JP2012183881A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which enables a user to obtain a comfortable steering feeling when a steering wheel is turned to the right or left, returned to the center position and held at the center position even when a steering speed is not detected.SOLUTION: When the product which is obtained by multiplying steering torque by the differential value of the steering torque is larger than zero, the state is determined that the steering wheel is turned to the right or left. When the product which is obtained by multiplying the steering torque by the differential value of the steering torque is smaller than zero, the state is determined that the steering wheel is returned to the center position. When the product is zero, the state is determined that the steering wheel is held at the center position. When it is determined that the steering wheel is turned to the right or left or held at the center position, a basic torque shift based on the steering torque is enabled.

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, in an electric power steering apparatus, a basic assist current is calculated from the steering torque and the vehicle speed, and the motor is rotated based on the calculated value to perform assist torque control. This method is common regardless of the vehicle steering situation.

  However, if the steering torque is uniquely determined from the steering torque and the vehicle speed in spite of the change of the steering wheel, the steering, and the switching back state, the steering feeling is uncomfortable. Therefore, for example, in the electric power steering apparatus described in Patent Document 1, it is described that the basic shift amount is calculated based on the steering speed, and the basic assist torque is changed in accordance with the turning of the steering wheel and the return of the steering wheel.

JP 2004-001630 A

  However, in the case of Patent Document 1, since the steering speed is generated from the steering angle sensor, if the steering angle sensor is not attached, the basic shift amount cannot be calculated, and there is a possibility that the steering feeling is lowered. It still left room for improvement.

  The present invention has been made in order to solve the above-described problems, and its object is to provide a comfortable steering fee, particularly when the steering wheel is turned, turned back, and held even when the steering speed cannot be detected. An object of the present invention is to provide an electric power steering device capable of obtaining a ring.

  In order to solve the above-mentioned problem, the invention according to claim 1 detects a vehicle speed, a motor (12) for applying a steering assist force to a steering system of a vehicle, a torque sensor (15) for detecting a steering torque, and the like. A vehicle speed sensor (16), a basic assist characteristic setting means (23) for setting a basic assist characteristic that is a basic characteristic of the motor drive target value with respect to the steering torque and the vehicle speed, and a steering state determination means for determining the steering state of the steering wheel (25), a basic torque shift amount calculating means (26) for calculating a basic torque shift amount based on the steering torque, a vehicle speed gain calculating means (27) for calculating a vehicle speed gain based on the vehicle speed, And a parameter (α) output from the steering state determination means (25) and a basic torque shift amount output from the basic torque shift amount calculation means (26). ΔTha) multiplied by the vehicle speed gain (Gv) output from the vehicle speed gain calculation means (27) is added to the basic assist characteristic set by the basic assist characteristic setting means (23), and an assist torque command is added. Value setting means (24), and motor control signal output means for generating a control signal for driving the motor (12) by the assist torque command value (Ta *) output from the assist torque command value setting means (24). 31) and motor drive means (40) for driving the motor (12) by the motor control signal generated by the motor control signal output means (31).

  According to the above configuration, it is possible to determine whether or not to add the torque shift amount to the basic assist characteristics by determining the steering state based on the steering torque without detecting the steering speed. As a result, the steering torque can be increased / decreased only when necessary, so that a comfortable steering feeling can be obtained.

  According to a second aspect of the present invention, when the product of the steering torque and the differential value of the steering torque is greater than zero, the steering state determination unit determines that the state is a cut state and writes “0” in the parameter. When the product of the steering torque and the differential value of the steering torque is smaller than zero, it is determined that the switch-back state has occurred, and “1” is written in the parameter, and the product of the steering torque and the differential value of the steering torque is In the case of zero, it is determined that the steering state is maintained and “1” is written in the parameter.

According to the above configuration, when the product of the steering torque and the differential value of the steering torque is larger than zero, it is determined as a cut-in state, and when the product of the steering torque and the differential value of the steering torque is smaller than zero, the switchback is performed. Judged as a state. When the product of the steering torque and the differential value of the steering torque is zero, it is determined that the steering is maintained.
As a result, it is possible to accurately determine whether the cutting state, the switching back state, or the steered state.

  According to the present invention, the steering torque can be increased by invalidating the basic torque shift amount when it is determined that the cut-in state is established, and when it is determined that the switch-back state or the steered state is determined. Since the steering torque can be reduced by making the basic torque shift amount effective, a comfortable steering feeling can be obtained.

The schematic block diagram of an electric power steering device (EPS). The block diagram which shows the electric constitution of EPS. Explanatory drawing of the assist torque command value setting part of embodiment of this invention. The flowchart figure which shows the process sequence of the steering state determination part of embodiment of this invention. Explanatory drawing of the torque shift amount calculating part with respect to the steering torque of embodiment of this invention. Explanatory drawing of the vehicle speed gain calculating part with respect to the vehicle speed of embodiment of this invention.

Hereinafter, an embodiment of the present invention embodied in a column type electric power steering apparatus 1 (hereinafter referred to as EPS) will be described with reference to the drawings.
As shown in FIG. 1, in the EPS 1 of the present embodiment, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. The rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4.

  The steering shaft 3 of this embodiment is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. Then, the reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 6 connected to both ends of the rack shaft 5, whereby the steering angle of the steered wheels 7. Is changed.

  Further, the EPS 1 includes an EPS actuator 13 that applies an assist force for assisting a steering operation to the steering system, and an ECU 11 that serves as a control unit that controls the operation of the EPS actuator 13.

  The EPS actuator 13 of the present embodiment is a column type EPS actuator, and the motor 12 that is a driving source thereof is drivingly connected to the column shaft 8 via a speed reduction mechanism 14. The EPS actuator 13 applies the motor torque as an assist force to the steering system by decelerating the rotation of the motor 12 by the speed reduction mechanism 14 and transmitting it to the column shaft 8.

  A vehicle speed sensor 16, a torque sensor 15, and a motor rotation angle sensor 18 are connected to the ECU 11. The ECU 11 detects the vehicle speed V, the steering torque τ, and the motor rotation angle θm based on the output signals of these sensors. For example, the torque sensor 15 of the present embodiment is a twin resolver type torque sensor in which a pair of resolvers are provided at both ends of a torsion bar (not shown). Further, the ECU 11 calculates a target assist force based on each detected state quantity, and controls the operation of the EPS actuator 13, that is, the assist force applied to the steering system through the supply of drive power to the motor 12. To do.

Next, an aspect of assist control in the EPS of the present embodiment will be described.
As shown in FIG. 2, the ECU 11 includes a microcomputer 21 that outputs a motor control signal and a drive circuit 40 that supplies drive power to the motor 12 based on the motor control signal.

  In the present embodiment, the ECU 11 includes a current sensor 41 for detecting the actual current value Im supplied to the motor 12 and a motor rotation angle sensor 18 for detecting the rotation angle θm of the motor 12 (see FIG. 1). Is connected. The microcomputer 21 drives the drive circuit 40 based on the vehicle state quantities and the actual current value Im of the motor 12 and the motor rotation angle θm detected based on the output signals of the current sensor 41 and the motor rotation angle sensor 18. A motor control signal to be output to is generated.

  Each control block shown below is realized by a computer program executed by the microcomputer 21. Then, the microcomputer 21 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control blocks every predetermined period.

  Specifically, the microcomputer 21 of the present embodiment calculates the assist torque to be generated by the motor 12, that is, the assist torque command value Ta * corresponding to the target assist force, based on the steering torque τ and the vehicle speed V. A command value calculation unit 22 and an assist current command value calculation unit 30 that calculates an assist current command value I * corresponding to the assist torque command value Ta * are provided.

  Then, the microcomputer 21 causes the motor control signal output unit 31 to make current feedback based on the current deviation ΔI so that the assist current command value I * follows the actual current value Im detected by the current sensor 41 of the motor 12. By executing the control, a motor control signal to be output to the drive circuit 40 is generated.

  Specifically, in the present embodiment, a brushless motor that rotates by supplying three-phase (U, V, W) driving power is used as the motor 12. The motor control signal output unit 31 converts the phase current value (Iu, Iv, Iw) of the motor 12 detected as the actual current value Im into d and q axis current values in the d / q coordinate system (d / q The current feedback control is performed by performing conversion.

  That is, the assist current command value I * is input to the motor control signal output unit 31 as a q-axis current command value, and the motor control signal output unit 31 is based on the motor rotation angle rotation angle θm detected by the rotation angle sensor 18. The phase current values (Iu, Iv, Iw) are d / q converted. The motor control signal output unit 31 calculates the d and q axis voltage command values based on the d and q axis current values and the q axis current command value. Then, the phase voltage command values (Vu *, Vv *, Vw *) are calculated by performing d / q inverse conversion on the d and q axis voltage command values, and a motor control signal is generated based on the phase voltage command values. To do.

  The motor control signal generated in this way is output from the microcomputer 21 to the drive circuit 40, and the drive circuit 40 supplies three-phase drive power based on the motor control signal to the motor 12. Then, when a motor torque corresponding to an assist current command value I * as an assist force target value based on the steering torque τ is generated, an assist force corresponding to the assist force target value is applied to the steering system. It has become.

(Assist torque command value calculation)
Next, a mode of assist torque command value calculation in the present embodiment will be described.
In the present embodiment, the assist torque command value calculation unit 22 is provided with a steering state determination unit 25 that determines steering wheel turning, steering wheel turning back, and steering wheel holding based on the steering torque τ and the steering torque change amount dτ / dt. It has been. When the steering state determination unit 25 determines that the steering wheel is cut, the steering state determination coefficient α is set to “0” (α = 0), while the steering wheel is turned back. Alternatively, when it is determined that the steering wheel is in the steered state, the steering state determination coefficient α is set to “1” (α = 1).

Next, a processing procedure of the steering state determination unit 25 in the assist torque command value calculation unit 22 configured as described above will be described.
As shown in the flowchart of FIG. 4, the microcomputer 21 takes in the steering torque τ (step S101). Next, the captured steering torque τ is differentiated to calculate the change amount dτ / dt of the steering torque τ (step S102). Then, it is determined whether or not the product of the steering torque τ and the change amount dτ / dt of the steering torque τ is greater than zero (step S103).

When the product of the steering torque τ and the change amount dτ / dt of the steering torque τ is greater than zero (τ · dτ / dt> 0, step S103, YES), the process proceeds to step S104.
In step S104, it is determined that the steering state is the infeed state, the steering state determination coefficient α is set to “0” (α = 0), and the process ends.

If the product of the steering torque τ and the amount of change dτ / dt of the steering torque τ is less than zero (τ · dτ / dt ≦ 0, step S103, NO), the process proceeds to step S105.
In step S105, it is determined whether or not the product of the steering torque τ and the change amount dτ / dt of the steering torque τ is smaller than zero.

When the product of the steering torque τ and the change amount dτ / dt of the steering torque τ is smaller than zero (τ · dτ / dt <0, step S105, YES), the process proceeds to step S106.
In step S106, it is determined that the steering state is the switchback state, the steering state determination coefficient α is set to “1” (α = 1), and the process ends.

When the product of the steering torque τ and the change amount dτ / dt of the steering torque τ is zero (τ · dτ / dt = 0, step S105, NO), the process proceeds to step S107.
In step S107, it is determined that the steering state is the holding state, the steering state determination coefficient α is set to “1” (α = 1), and the process ends.

In the present embodiment, the assist torque command value calculation unit 22 is provided with a torque shift calculation unit 26 that obtains a basic torque shift amount ΔTha based on the steering torque τ.
As shown in FIG. 5, the torque shift calculation unit 26 of the present embodiment associates a positive value of the basic torque shift amount ΔTha with a positive value of the steering torque τ. On the other hand, the torque shift calculation unit 26 of the present embodiment associates a negative value of the basic torque shift amount ΔTha with a negative value of the steering torque τ.

  Further, when the steering torque τ takes a value in the dead zone in the vicinity of zero, the torque shift calculation unit 26 of the present embodiment holds the basic torque shift amount ΔTha at zero. When the steering torque τ takes a value outside the dead zone in the vicinity of zero, the torque shift calculation unit 26 according to the present embodiment counters the increase of the steering torque within a range between the predetermined lower limit value and the upper limit value. It is determined to increase monotonously.

  In the present embodiment, the assist torque command value calculation unit 22 is provided with a vehicle speed gain calculation unit 27 that calculates a vehicle speed gain Gv based on the vehicle speed V. Then, as shown in FIG. 6, the vehicle speed gain calculation unit 27 of the present embodiment rapidly increases as the vehicle speed V increases in a range from zero to a predetermined speed, and thereafter gently increases to a constant value. It is determined to converge.

  As a result, the shift amount of the assist characteristic during low-speed traveling can be suppressed to be small. For example, even when the steering 2 is continuously cut in the same direction as in a U-turn operation, the steering burden becomes too heavy. There is no such thing.

  In the present embodiment, the assist torque command value calculation unit 22 is provided with a basic assist characteristic setting unit 23 based on the steering torque τ and the vehicle speed V, as shown in FIG. This basic assist characteristic associates a positive value of the assist torque command value Ta * with a positive value of the steering torque τ, and a negative value of the assist torque command value Ta * with a negative value of the steering torque τ. Are defined to be associated with each other. The basic assist characteristic setting unit 23 stores a plurality of basic assist maps corresponding to a plurality of vehicle speed ranges.

  In this embodiment, the assist torque command value calculation unit 22 outputs the steering state determination coefficient α output from the steering state determination unit 25 and the torque shift calculation unit 26 to the basic assist characteristic setting unit 23. The adder 29 adds the torque shift amount ΔTh (= α · ΔTha · Gv) obtained by multiplying the basic torque shift amount ΔTha and the vehicle speed gain Gv output from the vehicle speed gain calculation unit 27 by the multiplier 28. The torque shift amount ΔTh is added to the basic assist characteristic output from the basic assist characteristic setting unit 23 and input to the assist torque command value setting unit 24.

  Next, the function of the assist torque command value setting unit 24 of the present embodiment will be described based on FIG. FIG. 3 shows the basic assist characteristics and the corrected assist characteristics obtained by shifting the basic assist characteristics in the steering torque axis direction. The steering torque τ detected by the torque sensor 15 takes a positive value when a torque for steering in the right direction is applied to the steering 2, and takes a positive value when the torque for steering in the left direction is applied to the steering 2. Takes a negative value.

  The basic assist characteristic is indicated by a curve L10 in FIG. In this basic assist characteristic, a positive value of the assist torque command value Ta * is associated with a positive value of the steering torque τ, and a negative value of the assist torque command value Ta * is associated with a negative value of the steering torque τ. It is determined to associate the values of.

  As described above, the basic assist characteristic setting unit 23 stores a plurality of basic assist maps corresponding to a plurality of vehicle speed ranges. In FIG. 3, one basic assist applied in a certain vehicle speed range is stored. Show properties. In the basic assist characteristic shown by the curve L10, in the vicinity of the steering torque τ = 0, the assist torque command value Ta * = 0 is set regardless of the value of the steering torque τ. Such a range of steering torque is the dead zone NS.

  In the present embodiment, based on the steering torque τ, the virtual assist characteristic is shifted in the axial direction (positive direction or negative direction) of the steering torque τ by the torque shift amount ΔTh calculated by the torque shift calculation unit 26. The assist torque command value Ta * is set on the basis of various correction assist characteristics (for example, characteristics indicated by the curves L11 and L12).

  More specifically, in this embodiment, when the steering torque τ takes a positive value of a certain value or more, the virtual assist assist characteristic (in FIG. 3) is obtained by shifting the basic assist characteristic in the positive direction of the steering torque axis ( For example, the assist torque command value Ta * corresponding to the steering torque τ is determined according to the assist characteristic indicated by the curve L11. On the other hand, when the steering torque τ takes a negative value equal to or less than a certain value, the basic assist characteristic is shifted to the negative direction of the steering torque axis in FIG. The assist torque command value Ta * corresponding to the steering torque τ is determined according to the assist characteristics shown).

  More specifically, in the present embodiment, the steering torque τ takes a positive value during steering in which the steering 2 is turned away from the neutral position, so the virtual correction assist characteristic is the basic assist characteristic. Is shifted in the direction away from the origin along the steering torque axis direction. The torque shift amount ΔTh at this time increases as the absolute value of the steering torque τ increases.

  As a result, when the steering torque τ is the same, the assist torque command value Ta * has a smaller absolute value than the basic assist characteristic, and thus the steering assist force is small. As a result, it is possible to give the driver a good feeling of response when turning the steering wheel 2.

  On the other hand, in the present embodiment, at the time of turning-back steering in which the steering 2 is steered toward the steering angle midpoint, the steering torque τ gradually decreases and becomes a minute value. Accordingly, the virtual correction assist characteristic is a characteristic obtained by shifting the basic assist characteristic in the direction toward the origin along the steering torque axis direction.

  As a result, when the steering torque τ is the same, the assist torque command value Ta * has a larger absolute value than the basic assist characteristic, and thus the steering assist force is increased. As a result, when the steering wheel 2 is turned back, it is possible to give the driver a good feeling of response.

  In addition, when the steering torque is maintained, the assist torque command value Ta * has a larger absolute value than the basic assist characteristic when the steering torque τ is the same. Therefore, the steering assist force is increased. . As a result, it is possible to give the driver a good feeling of responsiveness when the steering 2 is held.

As described above, according to the present embodiment, the following operations and effects can be obtained.
When the product of the steering torque and the differential value of the steering torque is larger than zero, it is determined as a cut-in state, and when the product of the steering torque and the differential value of the steering torque is smaller than zero, it is determined as a switch-back state. When the product of the steering torque and the differential value of the steering torque is zero, it is determined that the steering is maintained. And when it determines with a switchback state or a steering hold state, the basic torque shift based on a steering torque was made effective.

  As a result, it is possible to accurately determine whether the cutting state, the switching back state, or the steered state. In addition, since the basic torque shift based on the steering torque becomes invalid in the cutting state, the absolute value of the assist torque command value Ta * is the same as that of the basic assist characteristic when the steering torque τ is the same. Since the steering assist force is reduced, the driver can feel good responsiveness when turning the steering wheel 2.

  In addition, since the basic torque shift based on the steering torque is effective in the switchback state or the steered state, the assist torque command value Ta * is compared with the basic assist characteristic when the steering torque τ is the same. Since the absolute value becomes large, the steering assist force becomes large, and a good feeling of response can be given to the driver when turning back the steering wheel 2 or at the time of steering.

In addition, you may change this embodiment as follows.
In each of the above embodiments, the present invention is embodied in a so-called column type EPS 1, but the present invention may be applied to a so-called pinion type or rack assist type EPS.

  In the above embodiment, the present invention is embodied in EPS using a brushless motor as a drive source. However, the present invention may be applied to EPS using a DC motor with a brush as a drive source.

1: Electric power steering device (EPS), 2: Steering,
3: Steering shaft, 4: Rack and pinion mechanism, 5: Rack shaft,
6: Tie rod, 7: Steering wheel, 8: Column shaft,
9: Intermediate shaft, 10: Pinion shaft, 11: ECU,
12: Motor, 13: EPS actuator, 14: Deceleration mechanism,
15: Torque sensor, 16: Vehicle speed sensor,
18: motor rotation angle sensor, 21: microcomputer, 22: assist torque command value calculation unit,
23: Basic assist characteristic setting unit, 24: Assist torque command value setting unit,
25: Steering state determination unit, 26: Torque shift calculation unit, 27: Vehicle speed gain calculation unit,
28: Multiplier, 29: Adder, 30: Assist current command value calculation unit,
31: Motor control signal output unit, 40: Drive circuit, 41: Current sensor,
V: vehicle speed, τ: steering torque, dτ / dt: steering torque change amount, θm: motor rotation angle,
Im: actual current value, I *: assist current command value, ΔI: current deviation,
Iu, Iv, Iw: Phase current value, Vu *, Vv *, Vw *: Phase voltage command value,
Ta *: assist torque command value, ΔTha: basic torque shift amount,
ΔTh: Torque shift amount, α: Steering state determination coefficient, Gv: Vehicle speed gain

Claims (2)

A motor for applying a steering assist force to the vehicle steering system;
A torque sensor for detecting steering torque;
A vehicle speed sensor for detecting the vehicle speed;
Basic assist characteristic setting means for setting a basic assist characteristic that is a basic characteristic of a motor drive target value with respect to the steering torque and the vehicle speed;
Steering state determination means for determining the steering state of the steering wheel;
Basic torque shift amount calculating means for calculating a basic torque shift amount based on the steering torque;
Vehicle speed gain calculating means for calculating a vehicle speed gain based on the vehicle speed,
A value obtained by multiplying the parameter output from the steering state determining means, the basic torque shift amount output from the basic torque shift amount calculating means, and the vehicle speed gain output from the vehicle speed gain calculating means is the basic assist characteristic. Assist torque command value setting means added to the basic assist characteristics set by the setting means;
Motor control signal output means for generating a control signal for driving the motor according to the assist torque command value output from the assist torque command value setting means;
Motor driving means for driving the motor by a motor control signal generated by the motor control signal output means,
An electric power steering device.   When the product of the steering torque and the differential value of the steering torque is greater than zero, the steering state determination unit determines that the steering state is a cut state, writes “0” in the parameter, and sets the steering torque and the steering torque. When the product of the differential values is smaller than zero, it is determined that the state is switched back, and “1” is written in the parameter. When the product of the steering torque and the differential value of the steering torque is zero, the steering holding state The electric power steering apparatus according to claim 1, wherein “1” is written in the parameter.

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