JP2019112000A - Steering assist device - Google Patents

Abstract

To perform steering assist control in consideration of driver's intention.SOLUTION: A steering assist device mounted in a vehicle includes a power steering device configured to turn wheels, and a control unit configured to control the power steering device. The control unit calculates a target traveling road on the basis of driving environment information indicating a driving environment of a vehicle. In addition, the control unit determines whether or not a start condition that a driver of the vehicle returns a steering wheel in accordance with a self-aligning torque during manual operation is established. In response to the establishment of the start condition, the control unit starts steering wheel return assist control. In the steering wheel return assist control, the control unit controls turning of the wheels by controlling the power steering device so that the vehicle travels following the target traveling road.SELECTED DRAWING: Figure 1

Description

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

  Patent Document 1 discloses a steer-by-wire vehicle steering apparatus. The vehicle steering system performs steering reaction force control for applying a steering reaction force to the steering wheel. More specifically, the vehicle steering system observes the turning amount of the vehicle based on the change in the yaw angle of the vehicle. If the observed turning amount is equal to or greater than the reference angle, the vehicle steering system increases the steering reaction force. Then, the vehicle steering system reduces the increased steering reaction force as time passes.

JP, 2013-100007, A

  According to the technology disclosed in Patent Document 1 above, the steering reaction force increases when the turning amount of the vehicle body becomes equal to or greater than the reference angle. Therefore, when it is necessary to maintain the turning state where the turning amount exceeds the reference angle for a while, the increased steering reaction force does not serve as an assist for the driver but rather becomes a load of the driver. This problem arises from the fact that the driver's intention is not taken into account correctly when implementing the steering reaction force control.

  It is important to consider the driver's intention in "steering assist control" which assists the steering of the vehicle as well as the steering reaction force control. If the steering assist control is performed regardless of the driver's intention, the driver feels a sense of discomfort. This is not preferable because it reduces the reliability of the steering assist control.

  One object of the present invention is to provide a technology capable of implementing 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 for turning the wheels of the vehicle;
And a control device for controlling the power steering device.
The controller is
Target runway calculation processing for calculating a target runway based on driving environment information indicating the driving environment of the vehicle;
A start condition determination process of determining whether a start condition for the driver of the vehicle to leave the self aligning torque and return the steering wheel during the manual operation is satisfied;
And an assist start process of starting the steering wheel return assist control in response to the establishment of the start condition.
In the steering wheel return assist control, the control device controls the turning of the wheels by controlling the power steering device such that the vehicle travels following the target travel path.

  According to the present invention, 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 travels following the target travel path. 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 starting condition of the steering wheel return assist control is that the driver entrusts the self aligning torque and returns the steering wheel. When leaving the steering wheel to the self aligning torque, the driver has no intention to steer by himself. Therefore, by performing the steering wheel return assist control with that as the start condition, the steering wheel can be naturally returned so that the vehicle travels following the target running road without causing the driver to feel discomfort.

It is a conceptual diagram for demonstrating the outline | summary of embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic for demonstrating the structure of the vehicle which concerns on embodiment of this invention, and a steering assist apparatus. It is a flowchart which shows the process example by the control apparatus of the steering assist apparatus 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 explaining step S41 in FIG. It is a conceptual diagram for demonstrating adjustment of the assist torque in step S60 (handwheel return assist control) in FIG. It is a conceptual diagram for demonstrating adjustment of the assist torque in step S60 (handwheel return assist control) in FIG. It is a flowchart which shows the detail of step S70 (end condition determination processing) in FIG.

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

1. Overview FIG. 1 is a conceptual diagram for describing an overview 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.

  Furthermore, the steering assist function according to the present embodiment also includes steering assist control that assists the steering so that the vehicle 1 travels following the target travel path at the time of turning. The steering assist control that assists the steering of the vehicle 1 to follow the target travel path is hereinafter referred to as “target travel path follow-up control”. The target runway is typically calculated by an automatic driving system mounted on the vehicle 1.

  However, the target track follow-up control according to the present embodiment is not performed unconditionally while the vehicle 1 is turning. When implementing the target travel path tracking control, the driver's intention of the vehicle 1 is considered. For the purpose of explanation, consider a situation where the vehicle 1 turns at an intersection or the like as shown in FIG. Although the vehicle 1 may be an autonomous driving vehicle, the situation in which the driver manually drives the vehicle 1 will be considered below.

  At timing ta, the driver of the vehicle 1 starts to cut the steering wheel. In response to the cut of the steering wheel, the vehicle 1 starts turning. After that, the driver holds the steering wheel for a while while cutting the steering wheel. While the driver cuts and holds the steering wheel, the driver has the intention to steer by himself. Therefore, target track following control is not performed in such a period.

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

  In the SAT steering wheel return state, the driver has no intention to steer by himself. Therefore, the target track follow-up control is started with the detection of the SAT handle return state as a trigger. In other words, the starting condition of the target track following control during turning is that a SAT handle return state is detected. By implementing the target travel path follow-up control triggered by the SAT steering wheel return state, the steering wheel can be returned naturally so that the vehicle 1 travels following the target travel path without causing the driver to feel discomfort. In that sense, the target track follow-up control in the SAT handle return state can also be called "handle return assist control".

  At timing tc, the turning of the vehicle 1 is finished, and the vehicle 1 starts straight traveling. Since the driver's SAT handle return operation is also completed, the steering wheel return assist control (target track follow-up control) is also completed.

  The steering assist control according to the present embodiment will be described in more detail below.

2. Steering Assist Device FIG. 2 is a schematic diagram 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 operation member used by a 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 movement of the pinion gear 4 is converted to the linear movement of the rack bar 5, whereby the steering angle of the wheel 6 is changed.

  The steering assist device 10 is mounted on the vehicle 1 and assists 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 wheel 6. More specifically, the EPS device 20 includes an electric motor, and generates assist torque by rotation of the electric motor. For example, the electric motor is coupled to the rack bar 5 via a conversion mechanism. When the rotor of the electric motor rotates, the conversion mechanism converts the rotational movement into the linear movement of the rack bar 5. In this way, assist torque is generated and 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 a 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 driving environment information ENV indicating the driving environment of the vehicle 1 necessary for performing automatic driving control. The driving environment information ENV includes position information indicating the position of the vehicle 1, map information, surrounding situation information indicating the situation around the vehicle 1, vehicle state information indicating the state of the vehicle 1, and the like. Position information is obtained, for example, by using a GPS (Global Positioning System). Map information is obtained from a map database. Ambient condition information can be obtained by using an external sensor such as a camera, a rider, or a radar. 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, the yaw rate, and the blinker state of the vehicle 1.

  The control device 100 is a microcomputer including a processor, a storage device, and an input / output interface. 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 performs operation control of the vehicle 1 based on the received information. In particular, in the present embodiment, control device 100 performs steering assist control by controlling the operation of 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 the control program stored in the storage device. The control program may be stored in a computer readable recording medium.

  The EPS control unit 110 performs general EPS control. More specifically, the EPS control unit 110 calculates an 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 an assist torque.

  The autonomous driving control unit 120 controls the autonomous driving of the vehicle 1. For example, based on the driving environment information ENV acquired by the driving environment information acquisition device 60, the automatic driving control unit 120 calculates a target travel path of the vehicle 1. Then, the automatic driving control unit 120 performs the above-described steering wheel return assist control (target travel path tracking control) as necessary. 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 and return the steering wheel 2 is satisfied. In response to the establishment of the start condition, the automatic driving 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 turning of the wheel 6 so that the vehicle 1 travels following the target travel path.

3. Process Flow Example FIG. 3 is a flowchart showing a process example of the control device 100 of the steering assist device 10 according to the present embodiment. The process flow shown in FIG. 3 is repeatedly executed every fixed cycle.

3-1. Step S10 (target runway calculation processing)
Control device 100 (automatic driving control unit 120) calculates a target travel path of vehicle 1 based on driving environment information ENV acquired by driving environment information acquisition device 60. In addition to the automatic driving mode, the calculation of the target running path is performed in the manual driving mode.

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

3-3. Step S30 (EPS control processing)
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 processing)
Control device 100 (automatic operation control unit 120) determines whether or not the steering wheel operation state of the driver is the SAT steering wheel return state. That is, the control device 100 determines whether the steering wheel return assist control start condition is satisfied. If the start condition is satisfied (step S40; Yes), the process proceeds to step S50. Otherwise (step S40; No), the process proceeds to step S30.

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

  In step S41, the control device 100 determines whether 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 and 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 of step S40 is “Yes”. Otherwise (step S41; No), the process proceeds to step S42.

  In step S42, the control device 100 determines whether the handle grip force of the driver has decreased. The reduction in the handle grip force of the driver can be recognized based on the detection information by the touch sensor 50. When the handle grip force decreases (step S42; Yes), it can be said that the handle return is due to the self aligning torque. Therefore, the determination result of step S40 is "Yes". In the other cases (step S42; No), the determination result of step S40 is "No".

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

3-6. Step S60 (steering wheel 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 target travel path tracking control based on the target travel path calculated in step S10. That is, control device 100 controls EPS device 20 to control turning of wheels 6 so that vehicle 1 travels following the target travel path. Since the target travel route is calculated based on the driving environment information ENV, appropriate steering wheel return assist control according to the road shape and the surrounding traffic conditions is realized.

  When the steering wheel return assist control is started, 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, adjustment of the assist torque may be performed to prevent a sudden change of the assist torque generated by the EPS device 20. The adjustment of the assist torque will be described below with reference to FIGS. 6 and 7.

  FIG. 6 conceptually shows the assist torque AT generated by the EPS device 20. As shown in FIG. The automatic driving control unit 120 calculates a first assist torque AT_1 that is an 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 ′. Furthermore, 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 expressed by the following equation (1).

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

  In equation (1), the parameter K is a gain which takes a value in the range of 0-1. An example of setting the gain K is shown in FIG. Normal EPS control is performed before time t1. 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. A period from time t1 to t2 is a switching period from EPS control to steering wheel return assist control. In 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_2 to the assist torque AT gradually decreases. Thus, sudden change of the assist torque AT is prevented.

  Note that, even during the steering wheel return assist control, the third assist torque AT_3 based on the steering torque MT is continuously incorporated into the assist torque AT. Thus, even when the steering wheel return assist control is canceled, the steering assist force can be secured.

3-7. Step S70 (end condition determination processing)
During the steering wheel return assist control, the control device 100 (the automatic driving control unit 120) determines whether an end condition for terminating the steering wheel return assist control is satisfied. If the end condition is satisfied (step S70; Yes), the process proceeds to step S80. Otherwise (step S70; No), the process returns to step S60. As described below, various examples of the termination condition can be considered.

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

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

  In step S73, control device 100 determines whether the curvature of the target runway ahead of vehicle 1 has increased by a threshold Cth2 or more. When the curvature of the forward target runway increases by a threshold Cth2 or more, the driver needs to stop the SAT handle return operation and turn the handle 2 to increase. At this time, if the steering wheel return assist control continues, it is difficult to turn the steering wheel 2 further, and the driver feels a sense of discomfort. Therefore, it is preferable to end the steering wheel return assist control. That is, an increase in the curvature of the forward target runway by the threshold Cth2 or more is a second end condition in which the turning increase of the steering wheel 2 is taken into consideration. When the second end condition is satisfied (step S73; Yes), the determination result of step S70 is "Yes". Otherwise (step S73; No), the process proceeds to step S74.

  In step S74, the control device 100 determines whether a steering torque MT equal to or greater than a threshold MTth has been 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 MTth, it means that the driver cancels the SAT steering wheel return operation and tries to steer by himself. Therefore, it is preferable to end the steering wheel return assist control. That is, detecting the steering torque MT equal to or higher than the threshold MTth is a third termination condition in consideration of the driver's steering intention. When the third end condition is satisfied (step S74; Yes), the determination result of step S70 is "Yes". In the other cases (step S74; No), the determination result of step S70 is "No".

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

  At the end of the steering wheel return assist control, switching from the steering wheel return assist control to the normal EPS control is performed. At this time, the assist torque AT may be adjusted as in the case of the start of the steering wheel return assist control (see FIGS. 6 and 7). Specifically, at time t3 in FIG. 7, the termination condition of the steering wheel return assist control is satisfied. A 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. Thus, sudden change of the assist torque AT is prevented.

4. 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 such that the vehicle 1 travels following the target travel path. 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 to the self aligning torque. When leaving the steering wheel 2 to the self aligning torque, the driver has no intention to steer by himself. Therefore, by performing the steering wheel return assist control using the above as a start condition, the steering wheel 2 can be naturally returned so that the vehicle 1 travels following the target running road without causing the driver to feel discomfort. .

  As an end condition of the steering wheel return assist control, various examples can be considered as described above. In the case of the first end condition in which the road shape is taken into consideration, it is possible to end the steering wheel return assist control at an appropriate timing at which the steering wheel return is ended. Further, in the case of the second end condition in which the turning of the steering wheel 2 is considered, it is possible to prevent the steering wheel return assist control from interfering with the turning of the steering wheel 2. In addition, in the case of the third termination condition in which the driver's steering intention is taken into consideration, it is possible to prevent the steering force from increasing due to the steering wheel return assist control at the time of driver's steering and causing discomfort. In any case, the driver is prevented from feeling uncomfortable.

1 Vehicle 2 steering wheel (steering wheel)
Reference Signs List 3 steering shaft 4 pinion gear 5 rack bar 6 wheel 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 driving control unit ENV driving environment information

Claims (1)

A steering assist device mounted on a vehicle,
A power steering device for turning the wheels of the vehicle;
A control device for controlling the power steering device;
The controller is
Target runway calculation processing for calculating a target runway based on driving environment information indicating the driving environment of the vehicle;
A start condition determination process of determining whether a start condition for the driver of the vehicle to leave the self aligning torque and return the steering wheel during the manual operation is satisfied;
Performing an assist start process of starting the steering wheel return assist control in response to the establishment of the start condition;
In the steering wheel return assist control, the control device controls the steering of the wheels by controlling the power steering device such that the vehicle travels following the target travel path.

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