JP4407935B2 - Electric power steering device - Google Patents

Description

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

FIG. 1 shows the results of examining how the steering torque T, which is the steering reaction force (reaction force received when the steering person steers), changes with respect to the steering angle θ.
The coordinates in FIG. 1 indicate the right steering angle θ with the steering wheel cut to the right from the neutral position of the origin on the right side of the horizontal axis, the vertical axis shows the steering torque T, and the origin is the steering torque 0 on the vertical axis. The direction above the origin is the right steering direction (direction in which the steering wheel is turned to the right), and the direction below the origin is the left steering direction (direction in which the steering wheel is turned to the left).

A characteristic of the steering torque T with respect to the right steering angle θ when the steering wheel is turned to the right (right steering) when there is no assist by a motor or the like is shown by a one-dot chain line curve.
When there is no assist at all, at the beginning of steering, the steering torque T suddenly increases with respect to the steering angle θ, that is, the steering wheel operation is heavy, and after that, it drops slightly for a moment and settles to a substantially constant steering torque T.

In the conventional electric power steering device, the assist motor is driven and controlled by the detected steering torque and vehicle speed (see, for example, Patent Document 1), and the steering wheel is cut to the right (right cut) when there is this conventional assist. The characteristics of the steering torque T with respect to the steering angle θ when the steering operation and the return of the steering wheel to the left (left return steering) are performed are indicated by a dashed curve.
Japanese Patent No. 3260206

  The shape of the characteristic curve at the time of right-turn steering is similar to the case without assist, and the steering torque T suddenly increases at the beginning of steering, and is almost constant after lowering slightly (lower by the amount of assistance compared to without assist) Torque value).

Even when the return steering is started, the steering torque T suddenly increases in the left steering direction at the beginning of the return steering and thereafter becomes substantially constant.
Further, the steering torque T is suddenly lost when shifting from cutting to returning.
Therefore, the steering torque characteristic curve with respect to the conventional rudder angle is substantially rectangular.

The steering torque characteristic with respect to the generally rectangular rudder angle is not suitable even if the steering operation is heavier as a whole at high vehicle speeds, and there is no problem even if the steering operation is heavy at the beginning of the incision. .
However, when the vehicle speed is low (about 40 km / h or less), the steering operation feels heavy at the beginning of steering, and then the steering torque suddenly becomes constant, which makes it strange.

  Ideally, it is appropriate that the weight gradually increases at the beginning of steering of turning and returning in steering operation, and it is appropriate that the weight is lost smoothly when shifting from cutting to returning. As shown by the solid line in FIG. 1, the steering torque characteristic with respect to is a smooth ellipse.

  The present invention has been made in view of the above points, and an object of the present invention is to gradually increase the steering torque with respect to the steering angle at a low vehicle speed by adding steering torque control based on the steering angle. An electric power steering device that enables a steering operation without a sense of incongruity 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 Base correction rudder angular velocity calculation means for calculating a base correction rudder angular speed based on the above, steering coefficient calculation means for calculating a multiplication coefficient value for multiplying and correcting the base correction rudder angular speed based on the steering torque and the vehicle speed, the steering torque and the Addition coefficient calculation means for calculating an addition coefficient value for adding and correcting the base correction rudder angular speed based on the vehicle speed; A target steering angular speed calculating means for calculating a target steering angular speed by multiplying the corrected steering angular speed by the multiplication coefficient value and then adding the addition coefficient value, and a correction current based on the difference between the target steering angular speed and the actual steering angular speed The electric power steering apparatus includes: a corrected current calculating unit that calculates a value; and an assist target current calculating unit that adds the corrected current value to the assist base current 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 calculates a vehicle speed addition coefficient value for the vehicle speed set in advance. Vehicle speed addition coefficient storage means for storing the relationship; and steering torque addition coefficient storage means for storing the relationship of the steering torque addition coefficient value with respect to the steering torque set in advance, the vehicle speed addition coefficient storage means storing A vehicle speed addition coefficient value is extracted based on the vehicle speed from the relationship between the vehicle speed addition coefficient value and the vehicle speed, and a steering torque addition coefficient value is extracted from the relationship between the steering torque addition coefficient value and the steering torque stored in the steering torque addition coefficient storage means. The addition coefficient value is calculated by multiplying the vehicle speed addition coefficient value obtained by the calculation and the extraction calculation by the steering torque addition coefficient value.

  According to the electric power steering apparatus of claim 1, the base correction rudder angular velocity calculated by the base correction rudder angular velocity calculation means based on the rudder angle is a base correction for correcting the steering torque characteristic with respect to the rudder angle to a substantially ideal characteristic. This is the rudder angular velocity, and the corrected current value is calculated based on the difference from the actual rudder angular velocity by correcting the base modified rudder angular velocity with the multiplication coefficient value and addition coefficient value obtained from the steering torque and vehicle speed. When the assist motor is driven based on the assist target current corrected by adding the value to the assist base current value, the steering torque is gradually increased with respect to the rudder angle, particularly at low vehicle speeds. This makes it possible to operate the steering wheel without any sense of incongruity.

  According to the electric power steering apparatus of the second aspect, since the base correction rudder angular speed storage means stores the relationship of the base correction rudder angular speed with respect to the rudder angle in a specific driving state set in advance, the detected rudder 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, the vehicle speed addition coefficient storage means stores the relationship of the vehicle speed addition coefficient value with respect to the vehicle speed, and can easily extract and calculate an appropriate vehicle speed addition coefficient value corresponding to the vehicle speed. Since the 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 can be easily extracted and calculated by associating the steering torque, and the vehicle speed addition coefficient value and the steering torque can be calculated. By multiplying the addition coefficient value, the addition coefficient value is calculated and added to the base correction steering angular speed, and the base correction steering angular speed can be easily added and corrected.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
FIG. 2 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 housed in a substantially cylindrical rack housing 2 oriented in the left-right direction of the vehicle (corresponding to the left-right direction in FIG. 2) 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 integrally attached with a steering wheel (not shown) 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 to the assist target current Io after being corrected based on the steering angle θ, and the difference between the assist target current Io and the motor current Im fed back by the current feedback control means 32 is set to zero. The drive current Id to be controlled is calculated and output to the motor drive circuit 33, and the assist motor M is driven by the 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 is provided for detecting the actual steering angle θ based on the motor rotation speed n detected by the rotation angle sensor 27.
A steering angle sensor that directly detects the actual steering angle θ may be provided.

The correction of the assist base current Ib is a correction based on the steering angle θ for realizing the characteristic curve of the steering torque T with respect to the elliptical steering angle θ shown by the solid line in FIG.
Therefore, a relation map of the base correction rudder angular speed ωmb with respect to the rudder angle θ serving as a base for correcting the assist base current Ib is obtained in advance and stored in the base correction rudder angular speed storage means 35a. Based on the relationship map, the base correction steering angular velocity ωmb is extracted and calculated from the actual steering angle θ calculated by the steering angle calculation means 34.

  FIG. 5 shows coordinates indicating the relationship of the base corrected steering angular speed ωmb with respect to the steering angle θ stored in the base corrected steering angular speed storage means 20a.

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 shape of the relationship curve of the base corrected steering angular speed ωmb with respect to the steering angle θ, a correction current for obtaining an ideal characteristic in which the steering torque gradually rises with respect to the steering angle when the vehicle is steered at a low speed of 10 km / h. Is determined for each steering angle, and the base correction rudder angular velocity is calculated backward from this correction current.
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. 4).

  Next, the addition coefficient calculation means 37 stores the relationship between the steering torque addition coefficient St with respect to the steering torque T as a map, and the vehicle speed that stores the relationship between the vehicle speed addition coefficient Sv with respect to the vehicle speed v as a map. And an addition coefficient storage means 37b.

A map stored in the steering torque addition coefficient storage means 37a is shown in FIG.
The horizontal steering torque T is the right steering torque that receives the right side from the origin in the right direction, the left steering torque that receives the left side from the origin in the left direction, the vertical axis indicates the steering torque addition coefficient St, and the upper side from the origin is positive. The value below is negative.

The steering torque addition coefficient St with respect to the steering torque T increases to the right shoulder as the right steering torque T increases from 0, and the left steering torque decreases to the left shoulder as it increases from 0, and is symmetrical to the origin. The curve is formed.
Therefore, the base correction rudder angular velocity ωmb is greatly shifted upward as the right steering torque is large, and the base correction rudder angular velocity ωmb is largely shifted downward as the left steering torque is large.

A map stored in the vehicle speed addition coefficient storage means 37b is shown in FIG.
The vehicle speed addition coefficient Sv with respect to the vehicle speed v shows a value of about 1.2 at a vehicle speed of 0, gradually decreases as the vehicle speed v increases, shows 0 at a vehicle speed of 40 km / h that separates the low vehicle speed and the high vehicle speed, and decreases when the vehicle speed further increases. Gradually decreases, and when it exceeds -1.0, it hardly decreases.

  Since this vehicle speed addition coefficient Sv is multiplied by the previous steering torque addition coefficient St and added to the base correction steering angular speed ωmb, the shift amount of the vehicle speed base correction steering angular speed ωmb close to the vehicle speed 40 km / h is suppressed, As the vehicle speed becomes lower, the shift is largely shifted upward without being suppressed, and as the vehicle speed becomes higher, the shift is largely shifted downward without being suppressed.

The addition coefficient calculation unit 37 calculates the addition coefficient S by multiplying the steering torque addition coefficient St obtained from the steering torque T and the vehicle speed addition coefficient Sv obtained from the vehicle speed v.
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. 4).

Therefore, referring to FIG. 4, the base correction rudder angular velocity calculation means 35 calculates the multiplication coefficient calculated by the multiplication coefficient calculation means 36 to the base correction rudder angular speed ωmb extracted and calculated from the rudder angle θ based on the base correction rudder angular speed storage means 35a. The target steering angular velocity ωm is obtained by multiplying k and then adding the addition coefficient S calculated by the addition coefficient calculation means 37.
That is, the target rudder angular velocity ωm is
ωm = ωmb · k + S (= ωmb · kv · kt + St · Sv)
It is.

On the other hand, the steering angle θ calculated by the steering angle calculation means 34 is time-differentiated by the steering angular speed calculation 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 the deviation calculating means 41 in FIG. 4), and the corrected current converting means 42 converts the deviation Δω into a current to obtain a corrected current. Is is determined.
This current conversion can be calculated by multiplying the deviation Δω by a predetermined conversion coefficient.

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 43 in FIG. 4), thereby obtaining the assist target current Io. .
The assist motor M is driven and controlled by the corrected assist target current Io.

Hereinafter, the characteristic of the steering torque T with respect to the steering angle θ will be obtained in the case of actual steering operation.
First, FIG. 10 shows a case where an operation of turning the steering wheel to the right from the neutral position is performed at a low vehicle speed (around 30 km / h).

  Since the vehicle speed is low at around 30 km / h, the vehicle speed multiplication coefficient kv is about three times 1.0 (see FIG. 6), and since the steering is steering, the steering torque multiplication coefficient is in a state other than letting go. kt is about 0.3 (see FIG. 7), the multiplication coefficient k obtained by multiplying the two shows a value of 1.0, which is close to 1.0, and ωmb · k multiplied by the base correction rudder angular velocity ωmb is also slightly smaller than ωmb. The shape of the relationship curve of the base correction rudder angular velocity ωmb with respect to the rudder angle θ shown in FIG.

Since the steering is in the right steering direction, the steering torque addition coefficient St shows a positive value (see FIG. 8), and the vehicle speed addition coefficient Sv is about +0.4 because the vehicle speed is around 30 km / h. (See FIG. 9), the addition coefficient S obtained by multiplying both is a positive value.
Therefore, when this addition coefficient S is added to the product obtained by multiplying the base correction rudder angular speed ωmb by the multiplication coefficient k, the relationship curve of the base correction rudder angular speed ωmb with respect to the rudder angle θ shown in FIG. The target rudder angular velocity ωm shifted by S is corrected.

FIG. 10 (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 indicated by a solid line.
In FIG. 10 (1), a relationship curve of the actual steering angular speed ω calculated by the steering angular speed calculation means 40 with respect to the steering angle θ is shown by a one-dot chain line.
In FIG. 10 (1), the actual steering angular velocity ω is a convex curve upward with respect to the downwardly convex target steering angular velocity ωm, and the two intersect at a small steering angle θp, and the deviation Δω (= ωm) between the two. The corrected current Is obtained by multiplying -ω) by the conversion factor by the corrected current converting means 42 is shown in FIG.

FIG. 10 (2) shows the change of the correction current Is with respect to the right steering angle θ. At the time of cutting, the upper side (positive side) from the origin of the vertical axis corresponds to the assist direction (the correction current Is works as an assist). The lower side (negative side) from the origin corresponds to the braking direction (the correction current Is works as a brake).
When the handle is returned, on the contrary, the upper side (positive side) from the origin is the brake direction, and the lower side (negative side) from the origin is the assist direction.

  Since the correction current Is is on the positive side in the steering angle range from the origin to the steering angle θp (0 <θ <θp) and is at the time of cutting, the correction current Is acts as an assist, and the steering angle range exceeding the steering angle θp (θ> θp). ) On the negative side and acts as a brake.

Therefore, as shown in FIG. 10 (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.
In other words, the correction current Is acts as an assist in the steering angle range (0 <θ <θp) from the initial origin to start steering from the neutral position to the steering angle θp. Has risen gently after the correction, and after the steering angle θp with this gentle rise, the steering torque T before the correction becomes larger.

A characteristic curve close to the ideal smooth elliptical characteristic curve shown in FIG. 1 is drawn, and the weight is gradually increased at the beginning of steering operation in steering operation, and there is no sudden change on the way and the curve is smooth. Since the steering torque is realized, it is possible to give the steering person a natural smooth steering feeling without a sense of incongruity.
Although the right steering angle has been described above, the same steering torque characteristic curve can be obtained only by turning the left steering angle left and right.

Next, FIG. 11 shows a case where an operation of cutting to the right at a high vehicle speed is performed.
Since steering is performed at a high vehicle speed, the vehicle speed multiplication coefficient kv shows a large value (see FIG. 6), but since the steering torque becomes large at a high vehicle speed, the steering torque multiplication coefficient kt shows a small value (see FIG. 7). Eventually, the multiplication coefficient k becomes a value somewhat 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. 5 changes somewhat flat.

  Since the steering torque increases at a high vehicle speed, the steering torque addition coefficient St shows a large value (see FIG. 8), and the vehicle speed addition coefficient Sv shows a negative value close to −1.0 (see FIG. 9). The coefficient S is a negative relatively large value. Therefore, the relationship curve of the base correction steering angular speed ωmb with respect to the steering angle θ shown in FIG. 5 is flattened and corrected to the target steering angular speed ωm shifted downward by the addition coefficient S ( (See FIG. 11 (1)).

The corrected current Is obtained by multiplying the deviation Δω (= ωm−ω) between the target rudder angular velocity ωm and the actual rudder angular velocity ω by the conversion factor by the correction current conversion means 42 is as shown in FIG. It is a convex flat curve and acts in the braking direction with negative values at all steering angles θ.
Therefore, as shown in FIG. 11 (3), the characteristic (solid line) of the steering torque T with respect to the steering angle θ corrected by the correction current Is moves upward in the characteristic curve before the correction indicated by the broken line, and starts slightly higher. It is smooth around the horizontal transition.

  When turning at high vehicle speeds, the steering torque T increases rapidly from the beginning of steering and settles smoothly to a large value, so the steering operation is heavy from the beginning and is relatively heavy to ensure a solid steering feeling. Like to do.

Next, a description will be given of a case where return steering is performed that is not in a released state after turning by right steering.
In the case of return steering, the steering angle returns to some extent even if it is let go, because the restoring force that tries to bring the rudder angle closer to 0 naturally works due to the self-aligning torque that the steered wheels receive from the road surface. In this case, the steering person applies a steering force to perform a return operation.

FIG. 12 shows a case where the vehicle speed is further low.
Since the vehicle speed is low, the vehicle speed multiplication coefficient kv shows a value around 1.0 (see FIG. 6), and since the vehicle speed is low in a state other than letting go, the steering torque multiplication coefficient kt shows around 0.3 (see FIG. 7). 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. 5 is corrected to be flat.

  And since it is a return steering, the left steering torque has arisen, the steering torque addition coefficient St shows a negative value, the vehicle speed addition coefficient Sv is a value of about +0.4, and the addition coefficient S shows a negative value after all, The relationship curve of the base correction rudder angular velocity ωmb with respect to the rudder angle θ shown in FIG. 5 is flattened and corrected to the target rudder angular velocity ωm that is shifted somewhat downward (see FIG. 12 (1)).

  Referring to FIG. 12 (1), the actual steering angular speed ω and the target steering angular speed ωm appearing in the left steering direction intersect each other 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), the correction current Is obtained by multiplying the conversion factor by the maximum steering angle θmax as shown in FIG. 12 (2) shows a large value in the assist direction (negative side), and the steering angle θ is small. It becomes smaller as the steering angle θq becomes 0, and the value in the brake direction (positive side) is shown until the steering angle returns to 0 thereafter.

Therefore, as shown in FIG. 12 (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.

  Thus, even during the return operation, a characteristic curve close to the ideal smooth elliptical characteristic curve shown in FIG. 1 is drawn, and the weight gradually increases at the beginning of the return steering in the steering operation, Since a smooth steering torque is realized without a sudden change, it is possible to give the steering person a natural smooth steering feeling without a sense of incongruity.

FIG. 13 shows a case where the return steering is performed at a high vehicle speed.
The target rudder angular velocity ωm is shown by flattening the relationship curve of the base correction rudder angular velocity ωmb with respect to the rudder angle θ shown in FIG. 5 and greatly shifting upward (see FIG. 13 (1)).
Therefore, as shown in FIG. 13 (2), the correction current Is is indicated by a curve that is convex upward in the braking direction (positive side). 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. 14 shows the case of a low vehicle speed.
Since the vehicle speed is low, the vehicle speed multiplication coefficient kv shows a value near 1.0 (see FIG. 6), and since it is in the almost released state, the steering torque multiplication coefficient kt shows about 1.0 (see FIG. 7). Accordingly, the shape of the relation curve of the base correction steering angular velocity ωmb with respect to the steering angle θ shown in FIG. 5 is corrected to be slightly flat.

  Since the steering torque addition coefficient St is 0 (see FIG. 8), the addition coefficient S is 0 regardless of the value of the vehicle speed addition coefficient Sv, and the steering angle θ shown in FIG. By simply flattening the relationship curve of the base correction rudder angular velocity ωmb, there is no vertical shift, and the target rudder angular velocity ωm passing through the origin is corrected (see FIG. 14 (1)).

  Referring to FIG. 14 (1), 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 is shown in FIG. As shown in 2), the maximum steering angle θmax at which the steering wheel starts to be returned shows a large value in the assist direction (negative side), and gradually approaches 0 as the steering angle θ becomes smaller. It is.

  Since the steering torque T is 0 because it is almost released, the self-aligning torque acts, and the steering wheel naturally returns and the steering angle θ decreases. However, the steering system usually becomes limited in the middle due to friction of the steering system, etc. until the neutral position is reached. Although this does not return, this correction current Is acts to force the steering angle to the neutral position where the steering torque T remains zero at all steering angles θ as shown in FIG. 14 (3). 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.
Further, in the relationship curve of the steering torque multiplication coefficient kt with respect to the steering torque T in FIG. 7, since the steering torque multiplication coefficient kt smoothly changes from 1.0 to near 0 with respect to the steering torque T, the steering torque is released during steering of the steering wheel. There is no abrupt change in steering torque when shifting from a state other than the state (the state where the steering person is applying the return steering force) to the releasing state and vice versa, so that the steering person feels uncomfortable Don't give.

FIG. 15 shows a case where the return operation is performed at a high vehicle speed and in a state of being almost released.
As shown in FIG. 15 (1), the target rudder angular velocity ωm is corrected to a curve that passes through the origin without any vertical shift by slightly expanding the relationship curve of the base correction rudder angular velocity ωmb with respect to the rudder angle θ shown in FIG. Has been.

  The target rudder angular velocity ωm intersects with the actual rudder angular velocity ω appearing in the left rotation direction at the rudder angle θr, and the corrected current Is obtained by multiplying the deviation Δω (= ωm−ω) between them by the conversion factor is shown in FIG. As shown in FIG. 15 (2), the maximum steering angle θmax at which the steering wheel starts to be returned shows a large value in the assist direction (negative side), gradually decreases as the steering angle θ decreases, and becomes zero at the steering angle θr. After increasing in the brake direction (positive side), it decreases and reaches the origin.

  As shown in FIG. 14 (3), the correction current Is acts, so that the steering torque T remains zero at all steering angles θ, that is, the neutral position where the steering angle is zero without applying any steering force to the steering wheel. The rudder angle can be returned to.

  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.

It is the coordinate which showed the change of the steering torque with respect to a 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. FIG. 5 is a diagram showing a map of a steering torque addition coefficient St with respect to the steering torque T. It is a figure which shows the map of the steering torque addition coefficient Sv with respect to the vehicle speed v. 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 performing operation which cuts a steering wheel to the right from a neutral position at low vehicle speed. It is a figure which shows the change of the steering angular speed (omega) with respect to the steering angle (theta), the correction electric current Is, and the steering torque T at the time of performing operation which cuts a steering wheel to the right from a neutral position 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 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. It is a figure which shows the change of the steering angular speed (omega) with respect to the steering angle (theta), the correction electric current Is, and the steering torque T at the time of return operation performed at a high vehicle speed in a substantially hand-off state.

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 37b ... vehicle speed 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 ... 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 steering angular speed based on the steering torque and the vehicle speed;
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 correction current value based on the difference between the target rudder angular speed and the actual rudder angular speed;
Assist target current calculation means for adding the corrected current value to the assist base current value to obtain an assist target current;
An electric power steering apparatus comprising: The base correction rudder angular velocity calculation means is
A base correction rudder angular speed storage means for storing a relationship of a base correction rudder angular speed to a rudder angle in a specific driving state set in advance;
The electric power steering apparatus according to claim 1, wherein a base correction rudder angular speed is extracted and calculated based on the rudder angle from a relation of a base correction rudder angular speed to a rudder angle stored in the base correction rudder angular speed storage means. The multiplication coefficient calculation means is
Vehicle speed multiplication coefficient storage means for storing a relationship of a vehicle speed multiplication coefficient value to the vehicle speed set in advance;
Steering torque multiplication coefficient storage means for storing the relationship of the 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 of the vehicle speed multiplication coefficient value to the vehicle speed stored in the vehicle speed multiplication coefficient storage means,
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,
3. The electric power steering apparatus according to claim 1, wherein a multiplication coefficient value is calculated by multiplying the extracted vehicle speed multiplication coefficient value and the steering torque multiplication coefficient value. The addition coefficient calculation means is
Vehicle speed addition coefficient storage means for storing a relationship of a vehicle speed addition coefficient value to the vehicle speed set in advance;
Steering torque addition coefficient storage means for storing the relationship of the steering torque addition coefficient value to the steering torque set in advance,
The vehicle speed addition coefficient value is extracted and calculated based on the vehicle speed from the relationship between the vehicle speed addition coefficient value and the vehicle speed stored in the vehicle speed addition coefficient storage means,
The steering torque addition coefficient value is extracted and calculated from the relationship of the steering torque addition coefficient value to 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 the addition coefficient value is calculated by multiplying the extracted vehicle speed addition coefficient value and the steering torque addition coefficient value.

Images