JP2012214093A - Control method for electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an operational feeling of an electric power steering system and improve the resistance thereof to power fluctuation.SOLUTION: A control unit 10 of the electric power steering system is capable of coping with the phenomenon that a duty ratio motor current value characteristic is varied along with variation in output voltage value of a power supply 50. Concretely, an F/F duty limit value setting unit 53 estimates a duty ratio of a break point indicative of a feedforward control range by using the output voltage value of the power supply 50 measured by a voltage value measuring unit 51. Furthermore, a gain correction value setting unit 54 estimates a gain correction value in feedback control on the basis of the output voltage value of the power supply 50 to cope with a variation in gradient subsequent to the break point. Then, the control unit 10 can equalize the current responsiveness of motor current Im by using the estimated duty ratio of the break point and the estimated gain correction value.

Description

  The present invention relates to a method for controlling an electric power steering device for a vehicle.

  The electric power steering device includes a motor in a steering system, and controls the power supplied from the motor by using a control device, thereby reducing the driver's steering force. In addition, the outline | summary of the content currently disclosed by patent document 1 is demonstrated below.

FIG. 5 is a diagram illustrating a schematic configuration of the electric power steering apparatus.
In FIG. 5, the electric power steering apparatus 1 is engaged with a steering wheel 110, a pinion 116 that is integrally rotatable via a steering shaft 111, universal joints 112 and 114, and a connecting shaft 113, and the pinion 116. And a rack and pinion mechanism having a rack shaft 117 which can be reciprocated in the vehicle width direction.
Both ends of the rack shaft 117 are connected to the knuckle arms 120 of the left and right front wheels 121 as steering wheels via tie rods 119, and the left and right front wheels 121 are steered according to the rotation operation of the steering wheel 110. ing. Further, a motor 118 that generates an auxiliary steering force for reducing the manual steering force of the steering wheel 110 is provided coaxially on the rack shaft 117.

  In FIG. 5, a manual steering torque detector 115 that detects manual steering torque acting on the pinion 116 is provided in a steering gear box (not shown). The manual steering torque detection unit 115 converts the detected manual steering torque into a manual steering torque detection value T, and outputs the manual steering torque detection value T to the control device 100. The control device 100 receives the manual steering torque detection value T as input and executes drive control of the motor 118 to control the output of the motor 118 (steering assist torque).

  The control device 100 includes a current target value determination unit 101 and a control unit 102. The current target value determination unit 101 determines a target auxiliary torque based on the manual steering torque detection value T, and outputs a target current value It necessary to supply the target auxiliary torque from the motor 118.

  FIG. 6 is a block configuration diagram of the control unit 102. The control unit 102 includes a motor control unit 130, a motor drive unit 140, and a motor current value measurement unit 150. The operation in each part will be described below (see FIG. 5 as appropriate). The motor 60 shown in FIG. 6 corresponds to the motor 118 shown in FIG.

The motor control unit 130 includes a feedback control unit 20, a feedforward control unit 30, and a PWM (Pulse Width Modulation) signal setting unit 40.
The feedback control unit 20 includes a deviation calculation unit 21, a proportional calculation unit 22, an integration calculation unit 23, and an addition calculation unit 24.

The deviation calculating unit 21 calculates a deviation between the current target value It output from the current target value determining unit 101 and the motor current value Im measured by the motor current value measuring unit 150, and outputs the deviation value.

  The proportional calculation unit 22 receives the output value of the deviation calculation unit 21 and outputs a value proportional to the input. The integral calculation unit 23 receives the output value of the deviation calculation unit 21 and outputs a value obtained by integrating the input. The addition calculation unit 24 adds the output value of the proportional calculation unit 22 and the output value of the integration calculation unit 23 to generate an output value 24 a of the feedback control unit 20. The output value 24a of the feedback control unit 20 is generated so that the output value of the deviation calculation unit 21 approaches zero.

  The feedforward control unit 30 includes an F / F (feedforward) limit processing unit 131 and an addition calculation unit 33.

  The F / F limit processing unit 131 receives the current target value It and calculates a value proportional to the current target value It. The F / F limit processing unit 131 includes a limiter 32. If the value proportional to the current target value It is within a predetermined range, the F / F limit processing unit 131 outputs a value proportional to the input value and is out of the predetermined range ( Outside the threshold value, a predetermined value indicating a saturated value is output.

  Further, the F / F limit processing unit 131 receives the signal value 41a input to the PWM signal setting unit 40 as an input. The signal value 41a is a signal value extracted from the branching unit 41, and is the same value as the final output value 33a that determines the duty ratio of the PWM signal used for PWM drive control. The signal value 41a varies with the variation of the counter electromotive voltage generated according to the rotation speed of the motor 60. Then, the fluctuation of the signal value 41a brings about a vibration at the turning and turning start at a small steering angle and an insufficient auxiliary steering force at the turning start at the time of steering. Therefore, the F / F limit processing unit 131 monitors the signal value 41a in order to prevent vibrations and lack of assist, and indicates a threshold indicating whether the feedforward control performs a proportional operation or a saturation operation (patent) In Reference 1, the threshold duty ratio) is compared with the signal value 41a, and the output value of the feedforward control set in the saturation operation is held at a predetermined value and limited according to the comparison result. Thus, after the final output value 33a reaches the threshold value (threshold duty ratio), the output value 131a of the F / F limit processing unit 131 is not increased even if the current target value It increases. The threshold value (threshold duty ratio) is defined between a predetermined range in the limiter 32 (a range in which a value proportional to the input value is output) and outside a predetermined range (a range in which a predetermined value indicating a saturated value is output). It is a boundary value.

  The addition calculation unit 33 adds the output value 24a of the feedback control unit 20 and the output value 131a of the F / F limit processing unit 131, and outputs the value as a final output value 33a. That is, the final output value 33a is a value used for determining the duty ratio of the PWM signal for PWM control of the motor current supplied to the motor 60.

  The PWM signal setting unit 40 generates a PWM signal for PWM driving the motor 60 based on the final output value 33a, and outputs the generated PWM signal value 40a as a drive control signal.

  The motor driving unit 140 includes a gate driving unit 141 and an H-type bridge circuit 142 including four FETs (Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors). The gate drive unit 141 selects two FETs by vertical drag according to the steering direction of the steering wheel 110, and drives the gates of the two selected FETs based on the PWM signal 40a to perform switching operation (upper and lower arm simultaneous switching). System operation).

  The motor current value measuring unit 150 measures the current value flowing through the motor 60 from the voltage generated at both ends of the shunt resistor 151 connected in series to the H-type bridge circuit 142, and outputs the measured current value as the motor current value Im. .

  As described above, the control device 100 (see FIG. 5) performs PWM control on the current supplied from the power supply 50 to the motor 60 based on the manual steering torque detection value T output from the manual steering torque detection unit 115, and steers by the motor 60. Auxiliary force can be controlled. The power supply 50 is an in-vehicle battery or alternator.

  FIG. 7 is a diagram illustrating a characteristic of the motor current value Im with respect to the duty ratio of the PWM signal 40a output from the PWM signal setting unit 40 (hereinafter referred to as duty ratio motor current value characteristic). The characteristics shown in FIG. 7 will be described below (see FIG. 6 as appropriate).

  The characteristic shown in FIG. 7 is that when the motor 60 is controlled by the simultaneous switching method of the upper and lower arms in the H-type bridge circuit 142 shown in FIG. This is obtained when the duty ratio is changed until the motor current flowing through the motor 60 is maximized.

  In FIG. 7, the horizontal axis indicates the duty ratio of the PWM signal 40 a, and the vertical axis indicates the motor current value Im flowing through the motor 60. The motor 60 rotates right when the duty ratio is positive and rotates left when the duty ratio is negative.

  As shown in FIG. 7, the motor current value Im increases as the duty ratio increases. Further, if the position (inflection point) where the slope of the characteristic changes suddenly is referred to as break points A1 and A2, the motor current value Im with respect to the duty ratio is within the range between the break points A1 and A2. The gradient of the change is smaller than the gradient in the range where the duty ratio is less than or equal to the breakpoint A1 or greater than or equal to the breakpoint A2.

  In the range from the break point A1 to the break point A2, the change in the motor current value Im with respect to the duty ratio is extremely small by only the feedback control by the feedback control unit 20. Therefore, the feedforward control unit 30 is used in combination so that the duty ratio is proportional to the current target value It in the range from the breakpoint A1 to the breakpoint A2. That is, both feedforward control and feedback control are performed in the range from the breakpoint A1 to the breakpoint A2.

  The boundary value of the limiter 32 (see FIG. 6), that is, the threshold value (threshold duty ratio) corresponds to the break point A1 and the break point A2. However, the boundary value of the limiter 32 is a value that is several percent larger than the duty ratio from the duty ratio of the break point A1 and a value that is several percent smaller than the duty ratio from the duty ratio of the break point A2 in actual implementation. . This is because variations in the characteristics of the control device 100 and the motor 60 are taken into consideration.

  In the range of the duty ratio below the break point A1 and the range of the duty ratio above the break point A2, the current F / B gain is set by feedback (F / B) control in accordance with the slope of the characteristic shown in FIG. Done.

Japanese Patent No. 3666806

  However, the duty ratio motor current value characteristic shown in FIG. 7 changes according to the voltage applied to the H-type bridge circuit 142 shown in FIG. 6, that is, the output voltage of the power supply 50, as shown in FIG.

  For example, FIG. 8A shows a duty ratio motor current value characteristic in which the duty ratio of the PWM signal 40a is positive when the output voltage of the power supply 50 (see FIG. 6) is changed as a parameter. In FIG. 8A, a solid line represents a case where the output voltage is a reference voltage (for example, 12.5 V), a broken line represents a case where the output voltage is lower than the reference voltage, and an alternate long and short dash line represents that the output voltage is the reference voltage. It represents a higher case. When the output voltage is lower than the reference voltage, as shown by the broken line, the duty ratio at the break point B (inflection point) of the duty ratio motor current value characteristic becomes larger than in the case of the reference voltage shown by the solid line, The inclination of the characteristic after the break point B becomes small. Also, when the output voltage is higher than the reference voltage, the duty ratio of the break point A (inflection point) of the duty ratio motor current value characteristic is larger than that of the reference voltage indicated by the solid line, as shown by the one-dot chain line. It becomes smaller and the inclination of the characteristic after the break point A becomes larger.

  Conventionally, the threshold value of the limiter 32 for F / B gain and F / F control has been set on the premise of the duty ratio motor current value characteristic at the reference voltage. Therefore, when the output voltage of the alternator changes for charging control of the vehicle-mounted battery, or when the output voltage decreases due to battery deterioration or the like, the duty ratio motor current value characteristic changes, and F / B control or F There is a problem that the current response by the / F control changes. Specifically, as shown in FIG. 8B, when the output voltage is lower than the reference voltage, F / F control is insufficient and the current responsiveness decreases, and when the output voltage is higher than the reference voltage, F / F control excess and current responsiveness become excessive and overshoot occurs. That is, there is a problem that the auxiliary steering force becomes excessive or insufficient when the power supply voltage of the vehicle fluctuates and the operation feeling is deteriorated.

  Accordingly, an object of the present invention is to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  In order to solve the above problem, a motor current value flowing in a motor controlled by PWM drive is measured, feedback control is performed according to a difference between the motor current value and the current target value, and the current target value increases. A method for controlling an electric power steering apparatus including feedforward control that outputs a value that increases in accordance with the electric power steering apparatus, wherein the electric power steering apparatus measures an output voltage value of a power source that supplies electric power to the electric power steering apparatus Determining a threshold of a duty ratio indicating a boundary between outputting a value proportional to the current target value in the feedforward control or outputting a predetermined value based on the output voltage value; and In forward control, the duty cycle of the PWM signal used for the PWM drive control After final output value determining the ratio reaches the threshold value also increases more, and executes the steps of: holding a value proportional to the current target value to the predetermined value.

  According to such a configuration, the electric power steering device determines a threshold value for limiting the output value of the feedforward control to a predetermined value based on the output voltage value of the power supply, and after the final output value reaches the threshold value, the electric power steering device is further Even if it increases, a value proportional to the current target value can be held at a predetermined value. Therefore, since the threshold is determined according to the fluctuation of the output voltage value of the power supply, it is possible to prevent the current response from being lowered or excessive. That is, it is possible to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  The electric power steering apparatus is characterized by executing a step of decreasing the threshold value in accordance with an increase in the output voltage value.

  According to such a configuration, the electric power steering apparatus can perform correction so as to reduce the threshold value in accordance with an increase in the output voltage value. This correction can prevent overshooting of current response due to excessive F / F control. That is, it is possible to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  In addition, the electric power steering apparatus is characterized by executing a step of reducing the gain of feedback control in accordance with an increase in the output voltage value.

  According to such a configuration, the electric power steering apparatus can perform correction for reducing the gain of the feedback control in accordance with the increase in the output voltage value. This correction can prevent the current response from being lowered or excessive. That is, it is possible to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  ADVANTAGE OF THE INVENTION According to this invention, while improving the operation feeling of an electric power steering apparatus, it becomes possible to improve the tolerance with respect to a power supply fluctuation.

It is a figure which shows the structural example of the control part of the control apparatus for implement | achieving the control method of the electric power steering apparatus of this embodiment. It is a figure which shows the structural example of a voltage averaging process part. It is a figure which shows an example of the relationship between a power supply voltage, a duty ratio, and a motor current value, (a) represents the relationship between a power supply voltage and a duty ratio motor current value characteristic, (b) is a power supply voltage and a breakpoint. (C) is a characteristic of the voltage applied to the motor at this time (Δ voltage value / (duty) corresponding to the characteristic after the break point shown in FIG. Ratio / 100)). It is a figure which shows an example of the current responsiveness of this embodiment. It is a figure showing a schematic structure of an electric power steering device. It is a figure which shows the structural example of the control part of the control apparatus for implement | achieving the control method of the conventional electric power steering apparatus. It is a figure which shows the characteristic of the motor electric current value with respect to the duty ratio of the PWM signal output from a PWM signal setting part. It is a figure which shows an example of the relationship between a power supply voltage and a motor current value, (a) represents the relationship between a power supply voltage and a duty ratio motor current value characteristic, (b) represents current responsiveness.

  Next, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings as appropriate.

  Since the structure of the electric power steering apparatus in the present embodiment is the same as that shown in FIG. 5 (however, the control unit 102 corresponds to the control unit 10), the illustration and description thereof are omitted.

  FIG. 1 shows a configuration example of the control unit 10 in the present embodiment. The control unit 10 shown in FIG. 1 corresponds to the control unit 102 shown in FIGS. 5 and 6, and the motor control unit 11 shown in FIG. 1 corresponds to the motor control unit 130 shown in FIG. The / F logic processing unit 31 corresponds to the F / F limit processing unit 131 shown in FIG. Moreover, when the code | symbol attached | subjected to each part shown in FIG. 1 is the same as the code | symbol attached | subjected to each part shown in FIG. 6, the same thing is represented and those description is abbreviate | omitted.

  Here, the F / F logic processing unit 31 shown in FIG. 1 is different from that shown in FIG. 6, and the voltage value measuring unit 51, the voltage averaging processing unit 52, and the F / F duty limit value setting unit that do not exist in FIG. The functions of the gain correction value setting unit 54 and the multiplication operation unit 55 will be described below.

  The voltage value measuring unit 51 measures the voltage of the power supply 50 at a predetermined cycle and outputs it as a voltage value Vps.

  The voltage averaging processing unit 52 calculates a value obtained by dividing the current value and the total of the past three times by 4, out of the voltage value Vps output from the voltage value measuring unit 51, that is, a moving average value for four times. Output as signal value 52a. The voltage averaging processing unit 52 includes three delay elements 521, an addition element 522, and a multiplication element 523 as shown in FIG. The addition element 522 receives as input the signal having the voltage value Vps as it is, the signal that has passed through the delay element 521 once, the signal that has passed through the delay element 521 twice, and the signal that has passed through the delay element 521 three times. Add the signals and output the sum. The multiplication element 523 outputs a value obtained by multiplying the addition value output from the addition element 522 by ¼ as the signal value 52a.

Returning to FIG. 1, the F / F duty limit value setting unit 53 sets the boundary value of the duty ratio for performing the feedforward control.
Specifically, as shown in FIG. 3A, the boundary value of the duty ratio at which the feedforward control is performed, that is, the break point of the duty ratio motor current value characteristic changes depending on the output voltage value of the power supply 50. To do. When the output voltage is smaller than the reference voltage, the duty ratio at the break point B of the duty ratio motor current value characteristic is larger than the duty ratio at the break point when the reference voltage is set. When the output voltage is higher than the reference voltage, the duty ratio at the break point A of the duty ratio motor current value characteristic is smaller than the duty ratio at the break point when the reference voltage is set.

Therefore, when the duty ratio of the break point is plotted for each output voltage value of the power supply 50 (marked with ●), it can be seen that there is a linear relationship between the two as shown in FIG. Therefore, the duty ratio of the break point can be estimated based on the output voltage value of the power supply 50. That is, the duty ratio of the break point is set as shown in the following formula (1).
Break point duty ratio = a × output voltage value + b Equation (1)
Here, a and b are constants.

Returning to FIG. 1, the gain correction value setting unit 54 sets a gain correction value for feedback control.
Specifically, as shown in FIG. 3A, the slope of the duty ratio motor current value characteristic after the break point changes depending on the output voltage value of the power supply 50. When the output voltage is smaller than the reference voltage, the slope of the duty ratio motor current value characteristic becomes small. Further, when the output voltage is higher than the reference voltage, the slope of the duty ratio motor current value characteristic increases.

Therefore, the relationship between the power supply voltage and the characteristic of the voltage applied to the motor at this time (Δ voltage value / (duty ratio / 100)) corresponding to the characteristic after the break point shown in FIG. Then, as shown in FIG. 3C, it can be seen that there is a linear relationship between the two. Therefore, Δ voltage value / (duty ratio / 100) can be estimated based on the output voltage value of the power supply 50. That is, Δvoltage value / (duty ratio / 100) is estimated as shown in the following equation (2).
Δ voltage value / (duty ratio / 100) = c × output voltage value + d (2)
Here, c and d are constants.

The correction value of the feedback control gain is calculated as shown in the following equation (3).
Gain correction value = (c × reference voltage value + d) / (c × output voltage value + d) Equation (3)
However, the reference voltage value may be 12.5 V, for example.

  The multiplication operation unit 55 multiplies the output value 54 a of the gain correction value setting unit 54 and the output value 24 a of the feedback control unit 20. That is, the output value 24a of the feedback control unit 20 is corrected so as to match the duty ratio motor current value characteristic at the reference voltage value.

  The F / F logic processing unit 31 has the same function as the F / F limit processing unit 131 shown in FIG. That is, the F / F logic processing unit 31 is configured to include a limiter 32. The F / F logic processing unit 31 is different from the F / F limit processing unit 131 shown in FIG. 6 in that the output value 53a of the F / F duty limit value setting unit 53 is input and the output value 53a is feedforward controlled. The limiter 32 is used as a threshold value.

  The addition operation unit 33 adds the output value of the multiplication operation unit 55 and the output value 31a of the F / F logic processing unit 31 to generate a final output value 33a.

  FIG. 4 shows the current responsiveness of the motor current Im with respect to the target current value It in the present embodiment. As shown in FIG. 4, the control unit 10 (see FIG. 1) according to the present embodiment has substantially the reference voltage both when the output voltage value is higher than the reference voltage (indicated by a one-dot chain line) and when it is lower (indicated by a broken line). It is possible to obtain the same current response as when. That is, it is possible to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  As described above, the control unit 10 of the electric power steering apparatus 1 according to the present embodiment copes with a phenomenon in which the break point in the duty ratio motor current value characteristic and the inclination after the break point change with the fluctuation of the output voltage value of the power supply 50. can do. Specifically, the F / F duty limit value setting unit 53 uses the output voltage value of the power supply 50 measured by the voltage value measurement unit 51 to estimate the duty ratio of the break point indicating the range in which the feedforward control is performed. To do. Further, the gain correction value setting unit 54 estimates a gain correction value in feedback control based on the output voltage value of the power supply 50 in order to cope with a change in inclination after the break point. And the control part 10 can cope with the fluctuation | variation of the output voltage value of the power supply 50 using the estimated duty ratio and gain correction value of a break point, and can make the current responsiveness of the motor current Im the same. That is, it is possible to improve the operation feeling of the electric power steering apparatus and to improve the resistance against power supply fluctuation.

  In FIG. 3 (c), the characteristics of the voltage applied to the motor at this time (Δ voltage value / (duty ratio / 100)) corresponding to the power supply voltage and the characteristics after the break point shown in FIG. 3 (a). It explained using the relationship. Instead, a linear relationship similar to FIG. 3C (however, the constants c and d are different) can be derived using the relationship between the power supply voltage and the duty ratio motor current value characteristic. Therefore, the gain correction value may be calculated from the relationship between the power supply voltage and the duty ratio motor current value characteristic.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 15 Motor current value measurement part 20 Feedback control part 30 Feedforward control part 32 Limiter 33 Signal value 50 Power supply 51 Voltage value measurement part 52 Voltage averaging process part 53 F / F duty limit value setting part 54 Gain correction Value setting section

Claims (3)

Measures the motor current value that flows to the motor controlled by PWM (Pulse Width Modulation) drive, performs feedback control according to the difference between the motor current value and the current target value, and increases as the current target value increases A control method for an electric power steering apparatus including feedforward control for outputting a value to be
The electric power steering device is
Measuring an output voltage value of a power source for supplying electric power to the electric power steering device;
Determining, based on the output voltage value, a duty ratio threshold value indicating a boundary between outputting a value proportional to the current target value in the feedforward control or outputting a predetermined value;
In the feedforward control, even if the final output value that determines the duty ratio of the PWM signal used for the PWM drive control reaches the threshold value, a value proportional to the target current value is set to the predetermined value even if the final output value increases further. Holding step;
The control method of the electric power steering apparatus characterized by performing this. The electric power steering device is
The method for controlling the electric power steering apparatus according to claim 1, wherein the step of reducing the threshold value is executed in accordance with an increase in the output voltage value. The electric power steering device is
The method for controlling the electric power steering apparatus according to claim 1, wherein a step of reducing a gain of the feedback control is executed in accordance with an increase in the output voltage value.

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