Braking control device

Abstract

To improve controllability of brake force of a brake control device.SOLUTION: At the time of abnormality of a brake control device 10, a first assistance device 31 boosts a pressure of brake liquid output from a master cylinder 22 and sends the boosted brake liquid to wheel cylinders 11L and 11R of front wheels, and a second assistance device 32 sends the brake liquid to wheel cylinders 12L and 12R of rear wheels independently from the master cylinder 22. At the time of abnormality of the brake control device 10, a second brake ECU 35 sets a higher liquid pressure of any of a first target wheel pressure set on the basis of a master pressure and a second wheel pressure set on the basis of a pedal stroke at a target pressure of the liquid pressures of the wheel cylinders 12L and 12R of the rear wheels, and controls the second assistance device 32.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brake control device that controls the braking force of a vehicle by adjusting the hydraulic pressure in a wheel cylinder. [Background technology]

[0002] Patent Document 1 describes a braking control device for a vehicle that includes two brake systems, a first brake system and a second brake system, and two types of cylinders, a master cylinder and an electric cylinder. The master cylinder pressurizes and discharges brake fluid drawn from a reserve tank in response to depression of the brake pedal. The electric cylinder electrically pressurizes and discharges the brake fluid drawn from the reserve tank. In this braking control device, both brake systems are connected to the electric cylinders under normal conditions, and braking forces of both brake systems are generated by hydraulic pressure generated by the electric cylinders. On the other hand, in the event of an abnormality such as a fluid leak, the master cylinder is connected to the first brake system, and the electric cylinder is connected to the second brake system. Braking force of the first brake system is generated by hydraulic pressure generated by the master cylinder, and braking force of the second brake system is generated by hydraulic pressure generated by the electric cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6202741 Summary of the Invention [Problem to be solved by the invention]

[0004] In the event of an abnormality, the second brake system of the braking control device is hydraulically separated from the master cylinder. Even in this state, it is desirable for the second brake system to generate braking force according to the driver's request. [Means for solving the problem]

[0005] A braking control device that solves the above problem controls the braking force of a vehicle by adjusting the hydraulic pressure in a first wheel cylinder and a second wheel cylinder. The braking control device includes a master cylinder that outputs brake fluid in response to depression of the brake pedal, a first pressurizing device that increases the pressure of the brake fluid output from the master cylinder and sends it to the first wheel cylinder, a second pressurizing device that sends brake fluid to the second wheel cylinder independently of the master cylinder, and a control unit that controls the second pressurizing device to set the target hydraulic pressure for the second wheel cylinder to the higher of a first target hydraulic pressure set based on the master pressure, which is the pressure of the brake fluid output from the master cylinder, and a second target hydraulic pressure set based on the pedal stroke, which is the amount of depression of the brake pedal.

[0006] If a fluid leak occurs in the fluid path connecting the master cylinder and the first wheel cylinder via the first pressure device, the master pressure may not increase even when the brake pedal is depressed. If the target fluid pressure for the second wheel cylinder is set based on the master pressure, the braking force generated by both the first wheel cylinder and the second wheel cylinder may be insufficient. In contrast, if the target fluid pressure for the second wheel cylinder is set based on the pedal stroke, the braking force generated by the second wheel cylinder can be appropriately controlled in accordance with the driver's request, even when the fluid leak occurs.

[0007] However, if the target hydraulic pressure for the second wheel cylinder is set based solely on the pedal stroke, the following problem can occur even when there is no fluid leakage and the master pressure rises normally in response to brake pedal depression. The first pressurizing device may return brake fluid to the master cylinder to adjust the hydraulic pressure in the first wheel cylinder. When brake fluid is returned to the master cylinder, the brake pedal is pushed back. Therefore, when the first pressurizing device returns brake fluid to the master cylinder, the pedal stroke decreases even if the driver's brake pedal force remains constant. Therefore, if the target hydraulic pressure for the second wheel cylinder is set based solely on the pedal stroke, the braking force generated by the second wheel cylinder decreases in response to this decrease in pedal stroke.

[0008] In this regard, with the above-described brake control device, even when the master cylinder pressure does not increase due to a fluid leak, the second target hydraulic pressure increases in response to an increase in pedal stroke, allowing the braking force generated by the second wheel cylinder to increase in response to depression of the brake pedal. Furthermore, when there is no fluid leak, even if the pedal stroke decreases due to the first pressurizing device returning brake fluid to the master cylinder, the master cylinder pressure does not decrease. Therefore, even if the second target hydraulic pressure decreases, the first target hydraulic pressure is maintained. Therefore, even if the first pressurizing device returns brake fluid to the master cylinder, the braking force generated by the second wheel cylinder does not decrease. In this way, the above-described brake control device can appropriately control the braking force generated by the second wheel cylinder in response to the driver's request, whether or not a fluid leak is occurring. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram schematically illustrating a configuration of a braking control device according to a first embodiment. [Figure 2] 3 is a diagram showing a schematic configuration of a second pressurizing unit included in the braking control device. FIG. [Figure 3] 4 is a flowchart showing the procedure of an abnormality wheel pressure control routine executed by the brake control device. [Figure 4] 6 is a graph showing the relationship between the master pressure and the first target wheel pressure in a first calculation map. [Figure 5] 10 is a graph showing the relationship between the pedal stroke and the second target wheel pressure in the second calculation map. [Figure 6] 10 is a diagram schematically showing the configuration of a modified example of the first pressurizing section included in the braking control device. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of a brake control device will be described with reference to FIGS. The configuration of a brake control device 10 of this embodiment will be described with reference to Figures 1 and 2. The brake control device 10 of this embodiment controls the braking force of a vehicle by adjusting the hydraulic pressure of wheel cylinders 11L, 11R of the left and right front wheels and wheel cylinders 12L, 12R of the left and right rear wheels. The brake control device 10 includes a first pressurizing unit 20 and a second pressurizing unit 30. In this embodiment, the wheel cylinders 11L, 11R of the left and right front wheels correspond to the first wheel cylinders. In addition, in this embodiment, the wheel cylinders 12L, 12R of the left and right rear wheels correspond to the second wheel cylinders.

[0011] <Configuration of first pressure unit 20> The configuration of the first pressurizing unit 20 will be described. The first pressurizing unit 20 is connected to the wheel cylinders 11L and 11R of the left and right front wheels via a first fluid passage 13. The first pressurizing unit 20 is also connected to the wheel cylinders 12L and 12R of the left and right rear wheels via a second fluid passage 14. The first pressurizing unit 20 includes a reserve tank 21, a master cylinder 22, an electric cylinder 23, a master cut valve 24, a system shutoff valve 25, a simulator cut valve 26, a stroke simulator 27, and a first brake ECU (Electronic Control Unit) 28. The reserve tank 21 is a tank that stores brake fluid, which is a liquid that serves as a transmission medium for hydraulic pressure. The master cylinder 22 is a mechanical pressurizing device that generates hydraulic pressure in response to depression of the brake pedal 15. The electric cylinder 23 is an electric pressurizing device that generates hydraulic pressure electrically. The master cut valve 24 and the system shutoff valve 25 are solenoid valves that constitute a switching mechanism that switches the state of the first pressurizing unit 20. The simulator cut valve 26 is an electromagnetic valve that switches between a state in which the master cylinder 22 and the stroke simulator 27 are hydraulically connected and a state in which the connection is cut off. The first brake ECU 28 is an electronic control device that controls the electric cylinder 23, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26.

[0012] <Configuration of master cylinder 22> Next, the configuration of the master cylinder 22 will be described. A master piston 221 is slidably provided inside the master cylinder 22. The master piston 221 defines a pressure chamber 222 into which brake fluid is introduced. The brake pedal 15 is mechanically connected to the master piston 221. The operating position of the master piston 221 in the master cylinder 22 changes in conjunction with the depression of the brake pedal 15. The operating position is the position of the master piston 221 within the range in which the master piston 221 can slide within the master cylinder 22. The volume of the pressure chamber 222 changes depending on the operating position of the master piston 221. The master cylinder 22 also has a biasing member 223 that biases the master piston 221 in a direction that increases the volume of the pressure chamber 222.

[0013] In the following description, the depression amount of the brake pedal 15 is represented by the pedal stroke S. The pedal stroke S is defined as follows: The operating position of the master cylinder 22 when the depression amount of the brake pedal 15 is "0" is defined as an operating position where the pedal stroke S is "0". The value of the pedal stroke S represents the operating amount of the master cylinder 22 in the direction where the volume of the pressure chamber 222 decreases from the operating position where the pedal stroke S is "0". The volume of the pressure chamber 222 is maximum when the pedal stroke S is "0". The volume of the pressure chamber 222 decreases as the pedal stroke S increases.

[0014] The master cylinder 22 also has two ports, an input port 224 and an output port 225, which connect the pressure chamber 222 to the outside. The pressure chamber 222 is connected to the reserve tank 21 via the input port 224. The input port 224 is open when the pedal stroke S is "0" but is closed by the master piston 221 when the pedal stroke S increases to a certain value or more. On the other hand, the output port 225 of the master cylinder 22 is always open regardless of the pedal stroke S. The output port 225 of the master cylinder 22 is connected to a stroke simulator 27 via a simulator cut valve 26. The stroke simulator 27 is a device that generates a reaction force in response to the operation of the brake pedal 15. The simulator cut valve 26 is a normally closed solenoid valve that opens when energized and closes when de-energized. The output port 225 of the master cylinder 22 is also connected to the first fluid path 13 via the master cut valve 24. The master cut valve 24 is a normally open solenoid valve that closes when energized and opens when de-energized.

[0015] <Configuration of electric cylinder 23> Next, the configuration of the electric cylinder 23 will be described. A piston 231 is slidably provided inside the electric cylinder 23. A fluid chamber 232 into which brake fluid is introduced is defined by the piston 231 inside the electric cylinder 23. The electric cylinder 23 is also provided with an electric motor 233 and a linear motion conversion mechanism 234 that converts the rotation of the electric motor 233 into linear motion of the piston 231. The operating position of the piston 231 in the electric cylinder 23 is changed by the electric motor 233. The volume of the fluid chamber 232 changes in response to the change in the operating position of the piston 231. The electric cylinder 23 also has a biasing member 235 that biases the piston 231 in a direction that increases the volume of the fluid chamber 232. In the following description, the operating position of the piston 231 at which the volume of the fluid chamber 232 is maximized will be referred to as the initial position of the piston 231. The amount of movement of the piston 231 from the initial position will be referred to as the piston stroke SP of the electric cylinder 23.

[0016] The electric cylinder 23 has two ports, an input port 236 and an output port 237, which connect the fluid chamber 232 to the outside. The fluid chamber 232 of the electric cylinder 23 is connected to the reserve tank 21 via the input port 236. The input port 236 is open when the piston stroke SP is "0" and is closed by the piston 231 when the piston stroke SP increases to a certain value or more. On the other hand, the output port 237 of the electric cylinder 23 is always open regardless of the piston stroke SP. The output port 237 of the electric cylinder 23 is connected to the second fluid path 14. The output port 237 of the electric cylinder 23 is also connected to the first fluid path 13 via a system shut-off valve 25. The system shut-off valve 25 is a normally closed solenoid valve that opens when energized and closes when de-energized. When the system shut-off valve 25 is open, the first fluid path 13 and the second fluid path 14 are in communication with each other.

[0017] <Configuration of First Brake ECU 28> Next, the configuration of the first brake ECU 28 provided in the first pressurizing unit 20 will be described. The first brake ECU 28 is an electronic control device including one or more processors that execute various controls and a memory that stores control programs and data. The first brake ECU 28 is controllably connected to the electric cylinder 23, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26. Detection signals from various sensors, such as a stroke sensor 280, a master pressure sensor 281, and an output pressure sensor 282, are input to the first brake ECU 28. The stroke sensor 280 detects the pedal stroke S. The master pressure sensor 281 detects a master pressure P0, which is the hydraulic pressure output from the output port 225 of the master cylinder 22. The output pressure sensor 282 detects the hydraulic pressure output from the output port 237 of the electric cylinder 23. The first brake ECU 28 is communicably connected to a second brake ECU 35 provided in the second pressurizing unit 30. In addition to these, the first brake ECU 28 also receives detection results of the wheel speed, vehicle body acceleration, and the like.

[0018] The first brake ECU 28 controls the electric cylinder 23, the master cut valve 24, the system shutoff valve 25, and the simulator cut valve 26 based on the detection results of the stroke sensor 280, the master pressure sensor 281, the output pressure sensor 282, etc. The first brake ECU 28 receives the control state of the second pressurizing unit 30 from the second brake ECU 35. The first brake ECU 28 may calculate the hydraulic pressure of each of the wheel cylinders 11L, 11R, 12L, and 12R based on the detection results of the stroke sensor 280, the master pressure sensor 281, and the output pressure sensor 282, and the control state of the second pressurizing unit 30.

[0019] <Configuration of second pressure unit 30> Next, the configuration of the second pressurizing unit 30 will be described. The second pressurizing unit 30 is a unit that can individually adjust the pressure of each of the wheel cylinders 11L, 11R, 12L, and 12R. The second pressurizing unit 30 can perform anti-skid control, anti-side slip control, traction control, etc.

[0020] The second pressurizing unit 30 includes a first assisting device 31, a second assisting device 32, a hydraulic pressure sensor 33, and a second brake ECU 35. The first assisting device 31 is a device that adjusts the hydraulic pressure in the wheel cylinders 11L, 11R of the left and right front wheels. The second assisting device 32 is a device that adjusts the hydraulic pressure in the wheel cylinders 12L, 12R of the left and right rear wheels. The hydraulic pressure sensor 33 is a sensor that detects the hydraulic pressure P1 that the first pressurizing unit 20 supplies to the first hydraulic path 13. The second brake ECU 35 is an electronic control device that controls the first assisting device 31 and the second assisting device 32.

[0021] <Configuration of second brake ECU 35> Like the first brake ECU 28, the second brake ECU 35 is also configured as an electronic control device. The second brake ECU 35 is controllably connected to the first assisting device 31 and the second assisting device 32. Detection signals from a stroke sensor 350 and a hydraulic pressure sensor 33 are input to the second brake ECU 35. The stroke sensor 350 is a sensor for detecting the pedal stroke S, separate from the stroke sensor 280 described above. The second brake ECU 35 calculates and determines the hydraulic pressures of the wheel cylinders 11L, 11R, 12L, and 12R based on the detection result of the hydraulic pressure sensor 33 and the control states of the first assisting device 31 and the second assisting device 32. In this embodiment, the control unit of the brake control device 10 is configured by these two electronic control units: the second brake ECU 35 and the first brake ECU 28 described above.

[0022] <Configuration of the first assisting device 31 and the second assisting device 32> Next, the configurations of the first assisting device 31 and the second assisting device 32 will be described with reference to Fig. 2. First, the configuration of the hydraulic circuit for the wheel cylinder 11L in the first assisting device 31 will be described. The hydraulic circuit includes a differential pressure control valve 301, a holding valve 302, a pressure reducing valve 303, a pump 304, a pressure regulating reservoir 306, and a return fluid path 307.

[0023] The first fluid line 13 is connected to a fluid line 308 via a differential pressure control valve 301. The differential pressure control valve 301 is a normally open linear solenoid valve. By controlling the opening degree of the differential pressure control valve 301, a differential pressure can be generated between the first fluid line 13 and the fluid line 308. A check valve 309 is installed in parallel with the differential pressure control valve 301. The check valve 309 is a valve that allows the flow of brake fluid from the first fluid line 13 to the fluid line 308, while preventing the flow of brake fluid in the opposite direction.

[0024] Fluid passage 308 is connected to wheel cylinder 11L via a retention valve 302. The retention valve 302 is connected to wheel cylinder 11L via a fluid passage 310. A check valve 311 is provided in parallel with retention valve 302 between fluid passage 308 and fluid passage 310. Check valve 311 is a valve that allows brake fluid to flow from fluid passage 310 toward fluid passage 308, while blocking brake fluid from flowing from fluid passage 308 toward fluid passage 310.

[0025] The fluid path 310 is connected to the pressure regulating reservoir 306 via a pressure reducing valve 303. The pressure reducing valve 303 is a normally closed solenoid valve that opens when energized and closes when de-energized. The pressure reducing valve 303 and the pressure regulating reservoir 306 are connected via a fluid path 312.

[0026] Fluid path 312 is connected to fluid path 308 through pump fluid path 313. Pump 304 is installed in pump fluid path 313. Pump 304 is operated by the rotation of electric motor 305. In response to its operation, pump 304 sucks brake fluid from pressure regulating reservoir 306 and discharges it into fluid path 308. A check valve 314 is installed in the portion of pump fluid path 313 between pump 304 and fluid path 308. Check valve 314 is a valve that allows brake fluid to flow from pump 304 to fluid path 308, while blocking brake fluid from flowing from fluid path 308 to pump 304.

[0027] The pressure regulating reservoir 306 is connected to the first fluid path 13 through the return fluid path 307. When there is a certain amount of brake fluid inside the pressure regulating reservoir 306, the pressure regulating reservoir 306 is in a state of blocking communication with the return fluid path 307. At this time, the pump 304 sucks the brake fluid inside the pressure regulating reservoir 306. On the other hand, when the brake fluid inside the pressure regulating reservoir 306 decreases due to suction by the pump 304, the pressure regulating reservoir 306 is in a state of communication with the return fluid path 307. This allows the pump 304 to suck the brake fluid from the first fluid path 13 through the return fluid path 307.

[0028] The hydraulic circuit for wheel cylinder 11R in first assisting device 31 has the same configuration as the hydraulic circuit for wheel cylinder 11L. The hydraulic circuits for wheel cylinder 11L and wheel cylinder 11R share differential pressure control valve 301, pump 304, pressure regulating reservoir 306, return fluid line 307, fluid lines 308 and 312, pump fluid line 313, and check valves 309 and 314. The hydraulic circuit for wheel cylinder 11L and the hydraulic circuit for wheel cylinder 11R each have separate retention valve 302, pressure reducing valve 303, fluid line 310, and check valve 311.

[0029] On the other hand, the hydraulic circuits for the wheel cylinders 12L and 12R in the second assisting device 32 have the same configuration as the hydraulic circuits for the wheel cylinders 11L and 11R in the first assisting device 31. The first assisting device 31 and the second assisting device 32 share the electric motor 305.

[0030] <Pressure Control by Second Pressurizing Unit 30> The second pressurizing unit 30 configured as described above can individually control the hydraulic pressure of each wheel cylinder 11L, 11R, 12L, and 12R. In the following description, the hydraulic pressure of each wheel cylinder 11L, 11R, 12L, and 12R will be referred to as wheel pressure. Here, the description will be made taking pressurization control of wheel cylinder 11L by the second pressurizing unit 30 as an example. Pressurization control of the other wheel cylinders 11R, 12L, and 12R is also performed in the same manner as for wheel cylinder 11L.

[0031] When pressurizing the wheel cylinder 11L, the second brake ECU 35 opens the holding valve 302 and closes the pressure-reducing valve 303. The second brake ECU 35 also sets a target differential pressure, which is a target value for the differential pressure between the wheel pressure in the wheel cylinder 11L and the hydraulic pressure P1 in the first hydraulic line 13. The target differential pressure is set so that the wheel pressure is higher than the hydraulic pressure P1 in the first hydraulic line 13. The second brake ECU 35 then applies a control current corresponding to the target differential pressure to the differential pressure control valve 301. In this state, the brake ECU 35 operates the pump 304 using the electric motor 305 to supply brake fluid from the first hydraulic line 13 to the hydraulic line 308 via the pressure regulating reservoir 306. At this time, the hydraulic line 308 is directly connected to the wheel cylinder 11L via the hydraulic line 310 due to the opening of the holding valve 302 and the closing of the pressure-reducing valve 303. Therefore, as the pump 304 supplies brake fluid to the fluid passage 308, the wheel cylinder 11L is pressurized.

[0032] If the differential pressure between the wheel pressure in the wheel cylinder 11L and the hydraulic pressure P1 in the first hydraulic line 13 attempts to exceed the target differential pressure, the differential pressure control valve 301 opens based on the magnitude relationship of the forces. The wheel pressure after pressurization is the sum of the hydraulic pressure P1 in the first hydraulic line 13, i.e., the basal hydraulic pressure, and the target differential pressure. In this way, the hydraulic circuit pressurizes the wheel cylinder 11L by generating a differential pressure between the basal hydraulic pressure and the wheel pressure. That is, the hydraulic circuit for the wheel cylinder 11L of the first assisting device 31 pressurizes the wheel cylinder 11L by increasing the hydraulic pressure P1 supplied to the first hydraulic line 13 by the first pressurizing unit 20 and outputting it to the wheel cylinder 11L.

[0033] <Normal braking force control> Next, we will explain the control of the vehicle braking force by the brake control device 10 when no abnormality is detected, i.e., during normal operation. During normal operation, the first brake ECU 28 closes the master cut valve 24 and opens the system shutoff valve 25 and simulator cut valve 26. As a result, the output port 237 of the electric cylinder 23 is connected to both the first fluid line 13 and the second fluid line 14. Meanwhile, the output port 225 of the master cylinder 22 is connected only to the stroke simulator 27, without being connected to either the first fluid line 13 or the second fluid line 14. In other words, the brake control device 10 connects both the first assisting device 31 and the second assisting device 32 to the reserve tank 21 via the electric cylinder 23. In this state, brake fluid discharged from the electric cylinder 23 is sent to the wheel cylinders 11L, 11R, 12L, and 12R. In this embodiment, this normal state of the brake control device 10 corresponds to the second state.

[0034] Under normal conditions, the first brake ECU 28 controls the braking force of the vehicle by adjusting the wheel pressure through control of the electric cylinder 23. In the following description, the hydraulic pressure in the wheel cylinders 11L, 11R of the left and right front wheels will be referred to as the front wheel pressure Pf, and the hydraulic pressure in the wheel cylinders 12L, 12R of the left and right rear wheels will be referred to as the rear wheel pressure Pr.

[0035] The first brake ECU 28 performs braking force control in the normal state in the following manner. That is, during braking force control in the normal state, the first brake ECU 28 reads the pedal stroke S detected by the stroke sensor 280 and the master pressure P0 detected by the master pressure sensor 281. Then, based on the master pressure P0 and the pedal stroke S, the first brake ECU 28 calculates a target wheel pressure Pt, which is a target value for the wheel pressures Pr, Pf of the front and rear wheels. Then, the first brake ECU 28 controls the electric cylinder 23 so that both the wheel pressures Pr, Pf of the front and rear wheels become equal to the target wheel pressure Pt.

[0036] The calculation of the target wheel pressure Pt at this time is performed, for example, in the following manner. First, the first brake ECU 28 calculates a third target wheel pressure Pt3 based on the master pressure P0, and calculates a fourth target wheel pressure Pt4 based on the pedal stroke S. The first brake ECU 28 also calculates a weighting coefficient α based on the master pressure P0. The first brake ECU 28 calculates the weighting coefficient α within a range of 0 to 1 so that the weighting coefficient α is smaller when the master pressure P0 is high than when it is low. The first brake ECU 28 then calculates a value that satisfies the relationship of Equation (1) as the value of the target wheel pressure Pt. That is, during braking force control in normal operation, the first brake ECU 28 sets the weighting coefficient α based on the master pressure P0. The first brake ECU 28 then calculates a weighted average of the third target wheel pressure Pt3 and the fourth target wheel pressure Pt4 according to the weighting coefficient α as the value of the target wheel pressure Pt.

[0037]

number

[0038] <Braking force control during abnormal conditions> During the normal braking force control as described above, the first brake ECU 28 checks whether or not there is an abnormality in the brake control device 10. For example, if there is a continuing deviation between the output hydraulic pressure of the electric cylinder 23 detected by the output pressure sensor 282 and the target wheel pressure Pt, the first brake ECU 28 determines that an abnormality has occurred in the brake control device 10. Note that the continuing deviation between the output hydraulic pressure and the target wheel pressure Pt occurs, for example, when the electric cylinder 23 no longer operates normally or when a hydraulic leak occurs in the hydraulic circuit of the brake control device 10.

[0039] When the first brake ECU 28 detects an abnormality in the brake control device 10, it stops the normal braking force control and returns the piston 231 of the electric cylinder 23 to its initial position. Specifically, the first brake ECU 28 stops the supply of electricity to the electric motor 233, causing the biasing member 235 to return the piston 231 to its initial position. If the electric cylinder 23 is controllable, the electric motor 233 may be driven to move the piston 231 toward its initial position. When the piston 231 is positioned at its initial position, the electric cylinder 23 is brought into a state in which the input port 236 and the output port 237 are in communication with each other. The first brake ECU 28 also opens the master cut valve 24 and closes the system shutoff valve 25 and the simulator cut valve 26. As a result, the first assisting device 31 is connected to the reserve tank 21 via the master cylinder 22. The second assisting device 32 is connected to the reserve tank 21 without passing through the master cylinder 22. In this embodiment, the state of the brake control device 10 at this time corresponds to the first state. Furthermore, the first brake ECU 28 notifies the second brake ECU 35 of the occurrence of an abnormality. Then, upon receiving the notification of the occurrence of an abnormality from the first brake ECU 28, the second brake ECU 35 starts controlling the braking force of the vehicle by adjusting the wheel pressures Pf, Pr using the first assisting device 31 and the second assisting device 32.

[0040] 3 shows a flowchart of an abnormality wheel pressure control routine executed by the second brake ECU 35 for controlling braking force in such an abnormality. After receiving an abnormality notification from the first brake ECU 28, the second brake ECU 35 repeatedly executes the processing of this routine at a predetermined control cycle.

[0041] When this routine starts, first in step S100, the second brake ECU 35 reads the detected value of the pedal stroke S by the stroke sensor 350. Also in step S100, the second brake ECU 35 reads the detected value of the hydraulic pressure by the hydraulic pressure sensor 33 as the value of the master pressure P0. At this time, the second brake ECU 35 may read the detected value of the master pressure sensor 281 as the value of the master pressure P0, instead of the detected value of the hydraulic pressure sensor 33.

[0042] Then, in the next step S110, the second brake ECU 35 calculates a first target wheel pressure Pt1 based on the master pressure P0 using the first calculation map MAP1. In the next step S120, the second brake ECU 35 calculates a second target wheel pressure Pt2 based on the pedal stroke S using the second calculation map MAP2.

[0043] Fig. 4 shows an example of the first calculation map MAP1. The first calculation map MAP1 is set to calculate a value proportional to the master pressure P0 as the value of the first target wheel pressure Pt1. Fig. 5 shows an example of the second calculation map MAP2. The second calculation map MAP2 is set to calculate a higher hydraulic pressure as the value of the second target wheel pressure Pt2 increases with an increase in the pedal stroke S.

[0044] Next, in step S130, the second brake ECU 35 sets the first target wheel pressure Pt1 as the target front wheel pressure Ptf, which is the target value for the front wheel wheel pressure Pf. In addition, in step S140, the second brake ECU 35 sets the higher of the first target wheel pressure Pt1 and the second target wheel pressure Pt2 as the target rear wheel pressure Ptr, which is the target value for the rear wheel wheel pressure Pr. In step S150, the second brake ECU 35 controls the first assisting device 31 to set the front wheel wheel pressure Pf to the target front wheel wheel pressure Ptf. In step S150, the second brake ECU 35 also controls the second assisting device 32 to set the rear wheel wheel pressure Pr to the target rear wheel pressure Ptr. Then, the second brake ECU 35 ends the processing of this routine for the current control cycle.

[0045] <Actions and Effects of the Embodiment> The operation and effects of this embodiment will be described. When no abnormality in the brake control device 10 is confirmed, the first brake ECU 28 sets the state of the brake control device 10 to a second state in which both the first assisting device 31 and the second assisting device 32 are connected to the reserve tank 21 via the electric cylinder 23. The first brake ECU 28 controls the braking force of the vehicle by adjusting the wheel pressures Pf, Pr using the electric cylinder 23. At this time, the first brake ECU 28 sets a target wheel pressure Pt common to the front and rear wheels based on the master pressure P0 and the pedal stroke S to control the braking force.

[0046] When an abnormality in the brake control device 10 is detected, the state of the brake control device 10 is switched from the second state to the first state. In the first state, the first assisting device 31 is connected to the reserve tank 21 via the master cylinder 22. The second assisting device 32 is connected to the reserve tank 21 without passing through the master cylinder 22. In this state, the hydraulic system for the front wheel cylinders 11L, 11R and the hydraulic system for the rear wheel cylinders 12L, 12R become independent hydraulic systems.

[0047] Also, at this time, adjustment of the wheel pressures Pf, Pr through control of the electric cylinder 23 is stopped. Instead, the second brake ECU 35 starts adjustment of the wheel pressures Pf, Pr through control of the first assisting device 31 and the second assisting device 32. At this time, the second assisting device 32 pressurizes the brake fluid drawn from the reserve tank 21 without passing through the master cylinder 22, and sends it to the wheel cylinders 12L, 12R of the rear wheels. In other words, at this time, the second assisting device 32 sends brake fluid to the wheel cylinders 12L, 12R independently of the master cylinder 22.

[0048] Furthermore, when an abnormality in the brake control device 10 is confirmed, the second brake ECU 35 sets a first target wheel pressure Pt1 based on the master pressure P0 and sets a second target wheel pressure Pt2 based on the pedal stroke S. The second brake ECU 35 then sets the first target wheel pressure Pt1 as the value of the front wheel target wheel pressure Ptf. The second brake ECU 35 then sets the higher hydraulic pressure of the first target wheel pressure Pt1 or the second target wheel pressure Pt2 as the value of the rear wheel target wheel pressure Ptr. The second brake ECU 35 then controls the first assisting device 31 to set the front wheel wheel pressure Pf to the front wheel target wheel pressure Ptf, and controls the second assisting device 32 to set the rear wheel wheel pressure Pr to the rear wheel target wheel pressure Ptr.

[0049] If a fluid leak occurs in the fluid path connecting the master cylinder 22 and the front wheel cylinders 11L, 11R via the first assisting device 31, the master pressure P0 may not increase even when the brake pedal 15 is depressed. If the target rear wheel pressure Ptr is set based on the master pressure P0, the braking forces generated by the front wheel cylinders 11L, 11R and the rear wheel cylinders 12L, 12R may both be insufficient. In contrast, if the target rear wheel pressure Ptr is set based on the pedal stroke S, the braking forces generated by the rear wheel cylinders 12L, 12R can be appropriately controlled in accordance with the driver's request, even when the fluid leak occurs.

[0050] However, if the target rear wheel pressure Ptr is set based only on the pedal stroke S, the following problem may occur even when there is no fluid leakage and the master pressure P0 increases normally in response to depression of the brake pedal 15. The first assisting device 31 may return brake fluid to the master cylinder 22 to adjust the fluid pressure in the front wheel cylinders 11L, 11R. For example, if anti-skid control is performed due to deceleration slippage of the front wheels, the first assisting device 31 may reduce the front wheel pressure Pf. To reduce the front wheel pressure Pf, the first assisting device 31 operates the pump 304 with the pressure-reducing valve 303 open and the pressure-holding valve 302 closed. This causes the brake fluid in the wheel cylinders 11L, 11R to be returned to the master cylinder 22 by the pump 304. When the brake fluid is returned to the master cylinder 22, the amount of fluid in the pressure chamber 222 of the master cylinder 22 increases. Therefore, even if the pedal force input by the driver to the brake pedal 15 is constant, the brake pedal 15 is pushed back, and the pedal stroke S is reduced. Therefore, if the rear wheel target wheel pressure Ptr is set based only on the pedal stroke S, the wheel pressure Pr will decrease in accordance with the reduction in the pedal stroke S at this time, and the braking force generated on the rear wheels will decrease.

[0051] In this embodiment, even if the master pressure P0 does not increase due to a fluid leak, the second target wheel pressure Pt2 increases in response to an increase in the pedal stroke S, thereby increasing the braking force generated by the wheel cylinders 12L, 12R of the rear wheels in response to depression of the brake pedal 15. Furthermore, even if the pedal stroke S decreases due to the return of brake fluid to the master cylinder 22 by the first assisting device 31 when there is no fluid leak, the master pressure P0 does not decrease as long as the pedal force input by the driver to the brake pedal 15 remains constant. Therefore, even if the second target wheel pressure Pt2 decreases, the first target wheel pressure Pt1 is maintained. Therefore, even if the first assisting device 31 returns brake fluid to the master cylinder 22, the braking force generated by the wheel cylinders 12L, 12R of the rear wheels does not decrease. Therefore, regardless of whether the brake control device 10 is malfunctioning and whether or not the brake fluid leak is occurring, the braking force generated by the wheel cylinders 12L, 12R of the rear wheels can be appropriately controlled in response to the driver's request.

[0052] As with the rear wheel target wheel pressure Ptr, if the higher of the first target wheel pressure Pt1 and the second target wheel pressure Pt2 is set as the front wheel target wheel pressure Ptf, the following problem occurs. The operating position of the master piston 221 in the master cylinder 22 is determined by the balance between the depression force of the brake pedal 15 and the master pressure P0. The pedal stroke S is also determined by the balance between the depression force of the brake pedal 15 and the master pressure P0. Meanwhile, when an abnormality occurs in the brake control device 10, the first assisting device 31 generates the wheel pressure Pf by increasing the pressure of the brake fluid output from the master cylinder 22. When the first assisting device 31 draws brake fluid from the master cylinder 22, the master pressure P0 decreases, and the pedal stroke S increases accordingly. If the first target wheel pressure Pt1 is increased in response to the increase in the pedal stroke S, the first assisting device 31 further draws in more brake fluid from the master cylinder 22 to further increase the wheel pressure Pf. Then, as the master pressure P0 decreases due to the suction of brake fluid, the pedal stroke S further increases. Repeating the above process causes the first target wheel pressure Pt1 to continue to rise and diverge. Therefore, in this embodiment, the target front wheel pressure Ptf is set based only on the master pressure P0, thereby preventing the above-described divergence of the target front wheel pressure Ptf.

[0053] As described above, in this embodiment, the wheel pressure Pr of the rear wheels can be appropriately controlled in response to the driver's request in both the event of an abnormality involving fluid leakage and the event of an abnormality not involving fluid leakage. Also, in the brake control device 10 of this embodiment, the wheel pressure Pf of the front wheels can be appropriately controlled in response to the driver's request in the event of an abnormality not involving fluid leakage.

[0054] In the embodiment described above, the first target wheel pressure Pt1 corresponds to the first target hydraulic pressure, and the second target wheel pressure Pt2 corresponds to the second target hydraulic pressure. The front wheel cylinders 11L and 11R correspond to the first wheel cylinders, and the rear wheel cylinders 12L and 12R correspond to the second wheel cylinders. In this embodiment, the first assisting device 31, which operates when an abnormality occurs in the brake control device 10, corresponds to the first pressurizing device that increases the pressure of the brake fluid output from the master cylinder 22 and sends it to the first wheel cylinder. Furthermore, in this embodiment, the second assisting device 32, which operates when an abnormality occurs in the brake control device 10, corresponds to the second pressurizing device that sends brake fluid to the second wheel cylinder independently of the master cylinder 22. Additionally, in this embodiment, the second brake ECU 35, which operates when an abnormality occurs in the brake control device 10, corresponds to the control unit that sets the first and second target hydraulic pressures and controls the first and second pressurizing devices based on these target hydraulic pressures.

[0055] (Modification of the embodiment) The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0056] <About the first pressure unit> The first pressure applying section 20 may be configured differently from that shown in Figure 1, as long as it is configured to send brake fluid output from the master cylinder 22 to the first fluid path 13 and to send brake fluid to the second fluid path 14 independently of the master cylinder 22.

[0057] FIG. 6 shows the configuration of a modified first pressurizing unit 20A that replaces the first pressurizing unit 20. The first pressurizing unit 20A includes a master cylinder 22A, a stroke simulator 27, and an electric cylinder 23. The configuration of the master cylinder 22A is described, for example, in Japanese Patent Application Laid-Open Publication No. 2021-49935. The master cylinder 22A includes a main cylinder 41, a cover cylinder 42, a master piston 43, and an input piston 44. The brake pedal 15 is connected to the input piston 44. Within the main cylinder 41, a master chamber 411, a first hydraulic pressure chamber 412, and a servo chamber 413 are defined by the master piston 43. Within the cover cylinder 42, a second hydraulic pressure chamber 421 and a third hydraulic pressure chamber 422 are defined. A master spring 45 is provided within the main cylinder 41 to bias the master piston 43 in a direction that expands the volume of the master chamber 411. An input spring 46 is provided within the cover cylinder 42, biasing the input piston 44 in a direction that expands the volume of the second hydraulic chamber 421. The electric cylinder 23 in the first pressurizing unit 20A is connected to the servo chamber 413. That is, the electric cylinder 23 can supply brake fluid to the wheel cylinders 12L, 12R of the rear wheels and the servo chamber 413. The first pressurizing unit 20A also has multiple control valves 52, 53. The control valves 52, 53 are provided in a fluid path that directly connects the second hydraulic chamber 421 and the reserve tank 21. The control valve 52 is a normally closed solenoid valve, and the control valve 53 is a normally open solenoid valve. The control valves 52, 53 switch between the following first and second states depending on their energized states. In the first state, the first hydraulic chamber 412 and the second hydraulic chamber 421 are connected to the stroke simulator 27 but are disconnected from the reserve tank 21. In the second state, the first hydraulic pressure chamber 412 and the stroke simulator 27 are connected to the reserve tank 21 while being disconnected from the second hydraulic pressure chamber 421 .

[0058] When the first pressurizing section 20A is normal, the control valve 52 is open and the control valve 53 is closed. In this state, the second hydraulic chamber 421 is hydraulically connected to the stroke simulator 27 and hydraulically disconnected from the reserve tank 21. When the pedal is operated in this state, the stroke simulator 27 provides a pedal feeling to the brake pedal 15. With the control valve 52 open and the control valve 53 closed, the electric cylinder 23 outputs brake fluid from the output port 237 in accordance with the amount of operation of the brake pedal 15. The output brake fluid is supplied to the second hydraulic line 14 and the servo chamber 413. As the brake fluid is supplied to the servo chamber 413, the master piston 43 slides so that the master chamber 411 becomes smaller. As the master piston 43 slides in this manner, brake fluid is supplied from the master chamber 411 to the first hydraulic line 13. In this way, under normal conditions, the first pressurizing unit 20A controls the electric cylinder 23 and the control valves 52 and 53 to supply brake fluid to the first fluid path 13 and the second fluid path 14, respectively.

[0059] In the first pressurizing unit 20A, when an abnormality occurs in the brake control device 10, the control valves 52 and 53 connect the first hydraulic pressure chamber 412 and the stroke simulator 27 to the reserve tank 21 and isolate them from the second hydraulic pressure chamber 421. Specifically, the control valves 52 and 53 are de-energized, the control valve 52 is closed, and the control valve 53 is open. This seals the second hydraulic pressure chamber 421, and the depression force applied to the brake pedal 15 is transmitted to the master piston 43 via the input piston 44 and the brake fluid sealed in the second hydraulic pressure chamber 421. At this time, the first hydraulic line 13 is connected to the master chamber 411 of the master cylinder 22A. Therefore, in the brake control device 10 at this time, the first assisting device 31 increases the pressure of the brake fluid output from the master cylinder 22A and sends it to the wheel cylinders 11L and 11R of the front wheels, thereby generating braking force for the front wheels. At this time, the brake control device 10 generates braking force for the rear wheels by causing the second assisting device 32 to send brake fluid to the wheel cylinders 12L, 12R of the rear wheels independently of the master cylinder 22A.

[0060] The braking force control in the abnormal state of the above embodiment can be similarly applied to the braking control device 10 including the first pressure section 20A, and in such a case, the same actions and effects as those of the above embodiment can be obtained.

[0061] Furthermore, the above-described embodiment and modified examples may be modified as follows. The brake control device 10 in Fig. 1 includes the master cut valve 24 and the system shutoff valve 25 as a switching mechanism. The configuration of such a switching mechanism may be changed as appropriate.

[0062] Instead of the electric cylinder 23, an electric pressure device using a pump operated by an electric motor may be provided. In the above embodiment, the braking control device 10 is provided with two control units, the first brake ECU 28 and the second brake ECU 35. The first brake ECU 28 controls the braking force in normal conditions, and the second brake ECU 35 controls the braking force in abnormal conditions. However, the same control unit may control both the braking force in normal conditions and the braking force in abnormal conditions. Alternatively, the braking control device 10 may be provided with only one control unit that controls all of the electric cylinder 23, the first assisting device 31, and the second assisting device 32.

[0063] In the above embodiment, the presence or absence of an abnormality in the brake control device 10 is determined based on the deviation between the target wheel pressure Pt and the output hydraulic pressure of the electric cylinder 23. The manner in which the presence or absence of an abnormality in the brake control device 10 is determined may be changed as appropriate.

[0064] In the above embodiment, the state of the braking control device 10 is switched between the first state and the second state depending on whether or not an abnormality exists. However, the state may be switched between the first state and the second state based on conditions other than whether or not an abnormality exists.

[0065] In the above embodiment, when an abnormality occurs in the brake control device 10, control of the electric cylinder 23 is stopped. However, control of the electric cylinder 23 may be continued even when an abnormality occurs. For example, when an abnormality occurs in the brake control device 10, the first brake ECU 28 may control the electric cylinder 23 so that the output hydraulic pressure of the electric cylinder 23 becomes the second target wheel pressure Pt2. In this case, the differential pressure control valve 301 hydraulically connected to the electric cylinder 23 may be de-energized and remain open. In this case, the electric cylinder 23 corresponds to the second pressurizing device. Furthermore, when an abnormality occurs in the brake control device 10, the electric cylinder 23 and the second assisting device 32 may be controlled individually so that the second target wheel pressure Pt2 is obtained by the sum of the brake pressures output by the electric cylinder 23 and the second assisting device 32. In this case, the second pressurizing device is composed of both the electric cylinder 23 and the second assisting device 32. In this case, the electric cylinder 23 corresponds to an electric pressurizing device that electrically pressurizes and discharges the brake fluid, and the second assisting device 32 corresponds to an assisting device that increases the pressure of the brake fluid discharged from the electric pressurizing device and sends it to the second wheel cylinder. Furthermore, the first brake ECU 28 corresponds to a control unit that sets the first target hydraulic pressure and the second target hydraulic pressure and controls the first pressurizing device and the second pressurizing device based on the settings.

[0066] The braking force control in the abnormal state of the above embodiment can be adopted as braking force control in a braking control device configured as follows. That is, the braking control device does not include a switching mechanism and is configured to be fixed in the first state in the braking control device 10 of the above embodiment. In this case, the braking force control in the abnormal state of the above embodiment can be adopted as control in normal state, not control in abnormal state.

[0067] In the above embodiment, the wheel cylinders 11L, 11R of the left and right front wheels are designated as first wheel cylinders, and the wheel cylinders 12L, 12R of the left and right rear wheels are designated as second wheel cylinders. However, the combination of wheel cylinders constituting the first and second wheel cylinders may be changed as appropriate. For example, the wheel cylinder 11L of the left front wheel and the wheel cylinder 12R of the right rear wheel may be designated as first wheel cylinders, and the wheel cylinder 11R of the right front wheel and the wheel cylinder 12L of the left rear wheel may be designated as second wheel cylinders.

[0068] The first brake ECU 28 and the second brake ECU 35 may be configured as the following circuits: one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware that executes at least some of the various processes, or a combination of these. Examples of dedicated hardware include an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0069] In the above embodiment, the first target hydraulic pressure is set based only on the master pressure, and the second target hydraulic pressure is set based only on the pedal stroke. However, the first target hydraulic pressure may be set based on both the master pressure and the pedal stroke. In this case, it is sufficient that the contribution of the master pressure to setting the first target hydraulic pressure is greater than the contribution of the pedal stroke. Also, the second target hydraulic pressure may be set based on the pedal stroke and the master pressure. In this case, it is sufficient that the contribution of the pedal stroke to setting the second target hydraulic pressure is greater than the contribution of the master pressure. [Explanation of symbols]

[0070] 10...Brake control device 11L, 11R... Wheel cylinder (first wheel cylinder) 12L, 12R... Wheel cylinder (second wheel cylinder) 13...1st liquid path 14…Second liquid path 15...Brake pedal 20, 20A...First pressure section 21...Reserve tank 22, 22A...Master cylinder 221...Master piston 222...Pressure chamber 223... Urging member 224...input port 225...Output port 23...Electric cylinder 231...Piston 232…liquid chamber 233...Electric motor 234...Linear motion conversion mechanism 235... Urging member 236...input port 237...Output port 24...Master cut valve (switching mechanism) 25...System shutoff valve (switching mechanism) 26...Simulator cut valve 27...Stroke simulator 28...First brake ECU (control unit) 280...Stroke sensor 281...Master pressure sensor 282...Output pressure sensor 30...Second pressure section 31…1st support device 32…Second assist device 33...Hydraulic pressure sensor 35...Second brake ECU (control unit) 301...Differential pressure control valve 302...Retention valve 303...Reducing valve 304...Pump 305...Electric motor 306...Pressure regulating reservoir 307...reflux liquid path 308, 310, 312…Liquid path 309, 311, 314...Check valve 313...Pump fluid path 350...Stroke sensor 41...Main cylinder 411...Master room 412...First hydraulic chamber 413...Servo Room 42...Cover cylinder 421...Second hydraulic chamber 422...Third hydraulic chamber 43...Master piston 44...Input piston 45...Master spring 46...Input spring 52, 53...Control valve

Claims

1. A braking control device that controls a braking force of a vehicle by adjusting hydraulic pressure in a first wheel cylinder and a second wheel cylinder, a master cylinder that outputs brake fluid in response to depression of the brake pedal; a first pressurizing device that increases the pressure of the brake fluid output from the master cylinder and sends the increased pressure to the first wheel cylinder; a second pressurizing device that supplies the brake fluid to the second wheel cylinder independently of the master cylinder; a control unit that controls the second pressurizing device by setting the target hydraulic pressure of the second wheel cylinder to a higher one of a first target hydraulic pressure that is set based on a master pressure that is the pressure of the brake fluid output from the master cylinder and a second target hydraulic pressure that is set based on a pedal stroke that is the depression amount of the brake pedal; and A braking control device comprising:

2. 2. The brake control device according to claim 1, wherein the control unit controls the first pressurizing device by setting the first target hydraulic pressure as a target hydraulic pressure for the first wheel cylinder.

3. The second pressurizing device includes an electric pressurizing device that electrically pressurizes and discharges the brake fluid, and an assisting device that increases the pressure of the brake fluid discharged from the electric pressurizing device and sends the increased pressure to the second wheel cylinder, a switching mechanism that switches between a first state in which the brake fluid discharged by the electric pressure device is sent to both the first wheel cylinder and the second wheel cylinder, and a second state in which the brake fluid discharged by the electric pressure device is sent only to the second wheel cylinder of the first wheel cylinder and the second wheel cylinder, When the switching mechanism is in the second state, the control unit sets the higher of the first target hydraulic pressure and the second target hydraulic pressure as the target hydraulic pressure of the second wheel cylinder, and controls at least one of the electric pressure applying device and the assisting device.

3. The braking control device according to claim 1 or 2.

4. The brake control device according to claim 3 , wherein the switching mechanism switches from the first state to the second state in response to the occurrence of an abnormality.

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