JP5029338B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus in which a steering assist force is applied by an electric motor to a steering mechanism that steers steered wheels, and in particular, even when the grip force of a tire is lost, the vehicle The present invention relates to an electric power steering apparatus capable of stabilizing the behavior.

2. Description of the Related Art Conventionally, as a steering device, an electric power steering device that gives a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque generated when a driver steers a steering wheel has been widely used.
Further, in such an electric power steering apparatus, in order to improve the steering performance and stabilize the behavior of the vehicle during cornering, a self-aligning torque that is a torque for returning the wheel attached to the vehicle to neutral is obtained. Further, there have been proposed ones that are used for steering control, and those that perform steering control in consideration of the grip state of the tire.

As a method for calculating the grip state of the tire, for example, a method of controlling the reaction force device using a deviation between the standard yaw rate and the actual yaw rate as a value corresponding to the grip state of the tire has been proposed (for example, see Patent Document 1). ). In addition, a vehicle steering reaction force control device that increases the steering force according to the rate of change of the yaw rate during understeer has been proposed (see, for example, Patent Document 2).
JP 2006-264392 A Japanese Patent No. 2894006

  However, as described above, when the deviation between the standard yaw rate and the actual yaw rate is used as a value corresponding to the grip state, these yaw rate deviations represent the grip state, but the error from the actual grip state is relatively large. The exact grip force of the tire cannot be detected. For example, when the vehicle is suddenly increased or decreased, or when making a large turn at a low speed such as a U-turn, the grip force of the tire is sufficient. Therefore, there is an unsolved problem that the correction control is turned on, and the driver feels uncomfortable.

  In addition, when the steering force is increased during oversteering, it is effective for preventing excessive steering during initial oversteering and suppressing the initial oversteering behavior, but the oversteering behavior by the driver after oversteering occurs. Even during so-called countersteering that is operated to stabilize the steering, the steering force is increased and the steering reaction force is felt, and there is an unsolved problem that countersteering operation becomes difficult.

  Accordingly, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and when the vehicle steer state is at least oversteer, it suppresses steering increase and facilitates countersteer steering. An object of the present invention is to provide an electric power steering device capable of improving the stability of vehicle behavior.

  In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention includes a steering torque detecting means for detecting a steering torque input to a steering mechanism for turning steered wheels, and steering to the steering mechanism. An electric power steering apparatus comprising: an electric motor that applies auxiliary force; and a control unit that calculates a steering auxiliary current command value based on the steering torque and controls the electric motor based on the calculated steering auxiliary current command value. A steering state detection means for detecting a steering state of the vehicle, a grip loss degree detection means for detecting a grip loss degree indicating a degree of loss of the grip force of the tire, and a steering torque detected by the steering torque detection means. And a differential torque compensation means for compensating the response near the steering neutral point and at least the steering state detection means. It is characterized in that a compensation value correcting means for correcting the torque differential compensation value of the torque differential value compensation means on the basis of the grip loss level detected by the steering state and the grip loss degree detecting means.

The electric power steering apparatus according to claim 2 is the electric power steering apparatus according to claim 1, wherein the compensation value correcting means determines whether the steering state is oversteer when the grip loss degree is a predetermined value or more. The torque differential compensation value correction mode is changed in accordance with whether it is understeer.
Furthermore, an electric power steering apparatus according to a third aspect of the present invention is the invention according to the first aspect, further comprising steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means has a predetermined value for the grip loss degree. When the steering state is oversteer as described above and the steering state detecting means detects an increased steering, the torque differential value compensation value is corrected to decrease according to the grip loss degree. It is characterized by being.

  Furthermore, an electric power steering apparatus according to a fourth aspect of the present invention is the invention according to the first aspect, further comprising steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means has a predetermined grip loss degree. The torque differential compensation value is increased and corrected in accordance with the grip loss degree when counter steering is detected by the steering state detection means when the steering state is oversteer. It is characterized by being.

  Still further, according to a fifth aspect of the present invention, there is provided an electric power steering apparatus according to the first aspect of the present invention, further comprising steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means has a predetermined grip loss degree. And when the steering state is oversteer and when the steering state detecting means detects an increased steering, the torque differential compensation value is corrected to decrease according to the grip loss degree, and the steering is detected. When the state detection means detects counter steer steering, the torque differential compensation value is increased and corrected in accordance with the grip loss degree.

  According to a sixth aspect of the present invention, there is provided the electric power steering apparatus according to any one of the first to fifth aspects, further comprising a steering state detecting unit that detects a steering state of the vehicle, wherein the compensation value correcting unit includes: When the degree of grip loss is equal to or greater than a predetermined value and the steering state is understeer, the torque differential compensation value is decreased according to the degree of grip loss when the steering state detecting means detects an increase in steering. It is characterized by being comprised so that it may correct | amend.

  Furthermore, an electric power steering apparatus according to a seventh aspect is the invention according to any one of the third to sixth aspects, wherein the steering state detecting means includes a yaw rate detecting means for detecting a yaw rate of the vehicle and a motor of the electric motor. Motor angular velocity detecting means for detecting the angular velocity, and is configured to detect increased steering and counter-steer steering based on the yaw rate and the sign of the motor angular velocity.

  Furthermore, an electric power steering apparatus according to an eighth aspect of the present invention is the invention according to any one of the third to sixth aspects, wherein the steering state detecting means includes a yaw rate detecting means for detecting a yaw rate of the vehicle, and a steering wheel. Steering speed detection means for detecting the steering speed, and is configured to detect the increased steering and counter-steer steering based on the yaw rate and the sign of the steering speed.

  Still further, an electric power steering apparatus according to a ninth aspect is the invention according to any one of the first to eighth aspects, wherein the self-aligning torque detecting means detects a self-aligning torque generated on the steered wheel side. A grip force degree detecting means, comprising: a lateral force detecting means for detecting a lateral force of the vehicle; and a self-aligning torque estimating means for estimating a self-aligning torque based on the lateral force detected by the lateral force detecting means. Is configured to detect the degree of grip loss based on the self-aligning torque detected value detected by the self-aligning torque detecting means and the self-aligning torque estimated value estimated by the self-aligning torque estimating means. It is characterized by having.

  According to the electric power steering device of the present invention, the torque differential compensation value of the torque differential compensation means for compensating the response near the steering neutral point with respect to the electric motor current command value calculated based on the steering torque Since the electric motor is driven and controlled based on the steering assist current command value obtained by the correction based on the steering state and the grip loss degree of the tire, when the grip loss degree exceeds a predetermined value, the vehicle steering Optimal steering assist control according to the state can be performed, and it is possible to obtain an effect that it is possible to easily perform counter-steer steering in oversteer while suppressing excessive steering.

Here, when the vehicle is oversteering and the grip loss degree is equal to or greater than a predetermined value, when the driver performs steering by increasing the steering, the torque differential compensation value is decreased to suppress the steering by increasing the countersteer steering. When performing, counter-steer steering is easily performed by increasing the torque differential compensation value.
Further, when the vehicle is understeer and the grip loss degree is equal to or greater than a predetermined value, when the driver increases and steers, the steering is suppressed by decreasing the torque differential compensation value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention, in which SM is a steering mechanism. This steering mechanism SM has a steering shaft 2 having an input shaft 2a to which a steering force applied from a driver is transmitted to the steering wheel 1 and an output shaft 2b connected to the input shaft 2a via a torsion bar (not shown). It has. The steering shaft 2 is rotatably mounted on the steering column 3, one end of the input shaft 2a is connected to the steering wheel 1, and the other end is connected to a torsion bar (not shown).

The steering force transmitted to the output shaft 2b is transmitted to the intermediate shaft 5 via the universal joint 4 composed of the two yokes 4a and 4b and the cross connecting portion 4c for connecting them, It is transmitted to the pinion shaft 7 through a universal joint 6 composed of yokes 6a and 6b and a cross connecting portion 6c for connecting them.
The steering force transmitted to the pinion shaft 7 is transmitted to the left and right tie rods 9 via the steering gear mechanism 8, and the left and right steered wheels WL and WR are steered by these tie rods 9. Here, the steering gear mechanism 8 is configured in a rack and pinion type having a pinion 8b coupled to the pinion shaft 7 and a rack shaft 8c meshing with the pinion 8b in the gear housing 8a, and is transmitted to the pinion 8b. The rotational motion obtained is converted into a linear motion in the vehicle width direction by the rack shaft 8 c and transmitted to the tie rod 9.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a speed reducer 11 such as a reduction gear connected to the output shaft 2b, and an electric motor 12 composed of, for example, a brushless motor that generates a steering assist force connected to the speed reducer 11. Yes.
A steering torque sensor 14 is disposed in a housing 13 connected to the steering wheel 1 side of the speed reducer 11. The steering torque sensor 14 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is converted into a torsional angular displacement, the torsional angular displacement is detected as a magnetic change or a resistance change, and converted into an electrical signal.

  Then, the steering torque detection value T output from the steering torque sensor 14 is input to a controller 15 constituted by, for example, a microcomputer as shown in FIG. In addition to the torque detection value T, the controller 15 detects the vehicle speed detection value Vx detected by the vehicle speed sensor 16, the motor currents Ia to Ic flowing through the electric motor 12, the rotation angle sensor 17 configured by a resolver, an encoder, and the like. The rotation angle θm of the electric motor 12 is also input.

  The controller 15 calculates a steering assist current command value Iref that causes the electric motor 12 to generate a steering assist force according to the input torque detection value T and the vehicle speed detection value Vx, and the calculated steering assist current command value Iref. Various compensation processes such as convergence compensation, inertia compensation, self-aligning torque compensation, and torque differential compensation based on the torque detection value T are performed based on the motor angular velocity ωm and the motor angular acceleration αm calculated based on the rotation angle θm. Are converted into dq axis command values, and these dq axis command values are converted into two-phase / three-phase to calculate motor current command values Iaref to Icref. Based on the calculated motor current command values Iaref to Icref Thus, the currents Ia to Ic flowing through the electric motor 12 are feedback-controlled to drive-control the electric motor 12.

  That is, the controller 15 calculates the steering assist current command value Iref for calculating the steering assist current command value Iref based on the steering torque T and the vehicle speed Vx, and the steering assist current command calculated by the steering assist current command value calculator 21. A command value compensation unit 22 for compensating the value Iref, a grip loss degree detection unit 23 as a grip loss degree detection means for detecting a grip loss degree representing the degree of tire grip loss, and a vehicle steer state are detected. The torque differential compensation value It of the torque differential compensation unit 37 in the command value compensation unit 22 based on the grip loss degree detected by the steering state detection unit 24 and the grip loss degree detection unit 23 and the steer state detected by the steering state detection unit 24. A compensation value correction unit 25 serving as a compensation value correction unit for correcting the steering assist current command after compensation compensated by the command value compensation unit 22 A dq-axis current command value calculation unit 26 that calculates a dq-axis current command value based on Iref ′, and a dq-axis command value output from the dq-axis current command value calculation unit 26 is 2 Two-phase / three-phase converter 27 for calculating motor current command values Iaref to Icref by phase / three-phase conversion, and motor current command values Iaref to Icref output from the two-phase / 3-phase converter 27 The motor current controller 28 generates motor currents Ia to Ic.

The steering assist current command value calculation unit 21 calculates a steering assist current command value Iref, which is a current command value, with reference to the steering assist current command value calculation map shown in FIG. 3 based on the steering torque T and the vehicle speed Vx.
As shown in FIG. 3, this steering assist current command value calculation map is a parabolic curve with the steering torque T on the horizontal axis, the steering assist current command value Iref on the vertical axis, and the vehicle speed Vx as a parameter. The steering assist current command value Iref is maintained at “0” while the steering torque T is between “0” and a set value Ts1 in the vicinity thereof, and the steering torque T is set at the set value Ts1. When it exceeds, the steering assist current command value Iref increases relatively slowly with the increase of the steering torque T, but when the steering torque T further increases, the steering assist current command value Iref increases steeply with the increase. The characteristic curve is set so that the inclination becomes smaller as the vehicle speed increases.

  The command value compensator 22 differentiates the motor rotation angle θm detected by the rotation angle sensor 17 to calculate the motor angular velocity ωm, and differentiates the motor angular velocity ωm calculated by the angular velocity calculator 31. The angular acceleration calculation unit 32 that calculates the motor angular acceleration αm and the motor angular velocity ωm calculated by the angular velocity calculation unit 31 compensates for the convergence of the yaw rate and brakes the operation of the steering wheel 1 swinging. Based on the motor angular acceleration αm calculated by the convergence compensation unit 33 and the angular acceleration calculation unit 32, an inertia compensation value Ii that compensates for the torque equivalent generated by the inertia of the electric motor 12 is calculated, and the sense of inertia or control response is obtained. Inertia compensation unit 34 for preventing the deterioration of the steering wheel, SAT detection unit 35 for detecting self-aligning torque (SAT) generated on the steered wheel side, and SA A SAT compensation unit 36 for calculating a self-aligning torque compensation value SATc for performing self-aligning torque compensation based on the self-aligning torque detected by the detection unit 35, and a steering torque T detected by the steering torque sensor 14 are differentiated. And a torque differential compensator 37 for calculating a torque differential compensation value It for compensating the responsiveness in the vicinity of the steering neutral point.

  Here, the convergence compensator 33 receives the vehicle speed Vx detected by the vehicle speed sensor 16 and the motor angular velocity ωm calculated by the angular velocity calculator 31, and the steering wheel 1 swings to improve the yaw convergence of the vehicle. A convergence compensation value Id is calculated by multiplying the motor angular velocity ωm by a convergence control gain Kv that is changed according to the vehicle speed Vx so as to apply a brake to the turning operation.

Further, the SAT detection unit 35 receives the steering torque T, the angular velocity ωm, the angular acceleration αm, and the steering assist current command value Iref calculated by the steering assist current command value calculation unit 21, and based on these, the self aligning torque SAT is calculated. Calculate.
The principle of calculating the self-aligning torque SAT will be described with reference to FIG. 4 showing the state of torque generated between the road surface and the steering. That is, when the driver steers the steering wheel 1, a steering torque T is generated, and the electric motor 12 generates an assist torque Tm according to the steering torque T. As a result, the wheel W is steered and a self-aligning torque SAT is generated as a reaction force. Further, at that time, torque serving as a steering resistance of the steering wheel 1 is generated by the inertia J and friction (static friction) Fr of the electric motor 12. Considering the balance of these forces, the following equation of motion can be obtained:

J ・ αm + Fr ・ sign (ωm) + SAT = Tm + T (1)
Here, when the above equation (1) is Laplace transformed with the initial value zero and the self-aligning torque SAT is solved, the following equation (2) is obtained.
SAT (s) = Tm (s) + T (s) − J · αm (s) − Fr · sign (ωm (s)) (2)
As can be seen from the above equation (2), the inertia J and static friction Fr of the electric motor 12 are obtained in advance as constants, so that the self-aligning torque is obtained from the motor angular velocity ωm, motor angular acceleration αm, assist torque Tm, and steering torque T. SAT can be detected, and this self-aligning torque detection value is SATd. Here, since the assist torque Tm is proportional to the steering assist current command value Iref, the steering assist current command value Iref is applied instead of the assist torque Tm.

  Then, the self-aligning torque compensation value SATc calculated by the SAT compensator 36 from the corrected torque differential compensation value It ′ obtained by correcting the torque differential compensation value It calculated by the torque differential compensator 37 by the compensation value corrector 25 described later. Is subtracted by the subtracter 38a, and the subtracted output of the subtractor 38a and the inertia compensation value Ii calculated by the inertia compensator 34 are added by the adder 38b. The added output of the adder 38b and the convergence compensator 33 are added. Is added by the adder 38c to calculate a command compensation value Icom, and this command compensation value Icom is output from the steering assist current command value calculation unit 21. Is added by an adder 38d to calculate a post-compensation steering assist current command value Iref '. The post-compensation steering assist current command value Iref' is calculated as a dq axis current command value. Is output to the calculation unit 26.

The grip loss degree detection unit 23 also includes a self-aligning torque detection value SATd input from the SAT detection unit 35 of the command value compensation unit 22 and a self-alignment torque input from the SAT estimation unit 41 that estimates the self-aligning torque. Based on the estimated aligning torque SATp, a grip loss degree that represents the degree of tire grip loss is calculated.
Here, the principle by which the SAT estimating unit 41 estimates the self-aligning torque estimated value SATp is as follows.

FIG. 5 and FIG. 6 show a model of a vehicle motion in which a tire rolls while skidding.
In FIG. 5, the lateral force generated on the entire ground contact surface of the tire becomes the deformation area (shaded portion) in the lateral direction of the tread portion, and the self-aligning torque SAT acts in the direction of decreasing the slip angle. . FIG. 6 also shows that the point of application of lateral force (the center point of the ground contact surface) is behind the tire centerline. The added value of the pneumatic trail and the caster trail is the trail.

  5 and 6 that the self-aligning torque SAT is a product of the lateral force Fy and the trail (lateral force Fy × trailer). That is, when the trail is εn, the self-aligning torque SAT can be calculated by the following equation (3). The self-aligning torque calculated by the equation (3) is assumed to be an estimated value SATp of the self-aligning torque.

SATp = εn · Fy (3)
When the distance from the center of gravity to the rear wheel is L2 (fixed value), the vehicle weight is m, the lateral acceleration is Gy, the vehicle inertia moment is Mo, the differential value of the yaw rate γ is dγ / dt, and the wheelbase is L, The lateral force Fy can be calculated by the following equation (4).
Fy = (L2 · m · Gy + Mo · dγ / dt) / L (4)
On the other hand, FIG. 7 is a characteristic diagram showing the characteristics of the lateral force Fy and the self-aligning torque SAT with respect to the slip angle, and the lateral force Fy and SAT are non-linear characteristics with respect to the slip angle. Since the SAT is the lateral force Fy × the trail εn and the caster trail is a fixed value, the non-linear characteristic of the self-aligning torque SAT with respect to the lateral force Fy directly represents a change in the pneumatic trail. Further, the characteristic of the self-aligning torque SAT with respect to the lateral force is caused by an increase in the slip area in FIG. 6 and a decrease in the pneumatic trail.

  Further, since the self-aligning torque SAT is a product of the lateral force Fy and the trail εn, the slip area does not increase in the linear region, and the pneumatic trail has a constant value. Therefore, the pneumatic trail and caster in the linear region are constant. FIG. 8 shows the estimated self-aligning torque SATp in accordance with the dimension of the self-aligning torque SAT with the sum with the trail, that is, the trail εn and the lateral force Fy in accordance with the dimension of the self-aligning torque SAT.

  Here, if the pneumatic trail is constant, the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp follow the same trajectory, but if the sliding area increases and the pneumatic trail decreases, self-aligning There is a difference between the detected torque value SATd and the estimated self-aligning torque value SATp. This difference represents the degree to which the grip is lost, and this is referred to as “grip loss degree” in the present invention. The self-aligning torque detection value SATd calculated by the above equation (2) and the self-aligning torque estimated value SATp calculated by the above equation (3) are compared by the following equation (5).

g = SATp−SATd (5)
The g calculated by the equation (5) is the grip loss degree, and the degree of loss of the grip force of the tire in the vehicle can be estimated from the grip loss degree g.
FIG. 8 is a characteristic diagram showing a comparison between the detected self-aligning torque value SATd and the estimated self-aligning torque value SATp (trail εn × lateral force Fy), and shows the self-aligning torque as the slip angle increases. It shows how the SAT is lost, and the difference between the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp calculated from the above equation (5) is used as the grip loss degree g (shaded portion in the figure). Show.

  For this reason, a yaw rate sensor 42 that detects the yaw rate of the vehicle and a lateral acceleration sensor 43 that detects the lateral acceleration of the vehicle are provided, and the yaw rate γ detected by the yaw rate sensor 42 and the lateral acceleration Gy detected by the lateral acceleration sensor 43 are obtained. This is input to the lateral force detection unit 44, and the lateral force detection unit 44 calculates the lateral force Fy by calculating the equation (4). The calculated lateral force Fy is input to the SAT estimation unit 41, and this SAT The estimation unit 41 calculates the equation (3) to calculate the self-aligning torque estimated value SATp.

  The self-aligning torque detection value SATd detected by the SAT detection unit 35 and the self-aligning torque estimation value SATp estimated by the SAT estimation unit 41 are input to the grip loss degree detection unit 23, and the grip loss degree detection unit 23. By calculating the equation (5), a grip loss degree g indicating the degree of tire grip loss is calculated, and the calculated grip loss degree g is applied to the compensation value correction unit 25 as compensation value correction means. input.

Further, the steering state detection unit 24 outputs the steering angle δ output from the steering angle sensor 45 that detects the steering angle δ of the steering mechanism SM, the yaw rate γ detected by the yaw rate sensor 42 described above, and the vehicle speed Vx detected by the vehicle speed sensor 16. Is input, and based on these, it is determined whether the steering state of the vehicle is understeer or oversteer.
The determination of the steer state is performed as follows. First, the standard yaw rate γ _{0 of the} vehicle can be expressed by the following equation (6).

γ ₀ = {1 / (1 + Ts)} {1 / (1 + A · Vx ² )} (Vxδ / Lα) (6)
Here, δ is a steering angle, Vx is a vehicle speed, L is a wheel base, T is a time constant, s is a Laplace operator, A is a stability factor, and α is a steering ratio.
The stability factor A is expressed by the following equation (7).
A = (m / 2L ² ) {(Lf · Kf−Lr · Kr) / Kf · Kr} (7)
Here, m is the vehicle weight, Lf is the distance between the vehicle center of gravity and the front wheel axle, Lr is the distance between the vehicle center of gravity and the rear wheel axle, Kf is the cornering power of the front tire, and Kr is the rear tire. Cornering power.

Then, by comparing the reference yaw rate γ ₀ and the actual yaw rate γ detected by the yaw rate sensor 42, the steering state of the vehicle can be determined as follows.
| Γ | − | γ ₀ |> 0: Oversteer | γ | − | γ ₀ | <0: Understeer A logical value “1” when the steering state of the vehicle is oversteer, and a logical value “0” when the vehicle is understeered. Is output to the compensation value correction unit 25.

  The compensation value correction unit 25 includes a grip loss degree g detected by the grip loss degree detection unit 23, a steering state signal SS corresponding to the steering state detected by the steering state detection unit 24, a yaw rate γ detected by the yaw rate sensor 42, and a command value. The torque differential for correcting the torque differential compensation value It output from the torque differential compensation unit 37 of the command value compensation unit 22 based on the motor angular velocity ωm calculated by the angular velocity calculation unit 31 of the compensation unit 22 is input. A compensation gain calculation unit 51 for calculating the compensation gain Kt; a multiplier 52 for multiplying the torque differential compensation value It calculated by the torque differential compensation unit 37 by the torque differential compensation gain Kt calculated by the compensation gain calculation unit 51; It has. Then, the multiplication output of the multiplier 52 is input to the subtractor 38a as the corrected torque differential compensation value It ′.

  Here, the compensation gain calculation unit 51 executes a compensation gain calculation process shown in FIG. In the compensation gain calculation process, first, in step S1, various input values of the yaw rate γ, the steering state signal SS, the grip loss degree g, and the motor angular velocity ωm are read, and then the process proceeds to step S2 to read the read grip loss degree. It is determined whether or not g is equal to or greater than a predetermined value g1 representing a preset grip limit. If g <g1, it is determined that the tire is in a normal steering state in which the grip force of the tire has not reached the grip limit. The process proceeds to S3, the torque differential compensation gain Kt is set to “1”, the set torque differential compensation gain Kt is output to the multiplier 52, and then the process returns to step S1.

When the determination result in step S2 is g ≧ g1, the process proceeds to step S4, and whether the steer state signal SS read in step S1 indicates oversteer with a logical value “1” or logical value “0”. It is determined whether or not understeer is indicated, and when the steer state signal SS is logical “0” and understeer is indicated, the process proceeds to step S5.
In this step S5, it is determined whether or not the signs of the yaw rate γ and the motor angular speed ωm are the same, and when the signs of the yaw rate γ and the motor angular speed ωm are different signs, the steering wheel 1 is steered in the switchback direction. The process proceeds to step S3.

  When the signs of the yaw rate γ and the motor angular velocity ωm are the same sign, it is determined that the steering wheel 1 is being steered in the increasing direction, and the process proceeds to step S6 to calculate the torque differential compensation gain shown in FIG. A characteristic line L2 is selected on the map, and a torque differential compensation gain K2 that decreases from “1” as the grip loss degree g increases from a predetermined value g1 according to the characteristic line L2 is calculated. K2 is output to the multiplier 52 as the torque differential compensation gain Kt, and the process returns to step S1.

  When the determination result in step S4 indicates that the steer state signal SS is a logical value “1” and indicates oversteer, the process proceeds to step S7, and the yaw rate γ and the motor angular velocity ωm are similar to those in step S5. It is determined whether or not the signs are the same, and when the signs of the yaw rate γ and the motor angular velocity ωm are different signs, it is determined that the steering wheel 1 is steered in the switchback direction, and the process proceeds to step S8. Then, the characteristic line L1 is selected in the torque differential compensation gain calculation map shown in FIG. 10, and the torque differential compensation gain K1 in which the grip loss degree g increases from the predetermined value g1 according to the characteristic line L1 is calculated. The compensation gain K1 is output to the multiplier 52 as the torque differential compensation gain Kt, and the process returns to step S1.

  When the determination result of step S7 is that the signs of the yaw rate γ and the motor angular velocity ωm are the same sign, it is determined that the steering wheel 1 is being steered in the increasing direction, and the process proceeds to step S9, and FIG. A characteristic line L2 is selected in the torque differential compensation gain calculation map shown in FIG. 4B, and a torque differential compensation gain K2 that decreases from “1” as the grip loss degree g increases from the predetermined value g1 is calculated according to the characteristic line L2. The calculated torque differential compensation gain K2 is output to the multiplier 52 as the torque differential compensation gain Kt, and the process returns to step S1.

  Here, the torque differential compensation gain calculation map of FIG. 10 has the grip loss degree g on the horizontal axis and the torque differential compensation gain Kt on the vertical axis, and when the grip loss degree g is less than the predetermined value g1, When the compensation gains K1 and K2 are maintained at “1” and the grip loss degree g is equal to or greater than the predetermined value g1, the torque differential compensation gain K1 increases from “1” as the grip loss degree g increases on the characteristic line L1. In the characteristic line L2, the torque differential compensation gain K2 is set to decrease from “1” as the grip loss degree g increases.

Here, the slopes of the characteristic lines L1 and L2 in the torque differential compensation gain calculation map are set according to the specifications of the vehicle, and both characteristic lines L1 and L2 are not limited to the linear form shown in FIG. .
Further, the dq axis current command value calculation unit 26 calculates a d axis current command value Idref based on the compensated steering assist current command value Iref ′ and the motor angular velocity ωm, Based on the electrical angle θe and the motor angular velocity ωm input from the electrical angle conversion unit 30, the d-axis EMF component ed (θ) and the q-axis EMF component eq (θ) of the dq-axis induced voltage model EMF (Electromotive Force) are obtained. The induced voltage model calculating unit 62 to calculate, the d-axis EMF component ed (θ) and the q-axis EMF component eq (θ) output from the induced voltage model calculating unit 62, and the d-axis current command value calculating unit 61 are output. A q-axis current command value calculation unit 63 for calculating a q-axis current command value Iqref based on the d-axis current command value Idref, the compensated steering assist current command value Iref ′, and the motor angular velocity ωm. I have.

The d-axis current command value Idref calculated by the d-axis current command value calculation unit 61 and the q-axis current command value Iqref calculated by the q-axis current command value calculation unit 63 are supplied to the 2-phase / 3-phase conversion unit 27. Is done.
The two-phase / three-phase conversion unit 27 performs two-phase / three-phase conversion on the input d-axis current command value Idref and the q-axis current command value Iqref based on the electrical angle θe input from the electrical angle conversion unit 30. The three-phase motor current command values Iaref, Ibref and Icref are calculated, and the calculated motor current command values Iaref, Ibref and Icref are output to the motor current control unit 28.

  The motor current control unit 28 includes a motor current detection unit 70 that detects motor currents Ia, Ib, and Ic supplied to the three-phase coils of the electric motor 12, and a motor current command input from the two-phase / three-phase conversion unit 27. Subtracters 71a, 71b, and 71c for obtaining respective phase current deviations ΔIa, ΔIb, and ΔIc by individually subtracting the motor currents Ia, Ib, and Ic detected by the motor current detector 70 from the values Iaref, Ibref, and Icref A current control unit 72 that performs proportional-integral control on the phase current deviations ΔIa, ΔIb, and ΔIc to calculate voltage command values Va, Vb, and Vc, and voltage command values Va, Vb output from the current control unit 72 And an inverter formed of a pulse width modulation (PWM) signal by calculating a duty ratio of each phase of the electric motor 12 by performing duty calculation based on Vc A pulse width modulation unit 73 that forms a control signal, and an inverter 74 that forms three-phase motor currents Ia, Ib, and Ic based on the inverter control signal output from the pulse width modulation unit 73 and outputs them to the electric motor 12; It has.

Next, the operation of the controller 15 will be described with reference to the flowchart of FIG.
First, steering torque T from the steering torque sensor 14, vehicle speed Vx from the vehicle speed sensor 16, motor rotation angle θm from the rotation angle sensor 17, yaw rate γ from the yaw rate sensor 42, lateral acceleration Gy from the lateral acceleration sensor 43, steering The steering angle δ from the angle sensor 45 is read (step S21). Next, the steering assist current command value Iref corresponding to the steering torque T and the vehicle speed Vx is calculated based on the read steering torque T and the vehicle speed Vx with reference to the steering assist current command value calculation map shown in FIG. 3 (step S22). The motor rotation angle θm from the rotation angle sensor 17 is differentiated to calculate the angular velocity ωm of the electric motor 12, and the calculated angular velocity ωm is differentiated to calculate the angular acceleration αm (step S23).

  Next, based on the steering torque T, the steering assist current command value Iref, the motor angular velocity ωm, and the motor angular acceleration αm, the calculation of the equation (2) is performed to detect the self-aligning torque detection value SATd (step S24). Based on the calculated self-aligning torque detection value SATd, a self-aligning torque compensation value SATc is calculated (step S25). Furthermore, the lateral force Fy is calculated based on the yaw rate γ and the lateral acceleration Gy, and the lateral force Fy is calculated. Based on the calculated lateral force Fy and the trail εn, the above equation (3) is calculated. Thus, the self-aligning torque estimated value SATp is calculated (step S26).

Subsequently, the grip loss degree g is detected from the deviation between the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp (step S27), and then based on the vehicle speed Vx and the steering angle δ, the equation (6) and The reference yaw rate γ ₀ is calculated by calculating the expression (7), and the calculated reference yaw rate γ ₀ and the actual yaw rate γ are compared to detect whether the vehicle steer state is oversteer or understeer. (Step S28).

  Next, the compensation gain calculation process shown in FIG. 9 is executed based on the grip loss degree g calculated in step S27, the steer state detected in step S28, the yaw rate γ read in step S21, and the motor angular velocity ωm calculated in step S23. Then, a torque differential compensation gain Kt for correcting the torque differential compensation value It is calculated (step S29).

  Next, a convergence compensation value Id for compensating the convergence of the yaw rate is calculated based on the motor angular velocity ωm, and the inertial feeling or the torque equivalent generated by the inertia of the electric motor 12 is compensated based on the motor angular acceleration αm. An inertia compensation value Ii for preventing deterioration of control responsiveness is calculated, and a torque differential compensation value It for differentiating the steering torque T to compensate for responsiveness near the steering neutral point is calculated (step S30), and then calculated. A corrected torque differential compensation gain Kt ′ is calculated by multiplying the torque differential compensation value It by the torque differential compensation gain Kt calculated in step S29 (step S31).

  Then, the command compensation value Icom is calculated by adding the convergence compensation value Id, the inertia compensation value Ii, and the corrected torque differential compensation value It ′, and subtracting the self-aligning torque compensation value SATc (step S32). The command compensation value Icom is added to the steering assist current command value Iref to calculate a compensated steering assist current command value Iref ′ (step S33).

  Next, the d-axis current command value Idref is calculated based on the calculated post-compensation steering assist current command value Iref ′, the q-axis current command value Iqref is calculated (step S34), and then the d-axis current command value Idref and q The shaft current command value Iqref is subjected to two-phase / three-phase conversion based on the electrical angle θe to calculate three-phase motor current command values Iaref, Ibref, and Icref (step S35).

  Next, the current deviations ΔIa, ΔIb, and ΔIc are calculated by subtracting the motor currents Ia, Ib, and Ic detected by the motor current detection unit 70 from the three-phase motor current command values Iaref, Ibref, and Icref (step S36). PI control processing is performed on the current deviations ΔIa, ΔIb, and ΔIc to calculate voltage command values Va, Vb, and Vc (step S37), and the calculated voltage command values Va, Vb, and Vc are subjected to pulse width modulation to obtain a pulse width. A modulation signal is formed, and the formed pulse width modulation signal is output to the inverter 74 (step S38).

  As a result, three-phase motor drive currents Ia, Ib, and Ic are output from the inverter 74 to the electric motor 12, and the electric motor 12 is driven and controlled, so that the optimum steering assist force according to the steering torque T and the vehicle speed Vx. This steering assist force is transmitted to the steering shaft 2 via the speed reducer 11.

  Therefore, when the grip loss degree g is less than the predetermined value g1, it is determined that the steering is in the normal steering state, and the compensation gain calculation process of FIG. 9 proceeds from step S2 to step S3, where the torque differential compensation gain Kt is “ Set to 1 ". For this reason, since the torque differential compensation gain Kt is multiplied by the torque differential compensation value It output from the torque differential compensation unit 37 by the multiplier 52, the torque differential compensation value It is directly used as the corrected torque differential compensation value It ′ as a subtractor. It is input to 38a.

  Therefore, the command value compensation unit 22 calculates a normal convergence compensation value Id, inertia compensation value Ii, self-aligning torque compensation value SATc, and corrected torque differential compensation value It ′, and converges compensation value Id and inertia compensation. The value Ii and the corrected torque differential compensation value It ′ are added and the self-aligning torque compensation value SATc is subtracted to calculate the command compensation value Icom. This command compensation value Icom is calculated by the steering assist current command value calculation unit 21. It is added to the calculated steering assist current command value Iref, and the command value compensation that is optimum for the steering state is performed, so that the driver's steering operation of the steering wheel 1 can be accurately assisted.

From this normal steering state, when the grip force of the front wheel exceeds the grip limit and becomes understeer, and the grip loss degree g detected by the grip loss degree detection unit 23 is equal to or greater than the predetermined value g1, the compensation gain calculation process of FIG. The process proceeds from step S2 to step S4, and the vehicle steer state is understeer. Therefore, the steer state detection unit 24 determines | γ | − | γ ₀ | <0 and determines that the vehicle is understeer. A steer state signal SS of 0 ″ is output to the compensation gain calculator 51.

  For this reason, the process proceeds from step S4 to step S5 in the compensation gain calculation process of FIG. 9 to determine whether the signs of the yaw rate γ and the motor angular velocity ωm are the same sign, and when the signs of the two are different signs. Then, it is determined that the steering wheel 1 is switched back to eliminate understeer, and the process proceeds to step S3, where the torque differential compensation gain Kt is set to “1” as in the normal state, and the normal state Similar steering assist control is performed.

  However, when the steering state of the vehicle is understeer and the steering wheel 1 is turned up and steered and the signs of the yaw rate γ and the motor angular velocity ωm are the same, the process proceeds from step S5 to step S6, and FIG. In the torque differential compensation gain calculation map, a characteristic line L2 is selected, and a torque differential compensation gain Kt that decreases from “1” as the grip loss degree g increases from the predetermined value g1 according to the characteristic line L2 is calculated. Since this torque differential compensation gain Kt is multiplied by the torque differential compensation value It output from the torque differential compensation unit 37, a corrected torque differential compensation value It ′ obtained by reducing and correcting the torque differential compensation value It is calculated.

  Then, the inertia compensation value Ii, the convergence compensation value Id, and the corrected torque differential compensation value It ′ are added, and the self-aligning torque compensation value SATc is subtracted to calculate the command compensation value Icom, and the calculated command compensation Since the value Icom is added to the steering assist current command value Iref calculated by the steering assist current command value calculation unit 21, the responsiveness near the steering neutral point of the steering wheel is reduced to the driver in the state of increasing understeer. The torque differential compensation is performed, and the steering wheel 1 is increased to make it difficult to steer, so that the steering can be suppressed and the vehicle behavior becomes unstable due to the loss of gripping force. it can.

On the other hand, when the rear wheel grip force exceeds the grip limit and the vehicle is oversteered, the steer state detection unit 24 determines | γ | − | γ ₀ | ≧ 0 and determines that the vehicle is oversteered. A steer state signal SS having a value “1” is input to the compensation gain calculation unit 51.

  Therefore, the process proceeds from step S4 to step S7 in the compensation gain calculation process of FIG. At this time, if the driver reverse-turns the steering wheel 1 to counter oversteer and countersteer steering, the sign of the yaw rate γ and the sign of the motor angular velocity ωm are different from each other. In step S8, the characteristic line L1 is selected in the inertia compensation gain calculation map of FIG. 10, and the torque differential compensation gain K1 that increases from “1” as the grip loss degree g increases from the predetermined value g1 is obtained. Calculated. Since this torque differential compensation gain K1 is multiplied by the torque differential compensation value It output from the torque differential compensation unit 37 as the torque differential compensation gain Kt, the corrected torque differential compensation value obtained by increasing the torque differential compensation value It is corrected. It ′ is calculated.

For this reason, torque differential compensation that improves the responsiveness in the vicinity of the steering neutral point from the normal state is performed, countersteering steering is facilitated, and oversteer can be easily eliminated.
Further, when the driver steers the steering wheel 1 while the vehicle is oversteered, the signs of the yaw rate γ and the motor angular speed ωm are the same, and therefore the compensation gain calculation process of FIG. Thus, the process proceeds from step S7 to step S9, and the characteristic line L2 is selected in the torque differential compensation gain calculation map of FIG. A torque differential compensation gain K1 that decreases from “1” as the value g1 increases is calculated. Then, the torque differential compensation gain K1 is multiplied by the torque differential compensation value It output from the torque differential compensation unit 37 as the torque differential compensation gain Kt, thereby correcting the torque differential compensation value It to be corrected. It ′ is calculated, and torque differential compensation is performed to reduce the responsiveness in the vicinity of the steering neutral point for the driver, and the steering wheel 1 is increased to make it difficult to steer and increase the steering force. It can suppress that vehicle behavior becomes unstable by being lost.

As described above, according to the above-described embodiment, the torque differential compensation value is corrected according to whether the vehicle steer state detected by the steer state detection unit 24 is understeer or oversteer, that is, the torque differential compensation gain Kt. Therefore, the optimum torque differential compensation value correction process according to the vehicle steering state can be performed.
In the above embodiment, the self-aligning torque SATd detected based on the steering torque T, the assist torque Tm, the angular velocity ωm and the angular acceleration αm of the electric motor 12, and the self-alignment based on the lateral force Fy generated in the vehicle. The grip loss degree g is calculated from the deviation from the estimated lining torque value SATp. Here, when the grip force of the tire is lost, the response of the self-aligning torque to this is faster than the response of the yaw rate to the loss of the grip force.

  Therefore, by calculating the grip loss degree using the self-aligning torque, it is possible to detect a change in the grip loss degree at an earlier stage than when calculating the grip loss degree using the yaw rate. Therefore, by calculating the degree of grip loss using the self-aligning torque, the grip situation can be detected with higher accuracy, and the steering assist current command value Iref is corrected in accordance with the grip situation thus detected. By reducing the steering assist force, it is possible to generate the steering assist force more accurately, avoiding excessive increase according to the degree of grip loss, and unstable vehicle behavior due to loss of grip force Can be suppressed, and vehicle running stability can be improved.

  Further, as described above, when the grip loss degree g is less than the predetermined value g1, the torque differential compensation gain Kt is set to “1” and the torque differential compensation value It is not corrected, so that grip loss occurs. The steering assist force is suppressed despite the fact that the grip loss is relatively small and does not adversely affect the driver, causing the driver to feel uncomfortable due to insufficient steering assist force being generated. Can be avoided.

  Here, the steering torque sensor 14 corresponds to the steering torque detection means, the processing of FIG. 11 corresponds to the control means, of which the processing in step S22 corresponds to the current command value calculation unit, and the processing in step S24 is the SAT detection. Corresponding to the unit 35 (self-aligning torque detecting means), the process of step S26 corresponds to the SAT estimating part 41 (self-aligning torque estimating means), and the process of step S27 is the grip loss degree detecting part 23 (grip loss degree). The processing of step S28 corresponds to the steer state detection unit 24 (steer state detection unit), the processing of steps S29 and S31 corresponds to the compensation value correction unit 25 (compensation value correction unit), The process of S30 corresponds to the torque differential compensation unit 37 (torque differential compensation means), and the process of step S34 is the dq-axis current command value calculation unit. 6, the process of step S35 corresponds to the 2-phase / 3-phase converter 27, the process of step S36 corresponds to the subtracters 71a to 71c, the process of step S37 corresponds to the PI current control unit 72, The processing in step S38 corresponds to the pulse width modulation unit 73.

  In the above embodiment, the case where the torque differential compensation value It is corrected by the torque differential compensation gain Kt calculated by the compensation gain calculation unit 51 has been described. However, the present invention is not limited to this, and the compensation gain calculation unit 51 is not limited thereto. The steering assist current command value Iref may be directly corrected with the torque differential compensation gain Kt calculated in step (1).

  Further, in the above-described embodiment, the case where the compensation gain calculation unit 51 determines the steer state and changes the correction mode according to the steering state in each of the understeer and the oversteer has been described. However, the understeer is increased. The torque differential compensation gain Kt may be set to “1” regardless of whether steering is performed or switchback steering is performed.

Furthermore, although the case where the lateral acceleration Gy of the vehicle is detected by the lateral acceleration sensor 43 has been described in the above embodiment, the present invention is not limited to this, and the lateral acceleration is determined based on the steering angle of the steering mechanism SM and the vehicle speed Vx. The acceleration Gy may be estimated.
In the above embodiment, the lateral force Fy is estimated based on the yaw rate γ, the lateral acceleration Gy, and the vehicle motion model, and the self-aligning torque that actually acts on the vehicle is estimated based on the lateral force Fy. However, a lateral force sensor may be provided in a hub or the like, and the lateral force may be directly detected by the lateral force sensor, and the self-aligning torque estimated value SATp may be calculated using this.

Alternatively, the self-aligning torque may be estimated using the vehicle motion model in the horizontal plane, the vehicle speed Vx, and the steering angle δ without using the lateral force Fy.
That is, the relationship among the yaw rate γ, the slip angle β, the vehicle speed Vx, and the steering angle δ can be expressed by the following equations (8) and (9).
mVx · (dβ / dt)
= − [MVx + [(Kf · Lf−Kr · Lr) / Vx]] · γ− (Kf + Kr) · β + Kf · δ / n
...... (8)
I · (dγ / dt)
= − [(Kf · Lf ² + Kr · Lr ² ) / Vx] · γ + (− Kf · Lf + Kr · Lr) · β
+ Kf · Lf · δ / n
...... (9)
In the equations (8) and (9), m is the vehicle weight, I is the moment of inertia about the Z axis passing through the center of gravity of the vehicle, L is the wheel base (L = Lf + Lr), and Lf and Lr are the front and rear axles. The horizontal distance from the center of gravity to the center of gravity, Kf and Kr are the cornering power of the front and rear tires, n is the overall steering gear ratio, δ / n is the actual steering angle of the front wheels, β is the slip angle of the center of gravity of the vehicle body, Vx is the vehicle speed, and γ is Yaw rate.

  Since the self-aligning torque can be expressed as a function of the yaw rate γ and the slip angle β, if the yaw rate γ and the slip angle β are arranged as a function of the vehicle speed Vx and the steering angle δ, the self-aligning torque estimated value SATp is obtained. Can be sought. When the self-aligning torque estimated value SATp is obtained from the vehicle speed Vx and the steering angle δ, it is as shown in FIG. This characteristic may be created by simulation using a vehicle motion model after measuring a characteristic value for each vehicle by experiment.

Therefore, in this case, as shown in FIG. 13, the vehicle speed Vx detected by the vehicle speed sensor (vehicle speed detection means) 21 and the steering angle δ detected by the steering angle sensor 45 (steering angle detection means) are used as the SAT estimation unit. 41, the SAT estimation unit 41 may calculate the self-aligning torque estimated value SATp according to the characteristic diagram of FIG.
Furthermore, in the above-described embodiment, the case where the self-aligning torque SAT is estimated based on the motor angular velocity ωm, the motor angular acceleration αm, the steering torque T, and the steering auxiliary current command value Iref has been described. Instead, instead of the steering assist current command value Iref, the motor currents Ia to Ic detected by the motor current detection unit 70 are three-phase / two-phase converted to calculate the q-axis current Iq, and the q-axis current Iq and the motor The motor assist torque Tma calculated by performing the calculation of the following equation (10) based on the angular acceleration αm may be applied.

Tma = Kmt · Iq−Jm · αm (10)
Here, Kmt is the torque constant of the motor, and Jm is the moment of inertia of the rotor portion of the motor.
In addition, a torque sensor such as a magnetostrictive torque sensor is provided on the torque transmission shaft such as the output shaft of the electric motor 12 and the input / output shaft of the speed reducer 11, and the motor assist torque Tma detected by the torque sensor is applied. It may be.

  Furthermore, in the above-described embodiment, the case where the present invention is applied to a column-type electric power steering apparatus in which the electric motor 12 is connected to the steering shaft 2 via the speed reducer 11 has been described, but the present invention is not limited thereto. The present invention is not limited to a pinion type electric power steering apparatus that connects an electric motor to the steering gear mechanism 8 via a speed reducer, or a rack type electric power steering apparatus that connects an electric motor to the rack shaft via a speed reducer. Can be applied.

  Furthermore, in the above embodiment, the case where the present invention is applied to a brushless motor has been described. However, the present invention is not limited to this, and when applied to a motor with a brush, as shown in FIG. Based on the motor current detection value Im output from the motor current detection unit 70 and the motor terminal voltage Vm output from the terminal voltage detection unit 90 in the calculation unit 31, the following equation (11) is calculated to calculate the motor angular velocity ωm. At the same time, the dq-axis current command value calculation unit 26 is omitted, and the compensated steering assist current command value Iref ′ is directly supplied to the motor current control unit 28, and each motor current control unit 28 is also connected to one subtraction unit 71. The current control unit 72, the pulse width modulation unit 73, and the H bridge circuit 91 in place of the inverter 74 may be used.

ωm = (Vm−Im · Rm) / K ₀ (11)
Here, Rm is the motor winding resistance, and K ₀ is the electromotive force constant of the motor.

It is a figure showing the schematic structure of the electric power steering device to which the present invention is applied. It is a block diagram which shows the specific structure of a controller. It is a characteristic diagram which shows the steering auxiliary current command value calculation map used in the steering auxiliary current command value calculating part of a controller. It is a schematic diagram with which it uses for description of the self-aligning torque. It is a figure which shows the relationship between the self-aligning torque and lateral force by the advancing direction of a tire, and a slip angle. It is a figure which shows the relationship between the landing force point of a lateral force, and a trail. It is a graph which shows the change of lateral force and the self-aligning torque with respect to the change of a slip angle. It is a graph showing the relationship between the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp. It is a flowchart which shows an example of the compensation gain calculating process performed with a compensation gain calculating part. It is a characteristic diagram which shows the torque differential compensation gain calculation map used with a compensation gain calculating part. It is a flowchart which shows an example of the process sequence of a controller. FIG. 5 is a characteristic diagram showing a relationship between a steering angle δ and an estimated value SATp of a self-aligning torque. It is a block diagram which shows the other example of the control unit in this invention. It is a block diagram which shows embodiment at the time of applying a motor with a brush.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 12 Electric motor 14 Steering torque sensor 15 Controller 16 Vehicle speed sensor 17 Rotation angle sensor 21 Steering auxiliary current command value calculation part 22 Command value compensation part 23 Grip loss detection part 24 Steer state detection part 25 Compensation value correction part 26 dq-axis current command value calculation unit 27 motor current control unit 33 convergence compensation unit 34 inertia compensation unit 35 SAT detection unit 36 SAT compensation unit 37 torque differential compensation unit 41 SAT estimation unit 42 yaw rate sensor 43 lateral acceleration sensor 44 lateral Force detector 45 Steering angle sensor 51 Compensation gain calculator 52 Multiplier

Claims (9)

Steering torque detection means for detecting steering torque input to a steering mechanism for turning steered wheels, an electric motor for applying steering assist force to the steering mechanism, and a steering assist current command value based on the steering torque And an electric power steering device having control means for controlling the electric motor based on the calculated steering assist current command value,
Steering state detecting means for detecting the steering state of the vehicle, grip loss degree detecting means for detecting the degree of grip loss indicating the degree of tire grip force loss, and the steering torque detected by the steering torque detecting means are differentiated. Torque differential value compensating means for compensating the response in the vicinity of the steering neutral point, and the torque differential value based on at least the steering state detected by the steering state detecting means and the grip loss degree detected by the grip loss degree detecting means. An electric power steering apparatus comprising: compensation value correcting means for correcting a torque differential compensation value of the compensating means.   The compensation value correction means is configured to change the correction mode of the torque differential compensation value depending on whether the steering state is oversteer or understeer when the grip loss degree is equal to or greater than a predetermined value. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is provided.   Steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means is the steering state detection means when the grip loss degree is a predetermined value or more and the steering state is oversteer. 2. The electric power steering apparatus according to claim 1, wherein when an increase steering is detected, the torque differential value compensation value is corrected so as to decrease according to the grip loss degree.   Steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means is the steering state detection means when the grip loss degree is a predetermined value or more and the steering state is oversteer. 2. The electric power steering apparatus according to claim 1, wherein the torque differential compensation value is increased and corrected in accordance with the grip loss degree when counter steering is detected.   Steering state detection means for detecting a steering state of the vehicle, wherein the compensation value correction means is the steering state detection means when the grip loss degree is a predetermined value or more and the steering state is oversteer. When increasing steering is detected, the torque differential compensation value is corrected to decrease according to the grip loss degree, and when countersteer steering is detected by the steering state detecting means, the torque according to the grip loss degree is detected. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to increase and correct the differential compensation value.   Steering state detecting means for detecting a steering state of the vehicle, and the compensation value correcting means is turned off by the steering state detecting means when the grip loss degree is a predetermined value or more and the steering state is understeer. The electric power according to any one of claims 1 to 5, wherein when the increased steering is detected, the torque differential compensation value is corrected to decrease according to the grip loss degree. Steering device.   The steering state detecting means includes a yaw rate detecting means for detecting a yaw rate of the vehicle and a motor angular speed detecting means for detecting a motor angular speed of the electric motor, and the steering state detecting means increases steering based on the yaw rate and the sign of the motor angular speed. The electric power steering apparatus according to any one of claims 3 to 6, wherein the electric power steering apparatus is configured to detect switchback or countersteer steering.   The steering state detecting means includes a yaw rate detecting means for detecting a yaw rate of the vehicle, and a steering speed detecting means for detecting a steering speed of the steering wheel, and the steering state detecting means is increased based on the signs of the yaw rate and the steering speed. The electric power steering apparatus according to any one of claims 3 to 6, wherein the electric power steering apparatus is configured to detect counter-steer steering.   Self-aligning torque detecting means for detecting self-aligning torque generated on the steered wheel side, lateral force detecting means for detecting lateral force of the vehicle, and self-alignment based on the lateral force detected by the lateral force detecting means. Self-aligning torque estimating means for estimating lining torque, and the grip loss degree detecting means is estimated by the self-aligning torque detected value detected by the self-aligning torque detecting means and the self-aligning torque estimating means. 9. The electric power steering apparatus according to claim 1, wherein the grip loss degree is detected based on the estimated self-aligning torque.

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