Vehicle steering system

Abstract

Provided is a steering device for a vehicle that can accurately determine the deterioration level of a steering actuator according to the traveling state of the vehicle. The steering device for a vehicle includes a steering mechanism that steers wheels, a steering actuator that applies a driving force to the steering mechanism, and a control device that controls the steering actuator, the steering mechanism having a rack shaft that is movable in the vehicle width direction from a predetermined reference position, and the control device calculates an evaluation value according to the usage state of the steering actuator and compares the evaluation value with at least one threshold value to determine the deterioration level of the steering actuator, the threshold value being set based on the amount of movement of the rack shaft from the reference position and the vehicle speed. [Representative diagram] Figure 5

Description

[Technical field]

[0001] The present invention relates to a steering device for a vehicle. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known a steering device for a vehicle that includes a steering mechanism for steering wheels and a steering actuator for applying a driving force to the steering mechanism.

[0003] For example, Patent Document 1 discloses an electric power steering device that includes a rack shaft to which a pair of wheels are connected, a steering shaft provided with a pinion gear that meshes with the rack shaft, and a motor that rotates the steering shaft. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-85917 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the steering device of the vehicle as described above, the steering actuator may deteriorate due to various reasons. Here, deterioration of the steering actuator refers to a decrease in the maximum output of the steering actuator. In order to take appropriate measures against such deterioration of the steering actuator, it is necessary to accurately determine the deterioration level of the steering actuator according to the running state of the vehicle.

[0006] In view of the above background, an object of the present invention is to accurately determine the deterioration level of a steering actuator in accordance with the running state of a vehicle. [Means for solving the problem]

[0007] In order to solve the above problem, one aspect of the present invention is a steering device (1) for a vehicle (2), comprising a steering mechanism (11) that steers wheels (3), a steering actuator (12) that applies a driving force to the steering mechanism, and a control device (15) that controls the steering actuator, wherein the steering mechanism has a rack shaft (26) that is movable in a vehicle width direction from a predetermined reference position, and the control device calculates an evaluation value according to a usage state of the steering actuator (step ST1) and determines a deterioration level of the steering actuator by comparing the evaluation value with at least one threshold value (TH1 to TH3) (step ST4), and the threshold value is set based on the amount of movement of the rack shaft from the reference position and the vehicle speed (step ST2).

[0008] According to this aspect, the threshold value can be set to an appropriate value based on the vehicle speed and the amount of movement of the rack shaft from the reference position, which change depending on the vehicle running state, so that the deterioration level of the steering actuator can be accurately determined depending on the vehicle running state.

[0009] In the above aspect, the at least one threshold value may include a plurality of threshold values, and the control device may determine the deterioration level of the steering actuator by comparing the evaluation value with the plurality of threshold values.

[0010] According to this aspect, the deterioration level of the steering actuator can be classified more finely, and the deterioration level of the steering actuator can be determined more accurately.

[0011] In the above aspect, the control device may periodically determine the deterioration level of the steering actuator, and only when the deterioration level of the steering actuator is determined to be at or above a predetermined level for a predetermined period of time or a predetermined number of times consecutively (step ST5), output a signal indicating that the deterioration level of the steering actuator is at or above the predetermined level (step ST6).

[0012] According to this aspect, when the deterioration level of the steering actuator accidentally becomes equal to or higher than a predetermined level, it is possible to suppress output of a signal indicating that the deterioration level of the steering actuator is equal to or higher than the predetermined level, thereby preventing erroneous detection of the deterioration level of the steering actuator.

[0013] In the above aspect, the control device may determine the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, and when the vehicle speed is less than a predetermined reference speed, the threshold value may be set to a higher value the greater the amount of movement of the rack shaft from the reference position.

[0014] In general, the greater the amount of movement of the rack shaft from the reference position, the greater the force required to move the rack shaft (the force required to steer the wheels). Therefore, when the vehicle speed is less than the reference speed, the greater the amount of movement of the rack shaft from the reference position, the higher the threshold value is set, thereby making it possible to more accurately determine the deterioration level of the steering actuator.

[0015] In the above aspect, when the vehicle speed is equal to or greater than the reference speed, the threshold value may be set to a constant value regardless of the amount of movement of the rack shaft from the reference position.

[0016] When the vehicle is traveling, a restoring force acts on the rack shaft to return it to a reference position depending on the wheel alignment (particularly the caster angle). In general, the effect of such a restoring force is greater than the effect of an increase in the force required to move the rack shaft. Therefore, by setting the threshold value to a constant value when the vehicle speed is equal to or greater than the reference speed, the deterioration level of the steering actuator can be determined more accurately.

[0017] In the above aspect, the control device may temporarily suspend the determination of the deterioration level of the steering actuator when the moving speed of the rack shaft is equal to or greater than a predetermined temporary determination suspension speed (step ST3).

[0018] When the moving speed of the rack shaft is high, the evaluation value may be higher than the threshold value even if the steering actuator is not deteriorated. In consideration of this, by temporarily suspending the determination of the deterioration level of the steering actuator when the moving speed of the rack shaft is equal to or higher than the determination temporary suspension speed, it is possible to prevent erroneous determination of the deterioration level of the steering actuator. For example, "temporarily suspending the determination of the deterioration level of the steering actuator" means "suspending the determination of the deterioration level of the steering actuator for the above-mentioned specified time or for the specified number of times."

[0019] In the above aspect, the control device may determine the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, and the evaluation value may be set to be larger as the value of the current flowing in response to driving of the steering actuator is larger.

[0020] When the frictional resistance inside the steering actuator and / or the force required to move the rack shaft becomes excessive, the drive torque of the steering actuator increases, and the value of the current that flows in response to the drive of the steering actuator also increases. By increasing the evaluation value accordingly, the deterioration level of the steering actuator can be accurately determined.

[0021] In the above aspect, the steering device of the vehicle further includes a temperature sensor (37) for detecting the temperature of the steering actuator or the control device, and the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, and when the temperature detected by the temperature sensor is higher than a predetermined reference temperature, the evaluation value may be set to be larger the higher the temperature detected by the temperature sensor.

[0022] If the temperature of the steering actuator or the control device is excessively high, the maximum output of the steering actuator is limited in order to protect the steering actuator or the control device. By increasing the evaluation value accordingly, the deterioration level of the steering actuator can be accurately determined.

[0023] In the above aspect, the steering device of the vehicle further includes a battery (35) that supplies power to the steering actuator, and the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, and when the voltage of the battery is lower than a predetermined reference voltage, the evaluation value may be set to be larger the lower the voltage of the battery.

[0024] When the battery voltage is excessively low, the maximum output of the steering actuator is limited to prevent the steering device from stopping. By increasing the evaluation value accordingly, the deterioration level of the steering actuator can be accurately determined.

[0025] In the above aspect, the evaluation value may be determined using a torque usage rate (TU).

[0026] According to this aspect, the torque usage rate is calculated based on the output torque of the steering actuator.

[0027] In the above aspect, the steering device of the vehicle may further include a steering member (10) that receives a steering operation, and the steering mechanism may be mechanically separated from the steering member.

[0028] According to this aspect, in a steer-by-wire steering device, the deterioration level of the steering actuator can be accurately determined in accordance with the running state of the vehicle. Effect of the Invention

[0029] According to the above aspect, the deterioration level of the steering actuator can be accurately determined in accordance with the running state of the vehicle. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram showing a steering device according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a block diagram showing a steering device according to an embodiment of the present invention; [Diagram 3] FIG. 2 is a flow chart showing level determination control according to an embodiment of the present invention. [Figure 4] (A) is a graph showing the relationship between the detected temperature and Ilim, and (B) is a graph showing the relationship between the battery voltage and Ilim. [Diagram 5] FIG. 1 is a diagram showing a first threshold table; [Figure 6] Table showing the relationship between PU range and steering actuator deterioration level [Figure 7] A table showing whether PU becomes higher than a first threshold value when the deterioration level of the steering actuator is at a first level. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, a steering device 1 of a vehicle 2 according to one embodiment of the present invention will be described. As shown in Fig. 1, the steering device 1 is a steer-by-wire (SBW) type steering device. The vehicle 2 on which the steering device 1 is provided is a four-wheeled automobile equipped with left and right front wheels 3 and left and right rear wheels (not shown). The left and right front wheels 3 are supported by a vehicle body 8 (only the outline of the lower part is shown in Fig. 1) via knuckles 7 so that the steering angle can be changed, and function as steered wheels. The steering angle refers to the angle of the front wheels 3 with respect to the fore-and-aft direction in a plan view. The steering device 1 changes the steering angle of the front wheels 3.

[0032] The steering device 1 has a steering member 10 rotatably provided on the vehicle body 8, a steering mechanism 11 that steers the front wheels 3, a steering actuator 12 that applies a driving force to the steering mechanism 11, a reaction force actuator 13 that applies a reaction torque to the steering member 10, and a steering control device 15 that controls the reaction force actuator 13 and the steering actuator 12. The steering device 1 may be a redundant system having a plurality of each of the steering actuators 12, the reaction force actuators 13, and the steering control devices 15.

[0033] The steering member 10 receives steering operations by the driver. The steering member 10 has a steering shaft 18 rotatably supported by the vehicle body 8, and a steering wheel 19 provided at one end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column (not shown) provided on the vehicle body 8, and its rear end protrudes rearward from the steering column. The steering wheel 19 is coupled to the rear end of the steering shaft 18 and rotates integrally with the steering shaft 18.

[0034] The reaction force actuator 13 is an electric motor, and is connected to the steering shaft 18 via a gear. When the reaction force actuator 13 is driven, the driving force is transmitted to the steering shaft 18 as a rotational force. The reaction force actuator 13 applies torque to the steering member 10 by rotating. The torque that the reaction force actuator 13 applies to the steering member 10 in response to the steering operation is called "reaction force torque."

[0035] The steering mechanism 11 has a rack shaft 26 extending in the vehicle width direction. The rack shaft 26 is supported by a gear housing (not shown) so as to be movable in the vehicle width direction. The left and right ends of the rack shaft 26 are connected to knuckles 7 that support the left and right front wheels 3, respectively, via tie rods 30. The steering angle of the front wheels 3 changes as the rack shaft 26 moves in the vehicle width direction from a predetermined reference position (a position where the orientation of the left and right front wheels 3 is parallel to the front-to-rear direction: see FIG. 1). The steering mechanism 11 is mechanically separated from the steering member 10.

[0036] The steering actuator 12 is an electric motor. The steering actuator 12 moves a rack shaft 26 in the vehicle width direction based on a signal from the steering control device 15, thereby changing the steering angle of the left and right front wheels 3.

[0037] 2, steering control device 15 is an ECU (Electronic Control Unit) including a CPU 32, a storage device 33, a drive circuit 34, etc. CPU 32 controls each part of steering device 1 based on programs and data stored in storage device 33. Drive circuit 34 is connected to battery 35 which supplies power to steering actuator 12. Direct current (hereinafter referred to as "battery current") flowing from battery 35 is converted to three-phase alternating current by drive circuit 34 and supplied to steering actuator 12.

[0038] The steering control device 15 is connected to a temperature sensor 37. The temperature sensor 37 may be provided integrally with the steering control device 15, or may be provided separately from the steering control device 15. The temperature sensor 37 detects the temperature of the CPU 32 or the drive circuit 34 (one example of the temperature of the steering control device 15), and outputs it to the steering control device 15. Note that in other embodiments, the temperature sensor 37 may detect the temperature of the steering actuator 12.

[0039] The steering control device 15 is connected to a voltage sensor 38. The voltage sensor 38 detects the voltage of the battery 35 (hereinafter referred to as "battery voltage") and outputs it to the steering control device 15. For example, the battery voltage is a voltage obtained by subtracting the voltage consumed by the harness connecting the battery 35 and the steering control device 15 from the terminal voltage of the battery 35.

[0040] The steering control device 15 is connected to a rack position sensor 39. The rack position sensor 39 detects the position of the rack shaft 26 in the vehicle width direction (hereinafter referred to as the "rack position") and outputs it to the steering control device 15. Based on the rack position detected by the rack position sensor 39, the steering control device 15 calculates the amount of movement of the rack shaft 26 in the vehicle width direction from a reference position (hereinafter referred to as the "rack stroke amount"), the moving speed of the rack shaft 26 in the vehicle width direction (hereinafter referred to as the "rack stroke speed"), and the steering angle of the front wheels 3.

[0041] The steering control device 15 is connected to a rack axial force sensor 40. The rack axial force sensor 40 detects a force in the vehicle width direction acting on the rack axle 26 (hereinafter referred to as "rack axial force") and outputs the force to the steering control device 15. For example, the rack axial force sensor 40 is a force sensor such as a piezoelectric sensor or a strain gauge sensor.

[0042] The steering control device 15 is connected to a vehicle speed sensor 41. The vehicle speed sensor 41 detects the vehicle speed (the speed of the vehicle 2) and outputs it to the steering control device 15.

[0043] The steering control device 15 is connected to a main control device 44. The main control device 44 is composed of multiple ECUs. The main control device 44 is connected to an HMI (Human Machine Interface) 45 including a display, speaker, warning lights, etc., and controls the HMI 45. The main control device 44 is connected to a drive device 46 and a braking device 47, and controls the drive device 46 and the braking device 47. The drive device 46 is a device that applies a driving force to the vehicle 2, and includes an electric motor and / or an internal combustion engine. The braking device 47 is a device that applies a braking force to the vehicle 2, and includes a mechanical brake.

[0044] Next, a description will be given of the level determination control executed by the steering control device 15. The level determination control is a control for determining the deterioration level of the steering actuator 12. For example, the level determination control is executed periodically after the ignition switch of the vehicle 2 is turned ON.

[0045] 3, when the level determination control is started, steering control device 15 executes an evaluation value calculation process (step ST1). In the evaluation value calculation process, steering control device 15 calculates a power usage rate (hereinafter referred to as "PU") of steering actuator 12 by the following equation (1). PU is an example of an evaluation value according to the usage state of steering actuator 12.

[0046]

number

[0047] Iact in the above formula (1) is the value of the battery current that actually flows in response to the driving of steering actuator 12. In other words, Iact is the value of the battery current that is actually consumed in response to the driving of steering actuator 12. Iact is equal to the value obtained by dividing the output of steering actuator 12 (more specifically, the output of the electric motor that constitutes steering actuator 12) by the battery voltage. Iact changes in response to the driving state of steering actuator 12. For example, if the frictional resistance inside steering actuator 12 or the force required to move rack shaft 26 in the vehicle width direction becomes excessive, the driving torque of steering actuator 12 increases and Iact increases accordingly. When Iact increases in this way, the numerator in the above formula (1) becomes larger, and therefore PU becomes larger.

[0048] Imax in the above formula (1) is the maximum value of the battery current that flows in response to the driving of steering actuator 12 (the battery current that can be consumed in response to the driving of steering actuator 12), and is determined based on the design capacity of steering actuator 12. Imax is constant regardless of the driving state of steering actuator 12.

[0049] Ilim in the above formula (1) is the maximum value of the battery current that flows in response to the driving of steering actuator 12 (the battery current that can be consumed in response to the driving of steering actuator 12), and is determined based on the limit amount of the maximum output of steering actuator 12. When the maximum output of steering actuator 12 is not limited, Ilim is equal to Imax. On the other hand, if the maximum output of steering actuator 12 is limited for some reason, Ilim becomes smaller than Imax. In other words, Ilim is equal to or smaller than Imax.

[0050] 4(A), Ilim is determined based on the temperature of the CPU 32 or the drive circuit 34 detected by the temperature sensor 37 (hereinafter referred to as the "detected temperature"). When the detected 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 constant and equal to Imax. When the detected temperature is lower than the first reference temperature T1, Ilim decreases as the detected temperature decreases. When the detected temperature is higher than the second reference temperature T2, Ilim decreases as the detected temperature increases. When Ilim decreases in this way, the numerator in the above formula (1) becomes larger, and PU becomes larger.

[0051] 4(B), 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 constant and equal to Imax. When the battery voltage is lower than the first reference voltage V1, Ilim decreases as the battery voltage decreases. When the battery voltage is higher than the second reference voltage V2, Ilim decreases as the battery voltage increases. When Ilim decreases in this way, the numerator in the above formula (1) increases, and PU increases.

[0052] 3, when the evaluation value calculation process (step ST1) is completed, the steering control device 15 executes a threshold setting process (step ST2). In the threshold setting process, the steering control device 15 sets first to third thresholds TH1 to TH3 based on the rack stroke amount and the vehicle speed.

[0053] The steering control device 15 determines the first threshold value TH1 by referring to a first threshold value table (see FIG. 5) based on the rack stroke amount and the vehicle speed. The first threshold value table is a two-dimensional table that defines the relationship between the rack stroke amount and the vehicle speed and the first threshold value TH1. In the first threshold value table, the rack stroke amount increases as the column goes to the right (i.e., 0 < L1 < L2 < L3 <... < Ln). In the first threshold value table, the vehicle speed increases as the row goes down (i.e., 0 < Y1 < Y2 < Y3 <... < Yn).

[0054] In the first threshold value table, A00 < A01 < A02. That is, when the vehicle speed is less than a predetermined reference speed Y1 and the rack stroke amount is less than a predetermined reference amount L3, the first threshold value TH1 is set to a higher value as the rack stroke amount increases.

[0055] In the first threshold value table, A02 < A03 and A03 = A04 =... = A0n. That is, when the vehicle speed is less than the reference speed Y1 and the rack stroke amount is greater than or equal to the reference amount L3, the first threshold value TH1 is set to a constant value regardless of the rack stroke amount.

[0056] The first threshold values TH1 (A10, A11,..., Ann) in the second to nth rows of the first threshold value table are all the same value. That is, when the vehicle speed is greater than or equal to the reference speed Y1, the first threshold value TH1 is set to a constant value regardless of the rack stroke amount. For example, the first threshold value TH1 in the second to nth rows of the first threshold value table is greater than A00 (the first threshold value TH1 when the vehicle speed and the rack stroke amount are 0) and less than A03 (the first threshold value TH1 when the vehicle speed is 0 and the rack stroke amount is the reference amount L3).

[0057] Note that the reference speed Y1 is the second lowest among the vehicle speeds displayed in the first threshold value table. Therefore, "when the vehicle speed is less than the reference speed Y1" corresponds to "when the vehicle 2 is stopped", and "when the vehicle speed is greater than or equal to the reference speed Y1" corresponds to "when the vehicle 2 is running".

[0058] The steering control device 15 determines the second and third threshold values ​​TH2 and TH3 by referring to second and third threshold value tables (not shown) based on the rack stroke amount and vehicle speed. The second and third threshold value tables are similar to the first threshold value table, and are two-dimensional tables that define the relationship between the rack stroke amount and vehicle speed and the second and third threshold values ​​TH2 and TH3. In this embodiment, the second threshold value TH2 is larger than the first threshold value TH1, and the third threshold value TH3 is larger than the second threshold value TH2.

[0059] 3, when the threshold setting process (step ST2) is completed, the steering control device 15 executes a speed determination process (step ST3). In the speed determination process, the steering control device 15 calculates a rack stroke speed based on the rack position detected by the rack position sensor 39, and determines whether or not the rack stroke speed is equal to or greater than a predetermined determination temporary interruption speed. If the rack stroke speed is equal to or greater than the determination temporary interruption speed (step ST3: Yes), the steering control device 15 does not execute the level determination process (step ST4) and the subsequent processes.

[0060] On the other hand, if the rack stroke speed is less than the judgment temporary interruption speed (step ST3: No), the steering control device 15 executes a level judgment process (step ST4). In the level judgment process, the steering control device 15 judges the deterioration level (first to fourth levels) of the steering actuator 12 by comparing PU with first to third threshold values ​​TH1 to TH3.

[0061] 6, when PU is equal to or less than first threshold value TH1, steering control device 15 determines that the deterioration level of steering actuator 12 is at the first level. The first level is the lowest level among the first to fourth levels, and indicates that steering actuator 12 is in a normal state.

[0062] When PU is greater than the first threshold value TH1 and equal to or less than the second threshold value TH2, the steering control device 15 determines that the deterioration level of the steering actuator 12 is at the second level. The second level is a level higher than the first level, and indicates that the steering actuator 12 is in a low deterioration state.

[0063] When PU is greater than the second threshold value TH2 and equal to or less than the third threshold value TH3, the steering control device 15 determines that the deterioration level of the steering actuator 12 is at the third level. The third level is a level higher than the second level, and indicates that the steering actuator 12 is in a moderately deteriorated state.

[0064] If PU is greater than the third threshold value TH3, the steering control device 15 determines that the deterioration level of the steering actuator 12 is at the fourth level. The fourth level is a level higher than the third level, and indicates that the steering actuator 12 is in a severely deteriorated state.

[0065] As described above, when PU is greater than each of threshold values ​​TH1 to TH3, steering control device 15 determines the deterioration level of steering actuator 12 to be higher than when PU is equal to or smaller than each of threshold values ​​TH1 to TH3.

[0066] With reference to FIG. 3, when the level determination process (step ST4) is completed, steering control device 15 executes signal determination process (step ST5). The signal determination process is a process for determining a signal (hereinafter referred to as an "output signal") that steering control device 15 outputs to main control device 44. In the signal determination process, steering control device 15 determines whether or not the continuous determination time is a predetermined time or more by referring to the determination results of the level determination process in the current and past level determination controls. The continuous determination time refers to the time during which a determination that the deterioration level of steering actuator 12 is the second deterioration level or more (i.e., a determination that steering actuator 12 is not in a normal state) continues. If the continuous determination time is the predetermined time or more, steering control device 15 determines the second to fourth level signals (signals indicating that the deterioration level of steering actuator 12 is the second to fourth levels) as output signals according to the determination results of the level determination process (step ST4). On the other hand, if the continuous judgment time is less than the predetermined time, the steering control device 15 determines the first level signal (a signal indicating that the deterioration level of the steering actuator 12 is the first level) as the output signal, regardless of the judgment result of the level judgment process (step ST4).

[0067] When the signal determination process (step ST5) is completed, the steering control device 15 executes a signal output process (step ST6). In the signal output process, the steering control device 15 outputs the output signals (first to fourth level signals) determined in step ST5 to the main control device 44. Note that in another embodiment, if the continuous determination time is less than a predetermined time in step ST5, the steering control device 15 does not need to output a signal to the main control device 44.

[0068] Main control device 44 recognizes the deterioration level of steering actuator 12 based on output signals (first to fourth level signals) from steering control device 15. When the deterioration level of steering actuator 12 is the first level (i.e. when steering actuator 12 is in a normal state), main control device 44 does not execute warning control and vehicle speed limit control. On the other hand, when the deterioration level of steering actuator 12 is the second to fourth levels (i.e. when steering actuator 12 is in a deteriorated state), main control device 44 executes warning control and / or vehicle speed limit control.

[0069] In the warning control, main control device 44 causes HMI 45 to execute a warning that steering actuator 12 is in a deteriorated state. For example, main control device 44 causes a warning message to be displayed on the display of HMI 45, causes a warning sound to be emitted from a speaker of HMI 45, or causes a warning light of HMI 45 to light up or flash. Main control device 44 may change the content of the warning control according to the deterioration level (second to fourth levels) of steering actuator 12.

[0070] In the vehicle speed limit control, main control device 44 controls drive device 46 and brake device 47 so that the vehicle speed is equal to or less than a predetermined speed limit. Main control device 44 may change the speed limit according to the deterioration level (second to fourth levels) of steering actuator 12. For example, main control device 44 may set the speed limit lower as the deterioration level of steering actuator 12 becomes higher.

[0071] Note that the warning control and vehicle speed limit control are merely examples of control executed by main control device 44 in accordance with the deterioration level of steering actuator 12. Therefore, main control device 44 may execute any control other than warning control and vehicle speed limit control. For example, main control device 44 may execute emergency stop control in which vehicle 2 autonomously travels to an appropriate stopping position and then stops. Furthermore, it may be a device other than main control device 44 (for example, steering control device 15, drive device 46, and / or braking device 47) that executes warning control, vehicle speed limit control, etc. in accordance with the deterioration level of steering actuator 12.

[0072] In the following, regarding the effects common to the first to third thresholds TH1 to TH3, only the first threshold TH1 will be described, and descriptions of the second and third thresholds TH2 and TH3 will be omitted.

[0073] In this embodiment, the first threshold value TH1 is set based on the rack stroke amount and the vehicle speed (step ST2). This makes it possible to set the first threshold value TH1 to an appropriate value based on the rack stroke amount and the vehicle speed which change according to the traveling state of the vehicle 2. Therefore, it is possible to accurately determine the deterioration level of the steering actuator 12 according to the traveling state of the vehicle 2.

[0074] Furthermore, steering control device 15 determines the deterioration level of steering actuator 12 by comparing PU with first to third threshold values ​​TH1 to TH3 (i.e. a plurality of threshold values). This makes it possible to classify the deterioration level of steering actuator 12 in more detail and to determine the deterioration level of steering actuator 12 more accurately.

[0075] Furthermore, steering control device 15 periodically determines the deterioration level of steering actuator 12, and only when the determination that the deterioration level of steering actuator 12 is at or above the second level continues for at least a predetermined time (step ST5), it outputs a signal indicating that the deterioration level of steering actuator 12 is at or above the second level (step ST6). This makes it possible to prevent a signal indicating that the deterioration level of steering actuator 12 is at or above the second level from being output when the deterioration level of steering actuator 12 accidentally becomes at or above the second level. This makes it possible to prevent erroneous detection of the deterioration level of steering actuator 12.

[0076] Generally, the greater the rack stroke amount, the greater the force required to move rack shaft 26 (the force required to steer front wheels 3). In consideration of this, when the vehicle speed is less than reference speed Y1, first threshold value TH1 is set to a higher value as the rack stroke amount increases. This makes it possible to more accurately determine the deterioration level of steering actuator 12.

[0077] When the vehicle 2 is running, a restoring force to the reference position acts on the rack shaft 26 according to the alignment of the front wheels 3 (especially the caster angle). Generally, the influence of such a restoring force is greater than the influence due to an increase in the force required to move the rack shaft 26. Considering this point, when the vehicle speed is equal to or higher than the reference speed Y1, the first threshold value TH1 is set to a constant value. Thereby, the deterioration level of the steering actuator 12 can be determined more accurately.

[0078] FIG. 7 shows whether the PU becomes higher than the first threshold value TH1 when the deterioration level of the steering actuator 12 is at the first level (that is, when the steering actuator 12 is in a normal state). In FIG. 7, the rack shaft force increases as the column goes to the right (that is, 0 < F1 < F2 < F3 <... < Fn-1 < Fn). In FIG. 7, the rack stroke speed increases as the row goes down (that is, 0 < X1 < X2 < X3 <... < Xn-1 < Xn).

[0079] As shown in FIG. 7, when the rack stroke speed is high, even if the deterioration level of the steering actuator 12 is at the first level, the PU may become higher than the first threshold value TH1. Considering this point, when the rack stroke speed is equal to or higher than a predetermined determination interruption speed (for example, X3 in FIG. 7), the steering control device 15 temporarily interrupts the determination of the deterioration level of the steering actuator 12 (step ST3). Thereby, an erroneous determination of the deterioration level of the steering actuator 12 can be prevented.

[0080] For example, if the temperature of steering actuator 12 drops and the grease inside steering actuator 12 hardens, the frictional resistance inside steering actuator 12 may become excessive. Also, if vehicle 2 is overloaded, for example, the force required to move rack shaft 26 may become excessive. When these situations occur, the drive torque of steering actuator 12 increases, and Iact (the value of the battery current that actually flows in response to the drive of steering actuator 12) also increases. Taking this into consideration, PU is set to be larger as Iact increases. This makes it possible to accurately determine the deterioration level of steering actuator 12.

[0081] Furthermore, if the detected temperature (the temperature of CPU 32 or drive circuit 34 detected by temperature sensor 37) is excessively high, the maximum output of steering actuator 12 is limited in order to protect CPU 32 or drive circuit 34. Taking this into consideration, when the detected temperature is higher than second reference temperature T2, PU is set to increase as the detected temperature increases. This makes it possible to accurately determine the deterioration level of steering actuator 12.

[0082] Furthermore, if the battery voltage is excessively low, the maximum output of the steering actuator 12 is limited to prevent the steering device 1 from stopping. Taking this into consideration, when the battery voltage is lower than the first reference voltage V1, PU is set to be larger as the battery voltage is lower. This makes it possible to accurately determine the deterioration level of the steering actuator 12.

[0083] In the above embodiment, steering control device 15 calculates PU (evaluation value) based on the current values ​​(Iact, Imax, Ilim). Meanwhile, in other embodiments, steering control device 15 may calculate the evaluation value based on the electric power or the torque by applying an equation similar to the above equation (1) to the electric power or the torque. Also, in other embodiments, steering control device 15 may calculate the evaluation value based on the battery voltage, the ambient temperature of steering actuator 12, the temperature of steering control device 15 or steering actuator 12, the rack axial force, friction resistance inside steering actuator 12 estimated based on the rack axial force, etc.

[0084] When the steering control device 15 calculates PU based on the electric power, the following formula (2) is used.

[0085]

number

[0086] The Actual Power in the above formula (2) means the actual power consumption of the steering actuator 12. The Maximum Power in the above formula (2) indicates the maximum power of the steering actuator 12 at the actual voltage determined by the specifications. The Power Degradation Limit in the above formula (2) is an actual limit value set for the steering actuator 12 to avoid undervoltage, overvoltage, and overheating of the steering actuator 12.

[0087] When steering control device 15 calculates the evaluation value based on the output torque of steering actuator 12, a torque usage rate (TU) is calculated based on the following equations (3) and (4). TU is an example of an evaluation value according to the usage state of steering actuator 12. The evaluation value is determined using TU, and TU is calculated based on the output torque of steering actuator 12.

[0088]

number

[0089]

number

[0090] Mmot_act in the above formula (3) is the actual torque value of the steering actuator 12. Mtrq_limit in the above formula (4) indicates the maximum torque of the steering actuator 12, and is basically the torque limit value of the steering actuator 12. Mpw_limit in the above formula (4) also indicates the torque limit value of the steering actuator 12, but indicates another limit, that is, the battery power limit value. In this case, the steering actuator 12 can provide the required torque, but the maximum value of the battery current flowing by the driving of the steering actuator 12 only allows a smaller torque to be output by the steering actuator 12. Mmax in the above formulas (3) and (4) is the maximum torque value of the steering actuator 12 at the actual speed according to the specifications. Mdeg in the above formulas (3) and (4) indicates the value of the actual torque degradation determined using the option. The torque limit values ​​Mtrq_limit and Mpw_limit are each subtracted from the maximum torque value Mmax. The larger of the results of these subtractions is used as Mdeg in formula (3).

[0091] In the above embodiment, in the signal determination process (step ST5), the steering control device 15 determines whether or not the continuous determination time is equal to or greater than a predetermined time. On the other hand, in another embodiment, in the signal determination process, the steering control device 15 may determine whether or not the number of continuous determinations is equal to or greater than a predetermined number. The number of continuous determinations is the number of consecutive determinations that the deterioration level of the steering actuator 12 is equal to or greater than a predetermined level.

[0092] In the above embodiment, steering control device 15 sets three thresholds. On the other hand, in other embodiments, steering control device 15 may set only one threshold, or may set two or four or more thresholds. For example, steering control device 15 may determine that steering actuator 12 is in a deteriorated state when PU (evaluation value) is greater than one threshold, and may determine that steering actuator 12 is not in a deteriorated state when PU is equal to or less than one threshold. In this way, "determining the deterioration level of steering actuator 12" includes "determining whether steering actuator 12 is in a deteriorated state or not."

[0093] In the above embodiment, PU (evaluation value) is set to increase as the deterioration level of steering actuator 12 increases. On the other hand, in other embodiments, the evaluation value may be set to decrease as the deterioration level of steering actuator 12 increases. In this case, when the evaluation value is smaller than a threshold value, steering control device 15 may determine the deterioration level of steering actuator 12 to be higher than when the evaluation value is equal to or greater than the threshold value.

[0094] In the above embodiment, the steering control device 15 calculates the rack stroke amount based on the rack position detected by the rack position sensor 39. On the other hand, in other embodiments, the steering control device 15 may calculate the rack stroke amount based on the steering angle of the front wheels 3, or may calculate the rack stroke amount based on the lateral acceleration applied to the vehicle 2, the yaw rate, and / or the vehicle speed.

[0095] In the above embodiment, when the rack stroke speed is equal to or greater than a predetermined judgment temporary suspension speed, the steering control device 15 temporarily suspends the judgment of the deterioration level of the steering actuator 12. On the other hand, in another embodiment, the steering control device 15 may temporarily suspend the judgment of the deterioration level of the steering actuator 12 when the rack axial force is equal to or greater than a predetermined judgment temporary suspension force.

[0096] In the above embodiment, the steering control device 15 directly acquires the rack axial force from the rack axial force sensor 40. On the other hand, in other embodiments, the steering control device 15 may estimate the rack axial force based on an evaluation value of the PU or the like, or may estimate the rack axial force based on a current value of the steering actuator 12 (for example, an effective value of a three-phase AC flowing through the steering actuator 12). In the latter case, the steering control device 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).

[0097] In the above embodiment, the configuration of the present invention is applied to a steering device 1 (a steer-by-wire type steering device 1) in which the steering mechanism 11 is mechanically separated from the steering member 10. On the other hand, in other embodiments, the configuration of the present invention may be applied to a steering device 1 in which the steering mechanism 11 is mechanically connected to the steering member 10.

[0098] Although the specific embodiment has been described above, the present invention is not limited to the above embodiment and its modified examples, and can be modified in a wide range of ways. [Explanation of symbols]

[0099] 1: Steering gear 2: Vehicle 3: Front wheel (example of a wheel) 10: Steering member 11: Steering mechanism 12: Steering actuator 15: Steering control device (an example of a control device) 26: Rack shaft 35: Battery 37: Temperature sensor

Claims

1. A steering device for a vehicle, comprising: A steering mechanism for steering the wheels; A steering actuator that applies a driving force to the steering mechanism; A control device for controlling the steering actuator, The steering mechanism has a rack shaft that is movable in a vehicle width direction from a predetermined reference position, the control device calculates an evaluation value according to a usage state of the steering actuator, and determines a deterioration level of the steering actuator by comparing the evaluation value with at least one threshold value; the threshold value is set based on a movement amount of the rack shaft from the reference position and a vehicle speed, The control device temporarily suspends the determination of the deterioration level of the steering actuator when the moving speed of the rack shaft is equal to or greater than a predetermined determination suspension speed.

2. the at least one threshold value includes a plurality of threshold values; The steering device for a vehicle according to claim 1 , wherein the control device determines the deterioration level of the steering actuator by comparing the evaluation value with the plurality of threshold values.

3. 3. The vehicle steering device according to claim 1 or 2, wherein the control device periodically determines the deterioration level of the steering actuator, and outputs a signal indicating that the deterioration level of the steering actuator is above a predetermined level only when the determination that the deterioration level of the steering actuator is above a predetermined level continues for a predetermined period of time or a predetermined number of times.

4. the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, 3. The steering apparatus for a vehicle according to claim 1, wherein when the vehicle speed is lower than a predetermined reference speed, the threshold value is set to a higher value as the amount of movement of the rack shaft from the reference position increases.

5. 5. The steering device for a vehicle according to claim 4, wherein when the vehicle speed is equal to or greater than the reference speed, the threshold value is set to a constant value regardless of the amount of movement of the rack shaft from the reference position.

6. the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, 3. The steering device for a vehicle according to claim 1, wherein the evaluation value is set to be larger as a value of a current flowing in response to driving of the steering actuator is larger.

7. A temperature sensor is further provided to detect a temperature of the steering actuator or the control device. the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, 3. The steering apparatus for a vehicle according to claim 1, wherein when the temperature detected by the temperature sensor is higher than a predetermined reference temperature, the evaluation value is set to be larger as the temperature detected by the temperature sensor becomes higher.

8. The steering actuator further includes a battery for supplying power to the steering actuator. the control device determines the deterioration level of the steering actuator to be higher when the evaluation value is greater than the threshold value than when the evaluation value is equal to or less than the threshold value, 3. The steering apparatus for a vehicle according to claim 1, wherein, when the voltage of the battery is lower than a predetermined reference voltage, the evaluation value is set to be larger as the voltage of the battery is lower.

9. The evaluation value is determined using a torque usage rate, The steering device for a vehicle according to claim 1 , wherein the torque usage rate is calculated based on an output torque of the steering actuator.

10. Further comprising a steering member that accepts a steering operation, 3. The vehicle steering apparatus according to claim 1, wherein the steering mechanism is mechanically separated from the steering member.

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