JPH08244643A - Auxiliary steering angle controller - Google Patents

Abstract

PURPOSE: To restrain a stationary vehicle slit angle while improving the transient behavior of a vehicle by comparing a stationary yaw rate corresponding to a value equivalent to the maximum lateral acceleration with an aimed stationary yaw rate to set lower one as the aimed stationary yaw rate for calculating an auxiliary steering angle. CONSTITUTION: The stationary lateral speed is presumed by the use of presumed cornering power Kf, Kr, steering angle θ and vehicle speed Vx detecting value to set an aimed stationary yaw rate ψ'rg (S3). For this aimed stationary yaw rate ψ'rn, is calculated the aimed stationary yaw rate ψ'rg base on a value equivalent to the maximum lateral acceleration. The lower one of the aimed stationary yaw rate ψ'rn by the lateral speed control and the aimed stationary yaw rate ψ'rg limiting the lateral acceleration is set to the aimed yaw rate ψ'r (S4). An auxiliary steering angle 5r is calculated on the basis of the aimed stationary yaw rate ψ'r.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary steering angle control device for controlling an operation characteristic of a vehicle by giving an auxiliary steering angle to at least one of front and rear wheels by using an estimated value of the cornering power of the vehicle.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to control a steering angle of a vehicle by giving an auxiliary steering angle to at least one of a rear wheel and a front wheel by yaw rate feedback control, for example, Japanese Unexamined Patent Publication No. 4-362470. An auxiliary steering angle control device disclosed in US Pat.

This is to calculate the target rear wheel steering angle by yaw rate feedback, and also calculate the target rear wheel steering angle by vehicle slip angle feedback, and switch these target rear wheel steering angles according to predetermined conditions. In the case where only the yaw rate is the target state quantity of the vehicle motion, particularly when the road friction coefficient μ is low and the cornering power is small, when the target yaw rate is achieved, the lateral speed, that is, the vehicle slip angle also increases, and Since the behavior becomes unstable, the behavior of the vehicle in such a state is stabilized by switching to the target rear wheel steering angle calculated based on the slip angle.

By the way, in this auxiliary steering angle control device, considering a case where the steering angle is input stepwise from a straight traveling state, there is a delay until a predetermined vehicle slip angle is generated after the start of steering. Immediately after the start of steering, the rear wheel steering angle is controlled so as to achieve the target yaw rate set by the yaw rate feedback control, and after the vehicle slip angle exceeds a predetermined value, the mode is switched to the slip angle feedback control to change the vehicle slip angle. In order to suppress it, the rear wheel steering angle is increased, and at the same time, the generated yaw rate is also suppressed with respect to the target yaw rate, so steady increase of the vehicle slip angle can be suppressed. There is a problem that transient vehicle behavior (for example, insufficient steering angle on a road surface having a low friction coefficient) is not improved.

In order to solve such a problem, the applicant of the present invention determines a steady lateral speed generated when a target steady yaw rate set by a steering angle and a vehicle speed is realized, as an estimated cornering power of each wheel, a steering angle, and a steering angle. Japanese Patent Application No. 6-16127 discloses an auxiliary steering angle control device capable of improving transient characteristics with respect to a steering input by predicting using a vehicle speed and resetting a target steady yaw rate in consideration of the magnitude of a steady lateral velocity Vy. As proposed.

[0006]

However, in the above-mentioned conventional auxiliary steering angle control device, at the target steady-state yaw rate reset in consideration of the steady lateral speed, the vehicle is in the low speed range (for example, 80 km / h or less). In the above, there is a problem that the target steady-state yaw rate becomes excessive and the stability of the vehicle may be impaired.

Therefore, the present invention has been made in view of the above problems, and it is possible to secure the stability of the vehicle in a low speed range while suppressing the steady vehicle slip angle and improving the transient vehicle behavior. It is an object of the present invention to provide a simple auxiliary steering angle control device.

[0008]

A first aspect of the present invention is a steering angle detecting means a for detecting a steering angle θ of a vehicle in FIG.
A vehicle speed detecting means b for detecting a vehicle speed Vx in the front-rear direction of the vehicle; a cornering power estimated value calculating means c for calculating an estimated cornering power value of each wheel of the vehicle; Auxiliary steering means d capable of auxiliary steering, target yaw rate calculating means e for calculating a steady-state value ψ′r ₀ of the target yaw rate and a target yaw rate ψ′r in consideration of transient characteristics, and the target yaw rate ψ′r are realized. Target auxiliary rudder angle calculating means f for calculating the auxiliary rudder angle δr required for the above from the detected steering angle θ, the vehicle speed detection value Vx, and the cornering power estimated value, and the target auxiliary rudder angle δ.
In an auxiliary steering angle control device provided with an auxiliary steering control means g for performing control so that the steering angle of the auxiliary steering means coincides with r, a steady lateral force generated when the steady value ψ′r ₀ of the target yaw rate is realized. and constant lateral speed calculation means h for calculating the speed Vy _0, the target steady-state yaw rate setting means i for setting the variable target steady yaw rate Pusai'r _n corresponding to the steering angle θ and the vehicle speed Vx and constant lateral speed Vy _0, the The target steady-state yaw rate ψ'r is calculated from the detected vehicle speed and the maximum lateral acceleration equivalent to the road surface.
_The maximum lateral acceleration equivalent value calculating means j for calculating _g is compared with the steady-state yaw rate ψ'r _g corresponding to the maximum lateral acceleration equivalent value and the set target steady-state yaw rate ψ'r _n, and the smaller one is compared. The target auxiliary yaw rate ψ'r is set, and the target auxiliary steering angle calculation means calculates the auxiliary steering angle δr based on the target steady yaw rate ψ'r set by the comparison setting means.

Further, in the second invention, as shown in FIG. 12, in the first invention, the maximum acceleration equivalent value calculating means j is a road surface friction coefficient calculating means j11 for calculating a road surface friction coefficient μ. , A lateral acceleration permissible value calculating means j12 for calculating a maximum lateral acceleration equivalent value at which the vehicle can turn from the vehicle speed and the road surface friction coefficient μ.

In a third aspect based on the second aspect, the road surface friction coefficient calculating means calculates a road surface friction coefficient from the cornering power estimated value.

In a fourth aspect based on the first aspect, the maximum lateral acceleration equivalent value calculating means includes longitudinal acceleration detecting means for detecting a deceleration of the vehicle based on the detected value of the vehicle speed, and a tire. And means for calculating the maximum lateral acceleration equivalent value corresponding to the deceleration from the friction circle.

The fifth invention is the first to fourth inventions.
In any one of the inventions described above, the steady lateral velocity calculating means calculates a lateral velocity allowable value for obtaining a predetermined vehicle slip angle, and the steady lateral velocity exceeds the allowable lateral velocity. And a lateral speed regulation unit that regulates the lateral speed.

[0013]

Therefore, in the first aspect of the invention, the target yaw rate calculating means calculates the target yaw rate in consideration of the transient characteristic from the set target steady yaw rate, and the target steady yaw rate setting means i operates the steering based on this target yaw rate. The steady lateral velocity Vy ₀ calculated by the steady lateral velocity calculating means h from the detected angle value, the detected vehicle speed value, and the cornering power estimated value, and the target steady state yaw rate by the lateral velocity control that is variable according to the detected steering angle value and the detected vehicle speed value. ψ'r _n is set.

On the other hand, the maximum lateral acceleration equivalent value calculating means j calculates the target steady-state yaw rate ψ'r _g corresponding to the lateral acceleration from the vehicle speed detection value and the maximum lateral acceleration equivalent value that the road surface can output, and the comparison setting means k. Comparing the steady-state yaw rate ψ'r _g according to the maximum lateral acceleration equivalent value and the target steady-state yaw rate ψ'r _n by lateral speed control, and setting the smaller one as the target steady-state yaw rate ψ'r and calculating the target auxiliary steering angle. The means calculates the auxiliary steering angle δr based on the target steady-state yaw rate ψ′r from the comparison setting means, and the calculated auxiliary steering angle and auxiliary steering means d.
The target steady-state yaw rate ψ'r _g corresponding to the maximum lateral acceleration equivalent value is selected in the low-speed range of the vehicle by controlling the steering angles of the two to match, and suppresses an excessive increase in the target yaw rate ψ'r. However, the steady vehicle slip angle can be suppressed and the transient vehicle behavior can be improved.

The second aspect of the invention is that the target steady-state yaw rate ψ'r at which the vehicle can turn according to the friction coefficient μ of the road surface and the vehicle speed.
_g is calculated and the target yaw rate ψ'in the low speed range of the vehicle is calculated.
Since r does not exceed the turning limit of the vehicle, the stability of the vehicle can be secured.

According to a third aspect of the present invention, the road surface friction coefficient calculating means calculates the road surface friction coefficient from the cornering power estimated value, so that the maximum lateral acceleration equivalent value corresponding to the turning limit of the vehicle can be reliably obtained. You can

According to a fourth aspect of the invention, the maximum lateral acceleration equivalent value calculating means changes the braking force obtained from the deceleration of the vehicle based on the detected value of the vehicle speed and the friction circle peculiar to the tire mounted on the vehicle to the tire. The maximum lateral acceleration equivalent value that can be turned can be calculated from the generated lateral force.

Further, in the fifth aspect of the invention, the steady lateral speed is limited so as not to exceed an allowable value such that a predetermined vehicle slip angle is obtained, and therefore, the target based on the lateral speed control from the target steady yaw rate setting means. The steady-state yaw rate ψ'r _n has its value reduced to ensure the stability of the vehicle in the high speed range.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 and 2 show an example in which the present invention is applied to a four-wheel steering system. In FIGS. 1 and 2, front wheels 30 are shown.
L and 30R are mechanical link type mechanisms that are operated by the driver's steering operation, while rear wheels 25
L and 25R are respectively steered by a hydraulic cylinder 15 that gives an auxiliary steering angle.

Here, the hydraulic cylinder 15 is driven in response to a command from a controller 13 mainly composed of a microprocessor and the like.

As shown in FIG. 2, the controller 13 has a steering angle θ detected by a steering angle sensor 1 as a means for detecting a steering angle and a vehicle speed Vx detected by a vehicle speed sensor 2 as a vehicle speed detecting means. , The rear wheel steering angle δr detected by the rear wheel steering angle sensor 16, the longitudinal acceleration Gx of the vehicle detected by the acceleration sensor 26, and the lateral acceleration Gy of the vehicle.
And the hydraulic pressures of the wheel cylinders 6c to 6d of the respective wheels detected by the pressure sensors 7a to 7c interposed in the brake system, respectively, and the rear wheel steering angle target value δ * which will be described later based on the respective detected values. r is calculated, and the hydraulic cylinder 15 is driven so that the rear wheel steering angle δr matches the rear wheel steering angle target value δ * r. In addition, the wheel cylinders 6a of each wheel
The hydraulic pressure from the master cylinder 5 according to the operation of the brake pedal 3 and the booster 4 is supplied to 6d.

Here, as shown in FIG. 1, the hydraulic cylinder 15 for giving an auxiliary steering angle to the rear wheels 25L, 25R is supplied with pressure from an oil pump 19 driven by an engine 20 through a supply passage 23. Oil to the controller 13
Is selectively supplied to the oil chambers 15L and 15R of the hydraulic cylinder 15 by the switching valve 17 which is driven in response to the command from the controller 13, and the controller 13 is driven by discharging pressure oil from the other oil chamber to the drain passage 24. The predetermined steering angle δr calculated in step S1 is given to the rear wheels 25L and 25R.

When a current having a predetermined sign is applied from the controller 13 to the switching valve 17, the supply passage 23 is communicated with the oil chamber 15L to supply the pressure oil, while the oil chamber 15R is connected to the drain passage 2L.
4, the pressure oil is discharged, and the rear wheels 25L and 25R are turned to the left. On the other hand, if the sign of the current to the switching valve 17 is reversed, the wheels are turned to the right. Then, at the neutral position of the switching valve 17, the pressure oil in the oil chambers 15L and 15R is held to maintain the rear wheel steering angle, and the controller 13 calculates the rear wheel steering angle target value δ * r and at the same time, the rear wheel steering angle is calculated. When the rear wheel steering angle δr detected by the sensor 16 matches the target value δ * r, the switching valve 17 is driven to the neutral position to maintain the predetermined rear wheel steering angle δr.

The oil pump 19 sucks the working oil from the reservoir 18 and discharges the pressure oil from the unload valve 2.
After the pressure is adjusted by 1, the pressure is accumulated in the accumulator 22 provided in the supply passage 23, and hydraulic oil of a predetermined pressure is supplied to the hydraulic cylinder 15.

[Vehicle Equation of Motion] Prior to the description of the rear wheel steering angle control, the equation of vehicle motion will be described when the vehicle motion is considered to have two degrees of freedom in yawing and lateral direction.

It is known that the equations of motion relating to the yawing and lateral directions of the vehicle are expressed by the following equations (1) and (2) when expressed in a continuous system at time t.

[0028]

[Equation 1]

However, Cf and Cr represent the cornering forces of the front and rear wheels, respectively, and these cornering forces are calculated by using the cornering powers Kf and Kr of the front and rear wheels and the sideslip angles βf and βr of the front and rear wheels. It is expressed by equations (3) and (4).

[0030]

[Equation 2]

The meanings of the above symbols are as follows.

Ψ ′; yaw rate ψ ″; yaw angular acceleration Vy; vehicle lateral velocity Lf; vehicle center of gravity position to front axle distance θ; steering angle Lr; vehicle center of gravity position to rear axle distance δr; rear wheel steering angle M; vehicle Weight Vx; vehicle speed Iz; yaw moment of inertia N; steering gear ratio Substituting equations (3) and (4) into equations (1) and (2), and considering it as a differential equation relating to yaw rate ψ'and lateral velocity Vy, It can be expressed as in the following expressions (5) and (6).

Ψ ″ = a ₁₁ ψ ′ + a ₁₂ · Vy + b _f1 · θ + b _r1 · δr (5) V′y = a ₂₁ · ψ ′ + a ₂₂ · Vy + b _f2 · θ + b _r2 · δr (6) However, , A ₁₁ = −2 (Kf · Lf ² + Kr · Lr ² ) / (I _Z · Vx) (7) a ₁₂ = −2 (Kf · Lf−Kr · Lr) / (I _Z · Vx) 8) a ₂₁ = -2 (Kf · Lf−Kr · Lr) / (M · Vx) −Vx (9) a ₂₂ = −2 (Kf + Kr) / (M · Vx) (10) b _f1 = 2Kf・ Lf / (I _Z · N) (11) b _f2 = 2Kf / (M · N) (12) b _r1 = -2Kr · Lr / Iz (13) b _r2 = 2Kr / M (14) Here, the cornering powers Kf, Kr of the front and rear wheels
Varies depending on the braking force and the driving force applied, but the estimated value can be calculated by detecting the state quantity of the vehicle during braking (cornering power estimating means c).
Equivalent to).

For example, the cornering power estimation value during braking is disclosed in Japanese Patent Laid-Open No. 4-126670 using the cornering power during non-braking, the detected value of the longitudinal acceleration G and the detected value of the wheel cylinder hydraulic pressure. It can be calculated by the method. The detailed calculation method is omitted here.

[Setting of Target Steady-State Yaw Rate Based on Steering Angle and Vehicle Speed] The target steady-state yaw rate ψ'r ₀ of the vehicle is set to a high μ value so as to have a preferable characteristic on a high μ road and when not braking.
The target steady-state yaw rate ψ'r ₀ can be expressed by the following equation (15) if it is set equal to the steady-state generation value when the steady-state rear wheel steering angle is set to zero during road / non-braking.

[0036]

(Equation 3)

Further, Kf ₀ and kr ₀ are the cornering powers of the front wheels and the rear wheels at the time of high μ road / non-braking.

[Setting of target steady-state yaw rate ψ'r ₀ in consideration of lateral speed] If the slip angle generated in the vehicle is set to a predetermined value β ₀ , the allowable lateral speed Vy _max0 for the vehicle speed Vx is allowed. Is calculated from the following equation.

Vy _max0 = −Vx · tan (β ₀ ) ... (18) Since the allowable lateral velocity Vy _max0 obtained by the equation (18) is proportional to the vehicle speed regardless of the friction coefficient μ of the road surface, Low μ
If the vehicle slip angle remains at the predetermined value β ₀ at high speeds on the road, it may not be appropriate and the stability of the vehicle may be impaired.

Therefore, the vehicle speed Vx or the road surface friction coefficient μ
To change the vehicle slip angle. An upper limit value is set for the allowable lateral speed Vy _max so that the set value of the vehicle slip angle becomes smaller as the vehicle speed Vx becomes higher.

Vy _max = min [| Vy _max0 |, Kvy] (19) However, Kvy is a preset value, and is a friction coefficient μ of the road surface or a lateral acceleration Gy generated in the vehicle or a value equivalent to the lateral acceleration. You may set as a variable or a map according to it.

Next, the steering angle θ and the target steady-state yaw rate ψ'r
_{From 0} , the steady rear wheel steering angle δr ₀ and the steady lateral speed Vy ₀ are set in the above
From the formula,

[0043]

[Equation 4]

By substituting this equation (20) into the above equation (3) and eliminating Vy ₀ , the steady rear wheel steering angle δr ₀ becomes the following equation.

[0045]

(Equation 5)

Similarly, when δr ₀ is deleted, the steady lateral velocity Vy ₀ is expressed by the following equation (23).

[0047]

(Equation 6)

On the other hand, the steady rear wheel steering angle δr ₁ and the steady yaw rate ψ′r ₁ are calculated from the steering angle θ and the steady allowable lateral velocity Vy _max obtained as described above. Considering the steady state in the above equations (1) and (2), if yaw angular acceleration ψ ″ = 0 and Vy = 0 are set and the steady yaw rate ψ ′ ₀ = 0, the above (1),
From the formula (2), Lf · Cf = Lr · Cr (24) MVxψ′r ₁ = 2 (Cf + Cr) (25) From these formulas (24) and (25), the steady-state yaw rate ψ′r ₁
About

[0049]

(Equation 7)

Then, this is substituted into the above equation (3) to sort out the cornering force Cf.

[0051]

(Equation 8)

Therefore, the steady yaw rate ψ'r ₁ is obtained from the equations (26) and (27) by the following equation (28).

[0053]

[Equation 9]

From the above equations (4) and (25), the sideslip angle βr of the rear wheel is

[0055]

[Equation 10]

Thus, the steady rear wheel steering angle δr ₁ is obtained from the above equation (4) using equations (27) and (29) as follows.

[0057]

[Equation 11]

The rear wheel steering angle δr is also mechanically limited, and this limit value is defined as the maximum rear wheel steering angle δr _max.
An allowable steering angle θ _max corresponding to the vehicle speed Vx is calculated from r _max and the steady allowable lateral speed Vy _max . Again in the same manner as above, as a steady yaw rate ψ'r ₁ = ψ'r _2, organize the steady yaw ψ'r _2.

[0059]

(Equation 12)

On the other hand, rearranging the above equation (4),

[0061]

(Equation 13)

Therefore, from equations (31) and (32), the steady-state yaw rate ψ'r ₂ becomes the following equation (33).

[0063]

[Equation 14]

Further, substituting the equation (31) into the equation (4) and rearranging the steady yaw rate ψ'r ₂ and the rear wheel cornering force Cr,

[0065]

(Equation 15)

From the above equations (3) and (24), the sideslip angle βf of the front wheels is

[0067]

[Equation 16]

From the above equation (3) using the above equations (33) and (34), the allowable steering angle θ _max can be obtained by the following equation (36).

[0069]

[Equation 17]

The steady-state yaw rates ψ'r _{0 to} ψ'r ₂ obtained by the above calculation are converted to the steady-state rear wheel steering angle δ calculated as above.
Based on the magnitude relationship among r ₀ , δr ₁ , the maximum rear wheel steering angle δr _max , the allowable steering angle θ _{max and the} steady lateral speed Vy ₀ , the steady allowable lateral speed Vy _max , the target steady yaw rate ψ′r is set as follows. Set.

1) δr ₀ ≦ δr _max , and | Vy ₀ | ≧ |
Vy _max | and δr ₁ ≦ δr _max ψ′r = ψ′r ₀ 2) δr ₀ ≦ δr _max and | Vy ₀ │ <│Vy _max | ψ′r = ψ′r ₀ 3) δr _0> δr _max, and if the theta ≦ theta case of _{max ψ'r = ψ'r 0 4) δr} 0> δr max, and _{θ> θ max ψ'r = ψ'r 2} 5) δr 0 ≦ δr _max , | Vy ₀ | ≧ | Vy _max |, δr ₁ > δ
When r _max and θ ≦ θ _max ψ'r = ψ'r ₀ 6) δr ₀ ≦ δr _max , │Vy ₀ │ ≧ │Vy _max │, δr ₁ > δ
In the case of r _max and θ> θ _max ψ′r = ψ′r _{2 The} target steady-state yaw rate in consideration of the transient characteristic is also used for steering angle input as disclosed in, for example, Japanese Patent Laid-Open No. 4-126670. On the other hand, the delay may be set to be a first-order delay, and the detailed description will be omitted.

Further, regarding the target rear wheel steering angle, Japanese Patent Laid-Open No.
Although it can be calculated in the same manner as that disclosed in Japanese Patent Publication No. 126670, detailed description thereof will be omitted as well.

[Limitation of Target Steady-State Yaw Rate Based on Lateral Acceleration] When the target steady-state yaw rate ψ′r ₀ considering the lateral velocity Vy is realized by the vehicle as described above, the vehicle is determined according to the vehicle speed Vx and the road surface friction coefficient μ. Limit value Gy _max / V set from the maximum lateral acceleration Gy _max preset according to the vehicle speed Vx and the road surface friction coefficient μ so as not to exceed the turning limit of
It is restricted from x as follows.

[0074]

(Equation 18)

That is, the target steady-state yaw rate ψ'r ₀ considering the limit value (Gy / Vx) corresponding to the maximum lateral acceleration Gy _max that the road surface can produce according to the vehicle speed Vx and the friction coefficient μ, and the lateral speed Vy _max. By setting the smaller one of them as the target steady-state yaw rate ψ'r again, it is possible to prevent the target steady-state yaw rate ψ'r from becoming excessive in the low speed range (80 km / h or less) as in the conventional example. .

Here, Gy _max / Vx represents a steady-state yaw rate ψr _g based on the limitation of the lateral acceleration Gy, and F = Mα = M (from the equation of the vehicle lateral motion shown in the above equation (2). Since V′y + Vxψ ′) (38), it can be treated as α≈Gy, and the lateral acceleration Gy can be expressed as Gy = Vy + Vxψ ′ (39). Therefore, considering the steady-state characteristics, it is considered that the lateral velocity Vy≈0. Therefore, the above equation (39) becomes Gy = Vxψ ′ ... (40), and if ψ = ψr _g and Gy = Gy _max , then ψ That is, 'r _g = Gy _max / Vx (41).

Here, as the lateral acceleration Gy _max , the detection value Gy of the acceleration sensor 26 may be used, and based on the estimated values of the cornering powers Kf and Kr, the maximum lateral acceleration corresponding to the road surface friction coefficient μ can be obtained. The value Gys _max may be used, and the road surface friction coefficient μ and the maximum lateral acceleration equivalent value Gys _max
The relationship between and can be realized as a function or a map set in advance by experiments or the like from the vehicle speed Vx, the steering angle θ and the generated lateral speed Vy.

Further, the lateral acceleration Gy _max is calculated by ABS (=
The anti-lock brake system may be realized by the maximum lateral acceleration equivalent value Gys _max set or estimated based on the vehicle deceleration (longitudinal acceleration Gx) during operation.

The maximum lateral acceleration equivalent value Gys _max based on the longitudinal acceleration Gx during the ABS operation is calculated based on the tire friction circle, and as shown in FIG. Let Fy be the force of Fy and Fy in the lateral direction,

[0080]

[Formula 19]

It is represented by Here, a indicates the maximum value of the braking force that can be generated by the tire, b indicates the maximum value of the lateral force that can be generated by the tire, and these a and b are the road surface friction coefficient μ, the vehicle weight w, It is expressed as follows from the cornering force C _F.

A = μw b = 2C _F Therefore, the above equation (41) is calculated from the equation of motion of the vehicle as follows.

[0083]

(Equation 20)

Then, the lateral acceleration Gy is

[0085]

[Equation 21]

It becomes By presetting these a and b to predetermined values according to the tire characteristics, the maximum lateral acceleration equivalent value Gys _max can be calculated from the detected longitudinal acceleration Gx.

Alternatively, the maximum lateral acceleration equivalent value Gys _max may be calculated by the following equation instead of the equation (43).

Gys _max = K × Gx (45) However, K = b / a Here, since the target steady-state yaw rate ψ'r is only limited by the maximum value of the lateral acceleration Gy, the estimation is made by the above equation (45). The calculated maximum lateral acceleration equivalent value Gys _max can speed up the calculation process.

[Target Rear Wheel Steering Angle Calculation Processing] Based on the equations (1) to (45) described above, the controller 13
Then, the target rear wheel steering angle δ * r is calculated according to the flowcharts shown in FIGS. These processes are executed every predetermined time ΔT by a timer interrupt or the like.

The flowchart of FIG. 3 shows the main routine, and FIG. 4 shows the subroutines for calculating the target steady-state yaw rate in which the lateral acceleration is limited in addition to the lateral velocity. Refer to the flowcharts of FIGS. 3 and 4 below. Meanwhile, the control performed by the controller 13 will be described in detail.

First, in step S1 of FIG. 3, the vehicle speed Vx, the steering angle θ, the wheel cylinder pressures P _FR and P of the respective wheels.
_{Read FL} , P _RR, vehicle longitudinal acceleration Gx, lateral acceleration Gy.

In step S2, the estimated values of the cornering powers Kf and Kr are calculated in the same manner as in Japanese Patent Laid-Open No. 4-126670 as described above. From these cornering powers Kf and Kr, in step S3, the above equation (15) is calculated. A target steady-state yaw rate ψ'r ₀ , which is a steady value at a higher μ road / non-braking, is calculated.

In step S6, the target steady-state yaw rate ψ'r is calculated by the equations (18) to (43) based on the flowchart of FIG.

First, in step S11, the above (1
8), (19) after performing the calculation of the allowable lateral speed Vy _{ma x} from the equation, based on the above (20) - (22) in step S12, necessary when the target steady yaw rate was Pusai'r ₀ The steady-state rear wheel steering angle δr ₀ and the lateral speed Vy ₀ are calculated.

In step S13, it is determined whether or not the steady rear wheel steering angle δr ₀ calculated in step S12 is less than or equal to the mechanically limited maximum rear wheel steering angle δr _{max. If 0} is less than or equal to the maximum rear wheel steering angle δr _max , the process proceeds to step S14 to determine the lateral speed, while if not, the process proceeds to step S17.

In step S14, the above step S12 is performed.
If the absolute value of the steady lateral velocity Vy ₀ obtained in step S1 is greater than or equal to the absolute value of the allowable lateral velocity Vy _max calculated in step S1, the process proceeds to step S15 and the target steady state yaw rate ψ is calculated from the equations (28) to (30). 'r ₁ , the steady rear wheel steering angle δ _r1 is calculated, and if the steady lateral speed Vy ₀ is less than the allowable lateral speed Vy _max , the routine proceeds to step S20 and the target steady yaw rate ψ'r computed at step S3. ₀ is the target steady-state yaw rate ψ '
Set as r.

In step S16, the steady rear wheel steering angle δ
r ₁ and the maximum rear-wheel steering angle δr _max are compared to determine the steady-state rear-wheel steering angle δr ₁
Is less than or equal to the maximum rear wheel steering angle δr _max , the process proceeds to step S19, and the target steady-state yaw rate ψ'r ₁ calculated in step S15 is set as the target steady-state yaw rate ψ'r, while
If not, the process proceeds to step S17.

In step S17, the above (31) to (3)
From equation 6), the target steady-state yaw rate ψ'r ₂ and the allowable steering angle θ
_After the calculation of _max , if the steering angle θ detected in step S18 is less than or equal to the allowable steering angle θ _max , step S20
On the other hand, if not, the process proceeds to step S21 to set the target steady-state yaw rate ψ'r ₂ calculated in step S17 as the target steady-state yaw rate ψ'r.

Thus, in steps S13 to S21, the steady lateral speed Vy ₀ , the steady rear wheel steering angle δr ₀ , and the steering wheel are steered as described in the section [Setting of the target steady yaw rate ψ'r ₀ in consideration of the lateral speed]. The target steady yaw rates ψ′r _{0 to} ψ′r ₂ that are variable according to the steering angle θ, the vehicle speed Vx and the steady lateral speed Vy ₀ are set by dividing the angle θ into 1) to 6).

Thus, after the target steady-state yaw rate ψ'r considering the steady lateral velocity Vy ₀ is obtained, A is obtained at step S22.
If all the channels of the BS are operating, and if all the channels are operating, the lateral acceleration is limited to the target steady-state yaw rate ψ'r obtained in steps S19 to S21 in step S23, while If not, the process is terminated and the process proceeds to step S5 of FIG.

The limitation of the lateral acceleration in step S23 is as follows.
As described in the section [Limitation of target steady-state yaw rate based on lateral acceleration], it is performed by the above equation (37), and corresponds to the road surface friction coefficient μ so that the target steady-state yaw rate ψ'r can be achieved within the turning limit. Limit value Gy / Vx to be set and the target steady-state yaw rate ψ'r set in steps S19 to S21.
The smaller one is set as the target steady-state yaw rate ψ'r.

The lateral acceleration Gy that determines the limit value Gy / Vx is, as described above, the maximum lateral acceleration equivalent value Gys _max based on the longitudinal acceleration Gx during the ABS operation and the estimated values of the cornering powers Kf and Kr. It may be calculated from the maximum lateral acceleration equivalent value Gys _max corresponding to the road surface friction coefficient μ, the acceleration sensor 26 detected value, or the like.

In this way, from the target steady-state yaw rate ψ'r obtained by adding the limitation due to the lateral acceleration to the target steady-state yaw rate ψ'r ₀ considering the lateral velocity, in step S5, the following equations (6) to (14) Based on the following equation, the target rear wheel steering angle δ * r is calculated.

[0104] δ * r = {ψ "r -a 11 · ψ'r-a 12 · Vy-b f1 · θ} / b r1 ... (46) Thus, wheel steering angle obtained after the target [delta] * r is , The limiter processing (δ is set so that its absolute value does not exceed the maximum rear wheel steering angle δr _max.
* r> δr _max → δ * r = δr _max ), the target rear wheel steering angle δ * r is matched with the actual rear wheel steering angle δ _R detected by the rear wheel steering angle sensor 16. The controller 13 drives the hydraulic cylinder 15 via the switching valve 17.

Simulation results in the case where the rear wheel steering angle is determined by such control are shown in FIGS.

FIG. 6 is a graph showing the relationship between the maximum value of the target steady-state yaw rate ψ'r (the maximum allowable yaw rate in the figure) in consideration of the lateral speed and the target steady-state yaw rate ψ'r to which the lateral acceleration is limited, and the vehicle speed. And the limit value of lateral acceleration is 0.2G,
Those shown as 0.3G, 0.4G and 0.5G are shown respectively.

In the case of the target steady-state yaw rate ψ'r in which only the lateral velocity is taken into consideration as in the conventional example, in the low speed region of 80 km / h or less, the target steady-state yaw rate ψ'r is obtained as in the conventional example.
However, if the target steady-state yaw rate ψ'r is limited by the maximum lateral acceleration Gy _max determined according to the vehicle speed Vx and the road friction coefficient μ, the vehicle stability may be impaired in the low speed range. Target steady-state yaw rate ψ'r
It can be seen that it is possible to suppress an increase in the vehicle and to ensure the stability of the vehicle.

7 to 10 show the relationship between the allowable lateral velocity Vy _max , the target steady-state yaw rate ψ'r, and the vehicle speed when the lateral acceleration is limited in addition to the lateral velocity control. 7 and 8 show the case where the allowable lateral speed Vy _max is not limited, and FIGS. 9 and 10 show the allowable lateral speed Vy _max =
Each case is shown to be limited to 0.06 m / s.

In both cases, the limit value due to lateral acceleration = Gy _max / Vx is smaller than the target steady-state yaw rate ψ'r considering the lateral velocity in the low speed region, and the lateral velocity is higher in the high speed region of 80 km / h or more. Since the target steady-state yaw rate ψ'r considered is smaller, the target steady-state yaw rate ψ'r is switched from the lateral acceleration limit value to a value considering the lateral speed in step S23 in accordance with the increase of the predetermined vehicle speed. , While suppressing the increase of the target steady-state yaw rate ψ'r in the low speed range to ensure the stability of the vehicle, it is possible to suppress the steady vehicle slip angle in the high speed range and improve the transient vehicle behavior. You can do it.

Further, in FIG. 7, since the allowable lateral speed Vy _max is not limited, the lateral speed is increased in the high speed range as compared with the case where the restriction is applied as shown in FIG. 9, and as a result, the target steady-state yaw rate in the high speed range is increased. ψ'r has a lower value when the allowable lateral speed is restricted as shown in FIG. 10, and the sideslip angle of the vehicle is restricted, resulting in a slight understeer tendency than that shown in FIG. It can be further improved.

As described above, the target steady-state yaw rate set in consideration of the magnitude of the steady-state lateral speed is limited by the lateral acceleration, thereby suppressing an excessive increase in the target steady-state yaw rate ψ'r in the low speed range. It is possible to suppress the steady increase in the vehicle slip angle and improve the transient vehicle behavior immediately after the start of steering, while ensuring the stability of the target steady yaw rate ψ The limit value of'r is the maximum lateral acceleration Gy _max determined by the vehicle speed Vx and the road surface friction coefficient μ, or the cornering power K.
By setting based on the maximum lateral acceleration equivalent value Gys _max determined from the road surface friction coefficient μ estimated from f and Kr, or the lateral acceleration Gy generated in the vehicle, the target steady-state yaw rate ψ'r can be set to the vehicle speed Vx and the road surface condition. It is possible to reliably ensure the stability of the vehicle without exceeding the corresponding turning limit.

The hydraulic cylinder 1 in the above embodiment.
Although not shown, 5 may be constituted by a driving means such as an electric motor.

[0113]

As described above, according to the first aspect of the present invention, the steady lateral speed generated when the target steady yaw rate set from the steering angle and the vehicle speed detection value is realized is calculated as the cornering power estimated value, the steering angle, and the steering angle. The target steady-state yaw rate is reset after making predictions using the vehicle speed detection value and considering the magnitude of this steady-state lateral speed, and the transient characteristics are taken into consideration in the target steady-state yaw rate ψ'r _n by this lateral speed control. While doing
The target steady-state yaw rate ψ'r _g based on the maximum lateral acceleration equivalent value determined according to the vehicle speed and the road surface friction coefficient is calculated, and the target steady-state yaw rate ψ'r _n by lateral speed control and the target steady-state yaw rate ψ'r with lateral acceleration limited. _Since the smaller of _g is set as the target yaw rate ψ'r, the target steady-state yaw rate ψ'r _g corresponding to the maximum lateral acceleration equivalent value is selected in the low-speed range of the vehicle, and the target yaw rate ψ'r increases excessively. Is suppressed, the stability of the vehicle can be improved as compared with the conventional example, the steady vehicle slip angle can be suppressed, and the transient vehicle behavior can be improved.

The second aspect of the invention is that the target steady-state yaw rate ψ'r at which the vehicle can turn according to the friction coefficient μ of the road surface and the vehicle speed.
_g is calculated and the target yaw rate ψ'in the low speed range of the vehicle is calculated.
Since r does not exceed the turning limit of the vehicle, the stability of the vehicle can be secured.

Further, in the third aspect of the invention, the road surface friction coefficient calculating means calculates the road surface friction coefficient from the cornering power estimated value, so that the maximum lateral acceleration equivalent value according to the turning limit of the vehicle is calculated from this friction coefficient. It is possible to obtain the value quickly and reliably, suppress the increase of the target steady-state yaw rate ψ′r _g in the low speed range, and improve the stability of the vehicle.

According to a fourth aspect of the present invention, the maximum lateral acceleration equivalent value calculating means changes the braking force obtained from the deceleration of the vehicle based on the detected value of the vehicle speed and the friction circle peculiar to the tire mounted on the vehicle to the tire. The maximum lateral acceleration equivalent value capable of turning can be calculated from the generated lateral force, and the target steady-state yaw rate ψ'r _g falls within the turning limit of the vehicle, and the stability of the vehicle can be improved.

In the fifth aspect of the present invention, the target steady-state yaw rate ψ'r _n is calculated after limiting the lateral speed so as not to exceed the allowable value that gives a predetermined vehicle slip angle. The target steady-state yaw rate ψ′r _n based on the lateral speed control selected by the means has its value reduced, and the transient behavior of the vehicle can be improved while ensuring the stability of the vehicle in the high speed range.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a four-wheel steering vehicle showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram similarly showing the arrangement of each sensor.

FIG. 3 is a flowchart showing an example of control similarly performed by the controller.

FIG. 4 is a flowchart for similarly calculating a target steady yaw rate.

FIG. 5 is a schematic view showing a friction circle of a tire.

FIG. 6 is a graph showing a relationship between a target steady-state yaw rate ψ′r due to maximum lateral acceleration or lateral speed limitation and a vehicle speed.

FIG. 7 is a graph showing a relationship between an allowable lateral speed and a vehicle speed when the lateral speed is not limited.

FIG. 8 is a dashed line showing the relationship between the vehicle speed and the target steady-state yaw rate ψ′r when the lateral speed is not limited and the maximum steady-state yaw rate ψ′r due to the maximum lateral acceleration limitation.
7 is a graph showing the result of selecting the target steady-state yaw rate ψ′r according to the present embodiment by a solid line.

FIG. 9 is a graph showing the relationship between the allowable lateral speed and the vehicle speed when the lateral speed is limited.

FIG. 10 is a broken line showing the relationship between the vehicle speed and the target steady-state yaw rate ψ'r when the lateral speed is restricted and the maximum steady-state yaw rate ψ'r due to the maximum lateral acceleration restriction.
7 is a graph showing the result of selecting the target steady-state yaw rate ψ′r according to the present embodiment by a solid line.

FIG. 11 is a claim correspondence diagram corresponding to the first invention.

FIG. 12 is a claim correspondence diagram corresponding to the second or third invention.

[Explanation of symbols]

 1 Steering angle sensor 2 Vehicle speed sensor 7a to 7c Pressure sensor 13 Controller 15 Hydraulic cylinder 16 Rear wheel steering angle sensor 17 Pressure control valve a Steering angle detecting means b Vehicle speed detecting means c Cornering power estimation value calculating means d Auxiliary steering means e Target yaw rate Calculation means f Target auxiliary steering angle calculation means g Auxiliary steering control means h Steady lateral speed calculation means i Target steady yaw rate setting means j Maximum lateral acceleration equivalent value calculation means k Comparison setting means j11 Road surface friction coefficient calculation means j22 Lateral acceleration calculation means j2 Lateral acceleration allowable value calculation means

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Claims (5)

[Claims] 1. A steering angle detecting means for detecting a steering angle θ of a vehicle, a vehicle speed detecting means for detecting a vehicle speed Vx in the longitudinal direction of the vehicle, and an estimated cornering power value for calculating an estimated cornering power value of each wheel of the vehicle. Calculation means, auxiliary steering means capable of assisting steering of at least one of the front wheels and the rear wheels, and a target for calculating the steady-state value ψ'r ₀ of the target yaw rate and the target yaw rate ψ'r considering the transient characteristics. A yaw rate calculation means, and a target auxiliary steering angle calculation means for calculating an auxiliary steering angle δr required to realize the target yaw rate ψ′r from the steering angle detection value θ, the vehicle speed detection value Vx, and the cornering power estimation value. And an auxiliary steering angle control device that includes an auxiliary steering control unit that controls the steering angle of the auxiliary steering unit to match the target auxiliary steering angle δr. A steady value ψ′r ₀ of the target yaw rate is realized. Steady-state lateral velocity Vy ₀ which is generated in the case of a constant steady-state lateral velocity Vy ₀ , and a steady-state lateral yaw rate ψ′r _n that is variable according to the steering angle θ, the vehicle speed Vx and the steady-state lateral velocity Vy ₀ Means, a maximum lateral acceleration equivalent value calculating means for calculating a target steady yaw rate ψ′r _g from a maximum lateral acceleration equivalent value that can be produced by the road surface according to the vehicle speed detection value, and a steady yaw rate corresponding to the maximum lateral acceleration equivalent value. ψ′r _g and the target steady-state yaw rate ψ′r _n set by the target steady-state yaw rate setting means.
And a comparison setting means for setting the smaller one as the target steady-state yaw rate ψ'r, and the target auxiliary steering angle calculation means is configured to assist the target steady-state yaw rate ψ'r based on the target steady-state yaw rate ψ'r set by the comparison setting means. An auxiliary steering angle control device characterized by calculating a steering angle δr. 2. The maximum acceleration equivalent value calculating means calculates a maximum lateral acceleration equivalent value at which the vehicle can turn from the road surface friction coefficient calculating means for calculating a road surface friction coefficient μ and the vehicle speed and the road surface friction coefficient μ. The auxiliary steering angle control device according to claim 1, wherein the auxiliary steering angle control device comprises: 3. The auxiliary steering angle control device according to claim 2, wherein the road surface friction coefficient calculation means calculates a road surface friction coefficient from the cornering power estimated value. 4. The maximum lateral acceleration equivalent value calculating means detects longitudinal deceleration of the vehicle based on the detected value of the vehicle speed, and a maximum lateral acceleration corresponding to the deceleration from a friction circle of a tire. The auxiliary rudder angle control device according to claim 1, further comprising: means for calculating a corresponding value. 5. The constant lateral speed calculating means calculates a lateral speed allowable value for calculating a lateral speed allowable value such that a predetermined vehicle slip angle is obtained, and the steady lateral speed does not exceed the allowable lateral speed. The auxiliary steering angle control device according to any one of claims 1 to 4, further comprising a lateral speed regulating means for regulating.