Steering system, control method thereof, and program

Abstract

To reduce a deterioration in steering feeling occurring due to the structure of an electric power steering, in a configuration in which the electric power steering is combined with a hydraulic power steering.SOLUTION: A steering system is equipped with: a steering mechanism including a steering shaft; a turning mechanism that turns a turning wheel in tandem with rotation of the steering shaft; a power steering device provided in the turning mechanism; an electric power steering device provided in the steering mechanism; and a control part that controls operation of the electric power steering device. The control part derives a compensation value of viscous friction caused by parts constituting the electric power steering device, and outputs a control value for controlling the parts by using the compensation value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a steering system, a control method thereof, and a program. [Background technology]

[0002] In recent years, various technologies have been developed for power steering devices in order to realize functions such as advanced driver-assistance systems (ADAS) and autonomous driving (AD) in vehicles. For example, consider implementing ADAS and AD in buses and trucks. Most mass-produced buses and trucks are equipped with hydraulic power steering (HPS). For such vehicles, it is conceivable to make them compatible with autonomous driving by retaining the existing HPS and installing a relatively low-output electric power steering (EPS) in the upper part of the power steering system. In such a configuration, for example, a column EPS can be used.

[0003] For example, Patent Document 1 discloses a configuration in which an EPS and an HPS are combined, and the torsion settings of the torsion bar are made different on the EPS side and the HPS side, thereby allowing the EPS to operate in the event of a failure of the HPS.

[0004] Furthermore, Patent Document 2 discloses a configuration that combines an EPS and an HPS, assuming vehicles such as large trucks and buses. In this configuration, it is described that the EPS operates as a steering actuator when a lane keeping assist function is activated, and cooperates with the HPS to provide steering assist during normal operation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6222427 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-264622 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a column EPS is installed above the HPS, problems with steering arise, such as heavier steering and poorer steering return, compared to a conventional HPS configuration with a manual column, due to friction from the reducer and motor that make up the column EPS.

[0007] Although the above-mentioned prior art documents disclose a configuration in which an EPS and an HPS are combined, they do not sufficiently consider the deterioration of steering performance that may result from the combination of these.

[0008] In view of the above problems, the present invention aims to reduce the deterioration of steering feel caused by the structure of electric power steering in a configuration in which electric power steering and power steering of a steering mechanism are combined. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following configuration: That is, a steering system comprising: a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a control unit that controls the operation of the electric power steering device; Equipped with The control unit derives a compensation value for viscous friction generated by a component of the electric power steering device, and uses the compensation value to output a control value for controlling the component.

[0010] Another aspect of the present invention has the following configuration: a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; A method for controlling a steering system comprising: A compensation value for viscous friction generated by a component of the electric power steering device is derived, and a control value for controlling the component is output using the compensation value.

[0011] Another aspect of the present invention has the following configuration: a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a computer for controlling a steering system comprising: A program is provided for causing the electric power steering device to function as a control unit that derives a compensation value for viscous friction generated by components that constitute the device and uses the compensation value to output a control value for controlling the components. [Effects of the Invention]

[0012] According to the present invention, in a configuration in which an electric power steering system and a power steering system of a steering mechanism are combined, it is possible to reduce deterioration in steering performance caused by the structure of the electric power steering system. [Brief explanation of the drawings]

[0013] [Figure 1A] 1 is a schematic diagram showing an example of the general configuration of a hydraulic power steering device; [Figure 1B] 1 is a schematic diagram showing an example of the general configuration of a steering system having the functions of both a hydraulic power steering device and an electric power steering device. [Figure 2] 1A to 1C are graphs illustrating various types of friction according to an embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing an example of a functional configuration according to an embodiment of the present invention. [Figure 4] FIG. 2 is a block diagram showing a schematic configuration of a viscous friction compensation function according to an embodiment of the present invention. [Figure 5] FIG. 4 is a graph showing an example of a conversion table of a viscous friction compensation function according to an embodiment of the present invention. [Figure 6] FIG. 10 is a graph illustrating verification results according to an embodiment of the present invention. [Figure 7] FIG. 10 is a graph illustrating verification results according to an embodiment of the present invention. [Figure 8] FIG. 4 is a graph illustrating an example of operating torque by a manual column. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that the embodiment described below is one embodiment for explaining the present invention and is not intended to be interpreted as limiting the present invention. Furthermore, not all of the configurations described in each embodiment are necessarily essential configurations for solving the problems of the present invention. Furthermore, in each drawing, the same components are assigned the same reference numerals to indicate correspondence.

[0015] First Embodiment A first embodiment of the present invention will be described below. Note that the configuration of the steering system shown below is an example, and the present invention is applicable to steering systems in general, including steering devices.

[0016] [Configuration overview] Before describing the configuration of the steering system of the present invention, the configuration of a conventional hydraulic power steering device will be described for comparison. As described above, it is assumed that vehicles such as buses and trucks are equipped with hydraulic power steering devices (HPS).

[0017] FIG. 1A is a diagram showing an example of the schematic configuration of a hydraulic power steering device 100. The steering wheel 1 is a steerable wheel used by a driver to perform steering operation. The steering shaft 2 of the steering wheel 1 includes a manual column and is connected to a rotary control valve 7 via a universal joint 4a, an intermediate shaft 5, a universal joint 4b, and a bevel gear 6. The steering shaft includes the steering shaft 2, the universal joint 4a, the intermediate shaft 5, the universal joint 4b, and the bevel gear 6. The rotary control valve 7 supplies oil, which is supplied from a tank 9 via a hydraulic pump 8, to a hydraulic chamber 10. The rotary control valve 7 controls the flow rate of oil to the hydraulic chamber 10 based on the steering force transmitted from the steering wheel 1, reaction force from the road surface, and the like. The hydraulic chamber 10 drives a power cylinder (not shown) inside a steering box 11. Although not shown in FIG. 1A, the steering box 11 also includes a pinion connected to a pinion shaft to which the steering force from the steering wheel 1 is transmitted, a rack fitted to the pinion, and the like. The rotational motion transmitted to the pinion is converted into linear motion in the vehicle width direction by the rack. The driving force from the power cylinder is connected to steered wheels 15a, 15b via left and right connecting parts 12a, 12b, tie rods 13a, 13b, and hub units 14a, 14b.

[0018] Next, a configuration example of an electric power steering system (EPS) according to this embodiment will be described. As described above, the electric power steering system according to this embodiment is intended to enable driving control by autonomous driving (AD) or advanced driver assistance systems (ADAS) for vehicles such as buses that have conventionally been equipped with an HPS. Examples of ADAS functions include a lane keeping function and a lane change function, but the types are not particularly limited.

[0019] 1B is a diagram showing an example of the schematic configuration of a steering system 110 according to this embodiment. The configuration of the HPS on the steered wheels 15 side (hereinafter also referred to as the downstream side) is the same as that shown in FIG. 1A, but on the steering wheel 1 side (hereinafter also referred to as the upstream side), an EPS functional unit 30 is provided instead of the manual column. In other words, the EPS functional unit 30 is provided on a steering shaft that includes a steering shaft 2, a universal joint 4a, an intermediate shaft 5, a universal joint 4b, a bevel gear 6, etc. Here, a description of the HPS located on the downstream side will be omitted.

[0020] The steering shaft 2 is provided with a torque sensor 31 that detects a steering torque T applied to a torsion bar (not shown). The torque sensor 31 also detects a steering angle θ , which indicates the rotation angle of the steering shaft 2 around the axis on the steering wheel 1 side (upstream side). h and an output shaft angle θ indicating the rotation angle around the axis of the universal joint 4a side (downstream side) of the steering shaft 2. c That is, the torque sensor 31 may be configured to detect the steering angle θ h and output shaft angle θ c The steering torque T is detected based on the twist of the torsion bar caused by the difference between the torques. Furthermore, information on the steering torque T and the rotation angle θ is sent to an EPS-ECU (Electronic Control Unit) 32 via a torque sensor 31.

[0021] In FIG. 1B, the torque sensor 31 is shown as a single sensor. h and output shaft angle θ cA steering angle sensor and an output shaft angle sensor may be configured separately as sensors for detecting each. Therefore, the configuration of the torque sensor 31 is not particularly limited, and for example, a sleeve type or a ring type that detects torque from the twist of a torsion bar may be used. In the above configuration, the steering torque T is calculated based on the steering angle θ h and output shaft angle θ c However, the present invention is not limited to this. For example, the steering torque T may be detected using the difference between the angle signal on the steering wheel 1 side of the torsion bar and the angle signal on the universal joint 4a side.

[0022] A steering assist motor 33 that assists the steering force applied to the steering wheel 1 is connected to the steering shaft 2 via a worm 34 and a worm wheel 35 that form a reduction gear. An EPS-ECU 32 that is a controller that controls the EPS is supplied with power from a battery (not shown). Note that the means for applying the steering assist force to the steering shaft 2 is not limited to a motor, and various types of actuators may be used.

[0023] The EPS-ECU 32 calculates a current command value as an assist command value based on the steering torque T and rotation angle θ detected by the torque sensor 31, and various information provided by the vehicle-side ECU 40. The information provided by the vehicle-side ECU 40 includes the vehicle speed V detected by a vehicle speed sensor (not shown), h The EPS-ECU 32 outputs an output voltage V according to a current command value based on the steering torque T and a current command value based on the driving assistance function. m The steering assist motor 33 controls the power supplied to the steering assist motor 33 based on the output voltage V m Based on this, the worm 34 and the worm wheel 35 are operated to perform assist control for the steering wheel 1. Also, the output voltage V m The motor current I applied to the steering assist motor 33 in accordance with mis detected by a motor current detection unit (not shown) and notified to the EPS-ECU 32. Also, the motor angle θ of the steering assist motor 33 m is detected by a motor angle sensor (not shown) configured by an encoder, resolver, etc., and notified to the EPS-ECU 32.

[0024] The EPS-ECU 32 may include, for example, a computer including a processor and peripheral components such as a storage device. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device may include any of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device may include memories such as a register, a cache memory, and a ROM (Read Only Memory) and a RAM (Random Access Memory) used as a main storage device. The functions of the EPS-ECU 32 described below are realized, for example, by the processor of the EPS-ECU 32 executing a computer program stored in the storage device.

[0025] The EPS-ECU 32 may be formed by dedicated hardware for executing each of the information processes described below. For example, the EPS-ECU 32 may include a functional logic circuit configured in a general-purpose semiconductor integrated circuit. For example, the EPS-ECU 32 may include a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0026] The vehicle-side ECU 40 may also have the same configuration as the EPS-ECU 32, or may have a different configuration depending on the functions realized by the AD or ADAS. Furthermore, the vehicle-side ECU 40 may be realized by a plurality of ECUs.

[0027] By providing the EPS functional unit 30 as described above around the steering shaft 2, more friction occurs around the steering shaft 2 than in the configuration of the hydraulic power steering device 100 as shown in FIG. 1A. As a result, it is expected that the friction will cause deterioration in steering performance. Friction at the contact surfaces between the steering shaft 2 and each part, such as the steering assist motor 33, the worm 34, and the worm wheel 35, can cause deterioration in steering performance. In this embodiment, control is performed to suppress such deterioration in steering performance. More specifically, in this embodiment, compensation values are derived for Coulomb friction (static friction and kinetic friction) and viscous friction caused by the functional unit 30 around the steering shaft 2, and the steering assist motor 33 is controlled based on the compensation values.

[0028] [friction] 2 is a diagram illustrating the relationship between the static friction, dynamic friction, and viscous friction considered in this embodiment and the steering torque T and steering speed ω. In FIG. 2, the vertical axis represents the steering torque T, with + (plus) representing a counterclockwise value and − (minus) representing a clockwise value. The horizontal axis represents the steering speed ω, with + (plus) representing a counterclockwise value and − (minus) representing a clockwise value.

[0029] Static friction increases in balance with the steering torque T until the steering torque T, i.e., the external force, reaches or exceeds a certain value (maximum static friction force). When the steering torque T exceeds the certain value, kinetic friction occurs. Viscous friction also occurs depending on the value of the steering speed ω. The viscous friction increases with an increase in the steering speed ω, based on the kinetic friction (for example, increases in direct proportion to the slope η). Note that, as will be described in detail later, when EPS is assumed, the increase in viscous friction is not necessarily linear, and therefore, in this embodiment, a compensation value that takes into account changes in viscous friction is used.

[0030] [Function Configuration] FIG. 3 is a block diagram showing an example of a functional configuration related to a friction compensation function in the EPS-ECU 32 according to this embodiment. In FIG. 3, the arrows indicate an example of data flow, but the flow is not limited to that shown here, and other data may be transmitted and received when components are linked together. Also, while FIG. 3 shows only the functions according to this embodiment, the EPS-ECU 32 may further include configurations for realizing other functions. For example, the EPS-ECU 32 may further include a component for calculating an assist command value and a component for performing various processes corresponding to the ADAS function.

[0031] The friction compensation function in the EPS-ECU 32 according to this embodiment is configured to include a Coulomb friction compensation unit 200, a viscous friction compensation unit 300, and an adder 400. The Coulomb friction compensation unit 200 receives the steering torque T and the steering speed ω detected by the torque sensor 31 as inputs, and calculates a Coulomb friction compensation value F due to Coulomb friction. c The viscous friction compensation unit 300 receives the steering speed ω as an input and derives a viscous friction compensation value F v The steering speed ω is calculated by multiplying the steering angle θ detected by the torque sensor 31. h The steering speed ω is calculated by a steering speed calculation unit (not shown) of the EPS-ECU 32 based on the motor angle θ. The steering speed ω may be calculated on the torque sensor 31 side and notified to the EPS-ECU 32. m The adder 400 may calculate the Coulomb friction compensation value F c and the viscous friction compensation value F derived by the viscous friction compensation unit 300. v The friction compensation value F is calculated by adding

[0032] The Coulomb friction compensation unit 200 calculates the Coulomb friction compensation value F due to the EPS functional unit 30. c is derived based on the values of dynamic friction and static friction. As shown in Figure 2, the static friction compensation value F s depends on the steering torque T. Also, the dynamic friction compensation value F ddepends on the steering torque T and the steering speed ω. Therefore, the Coulomb friction compensation unit 200 calculates a static friction compensation value F based on the steering torque T and the steering speed ω as shown in FIG. s and dynamic friction compensation value F d The static friction compensation value F is calculated from these inputs. s and dynamic friction compensation value F d can be derived.

[0033] Furthermore, the Coulomb friction compensation unit 200 may perform filtering using an LPF (Low Pass Filter) or a BPF (Band Pass Filter) to remove noise from each input value.

[0034] (Viscous friction compensation section) 4 is a diagram showing an example of the functional configuration of the viscous friction compensation unit 300 according to this embodiment. The viscous friction compensation unit 300 includes an input filter unit 301 and a viscous friction compensation value calculation unit 302.

[0035] The input filter unit 301 is configured for the purpose of removing noise from the input steering speed ω and correcting for phase delay. The input filter unit 301 is configured, for example, with an LPF (Low Pass Filter), a phase lead filter, or a BPF (Band Pass Filter), but is not particularly limited to these. The filter used here may be configured with a first or second order filter. The following equation (1) shows an example of the transfer function of a first order filter. In each of the following equations, z -1 indicates the value of each variable one sample in the past.

[0036]

number

[0037] The viscous friction compensation value calculation unit 302 calculates the viscous friction compensation value F based on the steering speed after the processing by the input filter unit 301 is applied. vAs shown in FIG. 2, viscous friction increases in proportion to the steering speed ω. However, the change in viscous friction in EPS is not necessarily linear, and can have nonlinear characteristics. Therefore, the viscous friction compensation unit 300 according to this embodiment uses a compensation value corresponding to the nonlinear viscous friction of EPS.

[0038] Fig. 5 shows an example of the configuration of a conversion table for compensation values related to viscous friction. In Fig. 5, the horizontal axis represents the steering speed [deg / s], and the vertical axis represents the viscous friction compensation torque [Nm] as a compensation value. Note that although positive values are shown here, the value of the viscous friction compensation torque also switches between positive and negative depending on the rotation direction of the steering wheel 1.

[0039] In FIG. 5, as the steering speed increases, the value of the viscous friction compensation torque increases. At this time, the increase ratio (the amount of change in the viscous friction compensation torque relative to the increase in the steering speed) is not constant, but varies according to the value of the steering speed. Furthermore, after the steering speed exceeds a value of approximately 700 [deg / s], the value of the viscous friction compensation torque becomes constant (here, 2.0 [Nm]). In other words, an upper limit is set for the value of the viscous friction compensation torque, and when the steering speed exceeds a threshold value (approximately 700 [deg / s] in the example of FIG. 5), control is performed using the upper limit compensation value. This conversion table is defined in advance and stored in a storage unit or the like.

[0040] Note that the steering assist motor 33 is controlled based on the value of the viscous friction compensation torque, but in some cases, for example, an EPS configuration uses positive feedback. In such a configuration, if control is performed using a high value of viscous friction compensation torque, it may affect the stability of the operation of the steering system 110. Therefore, in this embodiment, Coulomb friction compensation is performed, and then the value of viscous friction relative to the steering speed is derived through experiments, and the conversion table shown in FIG. 5 is constructed based on the results. This ensures the stability of the operation of the steering system even when a conversion table related to viscous friction is used.

[0041] Furthermore, in this embodiment, a table in which steering speeds are associated with compensation values is used, but the present invention is not limited to this. For example, the compensation value may be derived using a conversion equation that includes the steering speed as a variable. In this case, a configuration may be adopted in which multiple conversion equations are defined and different conversion equations are used depending on the value of the steering speed. For example, multiple conversion equations corresponding to the value (range) of the steering speed may be used, such as a conversion equation used when the steering speed value is 0 to 200 [deg / s] and a conversion equation used when the steering speed value is 201 to 400 [deg / s].

[0042] (Example of operation) Figure 6 shows the results of operation with and without Coulomb friction compensation. In Figure 6, the horizontal axis represents the rotation angle [deg] of the steering wheel 1, with + (plus) values representing counterclockwise (CCW) rotation angles and - (minus) values representing clockwise (CW) rotation angles. The vertical axis represents the torque value [Nm], with + (plus) values representing counterclockwise (CCW) torque values and - (minus) values representing clockwise torque values.

[0043] As shown in FIG. 6, without Coulomb friction compensation, an operating torque (friction torque) of ±1.3 Nm can be generated. On the other hand, with Coulomb friction compensation according to this embodiment, the operating torque is ±0.2 Nm, and the magnitude of this operating torque can be suppressed. Furthermore, without Coulomb friction compensation, the amplitude (fluctuation range) near the upper and lower limit values of +1.3 Nm and -1.3 Nm is large, and the amplitude is approximately 0.5 Nm. On the other hand, with Coulomb friction compensation, the amplitude near the upper and lower limit values of +0.2 Nm and -0.2 Nm is small. As a result, Coulomb friction compensation can improve steering performance even in a configuration that combines EPS and HPS.

[0044] FIG. 7 is a diagram showing the results of operation with and without Coulomb friction compensation and viscous friction compensation according to this embodiment. The rotational speed conditions in FIG. 7 are different from those in FIG. 6, and the rotational speed in FIG. 7 is higher. In FIG. 7, the horizontal axis represents the rotation angle [deg] of the steering wheel 1, with + (plus) values representing counterclockwise (CCW) rotation angles and - (minus) values representing clockwise (CW) rotation angles. The vertical axis represents the torque value [Nm], with + (plus) values representing counterclockwise (CCW) torque values and - (minus) values representing clockwise torque values.

[0045] As shown in Figure 7, without friction compensation, an actuation torque of ±1.5 Nm may be generated. With Coulomb friction compensation, an actuation torque of ±0.6 Nm is generated, and the magnitude of this actuation torque can be suppressed. Furthermore, with viscous friction compensation according to this embodiment, an actuation torque of ±0.18 Nm is generated, and the magnitude of this actuation torque can be further suppressed.

[0046] Without friction compensation, the amplitude (fluctuation) near the upper and lower limit values of +1.5 Nm and -1.5 Nm is large, at about 0.5 Nm. On the other hand, with Coulomb friction compensation and viscous friction compensation according to this embodiment, the amplitude near the upper and lower limit values of +0.18 Nm and -0.18 Nm is small. As a result, with Coulomb friction compensation and viscous friction compensation according to this embodiment, steering performance can be improved even in a configuration that combines EPS and HPS.

[0047] FIG. 8 shows the measurement results of the manual column of the hydraulic power steering device shown in FIG. 1A. In FIG. 8, the horizontal axis represents the rotation angle [deg] of the steering wheel 1, with + (plus) values representing counterclockwise (CCW) rotation and - (minus) values representing clockwise (CW) rotation. The vertical axis represents torque [Nm], with + (plus) values representing counterclockwise (CCW) torque and - (minus) values representing clockwise (CW) torque. Comparing FIG. 7 with FIG. 8, in a conventional configuration combining an EPS and an HPS, torque fluctuations were large when friction compensation control was not performed. However, by combining and applying Coulomb friction compensation and viscous friction compensation according to this embodiment, the steering performance is closer to that of an HPS without an EPS. This makes it possible to suppress deterioration in steering performance.

[0048] As described above, according to this embodiment, in a configuration in which electric power steering and hydraulic power steering are combined, it is possible to reduce the deterioration of steering performance that occurs due to the structure of the electric power steering.

[0049] <Other embodiments> Furthermore, the configuration of the electric power steering device is not limited to the configuration shown in Fig. 1. For example, the electric power steering device may be configured with a steer-by-wire (SBW) mechanism in which the steering wheel 1 side, i.e., the steering mechanism side, and the steered road wheels 15 side, i.e., the steering mechanism side, are mechanically separated.

[0050] In the steer-by-wire function, the downstream side may be a hydraulic power steering device or an electric power steering device using a motor. Even in this case, control may be performed to compensate for friction caused by the configuration of the motor or reduction gear of the electric power steering device on the upstream side, for example.

[0051] Furthermore, the present invention can also be realized by supplying a program or application for realizing the functions of one or more of the above-described embodiments to a system or device via a network or storage medium, etc., and having one or more processors in the computer of that system or device read and execute the program.

[0052] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought.

[0053] As described above, the present specification discloses the following: (1) a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a control unit that controls the operation of the electric power steering device; Equipped with a control unit that derives a compensation value for viscous friction generated by a component of the electric power steering device, and outputs a control value for controlling the component using the compensation value. According to this configuration, in a configuration in which electric power steering and power steering of a steering mechanism are combined, it is possible to reduce deterioration in steering performance that occurs due to the structure of the electric power steering.

[0054] (2) The steering system according to (1), wherein the control unit derives the compensation value for the viscous friction based on a steering speed of the steering shaft. According to this configuration, it is possible to more accurately derive a compensation value for viscous friction based on the steering speed of the steering shaft.

[0055] (3) The steering system described in (2), wherein the control unit derives the compensation value for viscous friction using a conversion table in which the steering speed and the compensation value for viscous friction correspond to each other. According to this configuration, it is possible to derive a compensation value for viscous friction at high speed and low load using a predefined conversion table.

[0056] (4) The steering system according to (3), wherein the conversion table is defined so that the compensation value for the viscous friction exhibits a nonlinear characteristic with respect to an increase in the steering speed. According to this configuration, it is possible to derive a nonlinear compensation value in response to changes in viscous friction and reflect this in control.

[0057] (5) The steering system according to (2), wherein the control unit derives the compensation value for the viscous friction using one or more conversion equations that include the steering speed as a variable. According to this configuration, it is possible to derive a compensation value for viscous friction using one or more conversion equations corresponding to the steering speed.

[0058] (6) The steering system according to any one of (2) to (5), wherein the control unit keeps the compensation value for the viscous friction constant when the steering speed exceeds a predetermined threshold value. According to this configuration, when the steering speed exceeds a certain value, the compensation value for viscous friction is made constant, thereby making it possible to ensure stability of steering control.

[0059] (7) A steering system according to any one of (1) to (6), characterized in that the control unit further derives a compensation value for Coulomb friction generated by the part, and outputs a control value for controlling the part using the compensation value for viscous friction and the compensation value for Coulomb friction. According to this configuration, the compensation value takes into consideration the compensation value for Coulomb friction that occurs due to the structure of the electric power steering, making it possible to further reduce deterioration in steering performance.

[0060] (8) The steering system described in (7), characterized in that the control unit derives the compensation value for the Coulomb friction using compensation values for static friction and dynamic friction of the part derived based on the steering speed and torque for the steering shaft. According to this configuration, it is possible to derive a compensation value for Coulomb friction with higher accuracy based on the steering speed and torque of the steering shaft provided with the electric power steering device.

[0061] (9) The steering system according to any one of (1) to (8), wherein the electric power steering device includes a motor and a reducer as the components. This configuration makes it possible to control the viscous friction caused by the motor and reducer included in the electric power steering device.

[0062] (10) a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; A method for controlling a steering system comprising: A control method for a steering system, comprising: deriving a compensation value for viscous friction generated by a component constituting the electric power steering device; and using the compensation value to output a control value for controlling the component. According to this configuration, in a configuration in which electric power steering and power steering of a steering mechanism are combined, it is possible to reduce deterioration in steering performance that occurs due to the structure of the electric power steering.

[0063] (11) a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a computer for controlling a steering system comprising: A program for causing the electric power steering device to function as a control unit that derives a compensation value for viscous friction generated by a component of the device and uses the compensation value to output a control value for controlling the component. According to this configuration, in a configuration in which electric power steering and power steering of a steering mechanism are combined, it is possible to reduce deterioration in steering performance that occurs due to the structure of the electric power steering. [Explanation of symbols]

[0064] 1...Steering wheel 2...Steering shaft 4a, 4b...Universal joint 5...Intermediate shaft 6...Bevel gear 7...Rotary control valve 8...Hydraulic pump 9. Tank 10...Hydraulic chamber 11...Steering box 12a, 12b...Connection 13a, 13b...Tie rod 14a, 14b...hub unit 15a,15b...Steering wheel 30...Functional part 31...Torque sensor 32…EPS-ECU(Electronic Control Unit) 33...Steering assist motor 34...Warm 35...worm wheel 40...Vehicle ECU 100...Hydraulic power steering device 110...Steering system

Claims

1. a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a control unit that controls the operation of the electric power steering device; Equipped with the control unit derives a compensation value for viscous friction generated by a component constituting the electric power steering device, and outputs a control value for controlling the component using the compensation value, A steering system, characterized in that the compensation value for the viscous friction is derived based on a steering speed of the steering shaft that is associated with the steering speed in a predefined conversion table.

2. 2. The steering system according to claim 1, wherein the conversion table is defined so that the compensation value for viscous friction exhibits a nonlinear characteristic with respect to an increase in the steering speed.

3. 2. The steering system according to claim 1, wherein the control unit derives the compensation value for the viscous friction using one or more conversion equations that include the steering speed as a variable.

4. 4. The steering system according to claim 1, wherein the control unit keeps the compensation value of the viscous friction constant when the steering speed exceeds a predetermined threshold value.

5. The steering system according to any one of claims 1 to 4, characterized in that the control unit further derives a compensation value for Coulomb friction generated by the part, and outputs a control value for controlling the part using the compensation value for viscous friction and the compensation value for Coulomb friction.

6. 6. The steering system according to claim 5, wherein the control unit derives the compensation value for the Coulomb friction using compensation values for static friction and dynamic friction of the part derived based on a steering speed and torque applied to the steering shaft.

7. 7. The steering system according to claim 1, wherein the electric power steering device includes a motor and a reducer as the components.

8. a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; A method for controlling a steering system comprising: deriving a compensation value for viscous friction generated by a component constituting the electric power steering device, and outputting a control value for controlling the component using the compensation value; 10. A method for controlling a steering system, comprising: deriving the compensation value for viscous friction based on a steering speed of the steering shaft associated with a predetermined conversion table.

9. a steering mechanism including a steering shaft; a steering mechanism that steers steered wheels in conjunction with rotation of the steering shaft; a power steering device provided in the steering mechanism; an electric power steering device provided in the steering mechanism; a computer for controlling a steering system comprising: a program for causing the electric power steering device to function as a control unit that derives a compensation value for viscous friction generated by a component of the device, and outputs a control value for controlling the component using the compensation value, The program, wherein the compensation value for viscous friction is derived based on a steering speed of the steering shaft associated with a predetermined conversion table.

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