Vehicle control system

Abstract

To perform proper vehicle attitude control when turning without changing each control parameter for each characteristic of an installed driving-motor.SOLUTION: A vehicle control device for controlling attitude of a vehicle (1), includes: wheel speed sensors (24) which each detect wheel speed of the vehicle during travel; brake actuators (8) which each actuate brake force on a wheel of the vehicle; and a brake control device (14a) which sends control signal to the brake actuators on the basis of a travel state of the vehicle to generate braking force. When the wheel speed of inner rear wheels of the vehicle becomes higher than the wheel speed of outer rear wheels during turning traveling of the vehicle, the brake control device executes vehicle attitude control which restrains lift of an inner rear part of the vehicle by applying the braking force to inner rear wheels of the vehicle. In the vehicle attitude control, when a slip ratio of the front and rear wheels of the vehicle is large, the brake control device increases the braking force to be applied to the inner rear wheels of the vehicle with respect to when the slip ratio of the front and rear wheels is small.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle control device, and more particularly to a vehicle control device for controlling the attitude of a vehicle. [Background technology]

[0002] Japanese Patent Publication No. 2020-20020 (Patent Document 1) describes a vehicle attitude control device. This vehicle attitude control device is configured to perform vehicle attitude control, turning control, and anti-skid control based on the lateral acceleration of the vehicle during a turn. In particular, as part of vehicle attitude control, the vehicle attitude control device applies braking force to the inner rear wheel of the vehicle during a turn, thereby suppressing the lift of the inner rear part of the vehicle body and generating appropriate diagonal roll during turning. Furthermore, as part of brake LSD (Limited-Slip Differential Gear) control, the vehicle attitude control device applies braking force to the inner rear wheel when the wheel speed of the inner rear wheel of the vehicle during a turn exceeds the wheel speed of the outer rear wheel, thereby suppressing slip of the inner rear wheel. This suppresses the lift of the inner rear part of the vehicle body during turning and stabilizes the vehicle's turning. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-20020 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the vehicle attitude control device described in Patent Document 1 has a problem in that the effect of brake LSD control differs depending on the torque of the installed engine, and sufficient effect cannot be obtained when a high-torque engine is installed. In other words, even if the vehicle body is the same, slip of the inner rear wheel is less likely to occur in models with a low-torque engine, while slip is more likely to occur in models with a high-torque engine. For this reason, if the same brake LSD control is applied to both models with a low-torque engine and models with a high-torque engine, and the same braking force is applied to the inner rear wheel, it is not possible to sufficiently suppress wheel slip and prevent the inner rear of the vehicle body from lifting.

[0005] Therefore, in order to obtain the appropriate effect of brake LSD control, it is conceivable to change the parameters of brake LSD control according to the torque of the engine installed in the vehicle. However, there is a problem in that there are many types of engines that can be installed in the same vehicle body, and it is extremely difficult to determine the appropriate control parameters for brake LSD control for each engine and install them in each vehicle.

[0006] Therefore, the present invention aims to provide a vehicle attitude control device that can perform appropriate vehicle attitude control during cornering without changing control parameters for each characteristic of the prime mover mounted on the vehicle body. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention provides a vehicle control device for controlling the attitude of a vehicle, comprising: a wheel speed sensor for detecting the wheel speed of a moving vehicle; a brake actuator for applying braking force to the wheels of the vehicle; and a brake control device that sends a control signal to the brake actuator and generates braking force based on the vehicle's driving state. The brake control device performs vehicle attitude control by applying braking force to the inner rear wheel of the vehicle when the wheel speed of the inner rear wheel of the vehicle becomes higher than the wheel speed of the outer rear wheel during turning, thereby suppressing the lifting of the inner rear of the vehicle body. In vehicle attitude control, when the front-to-rear wheel slip ratio of the vehicle is large, the braking force applied to the inner rear wheel of the vehicle is larger than when the front-to-rear wheel slip ratio is small. In vehicle attitude control, the braking force applied to the inner rear wheel of the vehicle is calculated by multiplying the basic command value by a predetermined gain. This predetermined gain increases when the front-to-rear wheel slip ratio is approximately 0.2 or higher, and remains constant when the front-to-rear wheel slip ratio is approximately 0.5 or higher. It is characterized by the following.

[0008] In the present invention configured as described above, when the wheel speed sensor detects that the wheel speed of the inner rear wheel has become higher than the wheel speed of the outer rear wheel while the vehicle is turning, the brake control device sends a control signal to the brake actuator as part of vehicle attitude control, applying braking force to the inner rear wheel of the vehicle and suppressing the lifting of the inner rear part of the vehicle body. In this vehicle attitude control, if the front-to-rear wheel slip ratio of the vehicle is large, the braking force applied to the inner rear wheel of the vehicle is greater than when the front-to-rear wheel slip ratio is small.

[0009] The inventors of this case have discovered that in vehicle attitude control, which applies braking force to the inner rear wheel when the wheel speed of the inner rear wheel becomes higher than the wheel speed of the outer rear wheel during a vehicle turn, the effect of the control differs depending on whether the installed engine is high torque or low torque, even with the same vehicle body. Specifically, it was found that in models equipped with a high torque engine, even if the same braking force is applied to the inner rear wheel of the vehicle, the effect of vehicle attitude control is reduced compared to models equipped with a low torque engine. As a result of diligent research, the inventors have determined that this is because, even with the same vehicle body, the slip of the inner rear wheel increases in models equipped with a high torque engine, and even if the same braking force is applied, the effect of vehicle attitude control is weakened. Therefore, in order to obtain the same effect of vehicle attitude control in models with high torque engines and models with low torque engines, a control device with different control parameters for each installed engine is required.

[0010] According to the present invention configured as described above, in vehicle attitude control, when the front-to-rear wheel slip ratio of the vehicle is large, the braking force applied to the inner rear wheel of the vehicle is greater than when the front-to-rear wheel slip ratio is small. As a result, the same vehicle attitude control effect can be obtained for models equipped with high-torque engines and models equipped with low-torque engines without having to prepare different brake control devices. That is, since the torque of the installed engine is reflected in the front-to-rear wheel slip ratio, by configuring the brake control device so that the braking force applied is changed according to the front-to-rear wheel slip ratio, it becomes possible to handle both models equipped with low-torque engines and high-torque models with a common brake control device. For this reason, according to the present invention, proper vehicle attitude control can be performed during cornering without changing the control parameters for each characteristic of the engine installed in the vehicle body. Furthermore, according to the present invention configured as described above, the gain increases when the front-to-rear wheel slip ratio is approximately 0.2 or higher. Therefore, when a high-torque prime mover is installed, the braking force applied to the inner rear wheel increases, and a sufficient vehicle attitude control effect can be obtained. Also, since the gain becomes constant when the front-to-rear wheel slip ratio is approximately 0.5 or higher, it is possible to prevent the braking force applied to the inner rear wheel from becoming too large, which would affect the vehicle's turning behavior itself rather than providing vehicle attitude control that suppresses the lifting of the inner rear of the vehicle body.

[0011] In the present invention, preferably, the front-to-rear slip ratio is calculated based on the wheel speed of the rear wheel with the slower wheel speed among the left and right rear wheels, and the wheel speed of the front wheel with the slower wheel speed among the left and right front wheels.

[0012] According to the present invention configured in this way, the front-to-rear wheel slip ratio is calculated based on the wheel speed of the rear wheel with the slower wheel speed among the left and right rear wheels, and the front wheel with the slower wheel speed among the left and right front wheels. As a result, the torque characteristics of the prime mover can be accurately reflected in the front-to-rear wheel slip ratio, and the torque characteristics of the prime mover can be accurately reflected in the vehicle attitude control. [Effects of the Invention]

[0015] According to the vehicle attitude control device of the present invention, proper vehicle attitude control can be performed during cornering without changing control parameters for each characteristic of the prime mover mounted on the vehicle body. [Brief explanation of the drawing]

[0016] [Figure 1] This is a layout diagram showing the overall configuration of a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention. [Figure 2] This diagram schematically shows, from the rear of the vehicle, a structure for suspending the rear axle of a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention. [Figure 3] This figure shows the roll axis of a vehicle body equipped with a vehicle attitude control device according to an embodiment of the present invention. [Figure 4] This diagram schematically illustrates the forces acting on the vehicle body when a braking force is applied to the rear wheels of a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention. [Figure 5] This is a block diagram showing a PCM (Personal Control Module) and sensors connected thereto, installed in a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention. [Figure 6] This flowchart shows the operation of a vehicle control device according to an embodiment of the present invention. [Figure 7] This is a flowchart of the subroutine called from the flowchart shown in Figure 6. [Figure 8] This is a time chart showing the operation of a vehicle control device according to an embodiment of the present invention. [Figure 9]This is a map for setting a threshold for the wheel speed difference in a vehicle attitude control device according to an embodiment of the present invention. [Figure 10] This is a map of steering angle gains multiplied by a basic command value in a vehicle attitude control device according to an embodiment of the present invention. [Figure 11] This is a map of the accelerator opening change speed gain multiplied by the basic command value in a vehicle attitude control device according to an embodiment of the present invention. [Figure 12] This is a map of accelerator opening gain multiplied by a basic command value in a vehicle attitude control device according to an embodiment of the present invention. [Figure 13] This is a map of the lateral acceleration gain multiplied by the basic command value in a vehicle attitude control device according to an embodiment of the present invention. [Figure 14] This is a map of the vehicle speed gain multiplied by the basic command value in a vehicle attitude control device according to an embodiment of the present invention. [Figure 15] This is a map of the differential rotation gain multiplied by the basic command value of brake LSD control in a vehicle attitude control device according to an embodiment of the present invention. [Figure 16] This is a map of the front-to-rear slip ratio gain multiplied by the basic command value of brake LSD control in a vehicle attitude control device according to an embodiment of the present invention. [Figure 17] This graph shows an example of the relationship between the front-to-rear slip ratio measured in a vehicle that performed a turn along a predetermined route and the difference in wheel speed between the left and right rear wheels. [Modes for carrying out the invention]

[0017] Next, preferred embodiments of the present invention will be described with reference to the attached drawings. First, with reference to Figure 1, a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention will be described. Figure 1 is a layout diagram showing the overall configuration of a vehicle equipped with a vehicle attitude control device according to an embodiment of the present invention.

[0018] In Figure 1, reference numeral 1 denotes a vehicle equipped with the vehicle attitude control device according to this embodiment. Vehicle 1 is equipped with left and right front wheels 2a and 2b, which are steering wheels, at the front of the vehicle body, and left and right rear wheels 2c and 2d, which are drive wheels, at the rear of the vehicle body. These front wheels 2a and 2b and rear wheels 2c and 2d of Vehicle 1 are supported by a suspension 3, which is a wheel suspension system, on the vehicle body 1a. An engine 4, which is the prime mover that drives the rear wheels 2c and 2d, is mounted on the front of the vehicle body 1a of Vehicle 1. In this embodiment, the engine 4 is a gasoline engine, but an internal combustion engine such as a diesel engine or an electric motor can also be used as the prime mover. In this embodiment, Vehicle 1 is a so-called FR vehicle in which the rear wheels 2c and 2d are driven by the engine 4 mounted on the front of the vehicle body 1a via a transmission 4a, a propeller shaft 4b, and a differential gear 4c. Preferably, the differential gear 4c is equipped with a mechanical limited-slip differential gear 4d (LSD). By providing the differential limiting device 4d, even if the ground contact of one rear wheel decreases, a sufficiently large driving force can be applied to the other rear wheel. However, the present invention can be applied to vehicles with any drive system, such as so-called RR vehicles where the rear wheels are driven by an engine mounted at the rear of the vehicle body, or four-wheel drive vehicles.

[0019] Vehicle 1 is also equipped with a steering system 7 that steers the front wheels 2a and 2b based on the rotational operation of the steering wheel 6. Furthermore, the vehicle 1 is equipped with a brake control system that supplies brake fluid pressure to the wheel cylinders and brake calipers (not shown) of the brake devices 8, which are brake actuators provided on each wheel. The brake control system includes a hydraulic pump 10 that generates the brake fluid pressure necessary to generate braking force in the brake devices 8 provided on each wheel. The hydraulic pump 10 is driven by power supplied from, for example, a battery (not shown), and is capable of generating the brake fluid pressure necessary to generate braking force in each brake device 8 even when the brake pedal (not shown) is not pressed.

[0020] The brake control system also includes a valve unit 12 (specifically a solenoid valve) installed in the hydraulic supply line to the brake device 8 of each wheel, for controlling the hydraulic pressure supplied from the hydraulic pump 10 to the brake device 8 of each wheel. 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 also includes a hydraulic pressure sensor 13 that detects the hydraulic pressure supplied from the hydraulic pump 10 to the brake device 8 of each wheel. The hydraulic pressure sensor 13 is located, for example, at the connection point between each valve unit 12 and the hydraulic supply line downstream of it, and detects the hydraulic pressure downstream of each valve unit 12, outputting the detected value to the PCM (Power-train Control Module) 14.

[0021] Furthermore, the brake control system calculates the hydraulic pressure to be supplied independently to each wheel cylinder and brake caliper based on the braking force command value input from the PCM14 and the detection value from the hydraulic pressure sensor13, and controls the rotation speed of the hydraulic pump10 and the opening degree of the valve unit12 according to these hydraulic pressures.

[0022] Next, with reference to Figures 2 to 4, the suspension structure of a vehicle equipped with the vehicle attitude control device according to this embodiment and the roll axis of the vehicle body will be described. FIG. 2 is a diagram schematically showing from the rear of the vehicle a structure for suspending the axles of the rear wheels 2c and 2d with respect to the vehicle body 1a of the vehicle 1. FIG. 3 is a diagram showing the roll axis of the vehicle body of the vehicle equipped with the vehicle attitude control device according to the present embodiment. FIG. 4 is a diagram schematically explaining the forces acting on the vehicle body when a braking force is applied to the rear wheels of the vehicle.

[0023] As shown in FIG. 2, the axle 2e of the left rear wheel 2c of the vehicle 1 is supported by the suspension 3 with respect to the vehicle body 1a of the vehicle 1. Specifically, in the example shown in FIG. 2, the axle 2e of the rear wheel 2c is supported by the upper arm 3a and the lower arm 3b which are link mechanisms constituting the suspension 3. Thus, the lines extending the upper arm 3a and the lower arm 3b connecting the vehicle body 1a and the rear wheel 2c intersect at the intersection point P1. The straight line connecting this intersection point P1 and the ground contact point P2 of the rear wheel 2c intersects with the vertical plane A passing through the center in the width direction of the vehicle body 1a at the point P rR . This point P rR is the center point of the rolling motion at the rear part of the vehicle body 1a, and the rear part of the vehicle body 1a rolls around this point P rR . Since the vehicle 1 is symmetric about the left and right, when finding the center point of the rolling motion for the right rear wheel 2d, the same point P rR becomes the center point of the rolling motion. Also, for the suspension 3 suspending the front wheels 2a and 2b of the vehicle 1, the center point P rF of the rolling motion can be obtained in the same manner.

[0024] FIG. 3 is a view projecting from the side of the vehicle 1 the center point P rR of the rolling motion at the rear part of the vehicle body 1a obtained in this way and the center point P rF of the rolling motion at the front part. The axis A rR connecting the center point P rF of the rolling motion at the rear part and the center point P r of the rolling motion at the front part of the vehicle body 1a becomes the central axis when the vehicle body 1a rolls. Therefore, the vehicle body 1a of the vehicle 1 basically rolls around this roll axis A rIt performs a rolling motion around the roll axis A of the vehicle 1. Also, as shown in Figure 3, in this embodiment, the roll axis A of the vehicle 1 is r The front of vehicle 1 is tilted forward so that it is lower. In this way, the roll axis A of vehicle 1 r By tilting forward, the vehicle 1 can naturally generate an appropriate diagonal roll when it turns, thereby improving the turning performance of the vehicle 1. In this embodiment, the roll axis A of the vehicle 1 r The present invention can also be applied to vehicles where the front is tilted forward, but the roll axis is not tilted forward.

[0025] Next, referring to Figure 4, we will explain the force acting on the vehicle body 1a when braking force is applied to the rear wheels 2c and 2d of vehicle 1. As described above, the rear wheels 2c and 2d are suspended by the upper arm 3a and lower arm 3b that constitute the suspension 3. Wheels may be suspended by various types of suspensions, but in any case, the axle of the wheel can be considered to be suspended so as to rotate around a hypothetical predetermined suspension center. As shown in Figure 4, in this embodiment, the rear wheel 2d is suspended at the suspension center point P. S It is suspended so as to rotate around the center point P. In this embodiment, the suspension center point P is S It is located above the axle 2e of the rear wheel 2d.

[0026] Here, when a braking force is applied to the rear wheel 2d, the rear wheel 2d has a contact point P2 with the road surface and a suspension center point P S The vehicle body 1a is pulled backward along the line segment l1 connecting the two points. The angle between this line segment l1 and the road surface is θ. al Let F be the frictional force acting between the road surface and the rear wheel 2d. x Therefore, the component of the force pulling the vehicle body 1a downwards is: It can be calculated using TIFF0007850371000001.tif6150. Furthermore, the wheelbase of vehicle 1 is l r The center of gravity G of vehicle 1 and the suspension center point P S The horizontal distance between X rTherefore, the moment M acts to pull down the rear of the vehicle body 1a. al This can be calculated using formula (1). TIFF0007850371000002.tif6150

[0027] In this way, by applying braking force to the rear wheels 2c or 2d of the vehicle 1, the rear of the vehicle body 1a can be pulled down. Also, in this embodiment, the suspension center point P S Because its position is higher than the rear axle 2e, the force pulling down the vehicle body 1a is relatively large.

[0028] Next, with reference to Figure 5, the various sensors installed in Vehicle 1 will be explained. Figure 5 is a block diagram showing the PCM14 mounted on vehicle 1, and the sensors and other components connected thereto.

[0029] As shown in Figure 5, the vehicle 1 is equipped with a steering angle sensor 16 for detecting the rotation angle of the steering wheel 6, an accelerator position sensor 18 for detecting the amount the accelerator pedal is depressed (accelerator opening), and a vehicle speed sensor 20 for detecting the vehicle speed, and these detection signals are input to the PCM 14. Furthermore, the vehicle 1 is equipped with a lateral acceleration sensor 22 for detecting the lateral acceleration acting on the vehicle 1, a wheel speed sensor 24 for detecting the wheel speed of each wheel of the vehicle 1, and a hydraulic pressure sensor 13 for detecting the hydraulic pressure downstream of the valve unit 12 (Figure 1), and these detection signals are also input to the PCM 14. In this embodiment, the vehicle 1 is equipped with a sensor that directly measures lateral acceleration as the lateral acceleration sensor 22. However, the lateral acceleration sensor 22 does not necessarily have to be a sensor that directly measures lateral acceleration, and lateral acceleration can also be determined from detection values ​​measured by other sensors. In this specification, "lateral acceleration sensor" includes any sensor used to determine lateral acceleration.

[0030] On the other hand, the PCM14 incorporates a brake control unit 14a, which is a brake control device for controlling the brake system 8; a turning control unit 14b, which performs turning control to improve the turning performance of the vehicle 1; and a skid prevention control unit 14c, which performs skid prevention control to suppress skidding when the vehicle 1 turns. As will be described later, each of these control units is configured to send control signals to the engine 4 and the brake system 8 to perform vehicle attitude control, turning control, and skid prevention control, respectively.

[0031] The vehicle control device according to an embodiment of the present invention consists of a steering angle sensor 16 that sends signals to the PCM 14, an accelerator opening sensor 18, a vehicle speed sensor 20, a lateral acceleration sensor 22, a wheel speed sensor 24, a brake control unit 14a built into the PCM 14, and an engine 4, a brake system 8, etc., controlled by the PCM 14. Note that some of the above components constituting the vehicle control device can be omitted depending on the application.

[0032] Each of these PCM14 control units is composed of a computer (not shown) equipped with a CPU, various programs interpreted and executed on the CPU (including basic control programs such as an OS, and application programs launched on the OS to realize specific functions), and internal memory such as ROM or RAM for storing programs and various data.

[0033] Next, the operation of the vehicle control device according to an embodiment of the present invention will be described with reference to Figures 6 to 17. Figure 6 is a flowchart showing the operation of the vehicle control device. Figure 7 is a flowchart of the subroutines called from the flowchart shown in Figure 6. Figure 8 is a time chart showing the operation of the vehicle control device. Figures 9 to 16 are maps showing the various gains used when determining the vehicle attitude control command values ​​by the vehicle control device.

[0034] The flowchart shown in Figure 6 is primarily executed repeatedly at predetermined time intervals in the PCM14 to automatically apply braking force to the vehicle 1 for purposes such as vehicle attitude control.

[0035] First, in step S1 of Figure 6, the detection signals from each sensor are read into the PCM 14. The detection signals read in step S1 are used for processing in steps S2 to S4. Specifically, in step S1, the steering angle signal (rotation angle of the steering wheel 6) [deg] from the steering angle sensor 16, the accelerator opening signal [%] from the accelerator opening sensor 18, and the vehicle speed signal [km / h] from the vehicle speed sensor 20 are read. Furthermore, in step S1, the lateral acceleration signal [G] from the lateral acceleration sensor 22, the wheel speed [m / sec] of each wheel from the wheel speed sensor 24, and the brake fluid pressure [MPa] from the hydraulic pressure sensor 13 are read.

[0036] Next, in step S2, the process of determining command values ​​based on vehicle attitude control is executed. Specifically, as part of vehicle attitude control, when vehicle 1 is turning based on the steering wheel 6 of vehicle 1, a braking force is applied to the inner rear wheel of vehicle 1 in order to suppress the lifting of the inner rear part of the vehicle body 1a during the turn. For example, when vehicle 1 turns to the left in Figure 1, a braking force is applied to the left rear wheel 2c, suppressing the lifting of the left rear part of the vehicle body 1a. In step S2, the flowchart shown in Figure 7 is called as a subroutine, and the command value of the braking force to be applied to the inner rear wheel for vehicle attitude control is determined. This vehicle attitude control is executed in a region where the lateral acceleration of vehicle 1 during the turn is relatively small, and a relatively small first braking force is applied to the inner rear wheel based on the difference in wheel speed between the inner and outer rear wheels. Therefore, vehicle attitude control does not substantially affect the yaw rate of the vehicle during the turn.

[0037] Preferably, for a vehicle 1 with a mass of approximately 960 kg to approximately 1060 kg, the braking force to be applied for vehicle attitude control is generated by applying a hydraulic pressure of 0.02 MPa to 0.1 MPa to the brake device 8 using a hydraulic pump 10. As a result, when the vehicle 1 turns, the inner rear of the vehicle body 1a tends to lift up with a certain acceleration, but by applying the braking force set as described above, a small deceleration of less than a predetermined value is applied to the vertical direction of the vehicle body 1a, suppressing the lifting of the inner rear of the vehicle body.

[0038] Next, in step S3, the process of determining command values ​​based on the turning control is executed. The turning control is a control performed by the turning control unit 14b of the PCM 14 when the steering angular velocity of the steering wheel 6 exceeds a predetermined value, with the aim of improving the turning performance of the vehicle 1. In addition, the torque generated by the engine 4 is adjusted, and / or braking force is applied by the brake device 8. When braking force is applied to the vehicle 1 in the turning control, the braking force is applied to the inner rear wheel of the turning vehicle 1, thereby generating a yaw moment in the turning direction of the vehicle 1 and improving the turning performance of the vehicle 1.

[0039] In step S2, during vehicle attitude control, which determines the command value, braking force is also applied to the inner rear wheel of the turning vehicle 1. However, turning control is performed in a region where lateral acceleration is relatively larger than that of vehicle attitude control, and therefore a larger braking force is applied during turning control. In other words, vehicle attitude control is performed to suppress the lifting of the inner rear part of the vehicle body 1a during turning of the vehicle 1, while turning control is performed to improve turning performance by applying a yaw moment to the vehicle 1, and is therefore completely different from turning control. In this embodiment, the braking force applied for turning control is generated by applying a hydraulic pressure of 0.2 MPa or more and 0.5 MPa or less, which is greater than that for vehicle attitude control, to the brake device 8 using a hydraulic pump 10.

[0040] Next, in step S4, the command value determination process based on the anti-skid control is performed. Anti-skid control is a control performed by the anti-skid control unit 14c of the PCM 14 in order to suppress or prevent the vehicle 1 from skidding during turns. This anti-skid control is performed based on the steering angle of the steering wheel 6 and the lateral acceleration of the vehicle 1, and is performed in a region where the lateral acceleration is much larger than that of the turning control. In anti-skid control, an appropriate braking force is applied to each wheel of the vehicle 1 in order to return the vehicle 1's driving state to the turning driving intended by the driver. The braking force applied in anti-skid control is much larger than that of the turning control. In this embodiment, the braking force applied for anti-skid control is generated by the hydraulic pump 10 applying a hydraulic pressure of 20 MPa or more, which is larger than that of the turning control, to the brake device 8.

[0041] Furthermore, in step S5, based on the command values ​​determined in steps S2 to S4, the PCM14 transmits a control signal to the brake device 8, applying braking force to the vehicle 1, and completing one process in the flowchart shown in Figure 6. It should be noted that the vehicle attitude control, turning control, and anti-skid control described above all apply braking force to the vehicle 1, but they are executed under different driving conditions, and these controls are not normally executed in conjunction.

[0042] Next, the process of determining command values ​​by vehicle attitude control will be explained with reference to Figures 7 to 17. As described above, the flowchart shown in Figure 7 is a subroutine called from step S2 of the flowchart in Figure 6, and is executed in the brake control unit 14a of the PCM 14. Figure 8 is a time chart showing an example of the braking force generated when vehicle attitude control is performed. In the time chart shown in Figure 8, the horizontal axis is time, and the vertical axis, from top to bottom, shows the detected value of the steering angle sensor 16, the detected value of the accelerator opening sensor 18, the wheel speed of the rear wheels detected by the wheel speed sensor 24, and the braking command value applied to the inner rear wheel.

[0043] First, in step S11 of Figure 7, the difference in wheel speed between the left and right rear wheels 2c and 2d of vehicle 1 is calculated. Specifically, in step S1 of Figure 6, the difference in wheel speed between the left and right rear wheels 2c and 2d is calculated based on the wheel speed of each wheel read from the wheel speed sensor 24.

[0044] Next, in step S12, it is determined whether the "vehicle attitude control flag" is "true" or not. The "vehicle attitude control flag" is changed to "true" when vehicle 1 starts turning and vehicle attitude control is started based on predetermined conditions, and is changed back to "false" when the turned steering wheel 6 is returned to its original position and the turn is completed. In the example time chart shown in Figure 8, vehicle 1 has not started turning at time t0, so the "vehicle attitude control flag" is "false", and the flowchart in Figure 7 proceeds to step S15.

[0045] In step S15, the wheel speeds of the inner and outer rear wheels of the turning vehicle are compared. If the outer wheel speed is higher, the process proceeds to step S16; if the inner wheel speed is higher, the process proceeds to step S20. When no slip occurs in any of the rear wheels, the outer rear wheel speed is higher, and when some slip occurs in the inner rear wheel, this relationship is reversed. In the example in Figure 8, at time t1, the driver begins turning the steering wheel 6, and the outer rear wheel speed of the turning vehicle 1 is higher, while the inner rear wheel speed is lower, so the flowchart process proceeds to step S16.

[0046] In step S16, the difference in wheel speed between the outer rear wheel and the inner rear wheel (outer wheel speed - inner wheel speed) is the first wheel speed difference T, which is the threshold for the wheel speed difference. a It is determined whether the difference is greater than [m / sec]. The difference in wheel speed between the outer and inner wheels is the first wheel speed difference T. aIf the following conditions are met, the processes from step S22 onward will be executed, and the process shown in the flowchart in Figure 7 will be completed without the application of braking force by vehicle attitude control. That is, the difference in wheel speed between the left and right rear wheels may also be caused by errors in the wheel speed sensor 24, and intervening in vehicle attitude control based on a small difference in wheel speed may cause discomfort to the driver, so vehicle attitude control is not executed when the difference in wheel speed is small. Note that the first wheel speed difference T is the threshold for the wheel speed difference. a This is changed based on the vehicle speed of vehicle 1. The specific setting of the wheel speed difference threshold will be described later, referring to Figure 9.

[0047] In the example shown in Figure 8, when the driver turns the steering wheel 6 at time t1, causing the vehicle 1 to begin turning, the wheel speed difference gradually increases, and the wheel speed difference becomes the first wheel speed difference T. a Once this limit is exceeded, the processes from step S17 onwards will be executed. In step S17, the lateral acceleration detected by the lateral acceleration sensor 22 is a predetermined first lateral acceleration GY a [G](1[G]=9.81[m / sec 2 The vehicle speed is higher than ]) and the vehicle speed detected by the vehicle speed sensor 20 is a predetermined first vehicle speed V a It is determined whether the lateral acceleration is higher than [km / h]. a The following conditions apply, or the vehicle speed is below the first vehicle speed V a In the following cases, the processes from step S22 onward are executed, and the process shown in the flowchart in Figure 7 is completed without the application of braking force by vehicle attitude control. That is, when the lateral acceleration or vehicle speed is very low, there is little need to intervene with vehicle attitude control, and unnecessary intervention may cause discomfort to the driver, so vehicle attitude control is not performed.

[0048] On the other hand, the lateral acceleration is the first lateral acceleration GY a If the vehicle speed exceeds the first vehicle speed V aIf it exceeds this value, the processes from step S18 onwards are executed, and braking force is applied by vehicle attitude control. First, in step S18, the vehicle attitude control flag is changed to "true". Note that when the vehicle attitude control flag is changed to "true" in step S18, the process in the flowchart in Figure 7 proceeds from step S12 to S13. Then, the lateral acceleration detected by the lateral acceleration sensor 22 is set to a predetermined second lateral acceleration GY b If the value is higher than [G], the process proceeds to step S13 → S14, and braking force is applied by Pre-Brake LSD control. Pre-Brake LSD control will be explained later.

[0049] Next, in step S19, the basic command value F for vehicle attitude control is determined based on the difference in wheel speed between the left and right rear wheels. b1 [N] is determined. That is, the braking force to be applied to the inner rear wheel of vehicle 1 is set based on the difference in wheel speed between the inner rear wheel and the outer rear wheel. This basic command value F b1 This is the command value for the braking force applied to the inner rear wheel of the turning vehicle 1, and the outer wheel speed V o and the inner wheel speed V i The difference is given by a predetermined coefficient C m1 By multiplying by , the result is calculated using formula (2). TIFF0007850371000003.tif6150

[0050] Furthermore, in step S24, the basic command value F calculated in step S19 is used. b1 Various gains are multiplied by this value to determine the final command value F1 for vehicle attitude control. The specific processing performed in step S24 will be described later. Next, in step S25, the command values ​​calculated in each control are compared, and the largest command value is selected as the final command value.

[0051] Specifically, in the flowchart shown in Figure 7, in addition to the first braking force calculated in step S19 due to vehicle attitude control, the lower limit braking force calculated in step S14 due to Pre-brake LSD control and the second braking force calculated in step S21 due to brake LSD control are also calculated, as will be described later. In step S26, the maximum braking force among these calculated braking forces is selected, and one process in the flowchart shown in Figure 7 is completed. Once the process in the flowchart of Figure 7 is completed, the process proceeds to step S5 in the flowchart of Figure 6, where the brake device 8 is controlled so that the selected braking force is applied.

[0052] In the example shown in Figure 8, after the steering wheel 6 is turned at time t1, the difference between the wheel speed of the outer rear wheel and the inner rear wheel of vehicle 1 increases, and therefore the command value of the braking force calculated by formula (2) also increases. As a result, the braking force applied to the inner rear wheel of vehicle 1 during the turn also increases (times t1-t2 in Figure 8). Next, at time t2 in Figure 8, the driver starts to press the accelerator pedal, and consequently the difference in wheel speed between the left and right rear wheels becomes constant (times t2-t3 in Figure 8). During this time, the command value of the braking force calculated by formula (2) also remains constant while maintaining its maximum value.

[0053] Next, at time t3 in Figure 8, when the driver finishes turning the steering wheel 6 and transitions to holding the steering wheel, the vehicle 1 enters a steady-state turning state. Consequently, the wheel speeds of the inner and outer rear wheels increase, and the difference in wheel speed between the inner and outer rear wheels decreases (times t3-t4 in Figure 8). As a result, the command value of the braking force calculated by equation (2) also decreases. Furthermore, at time t4 in Figure 8, the difference in wheel speed between the inner and outer rear wheels becomes the first wheel speed difference T. a As a result, the process in the flowchart of Figure 7 proceeds from step S16 to S22, and the command value based on vehicle attitude control becomes zero (see the bottom row of Figure 8, vehicle attitude control F1).

[0054] Next, at time t5 in Figure 8, the slip of the inner rear wheel increases, the wheel speeds of the inner and outer rear wheels reverse, and the wheel speed of the inner rear wheel becomes higher. As a result, the process in the flowchart in Figure 7 proceeds from step S15 to S20, and the processes from step S20 onwards in the flowchart in Figure 7 are executed. Note that the reversal of the wheel speeds of the inner and outer rear wheels occurs when road surface friction is low, and does not usually occur when road surface friction is high.

[0055] In step S20, the difference in wheel speed between the outer rear wheel and the inner rear wheel (inner wheel speed - outer wheel speed) is the second wheel speed difference T. b It is determined whether the difference is greater than [m / sec]. The difference in wheel speed between the outer and inner wheels is the second wheel speed difference T. b If the following conditions are met, the process from step S22 onwards will be executed, and the process shown in the flowchart in Figure 7 will be completed without the application of braking force by brake LSD control. In other words, the difference in wheel speed between the left and right rear wheels may also be caused by errors in the wheel speed sensor 24, and intervening with brake LSD control based on a small difference in wheel speed may cause discomfort to the driver, so brake LSD control is not executed when the difference in wheel speed is small.

[0056] On the other hand, the difference in wheel speed between the outer rear wheel and the inner rear wheel is the second wheel speed difference T. b If the value is greater than the specified value, the process proceeds to step S21, and a command value for the second braking force based on the brake LSD control is calculated. In this way, when the vehicle 1 is turning, the brake control unit 14a applies a second braking force to the inner rear wheel when the wheel speed of the inner rear wheel of the vehicle 1 becomes faster than the wheel speed of the outer rear wheel. Brake LSD control is a control that applies the brakes to a spinning wheel to reduce its wheel speed and avoid a spinning condition. That is, as shown in time t5 to t6 in Figure 8, when the wheel speed of the inner drive wheel (rear wheel in this embodiment) of the turning vehicle 1 exceeds the wheel speed of the outer drive wheel, the inner drive wheel begins to spin. When the wheel speed difference becomes large due to the spinning of the inner wheel, the driving force is no longer transmitted to the outer rear wheel via the differential gear 4c, so a braking force is applied to the inner wheel to reduce its wheel speed.

[0057] In step S21, the basic command value F for brake LSD control is determined based on the difference in wheel speed between the left and right rear wheels. b2 [N] is determined. This is the basic command value F for braking force under brake LSD control. b2 V is the command value for the braking force applied to the inner rear wheel of the turning vehicle 1, and the inner wheel speed V i and outer wheel speed V o The difference is given by a predetermined coefficient C m2 By multiplying by , the result is calculated using formula (3). TIFF0007850371000004.tif6150

[0058] In the example shown in Figure 8, at time t5, the basic command value F due to brake LSD control is b2 The calculation begins, and braking force is applied by brake LSD control. As a result, the wheel speed of the inner rear wheel decreases, and at time t6, the difference in wheel speed between the inner and outer rear wheels is almost zero. After the wheel speed difference becomes almost zero at time t6, the process in the flowchart of Figure 7 proceeds as follows: step S15 → S20 → S22, or step S15 → S16 → S22, and the basic command value F is determined by brake LSD control. b2 The calculation is not performed (see bottom row of Figure 8, time t6~t7, brake LSD control F2).

[0059] On the other hand, as described above, after the vehicle attitude control flag is changed to "true" in step S18 of Figure 7, the process in the flowchart shown in Figure 7 proceeds to step S12 → S13. In step S13, the lateral acceleration detected by the lateral acceleration sensor 22 is a predetermined second lateral acceleration GY b It is determined whether the lateral acceleration is higher than the second lateral acceleration GY. b If the following conditions are met, the process proceeds to step S15, and no braking force is applied by the Pre-Brake LSD control. In this embodiment, the second lateral acceleration GY b This is the first lateral acceleration GY aIt is set to a value smaller than that. In other words, when lateral acceleration is very low, there is little need to intervene with Pre-Brake LSD control, and unnecessary intervention may cause discomfort to the driver, so Pre-Brake LSD control is not performed.

[0060] Furthermore, the lateral acceleration is a predetermined second lateral acceleration GY b When it exceeds [G], the braking force by the Pre-brake LSD control is calculated in step S14. In step S14, the basic command value F b3 However, the most recently set basic command value F for vehicle attitude control b1 A predetermined coefficient C is applied to the maximum value. m3 By multiplying by , the result is calculated using formula (4). TIFF0007850371000005.tif6150

[0061] In this embodiment, the coefficient C m3 It is set to a positive value less than 1. That is, the basic command value F for Pre-Brake LSD control. b3 This is the basic command value F for vehicle attitude control. b1 It is always set to a value smaller than the maximum value. In the example shown in Figure 8, between times t1 and t2, the basic command value F for vehicle attitude control is set. b1 Because it is on an upward trend, its maximum value is updated from time to time, and the coefficient C is added to it. m3 The base command value F multiplied by b3 The value of also increases (see bottom row of Figure 8, time t1~t2, Pre-brake LSD control F3). Then, between time t2~t3, the basic command value F for vehicle attitude control increases. b1 Since it becomes constant at its maximum value, that maximum value is also a constant value, and the coefficient C is added to it. m3 The base command value F multiplied by b3 The value of also becomes a constant value. Furthermore, from time t3 onward, the basic command value F for vehicle attitude control b1 It tends to decrease, but its maximum value is maintained, and it is given by coefficient C m3 The base command value F multiplied by b3 The value of this Pre-Brake LSD control is also retained. b3This is maintained until the turning maneuver is completed at time t7 and the vehicle attitude control flag is changed to "false" (step S22 → S23). In this way, after the first braking force is applied by the vehicle attitude control, even if the difference in wheel speed between the inner and outer rear wheels decreases, a braking force above a predetermined lower limit braking force is maintained until the turning is completed.

[0062] Note that the basic command value F is determined by the Pre-Brake LSD control. b3 Although it is calculated from time t1 onwards, the basic command value F for vehicle attitude control b1 When the command value F1 for vehicle attitude control based on this is large, it is not adopted in the maximum value selection in step S25 and is not actually applied. After time t3, the value of the command value F1 for vehicle attitude control decreases, and the basic command value F b3 When the command value F3 for Pre-Brake LSD control based on this falls below this value, the command value F3 for Pre-Brake LSD control is adopted in step S25.

[0063] Furthermore, from time t5 in Figure 8, the basic command value F for brake LSD control is shown. b2 The calculation of this basic command value F begins. b2 As long as the command value F2 for brake LSD control is less than the command value F3 for pre-brake LSD control, the command value F3 for pre-brake LSD control is adopted in the maximum value selection in step S25, and braking force based on the command value F3 is applied. After time t5, when the command value F2 for brake LSD control increases and exceeds the command value F3 for pre-brake LSD control, the command value F2 for brake LSD control is adopted in the maximum value selection in step S25, and braking force based on the command value F2 is applied. Then, when the command value F2 for brake LSD control decreases and falls below the command value F3 for pre-brake LSD control, the command value F3 is adopted in the maximum value selection in step S25, and braking force based on the command value F3 is applied until the turn is completed.

[0064] Thus, the braking force based on Pre-Brake LSD control is applied after the application of braking force based on vehicle attitude control is completed (after time t4 in Figure 8), and when the application of braking force by brake LSD control begins (time t5 in Figure 8), the braking force applied to the inner rear wheel of vehicle 1 changes in a short period of time, which is intended to prevent the driver from feeling any discomfort.

[0065] Furthermore, in the example shown in Figure 8, the driver begins to turn the steering wheel 6 back at time t6, completes the turn back at time t7, returns to a straight-ahead position, and ends the turning maneuver. In step S22, it is determined whether the steering wheel 6 has been returned to its original position based on the value detected by the steering angle sensor 16. If the return to its original position is not complete, the process proceeds to step S24; if the return to its original position is complete, the process proceeds to step S23. In this embodiment, the brake control unit 14a generates a braking force at a brake fluid pressure of approximately 0.1 MPa or less during vehicle attitude control from the time t1 in Figure 8 when the steering wheel 6 is turned inward until the return to its original position is completed at time t7.

[0066] In step S23, since the counter-steering is complete and the turning maneuver is finished, the "vehicle attitude control flag" is changed to "false". Subsequently, if the flowchart shown in Figure 7 is executed, the process will proceed to steps S12 → S16. In this state, no braking force is applied based on the Pre-brake LSD control.

[0067] Next, referring to Figure 9, the threshold for the wheel speed difference used in step S16 of Figure 7 (first wheel speed difference T) a This explains the settings for ). Figure 9 is an example of a map for setting the threshold for the wheel speed difference, and the first wheel speed difference T in step S16 of Figure 7. a The value in [m / sec] is set based on the map in Figure 9. First wheel speed difference T a The value of is changed based on the vehicle speed of vehicle 1 detected by the vehicle speed sensor 20. As shown in Figure 9, the first wheel speed difference Ta The value is maximum at a vehicle speed of 0, decreases as the vehicle speed increases, and becomes substantially constant at a predetermined vehicle speed V1 or higher. Preferably, the value of the vehicle speed V1 is set to about 80 to about 110 [km / h] per hour, and at this value or higher, the first wheel speed difference T a is set to be about 0.02 to about 0.05 [m / sec].

[0068] Thus, by changing the threshold value of the wheel speed difference according to the vehicle speed, the condition for starting the execution of vehicle attitude control is changed. That is, the first wheel speed difference T a is set. In a low vehicle speed region, the vehicle attitude control executed at step S17 or lower in FIG. 7 is less likely to intervene. That is, in a low vehicle speed region, an error is likely to occur in the measured value of the wheel speed, and if vehicle attitude control is executed with a minute wheel speed difference, vehicle attitude control may be executed based on the measurement error. In order to suppress such unnecessary intervention of vehicle attitude control, in the present embodiment, the value of the first wheel speed difference T a is set as shown in FIG. 9.

[0069] Next, referring to FIGS. 10 to 16, the gains multiplied by each basic command value in step S24 of FIG. 7 will be described. FIG. 10 is a steering angle gain set based on the steering angle and multiplied by the basic command value F b1 by vehicle attitude control. FIG. 11 is a gain of the change speed of the accelerator opening set based on the change speed of the accelerator opening and multiplied by the basic command value F b1 by vehicle attitude control. FIG. 12 is a map of the accelerator opening gain set based on the accelerator opening and multiplied by the basic command value F b1 by vehicle attitude control. FIG. 13 is a map of the lateral acceleration gain set based on the lateral acceleration and multiplied by the basic command value F b1 by vehicle attitude control. FIG. 14 is a map of the vehicle speed gain set based on the vehicle speed and multiplied by the basic command value F b1 by vehicle attitude control.

[0070] Furthermore, FIG. 15 is a map of the differential rotation gain that is set based on the inner and outer wheel speed differences and is multiplied by the basic command value F by the brake LSD control. FIG. 16 is a map of the front-to-rear slip ratio gain that is set based on the slip ratios of the front and rear wheels of the vehicle and is multiplied by the basic command value F by the brake LSD control. FIG. 17 is a diagram showing an example of comparing the relationship between the slip ratios of the front and rear wheels and the wheel speed difference in a vehicle equipped with a high-power prime mover and a vehicle equipped with a low-power prime mover. b2 As shown in FIG. 10, the steering angle gain G b2 is zero in the region where the steering angle θ [deg] is less than or equal to the first steering angle θ1, increases when θ1 or more, and is set to converge to "1" when the steering angle is more than a predetermined steering angle. By setting the steering angle gain G

[0071] in this way, in the region where the steering angle is less than or equal to the first steering angle θ1, vehicle attitude control is not substantially executed and control intervention is not performed (by multiplying by the steering angle gain G θ , the command value of vehicle attitude control becomes zero). As a result, vehicle attitude control is suppressed from intervening due to fine steering of the steering wheel 6 and giving the driver a sense of discomfort. Preferably, the value of the first steering angle θ1 is set to about 3.5 to about 6.0 [deg], and below this value, the value of the steering angle gain G θ is set to zero. θ is set to zero. θ is set to zero.

[0072] As shown in FIG. 11, the accelerator opening change speed gain G AV is "1.2" in the region where the change speed A V [% / sec] of the accelerator opening is near zero, decreases as the change speed increases, and is set to converge to "0.5" when the change speed is more than a predetermined change speed. Here, when the accelerator pedal (not shown) of vehicle 1 is rapidly depressed (large accelerator opening change speed), the wheel speed difference (differential rotation) between the inner rear wheel and the outer rear wheel increases, and the differential limiting device 4d provided in the differential gear 4c operates. Due to the action of this differential limiting device 4d, the wheel speed difference rapidly decreases.

[0073] When the vehicle attitude control operates in conjunction with the action of such a differential limiting device 4d, and a large braking force is applied to the inner rear wheel, the rate of change in the wheel speed difference can become too large, which may cause discomfort to the driver. Therefore, the accelerator opening change rate gain G AV By setting this, when the accelerator pedal (not shown) is rapidly pressed, the braking force applied by the vehicle attitude control is reduced. That is, the accelerator opening change speed gain G is set as shown in Figure 11. AV By multiplying by this factor, the greater the rate of change in the accelerator opening detected by the accelerator opening sensor, the smaller the braking force applied to the inner rear wheel of the turning vehicle. This prevents the rate of change in the wheel speed difference from becoming too large, which could cause discomfort to the driver.

[0074] As shown in Figure 12, accelerator opening gain G a The accelerator opening gain G increases with increasing accelerator opening [%], becomes "1" at the first accelerator opening A1, and is set to converge to a predetermined value greater than "1" at accelerator openings A1 and above. a By setting this, the command value from vehicle attitude control decreases as the accelerator opening decreases. In other words, in the range of small accelerator openings, the lifting of the inner rear of the vehicle body 1a is less likely to occur, thus suppressing unnecessary intervention by vehicle attitude control that may cause discomfort to the driver. Preferably, the value of the first accelerator opening A1 is set to about 45 to about 60%, and below this value, the accelerator opening gain G aH Set this value to "1" or less; if it is greater than this value, the accelerator opening gain G a Set it so that it is "1" or greater.

[0075] As shown in Figure 13, the lateral acceleration gain G l is the lateral acceleration a l [G] is the first transverse acceleration a l1 In the following region, it is zero, and a l1 The lateral acceleration gain G increases above a certain threshold and is set to converge to "1" when the lateral acceleration exceeds a predetermined threshold. lBy setting this, when the lateral acceleration of vehicle 1 is large, a greater braking force is applied to the inner rear wheel of vehicle 1 during a turn than when the lateral acceleration of vehicle 1 is small. Also, as shown in Figure 13, the lateral acceleration gain G l By setting this, the lateral acceleration becomes the first lateral acceleration a l1 In the following region, vehicle attitude control intervention is effectively eliminated (lateral acceleration gain G). l By multiplying by this, the command value for vehicle attitude control becomes zero. ) That is, lateral acceleration a l In the smallest region, the lifting of the inner rear of the vehicle body 1a is unlikely to occur, thus suppressing unnecessary intervention by vehicle attitude control that would cause discomfort to the driver. Preferably, the first lateral acceleration a l1 Set the value to approximately 0.22 to 0.35 [G], and below this value, the lateral acceleration gain G l Set the value to zero.

[0076] As shown in Figure 14, the vehicle speed gain G V The vehicle speed gain G gradually increases with increasing vehicle speed [km / h], becoming "1" at the first vehicle speed V1, and is set to increase relatively rapidly above the first vehicle speed V1. V By setting this, the command value for vehicle attitude control increases with increasing vehicle speed, and at high vehicle speeds, a greater braking force is applied to the inner rear wheel of the turning vehicle than at low vehicle speeds. In other words, while the lift of the inner rear of the vehicle body 1a is less likely to occur in the low vehicle speed range, the problem of the inner rear of the vehicle body 1a lifting becomes more pronounced as the vehicle speed increases, so the command value is increased and vehicle attitude control is strongly intervened. Preferably, the value of the first vehicle speed V1 is set to about 95 to about 115 [km / h], and below this value, the vehicle speed gain G VH Set this value to "1" or less, and if it is greater than or equal to this value, the vehicle speed gain G V Set it to increase.

[0077] In step S24 of Figure 7, the basic command value F for vehicle attitude control is b1 The steering angle gain G is set based on Figure 10. θBased on Figure 11, the accelerator opening rate change gain G is set. AV Based on Figure 12, the accelerator opening gain G is set. a Based on Figure 13, the lateral acceleration gain G is set. l , and the vehicle speed gain G set based on Figure 14 V This is multiplied, and the command value F1 for vehicle attitude control is calculated using formula (5). TIFF0007850371000006.tif8150

[0078] Next, referring to Figures 15 and 16, the basic command value F for brake LSD control is shown. b2 The differential rotation gain G multiplied by this D , and front-to-rear slip ratio gain G S Explain.

[0079] Figure 15 shows the differential rotation gain G. D This is a map used to configure [something]. As shown in Figure 15, the differential rotation gain G D The differential rotation gain G is set to a value of approximately 0.8 or less in the region where the difference in rotation D [m / sec] between the inner and outer rings is low, and is set to converge to "1" as the difference in rotation D increases. D By setting this, the differential rotation increases and the command value for brake LSD control increases. Also, the differential rotation gain G D As the differential rotation D increases, the command value for brake LSD control will not become excessive.

[0080] Figure 16 shows the front-to-rear slip ratio gain G. S This is a map used to configure [something]. Front / rear slip ratio gain G S This is a gain set in accordance with the front-to-rear slip ratio, which is the slip ratio between the front and rear wheels. In this embodiment, the front-to-rear slip ratio is calculated based on equation (6). TIFF0007850371000007.tif12150 This means that if there is no slip in the rear wheels, the front-to-rear slip ratio is 0, and if the rear wheels are completely slipping, the front-to-rear slip ratio is 1. Generally, when a vehicle is driving on a dry road surface, the front-to-rear slip ratio will be at most about 0.2. Also, on low-μ road surfaces such as snowy roads, the front-to-rear slip ratio will be greater than 0.2, and on medium-μ road surfaces such as gravel roads, it will be about 0.1 to 0.3. This front-to-rear slip ratio tends to be larger when a vehicle equipped with a high torque / power engine is driving on a low-μ road surface, and it serves as an indicator of the torque / power of the engine installed in the vehicle.

[0081] Figure 17 is a graph showing an example of the relationship between the front-to-rear slip ratio and the difference in wheel speed between the left and right rear wheels, measured for a vehicle that traveled a predetermined path on a low-friction surface. In Figure 17, the relationship between the front-to-rear slip ratio and the difference in wheel speed measured for a vehicle equipped with a 1.5-liter engine is plotted with circles, and the relationship between the front-to-rear slip ratio and the difference in wheel speed measured for a vehicle equipped with a 2.0-liter engine on the same chassis is plotted with crosses.

[0082] As shown in Figure 17, during cornering on a road surface with low friction coefficient (μ), both vehicles exhibited a maximum wheel speed difference of approximately 50 km / h between the left and right rear wheels. On the other hand, the vehicle equipped with a high-torque 2.0-liter engine showed a front-to-rear slip ratio distributed between approximately 0 and 0.7, with a maximum of about 0.9, while the vehicle equipped with a low-torque 1.5-liter engine had a maximum front-to-rear slip ratio of only about 0.5. Thus, even when vehicles with the same body performed cornering on the same route, the vehicle equipped with a high-torque engine exhibited a large front-to-rear slip ratio, while the vehicle equipped with a low-torque engine exhibited a relatively small front-to-rear slip ratio. This is thought to be because, when cornering on a road surface with low friction coefficient (μ), the drive wheels of the vehicle equipped with a high-torque engine are more prone to slipping.

[0083] Thus, in vehicles equipped with engines with high torque, slip of the drive wheels (rear wheels in this embodiment) is more likely to occur, and therefore the effect of brake LSD control tends to be weaker compared to vehicles equipped with engines with low torque. In this embodiment, as shown in Figure 16, the front-to-rear slip ratio gain G is relative to the front-to-rear slip ratio. S This setting ensures that sufficient brake LSD control is achieved even in vehicles equipped with high-torque engines. Specifically, the front-to-rear slip ratio gain G S The value of is 1 up to a front-to-rear slip ratio of approximately 0.2, and increases when it exceeds approximately 0.2. Furthermore, the front-to-rear slip ratio gain G S The value plateaus when the front-to-rear slip ratio exceeds approximately 0.5, and then settles at a constant value of approximately 2.25.

[0084] The front-to-rear slip ratio gain G is set in this manner. S The basic command value F for brake LSD control b2 By multiplying by this, in vehicles equipped with high-torque engines that tend to have a large front-to-rear slip ratio, the command value F2 for brake LSD control is increased. Therefore, the front-to-rear slip ratio gain G is increased relative to the front-to-rear slip ratio as shown in Figure 16. S By setting this, a common brake control unit 14a can be applied to vehicles with both high-torque and low-torque engines on the same vehicle body. Also, the front-to-rear slip ratio gain G S Since the value is set to cap out at a predetermined value, it is possible to prevent the braking force from becoming excessive due to brake LSD control as the front-to-rear slip ratio increases. In other words, if excessive braking force is applied to the inner rear wheel as brake LSD control, the vehicle's yaw rate will change, affecting the vehicle's cornering performance. By applying a braking force of less than or equal to a predetermined value as brake LSD control to the inner rear wheel of the vehicle while it is cornering, it is possible to control the vehicle's attitude by suppressing the lift of the inner rear of the vehicle body without substantially affecting the vehicle's yaw rate.

[0085] In step S24 of Figure 7, the basic command value F for brake LSD control is b2 The differential rotation gain G is set based on Figure 15. D , and the front-to-rear slip ratio gain G set based on Figure 16 S This is multiplied, and the command value F2 for brake LSD control is calculated using formula (7). TIFF0007850371000008.tif8150

[0086] Thus, in step S24 of Figure 7, the basic command value F for vehicle attitude control is b1 Based on this, the command value F1 for vehicle attitude control is calculated using formula (5). Furthermore, the basic command value F for brake LSD control is calculated. b2 Based on this, the command value F2 is calculated using formula (7).

[0087] Furthermore, the command value F3 for Pre-Brake LSD control is the same as the basic command value F b3 It is calculated by multiplying it by the same gain as the vehicle attitude control. That is, the command value F3 is calculated by the following formula (8). As mentioned above, Pre-brake LSD control is applied to suppress changes in braking force between the completion of braking force application based on vehicle attitude control and the application of braking force by brake LSD control. For this reason, the command value for Pre-brake LSD control is also multiplied by the same gain as the vehicle attitude control to set the braking force so that it connects smoothly with the vehicle attitude control. TIFF0007850371000009.tif6150

[0088] Furthermore, in step S25 of Figure 7, the command value F1 for vehicle attitude control, the command value F2 for brake LSD control, and the command value F3 for pre-brake LSD control, calculated as described above, are compared, and the largest command value is finally determined as the command value for the braking force to be applied to the inner rear wheel. Once the command value for the braking force is determined in step S25 of Figure 7, the process returns to the flowchart in Figure 6. Furthermore, as described above, in the flowchart of Figure 6, the command value for turning control is determined in step S3, and the command value for anti-skid control is determined in step S4. Next, in step S5, the brake device 8 is controlled based on the determined command values.

[0089] As mentioned above, the vehicle attitude control (step S2), turning control (step S3), and anti-skid control (step S4) in Figure 6 are each performed under different driving conditions, and these controls are not normally performed in overlapping order. Therefore, when the command value for vehicle attitude control (step S2) is set according to the flowchart in Figure 7, the command values ​​for turning control (step S3) and anti-skid control (step S4) are not set (these command values ​​are set to "0").

[0090] According to the vehicle control device of the embodiment of the present invention, in vehicle attitude control, when the front-to-rear wheel slip ratio of the vehicle is large, the braking force applied to the inner rear wheel of the vehicle is greater than when the front-to-rear wheel slip ratio is small (Figure 16). As a result, the same vehicle attitude control effect can be obtained for models equipped with high-torque engines and models equipped with low-torque engines without having to prepare different brake control devices.

[0091] Furthermore, according to the vehicle control device of this embodiment, the front-to-rear wheel slip ratio is calculated based on the wheel speed of the rear wheel with the slower wheel speed among the left and right rear wheels, and the front wheel with the slower wheel speed among the left and right front wheels (equation (6)). Therefore, the torque characteristics of the engine can be accurately reflected in the front-to-rear wheel slip ratio, and the torque characteristics of the engine can be accurately reflected in the vehicle attitude control.

[0092] Furthermore, according to the vehicle control device of this embodiment, as shown in Figure 16, the gain increases when the front-to-rear wheel slip ratio is approximately 0.2 or higher. Therefore, when a high-torque engine is installed, the braking force applied to the inner rear wheel increases, and sufficient vehicle attitude control can be obtained. Also, since the gain becomes constant when the front-to-rear wheel slip ratio is approximately 0.5 or higher, it is possible to prevent the braking force applied to the inner rear wheel from becoming too large, which would affect the vehicle's turning behavior itself rather than controlling the lift of the inner rear of the vehicle body.

[0093] Although embodiments of the present invention have been described above, various modifications can be made to the embodiments described above. In particular, in the embodiments described above, the present invention was applied to a vehicle equipped with an engine (internal combustion engine) as the prime mover, but the present invention can also be applied to a vehicle equipped with an electric motor as the prime mover, or to a vehicle equipped with both an engine and a motor. Furthermore, in the embodiments described above, the rear wheels of the vehicle were driven by the prime mover, but the present invention can also be applied to a four-wheel drive vehicle in which driving force is also applied to the front wheels of the vehicle. [Explanation of Symbols]

[0094] 1 vehicle 1a Vehicle body 2a, 2b front wheel 2c, 2d rear wheel 2e axle 3 Suspension 3a Upper Arm 3b Lower Arm 4. Engine (prime mover) 4a Transmission 4b Propeller shaft 4c Differential Gear 4d Differential Limiter 6 Steering Wheel 7. Steering gear 8. Brake system (brake actuator) 10. Hydraulic pump 12 Valve Unit 13. Hydraulic pressure sensor 14 PCM 14a Brake control unit (brake control device) 14b Swing control unit 14c Anti-skid control unit 16 Steering angle sensor 18. Accelerator position sensor 20. Vehicle speed sensor 22. Lateral acceleration sensor 24 Wheel speed sensors

Claims

1. A vehicle control device for controlling the attitude of a vehicle, A wheel speed sensor that detects the wheel speed of a moving vehicle, A brake actuator that applies braking force to the wheels of a vehicle, The system includes a brake control device that sends a control signal to the brake actuator based on the vehicle's driving state and generates braking force, The above brake control device performs vehicle attitude control by applying braking force to the inner rear wheel when the wheel speed of the inner rear wheel of the vehicle becomes higher than the wheel speed of the outer rear wheel during the vehicle's turn, thereby suppressing the lifting of the inner rear of the vehicle body. In the above vehicle attitude control, when the front-to-rear wheel slip ratio of the vehicle is large, the braking force applied to the inner rear wheel of the vehicle is increased compared to when the front-to-rear wheel slip ratio is small. In the above-described vehicle attitude control, the braking force applied to the inner rear wheel of the vehicle is calculated by multiplying the basic command value by a predetermined gain, wherein the predetermined gain increases when the front-to-rear wheel slip ratio is approximately 0.2 or more, and becomes a constant value when the front-to-rear wheel slip ratio is approximately 0.5 or more.

2. The vehicle control device according to claim 1, wherein the front and rear wheel slip ratio is calculated based on the wheel speed of the rear wheel with the slower wheel speed among the left and right rear wheels, and the front wheel with the slower wheel speed among the left and right front wheels.

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