VALVE UNIT FOR AN ANTI-LOCK BRAKING SYSTEM

A valve unit for an anti-lock braking system has a valve body, a piston, and an elastic element acting on the piston. The valve body has an outlet port, an inlet port, a primary chamber communicating with the outlet port, an expansion chamber with an outflow passage establishing fluid communication between the primary chamber and the expansion chamber, and a bypass passage between the inlet port and the outlet port. The piston is movable in the primary chamber and has a longitudinal through cavity, a first transversal surface facing the outlet port, and a second transversal surface facing away from the outlet port. The first transversal surface has an area smaller than the area of the second transversal surface. The elastic element exerts an elastic force to move the piston away from the outlet port. The valve unit is activatable by pressure of a brake fluid in the primary chamber.

TECHNICAL FIELD

The present invention relates to a valve unit for a hydraulic braking system to control the anti-lock function of a wheel of a vehicle. The valve system is applicable to both motorized and non-motorized vehicles, such as bicycles.

BACKGROUND ART

Anti-lock Braking Systems (“ABS”) have been installed on vehicles with hydraulic brakes to prevent skidding, or uncontrolled slippage, reducing the effects of an abrupt stop. One such system is illustrated inFIG.1, where the four wheels of a motor vehicle are equipped with brake discs E1-E4and related sensors S1-S4operatively facing phonic wheels F1-F4or equivalent elements, rotationally integral with the brake discs. The sensors S1-S4, according to known modes, detect the rotation speeds of the wheels to which they are associated and send, for example through wiring N1-N4, signals indicative of the rotation speeds to an Electronic Control Unit (ECU) or module which processes the speed signals received. Each brake disc is associated with a brake caliper G1-G4. A master cylinder M operated by a foot control C activates the brake calipers through respective hydraulic lines H1-H4, on each of which a valve unit ABS1-ABS4is installed. Each ABS valve unit controls the flow and pressure of brake fluid to the associated brake caliper in response to electrical control signals from the electronic control unit ECU. When the ECU detects a condition indicative of an impending wheel lockup, it actuates the respective ABS valve to reduce the hydraulic pressure on the brake at the affected wheel, thereby reducing the braking force on this wheel, so that the wheel remains braked but may rotate. This process is repeated continuously during braking, several times per second, preventing the vehicle from slipping.

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

EP 3 392 105 A2 describes a hydraulic braking system for a bicycle, including two electrically operated valve assemblies. Each valve assembly is operated separately from the other by a respective electric actuator. A first valve assembly is used to block the brake fluid between the master cylinder and the brake calipers, and a second valve assembly is used to open a parallel channel that hydraulically connects the brake caliper to an accumulator. The two electric actuators are individually powered by the ECU in a predetermined sequence. The two valve assemblies are positioned on parallel branches of a hydraulic circuit that connects a main cylinder operated by a hand lever, and a brake caliper. During normal braking, a first valve assembly is open, allowing direct fluid communication between the master cylinder and the brake caliper, while the second valve assembly is closed. Under hard braking conditions, in an impending wheel lock-up, a first electric actuator closes the first valve assembly, thus blocking the pressure input from the hand lever, so that the pressure is blocked from the first valve assembly to the caliper, preventing a further increase in pressure acting on the caliper. A second electric actuator opens the second valve, allowing the pressure to discharge into the accumulator, which is located upstream of the second valve in the parallel channel. As a result, the pressure on the caliper is reduced, releasing the brake.

Other ABS systems comprise a valve unit comprising a piston that is mounted in the hydraulic line. The piston is controlled by an electric actuator (solenoid) that makes the piston move back and forth in order to change the volume in the hydraulic line and thus modulate the pressure in the braking circuit.

SUMMARY OF THE INVENTION

In light of the prior art, a primary object of this invention is to provide an ABS valve unit that may be activated, to intervene in conditions of locking a braked wheel, not by an electrical control of a conventional actuator.

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

According to one aspect, this invention discloses a valve unit for a hydraulic braking system to control the anti-lock function of a wheel of a vehicle, as defined in claim1. Preferred embodiments of the invention are defined in the dependent claims.

In summary, a valve unit for an anti-lock braking system of a vehicle comprises a valve body, a movable piston in the valve body, and an elastic element acting on the piston. The valve body has an outlet port that may be hydraulically connected to a brake caliper, an inlet port that may be hydraulically connected to a master cylinder, a primary chamber in fluid communication with the outlet port, an expansion chamber with an outflow passage that achieves fluid communication between the primary chamber and the expansion chamber, and a bypass passage that achieves fluid communication between the inlet port and the outlet port. The piston is movable longitudinally in the primary chamber and has a longitudinal cavity extending through the piston between an end face of the piston, facing the outlet port, and a transversal passage that opens onto a lateral surface of the piston. The piston has collectively a first transverse surface, facing away from the outlet port, and a second transversal surface opposite the first transversal surface and facing away from the outlet port, and where the first transversal surface has an area smaller than the area of the second transversal surface. The elastic element exerts an elastic force to move the piston away from the outlet port. The piston has two alternative operational positions:a first position, under normal braking conditions, in which the elastic force of the elastic element prevails over the longitudinal component of the hydraulic thrust of the brake fluid present in the primary chamber, whereby the piston is moved away from the outlet port and occludes the outflow passage without occluding the bypass passage, anda second position, in conditions of activation of the valve unit, in which the hydraulic thrust of the brake fluid present in the primary chamber has a longitudinal component that prevails over the force exerted by the elastic element, whereby the piston is displaced towards the outlet port and occludes the bypass passage while not occluding the outflow passage.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS.2to5, reference number10designates as a whole an ABS valve unit for an anti-lock braking system for a wheel of a vehicle. The valve unit10defines a longitudinal axis x and has an elongated shape in the direction defined herein as longitudinal or axial. In the sense used in this context, terms such as “longitudinal” and “transversal” will be understood in reference to the x-axis.

The valve unit10comprises a body11(or housing) made of plastic material defining an actuation direction referred to herein as “longitudinal.” The body11has, in this example, an overall cylindrical tubular shape, with a first end12and a second end13opposite the first end.

The end12of the body11forms an outlet port (or exit port)14, hydraulically connectable to a brake caliper (not shown) of a brake for a wheel of a vehicle, and an inlet port17, hydraulically connectable to a master cylinder (or principal cylinder, not shown), which is operatively associated with an actuation control by a foot pedal or hand lever (not shown) on the vehicle.

The body11includes a primary hydraulic chamber15and an expansion chamber16, or secondary hydraulic chamber. The primary hydraulic chamber15communicates directly with the outlet port14and longitudinally receives a piston18in a slidable manner.

The primary hydraulic chamber15forms a first end section19(or distal section) having a diameter D1closer to the outlet port14, a second intermediate section20having a diameter D2greater than the diameter D1, and a third section21(or proximal section) having a diameter D3less than the diameter D1, further away from the outlet port14.

The piston18comprises an end portion22received in the end section19of the primary chamber15, an intermediate portion23received in the intermediate section20of the primary chamber15, and a proximal portion24received in the proximal section21of the primary chamber15.

The end portion22of the piston18is provided with a pair of longitudinally adjacent sealing end gaskets26,27which are spaced a short distance apart; the gaskets26,27are in sliding contact with the end section19of the primary chamber15. The intermediate portion23of the piston18is provided with a pair of intermediate gaskets28,29longitudinally adjacent and spaced a short distance apart, which engage with the intermediate section20of the primary chamber15. A proximal sealing gasket30is mounted on the proximal portion24of the piston so as to sealingly engage with the proximal section21of the primary chamber15.

The piston18forms a longitudinal cavity31that extends through the piston between an end face32of the end portion of the piston, facing the outlet port14, and a transversal passage33that discharges onto a side surface of the piston. The transversal passage33flows onto the intermediate section20of the primary hydraulic chamber15.

In the portion13of the body11opposite the end having the inlet ports17and the outlet ports14, a primary elastic element34is received, which urges the piston18away from the outlet port14.

In the embodiment ofFIG.2-5, the primary elastic element34is formed as a single compression spring, compressed longitudinally between a shoulder35of the body11and a transversal contrast wall36, facing the shoulder35and longitudinally spaced therefrom. Alternative embodiments to the one shown may involve more than one elastic element, for example two springs, one of which is already pre-stressed and only one supported, to provide different levels of preload along a short longitudinal stroke.

The transversal contrast wall36is received with transversal play and is longitudinally movable within a chamber38advantageously formed by the body11.

A stem37connects the transversal contrast wall36to the piston18and makes it longitudinally integral therewith.

Longitudinal compression of the primary elastic element34pushes the transversal contrast wall36to the left, and this consequently pulls the piston18to the left via the stem37.

The longitudinal distance between the transversal contrast wall36and the shoulder35may be adjusted to vary the longitudinal elastic force with which the primary elastic element pulls the piston18away from the outlet port14.

According to an embodiment, the stem37may be made as a threaded stem that engages through a corresponding threaded through-hole39formed through the transversal contrast wall36.

The stem37may have an enlarged terminal head40with a circular cross section, for example spherical, engaged in a corresponding recess41formed in the portion24of the piston18.

An adjusting device42may be envisaged to adjust the elastic force with which the piston18is urged away from the outlet port14. The adjusting device42may vary the longitudinal position of the transversal contrast wall36along the stem37, thereby adjusting the distance between the transversal contrast wall36and the shoulder35and consequently the length of the primary elastic element34and its compression. By rotating the stem37in a given rotation direction about its longitudinal axis37A by means of the adjusting device42, so as to further compress the primary elastic element34and thus shorten it longitudinally, the traction force by which the piston18is moved away from the outlet port14is consequently increased. Conversely, by rotating the stem37in an opposite direction of rotation, the primary elastic element34is decompressed and allowed to elongate longitudinally, thereby reducing the traction force by which the piston18is pulled away from the outlet port14.

The stem37has a central longitudinal axis37A preferably eccentric with respect to the longitudinal central axis18A of the piston18. In this way, a rotation imparted to the stem37about its axis37A during the phase of adjusting the position of the transversal contrast wall36does not cause an undesired rotation also of the piston18about the axis18A thereof, with consequent wear on the sealing gaskets mounted on the piston18and acting against the walls of the primary hydraulic chamber15. As an alternative to the aforementioned eccentric arrangement of the axes, different embodiments (not shown) may provide for anti-rotation elements, such as, for example, transversal teeth projecting radially from the piston18and/or the transversal contrast wall36.

Transversal play between the edges of the transversal contrast wall36and the chamber38is desirable to reduce friction during the longitudinal movement of the piston18together with the wall36. To ensure that the rotation imparted to the stem37causes a screwing or unscrewing relative to the contrast wall36, it is preferred that this at least one portion of the peripheral edge of the wall36has a transversal distance P1from the axis37A greater than a minimum transversal distance P2between the axis37A and the inner surface of the chamber38. In this way, the inner surface of the chamber38acts as a contrast wall to rotationally block the transversal wall36when the stem37is rotated.

According to one embodiment, the adjusting device42that rotates the threaded stem37comprises an electric drive controlled by an electronic control unit (ECU,FIG.1), mounted on board the vehicle, which may adjust the elastic force of the primary elastic element34as needed, as explained below.

In the primary chamber15, the brake fluid present in the first end section19closer to the outlet port14acts on a circular area of the piston18having a circumference of diameter D1, defined by the gaskets26,27. The brake fluid present in the first section, between the outlet port14and the sealing gasket27, exerts a longitudinal thrust on the piston18directed to the left (direction A) in the accompanying drawings, away from the outlet port14.

The brake fluid contained in the second intermediate section20of the primary chamber15exerts a longitudinal hydraulic thrust on an area of the piston determined by a circular crown having an outer circumference of diameter D2, corresponding to the diameter of the second intermediate section20of the primary chamber15, and an inner circumference of diameter D3, corresponding to the diameter of the third section21of the primary chamber15, farther from the outlet port14. The hydraulic thrust of the brake fluid in the second intermediate section20of the primary chamber is directed to the right in the accompanying drawings and pushes the piston18closer to the outlet port14.

The diameters D1, D2, and D3of the respective three sections19,20, and21of the primary chamber, and the diameters of the corresponding portions22,23, and24of the piston18, are chosen such that the area of a circular crown delimited by the diameters D2and D3is greater than the area of a circle having diameter D1. Consequently, the overall hydraulic thrust acting on the piston18has a longitudinal resultant that acts on the piston18pushing it closer to the outlet port14.

The overall hydraulic thrust acting on the piston18is therefore directed in the direction opposite to the stress produced by the primary elastic element34, which acts on the piston18away from the outlet port14.

A first bypass passage50is formed in the body11of the valve assembly and opens onto the end section19of the primary hydraulic chamber15, placing this chamber in fluid communication with the inlet port17. An outflow passage51is formed in the body11of the valve unit and opens onto the intermediate section20of the primary hydraulic chamber15, placing this chamber in fluid communication with the expansion chamber16.

The expansion chamber16receives a floating valve element61having a sealing gasket62that engages with a cylindrical portion63of the expansion chamber16in a longitudinally slidable manner. The floating valve element61is movable within the expansion chamber16between a shoulder64formed closer to the inlet port17, and a transversal wall67farther from the inlet port17.

The outflow passage51flows onto the expansion chamber16at a point positioned longitudinally closer to the inlet port17. The outflow passage51opens at a first end of the cylindrical section63of the expansion chamber16further from the inlet port17.

A secondary spring element66, such as a compression spring, is elastically compressed between the floating valve element61and the transversal wall67of the valve body32. The secondary spring element66urges the floating valve element61in the direction B toward the end12of the body11, thus toward the inlet port17. As described below, the introduction of pressurized brake fluid from the primary chamber15into the expansion chamber16causes the floating valve element61to move in the direction A, longitudinally away from the outlet port14and the inlet port17, in contrast to the force of the secondary spring element66, resulting in an immediate reduction of the pressure in the primary chamber15and in the branch of the hydraulic circuit extending from the outlet port14to the brake caliper.

The expansion chamber16is in fluid communication with the inlet port17through a channel68formed in the body11, wherein a one-way valve69is mounted between the expansion chamber16and the inlet port17. The one-way valve69comprises a ball70and a spring71, which pushes the ball70away from the inlet port17so as to occlude the channel68. The one-way valve69allows brake fluid to flow through it in only one direction, from the expansion chamber16toward the inlet port17.

In the illustrated embodiment, a transversal passage72is cut into the body32for constructive reasons to facilitate the construction of the bypass passage50. The transversal passage72is permanently closed by a plug schematically represented with73.

For constructional reasons, the body11may comprise two or more complementary parts, in this example a main part11aand a connecting part11b. The main portion11aforms the primary hydraulic chamber15, the expansion chamber16and the inlet port17, and the outlet port14. The connecting portion11bis tightly coupled to the main portion11aby means of a gasket74.

FIG.2illustrates the valve unit10under normal braking conditions, i.e., when the vehicle is braking but the wheel receiving the brake fluid from the outlet port14is not locked, and therefore does not slip. Brake fluid fills the primary chamber15, both in the first terminal section19and in the second intermediate section20, due to the longitudinal through cavity31. The primary elastic element34exerts an action that pulls the piston18to the left (direction A), overriding the hydraulic thrust that as a whole produces a resultant that tends to push the piston18to the right (direction B).

For moderate hydraulic pressures, occurring in a normal braking condition, i.e., without reaching a locked condition of the braked wheel, the hydraulic thrust given by the pressure acting on a thrust area given by the difference between the area of the circular crown having diameters D2and D3and the area of the circle having diameter D1, has a resultant with longitudinal component of less intensity with respect to the longitudinal force exerted by the primary elastic element34.

Under normal braking conditions, the elastic force of the primary elastic element34overrides the hydraulic thrust and holds the piston18displaced to the left, away from the outlet port14, in a rest position (or retracted position). In the rest position, the piston18may be in abutment against a transversal shoulder75formed by the body11.

When the piston18is in the rest position (FIG.2), it does not occlude the bypass passage50, allowing direct transit of brake fluid from the inlet port17to the outlet port14. The anti-lock braking system is not active. In the rest position of the piston, the outflow passage51between the primary chamber15and the expansion chamber16is instead closed between the two gaskets28,29on the second portion23of the piston18.

In locked wheel braking conditions, the pressure of the brake fluid present in the primary hydraulic chamber15rises, reaches, and exceeds a value whereby the resultant of the overall hydraulic thrust acting on the piston18, from left and right, has a longitudinal component of greater intensity and opposite direction with respect to the elastic force exerted by the primary elastic element34. Therefore, the brake fluid pressure in the primary hydraulic chamber15thrusts the piston18to the right (direction B,FIG.3), moving it away from the outlet port14further compressing the primary elastic element34.

The piston18, by moving toward the outlet port14, closes the bypass passage50between the gaskets26,27(FIG.3), whereby the flow of brake fluid from the master cylinder to the brake caliper through the valve unit is interrupted. At the same time, the piston18opens the outflow passage51between the primary chamber15and the expansion chamber16, whereby some of the brake fluid vents from the primary hydraulic chamber15to the expansion chamber16.

The pressure of the brake fluid entering the expansion chamber16thrusts the floating valve element61away from the inlet port17(to the left, direction A), overcoming the elastic force of the secondary spring66. The volume of the expansion chamber16then increases and, as a result, the brake fluid pressure in the primary chamber15is instantaneously reduced.

Due to the longitudinal through cavity31in the piston18, the pressure reduction in the primary hydraulic chamber15also simultaneously reduces the brake fluid pressure in the branch of the hydraulic circuit extending from the outlet port14to the brake caliper. The braking force exerted by the brake caliper is thus decreased, unlocking the wheel.

The pressure reduction in the primary hydraulic chamber15causes the elastic force of the primary elastic element34to again prevail over the longitudinal resultant of the hydraulic thrust, whereby the primary spring element34relaxes, pulls the piston18to the left away from the outlet port14again, reopening the bypass passage50and closing the outflow passage51. As a result, the master cylinder is again in fluid communication with the brake caliper.

When the bypass passage50is reopened, the expansion chamber16(FIG.2) still contains some brake fluid because the floating valve element61has moved in the direction A. The volume of brake fluid contained in the expansion chamber16must be returned to the hydraulic circuit so that the brake control (foot or hand lever) may return to its initial rest position. Releasing the brake control decreases the pressure in the hydraulic circuit, so that the secondary spring66may expand and move the floating valve element61toward the inlet port17(direction B), essentially emptying the expansion chamber16(FIG.2) and reintroducing brake fluid into the hydraulic circuit. The emptying of the expansion chamber16is made possible by the one-way valve69, which closes automatically due to the action of the spring71associated with the ball70.

In the embodiment illustrated inFIG.2-5, the minimum force to cause the piston18to move, and thus to trigger the anti-locking function, is adjustable. The adjustment is made by applying greater or lesser elastic preload to the primary elastic element34, as required. If the compression preload of the primary elastic element34is low, a relatively low level in the hydraulic pressure of the brake fluid in the primary chamber15will be sufficient to overcome the elastic resistance that keeps the piston18(to the left) away from the outlet port14. A low level of preload is achievable in this example by means of the adjusting device42, which rotates the stem37in a direction that moves the transversal contrast wall36away from the transversal shoulder35(FIG.4). When the longitudinal length of the primary elastic element34is greater, the compressive force with which this elastic element holds the piston at rest is low. Therefore, a peak hydraulic pressure that is not high will be enough to trigger the ABS system. Such a low-pressure adjustment is preferable when the vehicle is traveling on slippery, icy, or unpaved roads, along which braked wheels may lock more easily with modest hydraulic pressures.

Conversely, for travel on paved road surfaces, with a higher grip coefficient, a wheel slip condition occurs at higher hydraulic pressure levels. Therefore, for driving on non-slippery asphalt roads, the preload on the primary elastic element34may be increased by rotating the stem37by means of the adjusting device42in such a way as to bring the transversal contrast wall36closer to the transversal shoulder35, thereby shortening and further pre-compressing the primary elastic element34. With a shorter longitudinal length of the primary elastic element34, the compressive force with which this elastic element holds the piston18in its rest position increases. Consequently, a higher peak hydraulic pressure will be required to overcome the elastic force and trigger the ABS system.

In embodiments where the adjusting device42is electrically controllable, it may be activated by an electrical signal from the vehicle's on-board electronic processing unit (ECU) when the ECU receives speed signals from the wheel sensors indicative of a locking or slipping situation.

The stem37and the transversal contrast wall36are longitudinally integral with the piston18. Preferably, the adjusting device42is rotationally coupled to the stem37but longitudinally disengaged therefrom, for example by means of a splined axial coupling44, so as not to increase the inertial mass longitudinally integral with the piston18.

As will be appreciated, the ABS system may be activated even in the absence of an electrical control and electrical power supply, since it is the pressure of the brake fluid in the primary hydraulic chamber15that causes the piston18to intervene. Some embodiments, such as the one shown inFIG.2-5, provide the ability to set the intervention level of the ABS valve unit according to road surface conditions.

Simplified embodiments may envisage the ABS valve unit being implemented on a vehicle in the absence of an electrical power supply. According to an alternative embodiment, the adjusting device42may comprise a manually rotatable knob42(FIG.6) that allows the user to select the degree of pre-compression of the primary elastic element34and thus the elastic force acting on the piston18. Embodiments may provide the possibility of rotating the knob42among a plurality of predefined angular positions, each corresponding to a respective level of precompression of the primary elastic element.

As an alternative to a threaded coupling39between the stem37and the transversal contrast wall36, an adjustment by means of a member with cam surfaces may be used.

According to a further embodiment (FIG.7), which does not require an electrical power supply, the primary elastic element34that stresses the piston18away from the outlet port14may be formed as a traction elastic element, having a first end constrained to the piston18and a second end constrained to a transversal contrast wall36. The transversal contrast wall may be fixed with respect to the body11or adjustable in a longitudinal position to adjust the pre-tensioning of the primary elastic element34and thus the traction force acting on the piston as it moves away from the outlet port, as required.

According to other embodiments (not shown), an adjusting device42may be associated with a primary elastic element34implemented as a traction spring, to adjust the pre-tensioning thereof.

While specific embodiments of the invention have been described, it should be understood that this disclosure has been provided purely for illustrative purposes and that the invention should not be limited in any way thereby. Various changes will become apparent to persons skilled in the art in light of the above examples. The scope of the invention is limited only by the appended claims.