Vehicle braking control device

Abstract

To provide a brake control device that is composed of two brake units connected to each other by communication and can execute two-system pressure regulation, which appropriately performs pressure regulation control at the time of communication abnormality.SOLUTION: A brake control device includes a first unit for individually outputting a front wheel supply pressure and a rear wheel supply pressure according to an operation amount of a brake operation member, a second unit which individually increases the front wheel supply pressure and the rear wheel supply pressure and outputs a front wheel pressure and a rear wheel pressure, a communication bus for performing signal transmission between the first unit and the second unit, an operation amount sensor for detecting the operation amount, a front wheel supply pressure sensor for detecting the front wheel supply pressure, and a rear wheel supply pressure sensor for detecting the rear wheel supply pressure. The first unit calculates a front wheel target pressure and a rear wheel target pressure on the basis of the operation amount, and controls the front wheel supply pressure and the rear wheel supply pressure so that they approach the front wheel target pressure and the rear wheel target pressure. The second unit calculates the front wheel target pressure and the rear wheel target pressure on the basis of the operation amount, when the communication bus is abnormal, and increases the front wheel pressure and the rear wheel pressure on the basis of the front wheel target pressure and the rear wheel target pressure.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a braking control device for a vehicle. [Background technology]

[0002] Patent Document 1 describes that, with the aim of "fully demonstrating the function of increasing brake fluid pressure even when a communication abnormality occurs in the operation of the VSA device regarding the operating state information of the VSA device," "vehicle braking system 10 comprises ESB device 16 that generates brake fluid pressure by operating brake motor 72, VSA device 18 that adjusts the brake fluid pressure by operating pump motor 135, CAN communication medium 33 used when communicating operating state information regarding VSA device 18 to ESB device 16, and first braking control unit 77 that performs pressurization control to increase the brake fluid pressure in the fluid supply flow path to VSA device 18 by operating brake motor 72 when ESB device 16 receives operation in-progress information indicating that VSA device 18 is operating via CAN communication medium 33. First braking control unit 77 continues to perform the pressurization control even when it recognizes that a communication abnormality has occurred in the operation state information."

[0003] The applicant has developed a brake control device as disclosed in Patent Document 2, which has a reduced longitudinal dimension and allows for separate control of the brake fluid pressure in the front wheel system and the brake fluid pressure in the rear wheel system. Specifically, the brake control device in Patent Document 2 includes "a master unit having a master chamber connected to the front wheel cylinder and a servo chamber that applies to the master piston a forward force that counteracts the backward force applied to the master piston by the master chamber," "a pressure adjustment unit that adjusts brake fluid discharged from an electric pump to a first fluid pressure using a first solenoid valve, introduces the first fluid pressure into the rear wheel cylinder, and reduces and adjusts the first fluid pressure to a second fluid pressure using a second solenoid valve and introduces the second fluid pressure into the servo chamber," and "a regenerative coordination unit that includes an input piston that operates in conjunction with a brake operating member and an input cylinder fixed to the master cylinder, and in which the gap between the master piston and the input piston is controlled by the second fluid pressure." Here, adjusting the brake fluid pressure of the front wheel system and the brake fluid pressure of the rear wheel system to be the same is called "single-system pressure regulation," and adjusting them separately is called "dual-system pressure regulation."

[0004] In the device of Patent Document 1, if a communication error occurs while the ESB device (also referred to as the "first brake unit") is receiving information from the VSA device (also referred to as the "second brake unit") via communication that the VSA device is operating, the ESB device continues to increase the brake fluid pressure. That is, the device of Patent Document 1 anticipates a situation in which a communication error occurs while the operation information of the second brake unit is being transmitted to the first brake unit. Therefore, the first brake unit can determine that the second brake unit is operating. However, once the operation of the first and second brake units is terminated, the operation status of the first and second units cannot be determined in the event of a communication error. Therefore, in a brake control device capable of realizing dual-system pressure regulation, it is desirable to be able to appropriately execute control even if a communication error occurs and it becomes impossible to determine the mutual operation status. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-147614 [Patent Document 2] Japanese Patent Application Publication No. 2019-137202 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a vehicle braking control device that is composed of two braking units connected by communication and is capable of performing two-system pressure regulation, and that can perform pressure regulation control appropriately even in the event of a communication abnormality. [Means for solving the problem]

[0007] The vehicle brake control device (SC) of the present invention comprises a first unit (SA) that outputs front and rear wheel supply pressures (Pm, Pv) individually in accordance with the operation amount (Sp) of a brake operating member (BP), a second unit (SB) that is provided between the first unit (SA) and front and rear wheel cylinders (CWf, CWr) and that increases the front and rear wheel supply pressures (Pm, Pv) individually to output front and rear wheel pressures (Pwf, Pwr), a communication bus (BS) that transmits signals between the first unit (SA) and the second unit (SB), an operation amount sensor (SP) that detects the operation amount (Sp), a front wheel supply pressure sensor (PM) that detects the front wheel supply pressure (Pm), and a rear wheel supply pressure sensor (PV) that detects the rear wheel supply pressure (Pv). The first unit (SA) calculates the front and rear wheel target pressures (Ptf, Ptr) based on the manipulated variable (Sp) and controls the front and rear wheel supply pressures (Pm, Pv) to approach the front and rear wheel target pressures (Ptf, Ptr). When the communication bus (BS) is abnormal, the second unit (SB) calculates the front and rear wheel target pressures (Ptf, Ptr) based on the manipulated variable (Sp) and increases the front and rear wheel pressures (Pwf, Pwr) based on the front and rear wheel target pressures (Ptf, Ptr). For example, the manipulated variable sensor (SP) is connected to both the first and second units (SA, SB), and the front wheel supply pressure sensor (PM) is connected to at least the second unit (SB). Then, the second unit (SB) calculates the front and rear wheel target pressures (Ptf, Ptr) based on the operation amount (Sp), and increases the front wheel pressure (Pwf) by an amount equivalent to the deviation (hPf) between the front wheel target pressure (Ptf) and the front wheel supply pressure (Pm).

[0008] In the vehicle brake control device (SC) according to the present invention, the operation amount sensor (SP) is connected to both the first and second units (SA, SB), the front wheel supply pressure sensor (PM) is connected only to the second unit (SB), and the rear wheel supply pressure sensor (PV) is connected only to the first unit (SA). The first unit (SA) acquires the front wheel supply pressure (Pm) from the second unit (SB) via the communication bus (BS), calculates front and rear wheel target pressures (Ptf, Ptr) based on the operation amount (Sp), and controls the front and rear wheel supply pressures (Pm, Pv) to approach the front and rear wheel target pressures (Ptf, Ptr) based on the deviation (hPf, hPr) between the front and rear wheel target pressures (Ptf, Ptr) and the front and rear wheel supply pressures (Pm, Pv). When the communication bus (BS) is abnormal, the second unit (SB) calculates the front and rear wheel target pressures (Ptf, Ptr) based on the operation amount (Sp), increases the front wheel pressure (Pwf) by an amount equivalent to the deviation (hPf) between the front wheel target pressure (Ptf) and the front wheel supply pressure (Pm), and increases the rear wheel pressure (Pwr) by an amount equivalent to the rear wheel target pressure (Ptr).

[0009] If the communication bus BS is abnormal, the second brake unit SB cannot grasp the operating state of the first brake unit SA. Therefore, in the event of a communication abnormality, the second brake unit SB calculates the front and rear wheel target pressures Ptf, Ptr, and increases the front and rear wheel pressures Pwf, Pwr based on the front and rear wheel target pressures Ptf, Ptr. With the above configuration, even if the operating state of the first brake unit SA cannot be grasped due to a communication abnormality, the second brake unit SB compensates in accordance with the decrease in its output. In other words, pressure regulation control is performed appropriately even during a communication abnormality. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram for explaining the entire vehicle JV equipped with a braking control device SC. [Figure 2] FIG. 2 is a schematic diagram for explaining a configuration example of a first braking unit SA. [Figure 3]4 is a schematic diagram for explaining a configuration example of a second braking unit SB. FIG. [Figure 4] FIG. 4 is a flowchart illustrating a pressure regulation control process. [Figure 5] FIG. 3 is a block diagram for explaining drive control of a control valve UB. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Symbols for components, etc., and suffixes at the end of the symbols> In the following description, components, calculation processes, signals, characteristics, and values ​​with the same symbols, such as "CW," have the same function. The suffixes "f" and "r" at the end of the symbols for each wheel are generic symbols that indicate whether the symbol relates to the front or rear wheel system. For example, a wheel cylinder CW provided on each wheel is written as a "front wheel cylinder CWf" and a "rear wheel cylinder CWr." Furthermore, the suffixes "f" and "r" at the end of the symbol can be omitted. When the suffixes "f" and "r" are omitted, each symbol represents a generic term. For example, "CW" is a generic term for wheel cylinders provided on the front and rear wheels of a vehicle.

[0012] In the fluid path from the master cylinder CM to the wheel cylinder CW, the side closer to the master cylinder CM (the side farther from the wheel cylinder CW) is referred to as the "upper side," and the side closer to the wheel cylinder CW (the side farther from the master cylinder CM) is referred to as the "lower side." Also, in the circulating flows KN, KL of brake fluid BF in the first and second fluid units YA, YB, the side closer to the discharge ports of the first and second fluid pumps QA, QB (the side farther from the suction ports) is referred to as the "upstream side," and the side closer to the suction ports of the first and second fluid pumps QA, QB (the side farther from the discharge ports) is referred to as the "downstream side."

[0013] The first hydraulic unit YA of the first brake unit SA, the second hydraulic unit YB of the second brake unit SB, and the wheel cylinder CW are connected by a fluid path (communication path HS). Furthermore, in the first and second hydraulic units YA and YB, various components (UJ, UK, etc.) are connected by fluid paths. Here, the "fluid path" is a path for moving the brake fluid BF, and corresponds to piping, flow paths in the actuator, hoses, etc. In the following explanation, the communication path HS, reflux path HK, return path HL, reservoir path HR, input path HN, servo path HV, pressure reduction path HG, etc. are fluid paths.

[0014] <Vehicle JV equipped with braking control device SC> With reference to the schematic diagram of FIG. 1, the overall configuration of a vehicle JV equipped with a braking control device SC according to the present invention will be described. The vehicle JV is a hybrid vehicle or an electric vehicle equipped with an electric motor for driving. The vehicle JV is equipped with a regenerative device KG. The regenerative device KG is composed of a generator GN and a control unit EG for the regenerative device (also referred to as a "regenerative controller"). The generator GN is also an electric motor for driving. In regenerative braking, the electric motor / generator GN operates as a generator, and the generated electric power is stored in a storage battery BG via the regenerative controller EG. For example, the regenerative device KG is provided on the front wheels WHf. In this configuration, the regenerative device KG generates a regenerative braking force Fg on the front wheels WHf.

[0015] A vehicle JV is equipped with front and rear wheel braking devices SXf, SXr (=SX). The braking device SX is composed of a brake caliper CP, a friction member MS (e.g., brake pad), and a rotating member (e.g., brake disc) KT. The brake caliper CP is provided with a wheel cylinder CW. The hydraulic pressure Pw (referred to as "wheel pressure") in the wheel cylinder CW presses the friction member MS against the rotating member KT fixed to each wheel WH. This generates a braking force Fm on the wheel WH. The braking force generated by the wheel pressure Pw is referred to as the "friction braking force Fm."

[0016] The vehicle JV is equipped with a brake operating member BP and various sensors (such as SP). The brake operating member (e.g., brake pedal) BP is a member that the driver operates to decelerate the vehicle JV. The vehicle JV is provided with an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP. The operation displacement Sp is one of the state quantities (state variables) that indicate the operation amount (braking operation amount) of the brake operating member BP, and in a brake-by-wire type brake control device SC, it is a signal that indicates the driver's intention to brake (i.e., a braking command).

[0017] The operation displacement sensor SP (corresponding to an "operation amount sensor") includes two detection units SPa and SPb (referred to as "first and second detection units"). That is, the operation displacement Sp is detected in two ways, making the operation displacement sensor SP redundant. The first detection unit SPa (referred to as "first displacement detection unit") of the operation displacement sensor SP is connected to the first braking unit SA (particularly, the first control unit EA) by a first displacement signal line LSpa. On the other hand, the second detection unit SPb (referred to as "second displacement detection unit") of the operation displacement sensor SP is connected to the second braking unit SB (particularly, the second control unit EB) by a second displacement signal line LSpb. Therefore, the signal Spa (referred to as "first operation displacement") of the first displacement detection unit SPa is directly input to the first control unit EA. On the other hand, the signal Spb (referred to as "second operation displacement") of the second displacement detection unit SPb is directly input to the second control unit EB. For example, "signal lines LSpa, LSpb" are electric wires (wire harnesses) for transmitting signals.

[0018] In addition to the operation displacement sensor SP, the hydraulic pressure Ps (referred to as "simulator pressure") of the stroke simulator SS is adopted as another state quantity representing the braking operation amount. The simulator pressure Ps is detected by a simulator pressure sensor PS. The simulator pressure sensor PS is connected to the first brake unit SA (particularly, the first control unit EA) by a simulator pressure signal line LPs. Therefore, the simulator pressure Ps is directly input to the first control unit EA. The simulator pressure Ps is a state quantity equivalent to the operating force of the brake operating member BP.

[0019] The vehicle JV is equipped with various sensors. For braking control (referred to as "independent wheel control") that individually controls the wheel pressure Pw of each wheel WH, such as antilock brake control and anti-skid control, each wheel WH is equipped with a wheel speed sensor VW that detects its rotational speed (wheel speed) Vw. The vehicle JV is also equipped with a steering amount sensor that detects the steering amount Sa (e.g., the steering wheel angle), a yaw rate sensor that detects the vehicle's yaw rate Yr, a longitudinal acceleration sensor that detects the vehicle's longitudinal acceleration Gx, and a lateral acceleration sensor that detects the vehicle's lateral acceleration Gy (all not shown). The signals for the wheel speed Vw, steering amount Sa, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy are input to the second braking unit SB (particularly, the second control unit EB) via their respective signal lines.

[0020] The vehicle JV is equipped with a brake control device SC. The brake control device SC employs a so-called front and rear type (also called "type II") brake system as two brake systems. The brake control device SC adjusts the actual wheel pressure Pw.

[0021] The brake control device SC is composed of two brake units SA and SB. The first brake unit SA is composed of a first fluid unit YA and a first control unit EA. The first fluid unit YA is controlled by the first control unit EA using a storage battery BT (braking storage battery) separate from the drive storage battery BG as its power source. The second brake unit SB is composed of a second fluid unit YB and a second control unit EB. Like the first brake unit SA, the second fluid unit YB is controlled by the second control unit EB using the storage battery BT as its power source.

[0022] The first brake unit SA (particularly, the first control unit EA) and the second brake unit SB (particularly, the second control unit EB) are connected to a communication bus BS. The regenerative device KG (particularly, the regenerative control unit EG) is also connected to the communication bus BS. The "communication bus BS" has a network structure in which multiple control units (also called "controllers") hang from communication lines terminated at both ends. Signals are transmitted between the multiple controllers (EA, EB, EG, etc.) via the communication bus BS. That is, the multiple controllers can transmit signals (detected values, calculated values, control flags, etc.) to the communication bus BS and can receive signals from the communication bus BS. For example, a vehicle bus (an internal communication network that interconnects controllers within a vehicle) is used as the communication bus BS, and CAN is used as the serial communication protocol. The communication bus BS is composed of communication lines (e.g., CAN bus cables) and transmitting / receiving microcontrollers in each controller.

[0023] <First braking unit SA> An example of the configuration of the first brake unit SA (corresponding to the "first unit") of the brake control device SC will be described with reference to the schematic diagram of FIG. 2. The first brake unit SA generates front and rear wheel supply pressures Pm and Pv in response to operation of the brake operating member BP (brake pedal). The front and rear wheel supply pressures Pm and Pv are ultimately supplied to the front and rear wheel cylinders CWf and CWr via a communication path HS (fluid path) and a second brake unit SB. The first brake unit SA is made up of a first fluid unit YA and a first control unit EA.

[0024] <First fluid unit YA> The first fluid unit YA (also referred to as the "first actuator") is composed of an apply part AP, a pressure adjustment part CA, and an input part NR.

[0025] [Apply Department AP] In response to operation of the brake operating member BP, the apply section AP outputs a front wheel supply pressure Pm, which is composed of a single master cylinder CM and a master piston NM.

[0026] A master piston NM is inserted into the single-type master cylinder CM. The master piston NM divides the interior of the master cylinder CM into three hydraulic chambers Rm, Ru, and Rs. The master chamber Rm is divided by the bottom of one side of the master cylinder CM and the master piston NM. The interior of the master cylinder CM is further divided into a servo chamber Ru and a reaction chamber Rs by a flange portion Tu of the master piston NM. In other words, the master chamber Rm and the servo chamber Ru are arranged opposite each other with the flange portion Tu in between. Here, the pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are made equal.

[0027] When braking is not in progress, the master piston NM is in its most retracted position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is in communication with the master reservoir RV. Brake fluid BF is stored inside the master reservoir RV (an atmospheric pressure reservoir, also simply referred to as the "reservoir"). When the brake operating member BP is operated, the master piston NM is moved forward in the Ha direction (a direction in which the volume of the master chamber Rm decreases). This movement blocks communication between the master chamber Rm and the reservoir RV. When the master piston NM is further moved forward in the Ha direction, the front wheel supply pressure Pm increases from "0 (atmospheric pressure)." As a result, brake fluid BF pressurized to the front wheel supply pressure Pm is output (pressurized and fed) from the master chamber Rm of the master cylinder CM. Because the front wheel supply pressure Pm is the hydraulic pressure of the master chamber Rm, it is also referred to as the "master pressure." [Pressure Regulating Unit CA] The pressure adjusting unit CA supplies rear wheel supply pressure Pv to the rear wheel cylinder CWr and downstream servo pressure Pk to the servo chamber Ru of the apply unit AP. The pressure adjusting unit CA is composed of a first electric motor MA, a first fluid pump QA, and upstream and downstream pressure adjusting valves UJ and UK.

[0028] A first electric motor MA drives a first fluid pump QA. The suction and discharge ports of the first fluid pump QA are connected by a return passage HK (fluid passage). The suction port of the first fluid pump QA is also connected to a master reservoir RV via a reservoir passage HR. A check valve is provided at the discharge port of the first fluid pump QA.

[0029] Two pressure regulating valves UJ, UK are provided in series in the return path HK. Specifically, a normally open downstream pressure regulating valve UK is provided in the return path HK. A normally open upstream pressure regulating valve UJ is provided between the downstream pressure regulating valve UK and the discharge port of the fluid pump QA. Therefore, in the circulating flow KN of brake fluid BF, the upstream pressure regulating valve UJ is located upstream (closer to the discharge port of the fluid pump QA) of the downstream pressure regulating valve UK. The upstream and downstream pressure regulating valves UJ, UK are linear solenoid valves whose valve opening (lift amount) is continuously controlled based on the energization state (e.g., supply currents Ij, Ik). The upstream and downstream pressure regulating valves UJ, UK are also called "differential pressure valves" because they adjust the hydraulic pressure difference between their upstream and downstream sides.

[0030] When the first electric motor MA drives the first fluid pump QA, a circulation flow KN (indicated by the dashed arrow) of brake fluid BF is generated in the return path HK through the fluid pump QA and the upstream and downstream pressure regulating valves UJ and UK. The fluid pressure Pk between the upstream pressure regulating valve UJ and the downstream pressure regulating valve UK (referred to as the "downstream servo pressure") is controlled by the downstream pressure regulating valve UK. The fluid pressure Pj between the upstream pressure regulating valve UJ and the discharge port of the first fluid pump QA (referred to as the "upstream servo pressure") is controlled by the upstream pressure regulating valve UJ.

[0031] When the downstream pressure regulating valve UK is fully open (the downstream pressure regulating valve UK is normally open and therefore not energized), the downstream servo pressure Pk is "0 (atmospheric pressure)." When the amount of electricity (supply current) to the downstream pressure regulating valve UK is increased, the downstream pressure regulating valve UK throttles the circulation flow KN (the flow of brake fluid BF circulating in the return flow path HK). In other words, the downstream pressure regulating valve UK narrows the flow path of the return flow path HK, and the downstream pressure regulating valve UK exerts an orifice effect. As a result, a differential pressure sPk (referred to as the "downstream differential pressure") is generated between the downstream hydraulic pressure (atmospheric pressure) and the upstream hydraulic pressure Pk (downstream servo pressure) for the downstream pressure regulating valve UK. The downstream differential pressure sPk is adjusted by the amount of electricity (supply current Ik) to the downstream pressure regulating valve UK.

[0032] Similarly, when the upstream pressure regulating valve UJ is fully open (the upstream pressure regulating valve UJ is normally open and therefore not energized), the upstream servo pressure Pj is equal to the downstream servo pressure Pk. When the amount of energization (supply current Ij) to the upstream pressure regulating valve UJ is increased, the upstream pressure regulating valve UJ throttles the circulation flow KN (the flow of brake fluid BF circulating in the return flow path HK). In other words, the upstream pressure regulating valve UJ narrows the flow path of the return flow path HK, thereby exerting an orifice effect. This generates a differential pressure sPj (referred to as the "upstream differential pressure") between the downstream hydraulic pressure Pk (downstream servo pressure) and the upstream hydraulic pressure Pj (upstream servo pressure) for the upstream pressure regulating valve UJ. The upstream differential pressure sPj is adjusted by the amount of energization (supply current Ij) to the upstream pressure regulating valve UJ. In terms of the magnitude relationship between the upstream servo pressure Pj and the downstream servo pressure Pk, the upstream servo pressure Pj is always equal to or greater than the downstream servo pressure Pk (i.e., "Pj≧Pk"). Here, when no power is supplied to the upstream pressure regulating valve UJ and it is in a fully open state, the upstream and downstream servo pressures Pj and Pk are made equal (i.e., "Pj=Pk").

[0033] The hydraulic pressure supplied from the first brake unit SA to the second brake unit SB is referred to as the "supply pressure." In the brake control device SC, the transmission path of the supply pressure is different between the brake system related to the front wheels WHf and the brake system related to the rear wheels WHr. In the brake system related to the front wheels WHf, the return path HK is connected to the servo chamber Ru via a servo path HV (fluid path) at a point pk between the upstream pressure regulating valve UJ and the downstream pressure regulating valve UK. Therefore, the downstream servo pressure Pk is introduced (supplied) to the servo chamber Ru. As the downstream servo pressure Pk increases, the master piston NM is pressed in the forward direction Ha, and the hydraulic pressure Pm (front wheel supply pressure) in the master chamber Rm increases. A front wheel connection path HSf is connected to the front wheel cylinder CWf via the second brake unit SB (particularly, the second fluid unit YB). Therefore, in the braking system for the front wheels WHf of the brake control device SC, the downstream servo pressure Pk is supplied to the front wheel cylinders CWf via the master cylinder CM as the front wheel supply pressure Pm. However, since "ru = rm", "Pk = Pm = Pwf" holds.

[0034] In the brake system for the rear wheels WHr, the return path HK is connected to the rear wheel cylinder CWr via the rear wheel connection path HSR (fluid path) and the second brake unit SB (particularly, the second fluid unit YB) at a location pj between the discharge port of the first fluid pump QA and the upstream pressure regulating valve UJ. Therefore, in the brake system for the rear wheels WHr of the brake control device SC, the upstream servo pressure PJ is directly supplied to the rear wheel cylinder CWr as the rear wheel supply pressure Pv (i.e., "Pj = Pv = Pwr").

[0035] A rear wheel supply pressure sensor PV (also referred to as a "servo pressure sensor") is provided in the rear wheel connection path HSr to detect the rear wheel supply pressure Pv (=Pj). The rear wheel supply pressure sensor PV is connected to the first controller EA by a rear wheel supply pressure signal line LPv (also referred to as a "servo pressure signal line"). Therefore, a signal of the rear wheel supply pressure Pv is directly input to the first controller EA.

[0036] [Input NR] The input unit NR operates the brake operating member BP to realize regenerative cooperative control, but creates a state in which wheel pressure Pw is not generated. "Regenerative cooperative control" coordinates the friction braking force Fm (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to generator GN) so that the kinetic energy of the vehicle JV can be efficiently recovered as electrical energy during braking. The input unit NR is composed of an input cylinder CN, an input piston NN, an intake valve VA, an open valve VB, a stroke simulator SS, and a simulator hydraulic pressure sensor PS.

[0037] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to the brake operating member BP (brake pedal) via a clevis (U-shaped link) so that it moves in conjunction with the brake operating member BP. There is a gap Ks (also called "separation displacement") between the end face of the input piston NN and the end face of the master piston NM. Regenerative cooperative control is achieved by adjusting the separation distance Ks using the downstream servo pressure Pk.

[0038] The input chamber Rn of the input unit NR is connected to the reaction chamber Rs of the apply unit AP via an input path HN (fluid path). A normally closed inlet valve VA is provided in the input path HN. The input path HN is connected to the master reservoir RV via a reservoir path HR between the inlet valve VA and the reaction chamber Rs. A normally open release valve VB is provided in the reservoir path HR. The inlet valve VA and the release valve VB are on-off solenoid valves. A stroke simulator SS (also simply referred to as "simulator") is connected to the input path HN between the inlet valve VA and the reaction chamber Rs.

[0039] When power is not supplied to the introduction valve VA and the release valve VB, the introduction valve VA is closed and the release valve VB is open. When the introduction valve VA is closed, the input chamber Rn is sealed and fluid locked. As a result, the master piston NM is displaced integrally with the brake operating member BP. When the release valve VB is open, the simulator SS is connected to the master reservoir RV. When power is supplied to the introduction valve VA and the release valve VB, the introduction valve VA is opened and the release valve VB is closed. As a result, the master piston NM can be displaced separately from the brake operating member BP. At this time, the input chamber Rn is connected to the stroke simulator SS, and the operating force Fp of the brake operating member BP is generated by the simulator SS.

[0040] The state in which the master piston NM and the brake operating member BP are displaced separately (when the solenoid valves VA and VB are energized) is called the "first mode (or by-wire mode)." In the first mode, the brake control device SC functions as a brake-by-wire type device (i.e., a device that can generate a frictional braking force Fm independently of the driver's braking operation). Therefore, in the first mode, the wheel pressure Pw is generated independently of the operation of the brake operating member BP. On the other hand, the state in which the master piston NM and the brake operating member BP are displaced together (when the solenoid valves VA and VB are not energized) is called the "second mode (or manual mode)." In the second mode, the wheel pressure Pw is linked to the driver's braking operation. The input unit NR selects one of the first mode (by-wire mode) and the second mode (manual mode) depending on whether or not power is supplied to the introduction valve VA and the release valve VB. If a power failure occurs in the braking control device SC (for example, failure of the storage battery BT), the input unit NR goes into the second mode.

[0041] A simulator pressure sensor PS is provided in the input line HN between the introduction valve VA and the reaction force chamber Rs to detect the hydraulic pressure Ps (simulator pressure) in the simulator SS. The simulator pressure sensor PS is connected to the first control unit EA by a simulator pressure signal line LPs. Therefore, the simulator pressure Ps is directly input to the first control unit EA via the simulator pressure signal line LPs.

[0042] <First control unit EA> The first actuator YA is controlled by a first control unit EA (also referred to as the "first controller"). The first controller EA is composed of a first microprocessor MPa and a first drive circuit DRa. The first controller EA is connected to a communication bus BS so that signals (detected values, calculated values, control flags, etc.) can be shared between the first controller EA and various controllers (EB, EG, etc.).

[0043] The first controller EA and the first detection unit SPa of the operation displacement sensor SP are connected via a signal line LSpa for the first detection unit SPa. The first controller EA and the rear wheel supply pressure sensor PV are connected via a signal line LPv for the rear wheel supply pressure sensor PV. The first controller EA and the simulator pressure sensor PS are connected via a signal line LPs for the simulator pressure sensor PS. Therefore, the first controller EA directly receives the first operation displacement Spa via the signal line LSpa, the rear wheel supply pressure Pv via the signal line LPv, and the simulator pressure Ps via the signal line LPs.

[0044] The first controller EA (particularly, the first microprocessor MPa) is programmed with a pressure regulation control algorithm. "Pressure regulation control" is a control for adjusting the front and rear wheel supply pressures Pm and Pv (resulting in front and rear wheel pressures Pwf and Pwr), and includes regenerative cooperative control. The pressure regulation control is performed based on the first and second operation displacements Spa and Spb, the simulator pressure Ps, the front and rear wheel supply pressures Pm and Pv, and the maximum regenerative braking force Fx.

[0045] Based on the pressure regulation control algorithm, the first drive circuit DRa drives the first electric motor MA constituting the first actuator YA and various solenoid valves (UJ, UK, etc.). The first drive circuit DRa includes an H-bridge circuit configured with switching elements (e.g., MOS-FETs) to drive the first electric motor MA. The first drive circuit DRa also includes switching elements to drive the various solenoid valves (UJ, UK, etc.). Additionally, the first drive circuit DRa includes a motor current sensor (not shown) that detects the supply current Im (actual value) to the first electric motor MA, and upstream and downstream current sensors (not shown) that detect the supply currents Ij and Ik (actual values, referred to as "upstream and downstream currents") to the upstream and downstream pressure regulation valves UJ and UK. The first electric motor MA is provided with a rotation speed sensor (not shown) that detects its rotation speed Na (actual value). The first electric motor MA may be provided with a rotation angle sensor (not shown) that detects the rotation angle Ka (actual value), and the motor rotation speed Na may be calculated based on the motor rotation angle Ka.

[0046] The first controller EA calculates upstream and downstream target currents Itj and Itk (target values) corresponding to the upstream and downstream currents Ij and Ik based on the operation displacement Sp (operation amount). The upstream and downstream currents Ij and Ik are then controlled so as to approach and match the upstream and downstream target currents Itj and Itk (so-called current feedback control). The first controller EA also calculates a target rotation speed Nta (target value) corresponding to the actual rotation speed Na based on the operation displacement Sp. The first controller EA controls the motor supply current Im so that the actual rotation speed Na approaches and matches the target rotation speed Nta (so-called rotation speed feedback control). Based on these control algorithms, a drive signal Ma for controlling the first electric motor MA and drive signals Uj, Uk, Va, and Vb for controlling the various solenoid valves UJ, UK, VA, and VB are calculated. Then, in response to the drive signal (Ma, etc.), the switching elements of the first drive circuit DRa are driven to control the first electric motor MA and the solenoid valves UJ, UK, VA, VB.

[0047] <Second braking unit SB> An example of the configuration of the second braking unit SB (corresponding to the "second unit") of the braking control device SC will be described with reference to the schematic diagram in Figure 3. The second braking unit SB is a general-purpose unit (device) for performing independent control of each wheel, such as anti-lock brake control, traction control, and anti-skid control. In addition, the second braking unit SB performs complementary control. The "complementary control" compensates for a shortage of the pressures Pm and Pv supplied to the front and rear wheels due to a communication abnormality.

[0048] The second brake unit SB is supplied with front and rear wheel supply pressures Pm and Pv from the first brake unit SA. Specifically, in the brake system for the front wheels WHf (i.e., the front wheel connecting path HSf), the front wheel supply pressure Pm is supplied from the master cylinder CM. On the other hand, in the brake system for the rear wheels WHr (i.e., the rear wheel connecting path HSR), the rear wheel supply pressure Pv is supplied from the pressure adjusting unit CA. The front and rear wheel supply pressures Pm and Pv are then adjusted (increased or decreased) by the second brake unit SB and output as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) in the front and rear wheel cylinders CWf and CWr. The second brake unit SB is composed of a second fluid unit YB and a second control unit EB.

[0049] <Second fluid unit YB> The second fluid unit YB (also referred to as the "second actuator") is provided in the communication path HS between the first actuator YA and the wheel cylinder CW. The second actuator YB is composed of a front wheel supply pressure sensor PM, a control valve UB, a second fluid pump QB, a second electric motor MB, a pressure regulating reservoir RB, an inlet valve VI, and an outlet valve VO.

[0050] Front and rear wheel control valves UBf, UBr (=UB) are provided in the front and rear wheel communication passages HSf, HSR (=HS). The control valve UB is a normally open linear solenoid valve (differential pressure valve), as are the upstream and downstream pressure regulating valves UJ, UK. The front and rear wheel control valves UBf, UBr enable the front and rear wheel pressures Pwf, Pwr to be increased individually from the front and rear wheel supply pressures Pm, Pv.

[0051] The front wheel supply pressure sensor PM is provided above the front wheel control valve UBf (at a portion of the communication passage HSf near the first actuator YA) so as to detect the actual hydraulic pressure Pm (front wheel supply pressure) supplied from the first actuator YA (particularly, the master chamber Rm). The front wheel supply pressure sensor PM is also referred to as a "master pressure sensor" and is built into the second actuator YB. The front wheel supply pressure sensor PM is connected to the second brake unit SB (particularly, the second control unit EB) by a front wheel supply pressure signal line LPm. In other words, the signal of the front wheel supply pressure Pm is directly input to the second control unit EB.

[0052] The front and rear wheel return paths HLf, HLr (=HL) connect the upper portions of the front and rear wheel control valves UBf, UBr (portions of the communication paths HS closer to the first actuator YA) with the lower portions of the front and rear wheel control valves UBf, UBr (portions of the communication paths HS closer to the wheel cylinders CW). The front and rear wheel return paths HLf, HLr are provided with front and rear wheel fluid pumps QBf, QBr (=QB) and front and rear wheel pressure regulating reservoirs RBf, RBr (=RB). The second fluid pump QB is driven by a second electric motor MB.

[0053] When the second electric motor MB is driven, the second fluid pump QB draws brake fluid BF from the top of the control valve UB and discharges it from the bottom of the control valve UB. As a result, a circulating flow KL of brake fluid BF (i.e., front and rear wheel circulating flows KLf and KLr, indicated by dashed arrows) containing the pressure regulating reservoir RB is generated in the communication line HS and the return line HL. When the control valve UB narrows the flow path of the communication line HS and throttles the circulating flow KL of brake fluid BF, the orifice effect created increases the hydraulic pressures Pqf and Pqr (referred to as "front and rear wheel regulating pressures") below the control valve UB from the hydraulic pressures Pm and Pv (front and rear wheel supply pressures) above the control valve UB. In other words, in the circulation flow KL, the hydraulic pressure difference (differential pressure) between the hydraulic pressures Pm, Pv (supply pressures) downstream of the control valve UB and the hydraulic pressures Pqf, Pqr (adjustment pressures) upstream of the control valve UB is adjusted by the control valve UB. Note that in terms of the magnitude relationship between the front and rear wheel supply pressures Pm, Pv and the front and rear wheel adjustment pressures Pqf, Pqr, the front and rear wheel adjustment pressures Pqf, Pqr are equal to or greater than the front and rear wheel supply pressures Pm, Pv (i.e., "Pqf≧Pm, Pqr≧Pv"). As explained above, the mechanism by which the adjustment pressure Pq is generated in the second actuator YB is the same as the mechanism by which the servo pressures Pj, Pk are generated in the first actuator YA.

[0054] Inside the second actuator YB, the front and rear wheel communication passages HSf and HSR are each branched into two, which are connected to the front and rear wheel cylinders CWf and CWr. A normally-open inlet valve VI and a normally-closed outlet valve VO are provided for each wheel cylinder CW so that each wheel pressure Pw can be individually adjusted. Specifically, the inlet valve VI is provided in the branched communication passage HS (i.e., on the side of the communication passage HS closer to the wheel cylinder CW). The communication passage HS is connected to the pressure-regulating reservoir RB via a pressure-reducing passage HG below the inlet valve VI (the portion of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO is provided in the pressure-reducing passage HG. The inlet valve VI and the outlet valve VO are on-off solenoid valves. The inlet valve VI and the outlet valve VO allow the wheel pressure Pw to be individually reduced from the front and rear wheel adjustment pressures Pm and Pv at each wheel.

[0055] When the inlet valve VI and the outlet valve VO are not powered and are not operating, the inlet valve VI is open and the outlet valve VO is closed. In this state, the wheel pressure Pw is equal to the regulated pressure Pq. By driving the inlet valve VI and the outlet valve VO, the wheel pressure Pw is independently regulated for each wheel cylinder CW. To decrease the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. The inflow of brake fluid BF into the wheel cylinder CW is blocked, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RB, thereby decreasing the wheel pressure Pw. To increase the wheel pressure Pw (however, the increase can be limited to the front and rear wheel regulated pressures Pqf and Pqr), the inlet valve VI is opened and the outlet valve VO is closed. The brake fluid BF is prevented from flowing out to the pressure regulating reservoir RB, and the regulated pressure Pq from the pressure regulating valve UB is supplied to the wheel cylinder CW, increasing the wheel pressure Pw. To maintain the wheel pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the wheel pressure Pw is maintained constant.

[0056] <Second control unit EB> The second actuator YB is controlled by a second control unit EB (also referred to as a "second controller"). Similar to the first controller EA, the second controller EB is composed of a second microprocessor MPb and a second drive circuit DRb. The second controller EB is connected to a communication bus BS. Therefore, the first controller EA and the second controller EB can share signals via the communication bus BS.

[0057] The second controller EB (particularly, the second microprocessor MPb) receives inputs of the wheel speed Vw, steering amount Sa, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy. The second controller EB calculates the vehicle speed Vx based on the wheel speed Vw. The second controller EB executes the following independent controls for each wheel. Specifically, the independent controls for each wheel include antilock brake control (so-called ABS control) that suppresses locking of the wheels WH, traction control that suppresses spin of the drive wheels, and anti-skid control (so-called ESC) that suppresses understeer and oversteer to improve the directional stability of the vehicle.

[0058] The second drive circuit DRb drives the second electric motor MB constituting the second actuator YB and various solenoid valves (UB, etc.) in accordance with a control algorithm programmed in the second microprocessor MPb. The second drive circuit DRb includes an H-bridge circuit configured with switching elements (e.g., MOS-FETs) to drive the second electric motor MB. The second drive circuit DRb also includes switching elements to drive the various solenoid valves (UB, etc.). In addition, the second drive circuit DRb includes a motor current sensor (not shown) that detects the supply current In (actual value) to the second electric motor MB, and a second current sensor (not shown) that detects the supply current Ib (actual value, referred to as the "second supply current") to the control valve UB. Based on the control algorithm of the second microprocessor MPb, a drive signal Ub for the control valve UB, a drive signal Vi for the inlet valve VI, a drive signal Vo for the outlet valve VO, and a drive signal Mb for the second electric motor MB are calculated. Then, based on the drive signal (Ub, etc.), the second electric motor MB and the solenoid valves UB, VI, and VO are controlled by the second drive circuit DRb.

[0059] The second controller EB and the second detection unit SPb of the operation displacement sensor SP are connected via a signal line LSpb (e.g., a wire harness) for the second detection unit SPb. Furthermore, the second controller EB and the front wheel supply pressure sensor PM are connected via a signal line LPm (e.g., a signal pin) for the front wheel supply pressure sensor PM. Therefore, the second operation displacement Spb is directly input to the second controller EB via the signal line LSpb, and the front wheel supply pressure Pm is directly input to the second controller EB via the signal line LPm. Then, the second operation displacement Spb and the front wheel supply pressure Pm are transmitted from the second controller EB to the first controller EA via the communication bus BS. That is, the first controller EA acquires the second operation displacement Spb and the front wheel supply pressure Pm from the second controller EB via the communication bus.

[0060] <Pressure regulation control processing> An example of the pressure regulation control process will be described with reference to Figures 4 and 5. In the brake control device SC, dual-system pressure regulation is achieved by the first brake unit SA. "Dual-system pressure regulation" is pressure regulation control in which the front and rear wheel pressures Pwf, Pwr are regulated independently and individually. In contrast to dual-system pressure regulation, single-system pressure regulation is pressure regulation control in which the front and rear wheel pressures Pwf, Pwr are regulated equally. In regenerative cooperative control, dual-system pressure regulation improves regenerative efficiency and optimizes the distribution of braking force between the front and rear wheels compared to single-system pressure regulation.

[0061] The voltage regulation control includes not only regenerative cooperative control but also complementary control to deal with abnormalities in signal transmission (also called "communication abnormalities") in the communication bus BS. The communication bus BS is composed of a communication line (e.g., a CAN bus cable) and communication microcontrollers in the first and second controllers EA and EB. Communication abnormalities occur due to disconnection of the communication line, failure of the communication microcontrollers (e.g., receiver / transmitter) in the first and second controllers EA and EB, etc.

[0062] If a communication abnormality occurs between the first and second brake units SA and SB (particularly the first and second controllers EA and EB), the second brake unit SB will be unable to grasp the operating state of the first brake unit SA. For example, if the communication abnormality is caused by a failure in the communication line, the first brake unit SA will be unable to perform closed-loop control (i.e., feedback control) based on the front wheel supply pressure Pm, but will be able to perform open-loop control (i.e., feedforward control). On the other hand, if the communication abnormality is caused by a failure in the first controller EA and the first brake unit SA is completely lost, the front wheel supply pressure Pm will be generated solely by the driver's muscle force. Complementary control is used to address this situation. Below, we will explain the pressure regulation control in the first brake unit SA and the pressure regulation control in the second brake unit SB separately. The pressure regulation control algorithm is programmed in the microprocessors MPa and MPb of the first and second controllers EA and EB.

[0063] In describing the example process, the following assumptions are made: The regenerative device KG is provided only on the front wheels WHf, so that the regenerative braking force Fg acts on the front wheels WHf but not on the rear wheels WHr. In the first actuator YA, the pressure-receiving area rm (also called the "master area") of the master chamber Rm and the pressure-receiving area ru (also called the "servo area") of the servo chamber Ru are set equal. Therefore, "rm = ru", and in a static state, "Pk = Pm" (here, friction of the seal member SL, etc. is ignored). The front wheel supply pressure sensor PM is built into the second braking unit SB, and the front wheel supply pressure Pm is input to the first braking unit SA via the communication bus BS. On the other hand, the rear wheel supply pressure sensor PV is built into the first braking unit SA, and the rear wheel supply pressure Pv is input directly to the first braking unit SA.

[0064] The various braking forces are as follows: - "Vehicle body total braking force Fu" is the actual braking force acting on the entire vehicle JV. A target value corresponding to the vehicle body total braking force Fu is "target vehicle body position force Fv." - "Friction braking force Fm" is the braking force that is actually generated according to the wheel pressure Pw. A target value corresponding to the friction braking force Fm is "target friction braking force Fn." - "Regenerative braking force Fg" is the braking force actually generated by the regenerative device KG. A target value corresponding to the regenerative braking force Fg is "target regenerative braking force Fh." The target regenerative braking force Fh is calculated by the first braking unit SA (particularly, the first controller) and transmitted to the regenerative device KG (particularly, the regenerative controller EG) via the communication bus BS. In the regenerative device KG, the regenerative controller EG controls the generator GN so that the actual regenerative braking force Fg approaches and matches the target regenerative braking force Fh. The "limit regenerative braking force Fx" is the maximum value (limit value) of the regenerative braking force Fg that can be generated by the regenerative device KG. Therefore, the regenerative device KG generates a regenerative braking force Fg within a range (limit) up to the limit regenerative braking force Fx. The limit regenerative braking force Fx is calculated by the regenerative device KG (particularly, the regenerative controller EG) and transmitted to the first braking unit SA (particularly, the first controller EA) via the communication bus BS.

[0065] <Pressure regulation control processing> The overall voltage regulation control will be described with reference to the flow chart in Figure 4. The voltage regulation control includes two types of control depending on the operating state of the communication bus BS. The first is voltage regulation control when signal transmission through the communication bus BS is normal (referred to as "normal state"), and is called "normal control." The second is voltage regulation control when there is an abnormality in signal transmission through the communication bus BS (referred to as "abnormal state"), and is called "complementary control." The complementary control is performed by the second braking unit SB.

[0066] The pressure regulation control in the first braking unit SA will now be described. The following processing is performed by the first controller EA.

[0067] In step S110, power is supplied to the inlet valve VA and the release valve VB. As a result, the normally closed inlet valve VA is opened, and the normally open release valve VB is closed, selecting a first mode in which the master piston NM and the brake operating member BP can be displaced separately. In the first mode, the front and rear wheel supply pressures Pm, Pv (i.e., front and rear wheel pressures Pwf, Pwr) are adjusted independently of the operation of the brake operating member BP. At this time, the operating force Fp of the brake operating member BP is generated by the stroke simulator SS.

[0068] In step S120, signals such as the first and second operation displacements Spa and Spb, the front wheel supply pressure Pm, and the rear wheel supply pressure Pv are read. The operation displacement sensor SP is provided with two operation displacement detection units SPa and SPb (first and second detection units). The first operation displacement Spa (detection value of the first detection unit SPa) and the rear wheel supply pressure Pv (detection value of the rear wheel supply pressure sensor PV) are directly acquired through the first displacement signal line LSpa and the rear wheel supply pressure signal line LPv. The second operation displacement Spb (detection value of the second detection unit SPb) and the front wheel supply pressure Pm (detection value of the front wheel supply pressure sensor PM) are acquired (received) from the second controller EB via the communication bus BS.

[0069] In step S120, the operation displacement Sp is calculated based on the first and second operation displacements Spa and Spb. Specifically, the average value of the first and second operation displacements Spa and Spb is determined as the operation displacement Sp (i.e., "Sp = (Spa + Spb) / 2"). Furthermore, if one of the first and second operation displacements Spa and Spb cannot be obtained, the operation displacement Sp is determined based on the other that can be obtained (i.e., "Sp = Spa" or "Sp = Spb"). Since the operation displacement sensor SP is redundant, the operation displacement Sp is determined based on at least one of the first and second operation displacements Spa and Spb. The operation displacement Sp is transmitted from the first controller EA to the communication bus BS.

[0070] In step S130, a target vehicle body posture force Fv (a target value of the braking force acting on the entire vehicle) is calculated based on the operation displacement Sp and the calculation map Zfv. When the operation displacement Sp is less than a predetermined displacement so, the target vehicle body posture force Fv is calculated to be "0" according to the calculation map Zfv. When the operation displacement Sp is equal to or greater than the predetermined displacement so, the target vehicle body posture force Fv is calculated to increase from "0" as the operation displacement Sp increases from "0". Here, the "predetermined displacement so" is a preset value (constant) that represents the play of the brake operating member BP.

[0071] In step S140, it is determined whether signal transmission via communication is normal. This determination process is referred to as "suitability determination." The suitability of communication is determined by determining whether "the first braking unit SA is capable of sending and receiving signals via the communication bus BS." If all signals can be sent and received, the suitability determination is affirmative, and the process proceeds to step S150. On the other hand, if there is an abnormality in the signal transmission and reception, the suitability determination is negative, and the process proceeds to step S180.

[0072] In step S140, if the suitability determination is affirmative, the determination flag FT is set to "0." On the other hand, if the suitability determination is negative, the determination flag FT is set to "1." The "determination flag FT" is a control flag that indicates the suitability of the communication function. With the determination flag FT, "0" indicates a normal state, and "1" indicates an abnormal communication state.

[0073] <Normal control process in first braking unit SA> Normal control will now be described. Normal control is pressure regulation control when all operations of the brake control device SC are normal. The processing of steps S150 to S170 corresponds to normal control. The following processing corresponds to the case when signal transmission via the communication bus BS is operating normally. In normal control, two-system pressure regulation is performed by the first brake unit SA.

[0074] In step S150, front-wheel and rear-wheel required braking forces Fqf, Fqr (=Fq) are calculated based on the target vehicle body position force Fv. Specifically, the front-wheel and rear-wheel required braking forces Fqf, Fqr are calculated so that the following two conditions are satisfied. The "front-wheel required braking force Fqf" is a target value of the total braking force acting on the front wheels WHf. Therefore, the front-wheel required braking force Fqf is equal to the sum of the target regenerative braking force Fh and the front-wheel target frictional braking force Fnf (i.e., "Fqf = Fh + Fnf"). The "rear-wheel required braking force Fqr" is a target value of the total braking force acting on the rear wheels WHr. Therefore, the rear-wheel required braking force Fqr is equal to the rear-wheel target frictional braking force Fnr (i.e., "Fqr = Fnf"). Condition 1: The sum of the front wheel required braking force Fqf and the rear wheel required braking force Fqr matches the target vehicle body position force Fv (that is, "Fv=Fqf+Fqr"). Condition 2: The ratio Kq (referred to as "requested distribution") of the rear wheel required braking force Fqr to the front wheel required braking force Fqf must match a predetermined value hb (i.e., "Kq = Fqr / Fqf = hb"). Here, the predetermined value hb is the ratio of the rear wheel friction braking force Fmr to the front wheel friction braking force Fmf when the regenerative braking force Fg is "0". Therefore, the predetermined value hb is a constant that is set in advance based on the specifications of the braking device SX. The front and rear wheel required braking forces Fqf and Fqr are determined by the following equation (1) so as to satisfy conditions 1 and 2. Fqf = Fv / (1 + hb), and Fqr = Fv hb / (1 + hb) ...Equation (1)

[0075] Furthermore, in step S150, a target regenerative braking force Fh and front-wheel and rear-wheel target frictional braking forces Fnf and Fnr are calculated based on the front-wheel and rear-wheel required braking forces Fqf and Fqr and the limit regenerative braking force Fx. Specifically, the target regenerative braking force Fh is determined to be a value equal to or less than the limit regenerative braking force Fx. For example, when the front-wheel required braking force Fqf is equal to or less than the limit regenerative braking force Fx, the target regenerative braking force Fh is set equal to the front-wheel required braking force Fqf, the front-wheel target frictional braking force Fnf is set to "0", and the rear-wheel frictional braking force Fnr is set equal to the rear-wheel required braking force Fqr (i.e., when "Fqf≦Fx", "Fh=Fqf, Fnf=0, Fnr=Fqr"). On the other hand, when the front wheel required braking force Fqf is greater than the limit regenerative braking force Fx, the target regenerative braking force Fh is set equal to the limit regenerative braking force Fx, the front wheel target frictional braking force Fnf is set to the value obtained by subtracting the limit regenerative braking force Fx (=Fh) from the front wheel required braking force Fqf, and the rear wheel frictional braking force Fnr is set equal to the rear wheel required braking force Fqr (i.e., when "Fqf>Fx", "Fh=Fx, Fnf=Fqf-Fx=Fqf-Fh, Fnr=Fqr").

[0076] In step S160, front and rear wheel target pressures Ptf, Ptr are calculated based on the front and rear wheel target friction braking forces Fnf, Fnr (=Fn). The front and rear wheel target pressures Ptf, Ptr are determined by converting the target friction braking force Fn into the dimensions of front and rear wheel supply pressures Pm, Pv (i.e., front and rear wheel pressures Pwf, Pwr) based on the specifications of the braking device SX, etc. (pressure-receiving area of ​​the wheel cylinder CW, effective braking radius of the rotating member KT, friction coefficient of the friction member MS, effective radius of the wheel (tire) etc.). Since the front wheel supply pressure Pm is equal to the front wheel pressure Pwf and the rear wheel supply pressure Pv is equal to the rear wheel pressure Pwr, the front and rear wheel target pressures Ptf, Ptr are also target values ​​of the front and rear wheel wheel pressures Pwf, Pwr.

[0077] In step S170, the front and rear wheel pressures Pwf, Pwr (actual values) are adjusted based on the front and rear wheel target pressures Ptf, Ptr (target values). The first controller EA drives the first electric motor MA and the upstream and downstream pressure regulating valves UJ, UK, and controls the front and rear wheel pressures Pwf, Pwr to approach and match the front and rear wheel target pressures Ptf, Ptr. Specifically, in step S170, the electric motor MA is driven to generate a circulation flow KN that includes the fluid pump QA and the upstream and downstream pressure regulating valves UJ, UK. Then, based on the front wheel target pressure Ptf and the front wheel supply pressure Pm, the downstream pressure regulating valve UK is hydraulically feedback controlled so that the front wheel supply pressure Pm (=Pwf) matches the front wheel target pressure Ptf. In other words, the supply current Ik (actual value, also referred to as the "downstream current") to the downstream pressure regulating valve UK is adjusted so that the deviation hPf (referred to as the "front wheel deviation") between the front wheel supply pressure Pm and the front wheel target pressure Ptf becomes "0". Furthermore, the upstream pressure regulating valve UJ is hydraulically feedback controlled based on the rear wheel target pressure Ptr and the rear wheel supply pressure Pv so that the rear wheel supply pressure Pv (= Pwr) matches the rear wheel target pressure Ptr. In other words, the supply current Ij (actual value, also referred to as the "upstream current") to the upstream pressure regulating valve UJ is adjusted so that the deviation hPr (referred to as the "rear wheel deviation") between the rear wheel supply pressure Pv and the rear wheel target pressure Ptr becomes "0".

[0078] <<Processing in the first braking unit SA when a communication error occurs>> The following describes the pressure regulation control in the first brake unit SA when signal transmission via communication does not function normally (i.e., when a communication abnormality occurs). If the appropriateness determination in step S140 is negative, the operation of the regenerative device KG is stopped in step S180. If communication between the first controller EA and the regenerative controller EG is functioning properly, "Fh=0" or "FT=1" is sent from the first controller EA to the regenerative controller EG, and power generation by the generator GN in the regenerative device KG is stopped. However, if the communication function of the first controller EA is malfunctioning, the regenerative controller EG cannot obtain the target regenerative braking force Fh. Based on this, the regenerative controller EG identifies a communication abnormality and stops power generation by the generator GN. In either case, when a communication abnormality occurs, the regenerative braking force Fg is set to "0" and the regenerative cooperative control is terminated. Since the operation of the regenerative device KG is stopped, the target frictional braking force Fn is set equal to the target vehicle body tension force Fv (i.e., "Fn=Fv").

[0079] Furthermore, in step S180, the power supply to the upstream pressure regulating valve UJ is stopped, and the upstream pressure regulating valve UJ is opened. Because the upstream pressure regulating valve UJ is a normally open solenoid valve, it is set to a fully open state when the power supply is stopped. This switches from dual-system pressure regulation to single-system pressure regulation.

[0080] In step S190, it is determined whether the first brake unit SA is operable (referred to as a "operability determination"). For example, if everything is normal except for the inability to acquire the supply pressure Pm via communication, it is determined that the first brake unit SA is operable (i.e., the "operability determination" is positive). However, if the drive voltage Ve of the first brake unit SA (the voltage that can be applied to the first controller EA and the first actuator YA) has dropped below a predetermined voltage Ve, the first brake unit SA is inoperable, and the "operability determination" is negative. Here, the "drive voltage Ve" is detected by a drive voltage sensor (not shown) provided in the first drive circuit DRa. The "predetermined voltage Ve" is a threshold value for the ability determination, and is a predetermined value (constant) that is set in advance. If the ability determination is positive, the process proceeds to step S200. On the other hand, if the ability determination is negative, the process proceeds to step S220.

[0081] In step S200, the first controller EA cannot acquire a signal of the second operation displacement Spb, so the operation displacement Sp is calculated based on the first operation displacement Spa. Specifically, the first operation displacement Spa is determined as the operation displacement Sp (i.e., "Sp = Spa"). Furthermore, in step S200, the front and rear wheel target pressures Ptf and Ptr are calculated based on the operation displacement Sp (= Spa) and the calculation map Zfv. Since the target regenerative braking force Fh is determined to be "0" and the target frictional braking force Fn is equal to the target vehicle body position force Fv, in the calculation map Zfv, the target vehicle body position force Fv (vertical axis of the calculation map Zfv) is replaced with the target frictional braking force Fn. Therefore, in step S200, the front and rear wheel target pressures Ptf and Ptr are determined based on the specifications of the braking device SX, etc. (pressure receiving area of ​​the wheel cylinder CW, effective braking radius of the rotating member KT, friction coefficient of the friction member MS, effective radius of the wheel (tire), etc.) so that "the front and rear wheel target pressures Ptf and Ptr are equal" and the target vehicle body position force Fv is satisfied.

[0082] In step S210, the first actuator YA is driven based on the rear wheel target pressure Ptr (=Ptf) and the rear wheel supply pressure Pv. During communication abnormality, the first controller EA cannot acquire the front wheel supply pressure Pm, so feedback control is performed based on the available rear wheel supply pressure Pv. In the pressure regulating section CA, the upstream pressure regulating valve UJ is fully open, so the upstream servo pressure Pj and the downstream servo pressure Pk are made equal (i.e., a state of "Pk = Pm = Pwf = Pj = Pv = Pwr"). Therefore, the downstream pressure regulating valve UK is hydraulically feedback controlled so that the rear wheel supply pressure Pv approaches and matches the rear wheel target pressure Ptr. In other words, the supply current Ik (downstream current) to the downstream pressure regulating valve UK is adjusted so that the deviation hPr (rear wheel deviation) between the rear wheel supply pressure Pv and the rear wheel target pressure Ptr becomes "0".

[0083] If the result of the determination in step S190 is negative, the power supply to the inlet valve VA and the release valve VB is stopped and the operation mode of the input unit NR is switched to the second mode in step S220, whereby the master piston NM is moved in conjunction with the brake operating member BP.

[0084] In step S230, the power supply to the first electric motor MA and the downstream pressure regulating valve UK is reduced. Except for cases where power cannot be supplied to the first braking unit SA at all, when power supply is possible, the power supply to the components (UK, MA, etc.) included in the first braking unit SA (particularly the pressure regulating unit CA) that increase the front and rear wheel supply pressures Pm and Pv is reduced compared to normal control. In other words, in the case of an abnormality, the power supply to the pressure regulating unit CA is stopped or the power output is reduced (for example, the first electric motor MA is driven at a low rotation speed nx). Note that if the communication abnormality is due to a failure of the first controller EA, power is not supplied to the components of the first actuator YA, so the input unit NR is set to the second mode and output from the pressure regulating unit CA is stopped (i.e., "Pj = Pk = 0").

[0085] <Complementary control processing> The complementary control will be described. The complementary control is a pressure regulation control in the second braking unit SB in the event of a communication abnormality. The processing of steps S310 to S370 corresponds to the complementary control. The complementary control is executed by the second controller EB.

[0086] In step S310, the second controller EB reads signals such as the first and second operation displacements Spa and Spb, the front and rear wheel supply pressures Pm and Pv, and the determination flag FT. The second operation displacement Spb (the detection value of the second displacement detection unit SPb) is acquired via a signal line LSpb. Similarly, the front wheel supply pressure Pm (the detection value of the supply pressure sensor PM) is acquired via a signal line LPm. The first operation displacement Spa, the rear wheel supply pressure Pv, and the determination flag FT are read from the communication bus BS. Note that in the event of a communication abnormality, the second controller EB cannot acquire signals such as the first operation displacement Spa, the rear wheel supply pressure Pv, and the determination flag FT.

[0087] In step S320, the second controller EB performs a suitability determination of "whether communication is normal or not" in the same manner as in step S140. If the second braking unit SB is able to receive and transmit signals via the communication bus BS, the suitability determination is affirmative, and the process returns to step S310. In this case, complementary control is not executed. If signal reception and transmission are not possible, the process proceeds to step S330. In step S320, if the suitability determination is affirmative, the determination flag FU is set to "0," which indicates a normal state. On the other hand, if the suitability determination is negative, the determination flag FU is set to "1," which indicates an abnormal state.

[0088] In step S330, the operation of the regenerative device KG is stopped. For example, "Fh=0" is transmitted from the second controller EB to the regenerative controller EG, and the power generating operation of the generator GN is stopped (i.e., "Fg=0"). Alternatively, "FU=1" may be transmitted, and the operation of the generator GN may be stopped.

[0089] In step S340, the operation displacement Sp is calculated. In the event of a communication abnormality, the second controller EB cannot receive the signal of the first operation displacement Spa, and therefore the second operation displacement Spb is determined to be the operation displacement Sp (i.e., "Sp = Spb"). Furthermore, in step S340, the target vehicle body position force Fv is calculated based on the operation displacement Sp (= Spb) and a method similar to that in step S130. Here, "similar method" means that a similar calculation map Zfv is adopted to calculate the target vehicle body position force Fv in a state where the regenerative braking force Fg is not generated (i.e., a state where "Fh = 0, Fg = 0"). However, the calculation map Zfv used in the first controller EA and the calculation map Zfv used in the second controller EB do not need to be completely identical, and it is sufficient if they are similar.

[0090] In step S350, the target vehicle body position force Fv and the front and rear wheel target pressures Ptf, Ptr are calculated using the same method as in step S160 (or the same method as in step S200). Note that, since the regenerative device KG is stopped in step S180 or step S330, in step S350 the target friction braking force Fn is equal to the target vehicle body position force Fv (i.e., "Fn = Fv"). Therefore, the "similar method to step S160" and the "similar method to step S200" are substantially the same. In other words, after the front wheel target pressure Ptf and the rear wheel target pressure Ptr are made equal, the front and rear wheel target pressures Ptf, Ptr are determined based on the specifications of the braking device SX so that the target vehicle body position force Fv is satisfied.

[0091] In step S360, a deviation hPf between the front wheel target pressure Ptf and the front wheel supply pressure Pm (referred to as the "front wheel deviation") is calculated based on the front wheel target pressure Ptf and the front wheel supply pressure Pm. During a communication abnormality, the second controller EB cannot acquire a signal for the rear wheel supply pressure Pv, but can acquire a signal for the front wheel supply pressure Pm. Therefore, the front wheel supply pressure Pm is subtracted from the front wheel target pressure Ptf to determine the front wheel deviation hPf (i.e., "hPf = Ptf - Pm"). Since the front wheel target pressure Ptf calculated by the first brake unit SA and the front wheel target pressure Ptf calculated by the second brake unit SB are equivalent, the front wheel deviation hPf is a state quantity that represents the difference between the supply pressure that should be output from the first brake unit SA (i.e., the front wheel target pressure Ptf at the first brake unit SA) at the front wheel pressure Pwf and the actually generated front wheel supply pressure Pm. In other words, the front wheel deviation hPf represents a deficiency in the front wheel supply pressure Pm that was to be output by the first brake unit SA.

[0092] In step S370, the second actuator YB is driven to increase the wheel pressure Pw. Specifically, the second actuator YB controls the front wheel control valve UBf based on the front wheel deviation hPf, and the rear wheel control valve UBf based on the rear wheel target pressure Ptr. That is, in the second braking unit SB, the front and rear wheel control valves UBf and UBr are driven separately.

[0093] In step S370, the second electric motor MB is driven, causing the second fluid pump QB to discharge brake fluid BF. This generates a circulating flow KL of brake fluid BF in the communication path HS and the return path HL. In the brake system for the front wheels WHf (i.e., the front wheel pressure Pwf), the front wheel deviation hPf is determined as a target value for the differential pressure of the front wheel control valve UBf. Then, a current Ibf (referred to as the "front wheel supply current") corresponding to this target value is supplied to the front wheel control valve UBf. As a result, the front wheel pressure Pwf is increased from the front wheel supply pressure Pm by an amount equivalent to the front wheel deviation hPf. Meanwhile, since the second brake unit SB cannot obtain the rear wheel supply pressure Pv, in the brake system for the rear wheels WHr (i.e., the rear wheel pressure Pwr), the rear wheel target pressure Ptr is determined as a target value for the differential pressure of the rear wheel control valve UBr. Then, a current Ibr (referred to as a "rear wheel supply current") corresponding to the target value is supplied to the rear wheel control valve UBr, thereby increasing the rear wheel pressure Pwr from the rear wheel supply pressure Pv by an amount corresponding to the rear wheel target pressure Ptr.

[0094] <Control valve UB drive control> With reference to the block diagram of FIG. 5, the details of the drive control of the control valve UB in the complementary control (particularly the processing of steps S360 and S370) will be described. The complementary control is executed by the second controller EB. Before a communication abnormality is determined (i.e., when "FT=0, FU=0"), the operation of the second actuator YB is stopped. When the appropriateness determination in step S320 is negative and a communication abnormality state is determined (i.e., when "FU=0" is switched to "FU=1"), the complementary control is started by the second actuator YB. Note that in the case of a communication abnormality, the second controller EB cannot receive the determination flag FT calculated by the first controller EA, and the signals of the first operation displacement Spa and the rear wheel supply pressure Pv input to the first controller EA.

[0095] The drive control of the control valve UB in complementary control is composed of a hydraulic pressure deviation calculation block HP, a front wheel target current calculation block ITF, a front wheel current feedback control block IFF, a rear wheel target current calculation block ITR, and a rear wheel current feedback control block IFR.

[0096] The increase adjustment of the front-wheel wheel pressure Pwf by the compensation control will be described. In the hydraulic pressure deviation calculation block HP, the deviation hPf (front-wheel deviation) between the front-wheel target pressure Ptf and the front-wheel supply pressure Pm is calculated. Specifically, the front-wheel supply pressure Pm is subtracted from the front-wheel target pressure Ptf to determine the front-wheel deviation hPf (that is, "hPf = Ptf - Pm"). Here, the front-wheel target pressure Ptf is calculated based on the same method as the calculation method of the front-wheel target pressure Ptf in the first braking unit SA. That is, in each of the first and second braking units SA and SB, the front-wheel target pressure Ptf is determined according to the same or similar calculation map. In the compensation control, the hydraulic pressure deviation hPf is treated as the target value of the differential pressure by the front-wheel control valve UBf.

[0097] In the front-wheel target current calculation block ITF, the front-wheel target current Itf is calculated based on the front-wheel deviation hPf and a preset calculation map Ztf. The "front-wheel target current Itf" is the target value related to the supply current Ibf (front-wheel supply current) to the front-wheel control valve UBf, which is necessary to generate a differential pressure corresponding to the front-wheel deviation hPf by the front-wheel control valve UBf. The front-wheel target current Itf is determined to increase according to the increase of the front-wheel deviation hPf according to the calculation map Ztf. The process of the front-wheel target current calculation block ITF corresponds to the feed-forward control in the front-wheel control valve UBf.

[0098] In the front-wheel current feedback control block IFF, based on the front-wheel target current Itf (target value) and the front-wheel supply current Ibf (actual value), the drive signal Ubf of the front-wheel control valve UBf is calculated so that the front-wheel supply current Ibf approaches and matches the front-wheel target current Itf. Here, the front-wheel supply current Ibf is detected by the front-wheel supply current sensor IBf provided in the second drive circuit DRb. In the front-wheel current feedback control block IFF, if "Itf > Ibf", the drive signal Ubf is determined so that the front-wheel supply current Ibf increases. On the other hand, if "Itf < Ibf", the drive signal Ubf is determined so that the front-wheel supply current Ibf decreases.

[0099] The increase adjustment of the rear-wheel wheel pressure Pwr by complementary control will be described. In the rear-wheel system, since the rear-wheel supply pressure Pv cannot be obtained during communication abnormalities, the hydraulic pressure deviation calculation block HP in the front-wheel system is omitted. In the adjustment of the rear-wheel wheel pressure Pwr, the rear-wheel target pressure Ptr is treated as the target value of the differential pressure in the rear-wheel control valve UBr. Here, the rear-wheel target pressure Ptr is calculated based on the same method as the calculation method of the rear-wheel target pressure Ptr in the first braking unit SA, similar to the front-wheel target pressure Ptf. That is, in each of the first and second braking units SA and SB, the rear-wheel target pressure Ptr is determined according to the same or similar calculation maps.

[0100] In the rear-wheel target current calculation block ITR, the rear-wheel target current Itr is calculated based on the rear-wheel target pressure Ptr and a preset calculation map Ztr. The "rear-wheel target current Itr" is the target value related to the supply current Ibr (rear-wheel supply current) to the rear-wheel control valve UBr, which is necessary to generate a differential pressure corresponding to the rear-wheel target pressure Ptr by the rear-wheel control valve UBr. The rear-wheel target current Itr is determined to increase according to the increase of the rear-wheel target pressure Ptr according to the calculation map Ztr. The process of the rear-wheel target current calculation block ITR corresponds to the feedforward control in the rear-wheel control valve UBr.

[0101] In the rear-wheel current feedback control block IFR, based on the rear-wheel target current Itr (target value) and the rear-wheel supply current Ibr (actual value), the drive signal Ubr of the rear-wheel control valve UBr is calculated so that the rear-wheel supply current Ibr approaches and matches the rear-wheel target current Itr. Here, the rear-wheel supply current Ibr is detected by the rear-wheel supply current sensor IBr provided in the second drive circuit DRb. In the rear-wheel current feedback control block IFR, if "Itr > Ibr", the drive signal Ubr is determined so that the rear-wheel supply current Ibr increases. On the other hand, if "Itr < Ibr", the drive signal Ubr is determined so that the rear-wheel supply current Ibr decreases.

[0102] When a communication abnormality occurs, the first and second brake units SA and SB are unable to grasp each other's operating status. Therefore, the second brake unit SB is unable to grasp the operating status of the first brake unit SA (the degree of output reduction, whether switching to single-system pressure regulation has been performed, etc.). Therefore, in the brake control device SC, the second brake unit SB calculates the front and rear wheel target pressures Ptf and Ptr based on the same method as the first brake unit SA. The second brake unit SB then increases the front and rear wheel pressures Pwf and Pwr based on the front and rear wheel target pressures Ptf and Ptr. Because the front and rear wheel target pressures Ptf and Ptr at the second brake unit SB are equivalent to the front and rear wheel target pressures Ptf and Ptr at the first brake unit SA, the second brake unit SB can compensate for the output reduction of the first brake unit SA in accordance with the degree of the output reduction. As a result, even when a communication abnormality occurs, the pressure regulation control can be performed appropriately.

[0103] Furthermore, in a configuration in which the rear wheel supply pressure sensor PV is built into the first brake unit SA and the second brake unit SB acquires the rear wheel supply pressure Pv via the communication bus BS, the second brake unit SB is unable to acquire the rear wheel supply pressure Pv in the event of a communication abnormality. In the complementary control of this configuration, the second brake unit SB increases the front wheel pressure Pwf by an amount corresponding to the deviation hPf (front wheel deviation) between the front wheel target pressure Ptf and the front wheel supply pressure Pm, and increases the rear wheel pressure Pwr by an amount corresponding to the rear wheel target pressure Ptr. Because the front wheel deviation hPf represents a deficiency in the front wheel supply pressure Pm, the complementary control compensates for the front wheel pressure Pwf without excess or deficiency. Meanwhile, because the rear wheel pressure Pwr is increased by an amount corresponding to the rear wheel target pressure Ptr, when the rear wheel supply pressure Pv is generated by the first brake unit SA, the difference between the actually generated rear wheel supply pressure Pv and the rear wheel target pressure Ptr becomes excessive. However, since the contribution of the rear wheel pressure Pwr to vehicle deceleration is small, its effect on the deceleration of the vehicle JV is minimal. From the above, even in a configuration in which the rear wheel supply pressure sensor PV is built into the first brake unit SA, the second brake unit SB can perform compensation according to the degree of output reduction of the first brake unit SA, so that pressure adjustment control is performed appropriately.

[0104] <Application to a vehicle JV with a regenerative device KG mounted on the rear wheels WHr> In the above-described embodiment, a vehicle (referred to as a "front-wheel regenerative vehicle") is assumed in which the regenerative device KG is provided on the front wheels WHf but not on the rear wheels WHr. Alternatively, the braking control device SC may be applied to a vehicle (referred to as a "rear-wheel regenerative vehicle") in which the regenerative device KG is provided on the rear wheels WHr but not on the front wheels WHf. Differences will be explained below. The single-system pressure adjustment process is the same for front-wheel and rear-wheel regenerative vehicles.

[0105] In the braking control device SC applied to a rear-wheel regenerative vehicle, as shown in the schematic diagram of FIG. 2, the servo path HV is connected to the return path HK at a point pj, and the rear-wheel connecting path HSr is connected to the return path HK at a point pk. That is, the upstream servo pressure Pj is supplied to the servo chamber Ru, and the downstream servo pressure Pk is supplied to the rear wheel cylinder CWr (i.e., "Pj = Pm = Pwf, Pk = Pv = Pwr"). Also, in the pressure regulation control process (particularly, dual-path pressure regulation) of FIG. 4, when "Fqr≦Fx" is satisfied, the front and rear wheel target frictional braking forces Fnf and Fnr are calculated as "Fh = Fqr, Fnf = Fqf, Fnr = 0." On the other hand, when "Fqf > Fx," the following are determined: "Fh = Fx, Fnf = Fqf, Fnr = Fqr - Fx = Fqr - Fh." Then, the front and rear wheel target friction braking forces Fnf and Fnr are converted into front and rear wheel target pressures Ptf and Ptr (where "Ptf≧Ptr").

[0106] In a vehicle equipped with a regenerative device KG (=KGf, KGr) on both the front and rear wheels WHf and WHr, one of the two configurations described above is adopted depending on the magnitude of the regenerative energy of the regenerative devices. Specifically, a brake control device SC for a front-wheel regenerative vehicle is applied to a vehicle in which the regenerative energy of the front-wheel regenerative device KGf is greater than that of the rear-wheel regenerative device KGf. Conversely, a brake control device SC for a rear-wheel regenerative vehicle is applied to a vehicle in which the regenerative energy of the front-wheel regenerative device KGf is smaller than that of the rear-wheel regenerative device KGf.

[0107] To summarize the above, in the first brake unit SA, normally open upstream and downstream pressure regulating valves UJ and UK are arranged in series in the circulating flow KN of brake fluid BF including the fluid pump QA. The upstream and downstream pressure regulating valves UJ and UK regulate the pressure of the brake fluid BF discharged by the fluid pump QA to upstream and downstream servo pressures Pj and Pk. The front wheel supply pressure Pm is output based on the hydraulic pressure on one side of the upstream and downstream servo pressures Pj and Pk. The rear wheel supply pressure Pv is output based on the hydraulic pressure on the other side of the upstream and downstream servo pressures Pj and Pk.

[0108] When the brake control device SC operates normally, the first brake unit SA performs dual-system pressure adjustment processing in the following order: Front and rear wheel required braking forces Fqf, Fqr are calculated based on the operation displacement Sp so as to satisfy conditions 1 and 2 (i.e., equation (1)) above. Front and rear wheel target frictional braking forces Fnf, Fnr are calculated based on the front and rear wheel required braking forces Fqf, Fqr, taking into account front and rear wheel target regenerative braking forces Fhf, Fhr. The front and rear wheel target frictional braking forces Fnf, Fnr are converted to front and rear wheel target pressures Ptf, Ptr based on the specifications of the front and rear wheel brake devices SXf, SXr. Based on the front and rear wheel target pressures Ptf, Ptr, the "hydraulic pressure on one side of the upstream and downstream servo pressures Pj, Pk" and the "hydraulic pressure on the other side of the upstream and downstream servo pressures Pj, Pk" are controlled. Specifically, one-side hydraulic pressure is adjusted by feedback control based on the front wheel supply pressure Pm so that the front wheel supply pressure Pm coincides with the front wheel target pressure Ptf, and the other-side hydraulic pressure is adjusted by feedback control based on the rear wheel supply pressure Pv so that the rear wheel supply pressure Pv coincides with the rear wheel target pressure Ptr.

[0109] <Other embodiments> Other embodiments will be described below, which also provide the same effects as those described above (such as the execution of appropriate pressure regulation control when a communication abnormality occurs).

[0110] In the above-described embodiment, the target values ​​of various braking forces (Fv, Fx, Fh, Fn, etc.) are calculated in terms of the longitudinal forces acting on the vehicle JV. Alternatively, they may be calculated in terms of the deceleration of the vehicle JV or the torque of the wheels WH. This is based on the fact that state quantities (referred to as "state quantities related to force") from longitudinal forces to vehicle deceleration are equivalent. Therefore, the front and rear wheel target pressures Ptf and Ptr are calculated based on state quantities related to forces from longitudinal forces acting on the vehicle JV to deceleration of the vehicle JV.

[0111] In the above-described embodiment, the rear wheel supply pressure sensor PV is connected only to the first brake unit SA, and the second brake unit SB acquires the rear wheel supply pressure Pv via the communication bus BS. Alternatively, the rear wheel supply pressure sensor PV may be built into the second brake unit SB, and the first brake unit SA acquires the rear wheel supply pressure Pv via the communication bus BS, and the second brake unit SB acquires the rear wheel supply pressure Pv directly. In this configuration, the rear wheel supply pressure Pv can be acquired even during a communication abnormality. Therefore, the rear wheel pressure Pwr is increased by an amount corresponding to the deviation hPr (rear wheel deviation) between the rear wheel target pressure Ptr and the rear wheel supply pressure Pv, similar to the front wheel pressure Pwf. However, in this configuration, the first brake unit SA cannot acquire the rear wheel supply pressure Pv during a communication abnormality, and therefore feedback control based on the rear wheel supply pressure Pv cannot be performed. For this reason, the above-described configuration (i.e., a configuration in which the rear wheel supply pressure sensor PV is directly connected only to the rear wheel supply pressure sensor SA, and the front wheel supply pressure sensor PM is directly connected only to the second brake unit SB) is preferable from the viewpoint of distributed arrangement of hydraulic pressure sensors and fail-safe. Note that at least one of the following may be adopted: "a configuration in which the rear wheel supply pressure sensor PV is directly connected to both the first and second brake units SA, SB" and "a configuration in which the front wheel supply pressure sensor PM is directly connected to both the first and second brake units SA, SB," but adopting these configurations would be disadvantageous in terms of simplifying the entire device.

[0112] In the above-described embodiment, the pressure regulating unit CA is exemplified as one that adjusts the front and rear wheel supply pressures Pm, Pv by throttling the circulating flow KN of brake fluid BF discharged by the fluid pump QA using the upstream and downstream pressure regulating valves UJ, UK (a so-called reflux type configuration). Alternatively, the pressure regulating unit CA may adjust the front and rear wheel supply pressures Pm, Pv based on the pressure accumulated in an accumulator (a so-called accumulator type configuration). Alternatively, the front and rear wheel supply pressures Pm, Pv may be adjusted by increasing or decreasing the volume within a cylinder using a piston directly driven by an electric motor (a so-called electric cylinder type configuration). In either configuration, the pressure regulating unit CA receives feedback of the detected values ​​Pm, Pv of the front and rear wheel supply pressure sensors PM, PV, and electrically adjusts them.

[0113] In the above-described embodiment, the pressure receiving area rm (master area) of the master chamber Rm and the pressure receiving area ru (servo area) of the servo chamber Ru in the apply section AP are set equal. The master area rm and the servo area ru do not have to be equal. In a configuration in which the master area rm and the servo area ru are different, a conversion calculation between the front wheel supply pressure Pm and the downstream servo pressure Pk (or the upstream servo pressure Pj) is possible based on the ratio between the servo area ru and the master area rm (i.e., conversion based on "Pm·rm=Pk·ru (or Pj·ru)").

[0114] In the above-described embodiment, the first brake unit SA outputs the front wheel supply pressure Pm via the master cylinder CM. That is, the apply unit AP and the pressure adjustment unit CA are arranged in series in the hydraulic pressure transmission path, and the downstream servo pressure Pk supplied from the pressure adjustment unit CA is transmitted as the front wheel supply pressure Pm via the master piston NM. This configuration is referred to as a "series configuration." Instead of the series configuration, the apply unit AP and the pressure adjustment unit CA may be arranged in parallel. This configuration is referred to as a "parallel configuration." In the parallel configuration, the apply unit AP (particularly, the master cylinder CM) and the pressure adjustment unit CA are each directly connected to the second actuator YB. In the first mode, "connection between the pressure adjustment unit CA and the second actuator YB" is selected, and in the second mode, "connection between the apply unit AP and the second actuator YB" is selected. For example, this selection is achieved by a solenoid valve (referred to as a "switching valve"). In the first mode of this configuration, the front and rear wheel supply pressures Pm and Pv generated by the pressure adjusting unit CA are directly output as the front and rear wheel supply pressures Pm and Pv without passing through the apply unit AP. At this time, the apply unit AP is connected to the stroke simulator SS, and the operating force Fp of the brake operating member BP is generated by the simulator SS. On the other hand, in the second mode, the hydraulic pressure in the master chamber Rm generated by operating the brake operating member BP is output as the front wheel supply pressure Pm. At this time, the apply unit AP is disconnected from the simulator SS.

[0115] <Summary of the embodiment> The following summarizes an embodiment of the brake control device SC: The brake control device SC is a brake-by-wire type device that can independently adjust the operation displacement Sp of the brake operating member BP and the hydraulic pressure Pw (wheel pressure) of the wheel cylinder CW.

[0116] The brake control device SC is equipped with a "first brake unit SA (first unit) that individually increases the front and rear wheel supply pressures Pm and Pv in accordance with the operation displacement Sp (operation amount) of the brake operating member BP," a "second brake unit SB (second unit) that is provided between the first brake unit SA and the front and rear wheel cylinders CWf and CWr and that individually increases the front and rear wheel supply pressures Pm and Pv and outputs front and rear wheel pressures Pwf and Pwr," a "communication bus BS that transmits signals between the first brake unit SA and the second brake unit SB," an "operation displacement sensor SP (operation amount sensor) that detects the operation displacement Sp (operation amount)," a "front wheel supply pressure sensor PM that detects the front wheel supply pressure Pm," and a "rear wheel supply pressure sensor PV that detects the rear wheel supply pressure Pv." In the first braking unit SA, front and rear wheel target pressures Ptf, Ptr are calculated based on the operation amount Sp, and the front and rear wheel supply pressures Pm, Pv are controlled so as to approach the front and rear wheel target pressures Ptf, Ptr. For example, in the first braking unit SA, feedback control is performed based on the deviation hPf (front wheel deviation) between the front wheel target pressure Ptf and the front wheel supply pressure Pm so that the front wheel supply pressure Pm coincides with the front wheel target pressure Ptf. Also, feedback control is performed based on the deviation hPr (rear wheel deviation) between the rear wheel target pressure Ptr and the rear wheel supply pressure Pv so that the rear wheel supply pressure Pv coincides with the rear wheel target pressure Ptr. Furthermore, in the braking control device SC, when the communication bus BS is abnormal, the second braking unit SB calculates the front and rear wheel target pressures Ptf, Ptr based on the operation amount Sp. Then, the front and rear wheel pressures Pwf and Pwr are increased based on the front and rear wheel target pressures Ptf and Ptr.

[0117] If the communication bus BS is abnormal (i.e., if signals cannot be transmitted between the first and second controllers EA and EB), even if an abnormality occurs in the first brake unit SA, the first brake unit SA cannot communicate this condition to the second brake unit SB. In other words, if there is a communication abnormality, the second brake unit SB cannot grasp the operating status of the first brake unit SA. For example, if the first brake unit SA (particularly the first controller EA) fails and a communication abnormality occurs, the operation of the first brake unit SA may be completely stopped. In this case, the first brake unit SA (particularly the input unit NR) is set to the second mode (manual mode), and the front and rear wheel supply pressures Pm and Pv are not generated electrically but are generated using the driver's muscle power as a power source. Also, even if the operation of the first brake unit SA is not completely stopped, the outputs Pm and Pv (front and rear wheel supply pressures) from the first brake unit SA may be lower than the front and rear wheel target pressures Ptf and Ptr. Therefore, the complementary control in the second brake unit SB must be performed in accordance with the degree of the decrease in the output of the first brake unit SA.

[0118] In the brake control device SC, when the communication bus BS is abnormal, the second brake unit SB employs the same method as the first brake unit SA to calculate the front and rear wheel target pressures Ptf, Ptr based on the operation amount Sp. More specifically, the second brake unit SB determines the front and rear wheel target pressures Ptf, Ptr based on a calculation map that is the same as (or similar to) the calculation map (Zfv, etc.) employed in the first brake unit SA. Therefore, the front and rear wheel target pressures Ptf, Ptr calculated by the second brake unit SB are equivalent to the front and rear wheel target pressures Ptf, Ptr calculated by the first brake unit SA. Then, the front and rear wheel pressures Pwf, Pwr are increased based on the front and rear wheel target pressures Ptf, Ptr. As a result, even if the operating status of the first brake unit SA cannot be determined due to a communication abnormality, the second brake unit SB compensates for the decrease in output of the first brake unit SA according to the degree of the decrease in output. In other words, the pressure regulation control is performed appropriately even during a communication abnormality.

[0119] The arrangement of various sensors (Sp, etc.) in the brake control device SC is summarized below. The operation displacement sensor SP (operation amount sensor) is connected to both the first and second brake units SA and SB. Therefore, even in the event of a communication abnormality, the first and second brake units SA and SB can acquire the operation displacement Sp (operation amount). The front wheel supply pressure sensor PM is connected to at least the second brake unit SB. The rear wheel supply pressure sensor PV may be connected to either brake unit.

[0120] The front and rear wheel supply pressures Pm and Pv are the hydraulic pressures actually output by the first brake unit SA. Therefore, the deviations hPf and hPr (front and rear wheel deviations) between the front and rear wheel target pressures Ptf and Ptr and the front and rear wheel supply pressures Pm and Pv represent the shortage of output from the first brake unit SA. In addition, the contribution of the front wheel pressure Pwf to deceleration of the vehicle JV is much greater than the contribution of the rear wheel pressure Pwr. Therefore, at least the front wheel pressure Pwf is increased by an amount corresponding to the front wheel deviation hPf. Note that a brake unit not connected to a sensor receives a signal from the sensor via the communication bus BS from a brake unit to which the sensor is connected. For example, in a configuration in which the front wheel supply pressure sensor PM is not connected to the first brake unit SA, the first brake unit SA receives a signal of the front wheel supply pressure Pm via the communication bus BS.

[0121] The second brake unit SB is a general-purpose unit for performing independent wheel control such as anti-lock brake control and anti-skid control, and is equipped with a front wheel supply pressure sensor PM to perform these controls. Therefore, the simplest configuration in terms of sensor arrangement and fail-safe is one in which the operation displacement sensor SP is connected to both the first and second brake units SA and SB, the front wheel supply pressure sensor PM is connected only to the second brake unit SB, and the rear wheel supply pressure sensor PV is connected only to the first brake unit SA. In this configuration, the first brake unit SA obtains the front wheel supply pressure Pm from the second brake unit SB via the communication bus BS, and can use it for feedback control in the two-system pressure regulation (particularly for control of the front wheel system).

[0122] In the above simplified configuration, in the event of a communication abnormality, the first brake unit SA cannot obtain the front wheel supply pressure Pm, and the second brake unit SB cannot obtain the rear wheel supply pressure Pv. In the event of a communication abnormality, the first brake unit SA should be able to switch from dual-system pressure regulation to single-system pressure regulation. However, the second brake unit SB cannot determine whether this switch has been made. In other words, the second brake unit SB cannot determine that single-system pressure regulation is being performed by the first brake unit SA. For this reason, in the event of a communication abnormality, the second brake unit SB is required to also deal with a situation in which dual-system pressure regulation continues.

[0123] In the brake control device SC, the front wheel pressure Pwf is increased by an amount corresponding to the deviation hPf (front wheel deviation) between the front wheel target pressure Ptf and the front wheel supply pressure Pm, and the rear wheel pressure Pwr is increased by an amount corresponding to the rear wheel target pressure Ptr. That is, for the front wheel cylinder CWf, the front wheel supply pressure Pm is increased by the amount of the front wheel deviation hPf and output from the second brake unit SB as the front wheel pressure Pwf. On the other hand, for the rear wheel cylinder CWr, the rear wheel supply pressure Pv is increased by the amount of the rear wheel target pressure Ptr and output from the second brake unit SB as the rear wheel pressure Pwr. As a result, even if dual-system pressure regulation continues in the first brake unit SA, the complementary control appropriately compensates for the output decrease of the first brake unit SA, and pressure regulation control is appropriately performed. The reason for this will be explained in detail below.

[0124] In the complementary control for the front wheel system, if the output Pm (front wheel supply hydraulic pressure) of the first brake unit SA is appropriate, the front wheel deviation hPf does not occur, and therefore adjustment by the second brake unit SB is not substantially performed. On the other hand, if the output Pm of the first brake unit SA is insufficient, the front wheel deviation hPf occurs, and accordingly, the front wheel supply pressure Pm is increased by an appropriate amount by the second brake unit SB. The complementary control ensures an appropriate front wheel pressure Pwf according to the amount of insufficiency in the front wheel supply pressure Pm, thereby effectively suppressing a decrease in the deceleration of the vehicle JV.

[0125] During a communication abnormality, the second brake unit SB cannot acquire the rear wheel supply pressure Pv signal, and therefore cannot calculate the deviation hPr (rear wheel deviation) between the rear wheel target pressure Ptr and the rear wheel supply pressure Pv. Therefore, in the complementary control for the rear wheel system, in order to ensure deceleration of the vehicle JV, the rear wheel supply pressure Pv from the first brake unit SA is assumed to be "0," and the second brake unit SB increases the rear wheel pressure Pwr by an amount equivalent to the rear wheel target pressure Ptr. When the output Pv of the first brake unit SA is being generated, this difference (i.e., hydraulic pressure "Ptr-Pv") becomes excessive. However, since the contribution of the rear wheel pressure Pwr to vehicle deceleration is small, the degree of its influence is minimal. The complementary control reliably suppresses the decrease in the rear wheel pressure Pwr, thereby ensuring appropriate deceleration of the vehicle JV. [Explanation of symbols]

[0126] SC...Brake control device, KG...Regeneration device, BP...Brake operating member (brake pedal), SA...First brake unit (first unit), SB...Second brake unit (second unit), YA...First fluid unit (first actuator), YB...Second fluid unit (second actuator), EA...First control unit (first controller), EB...Second control unit (second controller), BS...Communication bus, CM...Master cylinder, CW...Wheel cylinder, AP...Apply section, NR...Input section, CA...Pressure adjustment section, UJ, UK...Upstream side , downstream pressure regulating valve, MA, MB... first and second electric motors, QA, QB... first and second fluid pumps, VA... inlet valve, VB... release valve, UB... control valve, SP... operation displacement sensor (operation amount sensor), PM, PV... front wheel and rear wheel supply pressure sensors, Sp... operation displacement (operation amount), Pm, Pv... front wheel and rear wheel supply pressure, Pj, Pk... upstream and downstream servo pressure, Pq... adjustment pressure, Pw... wheel pressure, Ptf, Ptr... front wheel and rear wheel target pressure (target value corresponding to Pm, Pv), hPf, hPr... front wheel and rear wheel deviation (hydraulic pressure difference between Ptf, Ptr and Pm, Pv), FT... suitability flag (determination result of step S140), FU... suitability flag (determination result of step S320).

Claims

1. a first unit that outputs pressures to be supplied to the front wheels and the rear wheels individually in accordance with an operation amount of a brake operating member; a second unit provided between the first unit and the front and rear wheel cylinders, the second unit increasing the front and rear wheel supply pressures individually and outputting the front and rear wheel pressures; a communication bus for transmitting signals between the first unit and the second unit; an operation amount sensor connected to both the first and second units and configured to detect the operation amount; a front wheel supply pressure sensor for detecting the front wheel supply pressure; a rear wheel supply pressure sensor for detecting the rear wheel supply pressure; In a braking control device for a vehicle, the first unit calculates the front and rear wheel target pressures based on the operation amount, and controls the front and rear wheel supply pressures to approach the front and rear wheel target pressures; A vehicle braking control device, wherein when the communication bus is abnormal, the second unit calculates the front and rear wheel target pressures in a manner similar to the method of calculating the front and rear wheel target pressures by the first unit, and increases the front and rear wheel pressures based on the front and rear wheel target pressures.

2. 2. The vehicle brake control device according to claim 1, the front wheel supply pressure sensor is connected to at least the second unit; The second unit increases the front wheel pressure by an amount corresponding to a deviation between the front wheel target pressure and the front wheel supply pressure.

3. a first unit that outputs pressures to be supplied to the front wheels and the rear wheels individually in accordance with an operation amount of a brake operating member; a second unit provided between the first unit and the front and rear wheel cylinders, the second unit increasing the front and rear wheel supply pressures individually and outputting the front and rear wheel pressures; a communication bus for transmitting signals between the first unit and the second unit; an operation amount sensor connected to both the first and second units and configured to detect the operation amount; a front wheel supply pressure sensor connected only to the second unit and detecting the front wheel supply pressure; a rear wheel supply pressure sensor connected only to the first unit and detecting the rear wheel supply pressure; In a braking control device for a vehicle, The first unit is The front wheel supply pressure is acquired from the second unit via the communication bus; Calculating front and rear wheel target pressures based on the operation amount; controlling the front and rear wheel supply pressures to approach the front and rear wheel target pressures based on a deviation between the front and rear wheel target pressures and the front and rear wheel supply pressures; The second unit, when the communication bus is abnormal, calculates the front and rear wheel target pressures based on the operation amount, increases the front wheel pressure by an amount corresponding to the deviation between the front wheel target pressure and the front wheel supply pressure, and increases the rear wheel pressure by an amount corresponding to the rear wheel target pressure.