JP4577494B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that applies a steering assist force by a motor.

  In the electric power steering apparatus, the correspondence relationship between the steering torque and the basic assist torque is stored as an assist characteristic, the steering torque is detected by a torque sensor, and the steering according to the basic assist torque obtained based on the detected steering torque and the assist characteristic is performed. The steering assist force generation motor is controlled so that the assist force is generated.

In such an electric power steering device, it is desired to reduce the load acting on the driver from the road surface via the wheel in the steering holding state in which the steering angle does not change and the return steering state in order to return the steering angle to zero. Has been. Therefore, the stored assist characteristics are shifted so that the basic assist torque corresponding to a certain steering torque is larger in the return steering state and the steering holding state than in the infeed steering state in which the magnitude of the steering angle is increased. Has been proposed (see Patent Document 1).
JP 2004-1630 A

  However, the conventional technology has a problem that the steering feeling is deteriorated due to the transition of the assist characteristic. For example, if the steering assist force is increased in the steered state, the steering assist force becomes excessive at the beginning of the transition from the steered state to the turning steering state. Further, when the basic assist torque corresponding to a constant steering torque changes greatly due to the transition of the assist characteristic, the steering assist force changes abruptly. An object of the present invention is to provide an electric power steering apparatus that can solve such a problem.

  The present invention relates to a motor that generates a steering assist force, a torque sensor that detects steering torque, a means for storing a correspondence relationship between the steering torque and the basic assist torque as an assist characteristic, a detected steering torque and the assist characteristic. Means for controlling the motor so that a steering assist force corresponding to the required basic assist torque is generated, and the basic assist torque corresponding to a certain steering torque is set steering in the return steering state and the holding state. The present invention is applied to an electric power steering apparatus in which the stored assist characteristic is shifted so as to be larger than that in a cutting steering state exceeding the speed.

One feature of the present invention, the transition speed of the assist characteristic, when forward stroke steering is returned lies in being changed according to the setting condition that is faster than the time of steering. As a result, it is possible to prevent the steering assist force from becoming excessive at the beginning of the transition from the steered state to the turning steering state.

Another feature of the present invention is that the amount of change in the basic assist torque corresponding to a constant steering torque due to the transition of the assist characteristic is changed according to the driving state of the vehicle, and the transition speed of the assist characteristic is The change is in accordance with the setting condition that the larger the amount of change in the basic assist torque corresponding to the constant steering torque due to the transition of the assist characteristic, the slower the change is . Thus, even when the basic assist torque corresponding to a constant steering torque changes greatly due to the transition of the assist characteristic, the steering assist force does not change abruptly.

  Means for obtaining a shift amount of the detected steering torque value, a low-pass filter for removing a high-frequency component from the torque signal corresponding to the detected steering torque value shifted by the obtained shift amount, and a cutoff frequency of the low-pass filter Change means, a basic assist torque corresponding to the detected steering torque shifted by the shift amount is obtained from the assist characteristic, the stored assist characteristic is transitioned, and the cut-off frequency of the low-pass filter It is preferable that the transition speed of the assist characteristic is changed by changing. Thereby, the present invention can be implemented with a simple configuration.

  According to the electric power steering apparatus of the present invention, it is possible to prevent the steering feeling from being deteriorated with a simple configuration when the steering assist force in the return steering state or the steered state is different from the steering assist force in the turning steering state. .

  The vehicle electric power steering apparatus 1 according to the first embodiment shown in FIG. 1 includes a mechanism for transmitting the rotation of the steering wheel 2 by steering to the wheels 3 so that the steering angle changes. In the present embodiment, the rotation of the steering wheel 2 is transmitted to the pinion 5 via the steering shaft 4, so that the rack 6 meshing with the pinion 5 moves, and the movement of the rack 6 moves via the tie rod 7 and the knuckle arm 8. Then, the steering angle is changed by being transmitted to the wheel 3.

  A motor 10 is provided that generates a steering assist force that acts on a path for transmitting the rotation of the steering wheel 2 to the wheel 3. In this embodiment, the steering assist force is applied by transmitting the rotation of the output shaft of the motor 10 to the steering shaft 4 via the reduction gear mechanism 11.

The motor 10 is connected to a control device 20 configured by a computer via a drive circuit 21. The control device 20 includes a torque sensor 22 that detects the steering torque T of the steering wheel 2, a steering angle sensor 23 that detects the steering angle θ _h corresponding to the rotation angle of the steering wheel 2, a vehicle speed sensor 24 that detects the vehicle speed V, and a motor. A current sensor 26 for detecting ten drive currents i is connected.

2 and 3 are control block diagrams of the motor 10 by the control device 20.
As shown in FIG. 2, the value of the detected steering torque T is the shift amount ΔT by adding the shift amount ΔT obtained by the shift amount calculation unit 30 to the detected steering torque T by the torque sensor 22 in the addition unit 31. Shifted.

  As shown in FIG. 3, the shift amount calculation unit 30 includes a basic shift amount calculation element 30a, a shift vehicle speed gain calculation element 30b, and a steering speed gain calculation element 30c.

  In the basic shift amount calculation element 30a, the correspondence relationship between the steering torque T and the basic shift amount ΔTo is stored as, for example, a table or an arithmetic expression, and the basic shift amount ΔTo corresponding to the detected steering torque T is calculated. In the present embodiment, the basic shift amount ΔTo is zero until the steering torque T reaches the first set value T1, is proportional to the steering torque T until it reaches the second set value T2, and is constant thereafter. As a result, no steering assist force is generated in a straight traveling state where the steering angle is near zero. Further, the steering assist force is increased as the driver's load increases in the steering holding state and the return steering state. Since the sign of the steering torque T and the basic shift amount ΔTo may be reversed between the right steering and the left steering, only the correspondence when the steering is steered to the left and right is shown in the figure, and the steering is steered to the left and right. Illustration of the corresponding relationship is omitted. The correspondence relationship between the steering torque T and the basic shift amount ΔTo is not limited to that shown in the figure.

  In the shift vehicle speed gain calculation element 30b, the correspondence relationship between the vehicle speed V and the shift vehicle speed gain Gv ′ is stored as, for example, a table or an arithmetic expression, and the shift vehicle speed gain Gv ′ corresponding to the detected vehicle speed V is calculated. In the present embodiment, the shift vehicle speed gain Gv ′ is proportional to the vehicle speed V until the vehicle speed V reaches the set value V1, and is thereafter constant. As a result, the steering assist force is increased in the steered state and the return steering state when traveling stability is required at a high vehicle speed. The correspondence relationship between the vehicle speed V and the shift vehicle speed gain Gv ′ is not limited to that shown in the figure.

In the steering speed gain calculation element 30c, the correspondence relationship between the steering speed dθ _h / dt and the steering speed gain K is stored as, for example, a table or an arithmetic expression, and the steering obtained by differentiation of the detected steering angle θ _{h in} the differentiation element 30e. A steering speed gain K corresponding to the speed dθ _h / dt is calculated. In the present embodiment, the sign of the steering speed dθ _h / dt is positive in the infeed steering state and negative in the return steering state, and the sign is determined by the sign determining element 30f. For example, when the sign of the detected steering angle θ _h matches the sign of the detected steering torque T, the sign of the steering speed dθ _h / dt is determined to be positive in the turning steering state, and when it does not match, the return steering state Thus, the sign of the steering speed dθ _h / dt is determined to be negative. The state may be determined using the motor angular velocity or the angular velocity dθ _p / dt below the torsion bar instead of the steering velocity dθ _h / dt. The steering speed gain K is negative when the steering speed dθ _h / dt is negative, that is, in the return steering state, when the steering speed dθ _h / dt is zero, that is, when the steering speed is maintained, and when the steering speed dθ _h / dt is positive. And is constant until reaching the first set value ω1, and is inversely proportional to the steering speed dθ _h / dt until reaching the second set value ω2 from the first set value ω1, and after exceeding the second set value ω2. Is zero. As a result, in the return steering state and the steering holding state, the steering assist force is made larger than in the cutting steering state exceeding the set steering speed (second set value ω2 in the present embodiment). Further, even in the turning steering state, the steering speed gain K is kept constant until the steering speed dθ _h / dt reaches the first set value ω1, so that it is close to the steered state where the steering is performed slowly in the cutting direction. In this case, the steering assist force can be increased. The set steering speed may be set to zero, and the steering assist force may be made smaller than that in the steered state if the turning steering state is reached.

  The multipliers 30g and 30i obtain the product of the basic shift amount ΔTo, the shift vehicle speed gain Gv ′, and the steering speed gain K, and the shift amount ΔT is obtained through the low-pass filter 61 ′. As described above, the detected steering torque T is shifted by the shift amount ΔT by adding the obtained shift amount ΔT to the detected steering torque T by the torque sensor 22 in the adding unit 31. In the calculation unit 41, the correspondence relationship between the steering torque T and the basic assist current io is stored as, for example, a table or an arithmetic expression, and the basic assist current io corresponding to the shifted detected steering torque value (T + ΔT) is calculated. . The low-pass filter 61 removes unnecessary high-frequency components from the torque signal corresponding to the detected steering torque value (T + ΔT) shifted by the shift amount ΔT. The correspondence relationship between the steering torque T and the basic assist current io is such that, for example, as shown in the calculation unit 41, the magnitude of the basic assist current io increases as the magnitude of the steering torque T increases. The signs of the steering torque T and the basic assist current io are reversed between right steering and left steering.

  The basic assist current io becomes the target drive current of the motor 10, and the steering assist force is applied by feedback-controlling the motor 10 so as to reduce the deviation between the basic assist current io and the obtained drive current i. The basic assist current io corresponds to the basic assist torque To. The relationship between the steering torque T and the basic assist current io in the calculation unit 41 of FIG. 2 illustrates the case where the vehicle speed V is constant, but the relationship between the steering torque T and the basic assist current io varies with the vehicle speed V. For example, if the steering torque T is constant, the basic assist current io increases as the vehicle speed V decreases. In the calculation unit 41, for example, a correspondence relationship between the steering torque T and the basic assist current io is stored as a table for each of a plurality of predetermined set vehicle speeds. When the detected vehicle speed V is a value between the set vehicle speeds, an interpolation calculation is performed. A correspondence relationship between the steering torque T and the basic assist current io is obtained. As a result, the correspondence relationship between the steering torque T and the basic assist torque To is stored as an assist characteristic, and the motor is configured to generate a steering assist force corresponding to the basic assist torque To obtained based on the assist characteristic and the detected steering torque T. 10 will be controlled.

According to the above configuration, the motor 10 is controlled by the control device 20 so as to generate a steering assist force corresponding to the basic assist torque To corresponding to the detected steering torque T in the incision steering state exceeding the set steering speed ω2. . Further, in the return steering state, the steering holding state, and the turning steering state at the set steering speed ω2 or less, the steering assist according to the basic assist torque To corresponding to the detected steering torque value (T + ΔT) shifted by the shift amount ΔT. The motor 10 is controlled by the controller 20 to generate a force. That is, the basic assist torque To corresponding to a certain steering torque is obtained by obtaining the basic assist torque To corresponding to the value (T + ΔT) of the detected steering torque T shifted by the shift amount ΔT. In the return steering state and the steering holding state, the stored assist characteristic is shifted so as to be larger than that in the turning steering state exceeding the set steering speed ω2. For example, in the assist characteristic in the incision steering state exceeding the set steering speed ω2 indicated by the solid line L in FIG. 4, the value of the basic assist torque To at a certain value α of the steering torque T is β, and the constant steering torque T The value of the basic assist torque To at the value α + ΔT obtained by shifting the value α by the shift amount ΔT is β ′. In this case, the assist characteristic indicated by the solid line L in the incision steering state indicates the basic assist torque To at the constant steering torque T value α as indicated by the two-dot chain line L ′ in the return steering state and the holding state. The value is virtually transitioned to the assist characteristic of β ′. The amount of change in the basic assist torque To corresponding to the constant steering torque T due to the transition of the assist characteristic is the shift amount obtained by the product of the basic shift amount ΔTo, the shift vehicle speed gain Gv ′, and the steering speed gain K. since corresponding to [Delta] T, the vehicle speed V, the steering torque T, will be changed according to the driving state of the vehicle such as the steering angle theta _h.

The speed of the transition of the assist characteristic as shown in FIG. 4 between the assist characteristic indicated by the solid line L and the assist characteristic indicated by the two-dot chain line L ′ is changed according to the set condition. In the present embodiment, the transition speed of the assist characteristic is changed in accordance with a setting condition that the turning speed becomes faster during the turning steering than during the return steering. As shown in FIG. 2, the time constant t of the low-pass filter 61 is changed according to the determination result of the turning steering state or the return steering state in the steering state determination unit 45 of the control device 20, thereby cutting the low-pass filter 61. The off frequency 1 / (2πt) is changed. In addition, for example, when the sign of the steering speed dθ _h / dt and the sign of the detected steering torque T coincide with each other, it is determined that the engine is in the turning steering state. Is determined to be a return steering state. A torque signal corresponding to the detected steering torque value (T + ΔT) shifted by the shift amount ΔT is input to the calculation unit 41 via the low-pass filter 61, and the basic assist torque To corresponding to the value (T + ΔT) is obtained. Thus, the stored assist characteristic is changed. Therefore, when the cut-off frequency 1 / (2πt) of the low-pass filter 61 is changed, the transmission speed of the torque signal changes when the value of the detected steering torque T is shifted by the shift amount ΔT, and the assist characteristic transition speed. Is changed. In the present embodiment, the time constant t of the low-pass filter 61 is set so that the value at the time of turning steering is smaller than the value at the time of return steering. For example, in the Bode diagram showing the frequency response characteristics shown in FIG. 5, the horizontal axis represents the frequency (Hz) of the torque signal passing through the low-pass filter 61, and the vertical axis represents the amplitude ratio (dB) of the output with respect to the input of the torque signal. The characteristic at the time of return steering is represented by a two-dot chain line, and the characteristic at the time of turning steering is represented by a solid line.

The flowchart of FIG. 6 shows the control procedure of the motor 10 by the control device 20. First, the detected values V, θ _h , T, i by each sensor are read (step S1), and the steering state is a cut-in steering state or a return steering state based on the sign of the steering speed dθ _h / dt and the detected steering torque T. It is determined whether or not the vehicle is in the steered state (step S2). If the steering state is the cut-in steering state, the value of the time constant t of the low-pass filter 61 is set to a first preset value t1 (step S3). A predetermined second set value t2 larger than the set value t1 is set (step S4). Next, the steering speed dθ _h / dt is obtained by differentiating the steering angle θ _h obtained in time series (step S5), and the obtained steering speed dθ _h / dt, detected steering torque T, detected vehicle speed V, detected steering. A shift amount ΔT is obtained from the sign of the angle θ _h and the detected steering torque T (step S6). In addition, when it is a steering holding state by step S2, it progresses to step S5. Next, a detected steering torque value (T + ΔT) shifted by the shift amount ΔT is obtained (step S7), and a basic assist current io corresponding to the shifted detected steering torque value (T + ΔT) is obtained (step S8). Then, the motor 10 is feedback controlled so as to reduce the deviation between the basic assist current io and the detected drive current i (step S9). After that, whether or not to end the control is determined based on, for example, whether the ignition switch is on or off (step S10). If the control is not ended, the process returns to step S1.

  According to the first embodiment, the transition speed of the assist characteristic is changed according to the setting condition that the speed during the turning steering is faster than that during the return steering. It is possible to prevent the steering assist force from becoming excessively delayed due to the change in the steering assist force by increasing the transition speed of the assist characteristic.

  7 to 9 show a second embodiment. Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals and the differences will be described. The difference from the first embodiment is that, instead of the setting condition that the transition speed of the assist characteristic is faster than that of the return steering during the turning steering, the basic assist corresponding to a constant steering torque T due to the transition of the assist characteristic. The change is in accordance with the setting condition that the torque To becomes slower as the amount of change in the torque To increases. In the present embodiment, since the amount of change in the basic assist torque To corresponding to the constant steering torque T due to the transition of the assist characteristics corresponds to the shift amount ΔT, the shift is performed instead of the steering state determination unit 45 of the first embodiment. The time constant t of the low-pass filter 61 is changed according to the determination result of the quantity determination unit 46, and thereby the cutoff frequency 1 / (2πt) of the low-pass filter 61 is changed. That is, the time constant t of the low-pass filter 61 is increased as the shift amount ΔT is increased. For example, as shown in FIG. 8, the characteristic when the shift amount ΔT is zero is represented by a solid line, and the characteristic when the shift amount ΔT is increased is represented by a one-dot chain line. Note that the time constant t may change continuously or stepwise according to the magnitude of the shift amount ΔT. Others are the same as in the first embodiment.

The flowchart of FIG. 9 shows the control procedure of the motor 10 by the control device 20. First, the detection values V, θ _h , T, i from each sensor are read (step S101), and the time constant t of the low-pass filter 61 is set according to the magnitude of the shift amount ΔT (step S102). At the start of control, a predetermined initial value may be used as the shift amount ΔT. For example, the initial value is set to zero. Next, the steering speed dθ _h / dt is obtained by differentiating the steering angle θ _h obtained in time series (step S 103), the sign of the detected steering angle θ _h and the detected steering torque T, and the obtained steering speed dθ. _The shift amount ΔT is obtained from _h / dt, the detected steering torque T, and the detected vehicle speed V (step S104). Next, the detected steering torque value (T + ΔT) shifted by the shift amount ΔT is obtained (step S105), and the basic assist current io corresponding to the shifted detected steering torque value (T + ΔT) is obtained (step S106). Then, the motor 10 is feedback controlled so as to reduce the deviation between the basic assist current io and the detected drive current i (step S107). Thereafter, whether or not to end the control is determined based on, for example, whether the ignition switch is on or off (step S108). If the control is not ended, the process returns to step S101.

  According to the second embodiment, the transition speed of the assist characteristic is changed according to the setting condition that the shift speed becomes slower as the shift amount ΔT is larger. Therefore, the basic assist torque To corresponding to the constant steering torque T is the transition of the assist characteristic. Even when the steering assist force changes greatly, the steering assist force does not change abruptly, and an excess or deficiency of the steering assist force at the beginning of the transition of the assist characteristic can be prevented by slowing down the transition speed of the assist characteristic.

  The present invention is not limited to the above embodiment. For example, the mechanism for transmitting the rotation of the steering wheel to the wheel so that the steering angle changes is not limited to the embodiment, and the rotation of the steering wheel is transmitted from the steering shaft to the wheel via a link mechanism other than the rack and pinion. It may be a thing. Further, the mechanism for transmitting the output of the motor for generating the steering assist force to the steering system is not limited to the embodiment as long as the steering assist force can be applied. For example, a ball nut screwed to the ball screw integrated with the rack is attached to the motor. A steering assist force may be applied by driving with an output.

Configuration explanatory diagram of an electric power steering apparatus according to an embodiment of the present invention FIG. 1 is a control block diagram of the electric power steering apparatus according to the first embodiment of the present invention. Control block diagram for obtaining the shift amount in the electric power steering apparatus of the first embodiment of the present invention The figure which shows the relationship between the steering torque in the electric power steering device of embodiment of this invention, and a basic assist torque. The figure which shows the frequency response characteristic of the torque signal which passes a low-pass filter in the electric power steering apparatus of 1st Embodiment of this invention. The flowchart which shows the control procedure in the electric power steering device of 1st Embodiment of this invention. Control block diagram of electric power steering apparatus of second embodiment of the present invention The figure which shows the frequency response characteristic of the torque signal which passes a low-pass filter in the electric power steering apparatus of 2nd Embodiment of this invention. The flowchart which shows the control procedure in the electric power steering apparatus of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 10 Motor 20 Control apparatus 22 Torque sensor 61 Low pass filter

Claims (3)

A motor that generates steering assist force;
A torque sensor for detecting steering torque;
Means for storing a correspondence relationship between the steering torque and the basic assist torque as an assist characteristic;
Means for controlling the motor so as to generate a steering assist force according to a detected steering torque and a basic assist torque obtained based on the assist characteristics;
Electric power steering in which the stored assist characteristic is shifted so that a basic assist torque corresponding to a constant steering torque is larger in a return steering state and a holding state than in a notch steering state exceeding a set steering speed. In the device
The electric power steering device according to claim 1, wherein the transition speed of the assist characteristic is changed in accordance with a setting condition that a speed of turning steering is faster than that of returning steering . A motor that generates steering assist force;
A torque sensor for detecting steering torque;
Means for storing a correspondence relationship between the steering torque and the basic assist torque as an assist characteristic;
Means for controlling the motor such that a steering assist force according to a detected steering torque and a basic assist torque obtained based on the assist characteristic is generated;
Electric power steering in which the stored assist characteristics are transitioned so that a basic assist torque corresponding to a certain steering torque is larger in a return steering state and a holding state than in a notch steering state exceeding a set steering speed. In the device
The amount of change in basic assist torque corresponding to a constant steering torque due to the transition of the assist characteristic is changed according to the driving state of the vehicle,
An electric power steering apparatus characterized in that the transition speed of the assist characteristic is changed according to a setting condition that the amount of change in the basic assist torque corresponding to a constant steering torque due to the transition of the assist characteristic becomes slower as the amount of change increases. . Means for determining the shift amount of the detected steering torque value;
A low-pass filter for removing high-frequency components from the torque signal corresponding to the value of the detected steering torque shifted by the obtained shift amount;
And means for changing the cutoff frequency of the low-pass filter,
Since the basic assist torque corresponding to the detected steering torque shifted by the shift amount is obtained from the assist characteristic, the stored assist characteristic is transitioned,
The electric power steering apparatus according to claim 1 or 2 , wherein a transition speed of the assist characteristic is changed by changing a cutoff frequency of the low-pass filter .

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