Steering control device and steering control method

Abstract

A steering control device (10) performs an operation amount calculation process, a correction process, and an operation process. The operation amount calculation process is for calculating the operation amount of control in which a steering torque is used as a control amount and a target steering torque is used as a target value of the control amount. The correction process is for correcting the operation amount on the basis of a correction amount corresponding to the difference between the actual steering torque and the steering torque which is assumed by a nominal model while using the steering torque and the operation amount as input. The operation process is for operating a motor of a steering device so that a torque corresponding to the operation amount corrected by the correction process is generated. The correction process includes an intermediate process which is repeatedly performed at prescribed intervals and in which a correction amount calculated at one sampling timing of the operation amount is an intermediate correction amount value that is virtually calculated using values at two respective adjacent sampling timings of the operation amount.

Description

[Technical Field]

[0001] The present disclosure relates to a steering control device and a steering control method. [Background technology]

[0002] For example, Patent Document 1 listed below describes a device that operates a motor for steering steered wheels in accordance with a feedback control operation amount that uses steering torque as a control amount and a target value of steering torque as a control amount target value. More specifically, the feedback control operation amount is calculated in accordance with an output value of a proportional element, an output value of a differential element, and an output value of an integral element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-203089 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when setting a feedback gain or the like in order to satisfy requirements such as improving the responsiveness of the feedback control, there is a risk that the amount of work required to adapt the parameter values ​​that determine the feedback control to those requirements will become excessively large. [Means for solving the problem]

[0005] One aspect of the present disclosure provides a steering control device configured to execute a manipulation amount calculation process, a correction process, and a manipulation process, wherein the manipulation amount calculation process calculates a manipulation amount for control using a steering torque as a control amount and a target steering torque as a target value of the control amount, the steering torque being a torque input to a steering device by a driver, and the target steering torque being a target value of the steering torque, the correction process uses the steering torque and the manipulation amount as inputs and corrects the manipulation amount with a correction amount corresponding to a difference between the steering torque assumed by a nominal model and the actual steering torque, and the manipulation process operates a motor of the steering device so as to generate a torque corresponding to the manipulation amount corrected by the correction process, and the correction process is repeatedly executed at a predetermined cycle and includes an intermediate process that sets the correction amount calculated at one sampling timing of the manipulation amount to an intermediate value of correction amounts virtually calculated using the manipulation amounts obtained at two adjacent sampling timings.

[0006] Another aspect of the present disclosure provides a steering control method, the steering control method comprising steps of executing a manipulation amount calculation process, a correction process, and a manipulation process, wherein the manipulation amount calculation process calculates a manipulation amount for control using a steering torque as a control amount and a target steering torque as a target value of the control amount, the steering torque being a torque input to a steering device by a driver, the target steering torque being a target value of the steering torque, the correction process using the steering torque and the manipulation amount as inputs and correcting the manipulation amount with a correction amount corresponding to a difference between the steering torque assumed by a nominal model and the actual steering torque, the manipulation process operating a motor of the steering device so as to generate a torque corresponding to the manipulation amount corrected by the correction process, and the correction process is repeatedly executed at a predetermined cycle and includes an intermediate process of setting the correction amount calculated at one sampling timing of the manipulation amount to an intermediate value of correction amounts virtually calculated using the manipulation amounts obtained at two adjacent sampling timings. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing the configuration of a steering control device and a steering device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the processing executed by the steering control device of FIG. 1. [Figure 3] FIG. 3 is a block diagram showing an s-domain representation of the disturbance observer in FIG. 2. [Figure 4] FIG. 3 is a block diagram showing a discrete representation of the disturbance observer in FIG. 2. [Figure 5] FIG. 4 is a diagram showing the configuration of a steering control device and a steering device according to a second embodiment. [Figure 6] FIG. 6 is a block diagram showing the processing executed by the steering control device of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0008] First Embodiment The first embodiment will be described below with reference to the drawings. "Prerequisite configuration" As shown in FIG. 1, steering device 10 includes steering wheel 12. Steering wheel 12 is a means for transmitting steering instructions by the driver. A transmission shaft 14 is connected to steering wheel 12. Therefore, when steering wheel 12 rotates, transmission shaft 14 rotates integrally. The rotational power of transmission shaft 14 is transmitted to steering shaft 16. Steering shaft 16 extends in the vehicle width direction (left-right direction in FIG. 1). Steerable wheels 20 are connected to both ends of steering shaft 16 via tie rods 18.

[0009] Transmission shaft 14 is arranged so as to intersect with steered shaft 16. Transmission shaft 14 and steered shaft 16 have teeth formed thereon that mesh with each other. These teeth mesh with each other, enabling power to be transmitted from transmission shaft 14 to steered shaft 16. In other words, the rotational power of transmission shaft 14 is converted into power that displaces steered shaft 16 in the axial direction. The displacement of steered shaft 16 in the axial direction is transmitted to steered wheels 20 via tie rods 18. This changes the steering angle of steered wheels 20. The steering angle refers to the turning angle of the tires.

[0010] The steering device 10 also includes an assist motor 30. The assist motor 30 generates an assist force that assists the driver in steering. The rotational power of the assist motor 30 is applied to a drive shaft 34. The drive shaft 34 and the steered shaft 16 have teeth that mesh with each other. The meshing of these teeth enables power to be transmitted from the drive shaft 34 to the steered shaft 16. In other words, the rotational power of the drive shaft 34 is converted into displacement power in the axial direction of the steered shaft 16. As a result, the rotational power of the assist motor 30 is converted into displacement power in the axial direction of the steered shaft 16 via the drive shaft 34. More specifically, the assist motor 30 is, for example, a three-phase brushless motor. The output voltage of an inverter 32 is applied to the terminals of the assist motor 30.

[0011] The steering control device 40 controls the control amount of the steering device 10, which is the object to be controlled. In order to control the control amount, the steering control device 40 refers to the steering torque Th input to the steering wheel 12. The steering torque Th is detected by a torque sensor 50. The torque sensor 50 is a sensor that detects the steering torque Th according to the degree of torsion of a torsion bar 52, which is part of the transmission shaft 14. The steering control device 40 also refers to a vehicle speed SPD detected by a vehicle speed sensor 54. The steering control device 40 also refers to a rotation angle θa of the assist motor 30 detected by a rotation angle sensor 56. The steering control device 40 also refers to the currents iu, iv, and iw flowing through the assist motor 30.

[0012] The steering control device 40 includes a PU 42 and a storage device 44. The PU 42 is a software processing device such as a CPU, a GPU, and a TPU. The storage device 44 includes a storage medium such as an electrically rewritable nonvolatile memory and a disk medium. A steering control program 44a is stored in the storage device 44. The steering control device 40 controls the control amount by having the PU 42 execute the steering control program 44a stored in the storage device 44.

[0013] "Processing Executed by Steering Control Device 40" Fig. 2 shows the processing executed by the steering control device 40. The processing shown in Fig. 2 is realized by the PU 42 repeatedly executing the steering control program 44a, for example, at predetermined intervals.

[0014] The target steering torque calculation process M10 is a process for calculating a target steering torque Th*, which is a target value of the steering torque Th, based on the axial force Fa. The axial force Fa is a force applied to the steered shaft 16. The axial force Fa is an amount converted into torque of the transmission shaft 14. The target steering torque calculation process M10 includes a process for setting the target steering torque Th* to a different value depending on the vehicle speed SPD, even if the axial force Fa is the same. This setting is intended to allow the driver to experience an optimal steering feel depending on the vehicle speed SPD.

[0015] The open-loop operation amount calculation process M12 is a process for calculating the open-loop operation amount Mff. The open-loop operation amount Mff is an operation amount for open-loop control that uses the steering torque Th as a control amount and the target steering torque Th* as a target value for the control amount. The open-loop operation amount calculation process M12 is a process for calculating the open-loop operation amount Mff by inputting the target steering torque Th*. The open-loop operation amount calculation process M12 calculates the open-loop operation amount Mff based on an inverse model of the nominal model Pn. The nominal model Pn is a model that uses the assist torque Ta, which is the torque of the assist motor 30, as an input and outputs an estimated steering torque The, which is an estimated value of the steering torque Th. Here, the assist torque Ta is a value converted into the torque of the transmission shaft 14. The inverse model is a model that uses the estimated steering torque The as an input and outputs the assist torque Ta. The nominal model Pn will be described in detail later.

[0016] The deviation calculation process M14 is a process for calculating a deviation, which is a value obtained by subtracting the target steering torque Th* from the steering torque Th. The feedback manipulated variable calculation process M16 is a process that uses the deviation as an input to calculate a feedback manipulated variable Mfb. The feedback manipulated variable Mfb is a manipulated variable of feedback control that uses the steering torque Th as a controlled variable and the target steering torque Th* as a controlled variable target value. The feedback manipulated variable Mfb is the sum of the output value of a proportional element that uses the deviation as an input and the output value of a derivative element that uses the deviation as an input. The feedback manipulated variable Mfb is a value converted into the torque of the transmission shaft 14. More specifically, the feedback manipulated variable calculation process M16 includes a process that changes at least one of the gain of the proportional element and the gain of the derivative element in accordance with the vehicle speed SPD.

[0017] The torque command value calculation process M20 is a process that calculates the assist torque Ta using the open loop operation amount Mff, the feedback operation amount Mfb, and the estimated second disturbance torque de as inputs. In the torque command value calculation process M20, a value obtained by subtracting the estimated second disturbance torque de from the sum of the open loop operation amount Mff and the feedback operation amount Mfb is substituted for the assist torque Ta.

[0018] The assist torque Ta is input to the axial force calculation process M22, which is a process for substituting the sum of the assist torque Ta and the steering torque Th for the axial force Fa. The assist torque Ta is input to a disturbance observer M30. The disturbance observer M30 includes a steering torque estimation process M32, a first disturbance calculation process M34, and a second disturbance calculation process M36.

[0019] The steering torque estimation process M32 is a process for inputting the assist torque Ta to the nominal model Pn, thereby outputting the estimated steering torque The. The estimated steering torque The is the steering torque assumed by the nominal model Pn.

[0020] The first disturbance calculation process M34 is a process for calculating an estimated first disturbance torque dhe. The estimated first disturbance torque dhe is a disturbance component that is superimposed on the steering torque Th of the actual control object. The estimated first disturbance torque dhe is the difference between the torque estimated from the nominal model Pn and the actual steering torque Th. In other words, the estimated first disturbance torque dhe is the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th. More specifically, the first disturbance calculation process M34 is a process for substituting a value obtained by subtracting the estimated steering torque The from the steering torque Th into the estimated first disturbance torque dhe.

[0021] The second disturbance calculation process M36 is a process that uses the estimated first disturbance torque dhe as an input and calculates the estimated second disturbance torque de. The estimated second disturbance torque de is disturbance torque converted into the torque of the assist motor 30. The second disturbance calculation process M36 is a process that calculates the estimated second disturbance torque de using an inverse model of the nominal model Pn and a filter Hd.

[0022] The filter Hd is provided to reduce noise caused by the differential operation included in the nominal model Pn. In this embodiment, the filter Hd is, for example, a third-order low-pass filter.

[0023] As described above, the assist torque Ta is a value obtained by subtracting the estimated second disturbance torque de from the sum of the open-loop operation amount Mff and the feedback operation amount Mfb. On the other hand, the estimated second disturbance torque de is an amount obtained by converting the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th into the torque of the assist motor 30. This means that the estimated second disturbance torque de is an amount corresponding to the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th. Therefore, the assist torque Ta is an amount obtained by correcting the sum of the open-loop operation amount Mff and the feedback operation amount Mfb according to a correction amount corresponding to the difference between the steering torque assumed by the nominal model Pn and the actual steering torque Th.

[0024] The operation signal generation process M40 is a process for operating the inverter 32 by inputting the assist torque Ta. Specifically, the operation signal generation process M40 includes a process for calculating an operation amount using the torque of the assist motor 30 as a control amount and using a value obtained by converting the assist torque Ta into torque of the assist motor 30 as a target value for the control amount. The rotation angle θa and currents iu, iv, and iw are referenced in calculating the operation amount. The operation signal generation process M40 also includes a process for operating the inverter 32 so as to obtain the operation amount. The operation amount may be, for example, the time ratio of the ON operation time to one cycle of the ON / OFF operation of the switching elements of the inverter 32. FIG. 2 shows an operation signal MS for the inverter 32. However, in reality, the operation signal MS is a separate operation signal for each switching element of the inverter 32.

[0025] "Nominal Model Pn" The steering torque Th is expressed by the following equation (c1) using the inertia coefficient Jh, the viscosity coefficient Ch, and the steering angle θh. The inertia coefficient Jh indicates the inertia of a first portion of the transmission shaft 14, which is a portion closer to the steering wheel 12 than the torsion bar 52. The viscosity coefficient Ch indicates the viscosity of the first portion of the transmission shaft 14. The steering angle θh is the rotation angle of the steering wheel 12.

[0026] -Th=(Jh·s·s+Ch·s)·θh …(c1) On the other hand, the following equation (c2) is established using the rotation angle θl and the torsional rigidity coefficient Ktb of the torsion bar 52. Note that the rotation angle θl is the rotation angle of a second portion of the transmission shaft 14, which is a portion that is farther from the steering wheel 12 than the torsion bar 52.

[0027] Th=Ktb·(θh-θl) …(c2) Furthermore, using the inertia coefficient J, viscosity coefficient C, and elastic coefficient K, the following equation (c3) holds between the rotation angle θl and the assist torque Ta and steering torque Th. The inertia coefficient J represents the inertia of the second portion of the transmission shaft 14. The viscosity coefficient C represents the viscosity of the second portion of the transmission shaft 14. The elastic coefficient K represents the elasticity of the second portion of the transmission shaft 14. Note that the viscosity coefficient C and elastic coefficient K actually reflect the influences that the steered shaft 16, tie rod 18, steered wheels 20, etc. have on the transmission shaft 14.

[0028] Th+Ta=(J·s·s+C·s+K)·θl …(c3) Here, if the steering torque Th is input so that the steering angle θh is zero, the steering angle θh will always be zero. If the steering angle θh is set to zero and the transfer function from the assist torque Ta to the steering torque Th is calculated based on the above equations (c1) to (c3), the following equation (c4) is obtained.

[0029] Th / Ta=(-Ktb) / {J·s·s+C·s+K+Ktb} …(c4) In the above formula (c4), a differential operator s is used. The above formula (c4) is the nominal model Pn. The above formula (c4) also holds when "θh" and "θl" in the above formulas (c1) to (c3) are replaced as follows:

[0030] θh: Phase difference between the rotation angle of the first portion of the transmission shaft 14 and the rotation angle of the steering wheel 12. This is always zero. θl: Phase difference between the rotation angle of the second portion of the transmission shaft 14 and the rotation angle of the steering wheel 12.

[0031] Therefore, the above formula (c4) holds true for any steering angle θh. "Design of disturbance observer M30" FIG. 3 shows the s-domain representation of the disturbance observer M30 using observer gains L1, L2, and L3.

[0032] As shown in FIG. 3, the addition process M50 is a process for calculating a value obtained by adding the estimated second disturbance torque de to the assist torque Ta. The multiplication process M52 is a process of multiplying the output value of the addition process M50 by a value that is "-1" times the torsional stiffness coefficient Ktb.

[0033] The output value of the addition process M54, which is based on the output value of the multiplication process M52, is input to the multiplication process M56. The multiplication process M56 is a process in which the output value of the addition process M54 is multiplied by the reciprocal of the inertia coefficient J.

[0034] The output value of the addition process M58, which is based on the output value of the multiplication process M56, is input to an integration element M60. The output value of the addition process M62, which is based on the output value of the integral element M60, is output to an integral element M64, whose output value is the estimated steering torque The.

[0035] The multiplication process M66 is a process of multiplying the output value of the integral element M60 by the viscosity coefficient C. The multiplication process M68 is a process of multiplying the estimated steering torque The by "Ktb+K". The addition process M54 is a process of subtracting the output value of the multiplication process M66 and the output value of the multiplication process M68 from the output value of the multiplication process M52.

[0036] The multiplication process M70 is a process of multiplying the estimated first disturbance torque dhe by the observer gain L3. The output value of the multiplication process M70 is input to an integral element M76. The output value of the integral element M76 is the estimated second disturbance torque de.

[0037] The multiplication process M72 is a process of multiplying the estimated first disturbance torque dhe by the observer gain L2. The addition process M58 is a process of adding the output value of the multiplication process M72 to the output value of the multiplication process M56.

[0038] The multiplication process M74 is a process of multiplying the estimated first disturbance torque dhe by the observer gain L1. The addition process M62 is a process of adding the output value of the multiplication process M74 to the output value of the integral element M60.

[0039] The actual plant M80 is an actual controlled object. In this embodiment, the filter Hd is the cube of "ω / (s+ω)". Therefore, the observer gains L1, L2, and L3 are designed so that the transfer function from the actual disturbance torque d to the estimated second disturbance torque de in Fig. 3 is equal to the cube of "ω / (s+ω)". In this case, it is assumed that the above-mentioned nominal model Pn is equal to the actual plant M80.

[0040] "Representation of Discrete Systems" The disturbance observer M30 is actually digitally processed. Figure 4 shows a discrete system representation of the disturbance observer M30. The processing shown in Figure 4 is the processing actually executed by the PU 42. Note that in Figure 4, the same processes as those shown in Figure 3 are denoted by the same reference numerals for convenience.

[0041] As shown in Figure 4, the integral elements M60, M64, and M76 in Figure 3 have been replaced with bilinear transformation processes M60a, M64a, and M76a. In the bilinear transformation "(T / 2)·(1+Z^(-1)) / (1-Z^(-1))," "T" is the sampling period. Using the bilinear transformation, a value intermediate between the value obtained by approximating using the forward rectangular approximation "T·Z^(-1) / (1-Z^(-1))" and the value obtained by approximating using the backward rectangular approximation "T / (1-Z^(-1))" is calculated.

[0042] The use of bilinear transformation processing aims to prevent deviation of actual performance from the theoretical value in the continuous system shown in FIG. 3. Compared to using forward rectangular approximation or backward rectangular approximation, using bilinear transformation increases the computational load. However, compared to using forward rectangular approximation or backward rectangular approximation, using bilinear transformation reduces the error associated with discretization. Therefore, it is possible to improve the controllability of control using steering torque Th as a control variable.

[0043] Moreover, addition processing M50 shown in FIG. 4 is processing for adding the estimated second disturbance torque de to the assist torque Ta. Delay processing M92 is processing for outputting the value of the output value of addition processing M50 one sampling before. Addition processing M94 is processing for adding the output value of addition processing M50 and the output value of delay processing M92. Multiplication processing M96 is processing for multiplying the output value of addition processing M94 by "1 / 2". The output value of multiplication processing M96 is input to multiplication processing M52.

[0044] That is, the input of the multiplication process M52 is the average value of the values ​​obtained at two adjacent sampling timings for the assist torque Ta corrected by the estimated second disturbance torque de, which is intended to reduce errors associated with discretization.

[0045] <Actions and Effects of This Embodiment> The PU 42 calculates an estimated second disturbance torque de using, as an input, an estimated first disturbance torque dhe, which is the difference between the steering torque Th and the estimated steering torque The. The estimated second disturbance torque de indicates the disturbance element of the torque of the second portion of the transmission shaft 14. In other words, it indicates the disturbance element of the torque converted into a force that displaces the steered shaft 16.

[0046] The PU42 uses the value obtained by correcting the sum of the open-loop control input Mff and the feedback control input Mfb by the estimated second disturbance torque de as the assist torque Ta. Then, the PU42 operates the inverter 32 so that the torque of the assist motor 30 approaches the assist torque Ta. This makes it possible to execute control using the target steering torque Th* as the target value of the controlled variable while compensating for disturbance elements such as the error between the nominal model Pn and the actual controlled object. In other words, the disturbance observer M30 makes it possible to execute control using the target steering torque Th* as the target value of the controlled variable while compensating for the error of the nominal model Pn with respect to the actual controlled object.

[0047] Since the amount equivalent to the error is immediately compensated for in this manner, the responsiveness of the steering torque Th to the target steering torque Th* can be improved. Furthermore, compared to the case where a controller is designed in accordance with an actual control target without using the disturbance observer M30, the number of steps required to design the controller can be reduced.

[0048] Furthermore, when the expression in the s domain shown in FIG. 3 was replaced with actual digital processing, the PU42 used the average value of values ​​obtained at two adjacent sampling timings as input to the disturbance observer M30. That is, the PU42 calculated the estimated second disturbance torque de according to a value corresponding to the average value of the previous and current values ​​of the sum of the open-loop control input Mff and the feedback control input Mfb. As a result, the estimated second disturbance torque de is an intermediate value between the values ​​obtained when the sum of the open-loop control input Mff and the feedback control input Mfb is used individually at each of the two adjacent sampling timings, the first timing and the second timing.

[0049] That is, the estimated second disturbance torque de is an intermediate value between "de1" and "de2." Here, "de1" and "de2" are the following values. de1: Estimated second disturbance torque de calculated using the open loop control input Mff and the feedback control input Mfb at the first timing.

[0050] de2: Estimated second disturbance torque de calculated using the open loop control input Mff and the feedback control input Mfb at the second timing. When only a single set of the open-loop control input Mff and the feedback control input Mfb that change at the sampling period is used, the estimated second disturbance torque de may deviate significantly from the value expected by the continuous system. In contrast, by using an intermediate value between the value virtually calculated at the first timing and the value virtually calculated at the second timing as the estimated second disturbance torque de, it is possible to reduce the deviation from the value expected by the continuous system.

[0051] According to the present embodiment described above, the following further functions and effects are achieved. (1-1) PU42 replaces integral elements M60, M64, and M76 with bilinear transformation processes M60a, M64a, and M76a. This allows the performance indicated by the s-domain representation to be maintained as much as possible compared to when forward rectangular approximation or backward rectangular approximation is used.

[0052] When forward rectangular approximation or backward rectangular approximation is used, integration is performed using values ​​obtained at a single input timing. In contrast, when bilinear transformation is used, the median value of values ​​obtained at two adjacent timings is used. This means that the estimated second disturbance torque de is calculated as the median value between "de1" and "de2" even when the delay process M92, the addition process M94, and the multiplication process M96 in FIG. 4 are not used.

[0053] (1-2) The PU 42 calculates the open-loop control input Mff by inputting the target steering torque Th* to an inverse model of the nominal model Pn. The PU 42 also calculates the assist torque Ta according to the open-loop control input Mff. This makes it possible to use the estimated second disturbance torque de as a compensation component for the error in the open-loop control input Mff in control that targets the target steering torque Th* as the control input. This allows the controlled object to be pseudo-linearized.

[0054] (1-3) The assist torque Ta includes the feedback control input Mfb. This allows the error equivalent of the specified second disturbance torque de to be compensated for by the feedback control input Mfb. Therefore, the steering torque Th can be made to approximate the target steering torque Th* with higher accuracy.

[0055] (1-4) The nominal model Pn is configured to include not only the inertia coefficient J but also the viscosity coefficient C, elastic coefficient K, and torsional stiffness coefficient Ktb. This allows the nominal model Pn to be a model that closely approximates the actual controlled object.

[0056] Second Embodiment The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0057] "Prerequisite configuration" The configuration of the steering control system according to this embodiment is shown in Fig. 5. In Fig. 5, members corresponding to those shown in Fig. 1 are denoted by the same reference numerals for convenience.

[0058] As shown in Fig. 5, in the steering device 10, the transmission shaft 14 is separated into an input shaft 14a connected to the steering wheel 12 and an output shaft 14b engaged with the steered shaft 16. Note that in this embodiment, the output shaft 14b is not actually required. However, for convenience of the following explanation, the output shaft 14b is provided.

[0059] A reaction motor 70 is provided on the input shaft 14a. The reaction motor 70 is a motor for applying a reaction force, which is a torque in the opposite direction to the torque input by the driver, to the steering wheel 12. The reaction motor 70 is, for example, a three-phase brushless motor. The output voltage of an inverter 72 is applied to the terminals of the reaction motor 70.

[0060] Torque from steering motor 80 is applied to steering shaft 16 via drive shaft 34. As an example, steering motor 80 is a three-phase brushless motor. The output voltage of inverter 82 is applied to the terminals of steering motor 80.

[0061] The steering control device 40 controls the steering device 10. The steering control device 40 operates the inverter 72 to control the reaction force, which is the control variable of the control object. The steering control device 40 also operates the inverter 82 to control the steering angle of the steered wheels 20, which is the control variable of the control object.

[0062] Steering control device 40 refers to rotation angle θs of reaction force motor 70 detected by rotation angle sensor 90 in order to control the reaction force, which is a control variable. Steering control device 40 also refers to currents ius, ivs, iws flowing through reaction force motor 70 in order to control the reaction force. Steering control device 40 also refers to rotation angle θt of steering motor 80 detected by rotation angle sensor 92 in order to control the steering angle, which is a control variable. Steering control device 40 also refers to currents iut, ivt, iwt flowing through steering motor 80 in order to control the steering angle.

[0063] "Processing Executed by Steering Control Device 40" Fig. 6 shows the processing executed by the steering control device 40. In other words, Fig. 6 shows the processing executed by the steering control device 40 in a state where the transmission of power from the steering wheel 12 to the steered wheels 20 is interrupted. Note that in Fig. 6, the processing corresponding to the processing shown in Fig. 2 is denoted by the same reference numerals for convenience.

[0064] As shown in FIG. 6, deviation calculation processing M14 is processing for calculating a value obtained by subtracting steering torque Th from target steering torque Th*. Torque command value calculation processing M20 is processing for outputting reaction force command value Tr*. Torque command value calculation processing M20 is processing for substituting a value obtained by subtracting estimated second disturbance torque de from the sum of open loop operation amount Mff and feedback operation amount Mfb into reaction force command value Tr*. Reaction force command value Tr* is a command value for reaction torque to be applied to steering wheel 12. Reaction force command value Tr* is converted into the angle of transmission shaft 14.

[0065] The steering operation signal generation process M40a is a process for operating the inverter 72 in response to input of the reaction force command value Tr*. Specifically, the steering operation signal generation process M40a includes a process for calculating a control operation amount using the torque of the reaction force motor 70 as a control amount and a value obtained by converting the reaction force command value Tr* into the torque of the reaction force motor 70 as a target value for the control amount. The calculation of the operation amount refers to the rotation angle θs and the currents ius, ivs, and iws. The steering operation signal generation process M40a also includes a process for operating the inverter 72 in accordance with the operation amount. FIG. 6 shows an operation signal MSs for the inverter 72. Note that in reality, the operation signal MSs is a separate operation signal for each switching element of the inverter 72.

[0066] The target angle calculation process M100 is a process for calculating a target angle θp*, which is a target value for the rotation angle of the drive shaft 34. The rotation angle of the drive shaft 34 has a one-to-one correspondence with the steering angle. The target angle calculation process M100 may be a process for calculating the target angle θp* from the reaction force command value Tr* using, for example, a model of the steering device 10. In this model, for example, the reaction force command value Tr* may be regarded as a torque applied to the transmission shaft 14 when it is assumed that the input shaft 14a and the output shaft 14b are mechanically coupled.

[0067] The angle control process M102 is a process for calculating the manipulated variable for controlling the rotation angle of the drive shaft 34 to the target angle θp*. This manipulated variable is the steering torque command value Tt*, which is the torque command value for the steering motor 80.

[0068] Steering operation signal generation process M104 is a process for operating inverter 82 in response to input of steering torque command value Tt*. Steering operation signal generation process M104 includes a process for calculating a control operation amount using the torque of steering motor 80 as a control amount and a value obtained by converting steering torque command value Tt* into torque of steering motor 80 as a target value of the control amount. The calculation of the operation amount references rotation angle θt and currents iut, ivt, iwt. Steering operation signal generation process M104 also includes a process for operating inverter 82 in accordance with the operation amount. FIG. 6 shows operation signal MSt of inverter 82. Note that in reality, operation signal MSt is a separate operation signal for each switching element of inverter 82.

[0069] <Other embodiments> The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0070] "About intermediate processing" It is not necessary to replace the integral elements M60, M64, and M76 with the bilinear transformation processes M60a, M64a, and M76a, respectively. For example, the integral elements M60 and M64 may be replaced with the bilinear transformation processes M60a and M64a, respectively, while forward rectangular approximation or backward rectangular approximation may be adopted for the integral element M76.

[0071] It is not necessary to replace any of the integral elements M60, M64, and M76 with bilinear transformation processing. Even in this case, if the delay processing M92, the addition processing M94, and the multiplication processing M96 in Fig. 4 are employed, the estimated second disturbance torque de can be set to an intermediate value between "de1" and "de2".

[0072] In the example shown in Fig. 4, the simple average of the output values ​​of the addition process M50 is calculated by the delay process M92, the addition process M94, and the multiplication process M96, but this is not limiting. For example, a weighted average may be calculated. That is, for example, the sum of the value obtained by multiplying the previous value of the output value by a weighting coefficient α and the value obtained by multiplying the current value of the output value by "1-α" may be calculated. Here, the value of the weighting coefficient α is set to any value greater than "0" and less than "1."

[0073] It is not essential to employ the delay process M92, the addition process M94, and the multiplication process M96 in Fig. 4. Even in this case, for example, by replacing at least one of the three processes of the integral elements M60, M64, and M76 with a bilinear transformation process, the estimated second disturbance torque de can be set to an intermediate value between "de1" and "de2."

[0074] "About the target steering torque calculation process M10" It is not essential that the target steering torque calculation process M10 calculates the target steering torque Th* based on the axial force Fa. For example, the target steering torque calculation process M10 may be a process that calculates the target steering torque Th* using the steering torque Th and the assist torque Ta as inputs.

[0075] It is not essential that the target steering torque calculation process M10 uses the vehicle speed SPD as an input. The input to the target steering torque calculation process M10 is not limited to the above. For example, two or more sampled values ​​of the steering angle at different sampling times may be input to the target steering torque calculation process M10. In this case, a process for distinguishing between when the steering wheel 12 is turned and when it is returned to its original position can be realized in accordance with the input. Therefore, for example, the absolute value of the target steering torque Th* may be set to a larger value when the steering wheel 12 is turned to its original position than when it is returned to its original position.

[0076] "Open-loop operation amount calculation process" The open-loop manipulated variable calculation process M12 is not limited to a process that uses the target steering torque Th* as an input. For example, the open-loop manipulated variable calculation process M12 may be a process that uses the axial force Fa as an input. In that case, the transfer function of the open-loop manipulated variable calculation process M12 may be the product of a transfer function that calculates the target steering torque Th* from the axial force Fa and an inverse model of the nominal model Pn.

[0077] "Feedback manipulated variable calculation process" The feedback manipulated variable Mfb does not necessarily have to be the sum of the output value of a proportional element that uses the deviation as an input and the output value of a differential element that uses the deviation as an input. For example, the feedback manipulated variable Mfb may be the sum of the output value of a proportional element that uses the deviation as an input, the output value of a differential element that uses the deviation as an input, and the output value of an integral element that uses a value corresponding to the deviation as an input. Also, for example, the feedback manipulated variable Mfb may be the sum of the output value of a proportional element that uses the deviation as an input and the output value of an integral element that uses a value corresponding to the deviation as an input. In this case, the gain of the integral element may be variable depending on the vehicle speed SPD.

[0078] The differential element is not limited to one that receives a deviation as an input. For example, the differential element may use the steering torque Th as an input. In other words, the differential element may constitute a leading differential type controller.

[0079] The process of making at least one of the gains of the elements constituting the feedback manipulated variable calculation process variable in accordance with the vehicle speed SPD is not essential. "Operation volume calculation process" For example, the manipulated variable calculation process may be configured from only the open-loop manipulated variable calculation process without including the feedback manipulated variable calculation process.Further, for example, the manipulated variable calculation process may be configured from only the feedback manipulated variable calculation process without including the open-loop manipulated variable calculation process.

[0080] "About the nominal model Pn" The nominal model Pn is not limited to the model exemplified in the above embodiment, and may be, for example, a model expressed by the following equation (c6):

[0081] (-Ktb) / {J·s·s} …(c6) That is, the polynomial in the denominator of the transfer function of the nominal model Pn does not need to include the first-order and zero-order terms. Alternatively, "Ktb" may be added to the denominator of the above equation (c6). In other words, the polynomial in the denominator of the transfer function of the nominal model Pn may include the zero-order term.

[0082] It is not essential that the degree of the polynomial in the denominator of the transfer function of the nominal model Pn be quadratic. "About correction processing" The filter Hd does not necessarily have to have a transfer function in which the denominator is a third-order polynomial and the numerator is a zeroth-order polynomial. In other words, it is not essential that the numerator of the transfer function obtained by combining the filter Hd and the inverse model of the nominal model Pn be of second order and the denominator of the combined transfer function be of third order. For example, the filter Hd may be the square of "ω / (ω+s)". Furthermore, the filter Hd may be the fourth power or greater of "ω / (ω+s)".

[0083] The correction process is not limited to processes including the steering torque estimation process M32, the first disturbance calculation process M34, the second disturbance calculation process M36, and the torque command value calculation process M20. For example, first, the estimated motor torque Tae may be calculated by using the steering torque Th as an input to a combination process that combines an inverse model of the nominal model Pn with a filter Hd. In this case, second, a difference calculation process is executed that calculates the difference between the estimated motor torque Tae and the sum of the open-loop control input Mff and the feedback control input Mfb. In this case, third, the torque command value calculation process M20 is a process that corrects the sum of the open-loop control input Mff and the feedback control input Mfb using the output of the difference calculation process. In this case, the correction process is composed of the combination process, the difference calculation process, and the torque command value calculation process M20. Note that the output of the difference calculation process is an amount corresponding to the difference between the steering torque estimated by the nominal model Pn and the actual steering torque Th.

[0084] "About operation processing" In the process shown in FIG. 2 , the operation process uses the torque of the assist motor 30 as the control variable and the value obtained by converting the assist torque Ta into torque of the assist motor 30 as the target value of the control variable. However, this is not limited to this. For example, the operation process may include a process of calculating a target value for the rotation angle of the assist motor 30 from the axial force Fa. In this case, the operation process is a process of operating the assist motor 30 in accordance with a feedback control operation variable that uses the rotation angle of the assist motor 30 as the control variable. Note that the axial force Fa is the sum of the steering torque Th and a value obtained by correcting the operation variable determined from the open-loop operation variable Mff and the feedback operation variable Mfb with the estimated second disturbance torque de. Therefore, the operation process is a process of operating the inverter 32 in accordance with a value obtained by correcting the operation variable determined from the open-loop operation variable Mff and the feedback operation variable Mfb with the estimated second disturbance torque de. This is a process of controlling the torque of the assist motor 30 so as to generate a torque corresponding to a value obtained by correcting the operation amount determined from the open-loop operation amount Mff and the feedback operation amount Mfb according to the estimated second disturbance torque de.

[0085] Note that the embodiment to which the modification including the feedback control of the angle can be applied is not limited to the embodiment shown in Fig. 2. For example, it may be applied to the embodiment shown in Fig. 6. "About steering control devices" In the configuration shown in FIG. 5, the device that operates the reaction motor 70 and the device that operates the steering motor 80 may be separate devices.

[0086] The steering control device is not limited to a device that includes the PU 42 and the storage device 44 and executes software processing. For example, it may include a dedicated hardware circuit such as an ASIC that executes at least part of the processing executed in the above embodiment. That is, the control device may include a processing circuit having any of the following configurations (a) to (c):

[0087] (a) A processing circuit comprising a processing device that executes all of the above processes according to a program, and a program storage device such as a memory device that stores the program. (b) A processing circuit comprising a processing device and a program storage device that execute part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing.

[0088] (c) A processing circuit having dedicated hardware circuitry for performing all of the above processes. Here, there may be a plurality of software execution devices each having a processing device and a program storage device, and there may also be a plurality of dedicated hardware circuits.

[0089] "About steering control methods" The entity that executes the various controls described above is not limited to a steering control device attached to the vehicle. For example, some of the processing for control to the target steering torque Th*, such as the disturbance observer M30, may be executed by a mobile terminal of the driver.

[0090] "About the input section" The input unit to which the steering torque is input is not limited to the steering wheel 12. "About the power transmission cutoff state" The configuration for interrupting the power transmission between the input section to which the steering torque is input and the steered wheels 20 is not limited to the configuration illustrated in Fig. 4. For example, a clutch may be provided between the input shaft 14a and the output shaft 14b.

[0091] "About the steering device" The actuator used to steer steered wheels 20 may be, for example, one in which assist motor 30 or steering motor 80 is arranged coaxially with steering shaft 16. Alternatively, for example, one in which the power of assist motor 30 or steering motor 80 is transmitted to steering shaft 16 via a belt-type reducer using a ball screw mechanism may be used.

[0092] The steering device capable of changing the relationship between the steering angle and the turning angle is not limited to a steering device in which the transmission of power between the steering wheel 12 and the steered wheels 20 is blocked, as shown in Fig. 4. For example, a steering device capable of changing the relationship between the steering angle and the turning angle may be configured by using a variable gear as the gear that enables the transmission of power between the steering wheel 12 and the steered wheels 20.

Claims

1. configured to perform an operation amount calculation process, a correction process, and an operation process; the operation amount calculation process is a process for calculating an operation amount of control using a steering torque as a control amount and a target steering torque as a target value of the control amount, The steering torque is a torque input by a driver to a steering device, the target steering torque is a target value of the steering torque, the correction process is a process that uses the steering torque and the operation amount as inputs, and corrects the operation amount by a correction amount corresponding to a difference between the steering torque assumed by a nominal model and the actual steering torque, the operation processing is processing for operating a motor of the steering device so as to generate a torque corresponding to the operation amount corrected by the correction processing, The correction process is a process that is repeatedly executed at a predetermined cycle, and includes intermediate processing that sets the correction amount calculated at one sampling timing of the operation amount to an intermediate value of the correction amounts that are virtually calculated using each of the operation amounts obtained at two adjacent sampling timings.

2. 2. The steering control device according to claim 1, wherein the intermediate processing includes a process of setting the operation amount used in calculating the correction amount to an average value of the operation amounts obtained at two adjacent sampling times.

3. the transfer function of the correction process includes an integral element, 2. The steering control device according to claim 1, wherein the intermediate processing includes a process of discretizing the integral element by a bilinear transformation.

4. the correction process includes a steering torque estimation process and a disturbance estimation process, the steering torque estimation process is a process of calculating an estimated steering torque, which is an estimated value of the steering torque according to the operation amount, by utilizing the nominal model; the disturbance estimation process is a process of estimating a disturbance torque from a difference between the estimated steering torque and the steering torque by utilizing an inverse model of the nominal model and a filter, 2. The steering control device according to claim 1, wherein the degree of the polynomial in the denominator of the transfer function of the combination of the inverse model and the filter is greater than the degree of the polynomial in the numerator of the transfer function.

5. the degree of the polynomial in the denominator of the transfer function of the nominal model is second order; 5. The steering control device according to claim 4, wherein the degree of the polynomial in the denominator of the transfer function of the filter is third or higher.

6. 6. The steering control device according to claim 5, wherein the polynomial in the denominator of the transfer function of the nominal model includes a first-order term and a zeroth-order term.

7. the operation amount calculation process includes an open-loop operation amount calculation process, the open-loop operation amount calculation process is a process of calculating an open-loop operation amount by inputting the target steering torque into an inverse model of the nominal model, 2. The steering control device according to claim 1, wherein the open-loop manipulated variable is a manipulated variable of open-loop control that uses the steering torque as the controlled variable and a target value of the steering torque as a target value of the controlled variable.

8. the manipulated variable calculation process includes a feedback manipulated variable calculation process, the feedback manipulated variable calculation process is a process of calculating a feedback manipulated variable, 2. The steering control device according to claim 1, wherein the feedback manipulated variable is a manipulated variable of feedback control that uses the steering torque as the controlled variable and the target steering torque as a target value of the controlled variable.

9. 2. The steering control device according to claim 1, wherein the motor is a motor for steering steered wheels of a vehicle.

10. 2. The steering control device according to claim 1, wherein the motor is a motor that applies torque to the input part when power transmission between the steered wheels of the vehicle and the steering torque input part is cut off.

11. The method includes a step of performing an operation amount calculation process, a correction process, and an operation process, the operation amount calculation process is a process for calculating an operation amount of control using a steering torque as a control amount and a target steering torque as a target value of the control amount, The steering torque is a torque input by a driver to a steering device, the target steering torque is a target value of the steering torque, the correction process is a process that uses the steering torque and the operation amount as inputs, and corrects the operation amount by a correction amount corresponding to a difference between the steering torque assumed by a nominal model and the actual steering torque, the operation processing is processing for operating a motor of the steering device so as to generate a torque corresponding to the operation amount corrected by the correction processing, The correction process is a process that is repeatedly executed at a predetermined cycle, and includes intermediate processing that sets the correction amount calculated at one sampling timing of the operation amount to an intermediate value of the correction amounts that are virtually calculated using each of the operation amounts obtained at two adjacent sampling timings.

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