Vehicle braking control device

Abstract

To provide a braking control device, which is configured so that fluctuation of liquid pressure due to slide resistance of a seal member sealing a cylinder and a piston can be suppressed.SOLUTION: A braking control device, which is applied to a vehicle having a regenerative device arranged at a front wheel thereof, comprises an actuator that adjusts wheel pressures of a front wheel and a rear wheel, and a controller that controls the actuator so that the wheel pressures of the front wheel and rear wheel respectively matches target pressures of the front wheel and rear wheel. The actuator supplies a first liquid pressure that can be adjusted only with a first pressure-adjusting valve to a wheel cylinder of the front wheel through a cylinder and a piston and supplies a second liquid pressure that is adjusted with the first and second pressure-adjusting valves to a wheel cylinder of the rear wheel. The controller, when the regenerative device does not generate regenerative braking force, determines the target pressure for the rear wheel so that the pressure is larger by a predetermined quantity than the target pressure for the front wheel, and stops power distribution to the second pressure-adjusting valve.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] The applicant has developed a brake control device described in Patent Document 1 that has a reduced longitudinal dimension and can separately control the brake fluid pressure of the front wheel system (also called "wheel pressure") and the brake fluid pressure of the rear wheel system. Specifically, this brake control device includes "a master unit having a master chamber connected to the front wheel cylinder and a servo chamber that applies to the master piston a forward force that counteracts the backward force applied to the master piston by the master chamber," "a pressure adjustment unit that adjusts brake fluid discharged from an electric pump to a first fluid pressure using a first solenoid valve, introduces the first fluid pressure into the rear wheel cylinder, and reduces and adjusts the first fluid pressure to a second fluid pressure using a second solenoid valve and introduces the second fluid pressure into the servo chamber," and "a regenerative coordination unit that is composed of an input piston that operates in conjunction with a brake operating member and an input cylinder fixed to the master cylinder, and in which the gap between the master piston and the input piston is controlled by the second fluid pressure."

[0003] In such braking control devices, there are problems caused by the sliding resistance of the seal member that seals the cylinder and piston. First, referring to the schematic diagram and characteristic diagram of FIG. 7, the hydraulic pressure difference caused by the sliding resistance will be explained. The schematic diagram of FIG. 7(a) shows the following. The hydraulic pressures Pwf and Pwr in the front and rear wheel cylinders CWf and CWr are referred to as the "front and rear wheel pressures." - Brake fluid BF discharged by fluid pump QA driven by electric motor MA is adjusted to servo pressure Pc by pressure regulating valve UC (linear solenoid valve). Brake fluid BF adjusted to servo pressure Pc is directly supplied to rear wheel cylinder CWr as rear wheel pressure Pwr. The hydraulic pressure Pwf (front wheel pressure) in the front wheel cylinder CWf is adjusted by the servo pressure Pc via the master cylinder CM and the master piston NM. Specifically, the master piston NM is inserted into the master cylinder CM and sealed with a seal member SL. Two hydraulic chambers, a master chamber Rm and a servo chamber Ru, are formed inside the master cylinder CM. The pressure-receiving area rm of the master chamber Rm is equal to the pressure-receiving area ru of the servo chamber Ru. When the front wheel pressure Pwf increases, brake fluid BF adjusted to the servo pressure Pc is supplied to the servo chamber Ru. This pressurizes the master piston NM in the forward direction Ha, causing brake fluid BF to move from the master chamber Rm toward the front wheel cylinder CWf, increasing the front wheel pressure Pwf. When the front wheel pressure Pwf decreases, the servo pressure Pc in the servo chamber Ru decreases, causing the master piston NM to move in the reverse direction Hb (opposite the forward direction Ha). The brake fluid BF in the front wheel cylinder CWf is returned to the master chamber Rm, and the front wheel pressure Pwf is reduced. In other words, the hydraulic pressure is transmitted between the servo pressure Pc and the front wheel pressure Pwf via the master cylinder CM / master piston NM.

[0004] With reference to the characteristic diagram of Figure 7(b), the changes in front and rear wheel pressures Pwf and Pwr in response to changes in servo pressure Pc will be described. Servo pressure Pc is increased from "0" to a value p1 and then decreased to "0". Characteristic Zc in the diagram indicates that the wheel pressures Pwf, Pwr and servo pressure Pc have a "1:1" relationship. Brake fluid BF adjusted to servo pressure Pc is supplied directly to the rear wheel cylinder CWr (i.e., without passing through cylinder CM / piston NM). Therefore, rear wheel pressure Pwr is equal to servo pressure Pc and transitions along characteristic Zc. On the other hand, front wheel pressure Pwf is transmitted via cylinder CM / piston NM. Therefore, there is hysteresis in the transition (change) of front wheel pressure Pwf due to the sliding resistance of the seal member SL. Specifically, even if the servo pressure Pc is increased from "0," sliding resistance exists, so the front wheel pressure Pwf remains "0" until the servo pressure Pc reaches a value p2. Then, when the servo pressure Pc exceeds the value p2, the front wheel pressure Pwf increases as the servo pressure Pc increases. At this time, the front wheel pressure Pwf is smaller than the servo pressure Pc by a value psa (i.e., the front wheel pressure Pwf is smaller than the characteristic Zc). The value psa of the front wheel pressure Pwf is a pressure value corresponding to the sliding resistance of the seal member SL when the master piston NM moves in the forward direction Ha. When the servo pressure Pc begins to decrease, sliding resistance acts on the master piston NM in the reverse direction Hb, opposite to the forward direction Ha. As a result, the front wheel pressure Pwf is larger than the servo pressure Pc by a value psb (i.e., the front wheel pressure Pwf is larger than the characteristic Zc). The value psb of the front wheel pressure Pwf is a pressure value corresponding to the sliding resistance of the seal member SL when the master piston NM moves in the reverse direction Hb. Even if the servo pressure Pc is set to "0," hydraulic pressure of value p3 (=psb) remains in the front wheel cylinder CWf. The above explains the hysteresis of the front wheel pressure Pwf that occurs due to the sliding resistance of the seal member SL that seals the master cylinder CM and the master piston NM.

[0005] The first embodiment of Patent Document 1 describes a configuration in which the first and second hydraulic pressures are independently adjustable. The front wheel pressure Pwf, which is adjusted by the second hydraulic pressure via a cylinder / piston, is affected by the sliding resistance, while the rear wheel pressure Pwr, which is adjusted directly by the first hydraulic pressure, is not affected by the sliding resistance. The following describes the problem (i.e., the problem of the present invention) that occurs when a switching operation of the regenerative cooperative control is performed in this configuration. The "switching operation" compensates for a decrease in regenerative braking force due to the generator by increasing frictional braking force due to wheel pressure. During the switching operation, the first and second hydraulic pressures are independently adjusted, and when the switching operation ends, the first and second hydraulic pressures are set to the same hydraulic pressure. Due to the hydraulic pressure difference between the first and second hydraulic pressures during the switching operation, fluctuations in the wheel pressure Pw may occur at the end of the switching operation. Specifically, just before the end of the switching operation, the second hydraulic pressure is greater than the first hydraulic pressure by an amount corresponding to the sliding resistance. Therefore, if the first and second hydraulic pressures are made equal at the end of the switching operation, the rear wheel pressure Pwr (i.e., the first hydraulic pressure) may suddenly increase by an amount corresponding to the sliding resistance, which may result in a discontinuous increase in the deceleration of the vehicle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2019-137202 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a brake control device for a vehicle that can suppress fluctuations in hydraulic pressure caused by sliding resistance of a seal member that seals a cylinder and a piston. [Means for solving the problem]

[0008] The vehicle braking control device of the present invention is applied to a vehicle (JV) equipped with a regenerative device (KCf) on the front wheels (WHf), and comprises: "an actuator (HU) that adjusts the front and rear wheel pressures (Pwf, Pwr) of the front and rear wheel cylinders (CWf, CWr)"; and "a controller (ECU) that calculates front and rear wheel target pressures (Ptf, Ptr), which are target values ​​for the front and rear wheel pressures (Pwf, Pwr), based on the braking demand (Qg) of the vehicle (JV), and controls the actuator (HU) so that the front and rear wheel pressures (Pwf, Pwr) match the front and rear wheel target pressures (Ptf, Ptr)."

[0009] In the vehicle brake control device according to the present invention, the actuator (HU) comprises a fluid pump (QA) driven by an electric motor (MA), and first and second pressure regulating valves (UA, UB) provided in a return path (HK) connecting the intake and discharge ports of the fluid pump (QA). The actuator (HU) supplies a first fluid pressure (Pa) regulated only by the first pressure regulating valve (UA) to the front wheel cylinder (CWf) via a cylinder (CM) and a piston (NM) in a state in which brake fluid (BF) in the return path (HK) cannot move to the front wheel cylinder (CWf), and supplies a second fluid pressure (Pb) regulated by the first and second pressure regulating valves (UA, UB) to the rear wheel cylinder (CWr) in a state in which brake fluid (BF) in the return path (HK) can move to the rear wheel cylinder (CWr). The controller (ECU) then determines whether the rear wheel target pressure (Ptr) is greater than the front wheel target pressure (Ptf) when the regenerative device (KCf) does not generate a regenerative braking force (Fgf). Specified pressure (px) and then the power supply to the second pressure regulating valve (UB) is stopped.

[0010] The vehicle braking control device of the present invention is applied to a vehicle (JV) equipped with a regenerative device (KCr) on a rear wheel (WHr), and comprises "an actuator (HU) that adjusts the hydraulic pressure of a front wheel cylinder (CWf) as a front wheel pressure (Pwf) and adjusts the hydraulic pressure of a rear wheel cylinder (CWr) as a rear wheel pressure (Pwr)," and "a controller (ECU) that calculates front and rear wheel target pressures (Ptf, Ptr), which are target values ​​for the front and rear wheel pressures (Pwf, Pwr), based on the braking demand (Qg) of the vehicle (JV), and controls the actuator (HU) so that the front and rear wheel pressures (Pwf, Pwr) match the front and rear wheel target pressures (Ptf, Ptr)."

[0011] In the vehicle brake control device according to the present invention, the actuator (HU) comprises a fluid pump (QA) driven by an electric motor (MA), and first and second pressure regulating valves (UA, UB) provided in a return path (HK) connecting the intake and discharge ports of the fluid pump (QA). The actuator (HU) supplies a first fluid pressure (Pa) regulated only by the first pressure regulating valve (UA) to the rear wheel cylinder (CWr) in a state in which brake fluid (BF) in the return path (HK) can move to the rear wheel cylinder (CWr), and supplies a second fluid pressure (Pb) regulated by the first and second pressure regulating valves (UA, UB) to the front wheel cylinder (CWf) via a cylinder (CM) and a piston (NM) in a state in which brake fluid (BF) in the return path (HK) cannot move to the front wheel cylinder (CWf). Then, when the regenerative device (KCr) does not generate a regenerative braking force (Fgr), the controller (ECU) determines the rear wheel target pressure (Ptr) to be greater than the front wheel target pressure (Ptf) by a predetermined pressure (px), and stops the supply of electricity to the second pressure regulating valve (UB).

[0012] When the front and rear wheel pressures Pwf and Pwr are controlled to match the front and rear wheel target pressures Ptf and Ptr, the hydraulic pressure component (resistance component) due to the sliding resistance Ms of the seal member SL that seals the cylinder CM and the piston NM is compensated for. In other words, of the first servo pressure Pa and the second servo pressure Pb, the one-side hydraulic pressure supplied to the servo chamber Ru is adjusted to include a resistance component, but the other-side hydraulic pressure of the first servo pressure Pa and the second servo pressure Pb that is supplied to the rear wheel cylinder CWr is not affected by the sliding resistance Ms. For this reason, when the front and rear wheel target pressures Ptf and Ptr are set to the same pressure and the front and rear wheel pressures Pwf and Pwr are adjusted to be the same, the one-side hydraulic pressure is adjusted to be higher than the other-side hydraulic pressure.

[0013] According to the above configuration, when the regenerative devices KCf, KCr do not generate the regenerative braking forces Fgf, Fgr (i.e., when the switching operation of the regenerative cooperative control is terminated), the rear wheel pressure Pwr is increased above the front wheel pressure Pwf by a predetermined pressure px equivalent to the sliding resistance Ms of the seal member SL. At the end of the switching operation, the one-side hydraulic pressure and the other-side hydraulic pressure are equalized, thereby suppressing fluctuations in the rear wheel pressure Pwr. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram illustrating an entire vehicle JV equipped with a braking control device SC. [Figure 2] 1 is a schematic diagram for explaining a first embodiment of a braking control device SC. [Figure 3] FIG. 4 is a flowchart illustrating a process of regenerative cooperative control. [Figure 4] 3 is a time series diagram for explaining the operation of the regenerative cooperative control according to the first embodiment of the braking control device SC. FIG. [Figure 5] FIG. 4 is a schematic diagram for explaining a second embodiment of the braking control device SC. [Figure 6] FIG. 6 is a time series diagram for explaining the operation of the regenerative cooperative control according to the second embodiment of the braking control device SC. [Figure 7] 1A and 1B are a schematic diagram and a characteristic diagram for explaining the problem. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Symbols of components> In the following explanation, components, signals, values, and other elements with the same symbol, such as "CW," have the same function. The subscripts "f" and "r" added to the end of various symbols related to wheels are generic symbols that indicate whether the element relates to the front or rear wheels. Specifically, "f" indicates "element related to the front wheels," and "r" indicates "element related to the rear wheels." For example, a wheel cylinder CW is written as "front wheel cylinder CWf, rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" may be omitted. When omitted, each symbol represents its generic name.

[0016] <Vehicle JV equipped with braking control device SC> The overall configuration of a vehicle JV equipped with a braking control device SC according to the present invention will be described with reference to the schematic diagram of Figure 1. Here, the vehicle JV equipped with the braking control device SC will also be referred to as the "host vehicle" in order to distinguish it from other vehicles (for example, a preceding vehicle SV).

[0017] The vehicle JV is a hybrid vehicle or an electric vehicle equipped with a drive electric motor. The drive electric motor also functions as a generator (electric power generator) for energy regeneration. The generator GNf is provided on the front wheels WHf. The generator GNf (also referred to as a "front wheel generator") is controlled (driven) by a controller EGf for the generator GNf. Here, a device including the generator GNf and its controller EGf is referred to as the "regeneration device KCf (or front wheel regeneration device KCf)." The vehicle JV is equipped with a storage battery BT for the regeneration device KCf. In other words, the regeneration device KCf also includes the storage battery BT.

[0018] When the electric motor / generator GNf operates as a drive electric motor (when the vehicle JV is accelerating), power is supplied to the electric motor / generator GNf from the storage battery BT via a regeneration device controller EGf (referred to as a "regeneration controller" or "front wheel regeneration controller"). On the other hand, when the electric motor / generator GNf operates as a generator (when the vehicle JV is decelerating), power generated by the generator GNf is stored in the storage battery BT via the regeneration controller EGf (so-called regenerative braking is performed). In regenerative braking, the generator GNf generates a front wheel regenerative braking force Fgf independently and separately from a friction braking force Fm, which will be described later.

[0019] A vehicle JV is equipped with a braking device SX. The braking device SX generates front and rear wheel friction braking forces Fmf and Fmr on the front and rear wheels WHf and WHr. The braking device SX includes a rotating member (e.g., a brake disc) KT and a brake caliper CP. The rotating member KT is fixed to the wheel WH, and the brake caliper CP is provided to clamp the rotating member KT. The brake caliper CP is provided with a wheel cylinder CW. Pressurized braking fluid BF is supplied to the wheel cylinder CW from the brake control device SC. A friction member (e.g., a brake pad) MS is pressed against the rotating member KT by hydraulic pressure Pw (referred to as "wheel pressure") in the wheel cylinder CW. Because the rotating member KT and the wheel WH are fixed so as to rotate together, the frictional force generated at this time generates a frictional braking force Fm on the wheel WH. In other words, the friction braking force Fm is a braking force generated by friction between the rotating member KT and the friction member MS.

[0020] The vehicle JV is equipped with a brake operating member BP and various sensors (such as BA). The brake operating member (e.g., a brake pedal) BP is a member that the driver operates to decelerate the vehicle. The vehicle JV is provided with a brake operation amount sensor BA to detect the operation amount Ba (also referred to as the "braking operation amount") of the brake operating member BP. As the brake operation amount sensor BA, at least one of a simulator pressure sensor PS that detects the hydraulic pressure Ps (referred to as the "simulator pressure") of a stroke simulator SS (described later), an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP, and an operation force sensor FP that detects the operation force Fp of the brake operating member BP is adopted. In other words, the operation amount sensor BA detects at least one of the simulator pressure Ps, the brake operation displacement Sp, and the brake operation force Fp as the braking operation amount Ba. The braking operation amount Ba is input to a controller ECU (also simply referred to as the "brake controller" or "controller") for the brake control device SC. The vehicle JV is equipped with various sensors including a wheel speed sensor VW that detects the rotational speed (wheel speed) Vw of the wheels WH. The detection signals (Ba, etc.) of these sensors are input to a braking controller ECU. The braking controller ECU calculates the vehicle speed Vx based on the wheel speed Vw.

[0021] The vehicle JV is equipped with a brake control device SC so as to execute so-called regenerative cooperative control (control in which the regenerative braking force Fg and the friction braking force Fm are operated in cooperation with each other). The brake control device SC employs a so-called front and rear type (also called "type II") brake system as two systems. The brake control device SC supplies wheel pressure Pw to the brake device SX (particularly, wheel cylinder CW) via the front and rear wheel connection paths HSf and HSR in accordance with the operation amount Ba of the brake operating member BP. The brake control device SC is composed of a fluid unit HU (also called "actuator") including a master cylinder CM, and a brake controller ECU.

[0022] The hydraulic unit HU is controlled by a brake controller ECU. The brake controller ECU is composed of a microprocessor MP that processes signals and a drive circuit DD that drives the solenoid valves and the electric motor. The brake controller ECU is connected to a regenerative device controller EGf and a driving assistance device controller ECA via a communication bus BS. Therefore, information (detected values, calculated values) is shared between these controllers. For example, a vehicle speed Vx is calculated by the brake controller ECU and transmitted to a driving assistance device controller ECA (also simply referred to as a "driving assistance controller"). A target deceleration Gd is calculated by the driving assistance controller ECA and transmitted to the brake controller ECU. A target regenerative braking force Fhf is calculated by the brake controller ECU and transmitted to the regenerative controller EGf. A limit regenerative braking force Fxf is calculated by the regenerative controller EGf and transmitted to the brake controller ECU. The brake controller ECU receives inputs of the braking operation amount Ba, the wheel speed Vw, the target deceleration Gd, the limit regenerative braking force Fx, etc. Based on these signals, the brake controller ECU controls the hydraulic unit HU.

[0023] The vehicle JV is provided with a driving assistance device UD that performs automatic braking in place of or to assist the driver. The driving assistance device UD is composed of an object detection sensor OB that detects the distance Ds (relative distance) to an object OJ ahead of the host vehicle JV (including a preceding vehicle SV traveling ahead of the host vehicle JV), and a controller ECA for the driving assistance device. For example, a radar sensor, a millimeter-wave sensor, an image sensor, etc. are used as the object detection sensor OB. The driving assistance controller ECA calculates a target deceleration Gd (a target value of vehicle body acceleration in the longitudinal direction of the host vehicle JV) for the host vehicle JV based on the detection result Ds (relative distance) of the object detection sensor OB. The target deceleration Gd (target vehicle body longitudinal acceleration) is transmitted from the driving assistance controller ECA to a brake controller ECU via a communication bus BS. Then, a brake control device SC generates braking forces Fg and Fm according to the target deceleration Gd.

[0024] <First embodiment of braking control device SC> A first embodiment of the brake control device SC (particularly, a configuration example of the fluid unit HU) will be described with reference to the schematic diagram of FIG. 2. The brake control device SC includes a fluid unit HU as a pressure source for increasing the hydraulic pressure Pw (wheel pressure) of four wheel cylinders CW. In the illustrated brake control device SC, the fluid unit HU and the master cylinder CM are integrated. The brake control device SC also employs a front / rear type (also called "type II") brake system. The fluid unit HU is composed of an apply unit AU including the master cylinder CM, and a pressurizing unit KU.

[0025] The apply unit AU and the pressurizing unit KU are controlled by a brake controller ECU. Specifically, the controller ECU receives the braking operation amount Ba (at least one of the simulator pressure Ps, operation displacement Sp, and operation force Fp), the target deceleration Gd, the master pressure Pm, the second servo pressure Pb, and the front wheel limit regenerative braking force Fxf. Based on these signals, the controller ECU calculates drive signals Va and Vb for the first and second on-off valves VA and VB, drive signals Ua and Ub for the first and second pressure regulating valves UA and UB, a drive signal Ma for the electric motor MA, and a front wheel target regenerative braking force Fhf. The solenoid valves VA, VB, UA, and UB constituting the hydraulic unit HU and the electric motor MA are controlled (driven) in accordance with the drive signals Va, Vb, Ua, Ub, and Ma.

[0026] As will be described later, the hydraulic unit HU, wheel cylinders CW, etc. are connected by the reservoir path HR, communication path HS (= HSf, HSR), input path HN, servo path HV, and return path HK. These are fluid paths through which the brake fluid BF moves. Fluid paths (HS, etc.) include fluid piping, flow paths within the hydraulic unit HU, hoses, etc.

[0027] <<Apply Unit AU>> The apply unit AU is composed of a master reservoir RV, a master cylinder CM, a master piston NM, a master spring DM, an input cylinder CN, an input piston NN, an input spring DN, first and second on-off valves VA and VB, a stroke simulator SS, and a simulator pressure sensor PS.

[0028] The master reservoir (also called the "atmospheric pressure reservoir") RV is a tank for hydraulic fluid, and stores brake fluid BF therein. The master reservoir RV is connected to the master cylinder CM (particularly, the master chamber Rm).

[0029] The master cylinder CM (also simply referred to as "cylinder") is a cylinder member having a bottom. A master piston NM (also simply referred to as "piston") is inserted into the master cylinder CM, and the interior is sealed with a seal member SL to form a master chamber Rm. The master cylinder CM is a so-called single-type master cylinder. A master spring DM is provided in the master chamber Rm to pressurize the master piston NM in the backward direction Hb (the direction in which the volume of the master chamber Rm increases, which is the opposite direction to the forward direction Ha). The master chamber Rm is ultimately connected to the front wheel cylinder CWf via the front wheel communication passage HSf and a hydraulic pressure modulator MJ. When the master piston NM moves in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases), brake fluid BF is pumped from the fluid unit HU (particularly the master cylinder CM) toward the front wheel cylinder CWf at hydraulic pressure Pm. The hydraulic pressure Pm in the master chamber Rm is referred to as "master pressure."

[0030] The master piston NM is provided with a flange Tp. This flange Tp further divides the interior of the master cylinder CM into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru is disposed opposite the master chamber Rm across the master piston NM. The rear chamber Ro is sandwiched between the master chamber Rm and the servo chamber Ru and is disposed therebetween. The servo chamber Ru and the rear chamber Ro are also sealed by the seal member SL, as described above.

[0031] For example, the pressure-receiving area ru of the flange portion Tp of the master piston NM (i.e., the pressure-receiving area of ​​the servo chamber Ru, also called the "servo area") and the pressure-receiving area rm of the end portion of the master piston NM (i.e., the pressure-receiving area of ​​the master chamber Rm, also called the "master area") are set to be equal. In this case, the hydraulic pressure Pa (first servo pressure) in the servo chamber Ru and the hydraulic pressure Pm (master pressure) in the master chamber Rm are statically equal, ignoring friction and other factors.

[0032] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted inside the input cylinder CN and sealed with a seal member SL to form an input chamber Rn. The input piston NN is mechanically connected to the brake operating member BP via a clevis (U-shaped link). A flange Tn is provided on the input piston NN. An input spring DN is provided between the flange Tn and the mounting surface of the input cylinder CN relative to the master cylinder CM. The input spring DN presses the input piston NN in the backward direction Hb.

[0033] When the input piston NN and the master piston NM are pressed most in the backward direction Hb, there is a gap Ks (also referred to as the "separation distance") between the input piston NN and the master piston NM. The gap Ks creates a state in which the wheel pressure Pw does not change even when a displacement Sp of the brake operating member BP occurs. In other words, by separating the input piston NN and the master piston NM with the gap Ks, the brake control device SC is able to achieve regenerative cooperative control.

[0034] The apply unit AU is provided with hydraulic chambers: an input chamber Rn, a servo chamber Ru, a rear chamber Ro, and a master chamber Rm. Here, the "hydraulic chambers" are chambers filled with brake fluid BF and sealed with a seal member SL. The volume of each hydraulic chamber is changed by the movement of the input piston NN and the master piston NM. The hydraulic chambers are arranged along the central axis Jm of the master cylinder CM in the order of input chamber Rn, servo chamber Ru, rear chamber Ro, and master chamber Rm, from the side closest to the brake operating member BP.

[0035] The input chamber Rn and the rear chamber Ro are connected via an input path HN. A first on-off valve VA is provided in the input path HN. The input path HN is connected to a master reservoir RV via a reservoir path HR between the rear chamber Ro and the first on-off valve VA. A second on-off valve VB is provided in the reservoir path HR. The first and second on-off valves VA and VB are two-position solenoid valves (also called "on-off valves") having an open position (communicating state) and a closed position (blocking state). A normally closed solenoid valve is used as the first on-off valve VA. A normally open solenoid valve is used as the second on-off valve VB. The first and second on-off valves VA and VB are driven (controlled) by drive signals Va and Vb from a brake controller ECU.

[0036] A stroke simulator (also simply referred to as "simulator") SS is connected to the rear chamber Ro. An operating force Fp of the brake operating member BP is generated by the simulator SS. A piston and an elastic body (e.g., a compression spring) are provided inside the simulator SS. When brake fluid BF flows into the simulator SS, the piston is pushed by the brake fluid BF. A force is applied to the piston by the elastic body in a direction that prevents the inflow of brake fluid BF, thereby generating an operating force Fp of the brake operating member BP. The operating characteristics of the brake operating member BP (the relationship between the operating displacement Sp and the operating force Fp) are formed by the simulator SS.

[0037] A simulator pressure sensor PS is provided to detect the hydraulic pressure (referred to as "simulator pressure") Ps of the simulator SS. The simulator pressure Ps is a state quantity equivalent to the operation force Fp, and is also the hydraulic pressure in the input chamber Rn and the rear chamber Ro. The simulator pressure sensor PS is one of the above-mentioned braking operation amount sensors BA, and the simulator pressure Ps is input to the controller ECU for the brake control device SC as the braking operation amount Ba.

[0038] In addition to the simulator pressure sensor PS, the fluid unit HU is provided with a braking operation amount sensor BA, which includes an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP and / or an operation force sensor FP that detects the operation force Fp of the brake operating member BP. That is, the braking operation amount sensor BA is at least one of the simulator pressure sensor PS, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP. Therefore, the braking operation amount Ba is at least one of the simulator pressure Ps, the operation displacement Sp, and the operation force Fp.

[0039] <Pressure unit KU> The pressure applying unit KU adjusts the hydraulic pressure Pwf (front wheel pressure) of the front wheel cylinder CWf and the hydraulic pressure Pwr (rear wheel pressure) of the rear wheel cylinder CWr independently and individually. The pressure applying unit KU includes an electric motor MA, a hydraulic pump QA, first and second pressure adjusting valves UA and UB, and a servo pressure sensor PB.

[0040] The hydraulic pump QA is driven by an electric motor MA, and the hydraulic fluid BF discharged by the hydraulic pump QA increases the wheel pressure Pw. Therefore, the electric motor MA is the power source for increasing the hydraulic pressure (wheel pressure) Pw in the wheel cylinder CW. The electric motor MA is controlled by the brake controller ECU in response to a drive signal Ma.

[0041] The suction port of the fluid pump QA is connected to the master reservoir RV via a reservoir line HR. The suction port and discharge port of the fluid pump QA are also connected via a return path HK. Therefore, when the electric motor MA is driven, a circulating flow KN of brake fluid BF is generated in the return path HK by the brake fluid BF discharged by the fluid pump QA (see the dashed arrows in the figure). Here, the side of the circulating flow KN closer to the discharge port of the fluid pump QA is referred to as the "upstream side," and the side further away is referred to as the "downstream side."

[0042] Two pressure regulating valves UA and UB are provided in series in the return flow path HK. Specifically, a first pressure regulating valve UA is provided in the return flow path HK. A second pressure regulating valve UB is provided between the first pressure regulating valve UA and the discharge port of the fluid pump QA. Therefore, in the return flow KN, the second pressure regulating valve UB is disposed upstream of the first pressure regulating valve UA. The first and second pressure regulating valves UA and UB are linear solenoid valves (also called "proportional valves" or "differential pressure valves") whose valve opening amount (lift amount) is continuously controlled based on the energization state (e.g., supply current). Normally open solenoid valves are used as the first and second pressure regulating valves UA and UB. The first and second pressure regulating valves UA and UB are controlled by a braking controller ECU based on drive signals Ua and Ub.

[0043] The hydraulic pressure Pa between the first pressure regulating valve UA and the second pressure regulating valve UB is regulated solely by the first pressure regulating valve UA. The hydraulic pressure Pa is referred to as the "first servo pressure or first hydraulic pressure." In the braking system for the front wheels WHf, the return path HK is connected to the servo chamber Ru through the servo path HV between the first pressure regulating valve UA and the second pressure regulating valve UB. Therefore, the first servo pressure Pa is supplied to the servo chamber Ru. The first servo pressure Pa presses the master piston NM, generating a master pressure Pm. The master pressure Pm is supplied to the front wheel cylinder CWf. In other words, the first servo pressure Pa ultimately generates the front wheel pressure Pwf. In other words, the first servo pressure Pa (first hydraulic pressure) is supplied to the front wheel cylinder CWf via the master cylinder CM and the master piston NM, without allowing the brake fluid BF in the return path HK to move to the front wheel cylinder CWf. The pressurizing unit KU is provided with a master pressure sensor PM for detecting a master pressure Pm.

[0044] The hydraulic pressure Pb between the fluid pump QA and the second pressure regulating valve UB is controlled by both the first and second pressure regulating valves UA and UB. The hydraulic pressure Pb is referred to as the "second servo pressure or second hydraulic pressure." In the braking system for the rear wheel WHr, the return path HK is connected to the rear wheel cylinder CWr between the fluid pump QA (particularly the discharge portion) and the second pressure regulating valve UB via the rear wheel connection path HSR and the hydraulic pressure modulator MJ. In other words, the second servo pressure Pb is supplied directly to the rear wheel cylinder CWr, and the rear wheel pressure Pwr is generated by the second servo pressure Pb. In other words, the second servo pressure Pb (second hydraulic pressure) is supplied to the rear wheel cylinder CWr in a state in which the brake fluid BF in the return path HK can move to the rear wheel cylinder CWr. The pressurizing unit KU is provided with a servo pressure sensor PB (also referred to as a "second servo pressure sensor") to detect the second servo pressure Pb.

[0045] When the electric motor MA is driven and the fluid pump QA is operating, a circulation flow KN of brake fluid BF is generated through the fluid pump QA and the first and second pressure regulating valves UA and UB (a flow that circulates in the order "QA → UB → UA → QA"). When no power is supplied to the first and second pressure regulating valves UA and UB and they are fully open, the first and second servo pressures Pa and Pb are both approximately "0 (atmospheric pressure)" (i.e., "Ia = Ib = 0" and "Pa = Pb = 0"). Here, pressure loss when the first and second pressure regulating valves UA and UB are fully open is ignored.

[0046] When the second pressure regulating valve UB is de-energized, power begins to be supplied to the first pressure regulating valve UA, and the amount of power Ia increases, causing the first pressure regulating valve UA to throttle the circulation flow KN. This causes the first servo pressure Pa to increase from "0." In this state, when power begins to be supplied to the second pressure regulating valve UB, and the amount of power Ib increases, the second pressure regulating valve UB further throttles the circulation flow KN. This causes the second servo pressure Pb to increase from the first servo pressure Pa. In other words, the first servo pressure Pa is a differential pressure with respect to "0 (atmospheric pressure)" and is regulated only by the first pressure regulating valve UA. Meanwhile, the second servo pressure Pb is a differential pressure with respect to the first servo pressure Pa and is regulated by the first and second pressure regulating valves UA and UB. Therefore, in terms of the magnitude relationship between the first servo pressure Pa and the second servo pressure Pb, the second servo pressure Pb is always equal to or greater than the first servo pressure Pa (i.e., "Pb≧Pa"). When no power is supplied to the second pressure regulating valve UB and it is fully open, the first servo pressure Pa and the second servo pressure Pb are made equal (that is, "Ib=0" and "Pa=Pb").

[0047] A hydraulic pressure modulator MJ is provided between the brake control device SC and the front and rear wheel cylinders CWf, CWr so that the front and rear wheel pressures Pwf, Pwr can be individually controlled at each wheel cylinder CW. Inside the hydraulic pressure modulator MJ, the front and rear wheel communication paths HSf, HSR are each branched into two paths that are connected to the front and rear wheel cylinders CWf, CWr. The hydraulic pressure modulator MJ controls each wheel pressure Pw for anti-lock brake control, vehicle stability control, etc., independently and individually. Note that the hydraulic pressure modulator MJ is not activated during service brake (service brake) application.

[0048] <<Operation of the brake control device SC>> When braking is not being applied (for example, when the brake operating member BP is not being operated), the master piston NM is pressed by the master spring DM and returned to its initial position (the position where it has been moved furthest in the backward direction Hb). In this state, the master chamber Rm and the master reservoir RV are in communication, and the hydraulic pressure Pm (master pressure) in the master chamber is "0 (atmospheric pressure)." Furthermore, when the master piston NM is in its initial position, there is a gap Ks between the input piston NN and the master piston NM. When braking is not being applied, the first and second pressure regulating valves UA and UB are open, so the first and second servo pressures Pa and Pb are "0 (atmospheric pressure)."

[0049] During braking (i.e., when the brake operating member BP is operated), the first on-off valve VA is opened and the second on-off valve VB is closed. That is, the input chamber Rn and the rear chamber Ro are connected, and the rear chamber Ro is disconnected from the master reservoir RV. As the operating amount Ba of the brake operating member BP increases, the input piston NN is moved forward in the forward direction Ha, and brake fluid BF is discharged from the input chamber Rn. The discharged brake fluid BF is absorbed by the stroke simulator SS, increasing the hydraulic pressure Pn (input pressure) in the input chamber Rn and the hydraulic pressure Po (rear pressure) in the rear chamber Ro, and generating an operating force Fp on the brake operating member BP. At this time, the first and second pressure regulating valves UA and UB are controlled in accordance with the braking operating amount Ba (at least one of the simulator pressure Ps, operating displacement Sp, and operating force Fp), and the first and second servo pressures Pa and Pb are increased.

[0050] The first servo pressure Pa is supplied to the servo chamber Ru, which pressurizes and moves the master piston NM in the forward direction Ha. As the master piston NM moves in the forward direction Ha, the master pressure Pm increases. Brake fluid BF adjusted to the master pressure Pm is then supplied to the front wheel cylinder CWf, increasing its internal pressure Pwf. Brake fluid BF adjusted to the second servo pressure Pb is then supplied to the rear wheel cylinder CWr, increasing its internal pressure Pwr.

[0051] The braking control device SC is of a brake-by-wire type, and executes regenerative cooperative control. Because there is a gap Ks between the input piston NN and the master piston NM, the relative positional relationship between the input piston NN and the master piston NM can be adjusted arbitrarily within the range of this gap Ks by controlling the first servo pressure Pa. For example, when only the braking force Fgf from the front wheel regenerative device KCf is required, Pa is set to "0" and the master pressure Pm is left at "0." Because the front wheel pressure Pwf is not increased and remains at "0," no braking force (front wheel friction braking force) Fmf is generated due to friction between the rotating member KT and the friction member MS. Therefore, the front wheel braking force Fbf is generated only by the front wheel regenerative braking force Fgf.

[0052] <Sliding resistance Ms of seal member SL> In the brake control device SC, the pressure-receiving area (servo area) ru of the servo chamber Ru and the pressure-receiving area (master area) rm of the master chamber Rm are set to be the same. Therefore, if we assume that the sliding resistance Ms of the seal member SL (frictional resistance when sliding) is "0," the master pressure Pm (and consequently the front wheel pressure Pwf) and the first servo pressure Pa will be the same. However, in reality, the frictional resistance Ms of the seal member SL exists between the first servo pressure Pa and the master pressure Pm. Therefore, the difference between the first servo pressure Pa and the master pressure Pm is the hydraulic pressure component (referred to as the "resistance component") that corresponds to the sliding resistance Ms.

[0053] Specifically, the force Mu applied by the servo chamber Ru to the master piston NM (thrust force along the central axis Jm of the master piston NM) is expressed as "Pa × ru." Similarly, the force Mm applied by the master chamber Rm to the master piston NM (thrust force along the central axis Jm of the master piston NM) is expressed as "Pm × rm." The sliding resistance Ms (thrust force) of the seal member SL acts in a direction that prevents movement. If the sliding resistance Ms is independent of direction and has the same value whether the master piston NM moves in the forward direction Ha or the backward direction Hb, then when the master piston NM moves in the forward direction Ha (i.e., when the master pressure Pm is increased), then "Mu = Mm + Ms." Conversely, when the master piston NM moves in the backward direction Hb (i.e., when the master pressure Pm is decreased), then "Mu + Ms = Mm."

[0054] <Regenerative Cooperative Control Processing> The regenerative cooperative control process, including the switching operation, will be described with reference to the flow chart in Figure 3. In the "regenerative cooperative control," the regenerative braking force Fgf generated by the generator GNf and the frictional braking force Fmf generated by the brake control device SC are controlled in coordination so that the kinetic energy of the vehicle JV during braking is efficiently recovered (regenerated) as electrical energy. In the generator GNf, the regenerative braking force Fgf decreases as its rotational speed Ngf decreases, but the "switching operation" compensates for the decrease in the regenerative braking force Fgf (braking force generated by the generator GNf) by increasing the frictional braking force Fmf (braking force generated by the wheel pressure Pw). The algorithm for the regenerative cooperative control is programmed into the microprocessor MP of the brake controller ECU.

[0055] In step S110, signals such as the braking operation amount Ba, master pressure Pm, second servo pressure Pb, vehicle body speed Vx, and target deceleration Gd are read. The operation amount Ba is calculated based on the detected value of the operation amount sensor BA (simulator pressure sensor PS, operation displacement sensor SP, operation force sensor FP, etc.). The master pressure Pm is calculated based on the detected value of the master pressure sensor PM. The second servo pressure Pb is calculated based on the detected value of the servo pressure sensor PB. The vehicle body speed Vx is calculated based on the wheel speed Vw (detected value of the wheel speed sensor VW). The target deceleration Gd is transmitted from the driving assistance controller ECA via the communication bus BS.

[0056] In step S120, a target vehicle body posture force Fv is calculated based on the braking operation amount Ba. The "target vehicle body posture force Fv" is a target value corresponding to the braking force Fb acting on the body of the vehicle JV (i.e., the braking force of the vehicle JV as a whole). The target vehicle body posture force Fv is calculated to be "0" based on the braking operation amount Ba and the calculation map Zfv when the braking operation amount Ba is less than a predetermined amount bo. When the braking operation amount Ba is equal to or greater than the predetermined amount bo, the target vehicle body posture force Fv is calculated to increase from "0" as the braking operation amount Ba increases from "0". Here, the predetermined amount bo is a preset value (constant) that represents the play of the brake operating member BP.

[0057] When braking is automatically performed by the driving support device UD (i.e., in the case of automatic braking control that does not depend on the operation of the braking operation member BP), in step S120, similar to the case of the braking operation amount Ba, the target vehicle body braking force Fv is calculated based on the target deceleration Gd. Specifically, the target vehicle body braking force Fv is calculated to be "0" when "Gd < bo", and is calculated to increase from "0" as the target deceleration Gd increases when "Gd ≧ bo". Here, the predetermined amount bo is a predetermined value (constant) set in advance that represents the dead zone in the automatic braking control.

[0058] The braking operation amount Ba and the target deceleration Gd are collectively referred to as the "braking required amount Qg". That is, the braking required amount Qg is the target value required for braking to decelerate the host vehicle JV. The target vehicle body braking force Fv is calculated based on the braking required amount Qg.

[0059] In step S130, based on the target vehicle body braking force Fv, the front-wheel and rear-wheel required braking forces Fqf, Fqr (= Fq) are calculated. The "front-wheel and rear-wheel required braking forces Fqf, Fqr" are the target values corresponding to the actual front-wheel and rear-wheel braking forces Fbf, Fbr acting on the front wheels WHf and rear wheels WHr. Therefore, the required braking force Fq is the target value corresponding to the sum of the regenerative braking force Fg and the frictional braking force Fm. In the braking control device SC, since the braking forces of the left and right wheels are calculated as the same value, the front-wheel required braking force Fqf corresponds to two wheels in the front of the vehicle (i.e., the front two wheels WHf), and the rear-wheel required braking force Fqr corresponds to two wheels in the rear of the vehicle (i.e., the rear two wheels WHr). Step S130 calculates the front-wheel and rear-wheel required braking forces Fqf, Fqr so that the following two conditions are satisfied. Condition 1: The value obtained by adding the front-wheel required braking force Fqf and the rear-wheel required braking force Fqr is equal to the target vehicle body braking force Fv (i.e., "Fv = Fqf + Fqr"). Condition 2: The ratio Kq (also referred to as "braking force distribution") of the rear-wheel required braking force Fqr to the front-wheel required braking force Fqf is constant (value hb) (i.e., "Kq = Fqr / Fqf = hb, where the value hb is a predetermined value (constant) set in advance"). Specifically, in step S130, the ratio Kq is set to "hb (constant value)" and the front and rear wheel required braking forces Fqf and Fqr are calculated as shown in the following equation (1). Fqf = Fv / (1 + hb), and Fqr = Fv hb / (1 + hb) ...Equation (1)

[0060] In step S140, the limit regenerative braking force Fxf is acquired. The "limit regenerative braking force Fxf" is the maximum value (limit value) of the regenerative braking force Fgf that can be generated by the regenerative device KCf, and is also referred to as the "front wheel limit regenerative braking force." In other words, the limit regenerative braking force Fxf is a state quantity (variable) that represents the limit of the regenerative braking force Fgf of the front wheels WHf.

[0061] The limit regenerative braking force Fxf is restricted by the operating state of the front wheel regenerative device KCf. Therefore, the limit regenerative braking force Fxf is determined based on the operating state of the regenerative device KCf. Specifically, the operating state of the regenerative device KCf corresponds to at least one of the rotation speed Ngf of the front wheel generator GNf, the state (temperature, etc.) of the front wheel regenerative controller EGf (particularly, power transistors such as IGBTs), and the state (charge acceptance amount, temperature, etc.) of the storage battery BT. The limit regenerative braking force Fxf is determined (calculated) by the regenerative controller EGf and acquired by the brake controller ECU via the communication bus BS. For example, the front wheel regenerative controller EGf determines the front wheel limit regenerative braking force Fxf in the following manner.

[0062] The limit regenerative braking force Fxf (the upper limit value of the regenerative braking force Fgf) is determined based on the characteristic Zfx (operation map) of block X140. This is because the regenerative amount (resulting in the regenerative braking force Fgf) by the regenerator KCf is determined by the rating of the power transistor (such as IGBT) of the regenerative controller EGf and the charge acceptance amount of the storage battery BT (the remaining amount obtained by subtracting the current charge amount from the full charge). Specifically, in the operation map Zfx, when the rotational speed Ngf of the generator GNf is equal to or higher than the first predetermined speed vo, the regenerative power (work rate) by the regenerator KCf is made constant (that is, the product of the limit regenerative braking force Fxf and the rotational speed Ngf is made constant), and the limit regenerative braking force Fxf is determined. Therefore, when "Ngf ≧ vo", as the rotational speed Ngf decreases, the limit regenerative braking force Fxf is calculated to increase in an inverse proportional relationship to the rotational speed Ngf. Also, when the rotational speed Ngf decreases, the regenerative amount decreases. So, in the operation map Zfx, when the rotational speed Ngf is less than the second predetermined speed vp, the limit regenerative braking force Fxf is calculated to decrease as the rotational speed Ngf decreases. Furthermore, when the rotational speed Ngf is extremely low, energy regeneration becomes impossible. So, in the operation map Zfx, when the rotational speed Ngf is less than the third predetermined speed vq, the limit regenerative braking force Fxf is calculated to be "0". In addition, in order to prevent excessive deceleration slip (in extreme cases, wheel lock) from occurring in the front wheel WHf due to the regenerative braking force Fgf, an upper limit value fxf set in advance is provided in the operation map Zfx (that is, "vp ≦ Ngf < vo" and "Fxf = fxf"). The first, second, and third predetermined speeds vo, vp, vq, and the upper limit value fxf are predetermined values (constants).

[0063] As described above, the method for determining the limit regenerative braking force Fxf based on the rotational speed Ngf in the generator GNf has been explained. Furthermore, the limit regenerative braking force Fxf is determined based on the state of the regenerative controller EG such as temperature. When the temperature of the regenerative controller EGf is high, the limit regenerative braking force Fxf is further determined to decrease from the limit regenerative braking force Fxf determined according to the rotational speed Ngf. Also, when the temperature of the storage battery BT is high, similarly, the limit regenerative braking force Fxf is calculated to decrease.

[0064] In step S150, a target regenerative braking force Fhf and front-wheel and rear-wheel target frictional braking forces Fnf and Fnr are calculated based on the front-wheel and rear-wheel required braking forces Fqf and Fqr and the limit regenerative braking force Fxf. The "target regenerative braking force Fhf" is a target value corresponding to the actual regenerative braking force Fgf to be realized by the regenerative device KCf provided on the front wheels WHf. Furthermore, the "front-wheel and rear-wheel target frictional braking forces Fnf and Fnr (=Fn)" are target values ​​corresponding to the actual front-wheel and rear-wheel frictional braking forces Fmf and Fmr (=Fm) to be realized by the brake control device SC.

[0065] In step S150, it is determined whether the front wheel required braking force Fqf is greater than the limit regenerative braking force Fxf (referred to as "limit determination"). If the front wheel required braking force Fqf is equal to or less than the limit regenerative braking force Fxf (i.e., if the limit determination is negative), the target regenerative braking force Fhf is calculated to be equal to the front wheel required braking force Fqf, and the front wheel target frictional braking force Fnf is calculated to be "0". Furthermore, the rear wheel target frictional braking force Fnr is calculated to be equal to the rear wheel required braking force Fqr. That is, in step S150, if "Fqf≦Fxf", it is determined that "Fhf=Fqf, Fnf=0, Fnr=Fqr".

[0066] On the other hand, if the front wheel required braking force Fqf is greater than the limit regenerative braking force Fxf (i.e., if the limit determination is positive), the target regenerative braking force Fhf is calculated to be equal to the limit regenerative braking force Fxf, and the front wheel target frictional braking force Fnf is calculated to be equal to the front wheel required braking force Fqf minus the limit regenerative braking force Fxf. The rear wheel target frictional braking force Fnr is calculated to be equal to the rear wheel required braking force Fqr. That is, in step S150, if "Fqf>Fxf", it is determined that "Fhf=Fxf, Fnf=Fqf-Fxf, Fnr=Fqr".

[0067] The target regenerative braking force Fhf calculated in step S150 is transmitted from the braking controller ECU to the regenerative controller EGf via the communication bus BS. Then, the regenerative controller EGf controls the generator GNf so that the actual regenerative braking force Fgf approaches and matches the target regenerative braking force Fhf.

[0068] In step S160, front and rear wheel converted pressures Pkf and Pkr (=Pk) are calculated based on the front and rear wheel target frictional braking forces Fnf and Fnr (=Fn). The converted pressure Pk is a target value before the above-mentioned hysteresis effect is compensated for. The converted pressure Pk (=Pkf, Pkr) is determined by simply converting the target frictional braking force Fn (=Fnf, Fnr) into the dimension of the wheel pressure Pw (=Pwf, Pwr) based on the specifications of the braking device SX, etc. (pressure-receiving area of ​​the wheel cylinder CW, effective braking radius of the rotating member KT, friction coefficient of the friction member MS, effective radius of the wheel (tire), etc.).

[0069] In step S170, front and rear wheel target pressures Ptf, Ptr (=Pt) are calculated based on the front and rear wheel converted pressures Pkf, Pkr (=Pk). The front and rear wheel target pressures Ptf, Ptr are final target values ​​corresponding to the front and rear wheel pressures Pwf, Pwr (=Pw). Since the front wheel pressure Pwf is equal to the master pressure Pm, the front wheel target pressure Ptf is also the target value for the master pressure Pm. Furthermore, since the rear wheel pressure Pwr is equal to the second servo pressure Pb, the rear wheel target pressure Ptr is also the target value for the second servo pressure Pb.

[0070] The front wheel pressure Pwf (=Pm) is adjusted by the first servo pressure Pa, but since hydraulic pressure feedback control is performed so that the front wheel pressure Pwf coincides with the front wheel target pressure Ptf, the above-mentioned resistance component (hydraulic pressure component equivalent to the sliding resistance Ms of the seal member SL) is taken into account when adjusting the first servo pressure Pa. In other words, the influence of the sliding resistance Ms is compensated for by hydraulic pressure feedback control, and the front wheel pressure Pwf is adjusted. For this reason, when controlling the rear wheel pressure Pwr (=Pb), it is taken into account that the front wheel pressure Pwf includes a resistance component.

[0071] Specifically, in step S170, the front wheel target pressure Ptf is determined to be equal to the front wheel converted pressure Pkf (i.e., "Ptf = Pkf"). On the other hand, the rear wheel target pressure Ptr is determined by adding the hydraulic pressure Px (referred to as "heightening pressure") to the rear wheel converted pressure Pkr (i.e., "Ptr = Pkr + Px"). The heightening pressure Px increases the rear wheel target pressure Ptr by the hydraulic pressure component (i.e., the resistance component) related to the sliding resistance Ms. Note that the increase in the rear wheel target pressure Ptr (and thus the rear wheel pressure Pwr) from the rear wheel converted pressure Pkr by the heightening pressure Px (upper limit value px) is referred to as "heightening."

[0072] As shown in the calculation map Zpx in block X170, the padding pressure Px is calculated to increase from "0" at an increasing gradient kp (amount of change with respect to time T) as time T passes, and to become constant at a predetermined pressure px after a predetermined time to has passed. In other words, the padding pressure Px is calculated to increase smoothly from "0" toward the upper limit value px. After reaching the predetermined pressure px, the padding pressure Px is maintained constant at the predetermined pressure px. Here, the increasing gradient kp, the predetermined time to, and the predetermined pressure px are preset predetermined values ​​(constants). Furthermore, the predetermined pressure px is a hydraulic pressure value corresponding to the sliding resistance Ms of the seal member SL that seals the master cylinder CM and the master piston NM.

[0073] The pressure increase Px is calculated so that it reaches the predetermined pressure px at least by the time the switching operation of the regenerative cooperative control (an operation in which a decrease in the regenerative braking force Fg is compensated for by an increase in the frictional braking force Fm) is completed and before the actual front wheel regenerative braking force Fgf becomes "0." Therefore, at the time the switching operation is completed (i.e., when "Fgf = 0" is achieved), the state is "Px = px." For example, it is desirable that the pressure increase Px reaches the predetermined pressure px before the switching operation is started. This is because various fluctuation factors exist in the hydraulic pressure control related to the regenerative cooperative control during the switching operation.

[0074] In step S180, the front and rear wheel pressures Pwf, Pwr (actual values) are adjusted based on the front and rear wheel target pressures Ptf, Ptr (target values). The brake controller ECU drives the electric motor MA and the first and second pressure regulating valves UA, UB to control the front and rear wheel pressures Pwf, Pwr to approach and match the front and rear wheel target pressures Ptf, Ptr. Specifically, first, the electric motor MA is driven to generate a circulation flow KN that includes the fluid pump QA and the first and second pressure regulating valves UA, UB. Then, based on the front wheel target pressure Ptf and the master pressure Pm (the value detected by the master pressure sensor PM), the first pressure regulating valve UA is hydraulically feedback controlled so that the master pressure Pm (= Pwf) matches the front wheel target pressure Ptf. That is, the current Ia (also referred to as the "first current") supplied to the first pressure regulating valve UA is adjusted so that the deviation hPf between the master pressure Pm and the front wheel target pressure Ptf becomes "0." Furthermore, the second pressure regulating valve UB is hydraulically feedback controlled based on the rear wheel target pressure Ptr and the second servo pressure Pb (the value detected by the servo pressure sensor PB) so that the second servo pressure Pb (= Pwr) matches the rear wheel target pressure Ptr. That is, the current Ib (also referred to as the "second current") supplied to the second pressure regulating valve UB is adjusted so that the deviation hPr between the second servo pressure Pb and the rear wheel target pressure Ptr becomes "0." Note that when the switching operation of the regenerative cooperative control is terminated (i.e., when the front wheel regenerative braking force Fgf is no longer generated), the supply of current to the second pressure regulating valve UB is stopped, and the first servo pressure Pa and the second servo pressure Pb are made equal.

[0075] By feedback-controlling the front wheel pressure Pwf (=Pm) so that it coincides with the front wheel target pressure Ptf, the first servo pressure Pa is affected by the sliding resistance Ms of the seal member SL. In other words, when the first servo pressure Pa is increased, the first servo pressure Pa is adjusted to be greater than the front wheel target pressure Ptf by the resistance component (hydraulic pressure component equivalent to the sliding resistance Ms). On the other hand, even when the rear wheel pressure Pwr (=Pb) is feedback-controlled so that it coincides with the rear wheel target pressure Ptr, the second servo pressure Pb is not affected by the sliding resistance Ms. For this reason, the second servo pressure Pb is adjusted to be equal to the rear wheel target pressure Ptr. In other words, even if the front and rear wheel pressures Pwf and Pwr are the same, the first servo pressure Pa is greater than the second servo pressure Pb by the resistance component.

[0076] When the generator GNf can no longer generate the regenerative braking force Fgf and the switching operation ends, the supply current Ib to the second pressure regulating valve UB is set to "0." With "Ib = 0," the second pressure regulating valve UB is fully open, and the first servo pressure Pa and the second servo pressure Pb are forcibly made the same.

[0077] First, we will explain the case where the effect of sliding resistance Ms is not compensated. In this case, the brake control device SC calculates the target pressure Pt as "Ptf = Pkf, Ptr = Pkr." Just before the end of the switching operation, the second pressure regulating valve UB is not fully open, and the first servo pressure Pa is adjusted to compensate for the resistance component, so it is greater than the second servo pressure Pb by the resistance component. When the switching operation ends, the second pressure regulating valve UB is de-energized, forcing the first servo pressure Pa and the second servo pressure Pb (= Pwr) to become the same hydraulic pressure. In other words, the first servo pressure Pa, which is greater than the second servo pressure Pb, is supplied to the rear wheel cylinder CWr, so the rear wheel pressure Pwr increases.

[0078] However, in the braking control device SC, before the power supply to the second pressure regulating valve UB is stopped, the rear wheel target pressure Ptr is determined to be higher than the rear wheel converted pressure Pkr by a predetermined pressure px. In other words, since the rear wheel pressure Pwr is raised by the resistance component (i.e., the predetermined pressure px), the rear wheel pressure Pwr (i.e., the second servo pressure Pb) is adjusted to approximately match the first servo pressure Pa before the second pressure regulating valve UB is fully opened. This prevents an increase in the rear wheel pressure Pwr when the switching operation is completed. As a result, fluctuations in the vehicle deceleration are suppressed.

[0079] For example, the rear wheel target pressure Ptr is raised while the switching operation is being performed (when the regenerative braking force Fgf and the friction braking force Fmf are being generated simultaneously). During the switching operation, the raising pressure Px is calculated so as to gradually (smoothly) increase from "0" as time T passes. Finally, the raising pressure Px is determined so as to reach the predetermined pressure px before the switching operation ends (when the second pressure regulating valve UB is de-energized). Preferably, the raising pressure Px is controlled to reach the predetermined pressure px before the switching operation. In either case, since the raising pressure Px is gradually increased, a sudden change in the rear wheel target pressure Ptr (and consequently the rear wheel pressure Pwr) due to the switching operation can be suppressed.

[0080] The brake control device SC determines the target friction braking force Fn so that the braking force distribution Kq is constant. However, due to the increase in the rear wheel target pressure Ptr, the braking force distribution ratio Kq does not strictly equal the desired value. However, the pressure-receiving area of ​​the rear wheel cylinder CWr is smaller than that of the front wheel cylinder CWf, and the effective braking radius of the rear wheel rotating member KTr is smaller than that of the front wheel rotating member KTf. Therefore, the effect of the increase in the rear wheel target pressure Ptr on the braking force distribution ratio Kq is slight and can be ignored.

[0081] <Operation of the Brake Control Device SC in the Regenerative Cooperative Control According to the First Embodiment> The operation of the braking control device SC according to the first embodiment (particularly the calculation of the front and rear wheel target pressures Ptf and Ptr) during regenerative cooperative control will be described with reference to the time series diagram of Figure 4 (a diagram showing the transition of state quantities over time T). During regenerative cooperative control, target values ​​Ptf and Ptr are calculated, and actual values ​​Pwf and Pwr are controlled to match the target values ​​Ptf and Ptr, so the diagram of the target pressure Pt and the diagram of the wheel pressure Pw overlap.

[0082] In the example, it is assumed that: The regenerative device KCf is provided only on the front wheels WHf. Therefore, the regenerative braking force Fgf and the friction braking force Fmr act on the front wheels WHf, and only the friction braking force Fmr acts on the rear wheels WHr. In the brake control device SC, the pressure-receiving area ru of the servo chamber Ru is equal to the pressure-receiving area rm of the master chamber Rm. Therefore, if the frictional resistance (sliding resistance) Ms when the seal member SL slides is ignored, then "Pa = Pm". - The front wheel pressure Pwf (= Pm) is adjusted by the first servo pressure Pa. The first servo pressure Pa is feedback-controlled so that the master pressure Pm (detection value of the master pressure sensor PM) coincides with the front wheel target pressure Ptf. Therefore, the hydraulic pressure component of the front wheel pressure Pwf caused by the sliding resistance Ms of the seal member SL is compensated for by this feedback control. In other words, when the master pressure Pm is increased, the first servo pressure Pa is adjusted to be larger than the master pressure Pm by the resistance component (hydraulic pressure component caused by the sliding resistance Ms of the seal member SL) (see the dashed dotted line). The rear wheel target pressure Ptr is raised (i.e., the raising pressure Px is calculated) at the time t0 when the regenerative braking cooperative control starts (i.e., when braking starts). The raising pressure Px is gradually increased and finally reaches a predetermined pressure px (a preset constant) before the second pressure regulating valve UB is de-energized. At time t0, braking is initiated, and the braking operation amount Ba begins to increase. At time t2, the brake operating member BP is held, and the braking operation amount Ba is set to a constant value ba. At time t5, a switching operation in the regenerative cooperative control is initiated. The vehicle JV stops immediately after time t6. Therefore, this switching operation ends at time t6. - The two-dot chain line (A) represents the front wheel required braking force Fqf converted into the dimension of the front wheel pressure Pwf. Therefore, the area between the two-dot chain line (A) and the front wheel target pressure Ptf (resulting in the front wheel pressure Pwf) represents the target regenerative braking force Fhf (resulting in the regenerative braking force Fgf).

[0083] At time t0, operation of the brake operating member BP begins. Accordingly, from time t0, the front and rear wheel required braking forces Fqf, Fqr are calculated in accordance with the increase in the braking operation amount Ba (i.e., the braking request amount Qg). From time t0, the rear wheel target frictional braking force Fnr is increased, and the rear wheel converted pressure Pkr is increased. Then, the rear wheel converted pressure Pkr is added with the padding pressure Px to determine the rear wheel target pressure Ptr. From time t0 to time t1, the front wheel required braking force Fqf is equal to or less than the limit regenerative braking force Fxf, so the front wheel target frictional braking force Fnf remains "0". Therefore, the front wheel target pressure Ptf (= Pkf) is determined to be "0".

[0084] At time t1, "Fqf = Fxf." After time t1, the front wheel target friction braking force Fnf is increased, and the front wheel converted pressure Pkf is increased. Then, the front wheel converted pressure Pkf is determined as the front wheel target pressure Ptf. At time t2, the brake operating member BP is held. After time t2, as the vehicle speed Vx decreases, the generator rotation speed Ngf decreases, and the limit regenerative braking force Fxf is increased (see the calculation map Zfx in FIG. 3). Therefore, the front wheel regenerative braking force Fgf increases and the front wheel target pressure Ptf is decreased. From time t0 to time t3, the padding pressure Px is gradually increased (see the calculation map Zpx in FIG. 3). From time t2, the rear wheel converted pressure Pkr is maintained constant, but the padding pressure Px gradually increases the rear wheel target pressure Ptr until time t3.

[0085] At time t3, a predetermined time to has elapsed since the start of the padding operation, and the padding pressure Px reaches a predetermined hydraulic pressure px, which represents the upper limit of the padding pressure Px. After time t3, "Px = px (predetermined value)" is determined, and the rear wheel target pressure Ptr is calculated as a constant "Pkr + px." At time t4, the generator rotation speed Ngf decreases to a first predetermined speed vo, and the limit regenerative braking force Fxf reaches an upper limit value fxf. After time t4, the state "Fxf = fxf" is maintained, and the front wheel target pressure Ptf is calculated as a constant.

[0086] At time t5, the generator rotation speed Ngf decreases to the second predetermined speed vp, and the switching operation is initiated. From time t5, the switching operation increases the front wheel target friction braking force Fnf and the front wheel target pressure Ptf so as to compensate for the decrease in the front wheel limit regenerative braking force Fxf (resulting in the front wheel regenerative braking force Fgf). As a result, the first servo pressure Pa increases, and the front wheel pressure Pwf increases.

[0087] At time t6, just before the vehicle JV comes to a stop, the generator rotation speed Ngf reaches the third predetermined speed vq. In the state of "Ngf≦vq", "Fxf=0" holds, and therefore the regenerative braking force Fgf is no longer generated. At time t6, the switching operation is terminated. As a result, the second pressure regulating valve UB is de-energized, and the second pressure regulating valve UB is opened (fully open). With the second pressure regulating valve UB open, the first servo pressure Pa and the second servo pressure Pb become the same. At time t7, the brake operating member BP, which had been held, is returned to its original position. Accordingly, the front and rear wheel target pressures Ptf and Ptr are reduced toward "0".

[0088] <Effect of raising the height> First, we will explain the case where the rear wheel pressure Ptr (target value) and Pwr (actual value) are not raised. When raising is not performed, the rear wheel target pressure Ptr is calculated to be equal to the rear wheel converted pressure Pkr. The second pressure regulating valve UB controls the second servo pressure Pb (=Pwr) so that it matches the rear wheel converted pressure Pkr. Then, at time t6 when the switching operation ends, the power supply to the second pressure regulating valve UB is stopped and the second pressure regulating valve UB is set to the fully open state.

[0089] In the control of the first servo pressure Pa, feedback control is performed so that the master pressure Pm (=Pwf) coincides with the front wheel target pressure Ptf. Therefore, the first servo pressure Pa (shown by the dashed dotted line) is controlled taking into account a resistance component (a hydraulic pressure component corresponding to the sliding resistance Ms of the seal member SL). On the other hand, the control of the second servo pressure Pb does not include this resistance component. Therefore, just before the second pressure regulating valve UB is fully opened (i.e., just before time t6), the first servo pressure Pa is greater than the second servo pressure Pb by the resistance component. When the second pressure regulating valve UB is opened in this state, the rear wheel pressure Pwr (=Pb) is rapidly increased toward the first servo pressure Pa, as shown by line (B). The rapid increase in the rear wheel pressure Pwr causes a change in the deceleration of the vehicle JV, leading to a deterioration in ride comfort.

[0090] The brake control device SC increases the rear wheel pressures Ptr (target value) and Pwr (actual value) to avoid a sudden change in the rear wheel pressure Pwr. This increase smoothly increases the second servo pressure Pb (=Pwr) from the rear wheel converted pressure Pkr by a predetermined pressure px, which corresponds to the resistance component, before the switching operation is completed. In other words, the second servo pressure Pb is increased so that it becomes equal to the first servo pressure Pa at least until just before the time t6 when the switching operation is completed (i.e., the time when the regenerative braking force Fgf is set to "0"). This increase causes the first servo pressure Pa and the second servo pressure Pb to be substantially equal, so that a sudden increase in the rear wheel pressure Pwr does not occur even if the second pressure regulating valve UB is fully opened. As a result, fluctuations in the deceleration of the vehicle JV are avoided, improving ride comfort.

[0091] <Second embodiment of braking control device SC> A second embodiment of the braking control device SC will be described with reference to the schematic diagram of Fig. 5. In a vehicle JV equipped with the braking control device SC according to the first embodiment, a regenerative device KCf is provided on the front wheels WHf. Conversely, in a vehicle JV equipped with the braking control device SC according to the second embodiment, a regenerative device KCr is provided on the rear wheels WHr, as indicated by the dashed lines and bracketed symbols in the schematic diagram of Fig. 1. The regenerative device KCr (also referred to as the "rear wheel regenerative device") includes a generator GNr (also referred to as the "rear wheel generator"), a controller EGr for the generator GNr, and a storage battery BT for the regenerative device KCr.

[0092] In a vehicle JV equipped with a brake control device SC according to the second embodiment, no regenerative braking force is generated on the front wheels WHf, and only the regenerative braking force Fgr is generated on the rear wheels WHr. Therefore, in the second embodiment of the brake control device SC, the first servo pressure Pa is supplied to the rear wheel cylinder CWr, and the second servo pressure Pb is supplied to the servo chamber Ru. The following describes the differences between the first and second embodiments. Note that the first and second embodiments are the same except for the differences.

[0093] In the brake control device SC according to the second embodiment, in the brake system for the front wheels WHf, the return path HK is connected to the servo chamber Ru through the servo path HV between the discharge port of the fluid pump QA and the second pressure regulating valve UB. Therefore, the second servo pressure Pb is supplied to the servo chamber Ru. The second servo pressure Pb generates a master pressure Pm via the master piston NM. The master pressure Pm is supplied to the front wheel cylinder CWf, and ultimately generates the front wheel pressure Pwf. In other words, the second servo pressure Pb (second hydraulic pressure) is supplied to the front wheel cylinder CWf via the master cylinder CM and the master piston NM in a state in which the brake fluid BF in the return path HK cannot move to the front wheel cylinder CWf.

[0094] In the brake system for the rear wheel WHr, the return path HK is connected to the rear wheel cylinder CWr between the first pressure regulating valve UA and the second pressure regulating valve UB via the rear wheel connection path HSR and the hydraulic pressure modulator MJ. Therefore, the first servo pressure Pa is directly supplied to the rear wheel cylinder CWr. Therefore, the rear wheel pressure Pwr is generated by the first servo pressure Pa. In other words, the first servo pressure Pa (first hydraulic pressure) is supplied to the rear wheel cylinder CWr in a state in which the brake fluid BF in the return path HK can move to the rear wheel cylinder CWr. The pressurizing unit KU is provided with a servo pressure sensor PA (also referred to as the "first servo pressure sensor") to detect the first servo pressure Pa.

[0095] Next, the regenerative cooperative control in the second embodiment will be described with reference to the flow diagram of Fig. 3. The regenerative cooperative control in the second embodiment corresponds to the process in steps S140 to S160, where "front wheels" is replaced with "rear wheels", and the suffix "f" at the end of the symbols is replaced with "r", and the suffix "r" is replaced with "f".

[0096] In step S140, a limit regenerative braking force Fxr of the rear wheels WHr is calculated and acquired based on a calculation map similar to the calculation map Zfx and the rotation speed Ngr of the rear wheel generator GNr (or vehicle speed Vx). Then, in step S150, a limit determination is made as to whether the rear wheel required braking force Fqr is greater than the limit regenerative braking force Fxr. If the rear wheel required braking force Fqr is equal to or less than the limit regenerative braking force Fxr, the target regenerative braking force Fhr is calculated to be equal to the rear wheel required braking force Fqr, the front wheel target frictional braking force Fnf is calculated to be equal to the front wheel required braking force Fqf, and the rear wheel target frictional braking force Fnr is calculated to be "0." That is, if "Fqr≦Fxr," it is determined that "Fhr=Fqr, Fnf=Fqf, Fnr=0." On the other hand, when the rear wheel required braking force Fqr is greater than the limit regenerative braking force Fxr, the target regenerative braking force Fhr is calculated to be equal to the limit regenerative braking force Fxr, the front wheel target frictional braking force Fnf is calculated to be equal to the front wheel required braking force Fqf, and the rear wheel target frictional braking force Fnr is calculated to be a value obtained by subtracting the limit regenerative braking force Fxr from the rear wheel required braking force Fqr. In other words, when "Fqr > Fxr," "Fhr = Frf, Fnf = Fqf, Fnr = Fqr - Fxr" are determined. The target regenerative braking force Fhr is then transmitted from the brake controller ECU to the regenerative controller EGr via the communication bus BS. The regenerative controller EGr controls the generator GNi so that the actual regenerative braking force Fgr approaches and matches the target regenerative braking force Fhr.

[0097] In step S160, the converted pressure Pk is calculated based on the target frictional braking force Fn. As described above, the converted pressure Pk is a target value before the hysteresis of the seal member SL is compensated. The converted pressure Pk is calculated by converting the target frictional braking force Fn into the dimension of the wheel pressure Pw based on the specifications of the brake device SX, etc.

[0098] In step S170, target front and rear wheel pressures Ptf and Ptr are calculated based on the padding pressure Px so as to compensate for the effect of sliding resistance Ms. The target front and rear wheel pressures Ptf and Ptr are target values ​​for the front and rear wheel pressures Pwf and Pwr. The target front wheel pressure Ptf is also the target value for the master pressure Pm. The target rear wheel pressure Ptr is also the target value for the first servo pressure Pa.

[0099] In step S170, the front wheel target pressure Ptf is determined to be equal to the front wheel converted pressure Pkf (i.e., "Ptf = Pkf"). On the other hand, the rear wheel target pressure Ptr is determined by adding the padding pressure Px to the rear wheel converted pressure Pkr (i.e., "Ptr = Pkr + Px"). As in the first embodiment, the padding pressure Px is calculated to reach a predetermined pressure px (the upper limit of the padding pressure Px) before the switching operation of the regenerative cooperative control is completed (i.e., before the rear wheel regenerative braking force Fgr becomes "0"). For example, the padding pressure Px can be determined so that it reaches the predetermined pressure px before the switching operation is started. In any case, the state of "Px = px" is achieved at the end of the switching operation.

[0100] <Operation of the Brake Control Device SC in Regenerative Cooperative Control According to the Second Embodiment> The operation of the braking control device SC according to the second embodiment (particularly the calculation of the front and rear wheel target pressures Ptf and Ptr) during regenerative cooperative control will be described with reference to the time series diagram of Figure 6 (a diagram showing the transition of state quantities over time T). During regenerative cooperative control, target values ​​Ptf and Ptr are calculated, and actual values ​​Pwf and Pwr are controlled to match the target values ​​Ptf and Ptr, so the diagram of the target pressure Pt and the diagram of the wheel pressure Pw overlap.

[0101] In the example, it is assumed that: The regenerative braking device KCr is provided only on the rear wheels WHr. Therefore, only the friction braking force Fmf acts on the front wheels WHf, and the regenerative braking force Fgr and the friction braking force Fmr act on the rear wheels WHr. In the brake control device SC, the pressure-receiving area ru of the servo chamber Ru is equal to the pressure-receiving area rm of the master chamber Rm. Therefore, if the sliding resistance Ms of the seal member SL is ignored, then "Pb = Pm." The front wheel pressure Pwf (=Pm) is adjusted by the second servo pressure Pb. The second servo pressure Pb is feedback-controlled so that the master pressure Pm (the value detected by the master pressure sensor PM) coincides with the front wheel target pressure Ptf. Therefore, the hydraulic pressure component of the front wheel pressure Pwf caused by the sliding resistance Ms of the seal member SL is compensated for by this feedback control. In other words, when the master pressure Pm is increased, the second servo pressure Pb is adjusted to be larger than the master pressure Pm by the resistance component (the hydraulic pressure component caused by the sliding resistance Ms of the seal member SL) (see the dashed dotted line). The rear wheel target pressure Ptr is raised (i.e., the calculation of the pressure raising Px) at a time u3 after the start of the regenerative cooperative control and before the start of the switching operation. The pressure raising Px is gradually increased and finally reaches a predetermined pressure px (a preset constant) before the second pressure regulating valve UB is de-energized. At time u0, braking begins, and the braking operation amount Ba begins to increase. At time u2, the brake operating member BP is held, and the braking operation amount Ba is set to a constant value ba. At time u5, the switching operation in the regenerative cooperative control begins. The vehicle JV stops immediately after time u6. Therefore, the switching operation ends at time u6.

[0102] At time u0, operation of the brake operating member BP begins. Accordingly, from time u0, the front and rear wheel required braking forces Fqf, Fqr are calculated in accordance with the increase in the braking operation amount Ba (i.e., the required braking amount Qg). From time u0, the target friction braking force Fnf is increased, and the front wheel converted pressure Pkf is increased. From time u0 to time u1, the rear wheel required braking force Fqr is equal to or less than the limit regenerative braking force Fxr, so the rear wheel target friction braking force Fnr remains "0".

[0103] At time u3, the rear wheel conversion pressure Pkr is increased by the pressure increase Px. That is, the rear wheel conversion pressure Pkr is added to the pressure increase Px to determine the target rear wheel pressure Ptr. Also, at time u3, the rotation speed Ngr of the generator GNr decreases to a first predetermined speed vo, and the limit regenerative braking force Fxr reaches the upper limit value fxr. Since the condition "Fxr = fxr" is maintained after time u3, the rear wheel conversion pressure Pkr is calculated to be constant.

[0104] At time u4, a predetermined time to has elapsed since the start time u3 of the padding operation, and the padding pressure Px reaches the upper limit value px. Therefore, from time u4 onwards, the target rear wheel pressure Ptr is increased by the predetermined pressure px from the rear wheel converted pressure Pkr (i.e., "Ptr = Pkr + px"). At time u5, the switching operation is started. From time u5 onwards, the target rear wheel friction braking force Fnr is increased and the target rear wheel pressure Ptr is increased so as to compensate for the decrease in the limit regenerative braking force Fxr (and consequently the rear wheel regenerative braking force Fgr). Then, the first servo pressure Pa is increased, thereby increasing the rear wheel pressure Pwr.

[0105] At time u6, just before the vehicle JV comes to a stop, the rear wheel regenerative braking force Fgr is no longer generated. Therefore, the switching operation is terminated. As a result, the second pressure regulating valve UB is de-energized, the second pressure regulating valve UB is opened (fully open), and the first servo pressure Pa and the second servo pressure Pb are forcibly made equal. At time u7, the brake operating member BP, which had been held, is released. Accordingly, the front and rear wheel target pressures Ptf and Ptr are decreased toward "0".

[0106] In a configuration in which the vehicle is not raised using the raised pressure Px, immediately before the end of the switching operation at time u6, the second servo pressure Pb is greater than the first servo pressure Pa by a resistance component (corresponding to the sliding resistance Ms). When the second pressure regulating valve UB is de-energized at time u6, the rear wheel pressure Pwr (=Pa) increases rapidly toward the second servo pressure Pb, as shown by line (C). The rapid increase in the rear wheel pressure Pwr may cause a change in the deceleration of the vehicle JV, resulting in a deterioration in ride comfort.

[0107] The brake control device SC increases the rear wheel pressures Ptr (target value) and Pwr (actual value) to avoid a sudden change in the rear wheel pressure Pwr. This increase smoothly increases the first servo pressure Pa (=Pwr) from the rear wheel converted pressure Pkr by a predetermined pressure px, which corresponds to the resistance component, before the switching operation is completed. In other words, the first servo pressure Pa and the second servo pressure Pb are increased so that they are equal to each other at least immediately before the switching operation is completed (the time when the regenerative braking force Fgr is set to "0"). This prevents a sudden increase in the rear wheel pressure Pwr, since the first servo pressure Pa and the second servo pressure Pb are already substantially equal to each other even when the second pressure regulating valve UB is fully opened. As a result, fluctuations in the longitudinal deceleration of the vehicle JV are avoided, and a deterioration in ride comfort is avoided.

[0108] <Summary of the embodiment> The following summarizes embodiments of the braking control device SC. The braking control device SC is composed of an actuator HU and a controller ECU. The actuator HU (fluid unit) adjusts the hydraulic pressure (front wheel pressure) Pwf of the front wheel cylinder CWf and adjusts the hydraulic pressure (rear wheel pressure) Pwr of the rear wheel cylinder CWr. The controller ECU calculates front and rear wheel target pressures Ptf and Ptr, which are target values ​​for the front and rear wheel pressures Pwf and Pwr, based on the braking demand Qg (a collective term for the braking operation amount Ba and the target deceleration Gd) of the vehicle JV. The controller ECU then controls the actuator HU so that the front and rear wheel pressures Pwf and Pwr coincide with the front and rear wheel target pressures Ptf and Ptr.

[0109] The actuator HU includes a fluid pump QA driven by an electric motor MA, and first and second pressure regulating valves UA and UB provided in a return path HK connecting the suction and discharge ports of the fluid pump QA. The first and second pressure regulating valves UA and UB regulate first and second servo pressures Pa and Pb (first and second hydraulic pressures). Specifically, the first servo pressure (first hydraulic pressure) Pa is regulated only by the first pressure regulating valve UA. On the other hand, the second servo pressure (second hydraulic pressure) Pb is regulated by both the first and second pressure regulating valves UA and UB.

[0110] In a vehicle JV having a regenerative brake device KCf on a front wheel WHf, the first servo pressure Pa is supplied to the front wheel cylinder CWf via the cylinder CM and the piston NM in a state in which the brake fluid BF in the return path HK cannot move to the front wheel cylinder CWf. That is, the servo chamber Ru and the front wheel cylinder CWf are fluidically separated. On the other hand, the second servo pressure Pb is supplied to the rear wheel cylinder CWr in a state in which the brake fluid BF in the return path HK can move to the rear wheel cylinder CWr.

[0111] In a configuration in which the brake control device SC is applied to a vehicle JV having a regenerative device KCr on a rear wheel WHr, the second servo pressure Pb is supplied to the front wheel cylinder CWf via the cylinder CM and the piston NM in a state in which the brake fluid BF in the return path HK cannot move to the front wheel cylinder CWf, while the first servo pressure Pa is supplied to the rear wheel cylinder CWr in a state in which the brake fluid BF in the return path HK can move to the rear wheel cylinder CWr.

[0112] When the regenerative braking devices KCf, KCr do not generate regenerative braking forces Fgf, Fgr (i.e., when the switching operation is terminated), the controller ECU determines the rear wheel target pressure Ptr to be higher than the front wheel target pressure Ptf by a predetermined pressure px. Then, the controller ECU stops energizing the second pressure regulating valve UB to fully open the second pressure regulating valve UB. Specifically, the controller ECU calculates the padding pressure Px based on a characteristic Zpx (computation map) that increases over time T and has an upper limit value px. By the time the switching operation of the regenerative cooperative control (an operation that compensates for a decrease in regenerative braking force by increasing frictional braking force) is terminated, the rear wheel target pressure Ptr has been increased by the predetermined pressure px relative to the front wheel target pressure Ptf. Here, the predetermined pressure px is preset as a hydraulic pressure value corresponding to the sliding resistance Ms of the seal member SL that seals the cylinder CM and the piston NM.

[0113] In hydraulic pressure feedback control, front and rear wheel pressures Pwf and Pwr (actual values) are controlled to coincide with front and rear wheel target pressures Ptf and Ptr (target values). In the front wheel pressure Pwf, hydraulic pressure feedback control compensates for a hydraulic pressure component (resistance component) due to the sliding resistance Ms of the seal member SL that seals the cylinder CM and the piston NM. In other words, of the first servo pressure Pa and the second servo pressure Pb, one side hydraulic pressure supplied to the servo chamber Ru (the first servo pressure Pa described in the first embodiment and the second servo pressure Pb described in the second embodiment) is adjusted to include a resistance component. On the other hand, of the first servo pressure Pa and the second servo pressure Pb, the other side hydraulic pressure supplied to the rear wheel cylinder CWr (the second servo pressure Pb in the first embodiment and the first servo pressure Pa in the second embodiment) is not affected by the sliding resistance Ms. Therefore, even if the front wheel pressure Pwf and the rear wheel pressure Pwr are the same, the one-side hydraulic pressure is greater than the other-side hydraulic pressure by an amount equal to the resistance component. At the end of the switching operation, the second pressure regulating valve UB is de-energized, forcing the one-side hydraulic pressure and the other-side hydraulic pressure to be equal. However, if the pressure is not raised, the one-side hydraulic pressure greater than the other-side hydraulic pressure is introduced into the rear wheel cylinder CWr, to which the other-side hydraulic pressure is supplied, causing a sudden (step-like) increase in the rear wheel pressure Pwr.

[0114] In the braking control device SC, at the end of the switching operation, the rear wheel pressure Pwr is raised (hydraulic pressure increased) by an amount corresponding to the sliding resistance Ms of the seal member SL. Therefore, at the end of the switching operation, the rear wheel pressure Pwr is greater than the front wheel pressure Pwf, but the one-side hydraulic pressure and the other-side hydraulic pressure are approximately equal. As a result, changes in the rear wheel pressure Pwr are suppressed, which suppresses fluctuations in the longitudinal acceleration of the vehicle JV and improves ride comfort. [Explanation of symbols]

[0115] JV...vehicle, SC...brake control device, SX...brake device, CP...brake caliper, CW...wheel cylinder, KT...rotating member (brake disc), MS...friction member (brake pad), CM...master cylinder, NM...master piston, SL...sealing member, Rm...master chamber, Ru...servo chamber, HU...fluid unit (actuator), UA, UB...first and second pressure regulating valves, MA...electric motor, QA...fluid pump, ECU...controller for brake control device (brake controller), KCf, KCr...front and rear wheel regenerative device, GNf, GNr...front and rear wheel generators, EGf , EGr...controller for front and rear wheel regenerative devices (front and rear wheel regenerative controller), BS...communication bus, Fxf, Fxr...front and rear wheel limit regenerative braking force, Fnf, Fnr...front and rear wheel target friction braking force (target value), Pkf, Pkr...front and rear wheel converted pressure (target value), Ptf, Ptr...front and rear wheel target pressure (target value), Pwf, Pwr...front and rear wheel wheel pressure (actual value), Pa, Pb...first and second servo pressure (first and second hydraulic pressure), Pm...master pressure, PM...master pressure sensor, PA, PB...first and second servo pressure sensor (first and second servo pressure sensor), Px...heightening pressure, px...specified pressure.

Claims

1. A vehicle braking control device applied to a vehicle equipped with a regenerative device on a front wheel, an actuator for adjusting the front and rear wheel pressures in the front and rear wheel cylinders; a controller that calculates front and rear wheel target pressures, which are target values ​​for the front and rear wheel wheel pressures, based on a braking demand amount of the vehicle, and controls the actuators so that the front and rear wheel pressures coincide with the front and rear wheel target pressures; the actuator is composed of a fluid pump driven by an electric motor, and first and second pressure regulating valves provided in a return passage connecting a suction portion and a discharge portion of the fluid pump; a first hydraulic pressure adjusted only by the first pressure regulating valve is supplied to the front wheel cylinder in a state in which the brake fluid in the return flow path cannot move to the front wheel cylinder via a cylinder and a piston, and a second hydraulic pressure adjusted by the first and second pressure regulating valves is supplied to the rear wheel cylinder in a state in which the brake fluid in the return flow path can move to the rear wheel cylinder; A vehicle braking control device, wherein the controller determines the rear wheel target pressure to be greater than the front wheel target pressure by a predetermined pressure when the regenerative device does not generate regenerative braking force, and stops supplying electricity to the second pressure regulating valve.

2. A vehicle braking control device applied to a vehicle equipped with a regenerative device on a rear wheel, an actuator for adjusting the front and rear wheel pressures in the front and rear wheel cylinders; a controller that calculates front and rear wheel target pressures, which are target values ​​for the front and rear wheel wheel pressures, based on a braking demand amount of the vehicle, and controls the actuators so that the front and rear wheel pressures coincide with the front and rear wheel target pressures; Equipped with the actuator is composed of a fluid pump driven by an electric motor, and first and second pressure regulating valves provided in a return passage connecting a suction portion and a discharge portion of the fluid pump; a first hydraulic pressure regulated only by the first pressure regulating valve is supplied to the rear wheel cylinder in a state in which the brake fluid in the return flow path can move to the rear wheel cylinder, and a second hydraulic pressure regulated by the first and second pressure regulating valves is supplied to the front wheel cylinder in a state in which the brake fluid in the return flow path cannot move to the front wheel cylinder via a cylinder and a piston; A vehicle braking control device, wherein the controller determines the rear wheel target pressure to be greater than the front wheel target pressure by a predetermined pressure when the regenerative device does not generate regenerative braking force, and stops supplying electricity to the second pressure regulating valve.

3. 3. The vehicle braking control device according to claim 1, A braking control device for a vehicle, wherein the predetermined pressure is a hydraulic pressure corresponding to the sliding resistance of a seal member that seals the cylinder and the piston.

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