Anomaly detection apparatus

Abstract

An abnormality detection device includes a processing circuit configured to execute an abnormality detection process. The abnormality detection process includes a first state quantity acquisition process, a second state quantity acquisition process, a difference calculation process of calculating a difference between the first state quantity and the second state quantity, and a determination process of comparing an absolute value of the difference with a difference threshold value. The abnormality detection process is a process of detecting an abnormality of a turning unit (6) when the absolute value of the difference is greater than the difference threshold value, and the processing circuit is configured not to execute the determination process when an absolute value of an actual current value is greater than a current threshold value.

Description

TECHNICAL FIELD

[0001] The present application relates to an abnormality detection device. BACKGROUND

[0002] In related art, a steer-by-wire system in which a power transmission path between a steering unit connected to a steering wheel and a turning unit that turns a turning wheel is cut off is referred to as a steering system of a vehicle. For example, the turning unit of the steering system described in Japanese Unexamined Patent Application Publication No. 2015-160504 (JP 2015-160504 A) includes a motor as a drive source, a turning shaft connected to the turning wheel, and a power transmission mechanism that transmits torque of the motor to the turning shaft.

[0003] For example, due to an abnormality of the power transmission mechanism, torque of the motor can not be smoothly transmitted to the turning shaft. Therefore, the steering control device that controls the steering system described in JP 2015-160504 A detects an abnormality of the turning unit based on a relationship between a rotation angle of the motor and a turning angle of the turning wheel. Specifically, the steering control device stores in advance a relationship between the rotation angle of the motor and the turning angle when the power transmission mechanism is normal. The steering control device detects an abnormality of the turning unit by comparing the relationship between the rotation angle and the turning angle when the power transmission mechanism is normal with an actually detected relationship between the rotation angle and the turning angle. SUMMARY

[0004] Recently, detection of an abnormality of a steering system needs higher accuracy. Therefore, there is a demand for development of a new technology that can more accurately detect an abnormality of a turning unit. For example, this problem can similarly arise in a turning unit that constitutes an electric power steering system and a turning unit that constitutes a steer-by-wire system.

[0005] The present application provides an abnormality detection device that can accurately detect an abnormality of a turning unit.

[0006] According to an aspect of the present application, there is provided an abnormality detection device configured to detect an abnormality of a turning unit, the turning unit including: a motor as a drive source; a turning shaft connected to a turning wheel; a power transmission mechanism configured to transmit a torque of the motor to the turning shaft; a first sensor configured to detect a rotation angle of the motor; a second sensor configured to detect a joint state amount indicating position information about a joint member mechanically connected to the motor via the power transmission mechanism; and a current sensor configured to detect an actual current value that is a value of an actual current supplied to the motor. The abnormality detection device includes a processing circuit configured to execute an abnormality detection process. The abnormality detection process includes: a first state amount acquisition process of acquiring a first state amount indicating position information about a convertible member based on the rotation angle detected by the first sensor, the first state amount being convertible to a turning angle of the turning wheel; a second state amount acquisition process of acquiring a second state amount indicating position information about the convertible member based on the joint state amount detected by the second sensor; a difference calculation process of calculating a difference between the first state amount and the second state amount; and a determination process of comparing an absolute value of the difference with a difference threshold value. The abnormality detection process is a process of detecting an abnormality of the turning unit when the absolute value of the difference is greater than the difference threshold value. The processing circuit is configured not to execute the determination process when an absolute value of the actual current value is greater than a current threshold value.

[0007] The first state amount and the second state amount each indicate position information about the convertible member. Therefore, when the turning unit is normal, the absolute value of the difference between the first state amount and the second state amount is equal to or smaller than the difference threshold value. Here, when the absolute value of the actual current value that is the value of the actual current supplied to the motor is large, i.e., when the motor outputs a large torque, a large force acts on a constituent member of the power transmission mechanism, for example. Therefore, even when the rotation angle of the motor changes, the joint state amount indicating position information about the joint member can not change due to elastic deformation of the constituent member of the power transmission mechanism, for example. That is, although the first state amount changes, the second state amount can not change, and thus the absolute value of the difference can increase. Therefore, when the absolute value of the actual current value is large, the absolute value of the difference can be greater than the difference threshold value even when the turning unit is normal.

[0008] In this regard, by the above-described configuration, when the absolute value of the actual current value is greater than the current threshold value, the processing circuit does not execute the determination process. Therefore, it is possible to reduce the possibility of erroneously determining that the turning unit is abnormal due to elastic deformation of the constituent member of the power transmission mechanism, for example, when the turning unit is actually normal.

[0009] In the abnormality detection device according to the aspect, it is possible to cut off a power transmission path between the turning unit and a steering unit that is steered by a driver. BRIEF DESCRIPTION OF DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, in which like numerals designate like elements, and wherein:

[0011] Figure 1 is a diagram schematically showing a configuration of a steering system; and

[0012] Figure 2 is a flowchart showing an example of a process of an abnormality detection processing of a turning unit performed by a steering control device. DETAILED DESCRIPTION

[0013] Hereinafter, an abnormality detection device according to an embodiment of the present application will be described with reference to the accompanying drawings. As Figure 1 shown, a steering system 2 controlled by a steering control device 1 as a control target is configured as a steer-by-wire system. The steering system 2 includes a steering unit 4 on which a driver performs a steering operation via a steering wheel 3, and a turning unit 6 that turns a turning wheel 5 in accordance with the steering operation of the driver on the steering unit 4. The steering system 2 according to the present embodiment has a structure in which a power transmission path between the steering unit 4 and the turning unit 6 is generally mechanically cut off.

[0014] The steering unit 4 includes a steering shaft 11 connected to the steering wheel 3, and a steering-side actuator 12 that applies a steering reaction force as a force resisting the steering operation on the steering wheel 3.

[0015] The steering-side actuator 12 includes a steering-side motor 13 and a speed reducer 14. The speed reducer 14 employs, for example, a worm mechanism. The steering-side motor 13 is connected to the steering shaft 11 via the speed reducer 14. Thus, the steering reaction force is applied to the steering wheel 3 via the steering shaft 11.

[0016] The turning unit 6 includes a pinion shaft 21, a rack shaft 22 as a turning shaft connected to the pinion shaft 21, a rack housing 23 that houses the rack shaft 22 so that the rack shaft 22 can reciprocate, and a rack-and-pinion mechanism 24 including the pinion shaft 21 and the rack shaft 22. The rack shaft 22 and the pinion shaft 21 are arranged in the rack housing 23 at a predetermined crossing angle. The rack-and-pinion mechanism 24 has a configuration in which pinion teeth 21a formed in the pinion shaft 21 and rack teeth 22a formed in the rack shaft 22 engage with each other. Thus, the pinion shaft 21 rotates in accordance with the reciprocation of the rack shaft 22. A tie rod 26 is connected to both ends of the rack shaft 22 via a ball joint 25, respectively. A distal end of the tie rod 26 is connected to a knuckle (not shown) to which the turning wheel 5 is assembled.

[0017] The turning unit 6 includes a turning-side actuator 31 that applies a turning force, which is a force for turning the turning wheel 5, to the rack shaft 22. The turning-side actuator 31 includes a turning-side motor 32 that serves as a drive source, and a power transmission mechanism 33 that transmits the torque of the turning-side motor 32 to the rack shaft 22. The power transmission mechanism 33 according to the present embodiment includes a belt mechanism 34 and a ball screw mechanism 35.

[0018] The belt mechanism 34 includes a pair of pulleys 41 and 42 and a belt 43 that is wound around the pair of pulleys 41 and 42. The pair of pulleys 41 and 42 are formed of resin and the belt 43 is formed of rubber. The ball screw mechanism 35 includes a threaded portion 22b formed on the rack shaft 22 and a ball screw nut 46 that is screwed to the threaded portion 22b via a plurality of balls 45. The pulley 41 is connected to a rotation shaft 32a of the turning-side motor 32. The pulley 42 is fixed to the outer periphery of the ball screw nut 46. Thus, the pinion shaft 21 is mechanically connected to the turning-side motor 32 via the rack and pinion mechanism 24 and the power transmission mechanism 33. That is, in the present embodiment, the pinion shaft 21 corresponds to a conjunction member.

[0019] The turning-side actuator 31 applies the turning force to the turning unit 6 by transmitting the rotation of the turning-side motor 32 to the ball screw mechanism 35 via the belt mechanism 34 and causing the ball screw mechanism 35 to convert the transmitted rotation into the reciprocating motion of the rack shaft 22.

[0020] In the steering system 2 having the above-described configuration, the turning angle θi of the turning wheel 5 is changed by the reciprocating motion of the rack shaft 22 due to the application of the turning force from the turning-side actuator 31 in accordance with the steering operation of the driver. At this time, the steering reaction force against the steering operation of the driver is applied to the steering wheel 3 from the steering-side actuator 12.

[0021] An electrical configuration according to the present embodiment will be described below. The steering control device 1 is connected to and operates the steering-side motor 13 and the turning-side motor 32. The steering control device 1 detects an abnormality of the turning unit 6 due to which the torque of the turning-side motor 32 cannot be smoothly transmitted to the rack shaft 22. That is, the steering control device 1 corresponds to an abnormality detection device. Examples of the abnormality detected by the steering control device 1 include an increase in the permanent elongation of the belt 43 due to aging, that is, deterioration over time. The steering control device 1 is connected to a warning device 51 including a warning lamp or a speaker and the steering control device 1 operates the warning device 51.

[0022] The steering control device 1 can be configured to include processing circuitry that (1) operates according to a computer program (software), (2) executes at least some of various processes using one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC), or (3) a combination of the above. The processor includes a central processing unit (CPU) and a memory such as a RAM and a ROM, and the memory stores program codes or commands configured to cause the CPU to execute processes. The memory, i.e., a non-transitory computer readable medium, includes all available media that can be accessed by a general purpose computer or a special purpose computer. Various controls in the steering control device 1 are performed by causing the CPU to execute the programs stored in the memory at intervals of a predetermined operation cycle.

[0023] Detection results from various sensors are input to the steering control device 1. Examples of the various sensors include a vehicle speed sensor 52, a torque sensor 53, a steering-side rotation angle sensor 54, a turning-side rotation angle sensor 55, a pinion angle sensor 56, a steering-side current sensor 57, and a turning-side current sensor 58.

[0024] The vehicle speed sensor 52 detects a vehicle speed V that is a running speed of the vehicle. The torque sensor 53 detects a steering torque Th that is applied to the steering shaft 11. The steering-side rotation angle sensor 54 detects a rotation angle Θs of the rotation shaft 13a of the steering motor 13 as a relative angle in a range of 360°. The turning-side rotation angle sensor 55 detects a rotation angle Θt of the rotation shaft 32a of the turning motor 32 as a relative angle. The pinion angle sensor 56 detects a second pinion angle Θp2 that is a rotation angle of the pinion shaft 21 as an absolute angle in a range including more than 360°. For example, the second pinion angle Θp2 has a positive value when it is located on the right side with respect to a pinion angle midpoint that is an angle when the vehicle is straight, and has a negative value when it is located on the left side with respect to the pinion angle midpoint. In this embodiment, since the pinion shaft 21 corresponds to the link member, the second pinion angle Θp2 corresponds to a link state amount. The turning-side rotation angle sensor 55 corresponds to the first sensor and the pinion angle sensor 56 corresponds to the second sensor.

[0025] The turning side current sensor 57 detects an actual current value Is, which is a value of an actual current supplied to the turning side motor 13. The actual current value Is indicates the magnitude of the torque output from the turning side motor 13. The actual current value Is has a positive value when a torque that rotates the steering wheel 3 to the right side is generated, and has a negative value when a torque that rotates the steering wheel 3 to the left side is generated. The turning side motor sensor 58 detects an actual current value It, which is a value of an actual current supplied to the turning side motor 32. The actual current value It indicates the magnitude of the torque output from the turning side motor 32. The actual current value It has a positive value when a torque that turns the turning wheel 5 to the right is generated, and has a negative value when a torque that turns the turning wheel 5 to the left is generated.

[0026] A summary of reaction control by operation of the turning side motor 13 will now be described. The steering control device 1 calculates a target reaction torque, which is a target value of the steering reaction force, based on the steering torque Th and the vehicle speed V. The steering control device 1 operates the turning side motor 13 so that a motor torque corresponding to the target reaction torque is generated. Thus, the steering reaction force is applied to the steering unit 4.

[0027] A summary of turning control by operation of the turning side motor 32 will be described below. The steering control device 1 calculates a steering angle θh, which is a rotation angle of the steering shaft 11, based on the rotation angle θs of the turning side motor 13. Specifically, for example, the steering control device 1 counts the number of rotations of the turning side motor 13 with respect to a steering midpoint, and calculates a total angle, which is an angle obtained by totaling the rotation angle θs with respect to the steering midpoint. The steering midpoint is the steering angle θh when the steering wheel 3 is located at the center of the steerable range. The steering control device 1 calculates the steering angle θh of the steering wheel 3 by multiplying the total angle by a conversion factor based on the speed ratio of the decelerator 14. For example, the steering angle θh has a positive value when it is an angle located to the right with respect to the steering midpoint, and has a negative value when it is an angle located to the left with respect to the steering midpoint.

[0028] For example, the steering control device 1 counts the number of rotations of the turning side motor 32 with respect to the pinion angle midpoint, calculates a total angle, which is an angle obtained by totaling the rotation angle θt with respect to the pinion angle midpoint. The steering control device 1 calculates a first pinion angle θpl that is convertible to the turning angle θi of the turning wheel 5, by multiplying the total angle by conversion factors based on the speed ratio of the belt mechanism 34, the lead of the ball screw mechanism 35, and the speed ratio of the rack and pinion mechanism 24. That is, the first pinion angle θpl is substantially the same angle as the second pinion angle θp2 detected by the pinion angle sensor 56. For example, the first pinion angle θpl has a positive value when it is an angle located to the right with respect to the pinion angle midpoint, and has a negative value when it is an angle located to the left with respect to the pinion angle midpoint.

[0029] The turning control device 1 calculates a target pinion angle θp* as a target value of the first pinion angle θp1 based on the steering angle θh. For example, the turning control device 1 sets a value obtained by dividing the steering angle θh by a transmission ratio that varies depending on the steering angle θh and the vehicle speed V as the target pinion angle θp*. The turning control device 1 calculates a target turning torque as a target value of the turning force by executing feedback control that makes the first pinion angle θp1 coincide with the target pinion angle θp*. The turning control device 1 operates the turning side motor 32 so that a motor torque corresponding to the target turning torque is generated. Thus, the turning force is applied to the turning unit 6.

[0030] The abnormality detection processing of the turning unit 6 will be described below. Since the pinion shaft 21 rotates in accordance with the reciprocating motion of the rack shaft 22 as described above, the rotation angle of the pinion shaft 21 is convertible to (i.e., can be converted to) the turning angle θi of the turning wheel 5. Thus, in the present embodiment, the pinion shaft 21 serves as a convertible member. The first pinion angle θp1 calculated based on the rotation angle θt as described above corresponds to a first state quantity. The second pinion angle θp2 detected by the pinion angle sensor 56 corresponds to a second state quantity.

[0031] The turning control device 1 acquires the first pinion angle θp1 in the abnormality detection processing. The first pinion angle θp1 can be calculated in the course of executing the turning control, or can be calculated separately in the abnormality detection processing based on the rotation angle θt of the turning side motor 32. The turning control device 1 acquires the second pinion angle θp2 in the abnormality detection processing. The second pinion angle θp2 can be detected in the course of executing the turning control, or can be detected separately in the abnormality detection processing by the pinion angle sensor 56.

[0032] The turning control device 1 calculates a difference Δθp between the first pinion angle θp1 and the second pinion angle θp2. Subsequently, the turning control device 1 compares the absolute value of the difference Δθp with a difference threshold value Δθth. When the absolute value of the difference Δθp is greater than the difference threshold value Δθth, the turning control device 1 determines that the turning unit 6 is abnormal. In other words, when the absolute value of the difference Δθp is greater than the difference threshold value Δθth, the turning control device 1 detects an abnormality of the turning unit 6. The reason for this determination is that since the first pinion angle θp1 and the second pinion angle θp2 each indicate position information about the pinion shaft 21, the absolute value of the difference Δθp is equal to or less than the difference threshold value Δθth based on the tolerances of the constituent components of the turning unit 6 when the turning unit 6 is normal. For example, the difference threshold value Δθth is set to an angle equal to or greater than the maximum value of the difference Δθp that can occur within a range obtained by aggregating the tolerances of the constituent components of the turning unit 6.

[0033] When the absolute value of the actual current It supplied to the turning motor 32 is large, that is, when the turning motor 32 outputs a large torque, a large force acts on components such as the power transmission mechanism 33. Therefore, for example, even when the rotation angle θt of the turning motor 32 changes, the second pinion angle θp2 of the pinion shaft 21 may not change due to, for example, the elastic stretch of the belt 43. In other words, even if the first pinion angle θp1 changes, the second pinion angle θp2 may not change, and thus the absolute value of the difference Δθp increases. Therefore, when the absolute value of the actual current It is large, even if the turning unit 6 is operating normally, the absolute value of the difference Δθp may exceed the difference threshold Δθth.

[0034] Therefore, when the absolute value of the actual current value It exceeds the current threshold value Ith based on the rigidity of the components of the turning unit 6, the steering control device 1 according to this embodiment does not perform the determination process based on the comparison between the absolute value of the difference Δθp and the difference threshold value Δθth. In other words, the steering control device 1 performs this determination process only when the absolute value of the actual current value It is equal to or less than the current threshold value Ith. For example, the current threshold value Ith is set to a current value at which the torque generated causes the sum of the elastic deformation of the belt 43 and the elastic deformation of the pair of pulleys 41 and 42 to be excessive. When the sum of the elastic deformation amounts is excessive, this means that the absolute value of the difference Δθp caused by the elastic deformation of the belt 43 and the pair of pulleys 41 and 42 is greater than a predetermined proportion of the difference threshold value Δθth.

[0035] The following will refer to Figure 2 The flowchart shown describes an example of the procedure of the abnormality detection process performed by the steering control device 1. The abnormality detection process is repeatedly performed at intervals of a predetermined operation cycle. Figure 2 After obtaining the actual current value It of the turning motor 32 (step 101), the steering control device 1 determines whether the absolute value of the actual current value It is greater than the current threshold value Ith (step 102). If the absolute value of the actual current value It is equal to or less than the current threshold value Ith (step 102: No), the process proceeds to step 103.

[0036] In step 103, the steering control device 1 acquires the first pinion angle θpl as the first state quantity. Next, the steering control device 1 acquires the second pinion angle θp2 as the second state quantity (step 104), calculates the difference Δθp between the first pinion angle θpl and the second pinion angle θp2 (step 105). Then, the steering control device 1 compares the absolute value of the difference Δθp with the difference threshold value Δθth (step 106). That is, the processing of step 103 corresponds to first state quantity acquisition processing. The processing of step 104 corresponds to second state quantity acquisition processing. The processing of step 105 corresponds to difference calculation processing. The processing of step 106 corresponds to determination processing.

[0037] Then, when the absolute value of the difference Δθp is greater than the difference threshold value Δθth (step 106: Yes), the steering control device 1 outputs a signal for operating the warning device 51, thereby warning the driver that an abnormality of the turning unit 6 has been detected (step 107). On the other hand, when the absolute value of the difference Δθp is equal to or less than the difference threshold value Δθth (step 106: No), the steering control device 1 determines that the turning unit 6 is normal and ends the abnormality detection processing.

[0038] When the absolute value of the actual current value It is greater than the current threshold value Ith (step 102: Yes), the steering control device 1 does not perform the subsequent processing. That is, step 106 as determination processing is not performed.

[0039] The operation and advantages of this embodiment will be described below. (1) When the absolute value of the actual current value It of the turning side motor 32 is greater than the current threshold value Ith, the steering control device 1 does not perform the determination processing. Therefore, it is possible to reduce the possibility of erroneously determining that the turning unit 6 is abnormal due to elastic deformation of constituent members of the power transmission mechanism 33 when the turning unit 6 is normal, for example.

[0040] This embodiment can be modified as follows. Unless there is a technical contradiction, the embodiment and the following modification examples can be combined. In the foregoing embodiment, the pinion shaft 21 is used as a link member and the second pinion angle θp2 as a linked state quantity is detected by the pinion angle sensor 56 as a second sensor, but the application is not limited to this. For example, the rack shaft 22 can be used as a link member and the stroke position of the rack shaft 22 as a linked state quantity can be detected by a stroke sensor as a second sensor. In this case, the second pinion angle θp2 calculated on the basis of the stroke position detected by the stroke sensor can be used as the second state quantity. The stroke position detected by the stroke sensor can be used as the second state quantity, and the stroke position calculated on the basis of the rotation angle θt of the turning side motor 32 can be used as the first state quantity.

[0041] In the foregoing embodiment, the pinion shaft 21 serves as the convertible member, but the application is not limited thereto, and for example, the rack shaft 22 can serve as the convertible member. In this case, the stroke position calculated on the basis of the rotation angle θt of the turning side motor 32 can be used as the first state quantity, and the stroke position calculated on the basis of the second pinion angle θp2 can be used as the second state quantity.

[0042] In the foregoing embodiment, as long as the determination as to whether the absolute value of the actual current value It is greater than the current threshold value Ith (step 102) is performed before the determination process (step 106) in which the absolute value of the difference Δθp is compared with the difference threshold value Δθth, the order thereof can be appropriately changed, and the determination can be performed immediately after the difference Δθp is calculated (step 105).

[0043] In the foregoing embodiment, the steering system 2 adopts a connectionless structure in which the steering unit 4 and the turning unit 6 are generally mechanically disconnected from each other, but the application is not limited thereto, and a structure in which the steering unit 4 and the turning unit 6 can be mechanically disconnected by a clutch can be adopted. The application is not limited to a steer-by-wire system, and an electric power steering system in which a steering torque input by a driver is mechanically transmitted to the turning unit 6 can be adopted as the steering system 2. In the electric power steering system, the torque of a motor is applied as an assist force that assists the driver steering operation.

Claims

1. An anomaly detection apparatus configured to detect an anomaly of a turning unit (6), the turning unit (6) comprising: a motor as a drive source; a turning shaft connected to the turning wheel; a power transmission mechanism (33) configured to transmit a torque of the motor to the turning shaft; a first sensor configured to detect a rotation angle of the motor; a second sensor configured to detect a connection state amount indicating position information about a connection member mechanically connected to the motor via the power transmission mechanism (33); and a current sensor configured to detect an actual current value that is a value of an actual current supplied to the motor, the abnormality detection device characterized by comprising: a processing circuit configured to execute an abnormality detection process, wherein the abnormality detection process includes: a first state amount acquisition process that acquires a first state amount indicating position information about a convertible member based on the rotation angle detected by the first sensor, the first state amount being convertible to a turning angle of the turning wheel; a second state amount acquisition process that acquires a second state amount indicating position information about the convertible member based on the connection state amount detected by the second sensor; a difference calculation process that calculates a difference between the first state amount and the second state amount; and a determination process that compares an absolute value of the difference with a difference threshold value, wherein the abnormality detection process is a process of detecting an abnormality of the turning unit (6) when the absolute value of the difference is greater than the difference threshold value, and wherein the processing circuit is configured not to execute the determination process when an absolute value of the actual current value is greater than a current threshold value.

2. The abnormality detection device according to claim 1, characterized by, the power transmission path between the turning unit (6) and a steering unit subjected to a steering operation by a driver is cut off.

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