JP2008162562A - Brake control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the wheel cylinder pressure control performance in the case of controlling the hydraulic pressure of at least one wheel cylinder among a plurality of wheel cylinders so as to be different from that of other wheel cylinders. <P>SOLUTION: The brake control device 20 comprises a hydraulic pressure control system capable of controlling a plurality of wheel cylinders 23 to a common hydraulic pressure by performing the feed-back control, a plurality of ABS (anti-lock Brake System) holding valves 51-54 provided corresponding to each of the plurality of wheel cylinders 23 so as to supply the controlled hydraulic pressure from the hydraulic pressure control system to a corresponding wheel cylinder 23 when the valve is opened and so as to keep the hydraulic pressure in the corresponding wheel cylinder 23 when the valve is closed, and return check valves 81-84 for releasing the holding pressure to the controlled hydraulic pressure so that the holding pressure is reduced to the controlled hydraulic pressure in the case wherein the controlled hydraulic pressure is reduced to a value lower than the holding pressure by the ABS holding valves 51-54. The hydraulic control system changes a control gain of the pressure reduction control of the controlled pressure so as to reduce an influence to responsiveness of the controlled hydraulic pressure when the pressure is reduced by the return check valves 81-84. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a brake control device that controls braking force applied to wheels provided in a vehicle.

For example, Patent Document 1 discloses a brake control device using so-called brake-by-wire. The brake-by-wire detects a driver's brake operation and generates a driver's required braking force by electronic control. In this brake control device, it is possible to control each wheel cylinder pressure in common by a pair of pressure-increasing linear control valve and pressure-decreasing linear control valve, and the cost is reduced compared to providing a linear control valve for each wheel cylinder. It is preferable from the viewpoint.
JP 2006-123889 A

  By the way, for example, it may be desirable to change the braking force distribution of each wheel in order to stabilize the behavior of the vehicle or improve the riding comfort of the vehicle. This is realized by making the wheel cylinder pressures different, and for this purpose, for example, a holding valve provided upstream of each wheel cylinder is individually opened and closed. As a result, the controllability of the wheel cylinder pressure by the pressure increase control valve and the pressure reduction control valve common to each wheel cylinder may be affected.

  Therefore, the present invention provides a brake control technology that can improve the controllability of the wheel cylinder pressure when different hydraulic pressures of at least one of the plurality of wheel cylinders are used. Objective.

  A brake control device according to an aspect of the present invention can control a plurality of wheel cylinders that apply braking force to each of a plurality of wheels by supplying hydraulic fluid, and a plurality of wheel cylinders to a common control fluid pressure by feedback control. The hydraulic pressure control system is provided corresponding to each of the plurality of wheel cylinders. When the valve is opened, the control hydraulic pressure is supplied from the hydraulic pressure control system to the corresponding wheel cylinder and the valve cylinder is closed. If the control hydraulic pressure is reduced to a pressure lower than the holding pressure by the holding valve, and the holding pressure that holds the hydraulic pressure in the corresponding wheel cylinder, the holding pressure follows the control hydraulic pressure. Holding pressure reducing means for releasing the holding pressure to the control hydraulic pressure so that the pressure is reduced, and the hydraulic pressure control system is adapted to control fluid pressure responsiveness when pressure is reduced by the holding pressure reducing means. Should alleviate the impact It changes the control gain of the pressure reduction control of the control fluid pressure.

  According to this aspect, the brake force distribution of each wheel is achieved by controlling the hydraulic pressure of other wheel cylinders by the hydraulic pressure control system while closing some of the holding valves and holding the hydraulic pressure in the wheel cylinders. Can be changed. For example, when the control hydraulic pressure is controlled to be lower than the holding pressure by weakening the brake operation by the driver, it may be desirable to reduce the holding pressure by following the control hydraulic pressure in order to maintain a good braking state. is there. In this case, the holding pressure is reduced by, for example, being released to the control hydraulic pressure by the holding pressure reducing means. Responsiveness of the control hydraulic pressure, particularly during pressure reduction control, differs between a situation where the holding pressure is required to be reduced and a situation where the holding pressure is not required. This is because the volume to be subjected to pressure reduction control is different. For this reason, by appropriately changing the control gain of the feedback control by the hydraulic pressure control system, it becomes possible to reduce the influence on the responsiveness of the control hydraulic pressure when the holding pressure reducing means is reduced. Thereby, the controllability of the brake control hydraulic pressure can be improved.

  The hydraulic pressure control system performs pressure reduction control by switching the control gain according to the number of holding valves that are opened, and when the holding pressure by any holding valve exceeds the control hydraulic pressure The control gain may be switched assuming that any one of the holding valves is opened.

  The volume to be controlled by the hydraulic control system differs depending on the number of holding valves that are opened. For example, if all four wheel holding valves are opened, the control target volume is all four wheel cylinders. If only two front wheel holding valves are opened, the control target volume is the two front wheel wheels. Cylinder. Therefore, by switching the control gain according to the number of holding valves that are opened, it is possible to appropriately increase or decrease the command value in the control system according to the increase or decrease of the control target volume. Therefore, the controllability of the brake control hydraulic pressure can be improved.

  In addition, when the holding pressure by any holding valve exceeds the control hydraulic pressure, the holding pressure is released to the control hydraulic pressure through the holding pressure reducing means. This is substantially equivalent to the fact that the wheel cylinder in which the holding pressure is held is added to the target volume for pressure reduction control. For this reason, it is assumed that the holding valve that holds the holding pressure is opened, that is, the holding valve that holds the holding pressure is also one of the opened holding valves, and the control gain is switched in the number. As a result, the delay in decompression can be reduced and the controllability of the brake control hydraulic pressure can be further improved.

  The hydraulic pressure control system may execute pressure reduction control by switching to a control gain used when all the holding valves are opened when the holding pressure by any holding valve exceeds the control hydraulic pressure.

  When the holding pressure by any holding valve exceeds the control hydraulic pressure, the influence on the controllability of the control hydraulic pressure during the pressure reduction control is relatively large. Switching to the control gain that is used when all the holding valves are open corresponds to returning to the control gain before executing the control that requires the holding valves to be closed. As a result, it is possible to reduce the delay in pressure reduction and improve the controllability of the brake control hydraulic pressure.

  The holding pressure reducing means may be a plurality of check valves provided in parallel to each of the holding valves so as to relieve the holding pressure to the control hydraulic pressure when the holding pressure exceeds the control hydraulic pressure.

  Thus, by providing the check valve in parallel with each holding valve, the holding pressure can be mechanically reduced automatically through the check valve while maintaining the closed state of the holding valve. This is preferable in that the opening / closing control of the holding valve can be simplified. Further, since the holding pressure is reduced to the control hydraulic pressure when the holding pressure exceeds the control hydraulic pressure, the holding pressure is prevented from excessively deviating from the control hydraulic pressure. Since the control hydraulic pressure is controlled by reflecting the increase or decrease in the braking force required by the driver, a good braking state can be maintained by suppressing the holding pressure from deviating from the control hydraulic pressure.

  The hydraulic pressure control system may control the control hydraulic pressure by switching the control gain according to the control target volume that varies depending on the open / closed state of the plurality of holding valves.

  The hydraulic control system increases the control gain of the feedback control according to the open / closed state of the plurality of holding valves, that is, the number of open valves, for example, when the control target volume increases, while when the control target volume decreases, The control gain may be switched so as to decrease. In this way, the control gain of feedback control is switched according to the increase or decrease of the control target volume. As a result, the command value in the control system can be increased or decreased in accordance with the open / close state of the holding valve, so that the controllability can be improved by reducing fluctuations in the controllability of the brake control hydraulic pressure due to the opening / closing of the hold valve. it can.

  According to the present invention, it is possible to improve the controllability of the wheel cylinder pressure.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a system diagram showing a brake control device 20 according to an embodiment of the present invention. A brake control device 20 shown in the figure constitutes an electronically controlled brake system (ECB) for a vehicle, and controls braking force applied to four wheels provided on the vehicle. The brake control device 20 according to the present embodiment is mounted on, for example, a hybrid vehicle that includes an electric motor and an internal combustion engine as a travel drive source. In such a hybrid vehicle, each of regenerative braking that brakes the vehicle by regenerating kinetic energy of the vehicle into electric energy and hydraulic braking by the brake control device 20 can be used for braking the vehicle. The vehicle in the present embodiment can execute brake regenerative cooperative control that generates a desired braking force by using both the regenerative braking and the hydraulic braking together.

  As shown in FIG. 1, the brake control device 20 includes disc brake units 21FR, 21FL, 21RR and 21RL provided for each wheel, a master cylinder unit 27, a power hydraulic pressure source 30, a hydraulic pressure, Actuator 40.

  Disc brake units 21FR, 21FL, 21RR, and 21RL apply braking force to the right front wheel, the left front wheel, the right rear wheel, and the left rear wheel of the vehicle, respectively. The master cylinder unit 27 as the manual hydraulic pressure source in the present embodiment sends the brake fluid pressurized according to the amount of operation by the driver of the brake pedal 24 as the brake operation member to the disc brake units 21FR to 21RL. To do. The power hydraulic pressure source 30 can send the brake fluid as the working fluid pressurized by the power supply to the disc brake units 21FR to 21RL independently from the operation of the brake pedal 24 by the driver. is there. The hydraulic actuator 40 appropriately adjusts the hydraulic pressure of the brake fluid supplied from the power hydraulic pressure source 30 or the master cylinder unit 27 and sends it to the disc brake units 21FR to 21RL. Thereby, the braking force with respect to each wheel by hydraulic braking is adjusted.

  Each of the disc brake units 21FR to 21RL, the master cylinder unit 27, the power hydraulic pressure source 30, and the hydraulic actuator 40 will be described in more detail below. Each of the disc brake units 21FR to 21RL includes a brake disc 22 and wheel cylinders 23FR to 23RL incorporated in the brake caliper, respectively. The wheel cylinders 23FR to 23RL are connected to the hydraulic actuator 40 via different fluid passages. Hereinafter, the wheel cylinders 23FR to 23RL are collectively referred to as “wheel cylinders 23” as appropriate.

  In the disc brake units 21FR to 21RL, when brake fluid is supplied to the wheel cylinder 23 from the hydraulic actuator 40, a brake pad as a friction member is pressed against the brake disc 22 that rotates together with the wheel. Thereby, a braking force is applied to each wheel. In the present embodiment, the disc brake units 21FR to 21RL are used, but other braking force applying mechanisms including a wheel cylinder 23 such as a drum brake may be used.

  In this embodiment, the master cylinder unit 27 is a master cylinder with a hydraulic booster, and includes a hydraulic booster 31, a master cylinder 32, a regulator 33, and a reservoir. The hydraulic booster 31 is connected to the brake pedal 24, amplifies the pedal effort applied to the brake pedal 24, and transmits it to the master cylinder 32. When the brake fluid is supplied from the power hydraulic pressure source 30 to the hydraulic pressure booster 31 via the regulator 33, the pedal effort is amplified. The master cylinder 32 generates a master cylinder pressure having a predetermined boost ratio with respect to the pedal effort.

  A reservoir 34 for storing brake fluid is disposed above the master cylinder 32 and the regulator 33. The master cylinder 32 communicates with the reservoir 34 when the depression of the brake pedal 24 is released. On the other hand, the regulator 33 is in communication with both the reservoir 34 and the accumulator 35 of the power hydraulic pressure source 30, and the reservoir 34 is used as a low pressure source, the accumulator 35 is used as a high pressure source, and the hydraulic pressure is approximately equal to the master cylinder pressure. Is generated. Hereinafter, the hydraulic pressure in the regulator 33 is appropriately referred to as “regulator pressure”. The master cylinder pressure and the regulator pressure do not need to be exactly the same pressure. For example, the master cylinder unit 27 can be designed so that the regulator pressure is slightly higher.

  The power hydraulic pressure source 30 includes an accumulator 35 and a pump 36. The accumulator 35 converts the pressure energy of the brake fluid boosted by the pump 36 into the pressure energy of an enclosed gas such as nitrogen, for example, about 14 to 22 MPa and stores it. The pump 36 has a motor 36 a as a drive source, and its suction port is connected to the reservoir 34, while its discharge port is connected to the accumulator 35. The accumulator 35 is also connected to a relief valve 35 a provided in the master cylinder unit 27. When the pressure of the brake fluid in the accumulator 35 increases abnormally to about 25 MPa, for example, the relief valve 35 a is opened, and the high-pressure brake fluid is returned to the reservoir 34.

  As described above, the brake control device 20 includes the master cylinder 32, the regulator 33, and the accumulator 35 as a supply source of brake fluid to the wheel cylinder 23. A master pipe 37 is connected to the master cylinder 32, a regulator pipe 38 is connected to the regulator 33, and an accumulator pipe 39 is connected to the accumulator 35. These master pipe 37, regulator pipe 38 and accumulator pipe 39 are each connected to a hydraulic actuator 40.

  The hydraulic actuator 40 includes an actuator block in which a plurality of flow paths are formed, and a plurality of electromagnetic control valves. The flow paths formed in the actuator block include individual flow paths 41, 42, 43 and 44 and a main flow path 45. The individual flow paths 41 to 44 are respectively branched from the main flow path 45 and connected to the wheel cylinders 23FR, 23FL, 23RR, 23RL of the corresponding disc brake units 21FR, 21FL, 21RR, 21RL. Thereby, each wheel cylinder 23 can communicate with the main flow path 45.

  In addition, ABS holding valves 51, 52, 53 and 54 are provided in the middle of the individual flow paths 41, 42, 43 and 44. Each of the ABS holding valves 51 to 54 has a solenoid and a spring that are ON / OFF controlled, and both are normally open electromagnetic control valves that are opened when the solenoid is in a non-energized state. Each of the ABS holding valves 51 to 54 in the opened state can distribute the brake fluid in both directions. That is, the brake fluid can flow from the main flow path 45 to the wheel cylinder 23, and conversely, the brake fluid can also flow from the wheel cylinder 23 to the main flow path 45. When the solenoid is energized and the ABS holding valves 51 to 54 are closed, the flow of brake fluid in the individual flow paths 41 to 44 is blocked.

  Also, return check valves 81, 82, 83, and 84 are provided in parallel to the ABS holding valves 51, 52, 53, and 54, respectively. The return check valves 81 to 84 block the flow of brake fluid from the main flow path 45 toward the wheel cylinders 23. On the other hand, when the wheel cylinder pressure is higher than the hydraulic pressure in the main flow path 45, the valve is mechanically opened to allow the brake fluid to flow from the wheel cylinder 23 to the main flow path 45. When the hydraulic pressure at becomes equal, the valve is mechanically closed.

  When the ABS holding valves 51 to 54 are closed by the return check valves 81 to 84 and the wheel cylinder pressure is held, when the control hydraulic pressure in the main flow path 45 falls below the holding pressure, the ABS holding valve The holding pressure can be automatically reduced to the hydraulic pressure in the main flow path 45 while maintaining the closed states of 51 to 54. Since the holding pressure can be mechanically reduced automatically without opening the ABS holding valves 51 to 54, it is preferable in that the opening / closing control of the ABS holding valves 51 to 54 can be simplified.

  Further, the wheel cylinder 23 is connected to the reservoir channel 55 via pressure reducing channels 46, 47, 48 and 49 connected to the individual channels 41 to 44, respectively. ABS decompression valves 56, 57, 58 and 59 are provided in the middle of the decompression channels 46, 47, 48 and 49. Each of the ABS pressure reducing valves 56 to 59 has a solenoid and a spring that are ON / OFF controlled, and is a normally closed electromagnetic control valve that is closed when the solenoid is in a non-energized state. When the ABS pressure reducing valves 56 to 59 are closed, the flow of brake fluid in the pressure reducing flow paths 46 to 49 is blocked. When the solenoid is energized and the ABS pressure reducing valves 56 to 59 are opened, the brake fluid is allowed to flow through the pressure reducing flow paths 46 to 49, and the brake fluid flows from the wheel cylinder 23 to the pressure reducing flow paths 46 to 49 and It returns to the reservoir 34 via the reservoir channel 55. The reservoir channel 55 is connected to the reservoir 34 of the master cylinder unit 27 via a reservoir pipe 77.

  The main channel 45 has a separation valve 60 in the middle. By this separation valve 60, the main channel 45 is divided into a first channel 45 a connected to the individual channels 41 and 42 and a second channel 45 b connected to the individual channels 43 and 44. The first flow path 45a is connected to the front wheel wheel cylinders 23FR and 23FL via the individual flow paths 41 and 42, and the second flow path 45b is connected to the rear wheel wheel cylinder via the individual flow paths 43 and 44. Connected to 23RR and 23RL.

  The separation valve 60 has a solenoid and a spring that are ON / OFF controlled, and is a normally closed electromagnetic control valve that is closed when the solenoid is in a non-energized state. When the separation valve 60 is in the closed state, the flow of brake fluid in the main flow path 45 is blocked. When the solenoid is energized and the separation valve 60 is opened, the brake fluid can be circulated bidirectionally between the first flow path 45a and the second flow path 45b.

  In the hydraulic actuator 40, a master channel 61 and a regulator channel 62 communicating with the main channel 45 are formed. More specifically, the master channel 61 is connected to the first channel 45 a of the main channel 45, and the regulator channel 62 is connected to the second channel 45 b of the main channel 45. The master channel 61 is connected to a master pipe 37 that communicates with the master cylinder 32. The regulator channel 62 is connected to a regulator pipe 38 that communicates with the regulator 33.

  The master channel 61 has a master cut valve 64 in the middle. The master cut valve 64 is provided on the brake fluid supply path from the master cylinder 32 to each wheel cylinder 23. The master cut valve 64 has a solenoid and a spring that are ON / OFF-controlled, and the valve closing state is guaranteed by the electromagnetic force generated by the solenoid when supplied with a prescribed control current, so that the solenoid is in a non-energized state. It is a normally open electromagnetic control valve that is opened in some cases. The master cut valve 64 in the opened state can cause the brake fluid to flow in both directions between the master cylinder 32 and the first flow path 45 a of the main flow path 45. When a prescribed control current is applied to the solenoid and the master cut valve 64 is closed, the flow of brake fluid in the master flow path 61 is interrupted.

  A stroke simulator 69 is connected to the master channel 61 via a simulator cut valve 68 on the upstream side of the master cut valve 64. That is, the simulator cut valve 68 is provided in a flow path connecting the master cylinder 32 and the stroke simulator 69. The simulator cut valve 68 has a solenoid and a spring that are ON / OFF controlled, and the valve opening state is guaranteed by the electromagnetic force generated by the solenoid upon receipt of a specified control current, and the solenoid is in a non-energized state. It is a normally closed electromagnetic control valve that is closed in some cases. When the simulator cut valve 68 is closed, the flow of brake fluid between the master flow path 61 and the stroke simulator 69 is blocked. When the solenoid is energized and the simulator cut valve 68 is opened, the brake fluid can be circulated bidirectionally between the master cylinder 32 and the stroke simulator 69.

  The stroke simulator 69 includes a plurality of pistons and springs, and creates a reaction force corresponding to the depression force of the brake pedal 24 by the driver when the simulator cut valve 68 is opened. As the stroke simulator 69, in order to improve the feeling of brake operation by the driver, it is preferable to employ one having a multistage spring characteristic.

  The regulator flow path 62 has a regulator cut valve 65 in the middle. The regulator cut valve 65 is provided on the brake fluid supply path from the regulator 33 to each wheel cylinder 23. The regulator cut valve 65 also has a solenoid and a spring that are controlled to be turned on and off, and the closed state is guaranteed by the electromagnetic force generated by the solenoid when supplied with a prescribed control current, so that the solenoid is turned off. It is a normally open electromagnetic control valve that is opened in some cases. The regulator cut valve 65 that has been opened can cause the brake fluid to flow in both directions between the regulator 33 and the second flow path 45 b of the main flow path 45. When the solenoid is energized and the regulator cut valve 65 is closed, the flow of brake fluid in the regulator flow path 62 is blocked.

  In the hydraulic actuator 40, an accumulator channel 63 is also formed in addition to the master channel 61 and the regulator channel 62. One end of the accumulator channel 63 is connected to the second channel 45 b of the main channel 45, and the other end is connected to an accumulator pipe 39 that communicates with the accumulator 35.

  The accumulator flow path 63 has a pressure-increasing linear control valve 66 in the middle. Further, the accumulator channel 63 and the second channel 45 b of the main channel 45 are connected to the reservoir channel 55 via the pressure-reducing linear control valve 67. The pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 each have a linear solenoid and a spring, and both are normally closed electromagnetic control valves that are closed when the solenoid is in a non-energized state. In the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67, the opening degree of the valve is adjusted in proportion to the current supplied to each solenoid.

  The pressure-increasing linear control valve 66 is provided as a common pressure-increasing control valve for each of the wheel cylinders 23 provided corresponding to each wheel. Similarly, the pressure reducing linear control valve 67 is provided as a pressure reducing control valve common to the wheel cylinders 23. That is, in this embodiment, the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67 are a pair of common control valves that control the supply and discharge of the working fluid sent from the power hydraulic pressure source 30 to each wheel cylinder 23. It is provided as. If the pressure-increasing linear control valve 66 and the like are made common to each wheel cylinder 23 in this way, it is preferable from the viewpoint of cost as compared with the case where a linear control valve is provided for each wheel cylinder 23.

  Here, the differential pressure between the inlet and outlet of the pressure-increasing linear control valve 66 corresponds to the differential pressure between the pressure of the brake fluid in the accumulator 35 and the pressure of the brake fluid in the main flow path 45, and the inlet / outlet of the pressure-reducing linear control valve 67. The pressure difference therebetween corresponds to the pressure difference between the brake fluid pressure in the main flow path 45 and the brake fluid pressure in the reservoir 34. Further, the electromagnetic driving force according to the power supplied to the linear solenoid of the pressure increasing linear control valve 66 and the pressure reducing linear control valve 67 is F1, the spring biasing force is F2, and the pressure increasing linear control valve 66 and the pressure reducing linear control valve are Assuming that the differential pressure acting force according to the differential pressure between the inlet / outlet of 67 is F3, the relationship of F1 + F3 = F2 is established. Therefore, the differential pressure between the inlet and outlet of the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67 is controlled by continuously controlling the power supplied to the linear solenoids of the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67. can do.

  In the brake control device 20, the power hydraulic pressure source 30 and the hydraulic actuator 40 are controlled by a brake ECU 70 as a control unit in the present embodiment. The brake ECU 70 is configured as a microprocessor including a CPU, and includes a ROM that stores various programs, a RAM that temporarily stores data, an input / output port, a communication port, and the like in addition to the CPU. The brake ECU 70 can communicate with a host hybrid ECU (not shown) and the like, and based on control signals from the hybrid ECU and signals from various sensors, the pump 36 of the power hydraulic pressure source 30 and the hydraulic pressure The electromagnetic control valves 51 to 54, 56 to 59, 60, and 64 to 68 constituting the actuator 40 are controlled.

  Further, a regulator pressure sensor 71, an accumulator pressure sensor 72, and a control pressure sensor 73 are connected to the brake ECU 70. The regulator pressure sensor 71 detects the pressure of the brake fluid in the regulator flow path 62 on the upstream side of the regulator cut valve 65, that is, the regulator pressure, and gives a signal indicating the detected value to the brake ECU 70. The accumulator pressure sensor 72 detects the pressure of the brake fluid in the accumulator flow path 63, that is, the accumulator pressure on the upstream side of the pressure increasing linear control valve 66, and gives a signal indicating the detected value to the brake ECU 70. The control pressure sensor 73 detects the pressure of the brake fluid in the first flow path 45a of the main flow path 45, and gives a signal indicating the detected value to the brake ECU 70. The detection values of the pressure sensors 71 to 73 are sequentially given to the brake ECU 70 every predetermined time, and are stored and held in a predetermined storage area of the brake ECU 70 by a predetermined amount.

  When the separation valve 60 is opened and the first flow path 45 a and the second flow path 45 b of the main flow path 45 communicate with each other, the output value of the control pressure sensor 73 is the low pressure of the pressure-increasing linear control valve 66. This indicates the hydraulic pressure on the high pressure side of the pressure-reducing linear control valve 67 and the output value can be used to control the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67. When the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 are closed and the master cut valve 64 is opened, the output value of the control pressure sensor 73 indicates the master cylinder pressure. Further, the separation valve 60 is opened so that the first flow path 45a and the second flow path 45b of the main flow path 45 communicate with each other, and the ABS holding valves 51 to 54 are opened, while the ABS pressure reducing valves 56 are opened. When? 59 is closed, the output value of the control pressure sensor 73 indicates the working fluid pressure acting on each wheel cylinder 23, i.e., the wheel cylinder pressure.

  Further, the sensor connected to the brake ECU 70 includes a stroke sensor 25 provided on the brake pedal 24. The stroke sensor 25 detects a pedal stroke as an operation amount of the brake pedal 24 and gives a signal indicating the detected value to the brake ECU 70. The output value of the stroke sensor 25 is also sequentially given to the brake ECU 70 every predetermined time, and is stored and held in a predetermined storage area of the brake ECU 70 by a predetermined amount. A brake operation state detection unit other than the stroke sensor 25 may be provided in addition to the stroke sensor 25 or in place of the stroke sensor 25 and connected to the brake ECU 70. Examples of the brake operation state detection means include a pedal depression force sensor that detects an operation force of the brake pedal 24 and a brake switch that detects that the brake pedal 24 is depressed.

  The brake control device 20 configured as described above can execute brake regeneration cooperative control. The brake control device 20 starts braking in response to a braking request. The braking request is generated when a braking force should be applied to the vehicle, for example, when the driver operates the brake pedal 24. In response to the braking request, the brake ECU 70 calculates a required braking force, and calculates a required hydraulic braking force that is a braking force to be generated by the brake control device 20 by subtracting the braking force due to regeneration from the required braking force. Here, the braking force by regeneration is supplied to the brake control device 20 from the hybrid ECU. Then, the brake ECU 70 calculates the target hydraulic pressure of each wheel cylinder 23FR to 23RL based on the calculated required hydraulic braking force. The brake ECU 70 determines the value of the control current supplied to the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 based on the feedback control law so that the wheel cylinder pressure becomes the target hydraulic pressure.

  As a result, in the brake control device 20, the brake fluid is supplied from the power hydraulic pressure source 30 to the wheel cylinders 23 via the pressure-increasing linear control valve 66, and braking force is applied to the wheels. Further, brake fluid is discharged from each wheel cylinder 23 through the pressure-reducing linear control valve 67 as necessary, and the braking force applied to the wheel is adjusted. In the present embodiment, a hydraulic pressure control system is configured including the power hydraulic pressure source 30, the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67, the control pressure sensor 73, the brake ECU 70, and the like. This hydraulic pressure control system performs braking force control by so-called brake-by-wire. This hydraulic pressure control system is provided in parallel to the brake fluid supply path from the master cylinder unit 27 to the wheel cylinder 23.

  At this time, the brake ECU 70 closes the regulator cut valve 65 so that the brake fluid sent from the regulator 33 is not supplied to the wheel cylinder 23. Further, the brake ECU 70 closes the master cut valve 64 and opens the simulator cut valve 68. This is because the brake fluid sent from the master cylinder 32 in accordance with the operation of the brake pedal 24 by the driver is supplied not to the wheel cylinder 23 but to the stroke simulator 69. During the brake regeneration cooperative control, a differential pressure corresponding to the magnitude of the regenerative braking force acts between the upstream and downstream of the regulator cut valve 65 and the master cut valve 64.

  The brake control device 20 according to the present embodiment can naturally control the braking force by the wheel cylinder pressure control system even when the required braking force is provided only by the hydraulic braking force without using the regenerative braking force. . Regardless of whether or not the brake regeneration cooperative control is executed, the control mode for controlling the braking force by the wheel cylinder pressure control system will be appropriately referred to as a “linear control mode” below. Or it may be called control by brake-by-wire.

  In the linear control mode, the ABS holding valves 51 to 54 are normally opened, and the wheel cylinder pressures are controlled to a common hydraulic pressure. However, at least one wheel cylinder pressure may be different from other wheel cylinder pressures by appropriately opening and closing the ABS holding valves 51 to 54. In addition, the hydraulic pressure may be different for each wheel cylinder. As such a case, for example, there is a case where so-called EBD (Electronic Brake-Force Distribution) control or ABD (Automatic Brake Differential) control is executed.

  Both the EBD control and the ABD control are controls aimed at stabilizing the behavior of the vehicle or improving the riding comfort of the vehicle. The EBD control is control for changing the braking force distribution between the front wheels and the rear wheels by, for example, closing the rear wheel side ABS holding valves 53 and 54 and holding the wheel cylinder pressure on the rear wheels. The ABD control is a control for changing the left and right braking force distribution mainly by changing the open / closed state of the ABS holding valves 51 to 54 with the left and right wheels while the vehicle is turning. In the present embodiment, the brake ECU 70 can execute either EBD control or ABD control in the linear control mode, or both can be executed simultaneously. Hereinafter, for convenience, EBD control and ABD control are collectively referred to simply as EBD control.

  In the EBD control, the brake ECU 70 calculates a timing at which the EBD control should be started, and starts the EBD control at the timing. The brake ECU 70 closes the ABS holding valves 53 and 54 on the rear wheel side with the start of the EBD control, for example. At this time, since the ABS pressure reducing valves 56 to 59 are closed, the brake fluid is sealed in the wheel cylinders 23RL and 23RR on the rear wheel side so that the hydraulic pressure is maintained. On the other hand, since the ABS holding valves 51 and 52 on the front wheel side remain open, the wheel cylinder pressure on the front wheel side is controlled according to the control to the pressure increasing linear control valve 66 and the pressure reducing linear control valve 67. Is controlled to be equal to the hydraulic pressure in the main flow path 45.

  Hereinafter, for the sake of convenience, the hydraulic pressure held in the wheel cylinder 23 by closing the ABS holding valves 51 to 54 is referred to as “holding pressure”, and in particular, the holding pressure when the ABS holding valves 51 to 54 are closed is referred to as “holding start pressure”. May be called. Further, the hydraulic pressure in the main flow path 45 and the wheel cylinder pressure controlled to be equal to the hydraulic pressure may be referred to as “control hydraulic pressure”, and the hydraulic pressure in the main flow path 45 may be particularly referred to as “holding valve upstream pressure”. Since the holding valve upstream pressure is introduced into the wheel cylinder 23 in which the ABS holding valves 51 to 54 are opened, the holding valve upstream pressure and the control hydraulic pressure are equal.

  FIG. 2 is a diagram illustrating an example of a time change of the wheel cylinder pressure during the EBD control. As shown in FIG. 2, when the EBD control starts, the wheel cylinder pressure on the rear wheel side is held at the holding start pressure, while the wheel cylinder pressure on the front wheel side, that is, the control hydraulic pressure, is controlled and fluctuated according to the required braking force. To do. Thus, the braking force distribution between the front wheels and the rear wheels can be changed by making the wheel cylinder pressure on the front wheel side different from the wheel cylinder pressure on the rear wheel side.

  In the following, the volume of the wheel cylinder 23 and the main flow path 45, etc., to be controlled by the hydraulic pressure control system including the brake ECU 70, the pressure-increasing linear control valve 66, the pressure-decreasing linear control valve 67, etc. The volume in which the hydraulic fluid can be supplied and discharged by the linear control valve 66 and the pressure-reducing linear control valve 67 will be appropriately referred to as a control target volume hereinafter. The number of the ABS holding valves 51 to 54 that are opened is appropriately referred to as the number of opening of the ABS holding valves 51 to 54.

  With respect to the wheel cylinders 23 corresponding to the ABS holding valves 51 to 54 that are closed, the ABS holding valves 51 to 54 block the flow of the hydraulic fluid from the main flow path 45, so that the pressure increasing linear control valve 66 and the pressure reducing linear The hydraulic pressure cannot be controlled by the control valve 67. Therefore, the volume to be controlled by the hydraulic pressure control system according to the present embodiment varies depending on the number of opening of the ABS holding valves 51 to 54. If the number of opening of the ABS holding valves 51 to 54 increases, the control target volume increases. Conversely, if the number of opening of the ABS holding valves 51 to 54 decreases, the control target volume decreases.

  In such a situation, when the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67 are controlled by a constant control law, the control hydraulic pressure is controlled by the change in the control target volume accompanying the opening / closing of the ABS holding valves 51 to 54. Controllability will be different. For example, if the control gain of the hydraulic pressure feedback control by the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 is set to an optimal control gain for commonly controlling the wheel cylinder pressures of the four wheels, the number is When the ABS holding valves 51 to 54 are closed and the volume to be controlled is reduced, the control gain may be larger than the optimal control state.

  Therefore, in the present embodiment, the control valve pressure of the hydraulic pressure control is switched according to the control target volume to control the holding valve upstream pressure, that is, the control hydraulic pressure. Specifically, the brake ECU 70 increases the control gains of the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 when the volume to be controlled increases according to the open / close state of the ABS holding valves 51 to 54, while When the volume decreases, the control gain is switched so as to decrease the control gain. Note that the control gain of either the pressure-increasing linear control valve 66 or the pressure-decreasing linear control valve 67 may be changed.

  In the present embodiment, different control gain values are set for the following open / close states. As the open / close state, when all the ABS holding valves 51 to 54 are closed, when the number of opening of the ABS holding valves 51 to 54 is 1, when the number of opening of the ABS holding valves 51 to 54 is 2, When the number of opening of the ABS holding valves 51 to 54 is 3, all of the ABS holding valves 51 to 54 may be open.

  More specifically, when the number of the ABS holding valves 51 to 54 is one, only one of the front wheel side ABS holding valves 51 and 52 is open, and the rear wheel side ABS holding valve. There are two cases: only one of 53 and 54 is open. When the number of opening of the ABS holding valves 51 to 54 is 2, both the ABS holding valves 51 and 52 on the front wheel side are open, and both the ABS holding valves 53 and 54 on the rear wheel side are open. And the case where one of the ABS holding valves 51 and 52 on the front wheel side and the one of the ABS holding valves 53 and 54 on the rear wheel side are open. When the number of opening of the ABS holding valves 51 to 54 is 3, when the front wheel side ABS holding valves 51 and 52 and one of the rear wheel side ABS holding valves 53 and 54 are opened, the front wheel side The ABS holding valves 51 and 52 and the rear wheel ABS holding valves 53 and 54 are both open.

  In this way, the opening of the front wheel side ABS holding valves 51, 52 and the opening of the rear wheel side ABS holding valves 53, 54 are distinguished from each other by the volume of the front wheel side wheel cylinders 23FR, 23FL and the rear wheel. This is because the volume of the wheel cylinders 23RR, 23RL on the side is different. For example, the volume of the wheel cylinders 23RR and 23RL on the rear wheel side is approximately half the volume of the wheel cylinders 23FR and 23FL on the front wheel side. As a result, for example, when the front wheel side ABS holding valves 51 and 52 are opened and when the rear wheel side ABS holding valves 53 and 54 are opened, the number of opened valves is 2 However, the volume to be controlled is different.

  After all, in the present embodiment, different control gain values are preset for each of the above-described nine open / close states and stored in the brake ECU 70. The control gain can be determined in consideration of the relationship between the volume to be controlled and the wheel cylinder pressure in each open / close state. The value of the control gain may be determined so as to be proportional to the control target volume. In this case, the control gain may be appropriately adjusted and determined from the viewpoint of controllability and the like.

  FIG. 3 is a diagram illustrating an example of the control gain according to the present embodiment. The vertical axis in FIG. 3 indicates the control gain of feedback control, and the horizontal axis indicates the wheel cylinder pressure. FIG. 3 shows control gains in three cases, for example, when the control target volume is all four wheels, two front wheels, and one front wheel. As shown in FIG. 3, in this embodiment, the control gain is set to a larger value as the number of wheel cylinders to be controlled by the hydraulic pressure control system is larger, that is, the control target volume is larger. The control gain when the wheel cylinder pressure of the four wheels is the control target is set larger than the control gain when the two front wheels are the control target. Further, the control gain when the two front wheels are the control target is set larger than the control gain when only one of the front wheels is the control target.

  In FIG. 3, the control gain is set to increase as the wheel cylinder pressure decreases. This is because the rate of increase of the hydraulic pressure with respect to the amount of fluid flowing into the wheel cylinder 23 is smaller when the wheel cylinder pressure is relatively low than when the wheel cylinder pressure is relatively high. In FIG. 3, the control gain is set so as to continuously change in accordance with the wheel cylinder pressure. However, discrete control is performed so that one control gain is assigned to a predetermined hydraulic pressure range. A gain may be set.

  In this embodiment, in the normal linear control mode in which the EBD control is not executed, all the ABS holding valves 51 to 54 are opened, so the hydraulic pressure control system controls the wheel cylinder pressure of the four wheels. The wheel cylinder pressure is controlled using the control gain in the case of. The brake ECU 70 controls the wheel cylinder pressure by starting the EBD control and decreasing the control gain to a control gain set in accordance with the number of opening of the ABS holding valves 51 to 54, that is, the control target volume. Thereafter, the brake ECU 70 controls the wheel cylinder pressure by switching the control gain according to the increase / decrease of the control target volume due to the opening / closing of the ABS holding valves 51 to 54. With the end of the EBD control, the brake ECU 70 returns the control gain to the control gain in the normal linear control mode, that is, the control gain when the wheel cylinder pressure of the four wheels is the control target.

  In the present embodiment, the brake ECU 70 controls the wheel cylinder pressure by, for example, PD control. Therefore, brake ECU70 changes the value of a proportional gain and a differential gain according to the open / close state of ABS holding valves 51-54. When PID control is employed instead of PD control, the integral gain may be changed.

  As described above, according to the present embodiment, the control gain of the feedback control is changed according to the open / closed state of the ABS holding valves 51 to 54 during execution of the EBD control or the like, and the pressure-increasing linear control valve 66 and the pressure-reducing linear The control valve 67 is controlled. Thereby, the controllability of the brake control hydraulic pressure can be improved.

  By the way, in the present embodiment, the control hydraulic pressure may be controlled to be lower than the holding start pressure during EBD control. For example, the control hydraulic pressure may be controlled to be lower than the holding start pressure when the driver weakens the stepping operation on the brake pedal 24 compared to when the EBD control is started. The wheel cylinder pressure held at this time is released to the main flow path 45 through the return check valves 81 to 84 and is reduced to be equal to the control hydraulic pressure. Further, the brake ECU 70 controls the control hydraulic pressure to be reduced through the pressure-reducing linear control valve 67 in accordance with the driver's required braking force.

  Therefore, when the control hydraulic pressure becomes lower than the holding start pressure during the EBD control, the control target volume of the pressure reducing control by the pressure reducing linear control valve 67 is larger than when the control hydraulic pressure is higher than the holding start pressure. Will grow. On the other hand, when the control hydraulic pressure is increased again and becomes higher than the holding pressure, the pressure reduction through the return check valves 81 to 84 is not performed, so the target volume for the pressure reduction control is restored.

  When the control hydraulic pressure is higher than the holding start pressure, the target of pressure reduction control by the pressure reduction linear control valve 67 is the wheel cylinder 23 in which the ABS holding valves 51 to 54 are opened. For example, when the wheel cylinder pressure on the rear wheel side is maintained, the wheel cylinders 23FR and 23FL on the front wheel side are subject to pressure reduction control. In this case, since the control hydraulic pressure is higher than the holding pressure, the holding pressure is not reduced through the return check valves 81 to 84. On the other hand, when the control hydraulic pressure is lower than the holding start pressure, the wheel cylinder 23 holding the hydraulic pressure is also added to the target of pressure reduction control by the pressure reducing linear control valve 67. This is because the holding pressure is released to the main flow path 45 through the return check valves 81 to 84. As a result, the holding pressure is reduced to the control hydraulic pressure at that time.

  Thus, the control target volume may differ depending on the value of the control hydraulic pressure. For this reason, for example, when a constant control side is used regardless of the situation, a control delay may occur when the volume to be controlled increases. Alternatively, when the control target volume becomes small, there is a possibility that an excessive response occurs. It is desirable that more stable controllability can be realized during execution of EBD control or the like in which the control target volume varies.

  Therefore, in the present embodiment, the brake ECU 70 changes the control gain of the control fluid pressure reduction control to reduce the influence of the control fluid pressure on the responsiveness. The brake ECU 70 increases or decreases the control gain of the pressure reduction control according to the change in the control target volume accompanying the change in the control hydraulic pressure. The brake ECU 70 basically controls the pressure-reducing linear control valve 67 by switching the control gain according to the number of opening of the ABS holding valves 51 to 54. At this time, when the holding pressure by any of the ABS holding valves 51 to 54 exceeds the control hydraulic pressure, the brake ECU 70 switches the control gain on the assumption that any of the ABS holding valves 51 to 54 is opened. .

  As described above, in the present embodiment, the brake ECU 70 controls the pressure increase linear control valve 66 and the pressure reduction linear control valve in accordance with the control target volume in both the control fluid pressure increase control and the pressure reduction control. It is possible to control by switching the control gain of 67. In the present embodiment, in the case of pressure increase control, the control target volume does not change even if the control hydraulic pressure fluctuates. This is because the inflow of the brake fluid from the main flow path 45 to the wheel cylinder 23 where the hydraulic pressure should be maintained is blocked by the ABS holding valves 51 to 54 and the return check valves 81 to 84.

  Therefore, in the present embodiment, the brake ECU 70 controls the pressure-increasing linear control valve 66 by simply switching the control gain according to the number of opening of the ABS holding valves 51 to 54 when increasing the control hydraulic pressure. That's fine. Even if the control hydraulic pressure is lower than the holding start pressure, it is not necessary to switch the control gain for pressure increase control. When the control hydraulic pressure becomes lower than the holding start pressure, the brake ECU 70 switches the control gain on the assumption that the number of opening of the ABS holding valves 51 to 54 is different between the pressure increase control and the pressure reduction control.

  FIG. 4 is a diagram illustrating an example of a temporal change in the wheel cylinder pressure when the EBD control is executed. With reference to FIG. 4, an example of brake fluid pressure control according to the present embodiment will be described. FIG. 4 shows an example in which the rear wheel side ABS holding valves 53 and 54 are closed by EBD control and the hydraulic pressure is held in the rear wheel side wheel cylinders 23RR and 23RL. The vertical axis in FIG. 4 indicates the wheel cylinder pressure, and the horizontal axis indicates time. FIG. 4 shows changes over time in the wheel cylinder pressure on the front wheel side and the wheel cylinder pressure on the rear wheel side.

  As shown in FIG. 4, until the EBD control is started, the wheel cylinder pressure is controlled to a common control hydraulic pressure on both the front wheel side and the rear wheel side. In FIG. 4, this is the section from point O to point A. This is because in this embodiment, the wheel cylinder pressures of all four wheels are controlled in common in the normal linear control mode. When the timing for starting the EBD control arrives, the brake ECU 70 starts the EBD control. At this time, the brake ECU 70 closes the ABS holding valves 53 and 54 on the rear wheel side. As a result, the hydraulic pressure is maintained at the wheel cylinder pressure on the rear wheel side. The brake ECU 70 switches the control gain for feedback control of each of the pressure-increasing linear control valve 66 and the pressure-reducing linear control valve 67 from the normal control gain to the control gain for EBD control. Here, the normal control gain is a control gain that is optimally set when all four wheels used in the normal linear control mode are subject to hydraulic pressure control. As described above, a plurality of control gains for EBD control are set in accordance with the number of opening of the ABS holding valves 51 to 54, and here, they are optimally set when two front wheels are to be subjected to hydraulic pressure control. Switch to control gain.

  When the rear wheel side ABS holding valves 53 and 54 are closed, the rear wheel side wheel cylinder pressure is kept constant at the holding pressure Pa while the front wheel side wheel cylinder pressure is controlled to be higher than the holding start pressure. Retained. In FIG. 4, this is the section from point A to point B. The holding pressure Pa is the rear wheel side wheel cylinder pressure at the start of holding. At this time, since the front wheel side wheel cylinder pressure, that is, the control hydraulic pressure is higher than the holding start pressure, the volume to be controlled is the two wheel cylinders 23FR and 23FL on the front wheel side for both the pressure increase control and the pressure reduction control. Therefore, the brake ECU 70 controls the hydraulic pressure using the control gain when the two front wheels are to be controlled, whether the control hydraulic pressure is increased or controlled.

  For example, when the driver loosens the brake pedal operation and the front wheel side wheel cylinder pressure is reduced to a pressure lower than the holding start pressure Pa, the rear wheel side wheel cylinder pressure is also increased through the return check valves 83 and 84. The pressure is reduced following the side wheel cylinder pressure. In FIG. 4, this is the section from point B to point C. In this way, when the holding pressure is reduced even though the ABS holding valves 53 and 54 on the rear wheel side are closed, the brake ECU 70 sets the control gain for pressure reduction control to the four wheels before starting the EBD control. Restore control gain for use. This corresponds to switching the control gain on the assumption that the ABS holding valves 53 and 54 that are closed are opened.

  When the driver depresses the brake pedal 24 again to increase the front wheel side wheel cylinder pressure, the front wheel side wheel cylinder pressure is controlled to increase according to the driver's brake operation, but the rear wheel side wheel cylinder pressure is increased. Is kept constant at the holding pressure Pc at the start of pressure increase. This is because the ABS holding valves 53 and 54 are continuously closed. In FIG. 4, this is the section after point C. At this time, the brake ECU 70 switches the control gain to the control gain for the two front wheels again.

  In the present embodiment, when the holding pressure is reduced from the holding start pressure, the brake ECU 70 may update the reduced holding pressure value as the holding start pressure. According to the example of FIG. 4, in the section from point B to point C, the holding start pressure may be updated to the actual holding pressure as needed as the holding pressure is reduced. In the section after the point C, the holding pressure Pc may be updated as the holding start pressure.

  In this embodiment, the holding start pressure is used as a threshold value for switching the control gain. Thus, by updating the actual holding pressure as the holding start pressure, the control gain can be switched at a more appropriate timing. Can be done. For example, in the section after point C in FIG. 4, if the threshold value for switching the control gain is fixed to the holding start pressure Pa, an actual value is obtained by comparing the holding start pressure Pa with the front wheel side wheel cylinder pressure. The control gain is switched regardless of the holding pressure value Pc. On the other hand, when the threshold value is updated to the actual holding pressure Pc, the control gain is switched by comparing the actual holding pressure Pc with the front wheel side wheel cylinder pressure. Whether or not the retained rear wheel wheel cylinder pressure is included in the pressure reduction control target depends on whether or not the control hydraulic pressure is lower than the actual holding pressure Pc. For this reason, it is desirable to update the actual holding pressure as the holding start pressure and use the actual holding pressure as a threshold value for switching the control gain. In short, in this embodiment, the hydraulic pressure control system is such that when the holding pressure in any of the wheel cylinders exceeds the control hydraulic pressure, the ABS holding valve that holds the holding pressure is opened. To switch the control gain.

  Note that the holding start pressure Pa and the holding pressure Pc after the pressure reduction can be measured by the control pressure sensor 73 in this embodiment. The holding start pressure Pa is a measured value of the control pressure sensor 73 at the start of the EBD control, and the holding pressure Pc is a measured value of the control pressure sensor 73 at the start of re-pressure increase (point C in FIG. 4).

  However, the actual holding pressure here does not need to be a measured value of the holding pressure, but may be an estimated value. Since the brake control device 20 according to the present embodiment does not have means for directly measuring the retained rear wheel side wheel cylinder pressure, the brake ECU 70 estimates the retained pressure and uses it as a threshold for switching the control gain. It may be used. As shown in FIG. 5, for example, in order to ensure vehicle braking force, the ABS holding valves 53 and 54 may be opened in a pulse manner to gradually increase the holding pressure. FIG. 5 is a diagram illustrating another example of the time change of the wheel cylinder pressure when the EBD control is executed. As in FIG. 4, the vertical axis in FIG. 5 indicates the wheel cylinder pressure, and the horizontal axis indicates time. The brake ECU 70 can estimate the holding pressure after the pulse increase based on the holding pressure immediately before the holding valve is opened, the control hydraulic pressure, the opening time of the holding valve, the holding valve characteristics, and the like. The brake ECU 70 may update the estimated value of the holding pressure after the pulse pressure increase as the holding start pressure.

  FIG. 6 is a flowchart for explaining control gain switching processing according to the present embodiment. As described above, a specific example of the switching process according to the present embodiment will be described using the EBD control that maintains the hydraulic pressure on the rear wheel side as an example. The process shown in FIG. 6 is executed by the brake ECU 70 at a predetermined cycle during the brake control in the linear control mode, for example. When the process shown in FIG. 6 is started, the brake ECU 70 first determines whether or not the EBD control is being performed (S1). If it is determined that the EBD control is not being performed (No in S1), the brake ECU 70 controls the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 with a normal control gain (S2). That is, the hydraulic pressure control in the normal linear control mode is executed with the control gain for four wheels.

  If it is determined that the EBD control is being performed (Yes in S1), the brake ECU 70 further determines whether the EBD control was being performed in the previous process (S3). If the EBD control is not being performed in the previous process (No in S3), the brake ECU 70 sets and stores the current wheel cylinder pressure Pwc as the holding start pressure Pst (S5). In this case, since the EBD control is started in the current process, the wheel cylinder pressure Pwc, which is the measurement value of the control pressure sensor 73, is stored as the holding start pressure Pst.

  If the EBD control is also being performed in the previous process (Yes in S3), the brake ECU 70 determines the smaller of the current wheel cylinder pressure Pwc and the holding start pressure Pst stored at the end of the previous process. The value is set and stored as a holding start pressure (S4). As a result, if the holding pressure is maintained at the holding start pressure Pst because the control hydraulic pressure Pwc is higher, the value of the holding start pressure Pst is maintained and stored in the brake ECU 70 as it is. Conversely, when the control hydraulic pressure Pwc becomes lower, the holding start pressure Pst is updated to the value of the control hydraulic pressure Pwc.

  Next, the brake ECU 70 determines whether or not the control hydraulic pressure Pwc is equal to or lower than the holding start pressure Pst (S6). If the control hydraulic pressure Pwc is higher than the holding start pressure Pst (No in S6), the brake ECU 70 switches to the control gain for EBD control and switches the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67. Control (S7). Here, the control gain for EBD control means a control gain when the front wheels are controlled. In this example, if the control hydraulic pressure Pwc is higher than the holding start pressure Pst, both the pressure increase control and the pressure reduction control are controlled only by the two front wheels.

  On the other hand, when the control hydraulic pressure Pwc is lower than the holding start pressure Pst (Yes in S6), the brake ECU 70 further determines whether the target pressure Pref of the control hydraulic pressure Pwc is lower than the control hydraulic pressure Pwc. (S8). When the target pressure Pref is larger than the control hydraulic pressure Pwc (No in S8), the brake ECU 70 executes the pressure increase control and only the front wheels are controlled, so the brake ECU 70 performs the EBD control. The pressure-increasing linear control valve 66 is controlled by switching to the control gain (S7). When the target pressure Pref is lower than or equal to the control hydraulic pressure Pwc (Yes in S8), the brake ECU 70 executes the pressure reduction control, and the control target is four wheels. Therefore, the brake ECU 70 has a normal control gain. The pressure-reducing linear control valve 67 is controlled (S9).

  Further, the brake ECU 70 determines whether it is necessary to increase the holding pressure by the pulse opening of the ABS holding valves 53 and 54 on the rear wheel side, that is, so-called holding pressure pulse increase (S10). Whether or not the pulse increase is necessary is determined by the brake ECU 70 from the viewpoint of whether or not it is necessary to increase the braking force of the vehicle in accordance with the driver's pedal depression in the EBD control processing executed in parallel. Is done. If it is determined that a pulse increase is necessary (Yes in S10), the brake ECU 70 opens the ABS holding valves 53 and 54 for a very short time to increase the holding pressure (S11). In this case, the brake ECU 70 estimates the value of the increased holding pressure, updates the estimated value of the holding pressure as the holding start pressure Pst, and stores it for the next processing. If it is determined that the pulse increase is not necessary (No in S10), the brake ECU 70 ends the process as it is.

  As described above, according to the present embodiment, the brake ECU 70 controls the pressure-increasing linear control valve 66 and the pressure-decreasing linear control valve 67 by switching to an appropriate control gain according to the volume to be controlled by the hydraulic pressure. For this reason, even if it is a case where control object volume changes like EBD control, brake fluid pressure can be controlled favorably. The brake ECU 70 simply combines the selection of the control gain according to the number of opening of the ABS holding valves 51 to 54 and the selection of the control gain according to the relationship between the holding pressure and the control hydraulic pressure. May be executed, or only one of them may be executed.

  The brake ECU 70 may select an optimal control gain according to the relationship between the holding pressure and the control hydraulic pressure. In the above example, switching between the control gain for four wheels and the control gain for two front wheels has been described, but the present invention is not limited to this. For example, consider a case where the hydraulic pressures are held at different values in the first wheel cylinder and the second wheel cylinder, and the remaining wheel cylinders are controlled by the control hydraulic pressure Pwc. It is assumed that the first wheel cylinder is held at a holding pressure P1, and the second wheel cylinder is held at a holding pressure P2 that is higher than the holding pressure P1. At this time, when the control hydraulic pressure Pwc is higher than the holding pressure P1 and lower than the holding pressure P2, the target volume for the pressure reduction control is a three-wheel wheel cylinder other than the first wheel cylinder. Therefore, the brake ECU 70 executes the pressure reduction control by switching to the control gain for the three wheels. As described above, when the holding pressure is different for each wheel cylinder, the control gain is switched to the control gain corresponding to the control target volume without necessarily recovering the control gain for the four wheels as in the above-described embodiment. You may do it.

It is a distribution diagram showing a brake control device concerning one embodiment of the present invention. It is a figure which shows an example of the time change of the wheel cylinder pressure in EBD control. It is a figure which shows an example of the control gain which concerns on this embodiment. It is a figure which shows an example of the time change of a wheel cylinder pressure when performing EBD control. It is a figure which shows the other example of the time change of a wheel cylinder pressure when performing EBD control. It is a flowchart for demonstrating the switching process of the control gain which concerns on this embodiment.

Explanation of symbols

  20 brake control device, 23 wheel cylinder, 51-54 ABS holding valve, 66 pressure-increasing linear control valve, 67 pressure-reducing linear control valve, 70 brake ECU, 81-84 return check valve.

Claims (5)

A plurality of wheel cylinders for applying braking force to each of the plurality of wheels by supplying hydraulic fluid;
A hydraulic control system capable of controlling the plurality of wheel cylinders to a common control hydraulic pressure by feedback control; and
Provided corresponding to each of the plurality of wheel cylinders, and when the valve is opened, the control hydraulic pressure is supplied from the hydraulic pressure control system to the corresponding wheel cylinder and the valve cylinder is closed. A plurality of holding valves that hold the hydraulic pressure in the corresponding wheel cylinders,
When the control hydraulic pressure is reduced to a pressure lower than the holding pressure by the holding valve, the holding pressure is released to the control hydraulic pressure so that the holding pressure is reduced following the control hydraulic pressure. Holding pressure reducing means,
The hydraulic pressure control system changes a control gain of the pressure reduction control of the control hydraulic pressure in order to reduce the influence on the responsiveness of the control hydraulic pressure when the holding pressure is reduced by the holding pressure reducing means. Brake control device.   The hydraulic pressure control system performs the pressure reduction control by switching the control gain according to the number of the holding valves that are opened, and the holding pressure by any holding valve is the control hydraulic pressure. 2. The brake control device according to claim 1, wherein the control gain is switched on the assumption that any one of the holding valves is opened when the pressure exceeds the control value.   The hydraulic pressure control system executes the pressure reduction control by switching to a control gain used when all the holding valves are opened when the holding pressure by any holding valve exceeds the control hydraulic pressure. The brake control device according to claim 2.   The holding pressure reducing means is a plurality of check valves provided in parallel to each of the holding valves so as to relieve the holding pressure to the control hydraulic pressure when the holding pressure exceeds the control hydraulic pressure. The brake control device according to claim 1.   2. The brake control device according to claim 1, wherein the hydraulic pressure control system controls the control hydraulic pressure by switching a control gain in accordance with a control target volume that varies depending on an open / close state of the plurality of holding valves. .

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