Steering system for a vehicle

Abstract

A steering system for a vehicle capable of accurately determining a deterioration level of a steering actuator according to a running state of the vehicle is provided. The steering system for a vehicle includes a steering mechanism configured to turn a wheel, a steering actuator configured to apply a driving force to the steering mechanism, and a controller configured to control the steering actuator. The steering mechanism includes a rack shaft capable of moving in a vehicle width direction from a prescribed reference position. The controller is configured to calculate an evaluation value according to a usage state of the steering actuator, and determine a deterioration level of the steering actuator by comparing the evaluation value with at least one threshold value set based on an amount of movement of the rack shaft with respect to the reference position and a vehicle speed.

Description

Technical Field

[0001] This invention relates to a steering system for vehicles. Background Technology

[0002] Traditionally, there exists a steering system for vehicles that includes a steering mechanism configured to steer the wheels and a steering actuator configured to apply driving force to the steering mechanism.

[0003] For example, Patent Document 1 discloses an electric steering system comprising: a rack shaft, a pair of wheels connected to the rack shaft; a steering shaft having a pinion that meshes with the rack shaft; and a motor configured to rotate the steering shaft.

[0004] List of cited references

[0005] Patent documents

[0006] [Patent Document 1] JP2018-85917A Summary of the Invention

[0007] Technical issues

[0008] In the vehicle steering system described above, the steering actuator may deteriorate for various reasons. Deterioration of the steering actuator may mean a reduction in its maximum output. To take appropriate measures against steering actuator deterioration, the degree of deterioration needs to be accurately determined based on the vehicle's driving conditions.

[0009] In view of the above background, the object of the present invention is to accurately determine the degradation level of the steering actuator based on the vehicle's driving conditions.

[0010] Solution to the problem

[0011] To achieve this objective, one aspect of the present invention provides a steering system 1 for a vehicle 2, the steering system comprising: a steering mechanism 11 configured to steer wheels 3; a steering actuator 12 configured to apply a driving force to the steering mechanism; and a controller 15 configured to control the steering actuator, wherein the steering mechanism includes a rack shaft 26 movable from a predetermined reference position along the vehicle width direction, and the controller is configured to calculate an evaluation value based on the usage state of the steering actuator (step ST1), and determine the degradation level of the steering actuator by comparing the evaluation value with at least one threshold (TH1 to TH3) set based on the amount of movement of the rack shaft relative to the reference position and the vehicle speed (step ST2) (step ST4).

[0012] Based on this, a threshold value can be set appropriately based on the amount of movement of the rack shaft relative to a reference position and the vehicle speed, which vary according to the vehicle's driving conditions. Therefore, the degradation level of the steering actuator can be accurately determined according to the vehicle's driving conditions.

[0013] In the foregoing, preferably, the at least one threshold comprises a plurality of thresholds, and the controller is configured to determine the degradation level of the steering actuator by comparing the evaluation value with the plurality of thresholds.

[0014] Based on this, the degradation level of the steering actuator can be classified more finely, allowing the degradation level of the steering actuator to be determined more accurately.

[0015] In the foregoing, preferably, the controller is configured to periodically determine the degradation level of the steering actuator, and only output a signal indicating that the degradation level of the steering actuator is equal to or higher than the predetermined level (step ST6) when the determination that the degradation level of the steering actuator is equal to or higher than the predetermined level has been performed continuously for a predetermined period of time or longer, or has been performed continuously a predetermined number of times or more (step ST5).

[0016] Based on this aspect, in the event that the degradation level of the steering actuator unexpectedly reaches or exceeds a specified level, the output of a signal indicating that the degradation level of the steering actuator is equal to or higher than the specified level can be prevented. Therefore, erroneous detection of the degradation level of the steering actuator can be prevented.

[0017] In the foregoing, preferably, the controller is configured to determine the degradation level of the steering actuator as higher than the degradation level when the evaluation value is higher than the threshold, and the threshold is set to increase as the amount of movement of the rack shaft relative to the reference position increases when the vehicle speed is lower than a predetermined reference speed.

[0018] Typically, the force required to move the rack shaft (the force required to steer the wheel) increases with the amount of movement of the rack shaft relative to a reference position. Thus, when the vehicle speed is below a reference speed, the threshold increases with the amount of movement of the rack shaft relative to the reference position, allowing for a more accurate determination of the steering actuator's degradation level.

[0019] In the above aspects, preferably, when the vehicle speed is equal to or higher than the reference speed, the threshold is set to a constant value regardless of the amount of movement of the rack shaft relative to the reference position.

[0020] When the vehicle is in motion, a restoring force is applied to the rack shaft toward a reference position based on wheel alignment (especially the caster angle). Typically, this restoring force is greater than the increase in force required to move the rack shaft. Thus, by setting a constant threshold value when the vehicle speed is equal to or higher than the reference speed, the degradation level of the steering actuator can be determined more accurately.

[0021] In the above aspects, preferably, when the moving speed of the rack shaft is equal to or higher than a predetermined stopping speed, the controller suspends the determination of the deterioration level of the steering actuator (step ST3).

[0022] When the rack shaft travels at high speeds, the evaluation value may exceed the threshold even if the steering actuator is not deteriorated. Considering this, the determination of the steering actuator's deterioration level is suspended when the rack shaft travels at or above a predetermined pause speed, thus preventing erroneous determination of the steering actuator's deterioration level. For example, "suspending the determination of the steering actuator's deterioration level" means "postponing the determination of the steering actuator's deterioration level for a specified period or number of times."

[0023] In the foregoing, preferably, the controller is configured to determine the degradation level of the steering actuator as higher than the degradation level when the evaluation value is higher than the threshold, and the evaluation value is set to increase as the current value flowing according to the drive of the steering actuator increases.

[0024] When the frictional resistance within the steering actuator and / or the force required to move the rack shaft is excessive, the driving torque of the steering actuator increases, and the current flowing according to the drive of the steering actuator also increases. By using this increase to make the evaluation value high, the degradation level of the steering actuator can be accurately determined.

[0025] In the foregoing, preferably, the steering system for the vehicle further includes a temperature sensor 37 configured to detect the temperature of the steering actuator or the controller, wherein the controller is configured to determine a degradation level of the steering actuator as higher than a degradation level if the assessed value is higher than the threshold value, and the assessed value is set to increase as the temperature detected by the temperature sensor increases if the temperature detected by the temperature sensor is higher than a predetermined reference temperature.

[0026] In cases where the steering actuator or controller overheats, the maximum output of the steering actuator can be limited to protect it. By setting a high evaluation value based on this limitation, the degradation level of the steering actuator can be accurately determined.

[0027] In the foregoing, preferably, the steering system for the vehicle further includes a battery 35 configured to supply power to the steering actuator, wherein the controller is configured to determine a degradation level of the steering actuator as higher than a degradation level if the evaluation value is higher than the threshold value, and the evaluation value is set to increase as the battery voltage decreases if the battery voltage is lower than a predetermined reference voltage.

[0028] When the battery voltage is too low, the maximum output of the steering actuator can be limited to prevent the steering system from shutting off. By setting a high evaluation value based on this limitation, the degradation level of the steering actuator can be accurately determined.

[0029] In the above aspects, preferably, the torque utilization value TU is used to determine the evaluation value.

[0030] Based on this, the torque utilization value is calculated based on the output torque of the steering actuator.

[0031] In the foregoing, preferably, the steering system for a vehicle further includes a steering member 10 configured to receive steering operations, wherein the steering mechanism is mechanically separated from the steering member.

[0032] Based on this, in a steering system with online steering, the degradation level of the steering actuator can be accurately determined according to the vehicle's driving status.

[0033] Beneficial effects of the invention

[0034] Therefore, based on the above aspects, the degradation level of the steering actuator can be accurately determined according to the vehicle's driving condition. Attached Figure Description

[0035] [ Figure 1 This diagram shows a schematic representation of a steering system according to an embodiment of the present invention.

[0036] [ Figure 2 [A block diagram of a steering system according to an embodiment of the present invention is shown.]

[0037] [ Figure 3 The diagram shows a flowchart of a level determination control according to an embodiment of the present invention.

[0038] [ Figure 4AThe graph shows the relationship between the detection temperature and Ilim.

[0039] [ Figure 4B The graph shows the relationship between battery voltage and Ilim.

[0040] [ Figure 5 The graph shows the first threshold table.

[0041] [ Figure 6 The table shows the relationship between the range of PU and the degradation level of the steering actuator.

[0042] [ Figure 7 The table shows whether the PU becomes higher than the first threshold when the degradation level of the steering actuator is the first level. Detailed Implementation

[0043] The steering system 1 for a vehicle 2 according to an embodiment of the present invention will now be described. Figure 1 As shown, the steering system 1 includes a steer-by-wire (SBW) system. The vehicle 2 equipped with the steering system 1 is a four-wheeled vehicle comprising left and right front wheels 3 and left and right rear wheels (not shown in the figure). The left and right front wheels 3 are connected to the vehicle body 8 via their respective steering knuckles 7. Figure 1 (Only the lower outline of the front wheel 3 is shown in the diagram.) The front wheel 3 is supported so that its steering angle can be changed, and thus it functions as a steerable wheel. The steering angle is the angle of the front wheel 3 relative to the longitudinal direction in the top view. Therefore, the steering system 1 changes the steering angle of the front wheel 3.

[0044] The steering system 1 includes a steering member 10 rotatably mounted on the vehicle body 8, a steering mechanism 11 configured to steer the front wheels 3, a steering actuator 12 configured to apply a driving force to the steering mechanism 11, a reaction force actuator 13 configured to apply a reaction torque to the steering member 10, and a steering controller 15 configured to control the reaction force actuator 13 and the steering actuator 12. The steering system 1 may be a redundant system including multiple steering actuators 12, multiple reaction force actuators 13, and multiple steering controllers 15.

[0045] The steering member 10 is configured to receive steering inputs from the driver. The steering member 10 includes a steering shaft 18 rotatably supported by the vehicle body 8 and a steering wheel 19 disposed at an end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column (not shown) disposed on the vehicle body 8 and has a rear end projecting rearward from the steering column. The steering wheel 19 is connected to the rear end of the steering shaft 18 so as to rotate integrally with the steering shaft 18.

[0046] The reaction force actuator 13 is composed of an electric motor and is connected to the steering shaft 18 via a gear mechanism. When the reaction force actuator 13 is driven, its driving force is transmitted to the steering shaft 18 as a rotational force. The reaction force actuator 13 is configured to rotate, thereby applying torque to the steering member 10. The torque applied to the steering member 10 by the reaction force actuator 13 in response to steering operation is referred to as the "reaction torque".

[0047] The steering mechanism 11 includes a rack shaft 26 extending in the vehicle width direction. The rack shaft 26 is supported by a gearbox (not shown), allowing it to move in the vehicle width direction. The left and right ends of the rack shaft 26 are connected to steering knuckles 7, which support the left and right front wheels 3 respectively via tie rods 30. When the rack shaft 26 moves from a predetermined reference position (the position where the direction of the left and right front wheels 3 is parallel to the front-rear direction: see...) Figure 1 When moving along the width of the vehicle, the steering angle of the front wheel 3 changes. The steering mechanism 11 is mechanically separated from the steering component 10.

[0048] The steering actuator 12 includes an electric motor. The steering actuator 12 moves the rack shaft 26 along the vehicle width direction based on a signal from the steering controller 15, thereby changing the steering angle of the left and right front wheels 3.

[0049] See Figure 2 The steering controller 15 comprises an electronic control unit (ECU) including a CPU 32, a storage unit 33, and a drive circuit 34. The CPU 32 is configured to control each part of the steering system 1 based on programs and data stored in the storage unit 33. The drive circuit 34 is connected to a battery 35 configured to supply power to the steering actuator 12. The direct current (DC) flowing from the battery 35 (hereinafter referred to as "battery current") is converted into three-phase alternating current by the drive circuit 34 and then supplied to the steering actuator 12.

[0050] The steering controller 15 is connected to a temperature sensor 37. The temperature sensor 37 may be integrated with or separate from the steering controller 15. The temperature sensor 37 is configured to detect the temperature of the CPU 32 or the drive circuit 34 (an example of the temperature of the steering controller 15) and output the temperature to the steering controller 15. In another embodiment, the temperature sensor 37 may detect the temperature of the steering actuator 12.

[0051] The steering controller 15 is connected to a voltage sensor 38. The voltage sensor 38 is configured to detect the voltage of the battery 35 (hereinafter referred to as "battery voltage") and output the battery voltage to the steering controller 15. For example, the battery voltage is calculated by subtracting the voltage consumed by the wiring harness connecting the battery 35 and the steering controller 15 from the terminal voltage of the battery 35.

[0052] Steering controller 15 is connected to rack position sensor 39. Rack position sensor 39 is configured to detect the position of rack shaft 26 in the vehicle width direction (hereinafter referred to as "rack position") and output the rack position to steering controller 15. Steering controller 15 is configured to calculate the amount of movement of rack shaft 26 relative to a reference position in the vehicle width direction (hereinafter referred to as "rack travel"), the speed of movement of rack shaft 26 in the vehicle width direction (hereinafter referred to as "rack travel speed"), and the steering angle of front wheel 3 based on the rack position detected by rack position sensor 39.

[0053] The steering controller 15 is connected to the rack axial force sensor 40. The rack axial force sensor 40 is configured to detect the force (hereinafter referred to as "rack axial force") applied to the rack shaft 26 in the vehicle width direction and output the rack axial force to the steering controller 15. For example, the rack axial force sensor 40 is a force sensor such as a piezoelectric sensor or a strain gauge.

[0054] The steering controller 15 is connected to the vehicle speed sensor 41. The vehicle speed sensor 41 is configured to detect the vehicle speed (the speed of vehicle 2) and output the vehicle speed to the steering controller 15.

[0055] Steering controller 15 is connected to main controller 44. Main controller 44 includes multiple ECUs. Main controller 44 is connected to human-machine interface (HMI) 45, which includes a display, speaker, warning lights, etc., thereby controlling HMI 45. Main controller 44 is connected to drive unit 46 and braking unit 47, thereby controlling drive unit 46 and braking unit 47. Drive unit 46 is a device that applies driving force to vehicle 2 and includes an electric motor and / or internal combustion engine. Braking unit 47 is a device that applies braking force to vehicle 2 and includes a mechanical brake.

[0056] Next, the level determination control performed by the steering controller 15 will be described. The level determination control is used to determine the degradation level of the steering actuator 12. For example, the level determination control is performed periodically after the ignition switch of the vehicle 2 is turned on.

[0057] See Figure 3 When the start level determination control is initiated, the steering controller 15 performs an evaluation value calculation process (step ST1). In the evaluation value calculation process, the steering controller 15 calculates the power utilization rate (hereinafter referred to as "PU") of the steering actuator 12 based on the following equation (1). PU is an example of an evaluation value based on the usage state of the steering actuator 12.

[0058]

[0059] In equation (1) above, Iact is the value of the battery current actually flowing during the drive of the steering actuator 12. That is, Iact is the value of the battery current actually consumed during the drive of the steering actuator 12. Iact is equal to the value calculated by dividing the output of the steering actuator 12 (more specifically, the output of the electric motor constituting the steering actuator 12) by the battery voltage. Iact varies depending on the driving state of the steering actuator 12. For example, if the frictional resistance inside the steering actuator 12 or the force required to move the rack shaft 26 in the vehicle width direction is too large, the driving torque of the steering actuator 12 increases, and Iact increases accordingly. When Iact increases in this way, the numerator of equation (1) above increases, resulting in a higher PU.

[0060] In equation (1) above, Imax is the maximum value of the battery current flowing according to the drive of the steering actuator 12 (i.e., the battery current that can be consumed according to the drive of the steering actuator 12), and is determined based on the design capacity of the steering actuator 12. Imax is a constant regardless of the drive state of the steering actuator 12.

[0061] In equation (1) above, Ilim is the maximum value of the battery current flowing according to the driving of the steering actuator 12 (i.e., the battery current that can be consumed according to the driving of the steering actuator 12), and is determined based on the limitation of the maximum output of the steering actuator 12. When the maximum output of the steering actuator 12 is not limited, Ilim equals Imax. On the other hand, if the maximum output of the steering actuator 12 is limited for some reason, Ilim becomes less than Imax. That is, Ilim is equal to or less than Imax.

[0062] Reference Figure 4A Ilim is determined based on the temperature of the CPU 32 or drive circuit 34 detected by temperature sensor 37 (hereinafter referred to as the "detection temperature"). When the detection temperature is equal to or higher than the first reference temperature T1 and equal to or lower than the second reference temperature T2 (T2>T1), Ilim is a constant and equal to Imax. When the detection temperature is lower than the first reference temperature T1, Ilim decreases as the detection temperature decreases. When the detection temperature is higher than the second reference temperature T2, Ilim decreases as the detection temperature increases. When Ilim decreases in this way, the numerator of the above equation (1) increases, thereby increasing PU.

[0063] Reference Figure 4B, Ilim is determined based on the battery voltage detected by the voltage sensor 38. When the battery voltage is equal to or higher than the first reference voltage V1 and equal to or lower than the second reference voltage V2 (V2>V1), Ilim is a constant and equal to Imax. When the battery voltage is lower than the first reference voltage V1, Ilim decreases as the battery voltage becomes lower. When the battery voltage is higher than the second reference voltage V2, Ilim decreases as the battery voltage becomes higher. When Ilim decreases in this manner, the numerator of the above equation (1) increases, so that PU becomes higher.

[0064] See Figure 3 , when the evaluation value calculation process (step ST1) ends, the steering controller 15 executes a threshold setting process (step ST2). In the threshold setting process, the steering controller 15 sets the first threshold TH1 to the third threshold TH3 based on the rack travel amount and the vehicle speed.

[0065] The steering controller 15 refers to the first threshold table (see Figure 5 ) to determine the first threshold TH1. The first threshold table is a two-dimensional table that defines the relationship between the rack travel amount, the vehicle speed, and the first threshold TH1. In the first threshold table, the rack travel amount increases as the column goes to the right (i.e., 0<L1<L2<L3<……<Ln). In the first threshold table, the vehicle speed becomes higher as the row goes down (i.e., 0<Y1<Y2<Y3<……<Yn).

[0066] In the first threshold table, A00<A01<A02. That is, when the vehicle speed is lower than the specified reference speed Y1 and the rack travel amount is less than the specified reference amount L3, the first threshold TH1 is set to become higher as the rack travel amount increases.

[0067] In the first threshold table, A02<A03, and A03=A04=……=A0n. That is, when the vehicle speed is lower than the reference speed Y1 and the rack travel amount is equal to or greater than the reference amount L3, the first threshold TH1 is set to a constant value regardless of the rack travel amount.

[0068] The first thresholds TH1 (A10, A11, ..., Ann) in the second row to the nth row of the first threshold table are all the same value. That is, when the vehicle speed is equal to or higher than the reference speed Y1, the first threshold TH1 is set to a constant value regardless of the rack travel amount. For example, the first thresholds TH1 in the second row to the nth row of the first threshold table are higher than A00 (the first threshold TH1 when the vehicle speed and the rack travel amount are 0) and lower than A03 (the first threshold TH1 when the vehicle speed is 0 and the rack travel amount is the reference amount L3).

[0069] Incidentally, the reference speed Y1 is the second lowest value after 0 among the vehicle speeds listed in the first threshold table. Therefore, "the case where the vehicle speed is lower than the reference speed Y1" corresponds to "the case where vehicle 2 is stopped", and "the case where the vehicle speed is equal to or higher than the reference speed Y1" corresponds to "the case where vehicle 2 is moving".

[0070] The steering controller 15 determines a second threshold TH2 and a third threshold TH3 based on rack travel and vehicle speed, referring to a second threshold table and a third threshold table (not shown in the figure). The second and third threshold tables are similar to the first threshold table and are two-dimensional tables defining the relationship between rack travel and vehicle speed and the second and third thresholds TH2 and TH3. In this embodiment, the second threshold TH2 is higher than the first threshold TH1, and the third threshold TH3 is higher than the second threshold TH2.

[0071] See Figure 3 When the threshold setting process (step ST2) ends, the steering controller 15 executes the speed determination process (step ST3). In the speed determination process, the steering controller 15 calculates the rack travel speed based on the rack position detected by the rack position sensor 39 and determines whether the rack travel speed is equal to or higher than a predetermined stop speed. If the rack travel speed is equal to or higher than the predetermined stop speed (step ST3: Yes), the steering controller 15 does not execute the level determination process (step ST4) and its subsequent steps.

[0072] On the other hand, if the rack travel speed is lower than the determined pause speed (step ST3: No), the steering controller 15 performs a level determination process (step ST4). In the level determination process, the steering controller 15 determines the degradation level of the steering actuator 12 (one of the first to fourth levels) by comparing the PU with the first threshold TH1 to the third threshold TH3.

[0073] See Figure 6 When PU is equal to or below the first threshold TH1, the steering controller 15 determines that the degradation level of the steering actuator 12 is the first level. The first level is the lowest level among the first to fourth levels and indicates that the steering actuator 12 is in a normal state.

[0074] When the PU is higher than the first threshold TH1 and equal to or lower than the second threshold TH2, the steering controller 15 determines that the degradation level of the steering actuator 12 is the second level. The second level is higher than the first level and indicates that the steering actuator 12 is in a degraded state at a lower level.

[0075] If the PU is higher than the second threshold TH2 and equal to or lower than the third threshold TH3, the steering controller 15 determines that the degradation level of the steering actuator 12 is the third level. The third level is higher than the second level and indicates that the steering actuator 12 is in a medium-level degradation state.

[0076] When the PU is higher than the third threshold TH3, the steering controller 15 determines that the degradation level of the steering actuator 12 is level four. Level four is higher than level three, and indicates that the steering actuator 12 is in a degraded state at a higher level.

[0077] As described above, the steering controller 15 determines the degradation level of the steering actuator 12 to be higher when the PU is above each threshold TH1 to TH3 than when the PU is equal to or below each threshold TH1 to TH3.

[0078] See Figure 3 When the grade determination process (step ST4) ends, the steering controller 15 performs a signal determination process (step ST5). The signal determination process is used to determine the signal (hereinafter referred to as the "output signal") output by the steering controller 15 to the main controller 44. In the signal determination process, the steering controller 15 determines whether a continuous determination period is equal to or longer than a predetermined period by referring to the determination results of the grade determination processes in the current and past grade determination controls. A continuous determination period is a period during which the determination of the degradation grade of the steering actuator 12 is equal to or higher than the second degradation grade (i.e., the determination that the steering actuator 12 is not in a normal state) is performed continuously. If the continuous determination period is equal to or longer than the predetermined period, the steering controller 15 determines one of the second to fourth grade signals (i.e., the signal indicating that the degradation grade of the steering actuator 12 is one of the second to fourth grades) as the output signal based on the determination result of the grade determination process (step ST4). On the other hand, if the continuous determination period is shorter than the specified period, the steering controller 15 determines the first level signal (i.e., the signal indicating that the degradation level of the steering actuator 12 is the first level) as the output signal without considering the determination result of the level determination process (step ST4).

[0079] When the signal determination process (step ST5) ends, the steering controller 15 performs the signal output process (step ST6). In the signal output process, the steering controller 15 outputs the output signal (one of the first-level signal to the fourth-level signal) determined in step ST5 to the main controller 44. In another embodiment, if the continuous determination period in step ST5 is shorter than a predetermined period, the steering controller 15 may not output a signal to the main controller 44.

[0080] The main controller 44 identifies the degradation level of the steering actuator 12 based on the output signal (one of the first to fourth level signals) from the steering controller 15. If the degradation level of the steering actuator 12 is the first level (i.e., when the steering actuator 12 is in a normal state), the main controller 44 does not perform warning control and speed limit control. On the other hand, if the degradation level of the steering actuator 12 is one of the second to fourth levels (i.e., when the steering actuator 12 is in a degraded state), the main controller 44 performs warning control and / or speed limit control.

[0081] In the warning control, the main controller 44 causes the HMI 45 to issue a warning that the steering actuator 12 is in a deteriorated state. For example, the main controller 44 causes the HMI 45's display to show a warning message, causes the HMI 45's speaker to produce a warning sound, or turns on or flashes the HMI 45's warning light. The main controller 44 can change the content of the warning control according to the deterioration level of the steering actuator 12 (one of the second to fourth levels).

[0082] In speed limit control, the main controller 44 controls the drive unit 46 and the braking unit 47 to ensure that the vehicle speed is equal to or lower than the prescribed speed limit. The main controller 44 can change the speed limit according to the degradation level of the steering actuator 12 (one of the second to fourth levels). For example, the main controller 44 can set the speed limit such that it decreases as the degradation level of the steering actuator 12 increases.

[0083] Incidentally, warning control and speed limit control are merely examples of controls performed by the main controller 44 based on the degradation level of the steering actuator 12. Therefore, the main controller 44 can perform any control other than warning control and speed limit control. For example, the main controller 44 can perform emergency stop control to allow the vehicle 2 to autonomously drive to an appropriate stopping position and stop there. Furthermore, devices other than the main controller 44 (e.g., steering controller 15, drive unit 46, and / or braking unit 47) can perform warning control, speed limit control, etc., based on the degradation level of the steering actuator 12.

[0084] In the following text, regarding the combined effects of the first threshold TH1 to the third threshold TH3, only the effect of the first threshold TH1 will be described, and the effects of the second threshold TH2 and the third threshold TH3 will be omitted.

[0085] In this embodiment, a first threshold TH1 is set based on the rack travel and vehicle speed (step ST2). Therefore, the first threshold TH1 can be set to an appropriate value based on the rack travel and vehicle speed, which vary according to the vehicle's driving conditions. Thus, the degradation level of the steering actuator 12 can be accurately determined according to the vehicle's driving conditions.

[0086] Furthermore, the steering controller 15 determines the deterioration level of the steering actuator 12 by comparing PU with a first threshold TH1 to a third threshold TH3 (i.e., a plurality of thresholds). Accordingly, the deterioration level of the steering actuator 12 can be classified more finely, so that the deterioration level of the steering actuator 12 can be determined more accurately.

[0087] Furthermore, the steering controller 15 periodically determines the deterioration level of the steering actuator 12, and outputs a signal indicating that the deterioration level of the steering actuator 12 is equal to or higher than the second level (step ST6) only when the determination that the deterioration level of the steering actuator 12 is equal to or higher than the second level is continuously made for a prescribed period or longer (step ST5). Therefore, in a case where the deterioration level of the steering actuator 12 accidentally reaches or exceeds the second level, it is possible to prevent the output of the signal indicating that the deterioration level of the steering actuator 12 is equal to or higher than the second level. Accordingly, erroneous detection of the deterioration level of the steering actuator 12 can be prevented.

[0088] Generally, the force required to move the rack shaft 26 (the force required to steer the front wheels 3) increases as the rack stroke amount increases. In view of this, when the vehicle speed is lower than the reference speed Y1, the first threshold TH1 is set to become higher as the rack stroke amount increases. Accordingly, the deterioration level of the steering actuator 12 can be determined more accurately.

[0089] When the vehicle is traveling, a restoring force toward the reference position is applied to the rack shaft 26 according to the alignment (particularly the caster angle) of the front wheels 3. Generally, the effect of this restoring force is greater than the effect of the increase in the force required to move the rack shaft 26. In view of this, when the vehicle speed is equal to or higher than the reference speed Y1, the first threshold TH1 is set to a constant value. Accordingly, the deterioration level of the steering actuator 12 can be determined more accurately.

[0090] Figure 7 shows whether PU becomes higher than the first threshold TH1 when the deterioration level of the steering actuator 12 is the first level (i.e., when the steering actuator 12 is in a normal state). In Figure 7 , the rack axial force increases as proceeding rightward in the columns (i.e., 0<F1<F2<F3<……<Fn-1<Fn). In Figure 7 , the rack stroke speed becomes higher as proceeding downward in the rows (i.e., 0<X1<X2<X3<……<Xn-1<Xn).

[0091] As shown in Figure 7As shown, at high rack travel speeds, even if the degradation level of the steering actuator 12 is at level one, the PU may still exceed the first threshold TH1. Taking this into account, when the rack travel speed is equal to or higher than a predetermined stopping speed (e.g., ...), Figure 7 In the case of X3), the steering controller 15 suspends the determination of the degradation level of the steering actuator 12 (step ST3). Therefore, it is possible to prevent the incorrect determination of the degradation level of the steering actuator 12.

[0092] For example, when the temperature of the steering actuator 12 decreases and the grease inside the steering actuator 12 hardens, the frictional resistance inside the steering actuator 12 may become excessive. Furthermore, due to overload of the vehicle 2, the force required to move the rack shaft 26 may become excessive. When these conditions occur, the drive torque of the steering actuator 12 increases, and Iact (the actual battery current flowing according to the drive of the steering actuator 12) also increases. Taking this into account, PU is set to increase as Iact increases. Therefore, the degradation level of the steering actuator 12 can be determined more accurately.

[0093] If the detected temperature (the temperature of the CPU 32 or drive circuit 34 detected by temperature sensor 37) is too high, the maximum output of the steering actuator 12 can be limited to protect the CPU 32 or drive circuit 34. With this in mind, when the detected temperature is higher than the second reference temperature T2, the PU is set to increase as the detected temperature increases. Therefore, the degradation level of the steering actuator 12 can be determined more accurately.

[0094] In the event of a low battery voltage, the maximum output of the steering actuator 12 can be limited to prevent the steering system 1 from shutting down. With this in mind, when the battery voltage is below a first reference voltage V1, the PU is set to increase as the battery voltage decreases. Therefore, the degradation level of the steering actuator 12 can be determined more accurately.

[0095] In the above embodiment, the steering controller 15 calculates the PU (evaluation value) based on the current values ​​(Iact, Imax, Ilim). In another embodiment, the steering controller 15 can calculate the evaluation value based on electricity or torque by applying an equation similar to equation (1) above to electricity or torque. Additionally, in another embodiment, the steering controller 15 can also calculate the evaluation value based on battery voltage, ambient temperature of the steering actuator 12, temperature of the steering controller 15 or the steering actuator 12, rack axial force, and frictional resistance inside the steering actuator 12 estimated based on the rack axial force, etc.

[0096] When the steering controller 15 is based on the power calculation PU, the following equation (2) is used.

[0097]

[0098] The actual power in equation (2) represents the actual power consumed by the steering actuator 12. The maximum power in equation (2) refers to the maximum power of the steering actuator 12 at the actual voltage defined by its size. The power degradation limit in equation (2) is the actual limit set in the steering actuator 12 to avoid undervoltage, overvoltage, or overtemperature of the steering actuator 12.

[0099] When the steering controller 15 calculates an evaluation value based on the output torque of the steering actuator 12, the torque utilization value (TU) is calculated based on the following equations (3) and (4). TU is an example of an evaluation value based on the usage state of the steering actuator 12. The evaluation value is determined using TU, and TU is calculated based on the output torque of the steering actuator 12.

[0100]

[0101] Mdeg=MAXIMUM[(Mmax-Mtrq_limit); (Mmax-Mpw_limit)]...(4)

[0102] In equation (3) above, Mmot_act is the actual torque value of the steering actuator 12. In equation (4) above, Mtrq_limit refers to the maximum torque capability of the steering actuator 12, which is essentially the torque limit of the steering actuator 12. In equation (4) above, Mpw_limit also refers to the torque limit of the steering actuator 12, but introduces another constraint, namely the battery power limit. In this case, the steering actuator 12 will be able to provide the required amount of torque, but the maximum value of the battery current flowing according to the drive of the steering actuator 12 only allows the steering actuator 12 to output a smaller amount of torque. In equations (3) and (4) above, Mmax is the maximum torque value of the steering actuator 12 at its actual speed according to the size specification. In equations (3) and (4) above, Mdeg represents the value of actual torque degradation determined by selection. The torque limits Mtrq_limit and Mpw_limit are subtracted from the maximum torque value Mmax, respectively. The larger of these subtractions will be used as Mdeg in equation (3).

[0103] In the above embodiment, during the signal determination process (step ST5), the steering controller 15 determines whether the continuous determination period is equal to or longer than a predetermined period. In another embodiment, during the signal determination process, the steering controller 15 may determine whether the number of consecutive determinations is equal to or greater than a predetermined number. The number of consecutive determinations is the number of times the degradation level of the steering actuator 12 is determined to be equal to or higher than a predetermined level.

[0104] In the above embodiment, the steering controller 15 sets three thresholds. In another embodiment, the steering controller 15 may set only one threshold, two thresholds, or four or more thresholds. For example, the steering controller 15 may determine that the steering actuator 12 is in a deteriorated state when the PU (performance unit) is higher than a threshold, and may determine that the steering actuator 12 is not in a deteriorated state when the PU is equal to or lower than a threshold. Thus, "determining the deterioration level of the steering actuator 12" includes "determining whether the steering actuator 12 is in a deteriorated state".

[0105] In the above embodiment, the PU (evaluation value) is set to increase as the degradation level of the steering actuator 12 increases. In another embodiment, the evaluation value may be set to decrease when the degradation level of the steering actuator 12 increases. In this embodiment, the steering controller 15 may determine the degradation level of the steering actuator 12 as higher when the evaluation value is below a threshold and higher when the evaluation value is equal to or above a threshold.

[0106] In the above embodiment, the steering controller 15 calculates the rack travel based on the rack position detected by the rack position sensor 39. In another embodiment, the steering controller 15 may calculate the rack travel based on the steering angle of the front wheel 3, the lateral acceleration applied to the vehicle 2, the yaw rate, and / or the vehicle speed.

[0107] In the above embodiment, when the rack travel speed is equal to or higher than a predetermined stop speed, the steering controller 15 suspends the determination of the deterioration level of the steering actuator 12. In another embodiment, when the rack axial force is equal to or higher than a predetermined stop force, the steering controller 15 may suspend the determination of the deterioration level of the steering actuator 12.

[0108] In the above embodiment, the steering controller 15 obtains the rack axial force directly from the rack axial force sensor 40. In another embodiment, the steering controller 15 may estimate the rack axial force based on an evaluation value such as PU or the current value of the steering actuator 12 (e.g., the effective value of the three-phase AC current flowing through the steering actuator 12). In the latter case, the steering controller 15 may estimate the rack axial force by multiplying the current value of the steering actuator 12 by a power transmission coefficient (a coefficient set based on the power transmission efficiency from the steering actuator 12 to the rack shaft 26).

[0109] In the above embodiments, the configuration of the present invention is applied to a steering system 1 in which the steering mechanism 11 and the steering member 10 are mechanically separated (more specifically, a steer-by-wire steering system 1). In another embodiment, the configuration of the present invention can be applied to a steering system 1 in which the steering mechanism 11 is mechanically connected to the steering member 10.

[0110] The specific embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications and changes can be made within the scope of the present invention.

[0111] List of reference numerals

[0112] 1: Steering System

[0113] 2: Vehicles

[0114] 3: Front wheel (example of a wheel)

[0115] 10: Steering components

[0116] 11: Steering mechanism

[0117] 12: Steering actuator

[0118] 15: Steering Controller (Example of a Controller)

[0119] 26: Rack and pinion shaft

[0120] 35: Battery

[0121] 37: Temperature sensor

Claims

1. A steering system for a vehicle, the steering system for a vehicle comprising: A steering mechanism configured to steer the wheels; A steering actuator configured to apply a driving force to the steering mechanism; as well as A controller, configured to control the steering actuator, The steering mechanism includes a rack shaft, which is movable from a predetermined reference position along the vehicle width direction. The controller is configured to calculate an evaluation value based on the usage status of the steering actuator, and to determine the degradation level of the steering actuator by comparing the evaluation value with at least one threshold set based on the amount of movement of the rack shaft relative to the reference position and the vehicle speed. Specifically, when the moving speed of the rack shaft is equal to or higher than a predetermined stopping speed, the controller suspends the determination of the deterioration level of the steering actuator.

2. The steering system for a vehicle according to claim 1, wherein, The at least one threshold includes multiple thresholds, and The controller is configured to determine the degradation level of the steering actuator by comparing the evaluation value with the plurality of thresholds.

3. The steering system for a vehicle according to claim 1 or 2, wherein, The controller is configured to periodically determine the degradation level of the steering actuator, and only output a signal indicating that the degradation level of the steering actuator is equal to or higher than the predetermined level if the determination that the degradation level of the steering actuator is equal to or higher than the predetermined level has been performed continuously for a predetermined period of time or longer, or has been performed continuously a predetermined number of times or more.

4. The steering system for a vehicle according to claim 1 or 2, wherein, The controller is configured to determine the degradation level of the steering actuator to be higher than the degradation level when the evaluated value is higher than the threshold, and when the evaluated value is equal to or lower than the threshold. When the vehicle speed is lower than a predetermined reference speed, the threshold is set to increase as the amount of movement of the rack shaft relative to the reference position increases.

5. The steering system for a vehicle according to claim 4, wherein, When the vehicle speed is equal to or higher than the reference speed, the threshold is set to a constant value regardless of the amount of movement of the rack shaft relative to the reference position.

6. The steering system for a vehicle according to claim 1 or 2, wherein, The controller is configured to determine the degradation level of the steering actuator to be higher than the degradation level when the evaluated value is higher than the threshold, and when the evaluated value is equal to or lower than the threshold. The evaluation value is set to increase as the current flowing according to the drive of the steering actuator increases.

7. The steering system for a vehicle according to claim 1 or 2, further comprising a temperature sensor configured to detect the temperature of the steering actuator or the controller. in, The controller is configured to determine the degradation level of the steering actuator to be higher than the degradation level when the evaluated value is higher than the threshold, and when the evaluated value is equal to or lower than the threshold. If the temperature detected by the temperature sensor is higher than a predetermined reference temperature, the evaluation value is set to increase as the temperature detected by the temperature sensor increases.

8. The steering system for a vehicle according to claim 1 or 2, further comprising a battery configured to supply power to the steering actuator. in, The controller is configured to determine the degradation level of the steering actuator to be higher than the degradation level when the evaluated value is higher than the threshold, and when the evaluated value is equal to or lower than the threshold. When the battery voltage is lower than a specified reference voltage, the evaluation value is set to increase as the battery voltage decreases.

9. The steering system for a vehicle according to claim 1, wherein, The evaluation value is determined using the torque utilization value, and The torque utilization value is calculated based on the output torque of the steering actuator.

10. The steering system for a vehicle according to claim 1 or 2, further comprising a steering member configured to receive a steering operation. in, The steering mechanism is mechanically separated from the steering component.

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