PRESSURE REDUCER FOR INTERNAL COMBUSTION ENGINES FED WITH GAS, FOR EXAMPLE CNG, LPG AND LNG

Technical field

This invention relates to a pressure reducer, in particular a pressure reducer insertable in a feed system for an internal combustion engine running on gas, methane, LPG or LNG.

This invention is mainly applied in the automotive sector, and in particular in the production of low pressure stages in feed systems for internal combustion engines running on gas, methane, LPG or LNG.

Background art

In the prior art there are mainly two types of "mechanical" pressure reducers, of the piston or membrane type.

Piston-type reducers, commonly made by OEM (original equipment manufacturers), comprise a hollow valve body in which a piston can slide, the piston forming the sensitive element of the system.

To guarantee system sealing, the piston is provided, at the head (that is to say, at the part with the larger diameter on which the pressure and the spring act with an opposing force), with a lip seal, that is to say constrained to the head and abutting the valve body, mobile relative to it by sliding.

In other words, the change in pressure imparts a movement to the piston, which drags the seal with it, deforming the seal.

Obviously, that structure produces friction phenomena (static and dynamic) between the seal and the inner wall of the cavity, which particularly in low pressure applications have a high incidence on the balance of forces produced inside the reducer.

In fact, such a high incidence of friction force, in low pressure applications, results in a big variability of the reducer pressure output value, which harms its efficiency.

Moreover, it should be noticed that friction tends to increase as time passes due to deterioration of piston lubrication.

Alternatively, in particular in the aftermarket, membrane-type reducers are sold, in which the sensitive element is only the membrane, having a circular shape and forming a deformable separator between a higher pressure chamber and a lower pressure chamber (usually at atmospheric pressure), provided with a contact spring inside it.

Therefore, the membrane is connected to a shutter for regulating its position and defining the gas transit gap (and therefore the pressure drop). That solution, although having advantages from the point of view of the forces involved, having eliminated the friction of the seal, introduces considerable problems linked to the reliability of the component.

In fact, although being made with the most modern materials (e.g.: rubberised fabric), the membranes of the reducers are subject to regulations which, due to the high fatigue stress to which they are subjected, limit their use to no more than 20,000 km (on motor cars).

In light of this, while on one hand they facilitate pressure control, on the other they significantly reduce performance in terms of reliability and duration.

Considering the situation just described, the client/manufacturer is today forced to choose, depending on the type of application, between two solutions, neither of which is without disadvantages. Disclosure of the invention

This invention therefore has for an aim to provide a pressure reducer for internal combustion engines fed with gas, for example CNG, LPG and LNG, able to overcome the disadvantages of the prior art described above.

In particular, this invention has for an aim to provide a pressure reducer for internal combustion engines fed with gas, for example CNG, LPG and LNG, which is easy to make and highly efficient.

More precisely, the aim of this invention is to provide a pressure reducer for internal combustion engines fed with gas, for example CNG, LPG and LNG, of the piston type able to limit as far as possible the range of output pressures.

Said aims are achieved by a pressure reducer for internal combustion engines fed with gas, for example CNG, LPG and LNG with the features of one or more of the appended claims, and in particular comprising a valve body provided with an inner cavity delimited by a lateral wall, a piston housed in the inner cavity in such a way as to divide it into a first chamber and a second chamber and slidably associated with it for moving between a first position, in which said first chamber has a maximum volume, and a second position, in which said first chamber has a minimum volume.

Moreover, the reducer comprises at least one spring positioned inside the first chamber of the cavity, operatively interposed between the valve body and the piston and designed to act on the piston for pushing it towards the first position, and at least one sealing element interposed between the piston and the lateral wall of the valve body for preventing fluid leaks between the first and second chambers.

According to the invention, the sealing element is a flexible ring extending between an outer edge, fixed to the lateral wall of the cavity, and an inner edge, fixed to the piston in such a way that it deforms without sliding on said lateral wall during the movement of the piston between the first and second positions.

Advantageously, in that way, although keeping all of the advantages in terms of reliability and duration of the "piston-type" reducer, its disadvantages are reduced, since the friction components are eliminated from the balance of forces.

In fact, since both edges of the ring are constrained to the components of the reducer, it is not subject to sliding phenomena. Consequently, the only force involved opposing the movement of the piston is the sealing element resistance to deformation, which has a much smaller incidence than friction.

It should be noticed that the ring described above cannot in any way be compared with the membrane of a membrane-type regulator, since it is the piston which forms the sensitive element of the system and which is moved by the change in pressure. The ring is dragged and deformed by the piston as it moves.

To avoid strain on the material, the ring has a substantially bellows-style structure, mobile between a compact configuration, corresponding to the first position of the piston, and an extended configuration, corresponding to the second position of the piston.

More precisely, the substantially bellows-style structure of the ring is formed by a profile provided with at least one apex formed by two rising walls which are joined at the apex and elastically mobile between a near position, corresponding to the compact configuration, and a far position, corresponding to the extended configuration.

In other words, the apex is formed by two opposite annular separators, set at an angle to each other and joined at the apex, where the apex acts substantially as a pin (that is to say, a pivot or elbow) between the near position, where the two walls are substantially opposite each other, and the far position, where the two walls form an obtuse angle.

It should be noticed that, preferably, the apex forms a concavity of the ring facing towards the second chamber, that is to say, the pressurised chamber (low pressure) so that the fluid in the second chamber acts on said rising walls, pushing them towards the far position.

In fact, the pressure in the second chamber, greater than that in the first chamber (substantially atmospheric pressure) tends to make the concavity "open out", opening out the two annular walls (or two rising walls), keeping the inner edge and the outer edge of the ring adhering respectively to the piston and to the lateral wall of the cavity. Brief description of the drawings

These features of the invention will become more apparent from the following detailed description of a preferred, non-limiting embodiment of it, illustrated by way of example in the accompanying drawings, in which: - Figures 1 a and 1 b are longitudinal sections of a pressure reducer according to a first embodiment of this invention, in two successive operating configurations;

- Figures 2a to 2c are respectively a perspective view, a side view and a cross-section of a flexible ring of the reducer of Figures 1 a and 1 b;

- Figures 3a and 3b are longitudinal sections of a pressure reducer according to a second embodiment of this invention, in two successive operating configurations;

- Figures 4a to 4c are respectively a perspective view, a side view and a cross-section of a flexible ring of the reducer of Figures 3a and 3b;

- Figure 5 is a partial view in cross-section of a further embodiment of a flexible ring for a pressure regulator according to this invention;

- Figure 6 is a schematic view of a feed system for an internal combustion engine fed with gas, for example CNG, LPG and LNG, comprising the regulator of Figures 1 a and 1 b.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes a pressure reducer according to this invention.

The pressure reducer 1 is preferably designed to be inserted in a feed system for internal combustion engines running on gas, even more preferably, running on methane (CNG), LPG or LNG.

Said system 100 (also forming the subject matter of this invention) comprises a plurality of electromagnetic injectors 101 , at least one distribution manifold 102 in fluid communication with the injectors 101 and at least one feed tank 103 for feeding the manifold 102 containing a pressurised gas (CNG, LPG, LNG). To allow control of the input pressure of the injectors 101 , the system comprises at least one pressure regulating valve 104 interposed between said tank 103 and said manifold 102.

Said regulating valve comprises a regulator 1 according to this invention. In particular, in preferred applications, the regulating valve 104 comprises a high pressure stage 104a and a low pressure stage 104b.

In its main application, the reducer (or regulator) 1 according to this invention is positioned in the low pressure stage 104b, that is to say, it is designed for feeding the engine injectors with a pressure of between 1 and 10 bar, preferably between 1 .5 and 5 bar.

More precisely, the pressure regulator 1 comprises at least one inlet 105, in communication with said high pressure stage 104a or with said tank 103, and one outlet 106 in communication with the manifold 102.

The gas at the inlet 105 has a pressure of between 5 and 25 bar, and the gas at the outlet 106 has a pressure of between 1 and 10 bar, preferably between 1 .5 and 5 bar.

It should be noticed that the expression "in communication" in the previous paragraph means that the environments in communication with one another are at the same pressure.

Therefore, the reducer 1 comprises a (metal) valve body 2 provided with an inner cavity 3 delimited by a lateral wall 3a. The valve body 2 is therefore a box-style element, preferably cylindrical, provided with connecting means 2a for connection to a high pressure stage of the feed system (not illustrated). Preferably, the connecting means are formed by a screw thread or by a slot.

More precisely, the cavity 3 comprises a portion with larger diameter 4, delimited by said lateral wall 3a, and a portion with smaller diameter 5, close to which the above-mentioned connecting means 2a are preferably positioned.

Therefore, the cavity 3 comprises an inlet at the portion with smaller diameter 5 and an outlet at the portion with larger diameter 4. It should be noticed that the terms "inlet" and "outlet" are used in relation to a regulator 1 use condition, since the fluid (gas) tends to flow from the high pressure zone (close to said inlet) to the low pressure zone (close to said outlet). It should be noticed that the regulator 1 is of the piston type, that is to say, it comprises a piston 6 (also metal) housed in the inner cavity 3 in such a way as to divide it into a first chamber 7 and a second chamber 8.

In other words, the piston 6 comprises at least one head 6a housed in the cavity 3 and forming a separator between the first chamber 7 and the second chamber 8. Therefore, the head 6a has a first side facing into the first chamber 7 and a second side, opposite to the first 7, facing into the second chamber 8.

Said piston 6 is slidably associated with the cavity 3 for translating inside the cavity along a line of movement "A". Said line of movement "A" is substantially parallel with (and corresponds to) a central axis of extension of the valve body 2 (and in particular of the cavity 3).

Therefore, the piston 6 is mobile between a first position, in which the first chamber 7 has a maximum volume, and a second position, in which the first chamber 7 has a minimum volume. Similarly, in said first and second positions, the second chamber 8 respectively has a minimum and a maximum volume, the volumes of the chambers being complementary to form the volume of the cavity.

Therefore, the head 6a of the piston 6 forms a separator slidably mobile in the cavity between the first and the second positions.

Preferably, the piston 6 also comprises a rod 6b, with smaller diameter than the head 6a (the head therefore having a larger diameter) and extending along the axis of movement "A" of the piston 6 between a first end 9a, constrained to the head 6a, and a second end 9b, which is free, projecting outside the cavity 3.

More precisely, the second end 9b of the rod 6b forms the shutter of the reducer 1 since its position causes the pressure drop.

It should be noticed that the head 6a of the piston 6 is housed and slidable inside the portion with larger diameter 4 of the cavity 3. In contrast, the rod 6b is housed and slidable in the portion with smaller diameter 5 of the cavity 3.

In the preferred embodiment, the piston 6 (and in particular the rod 6b) comprises an inner through duct 10 extending between an inlet section, giving onto the outside of the cavity 3, and an outlet section opening into the second chamber 8 for putting in fluid communication the second chamber 8 and a high pressure stage of the reducer 1 .

In other words, the inlet section corresponds to the second end 9b of the rod 6b, whilst the outlet section is facing the inside of the second chamber 8 and is formed by an opening in the head 6a of the piston 6.

Therefore, the fluid in the second chamber 8 has a greater pressure than that in the first chamber 7.

It should be noticed that the second chamber 8 is, in use, in communication with said outlet 106, and therefore with the manifold 102. More precisely, the fluid in the second chamber 8 is, in use, low pressure engine feed gas (between 1 and 10 bar). In contrast, the fluid in the first chamber 7 is air at atmospheric pressure (around 1 bar).

The reducer 1 also comprises contact means 1 1 operatively interposed between the valve body 2 and the piston 6 and designed to apply an elastic force on the piston 6.

More precisely, the contact means are formed by an elastic unit (that is to say, a spring 11 a) housed in the cavity 3 (and in particular inside the first chamber 7).

Said spring 1 1 a is designed to act on the piston 6 for pushing it towards the first position. In other words, the spring 1 1 a is compressed between a top wall 2a of the valve body 2 and the head 6a of the piston 6.

Preferably, the spring 11 a extends along its own central axis corresponding to the central axis of the cavity 3. Therefore, the spring 1 1a is coaxial with the rod 6b of the piston 6.

Preferably, the valve body comprises a tubular portion 2b coaxial with the lateral wall 3a of the cavity 3 forming the portion with smaller diameter 4 of the cavity.

The spring 1 1 a is preferably positioned around said tubular portion 2b in such a way as to remain coaxial with the rod 6b.

To prevent fluid leaks between the first chamber 7 and the second chamber 8, the reducer 1 comprises at least one sealing element 12 interposed between the piston 6 and the lateral wall 3a of the cavity 3 of the valve body 2.

More precisely, the sealing element 12 is formed by a flexible ring 13 extending between an outer edge 13a, fixed to the lateral wall 3a of the cavity 3, and an inner edge 13b, fixed to the piston 6 in such a way that it deforms without sliding on said lateral wall 3a during the movement of the piston 6 between the first and second positions.

Advantageously, in that way the friction components of the movement of the piston 6 are eliminated, and are substituted by the elastic component arising from deformation of the flexible ring 13, the latter component having a much smaller incidence.

In other words, in that way it is possible to obtain a reducer which is guaranteed "for life" because it is of the piston type (the piston being the sensitive element) but has very high efficiency even at low pressures, since it is substantially free of friction components.

It should be noticed that, relative to what is mentioned above, it is particularly important to emphasise that in the reducer 1 according to this invention the element sensitive to changes in pressure is the piston 6, whilst the only function of the ring 13 is sealing (since it is a sealing element 12). In fact, it is the piston 6 which deforms the ring 13 during piston movement between the first and second positions and not the ring 13 which moves the piston 6.

Therefore, the ring 13 is made of an impermeable and elastically deformable (flexible) material.

Preferably, the ring 13 is made of polymeric material. Even more preferably, the ring 13 is made of a thermoplastic polymer.

In the preferred embodiment, but without limiting the use of other suitable materials, the ring 13 is made of polyurethane.

Therefore, the inner edge 13b and the outer edge 13a of the ring 13 are fixed (without the possibility of sliding) respectively to the piston 6 (that is to say, to the head 6a) and to the lateral wall 3a of the cavity 3.

Said edges 13a, 13b may be fixed using clamps or flanges or by interference fit.

Preferably, the outer edge 13a is mechanically constrained to the lateral wall 3a of the cavity 3 by clamp or flange means 14.

In a first embodiment, the inner edge 13b of the ring 13 is constrained to the piston 6, and in particular to the head 6a of the piston 6, by interference fit.

In other words, the ring 13 has an undeformed ("free") configuration which is different to the configuration it adopts inside the regulator 1 . Therefore, once inserted in the regulator 1 and constrained to the lateral wall 3a of the cavity 3, the ring is deformed and forced into contact on the piston 6 with "interference fit". Consequently, the inner edge 13b of the ring 13, in that embodiment, is shaped to apply a pressure (at least partly radial) on the piston 6 so as to remain anchored to it.

In one embodiment illustrated (Figure 5), the inner edge 13b comprises a cylindrical portion 18 from which at least one circumferential tooth 19 extends, forming a narrowing designed to increase the mounting seal. To facilitate said coupling (Figures 3a to 3c), preferably the head 6a of the piston 6 is provided with a circumferential groove 15 for housing the inner edge 13b of the ring 13.

Advantageously, the shoulders of the circumferential groove 15 form axial locking bodies (that is to say, along the line of movement "A") for the inner edge 13b of the ring 13.

Therefore, the ring 13 extends between the inner edge 13b and the outer edge 13a with a deformable intermediate portion 13c, more precisely elastically deformable.

In the preferred embodiment, the ring 13, and in particular the intermediate portion 13c, has a substantially bellows-style structure, for deforming between a compact configuration, corresponding to the first position of the piston 6, and an extended configuration, corresponding to the second position of the piston 6.

More precisely, the intermediate portion 13c of the ring 13 is formed by a profile provided with at least one apex 16 formed by two rising walls 16a which are joined at the apex 16 and elastically mobile between a near position, corresponding to the compact configuration, and a far position, corresponding to the extended configuration.

In other words, the two rising walls 16a are substantially rotatable relative to one another as they move towards and away from each other between the near position and the far position.

It should be noticed that the apex 16 substantially forms a pin (or pivot) of the rotation of the above-mentioned two rising walls 16a.

The term "rising walls 16a" in this text refers to two annular separators set at an angle to one another and inclined towards each other, which are joined at the apex 16.

Preferably, the apex 16 forms a concavity of the ring 13 facing towards the second chamber 8, in such a way that the fluid in the second chamber 8

(that is to say, the low pressure gas) acts on said rising walls 16a, pushing them towards the far position.

Preferably, the ring 13 has a single concavity facing towards the second chamber 8.

In fact, since the pressure in the second chamber 8 is higher than that in the first chamber (atmospheric pressure) the pressurised fluid in said second chamber 8 tends to make the concavity of the ring 13 "open out", helping to keep the outer edge 13a and the inner edge 13b anchored. It should be noticed that the intermediate portion 13c could also have a series of apexes and recesses (that is to say, a plurality of apexes 16). That must be established depending on the material and the stroke of the piston 6. In the embodiment illustrated, the ring 13 has a single apex 16 and the piston stroke is approximately 2 mm.

For a complete description, it should be noticed that the reducer 1 is provided with a further sealing element 17 operatively interposed between the rod 6b of the piston 6 and the tubular portion 2a of the valve body 2. Said further sealing element 17 is preferably a lip seal, or a sliding seal. However, alternatively, this sealing element too may be substituted with a ring similar to the one described above.

The invention achieves the preset aims and brings important advantages. In fact, the use of a flexible ring anchored both to the piston and the valve body inside a piston-type reducer allows a significant reduction in the regulator output pressure range, increasing its performance and facilitating control of it.

Moreover, the absence of a sliding seal between the piston head and the valve body allows an increase in construction tolerances, thereby reducing production costs for the component.

It should also be noticed that the use of a ring with a bellows-style structure avoids stressing the material in the many piston movement cycles, allowing the component to be guaranteed "for life" as in classic piston-type reducers.