JP7626976B2 - Vehicle steering guide torque control device - Google Patents

Description

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

As a steering reaction torque control device for vehicles such as automobiles, for example, as described in Patent Document 1 below, a steering reaction torque control device is known that predicts the appropriate steering operation amount of the 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 increased more than before until the steering operation amount comes into the appropriate steering operation amount range.

The steering reaction torque acts as a steering reaction torque that resists 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 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 the following Patent Document 1 may be called a steering guide torque control device.

A steering guide torque control device is known that 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 applying device so that the steering guide torque becomes the target steering guide torque.

The above-described steering reaction torque control device and steering guide torque control device can encourage the driver to steer the vehicle so that the actual steering angle becomes the target steering angle when the vehicle is traveling around a curve on a road.

JP 2019-209844 A

[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.

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

The main objective 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 uncomfortable as if he or she is being forced to steer back.

[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 application device (reaction force actuator 24) that applies a steering guide torque (Tsg) to the steering input member, a control unit (14) that controls the torque application device, and a detection device (camera sensor 46) that detects the curvature of a curve on the road ahead of the vehicle.

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) that reduces the 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 the control unit determines that the vehicle is approaching the exit of the curve (S10 to S40).

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 is calculated based on the deviation between the target steering operation amount calculated before a preset look-ahead time 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. Therefore, since a steering guide torque that reduces the deviation between the target steering operation amount and the actual steering operation amount is applied to the steering input member, the driver can be encouraged to steer so that the actual steering operation amount approaches the target steering operation amount for driving the vehicle along the curve.

Furthermore, according to the above configuration, when it is determined that the vehicle is approaching the exit of a curve, the look-ahead time is reduced. Therefore, even if the steering operation is delayed compared to an appropriate steering operation, or the rate of decrease in the curvature of the curve calculated based on the detection results of the camera sensor increases, the risk of the deviation between the target steering operation amount and the actual steering operation amount becoming large can be reduced compared to when the look-ahead time is not reduced. Therefore, it is possible to reduce the risk that the driver will feel 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.

In this application, "the vehicle is approaching the exit of a curve" means that the vehicle is traveling from the area where the curvature of the curve is at its maximum toward the area where the curvature of the curve is zero.

In the above description, in order to aid in understanding the present invention, the reference numerals used in the embodiments described below are enclosed in parentheses with respect to the configuration 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 enclosed 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.

1 is a schematic diagram showing an embodiment of a vehicle steering assist torque control device configured as a steering reaction torque control device; This is to explain the shooting reference position, etc. 5 is a flowchart showing a control routine for steering reaction torque in the embodiment. 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. 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. 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. 10A to 10C are diagrams for explaining the effects obtained by the embodiment. 10 is a flowchart showing a main part of a control routine for steering reaction torque in a first modified example. 13A to 13C are diagrams for explaining the effects obtained by the first modified example. 10 is a flowchart showing a main part of a control routine for steering reaction torque in a second modified example. 13A to 13C are diagrams for explaining the effects obtained by the second modified example.

The following describes in detail an embodiment of the present invention with reference to the attached drawings.

<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, "electronic control unit" will be abbreviated as "ECU."

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.

The steering wheel 20 is a steering input member that is steered by a driver (not shown) and may have a shape similar to a control stick. The reaction force actuator 24 includes an electric motor, and the 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.

The steering device 18 includes a steering mechanism 30 configured to receive steering torque Tst and steer the left and right front wheels 28FL and 28FR, which are steerable 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 steerable wheels.

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 the 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. The steering mechanism may have any structure known in the art.

Furthermore, the steering mechanism 30 includes tie rods 42L and 42R, the inner ends of which are pivotally attached 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 attached 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.

The steering mechanism 30 is configured to receive steering torque from the steering actuator 32 at the pinion shaft 38 to steer the front wheels 28FL and 28FR. There is a certain relationship between the rotation angle φ (not shown) 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 rotating shaft of the electric motor of the steering actuator 32.

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

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, the ECU 14 receives a signal indicating the vehicle speed V detected by the vehicle speed sensor 44, and a signal indicating the white line information of the lane ahead of the vehicle 12 acquired by the camera sensor 46. The vehicle speed sensor 44 detects the vehicle speed V based on, for example, the wheel speed.

As shown in FIG. 3, the camera sensor 46 is fixed to the upper part 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 a photographing 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 photographing reference Lca as necessary. The reference position of the vehicle 50 may be the position of the front wheels 28FL and 28FR, a midpoint between the front and rear wheels, etc.

The ECU 14 sets the steering gear ratio Rst to a standard steering gear ratio Rstn and controls the steering actuator 32 based on the steering angle θ detected by the steering angle detection device 22. Thus, the steering angle δ of the front wheels 28FL and 28FR is controlled to be θ/Rstn. The steering angle θ and the steering angle δ are 0 when the vehicle 50 is traveling straight, and are positive values when the vehicle 50 turns left. The standard steering gear ratio Rstn is a positive value that is preset to increase as the vehicle speed V increases, but may be a positive constant.

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, the derivative of the steering angle θ, and the second derivative of the steering angle θ. The basic steering reaction torque Treb is variably set according to the vehicle speed so that it 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.

As will be described in detail later, the ECU 14 also 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 the 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 approximately one tenth of the magnitude of the basic steering reaction torque Treb.

The target steering guide torque Tsgt acts in a direction that inhibits 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 that promotes 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.

In this embodiment, the ECU 14 calculates the curve curvature ρca of the road for the area centered on the shooting 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 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 the area centered on the shooting reference position Pca.

Furthermore, the ECU 14 reads out from the RAM the curve curvature ρca corresponding to the look-ahead time Δt 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 a curve. In this embodiment, the curvature in the direction in which the vehicle 50 turns left is positive.

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 the RAM a time Lca/V before it takes the vehicle 50 to travel 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 the RAM a time Lca/V before, i.e., the amount of change in the curve curvature per unit distance.
ρca=ρ ₀ +VΔtΔρ…(1)

As shown in FIG. 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, i.e., the curve curvature at the position where the center of gravity 48 of the vehicle 50 reaches after the look-ahead time Δt.

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/( ^m2 / ^s2 )] of the vehicle 50, 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+ ^AV2 )ρpreLw…(2)

<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.

First, in step S10, the CPU determines whether 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.

In an embodiment, whether or not the vehicle 50 is approaching the exit of a curve on the road is determined as follows. This determination may be made in any manner known in the art, for example, based on the curve curvature ρca, the curve curvature ρpre, or the steering angle θ. This determination may also be made 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.

For the sake of simplicity, the case will be described in which the curvature of the road changes into a trapezoidal shape, i.e., the vehicle 50 travels along 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 pre-reading 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 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.

4, when the curvature ρ is equal to or smaller than the reference value α and the curvature _ρ 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 t to time t, the determination in step S10 is positive.

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

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.

In step S50, the CPU calculates the rate of change Δρ of the curve curvature for the area centered on the shooting 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 this in the RAM.

In step S60, the curve curvature ρca of the road is calculated for the area centered on the shooting reference position Pca according to the above formula (1) and stored in RAM. Note that the curve curvature ρca may be set to 0 until the time Lca/V has elapsed since the control was started.

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.

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 Figure 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 Figure 4.

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 predicted position Ppre, in accordance with the above formula (2).

In step S90, 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.

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

In step S110, the CPU calculates the basic steering reaction torque Treb to be applied to the steering wheel 20 based on the steering angle θ, the derivative of the steering angle θ, the second derivative of the steering angle θ, and the vehicle speed V in any manner known in the art.

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.

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. Therefore, a steering reaction torque corresponding to the target steering reaction torque Tret is applied to the steering wheel 20, and a steering guide torque Tsg corresponding to the target steering guide torque Tsgt is applied to the steering wheel 20.

<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.

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 shows the change in the actual steering angle θ when the driver's return steering is not delayed, and the dashed line shows 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 shows the change in the target steering angle θt calculated based on the curve curvature predicted in advance at the prediction time Δt.

In addition, in Figures 5 and 6 and Figures 7, 9, and 11 described below, 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.

The steering guide torque Tsg, which is 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 Figure 5. Note that in the examples shown in Figures 5 and 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 turning-back steering. This is also true in Figures 7, 9, and 11, which will be described later.

In conventional steering guide torque control devices, 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 Figure 5. As a result, as can be seen from a comparison of the solid line and dashed line in the lower part of Figure 5, the target steering guide torque Tsgt becomes excessive, causing the steering guide torque Tsg acting in the return direction to become excessive, and the driver may feel uncomfortable as if he or she is being forced to perform return steering (first problem).

In addition, when the vehicle 50 transitions from a curved state to a straight-ahead state, the camera sensor 46 can detect white lines that are 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 of the solid line and the dashed line in the lower part of FIG. 6, the target steering guide torque Tsgt acting in the return direction becomes excessive, and the driver may feel uncomfortable as if he or she is being forced to steer back (second problem).

In Figure 6, the dashed line also shows the change in the actual steering angle θ when the driver's return steering is delayed. Therefore, Figure 6 illustrates both the first and second problems mentioned above.

<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). On the other hand, 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).

In the upper part of Figure 7, which shows the situation in which the actual steering angle θ and the target steering angle θt change in the same way as in Figures 5 and 6, the two-dot chain line shows 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 shows the change in the target steering angle θt when the standard look-ahead time Δts is not reduced, as in Figure 5.

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 Figure 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.

In the lower part of Figure 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 to turn, the target steering reaction torque Tret acts in the turning direction, so that steering guidance can be performed to encourage the driver to turn the wheel. Note that this effect can be obtained not only in the embodiment, but also when the look-ahead time Δt is not reduced.

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

According to the embodiment, the magnitude of the steering guide torque Tsg is rapidly decreased after passing through a state in which the torque increases rapidly and remains substantially constant or slightly decreases. Therefore, compared to the case of the first modified example described below in which the magnitude of the steering guide torque Tsg changes from a state in which the torque increases rapidly to a state in which the torque decreases rapidly, it is possible to reduce the risk that the driver will feel a sense of discomfort due to the increase or decrease in the magnitude of the steering guide torque Tsg.

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

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, in step S30, the correction coefficient Ka is set to 1 + Kaf - ΔKa. Note that Kaf is the previous value of the correction coefficient Ka, and is initialized to 0 when control starts and when the curve curvature ρpre or the target steering angle θt is 0. ΔKa is a positive constant, for example, about 0.001 to 0.01. Furthermore, when 1 + Kaf - ΔKa becomes a negative value, the correction coefficient Ka is set to 0.

According to the first modified example, the correction coefficient Ka gradually decreases from 1, so 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 rate of decrease is smaller than the rate of decrease of the target steering angle θt of the one-dot chain line.

As a result, as shown in the lower part of Figure 9, the magnitude of the target steering guide torque Tsgt calculated based on the steering angle deviation Δθ also decreases. This reduces the steering guide torque Tsg acting in the return direction, reducing the risk that the driver will feel uncomfortable as if he or she is being forced to perform return steering.

In addition, 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 target steering guide torque Tsgt and the rate of increase when 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 return direction can be reduced compared to the embodiment.

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

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 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.

According to the second modified example, the correction coefficient Ka gradually decreases from Kab, so 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 at a time later than 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, and the rate of decrease is smaller than the rate of decrease of the target steering angle θt of the one-dot chain line.

As a result, as shown in the lower part of Figure 11, the magnitude of the target steering guide torque Tsgt calculated based on the steering angle deviation Δθ also decreases. This reduces the steering guide torque Tsg acting in the return direction, reducing the risk that the driver will feel uncomfortable as if he or she is being forced to perform return steering.

In addition, as can be seen from a comparison of the bottom part of FIG. 11 with the middle part of FIG. 7 and the bottom 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 return direction can be reduced compared to the embodiment.

Furthermore, as in 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 decreases quickly. Therefore, compared to 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 risk that the driver will feel a sense of discomfort due to the increase or decrease in the magnitude of the steering guide torque Tsg.

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

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 a curve on the road, the look-ahead time Δt for determining 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 a curve on the road, the look-ahead distance Lpre is reduced from the standard look-ahead distance Lpreb, and the curve curvature ρca calculated in step 70 a time Lpre/V ago and stored in RAM may be read out from the RAM as the curve curvature ρpre.

In addition, 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.

In the above 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 causing the curve curvature ρpre to suddenly become 0.

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

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 driver's driving history is recorded, and the smaller the delay in the driver's return steering when the vehicle 50 is approaching the exit of a curve on the road, the smaller the reduction in the look-ahead time Δt may be, and when the delay in the driver's return steering is small, the reduction in the look-ahead time Δt may be omitted.

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 (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 such that, when the control unit determines that the vehicle is approaching the exit of a curve, the control unit reduces the look-ahead time.

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