

  However, since the electric power steering devices disclosed in Patent Document 1 and Patent Document 2 do not perform correction to remove torque ripple generated in the electric motor, the auxiliary torque cannot be controlled smoothly. In particular, the technique of Patent Document 2 feeds back a detected current by dq conversion (three-phase two-axis conversion) to control the torque of a three-phase brushless motor with high accuracy. Torque ripples that occur, torque ripples that occur due to gain variations in the detection system of the control device cannot be removed. For this reason, torque ripple is generated in the electric motor, and the steering feeling cannot be further improved.

  The electric power steering device disclosed in Patent Document 3 can remove the torque ripple generated in the electric motor, but corrects the detected current of the feedback system by the torque ripple component. The transfer function becomes considerably complicated due to the function of the torque ripple component. This complicates the control circuit and increases the cost of the electric power steering apparatus. In addition, since the torque ripple component is added (or subtracted) to the detected current that is fed back, a hunting phenomenon occurs due to the difference in the transfer function between the detected current and the torque ripple component that is added (or subtracted). There is also a possibility that subtle uneven rotation occurs in the electric motor. As a result, subtle unevenness in the magnitude of the assist torque for assisting the steering force may occur, and the steering feeling may be deteriorated.

  The present invention has been made in view of the above problems, and even if torque control of a motor is performed without adding or subtracting a torque ripple component to a feedback system, torque ripple does not occur in the motor. An object is to provide an electric power steering apparatus.

  The electric power steering device of the present invention was created to achieve the above-mentioned object, and the electric motor is driven by a feedback control system based on the target current calculated based on the magnitude of the steering input. An electric power steering device that applies the generated driving force to a steering system, the rotational position detecting means for detecting the rotational position of the electric motor, and the torque for calculating the torque ripple component corresponding to the rotational position detected by the rotational position detecting means Ripple calculation means and a target current is corrected based on a value obtained by multiplying a torque ripple component calculated by the torque ripple calculation means by a predetermined gain to generate a correction target current, and the feedback control system using the correction target current as a reference signal And a target current correcting means to be provided.

  According to such a configuration, the target current is corrected by subtracting the torque ripple component from the target current, and this is used as the corrected target current. As a result, even if a torque ripple component is included in the detection signal of the feedback system, the correction target current that is a reference for control of the feedback system is corrected with the torque ripple component, so that the transfer function of the feedback system does not change. The motor can be controlled with high accuracy so that torque ripple does not occur in the motor. That is, since the torque ripple component is not added or subtracted in the feedback system, the transfer function does not change. The torque ripple component is obtained in advance by experiments, simulations, etc., and stored in the torque ripple calculation means as a map corresponding to the rotational position of the motor. As a result, the rotational position detecting means can easily obtain the torque ripple component from the rotational position during actual operation.

  In the configuration of the invention, the gain is set to be larger than a predetermined value when the rotational speed of the electric motor is slower than the predetermined speed, and is set to be smaller than the predetermined value when the rotational speed of the electric motor is faster than the predetermined speed. Can be taken.

  That is, when the rotational speed increases, the rate of increase of the electric motor decreases, but torque ripple that generates sound is less likely to occur. Therefore, the correction of the target current can be weakened by reducing the gain value in the high speed rotation range. As a result, at high speed rotation, torque ripple limitation can be weakened or torque ripple limitation can be avoided.

  In the configuration of the invention, it is possible to adopt a configuration in which the gain becomes a smaller value as the rotational speed of the electric motor increases. According to such a configuration, the gain value decreases, for example, linearly as the rotational speed of the motor increases. Therefore, the torque ripple limit is gradually weakened as the rotational speed increases, and the torque is increased above a certain rotational speed. Ripple restriction can be avoided.

  Further, in addition to the configuration of the above invention, it further includes a current detection means for detecting a current supplied to the electric motor, and the gain is when the temperature of the current detection means or the ambient temperature of the current detection means is lower than a predetermined temperature. When the temperature of the current detection unit or the ambient temperature of the current detection unit is higher than the predetermined value, it can be set to a value smaller than the predetermined value.

  In other words, since the current sensor suppresses an increase in gain variation when the temperature increases (that is, gain variation decreases), the gain value can be reduced in the high temperature transition region to weaken the target current correction. In this way, even if the torque ripple restriction is weakened at high temperatures, the torque ripple component is originally small at high temperatures, so that the motor can be operated substantially with little torque ripple.

  In the configuration of the invention, the gain can be configured to become a linearly small value, for example, as the temperature of the current detection unit or the ambient temperature of the current detection unit increases. According to such a configuration, the gain value decreases linearly as the temperature of the current detection means increases, so that the torque ripple limitation can be gradually weakened as the temperature increases.

  In each of the inventions, the motor can be a three-phase brushless motor, and the rotational position detecting means can be a resolver. According to such a configuration, if a three-phase brushless motor is used as an electric motor, the detection signal can be DQ converted (three-phase two-axis conversion) to easily configure a feedback system, so that the control means is very simple. Become. Further, since a general-purpose resolver can be used as the rotational position detecting means, the cost of parts can be reduced.

  According to the electric power steering device of the present invention, even if a torque ripple component is included in the detection signal of the feedback system, the correction target current that becomes the reference signal of the feedback system is corrected by the torque ripple component. Therefore, the motor can be controlled with high accuracy so that torque ripple does not occur in the motor.

  Further, according to the electric power steering apparatus of the present invention, the electric motor uses the characteristic that the rate of increase decreases as the rotational speed increases, and the torque ripple that affects the steering feeling is less likely to occur. In the high speed rotation range of the electric motor, the gain value can be reduced to weaken the target current correction. As a result, at high speed rotation of the electric motor, torque ripple limitation can be weakened or torque ripple limitation can be avoided.

  Further, according to the electric power steering apparatus of the present invention, the current sensor for detecting the electric current of the motor can suppress the increase in gain variation when the temperature becomes high (that is, the gain variation decreases). The target current correction can be weakened by reducing the value of. In this way, even if the torque ripple restriction is weakened at high temperatures, the torque ripple component is originally small at high temperatures, so that the motor can be operated substantially with little torque ripple.

<< Summary of Invention >>
The electric power steering device of the present invention measures in advance the torque ripple inherent to the electric motor generated by the number of rotor poles and the stator configuration in the electric motor, and maps it into a map (or table) corresponding to the rotational angle of the electric motor. And store it. Then, the rotation angle of the electric motor is detected during operation, and a torque ripple component corresponding to the detected rotation angle is read with reference to a map (or table). Further, the torque ripple component is subtracted from the target current of the control circuit to correct the target current, and this is used as the corrected target current. As a result, even if a torque ripple component is included in the detection signal of the feedback system, the correction target current serving as the reference signal is corrected with the torque ripple component, so that the torque is applied to the motor without changing the transfer function of the feedback system. The electric motor can be controlled with high accuracy so as not to generate ripples.

  In addition, the torque ripple generated in the motor due to the gain shift of the current sensor inserted in two of the three phases is measured in advance, and stored as a map (or table, function) corresponding to the rotation angle of the motor. (Or make it a function). Then, the rotation angle of the electric motor is detected during operation, and a torque ripple component corresponding to the detected rotation angle is read with reference to a map (or table). Further, the torque ripple component is subtracted from the target current of the control circuit to correct the target current, and this is used as the corrected target current. As a result, even if the torque ripple component is included in the detection signal of the feedback system, the reference correction target current is corrected with the torque ripple component, so that the torque ripple is supplied to the motor without changing the transfer function of the feedback system. It is possible to control the electric motor with high accuracy so as not to occur.

  In the electric power steering device of the present invention, the d-axis and the q-axis expressed in the conventional electric power steering device are represented by D in the electric power steering device of the present invention in order to be distinguished from the conventional electric power steering device. The axis and Q axis are expressed in capital letters to distinguish them. In the electric power steering apparatus of the present invention, other alphabets are also expressed in capital letters. However, the lowercase letters of the alphabet are used for the numerical subscripts.

<< Embodiment of the Invention >>
Embodiments of an electric power steering apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of an electric power steering apparatus applied to an embodiment of the present invention. First, the overall configuration of the electric power steering apparatus 1 shown in FIG. 1 will be described. In FIG. 1, a steering shaft 4 provided integrally with a steering wheel 3 is connected to a pinion 7a of a rack and pinion mechanism 7 in a steering gear box via a connecting shaft 5 having universal joints 5a and 5b. The manual steering force generating means 2 is configured. Further, the rack teeth 7b that mesh with the pinion 7a and the rack shaft 9 that reciprocates due to these meshing are connected to the left and right front wheels W and W as rolling wheels at both ends via tie rods 10 and 10, respectively. It is configured such that the direction of the vehicle can be changed by rolling the left and right front wheels W via a rack and pinion type steering system. In order to reduce the steering force by the manual steering force generating means 2, an electric motor 8 for supplying an auxiliary steering force is provided, and an auxiliary torque corresponding to the steering torque T is generated by the control of the control means 12, and this auxiliary torque is generated by the rack shaft. 9, the steering force of the steering wheel 3 is reduced.

  That is, the electric power steering apparatus 1 of the present embodiment is provided with a steering system S from the steering wheel 3 to the left and right front wheels W, which are steering wheels, and assists the steering force by the manual steering force generating means 2. Yes. For this reason, the electric power steering apparatus 1 generates an electric motor voltage VM by the electric motor driving means 13 based on the electric motor control signal V0 from the control means 12, and drives the electric motor 8 by the electric motor voltage VM to thereby generate an auxiliary torque (auxiliary steering force). ) To assist the manual steering force by the manual steering force generation means 2. In the present embodiment, a three-phase brushless motor is used as the electric motor 8, and DQ control for controlling the D axis (field current axis) and the Q axis (torque axis) is performed as drive control of the electric motor 8.

  In the manual steering force generating means 2, a pinion 7 a of a rack and pinion mechanism 7 provided in the steering gear box 6 is connected to a steering shaft 4 provided integrally with the steering wheel 3 via a connecting shaft 5. The connecting shaft 5 includes universal joints 5a and 5b at both ends thereof. In the rack and pinion mechanism 7, rack teeth 7b that mesh with the pinions 7a are formed on the rack shaft 9, and the rotational movement of the pinions 7a is reciprocated in the lateral direction (vehicle width direction) of the rack shaft 9 by the engagement of the pinions 7a and 7b. I am in motion. Furthermore, left and right front wheels W and W as steering wheels are connected to the rack shaft 9 via tie rods 10 and 10 at both ends thereof.

  In the electric power steering apparatus 1, the electric motor 8 is disposed coaxially with the rack shaft 9 in order to generate an auxiliary steering force (auxiliary torque). Then, the electric power steering apparatus 1 converts the rotation of the electric motor 8 into a thrust through a ball screw mechanism 11 provided coaxially with the rack shaft 9, and this thrust is applied to the rack shaft 9 (ball screw shaft 11a). ing.

  The detection means V, T, and IMO of the vehicle speed sensor VS, the steering torque sensor TS, and the motor current detection means 14 are input to the control means 12. The control means 12 determines the magnitude and direction of the motor current IM applied to the motor 8 based on these detection signals V, T, and IMO, and outputs the motor control signal VO to the motor driving means 13. Furthermore, the control means 12 determines the assist in the electric power steering device 1 based on the steering torque signal T and the electric motor current signal IMO, and controls the driving of the electric motor 8. The control means 12 includes a CPU that performs various calculations and processes, an input signal conversion means, a signal generation means, and a storage means. Incidentally, the CPU performs main control in the electric power steering apparatus 1.

  The vehicle speed sensor VS detects the vehicle speed as the number of pulses per unit time, and transmits an analog electrical signal corresponding to the detected number of pulses to the control means 12 as the vehicle speed signal V. The vehicle speed sensor VS may be a dedicated sensor for the electric power steering device 1 or may use a vehicle speed sensor of another system.

  The steering torque sensor TS is disposed in the steering gear box 6 and detects the magnitude and direction of the manual steering torque by the driver. Then, the steering torque sensor TS transmits an analog electrical signal corresponding to the detected steering torque to the control means 12 as a steering torque signal T. The steering torque signal T includes information on the steering torque indicating the magnitude and the torque direction indicating the direction of the torque. The torque direction is represented by a plus value / minus value of the steering torque. The plus value is the steering torque direction to the right direction, and the minus value is the steering torque direction to the left direction.

  The motor current detection means 14 is formed of, for example, a current transformer (CT) provided for each winding of the motor 8, and detects the magnitude and direction of the motor current IM that actually flows through the motor 8. The motor current detection means 14 feeds back (negative feedback) the motor current signal IMO corresponding to the motor current IM to the control means 12.

  The motor driving means 13 drives the motor 8 by applying the motor voltage VM to the motor 8 based on the motor control signal VO. For example, the motor driving means 13 applies a sine wave current to each winding of the motor 8 via a pre-drive circuit and an FET bridge in the motor driving means 13 in accordance with the duty of a PWM (Pulse Width Modulation) signal, for example. Take control.

  Next, the control means 12 of FIG. 1 will be described in detail. FIG. 2 is a block diagram showing the configuration of the control device and its surroundings in the electric power steering device shown in FIG. The control means 12 includes a phase current detection means 21, a three-phase biaxial conversion means 22, a resolver (rotational position detection means) 23, an angle calculation means (torque ripple calculation means) 24, an electric motor speed calculation means 25, and a field current means 26. , Q-axis PI control means 27, D-axis PI control means 28, 2-axis three-phase conversion means 29, PWM conversion means 30, non-interference control means 31, and target current correction means 32. Further, as peripheral devices, the motor 8, the motor driving means 13, the motor current detecting means (current detecting means) 14 having current sensors 14 a and 14 b, and a battery are provided. The control means 12 operates in response to a command signal from the CPU, but the CPU is not shown in this figure.

  Such a control means 12 performs vector control of the electric motor 8 according to the command torque by vector control represented by a two-phase rotating magnetic flux coordinate system (hereinafter referred to as DQ coordinate system). That is, the steering torque T applied to the steering wheel of the steering system S is detected by the steering torque sensor TS, and the assist of the steering is performed by vector control of the electric motor 8 so that the assist torque corresponding to the detected steering torque T is obtained. Is going.

  First, in a CPU (not shown), a command torque is obtained from the steering torque T detected by the steering torque sensor TS, the steering angular velocity, the vehicle speed signal V detected and output by the vehicle speed sensor VS, and the like. Torque is converted into a Q-axis current command value by torque current conversion, and input to the Q-axis PI control means 27 of the control means 12. A command signal from the CPU and a speed signal from the motor speed calculation means 25 are input to the field current means 26, converted into a D-axis current command value, and input to the D-axis PI control means 28.

  Further, each phase current (for example, U phase current IU, W phase current IW) of the electric motor 8 is detected by the current sensors (CT) 14a, 14b of the electric motor current detecting means 14, and the phase current detecting means 21 at a predetermined cycle. Sampled. Each phase current (IU, IW) output from the phase current detection means 21 is input to the three-phase biaxial conversion means 22. On the other hand, the rotational position of the electric motor 8 detected by the resolver 23 is converted into an angle signal (ANGLE) by the angle calculation unit 24, and the angle signal is input to the three-phase biaxial conversion unit 22. The three-phase biaxial conversion means 22 performs DQ conversion on each phase current (IU, IW) based on the input angle signal, and outputs a D-axis current (ID) and a Q-axis current (IQ).

  Next, the Q-axis PI control means 27 performs a P (Proportional) control process and I ((proportional) control processing based on the Q-axis current command value input from the CPU and the Q-axis current (IQ) input by the feedback system. Integral (integral) control processing is executed, and as a result, a command voltage VQ for the Q axis is generated, and this command voltage VQ is input to the two-axis three-phase conversion means 29. Further, the D-axis PI control means 28 performs P (proportional) control processing and I based on the D-axis current command value input from the field current means 26 and the D-axis current (ID) input by the feedback system. (Integration) control processing is executed, and as a result, a command voltage VD for the D axis is generated, and this command voltage VD is input to the biaxial three-phase conversion means 29.

  Then, the two-axis three-phase conversion means 29 performs DQ inverse conversion on these command voltages VQ and VD to convert the command voltages VU, VV and VW for the U, V and W phases of the electric motor 8. To do. These command voltages VU, VV, and VW are converted into PWM duty signals by the PWM conversion means 30, and the PWM duty signal controls a pre-driving drive circuit and an FET bridge circuit (not shown) in the motor driving means 13. As a result, a PWM-controlled sinusoidal current is applied to each phase winding of the electric motor 8 such as a brushless motor, and predetermined vector control is performed on the electric motor 8.

  It should be noted that the non-interference control means 31 has one control input when there is mutual interference between a plurality of control inputs and a plurality of control amounts as in the Q-axis PI control means 27 and the D-axis PI control means 28. It works to eliminate mutual interference so that the influence reaches only one control amount. In the example of FIG. 2, the non-interference control means 31 is used to reduce the feedback loop of the motor angular velocity and the motor current (that is, to increase the response speed of the feedback loop).

  By the way, as shown in FIG. 2, the electric power steering apparatus 1 of the present embodiment has a target current correction means for correcting a target current that is a reference signal for vector control of the rotational torque of the electric motor 8 with a torque ripple component. 32. In other words, the target current correcting means 32 ripple-corrects the target current (reference signal) to obtain a corrected target current, and the corrected target current is used as the Q-axis PI control means 27 for controlling the torque axis current, and the field current. Is input to the reference input terminal of the field current means 26 (resulting in D-axis PI control means 28). In other words, the feedback system that feeds back the rotation angle and current of the motor 8 is not corrected by the torque ripple component, but the torque ripple component is input to the target current correction means 32 to ripple-correct the target current, and the corrected target current is The reference signal is used. Therefore, the transfer function of the feedback system in the control means 12 is not changed at all.

  Here, the torque ripple generated in the electric motor will be described. In the electric motor, torque ripple specific to the electric motor is generated depending on the number of magnetic poles on the rotor side, the number of slots (stator) on the stator side, and the arrangement structure thereof. Such torque ripple occurs because a slight change in magnetic field occurs in the process in which each magnetic pole and each slot face each other and move away when the rotor of the motor rotates. For example, in the case of an electric motor having an 8-pole 9-slot configuration, sixth-order torque ripple occurs. The configuration of such an 8-pole 9-slot motor is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-275325 by the applicant of the present invention, and an experiment with the 8-pole 9-slot motor shows a sixth-order torque ripple. It appears remarkably.

  FIG. 3 is a waveform of a sixth-order torque ripple appearing in an 8-pole 9-slot motor, and represents a correction coefficient. The horizontal axis represents the electrical angle (deg), and the vertical axis represents the torque ripple current value (A). That is, the electrical angle 360 deg is one rotation of the electric motor, and six primary torque ripples in one cycle (2π) are generated during this period. Therefore, it is said that such a continuous torque ripple is a sixth-order torque ripple. If the sixth-order torque ripple is input to the target current correcting means 32 in the control means 12 of FIG. 2 and the current of the sixth-order torque ripple is subtracted from the target current input from the CPU (not shown) in advance, The corrected target current is a value obtained by canceling the current component of the sixth-order torque ripple. That is, the vertical axis in FIG. 3 can be regarded as a corrected target current obtained by subtracting the current component of the sixth-order torque ripple from the target current. That is, the target current is normally at a linear level, but if the current component of the sixth-order torque ripple is subtracted from the target current, the envelope of the corrected target current has a waveform of the sixth-order torque ripple as shown in FIG. .

  Torque ripples are also caused by gain variations in current sensors that detect the current of the motor. FIG. 4 is a waveform of a secondary torque ripple that appears in the motor when the current sensor is inserted into two of the three phases, and represents a correction coefficient. The horizontal axis represents the electrical angle (deg), and the vertical axis represents the torque ripple current value (A). As described with reference to FIG. 2, in the case of a three-phase brushless motor, normally, the two current sensors 14a and 14b are inserted in two arbitrary phases, and therefore the gain (amplification factor) of each current sensor 14a and 14b. ) Causes two cycles of torque ripple during one revolution of the motor.

  That is, as shown in FIG. 4, the electrical angle 360 deg is one rotation of the motor, and two primary torque ripples of one cycle (2π) are generated during this period. Such a continuous torque ripple is said to be a secondary torque ripple. If this secondary torque ripple is input to the target current correcting means 32 in the control means 12 of FIG. 2 and the current of the secondary torque ripple is subtracted from the target current input from the CPU in advance, the corrected target The current becomes a value obtained by canceling the current component of the secondary torque ripple. That is, the vertical axis in FIG. 4 can be regarded as a corrected target current obtained by subtracting the current component of the secondary torque ripple from the target current. That is, the target current is normally at a linear level, but if the current component of the secondary torque ripple is subtracted from the target current, the envelope of the corrected target current has the waveform of the secondary torque ripple as shown in FIG. .

  Next, the process in which the target current correcting unit 32 generates the corrected target current will be described in more detail with reference to FIG. In the following description, a case will be described in which the electric motor 8 is a three-phase brushless motor, has a configuration of eight poles and nine slots, and a current sensor is inserted in two of the three phases. First, a procedure for removing sixth-order torque ripple caused by the structure of the electric motor 8 will be described. The sixth-order torque ripple is measured by rotating the motor 8 in advance, and the sixth-order torque ripple is made to correspond to the rotation angle of the motor 8 measured by the resolver 23 and stored in the angle calculation means 24 as a map. . The sixth-order torque ripple and the rotation angle of the electric motor 8 may be stored in correspondence with each other, but in the following description, a case where the map is stored as a map will be described. During operation, the resolver 23 detects the rotation angle of the electric motor 8, and the angle calculation means 24 reads out the sixth-order torque ripple component corresponding to the detected rotation angle with reference to the map. Further, the angle calculation unit 24 transmits a sixth-order torque ripple component to the target current correction unit 32.

  As a result, the target current correcting means 32 subtracts the sixth-order torque ripple component from the target current input from the CPU to obtain a corrected target current, and using this corrected target current as a reference signal, the Q-axis PI control means 27 Input to the reference terminal of the D-axis PI control means 28 via the reference terminal and field current means 26. That is, since the levels of the reference signals of the Q-axis PI control means 27 and the D-axis PI control means 28 fluctuate with the sixth-order torque ripple, the feedback signal of the motor 8 includes the sixth-order torque ripple. However, the feedback control is performed in a state where the sixth-order torque ripple is canceled out, and the sixth-order torque ripple due to the number of magnetic poles and stators is not generated in the motor 8.

  Next, a procedure for removing secondary torque ripple caused by variations in the gains of the current sensors 14a and 14b will be described. The motor 8 is rotated in advance to measure the secondary torque ripple caused by variations in the gains of the current sensors 14a and 14b, and this secondary torque ripple is associated with the rotation angle of the motor 8 and is mapped (or a table). And stored in the angle calculation means 24. During operation, the resolver 23 detects the rotation angle of the electric motor 8, and the angle calculation means 24 reads a secondary torque ripple component corresponding to the detected rotation angle with reference to the map. Further, the angle calculation unit 24 transmits a secondary torque ripple component to the target current correction unit 32.

  As a result, the target current correcting means 32 subtracts the secondary torque ripple component from the target current input from the CPU to obtain a corrected target current, and using this corrected target current as a reference signal, the Q-axis PI control means 27 Input to the reference terminal of the D-axis PI control means 28 via the reference terminal and field current means 26. That is, since the level of the reference signal of the Q-axis PI control means 27 and the D-axis PI control means 28 fluctuates due to the secondary torque ripple, the detection signal of the fed back motor 8 includes the secondary torque ripple. However, the feedback control is performed in a state where the secondary torque ripple is apparently cancelled, and the secondary torque ripple caused by variations in the gains of the current sensors 14a and 14b is not generated in the electric motor 8.

  FIG. 5 is a correction coefficient map used in the electric power steering apparatus of the present invention, where the horizontal axis represents the motor angle (deg) and the vertical axis represents the correction coefficient. The correction coefficient in FIG. 5 represents a combination of each ripple component such as a sixth-order torque ripple component caused by the structure of the motor at each motor angle and a second-order torque ripple component caused by the gain of the current sensor. Such torque ripple components are calculated and stored by the angle calculation means 24 of FIG. 2 by a simulation test. Therefore, during actual operation, the angle calculation unit 24 acquires the motor angle signal of the motor 8 from the resolver 23, reads the correction coefficient for each motor angle from the correction coefficient map of FIG. 5, and transmits it to the target current correction unit 32. To do.

  As a result, the target current correcting means 32 generates a corrected target current based on the target current input from the CPU and the correction coefficients A and B. For example, the correction coefficient for the sixth-order torque ripple may be read as the correction coefficient A, and the correction coefficient for the second-order torque ripple may be read as the correction coefficient B.

  FIG. 6 is a diagram showing correction of sixth-order torque ripple used in the electric power steering apparatus of the present invention, where the horizontal axis represents the motor speed (MVEL) and the vertical axis represents the correction coefficient. In other words, since the counter electromotive force of the armature coil increases when the rotational speed of the electric motor increases, the rotational speed does not easily increase. In addition, when the rotational speed of the electric motor increases, torque ripple that generates sound is less likely to occur. Therefore, the correction of the sixth-order torque ripple can be weakened in the high speed rotation range. That is, as shown by the solid line in FIG. 6, the correction coefficient for the sixth-order torque ripple is set to 1 up to a predetermined rotational speed, but from the target current by decreasing the correction coefficient as the rotational speed increases above the predetermined rotational speed. Reduce the ratio of subtracting the torque ripple component. As a result, at high speed rotation, torque ripple limitation is weakened or torque ripple limitation is not performed. As indicated by the broken line in FIG. 6, the correction gain may be varied, for example, linearly according to the rotation speed of the electric motor.

  FIG. 7 is a correction ratio map of the secondary torque ripple used in the electric power steering apparatus of the present invention. The horizontal axis represents the temperature of the ECU (control means 12), and the vertical axis represents the ratio of the correction coefficient. Yes. That is, since the current sensor can suppress the gain variation from increasing (ie, the gain variation is reduced) at a high temperature, the correction ratio of the secondary torque ripple is reduced to prevent torque ripple limitation at high temperatures. To. For example, as shown by the solid line in FIG. 7, torque ripple is limited by setting the correction ratio to 1 from -40 ° C to 0 ° C, and the correction ratio decreases with increasing temperature in the normal temperature range from 0 ° C to 40 ° C. Gradually reduce the torque ripple limit. When the temperature is 40 ° C. or higher, the correction ratio value is fixed to a certain level so that torque ripple is not limited. Alternatively, as indicated by a broken line in FIG. 7, as the temperature rises from −40 ° C., the value of the correction ratio may be gradually reduced to gradually weaken the torque ripple limit.

  Next, the flow of processing for correcting the target current and removing the torque ripple component will be described based on a flowchart. FIG. 8 is a flowchart showing the flow of processing for correcting the target current and realizing torque ripple correction in the electric power steering apparatus of the present invention. This flowchart shows the flow of torque ripple correction when the electric motor 8 is a three-phase brushless motor and has an 8-pole 9-slot configuration and the current sensor is inserted into two of the three phases. Yes.

  In FIG. 8, first, a sixth-order torque ripple like the waveform shown in FIG. 3 is read, the detected motor angle of the first-order torque ripple is multiplied by 6, and the rotation angle of the electric motor 8 is obtained (step S1). Next, the correction coefficient map of FIG. 5 is searched from the rotation angle of the electric motor (that is, the angle of the sixth-order torque ripple) obtained in step S1, and the correction coefficient A (that is, the correction coefficient of the sixth-order torque ripple). Is calculated (step S2). Further, the rotational speed of the electric motor 8 is read (step S3). Then, based on the rotational speed of the electric motor 8 read in step S3, a sixth-order torque ripple correction ratio G6 is calculated from the sixth-order correction ratio map of FIG. 6 (step S4). Further, target current− (correction coefficient A × correction ratio G6 × target current) = corrected target current P6 is calculated (step S5). Then, although not displayed in the flow, rotation control of the electric motor 8 is performed based on the calculated corrected target current P6.

  Next, a secondary torque ripple like the waveform shown in FIG. 4 is read, and the detected motor angle of the primary torque ripple is doubled to obtain the electrical angle of the secondary torque ripple (step S6). Next, from the electrical angle of the secondary torque ripple obtained in step S1, the correction coefficient map in FIG. 5 is searched to calculate the correction coefficient B (that is, the secondary torque ripple correction coefficient) (step S7). . Further, the temperature of the current sensor in the ECU (control means) is read (step S8). Based on the temperature read in step S8, a secondary torque ripple correction ratio G2 is calculated from the secondary correction ratio map of FIG. 7 (step S9). Further, target current− (correction coefficient B × correction ratio G2 × target current) = corrected target current P2 is calculated (step S10). Then, although not displayed in the flow, rotation control of the electric motor 8 is performed based on the calculated corrected target current P2.

  In the flow chart of FIG. 8, the correction target current is obtained separately for the sixth-order torque ripple and the second-order torque ripple. However, as shown in FIG. 5, all torque ripple components (in this embodiment, If the sixth-order torque ripple component and the second-order torque ripple component) are combined into a map, the corrected target current can be obtained by one calculation.

  In the above embodiment, for the sake of easy understanding, an electric power steering apparatus using an 8-pole 9-slot three-phase brushless motor and a current sensor for two phases has been described as an example. However, the present invention is limited to such a configuration. Is not to be done. No matter how many current sensors are used in a motor of any configuration, if the torque ripple inherently generated by that configuration is subtracted from the target current, no torque ripple will be generated in the motor without changing the feedback system at all. Thus, the rotation of the electric motor can be controlled with high accuracy. Note that the present invention can also be applied to a steer-by-wire (Steer_By_Wire) in which the steering wheel and the front wheel (rolling wheel) in the steering system S are mechanically separated.

It is a lineblock diagram of an electric power steering device applied to an embodiment of the invention. It is a block diagram which shows the control apparatus in the electric power steering apparatus shown in FIG. 1, and the structure of the periphery. It is a waveform of a 6th-order torque ripple appearing in an 8-pole 9-slot motor. It is a waveform of a secondary torque ripple that appears in the motor when the current sensor is inserted into two of the three phases. It is a figure which shows the correction coefficient map used for the electric power steering apparatus of this invention. It is a figure which shows the correction coefficient of the 6th-order torque ripple used for the electric power steering apparatus of this invention. It is a figure which shows the correction coefficient of the secondary torque ripple used for the electric power steering apparatus of this invention. It is a flowchart which shows the flow of a process which correct | amends a target current and implement | achieves a torque ripple correction in the electric power steering apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus 2 ... Manual steering force generation means 3 ... Steering wheel 4 ... Steering shaft 5 ... Connection shaft 5a, 5b ... Universal joint 6 ... Steering gear box 7 ... Rack & pinion mechanism 7a ... Pinion 8 ... Electric motor 9 ... Rack shaft 10 ... Tie rod 11 ... Ball screw mechanism 12 ... Control means 13 ... Electric motor drive means 14 ... Electric motor current detection means (current detection means)
14a, 14b ... current sensor 15 ... motor voltage detection means 21 ... phase current detection means 22 ... three-phase two-axis conversion means 23 ... resolver (rotational position detection means)
24. Angle calculation means (torque ripple calculation means)
25 ... Motor speed calculation means 26 ... Field current means 27 ... Q-axis PI control means 28 ... D-axis PI control means 29 ... 2-axis 3-phase conversion means 30 ... PWM conversion means 31 ... Non-interference control means 32 ... Target current correction Means S ... Steering system TS ... Steering torque sensor VS ... Vehicle speed sensor W ... Front wheel

Claims (6)

An electric power steering device that drives an electric motor by a feedback control system based on a target current calculated based on a magnitude of a steering input, and applies a driving force generated by the electric motor to a steering system,
Rotational position detecting means for detecting the rotational position of the electric motor;
Torque ripple calculating means for calculating a torque ripple component corresponding to the rotational position detected by the rotational position detecting means;
A corrected target current is generated by correcting the target current based on a value obtained by multiplying the torque ripple component calculated by the torque ripple calculating means by a predetermined gain, and the corrected target current is provided to the feedback control system as a reference signal. Target current correction means for
An electric power steering apparatus comprising:   The gain is set larger than a predetermined value when the rotational speed of the electric motor is slower than a predetermined speed, and is set smaller than the predetermined value when the rotational speed of the electric motor is faster than a predetermined speed. The electric power steering apparatus according to claim 1.   The electric power steering apparatus according to claim 2, wherein the gain decreases as the rotational speed of the electric motor increases. Furthermore, it comprises a current detection means for detecting the current supplied to the electric motor,
The gain is set to a value larger than a predetermined value when the temperature of the current detection unit or the ambient temperature of the current detection unit is lower than a predetermined temperature, and the temperature of the current detection unit or the ambient temperature of the current detection unit is predetermined. The electric power steering apparatus according to any one of claims 1 to 3, wherein when the temperature is higher than the temperature, the electric power steering apparatus is set to a value smaller than a predetermined value.   5. The electric power steering apparatus according to claim 4, wherein the gain decreases as the temperature of the current detection means or the ambient temperature of the current detection means increases.   6. The electric power steering apparatus according to claim 1, wherein the electric motor is a three-phase brushless motor, and the rotational position detecting means is a resolver.

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