JP2024136710A - Vehicular control device - Google Patents

Abstract

To provide a vehicular control device which is made up in view of the above-described technical problem, and which can appropriately stabilize the behavior of a vehicle even in a case in which a large earthquake occurs while the vehicle is travelling.SOLUTION: A vehicular control device includes a front wheel steering device 3 that turns front wheels 1, and a rear wheel steering device 4 that turns rear wheels 2, and actuates the front wheel steering device 3 and the rear wheel steering device 4 based on an aiming yaw rate calculated from the operation state of a steering device 5. This vehicular control device determines whether or not an earthquake occurs while a vehicle is travelling, calculates, when a deviation ΔYR1 between an aiming yaw rate YRstd and an actual yaw rate YR is larger than a control threshold Th1, a rear wheel steering amount to turn the rear wheels 2 in a direction in which the deviation ΔYR1 decreases, and controls the rear wheel steering device 4 based on the rear wheel steering amount (step S5).SELECTED DRAWING: Figure 3

Description

This invention relates to a control device for a vehicle (four-wheel steering vehicle) that can steer the rear wheels in addition to the front wheels.

Patent Document 1 describes a steering control device for a vehicle equipped with a four-wheel steering mechanism (four-wheel steering vehicle). The four-wheel steering vehicle described in Patent Document 1 is equipped with a front-wheel steering device, a rear-wheel steering device, and a VGRS device (variable gear ratio steering device). The steering control device described in Patent Document 1 controls the steering angle of the rear wheels so that the rear wheels are steered in phase (same steering direction) or opposite phase (opposite steering direction) to the steering direction of the front wheels based on the driving conditions of the vehicle. It also detects a state in which the vehicle should be moved laterally and determines a target movement distance in that lateral direction. When it detects a state in which the vehicle should be moved laterally, it steers the rear wheels in opposite phase to the front wheels for a period determined based on the target movement distance, and delays the timing of steering the rear wheels in phase with the front wheels.

Patent document 2 describes a vehicle driving control device that performs appropriate vehicle driving control when an emergency earthquake early warning is received, with the aim of suppressing panic that is feared to be caused by the emergency earthquake early warning. When an emergency earthquake early warning is received, the vehicle driving control device described in this patent document 2 corrects the vehicle operation input amount (accelerator pedal operation amount, brake pedal operation amount, steering wheel steering angle, etc.) when the vehicle operation input amount increases, so that the rate of increase decreases, and drives a control actuator according to the corrected operation input amount.

Patent document 3 describes a vehicle driving control device that detects lane markers displayed on a road and steers and controls the vehicle's traveling direction so that the vehicle follows the detected lane markers. The vehicle driving control device described in Patent document 3 detects whether the direction of the branching or merging is to the left or right of the traveling road when the required distance to a branching or merging position on the road on which the vehicle is traveling reaches a predetermined reference distance. Then, the steering and vehicle speed are controlled based on the lane marker on the opposite side of the branching or merging direction.

JP 2009-280102 A JP 2010-253964 A JP 2000-207692 A

In a four-wheel steering vehicle equipped with a rear-wheel steering system as described in Patent Document 1, the rear wheels are generally steered in the opposite direction (opposite phase) to the front wheels when traveling at low speeds. This action generates a yaw moment in the direction of turning of the vehicle, making it possible to reduce the turning radius of the vehicle. Also, when traveling at high speeds, the rear wheels are steered in the same direction (in phase) as the front wheels. This action reduces the yawing of the vehicle when steering, and improves the handling stability of the vehicle. However, even in such a four-wheel steering vehicle, if a large earthquake occurs while the vehicle is traveling, the behavior of the vehicle will be disturbed by the unexpected vibration of the earthquake. In particular, if a large yaw rate is generated in the vehicle due to the lateral vibration of the earthquake that vibrates the vehicle in the left-right direction, the excessive yaw rate cannot be suppressed even when the driver steers the vehicle, and as a result, there is a risk that the vehicle will deviate from the driving lane.

This invention was conceived with a focus on the above technical problems, and aims to provide a vehicle control device that can appropriately stabilize the behavior of a vehicle capable of rear-wheel steering, even if a large earthquake occurs while the vehicle is in motion.

To achieve the above object, the present invention provides a vehicle control device that includes a steering device operated by a driver, a front wheel steering device that steers the front wheels, and a rear wheel steering device that steers the rear wheels, and that operates the front wheel steering device and the rear wheel steering device based on a target yaw rate calculated from the operation state of the steering device. The vehicle control device includes a controller that controls the front wheel steering device and the rear wheel steering device, respectively. The controller determines whether an earthquake has occurred while traveling, and if it determines that an earthquake has occurred, calculates the deviation (or amount of deviation) between the target yaw rate and the actual yaw rate, and if the deviation is greater than a predetermined control threshold, calculates a rear wheel steering amount that steers the rear wheels in a direction that reduces the deviation, and controls the rear wheel steering device based on the rear wheel steering amount.

The vehicle control device of the present invention controls the front wheel steering device and the rear wheel steering device for a vehicle capable of steering the rear wheels in addition to steering the front wheels. By appropriately controlling the front and rear wheels according to the situation, the turning radius of the vehicle can be reduced and the vehicle's handling stability can be improved. However, as mentioned above, if a large earthquake occurs while the vehicle is traveling, accompanied by lateral vibration that causes the vehicle to vibrate in the left and right directions, the driver's steering may not be able to suppress the disturbance of the vehicle's behavior. Therefore, the vehicle control device of the present invention makes use of the characteristics of a vehicle capable of steering control of the rear wheels, and when a large earthquake occurs while traveling that causes the deviation between the target yaw rate of the vehicle and the actual yaw rate to exceed the control threshold, the rear wheels are steered to reduce the deviation of the yaw rates. In other words, the actual yaw rate is made to follow the target yaw rate. Therefore, even in a situation where a large yaw rate is generated by an earthquake and there is a risk that the vehicle's behavior will be significantly disturbed, the excessive yaw rate can be reduced by controlling the rear wheel steering device.

In theory, the control to suppress excessive yaw rates as described above can also be implemented by automatically controlling the front wheel steering device to steer the front wheels in a direction that reduces the yaw rate. However, the front wheel steering device is basically configured to operate in response to the driver's steering, and automatically controlling the front wheel steering device can cause interference between the driver's steering of the front wheels and the automatic control, which can cause the driver to feel uncomfortable or uneasy. In contrast, the vehicle control device of this invention does not automatically control the front wheel steering device, but instead automatically controls the rear wheel steering device as described above to reduce the yaw rate. As a result, excessive yaw rates caused by earthquake lateral shaking can be appropriately suppressed without interfering with the driver's steering.

Therefore, the vehicle control device of this invention can control a vehicle capable of rear wheel steering and appropriately stabilize the vehicle's behavior even if a large earthquake occurs while the vehicle is traveling.

FIG. 1 is a block diagram showing a schematic configuration of a vehicle to be controlled by a vehicle control device of the present invention. FIG. 2 is a diagram for explaining the behavior of a vehicle when an earthquake (lateral shaking) occurs and the mechanism by which yaw rate is generated. FIG. 2(a) illustrates the inertial force of the vehicle, the tire lateral force, and the amount of movement, and FIG. 2(b) illustrates the relationship between the tire lateral force and the ground contact load. FIG. 3 is a flow chart for explaining an example of control (in the case of manual steering) executed by the vehicle control device of the present invention. FIG. 4 is a diagram showing an image of a map applied when determining the rear wheel steering amount in the control shown in the flowchart of FIG. FIG. 5 is a flow chart for explaining another example of control (in the case of automatic steering) executed by the vehicle control device of the present invention. FIG. 6 is a diagram showing an image of a map applied when determining the rear wheel steering amount in the control shown in the flowchart of FIG.

The embodiment of the present invention will be described with reference to the drawings. Note that the embodiment shown below is merely an example of how the present invention can be realized, and is not intended to limit the present invention.

Figure 1 shows the general configuration of a vehicle Ve that is the subject of control in an embodiment of the present invention. The vehicle Ve shown in Figure 2 is a so-called "four-wheel steering vehicle" that is capable of steering both the front wheels 1 and the rear wheels 2. To this end, the vehicle Ve is equipped with a front wheel steering device 3 that steers the front wheels 1, a rear wheel steering device 4 that steers the rear wheels 2, and a steering device 5.

The front wheel steering device 3 steers the front wheels 1 according to the operating state of the steering device (steering wheel) 5 operated by the driver. In the example shown in FIG. 1, the front wheel steering device 3 has an electric actuator 6, a steering gear box 7, and the like. The electric actuator 6 assists the steering by the steering device 5, and causes the front wheel steering device 3 to function as a so-called "power steering device." The front wheel steering device 3 then steers the front wheels 1 according to the steering state (steering angle, or steering direction and steering amount) of the steering device 5.

The rear wheel steering device 4 steers the rear wheels 2 based on the steering state of the steering device 5 and the running state of the vehicle Ve, and in conjunction with the steering operation of the front wheels 1 by the front wheel steering device 3. In the example shown in FIG. 1, the rear wheel steering device 4 has an electric actuator 8. The rear wheel steering device 4 is a type of "steer-by-wire type steering device" and steers the rear wheels 2 by operating the electric actuator 8 with an electric signal from a controller 10 (described later).

The vehicle Ve to be controlled in the embodiment of the present invention may have the configuration of a "four-wheel steering vehicle" described in the aforementioned Patent Document 1, for example. In this case, the detailed configuration of the vehicle Ve is as described in the specification of the aforementioned Patent Document 1.

Although not shown in FIG. 1, the vehicle Ve actually has a driving force source such as an engine, a motor, or a hybrid drive unit, as well as a power transmission system that transmits the output torque of the driving force source to the drive wheels. The vehicle control device in the embodiment of the present invention can control a vehicle Ve with any driving method.

Furthermore, the vehicle Ve is equipped with a detection unit 9 and a controller (ECU) 10 to control the front wheel steering device 3 and the rear wheel steering device 4 based on the steering state of the steering device 5 and the running state of the vehicle Ve.

The detection unit 9 is a device or apparatus for acquiring various data and information required for controlling the vehicle Ve, and includes, for example, a power supply unit, a microcomputer, a sensor, and an input/output interface. In particular, the detection unit 9 in the embodiment of the present invention detects various data for controlling the front wheel steering device 3 and the rear wheel steering device 4. For example, the detection unit 9 has various sensors such as a vehicle speed sensor 9a for detecting the vehicle speed, an acceleration sensor 9b for detecting the acceleration of the vehicle Ve, a yaw rate sensor 9c for detecting the yaw rate of the vehicle Ve, a steering angle sensor 9d for detecting the steering angle of the steering device (steering wheel) 5 or the rotation angle of the steering shaft (not shown), and a steering angle sensor 9e for detecting the steering angles of the front wheels 1 and the rear wheels 2. Furthermore, the detection unit 9 in the embodiment of the present invention has an emergency earthquake warning receiver 9f for receiving an emergency earthquake warning in order to determine the occurrence of an earthquake in the controller 10 described later, and an in-vehicle camera 9g for photographing the external situation of the vehicle Ve or generating video data. The detector 9 is electrically connected to the controller 10 (described later) and outputs electrical signals corresponding to the detected or calculated values of the various sensors, devices, and equipment described above to the controller 10 as detection data.

The controller 10 is an electronic control device mainly composed of a microcomputer, for example, and controls the vehicle Ve as well as the front wheel steering device 3 and the rear wheel steering device 4. In particular, the controller 10 in the embodiment of the present invention determines whether an earthquake has occurred. For example, as disclosed in the specification of JP 2008-224353 A, the occurrence of an earthquake is determined based on the change in acceleration of the vehicle Ve and its duration, etc. Also, as disclosed in the specification of JP 2008-224353 A, the occurrence of an earthquake is determined based on the difference between the movement amount and attitude of the vehicle Ve based on the image captured by the on-board camera 9g and the movement amount and attitude of the vehicle Ve calculated from the detection values of each sensor of the vehicle Ve. Furthermore, as described below, when the controller 10 in the embodiment of the present invention determines that an earthquake has occurred while the vehicle Ve is traveling, it controls the rear wheel steering device 4 to steer the rear wheels 2. Various data detected or calculated by the above-mentioned detection unit 9 are input to the controller 10. The controller 10 performs calculations using various input data, pre-stored data, calculation formulas, etc. The controller 10 then outputs the calculation results as control command signals and is configured to control the vehicle Ve as described above. Note that while FIG. 1 shows an example in which one controller 10 is provided, multiple controllers 10 may be provided for each device or equipment to be controlled, or for each control content.

As described above, the vehicle control device in the embodiment of the present invention aims to appropriately stabilize the behavior of the vehicle Ve even in a situation where a large earthquake occurs while the vehicle is traveling. When an earthquake occurs while the vehicle is traveling, an unintended (not caused by the driver's steering) yaw rate occurs in the vehicle Ve due to the lateral vibration of the earthquake that vibrates the vehicle Ve in the left-right direction. For example, as shown in (a) of FIG. 2, if the front-to-rear weight distribution of the vehicle Ve is "6:4", a shift occurs in the center of the force point of the inertial force acting on the center of gravity of the vehicle Ve due to the lateral vibration of the earthquake and the total tire lateral force (the tire lateral force of the front wheel 1 and the tire lateral force of the rear wheel 2). As a result, an unintended yaw rate occurs in the vehicle Ve, and the behavior of the vehicle Ve becomes unstable. As shown in FIG. 2B, the relationship between the ground load and tire lateral force of the vehicle Ve is nearly linear in the region where both the ground load and tire lateral force are small, but as the ground load increases, the slope of the graph showing the relationship between the ground load and tire lateral force decreases (the relationship between the ground load and tire lateral force becomes an upwardly convex curve). Therefore, the tire lateral force relative to the ground load is greater on the rear wheel 2 than on the front wheel 1, and the total tire lateral force acts at a position closer to the rear wheel 2 than the center of gravity of the vehicle Ve. Therefore, the force center between the inertial force of the vehicle Ve and the total tire lateral force is shifted, and as a result, a yaw moment acts on the vehicle Ve, generating a yaw rate.

If the yaw rate generated by the lateral shaking of an earthquake as described above is minor, it can be absorbed within the range of play of the steering device 5, for example, or can be suppressed by the driver's steering. However, if the earthquake is large and an excessive yaw rate occurs, the yaw rate cannot be suppressed even by the driver's steering. As a result, the behavior of the vehicle Ve becomes significantly disturbed, and there is a risk that the vehicle Ve will deviate from its lane while traveling. Therefore, the controller 10 of the vehicle Ve in this embodiment of the present invention is configured to execute control to suppress the excessive yaw rate when an excessive yaw rate occurs due to the lateral shaking of an earthquake. An example of such yaw rate suppression control is shown in the flowchart of the following Figure 3.

The control shown in the flowchart of FIG. 3 is executed when an earthquake occurs while the vehicle Ve, whose front wheel steering device 3 is manually operated, is traveling. For example, the control is executed when it is determined that an earthquake has occurred while the vehicle Ve is traveling at a predetermined vehicle speed or faster. Therefore, in the flowchart of FIG. 3, when it is determined in step S1 that an earthquake has occurred, the process proceeds to the next step S2, and the routine shown in the flowchart of FIG. 3 is started. The determination of the occurrence of an earthquake in step S1 is made, for example, when the aforementioned emergency earthquake warning is received, or when the initial tremors (P waves) of an earthquake are detected by the acceleration sensor 9b or the like.

In step S2, it is determined whether an earthquake has actually occurred. For example, it is determined that an earthquake has actually occurred if the seismic intensity or magnitude is greater than a predetermined value, if the main motion of the earthquake (S waves) is detected, if it is determined that the waveform showing the change in acceleration of the vehicle Ve is a waveform specific to an earthquake, or if it is determined that there is a fluctuation specific to an earthquake based on the image data captured by the vehicle-mounted camera 9g. It may also be determined that an earthquake has occurred if at least one of the multiple determination conditions described above is met. Alternatively, it may be determined that an earthquake has occurred if two or more or three or more determination conditions are met.

If the answer to step S2 is "No" because no earthquake has actually occurred, for example, an emergency earthquake warning has been received but no earthquake has occurred that satisfies the above-mentioned criteria, i.e., no earthquake that would affect the behavior of the vehicle Ve, the routine shown in the flowchart of FIG. 3 is temporarily terminated without executing the control of the subsequent steps.

On the other hand, if the above judgment condition is met, for example, because an earthquake has occurred that may affect the behavior of the vehicle Ve, and the answer is "Yes" in step S2, the process proceeds to the next step S3.

In step S3, the target yaw rate YRstd and the deviation ΔYR1 are calculated. The target yaw rate YRstd is expressed as follows, where STR is the steering angle by the steering device 5, V is the vehicle speed, N is the steering gear ratio of the front wheel steering device 3, and L is the wheelbase of the vehicle Ve:
YRstd=STR×V/(N×L)
It is calculated as:

The deviation ΔYR1 is the difference between the target yaw rate YRstd and the actual yaw rate YR,
ΔYR1=YRstd-YR
It is calculated as:

Next, in step S4, it is determined whether the absolute value of the deviation ΔYR1 is greater than the control threshold Th1. The control threshold Th1 is a threshold for determining the yaw rate at which there is concern that the behavior of the vehicle Ve may be disturbed due to lateral shaking caused by an earthquake. If the absolute value of the yaw rate deviation ΔYR1 is greater than the control threshold Th1, that is, if the deviation of the actual yaw rate YR from the target yaw rate YRstd is large, it is determined that yaw rate suppression control is necessary. The control threshold Th1 is set in advance, for example, based on the results of driving experiments using an actual vehicle or simulations.

Therefore, if the absolute value of the yaw rate deviation ΔYR1 is equal to or less than the control threshold value Th1 and the answer to this step S4 is "No," yaw rate suppression control is not necessary, so the routine shown in the flowchart of FIG. 3 is temporarily terminated without executing any further control.

On the other hand, if the absolute value of the yaw rate deviation ΔYR1 is greater than the control threshold Th1 and the answer is "Yes" in step S4, the process proceeds to the next step S5.

Then, in step S5, yaw rate suppression control is executed. Specifically, the rear wheel steering amount is calculated, and the rear wheel steering device 4 is controlled based on the rear wheel steering amount. The rear wheel steering amount is a target value for steering the rear wheels 2 in a direction that reduces the yaw rate deviation ΔYR1, and is calculated, for example, from a map (MAP1) shown in FIG. 4. This map in FIG. 4 is preset, for example, based on the results of driving experiments using an actual vehicle, simulations, etc.

As described above, once the rear wheel steering amount is determined in step S5 and yaw rate suppression control is executed, the routine shown in the flowchart of FIG. 3 is temporarily terminated.

In addition, the controller 10 of the vehicle Ve in this embodiment of the invention can also execute the control shown in the flowchart in Figure 5 for a vehicle Ve in which the front wheel steering device 3 is automatically controlled, i.e., the vehicle is automatically driven without the driver touching the steering device 5 (hands-free).

The control contents of steps S11 and S12 in the flowchart of FIG. 5 are the same as those of steps S1 and S2 in the flowchart of FIG.

In the flowchart of Fig. 5, in step S13, a target trajectory yaw rate YRref and a deviation ΔYR2 are calculated. When an estimated turning radius of the front is R and a vehicle speed is V, the target trajectory yaw rate YRref is expressed as follows:
YRref=V/R
It is calculated as:

The deviation ΔYR2 is the difference between the target trajectory yaw rate YRref and the actual yaw rate YR,
ΔYR2=YRref−YR
It is calculated as:

Next, in step S4, it is determined whether the absolute value of the deviation ΔYR2 is greater than the control threshold Th2. Similar to the above-mentioned control threshold Th1, the control threshold Th2 is a threshold for determining the yaw rate at which there is concern that the behavior of the vehicle Ve may be disturbed due to lateral shaking caused by an earthquake. However, since this control threshold Th2 is a threshold for assuming the above-mentioned hands-free automatic driving, there is no need to take into account interference with steering by the driver. Therefore, the control threshold Th2 may be set to a value smaller than the above-mentioned control threshold Th1.

If the absolute value of the yaw rate deviation ΔYR2 is equal to or less than the control threshold value Th2 and therefore the answer to step S14 is "No," yaw rate suppression control is not necessary, so the routine shown in the flowchart of FIG. 5 is terminated without executing any further control.

On the other hand, if the absolute value of the yaw rate deviation ΔYR2 is greater than the control threshold Th2 and therefore the answer is "Yes" in step S14, the process proceeds to the next step S15.

Then, in step S15, yaw rate suppression control is executed. Specifically, the rear wheel steering amount is calculated, and the rear wheel steering device 4 is controlled based on the rear wheel steering amount. The rear wheel steering amount in this case is a target value for steering the rear wheels 2 in a direction that reduces the yaw rate deviation ΔYR2, and is calculated, for example, from the map (MAP2) shown in FIG. 6.

As described above, once the rear wheel steering amount is determined in step S15 and yaw rate suppression control is executed, the routine shown in the flowchart of FIG. 5 is temporarily terminated.

As described above, the vehicle control device in this embodiment of the invention takes advantage of the feature of the vehicle Ve that allows steering control of the rear wheels 2, and when a large earthquake occurs while the vehicle Ve is traveling such that the deviation between the target yaw rate and the actual yaw rate exceeds the control threshold, the rear wheels 2 are steered to reduce the deviation in the yaw rate. In other words, the actual yaw rate is made to follow the target yaw rate. Therefore, even in a situation where a large yaw rate is generated by an earthquake and there is a risk that the behavior of the vehicle Ve will be significantly disturbed, the excessive yaw rate can be reduced by controlling the rear wheel steering device 4.

Therefore, according to the vehicle control device of the embodiment of the present invention, the vehicle Ve capable of rear wheel steering is targeted as the control target, and the behavior of the vehicle Ve can be appropriately stabilized even if a large earthquake occurs while the vehicle is traveling.

1 Front wheel 2 Rear wheel 3 Front wheel steering device 4 Rear wheel steering device 5 Steering wheel (steering device)
6 Electric actuator (for front wheels)
7 Steering gear box 8 Electric actuator (for rear wheels)
9 Detection unit 9a (detection unit) vehicle speed sensor 9b (detection unit) acceleration sensor 9c (detection unit) yaw rate sensor 9d (detection unit) steering angle sensor 9e (detection unit) turning angle sensor 9f (detection unit) emergency earthquake alert receiver 9g (detection unit) vehicle-mounted camera 10 Controller (ECU)
Vehicle

Claims (1)

A control device for a vehicle including a steering device operated by a driver, a front wheel steering device for turning front wheels, and a rear wheel steering device for turning rear wheels, the control device operating the front wheel steering device and the rear wheel steering device based on a target yaw rate calculated from an operation state of the steering device,
a controller for controlling each of the front wheel steering device and the rear wheel steering device;
The controller:
Determine whether an earthquake has occurred while driving,
When it is determined that an earthquake has occurred, a deviation between the target yaw rate and an actual yaw rate is calculated;
When the deviation is greater than a predetermined control threshold, a rear wheel steering amount for steering the rear wheels in a direction that reduces the deviation is calculated;
A vehicle control device comprising: a rear wheel steering device that controls the rear wheel steering device based on the rear wheel steering amount.

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