JP2006290127A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering system capable of suppressing the heat emission from a motor properly without causing the device itself to be large sized. <P>SOLUTION: The electric power steering system is equipped with a target steering torque calculating means 40 to calculate the target steering torque Tm on the basis of the steering angle and the vehicle speed, a feedback control amount calculating means 58 to calculate the feedback control amount Dfb on the basis of the difference between the target steering torque Tm and the steering torque T, a motor current presuming means 54 to convert the steering angular velocity ω obtained through calculation as subjecting the steering angle θ to time difference into a motor revolving speed ω<SB>M</SB>of an assist motor, calculate the inverse electromotive voltage V<SB>M</SB>of the assist motor from the motor revolving speed ω<SB>M</SB>, and presume the motor current I<SB>M</SB>of the assist motor from the difference between the inverse electromotive voltage V<SB>M</SB>and the voltage V<SB>T</SB>between the motor terminals, and a motor control amount setting means 59 to calculate the upper limit amperage I<SB>L</SB>from the presumed motor current I<SB>M</SB>, suppress the feedback control amount Dfd on the basis of the motor current I<SB>M</SB>presumed as the upper limit amperage I<SB>L</SB>, and set the motor control amount D<SB>M</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering device that is mounted on an automobile and assists a steering force with an electric motor.

  Steering torque control of the electric power steering apparatus basically assists the steering force by applying an assisting force corresponding to the steering torque applied to the steering shaft from the motor to the steering mechanism when the steering wheel is steered.

  For example, in the electric power steering device disclosed in Patent Document 1, the control unit ECU estimates the target steering torque based on the steering angle and the vehicle speed, and based on the deviation between the target steering torque and the detected steering torque. The motor feedback control.

JP 2002-120743 A

When the motor is operated, the temperature rises due to the loss of each part, particularly the loss of the electric resistance.
If the temperature rise exceeds the limit, the insulation used in the winding may deteriorate and cause breakdown, so it must be used so that the limit specified for the insulation is not exceeded.
In addition, a motor used in an electric power steering apparatus is often provided with a control board equipped with a CPU or the like for controlling the motor in the vicinity. In order to protect electric elements such as the CPU from thermal destruction, the motor It is necessary to further suppress the heat generation.

Prior Patent Document 1 does not include means for suppressing motor heat generation.
In order to appropriately suppress the heat generation of the motor, it is necessary to increase the capacity of the motor or to detect and regulate the motor current that causes the loss of electric resistance that is the cause of the heat generation.
In the former case, the motor itself increases in size, and even in the latter case, if the motor current detection device is provided, the size of the electric power steering device increases, and in any case, the cost increases.

  The present invention has been made in view of the above points, and the object of the present invention is to provide an electric power steering device that can appropriately suppress the heat generation of the motor without increasing the size of the device itself at low cost. .

  In order to achieve the above object, according to a first aspect of the present invention, there is provided an electric power steering apparatus in which a driving force of an assist motor assists a steering force, a torque sensor for detecting a steering torque, a vehicle speed sensor for detecting a vehicle speed, A steering angle detection means for detecting a steering angle of the steering, a motor terminal voltage detection means for detecting a voltage between terminals of the assist motor, a steering angle detected by the steering angle detection means and a vehicle speed sensor. Feedback based on the difference between the target steering torque calculated by the target steering torque calculating means and the steering torque detected by the torque sensor; Feedback control amount calculation means for calculating a control amount, and the steering angle detection means Steering angular velocity calculation means for calculating the steering angular velocity by differentiating the detected steering angle by time, and motor rotation speed calculation means for converting the steering angular speed calculated by the steering angular velocity calculation means to the motor rotation speed of the assist motor; A counter electromotive voltage calculation means for calculating a counter electromotive voltage of the assist motor from a motor rotation speed calculated by the motor rotation speed calculation means; a voltage between the motor terminals detected by the voltage detection means between the motor terminals; Motor current estimation processing means for estimating the motor current of the assist motor from the difference from the counter electromotive voltage calculated by the electromotive voltage calculation means, and motor current integration by integrating the motor current estimated by the motor current estimation processing means Motor current integrating means for calculating a value, and the motor current integrating means An upper limit current value setting means for deriving and setting an upper limit current value from a predetermined relationship based on the motor current integrated value calculated by the above, an upper limit current value set by the upper limit current value setting means, and the motor current estimation Motor control amount setting means for setting the motor control amount by suppressing the feedback control amount based on the motor current estimated by the processing means; and the assist motor based on the motor control amount set by the motor control amount setting means. An electric power steering apparatus including motor driving means for driving is provided.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the motor control amount setting means sets the motor current estimated by the motor current estimation processing means by the upper limit current value setting means. A control amount suppression coefficient for suppressing the feedback control amount based on a current difference exceeding an upper limit current value is derived from a predetermined relationship, and the feedback control amount is multiplied by the control amount suppression coefficient to obtain a motor control amount. It is calculated and set.

  According to a third aspect of the present invention, in the electric power steering apparatus according to the first or second aspect, the target steering torque calculation processing means is based on a steering rudder angle detected by the steering rudder angle detecting means and the vehicle speed sensor. Self-aligning torque calculation means for calculating self-aligning torque based on the detected vehicle speed, and calculation of steering friction torque based on the angular speed detected by the steering angular speed calculation means and the vehicle speed detected by the vehicle speed sensor Friction torque calculating means for calculating the target steering torque by adding the friction torque calculated by the friction torque calculating means to the self-aligning torque calculated by the self-aligning torque calculating means. To do.

  According to the electric power steering apparatus of the first aspect, the motor current is estimated by the motor current estimation processing means from the back electromotive voltage calculated based on the steering angle and the voltage between the motor terminals, and the motor is obtained by integrating the motor current. Since the motor control amount is set by suppressing the feedback control amount by the motor control amount setting means from the upper limit current value derived from the integrated current value and the motor current, the heat generation of the assist motor is suppressed and the CPU or the like is thermally destroyed. Can be prevented.

  Since the motor current is estimated from the difference between the back electromotive voltage calculated based on the steering angle and the voltage between the motor terminals, the electric power steering is not required and the motor capacity is not increased. An increase in the size of the apparatus can be avoided.

  According to the electric power steering apparatus of the second aspect, the control amount suppression coefficient is derived from a predetermined relationship based on the current difference in which the motor current exceeds the upper limit current value, and is multiplied by the feedback control amount to control the motor. Therefore, it is possible to suppress heat generation more than necessary by the assist motor and prevent thermal destruction of the CPU or the like.

  According to the third aspect of the present invention, the target steering torque is obtained by adding the friction torque calculated based on the angular speed and the vehicle speed to the self-aligning torque calculated based on the steering angle and the vehicle speed. In particular, the friction torque is added so as to compensate for the self-aligning torque that is reduced at a low vehicle speed, and the influence of the tire friction on the road surface can be covered, so that a stable steering feeling can be realized at all times.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 shows a schematic rear view of the entire electric power steering apparatus 1 according to the present embodiment.

  In the electric power steering apparatus 1, a rack shaft 3 is accommodated in a substantially cylindrical rack housing 2 oriented in the left-right direction of the vehicle (corresponding to the left-right direction in FIG. 1) so as to be slidable in the left-right axis direction.

  Tie rods are connected to both ends of the rack shaft 3 projecting from the openings at both ends of the rack housing 2 via joints, respectively, and the tie rod is moved by the movement of the rack shaft 3, and the steered wheels of the vehicle are rotated via the steering mechanism. Steered.

A steering gear box 4 is provided at the right end of the rack housing 2.
In the steering gear box 4, an input shaft 5 connected via a joint to a steering shaft to which a steering wheel (not shown) is integrally attached is rotatably supported via a bearing. As shown, the input shaft 5 is connected to the steering pinion shaft 7 via the torsion bar 6 in the steering gear box 4 so as to be capable of relative twisting.

The helical teeth 7 a of the steering pinion shaft 7 are engaged with the rack teeth 3 a of the rack shaft 3.
Therefore, the steering force transmitted to the input shaft 5 by the turning operation of the steering wheel rotates the steering pinion shaft 7 via the torsion bar 6 and meshes with the helical teeth 7a of the steering pinion shaft 7 and the rack teeth 3a. The rack shaft 3 is slid in the left-right axis direction.

  The rack shaft 3 is pressed from behind by a rack guide 9 biased by a rack guide spring 8.

  An assist motor M is attached to an upper portion of the steering gear box 4, and a worm reduction mechanism 10 that decelerates the driving force of the assist motor M and transmits it to the steering pinion shaft 7 is configured in the steering gear box 4.

The worm speed reduction mechanism 10 is configured such that a worm wheel 11 fitted on the steering pinion shaft 7 is engaged with a worm 12 coaxially connected to a drive shaft of the assist motor M.
The driving force of the assist motor M is applied to the steering pinion shaft 7 via the worm reduction mechanism 10 to assist steering.

  Although not shown in FIG. 2, the assist motor M is provided with a motor terminal voltage detection device 27 for detecting the motor terminal voltages Vp and Vn, and the steering pinion shaft 7 has a steering rudder for detecting the steering rudder angle θ. An angle detection device 28 is provided.

A steering torque sensor 20 is provided further above the worm reduction mechanism 10.
The twist of the torsion bar 6 is converted into the movement of the core 21 in the axial direction, and the movement of the core 21 is changed into the inductance change of the coils 22 and 23 to detect the steering torque T.
A torque sensor that optically detects torsion of the torsion bar 6 may be used.

  A control board on which the control system CPU and the like of the steering torque control device 30 for assisting the steering force by driving and controlling the assist motor M as described above is accommodated in the steering gear box 4. .

A schematic block diagram of the steering torque control device 30 is shown in FIG.
The steering torque control device 30 includes a steering torque T detected by the steering torque sensor 20, a vehicle speed v detected by the vehicle speed sensor 25, a steering steering angle θ detected by the steering steering angle detection device 28, and a motor terminal voltage detection device 27. motor terminal voltage Vp is detected, Vn is input by, and data processing, and outputs the motor control amount D _M is the PWM control signal (duty signal) to the motor drive circuit 26, a motor drive circuit 26 is the PWM The assist motor M is driven according to the control signal.

  The steering torque control device 30 mainly includes a target steering torque calculation processing means 40, a feedback control amount calculation means 58, and a motor control amount setting means 59. In addition, a steering angular speed calculation means 50, a motor rotation speed calculation means 51 , Counter electromotive voltage calculation means 52, motor terminal voltage calculation means 53, motor current estimation processing means 54, motor current integration means 55, upper limit current value setting means 56, and the like.

The steering angular velocity calculation means 50 calculates the steering angular velocity ω by time-differentiating the steering angle θ detected by the steering angle detector 28.
Based on the steering angular velocity ω, the steering angle θ, and the vehicle speed v detected by the vehicle speed sensor 25, the target steering torque calculation processing means 40 calculates the target steering torque Tm.

The target steering torque calculation processing means 40 will be described with reference to FIGS.
FIG. 4 is a schematic block diagram of the target steering torque calculation processing means 40. As shown in FIG. 4, the target steering torque calculation processing means 40 includes two self-aligning torque calculation means 41 and friction torque calculation means 45. It consists of two computing means.

The self-aligning torque calculating unit 41 includes a self-aligning base torque extracting unit 42 and a self-aligning torque multiplication coefficient extracting unit 43.
The self-aligning base torque extracting means 42 is based on the steering angle θ from the self-aligning base torque (SABT) storage means 42a that stores the relationship of the self-aligning base torque with respect to the steering angle at the reference vehicle speed. To extract.

A relationship map of the self-aligning base torque Tsb with respect to the steering angle θ at the reference vehicle speed Vo stored in the self-aligning base torque storage means 42a is shown in the coordinates of FIG.
In FIG. 5, as for the steering angle θ on the horizontal axis, a positive value indicates a right steering angle (θ> 0), and a negative value indicates a left steering angle (θ <0).

Here, as for the self-aligning base torque Tsb on the vertical axis, the positive value is the right direction torque (Tsb> 0), the negative value is the left direction torque (Tsb <0), and the actual self-aligning torque ( This is the torque that the running wheel receives from the road surface, and is shown as the reaction force of the force that works to restore the running wheel to a straight running posture.
Therefore, for example, when the right steering angle θ (> 0) increases, the self-aligning base torque Tsb (> 0) in the right direction opposite to the actual direction increases.

  Another self-aligning torque multiplication coefficient extraction means 43 provided in the self-aligning torque calculation means 41 is changed from the self-aligning torque (SAT) multiplication coefficient storage means 43a for storing the self-aligning torque multiplication coefficient with respect to the vehicle speed to the vehicle speed v. Based on this, a self-aligning torque multiplication coefficient ks is extracted.

A relationship map of the self-aligning torque multiplication coefficient ks with respect to the vehicle speed v stored in the self-aligning torque multiplication coefficient storage means 43a is shown in the coordinates of FIG.
In FIG. 6, the value of the self-aligning torque multiplication coefficient ks increases as the vehicle speed v increases.
At the reference vehicle speed Vo, the self-aligning torque multiplication coefficient ks = 1.0.

The self-aligning torque calculating means 41 extracts the self-aligning base torque Tsb extracted by the self-aligning base torque extracting means 42 based on the steering angle θ, and the self-aligning torque multiplication coefficient extracting means 43 extracts based on the vehicle speed v. The self-aligning torque multiplication coefficient ks is multiplied by the multiplication means 44 to calculate the self-aligning torque Ts.
The self-aligning torque Ts is a self-aligning torque as a reaction force of the actual self-aligning torque.

  By multiplying the self-aligning base torque Tsb by the self-aligning torque multiplication coefficient ks, the self-aligning torque Ts decreases as the vehicle speed v becomes lower than the reference vehicle speed Vo, and the reference vehicle speed Vo. The larger it is, the more it will be amplified.

On the other hand, the friction torque calculation means 45 includes a friction base torque extraction means 46 and a friction torque multiplication coefficient extraction means 47.
The friction base torque extraction means 46 extracts the friction base torque Tfb based on the angular speed ω from the friction base torque (FBT) storage means 46a that stores the relationship of the friction base torque to the angular speed when the vehicle is stopped.

A relationship map of the friction base torque Tfb with respect to the angular speed ω at the time of stopping (vehicle speed v = 0) stored in the friction base torque storage means 46a is shown in the coordinates of FIG.
In FIG. 7, as for the angular velocity ω on the horizontal axis, a positive value indicates an angular velocity in the right direction (ω> 0), and a negative value indicates an angular velocity in the left direction (ω <0).

The friction base torque Tfb on the vertical axis indicates a right direction torque (Tfb> 0) as a positive value and a left direction torque (Tfb <0) as a negative value. ing.
Therefore, for example, when the angular velocity ω (> 0) in the right direction increases, the friction base torque Tfb (> 0) in the right direction opposite to the actual direction increases, and the torque is lower than the self-aligning base torque Tsb. It becomes almost constant.

  Another friction torque multiplication coefficient extraction means 47 provided in the friction torque calculation means 45 is a friction torque multiplication coefficient kf based on the vehicle speed v from the friction torque (FT) multiplication coefficient storage means 47a for storing the friction torque multiplication coefficient for the vehicle speed. To extract.

A relationship map of the friction torque multiplication coefficient kf with respect to the vehicle speed v stored in the friction torque multiplication coefficient storage means 47a is shown in the coordinates of FIG.
In FIG. 8, when the vehicle speed v = 0 (when the vehicle is stopped), the value of the friction torque multiplication coefficient kf is 1.0, and the value of the friction torque multiplication coefficient kf decreases as the vehicle speed v increases from when the vehicle stops. The value is almost constant (about 0.5) from around / h.

The friction torque calculation means 45 multiplies the friction base torque Tfb extracted by the friction base torque extraction means 46 based on the angular velocity ω by the friction torque multiplication coefficient kf extracted by the friction torque multiplication coefficient extraction means 47 based on the vehicle speed v. Multiply by means 48 to calculate the friction torque Tf.
The friction torque Tf is a friction torque as a reaction force of the actual friction torque.

  By multiplying the friction base torque Tfb by the friction torque multiplication coefficient kf, the friction torque Tf gradually decreases until the vehicle speed v is about 20 km / h, and is substantially halved after about 20 km / h. The state continues.

  The self-aligning torque Ts calculated by the self-aligning torque calculating means 41 and the friction torque Tf calculated by the friction torque calculating means 45 are added by the adding means 49 to calculate the target steering torque Tm.

  The self-aligning torque Ts decreases particularly at low vehicle speeds, but the friction torque Tf exhibits a relatively large value so as to compensate for this at low vehicle speeds. Therefore, the friction torque Tf is added to the self-aligning torque Ts. The effect of tire friction on the road surface that appears greatly at low vehicle speeds can be compensated.

FIG. 9 is a flowchart showing a processing procedure until the above target steering torque Tm is calculated.
First, the steering angle θ detected by the steering angle detection means 55 is read (step 1), the angular speed ω is calculated by the angular speed calculation means 56 (step 2), and the vehicle speed v detected by the vehicle speed sensor 25 is read (step 3). .

  Next, the self-aligning base torque extraction means 42 extracts the self-aligning base torque Tsb based on the steering angle θ (step 4), and the self-aligning torque multiplication coefficient extraction means 43 extracts the self-aligning torque multiplication coefficient based on the vehicle speed v. ks is extracted (step 5), and the self-aligning base torque Tsb is multiplied by the self-aligning torque multiplication coefficient ks to calculate the self-aligning torque Ts (step 6).

  Next, the friction base torque extraction means 46 extracts the friction base torque Tfb based on the angular velocity ω (step 7), and the friction torque multiplication coefficient extraction means 47 extracts the friction torque multiplication coefficient kf based on the vehicle speed v (step 8). ), The friction torque Tf is calculated by multiplying the friction base torque Tfb by the friction torque multiplication coefficient kf (step 9).

In step 10, the target steering torque Tm is calculated by adding the friction torque Tf to the self-aligning torque Ts.
The processes of the above steps are repeatedly executed.

  With respect to the target steering torque Tm thus calculated, a deviation ΔT (= Tm−T) from the steering torque T detected by the steering torque sensor 20 is calculated by the subtracting means 57 with reference to FIG. Input to means 58.

  The feedback control amount calculation means 58 includes PI (proportional / integral) control means and PWM control signal generation means, and the PI control means uses P (proportional) in order to obtain the target steering torque Tm by setting the deviation ΔT to 0 from the deviation ΔT. ) The optimum control amount of feedback is calculated by combining the operation and the I (integration) operation, and the optimum control amount is converted into the feedback duty Dfb of the PWM control duty by the PWM control signal generating means and output.

On the other hand, the motor current estimated value _IM is estimated and calculated based on the steering angular velocity ω calculated by the steering angular velocity calculating means 50 and the motor terminal voltages Vp and Vn detected by the motor terminal voltage detector 27. The processing procedure will be described with reference to the flowchart of FIG.

First, the steering angular velocity ω is read (step 21), and the motor terminal voltages Vp and Vn are read (step 22).
Then, the motor terminal voltage V _T (= Vp−Vn) is calculated from the motor terminal voltages Vp and Vn by the motor terminal voltage calculation means 53 (step 23), and then the calculated motor terminal voltage V _T is low-pass filtered. Process (step 24).

In the next step 25, the motor rotation speed ω _M is calculated by the motor rotation speed calculation means 51 from the steering angular speed ω read in step 21.
The motor rotation speed ω _M (= ω / p) is calculated by dividing the steering angular speed ω by the reduction ratio p of the worm reduction mechanism 10.

In step 26, it calculates the counter electromotive voltage V _M of the assist motor M by the counter electromotive voltage calculating unit 52 from the motor rotation speed omega _M.
The counter electromotive voltage V _M (= ω _M × k _E ) is calculated by multiplying the motor rotational speed ω _M by the induced voltage constant k _E.

Then, the motor terminal voltage V _T and the counter electromotive voltage V assist from the difference between the _M motor M of execution voltage V (= V T _{-V M)} is calculated by the motor current estimation processing unit 54 (step 27), the execution The voltage V is divided by the motor internal resistance Rm of the assist motor M, and a motor current estimated value I _M (= V / Rm) is estimated and calculated (step 28).

Feedback duty Dfb that the feedback control amount calculation means 58 is calculated, are suppressed calculation as necessary based on the motor current estimated value I _M, the motor control amount D _{M (PMW} control signal for driving and controlling the assist motor M Duty D _M ) is determined.

The motor control amount D _M will be described with reference to a flowchart of FIG. 11 the procedures set process.
First, the motor current integral Is is calculated according to the following equation by the motor current integration means 55 based on the motor current estimated value I _M in step 31.
Is (n) = Is (n−1) + (I _M −If) ²
Here, If is a motor current integration reference value.

The main loss of the motor during operation is copper loss, which is the square of the armature current (motor current) multiplied by the armature resistance. Therefore, the integrated value of the square of the motor current estimated value I _M is obtained by the above equation.
Each time this motor control amount setting routine is repeated, (I _M −If) ² is sequentially added to the previous value Is (n−1) to calculate the current value Is (n), which is the motor current integrated value Is. .

In step 32, the upper limit current value _IL is calculated from the motor current integrated value Is by the upper limit current value setting means 56.
Upper limit current value setting means 56 is provided with a function f to derive the upper limit current value I _L from the motor current integral Is, the upper limit by calculating putting the motor current integral Is the same function f previously determined A current value _IL is derived.

Figure 12 is a representation of the same function in the coordinate indicates the upper limit current value I _L motor current integral Is, the vertical axis on the horizontal axis.
Function curve shown in Figure 12, the motor current estimated value I _M is indicates the current value of the upper limit there is a risk of thermal destruction of the CPU or the like by the heat generation of the motor exceeds the upper limit current value I _L, determined in advance appropriate Keep it.

Next, the function limit determined by f current value I _L and the motor current estimated value I _M and the inhibition of the feedback control amount Dfb by the motor control amount setting means 59 based on is made, first, in step 33, A current difference ΔI (= I _M −I _L ) is obtained from the upper limit current value I _L obtained by the function f and the motor current estimated value I _M.

In step 34, a control amount suppression coefficient q is derived from a predetermined relationship based on the current difference ΔI.
FIG. 13 shows the relationship of the control amount suppression coefficient q with respect to the current difference ΔI.
That is, when ΔI ≦ 0, the control amount suppression coefficient q is always 1.0, and when ΔI> 0, the control amount suppression coefficient q decreases as the current difference ΔI increases.

In the next step 35, a motor control amount D _M (= Dfb × q) is calculated and set by multiplying the feedback control amount Dfb calculated by the feedback control amount calculation means 58 by the control amount suppression coefficient q.

Thus the motor control amount D _M that is set by the motor control amount setting means 59, (0 ΔI ≦) when the motor current estimated value I _M does not exceed the upper limit current value I _L, the control amount suppression coefficient q = 1.0 Since without feedback control quantity Dfb is suppressed, is a motor control amount D _M as it is, when the motor current estimated value I _M exceeds the upper limit current value I _L (ΔI> 0), the feedback control by the control amount controlling factor q <1.0 the amount Dfb is a motor control amount D _M with suppressed.

As it is also the current difference ΔI is large motor current estimated value I _M exceeds the upper limit current value I _L, the amount of suppressor for suppressing a feedback control amount Dfb also large.
The motor control amount D _M is the duty of the PWM control signal for driving and controlling the assist motor M.

That is, the duty D _M of the PMW control signal is output to the motor driving circuit 26, a motor driving circuit 26, the voltage V _B × D _M in accordance with the duty of the PWM control signal is applied to the assist motor M assist motor M To assist the steering force.

As described above, the motor current estimated value I _M until exceeds the upper limit current value I _L, since the influence of heat generation of the assist motor M is no concern, the assist motor M feedback control amount Dfb as the motor control amount D _M as had been driving control, when the motor current estimated value I _M is a risk of thermal destruction of the CPU or the like by the heat generation of the motor exceeds the upper limit current value I _L, the motor control amount D _M which suppresses feedback control amount Dfb By controlling the driving of the assist motor M, the heat generation of the assist motor M can be suppressed and the thermal destruction of the CPU or the like can be prevented.

Since the estimated motor current value I _M is estimated from the difference (execution voltage V) between the back electromotive voltage V _M calculated based on the steering angle θ and the motor terminal voltage V _T , a motor current detection device is not required. In addition, an increase in the size of the electric power steering device can be avoided without increasing the capacity of the motor.

  Further, in the present steering torque control device 30, the target steering torque calculation processing means 40 adds the friction torque Tf calculated by the friction torque calculation means 45 to the self-aligning torque Ts calculated by the self-aligning torque calculation means 41. Since the target steering torque Tm is obtained, the friction torque Tf compensates for the self-aligning torque Ts, which is particularly small at low vehicle speeds, and is always stable, covering the effects of tire friction on the road surface that appears at low vehicle speeds. The steering feeling can be realized.

1 is a schematic rear view of an entire electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing which shows the structure in a steering gear box. It is a schematic block diagram of a steering torque control device. It is a schematic block diagram of a target steering torque calculation processing means. It is a figure which shows the relationship map of the self-aligning base torque Tsb with respect to the steering angle (theta) in a reference | standard vehicle speed by a coordinate. It is a figure which shows the relationship map of the self-aligning torque multiplication coefficient ks with respect to the vehicle speed v by a coordinate. It is a figure which shows the relationship map of friction base torque Tfb with respect to angular velocity (omega) at the time of a stop by a coordinate. It is a figure which shows the relationship map of the friction torque multiplication coefficient kf with respect to the vehicle speed v by a coordinate. It is a flowchart which shows the calculation process sequence of target steering torque. It is a flowchart which shows the process sequence by which the motor current estimated value _IM is estimated and calculated. . It is a flowchart illustrating a procedure for setting processing of the motor control amount D _M. Is a diagram showing a predetermined relationship between the upper limit current value I _L to the motor current integral Is. It is a figure which shows the predetermined relationship of the controlled variable suppression coefficient q with respect to electric current difference (DELTA) I.

Explanation of symbols

M: Assist motor, 1 ... Electric power steering device, 2 ... Rack housing, 3 ... Rack shaft, 4 ... Steering gear box, 5 ... Input shaft, 6 ... Torsion bar, 7 ... Steering pinion shaft, 8 ... Rack guide spring, DESCRIPTION OF SYMBOLS 9 ... Rack guide, 10 ... Worm deceleration mechanism, 11 ... Worm wheel, 12 ... Worm, 20 ... Steering torque sensor, 21 ... Core, 22, 23 ... Coil, 25 ... Vehicle speed sensor, 26 ... Motor drive circuit, 27 ... Motor Terminal voltage detector, 28 ... Steering angle detector,
30 ... Steering torque control device,
40 ... Target steering torque calculation processing means, 41 ... Self-aligning torque calculation means, 42 ... Self-aligning base torque extraction means, 42a ... Self-aligning base torque storage means, 43 ... Self-aligning torque multiplication coefficient extraction means, 43a ... Self-aligning torque multiplication coefficient storage means 44 ... Multiplication means 45 ... Friction torque calculation means 46 ... Friction base torque extraction means 46a ... Friction base torque storage means 47 ... Friction torque multiplication coefficient extraction means 47a ... Friction Torque multiplication coefficient storage means, 48 ... multiplication means, 49 ... addition means,
50: Steering angular velocity calculating means, 51 ... Motor rotational speed calculating means, 52 ... Back electromotive force calculating means, 53 ... Motor terminal voltage calculating means, 54 ... Motor current estimation processing means, 55 ... Motor current integrating means, 56 ... Upper limit Current value setting means,
57 ... subtracting means, 58 ... feedback control amount calculating means, 59 ... motor control amount setting means.

Claims (3)

In the electric power steering device in which the driving force of the assist motor assists the steering force,
A torque sensor for detecting steering torque;
A vehicle speed sensor for detecting the vehicle speed;
Steering angle detection means for detecting the steering angle of the steering;
Motor terminal voltage detection means for detecting the terminal voltage of the assist motor;
Target steering torque calculation processing means for deriving a target steering torque based on the steering angle detected by the steering angle detection means and the vehicle speed detected by the vehicle speed sensor;
Feedback control amount calculation means for calculating a feedback control amount based on a difference between the target steering torque calculated by the target steering torque calculation means and the steering torque detected by the torque sensor;
Steering angular velocity calculating means for calculating a steering angular velocity by differentiating the steering angle detected by the steering angle detection means with respect to time;
Motor rotation speed calculation means for converting the steering angular speed calculated by the steering angular speed calculation means into the motor rotation speed of the assist motor;
Back electromotive force calculation means for calculating a back electromotive voltage of the assist motor from the motor rotation speed calculated by the motor rotation speed calculation means;
Motor current estimation processing means for estimating the motor current of the assist motor from the difference between the motor terminal voltage detected by the motor terminal voltage detection means and the counter electromotive voltage calculated by the counter electromotive voltage calculation means;
Motor current integration means for calculating a motor current integrated value by integrating the motor current estimated by the motor current estimation processing means;
Upper limit current value setting means for deriving and setting the upper limit current value from a predetermined relationship based on the motor current integrated value calculated by the motor current integrating means;
Motor control amount setting means for setting the motor control amount by suppressing the feedback control amount based on the upper limit current value set by the upper limit current value setting means and the motor current estimated by the motor current estimation processing means;
An electric power steering apparatus comprising: motor driving means for driving the assist motor based on a motor control amount set by the motor control amount setting means. The motor control amount setting means includes
A control amount suppression coefficient that suppresses the feedback control amount is predetermined based on a current difference in which the motor current estimated by the motor current estimation processing unit exceeds the upper limit current value set by the upper limit current value setting unit. Derived from the relationship,
2. The electric power steering apparatus according to claim 1, wherein a motor control amount is calculated and set by multiplying the feedback control amount by the control amount suppression coefficient. The target steering torque calculation processing means includes:
Self-aligning torque calculating means for calculating self-aligning torque based on the steering angle detected by the steering angle detecting means and the vehicle speed detected by the vehicle speed sensor;
Friction torque calculation means for calculating the friction torque of the steering based on the angular speed detected by the steering angular speed calculation means and the vehicle speed detected by the vehicle speed sensor;
3. The target steering torque is calculated by adding the friction torque calculated by the friction torque calculation means to the self-aligning torque calculated by the self-aligning torque calculation means. Electric power steering device.

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