IMPROVED FUEL-SUPPLY DEVICES IN DIESEL ENGINES OF THE COMMON-RAIL TYPE

Abstract: Pump for common-rail accumulator, comprising: - a pump casing with an inner housing (2) and containing a sliding plunger (4) adapted to compress and deliver the fuel to said high-pressure accumulator; (1) - a sliding piston (6) adapted to slide in a contiguous portion of said housing; - a first chamber (7) comprised between said plunger and said sliding piston; - a second chamber (8) adjacent to said sliding piston; (6) - a first conduit (9) adapted to convey a flow of fuel from a suitable low-pressure tank (10) to said second chamber; (8) - a second conduit, (21) or delivery conduit, adapted to convey said fuel from said second chamber (8) to said high-pressure accumulator, (1) in which there is provided a third conduit (15) adapted to inject oil under pressure, in synchronization with the movement of said plunger, (4) onto the inner surface of said housing. (2) Said third conduit (15) is connected to a hydraulic pressure amplifier (40).

Description: IMPROVED FUEL-SUPPLY DEVICES IN DIESEL ENGINES OF THE COMMON-RAIL TYPE DESCRIPTION The present invention refers in particular to an improved fuel pump and an improved fuel injector adapted to inject precise amounts of highly pressurized fuel into the cylinder of a two-stroke or four-stroke diesel engine. Conventional injection systems make use of a plunger pump to pressurize the fuel circuit and inject the same fuel at a sufficiently high pressure in the cylinder of the engine. In the most common one of these systems, the pump, which is operated by a cam driven by the same engine, pressurizes the injection circuit up to such an extent as to cause the spring-loaded needle of the nozzle to open, thereby starting the phase in which fuel is injected in the combustion chamber. Relieving the pressure acting on the pump causes the circuit to decompress and this in turn causes the needle of the nozzle to close and the injection phase to terminate. In all of the above described systems, the injection (phase and duration) control action is performed by the pump which must be appropriately synchronized with the engine. The injector itself has on the contrary a passive role from a control point of view and, through the motion of the needle of the nozzle brought about by the pressure waves generated by the pump, ensures that the injection starts and ends at well-defined pressure levels. In another type of operation used in connection with diesel engines, generally known under the term "common-rail" in the art, the fuel injection systems are actually constituted by a pressure accumulator or manifold, which is kept at a constant pressure by means of a mechanically or electronically controlled pump, and one or more injectors connected thereto through proper pipes. A properly controlled organ, which depending on the case may be constituted by a valve or the same needle of the nozzle, regulates the fuel flow from said accumulator to the nozzle and, therefore, the combustion chamber. The pressure control performed by the pump is fully independent of the operation of the injectors, which may be operated hydraulically, mechanically or electronically. Therefore, as anyone in the art knows very well, no correlation exists in this case between the timing of the pump and the timing of the engine, while the pump itself can be operated in an asynchronous manner independently of the engine. The injection control action, both in terms of timing and duration thereof or injected amount, is entirely performed by suitable valves and organs that are an integral part of the injector itself. Accordingly, the operating principle of these injection apparatuses is very simple and the currently available technique is such as to enable diesel engines to be produced which are not only very reliable, but also very good-value, in particular large-sized engines for use as stationary electric power generators or naval drives. However, all this motors must use, as a fuel, certain types of oil products that are normally sold on the market and do not give rise to any problem as far as their availability and utilization are concerned. As any fuel that may be anyway considered, these products tend however to determine a cost-related problem, which becomes extremely important whenever these engines are required to operate in a continuous or semi-continuous manner, as this is the case in the afore cited types of applications. In the search for cheaper fuels that would anyway prove technically capable of being used in conjunction with the current types of diesel engines, the exploitation and utilization of a particular fuel, which is generally known in the art under the denomination of "ORIMULSION", have been eventually developed. This fuel is obtained by extracting a particular kind of bitumen from a fossil deposit located at the outfall of the river Orinoco, and subjecting it to a treatment of emulsion in water and a treatment of stabilization with particular additive substances, until a semi-fluid fuel product is eventually obtained which is easily producible to high levels of availability, is capable of being stocked and transported normally, is not dangerous in handling and transporting, has a high heat value, is not only very cheap, but also quite likely to remain substantially stable in its cost in the future. It can be most easily appreciated that such characteristics of Orimulsion make it actually an ideal fuel for some typical applications and, as a matter of fact, it is being used prevailingly to supply large-sized boilers for the production of gas in thermal power plants, where it is ideally used as a replacement for coal, which actually features many of the above mentioned qualities and merits, but, as anyone is well aware of, is connected to a number of serious drawbacks from an environmental point of view, since it is considered a remarkable source of pollution. Its utilization as a fuel to supply stationary power-generation installations operating with high-to-medium power diesel engines being currently produced has of course being taken into consideration and investigated accordingly. In this connection, however, it has to be stressed that such an Orimulsion fuel shows following three peculiarities, ie.: - the first such peculiarity derives from the fact that the emulsion is not particularly stable to withstand the temperature, pressure and velocity conditions that prevail in an injection apparatus; this problem can be solved by inverting the emulsion, ie. dispersing the water in the bitumen: a marked increase in the stability is thereby obtained; - in the second place, the so obtained emulsion is however characterized by a high viscosity thereof at ambient temperature; such a problem can in turn be solved without any particular difficulty by appropriately pre-heating it before utilization, up to a temperature of anywhere between approx. 170°C and 180°C, so as to obtain the desired value of fluidity; - the third peculiarity lies in the fact that this fuel turns practically out as being rather corrosive, but above all abrasive, to such an extent that it would make it necessary for both the pump and the injectors of a fuel-supply apparatus of diesel engines of general kind to be replaced quite frequently; since such an occurrence, if it does not actually present any technical difficulty, gives rise to a still widely unsolved economic problem deriving from the need for the concerned spare parts to be replaced and the resulting downtimes of the related installation, the use of such a fuel has practically turned out as being largely unacceptable from an economic point of view owing to the whole number of above illustrated reasons, so that its utilization as a diesel fuel is still barred industrially, notwithstanding the other above mentioned, fully positive technical characteristics thereof. It therefore would be desirable, and it is actually a main purpose of the present invention, to remove the above cited hindrances and, in particular, to provide a pump and a kind of injectors for diesel engines, operating on a so-called common- rail supply, that is capable of doing away with the above mentioned drawbacks connected A/vith the use of highly abrasive fuels and, in particular, in which a kind of barrier is brought about which is capable of totally preventing such kind of fuels from being able to come into contact with and, as a result, contaminate some of the moving members of the pump of the injector of the fuel supply system; in addition, these organs shall be capable of being manufactured in a low-cost, reliable manner through the use of readily available, safe techniques and materials. This aim, along with further features of the present invention, is reached in a pump and an injector that are made and operate as recited in the appended claims. The present invention may be implemented according to a preferred, although not sole embodiment that is described below by way of non-limiting example with reference to the accompanying drawings, in which: - Figure 1 is a symbolic, schematic view of a pump according to the present invention; - Figure 2 is an enlarged symbolic schematic view of a device that is essential to the purposes of the present invention; - Figure 3 is a schematic view of the most significant component parts and assemblies of a pump and an injector according to the present invention, as correctly assembled together in their normal operation state; - Figure 4 is a view of the injector appearing in Figure 1 , in a different operating state thereof; - Figure 5 is a schematic view of the configuration of a hydraulically operating pressure amplifier. The term "fuel" will be used without distinction throughout the following description to mean each and any of various liquid fuels suitable for the diesel cycle and, in particular, the so-called Orimulsion type. Such a simplification will however by no means affect the clearness of what is being set forth therein, owing to the context in which such a term is used, as anyone skilled in the art is capable of readily understanding. Referring to Figure 1, which illustrates a preferred embodiment, a solution according to the present invention is described below, along with the related operating principle. In particular, the pump body 41 can be noticed to be provided with a cylindrical inner housing 2, which is closed on a side thereof by a sealed wall 3; in such a housing there are arranged: - a sliding plunger 4 adapted to be operated by an appropriate organ 5, typically a cam, - a piston 6 located between said plunger and said wall 3, - a first chamber 7 separating said plunger from said piston, - a second chamber 8 separating said piston from said sealed wall 3, - a first conduit 9 used to convey a flow of fuel from an appropriate low- pressure tank 10 to said second chamber 8, and provided with a non-return valve 19. Such a pump, owing to the pressurization of the fuel in the second chamber 8, has the drawback that the fuel, as compressed at the very high pressure that is typical of the common rail, ie. at approx. 1000 bar, is capable of seeping into the gap, however narrow it actually is, existing between the surface of the piston 6 and the inner surface, or liner, of the housing 2, so that, considering the very high corrosiveness and high temperature thereof, it would cause the pump itself to become unserviceable in quite short a time. In order to prevent such a seepage, the present invention provides for a form of "hydraulic seal or stopper" to be provided so as to cause it to flow in between said liner and said piston, in which said stopper or seal is preferably brought about by oil. For it to be effective, ie. for it to form an absolute barrier against the seepage of the fuel, the pressure at which said oil must be pumped into said gap must be greater, albeit just slightly, than the pressure prevailing in said second chamber 8m; furthermore, the pressure of said sealing oil must be pulsating and synchronized with the pattern followed by the pressure in said second chamber 8. According to the present invention, these results are obtained by providing an appropriate device consisting in an outer housing 40 that contains two distinct cavities 11, 12 separated from each other by a sliding partition element, as illustrated in Figure 2. These two cavities 11 and 12 are joined to each other by a passage provided with two longitudinal sectors, in which a first sector 14a has a certain cross-section area A and is adjacent to said first cavity 11, whereas a second sector 14b has a respective cross-section area B that is larger than said cross-section area A. The above cited partition element 13 is formed by two potions 13a and 13b adapted to fit into the two respective sectors 14a and 14b, in such a manner as to ensure that each portion closes, ie. plugs in a substantially tight manner the respective sector. In substance, the partition element 13a and 13b is able to slide along a certain distance H and, during such a sliding motion thereof, the two faces of said partition element move in such a manner as to delimit the respective variable-volume cavities. As regards what has not been explicitly described here, reference should be made to Figure 2, which is self-explaining. This Figure can be seen to symbolically illustrate a so-called "pressure amplifier", ie. a machine that conceptually resembles a hydraulic lever, for which following relations, referred to Figure 5, apply: FI = PI * SI and F2 = P2 * S in which P is the pressure, F the force and S the surface of the elements, the meanings of which can be clearly inferred from the Figure. Since the partition element formed by said portions 13a and 13b is a solid body, the force is transmitted therethrough without variations, and therefore: FI = F2 and therefore PI * SI = P2 * S2 so that in substance P2 = P1 * (S1 / S2) It therefore can be readily appreciated that the pressure P2 can be increased at will by appropriately adapting the S1/S2 ratio. Said first cavity 11 is connected, via a third conduit 15, to one or more appropriate apertures 16 provided in the liner of said housing 2, at the height of the motion, or displacement, of said piston 6. To conclude the description of the device, it should be added that there is provided a fourth permanently open conduit 17 between said second cavity 12 and said first chamber 7. At this point of the description, anyone skilled in the art will be fully capable of readily understanding the way in which the above exemplified invention actually works: when the plunger 4 is pressed by the cam 5, it transmits the pressure to the first chamber 7, which is filled with oil, and from this chamber on to the piston 6. From this piston the pressure is transmitted finally on to the second chamber 8, in which the therein contained fuel is then pressurized up to the desired, correct pressure for use in the injection nozzles connected to the common rail 1. At the same time as the pressure is so applied onto the oil in said first chamber 7, also the second cavity 12 is pressurized up to the same pressure owing to the connection of said fourth conduit 17. Owing to the action of the just described pressure amplifier 13a and 13b, the pressure in the cavity 11 is increased up to a pre-determined value, which is anyway greater than the value of the pressure existing in the second chamber 8 containing the fuel, so that a particular lubricant oil at a relatively high viscosity, which is contained in said first chamber 11, is pumped into said conduit 15 and, from here, into the apertures 16, from which said oil eventually flows out to spread out in an almost even, uniform manner between the outer surface of the piston and said liner, thereby bringing about a kind of oil stopper which, owing to its being pumped at a pressure that is higher than the pressure of the fuel in the second chamber 8, prevents this fuel from seeping therethrough and, as a result, deteriorating the moving parts. In this way, it has therefore been possible for a kind of sealing effect to be provided not through the use of a solid or elastic component part, but rather by means of a fluid that is pumped at an appropriate pressure into very narrow gaps, so as to provide the afore cited "absolute barrier or stopper" function against the seepage of foreign fluids, at a lower pressure, into the same gaps. As a result, since the fuel is in this way prevented by the existing pressure difference from seeping into the gap, the latter, duly lubricated by an appropriate and different fluid, is not damaged and the purpose of the present invention is therefore fully attained. It is further to point out that the pumping onto the surface of the piston of the oil contained in said first cavity occurs intermittently in synchronization with the pressurization pattern of the fuel in the second chamber 8, so that said lubricating and sealing action is exactly performed when required and appropriate. In this way, it further improves the effectiveness of the invention, while at the same time contributing to a lower usage of oil in said first cavity 11 , since such an oil is actually pressurized and pumped only in the pre-established, useful intervals. A particular improvement of the present invention can be obtained if the outer surface of the piston 6 is provided with a plurality of annular grooves 19 which, owing to them passing in front of said apertures 16 in an alternating manner, are able to more easily collect the oil therefrom, thereby promoting both the uniformity and the velocity of the distribution thereof on most of the outer surface of said piston, wherein such a circumstance actually contributes to a further improvement of the above described function of "fluid stopper" performed by said oil. The practical result obtained with the invention will at this point be fully obvious. In this connection, those skilled in the art will anyway be able to still more appreciate the usefulness and validity thereof, considering that the pressure of the flow injected by the conduit 15 is a pulsating one, duly synchronized with the actual pressurization phase or timing in said first chamber 7, ie. with the phase of actual temperature rise of the common rail and, therefore, just when it is actually needed. In fact, if the pressure on the conduit 15 were not a pulsating, but a continuous one, the result would be a totally useless sealing effect of said "oil stopper". What is still worse, the resulting useless seepage occurring during a single portion of the movement of the plunger 4, out of the compression phase, would generate a useless, but quite considerable usage of sealing oil flowing in from said cavity 11. The problem that so emerged in connection with the protection against the corrosive effects produced by a particular kind of fuel on the moving parts of a common-rail pump is also true in a quite similar manner, and to a quite similar extent, for a typical injector. With reference to Figures 3 and 4, it should be noticed that the injector 30 is provided with a lower body 31, in which the chamber 32A collecting said fuel is arranged around a needle valve 34, the conduit 33 for the fluid controlling the movement of the valve, and the final injection nozzle 35. Said needle valve is of course slidably housed in an appropriate seat 36 provided inside said lower body 31. The injector is provided with, further organs, which however are not relevant to the purposes of the present invention. Therefore, also in this case the high-pressure fuel that flows into the chamber 32A tends of course to seep into the however quite narrow gap existing between the needle valve 34 and said seat 36. In order to prevent such a drawback from arising, there is provided an annular cavity 39 contiguous to and open towards said seat 36 housing said needle valve, so that said seat 36 is intercommunicating with said annular cavity 39. The latter is furthermore connected, via a fifth conduit 37, to said first cavity 11„ so that said annular cavity 39 is constantly filled by the same lubrication oil which is present in the pump and, as in the previously considered case, is still at a pressure that is higher than the pressure of the fuel in the fuel supply conduit 32 coming from the accumulator 1. As a result, even in this case the sealing effect against fuel seepage in the seat 36 is ensured by the opposing pressure of said oil in said annular cavity 39 supplied via said fifth conduit 37 connected to said first cavity 11. In an advantageous manner, in order to ensure a substantial constancy of the pressure in said annular cavity, said conduit 37 is provided with an appropriate non-return valve 38. Therefore, the advantage deriving from such a solution is a substantial one, owing to the fact that to the high, but constant (since generated by the common rail) pressure prevailing in the chamber 3 A there is opposed a still higher, but anyway still constant pressure of the oil flowing in from the conduit 37 associated to the nonreturn valve 38. As a result, there are no phases or periods in which the pressure of Orimulsion in the chamber 3 A is not contrasted, so that, conclusively, the fuel is permanently prevented from being able to seep into said seat 36. The above proposed solution is such to anyway allow for a further advantageous improvement. As a matter of fact, both the hydraulic oil that is present in the first chamber 7 in communication with said second cavity 1 , and the oil that is present in said first cavity 11 are of course subject to become progressively exhausted due to the effect of the various seepages and leaks. In view of doing away with such a drawback, a further oil supply chamber 50, which is duly filled with oil at a low/medium pressure and operates as a fill-up reservoir, is provided in the arrangement. Said chamber 50 is connected to said first chamber 7 via an appropriate conduit 51 flowing into said first chamber 7 through an appropriate nozzle 52, which is arranged in a suitable position with respect to said pump body 41, and which shall be explained in greater detail further on. In addition, to said chamber 50 there is connected a further conduit 53 that, via the non-return valve 54, is in turn connected to said first cavity 11. The operation of this fill-up chamber 50 and the thereto connected conduits is as follows: when the sliding plunger 4 is in its upstroke phase, it generates a negative pressure in said first chamber 7 which therefore takes in the oil that is present in said fill-up chamber 50 via the conduit 51. Such an intake is possible owing to the position of the nozzle 52 being such as to ensure that it is open towards the chamber 7 during at least a portion of the upstroke period of the plunger 4, in such a manner as to ensure the due intake and enable the oil in the chamber 7 to be filled up, ie. restored to the due level. However, it should further be noticed that the position of said nozzle 52 is also such as to cause said nozzle to be automatically closed by the sliding plunger 4 at a certain stage of its downstroke movement, thereby ensuring the tightness of said first chamber 7 (apart from the conduit 17, which anyway does not impair said substantial tightness) and, therefore, preventing any high-pressure backflow towards said fill-up chamber 50. As far as the oil fill-up in the cavity 11 is on the contrary concerned, this is carried out through said conduit 53; in this case, however, the provision of the nonreturn valve 54 becomes absolutely necessary, since otherwise the oil would of course be free to flow back from the cavity 11 to said fill-up chamber 50, thereby depressurising said cavity 11 and, indirectly, also said first chamber 7, under resulting ruinous effects on the maintenance of the pressure in the common rail.

Claims: CLAIMS 1. Pump high-pressure accumulator (1) adapted to supply fuel to an injector for internal-combustion engine, in particular a diesel engine, comprising: - a pump body provided with a cylindrical inner housing (2) that is substantially closed on a side thereof by a wall (3) and accommodates a plunger (4) adapted to reciprocatingly slide therein and compress the fuel to deliver it to said high- pressure accumulator (1), - a piston (6) adapted to slide in the portion of said cylindrical housing that is comprised between said plunger and said sealed wall (3), - a first chamber (7) comprised between said plunger and said sliding piston, - a second chamber (8) comprised between said sliding piston and said wall (3), - a first conduit (9), or intake conduit, adapted to convey a flow of fuel from an appropriate low-pressure tank (10) to said second chamber (8), and provided with a first non-return valve (19), - a second conduit ( 1), or delivery conduit, adapted to convey a flow of said fuel from said second chamber to said high-pressure accumulator, and provided with a respective second non-return valve (22), characterized in that there are provided automatic means and a third conduit (15) that are adapted to deliver, in synchronization with the movement of said plunger, intermittent flows of pressurized lubricant fluid on to the liner or inner surface of said housing (2). 2. Pump according to claim 1, characterized in that said sliding piston (6) is provided in its outer surface, in contact with said liner of said cylindrical housing (2), with at least a preferably annular groove (19) adapted to enable said lubricant fluid flowing in from said third conduit (15) to be distributed over a portion of said liner. 3. Pump according to claim 1 or 2, characterized in that said automatic means are adapted to raise the pressure of said lubricant fluid in said third conduit (15) up to a value that is higher than the value of the pressure in said second chamber (8). 4. Pump according to any of the preceding claims, characterized in that said automatic means comprise two distinct cavities (11, 12) separated from each other by a partition element capable of performing a tightly sliding movement within an appropriate passage comprising two sectors (14a, 14b) that connects said cavities with each other, - in which said partition element is constituted by two portions, of which the first portion (13a) is adapted to be coupled tightly in said first sector (14a) and the second portion (13b) is adapted to be coupled tightly in said second sector (14b), - in which the first cavity (11) is connected to said third conduit (15), and said second cavity (12) is connected via an appropriate fourth conduit (17) to said first chamber (7), - and in which the area of the component of the surface which is orthogonal to the sliding direction of said first portion (13a), facing said first cavity (11), is smaller than the area of the corresponding orthogonal component of the surface, facing said second cavity (12), of said second portion (13b). 5. Pump according to the preamble of claim 1, and furthermore adapted to supply an injector (30) provided with a lower body (31) comprising a needle valve (34), which controls the flow of pressurized fuel and is capable of being selectively actuated into a first position and a second position in which said needle is moved so as to close and open, respectively, an outlet port for the pressurized fuel to flow from said high-pressure accumulator (1) to a combustion chamber of an internal- combustion engine, characterized in that: - a portion of said needle valve is housed in an appropriate seat (16) provided in a portion of the body of said injector, in which in said body there is provided an annular cavity (39) that is contiguous to and open towards said seat and, therefore, the outer surface of said needle valve, - and into said annular cavity (39) there is injected a flow of oil at a pressure that is higher than the pressure of said high-pressure accumulator (1). 6. Pump according to claim 5, characterized in that the pressure of the oil in said annular cavity (39) is substantially constant. 7. Pump according to any of the preceding claims or combination thereof, characterized in that: - said annular cavity (39) is connected, via a fifth conduit (37), to said first cavity (11), and - said fifth conduit (37) is provided with a non-return valve (38). 8. Pump according to any of the preceding claims, characterized in that there is provided a supply chamber (50), connected via a conduit (51) on the wall of said housing (2) to a nozzle (52), which is arranged in a position adapted to enable a connection thereof to be established with said first chamber (11) at least during a portion of the stroke of said sliding plunger. 9. Pump according to claim 8, characterized in that there is provided a further conduit (53) between said supply chamber (50) and said first cavity (11), in which said further conduit comprises an appropriate non-return valve (54) adapted to prevent the oil from flowing back towards said supply chamber (50).

Inventors: NOBILE MARINO, SORGO MARINO, NOBILE, MARINO, SORGO, MARINO
Applicants: NOBILE MARINO, SORGO MARINO, WAERTSILAE ITALIA S P A, NOBILE, MARINO, SORGO, MARINO, WAERTSILAE ITALIA S.P.A.
Application year: 2001
Main classification: F02M63
IPC codes: F02M59, F02M61, F02M63