Vehicle steering guide torque control device

Abstract

To provide a steering guide torque controller that is so improved as to reduce a risk that a driver has a feeling of physical disorder of an increase in steering reaction force due to steering guide torque when a vehicle makes a curve travel.SOLUTION: A control unit which controls a reaction force actuator imparting steering guide torque to a steering wheel is configured to: compute a target steering angle for letting a vehicle travel along a curve and then compute a target steering guide torque Tsgt based upon a deviation of actual steering from the target steering angle S70, S90; correct the target steering guide torque so that an index value Nin indicative of at least one of the number of times and the integrated time when the difference between an actual steering angle and the target steering angle exceeds a reference value is made smaller as it is larger S40 to S70; and control the reaction force actuator so that the steering guide torque reaches the target steering guide torque S140.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a steering guide torque control device for a vehicle such as an automobile. [Background technology]

[0002] As a steering reaction torque control device for vehicles such as automobiles, for example, as described in Patent Document 1 below, there is known a steering reaction torque control device that predicts an appropriate steering operation amount of a driver based on the detection results of an external sensor, and when the steering operation amount of the driver corresponding to the predicted time of the appropriate steering operation amount is not within the appropriate steering operation amount range, the steering reaction torque is configured to be larger than before until the steering operation amount comes into the appropriate steering operation amount range.

[0003] The steering reaction torque acts as a steering reaction torque that resists the steering operation when the steering operation amount changes from within the appropriate steering operation amount range to outside the range, and acts as a steering torque that encourages the steering operation when the steering operation amount changes from outside the appropriate steering operation amount range to within the range. Therefore, the steering reaction torque control device described in Patent Document 1 below may be called a steering guide torque control device.

[0004] A steering guide torque control device is known which calculates a target steering angle for driving the vehicle along a curve based on the curvature of the curve on the road ahead of the vehicle detected by a camera sensor, calculates a target steering guide torque for guiding the driver's steering so that the actual steering operation amount is within a predetermined range of steering operation amounts including the target steering operation amount based on the deviation between the target steering angle taking into account the look-ahead time and the actual steering angle, and controls a torque imparting device so that the steering guide torque becomes the target steering guide torque.

[0005] According to the steering reaction torque control device and the steering guide torque control device as described above, when the vehicle is traveling around a curve on a road, the driver can be encouraged to perform a steering operation so that the actual steering angle becomes the target steering angle. Therefore, the steering assistance can be performed so that the amount of steering operation by the driver becomes an appropriate amount of steering operation while maintaining the driver's sense of ownership of the steering. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-209844 A Summary of the Invention

[0007] [Problem to be solved by the invention] In the steering guide torque control device, the target steering angle is calculated as a steering angle for driving the vehicle along a curve based on the curvature of the curve of the road ahead of the vehicle. However, there are cases where the driver desires to drive the curve in a manner different from the curve driven by the target steering angle. For example, the target steering angle is calculated so that the vehicle drives the curve along the center of the lane, but the driver may wish to drive the curve in an out-in-out pattern, wide turn, or the like.

[0008] When a driver wishes to drive a curve different from the curve driven by the target steering angle, the driver performs steering operation so that the actual steering angle differs from the target steering angle. Therefore, when the driver performs steering to turn the vehicle further so that the actual steering angle deviates from the target steering angle, the driver cannot avoid feeling a sense of discomfort due to an increase in the steering reaction force caused by the steering guide torque.

[0009] A primary object of the present invention is to provide an improved steering guide torque control device that reduces the risk of a driver feeling uncomfortable due to an increase in steering reaction force caused by the steering guide torque when the vehicle is traveling around a curve.

[0010] [Means for solving the problems and effects of the invention] According to the present invention, a vehicle steering system includes a steering input member (steering wheel 20) that is steered by a driver, a steering device (18) that steers steered wheels (28FL, 28FR) in accordance with an amount of steering operation applied to the steering input member, a torque imparting device (reaction force actuator 24) that imparts a steering guide torque (Tsg) to the steering input member, a control unit (ECU 14) that controls the torque imparting device, and an imaging device (camera sensor 46) that captures an image of the front of the vehicle, and the control unit controls a vehicle steering system for driving the vehicle along a lane based on the image captured by the imaging device. There is provided a steering guide torque control device (10) for a vehicle configured to estimate a curvature (ρpre) of a lane ahead of both vehicles, calculate a target steering operation amount (θt) based on the lane curvature, calculate a target steering guide torque (Tsgt) for guiding the driver's steering so that the actual steering operation amount falls within a range of predetermined steering operation amounts including the target steering operation amount based on a deviation (Δθ) between the target steering operation amount and the actual steering operation amount (θ), and perform steering guide torque control for controlling a torque imparting device (reaction force actuator 24) so ​​that the steering guide torque becomes the target steering guide torque.

[0011] The control unit (ECU14) is configured to calculate an index value (Nin) indicating at least one of the number of times that the difference between the magnitude of the actual steering operation amount (θ) and the magnitude of the target steering operation amount (θt) has exceeded a reference value (θa) within a judgment time (Tc) up to the present and the accumulated time, and to correct the target steering guide torque in accordance with the index value so that the magnitude of the target steering guide torque (Tsgt) becomes smaller as the index value becomes larger (S10 to S40).

[0012] According to the above configuration, a target steering operation amount is calculated based on the curvature of the lane ahead of the vehicle for driving the vehicle along the lane, a target steering guide torque for guiding the driver's steering so that the actual steering operation amount falls within a range of predetermined steering operation amounts including the target steering operation amount is calculated based on the deviation between the target steering operation amount and the actual steering operation amount, and the torque applying device is controlled so that the steering guide torque becomes the target steering guide torque. Thus, the steering guide torque for driving the vehicle along the lane is applied to the steering input member, and the driver can be prompted to perform a steering operation so that the actual steering operation amount becomes the target steering operation amount.

[0013] Furthermore, according to the above configuration, an index value is obtained that indicates at least one of the number of times that the difference between the magnitude of the actual steering operation amount and the magnitude of the target steering operation amount exceeds a reference value within the judgment time up to the present, and the cumulative time. Furthermore, the target steering guide torque is corrected according to the index value so that the magnitude of the target steering guide torque becomes smaller as the index value increases. Therefore, compared to a case where the target steering guide torque is not corrected according to the index value, it is possible to reduce the risk that the driver will feel discomfort due to an increase in steering reaction force caused by the steering guide torque when the vehicle is traveling around a curve. Furthermore, in the above configuration, the control unit (ECU 14) is configured to variably set the judgment time (S40) in accordance with the frequency with which the vehicle (60) travels around a curve so that the judgment time (Tc) is longer as the frequency with which the vehicle (60) travels around a curve decreases. According to the above configuration, the determination time is variably set according to the frequency with which the vehicle turns a curve, so that the determination time is longer as the frequency with which the vehicle turns a curve is lower. Therefore, regardless of the number of curves on the road, the index value can be calculated as a value indicating the tendency of the driver to perform steering operation so that the actual steering angle differs from the target steering angle.

[0014] [Mode of the invention] In one aspect of the present invention, the control unit (ECU 14) is configured to decrease (S50 to S90) the ratio of the target steering guide torque (Tsgt) to the deviation (Δθ) as the index value (Nin) increases.

[0015] According to the above aspect, the ratio of the target steering guide torque to the deviation is reduced as the index value is increased. Therefore, the ratio of the target steering guide torque to the deviation can be reduced as the number of times that the difference between the magnitude of the actual steering operation amount and the magnitude of the target steering operation amount within the current judgment time exceeds the reference value and / or the cumulative time is increased. Therefore, the magnitude of the target steering guide torque can be reduced as the driver tends to drive a curve different from the curve drive according to the target steering angle.

[0016] In another aspect of the present invention, the control unit (ECU 14) is configured to increase and correct (S60, S100) the magnitude of the target steering operation amount (θt) by a correction amount (Δθa·signθt) that increases as the index value (Nin) increases.

[0017] According to the above aspect, the magnitude of the target steering operation amount is increased by a larger amount of correction as the index value increases, so that it is possible to reduce the magnitude of the target steering guide torque when the magnitude of the actual steering operation amount is greater than the magnitude of the target steering operation amount that is not increased.

[0020] In still another aspect of the present invention, the control unit (ECU 14) is configured to acquire information on the vehicle speed (V) and variably set the reference value (θa) according to the vehicle speed (S60) so that the higher the vehicle speed is, the smaller the reference value (θa) is.

[0021] In general, the steering angle when a vehicle is traveling around a curve becomes smaller as the turning radius of the curve becomes larger and the vehicle speed becomes higher. Also, the higher the vehicle speed, the smaller the difference between the actual steering operation amount and the target steering operation amount becomes.

[0022] According to the above aspect, the reference value is variably set according to the vehicle speed so that the reference value is smaller as the vehicle speed is higher. Therefore, regardless of the turning radius of the curve, the index value can be calculated as a value indicating the tendency of the driver to perform steering operation so that the actual steering angle differs from the target steering angle.

[0023] Furthermore, in another aspect of the present invention, the control unit (ECU14) is configured to execute automatic steering control in which the steering device (18) automatically steers the steered wheels (28FL, 28FR) so that the vehicle (60) travels along the lane even if the steering input member (steering wheel 20) is not steered by the driver, and is configured to stop the automatic steering control and start steering guide torque control (S20, S40 to S140) when it is determined that the driver has started steering the steering input member while the automatic steering control is being executed.

[0024] According to the above aspect, automatic steering control is executed in which the steering device (18) automatically steers the steered wheels so that the vehicle travels along the lane even if the steering input member is not steered by the driver. Furthermore, when it is determined that the driver has started to steer the steering input member during execution of the automatic steering control, the automatic steering control is stopped and the steering guide torque control is started.

[0025] Therefore, when the driver starts to operate the steering input member while the automatic steering control is being executed, the automatic steering control is automatically stopped and the steering guide torque control is automatically started without the need for a switch operation or the like.

[0026] In the above description, in order to facilitate understanding of the present invention, the names and / or symbols used in the embodiments described below are added in parentheses to the configurations of the invention corresponding to those embodiments. However, each component of the present invention is not limited to the components of the embodiments corresponding to the names and / or symbols added in parentheses. Other objects, other features, and associated advantages of the present invention will be easily understood from the description of the embodiments of the present invention described below with reference to the drawings. [Brief description of the drawings]

[0027] [Figure 1] 1 is a schematic diagram showing an embodiment of a vehicle steering guide torque control device configured as a steering reaction torque control device; [Diagram 2] FIG. 2 is a diagram for explaining a photographing reference position and the like. [Diagram 3] 5 is a flowchart showing a control routine for a steering reaction torque in the first embodiment. [Figure 4] 4 is a flowchart showing a routine for calculating a target basic steering guide torque Tsgtb, which is executed in step 70 of FIG. 3. [Diagram 5] 10 is a flowchart showing a control routine for steering reaction torque in the second embodiment. [Figure 6] 13 is a flowchart showing a control routine for steering reaction torque in a third embodiment. [Figure 7] 7 is a flowchart showing a calculation routine for a target steering guide torque Tsgt executed in step 100 of FIG. 6. [Figure 8] 13 is a flowchart showing a control routine for steering reaction torque in the fourth embodiment. [Figure 9] 13 is a map for calculating a conversion coefficient Ks based on an index value Nin. [Figure 10] 11 is a map for calculating a target basic steering guide torque Tsgtb based on a deviation Δθ of a steering angle. [Figure 11] 11 is a map for calculating a correction steering angle Δθa based on an index value Nin. [Figure 12] 11 is a map for calculating a target steering guide torque Tsgt based on a deviation Δθ of a steering angle. [Figure 13] FIG. 4 is a diagram showing a manner in which a target steering guide torque Tsgt is corrected in the first and second embodiments. [Figure 14] FIG. 13 is a diagram showing a manner in which the target steering guide torque Tsgt is corrected in the third and fourth embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0029] [First embodiment] <Configuration> 1, the steering guide torque control device 10 according to the first embodiment is configured as a steering reaction torque control device including a steer-by-wire type steering device 12 and an electronic control unit 14 that controls the steering device 12, and is applied to a vehicle 60. In the first embodiment, as will be described in detail later, the steering guide torque control device 10 also performs lane keeping control as an automatic steering control that automatically steers the steered wheels so that the vehicle 60 runs along the lane.

[0030] In the following explanation and drawings, the "electronic control unit" is abbreviated as "ECU." Also, "LKA" is an abbreviation for Lane Keeping Assist, and "lane keeping control" is abbreviated as LKA control.

[0031] The steering device 12 includes a steering input device 16 and a turning 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 a steering angle θ, and a reaction force actuator 24 that applies a steering reaction torque Tre to the steering wheel.

[0032] The steering wheel 20 is a steering input member that is steered by a driver (not shown) and may have a form similar to a control stick. The reaction force actuator 24 includes an electric motor, and a rotating shaft 26 of the electric motor is integrally connected to the steering wheel 20. The steering angle detection device 22 may be a rotary encoder built into the electric motor.

[0033] The steering device 18 includes a steering mechanism 30 configured to receive steering torque Tst to steer the left and right front wheels 28FL and 28FR, which are steered wheels, a steering actuator 32 that imparts steering torque to the steering mechanism, and a steering angle detection device 34 that detects the steering angle δ of the steered wheels.

[0034] In the illustrated embodiment, the steering mechanism 30 includes a rack and pinion device 40 having a rack bar 36 and a pinion shaft 38. Although not shown in the figure, the pinion shaft 38 has a pinion that meshes with rack teeth of the rack bar 36, and the rotational motion of the pinion shaft 38 is converted into the reciprocating motion of the rack bar 36, and the reciprocating motion of the rack bar 36 is converted into the rotational motion of the pinion shaft 38. Note that the steering mechanism may have any structure known in the art.

[0035] Further, the steering mechanism 30 includes tie rods 42L and 42R, the inner ends of which are pivotally connected to the left and right ends of the rack bar 36, respectively. Although not shown in the figure, 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 rotating shaft of which is integrally connected to the pinion shaft 38.

[0036] Thus, steering mechanism 30 is configured to steer front wheels 28FL and 28FR by receiving steering torque from steering actuator 32 at pinion shaft 38. There is a fixed relationship between rotation angle φ (not shown) of pinion shaft 38 and steering angle δ of front wheels 28FL and 28FR. Thus, in the illustrated embodiment, steering angle detection device 34 detects rotation angle φ of pinion shaft 38 or the rotating shaft of the electric motor of steering actuator 32 to detect steering angle δ of front wheels 28FL and 28FR.

[0037] 1, the ECU 14 includes a microcomputer and a drive circuit. The microcomputer has a CPU, a ROM, a RAM, an interface (I / F), and the like, and has a general configuration in which these are connected to each other by a bidirectional common bus.

[0038] The ECU 14 receives a signal indicating the steering angle θ detected by the steering angle detection device 22, and a signal indicating the steering angle δ of the front wheels 28FL and 28FR detected by the steering angle detection device 34. The ECU 14 also receives a signal indicating the vehicle speed V detected by the vehicle speed sensor 44, and a signal indicating white line information of the lane ahead of the vehicle 60 acquired by the camera sensor 46. The vehicle speed sensor 44 detects the vehicle speed V based on, for example, the wheel speed.

[0039] Furthermore, a signal indicating whether or not the LKA switch 48 is on is input to the ECU 14. When the LKA switch 48 is on, the ECU 14 executes the LKA control.

[0040] 3, the camera sensor 46 is fixed to an upper portion of the inner surface of the windshield 50a of the vehicle 60, and captures an image of the front of the vehicle 60, centered on an imaging reference position Pca that is a distance Lca (a positive constant) forward from the center of gravity 50b, which is the reference position of the vehicle 60. The distance Lca is referred to as an imaging reference distance Lca as necessary. The reference position of the vehicle 60 may be the positions of the front wheels 28FL and 28FR, a midpoint between the front and rear wheels, or the like.

[0041] When LKA switch 48 is off, ECU 14 sets steering gear ratio Rst to standard steering gear ratio Rstn and controls steering actuator 32 based on steering angle θ detected by steering angle detection device 22. Thus, steering angle δ of front wheels 28FL and 28FR is controlled to θ / Rstn. Note that steering angle θ and steering angle δ are 0 when vehicle 60 is traveling straight, and are positive values ​​when vehicle 60 turns left. Also, standard steering gear ratio Rstn is a positive value that is preset to increase as vehicle speed V increases, but may be a positive constant.

[0042] Furthermore, the ECU 14 calculates a basic steering reaction torque Treb to be applied to the steering wheel 20 based on the steering angle θ, a derivative of the steering angle θ, and a second-order derivative of the steering angle θ. The basic steering reaction torque Treb is variably set according to the vehicle speed so that the basic steering reaction torque Treb increases as the vehicle speed V increases. The basic steering reaction torque Treb may be controlled in any manner known in the art. For example, the basic steering reaction torque Treb may be a torque corresponding to the steering torque felt by the driver through the steering wheel in a vehicle in which the steering wheel is mechanically connected to the steered wheels and a steering assist torque is applied by a power steering device.

[0043] Furthermore, as will be described in detail later, the ECU 14 calculates a target steering guide torque Tsgt that guides the driver's steering when the vehicle 60 travels around a curve on a road. Furthermore, the ECU 14 controls the reaction force actuator 24 so that the steering reaction torque Tre generated by the reaction force actuator 24 and applied to the steering wheel 20 becomes a target steering reaction torque Tret, which is the sum of the basic steering reaction torque Treb and the target steering guide torque Tsgt. Thus, the reaction force actuator 24 functions as a torque applying device that applies a steering guide torque Tsg corresponding to the target steering guide torque Tsgt to the steering wheel 20. The magnitude of the target steering guide torque Tsgt is about one tenth of the magnitude of the basic steering reaction torque Treb.

[0044] The target steering guide torque Tsgt acts in a direction to suppress steering when the driver steers the vehicle further so that the actual steering angle θ moves away from the target steering angle θt. In contrast, the target steering guide torque Tsgt acts in a direction to promote steering when the driver steers the vehicle back so that the actual steering angle θ approaches the target steering angle θt. Therefore, the target steering guide torque Tsgt guides the driver's steering so that the actual steering angle θ falls within a predetermined range of steering operation amounts including the target steering angle θt.

[0045] In the embodiment, the ECU 14 calculates the curve curvature ρca of the road for an area centered on the photographing reference position Pca based on the white line information of the lane ahead of the vehicle 60 acquired by the camera sensor 46, and stores the calculated value in the RAM. Therefore, the camera sensor 46 and the ECU 14 function as a detection device that detects the curve curvature ρca of the road for an area centered on the photographing reference position Pca.

[0046] Furthermore, the ECU 14 reads out the curve curvature ρca corresponding to the look-ahead time Δt from the RAM as the look-ahead curve curvature ρpre, calculates the target steering angle θt based on the curve curvature ρpre, and calculates the steering guide torque Tsg based on the deviation Δθ between the target steering angle θt and the actual steering angle θ. The target steering angle θt is a target steering angle for making it easier for the actual steering angle to remain within an appropriate range so that the vehicle 60 travels along the curve. In this embodiment, the curvature in the direction in which the vehicle 60 turns left is positive.

[0047] The curve curvature ρca [1 / m] is calculated according to the following formula (1). In the following formula (1), V is the vehicle speed [m / s], and ρ0 is the curve curvature [1 / m] of the road at the center of gravity 50b of the vehicle 60. Therefore, ρ0 is the curve curvature ρca calculated and stored in RAM a time Lca / V before the vehicle 60 travels the shooting reference distance Lca shown in Fig. 1. Δρ is the rate of change [1 / m / m] of the curve curvature ρca calculated and stored in RAM a time Lca / V before, i.e., the amount of change in the curve curvature per unit distance. ρca=ρ0+VΔtΔρ …(1)

[0048] 1, the distance (read-ahead distance) Lpre between the center of gravity 50b of the vehicle 60 and the look-ahead position Ppre is smaller than the shooting reference distance Lca. Note that the look-ahead distance Lpre does not have to be constant. As can be seen from the above explanation, the curve curvature ρpre is the curve curvature at the look-ahead position Ppre, that is, the curve curvature at the position where the center of gravity 50b of the vehicle 60 reaches after the look-ahead time Δt.

[0049] The target steering angle θt [deg] is calculated according to the following formula (2). In the following formula (2), Rst is the steering gear ratio as described above, and A is the stability factor [deg / (m 2 / s 2 )], and Lw is the wheelbase of the vehicle 60. The stability factor A and the wheelbase Lw are known constant values ​​determined by the specifications of the vehicle 60. θt = Rst(1 + AV 2 )ρpreLw …(2)

[0050] In addition, the ECU 14 calculates the steering angle deviation Δθ, which is the deviation θ-θt between the actual steering angle θ and the target steering angle θt, and calculates the target basic steering guide torque Tsgtb by referring to the map shown in Figure 10 based on the steering angle deviation Δθ.

[0051] In particular, the ECU 14 calculates the number of times that 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 determination time Tc up to the present as the index value Nin. The ECU 14 calculates the correction coefficient Ks by referring to the map shown in FIG. 9 based on the index value Nin.

[0052] The determination time Tc may be constant, but in this embodiment and other embodiments described later, it is variably set according to the frequency at which the vehicle 60 travels around a curve, so that the determination time Tc is longer as the frequency at which the vehicle 60 travels around a curve decreases. Also, the reference value θa may be constant, but in this embodiment and other embodiments described later, it is variably set according to the vehicle speed, so that the reference value θa is smaller as the vehicle speed V is higher.

[0053] Furthermore, the ECU 14 calculates the target steering guide torque Tsgt as the product KsTsgtb of the correction coefficient Ks and the target basic steering guide torque Tsgtb. Furthermore, the ECU 14 controls the reaction force actuator 24 so that the steering reaction torque Tre becomes the target steering reaction torque Tret.

[0054] When the LKA switch 48 is on and the driver is not performing a steering operation, the ECU 14 performs the LKA control without performing the steering guide torque control. Furthermore, when the driver performs a steering operation in a situation where the LKA switch 48 is on and the LKA control is being performed, the ECU 14 stops the LKA control and performs the steering guide torque control.

[0055] <Steering reaction torque control routine> Next, a control routine for steering reaction torque in the first embodiment will be described. When an ignition switch (not shown) is on, the CPU of the ECU 14 executes a control routine for steering reaction torque shown in the flowchart of Fig. 3 every time a predetermined time elapses. The control program corresponding to the flowchart of Fig. 3 is stored in the ROM of the ECU 14.

[0056] First, in step S10, the CPU determines whether or not the LKA switch 48 is on. If the CPU determines negatively, the CPU advances the control of the steering reaction torque to step S40, and if the CPU determines positively, the CPU advances the control of the steering reaction torque to step S20.

[0057] In step S20, the CPU determines whether or not the driver has performed a steering operation that intervenes in the LKA control. If the CPU determines negative, it executes the LKA control in step S30, and if the CPU determines positive, it advances the control of the steering reaction torque to step S40. The LKA control may be performed in any manner known in the art, and the determination of whether or not the driver has performed a steering operation that intervenes in the LKA control may also be performed in any manner known in the art.

[0058] In step S40, the CPU determines the judgment time Tc based on the frequency with which the vehicle 60 travels around a curve, as described above, and also determines the reference value θa based on the vehicle speed V, as described above. Furthermore, the CPU calculates the number of times that the difference between the absolute value of the actual steering angle θ and the absolute value of the target steering angle θt has exceeded the reference value θa within the judgment time Tc up to the present, as an index value Nin.

[0059] In step S50, the CPU calculates a correction coefficient Ks based on the index value Nin by referring to a map shown in Fig. 9. As shown in Fig. 9, the correction coefficient Ks is 1 when the index value Nin is 0, and when the index value Nin is less than Nins (a positive constant), the correction coefficient Ks decreases as the index value Nin increases, and is calculated to a constant value of Ksmin when the index value Nin is equal to or greater than Nins.

[0060] In step S70, the CPU calculates the target basic steering guide torque Tsgtb in accordance with the flowchart shown in FIG.

[0061] In step S90, the CPU calculates a target steering guide torque Tsgt that guides the driver's steering when the vehicle 60 travels around a curve in the road, as a product KsTsgtb of the correction coefficient Ks and the target basic steering guide torque Tsgtb.

[0062] In step S120, the CPU calculates a 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, the second derivative of the steering angle θ, and the vehicle speed V in any manner known in the art.

[0063] In step S130, the CPU calculates the target steering reaction torque Tret as the sum Treb+Tsgt of the basic steering reaction torque Treb and the target steering guide torque Tsgt.

[0064] In step S140, the CPU controls the reaction force actuator 24 so that the steering reaction torque Tre generated by the reaction force actuator 24 becomes the target steering reaction torque Tret. Thus, a steering reaction torque corresponding to the target steering reaction torque Tret is applied to the steering wheel 20, and thereby a steering guide torque Tsg corresponding to the target steering guide torque Tsgt is applied to the steering wheel 20.

[0065] In step S72 of the flowchart shown in FIG. 4, the CPU calculates the rate of change Δρ of the curve's curvature for the area centered on the shooting reference position Pca based on the white line information of the lane ahead of the vehicle 60 acquired by the camera sensor 46, and stores the rate of change Δρ in the RAM.

[0066] In step S74, the curve curvature ρca of the road is calculated for the area centered on the photographing reference position Pca according to the above formula (1) and stored in the RAM. Note that the curve curvature ρca may be set to 0 until the time Lca / V has elapsed since the control was started.

[0067] In step S76, the CPU reads out from the RAM the curve curvature ρca that was calculated before the look-ahead time Δt and stored in the RAM as the curve curvature ρpre at the look-ahead position Ppre.

[0068] In step S78, the CPU calculates the target steering angle θt as a target steering operation amount for the vehicle 60 to travel along the curve of the road, in accordance with the vehicle speed V and the curve curvature ρpre at the read-ahead position Ppre, in accordance with the above equation (2).

[0069] In step S80, the CPU calculates a steering angle deviation Δθ, which is the deviation θ-θt between the actual steering angle θ detected by the steering angle detection device 22 and the target steering angle θt.

[0070] In step S82, the CPU calculates the target basic steering guide torque Tsgtb by referring to the map shown in Fig. 10 based on the steering angle deviation Δθ. As shown in Fig. 10, when the absolute value of the steering angle deviation Δθ is less than Δθc (a positive constant), the target basic steering guide torque Tsgtb is calculated so that the magnitude increases as the absolute value of the steering angle deviation Δθ increases, and when the absolute value of the steering angle deviation Δθ is equal to or greater than Δθc, the magnitude becomes a constant value of Tsgtbmax.

[0071] [Second embodiment] Fig. 5 is a flowchart showing a control routine for steering reaction torque in a second embodiment configured as a modified example of the first embodiment. In Fig. 5, the same steps as those shown in Fig. 3 are assigned the same step numbers as those assigned in Fig. 3. This also applies to other embodiments described later.

[0072] In the second embodiment and a fourth embodiment described later, the LKA control is not executed, and therefore, although not shown, the steering guide torque control device 10 according to these embodiments is not provided with an LKA switch 48.

[0073] As can be seen from a comparison between FIG. 5 and FIG. 3, steps 10 to 30 in the first embodiment are not executed, and steps 40 to 140 are executed in the same manner as steps 40 to 140 in the first embodiment, respectively.

[0074] According to the first and second embodiments, the number of times that 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 judgment time Tc up to the present is calculated as the index value Nin (step S40). The correction coefficient Ks is calculated based on the index value Nin (step S50), and the target basic steering guide torque Tsgtb is calculated (step S70). Furthermore, the target steering guide torque Tsgt is calculated as the product KsTsgtb of the correction coefficient Ks and the target basic steering guide torque Tsgtb (step S90).

[0075] Since the correction coefficient Ks is calculated so as to be smaller as the index value Nin is larger (FIG. 9), the ratio of the target steering guide torque Tsgt to the deviation Δθ decreases as the index value Nin is larger. Therefore, the magnitude of the target steering guide torque can be reduced as the driver tends to drive a curve different from the curve drive according to the target steering angle.

[0076] Fig. 13 shows the relationship between the absolute value of the actual steering angle θ, the index value Nin, and the absolute value of the target steering guide torque Tsgt. As shown in Fig. 13, the larger the index value Nin, the smaller the magnitude of the target steering guide torque Tsgt in the region where the magnitude of the actual steering angle θ exceeds the magnitude of the target steering angle θt. As can be seen from Fig. 13, when the steering operation is performed so that the magnitude of the actual steering angle θ is larger than the magnitude of the target steering angle θt, the larger the index value Nin, the smaller the reaction torque caused by the steering guide torque can be.

[0077] [Third embodiment] FIG. 6 is a flowchart showing a control routine for steering reaction torque in the third embodiment of the present invention.

[0078] As can be seen from a comparison of Figure 6 with Figure 3, in the second embodiment, steps 10 to 40 and steps 120 to 140 are performed in the same manner as in the first embodiment. After step 40 is completed, steps 60 and 100 are performed.

[0079] In step S60, the CPU calculates the corrective steering angle Δθa based on the index value Nin by referring to the map shown in Fig. 11. As shown in Fig. 11, the corrective steering angle Δθa is calculated to be 0 when the index value Nin is 0, and to be larger as the index value Nin increases when the index value Nin is less than Nina (a positive constant), and to be a constant value of Δθamax when the index value Nin is equal to or greater than Nina.

[0080] In step S100, the CPU calculates the target steering guide torque Tsgt in accordance with the flowchart shown in FIG.

[0081] As can be seen from a comparison of FIG. 7 with FIG. 4, steps 102 through 108 are performed in the same manner as steps 72 through 78, respectively, in the first embodiment.

[0082] In step S110 executed after step S108, the steering angle deviation Δθ is calculated according to the following equation (3) with sign θt as the sign of the target steering angle θt. That is, the steering angle deviation Δθ is calculated as the deviation θ-(θt+Δθa·signθt) between the actual steering angle θ detected by steering angle detection device 22 and the target steering angle θta (=θt+Δθa·signθt) whose magnitude has been increased and corrected by the correction steering angle Δθa. Δθ=θ-(θt+Δθa·signθt) =θ-θt-Δθa·signθt …(3)

[0083] In step S112, the CPU calculates the target steering guide torque Tsgt by referring to the map shown in Fig. 12 based on the steering angle deviation Δθ. As shown in Fig. 12, when the absolute value of the steering angle deviation Δθ is less than Δθc, the target steering guide torque Tsgt increases as the absolute value of the steering angle deviation Δθ increases, and when the absolute value of the steering angle deviation Δθ is equal to or greater than Δθc, the target steering guide torque Tsgt is calculated to be a constant value of Tsgtmax.

[0084] [Fourth embodiment] FIG. 8 is a flowchart showing a control routine for steering reaction torque in the fourth embodiment configured as a modified example of the third embodiment.

[0085] As can be seen from a comparison between FIG. 8 and FIG. 6, steps 10 to 30 in the third embodiment are not performed, and steps 40 to 140 are performed in the same manner as steps 40 to 140, respectively, in the third embodiment.

[0086] According to the third and fourth embodiments, the number of times that 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 judgment time Tc up to the present is calculated as an index value Nin (step S40). A correction steering angle Δθa is calculated based on the index value Nin (step S60), and a target steering guide torque Tsgt is calculated according to the flowchart shown in FIG. 7 (step S100).

[0087] The deviation Δθ of the steering angle is calculated as the deviation between the actual steering angle θ and the target steering angle θt+Δθa·signθt whose magnitude has been increased and corrected by the correction steering angle Δθa (step S110). Therefore, the magnitude of the target steering guide torque Tsgt can be reduced when the magnitude of the actual steering angle θ becomes larger than the magnitude of the target steering angle that is not increased and corrected.

[0088] According to the first and third embodiments described above, when the driver performs a steering operation to intervene in the LKA control while the LKA switch 48 is on, a positive determination is made in steps S10 and S20, and steps S40 to S140 are executed. Therefore, when the driver starts an intervening steering operation while the LKA control is being executed, the LKA control is automatically stopped, and the steering guide torque control can be automatically started without the need for a switch operation or the like. <Effects common to the first to fourth embodiments>

[0089] As can be seen from the above description, according to the first to fourth embodiments described above, the target steering guide torque can be corrected according to the index value so that the magnitude of the target steering guide torque Tsgt decreases as the index value Nin increases. Therefore, compared to a case in which the target steering guide torque is not corrected according to the index value, it is possible to reduce the possibility that the driver will feel uncomfortable due to an increase in steering reaction force caused by the steering guide torque when the vehicle is traveling around a curve.

[0090] According to the first to fourth embodiments, the judgment time Tc is variably set according to the frequency with which the vehicle 60 travels around a curve, so that the judgment time Tc is longer as the frequency with which the vehicle 60 travels around a curve decreases. Therefore, regardless of the number of curves, the index value can be calculated as a value indicating the tendency of the driver to perform a steering operation such that the actual steering angle differs from the target steering angle.

[0091] Furthermore, according to the first to fourth embodiments, the reference value θa is variably set according to the vehicle speed so as to be smaller as the vehicle speed V increases. Therefore, regardless of the turning radius of the curve, the index value can be calculated as a value indicating the tendency of the driver to perform steering operation so that the actual steering angle differs from the target steering angle.

[0092] Although the present invention has been described in detail above with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments, and that various other embodiments are possible within the scope of the present invention.

[0093] For example, in the above-described embodiment, the index value Nin is calculated as the number of times that 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 judgment time Tc up to the present. However, the index value Nin may be calculated as the accumulated time during which 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 judgment time Tc up to the present. In addition, the number of times and the accumulated time may be Nc and Tc, respectively, and α and β may be positive constants, and the index value Nin may be calculated based on both the number of times and the accumulated time as a linear sum αNc+βTc of the number of times and the accumulated time.

[0094] In the above-described embodiment, the automatic steering control in which the steering device (18) automatically steers the steered wheels (28FL, 28FR) so that the vehicle (60) travels along the lane even if the steering input member (steering wheel 20) is not steered by the driver is the LKA control. However, the automatic steering control may be any automatic steering control known in the art, such as an automatic driving control.

[0095] In the first and third embodiments described above, when the driver performs a steering operation that intervenes in the LKA control, the LKA control is stopped and the steering guide torque control of steps S40 to S140 is automatically started. However, the steering guide torque control that is started when the driver performs a steering operation that intervenes in the LKA control may be a steering guide torque control in which the target steering guide torque is not corrected according to the index value.

[0096] Furthermore, in the above-described embodiment, the steering guide torque control device 10 is configured as a steering reaction torque control device including a steer-by-wire type steering device 12. However, the steering guide torque control device 10 may be configured as a steering reaction torque control device including an electric power steering device in which the steering wheel and the left and right front wheels are mechanically connected. In that case, the target steering assist torque Tsat is calculated as the sum of the basic steering assist torque Tsab and the target steering guide torque Tsgt, which are calculated based on the steering torque and the vehicle speed. Furthermore, the electric power steering device is controlled so that the steering assist torque Tsa generated by the electric power steering device becomes the target steering assist torque Tsat. [Explanation of symbols]

[0097] 10...vehicle steering assist torque control device, 12...steering device, 14...ECU, 20...steering wheel, 22...steering angle detection device, 24...reaction force actuator, 28FL, 28FR...front wheels, 30...steering mechanism, 44...vehicle speed sensor, 46...camera sensor, 48...LKA switch, 60...vehicle

Claims

1. a steering input member that is steered by a driver, a steering device that steers steered wheels in accordance with an amount of steering operation applied to the steering input member, a torque imparting device that imparts a steering guide torque to the steering input member, a control unit that controls the torque imparting device, and an imaging device that captures an image of a front of the vehicle, a control unit for performing steering guide torque control for a vehicle, the control unit being configured to estimate a curvature of a lane ahead of the vehicle for driving the vehicle along the lane based on an image acquired by the imaging device, calculate a target steering operation amount based on the curvature of the lane, calculate a target steering guide torque for guiding steering by the driver so that the actual steering operation amount falls within a range of predetermined steering operation amounts including the target steering operation amount based on a deviation between the target steering operation amount and an actual steering operation amount, and perform steering guide torque control for controlling the torque applying device so that the steering guide torque becomes the target steering guide torque; the control unit is configured to obtain an index value indicating at least one of the number of times that a difference between a magnitude of an actual steering operation amount and a magnitude of the target steering operation amount has exceeded a reference value within a determination time up to the present and an integrated time, and to correct the target steering guide torque in accordance with the index value such that the magnitude of the target steering guide torque becomes smaller as the index value increases, A steering guide torque control device for a vehicle, wherein the control unit is configured to variably set the judgment time according to the frequency with which the vehicle travels around a curve, so that the judgment time is longer the lower the frequency with which the vehicle travels around a curve.

2. 2. The vehicle steering guide torque control device according to claim 1, wherein the control unit is configured to reduce a ratio of the target steering guide torque to the deviation as the index value increases.

3. 3. The vehicle steering guide torque control device according to claim 2, wherein the control unit is configured to increase and correct the magnitude of the target steering operation amount by a correction amount that increases as the index value increases.

4. 2. A steering guide torque control device for a vehicle according to claim 1, wherein the control unit is configured to acquire information on vehicle speed and variably set the reference value according to the vehicle speed so that the reference value becomes smaller as the vehicle speed increases.

5. In the steering guide torque control device for a vehicle described in any one of claims 1 to 4, the control unit is configured to execute automatic steering control in which the steering device automatically steers the steered wheels so that the vehicle travels along a lane even if the steering input member is not steered by the driver, and when it is determined that the driver has started steering the steering input member while the automatic steering control is being executed, the control unit is configured to stop the automatic steering control and start the steering guide torque control.

Images