Steering control device and steering control method

Abstract

This steering control device is configured so as to execute determination processing, first temperature acquisition processing, second temperature acquisition processing, and permission processing. The determination processing is processing for determining whether an abnormality has occurred in which the force required for steering increases due to freezing of a steering mechanism. The first temperature acquisition processing is processing for acquiring a first temperature, which is the temperature in the surroundings of the steering mechanism as detected by a first temperature sensor. The second temperature acquisition processing is processing for acquiring a second temperature, which is the temperature in the surroundings of the steering mechanism as detected by a second temperature sensor. The permission processing is processing for determining, on the basis of the first temperature and the second temperature as input variables, whether to permit execution of the determination processing.

Description

Steering control device and steering control method 【0001】 The present disclosure relates to a steering control device and a steering control method. 【0002】 For example, Patent Document 1 below describes a device that estimates icing of a steering system based on a temperature detection value by a temperature sensor and vibrates a motor. 【0003】 International Publication No. 2008 / 116554 【0004】 The above document does not disclose countermeasures when the reliability of the detection value by the temperature sensor is low. 【0005】 In one aspect of the present disclosure, a steering control device is provided. The steering mechanism is configured to convert the rotational power of a motor into the power for steering a steering wheel. The steering control device is configured to execute a determination process, a first temperature acquisition process, a second temperature acquisition process, and a permission process. The determination process is a process of determining whether an abnormality has occurred in which the force required for steering has increased due to icing of the steering mechanism. The first temperature acquisition process is a process of acquiring a first temperature, which is the temperature around the steering mechanism detected by a first temperature sensor. The second temperature acquisition process is a process of acquiring a second temperature, which is the temperature around the steering mechanism detected by a second temperature sensor. The permission process is a process of determining whether to permit the execution of the determination process based on the first temperature and the second temperature as input variables. 【0006】Another aspect of this disclosure provides a steering control method. The steering mechanism is configured to convert the rotational power of a motor into power to steer the steering wheels. The steering control method includes executing a determination process, executing a first temperature acquisition process, executing a second temperature acquisition process, and executing a permission process. The determination process is a process to determine whether or not an abnormality has occurred in which the force required for steering has increased due to freezing of the steering mechanism. The first temperature acquisition process is a process to acquire a first temperature, which is the temperature around the steering mechanism detected by a first temperature sensor. The second temperature acquisition process is a process to acquire a second temperature, which is the temperature around the steering mechanism detected by a second temperature sensor. The permission process is a process to determine whether or not to allow the execution of the determination process based on the first temperature and the second temperature as input variables. 【0007】 This is a block diagram showing the configuration of a steering control device and a steering device according to one embodiment. This is a block diagram showing a part of the processing performed by the steering control device of Figure 1. This is a flowchart showing the procedure for the processing related to permission of determination performed by the steering control device of Figure 1. This is a flowchart showing the procedure for the processing related to ice formation prediction determination performed by the steering control device of Figure 1. This is a flowchart showing the procedure for the processing related to lock determination performed by the steering control device of Figure 1. 【0008】 The following describes one embodiment 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. 【0009】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. 【0010】 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 purpose of the boot 52 is to prevent liquids such as rainwater from entering the rack housing 50. 【0011】 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. 【0012】 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 device by having the PU 62 execute the above program. 【0013】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 substrate temperature sensor 70. The control device 60 refers to the output line currents iu, iv, and iw of the inverter 36. 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 rotation angle θm rotates the steering shaft 14 to the right is the same as the sign of the steering torque Th when the steering shaft 14 rotates to the right due to the steering torque Th. The control device 60 refers to the vehicle speed V detected by the vehicle speed sensor 76. The control device 60 refers to the ambient temperature To detected by the ambient temperature sensor 78. It is desirable that the ambient temperature sensor 78 be placed in a location in the vehicle that is less affected by heat-generating elements. It is also desirable that the ambient temperature sensor 78 be placed in a well-ventilated area. 【0014】 "Basic Processing for Freezing Prevention" Figure 2 shows some 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. 【0015】 The basic assist amount calculation process M10 calculates the basic assist amount Ta0 based on the steering torque Th and vehicle speed V as input variables. The superposition process M12 is a process that superimposes the vibration torque Tf onto the basic assist amount Ta0 and substitutes that value into the assist amount Ta. Note that the vibration torque Tf may be zero in a steady state. 【0016】The operation signal generation process M14 generates and outputs an operation signal MS for operating the inverter 36 in order to bring the torque of the motor 32 closer to the assist amount Ta. The pre-fault determination process M20 determines whether or not there are 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. Furthermore, if the 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. 【0017】 The lock detection process M22 determines whether or not there is a seizure abnormality due to freezing of the steering mechanism. Hereafter, the determination that there is a seizure abnormality will be referred to as a lock detection. The vibration process M16 outputs a vibration torque Tf if it is determined that there is a sign of a seizure abnormality or if a lock detection is made. The vibration torque Tf is, as an example, a sinusoidal torque with amplitude Am. 【0018】 "Determination of whether to execute the premonitory sign detection process and the lock detection process" Figure 3 shows the procedure for determining whether to execute the premonitory sign detection process and the lock detection process. The process shown in Figure 3 is realized by the PU 62 repeatedly executing a program stored in the storage 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". 【0019】In the series of processes shown in Figure 3, PU62 first obtains the ambient temperature To and the substrate temperature Tb (S10). Next, PU62 determines whether the logical OR of the following conditions A and B is true or not (S12). 【0020】 Condition A is the condition that the ambient temperature To is below the first threshold Toth. The first threshold Toth is set to the temperature at which moisture in the steering mechanism may solidify if it is present. 【0021】 Condition B is that the substrate temperature Tb is less than or equal to the second threshold Tbth. The second threshold Tbth is set to the temperature at which moisture in the steering mechanism may solidify if moisture is present. 【0022】 The first threshold Toth is set to a lower value than the second threshold Tbth. This setting takes into account the tendency for the temperature inside the motor unit 30 to be higher than the ambient temperature due to heat generated by the inverter 36 and the motor 32. 【0023】 If PU62 determines that the above logical OR is true (S12: YES), it assigns "1" to the permission flag Fp (S14). When the permission flag Fp is "1", it indicates that the execution of the determination of whether there is a warning sign and whether there is a sticking abnormality is permitted. When the permission flag Fp is zero, it indicates that the execution of the determination of whether there is a warning sign and whether there is a sticking abnormality is not permitted. At the start of the trip, the permission flag Fp is initialized to zero. A trip is a single period during which the vehicle's start switch is in the ON state. The start switch may be, for example, a switch that opens and closes a system main relay that opens and closes the connection between the drive circuit of a rotating electric machine and a DC voltage source, if the vehicle's thrust generating device is equipped with a rotating electric machine. 【0024】 On the other hand, if PU62 determines that the above logical OR is false (S12: NO), it determines whether the logical OR of the following conditions C to H is true (S16). Condition C is a condition that the logical OR of the fact that there is a history of a warning judgment being made by the warning judgment process M20 and the fact that there is a history of a lock judgment being made by the lock judgment process M22 is true. 【0025】 Condition D indicates an abnormality in CAN communication or CAN power supply voltage. Incidentally, the output signal of the ambient temperature sensor 78 is transmitted to the control device 60 using CAN communication. This condition means that the ambient temperature To detected by the ambient temperature sensor 78 cannot be acquired properly. 【0026】 Condition E is the condition that the ambient temperature To is less than the lower limit of the value detected by the ambient temperature sensor 78. This condition indicates that the ambient temperature To is not showing a normal value. Condition F is the condition that the ambient temperature To is greater than the upper limit of the value detected by the ambient temperature sensor 78. This condition indicates that the ambient temperature To is not showing a normal value. 【0027】 Condition G indicates that there is an abnormality in the substrate temperature sensor 70. The presence or absence of an abnormality in the substrate temperature sensor 70 is determined by the PU 62. The PU 62 may determine that there is an abnormality in the substrate temperature sensor 70 if, for example, the output signal of the substrate temperature sensor 70 is fixed at ground potential. Alternatively, the PU 62 may determine that there is an abnormality in the substrate temperature sensor 70 if, for example, the output signal of the substrate temperature sensor 70 is fixed at the power supply voltage. 【0028】 Condition H is the condition that the value obtained by subtracting the ambient temperature To from the substrate temperature Tb is less than a predetermined value ΔTth. This condition indicates that there is a malfunction in the ambient temperature sensor 78. In particular, this condition is also true when the ambient temperature To indicated by the ambient temperature sensor 78 is above the lower limit and below the upper limit, but there is a malfunction in the ambient temperature sensor 78. That is, the control board 34 is affected by the heat generated by the inverter 36 and the motor 32, so the substrate temperature Tb becomes higher than the ambient temperature To. Therefore, the predetermined value ΔTth is set to a value smaller than the minimum value that is expected to be possible when the substrate temperature Tb is subtracted from the ambient temperature To if the ambient temperature sensor 78 is functioning normally. 【0029】 If PU62 determines that the above logical OR is true (S16: YES), it proceeds to process S14. Note that if PU62 determines that the result is negative in process S16, or if it completes process S14, it temporarily terminates the series of processes shown in Figure 3. 【0030】 "Predictive Determination Process M20" Figure 4 shows the detailed procedure of predictive determination process M20. The process shown in Figure 4 is realized by the PU 62 repeatedly executing a program stored in the memory device 64, for example, at a predetermined period. 【0031】 In the series of processes shown in Figure 4, PU 62 first determines whether the permission flag Fp is "1" (S20). If PU 62 determines that the permission flag Fp is "1" (S20: YES), it obtains the steering torque Th and the assist amount Ta (S22). Next, PU 62 substitutes the sum of the steering torque Th and the assist amount Ta into the combined torque Tt (S24). The combined torque Tt is the torque applied to steer the steering wheel 20. PU 62 also obtains the rotation angle θm (S26). 【0032】 PU62 determines whether the stick detection history flag F1 is "1" (S28). 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 steering angle θh is, for example, the rotation angle of the steering wheel 12 as an angular variable that correlates with the steering angle of the steering wheel 20. The stick detection history flag F1 is set to "0" when it is not determined that the system is in a stick state. 【0033】 If PU62 determines that the stick judgment history flag F1 is "0" (S28: NO), it determines whether the following condition I is met (S30). Condition I is 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 amount that would normally cause the steering angle θh to change. If PU62 determines that condition I is met (S30: YES), it determines whether the following condition J is met (S32). 【0034】Condition J is a condition that the change in the rotation angle θm is less than or equal to a predetermined amount Δθth. Specifically, PU62 quantifies the change in the rotation angle θm by the absolute value of the value obtained by subtracting the rotation angle θm(n-k) 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 more. In order to make the change in the rotation angle θm apparent, k may be set to around 5 to 15. 【0035】 If PU62 determines that the logical AND of condition I and condition J is true (S32: YES), it increments counter C1 (S34). Counter C1 is used to measure the duration of the state in which the logical AND of condition I and condition J is true. 【0036】 PU62 determines whether counter C1 is greater than or equal to threshold C1th (S36). This process determines whether the state in which the logical AND of condition I and condition J is true has continued for a predetermined period of time. If PU62 determines that counter C1 is greater than or equal to threshold C1th (S36: YES), it assigns "1" to the stick determination history flag F1 (S38). In other words, PU62 determines that a stick phenomenon has occurred if it determines that the state in which the logical AND of condition I and condition J is true has continued for a predetermined period of time. In addition, PU62 initializes counter C1 in the process of S38. Furthermore, PU62 assigns the current total torque Tt(n) to the total torque Tt0 at the time of stick determination. 【0037】On the other hand, if PU62 determines that the stick determination history flag F1 is "1" (S28: YES), it determines whether the determination condition for being in a stick state is no longer met (S39). This process determines whether the logical AND of the above conditions I and K is false. If PU72 determines that the determination condition for being in a stick state is not met (S39: YES), it increments counter C2 (S40). Counter C2 is used to measure the elapsed time after the stick determination is not met. PU62 determines whether counter C2 is less than the threshold C2th (S42). If PU62 determines that counter C2 is less than the threshold C2th (S42: YES), it determines whether the following conditions K, L and M are met (S44, S46, S48). 【0038】 Condition K 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. 【0039】 Condition L is the condition that the sign of the summation torque Tt0 at the time of stick detection and the sign of the angular acceleration αm of the motor 32 are the same. Condition M is the condition that the absolute value of the angular acceleration αm is greater than or equal to the threshold αmth. 【0040】 PU62 determines that there is a sign of a sticking abnormality if it determines that the logical AND of condition K to condition M is true (S44-S48: YES) (S50). In other words, PU62 determines that there is a sign of a sticking abnormality if the logical AND of condition K to condition M becomes true within a predetermined time defined by the threshold C2th after the sticking condition occurs. Then PU62 initializes the sticking determination history flag F1 (S52). Also, PU62 initializes the counter C2 (S54). 【0041】On the other hand, when the PU 62 determines that the counter C2 is equal to or greater than the threshold value C2th (S42: NO), it proceeds to the process of S52. Also, when the PU 62 makes a negative determination in the process of S30 or S32, it initializes the counter C1 (S56). 【0042】 In addition, when the PU 62 makes a negative determination in the processes of S20, S36, S39, S44, S46, and S48, and when the processes of S38, S54, and S56 are completed, the PU 62 temporarily ends the series of processes shown in FIG. 3. 【0043】 "Lock determination process M22" FIG. 5 shows the procedure of the lock determination process M22. The process shown in FIG. 5 is realized by the PU 62 repeatedly executing, for example, a program stored in the storage device 64 at a predetermined cycle. 【0044】 In the series of processes shown in FIG. 5, first, the PU 62 determines whether the permission flag Fp is "1" (S60). When the PU 62 determines that the permission flag Fp is "1" (S60: YES), it acquires the steering torque Th and the assist amount Ta (S62). Then, the PU 62 substitutes the sum of the steering torque Th and the assist amount Ta into the total torque Tt (S64). Also, the PU 62 acquires the steering angle θh (S66). The steering angle θh is calculated by the PU 62 using the integration process of the rotation angle θm. Note that the sign of the steering angle θh is consistent with the sign of the steering torque Th. That is, the sign of the change amount of the steering angle θh when the steering shaft 14 rotates to the right rotation side and the sign of the steering torque Th when the steering shaft 14 is rotated and steered to the right rotation side match. 【0045】PU62 determines whether there is a request to update the reference point (S68). PU62 determines that there is a request to update the reference point even when the reference point has not yet been set. When PU62 determines that there is a request to update the reference point (S68: NO), it determines whether the absolute value of the combined torque Tt is greater than or equal to a predetermined value Ttth (S70). The predetermined value Ttth is set to a value that is assumed to be able to change the steering angle θh in normal situations. When PU62 determines that it is greater than or equal to the predetermined value Ttth (S70: YES), it determines the reference point based on the combined torque Tt and the steering angle θh obtained in the processes of S64 and S66 (S72). Specifically, PU62 substitutes the combined torque Tt and the steering angle θh obtained in the processes of S64 and S66 into the combined torque Ttr and the steering angle θhr, respectively. Then PU62 sets that there is no request to update the reference point (S73). 【0046】 On the other hand, when PU62 determines that there is no request to set the reference point (S68: YES), it determines whether the following condition N holds (S74). Condition N is the condition that the absolute value of the difference between the steering angle θh and the steering angle θhr that determines the reference point is less than or equal to a predetermined amount Δθh. 【0047】 The process of S74 is a process of determining whether the steering angle θh has changed due to the combined torque Tt. When PU62 determines that the above condition N does not hold (S74: NO), it sets that there is a request to update the reference angle (S77). That is, based on the determination that the steering angle θh has changed due to the combined torque Tt, PU62 generates a request to update the reference point. 【0048】 On the other hand, when PU62 determines that the above condition N holds (S74: YES), it determines whether the logical sum of the following condition O and condition P is true (S75). Condition O is the condition that the combined torque Ttr that determines the reference point is positive and the combined torque Tt is positive. 【0049】 Condition P is the condition that the combined torque Ttr that determines the reference point is negative and the combined torque Tt is negative. Conditions O and P are processes of determining whether the combined torque Ttr and the combined torque Tt at the reference point have the same sign. 【0050】 If PU62 determines that the above logical OR is false (S75: NO), it proceeds to the process in S77. On the other hand, if PU62 determines that the above logical OR is true (S75: YES), it determines whether the following condition Q is satisfied (S76). 【0051】 Condition Q is the condition that the absolute value of the difference between the combined torque Tt and the combined torque Tt that defines the reference point is greater than a predetermined amount ΔTt. The process in S76 is to determine whether or not the steering angle θh does not change despite the application of a combined torque Tt with a large absolute value. In other words, the process in S76 is to determine whether or not a sticking abnormality has occurred. 【0052】 If PU62 determines that the above condition Q is met (S76: YES), it determines that a sticking abnormality has occurred (S78). Then, PU62 notifies the driver that the vehicle cannot be driven due to a sticking abnormality by operating the user interface 80 shown in Figure 1 (S80). Specifically, if the user interface 80 is equipped with a display device, PU62 may, for example, display visual information on the display device. 【0053】 Furthermore, PU62 terminates the series of processes shown in Figure 5 when the processes in S73, S77, and S80 are completed, and when a negative determination is made in the processes in S60 and S70. <Operation and Effects of this Embodiment> PU62 determines whether there are signs of a seizing abnormality caused by freezing, and whether a seizing abnormality has occurred. When PU62 makes a determination of signs of a seizing abnormality or a lock determination, it sets the assist amount Ta to a value obtained by superimposing the vibration torque Tf on the basic assist amount Ta0. As a result, the torque generated by the motor 32 vibrates with angular velocity ω and amplitude Am. This vibration can contribute to breaking the ice on the movable parts of the steering mechanism. Also, when the torque of the motor 32 is vibrated, the amount of heat generated by the motor 32 and inverter 36 is greater than when it is not vibrated. The heat generated by the motor 32 and inverter 36 can contribute to melting the ice on the movable parts of the steering mechanism or to suppressing the solidification of moisture on the movable parts. 【0054】 PU62 executes a process to determine whether or not to allow the determination of whether or not there is a warning sign and whether or not there is a sticking abnormality, in order to suppress misjudgments of the presence or absence of warning signs and misjudgments of the presence or absence of sticking abnormalities. Basically, PU62 allows the execution of the determination of whether or not there is a warning sign and whether or not there is a sticking abnormality when condition A is met. That is, for example, when the outside temperature To is at room temperature, it is considered that no abnormality caused by freezing will occur. Therefore, if condition A is not met, the execution of the determination of whether or not there is a warning sign and whether or not there is a sticking abnormality is not permitted, thereby suppressing misjudgments. However, if an abnormality occurs in the outside temperature sensor 78, there is a risk that the execution of the determination of whether or not there is a warning sign and whether or not there is a sticking abnormality will not be permitted when a warning sign or sticking abnormality could actually occur. 【0055】 Therefore, PU62 refers to the substrate temperature Tb. That is, if condition B is met, PU62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. As a result, even if an abnormality occurs in the ambient temperature sensor 78, the determination of whether there is a warning sign and whether there is a sticking abnormality can be performed. 【0056】 Furthermore, the above embodiment provides the following effects and benefits: (1) When condition H is met, PU 62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. This prevents a situation in which the determination of whether there is a warning sign and whether there is a sticking abnormality is prohibited due to a malfunction in the outside temperature sensor 78, even though the outside temperature To indicated by the outside temperature sensor 78 is above the lower limit and below the upper limit. 【0057】 (2) When condition E is met, PU62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. This prevents a situation in which the determination of whether there is a warning sign and whether there is a sticking abnormality is prohibited due to an abnormality in the outside temperature sensor 78. 【0058】 (3) When condition F is met, PU62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. This prevents a situation in which the determination of whether there is a warning sign and whether there is a sticking abnormality is prohibited due to an abnormality in the outside temperature sensor 78. 【0059】 (4) When condition G is met, PU 62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. This prevents a situation in which the determination of whether there is a warning sign and whether there is a sticking abnormality is prohibited due to an abnormality in the substrate temperature sensor 70. 【0060】 (5) When condition D is met, PU62 performs a determination of whether there is a warning sign and whether there is a sticking abnormality. This prevents a situation in which the determination of whether there is a warning sign and whether there is a sticking abnormality is prohibited due to the inability to obtain the outside temperature To via CAN communication. 【0061】 (6) The substrate temperature sensor 70 is susceptible to the heat generated by the motor 32 and the inverter 36. As a result, the substrate temperature Tb tends to be higher than the ambient temperature To. In particular, when the torque of the motor 32 is frequently increased, the substrate temperature Tb can become quite high. If the second threshold Tbth in condition B is set to an excessively large value, the effect of suppressing false judgments decreases. However, if the second threshold Tbth is set to a small value, condition B becomes less likely to be met, even though an abnormality caused by freezing may actually occur. Therefore, when the PU 62 assigned "1" to the permission flag Fp, it held the value of the permission flag Fp for the duration of the trip. In other words, once the PU 62 permitted the execution of the judgment for the presence or absence of warning signs and the judgment for the presence or absence of sticking abnormalities, it continued to permit the execution of the judgment for the presence or absence of warning signs and the judgment for the presence or absence of sticking abnormalities for the duration of the trip. This prevents situations where, even if the amount of heat generated by the motor 32 or the inverter 36 increases, making it difficult to satisfy condition B, the determination of whether there are any warning signs or whether there are any sticking abnormalities is prohibited if there is a history of permission being granted. 【0062】 (7) When condition C is met, PU62 performs a check for the presence or absence of warning signs and a check for the presence or absence of sticking abnormalities. This prevents a situation in which the check for warning signs and the check for sticking abnormalities are prohibited due to the substrate temperature Tb being high due to the heat generated by the vibration processing during the previous trip. 【0063】 Furthermore, if condition C is met, an abnormality has occurred in which water has entered the rack housing 50. This means that a situation has arisen in which abnormalities caused by freezing are likely to occur. Therefore, by performing a check for the presence or absence of warning signs and a check for the presence or absence of sticking abnormalities, vibration treatment can be reliably performed when it is necessary. 【0064】 <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. 【0065】 "Regarding the permission process" - The temperature variables used to determine whether the temperature around the steering mechanism is below a predetermined temperature are not limited to the ambient temperature To and the substrate temperature Tb. For example, the temperature variable used to determine whether the temperature around the steering mechanism is below a predetermined temperature may be either the ambient temperature To or the substrate temperature Tb. In other words, the process in S12 is not limited to determining whether the logical OR of condition A and condition B is true, but may also be, for example, determining whether condition A is true. 【0066】 The process for determining whether a reliable value cannot be obtained for the temperature around the steering mechanism is not limited to determining whether the logical OR of conditions D to H is true. For example, the process for determining whether a reliable value cannot be obtained may be a process for determining whether the logical OR of conditions D, F to H is true. 【0067】 - If condition C above is met, it is not mandatory to allow the execution of the process that determines whether there is a warning sign or a locking abnormality. In other words, it is not mandatory to unconditionally allow the execution of the process that determines whether there is a warning sign or a lock on the trip following a trip in which a warning sign or lock check was performed. 【0068】- In the above embodiment, when the value of the permission flag Fp is set to "1", the value of the permission flag Fp is maintained for the duration of the trip, but this is not limited to this. "Regarding vibration processing" - It is not essential that the vibration processing is a process that superimposes a sinusoidal periodic torque on the basic assist amount Ta0. For example, the vibration processing may be a process that superimposes a sawtooth-shaped periodic torque on the basic assist amount Ta0. 【0069】 It is not mandatory that the vibration processing involves superimposing a vibration component onto the basic assist amount Ta0. For example, if a lock is detected when the vehicle is started, the motor torque may be periodically varied while the vehicle is prohibited from driving and the basic assist amount Ta0 is set to zero. 【0070】 - For example, while the vehicle is in motion, the fact that a warning has been detected may be included as a condition for executing the process to determine whether or not the lock is present. "Regarding the first temperature sensor and the second temperature sensor" - The first temperature sensor and the second temperature sensor are not limited to the ambient temperature sensor 78 and the substrate temperature sensor 70. The second temperature sensor may be, for example, a temperature sensor attached to the motor 32. 【0071】 "Regarding the Prediction Judgment Process" (a) Regarding the Stick Judgment Process: In the process of determining whether the absolute value of the amount of rotation of the steering mechanism is less than or equal to a predetermined value, the variable indicating the amount of rotation is not limited to the change in the rotation angle θm. The variable indicating the amount of rotation may be, for example, the change in the steering angle θh. Alternatively, for example, the variable indicating the amount of rotation may be the change in the steering angle of the steering wheel 20. 【0072】- In the process of determining whether the absolute value of the torque for driving the steering mechanism is greater than or equal to a predetermined value, the variable indicating the torque for driving the steering mechanism is not limited to the summed torque Tt. The variables indicating the torque for driving the steering mechanism may be, for example, vehicle speed V and steering torque Th. That is, since the basic assist amount Ta0 is determined by the vehicle speed V and steering torque Th, the summed torque Tt can be determined by the vehicle speed V and steering torque Th. Therefore, for example, in the process of determining whether the absolute value of the steering torque Th is greater than or equal to a predetermined value, if the predetermined value is determined according to the vehicle speed V, a process equivalent to determining whether the summed torque Tt is greater than or equal to a predetermined value can be achieved. 【0073】 (b) Regarding the slip detection process: The variable representing the "torque for driving" in the process of determining whether the absolute value of the torque for driving the steering mechanism decreases is not limited to the summation torque Tt. The variable representing the torque for driving may be, for example, the steering torque Th. That is, since the basic assist amount Ta0 is determined by the vehicle speed V and the steering torque Th, the summation torque Tt can be determined by the vehicle speed V and the steering torque Th, but the change in vehicle speed V can be ignored in the time scale of the slip detection. Therefore, if the absolute value of the steering torque Th decreases, it can be assumed that the summation torque Tt decreases. 【0074】 - In the process of determining whether the rotation of the steering mechanism when the absolute value of the torque decreases matches the sign of the torque when it is determined that sticking has occurred, the variable indicating the rotation of the steering mechanism is not limited to angular acceleration αm. The variable indicating the rotation may be, for example, the second time derivative of the steering angle θh. Alternatively, the variable indicating the rotation may be, for example, the second time derivative of the steering angle of the steering wheel 20. Furthermore, it is not essential that the variable indicating the rotation has the dimension of acceleration. The variable indicating the rotation may be, for example, a variable with the dimension of velocity, such as the rotational speed of the motor 32. 【0075】The slip detection process is not limited to determining whether the logical AND of conditions K to M is true or not. For example, it may be a process that determines whether the logical AND of conditions K and L is true or not. 【0076】 "Regarding Assist Processing" - It is not mandatory for assist processing 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. Assist processing may, for example, include a process of substituting an input variable for feedback control of the steering torque Th to a target steering torque into the basic assist amount Ta0. 【0077】 "Regarding Motor Torque Control" - For example, as described in the "Regarding Steering Device" section below, if the steering device 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 vibration process may be a process that superimposes the vibration component of the torque onto 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". 【0078】"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 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. 【0079】 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 in which a steering mechanism is the target of control, wherein the steering mechanism is configured to convert the rotational power of a motor into power to steer the steering wheels, and is configured to perform a determination process, a first temperature acquisition process, a second temperature acquisition process, and a permission process, wherein the determination process is a process to determine whether or not an abnormality has occurred in which the force required for steering has increased due to freezing of the steering mechanism, the first temperature acquisition process is a process to acquire a first temperature, which is the temperature around the steering mechanism detected by a first temperature sensor, the second temperature acquisition process is a process to acquire a second temperature, which is the temperature around the steering mechanism detected by a second temperature sensor, and the permission process is a process to determine whether or not to permit the execution of the determination process based on the first temperature and the second temperature as input variables.

2. The steering control device according to claim 1, wherein the second temperature sensor is positioned closer to the motor than the first temperature sensor, and the permission process includes a process that permits the execution of the determination process when the logical OR of the first temperature being less than or equal to a first threshold and the second temperature being less than or equal to a second threshold is true, and the second threshold is greater than the first threshold.

3. The steering control device according to claim 1, wherein the second temperature sensor is positioned closer to the motor than the first temperature sensor, and the permission process includes a process that permits the execution of the determination process if the value obtained by subtracting the first temperature from the second temperature is less than or equal to a predetermined value.

4. The steering control device according to claim 3, wherein, if the permission process determines that the execution of the determination process is permitted, the execution of the determination process is permitted until the end of the trip, and the trip is the period during which the start switch of the vehicle on which the steering mechanism is installed is in the ON state.

5. Steering control device according to claim 1, configured to perform a history storage process, wherein the history storage process is a process of storing in a storage device the history in which the determination process has determined that the abnormality has occurred, and the permission process includes a process of permissioning the execution of the determination process if the history is stored in the storage device.

6. The steering control device according to claim 5, which is configured to perform vibration processing, wherein the vibration processing is a process of vibrating the torque of the motor when it is determined that the abnormality has occurred.

7. A steering control method in which a steering mechanism is the object of control, wherein the steering mechanism is configured to convert the rotational power of a motor into power to steer the steering wheels, and the method includes the execution of a determination process, the execution of a first temperature acquisition process, the execution of a second temperature acquisition process, and the execution of a permission process, wherein the determination process is a process of determining whether or not an abnormality has occurred in which the force required for steering has increased due to freezing of the steering mechanism, the first temperature acquisition process is a process of acquiring a first temperature, which is the temperature around the steering mechanism detected by a first temperature sensor, the second temperature acquisition process is a process of acquiring a second temperature, which is the temperature around the steering mechanism detected by a second temperature sensor, and the permission process is a process of determining whether or not to permit the execution of the determination process based on the first temperature and the second temperature as input variables.

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