JPH0361176A - Rear wheel steering method - Google Patents

Abstract

PURPOSE:To improve travel feeling and steering stability by steering rear wheels with a proportion constant, which decides a rear-wheel target steering speed when the rear wheels are steered so that a rear-wheel actual steered angle becomes a rear-wheel target steering angle, changed corresponding to a vehicle speed. CONSTITUTION:In a four-wheel steering vehicle, a front-wheel steering device 8, steering front wheels 10 corresponding to the operation of a steering wheel 4, and a rear-wheel steering device 12, steering rear wheels 14 corresponding to the steering of the front wheels 10, are provided, and a motor 36, controlled by a controller 44 based on the outputs of a front-wheel steering sensor 48 and a vehicle speed sensor 54, is equipped in the rear-wheel steering device 12. In this case, moreover a rear-wheel steering angle sensor 50 is provided, and a proportion constant, deciding a rear-wheel target steering speed when the rear wheels 14 are steered and controlled so that a rear-wheel actual steered angle is made a rear-wheel target steering angle set corresponding to a front- wheel steered angle, is to be changed according to a vehicle speed. This enables the rear wheels 14 to be stably steered, and travel feeling to be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear wheel steering method, and more particularly to a rear wheel steering method that can improve driving feeling and improve steering stability.

[Conventional technology]

BACKGROUND ART Vehicles such as automobiles usually have front wheels that are steerable in a desired direction of travel of the vehicle, and rear wheels that are provided parallel to the longitudinal direction of the vehicle body.

When the front wheels of such a vehicle are steered to turn, the traveling trajectories of the front and rear wheels do not match the turning circle, and at low vehicle speeds, the rear wheels enter the inside of the turning circle due to the difference between the inner wheels. When turning and at high vehicle speeds, centrifugal force causes the vehicle to turn with the front wheels inside the turning circle.

Therefore, even if the front wheels are steered in the turning direction, which is the traveling direction of the vehicle, there is a problem in that the attitude of the vehicle cannot be made to match the turning direction.

Therefore, a vehicle has been proposed in which the rear wheels are also steered when the front wheels are steered. Some vehicles that steer the rear wheels in this manner employ a rear wheel steering method in which the rear wheels are steered so that the actual rear wheel steering angle becomes the rear wheel target steering angle when the front wheels are steered. For example, in Japanese Patent Application Laid-Open No. 61-241274,
A method for steering the rear wheels by controlling an electric motor in a direction in which the difference between the rear wheel target steering angle and the rear wheel actual steering angle becomes zero is disclosed.

Furthermore, Japanese Patent Application Laid-Open No. 62-187657 discloses that when the difference between the actual rear wheel steering angle and the rear wheel target steering angle is large, the ratio of the control output for steering the rear wheels is made larger than when the difference is small. A method for controlling an electric motor and steering rear wheels is disclosed.

[Problem that the invention seeks to solve]

However, in the conventional steering method, there is a problem in that the driving feeling is impaired due to differences in the driving feeling depending on the steering method. In addition, if the target rear wheel steering speed when steering the rear wheels is constant regardless of the vehicle speed, the time required for the actual rear wheel steering angle to reach the target rear wheel steering angle will be constant regardless of the vehicle speed, resulting in stable steering. Therefore, in order to improve steering stability, it is desirable to set a relatively slow target rear wheel steering speed at low vehicle speeds, and a relatively high target rear wheel steering speed at high vehicle speeds. was.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to realize a rear wheel steering method that can improve driving feeling and steering stability.

[Means for solving problems]

In order to achieve this object, the present invention provides: 1); a rear wheel steering method for steering a rear wheel so that an actual rear wheel steering angle becomes a rear wheel target steering angle when steering one width; When the rear wheels are steered so that the steering angle becomes the rear wheel F' target steering angle, the rear wheels are steered by changing the proportional constant that determines the rear wheel steering speed according to the vehicle speed. shall be.

[Effect]

According to the method of the present invention, the proportional constant that determines the rear wheel target steering speed when the rear wheels are steered so that the rear wheel actual steering angle becomes the rear wheel target steering angle is changed according to the vehicle speed. By steering, the time required for the rear wheel actual steering angle to reach the rear wheel target steering angle can be changed depending on the vehicle speed. for example,
By setting a proportionality constant such that the rear wheel target steering speed is relatively slow at low vehicle speeds, it is possible to lengthen the time for the rear wheel actual steering angle to reach the rear wheel target steering angle, while at high vehicle speeds By setting the proportionality constant such that the rear wheel target steering speed becomes relatively high, the time required for the rear wheel actual steering angle to reach the rear wheel target steering angle can be shortened. Thereby, the time required for the rear wheel actual steering angle to reach the rear wheel target steering angle can be changed depending on the vehicle speed.

〔Example〕

Next, embodiments of the present invention will be explained in detail with reference to the drawings.

1 to 14 show embodiments of this invention.

In Figs. 4 to 6, 2 is a vehicle, 4 is a steering wheel, 6 is a steering shaft, 8 is a front wheel steering mechanism which is a front wheel steering means, 10 is a front wheel, 12 is a rear wheel steering mechanism which is a rear wheel steering means, and 14 is a rear wheel steering mechanism. It's a ring. This vehicle 2 uses a front wheel steering mechanism 8 to steer front wheels 10, 10, and a rear wheel steering mechanism 12 to also steer rear wheels 14, 14.

The front wheel steering mechanism 8 is provided with a front pinion 16 fixed to the tip side of the steering shaft 6 meshing with a front rack 20 provided on a front rack bar 18, and both ends of the front rack bar 18 are connected to front tie rods. 22, 22 and the front wheels 10, 1 via the front knuckle arms 24, 24.
It is set up by contacting 0.

The rear wheel steering mechanism 12 is provided with a rear pinion 26 meshing with a rear rack 30 provided on a rear rack 28,
Both ends of the rear rear wheels 28 are connected to the rear wheels 14 via rear tie rods 32 and rear knuckle arms 34, respectively.

Further, this rear wheel steering mechanism 12 is driven by an electric motor 36. This electric motor 36 is connected to the rear wheel steering mechanism 12 via a driving force transmission mechanism 38 . The driving force transmission mechanism 38 includes a driving pinion 4 provided on the electric motor 36 side.
0, and a driven hypoid gear 4 provided on the rear pinion 26 side to mesh with the drive pinion 40.
It consists of 2 and.

The electric motor 36 is configured to be driven by pulses, for example, and the electric motor drive unit 46 is connected to a control unit 44 as a control means.
connected via. This control unit 44 includes a front wheel steering angle sensor 48 provided in the front wheel steering mechanism 12 to detect the rotation amount of the steering shaft 6 due to the operation of the steering wheel 6 as a steering angle of the front wheels 10, and The amount of rotation of rear pinion 2G due to drive is calculated as rear wheel 1.
A rear wheel steering angle sensor 50 provided in the rear wheel steering mechanism 12 to detect the steering angle of 4.14, and a vehicle speed sensor 54 provided in the speedometer 52 to detect the vehicle speed of the vehicle 2. It is connected.

This control unit 44 inputs signals from the respective sensors 48, 50, and 54, and determines the rear wheel actual steering angle θ8 of the rear wheels 14, 14,
The ratio of the steering angle θ7 of the rear wheels 14 and 14 to the steering angle θr of the front wheels 10 and 10 is determined by the steering ratio C(
Determine the rear wheel target steering angle θ8* from (see Figure 2) and
Actual rear wheel steering angle θ when steering the front wheels 10. The rear wheels 14 are steered by controlling the drive of the electric motor vehicle 36 so that the rear wheels become the rear wheel target steering angle θ7*. Note that this control section 4
4) Not only the rear wheel target steering angle θ8*, but also the rear wheel target steering angle θ□*, the rear wheel target steering speed ω8ho, and the rear wheel target steering force l speed α. In combination with *, the rear wheels 14 are steered so that the rear wheel actual steering angle θ, becomes the rear wheel target steering angle θ, *.

That is, as shown in FIG. 7, the control unit 44 controls the front wheels 10.]
0, first, the rear wheel actual steering angle θ and the steering ratio C
The rear wheel target steering angle θ7* is determined from the rear wheel actual steering angle θ, the rear wheel target steering angle θ8* and the proportional constant 1 are used to calculate the rear wheel target steering speed ω8*, and then, The rear wheel target steering acceleration α8* is calculated from the rear wheel actual steering angle θ8, the rear wheel actual steering speed, the rear wheel target steering speed ω8*, and the proportional constant 2, and then the rear wheel actual steering acceleration and the rear wheel target are calculated. The motor control voltage V is calculated from the steering acceleration α, * and the proportional constant 3, and this motor control voltage V is used to control the drive of the electric motor [36] so that the actual rear wheel steering angle θ7 becomes the rear wheel target steering angle θ□*. to steer the rear wheels 14.

In this way, the rear wheel actual steering angle θ8 becomes the rear wheel target steering angle θ□*
In the rear wheel steering method in which the rear wheels 14, 14 are steered so that the rear wheels 14, 14 become 1 is set to the proportionality constant that determines the rear wheel target steering speed ωR* when the rear wheel target steering speed ωR* is set, and the vehicle speed is set to ■.

The electric motor 36 is driven and controlled so that the rear wheels 14 are steered by varying the steering angle (see FIG. 3).

Next, the effect will be explained.

As described above, when steering the front wheels 10, the control unit 44 first calculates the rear wheel target steering angle θ8*, and then calculates the rear wheel target steering angle θ8*.
The rear wheel target steering speed ω□* is calculated, then the rear wheel target steering acceleration α,* is calculated, and after that, the motor control voltage V is calculated, and the rear wheel actual steering angle θ8 is determined by this motor control voltage ■. The electric motor 36 is drive-controlled to steer the rear wheels 14 so that the rear wheel target steering angle θ□* is achieved.

When the rear wheels 14 are steered by this control unit 44 so that the rear wheel actual steering angle θ□ becomes the rear wheel target steering angle θ3*, the proportional constant that determines the rear wheel target steering speed ω8* is the vehicle speed. ■In order to change it according to (a) (see Fig. 3), as shown in Fig. 7, the vehicle speed (1) is taken in and the proportional constant is changed by 1 using the table to determine the rear wheel target steering speed ω8*. .

That is, as shown in FIG. 1, when the control starts (100), the control unit 44 inputs the rear wheel actual steering angle θ8 (101).
)L, vehicle speed VT is manually (102), rear wheel actual steering angle θ7
and the steering ratio C obtained from Table 1 as shown in FIG.
A rear wheel target steering angle θ8* is determined from (103).

When calculating the rear wheel target steering speed ω, * from the rear wheel actual steering angle θ8, the rear wheel target steering angle θ8*, and the proportional constant,
A proportional constant having a value corresponding to the vehicle speed Va is obtained from a table Z as shown in FIG. 3, and a rear wheel target steering speed ω,* is determined (104).

Thereafter, a rear wheel steering routine is executed (105) and the routine returns (106).

As a result, the rear wheel actual steering angle θ8 becomes the rear wheel target steering angle θ, *
The time it takes to reach can be changed depending on the vehicle speed.

In other words, 1 is added to the proportionality constant that determines the rear wheel target steering speed ω7*.
When VT is changed according to the vehicle speed VT, the time required for the actual rear wheel steering angle θ8 to reach the target rear wheel steering angle θ7* changes, as is clear from the staining results not shown in FIGS. 12 to 14. That is, as shown in FIG. 9, when the proportionality constant is changed to Kx>KHz>K's, the time required to reach the rear wheel target steering angle θ, * changes. Therefore, as shown in Fig. 8, when the proportional constant 1 is changed from small to large, the rear wheel target steering speed ω7* becomes slow →
It can be changed quickly.

Further, as shown in FIG. 10, the rear wheel target steering speed ω8* with respect to the vehicle speed Va changes from low to high with respect to the vehicle speed VT.
It is preferable to change the rear wheel target steering speed ω8* from slow to fast when driving.

Therefore, as shown in FIG. 11, by changing the proportional constant 1 that determines the rear wheel target steering speed ω, * from low to high in response to a low to high change in vehicle speed VT, for example, By setting the proportionality constant such that the rear wheel target steering speed ω8* is relatively slow at the vehicle speed, it is possible to lengthen the time for the rear wheel actual steering angle θ□ to reach the rear wheel target steering angle θ8*. , On the other hand, at high vehicle speed, the rear wheel target steering speed ω8*
By setting a proportionality constant of 1 such that the angle is relatively fast (1), it is possible to shorten the time for the rear wheel actual steering angle θ, to reach the rear wheel target steering angle θ,*.

Therefore, for example, by setting the proportionality constant KI such that the rear wheel target steering speed θ8* is relatively slow at low vehicle speeds, the rear wheels 14 can be stably steered.
On the other hand, at high vehicle speeds, by setting the proportionality constant to 1 so that the rear wheel target steering speed θ8* becomes relatively fast, the rear wheel
4 and 14 can be quickly steered, the driving feeling can be improved, and the steering stability can be improved.

〔Effect of the invention〕

As described above, according to the present invention, the proportional constant that determines the rear wheel target steering speed when the rear wheels are steered so that the rear wheel actual steering angle becomes the rear wheel target steering angle is changed according to the vehicle speed. By steering the wheels, the time required for the actual rear wheel steering angle to reach the rear wheel target steering angle can be changed depending on the vehicle speed. For example, by setting a proportionality constant such that the rear wheel target steering speed is relatively slow at low vehicle speeds, it is possible to lengthen the time it takes for the rear wheel actual steering angle to reach the rear wheel target steering angle; By setting a proportionality constant such that the rear wheel target steering speed becomes relatively high, the time required for the rear wheel actual steering angle to reach the rear wheel target steering angle can be shortened. Thereby, the time required for the rear wheel actual steering angle to reach the rear wheel target steering angle can be changed depending on the vehicle speed.

For this reason, for example, by setting a proportionality constant such that the rear wheel target steering speed is relatively slow at low vehicle speeds, it is possible to stably steer the rear wheels, while at high vehicle speeds, the rear wheel target steering speed is By setting the proportionality constant to be relatively fast, the rear wheels can be quickly steered, so the driving feeling can be improved, and the steering stability can also be improved.

[Brief explanation of drawings]

1 to 14 show embodiments of the present invention, FIG. 1 is a control flowchart, FIG. 2 is an explanatory diagram showing the relationship between the steering ratio and vehicle speed, and FIG. 3 is a diagram showing the relationship between the proportionality constant and vehicle speed. 4 is a block diagram of the control device, FIG. 5 is a schematic plan view of a vehicle that steers the rear wheels, FIG. 6 is a schematic perspective view of the rear wheel steering mechanism, and FIG. 7 is a block diagram of the control loop. Figure 8 is an explanatory diagram showing the relationship between the proportional constant and the rear wheel steering speed, Figure 9 is an explanatory diagram showing the relationship between the proportional constant and the rear wheel actual steering angle and time, and Figure 10 is an explanatory diagram showing the relationship between the proportional constant and the rear wheel steering speed. Figure 11 is an explanatory diagram showing the relationship between wheel steering speed, Figure 11 is an explanatory diagram showing the relationship between vehicle speed and the proportionality constant, and Figures 12 to 14 are explanatory diagrams of the similation results when the proportionality constant is changed. be. In the figure, 2 is the vehicle, 4 is the steering wheel, and 6 is the vehicle.
is a steering shaft, 8 is a front wheel steering mechanism as a front wheel steering means, 10 is a front wheel, 12 is a rear wheel steering mechanism as a rear wheel steering means,
14 is a rear wheel, 16 is a front binion, 18 is a front rack par, 20 is a front rank, 22 is a front tie rod, 24 is a front knuckle arm, 26 is a rear binion, 28 is a rear rack bar, 130 is a rear rack, 32 is a rear tie opening/nod; 34 is a rear knuckle arm; 36 is an electric motor; 38 is a driving force transmission mechanism; 40 is a drive binion; 42 is a driven hypoid gear; 44 is a control section; 46 is an electric motor drive section;
48 is a front wheel steering angle sensor, 50A is a rear wheel steering angle sensor, 52 is a steering angle sensor, and 54 is a vehicle speed sensor 54.

Claims (1)

[Claims] 1. In a rear wheel steering method in which the rear wheels are steered so that the actual rear wheel steering angle becomes the rear wheel target steering angle when the front wheels are steered, the rear wheels are steered so that the rear wheel actual steering angle becomes the rear wheel target steering angle. A rear wheel steering method characterized in that the rear wheels are steered by changing a proportionality constant that determines a rear wheel target steering speed when the rear wheels are steered according to the vehicle speed.