Hydraulic pressure generation device

Abstract

This hydraulic pressure generation device comprises: an electric motor that outputs rotational power; a conversion mechanism that outputs, as linear power for a linear motion member, rotational power input to a rotary member; a piston that is inserted into a cylinder and that moves under linear power to increase the hydraulic pressure of the cylinder; and an intermediate member that is disposed between the linear motion member and the piston and that is capable of sliding together with the linear motion member and the piston. The piston has a first bottom part and a first cylindrical part. The intermediate member has a second cylindrical part and is inserted into the first cylindrical part. In a gap between the inner peripheral surface of the first cylindrical part and the outer peripheral surface of the second cylindrical part, a gap Ska at a position close to the first bottom part is made narrower than a gap Skb which is at a position spaced apart from the first bottom part.

Description

Hydraulic Pressure Generator

[0001] The present disclosure relates to a hydraulic pressure generating device.

[0002] As described in Patent Document 1, the applicant has developed an electric cylinder device (also called a "hydraulic pressure generating device") that prevents a piston and a linearly moving member from moving away from each other, comprising "a housing in which a cylinder is provided, a piston disposed inside the cylinder, a rotating member that rotates around a rotation axis, a linearly moving member attached to the rotating member so as to move in a first direction along the rotation axis or a second direction opposite to the first direction in response to rotation of the rotating member, and that pushes the piston so as to reduce the volume of a liquid chamber of the cylinder by moving in the first direction, a first engaging portion provided on the piston, and a second engaging portion provided on the linearly moving member that abuts against the first engaging portion to restrict the linearly moving member from moving away from the piston in the second direction."

[0003] In this device, a spacer 46 (also referred to as an "intermediate member") is interposed between the end surface 45a of the nut member 45 and the inner surface 71a of the piston 22, and the nut member 45 pushes the piston 22 forward in the Df direction via the spacer 46. The diameter of the outer peripheral surface 92b of the spacer 46 is smaller than the diameter of the inner peripheral surface 72a of the piston 22, providing a gap between the outer peripheral surface 92b and the inner peripheral surface 72a. This allows relative radial movement between the piston 22 and the spacer 46. The spacer (intermediate member) also functions as a mechanism for compensating for the effects of axial misalignment (also referred to as an "axial misalignment compensation mechanism"). The larger the gap, the greater the effectiveness of the axial misalignment compensation mechanism. However, increasing the gap can result in issues with the accuracy of positioning the intermediate member when the load is small (including when no load is present).

[0004] Patent application No. 2023-054971

[0005] In view of the above-mentioned problems, an object of the present invention is to provide a hydraulic pressure generating device equipped with an axis deviation compensation mechanism that can improve the positioning accuracy of an intermediate member.

[0006] The hydraulic pressure generating device (PS) of the present invention comprises an electric motor (MT) that outputs rotational power (Tm), a conversion mechanism (GH) that outputs the rotational power (Tm) input to a rotating member (BK) as linear power (Fn) of a linearly moving member (BD), a piston (NC) that is inserted into a cylinder (CC) and moves by the linear power (Fn) to increase the hydraulic pressure (Pc) of the cylinder (CC), and an intermediate member (BE) that is arranged between the linearly moving member (BD) and the piston (NC) and is slidable with the linearly moving member (BD) and the piston (NC).

[0007] In the hydraulic pressure generating device (PS) according to the present invention, the piston (NC) has a first bottom (Btn) and a first cylindrical portion (Enn). The intermediate member (BE) has a second cylindrical portion (Ene) and is inserted into the first cylindrical portion (Enn). In addition, in a gap between an inner peripheral surface (Min) of the first cylindrical portion (Enn) and an outer peripheral surface (Moe) of the second cylindrical portion (Ene), the gap (Ska) at a position closer to the first bottom (Btn) is narrower than the gap (Skb) at a position farther away from the first bottom (Btn).

[0008] For example, at least one of the end surface (Mpe) of the intermediate member (BE) that contacts the first bottom portion (Btn) and the end surface (Mqe) of the intermediate member (BE) that contacts the linear motion member (BD) is a convex surface. According to the above configuration, the positioning accuracy of the intermediate member BE is improved. In addition, axial misalignment is appropriately compensated for.

[0009] In the hydraulic pressure generating device (PS) according to the present invention, the rotating member (BK) can enter the second cylindrical portion (Ene). This shortens the axial length of the device. Furthermore, the second cylindrical portion (Ene) has an air vent (Ae). This suppresses air pressure fluctuations inside the intermediate member BE.

[0010] It is a schematic diagram for explaining the overall configuration of the brake control device SC. It is a partial cross-sectional view for explaining an embodiment of a hydraulic pressure generating unit PS. It is a partial cross-sectional view for explaining a first configuration example relating to the positioning of an intermediate member BE. It is a partial cross-sectional view for explaining a second configuration example relating to the positioning of an intermediate member BE.

[0011] <Symbols of components, etc., and subscripts at the end of symbols> In the following description, components, arithmetic processes, signals, characteristics, and values ​​with the same symbol, such as "CW," have the same function. The subscripts "f" and "r" at the end of the symbol for each wheel are generic symbols that indicate whether the symbol relates to the front or rear wheel system. For example, a wheel cylinder CW provided on each wheel is written as "front wheel cylinder CWf, rear wheel cylinder CWr." Furthermore, the subscripts "f" and "r" at the end of the symbol can be omitted. When the subscripts "f" and "r" are omitted, each symbol represents a generic term. For example, "CW" is a generic term for wheel cylinders provided on the front and rear wheels of a vehicle. Furthermore, the generic term "CW" can also be written as "CW (= CWf, CWr)."

[0012] The first actuator YA of the first brake unit SA, the second actuator YB of the second brake unit SB, and the wheel cylinder CW are connected by a fluid path (communication path HS). Furthermore, the first and second actuators YA and YB are connected to various components (PS, etc.) by fluid paths. Here, the "fluid path" refers to a path for moving brake fluid BF (working fluid), and includes piping, flow paths within the actuators, hoses, etc. In the following explanation, the communication path HS, reservoir path HR, input path HN, servo path HU, supply path HH, etc. are fluid paths.

[0013] <Brake control device SC of vehicle> The overall configuration of the brake control device SC including the hydraulic pressure generating unit PS will be described with reference to the schematic diagram of Fig. 1. For example, the brake control device SC is applied to a hybrid vehicle equipped with an electric motor for driving, or an electric vehicle.

[0014] The vehicle is equipped with a regenerative device KG. The regenerative device KG is composed of a generator GN for energy regeneration (also called an "electric motor / generator" or "regenerative generator"), a control unit EG for the regenerative device KG (also called a "regenerative controller"), and a regenerative storage battery (not shown). The regenerative generator GN also functions as an electric motor for driving. During regenerative braking, the electric motor / generator GN operates as a generator, and the generated electric power is stored in the regenerative storage battery via the regenerative controller EG. At this time, a regenerative braking force Fg acts on the wheels. For example, the regenerative device KG is provided on the front wheels WHf, and a regenerative braking force Fg is generated on the front wheels WHf.

[0015] The front and rear wheels WHf, WHr of a vehicle are equipped with braking devices SX (=SXf, SXr). The braking devices SX are composed of a brake caliper, a friction member (e.g., brake pad), and a rotating member KT (e.g., brake disc). The brake caliper (not shown) is provided with a wheel cylinder CW (=CWf, CWr). A hydraulic pressure Pw (referred to as "wheel pressure") in the wheel cylinder CW presses the friction member (not shown) against a rotating member KT (=KTf, KTr) fixed to each wheel WH. This applies a braking torque Tb to the wheel WH. As a result, a hydraulic braking force Fp is generated in the wheel WH.

[0016] A vehicle is equipped with a brake operating member BP and various sensors (such as SP). The brake operating member BP (e.g., a brake pedal) is an operating member used by the driver to decelerate the vehicle. The vehicle is provided with an operation displacement sensor SP that detects an operation displacement Sp of the brake operating member BP. The operation displacement Sp is one of the state quantities (state variables) that indicate the operation amount of the brake operating member BP. In addition to the operation displacement sensor SP, a hydraulic pressure Pn (referred to as "input pressure") in an input chamber Rn (described later) is used as another state quantity that indicates the braking operation amount. The input pressure Pn is detected by an input pressure sensor PN. The operation displacement Sp, input pressure Pn, etc. are collectively referred to as the "braking operation amount Ba." Furthermore, a sensor that detects the braking operation amount Ba, such as the operation displacement sensor SP or the input pressure sensor PN, is referred to as the "braking operation amount sensor BA."

[0017] The vehicle is equipped with a brake control device SC. The brake control device SC employs a so-called front and rear type (also called "type II") dual brake system. The brake control device SC adjusts the actual wheel pressure Pw of each wheel cylinder CW. The brake control device SC is composed of two brake units SA and SB.

[0018] <First brake unit SA> The first brake unit SA adjusts the hydraulic pressures Pwf and Pwr (front and rear wheel pressures) of the front and rear wheel cylinders CWf and CWr in response to the operation of the brake operating member BP (brake pedal). The first brake unit SA is composed of a first actuator YA and a first controller EA.

[0019] <<First Actuator YA>> The first actuator YA is composed of an apply unit AP, a hydraulic pressure generating unit PS, and an input unit NR.

[0020] [Apply Unit AP] The apply unit AP outputs a supply pressure Pm in response to operation of the brake operating member BP. The apply unit AP is composed of a single master cylinder CM and a master piston NM.

[0021] A master piston NM is inserted into the single-type master cylinder CM. The master piston NM divides the interior of the master cylinder CM into three hydraulic chambers Rm, Ru, and Rs. The master chamber Rm is formed by the bottom of the master cylinder CM and the master piston NM. The interior of the master cylinder CM is further divided into a servo chamber Ru and a reaction chamber Rs by a flange Tu of the master piston NM. The pressure-receiving area rm of the master chamber Rm and the pressure-receiving area ru of the servo chamber Ru are set equal to each other.

[0022] When braking is not in progress, the master piston NM is in its most retracted position (i.e., the position where the volume of the master chamber Rm is maximum). In this state, the master chamber Rm of the master cylinder CM is connected to the master reservoir RV. Brake fluid BF is stored inside the master reservoir RV (also referred to as the "atmospheric pressure reservoir"). When the brake operating member BP is operated, the master piston NM is moved forward in the direction Ma (a direction in which the volume of the master chamber Rm decreases). This movement blocks communication between the master chamber Rm and the master reservoir RV. When the master piston NM is further moved forward in the direction Ma, the supply pressure Pm (the internal pressure of the master chamber Rm, also referred to as the "master pressure") increases from "0 (atmospheric pressure)." This causes brake fluid BF pressurized to the supply pressure Pm to be output (pressurized and fed) from the master cylinder CM (particularly the master chamber Rm).

[0023] [Hydraulic Pressure Generating Unit PS] The hydraulic pressure generating unit PS (also referred to as a "hydraulic pressure generating device") uses an electric motor MT as its power source to generate front and rear wheel pressures Pwf and Pwr. The front and rear wheel pressures Pwf and Pwr are adjusted by a servo pressure Pc generated by the electric motor MT. Specifically, the hydraulic pressure generating unit PS and the servo chamber Ru are connected via a servo path HU (fluid path). The hydraulic pressure generating unit PS and the rear wheel cylinder CWr are connected via a rear wheel communication path HSr (fluid path). Furthermore, the hydraulic pressure generating unit PS is connected to a master reservoir RV via a supply path HH (fluid path) so that brake fluid BF can be replenished in the event of a shortage of brake fluid BF in the hydraulic pressure generating unit PS.

[0024] When the hydraulic pressure generating unit PS is operating (i.e., during braking), the supply line HH is blocked. This disconnects the hydraulic pressure generating unit PS from the master reservoir RV. In the front brake system, servo pressure Pc is supplied to the servo chamber Ru to generate a supply pressure Pm (master pressure). This supply pressure Pm then generates a hydraulic pressure Pwf (front wheel pressure) in the front wheel cylinder CWf. Meanwhile, in the rear brake system, servo pressure Pc is directly supplied to the rear wheel cylinder CWr to generate a hydraulic pressure Pwr (rear wheel pressure) in the rear wheel cylinder CWr. The hydraulic pressure generating unit PS is provided with a servo pressure sensor PC to detect the servo pressure Pc. Details of the hydraulic pressure generating unit PS will be described later.

[0025] [Input Unit NR] The input unit NR realizes regenerative cooperative control. "Regenerative cooperative control" cooperates the hydraulic braking force Fp (braking force due to wheel pressure Pw) and the regenerative braking force Fg (braking force due to regenerative generator GN) so that the kinetic energy of the vehicle can be efficiently recovered as electrical energy during braking. In regenerative cooperative control, the brake operating member BP is operated, but a state is created in which the wheel pressure Pw is not generated. The input unit NR is composed of an input cylinder CN, an input piston NN, a first control valve VA, a second control valve VB, a stroke simulator SS, and an input pressure sensor PN.

[0026] The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted into the input cylinder CN. The input piston NN is mechanically connected to a brake operating member BP (brake pedal) so as to move in conjunction with the movement of the brake operating member BP. A gap Ks (also referred to as the "separation distance") is defined between the end face of the input piston NN and the end face of the master piston NM. The separation distance Ks is adjusted by the servo pressure Pc, thereby realizing regenerative cooperative control.

[0027] The input chamber Rn of the input unit NR is connected to the reaction force chamber Rs of the apply unit AP via an input path HN (fluid path). A normally closed first control 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 (fluid path) between the first control valve VA and the reaction force chamber Rs. A normally open second control valve VB is provided in the reservoir path HR. On-off solenoid valves are used for the first and second control valves VA and VB. A stroke simulator SS is connected to the input path HN between the first control valve VA and the reaction force chamber Rs.

[0028] When no power is supplied to the first and second control valves VA and VB, the first control valve VA is closed and the second control valve VB is open. Closing the first control valve VA seals the input chamber Rn, creating a fluid lock. This causes the master piston NM to displace integrally with the brake operating member BP. Opening the second control valve VB also connects the stroke simulator SS and the reaction chamber Rs to the master reservoir RV.

[0029] When power is supplied to the first and second control valves VA and VB, the first control valve VA is opened and the second control valve VB is closed. This allows the master piston NM to be displaced separately from the brake operating member BP. Since the input chamber Rn is connected to the stroke simulator SS, the operating force for the brake operating member BP is generated by the stroke simulator SS. An input pressure sensor PN is provided in the input line HN between the input chamber Rn and the first control valve VA to detect the input pressure Pn. The input pressure Pn is also the hydraulic pressure within the stroke simulator SS.

[0030] <<First Controller EA>> The first controller EA controls the first actuator YA. The first controller EA is composed of a microprocessor MP and a drive circuit DR. The first controller EA is connected to a communication bus BS so that signals (detection values, calculation values, control flags, etc.) can be shared with other controllers (EB, EG, etc.).

[0031] The first controller EA directly receives various signals such as the operation displacement Sp (detection value of the operation displacement sensor SP), the input pressure Pn (detection value of the input pressure sensor PN), the servo pressure Pc (detection value of the servo pressure sensor PC), and the motor rotation angle Ka (detection value of the rotation angle sensor KA). Furthermore, the first controller EA receives various signals such as the supply pressure Pm and the limit regenerative braking force Fx from the communication bus BS. The first controller EA also outputs a target regenerative braking force Fh (target value of the regenerative braking force Fg) to the communication bus BS. The regenerative controller EG controls the regenerative braking force Fg (actual value) based on the target regenerative braking force Fh (target value) acquired from the communication bus BS.

[0032] The first controller EA (particularly the microprocessor MP) is programmed with a pressure regulation control algorithm. "Pressure regulation control" is control for adjusting the wheel pressure Pw (=Pwf, Pwr) and includes regenerative cooperative control. Pressure regulation control is performed based on the various signals (Sp, Pc, etc.) described above. Based on the pressure regulation control algorithm, the drive circuit DR drives the electric motor MT and various solenoid valves (VA, etc.). The drive circuit DR includes an H-bridge circuit (also referred to as an "inverter circuit") formed with switching elements (e.g., MOS-FETs) to drive the electric motor MT. The drive circuit DR also includes switching elements to drive the various solenoid valves. Additionally, the drive circuit DR includes a motor current sensor (not shown) that detects the current Im (also referred to as "motor current") supplied to the electric motor MT. The electric motor MT is provided with a rotation angle sensor KA to detect the position Ka (rotation angle) of the motor shaft SM.

[0033] The first controller EA calculates drive signals Va and Vb for the first and second control valves VA and VB, and a drive signal Mt for the electric motor MT. The switching elements are then driven in response to the various drive signals (Mt, etc.). Specifically, in controlling the solenoid valves, power is supplied to the first and second control valves VA and VB based on the drive signals Va and Vb. This opens the first control valve VA and closes the second control valve VB. In controlling the electric motor MT, a target pressure Pt is calculated based on the operating displacement Sp, etc. The "target pressure Pt" is a target value corresponding to the servo pressure Pc (actual value). The first controller EA controls the electric motor MT in response to the target pressure Pt and the drive signal Mt calculated from the servo pressure Pc, so that the servo pressure Pc (actual value) approaches and matches the target pressure Pt (target value).

[0034] <Second Brake Unit SB> A second brake unit SB is provided between the first brake unit SA and the wheel cylinder CW. The second brake unit SB performs antilock brake control, traction control, and skid prevention control. In the brake system for the front wheels WHf (i.e., the front wheel connecting path HSf), a supply pressure Pm is supplied from the master cylinder CM to the second brake unit SB. Meanwhile, in the brake system for the rear wheels WHr (i.e., the rear wheel connecting path HSr), a servo pressure Pc is directly supplied from the hydraulic pressure generating unit PS to the second brake unit SB. The second brake unit SB adjusts (increases or decreases) the supply pressure Pm and the servo pressure Pc, and outputs them as hydraulic pressures Pwf and Pwr (front and rear wheel pressures) for the front and rear wheel cylinders CWf and CWr. The configuration of the second brake unit SB is well known, so a detailed description thereof will be omitted.

[0035] Normally, when the regenerative cooperative control is executed, the operation of the second actuator YB (electric motor, fluid pump, solenoid valve, etc.) is stopped, and therefore the supply pressure Pm is output from the second brake unit SB as the front wheel pressure Pwf, and the servo pressure Pc is output as the rear wheel pressure Pwr.

[0036] <Embodiment of Hydraulic Pressure Generating Unit PS> An embodiment of the hydraulic pressure generating unit PS will be described with reference to the partial cross-sectional view of Figure 2. In the hydraulic pressure generating unit PS (hydraulic pressure generating device), an electric motor MT is used as a pressure source (also referred to as a "power source") to generate a servo pressure Pc. The wheel pressure Pw (= Pwf, Pwr) is then adjusted by the servo pressure Pc.

[0037] <<Shapes and Directions of Movement of Constituent Members>> First, the shapes, directions of movement, etc. of the elements that constitute the hydraulic pressure generating unit PS will be defined. In the hydraulic pressure generating unit PS, when no axial misalignment occurs, the rotation axis Jm of the electric motor MT (particularly, the motor shaft SM), the rotation axis Jk of the rotating member BK, the central axis Jn of the control piston NC, the central axis Jc of the control cylinder CC, and the central axis Je of the intermediate member BE are aligned on a straight line. The direction along (i.e., the parallel direction to) the axes Jm, Jk, Jn, Jc, and Je is referred to as the "axial direction Hj." In contrast, the direction perpendicular to the axes Jm, Jk, Jn, Jc, and Je is referred to as the "radial direction Hk." Therefore, the radial direction Hk is perpendicular to the axial direction Hj.

[0038] In a member (NC, BE, BD, etc.) that is movable along the axial direction Hj, the direction toward the bottom surface Mbc of the control cylinder CC is referred to as the "advance direction Ha." Conversely, the direction away from the bottom surface Mbc of the control cylinder CC is referred to as the "retraction direction Hb." Therefore, when the control piston NC moves in the advancement direction Ha, the volume of the control chamber Rc decreases, and its internal pressure Pc (servo pressure) increases. In contrast, when the control piston NC moves in the retraction direction Hb, the volume of the control chamber Rc increases, and the servo pressure Pc decreases.

[0039] In the relationship between the rotational motion of the electric motor MT and the linear motion of the linearly moving member BD (and consequently the control piston NC), the forward rotation direction Hs of the electric motor MT corresponds to the forward direction Ha of the linearly moving member BD. Conversely, the rotational motion of the electric motor MT in the reverse direction Hg corresponds to the backward direction Hb of the linearly moving member BD. Therefore, when the electric motor MT rotates in the forward rotation direction Hs, the linearly moving member BD moves in the forward direction Ha. This reduces the volume of the control chamber Rc and increases the servo pressure Pc. Conversely, when the electric motor MT rotates in the reverse direction Hg, the linearly moving member BD moves in the backward direction Hb. This increases the volume of the control chamber Rc and decreases the servo pressure Pc.

[0040] <Configuration of Hydraulic Pressure Generating Unit PS> The hydraulic pressure generating unit PS is made up of a housing HG, an electric motor MT, a rotation angle sensor KA, a reducer GS, a conversion mechanism GH, a rotation preventing member MD, a control piston NC, and an intermediate member BE.

[0041] The housing HG holds the components (MT, GS, etc.) that make up the hydraulic pressure generating unit PS. The housing HG is divided into multiple parts so that the components can be assembled. For example, the housing HG is divided into a cylinder housing HGc and a motor housing HGm. The motor housing HGm and the cylinder housing HGc are assembled and ultimately integrated into the housing HG. In other words, the housing HG is a collective term for the cylinder housing HGc and the motor housing HGm.

[0042] Furthermore, the housing HG may be integrated with the first controller EA. Specifically, the first controller EA is composed of a control board on which the microprocessor MP and the drive circuit DR are mounted, and a controller housing (not shown) that houses the control board. The controller housing is then assembled and integrated with the housing HG. The housing HG (particularly, the cylinder housing HGc) holds the reducer GS and the conversion mechanism GH. The housing HG (particularly, the motor housing HGm) also holds the electric motor MT.

[0043] A control cylinder CC (corresponding to a "cylinder") is formed in the housing HG (particularly, the cylinder housing HGc). A control piston NC (corresponding to a "piston") is inserted into the control cylinder CC. The control cylinder CC and the control piston NC form a control chamber Rc (hydraulic pressure chamber). A discharge portion Au is provided in the control cylinder CC (particularly, the control chamber Rc). The servo path HU and the rear wheel communication path HSr are connected to the discharge portion Au. That is, the control chamber Rc is connected to the servo chamber Ru and the rear wheel cylinder CWr. As a result, the servo pressure Pc is supplied (output) to the servo chamber Ru and the rear wheel cylinder CWr.

[0044] The electric motor MT is a power source (pressure source) for generating the servo pressure Pc (hydraulic pressure in the control cylinder CC). Here, "power" refers to the energy required to move the movable members (NC, BK, BD, etc.) in the hydraulic pressure generating unit PS. For example, power is defined as a physical quantity, i.e., energy per unit time (also referred to as "power"). The electric motor MT outputs rotational power Tm (also referred to as "first rotational power"). The rotational power Tm of the electric motor MT is calculated by multiplying the shaft torque of the electric motor MT by the rotational speed of the electric motor MT (particularly, the motor shaft SM). The linear power Fn of the linearly moving member BD (described below) is calculated by multiplying the thrust of the linearly moving member BD (force acting in the axial direction Hj) by the linear speed of the linearly moving member BD (speed in the axial direction Hj).

[0045] A three-phase brushless motor is employed as the electric motor MT. The electric motor MT is mounted within a motor housing HGm. The electric motor MT includes a motor coil CL, a motor shaft SM, and a rotation angle sensor KA. The motor coil CL (also simply referred to as a "coil (winding)") is fixed within the motor housing HGm. The motor coil CL is also referred to as a "stator." A motor line Lm is connected to the motor coil CL. Power is supplied to the motor coil CL from a first controller EA (particularly, a drive circuit DR) via the motor line Lm.

[0046] The motor shaft SM (also simply referred to as the "shaft") is rotatably supported relative to the motor housing HGm (i.e., the motor coil CL) by bearings BB fixed within the motor housing HGm. A motor magnet Mm (permanent magnet) is fixed to the outer periphery of the shaft SM of the electric motor MT. For example, the motor magnet Mm is affixed to the motor shaft SM by adhesive or the like. The motor shaft SM is also referred to as the "rotor."

[0047] In the three-phase brushless motor MT, the magnetic pole position of the rotor SM (i.e., the rotation angle relative to the stator CL) is detected, and the current Im (motor current) flowing through the motor coil CL is switched accordingly. Here, the motor current Im is a collective term for the currents flowing through the U, V, and W phases. The three-phase motor current Im corresponding to the U, V, and W phases is switched based on the rotational position Ka (also referred to as the "rotation angle") of the motor shaft SM. The first controller EA drives the switching elements of the drive circuit DR (inverter circuit) in accordance with the rotational angle Ka. This switches the motor current Im flowing through the motor coil CL, driving the electric motor MT to rotate. A first rotational power Tm is then output from the electric motor MT to the reducer GS.

[0048] A rotation angle sensor KA is provided in the electric motor MT (brushless motor) to detect the motor rotation angle Ka. The rotation angle sensor KA is composed of a sensor disk Ds, a sensor magnet Ms, a sensor board Kb, and a sensor wire Ls. The sensor disk Ds is fixed to the motor shaft SM so as to rotate integrally with the motor shaft SM. The sensor disk Ds is provided with a sensor magnet Ms. The sensor board Kb is fixed to the motor housing HGm. A hole is formed in the sensor board Kb so that the motor shaft SM passes through. A detection unit using a magnetic field detection element is provided around the hole to detect changes in the magnetic field that occur when the motor shaft SM (i.e., the sensor magnet Ms) rotates. A signal detected by the magnetic field detection element is transmitted to the first controller EA (particularly, the microprocessor MP) via the sensor wire Ls.

[0049] The reducer GS reduces the speed of the first rotational power Tm output from the electric motor MT and outputs a second rotational power Tn. Specifically, the input shaft of the reducer GS is fixed to the motor shaft SM. The output shaft of the reducer GS is also fixed to the rotating member BK of the conversion mechanism GH. The reducer GS reduces the speed input from the electric motor MT and increases the torque input from the electric motor MT. The second rotational power Tn is then output from the reducer GS to the conversion mechanism GH.

[0050] For example, a planetary gear mechanism is used as the reducer GS. A "planetary gear mechanism" is a gear mechanism in which multiple planetary gears revolve around a sun gear while rotating on their axes. The reducer GS is composed of a sun gear, planetary gears, an internal gear, and a planetary carrier. For example, in the reducer GS, the internal gear (also called "inner gear") is fixed to the cylinder housing HGc. The sun gear (also called "sun gear") is fixed to the motor shaft SM, and a first rotational power Tm is input to the sun gear from the electric motor MT. Then, the planetary carrier of the reducer GS is fixed to the rotating member BK, and a second rotational power Tn is output from the planetary carrier to the conversion mechanism GH.

[0051] The conversion mechanism GH is composed of a rotating member BK that performs rotational motion and a linearly moving member BD that performs linear motion. In the conversion mechanism GH, the second rotational power Tn output from the reducer GS is input to the rotating member BK. The second rotational power Tn input to the rotating member BK is then converted into linear power Fn of the linearly moving member BD. The conversion mechanism GH is also called a "rotation-to-linear conversion mechanism."

[0052] For example, a "ball screw" is employed as the conversion mechanism GH. Specifically, in the conversion mechanism GH, a rotating member BK, which is a shaft member, is fixed to the output shaft of the reducer GS. The rotating member BK is inserted into a linearly moving member BD having a cylindrical shape. A ball screw groove Mzk is formed on the outer peripheral surface Mok of the rotating member BK. Similarly, a ball screw groove Mzd is also formed on the inner peripheral surface Mid of the linearly moving member BD. A plurality of balls BL (steel balls) are fitted into the ball screw grooves Mzk and Mzd (see blow-out section XGH for the above).

[0053] In the conversion mechanism GH, the member having a thread groove on its outer circumferential surface is referred to as the "inner member." The member having a thread groove on its inner circumferential surface is referred to as the "outer member." The outer member is disposed so as to cover the inner member, and the thread groove of the inner member and the thread groove of the outer member are engaged with each other. Specifically, in the ball screw mechanism, two thread grooves are engaged with each other via a plurality of balls BL.

[0054] In the ball screw mechanism employed as the conversion mechanism GH, a ball screw shaft (an inner member, also referred to as a "shaft member") serves as the rotating member BK, and a ball screw nut (an outer member, also referred to as a "nut member") serves as the linear motion member BD. In this configuration, a screw groove Mzk is formed on the outer peripheral surface Mok of the rotating member BK (inner member), and a screw groove Mzd is formed on the inner peripheral surface Mid of the linear motion member BD (outer member). The outer peripheral groove Mzk and the inner peripheral groove Mzd are engaged with each other via a ball BL.

[0055] A flange portion Fd is provided on the linear motion member BD at the end away from the control cylinder CC (particularly the control chamber Rc). The flange portion Fd is formed by extending the cylindrical end of the linear motion member BD in the radial direction Hk in a flange shape. A notch is formed in the flange portion Fd. The anti-rotation member MD is fitted into the notch.

[0056] The anti-rotation member MD is fixed to the cylinder housing HGc. For example, the anti-rotation member MD is a long, thin rod-shaped member (e.g., a pin member). The housing HG has a plurality of holes spaced equally around the rotation axis Jk on the side of the linear motion member BD away from the rotation axis Jk. A anti-rotation member MD is inserted into each of the holes and fixed. A semicircular notch is formed in the flange portion Fd of the linear motion member BD. The notch engages with the anti-rotation member MD, thereby preventing the linear motion member BD from rotating around the rotation axis Jk. As a result, when the rotating member BK is rotationally driven, the linear motion member BD moves along the axial direction Hj (forward direction Ha or backward direction Hb).

[0057] The control piston NC is inserted into a control cylinder CC formed in the cylinder housing HGc. Specifically, the control piston NC is composed of a bottom portion Btn (also referred to as a "first bottom portion") and a cylindrical portion Enn (also referred to as a "first cylindrical portion"). That is, the control piston NC has a cylindrical shape (cup shape) with the bottom portion Btn. The control piston NC (particularly the first bottom portion Btn) inserted into the control cylinder CC forms a control chamber Rc (hydraulic chamber) inside the control cylinder CC.

[0058] The outer peripheral surface Mon of the control piston NC and the inner peripheral surface Mic of the control cylinder CC are sealed by two seal members SL. The two seal members SL are fitted into seal grooves formed in the inner peripheral surface Mic of the control cylinder CC. Between the two seal grooves, a hole (not shown, also referred to as a "housing hole") penetrating into the control cylinder CC is provided in the cylinder housing HGc. The housing hole is connected to the master reservoir RV via a supply path HH. The control piston NC is provided with a hole (not shown, also referred to as a "piston hole") penetrating from the outer peripheral surface Mon to the bottom Btn to connect the housing hole and the control chamber Rc.

[0059] An intermediate member BE is provided between the linear moving member BD and the control piston NC in the axial direction Hj. The intermediate member BE transmits power between the linear moving member BD and the control piston NC. A linear power Fn from the linear moving member BD is transmitted to the control piston NC via the intermediate member BE. This allows the linear moving member BD, intermediate member BE, and control piston NC to move together in the forward direction Ha. Note that the linear moving member BD and the control piston NC are secured by a retaining member ND so that they can move together when returning in the backward direction Hb.

[0060] The control piston NC is sealed against the control cylinder CC by a seal member SL, but if axial misalignment occurs (particularly, if there is a misalignment between the direction of the linear power Fn and the direction of movement of the control piston NC), the contact between the outer circumferential surface Mon of the control piston NC and the seal member SL becomes uneven. This can cause a decrease in sealing performance, uneven wear of the seal member SL, etc. In order to suppress the effects of axial misalignment of the control piston NC, etc. (i.e., a decrease in sealing performance, uneven wear of the seal member SL, etc.), an intermediate member BE is provided in the power transmission path from the linear motion member BD to the control piston NC.

[0061] The intermediate member BE is composed of a bottom portion Bte (also referred to as a "second bottom portion") and a cylindrical portion Ene (also referred to as a "second cylindrical portion"). Like the control piston NC, the intermediate member BE has a cylindrical shape (i.e., a cup shape) with the second bottom portion Bte. The intermediate member BE is housed inside (inside) the control piston NC. In other words, the control piston NC and the intermediate member BE are nested. This structure is called a "nested structure." In the nested structure, the control piston NC located on the outside slides against the seal member SL, sealing the control chamber Rc, and the influence of axial misalignment is compensated for by the intermediate member BE located on the inside.

[0062] A through-hole Ae (also referred to as an "air vent") is provided in the intermediate member BE (particularly the cylindrical portion Ene). As the linearly moving member BD moves, the rotating member BK moves in and out of the intermediate member BE. Specifically, when the linearly moving member BD moves in the forward direction Ha (i.e., when the servo pressure Pc increases), the rotating member BK gradually moves out of the interior of the intermediate member BE. Conversely, when the linearly moving member BD moves in the backward direction Hb (i.e., when the servo pressure Pc decreases), the rotating member BK gradually moves into the interior of the intermediate member BE. In other words, as the linearly moving member BD moves, the volume of gas (e.g., air) present inside the intermediate member BE changes, and thus the air pressure inside the intermediate member BE changes. When negative pressure is generated inside the intermediate member BE, the lubricant (e.g., grease) in the conversion mechanism GH may be sucked out. An air vent Ae (e.g., a circular hole) is provided so that gas can easily move between the inside and outside of the intermediate member BE. The air vent Ae may be provided at the contact portion between the intermediate member BE and the linear motion member BD. In this configuration, a notch is formed at the end of the intermediate member BE as the air vent Ae.

[0063] <Adjustment of Servo Pressure Pc> In the brake control device SC, the wheel pressure Pw is adjusted by the servo pressure Pc, which is the output of the hydraulic pressure generating unit PS. In the hydraulic pressure generating unit PS, the rotational power Tm (i.e., shaft torque) of the electric motor MT is converted by the conversion mechanism GH into linear power Fn (i.e., thrust) of the linearly moving member BD (resulting in the control piston NC). The control piston NC is then moved by the linear power Fn, thereby generating and adjusting the servo pressure Pc. A servo pressure sensor PC is provided in the hydraulic pressure generating unit PS to detect the servo pressure Pc.

[0064] The conversion mechanism GH is capable of both converting rotary motion to linear motion and converting linear motion to rotary motion. The former operation of the conversion mechanism GH is called "direct operation," and the latter operation is called "reverse operation." Therefore, the movement of the control piston NC is determined by the magnitude relationship between the torque output from the electric motor MT (also called "direct operation torque Qmt") and the torque input to the electric motor MT by the servo pressure Pc (also called "reverse operation torque Qpc"). Adjustment (increase or decrease) of the servo pressure Pc will be described below.

[0065] [Increase in Servo Pressure Pc] In Figure 2, above the rotation axis Jk, a state in which the hydraulic pressure generating unit PS is not generating the servo pressure Pc is shown. In this state, the control chamber Rc is connected to the master reservoir RV via the housing hole and the piston hole, and the servo pressure Pc is "0 (atmospheric pressure)." The positions of the linearly acting member BD, the control piston NC, etc. in this state are referred to as the "initial position." In the initial position, the control piston NC is displaced to its maximum in the backward direction Hb, and the volume of the control chamber Rc is at its maximum.

[0066] As described above, the control piston NC and the intermediate member BE have a bottomed cylindrical shape (cup shape) and are nested within each other, so that the intermediate member BE is housed inside the control piston NC. Furthermore, when the control piston NC is in its initial position, the rotating member BK is housed inside the intermediate member BE. This structure reduces the dimension in the axial direction Hj (also referred to as the "axial length") of the hydraulic pressure generating unit PS.

[0067] When the braking demand value (a state quantity indicating a demand for braking force, for example, the operating displacement Sp of the brake operating member BP) increases, the target pressure Pt is increased from "0." The target pressure Pt is a target value corresponding to the servo pressure Pc (actual value). The target pressure Pt increases as the braking demand value increases. As the target pressure Pt increases, the forward acting torque Qmt becomes greater than the reverse acting torque Qpc, and the electric motor MT rotates in the forward rotation direction Hs. In other words, the electric motor MT generates rotational power Tm in the forward rotation direction Hs. The rotational power Tm is transmitted to the conversion mechanism GH via the reducer GS and output as linear power Fn of the linearly moving member BD. The linearly moving member BD then presses the intermediate member BE, which in turn presses the control piston NC. As a result, the control piston NC moves forward in the forward direction Ha (the direction in which the volume of the control chamber Rc decreases).

[0068] This movement first cuts off communication between the control chamber Rc and the master reservoir RV. As the control piston NC moves further forward in the direction Ha, the servo pressure Pc (internal pressure of the control chamber Rc) increases from "0 (atmospheric pressure)." Brake fluid BF pressurized to the servo pressure Pc is output (pressurized and fed) from the control chamber Rc of the control cylinder CC to the servo chamber Ru and the rear wheel cylinder CWr.

[0069] [Maintaining Servo Pressure Pc] When the braking demand value becomes constant, the target pressure Pt is maintained. The forward acting torque Qmt and the reverse acting torque Qpc become equal, and the rotation of the electric motor MT stops (i.e., the rotational speed of the electric motor MT becomes "0"). By stopping the movement of the control piston NC, the servo pressure Pc is maintained constant (see below the rotation axis Jk in Figure 2).

[0070] [Reduction of Servo Pressure Pc] When the braking demand value is reduced, the target pressure Pt is reduced. This reduces the rotational power Tm of the electric motor MT. The reverse acting torque Qpc due to the servo pressure Pc becomes greater than the forward acting torque Qmt due to the electric motor MT, causing the electric motor MT to rotate in the reverse direction Hg. The control piston NC is moved in the reverse direction Hb, increasing the volume of the control chamber Rc. The brake fluid BF that had been moved to the servo chamber Ru and the rear wheel cylinder CWr is returned toward the control chamber Rc, thereby reducing the servo pressure Pc.

[0071] <Compensation for the Effects of Axial Misalignment by the Intermediate Member BE> Suppression of the effects of axial misalignment by the intermediate member BE will be described with reference to the partial cross-sectional view of Figure 3. Here, suppression of the effects caused by axial misalignment is referred to as "axial misalignment compensation." Figure 3 shows a situation in which no axial misalignment has occurred, and the rotation axis Jk of the rotating member BK, the central axis Je of the intermediate member BE, the central axis Jn of the control piston NC, and the central axis Jc of the control cylinder CC are aligned on a straight line.

[0072] <Axis Misalignment> First, we will explain axis misalignment. In power transmission, it is desirable that the axes Jk, Jn, and Jc are aligned in a straight line. However, because the conversion mechanism GH, control piston NC, control cylinder CC, etc. are individual components, their axes Jk, Jn, and Jc may deviate from the straight line and become misaligned. Misalignment of the axes Jk, Jn, and Jc is called "axis misalignment." Axis misalignment is eccentricity (misalignment) between the axes, and is also called "misalignment."

[0073] For example, there are cases where two axes intersect but form an angle (i.e., lack of parallelism). This type of axis misalignment is called "declination misalignment (or declination error)." There are also cases where two axes are not parallel. This type of axis misalignment is called "parallel misalignment (or parallel error)." Usually, axis misalignment occurs as a combination of declination misalignment and parallel misalignment.

[0074] As described above, when axial misalignment (misalignment) occurs, the contact between the outer peripheral surface Mon of the control piston NC and the seal member SL becomes uneven, which may result in a decrease in the sealing performance of the seal member SL and uneven wear. Furthermore, the load on the conversion mechanism GH becomes uneven, which may result in uneven wear of the ball member BL, the screw grooves Mzk, Mzd, etc. The hydraulic pressure generating unit PS is provided with an intermediate member BE to compensate for the axial misalignment.

[0075] <Axis Misalignment Compensation Mechanism> The axis misalignment compensation mechanism, which is composed of the conversion mechanism GH, the control piston NC, and the intermediate member BE, will be described. The conversion mechanism GH is composed of a rotating member BK and a linearly moving member BD. The rotational movement of the rotating member BK is constrained relative to the housing HG (linear movement in the axial direction Hj), but rotational movement is maintained in a state where it is possible. On the other hand, the rotational movement of the linearly moving member BD is constrained relative to the housing HG, but translational movement is maintained in a state where it is possible. As a result, the conversion mechanism GH outputs the rotational power Tm input to the rotating member BK as linear power Fn of the linearly moving member BD. Here, in the conversion mechanism GH, the linearly moving member BD is arranged to cover the rotating member BK. For example, in a configuration in which a ball screw mechanism is adopted as the conversion mechanism GH, the rotating member BK is a ball screw shaft, and the linearly moving member BD is a ball screw nut.

[0076] A flange portion Fd is provided at the end of the linear moving member BD (more specifically, the end away from the bottom surface Mbc of the control cylinder CC or the bottom portion Btn of the control piston NC). A notch is formed on the outer periphery of the flange portion Fd. The notch engages with a rotation prevention member MD. The rotation prevention member MD is fixed to the housing HG. The rotation prevention member MD prevents the rotational movement of the linear moving member BD relative to the housing HG, so that the rotational movement of the rotating member BK can be converted into linear movement of the linear moving member BD.

[0077] The control piston NC is inserted into a control cylinder CC formed in the housing HG. The control piston NC has a bottomed cylindrical shape (cup shape) and is composed of a first bottom portion Btn and a first cylindrical portion Enn. Two seal grooves are formed in the inner circumferential surface Mic of the control cylinder CC. A seal member SL is fitted into each seal groove. The outer circumferential surface Mon of the cylindrical portion Enn and the inner circumferential surface Mic of the control cylinder CC are sealed by the seal member SL. The control piston NC (particularly the bottom portion Btn) forms a control chamber Rc (hydraulic pressure chamber) in the control cylinder CC. Note that a plane perpendicular to the central axis Jn of the control piston NC (i.e., the central axis of the first cylindrical portion Enn) is formed on the inner bottom surface Mtn of the first bottom portion Btn.

[0078] An annular groove is formed on the inner peripheral surface Min of the cylindrical portion Enn of the control piston NC. An annular groove is also formed on the outer peripheral surface Mod of the linear motion member BD. A retaining member ND (e.g., a snap ring) is fitted into these grooves. The retaining member ND limits the relative displacement between the control piston NC and the linear motion member BD so that the control piston NC and the linear motion member BD do not completely separate. The retaining member ND has a backlash (gap) with respect to the annular groove in the axial direction Hj and the radial direction Hk. Therefore, the control piston NC and the linear motion member BD can be displaced relative to each other within the range of the backlash in both the axial direction Hj and the radial direction Hk.

[0079] An intermediate member BE is provided between the control piston NC and the linearly moving member BD. Like the control piston NC, the intermediate member BE has a bottomed cylindrical shape (cup shape) and is composed of a second bottom portion Bte and a second cylindrical portion Ene. In a nested structure (i.e., a structure in which the intermediate member BE is disposed inside the control piston NC), the bottom portion Btn (first bottom portion) of the control piston NC and the bottom portion Bte (second bottom portion) of the intermediate member BE are in slidable contact with each other. Here, "sliding" refers to the movement in which two members move while sliding while in contact with each other.

[0080] Specifically, slippage can occur between the outer bottom surface Mpe (also referred to as the "pressing surface") of the intermediate member BE and the inner bottom surface Mtn (also referred to as the "pressure-receiving surface") of the control piston NC. A spherical convex portion with a radius Rq is formed on the pressing surface Mpe (corresponding to the "one end surface") of the intermediate member BE. Furthermore, a rounded corner (also referred to as a "corner") with a radius Rp is formed on the intermediate member BE at a portion (also referred to as a "corner") where the pressing surface Mpe and the outer circumferential surface Moe of the cylindrical portion Ene are connected. That is, the corner of the bottom portion Bte of the intermediate member BE is rounded. Here, the radius Rq of the convex spherical surface is significantly larger than the radius Rp of the rounded corner. The portion where the pressing surface Mpe (outer bottom surface) of the intermediate member BE and the pressure-receiving surface Mtn (inner bottom surface) of the control piston NC come into contact is referred to as a "first sliding portion Sda."

[0081] An end surface Mqe (also referred to as the "middle end surface") of the cylindrical portion Ene of the intermediate member BE is in slidable contact with an end surface Mpd (also referred to as the "linear end surface") of the linear moving member BD. For example, the middle end surface Mqe (corresponding to the "other end surface") is a plane perpendicular to the central axis Je of the intermediate member BE (i.e., the central axis of the second cylindrical portion Ene). Furthermore, the linear moving end surface Mpd is a plane perpendicular to the rotation axis Jk. Therefore, the linear moving end surface Mpd and the middle end surface Mqe contact on a plane perpendicular to the axial direction Hj and parallel to the radial direction Hk. Here, the portion where the middle end surface Mqe of the intermediate member BE and the linear moving end surface Mpd of the linear moving member BD contact each other is referred to as the "second sliding portion Sdb."

[0082] The configurations of the conversion mechanism GH, control piston NC, and intermediate member BE can be summarized as follows. The intermediate member BE is housed inside the control piston NC. The intermediate member BE is located between the linearly moving member BD (particularly, the linearly moving end surface Mpd) and the control piston NC (particularly, the pressure-receiving surface Mtn). When the servo pressure Pc increases, the linearly moving end surface Mpd (flat surface) presses the intermediate end surface Mqe (flat surface) in the forward direction Ha, and the pressing surface Mpe (convex surface) presses the pressure-receiving surface Mtn (flat surface) in the forward direction Ha. As a result, the control piston NC, intermediate member BE, and linearly moving member BD move in the forward direction Ha. Conversely, when the servo pressure Pc decreases, the pressure-receiving surface Mpe presses the pressing surface Mpe in the backward direction Hb, and the intermediate end surface Mqe presses the linearly moving end surface Mpd in the backward direction Hb. As a result, the control piston NC, the intermediate member BE, and the linearly moving member BD move in the backward direction Hb. Here, the intermediate member BE has two portions (i.e., first and second sliding portions Sda and Sdb) that can slide against the control piston NC and the linearly moving member BD.

[0083] <Axis Misalignment Compensation> The operation of the axis misalignment compensation mechanism will be described. The effects of axis misalignment are compensated for by "allowing slippage in the radial direction Hk between the power transmission members (BD, BE, NC, etc.)" and "allowing the intermediate member BE to rotate when the control piston NC is in contact with the intermediate member BE." The control piston NC and the intermediate member BE are arranged in a nested state, and there is a gap (also referred to as a "nested gap") between the control piston NC and the intermediate member BE in the radial direction Hk. In the hydraulic pressure generating unit PS, this nested gap allows slippage between the members.

[0084] At the first sliding portion Sda, the pressure-receiving surface Mtn of the control piston NC (e.g., a plane perpendicular to the central axis Jn of the first cylindrical portion Enn) and the pressing surface Mpe (e.g., a convex surface) of the intermediate member BE come into contact. The pressure-receiving surface Mtn and the pressing surface Mpe can be displaced relative to each other in the radial direction Hk within the range of the gap (i.e., the nesting gap) between the inner peripheral surface Min of the control piston NC and the outer peripheral surface Moe of the intermediate member BE. In addition, because the pressing surface Mpe is a convex surface (e.g., a spherical surface), they can be rotated and displaced relative to each other and tilt around the contact point between the pressure-receiving surface Mtn and the pressing surface Mpe. This rotational movement is referred to as "swinging." The swinging (tilting) and sliding (sliding) at the first sliding portion Sda suppress the effects of axial misalignment (angle misalignment and parallel misalignment) of the control piston NC and the like. Furthermore, when the inclination between the pressure-receiving surface Mtn and the pressing surface Mpe (i.e., the degree of swing) increases, the pressure-receiving surface Mtn comes into contact with the corner of the intermediate member BE. Because the corner is rounded (rounded), the contact pressure between the pressure-receiving surface Mtn and the pressing surface Mpe is suppressed even if the angular deviation becomes excessive.

[0085] At the second sliding portion Sdb, a linear end surface Mpd of the linear moving member BD (e.g., a plane perpendicular to the rotation axis Jk of the rotating member BK) and a middle end surface Mqe of the intermediate member BE (e.g., a plane perpendicular to the central axis Je of the second cylindrical portion Ene) come into contact. This contact allows the linear end surface Mpd and the middle end surface Mqe to slide relative to each other. Therefore, the linear end surface Mpd and the middle end surface Mqe can be displaced relative to each other in the radial direction Hk within the range of the gap (i.e., the nested gap) between the inner circumferential surface Min of the control piston NC and the outer circumferential surface Moe of the intermediate member BE.

[0086] The control piston NC is held in the housing HG by a seal member SL. The conversion mechanism GH is held in the housing HG by a bearing (e.g., a bearing). The intermediate member BE is not directly held in the housing HG but serves as a floating joint. Specifically, the intermediate member BE can slide and move parallel to both the control piston NC and the linearly moving member BD in the radial direction Hk. This effectively suppresses the effects of parallel misalignment. Furthermore, the intermediate member BE can oscillate relative to the control piston NC, thereby appropriately suppressing the effects of angular misalignment. Additionally, the presence of the second sliding portion Sdb does not impede the sliding and oscillating motion of the first sliding portion Sda. In other words, sliding and oscillating motion are facilitated, improving the compensation effect for angular misalignment. In the hydraulic pressure generating unit PS, the intermediate member BE provides two sliding portions Sda and Sdb, thereby not only suppressing the effects of parallel misalignment but also effectively compensating for the effects of angular misalignment.

[0087] <Positioning the Intermediate Member BE: First Configuration Example> A first configuration example relating to the positioning of the intermediate member BE relative to the control piston NC will be described. In an axial misalignment compensation mechanism, the larger the nesting gap, the greater the effect of axial misalignment compensation. However, if the nesting gap is set large, it becomes difficult to determine the position of the intermediate member BE when the linear force Fn is small. Therefore, in the hydraulic pressure generating unit PS, in the nesting gap between the inner circumferential surface Min of the cylindrical portion Enn (first cylindrical portion) of the control piston NC and the outer circumferential surface Moe of the cylindrical portion Ene (second cylindrical portion) of the intermediate member BE, the nesting gap Ska at a position close to the bottom Btn (first bottom) of the control piston NC is narrower than the nesting gap Skb at a position farther away from the first bottom Btn. Here, the nesting gap Ska at a position close to the bottom Btn is referred to as the "proximal gap," and the nesting gap Skb at a position farther away from the bottom Btn is referred to as the "remote gap." Specifically, in a cross section perpendicular to the central axis Jn, the difference between the inner diameter of the inner peripheral surface Min of the control piston NC and the outer diameter of the outer peripheral surface Moe of the intermediate member BE at a location relatively close to the contact portion of the first and second bottom portions Btn, Bte is the proximity gap Ska, and in a cross section perpendicular to the central axis Jn, the difference between the inner diameter of the inner peripheral surface Min of the control piston NC and the outer diameter of the outer peripheral surface Moe of the intermediate member BE at a location relatively far from the contact portion is the remote gap Skb.

[0088] The inner diameter (i.e., the diameter of the inner circumferential surface Min) of the cylindrical portion Enn of the control piston NC is formed in two stages, thereby setting the proximity gap Ska and the remote gap Skb. Specifically, the inner circumferential surface Min in a portion close to the bottom Btn (specifically, in a region from the contact point between the pressure-receiving surface Mtn and the pressing surface Mpe up to a predetermined distance La) has a diameter Da (also referred to as the "proximal inner diameter"). The inner circumferential surface Min in a portion away from the bottom Btn (specifically, in a region at least the predetermined distance La from the contact point between the pressure-receiving surface Mtn and the pressing surface Mpe) has a diameter Db (also referred to as the "remote inner diameter"). The proximal inner diameter Da is larger than the outer diameter De (i.e., the diameter of the outer circumferential surface Moe) of the cylindrical portion Ene of the intermediate member BE but is smaller than the remote inner diameter Db by a predetermined value rx (i.e., "De < Da < Db"). Here, the outer diameter De of the cylindrical portion Ene of the intermediate member BE is constant.

[0089] The intermediate member BE is inserted into the control piston NC and is disposed so as to contact the bottom Btn (particularly the pressure-receiving surface Mtn) of the control piston NC. Therefore, the proximity gap Ska in the region up to a predetermined distance La from the pressure-receiving surface Mtn is smaller than the remote gap Skb in the region at least the predetermined distance La away from the pressure-receiving surface Mtn. In other words, in the hydraulic pressure generating unit PS, the proximity gap Ska is set narrower than the remote gap Skb in the nesting gap. This improves the positioning accuracy of the intermediate member BE relative to the control piston NC in the hydraulic pressure generating unit PS.

[0090] The intermediate member BE can move parallel in the radial direction Hk by at least the amount of the proximity gap Ska to compensate for the effects of parallel misalignment. Furthermore, parallel misalignment can also be compensated for between the intermediate member BE and the rotating member BK. Additionally, the intermediate member BE can swing about the pressing surface Mpe to compensate for the effects of angular misalignment. During this swing, the amount of arcuate movement is small near the center (i.e., the contact point between the first and second bottom portions Btn and Bte), but the amount of arcuate movement increases with increasing distance from the center. In the hydraulic pressure generating unit PS, the remote gap Skb is relatively larger than the proximity gap Ska, ensuring a sufficient rotation angle (also referred to as the "swing angle") during swing (rotational movement). In other words, the hydraulic pressure generating unit PS improves the positioning accuracy of the intermediate member BE by appropriately compensating for the effects of axial misalignment (a combination of parallel misalignment and angular misalignment).

[0091] Suppression of Poor Lubrication Due to Negative Pressure: This section explains how to ensure the lubrication of the conversion mechanism GH in a configuration employing a nested structure. In the hydraulic pressure generating unit PS, the control piston NC and the intermediate member BE are cup-shaped and nested together, and the rotating member BK is housed inside the intermediate member BE, thereby reducing the axial dimension Hj. However, because the rotating member BK moves in and out of the cylindrical portion Ene of the intermediate member BE, air pressure fluctuations occur within the cylindrical portion Ene. These air pressure fluctuations can generate negative pressure, potentially resulting in the loss of lubricant (e.g., grease) that lubricates the conversion mechanism BH and other components. Furthermore, improving the positioning accuracy of the intermediate member BE increases the degree of contact between the linear end surface Mpd and the intermediate end surface Mqe.

[0092] In order to prevent the loss of lubricant (such as grease) due to negative pressure, an air vent Ae (e.g., a circular hole) is provided in the intermediate member BE (particularly the cylindrical portion Ene). When the servo pressure Pc is increased, gas (e.g., air) flows from the outside of the intermediate member BE to the inside of the intermediate member BE through the air vent Ae. On the other hand, when the servo pressure Pc is decreased, gas flows from the inside of the intermediate member BE to the outside of the intermediate member BE through the air vent Ae. Since gas can move freely between the inside and outside of the intermediate member BE through the air vent Ae, poor lubrication due to the ejection of lubricant is prevented. Note that, since the air vent Ae is intended to allow the movement of gas, an air vent Ae (e.g., a notch) may be provided in the contact surface between the intermediate member BE and the linearly moving member BD.

[0093] <Positioning of Intermediate Member BE: Second Configuration Example> A second configuration example relating to the positioning of the intermediate member BE will be described with reference to the partial cross-sectional view of Fig. 4. In the first configuration example, the inner diameter of the cylindrical portion Enn of the control piston NC is configured in two stages. Instead, in the second configuration example, the outer diameter of the cylindrical portion Ene of the intermediate member BE (i.e., the diameter of the outer circumferential surface Moe) is configured in two stages. The following description will focus on the differences.

[0094] The outer peripheral surface Moe of the intermediate member BE at a portion close to the bottom portion Bte (specifically, a region extending a predetermined distance Lc from the contact point between the first and second bottom portions Btn and Bte) has a diameter Dc (also referred to as the "proximal outer diameter"). In contrast, the outer peripheral surface Moe at a portion distant from the bottom portion Bte (specifically, a region at least the predetermined distance Lc from the contact point between the first and second bottom portions Btn and Bte) has a diameter Dd (also referred to as the "remote outer diameter"). The proximal outer diameter Dc is smaller than the inner diameter Dn of the cylindrical portion Enn of the control piston NC (i.e., the diameter of the inner peripheral surface Min), but is larger than the remote outer diameter Dd by a predetermined value rz (i.e., "Dn > Dc > Dd"). Here, the inner diameter Dn of the cylindrical portion Enn of the control piston NC is constant.

[0095] As in the first configuration example, in the second configuration example, the proximity gap Ska in the region up to the predetermined distance Lc from the pressure-receiving surface Mtn (= Mpe) (i.e., the nested gap at a position close to the first bottom Btn) is smaller than the remote gap Skb in the region at least the predetermined distance Lc away from the pressure-receiving surface Mtn (i.e., the nested gap at a position farther from the first bottom Btn). In other words, in the hydraulic pressure generating unit PS, the proximity gap Ska in the nested gaps is set narrower than the remote gap Skb, and therefore the same effects as in the first configuration example (improved positioning accuracy and ensured axial misalignment compensation effect) are achieved.

[0096] <Other Embodiments of the Hydraulic Pressure Generating Unit PS> Other embodiments of the hydraulic pressure generating unit PS will be described below. In these other embodiments, the hydraulic pressure generating unit PS also achieves the same effects as those described above (compensation for axial misalignment, improved positioning accuracy of the intermediate member BE, shortening the axial length of the hydraulic pressure generating unit PS, ensuring lubrication of the conversion mechanism GH, etc.).

[0097] In the above-described embodiment of the hydraulic pressure generating unit PS, a ball screw is used as the conversion mechanism GH. Alternatively, a sliding screw (e.g., a trapezoidal screw) may be used as the conversion mechanism GH. In a configuration in which a sliding screw mechanism is used, a male thread is formed as a screw groove on the inner member. Furthermore, a female thread is formed as a screw groove on the outer member. The male thread and the female thread are directly engaged with each other. Reverse operation occurs even in a conversion mechanism GH in which a sliding screw is used.

[0098] In the embodiment of the hydraulic pressure generating unit PS described above, a configuration is adopted in which the axis Jm and the axes Jc, Jn, and Jk are aligned in a straight line. This configuration is referred to as a "coaxial configuration (or single-shaft configuration)" because the axis Jm and the axis Jc, etc. are coaxial. In a coaxial configuration, a reducer GS is used in which the rotation axis of the input shaft and the rotation axis of the output shaft are coaxial (e.g., a planetary gear mechanism). Alternatively, a "separate-shaft configuration (or two-shaft configuration)" may be adopted in which the axis Jm and the axes Jc, Jn, and Jk are on separate axes. In a separate-shaft configuration, a reducer GS is used in which the rotation axis of the input shaft and the rotation axis of the output shaft are different (e.g., a gear train). In a separate-shaft configuration, the axis Jm and the axes Jc, Jn, and Jk are separate axes but arranged parallel to each other. Even in the separate shaft configuration, the axes Jc, Jn, and Jk are on the same straight line.

[0099] In the above-described embodiment of the hydraulic pressure generating unit PS, the close gap Ska is narrower than the remote gap Skb by "setting the inner diameters Da, Db of the control piston NC in two stages (see the first configuration example)" or "setting the outer diameters Dc, Dd of the intermediate member BE in two stages (see the second configuration example)." Alternatively, the first and second configuration examples may be combined. Therefore, in the hydraulic pressure generating unit PS, "Ska<Skb" is achieved by at least one of "setting the inner diameters Da, Db of the control piston NC in two stages" and "setting the outer diameters Dc, Dd of the intermediate member BE in two stages."

[0100] In the embodiment of the hydraulic pressure generating unit PS described above, the "inner diameters Da, Db of the control piston NC" and / or the "outer diameters Dc, Dd of the intermediate member BE" are set in two stages in the nested gap. Alternatively, these may be set in multiple stages. Alternatively, they may be set so as to gradually change without any stages. In any case, in the hydraulic pressure generating unit PS, the close gap Ska is narrower than the remote gap Skb.

[0101] In the embodiment of the hydraulic pressure generating unit PS described above, a configuration was exemplified in which the end face Mpe of the intermediate member BE in contact with the first bottom portion Btn is a convex surface, and the end face Mqe of the intermediate member BE in contact with the linearly moving member BD is a flat surface. In the hydraulic pressure generating unit PS, it is sufficient that at least one of the end face Mpe of the intermediate member BE in contact with the first bottom portion Btn and the end face Mqe of the intermediate member BE in contact with the linearly moving member BD is a convex surface. In other words, in the hydraulic pressure generating unit PS, "one of the end face Mpe of the intermediate member BE in contact with the first bottom portion Btn and the end face Mqe of the intermediate member BE in contact with the linearly moving member BD is a convex surface and the other is a flat surface," or "both the end face Mpe of the intermediate member BE in contact with the first bottom portion Btn and the end face Mqe of the intermediate member BE in contact with the linearly moving member BD are convex surfaces." By forming at least one of the end faces Mpe and Mqe on both sides of the intermediate member BE into a convex surface (for example, a convex spherical surface), it becomes easier for oscillation to occur, which can improve the effect of compensating for axial misalignment.

[0102] The above-described braking control device SC is applied to a vehicle in which a regenerative device KG is provided on the front wheels WHf and in which regenerative cooperative control is performed. In a vehicle in which regenerative cooperative control is performed, the regenerative device KG only needs to be provided on at least one of the front wheels WHf and the rear wheels WHr. The braking control device SC can also be applied to a vehicle in which the regenerative device KG is power-saving and in which regenerative cooperative control is not performed. In other words, the braking control device SC can be applied to various vehicles regardless of whether regenerative cooperative control is performed or not.

[0103] In the above-described exemplary configuration of the brake control device SC, a single-type master cylinder CM is employed. However, the brake control device SC may also employ a tandem-type master cylinder CM. In this configuration, two master chambers Rm are formed inside the CM. A servo pressure Pc is supplied from the hydraulic pressure generating unit PS to the servo chamber Ru, and a wheel pressure Pw is supplied from the master chamber Rm to the wheel cylinder CW. In this configuration, the brake control device SC may employ not only a front-rear type but also a diagonal type (also called an "X type") brake system as the two-system brake system. In a diagonal-type brake control device SC, one of the two master chambers Rm is connected to the right front wheel cylinder and the left rear wheel cylinder. The other of the two master chambers Rm is connected to the left front wheel cylinder and the right rear wheel cylinder.

[0104] In the above-described exemplary configuration of the brake control device SC, the first brake unit SA outputs the supply pressure Pm via the master cylinder CM. That is, the apply unit AP and the hydraulic pressure generating unit PS are arranged in series in the hydraulic pressure transmission path, and the servo pressure Pc supplied from the hydraulic pressure generating unit PS is transmitted as the supply pressure Pm via the master piston NM. Alternatively, the apply unit AP and the hydraulic pressure generating unit PS may be arranged in parallel. Specifically, the apply unit AP (particularly the master cylinder CM) and the hydraulic pressure generating unit PS are each directly connected to the second actuator YB. An on-off solenoid valve (referred to as a "switching valve") selects either the connection between the hydraulic pressure generating unit PS and the second actuator YB or the connection between the apply unit AP and the second actuator YB. When the former is selected, the servo pressure Pc generated by the hydraulic pressure generating unit PS is directly output as the supply pressure Pm without passing through the apply unit AP. In this case, the apply unit AP is connected to the stroke simulator SS, and the operating force of the brake operating member BP is generated by the stroke simulator SS. On the other hand, when the latter is selected, the hydraulic pressure in the master chamber Rm generated by the operation of the brake operating member BP is output as the supply pressure Pm. In this case, the apply unit AP is disconnected from the simulator SS.

[0105] Summary of the Embodiments The following summarizes the embodiments of the hydraulic pressure generating unit PS (hydraulic pressure generating device). The hydraulic pressure generating unit PS is applied to a braking control device SC that adjusts the wheel pressure Pw of the wheel cylinder CW to control the braking force of the wheel WH.

[0106] The hydraulic pressure generating unit PS includes an electric motor MT, a conversion mechanism GH, a control piston NC (corresponding to a "piston"), and an intermediate member BE. The electric motor MT outputs rotational power Tm. The conversion mechanism GH outputs the rotational power Tm input to the rotating member BK as linear power Fn of the linearly moving member BD. The control piston NC is inserted into a control cylinder CC (corresponding to a "cylinder"). The control piston NC increases the hydraulic pressure Pc (servo pressure) of the control cylinder CC by moving using the linear power Fn. Specifically, the control piston NC increases the servo pressure Pc by moving in the forward direction Ha (i.e., the direction toward the bottom surface Mbc of the control cylinder CC).

[0107] In the hydraulic pressure generating unit PS, the control piston NC has a first bottom portion Btn and a first cylindrical portion Enn. The intermediate member BE has a second cylindrical portion Ene and is inserted into the first cylindrical portion Enn. In the gap (nested gap) between the inner circumferential surface Min of the first cylindrical portion Enn and the outer circumferential surface Moe of the second cylindrical portion Ene, the gap Ska (proximal gap) closer to the first bottom portion Btn is narrower than the gap Skb (remote gap) farther from the first bottom portion Btn. Furthermore, at least one of the end surface Mpe (pressing surface) of the intermediate member BE that contacts the first bottom portion Btn and the end surface Mqe (middle end surface) of the intermediate member BE that contacts the linearly moving member BD is machined to a convex surface. For example, the pressing surface Mpe is machined to a convex surface, and the middle end surface Mqe is machined to a flat surface.

[0108] The intermediate member BE (particularly, the pressing surface Mpe) is in contact with the bottom Btn (particularly, the pressure-receiving surface Mtn) of the control piston NC. By setting the proximity gap Ska narrow, the position of the intermediate member BE relative to the control piston NC is appropriately determined. Furthermore, the intermediate member BE can move parallel in the radial direction Hk at least by the amount of the proximity gap Ska, thereby compensating for parallel misalignment. Furthermore, parallel misalignment is also compensated for between the intermediate member BE and the rotating member BK. Additionally, since "Skb > Ska," a sufficient swing angle about the pressing surface Mpe can be ensured. This allows for appropriate compensation for angular misalignment in addition to parallel misalignment. That is, in the hydraulic pressure generating unit PS, the positioning accuracy of the intermediate member BE is improved while the axial misalignment is appropriately compensated for.

[0109] In the hydraulic pressure generating unit PS, the rotating member BK can enter the second cylindrical portion Ene. This shortens the axial length of the hydraulic pressure generating unit PS. Furthermore, the intermediate member BE is provided with an air vent Ae (circular hole, notch, etc.) to reduce pressure changes in the gas within the intermediate member BE caused by volumetric changes in the gas within the intermediate member BE. The air vent Ae prevents expansion and compression of the gas, thereby preventing loss of lubricant (grease) from the conversion mechanism GH, etc., due to pressure fluctuations.

Claims

1. A hydraulic pressure generating device comprising: an electric motor which outputs rotational power; a conversion mechanism which outputs the rotational power input to a rotating member as linear power for a linear moving member; a piston which is inserted into a cylinder and moves by the linear power to increase the hydraulic pressure in the cylinder; and an intermediate member which is disposed between the linear moving member and the piston and is capable of sliding with the linear moving member and the piston, wherein the piston has a first bottom and a first cylindrical portion, and the intermediate member has a second cylindrical portion and is inserted into the first cylindrical portion, and in a gap between an inner circumferential surface of the first cylindrical portion and an outer circumferential surface of the second cylindrical portion, the gap at a position close to the first bottom is narrower than the gap at a position farther away from the first bottom.

2. A hydraulic pressure generating device as described in claim 1, wherein at least one of the end face of said intermediate member that contacts said first bottom portion and the end face of said intermediate member that contacts said linearly acting member is convex.

3. A hydraulic pressure generating device according to claim 1 or 2, wherein the rotating member can enter the second cylindrical portion.

4. A hydraulic pressure generating device as described in claim 3, wherein the second cylindrical portion has an air hole.

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