Vehicle braking control system

Abstract

To provide a braking control device that can suppress vehicle deceleration from varying at an extremely low temperature.SOLUTION: A braking control device comprises: a first pressure-regulation valve provided in a fluid passage through which an ejection part and a suction part of a fluid pump that is driven by an electric motor are connected to each other; a second pressure-regulation valve provided between the first pressure-regulation valve and the suction part, on the fluid passage; and a controller for controlling the first and second pressure-regulation valves. The controller selects either of second-system pressure regulation in which the first and second pressure-regulation valves control wheel pressure of front wheels and of rear wheels and first-system pressure regulation in which only the second pressure-regulation valve controls the wheel pressure of the front wheels and of the rear wheels. Further, the controller regulates the wheel pressure of the front wheels, on the basis of a temperature of operating fluid in the fluid passage, when selecting the first-system pressure regulation.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] In the invention described in Patent Document 1, when creating a control command value for a linear valve so that the actual value of the brake cylinder hydraulic pressure approaches the target value, the control gain is set to a large value when the temperature of the working fluid is below the set temperature. This can reduce the control delay caused by the low temperature of the working fluid and its high viscosity.

[0003] The applicant has developed a braking control device capable of individually controlling the braking hydraulic pressure of the front-wheel system (also referred to as "front-wheel wheel pressure") and the braking hydraulic pressure of the rear-wheel system (also referred to as "rear-wheel wheel pressure") as described in Patent Document 2. By the way, in the braking control device, an excess or deficiency of the wheel pressure may occur at extremely low temperatures, and the deceleration of the vehicle may change.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a braking control device in which a change in vehicle deceleration can be suppressed at extremely low temperatures.

Means for Solving the Problems

[0006] The vehicle braking control device (SC) according to the present invention comprises a first pressure regulating valve (UA) provided in a fluid passage (HK) connecting the discharge section (Qo) and the suction section (Qi) of a fluid pump (QA) driven by an electric motor (MA), a second pressure regulating valve (UB) provided in the fluid passage (HK) between the first pressure regulating valve (UA) and the suction section (Qi), and a controller (EA) that controls the first and second pressure regulating valves (UA, UB). The controller (EA) selects either a two-system pressure regulating system that controls the front and rear wheel pressures (Pwf, Pwr) using the first and second pressure regulating valves (UA, UB), or a one-system pressure regulating system that controls the front and rear wheel pressures (Pwf, Pwr) using only the second pressure regulating valve (UB). Then, when the controller (EA) selects the single-system pressure adjustment, it adjusts the front wheel pressure (Pwf) based on the temperature (Te) of the working fluid (BF) in the fluid passage (HK).

[0007] In the vehicle braking control device (SC) according to the present invention, the controller (EA) controls the rear wheel pressure (Pwr) by the first hydraulic pressure (Pa) between the discharge unit (Qo) and the first pressure regulating valve (UA), and controls the front wheel pressure (Pwf) by the second hydraulic pressure (Pb) between the first pressure regulating valve (UA) and the second pressure regulating valve (UA). Furthermore, when the temperature (Te) is low, the controller (EA) reduces the front wheel pressure (Pwf) compared to when the temperature (Te) is high.

[0008] In the vehicle braking control device (SC) according to the present invention, the controller (EA) controls the front wheel pressure (Pwf) by the first hydraulic pressure (Pa) between the discharge unit (Qo) and the first pressure regulating valve (UA), and controls the rear wheel pressure (Pwr) by the second hydraulic pressure (Pb) between the first pressure regulating valve (UA) and the second pressure regulating valve (UA). Furthermore, when the temperature (Te) is low, the controller (EA) increases the front wheel pressure (Pwf) compared to when the temperature (Te) is high.

[0009] With the above configuration, the wheel pressure is adjusted by the temperature of the working fluid, so changes in vehicle deceleration are suppressed at extremely low temperatures. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram illustrating a first embodiment of the braking control device SC. [Figure 2] This is a schematic diagram illustrating the pressure regulating section CA. [Figure 3] This is a flowchart illustrating pressure regulation control. [Figure 4] This is a schematic diagram illustrating a second embodiment of the braking control device SC. [Figure 5] This is a schematic diagram illustrating a modified version of the brake control device SC. [Modes for carrying out the invention]

[0011] <Symbols for constituent components, etc., and subscripts at the end of the symbols> In the following explanation, components, calculation processes, signals, characteristics, and values ​​that are denoted by the same symbol, such as "CW," represent components with the same function. The subscripts "f" and "r" at the end of the symbols related to each wheel are general symbols indicating whether they relate to the front or rear wheel system. For example, for the wheel cylinder CW provided on each wheel, it is written as "front wheel cylinder CWf" and "rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" at the end of the symbols may be omitted. When the subscripts "f" and "r" are omitted, each symbol represents a general term. For example, "CW" is a general term for the wheel cylinders provided on the front and rear wheels of a vehicle.

[0012] In the fluid path from the master cylinder CM to the wheel cylinder CW, the side closer to the master cylinder CM (the side further from the wheel cylinder CW) is referred to as the "upper part," and the side closer to the wheel cylinder CW (the side further from the master cylinder CM) is referred to as the "lower part." Furthermore, in the circulating flow KN of the braking fluid BF (also called "working fluid"), the side closer to the discharge port Qo of the fluid pump QA (the side further from the suction port Qi) is referred to as the "upstream side," and the side closer to the suction port Qi of the fluid pump QA (the side further from the discharge port Qo) is referred to as the "downstream side."

[0013] The first actuator YA of the first braking unit SA, the second actuator YB of the second braking unit SB, and the wheel cylinder CW are connected by a fluid passage (connecting passage HS). Furthermore, various components (UA, UB, etc.) in the first and second actuators YA and YB are connected by fluid passages. Here, a "fluid passage" is a path for moving the braking fluid BF, and includes piping, flow paths within actuators, hoses, etc. In the following explanation, the connecting passage HS, return passage HK, reservoir passage HR, input passage HN, servo passage HV, etc., are fluid passages.

[0014] <First Embodiment of Brake Control Device SC> A first embodiment of the braking control device SC will be described with reference to the schematic diagram in Figure 1. The vehicle equipped with the braking control device SC is a hybrid vehicle or electric vehicle equipped with an electric motor for driving.

[0015] The vehicle is equipped with a regenerative braking system KG. The regenerative braking system KG consists of an energy regeneration generator GN (also called an "electric motor / generator" or "regenerative generator"), a control unit EG for the regenerative braking system KG (also called a "regenerative controller"), and a battery BG for the regenerative braking system KG (also called a "regenerative battery"). The regenerative generator GN also serves as the electric motor for driving. During regenerative braking, the electric motor / generator GN acts as a generator, and the generated electricity is stored in the regenerative battery BG via the regenerative controller EG. At this time, a regenerative braking force Fg acts on the wheels. In other words, the regenerative braking system KG can generate a regenerative braking force Fg. For example, if the regenerative braking system KG is installed on the front wheels, a regenerative braking force Fg will be generated on the front wheels.

[0016] The front and rear wheels of a vehicle are equipped with braking systems. The braking system consists of a brake caliper, a friction member (e.g., brake pads), and a rotating member (e.g., brake discs). A wheel cylinder CW is provided in the brake caliper (not shown). The hydraulic pressure Pw (referred to as "wheel pressure") within the wheel cylinder CW presses the friction member (not shown) against the rotating member (not shown) fixed to each wheel. This generates a hydraulic braking force Fp on the wheel.

[0017] The vehicle is equipped with a braking control member BP and various sensors (SP, etc.). The braking control member BP (for example, the brake pedal) is an operating member used by the driver to decelerate the vehicle. The vehicle is equipped with an operating displacement sensor SP that detects the operating displacement Sp of the braking control member BP. The operating displacement Sp is one of the state variables that indicate the amount of operation of the braking control member BP (amount of braking operation), and in a brake-by-wire type braking control device SC, it is a signal that represents the driver's intention to brake (i.e., a braking instruction).

[0018] In addition to the operation displacement sensor SP, as another state quantity representing the braking operation amount, the hydraulic pressure Ps of the stroke simulator SS (referred to as "simulator pressure") is adopted. The simulator pressure Ps is detected by the simulator pressure sensor PS. The simulator pressure Ps is a state quantity corresponding to the operating force of the braking operation member BP.

[0019] The vehicle is equipped with various sensors for braking control (also referred to as "individual wheel control") that individually controls the wheel pressure Pw of each wheel, such as anti-lock brake control and anti-skid control. Specifically, each wheel is equipped with a wheel speed sensor VW that detects its rotational speed Vw (wheel speed). In addition, a steering amount sensor that detects the steering amount Sa (for example, the operating angle) of the steering operation member (for example, the steering wheel), a yaw rate sensor that detects the yaw rate Yr of the vehicle, a longitudinal acceleration sensor that detects the longitudinal acceleration Gx of the vehicle (also referred to as "deceleration"), and a lateral acceleration sensor that detects the lateral acceleration Gy of the vehicle are provided (not shown above).

[0020] The vehicle is equipped with a braking control device SC. In the braking control device SC, a so-called front-rear type (also referred to as "Type II") is adopted as the two braking systems. The actual wheel pressure Pw of each wheel cylinder CW is adjusted by the braking control device SC.

[0021] The braking control device SC is composed of two braking units SA and SB. The first braking unit SA is composed of a first actuator YA (fluid unit) and a first controller EA (control unit). The first actuator YA is controlled by the first controller EA using a battery BT different from the regenerative battery BG as a power source. The second braking unit SB is composed of a second actuator YB (fluid unit) and a second controller EB (control unit). The second actuator YB is controlled by the second controller EB using the battery BT as a power source, similar to the first braking unit SA.

[0022] The first braking unit SA (specifically the first controller EA) and the second braking unit SB (specifically the second controller EB) are connected to the communication bus BS. The regenerative braking unit KG (specifically the regenerative controller EG) is also connected to the communication bus BS. Signal transmission occurs between multiple controllers (EA, EB, EG, etc.) via the communication bus BS. In other words, multiple controllers can send signals (detected values, calculated values, control flags, etc.) to the communication bus BS and can also receive such signals from the communication bus BS.

[0023] <First Braking Unit SA> The first braking unit SA of the braking control device SC will now be described. The first braking unit SA adjusts the hydraulic pressures Pwf and Pwr (referred to as "front wheel and rear wheel pressure") of the front and rear wheel cylinders CWf and CWr in response to the operation of the braking operating member BP (brake pedal). The first braking unit SA consists of a first actuator YA and a first controller EA.

[0024] ≪First Actuator YA≫ The first actuator YA consists of an apply section AP, a pressure regulating section CA, and an input section NR.

[0025] [Apply Department AP] In response to the operation of the braking control member BP, the master pressure Pm is output from the apply unit AP. The apply unit AP consists of a single-type master cylinder CM and a master piston NM.

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

[0027] When not braking, the master piston NM is in its most retracted position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is in communication with the master reservoir RV. Braking fluid BF is stored inside the master reservoir RV (an atmospheric pressure reservoir, also simply called the "reservoir"). When the braking operating member BP is operated, the master piston NM is moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases). This movement disconnects the communication between the master chamber Rm and the reservoir RV. Then, when the master piston NM is moved further in the forward direction Ha, the master pressure Pm (internal pressure of the master chamber Rm) increases from "0 (atmospheric pressure)". As a result, the braking fluid BF, pressurized to the master pressure Pm, is output (pressurized) from the master chamber Rm of the master cylinder CM.

[0028] [Pressure Regulating Unit CA] The pressure regulating unit CA supplies a first hydraulic pressure Pa to the rear wheel cylinder CWr and a second hydraulic pressure Pb to the servo chamber Ru of the apply unit AP. The pressure regulating unit CA consists of an electric motor MA, a fluid pump QA, and first and second pressure regulating valves UA and UB. Details of the pressure regulating unit CA will be described later.

[0029] [Input Section NR] The input unit NR enables regenerative cooperative control. Regenerative cooperative control is a system that works in cooperation with hydraulic braking force Fp (braking force due to wheel pressure Pw) and regenerative braking force Fg (braking force due to regenerative generator GN) so that the kinetic energy of the vehicle is efficiently recovered as electrical energy during braking. In regenerative cooperative control, the braking operating member BP is operated, but a state is created in which no wheel pressure Pw is generated. The input unit NR consists of an input cylinder CN, an input piston NN, an introduction valve VA, an opening valve VB, a stroke simulator SS, and a simulator hydraulic pressure sensor PS.

[0030] The input cylinder CN is fixed to the master cylinder CM. The input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to the braking pedal BP via a clevis (U-shaped link) so as to move in conjunction with the braking pedal BP. There is a gap Ks (also called "separation displacement") between the end face of the input piston NN and the end face of the master piston NM. Regenerative braking coordinated control is achieved by adjusting the separation distance Ks with the second hydraulic pressure Pb.

[0031] The input chamber Rn of the input unit NR is connected to the reaction chamber Rs of the apply unit AP via the input path HN (fluid path). The input path HN is equipped with a normally closed inlet valve VA. Between the inlet valve VA and the reaction chamber Rs, the input path HN is connected to the master reservoir RV via the reservoir path HR (fluid path). The reservoir path HR is equipped with a normally open release valve VB. On / off type solenoid valves are used for the inlet valve VA and the release valve VB. Between the inlet valve VA and the reaction chamber Rs, a stroke simulator SS (also simply called "simulator") is connected to the input path HN.

[0032] If power is not supplied to the inlet valve VA and the release valve VB, the inlet valve VA will close and the release valve VB will open. Closing the inlet valve VA seals the input chamber Rn, locking the fluid. As a result, the master piston NM is displaced together with the braking operating member BP. Opening the release valve VB connects the simulator SS and the reaction chamber Rs to the master reservoir RV.

[0033] When power is supplied to the inlet valve VA and the release valve VB, the inlet valve VA opens and the release valve VB closes. This allows the master piston NM to be displaced independently of the braking operating member BP. At this time, the input chamber Rn is connected to the stroke simulator SS, so the operating force Fp of the braking operating member BP is generated by the simulator SS. A simulator pressure sensor PS is provided in the input path HN between the inlet valve VA and the reaction chamber Rs to detect the hydraulic pressure Ps (simulator pressure) inside the simulator SS.

[0034] ≪First Controller EA≫ The first actuator YA is controlled by the first controller EA. The first controller EA consists of a microprocessor MP and a drive circuit DR. The first controller EA is connected to a communication bus BS so that it can share signals (detected values, calculated values, control flags, etc.) with various controllers (EB, EG, etc.).

[0035] The first controller EA receives various signals directly, including operating displacement Sp, simulator pressure Ps, first and second hydraulic pressures Pa and Pb, and first and second temperatures Ta and Tb. Furthermore, the first controller EA receives various signals from the communication bus BS, including master pressure Pm, limiting regenerative braking force Fx, master temperature Tm, and execution flag FA. The first controller EA also outputs the target regenerative braking force Fh (target value of regenerative braking force Fg) to the communication bus BS. The regenerative controller EG controls the regenerative braking force Fg (actual value) based on the target regenerative braking force Fh (target value) obtained from the communication bus BS.

[0036] The first controller EA (specifically the microprocessor MP) is programmed with a pressure regulation control algorithm. Pressure regulation control is the control for adjusting the front and rear wheel pressures Pwf and Pwr, and includes regenerative braking control. Pressure regulation control is performed based on the various signals (Sp, Ps, etc.) mentioned above.

[0037] Based on a pressure regulation control algorithm, the drive circuit DR drives the electric motor MA and various solenoid valves (UA, UB, etc.). The drive circuit DR is configured with an H-bridge circuit using switching elements (e.g., MOS-FETs) to drive the electric motor MA. The drive circuit DR is also equipped with switching elements to drive various solenoid valves (UA, UB, etc.). In addition, the drive circuit DR includes a motor current sensor (not shown) for detecting the supply current Im (actual value, referred to as "motor current") to the electric motor MA, and first and second supply current sensors (not shown) for detecting the supply currents Ia and Ib (actual values, referred to as "first and second supply currents") to the first and second pressure regulating valves UA and UB. The electric motor MA is provided with a rotation speed sensor (not shown) for detecting its rotation speed Na (actual value). For example, the electric motor MA may be provided with a rotation angle sensor (not shown) for detecting the rotation angle Ka (actual value), and the motor rotation speed Na may be calculated based on the motor rotation angle Ka. Furthermore, the motor rotational speed Na can be estimated based on the motor current Im.

[0038] In the first controller EA, the first and second target currents Ita and Itb (target values) corresponding to the first and second pressure regulating valve currents Ia and Ib are calculated based on the operating displacement Sp (the amount of operation of the braking operating member BP). The first and second supply currents Ia and Ib are then controlled to approach and match the first and second target currents Ita and Itb (so-called current feedback control). In addition, the first controller EA calculates the target rotational speed Nta (target value) corresponding to the motor rotational speed Na (actual value) based on the operating displacement Sp. The motor current Im is then controlled to approach and match the motor rotational speed Nta (so-called rotational speed feedback control). Based on these control algorithms, the drive signal Ma for controlling the electric motor MA, and the drive signals Ua, Ub, Va, and Vb for controlling various solenoid valves UA, UB, VA, and VB are calculated. Then, in response to the drive signal (Ma, etc.), the switching elements of the drive circuit DR are driven, and the electric motor MA and the solenoid valves UA, UB, VA, and VB are controlled.

[0039] <Second braking unit SB> A second braking unit SB is provided between the first braking unit SA and the wheel cylinder CW. The second braking unit SB performs independent control of each wheel, including anti-lock brake control, traction control, and anti-skid control.

[0040] In the braking system for the front wheels (i.e., the front wheel connecting passage HSf), the master pressure Pm is supplied from the master cylinder CM to the second braking unit SB. On the other hand, in the braking system for the rear wheels (i.e., the rear wheel connecting passage HSr), the first hydraulic pressure Pa is supplied directly from the pressure regulating unit CA to the second braking unit SB. In the second braking unit SB, the master pressure Pm and the first hydraulic pressure Pa are adjusted (increased or decreased) and output as the hydraulic pressures Pwf and Pwr (front wheel and rear wheel pressures) for the front and rear wheel cylinders CWf and CWr, respectively. The second braking unit SB consists of a second actuator YB and a second controller EB.

[0041] The second actuator YB is positioned in the communication path HS between the first actuator YA and the wheel cylinder CW. The second actuator YB includes an electric motor, a fluid pump, a solenoid valve, a master pressure sensor PM, and a master temperature sensor TM. The master pressure sensor PM detects the master pressure Pm, and the master temperature sensor TM detects the master temperature Tm (the temperature of the brake fluid BF in the second actuator YB). The master pressure Pm and master temperature Tm are input to the second controller EB. The configuration of the second actuator YB is known, so its description is omitted.

[0042] The second controller EB controls the second actuator YB. The second controller EB is connected to the communication bus BS. Therefore, the first controller EA and the second controller EB can share signals via the communication bus BS.

[0043] The second controller EB receives various signals, including wheel speed Vw, steering angle Sa, yaw rate Yr, longitudinal acceleration Gx, and lateral acceleration Gy. Based on the wheel speed Vw, the second controller EB calculates the vehicle speed Vx. Based on the various signals (Vw, Yr, etc.), the second controller EB executes anti-lock brake control to suppress wheel lock, traction control to suppress wheelspin of the drive wheels, and anti-skid control (so-called ESC) to suppress understeer and oversteer and improve the directional stability of the vehicle. The execution of these controls is communicated from the second braking unit SB (especially the second controller EB) to the first braking unit SA (especially the first controller EA) via the communication bus BS using control flags, etc.

[0044] Normally, when regenerative braking is performed, the operation of the second actuator YB (electric motor, fluid pump, solenoid valve, etc.) is stopped. Therefore, the second braking unit SB outputs the master pressure Pm as the front wheel pressure Pwf, and the first hydraulic pressure Pa as the rear wheel pressure Pwr.

[0045] <Pressure Regulating Section CA> Referring to the schematic diagram in Figure 2, the pressure regulating unit CA, which is applied to a vehicle equipped with a regenerative generator GN on the front wheel, will be described. In addition to the pressure regulating unit CA, the master cylinder CM, wheel cylinder CW, etc. are schematically shown in Figure 2, and the hydraulic pressure transmission path is indicated. The pressure regulating unit CA outputs first and second hydraulic pressures Pa and Pb, and controls the front wheel and rear wheel pressures Pwf and Pwr. The pressure regulating unit CA consists of a fluid pump QA, an electric motor MA, first and second pressure regulating valves UA and UB, and first and second hydraulic pressure sensors PA and PB.

[0046] The fluid pump QA is driven by an electric motor MA. That is, the combination of the electric motor MA and the fluid pump QA forms an electric pump. In the fluid pump QA, the suction section Qi, which draws in the brake fluid BF, and the discharge section Qo, which discharges the brake fluid BF, are connected by a return passage HK (fluid passage). The suction section Qi of the fluid pump QA is also connected to the master reservoir RV via a reservoir passage HR. A check valve GA (also called a "check valve") is provided at the discharge section Qo of the fluid pump QA.

[0047] Two pressure regulating valves, UA and UB, are installed in series in the return channel HK. Specifically, a normally open second pressure regulating valve UB is installed in the return channel HK. A normally open first pressure regulating valve UA is installed between the second pressure regulating valve UB and the discharge port Qo of the fluid pump QA. Therefore, in the circulating flow KN of the bremflue BF (indicated by the dashed arrow), the first pressure regulating valve UA is positioned upstream of the second pressure regulating valve UB (closer to the discharge port Qo of the fluid pump QA). The first and second pressure regulating valves UA and UB are linear solenoid valves whose opening amount (lift amount) is continuously controlled according to the energized state (e.g., supply current Ia and Ib). The first and second pressure regulating valves UA and UB adjust the difference in fluid pressure (differential pressure) between their upstream and downstream sides, and are therefore also called "differential pressure valves".

[0048] When the fluid pump QA is driven by the electric motor MA, a circulating flow KN (the flow of bremsting fluid BF circulating in the return channel HK) of the fluid pump QA and the first and second pressure regulating valves UA and UB is generated in the return channel HK. The hydraulic pressure Pb (second hydraulic pressure) between the first pressure regulating valve UA and the second pressure regulating valve UB is controlled by the second pressure regulating valve UB. The hydraulic pressure Pa (first hydraulic pressure) between the first pressure regulating valve UA and the discharge part Qo of the fluid pump QA is controlled by the first pressure regulating valve UA.

[0049] When the second pressure regulating valve UB is fully open (since the second pressure regulating valve UB is normally open, this is when it is not energized), the second hydraulic pressure Pb is "0 (atmospheric pressure)". When the supply current Ib (second supply current) to the second pressure regulating valve UB is increased, the flow path of the return channel HK is narrowed by the second pressure regulating valve UB. As a result, a differential pressure ΔPub (referred to as the "second differential pressure") is generated between the downstream hydraulic pressure (atmospheric pressure "0") and the upstream hydraulic pressure Pb (second hydraulic pressure) with respect to the second pressure regulating valve UB. Therefore, the second hydraulic pressure Pb is equal to the second differential pressure ΔPub (i.e., "Pb = ΔPub"). Here, the second differential pressure ΔPub is regulated by the second supply current Ib.

[0050] Similarly, when the first pressure regulating valve UA is fully open (since the first pressure regulating valve UA is normally open, this is when it is not energized), the first hydraulic pressure Pa is equal to the second hydraulic pressure Pb. When the supply current Ia (first supply current) to the first pressure regulating valve UA is increased, the circulating flow KN is throttled by the first pressure regulating valve UA. This creates a differential pressure ΔPua (referred to as the "first differential pressure") between the downstream hydraulic pressure Pb (second hydraulic pressure) and the upstream hydraulic pressure Pa (first hydraulic pressure) with respect to the first pressure regulating valve UA. Therefore, the first hydraulic pressure Pa is equal to the sum of the second hydraulic pressure Pb and the first differential pressure ΔPua (i.e., "Pa = Pb + ΔPua = ΔPua + ΔPub"). Here, the first differential pressure ΔPua is regulated by the first supply current Ia. Furthermore, in the relationship between the first hydraulic pressure Pa and the second hydraulic pressure Pb, the first hydraulic pressure Pa is always greater than or equal to the second hydraulic pressure Pb (i.e., "Pa ≥ Pb").

[0051] In the braking control device SC, regenerative braking force Fg is generated at the front wheels, and the front wheel pressure Pwf is adjusted by the second hydraulic pressure Pb. In the braking system for the front wheels, the return passage HK is connected to the servo chamber Ru of the master cylinder CM via the servo passage HV (fluid passage) between the first pressure regulating valve UA and the second pressure regulating valve UB. Therefore, the second hydraulic pressure Pb is introduced (supplied) to the servo chamber Ru. As the second hydraulic pressure Pb increases, the master piston NM is pressed in the forward direction Ha, and the hydraulic pressure Pm (master pressure) in the master chamber Rm increases. The front wheel connecting passage HSf is connected to the master chamber Rm. The front wheel connecting passage HSf is connected to the front wheel cylinder CWf via the second braking unit SB. Therefore, in the front wheel braking system, the second hydraulic pressure Pb is supplied to the front wheel cylinder CWf as master pressure Pm via the master cylinder CM. In other words, in the front wheel braking system, the second hydraulic pressure Pb generated in the pressure regulating unit CA is transmitted to the front wheel cylinder CWf in the order "Pb → Pm → Pwf". Here, since "ru = rm", "Pb = Pm = Pwf".

[0052] In the braking control device SC, the rear wheel pressure Pwr is adjusted by the first hydraulic pressure Pa. In the braking system for the rear wheels, the return passage HK is connected to the rear wheel connecting passage HSr (fluid passage) between the discharge section Qo of the fluid pump QA and the first pressure regulating valve UA. The rear wheel connecting passage HSr is connected to the rear wheel cylinder CWr via the second braking unit SB. Therefore, in the rear wheel braking system, the first hydraulic pressure Pa is supplied directly to the rear wheel cylinder CWr. In other words, in the rear wheel braking system, the first hydraulic pressure Pa generated in the pressure regulating section CA is transmitted to the rear wheel cylinder CWr in the order "Pa → Pwr". Here, "Pa = Pwr".

[0053] The pressure regulating unit CA is equipped with first and second hydraulic pressure sensors PA and PB to detect the first and second hydraulic pressures Pa and Pb, respectively. The detected first and second hydraulic pressures Pa and Pb are input to the first controller EA. In addition, the master pressure Pm detected by the master pressure sensor PM of the second actuator YB is input to the first controller EA via the communication bus BS.

[0054] The pressure regulating section CA (particularly the return channel HK) is equipped with first and second temperature sensors TA and TB to detect the first and second temperatures Ta and Tb of the brake fluid BF (working fluid). The detected first and second temperatures Ta and Tb are input to the first controller EA. In addition, the master temperature Tm detected by the master temperature sensor TM of the second actuator YB is input to the first controller EA via the communication bus BS. For example, the first and second temperature sensors TA and TB and the master temperature sensor TM are built into the first and second hydraulic pressure sensors PA and PB and the master pressure sensor PM. The detected temperatures (Ta, etc.) are then used for temperature compensation of the hydraulic pressure sensors (PA, etc.).

[0055] In the first controller EA, at least one of the first and second temperatures Ta and Tb is determined as the temperature Te of the bremfluid BF (working fluid) in the reflux channel HK. Alternatively, the temperature Te of the bremfluid BF (working fluid) in the reflux channel HK may be estimated based on the master temperature Tm. In other words, the temperature Te of the bremfluid BF is determined based on at least one of the first and second temperatures Ta and Tb, and the master temperature Tm.

[0056] ≪Temperature Dependence of the First Differential Pressure ΔPua≫ The braking control device SC selectively switches between "two-system pressure regulation in which the front and rear wheel pressures Pwf and Pwr are individually controlled by the first and second pressure regulating valves UA and UB" and "one-system pressure regulation in which the front and rear wheel pressures Pwf and Pwr are controlled to the same extent by only the second pressure regulating valve UB". In one-system pressure regulation, the first pressure regulating valve UA is not powered and is kept in a fully open state. Even when the first pressure regulating valve UA is fully open, the size of the gap between the valve body and the valve seat (i.e., the amount of opening) is limited. Therefore, this gap acts as resistance to the circulating flow KN, and a small differential pressure ΔPua is generated at the first pressure regulating valve UA. In the return flow path HK, when the temperature Te of the braking fluid BF (working fluid) is normal (for example, at room temperature, 20°C), the first differential pressure ΔPua is negligible. However, as the temperature Te decreases, the viscosity of the brake fluid BF increases, causing the first differential pressure ΔPua to gradually increase. At extremely low temperatures (e.g., below -10°C), the magnitude of the first differential pressure ΔPua increases to the extent that it affects the vehicle's deceleration Gx.

[0057] In a single-system pressure regulation system, the second hydraulic pressure Pb is adjusted by the second pressure regulating valve UB based on the front wheel target pressure Ptf, which corresponds to the front wheel pressure Pwf. At this time, the first pressure regulating valve UA is fully open. At normal temperatures (room temperature), since "ΔPau ≈ 0", the first hydraulic pressure Pa is approximately equal to the second hydraulic pressure Pb. However, at low temperatures, the first differential pressure ΔPau becomes larger, so the first hydraulic pressure Pa is higher than the second hydraulic pressure Pb. As a result, due to the decrease in the temperature of the brake fluid BF, a situation may arise where the vehicle's deceleration Gx is not constant (for example, excessive). In the braking control device SC, this is taken into consideration, and the second hydraulic pressure Pb (and consequently the front and rear wheel pressures Pwf and Pwr) is adjusted accordingly.

[0058] <Pressure regulation control process> The pressure regulation control process will be explained with reference to the flowchart in Figure 3. In pressure regulation control, the first braking unit SA selects and executes either two-system pressure regulation or one-system pressure regulation. In "two-system pressure regulation," the first and second pressure regulating valves UA and UB independently and individually adjust the front and rear wheel pressures Pwf and Pwr. In contrast, in "one-system pressure regulation," only the second pressure regulating valve UB adjusts the front and rear wheel pressures Pwf and Pwr. For example, one-system pressure regulation is selected when anti-lock brake control is performed by the second braking unit SB, or when sufficient regenerative operation cannot be performed by the regenerative device KG. If one-system pressure regulation is not selected, two-system pressure regulation is selected.

[0059] In pressure regulation control, power is first supplied to the inlet valve VA and the release valve VB, causing the normally closed inlet valve VA to open and the normally open release valve VB to close. This allows the master piston NM and the braking operating member BP to be displaced separately, and the front and rear wheel pressures Pwf and Pwr are adjusted independently of the operation of the braking operating member BP. At this time, the operating force Fp of the braking operating member BP is generated by the stroke simulator SS.

[0060] In step S110, various signals are read. The first controller EA acquires the operating displacement Sp, the first and second hydraulic pressures Pa and Pb, and the first and second temperatures Ta and Tb from the operating displacement sensor SP, the first and second hydraulic pressure sensors PA and PB, and the first and second temperature sensors TA and TB. The first controller EA also acquires the master pressure Pm, master temperature Tm, execution flag FA, and limit regenerative braking force Fx from the communication bus BS.

[0061] The "execution flag FA" is a control flag that indicates whether or not anti-lock brake control is being performed in the second braking unit SB. The execution flag FA is transmitted from the second controller EB to the communication bus BS. For example, "FA=0" is transmitted if anti-lock brake control is not being performed, and "FA=1" is transmitted if anti-lock brake control is being performed. The first controller EA can identify the execution status of anti-lock brake control based on the execution flag FA.

[0062] The "limit regenerative braking force Fx" is the upper limit (limit value) of the regenerative braking force Fg that the regenerative device KG can generate. In other words, the regenerative device KG can generate a regenerative braking force Fg within the range from "0" to the limit regenerative braking force Fx. The amount of regeneration (and consequently the regenerative braking force Fg) from the regenerative device KG is limited by the rating of the power transistor (IGBT, etc.) of the regenerative controller EG and the charge acceptance capacity of the regenerative battery BG. For example, the regenerative braking force Fg from the regenerative device KG is controlled to a predetermined power (electrical energy per unit time). Since the power (work rate) is constant, the regenerative braking force Fg is inversely proportional to the rotational speed Ng of the regenerative generator GN (i.e., the rotational speed Vw of the wheels, which corresponds to the vehicle speed Vx). Also, if the rotational speed Ng of the regenerative generator GN decreases, the regenerative braking force Fg decreases. Furthermore, the limiting regenerative braking force Fx is subject to a maximum regenerative braking force fx (also called "maximum regenerative force"). The limiting regenerative braking force Fx is transmitted from the regenerative controller EG to the communication bus BS. The first controller EA can understand the operating status of the regenerative device KG based on the limiting regenerative braking force Fx.

[0063] In step S120, the target total braking force Fv is calculated based on the operating displacement Sp and the calculation map Zfv. The "target total braking force Fv" is the target value of the braking force acting on the entire vehicle. As shown in the target total braking force calculation block FV, the target total braking force Fv is calculated to be "0" according to the calculation map Zfv if the operating displacement Sp is less than a predetermined displacement so. If the operating displacement Sp is greater than or equal to the predetermined displacement so, the target total braking force Fv is calculated to increase from "0" as the operating displacement Sp increases from "0". Here, the "predetermined displacement so" is a predetermined value (constant) that represents the play of the braking operating member BP.

[0064] In step S130, it is determined whether or not to select "single-system pressure regulation". The process in step S130 is referred to as the "selection determination". In the selection determination, two-system pressure regulation is selected as the initial setting. The selection determination is performed based on at least one of the operating status of the second braking unit SB and the operating status of the regenerative device KG. For example, in the following cases, the selection determination is affirmed, and the system switches from two-system pressure regulation to one-system pressure regulation.

[0065] (A) When anti-lock brake control is performed by the second braking unit SB While anti-lock brake control is in operation, the pressure regulation control is switched to single-system pressure regulation. Here, the status of anti-lock brake control is determined based on the execution flag FA.

[0066] (B) When the regenerative braking force Fg cannot be generated by the regenerative braking device KG (or when there are limitations on the generation of the regenerative braking force Fg) If the regenerative braking system KG malfunctions, or if the regenerative battery BG is not charging properly, a single-system voltage regulator is used. For example, this situation is determined based on the limit regenerative braking force Fx.

[0067] When the selection determination in step S130 is negative, two - line pressure regulation is selected and the process proceeds to step S140. On the other hand, when the selection determination is positive, one - line pressure regulation is selected and the process proceeds to step S160.

[0068] ≪Two - line pressure regulation process≫ In step S140, based on the target total braking force Fv and the limit regenerative braking force Fx, the target regenerative braking force Fh and the front - wheel and rear - wheel target hydraulic braking forces Fnf, Fnr are calculated. Specifically, based on the following case - by - case analysis, the target values Fh, Fnf, Fnr are determined.

[0069] Case (1): When the target total braking force Fv is less than or equal to the limit regenerative braking force Fx, the target regenerative braking force Fh is made equal to the target total braking force Fv, and the front - wheel and rear - wheel target hydraulic braking forces Fnf, Fnr are made "0". That is, when "Fv≦Fx", "Fh = Fv, Fnf = Fnr = 0" is determined.

[0070] Case (2): When the target total braking force Fv is greater than the limit regenerative braking force Fx and less than or equal to the value (Fx / hf) obtained by dividing the limit regenerative braking force Fx by the front - wheel ratio hf, the target regenerative braking force Fh is made equal to the target total braking force Fv. Then, the front - wheel target hydraulic braking force Fnf is made "0", and the rear - wheel target hydraulic braking force Fnr is determined to be the value obtained by subtracting the target regenerative braking force Fh (=Fx) from the target total braking force Fv. That is, when "Fx < Fv≦(Fx / hf)", "Fh = Fx, Fnf = 0, Fnr = Fv - Fh = Fv - Fx" is determined. Note that the "front - wheel ratio hf" is the ratio of the front - wheel target braking force (i.e., the sum of the target regenerative braking force Fh and the front - wheel target hydraulic braking force Fnf) to the target total braking force Fv, and is a predetermined value (constant) set in advance based on the specifications of the braking device.

[0071] Case (3): If the target total braking force Fv is greater than the value obtained by dividing the limit regenerative braking force Fx by the front wheel ratio hf (Fx / hf), then the target regenerative braking force Fh is set to be equal to the target total braking force Fv. The front wheel target hydraulic braking force Fnf is then calculated by subtracting the target regenerative braking force Fh from the value obtained by multiplying the target total braking force Fv by the front wheel ratio hf (hf·Fv). The rear wheel target hydraulic braking force Fnr is then calculated by multiplying the value obtained by subtracting the front wheel ratio hf from "1" by the target total braking force Fv. That is, if "Fv > (Fx / hf)", then "Fh = Fx, Fnf = hf·Fv - Fh, Fnr = (1-hf)·Fv" are determined.

[0072] Ultimately, in step S140, the target front and rear wheel pressures Ptf and Ptr (=Pt) are calculated based on the target front and rear wheel hydraulic braking forces Fnf and Fnr (=Fn). The "target front and rear wheel pressures Ptf and Ptr" are the target values ​​for the front and rear wheel pressures Pwf and Pwr. The target front and rear wheel pressures Ptf and Ptr are determined by converting the target hydraulic braking forces Fnf and Fnr into the dimensions of the front and rear wheel pressures Pwf and Pwr based on the specifications of the braking system, etc. Here, the above specifications include the pressure-receiving area of ​​the wheel cylinder CW, the effective braking radius of the rotating member (brake disc), the coefficient of friction of the friction material (brake pad), and the effective radius of the wheel (tire).

[0073] In step S150, the front and rear wheel pressures Pwf and Pwr (actual values) are adjusted by the pressure regulating unit CA based on the front and rear wheel target pressures Ptf and Ptr (target values). Specifically, the first controller EA drives the electric motor MA and the first and second pressure regulating valves UA and UB, controlling the front and rear wheel pressures Pwf and Pwr to approach and match the front and rear wheel target pressures Ptf and Ptr. In other words, in the two-system pressure regulating, power is supplied to the first and second pressure regulating valves UA and UB.

[0074] In step S150, the electric motor MA is driven, generating a circulating flow KN including the fluid pump QA and the first and second pressure regulating valves UA and UB. For front wheel pressure regulation, the second pressure regulating valve UB is controlled so that the master pressure Pm (=Pwf) matches the front wheel target pressure Ptf, based on the front wheel target pressure Ptf and the master pressure Pm. In other words, the supply current Ib to the second pressure regulating valve UB is adjusted by feedback control so that the deviation hPf between the master pressure Pm and the front wheel target pressure Ptf becomes "0". Here, since the pressure-receiving area ru of the servo chamber Ru and the pressure-receiving area rm of the master chamber Rm are equal, hydraulic pressure control may be performed using the second hydraulic pressure Pb instead of the master pressure Pm.

[0075] Based on the rear wheel target pressure Ptr and the first hydraulic pressure Pa, the first pressure regulating valve UA is controlled so that the first hydraulic pressure Pa (=Pwr) matches the rear wheel target pressure Ptr. In other words, the supply current Ia to the first pressure regulating valve UA is adjusted by feedback control so that the deviation hPr between the first hydraulic pressure Pa and the rear wheel target pressure Ptr becomes "0".

[0076] <<Processing for adjusting voltage in one system>> If the selection decision in step S130 is affirmed, the power supply to the first pressure regulating valve UA is stopped, and the first pressure regulating valve UA opens. Since the first pressure regulating valve UA is a normally open solenoid valve, it is fully opened when the power supply is stopped. This switches from two-system pressure regulating to one-system pressure regulating.

[0077] In step S160, the sum of the target regenerative braking force Fh and the target hydraulic braking force Fn, Fnt (also called the "target sum"), is calculated based on the target total braking force Fv and the limit regenerative braking force Fx. Here, the "target sum Fnt" is the sum of the front wheel target hydraulic braking force Fnf and the rear wheel target hydraulic braking force Fnr (i.e., "Fnt = Fnf + Fnr"). In step S160, if the target total braking force Fv is less than or equal to the limit regenerative braking force Fx, the target regenerative braking force Fh is made equal to the target total braking force Fv, and the sum of the target hydraulic braking forces Fn, Fnt, is made "0" (i.e., if "Fv ≤ Fx", then "Fh = Fv, Fnt = 0"). On the other hand, if the target total braking force Fv is greater than the limiting regenerative braking force Fx, the target regenerative braking force Fh is set to be equal to the limiting regenerative braking force Fx, and the target sum Fnt is set to "the value obtained by subtracting the target regenerative braking force Fh (=Fx) from the target total braking force Fv" (i.e., if "Fv > Fx", then "Fh = Fx, Fnt = Fv - Fh = Fv - Fx").

[0078] In step S160, the front wheel target pressure Ptf is calculated based on the target total Fnt. Specifically, the front wheel target pressure Ptf is determined based on the specifications of the braking system so that the front wheel target pressure Ptf and the rear wheel target pressure Ptf are equal and the target total Fnt is satisfied. In other words, if "Fv ≤ Fx", the front wheel target pressure Ptf (= Ptr) is determined to be "0". On the other hand, if "Fv > Fx", the front wheel target pressure Ptf is determined so that "Ptf = Ptr" is satisfied and the total target hydraulic braking force Fn (target total) Fnt is equal to the value "Fv - Fh". As above, the specifications of the braking system include the pressure-receiving area of ​​the wheel cylinder CW, the effective braking radius of the rotating member, the friction coefficient of the friction material, and the effective radius of the wheel.

[0079] If single-system control is selected, in step S160, the target regenerative braking force Fh may be determined to be "0", and the operation of the regenerative device KG may be stopped. For example, when anti-lock brake control is started, "Fh=0" is transmitted to the regenerative device KG, and the regenerative device KG is stopped. Even in the case of "Fh=0", the front wheel target pressure Ptf is calculated based on the specifications of the braking system so that "Ptf=Ptr, Fnf+Fnr=Fv" is satisfied.

[0080] In step S170, a corrected target pressure Psf is calculated based on the front wheel target pressure Ptf and the temperature Te of the brake fluid BF (working fluid) in the return channel HK. The "corrected target pressure Psf" is a target value obtained by correcting the front wheel target pressure Ptf according to the temperature Te (i.e., the corrected target pressure). In step S170, first, the temperature Te of the brake fluid BF in the return channel HK is determined based on at least one of the first and second temperatures Ta and Tb, and the master temperature Tm. Here, the first and second temperatures Ta and Tb, and the master temperature Tm are detected by the first and second temperature sensors TA and TB, and the master temperature sensor TM.

[0081] Next, in step S170, based on the temperature Te, the corrected pressure eP is the hydraulic pressure used to correct the front wheel target pressure Ptf. Specifically, according to the calculation map Zep shown in the corrected pressure calculation block EP, if the temperature Te is greater than or equal to a predetermined temperature te, the corrected pressure eP is determined to be "0". If the temperature Te is less than the predetermined temperature te, the corrected pressure eP is calculated to increase as the temperature Te decreases. An upper limit pressure ep is also set for the corrected pressure eP. Here, the predetermined temperature te (also called the "first predetermined temperature") and the upper limit pressure ep are predetermined values ​​(constants) set in advance. The predetermined temperature te is a temperature lower than the freezing point (0°C). Finally, in step S170, the corrected target pressure Psf is calculated based on the front wheel target pressure Ptf and the corrected pressure eP. Specifically, the corrected target pressure Psf is determined by subtracting the corrected pressure eP from the front wheel target pressure Ptf (i.e., "Psf = Ptf - eP").

[0082] In step S180, the front wheel pressure Pwf (actual value) is adjusted by the pressure regulating unit CA based on the correction target pressure Psf (target value). In step S180, the electric motor MA and the second pressure regulating valve UB are driven and controlled so that the front wheel pressure Pwf (=Pm) approaches and matches the correction target pressure Psf. Here, the rear wheel pressure Pwr (actual value) is determined by the progression of the front wheel pressure Pwf. That is, in a single-system pressure regulating system, power is supplied only to the second pressure regulating valve UB.

[0083] In step S180, similar to step S150, the electric motor MA is driven, and a circulating flow KN is generated, including the fluid pump QA and the first and second pressure regulating valves UA and UB. At this time, the first pressure regulating valve UA is not supplied with power, so it is in a fully open state. In single-system pressure regulation, only the second pressure regulating valve UB is controlled so that the master pressure Pm (=Pwf) matches the corrected target pressure Psf, based on the corrected target pressure Psf and the master pressure Pm. Note that, similar to two-system pressure regulation, in single-system pressure regulation, the second hydraulic pressure Pb may be used instead of the master pressure Pm.

[0084] In a single-system pressure regulation, the first pressure regulating valve UA is fully open, and the second pressure regulating valve UB adjusts the second hydraulic pressure Pb (resulting in the front wheel pressure Pwf). At this time, the first hydraulic pressure Pa (resulting in the rear wheel pressure Pwr) is determined as a result of adjusting the second hydraulic pressure Pb. As described above, even when the first pressure regulating valve UA is fully open, a gap exists between the valve body and the valve seat. Therefore, this gap in the first pressure regulating valve UA acts as resistance to the circulating flow KN, generating a first differential pressure ΔPua. When the temperature Te is not very low, the first differential pressure ΔPua is negligible in relation to the vehicle's deceleration Gx. However, when the temperature Te becomes extremely low, the effect of the first differential pressure ΔPua on the vehicle's deceleration Gx becomes significant. Specifically, for the same operating displacement Sp, at extremely low temperatures, the vehicle deceleration Gx is greater than at normal temperatures by the amount corresponding to the first differential pressure ΔPua.

[0085] Therefore, in the braking control device SC, the second hydraulic pressure Pb is finely adjusted based on the temperature Te during single-system pressure regulation. First, the temperature Te is determined based on at least one of the first and second temperatures Ta, Tb, and the master temperature Tm. Next, the front wheel target pressure Ptf is corrected based on the corrected pressure eP calculated from the temperature Te of the circulating flow KN, and the corrected target pressure Psf is determined. Then, based on the corrected target pressure Psf, the second pressure regulating valve UB is controlled so that the master pressure Pm (or second hydraulic pressure Pb) matches the corrected target pressure Psf. In adjusting the second hydraulic pressure Pb by the second pressure regulating valve UB, the temperature Te of the working fluid BF is taken into consideration, so the effect of the first differential pressure ΔPua is compensated for. Therefore, even if the temperature Te decreases, the same vehicle deceleration Gx can be ensured for the same operating displacement Sp, regardless of the temperature Te. In other words, the vehicle's deceleration characteristics are always maintained constant without changing with ambient temperature.

[0086] In the two-system pressure regulation, the first and second hydraulic pressures Pa and Pb are adjusted individually, so the effect of the first differential pressure ΔPua does not affect the vehicle deceleration Gx. This is because even if the first differential pressure ΔPua increases, this effect is compensated for by feedback control based on the rear wheel target pressure Ptr and the first hydraulic pressure Pa.

[0087] <Second embodiment of the braking control device SC> Referring to the schematic diagram in Figure 4, a second embodiment of the braking control device SC will be described. While the first embodiment was applied to a vehicle equipped with a regenerative generator GN on the front wheels, the second embodiment is applied to a vehicle equipped with a regenerative generator GN on the rear wheels. The apply unit AP, input unit NR, first controller EA, and second braking unit SB according to the second embodiment are the same as those in the first embodiment, so the differences will be explained mainly.

[0088] Similar to the first embodiment, the pressure regulating unit CA according to the second embodiment is also composed of a fluid pump QA, an electric motor MA, and first and second pressure regulating valves UA and UB. The circulating flow KN generated by the electric motor MA and the fluid pump QA is regulated by the first pressure regulating valve UA and the second pressure regulating valve UB to control the first hydraulic pressure Pa and the second hydraulic pressure Pb. However, in the second embodiment, the first hydraulic pressure Pa is supplied to the servo chamber Ru, and the second hydraulic pressure Pb is supplied to the rear wheel cylinder CWr. In addition, at extremely low temperatures, the rear wheel pressure Pwr becomes excessive in the first embodiment, but a deficiency of the rear wheel pressure Pwr occurs in the second embodiment. This phenomenon will be explained below.

[0089] In the single-system pressure regulation of the second embodiment, power is stopped to the first pressure regulating valve UA, and power is supplied only to the second pressure regulating valve UB. The first hydraulic pressure Pa is then regulated solely by the second pressure regulating valve UB, and the front wheel pressure Pwf is generated by the first hydraulic pressure Pa. Specifically, the supply current Ib to the second pressure regulating valve UB is adjusted so that the master pressure Pm (=Pa) approaches and matches the front wheel target pressure Ptf. At this time, the second hydraulic pressure Pb (=Pwr) is determined as a result of adjusting the first hydraulic pressure Pa (=Pm=Pwf). As described above, the first differential pressure ΔPua is not a problem at room temperature, but at extremely low temperatures, the first differential pressure ΔPua increases due to the decrease in viscosity of the brake fluid BF.

[0090] In the first embodiment, when the second hydraulic pressure Pb (resulting in the front wheel pressure Pwf) is controlled so that the master pressure Pm matches the front wheel target pressure Ptf, the naturally occurring first hydraulic pressure Pa (resulting in the rear wheel pressure Pwr) becomes larger than the second hydraulic pressure Pb by the first differential pressure ΔPua. Therefore, at extremely low temperatures, the vehicle deceleration Gx is excessive by the amount corresponding to the first differential pressure ΔPua compared to normal temperatures (i.e., when "ΔPau ≈ 0"). In contrast, in the second embodiment, when the first hydraulic pressure Pa (resulting in the front wheel pressure Pwf) is controlled so that the master pressure Pm matches the front wheel target pressure Ptf, the naturally occurring second hydraulic pressure Pb (resulting in the rear wheel pressure Pwr) becomes smaller by the first differential pressure ΔPua. Therefore, at extremely low temperatures, the vehicle deceleration Gx is insufficient by the amount corresponding to the first differential pressure ΔPua compared to normal temperatures. To resolve this issue, in the second embodiment as well, the corrected target pressure Psf is determined according to the temperature Te of the working fluid BF.

[0091] In the second embodiment, the braking control device SC selectively performs two-system pressure regulation and one-system pressure regulation as pressure regulation control. In two-system pressure regulation, the front wheel pressures Pwf and Pwr are individually controlled by the first and second pressure regulating valves UA and UB within the range of "Pwf≧Pwr". In one-system pressure regulation, the front wheel pressures Pwf and Pwr are controlled by the second pressure regulating valve UB alone.

[0092] <<Processing of 2-system voltage regulation>> In the two-system pressure regulation according to the second embodiment, the target regenerative braking force Fh and the target hydraulic braking forces Fnf and Fnr for the front and rear wheels are determined based on the target total braking force Fv and the limit regenerative braking force Fx, divided into the following three cases. Then, based on the specifications of the braking system, etc., the target hydraulic braking forces Fnf and Fnr (=Fn) for the front and rear wheels are converted to target pressures Ptf and Ptr for the front and rear wheels.

[0093] Case (4): If the target total braking force Fv is less than or equal to the limit regenerative braking force Fx, the target regenerative braking force Fh is set to equal the target total braking force Fv, and the front and rear target hydraulic braking forces Fnf and Fnr are set to "0". That is, if "Fv ≤ Fx", then "Fh = Fv, Fnf = Fnr = 0" is determined.

[0094] Case (5): When the target total braking force Fv is greater than the limit regenerative braking force Fx and is less than or equal to the value obtained by dividing the limit regenerative braking force Fx by the rear wheel ratio hr (Fx / hr), the target regenerative braking force Fh is made equal to the target total braking force Fv. Then, the front wheel target hydraulic braking force Fnf is determined as the value obtained by subtracting the target regenerative braking force Fh (= Fx) from the target total braking force Fv, and the rear wheel target hydraulic braking force Fnr is determined as "0". That is, when "Fx < Fv ≤ (Fx / hr)", "Fh = Fx, Fnf = Fv - Fh = Fv - Fx, Fnr = 0" is determined. Note that the "rear wheel ratio hr" is the ratio of the rear wheel target braking force to the target total braking force Fv (i.e., the sum of the target regenerative braking force Fh and the rear wheel target hydraulic braking force Fnr), and is a predetermined value (constant) set in advance based on the specifications of the braking device.

[0095] Case (6): When the target total braking force Fv is greater than the value obtained by dividing the limit regenerative braking force Fx by the rear wheel ratio hr (Fx / hr), the target regenerative braking force Fh is made equal to the target total braking force Fv. Then, the front wheel target hydraulic braking force Fnf is calculated by multiplying the target total braking force Fv by the value obtained by subtracting the rear wheel ratio hr from "1". Also, the rear wheel target hydraulic braking force Fnr is calculated by subtracting the target regenerative braking force Fh from the value obtained by multiplying the target total braking force Fv by the rear wheel ratio hr (hr·Fv). That is, when "Fv > (Fx / hr)", "Fh = Fx, Fnf = (1 - hr)·Fv, Fnr = hr·Fv - Fh" is determined.

[0096] ≪Processing of pressure regulation for one system≫ In the single-system pressure adjustment process according to the second embodiment, the sum of the target regenerative braking force Fh and the target hydraulic braking force Fn, Fnt (target sum), is calculated based on the target total braking force Fv and the limit regenerative braking force Fx. If the target total braking force Fv is less than or equal to the limit regenerative braking force Fx, the target regenerative braking force Fh is made equal to the target total braking force Fv, and the sum of the target hydraulic braking forces Fn, Fnt, is made "0" (i.e., if "Fv ≤ Fx", then "Fh = Fv, Fnt = 0"). On the other hand, if the target total braking force Fv is greater than the limiting regenerative braking force Fx, the target regenerative braking force Fh is set to be equal to the limiting regenerative braking force Fx, and the target sum Fnt is set to "the value obtained by subtracting the target regenerative braking force Fh (=Fx) from the target total braking force Fv" (i.e., if "Fv > Fx", then "Fh = Fx, Fnt = Fv - Fh = Fv - Fx").

[0097] The front wheel target pressure Ptf is determined based on the brake system specifications such that both the target total pressure Fnt and the condition "Ptf = Ptr" are satisfied. Therefore, if "Fv ≤ Fx", the front wheel target pressure Ptf (= Ptr) is determined to be "0". If "Fv > Fx", the front wheel target pressure Ptf is determined such that the target total pressure Fnt is equal to the value "Fv - Fh" under the condition "Ptf = Ptr".

[0098] Based on the temperature Te and the calculation map Zep, the corrected pressure eP is calculated (see the corrected pressure calculation block EP in Figure 3). Then, the corrected pressure eP is added to the front wheel target pressure Ptf to determine the corrected target pressure Psf (i.e., "Psf = Ptf + eP"). In the first embodiment, the corrected target pressure Psf was determined such that the front wheel target pressure Ptf decreased due to the corrected pressure eP. Conversely, in the second embodiment, the corrected target pressure Psf was determined by correcting the front wheel target pressure Ptf to increase due to the corrected pressure eP. At extremely low temperatures, there is a shortage of vehicle deceleration Gx corresponding to the first differential pressure ΔPua, but in the adjustment of the first hydraulic pressure Pa by the second pressure regulating valve UB, the shortage of vehicle deceleration Gx is suppressed by the correction of increasing the front wheel target pressure Ptf according to the temperature Te. As a result, the vehicle's deceleration characteristics are always maintained constant without changing with ambient temperature.

[0099] <Variation> A modified example of the braking control device SC will be described with reference to the schematic diagram in Figure 5. In the first and second embodiments, the master pressure Pm was output from the first braking unit SA via the master cylinder CM. That is, in the hydraulic transmission path, the apply unit AP and the pressure regulating unit CA were arranged in series, and the first hydraulic pressure Pa or the second hydraulic pressure Pb supplied from the pressure regulating unit CA was output as the master pressure Pm from the master cylinder CM via the master piston NM. This configuration is referred to as the "series configuration". Instead of the series configuration, the apply unit AP and the pressure regulating unit CA may be arranged in parallel. This configuration is referred to as the "parallel configuration".

[0100] In a parallel configuration, the apply unit AP (especially the master cylinder CM) and the pressure regulating unit CA are directly connected to the wheel cylinder CW. Specifically, the master cylinder CM and the front wheel cylinder CWf are connected by the front wheel connecting passage HSf. The front wheel connecting passage HSf is equipped with a normally open on / off solenoid valve VM. Below the shut-off valve VM, the front wheel connecting passage HSf is connected to the pressure regulating unit CA via a connecting passage HC (fluid passage). The connecting passage HC is equipped with a normally closed on / off solenoid valve VC. The pressure regulating unit CA is directly connected to the rear wheel cylinder CWr.

[0101] During pressure regulation control, power is supplied to the shut-off valve VM and the communication valve VC. As a result, the shut-off valve VM is closed and the communication valve VC is opened. In vehicles equipped with a regenerative generator GN on the front wheels, the second hydraulic pressure Pb is supplied to the front wheel cylinder CWf, and the first hydraulic pressure Pa is supplied to the rear wheel cylinder CWr (see the first embodiment). In this single-system pressure regulation, the front wheel target pressure Ptf is modified to decrease based on the temperature Te of the brake fluid BF. In vehicles equipped with a regenerative generator GN on the rear wheels, the first hydraulic pressure Pa is supplied to the front wheel cylinder CWf, and the second hydraulic pressure Pb is supplied to the rear wheel cylinder CWr (see the second embodiment). In this single-system pressure regulation, the front wheel target pressure Ptf is modified to increase based on the temperature Te of the brake fluid BF. These modifications allow for the suppression of changes in vehicle deceleration Gx caused by the first differential pressure ΔPua at extremely low temperatures, even in modified versions.

[0102] <Other Embodiments> Other embodiments will be described below. In these other embodiments, the same effects as described above (suppression of changes in vehicle deceleration Gx at extremely low temperatures) are achieved.

[0103] In the above-described embodiment, a corrected target pressure Psf is determined based on a corrected pressure eP calculated from the temperature Te, and the second hydraulic pressure Pb or the first hydraulic pressure Pa is controlled so that the master pressure Pm matches the corrected target pressure Psf. That is, the effect of the first differential pressure ΔPua is compensated by correcting the target value Ptf (target value). Alternatively, the effect may be compensated by correcting the master pressure Pm (actual value). Specifically, in the first embodiment (configuration corresponding to a vehicle equipped with a regenerative generator GN on the front wheels), the value obtained by adding the corrected pressure eP to the master pressure Pm is controlled to approach and match the front wheel target pressure Ptf. As a result, the wheel pressure Pw is corrected to be smaller. In the second embodiment (configuration corresponding to a vehicle equipped with a regenerative generator GN on the rear wheels), the value obtained by subtracting the corrected pressure eP from the master pressure Pm is controlled to approach and match the front wheel target pressure Ptf. As a result, the wheel pressure Pw is corrected to be larger.

[0104] In the embodiment described above, the corrected pressure eP was calculated as a variable corresponding to the temperature Te. Alternatively, the corrected pressure eP may be determined to "0" when the temperature Te is equal to or greater than a predetermined temperature tg, and to a predetermined pressure ep when the temperature Te is less than the predetermined temperature tg (see the characteristics shown by the dashed line in the corrected pressure calculation block EP in Figure 3). Here, the predetermined temperature tg (also called the "second predetermined temperature") and the predetermined pressure ep are predetermined values ​​(constants) set in advance. The second predetermined temperature tg is a temperature less than 0°C, similar to the first predetermined temperature te.

[0105] Alternatively, the correction pressure eP may not be determined, and the target of the feedback control may be switched. Specifically, in the first embodiment (a configuration corresponding to a vehicle equipped with a regenerative generator GN on the front wheels), when the temperature Te is above a predetermined temperature tg, the master pressure Pm (or the second hydraulic pressure Pb) is controlled to approach and match the front wheel target pressure Ptf. On the other hand, when the temperature Te is below the predetermined temperature tg, the first hydraulic pressure Pa is controlled to approach and match the front wheel target pressure Ptf. Similarly, in the second embodiment (a configuration corresponding to a vehicle equipped with a regenerative generator GN on the rear wheels), when the temperature Te is above a predetermined temperature tg, the master pressure Pm (or the first hydraulic pressure Pa) is controlled to approach and match the front wheel target pressure Ptf. On the other hand, when the temperature Te is below the predetermined temperature tg, the second hydraulic pressure Pb is controlled to approach and match the front wheel target pressure Ptf.

[0106] As illustrated in the other embodiments described above, in a braking control device SC applied to a vehicle equipped with a regenerative device KG (particularly a regenerative generator GN) on the front wheels, when the temperature Te (liquid temperature) of the brake fluid BF is low, the front wheel pressure Pwf (=Pm) is adjusted (reduction correction) to be smaller compared to when the temperature is high. Conversely, in a braking control device SC applied to a vehicle equipped with a regenerative device KG (particularly a regenerative generator GN) on the rear wheels, when the temperature Te (liquid temperature) of the brake fluid BF is low, the front wheel pressure Pwf (=Pm) is adjusted (increase correction) to be larger compared to when the temperature is high. By optimizing the generation of the front wheel pressure Pwf according to the temperature Te of the brake fluid BF, changes in vehicle deceleration Gx at low temperatures are suppressed.

[0107] In the above-described embodiment, the target values ​​of various braking forces (Fv, Fx, Fh, Fn, etc.) were calculated in the dimension of the longitudinal forces acting on the vehicle. Alternatively, they may be calculated in the dimension of the vehicle's deceleration Gx or the dimension of the wheel torque. This is based on the fact that the state variables (referred to as "force-related state variables") from the longitudinal forces to the vehicle's deceleration Gx are equivalent. Therefore, the target pressures Ptf and Ptr are calculated based on the force-related state variables from the longitudinal forces acting on the vehicle to the vehicle's deceleration Gx.

[0108] In the above embodiment, in the apply unit AP, the pressure-receiving area rm (master area) of the master chamber Rm and the pressure-receiving area ru (servo area) of the servo chamber Ru are set to be equal. The master area rm and the servo area ru do not have to be equal. In configurations where the master area rm and the servo area ru are different, it is possible to perform a conversion calculation between the master pressure Pm and the second hydraulic pressure Pb (or the first hydraulic pressure Pa) based on the ratio of the servo area ru to the master area rm (i.e., a conversion based on "Pm·rm = Pb·ru (or Pa·ru)").

[0109] <Summary of Embodiments> This section summarizes the embodiments of the braking control device SC. The braking control device SC includes first and second pressure regulating valves UA and UB, and a controller EA that controls the first and second pressure regulating valves UA and UB.

[0110] The first pressure regulating valve UA is provided in the fluid passage HK connecting the discharge section Qo of a fluid pump QA, which is driven by an electric motor MA, to the suction section Qi of the fluid pump QA. The second pressure regulating valve UB is provided in the fluid passage HK between the first pressure regulating valve UA and the suction section Qi. Therefore, the first and second pressure regulating valves UA and UB are arranged in the order of the first pressure regulating valve UA and the second pressure regulating valve UB from the upstream side of the circulating flow KN of the brake fluid BF.

[0111] Controller EA selects either "two-system pressure regulation that controls the front and rear wheel pressures Pwf and Pwr by driving the first and second pressure regulating valves UA and UB," or "one-system pressure regulation that controls the front and rear wheel pressures Pwf and Pwr by driving only the second pressure regulating valve UB." When one-system pressure regulation is selected, Controller EA adjusts the front wheel pressure Pwf based on the temperature Te of the working fluid BF in the fluid path HK.

[0112] In the dual-system pressure regulation of the braking control device SC, power is supplied to the first and second pressure regulating valves UA and UB, and they are both driven. The front and rear wheel pressures Pwf and Pwr are then individually controlled by the first and second pressure regulating valves UA and UB. In contrast, in the single-system pressure regulation of the braking control device SC, power is supplied to the second pressure regulating valve UB, but not to the first pressure regulating valve UA. In other words, in single-system pressure regulation, the first pressure regulating valve UA is not driven, and only the second pressure regulating valve UB is driven. The front and rear wheel pressures Pwf and Pwr are then controlled solely by the second pressure regulating valve UB. Here, the rear wheel pressure Pwr is controlled as a result of the front wheel pressure Pwf.

[0113] When one-system pressure regulation is performed, the first pressure regulating valve UA, located upstream of the second pressure regulating valve UB, is fully open. However, even when the first pressure regulating valve UA is fully open, there is a limit to the amount it can open, so a first differential pressure ΔPua (hydraulic pressure difference) is generated between the upstream and downstream sides of the first pressure regulating valve UA. Furthermore, since the first differential pressure ΔPua depends on the viscosity of the brake fluid BF, the lower the temperature Te of the brake fluid BF, the larger the first differential pressure ΔPua becomes.

[0114] In a single-system pressure regulation, the front wheel pressure Pwf is adjusted based on the front target pressure Ptf, while the rear wheel pressure Pwr is adjusted automatically as a result of the front wheel pressure Pwf. Due to the first differential pressure ΔPua, an excess or deficiency of the rear wheel pressure Pwr occurs, and when the temperature Te of the brake fluid BF is extremely low, a change occurs in the overall deceleration Gx of the vehicle. In the brake control device SC, the front wheel pressure Pwf is finely adjusted (increased or decreased) based on the fluid temperature Te, so that the change in vehicle deceleration Gx at extremely low temperatures is suppressed.

[0115] For example, as shown in the first embodiment, the controller EA controls the rear wheel pressure Pwr by the first hydraulic pressure Pa between the discharge section Qo of the fluid pump QA and the first pressure regulating valve UA, and controls the front wheel pressure Pwf by the second hydraulic pressure Pb between the first pressure regulating valve UA and the second pressure regulating valve UA. When the temperature Te is low, the controller EA reduces the front wheel pressure Pwf (=Pb=Pm) compared to when the temperature Te is high.

[0116] In the braking control device SC (first embodiment) applied to a vehicle equipped with a regenerative braking device KG on the front wheels, the rear wheel pressure Pwr is controlled by the first hydraulic pressure Pa, and the front wheel pressure Pwf is controlled by the second hydraulic pressure Pb. In a single-system pressure regulation, the second hydraulic pressure Pb is controlled by the second pressure regulating valve UB so that the front wheel pressure Pwf (=Pm) matches the front wheel target pressure Ptf. At this time, the rear wheel pressure Pwr (=Pa) is greater than the second hydraulic pressure Pb by the amount of the first differential pressure ΔPua (i.e., "Pa = Pb + ΔPua"). Therefore, at extremely low temperatures, the vehicle deceleration Gx is relatively larger than at normal temperatures. In other words, the actual vehicle deceleration Gx is excessive compared to the target deceleration calculated from the operating displacement Sp. In the braking control device SC according to this configuration, when the fluid temperature Te is low, the front wheel pressure Pwf (=Pb=Pm) is modified to decrease compared to when the fluid temperature Te is high. As a result, the vehicle's deceleration Gx characteristics are maintained in a constant relationship with the operating displacement Sp of the braking operating member, regardless of the temperature Te. In other words, changes (increases) in the vehicle's deceleration Gx at extremely low temperatures are suppressed.

[0117] Furthermore, as shown in the second embodiment, the controller EA controls the front wheel pressure Pwf by the first hydraulic pressure Pa between the discharge section Qo and the first pressure regulating valve UA, and controls the rear wheel pressure Pwr by the second hydraulic pressure Pb between the first pressure regulating valve UA and the second pressure regulating valve UA. When the temperature Te is low, the controller EA increases the front wheel pressure Pwf (=Pa=Pm) compared to when the temperature Te is high.

[0118] Conversely to the first embodiment, in the braking control device SC (second embodiment) applied to a vehicle equipped with a regenerative braking device KG on the rear wheels, the front wheel pressure Pwf is controlled by the first hydraulic pressure Pa, and the rear wheel pressure Pwr is controlled by the second hydraulic pressure Pb. In a single-system pressure regulation, the first hydraulic pressure Pa is controlled by the second pressure regulating valve UB so that the front wheel pressure Pwf (=Pm) matches the front wheel target pressure Ptf. At this time, the rear wheel pressure Pwr (=Pb) is smaller than the first hydraulic pressure Pa by the amount of the first differential pressure ΔPua (i.e., "Pb = Pa - ΔPua"). Therefore, at extremely low temperatures, the vehicle deceleration Gx is relatively smaller than at normal temperatures. In other words, the actual vehicle deceleration Gx is insufficient compared to the target deceleration calculated from the operating displacement Sp. In the braking control device SC according to this configuration, when the fluid temperature Te is low, the front wheel pressure Pwf (=Pa=Pm) is modified to increase compared to when the fluid temperature Te is high. As a result, the vehicle's deceleration Gx characteristics are maintained in a constant relationship with the operating displacement Sp of the braking operating member, regardless of the temperature Te. In other words, changes (decreases) in the vehicle's deceleration Gx at extremely low temperatures are suppressed. [Explanation of Symbols]

[0119] SC... Brake control device, KG... Regenerative device, BP... Brake operating member (brake pedal), BF... Brake fluid (hydraulic fluid), SA, SB... 1st and 2nd braking units, YA, YB... 1st and 2nd actuators, EA, EB... 1st and 2nd controllers, BS... Communication bus, CM... Master cylinder, CW... Wheel cylinder, AP... Apply unit, NR... Input unit, CA... Pressure regulating unit, HK... Return channel (fluid path connecting Qo and Qi), UA, UB... 1st and 2nd pressure regulating valves, MA... Electric motor, QA... Fluid pump, Qo... Discharge part of QA, Qi... Suction part of QA, VA... Inlet valve, VB... Opening valve, SP... Operational displacement sensor, PA, PB... 1st and 2nd hydraulic pressure sensors, PM... Master pressure sensor, TA, TB... 1st and 2nd temperature sensors, TM... Master **Stand temperature sensor**, Sp...Operating displacement, Pa, Pb...First and second hydraulic pressure (detected values ​​of PA and PB), Pm...Master pressure (detected value of PM), ΔPua, ΔPub...First and second differential pressure (hydraulic pressure difference between the upstream and downstream sides in UA and UB), Ta, Tb...First and second temperature (detected values ​​of TA and TB), Tm...Master temperature (detected value of TM), Te...BF temperature, Pwf, Pwr...Front and rear wheel pressure, Ptf, Ptr...Front and rear target pressure (target values ​​corresponding to Pwf and Pwr), eP...Corrected pressure, Psf...Corrected target pressure (corrected Ptf), Fg...Regenerative braking force, Fx...Limit regenerative braking force (limit value of Fg that can generate KG), Fp...Hydraulic braking force, FA...Execution flag (control flag indicating the execution status of anti-lock brake control).

Claims

1. A first pressure regulating valve is provided in the fluid passage connecting the discharge section and the suction section of a fluid pump driven by an electric motor, In the fluid passage, a second pressure regulating valve is provided between the first pressure regulating valve and the suction portion, A controller that controls the first and second pressure regulating valves, In a braking control device for a vehicle equipped with, The aforementioned controller, Either a two-system pressure regulation system that controls the front and rear wheel pressure using the first and second pressure regulating valves, or a one-system pressure regulation system that controls the front and rear wheel pressure using only the second pressure regulating valve, is selected. A vehicle braking control device that, when selecting the aforementioned single-system pressure adjustment, adjusts the front wheel pressure based on the temperature of the working fluid in the fluid passage.

2. In the vehicle braking control device described in claim 1, The aforementioned controller, The rear wheel pressure is controlled by the first hydraulic pressure between the discharge section and the first pressure regulating valve, and the front wheel pressure is controlled by the second hydraulic pressure between the first pressure regulating valve and the second pressure regulating valve. A vehicle braking control device that reduces the front wheel pressure when the temperature is low compared to when the temperature is high.

3. In the vehicle braking control device described in claim 1, The aforementioned controller, The front wheel pressure is controlled by the first hydraulic pressure between the discharge section and the first pressure regulating valve, and the rear wheel pressure is controlled by the second hydraulic pressure between the first pressure regulating valve and the second pressure regulating valve. A vehicle braking control device that increases the front wheel pressure when the temperature is low compared to when the temperature is high.

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