Vehicle control device

Abstract

To provide a vehicle control device that is able to eliminate uncomfortable feeling of steering in 4WS.SOLUTION: In a vehicle employing 4WS that controls the steering angles of front wheels and rear wheels, based on the steering of a steering wheel by an occupant, when a parallel traveling state in which traveling is performed with a steering angle of the front wheels and a steering angle of the rear wheels coinciding with each other in a state in which the steering wheel is located at a position other than a neutral position as a result of the steering of the steering wheel, a torque corresponding to a self-alignment torque (SAT) is applied to the steering wheel in a direction in which the steering wheel is returned to the neutral position.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a vehicle control device for a vehicle capable of controlling the steering angles of the front wheels and the rear wheels respectively based on the steering of a steering wheel by a driver.

Background Art

[0002] Conventionally, as a vehicle steering method, there are two-wheel steering (2 Wheels Stearing, hereinafter referred to as 2WS) that controls only the steering angle of the front wheels based on the steering wheel operation by the driver, and four-wheel steering (4 Wheels Stearing, hereinafter referred to as 4WS) that controls the steering angles of the front wheels and the rear wheels respectively. Although 4WS has a problem that the structure becomes more complicated than 2WS, there are also many excellent merits such as reducing the inner wheel difference, being able to reduce the turning radius, preventing slip on icy roads, and enabling stable lane change at high speeds.

[0003] However, for the steering angle control of 4WS, there are, for example, in-phase control that controls the steering angles of the front wheels and the rear wheels in the same direction and reverse-phase control that controls the steering angles of the front wheels and the rear wheels in the opposite direction. However, for 4WS in which these controls are performed, there is a large difference in the driver's steering feeling from that of 2WS, and as a result, 4WS has been shunned by drivers who feel a sense of discomfort in the steering of 4WS. Therefore, for example, Japanese Patent Application Laid-Open No. 2010-285036 discloses a technique for realizing an appropriate steering feeling by applying a reaction torque to the steering wheel of a vehicle adopting 4WS.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, as one form of in-phase control by 4WS, it is known that parallel running (so-called crab running) is performed in which the steering angles of the front wheels and the rear wheels coincide while the steering wheel is in a position other than the neutral position. When this parallel running is performed, a torque called self-aligning torque (SAT) that acts in the direction of returning the steering wheel to the neutral position does not occur, which has been one of the factors causing the driver to feel a strong sense of discomfort in steering the 4WS.

[0006] Although Patent Document 1 discloses applying a reaction torque to the steering wheel of a vehicle, it does not address the countermeasure against the SAT in the above parallel running, and thus is insufficient to eliminate the sense of discomfort in steering the 4WS.

[0007] The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a vehicle control device capable of eliminating the sense of discomfort in steering the 4WS by applying a torque corresponding to the SAT to the steering wheel in a state where parallel running is being performed in the 4WS.

Means for Solving the Problems

[0008] To achieve the above object, a vehicle control device according to the present invention includes a steering angle control means for controlling the steering angles of the front wheels and the rear wheels respectively based on the steering of the steering wheel by a driver, and as a result of the steering of the steering wheel, when a parallel running state is entered in which the steering angles of the front wheels and the rear wheels coincide while the steering wheel is in a position other than the neutral position, a torque applying means for applying a torque to the steering wheel in the direction of returning the steering wheel to the neutral position. Note that "applying a torque to the steering wheel" includes not only directly applying a torque to the steering wheel but also applying a torque to the steering wheel by driving, for example, a shaft, a gear, or a rack connected to the steering wheel.

Effects of the Invention

[0009] According to the vehicle control device of the present invention having the above configuration, in a vehicle adopting 4WS that controls the steering angles of the front wheels and the rear wheels respectively based on the steering of the steering wheel by the occupant, when the vehicle is in a parallel running state where the steering angles of the front wheels and the rear wheels are the same while the steering wheel is in a position other than the neutral position, by applying torque to the steering wheel in the direction of returning it to the neutral position, it becomes possible to eliminate the discomfort of the 4WS steering.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

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Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0011] Hereinafter, a vehicle control device according to the present invention will be described in detail with reference to the drawings based on an embodiment in which it is embodied. First, a vehicle 2 equipped with the vehicle control device 1 according to the present embodiment will be described below. FIG. 1 is a schematic configuration diagram of the vehicle 2 according to the present embodiment.

[0012] Here, the vehicle 2 may be, for example, an automobile (internal combustion engine vehicle) having an internal combustion engine (engine, etc.) as a drive source, an automobile (electric vehicle, fuel cell vehicle, etc.) having an electric motor (motor, etc.) as a drive source, or an automobile (hybrid vehicle) having both of them as drive sources. Also, regardless of the vehicle type, it may be a passenger car, or a commercial large truck, bus, etc. Further, if it is equipped with front wheels and rear wheels respectively, it may be a forklift or construction machinery.

[0013] Also, the vehicle 2 of the present embodiment is a vehicle that adopts four-wheel steering (4 Wheels Stearing, hereinafter referred to as 4WS) that controls the steering angles of the front wheels and the rear wheels respectively based on the steering wheel operation by the occupant as a steering method. As the configuration of 4WS, there are a mechanical type in which the steering of the front wheels is mechanically transmitted to the rear wheels via an input gear box on the front wheel side and a steering gear box on the rear wheel side, and an electronic control type in which the rear wheels are steered by electric control by controlling an actuator, motor, various valves, etc. based on the steering amount. In the present embodiment, an example using the electronic control type will be described.

[0014] As shown in FIG. 1, the vehicle 2 includes a vehicle body 3, a steering wheel 4 that is an operation target by the occupant, a power steering device 5 that assists the steering of the steering wheel 4, a rear-wheel steering ECU (Electronic Control Unit) 6, a rear-wheel actuator 7, wheels 8A to 8D, and a liquid crystal display 9. In the following description, the left front wheel is 8A, the right front wheel is 8B, the left rear wheel is 8C, and the right rear wheel is 8D. Note that the vehicle control device 1 includes the power steering device 5, the rear-wheel steering ECU 6, the rear-wheel actuator 7, and other control parts related to the control of the wheels 8A to 8D.

[0015] The following describes each component included in the vehicle 2. First, the steering wheel 4 (also referred to as the steering wheel) is installed in the driver's seat and is a rudder that changes the traveling direction of the vehicle 2 when the occupant grips and turns it. Basically, when changing the traveling direction to the right, the steering wheel 4 is turned in the right direction (clockwise), and when changing it to the left, the steering wheel 4 is turned in the left direction (counterclockwise). Incidentally, a power steering device 5 described later is connected to the steering shaft 11 connected to the steering wheel 4. After being assisted by the power steering device 5, the rack gear and pinion gear 12 at the tip of the steering shaft 11 are driven in accordance with the turning of the steering wheel 4, thereby displacing the steering angles of the front wheels 8A and 8B in the direction corresponding to the turning direction of the steering wheel 4.

[0016] Also, a torque sensor 13 is installed on the steering shaft 11. It detects the steering torque related to the operation of the steering wheel 4 by the occupant and transmits it to the power steering device 5 and the rear wheel steering ECU 6. In addition to the steering torque, the torque sensor 13 can also detect the steering angle and the angular velocity of the steering angle, and transmits the information about them as well. The power steering device 5 controls the torque (assist force for steering) applied to the steering shaft 11 based on the steering torque, steering angle, and angular velocity of the steering angle detected by the torque sensor 13. The rear wheel steering ECU 6 controls the steering angles of the rear wheels 8C and 8D based on the steering torque, steering angle, and angular velocity of the steering angle detected by the torque sensor 13.

[0017] In addition, various operation buttons 15 that are to be operated by the occupant are arranged on the front surface of the steering wheel 4. In particular, in this embodiment, by operating the operation buttons 15, it is possible to arbitrarily change the control mode of the vehicle 2. Here, in this embodiment, the control modes set for the vehicle 2 include a "parallel running mode" in which the steering angles of the front wheels 8A and 8B and the steering angles of the rear wheels 8C and 8D are displaced in a state where they are the same with respect to the steering of the steering wheel 4, and a "normal running mode" in which the steering angles of the front wheels 8A and 8B and the steering angles of the rear wheels 8C and 8D are displaced in different manners with respect to the steering of the steering wheel 4. The control mode set for the vehicle 2 may be automatically switched based on the state of the vehicle in addition to being manually switched by the above operation buttons 15. The details of each control mode will be described later.

[0018] On the other hand, the power steering device 5 is a device that assists the steering of the steering wheel 4, and is roughly classified into a hydraulic type, an electro-hydraulic type, and an electric type. In this embodiment, the electric type will be particularly adopted. Further, the electric type is further divided into a column assist type, a pinion assist type, and a rack assist type depending on the position of the motor 16 that assists the steering, and any of these methods may be adopted. In the following description, the column assist type will be taken as an example for explanation.

[0019] In the power steering device 5, the motor 16 is driven after adjusting the current amount according to the steering torque, the steering angle, and the angular velocity of the steering angle detected by the above-described torque sensor 13. The motor 16 is connected to the steering shaft 11 via a worm gear or a wheel gear. When the motor 16 is driven, torque is applied to the steering shaft 11 to assist the occupant's steering of the steering wheel.

[0020] Further, in this embodiment, in addition to assisting the occupant's steering of the steering wheel, the power steering device 5 also applies torque (hereinafter referred to as reaction torque) in the direction of returning the steering wheel 4 to the neutral position with respect to the steering wheel 4 when the vehicle is in a parallel running state in which the steering angles of the front wheels and the steering angles of the rear wheels are the same while the steering wheel 4 is in a position other than the neutral position. The details of the application of the reaction torque will be described later.

[0021] Subsequently, the rear-wheel steering ECU 6 is a control device that controls the steering angles of the rear wheels 8C and 8D according to the steering torque detected by the aforementioned torque sensor 13, the steering wheel angle, and the angular velocity of the steering angle. The rear-wheel steering ECU 6 is connected to the power steering device 5, the rear-wheel actuator 7, the liquid crystal display 9, the torque sensor 13, and the operation button 15 via an in-vehicle network such as CAN. It is also connected to various sensors such as a vehicle speed sensor and an acceleration sensor mounted on the vehicle 2. In the present embodiment, the rear-wheel steering ECU 6 calculates, in addition to controlling the steering angles of the rear wheels 8C and 8D, the amount of torque of the reaction torque applied to the steering wheel 4. Details of the rear-wheel steering ECU 6 will be described later.

[0022] On the other hand, the rear-wheel actuator 7 is a drive device including, for example, a motor and gears, and is configured to be able to apply a driving force for moving the rear-wheel shaft 18 in the left-right direction to the rear-wheel shaft 18 that connects the left and right rear wheels 8C and 8D to each other. The left and right rear wheels connected to the rear-wheel shaft 18 via tie rods and knuckles turn and are steered in the same direction, respectively. The rear-wheel actuator 7 is electrically connected to the rear-wheel steering ECU 6, and the application of the driving force to the rear-wheel shaft 18 is controlled by the rear-wheel steering ECU 6.

[0023] The liquid crystal display 9 is provided on the instrument panel of the vehicle 2 and displays the control mode currently set in the vehicle 2. However, the liquid crystal display 9 may be used in combination with that for a navigation device. Instead of the liquid crystal display 9, a HUD or an HMD may be used. Further, as a means for notifying the control mode currently set in the vehicle 2, there may be a means for notifying by voice such as a speaker instead of the liquid crystal display 9.

[0024] In addition to the components shown in FIG. 1, the vehicle 2 includes basic components as a vehicle 2, but only the configuration related to the steering of the wheels 8A to 8D and its control, and the control related to the configuration will be described.

[0025] Next, among the components included in the vehicle 2, the configuration of the power steering device 5 in particular will be described. FIG. 2 is a schematic configuration diagram of the power steering device 5 according to the present embodiment.

[0026] As shown in FIG. 2, the power steering device 5 of the present embodiment employs a column assist type, and includes a torque sensor 13 that detects the steering torque generated by the driver on the steering shaft 11 with respect to the steering shaft 11, and a motor 16 that applies torque to the steering shaft 11. Then, by fitting a worm 21 provided on the shaft of the motor 16 and a worm wheel 22 connected to the steering shaft 11, it is possible to apply torque to the steering shaft 11 (including the steering wheel 4 connected to the steering shaft 11, the same applies hereinafter) by the rotational drive of the motor 16.

[0027] Also, by controlling the current flowing through the motor 16, it is possible to control the direction and the amount of torque applied to the steering shaft 11, and the current flowing through the motor 16 is adjusted by the power steering ECU 23 provided in the power steering device 5. Here, as the torque applied to the steering shaft 11 by the motor 16, in addition to the torque assisting the driver's steering wheel operation, when the vehicle is in a parallel running state, there is a reaction torque in the direction of returning the steering wheel 4 to the neutral position with respect to the steering wheel 4. Here, the torque applied to assist the steering wheel operation is in the same direction as the direction in which the driver operates the steering wheel 4, but the reaction torque is a torque in the direction of returning to the neutral position regardless of the operation of the steering wheel 4 by the driver. Note that the amount of torque applied to assist the steering is calculated by the power steering ECU 23 based on the detection value of the torque sensor 13. On the other hand, the amount of reaction torque applied is calculated by the rear wheel steering ECU 6 and transmitted to the power steering ECU 23. However, the amount of reaction torque applied may also be calculated by the power steering ECU 23.

[0028] In addition, the rack gear and pinion gear 12 at the tip of the steering shaft 11 are such that a disk-shaped pinion gear and a rack gear which is a rod-shaped gear are engaged with each other, and by converting the rotational motion of the steering shaft 11 into a linear motion, a driving force for moving the front wheel shaft 24 in the left-right direction can be applied to the front wheel shaft 24 that connects the left and right front wheels 8A and 8B to each other. Incidentally, the left and right front wheels connected to the front wheel shaft 24 via tie rods, knuckles, etc. turn and are steered in the same direction. Basically, the steering angles of the front wheels 8A and 8 change by "1 / gear ratio" with respect to the turning of the steering wheel 4.

[0029] Subsequently, the configuration of the vehicle control device 1 will be described in more detail with reference to FIG. 3. FIG. 3 is a block diagram showing the configuration of the vehicle control device 1 according to the present embodiment.

[0030] The vehicle control device 1 according to the present embodiment includes the above-described power steering device 5, a rear-wheel steering ECU 6, a rear-wheel actuator 7, and a control portion related to the control of the other wheels 8A to 8D. In particular, the rear-wheel steering ECU 6 is an electronic control unit (ECU: Electronic Control Unit) that performs various controls related to the running of the vehicle, such as steering angle control of the rear wheels 8C and 8D, application of reaction torque, and change of control mode, and has various means as processing algorithms together with the control portions included in the power steering device 5 and other vehicle control devices 1. For example, the steering angle control means controls the steering angles of the front wheels and the rear wheels respectively based on the steering of the steering wheel by the occupant. The torque application means applies torque in the direction of returning the steering wheel to the neutral position to the steering wheel when, as a result of the steering of the steering wheel, a parallel running state is achieved in which the steering angles of the front wheels and the rear wheels coincide and the vehicle runs with the steering wheel in a position other than the neutral position.

[0031] Specifically, as shown in FIG. 3, it includes a CPU 31 as an arithmetic unit and a control unit, a RAM 32 used as a working memory when the CPU 31 performs various arithmetic processes, a ROM 33 in which, in addition to control programs, a vehicle control processing program (see FIG. 4) described later, etc. are recorded, and an internal storage device such as a flash memory 34 that stores the programs read from the ROM 33. It also has a timer 35 as a means for measuring time. On the other hand, the rear-wheel steering ECU 6 is also connected via an in-vehicle network such as CAN to the power steering device 5, various sensors such as a torque sensor 13 and a vehicle speed sensor 36 installed in the vehicle 2, a rear-wheel actuator 7, a liquid crystal display 9, and an operation button 15 provided on the steering wheel 4.

[0032] Incidentally, the vehicle speed sensor 36 is a sensor for detecting the moving distance and vehicle speed of the vehicle 2. It generates pulses according to the rotation of the driving wheels of the vehicle 2 and outputs a pulse signal to the rear-wheel steering ECU 6. Then, the rear-wheel steering ECU 6 calculates the vehicle speed and moving distance of the vehicle by counting the generated pulses.

[0033] Subsequently, the vehicle control processing program particularly executed by the rear-wheel steering ECU 6 in the vehicle control device 1 having the above configuration will be described with reference to FIG. 4. FIG. 4 is a flowchart of the vehicle control processing program according to the present embodiment. Here, the vehicle control processing program is executed after the ACC power supply (accessory power supply) of the vehicle is turned on, and is a program for performing various controls related to the running of the vehicle, such as steering angle control of the rear wheels 8C and 8D, application of reaction torque, and change of control mode. Incidentally, the program shown in the flowchart in FIG. 4 below is stored in the RAM 32, ROM 33, etc. provided in the rear-wheel steering ECU 6 and is executed by the CPU 31.

[0034] First, in step (hereinafter abbreviated as S) 1, the CPU 31 determines whether the start condition of the "parallel running mode" is satisfied as the control mode of the vehicle. Here, in the present embodiment, the control modes set for the vehicle 2 include the "parallel running mode" in which the steering angles of the front wheels 8A and 8B and the steering angles of the rear wheels 8C and 8D are displaced in a state where they are the same with respect to the steering of the steering wheel 4, and the "normal running mode" in which the steering angles of the front wheels 8A and 8B and the steering angles of the rear wheels 8C and 8D are displaced in different manners with respect to the steering of the steering wheel 4. The initial state immediately after the ACC power of the vehicle is turned on is the "normal running mode".

[0035] And the case where the start condition of the "parallel running mode" is satisfied means that the current control mode is the "normal running mode", the occupant instructs the shift to the "parallel running mode" by operating the operation button 15, and the steering wheel angle is less than the threshold value (that is, not turning). Note that the steering wheel angle can be detected by the torque sensor 13. However, other conditions may be set as the start condition of the "parallel running mode". For example, even if the occupant does not operate the operation button 15, if it is determined that the vehicle is in a state where it should run in the "parallel running mode", it may be automatically shifted to the "parallel running mode". Specifically, when it is detected that the vehicle has slipped based on the operations of various devices such as ABS (Antilock Brake System), TRC (Traction Control), and VSC (Vehicle Stability Control), it may be shifted to the "parallel running mode". Alternatively, when it is predicted that a lane change will be performed at high speed, specifically, when an obstacle is detected in front of the traveling direction during traveling at a predetermined speed or higher, etc., it may be shifted to the "parallel running mode".

[0036] When it is determined that the start condition of the "parallel running mode" is satisfied (S1: YES), the control mode of the vehicle is shifted to the "parallel running mode" and then shifted to S3. When switching from the "normal running mode" to the "parallel running mode", a screen notifying the fact is displayed on the liquid crystal display 9. As a result, the occupant can be informed in advance that the current control mode of the vehicle is in the "parallel running mode", that is, the parallel running state where the steering angle of the front wheels and the steering angle of the rear wheels coincide when turning the steering wheel.

[0037] On the other hand, when it is determined that the start condition of the "parallel running mode" is not satisfied (S1: NO), the control mode of the vehicle remains in the "normal running mode". Then, vehicle running control based on the "normal running mode" is performed (S2). The vehicle running control based on the "normal running mode" is the conventional 4WS running control. Specifically, based on the steering torque detected by the torque sensor 13, the steering angle of the steering wheel, and the angular velocity of the steering angle, it is determined whether to perform either in-phase control for controlling the steering angles of the front wheels and the rear wheels in the same direction or anti-phase control for controlling the steering angles of the front wheels and the rear wheels in the opposite direction. Then, the direction and the amount of the steering angle of the rear wheels are determined, and a control signal is output to the rear-wheel actuator 7 according to the determined content. In the in-phase control, for example, the steering angle of the rear wheels is set to about 1 / 10 to 1 / 20 of the steering angle of the front wheels. In the "normal running mode", the application of reaction torque is not performed, but the application of reaction torque may be performed in the same manner as in the "parallel running mode". After that, it shifts to S15.

[0038] In S3, the CPU 31 acquires the current steering angle (the steering angle of the steering wheel 4) θ from the torque sensor 13, and determines whether the current steering angle θ is equal to or greater than the threshold value, that is, whether the occupant is performing a turning operation. The threshold value is, for example, 10 degrees (regardless of the steering direction), but the value can be set as appropriate.

[0039] And when it is determined that the current steering angle θ is less than the threshold value (S3: NO), the timer 35 performs a count-up (S4). Since the timer 35 is reset when the steering angle θ becomes equal to or greater than the threshold value as described later (S5), the current value of the timer 35 indicates the time during which the state where the steering angle has been less than the threshold value has continued up to the current point in the "parallel running mode".

[0040] On the other hand, when it is determined that the current steering angle θ is equal to or greater than the threshold value (S3: YES), a steering flag indicating that a turning operation is being performed by the occupant is turned ON (S5). The operation flag is stored in the RAM 32 or the like and is set to OFF in the initial state. Also, the steering direction (right direction (+) or left direction (-) when 0 is the positive position) is recorded, and the count of the timer 35 is also reset.

[0041] Next, in S6, the CPU 31 calculates the direction and amount of the rear wheel steering angle assuming that the "normal running mode" is set. Basically, it is the same process as S2 which is carried out in the state where the "normal running mode" is set. Based on the steering torque detected by the torque sensor 13, the steering angle, and the angular velocity of the steering angle, it is determined whether to perform either the in-phase control that controls the front and rear wheel steering angles in the same direction or the anti-phase control that controls the front and rear wheel steering angles in the opposite direction, and then the direction and amount of the rear wheel steering angle are calculated. In the in-phase control, for example, the rear wheel steering angle is set to about 1 / 10 to 1 / 20 of the front wheel steering angle.

[0042] Subsequently, in S7, the CPU 31 calculates the direction and amount of the rear wheel steering angle based on the "parallel running mode". Basically, based on the steering torque detected by the torque sensor 13, the steering angle, and the angular velocity of the steering angle, the direction and amount of the current front wheel steering angle are estimated, and the direction and amount of the rear wheel steering angle are calculated as being the same as those of the front wheel.

[0043] Thereafter, in S8, the CPU 31 reads the count value of the timer 35 and determines whether the count value has reached a certain time (for example, 60 sec) or more, that is, whether the state where the steering rudder angle θ is less than the threshold value has continued for a certain time or more.

[0044] And when it is determined that the count value of the timer 35 has reached a certain time or more (S8: YES), a degradation process is performed to degrade the 'parallel running mode' and approach the 'normal running mode'. In this degradation process, regarding the direction and amount of the rear wheel steering angle based on the 'parallel running mode' calculated in S7, the values are adjusted so as to gradually approach the direction and amount of the rear wheel steering angle based on the 'normal running mode' calculated in S6. Incidentally, if the direction and amount of the rear wheel steering angle after adjustment match the direction and amount of the rear wheel steering angle based on the 'normal running mode' calculated in S6, the degradation process ends.

[0045] Thereafter, in S10, the CPU 31 determines the direction and amount of the rear wheel steering angle. In the 'parallel running mode', basically, the direction and amount of the rear wheel steering angle based on the 'parallel running mode' calculated in S7 are used, but in the case where the degradation process is performed in S9, the direction and amount of the rear wheel steering angle after adjustment are used.

[0046] Subsequently, in S11, the CPU 31 outputs a control signal to the rear wheel actuator 7 according to the content determined in S10. The rear wheel actuator 7 applies a driving force for moving the rear wheel shaft 18 in the left - right direction to the rear wheel shaft 18 that connects the left and right rear wheels 8C, 8D. As a result, the rear wheel steering angle is controlled.

[0047] Next, in S12, the CPU 31 calculates the torque amount of the reaction torque applied to the steering wheel 4. Here, the reaction torque is a torque applied to the steering wheel 4 in the direction of returning the steering wheel 4 to the neutral position with respect to the parallel running state (so - called crab running) where the front wheel steering angle and the rear wheel steering angle match when the steering wheel 4 is in a position other than the neutral position.

[0048] The following describes the content of the reaction torque and the effects of applying the reaction torque with reference to FIGS. 5 to 10.

[0049] For example, when performing a right or left turn in a conventional 2WS, as shown in FIG. 5, an azimuth difference occurs between the traveling direction X of the vehicle body and the steering angle Y of the front wheels. As a result, deformation as shown in FIG. 5 occurs on the tire contact surface. Since the area of the contact surface gradually becomes wider on the side opposite to the traveling direction than the traveling direction, the shear stress generated due to the deformation of the contact surface also becomes larger on the side opposite to the traveling direction than the traveling direction in proportion to the area of the contact surface. When these shear stresses are combined, it becomes a moment acting in the direction opposite to the turning direction with respect to the center of the tire contact surface. This moment becomes a torque acting in the direction of aligning the vehicle body along the traveling direction received by the tire from the road surface, that is, the direction of returning the steering wheel to the neutral position, and is also called the self-aligning torque (hereinafter referred to as SAT). Due to this SAT, in 2WS, after the driver turns the steering wheel, the steering wheel returns to the neutral position without the driver particularly consciously applying a strong torque, and the vehicle path is corrected in the straight-ahead direction.

[0050] However, in the state where 4WS is performing parallel running, as shown in FIG. 6, no azimuth difference occurs between the traveling direction X of the vehicle body and the steering angle Y of the front wheels. Therefore, no deformation occurs on the tire contact surface, and the above SAT does not occur. The fact that SAT does not occur in the parallel running of the above 4WS has been one of the factors causing the driver to feel a great sense of discomfort in the steering of 4WS.

[0051] For example, taking the case of changing lanes to the left lane as shown in Fig. 7 as an example to explain the above-mentioned sense of discomfort, when changing lanes to the left lane with 2WS, the occupant first turns the steering wheel to the left, then turns the steering wheel back to the neutral position and then turns further in the reverse right direction, and finally turns the steering wheel back to the neutral position again. In the process, when the steering wheel is turned to the left, a torque to return to the neutral position is generated by SAT, so the occupant does not need to perform a steering wheel operation by consciously applying a particularly strong torque to return to the neutral position, and the steering wheel will return to the neutral position. Similarly, when the steering wheel is turned to the right, a torque to return to the neutral position is generated by SAT, so the occupant does not need to perform a steering wheel operation by consciously applying a particularly strong torque to return to the neutral position, and the steering wheel will return to the neutral position. Also, the steering torque when turning back is in the same direction as the movement of the vehicle (lateral G).

[0052] Here, Fig. 8 is a diagram showing the relationship between the steering angle and the steering torque when changing lanes with the above-mentioned 2WS. As shown in Fig. 8, in 2WS, due to the occurrence of SAT, the relationship between the steering angle and the steering torque when turning back becomes nearly linear. Although it also partly includes the second quadrant and the fourth quadrant, basically it only passes through the first quadrant and the third quadrant. The fact that the relationship between the steering angle and the steering torque only passes through the first quadrant and the third quadrant indicates that the steering torque when turning back is in the same direction as the movement of the vehicle (lateral G).

[0053] On the other hand, as shown in Fig. 9, when changing lanes to the left lane in the state where 4WS is performing parallel driving, the occupant first turns the steering wheel to the left, but no torque is generated by SAT, so the occupant must consciously operate the steering wheel, otherwise the steering wheel will not move and will maintain the turned state. Also, when turning the steering wheel back to the neutral position later, a stronger torque is required for the steering wheel operation compared to the above-mentioned 2WS, and the steering torque is in the opposite direction to the movement of the vehicle (lateral G), so it becomes difficult to recognize the movement of the vehicle. Furthermore, since it does not automatically return to the neutral position, it is difficult to determine whether it has returned to the neutral position.

[0054] Here, FIG. 9 is a diagram showing the relationship between the steering angle and the steering torque when performing the lane change of the above 4WS. In particular, it shows a comparison between the case where no reaction torque is applied and the case where reaction torque is applied. As shown in FIG. 9, in 4WS, SAT does not occur, so there is no application of torque when turning back, and the relationship between the steering angle and the steering torque becomes a shape close to a rectangle. As a result, it will pass through the second quadrant when turning back. The fact that the relationship between the steering angle and the steering torque passes through the second quadrant or the fourth quadrant indicates that the steering torque when turning back is in the opposite direction to the movement of the vehicle (lateral G), that is, it gives the driver a sense of discomfort in steering.

[0055] On the other hand, if the same 4WS applies a reaction torque corresponding to SAT, the relationship between the steering angle and the steering torque when turning back will be close to a linear shape, similar to the case of 2WS. Basically, it will only pass through the third quadrant, and it becomes possible to eliminate the sense of discomfort that occurred in 4WS.

[0056] And in this embodiment, for the purpose of eliminating the above-mentioned sense of discomfort, when the 4WS is in a state of parallel running, a torque corresponding to SAT is applied as the reaction torque. Specifically, in the above S12, the CPU 31 calculates the torque amount T of the reaction torque by the following formulas (1) and (2). Note that the fact that T is a negative value indicates that it is the torque in the direction of returning the steering wheel to the neutral position. T = sign(θ)×k1 + θ×g(V) + Δθ×k2····(1) g(V) = -k3×{1 + k4×max(0, V - c1) / c1}····(2) θ: Steering angle (deg), Δθ: Angular velocity of the steering angle (deg / sec), V: Vehicle speed (km / h), k1: Friction compensation coefficient, k2: Angular velocity coefficient of the steering, k3: Steering angle amount coefficient, k4: Speed coefficient, c1: Speed constant

[0057] The torque amount T of the reaction torque calculated by the above formulas (1) and (2) corresponds to the torque amount of SAT generated by 2WS. That is, the reaction torque becomes a torque that pseudo-reproduces SAT. Incidentally, the torque direction of the reaction torque is the direction toward the neutral position regardless of the steering direction. Also, the torque amount T of the reaction torque calculated by the above formulas (1) and (2) becomes a stronger torque in the direction of returning the steering wheel to the neutral position as the steering angle of the steering wheel increases, as the angular velocity of the steering angle increases, or as the current vehicle speed of the vehicle increases. This is the same for SAT.

[0058] Thereafter, in S13, the CPU 31 outputs a control signal to the power steering device 5 according to the content determined in the above S12. The power steering device 5 drives the motor 16 with a current amount corresponding to the instructed torque direction and torque amount, thereby applying a reaction torque to the steering wheel (Fig. 2). As a result, even in a state where parallel running is being performed with 4WS, a torque corresponding to the SAT of 2WS is applied to the steering wheel (i.e., SAT is pseudo-reproduced), and it becomes possible to eliminate the sense of discomfort as described above.

[0059] Subsequently, in S14, the CPU 31 determines whether or not the release condition of the "parallel running mode" is satisfied. Here, the case where the release condition of the "parallel running mode" is satisfied means that the current control mode is the "parallel running mode", the steering flag was turned ON in the above S5 and then the neutral position was straddled, that is, the first condition is that steering was performed in the direction opposite to the steering direction when the steering flag was turned ON. On the other hand, the second condition is that when the degradation process in the above S9 is completed, that is, when the state where the steering angle is less than the threshold value continues for a certain period of time and then the rear wheel steering angle that has been gradually adjusted reaches the same direction and the same steering angle amount as the rear wheel steering angle based on the "normal running mode". Incidentally, if at least one of the first and second conditions is satisfied, it is determined that the release condition is satisfied. However, other conditions may be set as the release condition of the "parallel running mode", for example, the condition that the occupant operates the operation button 15 may be set as the release condition.

[0060] When it is determined that the release condition of the "parallel running mode" is satisfied (S14: YES), the control mode of the vehicle is shifted to the "normal running mode" and then shifted to S2. In S2, as described above, the running control of the vehicle based on the "normal running mode" is performed. When switching from the "parallel running mode" to the "normal running mode", a screen notifying the fact is displayed on the liquid crystal display 9. As a result, the occupant can grasp that the current control mode of the vehicle has returned to the "normal running mode".

[0061] On the other hand, when it is determined that the release condition of the "parallel running mode" is not satisfied (S14: NO), the control mode of the vehicle remains in the "parallel running mode". Then, in S15, it is determined whether the vehicle has finished running. If it has not finished running (S15: NO), it returns to S1 and then shifts to S3, and the running control of the vehicle based on the "parallel running mode" is continuously performed. On the contrary, if the vehicle has finished running (S15: YES), the vehicle control processing program is terminated.

[0062] Subsequently, time charts showing specific examples when vehicle control is performed by the above vehicle control processing program are shown in FIGS. 9 and 10. The horizontal axis represents the elapsed time. In the example shown in FIG. 9, when the user operates the operation button 15 to satisfy the start condition of the "parallel running mode" and the occupant steers the steering wheel, as long as the "parallel running mode" continues, the steering wheel steering angle θ, that is, the steering angle of the front wheels and the steering angle of the rear wheels are displaced in agreement, resulting in a parallel running state. Then, when the steering wheel steering angle θ exceeds the threshold value in the parallel running state, the steering flag is turned ON (S5). After that, the parallel running state is maintained. However, for example, if the steering is reversed in the opposite direction due to reasons such as the completion of a lane change and the steering wheel steering angle θ crosses the neutral position, the release condition of the "parallel running mode" is satisfied, and the vehicle returns to the "normal running mode". In the example shown in FIG. 10, when the user operates the operation button 15 to satisfy the start condition of the "parallel running mode", as long as the "parallel running mode" continues when the occupant steers the steering wheel, the steering wheel angle θ, that is, the front wheel steering angle and the rear wheel steering angle are displaced in unison, resulting in a parallel running state. However, in the example shown in FIG. 10, when the steering wheel angle θ does not exceed the threshold value for a certain period of time or more in the parallel running state (S8: YES), the degradation process (S9) is performed. When the degradation process is performed, the rear wheel steering angle gradually displaces from the state where it coincides with the front wheel steering angle until it coincides with the direction and amount of the rear wheel steering angle based on the "normal running mode". And when the rear wheel steering angle coincides with the direction and amount of the rear wheel steering angle based on the "normal running mode", the release condition of the "parallel running mode" is satisfied, and the vehicle returns to the "normal running mode".

[0063] As described in detail above, in the vehicle control device 1 according to the present embodiment and the computer program executed by the vehicle control device 1, in a vehicle adopting 4WS that controls the steering angles of the front wheels and the rear wheels respectively based on the steering of the steering wheel by the occupant, as a result of the steering of the steering wheel, when a parallel running state occurs in which the front wheel steering angle and the rear wheel steering angle coincide and the vehicle runs with the steering wheel in a position other than the neutral position, torque is applied to the steering wheel in the direction of returning the steering wheel to the neutral position (S12, S13). Therefore, it is possible to eliminate the discomfort of the 4WS steering. In addition, the torque applied to the steering wheel is calculated based on at least one or more of the current steering angle of the steering wheel, the angular velocity of the steering angle of the steering wheel, and the current vehicle speed of the vehicle (S12). Therefore, it is possible to apply a torque having the same nature as the self-aligning torque (SAT) generated in 2WS. In addition, the torque applied to the steering wheel is such that the greater the current steering angle of the steering wheel, the faster the angular velocity of the steering angle of the steering wheel, or the faster the current vehicle speed of the vehicle, the stronger the torque is applied in the direction of returning the steering wheel to the neutral position (S12, S13). Therefore, it is possible to more accurately reproduce the self-aligning torque (SAT) generated in 2WS. In addition, the steering angle control of the front wheels and the rear wheels is executed based on a control mode set from among a plurality of control modes. The plurality of control modes include a parallel running mode in which the steering angles of the front wheels and the rear wheels are displaced in a state where they match with respect to the steering of the steering wheel, and a normal running mode in which the steering angles of the front wheels and the rear wheels are displaced in different manners with respect to the steering of the steering wheel. The control mode can be switched based on the operation of the occupant or the current state of the vehicle, and a liquid crystal display 9 is provided as notification means for notifying the occupant of the currently set control mode. Therefore, the occupant can grasp in advance that the current control mode of the vehicle is the parallel running mode, that is, the vehicle is in a parallel running state in which the steering angles of the front wheels and the rear wheels match when the steering wheel is turned. In addition, the occupant can also grasp that the parallel running mode has been released and the current control mode of the vehicle has returned to the normal running mode. In addition, in a state where the parallel running mode is set as the steering angle control of the front wheels and the rear wheels by the steering angle control means, when the steering angle of the steering wheel crosses the neutral position after the steering angle of the steering wheel becomes equal to or greater than the threshold value, or when the state where the steering angle of the steering wheel is less than the threshold value continues for a certain period of time or more, the currently set control mode is switched from the parallel running mode to the normal running mode. Therefore, when the device determines that there is no need or situation to perform the parallel running state, it is possible to automatically release the parallel running mode and return to the normal running mode.

[0064] Note that the present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, when calculating the reaction torque (S12), it is calculated using three elements: the current steering angle of the steering wheel, the angular velocity of the steering angle of the steering wheel, and the current vehicle speed of the vehicle. However, it is not necessarily required to calculate using all of these elements, and it may be calculated using only any one or two of the elements.

[0065] Also, in this embodiment, the execution entity of the vehicle control processing program shown in FIG. 4 was the rear-wheel steering ECU 6, but part or all of the processing may be performed by the ECU of the power steering device 5. Alternatively, another in-vehicle device such as a navigation device may be the execution entity. Further, part of the processing may be performed by an external server device.

Explanation of Signs

[0066] 1…Vehicle control device, 2…Vehicle, 3…Vehicle body, 4…Steering wheel, 5…Power steering device, 6…Rear-wheel steering ECU, 7…Rear-wheel actuator, 8A~8D…Wheels, 9…Liquid crystal display, 13…Torque sensor, 15…Operation button, 31…CPU

Claims

1. Steering angle control means for controlling the steering angles of the front wheels and the rear wheels respectively based on the steering of the steering wheel by the driver, When, as a result of the steering of the steering wheel, a parallel running state is reached in which the steering angles of the front wheels and the rear wheels coincide and the vehicle travels with the steering wheel in a position other than the neutral position, torque applying means for applying torque to the steering wheel in a direction to return the steering wheel to the neutral position. A vehicle control device comprising:

2. The vehicle control device according to claim 1, wherein the torque applied by the torque applying means is calculated based on at least one of the current steering angle of the steering wheel, the angular velocity of the steering angle of the steering wheel, and the current vehicle speed of the vehicle.

3. The vehicle control device according to claim 2, wherein the torque applied by the torque applying means applies a stronger torque in a direction to return the steering wheel to the neutral position as the current steering angle of the steering wheel increases, as the angular velocity of the steering angle of the steering wheel increases, or as the current vehicle speed of the vehicle increases.

4. The steering angle control of the front wheels and the rear wheels by the steering angle control means is executed based on a control mode set from among a plurality of control modes, The plurality of control modes include a parallel running mode in which the steering angles of the front wheels and the rear wheels are displaced in a state where they coincide with respect to the steering of the steering wheel, and a normal running mode in which the steering angles of the front wheels and the rear wheels are displaced in different manners with respect to the steering of the steering wheel, Switching means for switching the control mode based on the operation of the driver or the current state of the vehicle, The vehicle control device according to any one of claims 1 to 3, further comprising notification means for notifying the driver of the currently set control mode.

5. The switching means is configured such that, In a state where the parallel running mode is set as the steering angle control of the front wheels and the rear wheels by the steering angle control means, When the steering angle of the steering wheel crosses the neutral position after the steering angle of the steering wheel becomes equal to or greater than a threshold value, or when a state where the steering angle of the steering wheel is less than the threshold value continues for a certain period of time or more, the currently set control mode is switched from the parallel running mode to the normal running mode. The vehicle control device according to claim 4.

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