Vehicle steering assist device

Abstract

The present invention provides a vehicle steering assist device capable of achieving both controllability of steering assist control and steering feeling of a driver. When a target steering torque calculation unit (32b) is in an activated state, a DSS_ECU (11) switches a power steering torque calculation unit (31a) from an activated state to an inactivated state by using a power steering torque output control unit (33) to limit the output of the power steering torque. On the other hand, even if the target steering torque calculation unit (32b) is in an activated state, when it is detected that the driver is holding a steering wheel (4), the power steering torque calculation unit (31a) is switched from an inactivated state to an activated state by using the power steering torque output control unit (33).

Description

Technical Field

[0001] The present invention relates to a steering assist device for a vehicle, which applies a power steering torque corresponding to the steering of a steering wheel by a driver to a steering system when a driving assist control is in an inactive state. Background Art

[0002] Conventionally, there is known a so-called electric power steering (EPS) system that assists the steering force when a driver operates a steering wheel with a power steering torque generated by an electric motor.

[0003] Also known is lane keeping assist (ALK) control that sets a predetermined position of a lane (for example, the center of the lane) as a target driving trajectory and generates a target steering torque using an electric motor to assist steering so that the vehicle travels along the target driving position.

[0004] In recent years, in a steering assist device, the steering assist control can be kept activated even when the driver takes his hands off the steering wheel. Moreover, in such a driving assist device, when the driver holds the steering wheel and applies a steering torque exceeding a predetermined value to the steering system, it is determined as an override and the steering assist control is transferred to an inactive state, and only the power steering torque based on the electric power steering control is applied to the steering system.

[0005] However, even in the steering assist control such as the lane keeping assist (ALK) control, the steering system on the steering wheel side is rotated simultaneously when the electric motor is driven, so the steering torque sensor is affected by the friction force (static friction force) of the steering system. That is, if the target steering torque is transmitted to the steering system, the steering torque sensor detects a torque value in the opposite direction to the steering direction of the steering assist control as the steering torque based on the driver due to the influence of the static friction force of the steering system. And, if such a torque value is detected, the power steering torque 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 power steering torque during such steering assist control and thus improve the controllability during steering assist control, for example, Patent Document 1 discloses a technique in which the electric power steering control is actually inactivated from the time when the steering assist control becomes activated until it is determined to be overridden. Here, in the technique of Patent Document 1, the steering torque detected by the steering torque sensor through the driver's steering wheel operation is compared with the steering reaction torque set by reference to a map or the like based on the steering angle detected by the steering angle sensor and the vehicle speed detected by the vehicle speed sensor, and overriding is determined when the steering torque exceeds the steering reaction torque.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-171224 Summary of the invention

[0010] Technical issues

[0011] However, as in the technology disclosed in the above-mentioned patent document 1, when the electric power steering control is made inactive from the time the driving assistance control becomes active until it is determined to be over-control, no power steering torque is generated in response to the driver's steering wheel operation from the time the driver starts steering wheel operation until it is determined to be over-control, which may cause the steering wheel operation to become temporarily heavy and the steering feel to deteriorate.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a steering assist device for a vehicle that can ensure both controllability of steering assist control and steering feel of a driver.

[0013] Technical Solution

[0014] A steering assist device for a vehicle according to one embodiment of the present invention comprises: a steering torque detection device for detecting a steering torque based on a driver's steering wheel operation; a power steering torque calculation device for calculating a power steering torque for the steering torque; a target steering torque calculation device for independently calculating a target steering torque for steering control relative to the driver's steering wheel operation; a power steering torque output control device for limiting the output of the power steering torque by switching the power steering torque calculation device from an active state to an inactive state when the target steering torque calculation device is in an active state; an EPS torque setting device for setting an EPS torque for driving an EPS motor based on an output from the target steering torque calculation device and an output from the power steering torque output control device; and a hold steering detection device for detecting a hold steering state of the driver's steering wheel, wherein the power steering torque output control device switches the power steering torque calculation device from an inactive state to an active state when the hold steering detection device detects that the driver is holding the steering wheel, even when the target steering torque calculation device is in an active state.

[0015] Technical Effects

[0016] According to the steering assist device for a vehicle of the present invention, it is possible to ensure both the control performance of the steering assist control and the steering feeling of the driver. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of a vehicle equipped with a steering assist device.

[0018] Figure 2 This is a functional block diagram of a steering assist device.

[0019] Figure 3 This is a flowchart (part 1) showing the EPS torque setting routine.

[0020] Figure 4 This is a flowchart showing the EPS torque setting routine (part 2).

[0021] Figure 5 (a) is a timing diagram of the torque sensing value detected by the torque sensor. Figure 5 (b) is a timing diagram of the steering angle detected by the steering angle sensor. Figure 5 (c) is a timing chart of the power steering torque calculated by the power steering torque calculation unit.

[0022] Figure 6 (a) is a timing chart of the target steering torque calculated in the target steering torque calculation unit,

[0023] Figure 6 (b) is a timing diagram of the steering angle detected by the steering angle sensor. Figure 6 (c) is a timing diagram of the torque sensing value detected by the torque sensor. Figure 6 (d) is a timing chart of the power steering torque calculated by the power steering torque calculation unit.

[0024] Figure 7 (a) is a timing diagram of the hold steering detection sensor value detected by the hold steering detection sensor, Figure 7 (b) is a timing diagram of the torque sensing value detected by the torque sensor. Figure 7 (c) is the timing diagram of the power steering torque after output control. Figure 7 (d) is a timing chart of the target steering torque calculated in the target steering torque calculation unit, Figure 7 (e) is a timing diagram of the steering angle detected by the steering angle sensor.

[0025] Figure 8 (a) is a timing chart of the hold steering detection sensor value detected by the hold steering detection sensor of the comparative example, Figure 8 (b) is a timing diagram of the torque sensing value detected by the torque sensor. Figure 8 (c) is a timing diagram of the power steering torque of the comparative example, Figure 8 (d) is a time chart of the target steering torque calculated by the target steering torque calculation unit of the comparative example, Figure 8(e) is a timing chart of the steering angle detected by the steering angle sensor of the comparative example.

[0026] Explanation of symbols

[0027] 1…This vehicle

[0028] 2… Steering mechanism

[0029] 3…Tie rod

[0030] 4… Steering wheel

[0031] 5…Steering axle

[0032] 5a…Torsion bar

[0033] 6…Electric power steering

[0034] 7…EPS motor

[0035] 8…EPS_ECU

[0036] 11…DSS_ECU

[0037] 12…Steering angle sensor

[0038] 13…Yaw rate sensor

[0039] 14…Vehicle speed sensor

[0040] 15…EPS motor rotation angle sensor

[0041] 16…Steering torque sensor

[0042] 17…Standing detection sensor

[0043] 21…Front identification device

[0044] 22…Car Camera

[0045] 22a…Main camera

[0046] 22b…Secondary camera

[0047] 31…PSA Control Department

[0048] 31a…Power steering torque calculation unit

[0049] 32…Steering assist control unit

[0050] 32a ...target steering angle calculation unit

[0051] 32b ...target steering torque calculation unit

[0052] 32c ... Steering assist execution determination unit

[0053] 33…Power steering torque output control unit

[0054] 34…Torque addition unit DETAILED DESCRIPTION

[0055] Hereinafter, one embodiment of the present invention will be described based on the drawings. It should be noted that, in the following, ALK control will be described as an example of steering assist control.

[0056] exist Figure 1 In the figure, a vehicle (the vehicle itself) 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 driving wheels and are connected to a steering mechanism 2 such as a rack-and-pinion mechanism via a steering tie rod 3. In addition, a steering shaft 5 having a steering wheel 4 fixedly provided at the front end is connected to the steering mechanism 2. When the driver operates the steering wheel 4, the front wheels FL, FR are steered via the steering mechanism 2.

[0057] 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 includes 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 the DSS_ECU 11 via an in-vehicle network using CAN (Controller Area Network) communication or the like.

[0058] The EPS_ECU8 basically sets the assist torque for assisting the steering torque applied by the driver to the steering wheel 4 according to the driving signal from the DSS_ECU11 when the steering assist control is in an inactive state. On the other hand, when the ALK control is in an active state, a command signal corresponding to the assist torque set by the DSS_ECU11 is sent to the EPS_ECU8, and the EPS_ECU8 is used to generate the predetermined assist torque in the EPS motor 7, so as to control the vehicle 1 to follow the target driving trajectory (for example, the center of the lane) described later. It should be noted that although not shown in the figure, in the in-vehicle network, in addition to the EPS_ECU8 and the DSS_ECU11, the unit devices for controlling the driving state of the vehicle 1, such as the engine control unit, the transmission control unit, and the vehicle stability control (VDC: Vehicle Dynamics Control) unit including the braking control, are connected to each other in a communication manner, and these control units are mainly composed of microcomputers such as CPU, RAM, ROM, etc.

[0059] In DSS_ECU11, as various parameters required when performing ALK control, signals from sensor devices that detect the behavior of the vehicle 1 are received, and the sensor devices include a steering angle sensor 12 installed on the steering shaft 5 to detect the steering angle as the steering angle of the steering wheel 4, a yaw rate sensor 13 that detects the yaw rate acting on the vehicle 1, a vehicle speed sensor 14 that detects the vehicle speed, an EPS motor rotation angle sensor 15 that detects the rotation angle of the EPS motor 7, and a steering torque sensor 16 that uses the torsion angle of the torsion bar 5a installed on the steering shaft 5 as a steering torque detection device for detecting the steering torque applied to the steering wheel 4 by the driver, a holding steering detection sensor 17 that is composed of a contact sensor etc. arranged on the steering wheel 4 and serves as a holding steering detection device for detecting whether the driver holds the steering wheel, etc.

[0060] On the other hand, symbol 21 is a forward recognition device, which is mainly composed of a microcomputer having a CPU, RAM, ROM, etc. and has a vehicle-mounted camera composed of a stereo camera. The image captured by the vehicle-mounted camera 22 is processed to generate image information required for ALK control. The stereo camera is formed by a main camera 22a and a sub-camera 22b.

[0061] The two cameras 22a and 22b are arranged horizontally at equal intervals from the center of the vehicle width direction at the front of the vehicle and near the windshield. In addition, each camera 22a and 22b is provided with a shooting element such as CCD and / or CMOS, and these two shooting elements are used to shoot a three-dimensional image of the driving environment in front of the driving direction of the driving route of the vehicle. It should be noted that in the present embodiment, three-dimensional objects, obstacles, etc. including the driving lane of the vehicle 1 and / or the preceding vehicle are identified based on the image data captured by the vehicle-mounted camera 22. Therefore, as long as these objects can be identified, millimeter wave radar, infrared laser radar, or even a combination of these can be used instead of the vehicle-mounted camera 22.

[0062] The front recognition device 21 converts a pair of analog images captured by each camera 22a, 22b into a digital image of a predetermined brightness level, generates reference image data based on the output signal of the main camera 22a, and generates comparison image data based on the output signal of the auxiliary camera 22b. Then, based on the parallax between the reference image data and the comparison image data, the three-dimensional information of the same object in the two images, that is, the distance from the vehicle to the object, is calculated. The front recognition device 21 identifies the left and right dividing lines based on the generated image data, and calculates the width (diagonal line width) W between the dividing lines. It should be noted that the vehicle-mounted camera 22 can be a single-lens reflex camera, in which case the three-dimensional information can be obtained using the well-known motion stereo method, etc.

[0063] like Figure 2 As shown, DSS_ECU11 has a power steering assist control unit (hereinafter referred to as "PSA control unit") 31, a steering assist control unit 32, a power steering torque output control unit 33 as a power steering torque output control device, and a torque addition unit 34 as an EPS torque setting device as the function of executing ALK control.

[0064] In addition, the PSA control unit 31 is configured to include a power steering torque calculation unit 31a as a power steering torque calculation device. On the other hand, the steering assist control unit 32 is configured to include a target steering angle calculation unit 32a, a target steering torque calculation unit 32b as a target steering torque calculation device, and a steering assist execution determination unit 32c as a steering assist execution determination device.

[0065] The power steering torque calculation unit 31a of the PSA control unit 31 calculates the power steering torque as the power steering control amount corresponding to the driver's steering wheel 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.

[0066] In addition, the steering assist control unit 32 is a device that performs steering assist control (ALK control) in a manner so that the vehicle 1 travels along a target driving trajectory set in a driving lane in front of the vehicle 1, and the target steering angle calculation unit 32a calculates the target steering angle required for the vehicle 1 to travel along the target driving trajectory based on image data from the front recognition device 21, the vehicle speed of the vehicle 1 detected by the vehicle speed sensor 14, and the yaw rate detected by the yaw rate sensor 13.

[0067] Furthermore, the target steering torque calculation unit 32 b 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 32 a .

[0068] In addition, the steering assist execution determination unit 32c determines whether to start the execution of the steering assist control (ALK control) when, for example, the steering assist control switch (not shown) provided on the steering wheel 4 is turned on by the driver. On the other hand, during the execution of the steering assist control, when the holding steering detection sensor 17 detects that the driver is holding the steering wheel 4, the steering assist execution determination unit 32c compares the steering torque of the driver's steering wheel operation detected by the steering torque sensor 16 with the steering reaction torque set based on the steering angle detected by the steering angle sensor 12 and the vehicle speed detected by the vehicle speed sensor 14. Then, when the steering torque is greater than the steering reaction torque, it is determined to be an overriding control and the execution of the steering assist control (ALK control) is prohibited.

[0069] On the other hand, the power steering torque output control unit 33 checks whether the ALK control is being performed or whether the steering wheel 4 is being held by the driver even during the ALK control, and sets the power steering torque to active or inactive based on these results.

[0070] It should be noted that since the calculations performed by the power steering torque calculation unit 31a, the target steering angle calculation unit 32a, the target steering torque calculation unit 32b, and the steering assist execution determination unit 32c are well known, detailed descriptions thereof will be omitted.

[0071] Specifically, the EPS torque set in the DSS_ECU 11 is based on Figure 3 , Figure 4 The EPS torque setting program shown is set.

[0072] This routine is repeatedly executed at a unit set time. When the routine is started, the DSS_ECU 11 first detects parameters required for calculating the EPS torque based on the sensing signals from the sensors 12 to 17 .

[0073] Next, the process proceeds to step S102, where the DSS_ECU 11 calculates the power steering torque for the driver's steering wheel operation based on, for example, the vehicle speed of the 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. It should be noted that step S102 corresponds to the processing performed by the power steering torque calculation unit 31a.

[0074] On the other hand, when the process proceeds from step S101 to step S103, the DSS_ECU 11 estimates the driving 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 estimates the driving lane state in front of the host vehicle 1 based on the image data acquired by the front recognition device 21. Then, the DSS_ECU 11 calculates the target steering angle based on the driving state of the host vehicle 1 and the driving lane state in front of the host vehicle 1. It should be noted that step S103 corresponds to the processing performed by the target steering angle calculation unit 32a.

[0075] Next, the process proceeds to step S104, where the DSS_ECU 11 calculates a target steering torque for limiting the steering angle detected by the steering angle sensor 12 to a target steering angle through, for example, feedback control, etc. Step S104 corresponds to processing executed by the target steering torque calculation unit 32b.

[0076] Next, the process proceeds to step S105, where DSS_ECU11 makes a judgment on the action of the steering assist control. That is, when the steering assist control switch provided on the steering wheel 4 is turned on by the driver, for example, DSS_ECU11 makes a judgment on the intention to start the execution of the steering assist control (a judgment on the intention to activate the driving assist control). On the other hand, during the execution of the steering assist control, when the steering detection sensor 17 detects that the driver is holding the steering wheel 4, DSS_ECU11 compares the steering torque of the driver's steering wheel operation detected by the steering torque sensor 16 with the steering reaction torque set based on the steering angle detected by the steering angle sensor 12 and the vehicle speed detected by the vehicle speed sensor 14. Then, when the steering torque is greater than the steering reaction torque, it is judged as an overriding control and a judgment on the intention to prohibit the execution of the steering assist control is made (a judgment on the intention to inactivate the driving assist control). It should be noted that step S105 corresponds to the processing performed by the steering assist execution determination unit 32c.

[0077] Next, the process proceeds to step S106 , where the DSS_ECU 11 determines whether the steering assist control is currently in an activated state.

[0078] Then, in step S106 , when the DSS_ECU 11 determines that the steering assist control is not in the activated state, the process jumps to step S108 .

[0079] On the other hand, in step S106, if the DSS_ECU 11 determines that the steering assist control is activated, the process proceeds to step S107, and after outputting the target steering torque calculated in step S104, the process proceeds to step S108. It should be noted that step S104, step S106, and step S107 correspond to the processing executed by the target steering torque calculation unit 32b.

[0080] When the process proceeds to step S108 from step S102 , step S106 , or step S107 , the DSS_ECU 11 determines whether the steering assist control is currently in an active state based on the determination in step S105 .

[0081] Then, in step S108 , when the DSS_ECU 11 determines that the steering assist control is not in the activated state, the process proceeds to step S117 .

[0082] On the other hand, in step S108, when the DSS_ECU 11 determines that the steering assist control is in the activated state, the process proceeds to step S109 to confirm whether the driver is currently holding the steering wheel 4 based on the signal from the hold steering detection sensor 17. It should be noted that the process from step S108 to step S123 shown below corresponds to the processing executed by the power steering torque output control unit 33.

[0083] Then, in step S109 , when the DSS_ECU 11 determines that the driver is holding the steering wheel, the process proceeds to step S117 , and when the DSS_ECU 11 determines that the driver is not holding the steering wheel, the process proceeds to step S110 .

[0084] When the process proceeds from step S109 to step S110 , the DSS_ECU 11 prohibits the power steering torque from being input from the power steering torque calculation unit 31 a to the power steering torque output control unit 33 , thereby placing the power steering torque control in an inactive state.

[0085] Next, the process proceeds to step S111 , and the DSS_ECU 11 checks whether a flag Fdec for performing a step-down process on the power steering torque outputted in the transition period after the power steering torque control becomes inactive is set to “1”.

[0086] Then, in step S111 , when the DSS_ECU 11 determines that the flag Fdec is set to “1”, the process proceeds to step S112 , and when the DSS_ECU 11 determines that the flag Fdec is set to “0”, the process jumps to step S124 .

[0087] When the process proceeds from step S111 to step S112 , the DSS_ECU 11 checks whether the power steering torque control has been switched from the active state to the inactive state.

[0088] Then, in step S112 , when the DSS_ECU 11 determines that the state has not been switched to the inactive state, the process jumps to step S114 .

[0089] On the other hand, when the DSS_ECU 11 determines in step S112 that the state has been switched to the inactive state, the process proceeds to step S113 , sets the flag Fdec to “1”, and then proceeds to step S114 .

[0090] When the process proceeds from step S112 or step S113 to step S114 , the DSS_ECU 11 performs a decreasing process of decreasing the previous power steering torque at a preset decreasing rate.

[0091] Next, in step S115 , the DSS_ECU 11 checks whether the reduction process for the power steering torque has been completed.

[0092] Then, in step S115 , when the DSS_ECU 11 determines that the decrement process has not been completed, the process jumps to step S124 .

[0093] On the other hand, when the DSS_ECU 11 determines in step S115 that the decrement process is completed, the process proceeds to step S116, clears the flag Fdec to "0", and then proceeds to step S124. In this determination, for example, when the power steering torque becomes zero, the decrement process is determined to be completed.

[0094] When the process proceeds from step S108 or step S109 to step S117 , the DSS_ECU 11 activates the power steering torque control by, for example, allowing the power steering torque to be input from the power steering torque calculation unit 31 a to the power steering torque output control unit 33 .

[0095] Next, the process proceeds to step S118 , and the DSS_ECU 11 checks whether a flag Finc for performing a process of incrementally increasing the power steering torque output during the transition period after the power steering torque control becomes active is set to “1”.

[0096] Then, in step S118 , when the DSS_ECU 11 determines that the flag Finc is set to “1”, the process proceeds to step S119 , and when the DSS_ECU 11 determines that the flag Finc is set to “0”, the process jumps to step S124 .

[0097] When the process proceeds from step S118 to step S119 , the DSS_ECU 11 checks whether the power steering torque control has been switched from the inactive state to the active state.

[0098] Then, in step S119 , when the DSS_ECU 11 determines that the state has not been switched to the active state, the process jumps to step S121 .

[0099] On the other hand, when the DSS_ECU 11 determines in step S119 that the state has been switched to the active state, the process proceeds to step S120 , and after setting the flag Finc to “1”, the process proceeds to step S121 .

[0100] When the process proceeds from step S119 or step S120 to step S121 , the DSS_ECU 11 performs a gradual increase process of increasing the previous power steering torque at a preset gradual increase rate.

[0101] Next, in step S122 , the DSS_ECU 11 checks whether the process of increasing the power steering torque has been completed.

[0102] Then, in step S122 , when the DSS_ECU 11 determines that the increment process has not been completed, the process jumps to step S124 .

[0103] On the other hand, in step S122, when the DSS_ECU 11 determines that the incremental processing has been completed, it proceeds to step S123, and after clearing the flag Finc to "0", it proceeds to step S124. It should be noted that in this determination, for example, when the incremental power steering torque is consistent with the power steering torque input by the power steering torque calculation unit 31a, it is determined that the incremental processing has been completed.

[0104] If the process proceeds to step S124 from step S111, step S115, step S116, step S118, step S122 or step S123, the DSS_ECU 11 exits the program after outputting the value obtained by adding the target steering torque output by the target steering torque calculation unit 32b and the power steering torque output by the power steering torque output control unit 33 as the final power steering torque (EPS torque). It should be noted that step S124 corresponds to the processing performed by the torque addition unit 34.

[0105] That is, when the process proceeds from step S111 to step S124 , the target steering torque outputted from the target steering torque calculation unit 32 b is outputted as the EPS torque as it is.

[0106] When the process proceeds from step S116 to step S124 , a value obtained by adding a value obtained by decreasing the power steering torque immediately before the power steering torque control is deactivated to the target steering torque output by the target steering torque calculation unit 32 b is output as the EPS torque.

[0107] When the process proceeds from step S115 to step S124 , a value obtained by adding a value obtained by decrementing the previous power steering torque to the target steering torque output by the target steering torque calculation unit 32 b is output as the EPS torque.

[0108] When the process proceeds from step S118 to step S124 , a value obtained by adding the power steering torque output by the power steering torque calculation unit 31 a and the target steering torque output by the target steering torque calculation unit 32 b is output as the EPS torque.

[0109] When the process proceeds from step S123 to step S124 , a value obtained by adding the power steering torque (=0) to the target steering torque outputted from the target steering torque calculation unit 32 b is outputted as the EPS torque.

[0110] When the process proceeds from step S122 to step S124 , a value obtained by subtracting a value obtained by incrementally increasing the previous power steering torque from the target steering torque output by the target steering torque calculation unit 32 b is output as the EPS torque.

[0111] Next, refer to Figure 5 to Figure 7 , each torque set in the above-mentioned EPS torque setting program is explained.

[0112] For example, when the target steering torque calculation unit 32b is in an inactive state, the power steering torque calculation unit 31a calculates the target steering torque corresponding to the driver's steering torque (torque sensor value: see Figure 5 (a)) and steering angle (refer to Figure 5 (b)) corresponding to the power steering torque (refer to Figure 5 (c)).

[0113] For example, when the target steering torque calculation unit 32b is in an activated state, the target steering torque calculation unit 32b calculates the target steering torque (see Figure 6 (a)), the target steering torque is used to make the steering angle detected by the steering angle sensor (reference Figure 6 When the steering control is performed by using such a target steering torque, the steering torque (torque sensor value) in the opposite direction to the steering direction based on the steering assist control is detected by the steering torque sensor 16 under the influence of the static friction force of the steering system (refer to Figure 6 (c)). Thus, the power steering torque calculation unit 31a calculates the power steering torque in the direction of canceling the target steering torque (refer to Figure 6 (d)).

[0114] Thus, in this embodiment, by performing output control in the power steering torque output control unit 33 for the power steering torque calculated in the power steering torque calculation unit 31 a , controllability of the steering assist control and steering feeling of the driver can be achieved simultaneously.

[0115] That is, for example, when the driver holds the steering wheel 4 (see Figure 7 (a)) and the target steering torque calculation unit 32b is in an inactive state from time t1 to time t2, based on the steering torque detected by the steering torque sensor 16 (refer to Figure 7 (b)) and the power steering torque calculated by the power steering torque calculation unit 31a is directly output as the power steering torque after output control (refer to Figure 7 (c)).

[0116] In addition, when the driver's hands are removed from the steering wheel 4 (see Figure 7 (a)) and the target steering torque calculation unit 32b is in an activated state (refer to Figure 7 (d)) During the period from time t2 to time t3, the power steering torque calculation unit 31a is inactive, and the power steering torque after output control is gradually reduced and maintained at zero (see Figure 7 (c)). Thus, interference between the target steering torque and the power steering torque can be prevented, and the controllability of the steering assist control can be improved. Here, the actual steering angle is the steering angle detected by the steering angle sensor, and the target steering angle is the target steering angle calculated by the target steering angle calculation unit 32a.

[0117] In addition, when the target steering torque calculation unit 32b is in an active state (see Figure 7 In the case of (d)), when the driver holds the steering wheel 4 (refer to Figure 7 At time t3 of (a)), the power steering torque calculation unit 31a becomes activated again, and the power steering torque after output control increases to the power steering torque calculated by the power steering torque calculation unit 31a (refer to time t3 to time t4). After time t4, the power steering torque after output control, the power steering torque calculated by the power steering torque calculation unit 31a is directly output (refer to time t4 and after). As a result, when the driver turns the steering wheel 4, the temporary heaviness of the steering wheel operation caused by the lack of power steering torque output can be eliminated.

[0118] If it is determined to be an overriding state (see time t5 ), the target steering torque is in an inactive state.

[0119] It should be explained, such as Figure 8As shown in the comparative example of , when the power steering torque is directly output, the target steering torque and the power steering torque interfere with each other during the steering assist control.

[0120] According to such an embodiment, when the target steering torque calculation unit 32b is in an activated state, the power steering torque output control unit 33 switches the power steering torque calculation unit 31a from an activated state to an inactivated state to limit the output of the power steering torque. On the other hand, even if the target steering torque calculation unit 32b is in an activated state, when it is detected that the driver holds the steering wheel 4, the power steering torque output control unit 33 switches the power steering torque calculation unit 31a from an inactivated state to an activated state, thereby achieving both the controllability of the steering assist control and the steering feeling of the driver. It should be noted that the power steering torque calculation device is in an inactivated state, and when the driver holds the steering wheel, after a set time has passed, when a steering torque greater than a set value is detected by the steering torque detection device, the steering assist execution determination device can switch the target steering torque calculation device from an inactivated state to an activated state.

[0121] It should be noted that the present invention is not limited to the above-described embodiments, and various modifications and changes are possible, which are also within the technical scope of the present invention.

Claims

1. A steering assist device for a vehicle, characterized in that: have: a steering torque detection device that detects a steering torque based on a driver's steering wheel operation; a power steering torque calculation device that calculates a power steering torque for the steering torque; a target steering torque calculation device that calculates a target steering torque for performing steering control independently of a driver's steering wheel operation; A steering hold detection device, which detects the driver's steering hold state of the steering wheel; a power steering torque output control device, which switches the power steering torque calculation device from an activated state to an inactivated state to limit the output of the power steering torque when the target steering torque calculation device is in an activated state and the hold steering detection device does not detect that the driver is holding the steering wheel; an EPS torque setting device that sets an EPS torque for driving an EPS motor based on an output from the target steering torque calculation device and an output from the power steering torque output control device; as well as a steering assist execution determination device that performs switching determination between an activation state and an inactivation state of the target steering torque calculation device, the power steering torque output control device maintains the activation state of the target steering torque calculation device and switches the power steering torque calculation device from the inactive state to the active state when the target steering torque calculation device is in the active state, the power steering torque calculation device is in the inactive state, and the steering hold detection device detects that the driver is holding the steering wheel, The steering assist execution determination device switches the target steering torque calculation device from an activated state to an inactivated state when a steering torque equal to or greater than a set value is detected by the steering torque detection device in a state in which the driver holds the steering wheel.

2. The vehicle steering assist device according to claim 1, characterized in that: The power steering torque output control device decreases the output to zero when the power steering torque calculation device switches from an activated state to an inactivated state, and increases the output from zero to the power steering torque calculated by the power steering torque calculation device when the power steering torque calculation device switches from an inactivated state to an activated state.

3. The vehicle steering assist device according to claim 1 or 2, characterized in that: The EPS torque setting device sets a value obtained by adding an output from the target steering torque calculation device and an output from the power steering torque output control device as the EPS torque.

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