Vehicle brake control device

Abstract

To provide a brake control device of a vehicle capable of reducing possibility that deceleration of the vehicle due to an automatic brake function of ACC may exceed the prescribed limit value over prolonged period.SOLUTION: A brake control device of a vehicle comprises: a target brake torque setting parts (91, 101) which set target brake torque (T_out) on the basis of indication brake torque (T_req_in) which is set on the basis of target inter-vehicle distance between an own vehicle and a preceding vehicle; and control parts (93, 103) which control braking force of the vehicle on the basis of the target brake torque (T_out). The target brake torque setting parts (91, 101) set limit brake torque (T_lim) of a value smaller than the indication brake torque (T_req_in) to the target brake torque (T_out) when deceleration (Ax) of the own vehicle exceeds a prescribed limit value (Ax_lim).SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a braking control device for a vehicle. [Background technology]

[0002] Recent vehicles are equipped with an automatic braking function. The automatic braking function is a function in which a driving assistance device, also called an ADAS (Advanced Driver-Assistance System), transmits a braking request instruction to a brake fluid pressure control device based on information ahead of the vehicle detected by a camera or sensor mounted on the vehicle, and automatically applies brake fluid pressure. Known automatic braking functions include an automatic braking function of an ACC (Adaptive Cruise Control) that automatically drives a vehicle while maintaining a target distance from a preceding vehicle, and an emergency braking function that avoids a collision with an obstacle or reduces the impact.

[0003] Specifically, in the automatic braking function, the driving assistance device judges whether braking is necessary and calculates the required braking torque based on information detected by a camera or a sensor, and transmits a signal indicating the braking request and braking torque information to the brake fluid pressure control device. The brake fluid pressure control device receives a signal indicating the braking request and braking torque information from the driving assistance device, switches the control mode according to the type of the ACC automatic braking function or emergency braking function, converts the received braking torque information into brake fluid pressure, and transmits a drive command to an actuator that adjusts the brake fluid pressure. This activates an electric motor provided in the brake fluid pressure control device to increase the brake fluid pressure of each wheel, generating a braking force. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-227532 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, unlike the emergency braking function, the automatic braking function of the ACC requires control so that the deceleration does not exceed a predetermined limit value as much as possible in order to suppress instability of the vehicle body behavior due to sudden deceleration of the vehicle. In response to this, it is conceivable to set an upper limit on the braking torque set by the driving assistance device, but since the braking force generated in the vehicle can be affected by various factors, there is a risk that the deceleration will exceed the limit value for a long period of time if only the braking torque set by the driving assistance device is limited.

[0006] The present invention has been made in consideration of the above problems, and provides a vehicle braking control device that can reduce the risk that the vehicle deceleration caused by the automatic braking function of the ACC will exceed a predetermined limit value for a long period of time. [Means for solving the problem]

[0007] In order to solve the above problem, according to one aspect of the present invention, a target braking torque setting unit sets a target braking torque based on information of a braking request that is set based on a target inter-vehicle distance between the host vehicle and a preceding vehicle, Self A vehicle braking control device is provided which includes a control unit that controls the braking force of the vehicle, and a target braking torque setting unit that sets the target braking torque to a limited braking torque that is smaller than the braking torque corresponding to the braking request information when the deceleration of the vehicle exceeds a predetermined limit value. Effect of the Invention

[0008] As described above, according to the present invention, it is possible to reduce the risk that the deceleration of the vehicle caused by the automatic braking function of the ACC will exceed a predetermined limit value for a long period of time. [Brief description of the drawings]

[0009] [Figure 1]1 is an explanatory diagram showing an example of the configuration of a brake system to which a vehicle brake control device according to a first embodiment of the present invention can be applied. [Diagram 2] 2 is a block diagram showing an example of the configuration of a brake fluid pressure control device constituting the vehicle braking control device according to the embodiment; FIG. [Diagram 3] 4 is a flowchart showing an example of an automatic brake control process performed by the vehicle braking control device according to the embodiment. [Figure 4] 5 is a flowchart showing an example of a target braking torque setting process performed by the vehicle braking control device according to the embodiment; [Diagram 5] 3 is an explanatory diagram showing the operation of the vehicle braking control device according to the embodiment; FIG. [Figure 6] 2 is a block diagram showing an example of the configuration of a booster control device constituting the vehicle braking control device according to the embodiment; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0011] <<1. First embodiment>> <1-1. Brake system configuration example> First, with reference to FIG. 1, a configuration example of a brake system to which a vehicle brake control device according to a first embodiment of the present invention can be applied will be described.

[0012] Fig. 1 is a schematic diagram showing a configuration example of a vehicle brake system 1. The vehicle brake system 1 shown in Fig. 1 is a brake system for a four-wheeled vehicle. The brake system 1 is configured as a brake system having two brake systems, each of which controls the braking force for one front wheel and one rear wheel as one pair.

[0013] The brake system 1 may be a brake system of so-called X-pipe type, in which two brake systems each control the braking force of a pair of a left or right front wheel and a rear wheel diagonally opposite the front wheel. Alternatively, the brake system 1 may be a brake system of so-called H-pipe type, in which one system brakes the left front and rear wheels and the other system brakes the right front and rear wheels. The brake system may also be a brake system for a vehicle other than a four-wheeled vehicle.

[0014] The brake system 1 includes a booster 10, a master cylinder 14, and a brake hydraulic unit 20. The brake system 1 also includes a hydraulic control device 90 that controls the brake hydraulic unit 20, and a booster control device 100 that controls the booster 10. The hydraulic control device 90 and the booster control device 100 are each partially or entirely configured with a microcomputer or microprocessor unit including an arithmetic processing device such as a CPU (Central Processing Unit). The hydraulic control device 90 and the booster control device 100 may each be partially or entirely configured with updatable firmware or the like, or may be a program module executed by commands from a CPU or the like.

[0015] The hydraulic control device 90 and the booster control device 100 are configured to be able to communicate with each other via a communication bus 120 such as a CAN (Controller Area Network). The hydraulic control device 90 and the booster control device 100 are also configured to be able to communicate with a driving support device 110 via the communication bus 120. The driving support device 110 is configured to be able to acquire information detected by a sensor device 111 for detecting information on the environment in front of the vehicle, such as other vehicles, pedestrians, bicycles, and obstacles in front of the vehicle. The sensor device 111 includes at least one of a camera, a radar, and a RiDAR, for example.

[0016] The driving support device 110 is configured to be capable of executing ACC control for automatically driving the vehicle while maintaining at least a target inter-vehicle distance between the vehicle and the preceding vehicle. In this embodiment, the driving support device 110 is configured to be capable of executing emergency brake control for avoiding the vehicle from colliding with another vehicle or an obstacle, or for reducing the impact of the collision, in addition to the ACC control. The driving support device 110 is configured, for example, by a microcomputer or a microprocessor unit including an arithmetic processing device such as a CPU or a GPU (Graphics Processing Unit). A part or the whole of the driving support device 110 may be configured by an updatable firmware, or may be a program module executed by a command from a CPU, or the like.

[0017] In the brake system 1, the depression force applied to the brake pedal 11 is amplified by the booster 10 and transmitted to a master cylinder 14 serving as a hydraulic pressure generating source. A reservoir tank 60 that supplies brake fluid to the master cylinder 14 is attached to the upper part of the master cylinder 14. A primary chamber 47 and a secondary chamber 48, which are two pressurized chambers partitioned by a primary piston 43 and a secondary piston 44, are formed inside the master cylinder 14. When the driver depresses the brake pedal 11, the primary piston 43 and the secondary piston 44 are pressed, and the brake fluid stored in the primary chamber 47 and the secondary chamber 48 is pressurized, and the brake fluid is supplied into the brake hydraulic unit 20.

[0018] The booster 10 is connected to a brake pedal 11 via an input shaft 16. The pedal force amplified by the booster 10 is transmitted to a master cylinder 14 via a push rod 13 that abuts against a primary piston 43. The axial movement of the primary piston 43 also causes the secondary piston 44 to move axially. This causes the brake fluid in a primary chamber 47 and a secondary chamber 48 to be pressurized.

[0019] In this embodiment, an electric booster driven by an electric motor is used as the booster 10. The electric motor may be, for example, a brushless DCDC motor including a stator as a fixed element and a rotor as a movable element. The electric motor operates by receiving a supply of electric power (current) controlled by the booster control device 100. The electric motor is a motor that can rotate forward to advance the push rod 13 and reverse to retract the push rod 13 by switching the direction of the electric current. When the driver depresses the brake pedal 11, the booster control device 100 supplies electric power (current) to the stator of the electric motor, boosts the depressing force of the brake pedal 11, and transmits it to the master cylinder 14.

[0020] A first hydraulic circuit 28 and a second hydraulic circuit 30 extend from the primary chamber 47 and the secondary chamber 48 of the master cylinder 14 toward the hydraulic brakes 38a to 38d of the wheels RF, LR, LF, and RR, respectively. The hydraulic circuits of the vehicle brake system 1 according to this embodiment are of an X-type piping system, and brake fluid is supplied to the wheel cylinder of the hydraulic brake 38a of the right front wheel RF and the wheel cylinder of the hydraulic brake 38b of the left rear wheel LR via the first hydraulic circuit 28. Brake fluid is supplied to the wheel cylinder of the hydraulic brake 38c of the left front wheel LF and the wheel cylinder of the hydraulic brake 38d of the right rear wheel RR via the second hydraulic circuit 30. As a result, each of the hydraulic brakes 38a to 38d can generate a braking force on each of the wheels RF, LR, LF, and RR by hydraulic pressure.

[0021] The brake hydraulic unit 20 includes a first hydraulic circuit 28 and a second hydraulic circuit 30 having the same configuration. Brake fluid is supplied to the first hydraulic circuit 28 and the second hydraulic circuit 30 from the master cylinder 14. Below, the first hydraulic circuit 28 will be briefly described, and a description of the second hydraulic circuit 30 will be omitted.

[0022] The first hydraulic circuit 28 includes, as solenoid valves, a normally open linearly controllable circuit control valve 36a, a normally closed on / off controlled suction valve 34a, normally open linearly controllable booster valves (adjustment valves) 58aa, 58ba, and normally closed on / off controlled pressure reducing valves 54aa, 54ba. The first hydraulic circuit 28 also includes a pump 44a driven by a pump motor 96, a low pressure accumulator 71a, and a damper 73a. The number of pumps 44a is not limited to one.

[0023] A first pressure increase valve 58aa and a first pressure reduction valve 54aa provided adjacent to the hydraulic brake 38a of the right front wheel RF are used for ABS (Antilock Brake System) control or ESP (Electronic Stability Program) control of the right front wheel RF. A second pressure increase valve 58ba and a second pressure reduction valve 54ba provided adjacent to the hydraulic brake 38b of the left rear wheel LR are used for ABS control or ESP control of the left rear wheel LR.

[0024] The first pressure increase valve 58aa for the right front wheel RF is provided between the circuit control valve 36a and the hydraulic brake 38a for the right front wheel RF. The linearly controllable first pressure increase valve 58aa continuously adjusts the flow rate of brake fluid from the circuit control valve 36a side to the wheel cylinder side of the hydraulic brake 38a for the right front wheel RF. When the first pressure increase valve 58aa is closed, the first pressure increase valve 58aa allows brake fluid to flow from the hydraulic brake 38a side to the circuit control valve 36a side, while providing a bypass flow path equipped with a check valve that restricts the flow in the opposite direction.

[0025] The first pressure reducing valve 54aa for the right front wheel RF is a solenoid valve that can be switched only between a fully open or fully closed state, and is provided between the wheel cylinder of the hydraulic brake 38a for the right front wheel RF and the low pressure accumulator 71a. When the first pressure reducing valve 54aa is in the open state, it reduces the pressure of the brake fluid supplied to the wheel cylinder of the hydraulic brake 38a for the right front wheel RF. The first pressure reducing valve 54aa can adjust the flow rate of the brake fluid flowing from the wheel cylinder of the hydraulic brake 38a for the right front wheel RF to the low pressure accumulator 71a by repeatedly opening and closing the valve intermittently.

[0026] The second pressure increase valve 58ba for the left rear wheel LR is provided between the circuit control valve 36a and the hydraulic brake 38b for the left rear wheel LR. The linearly controllable second pressure increase valve 58ba continuously adjusts the flow rate of brake fluid from the circuit control valve 36a side to the wheel cylinder side of the hydraulic brake 38b for the left rear wheel LR. When the second pressure increase valve 58ba is closed, the second pressure increase valve 58ba allows brake fluid to flow from the hydraulic brake 38b side to the circuit control valve 36a side, while providing a bypass flow path equipped with a check valve that restricts the flow in the reverse direction.

[0027] The second pressure reducing valve 54ba for the left rear wheel LR is a solenoid valve that can be switched only between a fully open or fully closed state, and is provided between the wheel cylinder of the hydraulic brake 38b for the left rear wheel LR and the low pressure accumulator 71a. When the second pressure reducing valve 54ba is in the open state, it reduces the pressure of the brake fluid supplied to the wheel cylinder of the hydraulic brake 38b for the left rear wheel LR. The second pressure reducing valve 54ba can adjust the flow rate of the brake fluid flowing from the wheel cylinder of the hydraulic brake 38b for the left rear wheel LR to the low pressure accumulator 71a by repeatedly opening and closing the valve intermittently.

[0028] The circuit control valve 36a is provided to establish or block communication between the booster valves 58aa, 58ba and the master cylinder 14. The suction valve 34a is provided to establish or block communication between the master cylinder 14 and the suction side of the pump 44a. A hydraulic pressure sensor 24 is provided in the pipe between the circuit control valve 36a and the master cylinder 14, as well as between the suction valve 34a and the master cylinder 14. These are similar to the components of the brake hydraulic unit 20, so detailed description will be omitted.

[0029] The second hydraulic circuit 30 controls a hydraulic brake 38c for the left front wheel LF and a hydraulic brake 38d for the right rear wheel RR. The second hydraulic circuit 30 is configured similarly to the first hydraulic circuit 28, except that the wheel cylinder of the hydraulic brake 38a for the right front wheel RF in the description of the first hydraulic circuit 28 is replaced with the wheel cylinder of the hydraulic brake 38c for the left front wheel LF, and the wheel cylinder of the hydraulic brake 38b for the left rear wheel LR is replaced with the wheel cylinder of the hydraulic brake 38d for the right rear wheel RR.

[0030] In the brake system 1 configured in this manner, when the vehicle approaches too close to the preceding vehicle during execution of ACC, the driving support device 110 generates a signal indicating a braking request (hereinafter also referred to as a "braking request signal") to maintain the inter-vehicle distance between the vehicle and the preceding vehicle at a predetermined target inter-vehicle distance. In the first embodiment, the hydraulic control device 90 that controls the brake hydraulic unit 20 receives the braking request signal transmitted from the driving support device 110, and functions as a vehicle braking control device that controls the braking force so that the deceleration of the vehicle does not exceed a predetermined limit value for a long period of time.

[0031] <1-2. Vehicle Brake Control Device (Hydraulic Pressure Control Device)> (1-2-1. Configuration example) 2 is a block diagram showing a functional configuration related to the automatic brake control of the ACC in the brake system 1. In this embodiment, the automatic brake control of the ACC is performed by the driving assistance device 110 and the hydraulic pressure control device 90 communicating with each other and the hydraulic pressure control device 90 controlling the brake hydraulic pressure unit 20.

[0032] During execution of ACC, the driving support device 110 determines whether braking is required and calculates a required braking request command value based on information detected by sensor devices 111 such as a camera, radar, and RiDAR, and transmits a braking request signal indicating information on the braking request and the braking request command value to the hydraulic control device 90. The braking request command value may be, for example, a braking torque command value or a brake hydraulic pressure command value. In this embodiment, an example will be described in which the driving support device 110 calculates a braking torque command value (hereinafter also referred to as "command braking torque") T_req_in as information on the braking request command value, and transmits a braking request signal indicating information on the braking request S_brk and the command braking torque T_req_in to the hydraulic control device 90.

[0033] Specifically, the driving support device 110 obtains the vehicle distance D between the host vehicle and the preceding vehicle and the relative speed dV of the host vehicle with respect to the preceding vehicle based on information detected by the sensor device 111. The driving support device 110 determines whether braking is required based on the calculated vehicle distance D and relative speed dV. For example, the driving support device 110 determines that braking is required when the vehicle distance D between the host vehicle and the preceding vehicle becomes less than a braking start threshold D_brk_thr value set according to the vehicle speed V of the host vehicle, the relative speed dV, and the target vehicle distance D_tgt. The target vehicle distance D_tgt may be a variable value set according to the vehicle speed V of the host vehicle. The method of determining whether braking is required by the driving support device 110 is not particularly limited.

[0034] Furthermore, the driving support device 110 calculates the command braking torque T_req_in based on the vehicle speed V of the host vehicle, the relative speed dV, and the difference dD between the inter-vehicle distance D and the target inter-vehicle distance D_tgt. The rate of change in the inter-vehicle distance D when a braking torque is generated in the vehicle may differ depending on the relative speed dV. Furthermore, the braking torque for decelerating the vehicle may differ depending on the vehicle speed V. For this reason, the driving support device 110 may calculate the command braking torque T_req_in by referring to map information in which the command braking torque T_req_in is preset according to the vehicle speed V, the relative speed dV, and the difference dD between the inter-vehicle distance. Note that the method of calculating the command braking torque T_req_in by the driving support device 110 is not particularly limited.

[0035] The hydraulic control device 90 basically executes ABS control and ESP control by controlling the driving of the brake hydraulic unit 20. Furthermore, when the hydraulic control device 90 receives an ACC braking request signal from the driving support device 110, it sets a target braking torque T_out based on a command braking torque T_req_in, and converts the target braking torque T_out into a target brake hydraulic pressure P_tgt to control the driving of the brake hydraulic unit 20. In the automatic brake control of the ACC, the hydraulic control device 90 drives at least the pump motor 96 of the brake hydraulic unit 20 to supply brake fluid from the master cylinder 14 to the wheel cylinders of each wheel, thereby increasing the brake hydraulic pressure of each wheel and generating a braking force for the vehicle.

[0036] The hydraulic control device 90 includes a target braking torque setting unit 91 and a control unit 93. The target braking torque setting unit 91 and the control unit 93 are functions realized by a microcomputer executing a program. In addition, the hydraulic control device 90 includes a drive circuit and storage elements such as a RAM (Random Access Memory) and a ROM (Read Only Memory), which are not shown.

[0037] The hydraulic control device 90 is configured to be able to receive a braking request signal transmitted from the driving support device 110. The hydraulic control device 90 is also configured to be able to acquire information on the acceleration G in the longitudinal direction of the vehicle. The hydraulic control device 90 may acquire the information on the acceleration G by directly receiving a sensor signal from a wheel speed sensor provided in the vehicle and differentiating the detected value, or may acquire the information on the acceleration G transmitted from another control device via the communication bus 120.

[0038] The vehicle acceleration G calculated based on the detection value of the wheel speed sensor indicates a positive value when the vehicle is accelerating in the forward direction. In other words, the vehicle deceleration Ax means negative acceleration G. Therefore, when the deceleration Ax exceeds a predetermined limit value Ax_lim, it means that the acceleration G falls below a value obtained by inverting the positive and negative of the predetermined limit value Ax_lim (positive value).

[0039] The target braking torque setting unit 91 sets the target braking torque T_out based on information on the command braking torque T_req_in included in the braking request signal transmitted from the driving support device 110. The target braking torque setting unit 91 sets the target braking torque T_out so that the vehicle deceleration Ax does not exceed a predetermined limit value Ax_lim for a long period of time. The limit value Ax_lim is an upper limit value of the deceleration Ax that is set to prevent the vehicle behavior from becoming unstable due to the automatic brake control of the ACC, and is set to, for example, 4.8 to 5.0 m / s 2 The value is set to a value in the range.

[0040] Specifically, when the deceleration Ax of the host vehicle is equal to or smaller than a predetermined limit value Ax_lim, the target braking torque setting unit 91 sets the command braking torque T_req_in as the target braking torque T_out. On the other hand, when the deceleration Ax exceeds the predetermined limit value Ax_lim, the target braking torque setting unit 91 turns on the braking torque limit mode, calculates a limit braking torque T_lim that is smaller than the command braking torque T_req_in, and sets the limit braking torque T_lim as the target braking torque T_out. In other words, while the driving assistance device 110 calculates the command braking torque T_req_in (N·m) as a target value for decelerating the vehicle, the target braking torque setting unit 91 calculates the vehicle deceleration Ax (m / s) in a different unit. 2 ) is used to limit the braking torque. This reduces the risk that the deceleration Ax will exceed the limit value Ax_lim for a long period of time, even if the braking force generated varies depending on the vehicle running conditions, and makes it possible to suppress instability in the vehicle body behavior.

[0041] The calculation method of the limited braking torque T_lim is not particularly limited. For example, when the deceleration Ax of the vehicle exceeds a predetermined limit value Ax_lim, the target braking torque setting unit 91 may calculate the limited braking torque T_lim by decreasing the command braking torque T_req_in at a constant decreasing rate. Specifically, when the deceleration Ax of the vehicle exceeds the predetermined limit value Ax_lim, the target braking torque setting unit 91 sets the limited braking torque T_lim obtained by subtracting a preset constant correction value T_x from the value of the command braking torque T_req_in as the target braking torque T_out. In addition, the target braking torque setting unit 91 sets the limited braking torque T_lim obtained by subtracting the correction value T_x from the target braking torque T_out of the previous cycle as the target braking torque T_out for each subsequent calculation cycle. The correction value T_x in this case is set to an appropriate value so as not to suddenly decrease the deceleration Ax. By calculating the limit braking torque T_lim in this manner, it is possible to easily limit the braking torque without increasing the calculation load on the hydraulic control device 90. In addition, since the deceleration Ax of the vehicle is not suddenly decreased, it is possible to prevent the inter-vehicle distance D from the preceding vehicle from becoming too small.

[0042] However, the method of calculating the limited braking torque T_lim is not limited to the method of subtracting a fixed correction value T_x. For example, the correction value T_x may be a value that varies depending on the deceleration state of the vehicle. Specifically, the correction value T_x may be set to a larger value as the difference between the vehicle deceleration Ax and the predetermined limit value Ax_lim increases. This makes it possible to suppress the vehicle deceleration Ax to be equal to or less than the predetermined limit value Ax_lim more quickly than in the case of subtracting a fixed correction value T_x.

[0043] In this embodiment, the target braking torque setting unit 91 is configured to compare the deceleration Ax of the vehicle with the limit value Ax_lim when the deceleration Ax exceeds a control start threshold value Ax_0 set to a value smaller than the limit value Ax_lim, and to limit the braking torque when the deceleration Ax exceeds the limit value Ax_lim. This reduces the calculation load of the hydraulic control device 90 during the period when the deceleration Ax is small and it is not necessary to limit the braking torque.

[0044] Furthermore, the target braking torque setting unit 91 may start the braking torque limit mode when the state in which the deceleration Ax of the vehicle exceeds the limit value Ax_lim continues for a predetermined time t_thr_st or more. This prevents the braking torque from being limited when the deceleration Ax exceeds the limit value Ax_lim in a very short time, and prevents the braking torque from being limited more than necessary, causing the inter-vehicle distance D to become too small. The predetermined time t_thr_st is set to an appropriate value in advance by simulation or the like.

[0045] Furthermore, the target braking torque setting unit 91 may end the braking torque limit mode when the deceleration Ax of the vehicle exceeds the limit value Ax_lim and the deceleration Ax remains equal to or less than the limit value Ax_lim for a predetermined time t_thr_fn or more. This makes it possible to delay the timing for ending the braking torque limit, and to prevent the deceleration Ax, which has become equal to or less than the limit value Ax_lim, from exceeding the limit value Ax_lim again due to the end of the braking torque limit. The predetermined time t_thr_fn is set to an appropriate value in advance by simulation or the like.

[0046] Furthermore, after the braking torque limit mode is terminated, the target braking torque setting unit 91 may hold the limited braking torque T_lim until the command braking torque T_req_in output from the driving assistance device 110 becomes equal to or less than the target braking torque T_out (i.e., limited braking torque T_lim) set in the previous calculation cycle at the time of termination of the braking torque limit mode, and may hold this limited braking torque T_lim as the target braking torque T_out. This makes it possible to prevent the target braking torque T_out from rising sharply when the braking torque limit mode is terminated, and to transition to a state in which the command braking torque T_req_in is set to the target braking torque T_out without significantly changing the target braking torque T_out.

[0047] During execution of ABS control or ESP control, the vehicle deceleration Ax obtained by differentiating the detection value of the wheel speed sensor may become excessively large, and the reliability of the value of the deceleration Ax may decrease. For this reason, during execution of ABS control or ESP control, the target braking torque setting unit 91 sets the target braking torque T_out without using information on the deceleration Ax. For example, the target braking torque setting unit 91 compares the value of the command braking torque T_req_in output from the driving support device 110 with the value of the target braking torque T_out set in the previous calculation cycle, and sets the smaller of the two as the target braking torque T_out for the current calculation cycle.

[0048] The control unit 93 controls the driving of the brake hydraulic pressure unit 20 based on the target braking torque T_out set by the target braking torque setting unit 91. This controls the braking force of the vehicle. In this embodiment, the control unit 93 calculates a target brake hydraulic pressure P_tgt to be generated in each wheel based on the target braking torque T_out, and controls the driving of the pump motor 96 of the brake hydraulic pressure unit 20.

[0049] For example, the control unit 93 may determine a target brake fluid pressure P_tgt corresponding to the target braking torque T_out by referring to map information in which the relationship between the target braking torque T_out and the target brake fluid pressure P_tgt is preset. The control unit 93 sets a target flow rate V_tgt of the brake fluid to be supplied from the master cylinder 14 to the brake fluid pressure unit 20 based on the calculated target brake fluid pressure P_tgt. For example, the control unit 93 may set the target flow rate V_tgt of the brake fluid by referring to map information in which the relationship between the target brake fluid pressure P_tgt and the target flow rate V_tgt is preset.

[0050] The control unit 93 may set the target flow rate V_tgt according to the difference dP between the current brake fluid pressure P_act and the target brake fluid pressure P_tgt. The current brake fluid pressure P_act may alternatively use a pressure value detected by the fluid pressure sensor 24. If a brake fluid pressure sensor that detects the brake fluid pressure of any of the wheel cylinders is provided in addition to the fluid pressure sensor 24, the pressure value detected by the brake fluid pressure sensor may be used instead of the fluid pressure sensor 24.

[0051] The control unit 93 outputs a control signal to a drive circuit of the pump motor 96 of the brake hydraulic unit 20 in accordance with the set target flow rate V_tgt to drive the pumps 44a, 44b. This causes brake fluid to be supplied from the master cylinder 14 into the brake hydraulic unit 20, and the brake fluid is supplied to the wheel cylinders of each wheel. As a result, the brake fluid pressure of each wheel increases, and a braking force of the vehicle is generated. As described above, in the braking torque limit mode, when the deceleration Ax of the vehicle exceeds the limit value Ax_lim, the braking torque is limited, thereby reducing the possibility that the deceleration Ax will exceed the limit value Ax_lim for a long period of time.

[0052] (1-2-2. Example of operation) Next, a specific example of the operation of the hydraulic pressure control device 90 as the vehicle brake control device according to this embodiment will be described.

[0053] Figures 3 and 4 are flowcharts showing brake control processing executed by the hydraulic control device 90 while ACC is being executed. Figure 3 is a flowchart showing a main routine of the brake control processing executed by the hydraulic control device 90 while ACC is being executed. Figure 4 is a flowchart showing a routine of target braking torque setting processing. The brake control processing described below is always executed while ACC is being executed.

[0054] As shown in Fig. 3, first, the target braking torque setting unit 91 of the hydraulic control device 90 determines whether or not a braking request signal has been received from the driving support device 110 (step S11). If a braking request signal has not been received (S11 / No), the target braking torque setting unit 91 ends this routine and returns to the start. On the other hand, if a braking request signal has been received (S11 / Yes), the target braking torque setting unit 91 sets the target braking torque T_out based on the command braking torque T_req_in included in the braking request signal (step S13). The process of setting the target braking torque T_out is performed according to the flowchart shown in Fig. 4.

[0055] In the flowchart shown in Fig. 4, "(n)" indicates a value acquired or calculated in the current calculation cycle, and "(n-1)" indicates a value calculated in the previous calculation cycle. First, the target braking torque setting unit 91 acquires information on the deceleration Ax(n) of the vehicle, and determines whether the deceleration Ax(n) exceeds the control start threshold Ax_0 (step S21). If the deceleration Ax(n) does not exceed the control start threshold Ax_0 (S21 / No), the deceleration Ax is unlikely to exceed the limit value Ax_lim, so the target braking torque setting unit 91 sets the command braking torque T_req_in(n) included in the braking request signal received from the driving support device 110 as the target braking torque T_out(n) as it is (step S43).

[0056] On the other hand, if the deceleration Ax(n) exceeds the control start threshold Ax_0 (S21 / Yes), the target braking torque setting unit 91 calculates a difference dA(n) by subtracting the limit value Ax_lim from the deceleration Ax(n) (step S23). Next, the target braking torque setting unit 91 determines whether the difference dA(n) is a positive value (step S25). In step S25, it is determined whether the vehicle deceleration Ax(n) exceeds the limit value Ax_lim.

[0057] When the difference dA(n) is a positive value (S25 / Yes), that is, when the deceleration Ax(n) exceeds the limit value Ax_lim, the target braking torque setting unit 91 turns on the braking torque limit mode (step S27). At this time, the target braking torque setting unit 91 may turn on the braking torque limit mode when a predetermined time t_thr_st has elapsed since the deceleration Ax(n) exceeded the limit value Ax_lim. When the braking torque limit mode is on, the target braking torque setting unit 91 calculates the limited braking torque T_lim(n) (step S29). In the example of this embodiment, the target braking torque setting unit 91 calculates the limited braking torque T_lim(n) by subtracting a constant correction value T_x set in advance from the target braking torque T_out(n-1) set in the previous cycle. Next, the target braking torque setting unit 91 sets the calculated limit braking torque T_lim(n) as the target braking torque T_out(n) (step S31).

[0058] On the other hand, if the difference dA(n) is not a positive value (S25 / No), the target braking torque setting unit 91 determines whether or not the braking torque limit mode is currently on (step S33). If the braking torque limit mode is not on (S33 / No), the target braking torque setting unit 91 sets the command braking torque T_req_in(n) included in the braking request signal received from the driving support device 110 as the target braking torque T_out(n) as it is (step S43).

[0059] On the other hand, when the braking torque limit mode is on (S33 / Yes), the target braking torque setting unit 91 determines whether or not a predetermined time t_thr_fn has elapsed since the difference dA(n) became a value equal to or less than 0 (step S35). This predetermined time t_thr_fn is set in order to delay the timing of ending the braking torque limit, in order to prevent the deceleration Ax, which has become equal to or less than the limit value Ax_lim, from exceeding the limit value Ax_lim again due to the end of the braking torque limit.

[0060] If the predetermined time t_thr_fn has not elapsed since the difference dA(n) became equal to or less than 0 (S35 / No), the target braking torque setting unit 91 calculates the limited braking torque T_lim(n) by subtracting a preset constant correction value T_x from the target braking torque T_out(n-1) set in the previous cycle (step S29). Next, the target braking torque setting unit 91 sets the calculated limited braking torque T_lim(n) to the target braking torque T_out(n) (step S31).

[0061] In the method of calculating the limited braking torque T_lim(n) in this embodiment, in the first cycle in which the braking torque limit mode is switched from off to on, the target braking torque T_out(n-1) set in the previous cycle is the command braking torque T_req_in(n-1), so the limited braking torque T_lim(n) is the command braking torque T_req_in(n-1) minus the correction value T_x. Also, while the braking torque limit mode continues, the limited braking torque T_lim(n) is the target braking torque T_out(n-1) set in the previous cycle minus the correction value T_x. Therefore, while the braking torque limit mode is on, the limited braking torque T_lim is calculated by decreasing the command braking torque T_req_in at a constant decreasing speed.

[0062] On the other hand, if the predetermined time t_thr_fn has elapsed since the difference dA(n) became a value equal to or less than 0 (S35 / Yes), the target braking torque setting unit 91 turns off the braking torque limit mode (step S37). Next, the target braking torque setting unit 91 determines whether the command braking torque T_req_in(n) is greater than the target braking torque T_out(n-1) set in the previous cycle (step S39). If the command braking torque T_req_in(n) is greater than the target braking torque T_out(n-1) (S39 / Yes), even though the deceleration Ax is below the limit value Ax_lim, the target braking torque setting unit 91 retains the target braking torque T_out(n-1) set in the previous cycle as the target braking torque T_out(n-1) for the current cycle to prevent the deceleration Ax from exceeding the limit value Ax_lim again due to the target braking torque T_out increasing as a result of ending the braking torque limit (step S41).

[0063] On the other hand, if the command braking torque T_req_in(n) is equal to or less than the target braking torque T_out(n-1) (S39 / No), the command braking torque T_req_in(n) has a value equivalent to the limit braking torque T_lim(n-1), and the deceleration Ax can be suppressed even if the command braking torque T_req_in(n) is directly set as the target braking torque T_out(n). Therefore, the target braking torque setting unit 91 sets the command braking torque T_req_in(n) included in the braking request signal received from the driving support device 110 as the target braking torque T_out(n) (step S43).

[0064] 3, after the target braking torque T_out is set in step S13, the control unit 93 calculates a target brake fluid pressure P_tgt based on the target braking torque T_out (step S15). For example, the control unit 93 refers to map information in which a relationship between the target braking torque T_out and the target brake fluid pressure P_tgt is preset, and determines the target brake fluid pressure P_tgt corresponding to the target braking torque T_out.

[0065] Next, the control unit 93 controls the driving of the actuator of the brake hydraulic unit 20 based on the calculated target brake hydraulic pressure P_tgt (step S17). Specifically, the control unit 93 sets a target flow rate V_tgt of brake fluid to be supplied from the master cylinder 14 to the brake hydraulic unit 20 based on the calculated target brake hydraulic pressure P_tgt, and controls the driving of the pump motor 96 of the brake hydraulic unit 20. For example, the control unit 93 may set the target flow rate V_tgt of brake fluid by referring to map information in which the relationship between the target brake hydraulic pressure P_tgt and the target flow rate V_tgt is preset.

[0066] This increases the brake fluid pressure in the wheel cylinder of each wheel, and generates a braking force for the vehicle. In this embodiment, when the deceleration Ax exceeds the limit value Ax_lim and the braking torque limit mode is set, the command braking torque T_req_in calculated by the driving support device 110 is not used as is, but the limit braking torque T_lim, which is set to a value smaller than the command braking torque T_req_in, is set as the target braking torque T_out. This reduces the risk that the deceleration Ax of the vehicle will exceed the limit value Ax_lim for a long period of time. This makes it possible to control the distance from the preceding vehicle to a predetermined target distance while suppressing the vehicle behavior from becoming unstable during the execution of ACC.

[0067] During execution of ABS control or ESP control, the target braking torque setting unit 91 sets the target braking torque T_out without using information on the deceleration Ax. For example, the target braking torque setting unit 91 compares the value of the command braking torque T_req_in(n) output from the driving support device 110 with the value of the target braking torque T_out(n-1) set in the previous calculation cycle, and sets the smaller one as the target braking torque T_out(n) for the current calculation cycle. During execution of ABS control or ESP control, the deceleration Ax of the vehicle obtained by differentiating the detection value of the wheel speed sensor may become excessively large, and the reliability of the value of the deceleration Ax may decrease. Therefore, by setting the target braking torque T_out without using information on the deceleration Ax during execution of ABS control or ESP control, it is possible to reduce the risk of the vehicle behavior becoming unstable.

[0068] (1-2-3. Effect) Next, the operation of the brake control process executed by the hydraulic pressure control device 90 according to this embodiment will be described.

[0069] FIG. 5 is a diagram for explaining the action of the brake control process executed by the hydraulic control device 90 according to this embodiment, and shows the target braking torque T_out that is set during execution of ACC, and the change over time of the vehicle deceleration Ax.

[0070] At time t1 when the inter-vehicle distance between the host vehicle and the preceding vehicle falls below the target inter-vehicle distance or is about to fall below the target inter-vehicle distance, the driving assistance device 110 starts transmitting a braking request signal to the hydraulic control device 90. After time t1, the command braking torque T_req_in increases, and the driving of the brake hydraulic unit 20 is controlled with the command braking torque T_req_in set as the target braking torque T_out, thereby increasing the deceleration Ax of the vehicle.

[0071] At time t2 when the deceleration Ax exceeds the control start threshold Ax_0, the target braking torque setting unit 91 starts calculating the difference dA obtained by subtracting the limit value Ax_lim from the deceleration Ax. The deceleration Ax further increases, and at time t3 when the deceleration Ax exceeds the limit value Ax_lim, the target braking torque setting unit 91 starts counting the timer. At time t4 before the elapsed time from time t3 reaches a predetermined time t_thr_st, the increase in the command braking torque T_req_in ends, and thereafter the value of the command braking torque T_req_in is held at a constant value. Accordingly, at time t4, the vehicle deceleration Ax becomes equal to or less than the limit value Ax_lim, and the target braking torque setting unit 91 resets the timer value.

[0072] After that, when the deceleration Ax exceeds the limit value Ax_lim again at time t5, the target braking torque setting unit 91 starts a timer count. At time t6 when the time elapsed from time t5 reaches a predetermined time t_thr_st in a state where the deceleration Ax exceeds the limit value Ax_lim, the target braking torque setting unit 91 turns on the braking torque limit mode and sets the limited braking torque T_lim, which is set to a value smaller than the command braking torque T_req_in, to the target braking torque T_out. In the example shown in FIG. 5, the command braking torque T_req_in at time t6 when the braking torque limit mode is turned on is reduced at a constant reduction rate to the limited braking torque T_lim, and the limited braking torque T_lim is set to the target braking torque T_out.

[0073] As the braking torque is limited, the vehicle deceleration Ax starts to decrease, and at time t7 when the deceleration Ax reaches the limit value Ax_lim, the target braking torque setting unit 91 starts counting a timer. At time t8 when the time elapsed from time t7 reaches a predetermined time t_thr_fn with the deceleration Ax being equal to or less than the limit value Ax_lim, the target braking torque setting unit 91 turns off the braking torque limit mode, and holds the target braking torque T_out (i.e., the limited braking torque T_lim) set in the previous calculation cycle at that time, and sets this as the target braking torque T_out. Note that the magnitude relationship between the predetermined time t_thr_st set for turning on the braking torque limit mode and the predetermined time t_thr_fn set for turning off the braking torque limit mode is not particularly limited.

[0074] Thereafter, as the inter-vehicle distance between the host vehicle and the preceding vehicle approaches the target inter-vehicle distance, the command braking torque T_req_in decreases, and at time t9, the command braking torque T_req_in becomes equal to or less than the target braking torque T_out (limited braking torque T_lim), so the target braking torque setting unit 91 ends the calculation of the limited braking torque T_lim and returns the command braking torque T_req_in to the target braking torque T_out as is. Then, at time t10, the transmission of the braking request signal from the driving support device 110 is stopped, and the hydraulic control device 90 stops driving the brake hydraulic unit 20.

[0075] As shown by the dashed line in Fig. 5, if the braking torque is not limited and the command braking torque T_req_in is set as the target braking torque T_out to control the driving of the brake hydraulic unit 20, after the deceleration Ax exceeds the limit value Ax_lim at time t5, the deceleration Ax_def continues to exceed the limit value Ax_lim even if the command braking torque T_req_in itself decreases. If the deceleration Ax_def continues to exceed the limit value Ax_lim for a long period of time, the vehicle may suddenly decelerate, causing the vehicle behavior to become unstable. In contrast, in this embodiment, the braking torque is limited when the deceleration Ax of the vehicle exceeds the limit value Ax_lim, so that the risk of the deceleration Ax exceeding the limit value Ax_lim for a long period of time is reduced, and the vehicle behavior can be prevented from becoming unstable.

[0076] <1-3.Effects> As described above, according to this embodiment, when the deceleration Ax of the host vehicle exceeds the limit value Ax_lim, the target braking torque setting unit 91 of the hydraulic control device 90 sets the limit braking torque T_lim, which is smaller than the command braking torque T_req_in transmitted from the driving support device 110, to the target braking torque T_out. Furthermore, the control unit 93 controls the driving of the pump motor 96 of the brake hydraulic unit 20 in accordance with the set target braking torque T_out. This reduces the risk that the deceleration Ax of the vehicle will exceed the limit value Ax_lim for a long period of time, and makes it possible to suppress the vehicle body behavior from becoming unstable due to sudden deceleration.

[0077] Furthermore, according to this embodiment, the target braking torque setting unit 91 calculates the limited braking torque T_lim by decreasing the command braking torque T_req_in at a constant rate of decrease when the braking torque limit mode is turned on. This makes it possible to easily limit the braking torque without increasing the calculation load on the hydraulic control device 90. Also, since the deceleration Ax of the vehicle is not suddenly decreased, it is possible to prevent the inter-vehicle distance D from the preceding vehicle from becoming too small.

[0078] According to this embodiment, when the state in which the deceleration Ax is equal to or less than the limit value Ax_lim continues for a predetermined time t_thr_fn or more, the target braking torque setting unit 91 turns off the braking torque limit mode, holds the target braking torque T_out (i.e., the limited braking torque T_lim) set in the previous calculation cycle at that time, and sets this as the target braking torque T_out. This makes it possible to delay the timing for ending the limit of the braking torque, and to prevent the deceleration Ax, which has become equal to or less than the limit value Ax_lim, from exceeding the limit value Ax_lim again due to the end of the limit of the braking torque.

[0079] According to this embodiment, when the state in which the deceleration Ax of the vehicle exceeds the limit value Ax_lim continues for a predetermined time t_thr_st or more, the target braking torque setting unit 91 turns on the braking torque limit mode and sets the limit braking torque T_lim to the target braking torque T_out. This prevents the braking torque from being limited when the deceleration Ax exceeds the limit value Ax_lim in a very short time, and prevents the braking torque from being limited more than necessary and the inter-vehicle distance D from the preceding vehicle from becoming too small.

[0080] Furthermore, according to this embodiment, the target braking torque setting unit 91 ends setting the limited braking torque T_lim as the target braking torque T_out when the command braking torque T_req_in becomes equal to or less than the limited braking torque T_lim after the braking torque limit mode is turned on. This makes it possible to prevent the target braking torque T_out from rising sharply when the braking torque limit mode is ended, and to transition to a state in which the command braking torque T_req_in is set to the target braking torque T_out without significantly changing the target braking torque T_out.

[0081] Furthermore, according to this embodiment, when the deceleration Ax exceeds a control start threshold value Ax_0 that is smaller than the limit value Ax_lim, the target braking torque setting unit 91 compares the deceleration Ax with the limit value Ax_lim, and when the deceleration Ax exceeds the limit value Ax_lim, sets the limited braking torque T_lim to the target braking torque T_out. This reduces the calculation load of the hydraulic control device 90 during the period when the deceleration Ax is small and it is not necessary to limit the braking torque.

[0082] <<2. Second embodiment>> Next, a second embodiment of the present invention will be described. In the second embodiment, a booster control device 100 that controls an electric booster 10 receives a braking request signal transmitted from a driving support device 110, and functions as a vehicle braking control device that controls the braking force so that the deceleration of the vehicle does not exceed a predetermined limit value for a long period of time.

[0083] The brake system 1 according to this embodiment can be configured similarly to the brake system 1 described in the first embodiment, except that the vehicle brake control device that executes the automatic brake control of the ACC is the booster control device 100. Below, differences from the first embodiment will be mainly described.

[0084] 6 is a block diagram showing a functional configuration related to the automatic brake control of the ACC in the configuration of the brake system 1. In this embodiment, the automatic brake control of the ACC is executed by the driving assistance device 110 and the booster control device 100 communicating with each other and the booster control device 100 controlling the booster 10.

[0085] As in the first embodiment, while ACC is being executed, the driving assistance device 110 determines whether braking is necessary and calculates the command braking torque T_req_in based on information detected by sensor devices 111 such as cameras, radar, RiDAR, etc., and transmits a braking request signal indicating information on the braking request S_brk and the command braking torque T_req_in to the booster control device 100.

[0086] When the booster control device 100 receives an ACC braking request signal from the driving support device 110, it sets a target braking torque T_out based on a command braking torque T_req_in, and converts the target braking torque T_out into a target brake fluid pressure P_tgt to control the drive of the booster 10. Specifically, the booster control device 100 drives the electric motor of the booster 10 to pressurize the brake fluid in the master cylinder 14, and supplies brake fluid from the master cylinder 14 to the wheel cylinders of each wheel to increase the brake fluid pressure of each wheel, thereby generating a braking force for the vehicle.

[0087] The booster control device 100 includes a target braking torque setting unit 101 and a control unit 103. The target braking torque setting unit 101 and the control unit 103 are functions realized by a microcomputer executing a program. In addition, the booster control device 100 includes a drive circuit and memory elements such as a RAM and a ROM, which are not shown.

[0088] The target braking torque setting unit 101 is configured similarly to the target braking torque setting unit 91 of the hydraulic control device 90 described in the first embodiment. That is, the target braking torque setting unit 101 sets the target braking torque T_out so that the deceleration Ax of the vehicle does not exceed a predetermined limit value Ax_lim for a long period of time, based on information on the command braking torque T_req_in included in the braking request signal transmitted from the driving support device 110 and information on the acceleration G. A specific calculation method of the target braking torque T_out may be the same as that of the target braking torque setting unit 91 of the hydraulic control device 90 described in the first embodiment.

[0089] The control unit 103 controls the drive of the booster 10 based on the target braking torque T_out set by the target braking torque setting unit 101. This controls the braking force of the vehicle. In this embodiment, the control unit 103 calculates a target brake fluid pressure P_tgt to be generated in each wheel based on the target braking torque T_out, and controls the drive of the electric motor of the booster 10 to advance the push rod 13 into the master cylinder 14.

[0090] The control unit 103, like the control unit 93 of the hydraulic control device 90 described in the first embodiment, determines the target brake hydraulic pressure P_tgt based on the target braking torque T_out, for example by referring to map information, and sets a target flow rate V_tgt of brake fluid to be supplied from the master cylinder 14 to the brake hydraulic unit 20 based on the target brake hydraulic pressure P_tgt.

[0091] The control unit 103 outputs a control signal to a drive circuit of the electric motor of the booster 10 according to the set target flow rate V_tgt, and moves the push rod 13 forward. This pressurizes the brake fluid in the primary chamber 47 and the secondary chamber 48, and the brake fluid is supplied from the master cylinder 14 into the brake fluid pressure unit 20, and the brake fluid is supplied to the wheel cylinders of each wheel. As a result, the brake fluid pressure of each wheel increases, and a braking force is generated for the vehicle. In the present embodiment, too, in the braking torque limit mode, the braking torque is limited when the deceleration Ax of the vehicle exceeds the limit value Ax_lim, so that the risk of the deceleration Ax exceeding the limit value Ax_lim for a long period of time is reduced.

[0092] The operation examples and actions of the booster control device 100 as a vehicle braking control device in this embodiment are the same as those described in the first embodiment, except that the actuator to be driven is the electric motor of the booster 10 rather than the pump motor 96 of the brake hydraulic unit 20, and therefore detailed explanations will be omitted.

[0093] As described above, according to this embodiment, when the deceleration Ax of the host vehicle exceeds the limit value Ax_lim, the target braking torque setting unit 101 of the booster control device 100 sets the limit braking torque T_lim, which is smaller than the command braking torque T_req_in transmitted from the driving support device 110, to the target braking torque T_out. Furthermore, the control unit 103 controls the driving of the electric motor of the booster 10 in accordance with the set target braking torque T_out. The booster control device 100 according to this embodiment can provide the same effects as those provided by the first embodiment.

[0094] Furthermore, according to this embodiment, the booster 10 is driven to supply brake fluid from the master cylinder 14 to the brake hydraulic unit 20, thereby increasing the brake hydraulic pressure in the wheel cylinder of each wheel. Therefore, the responsiveness until the generation of braking force can be improved compared to the case where the pump motor 96 of the brake hydraulic unit 20 is driven to supply brake fluid from the master cylinder 14 to the brake hydraulic unit 20.

[0095] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0096] 10...electric booster, 13...push rod, 14...master cylinder, 20...brake hydraulic unit, 43...primary piston, 44...secondary piston, 47...primary chamber, 48...secondary chamber, 90...hydraulic pressure control device, 91...target braking torque setting unit, 93...control unit, 100...booster control device, 101...target braking torque setting unit, 103...control unit, 110...driving assistance device

Claims

1. a target braking torque setting unit (91, 101) for setting a target braking torque (T_out) based on braking request information (T_req_in) that is set based on a target inter-vehicle distance between the host vehicle and a preceding vehicle; a control unit (93, 103) that controls the braking force of the host vehicle based on the target braking torque (T_out); the target braking torque setting unit (91, 101) sets a limit braking torque (T_lim) having a value smaller than a braking torque corresponding to the braking request information (T_req_in) to the target braking torque (T_out) when the deceleration (Ax) of the host vehicle exceeds a predetermined limit value (Ax_lim). A vehicle braking control device.

2. The braking request information is a command braking torque (T_req_in), The target braking torque setting unit (91, 101) calculates the limit braking torque (T_lim) by reducing the command braking torque (T_req_in) at a constant reduction rate. The vehicle brake control device according to claim 1.

3. the target braking torque setting unit (91, 101) holds the value of the limited braking torque (T_lim) when a state in which the deceleration (Ax) is equal to or less than the predetermined limit value (Ax_lim) continues for a predetermined time (t_thr_fn) or more. The vehicle brake control device according to claim 2.

4. the target braking torque setting unit (91, 101) sets the limit braking torque (T_lim) to the target braking torque (T_out) when a state in which the deceleration (Ax) exceeds the predetermined limit value (Ax_lim) continues for a predetermined time (t_thr_st) or more. The vehicle braking control device according to any one of claims 1 to 3.

5. The braking request information is a command braking torque (T_req_in), the target braking torque setting unit (91, 101) terminates setting the limit braking torque (T_lim) as the target braking torque (T_out) when the command braking torque (T_req_in) becomes equal to or less than the limit braking torque (T_lim) which is set as the target braking torque (T_out). The vehicle brake control device according to any one of claims 1 to 4.

6. the target braking torque setting unit (91, 101) compares the deceleration (Ax) of the host vehicle with the predetermined limit value (Ax_lim) when the deceleration (Ax) exceeds a control start threshold value (Ax_0) which is smaller than the predetermined limit value (Ax_lim), and sets the limit braking torque (T_lim) to the target braking torque (T_out) when the deceleration (Ax) exceeds the predetermined limit value (Ax_lim). The vehicle braking control device according to any one of claims 1 to 5.

7. The vehicle braking control device is a control device (90) for a brake hydraulic unit (20), the target braking torque setting unit (91) receives a braking request signal transmitted from a driving assistance device (110) that outputs information (T_req_in) on the braking request based on the target inter-vehicle distance and sets the target braking torque (T_out); The control unit (93) controls the brake hydraulic unit (20) based on the target braking torque (T_out). The vehicle brake control device according to any one of claims 1 to 6.

8. The vehicle braking control device is a control device (100) for an electric booster (10), the target braking torque setting unit (101) receives a braking request signal transmitted from a driving assistance device (110) that outputs the braking request information (T_req_in) based on the target inter-vehicle distance, and sets the target braking torque (T_out); The control unit (103) controls the electric booster (10) based on the target braking torque (T_out). The vehicle brake control device according to any one of claims 1 to 6.

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