Steering system

Abstract

To provide a steering system with improved reliability. [Solution] The steering system 10 comprises a first drive system 150 and a second drive system 250, and a first torque sensor 121 and a second torque sensor 122. The first control unit 170 of the first drive system 150 calculates a first rate of change at a predetermined timing, which is the amount of change per unit time of the value detected by the first torque sensor, and a second rate of change at a predetermined timing, which is the value detected by the second torque sensor, which is the amount of change per unit time of the value detected by the second drive system. If the difference between the first rate of change and the second rate of change is greater than a first threshold, it is determined that a torque detection abnormality has occurred for the first torque sensor.

Description

[Technical Field]

[0001] This invention relates to a steering system mounted on a vehicle. [Background technology]

[0002] Patent Document 1 discloses an automatic steering system to be installed in a vehicle. This automatic steering system comprises a power supply mechanism that generates steering force, which includes a main motor and a sub-motor, and a control unit that controls the operation of the power supply mechanism. The control unit comprises a main steering ECU that controls the main motor and a sub-steering ECU that controls the sub-motor. The main steering ECU determines that an abnormality has occurred in the automatic steering system if its own command value does not match the command value of the sub-steering ECU obtained from the sub-steering ECU via communication.

[0003] Patent Document 2 discloses an abnormality detection device to be installed in a vehicle. This abnormality detection device detects abnormalities in a lane keeping control device. The lane keeping control device includes a control controller. The control controller detects an abnormality in a predetermined function by comparing the deviation between the previously received command value and the currently received command value with a predetermined threshold. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-109555 [Patent Document 2] Japanese Patent Publication No. 2005-343183 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the automatic steering device described in the above Patent Document 1, the ECUs of the two control systems communicate with each other regarding the calculation results of torque so that the occurrence of an abnormality can be determined. Therefore, it can be said that the determination accuracy is higher than in the case of determining the occurrence of an abnormality by comparing the previous command value and the current command value in one control system as in the abnormality detection device described in Patent Document 2. However, in the automatic steering device described in the above Patent Document 1, since one ECU receives a command value or the like from the other ECU via communication, there is a risk of erroneously determining the occurrence of an abnormality due to communication delay.

[0006] The present invention has been made by the inventors of the present application newly paying attention to the above problems, and an object thereof is to provide a steering system with improved reliability.

Means for Solving the Problems

[0007] A steering system according to an aspect of the present invention includes a first drive system and a second drive system that apply a steering force to a steered wheel, and a first torque sensor and a second torque sensor that detect a steering force when an operating member is operated. The first drive system includes a first motor that generates the steering force and a first control unit that controls the first motor based on a detection value of the first torque sensor. The second drive system includes a second motor that generates the steering force and a second control unit that controls the second motor based on a detection value of the second torque sensor. The first control unit calculates a first change rate that is a change amount per unit time of the detection value by the first torque sensor, which is a first change rate at a predetermined timing, and calculates a second change rate that is a detection value by the second torque sensor and is a change amount per unit time of the detection value output by the second drive system, which is a second change rate at the predetermined timing. When the difference between the first change rate and the second change rate is greater than a first threshold value, it is determined that a torque detection abnormality has occurred in the first torque sensor.

Effects of the Invention

[0008] According to the present invention, a steering system with improved reliability can be provided.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a diagram schematically showing the overall configuration of a steering system according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the functional configuration of a first drive system and a second drive system according to an embodiment. [Figure 3] FIG. 3 is a flowchart showing the basic processing flow in the abnormality determination process executed by the first drive system according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing the processing flow regarding the detection value of a second torque sensor executed by the first drive system according to an embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of the specific processing flow in the abnormality determination process executed by the first drive system according to an embodiment. [Figure 6] FIG. 6 is a block diagram showing the functional configuration of a first drive system and a second drive system according to a modification example of an embodiment.

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Note that all of the embodiments described below show comprehensive or specific examples of the present invention. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. In addition, among the components in the following embodiments, components not described in the independent claims indicating the most上位 concept are described as optional components.

[0011] In addition, the drawings are schematic diagrams that have been appropriately emphasized, omitted, or adjusted in ratio to show the present invention, and may be different from the actual shapes, positional relationships, and ratios.

[0012] (Embodiment) [1. Overview of the steering system configuration] First, the overall configuration of the steering system 10 according to this embodiment will be described using Figure 1. Figure 1 is a schematic diagram showing the overall configuration of the steering system 10 according to this embodiment.

[0013] As shown in Figure 1, the steering system 10 according to this embodiment is a device that steers the steering wheels 300 of a vehicle equipped with the steering system 10 in response to the operation of an operating member 110 such as a steering wheel. In this embodiment, the vehicle equipped with the steering system 10 has left and right steering wheels 300, but for the sake of explanation, the configuration and operation of the steering system 10 will be described below focusing on one steering wheel 300.

[0014] More specifically, the steering system 10 is a power steering device that assists the driver's force in rotating an operating member 110, such as a steering wheel, for steering. The steering system 10 includes a first drive system 150 and a second drive system 250 that apply steering force to the steering wheels 300, and a first torque sensor 121 and a second torque sensor 122 that detect the steering force caused by the operation of the operating member 110. The first torque sensor 121 is connected to the first drive system 150 by wiring (communication cable, etc., the same applies hereinafter) and can transmit detected values ​​to the first drive system 150. The second torque sensor 122 is connected to the second drive system 250 by wiring (not shown) and can transmit detected values ​​to the second drive system 250. Furthermore, the first drive system 150 and the second drive system 250 are each connected to an in-vehicle network 500.

[0015] The in-vehicle network 500 is a communication network in which multiple ECUs (Electronic Control Units) in the vehicle are connected via CAN (Controller Area Network) communication. The first drive system 150 and the second drive system 250 can receive control signals from, for example, a higher-level ECU via the in-vehicle network 500 and operate according to those control signals. For example, the first drive system 150 can acquire the detection value of the second torque sensor 122 transmitted by the second drive system 250 via the in-vehicle network 500. The second drive system 250 can acquire the detection value of the first torque sensor 121 transmitted by the first drive system 150 via the in-vehicle network 500.

[0016] As described above, the steering system 10 according to this embodiment is equipped with two control systems for driving the steering of the steering wheels 300. This ensures that even if a malfunction occurs in one control system, the other control system can still steer the steering wheels 300 based on the operation of the operating member 110.

[0017] More specifically, the steering system 10 includes a steering mechanism 100 that steers the steering wheels 300 in response to the operation of an operating member 110, and the first drive system 150 and the second drive system 250 provide the steering mechanism 100 with driving force for steering. The steering mechanism 100 includes a steering shaft 130 that rotates in conjunction with the rotation of the operating member 110, and a rack and pinion device 140a that converts the rotation of the steering shaft 130 into reciprocating motion (movement in the left and right direction) of the steering shaft 141.

[0018] The steering shaft 130 consists of three shafts: a column shaft 131, an intermediate shaft 132, and a pinion shaft 133. The position where the first drive system 150, which provides driving force, is attached is not particularly limited, but in this embodiment, it is connected to the pinion shaft 133. The second drive system 250 is connected to a pinion shaft 134, which is located at a different position from the pinion shaft 133. The steering mechanism 100 is equipped with a rack and pinion device 140b that converts the rotation of the pinion shaft 134 into the reciprocating motion of the steering shaft 141.

[0019] The first drive system 150 includes a first motor 180, which acts as the drive source to apply steering force to the pinion shaft 133. The second drive system 250 includes a second motor 280, which acts as the drive source to apply steering force to the pinion shaft 134. In other words, each of the first drive system 150 and the second drive system 250 applies steering force to the steering wheel 300 via the steering shaft 141, which is a steering member. Thus, according to the steering system 10 of this embodiment, a high steering force (assist torque) can be obtained by the cooperation of the first drive system 150 and the second drive system 250. Furthermore, if one of the first drive system 150 or the second drive system 250 is unable to operate normally, the steering of the steering wheel 300 is performed using the steering force generated by the other of the first drive system 150 or the second drive system 250. In other words, the safe driving of the vehicle equipped with the steering system 10 can continue.

[0020] [2. Configuration and Operation of the First and Second Drive Systems] Next, the configuration and operation of the first drive system 150 and the second drive system 250 according to this embodiment will be explained using Figures 2 to 5. Figure 2 is a block diagram showing the functional configuration of the first drive system 150 and the second drive system 250 according to this embodiment. Figure 3 is a flowchart showing the basic processing flow in the abnormality detection process performed by the first drive system 150 according to this embodiment. Figure 4 is a flowchart showing the processing flow related to the detected value of the second torque sensor 122 performed by the first drive system 150 according to this embodiment. Figure 5 is a flowchart showing an example of a specific processing flow in the abnormality detection process performed by the first drive system 150 according to this embodiment.

[0021] As shown in Figure 2, the first drive system 150 includes a first motor 180 that generates steering force and a first control unit 170 that controls the first motor 180 based on the detection value of the first torque sensor 121. The second drive system 250 includes a second motor 280 that generates steering force and a second control unit 270 that controls the second motor 280 based on the detection value of the second torque sensor 122. The first control unit 170 and the second control unit 270 are computers equipped with a CPU (Central Processing Unit) and memory, and are one of the various ECUs equipped in the vehicle. Various processes performed by the first control unit 170 are realized by the CPU of the first control unit 170 executing a predetermined program. Various processes performed by the second control unit 270 are realized by the CPU of the second control unit 270 executing a predetermined program.

[0022] In this embodiment, the first torque sensor 121 and the second torque sensor 122 are sensor devices attached to the pinion shaft 133. The first torque sensor 121 and the second torque sensor 122 detect the steering force caused by the operation of the operating member 110. More specifically, each of the first torque sensor 121 and the second torque sensor 122 outputs a signal as a detected value that corresponds to the amount of twist of the pinion shaft 133 caused by the operation of the operating member 110.

[0023] The first drive system 150 has a first interface (hereinafter referred to as "I / F") 155 and a second I / F 156 for transmitting and / or receiving information. The first I / F 155 is connected to the first torque sensor 121 via wiring (not shown). The first control unit 170 can receive the detection value of the first torque sensor 121 transmitted from the first torque sensor 121 via the first I / F 155. The second I / F 156 is connected to the in-vehicle network 500. The first control unit 170 can communicate with the in-vehicle network 500 via the second I / F 156.

[0024] The second drive system 250 has a third I / F 255 and a fourth I / F 256 for transmitting and / or receiving information. The third I / F 255 is connected to the second torque sensor 122 via wiring (not shown). The second control unit 270 can receive the detection value of the second torque sensor 122 transmitted from the second torque sensor 122 via the third I / F 255. The fourth I / F 256 is connected to the in-vehicle network 500. The second control unit 270 can communicate with the in-vehicle network 500 via the second I / F 156.

[0025] In this configuration, the first drive system 150 can transmit the detection value of the first torque sensor 121 to the second drive system 250 via the in-vehicle network 500. The second drive system 250 can transmit the detection value of the second torque sensor 122 to the first drive system 150 via the in-vehicle network 500.

[0026] In other words, in this embodiment, the first drive system 150 is directly connected to the first torque sensor 121, but not directly connected to the second torque sensor 122. However, the first drive system 150 can acquire the detected value of the second torque sensor 122 via the in-vehicle network 500. The second drive system 250 is directly connected to the second torque sensor 122, but not directly connected to the first torque sensor 121. However, the second drive system 250 can acquire the detected value of the first torque sensor 121 via the in-vehicle network 500.

[0027] In the above configuration, in the first drive system 150, the first control unit 170 controls the operation of the first motor 180 using the detected value of the first torque sensor 121. In other words, it performs an assist calculation, which is a calculation process related to the steering force that the first motor 180 should generate, based on the detected value of the first torque sensor 121. In the second drive system 250, the second control unit 270 controls the operation of the second motor 280 using the detected value of the second torque sensor 122. In other words, it performs an assist calculation, which is a calculation process related to the steering force that the second motor 280 should generate, based on the detected value of the second torque sensor 122.

[0028] In this way, the first drive system 150 and the second drive system 250 each control the motor (180 or 280) provided in their respective systems based on the detection value of a torque sensor (121 or 122) directly connected to their own system. As a result, the first drive system 150 and the second drive system 250 can provide the steering wheel 300 with an appropriate steering force (assist force in this embodiment) based on the operation of the operating member 110.

[0029] However, if a torque detection abnormality occurs, for example, due to an abnormality in the first torque sensor 121 or the second torque sensor 122, the first motor 180 or the second motor 280 may not generate the appropriate steering force. For example, consider a case where a torque detection abnormality occurs due to a malfunction in the first torque sensor 121, or a malfunction in the wiring connecting the first torque sensor 121 and the first I / F 155. In this case, for example, the first motor 180 generates an inappropriate steering force because the detected value of the first torque sensor 121 is not the correct detected value. As a result, the first drive system 150 and the second drive system 250 cannot cooperate properly, which may lead to problems such as a decrease in the stability of the vehicle's steering based on the operation of the operating member 110.

[0030] To address this problem, for example, in the first drive system 150, it is conceivable to compare the detected value of the first torque sensor 121 with the detected value of the second torque sensor 122 to determine whether or not a torque detection abnormality has occurred. More specifically, both the first torque sensor 121 and the second torque sensor 122 are mounted on the pinion shaft 133. Therefore, in principle, the detected values ​​of the first torque sensor 121 and the second torque sensor 122 at the same timing are substantially the same. For this reason, the first control unit 170 can determine, for example, that a torque detection abnormality has occurred for the first torque sensor 121 if the difference between the detected value of the first torque sensor 121 and the detected value of the second torque sensor 122 is greater than a predetermined threshold.

[0031] However, the first drive system 150 acquires the detection value of the first torque sensor 121 from the directly connected first torque sensor 121, while the detection value of the second torque sensor 122 is acquired via the in-vehicle network 500. Therefore, the acquisition of the detection value of the second torque sensor 122 is affected by communication delay due to the in-vehicle network 500. Consequently, the determination of the occurrence of a torque detection anomaly based on the difference between the detection value of the first torque sensor 121 and the detection value of the second torque sensor 122 is prone to misjudgment due to communication delay. The second drive system 250 is also affected by communication delay due to acquiring the detection value of the first torque sensor 121 via the in-vehicle network 500. Therefore, the determination of the occurrence of a torque detection anomaly based on the difference between the detection value of the first torque sensor 121 and the detection value of the second torque sensor 122 is prone to misjudgment due to communication delay.

[0032] To resolve the above problem, increasing the threshold used for the determination would reduce the possibility of misjudgment due to communication delay, but would also decrease the accuracy of the determination. Alternatively, directly connecting the first drive system 150 and the second torque sensor 122 with wiring, and directly connecting the second drive system 250 and the first torque sensor 121 with wiring, could effectively eliminate the problems caused by the above communication delay. However, in this case, other problems would arise, such as increased complexity in the arrangement of wiring and connectors in the steering system 10 and an increase in the cost of the steering system 10.

[0033] Therefore, in the steering system 10 according to this embodiment, the rate of change of the detected value of the first torque sensor 121 (amount of change per unit time) and the rate of change of the detected value of the second torque sensor 122 (amount of change per unit time) are calculated. Furthermore, the difference between these detected values ​​is calculated, and by comparing the calculated difference with a predetermined threshold, it is determined whether or not a torque detection abnormality has occurred. In other words, for example, even if there is a communication delay in acquiring the detected value of the second torque sensor 122 in the first drive system 150, under normal circumstances, the delay is relatively small. Therefore, if no torque detection abnormality has occurred, it is estimated that the first rate of change, which is the rate of change of the detected value of the first torque sensor 121, and the second rate of change, which is the rate of change of the detected value of the second torque sensor 122, are almost the same. Accordingly, in this embodiment, the presence or absence of a torque detection abnormality related to the first torque sensor 121 is determined by comparing the difference between the first rate of change and the second rate of change with a first threshold.

[0034] The following describes the process (abnormality determination process) performed by the first drive system 150 regarding the occurrence of torque detection abnormalities, using Figures 3 to 6. Note that the abnormality determination process performed by the second drive system 250 is the same as that performed by the first drive system 150. Therefore, the following description will primarily focus on the abnormality determination process performed by the first drive system 150 and explain its process flow.

[0035] As shown in Figure 3, in the first drive system 150, the first control unit 170 calculates the first rate of change (r_TS1) and the second rate of change (r_C_TS2) at a predetermined timing (for example, the time of calculation, the same applies hereinafter) (S300). The first rate of change (r_TS1) is the amount of change per unit time of the detected value by the first torque sensor 121, acquired by the first drive system 150 from the first torque sensor 121. Specifically, the latest value of the detected value acquired from the first torque sensor 121 (latest value) is used as TS1. n Then, the value of the detected value obtained immediately before (for example, before Δta) (the previous value) is used in TS1 n-1 In that case, r_TS1=(TS1 n -TS1 n-1) / Δta.

[0036] Also, the second change rate (r_C_TS2) is the detected value by the second torque sensor 122 and is the amount of change per unit time of the detected value output by the second drive system 250. That is, the second change rate (r_C_TS2) is the amount of change per unit time of the detected value of the second torque sensor 122 output by the second drive system 250 and acquired by the first drive system 150 via the in-vehicle network 500. Specifically, the first drive system 150 obtains the latest value (latest acquired value) of the detected value of the second torque sensor 122 acquired via the in-vehicle network 500 as C_TS2 n and the value of the detected value (previous acquired value) acquired immediately before that (for example, before Δtb) as C_TS2 n-1 In this case, r_C_TS2 = (C_TS2 n - C_TS2 n-1 ) / Δtb.

[0037] The values of Δta and Δtb above are not particularly limited. For example, Δta and Δtb may be the same or different from each other. The first control unit 170 of the first drive system 150 may acquire the detected value of the first torque sensor 121 from the first torque sensor 121, for example, every Δta = 1 millisecond to 10 milliseconds. The first control unit 170 of the first drive system 150 may acquire the detected value of the second torque sensor 122 via the in-vehicle network 500, for example, every Δtb = 1 millisecond to 10 milliseconds. It is not necessary that the values of Δta and Δtb are numerical values described in millisecond units. The value of Δta and the value of Δtb may be numerical values generally described in units smaller or larger than millisecond units.

[0038] The r_TS1 which is the first change rate calculated in the first drive system 150 does not necessarily have to be r_TS1 = (TS1 n - TS1 n-1 ) / Δta. For example, TS1 n which is the latest value of the first torque sensor 121 and TS1n-L The difference between this and TS1 n-L From obtaining TS1 n The first rate of change, r_TS1, can be calculated by dividing by Δtc, which is the time (unit time) until acquisition. The same applies to the second rate of change, r_C_TS2, and the latest acquired value of the second torque sensor 122, C_TS2, can be used to calculate r_C_TS2. n and the previously obtained value C_TS2 n-1 Using these methods is not mandatory. However, from the perspective of determining the first rate of change with greater accuracy, it is preferable to use a shorter unit time when calculating the first rate of change. Similarly, from the perspective of determining the second rate of change with greater accuracy, it is preferable to use a shorter unit time when calculating the second rate of change.

[0039] The first control unit 170 further compares the difference between the first rate of change, r_TS1, and the second rate of change, r_C_TS2, with the first threshold (S305). If the difference between the first rate of change and the second rate of change is greater than the first threshold (Yes in S305), the first control unit 170 determines that a torque detection abnormality has occurred for the first torque sensor 121 and performs various processes to address the torque detection abnormality (S310). If the difference between the first rate of change and the second rate of change is less than or equal to the first threshold (No in S305), the first control unit 170 determines that no torque detection abnormality has occurred for the first torque sensor 121. If the first control unit 170 determines that no torque detection abnormality has occurred, it returns the latest value of the detected value (TS1) obtained from the first torque sensor 121. n The operation of the first motor 180 is controlled using ).

[0040] As described above, the steering system 10 according to this embodiment includes two control systems for applying steering force to the steering wheels 300: a first control system comprising a first torque sensor 121 and a first drive system 150, and a second control system comprising a second torque sensor 122 and a second drive system 250. In other words, the control systems for applying steering force to the steering wheels 300 are redundant, so that even if a torque detection abnormality occurs in one control system, steering force can be applied to the steering wheels 300 by the other control system. Furthermore, the first drive system 150 can acquire the detected value of the second torque sensor 122 output by the second drive system 250. In addition, the first drive system 150 determines that a torque detection abnormality has occurred for the first torque sensor 121 if the difference between the first rate of change of the detected value of the first torque sensor 121 and the second rate of change of the detected value of the second torque sensor 122 output by the second drive system 250 is greater than the first threshold. Therefore, the decrease in the accuracy of judgment regarding torque detection abnormalities caused by delays in communication (communication via the in-vehicle network 500 in this embodiment) for acquiring the detected value of the second torque sensor 122 is suppressed. Thus, the steering system 10 according to this embodiment is a steering system with improved reliability.

[0041] Furthermore, the steering system 10 according to this embodiment can suppress a decrease in the accuracy of judgment regarding torque detection abnormalities without using wiring that directly connects the first drive system 150 and the second torque sensor 122, for example. As a result, the steering system 10 can be miniaturized and / or its cost can be reduced.

[0042] The first drive system 150 performs a process to acquire the detected value of the second torque sensor 122 from the second drive system 250 in order to execute the abnormality detection process shown in Figure 3. The first drive system 150 also performs a process to transmit the detected value of the first torque sensor 121 to the second drive system 250 so that the second drive system 250 can determine whether or not a torque detection abnormality has occurred for the second torque sensor 122.

[0043] Specifically, as shown in Figure 4, the first control unit 170 stores the previously acquired value C_TS2 in the memory (not shown) provided by the first control unit 170. n-1 The latest acquired value C_TS2 n Rewrite to (S100). In other words, the latest acquired value at this point C_TS2 n However, in the calculation of the rate of change (S300 in Figure 3), the previously acquired value C_TS2 n-1 The previously obtained value C_TS2 will be treated as such. n-1 The latest acquired value is C_TS2 n It is overwritten. The first control unit 170 further performs information transmission and reception processing for the second drive system 250 (S101). Specifically, the first control unit 170 transmits the detected value of the first torque sensor 121 to the second drive system 250 by outputting the detected value of the first torque sensor 121 to the in-vehicle network 500. The first control unit 170 acquires the detected value of the second torque sensor 122 output by the second drive system 250 via the in-vehicle network 500. The first control unit 170 further acquires the latest acquired value C_TS2 stored in memory. n This is overwritten with the newly acquired detection value of the second torque sensor 122 via the in-vehicle network 500 (S102). Through this process, the latest acquired value C_TS2 of the second torque sensor 122, which is used to calculate the rate of change (S300 in Figure 3), is obtained. n and the previously obtained value C_TS2 n-1 It will be refreshed.

[0044] More specifically, the first control unit 170 performs various processes as shown in Figure 5. A more specific example of the abnormality detection process performed by the first control unit 170 will be explained with reference to Figures 3 and 5.

[0045] The first control unit 170 stores the previous value TS1 in memory (not shown). n-1 Latest value TS1 n Rewrite to (S200). In other words, the latest value at this point is TS1 n However, in the calculation of the rate of change (S300 in Figures 3 and 5), the previous value TS1n-1 The previous value TS1 is treated as such. n-1 The latest value is TS1 n It is overwritten. The first control unit 170 further overwrites the latest value TS1 stored in memory. n The value obtained from the first torque sensor 121 is overwritten with the newly acquired detection value from the first torque sensor 121 (S201). Also, the latest value after this overwriting TS1 n This is transmitted to the second drive system 250 via the in-vehicle network 500 (S101 in Figure 4).

[0046] Next, the first control unit 170 determines whether the communication process is normal or not (S202). For example, if the reception of the detection value of the second torque sensor 122 via the in-vehicle network 500, which is repeatedly performed at predetermined intervals, is interrupted for a period longer than the predetermined interval, the first control unit 170 determines that the communication process via the in-vehicle network 500 is not normal (i.e., a communication error has occurred) (No in S202). If the first control unit 170 determines that the communication process is normal (Yes in S202), it resets the number of communication errors stored in memory to zero (S203). In other words, the number of communication errors becomes "0".

[0047] Next, the first control unit 170 calculates the first rate of change (r_TS1) and the second rate of change (r_C_TS2) (S300). The first control unit 170 further compares the difference between the first rate of change r_TS1 and the second rate of change r_C_TS2 with the first threshold (S305). If the difference between the first rate of change and the second rate of change is greater than the first threshold (Yes in S305), the first control unit 170 determines that a torque detection abnormality has occurred for the first torque sensor 121 and performs various processes to address the torque detection abnormality (S310). For example, the first control unit 170 transmits a signal indicating a torque detection abnormality to the higher-level ECU via the in-vehicle network 500. The first control unit 170 further executes abnormal operation control for the first motor 180 (S320). The first motor 180, under abnormal operation control, refrains from generating steering force and rotates its output shaft in a direction that does not hinder the application of steering force to the steering wheel 300 by the second drive system 250. The first control unit 170, as abnormal operation control, for example, prevents the first motor 180 from performing its normal assist operation (generating steering force based on the detection value of the first torque sensor 121) and rotates the output shaft of the first motor 180 in the direction of the torque received by the output shaft. Such control is also called zero torque control.

[0048] In this way, when the first drive system 150 determines that a torque detection abnormality has occurred, it does not generate steering force to apply to the steering wheel 300, while controlling the first motor 180 so as not to hinder steering using the steering force generated by the second drive system 250. As a result, steering of the steering wheel 300 using the steering force of the second drive system 250 is performed more smoothly.

[0049] The first control unit 170 determines whether a torque detection abnormality has occurred using another condition if the difference between the first rate of change and the second rate of change is less than or equal to the first threshold (No in S305). Specifically, the first control unit 170 determines that a torque detection abnormality has occurred if the difference between the value detected by the first torque sensor 121 at a predetermined timing and the value detected by the second torque sensor 122 at the same predetermined timing, which is output by the second drive system 250, is greater than the second threshold (Yes in S306). In other words, in this embodiment, the first control unit 170 determines that the latest value (latest value) of the detected value obtained from the first torque sensor 121 is TS1 n And, C_TS2 is the latest value (latest acquired value) of the detection value of the second torque sensor 122 acquired via the in-vehicle network 500. n The difference is calculated. The first control unit 170 further compares this difference with the second threshold (S306). As a result of this comparison, the latest value TS1 of the first torque sensor 121 is calculated. n And the latest acquired value C_TS2 from the second torque sensor 122 n If the difference is greater than the second threshold (Yes in S306), the first control unit 170 performs various processes to respond to the torque detection abnormality (S310). The first control unit 170 further executes abnormal operation control on the first motor 180 (S320). The latest value of the first torque sensor 121 TS1 n And the latest acquired value C_TS2 from the second torque sensor 122 n If the difference is less than or equal to the second threshold (S306No), the first control unit 170 determines that no torque detection abnormality has occurred for the first torque sensor 121, and the latest value of the first torque sensor 121 TS1 n Using the above, an assist calculation is performed, which is a calculation process related to the steering force that the first motor 180 should generate (S330).

[0050] Thus, in this embodiment, even if the difference between the first rate of change and the second rate of change is less than or equal to the first threshold (No in S305), if the difference between the detected value of the first torque sensor 121 and the detected value of the second torque sensor 122 at a predetermined timing is greater than the second threshold, it is determined that a torque detection abnormality has occurred. Therefore, compared to the case where the presence or absence of a torque detection abnormality is determined only by the process of comparing the difference between the first rate of change and the second rate of change with the first threshold (S305), the accuracy of determining whether a torque detection abnormality has occurred is further improved.

[0051] In the flowchart of Figure 5, returning to S202, if the first control unit 170 determines that the communication process is not normal (No in S202), it increments the number of communication errors stored in memory (S204). In other words, it increases the number of communication errors stored in memory by one. The first control unit 170 then retrieves the latest value TS1 of the first torque sensor 121 at that point. n and previous value TS1 n-1 The difference between the two values ​​is calculated, and the calculated difference is compared with threshold a (S205). In other words, if a communication error occurs, the first control unit 170 may not be able to obtain the detected value of the second torque sensor 122 via the in-vehicle network 500, or it may obtain an incorrect detected value. Therefore, the first control unit 170 determines whether or not a torque detection error has occurred by comparing the amount of change in the detected value of the first torque sensor 121 over a predetermined period with threshold a (S205).

[0052] As a result of this comparison, if the difference is greater than or equal to threshold a (No in S205), the first control unit 170 performs various processes to respond to the torque detection abnormality (S310). The first control unit 170 further executes abnormal operation control on the first motor 180 (S320).

[0053] The first control unit 170 receives the latest value TS1 from the first torque sensor 121. n and previous value TS1 n-1If the difference is smaller than threshold a (Yes in S205), the number of communication errors is compared with threshold b (S206). If the result of this comparison is that the number of communication errors is smaller than threshold b (No in S206), the first control unit 170 sets the latest value TS1 of the first torque sensor 121. n Using the above, an assist calculation is performed, which is a calculation process related to the steering force that the first motor 180 should emit (S340). If the number of communication errors is greater than or equal to threshold b (Yes in S206), the first control unit 170 performs various processes to respond to torque detection errors (S310). The first control unit 170 further executes abnormal operation control for the first motor 180 (S320).

[0054] In the explanation using Figure 5 above, it was stated that if the difference between the first rate of change r_TS1 and the second rate of change r_C_TS2 is greater than the first threshold (Yes in S305), the first control unit 170 determines that a torque detection abnormality has occurred for the first torque sensor 121. However, the first control unit 170 may also determine that a torque detection abnormality has occurred if the period during which the difference between the first rate of change and the second rate of change is greater than the first threshold is longer than a predetermined period. A period during which the difference between the first rate of change and the second rate of change is greater than the first threshold is longer than a predetermined period, for example, if the comparison result that the difference is greater than the first threshold is obtained M (where M is an integer of 2 or more) times consecutively, or if the time during which the comparison result that the difference is greater than the first threshold is continuously obtained is longer than a predetermined period.

[0055] As a result, the first control unit 170 can, for example, not determine that a torque detection abnormality has occurred if the difference between the first rate of change and the second rate of change instantaneously exceeds the first threshold. Consequently, control of the steering of the steering wheel 300 can be continued more stably.

[0056] As described above, the first drive system 150 according to this embodiment determines whether or not a torque detection abnormality has occurred for the first torque sensor 121 by using the difference between the first rate of change of the detected value of the first torque sensor 121 and the second rate of change of the detected value of the second torque sensor 122 output by the second drive system 250. Therefore, a decrease in the accuracy of the determination caused by the delay in communication for acquiring the detected value of the second torque sensor 122 is suppressed.

[0057] Furthermore, as described above, the second drive system 250 performs various processes common to the first drive system 150. Specifically, the second drive system 250 uses, for example, the difference between the second rate of change of the detected value of the second torque sensor 122 and the first rate of change of the detected value of the first torque sensor 121 output by the first drive system 150 to determine whether or not a torque detection abnormality has occurred for the second torque sensor 122. As a result, a decrease in the accuracy of the determination caused by the delay in communication for acquiring the detected value of the first torque sensor 121 is suppressed.

[0058] The first threshold used by the second drive system 250 for comparison with the difference between the first rate of change and the second rate of change may be the same value as, or different from, the first threshold used by the first drive system 150 for comparison with the difference between the first rate of change and the second rate of change (S305). Similarly, the second drive system 250 may use the latest value TS2 of the second torque sensor 122. n and the latest acquired value C_TS1 from the first torque sensor 121 n The second threshold used for comparison with the difference is the latest value TS1 of the first torque sensor 121 when the first drive system 150 is set. n and the latest acquired value C_TS2 from the second torque sensor 122 n The second threshold used for comparison with the difference (S306) may be the same as or different from the second threshold.

[0059] [3. Variant] Next, a modified version of the steering system 10 will be described, focusing on the differences from the above embodiment. Figure 6 is a block diagram showing the functional configuration of the first drive system 150a and the second drive system 250a according to a modified version of the embodiment.

[0060] The steering system 10a according to this modified example comprises a first drive system 150a and a second drive system 250a, and a first torque sensor 121 and a second torque sensor 122, similar to the steering system 10 according to the embodiment (see Figures 1 and 2). The first drive system 150a has a first motor 180, a first control unit 170, a first I / F 155, and a second I / F 156. The second drive system 250a has a second motor 280, a second control unit 270, a third I / F 255, and a fourth I / F 256. The first torque sensor 121 is connected to the first I / F 155 by wiring (not shown), and the second torque sensor 122 is connected to the third I / F 255 by wiring (not shown). Furthermore, an in-vehicle network 500 is connected to the second I / F 156 and the fourth I / F 256. These configurations are common to the steering system 10 according to the embodiment.

[0061] In the modified steering system 10a, the first drive system 150a further has a fifth I / F 157, and the second drive system 250a further has a sixth I / F 257. In this modified version, the fifth I / F 157 and the sixth I / F 257 are connected by wiring not shown. As a result, the first control unit 170 can acquire the detection value of the second torque sensor 122 via the fifth I / F 157 and the sixth I / F 257. In other words, the first drive system 150a can acquire the detection value of the second torque sensor 122 directly from the second drive system 250a, rather than through communication via the in-vehicle network 500. The second drive system 250a can acquire the detection value of the first torque sensor 121 directly from the first drive system 150a, rather than through communication via the in-vehicle network 500.

[0062] According to the above configuration, the first drive system 150a can acquire the detection value of the second torque sensor 122 via wiring that connects the first drive system 150a and the second drive system 250a on a one-to-one basis, without going through the in-vehicle network 500. Therefore, in the steering system 10a according to this modified example, wiring that connects the first drive system 150a and the second drive system 250a on a one-to-one basis is required, while the communication delay when the first drive system 150a acquires the detection value of the second torque sensor 122 is reduced. As a result, the possibility of the first control unit 170 misjudging whether or not a torque detection abnormality has occurred is further reduced.

[0063] The same applies to the second drive system 250a, and the communication delay when the second drive system 250a acquires the detected value from the first torque sensor 121 is reduced. As a result, the possibility of the second control unit 270 misjudging whether or not a torque detection abnormality has occurred is further reduced.

[0064] [4. Regarding other variations] The steering system according to the present invention has been described above based on embodiments and modifications thereof. However, the present invention is not limited to the above embodiments and modifications. Within the scope of the present invention, various modifications that a person skilled in the art can conceive of may be applied to the above embodiments or modifications, or forms constructed by combining the above-described plurality of components are also included in the scope of the present invention.

[0065] The steering system 10 according to this embodiment does not necessarily have to be a power steering device that always requires the driver's force to rotate the operating member 110. The steering system 10 may be provided in a vehicle that can switch between a manual driving mode and an automatic driving mode. In this case, the steering system 10 may function as a power steering device in manual driving mode and as an automatic driving steering device that steers the steering wheels 300 using only the steering system 10 in automatic driving mode.

[0066] The steering system 10 does not need to steer two wheels 300; it may be one, or three or more. For example, the steering system 10 may be installed on a tricycle that has one front wheel (which is a steering wheel 300) and two rear wheels. In this case, the steering system 10 only needs to steer one wheel 300.

[0067] The second drive system 250 of the steering system 10 employs a rack and pinion mechanism to apply steering force to the steering wheels 300, but this is not mandatory. The second drive system 250 may, for example, employ a structure in which the second motor 280 is positioned so that its output shaft is parallel to the steering shaft 141, and the torque of the output shaft is transmitted to the steering shaft 141 using a belt, thereby causing the steering shaft 141 to reciprocate in the left-right direction.

[0068] The first drive system 150 and the second drive system 250 may exchange information with the in-vehicle network 500 by wireless communication instead of wired communication. In the above modified example, the first drive system 150a and the second drive system 250a may exchange information by wireless communication instead of wired communication.

[0069] The first motor 180 and the second motor 280 of the first drive system 150 do not necessarily have to be separate motors. For example, a single electric motor having only one set of housing and output shaft, etc., and having two electrical systems, may function as both the first motor 180 and the second motor 280.

[0070] Each of the various supplementary details concerning the steering system 10 according to the above embodiment may be appropriately applied to the steering system 10a according to a modified example of the embodiment. Furthermore, the present invention also includes any combination of two or more claims from the claims described in the claims at the time of filing the present application, provided that such combinations are not technically contradictory. [Industrial applicability]

[0071] The steering system according to the present invention is useful as a steering system that steers the steering wheels in response to the operation of an operating member, and can be used, for example, as a steering system for vehicles such as automobiles, agricultural machinery, or construction machinery. [Explanation of Symbols]

[0072] 10,10a: Steering system, 100: Steering mechanism, 110: Operating member, 121: First torque sensor, 122: Second torque sensor, 130: Steering shaft, 131: Column shaft, 132: Intermediate shaft, 133,134: Pinion shaft, 140a,140b: Rack and pinion device, 141: Steering shaft, 150,150a: First drive system, 155: First I / F, 156: Second I / F, 157: Fifth I / F, 170: First control unit, 180: First motor, 250,250a: Second drive system, 255: Third I / F, 256: Fourth I / F, 257: Sixth I / F, 270: Second control unit, 280: Second motor, 300: Steering wheel, 500: In-vehicle network

Claims

1. A first drive system and a second drive system that apply steering force to the steering wheels, It comprises a first torque sensor and a second torque sensor that detect steering force caused by the operation of an operating member, The first drive system is, The first motor that generates the steering force, The system includes a first control unit that controls the first motor based on the detected value of the first torque sensor, The second drive system is, The second motor that generates the steering force, The system includes a second control unit that controls the second motor based on the detected value of the second torque sensor, The first control unit is, The first rate of change at a predetermined timing is calculated as the amount of change per unit time of the value detected by the first torque sensor. The second rate of change at the predetermined timing is calculated to be the value detected by the second torque sensor and the amount of change per unit time of the detected value output by the second drive system. If the difference between the first rate of change and the second rate of change is greater than the first threshold, it is determined that a torque detection abnormality has occurred with respect to the first torque sensor. Steering system.

2. The first control unit is, If the period during which the difference between the first rate of change and the second rate of change is greater than the first threshold is longer than a predetermined period, it is determined that a torque detection abnormality has occurred. The steering system according to claim 1.

3. The first control unit is, If the difference between the first rate of change and the second rate of change is less than or equal to the first threshold, If the difference between the value detected by the first torque sensor at the predetermined timing and the value detected by the second torque sensor at the predetermined timing, which is output by the second drive system, is greater than the second threshold, it is determined that a torque detection abnormality has occurred. The steering system according to claim 1 or 2.

4. The first control unit is, If it is determined that the torque detection abnormality has occurred, the abnormal operation control is executed on the first motor. The first motor, upon receiving the abnormal operation control, refrains from performing the operation that generates the steering force, and rotates the output shaft of the first motor in a direction that does not hinder the application of the steering force to the steering wheel by the second drive system. The steering system according to claim 1 or 2.

Images