JP2017065446A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of reducing driver's discomfort of steering feeling even in a case where a steering wheel is abruptly turned.SOLUTION: An electric power steering device of the invention provides a steering assist force to a steering shaft by supplying a voltage from a power source to an electric motor so that a motor current value flowing through the electric motor becomes equal to a target current value determined on the basis of a steering torque of a steering wheel for a vehicle. The electric power steering device comprises: a booster circuit for boosting a voltage of the power source; an estimation part for estimating, when the target current value is changed, a motor operation point where the motor current value reaches the target current value on the basis of a change in the motor operation point specified according to a rotational speed of the electric motor and the motor current value; and a determination part for causing the booster circuit to start boosting, when the motor operation point at the target current value corresponds a starting condition to control the booster circuit to start boosting.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, there has been an electric power steering device that detects a steering torque applied to a steering handle for steering by a driver or the like with a steering torque sensor, generates a steering assist force according to the detected steering torque by a motor, and applies the steering assist force to the steering handle. Are known. Recently, in order to avoid a shortage of steering assist force, an electric power steering device capable of obtaining a larger steering assist force by boosting the battery voltage with a booster circuit and supplying the boosted voltage to the motor drive circuit. Has been proposed (see, for example, Patent Document 1).

  In such a device, if boosting is always performed by a booster circuit so as to increase the voltage of the battery so that the steering assist force is not insufficient, the booster circuit is increased in size and the switching operation of the transistors constituting the booster circuit is performed. Based on switching loss always occurs. As a result, there is a problem that energy loss in the booster circuit increases. In order to solve the above-mentioned problem, Patent Document 1 discloses that it is necessary when the duty ratio of a PWM (pulse width modulation) signal for turning on / off a switching element of a motor driving circuit exceeds a predetermined threshold value of 100%. An electric power steering device that boosts the voltage of a battery with a booster circuit in order to obtain a proper steering torque is described. Thereby, since it is possible to prevent the voltage of the battery from being constantly boosted by the booster circuit, switching loss of the booster circuit can be reduced and energy loss can be suppressed.

Japanese Patent Laid-Open No. 2003-200845

  Here, in the electric power steering device described in Patent Document 1, the duty ratio of the PWM signal is set in advance based on the deviation between the target current value set based on the steering torque and the detected value of the current flowing through the electric motor. When the measured value exceeds 100%, the battery voltage is boosted. Therefore, it may take time for the duty ratio of the PWM signal to exceed 100%. Therefore, in a scene where the driver suddenly turns the steering wheel, the duty ratio of the PWM signal may not reach the predetermined threshold even if the steering assist force is actually required. That is, in the electric power steering device described in Patent Document 1, the voltage of the battery cannot be boosted at a desired timing, and the driver feels uncomfortable with the steering feeling due to the time lag until the voltage is actually boosted. An event is assumed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electric power steering device that can reduce a driver's uncomfortable feeling even when the steering wheel is suddenly turned off. Is to provide.

  According to one aspect of the present invention, steering is performed by supplying a voltage from a power source to the electric motor so that a motor current value flowing through the electric motor becomes a target current value determined based on a steering torque of a steering handle of a vehicle. An electric power steering device that applies a steering assist force to a shaft, wherein the booster circuit boosts the voltage of the power source, and when the target current value is changed, the rotational speed of the electric motor and the motor current value, An estimation unit for estimating a motor operating point when the motor current value reaches the target current value based on a change in the motor operating point defined on the basis of the motor operating point, and the motor operating point at the target current value is the An electric power steering apparatus comprising: a determination unit that starts boosting of the booster circuit when a start condition for controlling the start of boosting of the booster circuit is met It is.

  Moreover, one aspect of the present invention is the above-described electric power steering apparatus, wherein the start condition is out of a range of a preset motor characteristic of the electric motor.

  Further, one aspect of the present invention is the above-described electric power steering apparatus, wherein the start condition can vary a preset range of the motor characteristics in accordance with a voltage of the power source.

  One embodiment of the present invention is the above-described electric power steering device, wherein the determination unit is configured to change the target current value when the boosting circuit boosts the voltage of the power supply. When the motor operating point estimated by the estimation unit corresponds to a stop condition for stopping the boosting of the booster circuit, the boosting of the booster circuit is stopped.

  One embodiment of the present invention is the above-described electric power steering device, wherein the start condition and the stop condition have a hysteresis width.

  As described above, according to the present invention, it is possible to provide an electric power steering device that can reduce the driver's uncomfortable feeling even when the steering wheel is suddenly turned off.

It is a figure which shows an example of schematic structure of the electric power steering apparatus 1 in this embodiment. It is a figure which shows an example of schematic structure of the control apparatus 15 in this embodiment. It is a figure which shows an example of schematic structure of the motor drive part 21 in this embodiment. It is a figure which shows an example of schematic structure of the pressure | voltage rise control part 226 in this embodiment. It is a diagram for explaining a method of estimating the target operating point S ₃ estimation unit 301 in this embodiment. It is a flowchart figure of the pressure | voltage rise process of the pressure | voltage rise control part 226 in this embodiment. It is a 1st schematic diagram explaining the flow of the pressure | voltage rise process of the pressure | voltage rise control part 226 in this embodiment. It is a 2nd schematic diagram explaining the flow of the pressure | voltage rise process of the pressure | voltage rise control part 226 in this embodiment. It is a 3rd schematic diagram explaining the flow of the pressure | voltage rise process of the pressure | voltage rise control part 226 in this embodiment. It is a 4th schematic diagram explaining the flow of the pressure | voltage rise process of the pressure | voltage rise control part 226 in this embodiment. It is a boost stop process flowchart figure of the pressure | voltage rise control part 226 in this embodiment. It is a 1st schematic diagram explaining the boost stop process flow of the pressure | voltage rise control part 226 in this embodiment. It is a 2nd schematic diagram explaining the boost stop process flow of the pressure | voltage rise control part 226 in this embodiment. It is a 3rd schematic diagram explaining the boost stop process flow of the pressure | voltage rise control part 226 in this embodiment. It is a 4th schematic diagram explaining the boost stop process flow of the pressure | voltage rise control part 226 in this embodiment.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention. In the drawings, the same or similar parts may be denoted by the same reference numerals and redundant description may be omitted. In addition, the shape and size of elements in the drawings may be exaggerated for a clearer description.

In the electric power steering apparatus (EPS system: Electric Power Steering System) in the embodiment, the motor current value flowing through the electric motor becomes a target current value determined based on the steering torque of the steering handle for steering the vehicle. By supplying a voltage from the power source to the electric motor, a steering assist force is applied to the steering shaft by the torque of the electric motor. The electric power steering apparatus according to the embodiment estimates the motor operating point when the motor current value reaches the target current value based on the change in the motor operating point when the target current value is changed, and estimates When the motor operating point thus met satisfies the start condition, boosting of the booster circuit is started.
Hereinafter, an electric power steering apparatus according to an embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a schematic configuration of an electric power steering apparatus 1 according to the present embodiment. As shown in FIG. 1, the electric power steering apparatus 1 includes a steering handle 9, a torque sensor 10, a steering shaft 11, a gear box 12, a steering mechanism 13, an electric motor 14, a control device 15, a battery 16, and a rotation angle detection unit. 17 and a vehicle speed sensor 50 are provided.

The steering handle 9 is connected to the steering shaft 11.
The steering shaft 11 has one end connected to the steering handle 9 and the other end connected to the gear box 12. A steering torque F applied between the steering shaft 11 and the gear box 12 is generated when the steering handle 9 is operated by the driver. The steering shaft 11 rotates with a steering torque F.
The torque sensor 10 is for detecting a steering torque F generated in the steering shaft 11, and is composed of, for example, a torsion bar type torsional force detection sensor. The torque sensor 10 outputs the detected steering torque F to the control device 15.

  The steering mechanism 13 is connected to the gear box 12. The steering mechanism 13 steers the front wheels (not shown) of the vehicle according to the driver's steering handle operating force and the steering torque F transmitted through the gear box 12.

  The electric motor 14 is connected to the gear box 12. The electric motor 14 is electrically connected to the control device 15. The electric motor 14 is driven by a drive signal from the control device 15. The electric motor 14 assists the steering force with which the steering mechanism 13 steers the front wheels of the vehicle. That is, the rotation of the electric motor 14 is transmitted to the steering shaft 11 through the gear box 12. Thereby, the operation of the steering mechanism 13 is assisted, and the labor burden on the driver for steering is reduced. Hereinafter, in the present embodiment, a case where the electric motor 14 is a three-phase (U, V, W) brushless motor will be described.

  The rotation angle detector 17 is provided in the electric motor 14. The rotation angle detector 17 detects the rotation angle of the rotor of the electric motor 14. For example, the rotation angle detector 17 is a magnetic rotary encoder provided with a resolver or Hall IC. The rotation angle detector 17 outputs an output signal corresponding to the detected rotation angle to the control device 15.

The control device 15 is electrically connected to a battery 16 (a power source in the claims) mounted on the vehicle. The control device 15 controls the drive of the electric motor 14 so that the current flowing through the electric motor 14 becomes a target value. In addition, the control device 15 controls the drive of the electric motor 14 based on the steering torque F detected by the torque sensor 10, thereby applying a steering assist force that assists the steering force of the steering mechanism 13 to the steering shaft 11. To do.
The vehicle speed sensor 50 measures the vehicle speed E of the vehicle on which the electric power steering device 1 is mounted. The vehicle speed sensor 50 supplies the measured vehicle speed E to the control device 15.

FIG. 2 is a diagram illustrating an example of a schematic configuration of the control device 15 in the present embodiment.
As shown in FIG. 2, the control device 15 includes a booster circuit 20, a motor drive unit 21, and a control unit 22.
Booster circuit 20, the voltage from the battery 16 (hereinafter, referred to as "battery voltage".) _{V b} is supplied.
Booster circuit 20 boosts the battery voltage V _b on the basis of the boosting circuit driving signal supplied from the control unit 22, it boosted voltage (hereinafter, referred to as "boost voltage".) Supplying V _s to the motor driving unit 21 . However, the step-up circuit 20, when the booster circuit drive signal from the control unit 22 is not supplied, does not boost the battery voltage V _b. Therefore, the booster circuit 20 supplies the battery voltage _Vb as it is to the motor drive unit 21 when the booster circuit drive signal from the control unit 22 is not supplied.

  The motor drive unit 21 applies the voltage supplied from the booster circuit 20 to the electric motor 14 based on the drive signal supplied from the control unit 22. For example, the motor drive unit 21 is an inverter circuit including a plurality of switching elements. Based on the drive signal supplied from the control unit 22, the motor drive unit 21 drives a switching element (described later) by PWM (pulse width modulation), and applies a predetermined drive voltage to the electric motor 14. Drive.

FIG. 3 is a diagram illustrating an example of a schematic configuration of the motor driving unit 21 in the present embodiment.
As shown in FIG. 3, the motor drive unit 21 converts the DC voltage supplied from the booster circuit 20 into an AC voltage and applies it to the electric motor 14. The DC voltage supplied from the booster circuit 20, a battery voltage V _b or boosted voltage V _s.
The motor drive unit 21 includes six switching elements 121UH, 121UL, 121VH, 121VL, 121WH, and 121WL. The motor drive unit 21 switches the switching elements 121UH to 121WL on and off according to the drive signal and converts the DC voltage into the AC voltage.

  The switching elements 121UH and 121UL connected in series, the switching elements 121VH and 121VL connected in series, and the switching elements 121WH and 121WL connected in series are respectively connected via current measuring units 30U, 30V, and 30W. It is connected in parallel with the ground potential. The connection point of the switching elements 121UH and 121UL is connected to one end of the coil U. The connection points of the switching elements 121VH and 121VL and the connection points of the switching elements 121WH and 121WL are connected to one end of the coil V and one end of the coil W, respectively.

  Each of the switching elements 121UH to 121WL has a configuration in which, for example, a FET (Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) and a free wheel diode are connected in parallel. ing. In this embodiment, the case where an FET is used is described, and a parasitic diode inside the FET has a function of a free wheel diode. In addition, each of the switching elements 121UH to 121WL is switched on and off based on a drive signal input from the control unit 22.

The current measuring units 30U, 30V, and 30W are connected to the switching elements 121UH and 121UL, the switching elements 121VH and 121VL, and the switching elements 121WH and 121WL, respectively, between the ground levels in the motor driving unit 21. For example, the current measuring units 30U, 30V, and 30W are configured by shunt resistors. Current measuring unit 30 U, 30 V, 30 W, a current value flowing through the motor drive unit 21, i.e., to measure the motor current value _{I m,} which is input to the electric motor 14. The current measuring units 30U, 30V, and 30W output the measured motor current value _Im to the control unit 22. In addition, although this embodiment demonstrates the case where the current measurement parts 30U, 30V, and 30W are shunt resistances, this invention is not limited to this.

  Returning to FIG. 2, the control unit 22 includes an angle acquisition unit 221, a target current acquisition unit 222, a difference calculation unit 223, a PI calculation unit 224, a drive signal acquisition unit 225, and a boost control unit 226.

  The angle acquisition unit 221 acquires the rotation speed N of the electric motor 14 based on the rotation angle supplied from the rotation angle detection unit 17. For example, the angle acquisition unit 221 acquires an output signal corresponding to the rotation angle supplied from the rotation angle detection unit 17. The angle acquisition unit 221 detects a change amount per unit time of the output signal indicating the rotation angle supplied from the rotation angle detection unit 17, and the number of rotations of the electric motor 14 (the rotor of the electric motor 14) from the detected change amount. N is calculated. From this rotational speed N, the angular velocity ω of the electric motor 14 is obtained. The angle acquisition unit 221 supplies the calculated rotation speed N to the boost control unit 226.

The target current acquisition unit 222 is based on a vehicle current speed E measured by the vehicle speed sensor 50 and a steering torque F supplied from the torque sensor 10. current value "that.) to get the _{I t.} Target current acquisition unit 222 supplies the target current value _{I t} acquired the difference calculation unit 223. The target current acquisition unit 222 may be determined based on, for example, a preset calculation formula or table. These calculations and tables, for example, based on the vehicle speed E and the steering torque F, so that the target current value I _t of the electric motor 14 can be determined, it may be determined experimentally or theoretically. In the case of using a preset table look with each vehicle speed E, and the steering torque F, and a target current value I _t of the motor current values associated with each combination of the vehicle speed E and the steering torque F The up table may be stored in advance in a storage unit (not shown). Then, the target current acquisition unit 222, a target current value I _t corresponding to the steering torque F and the supply vehicle speed E from the torque sensor 10 acquired from the look-up table, the difference calculating a target current value I _t obtained To the unit 223.

Difference calculation unit 223 obtains the target electric current value _{I t} from the target current acquisition unit 222. Difference calculation unit 223 obtains a current measuring unit 30U of the motor drive unit 21, 30 V, 30 W motor current value _{I m} were measured.
Difference calculation unit 223, the target current acquisition unit 222 the target current value I _t supplied from the difference value by subtracting the motor current value I _m obtained from the motor drive unit 21 [Delta] I (= target current value I _t -motor current value I _m ) is acquired. The difference calculation unit 223 supplies the acquired difference value ΔI to the PI calculation unit 224.

The PI calculation unit 224 executes P (Proportional) control processing and I (Integral) control processing (hereinafter referred to as “PI control”) on the difference value ΔI supplied from the difference calculation unit 223. Then, a command value V _d that attempts to bring the difference value ΔI close to a predetermined value, for example, 0 is calculated. For example, the command value _Vd is a voltage value applied to the electric motor 14. The PI calculation unit 224 supplies the calculated command value _Vd to the boost control unit 226 and the drive signal acquisition unit 225. However, in this embodiment, it is not limited to PI control, PID control may be sufficient and other feedback control may be sufficient.

Drive signal acquiring unit 225, the command value V _d supplied from the PI calculation portion 224, a pulse width modulation the switching elements of the motor driving portion 21: each consisting of pulses for driving on and off by (PWM Pulse Width Modulation) It converts into a drive signal, ie, a pulse width modulation signal. The drive signal acquisition unit 225 supplies the converted drive signal to the motor drive unit 21.

Boost control unit 226, based on the current flowing in the electric motor 14 (motor current value I _m obtained from the motor drive unit ₂₁₎ and the rotational speed N of the electric motor 14, electric the current target current value I _t The motor operating point of the motor 14 is acquired. The motor operating point is an operating point indicating the operating state of the electric motor 14 indicated by the rotational speed N (or rotational speed) of the electric motor 14 and the output torque of the electric motor 14. In other words, the operating state of the electric motor 14 indicated by one point in the two-dimensional coordinates of the axis indicating the rotational speed N of the electric motor 14 and the axis indicating the output torque of the electric motor 14. Since the output torque of the electric motor 14 can be calculated from the current value flowing through the electric motor 14, the motor operating point is determined based on the rotation speed N (or rotation speed) of the electric motor 14 and the current flowing through the electric motor 14 (for example, , Motor current value I _m ).

Boost control unit 226, when a new target current value I _t is set based on the change of the motor operating point due to a new target current value I _t is set, the operating point to be finally reached (hereinafter , Referred to as “target operating point”). Then, the boost control unit 226 starts the boost operation of the battery voltage _Vb in the boost circuit 20 when the estimated target operating point meets the start condition. Further, when boosting of the booster circuit 20 is being performed, the boost control unit 226 stops boosting of the booster circuit 20 when the estimated target operating point meets the stop condition. Here, the starting condition, for example, a voltage higher than the battery voltage V _b is in the range of the operating point of the electric motor 14 that operates by being supplied to the electric motor 14. That is, the start condition is outside the preset motor characteristics range of the electric motor 14. That is, the estimated target operating point corresponds to the start condition when a steering assist force that is greater than the steering assist force that can be applied to the steering shaft 11 by driving the electric motor 14 with the battery voltage _Vb is required. It is. Therefore, the boost control unit 226 of this embodiment estimates the estimated target operating point, and determines whether or not the estimated target operating point corresponds to the start condition, thereby requiring a steering assist force earlier than before. The case can be predicted. Therefore, the electric power steering apparatus 1 can boost the voltage of the battery at a desired timing. Therefore, even when the steering wheel is suddenly turned off by the driver, the uncomfortable feeling of the steering feeling can be reduced. The stop condition is, for example, a range of operating points of the electric motor 14 that operates when the battery voltage _Vb is supplied to the electric motor 14. That is, the stop condition is within a preset motor characteristic range of the electric motor 14.
In addition, the boost control unit 226 acquires the value of the boost voltage V _s supplied from the boost circuit 20 to the motor drive unit 21 and controls the boost circuit 20 so that the acquired boost voltage V _s becomes a desired voltage. .

Hereinafter, the processing of the boost control unit 226 in the present embodiment will be specifically described.
FIG. 4 is a diagram illustrating an example of a schematic configuration of the boost control unit 226 in the present embodiment. As illustrated in FIG. 4, the boost control unit 226 includes an estimation unit 301, a storage unit 302, a determination unit 303, and a condition control unit 304.

Estimation unit 301 obtains the operating point of the electric motor 14 in the target current value I _t supplied from the target current acquisition unit 222. The operating point of the electric motor 14 in this embodiment is indicated by the rotational speed N of the electric motor 14 and the output torque F _m of the electric motor 14. Therefore, the estimating unit 301, the present target current value I _t, and the rotational speed N of the electric motor 14 supplied from the angle acquisition unit 221, and an output torque F _m of the electric motor 14 at that time to obtain. The output torque F _m of the electric motor 14 can be calculated based on the motor current value I _m supplied from the motor drive unit 21. For example, the estimation unit 301 may determine the output torque F _m based on, for example, a preset calculation formula or table. These formulas and tables, for example based on the current flowing through the electric motor 14, so that the output torque F _m of the electric motor 14 can be determined, it may be determined experimentally or theoretically.

The rotational speed N of the electric motor 14 and the rotational speed _{N 1} at the present target current value _{I t,} the output torque _{F m} of the electric motor 14 and the output torque _{F 1.} Estimating unit 301 stores the operating point of the electric motor 14 at the present target current value _{I t S} 1 to _{(N 1, F} 1) in the storage unit 302.

Estimation unit 301, if the different target current value I _t is newly supplied from the target current acquisition unit 222 from the current target current value I _t, and calculates the change ΔS of the operating point of the electric motor 14 per unit time . For example, the estimation unit 301 acquires the operating point S ₂ of the electric motor 14 every unit time, and the previous operating point S ₁ (N ₁ , F ₁ ) and the current operating point S ₂ (N ₂ ) every unit time. , F ₂ ) to obtain an operating point change (hereinafter referred to as “operating point change”) ΔS. Then, the estimation unit 301 estimates the target operating point S ₃ (N ₃ , F ₃ ) that is the operating point that finally reaches based on the acquired operating point change ΔS. In the present embodiment, the target operating point is estimated from one operating point change for convenience of explanation, but the present invention is not limited to this. That is, the estimation unit 301 may estimate the target operating point by performing the process of obtaining the operating point change ΔS by comparing the previous operating point with the current operating point multiple times. That is, the estimation unit 301 of the present embodiment is not limited to the number of acquired operating point changes ΔS. Further, the operating point to be finally reached, for example, an operating point when the current value the motor current value I _m of the current measuring unit 30 has measured reaches the newly set target current value I _t. Estimating unit 301 supplies information of the target operating point _{S 3} was estimated judging unit 303.
Hereinafter, the method of estimating the target operating point S ₃ estimation unit 301 in the present embodiment will be specifically described. Figure 5 is a diagram illustrating an example of a method for estimating the target operating point S ₃ estimation unit 301 in this embodiment.

For example, the new target current value I _t2 is set from the present target current value I _t1. In that case, the rotational speed N of the electric motor 14 and _{N 1} of the present target current value _{I t1,} the motor current value _{I m} of the electric motor 14 and the motor current value _{I m1.} Then, the rotational speed N of the electric motor 14 at the operating point S ₂ which has changed by being set as a new target current value I _t2 and N _2, and the motor current value I _m2 motor current value I _m of the electric motor 14 To do. Further, the rotational speed N of the electric motor 14 of the target operating point S ₃ to be finally reached the N ₃ by which is set as a new target current value I _t2, the current value of the motor current value I _m of the electric motor 14 The motor current value is _Im3 .

Here, if the current target current value I a new target current value from _t1 I _t2 is set, and the time until the operating point S ₁ is to reach the operating point S ₂ time t, the operating point S ₁ the time to reach the operating point S ₃ times the T. In this case, the ratio of time T to time t is expressed by the following formula (1).
T: t = (I _m3 −I _m1 ) :( I _m2 −I _m1 ) (1)

Therefore, the time T can be expressed by the following formula (2).
T = t × (I _m3 −I _m1 ) / (I _m2 −I _m1 ) (2)

Further, the ratio between the time T and the time t is also expressed by the following formula (3).
T: t = (N ₃ −N ₁ ) :( N ₂ −N ₁ ) (3)

Thus, the rotational speed N ₃ of the target operating point S ₃ can be expressed by the following equation (4).
N ₃ = T × (N ₂ −N ₁ ) / t + N ₁ (4)

Since operating point when the motor current value I _m of the current measuring unit 30 has measured reaches the target current value I _t2 newly set is the target operating point, the target current value the motor current value I _m3 The current value _It2 is obtained. Accordingly, the estimating unit 301, by using the formulas (2) and (4), it is possible to estimate the rotational speed _{N 3} of the target operating point _{S 3.} That is, it is possible to target current value _{I t2,} based on the operating point _{S 1} and the operating point _{S 2} for estimating the target operating point _{S 3.} The target operating point S ₃ is represented by the rotational speed N ₃ between the current value the motor current value I _m. However, since it is substantially the same value current motor current value I _m and the target current value I _t2 as described above, may represent a target operating point S ₃ as the rotation speed N _3.

The determination unit 303 determines whether or not the operation state of the electric motor 14 estimated by the estimation unit 301 can be realized by the battery voltage _Vb . That is, the determination unit 303 determines whether the target operating point S ₃ the estimation unit 301 has estimated true start condition. Determination unit 303, when the target operating point S ₃ the estimation unit 301 has estimated true start condition supplies a boosting circuit driving signal to the booster circuit 20. Start condition indicates the relationship between the output torque of the speed N and the electric motor 14 of the electric motor 14 when the voltage higher than the battery voltage V _b supplied. Accordingly, the determination unit 303, when the target operating point S ₃ corresponding to the start condition, in order to supply the battery voltage V _b higher than voltage (boosted voltage V _s) to the electric motor 14, the boost in the boost circuit 20 A circuit drive signal is supplied.

Determination unit 303, when the booster circuit 20 is executing the step-up of the battery voltage V _b, whether the operation state of the electric motor 14 estimated by the estimating unit 301 can be realized by the battery voltage V _b Determine. That is, the determination unit 303, the target operating point S ₃ the estimation unit 301 has estimated determines whether corresponding to the stop condition. Determination unit 303, when the target operating point S ₃ the estimation unit 301 estimates corresponding to the stop condition to stop the supply of the booster circuit drive signal to the step-up circuit 20. The stop condition indicates the relationship between the rotational speed N of the electric motor 14 and the output torque of the electric motor 14 when the battery voltage _Vb is supplied. Accordingly, the determination unit 303, in order when the target operating point S ₃ corresponding to the stop condition, to supply less than the boosted voltage V _s voltage (battery voltage V _b) to the electric motor 14, to the booster circuit 20 Then, the supply of the booster circuit drive signal is stopped.

  The condition control unit 304 changes the start condition according to the voltage applied to the electric motor 14. The motor characteristics of the electric motor 14 vary according to the voltage applied to the electric motor 14. For example, when the voltage applied to the electric motor 14 is increased, the electric motor characteristics are such that the output torque is larger and the number of rotations at no load is larger. On the other hand, when the voltage applied to the electric motor 14 is lowered, the electric motor characteristics are such that the output torque is smaller and the rotation speed at no load is smaller.

  Below, the process of the pressure | voltage rise control part 226 in this embodiment is demonstrated. First, a boost process for the booster circuit 20 in the boost controller 226 in the present embodiment will be described. FIG. 6 is a flowchart of the boosting process of the boosting control unit 226. FIG. 7 is a schematic diagram illustrating the flow of the boosting process of the boosting control unit 226.

Estimation unit 301, the target current value _{I t1} supplied from the target current acquisition unit 222 acquires the operating point _{S 1} of the electric motor 14 based on the rotational speed of the electric motor 14 _{N 1} and the output torque _{F m1} ( Step S101: See FIG. 7A). The output torque F _m1 is determined based on the motor current value I _m1 supplied from the motor driving unit 21.

Estimating unit 301 determines whether the target current value I _t is changed to the new target current value. For example, the estimation unit 301 determines whether or not a target current value _It2 that is different from the current target current value _It1 is newly supplied from the target current acquisition unit 222 (step S102).
Estimation unit 301, when the target current value I _t2 different from the present target current value I _t1 is newly supplied from the target current acquisition unit 222 (see FIG. 7B), to calculate the operating point change ΔS per unit time (Step S103). For example, the estimation unit 301 acquires the operating point S ₂ of the electric motor 14, by comparing the current and the operating point S ₂ and the operating point S ₁ of the previous per unit time, to obtain the operating point change ΔS .

Estimating unit 301 estimates the target operating point _{S 3} on the basis of the obtained operating point change [Delta] S (step S104). Estimating unit 301 supplies the target operating point _{S 3} was estimated judging unit 303. For example, the estimation unit 301 calculates the change ΔI ₁ in the motor current value from the motor current value I _m1 at the operating point S ₁ to the motor current value I _m2 at the operating point S ₂ . Further, the estimating unit 301 calculates the rotation speed of the change .DELTA.N ₁ of the electric motor 14 from the rotational speed _{N 1} at the operating point _{S 1} to the rotational speed _{N 2} at the operating point _{S 2.} The estimation unit 301 calculates the slope a (= ΔN ₁ / ΔI ₁ ) by dividing the change ΔI ₁ by the calculated change ΔN. Estimating unit 301 as a motor current value _{I m3} of the target operating point _{S 3} the target current value _{I t2,} the motor current value from the motor current value _{I m1} at the operating point _{S 1} to the motor current value _{I m3} change [Delta] I ₂ by adding the rotational speed N ₁ at the operating point S ₁ to a value obtained by multiplying the slope a with respect to estimate the rotational speed N ₃ of the target operating point S _3.

Determination unit 303 determines whether the start condition is satisfied based on the target operating point S _3. That is, the determination unit 303 determines that the start condition is satisfied when the target operating point S ₃ the estimation unit 301 has estimated true start condition (step S105).
Determination unit 303 supplies if the target operating point _{S 3} the estimation unit 301 has estimated true start condition (see FIG. 7C), a boosting circuit driving signal to the booster circuit 20 (step S106).

Determination unit 303 (see FIG. 7D) when the target operating point S ₃ the estimation unit 301 estimates do not correspond to the start condition, it does not supply the booster circuit drive signal to the step-up circuit 20. Thus, the step-up control unit 226, since the target operating point S ₃ estimated can initiate boosting of the booster circuit 20 when true start condition, predicting when fast steering assist force than conventional is required can do. Therefore, the electric power steering apparatus 1 can boost the voltage of the battery at a desired timing. Therefore, even when the steering wheel is suddenly turned off by the driver, the uncomfortable feeling of the steering feeling can be reduced.

Next, boost stop processing for the booster circuit 20 in the boost controller 226 in the present embodiment will be described. FIG. 8 is a flowchart of boost stop processing performed by the boost control unit 226. FIG. 9 is a schematic diagram for explaining the flow of the boost stop process of the boost control unit 226. As an initial condition, a case where the booster circuit drive signal is supplied to the booster circuit 20 and the battery voltage _Vb of the booster circuit 20 is boosted will be described.

Estimation unit 301, the target current value _{I t1} supplied from the target current acquisition unit 222 acquires the operating point _{S 1} of the electric motor 14 based on the rotational speed of the electric motor 14 _{N 1} and the output torque _{F m1} ( Step S201: See FIG. 9A). The output torque F _m1 is determined based on the motor current value I _m1 supplied from the motor driving unit 21.

Estimating unit 301 determines whether the target current value I _t is changed to the new target current value. For example, the estimation unit 301 determines whether or not a target current value _It2 that is different from the current target current value _It1 is newly supplied from the target current acquisition unit 222 (step S202).
Estimation unit 301, when the target current value I _t2 different from the present target current value I _t1 is newly supplied from the target current acquisition unit 222 (see FIG. 9B), to calculate the operating point change ΔS per unit time (Step S203). For example, the estimation unit 301 acquires the operating point S ₂ of the electric motor 14, by comparing the current and the operating point S ₂ and the operating point S ₁ of the previous per unit time, to obtain the operating point change ΔS .

Estimating unit 301 estimates the target operating point _{S 3} on the basis of the obtained operating point change [Delta] S (step S204). Estimating unit 301 supplies the target operating point _{S 3} was estimated judging unit 303. For example, the estimation unit 301 calculates the change ΔI ₁ in the motor current value from the motor current value I _m1 at the operating point S ₁ to the motor current value I _m2 at the operating point S ₂ . Further, the estimating unit 301 calculates the rotation speed of the change .DELTA.N ₁ of the electric motor 14 from the rotational speed _{N 1} at the operating point _{S 1} to the rotational speed _{N 2} at the operating point _{S 2.} The estimation unit 301 calculates the slope a (= ΔN ₁ / ΔI ₁ ) by dividing the change ΔI ₁ by the calculated change ΔN. Estimating unit 301 as a motor current value _{I m3} of the target operating point _{S 3} the target current value _{I t2,} the motor current value from the motor current value _{I m1} at the operating point _{S 1} to the motor current value _{I m3} change [Delta] I ₂ by adding the rotational speed N ₁ at the operating point S ₁ to a value obtained by multiplying the slope a with respect to estimate the rotational speed N ₃ of the target operating point S _3.

Determination unit 303 determines whether the stop condition is satisfied on the basis of the target operating point S _3. That is, the determination unit 303 determines that the stop condition is satisfied in a case where the target operating point S ₃ the estimation unit 301 estimates corresponding to the stop condition (step S205).
Determination unit 303, when the target operating point _{S 3} the estimation unit 301 estimates corresponding to the stop condition (see FIG. 9C), to stop the supply of the booster circuit drive signal to the step-up circuit 20 (step S206).

Determination unit 303, when the target operating point S ₃ the estimation unit 301 estimates do not correspond to the stop condition (see FIG. 9D), to continue the supply of the booster circuit drive signal to the step-up circuit 20. Thus, the step-up controller 226, the target operating point S ₃ estimated it is possible to stop the boosting of the booster circuit 20 when true stop condition. Therefore, since the electric power steering apparatus 1 can stop boosting the voltage of the battery at a desired timing, it can reduce the driver's uncomfortable feeling of steering.

As described above, the electric power steering apparatus 1 according to this embodiment, when the target current value I _t is changed, the motor operation is defined based on the rotational speed N and the motor current value I _m of the electric motor 14 based on a change of the point, the estimating unit 301 that estimates the motor operating point (target operating point) at which the motor current value I _m reaches the target current value I _t, the motor operating point estimated by the estimation unit 301 And a determination unit 303 that starts boosting of the booster circuit when a start condition for controlling the start of boosting of the booster circuit 20 is met. Therefore, since the voltage of the battery can be boosted at a desired timing, it is possible to reduce the driver's uncomfortable feeling of steering. That is, it is possible to perform pressure increase control without delay when assisting the steering force.

In the electric power steering apparatus 1 in the above-described embodiment, the target operating point S ₃ estimated based on the change ΔS of the operating point of the electric motor 14 when the booster circuit 20 boosts the battery voltage _Vb. Stops the boosting of the booster circuit 20 when the stop condition is satisfied. Therefore, since the boosting of the battery voltage can be stopped at a desired timing, it is possible to reduce the driver's uncomfortable feeling of steering.

In the above-described embodiment, the start condition and the stop condition may have a hysteresis width. That is, the range of the stop condition is made narrower than the start condition. Thus, since the repetition of the step-up and non-boosting of the booster circuit 20 while the target operating point S ₃ the estimation unit 301 has estimated in a short time can vary (chattering) can be prevented from being generated, The driver's uncomfortable feeling of steering feeling can be further reduced.

  In the above-described embodiment, the start condition and the stop condition may be the same condition. In other words, the case where the start condition is not satisfied may be set as the condition where the stop condition is satisfied.

  Each unit of the control unit 22 may be realized by hardware, or may be realized by a combination of hardware and software. Further, the computer may function as a part of the control unit 22 by executing the program. The program may be stored in a computer-readable medium, or may be configured to be stored in a storage device connected to a network.

  You may make it implement | achieve the pressure | voltage rise control part 226 in embodiment mentioned above with a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be a program for realizing a part of the above-described functions, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. You may implement | achieve using programmable logic devices, such as FPGA (Field Programmable Gate Array).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  The execution order of each process such as operation, procedure, step, and stage in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior to”. It should be noted that the output can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if it is described using “first”, “next”, etc. for the sake of convenience, it means that it is essential to carry out in this order. It is not a thing.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 9 Steering handle 10 Torque sensor 11 Steering shaft 12 Gear box 13 Steering mechanism 14 Electric motor 15 Controller 20 Booster circuit 21 Motor drive part 22 Control part 50 Vehicle speed sensor 221 Angle acquisition part 222 Target current acquisition part 223 Difference calculation unit 224 PI calculation unit 225 Drive signal acquisition unit 226 Boost control unit 301 Estimation unit 302 Storage unit 303 Determination unit 304 Condition control unit

Claims (5)

A steering assist force is applied to the steering shaft by supplying a voltage from the power source to the electric motor so that the motor current value flowing through the electric motor becomes a target current value determined based on the steering torque of the steering wheel of the vehicle. An electric power steering device that
A booster circuit for boosting the voltage of the power supply;
When the target current value is changed, the motor current value reaches the target current value based on a change in the motor operating point defined based on the rotation speed of the electric motor and the motor current value. An estimation unit for estimating a motor operating point at the time,
A determination unit that starts boosting of the booster circuit when the motor operating point at the target current value corresponds to a start condition for controlling the start of boosting of the booster circuit;
An electric power steering apparatus comprising:   The electric power steering apparatus according to claim 1, wherein the start condition is outside a preset motor characteristic range of the electric motor.   The electric power steering apparatus according to claim 2, wherein the start condition is capable of changing a preset range of the motor characteristic in accordance with a voltage of the power source.   The determination unit stops boosting of the booster circuit by the motor operating point estimated by the estimation unit when the target current value is changed when the booster circuit boosts the voltage of the power supply. The electric power steering apparatus according to any one of claims 1 to 3, wherein boosting of the booster circuit is stopped when a stop condition to be met is satisfied.   The electric power steering apparatus according to claim 4, wherein the start condition and the stop condition have a hysteresis width.

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