JP7674916B2 - Electric power steering device - Google Patents

Description

The present invention relates to an electric power steering device that generates steering torque using an electric motor.

Conventionally, in power steering devices mounted on vehicles such as automobiles, an electric power steering device is known that uses an electric motor to apply steering torque (motor steering torque) to a steering mechanism that moves a steering shaft to which a steering wheel is connected left and right. When a steering torque sensor detects the driver's steering torque (driver steering torque), the electric motor generates a motor steering torque corresponding to the driver steering torque as an assist torque. In addition, when a target torque, which is a control instruction value, is input from a cruise control unit or the like for performing driving assistance control of the vehicle, the electric power steering device generates a motor steering torque corresponding to the target torque by the electric motor.

In such an electric power steering device, it is desirable to detect abnormalities such as rattle caused by deterioration over time in order to maintain good controllability over the electric motor. For example, Patent Document 1 discloses a technology for detecting abnormalities caused by deterioration, which detects abnormalities in the electric power steering device under the conditions that the vehicle is not running, the vehicle is parked without being caused by a stop signal, the main switch is on, and the steering member is not steered. In the technology disclosed in Patent Document 1, when the above conditions are met, the relationship between the rotation angle of the electric motor and the amount of movement of the steering shaft is detected within the range of the amount of movement of the steering shaft (rack shaft) within which the wheels are maintained in contact with the road surface. Then, if the rotation angle of the electric motor when the amount of movement of the steering shaft is the set amount of movement is greater than a threshold value, it is determined that the transmission device of the electric power steering device is abnormal (deteriorated).

JP 2019-104488 A

However, the deterioration determination disclosed in the above-mentioned Patent Document 1 requires the electric motor to be operated while the vehicle is stopped, and therefore there is a risk that the motor driving noise, etc., may cause discomfort to the occupants. In addition, the deterioration determination disclosed in the above-mentioned Patent Document 1 measures the amount of movement of the steering shaft on the premise that the wheels are maintained in contact with the road surface, so there is a risk that it may be difficult to perform an accurate deterioration determination, for example, when the vehicle is stopped on a low μ road surface.

The present invention was made in consideration of the above circumstances, and aims to provide an electric power steering device that can accurately determine deterioration without causing discomfort to the occupants.

An electric power steering device according to one aspect of the present invention includes a steering mechanism that transmits a driver steering torque input to a steering wheel to a steering shaft, an electric motor that generates a motor steering torque, a gear pair that transmits the motor steering torque to the steering shaft, steering control means that is capable of executing steering control that does not require the driver to grip the steering wheel through drive control of the electric motor, steering torque detection means that detects the driver steering torque input to the steering mechanism, grip state detection means that detects the grip state of the steering wheel by the driver, motor rotation angle detection means that detects the rotation angle of the electric motor, and a deterioration judgment means that judges deterioration of the gear pair. and a deterioration determination means, when the vehicle is traveling and the steering control is being executed and the driver's grip on the steering wheel is not detected by the grip state detection means, obtains, based on the output of the motor rotation angle detection means, the rotation angle of the electric motor from when the steering direction is reversed due to the electric motor being turned back by the steering control and the steering torque detection means detects a sudden change in the steering torque until the steering torque change is detected again, calculates the difference between the rotation angle and a predetermined reference value as a deterioration angle, and determines that the gear pair is deteriorated when the deterioration angle is equal to or greater than a predetermined first threshold value.

The electric power steering device of the present invention can perform deterioration determination with high accuracy without causing discomfort to the occupants.

Overall configuration of the driving support device Schematic diagram of a driving support device installed in a vehicle Schematic diagram of an electric power steering device FIG. 2 is an explanatory diagram showing an example of characteristics of the steering torque and the basic current value of the electric motor; An explanatory diagram of the actual travel trajectory of the vehicle relative to the target route Diagram showing the deterioration angle A flowchart showing a routine for determining deterioration of a motor steering torque transmission system. Flowchart showing a motor drive control routine

The following describes the embodiments of the present invention with reference to the drawings. The drawings relate to one embodiment of the present invention, with FIG. 1 being an overall configuration diagram of a driving control system, and FIG. 2 being a schematic configuration diagram of a driving assistance device mounted on a vehicle. First, with reference to FIGS. 1 and 2, a driving assistance device 10 of a vehicle (host vehicle) 1 equipped with an electric power steering device 50 will be described.

The driving assistance device 10 has a camera unit 11 and a locator unit 12 as units for recognizing the driving environment outside the vehicle. The driving assistance device 10 also has a driving control unit (hereinafter referred to as "driving_ECU") 21, an engine control unit (hereinafter referred to as "E/G_ECU") 22, a power steering control unit (hereinafter referred to as "PS_ECU") 23, a brake control unit (hereinafter referred to as "BK_ECU") 24, and an alarm control unit (hereinafter referred to as "alarm_ECU") 25. Each of these control units 21 to 25 is connected to the camera unit 11 and the locator unit 12 via an in-vehicle communication line such as a CAN (Controller Area Network).

The camera unit 11 is fixed, for example, to the center of the upper front part of the vehicle interior. This camera unit 11 has an on-board camera (stereo camera) consisting of a main camera 11a and a sub-camera 11b, which are imaging means, an image processing unit (IPU) 11c, and a first driving environment recognition unit 11d.

The main camera 11a and the sub-camera 11b are, for example, autonomous sensors that sense the real space (driving environment) in front of the vehicle 1. The main camera 11a and the sub-camera 11b are, for example, arranged in symmetrical positions on either side of the center in the vehicle width direction, and capture stereo images of the driving environment in the area in front of the vehicle 1 from different viewpoints.

The IPU 11c processes the forward driving environment image information of the vehicle 1 captured by both cameras 11a and 11b in a predetermined manner, and generates forward driving environment image information (distance image information) that includes distance information calculated from the amount of deviation between the positions of corresponding objects.

The first driving environment recognition unit 11d determines the lane markings that divide the roads around the vehicle 1 based on distance image information received from the IPU 11c, etc.

The first driving environment recognition unit 11d also calculates the road curvature [1/m] of the dividing lines dividing the left and right of the road (host vehicle driving lane) on which the host vehicle 1 is traveling, and the width between the left and right dividing lines (lane width). There are various known methods for calculating this road curvature and lane width, but for example, the first driving environment recognition unit 11d recognizes the left and right dividing lines by binarizing the road curvature based on the forward driving environment image information using brightness difference, and calculates the curvature of the left and right dividing lines for each specified section using a curve approximation formula using the least squares method, etc.

The first driving environment recognition unit 11d also performs a predetermined pattern matching on the distance image information to recognize three-dimensional objects such as guardrails and curbs along the road, and pedestrians, motorcycles, and vehicles other than motorcycles that are on the road around the vehicle 1. Here, when the first driving environment recognition unit 11d recognizes three-dimensional objects, it recognizes, for example, the type of the object, the distance to the object, the speed of the object, and the relative speed between the object and the vehicle 1.

The locator unit 12 estimates the vehicle's position on a road map, and has a locator calculation unit 13 that estimates the vehicle's position. The input side of this locator calculation unit 13 is connected to sensors required for estimating the position of the vehicle 1 (vehicle position), such as an acceleration sensor 14 that detects the longitudinal acceleration of the vehicle 1, a wheel speed sensor 15 that detects the rotational speed of each of the front, rear, left and right wheels, a gyro sensor 16 that detects the angular velocity or angular acceleration of the vehicle, and a GNSS receiver 17 that receives positioning signals transmitted from multiple positioning satellites.

The locator calculation unit 13 is also connected to a high-precision road map database 18. The high-precision road map database 18 is a large-capacity storage medium such as an HDD, and stores high-precision road map information (dynamic map).

The locator calculation unit 13 includes a map information acquisition unit 13a and a second driving environment recognition unit 13b.

The map information acquisition unit 13a acquires route map information from the current location to the destination from the map information stored in the high-precision road map database 18, for example, based on the destination set by the driver during automatic driving.

The map information acquisition unit 13a also transmits the acquired route map information (lane data on the route map) to the second driving environment recognition unit 13b. The second driving environment recognition unit 13b performs map matching of the position coordinates of the vehicle 1 acquired based on the positioning signal received by the GNSS receiver 17 onto the route map information, and estimates the vehicle's position on the road map.

In addition, in an environment where a valid positioning signal from a positioning satellite cannot be received due to reduced sensitivity of the GNSS receiver 17, such as when driving inside a tunnel, the second driving environment recognition unit 13b switches to autonomous navigation, which estimates the vehicle's position based on the vehicle speed calculated based on the wheel speed detected by the wheel speed sensor 15, the angular velocity detected by the gyro sensor 16, and the longitudinal acceleration detected by the longitudinal acceleration sensor 14, and estimates the vehicle's position on the road map.

Furthermore, the second driving environment recognition unit 13b recognizes road map information of a set range centered on the estimated vehicle position as second driving environment information. This second driving environment information includes various information such as the left and right lane markings that divide the vehicle's driving path (driving lane), the road curvature in the center of the driving lane, and the road type.

The driving_ECU 21 reads the first driving environment information recognized by the first driving environment recognition unit 11d of the camera unit 11, and the second driving environment information recognized by the second driving environment recognition unit 13b of the locator unit 12, etc.

In addition, various switches and sensors such as a mode changeover switch 31, a steering torque sensor 32 as a steering torque detection means, a brake sensor 33, an accelerator sensor 34, a yaw rate sensor 35, and a touch sensor 36 as a grip state detection means are connected to the input side of the travel_ECU 21.

The mode changeover switch 31 is a switch that allows the driver to switch the driving assistance control on and off. The steering torque sensor 32 detects the steering torque as a driving operation amount by the driver. The brake sensor 33 detects the brake pedal depression amount as a driving operation amount by the driver. The accelerator sensor 34 detects the accelerator pedal depression amount as a driving operation amount by the driver. The yaw rate sensor 35 detects the yaw rate acting on the host vehicle 1. The touch sensor 36 is, for example, a sheet-shaped pressure sensor, pressure sensor, or capacitance sensor arranged on the steering wheel 55 (see FIG. 3), and detects the state of grip of the steering wheel 55 by the driver.

The driving modes set in the driving_ECU21 are a manual driving mode, a first driving assistance mode and a second driving assistance mode which are modes for driving assistance control, and an evacuation mode.

The manual driving mode is a driving mode that requires the driver to maintain steering (hold the steering wheel 55), and is a driving mode in which the vehicle 1 is driven according to driving operations such as steering, accelerator, and brake operations by the driver.

Similarly, the first driving assistance mode is also a driving mode that requires the driver to maintain steering. That is, the first driving assistance mode is a driving mode that reflects the driving operation by the driver and mainly performs an appropriate combination of adaptive cruise control (ACC), active lane keep centering (ALKC) control that keeps the vehicle in the current driving lane, and active lane keep bouncing control. That is, the first driving assistance mode is a so-called semi-automatic driving mode in which the host vehicle 1 is driven along a target driving route through control of, for example, the E/G_ECU 22, the PS_ECU 23, the BK_ECU 24, the alarm_ECU 25, etc.

The second driving control mode is a driving mode that does not require the driver to maintain steering, operate the accelerator, or operate the brakes, and mainly performs an appropriate combination of preceding vehicle following control, lane centering control, and lane departure prevention control. In other words, the second driving assistance mode is an automatic driving mode that drives the host vehicle 1 according to a target route (route map information) through control of, for example, the E/G_ECU 22, PS_ECU 23, BK_ECU 24, etc.

The evacuation mode is a mode for automatically stopping the vehicle 1 on a roadside or the like when, for example, while driving in the second driving control mode, driving in that mode cannot be continued and the driver cannot take over driving operations (i.e., when transition to the manual driving mode or the first driving control mode cannot be made).

A throttle actuator 27 is connected to the output side of the E/G_ECU 22. This throttle actuator 27 opens and closes the throttle valve of an electronically controlled throttle provided in the throttle body of the engine. The throttle actuator 27 opens and closes the throttle valve in response to a drive signal from the E/G_ECU 22 to adjust the intake air flow rate, thereby generating the desired engine output.

An electric motor 28 for driving an electric power steering device 50 (described later) is connected to the output side of the PS_ECU 23. A motor rotation angle sensor 37 is connected to the input side of the PS_ECU 23 as a motor rotation angle detection means for detecting the rotation angle of the electric motor 28. The electric motor 28 is driven and controlled by a drive signal from the PS_ECU 23, and applies a steering torque (motor steering torque) due to the motor rotation force to a steering mechanism 51 (described later).

For example, when the driver steering torque is detected by the steering torque sensor 32, the PS_ECU 23 calculates the control current Ipsb corresponding to the driver steering torque Td and the vehicle speed V as a drive signal based on a pre-set map or the like (for example, see FIG. 4). Then, the PS_ECU 23 outputs the calculated control current Ipsb to the electric motor 28. This causes the electric motor 28 to generate a motor steering torque corresponding to the driver steering torque.

For example, when the first or second driving assistance mode is selected, and a control signal such as a target yaw rate is input from the travel_ECU 21, the PS_ECU 23 calculates a target torque according to the control signal. The PS_ECU 23 then outputs a control current Ipsb according to the calculated target torque as a drive signal to the electric motor 28. This causes the electric motor 28 to generate a motor steering torque for performing lane centering control, lane departure suppression control, and the like. Here, the PS_ECU 23 performs well-known feedback control when calculating the control current Ipsb. This feedback control causes the electric motor 28 to travel the host vehicle 1 along the target route while gently and repeatedly reversing the steering direction (see FIG. 5, for example).

A brake actuator 29 is connected to the output side of the BK_ECU 24. This brake actuator 29 adjusts the brake hydraulic pressure supplied to the brake wheel cylinders provided on each wheel. When the brake actuator 29 is driven by a drive signal from the BK_ECU 24, the brake wheel cylinders generate braking force on each wheel, forcibly decelerating the host vehicle 1.

An alarm device 30 is connected to the output side of the alarm_ECU 25. The alarm device 30 is configured to include, for example, a speaker and a display. The alarm device 30 operates the speaker and the display by a drive signal from the alarm_ECU 25, and issues various types of alarms to the driver by sound and display.

The electric power steering device 50 of this embodiment, which is mounted on a vehicle 1 equipped with such a driving assistance function, has a steering mechanism 51 for transmitting the steering input by the driver (driver steering torque) to the steered wheels, as shown in FIG. 3, for example.

The steering mechanism 51 is configured with a steering gear box 57 arranged in the engine compartment.

The steering gear box 57 supports a steering shaft 58 that extends in the vehicle width direction and a pinion shaft 59 that extends in a direction intersecting the steering shaft 58.

The steering shaft 58 is inserted and supported in the steering gear box 57 so that it can move back and forth in the vehicle width direction. A rack gear 62 is provided midway along the steering shaft 58.

The left and right ends of the steering shaft 58 each protrude outside the steering gear box 57. Front knuckles 60 that rotatably support the left and right front wheels 56L, 56R, which are the steered wheels, are connected to the left and right ends of the steering shaft 58. Each front knuckle 60 is supported on the vehicle frame via a kingpin (not shown) so that it can be steered. As a result, when the steering shaft 58 moves left and right, each front knuckle 60 is rotated about the kingpin, and the left and right front wheels 56L, 56R are steered left and right.

The pinion shaft 59 is supported by the steering gear box 57 in a rotatable state. A pinion gear 63 that meshes with a rack gear 62 of the steering shaft 58 is provided at the tip of the pinion shaft 59.

The tip of an intermediate shaft 65 is connected to the base end of the pinion shaft 59 via a universal joint 66. The tip of a steering shaft 67 is connected to the base end of the intermediate shaft 65 via a universal joint 68.

The steering shaft 67 is rotatably supported on the vehicle body frame (not shown) via a steering column 69. The base end of the steering shaft 67 protrudes into the vehicle cabin. The steering wheel 55 is fixed to the base end of the steering shaft 67 that protrudes into the vehicle cabin.

As a result, in the steering mechanism 51 of this embodiment, the driver's steering input (driver steering torque) to the steering wheel 55 is transmitted to the pinion shaft 59 via the steering shaft 67 and intermediate shaft 65, and is further transmitted to the steering shaft 58 via the gear pair 61 consisting of the pinion gear 63 and rack gear 62.

In the steering mechanism 51 of the electric power steering device 50 configured in this manner, a worm wheel gear 71 is attached to the tip of the pinion gear 63. This worm wheel gear 71 is meshed with a worm gear 72 fixed to the motor shaft 28a of the electric motor 28.

As a result, the rotational force (motor steering torque) generated in the electric motor 28 is transmitted to the pinion shaft 59 via a gear pair 70 consisting of a worm gear 72 and a worm wheel gear 71, and is further transmitted to the steering shaft 58 via a gear pair 61 consisting of a pinion gear 63 and a rack gear 62.

Here, a motor rotation angle sensor 37 that detects the rotation angle of the motor shaft 28a is connected to the electric motor 28.

A torsion bar 59a is also installed midway along the pinion shaft 59. A steering torque sensor 32 is provided on the outer periphery of this torsion bar 59a. The steering torque sensor 32 detects the displacement between the tip and base ends that occurs around the axis of the pinion shaft 59 due to the twisting of the torsion bar 59a, making it possible to detect the steering torque input to the pinion shaft 59 of the steering mechanism 51.

In the electric power steering device 50 configured in this manner, a predetermined gap (backlash) is set between the tooth surfaces of the pinion gear 63 and rack gear 62 that constitute each gear pair 61, 70, and between the tooth surfaces of the worm gear 72 and worm wheel gear 71, to prevent interference between the tooth surfaces.

The gap between the tooth surfaces of these gear pairs 61, 70 increases due to deterioration over time, such as wear, which results in abnormalities such as increased backlash in the motor steering torque transmission system. In order to ensure suitable steering controllability against such deterioration, the PS_ECU 23 performs a deterioration determination of the motor steering torque transmission system. When the PS_ECU 23 determines that the motor steering torque transmission system has reached a first deterioration level set in advance, it performs deterioration compensation (so-called backlash reduction) for the gear pairs 61, 70 through drive control of the electric motor 28.

Furthermore, when the motor steering torque transmission system reaches a second deterioration level in which the backlash is greater than the first deterioration level, the PS_ECU 23 prohibits steering control in the second driving assistance mode and issues a warning to the occupant via the warning_ECU 25.

In this manner, in this embodiment, the travel_ECU 21 and the PS_ECU 23 function as steering control means. The PS_ECU 23 also functions as deterioration determination means. The warning_ECU 25 also functions as warning means.

Next, the deterioration judgment of the motor steering torque transmission system will be described with reference to the flowchart of the deterioration judgment routine shown in FIG. 7. This routine is executed periodically by the PS_ECU 23. That is, the deterioration judgment routine is executed, for example, every time the vehicle 1 travels a preset distance (e.g., several hundred km) after the previous deterioration judgment has been performed, or every time a preset period of time (e.g., several months) has elapsed.

When the routine starts, in step S101, the PS_ECU 23 checks whether the vehicle 1 is currently traveling in the second driving assistance mode, i.e., whether the vehicle is traveling in an autonomous driving mode that does not require the driver to hold the steering wheel 55.

Then, in step S101, if it is determined that the current driving mode is not the autonomous driving mode, that is, if it is determined that the current driving mode is the manual driving mode or the first driving assistance mode, etc., the PS_ECU23 remains in standby.

On the other hand, if it is determined in step S101 that the current driving mode is the automatic driving mode, the PS_ECU 23 proceeds to step S102 and checks whether the steering direction by the electric motor 28 has just been reversed due to the steering control of the automatic driving.

If it is determined in step S102 that the steering direction by the electric motor 28 has not immediately been reversed, the PS_ECU 23 returns to step S101.

On the other hand, if it is determined in step S102 that the steering direction by the electric motor 28 has just been reversed, the PS_ECU 23 proceeds to step S103 and checks whether a predetermined change in steering torque has been detected by the steering torque sensor 32. That is, in steering control, when the steering direction by the electric motor 28 is reversed by steering back, the meshing of each gear pair 61, 70 is released and the steering torque changes suddenly with respect to the motor rotation angle θ. After that, when the steering in the reverse direction by the electric motor 28 proceeds, the opposite tooth surfaces of each gear pair 61, 70 mesh with each other, causing the steering torque to change (suddenly change) again. In step S103, the PS_ECU 23 determines whether the steering torque has changed suddenly again in this way. Note that the sudden change in steering torque can be determined based on the actual measured value of the steering torque, but it can also be determined, for example, by whether the differential value of the steering torque with respect to the motor rotation angle θ is equal to or greater than a preset threshold value.

If it is determined in step S103 that a change in the specified steering torque has not been detected, the PS_ECU 23 continues to wait.

On the other hand, if it is determined in step S103 that a change in the predetermined steering torque has been detected, the PS_ECU 23 proceeds to step S104 and checks whether the driver has not gripped the steering wheel 55 between the time the steering direction was reversed and the time the change in the predetermined steering torque was detected.

If it is determined in step S104 that the driver is gripping the steering wheel 55, the PS_ECU 23 returns to step S101.

On the other hand, if it is determined in step S104 that the driver is not gripping the steering wheel 55, the PS_ECU 23 proceeds to step S105. In step S105, the PS_ECU 23 acquires the rotation angle θA of the electric motor 28 from when the steering direction by the electric motor 28 is reversed by steering back and the steering torque sensor 32 detects a sudden change in steering torque until a predetermined sudden change in steering torque is detected again, based on the signal from the motor rotation angle sensor.

That is, for example, as shown in FIG. 6, when the steering direction by the electric motor 28 is reversed by steering back, the meshing between the tooth surfaces of each gear pair 70, 61 is released, and the steering torque detected by the steering torque sensor 32 changes suddenly with respect to the motor rotation angle θ. Then, when the steering in the reverse direction by the electric motor 28 proceeds, each gear pair 70, 61 goes through backlash, and the meshing between the tooth surfaces on the opposite side to the previous tooth surfaces starts. At this time, the steering torque detected by the steering torque sensor 32 changes suddenly again. As is clear from these, the rotation angle θA from when the steering direction by the electric motor 28 is reversed and the steering torque changes suddenly to when the steering torque changes again becomes a parameter indicating the current interval (backlash) between the tooth surfaces of the gear pairs 61, 70. In addition, when calculating the rotation angle θA, the rotation angle θA may be appropriately corrected by referring to a map or the like that is set in advance based on experiments, simulations, etc. for each driving condition (e.g., vehicle speed, steering speed, etc.).

Here, in order to improve the accuracy of the rotation angle θA, the PS_ECU 23 can repeat the process from step S101 to step S105 multiple times (a set number of times) and use the average of the rotation angles obtained multiple times as the final rotation angle θA. For example, the driving scene in which the rotation angle θA is obtained can be limited to driving on a straight road where the steering direction is gently and repeatedly reversed by feedback control, and by repeating the process from step S101 to step S105 in such a driving scene, it is possible to obtain a rotation angle θA with high accuracy.

When the process proceeds from step S105 to step S106, the PS_ECU 23 calculates the deterioration angle |Δθ| based on the acquired rotation angle θA. That is, a reference value θ0 of the rotation angle in a normal state before deterioration (e.g., at the time of shipment) is preset in the PS_ECU 23, and the PS_ECU 23 calculates the absolute value |Δθ| of the difference between the rotation angle θA and the reference value θ0 as the deterioration angle.

When the process proceeds from step S106 to step S107, the PS_ECU 23 checks whether the deterioration angle |Δθ| is equal to or greater than a first angle threshold θth1 that is set in advance. Here, the angle threshold θth1 is set in advance based on experiments, simulations, etc., and is a threshold for determining that each gear pair 70, 61 has deteriorated to a level (first deterioration level) that requires a predetermined angle compensation in order to perform steering control appropriately.

If it is determined in step S107 that the deterioration angle |Δθ| is less than the first angle threshold θth1, the PS_ECU 23 determines that the gear pairs 70, 61 are not in a deteriorated state, and the routine is exited.

On the other hand, if it is determined in step S107 that the deterioration angle |Δθ| is equal to or greater than the first angle threshold θth1, the PS_ECU 23 proceeds to step S108 and checks whether the deterioration angle |Δθ| is equal to or greater than a preset second angle threshold θth2. Here, the angle threshold θth2 is set in advance based on experiments, simulations, etc., and is a threshold for determining that each gear pair 70, 61 has deteriorated to a level (second deterioration level) at which it is difficult to perform appropriate steering control even if a predetermined angle compensation is performed. For this reason, the second angle threshold θth2 is set to a value greater than the first angle threshold θth1.

If it is determined in step S108 that the deterioration angle |Δθ| is less than the second angle threshold θth2, the PS_ECU 23 proceeds to step S109, determines that each gear pair 70, 61 has deteriorated to the first deterioration level, and then exits the routine.

On the other hand, if it is determined in step S108 that the deterioration angle |Δθ| is equal to or greater than the second angle threshold θth2, the PS_ECU 23 proceeds to step S110, where it determines that each gear pair 70, 61 has deteriorated to the second deterioration level, and then exits the routine.

Next, the motor drive control performed on the electric motor 28 will be described with reference to the flow chart of the motor drive control routine shown in FIG. 8. This routine is repeatedly executed at set time intervals by the PS_ECU 23.

When the routine starts, in step S201, the PS_ECU 23 checks whether the gear pair 70, 61 has deteriorated to the second deterioration level.

If it is determined in step S201 that the gear pair 70, 61 has not deteriorated to the second deterioration level, the PS_ECU 23 proceeds to step S204.

On the other hand, if it is determined in step S201 that the gear pair 70, 61 has deteriorated to the second deterioration level, the PS_ECU 23 proceeds to step S202 and prohibits driving assistance control. In other words, if the gear pair 70, 61 has deteriorated to the second deterioration level, it is difficult to perform appropriate steering control, so the PS_ECU 23 prohibits control using the first, second driving assistance mode, etc., even if the driving mode is selected in the travel_ECU 21.

In the next step S203, the PS_ECU 23 outputs a warning through the warning_ECU 25. This warning may, for example, notify the driver that proper steering control is difficult due to an abnormality caused by deterioration of the steering system, and/or prompt the driver to have the steering system repaired by a dealer or the like.

When proceeding from step S201 or step S203 to step S204, the PS_ECU 23 sets the motor base current value. For example, when the manual driving mode is selected as the driving mode, the PS_ECU 23 calculates the motor base current value according to the driver steering torque. Also, for example, when the first or second driving assistance mode is selected as the driving mode, the PS_ECU 23 calculates the motor base current value according to the driver steering torque and the target yaw rate, etc.

In the next step S205, the PS_ECU 23 calculates the feedback current value. That is, for example, when the first or second driving assistance mode is set as the driving mode, the PS_ECU 23 calculates the feedback current value based on the difference between the yaw rate detected by the yaw rate sensor 35 and the target yaw rate.

Then, when the process proceeds from step S205 to step S206, the PS_ECU 23 checks whether the gear pair 70, 61 is in a deterioration state of the first deterioration level.

If it is determined in step S206 that the deterioration state is at the first deterioration level, the PS_ECU23 proceeds to step S208.

On the other hand, if it is determined in step S206 that the gear pair 70, 61 is not in a degraded state of the first degradation level, the PS_ECU 23 proceeds to step S207 and checks whether the gear pair 70, 61 is in a degraded state of the second degradation level.

If it is determined in step S207 that the deterioration state is not at the second deterioration level, the PS_ECU23 proceeds to step S210.

On the other hand, if it is determined in step S207 that the deterioration state is at the second deterioration level, the PS_ECU23 proceeds to step S208.

When the process proceeds from step S206 or step S207 to step S208, the PS_ECU 23 checks, based on the directions of the driver steering torque and the motor steering torque, whether the steering direction of the steering mechanism 51 has just been reversed by steering back.

If it is determined in step S208 that the steering direction has not immediately reversed, the PS_ECU23 proceeds to step S210.

On the other hand, if it is determined in step S208 that the steering direction has just been reversed, the PS_ECU 23 calculates an angle compensation current value for the deterioration of each gear pair 70, 61, and then proceeds to step S210. That is, when the steering direction is reversed, the PS_ECU 23 calculates a current value for pre-rotating the electric motor 28 in the new steering direction by an amount corresponding to an increase in backlash due to deterioration of each gear pair 70, 61. This angle compensation current value is calculated, for example, based on the most recent deterioration angle |Δθ| calculated in the deterioration determination routine described above. Alternatively, the angle compensation current value may be a fixed value that is preset according to, for example, the deterioration level.

When the process proceeds from step S207, step S208, or step S209 to step S210, the PS_ECU 23 calculates the drive current value for the electric motor 28 by adding up the above-mentioned current values, drives the electric motor 28 with the calculated drive current value, and then exits the routine. That is, if the feedback current value and the angle compensation current value have been calculated, the PS_ECU 23 calculates the drive current value by appropriately adding these current values to the motor base current value.

According to this embodiment, when the vehicle is traveling and the driving assistance control (steering control) is being executed, and the touch sensor 36 does not detect the driver's grip on the steering wheel 55, the PS_ECU 23 acquires the rotation angle θA of the electric motor 28 from the time when the steering direction of the electric motor 28 is reversed by the steering control and the steering torque sensor 32 detects a sudden change in steering torque until the sudden change in steering torque is detected again, based on the output of the motor rotation angle sensor 37, calculates the difference between the rotation angle θA and a preset reference value θ0 as the deterioration angle |Δθ|, and determines that the gear pair 70, 61 is deteriorated when the deterioration angle |Δθ| is abnormal to the preset first angle threshold value θth1, thereby making it possible to perform deterioration determination with high accuracy without causing discomfort to the occupants.

That is, by setting the conditions that the vehicle is traveling with driving assistance control (steering control) being executed and the touch sensor 36 is not detecting the driver's grip on the steering wheel 55, deterioration determination can be performed in a state where only the motor steering torque is detected by the steering torque sensor 32. Therefore, no steering is performed for deterioration determination while the vehicle 1 is stopped, and deterioration determination can be realized without causing discomfort to the occupants.

In addition, the rotation angle θA of the electric motor 28 is obtained from when the steering direction of the electric motor 28 is reversed by the steering control and the steering torque sensor 32 detects a sudden change in steering torque until the sudden change in steering torque is detected again, and the difference between the rotation angle θA and the reference value θ0 is calculated as the deterioration angle |Δθ|. The deterioration judgment of each gear pair 70, 61 is performed based on the calculated deterioration angle |Δθ|, so there is no need to assume that the wheels are maintained in a fixed position on the road surface, and deterioration judgment can be achieved with high accuracy.

In this case, when the gear pair 70, 61 is at the first deterioration level, the PS_ECU 23 performs angle correction (angle compensation) on the rotation angle of the electric motor 28 to cancel the deterioration angle |Δθ|, thereby maintaining a high level of controllability of the steering control.

More specifically, the PS_ECU 23 performs angle correction when the steering direction by the electric motor 28 is reversed, thereby enabling steering control to be performed while appropriately eliminating backlash caused by deterioration over time.

In addition, when the gear pair 70, 61 reaches a second deterioration level, which is more deteriorated than the first deterioration level, steering control is prohibited and a warning is issued to the occupant, thereby maintaining a high level of reliability of steering control.

In the above embodiment, the first driving environment recognition unit 11d of the camera unit 11, the locator unit 12, the driving_ECU 21, the E/G_ECU 22, the PS_ECU 23, the BK_ECU 24, the alarm_ECU 25, etc. are configured with a well-known microcomputer equipped with a CPU, RAM, ROM, a non-volatile storage unit, etc., and its peripheral devices, and the ROM stores programs to be executed by the CPU and fixed data such as data tables in advance. Note that all or part of the functions of the processor may be configured with logic circuits or analog circuits, and the processing of various programs may be realized by electronic circuits such as FPGAs.

The invention described in the above embodiment is not limited to the embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention.

1 ... Vehicle (own vehicle)
10 ... driving support device 11 ... camera unit 11a ... main camera 11b ... sub camera 11c ... IPU
Reference Signs List 11d ... first driving environment recognition unit 12 ... locator unit 13 ... locator calculation unit 13a ... map information acquisition unit 13b ... second driving environment recognition unit 14 ... acceleration sensor 14 ... longitudinal acceleration sensor 15 ... wheel speed sensor 16 ... gyro sensor 17 ... GNSS receiver 18 ... high-precision road map database 21 ... driving_ECU
22...E/G_ECU
23 ... PS_ECU
24 … BK_ECU
25 ... Alarm_ECU
Reference Signs List 27 ... throttle actuator 28 ... electric motor 28a ... motor shaft 29 ... brake actuator 30 ... warning device 31 ... mode changeover switch 32 ... steering torque sensor 33 ... brake sensor 34 ... accelerator sensor 35 ... yaw rate sensor 36 ... touch sensor 37 ... motor rotation angle sensor 50 ... electric power steering device 51 ... steering mechanism 55 ... steering wheels 56L, 56R ... left and right front wheels 57 ... steering gear box 58 ... steering shaft 59 ... pinion shaft 59a ... torsion bar 60 ... front knuckle 61 ... gear pair 62 ... rack gear 63 ... pinion gear 65 ... intermediate shaft 66 ... universal joint 67 ... steering shaft 68 ... universal joint 69 ... steering column 70 ... gear pair 71 ... worm wheel gear 72 ... worm gear

Claims (5)

a steering mechanism that transmits a driver steering torque input to a steering wheel to a steering shaft;
an electric motor that generates a motor steering torque;
a gear pair that transmits the motor steering torque to the steered shaft;
a steering control means capable of executing steering control that does not require a driver to grip the steering wheel through drive control of the electric motor;
a steering torque detection means for detecting a driver steering torque input to the steering mechanism;
a gripping state detection means for detecting a gripping state of the steering wheel by a driver;
a motor rotation angle detection means for detecting a rotation angle of the electric motor;
a deterioration determination means for determining deterioration of the gear pair,
The deterioration determination means, when the steering control is being executed and the driver's grip on the steering wheel is not detected by the grip state detection means, obtains, based on the output of the motor rotation angle detection means, a rotation angle of the electric motor from when the steering direction is reversed due to the electric motor being turned back by the steering control and when the steering torque detection means detects a sudden change in the steering torque until the steering torque change is detected again, calculates a difference between the rotation angle and a preset reference value as a deterioration angle, and determines that the gear pair is deteriorated when the deterioration angle is equal to or greater than a preset first threshold value. The electric power steering device according to claim 1, characterized in that, when the deterioration determination means determines that the gear pair is deteriorated, the steering control means performs an angle correction on the rotation angle of the electric motor to cancel out the deterioration angle. The electric power steering device according to claim 2, characterized in that the steering control means performs the angle correction when the steering direction by the electric motor is reversed. The electric power steering device according to any one of claims 1 to 3, characterized in that the steering control means prohibits the steering control when the deterioration angle becomes equal to or greater than a second threshold value that is greater than the first threshold value. The electric power steering device according to claim 4, further comprising a warning means for warning an occupant when the deterioration angle is equal to or greater than the second threshold value.

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