JP2017109581A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering apparatus capable of more accurately computing an estimated rotation angle of a motor on the basis of steering torque and controlling the motor using the estimated rotation angle, thus applying appropriate steering assist torque.SOLUTION: Electric angle estimation means 44 performs: pre-storing a relation between an increase amount of rotation angle of a motor 32 and steering-torque in a state where a steering wheel is in a steering-in state or in a steering-back state; calculating an increase amount of rotation angle of the motor on the basis of the relation and the steering torque detected by a steering torque sensor 30; and computing a rotation angle addition value Δθ by correcting the increase amount so that the increase amount is smaller in a case where an absolute value of a calculated steering power P is equal to or less than a positive first given value a than in the case of the steering power being larger than the first given value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric power steering apparatus that performs steering assist by controlling an electric motor using a rotation angle of a rotor of the electric motor.

  The electric power steering device includes a rack shaft connected to the left and right front wheels via tie rods, a pinion shaft meshing with the rack shaft, a steering shaft connected to the pinion shaft at the lower end and a steering handle fixed at the upper end, And an electric motor linked to the rack shaft via a speed reduction mechanism.

  The middle part of the steering shaft is constituted by a torsion bar. Further, a steering torque sensor that detects a torsion angle of the torsion bar and detects a steering torque acting on the steering shaft based on the detected torsion angle is provided in the vicinity of the torsion bar.

  For example, the electric power steering apparatus disclosed in Patent Document 1 employs a three-phase brushless DC motor as an electric motor. A rotation angle sensor is provided inside the electric motor. The rotation angle sensor detects the rotation angle position of the rotor of the electric motor (hereinafter referred to as “rotation angle” or “electric angle”).

  The steering torque sensor, the rotation angle sensor, and the electric motor are electrically connected to an electronic control unit (hereinafter referred to as ECU). The ECU calculates a target steering assist torque based on the detected steering torque. Further, the ECU uses the rotation angle of the rotor of the electric motor to control the electric motor so as to output the target steering assist torque. As a result, torque generated by the electric motor is transmitted to the rack shaft, and steering assist is performed.

  As described above, the power steering device recognizes the rotation angle of the rotor and controls the electric motor based on the target steering assist torque. Therefore, when the rotation angle sensor fails, it is necessary to detect the rotation angle of the electric motor by another means.

  Therefore, when the ECU of the power steering device determines that the rotation angle sensor has failed, the electric motor after the failure determination is based on the induced voltage generated with the rotation of the rotor of the electric motor after the determination time. Is calculated. Further, the ECU adds the rotation angle addition amount obtained by the calculation to the rotation angle of the electric motor (that is, the actual electrical angle) detected by the rotation angle sensor immediately before the failure determination, thereby obtaining the current time. An estimated rotation angle that is an estimated position of the rotation angle of the rotor of the electric motor is calculated. Then, the ECU controls the electric motor using the estimated rotation angle.

JP 2011-157004 A

  The induced voltage generated by the electric motor is proportional to the angular speed (that is, the rotational speed) of the rotor. For this reason, when the angular velocity of the electric motor is small, the induced voltage generated in the electric motor is extremely small, and the ECU may not be able to accurately calculate the estimated rotation angle based on the induced voltage.

  By the way, it is known that the estimated rotation angle can be calculated using the steering torque detected by the steering torque sensor. That is, there is a certain degree of correlation between the steering torque when the steering wheel is in the cut-in state or the back-off state and the rotation angle addition amount of the electric motor. Therefore, for example, by applying the specification information of each component of the power steering device (for example, an electric motor) to a predetermined calculation formula, it is possible to obtain the relationship between the steering torque and the rotation angle addition amount of the electric motor. is there.

  By storing a map (lookup table) representing this relationship in the ROM of the ECU and applying the steering torque detected by the steering torque sensor to the map, it is possible to calculate the rotation angle addition amount of the electric motor. It is. Therefore, when the angular velocity of the electric motor is small, the rotation angle addition amount calculated using this map is added to the rotation angle (actual electrical angle) of the rotor of the electric motor detected immediately before the rotation angle sensor fails. By doing so, the estimated rotation angle of the electric motor can be calculated.

  However, the map is created on the assumption that the steering wheel is in the cut-in state or the switch-back state (not in the steered state). For this reason, when the steering wheel is in the steering holding state, the rotation angle addition amount of the electric motor calculated based on the map is a value deviating from the actual rotation angle addition amount. For example, when the steering wheel is in the steering-holding state, the rotation angle addition amount of the electric motor calculated based on the map is a value greater than zero even though the actual rotation angle addition amount of the electric motor becomes zero. become. Accordingly, when the estimated rotation angle is calculated using the rotation angle addition amount of the electric motor calculated based on the map when the steering wheel is in the steering holding state, the estimated rotation angle is the actual rotation angle of the electric motor. Deviate from. As a result, when the electric motor is controlled using the estimated rotation angle, there is a risk that the electric motor will apply an excessive or excessive steering assist torque to the rack shaft.

  The present invention has been made to address the above-described problems. That is, one of the objects of the present invention is to more accurately calculate the estimated rotation angle of the electric motor based on the steering torque, and to control the electric motor using the estimated rotation angle, thereby providing an appropriate steering assist torque. An object of the present invention is to provide an electric power steering device that can be used.

In order to achieve the above object, an electric power steering apparatus according to the present invention includes:
Based on the degree of torsion of the torsion bar (29) interposed in the steering mechanism (21, 22, 23, 25, 26) that connects the steering handle (27) and the wheels (15L, 15R), the steering is performed from the steering handle. A steering torque sensor (30) for detecting a steering torque input to the mechanism;
A steering angle sensor (37) for detecting a steering angle of the steering wheel;
An electric motor (32) coupled to the steering mechanism on the wheel side of the torsion bar to give a steering assist torque;
Target steering assist torque calculating means (41) for calculating a target steering assist torque that is the steering assist torque to be generated by the electric motor based on the steering torque detected by the steering torque sensor;
A normal rotation angle detection means (33, 42) for detecting an actual electrical angle which is an actual rotation angle of the electric motor;
An abnormality detecting means (43) for detecting an abnormality of the normal rotation angle detecting means;
Electrical angle estimating means (44) for calculating an estimated rotational angle that is an estimated value of the rotational angle of the electric motor;
When the abnormality detecting means does not detect an abnormality of the normal rotation angle detecting means, the electric motor is controlled based on the detected actual electric angle so that the electric motor generates the target steering assist torque. When the abnormality detecting means detects an abnormality of the normal rotation angle detecting means, the electric motor is controlled based on the calculated estimated rotation angle so that the electric motor generates the target steering assist torque. Motor control means (46);
Steering power calculation means (47) for calculating a steering power that is a power based on the steering torque detected by the steering torque sensor and the steering angle detected by the steering angle sensor of the steering operation of the driver with respect to the steering wheel;
With
The electrical angle estimating means
The relationship between the steering torque detected by the steering torque sensor when the steering handle is in the cutting state or the returning state and the amount of increase in the rotation angle of the electric motor is stored in advance, and the steering torque sensor detects the relationship An increase amount of the rotation angle of the electric motor is obtained based on the steering torque and the relationship,
When the calculated absolute value of the steering power is equal to or less than a positive first predetermined value, the rotation is corrected by correcting the increase so that the increase is smaller than when the absolute value is larger than the first predetermined value. Calculate the angle addition amount (Δθ),
When the abnormality detecting means detects an abnormality of the normal rotation angle detecting means, the normal electric angle detected last by the normal rotation angle detecting means when the abnormality detecting means does not detect the abnormality. The estimated rotation angle (θ) is calculated by adding an integrated value of the rotation angle addition amount after the time when the normal rotation angle detection means detects the normal electrical angle to a normal electrical angle. Has been.

The electrical angle estimating means of the present invention obtains the amount of increase in the rotation angle of the electric motor when the steering handle is in the cutting state or the returning state based on the steering torque detected by the steering torque sensor. When the absolute value is equal to or smaller than the positive first predetermined value, the rotation angle addition amount is calculated by correcting the increase amount so as to be smaller than that when the absolute value is larger than the first predetermined value. Further, when the abnormality detecting means detects an abnormality of the normal rotation angle detecting means, the actual electric angle of the electric motor last detected by the normal rotation angle detecting means when the abnormality detecting means does not detect the abnormality. The estimated rotation angle is calculated by adding the integrated value of the rotation angle addition amount after the time when the normal rotation angle detection means detects the normal electrical angle to the normal electrical angle.
The increase amount of the rotation angle of the electric motor obtained based on the steering torque as described above is calculated on the assumption that the steering handle is in the cutting state or the switching back state. For this reason, when the steering torque is larger than a certain level (zero), the increase amount is larger than zero.
However, when the steering wheel is in the steering holding state, even if the steering torque is large, the actual amount of increase in the rotation angle of the electric motor becomes zero.
That is, when the steering wheel is in the steering-holding state, if the rotation angle addition amount of the electric motor is calculated without correcting the increase amount based on the steering power, this rotation angle addition amount is the actual rotation angle addition amount. It becomes a value deviating from. Therefore, the estimated rotation angle calculated based on this rotation angle addition amount is a value deviated from the actual rotation angle of the electric motor.

However, when the absolute value of the steering power is equal to or less than the positive first predetermined value (when the steering wheel is in the steering holding state), the electrical angle estimating means of the present invention has an absolute value of the steering power that is greater than the first predetermined value. The amount of rotation angle addition is corrected by correcting the amount of increase so that it is smaller than when it is larger.
For this reason, even when the steering handle is in the steering-holding state, the estimated rotation angle of the electric motor calculated based on the steering torque is an accurate value, in other words, (substantially) the same value as the actual electric angle of the electric motor.
Therefore, even when the steering handle is in the steering-holding state, the possibility that the electric motor applies an excessive or too small steering assist torque to the steering handle is small.

  The electrical angle estimation means is configured to correct the increase amount so that the rotation angle addition amount becomes zero when the calculated absolute value of the steering power is equal to or less than the first predetermined value. Also good.

An error inevitably occurs in the calculation result of the steering power calculation means. Therefore, for example, there is a possibility that the absolute value of the steering power is greater than zero and equal to or less than the first predetermined value even though the steering wheel is actually in a completely steered state. In other words, the steering power calculation means may erroneously determine that “the steering handle is slightly rotated”.
However, when the present invention is configured in this way, the increase amount is corrected so that the electrical angle estimation means sets the rotation angle addition amount to zero as in the case where the steering power is zero.
Therefore, in such a situation, it is possible to reduce the possibility that the electric motor erroneously applies an assist force larger than the torque for maintaining the steered state to the steering wheel.

The electrical angle estimating means
It becomes zero when the absolute value of the steering power is equal to or less than the first predetermined value, becomes 1 when the absolute value of the steering power is equal to or larger than a second predetermined value (b) greater than the first predetermined value, and When the absolute value of the steering power is larger than the first predetermined value and smaller than the second predetermined value, the absolute value gradually changes from zero to 1 as the absolute value changes from the first predetermined value side to the second predetermined value side. The gain (G) that changes to
The rotation angle addition amount may be calculated by multiplying the gain by the increase amount.

Theoretically, the gain can be suddenly switched from zero (0) to 1 when the absolute value of the steering power is the first predetermined value. However, in this case, when the absolute value of the steering power changes near the first predetermined value, the gain may frequently change between “zero” and “1” during a minute time. That is, so-called chattering occurs in the output value of the gain, and the estimated rotation angle may change drastically in a short time due to chattering. In this case, the rotational torque fluctuation of the electric motor becomes intense, and the steering handle may vibrate due to this torque fluctuation.
However, when the present invention is configured in this way, even if the absolute value of the steering power changes near the first predetermined value and the second predetermined value, the possibility of chattering is small. Therefore, there is almost no possibility that the steering handle vibrates.

In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiments in parentheses, but each constituent element of the invention is represented by the reference numerals. It is not limited to the embodiments specified.
Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

1 is a schematic plan view of an entire vehicle including an electric power steering device according to an embodiment of the present invention. It is a block diagram which shows the relationship between ECU represented functionally of the electric power steering device, and main components. It is a flowchart which shows the calculation method of the estimated rotation angle of an electric motor. It is a table | surface which shows the relationship between the steering power P and a steering wheel operation state. 3 is a graph (map) showing a relationship between a steering power P and a rotation angle correction gain G. It is a graph (map) which shows the relationship between steering torque Tr and rotation angle addition amount ( _DELTA ) ( _theta ) _trq .

  Hereinafter, an electric power steering apparatus (EPS) according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First, the whole structure of the vehicle 10 provided with this electric power steering device will be briefly described with reference to FIGS.
A suspension is provided at the front portion of the vehicle body 11 of the vehicle 10. A carrier (knuckle arm), which is a component of the suspension, is rotatably supported around the kingpin axis between the distal ends of the left and right upper arms and the lower arm, which are components of the suspension. Furthermore, the left and right carriers respectively support the front wheels 15R and 15L so as to be rotatable about a horizontal axis.
Further, a vehicle speed sensor 17 is provided at a predetermined portion of the vehicle body 11.

Next, the detailed structure of the electric power steering device 20 will be described.
The electric power steering 20 includes a rack shaft 21 that is a rod-shaped member extending in the left-right direction. The rack shaft 21 is slidable in the left-right direction with respect to the vehicle body 11 and cannot rotate about its own axis. A thread groove is formed on the outer peripheral surface of the rack shaft 21.
The left and right ends of the rack shaft 21 are connected to the inner ends of a pair of left and right tie rods 22, and the outer ends of the left and right tie rods 22 are connected to left and right carriers.

A pinion shaft 23 is engaged with the rack shaft 21 (thread groove).
One end (lower end) of a steering shaft 25 that is a rod-like member is connected to the pinion shaft 23 via a universal joint 26.
Further, a steering handle 27 is fixed to the other end (upper end) of the steering shaft 25.
Therefore, when the steering handle 27 is rotated, this rotational force is transmitted to the pinion shaft 23 via the steering shaft 25 and the universal joint 26, and the pinion shaft 23 rotates about its own axis. Then, since the rack shaft 21 meshing with the pinion shaft 23 slides in one direction in the left-right direction, the steering angles of the front wheels 15R and 15L linked to the rack shaft 21 through the tie rod 22 and the carrier change.

An intermediate portion of the steering shaft 25 is constituted by a torsion bar 29. Further, in the vicinity of the torsion bar 29, a steering torque sensor 30 for detecting the steering torque Tr of the steering shaft 25 based on the twist angle around the axis of the torsion bar 29 is provided. The steering torque sensor 30 can be configured by, for example, a resolver.
Therefore, when the steering shaft 25 rotates, the steering torque sensor 30 detects the steering torque Tr of the steering shaft 25.

Furthermore, the electric power steering 20 includes an electric motor 32 composed of a three-phase brushless DC motor. The electric motor 32 is linked to the rack shaft 21 (thread groove) via a reduction mechanism (not shown). The electric motor 32 is provided with a rotation angle sensor 33 for detecting the rotation angle of the rotor of the electric motor 32 (see FIG. 2). The rotation angle sensor 33 can be configured by a resolver, for example.
Furthermore, a current sensor 34 and a voltage sensor 35 are connected to the electric motor 32 (see FIG. 2). The current sensor 34 detects motor currents Iu, Iv, Iw of each phase (U phase, V phase, W phase) of the electric motor 32, and the voltage sensor 35 is a motor terminal voltage Vu, Vv, of each phase of the electric motor 32. Vw is detected.

  Further, a steering angle sensor 37 for detecting a steering angle MA that is a rotation angle of the steering shaft 25 (steering handle 27) is provided around the steering shaft 25.

  As shown in FIGS. 1 and 2, the vehicle speed sensor 17, the steering torque sensor 30, the electric motor 32, the rotation angle sensor 33, the current sensor 34, the voltage sensor 35, and the steering angle sensor 37 are connected to an electronic control unit 40 (hereinafter referred to as an ECU). Connected). The ECU 40 is an electronic control circuit having a microcomputer including a CPU, a ROM, a RAM, an interface, and the like as main components. The CPU implements various functions to be described later by executing instructions stored in a memory (ROM).

  Next, the structure of the ECU 40 that controls the operation of the electric power steering apparatus 20 and the contents of control by the ECU 40 will be described in detail.

  In terms of functionality, the ECU 40, as shown in FIG. 2, includes an assist command current calculation unit 41, a normal rotation angle calculation unit 42, a rotation angle sensor failure detection unit 43, an estimated rotation angle calculation unit 44, and a rotation angle selection unit 45. , A PWM control unit 46 and an active / passive discrimination unit 47 are provided.

  An assist map (lookup table) (not shown) is stored in the ROM of the ECU 40. The assist map is a table that defines the relationship between the steering torque Tr and the target steering assist torque Ta for each of a plurality of representative vehicle speeds v.

The vehicle speed v detected by the vehicle speed sensor 17 and the steering torque Tr detected by the steering torque sensor 30 are input to the assist command current calculation unit 41. The assist command current calculation unit 41 calculates the target steering assist torque Ta by applying the vehicle speed v and the steering torque Tr to the assist map.
Further, the assist command current calculation unit 41 calculates the assist command current Ia by dividing the target steering assist torque Ta by the torque constant.
Then, the assist command current calculation unit 41 outputs a signal representing the calculated assist command current Ia to the PWM control unit 46.

The output signal of the rotation angle sensor 33 is transmitted to the normal rotation angle calculation unit 42, the rotation angle sensor failure detection unit 43, and the estimated rotation angle calculation unit 44.
When the normal rotation angle calculation unit 42 receives the output signal of the rotation angle sensor 33, the actual electrical angle θ _{ea of} the electric motor 32 (that is, the actual rotation angle of the electric motor 32) based on the output signal of the rotation angle sensor 33. And a signal representing the calculated actual electrical angle θ _ea is output to the rotation angle selector 45.
When the rotation angle sensor failure detection unit 43 receives the output signal of the rotation angle sensor 33, it determines whether or not the rotation angle sensor 33 is operating normally based on the output signal of the rotation angle sensor 33. When a resolver is employed as the rotation angle sensor 33, the detection coil and the excitation coil in the resolver may be disconnected or cause an insulation failure at the time of failure. Therefore, when a resolver is used as the rotation angle sensor 33, the rotation angle sensor failure detection unit 43 monitors the amplitude of the output signal of the detection coil, and if the amplitude deviates from the preset allowable range (the allowable range If it is lower than the lower limit and higher than the upper limit of the allowable range, it is determined that an abnormality has occurred in the rotation angle sensor 33. When the rotation angle sensor failure detection unit 43 determines that the rotation angle sensor 33 is normal, the rotation angle sensor failure detection unit 43 outputs a normal signal to the rotation angle selection unit 45 and the PWM control unit 46, and an abnormality has occurred in the rotation angle sensor 33. If it is determined, the abnormal signal is output to the rotation angle selector 45 and the PWM controller 46.

When the rotation angle sensor failure detection unit 43 outputs a normal signal to the rotation angle selection unit 45 and the PWM control unit 46, the rotation angle selection unit 45 uses the actual electrical angle θ _ea received from the normal rotation angle calculation unit 42. A signal to be output is output to the PWM control unit 46.
Then, as will be described later, the PWM control unit 46 is based on a signal representing the assist command current Ia received from the assist command current calculation unit 41 and a signal representing the actual electrical angle θ _ea received from the rotation angle selection unit 45. 32 is PWM controlled.

On the other hand, when an abnormality occurs in the rotation angle sensor 33, the normal rotation angle calculation unit 42 cannot calculate the actual electrical angle θ _ea , so the PWM control unit 46 generates a PWM control signal based on the actual electrical angle θ _ea. become unable. Therefore, the ECU 40 calculates the estimated rotation angle θ by the estimated rotation angle calculation unit 44 and the active / passive discrimination unit 47. Further, when the rotation angle sensor failure detection unit 43 outputs an abnormal signal to the rotation angle selection unit 45 and the PWM control unit 46, the rotation angle selection unit 45 selects the estimated rotation angle θ instead of the actual electrical angle θ _ea. To the PWM control unit 46. In this case, the PWM control unit 46 performs PWM control on the electric motor 32 based on a signal representing the assist command current Ia and a signal representing the estimated rotation angle θ received from the rotation angle selection unit 45.

  The estimated rotation angle calculation unit 44 uses at least one of the steering torque Tr detected by the steering torque sensor 30 and the induced voltage generated in the electric motor 32 to estimate the rotation of the electric motor 32 at a constant calculation cycle (fixed time). The angle θ is calculated (estimated).

This estimated rotation angle θ is a rotation angle obtained by adding the rotation angle addition amount Δθ to the previous value θ _bf of the rotation angle after selection.
The previous value θ _bf of the rotation angle after selection is the rotation angle of the electric motor 32 selected by the rotation angle selection unit 45 described later in the immediately preceding calculation cycle. That is, the previous value θ _bf of the rotation angle after selection is calculated by the estimated rotation angle calculation unit 44 based on the actual electrical angle θ _ea obtained by the normal rotation angle calculation unit 42 and the procedure described later. This is the previous value of any one of the 32 estimated rotation angles θ, and is the rotation angle used for controlling the electric motor 32 in the immediately preceding calculation cycle.
The rotation angle addition amount Δθ is an addition angle of the rotation angle of the electric motor 32 obtained by the estimated rotation angle calculation unit 44 in the current calculation cycle (a change amount of the rotation angle in the current calculation cycle).
That is, the estimated rotation angle calculation unit 44 calculates the estimated rotation angle θ of the electric motor 32 at the current time using the following equation (1).

Estimated rotation angle θ = θ _bf + Δθ (1)

Hereinafter, a method for calculating the estimated rotation angle θ based on the equation (1) will be described with reference to FIGS. 3 to 6.

As shown in the flowchart of FIG. 3, the estimated rotation angle calculation unit 44 (actually the CPU) acquires the selected rotation angle (previous value) θ _bf from the rotation angle selection unit 45 in step 301. Next, the active / passive discriminating unit 47 (actually CPU) calculates the steering power P in step 302.

Here, the steering power P is an index representing the power of the steering operation of the driver with respect to the steering handle 27, and is a physical quantity representing energy used per unit time. The steering power P can be expressed by the following equation (2) using the steering work W when the time is “t”. Here, the steering work amount W is an index representing the work of the steering operation of the driver with respect to the steering handle 27 and is a physical quantity representing the used energy.

P = dW / dt (2)

Actually, the active / passive discrimination unit 47 calculates the steering power P as follows. That is, the steering power P is determined by the steering angular velocity (corresponding to the differential value of the steering angle) MAdot (= dMA / dt) corresponding to the steering angle MA detected by the steering angle sensor 37 and the steering torque Tr detected by the steering torque sensor 30. And the product of the steering angle MA detected by the steering angle sensor 37 and the steering torque differential value Trdot (= dTr / dt) corresponding to the steering torque Tr detected by the steering torque sensor 30. be able to. Here, the steering power based on the product [Tr · MAdot] of the steering torque Tr and the steering angular velocity MAdot is set to the first steering power P1, and the product [Trdot · MA] of the steering torque differential value Trdot and the steering angle MA. The steering power based on this is referred to as a second steering power P2. The active / passive discriminating unit 47 calculates the steering power P using a composite model represented by the following equation (3) as a composite model expressing active / passive for the steering operation by the driver.

P = P1 + P2
= Tr · MAdot + Trdot · MA (3)

Next, the active / passive discrimination unit 47 proceeds to step 303 and applies the calculated P1, P2, MAdot, and TRdot to the table of FIG. 4 so that the steering operation by the driver on the steering handle 27 at the current time is active ( It is determined whether it is in the state of cutting), passive (switching back), or steering. In FIG. 4, “+” indicates that the sign is “positive”, and “−” indicates that the sign is “negative”.
As shown in FIG. 4, when the sign of the steering power P is positive, the active / passive discrimination unit 47 determines the current steering state as the “active operation state (cut-in state)”, and the sign of the steering power P Is negative, the active / passive determination unit 47 determines that the current steering state is the “passive operation state (switchback state)”. When the absolute value of the steering power P is zero, the active / passive determination unit 47 determines that the current steering state is the “steering state”. Such a steering state determination method is well known as disclosed in JP-A-2015-048057, JP-A-2015-182517, and the like.
However, as will be described later, whether the sign of the steering power P is positive or negative, the active / passive discriminating unit 47 when the absolute value is equal to or smaller than a predetermined minute value (a first predetermined value a described later). Determines that the current steering state is the “steering state” (this is not well known).

  Subsequently, the estimated rotation angle calculation unit 44 estimates (calculates) the induced voltage generated in the electric motor 32 in step 304. More specifically, signals representing the motor currents Iu, Iv, Iw of each phase output from the current sensor 34, signals representing the motor terminal voltages Vu, Vv, Vw of each phase output from the voltage sensor 35, and well-known The induced voltage generated in the electric motor 32 is calculated based on the calculation formula (for example, the calculation formula described in paragraph 0066 of JP 2011-157004 A). Further, in step 304, the estimated rotation angle calculation unit 44 calculates the angular velocity of the rotor of the electric motor 32 based on the calculated induced voltage.

  Further, in step 305, the estimated rotation angle calculation unit 44 determines whether or not the angular velocity of the rotor obtained in step 304 is equal to or less than a positive first threshold value. That is, the estimated rotation angle calculation unit 44 determines whether or not “the angular velocity of the electric motor 32 is in the low speed range”.

  When the estimated rotation angle calculation unit 44 determines in step 305 that “the angular velocity of the electric motor 32 is in the low speed range” (step 305: “Yes”), the estimated rotation angle calculation unit 44 performs steps 306 to step described below. The processing of 309 is performed in order, and this routine is temporarily terminated.

  Step 306: The estimated rotation angle calculation unit 44 applies the steering power P obtained by equation (3) in step 302 to the map (lookup table) MapG (P) in FIG. A correction gain (gain) G is calculated. The map MapG (P) is stored in the ROM.

  In the horizontal axis of the map in FIG. 5, + (plus) represents the “active operation state (cut-in state)” of the steering handle 27, and − (minus) represents the “passive operation state (switch-back state)” of the steering handle 27. Further, zero indicates that the steering handle 27 is in the “steering state”.

  As shown in FIG. 5, the rotation angle correction gain G has a magnitude of 0 to 1. When the absolute value of the steering power P is zero, in other words, when the steering handle 27 is in the steering holding state, the rotation angle correction gain G is “0”. Further, when the absolute value of the steering power P is in the range of the first predetermined value a which is a minute value, the rotation angle correction gain G is set to “0” even if the absolute value of the steering power P is larger than zero. Maintained. That is, in the map MapG (P) of FIG. 5, a dead zone is set over a range where the absolute value of the steering power P is equal to or less than the first predetermined value a. In other words, in this map MapG (P), the entire range where the absolute value of the steering power P is equal to or less than the first predetermined value a represents the “steering state”. Therefore, as described above, whether the sign of the steering power P is positive or negative, when the absolute value is equal to or less than the first predetermined value a, the active / passive determination unit 47 determines the current steering state in step 303 as “ It is determined as “steering state”.

  On the other hand, when the absolute value of the steering power P is equal to or larger than the second predetermined value b slightly larger than the first predetermined value a, the rotation angle correction gain G is maintained at “1”.

  Further, when the absolute value of the steering power P is in a range larger than the first predetermined value a and smaller than the second predetermined value b, the steering power P increases from the first predetermined value a to the second predetermined value b. Accordingly, the rotation angle correction gain G gradually increases from “0” to “1”.

Step 307: The estimated rotation angle calculation unit 44 _{applies the} “map (look-up table) MapΔθ _trq (Tr) shown in FIG. 6” that represents the relationship between the steering torque Tr and Δθ _trq stored in the ROM of the ECU 40. By applying the “steering torque Tr transmitted from the steering torque sensor 30”, an increase amount Δθ _trq of the rotation angle of the rotor of the electric motor 32 in the current calculation cycle is calculated. When the angular velocity of the electric motor 32 is in the low speed range, the induced voltage generated by the electric motor 32 is small, and it is difficult to accurately calculate the rotation angle addition amount Δθ based on the induced voltage. Therefore, in this case, the rotation angle increase amount Δθ _trq (which is a calculation element of the rotation angle addition amount Δθ) is calculated based on the map MapΔθ _trq (Tr) and the steering torque Tr in FIG. The map MapΔθ _trq (Tr) is stored in the ROM.

Step 308: The estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ by multiplying the rotation angle increase amount Δθ _trq by the rotation angle correction gain G obtained in step 306. That is, the rotation angle addition amount Δθ is calculated using the following equation (4). The reason for correcting (correcting) the rotation angle increase amount Δθ _trq with the rotation angle correction gain G will be described later.

Δθ = Δθ _trq · G Formula (4)

Step 309: The estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ according to the equation (1). That is, the estimated rotation angle calculation unit 44 calculates the estimated rotation angle θ by adding the rotation angle addition amount Δθ to the previous value θ _bf of the rotation angle after selection. As described above, when the rotation angle sensor failure detection unit 43 outputs an abnormal signal to the rotation angle selection unit 45 and the PWM control unit 46, the rotation angle selection unit 45 replaces the actual electrical angle θ _ea with the estimated rotation angle. θ is selected and transmitted to the PWM controller 46. Therefore, the estimated rotation angle calculation unit 44 rotates at the normal time immediately before it is determined that an abnormality has occurred in the rotation angle sensor 33 (in other words, at the end when it is determined that the rotation angle sensor 33 is normal). By adding the integrated value of the rotation angle addition amount Δθ after the time when the normal electrical angle is calculated to the normal electrical angle that is the actual electrical angle θ _ea calculated by the angle calculation unit 42, the estimated rotation angle θ is obtained. calculate.

  On the other hand, if the determination result in step 305 is “No”, that is, if the estimated rotation angle calculation unit 44 determines in step 305 that “the angular speed of the electric motor 32 is in the medium speed range or the high speed range”, the estimation is performed. In step 310, the rotation angle calculation unit 44 sets “1” as the rotation angle correction gain G regardless of the map MapG (P) in FIG. 5 (that is, regardless of the magnitude of the steering power P).

  Next, the estimated rotation angle calculation unit 44 proceeds to step 311 and determines whether or not the angular velocity of the rotor obtained in step 304 is equal to or less than a second threshold value that is greater than the first threshold value. That is, the estimated rotation angle calculation unit 44 determines whether or not “the angular velocity of the electric motor 32 is in the middle speed range”.

  If the estimated rotation angle calculation unit 44 determines in step 311 that “the angular speed of the electric motor 32 is in the medium speed range” (step 311: “Yes”), the process of step 312 described below is performed, and step 309 is performed. move on.

Step 312: The estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ _{using the} rotation angle increase amount Δθ _trq , the rotation angle addition amount Δθ _ω , the rotation angle addition correction amount Δθ _β and the rotation angle correction gain G. . Specifically, the rotation angle addition amount Δθ is calculated using the following equation (5). The rotation angle correction gain G is set to “1”.

Δθ = {Δθ _trq + (Δθ _ω + Δθ _β )} · G / 2 Formula (5)

The rotation angle addition amount Δθ obtained by Expression (5) corresponds to the average value of Δθ _trq and (Δθ _ω + Δθ _β ). Therefore, in Equation (5), the total value of Δθ _trq and (Δθ _ω + Δθ _β ) (value obtained by multiplying the rotation angle correction gain G) is divided by “2”.

Here, Δθ _ω is the rotation angle addition amount of the rotor of the electric motor 32 in the current calculation cycle calculated based on the angular velocity ω of the rotor of the electric motor 32 calculated from the induced voltage of the electric motor 32. The rotation angle addition correction amount Δθ _β is the rotation angle addition amount of the rotor of the electric motor 32 (as an angle correction term) in the current calculation cycle calculated from the induced voltage of the electric motor 32. Note that the calculation method of the rotation angle addition amount Δθ _ω and the rotation angle addition correction amount Δθ _β is well known as described in, for example, Japanese Patent Application Laid-Open No. 2011-157004, and the description thereof is omitted (the same publication). “Δθ _a ” described in paragraph 0075 and the like corresponds to θ _ω and “Δθ _e ” described in paragraph 0087 and the like corresponds to Δθ _β ).

  Further, when the determination result in step 311 is “No”, that is, when the estimated rotation angle calculation unit 44 determines in step 311 that “the angular velocity of the electric motor 32 is in the high speed range”, the estimated rotation angle calculation unit 44. Performs the processing of step 313 described below, and proceeds to step 309.

Step 313: The estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ using the rotation angle addition amount Δθ _ω , the rotation angle addition correction amount Δθ _β and the rotation angle correction gain G. Specifically, the rotation angle addition amount Δθ is calculated using the following equation (6). The rotation angle correction gain G is set to “1”.

Δθ = (Δθ _ω + Δθ _β ) · G (6)

Incidentally, the map MapΔθ _trq (Tr) in FIG. 6 defines the relationship between the steering torque Tr and the rotation angle increase amount Δθ _trq of the rotor of the electric motor 32 when the steering state is in the cut-in state or the switch-back state. ing. In other words, the map MapΔθ _trq (Tr) is created assuming that the steering state is not the steered state.

Therefore, only when the steering handle 27 is in the cutting state or the returning state, the accurate rotation angle increase amount Δθ _trq is obtained from the map MapΔθ _trq (Tr). On the other hand, the steering torque Tr of the steering shaft 25 is generated even when the steering state is in the steered state (that is, when the steering shaft 25 and the steering handle 27 are not substantially rotated). Therefore, when the steering handle 27 is in the steering holding state, the rotation angle increase Δθ _trq of the electric motor 32 obtained using the map MapΔθ _trq (Tr) is obtained from the actual rotation angle increase amount (that is, the correct rotation angle addition amount). The value is different.

Therefore, according to the map MapG (P) in FIG. 5, when the absolute value of the steering power P is in the range of the first predetermined value a or less, that is, the active / passive discrimination unit 47 indicates that “the steering handle 27 is in the steering holding state. When it is determined that the rotation angle correction gain G is “0”, the rotation angle correction gain G is maintained at “0”. Therefore, when the steering handle 27 is in the steered state, the estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ (= 0) by multiplying the rotation angle increase amount Δθ _trq by “0”. In other words, the estimated rotation angle calculation unit 44 estimates that the rotation angle of the rotor of the electric motor 32 does not change when the steering handle 27 is in the steered state.

Further, according to the map MapG (P), when the absolute value of the steering power P is in the range equal to or greater than the second predetermined value b, that is, the active / passive discrimination unit 47 indicates that the steering handle 27 is in the cut state or the switch back state. When it is determined that “there is no steering holding state”, the rotation angle correction gain G is maintained at “1”. Therefore, the estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ by multiplying the rotation angle increase amount Δθ _trq by “1” when the steering handle 27 is in the “cut state or the return state”.
Accordingly, regardless of the magnitude of the steering power P, the rotation angle addition amount Δθ calculated when the angular velocity of the electric motor 32 is in the low speed range is the actual rotation angle of the rotor of the electric motor 32. It becomes a value close to the increase amount in the calculation cycle. That is, the value of the rotation angle addition amount Δθ is a value close to the actual rotation angle increase amount of the electric motor 32. As a result, the value of the estimated rotation angle θ is also close to the actual rotation angle of the rotor of the electric motor 32.

On the other hand, when the angular velocity of the electric motor 32 is in the high speed region, the induced voltage generated by the electric motor 32 is sufficiently large. Therefore, the rotation angle addition amount Δθ _ω and the rotation angle addition correction amount Δθ _β are accurate values. Therefore, when the angular velocity of the electric motor 32 is in the high speed range, the estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ in step 313 based only on the induced voltage of the electric motor 32 without using the steering torque Tr. calculate. Therefore, the value of the rotation angle addition amount Δθ in this case is a numerical value that is very close to the actual rotation angle increase amount of the electric motor 32.

Furthermore, when the angular velocity of the electric motor 32 is in the middle speed range, the induced voltage generated by the electric motor 32 becomes a certain level. Therefore, the rotation angle addition amount Δθ _ω and the rotation angle addition correction amount Δθ _β have values that are accurate to some extent. Furthermore, when the angular velocity of the electric motor 32 is in the middle speed range, there is a high possibility that the steering state is not in the steered state. Therefore, the rotation angle increase amount Δθ _trq is also an accurate value to some extent. Therefore, when the angular speed of the electric motor 32 is in the middle speed range, the estimated rotation angle calculation unit 44 calculates the rotation angle addition amount Δθ using both the induced voltage and the steering torque Tr in step 312. As a result, the value of the rotation angle addition amount Δθ is a value close to the actual rotation angle increase amount of the electric motor 32.

  Further, when the angular speed of the electric motor 32 is in the middle speed range and the high speed range, the steering handle 27 is not in the steering holding state. Therefore, as described above, the rotation angle correction gain G in the equations (5) and (6) is set to “1”.

As is apparent from FIG. 6, according to the map MapΔθ _trq (Tr), when the steering torque Tr is between zero and a minute value Tr1 slightly larger than zero, the rotation angle increase amount Δθ _trq becomes zero. Maintained. That is, in this map MapΔθ _trq (Tr), a dead zone is provided over a certain region between zero and the minute value Tr1. There is a certain amount of play between the components of the electric power steering apparatus 20 (for example, between the pinion shaft 23 and the rack shaft 21). Therefore, when the steering torque Tr is between zero and the minute value Tr1, the rotation angle of the electric motor 32 does not change in practice. Therefore, the dead zone is provided in the map of FIG.

Referring again to FIG. 2, when the rotation angle sensor failure detection unit 43 outputs a normal signal to the rotation angle selection unit 45, the rotation angle selection unit 45 receives the actual electric power received from the normal rotation angle calculation unit 42. The angle θ _ea is selected as the electrical angle information of the electric motor 32 and transmitted to the PWM control unit 46.

  On the other hand, when the rotation angle sensor failure detection unit 43 outputs an abnormal signal to the rotation angle selection unit 45, the rotation angle selection unit 45 uses the estimated rotation angle θ received from the estimated rotation angle calculation unit 44 as the electric motor. 32 is selected as electrical angle information and transmitted to the PWM controller 46.

The PWM control unit 46 either one of the signal representing the actual electrical angle θ _ea received from the rotation angle selection unit 45 and the signal representing the estimated rotation angle θ received from the rotation angle selection unit 45 (that is, the rotation angle after selection). And the PWM control of the electric motor 32 based on the signal representing the assist command current Ia received from the assist command current calculation unit 41. Specifically, the PWM control unit 46 generates a PWM control signal (U-phase current, V-phase current, W-phase current) and outputs the PWM control signal to the electric motor 32. Then, the electric motor 32 rotates, and the rotational driving force of the electric motor 32 is transmitted to the rack shaft 21 via the speed reduction mechanism.

  The rotational force of the electric motor 32 at this time is a force that assists the operation of the steering handle 27. For example, the rotation direction of the electric motor 32 when the steering handle 27 is in the cut state is a direction in which the steering handle 27 is rotated in the cut direction. Further, the rotation direction of the electric motor 32 when the steering handle 27 is in the steering-holding state is a direction for holding the steering angle of the steering handle 27 against the force that the front wheels 15R and 15L receive from the road surface.

  In order to generate a desired assist force in the electric motor 32, the PWM control unit 46 needs to perform PWM control of the electric motor 32 after accurately recognizing the rotation angle of the rotor of the electric motor 32.

As described above, in the present embodiment, when the rotation angle sensor 33 is out of order, the estimated rotation angle θ calculated by the estimated rotation angle calculation unit 44 is such that the angular speed of the electric motor 32 is in the low speed range, the medium speed range, and In any of the high speed ranges, the value is very close to the actual rotation angle of the rotor of the electric motor 32. In addition, the actual electrical angle θ _ea detected by the rotation angle sensor 33 when the rotation angle sensor 33 is operating normally accurately represents the actual rotation angle of the electric motor 32.

  Therefore, in both cases where the rotation angle sensor 33 is operating normally and not, the electric motor 32 whose rotation is controlled by the PWM controller 46 assists the rotation operation of the steering handle 27 without excess or deficiency.

  For example, when the driver cuts the steering handle 27, the electric motor 32 generally needs to generate a large target steering assist torque Ta. In this embodiment, the PWM control unit 46 performs PMW control of the electric motor 32 based on accurate rotational angle position information of the rotor of the electric motor 32. In such a case, the electric motor 32 has a desired size target. A steering assist torque Ta can be applied to the rack shaft 21. In other words, in such a case, an assist torque smaller than the target steering assist torque Ta is transmitted from the electric motor 32 to the rack shaft 21, and as a result, the driver is less likely to feel a catching feeling when the steering handle 27 is rotated.

  Further, for example, a determination error inevitably occurs in the determination result of the active / passive determination unit 47. Therefore, for example, there is a possibility that the absolute value of the steering power P is greater than zero and equal to or less than the first predetermined value a, even though the steering handle 27 is actually in a completely steered state. In other words, the active / passive determination unit 47 may erroneously determine that “the steering handle 27 is slightly rotated (in other words, the rotor of the electric motor 32 is rotated)”.

However, in this embodiment, in such a case, as in the case where the absolute value of the steering power P is zero, the active / passive discrimination unit 47 determines that “the steering state is in the steered state”, and the estimated rotation angle The calculation unit 44 sets the rotation angle correction gain G to zero (that is, sets the rotation angle addition amount Δθ to zero).
Therefore, in such a situation, there is almost no possibility that the electric motor 32 erroneously gives the steering handle 27 an assist force larger than the torque for maintaining the steered state.

  Further, as the map of FIG. 5, it is theoretically possible to adopt a map in which the rotation angle correction gain G is suddenly switched from “0” to “1” when the absolute value of the steering power P is the first predetermined value a. The above is possible. However, in this case, when the absolute value of the steering power P changes in the vicinity of a, the rotation angle correction gain G may frequently change between “0” and “1” during a very short time. That is, so-called chattering occurs in the output (value) of the rotation angle correction gain G obtained using the map of FIG. 5, and the estimated rotation angle θ calculated in step 305 due to chattering is within a short time. May change drastically. In this case, the rotational torque fluctuation of the motor 30 becomes intense, and the steering handle 27 may vibrate due to this torque fluctuation.

  However, in the map of FIG. 5 of this embodiment, when the absolute value of the steering power P is in a range larger than the first predetermined value a and smaller than the second predetermined value b, the rotation angle correction gain G is set to “0” and “ 1 ”is gradually changed. Therefore, even if the absolute value of the steering power P changes between values near the first predetermined value a and the second predetermined value b, the possibility of chattering is small. Therefore, there is almost no possibility that the steering handle 27 vibrates.

As mentioned above, although this invention was demonstrated based on said each embodiment, this invention is not limited to said each embodiment, A various change is possible unless it deviates from the objective of this invention.
For example, a brushless motor having a rotation angle sensor 33 other than a three-phase brushless DC motor may be used as the electric motor 32.

  The ECU 40 may be configured such that the estimated rotation angle calculation unit 44 calculates the estimated rotation angle θ only when an abnormality occurs in the rotation angle sensor 33.

  The design of the electric power steering device 20 may be changed to a column EPS in which the electric motor 32 is linked to the steering shaft 25 (via a speed reducer or the like).

  DESCRIPTION OF SYMBOLS 10 ... Vehicle, 17 ... Vehicle speed sensor, 20 ... Electric power steering device, 25 ... Steering shaft, 27 ... Steering handle, 29 ... Torsion bar, 30 ... Steering torque sensor 32 ... Electric motor, 33 ... Rotation angle sensor, 40 ... Electronic control unit (ECU), 41 ... Assist command current calculation unit, 42 ... Normal rotation angle calculation unit, 43. Rotation angle sensor failure detection unit 44... Estimated rotation angle calculation unit 45... Rotation angle selection unit 46... PWM control unit 47.

Claims (3)

A steering torque sensor that detects a steering torque that is input from the steering handle to the steering mechanism based on a degree of twist of a torsion bar that is interposed in a steering mechanism that connects the steering handle and wheels;
A steering angle sensor for detecting a steering angle of the steering wheel;
An electric motor connected to the steering mechanism on the wheel side of the torsion bar to give a steering assist torque;
Target steering assist torque calculating means for calculating a target steering assist torque that is the steering assist torque to be generated by the electric motor based on the steering torque detected by the steering torque sensor;
A normal rotation angle detection means for detecting an actual electrical angle that is an actual rotation angle of the electric motor;
An abnormality detection means for detecting an abnormality in the normal rotation angle detection means;
An electrical angle estimating means for calculating an estimated rotational angle that is an estimated value of the rotational angle of the electric motor;
When the abnormality detecting means does not detect an abnormality of the normal rotation angle detecting means, the electric motor is controlled based on the detected actual electric angle so that the electric motor generates the target steering assist torque. When the abnormality detecting means detects an abnormality of the normal rotation angle detecting means, the electric motor is controlled based on the calculated estimated rotation angle so that the electric motor generates the target steering assist torque. Motor control means,
Steering power calculation means for calculating a steering power that is a power based on the steering torque detected by the steering torque sensor and the steering angle detected by the steering angle sensor of the steering operation of the driver with respect to the steering wheel;
With
The electrical angle estimating means
The relationship between the steering torque detected by the steering torque sensor when the steering handle is in the cutting state or the returning state and the amount of increase in the rotation angle of the electric motor is stored in advance, and the steering torque sensor detects the relationship An increase amount of the rotation angle of the electric motor is obtained based on the steering torque and the relationship,
When the calculated absolute value of the steering power is equal to or less than a positive first predetermined value, the rotation is corrected by correcting the increase so that the increase is smaller than when the absolute value is larger than the first predetermined value. Calculate the angle addition amount,
When the abnormality detecting means detects an abnormality of the normal rotation angle detecting means, the normal electric angle detected last by the normal rotation angle detecting means when the abnormality detecting means does not detect the abnormality. The estimated rotation angle is calculated by adding an integrated value of the rotation angle addition amount after the time when the normal rotation angle detection unit detects the normal electrical angle to a normal electrical angle,
Electric power steering device. The electric power steering apparatus according to claim 1, wherein
The electrical angle estimating means
When the absolute value of the calculated steering power is equal to or less than the first predetermined value, the increase amount is corrected so that the rotation angle addition amount becomes zero;
Electric power steering device. The electric power steering apparatus according to claim 1, wherein
The electrical angle estimating means
It becomes zero when the absolute value of the steering power is equal to or less than the first predetermined value, and becomes 1 when the absolute value of the steering power is equal to or larger than a second predetermined value that is larger than the first predetermined value. Gradually changes from zero to 1 as the absolute value changes from the first predetermined value side to the second predetermined value side when the absolute value is greater than the first predetermined value and smaller than the second predetermined value. , Calculate the gain,
The rotation angle addition amount is calculated by multiplying the increase amount by the gain,
Electric power steering device.

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