Steering control device and steering control method

Abstract

A steering control device (40) is configured so as to execute feedback processing, operation processing, system state determination processing, and change processing. The feedback processing calculates an operation amount of feedback control in which a prescribed state amount is a control amount and a target value for the prescribed state amount is a target value for the control amount. The prescribed state amount includes steering torque. The steering torque is a torque that is input into the input member (12). The operation processing operates a steering device (10) in accordance with the operation amount. The system state determination processing determines the state of a steering system including the steering device. The change processing includes processing for changing the target value in accordance with the determined state.

Description

Steering control device and steering control method

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

[0002] The following Patent Document 1 describes a steering control device that operates the torque of a motor that assists steering in accordance with an operation amount of feedback control in which steering torque is a controlled variable. In this control device, a target steering torque is set in accordance with the sum of the operation amount of feedback control and the steering torque. Further, in this control device, a target value of the steered angle of the steered wheels is set using an ideal model based on the above sum as an input variable. Then, this control device performs control so that the steered angle approaches the target value.

[0003] Japanese Unexamined Patent Application Publication No. 2020-179830

[0004] Incidentally, limiting processing is generally performed on steering systems from the viewpoint of protection. For reasons such as performing such limiting processing, the state of the steering system is not constant. However, the driver cannot recognize that the state of the system is not constant.

[0005] According to one aspect of the present disclosure, a steering control device is provided. The steering control device is applied to a steering device that steers steered wheels in accordance with an operation of an input member by a driver. The steering control device is configured to execute feedback processing, operation processing, system state determination processing, and change processing. The feedback processing is processing for calculating an operation amount for feedback control in which a predetermined state quantity is a controlled variable, and a target value of the predetermined state quantity is a target value of the controlled variable. The predetermined state quantity includes steering torque. The steering torque is torque input to the input member. The operation processing is processing for operating the steering device in accordance with the operation amount. The system state determination processing is processing for determining a state of a steering system including the steering device. The change processing includes processing for changing the target value in accordance with the determined state.

[0006] Another aspect of this disclosure provides a steering control method. The steering control method is applied to a steering device that steers the steering wheels in response to an operation of an input member by a driver. The steering control method includes performing a feedback process, performing an operation process, performing a system state determination process, and performing a modification process. The feedback process is a process of calculating an operation amount for feedback control in which a predetermined state quantity is a control quantity and the target value of the predetermined state quantity is the target value of the control quantity. The predetermined state quantity includes steering torque. The steering torque is a torque input to the input member. The operation process is a process of operating the steering device in accordance with the operation amount. The system state determination process is a process of determining the state of the steering system including the steering device. The modification process includes a process of changing the target value in accordance with the determined state.

[0007] This is a diagram showing the configuration of the vehicle steering system according to the first embodiment. This is a block diagram showing a part of the processing performed by the control device shown in Figure 1. This is a flowchart showing the procedure of the processing performed by the control device shown in Figure 1. This is a diagram for explaining the setting of the NT limit sensitivity ΔTnt. This is a diagram for explaining the setting of the low temperature sensitivity ΔTL. This is a diagram showing the configuration of the vehicle steering system according to the second embodiment. This is a block diagram showing a part of the processing performed by the steering control device according to the second embodiment.

[0008] <First Embodiment> The first embodiment will be described below with reference to the drawings. "Configuration of the Steering System" As shown in Figure 1, the steering device 10 is equipped with a steering wheel 12. The steering wheel 12 is an input member that serves as hardware for the driver to communicate their intention to steer. A steering shaft 14 is connected to the steering wheel 12. Therefore, when the steering wheel 12 rotates, the steering shaft 14 rotates together with it. The rotational power of the steering shaft 14 is transmitted to the steering shaft 16. The steering shaft 16 extends along the vehicle width direction (left and right direction in Figure 1). Steering wheels 20 are connected to both ends of the steering shaft 16 via tie rods 18.

[0009] The steering shaft 14 is positioned to intersect with the steering shaft 16. Teeth are formed on both the steering shaft 14 and the steering shaft 16 that mesh with each other. The meshing of these teeth enables the transmission of power from the steering shaft 14 to the steering shaft 16. In other words, the rotational power of the steering shaft 14 is converted into axial displacement power of the steering shaft 16. The axial displacement of the steering shaft 16 is transmitted to the steering wheels 20 via the tie rods 18. This changes the steering angle of the steering wheels 20. The steering angle is the angle at which the tires turn.

[0010] Furthermore, the steering system 10 is equipped with an assist motor 30. The assist motor 30 generates an assist force, which is a force to assist the driver in steering. The rotational power of the assist motor 30 is applied to the drive shaft 34. Teeth that mesh with each other are formed on the drive shaft 34 and the steering shaft 16. The meshing of these teeth enables the transmission of power from the drive shaft 34 to the steering shaft 16. In other words, the rotational power of the drive shaft 34 is converted into axial displacement power of the steering shaft 16. Thus, the rotational power of the assist motor 30 is converted into axial displacement power of the steering shaft 16 via the drive shaft 34. Specifically, the assist motor 30 is, as an example, a three-phase brushless motor. In particular, in this embodiment, a surface magnet synchronous motor (hereinafter referred to as SPM) is used as an example. The output voltage of the inverter 32 is applied to the terminals of the assist motor 30. The inverter 32 converts the terminal voltage of the battery 33, which is a DC voltage source, into an AC voltage.

[0011] The steering control device 40 includes a PU 42 and a storage device 44. The PU 42 is a processing unit that executes software processing such as a CPU. The storage device 44 includes electrically rewritable non-volatile memory and a storage medium such as a disk medium. The storage device 44 stores a steering control program 44a. The steering control device 40 controls the control amount of the controlled object by having the PU 42 execute the steering control program 44a stored in the storage device 44.

[0012] The steering control device 40 refers to the steering torque Ts input to the steering wheel 12 in order to control the control amount. The steering torque Ts is detected by the torque sensor 50. The torque sensor 50 is a sensor that detects the steering torque Ts according to the degree of twisting of the torsion bar 52, which is part of the steering shaft 14. The steering control device 40 also refers to the vehicle speed SPD detected by the vehicle speed sensor 54. The steering control device 40 also refers to the rotation angle θa of the assist motor 30 detected by the rotation angle sensor 56. The steering control device 40 also refers to the currents iu, iv, and iw flowing through the assist motor 30. The currents iu, iv, and iw may be detected as the voltage drop across the shunt resistors provided on each leg of the inverter 32.

[0013] "Processing performed by the steering control device 40" Figure 2 shows the processing performed by the steering control device 40. The processing shown in Figure 2 is achieved by the PU 42 repeatedly executing the steering control program 44a at a predetermined period.

[0014] Rotation conversion process M10 is a process that converts currents iu, iv, and iw into the d-axis current id and the q-axis current iq. Target steering torque setting process M12 is a process that sets the target steering torque Ts* based on the steering axis force Taf and vehicle speed SPD as input variables. Specifically, the target steering torque setting process M12 includes a process that calculates the estimated lateral acceleration Lae based on the steering axis force Taf and vehicle speed SPD as input variables. PU42 changes the estimated lateral acceleration Lae according to the steering axis force Taf, provided that the absolute value of the estimated lateral acceleration Lae when the absolute value of the steering axis force Taf is large is greater than or equal to the absolute value of the estimated lateral acceleration Lae when the absolute value of the steering axis force Taf is small. This process may, for example, be a process that multiplies the steering axis force Taf by a coefficient corresponding to the vehicle speed SPD and assigns that value to the estimated lateral acceleration Lae.

[0015] Furthermore, in statements such as "Change B according to A, provided that when A is large, B is greater than or equal to when A is small," "when A is large" and "when A is small" refer to the relative magnitude relationship when comparing the two. For example, "when A is large" corresponds to "when A is the first value," and "when A is small" corresponds to "when A is the second value, which is smaller than the first value." Also, the above statement means that, depending on the settings of the first and second values, B when A is the first value may be larger than B when A is the second value. Furthermore, the above statement means that B is changed according to A so that when B is large, A is larger than A when B is small.

[0016] The target steering torque setting process M12 includes a process for calculating the target steering torque Ts* based on the estimated lateral acceleration Lae as an input variable. PU42 changes the target steering torque Ts* according to the estimated lateral acceleration Lae, provided that the absolute value of the target steering torque Ts* when the absolute value of the estimated lateral acceleration Lae is large is greater than or equal to the absolute value of the target steering torque Ts* when the absolute value of the estimated lateral acceleration Lae is small. This process, as an example, involves PU42 performing a map calculation on the target steering torque Ts* with map data stored in the storage device 44. The input variable for this map data is the estimated lateral acceleration Lae, and the output variable for the map data is the target steering torque Ts*.

[0017] Here, map data is a set of data consisting of discrete values ​​of input variables and corresponding values ​​of output variables for each of the input variable values. Furthermore, a map operation is a process that sets the value of the corresponding output variable of the map data as the calculation result if the value of an input variable matches any of the values ​​of the input variables in the map data. Alternatively, if the value of an input variable does not match any of the values ​​of the input variables in the map data, the map operation is a process that sets the value obtained by interpolation of the values ​​of multiple output variables included in the map data as the calculation result. Or, instead, if the value of an input variable does not match any of the values ​​of the input variables in the map data, the map operation may be a process that sets the value of the output variable of the map data corresponding to the closest value among the multiple values ​​of the input variables included in the map data as the calculation result.

[0018] The steering operation amount calculation process M16 calculates the steering operation amount Ms, which is the controlled amount of the control where the steering torque Ts is the controlled amount and the target steering torque Ts* is the target value of the controlled amount. This controlled amount is calculated based on the controlled amount of the closed-loop control. The closed-loop control may be a PD controller. The closed-loop controller may include a disturbance observer. The steering operation amount Ms may be the sum of the controlled amount of the closed-loop control and the controlled amount of the open-loop control. Note that the steering operation amount calculation process M16 corresponds to the torque feedback process.

[0019] The steering axis force calculation process M18 calculates the steering axis force Taf by adding the steering torque Ts to the steering operation amount Ms. Since the steering torque Ts is the torque applied to the steering shaft 14, in this embodiment the steering axis force Taf is a value obtained by converting the force applied in the axial direction of the steering shaft 16 into the torque applied to the steering shaft 14.

[0020] The normative model calculation process M20 calculates the target steering equivalent angle θp*, which is the target value of the steering equivalent angle θp, based on the steering axis force Taf as an input variable. The steering equivalent angle θp is a variable that indicates the steering angle of the steering wheel 20. The steering equivalent angle θp may, for example, be the rotation angle of the drive shaft 34. More specifically, the normative model calculation process M20 calculates the target steering equivalent angle θp* based on the model equation expressed in the following equation (c1).

[0021] Taf = K・θp* + C・θp*' + J・θp*'' …(c1) The model expressed by the above equation (c1) models the value shown by the equivalent steering angle θp when a torque equal to the steering axis force Taf is input to the steering shaft 14. In the above equation (c1), the viscosity coefficient C models the friction of the steering device 10. The inertia constant J models the inertia of the steering device 10. The elastic modulus K models the specifications of the suspension and wheel alignment of the vehicle on which the steering device 10 is mounted. This model is not an accurate representation of the actual steering device 10 or the vehicle on which the steering device 10 is mounted, but rather a normative model designed to make the behavior of the steering angle in response to the input ideal. In other words, in this embodiment, the steering feel can be adjusted through the design of the normative model.

[0022] Specifically, in the inertial torque calculation process M22, the viscous term "C・θp*'", the model axial force Fm, and the deviation compensation axial force Fc are subtracted from the steering axial force Taf. The target angular acceleration αp* (=θp*'') is calculated by dividing the output value of the inertial torque calculation process M22 by the inertial constant J in the inertial constant division process M24. The integration process M26 calculates the target angular velocity ωp* (=θp*') based on the target angular acceleration αp* as an input variable. The integration process M28 calculates the target steering equivalent angle θp* based on the target angular velocity ωp* as an input variable.

[0023] The viscosity coefficient multiplication process M30 calculates the viscosity term "C・θp*'" by multiplying the target angular velocity ωp* by the viscosity coefficient C. The model axial force calculation process M32 calculates the model axial force Fm based on the target steering equivalent angle θp* and the q-axis current iq as input variables. The model axial force calculation process M32 includes a process to change the model axial force Fm according to the target steering equivalent angle θp*, provided that the absolute value of the model axial force Fm when the absolute value of the target steering equivalent angle θp* is large is greater than or equal to the absolute value of the model axial force Fm when the absolute value of the target steering equivalent angle θp* is small. This process demonstrates the properties of the axial force according to the elastic modulus K described above. The model axial force calculation process M32 also includes a process to calculate the model axial force Fm based on the q-axis current iq as an input variable. The model axial force calculation process M32 includes a process to change the model axial force Fm according to the q-axis current iq, provided that the absolute value of the model axial force Fm when the absolute value of the q-axis current iq is large is greater than or equal to the model axial force Fm when the absolute value of the q-axis current iq is small.

[0024] The model axial force calculation process M32 is, as an example, a process in which the PU 42 performs a map calculation on the model axial force Fm with the map data stored in the memory device 44. Here, the map data is data in which the target steering equivalent angle θp* and the q-axis current iq are input variables and the model axial force Fm is the output variable.

[0025] The deviation calculation process M34 outputs the deviation Δ, which is the value obtained by subtracting the q-axis current iq from the q-axis current command value iq*. The deviation axial force calculation process M36 calculates the deviation compensation axial force Fc based on the deviation Δ as an input variable. The deviation axial force calculation process M36 changes the deviation compensation axial force Fc according to the deviation Δ, provided that the deviation compensation axial force Fc when the deviation Δ is large is greater than or equal to the deviation compensation axial force Fc when the deviation Δ is small.

[0026] The angle manipulation amount calculation process M40 calculates the angle manipulation amount Mt, which is the control amount where the steering equivalent angle θp is the control amount and the target steering equivalent angle θp* is the target value of the control amount. The addition process M42 is the process of adding the steering manipulation amount Ms to the angle manipulation amount Mt and substituting the result into the required torque Td. The steering equivalent angle θp is calculated by PU42 based on the rotation angle θa as the input variable.

[0027] The conversion process M44 converts the requested torque Td into a torque command value Tm0* for the assist motor 30 by dividing the requested torque Td by the reduction ratio Km. The limiting process M46 limits the magnitude of the torque command value Tm0*. The limiting process M46 includes NT limiting processing. NT limiting processing limits the absolute value of the torque command value Tm0* to less than or equal to the NT guard value, which is an upper limit guard value. PU42 changes the NT guard value according to the angular velocity ωp, provided that the NT guard value when the absolute value of the angular velocity ωp is large is less than or equal to the NT guard value when the absolute value of the angular velocity ωp is small. The angular velocity ωp is calculated by PU42 based on the steering equivalent angle θp as an input variable.

[0028] The limiting process M46 includes overheat protection processing. Overheat protection processing is a process that limits the magnitude of the current flowing through the inverter 32 to a small value when the temperature of the assist motor 30, inverter 32, etc. exceeds a threshold value. This process, as an example, lowers the upper limit guard value of the magnitude of the current flowing through the inverter 32. The temperature of the assist motor 30, inverter 32, etc. is calculated, as an example, by PU42 according to the integration process of the sum of the squares of the currents id and iq.

[0029] The torque command value Tm* output by the limiting process M46 is set based on the smaller of the absolute values ​​of the output value of the NT limiting process and the output value of the overheat protection process. The operation signal generation process M48, as an operation process, generates and outputs an operation signal MSt for the inverter 32 to bring the torque of the assist motor 30 closer to the torque command value Tm*. The operation signal generation process M48 includes, as an example, a current feedback process where the target values ​​of the controlled quantities are the q-axis current command value iq* determined from the torque command value Tm* and the d-axis current command value id* set to zero. Here, the q-axis current command value iq* as an input variable for the deviation calculation process M34 is calculated for current feedback control. The operation signal MSt is actually the operation signal for each arm of each leg of the inverter 32.

[0030] State-sensitive processing M50 is a process that changes the target steering torque Ts* and the target steering equivalent angle θp* according to the state of the steering system equipped with the steering device 10. "Details of State-Sensitive Processing M50" Figure 3 shows the procedure of state-sensitive processing M50. The process shown in Figure 3 is realized by the PU 42 repeatedly executing the steering control program 44a, for example, at a predetermined period.

[0031] In the series of processes shown in Figure 3, PU42 first calculates the NT limit sensitivity ΔTnt (S10). The NT limit sensitivity ΔTnt is a sensitivity corresponding to the NT limiting process. Figure 4 shows an example of setting the NT limit sensitivity ΔTnt. The solid line in Figure 4 represents the NT guard value. The NT guard value is set to a smaller value as the absolute value of the angular velocity ωp increases. Region A1 where the torque command value Tm0* is greater than the solid line is a region where the absolute value of the torque command value Tm* is smaller than the absolute value of the torque command value Tm0*. That is, it is a region where the torque command value Tm* is limited by the NT limiting process. In contrast, region A2, represented by a faint dot and slightly smaller than the solid line, is a region close to the region where the torque command value Tm* is limited by the NT limiting process. Regions where the torque is smaller than region A2 are region A3, which is shown as a blank area in Figure 4, and are regions where no NT limiting process is performed.

[0032] PU42 determines whether the torque command value Tm0* is in a first state where it is in region A1, a second state where it is in region A2, or a third state where it is in region A3. Then, PU42 sets the NT limit sensitivity ΔTnt to different values ​​depending on which of the three states is present. For example, PU42 sets the NT limit sensitivity ΔTnt to its maximum value in region A1 where the absolute value of the torque command value Tm0* is greater than the solid line in Figure 4. In that case, PU42 should set the NT limit sensitivity ΔTnt to a value between the blank region A3 and region A1 above the solid line in region A2 where the dots are faint in Figure 4.

[0033] Returning to Figure 3, PU42 calculates the overheat protection sensitivity ΔToh (S12). The overheat protection sensitivity ΔToh is set using the same concept as the NT limit sensitivity ΔTnt. That is, PU42 sets the overheat protection sensitivity ΔToh to different values ​​depending on whether the temperature of the assist motor 30, etc. is above the threshold, whether the temperature is below the threshold but close to the threshold, or otherwise. As an example, PU42 sets the overheat protection sensitivity ΔToh to a larger value in the region where the temperature is above the threshold, the region where the temperature is below the threshold but close to the threshold, and then the other regions.

[0034] PU42 calculates the low voltage sensitivity ΔTlv according to the terminal voltage of the battery 33 (S14). PU42 sets the low voltage sensitivity ΔTlv to different values ​​depending on whether the terminal voltage of the battery 33 is above or below the threshold voltage. The threshold voltage is the lower limit of an appropriate value for controlling the torque of the assist motor 30. In the region where the terminal voltage is above but close to the threshold voltage, PU42 may set the low voltage sensitivity ΔTlv to an intermediate value between the region where the terminal voltage is even higher and the region where it is significantly lower than the threshold voltage. As an example, PU62 sets the low voltage sensitivity ΔTlv in the region where the terminal voltage is above the threshold voltage to a smaller value than the low voltage sensitivity ΔTlv in the region close to the threshold voltage. Note that the limiting process M46 shown in Figure 2 may include a process to lower the upper limit guard value of the torque command value Tm* when the terminal voltage is below the threshold voltage.

[0035] PU42 calculates the low-temperature sensitivity ΔTL (S16). PU42 sets the low-temperature sensitivity ΔTL to a value corresponding to the viscosity of the grease applied to the parts of the steering device 10 where the gears mesh.

[0036] Figure 5 illustrates the setting of the low-temperature sensitivity ΔTL. In Figure 5, darker dots are assigned when the temperature T is low compared to when it is high. When the temperature T is equal to or above the specified temperature Tth, the area is blank. As an example, PU42 changes the low-temperature sensitivity ΔTL according to the temperature T, under the condition that the low-temperature sensitivity ΔTL at a low temperature T is greater than or equal to the low-temperature sensitivity ΔTL at a high temperature T. Figure 5 schematically shows that the darker the dot, the larger the value of the low-temperature sensitivity ΔTL.

[0037] Returning to Figure 3, PU 42 specifies the map data to be used in the target steering torque setting process M12 (S18). That is, there are multiple types of map data to be used in the target steering torque setting process M12, and the map data used to calculate the target steering torque Ts* is specified by the process in S18. PU 42 may specify map data in which, for example, the larger the maximum value of the NT limit sensitivity ΔTnt, the overheat protection sensitivity ΔToh, and the low voltage sensitivity ΔTlv, the larger the absolute value of the target steering torque Ts* relative to the absolute value of the estimated lateral acceleration Lae. PU 42 may also specify map data taking into account the low temperature sensitivity ΔTL.

[0038] PU42 specifies the values ​​of the model variables in the normative model calculation process M20 and the map data used by the model axial force calculation process M32 (S20). As an example, PU42 may set the value of the viscosity coefficient C according to the low temperature sensitivity ΔTL. Specifically, PU42 may change the viscosity coefficient C according to the low temperature sensitivity ΔTL, provided that the value of the viscosity coefficient C when the temperature T is low is greater than or equal to the value of the viscosity coefficient C when the temperature T is high. As an example, PU42 may change the inertia constant J according to at least one of the NT limit sensitivity ΔTnt, the overheat protection sensitivity ΔToh, and the low voltage sensitivity ΔTlv. Also, as an example, PU42 may specify the map data used by the model axial force calculation process M32 according to at least one of the NT limit sensitivity ΔTnt, the overheat protection sensitivity ΔToh, and the low voltage sensitivity ΔTlv.

[0039] Furthermore, when PU42 completes the process in S20, it terminates the series of processes shown in Figure 3. Processes S10 to S16 correspond to system state determination processes. Processes S18 and S20 correspond to modification processes.

[0040] <Operation and Effects of This Embodiment> When the absolute value of the torque command value Tm0*, which is used as a limiting judgment variable, is greater than the NT guard value, the PU 42 limits the absolute value of the torque command value Tm* to the NT guard value. As a result, depending on the torque of the assist motor 30, it may not be possible to achieve the required torque Td. In that case, the PU 42 specifies map data for map calculation of the target steering torque Ts* so that the absolute value of the target steering torque Ts* becomes larger than the absolute value of the estimated lateral acceleration Lae. As a result, the driver feels that the absolute value of the steering torque Ts required for turning the steering wheel 12 has become larger, and feels that turning the steering wheel has become heavier. Therefore, the driver can understand that it is more difficult to steer the steering wheels 20 compared to when there is no limitation by the NT guard value.

[0041] Furthermore, if the temperature of the assist motor 30 or inverter 32, which are limiting variables, is high, the PU 42 limits the current of the assist motor 30 to a lower value. As a result, depending on the torque of the assist motor 30, it may become difficult to achieve the required torque Td. In that case, the PU 42 specifies map data for mapping the target steering torque Ts* so that the absolute value of the target steering torque Ts* becomes larger with respect to the absolute value of the estimated lateral acceleration Lae. As a result, the driver feels that the absolute value of the steering torque Ts required for turning the steering wheel 12 has become larger, and feels that turning the steering wheel has become heavier. Therefore, the driver can understand that it is more difficult to steer the steering wheels 20 compared to when there is no overheating protection limitation.

[0042] Here, if the absolute value of the current flowing through the inverter 32 is less than or equal to the upper limit guard value, the assist motor 30 can achieve the required torque Td due to the overheat protection process, even if the upper limit guard value is set to a low value. However, when the upper limit guard value is set to a low value due to the overheat protection process, the torque of the assist motor 30 is more easily limited compared to when it is not set. Therefore, by specifying the map data above, the driver can be informed that the torque of the assist motor 30 is likely to be limited.

[0043] Furthermore, when the terminal voltage of the battery 33 is low, the PU 42 specifies map data for calculating the target steering torque Ts* so that the absolute value of the target steering torque Ts* becomes larger relative to the absolute value of the estimated lateral acceleration Lae. As a result, the driver feels that the absolute value of the steering torque Ts required to turn the steering wheel 12 is larger, and perceives that turning the steering wheel has become heavier. Therefore, the driver can understand that it is more difficult to steer the steering wheels 20 compared to when the terminal voltage of the battery 33 is normal.

[0044] Here, even when the terminal voltage of the battery 33 is low, if the absolute value of the required torque Td is small, the assist motor 30 can achieve the required torque Td. However, when the terminal voltage is low, the magnitude of the torque of the assist motor 30 is likely to be limited. Therefore, according to the specification of the map data described above, it is possible to notify the driver that the magnitude of the torque of the assist motor 30 is in a situation where it is likely to be limited.

[0045] According to the present embodiment described above, the following additional functions and effects can be obtained. (1-1) The PU 42 sets the viscosity coefficient C to a larger value when the temperature T is less than the specified temperature Tth. This allows the driver to physically feel that the viscosity of the steering device 10 is high due to the high viscosity of the grease caused by low temperature.

[0046] (1-2) Although the restriction by the restriction process M46 is not applied, the PU 42 sets the absolute value of the target steering torque Ts* relative to the absolute value of the estimated lateral acceleration Lae to a larger value in a situation close to where the restriction will be applied. Therefore, it is possible to suppress the driver from feeling that the steering feeling changes abruptly.

[0047] In particular, in the case of NT restriction processing that sets an NT guard value in accordance with the angular velocity ωp which is a continuous variable, unlike overheat protection processing, it is difficult to define whether restriction is implemented due to a decrease in the NT guard value. Therefore, it is defined that restriction is implemented when the absolute value of the actual torque is larger than the NT guard value. However, in this case, if the absolute value of the target steering torque Ts* is set to a larger value only when restriction is implemented, information cannot be conveyed to the driver until the assist motor 30 enters a situation where it cannot achieve the actual required torque Td. In contrast, by setting the absolute value of the target steering torque Ts* to a larger value in a situation close to where restriction will be applied, the driver can perceive a sign of NT restriction processing.

[0048] However, for overheat protection processing, PU42 specifies different map data depending on whether the temperature of the assist motor 30 or the like as a limit determination variable is equal to or higher than a threshold value, the temperature is equal to or lower than the threshold value but close to the threshold value, and other cases. Accordingly, when the temperature of the assist motor 30 or the like is equal to or lower than the threshold value but becomes close to the threshold value, PU42 sets the absolute value of the target steering torque Ts* to a larger value. This allows the driver to sense a sign of the overheat protection processing. Note that when the limiting process M46 includes a process of reducing the upper guard value of the torque command value Tm* if the terminal voltage is less than the threshold voltage, the same circumstances apply to this process as well. In this case, the limit determination variable is the terminal voltage.

[0049] <Second Embodiment> Hereinafter, a second embodiment will be described with a focus on differences from the first embodiment with reference to the drawings.

[0050] "Configuration of Steering System" Fig. 6 shows the configuration of a steering control system according to the present embodiment. In Fig. 6, members corresponding to those shown in Fig. 1 are denoted by the same reference numerals for convenience.

[0051] As shown in Fig. 6, in the steering device 10, a steering shaft 14 is separated into an input shaft 14a connected to a steering wheel 12 and an output shaft 14b engaged with a steered shaft 16. Note that the output shaft 14b may be omitted in the present embodiment.

[0052] A reaction force motor 70 is provided on the input shaft 14a. The reaction force motor 70 is a motor for applying a reaction force, which is a torque in a direction opposite to the torque input by the driver, to the steering wheel 12. As an example, the reaction force motor 70 is a three-phase brushless motor. Note that the output voltage of an inverter 72 is applied to the terminals of the reaction force motor 70.

[0053] Torque from a steered motor 80 is applied to the steered shaft 16 via a drive shaft 34. As an example, the steered motor 80 is a three-phase brushless motor. Note that the output voltage of an inverter 82 is applied to the terminals of the steered motor 80.

[0054] 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 a control quantity of the controlled object. The steering control device 40 also operates the inverter 82 to control the steering angle of the steering wheels 20, which is a control quantity of the controlled object.

[0055] The steering control device 40 refers to the rotation angle θb of the reaction force motor 70, detected by the rotation angle sensor 90, in order to control the reaction force, which is a control variable. The steering control device 40 also refers to the currents ius, ivs, and iws flowing through the reaction force motor 70, in order to control the reaction force. The currents ius, ivs, and iws may be detected as the voltage drop across the shunt resistors provided on each leg of the inverter 72. The steering control device 40 also refers to the rotation angle θc of the steering motor 80, detected by the rotation angle sensor 92, in order to control the steering angle, which is a control variable. The steering control device 40 also refers to the currents iut, ivt, and iwt flowing through the steering motor 80, in order to control the steering angle. The currents iut, ivt, and iwt may be detected as the voltage drop across the shunt resistors provided on each leg of the inverter 82.

[0056] "Processing performed by the steering control device 40" Figure 7 shows the processing performed by the steering control device 40. The processing shown in Figure 7 is achieved by the PU 42 repeatedly executing the steering control program 44a at a predetermined period, for example. In Figure 7, the same reference numerals are used for processing corresponding to the processing shown in Figure 2 for convenience.

[0057] As shown in Figure 7, in this embodiment, the steering axis force Taf is converted to a reaction torque command value Tr, which is the command value of the torque of the reaction motor 70, in the conversion process M60. The steering-side operation signal generation process M62, as an operation process, is a process that operates the inverter 72 based on the reaction torque command value Tr, which is an input variable. Specifically, the steering-side operation signal generation process M62 includes a process to calculate the control operation amount, the target value of which is the value obtained by converting the reaction torque command value Tr to the torque of the reaction motor 70. The rotation angle θb and currents ius, ivs, and iws are referenced in the calculation of the operation amount. The steering-side operation signal generation process M62 also includes a process to operate the inverter 72 according to the said operation amount. Figure 7 shows the operation signal MSs of the inverter 72. In reality, the operation signal MSs is a separate operation signal for each switching element of the inverter 72.

[0058] The target steering equivalent angle setting process M70 sets the target steering equivalent angle θp* based on the steering angle θs and vehicle speed SPD as input variables. This process includes, as an example, a process to change the target steering equivalent angle θp* according to the steering angle θs, under the condition that the absolute value of the target steering equivalent angle θp* when the absolute value of the steering angle θs is large is greater than or equal to the absolute value of the target steering equivalent angle θp* when the absolute value of the steering angle θs is small. The steering angle θs is calculated by PU42 based on the rotation angle θb as an input variable.

[0059] The steering input calculation process M72 calculates the required torque Td as an input variable for feedback control, where the steering equivalent angle θp is the controlled variable and the target steering equivalent angle θp* is the target value of the controlled variable. The steering equivalent angle θp is calculated by PU42 based on the rotation angle θc as an input variable.

[0060] The conversion process M74 converts the requested torque Td into a steering torque command value Tt0*, which is the torque command value for the steering motor 80. In this embodiment, the steering torque command value Tt0* output by the conversion process M74 is the input variable for the limiting process M46. The output variable of the limiting process M46 is the steering torque command value Tt*.

[0061] In this embodiment, the rotation conversion process M10 is a process that converts the currents iut, ivt, and iwt flowing through the steering motor 80 into the d-axis current id and the q-axis current iq. The steering-side operation signal generation process M80 is a process that operates the inverter 82 based on the steering torque command value Tt* as an input variable. The steering-side operation signal generation process M80 includes a process that calculates the amount of feedback control so that the currents id and iq approach the current command values ​​id* and iq* determined from the steering torque command value Tt*. Figure 7 shows the operation signal MSt of the inverter 82. In reality, the operation signal MSt is a separate operation signal for each switching element of the inverter 82.

[0062] The state-sensitive processing M50 in this embodiment is a process in which, in the target steering torque setting processing M12, map data is specified in which the estimated lateral acceleration Lae is the input variable and the target steering torque Ts* is the output variable.

[0063] <Other Embodiments> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0064] "Regarding Angle Feedback Processing" - It is not essential that angle feedback processing be applied to a steering system 10 in which the steering wheel 12 and the steering wheel 20 are mechanically connected. For example, in Figure 7, feedback control in which the steering angle is the controlled variable may be included. This can be realized by including, for example, a process of setting a target value for the steering angle using an ideal model based on the steering axis force Taf as an input variable, and a process of setting the manipulated variable of the steering angle feedback control to the reaction force torque command value Tr.

[0065] "Regarding the System State Determination Process" - The variables used by the system state determination process to quantify the system state are not limited to NT limit sensitivity ΔTnt, overheat protection sensitivity ΔToh, undervoltage sensitivity ΔTlv, and low temperature sensitivity ΔTL. For example, the variables used to quantify the system state may be limited to any three of the above four variables. Also, for example, the variables used to quantify the system state may be limited to any two of the above four variables. Also, for example, the variables used to quantify the system state may be limited to any one of the above four variables.

[0066] - The system state determination process does not necessarily require that the variables used to quantify the system state be some of the following four variables: NT limit sensitivity ΔTnt, overheat protection sensitivity ΔToh, undervoltage sensitivity ΔTlv, and low temperature sensitivity ΔTL.

[0067] - The system state determination process does not necessarily have to be a process that determines which of three or more distinct states the system is in. For example, in a redundant system where there are two inverters 82 that drive the steering motor 80, the system state determination process may be a process that determines whether or not one of them has malfunctioned and stopped. In other words, the system state determination process may be a process that determines which of two states the system is in.

[0068] - The situations in which the system to be protected by the system state determination process are not limited to situations in which the restriction process exemplified in the above embodiment is executed. If the system state determination process determines a situation in which any system should be protected, the driver can be given a steering feel that communicates the system's status by executing a modification process accordingly.

[0069] "Regarding the modification process" (a) When the steering wheel 12 and the steering wheel 20 are mechanically connected, it is not necessary for the modification process to include both a process to change the target steering torque Ts* and a process to change the target steering equivalent angle θp*.

[0070] (b) In the case of steer-by-wire, the change process does not necessarily have to be a process that changes the target steering torque Ts*. For example, as described in the section on "Angle Feedback Processing", if the process includes setting a target value of the steering angle using an ideal model based on the steering axis force Taf, then the change process may also include a process that changes the target value of the steering angle.

[0071] (c) Other - Modification processing is not limited to processing that modifies the target steering torque Ts* by the target steering torque setting processing M12. For example, if the target steering torque setting processing M12 sets the target steering torque Ts* to a value obtained by multiplying the estimated lateral acceleration Lae by a gain, the modification processing may be processing that modifies the gain.

[0072] - It is not necessary for the modification process to be a process that changes the viscosity coefficient C, or a process that sets the value of the viscosity coefficient C. For example, if the viscosity coefficient C is calculated using map data where the vehicle speed SPD is the input variable and the viscosity coefficient C is the output variable, the modification process may be a process that changes the map data.

[0073] - It is not necessary for the modification process to be a process that modifies the model axial force Fm, or a process that modifies the map data. For example, if the model axial force is set according to a value obtained by multiplying the q-axis current iq by a gain, the modification process may be a process that sets the gain. Also, for example, if the model axial force is set according to a value obtained by multiplying the target steering equivalent angle θp* by a gain, the modification process may be a process that sets the gain. This gain corresponds to the elastic modulus K.

[0074] - The modification process related to the limiting process is not limited to the process of deciding which of three different methods to use for setting the target value. For example, if the overheating protection process is a process that reduces the upper limit guard value of the magnitude of the current flowing through the inverter 32, the modification process may be a process that decides which of two methods to use depending on whether the upper limit guard value is large or small.

[0075] The modification process may involve adjusting two or more map data sets related to the viscosity coefficient C, the inertia constant J, and the model axial force Fm. Here, the map data related to the model axial force Fm may be replaced with gains such as the elastic modulus K.

[0076] "Regarding Torque Variables" - The torque variable, which is a variable that indicates the torque of the assist motor 30 or steering motor, which are motors used to steer the steering wheels, and for which a command value is set, is not limited to the motor torque itself. For example, if the motor is an SPM, the torque variable may be the q-axis current.

[0077] "Regarding the steering control device" The steering control device is not limited to one that performs various processes using a PU. For example, it may be equipped with a dedicated hardware circuit such as an ASIC that performs at least a part of the processes performed in the above embodiment. That is, the steering control device may be equipped with any of the following processing circuits (a) to (c): (a) A processing circuit comprising a processing unit that performs 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 unit and a program storage device that perform a part of the above processes according to a program, and a dedicated hardware circuit that performs the remaining processes. (c) A processing circuit equipped with a dedicated hardware circuit that performs all of the above processes. Here, there may be multiple software execution devices equipped with processing units and program storage devices, or multiple dedicated hardware circuits.

[0078] Regarding the entity that executes the processes: It is not required that the entity that executes each of the above processes be a single control device, nor is it required that all of the executing entities be installed in the vehicle.

Claims

1. A steering control device applied to a steering device that steers the steering wheels in response to an operation of an input member by a driver, the steering control device being configured to perform feedback processing, operation processing, system state determination processing, and modification processing, wherein the feedback processing is a process of calculating an operation amount for feedback control in which a predetermined state amount is a control amount and the target value of the predetermined state amount is the target value of the control amount, the predetermined state amount includes steering torque, the steering torque is a torque input to the input member, the operation processing is a process of operating the steering device in accordance with the operation amount, the system state determination processing is a process of determining the state of the steering system including the steering device, and the modification processing includes a process of changing the target value in accordance with the determined state.

2. The steering control device according to claim 1, which is configured to perform a limiting process, wherein the limiting process is a process that limits the output of the motor for steering the steering wheel to the smaller side.

3. The steering control device according to claim 2, wherein the limiting process is a process that limits the value of the torque variable to the smaller side with respect to the command value of the torque variable, the torque variable is a variable that indicates the torque of the motor, and the changing process includes a process that changes the target value when the situation is close to the situation in which the output of the motor is limited to the smaller side by the limiting process, or when the situation is far from the situation in which the limiting process is close to the situation in which the command value input to the limiting process and the command value output from the limiting process are the same.

4. The steering control device according to claim 2, wherein the limiting process is a process that limits the output of the motor to the smaller side based on a comparison of the magnitude of the value of a limiting determination variable and a threshold, the system state determination process includes a process that determines whether the state of the steering system is a first state, a second state, or a third state, the first state is a state in which the output of the motor is limited to the smaller side by the limiting process, the second state is a state in which the output of the motor is not limited to the smaller side by the limiting process, but the value of the limiting determination variable is close to the threshold, the third state is a state in which the output of the motor is not limited to the smaller side by the limiting process, and the value of the limiting determination variable is farther from the threshold compared to the second state, and the modification process is a process that modifies the target value so that the magnitude of the steering torque required to steer the steering wheel in the second state is smaller than the magnitude of the steering torque in the first state and larger than the magnitude of the steering torque in the third state.

5. The steering control device according to claim 3, wherein the limiting process includes an NT limiting process, the NT limiting process is a process of changing the upper limit guard value according to the rotational speed, provided that the upper limit guard value of the absolute value of the command value when the absolute value of the rotational speed of the motor is large is less than or equal to the upper limit guard value when the absolute value of the rotational speed is small, the system state determination process includes a process of determining whether the state of the steering system is a first state, a second state, or a third state, the first state is a state in which the absolute value of the command value is greater than the upper limit guard value, the second state is a state in which the absolute value of the command value is less than or equal to the upper limit guard value and close to the upper limit guard value, the third state is a state in which the absolute value of the command value is smaller than the second state, and the modification process is a process of changing the target value such that the magnitude of the steering torque required to steer the steering wheel in the second state is smaller than the magnitude of the steering torque in the first state and larger than the magnitude of the steering torque in the third state.

6. The steering control device according to claim 1, wherein the modification process includes a process to change the target value of the steering torque according to the determined state.

7. The steering control device according to claim 1, wherein the predetermined state quantity includes the rotation angle of the rotation axis of the steering device, the feedback process includes a torque feedback process and an angle feedback process, the torque feedback process is a process for calculating an manipulated variable of feedback control in which the steering torque is the controlled variable, the angle feedback process is a process for calculating an manipulated variable of feedback control in which the rotation angle is the controlled variable, and the device is configured to perform a target angle setting process, the target angle setting process is a process for calculating a target rotation angle which is the target value of the rotation angle using a reference model based on the manipulated variable calculated by the torque feedback process as an input variable, the operation process is a process for operating the steering device in accordance with the manipulated variable of feedback control in which the rotation angle is the controlled variable, and the change process includes a process for changing the value of a model variable of the reference model.

8. The steering control device according to claim 7, wherein the system state determination process includes a process for determining whether the temperature of the steering device is below a specified temperature, and the modification process includes a process for changing the value of the model variable depending on whether the temperature of the steering device is below the specified temperature.

9. A steering control device according to claim 7, configured to perform a limiting process, wherein the limiting process is a process that limits the output of the motor for steering the steering wheel to the smaller side based on a comparison of the magnitude of the value of a limiting determination variable and a threshold, the system state determination process includes a process that determines whether the state of the steering system is a first state, a second state, or a third state, the first state being a state in which the output of the motor is limited to the smaller side by the limiting process, the second state being a state in which the output of the motor is not limited to the smaller side by the limiting process, but the value of the limiting determination variable is close to the threshold, the third state being a state in which the output of the motor is not limited to the smaller side by the limiting process, and the value of the limiting determination variable is farther from the threshold compared to the second state, and the modification process is a process that modifies the target value so that the magnitude of the steering torque required to steer the steering wheel in the second state is smaller than the magnitude of the steering torque in the first state and larger than the magnitude of the steering torque in the third state.

10. A steering control method applied to a steering device that steers the steering wheels in response to an operation of an input member by a driver, comprising: execution of a feedback process, execution of an operation process, execution of a system state determination process, and execution of a modification process, wherein the feedback process is a process for calculating an operation amount for feedback control in which a predetermined state quantity is a control quantity and the target value of the predetermined state quantity is the target value of the control quantity, the predetermined state quantity includes steering torque, the steering torque is a torque input to the input member, the operation process is a process for operating the steering device in accordance with the operation amount, the system state determination process is a process for determining the state of the steering system including the steering device, and the modification process includes a process for changing the target value in accordance with the determined state.

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