Brake control device for vehicle

Abstract

To provide a brake control device for a vehicle which can determine at an early stage whether an instable behavior accompanied by rotation occurs in the vehicle.SOLUTION: A brake control device 10 for a vehicle comprises: a controller 12 which can switchably execute a brake force generation control T1 that makes a brake 5 installed in a vehicle 1 generate brake force and a brake force release control T2 that makes the brake 5 release the generated brake force; and a determination part 14 which determines that an instable behavior accompanied by rotation around a rotational axis along a vertical direction occurs in the vehicle 1, when a determination value D is a specified value D0 or more, based on the determination value D being determined based on a lateral acceleration Gy representing a status generated in the vehicle 1 and a friction coefficient μ representing a status of a road surface with which a wheel 3 of the vehicle 1 comes into contact. The controller 12 executes the brake force generation control T1 in response to the determination of the instable behavior to generate the brake force in the brake 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a brake control device for a vehicle. [Background technology]

[0002] For example, an anti-skid control device (hereinafter, referred to as a "conventional control device") disclosed in Patent Document 1 has been known in the past. The conventional control device is configured to determine whether or not unstable behavior accompanied by rotation occurs in the vehicle based on the continuation of a pressure reduction mode in accordance with anti-skid control and the respective decreasing gradients of the wheel speed and the vehicle body speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-35464 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional control device, it is determined whether or not the vehicle is experiencing unstable behavior accompanied by rotation, based on the pressure reduction mode according to the anti-skid control. However, in order to determine whether the unstable behavior of the vehicle is resolved midway or whether the vehicle is turning in a manner that does not result in unstable behavior, time is required to determine the unstable behavior. In this regard, in the conventional control device, if the driver's braking is delayed, the time until the pressure reduction mode is started is also delayed, and the time required for determination may not be secured. As a result, there is a risk that the conventional control device cannot determine the unstable behavior.

[0005] An object of the present disclosure is to provide a brake control device for a vehicle that can quickly determine whether or not unstable behavior accompanied by rotation is occurring in the vehicle. [Means for solving the problem]

[0006] The vehicle braking control device disclosed herein comprises a control unit capable of switching between braking force generation control, which generates a braking force in a braking device mounted on the vehicle, and braking force release control, which releases the braking force generated in the braking device, and a judgment unit that judges whether or not the vehicle is experiencing unstable behavior involving rotation around a rotation axis along the vertical direction, based on a judgment value that is determined using the condition occurring in the vehicle and the condition of the road surface with which the vehicle's wheels contact, and in response to the determination of unstable behavior, the control unit executes braking force generation control, causing the braking device to generate braking force. Effect of the Invention

[0007] According to the vehicle braking control device of the present disclosure, the determination unit can determine whether or not the vehicle is experiencing unstable behavior accompanied by rotation based on the determination value. In other words, the vehicle braking control device can determine whether or not the vehicle is experiencing unstable behavior accompanied by rotation at an early stage even before braking. This allows the vehicle braking control device to promptly cause the control unit to execute braking force generation control, and as a result, it becomes possible to promptly stop the vehicle experiencing unstable behavior accompanied by rotation. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a vehicle and a vehicle brake control device; [Diagram 2] 1 is a graph showing the relationship between slip ratio and friction coefficient. [Diagram 3] FIG. 1 is a diagram for explaining unstable behavior accompanied by rotation. [Figure 4] 4 is a flowchart of a braking control program. [Diagram 5] 10 is a flowchart of a brake control program according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a vehicle brake control device 10 according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In addition to the embodiment described below, the vehicle brake control device can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0010] The vehicle brake control device 10 is applied to a vehicle 1 shown in Fig. 1. The vehicle 1 may be driven manually by a driver in the vehicle, or may be driven automatically. In the embodiment described below, a case where the vehicle 1 is driven manually by a driver will be described as an example.

[0011] The vehicle 1 includes a body 2 and wheels 3. The body 2 is supported by the wheels 3 via a suspension mechanism (not shown). The wheels 3 include a right front wheel 31, a left front wheel 32, a right rear wheel 33, and a left rear wheel .

[0012] The vehicle 1 also includes a steering device 4. In this embodiment, the steering device 4 is configured to steer a right front wheel 31 and a left front wheel 32. The vehicle 1 is configured so that the right front wheel 31 and the left front wheel 32, the right rear wheel 33 and the left rear wheel 34, or the right front wheel 31, the left front wheel 32, the right rear wheel 33 and the left rear wheel 34 are driven by driving force from a driving force source (such as an engine or an electric motor) not shown.

[0013] Furthermore, the vehicle 1 is equipped with a braking device 5 for generating a braking force on each of the wheels 3. The braking device 5 is equipped with a right front wheel brake 51, a left front wheel brake 52, a right rear wheel brake 53, and a left rear wheel brake 54. In this embodiment, the braking device 5 is equipped with a brake pedal 55, a master cylinder 56, a hydraulic circuit 57, and brake piping 58. The right front wheel brake 51, the left front wheel brake 52, the right rear wheel brake 53, and the left rear wheel brake 54 can be exemplified by disc brakes or drum brakes, and can also be configured to enable regenerative braking.

[0014] The master cylinder 56 pumps hydraulic oil in response to a braking operation by the driver depressing the brake pedal 55. Although not shown in detail, the hydraulic circuit 57 includes a reservoir, a pump, various valve devices, etc., and functions as a brake actuator. The hydraulic circuit 57 adjusts the hydraulic pressure of the hydraulic oil applied to each of the brake pipes 58 in response to an instruction from the control unit 12 of the vehicle brake control device 10, which will be described later, for example.

[0015] That is, the hydraulic circuit 57 can generate braking forces in each of the right front wheel brake 51, the left front wheel brake 52, the right rear wheel brake 53, and the left rear wheel brake 54 in a pressure increase mode in which the hydraulic pressure is increased. Also, the hydraulic circuit 57 can release the braking forces in each of the right front wheel brake 51, the left front wheel brake 52, the right rear wheel brake 53, and the left rear wheel brake 54 in a pressure decrease mode in which the hydraulic pressure is decreased.

[0016] A vehicle braking control device 10 is mounted on a vehicle 1, as shown in FIG. 1. The vehicle braking control device 10 includes a sensor group 11, a control unit 12, a road surface condition detection unit 13, a judgment unit 14, and a command unit 15. Here, the vehicle braking control device 10 is mainly configured with a computer device equipped with a CPU, a ROM, a RAM, and various interfaces. The CPU sequentially executes predetermined programs including a braking control program described later, and reads data, performs numerical calculations, and outputs the results of the calculations. The ROM stores programs and maps executed by the CPU. The RAM temporarily stores data, etc. The various interfaces are connected to each of the sensor group 11.

[0017] 1, the sensor group 11 includes a wheel speed sensor 111, a wheel speed sensor 112, a wheel speed sensor 113, and a wheel speed sensor 114. The sensor group 11 also includes a lateral acceleration sensor 115 and a yaw rate sensor 116 as state quantity detection units that detect state quantities of the vehicle 1 having left-right components of the vehicle 1. The sensor group 11 further includes a steering angle sensor 117 and a brake sensor 118.

[0018] The wheel speed sensor 111 detects the wheel speed Vwfr, which is the rotation speed of the right front wheel 31. The wheel speed sensor 112 detects the wheel speed Vwfl, which is the rotation speed of the left front wheel 32. The wheel speed sensor 113 detects the wheel speed Vwrr, which is the rotation speed of the right rear wheel 33. The wheel speed sensor 114 detects the wheel speed Vwrl, which is the rotation speed of the left rear wheel 34. In the following description, when the wheel speeds Vwfr, Vwfl, Vwrr, and Vwrl are not to be distinguished from one another, they may simply be referred to as "wheel speed Vw."

[0019] The lateral acceleration sensor 115 detects a lateral acceleration Gy which represents a state occurring in the vehicle 1 and is a state quantity of the vehicle 1 having a component in the left-right direction of the vehicle 1. The lateral acceleration Gy is a state quantity occurring in the left-right direction of the vehicle 1. The yaw rate sensor 116 detects a yaw rate YR which represents a state occurring in the vehicle 1 and is a state quantity of the vehicle 1 having a component in the left-right direction of the vehicle 1. The yaw rate YR is a state quantity occurring around the center of gravity point CG of the vehicle 1.

[0020] The steering angle sensor 117 detects the steering angle TA of the right front wheel 31 and the left front wheel 32 steered by the steering device 4. Here, a predetermined relationship is established between the steering angle TA and, for example, the amount of steering wheel operation (steering angle) performed by the driver. Therefore, the steering angle sensor 117 can also detect the steering angle TA based on, for example, the amount of steering wheel operation (steering angle).

[0021] When the driver applies a braking operation to the brake pedal 55, the brake sensor 118 outputs an operation signal BO that indicates an operation state that requests braking. That is, the brake sensor 118 detects the hydraulic pressure of the master cylinder 56 and the hydraulic pressure of the brake pipes 58 that correspond to the braking operation to the brake pedal 55, and outputs the operation signal BO.

[0022] The control unit 12 executes braking force generation control T1, which generates braking force in the pressure increase mode for the braking device 5 mounted on the vehicle 1. The control unit 12 also executes braking force release control T2, which releases the braking device 5 in a pressure reduction mode. The control unit 12 can switch between the braking force generation control T1 and the braking force release control T2.

[0023] In this embodiment, the control unit 12 switches between and executes braking force generation control T1 and braking force release control T2 in accordance with a well-known anti-skid control (also called "ABS control") that prevents the wheels 3 from stopping rotating, i.e., from being locked. The control unit 12 outputs information indicating the braking force generation control T1 or braking force release control T2 being executed to the determination unit 14.

[0024] Under normal circumstances, the control unit 12 determines the required deceleration based on the amount of operation of the brake pedal 55 by the driver, the wheel speed Vw of the wheels 3, the vehicle body speed Vb of the vehicle 1 that can be estimated using the wheel speed Vw, etc. Then, the control unit 12 controls the hydraulic circuit 57 to generate braking force in each of the wheels 3 so that the actual deceleration matches the required deceleration. On the other hand, when the wheels 3 are in a locked state based on the wheel speed Vw and the vehicle body speed Vb, the control unit 12 controls the hydraulic circuit 57 in accordance with the ABS control, for example, by switching from braking force generation control T1 to braking force release control T2.

[0025] The road surface condition detection unit 13 detects a physical quantity representing the condition of the road surface with which each of the wheels 3 contacts, more specifically, the condition between the wheels and the road surface, using the wheel speeds Vw detected by the wheel speed sensors 141-144. That is, the road surface condition detection unit 13 functions as a physical quantity detection unit, and estimates and detects, as a physical quantity, a friction coefficient μ that represents the magnitude of friction of the road surface with which the wheels 3 contact.

[0026] Here, the friction coefficient μ can be estimated using a well-known calculation method that has been widely adopted in the past. For this reason, an example of the estimation calculation of the friction coefficient μ by the road surface condition detection unit 13 will be briefly described below. The road surface condition detection unit 13 estimates the vehicle body speed Vb based on the wheel speed Vw. Then, the road surface condition detection unit 13 estimates and calculates the slip ratio S of each wheel 3 by dividing the deviation between the wheel speed Vw and the vehicle body speed Vb by the vehicle body speed Vb. The slip ratio S can also be estimated and calculated based on the acceleration of the wheel speed Vw, the longitudinal acceleration or lateral acceleration Gy of the vehicle 1, etc.

[0027] 2 as the relationship between the friction coefficient μ of the road surface and the slip ratio S of the wheel 3, the road surface condition detection unit 13 estimates and calculates the friction coefficient μ of the road surface corresponding to the calculated slip ratio S of the wheel 3. The road surface condition detection unit 13 then outputs the estimated and detected friction coefficient μ of the road surface to the determination unit 14.

[0028] 1, the determination unit 14 determines whether or not the vehicle 1 is experiencing unstable behavior involving rotation around a rotation axis passing through the center of gravity CG of the vehicle 1 as the rotation axis along the vertical direction, such as spin behavior or drift behavior. The determination unit 14 determines that the vehicle 1 is experiencing unstable behavior involving rotation when a determination value D determined using a lateral acceleration Gy (state quantity) representing a state occurring in the vehicle 1 and a friction coefficient μ (physical quantity) representing a state of the road surface with which the wheels 3 are in contact is equal to or greater than a predetermined value D0.

[0029] Here, the judgment value D in this embodiment is the ratio of the state quantity to the physical quantity, that is, the ratio of the lateral acceleration Gy to the friction coefficient μ (Gy / μ). The judgment value D tends to become larger as the friction coefficient μ becomes smaller or the lateral acceleration Gy becomes larger. Therefore, when the judgment value D becomes larger, the vehicle 1 is more likely to experience unstable behavior accompanied by rotation. On the other hand, the judgment value D tends to become smaller as the friction coefficient μ becomes larger or the lateral acceleration Gy becomes smaller. Therefore, when the judgment value D becomes smaller, the vehicle 1 is more likely to return from unstable behavior to stable behavior.

[0030] The determination unit 14 of this embodiment determines whether or not a first situation (see FIG. 3) has occurred in which the decrease gradient α of the vehicle body speed Vb of the vehicle 1 (vehicle body 2) becomes smaller than the decrease gradient of the wheel speed Vw of the wheel 3 of the vehicle 1, and the difference between the wheel speed Vw and the vehicle body speed Vb becomes large, as described later. In addition, when the first situation has occurred, the determination unit 14 of this embodiment determines whether or not a second situation (see FIG. 3) has occurred in which the braking force release control T2 is executed in the braking device 5 according to the wheel speed Vw, more specifically, according to the locked state of the wheel 3, when the first situation has occurred, as described later. Then, when the first situation and the second situation have occurred and the situation in which the determination value D is equal to or greater than a predetermined value D0 continues for a certain period of time, the determination unit 14 of this embodiment determines that the vehicle 1 has an unstable behavior accompanied by rotation, and outputs determination information J to the command unit 15.

[0031] The command unit 15 inputs the determination information J from the determination unit 14. Then, when the vehicle 1 is behaving unstable according to the determination information J, the command unit 15 outputs a braking command C to the control unit 12 to instruct the braking device 5 to generate a braking force. As a result, the control unit 12 executes braking force generation control T1 to cause the braking device 5 to generate a braking force.

[0032] In this embodiment, the control unit 12 terminates the braking force release control T2 being executed (ongoing) in the second situation in accordance with the braking command C, i.e., terminates the anti-skid control, and promptly executes the braking force generation control T1. As a result, the right front wheel brake 51, the left front wheel brake 52, the right rear wheel brake 53, and the left rear wheel brake 54 of the braking device 5 generate braking forces on all of the wheels 3.

[0033] Next, we will explain unstable behavior accompanied by rotation that occurs in the vehicle 1. As shown in Fig. 3, when the friction coefficient μ of the road surface decreases, the lateral acceleration Gy occurs in the vehicle 1, or the steering angle TA increases while the vehicle 1 is traveling straight, the vehicle 1 may exhibit unstable behavior accompanied by rotation around a rotation axis passing through the center of gravity CG, such as spinning behavior.

[0034] In this case, in "State A" shown in Fig. 3, as the vehicle 1 starts to rotate (or turn) and gradually approaches a perpendicular direction to the traveling direction, the reaction force input from the road surface to the wheel 3 decreases. As a result, in "State A", as shown by the long dashed line, the wheel speed Vw of the wheel 3 decreases rapidly. Then, when the vehicle 1 turns perpendicular, the reaction force from the road surface disappears, and as a result, the wheel speed Vw becomes "0", that is, the wheel 3 stops rotating.

[0035] Here, in "State A", when the driver applies the brake pedal 55, the control unit 12 attempts to execute braking force generation control T1 in the pressure increase mode in the initial stage based on the operation signal BO. However, when the wheel speed Vw becomes "0", in other words, a locked state with an increased slip ratio S occurs, the control unit 12 executes braking force release control T2 in the pressure decrease mode according to the anti-skid control.

[0036] When unstable behavior involving rotation occurs in the vehicle 1, the vehicle body speed Vb decreases at a decrease gradient α determined based on the friction coefficient μ of the road surface in order to avoid a sudden decrease, as shown by the thick solid line in Fig. 3. On the other hand, when unstable behavior involving rotation occurs in the vehicle 1, the reaction force from the road surface to the wheels 3 decreases as described above, so that the wheel speed Vw decreases at a decrease gradient larger than the decrease gradient α. Therefore, when unstable behavior involving rotation occurs in the vehicle 1, the vehicle body speed Vb does not catch up with the decreasing wheel speed Vw and deviates upward.

[0037] Then, when the vehicle speed Vb deviates upward from the wheel speed Vw and the wheel speed Vw and the vehicle speed Vb deviate from each other, the wheel speed Vw does not recover to the vehicle speed Vb. As a result, the locked state of the wheels 3 continues, and the control unit 12 continues the braking force release control T2 in the pressure reduction mode in accordance with the anti-skid control. As a result, in "State A", the driver feels an uncomfortable feeling, a so-called plate brake feeling, in the decrease in the vehicle speed Vb in response to the braking operation of the brake pedal 55.

[0038] Also, in "State B" in Fig. 3, as shown by the long dashed line, for example, the input of reaction force from the road surface is restored to some of the wheels 3, so that the wheel speed Vw increases and the locked state is released. However, even if the locked state is released, there is a possibility that the unstable behavior may continue unintentionally. And in "State C" in Fig. 3, for example, even if the braking force generation control T1 is executed corresponding to some of the wheels 3 from which the locked state has been released, the braking force to stop the vehicle 1 traveling backwards, in other words, the deceleration, is insufficient, and as a result, the driver may feel a sense of free running or acceleration.

[0039] 3 proceed in order, a "first situation" occurs in "State A" where the decrease gradient α of the body speed Vb of the body 2 of the vehicle 1 becomes smaller than the decrease gradient of the wheel speed Vw of the wheels 3 of the vehicle 1, and the difference between the wheel speed Vw and the body speed Vb becomes larger. Also, a "second situation" occurs in "State A" where the braking force release control T2 corresponding to the rotation stop state of the wheels 3 is being executed in the braking device 5.

[0040] For example, in the above-mentioned conventional control device, if the first condition is the occurrence of the "first situation" and the second condition is the occurrence of the "second situation," then when the first and second conditions are satisfied, it is determined that the vehicle is unstable in behavior accompanied by rotation about a rotation axis passing through the center of gravity CG. For the second condition to be satisfied, it is necessary that the braking force release control T2 in the pressure reduction mode continues for a relatively long period of time, for example, by the driver applying the brake pedal 55. For this reason, if the driver's application of the brake pedal 55 is delayed, for example, the determination of unstable behavior accompanied by rotation in "state A" is delayed, and after the determination of unstable behavior accompanied by rotation, for example, the switching to the braking force generation control T1 in "state B" and "state C" may also be delayed.

[0041] Therefore, the vehicle brake control device 10 of this embodiment executes a brake control program shown in the flowchart of Fig. 4 so as to determine unstable behavior accompanied by rotation early on before the driver applies the brake pedal 55. The vehicle brake control device 10 (more specifically, the CPU of the computer device constituting the vehicle brake control device 10) starts execution of the brake control program in step S10.

[0042] In the next step S11, the determination unit 14 of the vehicle brake control device 10 determines whether or not the vehicle body speed Vb is decreasing at a decreasing gradient α. In other words, the determination unit 14 determines whether or not a "first situation" is occurring in the vehicle 1. When the determination unit 14 determines that the vehicle body speed Vb is decreasing at a decreasing gradient α and the determination is "Yes," the vehicle brake control device 10 executes the process of step S12.

[0043] In step S12, the control unit 12 of the vehicle brake control device 10 determines whether or not the driver is not braking by operating the brake pedal 55, based on the operation signal BO from the brake sensor 118. When the control unit 12 determines that the driver is not braking by operating the brake pedal 55, i.e., "Yes", the vehicle brake control device 10 executes the process of step S13.

[0044] In step S13, the determination unit 14 determines whether the determination value D (=Gy / μ) is equal to or greater than a predetermined value D0. For this purpose, the determination unit 14 acquires the lateral acceleration Gy from the lateral acceleration sensor 115, and acquires the friction coefficient μ of the road surface from the road surface condition detection unit 13. Then, when the determination unit 14 determines that the determination value D is equal to or greater than the predetermined value D0 and the result is "Yes", the vehicle brake control device 10 increments the value of the pre-braking counter value Kb by "1" in step S14. Also, when the determination unit 14 determines that the determination value D is less than the predetermined value D0 and the result is "No", the vehicle brake control device 10 sets the value of the pre-braking counter value Kb to "0" in step S15. Then, the vehicle brake control device 10 executes the process of step S19 after the process of step S14 or step S15.

[0045] On the other hand, if the control unit 12 determines "No" in step S12 that the driver is braking by applying the brake pedal 55, the vehicle brake control device 10 executes the process of step S16. In step S16, the determination unit 14 determines whether or not the braking force release control T2 is being executed by the control unit 12. In other words, the determination unit 14 determines whether or not the "second situation" has occurred in the vehicle 1.

[0046] When the determination unit 14 determines that the braking force release control T2 is being executed and the result is "Yes," the vehicle brake control device 10 increments the value of the post-braking counter value Ka by "1" in step S17. When the determination unit 14 determines that the braking force release control T2 is not being executed and the result is "No," the vehicle brake control device 10 sets the value of the post-braking counter value Ka to "0" in step S18. Then, after the process of step S17 or step S18, the vehicle brake control device 10 executes the process of step S19.

[0047] In step S19, the vehicle brake control device 10 calculates a total counter value Kt by adding the post-braking counter value Ka and the pre-braking counter value Kb. Then, the vehicle brake control device 10 executes the process of step S20.

[0048] In step S20, the determination unit 14 determines whether the braking force release control T2 is being continued by the control unit 12 and whether the total counter value Kt is greater than a predetermined value Kt0. That is, in the case where the total counter value Kt to which the pre-braking counter value Kb, which makes the determination value D equal to or greater than the predetermined value D0, is added in step S19 and is greater than the predetermined value Kt0, and in addition, the "first situation" occurs according to the determination process of step S11, and the "second situation" occurs according to the determination process of step S16, the determination unit 14 in this embodiment determines "Yes" since unstable behavior accompanied by rotation occurs in the vehicle 1. Then, when the determination unit 14 outputs the determination information J indicating that unstable behavior accompanied by rotation occurs to the command unit 15, the vehicle brake control device 10 executes the process of step S21.

[0049] In step S21, the command unit 15 of the vehicle brake control device 10 outputs a braking command C to the control unit 12 in accordance with the determination information J acquired in step S20. As a result, the control unit 12 ends the braking force release control T2 in accordance with the braking command C, in other words, ends the anti-skid control, and promptly executes the braking force generation control T1, thereby causing the brake device 5 to generate braking force. Then, in step S23, the vehicle brake control device 10 temporarily ends the execution of the brake control program, and starts the execution of the program again in step S10 after a predetermined short time has elapsed.

[0050] Furthermore, in step S20, when the determination unit 14 determines that the vehicle 1 is not experiencing unstable behavior involving rotation, the vehicle brake control device 10 temporarily ends execution of the program in step S23, and then starts execution of the program again in step S10 after a predetermined short time has elapsed.

[0051] On the other hand, when the determination unit 14 determines in step S11 that the vehicle speed Vb is not decreasing at the decreasing gradient α, that is, the "first situation" has not occurred and the result is "No," the vehicle brake control device 10 executes the process of step S22. In step S22, the vehicle brake control device 10 sets the post-braking counter value Ka to "0" and sets the pre-braking counter value Kb to "0" in response to the fact that the "first situation" has not occurred.

[0052] In this case, the total counter value Kt calculated in step S19 also becomes "0", and the determination in the subsequent determination process in step S20 is "No" because the total counter value Kt is equal to or less than the predetermined value Kt0. Therefore, the vehicle brake control device 10 temporarily ends the execution of the program in step S23, and starts the execution of the program again in step S10 after a predetermined short time has elapsed.

[0053] As can be understood from the above explanation, the vehicle braking control device 10 includes a control unit 12 that can switch between braking force generation control T1, which generates a braking force in the braking device 5 mounted on the vehicle 1, and braking force release control T2, which releases the braking force generated in the braking device 5, and a judgment unit 14 that judges whether or not unstable behavior involving rotation around a vertical axis (a rotation axis passing through the center of gravity CG of the vehicle 1) is occurring in the vehicle 1 based on a judgment value D that is determined using a lateral acceleration Gy that represents the state occurring in the vehicle 1 and a friction coefficient μ that represents the state of the road surface with which the wheels 3 of the vehicle 1 contact, and the control unit 12 generates a braking force in the braking device 5 by executing the braking force generation control T1 in response to the judgment of unstable behavior.

[0054] In this case, the vehicle brake control device 10 determines that unstable behavior is occurring when the judgment unit 14 not only determines that the judgment value D is greater than or equal to the predetermined value D0, but also when a first situation occurs in which the decrease gradient α of the vehicle body speed Vb of the vehicle 1 becomes smaller than the decrease gradient of the wheel speed Vw of the wheel 3, causing the vehicle body speed Vb to be greater than the wheel speed Vw, and a second situation occurs in which the braking force release control T2 is being executed in the braking device 5 in accordance with the wheel speed Vw.

[0055] In these cases, the vehicle brake control device 10 has a sensor group 11 as a state quantity detection unit that detects a state quantity having a component in the left-right direction of the vehicle 1 and representing a state occurring in the vehicle 1, and a road surface condition detection unit 13 as a physical quantity detection unit that detects a physical quantity representing a state between the wheels 3 and the road surface, and a determination unit 14 sets the ratio of the state quantity to the physical quantity as a determination value D. In this case, the state quantity is the lateral acceleration Gy, which is one of the lateral acceleration Gy and the yaw rate YR occurring in the vehicle 1, and the physical quantity is a friction coefficient μ representing the magnitude of friction of the road surface with which the wheels 3 come into contact.

[0056] Furthermore, in these cases, the vehicle brake control device 10 has the control unit 12 execute braking force generation control T1 and braking force release control T2 in accordance with anti-skid control that prevents the wheels 3 from becoming locked in a state in which they stop rotating, and when the judgment unit 14 judges that unstable behavior is occurring while the braking force release control T2 is being executed in accordance with the anti-skid control, the control unit 12 terminates the anti-skid control and executes the braking force generation control T1.

[0057] According to these, the vehicle brake control device 10 allows the determination unit 14 to determine whether or not the vehicle 1 is experiencing unstable behavior accompanied by rotation based on the determination value D. In other words, in the vehicle brake control device 10, the determination unit 14 can determine early on that the vehicle 1 is experiencing unstable behavior accompanied by rotation before braking, i.e., before the driver operates the brake pedal 55 to brake. As a result, the vehicle brake control device 10 can cause the control unit 12 to terminate the braking force release control T2 when the braking force release control T2 is being executed, in other words, to terminate the anti-skid control, and promptly execute the braking force generation control T1. As a result, the vehicle brake control device 10 can promptly stop the vehicle 1 experiencing unstable behavior accompanied by rotation.

[0058] Furthermore, the judgment unit 14 can judge whether or not unstable behavior accompanied by rotation occurs in the vehicle 1 by using the judgment value D (=Gy / μ) which indicates the ratio of the lateral acceleration Gy to the friction coefficient μ. Therefore, the judgment unit 14 can ensure robustness and make a judgment even when, for example, the friction coefficient μ is small. Furthermore, the judgment unit 14 can also judge whether or not the vehicle 1 returns to stable behavior from unstable behavior accompanied by rotation as the judgment value D decreases, for example. In other words, the vehicle braking control device 10 can ensure a room for behavior recovery when judging unstable behavior accompanied by rotation.

[0059] Next, a modified example will be described. In the modified example, the vehicle brake control device 10 determines whether or not the vehicle 1 is exhibiting unstable behavior accompanied by rotation based on the determination value D, regardless of whether or not the "first situation" and the "second situation" are occurring in the vehicle 1, in other words, regardless of whether or not braking is being performed.

[0060] In the modified example, the vehicle brake control device 10 executes a brake control program represented by a flowchart in Fig. 5. That is, the vehicle brake control device 10 starts execution of the program in step S100, and in the following step S101, the determination unit 14 determines whether the determination value D is equal to or greater than a predetermined value D0.

[0061] Then, when the judgment unit 14 judges that the judgment value D is equal to or greater than the predetermined value D0 and judges "Yes", the vehicle brake control device 10 increments the counter value K by "1" in step S102. When the judgment unit 14 judges that the judgment value D is less than the predetermined value D0 and judges "No", the vehicle brake control device 10 changes the counter value K to "0" in step S102. Then, after the processing of step S102 or step S103, the vehicle brake control device 10 executes the processing of step S104.

[0062] In step S104, the determination unit 14 determines whether the counter value K is greater than a predetermined value K0. That is, if the counter value K is greater than the predetermined value K0, in other words, if a state in which the ratio of the lateral acceleration Gy to the friction coefficient μ is large continues for a certain period of time or more, the determination unit 14 determines "Yes" since unstable behavior accompanied by rotation is occurring in the vehicle 1. Then, when the determination unit 14 outputs the determination information J to the command unit 15, the vehicle brake control device 10 executes the process of step S105.

[0063] In step S105, the command unit 15 outputs a braking command C to the control unit 12 according to the determination information J. As a result, the control unit 12 executes the braking force generation control T1 according to the braking command C, thereby causing the brake device 5 to generate a braking force. Then, in step S106, the vehicle brake control device 10 temporarily ends the execution of the braking control program, and starts the execution of the program again in step S100 after a predetermined short time has elapsed. Also, in step S104, when the determination unit 14 determines that unstable behavior accompanied by rotation has not occurred, the vehicle brake control device 10 temporarily ends the execution of the program in step S106, and starts the execution of the program again in step S100 after a predetermined short time has elapsed.

[0064] Therefore, in the modified example, regardless of the presence or absence of braking, for example, even if the driver does not perform a braking operation, the vehicle brake control device 10 can determine whether or not unstable behavior accompanied by rotation occurs in the vehicle 1. Therefore, in the modified example, the same effects as those of the above-mentioned embodiment can be expected.

[0065] In the above-described embodiment and modified example, the determination unit 14 determines whether or not unstable behavior accompanied by rotation of the vehicle 1 occurs based on the determination value D using the friction coefficient μ and the lateral acceleration Gy. However, it is also possible to use the yaw rate YR detected by the yaw rate sensor 116 instead of the lateral acceleration Gy. In this case, the determination unit 14 can determine whether or not unstable behavior accompanied by rotation of the vehicle 1 occurs using the determination value indicating the ratio of the yaw rate YR to the friction coefficient μ, in the same manner as in the above-described embodiment and modified example.

[0066] Incidentally, the lateral acceleration Gy and the yaw rate YR are state quantities detected in association with the turning (rotation) of the vehicle 1. Therefore, it can be said that the lateral acceleration Gy and the yaw rate YR have a predetermined relationship with the steering angle TA, which is a state quantity that turns (rotates) the vehicle 1. For this reason, the determination unit 14 can also determine whether or not unstable behavior accompanying rotation occurs in the vehicle 1 based on a determination value that expresses the lateral acceleration Gy or the yaw rate YR as a relational expression with the steering angle TA. Even in this case, the same effects as those of the above-mentioned embodiment and modified example can be expected.

[0067] Furthermore, in the above-described embodiment, the control unit 12 executes the braking force generation control T1 or the braking force release control T2 in accordance with ABS control. Alternatively or in addition to this, the control unit 12 can execute the braking force generation control T1 or the braking force release control T2 in accordance with a well-known vehicle stability control (also referred to as "VSC") that stabilizes the running behavior of the vehicle 1. In particular, in the above-described modified example, when the determination unit 14 determines that the vehicle 1 is experiencing unstable behavior accompanied by rotation, the control unit 12 can execute the braking force generation control T1 in accordance with VSC.

[0068] It can be said that the vehicle braking control device 10 includes a sensor group 11 and a computer. The computer can also be said to be configured to execute the functions (or processes) of the control unit 12, the road surface condition detection unit 13, the determination unit 14, and the command unit 15 described above. [Explanation of symbols]

[0069] 1...vehicle, 2...vehicle body, 3...wheel, 4...steering device, 5...braking device, 10...vehicle brake control device, 11...sensor group, 115...lateral acceleration sensor (state quantity detection unit), 116...yaw rate sensor (state quantity detection unit), 12...control unit, 13...road surface condition detection unit (physical quantity detection unit), 14...determination unit, 15...command unit, Vw...wheel speed, Vb...vehicle body speed, Gy...lateral acceleration (state quantity), YR...yaw rate (state quantity), μ...friction coefficient (physical quantity), D...determination value, D0...predetermined value, α...decrease gradient, T1...braking force generation control, T2...braking force release control

Claims

1. a control unit capable of switching between a braking force generation control for generating a braking force in a braking device mounted on a vehicle and a braking force release control for releasing the braking force generated in the braking device; a determination unit that determines whether or not the vehicle is experiencing unstable behavior involving rotation about a rotation axis along a vertical direction, based on a determination value that is determined using a state that occurs in the vehicle and a state of a road surface with which wheels of the vehicle are in contact, The control unit: A vehicle brake control device that, in response to the determination of the unstable behavior, executes the braking force generation control, thereby causing the brake device to generate the braking force.

2. The determination unit, In addition to the case where the judgment value is equal to or greater than the predetermined value, 2. The vehicle brake control device according to claim 1, wherein the unstable behavior is determined to be occurring when a first situation occurs in which a gradient of decrease in the vehicle body speed of the vehicle becomes smaller than a gradient of decrease in the wheel speed of the wheel, and the vehicle body speed becomes greater than the wheel speed, and a second situation occurs in which braking force release control is executed in the braking device in accordance with the wheel speed.

3. a state quantity detection unit that detects a state quantity having a component in a left-right direction of the vehicle and that represents a state occurring in the vehicle; a physical quantity detection unit that detects a physical quantity representing a state between the wheel and the road surface, The determination unit, 3. The vehicle brake control device according to claim 1, wherein the determination value is a ratio of the state quantity to the physical quantity.

4. the state quantity is one of a lateral acceleration and a yaw rate generated in the vehicle, 4. The vehicle brake control device according to claim 3, wherein the physical quantity is a friction coefficient that represents a magnitude of friction of the road surface with which the wheels come into contact.

5. The control unit: executing the braking force generation control and the braking force release control in accordance with an anti-skid control for preventing the wheel from stopping rotating; 2. The vehicle brake control device according to claim 1, wherein when the determination unit determines that the unstable behavior is occurring during execution of the braking force release control in accordance with the anti-skid control, the anti-skid control is terminated and the braking force generation control is executed.

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