Vehicle parking brake device

Abstract

To provide a parking brake device which uses pressure applied by a fluid unit when a parking brake is activated and which can suppress drawing-in of a braking operation member.SOLUTION: This parking brake device comprises: "a fluid unit that includes a fluid pump for sucking a braking liquid from a master cylinder using a first electric motor as a power source and a pressure regulator for increasing the pressure of the braking liquid discharged from the fluid pump and supplying it as braking liquid pressure to a wheel cylinder, and presses a friction member to a rotational member fixed to a wheel by means of the braking liquid pressure to generate a braking force"; "an electric unit that generates a braking force for a parking wheel on which a parking brake is applied among wheels using a second electric motor as a power source; and "a controller that controls the fluid unit and the electric unit". The controller increases only braking liquid pressure corresponding to the parking wheel of the wheel cylinder when the parking brake is activated.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a parking brake device for a vehicle. [Background technology]

[0002] Patent document 1 describes the following: "A method for operating an automobile brake mechanism having an electrically controllable service brake system (BBA) that generates braking force independent of driver operation, and an electrically controllable parking brake system (FBA) that generates and maintains braking force, in which when a braking force greater than the braking force that the parking brake system can generate must be maintained under a specified operating condition, the service brake system (BBA) generates the additional required braking force so that the parking brake system or the electromechanical drive unit need only respond to relatively small operating conditions."

[0003] Patent document 2 states that "the electric parking brake system 11 includes a drum-type brake device 6, an electric motor 52 that activates the brake device 6 by pulling a brake cable 51, a VSC-ECU 4 that activates the brake device 6 by applying hydraulic pressure, and an EPB-ECU 2 that controls the electric motor 52. The EPB-ECU 2 includes a parking feasibility determination unit 24 that determines whether or not the braking force required for parking can be obtained by operating the brake device 6 by the electric motor 52, and a braking control unit 25 that, when the parking feasibility determination unit 24 determines that the necessary braking force cannot be obtained, causes the EPB-ECU2 to activate the brake device 6 and, simultaneously or with a delay, causes the electric motor 52 to activate the brake device 6."

[0004] In the parking brake devices for vehicles described in Patent Documents 1 and 2, the hydraulic pressure (braking hydraulic pressure) in the wheel cylinder is increased by the service brake to compensate for a shortage of braking force (i.e., the pressing force of a friction member against a rotating member) when applying the parking brake. For example, in Patent Documents 1 and 2, a hydraulic unit for vehicle stabilization control (so-called ESC, also called "driving dynamic control" or "vehicle stability control") is used as a unit for automatically increasing the braking hydraulic pressure.

[0005] The applicant has developed a parking brake device for a vehicle as described in Patent Document 3. In the devices of Patent Documents 1 and 2, when the parking brake is applied, a lack of pressing force is compensated for by automatic pressurization of brake fluid pressure. In contrast, in the device of Patent Document 3, assistance by automatic pressurization is performed when the parking brake is released.

[0006] In a hydraulic unit for vehicle stabilization control, the brake fluid pressure is generally automatically increased by moving the brake fluid from the master cylinder side to the wheel cylinder side via a pressure regulating valve. For this reason, when the brake fluid pressure is increased, the displacement of the brake operating member (brake pedal) may be affected. Specifically, the brake operating member is moved slightly toward the master cylinder side due to the movement of the brake fluid. This phenomenon is called "pulling in" of the brake operating member. In a parking brake device in which the operation of the parking brake (i.e., application and / or release of the parking brake) is assisted by automatic pressurization in the fluid unit, it is desirable to suppress this pulling phenomenon. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2007-519568 [Patent Document 2] JP 2020-050004 A [Patent Document 3] JP 2013-244888 A Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a parking brake device in which pressurization by a fluid unit is utilized when the parking brake is operated, in which retraction of a brake operating member can be suppressed. [Means for solving the problem]

[0009] The parking brake device of the present invention comprises: "a fluid unit (HU) which is composed of a fluid pump (QA) powered by a first electric motor (MA) and which draws brake fluid (BF) from a master cylinder (CM), and a pressure regulating valve (UA) which increases the pressure of the brake fluid (BF) discharged by the fluid pump (QA) and supplies it to a wheel cylinder (CW) as brake fluid pressure (Pw), and which generates a braking force (Fm) by pressing a friction member (MS) against a rotating member (KT) fixed to a wheel (WH) of the vehicle with the brake fluid pressure (Pw)", "an electric unit (DU) which is powered by a second electric motor (ME) and which generates the braking force (Fm) on a parking wheel (WHp) among the wheels (WH) which applies the parking brake", and "a controller (ECU) which controls the fluid unit (HU) and the electric unit (DU)". When the parking brake is activated, the controller (ECU) increases only the brake fluid pressure (Pwp) in the wheel cylinder (CW) corresponding to the parking wheel (WHp).

[0010] In the parking brake device according to the present invention, the parking wheels (WHp) are the rear wheels (WHr) of the vehicle, and the non-parking wheels (WHn) are the front wheels (WHf) of the vehicle. The hydraulic unit (HU) includes normally open front and rear wheel pressure regulators (UAf, UAr) in front and rear brake systems (BKf, BKr) as the pressure regulators (UA). When the parking brake is activated, the controller (ECU) does not energize the front wheel pressure regulator valve (UAf) but energizes only the rear wheel pressure regulator valve (UAr).

[0011] In the parking brake device according to the present invention, the parking wheels (WHp) are the rear wheels (WHr) of the vehicle, and the non-parking wheels (WHn) are the front wheels (WHf) of the vehicle. The hydraulic unit (HU) includes normally open one-side and other-side pressure regulating valves (UAi, UAj) in diagonal brake systems (BKi, BKj) as the pressure regulating valves (UA). The hydraulic unit (HU) further includes normally open front and rear wheel inlet valves (VIf, VIr) between the one-side and other-side pressure regulating valves (UAi, UAj) and the wheel cylinders (CW). When the controller (ECU) operates the parking brake, it energizes the front wheel inlet valve (VIf) to close the front wheel inlet valve (VIf), it does not energize the rear wheel inlet valve (VIr) to leave the rear wheel inlet valve (VIr) open, and it energizes the one-side and other-side pressure regulating valves (UAi, UAj).

[0012] According to the above-mentioned configuration, the amount of brake fluid BF moving from the master reservoir RV to the master cylinder CM is limited in the application assist control when the parking brake is applied. This can reduce the retraction of the brake operating member BP. As a result, the driver's discomfort is suppressed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram for explaining a first embodiment of a parking brake device EP for a vehicle according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram including a cross-sectional view for explaining an electric unit DU and the like. [Diagram 3] FIG. 11 is a flow diagram for explaining a process of application control including auxiliary pressurization control. [Figure 4] FIG. 11 is a time series diagram for explaining the operation of adaptive control. [Diagram 5] FIG. 11 is a flow chart for explaining a process of release control including an auxiliary pressurization control. [Figure 6] FIG. 4 is a time series diagram for explaining the operation of the release control. [Figure 7]FIG. 4 is a schematic diagram for explaining a second embodiment of a vehicle parking brake device EP according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] An embodiment of a parking brake device EP for a vehicle according to the present invention will be described with reference to the drawings.

[0015] <Symbols for components, etc.> In the following explanation, components, signals, values, etc. with the same symbol, such as "CW", have the same function. The subscripts "f" and "r" at the end of various symbols related to wheels are generic symbols that indicate whether the element is related 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 these are omitted, each symbol represents its generic name.

[0016] -Front and rear braking system- Furthermore, in a configuration in which a front and rear type (also called "II type") is adopted as the two braking systems (brake piping) (see the first embodiment), the suffixes "f" and "r" at the end of the symbols are also generic symbols indicating which system it relates to. Specifically, the suffix "f" means "corresponding to the front wheel braking system BKf", and the suffix "r" means "corresponding to the rear wheel braking system BKr". For example, "CWf" is a wheel cylinder (i.e., a front wheel cylinder) related to the front wheel braking system BKf, and "CWr" is a wheel cylinder (i.e., a rear wheel cylinder) related to the rear wheel braking system BKr. As above, the suffixes "f" and "r" may be omitted. In this case, the symbol represents a generic term for the front and rear wheel braking systems BKf and BKr. In other words, "wheel cylinder CW" is a generic term for the front and rear wheel wheel cylinders CWf and CWr.

[0017] -Diagonal type braking system- In addition, in a configuration in which a diagonal type (also called "X type") is adopted as two braking systems (braking piping) (see the second embodiment), the suffixes "i" and "j" at the end of the symbols are generic symbols indicating which system it relates to. Specifically, the suffix "i" means "corresponding to one side of the braking system", and the suffix "j" means "corresponding to the other side of the braking system". In addition, in a configuration in which a diagonal type braking system is adopted, the suffix "f" means "corresponding to the front wheel WHf", and the suffix "r" means "corresponding to the rear wheel WHr". For example, "VIf" belonging to "BKi" indicates "front wheel inlet valve VIf in one side of the braking system BKi". As above, the suffixes "i" and "j" may be omitted. In this case, the symbol represents a generic name.

[0018] -Direction of movement / movement- In terms of the directions of motion and movement of the members related to the friction member MS (the friction member MS itself, the brake piston PN, the output member SB, etc.), the "forward direction Ha" corresponds to the "direction in which the friction member MS approaches the rotating member KT," and the "reverse direction Hb (the direction opposite to the forward direction Ha)" corresponds to the "direction in which the friction member MS moves away from the rotating member KT." Therefore, when the members related to the friction member MS move in the forward direction Ha, the pressing force Fm of the friction member MS against the rotating member KT (the force with which the friction member MS is pressed against the rotating member KT, also called the "braking force") increases. Conversely, when the members related to the friction member MS move in the reverse direction Hb, the braking force (pressing force) Fm decreases.

[0019] Regarding the rotation direction of the second electric motor ME, the "forward rotation direction Da" is Forward direction Ha The "reverse direction Db (opposite rotation direction to the forward direction Da)" of the second electric motor ME corresponds to the backward direction Hb. In other words, when the second electric motor ME rotates in the forward direction Da, the friction member MS moves in the forward direction Ha, and the braking force Fm is increased. Conversely, when the second electric motor ME rotates in the reverse direction Db, the friction member MS moves in the backward direction Hb, and the braking force Fm is decreased.

[0020] Finally, the relationship between the direction of movement and the braking force Fm of the first and second master pistons NP and NS of the master cylinder CM will be described. In the first and second master pistons NP and NS, the "forward direction Hf" is the "direction corresponding to the forward direction Ha of the friction member MS," and the "reverse direction Hr" is the "direction corresponding to the reverse direction Hb of the friction member MS." When the first and second master pistons NP and NS are moved in the forward direction Hf, the brake fluid BF is discharged from the master cylinder CM toward the wheel cylinder CW. This increases the hydraulic pressure Pw (referred to as "braking hydraulic pressure") in the wheel cylinder CW, moves the friction member MS in the forward direction Ha, and increases the braking force Fm. Conversely, when the first and second master pistons NP and NS are moved in the reverse direction Hr, the brake fluid BF is returned from the wheel cylinder CW toward the master cylinder CM. This decreases the hydraulic pressure Pw in the wheel cylinder CW, moves the friction member MS in the reverse direction Hb, and decreases the braking force Fm.

[0021] <First embodiment of parking brake device EP> A first embodiment of the parking brake device EP will be described with reference to the schematic diagram of FIG. 1. A vehicle equipped with the parking brake device EP includes a brake operating member BP, a parking brake switch SW, a master reservoir RV, a master cylinder CM, a braking device SX, a fluid unit HU, various sensors (VW, etc.), a controller ECU, and the parking brake device EP. In the first embodiment of the parking brake device EP, a so-called front and rear type (also called "II type") is adopted for the braking system related to the master cylinder CM and the fluid unit HU. That is, in the tandem type master cylinder CM, two hydraulic chambers (front and rear master chambers) Rmf, Rmr (=Rm) are connected to the front and rear wheel cylinders CWf, CWr (=CW), respectively, via the front and rear wheel communication passages HSf, HSR (=HS).

[0022] A brake operating member (e.g., a brake pedal) BP is a member that the driver operates to decelerate the vehicle. A parking brake switch (also simply referred to as a "parking switch") SW is a switch that is operated by the driver, and outputs an on or off signal Sw (referred to as a "parking signal"). Specifically, when the parking signal Sw is in the on state, application (activation) of the parking brake is instructed so that the parking brake is applied. Conversely, when the parking signal Sw is in the off state, release (activation) of the parking brake is instructed so that the parking brake is not applied.

[0023] The master reservoir (also called "atmospheric pressure reservoir") RV is a tank for hydraulic fluid, and brake fluid BF is stored therein. The master cylinder CM is a cylinder member having a bottom. First and second master pistons NP, NS are inserted inside the master cylinder CM, and the inside is sealed by cup seals CS, CK to separate the master chambers Rmf, Rmr into front and rear master chambers. In other words, the master cylinder CM is of a tandem type. The front and rear master chambers Rmf, Rmr of the master cylinder CM are connected to the master reservoir RV. The front and rear master chambers Rmf, Rmr (=Rm) are also ultimately connected to the front and rear wheel cylinders CWf, CWr (=CW), respectively, via the front and rear wheel communication passages HSf, HSR (=HS).

[0024] The first and second master pistons NP, NS are mechanically connected to the brake operating member BP via a brake rod RD, etc. The master cylinder CM is provided with a brake booster BB to boost the operating force Fp of the brake operating member BP by the driver. When the brake operating member BP is operated, the first and second master pistons NP, NS are moved forward Hf (in the direction in which the volume of the master chamber Rm decreases). As a result, the brake fluid BF is moved from the master cylinder CM to the wheel cylinder CW, and the hydraulic pressure (brake fluid pressure) Pw in the wheel cylinder CW is increased. In a vehicle equipped with a parking brake device EP, the relationship between the operating force Fp and the operating displacement Sp of the brake operating member BP (i.e., the operating characteristics of the brake operating member BP) is determined by the rigidity (spring constant) of the power transmission members (the brake operating member BP itself, the master cylinder CM, the brake piping, the brake caliper CP, the friction member MS, etc.) from the brake operating member BP to the friction member MS. In other words, the vehicle does not employ a brake-by-wire type brake control device in which the operation characteristics of the brake operating member BP are generated by a stroke simulator.

[0025] 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 so as to rotate integrally with the wheel WH. The brake caliper CP is provided so as to sandwich the rotating member KT. The brake caliper CP is provided with a wheel cylinder CW. As will be described later, the wheel cylinder CW is supplied with brake fluid BF adjusted to an adjusted hydraulic pressure Pq (=Pm+mQ) from the fluid unit HU as a brake hydraulic pressure Pw. In the braking device SX, a braking force Fm is generated on the wheel WH in accordance with the brake hydraulic pressure Pw. Here, the "braking force Fm" is a force with which a friction member (e.g., a brake pad) MS is pressed against the rotating member KT, and is also referred to as a "pressing force."

[0026] <Fluid unit HU> The fluid unit HU is provided between the master cylinder CM and the wheel cylinders CW. The fluid unit HU is used for antilock brake control (control for suppressing locking of the wheels WH, so-called ABS control), traction control (control for suppressing spinning of the wheels WH), vehicle stability control (control for suppressing excessive understeer / oversteer of the vehicle, so-called ESC), etc. To perform these controls, the fluid unit HU controls the brake fluid pressure Pw independently of the fluid pressure (master cylinder fluid pressure) Pm of the master cylinder CM and individually in each wheel cylinder CW.

[0027] The fluid unit HU is composed of a pressure regulating valve UA (=UAf, UAr), a fluid pump QA (=QAf, QAr), an electric motor MA, a pressure regulating reservoir RC (=RCf, RCr), a master cylinder hydraulic pressure sensor PM (=PMf, PMr), an inlet valve VI (=VIf, VIr), and an outlet valve VO (=VOf, VOr).

[0028] Front and rear wheel pressure regulating valves UAf, UAr (=UA) are provided in the front and rear wheel communication passages HSf, HSR (=HS). The pressure regulating valve UA (solenoid valve) is a normally open linear valve (also called a "differential pressure valve" or "proportional valve"). The upper part Bmf, Bmr (part of the communication passage HS closer to the master cylinder CM) of the pressure regulating valve UA and the lower part Bbf, Bbr (part of the communication passage HS closer to the wheel cylinder CW) of the pressure regulating valve UA are connected by the front and rear wheel return passages HKf, HKr (=HK). The return passage HK is provided with the front and rear wheel fluid pumps QAf, QAr (=QA) and the front and rear wheel pressure regulating reservoirs RCf, RCr (=RC). The fluid pump QA is driven by an electric motor MA.

[0029] In the fluid unit HU, front and rear wheel master cylinder hydraulic pressure sensors PMf, PMr (=PM) are provided between the master cylinder CM and the pressure regulating valve UA to detect the actual hydraulic pressure (master cylinder hydraulic pressure) Pm supplied from the master cylinder CM. Since the hydraulic pressure Pmf (front wheel master cylinder hydraulic pressure) in the front wheel master chamber Rmf and the hydraulic pressure Pmr (rear wheel master cylinder hydraulic pressure) in the rear wheel master chamber Rmr are substantially equal, either one of the front and rear wheel master cylinder hydraulic pressure sensors PMf, PMr may be omitted.

[0030] The electric motor MA drives the fluid pump QA. Here, the electric motor MA is also referred to as the "return electric motor" or the "first electric motor" to distinguish it from the electric motor ME (for parking brake) described later. When the first electric motor MA is driven to rotate, the fluid pump QA sucks brake fluid BF from the upper part Bm of the pressure regulating valve UA and discharges it to the lower part Bb of the pressure regulating valve UA. As a result, front-wheel and rear-wheel circulation flows KNf, KNr (=KN) of brake fluid BF (flow of circulating brake fluid BF, also simply referred to as "return flow") are generated in the communication path HS and the return path HK, including the pressure regulating valve UA, the fluid pump QA, and the pressure regulating reservoir RC. When the return flow KN is throttled by the pressure regulating valve UA, the orifice effect causes the hydraulic pressure Pq (called the "adjusted hydraulic pressure") at the lower part Bb of the pressure regulating valve UA to be increased from the hydraulic pressure Pm (master cylinder hydraulic pressure) at the upper part of the pressure regulating valve UA. In other words, the hydraulic pressure difference mQ (also called the "differential pressure") between the master cylinder hydraulic pressure Pm and the adjusted hydraulic pressure Pq is adjusted by the fluid unit HU. The adjusted hydraulic pressure Pq increased by the pressure regulating valve UA is supplied to the wheel cylinder CW as the braking hydraulic pressure Pw.

[0031] Inside the fluid unit HU, the front and rear wheel communication passages HSf and HSR are each branched into two and connected to the front and rear wheel cylinders CWf and CWr. An inlet valve VI and an outlet valve VO are provided for each wheel cylinder CW. The inlet valve VI (solenoid valve) is a normally open on-off valve. The inlet valve VI is provided in the branched communication passage HS (i.e., on the side closer to the wheel cylinder CW than the branch parts Bbf and Bbr of the communication passage HS). The communication passage HS is connected to the pressure regulating reservoir RC via a pressure reducing passage HG at a lower part of the inlet valve VI (the part of the communication passage HS closer to the wheel cylinder CW). An outlet valve VO is provided in the pressure reducing passage HG. The outlet valve VO (solenoid valve) is a normally closed on-off valve.

[0032] When the inlet valve VI and the outlet valve VO are not controlled (i.e., when both are not energized), the brake fluid pressure Pw is increased by the differential pressure mQ with respect to the master cylinder pressure Pm. On the other hand, when the brake fluid pressure Pw needs to be adjusted for each wheel cylinder CW due to antilock brake control or the like, the inlet valve VI and the outlet valve VO are controlled individually. Specifically, to reduce the brake fluid pressure Pw, the inlet valve VI is closed and the outlet valve VO is opened. The inflow of brake fluid BF into the wheel cylinder CW is prevented, and the brake fluid BF in the wheel cylinder CW flows out to the pressure regulating reservoir RC, so that the brake fluid pressure Pw is reduced. To increase the brake fluid pressure Pw, the inlet valve VI is opened and the outlet valve VO is closed. The brake fluid BF is prevented from flowing out to the pressure regulating reservoir RC, and the brake fluid pressure Pq adjusted by the pressure regulating valve UA is supplied to the wheel cylinder CW, increasing the brake fluid pressure Pw. To maintain the brake fluid pressure Pw, both the inlet valve VI and the outlet valve VO are closed. Since the wheel cylinder CW is fluidly sealed, the brake fluid pressure Pw is maintained constant.

[0033] -The cause of the brake operating part BP being pulled in-- The following will describe the pull-in phenomenon (the phenomenon in which the brake operating member BP is moved in the forward direction Hf) that may occur when the differential pressure mQ (the hydraulic pressure difference between the master cylinder hydraulic pressure Pm and the adjusted hydraulic pressure Pq) is increased.

[0034] When the brake fluid pressure Pw is increased, the brake piston PN in the wheel cylinder CW is moved forward in the forward direction Ha (see FIG. 2). At this time, the volume in the wheel cylinder CW is increased, and the amount of brake fluid BF in the wheel cylinder CW is increased. In other words, when the brake fluid pressure Pw is increased and the brake piston PN is moved forward, a volume of brake fluid BF corresponding to the amount of movement of the brake piston PN is consumed in the wheel cylinder CW.

[0035] Next, the cup seals CS and CK that seal the master cylinder CM and the first and second master pistons NP and NS will be described. The master cylinder CM has a bottomed cylindrical hole formed by a closed bottom surface and the inner peripheral surface of a cylindrical hole. The first and second master pistons NP and NS are inserted into the bottomed cylindrical hole of the master cylinder CM. The outer peripheral surfaces of the first and second master pistons NP and NS and the inner peripheral surface of the master cylinder CM are sealed by two types of cup seals CS and CK. Of the two types of cup seals, the one on the forward direction Hf side (the side closer to the bottom of the master cylinder CM and away from the brake operating member BP) is called the "front end seal CS," and the one on the backward direction Hr side (the side farther from the bottom of the master cylinder CM and closer to the brake operating member BP) is called the "rear end seal CK."

[0036] The sealing performance of the leading end seal CS (one of the two types of cup seals) depends on the flow direction of the brake fluid BF (i.e., it has directionality). In detail, the leading end seal CS exerts a sealing function (a function to prevent the liquid BF from leaking) in the direction from the master chamber Rm to the master reservoir RV. On the other hand, the movement of the brake fluid BF is permitted in the direction from the master reservoir RV to the master chamber Rm via the lip portion of the leading end seal CS (the portion that comes into sliding contact with the inner periphery of the master cylinder CM). On the other hand, the sealing function of the rear end seal SK (the other of the two types of cup seals) is exerted without depending on the flow direction of the brake fluid BF.

[0037] When the brake operating member BP is not operated (i.e., when "Ba = 0"), the master reservoir RV and the master chamber Rm (= Rmf, Rmr) are in communication with each other. Therefore, the brake fluid BF is sucked from the master reservoir RV through the master cylinder CM without load. In other words, when the brake operating member BP is not operated, the amount of brake fluid BF accompanying the increase in the volume in the wheel cylinder CW is supplied from the master reservoir RV, which is in communication with the master cylinder CM. Here, the amount of brake fluid BF sucked from the master reservoir RV accompanying the increase in the volume in the wheel cylinder CW is referred to as the "suction amount."

[0038] When the brake operating member BP is operated, the first and second master pistons NP and NS are moved in the forward direction Hf. The movement of the first and second master pistons NP and NS blocks communication between the master reservoir RV and the master chamber Rm. In this case, the amount of brake fluid BF (i.e., the suction amount) caused by the increase in the volume in the wheel cylinder CW is supplied from the master reservoir RV through the lip of the cup seal CS (tip seal). When the fluid pump QA is driven by the first electric motor MA, the fluid pump QA also draws brake fluid BF from the master chamber Rm. In other words, the brake fluid BF is also supplied from the master reservoir RV through the cup seal CS (tip seal). At this time, resistance (suction resistance) exists in the cup seal CS in the movement of the brake fluid BF. Therefore, the first and second master pistons NP and NS are moved in the forward direction Hf. As a result, the driver may feel discomfort when the brake operating member BP is retracted (moved in the forward direction Hf). The degree of the drawing phenomenon depends on the amount (suction amount) of the brake fluid BF flowing through the cup seal CS. That is, the greater the amount of the brake fluid BF that is drawn in, the greater the degree of drawing in of the brake operating member BP.

[0039] As described above, the pull-in phenomenon occurs when the brake fluid BF moves from the master reservoir RV to the master cylinder CM through the cup seal CS while communication between the master reservoir RV and the master cylinder CM is interrupted. For this reason, the brake operation characteristic (referred to as the "Sp-Fp characteristic"), which is the relationship between the operation displacement Sp and the operation force Fp, cannot be generated in a brake-by-wire configuration formed by a stroke simulator. Therefore, in a vehicle to which the parking brake device EP is applied, the brake operation characteristic (Sp-Fp characteristic) is generated by the rigidity (elasticity) of the power transmission members (brake caliper CP, friction member MS, etc.) from the brake operation member BP to the friction member MS.

[0040] <Various sensors> The vehicle is equipped with various sensors, as listed below. Detection signals (Vw, etc.) from these sensors are input to a controller ECU. - A braking operation amount sensor BA that detects an operation amount (braking operation amount) Ba of the brake operating member BP. Here, the braking operation amount Ba is a general term, and specifically, it corresponds to at least one of the master cylinder hydraulic pressure Pm, the operation displacement Sp of the brake operating member BP, and the operation force Fp of the brake operating member BP. Therefore, as the braking operation amount sensor BA, at least one of a master cylinder hydraulic pressure sensor PM that detects the master cylinder hydraulic pressure Pm, an operation displacement sensor SP that detects the operation displacement Sp, and an operation force sensor FP that detects the operation force Fp is provided. A steering operation amount sensor SA that detects the operation amount (steering operation amount, for example, steering angle) Sa of a steering operation member SH (not shown). - A wheel speed sensor VW detects the rotational speed (wheel speed) Vw of the wheels WH. In the vehicle (particularly the vehicle body), a yaw rate sensor YR that detects a yaw rate Yr, a longitudinal acceleration sensor GX that detects a longitudinal acceleration Gx, and a lateral acceleration sensor GY that detects a lateral acceleration Gy.

[0041] <Controller ECU> The controller ECU is composed of a microprocessor MP and a drive circuit DD. The controller ECU controls the fluid unit HU. Specifically, based on detection signals (Vw, etc.) from various sensors and a control algorithm in the microprocessor MP, a drive signal Ua for the pressure regulating valve UA, a drive signal Vi for the inlet valve VI, a drive signal Vo for the outlet valve VO, and a drive signal Ma for the electric motor MA are calculated to perform antilock brake control, traction control, vehicle stability control, etc.

[0042] The drive circuit DD is formed by switching elements (power semiconductor devices such as MOS-FETs and IGBTs). The drive circuit DD is controlled in response to the drive signal (Ua, etc.) to drive the solenoid valves "UA, VI, VO" constituting the fluid unit HU and the electric motor MA. The drive circuit DD is provided with front and rear wheel current flow sensors (e.g., current sensors) IAf and IAr (=IA) to detect the current flow (front and rear wheel current flow, e.g., current value) Iaf and Iar (=Ia) of the front and rear wheel pressure regulating valves UAf and UAr.

[0043] <Parking brake device EP> The parking brake device EP is composed of an electric unit DU, a fluid unit HU, and a controller ECU. The parking brake device EP adjusts (increases or decreases) the braking force Fm to activate the parking brake. The electric unit DU is provided on a brake caliper CPr (rear wheel caliper) of the braking device SXr provided on the rear wheels WHr so as to adjust the braking force Fm. The fluid unit HU is controlled to assist (assist) the adjustment of the braking force Fm by the electric unit DU in addition to performing vehicle stability control and the like. The control of the parking brake is programmed in the microprocessor MP of the controller ECU. The pressurization control by the fluid unit HU when the parking brake is activated is referred to as "auxiliary pressurization control."

[0044] -Parking wheels WHp and non-parking wheels WHn- In the following description, among the wheels WH of the vehicle, those to which the parking brake is applied (wheels equipped with the electric unit DU) are referred to as "parking wheels WHp", and those to which the parking brake is not applied (wheels not equipped with the electric unit DU) are referred to as "non-parking wheels WHn". Among the wheels CW, those corresponding to the parking wheels WHp are referred to as "parking wheel cylinders CWp", and those corresponding to the non-parking wheels WHn are referred to as "non-parking wheel cylinders CWn". Furthermore, the hydraulic pressure of the parking wheel cylinder CWp is referred to as "parking brake hydraulic pressure Pwp", and the hydraulic pressure of the non-parking wheel cylinder CWn is referred to as "non-parking brake hydraulic pressure Pwn". Generally, the parking brake is operated by the rear wheels WHr. In this configuration, the front wheels WHf are the non-parking wheels WHn, and the rear wheels WHr are the parking wheels WHp. The front wheel cylinder CWf is the non-parking wheel cylinder CWn, and the rear wheel cylinder CWr is the parking wheel cylinder CWp. Furthermore, the front wheel brake fluid pressure Pwf is the non-parking brake fluid pressure Pwn, and the rear wheel brake fluid pressure Pwr is the parking brake fluid pressure Pwp.

[0045] <Electric unit DU> The electric unit DU of the parking brake device EP will be described with reference to the schematic diagram of FIG. 2. The electric unit DU is controlled by a controller ECU. The electric unit DU is composed of an electric motor ME, a reducer GS, an input member NB, and an output member SB. Here, the electric unit DU is provided in the rear wheel caliper CPr. That is, in the example, the front wheels WHf are non-parking wheels WHn, the rear wheels WHr are parking wheels WHp, the front wheel cylinder CWf is the non-parking wheel cylinder CWn, and the rear wheel cylinder CWr is the parking wheel cylinder CWp.

[0046] The electric motor ME is a power source for generating the braking force Fm. The electric motor ME is also called the "parking electric motor" or the "second electric motor" to distinguish it from the reflux electric motor (first electric motor) MA. The output of the second electric motor ME (the rotational power of the output shaft SF) is input to the reduction gear GS. For example, a small diameter gear SK is fixed to the output shaft SF of the electric motor ME. The small diameter gear SK meshes with a large diameter gear DK. In other words, the small diameter gear SK and the large diameter gear DK constitute the reduction gear GS.

[0047] An input member NB is fixed to the large diameter gear DK. The rotational power of the second electric motor ME is reduced by the reducer GS and transmitted to the input member NB. The input member NB is inserted into the hydraulic chamber Rw through an insertion hole formed in the rear wheel cylinder CWr (particularly, the body portion of the wheel cylinder CWr). The input member NB is held by a bearing member BH and sealed by a seal member SL. A male thread Oj is formed on the outer circumferential surface of the input member NB.

[0048] The output member SB is meshed with the input member NB. Specifically, the output member SB is formed as a hollow cylindrical member, and a female screw Mj is formed on its inner wall surface. This female screw Mj is screwed with a male screw Oj of the input member NB. That is, the input member NB (particularly the male screw Oj) and the output member SB (particularly the female screw Mj) constitute a rotary-linear motion conversion mechanism HN (also called a "power conversion mechanism") that converts rotary motion into linear motion. The power conversion mechanism HN is provided with a rotation prevention mechanism (for example, a key mechanism, a mechanism having a two-face width). The power conversion mechanism HN employs a self-locking configuration (a configuration in which the friction member MS can move from the electric motor ME, but the electric motor ME cannot be rotated from the friction member MS, also called a "configuration with zero reverse efficiency").

[0049] The output member SB is inserted into the cylindrical portion of the brake piston PN. The output member SB moves linearly along the rotation axis of the input member NB (i.e., the central axis Jp of the brake piston PN), thereby generating a braking force Fm. In detail, the released state (inoperative state) of the parking brake is shown in (a) above the central axis Jp. In this state, the end face Mp of the protrusion Bp of the output member SB is separated from the cylindrical bottom surface Mb of the brake piston PN, and the brake piston PN is not pressed by the output member SB.

[0050] When the parking brake is activated, the output member SB is moved in the forward direction Ha and presses the brake piston PN. This state is shown in (b) below the central axis Jp. The protruding end face Mp of the output member SB abuts against the cylindrical bottom face Mb of the brake piston PN, and the brake piston PN is pressed by the output member SB. Since the brake piston PN is disposed so as to press the back plate UT of the friction member MS, the linear movement of the output member SB (and thus the brake piston PN) presses the friction member MS against the rotating member KT, generating a braking force Fm. Since a self-locking configuration is adopted for the power conversion mechanism HN, once a desired braking force Fm is achieved, the braking force Fm is maintained even if the drive (energization) of the second electric motor ME is stopped.

[0051] The rear wheel cylinder CWr (=CWp) is also used as a service brake (also called the "service brake"). The braking force Fm (the pressing force of the friction member MS against the rotating member KT) is also increased by increasing the pressure (parking brake hydraulic pressure) Pwr (=Pwp) in the hydraulic chamber Rw of the rear wheel cylinder CWr through the above-mentioned auxiliary pressurization control. In other words, the brake piston PN is pressed by both the electric unit DU (particularly the second electric motor ME) and the parking brake hydraulic pressure Pwp (hydraulic pressure supplied from the hydraulic unit HU). This generates a braking force Fm, which is the force with which the friction member MS presses the rear wheel rotating member KTr.

[0052] A controller ECU (electronic control unit) controls an electric unit DU (particularly, a second electric motor ME). A parking signal Sw is input from a parking switch SW to the controller ECU. Then, a drive signal Me for controlling the second electric motor ME is calculated according to the parking signal Sw. The controller ECU is also provided with a drive circuit DD to drive the electric motor ME. In the drive circuit DD, a bridge circuit is formed by switching elements. The energization state of each switching element is controlled according to the drive signal Me, and the output of the electric motor ME is controlled. The drive circuit DD is provided with an energization amount sensor IE that detects an actual energization amount Ie of the electric motor ME. Here, the energization amount Ie is a state quantity that indicates the degree of energization to the second electric motor ME, and is, for example, a current value. A current sensor is adopted as the energization amount sensor IE, and the supply current Ie to the electric motor ME is detected.

[0053] <Application control processing> The application control process will be described with reference to the flow diagram of FIG. 3. "Application control" is control for transitioning the parking brake from a released state where the parking brake is not applied to an applied state where the parking brake is applied. In other words, application control is control for applying the parking brake. Application control is started when the parking signal Sw is switched from off to on. Here, switching the parking signal Sw from off to on is called an "application instruction." As above, since the electric unit DU is provided in the rear wheel caliper CPr, "WHf=WHn, WHr=WHp", "CWf=CWn, CWr=CWp", and "Pwf=Pwn, Pwr=Pwp".

[0054] In step S110, various signals including the parking signal Sw, the master cylinder hydraulic pressure Pm, the pressure regulating valve energization amount (e.g., current value) Ia, and the motor energization amount (e.g., current value) Ie are read. For example, the energization amount Ia (actual value) of the pressure regulating valve UA and the energization amount Ie (actual value) of the second electric motor ME are detected by energization amount sensors IA and IE provided in the drive circuit DD. The energization amount sensor IE may also be built into the second electric motor ME.

[0055] In step S120, the auxiliary pressurization control is executed. In the auxiliary pressurization control, the rear wheel brake hydraulic pressure Pwr (i.e., the parking brake hydraulic pressure Pwp) is increased by the hydraulic unit HU, and the braking force Fm is increased. In the auxiliary pressurization control, a certain proportion of the braking force Fm is borne by the rear wheel brake hydraulic pressure Pwr. This reduces the burden on the second electric motor ME. Specifically, a rear wheel target differential pressure Qtr (target value) corresponding to the rear wheel differential pressure mQr (the difference between the master cylinder hydraulic pressure Pm and the rear wheel brake hydraulic pressure Pwr, which is an actual value) in the rear wheel brake system BKr (i.e., the rear wheel cylinder CWr) is calculated starting from the time when the application instruction is issued. Then, the rear wheel target differential pressure Qtr is increased at an increasing gradient kj until the rear wheel brake hydraulic pressure Pwr reaches the application specified hydraulic pressure pj, and is maintained constant after the application specified hydraulic pressure pj is reached. On the other hand, the front wheel target differential pressure Qtf for the front wheel braking system BKf (that is, the front wheel cylinder CWf) is calculated to be 0. Here, the applied predetermined hydraulic pressure pj is a predetermined value (constant) that is set in advance.

[0056] In step S120, the first electric motor MA starts to be driven when an application instruction is issued (when the parking signal Sw transitions from OFF to ON, which corresponds to the calculation cycle). Then, the front wheel pressure regulating valve UAf is not energized, but the energization amount Iar is energized to the rear wheel pressure regulating valve UAr. The front and rear wheel inlet valves VIf, VIr and the front and rear wheel outlet valves VOf, VOr are not energized. In detail, in the front wheel braking system BKf not provided with the electric unit DU, since "Qtf=0", no energization is performed to the front wheel pressure regulating valve UAf (i.e., "Iaf=0"). On the other hand, in the rear wheel braking system BKr provided with the electric unit DU, the rear wheel energization amount Iar corresponding to the rear wheel target pressure difference Qtr is energized to the rear wheel pressure regulating valve UAr. In the pressure regulating valve UA, the larger the current flow amount Ia (pressure regulating valve current flow amount), the larger the differential pressure mQ becomes. Therefore, the rear wheel current flow amount Iar is determined based on the relationship of the differential pressure mQ to the current flow amount Ia (the so-called IP characteristic of the pressure regulating valve UA) and the rear wheel target differential pressure Qtr.

[0057] A fluid pump QA driven by a first electric motor MA generates front and rear wheel circulation flows KNf and KNr of brake fluid BF in the front and rear brake systems BKf and BKr. Since the front wheel pressure regulating valve UAf is fully open, the front wheel differential pressure mQf is "0", and the front wheel brake fluid pressure Pwf is equal to the master cylinder fluid pressure Pm. On the other hand, the rear wheel current Iar is energized to reduce the valve opening amount of the rear wheel pressure regulating valve UAr, so that the rear wheel differential pressure mQr is generated and the rear wheel brake fluid pressure Pwr is increased from the master cylinder fluid pressure Pm. When the rear wheel brake fluid pressure Pwr is equal to or higher than the specified application fluid pressure pj, the rear wheel current Iar is maintained constant so that the rear wheel brake fluid pressure Pwr coincides with the specified application fluid pressure pj.

[0058] In step S130, the electric motor ME is energized so that the second electric motor ME is driven in the forward rotation direction Da. Specifically, at the time of the application instruction, a positive voltage (+) is applied to the second electric motor ME. After the start of energization, the application of the positive voltage to the electric motor ME continues. As a result, a positive current (+) is applied to the electric motor ME, and the electric motor ME continues to be driven in the forward rotation direction Da.

[0059] In step S140, it is determined whether or not the current section is an inrush current section. An "inrush current" is a large current that exceeds a steady-state current value and flows temporarily in the initial stage when power is applied to an electric device (e.g., an electric motor), and is also called a "starting current." The "inrush current section" is a section (period) during which the inrush current can occur. The determination of the inrush current section is made in order to eliminate the influence of the inrush current in the determination of step S150.

[0060] For example, in step S140, it is determined whether or not the section is an inrush current section based on the actual amount of current Ie (amount of current supplied to the motor). In step S140, after the second electric motor ME is energized, a comparison is made between the previous value Ie[n-1] of the amount of current Ie and the current value Ie[n] of the amount of current Ie (where "n" represents a calculation period). Then, the end of the inrush current section is determined when a change amount dI (a time differential value of the amount of current Ie, also referred to as "amount of current change") in the actual amount of current Ie over time T from the start of energization to the electric motor ME continues to be less than a predetermined change amount dj (referred to as "application determination change amount") for an application determination time tj. Here, the application determination time tj and the application determination change amount dj are constants (predetermined values) set in advance. In other words, it is determined that the inrush current section exists when "the amount of change in current dI is equal to or greater than the applicable judgment amount dj" and when "even if the amount of change in current dI is less than the applicable judgment amount dj, the applicable judgment time tj has not elapsed."

[0061] Also, the time (period) during which the inrush current flows is known. For this reason, in step S140, the end of the inrush current section may be determined based on the fact that the specific application time tm has elapsed since the start of energization of the second electric motor ME. Specifically, the application duration Tj is calculated (integrated) from the start of energization of the second electric motor ME, and if the application duration Tj is less than the predetermined time tm, it is determined that the section is an inrush current section. On the other hand, if the application duration Tj is equal to or greater than the predetermined time tm, it is determined that the section is not an inrush current section. Here, the specific application time tm is a threshold value corresponding to the application duration Tj for determining the end of the inrush current section, and is a predetermined value (constant) that is set in advance.

[0062] If it is determined in step S140 that the current period is an inrush current period, the process returns to step S110. On the other hand, if it is determined in step S140 that the current period is not an inrush current period, the process proceeds to step S150.

[0063] In step S150, based on the comparison between the motor energization amount Ie and the application threshold amount ix (the end threshold of the application control), it is determined whether to end the application control (referred to as "end determination"). The end determination is made based on whether the actual energization amount Ie is greater than or equal to the application threshold amount ix. The application threshold amount ix is preset as a value (a predetermined constant) corresponding to a state where the friction member MS and the rotating member KT are sufficiently pressed so that the parking brake is effective. When "Ie≥ix" and step S150 is affirmed, the process proceeds to step S160. On the other hand, when "Ie < ix" and step S150 is negated, the process returns to step S110.

[0064] In step S160, the pressurization by the fluid unit HU and the energization of the electric motor ME are stopped. That is, when the energization amount Ie reaches the application threshold amount ix, the application control is ended in step S160. Since the power transmission mechanism HN is self-locked, the state where the parking brake is effective (i.e., the applied state) is maintained even when the pressurization by the fluid unit HU and the energization of the electric motor ME are stopped.

[0065] Normally, an application instruction is given while the driver is operating the braking operation member BP, and the parking brake is applied. When the braking operation member BP is operated, since the master chamber Rm of the master cylinder CM and the master reservoir RV are in a non-communicating state (blocked state), the brake fluid BF is moved through the cup seal CS. Due to the suction resistance of the brake fluid BF at this time, the pulling-in phenomenon of the braking operation member BP occurs. Note that the degree of pulling-in of the braking operation member BP (i.e., the degree of suction resistance) depends on the flow rate of the brake fluid BF flowing through the cup seal CS.

[0066] In the application control of the parking brake device EP, the braking force Fm is generated by the hydraulic unit HU and the second electric motor ME. In the hydraulic unit HU, the front wheel cylinder CWf (=CWn) does not increase (pressurize) the front wheel brake hydraulic pressure Pwf (=Pwn), but the hydraulic pressure Pwr (=Pwp) is increased (pressurized) only by the rear wheel cylinder CWr (=CWp). Specifically, the first electric motor MA is driven, and the hydraulic pump QA (=QAf, QAr) sucks and discharges the brake fluid BF. At this time, the inlet valve VI, the outlet valve VO, and the front wheel pressure regulating valve UAf are not energized, and only the rear wheel pressure regulating valve UAr is energized. The rear wheel differential pressure mQr is increased by the orifice effect when the circulating flow KNr is throttled by the rear wheel pressure regulating valve UAr. As a result, the rear wheel brake fluid pressure Pwr is increased from the master cylinder fluid pressure Pm (=Pmr) by the rear wheel differential pressure mQr.

[0067] In the front wheel brake system BKf, since the front wheel pressure regulating valve UAf is fully open, the brake fluid BF is only circulated through the front wheel connection passage HSf and the front wheel return passage HKf. Therefore, since "mQf = 0", the volume of the front wheel cylinder CWf does not increase, and the suction amount corresponding to the front wheel cylinder CWf is "0". Since only the amount of brake fluid BF corresponding to the increase in the volume of the rear wheel cylinder CWr is sucked in, the suction amount is limited to the minimum necessary. As a result, the pull-in of the brake operating member BP is suppressed, and the discomfort of the driver can be reduced.

[0068] <Application control operation> The operation of the application control will be described with reference to the time series diagram (transition diagram of state quantity with respect to time T) in Fig. 4. In this example, the inrush current section in step S140 is determined based on the application duration Tj calculated from the start of energization of the second electric motor ME. In addition, the driver has been operating the brake operating member BP before the application command, and the master cylinder hydraulic pressure Pm is maintained at the value pm.

[0069] At time t0, the parking switch SW is switched from the OFF state to the ON state, an application operation command is issued, and application control is started. At time t0, the rear wheel target differential pressure Qtr starts to increase so that the rear wheel brake hydraulic pressure Pwr (=Pwp) is increased. As a result, the rear wheel brake hydraulic pressure Pwr is increased from the value pm (=Pm) by the rear wheel differential pressure mQr (actual value) corresponding to the rear wheel target differential pressure Qtr (target value) at an increasing gradient kj (a preset constant) (i.e., "Pwr = pm + Qtr = pm + mQr"). On the other hand, since pressurization of the front wheel cylinder CWf (=CWn) is not required, the front wheel target differential pressure Qtf is calculated to be "0". As a result, the hydraulic pressure difference mQf is not generated, remains "0", and the front wheel brake hydraulic pressure Pwf (=Pwn) is equal to the value pm (=Pm).

[0070] Also, at time t0, a positive voltage is applied to the electric motor ME so that the second electric motor ME rotates in the forward direction. This starts energizing the second electric motor ME in the forward rotation direction Da. From time t0, calculation of the application duration Tj starts. Here, time t0 corresponds to the "start time point." Note that in the example, pressurization by the fluid unit HU and driving of the second electric motor ME start simultaneously, but one of them may start first and then the other may start.

[0071] Immediately after time t0 (start time), an inrush current (starting current) flows through the second electric motor ME. This causes the motor current Ie to rise to a peak value ie and then decrease. However, since it has been determined in step S140 that the period from time t0 to time t2 is an inrush current period, the determination in step S150 (comparison of the current Ie) is not performed.

[0072] At time t1, when the rear wheel brake hydraulic pressure Pwr reaches the applied predetermined hydraulic pressure pj (a preset predetermined threshold value), the rear wheel target differential pressure Qtr is maintained constant. As a result, the rear wheel brake hydraulic pressure Pwr is maintained at the constant value pj.

[0073] At time t2 (called the "specific time point") when a specific application time tm, which is a predetermined time, has elapsed from time t0, it is determined that the inrush current section is no longer in effect. This determination indicates that the effect of the inrush current has been eliminated, and the determination in step S150 is performed.

[0074] From time t0 to time t3, the end face Mp of the output member SB and the bottom face Mb of the brake piston PN do not come into contact with each other (see state (a) in Figure 2). Therefore, the motor current Ie is approximately constant at the value ic. From time t3, the motor current Ie begins to increase. This is because after time t3, the end face Mp of the output member SB and the bottom face Mb of the brake piston PN come into contact with each other, increasing the load on the second electric motor ME (see state (b) in Figure 2).

[0075] Time t4 At this point, the amount of current Ie of the second electric motor ME reaches the application threshold amount ix, which is the termination threshold value. Time t4 At this point, step S160 is satisfied, and the application control is terminated. The power supply to the rear wheel pressure regulating valve UAr is stopped, and the drive of the first electric motor MA is terminated. In addition, the application of the positive voltage to the second electric motor ME is stopped, and the power supply Ie is set to "0".

[0076] <Release control processing> The release control process will be described with reference to the flow diagram of FIG. 5. "Release control" is control for transitioning from an applied state in which the parking brake is applied to a released state in which the parking brake is not applied. In other words, release control is control for releasing the parking brake. Release control is started when the parking signal Sw is switched from on to off. Here, switching the parking signal Sw from on to off is called a "release instruction." As in the case of the application control, the electric unit DU is provided in the brake caliper CPr of the rear wheel WHr.

[0077] In step S210, various signals including the parking signal Sw, the master cylinder hydraulic pressure Pm, the pressure regulating valve energization amount (e.g., current value) Ia, and the motor energization amount (e.g., current value) Ie are read. For example, the energization amount Ia (actual value) of the pressure regulating valve UA and the energization amount Ie (actual value) of the second electric motor ME are detected by energization amount sensors IA and IE provided in the drive circuit DD. The energization amount sensor IE may also be built into the electric motor ME.

[0078] In step S220, the auxiliary pressurization control is executed. In the auxiliary pressurization control, the rear wheel brake hydraulic pressure Pwr (i.e., the parking brake hydraulic pressure Pwp) is increased by the hydraulic unit HU, and the braking force Fm is increased. In the auxiliary pressurization control, a certain percentage of the braking force Fm generated by self-locking is borne by the rear wheel brake hydraulic pressure Pwr. This makes it easier to drive the second electric motor ME in the reverse direction Db. The rear wheel brake hydraulic pressure Pwr is increased in the same manner as in step S120. Specifically, a rear wheel target differential pressure Qtr (target value) corresponding to the rear wheel differential pressure mQr (the difference between the master cylinder hydraulic pressure Pm and the rear wheel brake hydraulic pressure Pwr, which is an actual value) is calculated starting from the time when the release command is issued. Then, the rear wheel target differential pressure Qtr is increased at an increasing gradient kk until the rear wheel brake hydraulic pressure Pwr reaches the release predetermined hydraulic pressure pk, and is maintained constant after the release predetermined hydraulic pressure pk is reached. On the other hand, the front wheel target differential pressure Qtf for the front wheel braking system BKf (that is, the front wheel cylinder CWf) is calculated to be 0. Here, the predetermined release hydraulic pressure pk is a predetermined value (constant) that is set in advance.

[0079] In step S230, the electric motor ME is energized so that the second electric motor ME is driven in the reverse direction Db. Specifically, at the time of the release command, a voltage of negative sign (-) is applied to the second electric motor ME. After the start of energization of the second electric motor ME, the application of the negative voltage to the electric motor ME continues. As a result, the amount of energization Ie (negative value) is applied to the second electric motor ME, and the electric motor ME continues to be driven in the reverse direction Db.

[0080] In step S240, it is determined whether or not the contact has been released (referred to as "contact release determination"). The "contact release state" is a state in which the end face Mp of the output member SB and the bottom face Mb of the brake piston PN, which had been in contact, are no longer in contact. For example, the contact release determination is performed based on the motor current Ie, based on whether the current Ie is constant. This is based on the fact that when the end face Mp of the output member SB and the bottom face Mb of the brake piston PN are separated, the output of the electric motor ME is used only for the friction (sliding friction) of the power transmission mechanism (electric motor ME, reducer GS, input member NB, output member SB, brake piston PN, etc.) from the electric motor ME to the friction member MS. In other words, the magnitude of the current Ie supplied to the electric motor ME in the contact release state is a value equivalent to the friction of the power transmission members.

[0081] For example, the "constant state of the current Ie (i.e., the contact resolved state)" is determined when the current Ie remains within a predetermined range (within the range of the judgment amount ih) for a predetermined time th (referred to as the "judgment time"). The contact resolved state may also be determined when the change dIe (time differential value of the current Ie) over time T in the current Ie is equal to or smaller than the judgment change amount dx for the judgment time th. Here, the judgment amount ih, the judgment time th, and the judgment change amount dx are predetermined values ​​(constants) that are set in advance.

[0082] When it is determined in step S230 that the contact has been resolved (also referred to as "contact resolution confirmed"), the control flag FF (also referred to as "determination flag") is changed from "0" to "1." Here, the determination flag FF is set to "0" to indicate that the contact has not been resolved or the contact state is unknown (also referred to as "contact resolution unconfirmed"), and set to "1" to indicate that the contact has been resolved. Note that the determination flag FF is set to "0 (contact resolution unconfirmed)" as an initial value before the execution of release control begins.

[0083] If step S240 is negated, the process returns to step S210. On the other hand, if step S240 is affirmed, the process proceeds to step S250.

[0084] At step S250, a release duration Tk is calculated. The release duration Tk is the time from when step S240 was first affirmed (which is the corresponding calculation cycle and is referred to as the "determination time"). In other words, the release duration Tk is the time elapsed from the determination time when the state switched (transited) from the state where contact release was not determined to the state where contact release was determined, with this determination time as the starting point (reference).

[0085] At step S260, it is determined whether "the release duration Tk is greater than or equal to a release threshold time tk or not". Here, the release threshold time tk is a preset predetermined value (constant) and is a threshold value corresponding to the release duration Tk for ending the release control (release operation). If "Tk < tk" and step S260 is negated, the process returns to step S210. On the other hand, if "Tk ≥ tk" and step S260 is affirmed, the process proceeds to step S270.

[0086] At step S270, the pressurization by the fluid unit HU and the energization of the second electric motor ME are stopped. That is, at the time when a predetermined time tk has elapsed from the time when contact release was determined, the release control is ended and the parking brake is made ineffective.

[0087] In the release control of the parking brake device EP, as in the application control, in the fluid unit HU, the front wheel cylinder CWf (=CWn) does not increase (pressurize) the front wheel brake fluid pressure Pwf (=Pwn), and the hydraulic pressure Pwr (=Pwp) is increased (pressurized) only in the rear wheel cylinder CWr (=CWp). The hydraulic pump QA (=QAf, QAr) sucks in and discharges the brake fluid BF, but the inlet valve VI, the outlet valve VO, and the front wheel pressure regulating valve UAf are not energized, and only the rear wheel pressure regulating valve UAr is energized. Since the front wheel brake fluid pressure Pwf is not increased, the volume of the front wheel cylinder CWf is not increased. In other words, the suction amount corresponding to the front wheel cylinder CWf (the amount of brake fluid BF supplied from the master reservoir RV via the cup seal CS) is "0". Therefore, the suction amount is limited to the amount corresponding to the increase in the rear wheel brake fluid pressure Pwr. Since the amount of brake fluid BF sucked in is limited, the pull-in of the brake operating member BP is suppressed, and the sense of discomfort felt by the driver can be reduced.

[0088] <Release control operation> The operation of the release control will be described with reference to the time series diagram in Fig. 6. In addition, in the rotation direction of the second electric motor ME, the positive sign (+) of the motor current Ie (e.g., current value) corresponds to the forward rotation direction Da, and the negative sign (-) corresponds to the reverse rotation direction Db. In this example, the driver has been operating the brake operating member BP before the release command, and the master cylinder hydraulic pressure Pm is maintained at the value pn.

[0089] At time u0, the parking switch SW is switched from the on state to the off state, a release operation command is issued, and release control is started. At time u0, the rear wheel target differential pressure Qtr starts to increase so that the rear wheel brake hydraulic pressure Pwr (=Pwp) is increased. As a result, the rear wheel brake hydraulic pressure Pwr is increased from the value pn (=Pm) by the rear wheel differential pressure mQr (actual value) corresponding to the rear wheel target differential pressure Qtr (target value) at an increase gradient kk (a preset constant) (i.e., "Pwr = pn + Qtr = pn + mQr"). As in the application control, the front wheel target differential pressure Qtf is calculated to "0", and the front wheel hydraulic pressure difference mQf is not generated. Therefore, the front wheel brake hydraulic pressure Pwf (=Pwn) is equal to the value pn (=Pm).

[0090] At time u1, when the rear wheel brake hydraulic pressure Pwr reaches the predetermined release hydraulic pressure pk (a preset threshold value), the rear wheel target differential pressure Qtr is maintained constant. As a result, the rear wheel brake hydraulic pressure Pwr is maintained at the constant value pk.

[0091] At time u2, a negative voltage is applied to the electric motor ME so that the second electric motor ME rotates in the reverse direction. This starts energization corresponding to driving the second electric motor ME in the reverse direction Db. In the example, the pressurization by the hydraulic unit HU and the driving of the second electric motor ME are started at different times, but they may be started simultaneously at time u0.

[0092] At time u3, the amount of current Ie of the second electric motor ME becomes substantially constant for the first time, and it is determined that the amount of current Ie has become constant. However, at time u3, the constant state of the amount of current Ie has not yet continued for the determination time th, so the contact-released state is not determined (confirmed).

[0093] At time u4, which is a judgment time th (a preset constant) after time u3, it is judged (confirmed) that the contact has been resolved, and step S240 is satisfied. Accordingly, at time u4 (confirmation time), the judgment flag FF is switched from "0 (contact resolution unconfirmed)" to "1 (contact resolution confirmed)", and calculation of the release duration Tk (accumulation of time) is started.

[0094] At time u5, when the release threshold time tk (a preset constant) has elapsed from time u4, step S260 is satisfied and the release control is terminated. The power supply to the rear wheel pressure regulating valve UAr is stopped and the drive of the first electric motor MA is terminated. In addition, the application of a negative voltage to the second electric motor ME is stopped and the power supply Ie is set to "0". At this time, the judgment flag FF is returned from "1" to the initial value "0".

[0095] <Second embodiment of parking brake device EP> A second embodiment of the parking brake device EP will be described with reference to the schematic diagram of FIG. 7. In the first embodiment, a front-rear type is adopted in the braking system related to the master cylinder CM and the fluid unit HU, but in the second embodiment, a diagonal type (also called "X type") is adopted. That is, in the tandem type master cylinder CM, of the two hydraulic pressure chambers, one side master chamber Rmi is connected to the wheel cylinders of the right front wheel and the left rear wheel, and the other side master chamber Rmj is connected to the wheel cylinders of the left front wheel and the right rear wheel. In the second embodiment, the parking brake acts on the rear wheels WHr as in the first embodiment. That is, the electric unit DU is provided in the rear wheel caliper CPr.

[0096] In the second embodiment, the method of increasing the rear wheel brake fluid pressure Pwr is different from that of the first embodiment. In the first embodiment, the inlet valve VI, the outlet valve VO, and the front wheel pressure regulating valve UAf are de-energized, and then the first electric motor MA and the rear wheel pressure regulating valve UAr are energized to increase the rear wheel brake fluid pressure Pwr. Instead of this, in the second embodiment, the two pressure regulating valves UA (i.e., the one-side and other-side pressure regulating valves UAi, UAj) and the front wheel inlet valve VIf corresponding to the front wheel cylinder CWf among the inlet valves VI are energized. Therefore, the rear wheel inlet valve VIr corresponding to the rear wheel cylinder CWr among the inlet valves VI, and all the outlet valves VO (=VOf, VOr) are in a de-energized state.

[0097] The increase in the braking force Fm on the parked wheels WHp (i.e., rear wheels WHr) will be described in detail below. The first electric motor MA is driven, and the one-side and other-side fluid pumps QAi, QAj (=QA) suck in and discharge the braking fluid BF. As a result, in the one-side and other-side brake systems BKi, BKj (=BK), one-side and other-side circulation flows KNi, KNj (=KN) are formed through the communication path HS (=HSi, HSj) and the return path HK (=HKi, HKj) as shown by the dashed arrows, including the pressure regulating valve UA, the fluid pump QA, and the pressure regulating reservoir RC. The one-side and other-side pressure regulating valves UAi, UAj (=UA) are energized to throttle the circulating flow KN, and the one-side and other-side regulated hydraulic pressures Pqi, Pqj (=Pq), which are the hydraulic pressures at the lower parts Bbi, Bbj of the one-side and other-side pressure regulating valves UAi, UAj, are increased from the one-side and other-side master cylinder hydraulic pressures Pmi, Pmj (=Pm). That is, the master cylinder hydraulic pressure Pm is increased by the one-side and other-side differential pressures mQi, mQj (=mQ), and the regulated hydraulic pressure Pq is generated. In the one-side and other-side brake systems BKi, BKj, the front wheel inlet valves VIf are energized, and therefore the front wheel inlet valves VIf are closed. Therefore, the one-side and other-side adjustment hydraulic pressures Pqi, Pqj (=Pq=Pm+mQ) are not supplied to the front wheel cylinder CWf (=CWn) but are supplied only to the rear wheel cylinder CWr (=CWp). In other words, the front wheel brake hydraulic pressure Pwf (=Pwn) is not increased, and only the rear wheel brake hydraulic pressure Pwr (=Pwp) is increased, thereby increasing the braking force Fm on the parked wheels WHp.

[0098] In the second embodiment, an increase in the front wheel brake fluid pressure Pwf is avoided by closing the inlet valve VIf corresponding to the non-parked wheels WHn. When the operation amount Ba of the brake operating member BP is increased during execution of the auxiliary pressurization control, the closed front wheel inlet valve VIf is opened. This allows the driver's braking intention to be reflected in the front wheel brake fluid pressure Pwf. Also, when the braking operation amount Ba is increased, the driver is less likely to feel the pull-in of the brake operating member BP. Therefore, even if pull-in occurs due to the opening of the front wheel inlet valve VIf, the uncomfortable feeling can be avoided.

[0099] The second embodiment also has the same effects as the first embodiment. In the operation of the parking brake device EP (at least one of the application operation and the release operation), the braking force Fm is increased not only by the electric unit DU but also by the fluid unit HU. Since the front wheel brake hydraulic pressure Pwf is not increased, the brake fluid BF sucked from the master reservoir RV is not consumed in the front wheel cylinder CWf (i.e., the non-parking wheel cylinder CWn). In other words, the brake fluid BF from the master reservoir RV is consumed only in the rear wheel cylinder CWr (i.e., the parking wheel cylinder CWp). The greater the amount of brake fluid BF sucked in, the greater the degree of sucking in. However, since the amount of sucking in is limited in the auxiliary pressurization control, the pull in of the brake operating member BP is suppressed, and the driver's discomfort is reduced.

[0100] <Other embodiments> Other embodiments will be described below. The other embodiments also provide the same effect as above (suppression of the retraction phenomenon of the brake operating member BP).

[0101] In the above embodiment, the auxiliary pressurizing control (i.e., the increase in the braking force Fm by the hydraulic unit HU) is performed by both the application control and the release control. Alternatively, the auxiliary pressurizing control may be configured to be performed by either the application control or the release control.

[0102] In the above embodiment, the non-parked wheels WHn (wheels for which the parking brake is not applied) are the front wheels WHf, and the parked wheels WHp (wheels for which the parking brake is applied) are the rear wheels WHr. Alternatively, the non-parked wheels WHn may be the rear wheels WHr, and the parked wheels WHp may be the front wheels WHf. In the auxiliary pressurization control according to this configuration, when the parking brake is operated, the rear wheel brake hydraulic pressure Pwr (=Pwn) is not increased, and only the front wheel brake hydraulic pressure Pwf (=Pwp) is increased. Furthermore, in the parking brake device EP according to the diagonal type brake system BK, when the braking operation amount Ba is increased during the auxiliary pressurization control, the energization of the closed rear wheel inlet valve VIr (corresponding to the non-parked wheels WHn) is stopped and the valve is opened in order to prioritize the braking operation of the driver. By opening the valve, the rear wheel brake hydraulic pressure Pwr (=Pwn) is increased with the increase in the master cylinder hydraulic pressure Pm.

[0103] In the above embodiment, a caliper type parking brake is used. Alternatively, a drum brake type may be used. In the drum brake type, the friction member MS is a brake lining, and the rotating member KT is a brake drum. The parking brake device EP in which the drum brake type is used is also applied to a vehicle (not a brake-by-wire type vehicle) in which the braking operation characteristic (Sp-Fp characteristic) is determined by the rigidity of the members (master cylinder CM, braking piping, brake lever, brake shoe, friction member MS, etc.) from the brake operation member BP to the friction member MS.

[0104] <Summary of embodiments related to parking brake device EP> An embodiment of the parking brake device EP is summarized below. The parking brake device EP is applied to a vehicle in which the relationship between the operating force Fp and the operating displacement Sp of the brake operating member BP is determined according to the rigidity (elasticity, the relationship between force and deformation amount) of the members from the brake operating member BP to the friction member MS. The parking brake device EP is composed of a fluid unit HU, an electric unit DU, and a controller ECU.

[0105] The fluid unit HU includes a fluid pump QA and a pressure regulating valve UA. The fluid pump QA uses a first electric motor MA (for return flow) as a power source to draw brake fluid BF from a master cylinder CM. The pressure regulating valve UA increases the pressure of the brake fluid BF discharged by the fluid pump QA and supplies it to the wheel cylinder CW as brake fluid pressure Pw. Then, the fluid unit HU uses the brake fluid pressure Pw to press a friction member MS against a rotating member KT fixed to the wheels WH of the vehicle, thereby generating a braking force Fm. The fluid unit HU can generate the braking force Fm for all wheels WH of the vehicle.

[0106] The electric unit DU generates a braking force Fm on the parking wheels WHp that apply the parking brake among the wheels WH, using a second electric motor ME (for parking brake) separate from the first electric motor MA as a power source. In other words, the electric unit DU does not generate the braking force Fm on all the wheels WH of the vehicle, but generates the braking force Fm only on the parking wheels WHp. The controller ECU controls the fluid unit HU and the electric unit DU.

[0107] In the parking brake device EP, when the controller ECU operates the parking brake (when performing at least one of the apply operation and the release operation), it increases only the brake fluid pressure (parking brake fluid pressure) Pwp of the parking wheel cylinder CWp corresponding to the parking wheel WHp among the wheel cylinders CW. In other words, when the controller ECU operates the parking brake, it does not increase the brake fluid pressure (non-parking brake fluid pressure) Pwn of the non-parking wheel cylinder CWn corresponding to the non-parking wheel WHn (wheel on which the parking brake is not applied) among the wheel cylinders CW.

[0108] When the brake fluid pressure Pw is increased by the fluid unit HU, the brake piston PN is moved in the forward direction Ha (the direction approaching the rotating member KT). This movement causes a shortage of the amount of brake fluid BF present in the brake system BK, and this shortage is made up for by the master reservoir RV. When the brake operating member BP is operated, the brake fluid BF flows from the master reservoir RV into the master cylinder CM via the cup seal CS, and this flow may cause the brake operating member BP to be pulled in (the brake operating member BP moves slightly in the forward direction Hf). The larger the amount of flow in (i.e., the amount of suction), the larger the movement of the brake operating member BP. For this reason, in the parking brake device EP, when auxiliary pressurization control (control for increasing the braking force Fm by the fluid unit HU in addition to the electric unit DU) is performed, the non-parking brake fluid pressure Pwn corresponding to the non-parking wheels WHn for which the parking brake is not applied is not increased, and the inflow of the brake fluid BF is limited to the minimum amount required. This reduces the degree of retraction and reduces discomfort to the driver.

[0109] The parking brake device EP is applied to a vehicle equipped with front and rear brake systems BKf, BKr. For example, in this vehicle, the rear wheels WHr are set as parking wheels WHp, and the front wheels WHf are set as non-parking wheels WHn. In this configuration, the fluid unit HU is equipped with normally open front and rear wheel pressure regulating valves UAf, UAr in the front and rear brake systems BKf, BKr as the pressure regulating valve UA. When operating the parking brake, the controller ECU does not energize the front wheel pressure regulating valve UAf, but energizes only the rear wheel pressure regulating valve UAr. As a result, in the auxiliary pressurization control, the front wheel brake fluid pressure Pwf (i.e., the non-parking brake fluid pressure Pwn) is not increased, and only the rear wheel brake fluid pressure Pwr (i.e., the parking brake fluid pressure Pwp) is increased.

[0110] The parking brake device EP is applied to a vehicle equipped with diagonal brake systems BKi and BKj. For example, in the vehicle, the rear wheels WHr are set as parking wheels WHp, and the front wheels WHf are set as non-parking wheels WHn, as in the above. In this configuration, the fluid unit HU is equipped with normally open one-side and other-side pressure regulating valves UAi and UAj in the diagonal brake systems BKi and BKj as the pressure regulating valve UA. In addition, normally open front and rear wheel inlet valves VIf and VIr are provided between the one-side and other-side pressure regulating valves UAi and UAj and the wheel cylinders CW. When the parking brake is operated, the controller ECU energizes the front wheel inlet valve VIf to close the front wheel inlet valve VIf, and does not energize the rear wheel inlet valve VIr to keep the rear wheel inlet valve VIr open. In this state, the one-side and other-side pressure regulating valves UAi and UAj are energized. As a result, in the auxiliary pressurization control, the front wheel brake fluid pressure Pwf (ie, the non-parking brake fluid pressure Pwn) is not increased, and only the rear wheel brake fluid pressure Pwr (ie, the parking brake fluid pressure Pwp) is increased. [Explanation of symbols]

[0111] EP...Parking brake device, WH...Wheel, BP...Brake operating member, SW...Parking brake switch (parking switch), SX...Braking device, CP...Brake caliper, KT...Rotating member, MS...Friction member, CM...Master cylinder, CW...Wheel cylinder, ECU...Controller, HU...Fluid unit, MA...First electric motor (for return flow), QA...Fluid pump, UA...Pressure regulating valve, VI...Inlet valve, VO...Outlet valve, DU...Electric unit, ME...Second electric motor (for parking brake), MP...Microprocessor, D D...drive circuit, Ia...amount of current flowing through pressure regulating valve UA (actual value, for example, current value), Ie...amount of current flowing through second electric motor ME (actual value, for example, current value), PM...master cylinder hydraulic pressure sensor, Pm...master cylinder hydraulic pressure (detected value of master cylinder hydraulic pressure sensor PM), Pp...adjusted hydraulic pressure (hydraulic pressure adjusted by pressure regulating valve UA), mQ...differential pressure (hydraulic pressure difference between master cylinder hydraulic pressure Pm and adjusted hydraulic pressure Pq), Pw...brake hydraulic pressure (hydraulic pressure in wheel cylinder CW), Fm...braking force (pressure of friction member MS against rotating member KT).

Claims

1. a fluid unit including a fluid pump that draws brake fluid from a master cylinder using a first electric motor as a power source, and a pressure regulating valve that increases the pressure of the brake fluid discharged by the fluid pump and supplies it to a wheel cylinder as brake fluid pressure, the fluid unit pressing a friction member against a rotating member fixed to a wheel of the vehicle by the brake fluid pressure to generate a braking force; an electric unit that uses a second electric motor as a power source to generate the braking force on a parking wheel that is among the wheels and has a parking brake applied; A controller that controls the hydraulic unit and the electric unit; In a parking brake device for a vehicle, The controller: A parking brake device for a vehicle, which increases only the brake fluid pressure in the wheel cylinders corresponding to the parked wheels when the electric unit is operated while a brake operating member is being operated by a driver of the vehicle.

2. 2. A parking brake device for a vehicle according to claim 1, Among the wheels of the vehicle, wheels on which the parking brake is not applied are non-parking wheels, the parked wheels are rear wheels of the vehicle and the unparked wheels are front wheels of the vehicle; The hydraulic unit includes normally open front and rear wheel pressure regulating valves in a front and rear brake system as the pressure regulating valves, The controller: A parking brake device for a vehicle, wherein when the electric unit is operated, no current is applied to the front wheel pressure regulating valve and only current is applied to the rear wheel pressure regulating valve.

3. 2. A parking brake device for a vehicle according to claim 1, Among the wheels of the vehicle, wheels on which the parking brake is not applied are non-parking wheels, the parked wheels are rear wheels of the vehicle and the unparked wheels are front wheels of the vehicle; the hydraulic unit includes normally open one-side and other-side pressure regulating valves in a diagonal brake system as the pressure regulating valves, and normally open front and rear wheel inlet valves between the one-side and other-side pressure regulating valves and the wheel cylinders, The controller: When the electric unit is operated, the front wheel inlet valve is energized to close the front wheel inlet valve, the rear wheel inlet valve is not energized to keep the rear wheel inlet valve open, and the one-side and other-side pressure regulating valves are energized.

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