Valve unit for bicycle anti-lock brake systems

Abstract

Valve unit for bicycle anti-lock brake system. The valve unit (20) comprises an outer valve body (21) that defines an axially elongated inner cavity (22) from which a piston valve member (23) is slidably driven. Three stationary annular seal gaskets, namely an upstream end seal gasket (31), a downstream end seal gasket (32), and an intermediate seal gasket (33) mounted in the inner cavity (22) between the inlet port (27) and the outlet port (26), are mounted in the outer valve body within the inner cavity and slidably seal-coupled with the piston valve member (23). The outer valve body (21) does not need to provide a sliding surface for moving the seal gaskets and may be made of plastic material.

Description

Technical Field

[0001] The present invention relates to a valve unit for a hydraulic brake system for controlling the anti-lock function of the wheels of a vehicle, particularly a bicycle or an e-bike.

Background Art

[0002] An anti-lock braking system ("ABS") is equipped on a vehicle equipped with a hydraulic brake, and prevents skidding by reducing the impact of sudden stops. In an ABS brake system, each wheel of the vehicle is equipped with a brake disk and an associated phonic wheel sensor or equivalent element that rotates integrally with the brake disk. The sensor detects the rotational speed of the associated wheel, sends a signal indicating the rotational speed to an electronic control unit (ECU), and the ECU processes the received rotational signal. Each brake disk is associated with a brake caliper. A master cylinder actuated by a control device (a handlebar in the case of a bicycle) actuates the brake caliper via a corresponding hydraulic circuit, and an ABS valve unit is attached to each of the brake calipers. Each ABS valve unit controls the flow rate and pressure of the brake fluid directed towards the associated brake caliper in response to an electrical control signal from the electronic control unit. When the ECU detects a condition indicating that a wheel is about to lock, it actuates the corresponding ABS valve to reduce the hydraulic pressure of the brake of the affected wheel, reduce the braking force of this wheel, and allow the vehicle to rotate while being braked. This process is repeated continuously several times per second during braking to prevent the vehicle from skidding.

[0003] International Publication No. 2021 / 205337 discloses an ABS actuator device for a bicycle hydraulic brake system, comprising an internal cavity in which a piston valve member is slidably housed within the internal cavity, separating an upstream chamber from a downstream chamber. An inlet opening establishes fluid communication between the upstream chamber and a hydraulic master cylinder operated by a brake lever. An outlet opening connects the downstream chamber to a hydraulic slave cylinder acting on a brake caliper. The position of the piston valve member is controlled by an electric motor. During normal braking, when ABS intervention is not required, the electric motor is deactivated, and the piston valve member is at its end position toward the downstream chamber. A seal ring mounted on the floating member of the piston valve member creates an annular gap between the seal ring and the cavity wall, which communicates the upstream and downstream chambers, allowing brake fluid pressurized by the master cylinder to flow through the piston valve member toward the brake caliper. When ABS activation is required, an electric motor activates, moving the piston valve member toward the upstream chamber, causing the seal ring to engage with the reduced diameter portion of the cavity, thereby blocking fluid communication between the upstream and downstream chambers. In this state, the volume of the downstream chamber increases, and the pressure of the brake fluid supplied to the brake caliper decreases. [Overview of the Initiative]

[0004] The first object of the present invention is to provide an improved and simplified ABS valve unit that has a simplified design and is easier to manufacture and assemble.

[0005] Another specific object of the present invention is to provide a valve unit that can be manufactured more economically, comprising a valve body made of plastic material.

[0006] A further object of the present invention is to provide a valve unit having a safety function that ensures effective braking even in the event of a malfunction or loss of power in the e-bike.

[0007] In one aspect, the present invention provides a valve unit for a hydraulic brake system that controls the anti-lock function of a vehicle wheel, as defined in claim 1. Preferred embodiments are defined in the dependent claims.

[0008] In summary, the valve unit of a bicycle anti-lock hydraulic brake system comprises an outer valve body defining an inner cavity having an axially elongated shape. A piston valve member is axially slidable within the inner cavity, separating the upstream chamber from the downstream chamber within the inner cavity. The piston valve member is connectable to an electric motor for controlling its axial position along the inner cavity. An inlet port is formed in the outer valve body to establish fluid communication between the upstream chamber and the brake actuating hydraulic master cylinder. An outlet port is also formed in the outer valve body to establish fluid communication between the downstream chamber and the brake caliper operatively associated with the valve unit. The inlet and outlet ports are spaced apart from each other axially along the inner cavity. The piston valve member has a downstream end with a predetermined diameter, an upstream end, and a central portion having a smooth cylindrical surface with a diameter greater than that of the downstream end. The central portion has one or more radially narrow surfaces formed thereon, extending axially from the smooth cylindrical surface toward the upstream end. Three stationary annular seal gaskets, i) an upstream end seal gasket engaging with the upstream end, (ii) a downstream end seal gasket engaging with the downstream end, and (iii) an intermediate seal gasket mounted in the inner cavity between the inlet and outlet ports, are mounted on the outer valve body within the inner cavity. The upstream end seal gasket and the downstream end seal gasket are axially spaced apart from each other such that the inlet and outlet ports are axially positioned between the upstream and downstream end seal gaskets. The piston valve member is axially driveable between a normal braking position and at least one fluid shut-off position.In the normal braking position, the smooth cylindrical surface is axially shifted relative to the intermediate seal gasket and is not engaged by the intermediate seal gasket, which is laterally aligned with one or more radially narrow surfaces and radially spaced apart, thereby defining one or more corresponding passages between the piston valve member and the intermediate seal gasket, thereby establishing fluid communication between the downstream chamber and the upstream chamber. In at least one fluid isolation position, the piston valve member is axially shifted toward the upstream chamber, and the intermediate seal gasket engages with the smooth cylindrical surface, thereby fluidly isolating the downstream chamber from the upstream chamber.

[0009] Next, in order to better understand the present invention, some preferred embodiments of the present invention will be described as an example with reference to the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram illustrating the operation of the vehicle's anti-lock braking system. [Figure 2] Figure 2 is a longitudinal cross-sectional view of a valve unit in different operating states. [Figure 3] Figure 3 is a longitudinal cross-sectional view of a valve unit in different operating states. [Figure 4] Figure 4 is a longitudinal cross-sectional view of a valve unit in different operating states. [Figure 5] Figure 5 is a magnified view of a portion of Figure 4, showing further details. [Figure 6] Figure 6 is an enlarged cross-sectional view of the piston valve member of the valve unit shown in Figures 2 to 5. [Figure 7] Figure 7 is a magnified view of the details of Figure 2. [Modes for carrying out the invention]

[0011] Referring first to Figure 1, the anti-lock braking system (ABS) comprises wheel rotation sensors 10 mounted on multiple wheels of the vehicle (in this example, an e-bike). Each of the multiple wheels comprises a brake disc (not shown) and an associated brake caliper 11, which applies braking force to brake pads on the caliper via a hydraulic brake circuit 15, thereby generating a braking torque acting on the wheel. A hand lever 12 operates a hydraulic master cylinder 12 for generating and controlling pressure in the hydraulic brake circuit 15. A pressure sensor 14 detects the brake fluid pressure in the hydraulic circuit. The rotation sensor 10 detects the rotational speed of the associated wheel and sends a signal indicating the rotational speed to a brake control unit (BBCU) 16, which is an electronic unit that receives and processes signals from the rotation sensor 10 and the pressure sensor 14. The electrical signal from the pressure sensor 14 is sent to the BBCU 16 via line 9.

[0012] Each brake caliper is fitted with an ABS valve unit 20. Each ABS valve unit controls the flow rate and pressure of brake fluid to the associated brake caliper in response to an electrical control signal from the brake control unit 16. When the BBCU detects a condition indicating that a wheel is about to lock up, it activates the corresponding ABS valve unit to reduce the hydraulic pressure of the brake on the affected wheel, thereby reducing the braking force on that wheel and allowing the vehicle to rotate while remaining braked. This process is repeated continuously several times per second during braking to prevent the vehicle from skidding.

[0013] Referring to Figure 2, each ABS valve unit 20 comprises an outer valve body (or housing) 21 defining an inner cavity 22 having an axially elongated shape. A piston valve member 23 is axially slidable within the inner cavity, separating the upstream chamber 25 from the downstream chamber 24. The outer valve body 21 forms an inlet port 27 that establishes fluid communication between the upstream chamber 25 and a hydraulic master cylinder 13 operated by the brake lever 12. An outlet port 26 fluidly connects the downstream chamber 24 to a single brake caliper 11 associated with the valve unit 20. The inlet port 27 and the outlet port 26 are axially spaced apart from each other along the inner cavity 22. In this context, the terms “upstream” and “downstream” refer to the flow of brake fluid from the master cylinder to the brake caliper.

[0014] An electric motor 28, fixed to the outer valve body 21, controls the axial position of the piston valve member 23. The electric motor 28 drives a rotary output shaft 29, which is coupled to the piston valve member 23 via a rotation-to-linear motion conversion mechanism 30 that converts the rotational motion of the rotary shaft into a linear displacement of the piston valve member 23 within the inner cavity 22. The mechanism 30 may include a screw connection. The electric motor 28 is energized and controlled by a BBCU 16 via line 8. The BBCU 16 receives power from a battery (not shown) via line 7.

[0015] The electric motor may be equipped with a position sensor for detecting the angular position of the output shaft 29, thereby detecting the axial position of the piston valve member 23.

[0016] According to one embodiment, the first or upstream hollow tubular insert 35 is fitted into the inner cavity 22 and engages with two seal gaskets in the outer valve body 21, providing an axial passage for guiding the upstream end 231 of the piston valve member 23, and is shaped to establish fluid communication between the upstream chamber 25 and the inlet port 27.

[0017] Attached to the outer valve body 21 within the inner cavity 22 are three stationary annular seal gaskets 31-33 that slidably seal-engage with the piston valve member 23. The first end (or upstream end) seal gasket 31 and the second end (or downstream end) seal gasket 32 ​​are spaced axially apart from each other so that the inlet port 27 and the outlet port 26 are axially located between the upstream end seal gasket 31 and the downstream end seal gasket 32. A third intermediate seal gasket 33 is installed within the inner cavity between the inlet port 27 and the outlet port 26. No seal gaskets are attached to the piston valve member 23.

[0018] The third intermediate seal gasket 33 can fluidly separate the downstream chamber 24 and the upstream chamber 25, and depending on the axial position of the piston valve member 23, it can open and close the passage between the piston valve member and the inner cavity, thereby establishing fluid communication between the downstream chamber 24 and the upstream chamber 25, or sealing and separating the upstream chamber from the downstream chamber to temporarily block fluid communication between the outlet port 26 and the inlet port 27.

[0019] According to one embodiment, the second or downstream hollow tubular insert 36 is fitted into the inner cavity 22 and fits into the downstream seal gasket 32 ​​within the outer valve body 21, and is shaped to provide an axial passage for guiding the downstream end 232 of the piston valve member 23.

[0020] The upstream chamber 25 communicating with the inlet port 27 is defined between the upstream end seal gasket 31 and the intermediate seal gasket 33. The downstream chamber 24 communicating with the outlet port 26 is defined between the downstream end seal gasket 32 and the intermediate seal gasket 33.

[0021] The upstream hollow tubular insert 35 and the downstream hollow tubular insert 36 are sealingly coupled to the outer valve body 21 by a number of static seal rings such as O-rings 39 acting on the interface between each insert and the inner cavity 22.

[0022] The piston valve member 23, in which the intermediate seal gasket 33 can exert a sliding or dynamic sealing action, may be made of metal, such as an aluminum alloy, or other suitable rigid materials, such as thermosetting plastic materials. The outer valve body 21 has the problem of stably accommodating the seal gasket, but the wall of the inner cavity 22 also does not have the problem of functioning as a smooth sliding surface of the gasket that can withstand high pressure without significant deformation. As a result, the outer valve body may be conveniently made of a relatively inexpensive thermoplastic material, such as PA66GF30, PA66GF50, PA6, PA66CF30.

[0023] According to the exemplary embodiment shown in FIG. 2, the outer valve body 21 is formed as a substantially tubular body having axially opposed open ends and a radially thick central wall portion 211 in which the outlet port 26 may be formed.

[0024] As shown in the embodiment of FIG. 2, the radially thick central wall portion 211 forms an upstream cross-section 212, and the intermediate seal gasket can be stably held at a predetermined position between the central wall portion 211 and the upstream hollow tubular insert 35 with respect to the upstream cross-section 212.

[0025] Preferably, the upstream seal gasket 31 is stably housed in an annular seat formed by an upstream end hollow tubular insert 35 and an upstream end plug 38 which can be used to close the upstream open end of the outer valve body 21 and slidably accommodate the upstream end 231 of the piston valve member 23.

[0026] According to a preferred embodiment, the downstream seal gasket 32 ​​may be stably housed within an annular sheet formed by a downstream end hollow tubular insert 36 and a downstream cross section 213 formed by a radially thick central wall portion 211 on the opposite side of the upstream cross section 212.

[0027] Preferably, each of the three stationary annular seal gaskets 31 to 33 has a corresponding conical lip designed to elastically engage radially with the corresponding surface of the piston valve member 23. The conical lip of the upstream end seal gasket 31 tapers toward the upstream chamber 25, while the conical lip of the downstream end seal gasket 32 ​​tapers toward the downstream chamber 24.

[0028] Preferably, the conical lip of the intermediate seal gasket 33 tapers towards the upstream chamber 25.

[0029] The piston valve member 23 has a central portion 233 having a smooth cylindrical surface 235 with a diameter D3 and one or more radially narrow surfaces 234 extending axially from the cylindrical surface 235 toward the upstream end of the piston valve member. The one or more radially narrow surfaces 234 are configured to define one or more corresponding passages 236 between the piston valve member 23 and the intermediate seal gasket 33 in a particular operating state of the valve unit.

[0030] According to one embodiment, as shown in Figure 6, the multiple radially narrow surfaces 234 may be provided in the form of grooves that extend axially and are arranged at equal intervals in the circumferential direction.

[0031] According to a preferred embodiment, the piston valve member 23 has a central portion 233 located substantially in the center along its axial length.

[0032] The downstream end 232 of the piston valve member 23 has a diameter D2 that is smaller than the diameter D3 of the central portion 233.

[0033] Preferably, the upstream end 231 of the piston valve member 23 has a diameter D1 that is smaller than the diameter D3 of the central portion 233.

[0034] More preferably, the upstream end 231 of the piston valve member 23 has a diameter D1 that is smaller than the diameter D2 of the downstream end 232.

[0035] Optionally, the brake control unit 16 (BBCU) may have an integrated inertial measurement unit (IMU) as shown in 6 that detects the acceleration and attitude of the e-bike. Based on these measurements, the BBCU can energize an electric motor to control the position of the piston valve member 23, activating the valve unit to prevent the bicycle from tipping over when the rider brakes excessively on high-friction surfaces, and to prevent the controlled wheel from locking when the rider brakes on low-friction surfaces.

[0036] The following describes exemplary operating modes of the ABS valve, namely the normal brake operation mode, the fluid shut-off state, and the pressure regulation operation mode.

[0037] During normal operation of a bicycle hydraulic brake, the ABS valve is in a standby state (Figure 2). The piston valve member 23 is retracted toward the downstream chamber 24 in the starting position. In this position, the free end of the conical lip of the intermediate seal gasket 33 is in an open position (Figure 7) where the smooth cylindrical surface 235 is axially shifted relative to the intermediate seal gasket 33 and is not locked by the intermediate seal gasket 33. In this open position or normal operating position, the intermediate seal gasket 33 is aligned laterally with one or more radially narrow surfaces 234 and radially spaced apart. As a result, one or more corresponding passages 236 defined between the piston valve member 23 and the intermediate seal gasket 33 establish fluid communication between the downstream chamber 24 and the upstream chamber 25, and therefore between the master cylinder and the brake caliper.

[0038] During normal brake operation, the piston valve member 23 remains in this retracted passive position, and the brake fluid pumped by the brake lever 12 can flow from the inlet port 27 to the outlet port 26 through the passage or groove 234 and then to the brake caliper 11 without any interference of any kind from the ABS system. In this operating mode, the BBCU control unit 16 constantly monitors the hydraulic system pressure, the wheel angular velocity, and optionally information from the IMU. The control algorithm processes this information and decides to switch to one of the remaining operating modes listed.

[0039] When a wheel locks up during braking, or an imminent rollover or other loss of control is detected during braking, the BBCU 16 energizes the control motor 28 of the wheel in question, sliding the associated piston valve member attached to that wheel from its initial non-operating position in Figure 2 toward the upstream chamber 25 (Figure 3). The piston valve member 23 reaches a position axially shifted toward the upstream chamber 25, where the free end of the conical lip of the intermediate seal gasket 33 is closed and seals with the smooth cylindrical surface 235 of the central portion 233 of the piston valve member 23. In this position of the piston valve member (Figure 3), the intermediate seal gasket 33 fluidly isolates the downstream chamber 24 from the upstream chamber 25. As a result, fluid communication between the master cylinder and the brake caliper is temporarily interrupted.

[0040] This fluid shutoff state is transient because the electric motor 28 further drives the piston valve member into the upstream chamber 25 (Figure 4). Since the downstream end 232 of the piston valve member 23 has a diameter D2 smaller than the diameter D3 of the central portion 233 (Figure 5), the volume of the downstream chamber 24 increases as the piston valve member 23 moves toward or further into the upstream chamber 25, thereby instantaneously releasing the pressure of the brake fluid communicating with the brake caliper.

[0041] According to the pressure adjustment operation mode, the BBCU16 controls the electric motor 28 to repeatedly reciprocate the piston valve member 23 several times per second during braking, thereby the position of the piston valve member 23 is The intermediate seal gasket 33 seals the downstream chamber 24 from the upstream chamber 25, as shown in the fluid isolation state in Figure 3. The intermediate seal gasket 33 still seals the downstream chamber 24 from the upstream chamber 25, but the piston valve member 23 is further inside the upstream chamber, which increases the volume in the downstream chamber 24 and decreases the pressure, as shown in Figure 4. It performs linear reciprocating motion between these points.

[0042] As a result, the braking torque intermittently transmitted to the brake caliper prevents the wheels from locking up, i.e., preventing the vehicle from rolling over.

[0043] During the pressure adjustment operation mode, the downstream chamber 24 remains fluidly separated or sealed from the upstream chamber 25, which means that the master cylinder cannot exert any effect on the brake caliper.

[0044] The BBCU detects, via a hydraulic sensor, that the pressure in the downstream chamber has fallen below a predetermined threshold, sends a control signal to the electric motor 28, returns the piston valve member 23 to its starting position (Figure 2), and controls the electric motor and piston valve member in pressure adjustment mode until it switches to the normal operating mode of the ABS valve.

[0045] The design and positioning of the intermediate seal gasket 33 ensure that the fluid barrier or sealing action it provides is maintained as long as the pressure in the upstream chamber 25 is greater than or equal to the pressure in the downstream chamber 24. Conversely, when the pressure in the upstream chamber 25 falls below the pressure in the downstream chamber 24, as occurs when the rider releases the brake lever, the intermediate seal gasket 33 allows brake fluid to flow back from the downstream chamber 24 to the upstream chamber 25. This function prevents braking torque from being applied to the brake caliper even when the rider releases the brake.

[0046] The algorithm manages the omniaxial movement of the piston until the intermediate seal gasket is positioned as shown in Figure 3 and the brake caliper reaches a shut-off operating mode in which it is fluidly shut off from the master cylinder. If this state is still insufficient to effectively control braking, the algorithm acts to adjust the pressure in the downstream chamber according to the pressure adjustment operating mode described above.

[0047] As an alternative to the pressure adjustment operating mode described above, the valve unit 20 may be controlled in a more conventional operating mode. According to the alternative operating mode, when a critical (sideslip or rollover) braking condition is detected, the BBCU energizes the electric motor 28 to drive the piston valve member 23 from its initial position in Figure 2 to the sealed or shut-off position in Figure 4, where the pressure in the hydraulic circuit between the intermediate seal gasket 33 and the brake caliper is released. As soon as the BBCU detects through the hydraulic sensor that the pressure in the downstream chamber has fallen below a predetermined threshold, it sends a control signal to the electric motor 28, causing the piston valve member 23 to return to its starting position (Figure 2), thereby restarting the flow of brake fluid through the passage or groove 234 and temporarily re-establishing direct fluid communication between the master cylinder and the brake caliper. If the BBCU detects that the critical braking condition persists, it immediately drives the piston valve member to the sealed or shut-off position in Figure 4, opening and closing the passage 234. This process is repeated several times per second during braking to prevent the vehicle from skidding.

[0048] The arrangement of the diameters D3>D2>D1 of the parts 233, 232, and 231 of the piston valve member 23 also provides a favorable safety failure condition. If power supply to the electric motor 28 is lost while the piston 23 is in the position shown in Figure 4, although the intermediate seal gasket 33 fluidly isolates the master cylinder from the brake caliper, the piston valve member 23 moves toward the downstream chamber 24 (to the right) until the passage 234 is reopened, because the diameter D3 of the central part 233 is wider than the diameter D1 of the upstream end 231.

[0049] Preferably, the diameter D2 of the downstream end 232 is greater than the diameter D1 of the upstream end 231. As a result, as soon as the passage 234 is opened again, the same hydraulic pressure is present in both the downstream and upstream chambers, effectively biasing the piston valve member 23 to move toward the downstream chamber 24 (to the right). This is because the area of ​​the annular section demarcated by diameters D1 and D3 (on the upstream chamber side) is greater than the area of ​​the annular section demarcated by diameters D2 and D3 (on the downstream chamber side). Consequently, the hydraulic pressure acting on both sides of the piston valve member 23 provides a net axial force that pushes the piston valve member 23 further toward the downstream chamber 24, reaching the position shown in Figure 2. As a result, the valve unit always ensures sufficient braking torque so that the vehicle can stop at a reasonable stopping distance, even in the event of an electrical failure.

[0050] While specific embodiments of the present invention have been disclosed, it should be understood that such disclosures are for illustrative purposes only and do not limit the present invention in any way. Various modifications will be apparent to those skilled in the art in consideration of the aforementioned examples. The scope of the present invention is limited only by the appended claims.

Claims

1. A valve unit (20) for a bicycle anti-lock hydraulic brake system, wherein the valve unit is An outer valve body (21) defines an inner cavity (22) having an elongated shape in the axial direction, A piston valve member (23) is housed axially slidably within the inner cavity (22) and separates the upstream chamber (25) from the downstream chamber (24) within the inner cavity (22), wherein the piston valve member (23) is connectable to an electric motor (28) for controlling the axial position of the piston valve member (23) along the inner cavity (22), In order to establish fluid communication between the upstream chamber (25) and the brake operating hydraulic master cylinder (13), an inlet port (27) is formed in the outer valve body (21), To establish fluid communication between the downstream chamber (24) and the brake caliper (11) operably associated with the valve unit (20), an outlet port (26) is formed in the outer valve body (21), wherein the inlet port (27) and the outlet port (26) are spaced apart from each other axially along the inner cavity (22), Here, the piston valve member (23) has a downstream end (232) having a diameter (D2), an upstream end (231), and a central portion (233) having a smooth cylindrical surface with a diameter (D3) and one or more radially narrow surfaces (234) extending axially from the smooth cylindrical surface (235) toward the upstream end (231), wherein the diameter (D3) of the central portion (233) is greater than the diameter (D2) of the downstream end (232). Three stationary annular seal gaskets (31, 32, 33) are attached to the outer valve body (21) within the inner cavity (22) and slidably seal-engage with the piston valve member (23), wherein the three stationary annular seal gaskets (31, 32, 33) are, (i) Upstream end seal gasket (31) that engages with the upstream end (231), (ii) A downstream end seal gasket (32) that engages with the downstream end (232), wherein the upstream end seal gasket (31) and the downstream end seal gasket (32) are spaced apart from each other in the axial direction such that the inlet port (27) and the outlet port (26) are located in the axial direction between the upstream end seal gasket (31) and the downstream end seal gasket (32), and (iii) An intermediate seal gasket (33) installed in the inner cavity (22) between the inlet port (27) and the outlet port (26). The three static annular seal gaskets (31, 32, 33) include and Equipped with, The piston valve member (23) is The normal braking position is such that the smooth cylindrical surface (235) is axially shifted relative to the intermediate seal gasket (33) and is not engaged by the intermediate seal gasket (33), and the intermediate seal gasket (33) is laterally aligned with one or more radially narrow surfaces (234) and radially spaced apart, thereby defining one or more corresponding passages (236) between the piston valve member (23) and the intermediate seal gasket (33), thereby establishing fluid communication between the downstream chamber (24) and the upstream chamber (25), and At least one fluid shut-off position in which the piston valve member (23) is axially shifted toward the upstream chamber (25) and the intermediate seal gasket (33) engages with the smooth cylindrical surface (235), thereby fluidly shutting off the downstream chamber (24) from the upstream chamber (25), and A valve unit that can be driven axially between.

2. The valve unit according to claim 1, wherein the outer valve body (21) defining the inner cavity (22) is made of a plastic material.

3. The valve unit according to claim 1 or 2, wherein the upstream end (231) of the piston valve member (23) has a diameter (D1) smaller than the diameter (D3) of the central portion (233).

4. The valve unit according to claim 3, wherein the diameter (D2) of the downstream end (232) is greater than the diameter (D1) of the upstream end (231).

5. The valve unit according to any one of claims 1 to 4, wherein the intermediate seal gasket (33) has a conical lip that tapers toward the upstream chamber (25).

6. The valve unit according to claim 1, wherein the one or more radially narrow surfaces (234) are provided with a plurality of grooves that extend in the axial direction and are spaced apart in the circumferential direction.

7. The outer valve body (21) is formed as a substantially tubular body having axially opposed open ends and a radially thick central wall portion (211) that provides a cross-section (212) facing the upstream chamber (25). The upstream hollow tubular insert (35) is fitted into the inner cavity (22) and provides an axial passage for accommodating the upstream end (231) of the piston valve member (23). The valve unit according to claim 1, wherein the intermediate seal gasket (33) is stably held in the axial position between the central wall portion (211) and the upstream hollow tubular insert (35).

8. The valve unit is configured such that the piston valve member (23) can be driven to perform linear reciprocating motion according to the pressure adjustment operating mode, and to repeatedly and alternately reach two fluid shut-off positions that are relatively displaced in the axial direction, and the two fluid shut-off positions are The first fluid shut-off position is such that the piston valve member (23) is shifted axially toward the upstream chamber (25), and the intermediate seal gasket (33) engages with the smooth cylindrical surface (235), thereby fluidly shutting off the downstream chamber (24) from the upstream chamber (25), A second fluidic shutoff position in which the piston valve member (23) is further shifted axially toward and into the upstream chamber (25), and the intermediate seal gasket (33) engages with the smooth cylindrical surface (235), thereby fluidly shutting off the downstream chamber (24) from the upstream chamber (25). A valve unit according to any one of claims 1 to 8, including the valve unit according to any one of claims 1 to 8.

9. The valve unit is configured such that the piston valve member (23) can be driven to perform linear reciprocating motion according to the operating mode, and to repeatedly and alternately reach two positions that are relatively displaced in the axial direction, and the two positions are The normal braking position, in which the smooth cylindrical surface (235) is axially shifted relative to the intermediate seal gasket (33) and is not engaged by the intermediate seal gasket (33), and the intermediate seal gasket (33) is laterally aligned with one or more radially narrow surfaces (234) and radially spaced apart, thereby defining one or more corresponding passages (236) between the piston valve member (23) and the intermediate seal gasket (33), thereby establishing fluid communication between the downstream chamber (24) and the upstream chamber (25), The at least one fluid shut-off position wherein the piston valve member (23) is shifted axially toward the upstream chamber (25), and the intermediate seal gasket (33) engages with the smooth cylindrical surface (235), thereby fluidly shutting off the downstream chamber (24) from the upstream chamber (25), and A valve unit according to any one of claims 1 to 7, including the valve unit according to any one of claims 1 to 7.

10. A bicycle anti-lock hydraulic brake system comprising a valve unit (20) according to any one of claims 1 to 9.

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