JP2006137359A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device enabling smooth returning steering operation having no sense of incongruity. <P>SOLUTION: A base correction steering angular velocity ωmb is operated based on a steering angle θ, a multiplication coefficient value k determined based on steering torque T and a vehicle speed v is multiplied on the base correction steering angular velocity ωmb and then an addition coefficient value S determined based on the steering torque T is added to operate a target steering angular velocity ωm. A base correction current value Isb is operated based on difference of the target steering angular velocity ωm and an actual steering angular velocity ω and when a steering returning determination means 43 determines the steering returning state, the base correction current value Isb is made to a returning correction current value Is. When it determines the non-steering returning state, the returning correction current value Is is made to 0. The returning correction current value Is is added to an assist base current value Ib to make it to an assist target current Io. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device mounted on an automobile, and more particularly to control of steering torque.

  A traveling vehicle has a restoring force that tries to bring the rudder angle closer to 0 (neutral position) due to the self-aligning torque received by the steered wheels from the road surface. The self-aligning torque is small especially at low vehicle speeds, and the actual position does not return to the neutral position due to steering system friction or the like.

In view of this, an example in which a vehicle equipped with an electric power steering apparatus performs drive control even when the steering wheel is returned using a motor that assists human power has been proposed (see, for example, Patent Document 1).
JP-A-5-213222

  In the embodiment described in Patent Document 1, the relationship of the return torque with respect to the steering angle is provided in a map in advance, and the steering angle (the neutral position is set to 0 and the right steering angle is detected as positive and the left steering angle is detected as negative). The steering torque is differentiated from the steering angular speed obtained by time differentiation of the steering angle, and if the steering wheel is in the return state, the return torque is multiplied by a coefficient based on the road friction coefficient and a coefficient based on the vehicle speed. The output torque of the motor.

Regardless of the return steering force applied by the steering person, return steering is performed with this output torque by the motor, so that the handle is controlled to return to the neutral position in the almost released state.
Therefore, when a return steering force is applied, an assist force corresponding to the steering force cannot be obtained, and there is a sense of incongruity that does not conform to the intention of the steering person.

  The present invention has been made in view of the above points, and the object of the present invention is that even when the handle is returned, an assist force is obtained according to the return steering force to enable a smooth and comfortable return handle operation. An electric power steering device is provided.

  In order to achieve the above object, the invention according to claim 1 includes steering assist control means for calculating an assist base current value based on the steering torque and the vehicle speed, and the assist motor is operated according to the assist target current based on the assist base current value. In an electric power steering device that is driven and assisted to assist human power, a steering angle detection means that detects a steering angle, an actual steering angular speed calculation means that calculates the actual steering angular speed by time-differentiating the steering angle, and the steering angle A base correction rudder angular velocity calculating means for calculating a base correction rudder angular velocity based on the steering torque, a multiplication coefficient calculating means for calculating a multiplication coefficient value for multiplying and correcting the base correction rudder angular velocity based on the steering torque and the vehicle speed, and Addition coefficient calculation means for calculating an addition coefficient value for adding and correcting the base correction rudder angular velocity; and the base correction rudder angle A target rudder angular speed calculating means for calculating a target rudder angular speed by multiplying the multiplication coefficient value by a degree and then adding the addition coefficient value, and a base correction current value based on a difference between the target rudder angular speed and the actual rudder angular speed A correction current calculation means for calculating the steering wheel, a steering wheel return determination means for determining whether or not the steering wheel is returned based on the steering angle detected by the steering angle detection means and the actual steering angular speed calculated by the actual steering angular speed calculation means, and the handle When the return determination means determines that the steering wheel is returned, the base correction current value is set as a return correction current value, and when it is determined that the steering wheel is not returned, the return correction current value is 0, and the assist base current The electric power steering apparatus is provided with assist target current calculation means for adding the return correction current value to the value to obtain an assist target current.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the base correction rudder angular velocity calculation means stores the relationship of the base correction rudder angular velocity with respect to the rudder angle in a specific driving state set in advance. Base correction rudder angular velocity storage means for extracting and calculating a base correction rudder angular velocity based on the rudder angle from the relationship of the base correction rudder angular velocity with respect to the rudder angle stored by the base correction rudder angular velocity storage means.

  According to a third aspect of the present invention, in the electric power steering apparatus according to the first or second aspect of the present invention, the multiplication coefficient computing means stores a vehicle speed multiplication coefficient value relationship with the vehicle speed set in advance. A vehicle speed multiplication coefficient value for a vehicle speed stored in the vehicle speed multiplication coefficient storage means, comprising coefficient storage means and a steering torque multiplication coefficient storage means for storing a relationship of a steering torque multiplication coefficient value to the steering torque set in advance; The vehicle speed multiplication coefficient value is extracted and calculated based on the vehicle speed from the relationship, and the steering torque multiplication coefficient value is extracted and calculated from the relationship of the steering torque multiplication coefficient value to the steering torque stored in the steering torque multiplication coefficient storage means. The multiplication coefficient value is calculated by multiplying the vehicle speed multiplication coefficient value and the steering torque multiplication coefficient value.

  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 of the present invention, the addition coefficient calculation means sets the addition coefficient value for the steering torque set in advance. Steering torque addition coefficient storage means for storing the relationship, and the addition coefficient value is calculated from the relationship of the addition coefficient value to the steering torque stored in the steering torque addition coefficient storage means.

  According to the electric power steering apparatus of the first aspect, the base correction rudder angular speed calculated by the base correction rudder angular speed calculation means based on the rudder angle is corrected to obtain an ideal steering torque characteristic with respect to the rudder angle when the steering wheel is returned. The base correction rudder angular speed is corrected based on the difference between the actual steering angular speed by correcting the base correction rudder angular speed with the multiplication coefficient value obtained from the steering torque and the vehicle speed and the addition coefficient value obtained from the steering torque. By calculating the corrected current value and adding this base corrected current value as the corrected current value to the assist base current value only in the handle return state, the assist motor is driven based on the assist target current corrected when the handle is returned and returned. Assist force can be obtained according to the steering force, and it is possible to operate the return handle smoothly and comfortably according to the intention of the steering person And the.

  According to the electric power steering apparatus of the second aspect, the base correction rudder angular velocity storage means stores the relationship of the base correction rudder angular velocity with respect to the rudder angle in the hand-released handle return state set in advance. An appropriate base correction rudder angular velocity can be easily extracted and calculated by making the angle correspond.

  According to the electric power steering apparatus of the third aspect, the vehicle speed multiplication coefficient storage means stores the relationship of the vehicle speed multiplication coefficient value with respect to the vehicle speed, and can easily extract and calculate an appropriate vehicle speed multiplication coefficient value corresponding to the vehicle speed. Since the torque multiplication coefficient storage means stores the relationship of the steering torque multiplication coefficient value with respect to the steering torque, it is possible to easily extract and calculate an appropriate steering torque multiplication coefficient value corresponding to the steering torque, and the vehicle speed multiplication coefficient value and the steering torque can be calculated. The multiplication coefficient value is multiplied to calculate the multiplication coefficient value, and the base correction rudder angular speed is multiplied to easily multiply and correct the base correction rudder angular speed.

  According to the electric power steering apparatus of the fourth aspect, since the steering torque addition coefficient storage means stores the relationship of the steering torque addition coefficient value with respect to the steering torque, an appropriate steering torque addition coefficient value corresponding to the steering torque is stored. Can be easily extracted and added to the base correction rudder angular velocity, and the base correction rudder angular velocity can be easily added and corrected.

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 the 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.
The assist motor M is provided with a rotation angle sensor 27 such as a rotary encoder or resolver that directly detects the rotation of the rotation drive shaft.

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.

The assist motor M, which is controlled based on the steering torque and assists the steering, is driven and controlled by the CPU. A schematic block diagram of the steering torque control device 30 is shown in FIG.
The steering assist control means 31 calculates and outputs an assist base current Ib based on the steering torque T detected by the steering torque sensor 20 and the vehicle speed v detected by the vehicle speed sensor 25.

  The assist base current Ib is a current that serves as a base for driving the assist motor M. The assist base current Ib is calculated based on the fact that the assist base current Ib increases as the steering torque T increases to reduce the burden on the steering person. However, since the steering wheel becomes heavier when the vehicle speed is low than when the vehicle speed is high, the assist base current Ib is increased to reduce the steering torque.

The steering assist control means 31 calculates an appropriate assist base current Ib from the steering torque T and the vehicle speed v in consideration of the above.
For example, an optimal relationship between the assist base current Ib and the steering torque T is determined in advance for each predetermined vehicle speed, and the assist base current Ib is calculated from the steering torque T and the vehicle speed v based on the relationship.
Furthermore, the assist base current Ib may be obtained by adding a calculation for compensating the inertia torque of the steering system and the inertia torque of the motor.

  The assist base current Ib is corrected based on the steering angle θ to be described later when the steering wheel is returned to become an assist target current Io. The difference between the assist target current Io and the motor current Im fed back by the current feedback control means 32 is calculated. A drive current Id to be controlled to 0 is calculated and output to the motor drive circuit 33, and the assist motor M is driven by PWM control of the motor drive circuit 33.

The assist motor M includes a motor current detection device 26 that detects a motor current Im, and a rotation angle sensor 27, and detects the rotation angle of the assist motor M, that is, the motor rotation number n.
A steering angle calculation means 34 for detecting the steering angle θ based on the motor rotation speed n detected by the rotation angle sensor 27 is provided.
A steering angle sensor that directly detects the steering angle θ may be provided.

  The correction of the assist base current Ib at the time of returning the steering wheel is a correction based on the steering angle θ for realizing an ideal steering torque characteristic with respect to the steering angle at the time of returning the steering wheel. Therefore, the rudder as a base for correcting the assist base current Ib. A relation map of the base correction rudder angular speed ωmb with respect to the angle θ is obtained in advance and stored in the base correction rudder angular speed storage means 35a, and the base correction rudder angular speed calculation means 35 calculates the rudder angle calculation means 34 based on this relation map. The base correction rudder angular velocity ωmb is extracted from the rudder angle θ.

  FIG. 4 shows coordinates indicating the relationship of the base corrected steering angular velocity ωmb to the steering angle θ stored in the base corrected steering angular velocity storage means 35a.

The horizontal axis indicates the steering angle θ, and on the horizontal axis, the origin is the neutral position of the steering angle 0, the right side from the origin is the right steering angle, and the left is the left steering angle.
The vertical axis indicates the base correction rudder angular velocity ωmb, where the origin is the base correction rudder angular velocity 0, the direction above the origin is the right rotation direction (the direction of turning the handle to the right), and the direction below the origin is the left rotation Direction (direction to turn the handle to the left).

At the same coordinates, the relationship of the base correction rudder angular velocity ωmb to the rudder angle θ serving as a base for correcting the assist base current Ib is represented by a curve.
The relation curve is formed as a smooth curve symmetrical to the origin in the second quadrant and the fourth quadrant.

Looking at the right steering angle, the base correction rudder angular velocity ωmb increases in the left steering direction as the right rudder angle θ increases, and the base correction rudder angular velocity ωmb suddenly increases at the beginning when the right rudder angle θ increases from the rudder angle 0. A curve is drawn which increases gradually and then gradually decreases.
The left rudder angle is symmetrical with the right rudder angle, and the base correction rudder angular velocity ωmb increases in the right steering direction as the left rudder angle θ increases.

Regarding the relation curve of the base correction rudder angular speed ωmb with respect to the rudder angle θ, the correction current for obtaining the ideal characteristic of the steering torque with respect to the rudder angle when the steering wheel is returned at a low vehicle speed of 10 km / h is obtained for each rudder angle. The base correction rudder angular velocity is calculated from this correction current and determined backward.
Therefore, the relationship curve of the base correction steering angular velocity ωmb with respect to the steering angle θ changes upon correction based on the vehicle speed v and the steering torque T.

This correction includes a multiplication correction for multiplying the base correction rudder angular velocity ωmb by a multiplication coefficient k to change the shape of the relation curve, and an addition correction for adding the addition coefficient S to shift the relation curve up and down.
The multiplication coefficient k for multiplication correction is calculated by the multiplication coefficient calculation means 36, and the addition coefficient S for addition correction is calculated by the addition coefficient calculation means 37.

  The multiplication coefficient calculating means 36 stores vehicle speed multiplication coefficient storage means 36a for storing the relationship between the vehicle speed multiplication coefficient kv and the vehicle speed v as a map, and steering torque multiplication coefficient storage for storing the relationship between the steering torque multiplication coefficient kt for the steering torque T as a map. Means 36b.

A map stored in the vehicle speed multiplication coefficient storage means 36a is shown in FIG.
The vehicle speed multiplication coefficient kv becomes larger with respect to the vehicle speed v as the vehicle speed v increases from the origin, the vehicle speed multiplication coefficient kv shows 1.0 at a vehicle speed of 10 km / h, increases rapidly when the vehicle speed v is lower, and then increases. The rate is gradually decreasing.

  Therefore, the vehicle speed multiplication coefficient kv works to suppress the base correction rudder angular speed ωmb at a value of less than 1.0 when the vehicle speed is less than 10 km / h, and increases the base correction rudder angular speed ωmb at a value of 1.0 or more at a vehicle speed of 10 km / h or more. Work in the direction.

A map stored in the steering torque multiplication coefficient storage means 36b is shown in FIG.
The steering torque multiplication coefficient kt with respect to the steering torque T is 1.0 when the steering torque T is 0 (completely released from the steering wheel), and slightly decreases from 1.0 while the steering torque T increases and corresponds to the first almost released state. The decrease is slight, it decreases rapidly when it is released and approaches 0, and then gradually approaches 0 as the steering torque T increases.

That is, the steering torque multiplication coefficient kt shows a value in the vicinity of 1.0 in the substantially released state, and shows a value close to 0 in a state other than the released state.
Therefore, the shape of the base correction rudder angular velocity ωmb is generally maintained in the released state, and the shape of the base corrected rudder angular velocity ωmb is flattened (not changed with respect to the rudder angle) in a state other than the hand released state.

The multiplication coefficient calculating means 36 multiplies the vehicle speed multiplication coefficient kv obtained from the above vehicle speed v and the steering torque multiplication coefficient kt obtained from the steering torque T to calculate the multiplication coefficient k.
The multiplication coefficient k is multiplied by the base correction steering angular speed ωmb to perform multiplication correction (see multiplication correction means 38 in FIG. 3).

  Next, the addition coefficient calculation means 37 includes a steering torque addition coefficient storage means 37a for storing the relationship of the addition coefficient S with respect to the steering torque T as a map.

A map stored in the steering torque addition coefficient storage means 37b is shown in FIG.
The horizontal axis is the steering torque T, the vertical axis is the coordinate with the addition coefficient S, and the addition coefficient S is proportional to the steering torque T, and is indicated by a straight line that rises to the right through the origin.

The addition coefficient S is added to the base correction steering angular speed ωmb to perform addition correction (see addition correction means 39 in FIG. 3).
Therefore, the base correction rudder angular velocity ωmb is largely shifted upward as the steering torque is increased.
Note that when the vehicle speed increases, the steering torque increases due to the increase of the self-aligning torque, so the base correction steering angular speed ωmb tends to shift upward.

From the above, referring to FIG. 3, the multiplication coefficient calculating means 36 calculates the base corrected rudder angular speed ωmb extracted and calculated from the rudder angle θ based on the base corrected rudder angular speed storage means 35a by referring to FIG. Is multiplied by the multiplication coefficient k, and the addition coefficient S calculated by the addition coefficient calculation means 37 is added to obtain the target steering angular speed ωm.
That is, the target rudder angular velocity ωm is
ωm = ωmb · k + S (= ωmb · kv · kt + S)
It is.

On the other hand, the steering angle θ calculated by the steering angle calculating means 34 is time-differentiated by the steering angular speed calculating means 40 to calculate the actual steering angular speed ω.
A deviation Δω (= ωm−ω) of the target rudder angular speed ωm with respect to the actual rudder angular speed ω is obtained (see deviation calculating means 41 in FIG. 3), and the corrected current converting means 42 converts the deviation Δω into a current to correct the base. The current Isb is obtained.
This current conversion can be calculated by multiplying the deviation Δω by a predetermined conversion coefficient.

  Further, a handle return determination means 43 for determining whether or not the steering wheel is in a return state based on the steering angle θ calculated by the steering angle calculation means 34 and the actual steering angular speed ω calculated by the steering angle speed calculation means 40 is provided. The handle return discriminating means 43 is provided with 1 in the multiplication coefficient h if the handle is in the return state, and 0 in other cases.

Whether or not the steering wheel is in the return state can be determined by a positive / negative combination of the steering angle θ and the actual steering angular velocity ω.
That is, when the steering angle θ is at the right steering angle (steering angle θ> 0), if the actual steering angular velocity ω is in the left rotation direction (actual steering angular velocity ω <0), the steering wheel is in the return state, and similarly If the steering angle θ is at the left steering angle (steering angle θ <0) and the actual steering angular velocity ω is in the right rotation direction (actual steering angular velocity ω> 0), the steering wheel is in the return state.

Therefore, if θ × ω <0, the steering wheel is returned, and if θ × ω> 0, the steering wheel is cut.
The handle return determining means 43 sets the multiplication coefficient h = 1 when θ × ω <0 and determines that the handle is returned, and otherwise sets the multiplication coefficient h = 0.

The base correction current Isb converted by the correction current conversion means 42 is multiplied by the multiplication coefficient h by the multiplication means 44 to obtain a correction current Is (= Isb · h).
Accordingly, the correction current Is is the value of the base correction current Isb when the handle is returned, and the correction current Is is 0 when the handle is not returned.

The corrected current Is thus obtained is added to the assist base current Ib calculated by the steering assist control means 31 to correct the assist base current Ib (see the adding means 45 in FIG. 3), thereby obtaining the assist target current Io. .
The assist motor M is driven and controlled by the corrected assist target current Io.
Therefore, the assist base current Ib is corrected by the correction current Is only in the steering wheel returning state.

Hereinafter, the characteristic of the steering torque T with respect to the steering angle θ will be obtained in the actual steering wheel return state.
First, a description will be given of a case where return steering that is not in the released state after turning by right steering is performed (steering angle θ> 0 and actual steering angular velocity ω <0).

  In the case of return steering, the steering angle returns to some extent even if it is let go, because a restoring force that tries to bring the rudder angle closer to 0 by the self-aligning torque that the steered wheel receives from the road surface works. The case indicated by 9 is a case where a steering person applies a steering force to perform a return operation.

FIG. 8 shows the case of a lower vehicle speed.
Since the vehicle speed is low, the vehicle speed multiplication coefficient kv shows a value around 1.0 (see FIG. 5), and since the vehicle speed is low in a state other than hand release, the steering torque multiplication coefficient kt shows around 0.3 (see FIG. 6). k is a value considerably smaller than 1.0. Therefore, the shape of the relationship curve of the base correction steering angular velocity ωmb with respect to the steering angle θ shown in FIG. 4 is corrected to be flat.

  And since the vehicle speed is low, the steering torque also changes small, the addition coefficient S also shows a small value (see FIG. 7), and the relationship curve of the base correction steering angular velocity ωmb with respect to the steering angle θ shown in FIG. It is corrected to the shifted target rudder angular velocity ωm (see FIG. 8 (1)).

FIG. 8 (1) shows the coordinates of the steering angular velocity ω with respect to the right steering angle θ, and the relationship curve of the target steering angular velocity ωm with respect to the steering angle θ is shown by a solid line.
In FIG. 8 (1), a relationship curve of the actual steering angular speed ω calculated by the steering angular speed calculating means 40 with respect to the steering angle θ is indicated by a one-dot chain line.

  Referring to FIG. 8 (1), the actual steering angular speed ω and the target steering angular speed ωm appearing in the left steering direction intersect at a steering angle θq near the maximum steering angle θmax at which the steering wheel starts to return, and the deviation Δω ( = Ωm−ω) is multiplied by the conversion factor, the base correction current Isb is in the handle return state (θ × ω <0), so that the multiplication factor h = 1 directly becomes the correction current Is, and the correction current Is is shown in FIG. As shown in (2), the maximum steering angle θmax shows a small value in the assist direction (negative side), decreases as the steering angle θ decreases, becomes 0 at the steering angle θq, and then brakes until the steering angle returns to 0. Indicates the value of (positive side).

Therefore, as shown in FIG. 8 (3), the characteristic of the steering torque T with respect to the steering angle θ is indicated by a solid line after correction by the correction current Is when the characteristic curve before correction is indicated by a broken line.
That is, the correction current Is acts as an assist in the steering angle range (θq <θ <θmax) from the maximum steering angle θmax to the first steering angle θq at which the steering is started. Although the torque T has increased, the left steering torque T gradually increases after the correction, and when the steering angle θq is passed with the left steering torque T increasing gradually, the left steering torque T before the correction Increased and weighted.

Next, FIG. 9 shows a case where return steering is performed at a high vehicle speed.
The target rudder angular speed ωm has a flat relationship curve of the base correction rudder angular speed ωmb with respect to the rudder angle θ shown in FIG. 4, the return steering torque increases at a high vehicle speed, and the addition coefficient S has a large value from FIG. The relationship curve of the base correction rudder angular velocity ωmb is shown shifted greatly upward (see FIG. 9 (1)).

  Therefore, as shown in FIG. 9 (2), the correction current Is is indicated by a curve that is convex upward in the braking direction (positive side). Therefore, the steering current T is corrected with respect to the steering angle θ corrected by this correction current Is. The characteristic (solid line) moves the characteristic curve before correction indicated by the broken line downward (to the left steering direction), and changes slightly smoothly at the beginning of the return from the maximum rudder angle, giving a sense of steering with a solid weight overall. I have it.

Next, a description will be given of a case where the return operation is performed in the almost released state after turning by right steering.
FIG. 10 shows the case of low vehicle speed.
Since the vehicle speed is low, the vehicle speed multiplication coefficient kv shows a value around 1.0 (see FIG. 5), and since it is in the almost released state, the steering torque multiplication coefficient kt shows about 1.0 (see FIG. 6). Therefore, the relationship curve shape of the base correction steering angular velocity ωmb with respect to the steering angle θ shown in FIG. 5 is slightly flattened.

  Since the steering torque T = 0 and the addition coefficient S is 0 (see FIG. 7), the relationship curve of the base correction steering angular velocity ωmb with respect to the steering angle θ shown in FIG. There is no vertical shift, and the target rudder angular velocity ωm passing through the origin is corrected (see FIG. 10 (1)).

  Referring to FIG. 10 (1), the base correction current Isb, that is, the correction current Is obtained by multiplying the deviation Δω (= ωm−ω) between the actual steering angular velocity ω and the target steering angular velocity ωm appearing in the left steering direction by a conversion factor. As shown in FIG. 10 (2), the maximum steering angle θmax at which the steering wheel starts to be returned has a large value in the assist direction (negative side), and gradually approaches 0 to reach the origin as the steering angle θ decreases. Shown as a convex curve.

  Since the return steering torque T is 0 because it is in the almost released state, the steering angle is naturally reduced by the self-aligning torque, but the steering angle θ is naturally reduced. As shown in FIG. 10 (3), when the correction current Is acts, the steering current is forcibly steered to the neutral position where the steering torque T remains zero at all steering angles θ. The corner can be returned.

  The return speed with respect to the steering angle θ is also appropriately controlled by the shape of the relationship curve of the base correction steering angular speed ωmb with respect to the steering angle θ shown in FIG.

  As described above, as shown in FIGS. 8 to 10, the characteristic of the correction current Is with respect to the steering angle θ can be changed according to the return steering force to obtain a corresponding assist force, and smooth according to the intention of the steering person. The handle can be operated without any discomfort.

  Although the above example was a case where all steered to the right steering angle, the same effect can be show | played about a left steering angle.

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 coordinate which shows the relationship of the base correction rudder angular velocity (omega) mb with respect to the rudder angle (theta). It is a figure which shows the map of the vehicle speed multiplication coefficient kv with respect to the vehicle speed v. 4 is a diagram showing a map of a steering torque multiplication coefficient kt with respect to a steering torque T. FIG. 6 is a diagram showing a map of a steering torque addition coefficient S with respect to a steering torque T. FIG. It is a figure which shows the change of the steering angular velocity (omega) with respect to the steering angle (theta), the correction electric current Is, and the steering torque T at the time of return steering not being in a hand-off state at low vehicle speed. It is a figure which shows the change of the steering angular velocity (omega) with respect to the steering angle (theta), the correction electric current Is, and the steering torque T at the time of return steering not being hand-released at high vehicle speed. It is a figure which shows the change of the steering angular velocity (omega) with respect to the steering angle (theta), the correction electric current Is, and the steering torque T at the time of return operation | movement in the substantially hand-off state at low vehicle speed.

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, 9 ... Rack guide, 10 ... Worm reduction mechanism, 11 ... Worm wheel, 12 ... Worm,
20 ... Torque sensor, 21 ... Core, 22, 23 ... Coil, 25 ... Vehicle speed sensor, 26 ... Motor current detector, 27 ... Rotation angle sensor,
30 ... Steering torque control device, 31 ... Steering assist control means, 32 ... Current feedback control means, 33 ... Motor drive circuit, 34 ... Steering angle calculation means, 35 ... Base correction steering angular speed calculation means, 35a ... Base correction steering angular speed storage Means 36: Multiplication coefficient calculation means 36a ... Vehicle speed multiplication coefficient storage means 36b ... Steering torque multiplication coefficient storage means 37 ... Addition coefficient calculation means 37a ... Steering torque addition coefficient storage means 38 ... Multiplication correction means 39 ... Addition correction means, 40 ... steer angular velocity calculation means, 41 ... deviation calculation means, 42 ... corrected current conversion means, 43 ... handle return determination means, 44 ... multiplication means, 45 ... addition means.

Claims (4)

In an electric power steering apparatus comprising steering assist control means for calculating an assist base current value based on a steering torque and a vehicle speed, wherein the assist motor is driven and controlled according to an assist target current based on the assist base current value to assist human power.
Rudder angle detecting means for detecting the rudder angle;
An actual rudder angular velocity calculating means for calculating an actual rudder angular velocity by differentiating the rudder angle with respect to time;
Base correction rudder angular velocity calculating means for calculating a base correction rudder angular velocity based on the rudder angle;
Multiplication coefficient computing means for computing a multiplication coefficient value for multiplying and correcting the base correction steering angular speed based on the steering torque and the vehicle speed;
Addition coefficient calculation means for calculating an addition coefficient value for adding and correcting the base correction rudder angular velocity based on the steering torque;
Target rudder angular velocity calculating means for calculating a target rudder angular velocity by multiplying the base correction rudder angular velocity by the multiplication coefficient value and then adding the addition coefficient value;
Correction current calculation means for calculating a base correction current value based on the difference between the target rudder angular speed and the actual rudder angular speed;
A steering wheel return determination means for determining whether or not the steering wheel is returned based on the steering angle detected by the steering angle detection means and the actual steering angular speed calculated by the actual steering angular speed calculation means;
A return correction current calculating means for setting the base correction current value to be a return correction current value when the handle return determination means is determined to be a handle return state;
An electric power steering apparatus comprising: an assist target current calculation unit that adds the return correction current value to the assist base current value to obtain an assist target current.   The base correction rudder angular speed calculation means includes base correction rudder angular speed storage means for storing the relationship of the base correction rudder angular speed with respect to the rudder angle in a specific operation state set in advance, and the base correction rudder angular speed storage means stores The electric power steering apparatus according to claim 1, wherein a base correction rudder angular velocity is extracted and calculated based on the rudder angle from a relationship of a base correction rudder angular velocity to a rudder angle to be operated.   The multiplication coefficient calculating means stores vehicle speed multiplication coefficient storage means for storing the relationship of the vehicle speed multiplication coefficient value with respect to the preset vehicle speed, and the relationship between the steering torque multiplication coefficient value with respect to the preset steering torque. Steering torque multiplication coefficient storage means for storing, extracting and calculating a vehicle speed multiplication coefficient value based on the vehicle speed from the relationship between the vehicle speed multiplication coefficient value and the vehicle speed stored in the vehicle speed multiplication coefficient storage means, and the steering torque multiplication coefficient storage means The steering torque multiplication coefficient value is extracted from the relationship between the steering torque multiplication coefficient value and the steering torque stored in the vehicle, and the multiplication coefficient value is calculated by multiplying the extracted vehicle speed multiplication coefficient value by the steering torque multiplication coefficient value. The electric power steering apparatus according to claim 1 or 2. The addition coefficient calculation means includes steering torque addition coefficient storage means for storing a preset relation of the addition coefficient value with respect to the steering torque, and an addition factor for the steering torque stored in the steering torque addition coefficient storage means. The electric power steering apparatus according to any one of claims 1 to 3, wherein an addition coefficient value is calculated from a numerical relationship.

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