CN112109684A

CN112109684A - Vehicle attitude control device

Info

Publication number: CN112109684A
Application number: CN202010447484.XA
Authority: CN
Inventors: 平贺直树; 梅津大辅; 加藤史律; 绪方博幸
Original assignee: Mazda Motor Corp
Current assignee: Mazda Motor Corp
Priority date: 2019-06-04
Filing date: 2020-05-25
Publication date: 2020-12-22
Anticipated expiration: 2040-05-25
Also published as: CN112109684B; JP7274103B2; JP2020200020A

Abstract

Provided is a vehicle attitude control device which can suppress the inner rear portion of a vehicle body from floating up during cornering in a vehicle in which a roll axis is set so as to tilt forward. The present invention is a vehicle attitude control device for controlling the attitude of a vehicle (1) in which a wheel suspension device (3) is configured such that a roll axis is tilted forward, the vehicle attitude control device comprising: a lateral acceleration sensor (22) that detects a lateral acceleration of the running vehicle; a brake actuator (8) that applies a braking force to a wheel of the vehicle; and a brake control device (14a) that transmits a control signal to the brake actuator based on a traveling state of the vehicle to generate a braking force, and that executes the following vehicle attitude control during turning traveling of the vehicle based on a cut-in operation of a steering wheel (6) of the vehicle: when the lateral acceleration of the vehicle is large, a braking force that is larger than the braking force when the lateral acceleration of the vehicle is small is applied to the inner rear wheel of the vehicle during turning, and the floating of the vehicle body inner rear portion is suppressed.

Description

Vehicle attitude control device

Technical Field

The present invention relates to a vehicle attitude control device, and more particularly to a vehicle attitude control device for controlling the attitude of a vehicle in which a wheel suspension device is configured such that a roll axis of a vehicle body is tilted forward.

Background

Japanese patent No. 5193885 (patent document 1) describes a vehicle motion control device. In this vehicle motion control device, different braking forces or driving forces are applied to the left and right wheels based on a control command value of yaw moment calculated from the side slip information of the vehicle. Thus, in the invention described in patent document 1, acceleration and deceleration in cooperation with steering wheel operation is automatically performed, so that sideslip is reduced in the limit driving range, and safety performance is improved. That is, in the invention described in patent document 1, different braking forces or driving forces are applied to the left and right wheels based on the steering wheel operation by the driver, and the yaw moment is directly applied to the vehicle, thereby attempting to control the yaw motion of the vehicle.

On the other hand, attempts have been made to improve the attitude of the vehicle during cornering by setting the bottom suspension of the vehicle. That is, the following is also performed: by setting the bottom suspension so that the vehicle is likely to cause a pitching motion, the vehicle body is naturally made to generate an appropriate diagonal roll (diagonall) even in a turning with a low lateral acceleration. Specifically, the vehicle bottom suspension is set in advance such that the roll axis of the vehicle body tilts forward (the front side of the vehicle body descends), so that pitching motion is likely to occur in the vehicle body, and an appropriate diagonal sway can be generated during cornering.

Documents of the prior art

Patent document

Patent document 1, japanese patent No. 5193885

However, if the bottom suspension is set in advance such that the vehicle body generates a pitch motion and generates an appropriate diagonal roll during turning in a low lateral acceleration region, the following problem occurs: in a region where the lateral acceleration is large to some extent, the inner rear portion of the vehicle body during turning is likely to float. Such a phenomenon is also generated in a region where the lateral acceleration is much smaller than the lateral acceleration at which the vehicle is skidding while turning. That is, even in a lateral acceleration region where the lateral acceleration is small and does not substantially affect the turning performance of the vehicle, the inner rear portion of the vehicle body during turning may float. In this way, in a vehicle in which the roll axis of the vehicle body is set so as to tilt forward, the vehicle inside rear portion of the vehicle that is turning may float even in a region where the lateral acceleration is not so large, and may give a driver or an occupant a feeling of uneasiness.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a vehicle attitude control device that: in a vehicle in which a suspension is set so that a roll axis of a vehicle body tilts forward, the inner rear portion of the vehicle body can be suppressed from floating during cornering.

In order to solve the above-described problems, the present invention is a vehicle attitude control device for controlling an attitude of a vehicle including a front wheel and a rear wheel, the vehicle attitude control device being configured such that a roll axis of a vehicle body is tilted forward, the vehicle attitude control device including: a lateral acceleration sensor that detects a lateral acceleration of the running vehicle; a brake actuator that applies a braking force to a wheel of a vehicle; and a brake control device that transmits a control signal to the brake actuator based on a running state of the vehicle to cause the brake actuator to generate a braking force, and that executes vehicle attitude control as follows during turning running of the vehicle based on a cut-in operation of a steering wheel of the vehicle: when the lateral acceleration of the vehicle is large, a braking force that is larger than the braking force when the lateral acceleration of the vehicle is small is applied to the inner rear wheel of the vehicle during turning, and the floating of the vehicle body inner rear portion is suppressed.

In a vehicle in which a wheel suspension device is configured such that a roll axis of a vehicle body is tilted forward, pitching motion is likely to occur, and a diagonal sway can be generated even when the vehicle is turning with a small lateral acceleration, thereby improving turning performance. However, in a vehicle in which the roll axis is tilted forward in this way, when the lateral acceleration during turning becomes large to some extent, the inner rear portion of the vehicle body tends to float, and an inherent technical problem arises in that the driver and the passenger are given a sense of unease. The present invention solves the technical problem inherent in such a vehicle in which the roll axis of the vehicle body is tilted forward. According to the present invention configured as described above, when the lateral acceleration of the vehicle is large during turning travel of the vehicle by the cut-in operation of the steering wheel, a braking force that is larger than a braking force when the lateral acceleration of the vehicle is small is applied to the inner rear wheel of the vehicle during turning. When a braking force is applied to the inner rear wheel of the vehicle, a force that pulls down the inner rear portion of the vehicle body via the wheel suspension device acts, and the inner rear portion of the vehicle body is suppressed from floating. The braking force applied to the inner rear wheel does not substantially affect the turning performance of the vehicle, but acts to suppress the inner rear portion of the vehicle body from floating and to make it less likely to give a driver or a passenger a sense of unease.

In the present invention, it is preferable that the vehicle further includes a wheel speed sensor that detects a wheel speed of a rear wheel of the vehicle, and the brake control device sets the braking force acting on the inner rear wheel of the vehicle based on a difference between the wheel speeds of the inner rear wheel and the outer rear wheel detected by the wheel speed sensor and a lateral acceleration of the vehicle.

The floating of the vehicle body affects the ground contact load of the rear wheels of the vehicle, and if the inner rear portion of the vehicle body floats, the difference in wheel speed between the inner rear wheel and the outer rear wheel of the vehicle changes. In the present invention configured as described above, the braking force to be applied to the inner rear wheel of the vehicle is set based on the difference in wheel speed between the inner rear wheel and the outer rear wheel and the lateral acceleration of the vehicle, and therefore the braking force for suppressing the inner rear lift of the vehicle body can be set more accurately.

In the present invention, it is preferable that a vehicle speed sensor that detects a speed of the vehicle is further provided, and the brake control device causes a braking force larger than a braking force when the vehicle speed is smaller to act on an inner rear wheel of the vehicle during turning when the vehicle speed detected by the vehicle speed sensor is larger.

According to the present invention thus constituted, when the vehicle speed is high, a braking force greater than that when the vehicle speed is low acts on the inner rear wheel of the vehicle during cornering, so that an appropriate braking force can be set according to the vehicle speed.

In the present invention, it is preferable that the vehicle further includes an accelerator opening sensor, and the brake control device applies a larger braking force to the inner rear wheel of the vehicle during turning than when the accelerator opening detected by the accelerator opening sensor is small.

According to the present invention thus constituted, when the accelerator opening is large, a braking force larger than that when the accelerator opening is small acts on the inner rear wheel of the vehicle during turning, so that an appropriate braking force can be set according to the accelerator opening.

In the present invention, it is preferable that the vehicle further includes a steering angle sensor that detects a steering angle of a steering wheel of the vehicle, and the brake control device does not execute the vehicle attitude control when the steering angle detected by the steering angle sensor based on the cut-in operation of the steering wheel is equal to or smaller than a predetermined value.

According to the present invention thus constituted, when the steering angle by the cut-in operation of the steering wheel is equal to or less than the predetermined value, the vehicle attitude control is not executed, so that the following can be prevented: the vehicle attitude control is involved based on the fine steering of the driver to an unintended degree, giving the driver a sense of incongruity.

In the present invention, it is preferable that the brake control device is configured to be able to execute a vehicle attitude control based on a low road surface friction mode in which different braking forces are generated for the same lateral acceleration and a vehicle attitude control based on a high road surface friction mode.

The effect of suppressing the floating, which is generated by the braking force applied to the inner rear wheel of the vehicle during turning, differs depending on the magnitude of the road surface friction. According to the present invention configured as described above, since different braking forces are generated for the same lateral acceleration in the low road surface friction mode and the high road surface friction mode, an appropriate braking force can be set according to the road surface friction.

In the present invention, it is preferable that the brake control device is configured to be able to execute a vehicle attitude control based on a high road surface friction mode in which the brake control device executes the vehicle attitude control when a lateral acceleration of the vehicle becomes a first lateral acceleration or more and a vehicle attitude control based on a low road surface friction mode; in the low road surface friction mode, the brake control device executes the vehicle attitude control when the lateral acceleration of the vehicle becomes equal to or greater than a second lateral acceleration that is different from the first lateral acceleration.

The effect of suppressing the floating, which is generated by the braking force applied to the inner rear wheel of the vehicle during turning, differs depending on the magnitude of the road surface friction, and the level of the lateral acceleration to be involved in the vehicle attitude control also differs. According to the present invention configured as described above, since the vehicle attitude control is executed when the vehicle attitude control is equal to or higher than the first lateral acceleration in the high road surface friction mode and when the vehicle attitude control is equal to or higher than the second lateral acceleration in the low road surface friction mode, the vehicle attitude control can be started at an appropriate timing in accordance with the road surface friction.

In the present invention, it is preferable that a vehicle speed sensor for detecting a speed of the vehicle is further provided, and the brake control device changes a condition for starting execution of the vehicle attitude control in accordance with the vehicle speed detected by the vehicle speed sensor.

The effect of suppressing the floating, which is generated by the braking force applied to the inner rear wheel of the vehicle during turning, also differs depending on the speed of the vehicle. According to the present invention configured as described above, since the condition for starting execution of the vehicle attitude control is changed according to the vehicle speed, the execution of the vehicle attitude control can be started at an appropriate timing according to the vehicle speed.

In the present invention, it is preferable that the wheel suspension device includes a link mechanism that suspends an axle of the rear wheel from the vehicle body, the link mechanism suspending the axle so that the axle rotates about a predetermined suspension center, and the suspension center being located above the axle.

According to the present invention thus constituted, the link mechanism suspending the axle of the rear wheel to the vehicle body suspends the axle so that the axle pivots about the predetermined suspension center. Since the suspension center is located above the axle, when a braking force is applied to the rear wheel, the component of the force that pulls the vehicle body downward via the link mechanism is increased, and therefore, the rear portion inside the vehicle body can be more effectively suppressed from floating.

In the present invention, it is preferable that the vehicle is provided with a mechanical differential limiting device that mechanically controls a wheel speed difference between the inner rear wheel and the outer rear wheel in accordance with torques respectively acting on the inner rear wheel and the outer rear wheel of the vehicle during turning, and the vehicle attitude control device further includes an accelerator opening sensor, and the brake control device reduces a braking force acting on the inner rear wheel of the vehicle during turning as a change speed of the accelerator opening detected by the accelerator opening sensor increases.

According to the present invention thus constituted, the vehicle is provided with the mechanical differential limiting device, and therefore, due to this action, the difference in wheel speed between the inner rear wheel and the outer rear wheel is reduced more rapidly as the accelerator opening degree is increased. If the brake control device applies the braking force to the inner rear wheel based on the vehicle attitude control in addition to the action of the differential limiting device, the change in the wheel speed difference between the inner rear wheel and the outer rear wheel becomes excessively large, and there is a possibility that the driver will be given an uncomfortable feeling. According to the present invention configured as described above, the braking force acting on the inner rear wheel is reduced as the change speed of the accelerator opening degree is increased, and therefore, the sense of incongruity given to the driver can be suppressed.

In the present invention, it is preferable that the brake control device is configured to: when the same lateral acceleration acts on the vehicle during running, the same braking force is generated regardless of the road surface friction of the running road surface, and when the wheel speed difference between the inner rear wheel and the outer rear wheel of the vehicle during turning is equal to or less than a predetermined threshold value, the brake control device does not apply the braking force.

According to the present invention thus constituted, it is constituted that: when the same lateral acceleration acts on the vehicle during traveling, the same braking force is generated regardless of the road surface friction of the road surface during traveling, and therefore, the control algorithm can be easily configured without changing the control according to the road surface friction. Further, according to the present invention configured as described above, since the braking force is not applied when the wheel speed difference is equal to or less than the predetermined threshold value, it is possible to suppress excessive intervention of the braking force generated by the brake control device, and to suppress the inner rear float of the vehicle during turning by applying an appropriate braking force in a situation where the braking force is required.

According to the vehicle attitude control device of the present invention, even in a vehicle in which the suspension is set such that the roll axis of the vehicle body is tilted forward, the inner rear portion of the vehicle body can be suppressed from floating during cornering.

Drawings

Fig. 1 is a layout diagram showing an overall configuration of a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention.

Fig. 2 is a view schematically showing a structure of an axle in which a rear wheel is suspended from a vehicle body of a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention from behind the vehicle.

Fig. 3 is a diagram showing a roll axis of a vehicle body of a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention.

Fig. 4 is a diagram schematically illustrating a force acting on a vehicle body when a braking force is applied to a rear wheel of a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention.

Fig. 5 is a block diagram showing a PCM, sensors, and the like mounted on a vehicle equipped with a vehicle posture control device according to a first embodiment of the present invention.

Fig. 6 is a flowchart showing an operation of the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 7 is a flowchart of a subroutine called from the flowchart shown in fig. 6.

Fig. 8 is a timing chart showing an action of the vehicle posture control device according to the first embodiment of the present invention on a normal road surface.

Fig. 9 is a time chart showing an action of the vehicle attitude control device according to the first embodiment of the present invention on a road surface with a low friction coefficient.

Fig. 10 is a map for setting the threshold value of the wheel speed difference in the vehicle attitude control device according to the first embodiment of the invention.

Fig. 11 is a map of a steering angle gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 12 is a map of an accelerator opening degree change speed gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 13 is a map of an accelerator opening degree gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 14 is a map of the lateral acceleration gain multiplied by the basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 15 is a map of a vehicle speed gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 16 is a map of an accelerator opening degree gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 17 is a map of a lateral acceleration gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 18 is a map of a vehicle speed gain multiplied by a basic command value in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 19 is a map of the difference rotation gain multiplied by the basic command value based on the brake LSD control in the vehicle attitude control device according to the first embodiment of the present invention.

Fig. 20 is a flowchart showing a process for determining a command value in the vehicle attitude control device according to the second embodiment of the present invention.

Fig. 21 is a map of the difference rotation gain multiplied by the basic command value based on the brake LSD control in the vehicle attitude control device according to the second embodiment of the present invention.

Description of the symbols

1 vehicle

1a vehicle body

2a, 2b front wheel

2c, 2d rear wheel

2e axle

3 suspension (wheel suspension device)

3a Upper arm (connecting rod mechanism)

3b lower arm (connecting rod mechanism)

4 engines

4a speed variator

4b drive shaft

4c differential gear

4d differential limiting device

6 steering wheel

7 steering device

8 brake device (brake actuator)

10 hydraulic pump

12-valve unit

13 hydraulic pressure sensor

14 PCM

14a brake control part (brake control device)

14b turning control unit

14c sideslip prevention control part

16 steering angle sensor

18-throttle opening sensor

20 vehicle speed sensor

22 lateral acceleration sensor

24-wheel speed sensor

26 mode setting switch

Detailed Description

Next, preferred embodiments of the present invention will be described with reference to the drawings.

First, a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention will be described with reference to fig. 1. Fig. 1 is a layout diagram showing an overall configuration of a vehicle mounted with a vehicle posture control device according to a first embodiment of the present invention.

In fig. 1, reference numeral 1 denotes a vehicle mounted with a vehicle posture control device according to the present embodiment.

Left and right

front wheels

2a and 2b as steering wheels are provided at a front portion of a vehicle body of the vehicle 1, and left and right

rear wheels

2c and 2d as driving wheels are provided at a rear portion of the vehicle body. The

front wheels

2a and 2b and the

rear wheels

2c and 2d of the vehicle 1 are supported by the vehicle body 1a via suspensions 3 as wheel suspensions, respectively. An engine 4 as a prime mover for driving the

rear wheels

2c and 2d is mounted on a front portion of the vehicle body 1a of the vehicle 1. In the present embodiment, the engine 4 is a gasoline engine, but an internal combustion engine such as a diesel engine or an electric motor driven by electric power may be used as the prime mover. In the present embodiment, the vehicle 1 is a so-called FR vehicle in which the

rear wheels

2c and 2d are driven by an engine 4 mounted on a front portion of the vehicle body 1a via a transmission 4a, a propeller shaft 4b, and a differential gear 4 c. In addition, a mechanical Differential Gear 4d (LSD: Limited-Slip Differential Gear) is preferably provided to the Differential Gear 4 c. By providing the differential limiting device 4d, even when the ground contact performance of one rear wheel is reduced, a large driving force to some extent can be applied to the other rear wheel. However, the present invention can be applied to any vehicle of any drive system, such as a so-called RR vehicle in which the rear wheels are driven by an engine mounted on the rear portion of the vehicle body, and an FF vehicle in which the front wheels are driven by an engine mounted on the front portion of the vehicle body.

A steering device 7 is mounted on the vehicle 1, and the steering device 7 steers the

front wheels

2a and 2b based on a turning operation of the steering wheel 6.

The vehicle 1 further includes a brake control system that supplies a brake fluid pressure to a wheel cylinder and a brake caliper (not shown) of a brake device 8 as a brake actuator provided in each wheel. The brake control system includes a hydraulic pump 10, and the hydraulic pump 10 generates a brake hydraulic pressure necessary for generating a braking force in the brake device 8 provided in each wheel. The hydraulic pump 10 is driven by electric power supplied from a battery (not shown), for example, and can generate a brake hydraulic pressure necessary for generating a braking force in each brake device 8 even when a brake pedal (not shown) is not depressed.

The brake control system includes a valve unit 12 (specifically, a solenoid valve), and the valve unit 12 is provided in a hydraulic pressure supply line that supplies hydraulic pressure to the brake devices 8 of the respective wheels, and controls the hydraulic pressure supplied from the hydraulic pump 10 to the brake devices 8 of the respective wheels. For example, the opening degree of the valve unit 12 is changed by adjusting the amount of power supplied from the battery to the valve unit 12. The brake control system further includes a hydraulic pressure sensor 13, and the hydraulic pressure sensor 13 detects the hydraulic pressure supplied from the hydraulic pump 10 to the brake device 8 of each wheel. The hydraulic pressure sensor 13 is disposed, for example, at a connection portion between each valve unit 12 and a hydraulic pressure supply line on the downstream side thereof, detects the hydraulic pressure on the downstream side of each valve unit 12, and outputs the detected value to a PCM (Power-train Control Module) 14.

The brake control system calculates the hydraulic pressures to be supplied to the wheel cylinders and the calipers of the respective wheels independently from each other based on the braking force command value input from the PCM14 and the detection value of the hydraulic pressure sensor 13, and controls the rotation speed of the hydraulic pump 10 and the opening degree of the valve unit 12 based on these hydraulic pressures.

Next, a suspension structure of a vehicle and a roll axis of a vehicle body, in which the vehicle posture control device according to the present embodiment is mounted, will be described with reference to fig. 2 to 4.

Fig. 2 is a view schematically showing a structure for suspending axles of the

rear wheels

2c and 2d from the vehicle body 1a of the vehicle 1 from the rear of the vehicle. Fig. 3 is a diagram showing a roll axis of a vehicle body of a vehicle mounted with the vehicle posture control device according to the present embodiment. Fig. 4 is a diagram schematically illustrating a force acting on a vehicle body in a case where a braking force is applied to a rear wheel of the vehicle.

As shown in fig. 2, an axle 2e of a left rear wheel 2c of the vehicle 1 is supported by a vehicle body 1a of the vehicle 1 via a suspension 3. Specifically, in the example shown in fig. 2, an axle 2e of the rear wheel 2c is supported by an upper arm 3a and a lower arm 3b as link mechanisms constituting the suspension 3. Thus, a line extending the upper arm 3a and the lower arm 3b connecting the vehicle body 1a and the rear wheel 2c is positioned at the intersection point P₁Where they intersect. Connect the intersection point P₁And a point P where a straight line connecting a grounding point P2 of the rear wheel 2c and the center axis A of the vehicle body 1a is at_rRAnd (4) crossing. The point P_rRIs the center point of the roll motion of the rear portion of the vehicle body 1a, at which point P the rear portion of the vehicle body 1a is located_rRA roll motion is performed as a center. Further, since the vehicle 1 is bilaterally symmetric, when the center point of the roll motion is obtained for the right rear wheel 2d, the same point P is obtained_rRAlso becomes the center point of the roll motion. In addition, the center point P of the roll motion can be similarly obtained also for the suspension 3 suspending the

front wheels

2a, 2b of the vehicle 1_rF。

FIG. 3 is a view showing the center point P of the roll motion of the rear portion of the vehicle body 1a, which is obtained as described above, from the side of the vehicle 1_rRAnd a center point P of the front roll motion_rFAnd (4) projecting the image. The center point P of the roll motion connecting the rear parts of these vehicle bodies 1a_rRAnd a center point P of the front portion_rFAxis A of_rWhich is the center axis of the vehicle body 1a when performing a rolling motion. Therefore, the vehicle body 1a of the vehicle 1 is substantially at the roll axis a_rA roll motion is performed as a center. In addition, as shown in fig. 3, in the present embodiment, the roll axis a of the vehicle 1_rThe front side of the vehicle 1 is tilted forward so as to be lowered. Thus, the roll axis A of the vehicle 1 is preliminarily adjusted_rBy tilting forward, an appropriate diagonal swing can be naturally generated when the vehicle 1 performs a turning motion, and the turning performance of the vehicle 1 can be improved.

Next, a force acting on the vehicle body 1a when a braking force is applied to the

rear wheels

2c and 2d of the vehicle 1 will be described with reference to fig. 4.

As described above, the

rear wheels

2c and 2d are suspended by the upper arm 3a and the lower arm 3b constituting the suspension 3. In any case, the axle of the wheel can be regarded as being suspended so as to rotate around a virtual predetermined suspension center. As shown in fig. 4, in the present embodiment, the rear wheel 2d is suspended around a suspension center point P_SAnd (4) rotating. In addition, in the present embodiment, the suspension center point P_SIs located above the axle 2e of the rear wheel 2 d.

Here, when the braking force is applied to the rear wheel 2d, the rear wheel 2d is suspended along the suspension center point P and the ground contact point P2 connecting the rear wheel 2d and the road surface_SLine segment l of₁And the vehicle body 1a is pulled back rearward. If the line segment l is divided₁The angle with the road surface is set to theta_alF represents a frictional force acting between the road surface and the rear wheel 2d_xA component of the force pulling down the vehicle body 1a can pass through F_x×tanθ_alTo calculate. Further, let the wheel base of the vehicle 1 be I_rThe center of gravity G and the suspension center point P of the vehicle 1_SSet to X horizontal distance between_rThe moment M acting to pull down the rear portion of the vehicle body 1a can be calculated by the mathematical expression (1)_al。

M_al＝(l_r-X_r)×F_x×tanθ_al (1)

By applying a braking force to the

rear wheels

2c or 2d of the vehicle 1 in this way, the rear portion of the vehicle body 1a can be pulled down. In addition, in the present embodiment, the suspension center point P is a point at which the suspension center is suspended_SIs located higher than the axle 2e of the rear wheel, the force pulling down the vehicle body 1a becomes relatively large.

Next, various sensors mounted on the vehicle 1 will be described with reference to fig. 5.

Fig. 5 is a block diagram showing the PCM14 mounted on the vehicle 1, a sensor connected to the PCM14, and the like.

As shown in fig. 5, the vehicle 1 is equipped with a steering angle sensor 16 that detects the rotation angle of the steering wheel 6, an accelerator opening sensor 18 that detects the amount of depression of an accelerator pedal (accelerator opening), and a vehicle speed sensor 20 that detects the vehicle speed, and these detection signals are input to a PCM 14. The vehicle 1 is further equipped with a lateral acceleration sensor 22 that detects a lateral acceleration acting on the vehicle 1, a wheel speed sensor 24 that detects a wheel speed of each wheel of the vehicle 1, and a hydraulic pressure sensor 13 that detects a hydraulic pressure on the downstream side of the valve unit 12 (fig. 1), and these detection signals are also input to the PCM 14. In the present embodiment, a sensor that directly measures lateral acceleration is mounted on the vehicle 1 as the lateral acceleration sensor 22. However, the lateral acceleration sensor 22 does not necessarily have to include a sensor that directly measures the lateral acceleration, and the lateral acceleration may be obtained from a detection value measured by another sensor. In the present specification, the "lateral acceleration sensor" includes any sensor for obtaining lateral acceleration.

The vehicle 1 is configured such that the driver can select the low road surface friction mode or the high road surface friction mode according to the state of the road surface during traveling, and the vehicle 1 is provided with a mode setting switch 26 for selecting these modes. When the driver selects the low road friction mode or the high road friction mode according to the state of the road surface by the mode setting switch 26, the setting is input to the PCM14, and as described later, vehicle attitude control according to the state of the road surface is performed.

On the other hand, the PCM14 incorporates a brake control unit 14a, a turning control unit 14b, and a sideslip prevention control unit 14c, wherein the brake control unit 14a is a brake control device for controlling the brake device 8, the turning control unit 14b executes turning control for improving turning performance of the vehicle 1, and the sideslip prevention control unit 14c executes sideslip prevention control for suppressing sideslip of the vehicle 1 during turning. As will be described later, each of these control units is configured to transmit a control signal to the engine 4 and the brake device 8 to execute vehicle attitude control, turning control, and anti-sideslip control, respectively.

A vehicle attitude control device according to a first embodiment of the present invention is constituted by: a steering angle sensor 16, an accelerator opening sensor 18, a vehicle speed sensor 20, a lateral acceleration sensor 22, a wheel speed sensor 24, and a mode setting switch 26 that send signals to the PCM 14; a brake control unit 14a, a turning control unit 14b, and a sideslip prevention control unit 14c incorporated in the PCM 14; and an engine 4, a brake device 8, etc. controlled by the PCM 14. Further, the above-described structure constituting the vehicle attitude control device can be partially omitted depending on the application.

Each control unit of the PCM14 is configured by a computer including: a CPU, various programs interpreted and executed on the CPU (including a basic control program such as an OS, an application program that is started on the OS and realizes a specific function), and an internal memory such as a ROM, a RAM for storing the programs and various data.

Next, the operation of the vehicle attitude control device according to the first embodiment of the present invention will be described with reference to fig. 6 to 19.

Fig. 6 is a flowchart showing an operation of the vehicle attitude control device. Fig. 7 is a flowchart of a subroutine called from the flowchart shown in fig. 6. Fig. 8 is a time chart showing an action of the vehicle attitude control device on a normal road surface. Fig. 9 is a time chart showing the action of the vehicle attitude control device on a road surface with a low friction coefficient. Fig. 10 to 19 are maps showing various gains used when determining the vehicle attitude control command value generated by the vehicle attitude control device.

The flowchart shown in fig. 6 is executed repeatedly at predetermined time intervals mainly in the PCM14, and is executed to automatically apply the braking force to the vehicle 1 for the purpose of vehicle attitude control and the like.

First, in step S1 of fig. 6, detection signals of the respective sensors are read from the various sensors into the PCM 14. The detection signal read in step S1 is used for the processing in steps S2 to S4. Specifically, in step S1, a signal of the steering angle (the rotation angle of the steering wheel 6) [ deg ] from the steering angle sensor 16, a signal of the accelerator opening [% ] from the accelerator opening sensor 18, and a signal of the vehicle speed [ km/h ] from the vehicle speed sensor 20 are read. In step S1, a signal of the lateral acceleration [ G ] from the lateral acceleration sensor 22, a signal of the wheel speed [ m/sec ] of each wheel from the wheel speed sensor 24, and a signal of the brake hydraulic pressure [ MPa ] from the hydraulic pressure sensor 13 are read. Further, a selection signal indicating whether the low road friction mode or the high road friction mode is currently selected by the driver is read from the mode setting switch 26.

Next, in step S2, a determination process based on the command value for the vehicle attitude control is executed. Specifically, as the vehicle posture control, when the vehicle 1 is running while turning by the cutting operation of the steering wheel 6 of the vehicle 1, a braking force is applied to the inner rear wheels of the vehicle 1 in order to suppress the inner rear part of the vehicle body 1a of the vehicle 1 from floating during turning. For example, when the vehicle 1 turns leftward in fig. 1, a braking force acts on the left rear wheel 2c, and floating of the left rear portion of the vehicle body 1a is suppressed. In step S2, the flowchart shown in fig. 7 is called as a subroutine, and a command value for applying a braking force acting on the inner rear wheel for vehicle attitude control is determined. This vehicle posture control is executed in a region where the lateral acceleration of the turning travel of the vehicle 1 is relatively small, and a relatively small first braking force is applied to the inner rear wheel based on the wheel speed difference between the inner rear wheel and the outer rear wheel.

Preferably, the hydraulic pump 10 applies a hydraulic pressure of 0.02MPa to 0.1MPa to the brake device 8 to generate a braking force acting to control the vehicle posture, in the vehicle 1 having a mass of about 960kg to about 1060 kg. Thus, when the vehicle 1 turns, the inside rear of the vehicle body 1a tends to float at a certain acceleration, but the braking force set as described above is applied, so that a small deceleration of a predetermined value or less is given in the vertical direction of the vehicle body 1a, and the inside rear of the vehicle body is suppressed from floating.

Next, in step S3, a command value determination process by the turning control is executed. The turning control is control as follows: the turning control unit 14b of the PCM14 executes the operation when the steering angular velocity of the steering wheel 6 is equal to or greater than a predetermined value in order to improve the turning performance of the vehicle 1. In addition, in this turning control, adjustment of the torque generated by the engine 4 and/or application of the braking force by the brake device 8 is performed. When a braking force is applied to the vehicle 1 during turning control, a yaw moment in the turning direction is generated in the vehicle 1 by applying a braking force to the inner rear wheels of the vehicle 1 during turning, thereby improving the turning performance of the vehicle 1.

Further, although the braking force is applied to the inner rear wheels of the turning vehicle 1 also in the vehicle posture control in which the command value is determined in step S2, the turning control is executed in a region where the lateral acceleration is relatively larger than the vehicle posture control, and the braking force larger than the vehicle posture control is applied in the turning control. That is, the vehicle posture control is performed for the purpose of suppressing the inner rear portion of the vehicle body 1a from floating when the vehicle 1 turns, and the turning control is performed for the purpose of applying a yaw moment to the vehicle 1 to improve the turning performance, and the vehicle posture control is completely different from the turning control. In the present embodiment, the braking force that acts for the turning control is generated by applying a hydraulic pressure greater than the hydraulic pressure for the vehicle attitude control by 0.2MPa to 0.5MPa to the brake device 8 by the hydraulic pump 10.

Next, in step S4, a determination process based on the command value of the sideslip prevention control is executed. The sideslip prevention control is control executed in the sideslip prevention control portion 14c of the PCM14 in order to suppress or prevent the vehicle 1 from sideslipping during turning. The anti-sideslip control is a control executed based on the steering angle of the steering wheel 6 and the lateral acceleration of the vehicle 1, and is executed in a region where the lateral acceleration is extremely larger than that of the turning control. In the anti-sideslip control, an appropriate braking force is applied to each wheel of the vehicle 1 in order to return the running state of the vehicle 1 to the turning running expected by the driver. The braking force applied in the anti-sideslip control is very large compared to the braking force of the turning control. In the present embodiment, the braking force that acts for the anti-slip control is generated by applying a hydraulic pressure of 20MPa or more, which is greater than the hydraulic pressure of the turning control, to the brake device 8 by the hydraulic pump 10.

Further, in step S5, a control signal is sent to the brake device 8 by the PCM14 based on the command values determined in steps S2 to S4 to apply a braking force to the vehicle 1, and the process of the flowchart shown in fig. 6 is ended. The vehicle posture control, the turning control, and the anti-sideslip control described above are all controls in which the braking force is applied to the vehicle 1, but are executed in different running states, and these controls are usually executed without overlapping.

Next, referring to fig. 7 to 19, a process of determining a command value by vehicle attitude control will be described.

As described above, the flowchart shown in fig. 7 is a subroutine called out from step S2 of the flowchart shown in fig. 6, and is executed by the brake control unit 14a of the PCM 14. Fig. 8 and 9 are time charts showing an example of the braking force generated when the vehicle posture control is executed. Fig. 8 shows a case where the vehicle 1 travels on a normal road surface (high-friction road surface), and fig. 9 shows a case where the vehicle 1 travels on a constant-friction road surface such as a snow road. In the timing charts shown in fig. 8 and 9, the horizontal axis represents time, and the vertical axis represents, in order from the top, the detection value of the steering angle sensor 16, the detection value of the accelerator opening sensor 18, the wheel speed of the rear wheel detected by the wheel speed sensor 24, and the brake command value applied to the inner rear wheel.

First, in step S11 of fig. 7, a wheel speed difference between the left and right

rear wheels

2c, 2d of the vehicle 1 is calculated. Specifically, in step S1 of fig. 6, the wheel speed difference between the left and right

rear wheels

2c, 2d is calculated based on the wheel speed of each wheel read from the wheel speed sensor 24.

Next, in step S11, it is determined whether or not the "vehicle posture control flag" is true. The "vehicle attitude control flag" is a flag as follows: the "true" is changed when the vehicle 1 starts turning and starts the vehicle posture control based on a predetermined condition, and the "false" is returned when the cut-in steering wheel 6 is turned back and the turning is finished. In the example of the timing chart shown in fig. 8, at time t₀Since the vehicle 1 does not start turning, the "vehicle posture control flag" is false, and the process of the flowchart of fig. 7 proceeds to step S16.

In step S16, the wheel speeds of the inside rear wheel and the outside rear wheel of the vehicle in a curve are compared, and if the outside wheel speed is high, the routine proceeds to step S17, where the inside wheelIf the speed is high, the process proceeds to step S21. The wheel speed of the outer rear wheel is high when no slip occurs in each of the rear wheels, and if a certain degree of slip occurs in the inner rear wheel, the relationship is reversed. In the example of fig. 8, at time t₁The driver starts cutting into the steering wheel 6, the wheel speed of the outer rear wheel of the vehicle 1, which starts turning, becomes high, and the wheel speed of the inner rear wheel becomes low, and the process of the flowchart proceeds to step S17.

In step S17, it is determined whether or not the difference between the wheel speeds of the outer rear wheel and the inner rear wheel (outer wheel speed — inner wheel speed) is greater than a first wheel speed difference T that is a threshold value of the wheel speed difference_a[m/sec]. The difference between the outside and inside wheel speeds is a first wheel speed difference T_aIn the following case, the processing of step S23 and below is executed, and the primary processing of the flowchart shown in fig. 7 is ended without applying the braking force by the vehicle attitude control. That is, the wheel speed difference between the left and right rear wheels may be caused by an error of the wheel speed sensor 24, and if the vehicle attitude control is involved based on a slight wheel speed difference, there is a possibility that the driver will be given a sense of incongruity, so that the vehicle attitude control is not executed when the wheel speed difference is slight. Furthermore, a first wheel speed difference T as a threshold value for the wheel speed difference_aBased on the vehicle speed of the vehicle 1. The specific setting of the wheel speed difference threshold will be described later with reference to fig. 10.

In the example of FIG. 8, when at time t₁When the driver performs the cut-in operation of the steering wheel 6 and the vehicle 1 starts the turning travel, the wheel speed difference gradually becomes large, and when the wheel speed difference exceeds the first wheel speed difference T_aThen, the processing in step S18 is executed.

In step S18, it is determined whether or not the lateral acceleration detected by the lateral acceleration sensor 22 is larger than a predetermined first lateral acceleration GY_a[G](1[G]＝9.81[m/sec²]) Whether the vehicle speed detected by the vehicle speed sensor 20 is higher than a predetermined first vehicle speed Va [ km/h ]]High. At a lateral acceleration of a first lateral acceleration GY_aThe following or vehicle speed is the first vehicle speed V_aIn the following case, the processing of step S23 or less is executed, and the braking force is not applied by the vehicle attitude controlThe process of the flowchart shown in fig. 7 is ended. That is, in a state where the lateral acceleration or the vehicle speed is very low, there is no need to intervene in the vehicle attitude control, and the driver may be given a sense of incongruity due to unnecessary intervention, and therefore the vehicle attitude control is not executed.

On the other hand, when the lateral acceleration exceeds the first lateral acceleration GY_aAnd the vehicle speed exceeds a first vehicle speed V_aIn the case of (3), the processing of step S19 or less is executed to apply the braking force by the vehicle attitude control. First, in step S19, the vehicle attitude control flag is changed to true. Further, in step S19, when the vehicle attitude control flag is changed to true, during this time, the process in the flowchart of fig. 7 proceeds to step S12 → S13. However, in the example shown in fig. 8, since the high road friction mode is selected by the mode setting switch 26, the process of the flowchart of fig. 7 proceeds to step S13 → S16, and the processes in steps S14, S15 are not performed.

Next, in step S20, a basic command value F for vehicle attitude control is determined based on the wheel speed difference between the left and right rear wheels_b1[N]. That is, the braking force to be applied to the inner rear wheel of the vehicle 1 is set based on the difference in wheel speed between the inner rear wheel and the outer rear wheel. The basic instruction value F_b1Is a command value of a braking force applied to the inner rear wheel of the turning vehicle 1 through the wheel speed V to the outer side_oWheel speed V with the inner side_iMultiplying the difference by a predetermined coefficient C_m1And is calculated by the equation (2).

F_b1＝C_m1×(V_o-V_i) (2)

Further, in step S25, the basic command value F calculated in step S20_b1Multiplying the various gains to determine the final command value F for vehicle attitude control₁. The specific processing executed in step S25 will be described later. Next, in step S26, the command values calculated in the respective controls are compared, and the largest command value is selected as the final command value.

That is, in the flowchart shown in fig. 7, in addition to the first braking force based on the vehicle attitude control calculated in step S20, the lower limit braking force based on the pre-brake LSD control calculated in step S15, and the second braking force based on the brake LSD control calculated in step S22 are calculated as described later. In step S26, the largest braking force among the calculated braking forces is selected, and the process of the flowchart shown in fig. 7 is ended. When the processing of the flowchart of fig. 7 is finished, the processing proceeds to step S5 of the flowchart of fig. 6, and the brake device 8 is controlled so that the braking force selected here acts.

In the example shown in fig. 8, at time t₁After the cutting of the steering wheel 6 is started, the difference between the wheel speed of the outer rear wheel and the wheel speed of the inner rear wheel of the vehicle 1 increases, and therefore the command value of the braking force calculated by the equation (2) also increases. This increases the braking force applied to the inner rear wheel of the vehicle 1 during turning (time t in fig. 8)₁～t₂). Next, at time t in FIG. 8₂When the driver starts to depress the accelerator pedal, the wheel speed difference between the right and left rear wheels is constant (time t in fig. 8)₂～t₃). During this period, the command value of the braking force calculated by the equation (2) is also constant while maintaining the maximum value.

Next, at time t of FIG. 8₃When the driver finishes the cut-in of the steering wheel 6 and shifts to the steering hold, the vehicle 1 enters a steady turning state. Along with this, the wheel speeds of the inner and outer rear wheels increase, and the wheel speed difference between the inner rear wheel and the outer rear wheel decreases (time t in fig. 8)₃～t₄). Thereby, the command value of the braking force calculated by the equation (2) is also reduced. Further, at time t of fig. 8₄The wheel speed difference between the inner rear wheel and the outer rear wheel is a first wheel speed difference T_aThereafter, the process in the flowchart of fig. 7 proceeds to step S17 → S23, and the command value based on the vehicle attitude control becomes zero.

Next, at time t in FIG. 8₅The slip of the inner rear wheel increases, the wheel speeds of the inner rear wheel and the outer rear wheel reverse, and the wheel speed of the inner rear wheel increases. Thus, the process in the flowchart of fig. 7 advances to stepS16 → S21, the processing below step S21 in the flowchart of fig. 7 is executed.

In step S21, it is determined whether the wheel speed difference between the outside rear wheel and the inside rear wheel (inside wheel speed — outside wheel speed) is greater than a second wheel speed difference T_b[m/sec]. The difference between the outside and inside wheel speeds is a second wheel speed difference T_bIn the following case, the processing of step S23 and below is executed, and the primary processing of the flowchart shown in fig. 7 is ended without applying the braking force by the brake LSD control. That is, the wheel speed difference between the left and right rear wheels may be caused by an error of the wheel speed sensor 24, and if the brake LSD control is involved based on a slight wheel speed difference, there is a possibility that the driver will feel uncomfortable, and therefore, the brake LSD control is not executed when the wheel speed difference is slight.

On the other hand, the wheel speed difference between the outside rear wheel and the inside rear wheel is larger than the second wheel speed difference T_bIn the case of (3), the process proceeds to step S22, where a command value of the second braking force based on the brake LSD control is calculated. In this way, when the wheel speed of the inner rear wheel of the vehicle 1 becomes faster than the wheel speed of the outer rear wheel during turning of the vehicle 1, the brake control portion 14a causes the second braking force to act on the inner rear wheel. The brake LSD control is a control for applying a brake to a wheel that is spinning to lower the wheel speed and avoid a spinning state. I.e. at time t as in fig. 8₅～t₆In such a state that the wheel speed of the inner driving wheel (rear wheel in the present embodiment) of the vehicle 1 during turning exceeds the wheel speed of the outer driving wheel, the inner driving wheel starts to spin. When the wheel speed difference becomes large due to the spin of the inner wheel, the driving force is no longer transmitted to the outer rear wheel via the differential gear 4c, and therefore the braking force is applied to the inner wheel to decrease the wheel speed of the inner wheel.

In step S22, a basic command value F for the brake LSD control is determined based on the wheel speed difference between the left and right rear wheels_b2[N]. The basic command value F of the braking force based on the brake LSD control_b2Is a command value of a braking force applied to the inner rear wheel of the turning vehicle 1 through the wheel speed V to the inner side_iSpeed V of wheel with outside_oMultiplying the difference by a predetermined coefficient C_m2And is measured by the formula (3)And (4) calculating.

F_b2＝C_m2×(V_i-V_o) (3)

In the example shown in fig. 8, at time t₅Application of braking force based on the brake LSD control is started, whereby the wheel speed of the inner rear wheel is decreased, at time t₆The difference between the wheel speeds of the inboard rear wheel and the outboard rear wheel is substantially zero. At time t₆After the upper wheel speed difference is substantially zero, the processing in the flowchart of fig. 7 proceeds as in step S16 → S21 → S23 or step S16 → S17 → S23, and the application of the braking force to the inner rear wheel is not performed (time t of fig. 8)₆～t₇)。

In the example shown in fig. 8, the driver starts from time t₆The return of the steering wheel 6 is started at time t₇The vehicle returns to the straight running state after the wheel return is completed, and the turning running is finished.

In step S23, it is determined whether or not the turning of the steering wheel 6 is completed based on the detection value of the steering angle sensor 16, and the process proceeds to step S25 if the turning is not completed, and proceeds to step S24 if the turning is completed. In the present embodiment, at time t in fig. 8₁After the start of the cut-in operation of the steering wheel 6, the operation is continued until time t₇In the vehicle attitude control during the period until the wheel return operation is completed, the brake control unit 14a generates a braking force at a brake fluid pressure of about 0.1MPa or less.

In step S24, since the return is completed and the turning travel is ended, the "vehicle posture control flag" is changed to "false". Thereafter, in the case where the flowchart shown in fig. 7 is executed, the process advances to step S12 → S16. In this state, even when the low road surface friction mode is set by the mode setting switch 26, the braking force by the pre-brake LSD control is not applied.

Next, vehicle attitude control in the case where the low road friction mode is set by the mode setting switch 26 will be described with reference to fig. 9.

Fig. 9 is a timing chart showing an example of vehicle attitude control in the case where the low road surface friction mode is set. The process from step S14 or less is executed in the flowchart of fig. 7 when the low road surface friction mode is set, unlike the timing chart of fig. 8. In the processing below step S14, the braking force based on the pre-brake LSD control is calculated. In the time chart of fig. 9, the command value by the vehicle attitude control is indicated by a solid line, the command value by the pre-brake LSD control is indicated by a broken line, and the command value by the brake LSD control is indicated by a one-dot chain line.

In the present embodiment, the low road surface friction mode and the high road surface friction mode are switched by setting the mode setting switch 26 by the driver. In contrast, as a modification, the present invention can be configured as follows: each mode is automatically selected together with the setting of the mode setting switch 26 or in place of the setting of the mode setting switch 26. For example, the brake control unit 14a may be configured as follows: the low road surface friction mode is automatically set when the friction coefficient of the road surface is estimated based on the operating conditions of an outside air temperature sensor, a rainfall sensor, a wiper, and the slip state of the drive wheels mounted on the vehicle 1, and the friction coefficient is equal to or less than a predetermined value. In this case, the brake control unit 14a also functions as a friction coefficient estimation unit that estimates the friction coefficient of the road surface on which the vehicle 1 is traveling.

First, when the driver is at time t of fig. 9₁₁When the cutting of the steering wheel 6 is started, a wheel speed difference is generated between the inner rear wheel and the outer rear wheel, and the vehicle attitude control is started. Thus, in the flowchart of fig. 7, the processing of step S11 → S12 → S16 → S17 → S18 → S19 → S20 → S25 → S26 is performed. If the vehicle attitude control flag is changed to true in step S19 by this processing, the processing proceeds to step S12 → S13 and the processing below step S13 when the flowchart of fig. 7 is executed next.

In step S13, it is determined whether the low road friction mode has been set. In the example of the time chart of fig. 9, since the low road surface friction mode has been set, the process proceeds to step S14. In step S14, it is determined whether or not the lateral acceleration detected by the lateral acceleration sensor 22 is larger than a predetermined second lateral acceleration GY_b[G]High. At a lateral acceleration of a second lateral acceleration GY_bIn the following case, the process proceeds to step S16, and the braking force is not applied by the pre-brake LSD control. Further, in the present embodiment, the second lateral acceleration GY_bIs set to be higher than the first lateral acceleration GY_aA small value. That is, in a state where the lateral acceleration is very low, the pre-brake LSD control is not executed because there is no need to intervene in the pre-brake LSD control and the driver may feel discomfort due to unnecessary intervention.

On the other hand, the lateral acceleration is larger than the second lateral acceleration GY_bIn the case of (3), the process proceeds to step S15, where the basic command value F of the lower limit braking force by the pre-brake LSD control is determined_b3. In step S15, the basic command value F_b3By multiplying the maximum value of the most recently set basic command value Fb1 for vehicle attitude control by a predetermined coefficient C_m3And is calculated by equation (4).

F_b3＝C_m3×F_b1 (4)

In the present embodiment, the coefficient C_m3Is set to a positive value less than 1. That is, the basic command value F based on the pre-brake LSD control_b3Basic command value F set to be always more controlled than the vehicle attitude_b1The maximum value of (a) is small. In the example shown in fig. 9, at time t₁₁～t₁₂Basic command value F of vehicle attitude control_b1Since the maximum value of the coefficient is updated at any time, the coefficient C is multiplied by the maximum value_m3The latter basic instruction value F_b3The value of (c) also increases. Then, at time t₁₂～t₁₃Basic command value F of vehicle attitude control_b1Is constant at the maximum value, and therefore the maximum value is also constant, and the maximum value is multiplied by a coefficient C_m3The latter basic instruction value F_b3Becomes a constant value. Further, at time t₁₃Thereafter, the basic command value F for the vehicle attitude control_b1To reduce the tendency, but with its maximum value held, the maximum value is multiplied by a factor C_m3The latter basic instruction value F_b3Also has a value ofIs held. The basic command value F based on the pre-brake LSD control_b3Is maintained until at time t₁₇Until the turning travel is completed and the vehicle posture control flag is changed to false (step S23 → S24). In this way, even if the wheel speed difference between the inner rear wheel and the outer rear wheel decreases after the first braking force is applied by the vehicle attitude control, the braking force equal to or greater than the predetermined lower limit braking force is maintained until the end of turning.

In this way, the braking force based on the pre-brake LSD control is applied for the purpose of suppressing: after the braking force is applied based on the vehicle attitude control (time t in fig. 9)₁₄Thereafter) the application of the braking force is started again by the brake LSD control (time t in fig. 9)₁₅) The braking force applied to the inner rear wheel of the vehicle 1 changes in a short time, giving an uncomfortable feeling to the driver. On the other hand, when the high road surface friction mode is selected, the application of the braking force by the brake LSD control is rarely performed after the application of the braking force by the vehicle posture control is completed, and the applied braking force becomes relatively small even when the brake LSD control is performed. Therefore, in the present embodiment, the lower limit braking force based on the pre-brake LSD control is set when the low road surface friction mode is selected, and the pre-brake LSD control is not executed when the high road surface friction mode is selected (step S13 → S16 in fig. 7). Alternatively, as a modification, the present invention may be configured to execute the pre-brake LSD control even when the high road surface friction mode is selected. In this case, the coefficient C in the high road friction mode is preferably set to_m3Set to the coefficient C in the mode of lower road surface friction_m3Is small.

Next, in the example shown in fig. 9, at time t₁₅～t₁₆When the slip of the inner rear wheel occurs, the basic command value Fb2 for the brake LSD control is set. Thus, in the example shown in FIG. 9, at time t₁₁～t₁₄Setting basic command value F based on vehicle attitude control_b1At time t₁₁～t₁₇Setting is based on pre-braking LBasic instruction value F of SD control_b3At time t₁₅～t₁₆Setting a basic command value F for brake LSD control_b2。

In step S25 of fig. 7, gains by which the basic command values are multiplied are set, and command values F by which the gains are multiplied are calculated₁、F₂、F₃. Further, in step S26, these instruction values F are compared₁、F₂、F₃The maximum command value is used, and the braking force is applied to the inner rear wheel based on the command value. The setting of the gain to be multiplied by each basic command value in step S25 will be described later with reference to fig. 11 to 19.

Next, referring to fig. 10, the threshold value of the wheel speed difference (first wheel speed difference T) used in step S17 of fig. 7 is set_a) The setting of (a) will be explained.

Fig. 10 is an example of a map for setting the threshold value of the wheel speed difference, and the first wheel speed difference T in step S17 in fig. 7_a[m/sec]Is set based on the map of fig. 10. First wheel speed difference T_aThe value of (d) is changed based on the vehicle speed of the vehicle 1 detected by the vehicle speed sensor 20. As shown in FIG. 10, the first wheel speed differential T_aIs maximum at a vehicle speed of 0, decreases as the vehicle speed increases, and is at a predetermined vehicle speed V₁The above is approximately a constant value. The setting is preferably performed as follows: will speed the vehicle V₁Is set to a value of about 80 to about 110 km/h]Left and right, above this value, the first wheel speed difference T_aAbout 0.02 to about 0.05[ m/sec [ ]]。

In this way, the condition for starting execution of the vehicle attitude control is changed by changing the threshold value of the wheel speed difference in accordance with the vehicle speed. That is, by setting the first wheel speed difference T as the threshold value of the wheel speed difference in advance_aThus, in the region where the vehicle speed is low, the vehicle attitude control executed below step S18 of fig. 7 becomes difficult to intervene. That is, in a region where the vehicle speed is low, an error is likely to occur in the measured value of the wheel speed, and if the vehicle attitude control is executed due to a slight difference in wheel speed, the vehicle attitude control may be executed based on the measurement error. In order to suppress such unneedingIn the present embodiment, the intervention of the vehicle attitude control is set with the first wheel speed difference T as shown in fig. 10_aThe value of (c).

Next, referring to fig. 11 to 19, the gain to be multiplied by each basic command value in step S25 in fig. 7 will be described.

FIG. 11 shows a basic command value F based on vehicle attitude control set according to a steering angle_b1Multiplied steering angle gain. FIG. 12 shows a basic command value F based on vehicle attitude control set according to the change speed of the accelerator opening_b1The multiplied gain of the change speed of the accelerator opening degree. Fig. 13 to 15 are maps applied when the high road friction mode is set. FIG. 13 shows a basic command value F set according to the accelerator opening degree and controlled based on the vehicle attitude_b1A map of multiplied accelerator opening gain. FIG. 14 shows a basic command value F set according to the lateral acceleration and based on the vehicle attitude control_b1Mapping of the multiplied lateral acceleration gain. FIG. 15 shows a basic command value F set according to the vehicle speed and based on the vehicle attitude control_b1A map of multiplied vehicle speed gains.

Fig. 16 to 18 are maps applied to the case where the low road surface friction mode is set. FIG. 16 shows a basic command value F set according to the accelerator opening degree and controlled based on the vehicle attitude_b1A map of multiplied accelerator opening gain. FIG. 17 shows a basic command value F set according to the lateral acceleration and based on the vehicle attitude control_b1Mapping of the multiplied lateral acceleration gain. FIG. 18 shows a basic command value F set according to the vehicle speed and controlled based on the vehicle attitude_b1A map of multiplied vehicle speed gains. Fig. 19 is a map of the differential rotation gain, which is set based on the difference between the inner and outer wheel speeds and is multiplied by the basic command value Fb2 by the brake LSD control.

As shown in fig. 11, the steering angle gain G_θIs set as: at steering angle theta deg]Is the first steering angle theta₁The following region is zero at θ₁The above points increase and converge to "1" at a predetermined steering angle or more. By setting the steering angle gain G in this way_θSo that the steering angle is the first steering angle theta₁The following region does not substantially perform vehicle attitude control and does not intervene in control (by multiplying steering angle gain G)_θAnd the command value for the vehicle attitude control is zero. ). This suppresses the driver from being confused by the intervention of the vehicle attitude control by the fine steering of the steering wheel 6. The setting is preferably performed as follows: the first steering angle theta₁Is set to a value of about 3.5 to about 6.0[ deg ]]On the left and right sides, below this value, the steering angle gain G_θIs zero.

As shown in fig. 12, the accelerator opening change speed gain G_AVIs set as: at the change speed A of the accelerator opening degree_V[％/sec]The region near zero is "1.2", decreases with an increase in the change rate, and converges to "0.5" at a predetermined change rate or higher. Here, when the difference in wheel speed (differential rotation) between the inner rear wheel and the outer rear wheel increases due to rapid depression of an accelerator pedal (not shown) (a large accelerator opening change speed) of the vehicle 1, the differential limiting device 4d provided in the differential gear 4c operates. The differential limiting device 4d acts to sharply reduce the wheel speed difference.

When the vehicle attitude control is operated in superimposition with the action of the differential limiting device 4d and a large braking force acts on the inner rear wheels, the rate of change in the wheel speed difference becomes excessively large, and the driver may be given an uncomfortable feeling. Therefore, the speed gain G is changed by setting the accelerator opening degree_AVAccordingly, in a situation where the accelerator pedal (not shown) is rapidly depressed, the braking force applied by the vehicle attitude control is reduced. That is, the accelerator pedal position is multiplied by the accelerator pedal position change speed gain G set as shown in fig. 12_AVAccordingly, the greater the speed of change of the accelerator opening detected by the accelerator opening sensor, the smaller the braking force acting on the inner rear wheel of the vehicle during turning. This suppresses the driver from feeling uncomfortable due to the excessive change speed of the wheel speed difference.

As shown in fig. 13, the accelerator opening gain G_aHIs set as: with accelerator opening [ ]]At the first throttleOpening degree A₁Becomes "1" at the first accelerator opening degree A₁The above converges to a prescribed value greater than "1". By setting the accelerator opening gain G in this way_aHSo that the command value based on the vehicle attitude control becomes smaller as the accelerator opening degree decreases. That is, in the region where the accelerator opening degree is small, the floating of the inner rear portion of the vehicle body 1a is less likely to occur, and therefore, the driver is restrained from being given an uncomfortable feeling due to unnecessary intervention of the vehicle attitude control. The setting is preferably performed as follows: the first accelerator opening degree A₁Is set to a value of about 45 to about 60 [% ]]On the left and right sides, below this value, the accelerator opening is increased by G_aHIs set to be less than 1; above this value, the accelerator opening gain G_aHIs more than 1.

As shown in fig. 14, the lateral acceleration gain G_lHIs set as: at a lateral acceleration a_l[G]Is a first lateral acceleration a_l1The following region is zero, at a_l1The above increases and converges to "1" at a prescribed lateral acceleration or more. By setting the lateral acceleration gain G in this way_lHAccordingly, when the lateral acceleration of the vehicle 1 is large, a braking force that is larger than a braking force when the lateral acceleration of the vehicle 1 is small acts on the inner rear wheels of the vehicle 1 that is turning. In addition, by setting the lateral acceleration gain G as shown in fig. 14_lHSo that the lateral acceleration is the first lateral acceleration a_l1A region where the intervention of the vehicle attitude control is not substantially performed (by multiplying by a lateral acceleration gain G)_lHAnd the command value for the vehicle attitude control is zero. ). I.e. in the lateral acceleration a_lIn the fine region, the floating of the inner rear portion of the vehicle body 1a is less likely to occur, and therefore, the driver is inhibited from being given an uncomfortable feeling due to unnecessary intervention of vehicle attitude control. The setting is preferably performed as follows: the first lateral acceleration a_l1Is set to a value of about 0.22 to about 0.35[ G ]]Left and right, below which is the lateral acceleration gain G_lHIs zero.

As shown in FIG. 15, the vehicle speed gain G_VHIs set as: with vehicle speed [ km/h]Is gradually increased at a first vehicle speed V₁Is "1" at a first vehicle speed V₁The above increases comparatively sharply. By setting the vehicle speed gain G in this way_VHTherefore, the command value based on the vehicle posture control becomes larger as the vehicle speed increases, and when the vehicle speed is high, a larger braking force acts on the inner rear wheel of the vehicle during turning than when the vehicle speed is low. That is, in a region where the vehicle speed is small, the floating of the inner rear portion of the vehicle body 1a is less likely to occur, and the problem of the floating of the inner rear portion of the vehicle body 1a becomes more pronounced as the vehicle speed increases, so that the command value is increased, and the vehicle attitude control is strongly involved. The setting is preferably performed as follows: will first vehicle speed V₁Is set to a value of about 95 to about 115[ km/h]Left and right, and below the value, the vehicle speed is gained by G_VHIs set to be less than 1; above this value, the vehicle speed gain G_VHAnd is increased.

In step S25 of fig. 7, when the high road friction mode is selected, the basic command value F for the vehicle attitude control is set_b1Multiplied by a steering angle gain G set based on fig. 11_θAccelerator opening degree change speed gain G set based on fig. 12_AVAccelerator opening gain G set based on fig. 13_aHAnd a lateral acceleration gain G set based on FIG. 14_lHAnd a vehicle speed gain G set based on FIG. 15_VHCalculating a command value F for vehicle attitude control by the mathematical expression (5)₁。

F₁＝G_θ×G_AV×G_aH×G_lH×G_VH×F_b1 (5)

On the other hand, when the low road surface friction mode is selected, the accelerator opening degree gain, the lateral acceleration gain, and the vehicle speed gain are set using maps shown in fig. 16 to 18 different from the case where the high road surface friction mode is selected.

As shown in fig. 16, when the low road friction mode is selected, the accelerator opening degree gain G_aLIs set as: with accelerator opening [ ]]Is increased and at a second accelerator opening a₂Is at "1" and at a second accelerator opening degree A₂The above parts becomeGreater than a prescribed value of "1". By setting the accelerator opening gain G in this way_aLSo that the command value based on the vehicle attitude control becomes smaller as the accelerator opening degree decreases. In addition, accelerator opening gain G in low road friction mode_aLSecond throttle opening A of "1₂Set as the accelerator opening gain G in the friction mode of the high road surface_aHFirst throttle opening A of "1₁Is large. The setting is preferably performed as follows: the second accelerator opening degree A₂Is set to a value of about 60 to about 75 [% ]]On the left and right sides, below this value, the accelerator opening is increased by G_aLIs set to be less than 1; above this value, the accelerator opening gain G_aLIs more than 1.

As shown in fig. 17, when the low road friction mode is selected, the lateral acceleration gain G_lLIs set as: at a lateral acceleration a_l[G]Is a second lateral acceleration a_l2The following region is zero at the second lateral acceleration a_l2The above increases and converges to "1" at a prescribed lateral acceleration or more. In this way, since the lateral acceleration gain is set in the low road surface friction mode differently from the high road surface friction mode, different braking forces are generated for the same lateral acceleration between the low road surface friction mode and the high road surface friction mode in the vehicle attitude control. In addition, by setting the lateral acceleration gain G in this way_lLSo that the lateral acceleration is the second lateral acceleration a_l2A region where the intervention of the vehicle attitude control is not substantially performed (by multiplying by a lateral acceleration gain G)_lLThe command value for vehicle attitude control is zero. ). In addition, in the present embodiment, the lateral acceleration gain G is set in the low road surface friction mode_lLA second lateral acceleration a greater than zero_l2And a lateral acceleration gain G in a high road friction mode_lHA first lateral acceleration a greater than zero_l1Is set to be higher than the first lateral acceleration a_l1Is small. That is, in the low road friction mode, the vehicle attitude control is performed from a state in which the lateral acceleration is smaller than that in the high road friction mode. The setting is preferably performed as follows: will be firstTwo lateral accelerations a_l2Is set to a value of about 0.02 to about 0.15[ G ]]Left and right, below which is the lateral acceleration gain G_lLIs zero.

As shown in fig. 18, when the low road friction mode is selected, the vehicle speed gain G_VLIs set as: at a second vehicle speed V₂Set to zero at the second vehicle speed V₂The above increases and converges to a predetermined value smaller than "1" at a predetermined vehicle speed or higher. Therefore, when the vehicle speed is high, a braking force that is greater than that when the vehicle speed is low acts on the inner rear wheels of the vehicle that is turning. In addition, the vehicle speed gain G is set in this way_VLThus, at the second vehicle speed V₂Hereinafter, the vehicle attitude control is not involved, and the command value based on the vehicle attitude control is reduced even in a region where the vehicle speed is large. That is, in the case where the low road friction mode is selected, the intervention of the vehicle attitude control can be suppressed at any vehicle speed as compared with the high road friction mode. That is, the slip of the inner rear wheel is suppressed by the braking force of the vehicle attitude control. Preferably, the second vehicle speed V is set₂Is set to a value of about 15 to about 30[ km/h]Left and right, and gain G in vehicle speed_VLThe vehicle speed gain G is set so as to converge to about 0.3 to about 0.6 in a region where the vehicle speed is large_VL。

In step S25 of fig. 7, when the low-road friction mode is selected, the basic command value F for the vehicle attitude control is set_b1Multiplied by a steering angle gain G set based on fig. 11_θAccelerator opening degree change speed gain G set based on fig. 12_AVAccelerator opening gain G set based on fig. 16_aLAnd a lateral acceleration gain G set based on FIG. 17_lLAnd a vehicle speed gain G set based on FIG. 18_VLCalculating a command value F for vehicle attitude control by the mathematical expression (6)₁。

F₁＝G_θ×G_AV×G_aL×G_lL×G_VL×F_b1 (6)

Next, referring to fig. 19, the comparison between the case where the low road surface friction mode is selected and the case where the low road surface friction mode is selectedBasic command value F based on brake LSD control_b2Multiplied difference rotation gain G_DLThe description is given. Further, in the case where the high road friction mode is selected, the differential rotation gain G_DHAlways is "1".

As shown in fig. 19, the difference rotation gain G_DLIs set as: the differential rotation D between the inner wheel and the outer wheel is a first differential rotation D₁[m/sec]The following is "1", and the rotation D is the first differential rotation₁The above is converged to a predetermined value larger than "1". By setting the differential rotation gain G in this way_DLSo that when the differential rotation becomes the first differential rotation D₁In the above case, the command value for the brake LSD control increases. That is, when the low road surface friction mode is selected, the braking force that acts when the inner wheel slips is set to be larger than that when the high road surface friction mode is selected, and the inner wheel slip is suppressed to a greater degree. Preferably, the value of the first differential rotation D1 is set to a value of about 8 to about 12[ m/sec [/sec ]]On the left and right sides, and above this value, the command value for brake LSD control is increased. In addition, preferably, the difference rotation gain G_DLThe difference rotation D is set to converge to about 1.3 to about 1.6 in a large region.

In step S25 of fig. 7, when the low road friction mode is selected, the basic command value F for the brake LSD control is set_b2Multiplied by the difference rotation gain G set based on fig. 19_DLThe command value F for the brake LSD control is calculated by the following equation (7)₂. On the other hand, when the high road friction mode is selected, the differential rotation gain G_DHIs always "1", so the basic instruction value F_b2The value is set directly to the instruction value F₂。

F₂＝G_DL×F_b2 (7)

Thus, in step S25 of fig. 7, the basic command value F based on the vehicle attitude control_b1And calculates a command value F for vehicle attitude control by the mathematical expression (5) or (6)₁. And, the basic command value F based on the brake LSD control_b2And calculates the instruction value F by the mathematical expression (7)₂Or else the basic instruction value F_b2Directly as instructionsValue F₂。

Further, when the low road friction mode is selected, the command value F of the pre-brake LSD control₃By applying to the basic instruction value F_b3Multiplied by the same gain as that for the vehicle attitude control. That is, the command value F is calculated by the following equation (8)₃. As described above, the pre-brake LSD control is applied for the following purposes: the braking force variation during the period until the braking force is applied by the brake LSD control after the application of the braking force based on the vehicle attitude control is completed is suppressed. Therefore, as for the command value for the pre-brake LSD control, the same gain as that for the vehicle attitude control is also multiplied to set the braking force in a smoothly connected manner with the vehicle attitude control.

F₃＝G_θ×G_AV×G_aL×G_lL×G_VL×F_b3 (8)

On the other hand, when the high road friction mode is selected, as described above, the pre-brake LSD control (command value F of the pre-brake LSD control) is not executed₃0). However, in the case where the present invention is configured as a modification to execute the pre-brake LSD control even when the high road surface friction mode is selected, the command value F can be calculated by the following equation (9)₃. Thus, even in the high road surface friction mode, the braking force can be set to be smoothly connected to the vehicle attitude control.

F₃＝G_θ×G_AV×G_aH×G_lH×G_VH×F_b3 (9)

Then, in step S26 of fig. 7, the command value F for vehicle attitude control calculated as described above is subjected to₁Command value F for brake LSD control₂Command value F for pre-brake LSD control₃The maximum command value is finally determined as the command value of the braking force acting on the inner rear wheel by comparison. When the command value of the braking force is determined in step S26 of fig. 7, the process proceeds to step S5 of the flowchart of fig. 6, and the brake device 8 is controlled based on the determined command value in step S5.

According to the vehicle attitude control device of the first embodiment of the present invention, the lateral acceleration a of the vehicle 1 during turning travel of the vehicle based on the cut-in operation of the steering wheel is set_lWhen the acceleration is large, the lateral acceleration a of the vehicle 1 is set to be larger than_lA large braking force in a small case acts on the inner rear wheel of the vehicle in turning (fig. 14 and 17). When braking force (command value F) is applied₁) When acting on the inner rear wheels of the vehicle 1, a force that pulls down the inner rear portion of the vehicle body 1a via the suspension 3 as a wheel suspension acts, and the inner rear portion of the vehicle body 1a is suppressed from floating.

In addition, according to the vehicle attitude control device of the present embodiment, the vehicle attitude control device is based on the difference in wheel speed between the inner rear wheel and the outer rear wheel (step S16 in fig. 7) and the lateral acceleration a of the vehicle 1_lTo set the braking force (command value F) to be applied to the inner rear wheel of the vehicle 1₁) Therefore, the braking force for suppressing the inner rear portion of the vehicle body 1a from floating can be set more accurately.

Further, according to the vehicle posture control device of the present embodiment, when the vehicle speed V is large, a braking force larger than that when the vehicle speed V is small acts on the inner rear wheel (fig. 15 and 18) of the vehicle 1 during turning, and therefore, an appropriate braking force according to the vehicle speed V can be set.

Further, according to the vehicle attitude control device of the present embodiment, when the accelerator opening degree is large, a braking force larger than that in the case where the accelerator opening degree is small acts on the inner rear wheel (fig. 13 and 16) of the vehicle in a curve, and therefore, an appropriate braking force according to the accelerator opening degree can be set.

Further, according to the vehicle attitude control device of the present embodiment, when the steering angle θ based on the cut-in operation of the steering wheel 6 is equal to or less than the predetermined value, the vehicle attitude control is not executed (the braking force based on the vehicle attitude control is equal to 0) (fig. 11), so that it is possible to prevent the following: vehicle attitude control gives the driver a sense of incongruity based on a fine steering intervention to an unintended degree.

Further, according to the vehicle posture control device of the present embodiment, since different braking forces are generated for the same lateral acceleration between the low road surface friction mode (fig. 17) and the high road surface friction mode (fig. 14), an appropriate braking force according to the road surface friction can be set.

Further, according to the vehicle attitude control device of the present embodiment, the first lateral acceleration a is regarded as the first acceleration in the high road friction mode_l1In the above (fig. 14), the second lateral acceleration a is obtained in the low road friction mode_l2Since the vehicle attitude control is executed in the above-described manner (fig. 17), the execution of the vehicle attitude control can be started at an appropriate timing in accordance with the road surface friction.

Further, according to the vehicle posture control device of the present embodiment, since the condition for starting execution of the vehicle posture control is changed in accordance with the vehicle speed V (step S17 in fig. 7, fig. 10), the execution of the vehicle posture control can be started at an appropriate timing in accordance with the vehicle speed.

Further, according to the vehicle attitude control device of the present embodiment, the upper arm 3a and the lower arm 3b as the link mechanism suspending the axles of the

rear wheels

2c and 2d from the vehicle body 1a are disposed around the predetermined suspension center P with the axles around the predetermined suspension center P_SThe axle 2e is suspended in a rotatable manner (fig. 4). The suspension center P_SSince the vehicle body 1a is located above the axle 2e, when braking force is applied to the

rear wheels

2c and 2d, the component of the force pulling the vehicle body 1a downward through the upper arm 3a and the lower arm 3b is increased, and therefore, the floating of the vehicle body inner rear portion can be more effectively suppressed.

In the vehicle attitude control device of the present embodiment, the vehicle 1 includes the mechanical differential limiting device 4d, and therefore, due to this action, the difference in wheel speed between the inner rear wheel and the outer rear wheel is reduced more rapidly as the accelerator opening degree is larger. If the brake control unit 14a applies the braking force to the inner rear wheel based on the vehicle attitude control in addition to the operation of the differential limiting device 4d, the change in the wheel speed difference between the inner rear wheel and the outer rear wheel becomes excessively large, which may give an uncomfortable feeling to the driver. According to the vehicle attitude control device of the present embodiment, the braking force acting on the inner rear wheel is made smaller as the change speed of the accelerator opening degree is larger (fig. 12), so that it is possible to suppress discomfort given to the driver.

Next, a vehicle posture control device according to a second embodiment of the present invention will be described with reference to fig. 20 and 21.

The vehicle attitude control device of the present embodiment is different from the first embodiment described above in that the braking force applied by the vehicle attitude control is determined by the same control algorithm regardless of the road surface friction of the road surface on which the vehicle 1 is traveling. Therefore, only the points of the second embodiment of the present invention which are different from the first embodiment will be described, and the same configurations, operations, and effects will not be described. That is, in the first embodiment described above, different vehicle attitude controls are executed in the case where the low road surface friction mode is selected and in the case where the high road surface friction mode is selected. In contrast, in the present embodiment, when the same lateral acceleration acts on the vehicle 1, the same braking force is applied regardless of the road surface friction of the running road surface.

Fig. 20 is a flowchart showing a process for determining a command value in vehicle attitude control in the present embodiment, and corresponds to fig. 7 of the first embodiment.

In the flowchart according to the first embodiment shown in fig. 7, it is determined whether or not the low road friction mode is selected in step S13, and when the low road friction mode is selected, a command value for the pre-brake LSD control is set in step S15. On the other hand, in the case where the low road friction mode is not selected (in the case of the high road friction mode), the pre-brake LSD control is not executed.

In contrast, in the present embodiment, the "low road surface friction mode" and the "high road surface friction mode" are not selected, and the command value for the pre-brake LSD control is set regardless of the road surface friction. That is, in the present embodiment, as shown in fig. 20, when the vehicle posture control flag is true (step S112) and the lateral acceleration detected by the lateral acceleration sensor 22 is larger than the predetermined second lateral acceleration GY_b[G]When the braking force is high (step S113), the basic lower limit braking force based on the pre-brake LSD control is always determined in step S114Instruction value F_b3. The flowchart shown in fig. 20 is the same as the flowchart shown in fig. 7, except that the low road friction mode and the high road friction mode are not selected. That is, in step S114, the basic command value F is set regardless of the road surface friction_b3All by the basic command value F for the most recently set vehicle attitude control_b1Is multiplied by a predetermined coefficient C_m3And is calculated by the equation (10).

F_b3＝C_m3×F_b1 (10)

In the present embodiment, the basic command value F for vehicle attitude control calculated in step S119 of fig. 20_b1[N]Similarly to step S20 of fig. 7, the wheel speed is determined based on the wheel speed difference between the left and right rear wheels. I.e. the basic instruction value F_b1Is a command value of a braking force applied to the inner rear wheel of the turning vehicle 1, and is transmitted to the outer wheel speed V_oWheel speed V with the inner side_iMultiplying the difference by a predetermined coefficient C_m1And is calculated by the equation (11).

F_b1＝C_m1×(V_o-V_i) (11)

In the present embodiment, the basic command value F of the brake LSD control calculated in step S121 of fig. 20_b2[N]Similarly to step S22 of fig. 7, the wheel speed is determined based on the wheel speed difference between the left and right rear wheels. That is, the basic command value F of the braking force based on the brake LSD control_b2Is a command value of a braking force applied to the inner rear wheel of the turning vehicle 1, by the wheel speed V to the inner side_iSpeed V of wheel with outside_oMultiplying the difference by a predetermined coefficient C_m2And is calculated by equation (12).

F_b2＝C_m2×(V_i-V_o) (12)

In step S124 of fig. 20, the basic command values F calculated as described above are compared with each other_b1、F_b2、F_b3Respectively multiplied by gains to thereby calculate a command value F for vehicle attitude control₁Command value F for brake LSD control₂Command value F for pre-brake LSD control₃。

Namely, the command value F for vehicle attitude control₁At the basic instruction value F_b1Up times steering angle gain G_θAccelerator opening change speed gain G_AVAccelerator opening gain G_aLateral acceleration gain G_lAnd vehicle speed gain G_VAnd is calculated by the mathematical formula (13).

F₁＝G_θ×G_AV×G_a×G_l×G_V×F_bl (13)

Here, the steering angle gain G in the formula (13)_θAnd accelerator opening change speed gain G_AVThe same gain as that set in the first embodiment described above can be used. In addition, the accelerator opening gain G_aLateral acceleration gain G_lAnd a vehicle speed gain G_VThe accelerator opening degree gain G set in the case where the high road surface friction mode is selected in the first embodiment can be used_aHLateral acceleration gain G_HAnd vehicle speed gain G_VHThe same gain. Alternatively, gains different from the gains set in the first embodiment may be set.

And, a command value F for brake LSD control₂Is at the basic command value F for the brake LSD control_b2Up multiplied by a difference rotation gain G_DAnd is calculated by the equation (14). Here, the difference rotation gain G_DThe setting is based on the map shown in fig. 21. In the first embodiment described above, the differential rotation gain G is obtained when the low road surface friction mode is selected_DLThe difference rotation gain G is set based on the map shown in fig. 19, and when the high road surface friction mode is selected_DHIs always set to "1". In contrast, in the present embodiment, the differential rotation gain G is not determined regardless of the road surface friction_DAre set based on the map shown in fig. 21.

F₂＝G_D×F_b2 (14)

FIG. 21 shows a rotation gain G for setting the difference_DBut the mapping used.

As shown in fig. 21, the difference rotation gain G_DIs set as: differential rotation D m/sec between the inner and outer wheels]The low range is set to a value of about 0.8 or less and converges to "1" as the differential rotation D becomes larger. By setting the differential rotation gain GD in this manner, the command value for the brake LSD control increases as the differential rotation increases. Further, since the differential rotation gain GD converges to "1" as the differential rotation D increases, the command value for the brake LSD control does not become excessively large even when the road surface friction is large.

The command value F3 for the pre-brake LSD control is set to the basic command value F_b3Multiplied by the same gain as the vehicle attitude control. That is, the command value F is calculated by the following equation (15)₃. The pre-brake LSD control is applied for the purposes of: the braking force variation during the period until the braking force is applied by the brake LSD control after the application of the braking force based on the vehicle attitude control is completed is suppressed. Therefore, the command value for the pre-brake LSD control is also multiplied by the same gain as the vehicle attitude control to set the braking force so as to smoothly connect to the vehicle attitude control.

F₃＝G_θ×G_AV×G_a×G_l×G_V×F_b3 (15)

Next, in step S125 of fig. 20, command value F for vehicle attitude control calculated by each of equations (13) to (15)₁Command value F for brake LSD control₂Command value F for pre-brake LSD control₃The largest command value is finally determined as the command value of the braking force acting on the inner rear wheel by comparison. The braking device 8 is controlled based on the command value of the braking force determined in step S125 in fig. 20, which is the same as the first embodiment described above.

In the first embodiment described above, different command values are calculated between the case where the high road surface friction mode is selected and the case where the low road surface friction mode is selected, and the braking force applied by the brake device 8 is also different. In contrast, in the present embodiment, there is no choice concerning the road surface friction, and if the running state of the vehicle 1 such as the lateral acceleration acting on the vehicle 1 is the same, the same braking force is generated by the brake device 8 regardless of the road surface friction of the running road surface.

In the present embodiment, in step S116 of fig. 20, the wheel speed difference between the inner rear wheel and the outer rear wheel of the vehicle 1 during cornering is the first wheel speed difference T_a[m/sec]In the following case, the process proceeds to step S122. Therefore, the basic command value F for the vehicle attitude control is not set in step S119_b1[N](F_b10). Similarly, in step S120 of fig. 20, the wheel speed difference between the outer rear wheel and the inner rear wheel (inner wheel speed — outer wheel speed) is the second wheel speed difference T_b[m/sec]In the following case, the process proceeds to step S122. Therefore, the basic command value F for the brake LSD control is not set in step S121_b2[N](F_b20). In addition, the basic command value F based on the pre-brake LSD control_b3By applying to the basic instruction value F_b1Is multiplied by a predetermined coefficient C_m3The basic instruction value is calculated, so that if the basic instruction value F_b1If 0, the basic command value F_b3Also zero.

As described above, in the present embodiment, when the wheel speed difference between the inner rear wheel and the outer rear wheel of the vehicle 1 during turning is equal to or less than the predetermined threshold value, the basic command value F is set_b1、F_b2、F_b3All of which are zero, and the braking force by the brake device 8 is not applied.

A vehicle control device according to a second embodiment of the present invention is configured to: when the same lateral acceleration acts on the vehicle 1 during traveling, the same braking force is generated regardless of the road surface friction of the road surface during traveling, and therefore, the control algorithm can be easily configured without changing the control according to the road surface friction. Further, according to the vehicle control device of the present embodiment, since the braking force is not applied when the wheel speed difference is equal to or less than the predetermined threshold value, it is possible to suppress excessive intervention of the braking force generated by the brake device 8, and to suppress the inner rear float of the vehicle 1 during turning by applying an appropriate braking force in a situation where the braking force is required.

Although the vehicle attitude control device according to the embodiment of the present invention has been described above, various modifications can be made to the above-described embodiment. In particular, although the vehicle attitude control device according to the present invention is applied to the rear wheel drive vehicle in the above-described embodiment, the present invention can be applied to any drive type vehicle such as a four-wheel drive vehicle.

Claims

1. A vehicle attitude control device for controlling the attitude of a vehicle having front wheels and rear wheels, the vehicle attitude control device being configured such that a roll axis of a vehicle body is tilted forward, the vehicle attitude control device comprising:

a lateral acceleration sensor that detects a lateral acceleration of the running vehicle;

a brake actuator that applies a braking force to a wheel of a vehicle; and

a brake control device that transmits a control signal to the brake actuator based on a traveling state of the vehicle to cause the brake actuator to generate a braking force,

the brake control device executes vehicle attitude control, at the time of turning travel of the vehicle based on a cut-in operation of a steering wheel of the vehicle, as follows: when the lateral acceleration of the vehicle is large, a braking force that is larger than the braking force when the lateral acceleration of the vehicle is small is applied to the inner rear wheel of the vehicle during turning, and the floating of the vehicle body inner rear portion is suppressed.

2. The vehicle attitude control device according to claim 1,

the brake control device sets a braking force acting on the inner rear wheel of the vehicle based on a difference between wheel speeds of the inner rear wheel and the outer rear wheel detected by the wheel speed sensor and a lateral acceleration of the vehicle.

3. The vehicle attitude control device according to claim 1,

the vehicle braking control device is further provided with a vehicle speed sensor for detecting a vehicle speed, and when the vehicle speed detected by the vehicle speed sensor is large, the braking control device causes a braking force larger than that when the vehicle speed is small to act on an inner rear wheel of the vehicle during turning.

4. The vehicle attitude control device according to claim 1,

the vehicle further includes an accelerator opening sensor, and the brake control device causes a braking force larger than a braking force when the accelerator opening detected by the accelerator opening sensor is large to act on an inner rear wheel of the vehicle during turning.

5. The vehicle attitude control device according to claim 1,

the vehicle control system further includes a steering angle sensor that detects a steering angle of a steering wheel of a vehicle, and the brake control device does not execute the vehicle attitude control when the steering angle detected by the steering angle sensor based on the cut-in operation of the steering wheel is equal to or less than a predetermined value.

6. The vehicle attitude control device according to claim 1,

the brake control device is configured to be able to execute vehicle attitude control based on a low road surface friction mode in which different braking forces are generated for the same lateral acceleration and vehicle attitude control based on a high road surface friction mode.

7. The vehicle attitude control device according to claim 1,

the brake control device is configured to be capable of executing a vehicle attitude control based on a high road surface friction mode in which the brake control device executes the vehicle attitude control when a lateral acceleration of a vehicle becomes a first lateral acceleration or more, and a vehicle attitude control based on a low road surface friction mode; in the low road surface friction mode, the brake control device executes the vehicle attitude control when a lateral acceleration of the vehicle becomes equal to or greater than a second lateral acceleration different from the first lateral acceleration.

8. The vehicle attitude control device according to claim 1,

the vehicle control system further includes a vehicle speed sensor for detecting a speed of the vehicle, and the brake control device changes a condition for starting execution of the vehicle attitude control in accordance with the vehicle speed detected by the vehicle speed sensor.

9. The vehicle attitude control device according to claim 1,

the wheel suspension device includes a link mechanism that suspends an axle of a rear wheel from a vehicle body, and the link mechanism suspends the axle so that the axle pivots about a predetermined suspension center that is located above the axle.

10. The vehicle attitude control device according to claim 1,

the vehicle is provided with a mechanical differential limiting device which mechanically controls a wheel speed difference between an inner rear wheel and an outer rear wheel of the vehicle in a turning state according to torques respectively acting on the inner rear wheel and the outer rear wheel of the vehicle in the turning state, and the vehicle posture control device is further provided with an accelerator opening degree sensor which decreases a braking force acting on the inner rear wheel of the vehicle in the turning state as a change speed of an accelerator opening degree detected by the accelerator opening degree sensor increases.

11. The vehicle attitude control device according to claim 1,

12. The vehicle attitude control device according to claim 1,

13. The vehicle attitude control device according to claim 1,

14. The vehicle attitude control device according to claim 1,

the brake control device is configured to: the brake control device does not apply the braking force when the same lateral acceleration acts on the running vehicle, the same braking force is generated regardless of the road surface friction of the running road surface, and the wheel speed difference between the inner rear wheel and the outer rear wheel of the turning vehicle is equal to or less than a predetermined threshold value.