JP6834936B2 - Steering assist device - Google Patents

Description

The present invention relates to steering assist control that assists steering of a vehicle.

Patent Document 1 discloses a steer-by-wire type vehicle steering device. The vehicle steering device performs steering reaction force control that applies a steering reaction force to the steering wheel. More specifically, the vehicle steering device observes the turning amount of the vehicle body based on the change in the yaw angle of the vehicle body. If the observed turning amount is equal to or greater than the reference angle, the vehicle steering device increases the steering reaction force. Then, the vehicle steering device reduces the increased steering reaction force with the passage of time.

Japanese Unexamined Patent Publication No. 2013-100007

According to the technique disclosed in Patent Document 1 described above, the steering reaction force increases when the turning amount of the vehicle body exceeds the reference angle. Therefore, when the turning state in which the turning amount exceeds the reference angle must be maintained for a while, the increased steering reaction force does not assist the driver, but rather becomes a load on the driver. This problem is caused by the fact that the driver's intention is not accurately taken into consideration when the steering reaction force control is performed.

It is important to consider the driver's intention not only in steering reaction force control but also in "steering assist control" that assists the steering of the vehicle. When the steering assist control is performed regardless of the driver's intention, the driver feels uncomfortable. This leads to a decrease in reliability for steering assist control, which is not preferable.

One object of the present invention is to provide a technique capable of performing steering assist control in consideration of the driver's intention.

In one aspect of the present invention, a steering assist device mounted on a vehicle is provided.
The steering assist device is
A power steering device that steers the wheels of the vehicle,
It is provided with a control device for controlling the power steering device.
The control device is
Target track calculation processing that calculates the target track based on the driving environment information indicating the driving environment of the vehicle, and
During manual driving, a start condition determination process for determining whether or not the start condition that the driver of the vehicle relies on the self-aligning torque to return the steering wheel is satisfied, and
The assist start process for starting the steering wheel return assist control in response to the satisfaction of the start condition is performed.
In the steering wheel return assist control, the control device controls the power steering device to control the steering of the wheels so that the vehicle travels following the target track.

According to the present invention, steering wheel return assist control is performed as steering assist control. In the steering wheel return assist control, steering assist is performed so that the vehicle follows the target track and travels. However, the steering wheel return assist control is not unconditionally performed. The steering wheel return assist control is started in consideration of the driver's intention.

Specifically, the start condition of the steering wheel return assist control is that the driver returns the steering wheel by entrusting it to the self-aligning torque. When returning the steering wheel by relying on the self-aligning torque, the driver has no intention of steering by himself. Therefore, by performing the steering wheel return assist control with that as the starting condition, it is possible to naturally return the steering wheel so that the vehicle follows the target track and travels without causing the driver to feel uncomfortable.

It is a conceptual diagram for demonstrating the outline of the Embodiment of this invention. It is a schematic diagram for demonstrating the structure of the vehicle and the steering assist device which concerns on embodiment of this invention. It is a flowchart which shows the processing example by the control device of the steering assist device which concerns on embodiment of this invention. It is a flowchart which shows the detail of step S40 (start condition determination processing) in FIG. It is a timing chart for demonstrating step S41 in FIG. It is a conceptual diagram for demonstrating the adjustment of the assist torque in step S60 (handle return assist control) in FIG. It is a conceptual diagram for demonstrating the adjustment of the assist torque in step S60 (handle return assist control) in FIG. It is a flowchart which shows the detail of step S70 (end condition determination process) in FIG.

Embodiments of the present invention will be described with reference to the accompanying drawings.

1. 1. Outline FIG. 1 is a conceptual diagram for explaining the outline of the present embodiment. The vehicle 1 according to the present embodiment has a steering assist function that assists steering when the vehicle 1 turns. For example, the steering assist function includes general EPS (Electric Power Steering) control.

Further, the steering assist function according to the present embodiment also includes steering assist control that assists steering so that the vehicle 1 follows the target track when turning. The steering assist control that assists the steering of the vehicle 1 so as to follow the target track is hereinafter referred to as "target track tracking control". The target track is typically calculated by an automated driving system mounted on the vehicle 1.

However, the target track tracking control according to the present embodiment is not unconditionally performed during the turning of the vehicle 1. When implementing the target track tracking control, the intention of the driver of the vehicle 1 is taken into consideration. For the purpose of explanation, consider a situation in which the vehicle 1 turns at an intersection or the like as shown in FIG. The vehicle 1 may be an autonomous driving vehicle, but in the following, a situation in which the driver is manually driving the vehicle 1 will be considered.

At the timing ta, the driver of the vehicle 1 starts cutting the steering wheel. In response to the notch in the steering wheel, vehicle 1 begins to turn. After that, the driver keeps the steering wheel turned for a while. The driver intends to steer himself while the driver cuts and holds the steering wheel. Therefore, the target track tracking control is not performed during such a period.

At timing tb, the driver begins to return the steering wheel. Here, it is assumed that the driver entrusts the self-aligning torque (SAT) to return the steering wheel. Such a driver operation is hereinafter referred to as a "SAT handle return operation". Further, the state in which the driver is performing the SAT handle return operation is hereinafter referred to as the "SAT handle return state".

In the SAT handle return state, the driver has no intention of steering by himself. Therefore, the target track tracking control is started with the detection of the SAT handle return state as a trigger. In other words, the start condition of the target track follow-up control during turning is that the SAT steering wheel return state is detected. By performing the target track tracking control using the SAT steering wheel return state as a trigger, it is possible to naturally return the steering wheel so that the vehicle 1 follows the target track and travels without causing the driver to feel uncomfortable. In that sense, the target track tracking control in the SAT steering wheel return state can also be called "steering wheel return assist control".

At the timing ct, the turning of the vehicle 1 is completed, and the vehicle 1 starts traveling straight. Since the driver's SAT steering wheel return operation is also completed, the steering wheel return assist control (target track tracking control) is also completed.

Hereinafter, the steering assist control according to the present embodiment will be described in more detail.

2. 2. Steering Assist Device FIG. 2 is a schematic view for explaining the configurations of the vehicle 1 and the steering assist device 10 according to the present embodiment.

The vehicle 1 includes a steering wheel 2 (steering wheel), a steering shaft 3, a pinion gear 4, a rack bar 5, and wheels 6. The steering wheel 2 is an operating member used by the driver to perform a steering operation. One end of the steering shaft 3 is connected to the steering wheel 2, and the other end is connected to the pinion gear 4. The pinion gear 4 meshes with the rack bar 5. Both ends of the rack bar 5 are connected to the left and right wheels 6 via tie rods. The rotation of the steering wheel 2 is transmitted to the pinion gear 4 via the steering shaft 3. The rotational motion of the pinion gear 4 is converted into a linear motion of the rack bar 5, which changes the steering angle of the wheels 6.

The steering assist device 10 is mounted on the vehicle 1 and assists the steering of the vehicle 1 (steering of the wheels 6). The steering assist device 10 includes an EPS device 20, a steering angle sensor 30, a steering torque sensor 40, a touch sensor 50, a driving environment information acquisition device 60, and a control device 100.

The EPS device 20 is a power steering device that mechanically steers the wheels 6. More specifically, the EPS device 20 includes an electric motor, and the rotation of the electric motor generates an assist torque. For example, the electric motor is connected to the rack bar 5 via a conversion mechanism. When the rotor of the electric motor rotates, the conversion mechanism converts the rotational motion into the linear motion of the rack bar 5. In this way, the assist torque is generated and the steering of the wheel 6 is assisted.

The steering angle sensor 30 detects the steering angle θ of the steering wheel 2. The steering angle sensor 30 outputs detection information indicating the detected steering angle θ to the control device 100.

The steering torque sensor 40 detects the steering torque MT applied to the steering shaft 3. The steering torque sensor 40 outputs detection information indicating the detected steering torque MT to the control device 100.

The touch sensor 50 detects the gripping state of the steering wheel 2 by the driver of the vehicle 1. The touch sensor 50 outputs detection information indicating the detected gripping state to the control device 100.

The driving environment information acquisition device 60 acquires the driving environment information ENV indicating the driving environment of the vehicle 1 necessary for carrying out the automatic driving control. The driving environment information ENV includes position information indicating the position of the vehicle 1, map information, surrounding condition information indicating the surrounding condition of the vehicle 1, vehicle condition information indicating the state of the vehicle 1, and the like. The position information can be obtained by using, for example, GPS (Global Positioning System). Map information is obtained from the map database. Surrounding condition information can be obtained by using external sensors such as cameras, riders, and radars. For example, the surrounding situation information includes information on surrounding vehicles. The vehicle state information is obtained based on the detection results of various sensors mounted on the vehicle 1. For example, the vehicle state information includes information on the speed, yaw rate, and winker state of the vehicle 1.

The control device 100 is a microcomputer including a processor, a storage device, and an input / output interface. The control device 100 is also called an ECU (Electronic Control Unit). The control device 100 receives various information through the input / output interface. Then, the control device 100 controls the operation of the vehicle 1 based on the received information. In particular, in the present embodiment, the control device 100 performs steering assist control by controlling the operation of the EPS device 20.

More specifically, the control device 100 includes an EPS control unit 110 and an automatic operation control unit 120 as functional blocks. These functional blocks are realized by the processor of the control device 100 executing a control program stored in the storage device. The control program may be stored on a computer-readable recording medium.

The EPS control unit 110 performs general EPS control. More specifically, the EPS control unit 110 calculates the assist control amount for controlling the operation of the EPS device 20 based on the detection information of the steering angle θ and the steering torque MT. The EPS control unit 110 outputs the assist control amount to the EPS device 20. The EPS device 20 drives the electric motor according to the assist control amount to generate the assist torque.

The automatic driving control unit 120 controls the automatic driving of the vehicle 1. For example, the automatic driving control unit 120 calculates the target driving path of the vehicle 1 based on the driving environment information ENV acquired by the driving environment information acquisition device 60. Then, the automatic driving control unit 120 performs the above-mentioned steering wheel return assist control (target track follow-up control) as needed. Specifically, during the manual operation, the automatic operation control unit 120 determines whether or not the start condition that the driver entrusts the self-aligning torque to return the steering wheel 2 is satisfied. In response to the establishment of the start condition, the automatic operation control unit 120 starts the steering wheel return assist control. In the steering wheel return assist control, the automatic driving control unit 120 controls the EPS device 20 to control the steering of the wheels 6 so that the vehicle 1 travels following the target track.

3. 3. Example of processing flow FIG. 3 is a flowchart showing a processing example by the control device 100 of the steering assist device 10 according to the present embodiment. The processing flow shown in FIG. 3 is repeatedly executed at regular cycle intervals.

3-1. Step S10 (Target track calculation process)
The control device 100 (automatic driving control unit 120) calculates the target runway of the vehicle 1 based on the driving environment information ENV acquired by the driving environment information acquisition device 60. The target track is calculated not only in the automatic driving mode but also in the manual driving mode.

3-2. Step S20 (right / left turn determination process)
The control device 100 (automatic driving control unit 120) determines whether or not the vehicle 1 is turning right or left at the intersection based on the driving environment information ENV. For example, the control device 100 can determine whether or not the vehicle 1 is turning left or right at an intersection by referring to the position information, the map information, and the vehicle state information (vehicle speed, yaw rate, winker state). If the vehicle 1 has not turned left or right at the intersection (step S20; No), the process proceeds to step S30. On the other hand, when the vehicle 1 is turning left or right at the intersection (step S20; Yes), the process proceeds to step S40.

3-3. Step S30 (EPS control process)
The control device 100 (EPS control unit 110) performs general EPS control. Then, the processing in this cycle ends.

3-4. Step S40 (Start condition determination process)
The control device 100 (automatic operation control unit 120) determines whether or not the steering wheel operation state of the driver has changed to the SAT handle return state. That is, the control device 100 determines whether or not the start condition of the steering wheel return assist control is satisfied. If the start condition is satisfied (step S40; Yes), the process proceeds to step S50. In other cases (step S40; No), the process proceeds to step S30.

FIG. 4 is a flowchart showing the details of this step S40. Various examples can be considered as a method for detecting the SAT handle return state. Here, two examples are considered.

In step S41, the control device 100 determines whether or not the product (MT × MT ′) of the steering torque MT and the steering torque differential amount MT ′ is negative. As shown in FIG. 5, when the handle 2 is returned by the self-aligning torque, the product MT × MT ′ becomes negative. Therefore, the SAT handle return state can be detected based on the positive / negative of the product MT × MT'. The steering torque MT is detected by the steering torque sensor 40. The steering torque differential amount MT'is calculated from the steering torque MT. When the product MT × MT ′ is negative (step S41; Yes), the determination result in step S40 is “Yes”. In other cases (step S41; No), the process proceeds to step S42.

In step S42, the control device 100 determines whether or not the steering wheel gripping force of the driver has decreased. The decrease in the steering wheel gripping force of the driver can be recognized based on the detection information by the touch sensor 50. When the steering wheel gripping force is reduced (step S42; Yes), it can be said that the steering wheel return is due to the self-aligning torque. Therefore, the determination result in step S40 is "Yes". In other cases (step S42; No), the determination result in step S40 is "No".

3-5. Step S50 (assist start processing)
In response to the establishment of the start condition, the control device 100 (automatic operation control unit 120) starts the steering wheel return assist control. After that, the process proceeds to step S60.

3-6. Step S60 (Handle return assist control)
The control device 100 (automatic operation control unit 120) performs steering wheel return assist control. In the steering wheel return assist control, the control device 100 performs the target track tracking control based on the target track calculated in step S10. That is, the control device 100 controls the EPS device 20 to control the steering of the wheels 6 so that the vehicle 1 travels following the target track. Since the target runway is calculated based on the driving environment information ENV, appropriate steering wheel return assist control according to the road shape and surrounding traffic conditions is realized.

When starting the steering wheel return assist control, it is necessary to switch from the normal EPS control to the steering wheel return assist control in order to prevent interference with the normal EPS control. In this switching, the assist torque may be adjusted in order to prevent a sudden change in the assist torque generated by the EPS device 20. Hereinafter, the adjustment of the assist torque will be described with reference to FIGS. 6 and 7.

FIG. 6 conceptually shows the assist torque AT generated by the EPS device 20. The automatic operation control unit 120 calculates the first assist torque AT_1, which is the assist torque for the steering wheel return assist control. The EPS control unit 110 calculates a second assist torque AT_2, which is an assist torque for normal EPS control and is an assist torque based on the steering angle θ and the steering angular velocity θ'. Further, the EPS control unit 110 calculates a third assist torque AT_3, which is an assist torque for normal EPS control and is an assist torque based on a change in the steering torque MT. At this time, the assist torque AT generated by the EPS device 20 is represented by the following equation (1).

Equation (1): AT = K × AT_1 + (1-K) × AT_2 + AT_3

In equation (1), the parameter K is a gain that takes a value in the range 0 to 1. FIG. 7 shows an example of setting the gain K. Before time t1, normal EPS control is performed. Specifically, the gain K is set to 0, and EPS control based on the second assist torque AT_2 and the third assist torque AT_3 is performed.

At time t1, the SAT handle return operation starts, that is, the start condition of the handle return assist control is satisfied. The period of time t1 to t2 is a switching period from EPS control to steering wheel return assist control. During this switching period, the gain K gradually increases from 0 to 1. As a result, the contribution of the first assist torque AT_1 to the assist torque AT gradually increases, while the contribution of the second assist torque AT_1 to the assist torque AT gradually decreases. This prevents sudden changes in the assist torque AT.

Even while the steering wheel return assist control is being executed, the third assist torque AT_3 based on the steering torque MT is continuously incorporated into the assist torque AT. As a result, even when the steering wheel return assist control is canceled, it is possible to secure the steering assist force.

3-7. Step S70 (End condition determination process)
During the steering wheel return assist control, the control device 100 (automatic operation control unit 120) determines whether or not the end condition for terminating the steering wheel return assist control is satisfied. When the end condition is satisfied (step S70; Yes), the process proceeds to step S80. In other cases (step S70; No), the process returns to step S60. As explained below, various examples can be considered as the termination conditions.

FIG. 8 is a flowchart showing the details of this step S70. In step S71, the control device 100 calculates the current position of the vehicle 1 and the curvature of the target track ahead. The target track is calculated by the same method as in step S10 described above.

In step S72, the control device 100 determines whether or not the curvature of the target runway at the current position is equal to or less than the threshold value Cth. When the curvature at the current position is equal to or less than the threshold value Cth, it means that the vehicle 1 finishes turning and moves straight ahead. Therefore, the steering wheel return assist control may be terminated. That is, it is the first end condition in consideration of the road shape that the curvature at the current position is equal to or less than the threshold value Cth. When the first end condition is satisfied (step S72; Yes), the determination result in step S70 is “Yes”. In other cases (step S72; No), the process proceeds to step S73.

In step S73, the control device 100 determines whether or not the curvature of the target runway in front of the vehicle 1 has increased by the threshold value Cth2 or more. When the curvature of the target runway ahead increases by the threshold value Cth2 or more, the driver needs to stop the SAT handle return operation and turn the steering wheel 2 more. At this time, if the steering wheel return assist control is continued, it is difficult to increase the number of steering wheels 2, and the driver feels uncomfortable. Therefore, it is preferable to end the steering wheel return assist control. That is, it is the second end condition in consideration of the additional turning of the steering wheel 2 that the curvature of the target runway in front increases by the threshold value Cth2 or more. When the second end condition is satisfied (step S73; Yes), the determination result in step S70 is “Yes”. In other cases (step S73; No), the process proceeds to step S74.

In step S74, the control device 100 determines whether or not the steering torque MT equal to or higher than the threshold value MTth is detected. The steering torque MT is detected by the steering torque sensor 40. When the steering torque MT becomes equal to or higher than the threshold value MTth, it means that the driver has stopped the SAT steering wheel return operation and is trying to steer by himself / herself. Therefore, it is preferable to end the steering wheel return assist control. That is, detecting a steering torque MT equal to or higher than the threshold MTth is a third end condition in consideration of the driver's steering intention. When the third end condition is satisfied (step S74; Yes), the determination result in step S70 is “Yes”. In other cases (step S74; No), the determination result in step S70 is “No”.

3-8. Step S80 (Assist end processing)
In response to the establishment of the end condition, the control device 100 (automatic operation control unit 120) ends the steering wheel return assist control.

When the steering wheel return assist control is terminated, the steering wheel return assist control is switched to the normal EPS control. At this time, the assist torque AT may be adjusted in the same manner as when the steering wheel return assist control is started (see FIGS. 6 and 7). Specifically, at time t3 in FIG. 7, the end condition of the steering wheel return assist control is satisfied. The period from time t3 to t4 is a switching period from the steering wheel return assist control to the EPS control. During this switching period, the gain K gradually decreases from 1 to 0. This prevents sudden changes in the assist torque AT.

4. Effect As described above, according to the present embodiment, the steering wheel return assist control is performed as the steering assist control. In the steering wheel return assist control, steering assist is performed so that the vehicle 1 follows the target track and travels. However, the steering wheel return assist control is not unconditionally performed. The steering wheel return assist control is started in consideration of the driver's intention.

Specifically, the start condition of the steering wheel return assist control is that the driver returns the steering wheel 2 by entrusting it to the self-aligning torque. When returning the steering wheel 2 by relying on the self-aligning torque, the driver has no intention of steering by himself / herself. Therefore, by implementing the steering wheel return assist control with that as the start condition, it is possible to naturally return the steering wheel 2 so that the vehicle 1 follows the target track and travels without causing the driver to feel uncomfortable. ..

As described above, various examples can be considered as the end condition of the steering wheel return assist control. In the case of the first end condition in consideration of the road shape, it is possible to end the steering wheel return assist control at an appropriate timing when the steering wheel return ends. Further, in the case of the second end condition in consideration of the additional turning of the steering wheel 2, it is possible to prevent the steering wheel return assist control from hindering the additional turning of the steering wheel 2. Further, in the case of the third end condition in consideration of the driver's steering intention, it is possible to prevent the steering force from being increased by the steering wheel return assist control when the driver is steering and causing a sense of discomfort. In either case, the driver is prevented from feeling uncomfortable.

1 vehicle 2 steering wheel (steering wheel)
3 Steering shaft 4 Pinion gear 5 Rack bar 6 Wheels 10 Steering assist device 20 EPS device 30 Steering angle sensor 40 Steering torque sensor 50 Touch sensor 60 Driving environment information acquisition device 100 Control device 110 EPS control unit 120 Automatic operation control unit ENV Driving environment information

Claims (1)

A steering assist device installed in a vehicle
A power steering device that steers the wheels of the vehicle,
A control device for controlling the power steering device is provided.
The control device is
Target track calculation processing that calculates the target track based on the driving environment information indicating the driving environment of the vehicle, and
During manual driving, a start condition determination process for determining whether or not the start condition that the driver of the vehicle relies on the self-aligning torque to return the steering wheel is satisfied, and
Assist start processing that starts the steering wheel return assist control in response to the satisfaction of the start condition is performed.
In the steering wheel return assist control, the control device is a steering assist device that controls the power steering device to control the steering of the wheels so that the vehicle travels following the target track.

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