Vehicle braking control device

Abstract

To early compensate abnormality of a brake control device.SOLUTION: A brake control device includes a first unit for outputting a supply pressure according to an operation amount of a brake operation member, a second unit which is provided between the first unit and a wheel cylinder, and increases the supply pressure and outputs a wheel pressure, and a communication bus for performing signal transmission between the first unit and the second unit. The first unit selects any one of a first mode in which the operation amount and the supply pressure are independent, and a second mode which is interlocked with the first mode. When the first unit is normal, the first unit selects the first mode, and increases the wheel pressure by increase of the supply pressure. When abnormality of the first unit is decided, the first unit selects the second mode, and the second unit increases the wheel pressure from the supply pressure. When the abnormality is not decided but the abnormality of the first unit is suspected, the first unit selects the first mode and continues operation of a normal state, and the second unit increases the wheel pressure from the supply 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 "maintaining a good braking operation feel for the driver even if some abnormality occurs in the hydraulic pressure generating device," "a vehicle braking force generating device 10 includes an ESB device 16 including an ESB-ECU 29, a VSA device 18 including a VSA-ECU 31, and a CAN communication medium 33. The VSA-ECU 31 includes a first diagnostic unit 75 that performs abnormality diagnosis on the ESB device 16 including the ESB-ECU 29. When abnormality state information is obtained that indicates that the ESB device 16 is in an abnormal state, the VSA-ECU 31 performs assist control to assist the braking force using the VSA device 18, and, when performing this assist control, if the abnormality state information is uncertain, the increase in brake hydraulic pressure caused by the VSA device 18 is reduced compared to the increase in brake hydraulic pressure in the event of a failure when the abnormality state information is certain."

[0003] In Patent Document 1, as examples of cases where abnormal state information is certain and uncertain, "when it is determined that the device is not normal and information related to a request for assistance has been acquired" and "when it is determined that the device is not normal but information related to a request for assistance has not been acquired," are given. In other words, in Patent Document 1, when the determination of the device's abnormal state is certain but a request for assistance to back up the device abnormality has not been acquired, the control amount of the assist control (also called "backup control") is reduced compared to when the request for assistance is acquired.

[0004] However, when determining whether a braking control device has an abnormality, a certain amount of time is required for the abnormality to be confirmed and for the abnormality to be determined. For this reason, it is desirable to compensate for the abnormality in the braking control device as soon as possible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2015-071382 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a vehicle brake control device that can compensate for device abnormalities at an early stage. [Means for solving the problem]

[0007] The vehicle brake control device (SC) of the present invention comprises a first unit (SA) that outputs a supply pressure (Pm) 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 a wheel cylinder (CW) and increases the supply pressure (Pm) to output a wheel pressure (Pw) to the wheel cylinder (CW), and a communication bus (BS) that transmits signals between the first unit (SA) and the second unit (SB).

[0008] In the vehicle brake control device (SC) according to the present invention, the first unit (SA) selects either a first mode in which the operation amount (Sp) and the supply pressure (Pm) are independent, or a second mode in which the operation amount (Sp) and the supply pressure (Pm) are linked. When the first unit (SA) is in a normal state, the first unit (SA) selects the first mode and increases the supply pressure (Pm) to increase the wheel pressure (Pw). When the first unit (SA) is in a confirmed state in which it is confirmed that it is abnormal, the first unit (SA) selects the second mode, and the second unit (SB) increases the wheel pressure (Pw) from the supply pressure (Pm). When the first unit (SA) is in a specific state in which it is not in the confirmed state but an abnormality of the first unit (SA) is suspected, the first unit (SA) selects the first mode and continues operation in the normal state, and the second unit (SB) increases the wheel pressure (Pw) from the supply pressure (Pm).

[0009] The vehicle brake control device (SC) according to the present invention includes an operation amount sensor (SP) that detects the operation amount (Sp) and a supply pressure sensor (PM) that detects the supply pressure (Pm). In the normal state, the first unit (SA) calculates a target pressure (Pt) based on the operation amount (Sp) and increases the supply pressure (Pm) so as to approach the target pressure (Pt), and in the specific state, the second unit (SB) increases the wheel pressure (Pw) by an amount corresponding to the target pressure (Pt) and a deviation (hP) from the supply pressure (Pm).

[0010] In the brake control device SC, complementary control is executed before transitioning to backup control. In complementary control, the operation of the first brake unit SA in normal control continues, and in the second brake unit SB, the wheel pressure Pw is increased from the supply pressure Pm based on the deviation hP between the target pressure Pt and the supply pressure Pm. With the above configuration, execution of complementary control is initiated when an abnormality in the first brake unit SA is suspected before the abnormality is confirmed, so the abnormality is quickly compensated. In addition, in complementary control, the first mode is selected, so discomfort to the driver is reduced. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an entire vehicle JV equipped with a braking control device SC. [Figure 2] 3 is a schematic diagram for explaining a configuration example of a first braking unit SA. FIG. [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. 4 is a block diagram for explaining drive control of a pressure regulating valve UA. [Figure 6] FIG. 3 is a block diagram for explaining drive control of a control valve UB. DETAILED DESCRIPTION OF THE INVENTION

[0012] <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.

[0013] 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."

[0014] 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 (UA, 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.

[0015] <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.

[0016] 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."

[0017] 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).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] <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 a supply pressure Pm in response to operation of the brake operating member BP (brake pedal). The supply pressure Pm is ultimately supplied to the wheel cylinder CW 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.

[0025] <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.

[0026] [Apply Department AP] In response to operation of the brake operating member BP, a supply pressure Pm is output from the apply section AP, which is composed of a tandem master cylinder CM and primary and secondary master pistons NM and NS.

[0027] Primary and secondary master pistons NM and NS are inserted into the tandem master cylinder CM. The interior of the master cylinder CM is divided into four hydraulic chambers Rmf, Rmr, Ru, and Rs by the two master pistons NM and NS. The front and rear wheel master chambers Rmf and Rmr (= Rm) are divided by the bottom of one side of the master cylinder CM and the master pistons NM and NS. The interior of the master cylinder CM is further divided into a servo chamber Ru and a reaction chamber Rs by the flange Tu of the master piston NM. The master chamber Rm and the servo chamber Ru are arranged opposite each other with the flange 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.

[0028] When braking is not in progress, the master pistons NM and NS are in their 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 pistons NM and NS are 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 pistons NM and NS are further moved forward in the Ha direction, the front and rear wheel supply pressures Pmf and Pmr (= Pm) are increased from "0 (atmospheric pressure)." As a result, brake fluid BF pressurized to the supply pressure Pm is output (pressurized and fed) from the master chamber Rm of the master cylinder CM. The supply pressure Pm is the hydraulic pressure in the master chamber Rm, and is therefore also called the "master pressure."

[0029] [Pressure Regulating Unit CA] A servo pressure Pu is supplied to the servo chamber Ru of the apply unit AP by a pressure adjusting unit CA, which is composed of a first electric motor MA, a first fluid pump QA, and a pressure adjusting valve UA.

[0030] 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.

[0031] A normally open pressure regulating valve UA is provided in the return path HK. The pressure regulating valve UA is a linear solenoid valve whose opening amount is continuously controlled based on the energization state (e.g., supply current). The pressure regulating valve UA adjusts the hydraulic pressure difference (differential pressure) between its upstream and downstream sides, so it is also called a "differential pressure valve."

[0032] When the first fluid pump QA discharges brake fluid BF, a circulating flow KN (indicated by the dashed arrow) of brake fluid BF is generated in the return path HK. When the pressure regulating valve UA is fully open (when not energized, since the pressure regulating valve UA is normally open), the fluid pressure Pu (referred to as "servo pressure") between the discharge port of the first fluid pump QA and the pressure regulating valve UA in the return path HK is "0 (atmospheric pressure)." When the amount of electricity (supply current) to the pressure regulating valve UA is increased, the pressure regulating valve UA throttles the circulating flow KN (the flow of brake fluid BF circulating in the return path HK). In other words, the pressure regulating valve UA narrows the flow path of the return path HK, thereby exerting an orifice effect. As a result, the fluid pressure Pu upstream of the pressure regulating valve UA increases from "0." That is, in the circulating flow KN, a hydraulic pressure difference (differential pressure) is generated between the hydraulic pressure Pu (servo pressure) on the upstream side and the hydraulic pressure (atmospheric pressure) on the downstream side with respect to the pressure regulating valve UA. This differential pressure is adjusted by the amount of current supplied to the pressure regulating valve UA.

[0033] The return path HK is connected to the servo chamber Ru via a servo path HV (fluid path) at a location between the discharge port of the first fluid pump QA and the pressure regulating valve UA. Therefore, the servo pressure Pu is introduced (supplied) to the servo chamber Ru. As the servo pressure Pu increases, the master pistons NM and NS are pressed forward Ha (in the direction in which the volume of the master chamber Rm decreases), and the hydraulic pressures Pmf and Pmr (front and rear wheel supply pressures) in the front and rear master chambers Rmf and Rmr increase.

[0034] The front and rear wheel master chambers Rmf and Rmr (=Rm) are connected to the front and rear wheel communication passages HSf and HSR (=HS). The front and rear wheel communication passages HSf and HSR are connected to the front and rear wheel cylinders CWf and CWr (=CW) via the second brake unit SB (particularly, the second fluid unit YB). Therefore, the front and rear wheel supply pressures Pmf and Pmr are supplied from the first brake unit SA to the front and rear wheel cylinders CWf and CWr. Here, the front wheel supply pressure Pmf and the rear wheel supply pressure Pmr are equal (i.e., "Pmf = Pmr").

[0035] [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.

[0036] 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 primary piston NM. Regenerative cooperative control is achieved by adjusting the separation distance Ks using the servo pressure Pu.

[0037] 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.

[0038] 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 pistons NM and NS are 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 pistons NM and NS 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.

[0039] The state in which the master pistons NM, NS and the brake operating member BP are displaced separately (when the solenoid valves VA, 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 pistons NM, NS and the brake operating member BP are displaced together (when the solenoid valves VA, 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 operation modes, the first mode (by-wire mode) or 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.

[0040] 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.

[0041] <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 with other controllers (EB, EG, etc.).

[0042] 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 simulator pressure sensor PS are connected via a signal line LPs for the simulator pressure sensor PS. The first operation displacement Spa and the simulator pressure Ps are directly input to the first controller EA through these signal lines LSpa and LPs.

[0043] 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 supply pressure Pm (and consequently the wheel pressure Pw), 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 supply pressure Pm, and the maximum regenerative braking force Fx.

[0044] The first drive circuit DRa drives the first electric motor MA constituting the first actuator YA and various solenoid valves (UA, etc.) based on a pressure regulation control algorithm. 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 (UA, 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 a first current sensor (not shown) that detects the supply current Ia (actual value, referred to as the "first supply current") to the pressure regulation valve UA. 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 also 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.

[0045] The first controller EA calculates a first target current Ita (target value) corresponding to the first supply current Ia based on the operation displacement Sp (operation amount). The first supply current Ia is then controlled so as to approach and match the first target current Ita (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 motor supply current Im is then controlled 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 Ua, Va, Vb for controlling the various solenoid valves UA, VA, VB are calculated. The switching elements of the first drive circuit DRa are then driven in response to the drive signals (Ma, etc.), thereby controlling the first electric motor MA and the solenoid valves UA, VA, VB.

[0046] <Second braking unit SB> An example of the configuration of the second brake unit SB (corresponding to the "second unit") of the brake control device SC will be described with reference to the schematic diagram of Figure 3. The second brake 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 brake unit SB performs backup control and complementary control. The "backup control" is a preliminary control in preparation for unforeseen circumstances. For example, if there is an abnormality in the operation of the first brake unit SA, the backup control takes over the function of the first brake unit SA and compensates for its performance degradation. Furthermore, the "complementary control" compensates for any excess or deficiency in the supply pressure Pm caused by an abnormality in the first brake unit SA.

[0047] The second brake unit SB is supplied with front and rear wheel supply pressures Pmf and Pmr (=Pm) from the first brake unit SA. The second brake unit SB then adjusts (increases or decreases) the front and rear wheel supply pressures Pmf and Pmr and outputs them as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) for 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.

[0048] <Second fluid unit YB> The second fluid unit YB (also referred to as the "second actuator") is provided in the communication passage HS between the first actuator YA and the wheel cylinder CW. The second actuator YB is composed of a 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.

[0049] Front and rear wheel control valves UBf and UBr (=UB) are provided in the front and rear wheel communication passages HSf and HSR (=HS). The control valves UB are normally open linear solenoid valves (differential pressure valves) like the pressure regulating valve UA. The control valves UB allow the wheel pressure Pw to be increased individually from the supply pressure Pm in the front and rear wheel systems.

[0050] Front and rear wheel supply pressure sensors PMf, PMr (=PM) are provided above the front and rear wheel control valves UBf, UBr (at the portion of the communication passage HS closer to the first actuator YA) to detect actual hydraulic pressures Pmf, Pmr (front and rear wheel supply pressures) supplied from the first actuator YA (particularly, front and rear wheel master chambers Rmf, Rmr). The supply pressure sensor PM is also referred to as a "master pressure sensor" and is built into the second actuator YB. The front and rear wheel supply pressure sensors PMf, PMr are connected to the second brake unit SB (particularly, the second control unit EB) by front and rear wheel supply pressure signal lines LPmf, LPmr (=LPm). In other words, the signals of the front and rear wheel supply pressures Pmf, Pmr (=Pm) are directly input to the second control unit EB. Since the front wheel supply pressure Pmf and the rear wheel supply pressure Pmr are substantially the same, either one of the front and rear wheel supply pressure sensors PMf and PMr may be omitted. For example, in a configuration in which the rear wheel supply pressure sensor PMr is omitted, only the front wheel supply pressure Pmf is detected by the front wheel supply pressure sensor PMf and input directly to the second control unit EB.

[0051] 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.

[0052] 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 to 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 resulting orifice effect increases the hydraulic pressure Pq (referred to as the "regulating pressure") below the control valve UB from the hydraulic pressure Pm (supply pressure) above the control valve UB. In other words, the hydraulic pressure difference (differential pressure) between the hydraulic pressure Pm (supply pressure) downstream of the control valve UB and the hydraulic pressure Pq (regulating pressure) upstream of the control valve UB is adjusted by the control valve UB. In terms of the magnitude relationship between the supply pressure Pm and the adjustment pressure Pq, the adjustment pressure Pq is equal to or greater than the supply pressure Pm (i.e., "Pq≧Pm"). As described 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 pressure Pu is generated in the first actuator YA.

[0053] Inside the second actuator YB, the front and rear wheel communication passages HSf and HSR are each branched into two passages 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 supply pressure Pm at each wheel.

[0054] When the inlet valve VI and the outlet valve VO are not energized and are deactivated, 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. The wheel pressure Pw is independently adjusted for each wheel cylinder CW by operating the inlet valve VI and the outlet valve VO. To decrease the wheel pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. This prevents brake fluid BF from flowing into the wheel cylinder CW and causes the brake fluid BF in the wheel cylinder CW to flow out to the pressure regulating reservoir RB, thereby decreasing the wheel pressure Pw. To increase the wheel pressure Pw (up to the regulated pressure Pq), 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.

[0055] <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.

[0056] 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.

[0057] 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.

[0058] The second controller EB and the second detection unit SPb of the operation displacement sensor SP are connected via a signal line LSpb for the second detection unit SPb. Furthermore, the second controller EB and the supply pressure sensor PM are connected via a signal line LPm (e.g., a signal pin) for the 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 supply pressure Pm is directly input to the second controller EB via the signal line LPm. The second operation displacement Spb and the supply pressure Pm are then transmitted from the second controller EB to the first controller EA via the communication bus BS. In other words, the first controller EA acquires the second operation displacement Spb and the supply pressure Pm from the second controller EB via the communication bus.

[0059] In addition to the above-described independent control of each wheel, the second controller EB also performs backup control and complementary control to deal with abnormalities in the brake control device SC. In these controls, the second brake unit SB compensates for any deterioration in the function and performance of the first brake unit SA. Specifically, the complementary control and backup control compensate for a decrease in the wheel pressure Pw and reduce the operating force Fp of the brake operating member BP.

[0060] <Pressure regulation control processing> An example of the pressure regulation control process will be described with reference to Figures 4 to 6. The pressure regulation control includes not only regenerative cooperative control, but also complementary control and backup control in response to an abnormality in the first braking unit SA. The pressure regulation control algorithm is programmed in the microprocessors MPa and MPb of the first and second controllers EA and EB.

[0061] 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. When the braking control device SC operates normally, the second actuator YB is not driven, and only the first actuator YA is driven. Therefore, when the braking control device SC operates normally, the wheel pressure Pw is adjusted only by the first actuator YA, so that the wheel pressure Pw and the supply pressure Pm are equal (i.e., "Pm = Pw"). 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, "Pm = Pu" (where friction of the seal member SL is ignored). The supply pressure sensor PM is built into the second actuator YB and is connected to the second controller EB by a signal line LPm. The first controller EA acquires the supply pressure Pm from the second controller EB via the communication bus BS. In the second actuator YB, the rear wheel supply pressure sensor PMr is omitted, and only the front wheel supply pressure sensor PMf is provided as the supply pressure sensor PM. Therefore, only the front wheel supply pressure Pmf is used as the signal of the supply pressure Pm.

[0062] 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.

[0063] The entire pressure regulation control will be described with reference to the flow chart in Figure 4. The pressure regulation control includes the following three types depending on the operating state of the first brake unit SA. The first is pressure regulation control when the operation of the first brake unit SA is normal (referred to as the "normal state"), and is called "normal control." The second is pressure regulation control when it is confirmed that the operation of the first brake unit SA is abnormal (referred to as the "confirmed state"), and is called backup control. And the third is pressure regulation control when an abnormality in the first brake unit SA has not been confirmed but is suspected (referred to as the "specific state"), and is called "complementary control."

[0064] "Backup control" is a preliminary control in preparation for unforeseen circumstances, and substitutes for the function of the first braking unit SA. However, it takes a certain amount of time for the definite state to be determined and for the backup control to be initiated. In addition, the abnormality may be short-term, and the system may return to normal before the definite state is reached. During the period from the normal state to the definite state (i.e., the period of the specific state), a complementary control other than the backup control is executed to compensate for the deterioration of the function and performance of the first braking unit SA. Below, normal control, complementary control, and backup control are each explained.

[0065] In step S110, the first controller EA supplies power 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, and a first mode is selected in which the master pistons NM, NS and the brake operating member BP can be displaced separately. In the first mode, the supply pressure Pm (i.e., the wheel pressure Pw) is 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.

[0066] In step S120, the first controller EA reads signals such as the first and second operational displacements Spa and Spb, and the supply pressure Pm (=Pmf). The operational displacement sensor SP is provided with two operational displacement detection units SPa and SPb (first and second detection units). The first operational displacement Spa (detection value of the first detection unit SPa) is directly acquired through the first displacement signal line LSpa. The second operational displacement Spb (detection value of the second detection unit SPb) and the supply pressure Pm (detection value of the supply pressure sensor PM) are acquired from the second controller EB via the communication bus BS.

[0067] In step S120, the first controller EA calculates the operation displacement Sp based on the acquired 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 acquired, the operation displacement Sp is determined based on the other that can be acquired (i.e., "Sp = Spa" or "Sp = Spb"). Since the operation displacement sensor SP is redundant, the operation displacement Sp is calculated based on at least one of the first and second operation displacements Spa and Spb. The calculated operation displacement Sp is transmitted from the first controller EA to the second controller EB via the communication bus BS.

[0068] 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 set to "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 set 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.

[0069] In step S140, the first controller EA determines whether the first brake unit SA is normal. This determination process is referred to as the "suitability determination." The suitability of the first brake unit SA is determined by constantly monitoring the operation (behavior) of each element (MA, UA, MPa, DRa, etc.) that constitutes the first brake unit SA. Then, the time Tj (duration) during which the first brake unit SA is in an abnormal state (referred to as an "improper state") is calculated. When the duration Tj of the improper state has continued for a predetermined time tj, the "normal state" is denied (i.e., the "improper state" is affirmed). Here, the predetermined time tj (also referred to as the "suitability determination time") is a predetermined value (constant) that has been set in advance. Note that a negative determination in step S140 does not immediately result in a determination of an operational abnormality of the first brake unit SA.

[0070] In step S140, in addition to the determination based on the operation of the first braking unit SA, suitability is determined based on the power supply voltage Vd (available voltage) of components (such as MA and UA) that are electrically operated by the first braking unit SA. For example, "when the power supply voltage Vd of the first electric motor MA is equal to or higher than a predetermined voltage vd (that is, "Vd ≥ vd"), or "when the power supply voltage Vd is less than the predetermined voltage vd but the duration Tj of this state is less than the suitability determination time tj", the suitability determination for the first braking unit SA (particularly, the first electric motor MA) is affirmed, and a normal state is determined. On the other hand, "when the power supply voltage Vd of the first electric motor MA is less than the predetermined voltage vd and this state continues over the suitability determination time tj", the suitability determination is negated, and a non-suitable state is determined. Here, the power supply voltage Vd is detected by a power supply voltage sensor (not shown). Also, the predetermined voltage vd is a threshold value for suitability determination and is a preset predetermined value (constant).

[0071] When the first braking unit SA is in a normal state, or when the duration Tj of the non-suitable state is shorter than the suitability determination time tj (predetermined time) (that is, "Tj < tj"), the suitability determination is affirmed, and the process proceeds to step S150. On the other hand, when the duration Tj of the non-suitable state is equal to or longer than the predetermined time tj (that is, "Tj ≥ tj"), the suitability determination is negated, and the process proceeds to step S180.

[0072] In step S140, when the suitability determination is affirmed, the determination flag FJ (also referred to as the "suitability flag") is determined to be "0". On the other hand, when the suitability determination is negated, the suitability flag FJ is determined to be "1". The "suitability flag FJ" is a control flag that indicates the suitability of the first braking unit SA. In the suitability flag FJ, "0" represents a normal state, and "1" represents a non-suitable state. The suitability flag FJ is transmitted from the first controller EA to the second controller EB via the communication bus BS.

[0073] ≪Processing of Normal Control≫ The processes of steps S150 to S170 correspond to normal control. The processes are executed by the first controller EA. For example, in normal control, only the first actuator YA is driven.

[0074] In step S150, a target regenerative braking force Fh and a target frictional braking force Fn are calculated based on the target vehicle body position dynamics Fv 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, if the target vehicle body position dynamics Fv is equal to or less than the limit regenerative braking force Fx, the target regenerative braking force Fh is set equal to the target vehicle body position dynamics Fv, and the target frictional braking force Fn is determined to be "0" (i.e., if "Fv≦Fx", "Fh=Fv, Fn=0"). On the other hand, when the target vehicle body position dynamics Fv 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, and the target frictional braking force Fn is determined to be "the value obtained by subtracting the limit regenerative braking force Fx (=Fh) from the target vehicle body position dynamics Fv" (i.e., when "Fv > Fx," "Fh = Fx, Fn = Fv - Fx = Fv - Fh"). The target regenerative braking force Fh is transmitted from the first controller EA to the regenerative controller EG via the communication bus BS. The regenerative controller EG then controls the generator GN so that the actual regenerative braking force Fg approaches and matches the target regenerative braking force Fh.

[0075] In step S160, a target pressure Pt (=Ptf, Ptr) is calculated based on the target frictional braking force Fn. The "target pressure Pt" is a target value corresponding to the supply pressure Pm. Furthermore, since "Pm=Pw" holds when the brake control device SC is operating normally, the target pressure Pt is also a target value corresponding to the wheel pressure Pw. Specifically, the target pressure Pt is determined by converting the target frictional braking force Fn into the dimension of the supply pressure Pm (i.e., the wheel pressure Pw) based on the specifications of the braking device SX and the like (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.). Note that since "Pmf=Pmr", the front wheel target pressure Ptf and the rear wheel target pressure Ptr are determined to be equal values ​​(i.e., "Ptf=Ptr").

[0076] In step S170, the first controller EA controls the first actuator YA so that the supply pressure Pm (actual value) approaches and matches the target pressure Pt (target value). Specifically, the first electric motor MA is driven, and the braking fluid BF is discharged from the first fluid pump QA. As a result, a circulating flow KN of the braking fluid BF is generated in the reflux passage HK. Then, the pressure regulating valve UA is driven, and the circulating flow KN is throttled to generate a servo pressure Pu. In driving the first actuator YA, the pressure regulating valve UA is controlled by feedback control based on the supply pressure Pm so that the supply pressure Pm approaches the target pressure Pt.

[0077] ≪Pressure Regulation Control in the Event of Malfunction of the First Braking Unit SA≫ The pressure regulation control when the first braking unit SA does not function properly will be described. The pressure regulation control for coping with the malfunction of the first braking unit SA includes two types: complementary control and backup control.

[0078] When the determination of the applicability in step S140 is negative, the operation of the regeneration device KG is stopped in step S180. For example, "Fh = 0" or "FJ = 1" is transmitted from the first controller EA to the regeneration controller EG, and in the regeneration device KG, the power generation by the generator GN is stopped. As a result, the regenerative braking force Fg is set to "0", and the regenerative cooperative control is terminated.

[0079] In step S190, the first controller EA determines "whether or not to confirm the abnormality of the first braking unit SA". This determination is called "confirmation determination". In the confirmation determination of step S190, the abnormality of the first braking unit SA is confirmed for the first time when the duration Tj of the inapplicable state of the first braking unit SA continues for a predetermined time tk. Here, the predetermined time tk (also referred to as "confirmation determination time") is a value larger than the predetermined time tj (applicability determination time). Therefore, when the duration Tj is equal to or greater than the applicability determination time tj but less than the confirmation determination time tk (that is, in the case of "tj ≦ Tj < tk"), the abnormality of the first braking unit SA is suspected, but the abnormality has not been confirmed (that is, a specific state).

[0080] When the duration Tj of the malfunction state of the first braking unit SA is shorter than the predetermined determination time tk and the determination is negative (i.e., it is a specific state, in the case of "Tj < tk"), the process proceeds to step S200. On the other hand, when the duration Tj of the malfunction state of the first braking unit SA is equal to or longer than the determination time tk and the determination is positive (i.e., in the case of "Tj ≥ tk"), the process proceeds to step S220.

[0081] In step S190, when the determination is negative (i.e., a specific state), the determination flag FK (also referred to as the "confirmation flag") is determined to be "0". On the other hand, when the determination is positive (i.e., a confirmed state), the confirmation flag FK is determined to be "1". The "confirmation flag FK" is a control flag that indicates the confirmation of an abnormality in the first braking unit SA. In the confirmation flag FK, "0" represents the unconfirmed state of an abnormality, and "1" represents the confirmed state of an abnormality. The confirmation flag FK is transmitted from the first controller EA to the second controller EB via the communication bus BS.

[0082] ≪Processing of Complementary Control≫ "FJ = 1, FK = 0" indicates a specific state (a state where an abnormality in the first braking unit SA is suspected but not certain). In the specific state, prior to the backup control, in steps S200 and S210, complementary control is executed to complement the performance degradation of the first braking unit SA. That is, the processing in steps S200 and S210 by the second braking unit SB corresponds to the complementary control. In the specific state, both the first and second actuators YA and YB are driven.

[0083] In step S200, the target pressure Pt is acquired. Here, the target pressure Pt of the first controller EA and the target pressure Pt of the second controller EB are determined to be the same value. In step S200, since "Fh = 0, Fg = 0," the target frictional braking force Fn is equal to the target vehicle body position dynamics Fv (i.e., "Fn = Fv"). Therefore, the target frictional braking force Fn calculated according to the operation displacement Sp and the calculation map Zfv is converted into the target pressure Pt and determined based on the specifications of the brake device SX. For example, the target pressure Pt is calculated by the same method in each of the first and second controllers EA and EB based on the operation displacement Sp. In the "similar method," when the regenerative braking force Fg is not generated, the same calculation map Zfv is adopted to calculate the target pressure Pt. 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, as long as they are similar. Furthermore, the target pressure Pt calculated by the first controller EA may be acquired by the second controller EB via the communication bus BS, or the target pressure Pt calculated by the second controller EB may be acquired by the first controller EA via the communication bus BS.

[0084] If the improper state of the first brake unit SA affects the communication function, the signals of the first and second operation displacements Spa and Spb cannot be transmitted via the communication bus BS. In this case, the first controller EA cannot acquire the second operation displacement Spb, so the first operation displacement Spa is determined as the operation displacement Sp. Similarly, the second controller EB cannot acquire the first operation displacement Spa, so the second operation displacement Spb is determined as the operation displacement Sp. Since the first operation displacement Spa and the second operation displacement Spb are substantially equal, the operation displacement Sp used in the first controller EA and the operation displacement Sp used in the second controller EB are the same.

[0085] For the above reasons, in step S200, the target pressures Pt are acquired (or calculated) in both the first and second controllers EA and EB by one of the above methods. That is, the target pressures Pt of the first and second brake units SA and SB are calculated using the same or similar calculation maps as those used in the normal control when "Fh = 0". Therefore, in either case, the target pressures Pt of the first brake unit SA and the target pressures Pt of the second brake unit SB are substantially equal in value.

[0086] In step S210, the first actuator YA and the second actuator YB are both driven based on the target pressure Pt. Specifically, the first actuator YA is controlled by the first controller EA in the same manner as in step S170. Therefore, a description of the driving method of the first actuator YA will be omitted.

[0087] In step S210, a deviation hP between the target pressure Pt and the supply pressure Pm (referred to as the "hydraulic pressure deviation") is calculated based on the target pressure Pt and the supply pressure Pm. Specifically, the supply pressure Pm is subtracted from the target pressure Pt to determine the hydraulic pressure deviation hP (i.e., "hP = Pt - Pm"). Then, in step S210, the second actuator YB is controlled by the second controller EB based on the hydraulic pressure deviation hP. The "hydraulic pressure deviation hP" 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 target pressure Pt) and the actually generated supply pressure Pm. Therefore, when the supply pressure Pm is smaller than the target pressure Pt and an increase in the supply pressure Pm is necessary (i.e., when the hydraulic pressure deviation hP is greater than "0"), the hydraulic pressure deviation hP is a target value for compensating for the shortage of the supply pressure Pm and increasing the wheel pressure Pw, and is also a target value related to the pressure difference of the control valve UB.

[0088] When an increase in the supply pressure Pm is required, in step S210, the second electric motor MB and the control valve UB are driven. Specifically, the second electric motor MB is driven, and the braking fluid BF is discharged from the second fluid pump QB. As a result, a circulating flow KL of the braking fluid BF is generated in the communication path HS and the return path HL. And when the hydraulic pressure deviation hP is greater than or equal to the predetermined deviation hp, the supply pressure Pm is increased by the amount corresponding to the hydraulic pressure deviation hP by the control valve UB. Here, the "predetermined deviation hp" is a preset constant with a positive sign and is a predetermined value for setting the dead zone of the complementary control.

[0089] In the complementary control, the control valve UB is driven and the circulating flow KL is throttled, thereby generating a hydraulic pressure difference between the upstream side and the downstream side of the control valve UB. As a result, the adjustment pressure Pq, which is the upstream side hydraulic pressure, is increased from the supply pressure Pm, which is the downstream side hydraulic pressure. That is, in the drive of the second actuator YB, the control valve UB is controlled so that the differential pressure between the adjustment pressure Pq and the supply pressure Pm (that is, the hydraulic pressure "Pq - Pm") becomes the hydraulic pressure deviation hP. Since the adjustment pressure Pq is equal to the wheel pressure Pw, from the second actuator YB, a hydraulic pressure obtained by adding the actual hydraulic pressure corresponding to the hydraulic pressure deviation hP (target value) to the supply pressure Pm (actual value) is output as the wheel pressure Pw (actual value) (that is, "Pw = Pm + hP"). In the complementary control, when the supply pressure Pm is smaller than the target pressure Pt, the control valve UB is appropriately driven, so that the wheel pressure Pw is increased by the amount corresponding to the hydraulic pressure deviation hP from the supply pressure Pm.

[0090] On the other hand, in step S210, when the supply pressure Pm is greater than the target pressure Pt (specifically, when the hydraulic pressure deviation hP is less than the predetermined deviation hp), the complementary control is not executed and the second actuator YB is not driven. Therefore, the supply pressure Pm is output as the wheel pressure Pw from the second actuator YB. The complementary control is executed only when the supply pressure Pm is smaller than the target pressure Pt (that is, "Pm < Pt", and specifically, when the hydraulic pressure deviation hP is greater than or equal to the predetermined deviation hp).

[0091] ≪Backup control process≫ "FK=1 (FJ=1)" indicates a confirmed state (a state in which an abnormality in the first braking unit SA is certain). In the confirmed state, instead of complementary control, backup control is executed in steps S230 and S240 to substitute for the function of the first braking unit SA. In other words, the processing of steps S230 and S240 by the second braking unit SB corresponds to backup control. In addition, in the confirmed state, the operation of the first actuator YA is stopped and only the second actuator YB is driven.

[0092] In step S220, the first controller EA stops the supply of power to the first actuator YA. The first controller EA stops the supply of power to the inlet valve VA and the release valve VB, closes the inlet valve VA, and opens the release valve VB. As a result, the input unit NR selects the second mode in which the master pistons NM and NS and the brake operating member BP are displaced together. In the second mode, the wheel pressure Pw is adjusted in conjunction with the operation of the brake operating member BP. Since the input chamber Rn is separated from the stroke simulator SS and fluid-locked, the operating force Fp of the brake operating member BP is generated by the rigidity of the brake device SX and other components. Furthermore, the first controller EA stops the supply of power to the first electric motor MA and the pressure regulating valve UA, and sets the servo pressure Pu to "0." That is, in the first brake unit SA, the operation of the first actuator YA is stopped.

[0093] In step S230, the second controller EB calculates the assisting pressure Pc based on the supply pressure Pm. The "assisting pressure Pc" is a target value related to the pressure difference of the control valve UB for increasing the supply pressure Pm. Specifically, the wheel pressure Pw (actual value) is increased from the supply pressure Pm (actual value) by an amount equivalent to the assisting pressure Pc due to the assisting pressure Pc (target value).

[0094] In step S240, the second controller EB drives the second actuator YB based on the assisting pressure Pc. Specifically, the second electric motor MB is driven, and brake fluid BF is discharged from the second fluid pump QB. As a result, a circulating flow KL of brake fluid BF is generated in the communication path HS and the return path HL. Then, the control valve UB is driven, and the circulating flow KL is throttled, thereby generating a hydraulic pressure difference between the upstream and downstream sides of the control valve UB. As a result, the adjustment pressure Pq, which is the upstream hydraulic pressure, is increased from the supply pressure Pm, which is the downstream hydraulic pressure. In other words, when the second actuator YB is driven, the control valve UB is controlled so that the pressure difference between the adjustment pressure Pq and the supply pressure Pm (i.e., the hydraulic pressure "Pq - Pm") becomes equal to the assisting pressure Pc. Since the adjustment pressure Pq is equal to the wheel pressure Pw, the second actuator YB outputs a hydraulic pressure obtained by adding an actual hydraulic pressure corresponding to the assisting pressure Pc (target value) to the supply pressure Pm (actual value) as the wheel pressure Pw (actual value) (i.e., "Pw = Pm + Pc"). In other words, by driving the second actuator YB, the supply pressure Pm required to generate the wheel pressure Pw is reduced by an amount equivalent to the assisting pressure Pc. This reduces the operating force Fp of the brake operating member BP.

[0095] The brake control device SC is a brake-by-wire type device that can independently control the operation of the brake operating member BP (brake pedal) and the hydraulic pressure (wheel pressure Pw) of the wheel cylinder CW. Specifically, in the first brake unit SA, an input unit NR selects either a first mode (by-wire mode) in which the master piston NM and the brake operating member BP are displaced separately, or a second mode (manual mode) in which the master piston NM and the brake operating member BP are displaced integrally. As a result, in the first mode, the operation displacement Sp and the supply pressure Pm are independent, while in the second mode, the operation displacement Sp and the supply pressure Pm are linked. Since the supply pressure Pm is supplied as the wheel pressure Pw, selecting the first mode controls the wheel pressure Pw independently of the operation of the brake operating member BP.

[0096] In a normal state (for example, when the duration Tj of the improper state is less than a predetermined propriety determination time tj), the first mode is selected in the first brake unit SA, and normal control is executed. In normal control, a target pressure Pt is calculated based on the operation displacement Sp (for example, the average value of the first and second operation displacements Spa and Spb), and the supply pressure Pm is controlled to approach the target pressure Pt. In other words, in normal control, hydraulic pressure feedback control is executed based on the supply pressure Pm so that the output supply pressure Pm approaches and matches the target pressure Pt calculated using the operation displacement Sp as an input.

[0097] For example, the first brake unit SA is provided with a master cylinder CM, a master chamber Rm separated by a master piston NM inserted into the master cylinder CM, and a servo chamber Ru. The supply pressure Pm is controlled by increasing the servo pressure Pu supplied to the servo chamber Ru. In this configuration, the servo pressure Pu is feedback-controlled based on the supply pressure Pm so that the supply pressure Pm approaches and matches the target pressure Pt.

[0098] In a specific state (i.e., when the duration Tj of the improper state is equal to or longer than the propriety determination time tj and shorter than the final determination time tk), the first mode continues to be selected in the first brake unit SA. Then, both the first brake unit SA and the second brake unit SB are driven. The above-described normal control continues in the first brake unit SA. That is, in the first brake unit SA, feedback control based on the supply pressure Pm is executed so that the supply pressure Pm approaches and matches the target pressure Pt. This feedback control should make the supply pressure Pm approximately match the target pressure Pt. However, when the first brake unit SA malfunctions, the supply pressure Pm may not be generated sufficiently, and a situation may arise in which the target pressure Pt is not met. Therefore, complementary control is executed in the second brake unit SB to compensate for the drop in supply pressure Pm.

[0099] In the complementary control, the second brake unit SB increases the wheel pressure Pw based on the target pressure Pt and the deviation hP of the supply pressure Pm. Since the hydraulic pressure deviation hP in the first controller EA and the hydraulic pressure deviation hP in the second controller EB are equal, the hydraulic pressure deviation hP represents the decrease in the supply pressure Pm to be output from the first brake unit SA. Therefore, when the supply pressure Pm is smaller than the target pressure Pt (when "hP≧hp"), the supply pressure Pm is insufficient, so the wheel pressure Pw is increased by the amount of the shortage (i.e., the hydraulic pressure deviation hP) (i.e., "Pw=Pm+hP"). This appropriately compensates for the decrease in supply pressure Pm caused by a malfunction of the first brake unit SA. Note that even if the first brake unit SA malfunctions, if the supply pressure Pm is not decreased, "hP=0" and therefore the wheel pressure Pw is not actually increased by the complementary control.

[0100] In the determined state (i.e., when the duration Tj of the improper state is equal to or longer than a predetermined determination determination time tk), the first braking unit SA selects the second mode instead of the first mode. Then, the second braking unit SB executes backup control. In the backup control, the wheel pressure Pw is increased based on the supply pressure Pm. Specifically, the second braking unit SB calculates the assisting pressure Pc using the supply pressure Pm as an input, and increases the wheel pressure Pw based on the assisting pressure Pc. The assisting pressure Pc is a target value corresponding to the increase amount of the supply pressure Pm (the difference between the wheel pressure Pw and the supply pressure Pm) when increasing the supply pressure Pm to the wheel pressure Pw. Note that in the determined state, the first braking unit SA stops supplying power to the elements (UA, MA, etc.) that constitute the first actuator YA, and does not generate the servo pressure Pu. In other words, the servo pressure Pu is set to "0 (zero)," and the supply pressure Pm is generated solely by the driver's muscle force. However, in the backup control, the supply pressure Pm is input, increased, and output as the wheel pressure Pw, so the operating force Fp required to obtain the wheel pressure Pw is reduced.

[0101] One method for accelerating the start of backup control so that an abnormality in the brake control device can be compensated for early is to shorten the confirmation determination time tk (predetermined time). However, there are cases where the malfunction of the first brake unit SA is short-term and the first brake unit SA immediately returns to normal. In a brake-by-wire type brake control device SC, the method for generating the operation characteristics of the brake operating member BP differs between normal control and backup control. That is, in normal control under normal conditions, the first mode is selected, and the operating force Fp of the brake operating member BP is generated by the simulator SS. On the other hand, in backup control under abnormality confirmation conditions, the second mode is selected, and the operating force Fp of the brake operating member BP is generated by the rigidity of the brake device SX, etc. Therefore, the operation characteristics of normal control and backup control differ. Considering the discomfort felt by the driver and the short-term malfunction of the first brake unit SA, it is difficult to shorten the confirmation determination time tk.

[0102] The brake control device SC switches from normal control to backup control via complementary control so as to compensate for an abnormality in the first brake unit SA as soon as possible. Because the first mode is selected in complementary control, switching to the second mode is not performed in the case of a short-term malfunction. Furthermore, the complementary control compensates for the decrease in supply pressure Pm from the first brake unit SA only when the supply pressure Pm from the first brake unit SA is reduced. By providing complementary control before an abnormality in the first brake unit SA is confirmed, the performance degradation of the first brake unit SA is compensated for as soon as possible while suppressing discomfort felt by the driver. Furthermore, when an abnormality in the first brake unit SA is confirmed, the control switches from complementary control to backup control. After the abnormality is confirmed, even if the first brake unit SA loses its function, the second brake unit SB takes over the function of the first brake unit SA. In other words, the backup control reduces the operating force Fp of the brake operating member BP required to ensure the wheel pressure Pw, thereby ensuring appropriate vehicle deceleration.

[0103] In the braking control system SC, the supply pressure sensor PM is built into the second actuator YB. In normal control and complementary control, the supply pressure sensor PM is used to detect output information for hydraulic pressure feedback control. On the other hand, in backup control, the supply pressure sensor PM is used to detect input information for calculating the assisting pressure Pc (target value). By using one supply pressure sensor PM for each type of pressure regulation control, the entire system is simplified.

[0104] <Drive control of pressure regulating valve UA> The details of the drive control of the pressure regulating valve UA (particularly the processing of steps S170 and S210) will be described with reference to the block diagram of Figure 5. The drive control processing is executed by the first controller EA in normal control and complementary control. The pressure regulating valve UA adjusts the servo pressure Pu, and ultimately adjusts the supply pressure Pm. The drive control of the pressure regulating valve UA is composed of a command current calculation block IS, a hydraulic pressure deviation calculation block HP, a compensation current calculation block IH, and a first current feedback control block IFA.

[0105] The command current calculation block IS calculates the command current Isa based on the target pressure Pt and a preset calculation map Zis. The "command current Isa" is a target value for the supply current Ia (first supply current) of the pressure regulating valve UA required to achieve the target pressure Pt. According to the calculation map Zis, the command current Isa is determined to increase as the target pressure Pt increases. The command current calculation block IS corresponds to feedforward control based on the target pressure Pt.

[0106] The hydraulic pressure deviation calculation block HP calculates the deviation hP (hydraulic pressure deviation) between the target pressure Pt and the supply pressure Pm. Specifically, the hydraulic pressure deviation hP is determined by subtracting the supply pressure Pm from the target pressure Pt (i.e., "hP = Pt - Pm").

[0107] The compensation current calculation block IH calculates the compensation current Ih based on the hydraulic pressure deviation hP and a preset calculation map Zih. The command current Isa is calculated corresponding to the target pressure Pt, but an error may occur between the target pressure Pt and the supply pressure Pm. The "compensation current Ih" is used to compensate for (reduce) this error. The compensation current Ih is determined to increase as the hydraulic pressure deviation hP increases according to the calculation map Zih. Specifically, when the target pressure Pt is greater than the supply pressure Pm and the hydraulic pressure deviation hP has a positive sign, a positive compensation current Ih is determined to increase the command current Isa. On the other hand, when the target pressure Pt is smaller than the supply pressure Pm and the hydraulic pressure deviation hP has a negative sign, a negative compensation current Ih is determined to decrease the command current Isa. Here, a dead band is provided in the calculation map Zih. The compensation current calculation block IH corresponds to feedback control based on the supply pressure Pm.

[0108] The first target current Ita is calculated by adding the compensation current Ih to the command current Isa (i.e., "Ita = Isa + Ih"). The "first target current Ita" is the final target value of the current supplied to the pressure regulating valve UA. In other words, the first target current Ita is determined as the sum of the feedforward term Isa and the feedback term Ih. Therefore, the drive control of the pressure regulating valve UA is composed of feedforward control (processing of the command current calculation block IS) and feedback control (processing of the compensation current calculation block IH) in terms of hydraulic pressure.

[0109] In the first current feedback control block IFA, based on the first target current Ita (target value) and the first supply current Ia (actual value), the first drive signal Ua is calculated so that the first supply current Ia approaches and matches the first target current Ita. Here, the first supply current Ia is detected by the first supply current sensor IA provided in the first drive circuit DRa. In the first current feedback control block IFA, if "Ita > Ia", the first drive signal Ua is determined so that the first supply current Ia increases. On the other hand, if "Ita < Ia", the first drive signal Ua is determined so that the first supply current Ia decreases. That is, in the first current feedback control block IFA, current-related feedback control is executed. Therefore, in the drive control of the pressure regulating valve UA, in addition to the feedback control related to hydraulic pressure, feedback control related to current is provided.

[0110] <Drive control of control valve UB> Referring to the block diagram of FIG. 6, the details of the drive control of the control valve UB in the complementary control and the backup control (particularly, the processing of steps S210, S230, and S240) will be described. The processing of the drive control in the complementary control and the backup control is executed by the second controller EB.

[0111] ≪In the case of complementary control≫ The drive control in the complementary control will be described. Before the specific state is determined (i.e., when "FJ = 0"), the operation of the second actuator YB is stopped, and the second electric motor MB and the control valve UB are not powered. When the determination of the applicability of step S140 is negative and the specific state is determined (i.e., the switching point from "FJ = 0" to "FJ = 1"), in the second actuator YB, the second electric motor MB and the control valve UB are driven, and the complementary control is started. The drive control of the control valve UB in the complementary control is composed of a hydraulic pressure deviation acquisition block HQ, a second target current calculation block IBT, and a second current feedback control block IFB.

[0112] The hydraulic pressure deviation acquisition block HQ acquires the deviation hP between the target pressure Pt and the supply pressure Pm. For example, the hydraulic pressure deviation hP is calculated by the first controller EA (particularly the hydraulic pressure deviation calculation block HP) and input to the second controller EB via the communication bus BS. Alternatively, the hydraulic pressure deviation hP may be calculated by the second controller EB using the same method as the first controller EA (i.e., calculation using a similar calculation map) based on the operation displacement Sp (or the target pressure Pt) transmitted from the first controller EA. In either case, the hydraulic pressure deviation acquisition block HQ acquires the hydraulic pressure deviation hP similar to the hydraulic pressure deviation hP used by the first controller EA in the second controller EB. In complementary control, the hydraulic pressure deviation hP is treated as a target value for the differential pressure between the supply pressure Pm and the regulated pressure Pq (i.e., the wheel pressure Pw).

[0113] When the supply pressure Pm is smaller than the target pressure Pt (more specifically, when the hydraulic pressure deviation hP is equal to or greater than the predetermined deviation hp and exceeds the dead band of the complementary control), the second target current calculation block IBT calculates a second target current Itb based on the hydraulic pressure deviation hP and a preset calculation map Zib. The "second target current Itb" is a target value for the supply current Ib (second supply current) of the control valve UB required to generate a differential pressure equivalent to the hydraulic pressure deviation hP by the control valve UB. According to the calculation map Zib, the second target current Itb is determined so as to increase as the hydraulic pressure deviation hP increases. The processing of the second target current calculation block IBT is the same as that of the command current calculation block IS described above (i.e., feedforward control based on hydraulic pressure).

[0114] In the second current feedback control block IFB, based on the second target current Itb (target value) and the second supply current Ib (actual value), the second drive signal Ub is calculated so that the second supply current Ib approaches and matches the second target current Itb. Here, the second supply current Ib is detected by the second supply current sensor IB provided in the second drive circuit DRb. In the second current feedback control block IFB, if "Itb > Ib", the second drive signal Ub is determined so that the second supply current Ib increases. On the other hand, if "Itb < Ib", the second drive signal Ub is determined so that the second supply current Ib decreases. In the second current feedback control block IFB, feedback control related to current similar to the above-described first current feedback control block IFA is executed.

[0115] Although the drive control of the control valve UB described above is open-loop control, it may be configured as closed-loop control including feedback control related to hydraulic pressure. In this configuration, a pressure regulating sensor (not shown) is provided below the control valve UB so as to detect the regulated pressure Pq. Then, in the same manner as the above-described compensation current calculation block IH, the second target current Itb is finely adjusted based on the deviation between the supply pressure Pm and the regulated pressure Pq.

[0116] ≪In the case of backup control≫ The drive control in backup control will be described. Before the determined state is determined (that is, when "FK = 0"), both the first and second actuators YA and YB are driven. When the determination in step S190 is affirmed and the abnormality of the first brake unit SA is determined (that is, at the time of switching from "FK = 0" to "FK = 1"), the operation of the first actuator YA is stopped. The power supply to the pilot valve VA and the relief valve VB is stopped, and the operation mode of the input unit NR is switched from the first mode to the second mode. The power supply to the pressure regulating valve UA is stopped, and the servo pressure Pu is set to "0". At this time, in the second brake unit SB, the control is switched from the complementary control to the backup control. The drive control of the control valve UB in backup control is constituted by the boost pressure calculation block PC, the second target current calculation block IBT, and the second current feedback control block IFB.

[0117] The assisting pressure calculation block PC calculates the assisting pressure Pc based on the supply pressure Pm and a preset calculation map Zpc. The "assisting pressure Pc" is a target value for increasing the wheel pressure Pw from the supply pressure Pm. More specifically, it is a target value for the differential pressure between the supply pressure Pm and the adjustment pressure Pq (i.e., the wheel pressure Pw). In accordance with the calculation map Zpc, the assisting pressure Pc is determined to increase as the supply pressure Pm increases. Increasing the supply pressure Pm by the assisting pressure Pc reduces the operating force Fp of the brake operating member BP.

[0118] The second target current calculation block IBT calculates a second target current Itb based on the assisting pressure Pc (target value) and a preset calculation map Zib. The "second target current Itb" is a target value for the supply current Ib (second supply current) to the control valve UB required to achieve the assisting pressure Pc. The second target current Itb is determined in accordance with the calculation map Zib so as to increase as the assisting pressure Pc increases. Note that the processing in the second current feedback control block IFB is the same as in the case of complementary control, and therefore a description thereof will be omitted. In addition, in a configuration where an adjustment pressure sensor is provided, hydraulic pressure feedback control may be performed by controlling the drive of the control valve UB even in backup control.

[0119] In the above processing example, the assisting pressure calculation block PC calculates the assisting pressure Pc (a target value of the hydraulic pressure increase amount from the supply pressure Pm in backup control) based on the supply pressure Pm and the calculation map Zpc. Alternatively, the assisting pressure Pc may be calculated based on the hydraulic pressure deviation hP. For example, the assisting pressure calculation block PC determines the hydraulic pressure deviation hP as the assisting pressure Pc. In the determined state, the regenerative device KG and the first actuator YA are stopped, and the input section NR of the first brake unit SA selects the second mode. In the second mode, the relationship between the operation displacement Sp and the supply pressure Pm is uniquely determined. Since the target pressure Pt is calculated based on the operation displacement Sp, the relationship between the supply pressure Pm and the hydraulic pressure deviation hP corresponds to the calculation map Zpc. Therefore, "calculating the assisting pressure Pc based on the supply pressure Pm and the calculation map Zpc" is equivalent to "calculating the assisting pressure Pc based on the hydraulic pressure deviation hP." In either process, the assisting pressure calculation block PC calculates the assisting pressure Pc based on the supply pressure Pm.

[0120] In at least one of the complementary control and the backup control, the front wheel pressure Pwf may be adjusted to be greater than the rear wheel pressure Pwr to improve vehicle stability. Specifically, the front and rear wheel supply currents Ibf and Ibr are individually adjusted so that the front wheel supply current Ibf is greater than the rear wheel supply current Ibr.

[0121] <Configuration of two-system pressure adjustment> In the above-described embodiment, when the first brake unit SA is in a normal state, the operation of the second actuator YB is stopped and only the first actuator YA is driven. In this case, the front and rear wheel supply pressures Pmf and Pmr (=Pm) are equal, and therefore the front and rear wheel pressures Pwf and Pwr (=Pw) ​​are equal. This type of pressure regulation control is referred to as "single-system pressure regulation." In the single-system pressure regulation configuration, the second actuator YB is not driven during normal control, so the target pressure Ptm (referred to as "target supply pressure") corresponding to the supply pressure Pm and the target pressure Ptw (referred to as "target wheel pressure") corresponding to the wheel pressure Pw are equal (i.e., "Pt=Ptm=Ptw").

[0122] Instead of the single-system pressure regulation configuration, when the first brake unit SA is operating normally, the second actuator YB may be driven in addition to the first actuator YA to separately regulate the front and rear wheel pressures Pwf and Pwr. Specifically, the first actuator YA supplies the same supply pressures Pmf and Pmr (=Pm) to the second actuator YB. The second actuator YB then regulates the wheel pressure of one system corresponding to a wheel equipped with a regenerative device KG (e.g., the front wheel pressure Pwf) to be lower than the wheel pressure of the other system corresponding to a wheel not equipped with a regenerative device KG (e.g., the rear wheel pressure Pwr). Pressure regulation control in which the front and rear wheel pressures Pwf and Pwr are independently and individually regulated by driving the second actuator YB is referred to as "dual-system pressure regulation." In regenerative cooperative control, dual-system pressure regulation improves regenerative efficiency and optimizes braking force distribution between the front and rear wheels compared to single-system pressure regulation.

[0123] In a dual-system pressure regulation configuration, the second actuator YB is driven even in a normal state, so the target pressure Ptm (target supply pressure) corresponding to the supply pressure Pm differs from the target pressure Ptw (target wheel pressure) corresponding to the wheel pressure Pw. For this reason, the first actuator YA executes feedforward control and feedback control so that the supply pressure Pm (= Pmf, Pmr) approaches and matches the target supply pressure Ptm. Then, the second actuator YB executes feedforward control based on pressure differences hPf, hPr (referred to as "front and rear wheel target pressure differences") between the front and rear wheel target wheel pressures Ptwf, Ptwr and the target supply pressure Ptm (or actual supply pressure Pm).

[0124] Complementary control and backup control are also applied in the dual-system pressure regulation configuration. When an abnormality in the first brake unit SA is suspected (i.e., when the suitability flag FJ is switched to "1"), the regenerative cooperative control is terminated and the generation of the regenerative braking force Fg is stopped. The first controller EA continues normal control, and the second controller EB starts complementary control. Note that the input unit NR continues to select the first mode. In complementary control, the second actuator YB increases the wheel pressure Pw (actual value) from the supply pressure Pm (actual value) by an amount equivalent to the hydraulic pressure deviation hP (target value) based on the hydraulic pressure deviation hP, so as to compensate for the decrease in the supply pressure Pm output from the first brake unit SA. When an abnormal state in the first brake unit SA is confirmed (i.e., when the confirmation flag FK is switched to "1"), backup control is started. In the backup control, the second actuator YB increases the wheel pressure Pw (actual value) from the supply pressure Pm (actual value) by an amount equivalent to the assisting pressure Pc (target value) so that the driver's operating force Fp is reduced. Even in the dual-system pressure regulation configuration, compensation for an abnormality in the first brake unit SA is performed early by complementary control, just as in the single-system pressure regulation configuration.

[0125] <Other embodiments> Other embodiments will be described below, which also provide the same effects as those described above (early compensation for device abnormalities, simplification of device configuration, etc.).

[0126] In the above-described embodiment, the target values ​​of various braking forces (Fv, Fx, Fh, Fn, etc.) are calculated in terms of the longitudinal force 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 the longitudinal force acting on the vehicle JV to the deceleration of the vehicle JV are equivalent. Therefore, the target pressure Pt is calculated based on state quantities related to the force from the longitudinal force acting on the vehicle JV to the deceleration of the vehicle JV.

[0127] In the above-described embodiment, a front-rear type brake system is used as the two-system brake system. Alternatively, a diagonal type (also called "X type") brake system may be used as the two-system brake system. In this configuration, one of the two master chambers Pm is connected to the left front wheel cylinder and the right rear wheel cylinder, and the other of the two master chambers Pm is connected to the right front wheel cylinder and the left rear wheel cylinder. However, in a configuration in which dual-system pressure regulation is used, the brake system is limited to the front-rear type.

[0128] In the above-described embodiment, the supply pressure sensor PM is built into the second actuator YB and connected to the second controller EB. The first controller EA acquires the supply pressure Pm through the communication bus BS. Conversely, the supply pressure sensor PM may be built into the first actuator YA and connected to the first controller EA. In this configuration, the second controller EB acquires the supply pressure Pm through the communication bus BS when performing complementary control and backup control. However, the former configuration is more advantageous than the latter configuration in terms of functional distribution and fail-safe. For example, if an improper state of the first brake unit SA leads to a communication abnormality, the second brake unit SB (particularly the second controller EB) cannot acquire the supply pressure Pm in the latter configuration. Therefore, complementary control and backup control based on the supply pressure Pm cannot be performed. Furthermore, although independent wheel control, such as antilock brake control and anti-skid control, in the second brake unit SB is performed based on the supply pressure Pm, independent wheel control cannot be performed if the supply pressure Pm cannot be acquired. Therefore, the former configuration is the simplest configuration that can deal with the improper state of the first brake unit SA.

[0129] In the above-described embodiment, the pressure regulating unit CA is exemplified as one that regulates the servo pressure Pu by throttling the circulating flow KN of the brake fluid BF discharged by the fluid pump QA with the pressure regulating valve UA (a so-called reflux type configuration). Alternatively, the pressure regulating unit CA may regulate the pressure accumulated in an accumulator with a linear solenoid valve (a so-called accumulator type configuration). Furthermore, the servo pressure Pu may be adjusted by increasing or decreasing the volume inside a cylinder with a piston directly driven by an electric motor (a so-called electric cylinder type configuration). In either configuration, the pressure regulating unit CA feeds back the supply pressure Pm as an output signal, and electrically adjusts the hydraulic pressure Pu (servo pressure) in the servo chamber Ru.

[0130] In the above-described embodiment, a tandem type master cylinder CM is exemplified. However, a single type master cylinder CM may be employed instead. In this configuration, the secondary master piston NS is omitted. One master chamber Rm is connected to four wheel cylinders CW. In this configuration, the master cylinder CM outputs the same supply pressures Pmf and Pmr (=Pm).

[0131] In a configuration in which a single-type master cylinder CM is used, the master chamber Rm may be connected to the front wheel cylinder CWf, and the servo pressure Pu may be directly supplied from the pressure adjusting unit CA to the rear wheel cylinder CWr. In this configuration, the master cylinder CM outputs a front wheel supply pressure Pmf. Meanwhile, the pressure adjusting unit CA outputs the servo pressure Pu as a rear wheel supply pressure Pmr.

[0132] In the above-described embodiment, the operation of the first actuator YA is stopped during backup control. Alternatively, during backup control, the components included in the pressure regulating unit CA and used to increase the supply pressure Pm (i.e., the first electric motor MA and the pressure regulating valve UA) may be continuously driven with their output reduced (lowered) compared to normal control. This allows a slight servo pressure Pu to be generated during backup control, thereby reducing the operating force Fp. Alternatively, power supply to the pressure regulating valve UA may be completely stopped, but power supply to the first electric motor MA may be continued. In this case, during backup control, the first electric motor MA continues to be driven at the low rotation speed nx. Here, the "low rotation speed nx" is a predetermined value (constant) that is significantly smaller than the rotation speed of the first electric motor MA during normal control (a predetermined rotation speed sufficient to ensure the startup responsiveness of the electric motor MA). By continuing to drive the first electric motor MA, normal control can be quickly resumed when the normal state is restored. In the backup control, power supply to the first electric motor MA and the like continues, but power supply to the inlet valve VA and the release valve VB is stopped, and the operation mode of the input unit NR is set to the second mode.

[0133] 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, it is possible to perform a conversion calculation between the supply pressure Pm and the servo pressure Pu based on the ratio of the servo area ru to the master area rm (i.e., conversion based on "Pm·rm=Pu·ru").

[0134] In the above-described embodiment, the first brake unit SA outputs the 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 servo pressure Pu supplied from the pressure adjustment unit CA is transmitted as the supply pressure Pm via the master piston NM. Alternatively, the apply unit AP and the pressure adjustment unit CA may be arranged in parallel. Specifically, 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, the connection between the pressure adjustment unit CA and the second actuator YB is selected, and in the second mode, the connection between the apply unit AP and the second actuator YB is selected. For example, this selection is achieved by an on-off solenoid valve (referred to as a "switching valve"). In the first mode of this configuration, the servo pressure Pu generated in the pressure adjustment unit CA is directly output as the supply pressure Pm without passing through the apply unit AP. In this mode, 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 supply pressure Pm. In this mode, the apply unit AP is disconnected from the simulator SS.

[0135] In the above-described embodiment, the brake control device SC is applied to a vehicle JV that does not have a regenerative device KG on the rear wheels WHr. The brake control device SC may also be applied to a vehicle JV that has a regenerative device KG on the rear wheels WHr.

[0136] <Summary of the embodiment> The brake control device SC is a brake-by-wire type device that can independently adjust the operation displacement Sp (operation displacement) of the brake operating member BP and the hydraulic pressure Pw (wheel pressure) of the wheel cylinder CW.

[0137] The brake control device SC includes a "first brake unit SA (first unit) that outputs a supply pressure Pm in response to an operation displacement Sp of a brake operating member BP," a "second brake unit SB (second unit) that is provided between the first brake unit SA and the wheel cylinder CW and that increases the supply pressure Pm and outputs a wheel pressure Pw to the wheel cylinder CW," and a "communication bus BS that transmits signals between the first brake unit SA and the second brake unit SB." Here, the first brake unit SA selects either a first mode in which the operation displacement Sp and the supply pressure Pm are independent, or a second mode in which the operation displacement Sp and the supply pressure Pm are linked.

[0138] In the brake control device SC, when the first brake unit SA is normal (in the normal state), the first brake unit SA selects the first mode and increases the wheel pressure Pw by increasing the supply pressure Pm (i.e., normal control is executed). When it is determined that the first brake unit SA is abnormal (in the determined state), the first brake unit SA selects the second mode and the second brake unit SB increases the wheel pressure Pw from the supply pressure Pm (i.e., backup control is executed). In addition, when it is not in the determined state but an abnormality in the first brake unit SA is suspected (in the specific state), the first brake unit SA selects the first mode and continues operation in the normal state. When the second brake unit SB increases the wheel pressure Pw from the supply pressure Pm (i.e., complementary control is executed).

[0139] The brake control device SC is equipped with an "operation displacement sensor SP (operation amount sensor) that detects an operation displacement Sp (operation amount)" and a "supply pressure sensor PM that detects a supply pressure Pm." In a normal state, the first brake unit SA calculates a target pressure Pt based on the operation displacement Sp, and increases the supply pressure Pm so that it approaches the target pressure Pt. In a specific state, the second brake unit SB increases the wheel pressure Pw from the supply pressure Pm by the amount of the target pressure Pt and a deviation hP (hydraulic pressure deviation) from the supply pressure Pm. The hydraulic pressure deviation hP in the specific state is determined as the same value in the first and second brake units (particularly, the first and second controllers EA and EB).

[0140] In addition to normal control, the brake control device SC executes backup control to replace the normal control function. The backup control is initiated when an abnormality in the first brake unit SA is confirmed (i.e., when it is determined that the first brake unit SA is definitely abnormal), so it takes a certain amount of time before it starts. In addition, since the backup control eliminates the brake-by-wire state, the operation characteristics of the brake operating member BP change from those of the normal control.

[0141] In the brake control device SC, complementary control is executed while transitioning from normal control to backup control. Complementary control is initiated when an abnormality in the first brake unit SA is suspected, although an abnormality in the first brake unit SA has not been confirmed. Complementary control continues operation of the first brake unit SA in normal control. In the first brake unit SA, feedback control is performed so that the supply pressure Pm matches the target pressure Pt, so the supply pressure Pm should ideally match the target pressure Pt. However, there are cases where the supply pressure Pm is not generated sufficiently due to a malfunction of the first brake unit SA. To deal with such cases, in the second brake unit SB, the wheel pressure Pw (=Pq) is increased from the supply pressure Pm by the amount of the hydraulic pressure deviation hP, based on the deviation hP between the target pressure Pt and the supply pressure Pm. This is based on the fact that the hydraulic pressure deviation hP represents the deviation between the supply pressure that should be output (i.e., the target pressure Pt) if the brake control device SC is normal and the actual supply pressure Pm (i.e., the shortfall in the supply pressure Pm).

[0142] In the brake control device SC, the abnormality of the first brake unit SA is quickly compensated for by complementary control. Furthermore, in complementary control, the first mode is selected and the brake-by-wire state is maintained. Therefore, if the abnormality of the first brake unit SA is short-term (for example, a drop in the power supply voltage Vd of the first electric motor MA) and is resolved immediately, the operation characteristics of the brake operating member BP are not changed. The complementary control compensates for the performance degradation of the first brake unit SA while minimizing discomfort to the driver.

[0143] In the brake control device SC, when an abnormality in the first brake unit SA is confirmed (FK=1), the output of the pressure adjusting unit CA included in the first brake unit SA and which generates the supply pressure Pm may be reduced, rather than being completely stopped, compared to when the first brake unit SA is normal. In the abnormal state, the first brake unit SA selects the second mode, so that the supply pressure Pm is generated by the driver's muscle force. Even when an abnormality is confirmed, if the pressure adjusting unit CA can be driven, the output of the pressure adjusting unit CA is reduced and its drive is continued. For example, the first electric motor MA, which generates the supply pressure Pm, is driven at a low rotation speed nx. This allows the first electric motor MA to be quickly started up when the abnormality is resolved. In addition, the driver's operating force Fp is slightly assisted. [Explanation of symbols]

[0144] 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, UA...Pressure adjustment valve, UB...Control valve , MA, MB...first and second electric motors, QA, QB...first and second fluid pumps, VA...inlet valve, VB...release valve, SP...operation displacement sensor (operation amount sensor), PM...supply pressure sensor, Sp...operation displacement (operation amount), Pm...supply pressure, Pu...servo pressure, Pq...adjusted pressure, Pw...wheel pressure, Pt...target pressure (target value corresponding to Pm), Pc...assisting pressure (target value corresponding to the differential pressure between Pw and Pm), hP...hydraulic pressure deviation (hydraulic pressure difference between Pt and Pm), FJ...suitability flag (determination result of step S140), FK...confirmation flag (determination result of step S190).

Claims

1. a first unit that outputs a supply pressure in accordance with an operation amount of a brake operating member; a second unit provided between the first unit and a wheel cylinder, the second unit increasing the supply pressure and outputting a wheel pressure to the wheel cylinder; a communication bus for transmitting signals between the first unit and the second unit; A braking control device for a vehicle comprising: the first unit selects either a first mode in which the manipulated variable and the supply pressure are independent of each other, or a second mode in which the manipulated variable and the supply pressure are linked to each other; In a normal state where the first unit is normal, the first unit selects the first mode, and of the first unit and the second unit, only the first unit operates to increase the supply pressure and increase the wheel pressure; In a determined state in which it is determined that the first unit is abnormal, the first unit selects the second mode, and the second unit increases the wheel pressure from the supply pressure, A vehicle braking control device, wherein when the vehicle is not in the determined state but in a specific state in which an abnormality in the first unit is suspected, the first unit selects the first mode and continues operation in the normal state, and the second unit increases the wheel pressure from the supply pressure.

2. 2. A vehicle braking control device according to claim 1, an operation amount sensor for detecting the operation amount; a supply pressure sensor for detecting the supply pressure; Equipped with In the normal state, the first unit calculates a target pressure based on the manipulated variable and increases the supply pressure so as to approach the target pressure, In the specific state, the second unit increases the wheel pressure by an amount corresponding to a deviation between the target pressure and the supply pressure.

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