Brake control device for a vehicle

Abstract

A brake control device (SC) includes a master cylinder having a master chamber divided by a master piston, and a first pressure regulating unit having a servo chamber located on an opposite side of the master chamber with respect to the master piston, and supplying a servo pressure to the servo chamber, thereby generating a master pressure in the master chamber. The first pressure regulating unit acquires the master pressure and the servo pressure, and judges a bottoming of the master piston according to a comparison of the master pressure and the servo pressure. For example, the first pressure regulating unit performs the comparison according to a pressure receiving area of the servo chamber and a pressure receiving area of the master chamber. In a structure in which the pressure receiving area of the servo chamber and the pressure receiving area of the master chamber are equal, the first pressure regulating unit judges an occurrence of the bottoming when a difference between the servo pressure and the master pressure is greater than or equal to a predetermined pressure.

Description

Technical Field

[0001] This disclosure relates to a braking control device for a vehicle. Background Technology

[0002] Patent Document 1 describes a hydraulic braking system comprising a cylinder assembly having a front chamber at the front and a rear chamber at the rear, wherein the presence or absence of fluid leakage in the braking system is detected based on the hydraulic pressure in the rear chamber. Specifically, if the value ΔP, which is the difference between the target rear hydraulic pressure and the actual rear hydraulic pressure, is greater than a first anomaly judgment threshold ΔPth for a period of time T1 or more, and then the actual rear hydraulic pressure Ps increases at a slope greater than or equal to a set slope, and the value ΔP is less than a recovery judgment threshold δp, it is determined that the pressurizing piston has bottomed out due to leakage of working fluid in the front chamber.

[0003] Patent Document 2 describes a method for determining whether the main pistons 12c and 12d are in a bottoming-out state based on the reaction hydraulic pressure detected by the reaction hydraulic pressure detection unit 25b and the main hydraulic pressure detected by the main hydraulic pressure detection unit Y. Specifically, in Patent Document 2, when the stroke is less than a predetermined value (for example, a value equivalent to the stroke at which piston 13a2 of stroke simulator 13a bottoms out), bottoming-out determination is made based on the increment of the stroke per unit time and the increment of the main hydraulic pressure per unit time. Conversely, when the stroke is greater than or equal to the predetermined value, bottoming-out determination is made based on the increment of the reaction hydraulic pressure per unit time and the increment of the main hydraulic pressure per unit time.

[0004] In Patent Document 1, the presence or absence of fluid leakage in the braking system is detected based on the difference between the control target (i.e., the hydraulic pressure following the target) and the control result (i.e., the actual hydraulic pressure following the target). In Patent Document 2, since the stroke and reaction hydraulic pressure are equivalent to the inputs in the brake pedal, these state quantities are used to determine the control target in hydraulic control. In contrast, the main hydraulic pressure is the result of pressure regulation control. Therefore, in Patent Document 2, similarly to Patent Document 1, the occurrence of bottoming out (i.e., the bottoming-out state) is determined based on the relationship between the control target and the control result.

[0005] However, reliable judgment based on the relationship between the control objective and the control result requires a certain amount of time. Specifically, due to errors and time delays in control, in order to reliably identify the cause of the difference between the control objective and the control result as bottoming out, it is necessary to wait until a judgment threshold that would not occur if bottoming out were not to be reached, or additional computational processing is required. For example, in Patent Document 1, a bottoming-out state is determined when the state of the estimated rear force minus the actual rear force being greater than or equal to a first anomaly judgment threshold continues for more than a first anomaly judgment time, and then becomes less than or equal to a first recovery judgment threshold. In addition, in Patent Document 2, a bottoming-out state is determined when the slope ratio of the increment of the main hydraulic pressure per unit time relative to the increment of the reaction hydraulic pressure per unit time is calculated and is less than or equal to a predetermined ratio. Therefore, it is desirable to be able to quickly and reliably determine the bottoming-out state with simple processing.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2012 / 172702

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-058465 Summary of the Invention

[0010] The technical problem to be solved by the present invention

[0011] The purpose of this invention is to provide a vehicle braking control device that can quickly and reliably determine when the master piston has bottomed out.

[0012] Technical means for solving technical problems

[0013] The braking control device SC according to the present invention includes a "master cylinder (CM) having a main chamber (Rm) divided by a master piston (NP, NS)" and a "first pressure regulating unit (YA) having a servo chamber (Ru) located on the opposite side of the main piston (NP, NS) from the main chamber (Rm) and supplying servo pressure (Pu) to the servo chamber (Ru) to generate a main pressure (Pm) in the main chamber (Rm)". The first pressure regulating unit (YA) acquires the main pressure (Pm) and the servo pressure (Pu), and determines whether the master piston (NP, NS) has bottomed out based on a comparison of the main pressure (Pm) and the servo pressure (Pu). For example, the first pressure regulating unit (YA) performs the comparison based on the pressure-bearing area (ru) of the servo chamber (Ru) and the pressure-bearing area (rm) of the main chamber (Rm). In a structure where the pressure-bearing area (ru) of the servo chamber (Ru) is equal to the pressure-bearing area (rm) of the main chamber (Rm), if the difference between the servo pressure (Pu) and the main pressure (Pm) (hP = Pu - Pm) is greater than or equal to the specified pressure (px), the first pressure regulating unit (YA) determines that the bottoming out has occurred.

[0014] In the braking control device SC, when the main piston does not bottom out, there is a predetermined relationship between the servo pressure Pu and the main pressure Pm (for example, when set to "ru = rm", the servo pressure Pu and the main pressure Pm are the same). However, when the main piston bottoms out, this predetermined relationship does not hold. Therefore, the bottoming-out state of the main piston is determined by comparing the servo pressure Pu and the main pressure Pm. Based on the above structure, bottoming-out determination is not performed by comparing the control target and the control result, thus eliminating the need for time required to avoid errors and delays in pressure regulation control. Therefore, a rapid and reliable bottoming-out determination can be achieved through simple calculations. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the overall structure of a vehicle JV equipped with a braking control device SC.

[0016] Figure 2 This is a schematic diagram illustrating a first structural example of the first voltage regulating unit YA.

[0017] Figure 3 This is a schematic diagram illustrating the structure of the second voltage regulating unit YB.

[0018] Figure 4 This is a flowchart used to illustrate voltage regulation control.

[0019] Figure 5 This is a flowchart used to illustrate the bottoming-out process.

[0020] Figure 6 It is a timing diagram used to illustrate the actions involved in determining when the market has bottomed out.

[0021] Figure 7 It is a timing diagram used to illustrate the actions of compensation control based on the bottoming-out judgment result.

[0022] Figure 8 This is a schematic diagram illustrating a second structural example of the first voltage regulating unit YA. Detailed Implementation

[0023] Hereinafter, with reference to the accompanying drawings, embodiments of the vehicle braking control device SC according to the present invention will be described.

[0024] <Illustrations and other reference numerals for constituent elements>

[0025] In the following description, components, signals, values, etc., assigned the same reference numerals such as "CW" refer to elements that have the same function. The subscripts "f" and "r" assigned to the end of various reference numerals related to wheels are general reference numerals indicating whether they pertain to an element of the front or rear wheel. Specifically, "f" indicates "elements related to the front wheel," and "r" indicates "elements related to the rear wheel." For example, in wheel cylinder CW, it is labeled "front wheel cylinder CWf, rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" may be omitted. In cases where these are omitted, the reference numerals indicate their general term.

[0026] Furthermore, in the connecting path HS, based on the wheel cylinder CW, the side furthest from it is referred to as the "upper part," and the side closest to it is referred to as the "lower part." For example, in the movement of brake fluid BF based on fluid pump QB, it is described as "Brake fluid BF is drawn in from the upper part of pressure regulating valve UB and discharged to the lower part of pressure regulating valve UB." Additionally, the first and second pressure regulating units YA and YB are also referred to as "upper and lower pressure regulating units YA and YB." The first and second pressure regulating units YA and YB are composed of an actuator (fluid unit) and a controller. That is, the first pressure regulating unit YA is composed of a combination of the first fluid unit HA and the first controller ECA, and the second pressure regulating unit YB is composed of a combination of the second fluid unit HB and the second controller ECB. Here, the first and second fluid units HA and HB are also referred to as "upper and lower fluid units HA and HB." Similarly, the first and second controllers ECA and ECB are also referred to as "upper and lower controllers ECA and ECB." Furthermore, the adjustment (increase, etc.) of the wheel pressure Pw based on the first pressure regulating unit YA is referred to as "upper pressure regulation", and the adjustment (increase, etc.) of the wheel pressure Pw based on the second pressure regulating unit YB is referred to as "lower pressure regulation".

[0027] <Vehicle equipped with brake control device SC>

[0028] Reference Figure 1The schematic diagram illustrates the overall structure of the vehicle JV equipped with the braking control device SC, which is relevant to this invention.

[0029] The vehicle (JV) includes a braking control unit (BP), a steering control unit (SH), and various sensors (BA, etc.). The braking control unit (e.g., brake pedal) BP is operated by the driver to decelerate the vehicle (JV). The steering control unit (e.g., steering wheel) SH is operated by the driver to turn the vehicle (JV).

[0030] The vehicle JV is equipped with various sensors listed below.

[0031] - A brake operation amount sensor BA detects the operation amount (brake operation amount) of the brake operation component BP and a steering operation amount sensor SA detects the operation amount (steering operation amount, e.g., steering angle) of the steering operation component SH.

[0032] - The wheel speed sensor VW detects the rotational speed (wheel speed) of wheel WH.

[0033] - For a vehicle JV (specifically, the vehicle body), a yaw rate sensor YR detects yaw rate Yr, a front-rear acceleration sensor GX detects front-rear acceleration Gx, and a lateral acceleration sensor GY detects lateral acceleration Gy.

[0034] The vehicle JV is equipped with a braking device SX and a braking control device SC. In the braking control device SC, the braking system, which is a two-system unit, adopts a so-called front and rear type (also known as "Type II").

[0035] The braking system SX (=SXf, SXr) is configured to include a rotating component (e.g., a brake disc) KT and a brake caliper CP. The rotating component KT is fixed to the vehicle's wheel WH, and the brake caliper CP is provided to clamp the rotating component KT. A wheel cylinder CW is provided in the brake caliper CP. Pressurized brake fluid BF is supplied to the wheel cylinder CW from the brake control device SC. Here, the hydraulic pressure of the wheel cylinder CW is referred to as "wheel pressure Pw". In the braking system SX, the wheel pressure Pw presses the friction component (e.g., a brake pad) MS against the rotating component KT. Since the rotating component KT and the wheel WH are fixed together in a rotating manner, the friction force generated at this time generates a braking torque Tb in the wheel WH (resulting in a braking force Fb).

[0036] The brake control unit SC adjusts the actual wheel pressure Pw based on the operation amount Ba of the brake operating component BP. Specifically, brake fluid BF, pressurized by the brake control unit SC, is supplied to the brake unit SX (specifically, the wheel cylinder CW) via the front and rear wheel connecting circuits HSf and HSR. The brake control unit SC consists of a master cylinder CM and first and second pressure regulating units YA and YB. The first pressure regulating unit YA includes a first fluid unit HA and a first controller ECA. The second pressure regulating unit YB includes a second fluid unit HB and a second controller ECB. Furthermore, the first controller ECA and the second controller ECB are connected via a communication bus BS to share signals (detected values, calculated values, etc.).

[0037] The master cylinder CM, first and second pressure regulating units YA and YB (especially the first and second fluid units HA and HB), wheel cylinder CW, etc., are connected via connecting lines HS, input lines HN, pressure reducing lines HG, return lines HK and HL, servo lines HU, etc. These are the fluid paths for the movement of brake fluid BF. Fluid piping, flow paths within fluid units HA and HB, hoses, etc., are equivalent to the fluid paths (HS, etc.).

[0038] The brake control unit SC generates wheel pressure Pw based on the braking operation amount Ba, causing the vehicle JV to decelerate. That is, the brake control unit SC acts as a service brake (also known as a "service brake"). Furthermore, the brake control unit SC performs vehicle stability control (ESC) by independently and individually adjusting the hydraulic pressure Pw of each wheel cylinder CW to improve the stability of the vehicle JV. Additionally, the brake control unit SC performs brake force distribution control (EBD control) by limiting the hydraulic pressure Pwr (rear wheel pressure) of the rear wheel cylinder CWr to ensure the stability of the vehicle JV during braking.

[0039] The service brake function of the braking control device SC is implemented through a first pressure regulating unit YA and a second pressure regulating unit YB. In the service brake, a braking operation quantity Ba is input to the first controller ECA, and a request pressure Ps is calculated. In the first controller ECA, based on the request pressure Ps, a target pressure Pt related to the first pressure regulating unit YA and a target differential pressure Qt related to the second pressure regulating unit YB (specifically, the pressure regulating valve UB) are calculated. Furthermore, the first controller ECA controls the first fluid unit HA based on the target pressure Pt. Additionally, the target differential pressure Qt is transmitted to the second controller ECB via the communication bus BS, and the second controller ECB controls the second fluid unit HB based on the target differential pressure Qt.

[0040] On the other hand, the second pressure regulating unit YB realizes the function of controlling the brakes (vehicle stability control, brake force distribution control, etc.) of the brake control device SC. Wheel speed Vw, steering input (steering angle) Sa, hydraulic pressure Pm of the master cylinder CM, yaw rate Yr, front-rear acceleration Gx, and lateral acceleration Gy are input to the second controller ECB. Furthermore, the second controller ECB controls the second fluid unit HB to improve the directional stability of the vehicle JV.

[0041] The hydraulic pressure Pm of the master cylinder CM is sent to the first controller ECA via the communication bus BS to determine the bottoming-out state of the first and second master pistons NP and NS. The bottoming-out state of the master piston inserted into the master cylinder CM is identified by the first controller ECA. Furthermore, as a result of the bottoming-out state determination, a determination flag FL is sent to the second controller ECB via the communication bus BS. Details of the above processing will be explained later.

[0042] <First structural example of the first voltage regulating unit YA>

[0043] Reference Figure 2 A schematic diagram is provided to illustrate a first structural example of the first pressure regulating unit (upper pressure regulating unit) YA. The first pressure regulating unit YA is a pressure source for increasing the hydraulic (wheel pressure) Pw of the four wheel cylinders CW. In this example, the first pressure regulating unit YA is integrated with the master cylinder CM. Furthermore, as two braking systems, a front-and-rear configuration is adopted. The first pressure regulating unit YA consists of a first fluid unit HA and a first controller ECA that controls the first fluid unit HA.

[0044] The first fluid unit HA is integrated with the master reservoir RV, master cylinder CM, first and second master pistons NP and NS, and first and second master springs DP and DS. The first fluid unit HA includes the input cylinder CN, input piston NN, input spring DN, input valve VN, open valve VR, stroke simulator SS, and analog pressure sensor PB.

[0045] The master reservoir (also known as the "atmospheric reservoir") RV is a tank for the working fluid, containing brake fluid BF. The master reservoir RV is connected to the master cylinder CM (specifically, the front wheel and rear wheel master chambers Rmf and Rmr).

[0046] The master cylinder CM is a cylinder component with a bottom. The first and second master pistons NP and NS are inserted inside the master cylinder CM, which is sealed by a sealing component SL and divided into front wheel and rear wheel main chambers Rmf and Rmr, respectively. Specifically, the front wheel main chamber Rmf is defined by the inner circumferential surface of the master cylinder CM, the end face of the first master piston NP, and one end face of the second master piston NS. The rear wheel main chamber Rmr is defined by the inner circumferential surface of the master cylinder CM, the bottom surface of the master cylinder CM, and the other end face of the second master piston NS. The master cylinder CM is a so-called tandem type. Here, the hydraulic pressure Pmf of the front wheel main chamber Rmf is referred to as the "front wheel main pressure," and the hydraulic pressure Pmr of the rear wheel main chamber Rmr is referred to as the "rear wheel main pressure." Therefore, as a general term, the hydraulic pressure Pm of the main chamber Rm is referred to as the "main pressure."

[0047] First and second master springs DP and DS are installed in the main chambers Rmf and Rmr of the front and rear wheels, respectively. The first and second master pistons NP and NS are pressed in the reverse direction Hb (the direction in which the volume of the main chamber Rm increases, opposite to the forward direction Ha) via the first and second master springs DP and DS. The main chambers Rmf and Rmr (=Rm) of the front and rear wheels are connected to the wheel cylinders CWf and CWr (=CW) via the front and rear wheel connecting circuits HSf and HSR (=HS) and the second pressure regulating unit YB (specifically, the second fluid unit HB), respectively.

[0048] A flange is provided in the first master piston NP. Further, for use with the first pressure regulating unit YA, this flange divides the interior of the master cylinder CM into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru of the first pressure regulating unit YA is configured to be positioned opposite the front wheel master chamber Rmf, across the first master piston NP, in a manner that generates hydraulic pressure Pmf and Pmr in the front and rear wheel master chambers Rmf and Rmr, respectively. Additionally, the rear chamber Ro of the first pressure regulating unit YA is sandwiched between the front wheel master chamber Rmf and the servo chamber Ru, and is positioned between them to absorb brake fluid BF discharged from the input chamber Rn. The servo chamber Ru and the rear chamber Ro are also sealed by a sealing member SL, as described above.

[0049] The input cylinder CN is fixed to the master cylinder CM. The input piston NN is inserted into the interior of the input cylinder CN and sealed by the sealing component SL, thereby forming the input chamber Rn. The input piston NN is mechanically connected to the brake operating component BP via a U-shaped clip (U-link). A flange is provided on the input piston NN. An input spring DN is provided between this flange and the mounting surface of the input cylinder CN relative to the master cylinder CM. The input piston NN is pressed in the backward direction Hb by the input spring DN.

[0050] The input chamber Rn, servo chamber Ru, rear chamber Ro, and front and rear wheel main chambers Rmf and Rmr are hydraulic chambers (hydraulic cavities). These hydraulic chambers are filled with brake fluid BF and sealed by the sealing component SL. The volume of each hydraulic chamber varies according to the movement of the input piston NN and the first and second master pistons NP and NS. In the configuration of the hydraulic chambers, along the central axis Jm of the master cylinder CM, starting from the side closest to the brake operating component BP, the order is: input chamber Rn, servo chamber Ru, rear chamber Ro, front wheel main chamber Rmf, and rear wheel main chamber Rmr.

[0051] The input chamber Rn and the rear chamber Ro are connected via the input path HN. An input valve VN is installed on the input path HN. The input path HN connects to the main reservoir RV via the open valve VR between the rear chamber Ro and the input valve VN. Both the input valve VN and the open valve VR are solenoid valves (also called "on / off valves") with two positions: an open position (connected state) and a closed position (off state). The input valve VN is a normally closed solenoid valve, and the open valve VR is a normally open solenoid valve. Furthermore, the input valve VN and the open valve VR are driven (controlled) by drive signals Vn and Vr from the first controller ECA.

[0052] A stroke simulator (also simply called a "simulator") SS is connected to the rear chamber Ro. The simulator SS generates the operating force Fp of the brake operating component BP. Inside the simulator SS are a piston and an elastic body (e.g., a compression spring). When brake fluid BF flows into the simulator SS, the brake fluid BF presses against the piston. Because the elastic body applies a force to the piston in the direction that prevents the flow of brake fluid BF, the operating force Fp of the brake operating component BP is generated. In other words, the simulator SS establishes the operating characteristics of the brake operating component BP (the relationship between the operating displacement Sp and the operating force Fp).

[0053] The analog pressure sensor PB is configured to detect the hydraulic pressure Pb (referred to as "analog pressure") of the simulator SS. The analog pressure sensor PB is one of the brake operation quantity sensors BA mentioned above. As the brake operation quantity Ba, the analog pressure Pb is input to the first controller ECA. Furthermore, the analog pressure Pb is equal to the hydraulic pressure Pn (input pressure) of the input chamber Rn and the hydraulic pressure Po (rear pressure) of the rear chamber Ro.

[0054] In the first pressure regulating unit YA, the brake operation quantity sensor BA, in addition to the analog pressure sensor PB, includes an operation displacement sensor SP that detects the operation displacement Sp of the brake operating component BP, and / or an operation force sensor FP that detects the operation force Fp of the brake operating component BP. That is, the brake operation quantity sensor BA employs at least one of the analog pressure sensor PB, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP (pedal force sensor). Therefore, the brake operation quantity Ba is at least one of the analog pressure Pb, the operation displacement Sp, and the operation force Fp.

[0055] Furthermore, the first fluid unit HA includes a pressure accumulator pump QA, a pressure accumulator motor MA, an accumulator AC, an accumulator pressure sensor PC, a pressure cylinder CK, a pressure piston NK, a pressure boosting valve UZ, a pressure reducing valve UG, and a servo pressure sensor PU, to supply servo pressure Pu to the servo chamber Ru, thereby generating main pressure Pm.

[0056] The accumulator AC is pressurized by a accumulator fluid pump QA. The accumulator fluid pump QA (also called the "first fluid pump") is driven by an accumulator motor MA (also called the "first motor"), drawing brake fluid BF from the main reservoir RV. The brake fluid BF discharged from the fluid pump QA is stored in the accumulator AC. The accumulator AC contains brake fluid BF pressurized to the accumulator pressure Pc. An accumulator pressure sensor PC is installed to detect the accumulator pressure Pc. The accumulator motor MA (first motor) is controlled to maintain the accumulator pressure Pc within a specified range.

[0057] The pressurizing piston NK is inserted into the pressurizing cylinder CK. The pressurizing piston NK divides the interior of the pressurizing cylinder CK into three hydraulic chambers: Rp (pilot chamber), Rv (annular chamber), and Rk (pressurizing chamber). The pilot chamber Rp and the pressurizing chamber Rk are positioned across the pressurizing piston NK. That is, the pilot chamber Rp is located on the opposite side of the pressurizing chamber Rk within the pressurizing cylinder CK relative to the pressurizing piston NK. Hydraulic pressure Pp (referred to as "pilot pressure"), regulated by the pressure boosting valve UZ and the pressure reducing valve UG, is supplied to the pilot chamber Rp. Here, the accumulator pressure Pc is set as the initial pressure, and the pilot pressure Pp is adjusted.

[0058] An annular recess (neck) is provided on the outer periphery of the pressurizing piston NK. This annular recess and the inner periphery of the pressurizing cylinder CK form an annular chamber Rv. Furthermore, a valve body Vv (e.g., a spool valve) is formed on the outer periphery of the pressurizing piston NK. Brake fluid BF, pressurized from the accumulator AC to the accumulator pressure Pc, is supplied to this valve body Vv. The accumulator pressure Pc is regulated by the valve body Vv and introduced into the annular chamber Rv. The annular chamber Rv communicates with the pressurizing chamber Rk via a through-hole provided in the pressurizing piston NK. Therefore, the hydraulic pressure in the annular chamber Rv is the same as the hydraulic pressure in the pressurizing chamber Rk. This hydraulic pressure is referred to as "servo pressure Pu".

[0059] Specifically, when the hydraulic pressure Pp (pilot pressure) through the pilot chamber Rp moves the pressurizing piston NK, the opening of the valve body Vv changes. Furthermore, through the valve body Vv of the pressurizing piston NK, brake fluid BF is supplied from the accumulator AC to match the pilot pressure Pp with the servo pressure Pu (hydraulic pressure in the annular chamber Rv and the pressurizing chamber Rk). In other words, the high-pressure accumulator pressure Pc is throttled by the valve body Vv and adjusted to the servo pressure Pu. A servo pressure sensor PU is installed to detect the actual servo pressure Pu. The pressurizing chamber Rk and the servo chamber Ru are connected via the servo circuit (fluid circuit) HU, thus brake fluid BF adjusted to the servo pressure Pu is supplied to the servo chamber Ru.

[0060] Along the central axis Jm of the master cylinder CM (which is also the central axis of the first and second master pistons NP and NS), the servo chamber Ru is positioned on the opposite side of the front and rear wheel master chambers Rmf and Rmr (=Rm), relative to the first and second master pistons NP and NS. Therefore, the thrust Fm (called "main thrust") generated by the hydraulic pressure Pmf and Pmr (front and rear wheel main pressure) within the front and rear wheel master chambers Rmf and Rmr is opposed to the thrust Fu (called "servo thrust") generated by the servo pressure Pu along the central axis Jm. Under normal conditions (i.e., before bottoming out), the main thrust Fm and the servo thrust Fu reach static equilibrium. In other words, by adjusting (increasing or decreasing) the servo pressure Pu, the main pressure Pm (=Pmf and Pmr) is adjusted (increased or decreased).

[0061] The relationship between servo pressure Pu and main pressure Pm is determined by the relationship between the pressure-bearing area ru of the servo chamber Ru (the area of ​​the flange of the first main piston NP, also known as the "servo area") and the pressure-bearing area rm of the main chamber Rm (the area of ​​the end face of the second main piston NS, also known as the "main area"). Statically, the servo thrust Fu is equal to the main thrust Fm, therefore the relationship "Pu·ru = Pm·rm" holds. Thus, the main pressure Pm output is the servo pressure Pu multiplied by the value of "servo area ru relative to main area rm".

[0062] For example, in the first pressure regulating unit YA, the pressure-bearing area ru (servo area) of the servo chamber Ru is set to be equal to the pressure-bearing area rm (main area) of the main chamber Rm. In this case, the main pressures Pmf and Pmr of the front and rear wheels are usually equal to the servo pressure Pu. That is, since "ru = rm", therefore "Pm = Pu".

[0063] Operation of the First Voltage Regulating Unit YA

[0064] In the first pressure regulating unit YA, the first fluid unit HA is controlled by the first controller ECA. The braking operation quantity Ba, accumulator pressure Pc, servo pressure Pu, and main pressure Pm are input to the first controller ECA. Here, the main pressure Pm is sent from the second controller ECB via the communication bus BS and input to the first controller ECA. In the first controller ECA, based on these signals, the drive signals Vn, Vr, Uz, Ug, and MA of the input valve VN, the opening valve VR, and the pressure boosting valve UZ are calculated. Furthermore, based on the drive signals “Vn, Vr, Uz, Ug, Ma”, the solenoid valves “VN, VR, UZ, UG” constituting the first pressure regulating unit YA and the accumulator motor MA are controlled (driven). Additionally, as described later, the first controller ECA calculates the requested pressure Ps, the target pressure Pt, and the bottoming-out state judgment result (judgment flag) FL, which are then sent to the second controller ECB via the communication bus BS.

[0065] When not braking (i.e., without operation of the braking component BP), the pistons NN, NP, and NS are pressed backward in the direction Hb by the springs DN, DP, and DS, returning them to their initial positions (the positions moved most backward in the direction Hb). In this state, the front and rear wheel main chambers Rmf and Rm are connected to the main reservoir RV, and the front and rear wheel main pressures Pmf and Pmr are "0 (atmospheric pressure)". Furthermore, at the initial positions of each piston, the input piston NN and the first main piston NP have a gap Ks.

[0066] In the non-braking state, the booster valve UZ is closed and the pressure reducing valve UG is open, thus the pilot chamber Rp is connected to the main reservoir RV, and the pilot pressure Pp is "0 (atmospheric pressure)". Furthermore, the pressure piston NK is pressed against the bottom of the pressure cylinder CK by the compression spring DK, closing the valve body Vv (spool valve). Since the pressure chamber Rk is connected to the main reservoir RV, the servo pressure Pu is also "0". Further, in the non-braking state, the input valve VN and the release valve VR are open, and the rear chamber Ro and the input chamber Rn are connected to the main reservoir RV, so the internal pressures Po and Pn of these hydraulic chambers are also "0". That is, in the non-braking state, it is a state of "Pmf = Pmr = Pp = Pu = Po = Pn = 0".

[0067] During braking (i.e., when the brake operating component BP is operated), the input valve VN is opened, and the release valve VR is closed. That is, the input chamber Rn is connected to the rear chamber Ro, while the connection between the rear chamber Ro and the main reservoir RV is severed, resulting in a non-connected state. As the operating amount Ba of the brake operating component BP increases, the input piston NN moves in the forward direction Ha, discharging brake fluid BF from the input chamber Rn. Since this brake fluid BF is absorbed into the stroke simulator SS, the hydraulic pressure Pn (input pressure) in the input chamber Rn and the hydraulic pressure Po (rear pressure) in the rear chamber Ro increase, generating an operating force Fp in the brake operating component BP corresponding to the operating displacement Sp.

[0068] During braking, based on the braking operation amount Ba (at least one of simulated pressure Pb, operating displacement Sp, and operating force Fp), the booster valve UZ and the pressure reducing valve UG are controlled, increasing the hydraulic pressure Pp (pilot pressure) in the pilot chamber Rp. As the pilot pressure Pp increases, the valve body Vv is opened, increasing the hydraulic pressure Pu (servo pressure) in the annular chamber Rv and the pressurized chamber Rk. The servo pressure Pu is supplied to the servo chamber Ru via the servo circuit HU. The first master piston NP is pressed and moved in the forward direction Ha by the servo thrust Fu corresponding to the servo pressure Pu. Accompanying the movement of the first master piston NP in the forward direction Ha, the main pressures Pmf and Pmr (=Pm) of the front and rear wheels increase. Furthermore, brake fluid BF, adjusted from the main pressure Pm by the first pressure regulating unit YA, is supplied to the second pressure regulating unit YB, ultimately increasing the hydraulic pressure Pw in the wheel cylinder CW.

[0069] The braking control device SC is a so-called brake-by-wire type. Therefore, in the case of an electric vehicle (e.g., an electric car, a hybrid vehicle), regenerative coordinated control can be performed. In the first fluid unit HA of the first pressure regulating unit YA, the input piston NN and the first main piston NP have a gap Ks. By controlling the servo pressure Pu, the relative positional relationship between the input piston NN and the first, second, and third main pistons NP and NS can be arbitrarily adjusted within this gap range. For example, if only the braking force based on regenerative braking is required, it is set to "Pu = 0", and the main pressure Pm is kept at "0". No braking force based on the friction between the rotating component KT and the friction component MS is generated; only the regenerative braking force of the drive motor, which operates as a generator, is generated as the braking force Fb.

[0070] <Second Voltage Regulating Unit YB>

[0071] Reference Figure 3A schematic diagram is provided to illustrate the structure of the second pressure regulating unit (lower pressure regulating unit) YB. The second pressure regulating unit YB is located in the connecting circuit HS (fluid circuit) between the first pressure regulating unit YA and the wheel cylinder CW. The brake control device SC can adjust (increase, maintain, or decrease) the main pressure Pm through the second pressure regulating unit YB. The second pressure regulating unit YB consists of a second fluid unit HB and a second controller ECB that controls the second fluid unit HB.

[0072] The second fluid unit HB includes a pressure regulating valve UB, a main pressure sensor PM, a return fluid pump QB (also known as the "second fluid pump"), a return motor MB (also known as the "second motor"), a pressure regulating reservoir RC, an inlet valve UI, and an outlet valve VO.

[0073] Front and rear wheel pressure regulating valves UBf and UBR (=UB) are located in the front and rear wheel connecting circuits HSf and HSR (=HS). The pressure regulating valve UB (solenoid valve) is a normally open linear valve (also known as a "differential pressure valve" or "proportional valve"). The upper part of the pressure regulating valve UB (the part in the connecting circuit HS near the first pressure regulating unit YA side) and the lower part of the pressure regulating valve UB (the part in the connecting circuit HS near the wheel cylinder CW side) are connected through the front and rear wheel return flow circuits HKf and HKr (=HK). Front and rear wheel return flow fluid pumps QBf and QBr (=QB) and front and rear wheel pressure regulating reservoirs RCf and RCr (=RC) are installed in the return flow circuit HK. The return flow fluid pump QB (second fluid pump) is driven by the return flow motor MB (second motor).

[0074] The front and rear wheel main pressure sensors PMf and PMr (=PM) are configured to detect the main pressures Pmf and Pmr (=Pm) of the front and rear wheels, respectively. The main pressure Pm (hydraulic pressure of the main chamber Rm) is supplied through the first pressure regulating unit YA (specifically, the servo pressure Pu). The main pressure sensor PM is located above the pressure regulating valve UB (between the master cylinder CM and the pressure regulating valve UB).

[0075] When the second motor MB is driven to rotate, brake fluid BF is drawn from the upper part of the pressure regulating valve UB through the second fluid pump QB and discharged to the lower part of the pressure regulating valve UB. This creates a circulating flow KN of brake fluid BF in the connecting circuit HS and the return circuit HK (i.e., a flow of circulating brake fluid BF, with front and rear wheel return flows KNf and KNr). When the circulating flow KN of brake fluid BF is throttled through the pressure regulating valve UB, the hydraulic pressure Pq (called the "adjusting pressure") at the lower part of the pressure regulating valve UB increases from the main pressure Pm at the upper part of the pressure regulating valve UB due to the orifice effect. In other words, the front and rear wheel pressures Pwf and Pwr (=Pw) can be increased and adjusted from the front and rear wheel main pressures Pmf and Pmr through the second pressure regulating unit YB.

[0076] Inside the second pressure regulating unit YB, the front wheel and rear wheel connecting circuits HSf and HSR are each branched into two circuits and connected to the front wheel and rear wheel cylinders CWf and CWr, respectively. Furthermore, an inlet valve UI and an outlet valve VO are provided for each wheel cylinder CW. Similar to the pressure regulating valve UB, the inlet valve UI (solenoid valve) is a normally open linear valve. However, the opening direction of the pressure regulating valve UB differs from that of the inlet valve UI. Specifically, since the pressure regulating valve UB opens in accordance with the flow of brake fluid BF from the wheel cylinder CW side (lower side) to the master cylinder CM side (upper side), in pressure regulation based on the pressure regulating valve UB, the adjusting pressure Pq is greater than or equal to the master pressure Pm (i.e., "Pq ≥ Pm"). On the other hand, the inlet valve UI opens in response to the flow from the pressure regulating valve UB side (upper side) to the wheel cylinder CW side (lower side), so in the pressure regulation based on the inlet valve UI, the wheel pressure Pw is less than or equal to the regulating pressure Pq (i.e., "Pq≥Pw").

[0077] The inlet valve UI is located on the branched connecting line HS (i.e., near the wheel cylinder CW side of the branch of the connecting line HS). The connecting line HS is connected to the pressure regulating reservoir RC via the pressure reducing line HG at the lower part of the inlet valve UI (the part of the connecting line HS near the wheel cylinder CW side). Furthermore, the outlet valve VO, which is a normally closed on / off valve, is arranged in the pressure reducing line HG.

[0078] The inlet valve UI and outlet valve VO are controlled individually to adjust the wheel pressure Pw for each wheel cylinder CW. To decrease wheel pressure Pw, inlet valve UI is closed and outlet valve VO is opened. The flow of brake fluid BF into wheel cylinder CW is prevented, and brake fluid BF in wheel cylinder CW flows out to the pressure regulating reservoir RC, thus decreasing wheel pressure Pw. To increase wheel pressure Pw, inlet valve UI is opened and outlet valve VO is closed. The flow of brake fluid BF into the pressure regulating reservoir RC is prevented, and the regulating pressure Pq from pressure regulating valve UB is supplied to wheel cylinder CW, thus increasing wheel pressure Pw. To maintain wheel pressure Pw, inlet valve UI and outlet valve VO are closed together. Wheel cylinder CW is fluidly sealed, thus maintaining a constant wheel pressure Pw.

[0079] In the second pressure regulating unit YB, the second fluid unit HB is controlled by the second controller ECB. Here, the second controller ECB is connected to the first controller ECA via a communication bus BS to share information. Wheel speed Vw, main pressure Pm, steering amount Sa, yaw rate Yr, front-rear acceleration Gx, and lateral acceleration Gy are input to the second controller ECB. Additionally, the requested pressure Ps, target pressure Pt, and judgment flag FL calculated by the first controller ECA are input to the second controller ECB via the communication bus BS. In the second controller ECB, based on these signals, the drive signals Ub for the pressure regulating valve UB, Ui for the inlet valve UI, Vo for the outlet valve VO, and Mb for the second motor MB are calculated. Furthermore, based on these drive signals (Ub, etc.), the solenoid valves "UB, UI, VO" and the second motor MB constituting the second fluid unit HB are controlled (driven).

[0080] <Processing of Voltage Regulation Control>

[0081] Reference Figure 4 The flowchart below illustrates an example of pressure regulation control in the braking control device SC. "Pressure regulation control" refers to the control that electrically generates and adjusts wheel pressure Pw by using the first pressure regulating unit YA and the second pressure regulating unit YB as pressure sources. The pressure regulation control algorithm is programmed into the microprocessors within the first and second controllers ECA and ECB. Furthermore, in the following description, it is assumed that the servo area ru is equal to the main area rm. In a structure where the servo area ru is different from the main area rm, the relationship between the requested pressure Ps (the target value of wheel pressure Pw) and the target pressure Pt (the target value of servo pressure Pu) changes according to the ratio of the servo area ru to the main area rm.

[0082] In step S110, various signals, including braking operation quantity Ba and servo pressure Pu, are read. Here, the braking operation quantity Ba (a general term for state quantities representing the degree of operation of the braking operation component BP) is detected by the braking operation quantity sensor BA. Additionally, the servo pressure Pu is detected by the servo pressure sensor PU.

[0083] In step S120, the requested pressure Ps (variable) is calculated based on the operating amount Ba of the brake operating component BP. The requested pressure Ps is a target value for the hydraulic pressure Pw (actual value) for all wheel cylinders CW corresponding to the vehicle deceleration requested by the driver, calculated to be equal in the front wheel braking system BKf to the rear wheel braking system BKr. Specifically, as shown in block X120, the requested pressure Ps is determined based on the brake operating amount Ba (variable) and a pre-set calculation diagram Zps. Specifically, when the brake operating amount Ba is between "0" and the clearance amount bo, the requested pressure Ps is calculated as "0". Furthermore, when the brake operating amount Ba is greater than or equal to the clearance amount bo, the requested pressure Ps increases from "0" as the brake operating amount Ba increases. That is, in the case of "Ba≥bo", according to the calculation diagram Zps, the larger the brake operating amount Ba, the larger the requested pressure Ps. Here, the clearance amount bo is a pre-set value (constant), equivalent to the clearance of the brake operating component BP.

[0084] In step S130, based on the requested pressure Ps, it is determined whether "the requested pressure Ps is less than the area judgment pressure ps (referred to as "low hydraulic pressure area judgment," or simply "area judgment")." If the requested pressure Ps is less than the area judgment pressure ps, and the area judgment is affirmative, the process proceeds to step S140. On the other hand, if the requested pressure Ps is greater than or equal to the area judgment pressure ps, and the area judgment is negative, the process proceeds to step S160. Here, the area judgment pressure ps is a threshold value used to determine the low hydraulic pressure area, and it is a pre-set value (constant).

[0085] In step S140, the target pressure Pt and target differential pressure Qt are calculated for the region (referred to as the "low hydraulic pressure region") where the requested pressure Ps (resulting in wheel pressure Pw) is relatively small. The target pressure Pt (=Ptf, Ptr) is the target value of the hydraulic pressure to be achieved by the first pressure regulating unit YA. The front wheel target pressure Ptf and the rear wheel target pressure Ptr are determined to be equal (i.e., "Ptf=Ptr"). Furthermore, the target differential pressure Qt (=Qtf, Qtr) is the target value of the differential pressure (the hydraulic difference between the main pressure Pm and wheel pressure Pw) to be achieved by the second pressure regulating unit YB. The front wheel target differential pressure Qtf and the rear wheel target differential pressure Qtr are determined to be equal (i.e., "Qtf=Qtr"). In other words, in step S140, the requested pressure Ps is decomposed into the target pressure Pt and the target differential pressure Qt. Therefore, the requested pressure Ps is equal to the sum of the target pressure Pt and the target differential pressure Qt, "Pt+Qt". In addition, since the calculation is "Ptf = Ptr, Qtf = Qtr", the wheel pressure Pw is controlled to be equal in all wheel cylinders CW.

[0086] In step S140, the target pressure Pt is determined to be "0", and the target differential pressure Qt is determined to be the value obtained by subtracting the target pressure Pt from the requested pressure Ps (i.e., "Pt = 0, Qt = Ps - Pt = Ps"). In other words, in the low hydraulic pressure region where the wheel pressure Pw is small, the first pressure regulating unit YA is not used in the adjustment of the wheel pressure Pw; only the second pressure regulating unit YB is used. This is to leverage the high pressure regulation accuracy based on the second pressure regulating unit YB in the low hydraulic pressure region.

[0087] In step S150, the first and second pressure regulating units YA and YB are controlled according to the target pressure Pt and the target differential pressure Qt. Specifically, since "Pt = 0", the booster valve UZ and the pressure reducing valve UG are not energized, and the pilot pressure Pp remains "0". As a result, the valve body Vv remains in a closed state, and therefore the servo pressure Pu is set to "0". Therefore, the main pressure Pm, which is the output from the first pressure regulating unit YA (in particular, the first fluid unit HA), is set to "0".

[0088] On the other hand, in step S150, the second pressure regulating unit YB (specifically, the second fluid unit HB) is controlled according to the target differential pressure Qt (=Ps). Specifically, firstly, the motor MB is driven. As a result, a circulating flow KN of brake fluid is generated by the fluid pump QB. Moreover, the pressure regulating valve UB is energized according to the target differential pressure Qt. In detail, the relationship between the supply current Ib of the pressure regulating valve UB and the target differential pressure Qt (the so-called IP characteristic) is preset as a calculation diagram Zip, so the current Ib flows through the pressure regulating valve UB according to the target differential pressure Qt and this calculation diagram Zip. Since the opening amount of the pressure regulating valve UB is reduced according to the supply current Ib, the circulating flow KN is throttled, and the actual differential pressure mQ (the actual difference between the main pressure Pm and the regulating pressure Pq) increases. Furthermore, in the calculation diagram Zip, it is set that the larger the target differential pressure Qt is, the larger the supply current Ib is.

[0089] In step S160, the target pressure Pt (=Ptf, Ptr) and target differential pressure Qt (=Qtf, Qtr) are calculated when the requested pressure Ps (result, wheel pressure Pw) is out of the low hydraulic pressure region. In step S160, similarly to step S140, the requested pressure Ps is achieved through the target pressure Pt and the target differential pressure Qt, thus the relationship "Ps = Pt + Qt" holds. In step S160, the target pressure Pt is determined as "the value of the region judgment pressure ps minus the requested pressure Ps", and the target differential pressure Qt is determined as the value of the requested pressure Ps minus the target pressure Pt (i.e., "Pt = Ps - ps, Qt = Ps - Pt = ps"). In the hydraulic region where the wheel pressure Pw is relatively large (the region exceeding the aforementioned low hydraulic pressure region), the first and second pressure regulating units YA and YB are used together during the adjustment of the wheel pressure Pw.

[0090] In step S170, the first and second pressure regulating units YA and YB are controlled based on the target pressure Pt and the target differential pressure Qt. Specifically, in the first pressure regulating unit YA (especially the first fluid unit HA), the booster valve UZ and the pressure reducing valve UG are controlled based on the target pressure Pt and the servo pressure Pu, and upper pressure regulation is performed to make the servo pressure Pu approach and match the target pressure Pt. In detail, when "Pu < Pt", the servo pressure Pu is increased by at least one of increasing the opening amount of the booster valve UZ and decreasing the opening amount of the pressure reducing valve UG. On the other hand, when "Pu > Pt", the servo pressure Pu is decreased by at least one of decreasing the opening amount of the booster valve UZ and increasing the opening amount of the pressure reducing valve UG.

[0091] Further, in step S170, in the second pressure regulating unit YB (specifically, the second fluid unit HB), the pressure regulating valve UB is controlled and lower pressure is adjusted according to the target differential pressure Qt (=ps). Similar to step S150, the second motor MB is driven to form a circulating flow KN of brake fluid BF, including the second fluid pump QB and the pressure regulating valve UB. Moreover, according to the target differential pressure Qt, the pressure regulating valve UB is energized to adjust the actual differential pressure mQ.

[0092] The second pressure regulating unit YB was originally a general-purpose unit used for vehicle stability control, but it offers excellent pressure regulation accuracy for wheel pressure Pw. In the brake control device SC, this feature is applied to the service brake. Specifically, in the region where wheel pressure Pw is relatively small ("Ps < ps"), upper pressure regulation based on the first pressure regulating unit YA is not used; instead, wheel pressure Pw is adjusted solely by lower pressure regulation based on the second pressure regulating unit YB. On the other hand, supplying high pressure through the second pressure regulating unit YB requires increasing the speed of the second electric motor MB, which is disadvantageous from the perspective of operating noise. Therefore, in the region where wheel pressure Pw is relatively large ("Ps ≥ ps"), wheel pressure Pw is adjusted using both upper and lower pressure regulation. By using the division between upper and lower pressure regulation, quiet and high-precision pressure regulation control is achieved in the brake control device SC.

[0093] <Bottoming Out Processing>

[0094] Reference Figure 5The flowchart illustrates the bottoming-out process of the first and second master pistons NP and NS. "Bottoming-out" refers to the state where the first and second master pistons NP and NS reach their movable limit in the forward direction Ha, also known as "master bottoming-out." Bottoming-out of the first and second master pistons NP and NS occurs when brake fluid leaks to the outside of the brake control device SC. Additionally, bottoming-out of the first and second master pistons NP and NS can also occur due to brake fade (also simply called "fade"). In the event of fade, the rubber, resin, etc., used as raw materials for the friction component MS (e.g., brake pad) exceed their heat resistance temperature, undergo thermal decomposition, and are vaporized. Furthermore, the gas enters between the friction component MS and the rotating component KT (e.g., brake disc), forming an air film. This air film acts as a lubricant, reducing the coefficient of friction. Further, when fade occurs, the raw materials of the friction component (especially the base material, such as phenolic resin, a thermosetting resin) decompose and become brittle. At this point, in addition to the decrease in the coefficient of friction, rapid wear may occur (for example, wear of several millimeters during a single braking operation is called "failure wear").

[0095] When a main piston bottoms out, it is difficult to increase the main pressure Pm. Specifically, when the first main piston NP bottoms out, the front wheel main pressure Pmf will not increase, and when the second main piston NS bottoms out, the rear wheel main pressure Pmr will not increase. Hereinafter, as "bottoming out processing," the identification of a main piston bottoming out and the handling of such bottoming out (referred to as "compensation control") will be explained. For example, the bottoming out processing is programmed into the microprocessor of the first controller ECA. Furthermore, in the following description, a structure of "ru = rm" is also envisioned in the first fluid unit HA.

[0096] In step S210, servo pressure Pu and main pressure Pm (=Pmf, Pmr) are read. Servo pressure Pu is the detection value of servo pressure sensor PU, which is directly input to the first controller ECA. Front wheel and rear wheel main pressures Pmf and Pmr are the detection values ​​of front wheel and rear wheel main pressure sensors PMf and PMr, respectively, which are directly input to the second controller ECB. Moreover, the front wheel and rear wheel main pressures Pmf and Pmr are sent from the second controller ECB to the first controller ECA via the communication bus BS.

[0097] In step S220, based on the servo pressure Pu and the main pressures Pmf and Pmr of the front and rear wheels respectively, it is determined whether the first and second main pistons NP and NS have reached a bottoming-out state (referred to as "bottoming-out judgment"). Specifically, if the difference hPf (front wheel pressure difference) between the servo pressure Pu and the main pressure Pmf exceeds a specified pressure px, the bottoming-out state of the first main piston NP is determined. Similarly, if the difference hPr (rear wheel pressure difference) between the servo pressure Pu and the main pressure Pmr exceeds a specified pressure px, the bottoming-out state of the second main piston NS is determined. Here, the specified pressure px is a threshold value used for bottoming-out judgment, which is a pre-set value (constant). In addition, to distinguish it from the "hydraulic difference mQ based on the pressure regulating valve UB" and the "hydraulic difference wO based on the inlet valve UI", the pressure differences hPf and hPr are also called "judgment hydraulic difference" or "judgment differential pressure".

[0098] When bottoming out occurs in the front wheel braking system BKf, the movement of the first master piston NP in the forward direction Ha is restricted by the second master piston NS, reaching a limit position. Since the first master piston NP and the second master piston NS move as a unit, the relationship "Pu = Pmf" does not hold. Therefore, when the front wheel pressure difference hPf (= Pu - Pmf) is greater than the specified pressure p, the bottoming out state of the first master piston NP is determined. Furthermore, even if bottoming out occurs in the front wheel braking system BKf but not in the rear wheel braking system BKr, the rear wheel master pressure Pmr can be adjusted via the servo pressure Pu.

[0099] If bottoming out occurs in the rear wheel braking system BKr, the movement of the second master piston NS in the forward direction Ha is restricted by the bottom surface of the master cylinder CM, therefore "Pu = Pmr" does not hold. Similarly, if the rear wheel pressure difference hPr (=Pu-Pmr) is greater than the specified pressure px, the bottoming out state of the second master piston NS is determined. If bottoming out occurs in the rear wheel braking system BKr but not in the front wheel braking system BKf, the front wheel master pressure Pmf can be adjusted by the servo pressure Pu.

[0100] If at least one of the first and second main pistons NP and NS is in a bottoming-out state, and step S220 is affirmative, the process proceeds to step S230. On the other hand, if neither the first nor the second main pistons NP nor NS has bottomed out, step S220 is negative, and the process returns to step S210.

[0101] In step S230, compensation control is performed. In the case of a bottoming-out condition, the calculation method for the target differential pressures Qtf and Qtr (=Qt) between the front and rear wheels is changed to reduce (compensate) their impact. The main pressure Pm is increased via the pressure regulating valve UB and supplied to the wheel cylinder CW as the adjusting pressure Pq (ultimately, as the wheel pressure Pw). However, the target differential pressure Qt is a target value representing the degree of increase in the main pressure Pm (i.e., the difference between the main pressure Pm and the adjusting pressure Pq), also known as the "first target differential pressure".

[0102] First, the determination of the bottoming-out state of the first master piston NP will be explained. In the service brake, in step S140 or S160, the front wheel target differential pressure Qtf is calculated by subtracting the front wheel target pressure Ptf from the requested pressure Ps (i.e., "Qtf = Ps - Ptf"). In the case of bottoming out in the front wheel braking system BKf, the front wheel main pressure Pmf (the detected value of the front wheel main pressure sensor PMf, the actual value) is used instead of the front wheel target pressure Ptf (target value). That is, the front wheel target differential pressure Qtf is determined by subtracting the front wheel main pressure Pmf from the requested pressure Ps (i.e., "Qtf = Ps - Pmf"). Due to rapid wear (failure wear) of the front wheel friction component MSf, the front wheel main pressure Pmf gradually decreases, but the front wheel target differential pressure Qtf increases to compensate for the decrease in the front wheel main pressure Pmf. This suppresses the decrease in the deceleration of the vehicle JV. Furthermore, since bottoming out did not occur in the rear wheel braking system BKr, the target differential pressure Qtr of the rear wheel was calculated by subtracting the target rear wheel pressure Ptr from the requested pressure Ps (i.e., "Qtr = Ps - Ptr").

[0103] Next, the determination of the bottoming-out state of the second master piston NS will be explained. Similar to the above, the target differential pressure Qtr for the rear wheels is calculated by subtracting the target rear wheel pressure Ptr (target value) from the requested pressure Ps. However, if bottoming-out occurs in the rear wheel braking system BKr, the target differential pressure Qtr for the rear wheels is determined by subtracting the detected actual value of the rear wheel main pressure Pmr from the requested pressure Ps (i.e., "Qtr = Ps - Pmr"). This increases the target differential pressure Qtr for the rear wheels to compensate for the decrease in the rear wheel main pressure Pmr, suppressing the decrease in vehicle deceleration. Furthermore, since bottoming-out does not occur in the front wheel braking system BKf, the target differential pressure Qtf for the front wheels is calculated by subtracting the target front wheel pressure Ptf from the requested pressure Ps (i.e., "Qtf = Ps - Ptf").

[0104] As explained above, when the first master piston NP is determined to be at its bottom, the calculation method for the front wheel target differential pressure Qtf is changed to increase Qtf. This, in turn, compensates for the decrease in the front wheel main pressure Pmf through the second pressure regulating unit YB. Conversely, when the second master piston NS is determined to be at its bottom, the calculation method for the rear wheel target differential pressure Qtr is changed to increase Qtr. This, in turn, compensates for the decrease in the rear wheel main pressure Pmr through the second pressure regulating unit YB.

[0105] In other words, in the second pressure regulating unit YB, if bottoming out is detected in either the first or second main piston NP or NS, compared to the case where bottoming out is not detected, the target differential pressure corresponding to the bottoming-out target differential pressure Qtf or Qtr (=Qt) between the front and rear wheels is increased. This increases the degree to which the main pressures Pmf and Pmr of the front and rear wheels (i.e., the actual differential pressures between the front and rear wheels) mQf and mQr (the actual difference between the main pressure Pm and the regulating pressure Pq) increase, thus compensating for the reduction in the main pressures Pmf and Pmr caused by bottoming out. Furthermore, since the determination of the bottoming-out state of the first and second main pistons NP and NS is a simple calculation, it can be performed quickly. Therefore, compensation for the reduction in main pressure Pm based on the second pressure regulating unit YB can be performed rapidly.

[0106] Considering the change in vertical force (wheel load) during braking, in vehicle JV, the braking load of the front wheel WHf is set to be higher than that of the rear wheel WHr. Therefore, the probability of the aforementioned failure wear occurring in the friction component MSf of the front wheel WHf is higher than that of the friction component MSr of the rear wheel WHr. The front wheel main pressure Pmf and the rear wheel main pressure Pmr are substantially equal under normal circumstances (i.e., when bottoming out does not occur), so the rear wheel main pressure sensor PMr can be omitted. In this structure, it is impossible to determine the bottoming-out state of the second master piston NS based on the comparison between the servo pressure Pu and the rear wheel main pressure Pmr. However, for the reasons mentioned above, the omission of the rear wheel main pressure sensor PMr is based on the fact that the determination of the bottoming-out state of the first master piston NP is of greater importance.

[0107] In the structure that omits the rear wheel main pressure sensor PMr, in step S230, further, based on the result of the bottoming-out judgment of the first main piston NP, the control method of the rear wheel inlet valve UIr in the brake force distribution control (so-called EBD control) is changed as a compensation control.

[0108] First, the execution of brake force distribution control will be explained. In the brake control unit SC, known brake force distribution control is performed based on the wheel speed Vw (detection result of wheel speed sensor VW) through the following calculation steps.

[0109] (1) Calculate the vehicle speed Vx based on the wheel speed Vw.

[0110] (2) Calculate the front wheel and rear wheel slips Slf and Slr based on the vehicle speed Vx and the front and rear wheel speeds Vwf and Vwr. The front wheel and rear wheel slips Slf and Slr are state variables representing the degree of deceleration slip of the front and rear wheels WHf and WHr.

[0111] (3) Calculate the target rear wheel pressure Pvr based on the front wheel slip Slf and the rear wheel slip Slr. The target rear wheel pressure Pvr is the target value in the brake force distribution control that corresponds to the actual rear wheel pressure Pwr. The target rear wheel pressure Pvr is determined when the rear wheel slip Slr falls within the specified range relative to the front wheel slip Slf.

[0112] (4) Calculate the target differential pressure Otr of the rear wheels based on the target wheel pressure Pvr. Reduce the rear wheel adjustment pressure Pqr (the hydraulic pressure between the rear wheel pressure regulating valve UBr and the rear wheel inlet valve UIr) through the rear wheel inlet valve UIr and supply it to the rear wheel cylinder CWr. The target differential pressure Otr of the rear wheels is a target value that represents the degree to which the rear wheel adjustment pressure Pqr is reduced (i.e., the difference between the rear wheel adjustment pressure Pqr and the rear wheel pressure Pwr). In order to distinguish it from the "first target differential pressure (target value of the differential pressure based on the pressure difference of the pressure regulating valve UBr)" mentioned above, it is also called the "second target differential pressure (target value of the differential pressure based on the pressure difference of the inlet valve UIr)".

[0113] (5) Control the rear wheel inlet valve UIr according to the target differential pressure Otr of the rear wheel. That is, control the supply current to the rear wheel inlet valve UIr so that the actual differential pressure wOr (the hydraulic difference between the rear wheel pressure Pwr and the rear wheel adjustment pressure Pqr) generated by the rear wheel inlet valve UIr is close to and consistent with the target differential pressure Otr of the rear wheel.

[0114] In the absence of determining the bottoming-out state of the first master piston NP, in the aforementioned calculation step (4), the second target differential pressure Otr is calculated based on the front wheel main pressure Pmf (the detected value of the front wheel main pressure sensor PMf). Specifically, the second target differential pressure Otr is calculated as the value of subtracting the front wheel main pressure Pmf from the rear wheel target wheel pressure Pvr (i.e., "Otr = Pvr - Pmf"). This is based on the fact that "Pmf = Pmr" when the first master piston NP has not bottomed out.

[0115] When the first master piston NP bottoms out, the relationship "Pmf = Pmr" no longer holds. Therefore, given the bottoming-out state of the first master piston NP, in the calculation of the second target differential pressure Otr, the front wheel main pressure Pmf is switched to the front wheel target pressure Ptf (i.e., "Otr = Pvr - Ptf"). Based on the bottoming-out state of the first master piston NP, the front wheel main pressure Pmf gradually decreases, but in the calculation of the second target differential pressure Otr, the front wheel main pressure Pmf is replaced by the front wheel target pressure Ptf, thus the rear wheel pressure Pwr will not unnecessarily increase.

[0116] <Actions for determining bottoming out>

[0117] Reference Figure 6 The timing diagram (a line graph representing the transition of state quantities relative to time T) explains the bottoming-out determination used to identify the bottoming-out states of the first and second master pistons NP and NS. The bottoming-out state is when the first and second master pistons NP and NS reach their limit positions in the forward direction Ha. In the bottoming-out state, the volumes of the front and rear wheel master chambers Rmf and Rmr are at their minimum, and brake fluid BF can no longer be pumped from the front and rear wheel master chambers Rmf and Rmr.

[0118] In this example, consider the following:

[0119] - The operation of the braking control component BP begins at time t0, and at time t6, the braking control component BP remains constant.

[0120] - At time point t3, a bottoming-out state occurs. Here, a bottoming-out state does not occur in the second master piston NS, but only in the first master piston NP. Therefore, in the following explanation and... Figure 6 In this context, unless otherwise specified, "PM" corresponds to "PMf", "Pt" to "Ptf", "Pm" to "Pmf", and "hP" to "hPf". Furthermore, in the case where the first master piston NP has not bottomed out, but the second master piston NS has bottomed out (the opposite of the above), the following explanation and... Figure 6 In the text, it can replace “NP” with “NS”, “PM” with “PMr”, “Pt” with “Ptr”, “Pm” with “Pmr”, and “hP” with “hPr”.

[0121] The signal (main pressure) Pm from the main pressure sensor PM is input to the second controller ECB and then transmitted to the first controller ECA via the communication bus BS. Furthermore, the first controller ECA performs a bottoming-out determination. Therefore, the main pressure Pm includes the delay time (time points t1 to t2) involved in the communication with the servo pressure Pu.

[0122] - In the structure of the first fluid unit HA, the servo area ru and the main area rm are set to be equal.

[0123] At time t0, the braking operation component BP begins operation, and the braking operation amount Ba begins to increase. Corresponding to the increase in the braking operation amount Ba, the request pressure Ps increases. However, at the initial stage of braking, the request pressure Ps is less than the area judgment pressure ps, and is in a low hydraulic pressure area (refer to step S130), therefore the target pressure Pt remains "0". As a result, the servo pressure Pu and the main pressure Pm are "0". Here, the servo pressure Pu is controlled to be consistent with the target pressure Pt, therefore the graphs of the target pressure Pt and the servo pressure Pu are illustrated in an overlapping manner.

[0124] At time t1, the requested pressure Ps is greater than or equal to the regional judgment pressure ps, and the system moves away from the low hydraulic pressure region. Simultaneously, the target pressure Pt and servo pressure Pu increase from "0". Because the main pressure Pm (shown as a dashed line) is received from the second controller ECB, there is a communication time delay between the servo pressure Pu and the main pressure Pm. Therefore, the main pressure Pm begins to increase at time t2, slightly delayed from the start of the increase in servo pressure Pu. Neither the first nor the second main piston NP nor NS has reached its bottom. Therefore, the difference hP between the servo pressure Pu and the main pressure Pm (i.e., the value of servo pressure Pu minus the main pressure Pm) caused by the communication delay is relatively small. In other words, the servo pressure Pu and the main pressure Pm are approximately the same.

[0125] At time t3, the first master piston NP bottoms out. The movement of the first master piston NP in the forward direction Ha is constrained, therefore... The relationship no longer holds. After the bottoming-out time point t3, it becomes difficult to generate the main pressure Pm, which decreases sequentially. Therefore, the pressure difference hP (=Pu-Pm) increases sequentially. At time point t4, the pressure difference hP (judgment differential pressure) is greater than or equal to the specified pressure px for the first time. However, at time point t4, the bottoming-out state of the first main piston NP is not immediately determined. To eliminate the influence of noise, etc., the bottoming-out state of the first main piston NP is determined at time point t5 after the state of "hP≥px" has lasted for a specified time tx. In detail, the duration Tx of this state is calculated from the time point when "hP≥px" is initially satisfied (the corresponding calculation cycle). Moreover, the bottoming-out state is determined at the time point when "Tx≥tx" is satisfied. Here, the specified time tx is a threshold corresponding to the duration Tx, which is a pre-set specified value (constant). For example, the specified time tx can also be set to a quantity of several calculation cycles.

[0126] At the bottoming-out determination time point t5, the determination flag FL, indicating the bottoming-out state, switches from "0" to "1". Here, the determination flag FL uses "0" to indicate that a bottoming-out state has not occurred, and "1" to indicate that a bottoming-out state has occurred. The determination flag FL is sent from the first controller ECA to the second controller ECB via the communication bus BS.

[0127] In the brake control unit SC, the bottoming-out state of the first master piston NP (or the second master piston NS) is determined by comparing the servo pressure Pu with the front wheel main pressure Pmf (or the rear wheel main pressure Pmr). That is, the bottoming-out state is not determined by comparing the control target with the control result. Therefore, the bottoming-out determination is not affected by errors or control delays in pressure regulation control. The bottoming-out determination is based on the following: when the first master piston NP (or the second master piston NS) has not bottomed out, the servo pressure Pu and the front wheel main pressure Pmf (or the rear wheel main pressure Pmr) are consistent; however, when the first master piston NP (or the second master piston NS) bottoms out, they are inconsistent. Therefore, the bottoming-out state of the first master piston NP (or the second master piston NS) can be quickly and reliably determined through simple calculations.

[0128] The calculation of differential pressure hP requires the main pressure Pm; however, the main pressure Pm is obtained from the universal second pressure regulating unit YB via the communication bus BS. For vehicle stability control and other functions, the brake control unit SC already includes a second pressure regulating unit YB containing the main pressure sensor PM. Therefore, it is unnecessary to install a new main pressure sensor PM in the brake control unit SC for bottoming-out detection. From this perspective, the bottoming-out state of the first master piston NP (or the second master piston NS) can be determined with a simple structure.

[0129] In the above explanation, the structure "ru = rm" is assumed. In structures where the servo area ru and the main area rm are different, the main pressure Pm is transformed into a value corresponding to the servo pressure Pu based on the ratio of the pressure-bearing area ru of the servo chamber Ru to the pressure-bearing area rm of the main chamber Rm, and then compared with the servo pressure Pu. Specifically, the main pressure Pm is transformed into "Pm·rm / ru", and the difference hP (hydraulic pressure difference used for judgment) between the servo pressure Pu and "Pm·rm / ru" is calculated. Furthermore, if the hydraulic pressure difference hP is greater than or equal to the specified pressure px (a pre-set constant), the bottoming-out state of the first main piston NP (or the second main piston NS) is determined.

[0130] Alternatively, the servo pressure Pu and the main pressure Pm can be compared at the level of the thrust acting on the first main piston NP (or the second main piston NS). Specifically, the thrust (servo thrust) Fu involved in the servo pressure Pu is calculated using "Pu·ru", and the thrust (main thrust) Fm involved in the main pressure Pm is calculated using "Pm·rm". Furthermore, the difference hF (=Fu-Fm) between the servo thrust Fu and the main thrust Fm is calculated. If the thrust difference hF is greater than or equal to a predetermined force fx, a bottoming-out state is determined. Here, similar to the predetermined pressure px, the predetermined force fx is a threshold value (constant) used for bottoming-out determination. In any case, the bottoming-out state of the first main piston NP (or the second main piston NS) is determined based on the comparison between the servo pressure Pu and the main pressure Pm.

[0131] <Compensation Control Actions>

[0132] Reference Figure 7 The timing diagram illustrates the actions of the compensation control based on the bottoming-out determination result. "Compensation control" is used to compensate for the effects of bottoming out (such as a decrease in vehicle deceleration) when a bottoming-out state is determined. In this example, consider the following:

[0133] - The braking operation of component BP begins at time point u0. The period from time point u0 to time point u1 is a low hydraulic pressure region (the region where "Ps < ps"), where wheel pressure Pw is pressurized only by the second pressure regulating unit YB. After time point u1, since the low hydraulic pressure region has ended, wheel pressure Pw is pressurized by both the first and second pressure regulating units YA and YB.

[0134] - At time point u2, the rear wheel pressure Pwr is limited by brake force distribution control. At time point u3, the first master piston NP reaches its bottoming-out state, and at the immediately following time point u4, the bottoming-out state of the first master piston NP is determined. At time point u6, the brake operation component BP remains constant.

[0135] - In the first fluid unit HA, the servo area ru and the main area rm are set to be equal.

[0136] - The rear wheel main pressure sensor PMr is not used in the second pressure regulating unit YB; only the front wheel main pressure sensor PMf is used. Therefore, the bottoming-out determination for the second master piston NS is omitted.

[0137] The signal (front wheel main pressure) Pmf from the front wheel main pressure sensor PMf is input to the second controller ECB, and then transmitted to the first controller ECA via the communication bus BS. Furthermore, the first controller ECA performs the bottoming-out determination of the first master piston NP. In addition, the front wheel main pressure Pmf has a communication delay time relative to the servo pressure Pu, but... Figure 7 The ' ' is omitted in the representation.

[0138] At time point u0, the braking operation component BP begins operation, and the braking operation amount Ba starts to increase. Corresponding to the increase in the braking operation amount Ba, the requested pressure Ps increases. The braking initially occurs in a low hydraulic pressure region, therefore the front wheel target pressure Ptf remains "0", and only the front wheel target differential pressure Qtf increases. Corresponding to the increase in the front wheel target differential pressure Qtf (target value), the front wheel actual differential pressure mQf (actual value) increases. The front wheel actual differential pressure mQf is controlled to be close to and consistent with the front wheel target differential pressure Qtf; therefore, the graphs of the front wheel target differential pressure Qtf and the front wheel actual differential pressure mQf overlap.

[0139] At time point u1, the target differential pressure Qtf (resulting in the actual differential pressure mQf) of the front wheels reaches the zone judgment pressure ps (a pre-set constant). From time point u1 onwards, in addition to the target differential pressure Qtf, the target pressure Ptf of the front wheels also increases. Corresponding to the increase in the target pressure Ptf (target value), the servo pressure Pu (actual value) increases. The servo pressure Pu is controlled to be close to and consistent with the target pressure Ptf of the front wheels, therefore the graphs of the target pressure Ptf and the servo pressure Pu overlap.

[0140] At time point u2, the rear wheel slip Slr (e.g., the speed difference between vehicle speed Vx and wheel speed Vwr) increases, initiating the execution of brake force distribution control (EBD control). After time point u2, the requested pressure Ps increases, but the increase in the actual rear wheel differential pressure wOt (the difference between the rear wheel adjustment pressure Pqr and the rear wheel pressure Pwr) is limited by the rear wheel inlet valve UIr to suppress the increase in rear wheel slip Slr. Specifically, a second target differential pressure Otr is calculated using the rear wheel target wheel pressure Pvr calculated based on the rear wheel slip Slr and the front wheel main pressure Pmf. Furthermore, the current applied to the rear wheel inlet valve UIr is controlled based on the second target differential pressure Otr. In addition, when the execution of brake force distribution control begins, the control flag (execution flag) FE indicating this execution switches from "0 (not executing)" to "1 (executing)".

[0141] At time point u3, the first master piston NP bottoms out, and the front wheel main pressure Pmf begins to decrease. At the immediately following time point u4, the front wheel hydraulic pressure difference hPf (=Pu-Pmf) (judgment differential pressure) reaches the specified pressure px (a pre-set constant), and the bottoming-out state of the first master piston NP is determined. At the affirmative bottoming-out judgment time point u4 (processing in step S220), the judgment flag (control flag) FL indicating the bottoming-out state switches from "0 (non-occurrence state)" to "1 (occurrence state)".

[0142] Simultaneously, at time point u4, compensation control (control to reduce the impact of bottoming out) begins execution. Specifically, in the drive control of the pressure regulating valve UBf, up to time point u4, the first front wheel target differential pressure Qtf is calculated according to "Qtf = ps - Ptf". However, after time point u4, the front wheel target differential pressure Qtf is calculated according to "Qtf = Ps - Pmf". Here, the first front wheel target differential pressure Qtf is a target value corresponding to the actual differential pressure mQf (actual value) generated by the front wheel pressure regulating valve UBf.

[0143] After time point u3, due to the bottoming out of the first master piston NP, it is difficult to generate the front wheel main pressure Pmf, resulting in insufficient front wheel pressure Pwf. However, after time point u4, when the bottoming out state of the first master piston NP is determined, the front wheel main pressure Pmf is used in the calculation of the front wheel target differential pressure Qtf to reflect its reduction. As a result, the front wheel main pressure Pmf based on the first pressure regulating unit YA decreases, but the front wheel target differential pressure Qtf increases to compensate for this decrease. Consequently, the actual front wheel differential pressure mQf based on the second pressure regulating unit YB increases, compensating for the reduction in front wheel pressure Pwf.

[0144] Furthermore, at time point u4, as a compensation control, the control method for the rear wheel inlet valve UIr in the brake force distribution control is changed. In the drive control of the rear wheel inlet valve UIr, up to time point u4, the second target differential pressure Otr is calculated according to "Otr = Pvr - Pmf". However, after time point u4, the second target differential pressure Otr is calculated according to "Otr = Pvr - Ptf". Here, the second target differential pressure Otr is a target value corresponding to the actual differential pressure mOt (actual value) generated by the rear wheel inlet valve UIr. Additionally, the rear wheel target wheel pressure Pvr is a target value corresponding to the rear wheel pressure Pwr (actual value) in the brake force distribution control.

[0145] When the first master piston NP has not bottomed out, the front wheel main pressure Pmf detected by the front wheel main pressure sensor PMf is equal to the rear wheel main pressure Pmr. Based on this, the rear wheel main pressure sensor PMr is omitted, and the front wheel main pressure Pmf is used for the drive control of the rear wheel inlet valve UIr involved in the brake force distribution control. On the other hand, when the first master piston NP bottoms out, the front wheel main pressure Pmf is no longer consistent with the rear wheel main pressure Pmr. Therefore, instead of the front wheel main pressure Pmf, the front wheel target pressure Ptf is used in the drive control of the rear wheel inlet valve UIr. When the front wheel main pressure Pmf is continued to be used even after the first master piston NP bottoms out, the rear wheel pressure Pwr increases unnecessarily, but the calculation method of the rear wheel target differential pressure Otr is changed according to the bottoming-out judgment result. Thus, the increase of the rear wheel pressure Pwr is suppressed.

[0146] The following is a summary of the bottoming-out judgment and the compensation control based on this judgment. The bottoming-out state of the first master piston NP is determined by comparing the servo pressure Pu with the front wheel main pressure Pmf through simple calculations, allowing for rapid and reliable judgment. Furthermore, based on the bottoming-out judgment result, the calculation method for the front wheel target differential pressure Qtf is changed, and the reduction in the front wheel main pressure Pmf in the first pressure regulating unit YA is compensated by the second pressure regulating unit YB. Specifically, in the second pressure regulating unit YB, compared to the case where the bottoming-out of the first master piston NP is not determined, the front wheel target differential pressure Qtf increases when the bottoming-out of the first master piston NP is determined. Therefore, the degree of increase in the front wheel main pressure Pmf (actual differential pressure) mQf (i.e., the actual difference between the front wheel main pressure Pmf and the front wheel adjustment pressure Pqf) is significantly adjusted. Because the bottoming-out of the first master piston NP is quickly determined, the increase in the front wheel pressure Pwf based on the second pressure regulating unit YB can be performed immediately.

[0147] Furthermore, based on the bottoming-out determination of the first master piston NP, the control method for the rear wheel inlet valve UIr in the brake force distribution control is modified. This appropriately controls the differential pressure Otr (target value) and mOr (actual value) based on the rear wheel inlet valve UIr. That is, by suppressing unnecessary increases in the rear wheel pressure Pwr, vehicle stability is ensured. Similarly, the bottoming-out of the first master piston NP is determined shortly after its occurrence, thus minimizing the possibility of erratic vehicle behavior.

[0148] The situation of the first master piston NP bottoming out has been explained above. In the structure using the rear wheel main pressure sensor PMR, the bottoming-out state of the second master piston NS is determined by comparing the servo pressure Pu with the rear wheel main pressure Pmr (e.g., the rear wheel differential pressure hPr). Furthermore, based on the result of determining the bottoming-out of the second master piston NS, the calculation method of the rear wheel target differential pressure Qtr is changed, and the reduction of the rear wheel main pressure Pmr in the first pressure regulating unit YA is compensated by the second pressure regulating unit YB. Specifically, in the second pressure regulating unit YB, compared to the case where the bottoming-out of the second master piston NS is not determined, the rear wheel target differential pressure Qtr increases when the bottoming-out of the second master piston NS is determined. As a result, the degree of increase in the rear wheel main pressure Pmr (actual differential pressure) mQr (i.e., the actual difference between the rear wheel main pressure Pmr and Pqr) is adjusted significantly. Similarly, the bottoming out of the second master piston NS is quickly determined, so the rear wheel pressure Pwr can be increased rapidly based on the second pressure regulating unit YB.

[0149] <Example of the second structure of the first voltage regulating unit YA>

[0150] Reference Figure 8A schematic diagram is provided to illustrate a second structural example of the first pressure regulating unit (upper pressure regulating unit) YA. In the first structural example, a master cylinder CM of the series type with two main chambers Rmf and Rmr is used. Furthermore, an accumulator type is used in the first fluid unit HA of the first pressure regulating unit YA. Specifically, in the first fluid unit HA, the accumulator pressure Pc from the accumulator AC is the initial pressure. The pilot pressure Pp is adjusted by the booster valve UZ and the depressurizer valve UZ, and finally, the servo pressure Pu is adjusted. Replacing this accumulator type structure, in the second structural example of the first pressure regulating unit YA (especially the first fluid unit HA), a single master cylinder CM is used, and the servo pressure Pu is adjusted by throttling the brake fluid discharged from the third fluid pump QC using the servo valve UC. The differences will be explained below.

[0151] In the second structural example of the first fluid unit HA, since the rear wheel main chamber Rmr is omitted, the rear wheel main pressure sensor PMr is not used; instead, only the front wheel main pressure sensor PMf, which detects the front wheel main chamber Rmf, is used. Similar to the second fluid unit HB, the brake fluid BF discharged by the third fluid pump QC, driven by the third motor MC, is throttled via the servo valve UC, thereby adjusting the servo pressure Pu. Specifically, in the fluid pump QC, the suction section and the discharge section are connected via the return path HL (fluid path), which is the same as the return path HK. A servo valve UC (a solenoid valve similar to the pressure regulating valve UB) is installed in the return path HL as a normally open linear valve. When the fluid pump QC is driven by the motor MC, a circulating flow KN of brake fluid is generated in the return path HL. The servo pressure Pu is adjusted by the orifice effect when this circulating flow KN is throttled via the servo valve UC. The return path HL is connected to the servo chamber Ru via the servo path HU between the discharge section of the fluid pump QC and the servo valve UC. Therefore, servo pressure Pu is supplied to the servo chamber Ru. Additionally, the return path HL, located between the discharge section of the fluid pump QC and the servo valve UC, is connected to the rear wheel cylinder CWr via the rear wheel connection path HSr. Thus, servo pressure Pu is directly supplied to the rear wheel cylinder CWr.

[0152] In the second structural example, the bottoming-out state of the first master piston NP is also quickly and reliably determined based on the relationship between the servo pressure Pu and the front wheel main pressure Pmf. Furthermore, when the bottoming-out state of the first master piston NP is determined, the decrease in the front wheel main pressure Pmf caused by bottoming out can be compensated because the increase in the degree of increase in the front wheel main pressure Pmf based on the second pressure regulating unit YB (pressure difference Qtf, mQf) is increased. In other words, it achieves the same effect as the first structural example described above.

[0153] <Other Implementation Methods>

[0154] The following describes other embodiments of the braking control device SC. In these other embodiments, the same effect as described above is achieved (rapidly and reliably determining the bottoming-out state of the first and second master pistons NP and NS, and suppressing the bottoming-out effect through compensation control based on this determination).

[0155] In the above embodiment, in the service brake, when "Ps < ps", pressure is applied only through the second pressure regulating unit YB; when "Ps ≥ ps", pressure is applied through both the first and second pressure regulating units YA and YB. Alternatively, pressure can always be applied through the first pressure regulating unit YA only. In this structure, the bottoming-out state of the first and second main pistons NP and NS is determined by comparing the servo pressure Pu with the main pressure Pm. Moreover, when the bottoming-out state of the first and second main pistons NP and NS is determined, the increase in the main pressure Pm based on the second pressure regulating unit YB (i.e., the differential pressure Qt and mQ) increases compared to the case where the bottoming-out state is not determined. In other words, when the bottoming-out state is not determined, the target differential pressure Qt (resulting in the actual differential pressure mQ) is "0", but when the bottoming-out state is determined, the target differential pressure Qt (resulting in the actual differential pressure mQ) increases from "0" to compensate for the decrease in the main pressure Pm.

[0156] In the above embodiment, the main pressure Pm is obtained via the communication bus BS in the first controller ECA. Alternatively, the main pressure sensor PM is connected to the first controller ECA, and the main pressure Pm can also be obtained directly through the first controller ECA. However, as a general-purpose unit, the second pressure regulating unit YB already has the main pressure sensor PM. Therefore, obtaining the main pressure Pm from the second controller via the communication bus BS simplifies the overall structure of the braking control device SC.

[0157] In the above-described embodiment, a front-to-back type structure is adopted as the braking fluid path for the two systems. Alternatively, a diagonal type (also known as "X-type") braking system can be used. In this structure, one of the two main chambers formed within the master cylinder CM is connected to the right front wheel cylinder and the left rear wheel cylinder, while the other is connected to the left front wheel cylinder and the right rear wheel cylinder. In the front-to-back type structure, the bottoming-out state of the master piston is also determined by comparing the hydraulic pressure Pm and the servo pressure Pu in the two main chambers.

[0158] In the above embodiment, a disc brake type braking device SX is used. Alternatively, a drum brake type braking device SX is used. In the drum brake type braking device SX, the rotating component KT is a brake drum, and the friction component MS is a brake lining disposed on the brake shoe.

[0159] Summary of the implementation methods of the braking control device SC

[0160] The following is a summary of the implementation methods of the braking control device SC.

[0161] The braking control device SC includes a "master cylinder CM having a main chamber Rm divided by master pistons NP and NS", and a "first pressure regulating unit YA having a servo chamber Ru located on the opposite side of the main pistons NP and NS from the main chamber Rm, and supplying a servo pressure Pu to the servo chamber Ru to generate a main pressure Pm in the main chamber Rm". The first pressure regulating unit YA acquires the main pressure Pm and the servo pressure Pu. Furthermore, it determines whether the master pistons NP and NS have bottomed out based on a comparison of the main pressure Pm and the servo pressure Pu. For example, in the first pressure regulating unit YA, the comparison of the main pressure Pm and the servo pressure Pu is performed based on the pressure-bearing area ru of the servo chamber Ru and the pressure-bearing area rm of the main chamber Rm. Additionally, in a configuration where "ru = rm", the first pressure regulating unit YA determines that bottoming out has occurred when the difference hP (= Pu - Pm) between the servo pressure Pu and the main pressure Pm is greater than or equal to a predetermined pressure px.

[0162] In the braking control device SC, when the main piston does not bottom out, the servo pressure Pu and the main pressure Pm maintain a predetermined relationship (e.g., when set to "ru = rm", the servo pressure Pu and the main pressure Pm are consistent). However, when the main piston bottoms out, this relationship no longer holds. Based on this, the bottoming-out state of the main piston is determined by comparing the servo pressure Pu and the main pressure Pm. In other words, bottoming-out determination is not based on a comparison between the control target and the control result. That is, in the braking control device SC, the time required to avoid the effects of pressure regulation control errors and time delays is not needed. Therefore, in the braking control device SC, reliable bottoming-out determination can be performed in a short time through simple calculation processing.

[0163] In the brake control device SC, a second pressure regulating unit YB is provided between the master cylinder CM and the wheel cylinder CW, which can increase the main pressure Pm and supply it to the wheel cylinder CW. Moreover, in the second pressure regulating unit YB, compared with the case where bottoming out is not detected, the increase in the main pressure Pm differential pressure Qt (target value) and mQ (actual value) is larger when bottoming out is detected.

[0164] In detail, when no main bottoming-out occurs, the pressure regulating valve UB is controlled according to "Qt = Ps - Pt". However, when main bottoming-out occurs, the pressure regulating valve UB is calculated according to "Qt = Ps - Pm". When main bottoming-out occurs, the main pressure Pm gradually decreases, reaching "0" in the worst case. However, when the bottoming-out state is determined, the calculation method changes, and therefore, based on the decrease in main pressure Pm, the target differential pressure Qt increases. Thus, the degree of increase in main pressure Pm based on the pressure regulating valve UB (i.e., the magnitude of the actual differential pressure mQ) increases, which can compensate for the effects of main bottoming-out (such as a decrease in vehicle deceleration).

Claims

1. A braking control device for a vehicle, comprising: The master cylinder has a main chamber divided by the master piston; A first pressure regulating unit has a servo chamber located on the opposite side of the main chamber relative to the main piston, and supplies servo pressure to the servo chamber, thereby generating main pressure in the main chamber; and The second pressure regulating unit between the master cylinder and the wheel cylinder is capable of increasing the master pressure and supplying it to the wheel cylinder. in, The first voltage regulating unit obtains the main voltage and the servo voltage. Based on the comparison between the main pressure and the servo pressure, the bottoming out of the main piston is determined. The second voltage regulating unit includes a main pressure sensor. Compared to the case where the bottoming out is not detected, when the bottoming out is detected, the second pressure regulating unit changes the calculation method of the target value, i.e., the target differential pressure, which represents the degree of increase in the main pressure. The target differential pressure is determined by subtracting the target value of the hydraulic pressure to be achieved by the first pressure regulating unit from the target value of the wheel pressure of the wheel cylinder, i.e., the requested pressure, from the target value of the hydraulic pressure to be achieved by the first pressure regulating unit, i.e., the requested pressure from the detection value of the main pressure sensor, so as to increase the degree of increase in the main pressure.

2. The vehicle braking control device according to claim 1, wherein, The first pressure regulating unit performs the comparison based on the pressure-bearing area of ​​the servo chamber and the pressure-bearing area of ​​the main chamber.

3. The vehicle braking control device according to claim 1, wherein, The first voltage regulating unit determines that the bottoming out has occurred when the difference between the servo pressure and the main pressure is greater than or equal to a specified pressure.

Images