Electric power steering device and control method for electric power steering device

Abstract

To provide an electric power steering device and a control method for the electric power steering device that are able to improve steering feeling of a steering wheel.SOLUTION: An electric power steering device 1 includes: a shaft 2 that transmits an operation of rotating a steering wheel 3 of a vehicle to a steering mechanism S; a motor 4 capable of applying assist torque; a first angle detection unit 5 and a second angle detection unit 6 that detect a first angle θs and a second angle θp, respectively, that are rotational angles at two points of the shaft 2; and a controller 7 that controls the motor 4; wherein the controller 7 includes: a target relative angle calculation unit 72 that obtains a target relative angle θref, which is a difference between target rotation angles at two points of the shaft 2, based on the first angle θs detected by the first angle detection unit 5; and a control unit 76 that controls the motor 4, based on the target relative angle θref and a relative angle θε, which is a difference between the first angle θs and the second angle θ p.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric power steering device and a control method for an electric power steering device. [Background technology]

[0002] A conventional electric power steering device includes, for example, an input shaft connected to the steering wheel of the vehicle, an output shaft connected to a pinion that meshes with a rack shaft that drives the vehicle wheels, a torsion bar connecting the input shaft and the output shaft, a torque sensor that detects the torsion of the torsion bar and thereby detects the steering torque applied by the driver to operate the steering wheel, a motor that rotates and drives a worm that meshes with a worm wheel provided on the outer periphery of the output shaft, and a controller that calculates the amount of current to be supplied to the motor using a map from the steering torque detected by the torque sensor and supplies the calculated amount of current to the motor (see, for example, Patent Document 1).

[0003] In the electric power steering device configured in this manner, the motor outputs an assist torque in accordance with the steering torque when the driver operates the steering wheel, so that steering can be assisted without impairing the driver's steering feel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-199968 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, conventional electric power steering devices and control methods for electric power steering devices detect the steering torque to grasp the amount of steering wheel operation by the driver, and cause the motor to output an assist torque corresponding to the steering torque.

[0006] However, the signal output by the torque sensor that detects the steering torque contains bias due to the installation condition of the torque sensor, temperature changes, or deterioration over time. For this reason, a dead band of a certain width including 0 is set for the steering torque in the map that calculates the amount of current to be applied to the motor from the steering torque detected by the torque sensor.

[0007] When the steering torque detected by the torque sensor is close to zero, the steering torque falls within the dead band and the motor cannot provide assist torque. Therefore, when the driver changes steering direction while turning the steering wheel, the steering torque changes to cross zero, causing the motor to suddenly output assist torque after the change of direction. As such, conventional electric power steering devices and control methods for electric power steering devices have problems such as giving the driver a heavy steering feel when turning the steering wheel or giving the impression that the steering wheel operation suddenly becomes lighter, leaving room for improvement in steering feel.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an electric power steering system and a control method for an electric power steering system that can improve the steering feel of the steering wheel. [Means for solving the problem]

[0009] In order to achieve the above object, the electric power steering device in the problem-solving means of the present invention comprises: a shaft that transmits the rotational operation of a vehicle's steering wheel to a steering mechanism connected to the vehicle's wheels; a motor that can apply an assist torque to the steering mechanism to assist in the operation of the steering wheel; a first angle detection unit that detects a first angle, which is the rotational angle at one of two locations on the shaft that is located closer to the steering wheel; a second angle detection unit that detects a second angle, which is the rotational angle at one of the two locations that is located closer to the steering mechanism than the location where the first angle detection unit detects the first angle; and a controller that controls the motor, wherein the controller comprises a target relative angle calculation unit that calculates a target relative angle, which is the difference between the target rotational angles of the two locations on the shaft, based on the first angle detected by the first angle detection unit; and a control unit that controls the motor based on the target relative angle and the relative angle that is the difference between the first angle and the second angle.

[0010] In the electric power steering device configured in this manner, the motor is controlled by processing only the angle signal without using a torque sensor, so there is no need to set a dead zone for the first angle, which is a control parameter for controlling the motor.

[0011] The electric power steering device may further be configured so that the controller has a smoothing processing unit that smoothes the first angle, and the control unit calculates the difference between the second angle and the smoothed first angle to determine the relative angle. With an electric power steering device configured in this way, the relative angle used for control can be determined with high accuracy even if the shaft does not have a torsion bar, so the torsion bar can be removed from the shaft to reduce the weight and cost of the electric power steering device.

[0012] The controller in the electric power steering device may also be equipped with a relative angle command filter that performs filtering to remove frequency components superimposed by steering from the target relative angle. With an electric power steering device configured in this way, by processing the target relative angle and providing a corrected target relative angle to the control unit, overshooting and undershooting of the relative angle, which is the output of the system, with respect to the target relative angle is suppressed, and the relative angle can be made to follow the target relative angle with good responsiveness, providing the driver with an even better steering feel.

[0013] In addition, the control method for an electric power steering device includes a first angle detection step of detecting a first angle, which is the rotation angle at one of two locations on a shaft that transmits the rotational operation of the vehicle's steering wheel to a steering mechanism connected to the vehicle's wheels, located closer to the steering wheel; a second angle detection step of detecting a second angle, which is the rotation angle at one of the two locations that is located closer to the steering mechanism than the location where the first angle is detected in the first angle detection step; a target relative angle calculation step of calculating a target relative angle, which is the difference between the target rotation angles of the two locations on the shaft, based on the first angle; and a control step of controlling a motor that can apply an assist torque to the steering mechanism to assist in operating the steering wheel, based on the target relative angle and the relative angle that is the difference between the first angle and the second angle.

[0014] According to the control method for an electric power steering device configured in this manner, the motor is controlled by processing only the angle signal without using a torque sensor, so there is no need to set a dead zone for the first angle, which is a control parameter, when controlling the motor. [Effects of the Invention]

[0015] As described above, the electric power steering device and the control method for the electric power steering device of the present invention can improve the steering feel of the steering wheel. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a diagram illustrating an electric power steering device according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of a controller in the electric power steering device according to the embodiment. [Figure 3] FIG. 10 is a diagram showing a map for determining a target relative angle from a first angle. [Figure 4] 3 is a flowchart showing an example of a processing procedure of the electric power steering device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described below based on the embodiments shown in the drawings. As shown in Fig. 1, an electric power steering device 1 of one embodiment is mounted on a vehicle (not shown), and is configured to include a shaft 2 that transmits the rotational operation of a steering wheel 3 of the vehicle to a steering mechanism S connected to wheels W of the vehicle, a motor 4 that can apply an assist torque to the steering mechanism S to assist the operation of the steering wheel 3, an angle sensor 5 and a second angle detection unit 6 as a first angle detection unit that detect the rotational angles of two positions on the shaft 2, and a controller 7 that controls the motor 4.

[0018] Below, a detailed description will be given of each part of the electric power steering device 1. First, a steering wheel 3 is rotatable about a shaft 2 relative to the vehicle and is installed inside the vehicle compartment (not shown).

[0019] The steering mechanism S includes a rack shaft 8 that is installed so as to be able to move back and forth laterally relative to the vehicle, and tie rods 9 that connect each end of the rack shaft 8 to knuckle arms (not shown) that rotatably hold wheels W located on the left and right sides of the front of the vehicle.

[0020] One end of the shaft 2 is connected to the center of rotation of the steering wheel 3, and the other end is provided on its outer periphery with a pinion gear 11 that meshes with a rack 8a of the rack shaft 8. When the steering wheel 3 is steered by the driver of the vehicle, the shaft 2 rotates about its axis and transmits the driver's steering torque to the rack shaft 8 via the pinion gear 11, driving the rack shaft 8 in the lateral direction of the vehicle. The rack shaft 8 is driven in the lateral direction of the vehicle, in the opposite direction to the rotational direction of the steering wheel 3, and applies a steering angle to the wheels W so that the vehicle travels in the steering direction of the steering wheel 3, depending on the amount of steering of the steering wheel 3 by the driver.

[0021] Although not shown, a universal joint is provided in the middle of the shaft 2 to prevent the shaft 2 from occupying space in an engine compartment or the like. A worm wheel 12 is provided on the outer periphery of the other end of the shaft 2, on the steering mechanism S side. A worm 13 is meshed with the worm wheel 12, which is connected to a rotor (not shown) of the motor 4. Therefore, when the motor 4 is energized to drive the worm 13, the power of the motor 4 can be transmitted to the shaft 2 via the worm wheel 12, and the motor 4 can apply to the shaft 2 an assist torque that assists the driver in operating the steering wheel 3. In this embodiment, the motor 4 includes an armature having a three-phase coil (not shown) and a rotor (not shown), and is equipped with an angle sensor 4a that detects the mechanical angle of the rotor because the mechanical angle of the rotor is necessary for driving.

[0022] The angle sensor 5 as a first angle detection unit detects a first angle θs, which is a rotation angle in the circumferential direction at an arbitrary position on the shaft 2 closer to the steering wheel 3 than the worm wheel 12. The angle sensor 5 may be, for example, an angle sensor such as a rotary encoder, a resolver, or a potentiometer. The angle sensor 5 detects the rotation angle of the shaft 2 at the position and inputs it to the controller 7 as the first angle θs.

[0023] In the electric power steering device 1 of this embodiment, the second angle detection unit 6 is made up of an angle sensor 4a that is attached to the motor 4 and is used to detect the position of the rotor for controlling the motor 4, and an angle calculation unit 71 that calculates a second angle θp, which is the rotation angle at the installation position of the worm wheel 12 on the shaft 2, from the mechanical angle θm of the rotor in the motor 4 detected by the angle sensor 4a. In this embodiment, the angle calculation unit 71 is integrated into the controller 7, but a calculation processing device that calculates the second angle θp from the mechanical angle of the rotor may be provided separately from the controller 7.

[0024] In this manner, the angle sensor 5 serving as the first angle detection unit and the second angle detection unit 6 detect the rotation angles of the shaft 2 at two positions spaced apart from each other. The angle sensor 5 serving as the first angle detection unit detects the rotation angle of one of the two positions on the shaft 2 located closer to the steering wheel 3 as the first angle θs, and the second angle detection unit 6 detects the rotation angle of one of the two positions on the shaft 2 located closer to the steering mechanism S than the position where the angle sensor 5 detects the first angle as the second angle θp. The first angle θs is the rotation angle at the position on the steering wheel 3 side of the shaft 2, and therefore indicates a value closer to the steering angle of the steering wheel 3 of the vehicle driver than the second angle θp. The first angle θs is a value used to calculate a target relative angle θref, which will be described later. It is preferable that the first angle detection unit can detect a rotation angle as close as possible to the steering angle of the steering wheel 3. Therefore, the closer the position on the shaft 2 where the rotation angle is detected by the angle sensor 5 is to the steering wheel 3, the more preferable. In reality, the shaft 2 is configured to include a universal joint between the worm wheel 12 and the steering wheel 3, so the angle sensor 5 may detect the rotation angle of a point on the shaft 2 between the worm wheel 12 and the universal joint and near the universal joint as the first angle θs. Furthermore, the relative angle θε, which is the difference between the first angle θs and the second angle θp, is used to control the motor 4, and the value of the relative angle θε tends to be larger as the axial distance between the point on the shaft 2 where the first angle θs is detected and the point on the shaft 2 where the second angle θp is detected is as long as possible, so that the accuracy of the value of the relative angle θε can be improved even if the resolution of the angle sensors 4a and 5 is low.

[0025] The second angle detection unit 6 may be an angle sensor that directly detects the rotation angle at a location located closer to the steering mechanism S than the location where the first angle θs of the first angle detection unit of the shaft 2 is detected, or may be an angle sensor that detects the displacement of the rack shaft 8 using a displacement sensor and detects the second angle θp from the displacement.

[0026] As shown in FIG. 2, the controller 7 includes the angle calculation unit 71 described above, a target relative angle calculation unit 72 that calculates the target relative angle θref based on the first angle θs detected by the angle sensor 5, and a corrected target relative angle θref by filtering the target relative angle θref. * a relative angle command filter 73 that outputs the first angle θs; a smoothing processing unit 74 that smooths the first angle θs; a relative angle calculation unit 75 that calculates the relative angle θε, which is the difference between the first angle θs processed by the smoothing processing unit 74 and the second angle θp; and a corrected target relative angle θref * and a control unit 76 that controls the motor 4 based on the relative angle θε.

[0027] The angle calculation unit 71 calculates the second angle θp by θp=θm / Rw from the mechanical angle θm of the rotor detected by the angle sensor 4a attached to the motor 4 and the reduction ratio Rw between the worm wheel 12 and the worm 13. Since the reduction ratio Rw is a design value and is known in advance, the angle calculation unit 71 can calculate the second angle θp from the mechanical angle θm detected by the angle sensor 4a. The angle calculation unit 71 then inputs the calculated second angle θp to the relative angle calculation unit 75.

[0028] The target relative angle calculation unit 72 obtains a target relative angle θref, which is the difference between the target rotation angles of two points on the shaft 2, by map calculation from the first angle θs detected by the angle sensor 5. The map used by the target relative angle calculation unit 72 defines the relationship between the first angle θs and the target relative angle θref, as shown in Fig. 3, and three maps are prepared in advance according to the vehicle speed classification.

[0029] The three maps are for low speed, which is referred to when the vehicle speed is low, for medium speed, which is referred to when the vehicle speed is medium, and for high speed, which is referred to when the vehicle speed is high, and target relative angle calculation unit 72 monitors the vehicle speed and determines the target relative angle θref by referring to a map appropriate for the vehicle speed when determining the target relative angle θref. In order for target relative angle calculation unit 72 to monitor the vehicle speed, for example, controller 7 may obtain a vehicle speed pulse signal detected by the vehicle from the vehicle side via a CAN (Controller Area Network) bus or the like, but a vehicle speed sensor may also be provided to independently detect the vehicle speed and use the detected speed in the calculation of target relative angle θref.

[0030] The map is created to suit the position of the shaft 2 where the angle sensor 5 serving as the first angle detection unit detects the first angle θs and the position of the shaft 2 where the second angle detection unit 6 detects the second angle θp. The map also shows the relationship between the first angle θs and the relative angles θε at two locations on the shaft 2 when the motor 4 applies an ideal assist torque to the shaft 2 in response to the steering of the steering wheel 3 by the driver. In other words, the map shows the relationship between the first angle θs and the target relative angle θref as the ideal relative angle. In other words, if the difference between the rotation angles of the shaft 2 at two locations when the first angle θs is detected is the target relative angle θref obtained by map calculation, then the motor 4 is outputting an ideal assist torque in response to the steering of the steering wheel 3 by the driver.

[0031] Then, target relative angle calculation unit 72 selects a map according to the low, medium, or high vehicle speed category, and refers to the selected map to perform map calculations using first angle θs as a parameter to determine target relative angle θref. Note that the speeds that define the boundaries between vehicle speed categories can be set arbitrarily, and the number of speed categories may be any number other than three, and a map is created for each category.

[0032] The relative angle command filter 73 filters the target relative angle θref to obtain a corrected target relative angle θref *Specifically, the relative angle command filter 73 is a filter for setting the tracking ability of the relative angle θε, which is the difference between the first angle θs and the second angle θp, which is the output of the system, to the target relative angle θref, taking into consideration the frequency response characteristics of the entire system including the controller 7 and the motor 4, which is the object of control, and is, for example, a filter for removing the frequency at which the driver steers from the signal of the target relative angle θref output by the target relative angle calculation unit 72. More specifically, it is designed from the transfer function of the entire system so that the relative angle θε, which is the output of the system, tracks the target relative angle θref with good responsiveness. Note that the frequency at which the driver steers is several Hz. By providing this relative angle command filter 73, the target relative angle θref is processed to set the corrected target relative angle θref * to the control unit 76, overshooting and undershooting of the relative angle θε with respect to the target relative angle θref is suppressed, and the relative angle θε follows the target relative angle θref with good responsiveness. In this way, when the relative angle command filter 73 is provided, the responsiveness and followability of the relative angle θε output by the system through the control of the motor 4 by the controller 7 are improved with respect to the target relative angle θref, but the relative angle command filter 73 may be omitted.

[0033] The smoothing unit 74 is a filter that smoothes the first angle θs and performs moving average processing or low-pass filtering of the first angle θs. In the electric power steering device 1 of this embodiment, the shaft 2 does not have a torsion bar. Compared to conventional electric power steering devices, the degree of torsion of the shaft 2 is small. If the resolution of the angle sensor 5 that detects the first angle θs is low, the value of the first angle θs becomes discontinuous. On the other hand, in this embodiment, the angle sensor 4a used to detect the second angle θp is a high-resolution sensor for detecting the mechanical angle of the motor 4. Therefore, if the relative angle θε is calculated by taking the difference between the first angle θs and the second angle θp, the value of the relative angle θε may change suddenly or slowly, making it difficult to accurately determine the value of the relative angle θε. The relative angle θε is calculated by a relative angle calculation unit 75 that calculates the difference between the first angle θs and the second angle θp processed by the smoothing unit 74. The result is input to the control unit 76 and used to control the motor 4. The smoothing processing unit 74 performs moving average processing or low-pass filter processing on the first angle θs, and therefore can mitigate sudden changes in the first angle θs and determine an accurate value for the first angle θs, even if the shaft 2 does not include a torsion bar and the value of the relative angle θε tends to be small, and in addition the resolution of the angle sensor 5 is low. Therefore, by providing the smoothing processing unit 74, the relative angle calculation unit 75 can determine the relative angle θε with high accuracy, even if the shaft 2 does not include a torsion bar and the value of the relative angle θε tends to be small, and in addition the resolution of the angle sensor 5 is low.

[0034] Note that the smoothing processing unit 74 may process the relative angle θε calculated by the relative angle calculation unit 75. Even if the smoothing processing unit 74 performs moving average processing and low-pass filter processing on the relative angle θε, which is the difference between the first angle θs and the second angle θp, the relative angle calculation unit 75 can calculate the relative angle θε with high accuracy, similar to when only the first angle θs is processed.

[0035] Next, the control unit 76 calculates the corrected target relative angle θref *and the relative angle θε to control the motor 4. Specifically, the control unit 76 includes an observer 76a that estimates the state quantities and disturbances that are the system outputs of the electric power steering device 1, and a feedback controller 76b that feeds back the state quantities and disturbances estimated by the observer 76a to calculate the corrected target relative angle θref * a current amount calculation unit 76c that calculates the amount of current to be given to the motor 4 from the value output by the adder 76b and generates a current command I; and a driver circuit 76d that, upon receiving the current command from the current amount calculation unit 76c, gives the motor 4 a current amount instructed by the current command I.

[0036] The observer 76a estimates the relative angle, which is the output of the system of the electric power steering device 1, and the disturbance superimposed on the relative angle, based on the current command I calculated by the current amount calculation unit 76c and the relative angle θε calculated by the relative angle calculation unit 75. The adder 76b calculates the relative angle and the disturbance calculated by the observer 76a as the corrected target relative angle θref * In this way, by providing the observer 76a, the control unit 76 can perform state feedback control, which stabilizes the system of the electric power steering device 1 and allows the convergence characteristics to be determined arbitrarily.

[0037] The current amount calculation unit 76c receives the calculation result of the adder 76b and calculates a current command I. The calculation result of the adder 76b is a signal indicating a relative angle, and the current amount calculation unit 76c, for example, refers to a map indicating the relationship between the relative angle and the amount of current to be applied to the motor 4, calculates the amount of current from the calculation result of the adder 76b, and generates a current command I indicating that amount of current.

[0038] The driver circuit 76d is a drive circuit that PWM drives the motor 4 based on the current command I, and includes a current sensor (not shown) that detects the current flowing through the motor 4, and supplies the motor 4 with an amount of current according to the current command I through current feedback. The driver circuit 76d also obtains the mechanical angle of the motor 4 from the angle sensor 4a of the motor 4, and drives the motor 4 by energizing three-phase coils (not shown) at energization timing appropriate for the mechanical angle of the motor 4.

[0039] In order to stabilize the system of the electric power steering device 1, the control unit 76 is provided with the observer 76a as described above. However, instead of the observer 76a and the adder 76b, the motor 4 may be controlled using a controller that feeds back the relative angle θε, performs PI compensation or PDI compensation, and generates a command indicating the final relative angle.

[0040] As shown in FIG. 4, the electric power steering device 1 configured as described above detects a first angle θs using the angle sensor 5 while the vehicle V is traveling (first angle detection step), and also detects the first angle θs and the mechanical angle θm of the motor 4 using the angle sensor 4a (step S1). Next, the controller 7 calculates a second angle θp from the mechanical angle θm (step S2). In this embodiment, the second angle detection step is configured by detecting the mechanical angle θm and calculating the second angle θp from the mechanical angle θm. However, if an angle sensor that directly detects the second angle θp is used, the second angle detection step may be configured by only detecting the second angle θp using the angle sensor. Furthermore, the controller 7 smoothes the first angle θs (step S3) and calculates the difference between the first angle θs and the second angle θp to determine the relative angle θε (step S4). Then, the controller 7 proceeds to step S5, where it performs map calculations by referring to a map selected according to the vehicle speed to determine a target relative angle θref from the first angle θs (target relative angle calculation step).

[0041] Next, the controller 7 filters the target relative angle θref to obtain a corrected target relative angle θref *(Step S6), and the corrected target relative angle θref * and the relative angle θε, estimates the state quantity and disturbance, feeds back the state quantity and disturbance, and generates a current command I that indicates the amount of current to be supplied to the motor 4 (step S7). The controller 7 supplies current to the motor 4 in accordance with the current command I to control the motor 4 (step S8). The electric power steering device 1 controls the motor 4 by repeatedly performing the processes from step S1 to step S8. The processes from step S6 to step S8 constitute a control step that controls the motor 4 based on the target relative angle θref and the relative angle θε that is the difference between the first angle θs and the second angle θp. The steps S2 to S4 for obtaining the second angle θp and the relative angle θε are carried out using the corrected target relative angle θref * and the relative angle θε, and can be processed independently from steps S5 and S6 that process the first angle θs, so the order of steps S5 and S6 may be reversed.

[0042] Although not shown, the hardware resources of the controller 7 in the electric power steering device 1, excluding the driver circuit 76d, may specifically include, for example, an interface for receiving signals output by the angle sensors 4a and 5, a storage device such as a ROM (Read Only Memory) that stores a program used for processing required to receive the first angle θs and the mechanical angle θm of the motor 4 and control the motor 4, an arithmetic unit such as a CPU (Central Processing Unit) that executes processing based on the program, and a storage device such as a RAM (Random Access Memory) that provides a storage area for the CPU, and each unit in the controller 7 can be realized by the CPU executing the program. Also, the controller 7 may be realized by analog electronic circuits instead of by the CPU executing the program.

[0043] In electric power steering device 1 configured as described above, when the driver turns steering wheel 3, shaft 2 rotates in response to the steering of steering wheel 3, and first angle θs and second angle θp are detected as rotation angles of two positions on shaft 2. Then, electric power steering device 1 calculates a target relative angle θref from the first angle θs detected by angle sensor 5 serving as a first angle detection unit, calculates a relative angle θε which is the difference between the first angle θs and the second angle θp, and controls motor 4 based on the target relative angle θref and the relative angle θε. In this way, electric power steering device 1 does not use a torque sensor whose output signal contains bias due to its installation condition, temperature change, or aging, and controls motor 4 by processing only signals from angle sensors 4a and 5 which are free from such problems. Therefore, there is no need to set a dead band for the first angle θs, which is a control parameter for controlling motor 4.

[0044] As described above, the electric power steering device 1 of this embodiment includes a shaft 2 that transmits the rotational operation of the vehicle's steering wheel 3 to the steering mechanism S connected to the vehicle's wheels W, a motor 4 that can apply an assist torque to the steering mechanism S to assist in the operation of the steering wheel 3, an angle sensor (first angle detection unit) 5 that detects a first angle θs, which is the rotational angle at one of two locations on the shaft 2 that is located closer to the steering wheel 3, a second angle detection unit 6 that detects a second angle θp, which is the rotational angle at one of the two locations that is located closer to the steering mechanism S than the location where the angle sensor (first angle detection unit) 5 detects the first angle θs, and a controller 7 that controls the motor 4. The controller 7 includes a target relative angle calculation unit 72 that calculates a target relative angle θref, which is the difference between the target rotation angles of the two locations on the shaft 2, based on the first angle θs detected by the angle sensor (first angle detection unit) 5, and a control unit 76 that controls the motor 4 based on the target relative angle θref and the relative angle θε, which is the difference between the first angle θs and the second angle θp.

[0045] The electric power steering device 1 configured in this manner does not use a torque sensor, but processes only the angle signal to control the motor 4, and therefore there is no need to set a dead zone for the first angle θs, which is a control parameter, when controlling the motor 4. Therefore, according to the electric power steering device 1 of this embodiment, since it is not necessary to set a dead zone for the control parameter, even when the driver changes the steering direction while steering the steering wheel 3, the driver is not given a heavy steering feel or the impression that the operation of the steering wheel 3 suddenly becomes lighter, and the steering feel of the steering wheel 3 can be improved.

[0046] In addition, the control method of the electric power steering device 1 of this embodiment includes a first angle detection step of detecting a first angle θs, which is the rotation angle at one of two locations on the shaft 2 that transmits the rotational operation of the vehicle's steering wheel 3 to the steering mechanism S connected to the vehicle's wheels W, located closer to the steering wheel; a second angle detection step of detecting a second angle θp, which is the rotation angle at one of the two locations that is closer to the steering mechanism than the location where the first angle θs is detected in the first angle detection step; a target relative angle calculation step of calculating a target relative angle θref, which is the difference between the target rotation angles at the two locations on the shaft 2, based on the first angle θs; and a control step of controlling the motor 4, which can apply an assist torque to the steering mechanism S to assist the operation of the steering wheel 3, based on the target relative angle θref and the relative angle θε, which is the difference between the first angle θs and the second angle θp.

[0047] According to the control method for the electric power steering device 1 configured in this manner, the motor 4 is controlled by processing only the angle signal without using a torque sensor, and therefore there is no need to set a dead zone for the first angle θs, which is a control parameter, when controlling the motor 4. Therefore, according to the control method for the electric power steering device 1 of this embodiment, since it is not necessary to set a dead zone for the control parameter, even when the driver changes the steering direction while steering the steering wheel 3, the driver is not given a heavy steering feel or the impression that the operation of the steering wheel 3 suddenly becomes lighter, and the steering feel of the steering wheel 3 can be improved.

[0048] Furthermore, in the electric power steering device 1 of this embodiment, the controller 7 has a smoothing processing unit 74 that smoothes the first angle θs, and the control unit 76 calculates the difference between the second angle θp and the smoothed first angle θs to determine the relative angle θε. According to the electric power steering device 1 of this embodiment, the first angle θs is smoothed, so that the value of the relative angle θε is small because the shaft 2 does not have a torsion bar, and the relative angle θε can be determined with high accuracy even if the resolution of the angle sensor (first angle detection unit) 5 is low. Therefore, according to the electric power steering device 1 of this embodiment, the relative angle θε used for control can be determined with high accuracy even if the shaft 2 does not have a torsion bar, so the torsion bar can be removed from the shaft 2 to reduce the weight and cost of the electric power steering device 1.

[0049] Furthermore, the controller 7 in the electric power steering device 1 of this embodiment is provided with a relative angle command filter 73 that performs filtering to remove frequency components superimposed by steering from the target relative angle θref. According to the electric power steering device 1 configured in this manner, the target relative angle θref is processed to obtain a corrected target relative angle θref * to the control unit 76, overshooting and undershooting of the relative angle θε, which is the output of the system, with respect to the target relative angle θref is suppressed, and the relative angle θε can be made to follow the target relative angle θref with good responsiveness, thereby providing the driver with an even better steering feel.

[0050] In the electric power steering device 1 described above, the motor 4 is installed to drive the worm 13 meshing with the worm wheel 12 attached to the outer periphery of the shaft 2. However, although not shown, instead of the motor 4 directly applying assist torque to the shaft 2, the motor 4 may be installed so that the power of the motor 4 is transmitted via a reducer to an assist pinion gear meshing with the rack 8a of the rack shaft 8, and the assist torque of the motor 4 may be transmitted to the shaft 2 via the rack shaft 8. If the installation of the reducer is not necessary, it can be omitted. However, the reducer may be configured, for example, with a worm driven by the motor 4 and a worm wheel meshing with the worm and connected to the pinion gear.

[0051] In this case, the angle calculation unit 71 in the controller 7 determines the second angle θp as the rotation angle of the other end of the shaft 2 where the pinion gear 11 is installed, by calculating θp=(Rp2×θm) / (Rp1×Rg) from the mechanical angle θm of the rotor detected by the angle sensor 4a attached to the motor 4, the reduction ratio Rp1 between the pinion gear 11 attached to the other end of the shaft 2 and the rack 8a, the reduction ratio Rp2 between the assist pinion gear and the rack 8a, and the reduction ratio Rg of the reducer. Because the reduction ratios Rp1, Rp2, and Rg are design values ​​and known in advance, the angle calculation unit 71 can determine the second angle θp from the mechanical angle θm detected by the angle sensor 4a. Furthermore, the map referenced by the target relative angle calculation unit 72 in the controller 7 may be created so as to be suitable for the position of the axis 2 at which the angle sensor 5 serving as the first angle detection unit detects the first angle θs and the position of the axis 2 at which the second angle detection unit 6 detects the second angle θp. Even if the installation position of the motor 4 differs in this way, the electric power steering device controls the motor 4 by processing only the angle signal without using a torque sensor, and therefore there is no need to set a dead zone for the first angle θs, which is a control parameter for controlling the motor 4, thereby improving the steering feel.

[0052] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims. [Explanation of symbols]

[0053] 1 electric power steering device, 2 shaft, 3 steering wheel, 4 motor, 5 angle sensor (first angle detection unit), 6 second angle detection unit, 7 controller, 72 target relative angle calculation unit, 73 relative angle command filter, 74 smoothing processing unit, 76 control unit

Claims

1. a shaft for transmitting the rotation of a steering wheel of a vehicle to a steering mechanism connected to wheels of the vehicle; a motor capable of applying an assist torque to the steering mechanism to assist in the operation of the steering wheel; a first angle detection unit that detects a first angle, which is a rotation angle at one of the two positions of the shaft that is located on the steering wheel side; a second angle detection unit that detects a second angle, which is a rotation angle at a location that is located closer to the steering mechanism than a location where the first angle detection unit detects the first angle, of the two locations; a controller for controlling the motor; The controller a target relative angle calculation unit that calculates a target relative angle that is a difference between target rotation angles of the two locations of the shaft based on the first angle detected by the first angle detection unit; a control unit that controls the motor based on the target relative angle and a relative angle that is a difference between the first angle and the second angle; An electric power steering device characterized by:

2. The controller a smoothing processing unit that smoothes the first angle; The control unit The relative angle is calculated by calculating the difference between the second angle and the smoothed first angle.

2. The electric power steering device according to claim 1.

3. The controller a relative angle command filter that performs filtering to remove frequency components superimposed by steering from the target relative angle; 3. The electric power steering device according to claim 1 or 2.

4. a first angle detection step of detecting a first angle, which is a rotation angle at a position located on the steering wheel side of one of two positions of a shaft that transmits a rotation operation of a steering wheel of a vehicle to a steering mechanism connected to wheels of the vehicle; a second angle detection step of detecting a second angle, which is a rotation angle at a location of the two locations that is located closer to the steering mechanism than the location where the first angle is detected in the first angle detection step; a target relative angle calculation step of calculating a target relative angle that is a difference between target rotation angles of the two locations of the shaft based on the first angle; and a control step of controlling a motor capable of applying an assist torque to the steering mechanism to assist in operation of the steering wheel, based on the target relative angle and a relative angle that is a difference between the first angle and the second angle. A control method for an electric power steering device comprising:

Images