JP4698321B2 - Electric power steering device - Google Patents

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 apparatus disclosed in Patent Document 1, the control unit ECU derives a 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

  In the electric power steering apparatus in which the feedback control of the steering torque is performed in this way, when the steering is turned into a state of letting it off while traveling, the detected steering torque becomes substantially zero, so that the deviation from the target steering torque In addition to the large amount of control, the self-aligning torque that the running wheel receives from the road surface is added, and the return speed of the steering may become higher than necessary.

  The present invention has been made in view of the above points, and the object of the present invention is to limit the control amount of the electric motor in a state where the steering is almost released and to avoid an excessive steering return speed. 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, Steering steering angle detection means for detecting a steering steering angle; target steering torque calculation processing for deriving a target steering torque based on the steering steering angle detected by the steering steering angle detection means and the vehicle speed detected by the vehicle speed sensor Means, a 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, and the steering angle detection Steering angle detected by the vehicle and the vehicle speed sensor The return upper limit output deriving means for deriving the return upper limit output of the assist motor based on the vehicle speed detected by the vehicle, and the feedback control amount calculating means calculated by the feedback control amount calculating means when it is determined that the steering is in a substantially released state. The electric power steering apparatus includes output limiting processing means for limiting the output to a return upper limit output or less derived by the upper limit output deriving means.

The invention according to claim 2
2. The electric steering apparatus according to claim 1, wherein the return upper limit power deriving unit is a steering rudder angle detected by the steering rudder angle detecting unit based on a preset relationship map of a base return upper limit steering angular velocity with respect to a steering rudder angle. A base return upper limit steering angular speed extraction means for extracting a base return upper limit steering angular speed according to the vehicle speed, and a base return upper limit steering angular speed extracted by the base return upper limit steering angular speed extraction means based on the vehicle speed detected by the vehicle speed sensor. Return upper limit motor angular speed calculation means for converting to a return upper limit motor angular speed, and return upper limit output calculation means for converting a return upper limit motor angular speed calculated by the return upper limit motor angular speed calculation means into a return upper limit output To do.

  According to a third aspect of the present invention, in the electric power steering apparatus according to the second aspect, the return upper limit motor angular speed calculating means is a vehicle speed detected by the vehicle speed sensor based on a preset relationship map of a vehicle speed correction coefficient with respect to the vehicle speed. Vehicle speed correction coefficient extracting means for extracting a vehicle speed correction coefficient corresponding to the vehicle speed correction coefficient, and multiplying the base return upper limit steering angular speed extracted by the base return upper limit steering angular speed extraction means by the vehicle speed correction coefficient extracted by the vehicle speed correction coefficient extraction means. Then, a return upper limit steering angular velocity is calculated, and the return upper limit steering angular velocity is multiplied by a reduction ratio to be converted into a return upper limit motor angular velocity.

  According to a fourth aspect of the present invention, in the electric power steering apparatus according to any one of the first to third aspects, the target steering torque calculation processing means is a steering rudder angle detected by the steering rudder angle detecting means. And self-aligning torque calculating means for calculating self-aligning torque based on the vehicle speed detected by the vehicle speed sensor, steering based on the angular speed detected by the steering angular speed calculating means and the vehicle speed detected by the vehicle speed sensor. Friction torque calculating means for calculating the friction torque of the engine, and 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 And features.

  According to the electric power steering apparatus of the first aspect, the return upper limit output of the assist motor is derived based on the steering angle and the vehicle speed, and the output of the feedback control amount is limited to the return upper limit output or less, so that the steering is substantially omitted. It is possible to avoid an excessive steering return speed by restricting the control amount of the electric motor when it is in the released state.

  According to the electric power steering apparatus according to claim 2, the base return upper limit steering angular velocity corresponding to the steering rudder angle is extracted based on a preset relation map, corrected based on the vehicle speed, converted to a return upper limit motor angular velocity, Since the return upper limit output is calculated by converting the return upper limit motor angular velocity, it is possible to reliably limit the control amount of the electric motor below the desired return upper limit output.

  According to the electric power steering apparatus of the third aspect, the vehicle speed correction coefficient for correcting the base return upper limit steering angular speed based on the vehicle speed is extracted based on a preset relationship map of the vehicle speed correction coefficient with respect to the vehicle speed. The steering angular velocity is appropriately corrected to the vehicle speed, and a more ideal return upper limit output can be obtained.

  According to the electric power steering apparatus of the fourth aspect, 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. Therefore, friction torque is added to compensate for the self-aligning torque that becomes smaller especially at low vehicle speeds, and the effect of tire friction on the road surface is covered while reflecting the road surface condition in feedback control, providing a stable steering feeling at all times. 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 (coincident with 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 steering pinion shaft 7 is provided with a steering angle detector 29 that detects the steering angle θ.

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 receives the steering torque T detected by the steering torque sensor 20, the vehicle speed v detected by the vehicle speed sensor 25, and the steering angle θ detected by the steering angle detector 29, and performs data processing. Te, and outputs a PWM control signal the motor of the feedback control amount D _M is (duty signal) to the motor drive circuit 26, a motor drive circuit 26 drives the assist motor M according to the PWM control signal.
The motor drive circuit 26 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 feedback control amount calculation means 57, and an output restriction processing means 58. In addition, a steering angular speed calculation means 50 and a return upper limit output derivation means 51 have.
The return upper limit output deriving means 51 includes a base return upper limit steering angular speed extraction means 52, a vehicle speed correction coefficient extraction means 53, a return upper limit motor angular speed calculation means 54, and a return upper limit output duty calculation means 55.

The steering angular velocity calculation means 50 calculates the steering angular velocity ω by time differentiation of the steering angle θ detected by the steering angle detector 29.
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 to the steering angle at the reference vehicle speed. Torque Tsb is extracted.

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 is based on 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 is based on the vehicle speed v. Multiplication means 44 multiplies the extracted self-aligning torque multiplication coefficient ks to calculate 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 steering angle detector 29 is read (step 1), the angular velocity ω is calculated by the angular velocity calculator 50 (step 2), and the vehicle speed v detected by the vehicle speed sensor 25 is read (step 2). 3).

  Next, the self-aligning base torque extracting means 42 extracts the self-aligning base torque Tsb based on the steering angle θ (step 4), and the self-aligning torque multiplication coefficient extracting means 43 extracts the self-aligning torque based on the vehicle speed v. The coefficient ks is extracted (step 5), and the self-aligning torque Ts is calculated by multiplying the self-aligning base torque Tsb by the self-aligning torque multiplication coefficient ks (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 56 with reference to FIG. Input to means 57.

  The feedback control amount calculating means 57 comprises PI (proportional / integral) control means and PWM control signal generating means, and P (proportional) is used for the PI control means 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 to the output restriction processing means 58 To do.

On the other hand, the return upper limit output duty _DL is derived by the return upper limit output deriving means 51 based on the steering angle θ detected by the steering angle detection device 29 and the vehicle speed v detected by the vehicle speed sensor 25. The processing procedure will be described with reference to the flowchart of FIG.

First, in step 21, extracting the base return upper steering angular velocity omega _BL from the steering angle θ by the base back upper steering angular velocity extraction device 52.
Base back upper steering angular velocity extraction device 52 is provided with a relation map of the base return upper steering angular velocity omega _BL for the steering angle θ in a predetermined reference vehicle speed, indicated by the coordinates of the same relation map in Figure 11.

11, the horizontal axis is the steering angle theta, the vertical axis represents the base return upper steering angular velocity omega _BL, their correspondence is shown in relation curve.
In other words, the steering angular speed ω _BL that is the upper limit with respect to the steering angle θ at the reference vehicle speed is set in advance so as to have a desired relationship.
Therefore, the base return upper limit steering angular velocity extraction means 52 extracts the base return upper limit steering angular velocity ω _BL from the steering angle θ based on the relationship map.

In the next step 22, the vehicle speed correction coefficient Kv is extracted from the vehicle speed v by the vehicle speed correction coefficient extraction means 53.
The vehicle speed correction coefficient extracting means 53 includes a relationship map of the vehicle speed correction coefficient Kv with respect to the vehicle speed v.
FIG. 12 shows the relationship map in coordinates, where the horizontal axis is the vehicle speed v, the vertical axis is the vehicle speed correction coefficient Kv, and the correspondence between the two is shown by a relationship curve.

In the next step 23, the return upper limit steering angular velocity ω _SL (= ω _BL × Kv) at the vehicle speed v is calculated by multiplying and correcting the base return upper limit steering angular velocity ω _BL by the vehicle speed correction coefficient Kv.
Further, in the next step 24, the return upper limit steering angular speed ω _SL is multiplied by the reduction ratio N (> 1) of the worm reduction mechanism 10 to convert it to the return upper limit motor angular speed ω _ML (= ω _SL × N).

The return upper limit steering angular speed ω _SL and the return upper limit motor angular speed ω _ML are calculated by the return upper limit motor angular speed calculating means 54 by inputting the steering angle θ and the vehicle speed v and performing arithmetic processing.

Then, in the next step 25, it converts the upper motor angular velocity omega _ML returns the return limit output duty calculating means 55 returns to the upper limit output duty D _L.
That is, the return upper limit motor angular speed ω _ML is multiplied by the induced voltage constant k _E to obtain a return upper limit motor voltage, and this return upper limit motor voltage is divided by the power supply voltage V _B of the motor M to return upper limit output duty D _L ( = Ω _ML × k _E / V _B ).
As described above, the upper limit output duty _DL is derived from the steering angle θ and the vehicle speed v.

Describing the example of deriving the limit output duty D _L below.
Reduction ratio N of the worm speed reduction mechanism 10 is 15: (15 1), the induced voltage constant k _E of the motor M is 0.3 (V / rps), the power supply voltage V _B is the 14 (V).
Vehicle speed v is determined an upper limit output duty D _L when the 60 (km / h).
The vehicle speed correction coefficient Kv is 2 when the vehicle speed v is 60 (km / h) from the relationship map of the vehicle speed correction coefficient Kv with respect to the vehicle speed v (FIG. 12).

Under the above conditions, when the steering angle θ is 360 (deg), the base return upper limit steering angular velocity ω _BL is 360 (deg / deg.) From the relationship map of the base return upper limit steering angular velocity ω _BL to the steering angle θ (FIG. 11). s) is extracted.

Then
Return upper limit steering angular velocity ω _SL = ω _BL × Kv = 360 × 2 = 720 (deg / s) = 2 (rps)
Return upper limit motor angular velocity ω _ML = ω _SL × N = 2 × 15 = 30 (rps)
Return upper limit output duty D _L = ω _ML × k _E / V _B = 30 × 0.3 / 14 = 9/14 = 64.3 (%)
Next, the return limit output duty _{D L,} a 64.3 (%).

Further, under the above conditions, when the steering angle θ is 20 (deg), the base return upper limit steering angular velocity ω _BL is 70 (from the relationship map of the base return upper limit steering angular velocity ω _BL to the steering angle θ (FIG. 11) ( deg / s) is extracted.

Therefore,
Return upper limit steering angular velocity ω _SL = ω _BL × Kv = 70 × 2 = 140 (deg / s) = 0.39 (rps)
Return upper limit motor angular velocity ω _ML = ω _SL × N = 0.39 × 15 = 5.83 (rps)
Return upper limit output duty D _L = ω _ML × k _E / V _B = 5.83 × 0.3 / 14 = 12.5 (%)
Thus, the return upper limit output duty _DL is 12.5 (%).

The upper limit output duty D _L derived by the upper limit output deriving means 51 back in this manner is input to the output restriction processing unit 58, input separately from the feedback control amount calculation means 57 as described above in the output restriction processing means 58 The output of the feedback duty Dfb to the motor drive circuit 26 is limited.

The output restriction processing procedure by the output restriction processing means 58 will be described with reference to the flowchart of FIG.
First, in step 31, it is determined whether or not the steering is in a state of letting it go.
The state where the steering is almost released can be determined based on whether the steering angle θ is not 0 (straight forward) or the steering torque T detected by the steering torque sensor 20 is 0 or in the vicinity of 0.
When the steering is in a state of letting go while traveling, the steering is normally in a return state unless it is going straight.

When it is determined that the hand is in the substantially released state, the process jumps to step 32, and when it is determined that the hand is not in the substantially released state, the process proceeds to step 33.
When it proceeds to step 33 is determined not to be substantially parted state, without limiting the feedback duty Dfb calculated by the feedback control amount calculation means 57 as the output duty D _M to be outputted to the motor drive circuit 26 is used as such ( D _M = Dfb).

When the steering flew and the determination step 32 is substantially parted state, feedback duty Dfb calculated by the feedback control amount calculation means 57, exceeds the upper limit output duty D _L derived by back upper output deriving means 51 It is determined whether or not.

If the feedback duty Dfb does not exceed the upper limit output duty _{D L (Dfb ≦ D L)} , the process proceeds to step 33 and used as a feedback duty Dfb as the output duty _{D M (D M = Dfb)} .
Conversely, if the feedback duty Dfb exceeds the upper limit output duty _{D L (Dfb> D} L), the process proceeds to step 34, using the upper limit output duty _{D L} as the output duty _{D M (D M = D L} ).

That is, when the steering is in a state of letting go, the output duty _DM is always limited to the upper limit output duty _DL or less.
Therefore, the control amount of the electric motor can be limited in a state in which the steering is almost released, and an excessive steering return speed can be avoided.

Feedback duty Dfb used in conventional steering as an output duty D _M, because it limits at the upper limit output duty D _L when the substantially parted state of the steering does not affect the normal steering.

  That is, not only at the time of turning the steering, but also when the self-aligning torque is small in the returning state of the steering, assistance by the motor can be obtained by driving the motor by torque feedback control.

  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 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. Return is a flowchart showing a processing procedure of deriving the maximum output duty D _L. It is a figure which shows the relationship map of base return upper limit steering angular velocity (omega) _BL with respect to steering angle (theta) by a coordinate. It is a figure which shows the relationship map of the vehicle speed correction coefficient Kv with respect to the vehicle speed v by a coordinate. It is a flowchart which shows the process sequence of the output restriction by an output restriction processing means.

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, 29 ... Steering Rudder 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: Return upper limit output deriving means 52 ... Base return upper limit steering angular speed extracting means 53: Vehicle speed correction coefficient extracting means 54: Return upper limit motor angular speed calculating means 55: Return upper limit output duty calculating means 56 ... Subtraction means, 57 ... Feedback control amount calculation means, 58 ... Output restriction processing means.

Claims (4)

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;
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;
Return upper limit output deriving means for deriving a return upper limit output of the assist motor based on the steering rudder angle detected by the steering rudder angle detecting means and the vehicle speed detected by the vehicle speed sensor;
Output limiting processing means for limiting the output of the feedback control amount calculated by the feedback control amount calculating means to be less than or equal to the return upper limit output derived by the upper limit output deriving means when it is determined that the steering is in a substantially released state. An electric power steering apparatus comprising: The return upper limit output deriving means includes:
A base return upper limit steering angular speed extraction means for extracting a base return upper limit steering angular speed according to the steering rudder angle detected by the steering rudder angle detection means based on a preset relation map of the base return upper limit steering angular speed relative to the steering rudder angle; ,
Return upper limit motor angular speed calculation means for correcting the base return upper limit steering angular speed extracted by the base return upper limit steering angular speed extraction means based on the vehicle speed detected by the vehicle speed sensor and converting it to a return upper limit motor angular speed;
2. The electric power steering apparatus according to claim 1, further comprising return upper limit output calculation means for converting the return upper limit motor angular speed calculated by the return upper limit motor angular speed calculation means into a return upper limit output. The return upper limit motor angular velocity calculating means is
Vehicle speed correction coefficient extracting means for extracting a vehicle speed correction coefficient corresponding to the vehicle speed detected by the vehicle speed sensor based on a preset relationship map of the vehicle speed correction coefficient with respect to the vehicle speed;
Multiplying the base return upper limit steering angular speed extracted by the base return upper limit steering angular speed extraction means by the vehicle speed correction coefficient extracted by the vehicle speed correction coefficient extraction means to calculate a return upper limit steering angular speed;
3. The electric power steering apparatus according to claim 2, wherein the return upper limit steering angular velocity is multiplied by a reduction ratio to be converted into a return upper limit motor angular velocity. 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 4. 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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