Brake control device for a vehicle

Abstract

Provided is a brake control device for a vehicle that can reduce the likelihood that the deceleration of the vehicle will exceed a predetermined limit value for a long time due to an automatic brake function of an ACC. The brake control device for the vehicle includes a target brake torque setting section (91, 101) that sets a target brake torque (T_out) based on a brake request (T_req_in) that is set based on a target inter-vehicle distance between the host vehicle and a preceding vehicle, and a control section (93, 103) that controls the braking force of the vehicle based on the target brake torque (T_out). The target brake torque setting section (91, 101) sets a limit brake torque (T_lim) that is a value smaller than the indicated brake torque (T_req_in) as the target brake torque (T_out) when the deceleration (Ax) of the host vehicle exceeds a predetermined limit value (Ax_lim).

Description

Technical Field

[0001] This invention relates to a braking control device for vehicles. Background Technology

[0002] Modern vehicles are equipped with automatic braking functions. Automatic braking functions, also known as ADAS (Advanced Driver-Assistance System), are driver assistance devices that, based on information detected by cameras and sensors mounted on the vehicle, transmit braking requirements to the brake hydraulic control unit, automatically increasing brake fluid pressure. Known automatic braking functions include ACC (Adaptive Cruise Control), which maintains a target distance from preceding vehicles while automatically moving the vehicle; and emergency braking functions, which prevent collisions with obstacles or mitigate impacts.

[0003] Specifically, in the automatic braking function, the driver assistance device (ADAS) determines whether braking is necessary and calculates the required braking torque based on information detected by cameras and sensors. It then transmits signals indicating the braking requirement and braking torque to the brake hydraulic control device. The brake hydraulic control device receives these signals from the ADAS and switches the control mode accordingly to the type of automatic braking or emergency braking function of the ACC. It converts the received braking torque information into brake hydraulic pressure and transmits the drive command to the actuator that regulates the brake hydraulic pressure. This causes the electric motor in the brake hydraulic control device to operate, increasing the brake hydraulic pressure at each wheel and generating braking force.

[0004] Patent document 1: Japanese Patent Application Publication No. 2018-227532.

[0005] Here, in the ACC automatic braking function, unlike the emergency braking function, in order to suppress vehicle instability caused by sudden deceleration, it is required to control the deceleration to not exceed a predetermined limit as much as possible. In contrast, it is considered to set an upper limit for the braking torque set by the driver assistance device. However, the braking force generated by the vehicle is affected by various factors, so if only the braking torque set by the driver assistance device is limited, there is a possibility that the deceleration will exceed the limit for a long time. Summary of the Invention

[0006] The present invention was made in view of the above-mentioned problems, and provides a vehicle braking control device that can reduce the possibility that the vehicle deceleration will exceed a predetermined limit for a long time due to the automatic braking function of ACC.

[0007] To solve the above problems, according to a certain aspect of the present invention, a vehicle braking control device is provided, comprising a target braking torque setting unit and a control unit. The target braking torque setting unit sets a target braking torque based on braking requirement information, which is set based on a target inter-vehicle distance between the vehicle and a preceding vehicle. The control unit controls the braking force of the vehicle based on the target braking torque. When the deceleration of the vehicle exceeds a predetermined limit value, the target braking torque setting unit sets a limit braking torque that is smaller than the braking torque corresponding to the braking requirement information as the target braking torque.

[0008] Invention Effects

[0009] As explained above, according to the present invention, it is possible to reduce the possibility that the vehicle deceleration will exceed the predetermined limit value for an extended period of time due to the automatic braking function of ACC. Attached Figure Description

[0010] Figure 1 This is an explanatory diagram showing a structural example of a braking system for a vehicle to which the braking control device of the first embodiment of the present invention can be applied.

[0011] Figure 2 This is a block diagram illustrating a structural example of the brake hydraulic control device of the vehicle constituting this embodiment.

[0012] Figure 3 This is a flowchart illustrating an example of the automatic braking control process performed by the braking control device of the vehicle in this embodiment.

[0013] Figure 4 This is a flowchart illustrating an example of the target braking torque setting process performed by the braking control device of the vehicle in this embodiment.

[0014] Figure 5 This is an explanatory diagram illustrating the function of the braking control device of the vehicle in this embodiment.

[0015] Figure 6 This is a block diagram illustrating a structural example of the power assist control device of the braking control device constituting the vehicle of this embodiment. Detailed Implementation

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in this specification and the accompanying drawings, overlapping descriptions are omitted by using the same reference numerals to denote structural elements that substantially have the same functional structure.

[0017] <<1. First Embodiment>>

[0018] <1-1. Example of Braking System Structure>

[0019] First, refer to Figure 1 This section describes a structural example of a braking system for a vehicle to which the braking control device of the first embodiment of the present invention can be applied.

[0020] Figure 1 This is a schematic diagram illustrating a structural example of the braking system 1 of a vehicle. Figure 1 The braking system 1 shown is a braking system for a four-wheeled vehicle. Braking system 1 has two braking systems, each of which uses one front wheel and one rear wheel as a group to form a braking system that controls the braking force.

[0021] Alternatively, braking system 1 can also be an X-type piping system, where two braking systems control the braking force of one of the left and right front wheels and the rear wheel diagonally opposite to that front wheel as a group. Or, braking system 1 can also be an H-type piping system, where one system brakes the left front and rear wheels while other systems brake the right front and rear wheels. Furthermore, the braking system can also be the braking system of a vehicle other than a four-wheeled vehicle.

[0022] The braking system 1 includes a power assist device 10, a master cylinder 14, and a brake hydraulic unit 20. Furthermore, the braking system 1 includes a hydraulic control device 90 that controls the brake hydraulic unit 20 and a power assist device control device 100 that controls the power assist device 10. Part or all of the hydraulic control device 90 and the power assist device control device 100 may be constituted, for example, a microcomputer or microprocessor unit including a central processing unit (CPU). Part or all of the hydraulic control device 90 and the power assist device control device 100 may be constituted by an updatable structure such as firmware, or may be a program module executed according to instructions from the central processing unit, etc.

[0023] The hydraulic control unit 90 and the power steering control unit 100 are configured to communicate with each other via a communication bus 120, such as a controller area network. Furthermore, the hydraulic control unit 90 and the power steering control unit 100 are configured to communicate with the driver assistance device 110 via the communication bus 120. The driver assistance device 110 is configured to acquire information detected by a sensor device 111 used to detect other vehicles, pedestrians, bicycles, obstacles, etc., in front of the vehicle, and the environment in front of the vehicle. The sensor device 111 includes, for example, at least one of a camera, radar, or RiDAR.

[0024] The driving assistance device 110 is configured to at least perform ACC control, which maintains the inter-vehicle distance between the vehicle and the preceding vehicle at a target inter-vehicle distance while enabling the vehicle to move automatically. In this embodiment, the driving assistance device 110 is configured to perform ACC control and emergency braking control, the latter being used to avoid collisions between the vehicle and other vehicles, obstacles, etc., or to mitigate the impact of a collision. The driving assistance device 110 may be configured, for example, as a microcomputer or microprocessor unit including a computing processing device such as a central processing unit or a graphics processing unit (GPU). Part or all of the driving assistance device 110 may be configured as an updatable structure such as firmware, or as a program module executed according to instructions from a central processing unit, etc.

[0025] In the braking system 1, the force applied to the brake pedal 11 is amplified by the booster device 10 and transmitted to the master cylinder 14, which serves as the hydraulic power source. A storage tank 60 for supplying brake fluid to the master cylinder 14 is installed on its upper part. Within the master cylinder 14, two pressurized chambers, namely a first chamber 47 and a second chamber 48, are formed, divided by a first piston 43 and a second piston 44. Corresponding to the driver's operation of pressing the brake pedal 11, the first piston 43 and the second piston 44 are pushed, pressurizing the brake fluid stored in the first chamber 47 and the second chamber 48 respectively, and supplying the brake fluid to the brake hydraulic unit 20.

[0026] The power assist device 10 is connected to the brake pedal 11 via the input shaft 16. The pedal force amplified by the power assist device 10 is transmitted to the master cylinder 14 via the push rod 13 abutting against the first piston 43. Due to the axial movement of the first piston 43, the second piston 44 also moves axially. As a result, the brake fluid in the first chamber 47 and the second chamber 48 is pressurized.

[0027] In this embodiment, an electric power assist device driven by an electric motor is used as the power assist device 10. The electric motor may be, for example, a brushless DC-DC motor comprising a stator as a fixed element and a rotor as a movable element. The electric motor operates by receiving power (current) supplied under the control of the power assist device control device 100. The electric motor is capable of forward rotation (forward rotation) and reverse rotation (backward rotation) of the push rod 13 by switching the direction of current flow. When the driver depresses the brake pedal 11, the power assist device control device 100 supplies power (current) to the stator of the electric motor, thereby assisting the driver in applying pressure to the brake pedal 11 and transmitting this force to the master cylinder 14.

[0028] The first hydraulic circuit 28 and the second hydraulic circuit 30 extend from the first chamber 47 and the second chamber 48 of the master cylinder 14 to the hydraulic brakes 38a-38d of each wheel RF, LR, LF, and RR, respectively. In this embodiment, the hydraulic circuit of the vehicle's braking system 1 is an X-type piping configuration, with brake fluid supplied via the first hydraulic circuit 28 to the wheel cylinders of the hydraulic brake 38a of the right front wheel RF and the hydraulic brake 38b of the left rear wheel LR. Furthermore, brake fluid is supplied via the second hydraulic circuit 30 to the wheel cylinders of the hydraulic brake 38c of the left front wheel LF and the hydraulic brake 38d of the right rear wheel RR. Thus, each hydraulic brake 38a-38d can hydraulically generate braking force for each wheel RF, LR, LF, and RR.

[0029] The brake hydraulic unit 20 includes a first hydraulic circuit 28 and a second hydraulic circuit 30 having the same structure. Brake fluid is supplied from the master cylinder 14 to the first hydraulic circuit 28 and the second hydraulic circuit 30. Hereinafter, the first hydraulic circuit 28 will be briefly described, and the description of the second hydraulic circuit 30 will be omitted.

[0030] The first hydraulic circuit 28 includes a normally open, linearly controllable circuit control valve 36a, a normally closed suction valve 34a controlled by opening and closing, normally open, linearly controllable pressure boosting valves (adjusting valves) 58aa and 58ba, and normally closed pressure reducing valves 54aa and 54ba controlled by opening and closing, which function as solenoid valves. Furthermore, the first hydraulic circuit 28 includes a pump 44a driven by a pump motor 96, a low-pressure accumulator 71a, and a shock absorber 73a. The number of pumps 44a is not limited to one.

[0031] A first pressure-boosting valve 58aa and a first pressure-reducing valve 54aa, located 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-boosting valve 58ba and a second pressure-reducing valve 54ba, located 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.

[0032] A first booster valve 58aa for the right front wheel RF is located between the circuit control valve 36a and the hydraulic brake 38a of the right front wheel RF. The linearly controllable first booster 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 of the right front wheel RF. The first booster valve 58aa has a bypass flow path, which includes a check valve. When the first booster valve 58aa is closed, the check valve allows brake fluid to flow from the hydraulic brake 38a side to the circuit control valve 36a side, while simultaneously restricting its reverse flow.

[0033] The first pressure relief valve 54aa of the right front wheel RF is a solenoid valve that can only switch the valve to a fully open or fully closed state. It is located between the wheel cylinder of the hydraulic brake 38a of the right front wheel RF and the low-pressure accumulator 71a. When the first pressure relief valve 54aa is open, the brake fluid supplied to the wheel cylinder of the hydraulic brake 38a of the right front wheel RF is depressurized. The first pressure relief valve 54aa can regulate the flow rate of brake fluid from the wheel cylinder of the hydraulic brake 38a of the right front wheel RF to the low-pressure accumulator 71a by intermittently repeating the opening and closing of the valve.

[0034] The second booster valve 58ba for the left rear wheel LR is located between the circuit control valve 36a and the hydraulic brake 38b of the left rear wheel LR. The second booster valve 58ba, which can be linearly controlled, continuously adjusts the flow rate of brake fluid from the circuit control valve 36a side towards the wheel cylinder side of the hydraulic brake 38b of the left rear wheel LR. The second booster valve 58ba has a bypass flow path, which includes a check valve. When the second booster valve 58ba is closed, the check valve allows brake fluid to flow from the hydraulic brake 38b side to the circuit control valve 36a side, while simultaneously restricting its reverse flow.

[0035] The second pressure-reducing valve 54ba of the left rear wheel LR is a solenoid valve that can only switch the valve to a fully open or fully closed state. It is located between the wheel cylinder of the hydraulic brake 38b of the left rear wheel LR and the low-pressure accumulator 71a. When the valve is open, the second pressure-reducing valve 54ba reduces the pressure of the brake fluid supplied to the wheel cylinder of the hydraulic brake 38b of the left rear wheel LR. The second pressure-reducing valve 54ba can regulate the flow rate of brake fluid from the wheel cylinder of the hydraulic brake 38b of the left rear wheel LR to the low-pressure accumulator 71a by intermittently repeating the opening and closing of the valve.

[0036] The circuit control valve 36a is configured to connect or disconnect the booster valves 58aa and 58ba from the master cylinder 14. The suction valve 34a is configured to connect or disconnect the master cylinder 14 from the suction side of the pump 44a. A hydraulic sensor 24 is installed on the pipeline between the circuit control valve 36a, the suction valve 34a, and the master cylinder 14. These components are identical to those of the brake hydraulic unit 20, so detailed descriptions are omitted.

[0037] The second hydraulic circuit 30 controls the hydraulic brake 38c of the left front wheel LF and the hydraulic brake 38d of the right rear wheel RR. The second hydraulic circuit 30 is constructed in the same way as the first hydraulic circuit 28, except that the wheel cylinder of the hydraulic brake 38a of the right front wheel RF described in the first hydraulic circuit 28 is replaced with the wheel cylinder of the hydraulic brake 38c of the left front wheel LF, and the wheel cylinder of the hydraulic brake 38b of the left rear wheel LR is replaced with the wheel cylinder of the hydraulic brake 38d of the right rear wheel RR.

[0038] In the braking system 1 configured in this way, when the driver assistance device 110 is executing ACC, if the vehicle gets too close to the preceding vehicle, it generates a signal (hereinafter also referred to as "brake request signal") indicating a braking requirement to maintain the vehicle's distance from the preceding vehicle at a predetermined target distance. In the first embodiment, the hydraulic control device 90 that controls the brake hydraulic unit 20 functions as a braking control device for a vehicle that receives the brake request signal transmitted from the driver assistance device 110 and controls the braking force so that the vehicle's deceleration does not exceed a predetermined limit for an extended period of time.

[0039] <1-2. Vehicle braking control device (hydraulic control device)>

[0040] (1-2-1. Structural Example)

[0041] Figure 2 This is a block diagram showing the functional structure of the braking system 1 associated with the automatic braking control of ACC. In this embodiment, the automatic braking control of ACC is executed by communicating with the driving assistance device 110 and the hydraulic control device 90, and the hydraulic control device 90 controls the brake hydraulic unit 20.

[0042] During ACC execution, the driver assistance device 110 determines whether braking is necessary and calculates the required braking requirement based on information detected by sensors 111 such as cameras, radar, and RiDAR. It then transmits a braking requirement signal, representing the braking requirement and the indicated braking requirement, to the hydraulic control device 90. The indicated braking requirement can be, for example, an indication of braking torque or an indication of braking hydraulic pressure. In this embodiment, the following example will be described: the driver assistance device 110 calculates the indicated braking torque (hereinafter also referred to as "indicated braking torque") T_req_in as the braking requirement indication and transmits a braking requirement signal, representing the braking requirement S_brk and the indicated braking torque T_req_in, to the hydraulic control device 90.

[0043] Specifically, the driving assistance device 110 calculates the inter-vehicle distance D between the vehicle and the preceding vehicle and the relative speed dV of the vehicle relative to the preceding vehicle based on information detected by the sensor device 111. The driving assistance device 110 then determines whether braking is required based on the calculated inter-vehicle distance D and relative speed dV. For example, if the inter-vehicle distance D between the vehicle and the preceding vehicle is less than a braking initiation threshold D_brk_thr set corresponding to the vehicle's speed V, relative speed dV, and target inter-vehicle distance D_tgt, the driving assistance device 110 determines that braking is required. The target inter-vehicle distance D_tgt can also be a variable value set corresponding to the vehicle's speed V. Furthermore, the method by which the driving assistance device 110 determines whether braking is required is not particularly limited.

[0044] Furthermore, the driver assistance device 110 calculates the indicated braking torque T_req_in based on the vehicle speed V, 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 of the inter-vehicle distance D that generates braking torque varies depending on the relative speed dV. Furthermore, the braking torque used to decelerate the vehicle varies depending on the vehicle speed V. Therefore, the driver assistance device 110 can also calculate the indicated braking torque T_req_in by referring to pre-set mapping information corresponding to the vehicle speed V, relative speed dV, and the difference dD between the inter-vehicle distances. Additionally, the calculation method for the indicated braking torque T_req_in performed by the driver assistance device 110 is not particularly limited.

[0045] The hydraulic control unit 90 essentially performs ABS and ESP control by controlling the drive of the brake hydraulic unit 20. Furthermore, upon receiving a braking request signal from the driver assistance device 110, the hydraulic control unit 90 sets a target braking torque T_out based on the indicated braking torque T_req_in, converts the target braking torque T_out into a target brake hydraulic pressure P_tgt, and controls the drive of the brake hydraulic unit 20. In the automatic braking control of ACC, the hydraulic control unit 90 at least drives the pump motor 96 of the brake hydraulic unit 20, supplying brake fluid from the master cylinder 14 to the wheel cylinders of each wheel, causing the brake hydraulic pressure of each wheel to rise and generating braking force for the vehicle.

[0046] 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 implemented by a program executed by a microcomputer. In addition, the hydraulic control device 90 includes a drive circuit (not shown) and storage elements such as RAM (Random Access Memory) and ROM (Read Only Memory).

[0047] The hydraulic control unit 90 is configured to receive braking request signals transmitted from the driver assistance device 110. Furthermore, the hydraulic control unit 90 is configured to acquire information about the vehicle's acceleration G in the longitudinal direction. The hydraulic control unit 90 can also acquire acceleration G information by directly receiving sensor signals from wheel speed sensors installed on the vehicle and differentiating the detected values, or it can acquire acceleration G information transmitted from other control devices via the communication bus 120.

[0048] Furthermore, the vehicle's acceleration G, calculated based on the wheel speed sensor readings, is represented as a positive value when the vehicle is accelerating in the forward direction. That is, the vehicle's deceleration Ax implies a negative acceleration G. Therefore, a deceleration Ax exceeding a predetermined limit Ax_lim means that the acceleration G is lower than the value that reverses the sign of the predetermined limit Ax_lim (a positive value).

[0049] The target braking torque setting unit 91 sets the target braking torque T_out based on the information of the indicated braking torque T_req_in contained in the braking request signal transmitted from the driver assistance device 110. The target braking torque setting unit 91 sets the target braking torque T_out so that the vehicle's deceleration Ax does not exceed a predetermined limit value Ax_lim for an extended period. The limit value Ax_lim is an upper limit value of the deceleration Ax set to avoid vehicle instability due to ACC automatic braking control, and is, for example, set to 4.8~5.0 m / s². 2 The value within the range.

[0050] Specifically, when the vehicle's deceleration Ax is below a predetermined limit value Ax_lim, the target braking torque setting unit 91 sets the indicated braking torque T_req_in to the target braking torque T_out. Conversely, when the deceleration Ax exceeds the predetermined limit value Ax_lim, the target braking torque setting unit 91 activates a braking torque limiting mode, calculates a limiting braking torque T_lim that is smaller than the indicated braking torque T_req_in, and sets this limiting braking torque T_lim as the target braking torque T_out. That is, in the driver assistance device 110, the indicated braking torque T_req_in (N·m) is calculated as the target value for decelerating the vehicle, while the target braking torque setting unit 91 uses a different vehicle deceleration Ax (m / s²) as the target value. 2 The information from the braking torque limits the braking force. Therefore, even if the generated braking force is scattered due to vehicle travel conditions, the likelihood of the deceleration Ax exceeding the limit value Ax_lim for an extended period is reduced, thus suppressing vehicle instability.

[0051] The method for calculating the limiting braking torque T_lim is not particularly limited. For example, the target braking torque setting unit 91 can also calculate the limiting braking torque T_lim by decreasing the indicated braking torque T_req_in at a constant rate when the vehicle deceleration Ax exceeds a predetermined limit value Ax_lim. Specifically, when the vehicle deceleration Ax exceeds the predetermined limit value Ax_lim, the target braking torque setting unit 91 sets the limiting braking torque T_lim obtained by subtracting a preset constant correction value T_x from the value of the indicated braking torque T_req_in as the target braking torque T_out. Furthermore, for each subsequent calculation cycle, the target braking torque setting unit 91 sets the limiting 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. The correction value T_x in this case is set to an appropriate value so that the deceleration Ax does not drop sharply. By calculating the limiting braking torque T_lim in this way, the braking torque can be easily limited without increasing the computational load on the hydraulic control device 90. Furthermore, it does not cause the vehicle's deceleration Ax to drop sharply, thus preventing the inter-vehicle distance D from becoming too small.

[0052] However, the method for calculating the limiting braking torque T_lim is not limited to subtracting a constant correction value T_x. For example, the correction value T_x can also be a value that varies corresponding to the vehicle's deceleration state. Specifically, the correction value T_x can be set such that the larger the difference between the vehicle's deceleration Ax and the predetermined limit value Ax_lim, the greater the difference. Thus, compared to subtracting a constant correction value T_x, the vehicle's deceleration Ax can be suppressed to below the predetermined limit value Ax_lim earlier.

[0053] Furthermore, in this embodiment, the target braking torque setting unit 91 is configured to compare the deceleration Ax with the limit value Ax_lim when the vehicle's deceleration Ax exceeds a control start threshold Ax_0, which is set to be smaller than the limit value Ax_lim; and to impose a limit on the braking torque when the deceleration Ax exceeds the limit value Ax_lim. This reduces the computational load on the hydraulic control device 90 during periods when the deceleration Ax is small and there is no need to impose a limit on the braking torque.

[0054] Furthermore, the target braking torque setting unit 91 can also activate the braking torque limiting mode if the vehicle's deceleration Ax exceeds the limit value Ax_lim for a predetermined time t_thr_st or more. Therefore, if the deceleration Ax exceeds the limit value Ax_lim for a very short time, the braking torque will not be limited, preventing the braking torque from being limited to an unnecessary degree and the distance D between the vehicle and the preceding vehicle from becoming too small. The predetermined time t_thr_st is preset to an appropriate value through simulation or the like.

[0055] Furthermore, the target braking torque setting unit 91 can also start the braking torque limiting mode when the vehicle's deceleration Ax exceeds the limit value Ax_lim, and then end the braking torque limiting mode if the deceleration Ax remains below the limit value Ax_lim for a predetermined time t_thr_fn or more. This delays the timing of ending the braking torque limiting, preventing the deceleration Ax below the limit value Ax_lim from exceeding the limit value Ax_lim again due to the end of the braking torque limiting. The predetermined time t_thr_fn is preset to an appropriate value through simulation or the like.

[0056] Furthermore, the target braking torque setting unit 91 may, after the braking torque limiting mode ends, maintain the limiting braking torque T_lim as the target braking torque T_out (i.e., the limiting braking torque T_lim) set in the previous calculation cycle where the indicated braking torque T_req_in output from the driving assistance device 110 is at the end time of the braking torque limiting mode, and keep the limiting braking torque T_lim as the target braking torque T_out. Thus, when the braking torque limiting mode ends, a sharp increase in the target braking torque T_out can be prevented, and a transition to the state where the indicated braking torque T_req_in is set to the target braking torque T_out can be achieved without causing a large change in the target braking torque T_out.

[0057] Furthermore, during the execution of ABS and ESP control, there are instances where the vehicle deceleration Ax, calculated by differentiating the wheel speed sensor readings, becomes excessively large, reducing the reliability of the deceleration Ax value. Therefore, the target braking torque setting unit 91 sets the target braking torque T_out without using the deceleration Ax information during ABS and ESP control execution. For example, the target braking torque setting unit 91 compares the indicated braking torque T_req_in value output from the driver assistance device 110 with the target braking torque T_out value set in the previous calculation cycle, and sets the smaller one as the target braking torque T_out for the current calculation cycle.

[0058] The control unit 93 controls the drive of the brake hydraulic unit 20 based on the target brake torque T_out set by the target brake torque setting unit 91. Thus, the braking force of the vehicle is controlled. In this embodiment, the control unit 93 calculates the target brake hydraulic pressure P_tgt generated for each wheel based on the target brake torque T_out and controls the drive of the pump motor 96 of the brake hydraulic unit 20.

[0059] For example, the control unit 93 may refer to the mapping information of the pre-set relationship between the target braking torque T_out and the target braking hydraulic pressure P_tgt to calculate the target braking hydraulic pressure P_tgt corresponding to the target braking torque T_out. Based on the calculated target braking hydraulic pressure P_tgt, the control unit 93 sets the target flow rate V_tgt of the brake fluid supplied from the master cylinder 14 to the brake hydraulic unit 20. For example, the control unit 93 may refer to the mapping information of the pre-set relationship between the target braking hydraulic pressure P_tgt and the target flow rate V_tgt to set the target flow rate V_tgt of the brake fluid.

[0060] Additionally, the control unit 93 can also set a target flow rate V_tgt corresponding to the difference dP between the current brake hydraulic pressure P_act and the target brake hydraulic pressure P_tgt. The current brake hydraulic pressure P_act can be replaced by the pressure value detected by the hydraulic sensor 24. Alternatively, if a brake hydraulic pressure sensor for detecting the brake hydraulic pressure of a specific wheel cylinder is provided in addition to the hydraulic sensor 24, the pressure value detected by that brake hydraulic pressure sensor can be used instead of the hydraulic sensor 24.

[0061] The control unit 93 outputs a control signal to the drive circuit of the pump motor 96 in the brake hydraulic unit 20 according to the preset target flow rate V_tgt, driving pumps 44a and 44b. As a result, brake fluid is supplied from the master cylinder 14 to the brake hydraulic unit 20, and then to the wheel cylinders of each wheel. Consequently, the brake hydraulic pressure of each wheel increases, generating braking force on the vehicle. As described above, in the braking torque limiting mode, a limit is imposed on the braking torque if the vehicle's deceleration Ax exceeds the limit value Ax_lim, thus reducing the possibility of deceleration Ax exceeding the limit value Ax_lim for an extended period.

[0062] (1-2-2. Example of an action)

[0063] Next, a specific example of the operation of the hydraulic control device 90, which is the braking control device of the vehicle in this embodiment, will be described.

[0064] Figure 3 and Figure 4 This is a flowchart illustrating the braking control process executed by the hydraulic control device 90 during the execution of ACC. Figure 3This is a flowchart representing the main path of the braking control processing executed by the hydraulic control device 90 during the execution of ACC. Figure 4 This is a flowchart showing the path of the target braking torque setting process. The braking control processes described below are always executed during ACC execution.

[0065] like Figure 3 As shown, firstly, the target braking torque setting unit 91 of the hydraulic control device 90 determines whether a braking request signal has been received from the driving assistance device 110 (step S11). If no braking request signal has been received (S11 / No), the target braking torque setting unit 91 terminates this path as before and returns to the beginning. 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 indicated braking torque T_req_in included in the braking request signal (step S13). The process of setting the target braking torque T_out is based on... Figure 4 The flowchart shown is followed.

[0066] Figure 4 In the flowchart shown, "(n)" represents the value obtained or calculated in the current calculation cycle, and "(n-1)" represents the value calculated in the previous calculation cycle. First, the target braking torque setting unit 91 obtains information about the vehicle's deceleration Ax(n) 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), it is a state where the possibility of the deceleration Ax exceeding the limit value Ax_lim is low. Therefore, the target braking torque setting unit 91 sets the indicated braking torque T_req_in(n) included in the braking request signal received from the driver assistance device 110 as the target braking torque T_out(n) (step S43).

[0067] 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 the difference dA(n) between the deceleration Ax(n) and the limit value Ax_lim (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's deceleration Ax(n) exceeds the limit value Ax_lim.

[0068] When the difference dA(n) is positive (S25 / Yes), that is, when the deceleration Ax(n) exceeds the limit value Ax_lim, the target braking torque setting unit 91 activates the braking torque limiting mode (step S27). At this time, the target braking torque setting unit 91 can also activate the braking torque limiting 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 limiting mode is activated, the target braking torque setting unit 91 calculates the limiting braking torque T_lim(n) (step S29). In this embodiment, the target braking torque setting unit 91 calculates the limiting 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. Then, the target braking torque setting unit 91 sets the calculated limiting braking torque T_lim(n) as the target braking torque T_out(n).

[0069] On the other hand, if the difference dA(n) is not positive (S25 / No), the target braking torque setting unit 91 determines whether the current braking torque limiting mode is activated (step S33). If the braking torque limiting mode is not activated (S33 / No), the target braking torque setting unit 91 sets the indicated braking torque T_req_in(n) included in the braking request signal received from the driving assistance device 110 to the target braking torque T_out(n) as is (step S43).

[0070] On the other hand, when the braking torque limiting mode is activated (S33 / Yes), the target braking torque setting unit 91 determines whether a predetermined time t_thr_fn has elapsed since the difference dA(n) is 0 or less (step S35). This predetermined time t_thr_fn is set to delay the timing of ending the braking torque limiting in order to prevent the deceleration Ax below the limit value Ax_lim from exceeding the limit value Ax_lim again due to the end of the braking torque limiting.

[0071] If a predetermined time t_thr_fn has not elapsed since the difference dA(n) is below 0 (S35 / No), the target braking torque setting unit 91 calculates the limiting 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). Then, the target braking torque setting unit 91 sets the calculated limiting braking torque T_lim(n) as the target braking torque T_out(n) (step S31).

[0072] In the calculation method of the limiting braking torque T_lim(n) in this embodiment, during the initial cycle when the braking torque limiting mode switches from off to on, the target braking torque T_out(n-1) set in the previous cycle is the indicated braking torque T_req_in(n-1). Therefore, the limiting braking torque T_lim(n) is obtained by subtracting the correction value T_x from the indicated braking torque T_req_in(n-1). Furthermore, during the period when the braking torque limiting mode is active, the limiting braking torque T_lim(n) is obtained by subtracting the correction value T_x from the target braking torque T_out(n-1) set in the previous cycle. Therefore, during the period when the braking torque limiting mode is active, the limiting braking torque T_lim is calculated by reducing the indicated braking torque T_req_in at a constant decreasing rate.

[0073] On the other hand, if a predetermined time t_thr_fn has elapsed since the difference dA(n) was below 0 (S35 / Yes), the target braking torque setting unit 91 closes the braking torque limiting mode (step S37). Next, the target braking torque setting unit 91 determines whether the indicated 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 indicated braking torque T_req_in(n) is greater than the target braking torque T_out(n-1) (S39 / Yes), the deceleration Ax is lower than the limit value Ax_lim. However, in order to prevent the target braking torque T_out from rising due to the end of the braking torque limiting, and thus the deceleration Ax from exceeding the limit value Ax_lim again, the target braking torque setting unit 91 maintains the target braking torque T_out(n-1) set in the previous cycle as the target braking torque T_out(n) for the current cycle (step S41).

[0074] On the other hand, if the indicated braking torque T_req_in(n) is less than or equal to the target braking torque T_out(n-1) (S39 / No), the indicated braking torque T_req_in(n) is equal to the limiting braking torque T_lim(n-1), and the deceleration Ax can be suppressed by using the indicated braking torque T_req_in(n) as the target braking torque T_out(n). Therefore, the target braking torque setting unit 91 sets the indicated braking torque T_req_in(n) contained in the braking request signal received from the driving assistance device 110 to the target braking torque T_out(n) (step S43).

[0075] return Figure 3After the target braking torque T_out is set in step S13, the control unit 93 calculates the target braking hydraulic pressure P_tgt based on the target braking torque T_out (step S15). For example, the control unit 93 refers to the mapping information of the pre-set relationship between the target braking torque T_out and the target braking hydraulic pressure P_tgt to calculate the target braking hydraulic pressure P_tgt corresponding to the target braking torque T_out.

[0076] Next, the control unit 93 controls the drive 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 the target flow rate V_tgt of the brake fluid 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 drive of the pump motor 96 of the brake hydraulic unit 20. For example, the control unit 93 may also set the target flow rate V_tgt of the brake fluid by referring to the mapping information of the pre-set relationship between the target brake hydraulic pressure P_tgt and the target flow rate V_tgt.

[0077] As a result, the brake hydraulic pressure in the wheel cylinders of each wheel increases, generating braking force for the vehicle. In this embodiment, when the deceleration Ax exceeds the limit value Ax_lim and the braking torque limiting mode is set, the indicated braking torque T_req_in calculated by the driver assistance device 110 is not used as is. Instead, the limiting braking torque T_lim, which is set to a value smaller than the indicated braking torque T_req_in, is set as the target braking torque T_out. Therefore, the possibility of the vehicle's deceleration Ax exceeding the limit value Ax_lim for an extended period can be reduced. Consequently, during the execution of ACC, vehicle instability can be suppressed, and the inter-vehicle distance with the preceding vehicle can be controlled to a predetermined target inter-vehicle distance.

[0078] Furthermore, the target braking torque setting unit 91 sets the target braking torque T_out without using deceleration Ax information during ABS control and ESP control. For example, the target braking torque setting unit 91 compares the value of the indicated braking torque T_req_in(n) output from the driver assistance 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 the execution of ABS control and ESP control, there is a possibility that the vehicle deceleration Ax, which is obtained by differentiating the detection value of the wheel speed sensor, becomes too large, and the reliability of the deceleration Ax value decreases. Therefore, by setting the target braking torque T_out without using deceleration Ax information during the execution of ABS control and ESP control, the possibility of vehicle instability can be reduced.

[0079] (1-2-3. Function)

[0080] Next, the function of the braking control process performed by the hydraulic control device 90 of this embodiment will be explained.

[0081] Figure 5 This diagram illustrates the effect of the braking control process performed by the hydraulic control device 90 of this embodiment, showing the time variation of the target braking torque T_out and the vehicle deceleration Ax during the execution of ACC.

[0082] At time t1, when the distance between this vehicle and the preceding vehicle is lower than the target distance, or is about to be lower, the transmission of the braking request signal from the driving assistance device 110 to the hydraulic control device 90 begins. After time t1, the indicated braking torque T_req_in increases, and this indicated braking torque T_req_in is used as the target braking torque T_out to control the drive of the brake hydraulic unit 20, increasing the vehicle's deceleration Ax.

[0083] At time t2, when the deceleration Ax exceeds the control start threshold Ax_0, the target braking torque setting unit 91 begins calculating the difference dA between the deceleration Ax and the limit value Ax_lim. At time t3, when the deceleration Ax further increases and exceeds the limit value Ax_lim, the target braking torque setting unit 91 begins timing. At time t4, before the elapsed time from time t3 reaches a predetermined time t_thr_st, the rise of the indicator braking torque T_req_in ends, and thereafter, the value of the indicator braking torque T_req_in is maintained at a constant value. Subsequently, at time t4, the vehicle's deceleration Ax falls below the limit value Ax_lim, so the target braking torque setting unit 91 resets the timing value.

[0084] Subsequently, at time t5, when the deceleration Ax exceeds the limit value Ax_lim again, the target braking torque setting unit 91 starts timing. When the elapsed time from time t5 reaches the predetermined time t_thr_st while the deceleration Ax exceeds the limit value Ax_lim, at time t6, the target braking torque setting unit 91 activates the braking torque limiting mode, setting the limiting braking torque T_lim, which was set to a value smaller than the indicated braking torque T_req_in, to the target braking torque T_out. Figure 5 In the example shown, the indicated braking torque T_req_in decreases at a constant rate from the moment the braking torque limiting mode is activated (t6), and is set as the limiting braking torque T_lim. This limiting braking torque T_lim is set as the target braking torque T_out.

[0085] As the braking torque is limited, the vehicle's deceleration Ax begins to decrease. At time t7, when the deceleration Ax reaches the limit value Ax_lim, the target braking torque setting unit 91 starts timing. When the elapsed time from time t7 to time t8, while the deceleration Ax is below the limit value Ax_lim, reaches a predetermined time t_thr_fn, the target braking torque setting unit 91 deactivates the braking torque limiting mode and maintains the target braking torque T_out (i.e., the limited braking torque T_lim) set in the previous calculation cycle at that time, setting it as the target braking torque T_out. Furthermore, the relationship between the predetermined time t_thr_st set to activate the braking torque limiting mode and the predetermined time t_thr_fn set to deactivate the braking torque limiting mode is not specifically limited.

[0086] Subsequently, as the distance between the vehicle and the preceding vehicle approaches the target distance, the indicated braking torque T_req_in decreases. At time t9, the indicated braking torque T_req_in falls below the target braking torque T_out (limited braking torque T_lim). Therefore, the target braking torque setting unit 91 terminates the calculation of the limited braking torque T_lim and returns to setting the indicated braking torque T_req_in to the target braking torque T_out as it was. Furthermore, at time t10, the transmission of the braking request signal from the driving assistance device 110 stops, and the hydraulic control device 90 stops the drive of the brake hydraulic unit 20.

[0087] like Figure 5 As shown by the dashed line, when the indicated braking torque T_req_in is set to the target braking torque T_out to control the drive of the brake hydraulic unit 20 without imposing a limit on the braking torque, at time t5, after the deceleration Ax exceeds the limit value Ax_lim, the state of deceleration Ax_def exceeding the limit value Ax_lim remains even if the indicated braking torque T_req_in itself decreases. Thus, if the state of deceleration Ax_def exceeding the limit value Ax_lim persists for a long time, there is a possibility of vehicle instability due to sudden deceleration. In contrast, in this embodiment, when the vehicle's deceleration Ax exceeds the limit value Ax_lim, the braking torque is limited, so the possibility of deceleration Ax continuously exceeding the limit value Ax_lim for a long time is reduced, and vehicle instability can be suppressed.

[0088] <1-3. Effects>

[0089] As explained above, according to this embodiment, when the vehicle's deceleration Ax 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 indicated braking torque T_req_in transmitted from the driver assistance device 110, to a target braking torque T_out. Furthermore, the control unit 93 controls the drive of the pump motor 96 of the brake hydraulic unit 20 based on the set target braking torque T_out. Therefore, the possibility of the vehicle's deceleration Ax exceeding the limit value Ax_lim for an extended period is reduced, and vehicle instability due to sudden deceleration can be suppressed.

[0090] Furthermore, according to this embodiment, the target braking torque setting unit 91 calculates the limiting braking torque T_lim by decreasing the indicated braking torque T_req_in when the braking torque limiting mode is activated at a constant decreasing rate. Therefore, the braking torque can be easily limited without increasing the computational load on the hydraulic control device 90. Furthermore, by preventing a sharp drop in the vehicle's deceleration Ax, it is possible to prevent the inter-vehicle distance D from becoming too small.

[0091] Furthermore, according to this embodiment, if the target braking torque setting unit 91 remains in a state where the deceleration Ax is below the limit value Ax_lim for a predetermined time t_thr_fn or more, it closes the braking torque limiting mode and maintains the target braking torque T_out (i.e., the limiting braking torque T_lim) set in the previous calculation cycle at that time, setting it as the target braking torque T_out. This delays the timing of ending the braking torque limiting, preventing the deceleration Ax below the limit value Ax_lim from exceeding the limit value Ax_lim again due to the end of the braking torque limiting.

[0092] Furthermore, according to this embodiment, when the vehicle's deceleration Ax exceeds the limit value Ax_lim for a predetermined time t_thr_st or more, the target braking torque setting unit 91 activates the braking torque limiting mode and sets the limiting braking torque T_lim to the target braking torque T_out. Therefore, when the deceleration Ax exceeds the limit value Ax_lim for a very short time, the braking torque is not limited, preventing the braking torque from being limited to an excessive degree, thus avoiding an excessively small inter-vehicle distance D with the preceding vehicle.

[0093] Furthermore, according to this embodiment, after activating the braking torque limiting mode, the target braking torque setting unit 91 stops setting the limiting braking torque T_lim to the target braking torque T_out when the indicated braking torque T_req_in is below the limiting braking torque T_lim. Therefore, when ending the braking torque limiting mode, a sharp increase in the target braking torque T_out can be prevented, and the transition to the state where the indicated braking torque T_req_in is set to the target braking torque T_out can be achieved without causing a large change in the target braking torque T_out.

[0094] Furthermore, according to this embodiment, the target braking torque setting unit 91 compares the deceleration Ax with the limit value Ax_lim when the deceleration Ax exceeds the control start threshold Ax_0, which is smaller than the limit value Ax_lim. When the deceleration Ax exceeds the limit value Ax_lim, the limiting braking torque T_lim is set to the target braking torque T_out. Therefore, there is no need to impose a limit on the braking torque, and the computational load on the hydraulic control device 90 can be reduced during periods when the deceleration Ax is small.

[0095] <<2. Second Implementation>>

[0096] Next, the second embodiment of the present invention will be described. In the second embodiment, the power assist control device 100 that controls the electric power assist device 10 functions as a braking control device for a vehicle that receives a braking request signal transmitted from the driving assistance device 110 and controls the braking force so that the vehicle's deceleration does not exceed a predetermined limit for an extended period of time.

[0097] The braking system 1 of this embodiment, except that the braking control device of the vehicle performing ACC automatic braking control is the power assist control device 100, can have the same structure as the braking system 1 described in the first embodiment. Hereinafter, the differences from the first embodiment will be mainly described.

[0098] Figure 6 This is a block diagram showing the functional structure of the braking system 1 associated with the automatic braking control of ACC. In this embodiment, the automatic braking control of ACC is executed by the power assist device 100 controlling the power assist device 10 through communication between the driving assistance device 110 and the power assist device control device 100.

[0099] Similar to the first embodiment, during the execution of ACC, the driving assistance device 110 determines whether braking is required and calculates the braking torque T_req_in based on information detected by sensor devices 111 such as cameras, radar, and RiDAR. It then transmits a braking request signal indicating the braking request S_brk and the braking torque T_req_in to the power assist device control device 100.

[0100] When the power assist control unit 100 receives the braking request signal from the ACC (Adaptive Cruise Control) device 110, it sets the target braking torque T_out based on the indicated braking torque T_req_in, and converts the target braking torque T_out into a target braking hydraulic pressure P_tgt, thereby controlling the drive of the power assist device 10. Specifically, the power assist control unit 100 drives the electric motor of the power assist device 10 to pressurize the brake fluid in the master cylinder 14. By supplying brake fluid from the master cylinder 14 to the wheel cylinders of each wheel, the braking hydraulic pressure of each wheel increases, generating the braking force of the vehicle.

[0101] The power assist 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 implemented by a program executed by a microcomputer. In addition, the power assist control device 100 includes a drive circuit (not shown) and storage elements such as RAM and ROM.

[0102] The target braking torque setting unit 101 is configured identically 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 based on the information of the indicated braking torque T_req_in and the acceleration G included in the braking request signal transmitted from the driver assistance device 110, such that the vehicle's deceleration Ax does not exceed a predetermined limit value Ax_lim for an extended period. The specific calculation method for the target braking torque T_out can be the same as that of the target braking torque setting unit 91 of the hydraulic control device 90 described in the first embodiment.

[0103] The control unit 103 controls the drive of the power assist device 10 based on the target braking torque T_out set by the target braking torque setting unit 101. Thus, the braking force of the vehicle is controlled. In this embodiment, the control unit 103 calculates the target braking hydraulic pressure P_tgt generated by each wheel based on the target braking torque T_out, and controls the drive of the electric motor of the power assist device 10, causing the push rod 13 to advance into the master cylinder 14.

[0104] The control unit 103, like the control unit 93 of the hydraulic control device 90 described in the first embodiment, calculates the target braking hydraulic pressure P_tgt based on the target braking torque T_out by referring to mapping information, etc., and sets the target flow rate V_tgt of the brake fluid supplied from the master cylinder 14 to the brake hydraulic unit 20 based on the target braking hydraulic pressure P_tgt.

[0105] The control unit 103 outputs a control signal to the drive circuit of the electric motor of the power assist device 10 according to the preset target flow rate V_tgt, causing the push rod 13 to move forward. This pressurizes the brake fluid in the first chamber 47 and the second chamber 48, and the brake fluid is supplied from the master cylinder 14 to the brake hydraulic unit 20, and then to the wheel cylinders of each wheel. As a result, the brake hydraulic pressure of each wheel increases, generating braking force for the vehicle. In this embodiment, in the braking torque limiting mode, the braking torque is also limited even when the vehicle deceleration Ax exceeds the limit value Ax_lim, thus reducing the possibility that the deceleration Ax will continuously exceed the limit value Ax_lim for an extended period.

[0106] The operation and function of the assist device control device 100 of the vehicle braking control device in this embodiment are the same as those described in the first embodiment, except that the actuator driven is not the pump motor 96 of the brake hydraulic unit 20 but the electric motor of the assist device 10. Therefore, detailed description is omitted.

[0107] As explained above, according to this embodiment, when the deceleration Ax of the vehicle exceeds the limit value Ax_lim, the target braking torque setting unit 101 of the power assist control device 100 sets the limit braking torque T_lim, which is smaller than the indicated braking torque T_req_in transmitted from the driving assistance device 110, to the target braking torque T_out. Furthermore, the control unit 103 controls the drive of the electric motor of the power assist device 10 based on the set target braking torque T_out. The power assist control device 100 according to this embodiment can achieve the same effects as those obtained according to the first embodiment.

[0108] Furthermore, according to this embodiment, the drive assist device 10 supplies brake fluid from the master cylinder 14 to the brake hydraulic unit 20, causing the brake hydraulic pressure in the wheel cylinders of each wheel to rise. Therefore, compared to the case where the pump motor 96 drives the brake hydraulic unit 20 to supply brake fluid from the master cylinder 14 to the brake hydraulic unit 20, the responsiveness to generate braking force can be improved.

[0109] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. Those skilled in the art to which this invention pertains will obviously be able to conceive of various modifications or alterations within the scope of the technical concept described in the claims, and these modifications clearly fall within the technical scope of the present invention.

[0110] Explanation of reference numerals in the attached figures

[0111] 10… Electric power steering, 13… Push rod, 14… Master cylinder, 20… Brake hydraulic unit, 43… First piston, 44… Second piston, 47… First chamber, 48… Second chamber, 90… Hydraulic control device, 91… Target braking torque setting unit, 93… Control unit, 100… Power steering control device, 101… Target braking torque setting unit, 103… Control unit, 110… Driving assistance device.

Claims

1. A braking control device for a vehicle, characterized in that, It includes a target braking torque setting unit (91, 101) and a control unit (93, 103). The aforementioned target braking torque setting unit (91, 101) sets the target braking torque (T_out) based on the braking requirement information (T_req_in), which is set based on the target inter-vehicle distance between the vehicle and the preceding vehicle. The aforementioned control unit (93, 103) controls the braking force of the vehicle based on the aforementioned target braking torque (T_out). When the deceleration (Ax) of the vehicle exceeds a predetermined limit value (Ax_lim), the aforementioned target braking torque setting unit (91, 101) sets a limit braking torque (T_lim) that is smaller than the braking torque corresponding to the aforementioned braking requirement information (T_req_in) as the target braking torque (T_out). The aforementioned braking requirement information indicates the braking torque (T_req_in). The aforementioned target braking torque setting unit (91, 101) calculates the aforementioned limiting braking torque (T_lim) by decreasing the aforementioned indicated braking torque (T_req_in) at a constant decreasing rate.

2. The vehicle braking control device as described in claim 1, characterized in that, If the aforementioned target braking torque setting unit (91, 101) maintains the value of the aforementioned limiting braking torque (T_lim) for a predetermined time (t_thr_fn) or more when the aforementioned deceleration (Ax) is below the aforementioned predetermined limit value (Ax_lim).

3. The vehicle braking control device as described in claim 1 or 2, characterized in that, If the aforementioned target braking torque setting unit (91, 101) continues for a predetermined time (t_thr_st) or more when the aforementioned deceleration (Ax) exceeds the aforementioned predetermined limit value (Ax_lim), the aforementioned limiting braking torque (T_lim) is set to the aforementioned target braking torque (T_out).

4. The braking control device for a vehicle as described in claim 1 or 2, characterized in that, The aforementioned braking requirement information is the indicated braking torque (T_req_in). When the aforementioned target braking torque setting unit (91, 101) stops setting the aforementioned limiting braking torque (T_lim) to the aforementioned target braking torque (T_out) when the aforementioned indicated braking torque (T_req_in) is below the aforementioned limiting braking torque (T_lim) that is set to the aforementioned target braking torque (T_out).

5. The braking control device for a vehicle as described in claim 1 or 2, characterized in that, When the aforementioned target braking torque setting unit (91, 101) compares the aforementioned deceleration (Ax) of the vehicle with the aforementioned predetermined limit value (Ax_lim) if the aforementioned deceleration (Ax) exceeds a control start threshold (Ax_0) smaller than the aforementioned predetermined limit value (Ax_lim), and sets the aforementioned limiting braking torque (T_lim) to the aforementioned target braking torque (T_out) when the aforementioned deceleration (Ax) exceeds the aforementioned predetermined limit value (Ax_lim).

6. The braking control device for a vehicle as described in claim 1 or 2, characterized in that, The aforementioned vehicle's braking control device is the control device (90) of the brake hydraulic unit (20). The aforementioned target braking torque setting unit (91) receives a braking request signal and sets the aforementioned target braking torque (T_out). The aforementioned braking request signal is transmitted from the driving assistance device (110) that outputs information about the aforementioned braking request (T_req_in) based on the aforementioned target inter-vehicle distance. The aforementioned control unit (93) controls the aforementioned brake hydraulic unit (20) based on the aforementioned target braking torque (T_out).

7. The braking control device for a vehicle as described in claim 1 or 2, characterized in that, The aforementioned vehicle's braking control device is a control device (100) for an electric power assist device (10). The aforementioned target braking torque setting unit (101) receives a braking request signal and sets the aforementioned target braking torque (T_out). The aforementioned braking request signal is transmitted from the driving assistance device (110) that outputs information about the aforementioned braking request (T_req_in) based on the aforementioned target inter-vehicle distance. The aforementioned control unit (103) controls the aforementioned electric power assist device (10) based on the aforementioned target braking torque (T_out).

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