JP2007008292A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device allowing a driver to acquire the road information intuitively and approximately accurately by reflecting the road surface situation on the steering feeling to an appropriate degree. <P>SOLUTION: The electric power steering device is equipped with a target steering torque calculating means 40 to obtain the target steering torque Tm on the basis of the steering angle θ and the vehicle speed v, a rack thrust force presuming means 55 etc. to presume the rack thrust force F from the difference between the back electromotive voltage V<SB>M</SB>of an assist motor calculated from the steering angle θ and the inter-terminal voltage V<SB>T</SB>of the motor, and a road surface load correction factor calculating means 56 to obtain a road surface load correction factor K<SB>L</SB>on the basis of the rack thrust force F, the steering angle θ, and the vehicle speed v, whereby the target steering torque Tm is corrected on the basis of the road surface load correction factor K<SB>L</SB>, and the feedback control amount Dfb is calculated on the basis of the difference between the corrected target steering torque Tms and the steering torque T, and the assist motor M is driven on the basis of the feedback control amount Dfb. <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.
As the steering mechanism, a rack and pinion type power transmission mechanism is generally adopted in which a steering force is transmitted from the pinion to the rack shaft, and the movement of the rack shaft steers the steered wheels via the tie rods.
In addition, there is a power transmission mechanism that moves the rack shaft by a ball screw mechanism.

In such a power transmission mechanism, the rack shaft load (rack thrust) balances with the reaction force received from the road surface, which reflects the road surface condition.
That is, when the friction coefficient is large such as a dry paved road surface, the rack shaft load is large. However, when the friction coefficient such as a frozen road surface is small, the rack shaft load is small.

  An example of capturing this change in road surface condition as a change in rack shaft load and controlling the steering resistance to increase as the change in rack shaft load increases so that the change in road surface condition does not affect the steering feeling (See Patent Document 1).

Japanese Patent Laid-Open No. 11-49000

  Therefore, the driver cannot detect the change in the road surface condition in the steering operation, and cannot obtain the road information intuitively and substantially accurately even if the road information can be obtained indirectly by visual or auditory sense. .

  The present invention has been made in view of the above points, and the object of the present invention is that the driver can obtain road information intuitively and substantially accurately by appropriately reflecting the road surface condition on the steering feeling. An electric power steering device is provided.

  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 the steering angle of the steering, a motor terminal voltage derivation means for deriving the inter-terminal voltage of the assist motor, a steering angle detected by the steering angle detection means, and the vehicle speed sensor Target steering torque calculation processing means for deriving a target steering torque based on the vehicle speed, steering angular speed calculation means for calculating a steering angular speed by differentiating the steering angle detected by the steering angle detection means with respect to time, and Assists the steering angular velocity calculated by the steering angular velocity calculation means Motor rotation speed calculation means for converting the motor rotation speed of the motor, back electromotive force calculation means for calculating a counter electromotive voltage of the assist motor from the motor rotation speed calculated by the motor rotation speed calculation means, and the motor terminal Motor torque estimating means for estimating motor torque from the difference between the motor terminal voltage derived by the inter-voltage deriving means and the counter electromotive voltage calculated by the counter electromotive voltage calculating means, and estimated by the motor torque estimation calculating means. Rack thrust estimation means for estimating the rack thrust from the motor torque, the rack thrust estimated by the rack thrust estimation calculation means, the steering angle detected by the steering angle detection means, and the vehicle speed detected by the vehicle speed sensor A road load correction coefficient calculating means for deriving a road load correction coefficient, and the road load correction coefficient calculating means. A corrected target steering torque calculating means for correcting the target steering torque calculated by the target steering torque calculating means based on a road surface load correction coefficient to calculate a corrected target steering torque, and a correction calculated by the corrected target steering torque calculating means Feedback control amount calculation means for calculating a feedback control amount based on the difference between the target steering torque and the steering torque detected by the torque sensor, and the assist based on the feedback control amount calculated by the feedback control amount calculation means The electric power steering apparatus includes a motor driving unit that drives the motor.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the road surface load correction coefficient calculating means corrects the target steering torque based on the rack thrust estimated by the rack thrust estimating means. A correction coefficient is extracted from a predetermined relationship, a vehicle speed correction coefficient is extracted from a predetermined relationship based on the vehicle speed detected by the vehicle speed sensor, and based on the steering angle detected by the steering angle detection means A steering angle correction coefficient is extracted from a predetermined relationship, and the road load correction coefficient is derived by multiplying the reference road load correction coefficient by the vehicle speed correction coefficient and the steering angle correction coefficient. .

  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 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 target steering torque is corrected based on the road surface load correction coefficient calculated from the rack thrust reflecting the road surface condition, and the corrected target steering torque and the detected steering torque are Since the assist motor is feedback-controlled based on the difference, the road surface condition can be reflected in the steering feeling even with feedback control based on the target steering torque and detected steering torque based on the steering angle and vehicle speed. Information can be obtained intuitively and substantially accurately, and driving can be performed while appropriately detecting changes in road surface conditions during steering operation.

  According to the electric power steering apparatus of the second aspect, the road surface load correction coefficient calculating means extracts a reference road surface load correction coefficient for correcting the target steering torque based on the estimated rack thrust from a predetermined relationship. Since the road load correction coefficient is derived by multiplying the standard road load correction coefficient by the vehicle speed correction coefficient based on the vehicle speed and the steering angle correction coefficient based on the rudder angle, the target steering torque is calculated by the road load correction coefficient taking into account the vehicle speed and the steering angle. Since correction and feedback control are performed, the road surface condition can be appropriately reflected in the steering feeling in accordance with the traveling state.

  According to the electric power steering apparatus of the third aspect, the target steering torque is obtained by adding the friction torque calculated based on the angular velocity and the vehicle speed to the self-aligning torque calculated based on the steering angle and the vehicle speed. In particular, friction torque is added to compensate for the self-aligning torque that decreases at low vehicle speeds, and the effects of tire friction on the road surface are covered while the road surface condition is appropriately reflected in the steering feeling, so that the steering wheel is always stable. A ring can be realized.

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 on both ends of the rack housing 2 via joints, the tie rods are 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 detecting device 27 for detecting the motor terminal voltages Vp and Vn, and the steering pinion shaft 7 detects the steering 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 a control system CPU and the like of the steering torque control device 30 that drives and controls the assist motor M as described above to assist the steering force is mounted 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 angle θ detected by the steering angle detector 28, and a motor terminal voltage detector 27. The motor terminal voltages Vp and Vn detected by the above are input and processed, and the motor feedback control amount Dfb, which is a PWM control signal (duty signal, etc.), is output to the motor drive circuit 26. The motor drive circuit 26 The assist motor M is driven according to the PWM control signal.
The motor drive circuit 26 and the motor terminal voltage detection device 27 may be provided on the steering torque control device 30 side.

  The steering torque control device 30 mainly includes a target steering torque calculation processing means 40, a corrected target steering torque calculation means 57, and a feedback control amount calculation means 59. In addition, a steering angular speed calculation means 50, a motor rotation speed calculation means. 51, back electromotive voltage calculation means 52, motor terminal voltage calculation means 53, motor torque estimation means 54, rack thrust estimation means 55, road load correction coefficient calculation 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 obtains the 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. 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 rudder angle detection means 28 is read (step 1), the angular speed ω is calculated by the angular speed calculation means 50 (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.

  On the other hand, the rack thrust force F 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. This 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 rotational speed ω _M (= ω × N) is calculated by multiplying the steering angular speed ω by the reduction ratio N (> 1) of the worm reduction mechanism 10.

In step 26, 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 torque estimating means 54, the low-pass filtering 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 (Step 27 ), The execution voltage V is divided by the motor internal resistance Rm of the assist motor M, and multiplied by the torque constant k _T to estimate and calculate the motor torque T _M (= (V / Rm) × k _T ) (step) 28).

When the motor torque T _M is estimated, the rack thrust estimation means 55 estimates and calculates the rack thrust F from the motor torque T _{M according} to the following equation (basic equation applied to the rack and pinion type electric power steering device) ( Step 29).
F = T _M × 2π × N / ST
Here, N is a reduction ratio of the worm reduction mechanism 10, and ST is a specific stroke.

Rack thrust F thus estimated reflects the status of the road surface, seeking road load correction factor K _L from the rack thrust F, the procedure for correcting the target steering torque Tm by the road load correction factor K _L Will be described with reference to the flowchart of FIG.

First, thereby determining said rack thrust F and the vehicle speed v and on the basis of the steering angle θ road load correction factor K _L by road load modification coefficient calculation unit 56.
In step 31, extracting a reference road load correction coefficient k _F from a predetermined relationship based on the rack thrust F.
The relation map of the reference road surface load correction coefficient k _F for the rack thrust F, shown in FIG. 12.

Reference road load correction coefficient k _F as 1.0 when the rack thrust force F is zero, after gradually increased from 1.0 in accordance with the rack thrust F is increased, somewhat increase the rate of rise, a relationship curve again becomes gradual rise Draw.
Namely, road surface shows a reference road load correction coefficient k _F is smaller as slippery and frozen (low friction coefficient), it shows a larger value as the friction coefficient increases.
A reference road load correction coefficient kF corresponding to the estimated rack thrust _F is extracted from the relationship map.

In the next step 32, extracting a vehicle speed correction coefficient r _v from a predetermined relationship based on the vehicle speed v of the vehicle speed sensor 25 has detected.
The relation map of the vehicle speed correction coefficient r _v for the vehicle speed v, shown in FIG. 13.
Vehicle speed correction coefficient r _v is the vehicle speed v indicates 1.0 when 0, approaching the final constant value and gradually increases in accordance with the vehicle speed v increases.

Further, in the next step 33, a steering angle correction coefficient _rθ is extracted from a predetermined relationship based on the steering angle θ detected by the steering angle detection device 28.
FIG. 14 shows a relationship map of the steering angle correction coefficient r _θ with respect to the steering angle θ.
The steering angle correction coefficient r _theta, steering angle theta indicates 1.0 when 0, approaching the final constant value slightly decreased rapidly to the steering angle theta increases.

Then, in step 34, the reference road load correction coefficient k _F extracted in step 31 is corrected by multiplying the vehicle speed correction coefficient r _v and the steering angle correction coefficient r _theta extracted in step 32, the road surface load A correction coefficient K _L (= k _F × r _v × r _θ ) is calculated.

The road load correction factor K _L as a reference value the reference road load correction coefficient k _F extracted from the estimated rack thrust F, a coefficient obtained by adding a correction based on the vehicle speed v and the steering angle theta, basically The smaller the friction coefficient of the road surface, the smaller the value, and the larger the value, the larger the value.

Road load correction factor K _L thus calculated is subjected to low-pass filtered in step 35, so as not to shift smoothly to suppress the fluctuation in a short time.
In step 36, the low-pass filtering road load correction factor K _L was made by the corrected target steering torque computing means 57, by multiplying the target steering torque target steering torque Tm to the arithmetic processing unit 40 has determined corrected Then, the corrected target steering torque Tms (= Tm × K _L ) is calculated.

Accordingly, the target steering torque Tm is modified to the value suppressed as the road friction coefficient is smaller by road load correction factor K _L, are largely corrected greater the friction coefficient of the road surface.
As shown in FIG. 3, the corrected target steering torque Tms corrected in this way is calculated as a deviation ΔT (= Tms−T) from the steering torque T detected by the steering torque sensor 20 by the subtracting means 58, and the feedback control amount. It is input to the calculation means 59.

  The feedback control amount calculating means 59 is composed of PI (proportional / integral) control means and PWM control signal generating means. The PI control means sets 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.

  The feedback duty Dfb of the PWM control signal is output to the motor drive circuit 26, and the motor drive circuit 26 applies the motor drive voltage according to the duty of the PWM control signal to the assist motor M to drive the assist motor M and steer. Assist the power.

As described above, the target steering torque Tm when the assist motor M is feedback control of the steering torque is corrected by the road load correction factor K _L, is corrected to the value suppressed as low coefficient of friction of the road surface, the road surface The larger the friction coefficient is, the larger the correction is made. Therefore, when driving on a freezing and slippery road surface, the driver's steering operation becomes lighter, and when driving on a dry road surface, the steering operation becomes slightly heavier.

  Therefore, the road surface condition can be reflected in the steering feeling, the driver can obtain road information intuitively and substantially accurately, and the driver can drive while appropriately detecting the change of the road surface condition in the steering operation. it can.

Since the control feedback by modifying the target steering torque by the vehicle speed v road load corrected considering and steering angle θ coefficient K _L, the road conditions can be appropriately reflected in the steering feeling in accordance with the running state.

  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 self-aligning torque Ts, which is reduced particularly at low vehicle speeds, is supplemented by the friction torque Tf, and the road surface condition appears on the road surface which appears greatly at low vehicle speeds while appropriately reflecting the road surface condition to the steering feeling. Covering the effects of tire friction, etc., a stable steering feeling can be achieved at all times.

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 which estimates and calculates a rack thrust. It is a flowchart illustrating a procedure for processing to correct the calculated target steering torque to a road surface load correction factor K _L. It is a diagram showing a predetermined relation map of the reference road surface load correction coefficient k _F for rack thrust F. It is a diagram showing a predetermined relation map of the vehicle speed correction coefficient r _v for the vehicle speed v. It is a figure which shows the predetermined relationship map of the steering angle correction coefficient r ( _theta) with respect to the steering angle ( _theta ).

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 torque estimating means, 55 ... Rack thrust estimating means, 56 ... Road load Correction coefficient calculation means 57... Correction target steering torque calculation means 58. Subtraction means 59. Feedback control amount calculation 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 deriving means for deriving 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;
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 torque estimating means for estimating motor torque from the difference between the motor terminal voltage derived by the motor terminal voltage deriving means and the counter electromotive voltage calculated by the counter electromotive voltage calculating means;
Rack thrust estimation means for estimating rack thrust from the motor torque estimated by the motor torque estimation calculation means;
Road load correction coefficient calculation means for deriving a road load correction coefficient based on the rack thrust estimated by the rack thrust estimation calculation means, the steering angle detected by the steering angle detection means, and the vehicle speed detected by the vehicle speed sensor;
Modified target steering torque calculating means for correcting the target steering torque calculated by the target steering torque calculating means based on the road load correction coefficient calculated by the road load correction coefficient calculating means and calculating a corrected target steering torque;
Feedback control amount calculating means for calculating a feedback control amount based on a difference between the corrected target steering torque calculated by the corrected target steering torque calculating means and the steering torque detected by the torque sensor;
Motor driving means for driving the assist motor based on the feedback control amount calculated by the feedback control amount calculating means;
An electric power steering apparatus comprising: The road surface load correction coefficient calculating means is
A reference road load correction coefficient for correcting the target steering torque based on the rack thrust estimated by the rack thrust estimating means is extracted from a predetermined relationship.
The vehicle speed correction coefficient is extracted from a predetermined relationship based on the vehicle speed detected by the vehicle speed sensor,
Extracting from a predetermined relationship a steering angle correction coefficient based on the steering angle detected by the steering angle detection means,
2. The electric power steering apparatus according to claim 1, wherein the road load correction coefficient is derived by multiplying the reference road load correction coefficient by the vehicle speed correction coefficient and the steering angle correction coefficient. The target steering torque calculation processing means calculates self-aligning torque based on the steering angle detected by the steering angle detection means and the vehicle speed detected by the vehicle speed sensor; Self-aligning calculated by the self-aligning torque calculating means, comprising: friction torque calculating means for calculating steering friction torque based on the angular speed detected by the steering angular speed calculating means and the vehicle speed detected by the vehicle speed sensor 3. The electric power steering apparatus according to claim 1, wherein the target steering torque is calculated by adding the friction torque calculated by the friction torque calculating means to the torque.

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