JP3601292B2 - Electric power steering control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering that performs light steering by detecting a steering torque applied to a steering system by a steering torque detecting unit and controlling a steering assist force generated by an electric motor according to the detected value. In particular, a stable return characteristic can be obtained at the time of steering return.
[0002]
[Prior art]
2. Description of the Related Art As a conventional electric power steering control device, there is a control device described in, for example, Japanese Patent Application Laid-Open No. 8-67266 (hereinafter simply referred to as a conventional example).
[0003]
In this conventional example, an electric motor for applying a steering assist force to a steering system is connected to an H-bridge circuit composed of four switching elements, and an ON signal is supplied to one of a pair of diagonal switching elements of the H-bridge circuit. In the electric power steering apparatus having the motor driving means for driving the motor forward and reverse by supplying the pulse width modulation signal to the other side, when the return state of the steering system is detected, the ON signal of the H-bridge circuit is turned on. By changing to a pulse width modulation signal based on a return control signal corresponding to the speed signal, a counter electromotive force generated by a regenerative action when the motor rotates in the opposite direction due to the reaction force from the tire is controlled. A power steering device is described.
[0004]
Here, the operation of the motor rotation speed signal is performed by inserting a resistor in series with the motor to detect the direction and level of the motor current as a voltage signal, and to apply this voltage signal to the motor or the measured system of the motor driving means. In order to detect the motor current without affecting the motor current, the motor current is detected by supplying the detection accuracy to the motor current detecting means with high accuracy and little change over time, and the motor voltage is detected by the motor voltage detecting means. This is performed by calculating the motor rotation speed by the motor rotation speed calculation unit based on the detection signals of the current detection unit and the motor voltage detection unit.
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional electric power steering apparatus, the regenerative current due to the back electromotive force of the motor at the time of the return of the steering system can be compensated to make the motor current converge to the target current. Since the motor current is as small as about 1 A at the maximum when the maximum current value is 35 A, for example, it is necessary to apply current detection means having high detection accuracy as described above, and there is an unsolved problem that the cost increases.
[0006]
By the way, if the detection accuracy of the motor current detecting means is poor, the control for compensating for the regenerative current due to the back electromotive force of the motor at the time of return is performed or the return characteristic of the steering system is unstable because it is not performed. Become.
[0007]
Further, in the conventional example described above, because the current feedback control is employed, if the target current is too large at the time of return, the current flows even if the return speed of the steering wheel is large and the motor rotation speed is large. There is also an unsolved problem that the return characteristic is too good and the convergence to the neutral position in the non-steering state is deteriorated.
[0008]
Therefore, the present invention has been made by focusing on the unsolved problem of the conventional example described above, and a stable return characteristic can be obtained even when the motor current is detected by current detection means having low detection accuracy. It is another object of the present invention to provide a control device for an electric power steering device which can improve the convergence of a non-steering state to a neutral position even when the motor rotation speed is high.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a control device for an electric power steering device according to claim 1 includes a steering torque detecting means for detecting a steering torque applied to a steering system, and a steering assist force applied to the steering system. And a motor control means for controlling the motor based on at least a steering torque detection value of the steering torque detection means and a current detection value of the current detection means. In the control apparatus for an electric power steering, the electric motor control means includes: a steering state detecting means for detecting a steering operation and a steering return operation of the steering system; a steering return operation detected by the steering state detecting means; Open-loop control for controlling the voltage applied to the electric motor when the steering torque detection value of the torque detection means is near the non-steering state value; A loop control unit, is characterized in that it comprises a feedback control means for said motor for feedback control based on the steering torque detection value and the current detection value when other than the above.
[0010]
In the invention according to the first aspect, the open-loop control state in which a predetermined voltage is applied to the electric motor in the steering return state in which the steering wheel is released from the steering state or in a state close to the steering wheel is set, so that the electric motor current is detected. The motor is controlled without using the current detecting means.
[0011]
Further, in the control device for the electric power steering apparatus according to claim 2, in the invention according to claim 1, the steering state detecting means is such that a steering torque detection value of the steering torque detecting means is near a non-steering state value; In addition, when the motor rotation speed exceeds the set rotation speed, it is configured to detect that it is in the steering return operation state.
[0012]
In the invention according to the second aspect, the steering return operation state can be reliably detected from the detected steering torque value and the motor rotation speed.
Further, a control device for an electric power steering device according to a third aspect is configured such that in the invention according to the first aspect, the open loop control means sets a voltage applied to the electric motor in accordance with a vehicle speed. It is characterized in that the applied voltage can be changed according to the vehicle speed.
[0013]
Further, in the control device for an electric power steering apparatus according to a fourth aspect, in the invention according to the third aspect, the open-loop control means sets a voltage applied to the electric motor to a predetermined value only in a low to middle vehicle speed range. The open-loop control is performed only in a vehicle speed range that requires steering return operation control.
[0014]
【The invention's effect】
According to the invention according to claim 1, when the steering torque detection value becomes close to the non-steering state value at the time of the return operation of the steering system, the feedback control using the current detection value of the current detection means to the electric motor is performed. Since the control is changed to the open-loop control for applying a predetermined voltage, the detection accuracy of the current detection means is not affected, and the voltage control is performed. As a result, the effect of improving the convergence to the neutral position in the non-steering state can be obtained even when the applied voltage is somewhat too large.
[0015]
According to the second aspect of the present invention, when the detected steering torque is near the non-steering state value and the motor rotation speed is higher than the set speed, the steering return operation state is determined, so that the steering return operation state can be accurately determined. The effect of being able to detect is obtained.
[0016]
Further, according to the third aspect of the present invention, since the open loop control means sets the voltage applied to the electric motor according to the vehicle speed, it is possible to perform control according to the presence or absence of the effect of the regenerative current at the time of return. The effect is obtained.
[0017]
Still further, according to the invention according to claim 4, the open loop control means sets the voltage applied to the electric motor to the predetermined value only in the low and middle vehicle speed ranges, so that the effect of the regenerative current at the time of return is large. The effect is obtained that the return characteristics can be reliably stabilized in the low to middle vehicle speed range.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing one embodiment of the present invention. A steering wheel 1 is connected to an upper end of a steering shaft 2, and the steering shaft 2 is supported by a fixed portion and extends downward. The pinion 3 is mounted on the section.
[0019]
The pinion 3 meshes with a rack 4 extending horizontally in the vehicle width direction to form a steering gear, and a rotational motion of the steering wheel 1 around the steering shaft 2 is converted into a linear motion (translational motion) of the rack 4. You.
[0020]
Both ends of the horizontally extending rack 4 are connected to knuckles and steered wheels 6 via tie rods 5, respectively, and the left and right steered wheels 6 are steered by the rack 4 moving horizontally (translational movement). Is done.
[0021]
A ring gear 11 constituting a speed reducer is coaxially fixed above the pinion 3 in the steering shaft 2, and a ring gear 10 connected to a drive shaft 9 of a steering assist motor 8 as an electric motor meshes with the ring gear 11. The steering assist motor 8 is controlled so as to generate a steering assist force according to the steering torque by the duty-controlled pulse power output from the control unit 7 described later.
[0022]
Further, a torque detection mechanism 12 is provided above the ring gear 11 in the steering shaft 2. The torque detection mechanism 12 includes a torsion bar (not shown) that connects the lower end of the steering shaft 2 and the upper end of the pinion 3, and a steering torque sensor 13 disposed on the outer periphery thereof.
[0023]
The steering torque sensor 13 detects the steering torque from the torsion amount of the torsion bar, and corrects the steering torque according to the magnitude of the steering torque and by turning the steering wheel 1 rightward (counterclockwise with respect to the input from the pinion 3). A value and a torque detection value T which is a negative analog voltage signal when the steering wheel 1 is turned left (clockwise with respect to the input from the pinion 3) are supplied to a controller unit 7 described later.
[0024]
Further, the vehicle is equipped with a vehicle speed sensor 14 for detecting the vehicle speed. The vehicle speed sensor 14 detects the vehicle speed in the front-rear direction of the vehicle, and a pulse signal corresponding to the vehicle speed is supplied to a controller unit 7 described later. You.
[0025]
Further, a current detecting circuit 15 is provided as current detecting means for detecting a current supplied to the steering assist motor 8, and the current detecting circuit 15 detects an actual current flowing through the steering assist motor 8, and according to the magnitude thereof. An actual current detection value i composed of the analog voltage signal is supplied to the controller unit 7.
[0026]
Further, there is provided a tachogenerator 16 for detecting the rotational speed of the steering assist motor 8, for example, as a motor rotational speed detecting means attached to the rotating shaft of the steering assist motor 8. The motor rotation speed ω, which is an analog voltage that is negative when rotating in the left-turn direction and positive when rotating in the right-turn direction, is output to the controller unit 7 according to the speed and the rotation direction.
[0027]
The battery voltage sensor 17 detects a voltage of a battery 22 described later. The battery voltage sensor 17 outputs a battery voltage V which is an analog voltage signal. _B Is supplied to the controller unit 7.
[0028]
As shown in FIG. 2, the controller unit 7 includes a steering torque detection value T output from the steering torque sensor 13, a pulse signal output from the vehicle speed sensor 14, an actual current detection value i output from the current detection circuit 15, Motor rotation speed ω output from tachogenerator 16 and battery voltage V output from battery voltage sensor 17 _B And a microcomputer 18 for outputting a duty control signal for duty-controlling the drive current to the steering assist motor 8 for controlling the rotation direction and rotation speed of the steering assist motor 8, and an output from the microcomputer 18. And a motor drive circuit 19 for controlling the rotation direction and rotation speed of the steering assist motor 8 based on the supplied duty control current pulse.
[0029]
Here, the microcomputer 18 includes an input-side interface circuit 18a having an F / V conversion function and an A / D conversion function, an arithmetic processing unit (CPU) 18b including a microprocessor unit and the like, and a storage device including RAM, ROM and the like. 18c and an output-side interface circuit 18c.
[0030]
The input interface circuit 18a includes a steering torque detection value T from the steering torque sensor 13, a pulse signal from the vehicle speed sensor 14, an actual current detection value i from the current detection circuit 15, and a motor rotation speed from the tachogenerator 16. ω and the battery voltage V from the battery voltage sensor 17 _B Is input from the output interface circuit 18d, and a left-turning direction signal LD and a right-turning direction signal RD representing the steering assist force generation direction, and a left-turning duty control current pulse LP for duty-controlling the current supplied to the steering assist motor 8. And a right-turn duty control current pulse RP and an energization control signal CS for controlling energization of the motor drive circuit 19 are output to the motor drive circuit 19.
[0031]
The arithmetic processing device 18b executes the arithmetic processing of FIG. 5 described later every predetermined sampling time ΔT (for example, 5 msec), and detects the steering torque detection value T of the steering torque sensor 13 and the motor rotation speed ω of the tachogenerator 16. It is determined whether the steering system including the steering wheel 1 is in the steering operation state in which the steering angle is increasing in the direction in which the steering angle is away from the neutral position in the non-steering state or in the steering return operation state in which the steering angle is returned to the neutral position side. When the vehicle is in the steering return operation state, the motor application voltage V corresponding to the vehicle speed V obtained by F / V converting the pulse signal of the vehicle speed detector 14 is obtained. _M Is applied to the steering assist motor 8, and at other times, the target current value i is determined based on the steering torque detection value T detected by the steering torque sensor 13 and the motor rotation speed ω. ^* Is calculated, and based on this and the actual current detection value i detected by the current detection circuit 15, current feedback control for controlling the steering assist motor 8 is performed.
[0032]
Further, the storage device 18c stores in advance control maps, arithmetic expressions, programs, and the like necessary for the arithmetic processing of the arithmetic processing device 18b, and sequentially stores the arithmetic results required in the arithmetic process of the arithmetic processing device 18b. .
[0033]
On the other hand, the motor drive circuit 19 forms two sets of series circuits by connecting two switching elements T1 to T4 such as four MOSFETs in series, and forms two sets of series circuits. The steering assist motor 8 is connected between T4 and T4. The input sides of the switching elements T1 and T3 are connected to each other, and the negative side is connected to the positive side of the grounded battery 22 via the motor relay 20 and the key switch 21. The output sides of the switching elements T2 and T4 are connected to each other and grounded to form a so-called H-bridge circuit.
[0034]
The left-turn direction signal LD and the right-turn direction signal RD output from the output interface circuit 18d of the microcomputer 18 to the switching elements T1 and T3, respectively, are output to the output interface circuit of the microcomputer 18 to the switching elements T4 and T2, respectively. A left-turn duty control current pulse LP and a right-turn duty control current pulse RP output from 18d are supplied, respectively, and one end of a relay coil of the motor relay 20 is connected to the key switch 21 via an NPN transistor 24 as a switching element. The transistor 23 is connected and the other end thereof is grounded. An energization control signal CS output from the output side interface circuit 18 d of the microcomputer 18 is supplied to the transistor 23.
[0035]
Further, a resistance R for current detection is connected in series with the steering assist motor 8, and both ends of the resistance are connected to a current detection circuit 15 composed of an operational amplifier or the like. An actual current detection value i, which is an analog signal represented by a sign, is output to the controller unit 7. Here, the current detection circuit 15 does not require high detection accuracy, and a current detection circuit having a relatively low detection accuracy and a relatively large error of about ± 1 A can be applied.
[0036]
Next, the operation of the above embodiment will be described with reference to FIG. 3 showing a steering assist control processing procedure executed by the arithmetic processing unit 18b in the microcomputer 18.
The steering assist control process of FIG. 3 is executed as a main program. First, in step S1, the energization control signal CS for turning on the motor relay 20 for starting energization of the motor drive circuit 19 is turned on, and then the process proceeds to S2. Then, the steering torque detection value T detected by the steering torque sensor 13 is read, and then the process proceeds to step S3, where the absolute value of the steering torque detection value T is set to a predetermined value T that defines a preset dead zone width. ₀ It is determined whether or not | T | ≧ T ₀ If so, it is determined that the steering wheel 1 is in the steering state, and the process proceeds to step S4.
[0037]
In this step S4, the vehicle speed detection value V obtained by F / V converting the pulse signal detected by the vehicle speed sensor 14 is read. Then, the process proceeds to step S5, and based on the read vehicle speed detection value V, the vehicle speed shown in FIG. Is the steering torque detection value T and the motor reference drive current i _T After performing a control map selection process of selecting any one of the characteristic lines of the control map representing the relationship with the control map, the process proceeds to step S6.
[0038]
Here, as shown in FIG. 4, the control map indicates that the detected steering torque T is a set value + T sandwiching “0” defining the dead zone. ₀ And -T ₀ , The reference drive current i _T Becomes “0” and the steering torque detection value T becomes the set value + T ₀ And -T ₀ , The reference drive current i increases in the positive or negative direction. _T Is set to increase in a polygonal line shape, and the inclination angle of the polygonal line is set to decrease as the vehicle speed increases.
[0039]
In step S6, the reference current i to the steering assist motor 8 is referred to by referring to the control map selected in step S5 based on the steering torque detection value T read in step S2. _T Then, the process proceeds to step S7 to read the motor rotation speed ω detected by the tachogenerator 16, and then proceeds to step S8 to perform the calculation of the following equation (1) to calculate the target current for the steering assist motor 8. i ^* Is calculated.
[0040]
i ^* = I _T -K _D ・ Ω ………… (1)
Where K _D Is a predetermined damping gain sufficient to achieve the steering stability required for the steering system.
[0041]
Next, the process proceeds to step S9 to read the actual current detection value i of the current detection circuit 15, and then proceeds to step S10 to calculate the duty ratio D by performing the calculation of the following equation (2).
[0042]
D = K _C (I ^* -I) ............ (2)
Where K _C Is a control gain, and a target current i ^* In consideration of the allowable error range (for example, about several A) between the actual current detection value i and the actual current detection value i, the value is set to about ten to several tens.
[0043]
Next, the process proceeds to step S11, where it is determined whether the steering torque detection value T read in step S2 is negative including zero, and when T ≦ 0, it is determined that the vehicle is in a left-turn state. In step S12, the left turn direction signal LD is turned on, the right turn direction signal RD is turned off, and a left turn duty control current pulse LP having the duty ratio D calculated in step S10 is output. Then, after outputting the right-turn duty control current pulse RP in the OFF state, the process proceeds to step S14. If T> 0, it is determined that the vehicle is in the right-turn state, and the process proceeds to step S13, where the right-turn direction signal RD Is turned on, the left turn direction signal LD is turned off, and the right turn duty control current pulse R of the duty ratio D calculated in step S10 is set. Outputs, and proceeds from the output of the left turn duty control current pulses LP in the OFF state in step S14.
[0044]
In step S14, it is determined whether or not to end the steering assist control process. If the steering assist control process is to be continued, the process returns to step S2. If the steering assist control process is to be ended, the process proceeds to step S15. Then, after the energization control signal CS to the motor drive circuit 19 is turned off, the steering assist control process ends.
[0045]
On the other hand, the result of the determination in step S3 is | T | <T ₀ When it is determined that the steering torque detection value T is within the dead zone and that the steering torque is in the non-steering state or the steering returning operation state, the process proceeds to step S16, and the motor rotation speed ω detected by the tachogenerator 16 is read. The process proceeds to S17, where the motor rotation speed ω is set at the preset speed ω. ₀ Ω ≦ ω ₀ , It is determined that the vehicle is not in the steering return state but in the mere non-steering state, and the routine proceeds to step S3, where ω> ω ₀ If, it is determined that the motor rotation speed is high and the steering is returned to the neutral position side, and the process proceeds to step S18.
[0046]
In this step S18, the vehicle speed detection value V detected by the vehicle speed sensor 14 is read, and then the process proceeds to step S19, where the vehicle speed detection value V shown in FIG. And motor applied voltage V _M Motor applied voltage V with reference to the applied voltage calculation map _M Is calculated.
[0047]
Here, the motor applied voltage calculation map is, as shown in FIG. ₁ When it is less than or equal to _M Becomes “0” and the set value V ₁ Exceeds the applied voltage V according to the increase of the vehicle speed detection value V. _M Increases relatively steeply, and the set value V ₂ Reaches the middle speed range V ₃ Applied voltage V _M Maintains a constant value, and the vehicle speed detection value V becomes the set value V ₃ Exceeds the applied voltage V as the vehicle speed detection value V increases. _M Decreases relatively steeply, and the vehicle speed detection value V becomes the set value V at which the vehicle speed is in the high speed range. ₄ Exceeds the applied voltage V _M Is set to return to “0” again.
[0048]
Next, the process proceeds to step S20, in which the battery voltage V detected by the battery voltage sensor 17 is detected. _B Then, the process proceeds to step S21, calculates the duty ratio D according to the following equation (3), and then proceeds to step S22.
[0049]
D = V _M / V _B ............ (3)
In this step S22, it is determined whether or not the motor rotational speed ω is negative including zero, and when ω ≦ 0, it is determined that the steering is returning to the left turning direction, and the process proceeds to step S12. If ω> 0, it is determined that the steering is returning to the right turning direction, and the process proceeds to step S13.
[0050]
The processing of FIG. 3 corresponds to the motor control means, of which the processing of steps S2, S3, S16, and S17 corresponds to the steering state detection means, and the processing of steps S4 to S13 corresponds to the feedback control means. The processing of S16 to S22 corresponds to the open loop control means.
[0051]
Therefore, assuming that the key switch 21 is off and the vehicle is in a stopped state, in this state, the power supply of the controller unit 7 is cut off and the motor relay 20 of the motor drive circuit 19 is also turned off. , The power supply to the electric motor 8 is cut off.
[0052]
When the key switch 21 is turned on in this stopped state, the power of each section of the controller unit 7 is turned on, and the microcomputer 18 starts processing. At this time, the arithmetic processing device 18b starts executing the steering assist control process shown in FIG. 3, and outputs an ON-state energization control signal CS to the transistor 23 of the motor drive circuit 19 in step S1.
[0053]
Therefore, the transistor 23 is turned on, the motor relay 20 is turned on, and the supply of DC power from the battery 22 to the H-bridge circuit is started. At this time, when the steering wheel 1 is not being steered, the steering torque detection value T of the steering torque sensor 13 is substantially “0”.
[0054]
For this reason, the process proceeds from step S3 to step S16, but since the steering assist motor 8 has stopped rotating and the motor rotation speed ω is “0”, the process proceeds from step S17 to step S4.
[0055]
At this time, since the vehicle speed detection value V is "0", the characteristic line L having the largest slope of the characteristic lines shown in FIG. ₁ Is selected, but since the detected steering torque T is "0", the motor reference drive current i calculated in step S6 is selected. _T Is also "0".
[0056]
On the other hand, since the steering assist motor 8 is stopped, the actual current detection value i detected by the current detection circuit 15 is also “0”, so that the duty ratio D calculated in step S10 is also “0”, The process proceeds from step S11 to step S12, in which the left direction signal LD is turned on, the right direction signal RD is turned off, the duty ratio "0", that is, the off state is maintained for the left turn duty control current pulse LP, and the right turn duty is further maintained. The control current pulse RP is maintained in the off state.
[0057]
Therefore, in the motor drive circuit 19, only the switching element T1 is turned on and the other switching elements T2 to T4 are turned off, so that no current flows through the H-type bridge circuit, and the electric motor 8 is turned off. , The steering assist torque generated by the electric motor 8 is maintained at "0", and the non-steering state is continued.
[0058]
In this stopped state, time t ₁ When the steering wheel 1 is turned to the left, so-called stationary steering is performed, the steering torque detection value T detected by the steering torque sensor 13 in response to this setting value T defines the dead zone. ₀ And increases in the negative direction.
[0059]
As described above, the absolute value of the detected steering torque T is equal to the set value T. ₀ When it becomes larger, the process proceeds from step S3 to step S4 in the process of FIG. 3, and based on the detected steering torque value T, the motor reference drive current i _T Is calculated, and based on this and the motor rotation speed ω (= 0), the motor target current i ^* Is calculated, and the duty ratio D is calculated based on the difference value between the current value and the actual current detection value i detected by the current detection circuit 15 (step S10). Then, since the detected steering torque value T is negative, the process proceeds from step S7 to step S8, where the left direction signal LD is turned on, the right direction signal RD is turned off, and the left turn duty control current pulse LD is calculated. The right / left duty control current pulse RD is maintained in an off state with an on / off ratio corresponding to the duty ratio D thus obtained.
[0060]
For this reason, the switching element T1 of the motor drive circuit 19 continues to be in the on state, and in addition, the switching element T4 is turned on and off at the duty ratio D. The drive current i flows, and the electric motor 8 is rotationally driven by the feedback control to generate a left-turn steering assist torque corresponding to the steering torque detection value T, thereby performing light steering.
[0061]
Thereafter, when the stationary steering is completed, the steering torque detection value T returns to the initial state of substantially “0”, and then the vehicle is driven straight ahead at, for example, a medium vehicle speed, and then the steering wheel 1 is turned right, for example, to a steady circular turning state. Then, in response to this, the steering torque detection value T increases in the positive direction and then becomes a constant value, and a control map according to the vehicle speed is selected, and the drive current of the electric motor 8 is feedback-controlled.
[0062]
Thereafter, in order to return from the steady circular turning state to the straight running state, when the steering wheel 1 is released or is in a state close to the released state and the steering wheel is returned to the steering operation state, the detected steering torque T at this time becomes substantially “0”. Therefore, in the process of FIG. 3, the process proceeds from step S3 to step S16, where the steering system rotates in the left-turn direction by the self-aligning torque, and returns to the neutral position side in the non-steering state.
[0063]
At this time, in the initial state in which the steering is returned from the steady circular turning state, the motor rotation speed ω is substantially “0”, so the process proceeds from step S17 to step S4, and the feedback control of the steering assist motor 8 described above is performed. Is continued, but since the steering torque detection value T is “0”, the target current i calculated in step S8 is calculated. ^* Becomes substantially "0", and the steering assist torque generated by the steering assist motor 8 becomes substantially zero.
[0064]
Therefore, the wheels are returned to the neutral position side by the self-aligning torque, so that the steering system rotates in the left-turning direction, whereby the steering assist motor 8 is also rotationally driven in the left-turning direction. Motor rotation speed ω is set speed ω ₀ Is exceeded, it is determined that the vehicle is in the steering-back operation state, and the process proceeds from step S17 to step S18. Since the vehicle is running at the medium vehicle speed, the motor application voltage V is relatively large with reference to the control map of FIG. _M Is set.
[0065]
This motor applied voltage V _M Is the battery voltage V _B , The duty ratio D is calculated, and then the process proceeds to step S22. Since the steering assist motor 8 is rotationally driven in the left-turn direction, the motor rotation speed ω becomes negative. The motor drive circuit 19 is controlled in the same manner as in the left-turning state described above, and the motor applied voltage V _M Is applied to the steering assist motor 8, the steering assist motor 8 enters an open loop control state, and the steering assist motor 8 is rotationally driven against the frictional force generated by the steering assist motor 8. A stable steering return operation can be performed.
[0066]
As described above, in the steering return operation state, the steering assist motor 8 is in an open-loop voltage control state, so that the rotation of the steering assist motor 8 generates a back electromotive force, and the back electromotive force constant at this time is K _E Assuming that the actual current value including the regenerative current generated by the steering assist motor 8 is i and the coil resistance is R, the motor applied voltage V _M Can be represented by the following equation (4).
[0067]
V _M = I · R + K _E ・ Ω ............ (4)
As is apparent from the equation (4), the applied voltage V _M Is controlled to a constant value, so that when the motor rotation speed ω increases, the actual current value i supplied to the steering assist motor 8 decreases.
[0068]
As a result, the motor applied voltage V _M Is slightly too large and the motor rotational speed ω becomes too fast, the actual current value i decreases accordingly, and the steering assist torque generated by the steering assist motor 8 decreases. The rotation speed ω can be reliably prevented from becoming excessively high, and the steering return operation is performed at an appropriate rotation speed.
[0069]
When the driver grips the steering wheel 1 again and stops the rotation of the steering wheel 1 when or during the return of the vehicle to the straight traveling state, the steering assist generated by the steering assist motor 8 at this time is provided. Since the torque is detected by the steering torque sensor 13, the detected steering torque value T is the set value T that defines the dead zone. ₀ Therefore, the process goes from step S3 to step S4 in the process of FIG. 3, and feedback control equivalent to right-turning is started, and the steering assist motor 8 is turned in the right-turning direction. An auxiliary torque is generated, and the rotation is stopped.
[0070]
Further, if the wheel release state continues even after returning to the neutral state in which the wheels are in a straight running state, the steering system further moves leftward because the steering assist motor 8 generates steering assist torque for turning left. In this state, the motor rotates against the self-aligning torque, so that the motor rotation speed ω of the steering assist motor 8 decreases. In this state, the process proceeds from step S17 to step S4 in the process of FIG. And returns to the feedback control state. At this time, since the regenerative current generated by the steering assist motor 8 is also small, the regenerative current is not affected even when the feedback control is performed.
[0071]
Furthermore, even in the steering return operation state, when the vehicle speed is a vehicle speed just before stopping close to zero or in a high vehicle speed state, the influence of the regenerative current generated by the steering assist motor 8 is small, and therefore, FIG. The open loop control of steps S18 to S22 in the processing is performed, but when the motor applied voltage calculation map shown in FIG. _M Becomes "0", the rotational drive of the steering assist motor 8 is stopped.
[0072]
As described above, according to the above-described embodiment, when the vehicle shifts from the steering operation state in which the vehicle is in a turning traveling state to the steering return operation state in which the steering wheel 1 is released, the steering assist motor 8 has its actual current value i. From the feedback control state using the predetermined motor applied voltage V _M Is switched to an open loop control state in which the current is applied to the steering assist motor 8, so that the motor control can be performed without using the current detection circuit 15, and a current detection circuit 15 having a high detection accuracy needs to be used. And the overall cost can be reduced.
[0073]
In the above embodiment, the case where the tachogenerator 16 is applied as the motor rotation speed detecting means for detecting the motor rotation speed ω has been described. However, the present invention is not limited to this. An encoder that outputs a corresponding pulse signal can be applied. Further, the motor current i and the motor voltage V _M0 May be detected, and the motor rotation speed ω may be estimated from these in accordance with the following equation (4).
[0074]
ω = (V _M0 −R · i) / K _V (K _V Is a constant) ............ (4)
In the above embodiment, the case where the controller unit 7 is configured using the microcomputer 18 has been described. However, the present invention is not limited to this, and the function generator, the subtractor, the multiplier, the pulse width modulation circuit, etc. Further, it is possible to omit forming the duty control current pulses LP and RP in the arithmetic processing unit 18b of the microcomputer 18 and to provide an external pulse width modulation circuit. Good.
[0075]
Further, the motor drive circuit 19 is not limited to the above-described configuration, and any other switching element such as a transistor or a relay can be applied as a switching element forming the H-type bridge circuit.
[0076]
Furthermore, in the above-described embodiment, the reference current i with respect to the detected steering torque T is determined using the control map. _T Has been described, but the present invention is not limited to this. _T Control using a proportional term and a derivative term of the steering torque detection value T, and PID control in which an integral term is added to the PD control. In this case, each of the proportional gain, the differential gain, and the integral gain May be changed according to the vehicle speed.
[0077]
Similarly, the motor applied voltage V _M Also, the characteristic line is not limited to the case where it is obtained by referring to the motor applied voltage calculation map of FIG. 5, and the characteristic line may be expressed by a mathematical expression, and the motor applied voltage may be calculated according to the mathematical expression.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a specific example of the controller unit of FIG. 1;
FIG. 3 is a flowchart illustrating an example of a steering assist control process of a microcomputer in a control unit.
FIG. 4 is a characteristic diagram illustrating a control map representing a relationship between a steering torque detection value using a vehicle speed as a parameter and a motor target drive current.
FIG. 5 is a characteristic diagram showing a control map representing a relationship between a vehicle speed and a motor applied voltage.
[Explanation of symbols]
1 Steering wheel
2 Steering shaft
7 Controller unit
8 steering assist motor
13 Steering torque sensor
14 Vehicle speed sensor
15 Current detection circuit
16 Tacho generator
17 Battery voltage sensor
18 Microcomputer
19 Motor drive circuit

Claims (4)

Steering torque detection means for detecting a steering torque applied to a steering system, an electric motor for applying a steering assist force to the steering system, current detection means for detecting a drive current of the electric motor, and at least the steering torque detection means And a motor control means for controlling the motor based on the detected steering torque value and the current detection value of the current detection means, wherein the motor control means performs a steering operation of the steering system and a steering operation. Steering state detection means for detecting a return operation; open loop control means for performing open loop control of a voltage applied to the electric motor when the steering state detection means detects a steering return operation; Feedback control means for performing feedback control of the electric motor based on the torque detection value and the current detection value. Electric power steering control apparatus characterized by. The steering state detection means detects that the steering return operation state is established when the steering torque detection value of the steering torque detection means is near the non-steering state value and the motor rotation speed exceeds the set rotation speed. The control device for an electric power steering according to claim 1, wherein the control device is configured as follows. 2. The electric power steering control device according to claim 1, wherein the open loop control means is configured to set a voltage applied to the electric motor in accordance with a vehicle speed. 4. The electric power steering control device according to claim 3, wherein the open loop control means is configured to set a voltage applied to the electric motor to a predetermined value only in a low to middle vehicle speed range.

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