Anti-lock braking unit for hydraulic braking systems, in particular for bicycles

Abstract

The invention relates to an anti-lock braking unit comprising a single actuating solenoid (31) acting on a piston (40) of an associated valve unit (30). The solenoid moves the piston within a primary chamber (38) in fluid communication with the brake caliper. Movement of the piston closes a bypass passage (50) formed within the valve unit, which under normal circumstances connects the master cylinder to the brake caliper. By closing the bypass passage (50), the pressure acting on the brake caliper stops building up. At the same time, the same actuating movement of the piston (40) opens an outflow passage within the valve unit, allowing brake fluid to be discharged from the primary chamber (38) into an expansion chamber. The expansion chamber gives the brake fluid contained between the valve unit (30) and the brake caliper an enlarged volume, thereby reducing the pressure of the brake fluid acting on the brake caliper.

Description

Technical Field

[0001] This invention relates to a valve system for controlling the anti-lock braking function of wheels, particularly but not limited to bicycle wheels. Background Technology

[0002] Bicycles equipped with hydraulic brakes are fitted with an anti-lock braking system (ABS) to prevent skidding or loss of control by mitigating the effects of sudden stopping. In these systems, a master cylinder actuated by the handlebars activates the brake calipers via hydraulic lines. The calipers convert fluid pressure into a normal force between the brake pads and the brake discs. The ABS unit includes hydraulic valves that control the flow and pressure of brake fluid delivered to the calipers. The operation of the ABS unit is controlled by an electronic control unit (ECU) in response to signals from speed sensors mounted on the bicycle wheels. When the ECU detects an indication that the wheels are about to lock up, it activates the valves to reduce the hydraulic pressure at the affected wheel, thereby reducing the braking force on that wheel and allowing the wheel to spin faster. This process is repeated continuously during braking, several times per second, to prevent the bicycle from skidding.

[0003] Patent document DE 101 58 382A1 discloses an anti-lock braking system for bicycles, including a hydraulic master cylinder and a slave cylinder integrated into a hydraulic actuator, which forms a compact hydraulic closed unit with an outlet valve, a check valve, and a low-pressure hydraulic reservoir. The system also includes an electronic controller, at least one wheel brake, at least one speed sensor, and the hydraulic actuator, whose low-pressure hydraulic reservoir is connected to a drain valve and an isolation valve. The check valve is connected in parallel with the drain valve, and the hydraulic slave cylinder is connected downstream of the isolation valve and the drain valve.

[0004] Patent document EP 3 392 105 A2 (corresponding to WO 2017 / 115171 A2) discloses a hydraulic braking system for a bicycle, comprising two electric valve units. Each valve unit operates independently of the others via its own electric actuator. The first valve unit locks the brake fluid between the master cylinder and the brake caliper, and the second valve unit opens a parallel channel that hydraulically connects the brake caliper to an accumulator. The two electric actuators are individually energized by an ECU in a redefined sequence. The two valve units are located on parallel branches of a hydraulic circuit that connects the handlebar-actuated master cylinder to the brake caliper. During normal braking, the first valve unit is open, allowing direct fluid communication between the master cylinder and the brake caliper, while the second valve unit is closed. Under emergency braking conditions, when the wheel approaches lock-up, the first electric actuator closes the first valve unit, thereby stopping the inlet pressure from the handlebars and locking the pressure from the first valve unit to the brake caliper, preventing further pressure buildup on the brake caliper. The second electric actuator opens the second valve unit, allowing pressure to be released into the accumulator located upstream of the second valve unit in the parallel channel. As a result, the pressure on the brake caliper decreases, and the brake unlocks.

[0005] Other known ABS systems include valve units containing pistons mounted within hydraulic lines. These pistons are controlled by an electric motor, causing them to move back and forth to change the volume within the hydraulic lines, thereby regulating the pressure in the braking circuit. Summary of the Invention

[0006] In view of the above background, the main objective of this invention is to provide an improved bicycle ABS system with structural and cost-saving advantages. Another objective of this invention is to provide a lightweight and compact ABS system. A specific objective of this invention is to use a single valve unit that requires only a single electric solenoid to control the braking lock / unlock sequence when necessary.

[0007] Another object of the present invention is to provide a different type of single valve that requires only a single electric actuator. This offers potential benefits in terms of power consumption and also reduces the complexity, cost, and weight of mechanical and electrical / electronic components.

[0008] According to one aspect, the present invention provides an anti-lock braking unit for hydraulic braking systems, particularly for bicycle hydraulic braking systems.

[0009] In summary, the anti-lock braking system (ABS) comprises a single actuation solenoid acting on an associated piston of a single associated valve unit. This solenoid moves the piston within a primary chamber, which is in fluid communication with the brake caliper. The piston's movement closes a bypass passage formed within the valve unit, which normally connects the master cylinder to the brake caliper. By closing the bypass passage, the pressure acting on the brake caliper stops accumulating. Simultaneously, the same actuation movement of the piston opens an outflow passage within the valve unit, allowing brake fluid to drain from the primary chamber into the expansion chamber. The expansion chamber provides increased volume for the brake fluid contained between the valve unit and the brake caliper, thereby reducing the pressure exerted by the brake fluid on the brake caliper.

[0010] According to another aspect, the present invention provides a valve unit.

[0011] According to another aspect, the present invention provides an anti-lock braking system, including an anti-lock braking unit.

[0012] According to another aspect, the present invention relates to a vehicle, such as a bicycle, including the aforementioned anti-lock braking system. Attached Figure Description

[0013] To clearly understand the present invention, several preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0014] In the picture:

[0015] Figure 1 A schematic diagram of the main components of a bicycle ABS system;

[0016] Figure 2 This is a cross-sectional schematic diagram of an ABS unit and its components;

[0017] Figure 3 This is a circuit diagram of the hydraulic system.

[0018] Figure 4 This is a schematic diagram of a hydraulic braking system in the brake-off state.

[0019] Figure 5 This is a schematic diagram of a hydraulic braking system during manual braking.

[0020] Figure 6 This is a schematic diagram of a hydraulic braking system under reduced braking pressure.

[0021] Figures 7 to 13 Axial cross-sectional views of the valve unit shown under different operating conditions. Detailed Implementation

[0022] Before detailing the embodiments of the present invention, it should be understood that the present invention is not limited to the structural details and component arrangements set forth in the following description of the drawings or specific embodiments. The present invention may include other embodiments and can be practiced or implemented in various ways. It should also be understood that the wording and terminology used herein are for descriptive purposes and should not be construed as limiting. The use of "comprising" and "including" and variations thereof should be understood to cover all items listed below and their equivalents and additions and their equivalents.

[0023] First refer to Figure 1 This invention can be applied, for example, to a bicycle 10, which has a hydraulic brake and an anti-lock braking system (ABS). A handlebar 11 is associated with a master cylinder 12, which converts the rider's hand force into fluid pressure. An ABS unit 13 controls the flow and pressure of hydraulic fluid to the front wheel brake caliper 14 in response to signals from speed sensors 15 and 16. The front wheel speed sensor 15 measures the rotational speed of the front wheel 7, for example, by sensing the movement of a groove in the adjacent brake disc 19. The rear wheel speed sensor 16 measures the rotational speed of the rear wheel 18, for example, by sensing the movement of a groove in the adjacent brake disc 20. Sensor wiring 21 relays the speed signals from the speed sensors to the ABS unit 13. A hydraulic line 22 transmits pressurized fluid between the master cylinder, the ABS unit, and the brake caliper. The brake caliper converts the fluid pressure into a normal force between the brake pads and the brake disc. The brake caliper also reacts to the sliding force on the brake pads, thereby generating braking torque on the brake disc.

[0024] Although this disclosure specifically illustrates an exemplary embodiment of providing anti-slip control for the front wheel of a bicycle, the system can also be applied to the rear wheel of a bicycle.

[0025] Figure 2 The main components of ABS unit 13 are schematically depicted. First, refer to... Figures 2 to 6 This describes the overall operation of the ABS unit. (Refer to...) Figures 7 to 13 This describes the structural and functional characteristics of the hydraulic valve unit.

[0026] The ABS unit 13 includes a housing 23, which includes a hydraulic valve unit 30 for controlling the flow and pressure of brake fluid transmitted to the brake caliper.

[0027] Housing 23 contains electronic and mechanical components and provides environmental protection for the internal components. Housing 23 may also provide mounting hardware (not shown) for securely attaching the ABS unit to a bicycle or e-bike.

[0028] The hydraulic housing may enclose the spool valve 24, check valve 69, accumulator 81, and valve body 32, for example, in which chambers and pipes are machined. Channels or pipes may also be machined within the body and housing to suitably connect the hydraulic components. A hydraulic connection inlet port 37 and outlet port 36 are also machined within the housing, allowing hydraulic lines to be connected to the master cylinder and brake caliper.

[0029] The spool valve includes a sliding piston 40 slidably housed within the valve body 32 (e.g., Figure 7 (See details below). As described below, the longitudinal movement of piston 40 within valve body 32 connects internal pipes and chambers to provide hydraulic functionality to the ABS unit.

[0030] The sliding piston has two positions: in the first position, or position 0, the hydraulic lines to the master cylinder and brake caliper are directly connected, while the line to the accumulator is closed; in the second position, or position 1, the line to the master cylinder is closed, while the lines to the brake caliper and accumulator are in fluid communication with each other. In the intermediate position between position 0 and position 1, all line connections are closed simultaneously. The sliding piston is spring-loaded to position 0. A magnet or magnetic feature 78 at one end of the valve core 24 interacts with a magnetic field generated by the actuating solenoid 31, which, when energized, forces the valve against its spring into position 1.

[0031] When no electromagnetic force is acting on the sliding element, the return spring 57 moves the piston 40 to position 0. The accumulator 81 includes a spring-loaded piston 61 surrounding the hydraulic chamber. The accumulator 81 absorbs pressurized hydraulic fluid by deflecting the spring. The volume behind the piston 61 of the accumulator can be open to the atmosphere to allow piston movement without generating reaction air pressure.

[0032] When the pressure in the master cylinder is higher than the pressure in the accumulator, the check valve 69 can close. When the pressure in the master cylinder is lower than the pressure in the accumulator, the valve opens to allow fluid stored in the accumulator cylinder to flow back to the master cylinder.

[0033] The Electronic Control Unit (ECU) powers the actuating solenoid 31. The ECU includes: a circuit board 84, a microcontroller 85 attached to the circuit board 84, input / output devices connected to the microcontroller, a connection mechanism to an external electrical connector 83, a pressure sensor 86, a connection mechanism 87 to the actuating solenoid 31, and a solid-state switching device that allows switching of current within the solenoid winding. In a preferred embodiment, all components of the ECU are housed within the housing 23 of the ABS unit 13.

[0034] The real-time control system can be loaded into the flash memory of a microcontroller, which controls the current in the solenoid and the position of the spool valve. This allows the ABS unit to control the connections between hydraulic lines according to the operational objectives of the ABS system.

[0035] The actuation solenoid 31 applies a magnetic force to the slide valve, causing it to move from position 0 to position 1. The winding of the solenoid can be directly connected to the ECU circuit board 84.

[0036] Pressure sensor 86 can be connected to the brake caliper port (not shown) via a pipe in the hydraulic housing, allowing it to measure the hydraulic pressure in the brake caliper. The pressure sensor can also be directly connected to the ECU circuit board.

[0037] Electrical connector 83 allows the ECU circuit board to be robustly connected to the wiring harness, which provides power to the circuit board and connects the ECU to the speed sensor.

[0038] Depending on the handle position and piston status, the hydraulic piping connection within the ABS unit allows for three functional braking states. Please refer to [link to hydraulic circuit connection details] for more information. Figure 3 The three possible braking states are as follows: Brake closed ( Figure 4 Manual braking () Figure 5 ), braking pressure decreased ( Figure 6 ).

[0039] With the brake off, the handle is not activated, and the one-way valve ( Figure 4 The fluid is discharged into the main cylinder reservoir, allowing all the pressure in the system to be released.

[0040] In "manual braking" mode, the handle is activated, and pressure is directly transmitted to the brake caliper. The electric solenoid is not activated. The check valve is closed, preventing hydraulic fluid from entering the accumulator from the master cylinder. Figure 5 ).

[0041] When the ECU detects that the front wheel is starting to slip or that the bicycle is at risk of tipping over, a "reduced brake pressure" situation occurs; the electric solenoid activates, and the spool valve moves against its spring. Fluid flow in the master cylinder is obstructed, allowing pressure in the brake caliper to escape into the accumulator cylinder until the pressure in the brake caliper becomes equal to the pressure generated by the accumulator spring force acting on the accumulator piston. Figure 6 ).

[0042] During braking on a slippery surface, the ECU detects front wheel slippage and energizes the electric solenoid (the system changes from manual braking to reduced braking pressure). Once traction is regained, the current to the solenoid is cut off, and the system returns to manual braking.

[0043] Now refer to Figures 7 to 13In a specific exemplary embodiment, reference numeral 30 denotes a valve unit for an anti-lock braking system on the front wheel of a bicycle. The valve unit 30 defines a longitudinal axis x, which is defined herein as having an elongated shape in the longitudinal or axial direction. As used herein, terms such as “longitudinal” and “lateral” will be interpreted relative to the axis x.

[0044] The valve unit 30 includes a linear electric actuator that acts in the longitudinal direction “B” and a valve body 32 made of plastic material integrated with and longitudinally aligned with the electric actuator. As shown in the example, the electric actuator and the valve body 32 can be connected by a threaded coupler 33.

[0045] The valve body 32 has various shapes. In this example, the valve body 32 is generally cylindrical, with one end 34 fixed to the electric actuator and the other end 35.

[0046] The opposite end 35 of the valve body 32 forms an outlet port (or output port) 36 for hydraulically connecting to the brake caliper 14 of the bicycle front wheel brake and for hydraulically connecting to the master cylinder 12. Figure 3 The master cylinder 12 is operatively associated with an actuation lever on the bicycle handlebar 11 via its inlet port 37.

[0047] The valve body 32 forms a primary chamber 38 and an expansion chamber 39 or a secondary hydraulic chamber. The primary chamber 38 is directly connected to the outlet port 36 and receives a piston 40 operated longitudinally by an electric actuator. Figure 13 As shown, the primary chamber 38 forms a first portion 42 with a diameter D1 (closer to the outlet port 36), a second portion 43 with a diameter D2 greater than that of diameter D1, and a third portion 44 with a diameter D3 less than that of diameter D1 (closer to the actuator).

[0048] The piston 40 includes a terminal portion 45 received in a first portion 42 of the primary chamber 38, a middle portion 46 received in a second portion 43 of the primary chamber 38, and a proximal portion 47 received in a third portion 44 of the primary chamber 38.

[0049] The piston 40 has an end sealing gasket 48 at its terminal portion 45 that slidably contacts the first portion 42 of the primary chamber 38. The intermediate portion 46 has an intermediate sealing gasket 49 that engages the second portion 43 of the primary chamber 38. The proximal portion 47 has a proximal sealing gasket 52 that engages the third portion 44 of the primary chamber 38.

[0050] The piston 40 forms a longitudinal cavity 53 that extends through the piston between the end face 54 of the piston's end portion 45 facing the outlet port 36 and a transverse channel 55 opening on the side of the piston. Preferably, the transverse channel 55 opens in the second portion 43 of the primary chamber 38.

[0051] The longitudinal cavity 53 houses a primary spring 57, in this example a compression spring, which elastically compresses between the piston shoulder 56 and the transverse wall 58 of the primary chamber, near the outlet port 36. The primary spring 57 pushes the piston 40 toward the actuator (in the direction of arrow A).

[0052] For structural reasons, piston 40 can be mechanically connected to longitudinally movable pin 59 of actuator via connector 60, which is generally Z-shaped or L-shaped in the exemplary embodiment shown in this figure.

[0053] A first bypass passage 50 is formed in the valve body 32 of the valve unit and opens on the first portion 42 of the primary chamber 38, allowing the primary chamber to be in fluid communication with the inlet port 37. An outlet passage 51 is formed in the valve body 32 of the valve unit and opens on the second portion 43 of the primary chamber 38, allowing the primary chamber to be in fluid communication with the expansion chamber 39.

[0054] The expansion chamber 39 houses a floating valve 61 with a sealing gasket 62 that engages the cylindrical portion 63 of the expansion chamber 39 in a longitudinally slidable manner. The floating valve 61 is movable within the expansion chamber 39 between a shoulder 64 formed toward the opposite end 35 of the valve body 32 and a transverse wall 65 arranged toward the actuator.

[0055] The outflow channel 51 opens longitudinally on the expansion chamber 39 near the inlet port 37. In the illustrated example, the outflow channel 51 opens at the end of the cylindrical portion 63 of the expansion chamber 39 near the outlet port 36.

[0056] The secondary spring 66 (e.g., a compression spring) is elastically compressed between the floating valve 61 and the transverse wall 67 of the valve body 32. The secondary spring 66 pushes the floating valve 61 in direction B toward the opposite end 35 of the valve body 32, thereby pushing it toward the inlet port 37. As described below, pressurized braking fluid is injected from the primary chamber 38 into the expansion chamber 39, causing the floating valve 61 to move longitudinally away from the opposite end 35 of the valve body 32, thereby away from the outlet port 36 and the inlet port 37, opposite to the force exerted by the secondary spring 66.

[0057] Expansion chamber 39 is in fluid communication with inlet port 37 via a passage 68 formed in valve body 32, wherein a one-way valve 69 is installed between expansion chamber 39 and inlet port 37. One-way valve 69 consists of a ball 70 and a spring 71, the spring 71 forcing ball 70 away from inlet port 37 to block passage 68. One-way valve 69 allows braking fluid to flow through the valve in only one direction, from expansion chamber 39 to inlet port 37.

[0058] In the illustrated embodiment, for structural reasons, a transverse orifice 72 is formed in the valve body 32 to facilitate the construction of a bypass passage 50. The transverse orifice 72 is permanently sealed by a plug (schematically shown as 73).

[0059] For structural reasons, the valve body 32 may consist of two or more complementary parts, in this example, a main part 32a and a connecting part 32b. The main part 32a forms a primary chamber 38, an expansion chamber 39, an inlet port 37, and an outlet port 36. The connecting part 32b is located between the main part 32a and the actuator. The connecting part 32b is hermetically sealed to the main part 32a. The connecting part 32b is connected to the actuator via a coupler, in this example, a threaded coupler 33.

[0060] Under normal braking conditions, i.e., when the bicycle is braking but the front wheel is not locked and therefore not slipping, the electric actuator will not be energized. The primary spring 57 in the primary chamber 38 pushes the piston 40 (to the left) into the retracted position or position 0, keeping the bypass passage 50 clear. This allows brake fluid to flow directly from the inlet port 37 to the outlet port 36. The anti-lock braking system is not activated. In the piston's retracted position, the intermediate sealing gasket 49 blocks the outflow passage 51 between the primary chamber 38 and the expansion chamber 39.

[0061] Due to the longitudinal passage 53, the braking fluid fills the primary chamber 38 in both the first part 42 and the second part 43.

[0062] When the actuator is powered on ( Figure 8 Piston 40 moves toward outlet port 36 (to the right, direction B), compressing primary spring 57. End sealing gasket 48 closes bypass passage 50, interrupting the flow of brake fluid from master cylinder through valve unit to brake caliper. Piston 40 moves away from actuator to extended position, where outflow passage 51 between primary chamber 38 and expansion chamber 39 opens, allowing brake fluid to flow from primary chamber to expansion chamber.

[0063] The brake fluid pressure entering the expansion chamber 39 pushes the floating valve 61 towards the actuator (to the left, direction A), overcoming the spring force of the secondary spring 66. The volume of the expansion chamber 39 increases, resulting in a momentary drop in brake fluid pressure in the primary chamber 38. Due to the longitudinal passage 53 in the piston 40, the pressure drop in the primary chamber also simultaneously reduces the brake fluid pressure downstream of the outlet port 36 in the line leading to the front brake caliper, thus releasing the front brake caliper and unlocking the front wheels.

[0064] When the front wheel is unlocked, the electronic control unit interrupts the power supply to the actuator solenoid 31, allowing the primary spring 57 to extend and bringing the piston 40 closer to the actuator, thereby reopening the bypass passage 50 and closing the outflow passage 51. As a result, the master cylinder is once again in fluid communication with the front brake caliper.

[0065] When bypass channel 50 is reopened, expansion chamber 39 ( Figure 10The expansion chamber 39 still contains a certain amount of brake fluid because the floating valve 61 has moved in direction A and abutted against the transverse wall 65. The volume of brake fluid contained in the expansion chamber 39 must be fed back into the hydraulic circuit so that the brake lever can return to its initial rest position. As the pressure in the hydraulic circuit decreases, the secondary spring 66 can extend and move the floating valve 61 toward the inlet port 37 (direction B), essentially emptying the expansion chamber 39. Figure 11 And reintroduce brake fluid into the hydraulic circuit. Expansion chamber 39 may be emptied via check valve 69, which closes automatically due to the action of spring 71 associated with ball 70. Figure 12 ).

[0066] Reference Figure 13 In the primary chamber 38, the circular area (diameter D1) defined by the end sealing gasket 48 is advantageously equal to the annular area (defined by diameters D2 and D3) acted upon by the intermediate sealing gaskets 49 and 52. Therefore, the longitudinal thrust exerted by the brake fluid hydraulic pressure acting on the piston 40 in the first part 42 of the primary chamber (starting from the delivery port 36 side) is equal to or substantially equal to the hydraulic thrust acting on the same piston 40 in the second part 43 of the primary chamber (starting from the part closest to the actuator). Thus, these two opposing longitudinal thrusts of opposite direction and equal magnitude cancel each other out, allowing the actuator to displace the piston 40 with only a small longitudinal force. Due to the above arrangement, the actuation solenoid 31 can be very small, as only a moderate axial thrust needs to be provided to the piston to move it, and only the reaction force of the primary spring 57 needs to be overcome.

[0067] While specific embodiments of the present invention have been disclosed herein, it should be understood that this disclosure is for illustrative purposes only, and the invention is not limited thereto. Various modifications will become apparent to those skilled in the art from the foregoing examples. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. An anti-lock braking unit (13) for a hydraulic braking system, said unit (13) comprising: A single actuation solenoid (31) can be electrically connected to an electronic control unit (ECU) that monitors wheel speed, can detect conditions indicating that the wheel is about to lock up, and provides a control signal to actuate the actuation solenoid (31). A single valve unit (30) includes: Valve body (32) has: The outlet port (36) can be hydraulically connected to the brake caliper (14). The inlet port (37) can be hydraulically connected to the master cylinder (12). The primary chamber (38) is in fluid communication with the outlet port (36). Expansion chamber (39), having an outflow channel (51) that establishes fluid communication between the primary chamber (38) and the expansion chamber (39). A bypass channel (50) is located at the inlet port (37) and the outlet port (36). Establish fluid connectivity between them; The piston (40) is longitudinally movable in response to the energization of the actuation solenoid (31) and is slidably housed in the primary chamber (38); The piston (40) has two alternative operating positions: In the first position (0), wherein the actuating solenoid (31) is de-energized, and the piston (40) blocks the outflow channel (51) without blocking the bypass channel (50), and The second position (1) is wherein the piston (40) moves along the primary chamber (38) in response to the energization of the actuation solenoid (31), and the piston (40) blocks the bypass passage (50) without blocking the outflow passage (51); The piston (40) forms a longitudinal cavity (53) and a transverse channel (55). The longitudinal cavity (53) extends through the piston between the end face (54) of the piston's end portion (45) facing the outlet port (36) and the transverse channel (55). The longitudinal cavity (53) opens on the end face (54), and the transverse channel (55) opens on the side of the piston.

2. The anti-lock braking unit (13) according to claim 1, wherein, The primary chamber (38) forms a first part (42), a second part (43), and a third part (44), wherein: The first portion (42) is the end portion having a first diameter (D1) and being closer to the outlet port (36). The third portion (44) is the portion with a third diameter (D3) and furthest from the outlet port (36), wherein the third diameter (D3) is smaller than the first diameter (D1). The second part (43) is the portion between the first part (42) and the third part (44), and the second diameter (D2) of the second part (43) is greater than the first diameter (D1).

3. The anti-lock braking unit (13) according to claim 2, wherein, The piston (40) includes a terminal portion (45) received in a first part (42) of the primary chamber (38), a middle portion (46) received in a second part (43) of the primary chamber (38), and a proximal portion (47) received in a third part (44) of the primary chamber (38).

4. The anti-lock braking unit (13) according to claim 2 or 3, wherein, The area of ​​the circle having the first diameter (D1) is equal to the area of ​​the torus having an outer circle with a diameter corresponding to the second diameter (D2) and an inner circle with a diameter corresponding to the third diameter (D3). Thus, the longitudinal thrust exerted by the hydraulic pressure of the brake fluid on the piston (40) in the first part (42) of the primary chamber (38) is equal to the longitudinal thrust exerted by the hydraulic pressure of the brake fluid on the piston (40) in the second part (43) of the primary chamber (38).

5. The anti-lock braking unit (13) according to claim 1, wherein, The primary spring (57) is elastically compressed between the piston (40) and the transverse wall (58) of the primary chamber adjacent to the outlet port (36).

6. The anti-lock braking unit (13) according to claim 5, wherein, The primary spring (57) is at least partially housed in the longitudinal cavity (53) and is elastically compressed between the shoulder (56) of the piston (40) and the transverse wall (58) of the primary chamber (38).

7. The anti-lock braking unit (13) according to any one of claims 1-3, wherein, The expansion chamber (39) contains: A longitudinally sliding floating valve (61), and The secondary spring (66) pushes the floating valve (61) toward the inlet port (37). The expansion chamber (39) is in fluid communication with the inlet port (37) through a channel (68), and a one-way valve (69) is installed in the channel (68) to allow brake fluid to flow from the expansion chamber (39) to the inlet port (37) in only one direction (B) through the channel (68).

8. The anti-lock braking unit (13) according to claim 7, wherein, The floating valve (61) is movable within the expansion chamber (39) between the shoulder (64) of the valve body (32) located closer to the inlet port (37) and the transverse wall (65) located further away from the inlet port (37) in the expansion chamber. The outflow channel (51) opens longitudinally on the expansion chamber (39) near the shoulder (64).

9. The anti-lock braking unit (13) according to claim 1, wherein the hydraulic braking system is a hydraulic braking system for a bicycle.

10. A valve unit (30), comprising: Valve body (32) has: The outlet port (36) can be hydraulically connected to the brake caliper (14). The inlet port (37) can be hydraulically connected to the master cylinder (12). The primary chamber (38) is in fluid communication with the outlet port (36). Expansion chamber (39), having an outflow channel (51) that establishes fluid communication between the primary chamber (38) and the expansion chamber (39). A bypass channel (50) establishes fluid communication between the inlet port (37) and the outlet port (36); as well as The piston (40) is longitudinally movable and slidably housed at least partially in the primary chamber (38); The piston (40) has two alternative operating positions: First position (0), wherein the piston (40) blocks the outflow channel (51) but not the bypass channel (50), and Second position (1), wherein the piston (40) moves along the primary chamber (38) and blocks the bypass passage (50) without blocking the outflow passage (51); The piston (40) forms a longitudinal cavity (53) and a transverse channel (55). The longitudinal cavity (53) extends through the piston between the end face (54) of the piston's end portion (45) facing the outlet port (36) and the transverse channel (55). The longitudinal cavity (53) opens on the end face (54), and the transverse channel (55) opens on the side of the piston.

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