JP5875931B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

In recent years, there has been proposed an electric power steering device that includes an electric motor in a steering system of a vehicle and assists a driver's steering force with the power of the electric motor.
The drive of the electric motor of this electric power steering device is controlled by a control device. In order to control the drive of the electric motor, the control device first sets a target current to be supplied to the electric motor according to the steering torque, the vehicle speed, and the like. For example, a control device for an electric power steering apparatus described in Patent Document 1 receives a torque signal τ from a torque sensor and a vehicle speed signal v from a vehicle speed sensor, and sets a current command value based on these values.

Japanese Patent Laid-Open No. 2-193768

Since the counter electromotive voltage is generated when the electric motor rotates, the current actually supplied to the electric motor may fluctuate and the electric motor may vibrate unless the current fluctuation due to the counter electromotive voltage is taken into consideration. Therefore, in determining the target current to be supplied to the electric motor, it is desirable to take into account fluctuations in current caused by the counter electromotive voltage. Furthermore, it is desirable to consider that the back electromotive voltage increases in proportion to the rotation speed of the electric motor when considering fluctuations in current caused by the back electromotive voltage.
It is an object of the present invention to provide an electric power steering device that can more accurately suppress the current actually supplied to the electric motor from being fluctuated due to the back electromotive voltage and causing the electric motor to vibrate. To do.

For this purpose, the present invention provides an electric motor that applies a steering assist force to a steering wheel, a determination unit that determines a target current to be supplied to the electric motor based on a steering torque of the steering wheel, and the determination unit includes: Correction means for correcting the determined target current using a correction current which is a current corresponding to a counter electromotive voltage generated in the electric motor, and the correction means is based on the rotation speed of the electric motor. A correction current is adjusted, and the correction means is based on a base correction value determination unit that determines a base correction value that is a base of a correction value for correcting the target current determined by the determination means, and a rotation speed of the electric motor. An adjustment coefficient determination unit that determines a correction value adjustment coefficient for adjusting the base correction value determined by the base correction value determination unit, the base correction value and the correction It is an electric power steering device according to claim which has a correction current determining unit configured to determine the correction current by multiplying the adjustment factor.

  Here, the correction means may decrease the correction current as the rotation speed of the electric motor decreases.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress more accurately that the electric current actually supplied to an electric motor fluctuates due to a back electromotive voltage, and an electric motor vibrates.

It is a figure showing the schematic structure of the electric power steering device concerning an embodiment. It is a schematic block diagram of the control apparatus of a steering device. It is a schematic block diagram of a target current calculation part. It is a schematic block diagram of a control part. It is a figure which shows the difference of the target electric current supplied to an electric motor, and the actual electric current which actually flows into an electric motor. (A) shows the target current, (b) shows the current corresponding to the back electromotive voltage, and (c) shows the actual current. (A) is a figure which shows the phase of base correction value (DELTA) Ib when it assumes that the electric current for a counter electromotive voltage fluctuates by the phase shown in FIG.5 (b). (B) is a figure which illustrates the phase of final correction value (DELTA) If (final correction current) when it assumes that base correction value (DELTA) Ib fluctuates with the phase shown to (a). (C) is a diagram illustrating the phase of final target current ITF when it is assumed that final correction value ΔIf (final correction current) fluctuates in the phase shown in (b). It is a figure which shows the correlation of the rotational speed of an electric motor, and a correction value adjustment coefficient.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an electric power steering apparatus 100 according to an embodiment.
An electric power steering device 100 (hereinafter, also simply referred to as “steering device 100”) is a steering device for arbitrarily changing the traveling direction of a vehicle. In the present embodiment, the configuration applied to an automobile is used. Illustrated.

  The steering device 100 includes a wheel-like steering wheel (handle) 101 operated by a driver, and a steering shaft 102 provided integrally with the steering wheel 101. The steering shaft 102 and the upper connection shaft 103 are connected via a universal joint 103a, and the upper connection shaft 103 and the lower connection shaft 108 are connected via a universal joint 103b.

  Steering device 100 includes tie rods 104 connected to left and right front wheels 150 as rolling wheels, and rack shaft 105 connected to tie rods 104. Further, the steering device 100 includes a pinion 106 a that constitutes a rack and pinion mechanism together with rack teeth 105 a formed on the rack shaft 105. The pinion 106 a is formed at the lower end portion of the pinion shaft 106.

  The steering device 100 also has a steering gear box 107 that houses the pinion shaft 106. The pinion shaft 106 is connected to the lower connection shaft 108 via a torsion bar in a steering gear box 107. Inside the steering gear box 107, a torque sensor 109 is provided as an example of a steering torque detecting means for detecting the steering torque T of the steering wheel 101 based on the relative angle between the lower connecting shaft 108 and the pinion shaft 106. .

The steering device 100 includes an electric motor 110 supported by the steering gear box 107, and a speed reducing mechanism 111 that decelerates the driving force of the electric motor 110 and transmits it to the pinion shaft 106. Electric motor 110 according to the present embodiment is a three-phase brushless motor. The magnitude and direction of the actual current that actually flows through the electric motor 110 is detected by the motor current detector 33 (see FIG. 4).
The steering device 100 includes a control device 10 that controls the operation of the electric motor 110. The control device 10 receives the output value of the torque sensor 109 and the output value of the vehicle speed sensor 170 that detects the vehicle speed Vc, which is the moving speed of the automobile.

  The steering device 100 configured as described above detects the steering torque T applied to the steering wheel 101 by the torque sensor 109, drives the electric motor 110 in accordance with the detected torque, and generates torque generated by the electric motor 110. Is transmitted to the pinion shaft 106. Thereby, the torque generated by the electric motor 110 assists the driver's steering force applied to the steering wheel 101.

Next, the control device 10 will be described.
FIG. 2 is a schematic configuration diagram of the control device 10 of the steering device 100.
The control device 10 is an arithmetic and logic circuit composed of a CPU, ROM, RAM, backup RAM, and the like.
The control device 10 includes a torque signal Td obtained by converting the steering torque T detected by the torque sensor 109 described above into an output signal, and a vehicle speed signal obtained by converting the vehicle speed Vc detected by the vehicle speed sensor 170 into an output signal. v or the like is input.
Then, the control device 10 calculates a target auxiliary torque based on the torque signal Td, a target current calculation unit 20 that calculates a target current ITF necessary for the electric motor 110 to supply the target auxiliary torque, and a target And a control unit 30 that performs feedback control based on the target current ITF calculated by the current calculation unit 20.

Next, the target current calculation unit 20 will be described in detail.
FIG. 3 is a schematic configuration diagram of the target current calculation unit 20.
The target current calculation unit 20 includes a base current calculation unit 21 that calculates a base current that serves as a reference for setting the target current, an inertia compensation current calculation unit 22 that calculates a current for canceling the inertia moment of the electric motor 110, and And a damper compensation current calculation unit 23 for calculating a current for limiting the rotation of the motor. The target current calculation unit 20 also determines a temporary target current ITA based on the values calculated by the base current calculation unit 21, inertia compensation current calculation unit 22, and damper compensation current calculation unit 23. And a correction unit 27 that corrects the provisional target current ITA determined by the target current determination unit 25 in consideration of the influence of the counter electromotive voltage generated in the electric motor 110.

  The target current calculation unit 20 converts the torque signal Td, the vehicle speed signal v, the rotational speed signal Nms obtained by converting the rotational speed Nm of the electric motor 110 into an output signal, and the electrical angle θ of the electric motor 110 converted into an output signal. The electrical angle signal θs is input. The rotational speed signal Nms is, for example, a sensor configured to detect a rotational position of a rotor (rotor) of the electric motor 110 that is a three-phase brushless motor (for example, a rotor configured by a resolver, a rotary encoder, or the like that detects the rotational position of the rotor). It can be exemplified that the value obtained by differentiating the rotation angle of the electric motor 110 detected by the position detection circuit) is converted into an output signal. Further, the electrical angle signal θs can be exemplified as a value obtained by dividing the rotation angle of the electric motor 110 detected by this sensor by the number of poles into an output signal. .

  The base current calculation unit 21 calculates a base current Ib based on the torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26 and the vehicle speed signal v from the vehicle speed sensor 170. For example, the base current calculation unit 21 creates a map showing the correspondence between the torque signal Ts and the vehicle speed signal v and the base current Ib, which is previously created based on an empirical rule and stored in the ROM, and the torque signal Ts and The base current is calculated by substituting the vehicle speed signal v.

  The inertia compensation current calculation unit 22 calculates an inertia compensation current for canceling the moment of inertia of the electric motor 110 and the system based on the torque signal Td and the vehicle speed signal v. For example, the inertia compensation current calculation unit 22 generates a torque signal Td on a map indicating the correspondence between the torque signal Td, the vehicle speed signal v, and the inertia compensation current, which is previously created based on an empirical rule and stored in the ROM. And the inertia compensation current is calculated by substituting the vehicle speed signal v.

  The damper compensation current calculation unit 23 calculates a damper compensation current that limits the rotation of the electric motor 110 based on the torque signal Td, the vehicle speed signal v, and the rotation speed signal Nms of the electric motor 110. The damper compensation current calculation unit 23 indicates, for example, the correspondence between the torque compensation signal Td, the vehicle speed signal v, and the rotation speed signal Nms, which are previously created based on empirical rules and stored in the ROM, and the damper compensation current. The damper compensation current is calculated by substituting the torque signal Td, the vehicle speed signal v, and the rotational speed signal Nms into the map.

The target current determination unit 25 includes a base current Ib calculated by the base current calculation unit 21, an inertia compensation current calculated by the inertia compensation current calculation unit 22, and a damper compensation current calculated by the damper compensation current calculation unit 23. Based on the above, a temporary target current ITA is determined. The target current determination unit 25, for example, creates a compensation current obtained by adding the inertia compensation current to the base current and subtracting the damper compensation current based on an empirical rule in advance and storing it in the ROM. The target current ITA is calculated by substituting it into a map showing the correspondence between the current and the target current.
As will be described in detail later, the correction unit 27 corrects the target current ITA calculated by the target current determination unit 25, determines the corrected value as the final target current ITF, which is the final target current, and outputs it. .

Next, the control unit 30 will be described in detail.
FIG. 4 is a schematic configuration diagram of the control unit 30.
The control unit 30 includes a motor drive control unit 31 that controls the operation of the electric motor 110, a motor drive unit 32 that drives the electric motor 110, and a motor current detection unit 33 that detects the actual current Im that actually flows through the electric motor 110. And have.
The motor drive control unit 31 is based on a deviation between the target current ITF finally determined by the target current calculation unit 20 and the actual current Im supplied to the electric motor 110 detected by the motor current detection unit 33. A feedback (F / B) control unit 40 that performs feedback control, and a PWM signal generation unit 60 that generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110.

  The feedback control unit 40 includes a deviation calculation unit 41 for obtaining a deviation between the target current ITF finally determined by the target current calculation unit 20 and the actual current Im detected by the motor current detection unit 33, and the deviation is A feedback (F / B) processing unit 42 that performs feedback processing so as to be zero.

The feedback (F / B) processing unit 42 performs feedback control so that the target current ITF and the actual current Im match. For example, the feedback (F / B) processing unit 42 is proportional to the deviation calculated by the deviation calculating unit 41. Is proportionally processed, integrated by an integral element, and these values are added by an addition operation unit.
The PWM signal generation unit 60 generates a PWM signal for driving the electric motor 110 by PWM (pulse width modulation) based on the output value from the feedback control unit 40, and outputs the generated PWM signal 60a.

The motor drive unit 32 is a so-called inverter, and includes, for example, six independent transistors (FETs) as switching elements. Three of the six transistors are a positive line of a power source, an electric coil of each phase, The other three transistors are connected to the electric coil of each phase and the negative side (ground) line of the power source. Then, the driving of the electric motor 110 is controlled by driving the gates of two transistors selected from the six and switching the transistors.
The motor current detection unit 33 detects the value of the actual current Im flowing through the electric motor 110 from the voltage generated at both ends of the shunt resistor connected to the motor drive unit 32.

Next, the correction unit 27 of the target current calculation unit 20 will be described.
Since the counter electromotive voltage is generated when the electric motor 110 is driven to rotate, a part of the applied voltage is canceled by the counter electromotive voltage, and the current flowing through the electric motor 110 is reduced by the counter electromotive voltage.
FIG. 5 is a diagram illustrating a difference between the target current ITF supplied to the electric motor 110 and the actual current Im that actually flows through the electric motor 110. FIG. 5A shows the target current ITF, FIG. 5B shows the current corresponding to the back electromotive voltage, and FIG. 5C shows the actual current Im.
Due to the influence of the counter electromotive voltage generated in the electric motor 110, a current corresponding to the counter electromotive voltage according to the electrical angle as shown in FIG. Therefore, even if the target current ITF supplied to the electric motor 110 is constant regardless of the electric angle of the electric motor 110 as shown in FIG. And a fluctuating current flows as shown in FIG.

Therefore, the correction unit 27 according to the present embodiment corrects the temporary target current ITA determined by the target current determination unit 25 in consideration of the back electromotive voltage of the electric motor 110.
In view of the fact that the counter electromotive voltage generated in the electric motor 110 increases in proportion to the rotation speed of the electric motor 110 increasing, the correction based on the counter electromotive voltage of the electric motor 110 is corrected. Adjust according to. That is, even if the target current ITA determined by the target current determination unit 25 is the same, the target current ITA determined by the target current determination unit 25 is corrected when the rotational speed of the electric motor 110 is low than when it is high. Reduce the amount.

Hereinafter, the correction unit 27 will be described in more detail.
Based on the target current ITA determined by the target current determination unit 25, the correction unit 27 determines a base correction value determination that determines a base correction value ΔIb that is a base of a correction value as an example of a correction current for correcting the target current ITA. And an adjustment coefficient determination unit 272 that determines a correction value adjustment coefficient α that is a coefficient for adjusting the base correction value ΔIb determined by the base correction value determination unit 271. Further, the correction unit 27 multiplies the base correction value ΔIb determined by the base correction value determination unit 271 by the correction value adjustment coefficient α determined by the adjustment coefficient determination unit 272 to thereby obtain a final correction value (correction current). The final correction value determining unit 273 that determines the final correction value ΔIf, the target current ITA determined by the target current determining unit 25, and the final correction value ΔIf determined by the final correction value determining unit 273 are added to finally determine the final correction value ΔIf. A final target current determination unit 274 that determines a final target current ITF, which is a large target current.

Based on the target current ITA determined by the target current determination unit 25 and the electrical angle of the electric motor 110, the base correction value determination unit 271 performs correction so as to compensate for the current that is reduced due to the influence of the counter electromotive voltage. A base correction value ΔIb (base correction current), which is a correction value as an example of the correction current, is determined. The base correction value ΔIb is, for example, a current value that decreases due to the influence of the counter electromotive voltage, and is a current value that is in reverse phase with respect to the decreasing current.
FIG. 6A is a diagram illustrating the phase of the base correction value ΔIb when it is assumed that the current corresponding to the counter electromotive voltage fluctuates in the phase illustrated in FIG.
The base correction value determination unit 271, for example, in a map showing the correspondence between the target current ITA and the electric angle of the electric motor 110 and the base correction value ΔIb, which is created based on an empirical rule and stored in the ROM in advance. The base correction value ΔIb is calculated by substituting the target current ITA (the output value from the target current determination unit 25) and the electric angle θ of the electric motor 110.

FIG. 7 is a diagram showing a correlation between the rotation speed of the electric motor 110 and the correction value adjustment coefficient α.
The adjustment coefficient determination unit 272 determines the correction value adjustment coefficient α based on the rotation speed of the electric motor 110. For example, the adjustment coefficient determination unit 272 creates a correspondence between the rotation speed of the electric motor 110 and the correction value adjustment coefficient α in a relative relationship as shown in FIG. The correction value adjustment coefficient α is calculated by substituting the rotation speed (rotation speed signal Nms) of the electric motor 110 into a map indicating

As shown in FIG. 7, the correction value adjustment coefficient α is set to 1 when the rotation speed of the electric motor 110 is Nm0, and decreases as the rotation speed becomes lower than Nm0. Yes.
Further, the map used by the base correction value determination unit 271 to calculate the base correction value ΔIb is the target current ITA, the electric angle θ of the electric motor 110, and the base correction value when the rotation speed of the electric motor 110 is Nm0. It is created based on the relative relationship with ΔIb.

The final correction value determination unit 273 finally corrects the value obtained by multiplying the base correction value ΔIb determined by the base correction value determination unit 271 by the correction value adjustment coefficient α determined by the adjustment coefficient determination unit 272. A final correction value ΔIf (final correction current) which is a value (correction current) is determined (ΔIf = ΔIb × α). Thereby, the final correction value ΔIf determined by the final correction value determination unit 273 is adjusted according to the rotation speed of the electric motor 110.
FIG. 6B is a diagram illustrating the phase of the final correction value ΔIf (final correction current) when it is assumed that the base correction value ΔIb varies with the phase shown in FIG.

The final target current determination unit 274 determines a value obtained by adding the target current ITA determined by the target current determination unit 25 and the final correction value ΔIf determined by the final correction value determination unit 273 as the final target current ITF. .
FIG. 6C is a diagram illustrating the phase of the final target current ITF when it is assumed that the final correction value ΔIf (final correction current) fluctuates in the phase shown in FIG.

  In the steering device 100 configured as described above, when the target current calculation unit 20 determines the target current to be supplied to the electric motor 110, the correction unit 27 counteracts the back electromotive force against the current fluctuation caused by the back electromotive force. Since correction is performed using a current having a phase opposite to that of the voltage, the actual current supplied to the electric motor 110 is constant, and inherent motor vibration depending on the rotation of the electric motor 110 is suppressed.

  Further, since the adjustment coefficient determination unit 272 of the correction unit 27 determines the correction value adjustment coefficient α according to the rotation speed of the electric motor 110, the correction of the influence of the counter electromotive voltage of the electric motor 110 is performed by rotating the electric motor 110. It is adjusted according to the speed. Thereby, the inherent motor vibration depending on the rotation of the electric motor 110 with higher accuracy is suppressed. That is, for example, the correction unit 27 does not include the adjustment coefficient determination unit 272 and the final correction value determination unit 273, and the target current ITA determined by the target current determination unit 25 and the base correction determined by the base correction value determination unit 271. When the value obtained by adding the value ΔIb is determined as the final target current ITF, the current corresponding to the counter electromotive voltage when the rotation speed of the electric motor 110 is Nm0 is corrected. Become. In such a case, if the rotational speed of the electric motor 110 is smaller than Nm0, an excessive amount of current is added to correct the current that decreases due to the influence of the counter electromotive voltage. Variations will occur. On the other hand, in the correction unit 27 according to the present embodiment, the adjustment coefficient determination unit 272 and the final correction value determination unit 273 are the target determined by the target current determination unit 25 according to the rotation speed of the electric motor 110. Since the base correction value ΔIb for correcting the current ITA is adjusted, the current fluctuation caused by the counter electromotive voltage can be suppressed with higher accuracy, and the motor vibration can be reduced with higher accuracy.

DESCRIPTION OF SYMBOLS 10 ... Control apparatus, 20 ... Target electric current calculation part, 25 ... Target electric current determination part, 27 ... Correction | amendment part, 30 ... Control part, 100 ... Electric power steering apparatus, 101 ... Steering wheel (handle), 109 ... Torque sensor, 110 ... Electric motor

Claims (2)

An electric motor that gives steering assist force to the steering wheel;
Determining means for determining a target current to be supplied to the electric motor based on a steering torque of the steering wheel;
Correction means for correcting the target current determined by the determination means using a correction current that is a current corresponding to a counter electromotive voltage generated in the electric motor;
With
The correction means adjusts the correction current based on the rotation speed of the electric motor ,
The correction means determines a base correction value determination unit that determines a base correction value that is a base of a correction value for correcting the target current determined by the determination means, and determines the base correction value based on the rotation speed of the electric motor. An adjustment coefficient determination unit that determines a correction value adjustment coefficient for adjusting the base correction value determined by the unit, and a correction current determination unit that determines the correction current by multiplying the base correction value and the correction value adjustment coefficient And an electric power steering device.   The electric power steering apparatus according to claim 1, wherein the correction unit decreases the correction current as the rotation speed of the electric motor decreases.

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