JP2008049914A - Control apparatus of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate an absolute steering angle without using an absolute steering angle sensor, and to promote a shock dampening when a steering limit is attained which makes a rack shaft reach a rack stroke end in reference to this absolute steering angle. <P>SOLUTION: A relative steering angle ϕ is calculated in reference to a motor rotating angle θ, and when a steering mechanism turns neutral or shows a maximum steering angle, a known-absolute steering angle under these conditions and a relative steering angle at this time are associated with each other, and subsequently an absolute steering angle ϕabs based on this condition is estimated. When an absolute value ¾ϕabs¾ of the steering angle is more than a threshold value ϕ11, a restriction gain K11 becoming smaller than "1" is multiplied to restrict a steering assisting torque instruction value I<SB>M</SB>and further the steering assisting torque instruction value I<SB>M</SB>is corrected to restrict a difference between a desired value ωr of a motor angular velocity and an actual motor angular velocity ω when the absolute steering angle is ϕabs, and a torque transmitted to a torque transmitting member between a steering shaft and a steering wheel is restricted to reduce a shock at a steering limit position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a current command value calculation unit that calculates a current command value based on at least a steering torque, an electric motor that applies a steering assist force to a steering mechanism, and a motor control unit that controls the electric motor based on the current command value And a control device for an electric power steering device.

2. Description of the Related Art 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 by which a driver steers a steering wheel has been widely used.
In general, in a steering mechanism, when the steering wheel is continuously steered in the left or right steering direction from the neutral position, when the steering wheel operation amount reaches a maximum steering angle corresponding to the maximum value, the steering mechanism is mechanically operated. It becomes a steering limit position where it cannot abut further by contacting the stopper. It is called a so-called end pad that the steering limit position is brought into contact with the mechanical stopper.

When the steering wheel is operated quickly, that is, when the steering speed is high, the steering assist force generated by the electric power steering device is also increased, and the impact force generated at the time of end contact is increased. The durability of the mechanism may decrease, and the driver may feel uncomfortable during the steering operation.
For this reason, conventionally, as an electric power steering device configured to relieve impact at the time of end-contact, an unloader correction unit that reduces and corrects the steering assist torque of the motor when the rudder angle exceeds a predetermined rudder angle near the maximum rudder angle There is known an electric power steering device in which the unloader correction unit increases and corrects the reduction correction amount of the auxiliary steering torque as the steering speed increases (see, for example, Patent Document 1).

In addition, when it is detected that the steered wheel approaches the predetermined maximum steering angle and exceeds the attenuation start steering angle, a damping unit that attenuates the driving force of the electric motor, the load on the steering wheel, and the steering wheel steering There is also known an electric power steering device including an attenuation start steering angle setting unit that sets the attenuation start steering angle according to speed (for example, see Patent Document 2).
JP 2001-253356 A JP 2001-30933 A

  However, since the conventional electric power steering apparatus uses the absolute steering angle information of the steering wheel, a highly accurate steering angle sensor or an absolute steering angle estimation function is required. As this rudder angle, for example, a relatively low-precision rudder angle sensor used in other control devices such as a low-precision rudder angle sensor for a skid prevention device cannot be used, and an expensive rudder angle sensor. And the absolute rudder angle estimation function is required, which increases the manufacturing cost.

  Further, as a method of reducing the impact caused by the end contact, a method of decreasing the current command value from a predetermined angle near the maximum steering angle and a method of decreasing the current command value according to the steering speed have been proposed. However, the force acting on the steering mechanism includes an external force from the tire in addition to the steering torque of the driver and the steering assist torque by the electric power steering device, and the steering angle moves as a result of the action of these forces. For this reason, for example, when the road surface friction coefficient is low and the external force from the tire is small, the electric motor only needs to be adjusted by adjusting the steering assist torque of the electric power steering device according to the absolute steering angle and the steering speed. Cannot be sufficiently decelerated, and there is a possibility that the impact associated with the end pad cannot be sufficiently mitigated.

  Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and even when the absolute steering angle sensor for directly detecting the absolute steering angle is not mounted, the steering limit position In this case, an object of the present invention is to provide a control device for an electric power steering device capable of appropriately mitigating impact force transmitted to a torque transmission member such as an intermediate shaft.

  In order to achieve the above object, a control device for an electric power steer device according to claim 1 of the present invention is detected by a steering torque detecting means for detecting a steering torque input to a steering mechanism, and at least detected by the steering torque detecting means. A current command value calculating means for calculating a current command value based on the steering torque, an electric motor for generating a steering assist torque to be applied to a steering shaft of the steering mechanism, and drive control of the electric motor based on the current command value An absolute rudder for estimating an absolute rudder angle of the steering mechanism using a relative rudder angle detecting means for detecting a relative rudder angle of the steering mechanism, and a relative rudder angle detected by the relative rudder angle detecting means. The absolute rudder angle estimated by the angle estimator and the absolute rudder angle estimator exceeds the limit judgment threshold value before the steering limit rudder angle. And a buffer control means for suppressing torque transmitted to a torque transmission member between the steering shaft and the steered wheels of the steering mechanism, wherein the absolute steering angle estimating means A steering state determination unit that determines whether or not the steering mechanism is in a reference state in which a relative steering angle detected by the relative steering angle detection unit and an absolute steering angle of the steering mechanism can be associated with each other; When the steering state determination means determines that the steering mechanism is in the reference state, a relative steering angle detected by the relative steering angle detection means and a known reference absolute steering angle in the reference state of the steering mechanism , And thereafter, using the reference absolute steering angle and the relative steering angle corresponding to the reference absolute steering angle Conversion means for converting the relative steering angle detected by the steering angle detection means into an absolute steering angle, and the buffer control means is in a state in which the absolute steering angle can be estimated by the absolute steering angle estimation means. Then, the buffer control is performed using the absolute steering angle.

In the control device for an electric power steering apparatus according to claim 2, the reference state of the steering mechanism is a steering limit state in which the steering mechanism cannot perform further steering or a neutral state. It is said.
According to a third aspect of the present invention, there is provided the control device for the electric power steering apparatus, wherein the steering state determination means is configured to calculate the current command value when the steering torque change rate detected by the steering torque detection means exceeds a threshold value. When the rate of change of the current command value calculated by the means exceeds the threshold value, the steering limit state is determined.

According to a fourth aspect of the present invention, there is provided a control device for an electric power steering apparatus comprising an external force estimating means for estimating an external force acting on the steering mechanism, wherein the steering state determining means is an external force estimated value estimated by the external force estimating means. When the value is equal to or greater than the threshold value, the steering limit state is determined.
According to a fifth aspect of the present invention, there is provided a control device for an electric power steering apparatus comprising an external force estimating means for estimating an external force acting on the steering mechanism, wherein the steering state determining means is a steering torque detected by the steering torque detecting means. When the rate of change exceeds the threshold value, or the rate of change of the current command value calculated by the current command value calculating unit exceeds the threshold value, and the estimated external force value estimated by the external force estimating unit When the value is equal to or greater than the threshold value, the steering limit state is determined.

  According to a sixth aspect of the present invention, there is provided a control device for an electric power steering apparatus comprising angular velocity detection means for detecting an angular velocity of the electric motor, wherein the steering state determination means is an absolute value of steering torque detected by the steering torque detection means. And the rate of change thereof exceeds both threshold values, and the absolute value of the angular velocity detected by the angular velocity detecting means is equal to or less than the threshold value, it is determined that the steering limit state is established. It is said.

According to a seventh aspect of the present invention, there is provided a control device for an electric power steering apparatus comprising vehicle speed detection means for detecting a vehicle speed, wherein the steering state determination means has an absolute value of the steering torque equal to or less than a threshold value and the vehicle speed detection means. When the vehicle speed detected in step (b) is equal to or higher than the threshold value and this state continues for a predetermined time or more, it is determined that the vehicle is in the neutral state.
Further, the control device for the electric power steering apparatus according to claim 8, wherein the buffer control means is configured such that the current command value calculated by the current command value calculation means when the absolute steering angle exceeds the limit determination threshold value. Current suppression means is provided that suppresses the value so that the suppression width increases as the absolute value of the absolute steering angle increases.

  Further, in the control device for an electric power steering apparatus according to claim 9, the buffer control means sets a motor angular speed setting means for setting an angular speed target value of the electric motor at the absolute steering angle from the absolute steering angle, An angular velocity detecting means for detecting an angular velocity of the electric motor, and when the absolute value of the absolute steering angle exceeds a threshold value, an angular velocity target value set by the motor angular velocity setting means and a motor angular velocity detected by the angular velocity detecting means; Angular velocity feedback control means for feedback-controlling the current command value so as to reduce the amount corresponding to the deviation.

Further, in the control device for the electric power steering apparatus according to claim 10, the motor angular speed setting means sets the angular speed target value so that the angular speed target value becomes smaller as the absolute value of the absolute steering angle becomes larger. It is characterized by that.
In the control device for an electric power steering apparatus according to claim 11, the angular velocity target value is set so that the motor angular velocity setting means decreases as the motor angular velocity detected by the angular velocity detection means increases. It is characterized by setting.

In the control device for the electric power steering apparatus according to claim 12, the angular velocity feedback control means has the same angular velocity direction according to the angular velocity target value and the angular velocity direction according to the motor angular velocity, and The feedback control is performed only when the motor angular velocity is larger than the angular velocity target value.
Furthermore, in the control device for an electric power steering apparatus according to claim 13, the relative rudder angle detecting means detects the relative rudder angle using a motor rotation angle detected by a motor rotation angle sensor of the electric motor. It is a feature.

  According to a first aspect of the present invention, there is provided a control device for a power steering device for an electric motor, the relative steering angle detected by the relative steering angle detection means when the steering mechanism is in the reference state, and the known steering mechanism in the reference state. Since the absolute rudder angle is estimated from the relative rudder angle using the relative rudder angle and the absolute rudder angle at this time, the absolute rudder angle for directly detecting the absolute rudder angle Even if the detection sensor is not mounted, the absolute steering angle can be obtained if the relative steering angle detection means is mounted. Then, after the steering mechanism is brought into the reference state, the relative rudder angle at this point is associated with the known absolute rudder angle in the reference state, and thereafter the absolute rudder angle can be estimated. Since the torque transmitted to the torque transmission member between the steering shaft and the steered wheels is suppressed by using the angle, torque suppression is not performed based on an incorrect absolute steering angle, and is inserted between the steering shaft and the steering gear. The steering assist torque generated by the electric motor can be reliably limited before excessive torque is transmitted to the torque transmission member such as the intermediate shaft, and is transmitted to the torque transmission member when the steering limit value is reached. The impact force can be reliably suppressed.

Further, when the steering mechanism is in the steering limit state or the neutral state, the control device for the electric power steering device according to claim 2 associates the known absolute rudder angle in this state with the relative rudder angle at this time point. Correspondence between the absolute rudder angle and the relative rudder angle can be accurately performed, and the absolute rudder angle can be estimated with high accuracy.
According to a third aspect of the present invention, there is provided a control device for an electric power steering apparatus, wherein the steering limit state is entered when the rate of change of the steering torque exceeds the threshold value or when the rate of change of the current command value exceeds the threshold value. Since it is determined that there is, it is possible to easily and accurately determine the steering limit state.

In addition, since the control device for the electric power steering apparatus according to claim 4 determines that the steering limit state exists when the external force acting on the steering mechanism is equal to or greater than the threshold value, the steering limit state is easily and accurately determined. can do.
According to a fifth aspect of the present invention, there is provided a control device for an electric power steering apparatus, wherein the rate of change of the steering torque exceeds the threshold value or the rate of change of the current command value exceeds the threshold value. When it is determined that the steering force is in the steering limit state when the external force acting on the motor is greater than or equal to the threshold value, the reliability of the determination of the steering limit state can be further improved.

  In the control device for an electric power steering apparatus according to claim 6, the absolute value of the steering torque and the rate of change thereof exceed both threshold values, and the absolute value of the angular velocity of the electric motor is less than the threshold value. Since it is determined that the vehicle is in the steering limit state at a certain time, the reliability of the determination as to whether the vehicle is in the steering limit state can be further improved by taking into consideration the rotation state of the electric motor.

Further, the control device for the electric power steering apparatus according to claim 7 is in a neutral state when the state where the absolute value of the steering torque is equal to or less than the threshold value and the vehicle speed is equal to or greater than the threshold value continues for a specified time or more. Since it is determined that there is, it is possible to easily and accurately determine the neutral state.
In addition, when the absolute steering angle is equal to or greater than the limit determination threshold, the control device for the electric power steering apparatus according to claim 8 suppresses the current command value so that the suppression width increases as the current command value increases. Therefore, the torque transmitted to the torque transmission member between the steering shaft and the steered wheels can be easily and accurately suppressed according to the current absolute steering angle.

  The control device for the electric power steering apparatus according to claim 9 sets an angular velocity target value of the electric motor at the current absolute steering angle, and feedback-controls the current command value so that the actual angular velocity becomes the angular velocity target value. Therefore, by changing the external force from the tire, such as when the road surface friction coefficient changes, even if the change characteristic of the steering mechanism relative to the control of the electric motor changes, by feedback control of the angular velocity component, It is possible to suppress a decrease in control performance by the buffer control means due to a change in the characteristics of the steering mechanism, and to reliably reduce the impact force when the steering limit position is reached regardless of the driving environment.

  Further, the control device for the electric power steering apparatus according to claim 10 sets the angular velocity target value so that the angular velocity target value becomes smaller as the absolute value of the absolute steering angle becomes larger. As the electric motor needs to be decelerated more quickly, the angular velocity target value becomes smaller and a large deceleration is generated by the electric motor. Therefore, the electric motor can be decelerated more reliably, that is, when the steering limit position is reached. The force can be reduced more reliably.

  In addition, since the control device for the electric power steering apparatus according to claim 11 sets the angular velocity target value so that the angular velocity target value becomes smaller as the motor angular velocity is larger, the electric motor is rotating at a relatively high speed. In order to decelerate this, a larger deceleration is generated when it is necessary to generate a larger deceleration, and the electric motor can be decelerated more reliably regardless of the rotation state of the electric motor. .

In the control device for the electric power steering apparatus according to claim 12, the direction of the angular velocity according to the angular velocity target value is the same as the direction of the angular velocity according to the motor angular velocity, and the motor angular velocity is greater than the absolute value of the angular velocity target value. Since the motor angular velocity feedback control is performed only when the absolute value of the motor is larger, that is, when it is necessary to decelerate the electric motor, it is possible to avoid unnecessary angular velocity control.
Furthermore, since the control device for the electric power steering apparatus according to claim 13 uses the rotation angle sensor for detecting the motor rotation angle of the electric motor as the relative steering angle detection means, a sensor for detecting the relative steering angle, etc. There is no need to provide a new one, and accordingly, the number of components and the cost can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment will be described.
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.
In the figure, SM is a steering mechanism, and the steering mechanism SM is connected to an input shaft 2a to which a steering force applied from a driver is transmitted to the steering wheel 1 and a torsion bar (not shown). And a steering shaft 2 having an output shaft 2b. 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 8, and steered wheels (not shown) are steered by these tie rods 9.

  Here, as shown in FIG. 2, the steering gear 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 a gear housing 8a. The rotary motion transmitted to the pinion 8b is converted into a straight motion by the rack shaft 8c. The tie rod 9 is connected to both ends of the rack shaft 8c via ball joints 9a, and the rack shaft 8c is positioned at the steering limit position, i. When the stroke end is reached, a stopper member 8f is formed on which the buffer member 8e formed on the inner end surface of the ball joint 9a attached to the rack shaft 8c comes into contact.

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 reduction gear 11 connected to the output shaft 2b, and an electric motor 12 composed of, for example, a brushless motor as an electric motor that generates a steering assist force connected to the reduction gear 11. .
A steering torque sensor 14 is disposed in a housing 13 connected to the steering wheel 1 side of the reduction gear 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, and this torsional angular displacement is detected by a non-contact magnetic sensor.

The steering torque T output from the steering torque sensor 14 is input to the controller 15 as shown in FIG.
In addition to the steering torque T, the controller 15 includes a vehicle speed V detected by a vehicle speed sensor 16, motor currents Iu to Iw flowing through the electric motor 12, an electric motor detected by a motor rotation angle sensor 17 including a resolver, an encoder, and the like. 12 is also input, and the controller 15 executes a steering assist control process for causing the electric motor 12 to generate a steering assist force corresponding to the input steering torque T and vehicle speed V. That is, the steering assist torque command value I _M ^* for driving the electric motor 12 is calculated based on the steering torque T and the vehicle speed V, and the calculated steering assist torque command value I _M ^* is based on the motor rotation angle θ. Various compensation processes are performed based on the calculated motor angular velocity ω and motor angular acceleration α, and then converted into dq-axis command values, followed by two-phase / three-phase conversion to obtain three-phase current command values Iu ^{* to} Iw ^* . The motor current Iu for controlling the drive of the electric motor 12 by performing feedback control processing on the drive current calculated and supplied to the electric motor 12 based on the three-phase current command values Iu ^{* to} Iw ^* and the motor currents Iu to Iw ^. , Iv and Iw are output. Further, a buffer control process is executed in order to mitigate an impact when the rack shaft 8c of the steering gear 8 reaches the rack stroke end. That is, the absolute steering angle φabs of the steering wheel 1 is estimated based on the motor rotation angle θ, and the steering torque T and the vehicle speed V are set in the steering angle range near the steering limit position based on the estimated absolute steering angle estimated value φabs. The corresponding steering assist torque command value I _M is limited, and this is output as the steering assist torque command value I _M ^* .

The controller 15, specifically, as shown in FIG. 3, the steering assist torque command value calculating section 21 for calculating a steering assist torque command value I _M based on the steering torque T and vehicle speed V, the the steering assist torque command For the steering assist torque command value I _M calculated by the value calculation unit 21, a limiting process for the steering assist torque command value I _M is performed as a buffer control process for reducing the impact when the steering angle reaches the steering limit position. a steering assist torque command value I _M after the limiting process, the current limiting unit 22 for outputting a steering assist torque command value I _M ^*, to compensate for the steering assist torque command value I _M ^* from the current limiting unit 22 instruction A value compensation unit 23, a dq-axis current command value calculation unit 24 that calculates a dq-axis current command value based on the post-compensation torque command value I _M ^* ′ compensated by the command value compensation unit 23, This dq axis current command The motor current control unit 25 that generates motor currents Iu to Iw based on the command current output from the value calculation unit 24, and the absolute value of the steering wheel 1 that is used to determine whether or not the current limiting unit 22 performs current limiting. An absolute steering angle estimation unit 26 that estimates an absolute steering angle that is a rotation angle is configured.

The steering assist torque command value calculation unit 21 is provided with a memory (not shown). The memory stores a steering assist current command value I _M corresponding to the steering torque T using the vehicle speed V as a parameter. The steering assist current command value I _M is calculated based on the stored data.
As will be described later, the current limiting unit 22 determines whether or not to limit the current based on the absolute steering angle φabs from the absolute steering angle estimation unit 26, and the steering assist torque command value input as necessary. I _M is limited and output as a steering assist torque command value I _M ^* .

  The command value compensation unit 23 differentiates the motor rotation angle θ detected by the motor rotation angle sensor 17 to calculate the motor angular velocity ω, and differentiates the motor angular velocity ω calculated by the angular velocity calculation unit 31. The angular acceleration calculation unit 32 that calculates the motor angular acceleration α, the convergence compensation unit 33 that compensates the convergence of the yaw rate based on the motor angular velocity ω calculated by the angular velocity calculation unit 31, and the angular acceleration calculation unit 32 Based on the calculated motor angular acceleration α, an inertia compensation unit 34 that compensates for the torque equivalent generated by the inertia of the electric motor 12 to prevent deterioration of the feeling of inertia or control responsiveness, and a self-aligning torque (SAT) And a SAT estimation feedback unit 35 for estimation.

Here, the convergence compensation unit 33 receives the vehicle speed V detected by the vehicle speed sensor 16 and the motor angular velocity ω calculated by the angular velocity calculation unit 31, and the steering wheel 1 shakes to improve the yaw convergence of the vehicle. The convergence compensation value Ic is calculated by multiplying the motor angular speed ω by the convergence control gain Kv that is changed according to the vehicle speed V so as to brake the turning motion.
The SAT estimation feedback unit 35 receives the steering torque T, the angular velocity ω, the angular acceleration α, and the steering assist torque command value I _M ^* from the current limiting unit 22, and estimates and calculates the self-aligning torque SAT based on these. To do.

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 · α + Fr · sign (ω) + 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 · ω ′ (s) + Fr · sign (ω (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 ω, rotational angular acceleration α, assist torque Tm, and steering torque T. The SAT can be estimated. Here, the assist torque Tm is proportional to the steering assist torque command value I _M ^*, to apply a steering assist torque command value I _M ^* in place of the assist torque Tm.

Then, the inertia compensation value Ii calculated by the inertia compensation unit 34 and the self-aligning torque SAT calculated by the SAT estimation feedback unit 35 are added by the adder 36, and the addition output of the adder 36 and the convergence compensation unit 33 are added. Is added by the adder 37 to calculate a command compensation value Icom, and this command compensation value Icom is added to the steering assist torque command value I _M ^* output from the current limiting unit 22. The compensated torque command value I _M ^* ′ is calculated by the adder 38 and this compensated torque command value I _M ^* ′ is output to the dq-axis current command value calculation unit 24.

Further, the dq-axis current command value calculation unit 24 includes a d-axis target current calculation unit 51 that calculates the d-axis target current Id ^* based on the compensated steering assist torque command value I _M ^* ′ and the motor angular velocity ω. , An induced voltage model for calculating a d-axis EMF component e _d (θ) and a q-axis EMF component e _q (θ) of a dq-axis induced voltage model EMF (ElectroMotion Force) based on the motor rotation angle θ and the motor angular velocity ω. a calculating unit 52, the d-axis target output from the d-axis EMF component e _d (theta) and a q-axis EMF component e _q (theta) between the d-axis target current calculation unit 51 output from the induced voltage model calculating unit 52 A q-axis target current calculation unit 53 that calculates a q-axis target current Iq ^* based on the current Id ^* , the compensated steering assist torque command value I _M ^* ′, and the motor angular velocity ω, and an output from the d-axis target current calculation unit 51 D-axis target current Id ^* and q-axis A two-phase / three-phase converter 54 that converts the q-axis target current Iq ^* output from the standard current calculator 53 into three-phase current command values Iu ^* , Iv ^*, and Iw ^* is provided.

The motor current control unit 25 is configured such that each phase coil Lu of the electric motor 12 detected by the motor current detection circuit 60 from the current command values Iu ^* , Iv ^* , and Iw ^* input from the dq-axis current command value calculation unit 24. Subtractors 61u, 61v, and 61w for subtracting motor phase currents Iu, Iv, and Iw flowing through Lv and Lw to obtain respective phase current deviations ΔIu, ΔIv, and ΔIw, and for the obtained respective phase current deviations ΔIu, ΔIv, and ΔIw The PI current control unit 62 that calculates the voltage command values Vu, Vv, and Vw by performing proportional integral control, and the voltage command values Vu, Vv, and Vw that are output from the PI current control unit 62 are input. A pulse width modulation circuit 63 that outputs a pulse width modulation signal that has been subjected to pulse width modulation, and a pulse width modulation signal that is output from the pulse width modulation circuit 63 are input, and three-phase motor currents Iu, Iv, and I And an inverter 64 to output to the electric motor 12.

  As shown in FIG. 5, the absolute steering angle estimation unit 26 includes a relative steering angle calculation unit 101 that calculates the relative steering angle φ of the steering wheel 1 based on the motor rotation angle θ. In the relative steering angle calculation unit 101, the motor rotation angle θ is input, the amount of change Δθ of the motor rotation angle θ is sequentially calculated, the reduction gear ratio between the motor shaft and the steering wheel 1, the motor shaft and steering In consideration of the backlash characteristics of the mechanical mechanism with the wheel 1, the change amount Δθ in the motor rotation angle is converted into the change amount Δφ in the steering angle of the steering wheel 1. Then, the steering angle change amount Δφ is sequentially integrated in consideration of the change direction, and the cumulative value from the integration start time is calculated as the relative steering angle φ with reference to the integration start time.

Further, the absolute steering angle estimating portion 26, and inputs the steering assist torque command value I _M from the steering torque T and the steering assist torque command value calculating unit 21 from the steering torque sensor 14 to the rack end judgment unit 102, based on these It is determined whether or not the vehicle is in the steering limit state, that is, whether or not the rack shaft 8c is in the rack end state in which the rack shaft 8c has reached the steering limit position, that is, the rack stroke end. Specifically, the rack end determination unit 102 calculates the absolute value | T ′ | of the differential value of the steering torque T and the absolute value | I _M ′ | of the differential value of the steering assist torque command value I _M to calculate the steering torque. The absolute value | T ′ | of the differential value of T is larger than a preset threshold value T′th for rack end determination or the absolute value of the differential value of the steering assist torque command value I _M | I _M ′ | Is larger than a preset threshold value I _M ′ for determining the rack end, it is determined that the rack end state exists, and the sampling hold circuit 103 for holding the relative steering angle φ when the rack end state is maintained. In response to this, a sampling hold signal is output. The threshold value T′th of the change rate of the steering torque T for determining the rack end is set as follows, for example. That is, when the driver steers more strongly than usual in order to further increase the steering wheel 1 even though the rack shaft 8c is in the rack end state where the steering shaft is in the steering limit position and cannot be steered any more. The absolute value of the change rate of the steering torque T becomes larger than usual. Therefore, a value that can be regarded as being in the rack end state is set as the threshold value T′th from the absolute value of the rate of change of the steering torque T. Similarly, the threshold value I _M th of the rate of change of the steering assist torque command value I _M for determining the rack end is large because the rate of change of the steering torque T increases as described above when in the rack end state. the rate of change of the steering assist torque command value I _M that is set to increase with an increase in the steering torque T becomes larger than normal. Therefore, the rate of change of the steering assist torque command value I _M, it is set to a possible value of that considered to be the rack end state.

  Accordingly, the sampling hold circuit 103 holds the relative steering angle φ at the time when the sampling hold signal is input as the rack end relative steering angle φrelRE. The rack end relative steering angle φrelRE held by the sampling and holding circuit 103 is input to the subtractor 104 and subtracted from a preset rack end absolute steering angle φabsRE. This rack end absolute rudder angle φabsRE is an absolute rudder angle when in the steering limit state, and is a specific value depending on the vehicle, and is set to, for example, 540 degrees.

The output of the subtracter 104 is input to the adder 105 and added here with the relative steering angle φ, and the output is input to the switching circuit 106 as an absolute steering angle φabs (RE) obtained by converting the relative steering angle φ into an absolute steering angle. Is output. That is, the sampling hold circuit 103 and the subtractors 104 and 105 constitute an absolute steering angle calculation unit 107 based on the rack end state, and the relative steering angle φ calculated from the motor rotation angle θ is set as the absolute steering angle. The converted absolute steering angle φabs (RE) is calculated by the following equation (3) from the relative steering angle φ, the rack end relative steering angle φrelRE, and the rack end absolute steering angle φabsRE.
φabs (RE) = φ + φabsRE−φrelRE (3)

  Further, as shown in FIG. 5, the absolute rudder angle estimation unit 26 inputs the steering torque T from the steering torque sensor 14 and the vehicle speed V from the vehicle speed sensor 16 to the rudder angle neutral point determination unit 111 and performs steering based on these. It is determined whether the wheel 1 is in a neutral state. Specifically, the steering angle neutral point determination unit 111 determines that the absolute value | T | of the steering torque T is equal to or less than a preset threshold value Tth for determining the neutral point and the vehicle speed V is set in advance. Sampling hold for determining that the vehicle is in a neutral state when this state is equal to or greater than the threshold value Vth and this state continues for a specified time or more, and holding the relative steering angle φ when the steering wheel 1 is in the neutral state A sampling hold signal is output to the circuit 112.

Thereby, the sampling hold circuit 112 holds the relative steering angle φ at the time when the sampling hold signal is input as the neutral relative steering angle φrelCT. The neutral relative steering angle φrelCT held by the sampling hold circuit 112 is input to the subtractor 113 and subtracted from a preset neutral absolute steering angle φabsCT.
The neutral absolute rudder angle φabsCT is an absolute rudder angle when the steering wheel 1 is in a neutral state, and is a value unique to the vehicle, and is set to 0 degrees, for example.

The output of the subtractor 113 is input to the adder 114, where it is added to the relative steering angle φ, and the output is input to the switching circuit 115 as an absolute steering angle φabs (CT) obtained by converting the relative steering angle φ into an absolute steering angle. Is output. That is, the sampling hold circuit 112, the subtractor 113, and the adder 114 constitute an absolute steering angle calculation unit 116 based on the neutral state, and the absolute steering angle φabs of the relative steering angle φ calculated from the motor rotation angle θ. (CT) is calculated by the following equation (4) from the relative steering angle φ, the neutral relative steering angle φrelCT, and the neutral absolute steering angle φabsCT.
φabs (CT) = φ + φabsCT−φrelCT (4)

The switching circuits 106 and 115 are switched by a control signal from the absolute steering angle estimated value setting determination unit 117. The control signal to the switching circuit 106 or 115 is also input to a current limiting unit 22 described later.
The absolute rudder angle estimated value setting determination unit 117 controls the switching circuits 106 and 115 to be normally open, and inputs a sampling hold signal from either the rack end determination unit 102 or the rudder angle neutral point determination unit 111. The switching circuit 106 or 115 corresponding to the rack end determination unit 102 or the rudder angle neutral point determination unit 111 that is the output source of the sampling hold signal on the input side is switched to the closed state, and the other maintains the open state. .

  That is, the absolute steering angle estimated value setting determination unit 117 enters the rack end state before the neutral state, the rack end determination unit 102 holds the rack end relative steering angle φrelRE first, and uses the rack end absolute steering angle φabsRE. When the absolute steering angle φabs (RE) can be estimated, the switching circuit 106 on the rack end determination side is controlled to be closed, and thereafter, the rack end absolute steering angle φabsRE and the rack end associated therewith are controlled. Using the relative steering angle φrelRE as a reference, the relative steering angle φ calculated from the motor rotation angle θ is converted into an absolute steering angle φabs (RE). Conversely, the neutral state is established before the rack end state, the neutral relative rudder angle φrelCT is held first in the rudder angle neutral point determination unit 111, and the absolute rudder angle φabs (CT) is estimated using the neutral absolute rudder angle φabsCT. When it becomes possible, the switching circuit 115 on the rudder angle neutral point determination side is controlled to be closed, and thereafter the motor rotation is performed with reference to the neutral absolute rudder angle φabsCT and the neutral relative rudder angle φrelCT associated therewith. The relative steering angle φ calculated from the angle θ is converted into an absolute steering angle φabs (CT).

The absolute steering angle φabs (RE) or the absolute steering angle φabs (CT) output from the switching circuits 106 and 115 is output as the absolute steering angle estimated value φabs. Note that the switching circuits 106 and 115 are both open while the sampling hold signal is not output in either the rack end determination unit 102 or the steering angle neutral point determination unit 111, and therefore the absolute steering angle estimation value φabs is estimated. Is not done.
The current limiting unit 22 performs current limiting using the absolute steering angle estimated value φabs estimated in this way. Specifically, as shown in FIG. 6, the absolute steering angle estimation value φabs estimated by the absolute steering angle estimation unit 26 is input to the suppression gain setting unit 121 and the angular velocity target value setting unit 126.

  The suppression gain setting unit 121 sets the suppression gain K11 according to the magnitude of the absolute steering angle estimated value φabs, and when the absolute value | φabs | of the absolute steering angle estimated value φabs is equal to or less than a preset threshold value φ11. When the suppression gain K11 is set to “1” and the absolute value | φabs | of the absolute steering angle estimation value φabs exceeds the threshold value φ11, the suppression gain K11 increases as the absolute value | φabs | of the absolute steering angle estimation value φabs increases. Is set to be small, and the suppression gain K11 is set to zero when the absolute value | φabs | of the absolute steering angle estimated value φabs becomes the maximum steering angle φmax. The threshold value φ11 is set to be equivalent to the steering angle at which the current limit for reducing the impact when the rack shaft 8c reaches the rack stroke end when the steering limit is reached. Is also set to the front position.

The suppression gain K11 set by the suppression gain setting unit 121 is input to the switching circuit 122. The switching circuit 122 is configured to be able to select either the suppression gain K11 set by the suppression gain setting unit 121 or a preset fixed gain “1”, and the suppression gain K11 selected by the switching circuit 122 or The fixed gain is input to the multiplier 123, where it is multiplied by the steering assist torque command value I _M calculated by the steering assist torque command value calculator 21 and output to the adder 124.

  On the other hand, the angular velocity target value setting unit 126 receives the absolute steering angle estimated value φabs and the motor angular velocity ω calculated by the angular velocity calculation unit 31 of the command value compensation unit 23, and based on these, the angular velocity target value ωr. Set. Here, when the absolute rudder angle estimated value φabs is a positive value, it indicates that the rudder angle is more rightward than neutral, and when it is a negative value, it is a rudder angle leftward than neutral. It shall represent. Further, when the angular velocity target value ωr is a positive value, it indicates rotation in the right steering direction, and when it is a negative value, it indicates rotation in the left steering direction.

  The angular velocity target value ωr is a constant value that is set in advance when the absolute steering angle estimate value φabs is a positive value and the motor angular velocity ω is constant, and the absolute steering angle estimate value φabs is less than or equal to a preset threshold value φ12. When the absolute rudder angle estimated value φabs exceeds the threshold value φ12, the angular speed target value ωr is set to be smaller as the absolute rudder angle estimated value φabs is larger, and the absolute rudder angle estimated value φabs is the maximum rudder. When the angle φmax is reached, the target angular velocity value ωr is set to zero. That is, as the absolute rudder angle estimated value φabs approaches the maximum rudder angle φmax and the rack shaft 8b approaches the rack end, the angular velocity target value ωr is decreased to generate a torque that reduces the steering speed. Further, when the motor angular speed ω is large, that is, when the electric motor 12 rotates at a higher speed, a larger torque is required to decelerate the steering speed. Therefore, as the motor angular speed ω increases, the angular speed target value ωr becomes smaller. Set to be smaller.

  The same applies to the case where the absolute rudder angle estimated value φabs is a negative value and the vehicle is steered leftward from the neutral position. When the absolute rudder angle estimated value φabs is equal to or larger than a preset threshold “−φ12”, the angular velocity target is set. The value ωr is set to a preset constant value “−ωr12”. When the absolute steering angle estimated value φabs falls below the threshold value “−φ12”, the angular velocity target value ωr increases as the absolute steering angle estimated value φabs decreases. When the absolute rudder angle estimate value φabs reaches the maximum rudder angle φmax, the target angular velocity value ωr is set to zero. Further, as the motor angular velocity ω increases, the absolute value of the target angular velocity value ωr increases. Is set to be small. Note that the threshold value φ12 is set to be equivalent to the steering angle at which the current limit for mitigating the impact when the rack shaft 8c reaches the rack stroke end when the steering limit is reached, and is greater than the maximum steering angle. Set to the front position.

The angular velocity target value ωr set by the angular velocity target value setting unit 126 in this way is input to the subtractor 127, and an angular velocity deviation obtained by subtracting the motor angular velocity ω from the angular velocity target value ωr is input to the amplifier 128. The gain is multiplied by G and input to the adder 124 via the switching circuit 129. In other words, the angular velocity target value setting unit 126, the subtractor 127, the amplifier 128, the switching circuit 129, and the adder 124 constitute the feedback unit 130, and the angular velocity deviation is fed back to the steering assist torque command value I _M to obtain the angular velocity. Feedback control based on the deviation is performed.

  The gain G of the amplifier 128 is a gain for feeding back the angular velocity deviation from the subtractor 127 to the current command value, and the absolute value of the absolute steering angle estimated value φabs is preset, and the current steering start steering is limited. When it is larger than the threshold value φ13 corresponding to the angle, it is set to a preset specified value g1. Further, when the absolute value of the absolute steering angle estimated value φabs is equal to or smaller than the threshold value φ13, the gain G is set to zero, that is, feedback control corresponding to the angular velocity deviation associated with the current limitation is not performed.

The adder 124 adds the output of the multiplier 123 and the output of the switching circuit 129, and outputs the addition result as a steering assist torque command value I _M ^* . The switching circuits 122 and 129 are switched according to a control signal for the switching circuits 106 and 115 from the absolute steering angle estimated value setting determination unit 117, and are controlled to be closed with respect to any of the switching circuits 106 and 115. When the control signal is output, that is, when the absolute steering angle estimated value can be obtained, the switching circuit 122 is switched to the side for selecting the suppression gain K11, and the switching circuit 129 is controlled to be closed. is, feedback control is performed by the current limit and the angular velocity deviation caused by suppression gain K11 to the steering assist torque command value I _M. On the other hand, when the control signal for controlling the closed state is not output to any of the switching circuits 106 and 115, that is, when the absolute steering angle estimation value cannot be obtained, the switching circuit 122 has the fixed gain “1”. is switched to the side of selecting, switching circuit 129 is controlled to the open state, it does not perform current limiting and feedback control of angular velocity with respect to the steering assist torque command value I _M.

Next, the operation of the first embodiment will be described.
Now, when the ignition switch IG is turned on to start traveling of the vehicle, the controller 15 is powered on and the steering assist control process is executed.
Therefore, the steering torque T detected by the steering torque sensor 14, the vehicle speed V detected by the vehicle speed sensor 16, the motor current detection values Iu to Iw detected by the motor current detection circuit 60, and the motor rotation angle detected by the motor rotation angle sensor 17. θ is supplied to the controller 15.

Therefore, to calculate the steering assist torque command value I _M based on the steering assist torque command value calculating unit 21 and the steering torque T and the vehicle speed V. At this time, when the vehicle is in a stopped state and the steering wheel 1 is not steered largely, the absolute rudder angle estimation unit 26 performs neither rack end determination nor rudder angle neutral point determination. The steering angle estimated value φabs is not estimated. For this reason, since the control signal which switches this to a closed state is not output with respect to the switching circuit 106 or 115 from the absolute steering angle estimated value setting determination part 117 in the current control part 22, the switching circuit 122 of the current limiting part 22 Control is performed to select the fixed gain “1”, and the switching circuit 129 maintains the open state. Therefore, the current limit is not performed with respect to the steering assist torque command value I _M calculated by the steering assist torque command value calculating unit 21.

Therefore, the steering assist torque command value I _M calculated according to the steering torque T and the vehicle speed V is output as it is as the steering assist torque command value I _M ^* .
On the other hand, the motor rotation angle θ detected by the motor rotation angle sensor 17 is input to the angular velocity calculation unit 31 to calculate the motor angular velocity ω, and the motor angular velocity ω is input to the angular acceleration calculation unit 32 to calculate the motor angular acceleration α. Is done. Then, the convergence compensation unit 33 calculates the convergence correction value Ic based on the motor angular velocity ω, the inertia compensation unit 34 calculates the inertia compensation value Ii based on the motor angular acceleration, and the SAT estimation feedback unit 35 further calculates the motor. The self-aligning torque SAT is calculated based on the angular velocity ω and the motor angular acceleration α, and these are added by the adders 36 and 37 to calculate the command value compensation value Icom. The adder 38 calculates the steering assist torque command value I. _M ^* summed with the compensated steering assist torque command value compensation value I _{M *} ^'in is calculated.

Then, the calculated post-compensation steering assist torque command value compensation value I _M ^* ′ is supplied to the dq axis current command value calculation unit 24.
At this time, when the vehicle is stopped and the steering wheel 1 is not steered, the steering torque T detected by the steering torque sensor 14 is “0”, and the vehicle speed V detected by the vehicle speed sensor 16 is also Since it is “0”, the steering assist torque command value I _M ^* calculated by the steering assist torque command value calculation unit 21 is also “0”, and the electric motor 12 continues to be stopped.

When the vehicle starts from this state, the steering assist torque command value _IM is calculated according to the steering torque T and the vehicle speed V input to the steering wheel 1, but the absolute steering angle in the absolute steering angle estimation unit 26 is calculated. during the calculation of the estimated value φabs it is not started, because the current limitation in the current limiting unit 22 to the steering assist torque command value I _M is not performed, the steering assist torque command value I corresponding to the steering torque T and the vehicle speed V _M is output as it is as the steering assist torque command value I _M ^* . Accordingly, the electric motor 12 is driven and controlled accordingly, and a steering assist force corresponding to the steering torque T and the vehicle speed V is applied to the steering shaft 2.

From this state, when the steering wheel 1 travels straight while being maintained in a neutral state, the absolute value of the steering torque T satisfies | T | ≦ Tth and satisfies V ≧ Vth, which is specified. When the steering wheel 1 has continued for more than the time, the steering wheel neutral point determination unit 111 of the absolute steering angle estimation unit 26 determines that the steering wheel 1 is in a neutral state, and outputs a sampling hold signal to the sampling hold circuit 112. Thereby, the sampling hold circuit 112 holds the relative steering angle φ at this time as the neutral relative steering angle φrelCT. The absolute steering angle estimated value setting determination unit 117 outputs a sampling hold signal from the steering angle neutral point determination unit 111, and at this time, no sampling hold signal is output from the rack end determination unit 102. A control signal for closing the switching circuit 115 corresponding to the neutral point determination side and opening the switching circuit 106 corresponding to the rack end side is output.
Therefore, the absolute steering angle φabs (CT) obtained by adding the relative steering angle φ to the value obtained by subtracting the neutral point relative steering angle φrelCT held by the sampling hold circuit 112 from the neutral absolute steering angle φabsCT is obtained via the switching circuit 115. Is output as an absolute steering angle estimated value φabs.

On the other hand, in the current limiting unit 22, the suppression gain K <b> 11 is set according to the absolute steering angle estimated value φabs calculated in this way, and the switching circuit 122 switches the switching circuit 115 from the absolute steering angle estimated value setting determination unit 117. the receiving the control signal for switching to the closed state, since the switches in the suppression gain K11 side, the steering assist torque command value I _M calculated by the steering assist torque command value calculating unit 21 and the suppression gain K11 is multiplied. Further, an angular velocity target value ωr is calculated according to the absolute steering angle estimated value φabs and the motor angular velocity ω, and the angular velocity deviation between the angular velocity target value ωr and the motor angular velocity ω is the magnitude of the absolute steering angle estimated value φabs. Depending on the feedback.

At this time, since the steering wheel 1 is in a neutral state, the absolute steering angle estimated value φabs is substantially zero. Thus, from being set to the suppression gain K11 is "1", the current limiting by suppression gain K11 to the steering assist torque command value I _M is not performed, also the absolute value of the absolute steering angle estimating value φabs threshold since φ13 is less, the steering assist torque command value velocity feedback frequency becomes zero the relative I _M, a feedback control of angular velocity is not performed. Therefore, there is a steering wheel 1 is in the neutral state, in potential is low the rack shaft 8c of the steering gear 8 reaches the rack stroke end, no steering assist torque command value I _M is limited. Also, a neutral state, the steering assist torque command value I _M when the steering is not being performed substantially zero next steering assist torque command value I _M ^* substantially becomes zero electric motor 12 also is not driven. For this reason, since the motor rotation angle θ does not change, the relative steering angle φ calculated by the relative steering angle calculation unit 101 does not change, and the absolute steering angle estimated value φabs does not change.

From this state, when the driver performs the steering, the steering assist torque command value I _M is increased steering assist torque command value along with this, which is calculated by the steering assist torque command value calculating unit 21 according to an increase of the steering torque T Since I _M ^* increases, the electric motor 12 is driven. When the motor rotation angle θ changes with the rotation of the electric motor 12, a change amount Δθ of the motor rotation angle θ is calculated by the relative steering angle calculation unit 101. For example, when the right steering is performed, the change of the motor rotation angle θ is calculated. Since the current change amount Δθ is added to the integrated value of the amount Δθ, the value converted to the relative steering angle φ of the steering wheel 1 increases in the positive direction representing the right steering, and conversely the left steering is When this is done, the current amount of change Δθ is subtracted from the integrated value of the amount of change Δθ, and the value obtained by converting this to the relative steering angle φ of the steering wheel 1 increases in the negative value direction representing left steering.

  The relative rudder angle φ calculated in this way is input to the adder 105 on the rack end determination side and the adder 114 on the rudder angle neutral point determination side. Since the switching circuit 106 is controlled in the open state, the output of the adder 114 on the switching circuit 115 side that is controlled in the closed state, that is, the absolute steering angle φabs (CT) continues as the absolute steering angle estimated value φabs. Is output.

Further, as the steering torque T increases, the steering assist torque command value _IM also increases. In response to this, the electric motor 12 is driven and controlled, and the current limiting unit 22 limits the current gain of the suppression gain K11. Calculation and calculation for the feedback of the angular velocity are performed. While the absolute value of the absolute steering angle estimated value φabs is smaller than the threshold value φ11, the suppression gain K11 is “1”, and the absolute steering angle estimated value φabs since it is made of gain G and feedback frequency is zero angular velocity is set to "0" in the case of the threshold φ13 or less, not performed correction for the steering assist torque command value I _M, the steering torque T and the vehicle speed A steering assist force corresponding to V is generated. For this reason, the driver can perform light steering.

From this state, the vehicle stops, and the steering wheel 1 is turned to the right or left to the steering limit value in a very low speed traveling state such as a so-called stationary operation in which the steering wheel 1 is turned to the right (or left), or in the garage. When steering is performed, the steering assist torque command value I _M is maintained while the absolute value of the absolute steering angle estimated value φabs falls below the threshold value φ11 for setting the suppression gain K11 and the threshold value φ13 for setting the gain G. Since the electric motor 12 is driven and controlled according to the steering torque T without being corrected for, the driver can perform light steering, but the absolute steering angle estimated value φabs is close to the steering limit, and the suppression gain K11 is set. When the threshold value φ11 is exceeded, the suppression gain K11 is set to a value smaller than “1” and the absolute steering angle estimated value φabs as shown in the control map in FIG. The larger the value is, the smaller the value is set. Therefore, the steering assist torque command value I _M set according to the steering torque T is suppressed as the absolute steering angle estimated value φabs increases, that is, the torque generated from the electric motor 12 as the steering limit is approached. Since the torque to be transmitted to the intermediate shaft 5 is reduced, the impact applied to the torque transmission member such as the intermediate shaft is suppressed when the rack shaft 8b reaches the steering limit position. The durability can be improved accordingly.

At this time, if the absolute value of the absolute steering angle estimated value φabs exceeds the threshold value for setting the gain G, a preset fixed value g1 is set as the gain G, and the absolute steering angle estimated value φabs is large. is to deviations between the motor angular velocity at this point and the angular velocity target value ωr which is set from the motor angular velocity ω is fed back to the steering assist torque command value I _M, further, the absolute steering angle estimated value φabs is that threshold φ12 Is larger, the motor angular velocity target value ωr is set to a smaller value. Therefore, the feedback amount of the angular velocity, is supposed to correct the steering assist torque command value I _M in a direction to decelerate the electric motor 12, more rapidly slow down the electric motor 12, the impact at the time of end contact more reliably Can be reduced. At this time, the larger the motor angular velocity ω, the smaller the angular velocity target value ωr. Therefore, it is predicted that the motor angular velocity ω is large, the angular velocity of the electric motor 12 is fast, and the impact at the end of the impact is large. As the operation is performed, the electric motor 12 is further decelerated, and it is possible to accurately avoid the occurrence of an impact due to the end contact depending on the angular velocity of the electric motor 12.

The force acting on the steering mechanism includes an external force from the tire in addition to the driver's steering torque and electric power steering assisting force. Thus, for example, when the road surface friction coefficient is small external force from the tire low, even a steering assist torque command value I _M according to the absolute steering angle estimating value φabs as restricted in the same way, the electric motor 12 may not be sufficiently decelerated, and the steering speed may not be sufficiently decelerated to a speed at which the impact due to the end pad can be suppressed. However, as described above, by performing feedback control on the angular velocity deviation, it is possible to accurately decelerate regardless of changes in external force.

Further, by setting the angular velocity target value ωr smaller the current of the motor angular speed ω is larger to a smaller value, to a greater angular velocity feedback amount, because they limit the steering assist torque command value I _M to a smaller value Since the electric motor 12 rotates at a relatively high speed and a relatively large torque is required to decelerate the electric motor 12, the angular speed target value ωr increases as the motor angular speed ω increases and a larger deceleration is required. By controlling so that a sufficient deceleration is applied, it is possible to accurately decelerate regardless of the rotation state of the electric motor 12, and as a result, it is possible to accurately suppress the impact force.

On the other hand, when the vehicle is stopped and the steering wheel 1 is not steered after the ignition switch IG is turned on, the rack end determination and the steering angle neutral point are performed at the time of starting the stationary operation. Since neither of the determinations is performed, the absolute steering angle estimated value φabs is not calculated. However, although the rack end position has been reached and the steering cannot be performed any more, the driver does not control the steering wheel 1. By turning the wheel, a stronger steering than usual is performed, so that the change rate of the steering torque T exceeds the threshold value and can be regarded as being at the rack end position. when a, or the rate of change of the steering assist torque command value I _M for driving the electric motor 12 with the increase in the steering torque threshold The rack end determination unit 102 outputs a sampling hold signal at a point in time when the rack end determination unit 102 is in a state in which the rack end position can be regarded as being in the rack end position, and the relative steering angle φ at this point is the relative steering angle φrelRE. And the estimation of the absolute steering angle estimated value φabs is started from the relative steering angle φrelRE and the absolute steering angle φabsRE.

For this reason, when a steering operation that repeatedly increases and decreases in the vicinity of the steering limit is performed, it is detected that the rack end state is detected when the increase to the steering limit is first performed, and the absolute steering angle is detected. estimate calculation of φabs is initiated, which subsequently, since the feedback control of the current limit and the angular velocity is performed with respect to the steering assist torque command value I _M, which subsequently, there in case that a repetition rack end state However, it is possible to accurately suppress the impact caused by reaching the rack end position.

  In the first embodiment, the absolute steering angle φabs of the steering wheel 1 is estimated using the rotation angle θ of the electric motor 12. Therefore, it is possible to reduce the impact in the rack end state without providing an absolute steering angle sensor for detecting the absolute steering angle φabs of the steering wheel 1, thereby reducing the number of parts and the cost. it can. At this time, since the absolute steering angle φabs is estimated using the motor rotation angle θ from the motor rotation angle sensor 17 used for driving control of the electric motor 12, the absolute steering angle φabs is estimated. Therefore, there is no need to newly provide a relative steering angle sensor.

In addition, since the current control unit 21 is configured to limit the current for shock mitigation after the estimation of the absolute rudder angle is started, in the state where the absolute rudder angle is not fixed, By performing the current limitation, it is possible to avoid that a sufficient steering assist force cannot be obtained.
In the first embodiment, the absolute steering angle estimated value φabs is estimated using the relative steering angle φrelRE or φrelCT in the neutral state or the rack end state detected earlier. However, for example, the relative steering angle φrelRE or φrelCT may be updated every time the vehicle enters the neutral state or the rack end state. In this way, the absolute steering angle estimated values φabsRE and φabsCT that increase with time are updated. The estimation error can be removed.

Next, a second embodiment of the present invention will be described.
In the second embodiment, as shown in FIG. 7, an external force estimation unit 131 that estimates an external force acting on the steering mechanism from the tire is newly provided in the first embodiment, and the absolute steering angle estimation unit 26 is provided. Then, the rack end determination is performed using the external force estimated by the external force estimation unit 131. Detailed description of the same part is omitted.

FIG. 8 is a functional configuration diagram illustrating a functional configuration of the external force estimation unit 131. The external force estimation method in the external force estimation unit 131 is the same as the processing in the SAT estimation feedback unit 35 of the command value compensation unit 23 described above, and the steering angle calculated by the motor rotation angle θ and the steering assist torque command value calculation unit 21. Based on the auxiliary torque command value I _M and the steering torque T from the steering torque sensor 14, the self-aligning torque SAT is estimated and calculated by using the equation (2), and this is used as the external force estimated value SAT (RE). . The external force estimation unit 131 uses a multiplication value of the steering assist torque command value _IM , the gear ratio, and the torque constant as the assist torque Tm.

The external force estimated value SAT (RE) calculated by the external force estimating unit 131 is input to the rack end determining unit 102a for the absolute steering angle estimated value 26.
In the rack end determination unit 102a, the external force estimation value SAT (RE) from the external force estimation unit 131 is equal to or greater than a threshold value SATth for determining that the rack end state is set in advance, and the steering torque T When the absolute value | T ′ | of the change rate of the vehicle is larger than the threshold value T′th, or the absolute value | I _M ′ | of the change rate of the steering assist torque command value I _M is the threshold value I _M When it is larger than ′, it is determined that the rack is in the end state.

In other words, no further steering can be performed when the rack end state is reached, and therefore the external force increases with respect to the driver's steering operation, so the estimated external force value SAT (RE) becomes the rack end state. When the threshold value SATth corresponding to the external force is exceeded, the rack end state can be considered. Therefore, not only the state of change of the steering torque T and the steering assist torque command value I _M, by determining whether the rack end state by using also the external force estimation value SAT (RE), whether the rack end state It is possible to judge accurately. It is also possible to determine whether the rack end state is based only on the external force. As described above, the external force condition is satisfied, and the steering torque T or the steering assist torque command value _IM is changed. By determining that the position is at the rack end position when both of the condition conditions are satisfied, it is possible to determine whether or not the rack end state is more accurately determined.

Next, a third embodiment of the present invention will be described.
Since the third embodiment is the same as the first embodiment except that the processing of the absolute steering angle estimation unit 26 and the current limiting unit 22 is different, detailed description of the same part is omitted. .
FIG. 9 is a block diagram showing a functional configuration of the absolute steering angle estimation unit 26 in the third embodiment. In the third embodiment, the rack end determination unit 102b receives the steering torque T from the steering torque sensor 14, the relative steering angle φ from the relative steering angle calculation unit 101, and the angular velocity calculation unit 31 of the command value compensation unit 23. Rack end determination is performed using the motor angular velocity ω.

  Specifically, the absolute value | T | of the steering torque T is larger than the threshold value Tth (| T |> Tth), and the absolute value | T ′ | of the rate of change is the threshold value T′th. Is larger than (| T ′ |> T′th) and the absolute value | ω | of the motor angular velocity ω is equal to or less than the threshold value ωth (| ω | ≦ ωth), it is determined that the rack end state is established. Then, a sampling hold signal is output to the sampling hold circuit 103.

  That is, even though the rack end position has been reached and no further steering is possible, the driver tries to turn the steering wheel 1 to perform steering stronger than usual. Since T exceeds the threshold value and the rate of change of the steering torque exceeds the threshold value and the steering wheel 1 cannot be rotated any more, the electric motor 12 does not rotate, and the actual motor angular speed ω When the absolute value of is less than or equal to the threshold value, it is determined that the rack is in the end state. Therefore, since it is determined whether or not the rack end state is considered in consideration of not only the change state of the steering torque T but also the rotation state of the electric motor 12, the rack end determination can be performed more accurately.

On the other hand, in the current calculation unit 22, as shown in FIG. 10, the absolute steering angle estimated value φabs estimated by the absolute steering angle estimation unit 26 is input to the suppression gain setting unit 121 and the angular velocity target value setting unit 126a, and the suppression gain setting is performed. In the unit 121, after the suppression gain K11 is set in the same procedure as in the first embodiment, it is input to the multiplier 123 via the switching circuit 122, where it is multiplied by the steering assist torque command value I _M. Is then input to the adder 124.

  On the other hand, the angular velocity target value setting unit 126a sets the angular velocity target value ωr according to the absolute steering angle estimated value φabs. That is, as shown in the control map for setting the angular velocity target value in FIG. 10, when the absolute value of the absolute steering angle estimated value φabs is equal to or less than the preset threshold value φ14, the preset constant value ωr13 is set to the angular velocity target value. Set as ωr. When the absolute value of the absolute rudder angle estimated value φabs is larger than the threshold value φ14, the larger the absolute value of the absolute rudder angle estimated value φabs, the smaller the target angular velocity value ωr and the zero at the maximum rudder angle φmax. Set to.

The angular velocity target value ωr set by the angular velocity target value setting unit 126a is input to the subtractor 127, where the motor angular velocity ω is subtracted from the angular velocity target value ωr, and the deviation of the motor angular velocity is supplied to the amplifier 128a. After the gain is multiplied by G, the signal is input to the adder 124 via the switching circuit 129. The output of the adder 124 is output as a steering assist torque command value I _M ^* .

  The gain G in the multiplier 128a is set according to the absolute steering angle estimated value φabs, the angular velocity target value ωr set by the angular velocity target value setting unit 126a, and the motor angular velocity ω. Specifically, the absolute value of the absolute steering angle estimated value φabs is larger than a preset threshold value φth, the sign of the angular velocity target value ωr of the electric motor 12 is a positive value, and is larger than the angular velocity target value ωr. When the actual motor angular speed ω is larger, or the absolute value of the absolute steering angle estimated value φabs is larger than a preset threshold value φth, and the sign of the target angular speed value ωr of the electric motor 12 is a negative value. When the actual motor angular velocity ω is smaller than the angular velocity target value ωr, that is, when the electric motor 12 is currently rotating at a higher speed than the angular velocity target value ωr and needs to be decelerated. As the gain G, a preset constant value g2 is set. On the other hand, when these conditions are not satisfied, zero is set as the gain G because there is no need to perform angular velocity feedback. The angular velocity target value setting unit 126a, the subtractor 127, the amplifier 128a, the switching circuit 129, and the adder 124 constitute a feedback control unit 130a.

That is, in the current limiting unit 22, it is possible to suppress the steering assist torque command value I _M according to the magnitude of the absolute steering angle estimated value Faiabs, the larger steering limit position near than the absolute steering angle estimating value Faiabs threshold When it is necessary to limit the torque for suppressing the impact and the current angular velocity of the electric motor 12 is higher than the angular velocity target value and it is necessary to decelerate, the steering is performed by feeding back the angular velocity deviation. The auxiliary torque command value _IM is suppressed.

Therefore, it is possible to accurately feedback control the angular velocity deviation according to the actual rotation state of the electric motor 12, and to avoid decelerating the electric motor 12 by feeding back the angular velocity deviation unnecessarily, It is possible to reliably avoid the occurrence of an impact when the steering limit is reached while generating the necessary steering assist force.
In the third embodiment, similarly to the first embodiment, when the angular velocity target value ωr is set, the angular velocity target value ωr is variable so as to decrease as the motor angular velocity ω increases. In this way, when the speed control of the electric motor 12 is necessary, the speed control can be accurately performed according to the rotation state of the electric motor 12, and the steering limit position can be set. It is possible to accurately avoid the occurrence of an impact when reaching the value.

  In the above embodiment, the steering torque sensor 14 corresponds to the steering torque detection means, the steering assist torque command value calculation unit 21 in FIG. 3 corresponds to the current command value calculation means, and the motor current control unit 25 controls the motor. The motor angular velocity sensor 17 and the relative steering angle calculation unit 101 correspond to the relative steering angle detection unit, the absolute steering angle estimation unit 26 corresponds to the absolute steering angle estimation unit, and the current limiting unit 22 corresponds to the buffer control unit. It corresponds to.

Each of the rack end determination units 102, 102a, 102b and the steering angle neutral determination unit 111 corresponds to a steering state determination unit, and the absolute steering angle calculation units 107 and 116 correspond to a conversion unit.
The external force estimation unit 131 corresponds to the external force estimation unit, the angular velocity calculation unit 31 corresponds to the angular velocity detection unit, and the vehicle speed sensor 16 corresponds to the vehicle speed detection unit.
Further, the target angular velocity setting units 126 and 126a correspond to motor angular velocity setting means, respectively, and the feedback control units 130 and 130a correspond to angular velocity feedback control means, respectively.

1 is a diagram showing a schematic configuration of an electric power steering apparatus according to a first embodiment of the present invention. It is the front view which made a part the section which shows the concrete composition of a steering gear. It is a block diagram which shows the specific example of the controller which concerns on this invention. It is a schematic diagram with which it uses for description of the self-aligning torque. It is a block diagram which shows the function structure of an absolute steering angle estimation part. It is a block diagram which shows the function structure of a current control part. It is a block diagram which shows the function structure of the absolute steering angle estimation part in 2nd Embodiment. It is a block diagram which shows the function structure of an external force estimation part. It is a block diagram which shows the function structure of the absolute steering angle estimation part in 3rd Embodiment. It is a block diagram which shows the function structure of the current control part in 3rd Embodiment.

Explanation of symbols

SM Steering Mechanism 1 Steering Wheel 2 Steering Shaft 12 Electric Motor 14 Steering Torque Sensor 15 Controller 16 Vehicle Speed Sensor 17 Motor Rotation Angle Sensor 21 Steering Auxiliary Torque Command Value Calculation Unit 22 Current Limiting Unit 26 Absolute Steering Angle Estimation Unit

Claims (13)

Steering torque detection means for detecting steering torque input to the steering mechanism;
Current command value calculation means for calculating a current command value based on at least the steering torque detected by the steering torque detection means;
An electric motor for generating a steering assist torque to be applied to a steering shaft of the steering mechanism;
Motor control means for driving and controlling the electric motor based on the current command value;
Relative steering angle detection means for detecting the relative steering angle of the steering mechanism;
Absolute steering angle estimation means for estimating the absolute steering angle of the steering mechanism using the relative steering angle detected by the relative steering angle detection means;
When the absolute rudder angle estimated by the absolute rudder angle estimating means exceeds the limit judgment threshold value before the steering limit rudder angle, the torque transmitted to the torque transmission member between the steering shaft and the steered wheels of the steering mechanism is suppressed. A control device for the electric power steering device comprising:
The absolute steering angle estimation means determines whether the steering mechanism is in a reference state in which the relative steering angle detected by the relative steering angle detection means and the absolute steering angle of the steering mechanism can be associated with each other. Steering state determination means;
When the steering state determination means determines that the steering mechanism is in the reference state, a relative steering angle detected by the relative steering angle detection means and a known reference absolute steering angle in the reference state of the steering mechanism Conversion means for converting the relative steering angle detected by the relative steering angle detection means into the absolute steering angle using the reference absolute steering angle and the relative steering angle corresponding thereto associated with each other. With
The buffer control means controls the electric power steering apparatus using the absolute steering angle after the absolute steering angle estimation means is able to estimate the absolute steering angle. apparatus.   2. The control device for an electric power steering apparatus according to claim 1, wherein the reference state of the steering mechanism is a steering limit state or a neutral state in which the steering mechanism cannot perform further steering.   The steering state determining means is configured such that when the rate of change of the steering torque detected by the steering torque detecting means exceeds the threshold value, or the rate of change of the current command value calculated by the current command value calculating means is the threshold value. 3. The control device for an electric power steering apparatus according to claim 2, wherein the control unit determines that the vehicle is in the steering limit state when exceeding the control range. An external force estimating means for estimating an external force acting on the steering mechanism;
4. The steering state determining means determines that the steering state is in the steering limit state when the external force estimated value estimated by the external force estimating means is equal to or greater than the threshold value. The control apparatus of the electric power steering apparatus as described. An external force estimating means for estimating an external force acting on the steering mechanism;
The steering state determining means is configured such that when the rate of change of the steering torque detected by the steering torque detecting means exceeds the threshold value, or the rate of change of the current command value calculated by the current command value calculating means is the threshold value. 3. The electric power according to claim 2, wherein the electric power is determined to be in the steering limit state when the external force estimated value estimated by the external force estimating means is equal to or greater than the threshold value. Control device for steering device. Angular velocity detection means for detecting the angular velocity of the electric motor,
The steering state determination means has both the absolute value of the steering torque detected by the steering torque detection means and the rate of change thereof exceeding the respective threshold values, and the absolute value of the angular speed detected by the angular speed detection means. The control device for an electric power steering apparatus according to any one of claims 2 to 5, wherein when it is equal to or less than a threshold value, the steering limit state is determined. Vehicle speed detection means for detecting the vehicle speed,
The steering state determination means has an absolute value of the steering torque equal to or lower than the threshold value, and the vehicle speed detected by the vehicle speed detection means is equal to or higher than the threshold value. The control device for an electric power steering apparatus according to any one of claims 2 to 6, wherein the controller is determined to be in the neutral state.   The buffer control means suppresses the current command value calculated by the current command value calculation means and increases the absolute value of the absolute steering angle when the absolute steering angle exceeds the limit determination threshold value. 8. The control device for an electric power steering apparatus according to claim 1, further comprising a current suppression unit that suppresses the suppression width to be increased. The buffer control means is a motor angular speed setting means for setting an angular speed target value of the electric motor at the absolute steering angle from the absolute steering angle;
Angular velocity detection means for detecting the angular velocity of the electric motor;
When the absolute value of the absolute steering angle exceeds the threshold value, the current command so as to reduce a deviation equivalent between the target angular speed set by the motor angular speed setting means and the motor angular speed detected by the angular speed detection means 9. The control device for an electric power steering apparatus according to claim 8, further comprising angular velocity feedback control means for feedback-controlling the value.   10. The control of the electric power steering apparatus according to claim 9, wherein the motor angular speed setting means sets the angular speed target value so that the angular speed target value decreases as the absolute value of the absolute steering angle increases. apparatus.   11. The angular velocity target value is set so that the angular velocity target value becomes smaller as the motor angular velocity detected by the angular velocity detection means becomes larger. Control device for electric power steering apparatus.   The angular velocity feedback control means only when the angular velocity direction according to the angular velocity target value is the same as the angular velocity direction according to the motor angular velocity, and the motor angular velocity is larger than the angular velocity target value. The control device for an electric power steering apparatus according to any one of claims 9 to 11, wherein the feedback control is performed.   The said relative rudder angle detection means detects the said relative rudder angle using the motor rotation angle detected with the motor rotation angle sensor of the said electric motor, The any one of Claims 1-12 characterized by the above-mentioned. The control apparatus of the electric power steering apparatus as described.

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