JP2871230B2 - Front and rear wheel steering control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front and rear wheel steering control device for giving an auxiliary steering angle to at least one of front and rear wheels at the time of steering input or disturbance input.

[0002]

2. Description of the Related Art Conventionally, as this kind of front and rear wheel steering control device, for example, a device described in Japanese Patent Application Laid-Open No. 60-193773 is known.

[0003] The above-mentioned conventional source discloses a technique for controlling an auxiliary steering angle applied to a rear wheel by an addition value of a steering angle feedforward term and a yaw rate feedback term. In this conventional technique, the following equation is used. Rear wheel auxiliary steering angle δ
Is required.

Δ = k1 · δf + k2 · ψ 'where (k1 · δf); steering angle feed forward term k1; first proportional constant (corresponding to vehicle speed) δf; steering wheel steering angle (k2 · ψ'); yaw rate feedback term k2: second proportional constant (fixed value or selected value based on running conditions) ψ ': yaw rate

[0005]

However, in the above-described conventional front and rear wheel steering control device, both the first proportional constant k1 as the feedforward gain and the second proportional constant k2 as the feedback gain are reduced to the lateral acceleration. On the other hand, since it is given by a constant value, for example, in the limit driving region (high lateral acceleration region), the turning performance is not improved, for example, the vehicle does not turn in the turning direction as intended by the driver. There is a problem of sufficient.

That is, in the limit traveling region, the turning radius is usually large and the understeer is strong.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In a front-rear wheel steering control device which provides an auxiliary steering angle to at least one of the front and rear wheels at the time of steering input or disturbance input, the present invention relates to It is an object to improve the turning performance of the vehicle.

[0008]

In order to solve the above problems, a front and rear wheel steering control device according to the present invention controls an auxiliary steering angle based on an added value of a steering angle feed forward term and a yaw rate feedback term. The gain of at least one of the terms is changed to increase the yaw moment in accordance with the magnitude of the lateral acceleration.

That is, as shown in the claim correspondence diagram of FIG. 1, an auxiliary steering means a for giving an auxiliary steering angle to at least one of the front and rear wheels by an external command without depending on a steering wheel input, Steering wheel steering angle detecting means b for detecting an angle, yaw rate detecting means c for detecting a yaw rate, lateral acceleration detecting means d for detecting a lateral acceleration,
A lateral acceleration corresponding gain setting means e for changing at least one of the feedback gain and the feed forward gain in a direction to increase the yaw moment of the vehicle according to the magnitude of the lateral acceleration, and a set lateral acceleration corresponding gain, Auxiliary for outputting to the auxiliary steering means a a command to give an auxiliary steering angle to at least one of the front and rear wheels based on an addition value of a steering angle feedforward term based on the steering wheel steering angle and a yaw rate feedback term based on the detected yaw rate. And a steering angle control means f.

[0010]

At the time of steering input or disturbance input, the gain setting means for lateral acceleration changes at least one of the feedback gain and the feedforward gain in a direction to increase the yaw moment of the vehicle according to the magnitude of the lateral acceleration. The auxiliary steering angle control means f detects the steering angle feedforward term based on the steering wheel steering angle using the lateral acceleration corresponding gain set by the lateral acceleration corresponding gain setting means e. A command to give an auxiliary steering angle to at least one of the front and rear wheels is output to the auxiliary steering means a based on the added value with the yaw rate feedback term based on the yaw rate.

Therefore, when turning acceleration is performed in the limit traveling region in which high lateral acceleration is generated, an auxiliary steering angle is applied to at least one of the front and rear wheels in a direction to promote the generation of the yaw rate of the vehicle. On the other hand, in the limit traveling region, a load shift occurs from the front wheels to the rear wheels, and the understeer becomes strong. Therefore, the understeer tendency can be reduced by this auxiliary steering angle control, and the limit turning performance is improved.

[0012]

【Example】

 (First Embodiment) The configuration will be described.

FIG. 2 is an overall system diagram showing a front and rear wheel steering control device according to a first embodiment of the present invention for giving an auxiliary steering angle only to rear wheels.

The front wheels 1L, 1R of the vehicle to which the front and rear wheel steering control device of the first embodiment is applied are connected to the front wheels 1L, 1R via left and right front wheel steering mechanisms 3L, 3R based on a steering input to a steering wheel 2. A steering unit 4 for steering is provided, and left and right rear wheel steering mechanisms 9L, 9R are provided on rear wheels 8L, 8R.
A rear wheel-side hydraulic cylinder 10 (corresponding to an auxiliary steering unit) that provides an auxiliary steering angle to the rear wheels 8L and 8R via R is provided.

The rear wheel side hydraulic cylinder 10 is driven by applying a control pressure from a hydraulic source unit (not shown) via a rear wheel side servo valve 15.

The rear-wheel servo valve 15 is controlled by a command from the control unit 17 to, for example,
Switching between the three positions of holding and left steering is controlled.

The control unit 17 includes a steering angle sensor 21 (corresponding to a steering angle detecting means), a yaw rate sensor 22 (corresponding to a yaw rate detecting means), a vehicle speed sensor 20, and a lateral acceleration sensor 23 (corresponding to a lateral acceleration detecting means). ) Is input.

The auxiliary steering angle control law incorporated in the control unit 17 as a control program will be described.

In the first embodiment, the gain k corresponding to the lateral acceleration
_1, using the k _2, the rear wheel auxiliary steering according to the control law represented by the following formula is a sum of the yaw rate feedback term based on the yaw rate detected as the steering angle feedforward term based on the steering angle [delta] _f [psi ' angle [delta] _r is applied (corresponding to the auxiliary steering angle control means).

Δ _r = −k ₁ · C 1 · δ _f + k ₂ · C 2 · ψ '(1) where k ₁ ; gain corresponding to the lateral acceleration of the feedforward term C 1; first proportional constant k ₂ ; Lateral gain corresponding to lateral acceleration C2; second proportionality constant C1 and C2 are prior art materials disclosed in Japanese Patent Application Laid-Open No. 60-193773.
These correspond to k1 and k2 of the numbers.

As shown in FIG. 3, the gain k ₁ corresponding to the lateral acceleration is given by a value whose value gradually increases in a quadratic function from 1 in a region where the lateral acceleration YG is large. The gain k ₂ is, as shown in FIG.
In a region where YG is large, the value is given as a value that gradually decreases from 1 in a quadratic function (corresponding to a lateral acceleration corresponding gain setting means).

The operation will be described.

In the limit traveling region where high lateral acceleration YG occurs, the turning radius becomes large and understeer becomes strong.

However, among the control rules according to the above equation (1),
The steering angle feedforward term due to {−k ₁ · C 1 · δ _f } represents the rear wheels 8L, 8R with respect to the steering direction of the front wheels 1L, 1R.
Has a meaning as a reverse phase term which gives a reverse phase auxiliary steering angle.
In addition, the yaw rate feedback term by {k ₂ · C ₂ · {'} represents the rear wheels 8L, 8R with respect to the steering direction of the front wheels 1L, 1R.
It has a meaning as an in-phase term that gives an in-phase auxiliary steering angle to R.

[0025] Moreover, as shown in FIG. 3, the lateral acceleration corresponding gain k ₁ whereas a larger value becomes higher the lateral acceleration YG, lateral acceleration corresponding gain k ₂ is the lateral acceleration YG
Is higher, the smaller the value is, and in the high lateral acceleration region, the weight of {-k ₁ · C 1 · δ _f }, which is the opposite phase term, increases.

Therefore, the yaw rate ψ '
An auxiliary steering angle is given to the rear wheels 8L and 8R in a direction to promote the occurrence of the vehicle, so that the understeer tendency is weakened, the turning performance of the vehicle can be increased, and the limit turning performance is improved.

The effect will be described.

(1) The rear wheels 8 at the time of steering input or disturbance input
In the front and rear wheel steering control device that gives an auxiliary steering angle to L and 8R, the steering angle feed forward term ｛-k ₁ · C1 is used by using lateral acceleration corresponding gains k ₁ and k ₂ that increase the yaw moment of the vehicle in the high lateral acceleration region. · [delta] _f} and the order apparatus for controlling the rear wheel auxiliary steering angle [delta] _r by the yaw rate sum of the feedback term _{{k 2 · C2 · ψ '} }, is possible to improve the turning performance on maximal running region it can.

(Second Embodiment) The overall system configuration of the front and rear wheel steering control device according to the second embodiment of the present invention is similar to that shown in FIG. I do.

The auxiliary steering angle control law incorporated in the control unit 17 as a control program will be described.

In the second embodiment, the gain k corresponding to the lateral acceleration
_1, using the k _2, the rear wheel auxiliary steering according to the control law represented by the following formula is a sum of the yaw rate feedback term based on the yaw rate detected as the steering angle feedforward term based on the steering angle [delta] _f [psi ' angle [delta] _r is applied (corresponding to the auxiliary steering angle control means).

[0032] _{δ r = k 1 · G ·} δ f + k 2 · r (ψ'-Ψ T ') ... (2) where, k _1; lateral acceleration of the feed-forward term corresponding gain G; feedforward transfer function k ₂ ; lateral acceleration corresponding gain r of the feedback section; feedback gain _{(r> 0) Ψ T '} ; target yaw rate characteristics the lateral acceleration corresponding gain k _1, as shown in FIG. 4, the lateral acceleration YG is its value in a large area As shown in FIG. 4, the lateral acceleration-dependent gain k ₂ is given as a quadratic function in a region where the lateral acceleration YG is large, as shown in FIG. It is given by a gradually increasing value (corresponding to a lateral acceleration corresponding gain setting means).

The operation will be described.

In the limit traveling region where high lateral acceleration YG occurs, the turning radius becomes large and understeer becomes strong.

However, among the control rules according to the above equation (2),
The steering angle feedforward term due to {k ₁ · G · δ _f } increases vehicle stability in the critical driving range, ie,
It has the meaning as an in-phase term that gives the in-phase auxiliary steering angles to the rear wheels 8L and 8R with respect to the steering directions of L and 1R. Also, ｛k ₂
r (ψ'-Ψ _T ') the yaw rate feedback term due}, even marginal running region the actual yaw rate [psi' match with the target yaw rate characteristics [psi _T ', i.e., to the front wheels 1L, steering direction of the 1R when understeer is strong Rear wheel 8L, 8
It has a meaning as a negative-phase term that gives a reverse-phase auxiliary steering angle to R.

[0036] Moreover, as shown in FIG. 4, while the lateral acceleration corresponding gain k ₂ becomes a greater value as becomes higher the lateral acceleration YG, lateral acceleration corresponding gain k ₁ is the lateral acceleration YG
Becomes smaller the value is the higher, the higher the lateral acceleration region, the weighting of the reverse-phase term _{{k 2 · r (ψ'-} Ψ T ')} increases.

Therefore, the yaw rate ψ '
An auxiliary steering angle is given to the rear wheels 8L and 8R in a direction to promote the occurrence of the vehicle, so that the understeer tendency is weakened, the turning performance of the vehicle can be increased, and the limit turning performance is improved.

The effect will be described.

(2) The rear wheels 8 are input when a steering input or disturbance is input.
In the front and rear wheel steering control device that gives the auxiliary steering angle to L and 8R, the steering angle feed forward term ｛k ₁ · G · is used by using the lateral acceleration corresponding gains k ₁ and k ₂ that increase the yaw moment of the vehicle in the high lateral acceleration region. [delta] _f} and yaw rate feedback term _{{k 2 · r (ψ'-} Ψ T ')} apparatus for controlling a rear wheel auxiliary steering angle [delta] _r by the sum of the and the reason, improvement of turning performance on maximal running region Can be achieved.

(Third Embodiment) The configuration will be described.

FIG. 5 is an overall system diagram showing a front and rear wheel steering control device according to a third embodiment of the present invention which gives an auxiliary steering angle to both front and rear wheels.

The front wheels 1L and 1R of the vehicle to which the front and rear wheel steering control device of the third embodiment is applied are connected to the front wheels 1L and 1R via left and right front wheel steering mechanisms 3L and 3R based on the steering input to the steering wheel 2. In addition to the steering unit 4 to steer,
A front-wheel-side hydraulic cylinder 7 that provides an auxiliary steering angle to the front wheels 1L and 1R by stroking a rack tube (supported on the vehicle body 5 via the elastic body 6) of the steering unit 4 is provided, and rear wheels 8L and 8R are provided. , Left and right rear wheel steering mechanism 9
A rear-wheel-side hydraulic cylinder 10 that provides an auxiliary steering angle to the rear wheels 8L and 8R via L and 9R is provided.

The front-wheel hydraulic cylinder 7 and the rear-wheel hydraulic cylinder 10 have a common hydraulic power source unit 11, and are controlled from the hydraulic power unit 11 via a front-wheel failsafe valve 12 and a front-wheel servo valve 13. The front wheel hydraulic cylinder 7 is driven by applying pressure, and the rear wheel hydraulic cylinder 10 is driven by applying control pressure from the hydraulic power source unit 11 through the rear wheel fail-safe valve 14 and the rear wheel servo valve 15. I try to make it. still,
The hydraulic power source unit 11 includes a hydraulic pump 11a driven by an engine 16, an unload valve 11b, a pressure switch 11c, an accumulator 11d, and a reservoir 1
1e to supply a constant-pressure hydraulic oil.

The front-wheel-side failsafe valve 12 and the rear-wheel-side failsafe valve 14 are switched between two positions, ON / OFF, according to a command from the control unit 17.
The front wheel side servo valve 13 and the rear wheel side servo valve 1
5 is the servo amplifier 1 from the control unit 17
The three positions of right steering, holding, and left steering are controlled to be switched in accordance with commands via the switches 8 and 19.

The control unit 17 includes a vehicle speed sensor 20, a steering angle sensor 21 (corresponding to a steering angle detecting means), a yaw rate sensor 22 (corresponding to a yaw rate detecting means), and a lateral acceleration sensor 23 (corresponding to a lateral acceleration detecting means). ), Front wheel side displacement sensor 24, rear wheel side displacement sensor 2
5, neutral switch 26, clutch switch 2
7. A detection signal from the stop lamp switch 28 is input. The sensor signal from the yaw rate sensor 22 is amplified and input via the amplifier 29.

The auxiliary steering angle control law incorporated in the control unit 17 as a control program will be described.

In the third embodiment, the gain k corresponding to the lateral acceleration
_{1, k 2, k 3,} k 4 using the control represented by the following formula is a sum of the yaw rate feedback term based on the yaw rate detected as the steering angle feedforward term based on the steering angle [delta] _f [psi ' The front wheel auxiliary steering angle δ _f0 and the rear wheel auxiliary steering angle δ _r are given according to the law (corresponding to auxiliary steering angle control means).

Δ _f0 = k ₁ · G _f · δ _f -k ₂ · R _f · (ψ'-Ψ _T ') δ _r = k ₃ · G _r · δ _f + k ₄ · R _r · (ψ'- Ψ _T ') ... (3) where, k _1, k _3; lateral acceleration of the feed-forward term corresponding gain G _f, G _r; feedforward transfer function k _2, k _4; lateral acceleration corresponding gain of the feedback term R _f, R _r ; feedback gain (R _f > 0, R _r >
0) Ψ _T '; target yaw rate characteristic As shown in FIG. 6, the lateral acceleration corresponding gains k ₁ and k ₄ gradually increase quadratically from 1 in a region where the lateral acceleration YG is large (see FIG. 6). k ₁ > k ₄ ), and the lateral acceleration corresponding gains k ₂ and k ₃ gradually decrease from 1 in a quadratic function in a region where the lateral acceleration YG is large, as shown in FIG. (K ₂ <k ₃ ) (corresponding to a lateral acceleration gain setting means).

The operation will be described.

(A) Limit Traveling In the limit travel region where high lateral acceleration YG occurs, the turning radius becomes large and understeer becomes strong.

However, on the front wheel side of the control law of the above equation (3), the lateral acceleration corresponding gain of k ₁ > k ₂ is set in the high lateral acceleration range, so that ｛k ₁ · G _f · δ _f before sliced widening term due} is _{{-k 2 · R f · (} ψ'-Ψ T ') weighting than before slicing back section according} increases.

Further, on the rear wheel side of the control law according to the above equation (3), the lateral acceleration corresponding gain of k ₄ > k ₃ is set in the high lateral acceleration range, so that ｛k ₄ · R _r · ( The weight of the anti-phase term due to {'-{ _T ')} is higher than that of the in-phase term due to {k ₃ · G _r · δ _f }.

Therefore, the yaw rate ψ '
The front wheels 1L, 1R and the rear wheels 8
The auxiliary steering angle is given to L and 8R, the tendency of understeer is reduced, the turning performance of the vehicle can be increased, and the limit turning performance can be improved.

(B) During steering of the steering wheel When a steering input is given to the steering wheel 2 and the actual yaw rate ψ ′ always matches the target yaw rate characteristic Ψ _T ′,
ψ '= Ψ _T', and the above (3) the front wheel auxiliary steering angle by equation [delta] _f0
And the rear wheel auxiliary steering angle [delta] _r becomes _{δ f0 = k 1 · G f} · δ f δ r = k 3 · G r · δ f.

That is, the feedback component is eliminated, and the feedforward control is mainly performed, so that the vehicle moves as the driver intends.

Here, the relationship between G _f , G _r , and ' _T ' is disclosed in Japanese Patent Laid-Open No. 1-215672. That is,
In a linear two-degree-of-freedom motion equation using a simple two-wheel model, the results obtained by performing feedforward control on the front and rear wheels to obtain the target characteristic Ψ _T 'are transfer functions G _f and G _r . is there.

In other words, the transfer function G _f ,
Equation (1) can be applied to the case where _Gr is analytically obtained.

(C) At the time of disturbance input If a disturbance is applied to the vehicle and the yaw rate occurs even though the steering wheel 2 is not steered, the steering wheel steering angle δ
_Assuming that _f is δ _f = 0 and ψ ′ <0, the front wheel auxiliary steering angle δ _f0 and the rear wheel auxiliary steering angle δ _r are _calculated as δ _f0 = −k ₂ · R _f ψ ′ according to the above equation (3). > 0 δ _r = k ₄ · R _r · ψ '<0.

Accordingly, for the yaw rate ψ ′ <0 (counterclockwise) applied to the vehicle, the front wheels 1L and 1R are provided with the right front wheel auxiliary steering angle δ _f0 , and the rear wheels 8L and 8R are provided with the left direction. as that rear wheel auxiliary steering angle [delta] _r is given in, it is automatically corrected steering direction suppressing yaw rate [psi 'front and rear wheels, disturbing the route of the vehicle is reduced by the disturbance such as rough road and crosswind .

(D) Vehicle yaw rate characteristics As shown in equation (3), the vehicle yaw rate characteristics at the time of turning or the like include a deviation term between the actual yaw rate ψ ′ and the target yaw rate characteristic Ψ _T ′ in a control law. Because of the so-called feedback control, the target yaw rate characteristics can be achieved with high accuracy, and even if the vehicle characteristics deteriorate over time due to tire wear etc., the system is designed to approach the model of the target yaw rate characteristics Ψ _T '. It is adaptable.

The effect will be described.

(3) At the time of steering input or disturbance input, the front wheel 1
In the front and rear wheel steering control device for giving an auxiliary steering angle to the rear wheels L, 1R and the rear wheels 8L, 8R, gains k ₁ , k ₂ , k ₃ , k ₃ , k ₃ , k ₃ , k ₂ , k ₃ , which increase the yaw moment of the vehicle in the high lateral acceleration region.
Using k ₄ , the steering angle feed forward term ｛k ₁ · G _f · δ
_f ｝ and the yaw rate feedback term ｛−k ₂ · R _f · (ψ '
-Ψ _T ') controls the front wheel auxiliary steering angle [delta] _f0 by the sum of the}, yaw rate feedback term and the steering angle feed-forward term _{{k 3 · G r · δ} f} {k 4 · R r · (ψ' −Ψ _T ')｝
Because it and apparatus for controlling the rear wheel auxiliary steering angle [delta] _r by the sum of the, it is possible to improve the turning performance on maximal running region.

(4) Since the apparatus provides the auxiliary steering angles δ _f0 , δ _r to the front and rear wheels at the control speed represented by the above equation (3), it is possible to improve disturbance resistance and adaptability to deterioration of vehicle performance over time. In addition, the target characteristics can be achieved with high accuracy.

(5) One linear 2 using a simple two-wheel model
The motion equation of freedom, because the results of solving as target yaw rate characteristics [psi _T 'is obtained by feedforward control front and rear wheels transfer function G _f, and G _r, the control circuit requires only simple, Cost performance can be improved.

When the analysis model is complicated and the target characteristic Ψ _T ′ is a high-order component, naturally, the transfer functions G _f and G _r
Can be derived analytically in the same way, but of higher order. In this case, the control accuracy is improved on the one hand, but the control circuit is complicated and the cost performance is reduced. In that respect, the control law of the embodiment of the present invention is practical.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and any change or addition without departing from the gist of the present invention is included in the present invention. It is.

For example, in the embodiment, an example is shown in which a lateral acceleration sensor is used as the lateral acceleration detecting means. However, as shown in FIG. 7, a lateral acceleration sensor is not used, and the steering angle δ _f
And it detects a vehicle speed V, the by equation _{YG = n · δ f · V} 2 ( constant determined by the vehicle specification) may be obtained by calculation. In this case, the cost is reduced and the system is simplified, so that the reliability is improved.

In the embodiment, the example has been described in which the gains of both the steering angle feed forward term and the yaw rate feedback term are set to the gain corresponding to the lateral acceleration. However, the gain of only one of the terms is set to the gain corresponding to the lateral acceleration. An example may be used.

[0069]

As described above, according to the present invention, there is provided a front and rear wheel steering control device for providing an auxiliary steering angle to at least one of the front and rear wheels at the time of steering input or disturbance input. Since the auxiliary steering angle is controlled by the added value with the feedback term, and the gain of at least one of the two terms is changed in a direction to increase the yaw moment in accordance with the magnitude of the lateral acceleration, the limit traveling area The effect that the turning performance in the can be improved can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim showing a front and rear wheel steering control device of the present invention.

FIG. 2 is an overall system diagram showing the front and rear wheel steering control device of the first embodiment.

FIG. 3 is a gain characteristic diagram corresponding to a lateral acceleration in the device of the first embodiment.

FIG. 4 is a gain characteristic diagram corresponding to a lateral acceleration in the device of the second embodiment.

FIG. 5 is an overall system diagram showing a front and rear wheel steering control device according to a third embodiment.

FIG. 6 is a graph showing gain characteristics corresponding to lateral acceleration in the device of the third embodiment.

FIG. 7 is an overall system diagram showing another embodiment of the front and rear wheel steering control device.

[Explanation of symbols]

 a auxiliary steering means b steering wheel steering angle detecting means c yaw rate detecting means d lateral acceleration detecting means e gain setting means corresponding to lateral acceleration f auxiliary steering angle controlling means

Claims (1)

(57) [Claims] An auxiliary steering means for giving an auxiliary steering angle to at least one of the front and rear wheels by an external command without depending on a steering wheel input, a steering wheel angle detecting means for detecting a steering wheel angle, a yaw rate Detecting means for detecting a lateral acceleration, detecting lateral acceleration, and changing at least one of a feedback gain and a feedforward gain in a direction to increase the yaw moment of the vehicle according to the magnitude of the lateral acceleration. At least one of the front and rear wheels is obtained by using a lateral acceleration corresponding gain setting means and an added value of a steering angle feed forward term based on the steering angle and a detected yaw rate feedback term based on the detected yaw rate using the set lateral acceleration corresponding gain. Output a command to give an auxiliary steering angle to the auxiliary steering means Front and rear wheel steering control apparatus characterized by comprising a control means, a.