Vehicle steering assist torque control device

Abstract

A vehicle steering guidance torque control device. A control unit that controls a reaction force actuator that applies a steering guidance torque to a steering wheel calculates a target steering angle for causing a vehicle to travel along a curve, calculates a target steering guidance torque based on a deviation between the target steering angle and an actual steering angle, corrects the target steering guidance torque in such a manner that the target steering guidance torque becomes smaller as an index value of at least one of a number of times and an accumulated time that a difference between a magnitude of the actual steering angle and a magnitude of the target steering angle exceeds a reference value becomes larger, and controls the reaction force actuator in such a manner that the steering guidance torque becomes the target steering guidance torque.

Description

Technical Field

[0001] This invention relates to a steering torque control device for automobiles and other vehicles. Background Technology

[0002] As a steering reaction torque control device for automobiles and other vehicles, such a device as described in Japanese Patent Application Publication No. 2019-209844 is known. This steering reaction torque control device is configured to predict the appropriate (suitable) steering input of the driver based on the detection results of external sensors. When the steering input of the driver corresponding to the predicted time of the appropriate steering input is not within the range of the appropriate steering input, the steering reaction torque before the steering input reaches the range of the appropriate steering input is greater than before.

[0003] When the steering reaction torque changes from the appropriate steering operation range to outside that range, it functions as a steering reaction torque that resists the steering operation; when the steering operation changes from outside the appropriate steering operation range to within that range, it functions as a steering torque that promotes the steering operation. Therefore, the steering reaction torque control device described in Japanese Patent Application Laid-Open No. 2019-209844 can also be referred to as a steering guide torque control device.

[0004] As a steering guidance torque control device, a known steering guidance torque control device is as follows: a target steering angle for driving the vehicle along the curve is calculated based on the curvature of the curve of the road ahead of the vehicle detected by a camera sensor; a target steering guidance torque is calculated based on the deviation between the target steering angle and the actual steering angle, taking into account the pre-reading time; the target steering guidance torque is a torque that guides the driver's steering in a manner that makes the actual steering operation amount within a predetermined steering operation amount that includes the target steering operation amount; and a torque application device is controlled in such a manner that the steering guidance torque becomes the target steering guidance torque.

[0005] Based on the aforementioned steering reaction torque control device and steering guide torque control device, when the vehicle is traveling on a curve, it can prompt the driver to perform steering operations in a manner that makes the actual steering angle the target steering angle. Thus, steering support can be provided in a way that maintains the driver's sense of control while ensuring that the driver's steering input is appropriate. Summary of the Invention

[0006] In steering torque control systems, a target steering angle is calculated based on the curvature of the curve in the road ahead of the vehicle to determine the steering angle for driving the vehicle along the curve. However, drivers sometimes desire to perform curve driving differently than that based on the target steering angle. For example, sometimes the target steering angle is calculated to make the vehicle curve along the center of the lane, but the driver wants to perform curve driving in an out-in-out, sharp turn, or other similar pattern.

[0007] When a driver wants to navigate a curve that differs from the target steering angle, they will operate the steering wheel with an actual steering angle different from the target steering angle. Therefore, when the driver increases steering by deviating the target steering angle from the actual steering angle, they will inevitably feel an increased steering reaction force due to the steering guide torque.

[0008] The main objective of this invention is to provide an improved steering torque control device that reduces the likelihood of the driver feeling an increased steering reaction force due to steering torque when the vehicle is cornering.

[0009] According to the present invention, a steering torque control device (10) for a vehicle is provided, comprising: a steering input member (steering wheel 20) for steering operation by a driver; a steering device (18) for turning steering wheels (28FL, 28FR) according to the steering operation amount applied to the steering input member; a torque application device (reaction actuator 24) for applying steering torque (Tsg) to the steering input member; a control unit (ECU 14) for controlling the torque application device; and an imaging device (camera sensor 46) for acquiring an image of the front of the vehicle. The control unit is configured to perform steering torque control, wherein the steering torque control is as follows: The curvature (ρpre) of the lane in front of the vehicle used to drive the vehicle along the lane is estimated based on the image obtained by the imaging device. The target steering input (θt) is calculated based on the curvature of the lane. The target steering guide torque (Tsgt) is calculated based on the deviation (Δθ) between the target steering input and the actual steering input (θ). The target steering guide torque (Tsgt) is the torque that guides the driver's steering in a way that makes the actual steering input within a predetermined steering input range that includes the target steering input. The torque application device (reaction actuator 24) is controlled in such a way that the steering guide torque becomes the target steering guide torque.

[0010] The control unit (ECU14) is configured to calculate an index value (Nin) that indicates at least one of the number of times the difference between the actual steering operation amount (θ) and the target steering operation amount (θt) exceeds a reference value (θa) within the judgment time (Tc) up to now, and the cumulative time, so that the larger the index value, the smaller the target steering guidance torque (Tsgt), and then correct the target steering guidance torque (S10 to S40).

[0011] Based on the above configuration, a target steering input is calculated based on the curvature of the lane in front of the vehicle used to propel the vehicle along the lane. A target steering guide torque is calculated based on the deviation between the target steering input and the actual steering input. The target steering guide torque is a torque that guides the driver's steering in a manner that keeps the actual steering input within a predetermined range including the target steering input. The torque application device is controlled in such a way that the steering guide torque becomes the target steering guide torque. Therefore, a steering guide torque for propulsing the vehicle along the lane can be applied to the steering input member, prompting the driver to perform steering operations in a manner that makes the actual steering input the target steering input.

[0012] Furthermore, based on the above structure, an index value is calculated that represents at least one of the number of times the difference between the actual steering input and the target steering input exceeds a reference value within the judgment time up to now, and the cumulative time. Then, the target steering torque is corrected based on the index value in a manner that a larger index value results in a smaller target steering torque. Therefore, compared to not correcting the target steering torque based on the index value, the likelihood of the driver experiencing an increased steering reaction force due to the steering torque when the vehicle is cornering is reduced.

[0013] [Technical solution of the invention]

[0014] In one embodiment of the present invention, the control unit (ECU14) is configured such that the larger the index value (Nin) is, the lower the ratio of the target steering guidance torque (Tsgt) to the deviation (Δθ) (S50~S90).

[0015] According to the above technical solution, the larger the index value, the lower the ratio of the target steering guidance torque to the deviation. Therefore, "the greater the number of times the difference between the actual steering input and the target steering input exceeds the reference value within the current judgment time, and the greater the cumulative time, the lower the ratio of the target steering guidance torque to the deviation." Thus, "the higher the driver's tendency to perform cornering different from the cornering based on the target steering angle, the smaller the magnitude of the target steering guidance torque."

[0016] In another technical solution of the present invention, the control unit (ECU14) is configured to increase and correct the magnitude of the target steering operation (θt) by a correction amount (Δθa·signθt) that becomes larger as the index value (Nin) increases (S60, S100).

[0017] According to the above technical solution, the magnitude of the target steering operation is increased by using a correction factor that increases with the size of the index value. This reduces the magnitude of the target steering torque when the actual steering operation is larger than the target steering operation without this correction.

[0018] Furthermore, in another technical solution of the present invention, the control unit (ECU14) is configured to variably set the determination time (S40) according to the frequency of the vehicle (60) cornering, such that the lower the frequency of the vehicle (60) cornering, the longer the determination time (Tc).

[0019] According to the above technical solution, the judgment time is set variably based on the frequency of the vehicle's cornering, so that the lower the frequency of the vehicle's cornering, the longer the judgment time. Therefore, regardless of the number of curves on the road, the index value can be calculated as a value representing the driver's tendency to perform steering operations in a manner different from the actual steering angle and the target steering angle.

[0020] Furthermore, in another technical solution of the present invention, the control unit (ECU14) is configured to acquire information about the vehicle speed (V) and to variably set the reference value (S60) according to the vehicle speed in such a way that the higher the vehicle speed, the smaller the reference value (θa).

[0021] Generally, the larger the turning radius of a curve and the higher the vehicle speed, the smaller the steering angle when the vehicle is cornering. In addition, the higher the vehicle speed, the smaller the difference between the actual steering input and the target steering input.

[0022] According to the above technical solution, the reference value is set variably based on the vehicle speed, so that the higher the vehicle speed, the smaller the reference value becomes. Therefore, regardless of the turning radius of the curve, the index value can be calculated as a value representing the driver's tendency to perform steering operations in a manner different from the actual steering angle and the target steering angle.

[0023] Furthermore, in another technical solution of the present invention, the control unit (ECU14) is configured to perform automatic steering control, which automatically turns the steering wheel (28FL, 28FR) by the steering device (18) so that the vehicle (60) travels along the lane even if the driver does not perform steering operation on the steering input member (steering wheel 20). It is also configured to stop the automatic steering control and start steering guide torque control (S20, S40 to S140) when it is determined that the driver's steering operation on the steering input member has started during the execution of the automatic steering control.

[0024] According to the above technical solution, automatic steering control is performed. The automatic steering control automatically turns the steering wheel through the steering device (18) so that the vehicle travels along the lane even without the driver's steering input component. Furthermore, when it is determined that the driver's steering input component has started during the execution of automatic steering control, automatic steering control is stopped and steering guide torque control is started.

[0025] Therefore, when the driver initiates steering operation of the steering input component during the execution of automatic steering control, automatic steering control can be automatically stopped, and steering guide torque control can be automatically started without the need for switching operations.

[0026] In the foregoing description, to aid in understanding the invention, the names and / or reference numerals (drawing reference numerals) used in the embodiments described below are indicated in parentheses to represent the components of the invention. However, the constituent elements of the invention are not limited to the constituent elements of the embodiments indicated in parentheses. Other objects, features, and incidental advantages of the invention should be readily understood from the following description of embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0027] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements, and wherein:

[0028] Figure 1 This is a general configuration diagram showing an embodiment of a vehicle steering guide torque control device configured as a steering reaction torque control device.

[0029] Figure 2 It is a diagram used to illustrate the shooting reference position, etc.

[0030] Figure 3 This is a flowchart illustrating the control routine for the steering reaction torque in the first embodiment.

[0031] Figure 4 It is shown in Figure 3 The flowchart of the calculation routine for the target basic steering guide torque Tsgtb executed in step 70.

[0032] Figure 5 This is a flowchart illustrating the control routine for the steering reaction torque in the second embodiment.

[0033] Figure 6 This is a flowchart illustrating the control routine for the steering reaction torque in the third embodiment.

[0034] Figure 7 It is shown in Figure 6 The flowchart of the calculation routine for the target steering guide torque Tsgt executed in step 100.

[0035] Figure 8 This is a flowchart illustrating the control routine for the steering reaction torque in the fourth embodiment.

[0036] Figure 9 It is a mapping used to calculate the correction coefficient Ks based on the index value Nin.

[0037] Figure 10 It is used to calculate the target basic steering guidance torque Tsgtb based on the deviation Δθ of the steering angle.

[0038] Figure 11 It is used to calculate the corrected steering angle Δθa based on the index value Nin.

[0039] Figure 12 It is a mapping used to calculate the target steering guidance torque Tsgt based on the deviation Δθ of the steering angle.

[0040] Figure 13 This is a diagram illustrating the key points of correcting the target steering guide torque Tsgt in the first and second embodiments.

[0041] Figure 14 This is a diagram illustrating the key points of correcting the target steering guide torque Tsgt in the third and fourth embodiments. Detailed Implementation

[0042] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0043] [First Implementation Method]

[0044] <Composition>

[0045] like Figure 1As shown, the steering torque control device 10 according to the first embodiment is configured as a steering reaction torque control device including a "steer-by-wire (electronic steering) steering device 12" and an "electronic control unit 14 for controlling the steering device 12", and this steering torque control device 10 is applied to a vehicle 60. In the first embodiment, as will be explained in detail later, the steering torque control device 10 also performs lane keeping control as automatic steering control, which is control that automatically turns the steering wheel to make the vehicle 60 travel along the lane.

[0046] Furthermore, in the following description and accompanying drawings, "electronic control unit" is referred to as "ECU". Additionally, "LKA" is an abbreviation for Lane Keeping Assist, and "lane keeping control" is referred to as LKA control.

[0047] The steering device 12 includes a steering input device 16 and a steering device 18 that are not mechanically connected to each other. The steering input device 16 includes a steering wheel 20, a steering angle detection device 22 that detects the rotation angle of the steering wheel as the steering angle θ, and a reaction force actuator 24 that applies a steering reaction torque Tre to the steering wheel.

[0048] The steering wheel 20, not shown, is a steering input component operated by the driver and can also be shaped like a joystick. The reaction actuator 24 includes an electric motor, the rotation shaft 26 of which is integrally connected to the steering wheel 20. The steering angle detection device 22 can also be a rotary encoder built into the electric motor.

[0049] The steering device 18 includes: a steering mechanism 30 configured to receive a steering torque Tst to turn the left and right front wheels 28FL and 28FR, which are steering wheels; a steering actuator 32 that applies a steering torque to the steering mechanism; and a steering angle detection device 34 that detects the steering angle δ of the steering wheels.

[0050] In the illustrated embodiment, the steering mechanism 30 includes a rack and pinion assembly 40 having a rack 36 and a pinion shaft 38. Although not shown, the pinion shaft 38 has a pinion that meshes with the rack teeth of the rack 36, and the rotational motion of the pinion shaft 38 is converted into the reciprocating motion of the rack 36, and the reciprocating motion of the rack 36 is converted into the rotational motion of the pinion shaft 38. Furthermore, the steering mechanism can have any construction known in the art.

[0051] Furthermore, the steering mechanism 30 includes tie rods 42L and 42R, the inner ends of which are pivotally connected to the left and right top ends of the rack 36, respectively. Although not shown, the outer ends of the tie rods 42L and 42R are pivotally connected to the knuckle arms of the front wheels 28FL and 28FR. The steering actuator 32 includes an electric motor, the rotation shaft of which is integrally connected to the pinion shaft 38.

[0052] Thus, the steering mechanism 30 is configured to receive steering torque from the steering actuator 32 via the pinion shaft 38, causing the front wheels 28FL and 28FR to turn. The rotation angle of the pinion shaft 38... (Not shown) There is a certain relationship between the rudder angle δ of the front wheels 28FL and 28FR. Therefore, in the illustrated embodiment, the rudder angle detection device 34 detects the rotation angle of the rotating shaft of the pinion shaft 38 or the motor of the rudder actuator 32. To detect the rudder angle δ of the front wheels 28FL and 28FR.

[0053] exist Figure 1 Not shown in detail, ECU14 includes a microcomputer and drive circuitry. The microcomputer has a CPU, ROM, RAM, and interfaces (I / F), and has a general configuration that connects them to each other via a bidirectional common bus.

[0054] The ECU 14 receives a signal representing the steering angle θ detected by the steering angle detection device 22, and a signal representing the steering angle δ of the front wheels 28FL and 28FR detected by the steering angle detection device 34. Additionally, the ECU 14 receives a signal representing the vehicle speed V detected by the vehicle speed sensor 44, and a signal representing the white line information of the lane ahead of the vehicle 60 obtained by the camera sensor 46. The vehicle speed sensor 44 detects the vehicle speed V, for example, based on wheel speed.

[0055] Then, a signal indicating whether the LKA switch 48 is on is input to the ECU 14. When the LKA switch 48 is on, the ECU 14 performs LKA control.

[0056] like Figure 3 As shown, the camera sensor 46 is fixed to the upper part of the inner surface of the windshield 50a of the vehicle 60, and captures images of the front of the vehicle 60 from a shooting reference position Pca centered at a distance Lca (a positive constant) forward from the center of gravity 50b, which serves as the reference position of the vehicle 60. The distance Lca is referred to as the shooting reference distance Lca as needed. The reference position of the vehicle 60 can also be the position of the front wheels 28FL and 28FR, the middle position of the front and rear wheels, etc.

[0057] When the LKA switch 48 is open, the ECU 14 sets the steering gear ratio Rst to the standard steering gear ratio Rstn, and controls the steering actuator 32 based on the steering angle θ detected by the steering angle detection device 22. Therefore, the steering angle δ of the front wheels 28FL and 28FR is controlled to θ / Rstn. Furthermore, the steering angles θ and δ are 0 when the vehicle 60 is traveling straight, and become positive values ​​when the vehicle 60 turns left. Additionally, the standard steering gear ratio Rstn is a pre-set positive value that increases with increasing vehicle speed V, but it can also be a positive constant.

[0058] Furthermore, ECU14 calculates the basic steering reaction torque Treb to be applied to the steering wheel 20 based on the steering angle θ, the derivative of the steering angle θ, and the second derivative of the steering angle θ. The basic steering reaction torque Treb is variably set according to the vehicle speed, such that the higher the vehicle speed V, the greater the basic steering reaction torque Treb. Moreover, the basic steering reaction torque Treb can be controlled using any method known in the art. For example, the basic steering reaction torque Treb can be the torque corresponding to the steering torque felt by the driver via the steering wheel in a vehicle where the steering wheel is mechanically connected to the steering wheel and steering assist torque is applied by the power steering system.

[0059] Furthermore, as explained in detail later, ECU 14 calculates the target steering torque Tsgt to guide the driver's steering when the vehicle 60 is traveling on a curve of the road. Then, ECU 14 controls the reaction actuator 24 such that the steering reaction torque Tre generated by the reaction actuator 24 and applied to the steering wheel 20 becomes the target steering reaction torque Tret, which is the sum of the basic steering reaction torque Treb and the target steering torque Tsgt. Thus, the reaction actuator 24 functions as a torque application device that applies the steering torque Tsg corresponding to the target steering torque Tsgt to the steering wheel 20. Moreover, the magnitude of the target steering torque Tsgt is approximately one-tenth the magnitude of the basic steering reaction torque Treb.

[0060] Furthermore, when the pilot increases steering to make the actual steering angle θ deviate from the target steering angle θt, the target steering guide torque Tsgt acts in the direction of inhibiting steering. Conversely, when the pilot increases steering to make the actual steering angle θ approach the target steering angle θt, the target steering guide torque Tsgt acts in the direction of promoting steering. Thus, the target steering guide torque Tsgt guides the pilot's steering in a way that keeps the actual steering angle θ within a predetermined steering operation amount that includes the target steering angle θt.

[0061] In this implementation, the ECU 14 calculates the curvature ρca of the driving path for the area centered on the shooting reference position Pca based on the white line information of the lane in front of the vehicle 60 obtained by the camera sensor 46, and stores it in RAM. Thus, the camera sensor 46 and the ECU 14 function as a detection device for detecting the curvature ρca of the driving path for the area centered on the shooting reference position Pca.

[0062] Furthermore, ECU14 reads the curve curvature ρca corresponding to the pre-read time Δt from RAM as the pre-read curve curvature ρpre. Based on this curve curvature ρpre, it calculates the target steering angle θt, and based on the deviation Δθ between the target steering angle θt and the actual steering angle θ, it calculates the steering guidance torque Tsg. The target steering angle θt is the target steering angle used to make it easier for the actual steering angle to stay within a suitable range so that the vehicle 60 can travel along the curve. In addition, in this embodiment, the curvature of the direction in which the vehicle 60 turns left is positive.

[0063] The curvature ρca [1 / m] is calculated according to the following equation (1). Furthermore, in the following equation (1), V is the vehicle speed [m / s], and ρ0 is the curvature [1 / m] of the road surface at the center of gravity 50b of vehicle 60. Therefore, ρ0 is the curvature of the road surface at which vehicle 60 travels during its journey. Figure 1 The curve curvature ρca is calculated and stored in RAM before the time Lca / V required to shoot the reference distance Lca. Δρ is the rate of change of the curve curvature ρca [1 / m / m] calculated and stored in RAM before the time Lca / V, that is, the amount of change of the curve curvature per unit distance.

[0064] ρca=ρ0+VΔtΔρ…(1)

[0065] like Figure 1 As shown, the distance Lpre between the center of gravity 50b of vehicle 60 and the pre-reading position Ppre is smaller than the shooting reference distance Lca. Furthermore, the pre-reading distance Lpre may not be constant. From the above explanation, it can be seen that the curve curvature ρpre is the curve curvature at the pre-reading position Ppre, that is, the curve curvature at the position reached by the center of gravity 50b of vehicle 60 after the pre-reading time Δt.

[0066] The target steering angle θt [deg] is calculated according to equation (2) below. Furthermore, in equation (2) below, as mentioned earlier, Rst is the steering gear ratio, and A is the vehicle's stability factor [deg / (m...]. 2 / s 2 [)], where Lw is the wheelbase of vehicle 60. The stability factor A and wheelbase Lw are known constant values ​​determined by the specifications of vehicle 60.

[0067] θt=Rst(1+AV 2 )ρpreLw···(2)

[0068] In addition, ECU14 calculates the deviation θ-θt between the actual steering angle θ and the target steering angle θt, i.e., the steering angle deviation Δθ. Based on the steering angle deviation Δθ, it refers to... Figure 10 The mapping shown is used to calculate the target basic steering and guidance torque Tsgtb.

[0069] In particular, ECU14 calculates the number of times the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt exceeds the reference value θa within the current determination time Tc as the index value Nin. ECU14 then uses this index value Nin and references... Figure 9 The mapping shown is used to calculate the correction coefficient Ks.

[0070] Furthermore, the decision time Tc can be constant, but in this embodiment and other embodiments described later, the decision time Tc is set variably according to the frequency of the vehicle's cornering, so that the lower the frequency of the vehicle 60 cornering, the longer the decision time Tc. Additionally, the reference value θa can also be constant, but in this embodiment and other embodiments described later, the reference value θa is set variably according to the vehicle speed, so that the higher the vehicle speed V, the lower the reference value θa.

[0071] Furthermore, ECU14 calculates the target steering guide torque Tsgt as the product of the correction coefficient Ks and the target basic steering guide torque Tsgtb, KsTsgtb. Then, ECU14 controls the reaction force actuator 24 in a manner that makes the steering reaction torque Tre the target steering reaction torque Tret.

[0072] Furthermore, when the LKA switch 48 is on and the driver is not performing steering operations, the ECU 14 does not perform steering guide torque control, but instead performs LKA control. Conversely, when the LKA switch 48 is on and LKA control is being performed, if the driver performs steering operations, the ECU 14 stops LKA control and performs steering guide torque control.

[0073] <Control Routine for Steering Reaction Torque>

[0074] Next, the control routine for the steering reaction torque of the first embodiment will be described. When the ignition switch (not shown) is turned on, the CPU of ECU14 executes the following routine at predetermined intervals: Figure 3 The flowchart shows the control routine for the steering reaction torque. Furthermore, with... Figure 3 The control program corresponding to the flowchart is stored in the ROM of ECU14.

[0075] First, in step S10, the CPU determines whether the LKA switch 48 is turned on. If the CPU determines that it is not turned on, it advances the control of the steering reaction torque to step S40; if it determines that it is turned on, it advances the control of the steering reaction torque to step S20.

[0076] In step S20, the CPU determines whether the pilot has performed a steering operation that intervenes in LKA control. If the determination is no, the CPU executes LKA control in step S30; if the determination is yes, the control of the steering reaction torque proceeds to step S40. Furthermore, LKA control can be performed according to any method known in the art, and the determination of whether the pilot has performed a steering operation that intervenes in LKA control can also be performed according to any method known in the art.

[0077] In step S40, the CPU determines the decision time Tc based on the frequency of vehicle 60 cornering, as described above, and determines the reference value θa based on vehicle speed V, as described above. Furthermore, the CPU calculates the number of times the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt within the decision time Tc up to now exceeds the reference value θa as the index value Nin.

[0078] In step S50, the CPU, based on the index value Nin and referring to... Figure 9 The mapping shown is used to calculate the correction coefficient Ks. For example... Figure 9 As shown, when the index value Nin is 0, the correction coefficient Ks is 1. When the index value Nin is less than Nins (a positive constant), the larger the index value Nin is, the smaller the correction coefficient Ks is. When the index value Nin is greater than Nins, the correction coefficient Ks is calculated to be the constant value Ksmin.

[0079] In step S70, the CPU according to Figure 4 The flowchart shown is used to calculate the target basic steering guidance torque Tsgtb.

[0080] In step S90, the CPU calculates the target steering guidance torque Tsgt as the product of the correction coefficient Ks and the target basic steering guidance torque Tsgtb, KsTsgtb, where the target steering guidance torque Tsgt is the torque used to guide the driver's steering when the vehicle 60 is driving on a curve of the road.

[0081] In step S120, the CPU calculates the basic steering reaction torque Treb to be applied to the steering wheel 20 based on the steering angle θ, the differential value of the steering angle θ, the second derivative value of the steering angle θ, and the vehicle speed V, according to any method known in the art.

[0082] In step S130, the CPU calculates the target steering reaction torque Tret as the sum of the basic steering reaction torque Treb and the target steering guidance torque Tsgt: Treb + Tsgt.

[0083] In step S140, the CPU controls the reaction force actuator 24 in such a way that the steering reaction torque Tre generated by the reaction force actuator 24 becomes the target steering reaction torque Tret. Therefore, by applying a steering reaction torque corresponding to the target steering reaction torque Tret to the steering wheel 20, a steering guide torque Tsg corresponding to the target steering guide torque Tsgt can be applied to the steering wheel 20.

[0084] exist Figure 4 In step S72 of the flowchart shown, the CPU calculates the rate of change Δρ of the curvature of the curve for the area centered on the shooting reference position Pca based on the white line information of the lane in front of the vehicle 60 obtained by the camera sensor 46 and saves it in RAM.

[0085] In step S74, according to the above formula (1), the curvature ρca of the driving path is calculated for the area centered on the shooting reference position Pca and stored in RAM. Furthermore, during the period from the start of control to the elapsed time Lca / V, the curvature ρca can be set to 0.

[0086] In step S76, the CPU reads the curvature ρca of the curve that was calculated and stored in RAM before the pre-reading time Δt from RAM as the curvature ρpre at the pre-reading position Ppre.

[0087] In step S78, the CPU calculates the target steering angle θt as the target steering operation amount for making the vehicle 60 travel along the curve of the driving path, based on the vehicle speed V and the curve curvature ρpre at the pre-read position Ppre, according to the above formula (2).

[0088] In step S80, the CPU calculates the deviation θ-θt between the actual steering angle θ detected by the steering angle detection device 22 and the target steering angle θt, i.e., the deviation Δθ of the steering angle.

[0089] In step S82, the CPU uses the deviation Δθ based on the steering angle and refers to... Figure 10 The mapping shown is used to calculate the target's basic steering guidance torque Tsgtb. For example... Figure 10 As shown, when the absolute value of the deviation of the steering angle Δθ is less than Δθc (a positive constant), the larger the absolute value of the deviation of the steering angle Δθ, the larger the magnitude of the target's basic steering guidance torque Tsgtb. When the absolute value of the deviation of the steering angle Δθ is greater than Δθc, the magnitude of the target's basic steering guidance torque Tsgtb is calculated as the constant value Tsgtbmax.

[0090] [Second Implementation]

[0091] Figure 5 This is a flowchart illustrating the control routine for the steering reaction torque in a second embodiment, which is a variation of the first embodiment. Furthermore, in Figure 5 In the middle, to and Figure 3 The steps shown are the same as the step labels. Figure 3 The step numbers are the same as those marked in the diagram. This also applies to other embodiments described later.

[0092] In the second and fourth embodiments described later, LKA control is not performed. Therefore, although not illustrated, the steering torque control device 10 in these embodiments does not include an LKA switch 48.

[0093] from Figure 5 and Figure 3 A comparison shows that steps 10 to 30 in the first embodiment are not performed, but steps 40 to 140 are performed in the same way as steps 40 to 140 in the first embodiment.

[0094] According to the first and second embodiments, the number of times the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt exceeds the reference value θa within the current determination time Tc is calculated as an index value Nin (step S40). Based on the index value Nin, a correction coefficient Ks is calculated (step S50), and the target basic steering guidance torque Tsgtb is calculated (step S70). Furthermore, the target steering guidance torque Tsgt is calculated as the product of the correction coefficient Ks and the target basic steering guidance torque Tsgtb, KsTsgtb (step S90).

[0095] The correction coefficient Ks is calculated as follows: the larger the index value Nin, the smaller the correction coefficient Ks. Figure 9 Therefore, the larger the index value Nin, the lower the ratio of the target steering guidance torque Tsgt to the deviation Δθ. Thus, the higher the tendency of the driver to perform cornering different from the cornering based on the target steering angle, the smaller the target steering guidance torque becomes.

[0096] Figure 13 This shows the relationship between the absolute value of the actual steering angle θ and the index value Nin, and the absolute value of the target steering guidance torque Tsgt. For example... Figure 13 As shown, the larger the index value Nin, the smaller the target steering torque Tsgt in the region where the actual steering angle θ exceeds the target steering angle θt. From Figure 13It can be seen that when steering is performed in a manner that makes the actual steering angle θ larger than the target steering angle θt, the larger the index value Nin is, the smaller the reaction torque generated by the steering guidance torque will be.

[0097] [Third Implementation Method]

[0098] Figure 6 This is a flowchart illustrating the control routine for steering reaction torque in the third embodiment of the present invention.

[0099] from Figure 6 and Figure 3 A comparison shows that in the second embodiment, steps 10 to 40 and steps 120 to 140 are performed in the same way as in the first embodiment. When step 40 is completed, steps 60 and 100 are performed.

[0100] In step S60, the CPU, based on the index value Nin and referring to... Figure 11 The mapping shown is used to calculate the corrected steering angle Δθa. For example... Figure 11 As shown, when the index value Nin is 0, the corrected steering angle Δθa is 0. When the index value Nin is less than Nina (a positive constant), the larger the index value Nin is, the larger the corrected steering angle Δθa is. When the index value Nin is greater than Nina, the corrected steering angle Δθa is calculated to the constant value Δθamax.

[0101] In step S100, the CPU according to Figure 7 The flowchart shown is used to calculate the target steering torque Tsgt.

[0102] from Figure 7 and Figure 4 A comparison shows that steps 102 to 108 are performed in the same manner as steps 72 to 78 in the first embodiment.

[0103] In step S110, which follows step S108, signθt is set as the sign (positive or negative) of the target steering angle θt, and the deviation Δθ of the steering angle is calculated according to the following formula (3). That is, the deviation Δθ of the steering angle is calculated as the deviation θ-(θt+Δθa·signθt) between the actual steering angle θ detected by the steering angle detection device 22 and the target steering angle θta (=θt+Δθa·signθt) whose size has been increased by the correction steering angle Δθa.

[0104] Δθ=θ-(θt+Δθa·signθt)

[0105] =θ-θt-Δθa·signθt···(3)

[0106] In step S112, the CPU uses the deviation Δθ based on the steering angle and refers to... Figure 12 The mapping shown is used to calculate the target steering torque Tsgt. For example... Figure 12 As shown, when the absolute value of the deviation of the steering angle Δθ is less than Δθc, the larger the absolute value of the deviation of the steering angle Δθ, the larger the target steering guidance torque Tsgt. When the absolute value of the deviation of the steering angle Δθ is greater than Δθc, the target steering guidance torque Tsgt is calculated to be the constant value Tsgtmax.

[0107] [Fourth Implementation Method]

[0108] Figure 8 This is a flowchart illustrating the control routine for the steering reaction torque in a fourth embodiment, which is a variation of the third embodiment.

[0109] from Figure 8 and Figure 6 A comparison shows that steps 10 to 30 in the third embodiment are not performed, but steps 40 to 140 are performed in the same way as steps 40 to 140 in the third embodiment.

[0110] According to the third and fourth embodiments, the number of times the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt exceeds the reference value θa within the current determination time Tc is calculated as the index value Nin (step S40). The corrected steering angle Δθa is calculated based on the index value Nin (step S60), according to... Figure 7 The flowchart shown is used to calculate the target steering guidance torque Tsgt (step S100).

[0111] The deviation of the steering angle Δθ is calculated as the deviation between the actual steering angle θ and the target steering angle θt + Δθa·signθt, which has been increased in size using the corrected steering angle Δθa (step S110). This reduces the magnitude of the target steering torque Tsgt when the actual steering angle θ is larger than the target steering angle without the increase correction.

[0112] Furthermore, according to the first and third embodiments described above, when the LKA switch 48 is turned on, if the driver performs a steering operation to intervene in LKA control, it is determined in steps S10 and S20 that this is the case, and steps S40 to S140 are executed. Therefore, when the driver initiates a steering operation during the execution of LKA control, LKA control can be automatically stopped, and steering torque control can be automatically started without the need for switch operations or the like.

[0113] <Common effects of the first to fourth embodiments>

[0114] As explained above, according to the first to fourth embodiments described above, the target steering torque can be corrected based on the index value in a way that the larger the index value Nin is, the smaller the target steering torque Tsgt is. Therefore, compared to the case where the target steering torque is not corrected based on the index value, the possibility of the driver feeling an increased steering reaction force due to the steering torque when the vehicle is cornering can be reduced.

[0115] Furthermore, according to the first to fourth embodiments described above, the determination time Tc is variably set according to the frequency of the vehicle's cornering, such that the lower the frequency of the vehicle 60 cornering, the longer the determination time Tc. Therefore, regardless of the number of corners, the index value can be calculated as a value representing the driver's tendency to perform steering operations in a manner different from the actual steering angle and the target steering angle.

[0116] Furthermore, according to the first to fourth embodiments described above, the reference value θa is variably set according to the vehicle speed, such that the higher the vehicle speed V, the smaller the reference value θa. Therefore, regardless of the turning radius of the curve, the index value can be calculated as a value representing the driver's tendency to perform steering operations in a manner different from the actual steering angle and the target steering angle.

[0117] The present invention has been described in detail above with respect to specific embodiments, but the present invention is not limited to the embodiments described above. It will be obvious to those skilled in the art that various other embodiments can be implemented within the scope of the present invention.

[0118] For example, in the above implementation, the index value Nin is calculated as the number of times the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt exceeds the reference value θa within the current determination time Tc. However, the index value Nin can also be calculated as the cumulative time for the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt exceeds the reference value θa within the current determination time Tc. Alternatively, the number of occurrences and the cumulative time can be set as Nc and Tc, respectively, and α and β can be set as positive constants, and the index value Nin can be calculated as the linear sum of the number of occurrences and the cumulative time, αNc + βTc.

[0119] In the above embodiment, the automatic steering control is LKA control, which automatically turns the steering wheels (28FL, 28FR) via the steering device (18) so that the vehicle (60) travels along the lane even without the driver's steering input component (steering wheel 20). However, the automatic steering control can also be any automatic steering control known in the art, such as automatic driving control.

[0120] Furthermore, in the first and third embodiments described above, when the pilot performs a steering operation to intervene in LKA control, LKA control is aborted, and steering guide torque control in steps S40 to S140 automatically begins. However, the steering guide torque control that begins when the pilot performs a steering operation to intervene in LKA control can also be a steering guide torque control that does not correct the target steering guide torque based on the index value.

[0121] Furthermore, in the above-described embodiment, the steering guide torque control device 10 is configured as a steering reaction torque control device including a steering steer-by-wire type steering device 12. However, the steering guide torque control device 10 may also be configured as a steering reaction torque control device that mechanically connects the steering wheel to the left and right front wheels and includes an electric power steering device. In this case, the target steering assist torque Tsat is calculated as the sum of the basic steering assist torque Tsab calculated based on the steering torque and vehicle speed and the target steering guide torque Tsgt. Furthermore, the electric power steering device is controlled in such a way that the steering assist torque Tsa generated by the electric power steering device becomes the target steering assist torque Tsat.

Claims

1. A steering torque control device for a vehicle. include: The steering input component is used by the driver to operate the steering gear. The system includes a steering mechanism that turns the steering wheel according to a steering input amount applied to the steering input member; a torque application device that applies steering guide torque to the steering input member; a control unit that controls the torque application device; and an imaging device that acquires an image of the front of the vehicle. The control unit is configured to perform steering guide torque control, which involves: estimating the curvature of the lane ahead of the vehicle for driving the vehicle along the lane based on an image acquired by the imaging device; calculating a target steering input based on the lane curvature; calculating a target steering guide torque based on the deviation between the target steering input and the actual steering input; the target steering guide torque being a torque that guides the driver's steering in a manner that makes the actual steering input fall within a predetermined range including the target steering input; and controlling the torque application device in such a manner that the steering guide torque becomes the target steering guide torque. The control unit is configured to calculate an index value representing at least one of the number of times the difference between the actual steering operation and the target steering operation exceeds a reference value within the current determination time, and the cumulative time, such that a larger index value corresponds to a smaller target steering guidance torque, and to correct the target steering guidance torque based on the index value. The control unit is configured such that the larger the index value, the lower the ratio of the target steering torque to the deviation.

2. The vehicle steering torque control device according to claim 1, The control unit is configured to increase the magnitude of the target steering operation by using a correction amount that becomes larger as the index value increases.

3. The vehicle steering torque control device according to claim 1, The control unit is configured to variably set the determination time according to the frequency of the vehicle's cornering, such that the lower the frequency of the vehicle's cornering, the longer the determination time.

4. The vehicle steering torque control device according to claim 3. The control unit is configured to acquire vehicle speed information and variably set the reference value according to the vehicle speed, such that the higher the vehicle speed, the smaller the reference value.

5. The vehicle steering torque control device according to claim 1. The control unit is configured to perform automatic steering control, which automatically turns the steering wheel via the steering device so that the vehicle travels along the lane even without steering operation by the driver on the steering input component. Furthermore, it is configured to abort the automatic steering control and initiate steering guide torque control when it is determined that steering operation by the driver on the steering input component has begun during the execution of the automatic steering control.

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