JPH0361175A - Rear-wheel steering method - Google Patents

Abstract

PURPOSE:To prevent the hunting of the actual steered angle of rear wheels in the vicinity of a target steering angle and to improve maneuverability by feeding back the steered angle, steering speed, and steering acceleration of rear wheels steered at a target steering angle so that the rear wheels can be steering-controlled at the target steering angle. 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 the rear-wheel steering device 12 has a motor 36 controlled with a controller 44 based on the outputs of a front-wheel steering sensor 48 and a vehicle speed sensor 54. In this case, moreover a rear-wheel steering angle sensor 50 is provided, and when the rear wheels 14 are steered and controlled with a target steering angle corresponding to a front-wheel steered angle, the rear wheels 14 are controlled so as to be steered with the target steering angle by feeding back the steered angle, steering speed, and steering acceleration of the rear wheels 14. This prevents the hunting of the actual steered angle of the rear wheels 14 in the vicinity of the target steering angle.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rear wheel steering method, in particular, the rear wheels are steered to a target steering angle in consideration of the steering angle, the steering speed, and the steering acceleration. The present invention relates to a rear wheel steering method capable of reliably steering the rear wheels to a target steering angle, stably holding the rear wheels at the target steering angle, and improving 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.

As such a rear wheel steering method, for example, Japanese Patent Application Laid-open No. 61
It is disclosed in Japanese Patent Application Laid-Open No. 187657/1983.

In the system disclosed in Japanese Patent Laid-Open No. 61-24.1274, the electric motor is controlled in a direction in which the difference between the rear wheel target steering angle and the rear wheel actual steering angle becomes zero, and the rear wheels are steered. That is, the first
As shown in FIG.
The control voltage V output to operate the electric motor 72 at 0 is calculated as V=A (θR*-θR), where A: constant, and the calculated control voltage V is used to control the electric motor 72.
2 is driven and controlled.

Furthermore, the method described in JP-A-62-187657 calculates the ratio of control output for steering the rear wheels when the difference between the actual rear wheel steering angle and the rear wheel target steering angle is larger than when the difference is small. It is made larger to control the electric motor and steer the rear wheels.

That is, as shown in FIG. 11, the rear wheel target steering angle θR* and the rear wheel actual steering angle θR are manually inputted to the control section 74, and the rear wheel target steering angle θR* and the rear wheel actual steering angle .theta. The steering angle difference S with respect to the steering angle θR is calculated, and according to this steering angle difference S, a control voltage V to the electric motor 72 is obtained as shown in FIG. 12, and the electric motor 72 is driven and controlled by this control voltage V. are doing.

[Problem that the invention seeks to solve]

However, in the conventional rear wheel steering method, the rear wheel steering is controlled by simply comparing the rear wheel actual steering angle θR and the rear wheel target steering angle θR*, as shown in FIG. Due to disturbances such as changes in tire side force due to road surface conditions and changes in tire load due to changes in steering reaction force (lateral G), the rear wheels cannot be reliably steered to the target steering angle θR*, and the steering There was an inconvenience that a shortage occurred.

Furthermore, as shown in FIG. 14, since the steering speed of the rear wheels is not taken into consideration, the actual steering angle θR of the rear wheels is the target steering angle θ of the rear wheels.
With R* as the boundary, due to the change in load (disturbance) mentioned above,
There is a problem in that the actual rear wheel steering angle θR causes hunting in the vicinity of the rear wheel target steering angle θR*, resulting in insufficient steering.

Furthermore, as shown in Figures 15 and 16, in a simulation for rear wheel steering control, when a force of 250 Newtons (for example, 250 Newtons) is applied as a disturbance from the side of the tire 76, that is, from the vertical direction of the front and back direction of the tire 76, , as shown in FIG. 16, the rear wheel target steering angle θR* is set to 0.05.
(rad), the rear wheel actual steering angle θR becomes smaller than the rear wheel target steering angle θR* (0.05rad) from time t1 to time t2 when 250ON is applied, resulting in insufficient steering. There was an inconvenience that (indicated by the P position) occurred.

[Purpose of the invention]

Therefore, an object of the present invention is to eliminate the double disadvantage by considering the steering angle, steering speed, and steering acceleration of the rear wheels when controlling the steering of the rear wheels to a target steering angle. This system ensures steering to the target steering angle, prevents the actual steering angle of the rear wheels from hunting near the target steering angle, and stably maintains the actual steering angle of the rear wheels at the target steering angle, improving steering stability. The purpose of this invention is to realize a rear wheel steering method that can improve the performance.

[Means for solving problems]

To achieve this object, the present invention provides a rear wheel steering method for steering a rear wheel to a target steering angle according to a steering angle of the front wheel when the front wheels are steered. The present invention is characterized in that the rear wheels are steered to the target steering angle by feeding back the steering angle of the wheels, the steering speed of the rear wheels, and the steering acceleration of the rear wheels.

[Effect]

According to the method of the present invention, when the front wheels are steered, the rear wheels try to be controlled to the target steering angle according to the steering angle of the front wheels. The target steering angle is controlled by feed-hacking the speed and steering acceleration. This allows the rear wheels to be reliably steered to the target steering angle, prevents the actual rear wheel steering angle from hunting near the target steering angle, and also stabilizes the rear wheels at the target steering angle even in the face of external disturbances. It can be held in place to improve handling stability.

〔Example〕

Embodiments of the present invention will be described in detail and specifically below based on the drawings.

1 to 9 show embodiments of this invention. 6 to 8, 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 and 10 are front wheels, 12 is a rear wheel steering mechanism which is a rear wheel steering means, and 14 is a front wheel steering mechanism.・14 is the rear wheel. This vehicle 2 is
The front wheels 10 are steered by the front wheel steering mechanism, and the rear wheels 14 are also steered by the rear wheel steering mechanism 12.

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 front knuckle arms 24, 24 to communicate with the front wheels 10, 10.

The rear wheel steering mechanism 12 is installed with a rear pinion 26 meshing with a rear rack 30 provided on a rear rack bar 28).
Both ends of the rear rack bar 28 are connected to the rear wheels 14 via rear quirods 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 3B includes a driving pinion 4 installed 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 the rear pinion 26 due to the drive is expressed as the 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 are connected. has been done.

This control unit 44 manually receives signals from the sensors 48, 50, and 54, and calculates the actual rear wheel steering angle θR, which is the current steering angle of the rear wheels 4, 14, and the current steering angle of the front wheels 10, 10. The rear wheel target steering angle θR* is determined from the steering ratio C (see Fig. 9), which is the ratio of the rear wheel actual steering angle θR to the front wheel actual steering angle θf, which is set for the vehicle speed, and the front wheels 10 and 10 are steered. When doing so, the electric motor 36 is drive-controlled to steer the rear wheels 14 so that the rear wheel actual steering angle θR becomes the rear wheel target steering angle θR*.

The control unit 44 feed-hacks the rear wheel actual steering angle θR, the rear wheel actual steering speed ωR, and the rear wheel actual steering acceleration αR to the rear wheel target steering angle θR*.
4 to the rear wheel target steering angle θR*.

That is, the control unit 44 controls the front wheels 10.1 as shown in FIG.
0, first, the rear wheel actual steering angle θR and the steering ratio C
(See Figure 9) to determine the rear wheel target steering angle θR*,
Next, the rear wheel target steering speed ωR* is calculated from the rear wheel actual steering angle θR, the rear wheel target steering angle θR*, and a proportional constant of 1, and then the rear wheel actual steering angle θR and the rear wheel actual steering speed ωR are calculated. The rear wheel target steering acceleration αR* is calculated from the rear wheel target steering speed ωR* and the proportional constant 2, and then the rear wheel actual steering acceleration α
The control voltage V of the electric motor 36 is calculated from R, the rear wheel target steering acceleration αR*, and the proportionality constant 3, and this motor control voltage V
Accordingly, the electric motor 36 is drive-controlled to steer the rear wheels 14 so that the rear wheel actual steering angle θR becomes the rear wheel target steering angle θR*.

Next, the operation of this embodiment will be explained based on the flowchart in FIG. 1 and the loop block diagram number in the control software in FIG. 2.

When the program starts (step 201), first, the front wheel actual steering angle θr of the front wheels 10, 10 from the front wheel steering angle sensor 48 is manually determined (step 202), and then, in the first table (301), ring 14
・Determine rear wheel target steering angle θR* of 14 (Step 2
03).

0 Then, in step 204, the rear wheel actual steering angle θR of the rear wheels 14, 14 is manually determined, that is, the rear wheel target steering angle θR* and the rear wheel actual steering angle θR are compared in FIG.
), then in step 205, the rear wheels 14 and I4
The rear wheel actual target steering speed ωR is calculated as ωR = θR - (the previous θR), and the rear wheel actual steering acceleration αR of the rear wheels 14 and 14 is calculated as αR = ωR - (the previous ωR). ) is calculated.

Then, in the second table (303) in FIG. 3, the rear wheel target steering speed ωR* of the rear wheels 14 and 14 is expressed as ω1lk
=1 (θR*−θR) where Kl is a proportionality constant (step 206).

In FIG. 3, the rear wheel target steering speed ωR* and the rear wheel actual steering speed ωR are compared (304), and the rear wheel target steering acceleration αR* of the rear wheels 14 and 14 is compared in the third table (305). ■ + (previous αR*) Here, Kl: proportionality constant T; constant Δt: calculation period en: ωR*−ωR en−1 Calculate with en−1 previous en (step 207>. At this time, Ring 14・
The rear wheel actual steering speed ωR of 14 is determined by the value obtained by taking the Laplace operator S into consideration in the first Laplace calculation unit (306) on the rear wheel actual steering angle θR of the rear wheels 14.

In FIG. 3, the rear wheel target steering acceleration αR* is compared with the rear wheel actual steering acceleration αR in which the Laplace operator S is taken into account in the second Laplace calculation unit (308).
B), and in the fourth table (309) electric motor 3
In order to drive and control the controller 6, the control voltage V is calculated as follows: V=3 (αR*−αR) K3: proportionality constant (step 208).

Then, in step 209, the control voltage V is set to V>O
■ If V<O, then control voltage IV
I drives the electric motor 36 in the normal rotation (step 210), while when V<O, the electric motor 8136 is driven in the reverse rotation with the control voltage IVI (step 211), and returns (step 212).

On the other hand, when the control section 44 is controlled by hardware, the control section 44 is configured as shown in FIG. 3. That is,
The control section 44 is composed of a table section 102, a first comparison section 104, a proportional-integral (P, I) controller 106, a second comparison section 108, a first differentiator 110, and a second differentiator 112.

As shown in FIG. 4, the table section 102 determines the target rear wheel steering angle θR* of the rear wheels 14, 143 according to the signal from the front actual steering angle θf of the front wheels 10, 10 detected by the front wheel steering angle sensor 48. It is up to you to decide.

At this time, the rear wheel target steering angle θR* is θR*=Ko・θr Here, KO: front and rear steering ratio It is calculated by

The first comparison unit 104 inputs and compares the signal of the rear wheel target steering angle θR* from the table unit 102 and the signal of the rear wheel actual steering angle θR from the rear wheel steering angle sensor 50, and sets the proportionality constant by 1. The rear wheel target steering speed ωR* of the rear wheels 14, 14 is calculated by taking this into account, and is output to the proportional-integral controller 106.

The proportional-integral controller 106 inputs the rear wheel target steering speed ωR* and the rear wheel actual steering speed ωR obtained by differentiating the rear wheel actual steering angle θR from the rear wheel steering angle sensor 50 by the first differentiator 110, Then, the rear wheel target steering acceleration αR* is calculated and outputted to the second comparison section 108.

The second comparison unit 108 manually calculates the rear wheel target steering acceleration αR* and the rear wheel actual steering acceleration αR obtained by differentiating the rear wheel actual steering speed ωR by the second differentiator 112, and controls the four electric motors 36-5. It calculates the voltage ■ and outputs it to the electric motor 36.

Therefore, in the control section 44, the front wheel steering angle sensor 4
When the signal of the front wheel actual steering angle θf from 8 is manually inputted to the table unit 102, this table unit 102 calculates the rear wheel target steering angle θR* and compares the signal of the rear wheel target steering angle θR* with the signal of the rear wheel target steering angle θR*. The signal of the rear wheel target steering angle θR* and the rear wheel steering angle sensor 5o are output to the first comparison unit 104.
A rear wheel target steering speed ωR* is calculated while inputting a signal of the rear wheel actual steering angle θR from However, this proportional-integral control section 106 controls the rear wheel target steering speed ω.
The signal of R* and the signal of the rear wheel actual steering speed ωR obtained by differentiating the rear wheel actual steering angle θR with the first differentiator 112 are manually inputted to calculate the rear wheel target steering acceleration αR*, and this proportional integral is calculated. The controller 10G compares the rear wheel target steering acceleration αR* with the second comparison unit 108.
The second comparison unit 108 outputs a signal of the rear wheel target steering acceleration αR* and a signal of the rear wheel actual steering acceleration αR obtained by differentiating the rear wheel actual steering speed ωR by the second differentiator 112. , the second comparator 108 calculates the control voltage V, outputs this control voltage V to the motor 36, and controls the drive of the motor 36.

As a result, in order to control the rear wheels 14, 14 to the rear wheel target steering angle θR*, the rear wheel actual steering angle θR, the rear wheel actual steering speed ωR, and the rear wheel actual steering acceleration αR of the rear wheels 14, 14 are adjusted. By considering, as shown in FIG. 5, the rear wheels 14 are reliably steered to the rear wheel target steering angle θR* (=0.05°) at time To, and as shown in FIG. 250O
Even if an external force of N is applied to the side surface of the tire, that is, in a direction perpendicular to the longitudinal direction, the actual rear wheel steering angle θR will not deviate from the rear wheel target steering angle θR*, and insufficient steering will not occur. (See Figure 5).

Therefore, the steering control of the rear wheels 14, 14 is stabilized, and the vehicle 2
The steering stability of the vehicle can be improved.

〔Effect of the invention〕

As is clear from the following detailed description, according to the present invention, the rear wheels are controlled by feed-hacking the steering angle of the rear wheels steered to the target steering angle, the steering speed of the rear wheels, and the steering acceleration of the rear wheels. By controlling the steering to the target steering angle, the rear wheels are reliably steered to the target steering angle, and the actual steering angle of the rear wheels is prevented from hunting near the target steering angle. The steering angle can be stably maintained at the target steering angle, thereby improving steering stability.

[Brief explanation of drawings]

1 to 9 show embodiments of the present invention, FIG. 1 is a flowchart explaining the invention in detail, FIG. 2 is a loop block diagram of a control section connected to control software, and FIG. 3 is a flowchart explaining the invention in detail. A circuit diagram of the control unit in the control hardware, Fig. 4 is a diagram of the front wheel actual steering angle and rear wheel target steering angle of the table section in Fig. 3, and Fig. 5 is a simulation result of the rear wheel actual steering angle state. Figure 6 is a schematic diagram of the vehicle.
FIG. 7 is a perspective view of the driving force transmission mechanism, FIG. 8 is a block diagram of the control device, and FIG. 9 is a diagram of the steering ratio. Figures 10 to 16 are conventional explanatory diagrams, and the 10th
The figure is a block diagram of a control device that determines the control voltage to the electric motor by the comparison section, FIG. 11 is a block diagram of the control device that determines the control voltage to the electric motor by the control section, and FIG. FIG. 13 is a diagram showing the state of voltage determination; FIG. 13 is a diagram showing the actual steering angle state of the rear wheels when the rear wheels are steered to the target steering angle due to load changes;
Fig. 14 is a diagram showing the state in which the rear wheels are hunting around the target steering angle, Fig. 15 is an explanatory diagram when applying an external force to the tires, and Fig. 16 is a diagram showing changes in the actual steering angle of the rear wheels. It is a diagram of the simulation result when external force is applied. In the figure, 2 is the vehicle, 4 is the steering wheel, and 6 is the vehicle.
1 is a steering shaft, 8 is a front wheel steering mechanism as a front wheel steering means, 10 and 1o are front wheels, 12 is a rear wheel steering mechanism as a rear wheel steering means, 14 and 14 are rear wheels, 16 is a front pinion, and 18 is a front rack bar 320 is the front rack, 22 is the front tie rod, 24 is the front knuckle arm, 26 is the rear pinion, 28 is the rear rack bar, 13o is the rear rank, 32 is the rear tie rod, 34 is the rear knuckle arm, 8 36 is the electric motor , driving pinion, 4 is a control unit, 4 is an angle sensor, 50 is a dometer, 54 and 38 are driving force transmission mechanisms, 40 is a drive 42 is a driven hypoid gear, 4 and 6 are electric motor drive units, and 48 is a front wheel steering angle sensor, and 48 is a rear wheel steering angle sensor. , 52 is a vehicle speed sensor.

Claims (1)

[Claims] 1. In a rear wheel steering method in which the rear wheels are steered to a target steering angle according to the steering angle of the front wheels when steering the front wheels, the steering angle of the rear wheels steered to the target steering angle and the steering angle of the rear wheels are A rear wheel steering method, comprising: steering the rear wheels to the target steering angle by feeding back a steering speed and a steering acceleration of the rear wheels.