Torque sensor failure detection method

Abstract

A torque sensor fault detection method. When the vehicle is driving straight, the torque sensor is normal, and the torque center point is pointed to the center. When driving straight on an inclined road, the torque center point deviates due to the inclination of the road, and the torque sensor fault is misdetected. If the direction of the rudder angle is opposite to the deviation direction of the torque sensor detection value, it can be determined that the torque sensor has failed. If in the same direction, driving on an inclined road, it can be determined that the torque sensor is normal and no fault is misdetected.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a failure detection method, and particularly to a failure detection method of a torque sensor in an electric power steering apparatus. BACKGROUND

[0002] Steering force applied by an operator to a steering wheel is detected by a torque sensor provided to a steering shaft to which the steering wheel is coupled. Based on the steering force (steering torque) detected by the torque sensor, in an electric power steering apparatus, an electric motor is driven by a control device, and an assist torque generated by the electric motor is transmitted to the steering shaft (steering system) via a worm reduction mechanism or the like, to reduce the steering force applied by the operator to the steering wheel.

[0003] In this case, as the torque sensor, as shown in Patent Document 1 (JP 3055752 B2), a configuration in which an input shaft and an output shaft are coupled by a torsion bar, and a magnet that engages the input shaft and the output shaft is provided, and the magnet is displaced when a torque acts between the input and output shafts, and the displacement of the magnet is electrically detected by a detection coil, is known.

[0004] In Patent Document 2 (JP H09-231452), a technology is proposed in which, in an electric power steering (EPS) apparatus in which an assist steering force is generated based on a steering torque detected by a torque sensor to assist steering, it is determined whether the torque sensor is normal or defective based on the steering torque, the vehicle speed, and the steering angle.

[0005] Although the prior art can detect that the torque sensor has failed when a mechanical failure occurs in a torque sensor member inside the torque sensor (for example, when a magnet for detecting the rotational speed inside the torque sensor is displaced), it is possible to erroneously detect that the torque sensor has failed under a running condition in which the torque sensor is directed to a point other than the midpoint.

[0006] [Related Art Documents]

[0007] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent No. 3055752

[0009] [Patent Document 2] Japanese Laid-Open Patent Publication No. H09-231452 SUMMARY

[0010] [Problems to be Solved by the Invention]

[0011] Although there is a stop structure in the torque sensor, when the magnet is peeled off, a shift of about 3 to 4 Nm occurs, and an unbalanced state of the steering force is maintained. At this time, if the hand is released, automatic steering occurs. Since the torque sensor receives an electrically normal signal due to a mechanical failure, the failure cannot be detected.

[0012] [Technical means for solving the problem]

[0013] When a large torque occurs while the vehicle is traveling straight, the shift failure can be recognized, and the backup control at the time of the torque sensor failure is executed.

[0014] The present application provides a torque sensor failure detection method for a control device of an electric power steering provided with a torque sensor that detects a steering torque and a rudder angle based on an operation amount of a steering provided in a vehicle, the method including the steps of: determining whether the vehicle is traveling straight by a yaw rate detection device for detecting a yaw rate of the vehicle, the torque sensor, and a vehicle speed of the vehicle, and determining a shift of the torque sensor from a steering torque, wherein in the determination of the shift, a torque detection range of the torque sensor is set to include a first direction in which the torque detection range is shifted to one side from a torque midpoint of a detection value of the torque sensor and a second direction in which the torque detection range is shifted to the other side, and when a direction of the steering torque is opposite to a detection direction in the torque detection range, it is determined that the torque sensor has a failure, wherein the detection direction is determined by comparing the rudder angle with the torque detection range.

[0015] The torque sensor failure detection method of an embodiment of the present application, wherein when the detection value of the torque sensor is in the first direction, the torque detection range of the torque sensor is larger in the second direction than in the first direction; and when the detection value of the torque sensor is in the second direction, the torque detection range is larger in the first direction than in the second direction.

[0016] The torque sensor failure detection method of an embodiment of the present application includes: when the yaw rate detection device detects that the yaw rate is equal to or higher than a threshold value, the control device does not perform the failure detection of the torque sensor.

[0017] [Effects of the invention]

[0018] By the above method, the present application can prevent the unbalanced state of the steering force from being maintained, and prevent automatic steering after the hand is released.

[0019] In order to make the disclosure more apparent, the following embodiments are specifically described below, and the detailed description is made below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a whole schematic configuration view of an electric power steering device mounted on a vehicle according to an embodiment of the present application.

[0021] Figure 2 is a flowchart of a torque sensor failure detection program of an embodiment of the present application.

[0022] Figure 3 is a plot of a detected value of a torque sensor of an embodiment of the present application.

[0023] Figure 4 is a flowchart of a torque sensor failure detection program of an embodiment of the present application.

[0024] Symbol Explanation

[0025] 10: Electric power steering apparatus

[0026] 12: Steering wheel

[0027] 14, 15: Steering shaft

[0028] 16: Steering wheel

[0029] 18: Steering system

[0030] 19: Steering angle sensor

[0031] 20: Torque sensor

[0032] 22: Control device

[0033] 23: Rotor

[0034] 24: Electric motor

[0035] 25: Rotation axis

[0036] 28: Pinion mechanism

[0037] 30: Pinion

[0038] 32, 34: Curve

[0039] 36: Area

[0040] 41: Input shaft

[0041] 42: Output shaft

[0042] 46: Universal joint

[0043] 50: Rack shaft

[0044] 50a: Rack tooth

[0045] 52: Tie rod

[0046] 58: Resolver

[0047] 91, 92, 93, 94: Wire harness

[0048] T1, T2: Time point

[0049] Tr: Torque

[0050] θs: steering angle

[0051] θr: Rotation angle

[0052] S202~S214, S402~S418: Steps Detailed Implementation

[0053] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0054] Figure 1 This is a schematic diagram of the overall configuration of an electric power steering (EPS) device mounted on a vehicle according to an embodiment of the present invention.

[0055] like Figure 1 As shown, the electric power steering system 10 basically includes: a steering system 18 extending from the steering wheel 12 (an operating component used by the driver to control the vehicle) via steering shafts 14 and 15 to the steering wheels 16; a torque sensor 20 mounted on the rotation shaft of the steering system 18 and containing a steering angle sensor 19, which detects the torque Tr and steering angle θs of the rotation shaft; a control device 22 that determines the auxiliary torque Ta based on the output from the torque sensor 20; and a brushless motor, i.e., an electric motor 24, driven by the control device 22. The motor 24 can also be a brushed motor.

[0056] The torque sensor 20 has the following known structure: the input shaft 41 and the output shaft 42, which are the rotation shafts of the steering system 18, are internally connected by a torsion bar, and two detection coils (not shown) supported in the housing are arranged in such a way that they surround and engage with the cylindrical magnets (not shown) of the input and output shafts 41 and 42.

[0057] The steering angle sensor 19 has a known configuration that detects the rotation angle of the input shaft 41 as the steering angle θs.

[0058] The torque Tr and steering angle θs signals, which are the output signals of torque sensor 20 and steering angle sensor 19, are provided to control device 22 through wiring harness 91.

[0059] The steering wheel 12 is constructed by connecting the main steering shaft 15, the input shaft 41, and the output shaft 42, which serve as rotation axes respectively. The main steering shaft 15 is integrally integrated with the steering wheel 12, the input shaft 41 is connected to the main steering shaft 15 via a universal joint 46, and the output shaft 42 is provided with a pinion 30 of a rack and pinion mechanism 28.

[0060] A pinion 30 is provided at the lower end of the output shaft 42. The pinion 30 meshes with the rack teeth 50a of the rack shaft 50, which can reciprocate in the vehicle width direction. At both ends of the rack shaft 50, the left and right front wheels, i.e., the steering wheels 16, are connected via tie rods 52.

[0061] More specifically, the steering system 18 described above comprises, starting from the steering wheel 12, a steering shaft 14 (main steering shaft 15, universal joint 46, input shaft 41, output shaft 42 with pinion 30), a rack shaft 50 with rack teeth 50a, a tie rod 52, and a steering wheel 16.

[0062] With this configuration, when steering with the steering wheel 12, normal rack and pinion steering operations can be performed, allowing the steering wheel 12 to turn the steering wheel 16 and thus change the vehicle's direction. Here, the rack shaft 50, rack teeth 50a, and tie rod 52 constitute the steering mechanism in the steering system 18.

[0063] As described above, the electric power steering 10 includes an electric motor 24 that provides steering assistance force (also referred to as assistance force) to reduce the steering force of the steering wheel 12.

[0064] The resolver 58 detects the rotation angle θrm (also called the motor mechanical angle) of the rotor 23 of the electric motor 24, which rotates integrally with the rotating shaft 25, as the rotation angle θr (also called the motor electrical angle) of the rotor 23, and provides it to the control device 22 through the wiring harness 92. Alternatively, the resolver 58 is a relative angle detection sensor, but a rotary encoder with an absolute angle detection sensor can be used instead.

[0065] The control device 22 is, for example, a computer containing a microcomputer. In addition to a CPU (central processing unit), ROM (including EEPROM) and RAM (random access memory) as memory, it also has input / output devices such as an A / D converter and a D / A converter, a timer as a timing unit, etc. The CPU implements various functions by reading and executing programs recorded in the ROM.

[0066] The control device 22 generates a signal corresponding to the torque Tr based on the differential signal associated with the torque Tr output from the detection coil (not shown) of the torque sensor 20 through the wiring harness 91.

[0067] When the steering angle sensor 19, which is operating normally, provides a steering angle (also called the steering angle, steering angle, or steering wheel angle of the steering shaft 14) θs, the control device 22 differentiates the steering angle θs output from the steering angle sensor 19 through the wiring harness 91 to generate a steering angular velocity θs' (θs' = dθs / dt, where d is the differentiation operator and t is time).

[0068] The control device 22 further receives an output of the vehicle speed sensor 86, i.e., a vehicle speed Vs, through a wire harness 93, and an output of the yaw rate detection device 88, i.e., a yaw rate Ys, through a wire harness 94.

[0069] The electric motor 24 generates an assist torque Ta corresponding to the supplied assist current, and imparts the assist torque Ta to the output shaft 42 through the reduction transmission mechanism 26, thereby causing the steering shaft 14 to generate a steering assist force.

[0070] Basically, the electric power assisted steering device 10 is configured and operates to implement steering assist as described above.

[0071] Figure 2 is a flowchart of a torque sensor fault detection routine according to an embodiment of the present application. Referring to Figure 1 and Figure 2 , the fault detection routine according to the embodiment is applicable to the electric power assisted steering device 10 of Figure 1 , and the detailed steps of the fault detection routine according to the embodiment will be described below in conjunction with the components in the electric power assisted steering device 10.

[0072] In step S202, the control device 22 determines whether the vehicle is straight running based on the yaw rate Ys detected by the yaw rate detection device 88, the steering torque detected by the torque sensor 20, and the vehicle speed Vs detected by the vehicle speed sensor 86. In some embodiments, the control device 22 determines that the vehicle is straight running, for example, when the vehicle yaw rate Ys is less than a predetermined value (e.g., 0.25), the steering angle of the vehicle is less than a predetermined angle (e.g., 4 degrees), and the vehicle speed Vs is higher than a predetermined speed (e.g., 20 km / h), but is not limited thereto. In other embodiments, the control device 22 can use other values as the predetermined values for determination or add other parameters to determine whether the vehicle is straight running.

[0073] In step S204, the control device 22 determines the offset of the torque sensor 20 based on the steering torque. For example, when the detected value output by the torque sensor 20 is positive, it is determined that the torque sensor 20 is offset to the right, and when the detected value output by the torque sensor 20 is negative, it is determined that the torque sensor 20 is offset to the left.

[0074] In the offset determination, the torque detection range of the torque sensor 20 is set to include a first direction offset to one side from the torque midpoint of the detected value of the torque sensor 20 and a second direction offset to the other side. The first direction is, for example, the right side direction, and the second direction is, for example, the left side direction, but is not limited thereto.

[0075] In step S206, the control device 22 determines whether the direction of the steering torque is opposite to the detection direction within the torque detection range. The control device 22, for example, acquires the steering angle from the steering angle sensor 19 of the torque sensor 20, and compares the steering angle with the predetermined torque detection range to determine the detection direction within the torque detection range. If the steering angle is within the torque detection range, the direction of the steering angle is taken as the detection direction. If the direction of the steering torque is opposite to the detection direction within the torque detection range, the process proceeds to step S208, and the control device 22 increments the count for determining whether the torque sensor is malfunctioning.

[0076] If, on the other hand, the direction of the steering torque is opposite to the detection direction within the torque detection range, the process proceeds to step S208, and the control device 22 increments the count for determining whether the torque sensor is malfunctioning. In step S210, the control device 22 determines whether the accumulated count is greater than a predetermined count.

[0077] If the accumulated count is greater than the predetermined count, the control device 22 determines in step S212 that the torque sensor 20 is malfunctioning, and ends the malfunction detection program. At this time, the control device 22, for example, turns on a warning light to indicate that the torque sensor 20 is malfunctioning, or activates a backup control in the event of a torque sensor 20 malfunction to implement electric power steering (EPS) assistance that does not continue in the state of imbalance of the steering force.

[0078] If, on the other hand, the accumulated count is not greater than the predetermined count, the process returns to step S202, and the next determination is made. Further, if it is determined in step S202 that the vehicle is not traveling straight, or if it is determined in step S204 that the detection value of the torque sensor 20 is not offset, or if it is determined in step S206 that the direction of the steering torque is opposite to the detection direction within the torque detection range, the process proceeds to step S214, and the control device 22 clears the accumulated count, and ends the malfunction detection program.

[0079] Figure 3 FIG. 32 is a graph showing the change in the detection value of the torque sensor according to an embodiment of the present application. Referring to FIG. 32, curves 32 and 34 show the detection values of the torque sensor when the vehicle is traveling straight on a flat road and on an incline, respectively. The curve 32 shows the detection value of the torque sensor when the vehicle is traveling straight on a flat road. The curve 34 shows the detection value of the torque sensor when the vehicle is traveling straight on an incline. Figure 3 The curve 34 maintains a constant value within a region 36 after a change over a period of time, which represents that the vehicle is traveling straight on an incline. Normally, the detection value of the torque sensor should be zero when the vehicle is traveling straight, but the detection value of the curve 34 within the region 36 is maintained at a negative value. This indicates that the direction of the steering torque is opposite to the offset direction of the detection value of the torque sensor, and thus it is determined that the torque sensor is malfunctioning.

[0080] By the above method, if the direction of the steering torque generated is opposite to the direction of the shift of the detected value of the torque sensor 20, it is determined that the torque sensor 20 is malfunctioning, but if it is in the same direction, when driving on the inclined road, the torque sensor 20 is determined to be normal and will not be mis-detected as malfunctioning.

[0081] Figure 4 is a flowchart of the torque sensor malfunction detection program of an embodiment of the present application. Please refer to Figure 1 and Figure 4 The malfunction detection program of the present embodiment is applicable to the electric power steering apparatus 10 of Figure 1 The detailed steps of the malfunction detection program of the present embodiment will be described below in conjunction with the components in the electric power steering apparatus 10.

[0082] In step S402, the control device 22 determines whether the vehicle is driving straight based on the vehicle yaw rate Ys detected by the yaw rate detection device 88, the vehicle speed Vs detected by the torque sensor 20 and the vehicle speed sensor 86. The implementation of determining whether the vehicle is driving straight is the same as or similar to that of step S202 of the foregoing embodiment, and thus the details thereof will not be described herein.

[0083] Different from the foregoing embodiment, the present embodiment adds the rudder angle condition as a countermeasure to prevent mis-detection on the inclined road. Since the steering is performed on the opposite side of the shift direction, the twist of the torque sensor 20 and the rudder angle condition on the opposite side of the torque sensor 20 increase. That is, after determining that the vehicle is driving straight, the control device 22 sets the corresponding torque detection range according to the shift direction of the detected value of the torque sensor 20, and determines whether the torque sensor 20 is malfunctioning according to whether the rudder angle detected by the rudder angle sensor 19 falls within the torque detection range.

[0084] In detail, in step S404, the control device 22 determines whether the detected value of the torque sensor 20 is right-side large, i.e., right-side shift. If the control device 22 determines that the detected value of the torque sensor 20 is not right-side large, in step S410, the control device 22 determines whether the detected value of the torque sensor 20 is left-side large, i.e., left-side shift.

[0085] If the control device 22 determines that the detected value is right-side large, in step S408, the control device 22 determines whether the rudder angle is within the torque detection range (i.e., between -A and B, where A and B are arbitrary numbers and A is greater than B). If the control device 22 determines that the detected value is left-side large, in step S412, the control device 22 determines whether the rudder angle is within another torque detection range (i.e., between -B and A).

[0086] For example, when the control device 22 determines that the detection value of the torque sensor 20 is positive and greater than a predetermined value, the control device 22 determines whether the rudder angle is between -4 degrees and 2 degrees (i.e., the opposite side rudder angle condition is increased). When the control device 22 determines that the detection value of the torque sensor 20 is negative, the control device 22 determines whether the rudder angle is between -2 degrees and 4 degrees (i.e., the opposite side rudder angle condition is increased).

[0087] If the control device 22 determines in step S402 that the vehicle is not traveling straight, or determines in step S408 that the detection value is not greater on the left side, or determines in step S408 that the rudder angle is not within the torque detection range, or determines in step S412 that the rudder angle is not within the other torque detection range, the accumulated count is cleared in step S418, and the failure detection routine ends.

[0088] If the control device 22 determines in step S406 that the rudder angle is within the torque detection range, or determines in step S410 that the rudder angle is within the other torque detection range, the control device 22 increments the count for determining whether the torque sensor is failing in step S412, and determines in step S414 whether the accumulated count is greater than a prescribed count.

[0089] If the control device 22 determines that the accumulated count is greater than the prescribed count, the control device 22 determines that the torque sensor 20 is failing in step S416, and the failure detection routine ends. If the control device 22 determines that the accumulated count is not greater than the prescribed count, the routine returns to step S402, and the next determination is performed.

[0090] With the above-described method, when the vehicle is traveling straight on a sloped road, the torque sensor 20 turns in the opposite direction of the yawing direction due to the inclination of the road, and by correcting the detection value to the torque midpoint side, the accuracy of the failure detection of the torque sensor 20 is improved on a sloped road.

[0091] In some embodiments, the control device 22 does not perform the failure detection of the torque sensor 20 when the yaw rate detected by the yaw rate detection device 88 is equal to or higher than a predetermined threshold value. In detail, when the yaw rate detected by the yaw rate detection device 88 is equal to or higher than a predetermined threshold value (e.g., exceeds 0.25 degrees / second), it can be determined that the vehicle is in a turning state (e.g., is traveling on a curve). By stopping the failure detection of the torque sensor 20 at this time, the computational load on the control device 22 can be reduced.

[0092] In summary, the torque sensor fault detection method of the present application can determine whether the torque sensor is faulty by judging whether the direction of the steering torque and the detection direction of the torque sensor are opposite. By adding the rudder angle condition in the above judgment, false detection on the inclined road can be further prevented. When determining the torque sensor fault, the warning light can be turned on to allow the driver to identify the fault and perform maintenance, or the standby control that does not use the torque sensor can be enabled to implement the EPS assistance without continuing the steering force imbalance state, thereby avoiding or reducing the impact of the torque sensor fault on the driver.

[0093] Although the present disclosure has been disclosed with examples as above, it is not intended to limit the present disclosure, and any person skilled in the art can make some changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure is defined by the claims and their equivalent scope appended hereto.

Claims

1. A method for detecting torque sensor faults, used in a control device for electric power steering equipped with a torque sensor, wherein the torque sensor detects steering torque and rudder angle based on the amount of steering input to the vehicle's steering wheel, characterized in that, The method includes the following steps: The control device determines whether the vehicle is traveling straight based on the yaw rate detection device used to detect the vehicle's yaw rate, the torque sensor, and the vehicle's speed. When it is determined that the vehicle is traveling straight, the offset of the torque sensor is determined based on the detection value of the torque sensor, wherein... In the determination of the offset, the torque detection range of the torque sensor is set to include an offset in a first direction to one side and an offset in a second direction to the other side from the midpoint of the torque detected by the torque sensor. When the torque sensor detects a value in the first direction, the torque detection range of the torque sensor is offset in the second direction more than it is offset in the first direction. When the torque sensor detects a value in the second direction, the torque detection range of the torque sensor is offset in the first direction more than it is offset in the second direction. Determine whether the rudder angle is within the torque detection range; as well as When the rudder angle is within the torque detection range, the torque sensor is determined to be faulty.

2. The torque sensor fault detection method according to claim 1, characterized in that, The method includes the following steps: When the yaw rate detection device detects that the yaw rate is equal to or higher than the threshold, the control device does not perform fault detection of the torque sensor.

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