Vehicle braking control system

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 braking control device for a vehicle.

Background Art

[0002] Conventionally, for example, an anti-skid control device (hereinafter referred to as the "conventional control device") disclosed in Patent Document 1 has been known. The conventional control device determines whether an unstable behavior accompanied by rotation occurs in the vehicle based on the continuation of the pressure reduction mode according to the 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

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional control device, it is determined whether an unstable behavior accompanied by rotation occurs in the vehicle based on the pressure reduction mode according to the anti-skid control. By the way, for example, in order to determine that the unstable behavior is canceled halfway or a turn that does not reach the unstable behavior in the vehicle, time required for the determination of the unstable behavior is necessary. In this regard, in the conventional control device, for example, when the braking by the driver is delayed, the time until the pressure reduction mode is started is also delayed, and there is a case where the time required for the determination cannot be secured. As a result, in the conventional control device, there is a possibility that the determination of the unstable behavior cannot be made.

[0005] An object of the present disclosure is to provide a braking control device for a vehicle capable of early determining whether an unstable behavior accompanied by rotation occurs in the vehicle.

Means for Solving the Problems

[0006] The vehicle braking control device of this disclosure includes a control unit capable of switching between brake force generation control, which generates a braking force in a braking device mounted on a vehicle, and brake force release control, which releases the braking force generated in the braking device; and a determination unit that determines whether or not unstable behavior accompanied by rotation around a rotation axis along the vertical direction is occurring in the vehicle, based on a determination value determined using the conditions occurring in the vehicle and the condition of the road surface in contact with the vehicle's wheels. The control unit generates a braking force in the braking device by executing brake force generation control in response to the determination of unstable behavior. [Effects of the Invention]

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

[0008] [Figure 1] This is a schematic diagram of the vehicle and the vehicle's braking control system. [Figure 2] This graph shows the relationship between slip ratio and coefficient of friction. [Figure 3] This diagram illustrates unstable behavior involving rotation. [Figure 4] This is a flowchart of the braking control program. [Figure 5] This is a flowchart of a modified braking control program. [Modes for carrying out the invention]

[0009] Hereinafter, a vehicle braking control device 10, which is one embodiment of the present disclosure, will be described in detail with reference to the drawings. In addition to the embodiment described below, the vehicle braking 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 braking control device 10 is applied to the vehicle 1 shown in Figure 1. The vehicle 1 may be driven by manual operation by a driver or by automatic operation. The embodiments described below will illustrate the case where the vehicle 1 is driven by manual operation by a driver.

[0011] Vehicle 1 comprises a body 2 and wheels 3. The body 2 is supported by the wheels 3 via a suspension mechanism (not shown). The wheels 3 consist of a right front wheel 31, a left front wheel 32, a right rear wheel 33, and a left rear wheel 34.

[0012] Furthermore, the vehicle 1 is equipped with a steering device 4. In this embodiment, the steering device 4 is configured to steer the right front wheel 31 and the 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 a driving force from a power source (engine or electric motor, etc.) which is not shown.

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

[0014] The master cylinder 56 pumps hydraulic fluid in response to the braking operation performed by the driver by pressing the brake pedal 55. The hydraulic circuit 57, although not shown in detail, includes a reservoir, pump, and various valve devices, and functions as a brake actuator. The hydraulic circuit 57 adjusts the hydraulic pressure of the hydraulic fluid supplied to each of the brake lines 58 in response to instructions from, for example, the control unit 12 of the vehicle braking control device 10, which will be described later.

[0015] In other words, the hydraulic circuit 57 can generate braking force on each of the right front wheel brake 51, left front wheel brake 52, right rear wheel brake 53, and left rear wheel brake 54 by increasing the operating hydraulic pressure in a pressure-boosting mode. Conversely, the hydraulic circuit 57 can release the braking force on each of the right front wheel brake 51, left front wheel brake 52, right rear wheel brake 53, and left rear wheel brake 54 by decreasing the operating hydraulic pressure in a pressure-boosting mode.

[0016] As shown in Figure 1, the vehicle braking control device 10 is mounted on the vehicle 1. The vehicle braking control device 10 consists of a sensor group 11, a control unit 12, a road surface condition detection unit 13, a determination unit 14, and a command unit 15. Here, the vehicle braking control device 10 is mainly composed of a computer device equipped with a CPU, ROM, RAM, and various interfaces. The CPU sequentially executes a predetermined program including a braking control program, which will be described later, and performs data reading, numerical calculations, and output of calculation results. 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] As shown in Figure 1, the sensor group 11 comprises 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 comprises a lateral acceleration sensor 115 and a yaw rate sensor 116, which act as a state quantity detection unit for detecting state quantities of the vehicle 1 having a lateral component. Furthermore, the sensor group 11 comprises a steering angle sensor 117 and a brake sensor 118.

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

[0019] The lateral acceleration sensor 115 detects the lateral acceleration Gy which represents the state generated 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 generated in the left - right direction of the vehicle 1. The yaw rate sensor 116 detects the yaw rate YR which represents the state generated 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 generated 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, the steering angle TA has a predetermined relationship with, for example, the operation amount (steering angle) of the steering wheel by the driver. Therefore, the steering angle sensor 117 can also detect the steering angle TA based on, for example, the operation amount (steering angle) of the steering wheel.

[0021] When the brake pedal 55 is being brake - operated by the driver, the brake sensor 118 outputs an operation signal BO representing an operation state requiring braking. That is, the brake sensor 118 detects the hydraulic pressure of the master cylinder 56 and the hydraulic pressure of each of the brake pipes 58 corresponding to the brake operation on the brake pedal 55 and outputs the operation signal BO.

[0022] The control unit 12 executes a braking force generation control T1 on the braking device 5 mounted on the vehicle 1, generating braking force using the pressure boosting mode described above. The control unit 12 also executes a braking force release control T2 on the braking device 5, releasing the braking force using the pressure reduction mode. The control unit 12 can switch between executing the braking force generation control T1 and the braking force release control T2.

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

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

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

[0026] Here, for the estimation of the friction coefficient μ, a well-known calculation method that has been widely adopted in the past can be used. For this reason, an example of the estimation calculation of the friction coefficient μ by the road surface condition detection unit 13 is briefly shown below. The road surface condition detection unit 13 estimates the vehicle 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 difference between the wheel speed Vw and the vehicle speed Vb by the vehicle speed Vb. Note that the slip ratio S can also be estimated based on the acceleration of the wheel speed Vw, the longitudinal acceleration or lateral acceleration Gy of the vehicle 1, etc.

[0027] The road surface condition detection unit 13 then estimates and calculates the road surface friction coefficient μ corresponding to the calculated slip ratio S of the wheel 3, based on the S-μ characteristic determined as shown in Figure 2, which is the relationship between the road surface friction coefficient μ and the slip ratio S of the wheel 3. The road surface condition detection unit 13 then outputs the estimated and detected road surface friction coefficient μ to the determination unit 14.

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

[0029] In this embodiment, the determination value D is the ratio of a state variable to a physical quantity, that is, the ratio of the lateral acceleration Gy to the friction coefficient μ (Gy / μ). The determination value D tends to be larger as the friction coefficient μ decreases or as the lateral acceleration Gy increases. Therefore, when the determination value D is large, unstable behavior accompanied by rotation is more likely to occur in vehicle 1. On the other hand, the determination value D tends to be smaller as the friction coefficient μ increases or as the lateral acceleration Gy decreases. Therefore, when the determination value D is small, it is easier to return from unstable behavior to stable behavior.

[0030] As will be described later, the determination unit 14 of this embodiment determines whether a first situation (see Figure 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 larger. Furthermore, as will be described later, the determination unit 14 of this embodiment determines whether a second situation (see Figure 3) has occurred, in which the braking device 5 executes brake force release control T2 in accordance with the wheel speed Vw, or more specifically, in accordance with the locked state of the wheel 3. Then, if both the first and second situations have occurred and the determination value D is greater than or equal to a predetermined value D0, the determination unit 14 of this embodiment determines that unstable behavior accompanied by rotation is occurring in the vehicle 1 and outputs determination information J to the command unit 15.

[0031] The command unit 15 receives judgment information J from the judgment unit 14. If the command unit 15 detects that the vehicle 1 is exhibiting unstable behavior according to the judgment information J, it outputs a braking command C to the control unit 12 instructing the braking device 5 to generate braking force. As a result, the control unit 12 generates braking force in the braking device 5 by executing braking force generation control T1.

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

[0033] Next, we will explain the unstable behavior involving rotation that occurs in vehicle 1. As shown in Figure 3, when vehicle 1 is traveling in a straight line, if the coefficient of friction μ of the road surface decreases, or if a lateral acceleration Gy occurs in vehicle 1, or if the steering angle TA increases, vehicle 1 may exhibit unstable behavior involving 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 Figure 3, as vehicle 1 begins to rotate (or turn) and gradually approaches a direction perpendicular to the direction of travel, the reaction force input from the road surface to wheel 3 decreases. As a result, in "State A," the wheel speed Vw of wheel 3 decreases rapidly, as shown by the long dashed line. When vehicle 1 is facing perpendicular, the reaction force from the road surface disappears, and as a result, the wheel speed Vw becomes "0," meaning wheel 3 stops rotating.

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

[0036] When unstable rotation occurs in vehicle 1, as shown by the thick solid line in Figure 3, the vehicle speed Vb decreases at a rate determined by the coefficient of friction μ of the road surface in order to avoid a sudden drop. On the other hand, when unstable rotation occurs in vehicle 1, as described above, the reaction force from the road surface on the wheels 3 decreases, so the wheel speed Vw decreases at a rate greater than the rate of decrease α. Therefore, when unstable rotation occurs in vehicle 1, the vehicle speed Vb cannot keep up with the decreasing wheel speed Vw and ends up shifting upwards.

[0037] Then, when the vehicle speed Vb is higher than the wheel speed Vw, and a discrepancy occurs between the wheel speed Vw and the vehicle speed Vb, the wheel speed Vw does not recover to the vehicle speed Vb. As a result, the wheel 3 remains locked, and the control unit 12 continues the brake force release control T2 in depressurization mode according to the anti-skid control. Consequently, in "state A", the driver will feel an abnormality, a so-called plate brake sensation, in response to the decrease in vehicle speed Vb in response to braking operation with the brake pedal 55.

[0038] Furthermore, in "State B" of Figure 3, as shown by the long dashed line, for example, the wheel speed Vw increases and the locked state is resolved when the reaction force input from the road surface is restored to some of the wheels 3. However, even if the locked state is resolved, there is a possibility that unstable behavior may continue unintentionally. And in "State C" of Figure 3, for example, even if braking force generation control T1 is executed in response to some of the wheels 3 whose locked state has been resolved, the braking force required to stop the moving vehicle 1, in other words, the deceleration, is insufficient, and as a result the driver may feel a sense of coasting or acceleration.

[0039] In other words, when "State A," "State B," and "State C" shown in Figure 3 proceed in order, in "State A," a "first situation" occurs where the decrease gradient α of the vehicle body speed Vb of vehicle 1 becomes smaller than the decrease gradient of the wheel speed Vw of vehicle 1's wheel 3, and the difference between the wheel speed Vw and the vehicle body speed Vb becomes larger. Also, in "State A," a "second situation" occurs where the braking device 5 executes a brake force release control T2 corresponding to the rotation stop state of wheel 3.

[0040] For example, in the conventional control device described above, if the occurrence of the "first situation" is the first condition and the occurrence of the "second situation" is the second condition, then when both the first and second conditions are met, unstable behavior involving rotation around the axis of rotation passing through the center of gravity CG is determined. However, for the second condition to be met, for example, the driver must operate the brake pedal 55 to depressurize, which requires the brake force release control T2 to continue for a relatively long period of time. Therefore, if the driver's operation of the brake pedal 55 is delayed, for example, the determination of unstable behavior involving rotation in "state A" may be delayed, and after determining the unstable behavior involving rotation, the switch to the brake force generation control T1 in "state B" and "state C" may also be delayed.

[0041] Therefore, the vehicle braking control device 10 of this embodiment executes the braking control program shown in the flowchart of Figure 4 in order to determine unstable behavior accompanied by rotation early on, even before the driver performs a braking operation using the brake pedal 55. The vehicle braking control device 10 (more specifically, the CPU of the computer device constituting the vehicle braking control device 10) starts executing the braking control program in step S10.

[0042] In the following step S11, the determination unit 14 of the vehicle braking control device 10 determines whether the vehicle speed Vb is decreasing at a decreasing gradient α. In other words, the determination unit 14 determines whether the "first situation" is occurring in vehicle 1. If the determination unit 14 determines that the vehicle speed Vb is decreasing at a decreasing gradient α and the result is "Yes", the vehicle braking control device 10 executes the process in step S12.

[0043] In step S12, the control unit 12 of the vehicle braking control device 10 determines whether the driver has applied the brake pedal 55 based on the operation signal BO from the brake sensor 118. If the control unit 12 determines that the driver has not applied the brake pedal 55 and the result is "Yes", the vehicle braking control device 10 executes the process in step S13.

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

[0045] On the other hand, in step S12, if the control unit 12 determines that the driver is performing a braking operation with the brake pedal 55 and the vehicle braking control device 10 determines "No", it executes the process in step S16. In step S16, the determination unit 14 determines whether or not the control unit 12 is performing brake force release control T2. In other words, the determination unit 14 determines whether or not the "second situation" is occurring in the vehicle 1.

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

[0047] In step S19, the vehicle braking 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 braking control device 10 executes the process of step S20.

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

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

[0050] Furthermore, in step S20, if the determination unit 14 determines that no unstable behavior involving rotation is occurring in the vehicle 1, the vehicle braking control device 10 temporarily terminates program execution in step S23. Then, after a predetermined short period of time has elapsed, program execution is restarted in step S10.

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

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

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

[0054] In this case, the vehicle braking control device 10 determines that unstable behavior is occurring when the determination value D is greater than or equal to a predetermined value D0, and 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 become greater than the wheel speed Vw, and a second situation occurs in which the braking force release control T2 is executed in the braking device 5 according to the wheel speed Vw.

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

[0056] Furthermore, in these cases, the vehicle braking control device 10 has a control unit 12 that executes braking force generation control T1 and braking force release control T2 in accordance with anti-skid control to prevent the wheel 3 from entering a locked state where it stops rotating. If the determination unit 14 determines that unstable behavior is occurring while the braking force release control T2 is being executed in accordance with the anti-skid control, the anti-skid control is terminated and braking force generation control T1 is executed.

[0057] According to these findings, the vehicle braking control device 10 can determine whether or not the vehicle 1 is exhibiting unstable behavior accompanied by rotation, based on the determination value D, using the determination unit 14. In other words, the vehicle braking control device 10 can determine early on whether or not the vehicle 1 is exhibiting unstable behavior accompanied by rotation, before braking occurs, that is, before the brake pedal 55 is operated by the driver. As a result, the vehicle braking control device 10 can instruct the control unit 12 to terminate the brake force release control T2 if it is currently performing the brake force release control T2, or in other words, to terminate the anti-skid control, and to quickly execute the brake force generation control T1.

[0058] Furthermore, the determination unit 14 can determine whether or not the vehicle 1 is experiencing unstable behavior accompanied by rotation, using a determination value D (=Gy / μ) that represents the ratio of the lateral acceleration Gy to the friction coefficient μ. Therefore, the determination unit 14 can ensure robustness and make a determination even when, for example, the friction coefficient μ is small. In addition, the determination unit 14 can also determine, for example, whether or not the vehicle 1 will return from unstable behavior accompanied by rotation to stable behavior as the determination value D decreases. In other words, the vehicle braking control device 10 can ensure room for behavioral recovery when determining unstable behavior accompanied by rotation.

[0059] Next, a modified example will be described. In this modified example, the vehicle braking control device 10 determines whether or not unstable behavior involving rotation is occurring in the vehicle 1 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 braking control device 10 executes a braking control program represented by the flowchart in Figure 5. Specifically, the vehicle braking control device 10 starts executing the program in step S100, and in the following step S101, the determination unit 14 determines whether the determination value D is greater than or equal to a predetermined value D0.

[0061] Then, if the determination unit 14 determines that the determination value D is greater than or equal to a predetermined value D0 and is therefore "Yes", the vehicle braking control device 10 increments the value of the counter K by "1" in step S102. If the determination unit 14 determines that the determination value D is less than the predetermined value D0 and is therefore "No", the vehicle braking control device 10 changes the value of the counter K to "0" in step S102. After processing in step S102 or step S103, the vehicle braking control device 10 executes the processing in 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 the ratio of the lateral acceleration Gy to the coefficient of friction μ is large, the determination unit 14 determines "Yes" because 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 braking control device 10 executes the process in 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 generates braking force in the braking device 5 by executing braking force generation control T1 according to the braking command C. Then, in step S106, the vehicle braking control device 10 temporarily terminates the execution of the braking control program and restarts the program execution in step S100 after a predetermined short period of time has elapsed. Also, in step S104, if the determination unit 14 determines that no unstable behavior accompanied by rotation has occurred, the vehicle braking control device 10 temporarily terminates the program execution in step S106 and restarts the program execution in step S100 after a predetermined short period of time has elapsed.

[0064] Therefore, in the modified configuration, regardless of whether braking is performed or not, for example, even if the driver does not perform a braking operation, the vehicle braking control device 10 can determine whether or not unstable behavior involving rotation is occurring in the vehicle 1. Therefore, the same effects as in the above-described embodiment can be expected in the modified configuration as well.

[0065] Furthermore, in the embodiments and modifications described above, the determination unit 14 determines whether or not unstable behavior involving rotation of the vehicle 1 is occurring based on a 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 involving rotation of the vehicle 1 is occurring, similar to the embodiments and modifications described above, using a determination value representing the ratio of the yaw rate YR to the friction coefficient μ.

[0066] Furthermore, the lateral acceleration Gy and yaw rate YR are state variables detected in conjunction with the turning (rotation) of the vehicle 1. Therefore, it can be said that the lateral acceleration Gy and yaw rate YR have a predetermined relationship with the steering angle TA, which is a state variable that causes the vehicle 1 to turn (rotate). For this reason, the determination unit 14 can also determine whether or not unstable behavior accompanied by rotation is occurring in the vehicle 1 based on a determination value expressed by a relationship equation between the lateral acceleration Gy or yaw rate YR and the steering angle TA. In this case as well, the same effects as those of the above-described embodiment and modified example can be expected.

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

[0068] Furthermore, the vehicle braking control device 10 can be said to include 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, road surface condition detection unit 13, determination unit 14, and command unit 15 described above. [Explanation of symbols]

[0069] 1...Vehicle, 2...Vehicle body, 3...Wheels, 4...Steering device, 5...Braking device, 10...Vehicle braking 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...Coefficient of friction (physical quantity), D...Determination value, D0...Determined value, α...Decreasing gradient, T1...Braking force generation control, T2...Braking force release control

Claims

1. A control unit capable of switching between and executing braking force generation control, which generates braking force in a braking device mounted on a vehicle, and braking force release control, which releases the braking force generated in the braking device, A determination unit determines whether or not unstable behavior involving rotation around a rotation axis in the vertical direction is occurring in the vehicle, based on a determination value determined using the conditions occurring in the vehicle and the condition of the road surface in contact with the vehicle's wheels. A state quantity detection unit that detects one of the state quantities, which is the lateral acceleration and yaw rate, that occur in the vehicle, A physical quantity detection unit that detects a physical quantity which is the coefficient of friction representing the magnitude of friction of the road surface in contact with the wheel, Equipped with, If we define the first situation as the decrease in the vehicle body speed being smaller than the decrease in the wheel speed of the aforementioned wheels, resulting in the vehicle body speed being greater than the wheel speed, and define the second situation as the braking system performing brake force release control according to the wheel speed, then, The determination unit, If it is determined that the first situation described above has occurred, it is determined whether or not the driver is applying the brakes using the brake pedal. If it is determined that the driver has not performed a braking operation using the brake pedal, and the determination value, which is the ratio of the state quantity to the physical quantity, is determined to be equal to or greater than a predetermined value, the pre-braking counter value is increased. If it is determined that the driver is applying the brakes using the brake pedal, and that the second situation has occurred, the post-braking counter value is increased. If the total counter value, which is the sum of the pre-braking counter value and the post-braking counter value, is greater than a predetermined threshold, and both the first and second conditions are occurring, it is determined that the unstable behavior is occurring. The control unit, A vehicle braking control device that generates the braking force in the braking device by executing the braking force generation control in response to the determination of the unstable behavior.

2. The control unit, The braking force generation control and the braking force release control are executed in accordance with anti-skid control that prevents the wheel from coming to a rotational stop state. The vehicle braking control device according to claim 1, wherein if the determination unit determines that the unstable behavior is occurring while the braking force release control is being executed 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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