JP4969410B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device mounted on a vehicle.

  Conventionally, a control system of this type of electric power steering apparatus (hereinafter referred to as EPS) is configured as schematically shown in FIG. 3, and assists the driver's steering operation by the rotational drive of a motor (DC motor) 1.

  That is, the steering torque of the driver's steering is detected by the torque sensor 2, and the detected torque is A / D converted and input to the current target value setting unit 4 of the control ECU 3A having a microcomputer configuration. The detected torque includes information on the direction of the force (forward or reverse).

  The current target value setter 4 holds, for example, a characteristic map or arithmetic expression of the target value of the drive current of the motor 1 with respect to the detected torque of the torque sensor 2, and the target value of the drive current of the motor 1 according to the input detected torque. The Ir data is output to the subtracter 5.

  The subtractor 5 calculates an error ΔIrx (= Ir−Ix) between a target value Ir and a detection value Ix of a drive current described later, and outputs data of the error ΔIrx to the controller 6.

  The controller 6 forms a drive current controller for the motor 1 and applies a known PI control or PID control to the error ΔIrx (P is proportional, I is integral, D is derivative), and is detected as an operation amount of feedback control. A drive voltage value of the motor 1 that controls the value Ix to the target value Ir is obtained, a control output of, for example, PWM control is formed as a voltage control output corresponding to this drive voltage value, and this control output is used as a motor drive circuit of the drive ECU 7. 8 is output.

  For example, as shown in FIG. 4, the motor drive circuit 8 includes a series circuit of one two bridge sides 8a and 8b and a series circuit of the other two bridge sides 8c and 8d between a pair of power supply terminals a and b. They are connected in parallel and provided with semiconductor switches Q1 to Q4 on each of the bridge sides 8a to 8d to form a so-called full bridge.

  Each of the semiconductor switches Q1 to Q4 includes a power FET, IGBT, power transistor, and the like, and diodes D1 to D4 for discharge paths are connected in antiparallel.

  One end of the motor 1 is connected to a connection point α between the bridge sides 8a and 8b, and the other end of the motor 1 is connected to a connection point β between the two bridge sides 8c and 8d.

  The control output is a four-phase output pulsed to the control terminals (gate terminals) of the semiconductor switches Q1 to Q4 of the bridge sides 8a to 8d, and the semiconductor switches Q1 to Q4 based on their high level and low level. The drive voltage applied to the motor 1 is manipulated and variably controlled by the combination of ON and OFF.

  At this time, when the semiconductor switches Q1 and Q4 of the opposing two bridge sides 8a and 8d are simultaneously turned on, the driving current in the direction indicated by the arrow line ia in FIG. Driven forward.

  Further, when the semiconductor switches Q2 and Q3 of the opposing two bridge sides 8b and 8c are turned on at the same time, the driving current in the direction shown by the arrow line ib in FIG. Driven by rotation.

  Next, the drive current (motor current) flowing through the motor 1 is detected by, for example, the motor current detector 9 of FIG. 3 formed by the resistor R of FIG. 4, and the detected output is an A / D converter of the control ECU 3A. 10 is converted into data of the detected value Ix of the drive current, and the data of the detected value Ix is supplied to the subtracter 5. In practice, a sign adder is provided at the subsequent stage of the A / D converter 10, and the sign adder detects whether the rotation of the motor 1 is forward or reverse from the relationship between the output of the controller 6 and the detected value Ix. Although the output of the A / D converter 10 has positive and negative polarities according to the rotation direction of the motor 1, a sign adder and the like are omitted in FIG. 3 for simplicity of explanation.

  The EPS configured as described above is based on closed-loop digital feedback control that returns from the subtractor 5 to the subtractor 5 via the controller 6, the motor drive circuit 8, the motor 1, the motor current detector 9, and the A / D converter 10. The drive current which is a control amount of feedback control based on an error ΔIrx between the target value Ir of the drive current of the motor 1 corresponding to the steering operation torque and the detected value Ix of the drive current (control amount) of the motor 1 To the target value Ir.

  At that time, the control output of the PWM control for setting the driving voltage (operation amount of feedback control) of the motor 1 may be updated every minute unit period τ of the PWM control of about 50 μs set in the control ECU 3A. However, considering the followability of the entire control system and the like, practically, for example, the control output is updated by reading the target value Ir and the detection value Ix every control period of 10 unit periods 10 × τ (500 μs).

  By the way, in this type of EPS, as shown in FIG. 3, attenuating means (consisting of a phase delay circuit or a low-pass filter) indicated by a broken line in a feedback path 11 of feedback control from the motor current detector 9 to the subtractor 5. 12a is provided to reduce the external noise na mixed in the feedback path, to improve the quality of the electric power steering (steering operation feeling), and to the path from the current target value setting unit 4 to the controller 6 It has been proposed to provide a similar attenuating means 12b indicated by a broken line to reduce the external noise nb mixed in the route and improve the quality of the electric power steering (for example, see Patent Document 1).

  When the attenuating unit 12a is provided, the external noise na mixed in the feedback path detection value Ix output from the motor current detector 9 is reduced by the phase delay of the attenuating unit 12a or the low pass filter integration process. By reducing na, fluctuations due to the error ΔIrx of the subtracter 5 and the noise na of the control output output from the controller 6 to the motor drive circuit 8 are prevented, and disturbance of feedback control and the like are suppressed.

  Even when the attenuating means 12b is provided, the external high-frequency noise nb mixed (superposed) on the target value Ir of the current target value setter 4 is reduced by the phase delay of the attenuating means 12b or the integration process of the low-pass filter. Thus, disturbance of feedback control or the like is suppressed.

JP-A-7-329799 (claims, paragraphs [0027]-[0048], FIG. 1, FIG. 2, FIG. 3, FIG. 4)

  When the attenuating means 12a and 12b of FIG. 3 are provided in this type of EPS, the target value Ir of the control current target value setter 4 is changed from the previous value by the steering operation, and the control of the PWM control is accompanied by this change. When the output changes, the fluctuation of the detected value Ix based on the fluctuation of the control output is suppressed by the integration process of the attenuation means 12a, so that the motor driving current (detected value Ix) is drawn to the target value Ir and stabilized. Until then, the fluctuation of the feedback control is prolonged, and during that time, the steering is slightly vibrated and the operation feeling becomes worse.

  Even when the attenuating means 12b is provided, the change in the target value Ir of the current target value setter 4 due to the steering operation is suppressed by the integration process of the attenuating means 12b, so that the motor drive current is drawn into the target value Ir. Thus, the fluctuation of the feedback control until it becomes stable is prolonged, and during that time, the steering is slightly vibrated and the operation feeling becomes worse.

  That is, when the attenuating means 12a and 12b are provided, the target value Ir of the current target value setter 4 in each control cycle is changed from the previous value by the steering operation, and the drive voltage of the motor 1 (operation amount of feedback control) is changed. When the control output of the PWM control to be set changes and the drive current of the motor, which is the control amount of the feedback control, fluctuates, the original change of the control amount or the operation amount of the feedback control by the integration processing of the attenuation means 12a and 12b. Fluctuations in the feedback control until the motor drive current (detected value Ix) is drawn to the target value Ir and stabilizes, and the steering slightly vibrates and the operation feeling becomes worse. There is a problem that the steering operation performance deteriorates. Note that the phenomenon that the steering feels slightly worse due to the slight vibration of the steering is conspicuous in a normal gentle steering operation in which the change in the operating torque is not large.

  Since noise na and nb can be reduced by taking a so-called shield measure, the attenuating means 12a and 12b can be omitted.

  However, when the target value of the current target value setter 4 (target value of the feedback control) Ir is changed from the previous value, the fluctuation of the feedback control accompanying the change of the drive current omits the attenuating means 12a and 12b, and measures against shielding. It always appears during driving, and a slight vibration of the steering occurs.

  Therefore, in this type of EPS, how is the phenomenon that the steering feeling is deteriorated due to the slight vibration of the steering due to the change of the target value Ir of the current target value setter 4 and the steering operation performance is deteriorated? It is important to improve. The same applies to the case where the drive voltage of the motor 1 (operation amount of feedback control) is controlled by a control method other than the PWM control method.

  The present invention is an electric power steering apparatus that feedback-controls the motor drive current according to the steering operation torque, and prevents the steering vibration when the drive current target value changes as much as possible. The purpose is to improve.

  In order to achieve the above object, the EPS of the present invention includes a motor that assists the steering operation, a drive unit that drives the motor to be energized, and a control unit that controls the drive unit. In the EPS that feedback-controls the drive current based on an error between a target value of the motor drive current corresponding to the steering operation torque and a detected value of the motor drive current, Differentiating means for differentiating the detected value, adding means for adding the differentiated value of the differentiating means to the detected value, and error calculating means for calculating an error between the target value and the added value of the adding means, The control unit is configured to perform feedback control of the drive current based on an error between the target value and the addition value of the addition means (claim 1).

  The EPS of the present invention is characterized in that a low-pass filter that suppresses an excessive component of the differential value is provided after the differentiating means (claim 2).

  In the case of the EPS of the present invention of claim 1, the target value of the drive current changes according to the steering operation torque, and the motor drive control output (for example, the feedback control operation amount) is set. When the motor control current (PWM control output) changes and the motor drive current (control amount for feedback control) changes, the change is amplified by the differentiation of the differentiating means and is output from the differentiating means as a differential value.

  Then, the detected value of the driving current and the differential value of the differentiating means are added by the adding means, and the added value of the adding means is fed back to the error calculating means instead of the detected value of the driving current.

  Further, the change in the control output of the motor drive based on the error between the target value of the drive current to be feedback-controlled and the addition value of the adding means input by feedback is the target value of the feedback control and the detected value of the drive current. As a result, the drive current of the motor is quickly drawn to the target value by the control output, and the feedback control is stabilized in a very short time.

  Therefore, it is possible to prevent the occurrence of fine vibrations of the steering accompanying the fluctuation of the feedback control when the target value of the driving current is changed, thereby improving the steering feeling and improving the steering operation performance.

  In the EPS of the present invention according to claim 2, the differential value of the differentiating means is saturated at a constant magnitude by the integration processing of the low-pass filter provided at the subsequent stage of the differentiating means, and the differential value becomes extremely excessive. Therefore, it is possible to prevent the occurrence of a situation in which normal feedback control cannot be performed, improve the steering operation feeling with a more practical configuration, and improve the steering operation performance of this type of EPS.

  Next, in order to describe the present invention in more detail, an embodiment thereof will be described in detail with reference to FIGS.

  FIG. 1 is a block diagram of motor drive current control of an EPS mounted on a vehicle, and FIG. 2 shows an example of the transfer characteristic of FIG.

(Constitution)
In FIG. 1, the same reference numerals as those in FIG. 3 denote the same components, and the EPS in FIG. 1 differs from the conventional EPS in FIG. 3 in that a control unit of the present invention is formed instead of the control ECU 3A in FIG. A control ECU 3B having a microcomputer configuration is provided.

  This control ECU 3B is different from the control ECU 3A in FIG. 3 in that a low-pass filter (hereinafter referred to as “return filter”) is sequentially provided from the A / D converter 10 side to the original feedback path 11 of the feedback control from the A / D converter 10 to the subtractor 5. , LPF) 13 and an adder 14, and a differentiator 16 is sequentially provided from the A / D converter 10 side to a second feedback path 15 branched from the A / D converter 10 of the feedback path 11 to the adder 13. , LPF 17 and limiter 18 are provided.

  The control ECU 3B is not provided with the attenuating means 12a and 12b shown by broken lines in FIG. Each part in the control ECU 3B is actually realized by software processing of a microcomputer, and the control ECU 3B feedback-controls the driving current of the motor 1 by digital processing.

  The subtractor 5 is the error calculation means of the present invention, and the differentiator 16 is the differentiation means of the present invention. The adder 14 is the adding means of the present invention, and the LPF 17 is the LPF of the present invention that suppresses an excessive component of the differential value.

(Operation)
The EPS in FIG. 1 A / D converts the detected torque force of the torque sensor 2 and inputs it to the current target value setter 4, which sets the drive current of the motor 1 according to the detected torque force. Data of the target value Ir is output to the subtracter 5.

  The subtractor 5 calculates an error ΔIrz (= Ir−Iz) between the target value Ir and the output Iz of the adder 13 and outputs data of the error ΔIrz to the controller 6.

  The controller 6 forms a current control unit of the motor 1, performs known PI control (or PID control) on the error ΔIrz, and controls the output Irz to the target value Ir as an operation amount of feedback control. A value is obtained, a control output of PWM control is formed as a voltage control output of the motor 1 corresponding to this drive voltage value, and this control output is output to the motor drive circuit 8 of the drive ECU 7.

  The motor drive circuit 8 is formed as a full bridge of the semiconductor switches Q1 to Q4 shown in FIG. 4, and the motor 1 is connected to the motor 1 by a combination of ON and OFF of the semiconductor switches Q1 to Q4 of the bridge sides 8a to 8d based on the control output. The applied drive voltage is manipulated and variably controlled.

  Further, the drive current (motor current) flowing through the motor 1 is detected by the motor current detector 9, and the detected output is converted to data of the detected value Ix of the drive current by the A / D converter 10.

  The data of the detection value Ix is supplied to one input terminal of the adder 14 through the LPF 13 and is supplied to the other input terminal of the adder 14 through the differentiator 16, the LPF 17, and the limiter 18. .

  In practice, a sign adder is provided at the subsequent stage of the A / D converter 10, and the sign adder detects whether the rotation of the motor 1 is forward or reverse from the relationship between the output of the controller 6 and the detected value Ix. The output of the A / D converter 10 has positive and negative polarities according to the rotation direction of the motor 1, but in FIG. 1, a sign adder and the like are omitted for the sake of simplicity.

  The differentiator 16 differentiates the detected value Ix of the digital output of the A / D converter 10, and when the detected value Ix fluctuates, the output of the differentiator 15 changes greatly. Therefore, the differentiator 16 amplifies the fluctuation of the detection value Ix and outputs the differential value of the amplification result to the LPF 17.

  The LPF 17 has a characteristic that the output saturates to a certain level with respect to an excessive differential value exceeding a predetermined value, suppresses an excessive component of the differential value of the differentiator 16, and the feedback control of the control ECU 3B becomes an abnormal state of excessive input. To prevent becoming.

  In order to further improve the stability of feedback control of the control ECU 3B, the output of the differential value via the LPF 17 is cut to a component larger than the upper limit value set by the limiter 18 and is limited to the upper limit value or less. 14 is input.

  On the other hand, the LPF 13 has the same characteristics as the LPF 17, and acts on the detection value Ix of the digital output of the A / D converter 10 in the same manner as the LPF 17, and the detection value Ix input to the adder 14 through the LPF 13 and the limiter 18. To the phase difference with the differential value input to the adder 14.

  The adder 14 then detects the detected value Ix of the A / D converter 10 input via the LPF 13 and the differential value of the differentiator 16 (that is, the differential of the detected value Ix) input via the LPF 17 and the limiter 18. Value).

  Then, the added value Iz of the adder 14 is fed back to the subtracter 5 instead of the detected value Ix, and the subtracter 5 is fed back with the target value Ir of the current target value setter 4 as described above. An error ΔIrz with Iz is output to the controller 6, the controller 6 outputs a control output of the PWM control according to the error ΔIrz to the motor drive circuit 8, and operates the drive voltage of the motor 1 according to the error ΔIrz, The drive current of the motor 1 is drawn to the target value Ir by feedback control.

  At this time, the added value Iz is a value obtained by amplifying (emphasizing) the fluctuation of the detected value Ix by adding the differential value, and the error ΔIrz is formed by making the fluctuation of the detected value Ix larger than the actual value.

  Therefore, for example, when the control output of the PWM control is updated by reading the target value Ir and the detection value Ix at every control cycle of 10 × τ (500 μs), the operation torque is changed by a gentle steering operation during driving. Based on the change in the operation torque, when the target value Ir of the drive current in each control cycle changes from the previous value, the control output of the PWM control changes, and the detected value Ix of the drive current of the motor 1 fluctuates, the detected value Ix Due to the error ΔIr formed by amplifying the fluctuation of the signal and making it larger than the actual value, the control output of the PWM control changes greatly, the drive current of the motor 1 is quickly drawn to the target value Ix, and the feedback control is performed in a very short time. Stabilize.

  Therefore, it is possible to prevent the slight vibration of the steering accompanying the change of the driving current, and particularly to improve the operation feeling for the gentle steering operation during the normal driving, thereby improving the steering operation performance.

  The EPS of the present embodiment in FIG. 1 to which compensation by the differentiator 16 is added, the uncompensated EPS in which the LPFs 13 and 17, the adder 14, the differentiator 16, and the limiter 18 are omitted from the EPS of the present embodiment, For the EPS without compensation and the EPS in which the attenuation means 12a of FIG. 3 is added, noise is added to the control output of the motor drive circuit 8, the detected value Ix is observed, and the response of the feedback control system is simulated. Transfer characteristics were obtained. In the figure, the solid line represents the EPS transfer characteristic of the present embodiment, the broken line represents the EPS transfer characteristic without compensation, and the dashed line represents the EPS transfer characteristic with the attenuation means 12a added.

  As is clear from FIG. 2, the EPS of the present embodiment to which compensation by the differentiator 16 is added is minimized because fluctuation due to noise is minimized. Note that the EPS to which the attenuating means 12a is added has a greater fluctuation in the drive current due to noise than the EPS without compensation by the addition of the attenuating means 12a.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention.

  For example, when the configuration is simplified, the limiter 18 may be omitted, and the LPFs 13 and 17 may be omitted depending on circumstances.

  Further, the configuration of the differentiator 16, the LPFs 13, 17 and the like may be any, and the configuration of the motor drive circuit 8 and its drive system may be any. Furthermore, the control cycle of the motor 1 is not limited to the embodiment. Of course, each part of the control ECU 3B may be formed by hardware.

  Next, in the above-described embodiment, the present invention is applied to ESP that performs digital feedback control. However, the present invention can also be applied to ESP that performs analog feedback control.

  The present invention can be applied to EPS of various vehicles.

It is a block diagram of one embodiment of this invention. It is explanatory drawing of the transfer characteristic of FIG. It is a block diagram of a prior art example. FIG. 4 is a connection diagram of the motor drive circuit of FIG. 3.

Explanation of symbols

1 Motor 3B Control ECU
5 Subtractor 14 Adder 16 Differentiator 17 LPF
Ir target value Ix detection value Iz addition value

Claims (2)

A motor for assisting steering operation; a drive unit for energizing and driving the motor; and a control unit for controlling the drive unit. The control unit is configured to control the drive current of the motor according to the steering operation torque. In the electric power steering device that feedback-controls the drive current based on an error between a target value and a detected value of the drive current of the motor,
In the control unit,
Differentiating means for differentiating the detected value;
Adding means for adding the differential value of the differentiating means to the detected value;
An error calculating means for calculating an error between the target value and the added value of the adding means;
An electric power steering apparatus, wherein the drive current is feedback-controlled by the control unit based on an error between the target value and an addition value of the addition means. The electric power steering apparatus according to claim 1,
An electric power steering apparatus comprising a low-pass filter for suppressing an excessive component of the differential value at a subsequent stage of the differentiating means.

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