CN112109684B - Vehicle attitude control device - Google Patents
Vehicle attitude control device Download PDFInfo
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- CN112109684B CN112109684B CN202010447484.XA CN202010447484A CN112109684B CN 112109684 B CN112109684 B CN 112109684B CN 202010447484 A CN202010447484 A CN 202010447484A CN 112109684 B CN112109684 B CN 112109684B
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- braking force
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- 230000001133 acceleration Effects 0.000 claims abstract description 142
- 239000000725 suspension Substances 0.000 claims abstract description 23
- 230000008859 change Effects 0.000 claims description 22
- 230000007246 mechanism Effects 0.000 claims description 10
- 238000005520 cutting process Methods 0.000 claims description 9
- 230000007423 decrease Effects 0.000 claims description 8
- 238000000034 method Methods 0.000 description 27
- 230000008569 process Effects 0.000 description 27
- 238000012545 processing Methods 0.000 description 18
- 238000001514 detection method Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 8
- 230000009471 action Effects 0.000 description 7
- 230000002265 prevention Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000000994 depressogenic effect Effects 0.000 description 3
- 238000013507 mapping Methods 0.000 description 3
- 239000012530 fluid Substances 0.000 description 2
- 230000006870 function Effects 0.000 description 2
- 238000009987 spinning Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 230000008685 targeting Effects 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
- B60T8/17554—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve specially adapted for enhancing stability around the vehicles longitudinal axle, i.e. roll-over prevention
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
- B60T8/17555—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve specially adapted for enhancing driver or passenger comfort, e.g. soft intervention or pre-actuation strategies
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
- B60W30/02—Control of vehicle driving stability
- B60W30/025—Control of vehicle driving stability related to comfort of drivers or passengers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
- B60W30/02—Control of vehicle driving stability
- B60W30/04—Control of vehicle driving stability related to roll-over prevention
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
- B60W30/02—Control of vehicle driving stability
- B60W30/045—Improving turning performance
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2520/00—Input parameters relating to overall vehicle dynamics
- B60W2520/10—Longitudinal speed
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2520/00—Input parameters relating to overall vehicle dynamics
- B60W2520/12—Lateral speed
- B60W2520/125—Lateral acceleration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2520/00—Input parameters relating to overall vehicle dynamics
- B60W2520/28—Wheel speed
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2540/00—Input parameters relating to occupants
- B60W2540/10—Accelerator pedal position
- B60W2540/106—Rate of change
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60W2540/00—Input parameters relating to occupants
- B60W2540/18—Steering angle
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- Engineering & Computer Science (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Automation & Control Theory (AREA)
- Regulating Braking Force (AREA)
- Vehicle Body Suspensions (AREA)
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) having a wheel suspension device (3) in which a roll axis is tilted forward, comprising: a lateral acceleration sensor (22) that detects a lateral acceleration of the vehicle while the vehicle is traveling; a brake actuator (8) that applies a braking force to a wheel of the vehicle; and a brake control device (14 a) 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
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 region, 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 literature
However, if the bottom suspension is set in advance such that the vehicle body generates a pitching motion and generates an appropriate diagonal sway 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 tends 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 inner rear portion of the vehicle that is turning may float even in a region in which the lateral acceleration is not so large, and may give a sense of unease to the driver and the passenger.
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 traveling state of the vehicle to cause the brake actuator to generate a braking force, and that executes vehicle posture control as follows during turning traveling of the vehicle based on a cutting 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 cutting 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 feeling of uneasiness.
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 applied to the inner rear wheel of the vehicle on the basis of 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 an appropriate braking force can be set in accordance with 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 posture 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 the vehicle control device 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.
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 according to 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 discomfort may be given to the driver. 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 increases, and therefore, the discomfort 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 of a rear wheel 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 time 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 posture control apparatus 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 a threshold value of a 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 with a steering wheel
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. Engine
4a speed variator
4b drive shaft
4c differential gear
4d differential limiting device
6. Steering wheel
7. Steering device
8. Brake equipment (brake actuator)
10. Hydraulic pump
12. Valve unit
13. Hydraulic sensor
14 PCM
14a brake control part (brake control device)
14b turning control unit
14c sideslip prevention control part
16. Steering angle sensor
18. Accelerator 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 in which a vehicle posture control device according to a first embodiment of the present invention is mounted.
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, 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, or 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 in which the vehicle posture control device according to the present embodiment is mounted and a roll axis of a vehicle body 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 P 1 Where they intersect. Connect the intersection point P 1 And a point P where a straight line to a grounding point P2 of the rear wheel 2c intersects the central axis A of the vehicle body 1a rR And (4) crossing. The point P rR Is 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 rR A roll motion is performed for the 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 rR Also becoming the center point of 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 rR And a center point P of the front roll motion rF And (4) projecting the image. A center point P of roll motion connecting the rear portions of these vehicle bodies 1a rR And a center point P of the front portion rF Axis A of r Which 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 r A 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 r The 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 r By 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 S And (4) rotating. In addition, in the present embodiment, the suspension center point P S Is located above the axle 2e of the rear wheel 2d.
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 S Line segment l of 1 And the vehicle body 1a is pulled back rearward. If the line segment l is determined 1 The angle with the road surface is set to theta al F represents a frictional force acting between the road surface and the rear wheel 2d x Then, the vehicle body 1a is pulled down downwardCan pass through F x ×tanθ al To calculate. Further, let the wheel base of the vehicle 1 be I r Connecting the center of gravity G and the suspension center point P of the vehicle 1 S Set to X horizontal distance therebetween r The 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)
In this way, the rear portion of the vehicle body 1a can be pulled down by applying a braking force to the rear wheels 2c or 2d of the vehicle 1. In addition, in the present embodiment, the suspension center point P is a point at which the suspension center is suspended S Is 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 and a sensor or the like connected to the PCM14.
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 the PCM14. 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 PCM14. 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 a 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 through 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.
Meanwhile, 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 transmit 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 PCM14. 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 constituted by a computer including: a CPU, various programs (including a basic control program such as an OS, an application program that starts up and realizes a specific function on the OS) that are interpreted and executed on the CPU, and an internal memory such as a ROM, a RAM, etc. 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 PCM14. The detection signal read in step S1 is used for the processing in steps S2 to S4. Specifically, in step S1, a signal of a steering angle (a rotation angle of the steering wheel 6) [ deg ] from the steering angle sensor 16, a signal of an accelerator opening [% ] from the accelerator opening sensor 18, and a signal of a 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 process of determining a command value based on 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 the left rear portion of the vehicle body 1a is prevented from floating. In step S2, the flowchart shown in fig. 7 is called as a subroutine to determine a command value for applying the braking force acting on the inner rear wheel for the vehicle attitude control. 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, although the inside rear of the vehicle body 1a is floated at a certain acceleration, the inside rear floating of the vehicle body is suppressed by applying a small deceleration of a predetermined value or less in the vertical direction of the vehicle body 1a by applying the braking force set as described above.
Next, in step S3, a process of determining a command value based on the turning control is executed. The turning control is as follows: in order to improve the turning performance of the vehicle 1, 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 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, which are 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 anti-sideslip control is executed. The anti-sideslip control is control executed in the anti-sideslip 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 transmitted to the brake device 8 by the PCM14 based on the command values determined in steps S2 to S4, a braking force is applied to the vehicle 1, and the primary processing of the flowchart shown in fig. 6 is ended. The vehicle posture control, the turning control, and the anti-slip control 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 in step S2 of the flowchart shown in fig. 6 and executed by the brake control unit 14a of the PCM14. 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. The time charts shown in fig. 8 and 9 have the horizontal axis representing 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, the 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 t 0 Since 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 turning are compared, and the process proceeds to step S17 when the wheel speed on the outside is high, and proceeds to step S21 when the wheel speed on the inside is high. 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 t 1 The 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 a In the following case, the processing of step S23 and the following steps are 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 difference in wheel speed between the left and right rear wheels may be caused by an error of the wheel speed sensor 24, and may be based on a minute differenceSince the vehicle attitude control is involved due to a small wheel speed difference, there is a possibility that the driver will be given a sense of incongruity, and therefore the vehicle attitude control is not performed in the case where the wheel speed difference is slight. Furthermore, a first wheel speed difference T as a threshold value for the wheel speed difference a Based on the vehicle speed of the vehicle 1. The specific setting of the wheel speed difference threshold value will be described later with reference to fig. 10.
In the example of FIG. 8, when at time t 1 When 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 a Then, 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/sec 2 ]) Whether the vehicle speed detected by the vehicle speed sensor 20 is higher than a predetermined first vehicle speed Va [ km/h ]]Is high. At a lateral acceleration of a first lateral acceleration GY a The following or vehicle speed is the first vehicle speed V a In 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, 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 a And the vehicle speed exceeds a first vehicle speed V a In the case of (3), the process of step S19 and the following steps are executed to apply the braking force by the vehicle posture 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 and S15 are not executed.
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 b1 Is 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 o With the wheel speed V on the inside i Multiplying the difference by a predetermined coefficient C m1 And 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 is set b1 Multiplying the various gains to determine the final command value F for vehicle attitude control 1 . 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 posture 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 primary processing in 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 t 1 After 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 ～t 2 ). Next, at time t in FIG. 8 2 When 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 ～t 3 ). 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. 8 3 When the driver finishes cutting the steering wheel 6 and shifts to 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 ～t 4 ). Thereby, the command value of the braking force calculated by the equation (2) is also reduced. Further, at time t of fig. 8 4 The wheel speed difference between the inner rear wheel and the outer rear wheel is a first wheel speed difference T a Thereafter, the process in the flowchart of fig. 7 proceeds to step S17 → S23, and the command value based on the vehicle posture control becomes zero.
Next, at time t in FIG. 8 5 The 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 proceeds to step S16 → S21, and the processes following step S21 in the flowchart of fig. 7 are executed.
In step S21, it is determined whether or not 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 wheel speed and the inside wheel speed is a second wheel speed difference T b In the following case, the processing from step S23 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 b In 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. 8 5 ～t 6 In 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 b2 Is 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 i Speed V of wheel with outside o Multiplying the difference by a predetermined coefficient C m2 And is calculated by equation (3).
F b2 ＝C m2 ×(V i -V o ) (3)
In the example shown in fig. 8, at time t 5 When the application of the braking force by the brake LSD control is started, the wheel speed of the inner rear wheel is lowered and the wheel speed is increased at time t 6 The difference between the wheel speeds of the inboard rear wheel and the outboard rear wheel is substantially zero. At time t 6 After the upper wheel speed difference becomes substantially zero, the process in the flowchart of fig. 7 proceeds as in step S16 → S21 → S23 or step S16 → S17 → S23, and the braking force is not applied to the inner rear wheel (time t in fig. 8) 6 ～t 7 )。
In the example shown in fig. 8, the driver starts from time t 6 The return of the steering wheel 6 is started at time t 7 The vehicle returns to the straight running state after the wheel return is completed, and the turning running is finished.
In step S23, the steering wheel is determined based on the detection value of the steering angle sensor 16If the round of the round 6 is completed, the process proceeds to step S25 if the round is not completed, and proceeds to step S24 if the round is completed. In the present embodiment, at time t in fig. 8 1 After the start of the cut-in operation of the steering wheel 6, the operation is continued until time t 7 In 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 proceeds to step S12 → S16. In this state, even when the low road 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 surface 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 and the following steps are 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. 9 11 When 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. When 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 following 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 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 b In 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 b Is set to be higher than the first lateral acceleration GY a A 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 b In 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 instruction value F b3 By multiplying the maximum value of the basic command value Fb1 of the vehicle attitude control set most recently by a prescribed coefficient C m3 And is calculated by equation (4).
F b3 ＝C m3 ×F b1 (4)
In the present embodiment, the coefficient C m3 Is set to a positive value less than 1. That is, the basic command value F based on the pre-brake LSD control b3 Basic command value F set to be always more controlled than the vehicle attitude b1 The maximum value of (a) is small. In the example shown in fig. 9, at time t 11 ～t 12 Basic command value F of vehicle attitude control b1 Since the maximum value of the coefficient is updated at any time, the coefficient C is multiplied by the maximum value m3 The latter basic instruction value F b3 The value of (c) also increases. Then, at time t 12 ～t 13 Basic command value F of vehicle attitude control b1 The maximum value is constant, and therefore, the maximum value is also constant, and the maximum value is multiplied by a coefficient C m3 The latter basic instruction value F b3 Becomes a constant value. Further, at time t 13 Thereafter, the basic command value F for vehicle attitude control b1 To reduce the tendency, but with its maximum value held, the maximum value is multiplied by a factor C m3 The latter basic instruction value F b3 The value of (d) is also maintained. The basic command value F based on the pre-brake LSD control b3 Is maintained until at time t 17 The turning 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) 14 Thereafter) 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 friction mode is selected, the friction coefficient is set toAfter the application of the braking force in the vehicle posture control is completed, the application of the braking force by the brake LSD control is rarely performed, 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 m3 Set to the coefficient C in the lower road friction mode m3 Is small.
Next, in the example shown in fig. 9, at time t 15 ～t 16 When 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 t 11 ～t 14 Setting a basic command value F based on vehicle attitude control b1 At time t 11 ～t 17 Setting a basic command value F based on pre-brake LSD control b3 At time t 15 ～t 16 Setting 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 the command value F by which the gains are multiplied is calculated 1 、F 2 、F 3 . Further, in step S26, these command values F are compared 1 、F 2 、F 3 The maximum command value is used, and a 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 a threshold value of the wheel speed difference, and fig. 7 showsFirst difference in rotational speed T in step S17 a [m/sec]Is set based on the map of fig. 10. First wheel speed difference T a The 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 a Is maximum at a vehicle speed of 0, decreases as the vehicle speed increases, and is at a predetermined vehicle speed V 1 The above is approximately a constant value. The setting is preferably performed as follows: will speed the vehicle V 1 Is set to a value of about 80 to about 110[ km/h ] per hour]Left and right, above this value, the first wheel speed difference T a 2 of = about 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 a Thus, in the region where the vehicle speed is low, it becomes difficult to intervene in the vehicle attitude control executed below step S18 of fig. 7. 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 the wheel speed, the vehicle attitude control may be executed based on the measurement error. In order to suppress such unnecessary intervention of the vehicle attitude control, in the present embodiment, the first wheel speed difference T is set as shown in fig. 10 a The value of (c).
Next, the gain to be multiplied by each basic command value in step S25 in fig. 7 will be described with reference to fig. 11 to 19.
FIG. 11 shows a basic command value F based on vehicle attitude control set according to a steering angle b1 Multiplied 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 b1 The 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 b1 And (4) mapping of the 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 b1 Multiplied lateral acceleration gainMapping of (2). FIG. 15 shows a basic command value F set according to the vehicle speed and based on the vehicle attitude control b1 A 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 b1 A 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 b1 Mapping 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 b1 A 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 θ Is set as: at steering angle theta deg]Is the first steering angle theta 1 The following region is zero at θ 1 The above points increase and converge to "1" at a predetermined steering angle or more. By setting the steering angle gain G in this way θ So that the steering angle is the first steering angle theta 1 The following region does not substantially perform vehicle attitude control and does not intervene in control (by multiplying steering angle gain G) θ And 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 theta 1 Is set to a value of about 3.5 to about 6.0[ deg. ]]Left and right, below this value, steering angle gain G θ Is zero.
As shown in fig. 12, the accelerator opening change speed gain G AV Is set to: 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 an accelerator pedal (not shown) of the vehicle 1 is rapidly depressed (the accelerator opening degree change speed is large), the inner rear wheel and the outer rear wheel are drivenWhen the wheel speed difference (differential rotation) of the rear wheels becomes large, 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 AV Accordingly, 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 opening degree change speed gain G set as shown in FIG. 12 is multiplied AV Accordingly, 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 being confused by the excessive change speed of the wheel speed difference.
As shown in fig. 13, the accelerator opening gain G aH Is set to: with accelerator opening [ ]]Is increased at a first accelerator opening a 1 Becomes "1" at the first accelerator opening degree A 1 The above converges to a prescribed value greater than "1". By setting the accelerator opening gain G in this way aH So 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 A 1 Is set to a value of about 45 to about 60[% ]]On the left and right, below this value, the accelerator opening is increased by a gain G aH Set to "1" or less; above this value, the accelerator opening gain G aH Is more than 1.
As shown in fig. 14, the lateral acceleration gain G lH Is set to: at a lateral acceleration a l [G]Is a first lateral acceleration a l1 The following region is zero, at a l1 Increased at the above points and specifiedThe point above the lateral acceleration converges to "1". By setting the lateral acceleration gain G in this way lH Accordingly, when the lateral acceleration of the vehicle 1 is large, a larger braking force acts on the inner rear wheels of the vehicle 1 during turning than when the lateral acceleration of the vehicle 1 is small. In addition, by setting the lateral acceleration gain G as shown in fig. 14 lH So that the lateral acceleration is the first lateral acceleration a l1 A region where the intervention of the vehicle attitude control is not substantially performed (by multiplying by a lateral acceleration gain G) lH And the command value for vehicle attitude control is zero. ). I.e. in the lateral acceleration a l In the minute region, floating of the inner rear portion of the vehicle body 1a is difficult to occur, and therefore discomfort to the driver due to unnecessary intervention of vehicle attitude control is suppressed. The setting is preferably performed as follows: the first lateral acceleration a l1 Is set to a value of about 0.22 to about 0.35[ G ]]Left and right, below which is the lateral acceleration gain G lH Is zero.
As shown in FIG. 15, the vehicle speed gain G VH Is set as: with vehicle speed [ km/h]Is gradually increased at a first vehicle speed V 1 Is "1" at a first vehicle speed V 1 The above increases comparatively sharply. By setting the vehicle speed gain G in this way VH Therefore, the command value by 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 V 1 Is 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 VH Set to "1" or less; above this value, the vehicle speed gain G VH And is increased.
In step S25 of fig. 7, when the high road friction mode is selected, a basic command for vehicle attitude control is givenValue F b1 Multiplied by a steering angle gain G set based on FIG. 11 θ Accelerator opening degree change speed gain G set based on fig. 12 AV Accelerator opening gain G set based on fig. 13 aH Lateral acceleration gain G set based on fig. 14 lH And a vehicle speed gain G set based on FIG. 15 VH Calculating a command value F for vehicle attitude control by the mathematical expression (5) 1 。
F 1 ＝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 gain G aL Is set to: with accelerator opening [ ]]And at a second accelerator opening degree A 2 Is at "1" and at a second accelerator opening degree A 2 The above value is a predetermined value greater than "1". By setting the accelerator opening gain G in this way aL So 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 aL Second throttle opening degree A of "1 2 Set as the accelerator opening gain G in the friction mode of the high road surface aH First throttle opening A of "1 1 Is large. The setting is preferably performed as follows: the second accelerator opening degree A 2 Is 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 aL Is set to be less than 1; above this value, the accelerator opening gain G aL Is more than 1.
As shown in fig. 17, when the low road friction mode is selected, the lateral acceleration gain G lL Is set as: at a lateral acceleration a l [G]Is a second lateral acceleration a l2 The following region is zero at the second lateral acceleration a l2 The 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 lL So that the lateral acceleration is the second lateral acceleration a l2 A region where the intervention of the vehicle attitude control is not substantially performed (by multiplying by a lateral acceleration gain G) lL The 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 lL A second lateral acceleration a greater than zero l2 And a lateral acceleration gain G in a high road friction mode lH A first lateral acceleration a greater than zero l1 Is set to be higher than the first lateral acceleration a l1 Is 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: the second lateral acceleration a l2 Is set to a value of about 0.02 to about 0.15[ G ]]Left and right, below which is the lateral acceleration gain G lL Is zero.
As shown in fig. 18, when the low road friction mode is selected, the vehicle speed gain G VL Is set as: at a second vehicle speed V 2 Set to zero at the second vehicle speed V 2 The 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, vehicle speed gain G is set in this way VL Thus, at the second vehicle speed V 2 Hereinafter, 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 surface friction mode is selected, the vehicle attitude control can be suppressed at any vehicle speed as compared with the high road surface friction modeAnd (4) intervening. 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 set 2 Is set to a value of about 15 to about 30[ km/h ]]Left and right, and gain G in vehicle speed VL The 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 b1 Multiplied by a steering angle gain G set based on FIG. 11 θ Accelerator opening change speed gain G set based on fig. 12 AV Accelerator opening gain G set based on fig. 16 aL And a lateral acceleration gain G set based on FIG. 17 lL And a vehicle speed gain G set based on FIG. 18 VL Calculating a command value F for vehicle attitude control by the mathematical expression (6) 1 。
F 1 ＝G θ ×G AV ×G aL ×G lL ×G VL ×F b1 (6)
Next, referring to fig. 19, the basic command value F based on the brake LSD control when the low road friction mode is selected is compared with b2 Multiplied difference rotation gain G DL The description is given. Further, in the case where the high road friction mode is selected, the differential rotation gain G DH Always is "1".
As shown in fig. 19, the difference rotation gain G DL Is set as: the differential rotation D between the inner wheel and the outer wheel is a first differential rotation D 1 [m/sec]The following is "1", and the rotation D is the first differential rotation 1 The above converges to a predetermined value greater than "1". By setting the differential rotation gain G in this way DL So that when the differential rotation becomes the first differential rotation D 1 In 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 about 8 to about 12[ m/sec ]]To the left and right, and, at this valueAs described above, the command value for the brake LSD control is increased. In addition, preferably, the difference rotation gain G DL The 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 b2 Multiplied by the difference rotation gain G set based on fig. 19 DL The 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 DH Is always "1", so the basic instruction value F b2 The value is set directly to the instruction value F 2 。
F 2 ＝G DL ×F b2 (7)
Thus, in step S25 of fig. 7, the basic command value F based on the vehicle attitude control b1 And 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 b2 And calculates the instruction value F by the mathematical expression (7) 2 Or else the basic instruction value F b2 Directly as instruction value F 2 。
Further, when the low road friction mode is selected, the command value F of the pre-brake LSD control 3 By applying to the basic instruction value F b3 Multiplied 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.
F 3 ＝G θ ×G AV ×G aL ×G lL ×G VL ×F b3 (8)
On the other hand, when high road friction mode is selectedIn this case, as described above, the pre-brake LSD control (the command value F of the pre-brake LSD control) is not executed 3 = 0). 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.
F 3 ＝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 controlling the vehicle posture calculated as described above is subjected to 1 Command value F for brake LSD control 2 Command value F for pre-brake LSD control 3 The 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 braking device 8 is controlled based on the determined command value in step S5.
According to the vehicle posture control device of the first embodiment of the present invention, the lateral acceleration a of the vehicle 1 is determined during the turning operation of the vehicle based on the cutting operation of the steering wheel l When the acceleration is large, the lateral acceleration a of the vehicle 1 is set to be larger than l A large braking force acts on the inner rear wheel of the vehicle during turning when the braking force is small (fig. 14 and 17). When braking force (command value F) is applied 1 ) 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 posture control device of the present embodiment, 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 are based on l To set a braking force (command value F) to be applied to the inner rear wheel of the vehicle 1 1 ) Therefore, the rear inner side for suppressing the floating of the vehicle body 1a can be set more accuratelyBraking force.
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 wheels (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 (the braking force =0 based on the vehicle attitude control) is not executed (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 l1 In the above (fig. 14), the second lateral acceleration a is obtained in the low road friction mode l2 Since the vehicle posture control is executed in the above case (fig. 17), the execution of the vehicle posture control can be started at an appropriate timing in accordance with the road surface friction.
Further, according to the vehicle attitude control device of the present embodiment, since the condition for starting execution of the vehicle attitude control is changed in accordance with the vehicle speed V (step S17 in fig. 7, fig. 10), the execution of the vehicle attitude 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 vehicle attitude control device is to be provided withAxles of the rear wheels 2c, 2d are suspended from an upper arm 3a and a lower arm 3b as link mechanisms of the vehicle body 1a so that the axles surround a predetermined suspension center P S The axle 2e is suspended in a rotatable manner (fig. 4). The suspension center P S Since the vehicle body 1a is located above the axle 2e, when a braking force is applied to the rear wheel 2c or 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 thus, the floating of the vehicle body inner rear portion can be more effectively suppressed.
In addition, in the vehicle attitude control device of the present embodiment, since the vehicle 1 includes the mechanical differential limiting device 4d, the wheel speed difference between the inner rear wheel and the outer rear wheel is rapidly reduced as the accelerator opening degree is larger due to the operation thereof. 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 reduced as the change speed of the accelerator opening degree is increased (fig. 12), and therefore discomfort given to the driver can be suppressed.
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 posture control device of the present embodiment is different from the first embodiment described above in that the braking force applied by the vehicle posture 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 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 posture 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 if 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), in step S114, the basic command value F of the lower limit braking force by the pre-brake LSD control is always determined 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 b3 All by the basic command value F for the most recently set vehicle attitude control b1 Is multiplied by a predetermined coefficient C m3 And 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 b1 Is 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 o Wheel speed V with the inner side i Multiplying the difference by a predetermined coefficient C m1 And 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 in 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 b2 Is 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 i Speed V of wheel with outside o Multiplying the difference by a predetermined coefficient C m2 And 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 b3 Respectively multiplied by gains to thereby calculate a command value F for vehicle attitude control 1 And a command value F for brake LSD control 2 Command value F for pre-brake LSD control 3 。
Namely, the command value F for vehicle attitude control 1 At the basic instruction value F b1 Up times steering angle gain G θ Accelerator opening change speed gain G AV Accelerator opening gain G a Lateral acceleration gain G l And a vehicle speed gain G V And is calculated by the mathematical formula (13).
F 1 ＝G θ ×G AV ×G a ×G l ×G V ×F bl (13)
Here, the steering angle gain G in the formula (13) θ And accelerator opening change speed gain G AV The same gain as that set in the first embodiment described above can be used. In addition, the accelerator opening gain G a Lateral acceleration gain G l And a vehicle speed gain G V The accelerator opening degree set in the case where the high road friction mode is selected in the first embodiment can be usedGain G aH Lateral acceleration gain G H And a vehicle speed gain G VH The same gain. Alternatively, a gain different from each gain set in the first embodiment may be set.
And, a command value F for brake LSD control 2 Is at the basic command value F for the brake LSD control b2 Up multiplied by a difference rotation gain G D And is calculated by the equation (14). Here, the difference rotation gain G D The 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 DL The difference rotation gain G is set based on the map shown in fig. 19, and when the high road surface friction mode is selected DH Is always set to "1". In contrast, in the present embodiment, the differential rotation gain G is not determined regardless of the road surface friction D Are set based on the map shown in fig. 21.
F 2 ＝G D ×F b2 (14)
FIG. 21 shows a rotation gain G for setting the difference D But the mapping used.
As shown in fig. 21, the difference rotation gain G D Is set as: differential rotation D m/sec between 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 b3 Multiplied 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. Thus, with respect to targeting preThe command value for the brake LSD control is also multiplied by the same gain as that for the vehicle attitude control, and the braking force is set so as to smoothly connect to the vehicle attitude control.
F 3 ＝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) 1 And a command value F for brake LSD control 2 Command value F for pre-brake LSD control 3 The 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, the command values are calculated differently 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 b1 = 0). 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 b2 = 0). In addition, the basic command value F based on the pre-brake LSD control b3 By applying to the basic instruction value F b1 Is multiplied by a predetermined coefficient C m3 The basic instruction value is calculated, so if the basic instruction value F b1 If =0, the basic instruction value F b3 Also 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 b3 All 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 (11)
1. A vehicle attitude control device for controlling the attitude of a vehicle having a front wheel and a rear wheel, the vehicle 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 is configured to execute a vehicle posture control and a pre-brake LSD control during turning of the vehicle based on a cutting operation of a steering wheel of the vehicle,
in the vehicle posture control, the brake control device applies a braking force larger than a braking force in a case where a lateral acceleration of the vehicle is small to an inner rear wheel of the vehicle during turning to suppress floating of a vehicle body inner rear portion when the lateral acceleration of the vehicle is large,
in the pre-brake LSD control, the brake control device causes a braking force smaller than a braking force applied by the vehicle posture control to act on an inner rear wheel of the vehicle during turning travel of the vehicle until the turning travel is completed.
2. The vehicle attitude control apparatus according to claim 1, characterized in 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 a 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.
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 apparatus according to claim 1, characterized in that,
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 apparatus according to claim 1, characterized in that,
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,
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.
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| JP2019104205 | 2019-06-04 | ||
| JP2019-104205 | 2019-06-04 | ||
| JP2020026921A JP7274103B2 (en) | 2019-06-04 | 2020-02-20 | Vehicle attitude control device |
| JP2020-026921 | 2020-02-20 |
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| CN112109684A CN112109684A (en) | 2020-12-22 |
| CN112109684B true CN112109684B (en) | 2023-02-03 |
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| KR20220081113A (en) * | 2020-12-08 | 2022-06-15 | 현대자동차주식회사 | Braking control method using predicted friction coeffieient of brake pad |
| JP7145993B2 (en) * | 2021-01-20 | 2022-10-03 | 本田技研工業株式会社 | vehicle controller |
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| JP3061841B2 (en) * | 1990-08-29 | 2000-07-10 | 日産自動車株式会社 | Vehicle attitude control device |
| JP3047480B2 (en) * | 1991-02-27 | 2000-05-29 | 株式会社ユニシアジェックス | Vehicle suspension system |
| JP4292907B2 (en) * | 2003-07-17 | 2009-07-08 | 株式会社アドヴィックス | Vehicle motion control device |
| US7590481B2 (en) * | 2005-09-19 | 2009-09-15 | Ford Global Technologies, Llc | Integrated vehicle control system using dynamically determined vehicle conditions |
| JP4887719B2 (en) * | 2005-10-13 | 2012-02-29 | トヨタ自動車株式会社 | Vehicle control device |
| JP5057436B2 (en) * | 2007-03-27 | 2012-10-24 | 富士重工業株式会社 | Suspension device |
| CN104105609B (en) * | 2012-02-24 | 2016-07-27 | 丰田自动车株式会社 | Vehicular behavior controls device |
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| US8554414B2 (en) * | 2010-09-09 | 2013-10-08 | Advics Co., Ltd. | Rollover suppression control apparatus and rollover suppression control method |
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| JP2020200020A (en) | 2020-12-17 |
| CN112109684A (en) | 2020-12-22 |
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