JP2012126161A - Setting method and manufacturing method of electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a setting method and a manufacturing method of an electric power steering device, for properly correcting an assist force in response to a variation in characteristics for each product and gradually reducing steering resistance as operation of a steering mechanism is repeated.SOLUTION: The electric power steering device includes an assist torque correcting means for correcting assist torque based on assist torque correction characteristics (an assist torque correction map) set in advance in accordance with a steering quantity integral value. The setting method of the electric power steering device includes: an initial steering resistance measuring process P2 for measuring steering resistance R1 of the steering mechanism by actuating the steering mechanism before being installed in a vehicle after manufacturing the electric power steering device; and an assist torque correction characteristic setting process P8 for setting assist torque correction characteristics based on the measured steering resistance.

Description

  The present invention relates to a setting method and a manufacturing method of an electric power steering device in which an assist torque is applied to a steering mechanism of a vehicle by an electric motor.

  This type of electric power steering apparatus is configured to control the output of the electric motor in accordance with the input torque detected by the torque sensor, and the electric motor applies a predetermined assist torque.

  In the steering mechanism of the electric power steering apparatus, a steering resistance such as a frictional resistance against the steering force is generated. This steering resistance is abruptly reduced at the initial stage of driving of the vehicle (at the time of running-in) as a change with time, and gradually decreases as steering is repeated by subsequent driving.

  The electric power steering device disclosed in Patent Document 1 corrects the assist torque of the electric motor with a correction amount that changes according to the accumulated usage time so as to cancel out the steering resistance that shows a change over time. .

JP 2001-2119867

  However, the characteristic that the steering resistance decreases according to the accumulated usage time varies depending on the product of the electric power steering device (see FIG. 4).

  In the electric power steering device disclosed in Patent Document 1, when the characteristic (map) in which the correction amount of the assist torque changes based on the accumulated usage time is uniquely determined, the assist torque becomes excessive depending on the product, There may be a shortage.

  The present invention has been made in view of the above problems, and an appropriate assist force correction can be made in response to variations in characteristics of each product in which the steering resistance gradually decreases as the operation of the steering mechanism is repeated. It is an object of the present invention to provide a setting method and a manufacturing method of an electric power steering device to be performed.

  The present invention relates to a steering mechanism that converts input torque into steering force and transmits it to a wheel, an electric motor that applies assist torque to the steering mechanism, a torque sensor that detects input torque and outputs a torque detection signal, torque A controller that inputs a detection signal of the sensor and controls the output of the electric motor, and the controller includes an assist torque control unit that controls the assist torque in accordance with the torque detection signal, and an integration of a steering amount that the steering mechanism operates. A steering amount integrating unit that calculates a value as a steering amount integrated value; and an assist torque correcting unit that corrects an assist torque based on an assist torque correction characteristic that is preset according to the calculated steering amount integrated value. A power steering device is assumed.

  A method for setting an electric power steering device, wherein a steering resistance measuring step of measuring a steering resistance of a steering mechanism by operating a steering mechanism after the electric power steering device is manufactured, and an assist torque based on the measured steering resistance And an assist torque correction characteristic setting step for setting correction characteristics.

  In addition, a method for manufacturing an electric power steering apparatus includes an assembling step of assembling an electric motor and a torque sensor to a steering mechanism, and measuring the steering resistance of the steering mechanism by operating the steering mechanism before the steering mechanism is assembled to the vehicle. A method for manufacturing an electric power steering apparatus, comprising: an initial steering resistance measurement step that performs an assist torque correction characteristic setting step that sets an assist torque correction characteristic based on the measured steering resistance.

  According to the present invention, the assist torque correction characteristic is set based on the measured steering resistance, so that the steering resistance generated for each product of the electric power steering apparatus is mounted on the vehicle in response to the variation in the characteristic. Appropriate assist torque is maintained throughout the initial, intermediate and late use of the electric power steering device. Thereby, it is avoided that the assist torque becomes excessive or insufficient depending on the product.

1 is a schematic configuration diagram of an electric power steering apparatus showing an embodiment of the present invention. It is a block diagram which similarly shows the structure of a controller. The flowchart which shows the control content similarly performed with a controller. FIG. 5 is a characteristic diagram showing the relationship between the steering amount integrated value and the steering resistance of the steering mechanism. It is a schematic block diagram of a setting apparatus similarly. The flowchart which similarly shows the procedure which sets an assist torque correction characteristic.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an example of an electric power steering device for a vehicle to which the present invention is applied. The electric power steering apparatus 1 includes a steering mechanism 3 for steering a wheel (not shown) in cooperation with a steering handle (not shown), a torque sensor 2 for detecting input torque, and assist torque for the steering mechanism 3. An electric motor 4 to be applied, and a controller (ECU) 5 that inputs the detection signal of the torque sensor 2 and controls the output of the electric motor 4 are provided.

  In the steering mechanism 3, the input shaft 11 and the output shaft 12 rotate in conjunction with the steering handle, and the rack 14 that meshes with the pinion 17 formed on the output shaft 12 moves in the axial direction (the left-right direction of the vehicle). The wheel is steered through a tie rod (not shown) or the like connected to the wheel.

  The steering mechanism 3 includes a worm wheel 15 connected to the output shaft 12 and a worm 16 that meshes with the worm wheel 15. The electric motor 4 rotates the worm 16 and applies an assist torque to the output shaft 12 via the worm wheel 15.

  The torque sensor 2 is interposed between the input shaft 11 and the output shaft 12, and detects an input torque applied to the input shaft 11 by the driver via the steering handle.

  The controller 5 receives a torque detection signal output from the torque sensor 2 and communicates with another controller (not shown) mounted on the vehicle via a communication system (not shown) mounted on the vehicle. Information is transmitted and received, and various driving state detection signals such as a vehicle speed (vehicle speed) signal and a steering angle signal of the steering wheel are input. The controller 5 calculates a command value of the assist force based on a map set in advance according to these signals, and controls the output of the electric motor 4.

  FIG. 2 is a block diagram showing the configuration of the controller 5. The controller 5 calculates an assist torque basic command value Tb in accordance with a vehicle speed detection signal and an input torque detection signal as a driving state of the vehicle, and controls assist torque (output of the electric motor 4). Is provided. As a result, the electric motor 4 applies assist torque according to the input torque and the vehicle speed to the steering mechanism 3.

  By the way, in the steering mechanism 3 and the like of the electric power steering apparatus 1, a frictional resistance generated at a portion where the pinion 17 and the rack 14 mesh with each other is generated as a steering resistance against the steering force. This frictional resistance decreases abruptly according to the number of times the steering with a large steering angle is performed at the initial stage of the vehicle operation (at the time of running-in), and thereafter the steering with a large steering angle is repeated by the driving. Decrease gradually.

  That is, the steering resistance of the steering mechanism 3 has a characteristic that decreases according to the integrated value of the distance (steering amount) by which the rack 14 moves beyond a certain stroke from the neutral position (position where the steering angle becomes zero).

  Here, the integrated value of the steering amount for operating the steering mechanism 3 to steer the wheel is referred to as a steering amount integrated value M. Specifically, a parameter representing the steering amount is set as a steering angle of the steering wheel. The steering amount integrated value M is an integrated value of a steering angle at which the steering handle is operated beyond a predetermined value from a neutral position (a position at which the steering angle becomes zero).

  The controller 5 calculates the steering amount integrated value M according to the steering angle signal of the steering wheel, and corrects the assist force based on the assist torque correction map set in advance according to the calculated integrated amount.

  As shown in the block diagram of FIG. 2, the controller 5 includes a steering amount integration unit 24 that calculates a steering amount integration value M in accordance with the steering angle signal of the steering wheel, and a predetermined amount in accordance with the calculated steering amount integration value M. An assist torque correction value calculation means 25 for calculating an assist torque correction value F based on the set assist torque correction map, and a command by correcting the basic command value Tb of the assist torque based on the calculated assist torque correction value F. Assist torque correction means 22 for outputting a value Tf. The drive means 23 outputs a motor current to the electric motor 4 according to the corrected command value Tf.

  The steering amount integrating means 24 receives the steering angle signal of the steering wheel, and calculates the integrated value of the steering angle at which the steering angle increases beyond a predetermined angle from the neutral position as the steering amount integrated value M.

  The steering amount integrated value M calculated by the steering amount integrating means 24 is an integrated value of the distance that the rack 14 moves over a predetermined stroke from the neutral position, and based on this, the steering resistance of the steering mechanism 3 is reduced. The amount can be determined.

  The assist torque correction value calculation means 25 uses an assist torque correction map in which the relationship between the steering amount integrated value M and the assist torque correction value F is set in advance. This assist torque correction map performs a test for operating the electric power steering apparatus 1, measures the steering resistance of the steering mechanism 3 according to the steering amount integrated value M, and sets the assist torque correction value F based on this measurement data. Is done.

  The flowchart shown in FIG. 3 shows the content of the control performed by the controller 5. This will be described. First, in step 1, the steering amount integrated value M is counted according to the steering angle signal of the steering wheel. This process corresponds to the steering amount integrating means 24.

  In the subsequent step 2, the assist torque correction value F is calculated based on the assist torque correction map set in advance according to the calculated steering amount integrated value M. Here, every time the steering amount integrated value M reaches a predetermined value, the assist torque correction value F is read based on a preset assist torque correction map. This process corresponds to the assist torque correction value calculation means 25.

  In the subsequent step 3, the basic command value Tb of the assist torque is corrected based on the calculated assist torque correction value F, and the final command value Tf is output. This process corresponds to the assist torque correction means 22.

  The steering amount integrating means 24 may use the rotation angle of the electric motor 4 as a parameter representing the steering amount. In this case, the steering amount integrating means 24 calculates an integrated value of an angle at which the rotation angle of the electric motor 4 increases beyond a predetermined angle from the neutral position as the steering amount integrated value M.

  Based on the above configuration, the controller 5 controls the motor current so that the assist torque correction value F decreases in accordance with the characteristic that the steering resistance of the steering mechanism 3 decreases in accordance with the steering amount integrated value M, and is always appropriate. The assist characteristic is maintained.

  By the way, the characteristic in which the steering resistance of the steering mechanism 3 decreases according to the steering amount integrated value M varies depending on the product of the electric power steering device 1 shipped.

  FIG. 4 shows three characteristics in which the steering resistance of the steering mechanism 3 decreases according to the steering amount integrated value M as an example of the variation occurring for each product of the electric power steering apparatus 1. The steering resistance of the steering mechanism 3 rapidly decreases at the initial stage of use where the steering amount integrated value M is small, and gradually decreases as the steering amount integrated value M increases at the middle stage of use. However, in the stage from the initial stage of use to the middle stage of use, there is a large variation in steering resistance generated for each product.

  By measuring the initial steering resistance R1 of the steering mechanism 3 in the initial stage of use where the steering amount integrated value M is small, the steering resistance of the steering mechanism 3 decreases according to the steering amount integrated value M over the middle period of use and the latter period of use. The characteristic (decrease degree) to be performed can be determined.

  Focusing on this point, the setting method of the present invention measures the initial steering resistance R1 by operating the steering mechanism 3 at a stage after the electric power steering device 1 is manufactured and before being assembled to the vehicle. An assist torque correction map (assist torque correction characteristic) for correcting the assist torque according to the steering amount integrated value M is set based on the initial steering resistance R1.

  FIG. 5 shows a schematic configuration of a setting device 50 that adjusts the output of the electric power steering device 1. To explain this, the setting device 50 operates the steering mechanism 3 to measure the steering resistance of the steering mechanism 3 before being assembled to the vehicle, and assist torque correction based on the measured steering resistance. And a setting device 54 for setting characteristics.

  The steering resistance measuring device 40 includes an input-side actuator 51 that applies input torque for rotating the input shaft 11, an input torque detector 55 that detects input torque applied to the input shaft 11, and steering of the input shaft 11. A steering angle detector 56 for detecting an angle; an output-side actuator 57 for applying a rack thrust force that pushes the rack 14; and a steering force detector 52 for detecting a steering force (rack thrust force) applied to the rack 14. The actuator controller 60 for controlling the operation of the input-side actuator 51 or the output-side actuator 57, the detection data of the input torque detector 55, the detection data of the steering angle detector 56, and the steering force detector 52 A measuring device 53 that reads the detection data and measures the steering resistance according to the read detection data.

  The steering resistance measuring device 40 applies an input torque by which the input-side actuator 51 rotates the input shaft 11, and the measuring device 53 detects the input torque value detected by the input torque detector 55 and the steering angle detector 56. Based on the steering angle of the input shaft 11 detected by the above, the initial steering resistance R1 of the steering mechanism 3 is determined.

  Instead of the steering angle detector 56, a detector for detecting the displacement amount of the rack 14 may be provided, and the initial steering resistance R1 of the steering mechanism 3 may be determined based on the detected displacement amount of the rack 14.

  Not limited to this, the steering resistance measuring device 40 applies a steering force (rack thrust) by which the output-side actuator 57 pushes the rack 14, and the measuring device 53 detects the steering force value detected by the steering force detector 52. The initial steering resistance R1 of the steering mechanism 3 may be determined based on (rack thrust) and the steering angle of the input shaft 11 detected by the steering angle detector 56.

  Since the steering resistance of the steering mechanism 3 varies depending on the position of the rack 14, the setting device 50 sets the average value of the steering resistance measured according to the position of the rack 14 as the initial steering resistance R1. Further, the setting device 50 may use the maximum value of the steering resistance measured according to the position of the rack 14 as the initial steering resistance R1.

  The flowchart of FIG. 6 shows a procedure for setting the assist torque correction characteristics of the electric power steering device 1 using the setting device 50 before the electric power steering device 1 is assembled to the vehicle. This will be described below.

  First, in the process 1, an assembling step for assembling the electric power steering device 1 in which the respective parts are assembled to the setting device 50 is performed.

  In this assembling process, the input side actuator 51 and the steering angle detector 56 are connected to the input shaft 11 and the input torque detector 55 is attached, and the output side actuator 57 is connected to one end of the rack 14. A steering force detector 52 is connected to the other end.

  Next, it progresses to the process 2 and an initial steering resistance measurement process is performed. In this initial steering resistance measurement step, the steering mechanism 3 is operated via the input-side actuator 51 or the output-side actuator 57, and the measuring device 53 receives the measurement data of the input torque detector 55 or the steering force detector 52. Based on this, the post-operation resistance of the steering mechanism 3 is measured as the initial steering resistance R1.

  Next, it progresses to the process 3 and a break-in process is performed. In this break-in process, the steering operation is performed a predetermined number of times (for example, several tens of times) by reciprocating the input-side actuator 51 or the output-side actuator 57 and operating the steering mechanism 3 alternately to a predetermined steering angle in the left-right direction. Times) done. At this time, the number of steering operations is measured.

  Next, it progresses to the process 4 and a post-break-in steering resistance measurement process is performed. In this post-break-in steering resistance measurement step, as in the first initial steering resistance measurement step, the steering mechanism 3 is operated via the input-side actuator 51 or the output-side actuator 57, and the measuring instrument 53 detects the input torque. The operating resistance of the steering mechanism 3 is acclimated based on the measurement data of the detector 55 or the steering force detector 52 and then measured as the steering resistance R2.

  Next, it progresses to the process 5 and performs the defect determination process which determines the defect of a product. In this failure determination step, the difference between the initial steering resistance R1 and the post-break-in steering resistance R2 (R1-R2) is calculated as a decrease after break-in, and the calculated decrease after break-in (R1-R2) is a preset reference. It is determined whether it is within the range.

  In this process 5, when it is determined that the calculated after-break-down decrease range (R1-R2) is not within the reference range, the process proceeds to process 6 assuming that there is a manufacturing defect portion in the steering mechanism 3. Stop shipping products and conduct re-inspection.

  On the other hand, if it is determined in process 5 that the calculated decrease after running-in (R1-R2) is within the reference range, the process proceeds to process 7 assuming that there is no manufacturing defect in the steering mechanism 3. Then, an assist torque correction characteristic setting step is performed.

  In the assist torque correction characteristic setting step of process 7, the setting device 54 sets the assist torque correction characteristic of the controller 5 in accordance with the measured initial steering resistance R1.

  The assist torque correction characteristic is set based on the initial steering resistance on the assist torque correction map based on two points of the measured initial steering resistance R1 and the post-break-in steering resistance R2 from a plurality of prepared assist torque correction maps. Is selected, and the selected assist torque correction map is stored in the memory of the controller 5.

  The plurality of assist torque correction maps prepared in advance are set based on the characteristic diagram shown in FIG. 4 with the steering amount integrated value S and the steering resistance of the steering mechanism 3 as parameters.

  Then, the setter 54 stores the number of steering operations performed in the break-in process in the memory of the controller 5 as an initial value of the steering amount integrated value M.

  Next, the process proceeds to process 8, and the product for which the assist torque correction characteristic of the controller 5 has been set is shipped.

  Hereinafter, the gist, operation, and effect of the present embodiment will be described.

  In the present embodiment, the steering mechanism 3 that converts input torque into steering force and transmits it to the wheels, the electric motor 4 that applies assist torque to the steering mechanism 3, and the torque that detects the input torque and outputs a torque detection signal. A sensor 5 and a controller 5 that inputs a detection signal of the torque sensor 2 and controls an output of the electric motor 4, and the controller 5 has an assist torque control means 21 that controls the assist torque in accordance with the torque detection signal; Steering amount integrating means 24 for calculating the integrated value of the steering amount at which the steering mechanism 3 operates as the steering amount integrated value M, and assist torque correction characteristics (assist torque set in advance according to the calculated steering amount integrated value M) It is assumed that the electric power steering apparatus 1 includes assist torque correction means 22 that corrects assist torque based on a correction map.

  Then, a setting device 50 for setting an assist torque correction characteristic at the time of manufacturing the electric power steering device 1, which is measured with a steering resistance measuring device 40 that operates the steering mechanism 3 to measure the steering resistance of the steering mechanism 3. And a setting device 54 for setting the assist torque correction characteristic based on the steering resistance.

  Further, it is a setting method for setting the assist torque correction characteristic at the time of manufacturing the electric power steering apparatus 1, and the steering resistance measurement step of measuring the steering resistance of the steering mechanism 3 by operating the steering mechanism 3 before being assembled to the vehicle. And an assist torque correction characteristic setting step for setting an assist torque correction characteristic based on the measured steering resistance.

  The method for manufacturing the electric power steering apparatus 1 includes an assembling step of assembling the electric motor 4 and the torque sensor 2 to the steering mechanism 3, and operating the steering mechanism 3 before the steering mechanism 3 is assembled to the vehicle. 3, an initial steering resistance measurement step for measuring the steering resistance and an assist torque correction characteristic setting step for setting the assist torque correction characteristic based on the measured steering resistance.

  Based on the above configuration, the assist torque correction characteristic is set based on the measured steering resistance, so that the steering resistance generated for each product of the electric power steering device 1 is mounted on the vehicle in response to variations in characteristics. Appropriate assist torque is maintained over the initial use, middle use, and late use of the electric power steering apparatus 1 that has been used. Thereby, it is avoided that the assist torque becomes excessive or insufficient depending on the product.

  In addition, the process of connecting the controller 5 to the electric motor 4 and the torque sensor 2 and assembling finally may be performed before the steering mechanism 3 is assembled to the vehicle, or may be performed after the steering mechanism 3 is assembled to the vehicle. .

  When the step of finally connecting the controller 5 to the electric motor 4 and the torque sensor 2 and assembling is performed before the steering mechanism 3 is assembled to the vehicle, the electric power provided with the controller 5 in which the assist torque correction characteristic is set. After the steering device 1 is shipped as a product, it is assembled to the vehicle.

  When the process of finally connecting the controller 5 to the electric motor 4 and the torque sensor 2 and assembling is performed after the steering mechanism 3 is assembled to the vehicle, the electric power steering apparatus 1 without the controller 5 is shipped as a product. Is done. Then, after the steering mechanism 3 is assembled to the vehicle, the controller 5 in which the assist torque correction characteristic is set is connected to the electric motor 4 and the torque sensor 2 and assembled.

  In the present embodiment, the steering operation in which the steering mechanism 3 is alternately operated in the left-right turning direction is repeatedly performed, and the steering mechanism 3 is operated before the running-in process is performed, so that the steering resistance of the steering mechanism 3 is initialized. An initial steering resistance measurement step for measuring as the steering resistance R1, a post-acclimation steering resistance measurement step for measuring the steering resistance of the steering mechanism 3 by operating the steering mechanism 3 after the running-in step is performed, and measuring the steering resistance R2 after the running-in step. An assist torque correction characteristic setting step of setting an assist torque correction characteristic based on the initial steering resistance R1 and the post-break-in steering resistance R2 is performed.

  Based on the above configuration, the steering resistance of the steering mechanism 3 is rapidly reduced by performing the break-in process after the electric power steering apparatus 1 is assembled. Therefore, the initial steering resistance R1 measured before and after the break-in process is performed. The assist torque correction characteristic can be accurately set based on the two points of the post-break-in steering resistance R2.

  The setter 54 may set the assist torque correction characteristic of the controller 5 according to the average value of the initial steering resistance R1 and the post-break-in steering resistance R2 that are measured.

  The setting device 54 may set the assist torque correction characteristic of the controller 5 in accordance with either the initial steering resistance R1 or the post-break-in steering resistance R2 that is measured.

  In the present embodiment, a defect determination step of determining a defect of a product based on the difference between the initial steering resistance R1 and the post-break-in steering resistance R2 is performed.

  Based on the above configuration, it is possible to prevent a defective product from being accurately determined based on the degree to which the steering resistance of the steering mechanism 3 is reduced in the course of the break-in process, and to prevent the defective product from being shipped.

  In this embodiment, the number of steering operations performed in the break-in process is set as an initial value of the steering amount integrated value M.

  Based on the above configuration, after the electric power steering device 1 is mounted on the vehicle, the steering amount integrated value M reflecting the number of steering operations performed in the break-in process is calculated, and the calculated steering amount integrated value M is calculated. Accordingly, the accuracy of correcting the assist torque is increased.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Torque sensor 3 Steering mechanism 4 Electric motor 5 Controller 21 Assist torque control means 22 Assist torque correction means 24 Steering amount integration means 25 Assist torque correction value calculation means 40 Steering resistance measurement apparatus 50 Setting apparatus 51 Input side Actuator 52 Steering force detector 53 Measuring instrument 54 Setting device 55 Input torque detector 57 Actuator on output side

Claims (5)

A steering mechanism that converts input torque into steering force and transmits it to the wheels;
An electric motor for applying assist torque to the steering mechanism;
A torque sensor that detects the input torque and outputs a torque detection signal;
A controller that inputs the detection signal of the torque sensor and controls the output of the electric motor,
The controller is
Assist torque control means for controlling the assist torque in accordance with the torque detection signal;
Steering amount integration means for calculating an integrated value of the steering amount for operating the steering mechanism as a steering amount integrated value;
An assist torque correction means for correcting the assist torque based on an assist torque correction characteristic set in advance according to the calculated steering amount integrated value,
An initial steering resistance measurement step of measuring the steering resistance of the steering mechanism by operating the steering mechanism;
An assist torque correction characteristic setting step of setting the assist torque correction characteristic according to the measured initial steering resistance. A break-in process in which a turning operation for alternately operating the steering mechanism in the left-right turning direction is repeatedly performed,
An initial steering resistance measuring step of measuring the steering resistance of the steering mechanism as an initial steering resistance by operating the steering mechanism before the running-in step is performed;
An initial steering resistance measurement step of operating the steering mechanism after the running-in step and measuring the steering resistance of the steering mechanism as a post-steering resistance;
The method for setting an electric power steering apparatus according to claim 1, wherein the assist torque correction characteristic setting step of setting an assist torque correction characteristic based on the initial steering resistance and the post-break-in steering resistance is performed.   The method for setting an electric power steering apparatus according to claim 2, wherein a defect determination step of determining a defect of a product based on a difference between the initial steering resistance and the post-break-in steering resistance is performed.   The method for setting an electric power steering apparatus according to claim 2 or 3, wherein the number of times of the steering operation performed in the break-in process is set as an initial value of the steering amount integrated value. A steering mechanism that converts input torque into steering force and transmits it to the wheels;
An electric motor for applying assist torque to the steering mechanism;
A torque sensor that detects the input torque and outputs a torque detection signal;
A controller that inputs the detection signal of the torque sensor and controls the output of the electric motor,
The controller is
Assist torque control means for controlling the assist torque in accordance with the torque detection signal;
Steering amount integration means for calculating an integrated value of the steering amount for operating the steering mechanism as a steering amount integrated value;
An assist torque correction means for correcting the assist torque based on an assist torque correction characteristic set in advance according to the calculated steering amount integrated value,
An assembly step of assembling the electric motor and the torque sensor to the steering mechanism;
An initial steering resistance measurement step of measuring the steering resistance of the steering mechanism by operating the steering mechanism before the steering mechanism is assembled to a vehicle;
And an assist torque correction characteristic setting step of setting the assist torque correction characteristic based on the measured steering resistance.

Images