JP2017065433A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device with high reliability.SOLUTION: An electric power steering device of the invention drives an electric motor using electric power supplied from a power source on the basis of a detected value of a torque sensor to detect a steering torque of a steering wheel for a vehicle, and applying a steering assistance force to a steering shaft. The electric power steering device comprises: a booster circuit for boosting a voltage of the power source; and a booster control part for setting a boost continuing time for allowing boosting calculated from a boost power value of the booster circuit and boost allowable time, and interrupting the booster circuit from performing the boost control when the boost continuing time has passed since a boost start time.SELECTED DRAWING: Figure 2

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, electric power steering can obtain a larger steering assist force by boosting the battery voltage with a booster circuit and supplying the boosted voltage to the motor drive circuit. An apparatus 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-described problem, Patent Document 1 discloses that a duty ratio of a PWM (pulse width modulation) signal for turning on / off a switching element of a motor drive circuit exceeds a predetermined threshold value of 100%. An electric power steering device is described in which the voltage of the battery is boosted by a booster circuit because torque cannot be obtained. 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, in the booster circuit, a high voltage generated at the drain of the field effect transistor (HI-MOS 312 in FIG. 2 of Patent Document 1) constituting the booster circuit is generated. The motor driving circuit is supplied. In such a case, if the boosting control of the motor is continued by the boosting circuit, the heat generation of the field effect transistor increases, and there is a concern that the boosting circuit itself may fail to function.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an electric power steering device with high reliability.

  According to one aspect of the present invention, an electric motor is driven by electric power supplied from a power source based on a detection value of a torque sensor for detecting a steering torque of a steering handle of a vehicle, and an electric assisting force is applied to a steering shaft. A power steering device, wherein a booster circuit for boosting the voltage of the power supply, a boostable boost duration time calculated from a boosted power value of the booster circuit and a boostable time is set, and the booster starts from a boost start time An electric power steering apparatus comprising: a boost control unit that interrupts boost control by the boost circuit when a duration time has elapsed.

  One embodiment of the present invention is the above-described electric power steering device, wherein the boost control unit counts the boost duration time according to an increase or decrease of the boost power value, and the count value is counted up. Is set as the step-up duration.

  As described above, according to the present invention, an electric power steering device with high reliability can be provided by setting an appropriate boosting duration.

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 a pressure | voltage rise possible time map. It is a figure which shows an example of a pressure | voltage rise time time chart.

  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.

The electric power steering device (EPS system: Electric Power Steering System) in the embodiment drives an electric motor by electric power supplied from a power source based on a detection value of a torque sensor that detects a steering torque of a steering wheel for steering a vehicle. The steering assist force is applied to the steering shaft by the torque of the electric motor. Then, the electric power steering apparatus according to the embodiment determines a boosting circuit that boosts the voltage of the power supply and a start condition for controlling the start of boosting of the booster circuit based on the angular acceleration of the electric motor, and the determined start condition is And a boost control unit that starts boosting of the booster circuit when established.
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 drive signal acquisition unit 225 of 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 current value _{I m,} which is input to the electric motor 14. Current measuring unit 30 U, 30 V, 30 W, and outputs the measured current value _{I m} on the difference calculation unit 223 of 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 angular acceleration A 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 calculates the angular acceleration A of the electric motor 14 based on the calculated change amount per unit time of the rotation speed N. The angle acquisition unit 221 supplies the calculated angular acceleration A to the boost control unit 226.

The target current acquisition unit 222 is based on the vehicle speed E measured by the vehicle speed sensor 50 and the steering torque F supplied from the torque sensor 10. that the value ".) 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 acquire the target current value It 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. When using a preset table, the target current acquisition unit 222 uses a target current value I of a motor current associated with each vehicle speed, each steering torque F, and each combination of the vehicle speed E and the steering torque F. _A lookup table including _t 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, the current value _{I m} of 30W was measured.
Difference calculation unit 223, with respect to supplied from the target current acquisition unit 222 the target current value I _t, a difference value by subtracting the current value I _m obtained from the motor drive unit 21 [Delta] I (= target current value I _t -Obtain the current value I _m ). 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.

The step-up control unit 226 estimates the high-speed rotation of the electric motor 14 based on the increase in the angular acceleration A of the electric motor 14 and determines the timing for starting the operation of the step-up circuit 20. Further, the boost control unit 226 estimates the low speed rotation of the electric motor 14 based on the decrease in the angular acceleration A of the electric motor 14 and determines the timing for stopping the operation of the booster circuit 20. That is, the boost control unit 226 controls driving of the booster circuit 20 based on the angular acceleration A of the electric motor 14. The case where the electric motor 14 rotates at a high speed is a case where the steering handle 9 is largely turned in a short time by the driver. That is, the case where the electric motor 14 rotates at a high speed is a case where the steering assist force is required immediately. For example, a case where the steering handle is suddenly turned off by the driver in the traveling vehicle is assumed. Therefore, when it is estimated that the electric motor 14 is rotating at high speed based on the angular acceleration A of the electric motor 14, the boost control unit 226 immediately starts boosting of the booster circuit 20, thereby immediately steering. A steering assist force can be applied to the shaft 11.
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.

The step-up control unit 226 determines a control condition for controlling the step-up of the step-up circuit 20 based on the angular acceleration A supplied from the angle acquisition unit 221. The control condition includes a first start condition and a first stop condition. The first start condition is a condition for controlling the timing at which the booster circuit 20 starts boosting the battery voltage _Vb . The first stop condition is a condition for controlling the timing at which the boosting of the battery voltage _Vb by the booster circuit 20 is stopped. Therefore, the first start condition is a condition used when the booster circuit 20 does not boost the battery voltage _Vb . On the other hand, the first stop condition is a condition used when the booster circuit 20 boosts the battery voltage _Vb .

The first start condition changes in real time according to the angular acceleration A supplied from the angle acquisition unit 221. For example, a first start map including the angular acceleration of each electric motor 14 and a first start condition associated with each angular acceleration is stored in advance in a storage unit (not shown) in the boost control unit 226. And the pressure | voltage rise control part 226 is determined by acquiring the 1st start condition corresponding to the angular acceleration A supplied from the angle acquisition part 221 from the said 1st start map. Boost control unit 226, when the command value V _d supplied from the PI calculation unit 224 corresponds to the first start condition, it supplies the boosting circuit driving signal to the booster circuit 20. Incidentally, a case where the command value V _d corresponds to the first start condition, referred to as a first starting condition is satisfied. The first start condition is set such that the range of the condition is wider as the angular acceleration A is higher. That is, the first starting condition as the angular acceleration A is higher command value V _d corresponding to the first starting condition is increased is higher value is set. Thus, since the command value V _d that the angular acceleration A corresponds to the first starting condition as is the high value increases, the boosting of the booster circuit 20 is started earlier.

The first stop condition changes in real time according to the angular acceleration A supplied from the angle acquisition unit 221. For example, a first stop map including the angular acceleration of each electric motor 14 and a first stop condition associated with each angular acceleration is stored in advance in a storage unit (not shown) in the boost control unit 226. And the pressure | voltage rise control part 226 is determined by acquiring the 1st stop condition corresponding to the angular acceleration A supplied from the angle acquisition part 221 from the said 1st stop map. Boost control unit 226, the command value V _d supplied from the PI calculation portion 224 in the case of corresponding to the first stop condition, it stops the supply of the booster circuit drive signal to the step-up circuit 20. Incidentally, a case where the command value V _d corresponds to the first stop condition, that the first stop condition is satisfied. The first stop condition is set to have a wider range of conditions as the angular acceleration A is lower. That is, the first stop condition as the angular acceleration A is higher command value V _d corresponding to the first stop condition is increased is at a lower value is set. Thus, since the command value V _d that the angular acceleration A corresponds to the first starting condition as is the lower value increases, the boosting of the booster circuit 20 is stopped earlier.

  As described above, the electric power steering apparatus 1 according to the present embodiment determines the first start condition for controlling the start of boosting of the booster circuit 20 based on the angular acceleration of the electric motor 14, and the determined first start condition is When it is established, boosting of the booster circuit 20 is started. 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 feeling. That is, it is possible to perform pressure increase control without delay when assisting the steering force.

Further, the electric power steering apparatus 1 according to the present embodiment described above is configured to stop the boosting of the booster circuit 20 based on the angular acceleration of the electric motor 14 when the booster circuit 20 boosts the battery voltage _Vb . The stop condition is further determined, and the boost of the booster circuit 20 is stopped when the determined first 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 feeling.

Furthermore, as described below, the electric power steering apparatus 1 of the present embodiment can provide a highly reliable electric power steering apparatus by setting an appropriate boosting duration.
The boost control unit 226 calculates a boost power value when the battery voltage _Vb is boosted by the boost circuit 20 (when the boost control unit 226 supplies a boost circuit drive signal to the boost circuit 20). The boostable time is calculated from the possible boostable time map. Boost controller 226, a boost power value is calculated by multiplying the boosted voltage V _s to the current value I _m of the current measuring section 30 measures. The boost control unit 226 calculates a boostable time corresponding to the calculated boosted power value.

  Here, the boostable time is a value obtained based on reliability data obtained in advance by experiments or the like for the booster circuit 20. FIG. 4 is a diagram illustrating an example of a boostable time map. In FIG. 4, the horizontal axis represents the boosted power value, and the vertical axis represents the boostable time. As shown in FIG. 4, the boostable time tends to become shorter as the boosted power value becomes larger and becomes longer as the boosted power value becomes smaller. The boost control unit 226 has a storage unit that stores a boostable time map in which the boosted power value and the boostable time are associated with each other as shown in FIG. The boost control unit 226 refers to, for example, a boostable time map shown in FIG. 4 and calculates an appropriate boostable time that can actually be boosted corresponding to the calculated boosted power value. However, in this embodiment, the boostable time map is stored in the storage unit in advance, but the boostable time is calculated from the boosted power value and the boostable time without using the map. Also good.

When the boostable time calculated from the boost start time has elapsed, the boost control unit 226 stops supplying the booster circuit drive signal to the booster circuit 20 and the booster circuit 20 does not boost the battery voltage _Vb. To. FIG. 5 is a diagram illustrating an example of a boost time time chart. FIG. 5 shows the time on the horizontal axis and the boosted power value and the boost time on the vertical axis. The boosting time shown on the vertical axis indicates the boostable time corresponding to the boosted power value and the boosting continuation counter. The boost control unit 226 uses a built-in counter to count the boost duration (the boost time from the boost start time), and when the boost duration, which is the result of counting, exceeds the boostable time, the battery voltage generated by the boost circuit 20 The boosting of _Vb is interrupted. As shown in FIG. 5, time t0 represents the boost start time, and time t1 represents the time when the boost of the battery voltage _Vb by the boost circuit 20 is interrupted.

  As described above, the boost control unit 226 uses the boostable time map in which the boosted voltage value of the booster circuit 20 and the boostable time are associated with each other, sets the boostable duration time that can be actually boosted, and boosts from the boost start time. When the duration time has elapsed, the boost control by the boost circuit 20 is interrupted. Here, the boost control unit 226 counts the boost duration time by the counter in accordance with the increase / decrease of the boost power value during the period of time t0 to t1, and until the count value is counted up (exceeds the boostable time). Is set as the boosting duration.

  As described above, according to the electric power steering apparatus 1 of the present embodiment, the boosting time is ensured by limiting the maximum boosting time (boosting duration) by the boostable time calculated from the boosted power value. The overheating of the booster circuit 20 can be prevented. Therefore, according to the electric power steering apparatus 1 of the present embodiment, it is possible to provide a highly reliable electric power steering apparatus by setting an appropriate boosting duration.

  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.

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 16 Battery 20 Booster circuit 21 Motor drive part 22 Control part 50 Vehicle speed sensor 221 Angle acquisition part 222 Target current acquisition Unit 223 Difference calculation unit 224 PI calculation unit 225 Drive signal acquisition unit 226 Boost control unit

Claims (2)

An electric power steering device that drives an electric motor with electric power supplied from a power source based on a detected value of a torque sensor for detecting a steering torque of a steering wheel of a vehicle and applies a steering assist force to a steering shaft,
A booster circuit for boosting the voltage of the power supply;
A boostable boost duration calculated from the boost power value of the booster circuit and the boostable time is set, and when the boost duration has elapsed from the boost start time, the boost control by the booster is interrupted A boost control unit;
An electric power steering apparatus comprising: The boost control unit counts the boost duration according to the increase or decrease of the boost power value, and sets the time until the count value is counted up as the boost duration.
The electric power steering apparatus according to claim 1.

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