Vehicle steering assistance device

Abstract

To provide a steering assistance device for a vehicle, by which both controllability of steering assistance control and steering feeling of a driver can be achieved.SOLUTION: When a target steering torque calculation unit 32b is in an active state, a DSS_ECU 11 switches an assist steering torque calculation unit 31a from an active state to a non-active state through an assist steering torque output control unit 33 to limit output of assist steering torque. Meanwhile, in a case where a condition in which a steering is held with a handle 4 by a driver is detected even when the target steering torque calculation unit 32b is in an active state, the ECU switches the assist steering torque calculation unit 31a from a non-active state to an active state through the assist steering torque output control unit 33.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steering assist device for a vehicle that applies an assist steering torque to a steering system in response to steering by a driver when driving assist control is in an inactive state. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known a so-called electric power steering device (EPS) that assists the steering force exerted by a driver by using an assist steering torque generated by an electric motor.

[0003] Also known is lane keeping assist (ALK) control, which provides steering assistance by setting a predetermined position on the lane (e.g., the center of the lane) as a target driving trajectory and generating a target steering torque by an electric motor so that the vehicle drives along the target driving position.

[0004] In recent years, steering assist devices have become capable of maintaining the active state of steering assist control even when the driver takes his / her hands off the steering wheel. When the driver grips the steering wheel and applies a steering torque of a predetermined level or more to the steering system, such driving assist devices determine an override, transition the steering assist control to a non-active state, and apply only the assist steering torque by the electric power steering control to the steering system.

[0005] Incidentally, even in steering assist control such as lane keeping assist (ALK) control, when the electric motor is driven, the steering system on the steering wheel side rotates at the same time, so the steering torque sensor is affected by the frictional force (static frictional force) of the steering system. That is, when the target steering torque is transmitted to the steering system, due to the influence of the static frictional force of the steering system, the steering torque sensor detects a torque value in the opposite direction to the steering direction by the steering assist control as the steering torque by the driver. Then, when such a torque value is detected, an assist steering torque in a direction that offsets the target steering torque calculated in the steering assist control is calculated in the electric power steering control.

[0006] In order to prevent the generation of unnecessary assist steering torque during such steering assist control and improve controllability during steering assist control, for example, Patent Document 1 discloses a technique for substantially deactivating electric power steering control from the time when steering assist control becomes active until override is determined. Here, the technique of Patent Document 1 compares the steering torque detected by a steering torque sensor due to the driver's steering wheel operation with a steering reaction torque set by referring to a map or the like based on the steering angle detected by a steering angle sensor and the vehicle speed detected by a vehicle speed sensor, and determines that an override has occurred if the steering torque exceeds the steering reaction torque. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-171224 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, as with the technology disclosed in Patent Document 1 mentioned above, if the electric power steering control is inactive from the time when the driving assist control becomes active until an override is determined, no assist steering torque is generated in response to the driver's steering wheel operation from the time when the driver starts steering until an override is determined, which may temporarily make the steering wheel operation heavier and deteriorate the steering feeling.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a steering assist device for a vehicle that can achieve both the controllability of the steering assist control and the steering feeling for the driver. [Means for solving the problem]

[0010] A vehicle steering assist device according to one aspect of the present invention includes a steering torque detection means for detecting a steering torque caused by a driver's steering wheel operation, an assist steering torque calculation means for calculating an assist steering torque for the steering torque, and a target steering torque calculation means for calculating a target steering torque for performing steering assist control independent of the driver's steering wheel steering. before The assist steering torque calculation means of Active State and Inactive state And switching Rthe steering assist execution determination means for determining whether to switch between an active state and an inactive state of the target steering torque calculation means, when the target steering torque calculation means is in an active state and the steering assist execution determination means has not detected a state in which the driver has held the steering wheel, the assist steering torque output control means maintains the active state of the target steering torque calculation means to permit input of the target steering torque calculated by the target steering torque calculation means to the EPS torque setting means, while setting the assist steering torque calculation means to an inactive state and prohibiting input of the assist steering torque calculated by the assist steering torque calculation means to the EPS torque setting means, thereby causing the EPS torque setting means to input the target steering torque calculated by the assist steering torque calculation means to the EPS torque setting means. The assist steering torque output control means, when the target steering torque calculation means is in an active state and the steering detection means has detected a state in which the driver is steering the steering wheel, maintains the active state of the target steering torque calculation means and permits input of the target steering torque calculated by the target steering torque calculation means to the EPS torque setting means, while switching the assist steering torque calculation means from an inactive state to an active state and permits input of the assist steering torque calculated by the assist steering torque calculation means to the EPS torque setting means, thereby causing the EPS torque setting means to set a value obtained by adding the assist steering torque to the target steering torque as the EPS torque, and the steering assistance execution determination means, when a steering torque detection means detects a steering torque equal to or greater than a set value while the driver is steering the steering wheel, switches the target steering torque calculation means from an active state to an inactive state. Effect of the Invention

[0011] According to the vehicle steering assist device of the present invention, it is possible to achieve both the controllability of the steering assist control and the steering feeling for the driver. [Brief description of the drawings]

[0012] [Figure 1] Schematic diagram of a vehicle equipped with a steering assist device [Diagram 2] Functional block diagram of steering assist device [Diagram 3] Flowchart showing the EPS torque setting routine (part 1) [Figure 4] Flowchart showing EPS torque setting routine (part 2) [Diagram 5] FIG. 1A is a time chart of a torque sensor value detected by a torque sensor, FIG. 1B is a time chart of a steering angle detected by a steering angle sensor, and FIG. 1C is a time chart of an assist steering torque calculated in an assist steering torque calculation unit. [Figure 6] 1A is a time chart of a target steering torque calculated in a target steering torque calculation unit, FIG. 1B is a time chart of a steering angle detected by a steering angle sensor, FIG. 1C is a time chart of a torque sensor value detected by a torque sensor, and FIG. 1D is a time chart of an assist steering torque calculated in an assist steering torque calculation unit. [Figure 7] FIG. 1A is a time chart of a steering angle detection sensor value detected by a steering angle detection sensor; FIG. 1C is a time chart of an assist steering torque after output control; FIG. 1D is a time chart of a target steering torque calculated by a target steering torque calculation unit; and FIG. 1E is a time chart of a steering angle detected by a steering angle sensor. [Figure 8] FIG. 1A is a time chart of a steering angle detection sensor value detected by a steering angle detection sensor according to a comparative example; FIG. 1C is a time chart of an assist steering torque; FIG. 1D is a time chart of a target steering torque calculated by a target steering torque calculation unit; and FIG. 1E is a time chart of a steering angle detected by a steering angle sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An embodiment of the present invention will be described below with reference to the drawings. Note that, in the following, ALK control will be described as an example of steering assist control.

[0014] In Fig. 1, a vehicle (own vehicle) 1 has left and right front wheels FL, FR and left and right rear wheels RL, RR. The left and right front wheels FL, FR are drive wheels and are connected to a steering mechanism 2 such as a rack and pinion mechanism via a tie rod 3. A steering shaft 5 having a handlebar 4 fixed to its tip is also connected to the steering mechanism 2. When the driver operates the handlebar 4, the front wheels FL, FR are steered via the steering mechanism 2.

[0015] In addition, an EPS motor 7 of an electric power steering (EPS) device 6 is connected to the steering shaft 5 via a transmission mechanism (not shown). The EPS device 6 has the EPS motor 7 and an EPS control unit (EPS_ECU) 8, and the EPS_ECU 8 controls the assist torque (EPS torque) applied by the EPS motor 7 to the steering shaft 5. The EPS_ECU 8 is connected to a DSS_ECU 11 via an in-vehicle network using, for example, CAN (Controller Area Network) communication or the like.

[0016] The EPS_ECU8 basically sets an assist torque for assisting the steering torque applied by the driver to the steering wheel 4 when the steering assist control is inactive, according to a drive signal from the DSS_ECU11. On the other hand, when the ALK control is active, a command signal corresponding to the assist torque set by the DSS_ECU11 is sent to the EPS_ECU8, and the EPS_ECU8 generates a predetermined assist torque in the EPS motor 7, so that the host vehicle 1 runs while tracing a target travel path (for example, the center of the lane) described below. Although not shown, in addition to the EPS_ECU8 and the DSS_ECU11, units for controlling the running state of the host vehicle 1, such as an engine control unit, a transmission control unit, and a vehicle dynamics control (VDC) unit including brake control, are connected to the in-vehicle network so as to be able to communicate with each other, and these control units are mainly composed of a microcomputer equipped with, for example, a CPU, a RAM, a ROM, etc.

[0017] The DSS_ECU 11 receives signals from sensors that detect the behavior of the vehicle 1, such as a steering angle sensor 12 attached to the steering shaft 5 to detect the steering angle of the steering wheel 4, a yaw rate sensor 13 to detect the yaw rate acting on the vehicle 1, a vehicle speed sensor 14 to detect the vehicle speed, an EPS motor rotation angle sensor 15 to detect the rotation angle of the EPS motor 7, a steering torque sensor 16 as a steering torque detection means that detects the steering torque applied to the steering wheel 4 by the driver from the torsion angle of the torsion bar 5a attached to the steering shaft 5, and a steering detection sensor 17 composed of a touch sensor or the like provided on the steering wheel 4 and serving as a steering detection means that detects whether the driver is holding the steering wheel, as various parameters required when performing ALK control.

[0018] On the other hand, reference numeral 21 denotes a forward recognition device, which is mainly composed of a microcomputer equipped with a CPU, RAM, ROM, etc., and has an on-board camera composed of a stereo camera consisting of a main camera 22a and a sub-camera 22b, and processes the image captured by this on-board camera 22 to generate image information necessary for ALK control.

[0019] The cameras 22a and 22b are installed horizontally at equal intervals from the center of the vehicle width direction at a position close to the windshield, for example, at the front of the vehicle. Each of the cameras 22a and 22b is provided with an image pickup element such as a CCD or a CMOS, and these image pickup elements capture a three-dimensional image of the driving environment ahead in the traveling direction, including the driving lane in which the vehicle is traveling. In this embodiment, the driving lane of the vehicle 1 and three-dimensional objects including a preceding vehicle, obstacles, etc. are recognized based on the image data captured by the vehicle-mounted camera 22. Therefore, as long as they can recognize these, a millimeter wave radar, an infrared laser radar, etc. may be adopted instead of the vehicle-mounted camera 22, or a combination of these may be used.

[0020] The forward recognition device 21 converts a pair of analog images captured by the cameras 22a and 22b into digital images of a predetermined brightness level, generates reference image data from the output signal of the main camera 22a, and generates comparison image data from the output signal of the sub-camera 22b. Then, based on the parallax between the reference image data and the comparison image data, it calculates three-dimensional information of the same object in both images, that is, the distance from the vehicle to the object. The forward recognition device 21 recognizes the left and right lane lines based on the generated image data, and calculates the width (diagonal line width) W between the lane lines. The on-board camera 22 may be a monocular camera, in which case three-dimensional information can be obtained using a well-known motion stereo method or the like.

[0021] As shown in FIG. 2, the DSS_ECU 11 has, as functions for executing ALK control, a power steering assist control unit (hereinafter referred to as the "PSA control unit") 31, a steering assist control unit 32, an assist steering torque output control unit 33 as an assist steering torque output control means, and a torque addition unit 34 as an EPS torque setting means.

[0022] Furthermore, the PSA control unit 31 is configured to have an assist steering torque calculation unit 31a as an assist steering torque calculation means. On the other hand, the steering assist control unit 32 is configured to have a target steering angle calculation unit 32a, a target steering torque calculation unit 32b as a target steering torque calculation means, and a steering assist execution determination unit 32c as a steering assist execution determination means.

[0023] The assist steering torque calculation unit 31a of the PSA control unit 31 calculates an assist steering torque as an assist control amount corresponding to the driver's steering operation based on the vehicle speed of the vehicle 1 detected by the vehicle speed sensor 14, the steering torque (torque sensor value) detected by the steering torque sensor 16, and the rotation angle of the EPS motor 7 detected by the EPS motor rotation angle sensor 15.

[0024] In addition, the steering assist control unit 32 performs steering assist control (ALK control) so that the host vehicle 1 travels along a target driving trajectory set in the driving lane ahead of the host vehicle 1, and the target steering angle calculation unit 32a calculates the target steering angle required for the host vehicle 1 to travel along the target driving trajectory based on image data from the forward recognition device 21, the vehicle speed of the host vehicle 1 detected by the vehicle speed sensor 14, and the yaw rate detected by the yaw rate sensor 13.

[0025] Further, the target torque calculation unit 32b calculates a target steering torque for driving the EPS motor 7 in accordance with the target steering angle calculated by the target steering angle calculation unit 32a.

[0026] Furthermore, the steering assist execution determination unit 32c determines to start execution of steering assist control (ALK control) when, for example, a steering assist control switch (not shown) provided on the steering wheel 4 is turned on by the driver. On the other hand, when the steering wheel holding detection sensor 17 detects that the driver is holding the steering wheel 4 during execution of the steering assist control, the steering assist execution determination unit 32c compares the steering torque associated with the driver's steering wheel operation detected by the steering torque sensor 16 with the steering angle detected by the steering angle sensor 12 and the steering reaction torque set based on the vehicle speed detected by the vehicle speed sensor 14. Then, when the steering torque exceeds the steering reaction torque, the steering assist execution determination unit 32c determines an override and determines to prohibit execution of the steering assist control (ALK control).

[0027] On the other hand, the assist steering torque output control unit 33 checks whether ALK control is in progress or not, or whether the steering wheel 4 is being maintained by the driver even during ALK control, and sets the assist steering torque to active or inactive based on the results.

[0028] Incidentally, the calculations in the above-mentioned assist steering torque calculation unit 31a, target steering angle calculation unit 32a, target steering torque calculation unit 32b, and steering assist execution determination unit 32c are well known, so detailed explanations will be omitted.

[0029] The EPS torque set in the DSS_ECU 11 is specifically set in accordance with an EPS torque setting routine shown in FIGS.

[0030] This routine is repeatedly executed at set time intervals. When the routine starts, the DSS_ECU 11 first detects parameters required for calculating the EPS torque from the sensor signals from the sensors 12-17.

[0031] Next, the process proceeds to step S102, where the DSS_ECU 11 calculates an assist steering torque for the driver's steering operation based on, for example, the vehicle speed of the host vehicle 1 detected by the vehicle speed sensor 14, the steering torque detected by the steering torque sensor 16, and the rotation angle of the EPS motor 7 detected by the EPS motor rotation angle sensor 15. Note that this step S102 corresponds to the process executed by the assist steering torque calculation unit 31a.

[0032] On the other hand, when the process proceeds from step S101 to step S103, the DSS_ECU 11 estimates the running state of the host vehicle 1 based on the steering angle detected by the steering angle sensor 12, the yaw rate detected by the yaw rate sensor 13, and the vehicle speed detected by the vehicle speed sensor 14, and also estimates the state of the lane ahead of the host vehicle 1 from image data acquired by the forward recognition device 21. Then, the DSS_ECU 11 calculates a target steering angle based on the running state of the host vehicle 1 and the state of the lane ahead of the host vehicle 1. Note that this step S103 corresponds to the process executed by the target steering angle calculation 32a.

[0033] Next, the process proceeds to step S104, where the DSS_ECU 11 calculates a target steering torque for converging the steering angle detected by the steering angle sensor 12 to the target steering angle, for example, by feedback control or the like. Note that this step S104 corresponds to the process executed by the target steering torque calculation unit 32b.

[0034] Next, the process proceeds to step S105, where the DSS_ECU 11 performs a determination as to whether or not to operate the steering assist control. That is, for example, when the steering assist control switch provided on the steering wheel 4 is turned on by the driver, the DSS_ECU 11 performs a determination as to whether or not to start the execution of the steering assist control (determination as to whether or not to activate the driving assist control). On the other hand, when the steering wheel holding detection sensor 17 detects that the driver is holding the steering wheel 4 during the execution of the steering assist control, the DSS_ECU 11 compares the steering torque associated with the steering wheel operation of the driver detected by the steering torque sensor 16 with the steering angle detected by the steering angle sensor 12 and the steering reaction torque set based on the vehicle speed detected by the vehicle speed sensor 14. Then, when the steering torque exceeds the steering reaction torque, the DSS_ECU 11 performs a determination as to whether or not to override and to prohibit the execution of the steering assist control (determination as to whether or not to deactivate the driving assist control). Note that this step S105 corresponds to the processing executed by the steering assist execution determination unit 32c.

[0035] Next, the process proceeds to step S106, where the DSS_ECU 11 determines whether or not the steering assist control is currently in an active state.

[0036] Then, when it is determined in step S106 that the steering assist control is not in the inactive state, the DSS_ECU 11 jumps to step S108.

[0037] On the other hand, when the DSS_ECU 11 determines in step S106 that the steering assist control is in the active state, the process proceeds to step S107, where the DSS_ECU 11 outputs the target steering torque calculated in step S104, and then proceeds to step S108. Note that steps S104, S106, and S107 correspond to the processes executed by the target steering torque calculation unit 32b.

[0038] When the process proceeds from step S102, step S106, or step S107 to step S08, the DSS_ECU 11 determines whether or not the steering assist control is currently in an active state based on the determination in the above-mentioned step S105.

[0039] Then, when it is determined in step S108 that the steering assist control is not in the inactive state, the DSS_ECU 11 proceeds to step S117.

[0040] On the other hand, when the DSS_ECU 11 determines in step S108 that the steering assist control is in the active state, the process proceeds to step S109, where it checks whether or not the driver is currently maintaining the steering wheel 4, based on a signal from the maintaining steering detection sensor 17. Note that steps S108 to step S123 shown below correspond to the processes executed by the assist steering torque output control unit 33.

[0041] If the DSS_ECU 11 determines in step S109 that the driver is maintaining the steering angle, the process proceeds to step S117, and if the DSS_ECU 11 determines that the driver is not maintaining the steering angle, the process proceeds to step S110.

[0042] When proceeding from step S109 to step S110, the DSS_ECU 11 makes the assist steering torque control inactive by, for example, prohibiting the input of the assist steering torque from the assist steering torque calculation unit 31a to the assist steering torque output control unit 33.

[0043] Next, the process proceeds to step S111, where the DSS_ECU 11 checks whether or not a flag Fdec for gradually reducing the assist steering torque output during a transition period after the assist steering torque control becomes inactive is set to "1".

[0044] If the DSS_ECU 11 determines in step S111 that the flag Fdec is set to "1", the process proceeds to step S112, and if the DSS_ECU 11 determines that the flag Fdec is cleared to "0", the process jumps to step S124.

[0045] When the process proceeds from step S111 to step S112, the DSS_ECU 11 checks whether or not the assist steering torque control has just been switched from the active state to the inactive state.

[0046] If it is determined in step S112 that the state has not just been switched to the inactive state, the DSS_ECU 11 jumps to step S114.

[0047] On the other hand, if the DSS_ECU 11 determines in step S112 that the state has just been switched to the inactive state, the process proceeds to step S113, where the flag Fdec is set to "1", and the process proceeds to step S114.

[0048] When the process proceeds from step S112 or step S113 to step S114, the DSS_ECU 11 performs a gradual reduction process for reducing the previous assist steering torque using a preset gradual reduction rate.

[0049] Next, in step S115, the DSS_ECU 11 checks whether the gradual reduction process for the assist steering torque has been completed.

[0050] If the DSS_ECU 11 determines in step S115 that the gradual decrease process has not ended, the DSS_ECU 11 jumps to step S124.

[0051] On the other hand, when the DSS_ECU 11 determines in step S115 that the gradual reduction process has ended, the process proceeds to step S116, where the flag Fdec is cleared to "0", and the process proceeds to step S124. In this determination, for example, when the assist steering torque becomes zero, the process determines that the gradual reduction process has ended.

[0052] Furthermore, when the process proceeds from step S108 or step S109 to step S117, the DSS_ECU 11 activates the assist steering torque control by, for example, permitting input of the assist steering torque from the assist steering torque calculation unit 31a to the assist steering torque output control unit 33.

[0053] Next, the process proceeds to step S118, where the DSS_ECU 11 checks whether or not a flag Finc for gradually increasing the assist steering torque output during a transition period after the assist steering torque control becomes active is set to "1".

[0054] If the DSS_ECU 11 determines in step S118 that the flag Finc is set to "1", the process proceeds to step S119, and if the DSS_ECU 11 determines that the flag Finc is cleared to "0", the process jumps to step S124.

[0055] When the process proceeds from step S118 to step S119, the DSS_ECU 11 checks whether or not the assist steering torque control has just been switched from the inactive state to the active state.

[0056] If it is determined in step S119 that the state has not just been switched to the active state, the DSS_ECU 11 jumps to step S121.

[0057] On the other hand, if the DSS_ECU 11 determines in step S119 that the state has just been switched to the active state, the process proceeds to step S120, where the flag Finc is set to "1", and the process proceeds to step S121.

[0058] When the process proceeds to step S119 or step S121 from step S120, the DSS_ECU 11 performs a gradual increase process for increasing the previous assist steering torque at a preset gradual increase rate.

[0059] Next, in step S122, the DSS_ECU 11 checks whether the gradual increase process for the assist steering torque has ended.

[0060] If the DSS_ECU 11 determines in step S122 that the gradual increase process has not ended, the DSS_ECU 11 jumps to step S124.

[0061] On the other hand, when the DSS_ECU 11 determines in step S122 that the gradual increase process has ended, the process proceeds to step S123, where the flag Finc is cleared to "0", and the process proceeds to step S124. In this determination, for example, when the gradually increased assist steering torque matches the assist steering torque input from the assist steering torque calculation unit 31a, the process determines that the gradual increase process has ended.

[0062] When the process proceeds from step S111, step S115, step S116, step S118, step S122, or step S123 to step S124, the DSS_ECU 11 outputs the sum of the target steering torque output from the target steering torque calculation unit 32b and the assist steering torque output from the assist steering torque output control unit 33 as the final assist torque (EPS torque), and then exits the routine. Note that step S124 corresponds to the process executed by the torque addition unit 34.

[0063] That is, when the process proceeds from step S111 to step S124, the target steering torque output from the target steering torque calculation section 32b is output as is as the EPS torque.

[0064] Also, when the process proceeds from step S116 to step S124, the value obtained by adding the gradually decreasing value of the assist steering torque just before the assist steering torque control becomes inactive to the target steering torque output from the target steering torque calculation unit 32b is output as the EPS torque.

[0065] Also, when the process proceeds from step S115 to step S124, a value obtained by adding a value obtained by gradually decreasing the previous assist steering torque to the target steering torque output from the target steering torque calculation unit 32b is output as the EPS torque.

[0066] Also, when the process proceeds from step S118 to step S124, the value obtained by adding the assist steering torque output from the assist steering torque calculation unit 31a to the target steering torque output from the target steering torque calculation unit 32b is output as the EPS torque.

[0067] Also, when the process proceeds from step S123 to step S124, a value obtained by gradually increasing the assist steering torque (=zero) to the target steering torque output from the target steering torque calculation unit 32b is output as the EPS torque.

[0068] Also, when the process proceeds from step S122 to step S124, a value obtained by subtracting a value obtained by gradually increasing the previous assist steering torque from the target steering torque output from the target steering torque calculation unit 32b is output as the EPS torque.

[0069] Next, the torques that are set in the above-mentioned EPS torque setting routine will be described with reference to FIGS.

[0070] For example, when the target steering torque calculation unit 32b is in an inactive state, the assist steering torque calculation unit 31a calculates the assist steering torque (see FIG. 5(c)) according to the steering torque (torque output value: see FIG. 5(a)) by the driver and the steering angle (see FIG. 5(b)).

[0071] Also, for example, when the target steering torque calculation unit 32b is in an active state, the target steering torque calculation unit 32b calculates a target steering torque (see FIG. 6(a)) for converging the steering angle (see FIG. 6(b)) detected by the steering angle sensor to the target steering angle. When steering control is performed using such a target steering torque, the steering torque sensor 16 detects a steering torque (torque sensor value) in the opposite direction to the steering direction by the steering assist control due to the influence of static friction force of the steering system (see FIG. 6(b)). As a result, the assist steering torque calculation unit 31a calculates a steering assist torque in a direction that cancels out the target steering torque (see FIG. 6(c)).

[0072] In this embodiment, the assist steering torque calculated in the assist steering torque calculation unit 31a is output controlled in the assist steering torque output control unit 33, thereby achieving both the controllability of the steering assist control and the steering feeling for the driver.

[0073] That is, for example, in the section from timing t1 to t2 in which the steering wheel 4 is being steered by the driver (see FIG. 7(a)) and the target steering torque calculation unit 32b is inactive, the assist steering torque calculated by the assist steering torque calculation unit 31a in accordance with the steering torque detected by the steering torque sensor 16 (see FIG. 7(b)) is output as is as the ice steering torque after output control (see FIG. 7(c)).

[0074] In addition, in the section from timing t2 to t3 when the driver's hands are released from the steering wheel 4 (see FIG. 7(a)) and the target steering torque calculation unit 32b is in the active state (see FIG. 7(d)), the assist steering torque calculation unit 31a becomes inactive, and the assist steering torque after the output control is gradually decreased and then maintained at zero (see FIG. 7(c)). This makes it possible to prevent interference between the target steering torque and the assist steering torque, thereby improving the controllability of the steering support control.

[0075] Furthermore, when the target steering torque calculation unit 32b is in the active state (see FIG. 7(d)), at timing t3 when the driver holds the steering wheel 4 (see FIG. 7(a)), the assist steering torque calculation unit 31a becomes active again, and the assist steering torque after the output control is gradually increased to the assist steering torque calculated by the assist steering torque calculation unit 31a (see timing t3 to timing t4). After that, from timing t4 onwards, the assist steering torque after the output control is the assist steering torque calculated by the assist steering torque calculation unit 31a that is output as it is (see timing t4 onwards). As a result, even when the driver steers the steering wheel 4, the temporary heavy steering operation caused by the absence of the assist steering torque being output is eliminated.

[0076] Furthermore, when an override is determined (see timing t5), the target steering torque becomes inactive.

[0077] As shown in the comparative example of FIG. 8, when the assist steering torque is output as is, the target steering torque and the assist steering torque interfere with each other during steering assist control.

[0078] According to this embodiment, when the target steering torque calculation unit 32b is in an active state, the assist steering torque output control unit 33 switches the assist steering torque calculation unit 31a from an active state to an inactive state to limit the output of the assist steering torque, while when the target steering torque calculation unit 32b is in an active state but a state in which the driver is maintaining the steering wheel 4 is detected, the assist steering torque output control unit 33 switches the assist steering torque calculation unit 31a from an inactive state to an active state, thereby achieving both controllability of the steering assist control and steering feeling for the driver.

[0079] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible, which are also within the technical scope of the present invention. [Explanation of symbols]

[0080] 1 … Vehicle 2 … Steering mechanism 3 … Tie rod 4 … Handle 5 … Steering axis 5a … Torsion bar 6... Electric power steering device 7 ... EPS motor 8 … EPS_ECU 11 … DSS_ECU 12 ... Steering angle sensor 13 … Yaw rate sensor 14 ... Vehicle speed sensor 15 ... EPS motor rotation angle sensor 16 ... Steering torque sensor 17 … Steering wheel detection sensor 21 … Forward recognition device 22 … Car camera 22a … Main camera 22b … Sub camera 31 ... PSA control section 31a … Assist steering torque calculation unit 32 ... Steering assistance control unit 32a … Target steering angle calculation unit 32b … Target steering torque calculation unit 32c … Steering assistance execution determination unit 33 ... Assist steering torque output control section 34 … Torque adder

Claims

1. A steering torque detection means for detecting a steering torque generated by a driver's steering wheel operation; an assist steering torque calculation means for calculating an assist steering torque with respect to the steering torque; a target steering torque calculation means for calculating a target steering torque for performing steering assist control independently of a driver's steering wheel; an assist steering torque output control means for switching the assist steering torque calculation means between an active state and a non-active state; an EPS torque setting means for setting an EPS torque for driving an EPS motor based on an output from the target steering torque calculation means and an output from the assist steering torque output control means; A steering detection means for detecting a steering state of a driver; a steering assistance execution determination means for determining whether the target steering torque calculation means is switched between an active state and a non-active state; Equipped with when the target steering torque calculation means is in an active state and the steering detection means has not detected a state in which the driver is steering the steering wheel, the assist steering torque output control means maintains the active state of the target steering torque calculation means to permit input of the target steering torque calculated by the target steering torque calculation means to the EPS torque setting means, while setting the assist steering torque calculation means to an inactive state and prohibiting input of the assist steering torque calculated by the assist steering torque calculation means to the EPS torque setting means, thereby causing the EPS torque setting means to set a value equivalent to the target steering torque as the EPS torque, when the target steering torque calculation means is in an active state and the steering detection means has detected a state in which the driver has maintained the steering wheel in a held state, the assist steering torque output control means maintains the active state of the target steering torque calculation means and permits the target steering torque calculated by the target steering torque calculation means to be input to the EPS torque setting means, while switching the assist steering torque calculation means from a non-active state to an active state and permits the assist steering torque calculated by the assist steering torque calculation means to be input to the EPS torque setting means, thereby causing the EPS torque setting means to set a value obtained by adding the assist steering torque to the target steering torque as the EPS torque, The steering assist device for a vehicle, characterized in that the steering assist execution determination means switches the target steering torque calculation means from an active state to a non-active state when a steering torque detection means detects a steering torque equal to or greater than a set value while the driver is maintaining the steering wheel.

2. 2. The vehicle steering assist device according to claim 1, wherein the assist steering torque output control means gradually reduces an output to zero when the assist steering torque calculation means switches from an active state to an inactive state, and gradually increases an output from zero to the assist steering torque calculated by the assist steering torque calculation means when the assist steering torque calculation means switches from an inactive state to an active state.

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