ELECTROMAGNETIC SLEEVE FOR HYDROGEN VALVE

Technical field

[0001] The invention is directed to the field of electromagnetic devices, like electromagnetic actuators and valves, in particular to sleeves thereof. More specifically the invention is directed to the field of electromagnetic devices or valves for compressed gas, in particular for high pressure gases, e.g. compressed natural gas (CNG) and compressed hydrogen gas at pressures of up to 70 MPa.

Background art

[0002] Prior art patent document published WO 2016/180737 A1 discloses an electromagnetic valve for high pressure gases like compressed natural gas (CNG) and compressed hydrogen where the valve is operated by a pilot. The valve comprises a main valve member with a front face cooperating with a main seat, and with a pilot passage for the gas extending between the front face of said member and a pilot seat on a rear face thereof. The pilot valve member cooperates with the pilot seat on the rear face of the main valve member so as to close the pilot passage. The pilot valve member comprises a core that forms an air-gap with a counter-core rigidly fixed with the main valve member. Upon energization of a solenoid, the core is magnetically attracted towards the counter-core and the pilot valve member moves away from the pilot seat so as to open the pilot passage. The inlet pressure of the gas builds up on at the outlet so that the main valve member can move away from the seat so as to open the valve. The main valve member, the core and the counter-core are housed in a metallic sleeve. The sleeve comprises a cylindrical wall made predominantly of ferromagnetic material with however an intermediate ring of non- or poor-ferromagnetic material for promoting the development of magnetic field inside the cavity formed by the cylindrical wall, i.e. in the core, counter-core and in the air- gaps between said cores and between the counter-core and the bottom of the cavity. The ring of non- or poor-ferromagnetic material can be welded to the other portions of the sleeve for providing a gas tight sleeve. This operation can however be cumbersome, depending in particular on the materials involved and on the geometric accuracy to be achieved.

[0003] Prior art patent document published JPH07103354A discloses a process for manufacturing a sleeve of a solenoid valve. The process consists essentially in forming an external groove on a plain rod of ferromagnetic material, to weld non-ferromagnetic material in the groove and then to machine the blank so as to form a sleeve with an intermediate ring of non- ferromagnetic material. This process shows the advantage that the deformation of the blank further to the welding operation is very limited and is anyway compensated by the machining operations that are carried out afterwards.

[0004] With certain applications with high pressure gases, like hydrogen at pressures of up to 70 MPa, the material of the valve can be subject to embrittlement. Hydrogen embrittlement is a process by which various metals, for instance high-strength steel, become brittle and facture following exposure to hydrogen at high pressure.

[0005] Prior art patent document published WO 2015/082469 A1 discloses a pilot operated electromagnetic valve for high pressure gases like hydrogen where the sleeve housing the magnetic plunger and the compressed gas is a thin-walled sleeve of austenitic stainless steel which is resistant to hydrogen embrittlement. For promoting the magnetic field inside the sleeve, the sleeve is surrounded by a ring of non-ferromagnetic material and two ring of ferromagnetic material on both sides of said ring. This construction shows however as drawback that narrow dimensional tolerances are required for allowing a proper mounting of the sleeve, leading to high manufacturing costs.

Summary of invention

Technical Problem

[0006] The invention has for technical problem to provide a sleeve for an electromagnetic device, i.e. comprising a cylindrical wall forming a cavity for receiving a magnetic plunger and configured for being surrounded by an electromagnet, that overcomes at least one of the drawbacks of the above cited prior art. More specifically, the invention has for technical problem to provide a sleeve for an electromagnetic device that is resistant to embrittlement and cheap to manufacture while promoting the development of magnetic field inside said sleeve.

Technical solution

[0007] The invention is directed to a sleeve for an electromagnetic device, comprising a cylindrical wall forming a cavity for receiving a magnetic plunger, and configured for being surrounded by an electromagnet; wherein the cylindrical wall is made of a non-ferromagnetic material and comprises at least one external groove filled with ferromagnetic material.

[0008] The ferromagnetic material shows a relative permeability (m/mo) larger than 100, preferably larger than 500, more preferably larger than 1000. The non- ferromagnetic material shows a relative permeability (m/mo) equal to, or lower than 1.

[0009] According to a preferred embodiment, the ferromagnetic material filling the at least one groove is metallurgically bonded to the non-ferromagnetic material forming the at least one groove.

[0010] According to a preferred embodiment, the non-ferromagnetic material is stainless steel and the ferromagnetic material is iron and/or ferrite.

[0011] According to a preferred embodiment, the at least one groove extends radially only over a portion of a thickness of the cylindrical wall adjacent said groove, so that a bottom of said groove is formed by a reduced thickness portion of the non-ferromagnetic material.

[0012] According to a preferred embodiment, the reduced thickness is less than 30%, preferably less than 20%, more preferably less than 15%, of the thickness of the cylindrical wall adjacent the at least one groove.

[0013] According to a preferred embodiment, the at least one groove shows a trapezoid cross-section flaring radially outwardly.

[0014] According to a preferred embodiment, the cylindrical wall has an inner surface and an outer surface, at least one of said surfaces showing a constant diameter axially over the at least one groove and at each side of said groove. [0015] According to a preferred embodiment, the cylindrical wall comprises, at one axial end, a fastening element comprised of one of the following: an outer thread, an inner thread, an outer shoulder, or any combination thereof.

[0016] The invention is also directed to an electromagnetic device comprising: a sleeve; a magnetic plunger housed in the sleeve; an electromagnet mounted around the sleeve and configured for magnetically actuating the plunger; wherein the sleeve is according to the invention.

[0017] According to a preferred embodiment, the electromagnetic device further comprises a plug of ferromagnetic material mounted on the sleeve at one open end of the cavity, said plug forming with the magnetic plunger an air- gap.

[0018] According to a preferred embodiment, the electromagnetic device further comprises a ferromagnetic yoke forming with the sleeve and the magnetic plunger a magnetic circuit around the electromagnet, said yoke contacting the ferromagnetic material in at least one groove.

[0019] According to a preferred embodiment, the sleeve is a first sleeve, the yoke comprising a second sleeve, said sleeve being mounted around the at least one groove and made of ferromagnetic material.

[0020] According to a preferred embodiment, the second sleeve comprises a first portion in contact with the at least one groove and a second portion extending axially at a radial distance from the first sleeve so as to form a cavity housing the electromagnet.

[0021] According to a preferred embodiment, the magnetic plunger is axially located, in any operational position, in front of the at least one groove.

[0022] According to a preferred embodiment, the electromagnetic device is a valve and further comprises a closure element housed in the sleeve, attached to the magnetic plunger and with a front face configured for cooperating with a valve seat.

[0023] According to a preferred embodiment, with the closure element is a main closure element with a channel fluidly interconnecting the front face and an opposed rear face, the device further comprising a pilot closure element cooperating with a pilot seat on the rear face of the main closure element, the magnetic plunger comprising a core attached to the pilot closure element and a counter-core attached to the main closure element. [0024] The invention is also directed to a method of manufacturing a sleeve for an electromagnetic device, comprising the following steps: (a) forming at least one external groove on a rod-shaped blank of a first material; (b) filling the at least one groove with a second material by a welding process; (c) machining an outer surface and optionally an inner surface of the blank so as to form the sleeve; wherein the first material is non-ferromagnetic and the second material is ferromagnetic.

[0025] According to a preferred embodiment, step (c) comprising forming a bore extending through the whole blank.

[0026] According to a preferred embodiment, at step (a) the blank is plain.

Advantages of the invention

[0027] The invention is particularly interesting in that it provides a sleeve for an electromagnetic device, like an actuator or a valve, that is resistant to embrittlement, easy to manufacture and promotes the development of magnetic field induced by the electromagnet of the device. By being predominantly of non-ferromagnetic material, the sleeve can be made of a material selected among materials, like stainless steel, which resist to embrittlement. Also, the cylindrical wall does not need to be thin, at the contrary it can be thick enough to self-support the constraints resulting from the high pressure inside the sleeve. Narrow geometrical tolerances of the sleeve can be achieved in that the filling operation of the groove with ferromagnetic material can be achieved using a plain rod-shaped blank or at least thick-walled blank.

[0028] The sleeve can feature more than one groove filled with ferromagnetic material. In that case, the magnetic field can enter in the cavity by one of these grooves and exit said cavity by another of these grooves. In such a case, the cavity of the sleeve can be closed at one end, i.e. be formed by a blind bore.

Brief description of the drawings

[0029] Figure 1 is a sectional view of an electromagnetic valve according to the invention.

[0030] Figure 2 is a sectional view of the operating part of the valve of figure 1 , the valve being in a closed position. [0031] Figure 3 is a sectional view of the operating part of the valve of figure 2, similar to figure 1 , in an intermediate position before opening.

[0032] Figure 4 is a sectional view of the operating part of the valve of figure 1 , similar to figures 2 and 3, in a fully opening position.

[0033] Figures 5 to 7 illustrate the different steps for manufacturing the first sleeve 8.1 .

Description of an embodiment

[0034] Figure 1 depicts with a sectional view an electromagnetic valve according to the invention. The valve 2 comprises an operating part 4 and a connector 6 attached thereto. The operating part 4 comprises essentially a sleeve- shaped body 8 receiving a coil or solenoid 10 and housing a main closure element 12, a pilot valve element 14 and a magnetic core 16 attached to the pilot valve member 14.

[0035] Figure 2 to 4 illustrate the operating part 4 of the valve 2 in three different states, namely in the closed state (figure 2), in an intermediate state before opening (figure 3) and in a fully opened state (figure 4).

[0036] With reference to figure 2, the valve body 8 comprises a first sleeve 8.1 and a second sleeve 8.2 mounted there over. The first sleeve 8.1 comprises a shoulder portion 8.1.1 and the second sleeve 8.2 comprises a first portion 8.2.1 also with a shoulder that abuts against the shoulder portion 8.1.1 of the first sleeve when the second sleeve 8.2 is slid over the first sleeve 8.1. The second sleeve 8.2 comprises a second portion 8.2.2 that forms with the first sleeve 8.1 an annular cavity that extends longitudinally, said cavity housing the coil 10. The second sleeve 8.2 can comprise on its outer surface, advantageously on the first portion 8.2.1 , at the level of the shoulder potion, an outer thread 8.2.3 for engaging with an inner thread of body 18 on which the valve is mounted. The shoulder portions 8.1.1 and 8.2.1 are configured such that the second sleeve retains axially the first sleeve in contact with the body 18.

[0037] The inner sleeve 8.1 can comprise a front groove 8.1.2 housing a gasket that cooperates in a gas tight manner with a corresponding front surface of the body 18 onto which the valve is mounted. [0038] The second sleeve 8.2 is made of ferromagnetic material whereas the first sleeve 8.1 can be made of non-ferromagnetic material and shows an external groove filled with a ring of ferromagnetic material 8.1.3. The groove is such that it leaves a thin wall 8.1.4 of material unitary with the rest of the sleeve 8.1. The groove and the corresponding ring of ferromagnetic material 8.1.3 is advantageously located longitudinally at the level of the shoulder portion 8.2.1 of the second sleeve 8.2. Thanks to this construction, the first sleeve 8.1 can be made of stainless steel, e.g. austenitic stainless steel, that is particularly resistant to embrittlement in the presence of hydrogen under high pressure while still allowing the magnetic field produced by the coil to reach the inner cavity delimited by said sleeve. More specifically, the presence of the ferromagnetic ring 8.1.3 guides the magnetic field radially through the sleeve 8.1 until the thin wall 8.1.4 of non-ferromagnetic material. The low permeability of the material of that thin wall 8.1.4 is of a limited effect on the building up of the magnetic field so that said field can reach the inner cavity of the first sleeve 8.1 while said sleeve shows a perfect and continuous integrity and gas tightness to the high pressure in said cavity. The groove in the first sleeve 8.1. can be formed by machining and the ring of ferromagnetic material 8.1.3 can be applied by welding so as to restore, at least partially, the initial stability and rigidity of the sleeve.

[0039] The shut-off device of the valve, housed in the inner cavity of the first sleeve 8.1 will be described here.

[0040] The shut-off device comprises the main closure element 12 which is axially slidable in the inner cavity of the sleeve 8.1. More specifically, the main closure element 12 is generally elongate with a front conical face 12.1 engaging with a corresponding main seat 20 that is for instance formed in the body 18. The main closure element 12 comprises also a gasket 12.2 on the front face 12.1 , said gasket cooperating in a gas tight manner with the main seat 20. The gas tight cooperation of the main closure element 12 with the main seat 20 shuts-off the gas passage between a gas inlet 22 and a gas outlet 24.

[0041] The shut-off device further comprises the pilot closure element 14 that is slidable relative to the main closure element 12 so as to selectively close and open the channel 12.3 through the main closure element 12, interconnecting the inlet 22 with the outlet 24. More specifically, the pilot closure element 14 cooperates with a pilot seat that is advantageously formed on an element 26 that is inserted into a bore formed in the rear face of the main closure element 12. That element 26 is advantageously made of a material that is softer than the material of the main closure element. It can show a rear face 26.1 with a through-hole 26.2 which both cooperate with a conical tip of the pilot closure element. The element 26 can also show a conical front face 26.3 and a generally cylindrical outer surface 26.4 with circular lips.

[0042] The pilot closure element 14 can show a conical tip that engages with a corresponding conical surface of the pilot seat 26.

[0043] The pilot closure element 14 is rigidly fixed to a magnetic core 16 that forms an airgap with a counter-core 30 rigidly attached to the main closure element 12. For instance, the core 16 is cylindrical and surrounds the main closure element 12. It is attached to the pilot closure element 14 by means of a pin 32 extending radially through the core 16 and the pilot closure element 14. As is apparent figure 2, the pilot closure element 14 is slidably housed in a bore formed in the main closure element 12 and said element comprises two oblong holes through which the pin 32 extends. The core 16 forms with the counter-core 30 a first air-gap 28.

[0044] Still with reference to figure 2, the counter-core 30 is housed directly in the inner bore of the sleeve 8.1 , like the core 16. The bore of the sleeve 8.1 is closed in a gas tight manner by a plug 34 made of ferromagnetic material, said plug forming the bottom of the cavity. The plug 34 can be attached to the sleeve 8.1 by a threaded engagement as is visible in figure 2. For instance, the plug 34 can be generally cylindrical with an external thread 34.1 engaging with a corresponding internal thread formed in the sleeve 8.1. The plug 34 can also show a projecting portion 34.2 housed in the sleeve 8.1. More specifically, the internal thread of the sleeve 8.1 can be formed in an end portion 8.1.5 of said sleeve 8.1 that forms a bore of a larger diameter. The projecting portion 34.2 of the plug 34 shows then a reduced diameter compared with the portion of the external thread and mates with the nominal bore of said sleeve. The projecting portion 34.2 can have an external groove 34.3 housing a gasket for a gas tight cooperation with the sleeve 8.1. The plug 34 can also feature a cavity, for instance a bore 34.4, that receives an end of a spring 36 whose other ends engages with the counter-core 30. The compression spring 36 urges the main closure element 12, which is rigidly attached to the counter-core 30, against the main seat 20.

[0045] The main closure element 12 comprises a spring 38, for instance a compression spring, that urges the pilot closure element 14 against the pilot seat 26. More specifically, the main closure element 12 can comprise at its end opposite to the tip engaging with the pilot seat 26 an external thread that engages with an internal thread in a bore 30.1 formed in the counter- core 30, so as to provide a rigid attachment. The spring 38 rests then on one side against the bottom of the bore in the counter-core 30 and on the other side on the pilot closure element 14. In particular, the pilot closure element 14 can comprise an elongated end with a shoulder, the spring 38 being then slip on said elongated end and resting on said shoulder.

[0046] Still with reference to figure 2, the counter-bore 30 forms with the plug 34 a second air-gap 40. That second air-gap 40 is advantageously axially longer than the first one 28. More specifically, the counter-core 30 can show a circular protrusion 30.2 that extends axially in the second air-gap 40 where said protrusion engages around and along the projection portion 34.2 of the plug 34.

[0047] The main closure element 12 comprises a piston 44 at the centre of the front face 12.1 of said element, configured for cooperating with the main seat 20. The piston 44 can comprise a head portion 44.1 and an elongate portion 44.2, said elongate portion being housed in a bore formed in the main closure element 12. The head or main portion 44.1 of the piston 44 shows front face that contacts the main seat 20 so as to form a cavity 48 fluidly connected to the channel 12.3 through the main closure element 12, interconnecting the inlet 22 with the outlet 24. A building up of an inlet fluid pressure in the cavity 48 biases the main closure element 12 away from the main seat 20.

[0048] The piston 44 advantageously comprises a through-hole 44.3 fluidly interconnecting a front face and a rear face of said piston. This hole allows a counter pressure to build up at the outlet 24 once the pilot closure element 14 releases the pilot seat 26 while keeping a pressure in the cavity 48 that is higher than the counter pressure at the outlet 24.

[0049] The elongate portion 44.2 of the piston 44 can comprise an oblong hole through which an anchoring pin 46 extends. Said pin extends diametrically through the main closure element 12, advantageously through a circular external groove of the main closure element 12 housing the gasket 12.2 on the front face 12.1 of said element. The pin 46 extends diametrically at each end until the bottom of the groove housing the gasket 12.2. The latter is advantageously vulcanised in said groove so as to ensure a gas tightness between the inlet 22 and the channel 12.3 in the main closure element 12.

[0050] In figure 2, the valve is in a closed state, i.e. the fluid passage between the inlet 22 and the outlet 24 is shut-off. The spring 36 urges the main closure element 12 against the main seat 20 and the spring 38 urges the pilot closure element 14 against the pilot seat 26. The pressure at the inlet 22 is higher than the pressure at the outlet 24 so that both main and pilot closure elements 12 and 14 are further urged against their respective seats 20 and 26 by the difference between the inlet and outlet.

[0051] Upon energisation of the coil 10, a magnetic field is produced around said coil. More specifically, the coil 10 is generally ring-shaped and would around the axis of the ring. The magnetic field produced therefore naturally encircles the coil 10. In fact, the magnetic field extends axially along the second outer sleeve 8.2 and forms a loop at the axial ends of the coil 8. Starting from the left end of the coil 10, the magnetic field develops in the portion of the second sleeve 8.2 located at the left side of the coil 10, in the ring of ferromagnetic material 8.1.3 as well as in the core 16, the counter- core 30 and then loops back at the right end of the coil 10 in the back plate 42 (figure 1 ) made also of ferromagnetic material. The low permeability of the non-ferromagnetic material of the thin wall 8.1.4 is of a limited effect on the building up of the magnetic field in view of its reduced thickness. The same applies to the first air-gap 28. The negative influence of the second air-gap 40 on the development of magnetic field inside the sleeve 8.1 can be reduced by providing the engagement of the circular protrusion 30.2 with the plug 34, as detailed above. [0052] With reference now to figure 3, in the presence of a magnetic field in the core 16 and the counter-core 30, at the level of the first air-gap 28, a magnetic attracting force develops, tending to reduce said air-gap and bring the core 16 and the counter-core 30 into a mutual contact. In that sense, the core 16 is attracted towards the counter-core 30 so as to cancel the air-gap 28. By that movement of the core 16, the pilot valve element 14 is moved away from the pilot seat 26 against the resilient force of the spring 38. The gas under pressure at the inlet 22 flows through the channel 12.3 towards the piston 44, more precisely towards the through-hole 44.3 and the cavity 48. Upon development of a counter-pressure in the cavity 48, an opening force is exerted on the main closure element 12 against the closing force resulting from the gas pressure at the inlet against the main closure element 12 and also against the resilient force of the spring 36. This opening force resulting from the pressure in the cavity 48 adds to the magnetic force between the counter-bore 30 and the plug 34 at the second air-gap 40. The maximum cross-section of the through-hole 44.3 is advantageously smaller than the minimum cross-section of the through-hole 26.2 of the element 26, so as to promote the development of a counter-pressure in the cavity 48.

[0053] In other words, the piston 44 allows the building-up of a counter-pressure on a portion of the front face of the main closure element 12, facilitating the opening movement of the main closure element. The cavity 48 is active over a limited portion of the stroke of the main closure element 12, i.e. from the closed position (as illustrated in figure 2) in the opening direction as long as the gasket 12.2 is in tight contact with the seat 20 (as illustrated in figure 3).

[0054] The slidable attachment of the piston 44 to the main closure element 12 is configured so as to stop the relative movement between the piston and the main closure element once or shorty after that the gasket 12.2 does to cooperate anymore with the seat 20 in a gas tight manner. In figure 3, we can see that the attachment pin 46 is close to the end of the oblong holes in the elongate portion 44.2 of the piston.

[0055] With reference to figure 4, once the gasket 12.2 leaves the seat 20, the gas can flow directly from the inlet 22 to the outlet 24 between the seat 20 and the front face 12.1 of the main closure element 12. The cavity formed with the main seat 20, between the piston 44 and the gasket 12.2 does not exist anymore. Also the inlet pressure is present on both sides of the main closure element 12, so that essentially only the resilient force of the spring needs to be counter-acted by the magnetic force in the second air-gap 40 until said air-gap is cancelled and the counter-core 30 contacts the plug 34. During that movement, the main closure element 12 is moved away from the main seat 20 and the piston 44 is driven away by the main closure element 12.

[0056] Upon interruption of energization of the coil 10, the magnetic forces between the core 16 and counter-core 30 as well as between said counter-counter core 30 and the bottom 34 of the cavity disappears and the resilient forces of both springs 36 and 38 is not counter-acted anymore. As a consequence, the pilot closure element 14 is moved towards the pilot seat 26 and the main closure element 12 is moved towards the main seat 20, so that the gas passage between the inlet and the outlet is totally shut-off.

[0057] The electromagnetic core 16 can comprise a front portion 16.1 axially overlapping a ring portion 20 of the body 18 forming the main seat 20. This overlapping is advantageously also when the valve is in a fully open position as illustrated in figure 4. The section for the fluid flowing between the outer surface of the ring portion 20 and the inner surface of the front portion 16.1 is less than the section of the passage between the front portion 12.1 of the main closure element 12 and the seat 20. This provides a protection of the gasket 12.2 in that the fluid is accelerated and then decelerated towards the bottom of the chamber 16.2 formed by the front portion 16.1 . The chamber 16.2 forms than a stabilizing chamber that is beneficial for the gasket 12.2 and possible other sensible parts in the gas passage. The front potion 16.1 , the inner surface therefore and the outer surface of the ring portion 20 are advantageously generally cylindrical.

[0058] Figures 5 to 7 illustrate various steps for manufacturing the first sleeve 8.1 .

[0059] Figure 5 depicts a first step where a rod-shaped blank is machined to form the groove 8.1 .3. The general shape of the blank, i.e. with the two cylindrical portions, can be obtained by forging or by machining.

[0060] Figure 6 depicts a second step where the groove 8.1 .3 is filled with ferromagnetic material, like iron and/or ferrite. This filling is a deposition process that provides a metallurgic bonding of the material itself and also between that material and the material of the blank forming the groove. This can be achieved by a welding or sintering process.

[0061] Figure 7 depicts a third step where the blank is further machined to obtain the final sleeve 8.1 as illustrated in figures 1 to 4. For instance, a central bore is machined so to form the cylindrical wall of the sleeve and the cavity for receiving the different components of the electromagnetic device. Care can be taken to leave a thin-wall portion 8.1.4 at the bottom of the groove 8.1.3. This provides a continuity of material on the inner surface of the wall and thereby a gas tight and embrittlement resistant barrier. Also, the front end can be machined to form the groove 8.1.2. The outer surface of the cylindrical wall can also be machined, in particular at the level of the groove 8.1.3 in order to provide a proper cylindrical outer surface. Also the rear end portion 8.1.5 can be machined, for instance with a bore portion of a larger diameter and/or with an inner thread.