Steering control system

Abstract

To provide a steering control device that can meet the demand for increased heat generation. [Solution] The PU superimposes a warm-up torque Tw(1) onto the torque generated by energizing the first stator coil. The PU superimposes a warm-up torque Tw(2) onto the torque generated by energizing the second stator coil. The warm-up torque Tw(1) and warm-up torque Tw(2) are set to have the same amplitude and opposite phase.

Description

Technical Field

[0001] The present invention relates to a steering control device.

Background Art

[0002] Patent Document 1 describes a steering mechanism driven by a motor having two systems of stator coils insulated from each other. Patent Document 2 describes a device that vibrates the torque of a motor that drives a steering mechanism when the steering mechanism freezes.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a steering mechanism is driven by a motor having a plurality of systems of stator coils as in Patent Document 1 above, Patent Document 2 does not disclose how to deal with freezing.

Means for Solving the Problems

[0005] Hereinafter, means for solving the above problems and their effects will be described. 1. A steering control device in which a steering mechanism is the target of control, wherein the steering mechanism is configured such that the rotational power of a motor having a plurality of independent stator coil systems is converted into power to steer the steering wheels, and is configured to perform a request determination process and an energization process, wherein the request determination process is a process of determining whether or not an increase in heat generation is required, and the energization process is a process of energizing the first stator coil and the second stator coil such that the magnitude of the torque generated by energizing the first stator coil of the plurality of systems is reduced by the torque generated by energizing the second stator coil of the plurality of systems, and the torque generated by energizing the first stator coil is a periodically fluctuating torque.

[0006] In the above configuration, the torque generated by energizing the first stator coil is reduced by the torque generated by energizing the second stator coil. Therefore, the amount of heat generated tends to be large relative to the magnitude of the motor torque generated by the energizing process. Moreover, the torque generated by energizing the first stator coil fluctuates periodically. Therefore, it is possible to prevent the sum of the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil from being fixed to a constant right-hand or left-hand turning torque.

[0007] 2. The steering control device according to paragraph 1, wherein the energizing process includes energizing the first system of stator coils such that the torque generated by energizing the first system of stator coils oscillates periodically, and energizing the second system of stator coils such that the torque generated by energizing the second system of stator coils oscillates periodically.

[0008] In the above configuration, both the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil oscillate periodically. Therefore, it is possible to further suppress the situation in which their sum torque is fixed to a constant rightward or leftward turning torque.

[0009] 3. The steering control device according to item 2, wherein the energizing process includes energizing the first stator coil and the second stator coil such that the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil are in opposite phases to each other.

[0010] In the above configuration, since the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil are in opposite phases, it is possible to suppress the absolute value of their sum of torques from becoming too large.

[0011] 4. The steering control device according to 2 or 3 above, wherein the torque generated by energizing the first stator coil has a value obtained by superimposing a periodic signal on a first DC component which is a DC component greater than zero, and the torque generated by energizing the second stator coil has a value obtained by superimposing a periodic signal on a second DC component which is a DC component with the opposite sign to the first DC component.

[0012] In the above configuration, since the first DC component and the second DC component have opposite signs, the absolute value of their net torque can be reduced. Moreover, the torque generated by energizing the first stator coil has a value in which a periodic signal is superimposed on the first DC component, and the torque generated by energizing the second stator coil has a value in which a periodic signal is superimposed on the second DC component. Therefore, even if there is a difference between the absolute values ​​of the first DC component and the second DC component, it is possible to prevent their sum from being fixed to a torque on the right-hand side or a torque on the left-hand side on a steady basis.

[0013] 5. The steering control device according to item 4 above, wherein the energizing process includes a process to change the DC component of the one that is not abnormal to zero if an abnormality occurs in either the energizing of the first stator coil or the energizing of the second stator coil.

[0014] In the above configuration, if an abnormality occurs in either the energization of the first stator coil or the energization of the second stator coil, the torque generated by the energization of the abnormal system becomes zero. Therefore, if the torque of the system that is not abnormal has a DC component, there is a risk that it will be permanently fixed as either a right-hand or left-hand turn torque. To address this, the above configuration changes the DC component of the system that is not abnormal to zero. This prevents the torque generated by the system that is not abnormal from being permanently fixed as either a right-hand or left-hand turn torque.

[0015] 6. The steering control device according to item 1, wherein the torque generated by energizing the first stator coil has a value obtained by superimposing a periodic signal on a first DC component which is a DC component greater than zero, and the torque generated by energizing the second stator coil has a second DC component which is a DC component with the opposite sign to the first DC component.

[0016] In the above configuration, since the first DC component and the second DC component have opposite signs, the absolute value of their net torque can be reduced. Moreover, since the torque generated by energizing the first stator coil has a value in which a periodic signal is superimposed on the first DC component, even if the first DC component and the second DC component do not cancel each other out, it is possible to suppress the total torque from being fixed steadily to either a right-hand or left-hand turning torque.

[0017] 7. The steering control device according to any one of the above 1 to 6, wherein the request determination process is a process for determining whether or not an abnormality occurs in which the force required for steering increases due to freezing of the steering mechanism, and the request for an increase in the amount of heat generated means that the abnormality occurs.

[0018] In the above configuration, when an abnormality occurs due to freezing of the steering mechanism, the abnormality can be eliminated by increasing the calorific value.

Brief Description of the Drawings

[0019] [Figure 1] It is a block diagram showing the configuration of a steering control device and a steering device according to an embodiment. [Figure 2] It is a block diagram showing a part of the processing executed by the steering control device in FIG. 1. [Figure 3] It is a flowchart showing the procedure of the processing related to the prediction determination of freezing executed by the steering control device in FIG. 1. [Figure 4] It is a flowchart showing the procedure of the processing related to the lock determination executed by the steering control device in FIG. 1. [Figure 5] It is a flowchart showing the procedure of the heat generation processing in FIG. 2. [Figure 6] It is a time chart illustrating the heat generation processing in FIG. 2. [Figure 7] It is a time chart showing a comparative example of the heat generation processing in FIG. 2. [Figure 8] It is a time chart showing the merits of this embodiment with respect to the comparative example in FIG. 6. [Figure 9] It is a time chart illustrating the heat generation processing according to the second embodiment. [Figure 10] It is a time chart illustrating the heat generation processing at the time of a second system abnormality in the second embodiment. [Figure 11] It is a time chart illustrating the heat generation processing according to the third embodiment.

Mode for Carrying Out the Invention

[0020] <First Embodiment> Hereinafter, the first embodiment will be described with reference to the drawings. “Steering System” Figure 1 shows the configuration of the steering system according to this embodiment. As shown in Figure 1, the electric power steering device 10 includes a steering shaft 14 that rotates integrally with the steering wheel 12. The rotational power of the steering shaft 14 is converted into axial displacement power of the rack shaft 16. The axial displacement power of the rack shaft 16 is converted into power to steer the steering wheels 20 via the tie rods 18.

[0021] The motor unit 30 houses the motor 32 and the control board 34 within its casing. The drive pulley 40 is connected to the rotating shaft 32a of the motor 32 so as to be able to rotate integrally with the rotating shaft 32a. The rotational power of the drive pulley 40 is transmitted to the driven pulley 44 via the belt 42. The rotational power of the driven pulley 44 is converted into axial displacement power of the rack shaft 16 via the ball screw mechanism 46. The drive pulley 40 and the motor 32 are located vertically below the rack shaft 16.

[0022] The rack shaft 16, drive pulley 40, belt 42, driven pulley 44, and ball screw mechanism 46 are housed in the rack housing 50. The connection between the rack shaft 16 and the tie rod 18 is surrounded by a bellows-shaped boot 52 that spans both the rack housing 50 and the tie rod 18. The boot 52 is intended to prevent liquids such as rainwater from entering the rack housing 50.

[0023] The motor 32 described above is equipped with two independent stator coil systems 32b(1) and 32b(2) for one rotating shaft 32a. Here, the numbers in parentheses in the symbols are identifiers for identifying the systems. On the other hand, an inverter 36 is mounted on the control board 34. The inverter 36 is equipped with inverters 36(1) and 36(2), which are connected to the stator coils 32b(1) and 32b(2), respectively. Note that inverter 36 is a collective notation for inverters 36(1) and 36(2).

[0024] A control device 60 is mounted on the control board 34. The control device 60 includes a PU 62 and a storage device 64. The PU 62 is a software processing unit such as a CPU. The storage device 64 stores a program that commands the processing to be performed by the PU 62.

[0025] The control device 60 controls the motor 32. The control device 60 operates the inverter 36 mounted on the control board 34 in order to control the amount controlled by the control unit 62 executing the above program.

[0026] The control device 60 refers to the following detected values ​​for controlling the controlled quantity. Specifically, the control device 60 refers to the substrate temperature Tb, which is the temperature of the control board 34 detected by the temperature sensor 70. The control device 60 refers to the output line currents iu(1), iv(1), iw(1) of inverter 36(1) and the output line currents iu(2), iv(2), iw(2) of inverter 36(2). The control device 60 refers to the rotation angle θm of the rotation shaft 32a of the motor 32 detected by the rotation angle sensor 72. The control device 60 refers to the steering torque Th detected by the torque sensor 74. The steering torque Th is the torque input by the driver via the steering wheel 12. In this embodiment, the sign of the steering torque Th and the sign of the rotation angle θm are aligned. That is, the sign of the change in the rotation angle θm when the steering shaft 14 rotates to the right coincides with the sign of the steering torque Th when the steering shaft 14 is rotated to the right. The control device 60 refers to the vehicle speed V detected by the vehicle speed sensor 76.

[0027] "Basic procedures for preventing freezing" Figure 2 shows a portion of the processing performed by the control device 60. The processing shown in Figure 2 is achieved by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined period.

[0028] The basic assist amount calculation process M10 is a process that calculates the basic assist amount Ta0 based on the steering torque Th and vehicle speed V as input variables. Superposition process M12(1) is a process in which the value obtained by superimposing the warm-up torque Tw(1) onto the basic assist amount Ta0 is substituted into the assist amount Ta(1). The assist amount Ta(1) is the target value of the torque generated by the first system's stator coil 32b(1). Superposition process M12(2) is a process in which the value obtained by superimposing the warm-up torque Tw(2) onto the basic assist amount Ta0 is substituted into the assist amount Ta(2). The assist amount Ta(2) is the target value of the torque generated by the second system's stator coil 32b(2). Note that the warm-up torques Tw(1) and Tw(2) may be zero in a steady state.

[0029] The operation signal generation process M14(1) generates and outputs an operation signal MS(1) for operating the inverter 36(1) in order to bring the torque of the motor 32 generated by energizing the first stator coil 32b(1) closer to the assist amount Ta(1). The operation signal generation process M14(2) generates and outputs an operation signal MS(2) for operating the inverter 36(2) in order to bring the torque of the motor 32 generated by energizing the second stator coil 32b(2) closer to the assist amount Ta(2).

[0030] The predictive action determination process M20 is a process that determines whether or not there are any signs of a seizure abnormality caused by freezing of the steering mechanism. Here, the steering mechanism includes a steering shaft 14, a rack shaft 16, a tie rod 18, a drive pulley 40, a belt 42, a driven pulley 44, and a ball screw mechanism 46, etc. Freezing of the steering mechanism causes an abnormality in which the force required for steering increases. In other words, freezing of the steering mechanism interferes with the rotational drive of the movable parts of the steering mechanism by the motor 32. In this embodiment, the drive pulley 40 is provided in the vertically downward direction of the rack shaft 16. Therefore, if moisture enters the rack housing 50 through a scratch in the boot 52, water is likely to accumulate near the drive pulley 40. If this water freezes, it becomes difficult for the motor 32 to assist steering by rotating the drive pulley 40. Also, if the water freezes, it becomes difficult to steer the steering wheels 20 by rotating the steering wheel 12.

[0031] Lock detection process M22 is a process that determines whether or not there is a seizure abnormality due to freezing of the steering mechanism. In the following, the determination that there is a seizure abnormality will be referred to as lock detection. The heat treatment M16 is a process that outputs warm-up torques Tw(1) and Tw(2) if it is determined that there is a sign of seizing or if a lock is detected.

[0032] "Predictive detection process M20" Figure 3 shows the detailed procedure of the predictive error detection process M20. The process shown in Figure 3 is realized by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. In the following, the step number of each process is represented by a number preceded by "S".

[0033] In the series of processes shown in Figure 3, the PU62 first obtains the steering torque Th and the assist amount Ta (S10). Next, the PU62 substitutes the sum of the steering torque Th and the assist amount Ta into the combined torque Tt (S12). The combined torque Tt is the torque applied to steer the steering wheel 20. The PU62 also obtains the rotation angle θm (S14).

[0034] PU62 determines whether the stick detection history flag F1 is "1" (S16). The stick detection history flag F1 is set to "1" when it is determined that the system is in a stick state. The stick state is a state in which the steering angle θh hardly changes even when the absolute value of the steering torque Th increases. The stick detection history flag F1 is set to "0" when it is not determined that the system is in a stick state.

[0035] If PU62 determines that the stick detection history flag F1 is "0" (S16:NO), it determines whether the following condition A is met (S18). Condition A: This condition states that the absolute value of the combined torque Tt is greater than or equal to the threshold Tth. The threshold Tth is set to an magnitude that would normally cause the steering angle θh to change. If PU62 determines that condition A is true (S18: YES), it then determines whether the following condition B is true (S20).

[0036] Condition B is the condition that the change in rotation angle θm is less than or equal to a predetermined amount Δθth. Specifically, PU62 quantifies the change in rotation angle θm by subtracting the rotation angle θm(nk) at the previous execution timing from the rotation angle θm(n) at the current execution timing of the series of processes shown in Figure 3. Here, k is an integer of 1 or greater. To make the change in rotation angle θm apparent, k may be set to around 5 to 15.

[0037] If PU62 determines that the logical AND of condition A and condition B is true (S20: YES), it increments counter C1 (S22). Counter C1 is used to measure the duration of the state in which the logical AND of condition A and condition B is true.

[0038] PU62 determines whether counter C1 is greater than or equal to the threshold C1th (S24). This process determines whether the state in which the logical AND of condition A and condition B is true has continued for a predetermined period of time. If PU62 determines that counter C1 is greater than or equal to the threshold C1th (S24: YES), it assigns "1" to the stick determination history flag F1 (S26). In other words, PU62 determines that a stick phenomenon has occurred if it determines that the state in which the logical AND of condition A and condition B is true has continued for a predetermined period of time. PU62 also initializes counter C1. Furthermore, PU62 assigns the current total torque Tt(n) to the total torque Tt0 at the time of stick determination.

[0039] On the other hand, if PU62 determines that the stick detection history flag F1 is "1" (S16:YES), it determines whether the condition for determining that the device is in a stick state is no longer met (S27). This process determines whether the logical AND of the above conditions A and B is false. If PU72 determines that the condition for determining that the device is in a stick state is not met (S27:YES), it increments counter C2 (S28). Counter C2 is used to measure the elapsed time since the stick detection was not met. If PU62 determines that counter C2 is less than the threshold C2th (S30:YES), it determines whether the following conditions C, D and E are met (S32, S34, S36).

[0040] Condition C is a condition that the absolute value of the combined torque Tt is decreasing. Specifically, PU62 may determine that condition C is true, for example, if the current absolute value of the combined torque Tt is smaller than the absolute value of the combined torque Tt at the point when the logical AND of conditions A and B becomes false.

[0041] Condition D is the condition that the sign of the combined torque Tt0 at the time of stick detection and the sign of the angular acceleration αm of the motor 32 are the same. Condition E is the condition that the absolute value of the angular acceleration αm is greater than or equal to the threshold αmth.

[0042] PU62 determines that there is a sign of steering mechanism freezing if the logical AND of conditions C to E is true (S32-S36: YES) (S38). In other words, PU62 determines that there is a sign of steering mechanism freezing if the logical AND of conditions C to E is true within a predetermined time defined by the threshold C2th after the stick condition occurs. Then PU62 initializes the stick condition history flag F1 (S40). Also, PU62 initializes counter C2 (S42).

[0043] On the other hand, if PU62 determines that counter C2 is greater than or equal to the threshold C2th (S30: NO), it proceeds to process S40. Also, if PU62 makes a negative determination in process S18 or S20, it initializes counter C1 (S44).

[0044] Furthermore, when PU62 determines that a negative result is obtained in processes S24, S27, S32, S34, and S36, and when it completes processes S26, S42, and S44, it temporarily terminates the series of processes shown in Figure 3.

[0045] "Lock detection process M22" Figure 4 shows the procedure for the lock determination process M22. The process shown in Figure 4 is achieved by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period.

[0046] In the series of processes shown in Figure 4, the PU62 first obtains the steering torque Th and the assist amount Ta (S50). Then, the PU62 substitutes the sum of the steering torque Th and the assist amount Ta into the combined torque Tt (S52). The PU62 also obtains the steering angle θh (S54). The steering angle θh is calculated by the PU62 using the integration process of the rotation angle θm. The sign of the steering angle θh is consistent with the sign of the steering torque Th. That is, the sign of the change in the steering angle θh when the steering shaft 14 rotates to the right coincides with the sign of the steering torque Th when the steering shaft 14 is steered to the right.

[0047] PU62 determines whether or not there is a request to update the reference point (S56). PU62 determines that there is a request to update the reference point even if the reference point has not yet been set. If PU62 determines that there is a request to update the reference point (S56: NO), it determines whether or not the absolute value of the combined torque Tt is greater than or equal to a predetermined value Ttth (S58). The predetermined value Ttth is set to a value that is assumed to allow the steering angle θh to be changed under normal circumstances. If PU62 determines that it is greater than or equal to the predetermined value Ttth (S58: YES), it sets the reference point using the combined torque Tt and steering angle θh obtained in the S52 and S54 processes (S60). Specifically, PU62 substitutes the combined torque Tt and steering angle θh obtained in the S52 and S54 processes into the combined torque Ttr and steering angle θhr, respectively. Then PU62 sets the system to indicate that there is no request to update the reference point (S61).

[0048] On the other hand, if PU62 determines that there is no request to set a reference point (S56:YES), it determines whether the following condition F is met (S62). Condition F is a condition that the absolute value of the difference between the steering angle θh and the steering angle θhr used to define the reference point is less than or equal to a predetermined amount Δθh.

[0049] The process in S62 determines whether or not the steering angle θh has changed due to the combined torque Tt. If PU62 determines that the above condition F is not met (S62: NO), it sets a request to update the reference angle (S65). In other words, PU62 generates a request to update the reference point based on the determination that the steering angle θh has changed due to the combined torque Tt.

[0050] On the other hand, if PU62 determines that the above condition F is true (S62: YES), it determines whether the logical OR of the following conditions G and H is true or not (S63). Condition G is the condition that the sum of torques Ttr used to define the reference point is positive AND the sum of torques Tt is positive.

[0051] Condition H is the condition that the sum of torques Ttr used to define the reference point is negative AND the sum of torques Tt is negative. Conditions G and H are processes that determine whether the summation torque Ttr and summation torque Tt at the reference point have the same sign.

[0052] If PU62 determines that the above logical OR is false (S63: NO), it proceeds to processing S65. On the other hand, if PU62 determines that the above logical OR is true (S63: YES), it then determines whether the following condition I is true (S64).

[0053] Condition I is the condition that the absolute value of the difference between the total torque Tt and the total torque Ttr that defines the reference point is greater than a predetermined amount ΔTt. The S64 process determines whether or not the steering angle θh remains unchanged despite the application of a large absolute torque Tt. In other words, the S64 process determines whether or not a seizing abnormality has occurred.

[0054] If PU62 determines that the above condition I is met (S64: YES), it determines that a sticking abnormality has occurred (S66). Then, PU62 notifies the driver that the vehicle cannot be driven due to the sticking abnormality by operating the user interface 80 shown in Figure 1 (S68). Specifically, if the user interface 80 is equipped with a display device, PU62 may, for example, display visual information on the display device.

[0055] Furthermore, PU62 terminates the series of processes shown in Figure 4 when the processes in S61, S65, and S68 are completed, or when a negative determination is made in the process of S58. "Heat treatment M16" Figure 5 shows the procedure for the heat treatment M16. The process shown in Figure 5 is achieved by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period.

[0056] In the series of processes shown in Figure 5, PU62 first determines whether a pre-announcement or lock-up determination has been made (S70). If PU62 determines that a pre-announcement or lock-up determination has been made, it sets the warm-up torque Tw (S72). That is, PU62 assigns the value obtained by multiplying the amplitude Am by "sinωt", which is a sine wave of angular velocity ω, to the warm-up torque Tw(1) for the first system. Here, the variable t represents time. PU62 also assigns the value obtained by multiplying the amplitude Am by "sin(ωt+π)", which is a sine wave with the opposite phase, to the warm-up torque Tw(2) for the second system.

[0057] Furthermore, when PU62 completes the process in S72, it terminates the series of processes shown in Figure 5. "The operation and effects of this embodiment" PU62 determines whether there are any signs of a seizure abnormality caused by freezing, and whether a seizure abnormality has occurred. When PU62 determines whether there are signs of a seizure abnormality or whether the system is locked, it sets the assist amount Ta to a value obtained by superimposing the warm-up torque Tw onto the basic assist amount Ta0. As a result, the amount of heat generated by the motor 32 and inverter 36 is increased compared to when the warm-up torque Tw is not superimposed. The heat generated by the motor 32 and inverter 36 can contribute to melting ice on the movable parts of the steering mechanism or to suppressing the solidification of moisture on the movable parts.

[0058] As shown in Figure 6, the warm-up torque Tw(1) of the first system and the warm-up torque Tw(2) of the second system are in opposite phase and have equal amplitudes Am. As a result, the net torque generated in the motor 32 by the warm-up torques Tw(1) and Tw(2) is zero. Therefore, interference between the warm-up torques Tw(1) and Tw(2) and the driver's steering can be suppressed.

[0059] Furthermore, by setting the warm-up torques Tw(1) and Tw(2) to AC, compared to setting them to DC, even if torque control errors occur, interference between the warm-up torques Tw(1) and Tw(2) and the driver's steering can be suppressed for the following reasons.

[0060] Figure 7 shows the case where the warm-up torques Tw(1) and Tw(2) are DC components with equal absolute values ​​and opposite signs. In Figure 7, the actual warm-up torque Twr(1) represents the amount of torque actually generated by energizing the first stator coil 32b(1) that is attributable to the warm-up torque Tw(1). The actual warm-up torque Twr(2) represents the amount of torque actually generated by energizing the second stator coil 32b(2) that is attributable to the warm-up torque Tw(2). In the example shown in Figure 7, the actual warm-up torque Twr(1) is a DC component of a predetermined amount Δ, while the actual warm-up torque Twr(2) has an absolute value smaller than the predetermined amount Δ. In this case, the net torque of the motor 32 generated by the warm-up torques Tw(1) and Tw(2) is a small positive value. Therefore, this torque is the amount by which the steering wheels 20 can be turned either to the right or to the left on a steady basis. This can be a factor in self-steering.

[0061] In contrast, in this embodiment, the warm-up torque Tw(1) and warm-up torque Tw(2) are set to AC components. This makes it possible to suppress the fact that the net torque of the motor 32 generated due to the warm-up torques Tw(1) and Tw(2) has a constant sign even when errors occur in torque control.

[0062] Figure 8 shows an example where the amplitude of the actual warm-up torque Twr(1) is greater than the amplitude of the actual warm-up torque Twr(2). In this case, the net torque of the motor 32 generated due to the warm-up torques Tw(1) and Tw(2) is shown by the dashed line. As shown in Figure 8, the net torque of the motor 32 generated due to the warm-up torques Tw(1) and Tw(2) has an AC component, which can suppress the occurrence of self-steer.

[0063] <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings.

[0064] Figure 9 shows the warm-up torque Tw(1) and warm-up torque Tw(2) according to this embodiment. As shown in Figure 9, the warm-up torque Tw(1) is set to a torque in which a sinusoidal component is superimposed on a DC component of a predetermined amount Δ. The warm-up torque Tw(2) is set to a torque in which a sinusoidal component with the opposite phase to the above sinusoidal component is superimposed on a DC component of a predetermined amount "(-1)·Δ".

[0065] In this case, compared to the case where the warm-up torques Tw(1) and Tw(2) consist only of sinusoidal components, the amount of heat generated by the motor 32 and inverter 36 can be increased. Furthermore, even if control errors occur in the actual warm-up torques Twr(1) and Twr(2), the net torque of the motor 32 generated due to the warm-up torques Tw(1) and Tw(2) is suppressed from having a constant sign. Therefore, self-steer is suppressed.

[0066] Figure 10 shows a case where the power supply to the stator coil 32b(2) of the second system is stopped due to an abnormality in the control of the second system. In this case, the PU 62 sets the DC component of the warm-up torque Tw(1) to zero. This prevents the torque of the motor 32 generated due to the warm-up torque Tw(1) from being biased towards the right-hand and left-hand turning sides.

[0067] <Third Embodiment> The third embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings.

[0068] Figure 11 shows the warm-up torque Tw(1) and warm-up torque Tw(2) according to this embodiment. As shown in Figure 11, the warm-up torque Tw(1) is set to a torque in which a sinusoidal component is superimposed on a DC component of a predetermined amount Δ. The warm-up torque Tw(2) is set to a DC component of a predetermined amount "(-1)·Δ".

[0069] In that case, the sum of the warm-up torques Tw(1) and Tw(2) becomes a sine wave with a center of zero, as shown by the dashed line in Figure 11. Therefore, the net torque of the motor 32 generated due to the warm-up torques Tw(1) and Tw(2) is suppressed from having a constant sign. Consequently, self-steer is suppressed.

[0070] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" section is as follows. Below, the correspondence is shown for each number of the solution means described in the "Means for Solving the Problem" section. [1,7] The request determination process corresponds to the process in S70. The power supply process corresponds to the operation signal generation processes M14(1) and M14(2) corresponding to the process in S72. [2,3] The power supply process corresponds to the processes illustrated in Figures 6 and 9. [4] The power supply process corresponds to the process illustrated in Figure 9. [5] The matters described in Solution 5 correspond to the processes illustrated in Figure 10. [6] The matters described in Solution 6 correspond to the processes illustrated in Figure 11.

[0071] <Other Embodiments> Furthermore, 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.

[0072] "Regarding the request determination process" Whether or not an increase in heat generation is required is not limited to the process of determining whether or not a seizure abnormality has occurred or whether or not there are signs of a seizure abnormality. The requirement determination process may, for example, be a process of determining whether or not it is assumed that the viscosity of the grease provided in the movable part will be high and the load will be increased due to the low temperature around the steering mechanism.

[0073] "Regarding the power supply process" It is not essential that the energizing process is a process that sets the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil to be in opposite phases to each other. For example, in the process of S72, PU62 may substitute the value obtained by multiplying the amplitude Am by "sin(ωt+α):π / 2≦α<π" into the warm-up torque Tw(2) for the second system.

[0074] "Regarding Assist Processing" It is not mandatory for the assist process to include a basic assist amount calculation process M10 that calculates a basic assist amount Ta0 based on the steering torque Th and vehicle speed V as input variables. The assist process may include, for example, a process that substitutes an manipulated variable for feedback control of the steering torque Th to a target steering torque into the basic assist amount Ta0.

[0075] "Regarding motor torque control" For example, as described in the "About the Steering System" section below, if the steering system is a steer-by-wire system, the motor torque control may be performed as follows instead of the above assist process. That is, the motor torque control may be a process that sets the motor torque to the amount used to control the actual steering angle to a target steering angle determined according to the steering angle θh. In that case, the energizing process may be a process that superimposes the warm-up torque Tw on the amount used to control the steering angle to the target steering angle. Also, in that case, the steering mechanism subject to freezing determination may be a mechanism that transmits the motor's power to the steering wheels. In the case of a steer-by-wire system, the angle variable correlated with the steering angle is a variable that indicates the angle of the member mechanically connected to the steering wheel 20. That is, the above-mentioned "state in which the steering angle θh hardly changes" should be read as, for example, "state in which the steering angle hardly changes".

[0076] "About motors" A motor with multiple stator coil systems is not limited to a motor consisting of two stator coil systems that are insulated from each other. For example, a motor with multiple stator coil systems may consist of three or more stator coil systems that are insulated from each other.

[0077] A motor with multiple stator coil systems is not limited to a motor in which multiple stator coil systems share a single rotation axis. A motor with multiple stator coil systems may, for example, be a motor with multiple rotation axes and stator coil systems.

[0078] "Regarding steering control systems" The steering control device is not limited to one that performs various processes using a PU. For example, it may include 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 control device may include 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 comprising a dedicated hardware circuit that performs all of the above processes. Here, there may be multiple software execution devices comprising a processing unit and a program storage device, or multiple dedicated hardware circuits. [Explanation of symbols]

[0079] 10…Electric power steering system 12… Steering wheel 14… Steering axis 16... Rack axis 18…Tie rod 20... Steering wheel 30…Motor Unit 32…motor 32a... Rotation axis 32b... Stator coil 34…Control board 3. Instructions…Inverter 40… Drive pulley 42... belt 44... Driven pulley 46...Ball screw mechanism 50... Rack Housing 52... Boots 60...Control device

Claims

1. A steering control device in which the steering mechanism is the object of control, The steering mechanism is configured such that the rotational power of motors, each having multiple independent stator coil systems, is converted into power to steer the steering wheels. It is configured to perform request determination processing and power supply processing, The aforementioned request determination process is a process that determines whether or not an increase in heat generation is required. The energizing process, when it is determined that an increase in heat generation is required, is a process of energizing the stator coils of the first and second systems such that the magnitude of the torque generated by energizing the stator coil of the first system among the multiple systems is reduced, and the torque generated by energizing the stator coil of the second system among the multiple systems is reduced. The torque generated by energizing the first system of stator coils is a periodically fluctuating torque in the steering control device.

2. The steering control device according to claim 1, wherein the energizing process includes energizing the first system of stator coils such that the torque generated by energizing the first system of stator coils oscillates periodically, and energizing the second system of stator coils such that the torque generated by energizing the second system of stator coils oscillates periodically.

3. The steering control device according to claim 2, wherein the energizing process includes energizing the first stator coil and the second stator coil such that the torque generated by energizing the first stator coil and the torque generated by energizing the second stator coil are in opposite phases to each other.

4. The torque generated by energizing the first stator coil has a value obtained by superimposing a periodic signal on a first DC component, which is a DC component greater than zero. The steering control device according to claim 2, wherein the torque generated by energizing the second stator coil has a value obtained by superimposing a periodic signal on a second DC component which is a DC component with the opposite sign to the first DC component.

5. The steering control device according to claim 4, wherein the energizing process includes, if an abnormality occurs in either the energizing of the first stator coil or the energizing of the second stator coil, the process of changing the DC component of the one that is not abnormal to zero.

6. The torque generated by energizing the first stator coil has a value obtained by superimposing a periodic signal on a first DC component, which is a DC component greater than zero. The steering control device according to claim 1, wherein the torque generated by energizing the second stator coil is a second DC component having the opposite sign to the first DC component.

7. The aforementioned request determination process is a process that determines whether or not an abnormality occurs in which the force required for steering increases due to the freezing of the steering mechanism. The steering control device according to claim 1, wherein the requirement for an increase in the amount of heat generated is that the abnormality occurs.

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