Vehicle Steering Guide Torque Control Device

Abstract

To provide a steering guide torque controller improved to minimize the risk that a driver may feel a steering resistance attributable to a steering guide torque in a situation where the driver performs a steering maneuver to deviate from a lane by correcting the steering guide torque according to the possibility the driver may perform the steering maneuver for lane deviation.SOLUTION: A control unit that controls a reaction force actuator which applies a steering guide torque to a steering wheel computes a target steering guide torque Tsgt, which is used to force a vehicle to travel along a lane, on the basis of information on the lane ahead of a vehicle which is detected by a camera sensor (S50 to S120), corrects the target steering guide torque so that the target steering guide torque will get smaller as the possibility that a driver may perform a steering maneuver to deviate from a lane is higher (S100 to S150), and controls the reaction force actuator so that the steering guide torque will be equal to the target steering guide torque (S160 to S180).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a steering guide torque control device for vehicles such as automobiles.

Background Art

[0002] As a steering reaction force torque control device for vehicles such as automobiles, for example, as described in Patent Document 1 below, an appropriate steering operation amount of a driver is predicted based on a detection result of an external sensor, and when the steering operation amount of the driver corresponding to the prediction time of the appropriate steering operation amount is not within the appropriate steering operation amount range, a steering reaction force torque control device is configured to increase the steering reaction force torque until the steering operation amount reaches within the appropriate steering operation amount range more than conventionally is known.

[0003] The steering reaction force torque acts as a steering reaction force torque against 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 promotes the steering operation when the steering operation amount reaches within the appropriate steering operation amount range from outside the range. Therefore, the steering reaction force torque control device described in Patent Document 1 below may be called a steering guide torque control device.

[0004] As a steering guide torque control device, based on the curvature of a curve of a traveling road ahead of a vehicle detected by a camera sensor, a target steering angle for traveling the vehicle along the curve is calculated, and based on the deviation between the target steering angle considering the prediction time and the actual steering angle, a target steering guide torque for guiding the driver's steering so that the actual steering operation amount is within a predetermined steering operation amount range including the target steering operation amount is calculated, and a steering guide torque control device that controls a torque applying device so that the steering guide torque becomes the target steering guide torque is known.

[0005] According to the steering reaction torque control device and the steering guide torque control device as described above, when the vehicle is traveling on a curve of a road, it is possible to prompt the driver to perform a steering operation so that the actual steering angle is within the range of an appropriate steering operation amount. Therefore, it is possible to perform steering assistance so that the driver's steering operation amount becomes an appropriate steering operation amount while maintaining the driver's sense of steering initiative.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] 〔Problems to be Solved by the Invention〕 Even in a situation where the steering guide torque control device is operating, for example, when the driver makes a steering operation to deviate from the lane in which the vehicle is currently traveling, such as changing the course to the side road. Since the steering guide torque control device generates a steering guide torque suitable for traveling along the lane in which the vehicle is currently traveling, when a steering operation for lane departure is performed, the steering guide torque acts as a torque that interferes with the lane departure. Therefore, it is inevitable that the driver feels the steering resistance caused by the steering guide torque.

[0008] The main problem of the present invention is to reduce the steering resistance caused by the steering guide torque in a situation where the driver performs a steering operation for lane departure by correcting the steering guide torque according to the possibility that the driver performs a steering operation for lane departure. It is to provide an improved steering guide torque control device.

[0009] 〔Means for Solving the Problems and Effects of the Invention〕 According to the present invention, a steering input member (steering wheel 20) steered by a driver, a steering device (18) that steers steered wheels (28FL, 28FR) according to a steering operation amount applied to the steering input member, a torque applying device (reaction actuator 24) that applies steering guide torque (Tsg) to the steering input member, a control unit (ECU14) that controls the torque applying device, and a photographing device (camera sensor 46) that acquires an image in front of the vehicle (60) are included. The control unit (ECU14) calculates a target steering guide torque (Tsgt) for guiding the driver's steering so that the vehicle (60) travels along the lane recognized based on the image acquired by the imaging device, and is configured to control the torque applying device (reaction actuator 24) so that the steering guide torque becomes the target steering guide torque A vehicle steering guide torque control device (10) is provided.

[0011] The control unit (ECU14) estimates the possibility that the driver performs a steering operation of deviating from the lane based on at least one of the vehicle speed (V) and the deceleration amount (deceleration ΔV) of the vehicle, and when it is determined that it is necessary to correct the target steering guide torque, the target steering guide torque (Tsgt) is configured to be corrected according to the possibility such that the higher the possibility, the smaller the target steering guide torque. ( S10~S40) Further, the control unit (ECU14) is configured to acquire information on the deceleration rate (deceleration amount ΔV) of the vehicle and determine that the higher the deceleration rate of the vehicle, the higher the possibility (S100). 。

[0012] According to the above configuration, the torque applying device is controlled so that the vehicle travels along the lane recognized based on the image acquired by the photographing device. Therefore, steering guide torque for causing the vehicle to travel along the lane can be 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 an appropriate steering operation amount.

[0013] Furthermore, according to the above configuration, based on at least one of the vehicle speed and the deceleration amount of the vehicle, the possibility that the driver performs a steering operation of deviating from the lane is estimated, and when it is determined that it is necessary to correct the target steering guide torque, the target steering guide torque is corrected according to the possibility such that the higher the possibility, the smaller the target steering guide torque. Therefore, based on at least one of the vehicle speed and the deceleration amount of the vehicle, the possibility that the driver performs a steering operation of deviating from the lane can be estimated, and the risk of feeling steering resistance caused by the steering guide torque in a situation where the driver performs a steering operation of deviating from the lane can be reduced.

[0014] When a driver attempts a lane departure such as changing lanes to the side road, the vehicle is decelerated, so the vehicle speed decreases. Also, the greater the number of selectable lanes within a predetermined distance range from the vehicle, the higher the possibility that the driver will perform a steering operation for lane departure. Therefore, the "possibility that the driver will perform a steering operation for lane departure" may be estimated based on the vehicle speed, the deceleration of the vehicle, the number of selectable lanes within a predetermined distance range from the vehicle, and the like. Furthermore, according to the above configuration, since it is determined that the higher the deceleration rate of the vehicle, the higher the possibility, the higher the deceleration rate, the smaller the target steering guide torque, and in a situation where the driver performs a steering operation of deviating from the lane, it is possible to reduce the risk of feeling the steering resistance caused by the steering guide torque.

[0015] In one aspect of the present invention, the control unit (ECU14) is configured to acquire information on the vehicle speed (V) and determine that the lower the vehicle speed, the higher the possibility (S90).

[0016] According to the above aspect, since it is determined that the lower the vehicle speed, the higher the possibility, the lower the vehicle speed, the smaller the target steering guide torque, and the risk of feeling the steering resistance caused by the steering guide torque in a situation where the driver performs a steering operation for lane departure can be reduced.

[0019] Furthermore, in another aspect of the present invention, the control unit (ECU14) acquires information on the number (Nr) of selectable lanes within a predetermined distance range (70) from the vehicle, sets a limit guide torque (Tsgmax) to decrease as the number of selectable lanes increases, and determines that it is necessary to correct the target steering guide torque (Tsgt) when the magnitude of the target steering guide torque exceeds the limit guide torque, and corrects the target steering guide torque by limiting the magnitude of the target steering guide torque to the limit guide torque (S120 - S140).

[0020] According to the above aspect, the limit guide torque is set so as to decrease as the number of selectable lanes increases. When the magnitude of the target steering guide torque exceeds the limit guide torque, it is determined that it is necessary to correct the target steering guide torque, and the target steering guide torque is corrected by limiting the magnitude of the target steering guide torque to the limit guide torque. Therefore, when the magnitude of the target steering guide torque exceeds the limit guide torque, the target steering guide torque can be limited so that the magnitude of the target steering guide torque decreases as the number of selectable lanes increases.

[0021] Furthermore, in another aspect of the present invention, the control unit (ECU14) is configured to acquire information on the vehicle speed (V) and decrease the limit guide torque (Tsgmax) as the vehicle speed is lower (S120).

[0022] According to the above aspect, since the limit guide torque is decreased as the vehicle speed is lower, the maximum value of the magnitude of the target steering guide torque can be decreased as the vehicle speed is lower.

[0023] In the above description, for the purpose of assisting the understanding of the present invention, reference numerals used in the embodiments corresponding to the configurations of the invention to be described later are attached in parentheses. However, each component of the present invention is not limited to the component of the embodiment corresponding to the reference numeral attached in parentheses. Other objects, other features, and attendant advantages of the present invention will be easily understood from the description of the embodiments of the present invention described with reference to the following drawings.

Brief Description of the Drawings

[0024]

Figure 1

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Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0025] Embodiments of the present invention will be described in detail below with reference to the attached drawings. <Configuration>

[0026] A vehicle steering guide torque control device 10 according to an embodiment is configured as a steering reaction force torque control device including a steer-by-wire type steering device 12 and an electronic control unit 14 for controlling the same, as shown in FIG. 1, and is applied to a vehicle 60. In the following description and drawings, the "electronic control unit" is denoted as "ECU".

[0027] The steering device 12 includes a steering input device 16 and a steering gear 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.

[0028] The steering wheel 20 is a steering input member that is steered by a driver (not shown), and may be in the form of a steering column. The reaction force actuator 24 includes an electric motor, and the rotation 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.

[0029] The steering gear 18 includes a steering mechanism 30 configured to steer the left and right front wheels 28FL and 28FR, which are steering wheels, in response to a steering torque Tst, 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.

[0030] 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. The pinion shaft 38 has a pinion that meshes with the rack teeth of the rack bar 36 (not shown in the figure). The rotational movement of the pinion shaft 38 is converted into the reciprocating movement of the rack bar 36, and the reciprocating movement of the rack bar 36 is converted into the rotational movement of the pinion shaft 38. Note that the steering mechanism may have any structure known in the art.

[0031] Furthermore, the steering mechanism 30 includes tie rods 42L and 42R. The inner ends of the tie rods 42L and 42R are pivotally attached to the left and right ends of the rack bar 36, respectively. The outer ends of the tie rods 42L and 42R are pivotally attached to the knuckle arms of the front wheels 28FL and 28FR (not shown in the figure). The steering actuator 32 includes an electric motor, and the rotation shaft of the electric motor is integrally connected to the pinion shaft 38.

[0032] Therefore, the steering mechanism 30 is configured to receive the steering torque from the steering actuator 32 via the pinion shaft 38 and steer the front wheels 28FL and 28FR. There is a certain relationship between the rotation angle φ (not shown in the figure) of the pinion shaft 38 and the steering angle δ of the front wheels 28FL and 28FR. Therefore, in the illustrated embodiment, the steering angle detection device 34 detects the steering angle δ of the front wheels 28FL and 28FR by detecting the rotation angle φ of the pinion shaft 38 or the rotation shaft of the electric motor of the steering actuator 32.

[0033] Although not shown in detail in FIG. 1, the ECU 14 includes a microcomputer and a drive circuit. The microcomputer has a general configuration having a CPU, a ROM, a RAM, and an interface (I / F), etc., which are connected to each other by a bidirectional common bus.

[0034] A signal indicating the steering angle θ detected by the steering angle detection device 22 is input to the ECU 14, and a signal indicating the steering angle δ of the front wheels 28FL and 28FR detected by the steering angle detection device 34 is input. Further, a signal indicating the vehicle speed V detected by the vehicle speed sensor 44 is input to the ECU 14, and a signal indicating the white line information of the lane in front of the vehicle 60 acquired by the camera sensor 46 is input. The vehicle speed sensor 44 detects the vehicle speed V based on, for example, the wheel speed.

[0035] Furthermore, a signal indicating whether the turn signal lamp is flashing from the turn signal lamp 48 is input to the ECU 14, and a signal indicating the position information of the vehicle 60 and the road information of the road on which the vehicle is traveling and its surroundings by the navigation device 50 is input.

[0036] As shown in FIG. 3, the camera sensor 46 is fixed to an upper portion of the inner surface of the front glass 50a of the vehicle 60, and captures an image in front of the vehicle 60 with the imaging reference position Pca, which is at a distance Lca (positive constant) forward from the center of gravity 50b, which is the reference position of the vehicle 60, as the center. The distance Lca is referred to as the imaging reference distance Lca as needed. The reference position of the vehicle 60 may be the positions of the front wheels 28FL and 28FR, the intermediate position between the front and rear wheels, etc.

[0037] The ECU 14 controls the steering actuator 32 based on the steering angle θ detected by the steering angle detection device 22 by setting the steering gear ratio Rst to the standard steering gear ratio Rstn. Therefore, the steering angles δ of the front wheels 28FL and 28FR are controlled to be θ / Rstn. Note that the steering angle θ and the steering angle δ become 0 when the vehicle 60 is in a straight-ahead state, and become positive values when the vehicle 60 turns left. The standard steering gear ratio Rstn is a positive value preset to increase as the vehicle speed V increases, but may be a positive constant.

[0038] Furthermore, the ECU 14 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, and the second-order differential value of the steering angle θ. The basic steering reaction torque Treb is variably set according to the vehicle speed so as to increase as the vehicle speed V increases. Note that the basic steering reaction torque Treb may be controlled in any known manner in the art. For example, 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, the basic steering reaction torque Treb may be a torque corresponding to the steering torque felt by the driver via the steering wheel.

[0039] Further, 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 on a curve of a road. Further, the ECU 14 controls the reaction force actuator 24 so that the steering reaction force torque Tre generated by the reaction force actuator 24 and applied to the steering wheel 20 becomes a target steering reaction force torque Tret that is the sum of the basic steering reaction force torque Treb and the target steering guide torque Tsgt. Therefore, 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. Note that the magnitude of the target steering guide torque Tsgt is about one-tenth of the magnitude of the basic steering reaction force torque Treb.

[0040] Note that the target steering guide torque Tsgt acts in a direction to suppress steering when the driver makes an additional steering so that the actual steering angle θ deviates from the target steering angle θt, and acts in a direction to promote steering when the driver makes a return steering 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 becomes the target steering angle θt.

[0041] In the embodiment, the ECU 14 calculates the curve curvature ρca of the road on a region centered on the imaging reference position Pca based on the white line information of the lane in front of the vehicle 60 acquired by the camera sensor 46, and stores it 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 on a region centered on the imaging reference position Pca.

[0042] 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 stay within a range suitable for running the vehicle 60 along a curve. In the embodiment, the curvature in the left-turning direction of the vehicle 60 is positive.

[0043] 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 traveling path at the center of gravity 50b of the vehicle 60. Therefore, ρ0 is the curve curvature ρca calculated and stored in the RAM before the time Lca / V required for the vehicle 60 to travel the imaging reference distance Lca shown in FIG. 1. Δρ is the change rate [1 / m / m] of the curve curvature ρca calculated and stored in the RAM before the time Lca / V, that is, the change amount per unit distance of the curve curvature. ρca = ρ0 + VΔtΔρ …(1)

[0044] As shown in FIG. 1, the distance (look-ahead distance) Lpre between the center of gravity 50b of the vehicle 60 and the look-ahead position Ppre is smaller than the imaging reference distance Lca. Note that the look-ahead distance Lpre does not have to be constant. As can be understood from the above description, 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.

[0045] 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, A is the stability factor [deg / (m 2 / s 2 )] of the vehicle 60, 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 + AV2 )ρpreLw …(2)

[0046] Furthermore, the ECU 14 calculates a target basic steering guide torque Tsgtb based on a steering angle deviation Δθ, which is the deviation θ - θt between the actual steering angle θ and the target steering angle θt. Further, the ECU 14 calculates a target steering guide torque Tsgt as the product KvKaTsgtb of the vehicle speed coefficient Kv, the correction coefficient Ka, and the target basic steering guide torque Tsgtb. Furthermore, the ECU 14 controls the reaction actuator 24 so that the steering reaction torque Tre becomes the target steering reaction torque Tret.

[0047] Note that as shown in FIG. 4, the target basic steering guide torque Tsgtb increases as the absolute value of the steering angle deviation Δθ increases when the absolute value of the steering angle deviation Δθ is less than Δθs, and is calculated to a constant value of Tsgtbmax when the absolute value of the steering angle deviation Δθ is greater than or equal to Δθs. As shown in FIG. 5, the vehicle speed coefficient Kv is a value between 0 and 1 that decreases as the vehicle speed V decreases. As shown in FIG. 6, the correction coefficient Ka is a positive value less than or equal to 1 that decreases as the deceleration amount ΔV of the vehicle 60 increases. <Control Routine for Steering Reaction Torque>

[0048] Next, the control routine for the steering reaction torque of the embodiment will be described. The CPU of the ECU 14 executes the control routine for the steering reaction torque shown in the flowchart of FIG. 3 every time a predetermined time elapses when the ignition switch (not shown in the figure) is on. Note that the control program corresponding to the flowchart of FIG. 3 is stored in the ROM of the ECU 14.

[0049] First, in step S10, the CPU determines whether the white line information of the lane in front of the vehicle 60 can be obtained by the camera sensor 46 and whether the traveling route of the vehicle can be estimated normally. When the CPU makes a negative determination, it proceeds to step S30 for the control of the steering reaction torque, and when it makes a positive determination, it proceeds to step S20 for the control of the steering reaction torque.

[0050] In step S20, the CPU determines whether the turn signal lamp 48 is blinking, that is, whether the driver is determining the lane in which the vehicle is about to travel. When the CPU makes a negative determination, it proceeds to step S40 to control the steering reaction torque. When the CPU makes an affirmative determination, in step S30, after setting the target steering guide torque Tsgt to 0, it proceeds to step S160 to control the steering reaction torque.

[0051] In step S40, the CPU calculates the change rate Δρ of the curve curvature for the area centered on the imaging reference position Pca based on the white line information of the lane in front of the vehicle 60 acquired by the camera sensor 46, and stores it in the RAM.

[0052] In step S50, according to the above formula (1), the CPU calculates the curve curvature ρca of the driving road for the area centered on the imaging reference position Pca, and stores it in the RAM. Note that the curve curvature ρca may be set to 0 until the time Lca / V has elapsed since the start of the control.

[0053] In step S60, the CPU reads from the RAM the curve curvature ρca calculated and stored in the RAM at the look-ahead time Δt as the curve curvature ρpre at the look-ahead position Ppre.

[0054] In step S70, the CPU calculates the target steering angle θt as the target steering operation amount for the vehicle 60 to travel along the curve of the driving road according to the above formula (2) based on the vehicle speed V and the curve curvature ρpre at the look-ahead position Ppre.

[0055] In step S80, the CPU calculates the 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.

[0056] In step S90, the CPU calculates the target basic steering guide torque Tsgtb by referring to the map shown in FIG. 4 based on the steering angle deviation Δθ.

[0057] In step S100, the CPU calculates the vehicle speed coefficient Kv by referring to the map shown in FIG. 5 based on the vehicle speed V. Note that V1 and V2 shown in FIG. 5 may be, for example, 20 km / h and 60 km / h, respectively. Also, in FIG. 5, the vehicle speed coefficient Kv is 0 in the region where the vehicle speed V is low, but may also be a positive value in the region where the vehicle speed V is low.

[0058] In step S110, the CPU calculates the deceleration amount ΔV of the vehicle 60 as the deviation between the vehicle speed V before a preset time and the current vehicle speed V, and calculates the correction coefficient Ka by referring to the map shown in FIG. 6 based on the deceleration amount ΔV. As shown in FIG. 6, the correction coefficient Ka is calculated as a positive value of 1 or less such that it becomes smaller as the deceleration amount ΔV increases. Note that the correction coefficient Ka is set to 1 when the deceleration amount ΔV is a negative value, that is, when the vehicle 60 is in an accelerating state, in the same manner as when the deceleration amount ΔV is 0 or a small positive value.

[0059] In step S120, the CPU calculates the target steering guide torque Tsgt for guiding the driver's steering when the vehicle 60 travels on a curve of the traveling road as the product KvKaTsgtb of the deviation Δθ of the steering angle, the vehicle speed coefficient Kv, the correction coefficient Ka, and the target basic steering guide torque Tsgtb.

[0060] In step S130, the CPU determines the number Nr of selectable lanes within a range of a predetermined distance from the vehicle based on road information around the vehicle 60 acquired from the navigation device 50. The range of the predetermined distance may be, for example, a fan-shaped region 70 within an angular range of 180 degrees on the front side of the vehicle within a range of a reference radius Rc from the center of gravity 60b which is the reference position of the vehicle 60, as shown in FIGS. 11 and 12. The reference radius Rc is a positive constant, but may be variably set according to the vehicle speed V such that it becomes larger as the vehicle speed V increases.

[0061] In the case of the examples shown in FIGS. 11 and 12, the number of lanes Nr is determined to be 2 and 3, respectively. Note that when there are a plurality of lanes on one side, "the number of those lanes - 1" may also be counted as the selectable number of lanes Nr.

[0062] Furthermore, in step S130, the CPU calculates the restricted guide torque Tsgmax by referring to the map shown in FIG. 7 based on the selectable number of lanes Nr. As shown in FIG. 7, the restricted guide torque Tsgmax is calculated such that it becomes smaller as the selectable number of lanes Nr increases and smaller as the vehicle speed V decreases.

[0063] In step S140, the CPU determines whether or not the absolute value of the target steering guide torque Tsgt calculated in step S90 exceeds the restricted guide torque Tsgmax. When the CPU makes a negative determination, it proceeds to step S160 for the control of the steering reaction torque, and when it makes an affirmative determination, it proceeds to step S150 for the control of the steering reaction torque.

[0064] In step S150, the CPU restricts the target steering guide torque Tsgt to the restricted guide torque Tsgmax so that the absolute value of the target steering guide torque Tsgt becomes the restricted guide torque Tsgmax.

[0065] In step S160, the CPU calculates the basic steering reaction torque Treb to be applied to the steering wheel 20 in any known manner in the art based on the steering angle θ, the differential value of the steering angle θ, the second differential value of the steering angle θ, and the vehicle speed V.

[0066] In step S170, 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.

[0067] In step S180, the CPU controls the reaction force actuator 24 so that the steering reaction force torque Tre generated by the reaction force actuator 24 becomes the target steering reaction force torque Tret. Therefore, by applying the steering reaction force torque corresponding to the target steering reaction force torque Tret to the steering wheel 20, the steering guide torque Tsg corresponding to the target steering guide torque Tsgt is applied to the steering wheel 20. <Operation and effects of the embodiment>

[0068] According to the embodiment, when the traveling route of the vehicle can be normally estimated (step S10), the curve curvature ρpre at the preview position Ppre is obtained, and the target steering angle θt for the vehicle 60 to travel along the curve of the traveling route is calculated (steps S20 to S70). Based on the deviation Δθ of the steering angle, which is the deviation θ - θt between the actual steering angle θ and the target steering angle θt, the target basic steering guide torque Tsgtb is calculated (steps S80, S90). The target steering guide torque Tsgt is calculated as the product KvKaTsgtb of the vehicle speed coefficient Kv, the correction coefficient Ka, and the target basic steering guide torque Tsgtb (steps S100 to S120).

[0069] Furthermore, the target steering reaction force torque Tret is calculated as the sum of the basic steering reaction force torque Treb to be applied to the steering wheel 20 and the target steering guide torque Tsgt, and the reaction force actuator 24 is controlled so that the steering reaction force torque Tre becomes the target steering reaction force torque Tret (steps S160 to S180).

[0070] As described above, when the driver tries to deviate from the currently traveled lane, such as changing the driving route to a lane or a sidewalk, the driver performs a deceleration operation, so the vehicle speed V decreases. According to the embodiment, as shown in FIG. 5, the vehicle speed coefficient Kv is variably set to a value between 0 and 1 so that it becomes smaller as the vehicle speed V decreases.

[0071] Therefore, according to the embodiment, as the possibility of the lane in which the vehicle 60 travels being changed increases, such as when the driver is about to deviate from the currently traveling lane, the vehicle speed coefficient Kv decreases, and the magnitude of the target steering guide torque Tsgt becomes smaller. Thus, the target steering guide torque Tsgt that encourages the vehicle 60 to travel along the currently traveling lane decreases. Therefore, in a situation where the driver is about to deviate from the currently traveling lane, the possibility that the steering guide torque corresponding to the target steering guide torque Tsgt interferes with the driver's steering operation is reduced, and the possibility that the driver feels the steering resistance caused by the steering guide torque can be reduced.

[0072] Note that even when the vehicle 60 travels at a low speed, the target steering guide torque Tsgt becomes smaller, so the steering guide torque Tsg becomes smaller. However, since the basic steering reaction torque Treb is not increased, the driver does not feel the difficulty of the steering operation.

[0073] In particular, according to the embodiment, in step S110, the correction coefficient Ka is calculated as a positive value of 1 or less so as to become smaller as the deceleration amount ΔV is larger, and in step S120, the target steering guide torque Tsgt is calculated as the product of the vehicle speed coefficient Kv, the correction coefficient Ka, and the basic steering reaction torque Treb. Therefore, the larger the deceleration amount of the vehicle is, the smaller the magnitude of the target steering guide torque Tsgt is, and the possibility that the steering guide torque interferes with the driver's steering operation can be effectively reduced.

[0074] Also, according to the embodiment, since there may be one map for calculating the vehicle speed coefficient Kv as shown in FIG. 5, it is not necessary to set a plurality of different maps for each vehicle speed range as in the map shown in FIG. 9 of the modification example described later. Therefore, the target steering guide torque Tsgt can be calculated more easily than in the modification example. [Modification Example]

[0075] FIG. 8 is a flowchart showing a control routine for steering reaction torque in a modified example. In FIG. 8, the same steps as those shown in FIG. 3 are assigned the same step numbers as those assigned in FIG. 3.

[0076] In the modified example, the CPU executes step S95 instead of step S90, and calculates a target basic steering guide torque Tsgtb by referring to the map shown in FIG. 9 based on the deviation Δθ of the steering angle and the vehicle speed V. As shown in FIG. 9, the target basic steering guide torque Tsgtb is calculated such that the larger the absolute value of the deviation Δθ of the steering angle, the larger it becomes, and the lower the vehicle speed V, the smaller the absolute value.

[0077] Further, the CPU executes step S125 instead of step S120, and calculates a target steering guide torque Tsgt for guiding the driver's steering when the vehicle 60 travels on a curve of the traveling road as the product KaTsgtb of the correction coefficient Ka and the target basic steering guide torque Tsgtb.

[0078] According to the modified example, as shown in FIG. 9, the lower the vehicle speed V, the smaller the absolute value of the target basic steering guide torque Tsgtb, and thus the lower the vehicle speed V, the smaller the absolute value of the target steering guide torque Tsgt. Therefore, when the driver tries to deviate from the currently traveled lane and decelerates the vehicle 60, and the vehicle speed V decreases, the target steering guide torque Tsgt that prompts the vehicle 60 to travel along the currently traveled lane decreases. Therefore, in a situation where the driver tries to deviate from the currently traveled lane, the risk that the steering guide torque corresponding to the target steering guide torque Tsgt interferes with the driver's steering operation can be reduced, and the risk that the driver feels the steering resistance caused by the steering guide torque can be reduced.

[0079] In particular, according to the modification example, in step S110, the correction coefficient Ka is calculated to be a positive value of 1 or less such that the greater the deceleration amount ΔV, the smaller it becomes. In step S125, the target steering guide torque Tsgt is calculated as the product of the correction coefficient Ka and the target basic steering guide torque Tsgtb. Therefore, the greater the deceleration amount of the vehicle, the smaller the magnitude of the target steering guide torque Tsgt, and the risk of the steering guide torque interfering with the driver's steering operation can be effectively reduced.

[0080] Also, according to the above-described embodiment and modification example, in step S130, the number of selectable lanes Nr within a predetermined distance range from the vehicle 60 is determined, and the limit guide torque Tsgmax is calculated such that the greater the number of selectable lanes Nr, the smaller it becomes. Further, in steps S140 and S150, the target steering guide torque Tsgt is limited by the limit guide torque Tsgmax so that the absolute value of the target steering guide torque Tsgt does not exceed the limit guide torque Tsgmax.

[0081] Therefore, the target steering guide torque can be corrected so that the greater the number of selectable lanes Nr and the higher the possibility that the lane in which the vehicle 60 is traveling will be changed, the smaller the magnitude of the target steering guide torque Tsgt.

[0082] Furthermore, according to the embodiment and the modification example, as shown in FIG. 7, the limit guide torque Tsgmax is calculated such that it becomes smaller as the vehicle speed V is lower. Therefore, the target steering guide torque can be corrected so that the smaller the vehicle speed V, the smaller the magnitude of the target steering guide torque Tsgt.

[0083] In the above, the present invention has been described in detail with respect to specific embodiments. However, it is obvious to those skilled in the art that the present invention is not limited to the above-described embodiments, and various other embodiments are possible within the scope of the present invention.

[0084] For example, in the above-described embodiment, the target steering guide torque Tsgt is calculated as the product KvKaTsgtb of the vehicle speed coefficient Kv, the correction coefficient Ka, and the target basic steering guide torque Tsgtb in step S120. However, the correction coefficient Ka may be omitted, and the target steering guide torque Tsgt may be calculated as the product KaTsgtb.

[0085] In the above-described modification, the target steering guide torque Tsgt is calculated as the product KaTsgtb of the correction coefficient Ka and the target basic steering guide torque Tsgtb in step S125. However, the correction coefficient Ka may be omitted, and the target steering guide torque Tsgt may be set to the target basic steering guide torque Tsgtb.

[0086] Also, in the above-described embodiment and modification, as shown in FIG. 7, the limit guide torque Tsgmax is variably set according to the vehicle speed V such that it becomes smaller as the vehicle speed V is lower. However, the limit guide torque Tsgmax may not be variably set according to the vehicle speed V.

[0087] Also, in the modification, the target basic steering guide torque Tsgtb is calculated by referring to the map shown in FIG. 9 based on the steering angle deviation Δθ and the vehicle speed V. However, the target basic steering guide torque Tsgtb may be calculated by referring to the map shown in FIG. 10 based on the steering angle deviation Δθ, and the target basic steering guide torque Tsgtb may be limited by a limit value Tglim whose absolute value becomes smaller as the vehicle speed V is lower.

[0088] Furthermore, in the above-described embodiments and modifications, the steering assist torque control device 10 is configured as a steering reaction force torque control device including a steer-by-wire type steering device 12. However, the steering assist torque control device 10 may be configured as a steering reaction force torque control device in which the steering wheel and the left and right front wheels are mechanically connected and which includes an electric power steering device. In that 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 the vehicle speed and the target steering guide torque Tsgt. Further, 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.

Description of Signs

[0089] 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…Turn signal lamp, 50…Navigation device, 60…Vehicle

Claims

1. A steering guide torque control device for a vehicle includes 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 image capturing device that captures an image of a front of a vehicle, wherein the control unit calculates a target steering guide torque that guides the driver's steering so as to cause the vehicle to travel along a recognized lane based on an image captured by the image capturing device, and controls the torque imparting device so that the steering guide torque becomes the target steering guide torque, the control unit is configured to estimate a possibility that the driver will perform a steering operation to deviate from the lane based on at least one of a vehicle speed and a deceleration rate of the vehicle, and when it is determined that the target steering guide torque needs to be modified, to modify the target steering guide torque in accordance with the possibility such that the target steering guide torque becomes smaller as the possibility becomes higher; Furthermore, the control unit is configured to acquire information on the degree of deceleration of the vehicle, and determine that the higher the degree of deceleration of the vehicle, the higher the possibility of the occurrence of the steering guide torque control device for a vehicle.

2. 2. The vehicle steering guide torque control device according to claim 1, wherein the control unit is configured to acquire information on a vehicle speed and determine that the lower the vehicle speed is, the higher the possibility of the occurrence of the steering guide torque.

3. In the steering guide torque control device for a vehicle as described in claim 1 or 2, the control unit obtains information on the number of selectable lanes within a predetermined distance range from the vehicle, sets a limit guide torque so that the limit guide torque becomes smaller as the number of selectable lanes increases, and when the magnitude of the target steering guide torque exceeds the limit guide torque, determines that the target steering guide torque needs to be corrected, and corrects the target steering guide torque by limiting the magnitude of the target steering guide torque to the limit guide torque.

4. 4. The vehicle steering guide torque control device according to claim 3, wherein the control unit is configured to acquire information on a vehicle speed and to reduce the limit guide torque as the vehicle speed decreases.

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