JP2001213342A - Steering system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering system for a vehicle capable of stabilizing the behavior of the vehicle when a friction coefficient between a road surface and a wheel is lowered in the vehicle adopting a steer-by wire system. SOLUTION: The motion of a steering actuator M is transmitted to wheels 34 so as to change a steering angle according to the motion of the steering actuator M without mechanically connecting an operating member 1 to the wheels 4. A target yaw rate corresponding to the detected operating quantity of the operating member 1 is computed, and the steering actuator M is controlled so that the steering angle corresponds to the target steering angle corresponding to the deviation between the computed target yaw rate and the detected yaw rate. At least one of the braking force of the wheels 4 and the driving force of the wheels 4 is controlled to reduce the deviation between the computed target yaw rate and the detected yaw rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vehicle steering system employing a so-called steer-by-wire system.

[0002]

2. Description of the Related Art In a vehicle steering system employing a steer-by-wire system, the movement of a steering actuator in accordance with the operation of an operating member simulating a steering wheel is controlled without mechanically connecting the operating member to wheels. ,
The steering angle is transmitted to the wheels so as to change. In a vehicle employing such a steer-by-wire system, a target yaw rate corresponding to the operation amount of the operation member is calculated so that the vehicle behavior is stabilized, and the steering yaw rate is adjusted so that the actual yaw rate matches the target yaw rate. It has been proposed to control an actuator.

[0003]

When the friction coefficient between the road surface and the wheels decreases, the vehicle yaw rate becomes saturated without reaching the target yaw rate, and the behavior of the vehicle follows the operation of the operation member. Otherwise, the driver may feel uneasy, and the steering angle may diverge, leading to unstable vehicle behavior.

[0004] It is an object of the present invention to provide a vehicle steering system that can solve the above-mentioned problems.

[0005]

According to the present invention, there is provided a steering apparatus for a vehicle, comprising an operating member, a steering actuator driven in accordance with an operation of the operating member, and mechanically connecting the operating member to wheels. Without, so that the steering angle changes according to the movement of the steering actuator, means for transmitting the movement to the wheels, means for detecting the operation amount of the operating member, means for detecting the yaw rate of the vehicle, Means for calculating a target yaw rate corresponding to the detected operation amount of the operation member based on the stored relationship between the operation amount and the target yaw rate; and a means for calculating a target yaw rate according to a deviation between the calculated target yaw rate and the detected yaw rate. Means for calculating the target rudder angle based on the stored relationship between the deviation and the target rudder angle;
The steering angle corresponds to the calculated target steering angle,
Means for controlling the steering actuator, and means for controlling at least one of the braking force of the wheels and the driving force of the wheels so as to reduce the deviation between the calculated target yaw rate and the detected yaw rate. It is characterized by. According to the configuration of the present invention, when the yaw rate of the vehicle does not change due to a decrease in the friction coefficient between the road surface and the wheels even when the operation member is operated, the target yaw rate corresponding to the operation amount of the operation member is the detected vehicle yaw rate. It will be larger than the actual yaw rate. In this case, the deviation between the target yaw rate and the detected yaw rate is reduced by controlling at least one of the braking force of the wheels and the driving force of the wheels, and the divergence of the steering angle is prevented to stabilize the vehicle behavior. Can be planned.

There are provided means for calculating a time integrated value of a deviation between the calculated target yaw rate and the detected yaw rate for a set time, and means for determining whether or not the time integrated value has exceeded a set value. Only when the time integration value exceeds the set value, at least one of the braking force of the wheel and the driving force of the wheel is controlled so as to reduce the deviation between the calculated target yaw rate and the detected yaw rate. preferable. This eliminates the need for unnecessary control when the deviation between the target yaw rate and the detected yaw rate is small and does not affect the vehicle behavior.

Means for judging the steering direction, means for detecting the braking pressure of each wheel, means for detecting the wheel rotational speed of each wheel, and when the time integration value exceeds a set value, the steering direction and each Based on the stored relationship between the wheel braking pressure and the wheel rotation speed of each wheel, the braking force of each wheel is controlled according to the determined steering direction and the detected braking pressure and wheel rotation speed of each wheel. Means, and by controlling the braking force,
At the time of right steering, the wheel rotation speed of the left wheel is made larger than that of the right wheel so that a yaw moment for turning the vehicle to the right is generated. It is preferable that the wheel rotation speed of the right wheel be higher than that of the wheel. This allows
The deviation between the target yaw rate and the detected yaw rate can be reduced by simple control.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a vehicle steering apparatus shown in FIG. 1, a movement of a steering actuator M driven in response to a rotation operation of a steering wheel (operation member) 1 is controlled by mechanically moving the steering wheel 1 to a wheel 4. The steering wheel 3 transmits the steering angle to the front left and right wheels 4 without changing the steering angle.

The steering actuator M can be constituted by an electric motor such as a known brushless motor. The steering gear 3 has a motion conversion mechanism that converts the rotational motion of the output shaft of the steering actuator M into a linear motion of the steering rod 7. The movement of the steering rod 7 is transmitted to the wheel 4 via the tie rod 8 and the knuckle arm 9. The steering gear 3 can use a known gear, and the configuration is not limited as long as the steering angle can be changed by the movement of the steering actuator M. For example, a nut that is rotationally driven by an output shaft of the steering actuator M, And a screw shaft integrated with the steering rod 7. Note that, when the steering actuator M is not driven, the wheel alignment is set so that the wheels 4 can return to the straight steering position by the self-aligning torque.

The steering wheel 1 is connected to a rotating shaft 10 rotatably supported by the vehicle body. In order to apply an operation reaction force required to operate the steering wheel 1, the rotating shaft 10
An operation actuator R for applying a torque to the motor is provided. The operating actuator R can be constituted by an electric motor such as a brushless motor having an output shaft integrated with the rotating shaft 10, for example.

An elastic member 30 is provided for giving elasticity in a direction for returning the steering wheel 1 to a straight steering position. The elastic member 30 can be constituted by, for example, a spring that gives elasticity to the rotating shaft 10. When the operating actuator R does not apply torque to the rotary shaft 10, the steering wheel 1 returns to the straight steering position due to its elasticity.

An angle sensor 11 for detecting an operation angle corresponding to a rotation angle of the rotary shaft 10 as an operation amount of the steering wheel 1 is provided. A torque sensor 12 for detecting an operation torque of the steering wheel 1 is provided. The steering direction can be determined from the sign of the torque detected by the torque sensor 12.

A steering angle sensor 13 for detecting an operation amount of the steering rod 7 is provided as a steering angle of the vehicle. The steering angle sensor 13 can be constituted by a potentiometer.

The angle sensor 11, the torque sensor 12 and the steering angle sensor 13 are connected to a steering system control device 20 constituted by a computer. A yaw rate sensor 16 for detecting the yaw rate of the vehicle and a speed sensor 14 for detecting the vehicle speed are connected to the control device 20. The control device 20 controls the steering actuator M and the operation actuator R via the drive circuits 22 and 23.
Control.

A hydraulic braking system for braking the front, rear, left and right wheels 4 of the vehicle is provided. In the braking system, a master cylinder 52 generates a braking pressure according to the depression force of a brake pedal 51. The braking pressure is amplified by the braking pressure control unit B and distributed to the brake devices 54 of the wheels 4, and the brake devices 54 apply a braking force to the wheels 4. The braking pressure control unit B
Is a traveling system control device 6 configured by a computer.
Connected to 0. The traveling system control device 60 includes a steering system control device 20, a braking pressure sensor 61 for individually detecting the braking pressure of each wheel 4, and a wheel rotation speed sensor 62 for individually detecting the rotation speed of each wheel 4. Is connected. The traveling system control device 60 amplifies and distributes the braking pressure according to the rotation speed of each wheel 4 detected by the wheel rotation speed sensor 62 and the feedback value from the braking pressure sensor 61. The pressure control unit B is controlled. Thereby, it is possible to individually control the braking force of each of the front, rear, left and right wheels 4. The braking pressure control unit B can generate a braking pressure corresponding to a signal from the traveling system control device 60 by a built-in pump even when the brake pedal 51 is not operated.

The travel system controller 60 is connected to an actuator E for driving a throttle valve of an engine for generating power for the travel system of the vehicle. When the actuator E is driven by a signal from the traveling system control device 60 to change the opening of the throttle valve, the engine output,
Consequently, the driving force of each wheel 4 can be controlled.

FIG. 2 is a control block diagram of the steering device. The symbols in the control block diagram are as follows. δh: operating angle δ: steering angle δ ^* : target steering angle Th: operating torque Th ^* : target operating torque γ: yaw rate γ ^* : target yaw rate V: vehicle speed ω1, ω2, ω3, ω4: wheel rotation speed im ^* : steering Drive current of actuator M for operation ih ^* : target drive current of actuator R for operation ie ^* : target drive current of actuator E for driving throttle valve P1, P2, P3, P4: braking pressure ΔP1, ΔP2, ΔP3, ΔP4: instruction Braking pressure

K1 is a gain of the target yaw rate γ ^* with respect to the operation angle δh of the steering wheel 1,
The control device 20 calculates the target yaw rate γ ^* from the stored relationship of γ ^* = K1 · δh and the operation angle δh detected by the angle sensor 11. That is, the control device 20, predetermined relationship stored gain K1 representing the, calculates the target yaw rate gamma ^* corresponding to the detected operating angle δh on the basis of the relationship between its operating angle δh and the target yaw rate gamma ^* I do.

K2 is the gain of the target operation torque Th ^{* with} respect to the operation angle δh, and the target operation torque Th ^* is calculated from the relationship of Th ^* = K2 · δh and the operation angle δh detected by the angle sensor 11. That is, the control device 20
Stores a gain K2 representing a predetermined relationship between the target operation torque Th ^* and the operation angle δh, and stores the target operation torque Th ^* based on the relationship and the detected operation angle δh ^.
Is calculated. K2 is adjusted so as to perform optimal control. Note that the operation torque Th is used in place of the operation angle δh, the relationship between the target operation torque Th ^* and the operation torque Th is determined and stored in advance, and the target operation torque Th ^* is calculated from the relationship and the operation torque Th. It may be.

G1 is the target yaw rate γ^* And vehicle 100
Target steering angle δ for deviation from yaw rate γ^* Communication
The control device 20 stores the stored δ^* = G1 · (γ^* 
−γ) and the calculated target yaw rate γ^* And yaw
Target from yaw rate γ detected by rate sensor 16
Steering angle δ^* Is calculated. The transfer function G1 is, for example, PI
When performing control, the gain is Ka, the Laplace operator is s,
Assuming that the time constant is Ta, G1 = Ka [1 + 1 / (Ta ·
s)]. The gain Ka and the time constant Ta are optimal.
It is adjusted so that control can be performed. That is, the control device 2
0 is the deviation (γ ^* −γ) and target steering angle δ^* Between
A transfer function G1 representing a predetermined relationship is stored, and
Based on the relationship (γ^* −γ)
Angle δ^* Is calculated. In the present embodiment, the gain Ka is
It is a function of the vehicle speed V and is used to secure stability at high vehicle speeds.
The gain Ka is set so as to decrease as the speed V increases.
You.

G2 is a transfer function of a target drive current im ^* of the steering actuator M with respect to a deviation between the target steering angle δ ^* and the steering angle δ, and the control device 20 stores im = G2 ·
(Δ ^* −δ), the calculated target steering angle δ ^*, and the steering angle δ detected by the steering angle sensor 13, the target drive current i
Calculate m ^* . For example, when PI control is performed, the transfer function G2 is G2 = Kb [1 + 1 / (Tb · s)], where Kb is a gain, s is a Laplace operator, and Tb is a time constant.
become. The gain Kb and the time constant Tb are adjusted so that optimal control can be performed. That is, the control device 20
A transfer function G2 representing a predetermined relationship between the deviation (δ ^* −δ) and the target drive current im ^* is stored, and a target corresponding to the deviation (δ ^* −δ) calculated based on the relationship is stored. The driving current im ^* is calculated.

G3 is a transfer function of the target drive current ih ^* of the operation actuator R with respect to the deviation between the target operation torque Th ^* and the operation torque Th, and the control device 20 stores ih ^* = G3 · (Th ^* − Th), the calculated target operation torque Th ^*, and the operation torque Th detected by the torque sensor 12 to calculate the target drive current ih ^* . For example, when performing PI control, the transfer function G3 indicates a gain Kc, a Laplace operator s, and a time constant Tc.
G3 = Kc [1 + 1 / (Tc · s)].
The gain Kc and the time constant Tc are adjusted so as to perform optimal control. That is, the control device 20 stores a transfer function G3 representing a predetermined relationship between a deviation obtained by subtracting the detected operation torque Th from the target operation torque Th ^* and the target drive current ih ^*, and based on the relationship, The calculated target operation torque Th ^* and the detected operation torque Th
And the target drive current ih ^* corresponding to The operation actuator R is driven according to the target drive current ih ^* .

F1 is the target yaw rate γ ^* calculated according to the operation amount of the steering wheel 1 and the vehicle 10
Command braking pressures ΔP1, ΔP2, ΔP3 to the front, rear, left and right wheels 4 according to the deviation (γ ^* −γ) from the yaw rate γ of 0
This is a calculation unit for ΔP4. In the calculation unit F1, the deviation (γ ^* −) between the target yaw rate γ ^* and the yaw rate γ
Calculates the time integral value at the set time of γ), determines whether the time integrated value exceeds the stored set value, and if it exceeds the set value, reduces the deviation (γ ^* −γ) Preferably, the instructed braking pressure ΔP1 of each wheel 4 is set so that the canceling yaw moment is generated by the braking force control of each wheel 4.
Calculate ΔP2, ΔP3, ΔP4. That is, the braking pressure of the right wheel is made larger than that of the left wheel so that a yaw moment for turning the vehicle 100 to the right is generated during right steering, and a yaw moment for turning the vehicle 100 to the left is generated during left steering. Thus, the commanded braking pressures ΔP1 and ΔP
2, ΔP3 and ΔP4 are calculated. Each command braking pressure ΔP
1, ΔP2, ΔP3, ΔP4 are obtained as deviations from the braking pressures P1, P2, P3, P4 detected by the braking pressure sensor 61. That is, the control device 60 stores the relationship between the steering direction, the braking pressure of each wheel 4, and the wheel rotation speed of each wheel 4, and stores the relationship between the stored relationship and the operation torque Th detected by the torque sensor 12. The steering direction determined from the sign and the braking pressure P detected by the braking pressure sensor 61
From P1, P2, P3, and P4 and the wheel rotation speeds ω1, ω2, ω3, and ω4 detected by the wheel rotation speed sensor 62, command braking pressures ΔP1, ΔP2, ΔP3, and ΔP4 are calculated.

G4 is the target yaw rate γ ^* set according to the operation amount of the steering wheel 1 and the vehicle 10
Target drive current ie of the throttle valve drive actuator E with respect to a deviation (γ ^* −γ) from the yaw rate γ of 0
^{* Is} the transfer function. That is, ie ^* = G4 · (γ ^*
−γ), the calculated target yaw rate γ ^*, and the detected yaw rate γ, the target drive current ie ^* is obtained. The transfer function G4 is, for example, when performing PI control,
Assuming that the gain is Ke, the Laplace operator is s, and the time constant is Te, G4 = Ke [1 + 1 / (Te · s)]. The gain Ke and the time constant Te are adjusted so as to perform optimal control. That is, the control device 60 determines the deviation (γ ^*
-Γ) and a transfer function G4 representing a predetermined relationship between the target drive current ie ^* and a target corresponding to a deviation between the calculated target yaw rate γ ^* and the detected yaw rate γ based on the relationship. The drive current ie ^* is calculated. The actuator E for driving the throttle valve is driven by a signal corresponding to the target drive current ie ^* . As a result, the deviation between the target yaw rate γ ^* and the yaw rate γ (γ ^* −
When the deviation (γ ^* −γ) increases so as to reduce γ), control is performed so that the output of the engine for generating power to the traveling system of the vehicle 100 and, consequently, the driving force of the corresponding wheels 4 increase.

The control procedure of the steering device will be described with reference to the flowchart of FIG. First, each of the sensors 11 to 1
Operation angle δh and operation torque T by 4, 16, 61 and 62
h, steering angle δ, vehicle speed V, yaw rate γ, braking pressures P1, P
2, P3, P4, wheel rotation speeds ω1, ω2, ω3, ω4
Is read (step 1). Next, based on the transfer function G3, the operation is performed according to the deviation so that the deviation obtained by subtracting the operation torque Th from the target operation torque Th ^* obtained based on the gain K2 according to the detected operation angle δh becomes zero. The target drive current ih ^* of the actuator R is obtained (step 2). The operation actuator R is controlled by applying the target drive current ih ^* . Next, a target yaw rate γ ^* is obtained based on the gain K1 according to the operation angle δh (step 3). The deviation between the target yaw rate γ ^* and the detected yaw rate γ is calculated (step 4). The deviation and the transfer function G1
The target steering angle δ ^* is calculated according to (step 5).
Based on the transfer function G2, the target drive current im ^* of the steering actuator M is obtained based on the transfer function G2 so that the deviation obtained by subtracting the steering angle δ from the target steering angle δ ^* becomes zero (step 6). By applying the target drive current im ^* , the steering actuator M is controlled so as to cause a change in the steering angle. Next, the integral value Iγ of the deviation (γ ^* −γ) between the target yaw rate γ ^* and the detected yaw rate γ during the set time Δt is calculated (step 7), and the integral value Iγ exceeds the set value α. Is determined (step 8). The set time Δt and the set value α may be set in advance to appropriate values by experiments. Note that the integrated value Iγ is set to the initial value of zero until the set time Δt elapses from the start of the control. If the integrated value Iγ is equal to or smaller than the set value α, the process returns to step 1. When the integral value Iγ exceeds the set value α, the yaw moment for reducing the deviation (γ ^* −γ) between the target yaw rate γ ^* and the yaw rate γ is generated by controlling the braking force of each wheel 4. Of the command braking pressures ΔP1, ΔP2, ΔP3, and ΔP4 are calculated (step 9). The calculated instruction braking pressures ΔP1, ΔP
2, the braking force of each wheel 4 is controlled by the braking pressure control unit B changing the braking force of the wheel 4 according to ΔP3 and ΔP4. Next, the target drive current ie ^{* of the} throttle valve drive actuator E is obtained based on the transfer function G4 according to the deviation (γ ^* −γ) between the target yaw rate γ ^* and the yaw rate γ (step 10). When the target drive current ie ^* is applied, the throttle valve driving actuator E changes the opening degree of the throttle valve so that the deviation (γ ^* −γ) is reduced by a change in engine output. The driving force of each wheel 4 is controlled. Next, it is determined whether or not to end the control (step 11). If not, the process returns to step 1. The end determination can be made based on, for example, whether or not the key switch for starting the vehicle is on.

According to the above configuration, if the yaw rate of the vehicle 100 does not change due to a decrease in the coefficient of friction between the road surface and the wheels 4 even when the steering wheel 1 is operated, the target yaw rate corresponding to the operation amount of the steering wheel 1 γ
^* Becomes larger than the actual yaw rate γ of the detected vehicle. In this case, the deviation (γ ^* −γ) between the target yaw rate γ ^* and the detected yaw rate γ is reduced by controlling the braking force and the driving force of the wheels 4, preventing the divergence of the steering angle and stabilizing the vehicle behavior. Can be achieved. Further, the braking force and the driving force of the wheel 4 are controlled only when the time integral Iγ of the deviation between the target yaw rate γ ^* and the detected yaw rate γ during the set time Δt exceeds the set value, so that the target yaw rate γ ^* When the deviation between the detected yaw rate γ and the detected yaw rate γ is small and does not affect the vehicle behavior, unnecessary control need not be performed. Further, according to the above configuration, the deviation between the target yaw rate γ ^* and the detected yaw rate γ can be reduced by simple control. FIG. 4 is an example showing the time change of the target yaw rate γ ^* and the detected yaw rate γ. According to the present invention, the hatched portions in the figure can be reduced and eliminated.

The present invention is not limited to the above embodiment. For example, it is assumed that the operation torque Th corresponds to the operation amount instead of the operation angle δh, and the operation torque Th and the target yaw rate γ ^*
May be determined and stored in advance, and a target yaw rate γ ^* corresponding to the detected operation torque Th may be calculated based on the relationship. Further, only the braking force or only the driving force of each wheel may be controlled so as to reduce the deviation between the target yaw rate γ ^* and the detected yaw rate γ.

[0028]

According to the present invention, in a vehicle employing a steer-by-wire system, when the coefficient of friction between the road surface and the wheels is reduced, the vehicle behavior can be effectively stabilized. A steering device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view of a steering device according to an embodiment of the present invention.

FIG. 2 is a control block diagram of the steering device according to the embodiment of the present invention.

FIG. 3 is a flowchart showing a control procedure of the steering device according to the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a temporal change of a target yaw rate and a detected yaw rate of a vehicle

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 3 Steering gear 4 Wheel 11 Angle sensor 13 Steering angle sensor 16 Yaw rate sensor 20 Steering system control unit 60 Running system control unit 100 Vehicle B Braking pressure control unit E Throttle valve drive actuator M Steering actuator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B62D 101: 00 B62D 101: 00 105: 00 105: 00 113: 00 113: 00 119: 00 119: 00 137: 00 137: 00 (72) Inventor Masaya Segawa 3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka Inside Koyo Seiko Co., Ltd. (72) Inventor Shiro Nakano 3-5-minamisenba, Chuo-ku, Osaka-shi, Osaka No. 8 F-term in Koyo Seiko Co., Ltd. (Reference) 3D032 CC05 DA03 DA04 DA15 DA29 DC01 DD02 FF01 3D033 CA16 CA18 CA20 CA28 CA29 CA31 3D045 BB40 EE21 GG25 GG26 GG28 3D046 BB21 BB23 GG02 GG10 HH08 HH13 H09 DB03 DB23 EA09 EB04 EC01 EC04 FA04 FA11

Claims (3)

[Claims] An operating member, a steering actuator driven in accordance with the operation of the operating member, and a steering angle corresponding to the movement of the steering actuator without mechanically connecting the operating member to wheels. , Means for transmitting the movement to the wheels, means for detecting the operation amount of the operation member, means for detecting the yaw rate of the vehicle, and a target yaw rate corresponding to the operation amount of the detected operation member. To
Means for calculating based on the stored relationship between the manipulated variable and the target yaw rate; and a target steering angle corresponding to the deviation between the calculated target yaw rate and the detected yaw rate, and calculating the target steering angle between the deviation and the target yaw rate. Means for calculating based on the stored relationship; means for controlling the steering actuator such that the steering angle corresponds to the calculated target steering angle; and a deviation between the calculated target yaw rate and the detected yaw rate. Means for controlling at least one of the braking force of the wheel and the driving force of the wheel so as to reduce the force. Means for calculating a time integrated value of a deviation between the calculated target yaw rate and the detected yaw rate for a set time; and means for determining whether or not the time integrated value exceeds a set value. Only when the time integrated value exceeds the set value, at least one of the wheel braking force and the wheel driving force is controlled so as to reduce the deviation between the calculated target yaw rate and the detected yaw rate. Claim 1
The vehicle steering system according to claim 1. 3. A means for judging a steering direction, a means for detecting a braking pressure of each wheel, a means for detecting a wheel rotation speed of each wheel, and a method for detecting a steering direction when a time integral value thereof exceeds a set value. Based on the stored relationship between the braking pressure of each wheel and the wheel rotation speed of each wheel, the braking force of each wheel is determined according to the determined steering direction and the detected braking pressure and wheel rotation speed of each wheel. Control means, and by controlling the braking force,
At the time of right steering, the wheel rotation speed of the left wheel is made larger than that of the right wheel so that a yaw moment for turning the vehicle to the right is generated. 3. The vehicle steering system according to claim 2, wherein the wheel rotation speed of the right wheel is higher than that of the wheel.