Dual piston valve unit for an anti-lock braking system for bicycles

Abstract

The valve unit (20) comprises an outer valve body (21) with an axially elongated inner cavity (22) in which a main piston valve element (23) slides, separating an upstream chamber (25) from a downstream chamber (24). The main piston valve element (23) forms an inner axial channel (40) in which a secondary piston valve element (41) slides. An electric motor (28) causes simultaneous linear displacements of the main piston valve element (23) and the secondary piston valve element (41) in respective axially opposite directions. When in use, the upstream chamber (25) is in fluid communication with a driver-operated master cylinder. The volume available for brake fluid within the upstream chamber (25) remains constant, so the driver's hand on the brake control lever does not feel that the ABS system is operating.

Description

Technical field

[0001] The present invention relates to a valve unit for a hydraulic braking system for controlling the anti-lock braking function of a wheel of a vehicle, in particular a bicycle or an e-bike. background

[0002] Anti-lock braking systems (“ABS”) are installed on vehicles with hydraulic brakes to prevent skidding by reducing the effects of an abrupt stop. In an ABS braking system, all wheels of a vehicle are equipped with brake discs and associated wheel speed sensors or equivalent elements that are rotationally integrated with the brake discs. The sensors detect the rotational speeds of the wheels to which they are associated and send signals indicating these speeds to an electronic control unit (ECU), which processes the received rotational signals. Each brake disc is associated with a brake caliper. A master cylinder, actuated by a control unit (hand lever control in a bicycle), activates the brake calipers through a separate hydraulic circuit, each of which has an ABS valve unit installed.Each ABS valve unit controls the flow and pressure of brake fluid toward its associated brake caliper in response to electrical control signals from the electronic control unit (ECU). When the ECU detects a condition indicating impending wheel lockup, it actuates the relevant ABS valve to reduce the hydraulic pressure on the brake at the affected wheel, thereby decreasing the braking force at that wheel so that the wheel remains braked but can still rotate. This process is continuously repeated several times per second during braking to prevent the vehicle from skidding.

[0003] WO 2021 / 205334 A1 discloses an ABS actuator device for a hydraulic bicycle brake system, comprising a floating component carrying a sealing ring that separates an upstream chamber, communicating with an inlet port, from a downstream chamber, communicating with an outlet port. The inlet port is connected to a pump device associated with the brake lever. The outlet port is connected to the hydraulic cylinder actuator of a brake caliper. The position of the floating component is controlled by an electric motor. The floating component has a body with a passage for a hydraulic connection between the upstream and downstream chambers and is provided with a coaxial internal valve component that interacts with a valve seat formed in the body of the floating component to control the hydraulic connection through the passage.The valve component is associated with a spring that tends to hold the valve component in a closed position, engaged against the valve seat, thus interrupting the hydraulic connection between the upstream and downstream chambers. During normal brake operation, the electric motor is inactive, and the floating component is in an end position towards the downstream chamber. In this position, the valve component of the floating component interacts with a counter-element of the actuator body, which holds the valve component in an open position, spaced away from the valve seat, against the spring action. This allows the fluid pumped by the pump unit to flow from the inlet port to the outlet port in the direction of the hydraulic brake during normal brake operation.In situations requiring ABS activation, the electric motor is activated, causing the floating component to move towards the upstream chamber and away from its end position. This forces the valve component into its closed position via the spring, thus interrupting the connection between the upstream and downstream chambers. The downstream chamber consequently increases its volume, reducing the pressure of the fluid supplied to the hydraulic brake.

[0004] In most ABS systems on bicycles, when the ABS function is activated, a disadvantage arises because the ABS valve increases the pressure in the brake fluid upstream of the valve, causing the brake control lever to rotate back to some extent towards a brake release position, which opposes the effect exerted by the rider's hand. Overview of the invention

[0005] A primary object of the present invention is to provide an ABS valve unit that is able to overcome the aforementioned disadvantage.

[0006] According to one aspect, the present invention provides a valve unit for a hydraulic braking system for controlling the anti-lock braking function of a bicycle wheel, as defined in claim 1. Preferred embodiments are defined in the dependent claims.

[0007] In summary, a valve unit comprises an outer valve body with an axially elongated inner cavity in which a main piston valve element slides, separating an upstream chamber from a downstream chamber. The main piston valve element forms an inner axial channel in which a secondary piston valve element slides. An electric motor causes simultaneous linear displacements of the main piston valve element and the secondary piston valve element in axially opposite directions. When in use, the upstream chamber is in fluid communication with a driver-operated master cylinder. The volume available for brake fluid within the upstream chamber remains constant, so the driver's hand on the brake control lever does not feel the ABS system operating. Brief description of the drawings

[0008] In order to ensure a good understanding of the present invention, some preferred embodiments thereof will now be described by way of example, with reference to the accompanying drawings, in which: Fig. 1 a diagram that schematically illustrates the operation of an anti-lock braking system on a vehicle; Fig. 2 to Fig. Four longitudinal sectional views of a valve unit in different operating states are shown; Fig. 5 a partially enlarged view of Fig. 4 is the one that shows further details; Fig. 6 An enlarged transverse cross-sectional view of a main piston valve component along line VI-VI in Fig. 5 is; Fig. 7 an enlarged transverse cross-sectional view of a component of the valve unit along line VII-VII in Fig. 5 is; and Fig. 8 is an enlarged view of a detail that appears at VIII in Fig. 2 is circled. Detailed description

[0009] Initially referring to Fig. The system comprises an anti-lock braking system (ABS) with wheel rotation sensors 10, which are applied to the wheels of a vehicle, in this example an e-bike. The wheels are each equipped with brake discs (not shown) and associated brake calipers 11, which apply a braking force to brake pads on the caliper through a hydraulic brake circuit 15, consequently generating a braking torque that acts on the wheel. A hand lever 12 actuates a hydraulic master cylinder 12 to generate and control pressure within the hydraulic brake circuit 15. A pressure sensor 14 detects the brake fluid pressure in the hydraulic circuit. The rotation sensors 10 detect the rotational speeds of the wheels to which they are associated and send signals indicating the rotational speeds to a brake control unit (BBCU) 16, which is an electronic unit that receives and processes signals from the rotation sensors 10 and the pressure sensor 14.Electrical signals from the pressure sensor 14 are sent to the BBCU 16 through a line 9.

[0010] Each brake caliper is associated with an ABS valve unit 20. Each ABS valve unit controls the flow and pressure of brake fluid toward its associated brake caliper in response to electrical control signals from the brake control unit 16. When the BBCU detects a condition indicating impending wheel lockup, it actuates the respective ABS valve unit to reduce the hydraulic pressure on the brake at the affected wheel, thereby reducing the braking force on that wheel so that the wheel remains braked but can still rotate. This process is continuously repeated during braking, several times per second, thus preventing the vehicle from skidding.

[0011] With reference to Fig. 2 Each ABS valve unit 20 comprises an outer valve body 21, which defines an inner cavity 22 having an axially elongated shape. A main piston valve component 23 is axially displaceable within the inner cavity, separating an upstream chamber 25 from a downstream chamber 24. The outer valve body 21 forms an inlet port 27, which establishes a fluid connection between the upstream chamber 25 and the hydraulic master cylinder 13, which is actuated by the brake lever 12. An outlet port 26 fluidically connects the downstream chamber 24 to a 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.

[0012] The main piston valve component 23 has a substantially tubular shape with an inner channel 40 extending axially through it. A secondary piston valve component 41 is axially slidably mounted within the inner channel 40. The secondary piston valve component 41 has an upstream end region fitted with a seal 42, which slidably and sealingly engages with the inner axial channel 40 of the main piston valve component 23.

[0013] An electric motor 28, which is attached to the outer valve body 21, simultaneously controls the axial positions of both the main piston valve component 23 and the secondary piston valve component 41 with respect to the outer valve body 21.

[0014] The electric motor 28 drives a rotating output shaft 29, which is coupled to the main piston valve component 23 by a first or outer rotary-to-linear motion conversion mechanism 30, which converts a rotary motion of the rotating shaft 29 into a linear displacement of the main piston valve component 23 within the inner cavity 22.

[0015] Through a second or inner rotary-to-linear motion conversion mechanism 43, the electric motor 28 simultaneously controls the axial position of the secondary piston valve component 41. The second rotary-to-linear motion conversion mechanism 43 converts a rotary motion of the rotating shaft 29 into a linear displacement of the secondary piston valve component in an axial direction opposite to the axial direction in which the main piston valve component 23 is driven.

[0016] The rotary-to-linear motion conversion mechanisms 30 and 43 can each include threaded couplings with helically opposing threads, whereby the rotation of the shaft 29 simultaneously causes the main piston valve component 23 to move forward in a given axial direction, for example towards the downstream chamber 24, while the secondary piston valve component 41 is caused to retract in the opposite axial direction, in this example towards the upstream chamber 25.

[0017] According to the Fig. 2 to Fig. In the preferred embodiment shown in Figure 5, the output shaft 29 has a tubular, axially extending end region 44 with a radially outer cylindrical surface on which the first, outer rotary-to-linear motion conversion mechanism 30 is provided, and an axially extending end cavity 45 in which the inner rotary-to-linear motion conversion mechanism 43 is arranged.

[0018] The electric motor 28 is powered and controlled by the BBCU 16 via line 8. The BBCU 16 receives power from a battery (not shown) via line 7.

[0019] The electric motor can be equipped with a position sensor to detect the angular position of the output shaft 29 and consequently to detect the axial position of the main piston valve component 23.

[0020] A first or upstream hollow tubular insert 35 is fitted within the inner cavity 22 and is suitably shaped to accommodate two seals within the outer valve body 21 and to provide an axial passage for guiding an upstream end section 231 of the main piston valve component 23 and for establishing a fluid connection between the upstream chamber 25 and the inlet port 27.

[0021] Within the inner cavity 22, three stationary annular seals 31-33 are mounted, which engage with the main piston valve component 23 in a sliding and sealing manner: a first end seal (or upstream end seal) 31 and a second end seal (or downstream end seal) 32, which are arranged axially spaced apart from each other such that the inlet port 27 and the outlet port 26 are located axially between the upstream and downstream end seals 31, 32. A third intermediate seal 33 is mounted within the inner cavity between the inlet port 27 and the outlet port 26. No seals are mounted on the main piston valve component 23.

[0022] The third intermediate seal 33 can fluidically separate the downstream and upstream chambers 24, 25 and, depending on the axial position of the main piston valve component 23, can open and close a passage between the main piston valve component and the inner cavity, thereby establishing a fluid connection between the downstream and upstream chambers 24, 25 or temporarily interrupting the fluid connection between the outlet and inlet ports 26, 27 by sealingly separating the upstream chamber from the downstream chamber.

[0023] Due to the seal 42 on the secondary piston valve component 41, no flow of brake fluid is allowed to flow directly between the downstream and upstream chambers through the inner axial channel 40 of the main piston valve component 23.

[0024] A second or downstream hollow tubular insert 36 is fitted within the inner cavity 22 and is suitably shaped to fit the downstream seal 32 within the outer valve body 21 and to provide an axial passage for guiding a downstream end section 232 of the main piston valve component 23.

[0025] The downstream chamber 24, which is connected to the outlet port 26, is bounded between the downstream end seal 32 and the intermediate seal 33.

[0026] The upstream chamber 25, which is connected to the inlet port 27, is bounded between the upstream end seal 31 and the intermediate seal 33. At least one, and preferably a plurality, of radial openings 48 are formed by the upstream end section 231 of the main piston valve component 23, thereby bringing the upstream end region of the axial inner channel 40 into fluid communication with the upstream chamber 25. As a result, the upstream chamber 25 also contains a variable volume, the amount of which depends on the relative axial position of the main and secondary piston valve components 23, 41, which are contained within the upstream end region 231 of the secondary main piston valve component 41, between the seal 42 on the secondary piston valve component 41 and the upstream seal 31.

[0027] The upstream and downstream hollow tubular inserts 35, 36 are hermetically sealed to the outer valve body 21 by a number of static sealing rings such as O-rings 39, which act at the interfaces between each insert and the inner cavity 22.

[0028] The main piston valve component 23, on which the intermediate seal 33 can exert a sliding or dynamic sealing effect, can be made of metal, for example an aluminum alloy, or another suitable rigid material, for example a thermosetting plastic material.

[0029] The outer valve body 21 serves to continuously accommodate the seals, but the wall of the inner cavity 22 does not also serve as a smooth sliding surface for a seal capable of withstanding high pressures without significant deformation. Consequently, the outer valve body can expediently be made of a relatively inexpensive thermoplastic material, such as PA 66 GF30, PA 66 GF50, PA 6, or PA 66 CF30.

[0030] According to the in Fig. In the exemplary embodiment shown in Figure 2, the outer valve body 21 is formed as a substantially tubular body with axially opposite open ends and a central, radially thicker wall area 211 in which the outlet port 26 is formed.

[0031] As in the embodiment of Fig. As shown in Figure 2, the central, radially thicker wall region 211 forms an upstream transverse surface 212 against which the intermediate seal between the central wall region 211 and the upstream hollow tubular insert 35 can be held continuously in position.

[0032] Preferably, the upstream seal 31 is continuously received in an annular seat formed by the upstream hollow tubular end 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 to slidably receive the upstream end section 231 of the main piston valve component 23.

[0033] The upstream end plug 38 can form a cylindrical projection 47 that extends axially towards the upstream chamber 25, which is axially aligned with the inner axial channel 40, and projects into the inner axial channel 40 at the upstream end section 231 of the main piston valve component 23 to guide its linear movement. The cylindrical projection 47 can provide a sealing ring 46 that seals the inner axial channel 40 at the upstream end section 231 of the main piston valve component 23.

[0034] According to a preferred embodiment, the downstream seal 32 can be continuously received in an annular seat formed by the downstream hollow tubular end insert 36 and a downstream transverse surface 213 formed by the central, radially thicker wall region 211 opposite the upstream transverse surface 212.

[0035] The three stationary annular seals 31-33 are each preferably formed with a respective conical lip designed to engage elastically and radially with a respective surface of the main piston valve component 23. The conical lip of the upstream end seal 31 tapers towards the upstream chamber 25, whereas the conical lip of the downstream end seal 32 tapers towards the downstream chamber 24.

[0036] Preferably, the conical lip of the intermediate seal 33 tapers towards the upstream chamber 25.

[0037] The main piston valve component 23 has a central section 233 with a smooth cylindrical surface 235 having a diameter D3 and one or more radially narrower surfaces 234 extending axially from the cylindrical surface 235 towards the upstream end of the main piston valve component. The one or more radially narrower surfaces 234 are configured to define one or more corresponding passages 236 between the main piston valve component 23 and the intermediate seal 33 in certain operating conditions of the valve assembly.

[0038] According to one embodiment, as in Fig. As shown in Figure 8, the radially narrower surfaces 234 can be provided in the form of axially extending grooves spaced evenly in the circumferential direction.

[0039] According to a preferred embodiment, the main piston valve component 23 provides the central section 233 in a substantially central position along its axial length.

[0040] The downstream end section 232 of the main piston valve component 23 has an outer diameter D2 that is smaller than the outer diameter D3 of the central section 233.

[0041] Preferably, the upstream end section 231 of the main piston valve component 23 has an outer diameter D1 that is smaller than the outer diameter D3 of the central section 233.

[0042] Even more preferably, the upstream end section 231 of the main piston valve component 23 has an outer diameter D1 that is smaller than the outer diameter D2 of the downstream end section 232.

[0043] According to one embodiment, as in Fig. As shown in Figure 7, antirotation mechanisms, preferably in the form of wedge connections 49, 50, can be provided at the interface between the outer valve body 21 and the main piston valve component 23 and at the interface between the main and secondary piston valve components 23 and 41 to prevent relative rotation of the piston valve components while allowing relative axial movement between the parts.

[0044] Optionally, the brake control unit 16 (BBCU) can include an integrated inertial measurement unit (IMU), designated 6, which detects the acceleration and orientation of the e-bike. Based on these measurements, the BBCU can supply energy to the electric motor to control the positions of the main and secondary piston valve components 23, 41, thereby activating the valve unit to prevent the bike from tipping over when the rider brakes excessively on high-friction road surfaces, and to prevent the controlled wheel from locking up when the rider brakes on low-friction surfaces.

[0045] The following are examples of operating modes of the ABS valve: a normal braking mode, a fluid-isolated state, and a pressure modulation mode.

[0046] During normal operation of the hydraulic bicycle brake, the ABS valve is in a resting state ( Fig. 2) The main piston valve component 23 is retracted in a starting position towards the downstream chamber 24, whereas the secondary piston valve component 41 is advanced in a starting position towards the upstream chamber 25. The upstream end of the secondary piston component 4 can be in a final stroke position, resting against the upstream end plug 38, in this example against the cylindrical projection 47.

[0047] In all positions that the secondary piston component 41 can reach in operation with respect to the main piston valve component 23, including the initial position of Fig. 2, the seal 42 on the secondary piston valve component 41 is always further away from the upstream end seal than the radial openings 48.

[0048] In this position, the free end of the conical lip of the intermediate seal 33 is in an open position ( Fig. 8), in which the smooth cylindrical surface 235 is axially displaced with respect to the intermediate seal 33 and is not engaged with it. In this open or normal operating position, the intermediate seal is transversely aligned with and radially separated from the one or more radially narrower surfaces 234. Consequently, the one or more corresponding passages 236 defined between the main piston valve component 23 and the intermediate seal 33 establish a fluid connection between the downstream and upstream chambers 24, 25, and thus between the master cylinder and the brake caliper.

[0049] During normal brake operation, the main piston valve assembly 23 remains in a 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 passages or grooves 234 and then to the brake caliper 11 without any interference from the ABS system. The secondary piston valve assembly 41 remains in an extended, passive position, close to or adjacent to the upstream end plug 38. The volume of brake fluid within the upstream end of the inner axial channel 40 is minimal.

[0050] In this normal operating mode, the BBCU control unit 16 continuously monitors the pressure in the hydraulic system, the angular velocity of the wheels, and optionally information from the IMU. A control algorithm processes this information by deciding to switch to one of the remaining listed operating modes.

[0051] In locked wheel brake conditions, or when a condition of impending rollover or other loss of control is perceived during braking, the BBCU 16 supplies energy to the control motor 28 of the affected wheel, causing the relevant main piston valve component associated with that wheel to move towards the upstream chamber 25 ( Fig. 3) away from the initial inactive position of Fig. 2 to slide. At the same time, the rotation of the output shaft 29 causes the secondary piston valve component 41, which is associated with this wheel, to slide within the inner axial channel 40 in the direction of the downstream chamber 24 ( Fig. 3) slides away from the upstream end plug 38.

[0052] The main piston valve component 23 reaches an axially displaced position towards the upstream chamber 25, in which the free end of the conical lip of the intermediate seal 33 is in a closed position, engaging sealingly with the smooth cylindrical surface 235 of the central section 233 of the main piston valve component 23. In this position of the main piston valve component ( Fig. 3) The intermediate seal 33 fluidically isolates the downstream chamber 24 from the upstream chamber 25. Consequently, the fluid connection between the master cylinder and the brake caliper is temporarily interrupted.

[0053] This fluid-isolated state is a transitional state, as the electric motor 28 moves the main piston valve component further into the upstream chamber 25 ( Fig. 4) is driven and simultaneously the secondary piston valve component 41 is drawn further into the axial inner channel 40 of the main piston valve component 23. Since the downstream end section 232 of the main piston valve component 23 has a diameter D2 that is smaller than the diameter D3 of the central section 233 ( Fig. 5), causes the movement of the main piston valve component 23 towards the upstream chamber 25 or further into it, so that the volume of the downstream chamber 24 increases, thereby immediately releasing the pressure of the brake fluid associated with the brake caliper.

[0054] Conversely, the total volume of the upstream chamber 25 remains essentially unchanged because, although the main piston valve component 23 moves further into the upstream chamber 25, the reduction in the volume available for the brake fluid in the upstream chamber 25 outside the main piston valve component is compensated by an increase in the volume available inside the upstream end region of the axial inner channel 40.

[0055] More generally, depending on the directions in which the main and secondary piston valve components are linearly displaced, a variation (decrease or increase) in the volume available for the brake fluid in the upstream chamber 25 outside the main piston valve component is compensated by an substantially equivalent or corresponding variation (increase or decrease) in the volume available inside the upstream end region of the axial inner channel 40.

[0056] Consequently, the pressure of the brake fluid in the hydraulic system between the valve unit 20 and the master cylinder 13 remains unchanged. Accordingly, the driver does not feel the hand lever 12 moving back towards a brake release position, which counteracts the braking force the driver applies to the hand lever.

[0057] Volume compensation can be achieved in different ways. According to one embodiment, the threaded couplings 30 and 43 can include helically opposed threads with the same pitch, and the cross-sectional area of ​​the inner axial channel 40 can be equivalent to the cross-sectional area of ​​a circular ring having an outer circumference with the D3 diameter of the central section 233 of the main piston valve component 33 and an inner circumference with the D1 diameter of the upstream end section 231 of the main piston valve component 33.

[0058] According to an alternative embodiment, considering that the inner axial channel 40 may be relatively narrow, the pitch of the second or inner threaded coupling 43 can be chosen to be longer than that of the first or outer threaded coupling 30. Consequently, the linear velocity of the secondary piston valve component 41 can be higher than that of the main piston valve component 23, which moves in the opposite axial direction but leaves the volume of the upstream chamber 25 unchanged during activation of the valve unit.

[0059] According to a pressure modulation operating mode, the BBCU 16 controls the electric motor 28 in such a way as to repeatedly drive the main and secondary piston valve components 23, 41 back and forth several times per second during braking, causing the position of the main piston valve component 23 to perform a linear back-and-forth movement between - the fluid-isolated state of Fig. 3, in which the intermediate seal 33 seals the downstream chamber 24 from the upstream chamber 25, and - the position of Fig. 4, in which the intermediate seal 33 still seals the downstream chamber 24 from the upstream chamber 25, but the main piston valve component 23 is located further into the upstream chamber, thereby increasing the volume and reducing the pressure in the downstream chamber 24.

[0060] Consequently, the braking torque, which is intermittently transferred to the brake caliper, prevents wheel lock-up or rollover.

[0061] Simultaneously, the secondary piston valve component 41 is caused to move repeatedly back and forth within the axial inner channel 40. Due to the compensated and constant volume and pressure of the upstream chamber 25, the driver's hand does not feel the operating ABS valve unit.

[0062] It can be seen that during the pressure modulation operating mode, the downstream chamber 24 remains fluidly separated or sealed from the upstream chamber 25, thus preventing the master cylinder from acting on the brake caliper.

[0063] The BBCU unit controls the electric motor and the main piston valve component in pressure modulation mode until the BBCU detects, via the hydraulic pressure sensor, that the pressure in the downstream chamber falls below a predetermined threshold, and sends a control signal to the electric motor 28, causing the main piston valve component 23 to return to its starting position ( Fig. 2) to return, thereby switching back to the normal operating mode of the ABS valve.

[0064] Due to the design and position of the intermediate seal 33, the fluid isolation or sealing effect provided by the intermediate seal 33 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 becomes less than the pressure in the downstream chamber 24, which occurs when the rider releases the brake lever, the intermediate seal 33 allows the brake fluid to flow from the downstream chamber 24 back to the upstream chamber 25. This capability prevents a braking torque from being applied to the brake caliper, even when the rider releases the brake.

[0065] An algorithm manages the full axial movement of the piston until the fluid-isolated operating mode is reached, with the intermediate seal as in Fig. Figure 3 shows the arrangement in which the brake caliper is fluidly isolated from the master cylinder. If this condition is still insufficient to effectively control braking, the algorithm operates to adjust the pressure within the downstream chamber according to the pressure modulation operating mode described above.

[0066] As an alternative to the pressure modulation operating mode described above, the valve unit 20 can be controlled in a more conventional operating mode. According to this alternative operating mode, upon detecting a critical braking condition (skidding or rollover), the BBCU supplies energy to the electric motor 28 to move the main and secondary piston valve components 23, 41 from their initial positions. Fig. 2 to the sealed or insulated position of Fig. 4 to drive, in which the pressure in the hydraulic circuit between the intermediate seal 33 and the brake caliper is released. As soon as the BBCU detects by the hydraulic pressure sensor that the pressure in the downstream chamber falls below a predetermined threshold, it sends a control signal to the electric motor 28, causing the main and secondary piston valve components 23, 41 to move to their starting positions ( Fig. 2) to return, thereby reopening the flow of brake fluid through the passages or grooves 234 and temporarily re-establishing a direct fluid connection between the master cylinder and the brake caliper. Upon detecting a sustained critical brake condition, the BBCU immediately drives the main piston valve assembly 23 (and the secondary piston valve assembly 41) back to the sealed or isolated position of Fig. 4, and this process of opening and closing the passages 234 is continuously repeated during braking, several times per second, thus preventing the vehicle from skidding.

[0067] The arrangement of the diameters D3 > D2 > D1 of sections 233, 232, and 231 of the main piston valve component 23 also provides an advantageous safe failure condition. In the event of a power failure of the electric motor 28, while the piston valve component 23 is in the position of Fig. 4, although the intermediate seal fluidly isolates the master cylinder from the brake caliper, the diameter D3 of the central section 233, which is wider than the diameter D1 of the upstream end section 231, causes the main piston valve component 23 to move (to the left) towards the downstream chamber 24 until the passages 234 are reopened.

[0068] Preferably, the diameter D2 of the downstream end section 232 is larger than the diameter D1 of the upstream end section 231. Consequently, once the passages 234 are reopened, since the same hydraulic pressure is present in the downstream and upstream chambers, the main piston valve component 23 is effectively caused to move (to the left) towards the downstream chamber 24. This is because the area of ​​a circular annulus bounded by diameters D1 and D3 (on the upstream chamber side) is larger than the area of ​​a circular annulus bounded by diameters D2 and D3 (on the downstream chamber side). Consequently, the hydraulic forces acting on opposite sides of the main piston valve component 23 provide a net axial force that pushes it towards and further into the downstream chamber 24, thereby changing the position of Fig.2 is achieved. Consequently, the valve unit always guarantees sufficient braking torque to allow the vehicle to stop at a reasonable stopping distance, even in the event of an electrical failure.

[0069] Although specific embodiments of the invention have been disclosed, it is understood that such disclosure serves only for illustrative purposes and is not intended to limit the invention in any way. Various modifications will be obvious to the person skilled in the art in view of the foregoing examples. The scope of the invention is intended to be limited only by the appended claims. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2021 / 205334 A1

[0003]

Images