WO2024204787A1

WO2024204787A1 - Braking control device

Info

Publication number: WO2024204787A1
Application number: PCT/JP2024/013234
Authority: WO
Inventors: 翔太丹山
Original assignee: 株式会社アドヴィックス
Priority date: 2023-03-31
Filing date: 2024-03-29
Publication date: 2024-10-03
Also published as: JP2024144951A

Abstract

A vehicle 10 to which a braking control device 50 is applied comprises: friction brakes 20 for applying front-wheel friction braking force; and friction brakes 20 for applying rear-wheel friction braking force. A processing circuit 51 of the braking control device 50 functions as: a target pitch angle acquisition unit M15 for acquiring a target pitch angle during turning of the vehicle 10; and a control unit M21 for operating the friction brakes 20 and the friction brakes 20 such that request braking force is distributed, during braking of the vehicle 10, to the front-wheel friction braking force and the rear-wheel friction braking force according to the target pitch angle.

Description

Brake Control Device

The present invention relates to a braking control device that controls the braking force applied to a vehicle.

Patent Document 1 discloses an attitude control device that controls the acceleration in the longitudinal direction of a vehicle so that the pitch angle of the vehicle becomes a target pitch angle corresponding to the roll angle of the vehicle. This attitude control device sets the target pitch angle so that the angle becomes larger as the roll angle of the vehicle becomes larger.

JP 2007-237933 A

When a vehicle is turning, the roll angle of the vehicle increases or decreases. Therefore, in a vehicle equipped with the above-mentioned attitude control device, the target pitch angle changes in conjunction with the fluctuation in the roll angle, causing the longitudinal acceleration of the vehicle to fluctuate while turning. This fluctuation in the longitudinal acceleration of the vehicle while turning may cause discomfort to the vehicle occupants.

A braking control device for solving the above problem includes a first braking unit that applies a first braking force to a vehicle and a second braking unit that applies a second braking force to the vehicle, and is applied to a vehicle in which the pitch behavior of the vehicle in the pitch direction associated with application of a desired amount of the first braking force to the vehicle by the first braking unit is different from the pitch behavior of the vehicle in the pitch direction associated with application of the desired amount of the second braking force to the vehicle by the second braking unit. The braking control device includes a target pitch angle acquisition unit that acquires a target pitch angle that is a target for the pitch angle of the vehicle when the vehicle turns, and a control unit that operates the first braking unit and the second braking unit so that a required braking force that is a required value of the braking force to be applied to the vehicle is distributed between the first braking force and the second braking force in accordance with the target pitch angle when the vehicle is braked.

The braking control device has the effect of adjusting the pitch angle of the vehicle while suppressing fluctuations in the longitudinal acceleration of the vehicle while the vehicle is turning.

FIG. 1 is a schematic diagram showing a brake control device according to a first embodiment and a vehicle to which the brake control device is applied. FIG. 2 is a schematic diagram illustrating forces acting on a vehicle when a braking force is applied. FIG. 3 is a flowchart showing a flow of processing executed by a processing circuit included in the brake control device of the first embodiment. FIG. 4 is a graph showing the relationship between the front wheel friction braking force and the rear wheel friction braking force. FIG. 5 is a timing chart when a vehicle turns during braking. FIG. 6 is a block diagram showing a part of the functional configuration of a processing circuit provided in the brake control device of the second embodiment.

An embodiment of a brake control device will be described below with reference to Figs.
1 illustrates a vehicle 10 equipped with a brake control device 50. The vehicle 10 is equipped with a brake operating member 11, a steering member 12, a plurality of friction brakes 20, and a braking device 30. The brake operating member 11 is a member that is operated by the driver when applying a braking force to the vehicle 10. An example of the brake operating member 11 is a brake pedal. The steering member 12 is a member that is operated by the driver when turning the vehicle 10. An example of the steering member 12 is a steering wheel.

The vehicle 10 has a left front wheel 14 and a right front wheel 15 as front wheels, and a left rear wheel 16 and a right rear wheel 17 as rear wheels.
<Friction brake>
The plurality of friction brakes 20 apply frictional braking force to the corresponding wheels. The friction brakes 20 have a wheel cylinder 21, a rotating body 22, and a friction portion 23. Since the rotating body 22 rotates integrally with the wheel, the friction portion 23 is pressed against the rotating body 22 to apply frictional braking force to the wheel. The force pressing the friction portion 23 against the rotating body 22 increases as the wheel hydraulic pressure, which is the hydraulic pressure in the wheel cylinder 21, increases. Therefore, the friction brake 20 can apply a larger frictional braking force to the wheel as the wheel hydraulic pressure increases. The frictional braking force applied to the

front wheels

14, 15 is referred to as the "front wheel frictional braking force", and the frictional braking force applied to the

rear wheels

16, 17 is referred to as the "rear wheel frictional braking force".

In this embodiment, the front wheel friction braking force corresponds to the "first braking force," and the rear wheel friction braking force corresponds to the "second braking force." Therefore, the friction brake 20 for the front wheels corresponds to the "first braking unit," and the friction brake 20 for the rear wheels corresponds to the "second braking unit."

<Braking device>
The braking device 30 controls the frictional braking force applied to the

wheels

14, 15 by controlling the wheel hydraulic pressures in the multiple wheel cylinders 21. For example, the braking device 30 has a pressure source that supplies brake fluid to the multiple wheel cylinders 21. The pressure source is, for example, an electric pump and an electric cylinder. The braking device 30 can individually adjust the wheel hydraulic pressures in the wheel cylinders 21 for the front wheels and the wheel hydraulic pressures in the wheel cylinders 21 for the rear wheels.

In the following description, the sum of the braking forces applied to the multiple wheels 14 to 17 will also be referred to as the "braking force Fx applied to the vehicle 10."
<Changes in vehicle posture when braking>
The forces acting on the vehicle 10 during vehicle braking and the sprung motion of the vehicle 10 will be described with reference to Fig. 2. Fig. 2 shows the center of gravity GC of the vehicle 10. In Fig. 2, the horizontal distance between the center of gravity GC of the vehicle 10 and the axles of the

front wheels

14, 15 in the longitudinal direction of the vehicle 10 is shown as a first distance Lf, and the horizontal distance between the center of gravity GC of the vehicle 10 and the axles of the

rear wheels

16, 17 in the longitudinal direction of the vehicle 10 is shown as a "second distance Lr". The sum of the first distance Lf and the second distance Lr corresponds to the "wheelbase L of the vehicle 10".

When the vehicle brakes, a pitching moment My is generated around the vehicle center of gravity GC as shown by the arrow in Figure 2. When pitching moment My is generated in the vehicle 10, the vehicle 10 pitches toward the nose dive side. Nose dive is a behavior of the vehicle 10 that displaces the front of the body 19 of the vehicle 10 downward and the rear of the body 19 upward. On the other hand, a behavior of the vehicle 10 that displaces the front of the body 19 upward and the rear of the body 19 downward is called "nose lift". The larger the magnitude of the pitching moment My, the larger the pitch angle θ becomes, and the faster the rate at which the pitch angle θ increases becomes. On the other hand, when the attitude of the vehicle 10 changes toward the nose lift side, the pitch angle θ becomes smaller.

In FIG. 2, the front wheel friction braking force of the left front wheel 14 is shown as "front wheel friction braking force Fxflb," and the rear wheel friction braking force of the left rear wheel 16 is shown as "rear wheel friction braking force Fxrlb." The friction braking forces act on the contact points between the wheels and the road surface. In FIG. 2, the contact point where the front wheel friction braking force Fxflb acts is shown as the first contact point PA1, and the contact point where the rear wheel friction braking force Fxrlb acts is shown as the second contact point PA2.

In Figure 2, the instantaneous rotation center of the wheels is shown. The instantaneous rotation center of the left front wheel 14 when the vehicle is braking is shown as the front wheel rotation center Cf. The angle between the road surface 100 and the straight line connecting the first application point PA1 and the front wheel rotation center Cf is shown as the first angle θfb. Similarly, the instantaneous rotation center of the left rear wheel 16 when the vehicle is braking is shown as the rear wheel rotation center Cr. The angle between the road surface 100 and the straight line connecting the second application point PA2 and the rear wheel rotation center Cr is shown as the second angle θrb.

The positions of the multiple instantaneous rotation centers are each determined by the characteristics of the suspension device. The positions of the multiple instantaneous rotation centers shown in FIG. 2 are only an example, and do not represent the actual positions of the instantaneous rotation centers. Therefore, the magnitudes of the first angle θfb and the second angle θrb do not represent the actual angle magnitudes.

As shown by the white arrows in FIG. 2, when the vehicle is braking, an anti-dive force FAD acts on the front of the vehicle 10 by the front wheel suspension device. Also, when the vehicle is braking, an anti-lift force FAL acts on the rear of the vehicle 10 by the rear wheel suspension device.

The anti-dive force FAD is a force that acts when a braking force is applied to the

front wheels

14, 15. The anti-dive force FAD is a force that prevents the front of the vehicle body from sinking. The direction in which the anti-dive force FAD acts is a direction that displaces the front of the vehicle body away from the road surface 100.

The anti-lift force FAL is a force that acts when a braking force is applied to the

rear wheels

16, 17. The anti-lift force FAL is a force that prevents the rear of the vehicle body from lifting up. The direction in which the anti-lift force FAL acts is a direction that displaces the rear of the vehicle body so as to move it closer to the road surface 100.

The anti-dive force FAD can be expressed as the following relational expression (F1). In relational expression (F1), "Fxfb" is the sum of the front wheel frictional braking force Fxflb of the left front wheel 14 and the front wheel frictional braking force Fxfrb of the right front wheel 15. The anti-lift force FAL can be expressed as the following relational expression (F2). In relational expression (F2), "Fxrb" is the sum of the rear wheel frictional braking force Fxrlb of the left rear wheel 16 and the rear wheel frictional braking force Fxrrb of the right rear wheel 17. As is clear from relational expression (F1), the greater the front wheel frictional braking force Fxfb, the greater the anti-dive force FAD. As is clear from relational expression (F2), the greater the rear wheel frictional braking force Fxrb, the greater the anti-lift force FAL.

The vehicle 10 is a vehicle in which the pitch behavior of the vehicle 10 in the pitch direction caused by the application of a desired amount of the front wheel friction braking force Fxfb to the vehicle 10 is different from the pitch behavior of the vehicle 10 in the pitch direction caused by the application of a desired amount of the rear wheel friction braking force Fxrb to the vehicle 10. For example, the vehicle 10 is configured so that the attitude change of the vehicle 10 can be suppressed as the braking ratio, which is the ratio of the rear wheel friction braking force Fxrb to the total braking force, which is the sum of the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb, increases. In other words, the vehicle 10 is configured so that the pitching suppression force increases as the braking ratio increases. The pitching suppression force is the sum of the anti-dive force FAD and the anti-lift force FAL. Therefore, under the condition that the total braking force is the same, the pitch angle θ is suppressed from increasing as the rear wheel friction braking force Fxrb increases, and the increasing speed of the pitch angle θ decreases.

<Detection system>
The detection system of the vehicle 10 will be described with reference to Fig. 1. A detection signal is input from the detection system to the braking control device 50. The detection system has a plurality of sensors. The plurality of sensors includes a brake sensor 101, a steering angle sensor 102, a plurality of wheel speed sensors 103, a longitudinal acceleration sensor 104, and a lateral acceleration sensor 105.

The brake sensor 101 detects information related to the driver's operation of the brake operating member 11. For example, the brake sensor 101 can be a sensor that detects the amount of operation of the brake operating member 11 by the driver, and a sensor that detects the operating force of the brake operating member 11 by the driver.

The steering angle sensor 102 outputs a detection signal corresponding to the steering angle of the steering member 12. The steering angle based on the detection signal of the steering angle sensor 102 is referred to as a "steering angle STR."
A wheel speed sensor 103 is provided for each of the wheels 14 to 17. The wheel speed sensors 103 output detection signals corresponding to the rotation speeds of the corresponding wheels. The rotation speeds of the wheels based on the detection signals of the wheel speed sensors 103 are referred to as "wheel speeds VW."

The longitudinal acceleration sensor 104 outputs a detection signal corresponding to the longitudinal acceleration of the vehicle 10 among the accelerations acting on the vehicle 10. The lateral acceleration sensor 105 outputs a detection signal corresponding to the lateral acceleration of the vehicle 10 among the accelerations acting on the vehicle 10. The longitudinal acceleration of the vehicle 10 based on the detection signal of the longitudinal acceleration sensor 104 is referred to as "longitudinal acceleration Gx." The lateral acceleration of the vehicle 10 based on the detection signal of the lateral acceleration sensor 105 is referred to as "lateral acceleration Gy."

<Brake control device>
As shown in Fig. 1, the braking control device 50 includes a processing circuit 51. For example, the processing circuit 51 is an electronic control device. In this case, the processing circuit 51 includes a CPU 52 and a memory 53. The memory 53 stores a control program executed by the CPU 52. When the CPU 52 executes the control program, the processing circuit 51 controls the braking device 30 to activate the multiple friction brakes 20. In other words, the processing circuit 51 can adjust the braking force Fx applied to the vehicle 10 by activating the multiple friction brakes 20.

<Functional configuration of the processing circuit>
1, the processing circuit 51 functions as a required braking force acquisition unit M11, a roll angle acquisition unit M13, a target pitch angle acquisition unit M15, a target pitch moment acquisition unit M17, a target allocation ratio setting unit M19, and a control unit M21 by the CPU 52 executing a control program. Hereinafter, the target pitch moment acquisition unit M17 will be referred to as a "target PM acquisition unit M17."

The required braking force acquisition unit M11 acquires a required braking force FxRq, which is a required value of the braking force Fx to be applied to the vehicle 10. When the driver is operating the brake operating member 11, the required braking force acquisition unit M11 acquires a braking force corresponding to the detection signal of the brake sensor 101 as the required braking force FxRq. When the vehicle 10 is traveling autonomously through automatic driving, deceleration of the vehicle 10 may be requested from another control device. In this case, the required braking force acquisition unit M11 acquires a braking force corresponding to the deceleration of the vehicle 10 requested by the other control device as the required braking force FxRq.

The roll angle acquisition unit M13 acquires the roll angle φ of the vehicle 10. For example, the roll angle acquisition unit M13 estimates and calculates the roll angle φ based on the lateral acceleration of the vehicle 10. The lateral acceleration used in the estimation of the roll angle φ may be the lateral acceleration Gy detected by the lateral acceleration sensor 105, or a calculated value of the lateral acceleration derived based on the vehicle speed VS and steering angle STR of the vehicle 10. The roll angle φ is an example of a parameter whose magnitude changes when the vehicle 10 turns. Therefore, the roll angle acquisition unit M13 can be said to be an example of a "parameter acquisition unit" that acquires the parameter.

The target pitch angle acquisition unit M15 acquires a target pitch angle θTr, which is a target for the pitch angle θ of the vehicle 10. The target pitch angle acquisition unit M15 acquires a pitch angle corresponding to a parameter whose value changes when the vehicle 10 turns, as the target pitch angle θTr. When a roll angle φ is used as the parameter, the target pitch angle acquisition unit M15 acquires a larger pitch angle as the target pitch angle θTr as the roll angle φ increases. In this case, it is preferable for the target pitch angle acquisition unit M15 to acquire the product of the roll angle φ and a predetermined conversion gain α1 as the target pitch angle θTr. This allows the target pitch angle acquisition unit M15 to acquire the target pitch angle θTr when the roll angle φ is greater than 0 (zero) because the vehicle 10 is turning.

The predetermined conversion gain α1 is a gain for converting the roll angle into a pitch angle, and is set based on the specifications of the vehicle 10. A value greater than 0 (zero) and less than 1 is set as the conversion gain α1.

The target PM acquisition unit M17 acquires the pitching moment My corresponding to the target pitch angle θTr as the target pitching moment MyTr. For example, the target PM acquisition unit M17 can derive the target pitching moment MyTr using the following relational expression (F3). The pitch stiffness Ky of the vehicle 10 in relational expression (F3) can be calculated using the following relational expression (F4). In relational expression (F4), "Ksf" is the wheel rate of the

front wheels

14, 15, and "Ksr" is the wheel rate of the

rear wheels

16, 17. The first angle θfb and the second angle θrb are the angles shown in FIG. 2 and are angles determined from the specifications of the vehicle 10. By using relational expression (F3), the target PM acquisition unit M17 can acquire a target pitching moment MyTr that is a larger value as the target pitch angle θTr is larger.

The target allocation ratio setting unit M19 sets a target allocation ratio DfTr, which is a target of the allocation ratio, which is the ratio of the front wheel friction braking force Fxfb to the total braking force, which is the sum of the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb. In other words, the allocation ratio is the value obtained by dividing the front wheel friction braking force Fxfb by the total braking force. In this embodiment, the total braking force is equal to the required braking force FxRq. The process of setting the target allocation ratio DfTr will be described later.

When braking the vehicle, the control unit M21 activates the friction brakes 20 for the front wheels and the friction brakes 20 for the rear wheels so that the required braking force FxRq is distributed to the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb in accordance with the target pitch angle θTr. This enables the control unit M21 to set the distribution ratio Df to the target distribution ratio DfTr. Specifically, the control unit M21 controls the braking device 30 so that both the braking force Fx applied to the vehicle 10 is equal to the required braking force FxRq and the distribution ratio Df is equal to the target distribution ratio DfTr. Therefore, the control unit M21 increases the front wheel friction braking force Fxfb as the target distribution ratio DfTr increases. In other words, the control unit M21 distributes the required braking force FxRq between the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb by setting the distribution amount to the front wheel friction braking force Fxfb and the distribution amount to the rear wheel friction braking force Fxrb based on the target distribution ratio DfTr.

<Target Allocation Ratio Setting Process>
The process of setting the target allocation ratio DfTr will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a flowchart showing the setting process. The CPU 52 executes a control program in the memory 53, and the processing circuit 51 repeatedly executes the setting process. The processing circuit 51 functions as the target allocation ratio setting unit M19, and sequentially executes a number of steps S11 to S19 constituting the setting process.

In step S11, the processing circuit 51 acquires a base distribution ratio DfB, which is a base value of the distribution ratio. For example, a distribution ratio that makes the front wheel friction braking force Fxfb equal to the rear wheel friction braking force Fxrb is set as the base distribution ratio DfB. Note that the base distribution ratio DfB may be set to a corrected ideal distribution ratio, which is a front/rear braking force distribution that can prevent the rear wheel friction braking force Fxrb from becoming larger than the ideal braking distribution.

In the next step S13, the processing circuit 51 derives an allocation ratio correction amount ΔDf, which is a correction amount for the above-mentioned allocation ratio. The larger the target pitching moment MyTr is, the larger the value that the processing circuit 51 derives as the allocation ratio correction amount ΔDf. Furthermore, the smaller the required braking force FxRq is, the larger the value that the processing circuit 51 derives as the allocation ratio correction amount ΔDf. For example, the processing circuit 51 can derive the allocation ratio correction amount ΔDf using the following relational expression (F5). Note that the constant T in the relational expression (F5) can be expressed by the relational expression (F6).

As described above, the larger the target pitch angle θTr, the larger the target pitching moment MyTr. Therefore, the larger the target pitch angle θTr, the larger the distribution ratio correction amount ΔDf. The smaller the required braking force FxRq, the smaller the pitching moment My. The smaller the pitching moment My, the less likely it is that the pitch angle θ of the vehicle 10 will become large. In order to increase the pitch angle θ even when the pitching moment My is relatively small, it is necessary to increase the distribution ratio Df as the required braking force FxRq correlated with the pitching moment My becomes smaller. Therefore, by using the above relational expression (F5), the processing circuit 51 can derive, as the distribution ratio correction amount ΔDf, a value that is larger as the required braking force FxRq becomes smaller.

After deriving the distribution ratio correction amount ΔDf, the processing circuit 51 transitions to step S15.
In step S15, the processing circuit 51 derives the sum of the base allocation ratio DfB and the allocation ratio correction amount ΔDf as a provisional value DfTrA of the target allocation ratio. In the next step S17, the processing circuit 51 derives a lower limit allocation ratio DfLd and an upper limit allocation ratio DfLu. The region of the allocation ratio Df for ensuring the stability of the behavior of the vehicle 10 is set as a predetermined "allocation ratio region." At this time, the lower limit allocation ratio DfLd corresponds to the lower limit allocation ratio of the allocation ratio region, while the upper limit allocation ratio DfLu corresponds to the upper limit allocation ratio of the allocation ratio region.

With reference to Figure 4, the derivation of the lower limit distribution ratio DfLd and the upper limit distribution ratio DfLu will be explained. The multiple dashed lines shown in Figure 4 are contour lines of the braking force Fx applied to the vehicle 10. In Figure 4, the thick solid line is the ideal distribution line L1 indicating the ideal braking force distribution, and the thick dotted line is the same-pressure distribution line L2 indicating the same-pressure braking force distribution. In addition, the thick dashed line is the corrected ideal distribution line L3 indicating the corrected ideal braking force distribution. Same-pressure braking force distribution is the front and rear braking force distribution when the wheel hydraulic pressure for the front wheels and the wheel hydraulic pressure for the rear wheels are the same. The corrected ideal braking force distribution is a front and rear braking force distribution that is close to the ideal braking force distribution, but is a front and rear braking force distribution that can prevent the rear wheel friction braking force Fxrb from becoming larger than the ideal braking force distribution. When the front wheel friction braking force Fxfb indicated by the intersection of the corrected ideal distribution line L3 and the same pressure distribution line L2 is set as a predetermined braking force Fxfb1, the corrected ideal braking force distribution is set to satisfy the following two points.

- When the front wheel friction braking force Fxfb is less than a predetermined braking force Fxfb1, the rear wheel friction braking force Fxrb based on the corrected ideal braking force distribution is greater than the rear wheel friction braking force Fxrb based on the equal pressure braking force distribution.

- When the front wheel friction braking force Fxfb is equal to or greater than a predetermined braking force Fxfb1, the rear wheel friction braking force Fxrb based on the corrected ideal braking force distribution is equal to or less than the rear wheel friction braking force Fxrb based on the equal pressure braking force distribution.

For example, the processing circuit 51 obtains the intersection of the contour line of the required braking force FxRq and the equal pressure distribution line L2 as the first intersection. The processing circuit 51 derives the distribution ratio corresponding to the first intersection as the upper limit distribution ratio DfLu. This allows the processing circuit 51 to set the upper limit distribution ratio DfLu so that the greater the required braking force FxRq, the greater the front wheel friction braking force Fxfb.

The processing circuit 51 obtains the intersection of the contour line of the required braking force FxRq and the corrected ideal allocation line L3 as the second intersection. The processing circuit 51 derives the allocation ratio corresponding to the second intersection as the lower limit allocation ratio DfLd. This allows the processing circuit 51 to set the upper limit allocation ratio DfLu according to the ideal braking force allocation of the vehicle 10.

The distribution ratio corresponding to the intersection is the ratio of the front wheel friction braking force Fxfb to the total braking force, which is the sum of the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb at the intersection.

Returning to FIG. 3, after deriving the lower limit allocation ratio DfLd and the upper limit allocation ratio DfLu, the processing circuit 51 transitions to step S19.
In step S19, the processing circuit 51 sets the target allocation ratio DfTr based on the provisional value DfTrA of the target allocation ratio, the lower limit allocation ratio DfLd, and the upper limit allocation ratio DfLu. Specifically, the processing circuit 51 sets the second largest allocation ratio among the provisional value DfTrA, the lower limit allocation ratio DfLd, and the upper limit allocation ratio DfLu as the target allocation ratio DfTr. After that, the processing circuit 51 temporarily ends the process of setting the target allocation ratio DfTr.

<Actions and Effects of the Present Embodiment>
The operation and effect of the brake control device 50 will be described with reference to Fig. 5. The example shown in Fig. 5 is a case where the vehicle 10 is decelerated by braking, and the vehicle 10 turns by steering the steering member 12 by the driver.

As shown in (C) and (D) of FIG. 5, at timing t11 while the vehicle 10 is traveling, the driver begins to operate the brake operating member 11, etc., requesting deceleration of the vehicle 10. The processing circuit 51 then acquires the required braking force FxRq and operates the braking device 30 based on the required braking force FxRq. As a result, a braking force Fx is applied to the vehicle 10, and the vehicle speed VS of the vehicle 10 begins to decrease. In addition, when the braking force Fx is applied to the vehicle 10, a pitching moment My is generated in the vehicle 10. As a result, the vehicle 10 goes into a nose dive state, and the pitch angle θ of the vehicle 10 increases, as shown in (F) of FIG. 5.

Here, the vehicle 10 is equipped with a friction brake 20 for the front wheels and a friction brake 20 for the rear wheels such that when the wheel hydraulic pressure for the front wheels is the same as the wheel hydraulic pressure for the rear wheels, the front wheel friction braking force Fxfb is greater than the rear wheel friction braking force Fxrb.

Therefore, when the processing circuit 51 adjusts the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb so that the wheel hydraulic pressure for the front wheels is equal to the wheel hydraulic pressure for the rear wheels, the rate of increase of the front wheel friction braking force Fxfb becomes greater than the rate of increase of the rear wheel friction braking force Fxrb, as shown in FIG. 5 (I).

From timing t12, the required braking force FxRq is maintained. As shown in FIG. 5A, from timing t13 thereafter, the driver starts to operate the steering member 12, and the vehicle 10 starts to turn. When the steering angle STR increases as shown in FIG. 5A, the lateral acceleration Gy of the vehicle 10 increases as shown in FIG. 5B, and the roll angle φ of the vehicle 10 increases as shown in FIG. 5E.

In this way, when the vehicle 10 starts to turn and the roll angle φ becomes greater than 0 (zero), the processing circuit 51 sets a value greater than 0 (zero) as the target pitch angle θTr. The processing circuit 51 derives the pitching moment My for setting the pitch angle θ of the vehicle 10 to the target pitch angle θTr as the target pitching moment MyTr. The processing circuit 51 sets the distribution ratio Df according to the target pitching moment MyTr as the target distribution ratio DfTr. Specifically, as shown in (G) and (H) of FIG. 5, the larger the target pitching moment MyTr, the larger the target distribution ratio DfTr becomes. Then, the processing circuit 51 activates the front wheel friction brakes 20 and the rear wheel friction brakes 20 so that the distribution ratio Df becomes the target distribution ratio DfTr.

The larger the distribution ratio Df, the larger the front wheel friction braking force Fxfb. Therefore, as shown in (H) and (I) of FIG. 5, the larger the target distribution ratio DfTr, the larger the front wheel friction braking force Fxfb becomes, while the rear wheel friction braking force Fxrb becomes smaller. When the rear wheel friction braking force Fxrb becomes smaller in this way, the pitching suppression force, which is the sum of the anti-dive force FAD and the anti-lift force FAL, becomes smaller. As a result, the pitch angle θ of the vehicle 10 increases toward the target pitch angle θTr.

In the example shown in FIG. 5, since the pitch angle θ is smaller than the target pitch angle θTr, the pitching suppression force is reduced by increasing the front wheel friction braking force Fxfb. However, there are also cases where the pitch angle θ is greater than the target pitch angle θTr. In this case, the pitching suppression force is increased by increasing the rear wheel friction braking force Fxrb. This reduces the pitch angle θ toward the target pitch angle θTr.

The brake control device 50 can adjust the pitch angle θ of the vehicle 10 without changing the braking force Fx applied to the vehicle 10. Therefore, when the vehicle 10 turns while the vehicle 10 is decelerating due to braking, the brake control device 50 can control the pitch angle θ of the vehicle 10 without changing the deceleration of the vehicle 10. In other words, even if the pitch angle θ is adjusted, the deceleration of the vehicle 10 does not change, so the occupants of the vehicle 10 are less likely to feel uncomfortable.

When a braking force Fx is applied to the vehicle 10 by the driver operating the brake operating member 11, if the deceleration of the vehicle 10 changes to control the pitch angle θ even though the amount of operation of the brake operating member 11 by the driver has not changed, the driver may feel uncomfortable about the change in deceleration. In this regard, the brake control device 50 can control the pitch angle θ without changing the deceleration of the vehicle 10. Therefore, when the vehicle 10 is turning, the pitch angle θ of the vehicle 10 can be controlled without causing the driver to feel uncomfortable as described above.

In addition, when the vehicle 10 is traveling autonomously through automatic driving, when a command value for the deceleration of the vehicle 10 is input to the brake control device 50, the processing circuit 51 obtains a braking force based on the command value for the deceleration as a required braking force FxRq. The processing circuit 51 then controls the brake device 30 based on the required braking force FxRq. If the brake control device 50 varies the deceleration of the vehicle to control the pitch angle θ at this time, the actual deceleration of the vehicle 10 will deviate from the command value for the deceleration. In this regard, the brake control device 50 can control the pitch angle θ without changing the deceleration of the vehicle 10. Therefore, when the vehicle 10 is turning, the pitch angle θ of the vehicle 10 can be controlled while suppressing the actual deceleration of the vehicle 10 from deviating from the command value for the deceleration.

In the example shown in FIG. 5, turning of the vehicle 10 ends at timing t14 during vehicle braking. Then, the roll angle φ of the vehicle 10 becomes 0 (zero), so the processing circuit 51 adjusts the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb so that the wheel hydraulic pressure for the front wheels is equal to the wheel hydraulic pressure for the rear wheels.

In this embodiment, the following effects can be further obtained.
(1-1) In the braking control device 50, the larger the roll angle φ, the larger the pitch angle set as the target pitch angle θTr. This makes it possible to increase the correlation between the roll angle φ and the pitch angle θ while the vehicle 10 is turning. In particular, when the vehicle 10 is being driven by the driver's manual operation, the drivability of the driver can be improved.

(1-2) A predetermined distribution ratio region is set in the braking control device 50. Then, the processing circuit 51 sets the distribution ratio included in the distribution ratio region as the target distribution ratio DfTr. This allows the braking control device 50 to control the pitch angle θ of the vehicle 10 while ensuring the stability of the behavior of the vehicle 10 during cornering.

(1-3) The lower limit distribution ratio DfLd and the upper limit distribution ratio DfLu of the specified distribution ratio range can be set to distribution ratios according to the required braking force FxRq at that time. Therefore, the brake control device 50 can improve compatibility between ensuring the stability of the behavior of the vehicle 10 during turning and controlling the pitch angle θ of the vehicle 10.

Second Embodiment
A second embodiment of the brake control device will be described with reference to Fig. 6. The second embodiment differs from the first embodiment in that the distribution ratio between the front wheel friction braking force and the rear wheel friction braking force can be adjusted without deriving a target distribution ratio. In the following description, the differences from the first embodiment will be mainly described, and the same reference numerals will be used to designate the same members as those in the first embodiment, and repeated description will be omitted.

FIG. 6 shows part of the functional configuration of the processing circuit 51 in the braking control device 50 of this embodiment. When the CPU 52 executes the control program in the memory 53, the processing circuit 51 functions as a braking force correction amount derivation unit M31, four calculation units M33, M34, M35, M36, and a guard processing unit M38.

The braking force correction amount derivation unit M31 derives the braking force correction amount ΔFx based on the target pitching moment MyTr acquired by the target PM acquisition unit M17. The braking force correction amount derivation unit M31 derives a larger value as the braking force correction amount ΔFx as the target pitching moment MyTr increases. For example, the braking force correction amount derivation unit M31 can derive a value corresponding to the target pitching moment MyTr as the braking force correction amount ΔFx by using the following relational expression (F7). The constant T in relational expression (F7) can be expressed by the above relational expression (F6).

The calculation unit M33 derives the sum of a front wheel friction braking force base value FxflbB, which is a base value of the front wheel friction braking force Fxflb of the left front wheel 14, and the braking force correction amount ΔFx, as a provisional value FxflbA of the front wheel friction braking force Fxflb of the left front wheel 14. The front wheel friction braking force base value FxflbB is the front wheel friction braking force of the left front wheel 14 when the braking forces applied to the multiple wheels 14-17 are made the same.

Calculation unit M34 derives the sum of front wheel friction braking force base value FxfrbB, which is the base value of the front wheel friction braking force Fxfrb of the right front wheel 15, and the braking force correction amount ΔFx as a provisional value FxfrbA of the front wheel friction braking force Fxfrb of the right front wheel 15. The front wheel friction braking force base value FxfrbB is the front wheel friction braking force of the right front wheel 15 when the same braking force is applied to the multiple wheels 14 to 17.

Calculation unit M35 derives the difference between rear wheel friction braking force base value FxrlbB, which is the base value of the rear wheel friction braking force Fxrlb of the left rear wheel 16, and the braking force correction amount ΔFx as a provisional value FxrlbA of the rear wheel friction braking force Fxrlb of the left rear wheel 16. The rear wheel friction braking force base value FxrlbB is the rear wheel friction braking force of the left rear wheel 16 when the same braking force is applied to the multiple wheels 14 to 17.

Calculation unit M36 derives the difference between rear wheel friction braking force base value FxrrbB, which is the base value of the rear wheel friction braking force Fxrrb of the right rear wheel 17, and the braking force correction amount ΔFx as a provisional value FxrrbA of the rear wheel friction braking force Fxrrb of the right rear wheel 17. The rear wheel friction braking force base value FxrrbB is the rear wheel friction braking force of the right rear wheel 17 when the same braking force is applied to the multiple wheels 14 to 17.

The guard processing unit M38 derives the sum of the provisional value FxflbA of the front wheel friction braking force of the left front wheel 14 and the provisional value FxfrbA of the front wheel friction braking force of the right front wheel 15 as the provisional value FxfbA of the front wheel friction braking force. The guard processing unit M38 derives the sum of the provisional value FxrlbA of the rear wheel friction braking force of the left rear wheel 16 and the provisional value FxrrbA of the rear wheel friction braking force of the right rear wheel 17 as the provisional value FxrbA of the rear wheel friction braking force. The guard processing unit M38 then corrects the multiple friction braking forces so that the distribution ratio Df falls within a predetermined distribution ratio region, thereby deriving the four friction braking forces Fxflb, Fxfrb, Fxrlb, Fxrrb.

The control unit M21 operates the braking device 30 based on the four friction braking forces Fxflb, Fxfrb, Fxrlb, and Fxrrb derived by the guard processing unit M38. As a result, when braking the vehicle, the control unit M21 can operate the front wheel friction brakes 20 and the rear wheel friction brakes 20 so that the required braking force FxRq is distributed to the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb in accordance with the target pitch angle θTr. As a result, the distribution ratio Df becomes the distribution ratio that corresponds to the target pitch angle θTr.

The brake control device 50 of this embodiment can obtain the same effects as the brake control device 50 of the first embodiment.
(Example of change)
The above-described embodiments may be modified as follows: The above-described embodiments and the following modifications may be combined with each other to the extent that they are not technically inconsistent.

- In the first embodiment, the processing circuit 51 may set, as the lower limit allocation ratio DfLd of the specified allocation ratio region, an allocation ratio different from the allocation ratio corresponding to the intersection between the contour line of the required braking force FxRq at that time and the corrected ideal allocation line L3. For example, the processing circuit 51 may set, as the lower limit allocation ratio DfLd, an allocation ratio corresponding to the intersection between the contour line of the required braking force FxRq at that time and the ideal allocation line L1.

- In the first embodiment, the processing circuit 51 may set the upper limit distribution ratio DfLu of the specified distribution ratio region to a distribution ratio different from the distribution ratio corresponding to the intersection of the contour line of the required braking force FxRq at that time and the distribution line L2 at equal pressure.

In the first embodiment, when setting the target allocation ratio DfTr, the processing circuit 51 does not need to impose limitations using the upper limit allocation ratio DfLu and the lower limit allocation ratio DfLd.
When the roll angle φ of the vehicle 10 increases, the target pitch angle θTr is changed in conjunction with the increase in the roll angle φ. However, even if the distribution ratio Df is adjusted according to the target pitch angle θTr, there is a possibility that the increase in the actual pitch angle of the vehicle 10 is delayed with respect to the increase in the roll angle φ. Therefore, the processing circuit 51 may derive the product of the roll angle φ, the conversion gain α1, and the compensation gain α2 as the target pitch angle θTr. In this case, a value of 1 or more is set as the compensation gain α2. Furthermore, the processing circuit 51 sets a value greater than 1 as the compensation gain α2 immediately after the roll angle φ increases, and then gradually reduces the compensation gain α2 to 1 as time passes. This allows the brake control device to improve the controllability of the pitch angle θ of the vehicle 10 when the roll angle φ increases.

The vehicle to which the brake control device is applied may be a vehicle in which the pitch behavior of the vehicle 10 in the pitch direction caused by the application of a desired amount of rear wheel friction braking force Fxrb to the vehicle 10 is different from the pitch behavior of the vehicle 10 in the pitch direction caused by the application of a desired amount of front wheel friction braking force Fxfb to the vehicle 10. Specifically, the vehicle may be a vehicle configured so that the greater the proportion of the front wheel friction braking force Fxfb in the total braking force, which is the sum of the front wheel friction braking force Fxfb and the rear wheel friction braking force Fxrb, the more the attitude change of the vehicle 10 can be suppressed. In this case, the rear wheel friction braking force Fxrb corresponds to the first braking force, and the front wheel friction braking force Fxfb corresponds to the second braking force. Also, the friction brake 20 for the rear wheels corresponds to the first braking unit, and the friction brake 20 for the front wheels corresponds to the second braking unit.

Even in this case, it is preferable that the processing circuit 51 sets an allocation ratio included in the predetermined allocation ratio region as the target allocation ratio. Furthermore, it is preferable that the upper limit allocation ratio of the predetermined allocation ratio region is set so that the rear wheel friction braking force Fxrb can be increased as the required braking force FxRq increases. Furthermore, it is preferable that the lower limit allocation ratio of the predetermined allocation ratio region is set according to the ideal braking force allocation.

- The brake control device can also be applied to a vehicle that can apply regenerative braking force in addition to friction braking force. For example, when the regenerative braking force applied to the

front wheels

14, 15 is a front wheel regenerative braking force, the pitch angle θ of the vehicle can be changed by adjusting the distribution between the front wheel regenerative braking force and the front wheel friction braking force. In other words, the greater the proportion of the front wheel friction braking force in the total front wheel braking force, which is the sum of the front wheel regenerative braking force and the front wheel friction braking force, the more the attitude change of the vehicle 10 can be suppressed. This is because the point of application of the regenerative braking force is the axle of the wheel, and therefore the point of application of the friction braking force and the regenerative braking force are different. In a brake control device applied to such a vehicle, the distribution ratio, which is the ratio of the front wheel regenerative braking force to the total front wheel braking force, can be set to the target distribution ratio DfTr corresponding to the target pitch angle θTr at that time. In this case, the front wheel regenerative braking force corresponds to the first braking force, and the front wheel friction braking force corresponds to the second braking force. In addition, the generator that generates the front wheel regenerative braking force corresponds to the first braking unit, and the friction brake 20 for the front wheels corresponds to the second braking unit.

The same applies to vehicles that can apply regenerative braking force to the

rear wheels

16, 17. In this case, the regenerative braking force applied to the

rear wheels

16, 17 corresponds to the first braking force, and the rear wheel friction braking force corresponds to the second braking force. Also, the generator that adjusts the regenerative braking force applied to the

rear wheels

16, 17 corresponds to the first braking unit, and the friction brake 20 for the rear wheels corresponds to the second braking unit.

Note that the process of controlling the pitch angle θ of the vehicle 10 by adjusting the distribution of the regenerative braking force and the frictional braking force is preferably performed when the regenerative braking force applied to the vehicle is relatively large. In other words, when the regenerative braking force applied to the vehicle is relatively small, it is preferable to control the pitch angle θ by adjusting the distribution of the front wheel frictional braking force Fxfb and the rear wheel frictional braking force Fxrb, as described in the above multiple embodiments.

- The vehicle to which the brake control device is applied may be a vehicle in which the regenerative braking force applied to the

front wheels

14, 15 and the regenerative braking force applied to the

rear wheels

16, 17 can be adjusted separately. In this vehicle, when regenerative braking force is applied to both the

front wheels

14, 15 and the

rear wheels

16, 17, the pitch behavior of the vehicle in the pitch direction associated with the application of a desired amount of front wheel regenerative braking force to the vehicle differs from the pitch behavior of the vehicle in the pitch direction associated with the application of a desired amount of rear wheel regenerative braking force to the vehicle. In this case, for example, the front wheel regenerative braking force is the first braking force, and the rear wheel regenerative braking force is the second braking force. In this case, the brake control device sets a target distribution ratio, which is a target ratio of the front wheel regenerative braking force to the total braking force, which is the sum of the front wheel regenerative braking force and the rear wheel regenerative braking force, based on the target pitch angle θTr. Then, the brake control device adjusts the front wheel regenerative braking force and the rear wheel regenerative braking force based on the target pitch angle θTr.

- A vehicle to which the brake control device is applied may be a vehicle in which the regenerative braking force applied to the

front wheels

14, 15 and the regenerative braking force applied to the

rear wheels

16, 17 can be adjusted separately. In such a vehicle, the front wheel braking force, which is the sum of the front wheel friction braking force and the front wheel regenerative braking force, may be set as the first braking force, and the rear wheel braking force, which is the sum of the rear wheel friction braking force and the rear wheel regenerative braking force, may be set as the second braking force. In this case, the brake control device sets a target distribution ratio, which is a target for the ratio of the front wheel braking force to the total braking force, which is the sum of the front wheel braking force and the rear wheel braking force, based on the target pitch angle θTr. Then, the brake control device adjusts the front wheel friction braking force, front wheel regenerative braking force, rear wheel friction braking force, and rear wheel regenerative braking force based on the target pitch angle θTr. For example, the brake control device can adjust the front wheel friction braking force when the target pitch angle θTr cannot be achieved by adjusting only the front wheel regenerative braking force, and can adjust the rear wheel friction braking force when the target pitch angle θTr cannot be achieved by adjusting only the rear wheel regenerative braking force.

- Processing circuitry 51 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for executing at least some of the various processes, or a combination of these. An example of dedicated hardware is an ASIC, which is an application specific integrated circuit. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium accessible by a general purpose or dedicated computer.

<Other technical ideas>
Next, the technical ideas that can be understood from the above-described embodiments and modified examples will be described.
(Additional Note 1) It is preferable that the distribution ratio region is set so that the first braking force can be made larger than in a case where the first braking force and the second braking force are set according to an ideal braking force distribution of the vehicle.

(Additional Note 2) It is preferable that the target pitch angle derivation unit derives, as the target pitch angle, a value according to a parameter whose magnitude changes when the vehicle turns.
(Additional Note 3) The present invention is applied to a vehicle including a first braking unit that applies a first braking force to a vehicle and a second braking unit that applies a second braking force to the vehicle, wherein a pitch behavior of the vehicle in a pitch direction caused by application of a desired amount of the first braking force by the first braking unit to the vehicle is different from a pitch behavior of the vehicle in the pitch direction caused by application of the desired amount of the second braking force by the second braking unit to the vehicle,
a parameter acquisition unit that acquires a parameter whose magnitude changes when the vehicle turns;
a target PM acquisition unit that sets a pitching moment according to the parameters acquired by the parameter acquisition unit as a target pitching moment that is a target of the pitching moment;
a control unit that operates the first braking unit and the second braking unit so that a required braking force, which is a required value of the braking force to be applied to the vehicle, is distributed between the first braking force and the second braking force in accordance with the target pitching moment when the vehicle is braked.

The expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Claims

the vehicle is provided with a first braking unit that applies a first braking force to a vehicle and a second braking unit that applies a second braking force to the vehicle, and a pitch behavior of the vehicle in a pitch direction associated with application of a desired amount of the first braking force to the vehicle by the first braking unit differs from a pitch behavior of the vehicle in the pitch direction associated with application of the desired amount of the second braking force to the vehicle by the second braking unit;
a target pitch angle acquisition unit that acquires a target pitch angle that is a target for the pitch angle of the vehicle when the vehicle is turning;
a control unit that operates the first braking unit and the second braking unit so that a required braking force, which is a required value of a braking force to be applied to the vehicle, is distributed between the first braking force and the second braking force in accordance with the target pitch angle when braking the vehicle.
a target distribution ratio setting unit that sets a target distribution ratio, which is a target of a distribution ratio of the first braking force to a total braking force that is a sum of the first braking force and the second braking force, based on the target pitch angle,
2. The brake control device according to claim 1, wherein, when braking the vehicle, the control unit distributes the required braking force to the first braking force and the second braking force by setting a distribution amount to the first braking force and a distribution amount to the second braking force based on the target distribution ratio.
The brake control device according to claim 2 , wherein the target allocation ratio setting unit sets the allocation ratio included in a predetermined allocation ratio region as the target allocation ratio.
the first braking unit applies the first braking force to a front wheel of the vehicle,
an upper limit distribution ratio that is an upper limit of the distribution ratio region is set so that the first braking force can be increased as the required braking force increases,
The brake control device according to claim 3 , wherein a lower limit distribution ratio that is a lower limit of the distribution ratio region is set according to an ideal braking force distribution of the vehicle.