Braking control system

Abstract

To enable the vehicle to remain stationary even if communication between the first control device and the second control device is interrupted. [Solution] The braking control system 60 includes a first braking ECU 70 which operates the first electric parking actuator 31 and has an acceleration sensor 75, and a redundant ECU 90 which can communicate with the first braking ECU 70 and operates the second electric parking actuator 32. When generating parking braking force while communication between ECUs 70 and 90 is interrupted, the redundant ECU 90 generates parking braking force at the second wheel according to the control information that was last acquired. The first braking ECU 70 derives a first parking braking force by considering the difference between the predicted parking braking force, which is the parking braking force that can be predicted to be generated at the second wheel, and the stopping holding braking force, and generates the first parking braking force at the first wheel.

Description

Technical Field

[0004] , , ,

[0005] , , ,

[0001] The present invention relates to a braking control system mounted on a vehicle.

Background Art

[0002] Patent Document 1 discloses a system applied to a vehicle including a first electric parking actuator that generates a parking braking force on a first wheel and a second electric parking actuator that generates a parking braking force on a second wheel. The system includes a first control device that controls the first electric parking actuator and a second control device that controls the second electric parking actuator. The first control device and the second control device can communicate with each other via an in-vehicle network.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the vehicle is parked on a slope and the communication between the first control device and the second control device via the in-vehicle network is interrupted. In such a system as described above, even when a parking braking request occurs under such a situation, it is desired to be able to hold the vehicle in a parked state by parking braking.

Means for Solving the Problems

[0005] A braking control system for solving the above problems is applied to a vehicle comprising a first wheel and a second wheel, a first electric parking actuator configured to generate parking braking force with the first wheel, and a second electric parking actuator configured to generate parking braking force with the second wheel. The braking control system comprises a first control device that operates the first electric parking actuator and has an acceleration sensor, and a second control device that is configured to communicate with the first control device via an in-vehicle network and operates the second electric parking actuator. The first control device transmits control information, which is information regarding an acceleration detection value that is the acceleration based on the detection signal of the acceleration sensor, to the second control device at predetermined intervals. When communication between the first control device and the second control device via the in-vehicle network is interrupted, and a parking brake request occurs which is a request to park the vehicle, the second control device operates the second electric parking actuator to generate a second parking brake force at the second wheel, which is a parking brake force corresponding to the control information that was last obtained via the in-vehicle network. The first control device derives a first parking brake force such that it increases as the difference between the predicted parking brake force, which is a parking brake force that can be predicted to be generated at the second wheel by the operation of the second electric parking actuator, and the reference parking brake force, which is a parking brake force corresponding to the latest value of the acceleration detection value, increases, and operates the first electric parking actuator to generate the first parking brake force at the first wheel. [Effects of the Invention]

[0006] The above braking control system has the effect of being able to maintain the vehicle's stop even if communication between the first control device and the second control device is interrupted. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing a vehicle equipped with one embodiment of a braking control system. [Figure 2]Figure 2 is a configuration diagram showing the braking control system of Figure 1 and the electric parking device controlled by the braking control system. [Figure 3] Figure 3 is a sequence diagram showing the processing flow when generating parking braking force in the braking control system of Figure 1. [Figure 4] Figure 4 is a flowchart showing the series of processes involved in generating parking braking force with the second wheel in the braking control system shown in Figure 1. [Figure 5] Figure 5 is a flowchart showing the series of processes involved in generating parking braking force with the first wheel in the braking control system shown in Figure 1. [Figure 6] Figures 6(a) to 6(h) are timing charts for generating parking braking force in the vehicle in the braking control system shown in Figure 1. [Modes for carrying out the invention]

[0008] One embodiment of the braking control system will be described with reference to Figures 1 to 6. <Vehicle Configuration> Figure 1 shows a vehicle 10 to which the braking control system 60 is applied. Figure 2 shows the braking control system 60. As shown in Figures 1 and 2, the vehicle 10 further comprises a plurality of wheels, the same number of friction brakes 20 as the wheels, a hydraulic braking device 25, and an electric parking device 30. The plurality of wheels include first wheels 11 and second wheels 12. An example of the first wheels 11 and second wheels 12 is the rear wheels.

[0009] Each of the multiple friction brakes 20 includes a rotating body 21 that rotates integrally with the corresponding wheel, a friction material 22, and a wheel cylinder 23. The friction brake 20 is configured to generate braking force on the corresponding wheel by pressing the friction material 22 against the rotating body 21. The higher the hydraulic pressure of the wheel cylinder 23, the greater the force pressing the friction material 22 against the rotating body 21, resulting in a greater braking force being generated on the wheel.

[0010] The hydraulic braking system 25 includes a first hydraulic braking system 26 and a second hydraulic braking system 27. Each of the first hydraulic braking system 26 and the second hydraulic braking system 27 is configured to adjust the hydraulic pressure of a plurality of wheel cylinders 23. The first hydraulic braking system 26 is configured to adjust the hydraulic pressure of a plurality of wheel cylinders 23 individually. The second hydraulic braking system 27 is configured to generate hydraulic pressure in a plurality of wheel cylinders 23 corresponding to the required braking force, which is the required value of the braking force for the vehicle 10. An example of the configuration of the first hydraulic braking system 26 and the second hydraulic braking system 27 is disclosed in "Japanese Patent Application Publication No. 2024-76857".

[0011] The electric parking device 30 includes a first electric parking actuator 31 and a second electric parking actuator 32. The first electric parking actuator 31 is configured to generate parking braking force at the first wheel 11. The second electric parking actuator 32 is configured to generate parking braking force at the second wheel 12. Each of the multiple electric parking actuators 31, 32 has an electric motor. The multiple electric parking actuators 31, 32 can generate parking braking force at the wheels in accordance with the drive of the electric motors. For example, when the electric motor is driven, the friction material 22 of the friction brake 20 is pressed against the rotating body 21, so that parking braking force is generated at the wheels 11, 12. An example of the configuration of the electric parking actuators 31, 32 is disclosed in "Japanese Patent Application Publication No. 2022-85637".

[0012] <In-car network> The in-vehicle network of vehicle 10 will be described with reference to Figures 1 and 2. Vehicle 10 is equipped with multiple electronic control units. Hereafter, these electronic control units will be referred to as "ECUs." ECU is an abbreviation for "Electronic Control Unit." Vehicle 10 is equipped with an in-vehicle network for communication between the multiple ECUs. The in-vehicle network has multiple global communication lines. An example of a global communication line is the CAN bus. "CAN" is an abbreviation for "Control Area Network."

[0013] The multiple global communication lines include a first global communication line 201 and a second global communication line 202. <ECUs other than the ECU that make up the braking control system> Vehicle 10 is equipped with an integrated ECU 51 and a shift ECU 52 as ECUs other than those that constitute the braking control system 60. The integrated ECU 51 transmits various information, requests, and commands to other ECUs via the in-vehicle network. For example, when an occupant of vehicle 10 operates the parking brake operation switch 41, the integrated ECU 51 transmits a parking brake operation request, which is a request related to parking braking, to the first global communication line 201 and the second global communication line 202, as shown by arrow X1 in Figure 2. The parking brake operation switch 41 is an operating unit that the occupant operates to activate the electric parking device 30. For example, the parking brake operation switch 41 is installed inside the vehicle.

[0014] A parking brake action request includes an apply request and a release request. The apply request is a request to generate parking brake force. The release request is a request to release the state in which parking brake force is generated. In this embodiment, the apply request corresponds to the "parking brake action request".

[0015] The shift ECU 52 controls the shift device installed in the vehicle 10. The shift ECU 52 transmits range information, which is information corresponding to the shift range selected by the shift device, to the second global communication line 202.

[0016] <Braking control system> As shown in FIGS. 1 and 2, the braking control system 60 includes a plurality of ECUs related to vehicle braking. The plurality of ECUs includes a first braking ECU 70, a second braking ECU 80, and a redundant ECU 90.

[0017] The first braking ECU 70 operates the first hydraulic braking device 26. The first braking ECU 70 operates only the first electric parking actuator 31 among the plurality of electric parking actuators 31, 32, 33. In this regard, the first braking ECU 70 corresponds to the "first control device".

[0018] The first braking ECU 70 has a processing circuit 71, a drive circuit 73, and an acceleration sensor 75. The processing circuit 71 has a CPU and a memory that stores a control program executed by the CPU. The control program includes a control program for operating the first hydraulic braking device 26 and a control program for operating the first electric parking actuator 31. By the CPU executing the control program in the memory, the processing circuit 71 can operate the first hydraulic braking device 26 or operate the first electric parking actuator 31.

[0019] The drive circuit 73 is a circuit for driving the electric motor of the first electric parking actuator 31. When the drive circuit 73 operates based on a command from the processing circuit 71, the drive circuit 73 outputs a drive signal. The first electric parking actuator 31 operates when the electric motor is driven based on the drive signal.

[0020] The acceleration sensor 75 detects the acceleration of the vehicle 10 in the front-rear direction. The acceleration sensor 75 outputs a detection signal corresponding to the detection result to the processing circuit 71. The acceleration in the front-rear direction based on the detection signal of the acceleration sensor 75 is referred to as the "acceleration detection value Gx".

[0021] The second braking ECU 80 activates the second hydraulic braking device 27. However, the second braking ECU 80 does not control the electric parking device 30. The second braking ECU 80 has a processing circuit 81. The processing circuit 81 has a CPU and memory. The memory stores a control program for activating the second hydraulic braking device 27. By executing this control program, the CPU can activate the second hydraulic braking device 27.

[0022] The redundant ECU 90 does not control the hydraulic braking device 25. On the other hand, the redundant ECU 90 operates only the second electric parking actuator 32 among the multiple electric parking actuators 31 and 32. In this respect, the redundant ECU 90 corresponds to the "second control device".

[0023] The redundant ECU 90 has a processing circuit 91 and a drive circuit 93. On the other hand, the redundant ECU 90 does not have a sensor that can detect the longitudinal acceleration of the vehicle 10. The processing circuit 91 has a CPU and a memory. The memory stores a control program for operating the second electric parking actuator 32. By executing this control program, the CPU can operate the second electric parking actuator 32.

[0024] The drive circuit 93 is a circuit for driving the electric motor of the second electric parking actuator 32. When the drive circuit 93 operates based on a command from the processing circuit 91, the drive circuit 93 outputs a drive signal. The electric motor is driven based on this drive signal, thereby operating the second electric parking actuator 32.

[0025] The braking control system 60 has a braking communication line 61 as an in-vehicle network for communication between multiple ECUs involved in vehicle braking. An example of the braking communication line 61 is a CAN bus. The first braking ECU 70, the second braking ECU 80, and the redundant ECU 90 can communicate via the braking communication line 61. On the other hand, the braking communication line 61 cannot be used for communication with ECUs other than those that make up the braking control system 60. In other words, the braking communication line 61 corresponds to the "in-vehicle network" that enables communication between the first braking ECU 70 and the redundant ECU 90.

[0026] <Processing flow for parking brakes under normal conditions> Referring to Figure 3, the process flow during parking braking when the vehicle 10 is stopped and the braking control system 60 is functioning normally will be explained.

[0027] In step ST101, the processing circuit 71 of the first braking ECU 70 derives an acceleration detection value Gx. The processing circuit 71 transmits control information, which is information related to the acceleration detection value Gx derived in step ST101, to the redundant ECU 90 via the braking communication line 61 (ST102). For example, in step ST102, the processing circuit 71 transmits the acceleration detection value Gx as control information to the redundant ECU 90.

[0028] When the processing circuit 91 of the redundant ECU 90 receives control information via the braking communication line 61, it sends a reply to the first braking ECU 70 via the braking communication line 61 indicating that it has received the control information (ST103). When the first braking ECU 70 transmits an acceleration detection value Gx to the redundant ECU 90, the processing circuit 91 of the redundant ECU 90, upon receiving the acceleration detection value Gx, sends a reply to the first braking ECU 70 in step ST103 indicating that it has received the acceleration detection value Gx.

[0029] In step ST105, which is later than step ST101, the processing circuit 71 of the first braking ECU 70 derives a first parking braking force Fpk1 based on the latest value of the acceleration detection value Gx derived in step ST101. The first parking braking force Fpk1 is the target value of the parking braking force generated at the first wheel 11 by the operation of the first electric parking actuator 31.

[0030] The processing circuit 91 of the redundant ECU 90 sends a reply to the first braking ECU 70 indicating that it has received control information, and then executes the process in step ST106. In step ST106, the processing circuit 91 derives the second parking braking force Fpk2 based on the acceleration detection value Gx indicated by the control information last received from the first braking ECU 70. That is, the processing circuit 91 derives the second parking braking force Fpk2 based on the acceleration detection value Gx last received from the first braking ECU 70. The second parking braking force Fpk2 is the target value of the parking braking force generated at the second wheel 12 by the operation of the second electric parking actuator 32.

[0031] Here, when vehicle 10 is stopped, the magnitude of the detected acceleration value Gx corresponds to the road surface gradient θ, which is the gradient of the road surface on which vehicle 10 is stopped. In other words, the larger the magnitude of the detected acceleration value Gx, the larger the road surface gradient θ.

[0032] Therefore, the processing circuit 71 of the first braking ECU 70 derives a first parking braking force Fpk1 such that its magnitude increases as the magnitude of the acceleration detection value Gx increases. Similarly, the processing circuit 91 of the redundant ECU 90 derives a second parking braking force Fpk2 such that its magnitude increases as the magnitude of the acceleration detection value Gx increases. However, the multiple processing circuits 71 and 91 derive parking braking forces Fpk1 and Fpk2 such that the sum of the first parking braking force Fpk1 and the second parking braking force Fpk2 is greater than the stationary holding braking force FpkAL. The stationary holding braking force FpkAL is the lower limit of the total sum of braking forces of the vehicle 10 that can maintain the vehicle 10 in a stationary state.

[0033] When the processing circuit 91 of the redundant ECU 90 derives the second parking brake force Fpk2 in step ST106, it transmits information indicating the second parking brake force Fpk2 to the first braking ECU 70 via the braking communication line 61 (ST107). When the processing circuit 71 of the first braking ECU 70 receives information regarding the second parking brake force Fpk2 via the braking communication line 61, it replies to the redundant ECU 90 via the braking communication line 61 that it has received the information (ST108).

[0034] In the braking control system 60, the series of processes from step ST101 to step ST108 are repeatedly executed at predetermined intervals until an apply request is generated. When an apply request occurs, the processing circuit 71 of the first braking ECU 70 receives the apply request via the first global communication line 201 (ST111). The processing circuit 91 of the redundant ECU 90 receives the apply request via the second global communication line 202 (ST112).

[0035] When the processing circuit 71 of the first braking ECU 70 receives an apply request (ST111), it executes the process in step ST113. In step ST113, the processing circuit 71 executes apply control based on the first parking braking force Fpk1 derived in step ST105. In this apply control, the processing circuit 71 activates the first electric parking actuator 31 to generate the first parking braking force Fpk1 at the first wheel 11.

[0036] When the processing circuit 91 of the redundant ECU 90 receives an apply request (ST112), it executes the process in step ST114. In step ST114, the processing circuit 71 executes apply control based on the second parking brake force Fpk2 derived in step ST106. In this apply control, the processing circuit 71 activates the second electric parking actuator 32 to generate the second parking brake force Fpk2 at the second wheel 12.

[0037] As a result, the braking control system 60 can maintain the parked state by generating parking braking force on the vehicle 10. When a release request subsequently occurs, the processing circuit 71 of the first braking ECU 70 receives the release request via the first global communication line 201. The processing circuit 91 of the redundant ECU 90 receives the release request via the second global communication line 202. Then, the multiple processing circuits 71 and 91 perform release control. In the release control, the multiple processing circuits 71 and 91 activate the electric parking actuators 31 and 32 to release the parking braking force.

[0038] <Parking brakes in the event of a malfunction in the braking communication line> Referring to Figure 4, a series of processes performed by the redundant ECU 90 under the condition that communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted will be explained. When communication via the braking communication line 61 is interrupted, the processing circuit 91 of the redundant ECU 90 cannot obtain the acceleration detection value Gx from the first braking ECU 70.

[0039] In step S11, the processing circuit 91 of the redundant ECU 90 holds the second parking brake force Fpk2 derived based on the last received acceleration detection value Gx. In the following step S13, the processing circuit 91 determines whether or not it has received an apply request via the second global communication line 202. If the redundant ECU 90 has received an apply request (S13: YES), the processing circuit 91 proceeds to step S15. On the other hand, if the redundant ECU 90 has not received an apply request (S13: NO), the processing circuit 91 terminates the series of processes shown in Figure 4. Then, after a predetermined control cycle has elapsed, the processing circuit 91 executes the series of processes.

[0040] In step S15, the processing circuit 91 activates the second electric parking actuator 32 by performing apply control. This allows the processing circuit 91 to generate the second parking braking force Fpk2 held in step S11 at the second wheel 12. After completing the operation of the second electric parking actuator 32, the processing circuit 91 terminates the series of processes shown in Figure 4.

[0041] Referring to Figure 5, a series of processes performed by the first braking ECU 70 under the condition that communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted will be described. When communication via the braking communication line 61 is interrupted, the processing circuit 71 of the first braking ECU 70 cannot obtain the second parking braking force Fpk2 from the redundant ECU 90.

[0042] In step S31, the processing circuit 71 of the first braking ECU 70 derives a first parking braking force Fpk1 based on the latest value of the acceleration detection value Gx. In the following step S33, the processing circuit 71 derives a stationary holding braking force FpkAL based on the latest value of the acceleration detection value Gx. At this time, the processing circuit 71 derives the stationary holding braking force FpkAL such that its magnitude increases as the magnitude of the acceleration detection value Gx increases.

[0043] In the next step S35, the processing circuit 71 derives the predicted parking braking force Fpk2A. The processing circuit 71 obtains the acceleration detection value Gx that was last transmitted to the redundant ECU 90 via the braking communication line 61 as the final acceleration value GxA. The processing circuit 71 derives a second parking braking force Fpk2 based on the final acceleration value GxA as the predicted parking braking force Fpk2A. At this time, the processing circuit 71 derives the predicted parking braking force Fpk2A such that its magnitude increases as the magnitude of the final acceleration value GxA increases.

[0044] In the following step S37, the processing circuit 71 determines whether the first braking ECU 70 has received the apply request via the first global communication line 201. If the first braking ECU 70 has received the apply request (S37: YES), the processing circuit 71 proceeds to step S39. On the other hand, if the first braking ECU 70 has not received the apply request (S37: NO), the processing circuit 71 terminates the series of processes shown in Figure 5. Then, after a predetermined control cycle has elapsed, the processing circuit 71 executes the series of processes.

[0045] In step S39, the processing circuit 71 determines whether the predicted parking braking force Fpk2A is less than or equal to the reference parking braking force FpkB. The reference parking braking force FpkB is the parking braking force corresponding to the magnitude of the latest acceleration detection value Gx. For example, the reference parking braking force FpkB may be the value obtained by dividing the stopping holding braking force FpkAL by 2, or the value obtained by subtracting the first parking braking force Fpk1 from the stopping holding braking force FpkAL.

[0046] If the predicted parking braking force Fpk2A is less than or equal to the reference parking braking force FpkB (S39: YES), the processing circuit 71 proceeds to step S41. On the other hand, if the predicted parking braking force Fpk2A is greater than the reference parking braking force FpkB (S39: NO), the processing circuit 71 proceeds to step S43.

[0047] In step S41, the processing circuit 71 corrects the first parking braking force Fpk1 derived in step S31 based on the magnitude ΔFpk of the difference between the stationary holding braking force FpkAL and the predicted parking braking force Fpk2A. For example, the processing circuit 71 corrects the first parking braking force Fpk1 such that the larger the magnitude ΔFpk of the difference, the larger the increase in correction amount. For example, the processing circuit 71 sets the corrected first parking braking force Fpk1 to the sum of the first parking braking force Fpk1 before correction and the magnitude ΔFpk of the difference. Alternatively, the processing circuit 71 may set the corrected first parking braking force Fpk1 to the sum of the first parking braking force Fpk1 before correction, the magnitude ΔFpk of the difference, and the offset value α. Then, the processing circuit 71 proceeds to step S43.

[0048] In step S43, the processing circuit 71 activates the first electric parking actuator 31 by apply control. This allows the processing circuit 71 to generate the first parking braking force Fpk1 at the first wheel 11. After completing the operation of the first electric parking actuator 31, the processing circuit 71 terminates the series of processes shown in Figure 5.

[0049] <Operation and Effects of This Embodiment> Referring to Figure 6, the operation and effects of an apply request occurring when communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted will be explained. Figure 6(a) shows the timing of the apply control execution in the first braking ECU 70, while Figure 6(f) shows the timing of the apply control execution in the redundant ECU 90. Figure 6(b) shows the trend of the acceleration detection value Gx grasped by the first braking ECU 70, while Figure 6(g) shows the trend of the acceleration detection value Gx grasped by the redundant ECU 90. Figure 6(c) shows the trend of the predicted parking braking force Fpk2A derived by the first braking ECU 70. The solid line in Figure 6(e) shows the trend of the first current target value Ipk1, which is the value obtained by converting the first parking braking force Fpk1 into a current value. The first current target value Ipk1 is the target current flowing to the electric motor of the first electric parking actuator 31. The solid line in Figure 6(h) shows the change in the second current target value Ipk2, which is the value obtained by converting the second parking braking force Fpk2 into a current value. The second current target value Ipk2 is the target current flowing to the electric motor of the second electric parking actuator 32.

[0050] In the example shown in Figure 6, communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is performed normally until timing t11. For the sake of clarity, this explanation assumes that there is no delay due to communication via the braking communication line 61.

[0051] As shown in Figures 6(b) and 6(g), before timing t11, the acceleration detection value Gx obtainable by the redundant ECU 90 is substantially the same as the acceleration detection value Gx obtainable by the first braking ECU 70. Therefore, the predicted parking braking force Fpk2A derived by the first braking ECU 70 is substantially the same as the second parking braking force Fpk2 derived by the redundant ECU 90. In addition, the first braking ECU 70 derives the first parking braking force Fpk1 and the first current target value Ipk1 based on the latest value of the acceleration detection value Gx. The redundant ECU 90 derives the second parking braking force Fpk2 and the second current target value Ipk2 based on the latest value of the acceleration detection value Gx received via the braking communication line 61.

[0052] After timing t11, communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted. As a result, the acceleration detection value Gx and the second parking braking force Fpk2 can no longer be shared between the first braking ECU 70 and the redundant ECU 90. In other words, as shown in Figure 6(g), the acceleration detection value Gx that can be obtained by the redundant ECU 90 is retained at the value at timing t11. Also, as shown in Figure 6(c), the predicted parking braking force Fpk2A derived by the first braking ECU 70 is retained at the value at timing t11.

[0053] In the example shown in Figure 6, the vehicle 10 stops just before timing t11. Therefore, the acceleration detection value Gx fluctuates due to the vehicle's behavior accompanying the stopping of the vehicle 10. Then, at timing t11, while the acceleration detection value Gx is fluctuating, communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted. Therefore, as shown in Figure 6(g), the magnitude of the final acceleration value GxA, which is the last acceleration detection value Gx obtained by the redundant ECU 90, is smaller than the magnitude of the acceleration corresponding to the road surface gradient θ. Therefore, as shown in Figure 6(h), the second parking braking force Fpk2 derived by the redundant ECU 90 after timing t11 is smaller than the reference parking braking force FpkB mentioned above. Similarly, as shown in Figure 6(c), the predicted parking braking force Fpk2A derived by the first braking ECU 70 after timing t11 is also smaller than the reference parking braking force FpkB mentioned above.

[0054] At timing t12, the first braking ECU 70 and the redundant ECU 90 receive the apply request. The redundant ECU 90 then executes apply control, causing the second electric parking actuator 32 to operate so that the second parking braking force Fpk2 is generated at the second wheel 12. The dashed line in Figure 6(h) shows the change in the actual value of the current flowing to the electric motor of the second electric parking actuator 32. At timing t13, the actual value of the current exceeds the second current target value Ipk2, so the redundant ECU 90 determines that the second parking braking force Fpk2 is now being generated at the second wheel 12. Therefore, the redundant ECU 90 terminates the apply control.

[0055] In the first braking ECU 70, if communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted, the first parking braking force Fpk1 is derived such that it increases as the magnitude of the difference ΔFpk between the predicted parking braking force Fpk2A and the reference parking braking force FpkB increases. Specifically, from the timing t12 onward when the apply request is received, as shown in Figures 6(d) and 6(e), the first parking braking force Fpk1 and the first current target value Ipk1 are increased by the magnitude of the difference ΔFpk. The dashed line in Figure 6(e) shows the change in the first current target value Ipk1 when no correction of the first parking braking force Fpk1 and the first current target value Ipk1 based on the magnitude of the difference ΔFpk is performed.

[0056] In the first braking ECU 70, apply control is performed based on the corrected first parking brake force Fpk1. This apply control causes the first electric parking actuator 31 to operate so that the corrected first parking brake force Fpk1 is generated at the first wheel 11. The dashed line in Figure 6(e) shows the change in the actual value of the current flowing to the electric motor of the first electric parking actuator 31. At timing t14, the actual value of the current exceeds the first current target value Ipk1, so the first braking ECU 70 determines that the first parking brake force Fpk1 is now being generated at the first wheel 11. Therefore, the apply control is terminated in the first braking ECU 70.

[0057] If communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted, a braking force smaller than the parking braking force corresponding to the road surface gradient θ may be derived as the second parking braking force Fpk2. If an apply request occurs in this state, the parking braking force generated at the second wheel 12 will be smaller than the reference parking braking force FpkB, which is the parking braking force corresponding to the road surface gradient θ.

[0058] In this regard, in the braking control system 60, the processing circuit 71 of the first braking ECU 70 obtains a predicted parking braking force Fpk2A based on the last acceleration detection value Gx that could be transmitted to the redundant ECU 90. The processing circuit 71 derives a first parking braking force Fpk1 such that it increases as the magnitude of the difference ΔFpk between the predicted parking braking force Fpk2A and the reference parking braking force FpkB increases. Then, the processing circuit 71 operates the first electric parking actuator 31 so that the first parking braking force Fpk1 is generated at the first wheel 11.

[0059] As a result, the braking control system 60 can make the sum of the parking braking force actually generated at the first wheel 11 and the parking braking force actually generated at the second wheel 12 greater than the stopping holding braking force FpkAL. Therefore, the braking control system 60 can maintain the stopping of the vehicle 10 even if communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted.

[0060] Furthermore, even when communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted, the second parking braking force Fpk2 derived by the redundant ECU 90 and the predicted parking braking force Fpk2A derived by the first braking ECU 70 may be greater than or equal to the reference parking braking force FpkB. In such cases, the processing circuit 71 of the first braking ECU 70 in the braking control system 60 does not correct the first parking braking force Fpk1. This prevents an increase in the control load of the processing circuit 71.

[0061] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0062] In situations where communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted, the processing circuit 71 of the first braking ECU 70 may acquire the second parking braking force Fpk2 indicated by the last information on the second parking braking force Fpk2 that could be received via the braking communication line 61 as the predicted parking braking force Fpk2A.

[0063] The processing circuit 71 of the first braking ECU 70 may correct the first parking braking force Fpk1 based on the magnitude of the difference ΔFpk, even if the predicted parking braking force Fpk2A is greater than the reference parking braking force FpkB. For example, if the predicted parking braking force Fpk2A is greater than the reference parking braking force FpkB, the processing circuit 71 may reduce the first parking braking force Fpk1 based on the magnitude of the difference ΔFpk.

[0064] - In situations where communication between the first braking ECU 70 and the redundant ECU 90 via the braking communication line 61 is interrupted, the processing circuit 71 of the first braking ECU 70 may set the value obtained by subtracting the second parking braking force Fpk2 from the stationary holding braking force FpkAL as the first parking braking force Fpk1. Alternatively, the processing circuit 71 may set the sum of the value obtained by subtracting the second parking braking force Fpk2 from the stationary holding braking force FpkAL and a predetermined offset value as the first parking braking force Fpk1. Even in such cases, the processing circuit 71 can derive the first parking braking force Fpk1 such that it increases as the magnitude of the above difference ΔFpk increases.

[0065] In the above embodiment, the processing circuit 71 of the first braking ECU 70 corrects the first parking braking force Fpk1 based on the magnitude of the difference ΔFpk when it receives an apply request, but it is not limited to this. For example, the processing circuit 71 may correct the first parking braking force Fpk1 based on the magnitude of the difference ΔFpk even before it receives an apply request.

[0066] The processing circuit 71 of the first braking ECU 70 may transmit information other than the acceleration detection value Gx as control information to the redundant ECU 90, as long as it is related to the acceleration detection value Gx. For example, the processing circuit 71 of the first braking ECU 70 may transmit the parking braking force corresponding to the acceleration detection value Gx as control information to the redundant ECU 90. In this case, the processing circuit 91 of the redundant ECU 90 only needs to operate the second electric parking actuator 32 based on the parking braking force received from the first braking ECU 70. Therefore, the processing circuit 91 does not need to perform the process of deriving the parking braking force.

[0067] In the braking control system, the second braking ECU 80 may have the function of operating the second electric parking actuator 32. In this case, the second braking ECU 80 corresponds to the "second braking device". Furthermore, the braking control system may be configured without a redundant ECU 90.

[0068] In the braking control system, the second braking ECU 80 may have the function of operating the first electric parking actuator 31. In this case, the second braking ECU 80 corresponds to the "first braking device".

[0069] The processing circuits 71, 81, and 91 are not limited to those that include a CPU and ROM and execute software processing. In other words, the processing circuits 71, 81, and 91 may have any of the following configurations: (a), (b), and (c).

[0070] (a) The processing circuits 71, 81, and 91 each include one or more processors that perform various processes according to a computer program. The processors include a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0071] (b) The processing circuits 71, 81, and 91 each include one or more dedicated hardware circuits that perform various processes. Examples of dedicated hardware circuits include application-specific integrated circuits, i.e., ASICs or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit," and FPGA is an abbreviation for "Field Programmable Gate Array."

[0072] (c) Each processing circuit 71, 81, 91 comprises one or more processors that execute a portion of the various processes according to a computer program, and one or more dedicated hardware circuits that execute the remaining processes of the various processes. [Explanation of symbols]

[0073] 10... Vehicles 11...1st wheel 12…Second wheel 30…Electric parking system 31…First electric parking actuator 32...Second electric parking actuator 60… Braking control system 61… Brake communication line (an example of an in-vehicle network) 70…First braking ECU (an example of the first control unit) 71…Processing circuit 75…Accelerometer 90…Redundant ECU (an example of a second control unit) 91…Processing circuit

Claims

1. This invention is applied to a vehicle comprising a first wheel and a second wheel, a first electric parking actuator configured to generate parking braking force with the first wheel, and a second electric parking actuator configured to generate parking braking force with the second wheel. The first electric parking actuator is operated, and the first control device has an acceleration sensor, The system comprises a second control device which is configured to communicate with the first control device via an in-vehicle network and which operates the second electric parking actuator, The first control device is Control information, which is information regarding the acceleration detection value, which is the acceleration based on the detection signal of the acceleration sensor, is transmitted to the second control device at predetermined intervals. When communication between the first control device and the second control device via the in-vehicle network is interrupted, and a parking brake request occurs, which is a request to park the vehicle, The second control device activates the second electric parking actuator to generate a second parking braking force at the second wheel, which is a parking braking force corresponding to the control information that was last acquired via the in-vehicle network. The first control device derives a first parking braking force such that the first parking braking force increases as the difference between the predicted parking braking force, which is the parking braking force that can be predicted to be generated at the second wheel by the operation of the second electric parking actuator, and the reference parking braking force, which is the parking braking force corresponding to the magnitude of the latest value of the acceleration detection value, increases, and operates the first electric parking actuator to generate the first parking braking force at the first wheel. Braking control system.

2. The first control device is The parking braking force corresponding to the magnitude of the acceleration detection value is derived as the first parking braking force. When a parking brake request occurs while communication between the first control device and the second control device via the in-vehicle network is interrupted, the first parking brake force is corrected based on the magnitude of the difference, and the first electric parking actuator is activated to generate the first parking brake force at the first wheel. The braking control system according to claim 1.

3. If the parking brake request occurs while communication between the first control unit and the second control unit via the in-vehicle network is interrupted, the first control unit will not correct the first parking brake force based on the magnitude of the difference if the predicted parking brake force is greater than the reference parking brake force. The braking control system according to claim 2.

4. When a parking braking request occurs while communication between the first control device and the second control device via the in-vehicle network is interrupted, the first control device acquires the predicted parking braking force as the magnitude of the acceleration detection value indicated by the last control information that was able to be transmitted to the second control device via the in-vehicle network. A braking control system according to any one of claims 1 to 3.

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