WO2022112984A1

WO2022112984A1 - Valve unit for an anti-lock braking system

Info

Publication number: WO2022112984A1
Application number: PCT/IB2021/060958
Authority: WO
Inventors: Sandro Bonardo
Original assignee: RAICAM DRIVELINE S.r.l.
Priority date: 2020-11-27
Filing date: 2021-11-25
Publication date: 2022-06-02
Also published as: IT202000028739A1; TW202229059A

Abstract

A valve unit for an anti-lock braking system of a vehicle comprises a piston (18) longitudinally movable in a primary chamber (15) connectable to an outflow chamber (16). The piston has an internal channel (40) having a first opening (41) formed in a transversal surface (36) of the piston and facing longitudinally to a stationary sealing element (39), and a second opening (42) arranged on a lateral surface (37) of the piston which is received in a section (20) of the primary chamber (15) where an outflow passage (51) opens between the primary chamber and the outflow chamber.

Description

Valve unit for an anti-lock braking system

Technical field

The present invention relates to a valve unit for a hydraulic braking system for controlling the anti-lock function of a vehicle wheel. The valve system is applicable to both motor vehicles and vehicles without an engine, such as bicycles.

Backround art

Anti-lock Braking Systems (ABS) have been installed on vehicles with hydraulic brakes to prevent skidding, or uncontrolled skidding, reducing the effects of an abrupt stop. A system of this type is illustrated in Figure 10, where the four wheels of a motor vehicle are provided with brake discs E1-E4 and relative sensors S1-S4 operationally facing phonic wheels Fl- F4 or equivalent elements, rotationally integral with the brake discs. Sensors S1-S4, according to known methods, detect the rotation speeds of the wheels to which they are associated and send, for example via wiring N1-N4, signals indicative of the rotation speeds to a module or Electronic Control Unit (ECU) which processes the speed signals received. A brake caliper G1-G4 is associated with each brake disc. A master cylinder M operated by a foot control C activates the brake calipers through respective hydraulic lines H1-H4, each of which is fitted 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 electrical command signals from the electronic control unit ECU. When the ECU detects a condition indicative of an imminent locking of a wheel, it activates the respective ABS valve to reduce the hydraulic pressure on the brake at the affected wheel, thus reducing the braking force on this wheel, whereby the wheel remains braked but may rotate. This process is repeated continuously during braking, several times per second, preventing the vehicle from skidding.

Valve units have recently been proposed for an anti-lock braking system of a vehicle, where the valve unit comprises a valve body with a delivery port hydraulically connectable to a brake caliper, an inlet port hydraulically connectable to a master cylinder, a primary hydraulic chamber in fluid communication with the delivery port and an expansion chamber. An outflow passage establishes fluid communication between the primary chamber and the expansion chamber, and a bypass passage provides fluid communication between the inlet port and the delivery port. A piston is longitudinally movable in the primary chamber, operated by a solenoid controlled by an electronic control unit, in contrast to the force of an elastic element. Under normal braking conditions, the force of the elastic element holds the piston in a position where the piston occludes the outflow passage but does not occlude the bypass passage. Under locked-wheel braking conditions, the piston is moved to a position where it occludes the bypass passage while opening the outflow passage, allowing pressure to drain from the primary hydraulic chamber into the outflow chamber. As a result, the pressure on the caliper is reduced, thus releasing the brake.

Summary of the invention

A primary object of the present invention is to provide an ABS valve unit which may be activated in a particularly rapid and effective manner, to intervene in conditions of locking of a braked wheel.

The present invention provides an ABS valve unit comprising an internal piston the actuation stroke whereof is significantly shorter than the currently known ABS valve units. The shortening of the piston stroke makes the intervention of the valve unit faster. This feature is particularly useful for driving the vehicle on slippery surfaces, where the wheels are more likely to lock up during braking.

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

In summary, the valve unit has a piston longitudinally movable in a primary chamber connectable to an outflow chamber. The piston has an internal channel having a first opening formed in a transversal surface of the piston and facing longitudinally to a stationary sealing element, and a second opening arranged on a lateral surface of the piston received in a section of the primary hydraulic chamber where an outflow passage opens between the primary chamber and the outflow chamber.

In valve units of the type discussed in the introduction, the fluid communication between the primary hydraulic chamber and the outflow chamber is determined by one or two sealing rings mounted on the piston. When the piston is operated, it slides into the primary chamber making a stroke that causes a seal to reach and go beyond the opening of the outflow passage in the primary chamber. It is therefore required that the piston stroke has a greater length than the length (measured in the longitudinal direction) of the seal, which must be brought beyond the opening of the outflow passage.

According to an aspect of the present valve unit, the occlusion of the outflow passage is determined by the abutment of the piston in the longitudinal direction against a stationary sealing element. Therefore, a minimum longitudinal distance of the piston from the stationary sealing element is sufficient to open the outflow passage from the primary chamber to the outflow chamber. The piston then performs a very short stroke between the closed and open positions of the outflow passage, which allows a faster succession of the forward and backward movements of the piston, with consequent faster actuation of the valve unit.

Brief description of the drawings

For a better understanding of the present invention, some preferred embodiments will now be described, given by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a valve unit associated with an actuation solenoid;

Figure 2 is a view of the valve unit according to arrow II in Figure 1 ;

Figure 3 is an enlarged longitudinal sectional view of the valve unit of Figure 1, along the section line III- III in Figure 2, in a first operating condition;

Figure 4 is a longitudinal sectional view of the valve unit of Figure 3, in a second operating condition;

Figure 5 is a view of the valve unit according to arrow II in Figure 1 ; Figure 6 is an enlarged longitudinal sectional view of the valve unit of Figure 1, along the section line VI- VI in Figure 5, in a first operating condition;

Figure 7 is an enlarged view of a detail of Figure 6;

Figure 8 is a longitudinal sectional view of the valve unit of Figure 3, in a second operating condition;

Figure 9 is an enlarged view of a detail of Figure 8; and

Figure 10 is a diagram schematically representing the operation of an anti-lock braking system on a vehicle.

Detailed description of the invention

Referring now to Figures 1 to 4, reference numeral 10 indicates as a whole an ABS valve unit for an anti-lock braking system of a vehicle wheel. The valve unit 10 defines 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 with reference to the axis x.

The valve unit 10 comprises a body 11 (or housing) of plastic material defining an actuation direction herein defined as “longitudinal”. In this example, the body 11 has a generally cylindrical tubular shape, with a first end 12 and a second end 13 opposite the first.

The end 12 of the body 11 forms a delivery port (or outlet port) 14, hydraulically connectable to a brake caliper of a vehicle wheel, and an inlet port 17, hydraulically connectable to a master cylinder (or main cylinder), which is operationally associated with a pedal or manual lever actuation control on the vehicle.

The body 11 includes a primary hydraulic chamber 15 and an expansion chamber 16, or secondary hydraulic chamber. The primary hydraulic chamber 15 communicates directly with the delivery port 14 and slidably longitudinally receives a piston 18.

To the valve unit 10 there may be associated an actuating solenoid 80 which may be electrically activated to move the piston 18 in the longitudinal direction indicated with “B.” The actuation solenoid 80 and the valve unit body 11 may be joined by a threaded coupling 81. The actuation solenoid 80 may be electrically connected to an electronic control unit (ECU) which controls the rotation speed of the wheels and is able to detect a condition indicative of an imminent locking of a wheel and to provide a control signal to power the actuation solenoid 80.

For constructional reasons, the piston 18 may be mechanically connected to a longitudinally movable pin 59 of the actuator by means of a connecting element which, as in the exemplary embodiment illustrated herein, comprises a screw 60.

The primary hydraulic chamber 15 forms a first end section 19 (or distal section) with a diameter D1 closer to the delivery port 14, a second intermediate section 20 with a diameter D2 greater than the diameter Dl, and a third section 21 (or proximal section) with a diameter D3 smaller than the diameter Dl, further away from the delivery port 14.

The piston 18 comprises an end portion 22 received in the end section 19 of the primary chamber 15, an enlarged intermediate portion 23 received in the intermediate section 20 of the primary chamber 15, and a proximal portion 24 received in the proximal section 21 of the primary chamber 15.

A longitudinal cavity 31 extends longitudinally through the piston 18 between an end face 32 of the end portion of the piston, facing the delivery port 14, and a transversal passage 33 which opens onto a lateral surface 37 of the second enlarged intermediate portion 23 of the piston. The transversal passage 33 opens onto the intermediate section 20 of the primary hydraulic chamber 15.

Received in the longitudinal through cavity 31 is a primary elastic element 34, in this example a compression spring, elastically compressed between a shoulder 56 of the piston and a transversal wall 58 of the primary hydraulic chamber, adjacent to the delivery port 14. The primary elastic element 34 urges the piston 18 away from the delivery port 14 (in the direction of arrow A). The end portion 22 of the piston 18 has a pair of annular grooves longitudinally adjacent and spaced by a short distance. An annular element 26 of a low friction material, for example polytetrafluoroethylene (PTFE), preferably having a square or rectangular section, is received in a first annular groove, closer to the end face 32 of the piston and to the delivery port 14, so as to have a radially outer surface flush with the cylindrical surface of the first end portion 22 of the piston 18.

In a second annular groove, farther away from the end face 32 of the piston and from the delivery port 14, an annular sealing gasket 27 is accommodated in sliding contact with the end section 19 of the primary chamber 15.

The second enlarged intermediate portion 23 of the piston 18 is provided with a pair of sealing gaskets 28, 29 longitudinally adjacent and spaced by a short distance, which engage with the intermediate section 20 of the primary chamber 15. A proximal seal 30 is mounted on the proximal portion 24 of the piston so as to sealingly engage the proximal section 21 of the primary chamber 15.

A first bypass passage 50 is formed in the body 11 of the valve unit and opens onto the end section 19 of the primary hydraulic chamber 15, putting such chamber in fluid communication with the inlet port 17.

The bypass passage 50 opens onto the primary hydraulic chamber 15 at a point longitudinally positioned in proximity to the inlet port 17.

An outflow passage 51 is formed in the body 11 of the valve unit and opens onto the intermediate section 20 of the primary hydraulic chamber 15, setting such chamber in fluid communication with the expansion chamber 16.

The expansion chamber 16 receives a floating shutter 61 having a seal 62 which slidingly longitudinally engages with a cylindrical section 63 of the expansion chamber 16. The floating shutter 61 is movable within the expansion chamber 16 between a shoulder 64 formed closer to the inlet port 17, and a transversal wall 67, further away from the inlet port 17.

The outflow passage 51 opens onto the expansion chamber 16 at a point longitudinally positioned closer to the inlet port 17. In the illustrated embodiment, the outflow passage 51 opens at a first end of the cylindrical section 63 of the expansion chamber 16 further away from the inlet port 17.

The outflow passage 51 opens onto the primary hydraulic chamber 15 at a point positioned longitudinally intermediate between the two sealing gaskets 28, 29 on the piston 18.

The body 11 forms a transversal shoulder 35 which faces the delivery port 14 and faces the second intermediate section 20, larger and having the largest diameter D2, of the primary hydraulic chamber 15. The piston 18 forms a transversal or radial annular surface 36 which joins the second intermediate section 20 and the third 21 (or proximal section) of the piston 18 and faces the transversal shoulder 35 of the body 11.

An internal channel 40 (Figures 6 and 8) extends through the piston 18 between the transversal annular surface 36 and the lateral surface 37 of the second enlarged intermediate portion 23. The internal channel 40 forms a first opening 41 on the transversal annular surface 36 (Figures 7 and 9) and a second opening 42 arranged on the lateral surface 37 of the second enlarged intermediate portion 23 between the two annular sealing gaskets 28 and 29.

A stationary resilient sealing element 39 is fixed to the body 11 and partially protrudes from the transversal shoulder 35 in the longitudinal direction towards the first opening 41 of the internal channel 40. More particularly, the stationary resilient sealing element 39 is longitudinally aligned with the first opening 41 of the internal channel 40.

A secondary spring element 66, for example a compression spring, is elastically compressed between the floating shutter 61 and the transversal wall 67 of the valve body 32. The secondary spring element 66 urges the floating shutter 61 in the direction B towards the end 12 of the body 11, therefore towards the inlet port 17. As described later herein, the introduction of brake fluid under pressure from the primary chamber 15 into the expansion chamber 16 causes the floating shutter 61 to move in the direction A, moving it longitudinally away from the delivery port 14 and from the inlet port 17, in contrast with the strength of the secondary spring element 66.

The expansion chamber 16 is in fluid communication with the inlet port 17 through a channel 68, formed in the body 11, in which a one-way valve 69 is mounted between the expansion chamber 16 and the inlet port 17. The one-way valve 69 consists of a ball 70 and a spring 71, which pushes the ball 70 away from the inlet port 17 so as to occlude the channel 68. The one-way valve 69 allows brake fluid to flow through it only in one direction, from the expansion chamber 16 to the inlet port 17.

In the illustrated embodiment, a transversal bore 72 is formed in the body 11 for construction reasons, in order to facilitate the construction of the bypass passage 50. The transversal bore 72 is closed permanently by a plug schematically represented with 73.

For constructional reasons, the body 11 may consist of two or more complementary parts, in this example a main part 11a and a connection part lib mounted on the actuation solenoid 80. The main part 11a forms the primary hydraulic chamber 15, the expansion chamber 16 and the inlet port 17 and the delivery port 14. The connection part 1 lb, which in the example illustrated herein has the resilient stationary element 39, is sealingly coupled with the main part 1 la by means of a gasket 74.

Figures 3 and 6 illustrate the valve unit 10 in normal braking conditions, i.e. when the vehicle is braking but the wheel which receives the brake fluid from the delivery port 14 is not blocked, and therefore does not slip. The brake fluid fills the primary chamber 15, both in the first end section 19 and in the second intermediate section 20, by virtue of the longitudinal through cavity 31. The primary elastic element 34 exerts an action which pushes the piston 18 towards the left (arrow A) and keeps the piston 18 away from the delivery port 14, in a rest position (or retracted position). In the rest position, the piston 18 abuts against the transversal shoulder 35 of the body 11. When the piston 18 is in the rest position, it does not obstruct the bypass passage 50, thus allowing the direct passage of the brake fluid from the inlet port 17 to the delivery port 14. The anti-lock braking system is not active. In the rest position of the piston, the internal channel 40 is closed (Figures 6 and 7), because the stationary resilient sealing element 39 occludes the first opening 41 of the internal channel 40. Therefore, the brake fluid cannot flow from the primary hydraulic chamber 15 to the outflow passage 51 and then to the expansion chamber 16.

In locked wheel braking conditions, the actuation solenoid 80 is activated, whereby (Figures 4 and 8) the piston 18 is made to move towards the delivery port 14 (towards the right, direction B), compressing the primary elastic element 34. The annular member 26 temporarily closes the bypass passage 50, whereby the flow of brake fluid from the master cylinder to the brake caliper through the valve unit is interrupted. The piston 18 moves away from actuation solenoid 80.

As soon as the transversal surface 36 moves away from the stationary resilient member 39, the internal channel 40 is opened. The second opening 42 of the internal channel 40 moves at the outflow passage 51, and therefore the brake fluid may flow from the second contact 20 of the primary chamber 15 and to the expansion chamber 16 passing through the internal channel 40 and the outflow passage 51.

The pressure of the brake fluid entering the expansion chamber 16 pushes the floating shutter 61 towards the actuator (towards the left, direction A), overcoming the elastic force of the secondary spring 66. The volume of the expansion chamber 16 then increases and, as a result, the brake fluid pressure in the primary chamber 15 is instantly reduced. Due to the longitudinal through cavity 31 in the piston 18, the pressure drop in the primary chamber also simultaneously reduces the pressure of the brake fluid downstream of the delivery port 14 in the piping directed towards the brake caliper. The front brake caliper is therefore released, unlocking the wheel.

When the front wheel is unlocked, the electronic control unit cuts off the power supply to the actuation solenoid 80, so that the primary elastic element 34 may stretch, moving the piston 18 away from the delivery port 14, thus reopening the bypass passage 50. The piston 18 abuts against the transversal shoulder 35, whereby the stationary resilient sealing element 39 closes the internal channel 40 again. As a result, the master cylinder is again in fluid communication with the brake caliper.

When the bypass passage 50 is reopened, the expansion chamber 16 still contains a certain amount of brake fluid since the floating shutter 61 has moved in the direction A. The volume of brake fluid contained in the expansion chamber 16 must be returned to the hydraulic circuit so that the brake control (pedal or manual lever) may return to its initial rest position. As the pressure in the hydraulic circuit decreases, the secondary spring 66 may expand and cause the floating shutter 61 to move towards the inlet port 17 (direction B), substantially emptying the expansion chamber 16 (Figure 2) and reintroducing the brake fluid in the hydraulic circuit. The emptying of the expansion chamber 16 is made possible by the one way valve 69, which closes automatically by virtue of the action of the spring 71 associated with the ball 70.

In the illustrated embodiment, the opening of the outflow channel 51 on the primary hydraulic chamber always remains intermediate between the two annular sealing gaskets 28 and 29.

As it will be appreciated, a minimum longitudinal distance of the piston 18 from the stationary sealing element 39 is sufficient to put the primary chamber 15 in fluid communication with the outflow chamber 16. The outflow through the outflow channel 51 is not determined by the passage of gaskets beyond the outflow channel 51, but simply by the abutment or not of the piston 18 against the resilient and stationary sealing element 39. Therefore, the piston makes a very short stroke between the closed position of the outflow passage and an open position, which allows a faster succession of the forward and backward movements of the piston, with consequent rapid activation of the valve unit.

Advantageously, the operating stroke of the piston may be reduced to about 1 mm - 1.5 mm. In the illustrated embodiment, in the open position of the outflow passage the bypass passage 50 is blocked by the annular Teflon element 26. Since the piston is in this position for a few hundredths of a second, the annular element 26 is not required to seal the bypass passage 50. Therefore, the annular element 26 is not required to be a sealing element. The annular element 26 is optional. If provided, it is preferably of a low friction material, and has a radially outer surface arranged flush with the piston surface in that portion 22.

While specific embodiments of the invention have been described, it is to be understood that this disclosure has been provided for illustrative purposes only and that the invention is not to be limited in any way by it. Various modifications will be evident to those skilled in the art in the light of the preceding examples. The scope of the invention is limited only by the appended claims.

Claims

1. A valve unit for an anti-lock braking system of a vehicle, the valve unit comprising: a valve body (11) with a delivery port (14) hydraulically connectable to a brake caliper (G), an inlet port (17) hydraulically connectable to a master cylinder (M), a primary chamber (15) in fluid communication with the delivery port (14), an expansion chamber (16) with an outflow passage (51) establishing fluid communication between the primary chamber (15) and the expansion chamber (16), a bypass passage (50) providing fluid communication between the inlet port (17) and the delivery port (14), wherein the valve body (11) forms a transversal shoulder (35) fitted with a stationary sealing element (39) arranged at least partially in the primary hydraulic chamber (15); a piston (18) longitudinally movable in the primary chamber (15) and having an internal channel (40) with a first opening (41) formed in a transversal surface (36) of the piston and longitudinally facing the stationary sealing element (39) and a second opening (42) arranged on a lateral surface (37) of the piston received in a portion (20) of the primary hydraulic chamber (15) where the outflow passage (51) opens; an elastic element (34) exerting a longitudinal elastic force to move the piston (18) away from the delivery port (14).

2. A valve unit according to claim 1, wherein the piston (18) has two alternative operating positions: a first position, under normal braking conditions, in which the longitudinal force of the primary elastic element (34) keeps the piston (18) away from the delivery port (14) with said transversal surface (36) of the piston abutting against the stationary sealing element (39), whereby the stationary sealing element (39) occludes the outflow passage (51) and the piston (18) does not occlude the bypass passage (50), and a second position, in locked wheel braking conditions, in which the piston (18) is moved closer to the delivery port (14), the transversal surface (36) of the piston is moved away from the stationary sealing element (39), whereby the stationary sealing element (39) does not block the outflow passage (51), the inner channel (40) of the piston is in fluid communication with the outflow passage (51), and the piston (18) occludes the bypass passage (50).

3. A valve unit according to claim 1 or 2, wherein the piston (18) forms a longitudinal cavity (31) which extends through the piston between an end face (32) of the piston, facing the delivery port (14), and a transversal passage (33) which opens onto a lateral surface of the piston.

4. A valve unit according to claim 1, wherein: the primary hydraulic chamber (15) forms a first section (19) arranged closer to the delivery port (14) and having a first diameter (Dl), a third section (21) arranged farther from the delivery port (14) and having a third diameter (D3) smaller than the first diameter (Dl), and a second section (20), intermediate between the first section (19) and the third section (21), having a second diameter (D2) greater than the first diameter (Dl); and the piston (18) includes a first portion (22) sealingly sliding in the first portion (19) of the primary chamber (15), an intermediate portion (23) sealingly sliding in the second intermediate section (20) of the primary chamber, and a third portion (24) sealingly sliding in the third section (21) of the primary chamber.

5. A valve unit according to claim 4, wherein the second opening (42) of the inner channel (40) opens on a lateral surface (37) of the intermediate portion (23) of the piston between two sealing rings (28, 29) which slidingly engage the second section (20) of the primary chamber (15).

6. A valve unit according to claim 4, wherein the first portion (22) of the piston (18) has a pair of longitudinally adjacent annular grooves, with a first annular groove, closer to an end face (32) of the piston and to the delivery port (14), which accommodates an annular element (26) of a low friction material, a second annular groove, farther away from the end face (32) of the piston and from the delivery port (14), which accommodates an annular sealing gasket (27) in sliding contact with the first section (19) of the primary hydraulic chamber (15).

7. A valve unit according to claim 6, wherein the annular element (26) made of low friction material has a radially outer surface arranged flush with the side surface of the first portion (22) of the piston.

8. Valve unit according to any one of the preceding claims, wherein the stationary sealing element (39) is a resilient element that partially protrudes from the transversal shoulder (35) of the valve body (11) in a longitudinal direction towards the first opening (41) of the inner channel (40) of the piston (18).