Vehicle steering guide torque control device

Abstract

To provide vehicular steering guide torque control capable of securing an appropriate torque amount in a curve exit.SOLUTION: A control unit controls a reaction force actuator that applies a steering guide torque to a steering wheel. The control unit calculates a target steering angle θt for a vehicle traveling along a curve on the basis of a curvature of a curve in front of the vehicle detected by a camera sensor (S50 to S80), calculates a target steering guide torque Tsgt on the basis of a deviation between the target steering angle calculated read-ahead time Δt before and an actual steering angle θ (S90, S100), and controls the reaction force actuator such that a steering guide torque is the target steering guide torque (S110 to S130). Furthermore, the control unit reduces the read-ahead time when the vehicle is approaching an exit of a curve (S10 to S40).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 that reduces the deviation between the target steering angle calculated before the look-ahead time and the actual steering angle, and controls a torque application 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. [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] When a vehicle travels along a curve in a road, the steering operation when the vehicle exits the curve is likely to be delayed compared to an appropriate steering operation. In the conventional steering guide torque control device described in the above-mentioned Patent Document 1, the look-ahead time is constant. Therefore, if the steering operation is delayed, the deviation between the target steering angle calculated based on the curvature of the curve and the actual steering angle becomes large, and the steering guide torque becomes excessive, which may cause the driver to feel uncomfortable as if he or she is being forced to steer back.

[0008] When the vehicle approaches the exit of a curve on the road, the distance of the road ahead of the vehicle that can be detected by the camera sensor becomes larger compared to the situation before the vehicle approached the exit of the curve, so the rate of decrease in the curvature of the curve calculated based on the detection result of the camera sensor becomes larger. As a result, the deviation between the target steering angle calculated based on the curvature of the curve and the actual steering angle becomes larger, and the steering guide torque becomes excessive, which may cause the driver to feel uncomfortable as if he or she is being forced to steer back.

[0009] The main object of the present invention is to provide an improved steering guide torque control device that reduces the risk of the steering guide torque becoming excessive when the vehicle is approaching the exit of a curve on the road, causing the driver to feel an uncomfortable sensation as if he or she is being forced to steer back.

[0010] [Means for solving the problems and effects of the invention] According to the present invention, there is provided a steering guide torque control device (10) for a vehicle, which includes a steering input member (steering wheel 20) that is steered by a driver, a steering device (18) that steers the steered wheels (front wheels 28FL and 28FR) in accordance with the steering operation amount (steering angle θ) 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 (14) that controls the torque imparting device, and a detection device (camera sensor 46) that detects the curvature of a curve on a road ahead of the vehicle.

[0011] The control unit (14) is configured to calculate a target steering operation amount (target steering angle θt) for driving the vehicle (50) along the curve based on the curvature of the curve detected by the detection device (S50 to S80), calculate a target steering guide torque (Tsgt) for reducing a deviation between the target steering operation amount calculated a preset look-ahead time (Δt) before and the actual steering operation amount (steering angle θ) based on the deviation (S90, S100), and control the torque application device (reaction force actuator 24) so ​​that the steering guide torque becomes the target steering guide torque (S110 to S130), and further reduce the look-ahead time when it is determined that the vehicle is approaching the exit of the curve (S10 to S40).

[0012] According to the above configuration, a target steering operation amount for driving the vehicle along the curve is calculated based on the curvature of the curve detected by the detection device, a target steering guide torque for reducing the deviation between the target steering operation amount calculated before a preset look-ahead time and the actual steering operation amount is calculated, and the torque applying device is controlled so that the steering guide torque becomes the target steering guide torque. Thus, since a steering guide torque for reducing the deviation between the target steering operation amount and the actual steering operation amount is applied to the steering input member, it is possible to encourage the driver to perform a steering operation so that the actual steering operation amount approaches the target steering operation amount for driving the vehicle along the curve.

[0013] Furthermore, according to the above configuration, when it is determined that the vehicle is approaching the exit of the curve, the look-ahead time is reduced. Therefore, even if the steering operation is delayed compared to the appropriate steering operation or the rate of decrease in the curvature of the curve calculated based on the detection result of the camera sensor becomes large, the risk of the deviation between the target steering operation amount and the actual steering operation amount becoming large can be reduced compared to the case where the look-ahead time is not reduced. Therefore, it is possible to reduce the risk that the driver feels uncomfortable as if he or she is being forced to steer back due to the deviation between the target steering angle and the actual steering angle becoming large and the steering guide torque becoming excessive.

[0014] In this application, "the vehicle is approaching the exit of a curve" means that the vehicle is traveling from an area where the curvature of the curve is maximum toward an area where the curvature of the curve becomes zero.

[0015] In the above description, in order to facilitate understanding of the present invention, the reference numerals used in the following embodiments are added in parentheses to the configurations of the invention corresponding to the embodiments. However, each component of the present invention is not limited to the components of the embodiments corresponding to the reference numerals 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]

[0016] [Figure 1] 1 is a schematic diagram showing an embodiment of a vehicle steering assist torque control device configured as a steering reaction torque control device; [Diagram 2] This is to explain the shooting reference position, etc. [Diagram 3] 5 is a flowchart showing a control routine for steering reaction torque in the embodiment. [Figure 4] 4 is a diagram for explaining a method for determining whether or not a vehicle is approaching the exit of a curve on a road in an embodiment. FIG. [Diagram 5]1 is a diagram for explaining a first problem in the control of steering assist torque in a conventional steering assist torque control device. FIG. [Figure 6] FIG. 11 is a diagram for explaining a second problem of the control of the steering assist torque in the conventional steering assist torque control device. [Figure 7] 10A to 10C are diagrams for explaining the effects obtained by the embodiment. [Figure 8] 10 is a flowchart showing a main part of a control routine for steering reaction torque in a first modified example. [Figure 9] 13A to 13C are diagrams for explaining the effects obtained by the first modified example. [Figure 10] 10 is a flowchart showing a main part of a control routine for steering reaction torque in a second modified example. [Figure 11] 13A to 13C are diagrams for explaining the effects obtained by the second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0018] <Configuration> As shown in Fig. 1, a vehicle steering guide torque control device 10 according to an 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, and is applied to a vehicle 50. Hereinafter, the "electronic control unit" will be abbreviated as "ECU."

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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. In addition, a signal indicating the vehicle speed V detected by a vehicle speed sensor 44, and a signal indicating white line information of the lane ahead of the vehicle 12 acquired by a camera sensor 46 are also input. The vehicle speed sensor 44 detects the vehicle speed V based on, for example, the wheel speed.

[0027] 3, the camera sensor 46 is fixed to an upper portion of the inner surface of the windshield 50a of the vehicle 50, and captures an image of the front of the vehicle 12, centered on an imaging reference position Pca that is a distance Lca (a positive constant) forward from the center of gravity 48, which is the reference position of the vehicle 50. The distance Lca is referred to as the imaging reference Lca as necessary. The reference position of the vehicle 50 may be the positions of the front wheels 28FL and 28FR, a midpoint between the front and rear wheels, or the like.

[0028] 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 be θ / Rstn. Note that steering angle θ and steering angle δ are 0 when vehicle 50 is traveling straight, and are positive values ​​when vehicle 50 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.

[0029] 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.

[0030] 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 50 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.

[0031] In addition, the target steering guide torque Tsgt acts in a direction to suppress steering when the driver steers so that the actual steering angle θ moves away from the target steering angle θt, and acts in a direction to promote steering when the driver steers so that the actual steering angle θ moves closer to 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.

[0032] 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 50 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.

[0033] 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 steering angle for driving the vehicle 50 along the curve. In this embodiment, the curvature in the direction in which the vehicle 50 turns left is positive.

[0034] 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 48 of the vehicle 50. Therefore, ρ0 is the curve curvature ρca calculated and stored in RAM a time Lca / V before the vehicle 50 travels the 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)

[0035] 1, the distance (read-ahead distance) Lpre between the center of gravity 48 of the vehicle 50 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 48 of the vehicle 50 reaches after the look-ahead time Δt.

[0036] 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 50. The stability factor A and the wheelbase Lw are known constant values ​​determined by the specifications of the vehicle 50. θt = Rst(1 + AV 2 )ρpreLw …(2)

[0037] <Steering reaction torque control routine> Next, a control routine for steering reaction torque according to the 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.

[0038] First, in step S10, the CPU determines whether or not the vehicle 50 is approaching the exit of a curve on the road. If the CPU determines yes, the control proceeds to step S40, and if the CPU determines no, in step S20, the CPU sets the look-ahead time Δt to the standard look-ahead time Δts. The standard look-ahead time Δts may be constant.

[0039] In the embodiment, whether or not the vehicle 50 is approaching the exit of the curve on the road is determined in the following manner. This determination may be performed in any manner known in the art, for example, based on the curve curvature ρca, the curve curvature ρpre, the steering angle θ, etc. This determination may also be performed by determining a situation in which the curvature of the curve is decreasing, based on position information from a GPS and map information from a navigation device.

[0040] For the sake of simplicity, the case will be described in which the curvature of the road changes to a trapezoidal shape, that is, the vehicle 50 travels on a curve including a region of constant curvature and transition curve regions before and after the region, as shown in the top row of Fig. 4. In Fig. 4, the solid line indicates the curvature ρ0 at the center of gravity 48 of the vehicle 50, the dashed line indicates the curvature ρpre at the look-ahead position Ppre, and the dashed line indicates the curvature ρca at the photographing reference position Pca. α is a reference value for determining the magnitude of the curvature. The reference value α may be a constant, or may be set to a value smaller than the value based on the value of the curvature ρpre or Pca when the rate of increase of the curvature ρpre or Pca becomes equal to or smaller than the reference value.

[0041] 4, when the curvature ρca is equal to or smaller than the reference value α and the curvature ρ0 is equal to or larger than the reference value α, it is determined that the vehicle 50 is approaching the exit of the curve on the road (exit determination). Therefore, from time t1 to time t2, the determination in step S10 is positive.

[0042] In step S40, the CPU reduces the look-ahead time Δt by setting the look-ahead time Δt to the product KaΔts of the modification coefficient Ka and the standard look-ahead time Δts. Note that the modification coefficient Ka may be a positive constant greater than or equal to 0 and less than 1, for example, 0 to 0.8.

[0043] Therefore, in the example of Figure 4, as shown in the third row, the look-ahead time Δt is set to the standard look-ahead time Δts before time t1 and after time t2, and is set to the product KaΔts of the correction coefficient Ka and the standard look-ahead time Δts from time t1 to time t2.

[0044] In step S50, the CPU calculates the rate of change Δρ of the curve curvature for the area centered on the photographing reference position Pca based on the white line information of the lane ahead of the vehicle 12 acquired by the camera sensor 46, and stores it in the RAM.

[0045] In step S60, 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.

[0046] In step S70, 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.

[0047] Therefore, when the vehicle 50 is not approaching the exit of the curve, the curve curvature ρca calculated and stored in the RAM before the standard look-ahead time Δts is read out from the RAM as the curve curvature ρpre. Therefore, the curve curvature ρpre decreases as shown by the dashed line at the bottom of Fig. 4. In contrast, when the vehicle 50 is approaching the exit of the curve, the curve curvature ρca calculated and stored in the RAM before the time KaΔts, which is the product of the correction coefficient Ka and the standard look-ahead time Δts, is read out from the RAM as the curve curvature ρpre. Therefore, the curve curvature ρpre decreases as shown by the two-dot chain line at the bottom of Fig. 4.

[0048] In step S80, the CPU calculates the target steering angle θt for the vehicle 50 to travel around the curve of the road, based on the vehicle speed V and the curve curvature ρpre at the pre-read position Ppre, in accordance with the above formula (2).

[0049] In step S90, 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.

[0050] In step S100, the CPU calculates a target steering guide torque Tsgt that guides the driver's steering when the vehicle 50 travels around a curve in the road, as a product KsΔθ of a positive conversion coefficient Ks and a steering angle deviation Δθ.

[0051] In step S110, 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.

[0052] In step S120, 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.

[0053] In step S130, 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.

[0054] <Steering guide torque control and its problems in the prior art> In order to facilitate understanding of the operation and effects of the embodiment, prior to describing the operation and effects of the embodiment, the control of steering guide torque and its problems in a conventional steering guide torque control device such as the device described in the aforementioned Patent Document 1 will be described with reference to Figures 5 and 6.

[0055] When the vehicle 50 travels along a curve in the road, the driver's return steering is likely to be delayed when the vehicle 50 transitions from a curved state to a straight-ahead state. In the upper part of Fig. 5, the solid line indicates the change in the actual steering angle θ when the driver's return steering is not delayed, and the dashed line indicates the change in the actual steering angle θ when the driver's return steering is delayed. Furthermore, in the upper part of Fig. 5, the dashed line indicates the change in the target steering angle θt calculated based on the curve curvature predicted in advance during the predictive time Δt.

[0056] 5 and 6 and later-described Figures 7, 9, and 11, the magnitude of the target steering angle θt is the same as the actual steering angle θ. However, the target steering angle θt may be calculated to be smaller than the actual steering angle θ so that the steering angle θ is prevented from increasing in the direction of turning the steering wheel while the actual steering angle θ is held constant.

[0057] The steering guide torque Tsg calculated based on the steering angle deviation Δθ, which is the deviation θ-θt between the steering angle θ detected by the steering angle detection device 22 and the target steering angle θt, changes as shown in the lower part of Fig. 5. In the examples shown in Fig. 5 and Fig. 6, the steering guide torque Tsg on the lower side of the time axis is a torque that guides turning-in steering, and the steering guide torque Tsg on the upper side of the time axis is a torque that guides returning steering. This also applies to Fig. 7, Fig. 9, and Fig. 11 described later.

[0058] In the conventional steering guide torque control device, the look-ahead time Δt is constant. Therefore, if the driver's return steering is delayed when the vehicle 50 transitions from a curved driving state to a straight driving state, the deviation Δθ between the actual steering angle θ and the target steering angle θt becomes large, as shown by the dashed line in the upper part of Fig. 5. As a result, as can be seen from a comparison between the solid line and the dashed line in the lower part of Fig. 5, the target steering guide torque Tsgt becomes excessive, so that the steering guide torque Tsg acting in the return direction becomes excessive, and the driver may feel a sense of discomfort as if he or she is being forced to perform return steering (first problem).

[0059] In addition, when the vehicle 50 transitions from a curved state to a straight running state, the camera sensor 46 can detect a white line that is farther away than when the vehicle 50 is curved, so the rate of decrease in the predicted curve curvatures ρca and ρpre increases. Therefore, as shown by the dashed line in the upper part of Fig. 6, the rate of decrease in the magnitude of the target steering angle θt calculated based on the curve curvature ρpre increases, and the deviation Δθ between the actual steering angle θ and the target steering angle θt increases. As a result, as can be seen from a comparison between the solid line and the dashed line in the lower part of Fig. 6, the target steering guide torque Tsgt acting in the steering back direction becomes excessive, and the driver may feel a sense of discomfort as if he or she is being forced to steer back (second problem).

[0060] In addition, in Fig. 6, the dashed line also shows the change in the actual steering angle θ when the driver's return steering is delayed. Therefore, Fig. 6 illustrates both the first and second problems described above.

[0061] <Operation and Effects of the Embodiment> According to the embodiment, when it is determined that the vehicle 50 is not approaching the exit of the curve on the road, the look-ahead time Δt is set to the standard look-ahead time Δts (steps S10, S20). In contrast, when it is determined that the vehicle 50 is approaching the exit of the curve on the road, the look-ahead time Δt is reduced by being set to the product KaΔts of the correction coefficient Ka and the standard look-ahead time Δts (steps S10, S40).

[0062] In the upper part of Fig. 7, which shows a situation in which the actual steering angle θ and the target steering angle θt change in the same manner as in Fig. 5 and Fig. 6, the two-dot chain line indicates the change in the target steering angle θt when it is determined that the vehicle 50 is approaching the exit of a curve on the road and the standard look-ahead time Δts is reduced. Note that the one-dot chain line indicates the change in the target steering angle θt when the standard look-ahead time Δts is not reduced, as in Fig. 5.

[0063] When it is determined that the vehicle 50 is approaching the exit of a curve on the road and the look-ahead time Δt is reduced, the deviation Δθ between the steering angle θ and the target steering angle θt also becomes smaller even if the driver's return steering is delayed. Therefore, as shown in the middle part of Fig. 7, the magnitude of the target steering guide torque Tsgt calculated based on the steering angle deviation Δθ also becomes smaller. Therefore, since the steering guide torque Tsg acting in the return direction can be reduced, the risk of the driver feeling uncomfortable as if he or she is being forced to perform return steering can be reduced.

[0064] In the lower part of Fig. 7, the dashed line indicates the target steering reaction torque Tret in the embodiment, and the solid line indicates the basic steering reaction torque Treb. Furthermore, the dashed line indicates the target steering reaction torque Tret when the look-ahead time Δt is not reduced. When the vehicle 50 starts turning, the target steering reaction torque Tret acts in the turning direction, so that steering can be guided to promote turning steering by the driver. This effect can be obtained not only in the embodiment, but also in the case where the look-ahead time Δt is not reduced.

[0065] Furthermore, when the look-ahead time Δt is not reduced, the target steering reaction torque Tret increases in the return direction when the vehicle 50 is approaching the exit of a curve on the road, whereas in the embodiment, the target steering reaction torque Tret does not substantially increase in the return direction. Therefore, it is understood that it is possible to reduce the possibility that the driver feels uncomfortable as if he or she is being forced to perform return steering.

[0066] According to the embodiment, the magnitude of the steering guide torque Tsg is rapidly decreased through a state in which the magnitude of the steering guide torque Tsg is substantially constant or slightly decreased from a state in which the magnitude of the steering guide torque Tsg is rapidly increased. Therefore, compared to the case of a first modified example described later in which the magnitude of the steering guide torque Tsg is rapidly increased from a state in which the magnitude of the steering guide torque Tsg is rapidly decreased, it is possible to reduce the possibility that the driver feels a sense of discomfort due to the increase or decrease in the magnitude of the steering guide torque Tsg.

[0067] [First modified example] FIG. 8 is a flowchart showing a main part of a control routine for steering reaction torque in the first modified example.

[0068] In the first modified example, when the CPU determines in step S10 that the vehicle 50 is approaching the exit of a curve on the road, the CPU sets the modification coefficient Ka to 1+Kaf-ΔKa in step S30. Note that Kaf is the previous value of the modification coefficient Ka, and is initialized to 0 when the control starts and when the curve curvature ρpre or the target steering angle θt is 0. ΔKa is a positive constant of, for example, about 0.001 to 0.01. Furthermore, when 1+Kaf-ΔKa becomes a negative value, the modification coefficient Ka is set to 0.

[0069] According to the first modified example, the correction coefficient Ka gradually decreases from 1, so that the look-ahead time Δt gradually decreases from the standard look-ahead time Δts. Therefore, the target steering angle θt (two-dot chain line) calculated based on the curve curvature ρpre starts to decrease at the time when the target steering angle θt (one-dot chain line) starts to decrease when the look-ahead time Δt is the standard look-ahead time Δts, but the decrease rate is smaller than the decrease rate of the target steering angle θt of the one-dot chain line.

[0070] Therefore, the magnitude of the target steering guide torque Tsgt calculated based on the steering angle deviation Δθ also decreases as shown in the lower part of Fig. 9. Therefore, the steering guide torque Tsg acting in the steering back direction can be reduced, so that the possibility that the driver feels uncomfortable as if he or she is being forced to perform steering back can be reduced.

[0071] Also, as can be seen from a comparison between the lower part of Fig. 9 and the middle part of Fig. 7, the maximum value of the magnitude of the target steering guide torque Tsgt and the rate of increase when the magnitude of the target steering guide torque Tsgt increases can be reduced compared to the embodiment. Therefore, the magnitude and rate of increase of the steering guide torque Tsg acting in the returning direction can be reduced compared to the embodiment.

[0072] [Second modified example] FIG. 10 is a flowchart showing a main part of a control routine for steering reaction torque in the second modified example.

[0073] In the second modified example, when the CPU determines in step S10 that the vehicle 50 is approaching the exit of a curve on the road, in step S35, the correction coefficient Ka is set to Kab+Kaf-ΔKa. Note that Kaf and ΔKa are the same as those in the first modified example, and when Kab+Kaf-ΔKa is a negative value, the correction coefficient Ka is set to 0. Kab is a basic correction coefficient of, for example, about 0.2 to 0.8. Note that ΔKa in the second modified example may be larger than ΔKa in the first modified example.

[0074] According to the second modified example, the correction coefficient Ka gradually decreases from Kab, so that the look-ahead time Δt gradually decreases from the product KabΔts of Kab and the standard look-ahead time Δts. Therefore, the target steering angle θt (two-dot chain line) calculated based on the curve curvature ρpre starts to decrease later than the target steering angle θt (one-dot chain line) starts to decrease when the look-ahead time Δt is the standard look-ahead time Δts, and the decrease rate is smaller than the decrease rate of the target steering angle θt of the one-dot chain line.

[0075] Therefore, the magnitude of the target steering guide torque Tsgt calculated based on the steering angle deviation Δθ also decreases as shown in the lower part of Fig. 11. Therefore, the steering guide torque Tsg acting in the steering back direction can be reduced, so that the risk of the driver feeling uncomfortable as if he or she is being forced to perform steering back can be reduced.

[0076] Also, as can be seen from a comparison between the lower part of Fig. 11 and the middle part of Fig. 7 and the lower part of Fig. 9, the maximum value of the magnitude of the target steering guide torque Tsgt and the rate of increase when the magnitude of the target steering guide torque Tsgt increases can be reduced compared to the embodiment. Therefore, the magnitude and rate of increase of the steering guide torque Tsg acting in the returning direction can be reduced compared to the embodiment.

[0077] Furthermore, similarly to the embodiment, the magnitude of the target steering guide torque Tsgt goes from a state in which it increases quickly to a state in which it remains substantially constant or decreases slightly, and then quickly decreases. Therefore, compared to the case of the first modified example in which the magnitude of the steering guide torque Tsg changes from a state in which it increases quickly to a state in which it decreases quickly, it is possible to reduce the possibility that the driver feels a sense of discomfort due to the increase or decrease in the magnitude of the steering guide torque Tsg.

[0078] 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.

[0079] For example, in the above-described embodiment and the first and second modified examples, when it is determined that the vehicle 50 is approaching the exit of the curve on the road, the look-ahead time Δt for obtaining the curvature ρpre at the look-ahead position Ppre is reduced. However, when it is determined that the vehicle 50 is approaching the exit of the curve on the road, the look-ahead distance Lpre is reduced from the standard look-ahead distance Lpreb, and the curve curvature ρca calculated a time Lpre / V ago and stored in the RAM in step 70 may be read out from the RAM as the curve curvature ρpre.

[0080] In the above-described embodiment and the first and second modified examples, the steering guide torque control device 10 is configured as a steering reaction torque control device including a steer-by-wire 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.

[0081] Also, in the above-described embodiment, when the determination in step S10 is a positive determination, the look-ahead time Δt is reduced in step S40. However, once a positive determination is made in step S10, the look-ahead time Δt may be reduced without making the determination in step S10 until the vehicle 50 finishes traveling around the curve, for example, until the target steering angle θt becomes 0. With this configuration, it is possible to prevent the determination in step S10 from becoming a negative determination before the curve curvature ρpre becomes 0, causing the look-ahead time Δt to become the standard look-ahead time Δts and the curve curvature ρpre to suddenly become 0.

[0082] In the above embodiment, the modification coefficient Ka is a positive constant greater than or equal to 0 and less than 1. However, the modification coefficient Ka may be variably set according to the maximum absolute value of the target steering angle θt, for example, so that the modification coefficient Ka decreases as the maximum absolute value of the target steering angle θt increases.

[0083] Furthermore, in the above-described embodiment and the first and second modified examples, when it is determined that the vehicle 50 is approaching the exit of a curve on the road, the look-ahead time Δt is reduced. However, for example, the driving history of the driver is recorded, and the smaller the delay in the driver's return steering in a situation where the vehicle 50 is approaching the exit of a curve on the road, the smaller the reduction amount of the look-ahead time Δt may be, and when the delay in the driver's return steering is small, the reduction of the look-ahead time Δt may be omitted. [Explanation of symbols]

[0084] 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...center of gravity, 50...vehicle

Claims

[Claim 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 a detection device that detects a curvature of a curve on a road ahead of the vehicle, the control unit is configured to calculate a target steering operation amount for causing the vehicle to travel along the curve based on a curvature of the curve detected by the detection device, calculate a target steering guide torque for reducing a deviation between the target steering operation amount calculated before a preset look-ahead time and an actual steering operation amount, and control the torque applying device so that the steering guide torque becomes the target steering guide torque; The vehicle steering guide torque control device is further configured to reduce the look-ahead time when the control unit determines that the vehicle is approaching the exit of a curve.

Images