JPH11105689A - Steering characteristic control device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optimum steering characteristic control regardless of a road surface condition, by deciding a steering characteristic based on the comparison result between a first condition quantity based on a deviation of an actual/target yaw rate and a second condition quantity based on cross acceleration, and controlling brake force based on this decision result. SOLUTION: In a microcomputer 52 of an electric control device 50, a signal showing a yaw rate is input from a yaw rate sensor 60. A target yaw rate γt, deviation E between the target yaw rate γt and an actual yaw rate γ, and a condition quantity Y based on the deviation E, are calculated, an operating characteristic of a vehicle is discriminated from the condition quantity Y. Further in a CPU of the microcomputer 52, a condition quantity stabilizing the operating characteristic of the vehicle is calculated, brake force of each vehicle is controlled. Here, a control signal is output to control valves 40FL to 40RR in a hydraulic control device, opening/closing valves 44FL to 44RR of a control wheel, and opening/closing valves 46FL to 46RR, wheel cylinders 38FL to 38RR are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering characteristic control device for ensuring steering stability when the vehicle turns (steering).

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open Publication No. Hei 8-310360, for example, a steering characteristic control technique for turning a vehicle includes an actual yaw rate (hereinafter, referred to as an actual yaw rate) of the vehicle when turning. Based on the deviation from the target yaw rate, which is the target value, the steering characteristic (understeer or oversteer) of the vehicle is estimated, and the actual yaw rate is controlled by controlling the difference in the braking force of each wheel according to the characteristic. The vehicle is configured to follow the yaw rate to improve the steerability of the vehicle when turning.

[0003] The steering characteristics of a vehicle are controlled by a tire force defined by a frictional force between a tire and a road surface. Therefore, a low μ road where the tire force is limited to a small value (that is, a road surface with a small friction coefficient μ where the lateral acceleration Gy is limited to a small value).
In this case, since the steering characteristics of the vehicle tend to be unstable, it is necessary to start the control early. On the other hand, on a high μ road where the tire force increases (that is, the friction coefficient μ where the lateral acceleration Gy increases).
In the case of a road surface with a large road), it is preferable to refrain from controlling the vehicle near the limit of the tire force because a natural driving feeling can be obtained.

[0004]

However, the conventional steering characteristic control device as described in the above-mentioned publication is
Control is performed when the deviation between the actual yaw rate and the target yaw rate becomes larger than a predetermined value, regardless of the friction coefficient μ between the tire of the vehicle and the road surface at the time of turning (that is, regardless of the lateral acceleration), In addition, since the predetermined value is set so as not to be inadvertently controlled on a road surface having a high friction coefficient μ, the setting value is too large on a road surface having a low friction coefficient μ, and the control start is delayed. was there.

Accordingly, the present invention has been made in view of the above-described problems in the conventional steering characteristic control device, and has a controllability of the steering characteristic at an optimum timing irrespective of the road surface condition. It is an object of the present invention to provide a vehicle steering characteristic control device that is excellent in control and that optimally controls the steering characteristic of the vehicle.

[0006]

A vehicle steering characteristic control apparatus according to the present invention includes a yaw rate detecting means for detecting an actual yaw rate of a vehicle, and a target yaw rate for calculating a target yaw rate of the vehicle based on a speed and a steering angle of the vehicle. Arithmetic means;
State quantity calculating means for calculating a first state quantity based on a deviation between the actual yaw rate and the target yaw rate, and calculating a second state quantity based on a lateral acceleration of the vehicle; A steering characteristic determining unit that determines a steering characteristic of the vehicle based on a comparison result of the second state quantity; and a braking force control unit that controls a braking force of a wheel based on a determination result of the steering characteristic determining unit. Prepare.

The state quantity calculating means calculates a second state quantity based on a state quantity characteristic in which the absolute value of the value on the high lateral acceleration side is larger than that on the low lateral acceleration side.

[0008] The state quantity characteristics are provided for starting and ending the steering characteristic control of the vehicle, respectively.

Further, the state quantity characteristic is provided for each of the case where the steering characteristic of the vehicle is oversteer and the case where the vehicle is understeer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. FIG. 1 is a configuration diagram schematically showing a configuration of a vehicle steering characteristic control device according to Embodiment 1 of the present invention. In the figure, a steering characteristic control device 10 includes a master cylinder 14. The master cylinder 14 is for pumping brake oil from the first and second ports in response to a driver's depressing operation of the brake pedal 12. The first port is connected to the brake hydraulic control device 1 for the left and right front wheels via the brake hydraulic control conduit 16 for the front wheels.
8 and 20, the second port is a brake hydraulic control conduit 2 for the rear wheels with a proportional valve 22.
4, a brake hydraulic control device 26 for the left and right rear wheels,
28.

The braking device 10 includes an oil pump 34.
Is provided. The oil pump 34 pumps up the brake oil stored in the reservoir 30 and supplies high-pressure brake oil to the hydraulic control devices 18, 20, 26, 28 of each brake via the high-pressure conduit 32. The high pressure conduit 32 has an accumulator 3 for buffering pressure.
6 are connected.

A hydraulic control device 18 for a brake for each wheel,
20, 26, 28 are wheel cylinders 38FL, 38FR, 38RL, 3 for supplying braking force to respective wheels.
8RR and electromagnetic control valves 40FL, 40FR, 40RL, 40
RR and normally open electromagnetic on-off valves 44FL, 44FR, 44R
L, 44RR, normally closed solenoid on-off valves 46FL, 46F
R, 46RL, 46RR (hereinafter referred to as 46FL to 46RR. 3
8, 40, 44, 46 and 48 described later).

The control valves 40FL-40RR are three-port two-position switching control valves for controlling the pressure of the brake oil supplied from the master cylinder 14 to each of the wheel cylinders 38FL-38RR. Normally open type on-off valve 4
The high pressure conduits 35FL-35RR connecting the 4FL-44RR and the normally closed on-off valves 46FL-46RR are connected to the connection conduits 48FL, 4FL.
The control valves 40FL to 40RR are connected via 8FR, 48RL, and 48RR.

A control valve 40FL of a three-port two-position switching type,
In the first position (the position shown), the front wheel brake hydraulic control conduit 16 and the wheel cylinder 38F
L, 38FR and wheel cylinder 38F
L, 38FR and connecting conduit 48FL, 48FR are cut off,
In a second position (not shown), the brake hydraulic control conduit 16 is disconnected from the wheel cylinders 38FL, 38FR and the wheel cylinders 38FL, 38FR are connected to the connecting conduit 4.
The system is switched so that 8FL and 48FR can communicate with each other.

Similarly, the control valves 40RL and 40RR connect the rear wheel brake hydraulic control conduit 24 and the wheel cylinders 38RL and 38RR in the first position and connect the wheel cylinders 38RL and 38RR to the connection conduit 48RL.
48RR, but in a second position (not shown), brake hydraulic control conduit 24 and wheel cylinder 38R.
L, 38RR and the wheel cylinder 38R
L, 38RR are connected to the connecting conduits 48RL, 48RR.

In the steering characteristic control device having such a structure, when the control valves (40FL to 40RR) are at the first position, the driver depresses the brake pedal 12 so that the pedaling force input to the master cylinder 14 is obtained. Is supplied from the wheel cylinders (38FL to 38RR).

On the other hand, when the control valves (40FL-40RR) are in the second position, the normally open / closed valves (44FL-44RR) corresponding to each control valve are opened and the normally closed valves are closed. Are closed (the state shown in the figure), the control valves (40FL-40RR) and the connecting conduit (48) are closed.
Wheel cylinder (38FL-38) via FL-48RR
RR) and the high-pressure conduit 32 are connected so that the pressure inside the wheel cylinders (38FL-38RR) is increased.

When the control valves 40FL to 40RR are in the second position, the on-off valves 44FL to 44RR and the on-off valves (46
When both FL-46RR) are closed, the wheel cylinders (38FL-3RR) are disconnected from both the high-pressure conduit 32 and the low-pressure conduit 42, so that the wheel cylinders (38FL-3RR) are closed.
8RR) Internal pressure is maintained.

When the on-off valves (44FL-44RR) corresponding to the control valves 40FL-40RR are closed and the on-off valves 46FL-46RR are opened, the wheel cylinder 38
Is connected to the low-pressure conduit 42 via the control valves 40FL to 40RR and the connection conduit, so that the wheel cylinder (38
FL-38RR) The internal pressure is reduced.

In the brake system having such a structure,
When the control valve (40FL-40RR) of the brake hydraulic control device (18, 20, 26, 28) is in the second position,
On-off valve (44FL-44RR) and on-off valve (46FL-46R)
By controlling the opening and closing of R), the braking state of each wheel can be individually controlled regardless of the amount of depression of the brake pedal 12.

Next, the control valves 40FL-40RR, the on-off valve 44
The opening / closing control system of FL-44RR and on-off valves 46FL-46RR will be described. The electric control device 50 includes these control valves 40FL-40RR and on-off valves 44FL-44RR, 46FL-4
To control the opening and closing of the 6RR, a microcomputer 52
And a drive circuit 54. Microcomputer 52
Is, for example, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM)
And an input / output port. These are connected to each other by a bidirectional common bus or the like.

The microcomputer 52 receives signals indicating the longitudinal acceleration Gx and the lateral acceleration Gy of the vehicle from a longitudinal acceleration sensor 56 and a lateral acceleration sensor 58 substantially attached to the center of gravity of the vehicle, and a yaw rate sensor 60. The signal γ indicating the yaw rate of the vehicle body, the signal indicating the steering angle δ of the steering angle sensor 62, the wheel speed sensors 64FL
A signal indicating the wheel speeds VFL to VRR of each wheel is input from 64RR, and a signal indicating the pressure Pm in the master cylinder 14 is input from the pressure sensor 66.

The ROM of the microcomputer 52 includes:
A program and a map for performing a series of controls are stored and held. Further, the CPU calculates a target yaw rate γt, a deviation E between the target yaw rate γt and the actual yaw rate γ, and a state amount Y based on the deviation E based on the parameters detected by the sensors, and calculates the steering amount of the vehicle based on the state amount Y. The characteristic (understeer, oversteer, or neutral steer) is determined. Further, the CPU calculates a state quantity for stabilizing the steering characteristics of the vehicle, and controls the braking force of each wheel to stabilize the steering characteristics of the vehicle.

FIG. 2 is a flowchart showing the control contents of the vehicle steering characteristic control device of the present invention. The illustrated control is started by closing an ignition switch (not shown), and is repeatedly executed at predetermined time intervals.

FIG. 3 is a characteristic diagram showing a relationship between the absolute value of the lateral acceleration Gy and each state quantity (YUS, YUE, YOS, YOE) for performing the control start determination and the control end determination. The values indicated by these characteristics have a form in which the absolute value increases as the lateral acceleration Gy increases, and the control is performed on a low μ road even if the deviation between the actual yaw rate and the target yaw rate is small. As described above, on a high μ road, control is performed after the deviation between the actual yaw rate and the target yaw rate has increased to some extent. In the characteristics shown here, the state quantities (YUS, YUE, YOS, YOE) are constant on the side where the absolute value of the lateral acceleration Gy is small and on the side where the absolute value of the lateral acceleration Gy is large. As long as the characteristic is such that the absolute value of the state quantity increases as a whole, the same control can be performed by using a characteristic other than the characteristic shown in FIG.

In addition, as these characteristics, map values corresponding to two types of steering characteristics for understeer control determination and oversteer control determination are shown in order to match the steering characteristics specific to the vehicle and the driver's preference. Have been. In FIG. 2, in step 10, the vehicle speed sensor 56
A signal indicating the vehicle speed V detected by the above is read.

In step 20, the CPU of the microcomputer 52 first calculates the target yaw rate γt,
Based on this, the deviation E between the target yaw rate γt and the actual yaw rate γ is obtained. The target yaw rate γt is γt = V * δ with respect to the stability factor Kh and the wheelbase L.
* (1 + Kh * V2) * L / (1 + T * s) (T is a time constant, s is a Laplace operator).

The deviation E between the target yaw rate γt and the actual yaw rate γ is calculated by E = (γt−γ) * SIGN (γ). Here, SIGN (γ) is a function that represents the sign of the argument γ as a function value, and when γ is a negative value, SIGN (γ)
= -1 and γ = 0, SIGN (γ) = 0, and if γ is a positive value, SIGN (γ) = + 1.

In step 30, the CPU calculates a state quantity Y as a first state quantity. The state quantity Y is expressed as a linear combination of the deviation E and its time derivative, and Y = A * E + B *
It is calculated by dE / dt. Here, A and B represent weighting constants. In step 40, the understeer control start determination value YUS and the understeer end determination value YUE, which are the second state quantities, or the oversteer control start determination value YOS
And an oversteer end determination value YOE. These values are determined from the characteristic diagram shown in FIG. 3 based on the lateral acceleration Gy.

In step 50, the state quantity Y is compared with the understeer control determination values YUS and YUE. When the flag F_US indicating the understeer control state is 0, the state quantity Y is compared with the understeer control start determination value YUS, and when the flag F_US is 1, the state quantity Y is compared with the understeer control end determination value YUE. Is done. And these results,
If the state quantity Y is smaller, the flow proceeds to step 60. If the state quantity Y is larger, the flow proceeds to step 9.
Go to 0.

In step 60, the state quantity Y is compared with the oversteer control start determination value YOS and the oversteer control end determination value YOE. When the flag F_OS indicating the oversteer control state is 0, the state quantity Y is compared with the oversteer control start determination value YOS, and when the flag F_OS is 1, the state quantity Y is compared with the oversteer control end determination value YOE.

Then, as a result of step 60, if the state quantity Y is larger, the flow proceeds to step 70, and if the state quantity Y is smaller, the flow proceeds to step 80. When the flow proceeds to step 70, it is determined that the steering characteristic of the vehicle is neither understeer nor oversteer, and the flags F_OS, F_
US are both set to zero. Also, the target slip ratio R
sj is all cleared to 0.

When the flow proceeds to step 80, it is determined that the steering characteristic of the vehicle is oversteer, and the flag F_OS is set to 1. Further, the target slip ratio Rsfo of the front outer wheel is Rsfo = | E * Kp +
∫Ki * Edt | (Kp proportional gain, Ki is an integral gain). Further, the target slip rates of the other wheels are set to 0, and the flow proceeds to step 100.

On the other hand, if it is determined in step 50 that the state quantity Y is larger and the flow proceeds to step 90, it is determined that the steering characteristic of the vehicle is understeer, and the flag F_US is set to Set to 1.
The target slip ratio Rsri of the rear inner wheel is Rsri = | E
* Kp + ∫Ki * Edt | (Kp proportional gain, Ki is an integral gain), the target slip rates of the other wheels are set to 0, and the flow proceeds to step 100.

In step 100, the target slip ratio is 0
In the case of, the wheel speed is V0, and the target wheel speed Vwt of each wheel is
j is calculated. The target wheel speed is Vwtj = (1-Rsj) *
V0, and the duty ratio Rdj is Rdj
= Gp * (Vwj-Vwtj) + Gd * d (Vwj-Vwtj) /
dt (Gp: proportional gain in wheel speed feedback control, Gd: differential gain in wheel speed feedback control).

In step 100, the control valve 40FL in the hydraulic control device for the wheel whose braking force is to be controlled is controlled.
When the control signal is transmitted to the control wheels, the control valve is switched to the second position, and the duty ratio is set to the open / close valves (44FL to 44RR) and the open / close valves (46FL to 46RR) of the control wheels. By outputting a control signal corresponding to Rdj and controlling the pressure in the corresponding wheel cylinders 38FL to 38RR, the braking force of the control wheel is controlled.

When the duty ratio Rdj is between a negative reference value and a positive reference value, the control valve (40FL to 40FL)
40RR), the on-off valve (44FL-44RR) on the upstream side is closed, and the on-off valve (46FL-46RR) on the downstream side of the control valve (40FL-40RR) is kept closed. The pressure in the cylinder (38FL-38RR) is maintained.

When the duty ratio Rdj is equal to or more than the positive reference value, the on-off valves (44FL to 44RR) located upstream of the control valves (40FL to 40RR) are kept open and the control valves are controlled. By holding the on-off valves (46FL-46RR) located downstream of (40FL-40RR) in a closed state (both positions shown in FIG. 1),
The pressure in the corresponding wheel cylinder (38FL-38RR) is increased.

On the other hand, when the duty ratio Rdj is less than the negative reference value, the on-off valves (44FL to 44RR) located upstream of the control valves (40FL to 40RR) are closed and the control valves (40FL to 40RR) are closed. When the on-off valve (46FL-46RR) located on the downstream side is opened, the brake oil in the corresponding wheel cylinder (any of 38FL-38RR) is discharged to the low-pressure conduit 42, and thereby the wheel cylinder ( 38FL-38RR)
The pressure inside is reduced.

As described above, according to the vehicle steering characteristic control apparatus of the present invention, the state quantity based on the deviation between the target yaw rate and the actual yaw rate, and the threshold value whose absolute value is provided as a function of increasing the lateral acceleration. By comparing with, the start or end of the yaw rate control is performed.
If the start and end times of understeer and oversteer control are set separately, the coefficient of friction μ
Regardless of this, the steering characteristics of the vehicle can be satisfactorily controlled by performing good vehicle steering characteristics control according to the driver's preference in a timely manner and with a natural feeling for the driver.

In the above-described embodiment, in a state where the actual yaw rate at the time of turning of the vehicle cannot follow the target yaw rate, if the steering characteristic of the vehicle is determined to be understeer, the braking force of the turning inner rear wheel is reduced. Control is performed based on the deviation, and when it is determined that the vehicle is oversteering, the actual yaw rate follows the target yaw rate by controlling the braking force of the front wheel on the outside of the turn. The braking force of the turning inner front wheel may be reduced while increasing the braking force of the turning outer front wheel, and the braking force of the turning inner front and rear wheels may be controlled during oversteer. The same effect as in the embodiment can be obtained.

Although the predetermined value of the control start or end is a function of the lateral acceleration Gy, the longitudinal acceleration Gx
May be combined with, for example, a function of the square root of Gy2 + Gx2, which is usually used as an amount corresponding to the friction coefficient μ of the road surface. In these cases, the same control is performed as in the above-described embodiment. The effect of can be obtained.

[0043]

According to the vehicle steering characteristic control apparatus of the present invention,
Yaw rate detection means for detecting the actual yaw rate of the vehicle,
Target yaw rate calculation means for calculating a target yaw rate of the vehicle based on the speed and steering angle of the vehicle; a first state quantity based on a deviation between the actual yaw rate and the target yaw rate; Means for calculating a second state quantity, and a first state quantity and a second state quantity.
A steering characteristic determining means for determining a steering characteristic of the vehicle based on a comparison result of the state quantities of the vehicle, and a braking force control means for controlling a braking force of the wheels based on the determination result of the steering characteristic determining means. Thus, it is possible to optimally control the steering characteristics of the vehicle irrespective of the coefficient of friction between the road surface and the tire.

The state quantity calculating means calculates the second state quantity based on the state quantity characteristic in which the absolute value of the value on the high lateral acceleration side is larger than that on the low lateral acceleration side. Irrespective of the friction coefficient of the vehicle.

Further, since the state quantity characteristics are provided for starting and ending the steering characteristic control of the vehicle, the control of the steering characteristics of the vehicle can be started and terminated at an optimal timing, and the driver can be controlled. Natural steering characteristic control suited to the user's preference can be performed.

Further, since the state quantity characteristic is provided for each of the case where the steering characteristic of the vehicle is oversteer and the case where the vehicle is understeer, it is possible to control the steering characteristic with a finer grain, and the steering characteristic can be changed by the driver. The vehicle can be adjusted to the user's preference, and the steering stability of the vehicle during turning can be greatly improved.

[0047]

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a vehicle steering characteristic control device of the present invention.

FIG. 2 is a flowchart showing a control flow of the vehicle steering characteristic control device of the present invention.

FIG. 3 is a diagram schematically showing a characteristic of a state quantity with respect to an absolute value of a lateral acceleration for performing a control start determination and a control end determination.

[Explanation of symbols]

10 braking device, 14 master cylinder, 18, 20,
26, 28 Hydraulic control device, 34 Oil pump, 38
FL, 38FR, 38RL, 38RR Wheel cylinder, 40
FL, 40FR, 40RL, 40RR Control valve, 44FL, 44F
R, 44RL, 44RR open / close valve, 46FL, 46FR, 46R
L, 46RR open / close valve, 50 electric control device, 56 vehicle speed sensor, 58 lateral acceleration sensor, 60 yaw rate sensor, 62 steering angle sensor, 64FL, 64FR, 64RL, 6
4RR Wheel speed sensor, 66 pressure sensor.

Claims (4)

[Claims] A yaw rate detecting means for detecting an actual yaw rate of the vehicle; a target yaw rate calculating means for calculating a target yaw rate of the vehicle based on a speed and a steering angle of the vehicle; and a deviation between the actual yaw rate and the target yaw rate. A first state quantity based on the lateral acceleration of the vehicle, and a state quantity calculating means for calculating a second state quantity based on the lateral acceleration of the vehicle; and a comparison result of the first state quantity and the second state quantity. A steering characteristic control device for a vehicle, comprising: a steering characteristic determining unit configured to determine a steering characteristic of a vehicle based on the steering characteristic; and a braking force control unit configured to control a braking force of a wheel based on a determination result of the steering characteristic determining unit. . 2. The state quantity calculating means according to claim 1, wherein the second state quantity is calculated based on a state quantity characteristic in which the absolute value of the value on the high lateral acceleration side is larger than that on the low lateral side. The steering characteristic control device for a vehicle according to the above. 3. The steering characteristic control device for a vehicle according to claim 1, wherein the state quantity characteristic includes one for starting and one for ending the steering characteristic control of the vehicle. 4. The steering characteristic control device for a vehicle according to claim 1, wherein the state quantity characteristic is provided for each of a case where the steering characteristic of the vehicle is oversteer and a case where the steering characteristic of the vehicle is understeer.