JPH0569849A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To provide a steering characteristic good and stable even at deceleration time during turning of a vehicle, relating to a rear wheel steering device for the vehicle wherein a rear wheel can be controlled in the same phase to a front wheel. CONSTITUTION:In the case of a rear wheel steering device for a vehicle wherein rear wheels 3, 4 can be controlled in the same phase to front wheels 1, 2, a deceleration detecting means 9E' for detecting deceleration of the vehicle and a same phase steering angle setting means 9J for setting a same phase steering angle so as to control the rear wheels 3, 4 in the same phase, when the deceleration detected by the deceleration detecting means 9E' is larger than a predetermined value, are provided, and the same phase steering angle setting means 9J is constituted such that the same phase steering angle can be set so as to increase the same phase steering angle of the rear wheel in accordance with increase of the deceleration detected by the deceleration detecting means 9E'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering system capable of controlling rear wheels in phase with front wheels.

[0002]

2. Description of the Related Art In recent years, a four-wheel steering device for steering not only front wheels but also rear wheels has been developed as a steering device for automobiles. The rear wheel steering means in such a four-wheel steering device is a tie rod for the rear wheels. There is a configuration in which such a steering shaft is provided and the steering shaft is driven in the axial direction by, for example, hydraulic pressure to steer the rear wheels.

Further, such steering of the rear wheels includes reverse-phase steering that steers in the opposite direction to the front wheels and in-phase steering that steers in the same direction as the front wheels. Generally, the reverse steering is performed so that the vehicle can make a small turn when the vehicle speed is low. In-phase steering is performed so that at medium and high speeds, in-phase steering is performed so that the vehicle can turn or change lanes without losing the running posture of the vehicle.

In particular, in general, the steering angle (hereinafter, abbreviated as steering angle) θr of the in-phase steering at the middle and high speeds starts the in-phase steering when the vehicle speed reaches a predetermined speed, and the in-phase steering is performed. After the start, the steering angle θr is increased with the increase of the vehicle speed, the increase of the steering angle θr with respect to the increase of the vehicle speed is gradually reduced, and the steering angle θr is set to be constant regardless of the increase of the vehicle speed in the high speed range. ..

On the other hand, as a matter of course, since the rear wheel steering angle θr needs to correspond to the front wheel steering angle, in general, the rear wheel steering angle θ is proportional to the steering wheel angle θ _H corresponding to the front wheel steering angle.
Set r.

Therefore, for in-phase steering at medium and high speeds, for example, the in-phase coefficient K ₁ for the vehicle speed is set as follows, and the in-phase coefficient K ₁ is multiplied by the steering wheel angle θ _H (K ₁ × θ _H ) Can be set as the rear wheel steering angle θr.

The in-phase coefficient K ₁ is 0 until the vehicle speed reaches a predetermined value, rises from the point where the vehicle speed reaches a predetermined value, and increases as the vehicle speed increases, and the vehicle speed increases as the vehicle speed increases. The steering angle is set to be substantially constant in the high speed range by gradually increasing the steering angle with respect to.

[0008]

By the way, the steering control of the rear wheels as described above is usually performed on the assumption that the vehicle speed is in a steady state.

That is, the steering angle of the rear wheels is set in accordance with the vehicle speed, for example, when the vehicle speed is low, the rear wheels are set to the opposite phase with a relatively large steering angle, and the steering to the opposite phase side is performed as the vehicle speed increases. The steering angle of the rear wheels is reduced to 0 in the medium speed range by decreasing the angle, and when the vehicle speed further increases, the steering angle is increased to the in-phase side and the steering angle to the in-phase side is increased in accordance with the increase of the vehicle speed. Is being done.

However, at present, since the change in vehicle speed, that is, the control according to the acceleration / deceleration state is not particularly considered, for example, the problem that the vehicle is oversteered when the vehicle is suddenly braked during turning is In-phase control of the rear wheels corresponding to the vehicle speed cannot handle this.

The present invention was devised in view of the above-mentioned problems, and it is an object of the present invention to provide a rear wheel steering device for a vehicle, which can obtain good and stable steering characteristics even during deceleration during turning of the vehicle. To aim.

[0012]

Therefore, the vehicle rear wheel steering system of the present invention detects the deceleration of the vehicle in the vehicle rear wheel steering system capable of controlling the rear wheels of the vehicle in phase with the front wheels. Deceleration detecting means, and the in-phase steering angle setting means for setting the in-phase steering angle so as to control the rear wheels in-phase when the deceleration detected by the deceleration detecting means is larger than a predetermined value. The in-phase steering angle setting means is configured to set the in-phase steering angle such that the in-phase steering angle of the rear wheels increases in response to an increase in the deceleration detected by the deceleration detecting means. It is characterized by being.

[0013]

In the above-described vehicle rear wheel steering system of the present invention, when the deceleration detected by the deceleration detecting means is larger than the predetermined value, the in-phase steering angle setting means detects the deceleration detected by the deceleration detecting means. The in-phase steering angle is set so that the in-phase steering angle of the rear wheels increases as the speed increases, and the rear wheels are in-phase controlled according to the set in-phase steering angle.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle rear wheel steering system according to an embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram schematically showing the main structure of its control means, and FIG. 2 is its structure. FIG. 3 is a schematic configuration diagram showing the vehicle in plan view, FIG. 3 is a block diagram schematically showing the overall configuration of the control means, and FIGS. 4 and 5 are diagrams showing control characteristics thereof. 6 is a diagram showing a specific example of the control amount.

First, the first embodiment will be described. In FIG. 2, 1 and 2 are front wheels, 3 and 4 are rear wheels, and 5 is a steering wheel (hereinafter referred to as a steering wheel). Front wheels 1,2
In addition to a mechanical drive mechanism (not shown) such as a rack and pinion, a hydraulic cylinder 6 for power steering is attached to the front wheel steering tie rod arranged so as to be connected to each other. The hydraulic cylinder 6 is provided with a phase advancing valve 13 that supplies and discharges hydraulic pressure according to the steering state of the handle 5. Further, a hydraulic cylinder 7 for steering the rear wheels is attached to the tie rod for steering the rear wheels arranged so as to connect the rear wheels 3 and 4, and a valve 8 for steering the rear wheels is also attached to the hydraulic cylinder 7. It is provided.

The phase advancing valve 13 and the rear wheel steering valve 8 are controlled by the controller 9 by the steering wheel angle θ _H , vehicle speed V, power steering pressure (power steering pressure), rear wheel steering angle (hereinafter, steering angle is referred to as steering angle). (Abbreviated) and L of alternator
It is controlled based on the terminal output and the like.

For this reason, the controller 9 includes a steering wheel angle sensor 10, a vehicle speed sensor (vehicle speed detecting means) 11, a power steering pressure sensor 12, a rear wheel steering angle sensor 14, and an L terminal output (not shown in FIG. 2) of an alternator. Is connected,
Each of these pieces of detection information is input to the controller 9.

A schematic configuration of steering of the front and rear wheels of the controller 9 will be described. As shown in FIG. 3, each of the steering wheel angle sensor 10, the vehicle speed sensor 11, and the L terminal output 15 of the alternator input as digital signals. While the rear wheel steering mode is determined based on the information, the road surface roughness (based on the information from the power steering pressure sensor 12 and the information from the steering wheel angle sensor 10 and the vehicle speed sensor 11 input as analog signals ( Road surface μ) is estimated, and based on the determined rear wheel steering mode, the estimated road surface μ value, and each information from the steering wheel angle sensor 10, the vehicle speed sensor 11, and the rear wheel steering angle sensor 14 described above. Then, the control amount of each control is set, and this is digital-to-analog converted, and output to the front-phase advancing valve 13 and the rear-wheel steering valve 8. There is.

The rear-wheel steering performed through the controller 9 includes reverse-phase steering for steering in the opposite direction to the front wheels and in-phase steering for steering in the same direction as the front wheels. The reverse-phase steering allows the vehicle to make a small turn when the vehicle is running at low speed. Steering is performed, and in-phase steering is performed so that the vehicle can turn or change lanes without disturbing the running posture of the vehicle at medium and high speeds.

Further, in this device, in addition to the steering corresponding to the vehicle speed, the rear wheel steering control is performed in which the rear wheels are in-phase steered when decelerating during turning, and the rear wheels are steered in reverse phase when accelerating during turning. Is becoming

The rear wheel steering control corresponding to acceleration / deceleration is performed in addition to the vehicle speed corresponding steering control. That is,
The steering angle of the rear wheel corresponding to the vehicle speed is set and the steering angle of the rear wheel corresponding to acceleration / deceleration is set, and the steering angle of the rear wheel corresponding to acceleration / deceleration is set as the additional steering amount to the steering angle of the rear wheel corresponding to the vehicle speed. The final rear wheel steering angle is determined by adding to the corresponding rear wheel steering angle, and the rear wheel steering is performed.

The central portion of the controller 9 related to the acceleration / deceleration-compatible rear wheel steering is constructed as shown in FIG.

That is, as shown in FIG. 1, the controller 9 estimates the road surface μ from the steering wheel angle sensor 10, the vehicle speed sensor 11, the power steering pressure sensor 12, and the steering wheel angle θ _H , vehicle speed V, and power steering pressure information. Road surface estimation unit 9A
And the lateral acceleration (hereinafter referred to as lateral G) generated on the vehicle from the estimated road surface μ, steering wheel angle θ _H , and vehicle speed V.
And a lateral acceleration calculating unit (lateral acceleration detecting means) 9B for calculating the acceleration and deceleration V '(dV / dt) obtained by differentiating the information from the vehicle speed V (that is, the longitudinal acceleration of the vehicle) V' (dV / dt). Calculation unit (deceleration detection means and acceleration detection means)
9E ', and steering from which the in-phase steering angle θr of the rear wheels during deceleration or the anti-phase steering angle θr of the rear wheels during acceleration is set based on the information from the acceleration / deceleration calculation unit 9E' and the information from the lateral G calculation unit 9B. An angle setting section (in-phase steering angle setting means and anti-phase steering angle setting means) 9J is provided.

The lateral G is calculated by the lateral G calculating section 9B when the vehicle turns normally, lateral G: GY, vehicle speed: V, and steering wheel angle:
Since it is given as a function of θ _H and the road surface μ: μ, the lateral G is obtained from the following equation (1) or (1) ′ which is this function. GY = V ² · θ _H / [{1+ (A / μ) V ² } · L · ρ] (1) where A: Stability factor L: Wheel base ρ: Steering gear ratio From this, GY = Θ _H / [(L · ρ / V ² ) + (A · L · ρ / μ)] (1) ′ where −1 ≦ GY ≦ 1

In the steering angle setting unit 9J, the acceleration / deceleration calculation unit 9
The acceleration / deceleration V ′ calculated in E ′ and the lateral G calculation unit 9 described above.
The in-phase steering angle θr of the rear wheels during acceleration / deceleration is set based on the lateral G calculated in B. Specifically, the steering angle setting unit 9J is shown in FIGS. 4 (a) to 4 (c). Such maps are provided, and the in-phase steering angle θr of the rear wheels is set by the steering angle setting unit 9J based on one of these maps.

In the map of FIG. 4, (a) is for a small lateral G, (b) is for a medium lateral G, and (c) is for a large lateral G. belongs to. As shown in the figure, in both cases, the acceleration / deceleration corresponding steering of the rear wheels is not performed in a region where the longitudinal acceleration (hereinafter, longitudinal G) is small, but when the longitudinal acceleration (hereinafter, longitudinal G) becomes larger than the set value. By controlling the rear wheels in phase during deceleration and controlling the rear wheels in reverse phase during acceleration, the steering characteristics are stabilized.

In particular, when the lateral G is small, the boundary value between the front and rear G at which the acceleration / deceleration corresponding steering of the rear wheels is started becomes large, and the acceleration / deceleration corresponding steering is started as the lateral G increases. The boundary value between the front and rear G is small. Also,
When steering the rear wheels for acceleration / deceleration, the steering angle increases linearly with an increase in the front-rear G, but the rate of this increase (the slope of the characteristic line in the map) increases in the lateral G. Therefore it is getting bigger.

Therefore, the in-phase control of the rear wheels during deceleration and the anti-phase control of the rear wheels during acceleration are performed from a smaller front and rear G stage as the lateral G acting on the vehicle is larger, and the lateral G acting on the vehicle is also larger. Is larger, the in-phase control amount (in-phase steering angle) or the anti-phase control amount (reverse-phase steering angle) that accompanies an increase in the front-rear G
Is increasing rapidly.

The steering angle setting section 9J outputs a corresponding signal to the rear wheel steering valve 8 so that the in-phase steering angle or the anti-phase steering angle thus set is realized.

In order to secure the running stability at the time of medium and high speed, the same steering angle (control amount) is added to the total steering angle (control amount) to which the above-mentioned rear wheel steering angle corresponding to acceleration / deceleration and the steering angle corresponding to vehicle speed are added. To the opposite side and to the opposite phase side (eg 0.8
°) is provided to limit the upper limit clipping to limit the rear-wheel steering angle, etc. that supports acceleration / deceleration. Fixed limits (eg 0.8 ° / sec each)
Is provided, and the reduction degree is set to be clipped.

Since the vehicle rear wheel steering system as one embodiment of the present invention is configured as described above, the rear wheel steering performed by the controller 9 is controlled by the vehicle speed corresponding control to reverse the vehicle when the vehicle speed is low. By the phase steering, the vehicle can make a small turn, and at the middle and high speeds, the in-phase steering makes it possible to turn or change the lane without losing the running posture of the vehicle.

In addition, when the vehicle brakes or accelerates during turning, the rear wheels are controlled in phase during deceleration and the rear wheels are controlled in reverse phase during acceleration according to the acceleration / deceleration.
The steering characteristics of the vehicle are stabilized.

That is, for example, when sudden braking is applied during turning, when the front-rear G (in this case, deceleration) becomes large to some extent, the in-phase control of the rear wheels is performed, so that the vehicle is generated during sudden braking during turning. Oversteering is avoided by in-phase steering of the rear wheels, and the steering characteristics of the vehicle can be stabilized within a certain range.

In particular, the larger the lateral G acting on the vehicle (that is, the smaller the turn or the higher the speed is), the more in-phase control of the rear wheels is performed from the small front-rear G stage, and The larger the lateral G acting on the vehicle, the more rapidly the in-phase control amount (in-phase steering angle) increases with the increase in the front-rear G. Therefore, the larger the lateral G during sharp braking during turning, the more the vehicle oversteers. Can respond appropriately.

On the other hand, when sudden acceleration is performed during turning, the reverse phase control of the rear wheels is performed when the front-rear G (acceleration in this case) becomes large to some extent. The reverse steering of the rear wheels can prevent the steerability of the vehicle and stabilize the steering characteristic of the vehicle within a certain range.

Also in this case, the larger the lateral G acting on the vehicle (that is, the smaller the turn or the higher the turn), the more in-phase control of the rear wheels is started from the small front-rear G stage. As the lateral G acting on the vehicle increases and the lateral G acting on the vehicle increases, the in-phase control amount (in-phase steering angle) increases rapidly with the increase in the front-rear G. Therefore, the larger the lateral G during sudden acceleration during turning, the stronger the lateral G occurs. Appropriately respond to understeering of vehicles.

As described above, even if sudden braking or sudden acceleration is performed during turning, the rear wheels are controlled in-phase or anti-phase by an appropriate amount, and the steering characteristics of the vehicle are stabilized within a certain range. It is.

Further, since the acceleration / deceleration-corresponding steering of the rear wheels is not performed in the small front-rear G area, control is not unnecessarily performed during normal non-abrupt deceleration or acceleration, and the stability of control is ensured. ..

Here, the embodiment of the rear wheel deceleration-corresponding steering will be explained. As shown in FIG. 6, when the deceleration G occurs within a certain time as shown by the bending line a, the vehicle speed decreases during this period. The rear wheel steering angle corresponding to the vehicle speed decreases in response to the occurrence of a certain deceleration G as indicated by a bending line b shown by a chain line. On the other hand, the deceleration-corresponding steering angle is added to the bending line b corresponding to the bending line a, and largely protrudes like a bending line c shown by a broken line.

However, the upper limit clip limits the steering angle within a fixed limit, and the deceleration speed clip limits the deceleration speed of the steering angle within a fixed limit. Since the change does not become excessive as in the case of d and changes gradually, it is possible to perform control while stabilizing the behavior of the vehicle body and maintaining a good steering feeling.

As shown in FIG. 4, the map relating to the setting of the in-phase steering angle θr performed by the steering angle setting unit 9J shows the case where the lateral G is small, the lateral G is medium, and the lateral G is large. There are only 3 ways, but this map is the horizontal G
And make it more detailed regarding the size of
It is also conceivable to prepare only two ways, one for a small lateral G and one for a large lateral G.

Further, the in-phase steering angle θr may be set by the steering angle setting unit 9J based on a map as shown in FIG. In other words, the boundary value between the front and rear G that starts the acceleration / deceleration-corresponding steering of the rear wheels is constant regardless of the lateral G. Then, when the front-rear G becomes larger than the boundary value, the magnitude of the steering angle corresponding to the acceleration / deceleration of the rear wheels linearly increases with the increase in the front-rear G, but this increase rate (the slope of the characteristic line in the map) Becomes larger as the lateral G increases.

Even with such setting of the steering angle corresponding to acceleration / deceleration,
To a certain extent, understeering of the vehicle, which occurs more strongly as the lateral G increases during sudden acceleration during turning, can be dealt with.

Further, since the lateral G (lateral acceleration) is calculated from the lateral G, the vehicle speed, the steering wheel angle, and the road surface μ as described above, the lateral G sensor is not required, which is advantageous in terms of cost. It is also possible to provide a lateral G sensor in and to obtain the lateral G directly from the lateral G sensor.

[0045]

As described above in detail, according to the vehicle rear wheel steering system of the present invention, in the vehicle rear wheel steering system capable of controlling the rear wheels of the vehicle in phase with the front wheels, the deceleration of the vehicle is performed. A deceleration detecting means for detecting the in-phase steering angle setting means for setting the in-phase steering angle so that the rear wheels are in-phase controlled when the deceleration detected by the deceleration detecting means is larger than a predetermined value. The in-phase steering angle setting means can set the in-phase steering angle such that the in-phase steering angle of the rear wheels increases in accordance with the increase in the deceleration detected by the deceleration detecting means. As a result, even if sudden braking is performed during turning, the rear wheels are in-phase controlled by an appropriate amount, the steering characteristics of the vehicle are stabilized within a certain range, and a good steering feeling is maintained. ..

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a main configuration of a control means of a vehicle rear wheel steering system as an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a configuration of a vehicle rear wheel steering device as an embodiment of the present invention in a state corresponding to a plan view state of the vehicle.

FIG. 3 is a block diagram schematically showing an overall configuration of a control means of a vehicle rear wheel steering system as one embodiment of the present invention.

FIG. 4 is a diagram showing control characteristics of a vehicle rear wheel steering system according to an embodiment of the present invention.

FIG. 5 is a diagram showing a modification of the control characteristics of the vehicle rear wheel steering system as one embodiment of the present invention.

FIG. 6 is a diagram showing a specific example of a control amount of a vehicle rear wheel steering system as one embodiment of the present invention.

[Explanation of symbols]

1, 2 front wheels 3, 4 rear wheels 5 steering handle (handle) 6 hydraulic cylinder for power steering 7 hydraulic cylinder for steering rear wheels 8 rear wheel steering valve 9 controller 9A road surface μ estimation unit 9B lateral G calculation unit (horizontal) Acceleration detecting means) 9E 'Acceleration / deceleration calculating section (deceleration detecting means and acceleration detecting means) 9J Steering angle setting section (in-phase steering angle setting means and anti-phase steering angle setting means) 10 Steering wheel angle sensor 11 Vehicle speed sensor (vehicle speed detecting means) ) 12 power steering pressure sensor 13 advance valve 14 rear wheel steering angle sensor 15 L terminal output of alternator

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Claims (1)

[Claims] 1. A vehicle rear wheel steering system capable of controlling the rear wheels of a vehicle in phase with the front wheels, and deceleration detecting means for detecting deceleration of the vehicle, and deceleration detected by the deceleration detecting means. Is larger than a predetermined value, the in-phase steering angle setting means sets the in-phase steering angle so that the rear wheels are controlled in-phase, and the in-phase steering angle setting means detects the deceleration detected by the deceleration detecting means. A rear wheel steering device for a vehicle, wherein the in-phase steering angle can be set such that the in-phase steering angle of the rear wheels increases in accordance with an increase in speed.