Valve unit for an anti-lock braking system

Abstract

A valve unit (10) for an anti-lock braking system (ABS) includes a valve body (11), a piston (18) movable in the valve body, and a resilient element (34) acting on the piston. The valve body has an outlet port (14), an inlet port (17), a main chamber (15) in communication with the outlet port, an expansion chamber (16) having an outflow passage (51) effecting fluid communication between the main chamber and the expansion chamber, and a bypass passage (50) between the inlet port and the outlet port. The piston (18) is movable in the main chamber (15) and has a longitudinal through cavity (31). The piston has a first lateral surface facing away from the outlet port and a second lateral surface opposite the first lateral surface and facing away from the outlet port, wherein the area of the first lateral surface is less than the area of the second lateral surface. The resilient element (34) exerts a resilient force to move the piston (18) away from the outlet port (14). The valve unit (10) is activatable by pressure of brake fluid in the main chamber (15).

Description

Technical Field

[0001] This invention relates to a valve unit for a hydraulic braking system to control the anti-lock braking function of a vehicle's wheels. This valve system is suitable for both motorized and non-motorized vehicles, such as bicycles. Background Technology

[0002] Anti-lock braking systems (“ABS”) have been installed on vehicles with hydraulic brakes to prevent skidding or uncontrolled slippage, thereby reducing the impact of sudden stops. One such system is... Figure 1 The diagram illustrates a motor vehicle where four wheels are equipped with brake discs E1-E4 and associated sensors S1-S4, operably facing wheels F1-F4 or equivalent elements rotatably integrated with the brake discs. According to known models, sensors S1-S4 detect the rotational speed of their associated wheels and, for example, transmit signals representing the rotational speed via lines N1-N4 to an electronic control unit (ECU) or module that processes the received speed signals. Each brake disc is associated with a brake caliper G1-G4. A master cylinder M, operated by a foot pedal controller C, actuates the brake calipers via respective hydraulic lines H1-H4, each equipped with a valve unit ABS1-ABS4. Each ABS valve unit controls the flow and pressure of brake fluid to the associated brake caliper in response to electronic control signals from the ECU. When the ECU detects an indication of impending wheel lock-up, it activates the corresponding ABS valve to reduce the hydraulic pressure on the brake at the affected wheel, thereby reducing the braking force on that wheel, allowing the wheel to remain braked but still rotate. During braking, this process is repeated continuously, several times per second, to prevent the vehicle from skidding.

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

[0004] EP 3 392 105 A2 describes a hydraulic braking system for a bicycle comprising two electrically operated valve assemblies. Each valve assembly is independently operated by its respective electric actuator. A first valve assembly blocks brake fluid between the master cylinder and the brake caliper, and a second valve assembly opens a parallel passage hydraulically connecting the brake caliper and an accumulator. The two electric actuators are powered by an ECU in a predetermined sequence. The two valve assemblies are located on a parallel branch of a hydraulic circuit connecting the master cylinder, operated by a lever, and the brake caliper. During normal braking, the first valve assembly is open to allow direct fluid communication between the master cylinder and the brake caliper, while the second valve assembly is closed. Under emergency braking conditions, in the event of impending wheel lock-up, the first electric actuator closes the first valve assembly, thereby blocking pressure input from the lever and thus blocking pressure from the first valve assembly to the caliper to prevent further increase in pressure acting on the caliper. The second electric actuator opens the second valve to allow pressure release into the accumulator, which is located upstream of the second valve in the parallel passage. Therefore, the pressure on the caliper decreases, releasing the brakes.

[0005] Other ABS systems include a valve unit that comprises a piston mounted in a hydraulic line. The piston is controlled by an electric actuator (solenoid valve) that moves the piston back and forth to change the volume in the hydraulic line, thereby regulating the pressure in the braking circuit. Summary of the Invention

[0006] According to the prior art, the main objective of this invention is to provide an ABS valve unit that can be actuated to intervene in the case of locked braked wheels, rather than through electric control of a conventional actuator.

[0007] The present invention provides an ABS valve unit that is actuated by the brake fluid pressure present in the hydraulic circuit of the braking system.

[0008] According to one aspect, the present invention discloses a valve unit for a hydraulic braking system to control the anti-lock braking function of a vehicle's wheels, as defined in claim 1. Preferred embodiments of the invention are defined in the dependent claims.

[0009] Generally, the valve unit for an anti-lock braking system (ABS) in a vehicle includes a valve body, a movable piston within the valve body, and an elastic element acting on the piston. The valve body has an outlet port hydraulically connected to the brake caliper, an inlet port hydraulically connected to the master cylinder, a main chamber in fluid communication with the outlet port, an expansion chamber having an outflow passage enabling fluid communication between the main chamber and an expansion chamber, and a bypass passage enabling fluid communication between the inlet port and the outlet port. The piston is longitudinally movable within the main chamber and has a longitudinal cavity extending through the piston between a lateral passage leading to a side surface of the piston facing the outlet port. The piston generally has a first lateral surface facing away from the outlet port and a second lateral surface opposite to and facing away from the outlet port, wherein the area of ​​the first lateral surface is smaller than the area of ​​the second lateral surface. The elastic element applies an elastic force to move the piston away from the outlet port. The piston has two selectable operating positions:

[0010] In the first position, under normal braking conditions, the elastic force of the elastic element exceeds the longitudinal component of the hydraulic thrust of the brake fluid present in the main chamber. Consequently, the piston moves away from the outlet port and blocks the outflow passage without blocking the bypass passage.

[0011] In the second position, when the valve unit is actuated, the hydraulic thrust of the braking fluid present in the main chamber has a longitudinal component exceeding the force applied by the elastic element, thereby causing the piston to shift toward the outlet port and block the bypass passage, but not the outflow passage. Attached Figure Description

[0012] To clearly understand the present invention, several preferred embodiments will now be described with reference to the accompanying drawings, which are provided by way of example, wherein:

[0013] Figure 1 It is a schematic diagram illustrating the operation of the anti-lock braking system on a vehicle;

[0014] Figure 2 This is a longitudinal sectional view of the valve unit in the first operating state according to the first embodiment of the present invention;

[0015] Figures 3 to 5 It shows other operating conditions Figure 2 Valve unit;

[0016] Figure 6 This is a longitudinal sectional view of a valve unit according to another embodiment; and

[0017] Figure 7 This is a longitudinal sectional view of a valve unit according to another embodiment. Detailed Implementation

[0018] Reference Figures 2 to 5 Reference numeral 10 generally denotes an ABS valve unit for an anti-lock braking system used in the wheels of a vehicle. Valve unit 10 defines a longitudinal axis x and has an elongated shape in the direction defined herein as longitudinal or axial. In this context, terms such as “longitudinal” and “lateral” will be understood with reference to the x-axis.

[0019] Valve unit 10 includes a body 11 (or housing) made of plastic material, which defines an actuation direction referred to herein as "longitudinal". In this example, body 11 has an overall cylindrical tubular shape, having a first end 12 and a second end 13 opposite to the first end.

[0020] The end 12 of the main body 11 forms an outlet port (or exit port) 14 and an inlet port 17, the outlet port being hydraulically connected to a brake caliper (not shown) of the brake of the vehicle's wheel, and the inlet port being hydraulically connected to a master cylinder (or main cylinder, not shown), which is operatively associated with an actuation controlled by a foot pedal or handle (not shown) on the vehicle.

[0021] The main body 11 includes a main hydraulic chamber 15 and an expansion chamber 16, or an auxiliary hydraulic chamber. The main hydraulic chamber 15 is directly connected to the outlet port 14 and longitudinally accommodates the piston 18 in a slidable manner.

[0022] The main hydraulic chamber 15 forms a first end section 19 (or distal section) having a diameter D1 closer to the outlet port 14; a second intermediate section 20 having a diameter D2 greater than the diameter D1; and a third section 21 (or proximal section) having a diameter D3 less than the diameter D1 and further away from the outlet port 14.

[0023] The piston 18 includes an end portion 22 housed in an end section 19 of the main chamber 15, an intermediate portion 23 housed in an intermediate section 20 of the main chamber 15, and a proximal portion 24 housed in a proximal section 21 of the main chamber 15.

[0024] The end portion 22 of the piston 18 is provided with a pair of longitudinally adjacent sealing end washers 26 and 27, which are spaced apart by a short distance; the washers 26 and 27 are in sliding contact with the end portion 19 of the main chamber 15. The middle portion 23 of the piston 18 is provided with a pair of intermediate washers 28 and 29, which are longitudinally adjacent and spaced apart by a short distance and engage with the middle portion 20 of the main chamber 15. A proximal sealing washer 30 is mounted on the proximal portion 24 of the piston, thereby sealingly engaging with the proximal portion 21 of the main chamber 15.

[0025] The piston 18 forms a longitudinal cavity 31 that extends through the piston between an end surface 32 of the piston's end portion facing the outlet port 14 and a transverse channel 33 that discharges onto the side surface of the piston. The transverse channel 33 flows onto the middle section 20 of the main hydraulic chamber 15.

[0026] In the portion 13 of the main body 11 opposite to the end having an inlet port 17 and an outlet port 14, a main elastic element 34 is housed, which causes the piston 18 to move away from the outlet port 14.

[0027] exist Figure 2-5 In one embodiment, the main elastic element 34 is formed as a single compression spring that is longitudinally compressed between the shoulder 35 of the body 11 and the contrast wall 36, which faces the shoulder 35 and is longitudinally spaced from the shoulder. Alternative embodiments of the illustrated embodiment may include more than one elastic element, such as two springs, one of which is prestressed and only one is supported, to provide different levels of preload along a short longitudinal stroke.

[0028] The transverse liner 36 is received with transverse clearance and is advantageously movable longitudinally within the chamber 38 formed by the body 11.

[0029] The valve stem 37 connects the transverse liner 36 to the piston 18 and makes it longitudinally integrated with the piston.

[0030] The longitudinal compression of the main elastic element 34 pushes the transverse liner 36 to the left, and this in turn pulls the piston 18 to the left via the valve stem 37.

[0031] The longitudinal distance between the transverse liner 36 and the shoulder 35 can be adjusted to change the longitudinal elastic force by which the main elastic element pulls the piston 18 away from the outlet port 14.

[0032] According to one embodiment, the valve stem 37 may be made as a threaded valve stem, which engages through a corresponding threaded through-hole 39 formed through the transverse liner 36.

[0033] The valve stem 37 may have an enlarged end head 40 with a circular cross-section, such as a sphere, to engage in a corresponding groove 41 formed in a portion 24 of the piston 18.

[0034] An adjusting device 42 can be conceived to adjust the elastic force that pushes the piston 18 away from the outlet port 14. The adjusting device 42 can change the longitudinal position of the transverse liner 36 along the valve stem 37, thereby adjusting the distance between the transverse liner 36 and the shoulder 35, and thus adjusting the length and compression of the main elastic element 34. By means of the adjusting device 42 rotating the valve stem 37 about its longitudinal axis 37A in a given direction of rotation, the main elastic element 34 is further compressed and thus shortened longitudinally, thereby increasing the traction force that moves the piston 18 away from the outlet port 14. Conversely, by rotating the valve stem 37 in the opposite direction of rotation, the main elastic element 34 is depressurized and allowed to lengthen longitudinally, thereby reducing the traction force that pulls the piston 18 away from the outlet port 14.

[0035] The valve stem 37 has a central longitudinal axis 37A that is preferably eccentric relative to the longitudinal central axis 18A of the piston 18. In this way, during the phase of adjusting the position of the transverse liner 36, the rotation of the valve stem 37 about its axis 37A will not cause the piston 18 to also rotate undesirably about its axis 18A (which would cause wear on the gaskets mounted on the piston 18 and acting on the wall of the main hydraulic chamber 15). As an alternative to the aforementioned eccentric arrangement, different embodiments (not shown) may provide anti-rotation elements, such as transverse teeth projecting radially from the piston 18 and / or the transverse liner 36.

[0036] The lateral clearance between the transverse liner 36 and the edge of the chamber 38 is desirable to reduce friction during the longitudinal movement of the piston 18 with the wall 36. To ensure that rotation applied to the valve stem 37 causes tightening or loosening relative to the liner 36, it is preferable that at least a portion of the outer peripheral edge of the wall 36 has a lateral distance P1 greater than the minimum lateral distance P2 between the axis 37A and the inner surface of the chamber 38. In this way, as the valve stem 37 rotates, the inner surface of the chamber 38 acts as a liner to rotatably block the transverse wall 36.

[0037] According to one embodiment, the adjusting device 42 for the rotary threaded valve stem 37 includes an electronic control unit (ECU) mounted on the vehicle. Figure 1 An electrically driven actuator controlled by a main elastic element 34 can adjust the elastic force of the main elastic element 34 as needed, as described below.

[0038] In the main chamber 15, the brake fluid present in the first end section 19 closer to the outlet port 14 acts on the circular area of ​​the piston 18, which has a circumference of diameter D1 defined by washers 26 and 27. The brake fluid present in the first section between the outlet port 14 and the sealing washer 27 exerts a longitudinal thrust on the piston 18, which points to the left (direction A) in the figure, away from the outlet port 14.

[0039] The brake fluid contained in the second intermediate section 20 of the main chamber 15 applies a longitudinal hydraulic thrust to the piston over an area defined by an annular crown having an outer circumference of diameter D2 corresponding to the diameter of the second intermediate section 20 of the main chamber 15, and an inner circumference of diameter D3 corresponding to the diameter of the third section 21 of the main chamber 15 away from the outlet port 14. The hydraulic thrust of the brake fluid in the second intermediate section 20 of the main chamber is directed to the right in the figure and pushes the piston 18 closer to the outlet port 14.

[0040] The diameters D1, D2, and D3 of the corresponding three sections 19, 20, and 21 of the main chamber, and the diameters of the corresponding sections 22, 23, and 24 of the piston 18, are selected such that the area of ​​the annular crown defined by diameters D2 and D3 is larger than the area of ​​the circle having diameter D1. Therefore, the total hydraulic thrust acting on the piston 18 has a longitudinal resultant force acting on the piston 18, which pushes the piston closer to the outlet port 14.

[0041] Therefore, the total hydraulic thrust acting on piston 18 is directed in the opposite direction to the stress generated by the main elastic element 34, which acts on piston 18 to move it away from outlet port 14.

[0042] A first bypass passage 50 is formed in the body 11 of the valve assembly and leads to the end section 19 of the main hydraulic chamber 15, thereby enabling fluid communication between the chamber and the inlet port 17. An outlet passage 51 is formed in the body 11 of the valve unit and leads to the middle section 20 of the main hydraulic chamber 15, thereby enabling fluid communication between the chamber and the expansion chamber 16.

[0043] The expansion chamber 16 houses a floating valve element 61 with a sealing gasket 62, which engages longitudinally slidably with the cylindrical portion 63 of the expansion chamber 16. The floating valve element 61 is movable within the expansion chamber 16 between a shoulder 64 formed closer to the inlet port 17 and a transverse wall 67 farther from the inlet port 17.

[0044] The outflow channel 51 is positioned at a point closer in the longitudinal direction to the inlet port 17 to flow into the expansion chamber 16. The outflow channel 51 opens at the first end of the cylindrical section 63 of the expansion chamber 16, away from the inlet port 17.

[0045] A secondary spring element 66 (e.g., a compression spring) is elastically compressed between the float valve element 61 and the transverse wall 67 of the valve body 32. The secondary spring element 66 is directed in direction B toward the end 12 of the body 11, thus pushing the float valve element 61 toward the inlet port 17. As described below, pressurized brake fluid is introduced from the main chamber 15 into the expansion chamber 16, causing the float valve element 61 to move longitudinally away from the outlet port 14 and the inlet port 17, opposite to the force of the secondary spring element 66. This results in an immediate decrease in pressure in the main chamber 15 and in the branch of the hydraulic circuit extending from the outlet port 14 to the brake caliper.

[0046] Expansion chamber 16 is in fluid communication with inlet port 17 via passage 68 formed in body 11, wherein a one-way valve 69 is installed between expansion chamber 16 and inlet port 17. One-way valve 69 includes a ball 70 and a spring 71, which pushes the ball 70 away from inlet port 17, thereby closing passage 68. One-way valve 69 allows braking fluid to flow from expansion chamber 16 to inlet port 17 in only one direction.

[0047] In the illustrated embodiment, a transverse channel 72 is cut out in the body 32 for construction purposes to facilitate the construction of the bypass channel 50. The transverse channel 72 is permanently closed by a plug schematically indicated by 73.

[0048] For structural reasons, the main body 11 may include two or more complementary parts, in this example a main part 11a and a connecting part 11b. The main part 11a forms the main hydraulic chamber 15, the expansion chamber 16, the inlet port 17, and the outlet port 14. The connecting part 11b is tightly connected to the main part 11a by means of a washer 74.

[0049] Figure 2 The valve unit 10 is shown under normal braking conditions, i.e., when the vehicle is braking, but the wheels receiving brake fluid from the outlet port 14 are not locked and therefore do not slip. Brake fluid fills the first end section 19 and the second intermediate section 20 of the main chamber 15 due to the longitudinally penetrating cavity 31. The main elastic element 34 applies an action that pulls the piston 18 to the left (direction A), thereby overcoming the hydraulic thrust, which as a whole generates a resultant force tending to push the piston 18 to the right (direction B).

[0050] For moderate hydraulic pressure occurring under normal braking conditions (i.e., when the locking condition of the braked wheel is not met), the hydraulic thrust given by the pressure acting on the thrust area has a resultant force, which has a longitudinal component that is smaller than the longitudinal force intensity applied by the main elastic element 34, the thrust area being given by the difference between the area of ​​the annular crown with diameters D2 and D3 and the area of ​​the circle with diameter D1.

[0051] Under normal braking conditions, the elastic force of the main elastic element 34 exceeds the hydraulic thrust, keeping the piston 18 displaced to the left away from the outlet port 14 and in a stationary (or retracted) position. In the stationary position, the piston 18 can abut against the lateral shoulder 75 formed by the body 11.

[0052] When piston 18 is in a stationary position ( Figure 2 When the piston is in its resting position, the piston does not block the bypass passage 50, thus allowing brake fluid to be delivered directly from the inlet port 17 to the outlet port 14. The anti-lock braking system is not activated. In the piston's resting position, the outflow passage 51 between the main chamber 15 and the expansion chamber 16 is closed between two washers 28, 29 on the second part 23 of the piston 18.

[0053] When the wheels lock up during braking, the pressure of the brake fluid in the main hydraulic chamber 15 rises, reaches, and exceeds a certain value. Consequently, the resultant force of the total hydraulic thrust acting on the piston 18 from left and right has a longitudinal component that is stronger and opposite in direction to the elastic force applied by the main elastic element 34. Therefore, the brake fluid pressure in the main hydraulic chamber 15 pushes the piston 18 to the right. Figure 3 In the direction B), move it away from the outlet port 14 to further compress the main elastic element 34.

[0054] Piston 18 closes the bypass passage 50 between washers 26 and 27 by moving toward outlet port 14. Figure 3 This interrupts the flow of brake fluid from the master cylinder to the brake caliper through the valve unit. At the same time, piston 18 opens the outflow passage 51 between the main chamber 15 and the expansion chamber 16, thereby discharging some brake fluid from the main hydraulic chamber 15 into the expansion chamber 16.

[0055] The pressure of the brake fluid entering the expansion chamber 16 pushes the floating valve element 61 away from the inlet port 17 (to the left, direction A), thereby overcoming the elastic force of the secondary spring 66. The volume of the expansion chamber 16 then increases, resulting in a momentary decrease in the brake fluid pressure in the main chamber 15.

[0056] Due to the longitudinally penetrating cavity 31 in piston 18, the pressure reduction in the main hydraulic chamber 15 also simultaneously reduces the brake fluid pressure in the branch of the hydraulic circuit extending from outlet port 14 to the brake caliper. Therefore, the braking force applied by the brake caliper is reduced, thereby unlocking the wheel.

[0057] The pressure drop in the main hydraulic chamber 15 causes the elastic force of the main elastic element 34 to exceed the longitudinal resultant force of the hydraulic thrust again. As a result, the main spring element 34 relaxes, pulling the piston 18 to the left again away from the outlet port 14, 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 brake caliper.

[0058] When the bypass channel 50 reopens, the expansion chamber 16 ( Figure 2 The expansion chamber 16 still contains some brake fluid because the floating valve element 61 has moved in direction A. The volume of brake fluid contained in the expansion chamber 16 must return to the hydraulic circuit so that the brake control device (foot or handle) can return to its initial rest position. Releasing the brake control device reduces the pressure in the hydraulic circuit, allowing the secondary spring 66 to expand and move the floating valve element 61 toward the inlet port 17 (direction B), essentially emptying the expansion chamber 16. Figure 2 It also reintroduces brake fluid into the hydraulic circuit. A check valve 69, which allows the expansion chamber 16 to be emptied, automatically closes due to the action of a spring 71 associated with the ball 70.

[0059] exist Figure 2-5 In the illustrated embodiment, the minimum force required to move piston 18 and thus trigger the anti-lock braking function is adjustable. Adjustment is made as needed by applying a larger or smaller elastic preload to the main elastic element 34. If the compression preload of the main elastic element 34 is low, the relatively low level of hydraulic pressure of the brake fluid in the main chamber 15 will be sufficient to overcome the elastic resistance that keeps piston 18 (to the left) away from outlet port 14. In this example, a low level of preload can be achieved by means of an adjusting device 42 that rotates valve stem 37 in a direction that moves the transverse liner 36 away from the transverse shoulder 35. Figure 4 When the longitudinal length of the main elastic element 34 is large, the compressive force required to keep the piston stationary is low. Therefore, a low peak hydraulic pressure will be sufficient to trigger the ABS system. This low-pressure regulation is preferred when the vehicle is traveling on wet, icy, or unpaved roads, where the braked wheels are more likely to lock up under moderate hydraulic pressure.

[0060] Conversely, on paved roads with a higher coefficient of grip, wheels slip at higher hydraulic pressure levels. Therefore, on non-slip asphalt roads, the preload on the main elastic element 34 can be increased by rotating the valve stem 37 using the adjusting device 42, thereby bringing the lateral liner 36 closer to the lateral shoulder 35, thus shortening and further pre-compressing the main elastic element 34. The shorter the longitudinal length of the main elastic element 34, the greater the compressive force required to hold the piston 18 in its stationary position. Therefore, a higher peak hydraulic pressure is needed to overcome the elastic force and trigger the ABS system.

[0061] In an embodiment where the regulating device 42 is electrically controllable, the regulating device can be activated by an electrical signal from the vehicle's onboard electronic processing unit (ECU) when the ECU receives a speed signal from the wheel sensor indicating a locking or slipping condition.

[0062] The valve stem 37 and the transverse liner 36 are integral with the piston 18 in the longitudinal direction. Preferably, the adjusting device 42 is rotatably coupled to the valve stem 37, but longitudinally disengaged from it, for example by means of a splined axial coupling 44, so as not to increase the inertial mass integral with the piston 18 in the longitudinal direction.

[0063] It should be understood that the ABS system can even be activated without electric control and power supply, because the pressure of the brake fluid in the master hydraulic chamber 15 causes the piston 18 to engage. Some embodiments (e.g.) Figure 2-5 The illustrated embodiment provides the ability to set the intervention level of the ABS valve unit according to road surface conditions.

[0064] A simplified embodiment envisions implementing the ABS valve unit in a vehicle without a power supply. According to an alternative embodiment, the adjustment device 42 may include a manually rotatable knob 42. Figure 6 This allows the user to select the degree of pre-compression of the main elastic element 34, thereby selecting the elastic force acting on the piston 18. Embodiments may provide the possibility of rotating the knob 42 between a plurality of predetermined angular positions, each corresponding to a specific pre-compression level of the main elastic element.

[0065] As an alternative to the threaded connection 39 between the valve stem 37 and the transverse liner 36, adjustment can be made by means of a component having a cam surface.

[0066] According to another embodiment that does not require a power supply ( Figure 7 The main elastic element 34, which pulls the piston 18 away from the outlet port 14, can be configured as a traction elastic element having a first end constrained to the piston 18 and a second end constrained to the transverse liner 36. The transverse liner can be fixed relative to the body 11 or adjustable in the longitudinal position to adjust the pretension of the main elastic element 34, thereby adjusting the traction force acting on the piston as it moves away from the outlet port as needed.

[0067] According to other embodiments (not shown), the adjusting device 42 may be associated with the main elastic element 34 of the traction spring to adjust its pretension.

[0068] While specific embodiments of the invention have been described, it should be understood that this disclosure is provided for illustrative purposes only and the invention should not be limited thereto. Various variations will become apparent to those skilled in the art from the above examples. The scope of the invention is defined only by the appended claims.

Claims

1. A valve unit for a vehicle anti-lock braking system, the valve unit comprising: The valve body (11) has an outlet port (14) that can be hydraulically connected to a brake caliper (G), an inlet port (17) that can be hydraulically connected to a master cylinder (M), a main chamber (15) in fluid communication with the outlet port (14), an expansion chamber (16) having an outlet passage (51) that establishes fluid communication between the main chamber (15) and the expansion chamber (16), and a bypass passage (50) that establishes fluid communication between the inlet port (17) and the outlet port (14). A piston (18) is longitudinally movable in the main chamber (15) and has a longitudinal cavity (31) extending through the piston between an end face (32) of the piston facing the outlet port (14) and a transverse channel (33) leading to a side surface of the piston. The piston (18) generally has a first transverse surface facing the outlet port (14) and a second transverse surface opposite to and away from the outlet port (14), wherein the area of ​​the first transverse surface is smaller than the area of ​​the second transverse surface. At least one elastic element (34) applies an elastic force to move the piston (18) away from the outlet port (14). The piston (18) has two selectable operating positions: In the first position under normal braking conditions, where the force of the elastic element exceeds the longitudinal component of the hydraulic thrust of the braking fluid present in the main chamber (15), the piston (18) moves away from the outlet port (14) and blocks the outflow passage (51) without blocking the bypass passage (50), and In the second position under the starting conditions of the valve unit, wherein the hydraulic thrust of the braking fluid present in the main chamber (15) has a longitudinal component exceeding the force applied by the elastic element (34), thereby the piston (18) moves toward the outlet port (14) and blocks the bypass passage (50) without blocking the outflow passage (51).

2. The valve unit according to claim 1, wherein: The main chamber (15) is formed as follows: The first section (19) is arranged closer to the outlet port (14) and has a first diameter (D1). The third segment (21), which is arranged away from the outlet port (14) and has a third diameter (D3) smaller than the first diameter (D1), and The second intermediate segment (20), located between the first segment (19) and the third segment (21), has a second diameter (D2) that is larger than the first diameter (D1). The piston (18) comprises: The first part (22) slides in a sealed manner within the first section (19) of the main chamber (15). The intermediate portion (23), which slides in a sealing manner within the second intermediate section (20) of the main chamber, and The third part (24) slides in a sealed manner within the third section (21) of the main chamber; thus The first transverse surface has a circular area, the circle having a first diameter (D1), and The second transverse surface has an area of ​​an annular crown, which has an outer circumference with a diameter corresponding to the second diameter (D2) and an inner circumference with a diameter corresponding to the third diameter (D3).

3. The valve unit according to claim 1, further comprising means (42) for adjusting the elastic force applied to the piston (18) by the elastic element (34).

4. The valve unit according to claim 3, wherein, The valve unit includes: A lateral shoulder (35) is located away from the outlet port (14) and is integral with the valve body (11). A transverse liner (36) faces the transverse shoulder (35) and is longitudinally spaced from the transverse shoulder. The valve stem (37) connects the transverse liner (36) to the piston (18) and makes the piston and transverse liner (36) longitudinally integral. Furthermore, the elastic element (34) is a compression spring that is longitudinally compressed between the transverse liner (36) and the transverse shoulder (35).

5. The valve unit according to claim 4, wherein, The device (42) for adjusting the elastic force applied to the piston (18) by the elastic element (34) is configured to adjust the longitudinal distance between the transverse liner (36) and the transverse shoulder (35).

6. The valve unit according to claim 5, wherein, The valve stem (37) includes a threaded valve stem portion that engages in a corresponding threaded through-hole (39) formed through the transverse liner (36), thereby causing a change in the longitudinal distance between the transverse liner (36) and the piston (18) due to rotation applied to the valve stem about its own central longitudinal axis (37A).

7. The valve unit according to claim 6, wherein, The valve stem (37) has an enlarged end head (40) with a circular cross-section, which engages in a groove (41) formed in the piston (18).

8. The valve unit according to claim 6 or 7, wherein, The valve stem (37) has a central longitudinal axis (37A) that is eccentric to the longitudinal central axis (18A) of the piston (18).

9. The valve unit according to claim 6 or 7, wherein, The valve stem (37) has a central longitudinal axis (37A), and the transverse liner (36) has an outer peripheral edge, at least a portion of which is laterally distance (P1) from the central longitudinal axis (37A) greater than the minimum transverse distance (P2) between the central longitudinal axis (37A) and the surface of the valve body (11), the surface of the valve body facing the valve stem (37) in the transverse direction and acting as a stop to prevent the transverse liner (36) from rotating when the valve stem (37) rotates.

10. The valve unit according to claim 6, wherein, The device (42) is rotatably connected to the valve stem (37) via a splined longitudinal coupling (44), which allows relative longitudinal movement between the device (42) and the valve stem (37).

11. The valve unit according to any one of claims 4 to 7, wherein, The transverse liner (36) is accommodated with transverse clearance in the chamber formed by the valve body and is longitudinally movable within the chamber (38) formed by the valve body (11).

12. The valve unit according to claim 1, 2, or 3, wherein, The elastic element (34) is an elastic traction element having a first end constrained to the piston (18) and a second end constrained to a transverse liner (36) integral with the valve body (11).

13. The valve unit according to claim 12, wherein, The transverse liner (36) is fixed relative to the valve body (11) or adjustable in the longitudinal position, thereby adjusting the pretension of the elastic element (34) and thus the traction force acting on the piston away from the outlet port (14).

14. The valve unit according to claim 3, wherein, The device (42) includes an electric actuator that can be electrically connected to an electronic control unit (ECU) mounted on a vehicle carrier.

15. The valve unit according to claim 3, wherein, The device (42) includes a manual adjustment mechanism.

16. The valve unit according to claim 1, wherein, The expansion chamber (16) contains: A longitudinally sliding floating valve element (61), and A secondary spring element (66) pushes the floating valve element (61) toward the inlet port (17). Furthermore, the expansion chamber (16) is in fluid communication with the inlet port (17) via a passage (68), wherein a one-way valve (69, 70, 71) is installed to allow braking fluid to flow from the expansion chamber (16) toward the inlet port (17) through the passage in only one direction (B).

17. The valve unit according to claim 16, wherein: The floating valve element (61) is movable within the expansion chamber (16) between a shoulder (64) and a transverse wall (67) of the valve body (11), the shoulder being arranged closest to the inlet port (17) in the expansion chamber, and the transverse wall being arranged furthest from the inlet port in the expansion chamber, wherein... The outflow channel (51) is positioned longitudinally adjacent to the shoulder (64) and leads to the expansion chamber (16).

18. The valve unit according to claim 4, wherein, The elastic element (34) includes at least two compression springs located between the transverse liner (36) and the transverse shoulder (35), wherein the first spring is always longitudinally pre-compressed between the transverse liner (36) and the transverse shoulder (35), and the second spring has a shorter free length than the first spring and is not longitudinally pre-compressed between the transverse liner (36) and the transverse shoulder (35).

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