Steering control device and steering control method

Abstract

This steering control device is configured to execute a torque acquisition process, steering angle acquisition process, and determination process. In the torque acquisition process, the value of a torque variable is acquired. The torque variable indicates the drive torque, which is the torque for driving a steering mechanism. In the steering angle acquisition process, a steering angle variable is acquired. On the basis of the torque variable and the steering angle variable, which are used as input variables, the determination process determines that a fault leading to an increase in force required for steering increases has occurred, provided that the logical product of the torque gradient being equal to or greater than a predetermined value and the amount of increase in the absolute value of the drive torque exceeding a predetermined amount is true. The torque gradient is the ratio of the amount of increase in the absolute value of the drive torque to the absolute value of the amount of change in the steering angle indicated by the steering angle variable.

Description

Steering control device and steering control method 【0001】 The present disclosure relates to a steering control device and a steering control method. 【0002】 Patent Document 1 below describes a device that determines the presence or absence of a sticking abnormality in a steering mechanism based on the gradient of the torque of a motor that drives the steering mechanism. This device calculates the torque gradient based on the difference between values that are temporally before and after among the actual currents sampled at a predetermined time period. Then, this device determines that a sticking abnormality has occurred when the torque gradient is greater than or equal to a gradient threshold value. 【0003】 Japanese Unexamined Patent Application Publication No. 2021 - 138168 【0004】 The inventor has found that when determining the presence or absence of a sticking abnormality using the difference between values that are temporally before and after among the current values sampled at the time period as described above, the determination accuracy is not high. 【0005】 In one aspect of the present disclosure, a steering control device is provided. The steering mechanism is configured such that the rotational power of the motor is converted into the power for steering the steering wheel. The steering control device is configured to execute torque acquisition processing, steering angle acquisition processing, and determination processing. The torque acquisition processing is a process of acquiring the value of a torque variable. The torque variable is a variable indicating the driving torque, which is the torque for driving the steering mechanism. The steering angle acquisition processing is a process of acquiring a steering angle variable. The steering angle variable is a variable indicating the steering angle of the steering wheel. The determination processing is a process of determining that an abnormality has occurred in which the force required for steering has increased, on the condition that the logical product of the torque gradient being greater than or equal to a predetermined value and the increase amount of the absolute value of the driving torque exceeding a predetermined amount is true, based on the torque variable and the steering angle variable as input variables. The torque gradient is the ratio of the increase amount of the absolute value of the driving torque to the absolute value of the change amount of the steering angle indicated by the steering angle variable. 【0006】Another aspect of this disclosure provides a steering control method. The steering mechanism is configured such that the rotational power of a motor is converted into power to steer the steering wheels. The steering control method includes executing a torque acquisition process, a steering angle acquisition process, and a determination process. The torque acquisition process is a process of acquiring the value of a torque variable. The torque variable is a variable that indicates the drive torque, which is the torque for driving the steering mechanism. The steering angle acquisition process is a process of acquiring a steering angle variable. The steering angle variable is a variable that indicates the steering angle of the steering wheels. The determination process is a process of determining that an abnormality has occurred in which the force required for steering is large, based on the torque variable and the steering angle variable as input variables, on the condition that the logical AND of the torque gradient being greater than or equal to a predetermined value and the increase in the absolute value of the drive torque being greater than a predetermined amount is true. The torque gradient is the ratio of the increase in the absolute value of the drive torque to the absolute value of the change in the steering angle indicated by the steering angle variable. 【0007】 This is a block diagram showing the configuration of a steering control device and 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 processing related to the prediction of freezing performed by the steering control device of Figure 1. This is a flowchart showing the procedure for processing related to locking performed by the steering control device of Figure 1. This is a flowchart showing the procedure for setting the torque amplitude performed by the steering control device of Figure 1. This is a time chart showing the problem that the processing in Figure 4 aims to solve. This is a time chart showing the processing in Figure 4. This is a flowchart showing the procedure for processing related to locking according to a second embodiment. This is a flowchart showing the procedure for processing related to locking according to the same embodiment. 【0008】<First Embodiment> The first embodiment will now 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. 【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 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】 "Predictive Determination Process M20" Figure 3 shows the detailed procedure of predictive determination 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". 【0019】In the series of processes shown in Figure 3, the PU 62 first obtains the steering torque Th and the assist amount Ta (S10). Next, the PU 62 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 PU 62 also obtains the rotation angle θm (S14). 【0020】 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 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. 【0021】 If PU62 determines that the stick judgment history flag F1 is "0" (S16: NO), it determines whether the following condition A is met (S18). Condition A 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 A is met (S18: YES), it determines whether the following condition B is met (S20). 【0022】 Condition B is the 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. 【0023】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. 【0024】 PU62 determines whether counter C1 is greater than or equal to 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 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. 【0025】 On the other hand, if PU62 determines that the stick determination history flag F1 is "1" (S16: YES), it determines whether the determination condition for being 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 determination condition for being in a stick state is not met (S27: YES), it increments counter C2 (S28). 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 (S30). 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). 【0026】 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. 【0027】 Condition D is that the sign of the total 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 that the absolute value of the angular acceleration αm is greater than or equal to the threshold αmth. 【0028】 PU62 determines that there is a sign of the steering mechanism freezing if it determines that the logical AND of conditions C to E is true (S32-S36: YES). In other words, PU62 determines that there is a sign of the steering mechanism freezing if the logical AND of conditions C to E becomes true within a predetermined time defined by the threshold C2th after the stick condition occurs. Then PU62 initializes the stick determination history flag F1 (S40). Also, PU62 initializes the counter C2 (S42). 【0029】 On the other hand, if PU62 determines that counter C2 is greater than or equal to the threshold C2th (S30: NO), it proceeds to the process in S40. Also, if PU62 determines that the result is negative in the process in S18 or S20, it initializes counter C1 (S44). 【0030】 Furthermore, when PU62 determines that a negative result is obtained in processes S24, S27, S32, S34, and S36, or when it completes processes S26, S42, and S44, it temporarily terminates the series of processes shown in Figure 3. 【0031】 "Lock determination process M22" Figure 4 shows the procedure for the lock determination process M22. The process shown in Figure 4 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined period. 【0032】In the series of processes shown in Figure 4, the PU 62 first obtains the steering torque Th and the assist amount Ta (S50). Then, the PU 62 substitutes the sum of the steering torque Th and the assist amount Ta into the combined torque Tt (S52). The PU 62 also obtains the steering angle θh (S54). The steering angle θh is calculated by the PU 62 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. 【0033】 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 processes of S52 and S54 (S60). Specifically, PU62 substitutes the combined torque Tt and steering angle θh obtained in the processes of S52 and S54 into the combined torque Ttr and steering angle θhr, respectively. Then PU62 sets that there is no request to update the reference point (S61). 【0034】 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 that the absolute value of the difference between the steering angle θh and the steering angle θhr used to determine the reference point is less than or equal to a predetermined amount Δθh. 【0035】The process in S62 is to determine 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. 【0036】 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 (S63). Condition G is the condition that the summation torque Tt that defines the reference point is positive AND the summation torque Tt is positive. 【0037】 Condition H is a condition that the summation torque Tt used to define the reference point is negative and the summation torque Tt is also negative. Conditions G and H are processes to determine whether the summation torque Tt and the summation torque Tt at the reference point have the same sign. 【0038】 If PU62 determines that the above logical OR is false (S63: NO), it proceeds to the process in S65. On the other hand, if PU62 determines that the above logical OR is true (S63: YES), it determines whether the following condition I is satisfied (S64). 【0039】 Condition I is the condition that the absolute value of the difference between the total torque Tt and the total torque Tt that defines the reference point is greater than a predetermined amount ΔTt. The process in S64 is to determine whether or not the steering angle θh does not change despite the application of a total torque Tt with a large absolute value. In other words, the process in S64 is to determine whether or not a sticking abnormality has occurred. 【0040】 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 a 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, as an example, display visual information on the display device. 【0041】 Furthermore, when the processes in S61, S65, and S68 are completed, or when a negative determination is made in the process of S58, the PU 62 temporarily terminates the series of processes shown in Figure 4. "Details of Vibration Processing M16" Figure 5 shows the procedure for the process of setting the amplitude of vibration by vibration processing M16. The process shown in Figure 5 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined period. 【0042】 In the series of processes shown in Figure 5, PU62 first determines whether the logical OR of the following conditions J and K is true (S70). Condition J is a condition indicating that a warning has been detected. 【0043】 Condition K is a condition indicating that a lock has been determined. If PU62 determines that the above logical OR is true (S70: YES), it obtains the outside temperature To (S72). Next, PU62 determines whether or not a warning check has been performed (S74). If PU62 determines that a warning check has been performed (S74: YES), it performs a map calculation on the amplitude Am of the vibration component of the torque of the motor 32 using map data specifically for cases where there is a warning (S76). The map data is data in which the outside temperature To is the input variable and the amplitude Am is the output variable. In the process of S76, PU62 changes the amplitude Am according to the outside temperature To, provided that the amplitude Am when the outside temperature To is low is greater than or equal to the amplitude Am when the outside temperature To is high. 【0044】 Furthermore, in statements such as "change B according to A while satisfying the condition that B when A is large is greater than or equal to B 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. Also, the above statement means that change B according to A so that A when B is large is larger than A when B is small. 【0045】 Also, map data is paired data consisting of discrete values of input variables and values of output variables corresponding to each of the values of the input variables. Also, the map operation may be any process as long as when the value of the input variable matches any of the values of the input variables of the map data, the value of the output variable of the corresponding map data is the operation result. Also, the map operation may be any process as long as when the value of the input variable does not match any of the values of the input variables of the map data, the value obtained by interpolation of the values of a plurality of output variables included in the map data is the operation result. Also, alternatively, the map operation may be any process as long as when the value of the input variable does not match any of the values of the input variables of the map data, the value of the output variable of the map data corresponding to the closest value among the values of a plurality of input variables included in the map data is the operation result. 【0046】 On the other hand, when it is determined that the lock determination has been made (S74: NO), if the PU62 determines that there is a sticking abnormality, the PU62 performs a map operation on the amplitude Am of the torque vibration of the motor 32 using dedicated map data (S78). The map data is data in which the outside air temperature To is an input variable and the amplitude Am is an output variable. In the process of S78, the PU62 changes the amplitude Am according to the outside air temperature To on the condition that the amplitude Am when the outside air temperature To is low is greater than or equal to the amplitude Am when the outside air temperature To is high. In particular, when the outside air temperature To is the same, the PU62 sets the amplitude Am to a larger value when the lock determination has been made than when the prediction determination has been made. 【0047】 When the processes of S76 and S78 are completed, the PU62 substitutes, into the vibration torque Tf, a value obtained by multiplying the amplitude Am by the unit sine wave "sinωt" (S80). Here, the angular velocity ω is set to satisfy a predetermined condition such as not overlapping with the resonance frequency of the vehicle. Also, "t" is a variable indicating time. 【0048】Incidentally, when the processing of S80 is completed, PU62 temporarily ends the series of processing shown in FIG. 5. <Operations and Effects of the Present Embodiment> PU62 determines the presence or absence of a sign of fixation abnormality caused by freezing and whether a fixation abnormality has occurred. When performing a sign determination or a lock determination of a fixation abnormality, PU62 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 at the angular velocity ω and the amplitude Am. This vibration can contribute to breaking the ice on the movable part of the steering mechanism. Further, when vibrating the torque of the motor 32, the heat generation amount of the motor 32 and the inverter 36 becomes larger than when not vibrating. The heat generated by the motor 32 and the inverter 36 can contribute to melting the ice on the movable part of the steering mechanism or suppressing the moisture on the movable part from freezing. 【0049】 When a fixation abnormality occurs, the torque gradient, which is the ratio of the absolute value of the change amount of the total torque Tt to the change amount of the steering angle θh, can become a very large value. However, when determining that a fixation abnormality has occurred based on the magnitude of the torque gradient, the determination accuracy may decrease depending on the method of quantifying the torque gradient. 【0050】Figure 6 shows a case in which the torque gradient is quantified by sampling the steering angle θh and the combined torque Tt at a predetermined sampling period. In Figure 6, the steering angles θh0 and θh1 are steering angles θh sampled at time-series adjacent timings, and the change in combined torque Tt dTt is the difference between corresponding combined torques Tt. In this case, the torque gradient can be quantified by "|dTh / (θh0-θh1)|". The torque gradient thus quantified becomes larger the smaller the absolute value of the difference between the steering angles θh sampled at time-series adjacent timings is, even if the absolute value of the torque change dTh itself is not very large. Therefore, using the torque gradient quantified in this way increases the likelihood of a lock being detected when the absolute value of the combined torque Tt momentarily increases due to slight sticking in the steering mechanism or fluctuations in the reaction force received by the steering wheels 20 from the road surface. Figure 6 shows an example where the change in steering angle at the moment when the absolute value of the combined torque Tt momentarily increases due to a slight sticking in the steering mechanism or fluctuations in the reaction force that the steering wheel 20 receives from the road surface is equal to the difference between steering angles θh0 and θh1. 【0051】 Therefore, PU62 determines that there is a sticking abnormality if the logical AND of condition F and condition I is true. The necessary condition for this logical AND to be true is that the absolute value of the change in the summation torque Tt, dTt, is greater than a predetermined amount ΔTt. In other words, for this logical AND to be true means that in addition to the condition that the torque gradient is greater than "ΔTt / Δθh", the condition that the absolute value of the change in the summation torque Tt, dTt, is greater than a predetermined amount ΔTt is also met. 【0052】 Figure 7 shows the changes in steering angle θh and total torque Tt with solid lines. The curves shown with solid lines are the same as the curves shown in Figure 6. The white circles in Figure 7 indicate the reference point. The dashed line in Figure 7 indicates a value where the absolute value of the total torque Tt is greater than the reference point by a predetermined amount ΔTt. The double dashed line in Figure 7 indicates a position where the steering angle θh is separated from the reference point by a predetermined amount Δθh. 【0053】As shown in Figure 7, in this embodiment, the amount by which the absolute value of the combined torque Tt exceeds the reference point does not exceed a predetermined amount ΔTt. Therefore, in the example shown in Figure 7, PU62 does not determine that a sticking abnormality has occurred. 【0054】 Incidentally, the process of updating the reference point when the logical AND of condition F and condition I is false sets the lower limit of the torque gradient at which locking is determined to be "ΔTt / Δθh". 【0055】 <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings. 【0056】 Figures 8 and 9 show the detailed procedure of the lock determination process M22 according to this embodiment. The process shown in Figures 8 and 9 is realized by the PU 62 repeatedly executing a program stored in the storage device 64, for example, at a predetermined period. In Figure 8, the same reference numerals are used for the processes corresponding to the process shown in Figure 4 for convenience. 【0057】 In the series of processes shown in Figure 8, if PU 62 makes a positive determination in process S64, it makes a provisional determination that a sticking abnormality has occurred (S66a). If PU 62 completes process S66a, it terminates the series of processes shown in Figure 8. 【0058】 On the other hand, in the series of processes shown in Figure 9, PU62 determines whether the provisional judgment flag F2 is "1" or not (S90). If the provisional judgment flag F2 is "1", it indicates that a provisional determination of a sticking abnormality has been made. If the provisional judgment flag F2 is "0", it indicates that a provisional determination of a sticking abnormality has not been made. 【0059】 If PU62 determines that the provisional determination flag F2 is "0" (S90: NO), it determines whether a provisional determination has been made by the process shown in Figure 8 (S92). If PU62 determines that a provisional determination has been made (S92: YES), it assigns "1" to the provisional determination flag F2 (S94). Then, PU62 assigns the current steering angle θh to the steering angle θhr at the time of past lock determination (S96). 【0060】On the other hand, if PU62 determines that the provisional judgment flag F2 is "1" (S90: YES), it determines whether the pressing is continuing or not (S98). PU62 determines that the pressing is continuing if the current total torque Tt has the same sign as the total torque Tt at the time of the provisional judgment, and the amount exceeding the reference point exceeds a predetermined amount ΔTt. If PU62 determines that the pressing is continuing (S98: YES), it increments the counter T (S100). The counter T measures the duration of the pressing. PU62 determines whether the counter T is greater than or equal to the threshold Tth (S102). If PU62 determines that the counter T is greater than or equal to the threshold Tth (S102: YES), it performs vibration processing (S104). The vibration torque Tf produced by the vibration processing here may be the same torque as when, for example, a premonitory judgment is performed. 【0061】 PU62 determines whether the change in steering angle θh due to vibration processing is below a predetermined value (S106). Note that whether the change in steering angle θh is below a predetermined value may be determined by whether the change in rotation angle θm is below a specified value. 【0062】 If PU62 determines that the change in steering angle θh is below a predetermined value (S106: YES), it makes a final determination that a sticking abnormality has occurred (S108). Then, PU62 proceeds to the process in S68. 【0063】 On the other hand, if PU62 determines that the pressing is not continuing (S98: NO), it determines whether a second provisional determination has been made after the return (S110). A return means that the absolute value of the combined torque Tt falls below a threshold. The threshold here may be the same as the predetermined value Ttth in the process of S58. For example, PU62 may make an affirmative determination in the process of S110 on the condition that a second provisional determination is made within a predetermined time from the first provisional determination. 【0064】If PU62 determines that a second provisional determination has been made (S110: YES), it determines whether the absolute value of the difference between the steering angle θhr at the time of the previous lock determination and the current steering angle θh is less than or equal to a predetermined value Δth (S112). If PU62 determines that the absolute value of the difference is less than or equal to the predetermined value Δth (S112: YES), it proceeds to the process in S104. 【0065】 On the other hand, if PU62 determines that the result is negative in the processes of S106 and S112, it assigns zero to the provisional determination flag F2 (S114). Note that when PU62 completes the processes of S68, S96 and S114, or when it determines that the result is negative in the processes of S92, S102 and S110, it temporarily terminates the series of processes shown in Figure 9. 【0066】 <Operation and Effects of the Second Embodiment> PU62 makes a determination that a sticking abnormality has occurred if the state in which the logical AND of condition F and condition I is true continues for a predetermined time or longer determined by the threshold Tth. This makes it possible to suppress the misdetermination that a sticking abnormality has occurred due to sudden phenomena such as the influence of road surface reaction force. 【0067】 PU62 makes a final determination that a sticking abnormality has occurred, provided that multiple preliminary determinations are made and the absolute value of the difference between the steering angles θh at each of those preliminary determinations is less than or equal to a predetermined value. This prevents misdetermining that a sticking abnormality has occurred due to sudden phenomena such as the influence of road surface reaction force. 【0068】 PU62 makes a determination that a sticking abnormality has occurred when the absolute value of the change in steering angle θh due to vibration processing is less than or equal to a predetermined value. This makes it possible to more reliably suppress the erroneous determination that a sticking abnormality has occurred when no sticking abnormality has occurred. 【0069】 <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. 【0070】"Regarding the Judgment Process" In Figure 9, when the number of provisional judgments reached two, a final judgment was made that a sticking abnormality had occurred, provided that the absolute value of the difference between the steering angles θhr at each of those provisional judgments was less than or equal to a predetermined value. However, instead, when the number of provisional judgments reached three or more predetermined times, a final judgment may be made that a sticking abnormality had occurred, provided that the absolute value of the difference between the steering angles θhr at each of those provisional judgments was less than or equal to a predetermined value. 【0071】 - In the process shown in Figure 9, if processes S104 and S106 are omitted and a positive determination is made in processes S102 and S112, a final determination that a sticking abnormality has occurred may be made. - If a provisional determination is made by the process shown in Figure 8, processes S104 and S106 may be executed immediately, and if a positive determination is made in process S106, a final determination that a sticking abnormality has occurred may be made. 【0072】 The process of determining whether the logical AND of the conditions that the torque gradient is greater than or equal to a predetermined value and that the increase in the absolute value of the driving torque exceeds a predetermined amount is true is not limited to the process of determining whether the logical AND of condition I is true. For example, it may be a process of determining whether the absolute value of the difference between the minimum and maximum values ​​of the combined torque Tt exceeds a predetermined amount, and if it is determined that it exceeds the predetermined value, a process of determining whether the torque gradient is greater than or equal to a predetermined value. 【0073】 "Regarding vibration processing" - It is not essential that vibration processing involves superimposing a sinusoidal periodic torque onto the basic assist amount Ta0. For example, vibration processing may involve superimposing a sawtooth-shaped periodic torque onto the basic assist amount Ta0. 【0074】 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. 【0075】- For example, while the vehicle is in motion, the fact that a warning has been made may be included as a condition for executing the process of determining whether or not the vehicle is locked. "Regarding the warning determination process" (a) Regarding the stick determination process - In the process of determining whether or not 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. Also, for example, the variable indicating the amount of rotation may be the change in the steering angle of the steering wheel 20. 【0076】 - In the process of determining whether the absolute value of the drive torque, which is the torque used to drive the steering mechanism, is greater than or equal to a predetermined value, the variable indicating the drive torque is not limited to the summed torque Tt. The variables indicating the drive torque may be, for example, the vehicle speed V and 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 summed torque Tt can be determined by the vehicle speed V and the 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. 【0077】 (b) Regarding the slip detection process: The variable representing the drive torque in the process of determining whether the absolute value of the drive torque, which is the torque used to drive the steering mechanism, decreases is not limited to the summed torque Tt. The variable representing the drive torque 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 summed 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 summed torque Tt decreases. 【0078】- In the process of determining whether the rotation of the steering mechanism when the absolute value of the drive torque decreases matches the sign of the drive 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. 【0079】 The slip determination process is not limited to determining whether the logical AND of conditions C to E is true or not. The slip determination process may, for example, be a process that determines whether the logical AND of conditions C and D is true or not. 【0080】 "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. 【0081】"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". 【0082】 "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. 【0083】 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 a steering wheel, and is configured to perform torque acquisition processing, steering angle acquisition processing, and determination processing, wherein the torque acquisition processing is processing to acquire the value of a torque variable, the torque variable is a variable indicating a drive torque which is the torque for driving the steering mechanism, the steering angle acquisition processing is processing to acquire a steering angle variable, the steering angle variable is a variable indicating the steering angle of the steering wheel, and the determination processing is processing to determine that an abnormality has occurred in which the force required for steering is large, based on the torque variable and the steering angle variable as input variables, on the condition that the logical AND of the torque gradient being greater than or equal to a predetermined value and the increase in the absolute value of the drive torque being greater than a predetermined amount is true, and the torque gradient is the ratio of the increase in the absolute value of the drive torque to the absolute value of the change in the steering angle indicated by the steering angle variable.

2. A steering control device according to claim 1, configured to perform a reference point update process, wherein the reference point update process updates the reference point to a point determined from the current torque variable value and the steering angle variable value, based on the torque variable and the steering angle variable as input variables, when the amount by which the absolute value of the torque variable exceeds the reference point is less than or equal to a predetermined amount and the value of the steering angle variable is more than or equal to a predetermined angle from the reference point, and the determination process includes determining that the abnormality has occurred, on the condition that the amount by which the absolute value of the torque variable exceeds the reference point exceeds the predetermined amount.

3. The steering control device according to claim 2, wherein the determination process includes a process that determines that an abnormality has occurred if the amount by which the absolute value of the torque variable exceeds the reference point exceeds a predetermined amount reaches multiple times, and the absolute value of the difference between the values ​​of the steering angle variables when the amount exceeds the predetermined amount is less than or equal to a predetermined value.

4. The steering control device according to claim 2, wherein the determination process includes a process of determining that the abnormality has occurred on the condition that the amount by which the absolute value of the torque variable exceeds the reference point exceeds the predetermined amount continues for a predetermined period of time.

5. The steering control device according to claim 2, wherein the determination process includes a provisional determination process and a final determination process, the provisional determination process is a process that provisionally determines that the abnormality has occurred on the condition that the amount by which the absolute value of the torque variable exceeds the reference point exceeds a predetermined amount, and the final determination process is a process that, if the provisional determination has been made, makes a final determination that the abnormality has occurred when the absolute value of the change in the steering angle variable is less than or equal to a predetermined value when the torque of the motor is vibrated.

6. The steering control device according to claim 5, configured to perform a notification process and a vibration process, wherein the notification process is a process that notifies that the abnormality has occurred when the determination is made, and the vibration process is a process that vibrates the torque of the motor when the determination is made.

7. The steering control device according to claim 1, wherein the determination process is a process for determining an abnormality in the steering mechanism's sticking.

8. The steering control device according to claim 7, wherein the determination process is a process for determining a sticking abnormality caused by freezing of the steering mechanism.

9. 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 a steering wheel, and includes the execution of a torque acquisition process, a steering angle acquisition process, and a determination process, wherein the torque acquisition process is a process of acquiring the value of a torque variable, the torque variable is a variable indicating a drive torque which is the torque for driving the steering mechanism, the steering angle acquisition process is a process of acquiring a steering angle variable, the steering angle variable is a variable indicating the steering angle of the steering wheel, and the determination process is a process of determining that an abnormality has occurred in which the force required for steering is large, based on the torque variable and the steering angle variable as input variables, on the condition that the logical AND of the torque gradient being greater than or equal to a predetermined value and the increase in the absolute value of the drive torque being greater than a predetermined amount is true, and the torque gradient is the ratio of the increase in the absolute value of the drive torque to the absolute value of the change in the steering angle indicated by the steering angle variable.

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