JP5245898B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device in which a steering assist force is applied to a vehicle steering mechanism by an electric motor, and in particular, stabilizes vehicle behavior even when tire grip is lost. The present invention relates to an electric power steering apparatus capable of performing the above.

Conventionally, as a steering device, an electric power steering device that applies a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque when a driver steers a steering wheel has been widely used.
In addition, in such an electric power steering device, in order to improve the steering performance and stabilize the behavior of the vehicle during cornering, a steering control that takes into account the grip state of the tire has been proposed. .

  For example, the lateral force utilization factor of the front wheels is calculated, and the normal auxiliary steering torque command value determined based on the vehicle speed and the manual steering torque is corrected to be smaller as the lateral force utilization factor increases and approaches the grip limit. In this way, by making the driver aware of this by increasing the steering force before the vehicle characteristics reach the limit, it is possible to suppress changes in vehicle behavior according to the road surface conditions (for example, patents) Reference 1), for example, the deviation between the standard yaw rate and the actual yaw rate is set to a value corresponding to the grip state of the tire. In order to increase the reaction force, a steering assist torque is corrected to improve running stability (see, for example, Patent Document 2).

Japanese Patent No. 3730341 JP 2006-264392 A

However, as described above, when the road surface condition is estimated from the lateral force utilization rate and the steering assist torque command value is corrected, the robustness is low because the tire characteristics are not considered, and the road surface Since the situation estimation accuracy is relatively low, there is a possibility that the vehicle behavior change cannot be suppressed accurately.
Further, as described above, when the deviation between the standard yaw rate and the actual yaw rate is used as the value corresponding to the grip state, the deviation of the yaw rate represents the grip state, but the error from the actual grip state is relatively large.

Also, if the steering reaction force is increased so that the tire slips closer to the grip limit as the tire becomes closer to the grip limit in this way, the driver's steering wheel can be prevented from being increased, but the driver can slip. There is an unresolved problem that it is not possible to determine whether or not it is.
Accordingly, the present invention has been made paying attention to the unsolved problems of the conventional example described above, and an object of the present invention is to provide an electric power steering device that allows the driver to accurately sense the skid state of the vehicle. It is said.

In order to achieve the above object, an electric power steering apparatus according to claim 1 calculates a steering assist command value based on steering torque detection means for detecting steering torque input to a steering mechanism of a vehicle, and the steering torque. A control device for an electric power steering apparatus, comprising: a steering assist command value calculating means for driving; and a motor control means for driving an electric motor for applying a steering assist force to the steering mechanism based on the steering assist command value, and grip loss degree detecting means for detecting the grip loss degree representing the degree of grip is lost in the tire, and grip loss degree variation calculation means for calculating a change in the grip loss level detected by the grip loss degree detecting means, grid calculated in the detected grip loss degree and the grip loss degree variation calculation means by the grip loss degree detecting means And sideslip index calculating means for calculating a lateral slip indicator based on the loss of variation, to provide a stopper feeling of steering force after giving the missing sense of steering force according to an increase in the side slip indicator calculated in lateral slippage index computing means Command value correcting means for correcting the steering assist command value; self-aligning torque detecting means for detecting self-aligning torque input to the steering mechanism from a road surface; and a sudden value for detecting a sudden steering state of the steering mechanism. Steering command means, and the command value correction unit performs self-aligning torque compensation for the steering assist command value based on the self-aligning torque detection value detected by the self-aligning torque detection means. Self-aligning torque compensation means, and the self-aligning torque compensation means includes the self-aligning torque compensation means. A band-pass filter processing unit that performs band-filter processing on a detected torque value, and a gain adjustment unit that performs gain adjustment, and when the sudden steering state is detected by the sudden steering detection unit, the band-pass filter processing Compensation value correcting means for adjusting at least one of the adjustment unit and the gain adjustment unit in a direction to reduce the self-aligning torque compensation value is provided .

Further, the electric power steering apparatus according to claim 2, wherein the skid index calculating means, either the sum and product of the value multiplied by the gain to grip loss level and the value obtained by multiplying a gain to the grip loss of variation On the other hand, it is characterized by calculating a skid index.
The electric power steering apparatus according to claim 3, wherein the command value correcting means, among from the sideslip index started increasing to a predetermined threshold value, in order to give a sense of loss of steering force, the steering assist command value And a command value increase correction unit that calculates a correction value for returning to a normal value after abrupt increase.

According to a fourth aspect of the present invention, in the electric power steering apparatus, the command value correction means calculates a correction value for decreasing the steering assist command value in accordance with an increase in the skid index when the skid index exceeds a predetermined threshold. It has a command value reduction correction unit.
Further, the electric power steering apparatus according to claim 5 is characterized in that the command value decrease correction unit is configured to hold a constant value when the correction value exceeds a predetermined value.

The electric power steering apparatus according to claim 6, before Symbol grip loss degree detecting means, self-aligning torque estimation for estimating a self aligning torque resulting from the road surface as a self-aligning torque estimated value based on the vehicle motion model The grip loss degree is calculated based on a deviation between the self-aligning torque detected value detected by the self-aligning torque detecting unit and the self-aligning torque estimated value estimated by the self-aligning torque estimating unit. And a grip loss degree detection unit.

Further, in the electric power steering apparatus according to claim 7 , the sudden steering detection unit is configured to perform a sudden steering state when an absolute value of the motor angular velocity exceeds a predetermined value and an absolute value of the steering torque exceeds a predetermined value. It is characterized by being comprised so that it may judge.

According to the present invention, the vehicle slip index is calculated based on the grip loss degree and the grip loss degree change rate, and when the skid index starts to increase, the driver is first given a feeling of lack of steering force. Since the steering assist command value is corrected so as to give a stopper feeling of the steering force, an effect that the driver can be surely recognized that the skid index has increased is obtained.
Further, when the driver steers suddenly, this sudden steering state is detected, and the compensation value of the steering assist command value based on the self-aligning torque is suppressed, thereby making it possible to ensure rapid steering. can get.

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 block diagram which shows the specific structure of a SAT compensation value calculating part. 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 characteristic diagram which shows the correction value calculation map used in an electric current command correction | amendment part. It is a flowchart which shows an example of the process sequence of a controller. FIG. 6 is a characteristic diagram showing a transfer function of steering assist torque / steering torque. It is a block diagram which shows the other example of the control unit in this invention. 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 further another 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.

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 connected 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. The controller 15 detects the vehicle speed detection value V detected by the vehicle speed sensor 16 in addition to the torque detection value T, the motor currents Ia to Ic flowing through the electric motor 12, and the rotation angle sensor 17 constituted 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. After performing various compensation processes such as convergence compensation, inertia compensation, and self-aligning torque compensation based on the motor angular velocity ωm and motor angular acceleration αm calculated based on the rotation angle θm, it is converted into a dq axis command value, These dq axis command values are converted into two-phase / three-phase to calculate motor current command values Iaref to Icref, and currents Ia to Ic flowing through the electric motor 12 are fed back based on the calculated motor current command values Iaref to Icref. The electric motor 12 is driven and controlled.

  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 g representing the degree of tire grip loss, and the grip loss degree detection unit For example, the grip loss degree change rate calculating unit 24 as a grip loss degree change rate calculating means for calculating the grip loss degree change rate Δg by differentiating the grip loss degree g detected in 23, and the grip loss degree g and the change in the grip loss degree A skid index calculating unit 25 serving as a skid index calculating means for calculating a skid index representing the degree of the skid state based on the rate Δg. A side slip index recognition correction unit 26 as command value correction means for calculating a correction value for side slip index recognition for correcting the steering assist command value based on the calculated side slip index, and post-compensation steering compensated by the command value compensation unit 22 A dq-axis current command value calculator 27 that calculates a dq-axis current command value based on the auxiliary current command value Iref ′, and a dq-axis output from the dq-axis current command value calculator 27. A two-phase / three-phase converter 28 for calculating the motor current command values Iaref to Icref by converting the command value into two-phase / three-phase, and a motor current command value Iaref to be output from the two-phase / three-phase converter 28 The motor current control unit 29 generates motor currents Ia to Ic based on Icref.

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 θ 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, the convergence compensation unit 33 that compensates the convergence of the yaw rate based on the motor angular velocity ωm calculated by the angular velocity calculation unit 31, and the angular acceleration calculation unit 32 Inertia compensator 34 for compensating for the torque equivalent generated by the inertia of the electric motor 12 based on the motor angular acceleration αm, and preventing deterioration of the feeling of inertia or control responsiveness, and self-aligning generated on the steered wheel side SAT detector 35 for calculating torque (SAT), and self-aligning torque compensation based on the self-aligning torque calculated by SAT detector 35 And a SAT compensation unit 36 that calculates a self aligning torque compensation value SATc performed.

  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 Ic 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 calculated, 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.

  Further, as shown in FIG. 5, the SAT compensator 36 has a band pass filter and a phase adjuster for performing a band pass filter process on the self-aligning torque detection value SATd input from the SAT detector 35. A damping control unit 36a that calculates a self-aligning torque compensation value that suppresses steering vibration such as shimmy, brake jitter, and road surface vibration, and a gain Ks for the self-aligning torque compensation value output from the damping control unit A gain adjustment unit 36b to adjust, and a sudden steering detection unit as a sudden steering state detection unit that detects a sudden steering state based on the steering torque T detected by the steering torque sensor 14 and the motor angular velocity ωm calculated by the angular velocity calculation unit 31 36c and when the sudden steering state is not detected by the sudden steering detection unit 36c, Large gain Ks1 set, and a gain setting unit 36d for setting a gain Ks1 smaller gain Ks2 while detecting the quick steering state manner.

  Then, a self-aligning torque compensation value output from the gain adjustment unit 36b and a side slip index recognition correction value SA from a side slip index recognition correction unit 26, which will be described later, are added by an adder 37. The convergence compensation value Ic calculated by the convergence compensation unit 33 is added by the adder 38, and the output of the adder 38 and the inertia compensation value calculated by the inertia compensation unit 34 are added by the adder 39 to give a command. The compensation value Icom is calculated, and this command compensation value Icom is added to the steering assist current command value Iref output from the steering assist current command value calculation unit 21 by the adder 40 to calculate the compensated steering assist current command value Iref ′. The compensated steering assist current command value Iref ′ is output to the dq axis current command value calculation unit 27.

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. 6 and FIG. 7 show a model of a vehicle motion in which the tire rolls while skidding.
In FIG. 6, the lateral force generated on the entire ground contact surface of the tire becomes a 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. 7 also shows that the point of application of lateral force (the center point of the contact surface) is behind the tire centerline. The added value of the pneumatic trail and the caster trail is the trail.

6 and 7, it can be seen 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. 8 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. 7 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. 9 shows the estimated sum SATp as the self-aligning torque SATp in accordance with the dimension of the self-aligning torque SAT with the sum of the trails, that is, with the trail εn.

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. 9 is a characteristic diagram showing a comparison between the detected self-aligning torque value SATd and the estimated self-aligning torque value SATp (lateral force Fy × trailer εn). The self-aligning torque increases 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.

  Then, the self-aligning torque detection value SATd calculated 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 representing the degree of tire grip loss is calculated, and the calculated grip loss degree g is input to the grip loss degree change rate calculation unit 24. And output to the skid index calculation unit 25.

  The skid index calculation unit 25 includes a gain adjuster 25a that multiplies the grip loss degree g detected by the grip loss degree detection unit 23 by a gain Kg1 that changes according to the vehicle speed, and a grip that is calculated by the grip loss degree conversion rate calculation unit 24. A gain adjuster 25b that multiplies the loss degree change rate Δg by a gain Kg2 that is converted according to the vehicle speed; and an adder 25c that calculates the skid index Si by adding the output of the gain adjuster 25a and the output of the gain adjuster 25b. It consists of

  The current command correction unit 26 calculates a current command correction value Ai for correcting the steering assist current command value Iref with reference to the correction value calculation map based on the input skid index Si. Here, as shown in FIG. 10, the correction value calculation map has a two-dimensional map configuration in which the horizontal axis indicates the side slip index Si and the vertical axis indicates the current command correction value Ai, and the side slip index Si is “0”. When the side slip index Si increases to “0” in the positive direction, the current command correction value Ai increases in the positive direction according to the increase of the side slip index Si until the predetermined value Si1. If the skid index Si increases rapidly and then increases beyond the predetermined value Si1, the current command correction value Ai rapidly decreases according to the increase of the skid index Si up to the predetermined value Si2, and returns to "0". When the index Si increases, the current command correction value Ai rapidly decreases in the negative direction according to the increase of the skid index Si until the predetermined value Si3, and when the skid index Si exceeds the predetermined value Si3, the current command correction value Ai becomes negative. A constant value of Characteristic line is set to.

Then, the current command correction value Ai is supplied to the adder 37 to which the self-aligning torque compensation value output from the self-aligning torque compensation unit 36 of the command value compensation unit 22 is input.
The dq-axis current command value calculation unit 27 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 that calculates 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. It is. Then, 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 26. Is done.

  The two-phase / three-phase converter 26 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 converter 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 29.

  The motor current control unit 29 includes a motor current detection unit 70 that detects motor currents Ia, Ib, and Ic supplied to the three-phase coil of the electric motor 12 and a motor current command input from the two-phase / three-phase conversion unit 26. 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, the steering torque T from the torque sensor 14, the vehicle speed Vx from the vehicle speed sensor 16, the motor rotation angle θm from the rotation angle sensor 17, the yaw rate γ from the yaw rate sensor 42, and the lateral acceleration Gy from the lateral acceleration sensor 43 are read. (Step S1). Next, the steering assist current command value Iref corresponding to the steering torque T and the vehicle speed Vx is calculated based on the input steering torque T and the vehicle speed Vx with reference to the steering assist current command value calculation map shown in FIG. 3 (step S2). Based on the motor rotation angle θm from the rotation angle sensor 17, the angular velocity ωm of the electric motor 12 is calculated and the angular acceleration αm is calculated (step S3).

  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 calculate the self-aligning torque detection value SATd (step S4). Further, it is determined whether or not the vehicle is in a sudden steering state in which the absolute value | T | of the steering torque T is equal to or greater than the predetermined value Ts and the absolute value | ωm | of the motor angular velocity ωm is equal to or greater than the predetermined value ωms (step S5). When not in the sudden steering state, the SAT compensation gain Ks1 is selected (step S6), and when in the sudden steering state, the SAT compensation gain Ks2 is selected (step S7). Then, the self-aligning torque detection value SATd is subjected to a band-pass filter process and a phase adjustment process, and further multiplied by the selected compensation gain to calculate a self-aligning torque compensation value SATc (step S8). 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 S9).

Subsequently, the grip loss degree g is calculated from the deviation between the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp (step S10), and then the grip loss degree g is differentiated to obtain the grip loss degree change rate Δg. Then, the gains Kg1 and Kg2 are calculated based on the vehicle speed Vx (step S12).
Subsequently, a skid index Si is calculated based on the following equation (6) (step S13).
Si = Kg1 · g + Kg2 · Δg (6)

  Next, the current command correction value Ai is calculated with reference to the correction value calculation map of FIG. 10 based on the calculated skid index Si (step S14), and then the convergence of the yaw rate is compensated based on the motor angular velocity ωm. In addition to calculating the convergence compensation value Ic, the inertia compensation value Ii that compensates for the torque equivalent generated by the inertia of the electric motor 12 based on the motor angular acceleration αm to prevent deterioration of the feeling of inertia or control responsiveness is calculated. (Step S15), the convergence compensation value Ic and the inertia compensation value Ii are added, and the compensation value Icom is calculated by adding the current command correction value Ai and the self-aligning torque compensation value SATc (Step S16). The compensated steering assist current command value Iref ′ is calculated by adding the compensation value Icom to the steering assist current command value Iref (step S17).

  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 S18), 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 S19).

  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 S20). PI control processing is performed on the current deviations ΔIa, ΔIb, and ΔIc to calculate voltage command values Va, Vb, and Vc (step S21), and the calculated voltage command values Va, Vb, and Vc are subjected to pulse width modulation to generate a pulse width. A modulation signal is formed, and the formed pulse width modulation signal is output to the inverter 74 (step S22).

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 so that light steering can be performed.
Therefore, when the steering wheel 1 is held at the neutral position and the vehicle is traveling straight, the steering torque T detected by the steering torque sensor 14 is substantially “0” and is calculated by the steering assist current command value calculation unit 21. The steering assist current command value Iref is also substantially “0”.

  In addition, the self-aligning torque detection value SATd calculated by the SAT detection unit 35 and the self-aligning torque estimation value SATp estimated by the SAT estimation unit 41 are substantially “0”, and the grip loss degree detection unit 23 is corresponding to this. The grip loss degree g detected in step (1) maintains substantially “0”, and the grip loss degree change rate Δg calculated by the grip loss degree change rate calculation unit 24 also maintains substantially “0”. Therefore, the skid index Si calculated by the skid index calculating unit 25 is also substantially “0”, and the current command correction value Ai calculated by the current command correcting unit 26 is also substantially “0”.

On the other hand, since the self-aligning torque detection value SATd is substantially “0” in the straight traveling state, the self-aligning torque compensation value SATc calculated by the SAT compensation unit 36 is also substantially “0”.
Therefore, the post-compensation steering assist current command value Iref ′ calculated by the adder 40 is also substantially “0”, and the d-axis current command value Idref and the q-axis current output from the dq command value calculation unit 27. The command value Iqref is also substantially “0”, and the three-phase current command values Iaref, Ibref and Icref converted by the two-phase / three-phase converter 28 are also substantially “0”. Further, since the electric motor 12 is also stopped rotating, the motor currents Ia, Ib and Ic detected by the motor current detection unit 70 are also substantially “0”, and are thus calculated by the subtracters 71a, 71b and 71c. The current deviations ΔIa, ΔIb, and ΔIc are also substantially “0”, and the voltage command values Va, Vb, and Vc output from the PI current control unit 72 are also substantially “0”. Is not output to the inverter 74, and the motor currents Ia, Ib and Ic output from the inverter 74 become substantially “0”, and the electric motor 12 maintains the stopped state.

When the vehicle travels on a curve having a relatively large turning radius from this straight traveling state, the steering torque sensor 14 detects a relatively small steering torque T by steering the steering wheel 1 relatively gently. Thus, the steering assist current command value calculation unit 21 calculates a relatively small steering assist current command value Iref.
At the same time, the SAT detection unit 35 calculates a relatively small self-aligning torque detection value SATd, and the SAT estimation unit 41 also calculates a relatively small self-aligning torque estimation value SATp based on the lateral force Fy. Calculated.

  Even in this case, the self-aligning torque detection value SATd and the self-aligning torque estimated value SATp are substantially equal, and the grip loss degree g detected by the grip loss degree detection unit 23 maintains substantially “0”. The grip loss degree change rate Δg calculated by the grip loss degree change rate calculating unit 24 also maintains substantially “0”, and the skid index Si calculated by the side slip index calculating unit 25 also continues to substantially “0”. The current command correction value Ai calculated by the current command correction unit 26 also continues to be substantially “0”.

  On the other hand, in the SAT compensator 36, the self-aligning torque detection value SATd is a relatively small value, the steering torque T is less than the predetermined value Ts, and the motor angular velocity ωm is less than the predetermined value ωms. Therefore, a relatively large gain Ks1 is selected and supplied to the gain adjusting unit 36c. For this reason, the brake adjuster 36c outputs a brake aligner and a self-aligning torque compensation value SATc that suppresses road surface vibration, and this is added to the compensation values Ii and Ic of the command value compensation unit 22.

  Then, the compensation value Icom calculated by the current compensation unit 22 is added to the steering assist current command value Iref calculated by the steering assist current command value calculation unit 21, and the command value compensation optimal for the steering state is performed. The steering operation of the steering wheel 1 can be accurately assisted.

  However, when the vehicle is in a state where a side slip occurs due to traveling at a corner having a small turning radius or turning at a high speed although it has a middle turning radius, the steering assist current command value calculation unit 21 outputs the result. The steering assist current command value Iref increases, and, as shown in FIG. 9 described above, the SAT estimation unit 41 compares the SAT with the estimated self-aligning torque SATp estimated based on the lateral force Fy of the vehicle. The self-aligning torque detection value SATd calculated by the detection unit 35 starts to decrease, the grip loss degree g detected by the grip loss degree detection unit 23 starts to increase in the positive direction, and the grip loss degree change rate is increased. The grip loss degree change rate Δg calculated by the calculation unit 24 also increases in the positive direction.

For this reason, the skid index calculation unit 25 performs the calculation of the above equation (6), and the skid index Si increases in the positive direction from “0”, and the current command correction unit 26 as shown in FIG. In addition, the current command correction value Ai increases rapidly based on the skid index Si.
Then, since the current command correction value Ai is added to the steering assist current command value Iref, the post-compensation steering assist current command value Iref ′ increases rapidly, and thus is calculated by the dq axis current command value calculation unit 27. The d-axis current command value Idref and the q-axis current command value Iqref are increased, and the three-phase current command values Iaref to Icref converted by the two-phase / three-phase conversion unit 28 are increased. Accordingly, when current deviations ΔIa to ΔIc increase, voltage command values Va to Vc output from PI current control unit 72 also increase, and motor currents Ia to Ic output from inverter 74 increase. The electric motor 12 is rotated at a rotational speed faster than the normal rotational speed, and a large steering assist force is generated. This large steering assist force is transmitted to the steering shaft 2b via the speed reducer 11, so that the steering is suddenly lightened and the driver feels that the steering force is lost.

  Thereafter, when the skid index Si further increases and exceeds the predetermined value Si1, the current command correction value Ai rapidly decreases and returns to “0” at the predetermined value Si2, thereby returning to the normal steering assist state. When the skid index Si further increases, the current command correction value Ai decreases in the negative direction. Therefore, the current command correction value Ai is subtracted from the steering assist current command value Iref calculated by the steering assist current command value calculation unit 21, and the compensated steering assist current command value Iref ′ is decreased to The steering assist force generated by the motor 12 is reduced from the normal steering assist force, thereby increasing the steering reaction force and giving the driver a sense of stopper so that the driver can be surely recognized that the vehicle is at the steering limit. .

As described above, when the side slip increases, the steering force is given a sense of slipping after giving a sense of slipping of the steering force once according to the increase of the side slip index Si, so that the driver can surely recognize the limit state of the side slip. Can provide safe driving support.
On the other hand, when the driver wants to steer suddenly at the driver's will when the driver avoids a collision with the preceding vehicle by sudden braking of the preceding vehicle or avoids a collision due to a sudden approach of an oncoming vehicle When the sudden steering state is detected by the sudden steering detecting unit 36b, the gain of the gain adjusting unit 36c is changed from the normal gain Ks1 to the emergency gain Ks2 having a small value. For this reason, the self-aligning torque compensation value SATc for suppressing shimmy, brake jitter, and road surface vibration based on the self-aligning torque detection value SATd calculated by the SAT compensation unit 36 is corrected to decrease. Since the compensation value for the minute steering assist current command value Iref is decreased, high steering response can be ensured without impeding sudden steering by the driver's will.

  In this case, the transfer function of the steering assist torque / steering torque by the gain change is as shown in FIG. 12, and the response characteristic is improved when the emergency gain Ks2 is selected as compared with the normal gain Ks1. can do.

  Here, the steering torque sensor 14 corresponds to the steering torque detection means, the processing in FIG. 11 corresponds to the control means, among which the processing in step S2 corresponds to the current command value calculation unit, and the processing in step S4 corresponds to the SAT detection. Corresponding to the unit 35 (self-aligning torque detecting means), the processing in step S5 corresponds to the sudden steering detecting unit 36c (rapid steering detecting means), the processing in steps S6 and S7 corresponds to the gain setting unit 36d, The process of S8 corresponds to the SAT compensator 36 (self-aligning torque compensator), the process of step S9 corresponds to the SAT estimator 41, and the process of step S10 is the grip loss degree detector 23 (grip loss degree detector). ), The process of step S11 corresponds to the grip loss degree change rate calculation unit 24 (grip loss degree change calculation means), and step S12. S13 corresponds to the skid index calculation unit 25 (side slip index calculation means), the process of step S14 corresponds to the current command correction value calculation unit 26 (command value correction means), and the processes of steps S15 to S17 are commanded. Corresponding to the value compensator 22, the process of step S18 corresponds to the dq-axis current command value calculator 25, the process of step S19 corresponds to the 2-phase / 3-phase converter 26, and the process of step S20 is subtracted. The processing of step S21 corresponds to the PI current control unit 72, and the processing of step S22 corresponds to the pulse width modulation unit 73, corresponding to the devices 71a to 71c.

  In the above embodiment, the case where the skid index Si is calculated by the sum of the grip loss degree g and the grip loss degree change rate Δg has been described. However, the present invention is not limited to this, and as shown in FIG. Further, the value obtained by multiplying the grip loss degree g by the gain Kg1 and the value obtained by multiplying the grip loss degree change rate Δg by the gain Kg2 are multiplied by the multiplier 80, and the skid index Si is calculated by the product of both. Good.

In the above embodiment, the case of calculating the grip loss change rate Δg has been described. However, the present invention is not limited to this, and the grip loss change amount may be applied instead of the grip loss change rate. .
Furthermore, in the above-described embodiment, the case where the SAT compensation unit 36 selects the normal gain Ks1 when not suddenly steered and selects the emergency gain Ks2 while suddenly steered is described. However, the present invention is not limited to this. Alternatively, vibration suppression control such as shimmy, brake jitter, and road surface vibration may be suppressed by changing the filter characteristics of the bandpass filter.

In the above embodiment, the case has been described in which the characteristic line of the correction value calculation map of FIG. 10 in which the current command correction unit 26 calculates the current command correction value Ai based on the skid index Si is set linearly. However, the present invention is not limited to this, and the characteristic line may be set non-linearly.
In the above embodiment, the case where the lateral acceleration of the vehicle is detected by the lateral acceleration sensor 43 has been described. However, the present invention is not limited to this, and the lateral acceleration is based on the steering angle of the steering mechanism SM and the vehicle speed Vx. May be estimated.

Furthermore, 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. As described above, 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 (7) and (8).
mVx · (dβ / dt)
= − [MVx + [(Kf · Lf−Kr · Lr) / Vx]] · γ− (Kf + Kr) · β + Kf · δ / n
...... (7)
I · (dγ / dt)
= − [(Kf · Lf ² + Kr · Lr ² ) / Vx] · γ + (− Kf · Lf + Kr · Lr) · β
+ Kf · Lf · δ / n
...... (8)

  In the equations (7) and (8), 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. 15, the vehicle speed Vx detected by the vehicle speed sensor (vehicle speed detection means) 21 and the steering angle δ detected by a steering angle sensor (steering angle detection means) (not shown) are estimated by SAT. The SAT estimating unit 41 may calculate the self-aligning torque estimated value SATp according to the characteristic diagram of FIG.

Furthermore, in the above embodiment, the case where the self-aligning torque SAT is calculated 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, but the present invention is not limited to this. 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 (9) based on the angular acceleration αm may be applied.
Tma = Kt · Iq−Jm · αm (9)
Here, Kt 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 (10) is calculated to calculate the motor angular velocity ωm. At the same time, the dq-axis current command value calculation unit 25 is omitted, the compensated steering assist current command value Iref ′ is directly supplied to the motor current control unit 27, and each motor current control unit 27 is also subtracted by 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 (10)
Here, Rm is the motor winding resistance, and K ₀ is the electromotive force constant of the motor.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 12 Electric motor 14 Steering torque sensor 15 Controller 17 Rotation angle sensor 19 Vehicle speed sensor 21 Steering auxiliary current command value calculation part 22 Command value compensation part 23 Grip loss detection part 24 Grip loss degree change rate calculation part 25 Side slip Index calculation unit 26 Current command value correction unit 27 dq axis current command value calculation unit 28 Motor current control unit 35 SAT detection unit 36 SAT compensation unit 41 SAT estimation unit 42 Yaw rate sensor 43 Lateral acceleration sensor 44 Lateral force detection unit

Claims (7)

Steering torque detecting means for detecting a steering torque input to a steering mechanism of the vehicle, steering assist command value calculating means for calculating a steering assist command value based on the steering torque, and the steering based on the steering assist command value A control device for an electric power steering apparatus comprising: a motor control means for driving an electric motor that applies a steering assist force to the mechanism;
A grip loss degree detecting means for detecting a grip loss degree indicating the degree of tire grip loss;
A grip loss degree change calculating means for calculating a change in the grip loss degree detected by the grip loss degree detecting means;
And sideslip index calculating means for calculating a lateral slip indicator based on the grip loss of variation calculated in the detected grip loss degree and the grip loss degree variation calculation means by the grip loss degree detecting means,
Command value correcting means for correcting the steering assist command value so as to give a feeling of stopper of the steering force after giving a feeling of loss of the steering force according to the increase of the side slip index calculated by the side slip index calculating means;
Self-aligning torque detecting means for detecting self-aligning torque input to the steering mechanism from the road surface;
Sudden steering detection means for detecting a sudden steering state of the steering mechanism,
The command value correction unit has self-aligning torque compensation means for performing self-aligning torque compensation for the steering assist command value based on the self-aligning torque detection value detected by the self-aligning torque detection means. ,
The self-aligning torque compensating means has at least a band-pass filter processing unit for performing band-filter processing and a gain adjusting unit for adjusting gain with respect to the self-aligning torque detection value. Compensation value correction means for adjusting at least one of the band-pass filter processing unit and the gain adjustment unit in a direction to reduce the self-aligning torque compensation value when a steering state is detected is provided. Electric power steering device. The side slip indicator calculation means, claims and calculates either one at a skid indication of the sum and product of the value multiplied by the gain to grip loss level and the value obtained by multiplying a gain to the grip loss of variation Item 4. The electric power steering device according to Item 1. The command value correcting means, among from the sideslip index started increasing to a predetermined threshold value, in order to give a sense of loss of steering force, a correction value for returning the by rapidly increasing the steering assist command value to the normal value The electric power steering apparatus according to claim 1, further comprising a command value increase correction unit for calculating.   The command value correction means includes a command value decrease correction unit that calculates a correction value for decreasing the steering assist command value in accordance with an increase in the skid index when the skid index exceeds a predetermined threshold. Item 4. The electric power steering device according to Item 3.   The electric power steering apparatus according to claim 4, wherein the command value decrease correction unit is configured to hold a constant value when the correction value exceeds a predetermined value. Before Symbol grip loss degree detecting means includes a self-aligning torque estimating unit for estimating a self aligning torque resulting from the road surface as a self-aligning torque estimated value based on the vehicle motion model, detected by the self-aligning torque detecting unit A grip loss degree detection unit that calculates the grip loss degree based on a deviation between the self-aligning torque detection value and the self-aligning torque estimation value estimated by the self-aligning torque estimation unit. The electric power steering apparatus according to any one of claims 1 to 5. The abrupt steering detection means is configured to determine a sudden steering state when the absolute value of the motor angular velocity exceeds a predetermined value and the absolute value of the steering torque exceeds a predetermined value. The electric power steering apparatus according to any one of claims 1 to 6 .

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