JP7540973B2 - Vehicle steering device - Google Patents

Description

The present invention relates to a vehicle steering device.

Conventionally, devices capable of switching the turning center are known for independently steering vehicles in which each wheel can be steered independently.

For example, in the vehicle steering device disclosed in Patent Document 1, a slider (vehicle longitudinal direction position input means) that can be operated by the driver to indicate the position of the turning center in the vehicle longitudinal direction is provided next to the steering wheel. The steering controller controls the steering angle of each wheel based on the input turning center position.

Patent No. 4380175

In the device described in Patent Document 1, the lateral acceleration applied to the occupant changes depending on the turning center, which may result in a worsening of ride comfort.

The present invention was created in consideration of the above points, and its purpose is to provide a vehicle steering device that reduces the lateral acceleration applied to the occupant when turning an independently steered vehicle, thereby improving the ride comfort.

The vehicle steering device according to the present invention steers each tire of an independently steering vehicle (100) having three or more tires (91-94) that can be steered independently. This vehicle steering device is mounted on a vehicle equipped with an occupant riding position detection device (30) that detects the riding position of an occupant, and a vehicle center of gravity measurement device (40) that measures the center of gravity of the vehicle, and includes a steering angle control unit (15), a turning radius indication unit (17), and a target occupant position indication unit (18) . The steering angle control unit calculates a steering angle for individually steering each tire based on vehicle characteristics acquired from a vehicle characteristic storage device (20). The turning radius indication unit indicates the turning radius of the vehicle. The target occupant position indication unit indicates a target occupant position from a plurality of occupant positions stored in the vehicle characteristic storage device.

The steering angle control unit determines the position of the turning center in the vehicle longitudinal direction on the vehicle left-right axis passing through any one of the following: [A] a preset standard position, [B] an occupant position instructed by the target occupant position instructing unit , [C] an occupant riding position obtained from an occupant riding position detection device or a representative position in a riding range of a plurality of occupants, or [D] a center of gravity of the vehicle obtained from a vehicle center of gravity measuring device . The steering angle control unit calculates the turning angle of each tire from the turning center and the turning radius instructed by the turning radius instructing unit .

The steering angle control unit arbitrates to select one of the turning center positions given priority when the positions of the turning center determined based on information from the target occupant position indication unit, the occupant riding position detection device, or the vehicle center of gravity measurement device are different.

On the vehicle's left-right axis where the turning center is determined, the lateral acceleration caused by the change in turning radius during steering or due to corrective steering is reduced. Therefore, the lateral acceleration applied during turning can be reduced for an occupant who is seated at a target position on the vehicle's left-right axis including the turning center, thereby improving the ride comfort.

1 is a block diagram of a vehicle steering device according to an embodiment; 1A is a diagram showing an example of setting the turning center when only the driver is seated in the driver's seat, and FIG. 1B is a diagram showing an example of setting the turning center when all seats are occupied by passengers. 1A is a diagram showing the relationship between the turning center and changes in lateral acceleration when the turning center is on the vehicle's left-right axis passing through the driver's seat and on the vehicle's left-right axis passing through the rear wheel axle; 5A and 5B are diagrams for explaining calculation of a steering angle during turning. 6 is a time chart showing the steering angles of each tire when the turning center is (a) on the vehicle's left-right axis passing through the driver's seat, and (b) on the vehicle's left-right axis passing through the rear wheel axle. 4A is a time chart showing the turning radius and FIG. 4B is a time chart showing the lateral acceleration acting on the driver when turning. 6A is an enlarged view of a portion VIIa in FIG. 6A , and FIG. 6B is an enlarged view of a portion VIIb in FIG. 6B . 6 is a time chart showing the lateral acceleration acting on an occupant in (a) the right front seat (driver's seat) and (b) the right rear seat during turning. A diagram showing the relationship between wheel load and center of gravity. 4 is a flowchart of a steering process during turning according to one embodiment.

Below, a vehicle steering device according to one embodiment of the present invention will be described with reference to the drawings. The vehicle steering device of this embodiment steers each tire on an independently steering vehicle in which each tire can be steered independently.

Conventionally, in a typical vehicle, the pair of left and right tires are mechanically connected via a link, and the tires are turned by steering the steering wheel. In the future, developments are expected to progress to steer-by-wire, in which the steering wheel and the link between the pair of left and right tires are mechanically separated, and to four-wheel independently steering vehicles in which the left and right rear wheels can be steered independently in addition to the left and right front wheels.

In conventional front-wheel steering vehicles, where only the front wheels can be steered, the turning center during turning can only be set on the vehicle's left-right axis that passes through the rear axle. In contrast, in four-wheel independently steering vehicles, the rear wheels can be steered in addition to the front wheels, allowing the position of the turning center in the vehicle's fore-aft direction to be freely set. The purpose of this embodiment is to take advantage of the characteristics of such independently steering vehicles and improve the riding comfort of the occupants when turning.

(One embodiment)
The configuration of a vehicle steering device 10 according to one embodiment will be described with reference to Figure 1. In the four-wheel independently steerable vehicle 100 shown in Figure 1, all four tires 91-94 can be steered independently. The front left tire 91 is marked "FL", the front right tire 92 is marked "FR", the rear left tire 93 is marked "RL", and the rear right tire 94 is marked "RR".

In addition to the vehicle steering device 10, the vehicle 100 is equipped with a vehicle characteristic storage device 20 that stores vehicle characteristics and occupant positions, an occupant riding position detection device 30 that detects the riding positions of occupants, and a vehicle center of gravity measurement device 40 that measures the center of gravity of the vehicle. The vehicle characteristics stored in the vehicle characteristic storage device 20 include vehicle dimensions such as wheelbase and tread width. Occupant positions are stored as the coordinates of each seat. Detection signals output by the occupant riding position detection device 30 include a seat belt seating signal and a person authentication signal from an in-vehicle camera. An example of the configuration of the vehicle center of gravity measurement device 40 will be described later.

The vehicle steering device 10 is equipped with a steering angle control unit 15 and a turning radius instruction unit 17 as standard components. The steering angle control unit 15 calculates the steering angle for individually steering each tire 91-94 based on the vehicle characteristics acquired from the vehicle characteristics storage device 20. The turning radius instruction unit 17 is composed of a steering wheel or the like, and indicates the turning radius of the vehicle 100.

The vehicle steering device 10 also includes a target occupant position indicator 18 as an optional component. The target occupant position indicator 18 indicates a target occupant position from multiple occupant positions stored in the vehicle characteristics storage device 20. The target occupant position may be manually set by the driver to the driver's seat or a seat occupied by an important family member or guest, or may be automatically set by the system.

The steering angle control unit 15 determines the position of the turning center in the vehicle's longitudinal direction on the vehicle's left-right axis that passes through the target position. As the target position, one of the following positions A to D is used. Each of the target positions A to D may overlap.

Target position A: A preset standard position (e.g., the driver's seat).
Target position B: an occupant position indicated by the target occupant position indicating unit 18 .
Target position C: The passenger's riding position obtained from the passenger riding position detection device 30, or a representative position within the riding range of multiple passengers.
Target position D: the center of gravity of the vehicle obtained from the vehicle center of gravity measuring device 40.

Figure 2(a) shows an example of setting the turning center when only the driver is seated in the driver's seat 82. For example, it is possible to set the turning center on the vehicle's left-right axis (solid line) passing through the driver's seat 82 as target positions A, B, and C. As a comparative example, the vehicle's left-right axis passing through the axes of the rear wheels 93, 94 is shown by a dashed line. The effect of this setting example will be described later with reference to Figures 5 to 7.

Figure 2(b) shows an example of setting the turning center when four passengers are seated in all seats 81-84, the two in the front row and the two in the back row. For example, the turning center can be set on the vehicle's left-right axis (solid line) passing through the center of the vehicle as target positions A and C (or as a position close to target position D). As a comparative example, the vehicle's left-right axis passing through the axes of the rear wheels 93 and 94 is shown with a dashed line. The effect of this setting example will be described later with reference to Figure 8.

The steering angle control unit 15 calculates the steering angle of each tire 91-94 from the turning center and the turning radius specified by the turning radius specification unit. The steering angle control unit 15 issues steering angle commands to each tire 91-94, causing the vehicle 100 to turn in the desired direction.

Next, referring to Figure 3, we will explain a method for improving the ride comfort of an independently steered vehicle when it turns. As a factor related to the ride comfort of the occupants, it is important to reduce the magnitude and rate of change of the vehicle behavior, such as reducing the roll rate and pitch rate.

There are two types of lateral acceleration acting on a passenger (e.g. the driver) when turning. One is the centrifugal force associated with the turning radius and speed. The other is the lateral acceleration caused by a change in direction of travel due to the movement of the turning center. For example, as shown in Figure 3(b), if the turning center is on the vehicle's left-right axis that passes through the rear wheel axle, when the turning center moves from C1 to C2, the direction of travel changes from P1 to P2, and a lateral acceleration αx is generated accordingly. Examples of situations in which the turning center moves include when the steering angle is gradually increased at the beginning of steering or gradually decreased at the end of steering, and when corrective steering is applied during a constant turn.

In contrast, as shown in FIG. 3(a), if the turning center is set on the vehicle's left-right axis that passes through the driver's seat 82, the driver's traveling directions P1, P2 are always the same even if the turning center moves from C1 to C2. Therefore, no lateral acceleration is generated at the beginning of a turn or when corrective steering is applied, and acceleration other than centrifugal force is prevented from being applied to the driver. This improves the driver's ride comfort.

In this way, in this embodiment, the turning radius of the independently steered vehicle 100 can be freely adjusted, and the position of the turning center in the longitudinal direction of the vehicle is determined on the vehicle's lateral axis that passes through the set target position, and the steering angle of the four wheels is controlled. This reduces the lateral acceleration applied to the occupants when turning, improving ride comfort.

The calculation of the steering angle during turning will be described with reference to Figure 4. The steering angle is calculated so that the direction of rotation of each tire 91-94 is perpendicular to the line connecting the center of each tire 91-94 and the turning center. The xy coordinate system is defined with the vehicle's center of gravity as the origin (0,0), the vehicle's left-right axis as the x axis, and the vehicle's front-rear axis as the y axis. On the x axis, the right is positive and the left is negative, and on the y axis, the front is positive and the rear is negative. The coordinates of the turning center are (x1, y1), and the driver's seat coordinates are (x2, y2). For example, in the state shown in Figure 2(a), "y2 = y1".

The turning radius Rt is the distance between the turning center and the center of gravity, and is expressed by equation (1).
Rt=√(x1 ² +y1 ² )...(1)

The wheelbase L and tread widths Df, Dr of the vehicle are obtained from the vehicle characteristics storage device 20. The distance from the center of gravity to the axles of the front wheels 91, 92 in the y-axis direction is represented as Lf, and the distance from the center of gravity to the axles of the rear wheels 93, 94 is represented as Lr. The steering angles δFL, δFR, δRL, δRR of each tire 91-94 are expressed as tangent values using equations (2.1) to (2.4), with the clockwise direction being positive. The subscripts "FL, FR, RL, RR" in Figures 4 and 9 will be written in normal characters in the specification.

tanδFL= (Lf-y1)/{x1+(Df/2)}...(2.1)
tan δFR= (Lf-y1)/{x1-(Df/2)}...(2.2)
tanδRL=-(Lr+y1)/{x1+(Dr/2)}...(2.3)
tan δRR=-(Lr+y1)/{x1-(Dr/2)}...(2.4)

Next, referring to Figures 5 to 7, the effect of reducing lateral acceleration during turning according to this embodiment will be described based on the results of a simulation analysis. In this simulation, it is assumed that a right turn (clockwise turn) is initiated with a constant turning radius about 5 seconds after driving straight ahead, and corrective steering is applied about 15 seconds later. The corrective steering is performed by turning the steering wheel once each to the left and right per second. No numerical values other than 0 are listed on the vertical axis in each figure. However, only units are listed to indicate the dimension of the quantity.

The turning center in the vehicle's longitudinal direction is set to two points: [d] on the vehicle's left-right axis passing through the driver's seat, and [r] on the vehicle's left-right axis passing through the rear wheel axle. Hereinafter, the setting for [d] will be abbreviated to "driver's seat center" and the setting for [r] to "rear wheel axle center." In Figure 4, when it is the driver's seat center, "y1 = y2", and when it is the rear wheel axle center, "y1 = -Lr".

Figure 5(a) shows the steering angles of the tires 91-94 when turning with the driver's seat at the center, and Figure 5(b) shows the rear wheel axle at the center. When the driver's seat is at the center, the front wheels 91, 92 (FL, FR) turn to the right, and the rear wheels 93, 94 (RL, RR) turn to the left. The absolute value of the steering angle of the right wheels 92, 94 (FR, RR) that are closer to the turning center is greater than the absolute value of the steering angle of the left wheels 91, 93 (FL, RL) that are farther from the turning center. When the rear wheel axle is at the center, the front wheels 91, 92 (FL, FR) turn to the right, and the rear wheels 93, 94 (RL, RR) remain in a straight line.

Figures 6(a) and 7(a) show the change in turning radius over time under simulation conditions. Figures 6(b) and 7(b) show the lateral acceleration acting on the driver when turning. Analysis results show that when the gradual change in steering angle is completed, lateral acceleration overshoot is suppressed at the center of the driver's seat (solid line) compared to the center of the rear axle (dashed line). When corrective steering is applied, the lateral acceleration αx_d at the center of the driver's seat is reduced to less than half of the lateral acceleration αx_r at the center of the rear axle.

Next, referring to Figure 8, we will explain the results of an analysis of the lateral acceleration acting on occupants during turning when multiple occupants are seated in multiple seats. As an example, we will assume that there are four occupants seated in all seats, the left front seat (passenger seat) 81, the right front seat (driver's seat) 82, the left rear seat 83, and the right rear seat 84, as shown in Figure 2(b).

As shown in FIG. 2(b), the turning center in the longitudinal direction of the vehicle is set to two positions: [c] on the left-right axis of the vehicle passing through the center of the vehicle, and [r] on the left-right axis of the vehicle passing through the rear wheel axle. The center of the vehicle is, for example, the median of the wheelbase, and is selected as the "representative position in the riding range of multiple occupants." Hereinafter, the setting of [c] will be abbreviated to "vehicle center center," and the setting of [r] will be abbreviated to "rear wheel axle center" as in the explanation of FIG. 5 to FIG. 7. The simulation conditions other than the turning center are the same as those in FIG. 5 to FIG. 7, and the vehicle goes from straight ahead to a right turn and corrective steering is applied.

Figure 8(a) shows the lateral acceleration acting on an occupant in the right front seat (driver's seat) 82, and Figure 8(b) shows the lateral acceleration acting on an occupant in the right rear seat 84. In the right front seat (driver's seat) 82, the lateral acceleration αx_c at the vehicle center (solid line) was reduced to less than half of the lateral acceleration αx_r at the rear axle center (dashed line). In the right rear seat 84, the lateral acceleration αx_c at the vehicle center (solid line) was equivalent to the lateral acceleration αx_r at the rear axle center (dashed line). The lateral acceleration in the left front seat (passenger seat) 81 was offset overall lower than the lateral acceleration in the right front seat (driver's seat) 82, and the lateral acceleration in the left rear seat 83 was offset overall lower than the lateral acceleration in the right rear seat 84.

In this way, when multiple occupants are seated in multiple seats, the lateral acceleration acting on the multiple occupants during turning can be reduced overall by setting the turning center on the vehicle's left-right axis that passes through a representative position in the passenger area of the multiple occupants. For vehicles with three passengers in the back seat or three rows of seats, the representative position can be set appropriately.

Next, the measurement of the center of gravity of the vehicle by the vehicle center of gravity measurement device 40 will be described. The vehicle center of gravity measurement device 40 may derive the center of gravity position in the horizontal plane from the vehicle characteristics in advance. Alternatively, as shown in FIG. 9, the vehicle center of gravity measurement device 40 may estimate the center of gravity by calculating the center of gravity positions Lf, Lr in the longitudinal direction and the center of gravity positions Tl, Tr in the vehicle width direction based on the wheel loads WFR, WFL, WRR, WRL of each tire. The wheel loads of each tire may be detected by a sensor, or may be calculated from the suspension stroke sensor and spring constant. For convenience, FIG. 9 uses "T" as the symbol for the tread width, which is different from "Df, Dr" in FIG. 4.

The relationships between the wheel loads WFR, WFL, WRR, and WRL and the center of gravity positions Lf, Lr, Tl, and Tr are expressed by equations (3.1) to (3.4).
(WFR+WFL)Lf=(WRR+WRL)Lr...(3.1)
Lf+Lr=L...(3.2)
(WFR+WRR)Tr=(WFL+WRL)Tl...(3.3)
Tr+Tl=T...(3.4)

The flowchart in Figure 10 shows a routine for steering processing during turning by the steering angle control unit 15 of this embodiment. In the explanation of the flowchart, the symbol "S" means a step. In S1, the steering angle control unit 15 sets the vehicle's left-right axis to pass through one of the target positions A, B, C, or D.

As described above, target position A is a preset standard position. Target position B is an occupant position indicated by the target occupant position indication unit 18. Target position C is an occupant riding position obtained from the occupant riding position detection device 30, or a representative position in the riding range of multiple occupants. Target position D is the center of gravity of the vehicle obtained from the vehicle center of gravity measurement device 40.

At S2, the steering angle control unit 15 determines the position of the turning center in the vehicle longitudinal direction on the set vehicle left-right axis. At S3, the steering angle control unit 15 acquires the turning radius indicated by the turning radius indication unit 17. At S4, the steering angle control unit 15 calculates the turning angle of each tire 91-91 from the turning center and turning radius. At S5, the steering angle control unit 15 steers each tire 91-94 to the calculated turning angle.

(Effects of this embodiment)
(1) The steering angle control unit 15 determines the position of the turning center in the vehicle longitudinal direction on the vehicle's left-right axis, which passes through a preset standard position, for example. On the vehicle's left-right axis where the turning center is determined, the lateral acceleration caused by a change in turning radius during steering or due to a corrective steering is reduced. Therefore, for an occupant who is seated at a target position on the vehicle's left-right axis including the turning center, the lateral acceleration applied during turning can be reduced, improving the ride comfort.

In vehicles where only the driver sits in the driver's seat, or where two passengers sit in the driver's seat and the passenger seat, the driver's seat can be set as the standard position in advance to improve the comfort of the driver and the passenger in the passenger seat. Also, in vehicles where guests, elderly people, children, sick people, etc. often sit in the rear seats, the rear seats can be set as the standard position in advance.

(2) Alternatively, the steering angle control unit 15 determines the position of the turning center in the vehicle longitudinal direction on the vehicle left-right axis that passes through the occupant position indicated by the target occupant position indication unit 18. The driver can manually set the seat of, for example, an important family member or guest as "a person who gives top priority to improving ride comfort," and can change the turning center by indicating the target occupant position each time.

(3) Alternatively, the steering angle control unit 15 determines the position of the turning center in the vehicle longitudinal direction on the vehicle left-right axis that passes through the passenger's riding position obtained from the passenger riding position detection device 30 or a representative position in the riding range of multiple passengers. For example, when multiple passengers are riding, the turning center is determined on the vehicle left-right axis that passes through the center of the riding range, thereby making it possible to reduce the overall lateral acceleration acting on multiple passengers when turning.

(4) Alternatively, the steering angle control unit 15 determines the position of the turning center in the vehicle longitudinal direction on the vehicle's left-right axis that passes through the center of gravity of the vehicle obtained from the vehicle center of gravity measurement device 40. By determining the turning center on the vehicle's left-right axis that passes through the center of gravity of the vehicle, the lateral acceleration acting on the occupants and luggage during turning can be minimized.

Other Embodiments
(a) An independently steered vehicle whose tires are steered and controlled by the vehicle steering device 10 of the present invention is not limited to a four-wheeled vehicle, but may be any vehicle whose tires on three or more wheels are capable of being steered independently.

(b) In the case where the positions of the turning center determined based on information from the target occupant position indication unit 18, the occupant riding position detection device 30 or the vehicle center of gravity measurement device 40 are different, the steering angle control unit 15 may arbitrate to select one of them as a priority.

The present invention is not limited to the above-mentioned embodiment, and can be implemented in various forms without departing from the spirit of the invention.

10...vehicle steering device,
15...Steering angle control unit,
17...Turning radius indication unit,
20... Vehicle characteristic storage device,
91-94... Tires,
100...Vehicle with independent steering.

Claims (1)

A vehicle steering device for steering each tire of an independently steering vehicle (100) having three or more tires (91-94) that can be steered independently, the vehicle steering device being mounted on a vehicle equipped with an occupant riding position detection device (30) that detects the riding position of an occupant, and a vehicle center of gravity measurement device (40) that measures the center of gravity of the vehicle,
a steering angle control unit (15) that calculates a steering angle for individually steering each tire based on vehicle characteristics acquired from a vehicle characteristics storage device (20); and a turning radius instruction unit (17) that instructs a turning radius of the vehicle.
a target occupant position designation unit (18) for designating a target occupant position from among a plurality of occupant positions stored in the vehicle characteristic storage device;
Equipped with
The steering angle control unit is
The position of the turning center in the fore-and-aft direction of the vehicle is
Pre-set standard positions ,
an occupant position indicated by the target occupant position indicating unit ;
The passenger's riding position acquired from the passenger riding position detection device , or a representative position in a riding range of a plurality of passengers;
The center of gravity of the vehicle obtained from the vehicle center of gravity measuring device;
It is determined on the left and right axis of the vehicle passing through either of the
Calculating a steering angle of each tire from the turning center and the turning radius indicated by the turning radius indication unit ;
A vehicle steering device that arbitrates between the positions of the turning center determined based on information from the target occupant position indication unit, the occupant riding position detection device, or the vehicle center of gravity measurement device in order to select one of the positions of the turning center as a priority when the positions of the turning center determined based on information from the target occupant position indication unit, the occupant riding position detection device, or the vehicle center of gravity measurement device are different .

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