Pneumatic double check valve and electro-pneumatic brake pressure modulator comprising such pneumatic double check valve

Abstract

A pneumatic double check valve comprising a valve body having a longitudinal axis, a cavity, a first inlet opening, a second inlet opening and an outlet opening, the cavity being in fluid communication with the first inlet opening, the second inlet opening and the outlet opening. A first and a second shuttle are placed within the valve body, and a preloaded helical spring is interposed between and acting on them. The first and second shuttles are movable, by loading with pneumatic-induced pressures greater than respective shuttle crack off pressures, between first and second positions spaced therefrom, so that to alternatively close and open the first and the second inlet openings, respectively. The pneumatic double check valve is designed to avoid shuttle swimming failure, improve response time behaviour and facilitate port interchangeability.

Description

[0001] Pneumatic double check valve and electro-pneumatic brake pressure modulator comprising such pneumatic double check valve

[0002] The present invention relates to a pneumatic double check valve, to an electropneumatic brake pressure modulator comprising such a pneumatic double check valve, to a brake system comprising such an electro-pneumatic brake pressure modulator, and to a vehicle, in particular a passenger car or commercial vehicle, comprising such a brake system.

[0003] In general, pneumatic double check valves (also known as pneumatic DCVs) may come in different kinds. For instance, they may be of the kind labelled “Select High DCV”, i.e. pneumatic DCVs that only allow a high pressure to the delivery connections. In other known kinds, pneumatic double check valves of the “Select High DCV” are also frequently equipped with a preloaded spring acting on the guide piece. Also other known kinds are “Select low DCV”, i.e. pneumatic DCVs that only allows a low pressure to the delivery connections.

[0004] Double check valves are widely used in pneumatic circuits to prevent backflow or to provide backup connections. Pneumatic double check valves usually comprise two inlets or inlet openings as control ports and one outlet or outlet opening. They are often used in pneumatic brake circuits of passenger or commercial vehicles for various control purposes, e.g. for connection and separation of multiple air circuits with compressed air reservoirs. Pneumatic DCVs are often used in parking brake systems, service brakes, secondary consumers, clutches and transmissions, etc. Select high DCVs are used in anti-compounding relay valves of air brake systems, or in quadruple system protect valves used to prevent back flow of compressed air into upstream. Select high DCVs are also used in back up supply circuits of axle modulators in air brake systems.

[0005] A pneumatic double check valve can usually close one or the other of the two inlet openings by way of a spring or pressure force acting in the closing direction, and be opened in the other direction by an airflow, such as compressed air, which overcomes the closing force at one or both inlets. Closing usually takes place e.g. in that a guide piece is arranged in a respective blocking position in which the guide piece closes one of the inlets.

[0006] Known pneumatic double check valves generally comprise a preferably cylindrical guide piece that is inserted so as to be longitudinally movable within the cylindrical bore of the valve body or within an additional support sleeve member bore inserted within the cylindrical bore of the valve body. The guide piece end faces can form two check valves in series acting opposite one another. Also known are pneumatic double check valves where two separate guide pieces are arranged in the same valve body's cylindrical bore or cylindrical sleeve bore.

[0007] The pneumatic double check valves according to the prior art work as a function of a pneumatic force and require an air flow and associated pressurized air-induced pressure in order to set, maintain and / or change the state of the pneumatic double check valve in well-defined fashion. Pneumatic DCVs may be used in both pneumatic control applications and pneumatic supply applications. In pneumatic control applications, air pressure is instantly applied with a high apply rate (i.e. pressure gradients such as >25 bar / s). In such cases, the guide piece (also known as shuttle) instantly reacts and closes the opposite side. However, in pneumatic supply application, air pressure may be applied at a very slow rate (i.e. ~0.1 bar / s). In such cases, the shuttle may not react properly and sometimes close the DCV side which is opposite to the intended side. This often results in the shuttle swimming in-between the two supply connections. In the field of pneumatic DCVs, such a failure is called “shuttle swimming failure” and may result in damaging all connected pneumatic circuits in the system.

[0008] To avoid shuttle swimming, prior art solutions are known, that include providing shuttles having very tight radial and axial sealings. Such designs however suffer the issue of different pressures required to switch the shuttle, depending whether air is trapped between the axial and radial sealings, which is undesired in a vehicle braking scenario. Another known issue of the solutions with very tight radial and axial sealings, lies in the poor response time of the pneumatic DCV. The issues of the different pressures required to switch the shuttle, together with the issue of poor response time, make such DCVs unattractive in the context of pneumatic applications. Other issues of prior art pneumatic DCVs, both in the case of pneumatic control applications and pneumatic supply applications, reside in the difficulty to achieve the desired response behavior in devices with complex parts and / or multiple components. Similarly, port interchangeability is generally not possible with exiting pneumatic DCVs, especially with those equipped with a spring, due to the fact of their non-sym metrical air flow design.

[0009] An object of the present invention is therefore to eliminate or at least minimize the issue of pneumatic DCV shuttle swimming failure.

[0010] Another object of the present invention is to provide a pneumatic DCV that can effectively be used and perform well in both pneumatic control applications and pneumatic supply applications. Another object of the present invention is to provide a pneumatic DCV that does not suffer the issue of different pressures required to switch the shuttle, depending whether air is trapped between the axial and radial sealings. A further object of the present invention is to provide a pneumatic DCV having a fast response time. Another object of the present invention is to provide a pneumatic DCV that exhibit a predictable response behavior in devices with complex parts and / or multiple components. A further object of the present invention is to provide a pneumatic DCV enabling a good port interchangeability. Another object of the present invention is to provide an electro-pneumatic brake pressure modulator comprising such a pneumatic double check valve, a brake system comprising such an electro-pneumatic brake pressure modulator, and a vehicle, in particular a passenger car or commercial vehicle, comprising such a brake system.

[0011] These and other objects are achieved by a pneumatic double check valve according to claim 1 . The double check valve preferably comprises a valve body having a longitudinal axis, a cavity, a first inlet opening, a second inlet opening and an outlet opening, the cavity being in fluid communication with the first inlet opening, the second inlet opening and the outlet opening. The pneumatic DCV of the invention also comprises a first guide piece, or first shuttle, located in proximity to the first inlet opening and a second guide piece, or second shuttle, located in proximity to the second inlet opening. The first guide piece and the second guide piece are movably arranged in the cavity of the valve body along its longitudinal axis, the first guide piece comprising a first axial end proximal to the first inlet opening and a second axial end distal to the first inlet opening, and the second guide piece comprising a third axial end proximal to the second inlet opening and a fourth axial end distal to the second inlet opening. A preloaded spring is interposed between, and acting on, the first guide piece and the second guide piece.

[0012] The first guide piece of the pneumatic DCV of the invention is movable, by loading with a pneumatic-induced pressure greater than a first guide piece crack off pressure, between a first position and a second position spaced therefrom, the first guide piece preferably comprising at least a first axial seal. Similarly, the second guide piece of the pneumatic DCV of the invention is movable, by loading with a pneumatic-induced pressure greater than a second guide piece crack off pressure, between a third position and a fourth position spaced therefrom, the second guide piece preferably comprising at least a second axial seal. The term “crack off pressure” generally refers to the pressure force that is required to move a part. In the pneumatic DCV of the invention, the first inlet opening is closed by the first guide piece when the first guide piece is in the first position and the second inlet opening is closed by the second guide piece when the second guide piece is in the third position.

[0013] According to an embodiment, the first and / or the second axial seals are placed on an interior surface of the cavity of the valve body.

[0014] According to an aspect, the first position of the first guide piece is a position that is close to the first inlet opening and away from the second guide piece.

[0015] According to an aspect, the second position of the first guide piece is a position that is away from the first inlet opening and close to the second guide piece.

[0016] According to an aspect, the third position of the second guide piece is a position that is close to the second inlet opening and away from the first guide piece.

[0017] According to an aspect, the fourth position of the second guide piece is a position that is away from the second inlet opening and close to the first guide piece.

[0018] In other words, the second position approximately corresponds to the fourth position and, in spatial terms, can be defined as the in-between space between the first guide piece and the second guide piece, when the pneumatic double check valve of the invention is in an idle state.

[0019] In the pneumatic DCV of the invention, when the first guide piece is in the first position and the pneumatic-induced pressure greater than the second guide piece crack off pressure is provided at the second inlet opening, the second inlet opening is opened and in fluid communication with the outlet opening, and when the second guide piece is in the third position and the pneumatic-induced pressure greater than the first guide piece crack off pressure is provided at the first inlet opening, the first inlet opening is opened and in fluid communication with the outlet opening.

[0020] According to an embodiment, the cavity of the valve body is shaped as a cylindrical sleeve and both the first and second guide pieces are shaped as an elongate, cylindrical shuttle. This means, they may have projections on their circumference but in general have a cylindrical configuration with two opposite axial end faces, which however do not need to be flat surfaces.

[0021] As an alternative embodiment, the cavity of the valve body as well as the shuttle do not have a cylindrical shape, for instance they may have a different shape such as a squared shape or other shapes.

[0022] According to an embodiment, the preloaded spring is interposed between, and acting on, the second axial end of the first guide piece and the fourth axial end of the second guide piece. The preloaded spring may be attached to the first and second guide pieces or may just be positioned between them.

[0023] According to an embodiment, the first axial seal and the second axial seal are fluid-tight seals.

[0024] According to an embodiment, the first guide piece crack off pressure and the second guide piece crack off pressure are defined as a function of at least an elastic force of the preloaded spring.

[0025] Preferably, the first guide piece crack off pressure and the second guide piece crack off pressure are defined as a function of the elastic force of the preloaded spring, the weight of the first and of the second guide piece, respectively, and the internal friction acting between the first and the second guide piece and the internal surface of the cavity of the valve body.

[0026] According to an embodiment, the first guide piece crack off pressure is equal to the second guide piece crack off pressure. According to an alternative embodiment, the first guide piece crack off pressure is different from the second guide piece crack off pressure.

[0027] According to an embodiment, the first guide piece comprises a first plurality of ribs and / or a first plurality of cutouts to allow delivery of airflow from the first inlet opening to the outlet opening, and / or the second guide piece comprises a second plurality of ribs and / or a second plurality of cutouts to allow delivery of airflow from the second inlet opening to the outlet opening. This may reduce a necessary travel distance of the first and / or second guide piece for establishing the fluid flow from the first or second inlet to the outlet and thus may reduce reaction time.

[0028] According to an embodiment, the first plurality of ribs and / or the first plurality of cutouts of the first guide piece are placed at least in correspondence with the second axial end distal to the first inlet opening. Preferably, the second plurality of ribs and / or the second plurality of cutouts of the second guide piece are placed at least in correspondence with the fourth axial end distal to the second inlet opening.

[0029] According to a preferred embodiment, the first guide piece comprises a third plurality of ribs and / or a third plurality of cutouts placed in correspondence with the first axial end proximal to the first inlet opening. Preferably, the second guide piece comprises a fourth plurality of ribs and / or a fourth plurality of cutouts placed in correspondence with the third axial end proximal to the second inlet opening.

[0030] According to another embodiment, the circumferential dimension of the third plurality of ribs is shorter than the circumferential dimension of the first plurality of ribs of the first guide piece. Preferably, the circumferential dimension of the fourth plurality of ribs is shorter than the circumferential dimension of the second plurality of ribs of the second guide piece. For example, the circumferential dimension of the third plurality of ribs is shorter by 10%, 15%, 20% or more than the circumferential dimension of the first plurality of ribs of the first guide piece. For example, the circumferential dimension of the fourth plurality of ribs is shorter by 10%, 15%, 20% or more than the circumferential dimension of the second plurality of ribs of the second guide piece.

[0031] According to another embodiment, the first guide piece and / or the second guide piece comprise, on respective outer surfaces, a plurality of ribs extending from the first axial end to the second axial end and from the third axial end to the fourth axial end, respectively, along a direction parallel to the longitudinal axis of the valve body. It should be understood that the ribs do not need to extend over the entire length from the first to the second end, and the third to the fourth axial end, respectively, even though this is possible. Rather, the ribs may also extend just a portion, e.g. 50% or even less, or may be intersected.

[0032] According to a further embodiment, the first guide piece and / or the second guide piece comprise, on respective outer surfaces, a plurality of cutouts extending from the first axial end to the second axial end and from the third axial end to the fourth axial end, respectively, along a direction parallel to the longitudinal axis of the valve body. Also the cutouts do not need to extend over the entire length, even though they could. Preferably, the cutouts extend for the same length as the ribs, if provided.

[0033] According to an embodiment, both the first plurality of ribs and the first plurality of cutouts of the first guide piece, are placed in correspondence of respective same angular positions, with respect of both the third plurality of ribs and the third plurality of cutouts, in order to define airflow channels on the outer surface of the first guide piece, thus allowing air to flow from the first axial end to the second axial end of the first guide piece, without encountering obstacles and thus maximizing airflow.

[0034] According to an embodiment, both the second plurality of ribs and the second plurality of cutouts of the second guide piece are placed in correspondence of respective same angular positions, with respect of the fourth plurality of ribs and the fourth plurality of cutouts, in order to define airflow channels on the outer surface of the second guide piece, thus allowing air to flow from the third axial end to the fourth axial end of the second guide piece, without encountering obstacles and thus maximizing airflow.

[0035] According to one aspect, the first guide piece and / or the second guide piece have a shape adapted to maximize airflow, within the cavity of the valve body, from either the first inlet opening and / or the second inlet opening to the outlet opening.

[0036] According to another aspect, the first guide piece and the second guide piece have a shape adapted to minimize their respective weight, while preferably still have the same axial length as in the above embodiments. According to a further aspect, the first guide piece and the second guide piece have a shape adapted to provide a sufficient sealing with their respective mating surfaces in the valve body.

[0037] According to an embodiment, the valve body comprises an adaptor placed at either the first inlet opening and / or the second inlet opening.

[0038] According to an embodiment, the first and / or the second axial seals are placed on a surface of the adaptor.

[0039] According to another embodiment, the first guide piece and the second guide piece are placed within a sleeve placed in the cavity of the valve body. According to an embodiment, the sleeve placed in the cavity of the valve body comprises a plurality of cutouts. According to an aspect of the above embodiment, the plurality of cutouts are placed at least in correspondence with one end of the sleeve. According to a preferred aspect of the above embodiment, the plurality of cutouts of the sleeve are placed at least in correspondence with both ends of the sleeve. According to a preferred aspect of the above embodiments, the plurality of cutouts of the sleeve are placed at least in correspondence with a central position, with respect to a longitudinal axis of the sleeve. According to an embodiment, the first inlet opening and / or the second inlet opening comprises an air filter.

[0040] The objects of the present invention are also achieved by an electro-pneumatic brake pressure modulator, for instance an axle modulator, comprising an electro-pneumatic pressure control circuit. In general, an axle modulator is an electro-pneumatic pressure control circuit (channel) to control brake pressure of the front and / or the rear axle(s) of a vehicle.

[0041] The electro-pneumatic pressure control circuit of the invention is a combination of a relay valve, an inlet solenoid valve, an outlet solenoid valve, a backup solenoid valve. The relay valve comprises a pneumatic supply port system with a double check valve according to the invention, a delivery port system and a backup pneumatic port. The supply double check valve is adapted to connect a first and a second supply port of the relay valve and vice versa, mainly to provide a backup supply connection to the relay valve. Also, the electro-pneumatic pressure control unit is provided with a pressure sensor that monitors the delivery brake pressure of the relay valve in a closed loop manner.

[0042] The objects of the present invention are also achieved by a brake system comprising an electro-pneumatic brake pressure modulator as described above, the brake system being adapted to control the brake pressure at an axle of a vehicle. According to one aspect, the axle of the vehicle is a front axle. According to another aspect, the axle of the vehicle is a rear axle. According to a further aspect, the brake system is adapted to control the brake pressure at both the front and the rear axles of a vehicle. The objects of the present inventions are also achieved by a vehicle, in particular a passenger car or commercial vehicle, comprising a brake system as described above.

[0043] The objects of the present invention are also achieved by an industrial pneumatic system comprising the double check valve of the invention, for instance other automobile pneumatic systems comprising such a double check valve, e.g. an air suspension system in a vehicle, a door control system, and others.

[0044] For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed hereinafter. Further, the features described in the description, the drawings and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording “comprising” does not exclude other elements or steps. The word “a” or “an” does not exclude the plurality. The wording “a number of” items comprising also the number 1 , i.e. a single item, and further numbers like 2, 3, 4 and so forth. In the accompanying drawings:

[0045] Figure 1 shows a cutout view of a pneumatic double check valve according to the invention, shown in an idle state, i.e. without application of pressure; Fig. 2 shows a cutout view of the pneumatic double check valve of Fig. 1 , shown in an exemplary working state, i.e. when pressure is applied at one of the inlet openings and, specifically, at the first inlet opening;

[0046] Figure 3 shows, in perspective view, a detail of a component, i.e. a first guide piece, of the pneumatic double check valve according to a first embodiment of the invention;

[0047] Figure 4 shows, in perspective view, a detail of a component, i.e. a first and a second guide piece, of the pneumatic double check valve according to a first embodiment of the invention

[0048] Figure 5 shows, in perspective view, a detail of a component, i.e. a first guide piece, of the pneumatic double check valve according to a second embodiment of the invention;

[0049] Figure 6 shows, in perspective view, a detail of a component, i.e. a first guide piece, of the pneumatic double check valve according to a third embodiment of the invention;

[0050] Figure 7 shows a simplified pneumatic diagram of an electro-pneumatic brake pressure modulator according to the invention.

[0051] An embodiment of a pneumatic double check valve 1 of the invention is represented in Fig. 1 and comprises a valve body 2 having a longitudinal axis L, a cavity 7, a first inlet opening 3, a second inlet opening 4 and an outlet opening 5. The cavity 7 of the valve body 2 is in fluid communication with the first inlet opening 3, the second inlet opening 4 and the outlet opening 5.

[0052] In correspondence with the first inlet opening 3, an optional first air filter 210 is provided. An optional second air filter 220 is provided in correspondence with the second inlet opening 5. Also in correspondence with the second inlet opening 4, an adaptor 20 is provided.

[0053] The pneumatic double check valve 1 of the invention comprises a first guide piece 80 located in proximity to the first inlet opening 3 and a second guide piece 90 located in proximity to the second inlet opening 4. The first guide piece 80 and the second guide piece 90 are movably arranged in the cavity 7 of the valve body 2 along its longitudinal axis L. The first guide piece 80 comprises a first axial end 81 proximal to the first inlet opening 3 and a second axial end 82 distal to the first inlet opening, and the second guide piece 90 comprises a third axial end 91 proximal to the second inlet opening 4 and a fourth axial end 92 distal to the second inlet opening 4.

[0054] The first guide piece 80 and the second guide piece 90 are provided with respective first and second axial seals 800, 900 adapted to engage with the first inlet opening 3 and with the second inlet opening 4, respectively. The axial seals 800, 900 may be provided as separate components that are mounted and / or glued together with the respective first and second guide pieces or else overmoulded together with the respective guide pieces.

[0055] A preloaded spring 8 is interposed between, and acting on, the second axial end 82 of the first guide piece 80 and the fourth axial end 92 of the second guide piece 90. The preloaded spring 8 is preferably a helical spring.

[0056] In Fig.1 , the pneumatic double check valve 1 according to the invention is shown in an idle state, i.e. without application of pressure at neither the first inlet opening 3 nor at the second inlet opening 4. In such an idle state, the preloaded spring 8 pushes both guide pieces 80, 90 towards the first inlet opening 3 and the second inlet opening 4, respectively. In other words, in the idle state the first guide piece 80 is located in a first position closing the first inlet opening 3 and the second guide piece 90 is located in a third position closing the second inlet opening 4. In terms of contact surfaces, it is the first and second axial seals 800, 900 to close the first and the second inlet openings 3, 4, respectively.

[0057] As shown in Fig. 2, when sufficient pneumatic pressure is provided at the first inlet opening 3, the first guide piece 80 pushes against the preloaded spring 8, leaves the first position and moves, along a direction that is parallel to the longitudinal axis L of the valve body 2, towards a second position spaced therefrom and that is closer to the second guide piece 90, therefore allowing an airflow to enter the cavity 7 of the valve body 2 through the first inlet opening 3, pass around the guide piece 80 and exit the valve body 2 through the outlet opening 5. In order for the first guide piece 80 to leave the first position, open he first inlet opening 3 and reach the second position, the pneumatic-induced pressure at the first inlet opening 3 should be greater than the first guide piece crack off pressure. The first guide piece crack off pressure is defined as a function of the elastic force of the preloaded spring 8, the weight of the first guide piece 80, and the internal friction acting between the first guide piece 80 and the internal surface of the cavity 7 of the valve body 2. Specifically, the first guide piece crack off pressure is the threshold pressure at which the first guide piece 80 is able to equalize and overcome the forces keeping it in the first position. When the pneumatic-induced pressure is greater than the first guide piece crack off pressure, the first guide piece 80 starts moving towards the second position. The movement of the first guide piece 80 also depends on the delivery pressure at the outlet opening 5 or, more precisely, on the delivery pressure that is present in the delivery line (not shown) that is connected to the outlet opening 5. As soon as the delivery pressure at the outlet opening 5 equals the supply pressure from the first inlet opening 3, the first guide piece 80 will go back to its original position i.e. the first position closing the first inlet opening 3. This is known as a pressure balancing condition. When the first guide piece 80 is located in the second position, the second guide piece 90 is located in the third position and the second inlet opening 4 is closed, since no pressure or a sufficiently low pressure is applied at the second inlet opening 4. In such a configuration, the first guide piece 80 may be in contact with the second guide piece 90.

[0058] Similarly, the second guide piece 90 of the pneumatic double check valve 1 of the invention is movable, by providing sufficient pneumatic pressure at the second inlet opening 4. Such a working condition is not shown in the figures, however it is analogous, mutatis mutandis, to what already shown in Fig. 2 in connection with the first guide piece 80. In order to move the second guide piece 90 from the third position to a fourth position spaced therefrom and that is closer to the first guide piece 80, the pneumatic-induced pressure should be greater than a second guide piece crack off pressure. The second guide piece crack off pressure is defined, mutatis mutandis, in the same way as the first guide piece crack off pressure. With the first guide piece 80 located in the first position and closing the first inlet opening 3, with no pressure or sufficiently low pressure induced at the first inlet opening 3, the second guide piece 90 is located in the fourth position and the second inlet opening 4 is therefore opened and in fluid communication with the outlet opening 5. In this configuration, the second guide piece 90 may be in contact with the first guide piece 80. Also in this case, depending on the delivery pressure that is present in the delivery line (not shown) that is connected to the outlet opening 5, a pressure balancing condition may be reached, as explained above.

[0059] In practical terms, the second position of the first guide piece 80 and the fourth position of the second guide piece 90 basically both correspond, in spatial terms and with respect to the longitudinal axis L of the valve body 2, to the in-between space that is present between the first guide piece 80 and the second guide piece 90 when the pneumatic double check valve is in an idle state.

[0060] Generally, the second guide piece crack off pressure is chosen to be equal to the first guide piece crack off pressure. However, the crack off pressures of the first and second guide pieces may also be chosen to be different. In order to select different crack off pressures, different solutions may be adopted. For instance, a preloaded spring 8 having variable stiffness may be used. Or else, first and second guide pieces 80, 90 having a different weight or a different shape, so that to differently interact with the airflow, or different area sizes of functional surfaces may be provided. Another option could be that of providing first and second guide pieces having radial seals with different tightness, so that respective frictional forces acting between the internal surface of the cavity 7 of the valve body 2 and the guide pieces 80, 90 may be different. Any combination of the above-described solutions may be also envisaged.

[0061] In the embodiment shown in Fig. 1 , the crack off pressure of the first guide piece 80 is equal to the crack off pressure of the second guide piece 90. Preferably, the crack off pressure of the first and second guide pieces is lower than 0.05 bar, even more preferably lower than 0.04 bar. In an embodiment, the crack off pressure of the first and second guide pieces is approximately equal to 0.03 bar. Preferably, the crack off pressure is in a range of 0.03 to 0.05 bar, preferable 0.03 to 0.04 bar. The elastic force exerted by the preloaded spring 8 in its initial configuration, i.e. when the pneumatic double check valve 1 is in an idle state, as shown in Fig. 1 , is preferably in the range of 0.8 to 2 N, preferably, 0.8 to 1 .5 N, even more preferred 1 .0 N to 1 .3 N. In an embodiment, the spring force exerted by the preloaded spring 8 is approximately equal to 1 .2 N. The sealing pressure exerted by guide pieces 80, 90 on the respective edges of the cavity 7 of the valve body 2, is in general not evenly distributed over the entire contact surface. As an example, when the spring force exerted by the preloaded spring 8 in its initial configuration is equal to 1 .0 N, the sealing pressure exerted by guide pieces 80, 90 on the respective edges of the cavity 7 of the valve body 2 may vary between less than 0.03 MPa and 0.1 MPa, the latter, higher value, being found in the most stressed areas. In this respect, the portions of the first and second axial seals 800, 900 that face the first and second inlet openings 3, 4, respectively, are the portions of the axial seals taking up the most sealing pressure.

[0062] As previously mentioned, the axial seals 800, 900 may be provided as separate components that are mounted and / or glued on the main body of the guide pieces 80, 90 or else directly overmoulded together with the guide pieces.

[0063] With reference to Fig.1 , the axial seals 800, 900 are shaped as disc-like parts having a round sealing lip (not visible in the drawing). The material used to form the axial seals 800, 900 is generally different from the material used to form the main body of the guide pieces 80, 90. Preferably, the material used to form the axial seals 800, 900 is softer than the material used to form the main body of the guide pieces and may exhibit fluid- tight properties.

[0064] The preloaded spring 8 which is interposed between the first and the second guide pieces rests, and acts on, respective portions of the second axial end 82 of the main body of the first guide piece 80 and on the fourth axial end 92 of the main body of the second guide piece 90. Preferably, the main body of first and second guide pieces 80, 90 is made with a stiffer material than that of the axial seals. With reference to Fig. 4, the second axial end 82 of the main body of the first guide piece 80 comprises a first plurality of spring locking beads 829 and the fourth axial end 92 of the main body of the second guide piece 90 comprises a second plurality of spring locking beads 929, upon which the preloaded spring 8 rests.

[0065] With reference to Fig. 3, a first embodiment of the first guide piece 80 is shown. The same first embodiment is also shown in Fig. 4. and it is to be understood that what follows can be interpreted as applying to the second guide piece 90 as well (which is not depicted in Fig. 3), since in this particular embodiment the first guide piece 80 is identical to the second guide piece 90. The first guide piece 80 comprises a third plurality of ribs 861 and a third plurality of cutouts 871 placed in correspondence with the first axial end 81 proximal to the first inlet opening 3. The first guide piece 80 also comprises a plurality of longitudinal cutouts 89 extending from the first axial end 81 that is proximal to the first inlet opening 3, to the second axial end 82 that is distal from the first inlet opening 3, along a direction parallel to the longitudinal axis L of the valve body 2, and a plurality of longitudinal ribs 88, also extending from the first axial end 81 to the second axial end 82, along a direction parallel to the longitudinal axis L of the valve body 2. According to the present embodiment, the second axial end 82 has a disc-like shape. The first axial end 81 of the first guide piece 80 exhibits a “gear shape” design, to facilitate the flow of air through the cutouts 871 between the ribs 861 , over the plurality of longitudinal ribs 88 and through the plurality of longitudinal cutouts 89, in what could be defined as airflow channels, substantially without meeting any obstacle. As discussed, the same applies, mutatis mutandis, to the second guide piece 90 as well (not shown in Fig. 3),

[0066] With reference to Fig. 5, a second embodiment of the first guide piece 80 is shown. It is to be understood that what follows can be applied to the second guide piece 90 as well (not shown in Fig. 5), since in this particular embodiment the first guide piece is identical to the second guide piece.

[0067] In Fig. 5, the first guide piece 80 comprises an outer surface 85 having a cylindrical shape and extending along a direction that is parallel with the direction of the longitudinal axis L of the valve body 2, between the first axial end 81 that is proximal to the first inlet opening 3 and the second axial end 82 that is distal to the first axial opening 3. The first guide piece 80 also comprises a first plurality of ribs 86 and a first plurality of cutouts 87 to allow delivery of the airflow from the first inlet opening 3 to the outlet opening 5. The first plurality of ribs 86 and cutouts 87 are located in correspondence with the second axial end 82 distal to the first inlet opening 3. The first guide piece 80 also comprises a third plurality of ribs 861 and a third plurality of cutouts 871 placed in correspondence with the first axial end 81 proximal to the first inlet opening 3.

[0068] Specifically, the first axial end 81 and the second axial end 82 of the first guide piece 80 exhibits a “gear shape” design, to facilitate the flow of air through the cutouts 87, 871 between the ribs 86, 861 and over the outer surface 85 of the first guide piece 80. Conveniently, the first plurality of ribs 86 and the third plurality of ribs 861 are placed in corresponding angular positions along the circumferential contour of both the first and the second axial ends, respectively, so that air can flow from the first axial end 81 to the second axial end 82 of the first guide piece 80, over the outer surface 85 and from the third plurality of cutouts 871 to the first plurality of cutouts 87, in what could be defined as airflow channels, substantially without meeting any obstacle. Furthermore, in order to improve air flow, substantially circular cutouts 890 can be provided on the outer surface 85, preferably in correspondence with and in proximity to each rib of the first plurality of ribs 86. Preferably, the first guide piece 80 comprises, in addition to the first axial seal 800 placed in correspondence with the first axial end 81 , an additional axial seal 801 placed in correspondence with the second axial end 82. The additional axial seal, when present, can be mounted and / or glued or else directly overmoulded on the main body of the guide piece. As discussed, all of the above description applies, mutatis, mutandis, to the second guide piece 90 as well (not shown in Fig. 5).

[0069] With reference to Fig. 6, a third embodiment of the first guide piece 80 is shown. It is to be understood that what follows can be interpreted as applying to the second guide piece 90 as well (which is not depicted in Fig. 6), since in this particular embodiment the first guide piece 80 is identical to the second guide piece 90.

[0070] In Fig. 6, the first guide piece 80 comprises a plurality of longitudinal cutouts 89 extending from the first axial end 81 that is proximal to the first inlet opening 3, to the second axial end 82 that is distal from the first inlet opening 3, along a direction parallel to the longitudinal axis L of the valve body 2, and a plurality of longitudinal ribs 88, also extending from the first axial end 81 to the second axial end 82, along a direction parallel to the longitudinal axis L of the valve body 2. According to the present embodiment, the second axial end 82 has a disc-like shape.

[0071] According to the embodiment shown in Fig. 6, the first guide piece 80 comprises a first plurality of ribs 86 and cutouts 87 that are located in correspondence with the second axial end 82 distal to the first inlet opening 3. Conveniently, each rib of the first plurality of ribs 86, is placed in an angular position, along the circumferential contour of the second axial end 82, corresponding to the position of a respective longitudinal rib of the plurality of longitudinal ribs 88. The first guide piece 80 also comprises a third plurality of ribs 861 , each rib of the third plurality of ribs 861 being placed on a corresponding rib of the plurality of longitudinal ribs 88, in a position which is proximal to the first axial end 81 of the guide piece. As discussed in the context of the previous embodiments, the above description also applies, mutatis mutandis, to the second guide piece 90 as well (not shown in Fig. 6). Depending on the specific applications, these different embodiments of the guide pieces 80, 90 may be chosen with a view of maximizing the airflow, within the cavity 7 of the valve body 2, from either the first inlet opening 3 and / or the second inlet opening 4 to the outlet opening 5, around the guide pieces 80, 90 and within airflow channels defined by the interior surface of the valve body 2, the surfaces 85, 95 of the guide pieces 80, 90 and / or by the presence, position and dimension of ribs and / or cutouts in the guide pieces.

[0072] The weight of the guide pieces 80, 90 also may play an important role and may influence the performance of the pneumatic double check valve 1 of the invention. The weight of each guide piece is preferably comprised between 4 and 7 grams, preferably between 5 and 6 grams. The stroke of the guide pieces is generally comprised between 6 mm and 10 mm, preferably between 7 mm and 9.5 mm. As discussed, the shape and dimension of the guide pieces are important factors to define the performances of the pneumatic double check valve. The guide pieces of the invention have a ratio between length and diameter that is comprised between 0.400 and 0.700, preferably between 0.450 and 0.650, even more preferably between 0.470 and 0.500. In the pneumatic double check valve of the invention, shuttle swimming failure is avoided even if air pressure is applied at a very slow rate, i.e. at a gradient less than 0.1 bar / s.

[0073] With reference to Fig. 7 the pneumatic double check valve 1 of the invention can be incorporated in an electro-pneumatic brake pressure modulator 100 which controls the brake pressure at an axle of a vehicle.

[0074] In general, an axle modulator comprises an electro-pneumatic pressure control circuit 101 to control brake pressure of the front and / or the rear axle(s) of a vehicle.

[0075] The electro-pneumatic pressure control circuit 101 comprises a relay valve 105, an inlet solenoid valve 103, an outlet solenoid valve 104, and a backup solenoid valve 102. The relay valve 105 comprises a pneumatic supply port system a first supply port 111 and a second supply port 112 connected to a double check valve 1 according to the invention. The relay valve 105 also comprises a delivery port system comprising a first delivery port 212 and a second delivery port 222 and a backup pneumatic port 400. The double check valve 1 is adapted to connect to the first and to the second supply port 111 , 112 of the relay valve 105 and vice versa, mainly to provide a backup supply connection to the relay valve.

[0076] Also, the electro-pneumatic pressure control circuit 101 is provided with a pressure sensor P that monitors the delivery brake pressure of the relay valve 105 in a closed loop manner.

[0077] In the event of vehicle braking, when in electronic braking mode, the electro-pneumatic pressure control circuit 101 facilitates the delivery of the required brake pressure. In this case, pneumatic control pressure, the via the backup pneumatic port 400 from a brake signal transmitter (which is, for example, a foot brake valve controlled by the driver) is blocked by the backup solenoid valve 102 in the electro-pneumatic pressure control circuit.

[0078] In the event of vehicle braking, when in redundancy mode (which is what happens when the electro-pneumatic pressure control circuit fails or is deactivated), the pneumatic back-up pressure via the backup pneumatic port 400 generated by the brake signal transmitter shall control the internal relay valve 105 and is adapted to deliver the required brake pressure.

[0079] List of reference signs (Part of the description)

[0080] 1 pneumatic double check valve

[0081] 2 valve body

[0082] 20 adaptor

[0083] 210 air filter

[0084] 220 air filter

[0085] 3 first inlet opening

[0086] 4 second inlet opening

[0087] 5 outlet opening

[0088] 7 cavity of the valve body

[0089] 8 preloaded spring

[0090] 80 first guide piece

[0091] 90 second guide piece

[0092] 81 first axial end of the first guide piece 82 second axial end of the first guide piece

[0093] 85 outer surface of first guide piece

[0094] 86 first plurality of ribs

[0095] 87 first plurality of cutouts

[0096] 88 plurality of longitudinal ribs of first guide piece

[0097] 89 plurality of longitudinal cutouts of first guide piece

[0098] 829 first plurality of spring locking beads

[0099] 861 third plurality of ribs

[0100] 871 third plurality of cutouts

[0101] 91 third axial end of the second guide piece

[0102] 92 fourth axial end of the second guide piece

[0103] 98 plurality of longitudinal ribs of second guide piece

[0104] 99 plurality of longitudinal cutouts of second guide piece

[0105] 929 second plurality of spring locking beads

[0106] 961 fourth plurality of ribs

[0107] 971 fourth plurality of cutouts

[0108] 800 first axial seal

[0109] 801 additional axial seal

[0110] 890 circular cutouts

[0111] 900 second axial seal

[0112] 100 electro-pneumatic brake pressure modulator

[0113] 101 pressure control circuit

[0114] 102 backup solenoid valve

[0115] 103 inlet solenoid valve

[0116] 104 outlet solenoid valve

[0117] 105 relay valve

[0118] 111 first supply port

[0119] 112 second supply port

[0120] 221 first delivery port

[0121] 222 second delivery port

[0122] 400 backup pneumatic port

[0123] L longitudinal axis of the valve body

[0124] P pressure sensor

Claims

Claims1 . A pneumatic double check valve (1 ) comprising a valve body (2) having a longitudinal axis (L), a cavity (7), a first inlet opening (3), a second inlet opening (4) and an outlet opening (5), the cavity (7) being in fluid communication with the first inlet opening (3), the second inlet opening (4) and the outlet opening (5); a first guide piece (80) located in proximity to the first inlet opening (3) and a second guide piece (90) located in proximity to the second inlet opening(4), the first guide piece (80) and the second guide piece (90) being movably arranged in the cavity (7) of the valve body (2) along the longitudinal axis (L), the first guide piece (80) comprising a first axial end (81 ) proximal to the first inlet opening (3) and a second axial end (82) distal to the first inlet opening (3), and the second guide piece (90) comprising a third axial end (91 ) proximal to the second inlet opening (4) and a fourth axial end (92) distal to the second inlet opening (4); a preloaded spring (8) interposed between, and acting on, the first guide piece (80) and the second guide piece (90); the first guide piece (80) being movable, by loading with a pneumatic- induced pressure greater than a first guide piece crack off pressure, between a first position and a second position spaced therefrom, and the second guide piece (90) being movable, by loading with a pneumatic- induced pressure greater than a second guide piece crack off pressure, between a third position and a fourth position spaced therefrom, , wherein the first inlet opening (3) is closed by the first guide piece (80) when the first guide piece (80) is in the first position and the second inlet opening (4) is closed by the second guide piece (90) when the second guide piece (90) is in the third position, wherein when the first guide piece (80) is in the first position and the pneumatic-induced pressure greater than the second guide piece crack off pressure is provided at the second inlet opening (4), the second inlet opening (4) is opened and in fluid communication with the outlet opening(5), and wherein when the second guide piece (90) is in the third position and the pneumatic-induced pressure greater than the first guide piece crack offpressure is provided at the first inlet opening (3), the first inlet opening (3) is opened and in fluid communication with the outlet opening (5).

2. The pneumatic double-check valve (1 ) of claim 1 , wherein the first guide piece crack off pressure and the second guide piece crack off pressure are defined as a function of at least an elastic force of the preloaded spring (8).

3. The pneumatic double-check valve (1 ) of claims 1 or 2, wherein the first guide piece crack off pressure is equal to the second guide piece crack off pressure.

4. The pneumatic double check valve (1 ) of claims 1 to 3, wherein the first guide piece (80) comprises a first plurality of ribs (86) and a first plurality of cutouts (87) to allow delivery of airflow from the first inlet opening (3) to the outlet opening (5), and the second guide piece (90) comprises a second plurality of ribs (96) and a second plurality of cutouts (97) to allow delivery of airflow from the second inlet opening (4) to the outlet opening (5).

5. The pneumatic double check valve (1 ) of claim 4, wherein the first plurality of ribs (86) and the first plurality of cutouts (87) of the first guide piece (80) are placed at least in correspondence with the second axial end (82) distal to the first inlet opening (3), and wherein the second plurality of ribs (96) and the second plurality of cutouts (97) of the second guide piece (90) are placed at least in correspondence with the fourth axial end (92) distal to the second inlet opening (4).

6. The pneumatic double check valve (1 ) of claims 4 or 5, wherein the first guide piece (80) comprises a third plurality of ribs (861 ) and a third plurality of cutouts (871 ) placed in correspondence with the first axial end (81 ) proximal to the first inlet opening (3) and wherein the second guide piece (90) comprises a fourth plurality of ribs (961 ) and a fourth plurality of cutouts (971 ) placed in correspondence with the third axial end (91 ) proximal to the second inlet opening (4).

7. The pneumatic double check valve (1 ) of any of claims 4 to 6, wherein a circumferential dimension of the third plurality of ribs (861 ) is shorter than acircumferential dimension of the first plurality of ribs (86) of the first guide piece (80), and wherein a circumferential dimension of the fourth plurality of ribs (961 ) is shorter than a circumferential dimension of the second plurality of ribs (96) of the second guide piece (90).

8. The pneumatic double check valve (1 ) of claim 7, wherein the first guide piece (80) and the second guide piece (90) comprise, on respective outer surfaces (85, 95), a plurality of ribs (88, 98) extending from the first axial end (81 ) to the second axial end (82) and from the third axial end (91 ) to the fourth axial end (92), respectively, along a direction parallel to the longitudinal axis (L).

9. The pneumatic double check valve (1 ) of claim 8, wherein the first guide piece (80) and the second guide piece (90) comprise, on respective outer surfaces (85, 95), a plurality of cutouts (89, 99) extending from the first axial end (81 ) to the second axial end (82) and from the third axial end (91 ) to the fourth axial end (92), respectively, along a direction parallel to the longitudinal axis (L).

10. The pneumatic double check valve (1 ) of any of claims 4 to 9, wherein the first guide piece (80) and the second guide piece (90) have a shape adapted to maximize airflow, within the cavity (7) of the valve body (2), from either the first inlet opening (3) and / or the second inlet opening (4) to the outlet opening (5).11 . The pneumatic double check valve (1 ) of any of the preceding claims, wherein the first guide piece (80) comprises at least a first axial seal (800) and the second guide piece (90) comprises at least a second axial seal (900).

12. The pneumatic double check valve (1 ) of any of the preceding claims, wherein the first guide piece (80) and the second guide piece (90) are placed within a sleeve placed in the cavity (7) of the valve body (2).

13. An electro-pneumatic brake pressure modulator (100) comprising an electro-pneumatic pressure control circuit (101 ) comprising a relay valve (105), an inlet solenoid valve (103), an outlet solenoid valve (104) and a backup solenoid valve (102), and having a pressure sensor (P) adapted to control pressure in a closed loop manner,wherein the relay valve (105) comprises a pneumatic double check valve (1 ) according to any one of claims 1 to 12, the pneumatic double check valve (1 ) being operatively connected to the pressure control circuit (101 ) and adapted to connect a first supply port (111) and a second supply port (112) to supply pressure to the control circuit (101 ).

14. A brake system comprising an electro-pneumatic brake pressure modulator (100) according to claim 13, the brake system being adapted to control the brake pressure at an axle of a vehicle.

15. A vehicle, in particular a passenger car or commercial vehicle, comprising a brake system according to claim 14.

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