Braking control device and braking control method

Abstract

To suppress a vehicle from approaching a front vehicle during automatic traveling of the vehicle.SOLUTION: A braking control device 1 for controlling a regenerative brake and a friction brake on the basis of a distance to a front vehicle, includes: an identification part 111 configured to identify a battery residual amount; and a braking control part 112 configured to operate, when the identified battery residual amount is larger than a predetermined value, the friction brake at a special timing which is earlier than a reference timing for operating the friction brake when the battery residual amount is equal to or less than a predetermined value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a braking control device and a braking control method for controlling a regenerative brake and a friction brake. [Background technology]

[0002] In a vehicle equipped with a regenerative brake, when the battery is fully charged, the vehicle may not be able to be sufficiently decelerated by the regenerative brake. Patent Document 1 proposes controlling a brake modulator so as to apply a friction braking force equivalent to engine braking to each wheel when the driver releases the accelerator pedal when the battery is fully charged. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-137312 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the vehicle is automatically driven to maintain a constant distance from the vehicle ahead, the driver may not release the accelerator. In the invention described in Patent Document 1, if the battery becomes fully charged during such automatic driving, the vehicle cannot be sufficiently decelerated by regenerative braking, and the vehicle may approach the vehicle ahead and suddenly brake. This may cause the driver to feel scared.

[0005] The present invention has been made in consideration of this point, and aims to provide a braking control device or a braking control method that can prevent a vehicle from approaching too closely to a vehicle ahead while the vehicle is autonomously traveling. [Means for solving the problem]

[0006] A first aspect of the braking control device of the present invention is a braking control device that controls at least one of a regenerative brake and a friction brake based on the distance to a forward vehicle, and includes a determination unit that determines a remaining battery charge, and a braking control unit that, when the determined remaining battery charge is greater than a predetermined value, operates the friction brake at a special timing that is earlier than a standard timing for operating the friction brake when the remaining battery charge is equal to or less than the predetermined value.

[0007] The brake control unit may stop operation of the regenerative brake at the special timing. The specification unit may specify a regenerative braking force value at which the regenerative brake can be generated based on the remaining battery charge, and the brake control unit may operate the friction brake at the special timing on the condition that the regenerative braking force value becomes less than a first threshold value.

[0008] The determination unit may determine a regenerative braking force value that can be generated by the regenerative brake based on the remaining battery charge and the rotation speed of the motor. The first threshold value may be a value corresponding to a maximum value of the regenerative braking force value. The first threshold value may be a value obtained by multiplying the maximum value of the regenerative braking force value by a coefficient smaller than 1.

[0009] The brake control unit may operate the regenerative brake on condition that the regenerative braking force value becomes greater than a second threshold value that is greater than the first threshold value after the regenerative braking force value becomes less than the first threshold value. The brake control unit may operate the regenerative brake on condition that the regenerative braking force value becomes greater than the second threshold value after the regenerative braking force value becomes smaller than the first threshold value and the friction brake is not operating.

[0010] The brake control unit may operate the regenerative brake on the condition that the regenerative braking force value becomes larger than the second threshold value after the regenerative braking force value becomes smaller than the first threshold value, the friction brake is not operating, and the regenerative brake is not malfunctioning. The brake control unit may operate the regenerative brake after the regenerative braking force value becomes smaller than the first threshold value and the vehicle starts accelerating.

[0011] A second aspect of the braking control device of the present invention is a braking control device that controls at least one of a regenerative brake and a friction brake based on the distance to a preceding vehicle, and includes a determination unit that determines a remaining battery charge, and a braking control unit that activates the friction brake when the remaining battery charge is greater than a predetermined value and the distance to the preceding vehicle is equal to or less than a first distance, and that activates the friction brake when the remaining battery charge is equal to or less than the predetermined value and the distance to the preceding vehicle is equal to or less than a second distance longer than the first distance.

[0012] A braking control method of a third aspect of the present invention is a braking control method for controlling at least one of a regenerative brake and a friction brake based on a distance to a forward vehicle, and includes the steps of: determining a remaining battery charge; and, when the determined remaining battery charge is greater than a predetermined value, operating the friction brake at a special timing earlier than a standard timing for operating the friction brake when the remaining battery charge is equal to or less than the predetermined value.

[0013] A braking control method of a fourth aspect of the present invention is a braking control method for controlling at least one of a regenerative brake and a friction brake based on the distance to a forward vehicle, and includes the steps of: determining a remaining battery charge; and, if the remaining battery charge is greater than a predetermined value and the distance to the forward vehicle is equal to or less than a first distance, activating the friction brake; and, if the remaining battery charge is equal to or less than the predetermined value and the distance to the forward vehicle is equal to or less than a second distance longer than the first distance, activating the friction brake. Effect of the Invention

[0014] According to the present invention, an effect of preventing a vehicle from approaching too closely to a vehicle ahead while the vehicle is autonomously traveling is achieved. [Brief description of the drawings]

[0015] [Figure 1] 1 shows an overview of a vehicle equipped with a brake control device according to a first embodiment. [Diagram 2] The vehicle configuration is shown. [Diagram 3] 1 shows the relationship between the remaining battery charge and the regenerative braking force value when the motor is operating at a certain rotation speed. [Figure 4] 13 shows an example of switching on and off a regenerative brake flag by a braking control unit. [Diagram 5] 5 is a flowchart showing an example of a processing procedure for switching on and off a regenerative brake flag by a braking control unit of the first embodiment. [Figure 6] 4 shows the configuration of a vehicle including a braking control device according to a second embodiment. [Figure 7] 10 is a second flowchart showing the braking control flow of the braking control device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <First embodiment> [Vehicle Overview] 1 shows an overview of a vehicle 100 equipped with a brake control device 1 according to a first embodiment. The vehicle 100 is, for example, a commercial vehicle such as a truck. The vehicle 100 travels so as to maintain a constant distance to a preceding vehicle 200 by using an adaptive cruise control (ACC).

[0017] The braking control device 1 is, for example, an ECU (Electronic Control Unit). The braking control device 1 controls at least one of regenerative braking and friction braking based on the distance between the vehicle 100 and the preceding vehicle 200. During automatic traveling in which at least one of regenerative braking and friction braking is controlled based on the distance to the preceding vehicle 200, the braking control device 1 identifies information indicating the remaining battery charge of a battery mounted on the vehicle 100. The information indicating the remaining battery charge is, for example, SOC (State Of Charge).

[0018] The braking control device 1 judges whether the remaining battery charge is equal to or less than a threshold Vth1. Based on the result of this judgment, the braking control device 1 decides whether or not to apply friction braking at an earlier timing than normal. The threshold Vth1 is the maximum remaining battery charge at which a regenerative brake, which generates braking force by generating electricity from a motor mounted on the vehicle 100, can generate sufficient braking force. The threshold Vth1 is determined, for example, according to the type of the motor 3 that operates as a regenerative brake.

[0019] When the remaining battery charge is equal to or less than the threshold Vth1, the battery has sufficient free capacity to charge the battery with the power generated by the regenerative brake. Therefore, at this time, it is possible to obtain sufficient braking force by activating the regenerative brake. When the remaining battery charge is equal to or less than the threshold Vth1, the brake control device 1 turns on the regenerative brake flag stored in the memory unit. The brake control device 1 calculates the braking force required to maintain the inter-vehicle distance from the forward vehicle 200 when the regenerative brake flag is on, and activates the regenerative brake to generate the calculated braking force. When the regenerative brake flag is on, the brake control device 1 operates in a normal mode in which the friction brake is not activated.

[0020] When the remaining battery charge is greater than the threshold Vth1, there is not enough free capacity to charge the battery with the power generated by the regenerative brake. Therefore, even if the regenerative brake is operated, a sufficient braking force cannot be generated. In this case, the brake control device 1 turns off the regenerative brake flag.

[0021] When the regenerative brake flag is off, the braking control device 1 operates in a special mode in which the friction brake is activated at a special timing. The special timing is earlier than the timing (hereinafter also referred to as the reference timing) at which the friction brake is activated when the vehicle 100 approaches the preceding vehicle 200 while the regenerative brake flag is on.

[0022] In this way, when the remaining battery charge is greater than a predetermined value, the brake control device 1 activates the friction brake earlier than when the remaining battery charge is equal to or less than the predetermined value. Therefore, even in a state in which the vehicle 100 cannot be braked by regenerative braking, the brake control device 1 can prevent the vehicle 100 from approaching too close to the vehicle ahead, thereby preventing the driver from feeling scared.

[0023] [Vehicle 100 Configuration] 2 shows the configuration of a vehicle 100. The vehicle 100 includes a braking control device 1, a voltage sensor 2, a motor 3, a friction brake 4, and a battery 5. The braking control device 1 includes a storage unit 10 and a control unit 11. The control unit 11 includes an identification unit 111 and a braking control unit 112.

[0024] The voltage sensor 2 measures the output voltage of the battery 5 mounted on the vehicle 100. The voltage sensor 2 inputs to the identification unit 111 information indicating the output voltage.

[0025] The motor 3 generates a propulsive force for propelling the vehicle 100. The motor 3 also operates as a regenerative brake, generating power to generate a regenerative braking force. The friction brake 4 generates a braking force that decelerates the vehicle 100 by frictional force.

[0026] The battery 5 is an electricity storage device that supplies the motor 3 with electric power for driving the motor 3. The battery 5 is also capable of storing electric power generated by the motor 3 when the motor 3 performs a regenerative operation. The battery 5 may be fixed to the vehicle, or may be mounted detachably on the vehicle.

[0027] The storage unit 10 is configured with, for example, a Read Only Memory (ROM) and a Random Access Memory (RAM). The storage unit 10 stores a program to be executed by the control unit 11. The control unit 11 is, for example, a processor mounted on an ECU. The control unit 11 executes the program stored in the storage unit 10 to function as a determination unit 111 and a braking control unit 112.

[0028] The identifying unit 111 identifies information indicating the remaining battery charge of the battery mounted on the vehicle 100. For example, the identifying unit 111 identifies the information indicating the remaining battery charge based on the output voltage of the battery input from the voltage sensor 2. The information indicating the remaining battery charge is, for example, the SOC.

[0029] The identifying unit 111 identifies a regenerative braking force value that can be generated by regenerative braking based on the identified remaining battery charge. The regenerative braking force value is a value indicating the magnitude of braking force that can be generated by regenerative braking. For example, the regenerative braking force value is a ratio of the current braking force that can be generated by regenerative braking to the maximum braking force that can be generated by regenerative braking. When the remaining battery charge is greater than the threshold Vth1, there is not enough free capacity to further charge the battery. Therefore, when the remaining battery charge is greater than the threshold Vth1, the regenerative braking force value is smaller than when the remaining battery charge is equal to or less than the threshold Vth1.

[0030] 3 is a schematic diagram showing the relationship between the remaining battery charge and the regenerative braking force value when the motor 3 is operating at a certain rotation speed. The horizontal axis represents the remaining battery charge. The vertical axis represents the regenerative braking force value. When the remaining battery charge is equal to or less than a predetermined value (Vth0), the battery can be charged with the generated power even when the regenerative brake is operating at maximum braking force. Therefore, since the regenerative brake can be operated at maximum braking force, the regenerative braking force value is the maximum braking force value Pmax.

[0031] In addition, when the remaining battery charge is greater than a predetermined value Vth0, the battery cannot be charged with the power generated when the regenerative brake operates at maximum braking force. Therefore, the braking force that the regenerative brake can generate is limited and becomes smaller than the maximum braking force. Here, when the remaining battery charge is a threshold value Vth1, the regenerative braking force value that the regenerative brake can generate is assumed to be a first threshold value Pth1.

[0032] Also, the regenerative braking force value at which regenerative braking can be performed when the battery remaining charge is a threshold Vth2 that is smaller than the threshold Vth1 is set to a second threshold Pth2. Note that in FIG. 3 and the above description, for the sake of simplicity, the relationship between the battery remaining charge and the regenerative braking force value is shown linearly, but this is not limiting. As will be described later, the higher the rotation speed of the motor 3, the larger the regenerative braking force value generated by the regenerative brake. Therefore, the relationship between the battery remaining charge and the regenerative braking force value shown in FIG. 3 shows a different relationship depending on the rotation speed of the motor 3. Therefore, the threshold value of the battery remaining charge corresponding to the threshold value of the regenerative braking force value may take a different value depending on the rotation speed of the motor 3.

[0033] The determination unit 111 may determine the regenerative braking force value based on the rotation speed of the motor 3 in addition to the remaining battery charge. The higher the rotation speed of the motor 3, the larger the regenerative braking force value. The determination unit 111 outputs the determined regenerative braking force value to the braking control unit 112.

[0034] [Braking force control] The braking control unit 112 controls the friction brake 4 and the regenerative brake. When the remaining battery charge of the battery mounted on the vehicle 100 is greater than a threshold Vth1, the braking control unit 112 operates the friction brake 4 at a special timing that is earlier than a reference timing for operating the friction brake 4 when the remaining battery charge is equal to or less than the threshold Vth1. In order to realize control for operating the friction brake 4 at such a timing, the braking control unit 112 determines whether or not to operate the friction brake 4 based on the regenerative braking force value identified by the identification unit 111, for example.

[0035] Specifically, the braking control unit 112 transitions to a special mode in which the friction brake 4 is operated at a special timing earlier than the reference timing for operating the friction brake 4 when the regenerative braking force value is equal to or greater than the first threshold value Pth1, on the condition that the regenerative braking force value identified by the identification unit 111 becomes less than the first threshold value Pth1 stored in the storage unit 10. Here, the first threshold value Pth1 is a value set according to the maximum value of the regenerative braking force value. For example, the first threshold value Pth1 is a value obtained by multiplying the maximum value of the regenerative braking force value by a predetermined coefficient smaller than 1. The maximum value of the regenerative braking force value is a regenerative braking force value that can be generated when the remaining battery charge, the rotation speed of the motor 3, etc. are ideal values.

[0036] The reference timing is, for example, a timing when the distance between the vehicle 100 and the vehicle ahead becomes smaller than a predetermined first distance. The special timing is a timing when the distance between the vehicle 100 and the vehicle ahead becomes smaller than a predetermined second distance that is larger than the first distance. In other words, the braking control unit 112 according to this embodiment determines whether the remaining battery charge is greater than the threshold Vth1. is less than or equal to In this case, the friction brake is operated in response to the distance to the forward vehicle becoming smaller than the first distance, and the remaining battery charge is set to a value lower than the threshold Vth1 A larger fieldIn this case, it can be said that the friction brake 4 is operated in response to the distance to the forward vehicle becoming smaller than a second distance that is longer than the first distance. The braking control unit 112 transitions to a normal mode in which the friction brake 4 is operated at a reference timing on the condition that the regenerative braking force value identified by the identification unit 111 becomes larger than a first threshold value Pth1 stored in the storage unit 10 while operating in the special mode.

[0037] When the regenerative braking force value is greater than a first threshold value Pth1 stored in the memory unit 10, the braking control unit 112 turns on the regenerative brake flag and operates in a normal mode. When the identified regenerative braking force value is less than the first threshold value Pth1, the braking control unit 112 turns off the regenerative brake flag and operates in a special mode. When the regenerative brake flag is off, the braking control unit 112 activates the friction brake 4 at a special timing that is earlier than the reference timing.

[0038] When the rotation speed of the motor 3 satisfies a predetermined condition, the regenerative braking force value decreases as the remaining battery charge increases. In this case, the regenerative braking force value being less than the first threshold value Pth1 corresponds to the remaining battery charge identified by the identification unit 111 being greater than the threshold value Vth1. When the remaining battery charge is greater than the threshold value Vth1, the braking control unit 112 may stop the operation of the regenerative brake, or may operate the regenerative brake as an auxiliary to the friction brake 4.

[0039] The braking control unit 112 operates the regenerative brake on the condition that the regenerative braking force value becomes greater than a second threshold value Pth2 after the regenerative braking force value becomes less than a first threshold value Pth1. The second threshold value Pth2 is greater than the first threshold value Pth1.

[0040] Fig. 4 shows an example of on / off switching of the regenerative braking flag by braking control unit 112. The upper graph in Fig. 4 shows changes in the regenerative braking force value. The lower graph in Fig. 4 shows on / off switching of the regenerative braking flag. The horizontal axis in Fig. 4 shows time.

[0041] As shown in FIG. 4, when the regenerative braking force value falls to or below a first threshold value Pth1, the braking control unit 112 switches the regenerative brake flag from ON to OFF. Thereafter, when the regenerative braking force value rises to or above a second threshold value Pth2, the braking control unit 112 switches the regenerative flag from OFF to ON again. The second threshold value Pth2 is a value greater than the first threshold value Pth1. Because a value greater than the first threshold value Pth1 is set as the second threshold value Pth2, the braking control unit 112 can suppress frequent switching of the regenerative flag between ON and OFF. As a result, the braking control unit 112 can suppress the behavior of the vehicle 100 from becoming unstable.

[0042] The braking control unit 112 may operate the regenerative brake by turning on the regenerative brake flag under the condition that the friction brake 4 is not in operation, in addition to the condition that the regenerative braking force value becomes greater than a second threshold value Pth2 greater than the first threshold value Pth1 after the regenerative braking force value becomes less than the first threshold value Pth1. In this way, the braking control unit 112 can suppress the regenerative brake flag from being turned on while the friction brake 4 is in operation. Therefore, the braking control unit 112 can suppress the behavior of the vehicle 100 from becoming unstable due to the friction brake 4 being suddenly switched off.

[0043] The braking control unit 112 may activate the regenerative brake by turning on the regenerative brake flag on the condition that the regenerative braking force becomes less than the first threshold value Pth1 and the vehicle 100 starts accelerating. Since it is considered that the friction brake 4 is not activated while the vehicle 100 is accelerating, the braking control unit 112 can also suppress the behavior of the vehicle 100 from becoming unstable by turning on the regenerative brake flag during acceleration.

[0044] Furthermore, the braking control unit 112 may operate the regenerative brake by turning on a regenerative brake flag on the condition that the regenerative brake is not malfunctioning, in addition to the conditions of the regenerative braking force and the friction brake 4. In this way, the braking control unit 112 does not turn on the regenerative brake flag when the regenerative brake is malfunctioning, and the friction brake 4 operates, so that it is possible to prevent the vehicle 100 from approaching the preceding vehicle 200.

[0045] [Regenerative braking flag switching procedure] 5 is a flowchart showing an example of a processing procedure for switching on and off the regenerative brake flag by the braking control unit 112. This processing procedure starts, for example, when the vehicle 100 starts automatic driving using adaptive cruise control and is operating in the normal mode.

[0046] First, the identifying unit 111 identifies the remaining battery charge of the vehicle 100 (S101). The identifying unit 111 identifies the rotation speed of the motor 3 (S102). The identifying unit 111 identifies a regenerative braking force value based on the identified remaining battery charge and the rotation speed of the motor 3 (S103).

[0047] The braking control unit 112 determines whether the regenerative braking force value identified by the identification unit 111 is less than the first threshold value Pth1 (S104). When the braking control unit 112 determines that the regenerative braking force value identified by the identification unit 111 is less than the first threshold value Pth1 (YES in S104), the braking control unit 112 turns off the regenerative brake flag and transitions to the special mode (S105).

[0048] While operating in the special mode, the braking control unit 112 determines whether or not the regenerative braking force value identified by the identification unit 111 is equal to or greater than the second threshold value Pth2 (S106). When the braking control unit 112 determines that the regenerative braking force value identified by the identification unit 111 is equal to or greater than the second threshold value Pth2 (YES in S106), the braking control unit 112 turns on the regenerative brake flag (S107) and transitions to the normal mode (S107). The braking control unit 112 determines whether or not the autonomous driving of the vehicle 100 has ended (S108). When the braking control unit 112 determines that the autonomous driving of the vehicle 100 has ended (YES in S108), the braking control unit 112 ends the process.

[0049] When the braking control unit 112 determines in the determination of S104 that the regenerative braking force value identified by the identification unit 111 is equal to or greater than the first threshold value Pth1 (NO in S104), the braking control unit 112 maintains the normal mode and returns to S101. When the braking control unit 112 determines in the determination of S106 that the regenerative braking force value identified by the identification unit 111 is less than the second threshold value Pth2 (NO in S106), the braking control unit 112 maintains the special mode and repeats the process of S106. The braking control unit 112 repeats the processes from S101 to S107 until the automatic driving ends (NO in S108). When the automatic driving ends (YES in S108), the braking control unit 112 ends the control of the friction brake 4 linked to the remaining battery power.

[0050] [Variations] In the above description, the case has been exemplified where the threshold value Vth1 of the remaining battery charge used by the braking control unit 112 to determine the timing to generate the friction brake 4 is a fixed value, but the threshold value Vth1 may be a value that changes depending on the state of the vehicle 100. As an example, the threshold value Vth1 may be a value that changes depending on the distance between the vehicle 100 and the preceding vehicle 200. Since a larger braking force is required as the distance between the vehicle 100 and the preceding vehicle 200 becomes smaller, the braking control unit 112 may set the threshold value Vth1 to be smaller as the distance between the vehicle 100 and the preceding vehicle 200 becomes smaller.

[0051] Furthermore, the threshold value Vth1 may be determined based on the speed at which the vehicle 100 travels. Since the higher the speed of the vehicle 100, the greater the braking force required to stop the vehicle 100, the braking control unit 112 may set the threshold value Vth1 to be smaller as the speed of the vehicle 100 increases.

[0052] [Effects of the brake control device 1 of the present disclosure] When the identified remaining battery charge is greater than the threshold Vth1, the braking control unit 112 activates the friction brake 4 at a special timing that is earlier than the reference timing for activating the friction brake 4 when the remaining battery charge is equal to or less than the threshold Vth1, so that the vehicle 100 can be prevented from approaching the preceding vehicle 200 during the automatic traveling of the vehicle 100. As a result, the driver can be prevented from feeling a sense of fear.

[0053] <Second embodiment> A second embodiment of the present invention will be described. The braking control device 1000 according to the second embodiment is a braking control device that specifies a braking force (required braking force) required for a vehicle (hereinafter, host vehicle) that operates by the driving force of a motor 3 driven by a battery based on the distance between the host vehicle and a vehicle ahead of the host vehicle (hereinafter, forward vehicle) and executes brake control. The braking control device 1000 determines whether or not the required braking force can be generated by regenerative braking based on the remaining battery charge. Then, when the required braking force cannot be generated by regenerative braking, the braking control device 1000 executes brake control so that the required braking force is generated by the friction brake 4.

[0054] 6 is a configuration diagram showing the configuration of a vehicle including a braking control device 1000 according to the second embodiment. The vehicle includes a braking control device 1000, a voltage sensor 2, a motor 3, a friction brake 4, a battery 5, a vehicle speed sensor 6, and a distance sensor 7. Here, the voltage sensor 2, the motor 3, and the friction brake 4 have the same functions as those of the same components in the first embodiment, so their explanations are omitted.

[0055] The battery 5 is a power storage device that supplies the motor 3 with power for driving the motor 3. The battery 5 can also be charged with power generated by the motor 3 when the motor 3 performs a regenerative operation. A battery voltage V corresponding to the remaining power of the battery 5 is detected by the voltage sensor 2 and input to the braking control device 1000.

[0056] The vehicle speed sensor 6 is a detection device that detects the relative vehicle speed Vm between the host vehicle and a vehicle ahead. The relative vehicle speed Vm can be detected by various known techniques. The vehicle speed sensor 6 inputs the relative vehicle speed Vm to the brake control device 1000.

[0057] The distance sensor 7 is a detection device that detects the distance L between the vehicle itself and the vehicle ahead. Various known techniques can be adopted as a method for detecting the distance L. The distance sensor 7 inputs the distance L to the braking control device 1000.

[0058] The braking control device 1000 includes a control unit 1100 and a storage unit 10. The control unit 1100 includes one or more processors. The control unit 1100 may include an electric circuit. The control unit 1100 reads out a program stored in the storage unit 10 and executes the functions of an acquisition unit 1101, a required braking force specification unit 1102, a regenerative braking force specification unit 1103, and a braking control unit 1104. The storage unit 10 is a storage medium that stores the program executed by the control unit 1100 and parameters used by the control unit 1100 to execute the program.

[0059] The control unit 1100 executes the functions of an acquisition unit 1101 , a required braking force specification unit 1102 , a regenerative braking force specification unit 1103 , and a braking control unit 1104 .

[0060] The acquisition unit 1101 is an interface that acquires each parameter from each of the motor 3, the voltage sensor 2, the distance sensor 7, and the vehicle speed sensor 6. The acquisition unit 1101 acquires information indicating the rotation speed M of the motor 3 from the motor 3. The acquisition unit 1101 acquires information indicating the battery voltage V from the voltage sensor 2. The acquisition unit 1101 acquires information indicating the distance L between the host vehicle and the vehicle ahead from the distance sensor 7. The acquisition unit 1101 acquires information indicating the relative vehicle speed Vm between the host vehicle and the vehicle ahead from the vehicle speed sensor 6. The acquisition unit 1101 outputs the information indicating the distance L and the information indicating the relative vehicle speed Vm to the required braking force identification unit 1102. The acquisition unit 1101 outputs the information indicating the rotation speed M and the information indicating the battery voltage V to the regenerative braking force identification unit 1103.

[0061] The required braking force specifying unit 1102 specifies a braking force required to maintain a distance between the host vehicle and a preceding vehicle at a predetermined distance or more, based on information indicating the distance L and information indicating the relative vehicle speed Vm. Here, it is assumed that the correspondence relationship between the distance L, the relative vehicle speed Vm, and the required braking force Pw is stored as a table in the storage unit 10. It is assumed that the required braking force specifying unit 1102 sets the required braking force Pw based on the input information indicating the distance L and the information indicating the relative vehicle speed Vm, and the table.

[0062] If the distance L is the same, the greater the relative vehicle speed Vm, the greater the required braking force Pw. Also, if the relative vehicle speed Vm is the same, the shorter the distance L, the greater the required braking force. The correspondence relationship between the distance L, the relative vehicle speed Vm, and the required braking force Pw may be set discretely (in steps). Also, the required braking force Pw may be specified for the distance threshold Lth and the speed threshold Vmth using a predetermined function. The required braking force specification unit 1102 outputs the required braking force Pw to the braking control unit 1104.

[0063] The regenerative braking force specification unit 1103 specifies a braking force P that can be generated by regenerative braking, based on information indicating the rotation speed M of the motor 3 and information indicating the battery voltage V. The battery voltage V corresponds to the remaining capacity of the battery. The relationship between the braking force P that can be generated by regenerative braking and the rotation speed M of the motor 3 and the remaining capacity of the battery is similar to that described in the first embodiment, and therefore description thereof will be omitted.

[0064] Here, it is assumed that the correspondence relationship between the rotation speed M of the motor 3, the battery voltage V, and the braking force P is stored as a table in the storage unit 10. The regenerative braking force specifying unit 1103 specifies the braking force P based on the input information indicating the rotation speed M of the motor 3 and the information indicating the battery voltage V, and the table. The correspondence relationship between the rotation speed M of the motor 3, the battery voltage V, and the braking force P may be set discretely. Also, the braking force P may be specified for the rotation speed M of the motor 3 and the battery voltage V using a predetermined function. The regenerative braking force specifying unit 1103 outputs the braking force P to the braking control unit 1104.

[0065] The braking control unit 1104 controls the regenerative brake and the friction brake 4 based on the input required braking force Pw and the braking force P. Specifically, the braking control unit 1104 outputs a control signal for controlling the regenerative brake and the friction brake 4 to the motor 3 and the friction brake 4 based on the input required braking force Pw and the braking force P.

[0066] The braking control unit 1104 determines whether the braking force P is greater than the required braking force Pw. If the braking force P is greater than the required braking force Pw, the braking control unit 1104 sends a control signal to the motor 3 to operate the regenerative brake so as to obtain the required braking force Pw by the regenerative brake (normal mode). If the braking force P is not greater than the required braking force Pw, the braking control unit 1104 sends a control signal to the friction brake 4 to operate the friction brake 4 so as to obtain the required braking force Pw by the friction brake 4 (special mode).

[0067] Next, a braking control flow of the braking control device 1000 according to the second embodiment will be described. Fig. 7 is a flowchart showing the braking control flow of the braking control device 1000 according to the second embodiment. This flowchart is executed repeatedly while the vehicle is in the ACC (Auto Cruise Control) function mode. Note that a description of the drive control that is different from the brake control in the ACC function will be omitted.

[0068] In S201, the acquisition unit 1101 acquires information indicating the distance L from the distance sensor 7. The acquisition unit 1101 also acquires information indicating the relative vehicle speed Vm from the vehicle speed sensor 6. The acquisition unit 1101 outputs the information indicating the distance L and the information indicating the relative vehicle speed Vm to the required braking force identification unit 1102. The process proceeds to S202.

[0069] In S202, the required braking force specifying unit 1102 specifies a braking force (required braking force Pw) required to maintain the distance between the host vehicle and the preceding vehicle at a predetermined distance or more, based on information indicating the distance L and information indicating the relative vehicle speed Vm. The required braking force specifying unit 1102 outputs the required braking force Pw to the braking control unit 1104.

[0070] In S203, the braking control unit 1104 determines whether the required braking force Pw is greater than 0. If the required braking force Pw is 0, this indicates that braking is not necessary, that is, brake control is not necessary. If the braking control unit 1104 determines that the required braking force Pw is not greater than 0 (is 0) (No in S203), this flow ends. If the braking control unit 1104 determines that the required braking force Pw is greater than 0 (Yes in S203), the process proceeds to S204.

[0071] In S204, the acquisition unit 1101 acquires information indicating the battery voltage V from the voltage sensor 2. The battery voltage V indicates the remaining battery capacity, and the acquisition unit 1101 may acquire the remaining battery capacity (SOC) based on the battery voltage V. The acquisition unit 1101 outputs the information indicating the battery voltage V to the regenerative braking force identification unit 1103. The process proceeds to S205.

[0072] In S205, the acquisition unit 1101 acquires information indicating the rotation speed M of the motor 3 from the motor 3. The acquisition unit 1101 outputs the information indicating the rotation speed M of the motor 3 to the regenerative braking force identification unit 1103. The process proceeds to S206.

[0073] In S206, the regenerative braking force specifying unit 1103 specifies the braking force P that can be generated by the regenerative brake based on the information indicating the battery voltage V and the information indicating the rotation speed M of the motor 3. The method in which the regenerative braking force specifying unit 1103 specifies the braking force P is as described above. The regenerative braking force specifying unit 1103 outputs the braking force P to the braking control unit 1104. The process proceeds to S207.

[0074] In S207, the braking control unit 1104 determines whether the braking force P is equal to or greater than the required braking force Pw. If the braking force P is smaller than the required braking force Pw, this means that the braking force required by the ACC function cannot be obtained by braking using regenerative braking. This may result in the host vehicle unintentionally approaching the vehicle ahead. On the other hand, if the braking force P is equal to or greater than the required braking force Pw, this means that the braking force required by the ACC function can be obtained by using regenerative braking.

[0075] Here, as described above, the braking force P that can be generated by regenerative braking is determined based on the remaining charge of the battery 5. Therefore, it can be said that the braking control unit 1104 determines whether or not the required braking force Pw can be generated by regenerative braking based on the remaining charge of the battery. If it is determined that the braking force P is equal to or greater than the required braking force Pw (Yes in S207), the process proceeds to S208. If it is determined that the braking force P is smaller than the required braking force Pw (No in S207), the process proceeds to S209.

[0076] In S208, the braking control unit 1104 controls the regenerative brake so as to generate the required braking force Pw. The braking control unit 1104 transmits a control signal to the motor 3 for controlling the motor 3 so as to generate the required braking force Pw. The motor 3 receives the control signal and operates the regenerative brake to generate a braking force. This ends the flow. As described above, this flow is repeatedly executed while the ACC operation is being performed.

[0077] In S209, the braking control unit 1104 controls the friction brake 4 so as to generate the required braking force Pw. The braking control unit 1104 transmits a control signal to the friction brake 4 for controlling the friction brake 4 so as to generate the required braking force Pw. The friction brake 4 operates in response to the control signal and generates a braking force. This ends the flow.

[0078] With the above-described control, even when the remaining battery charge is high and the required braking force cannot be obtained by regenerative braking, the required braking force can be obtained by operating the friction brake 4. Furthermore, since regenerative braking can be used when the remaining battery charge is low, it is possible to suppress wear on the friction brake 4 caused by constantly using the friction brake 4 in ACC control.

[0079] In the above-described control, the regenerative brake and the friction brake 4 are controlled based on whether or not the braking force P at which the regenerative brake can be generated is equal to or greater than the required braking force Pw. As described in the first embodiment, the braking force P at which the regenerative brake can be generated is determined according to the remaining battery charge. Therefore, determining whether or not the braking force P at which the regenerative brake can be generated is equal to or greater than the required braking force Pw can be said to be determining whether or not the remaining battery charge is smaller than the battery remaining charge threshold at which the regenerative brake can be generated. In other words, the brake control device 1000 according to the second embodiment operates the regenerative brake when the remaining battery charge is smaller than the battery remaining charge threshold at which the regenerative brake can be generated, and operates the friction brake 4 when the remaining battery charge is not smaller than the battery remaining charge threshold at which the regenerative brake can be generated.

[0080] In addition, by controlling as described above, when the remaining battery charge is greater than the battery charge threshold at which the required braking force Pw can be generated by regenerative braking, the friction brake is operated instead of the regenerative brake. Therefore, the timing at which the friction brake starts operating is earlier than when the remaining battery charge is sufficient to generate the required braking force Pw by regenerative braking.

[0081] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0082] 1 Braking control device 2 Voltage Sensor 3 Motor 4 Friction brakes 5 Battery 6 Vehicle speed sensor 7 Distance Sensor 10 Storage section 11 Control section 100 vehicles 111 Specific section 112 Braking control unit 200 Front vehicle 1000 Braking control device 1100 Control section 1101 Acquisition Department 1102 Requested braking force specification section 1103 Regenerative braking force identification section 1104 Braking control unit

Claims

1. A braking control device that controls a regenerative brake and a friction brake based on a distance to a forward vehicle, a determination unit that determines a remaining battery charge of a battery that can be charged with electric power generated from the regenerative brake when the regenerative brake performs a regenerative operation; a braking control unit that controls the regenerative brake and the friction brake, and when the identified remaining battery charge is greater than a predetermined value, operates the friction brake at a special timing that is earlier than a reference timing for operating the friction brake when the remaining battery charge is equal to or less than the predetermined value; A braking control device comprising:

2. The braking control unit stops the operation of the regenerative brake at the special timing.

2. The braking control device according to claim 1.

3. The determination unit determines a regenerative braking force value that can be generated by the regenerative brake based on the remaining battery charge, The braking control unit operates the friction brake at the special timing on condition that the regenerative braking force value becomes less than a first threshold value.

2. The braking control device according to claim 1.

4. The determination unit determines a regenerative braking force value that can be generated by the regenerative brake based on the remaining battery charge and the rotation speed of the motor.

4. The braking control device according to claim 3.

5. The first threshold value is a value corresponding to a maximum value of the regenerative braking force value.

5. The brake control device according to claim 3 or 4.

6. The first threshold value is a value obtained by multiplying the maximum value of the regenerative braking force value by a coefficient smaller than 1.

6. The braking control system according to claim 5.

7. The braking control unit operates the regenerative brake on the condition that the regenerative braking force value becomes greater than a second threshold value that is greater than the first threshold value after the regenerative braking force value becomes less than the first threshold value.

5. The brake control device according to claim 3 or 4.

8. The braking control unit operates the regenerative brake under the condition that the regenerative braking force value becomes larger than the second threshold value after the regenerative braking force value becomes smaller than the first threshold value and the friction brake is not operating.

8. The braking control system according to claim 7.

9. The braking control unit operates the regenerative brake under the condition that, after the regenerative braking force value becomes smaller than the first threshold value, the regenerative braking force value becomes larger than the second threshold value, the friction brake is not operating, and the regenerative brake is not malfunctioning.

8. The braking control system according to claim 7.

10. The braking control unit operates the regenerative brake after the regenerative braking force value becomes less than the first threshold value and the vehicle starts accelerating.

5. The brake control device according to claim 3 or 4.

11. A braking control device that controls a regenerative brake and a friction brake based on a distance to a forward vehicle, a determination unit that determines a remaining battery charge of a battery that can be charged with electric power generated from the regenerative brake when the regenerative brake performs a regenerative operation; a braking control unit that controls the regenerative brake and the friction brake, and activates the friction brake when the remaining battery charge is equal to or less than a predetermined value and the distance to the forward vehicle is shorter than a first distance, and activates the friction brake when the remaining battery charge is greater than the predetermined value and the distance to the forward vehicle is shorter than a second distance longer than the first distance; A braking control device comprising:

12. A braking control method for controlling a regenerative brake and a friction brake based on a distance to a forward vehicle, comprising: determining a remaining battery charge of a battery that can be charged with electric power generated from the regenerative brake when the regenerative brake performs a regenerative operation; controlling the regenerative brake and the friction brake, and when the identified remaining battery charge is greater than a predetermined value, operating the friction brake at a special timing that is earlier than a reference timing for operating the friction brake when the remaining battery charge is equal to or less than the predetermined value; A braking control method comprising:

13. A braking control method for controlling a regenerative brake and a friction brake based on a distance to a forward vehicle, comprising: determining a remaining battery charge of a battery that can be charged with electric power generated from the regenerative brake when the regenerative brake performs a regenerative operation; controlling the regenerative brake and the friction brake, and activating the friction brake when the remaining battery charge is equal to or less than a predetermined value and the distance to the preceding vehicle becomes smaller than a first distance, and activating the friction brake when the remaining battery charge is greater than the predetermined value and the distance to the preceding vehicle becomes smaller than a second distance that is longer than the first distance; A braking control method comprising:

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