Fuel injection system for internal combustion engines

Abstract

 The invention concerns a system for the supply of fuel-injection, internal combustion engines, comprising a pump unit and an injector unit which are part of an integrated assembly. In the pump unit, an intake and supply piston (15) forms a movable anchor, displaced by an electromagnet (13) which exercises its force of attraction against a contrast spring (12). The operation of the electromagnet (13) acts on the piston in the intake direction, while the supply stroke of the piston (15) is driven by the sole elastic energy stored in said spring (12). The instant starting fuel injection coincides with the opening instant of the needle (28) of the injector (27).

Description

[0001] The device subject of the present invention falls in the sector of fuel supply systems for internal combustion engines. A large part of internal combustion engines is currently supplied with fuel injection systems which, according to applications, have operating pressures varying between 2 bar and 150 bar. The need arises therefrom to equip the above-mentioned systems with pumps to supply pressurised fuel.

[0002] Depending on the desired pressure level, different types of variously-operated pumps are used. In particular, for pressure levels between 2 and 5 bar, roller rotary electropumps operated by a direct-current motor (as well as go-devil pumps or liquid-ring pumps) are widely used in the technical practice. For higher pressure levels, mechanically-operated alternative pumps are nearly always employed. In this type of systems, by-pass pressure adjusters are normally employed.

[0003] Current anti-pollution regulations impose to adopt ever more advanced fuel-injection systems even in small motorcycle engines. The need to limit costs and to keep such engines efficient requires such systems not only to be functional and to have construction simplicity, but also to consume little power.

[0004] Fig. 1 shows the diagram of a conventional fuel-injection system. The fuel to be processed is drawn from tank 1 and arrives, through a filtering system 2, at pump 3 which provides to pressurise it and to send it to injector 4. Injector 4 adjusts the fuel flow, which reaches the engine through the intake manifolds or is directly injected into the combustion chamber.

[0005] Supply pressure adjustment is the task, as already mentioned, of a pressure adjuster 5 which, arranged downstream of the pump, is generally integrated in a by-pass circuit. Pressure adjustment through a by-pass system provides for the pump capacity to be oversize, according to the maximum flow rate required by the injector. In substance, pump capacity is defined according to the value of the flow rate required by the injector upon maximum power delivery by the engine, and is further suitably increased in order to take into account the part of fuel which is in any case led into the by-pass circuit by the adjuster. When, at low engine loads, the flow rate of the fuel to be injected is smaller than the maximum flow rate, the exceeding flow is recirculated through the by-pass; thereby, maximum pump capacity is always processed, but only a part thereof is actually used. Thereby, all the energy imparted to the recirculated part of fuel is lost. The pump will always operate at maximum power causing large energy consumption with low engine loads.

[0006] It is an object of the present invention to propose a pump-injector assembly and a supply system for internal combustion engines which overcome the mentioned drawbacks and which are both simpler - and hence cheaper from the point of view of the manufacture thereof - and more easily controllable in their use, so as to achieve pressurisation and adjustment of fuel pressure, as well as being cheaper from an energy point of view. These objects are achieved through the features mentioned in claims 1 and 7.

[0007] In other words, the object of the present invention is achieved by employing a fuel pressurisation system which provides both to pressurise the fuel and to adjust the desired pressure value without using additional external devices, of the type of known pressure adjusters.

[0008] Further features and advantages of the invention are in any case more evident from the following detailed description of a preferred embodiment, given merely by way of a non-limiting example and shown in the accompanying drawings, wherein:

fig. 1 shows, as already mentioned, a fuel supply system according to the known art;

fig. 2 shows, in an extremely diagrammatic manner similar to that of fig. 1, a supply system according to the present invention;

fig. 3 shows an axial section of a possible practical embodiment of the pump-injector assembly according to the invention;

fig. 4 shows a diagram of the excitation current of the electromagnet operating the supply pump, in a system according to the present invention, as well as the piston displacement diagram of an internal combustion engine supplied by such pump; and

fig. 5 is a diagram of the synchronisation signals of the supply pump and of the injector, in a system according to the present invention.

[0009] As outlined in fig. 2, the system according to the present invention consists of the same essential elements already seen in connection with fig. 1 of the known art, i.e.:

· a tank 1;

· a filter 2;

· an electromagnetic pump 3;

· an injector assembly 4;

but is devoid of the by-pass pressure adjuster 5; this remarkably simplifies system architecture and reduces the manufacturing and mounting costs thereof, but also carries the further advantages highlighted in the following.

[0010] The operation of the proposed system provides that the fuel taken from tank 1 flows through filtering system 2 and arrives at pump-injector assembly 3-4, which is capable of adjusting the pressure to a preset value.

[0011] This result is possible if a pump is adopted such as the one described for example in patents EP-0.288.216 in the name of EATON, or EP-0.953.764-B1 in the name of MARELLI; in the known art resulting from these patents, excitation of the operating electromagnet causes displacement of the piston in its fuel intake run, whereas the fuel supply run occurs under the thrust of a pressure spring, which has been loaded during the intake run.

[0012] The arrangement is better understandable if reference to the practical embodiment shown in fig. 3 is made, wherefrom it can be appreciated that pump body 3 and injector body 4 build a single assembly.

[0013] In body 3, a bell body 10 is housed, wherein a chamber 11 is formed, where the fuel arrives, within which a contrast spring 12 is housed; said spring rests above against a fixed collar 3b of the fuel supply conduit 3a to pump unit 3, and rests below against the upper surface of a piston 15. Said piston has at the same time the function both of intake and supply piston of the fuel coming from conduit 3a, and that of movable anchor, sensitive to the magnetic field generated by an electromagnet. As a matter of fact, on the outside of body 10 and of piston 15, reel 13 of said electromagnet is arranged, inwardly closed by a metal sheet 13a and housed in a supporting body 14. The wall of said metal sheet 13a builds, together with wall 14a of body 14, a cylinder guiding the displacements of piston 15.

[0014] Piston 15 is hollow and its inner cylindrical chamber in turn builds a guide of the same piston 15 on a cylindrical extension 16 of closing base 17 of body 3. In extension 16, a central cavity 18 is formed, which extends into an axial hole 18a in the same base 17; hole 18a puts in communication chamber 18 with end chamber 19 mounting injector unit 4, as better described in the following. In chamber 18, a non-return valve is housed, consisting of a valve body 20, for example a spherical one, and of a contrast spring 21.

[0015] When electromagnet reel 13 is electrically energised, it causes the upward (with reference to the drawing) displacement of anchor 15; structure, size and arrangement of spring 12 and valve 20-21, known per se, are such that the upward displacement of anchor 15 determines, in addition to compression of spring 12, the opening of valve 20 and the flow of fuel from chamber 11, i.e. from conduit 3a, to chamber 18.

[0016] When piston 15 has reached the upper end stop and stops, spring 21 causes the closure of valve 20. If, at this stage, electromagnet reel 13 is de-energised, the fuel in chamber 18, 18a, 19 - not being able to be released towards the injector (as better explained in the following), nor backwards towards chamber 11 - remains pressurised, under the action of piston 15, pushed by spring 12. The value of this pressure is determined by the ratio between the load of said spring 12 on piston 15 and the useful surface of piston 15.

[0017] Injector unit 4 is directly connected with pump unit 3 by way of the engagement of extension 4a of body 4 into chamber 19, for example by simple screwing in.

[0018] The structure of the injector unit, known per se and hence not described in further detail, essentially comprises: a first hollow cylindrical body 22, forming a first injector supply chamber 22a; a bell body 23, in whose central chamber a contrast spring 24 is housed; a movable anchor 25, shaped as a cylinder and equipped with an axial boring 25a; an electromagnet reel 26, which partly surrounds the chamber housing spring 24 and partly anchor 25; and a fuel injection nozzle 27, with corresponding closing needle 28, housed in a chamber 29 formed at the bottom of the sliding seat of anchor 25: needle 28 is integral with anchor 25 and is therefore normally closed when electromagnet 26 is not energised and spring 24 pushes anchor 25 downwards.

[0019] According to the present invention, chamber 18 of the pump unit is directly and freely in communication with conduit 18a, with chamber 19, with chamber 22a, with the chamber housing spring 24, with conduit 25a and with chamber 29 supplying injector 4. Therefore, when the fuel is pressurised in chamber 18, it is equally so in chamber 29.

[0020] Thanks to this arrangement, it can be appreciated that, according to the main feature of the present invention, an integrated assembly of pump and injector is accomplished, in which, however, the operation of the pump unit can be considered somewhat distinct from injector operation, due to the reasons set forth in the following.

[0021] The sizing of the pump unit, in relation to the delivery capability of the injector, is such that, when the engine is operated at high rpm, i.e. when the maximum quantity of supply fuel is required, a pump supply impulse must occur at each opening of the injector. However, it is not necessary to guarantee the coincidence of the actuation instant of electromagnet 13 controlling the displacements of piston 15, with the actuation instant of electromagnet 26 controlling the opening of the injector; but rather, the two actuation instants are preferably alternate, as appears clearly from the diagrams of figs. 4 and 5, shown below.

[0022] With such a sizing of the pump unit, it then becomes also possible - when the engine is operated at low rpm, i.e. at idle, and the fuel flow injected by the injector is consequently relatively small - to actuate electromagnet 13 which controls the displacements of piston 15 not following each actuation of electromagnet 26 which controls the opening of the injector, but rather following a sequence of an integer number of actuations of electromagnet 26, for example every two or three times. As a matter of fact, the full run capacity of piston 15 may correspond - at these low rpm - to two or three fuel injections into the engine, and at each fuel fuel-injection, piston 15 will cover only half or a third of its run, to stop as soon as needle 28 of the injector closes.

[0023] In general, if the duration of the fuel injection phase is short and injector capacity is accordingly small, only part of the fuel contained in chamber 18 will be released and, as a result, in the following intake phase, piston 15 will suck only the fuel amount required to replenish chamber 18. Thereby, flow rate adjustment occurs only according to injector opening time. The energy used during each intake run is constant upon varying of actuation frequency. If frequency decreases, cycle duration increases and, once intake duration has been set, the time in which the magnet is not actuated increases and, as a result, the energy used decreases. This is an obvious great advantage over the known art in which, even at low engine rpm, when fuel demand is low, the pump processes the entire flow even if most of it is bypassed, so that the entire energy employed in such process is wasted.

[0024] The diagram of fig. 4 - which refers to the case of engine supply at the highest rpm, and shows the piston position on the y axis and the progress of time on the x axis - shows in the upper half that the displacement of piston 13 comprises an initial supply phase a), a subsequent holding phase b), and a final return phase c). Phase a) corresponds to piston rise, with reload of spring 15 and simultaneous fuel intake towards chamber 18; phase b) is a piston holding phase while waiting to supply the injector with fuel; and phase c) corresponds to the fuel injection phase, wherein the fuel is released and the piston is moved downwards. It must here be remembered that holding of piston 15 is carried out hydraulically, in the sense that it is determined simply by closure of injector needle 28, which prevents the fuel from flowing. The lower half of the diagram of fig. 4, to be compared directly with the upper half thereof, shows the development of the excitation current (value on the y axis) over time (value on the x axis); here it shows clearly that the excitation current increases dramatically during phase a) which controls and displaces the piston, then drops to zero in phase b) which holds the pressure of the piston, and in phase c) when the injector control is activated.

[0025] The diagram of fig. 5 shows instead the time ratio between the activation signals of electromagnet 13 of the pump and of injector 26, respectively; here it is evident that the pump activation signal is generated immediately after the end of the injector one. In other words, electromagnet 26 controlling the opening of injector needle 28 is energised and kept energised for the time necessary for the injection of the required fuel amount according to the engine rpm; for all this time, fuel supply is guaranteed by the displacement of piston 15 under the action of spring 12, which extends itself. Following de-energising of electromagnet 26, pump unit electromagnet 13 is then energised, which causes piston 15 to rise and spring 12 to reload.

[0026] By the described structure of the pump-injector assembly according to the present invention, various advantages are hence obtained, which may be summed up in the following:

• the use of a pressure adjuster is abandoned. By opening electrically-controlled injector 27, the fuel is pumped thanks to the extension of spring 12, which provides to automatically keep the pressure at the desired value; this value, determined according to the preload assigned to the spring, remains virtually constant, given the modest variability of the spring load during extension thereof;
• the injector supply phase can be completed in a very short time because the energy required is already available and stored in the previously loaded spring. Since the spring can be reloaded between an injection phase and the other, it is therefore not necessary to keep to the characteristic movement times of electromagnet 13;
• the electric power installed to activate electromagnet 13 can be remarkably lower because the work required for displacing piston 15 and for compressing spring 12 can be produced over a longer time, i.e. precisely in the time between an injection phase and the other;
• considerable energy savings are made, due to the following factors: the fact that the pump must not treat excess fuel (i.e. the one normally recycled from the pressure adjuster of the prior art); the fact that a single run of pump piston 15 can be used, at low engine rpm, for multiple injector supplies; and the fact that, at intermediate rpm, the supply run of piston 15 is limited and spring 12 does not extend completely, hence the intake run is also limited to the one strictly necessary for the partial reload of spring 12;
• further energy savings are obtained, due to the fact that no power consumption exists in phase b) of holding of the cycle time, the holding being guaranteed hydraulically by the temporary closure of the injector.
• it is further possible to simplify the control algorithm in the electronic control unit, since the injector closure signal can be used as a control signal for the activation of electromagnet 13, simplifying the synchronisation between pump and injector;
• reduced cost of the system, due to the reduction of the components (doing without the pressure adjuster) and to the greater construction simplicity (integrated pump-injector assembly);

[0027] It is understood, however, that the invention is not to be considered limited to the particular arrangement illustrated above, which represents only an exemplary embodiment thereof, but that different variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection of the present invention, as defined in the following claims.

Claims

1. System for the supply of fuel-injection, internal combustion engines, of the type comprising a pump unit (3) cooperating with an injector unit (4), the pump unit comprising a piston-cylinder assembly (15; 13a-14a), an electromagnet (13) exercising its force of attraction on a movable anchor (15), consisting of the piston or integral therewith, a spring (12) acting on the anchor or piston (15) with an elastic force of a sign opposite to that of the force of attraction of the electromagnet, the run of said anchor-piston upon electromagnet actuation being used to load said spring (12) during the fuel intake phase,
characterised in that the supply run of the piston (15) is driven by the elastic energy stored in said spring (12),
that said supply run pressurises the fuel so as to supply it directly to the injector unit (4), and
in that fuel injection start is driven only by the opening of the injector unit needle (28).

2. System for the supply of fuel-injection, internal combustion engines as in claim 1), characterised in that adjustment of the injector supply pressure is determined by the ratio between the load of said spring (12) and the useful surface of the piston (15).

3. System for the supply of fuel-injection, internal combustion engines as in claim 1) or 2), characterised in that the closure signal of the injector needle (28) is used, in an electronic control unit, as a signal activating the pump unit (3).

4. System for the supply of fuel-injection, internal combustion engines as in any one of the preceding claims, characterised in that, at the maximum engine rpm, said electronic control unit sends a signal activating the electromagnet (13) of the pump unit (3) following each deactivation signal of the electromagnet (26) of the injector unit (4).

5. System for the supply of fuel-injection, internal combustion engines as in any one of claims 1) to 3), characterised in that, at the minimum engine rpm, said electronic control unit sends a signal activating the electromagnet (13) of the pump unit (3) following a multiple integer of deactivation signals of the electromagnet (26) of the injector unit (4).

6. System for the supply of fuel-injection, internal combustion engines as in any one of the preceding claims, characterised in that between said pump unit (3) and a fuel tank (1), there is a filter (2) only.

7. Pump-injector assembly, for the supply of internal combustion engines, of the type comprising a pump unit (3) equipped with a cylinder-piston assembly (15; 13a-14a), an electromagnet (13) exercising its force of attraction on a movable anchor (15), against the action of a contrast spring (12), the run of said anchor (15), upon excitation of said electromagnet (13), being used for the intake of fuel into a fuel chamber (18) formed in the pump unit (3),
characterised in that an injector unit (4) is directly associated with said pump unit (3),
in that said movable anchor consists of - or is integral with - a fuel supply piston (15),
in that said fuel chamber (18) of the pump unit (3) is closed upstream by a non-return valve (20) and is in direct communication, downstream, with a supply chamber (29) formed in said injector unit (4),
in that the fuel in said fuel chamber (18) and in said supply chamber (29) is kept pressurised by the action of the piston (15) of the pump unit, under the thrust of said contrast spring (12), and
in that an electromagnetically-operated needle (28) is associated with the injector, the opening of said needle controlling the supply run of said piston (15) of the pump unit.

8. Pump-injector assembly for the supply of fuel-injection, internal combustion engines as in claim 7), characterised in that said non-return valve (20) is placed between said fuel chamber (18) and a cylinder chamber (11), wherein said contrast spring (12) is housed, said chamber being directly connected with a fuel tank (1).

9. Pump-injector assembly for the supply of fuel-injection, internal combustion engines as claimed in claim 7), characterised in that said piston (15) is hollow and is guided on the outside within a cylinder consisting at least in part of the wall (13a) of the electromagnet reel (13).

10. Pump-injector assembly for the supply of fuel-injection, internal combustion engines as claimed in claim 9), characterised in that the electromagnet reel (13), closed on the inside by a metal sheet forming said wall (13a), is housed in a support body (14), the base of which forms a further cylindrical wall (14a) guiding the movements of piston (15).

11. Pump-injector assembly, for the supply of fuel-injection, internal combustion engines as claimed in claim 9), characterised in that said piston (15) is further guided, on the inside, along a cylindrical appendix (16) of a base (17) closing the pump unit body (3).

12. Pump-injector assembly, for the supply of fuel-injection, internal combustion engines as claimed in claim 7) or 11), characterised in that said fuel chamber (18) of the pump unit is formed in said appendix (16) guiding the piston (15), in said chamber being housed said non-return valve (20) and a respective pressure spring (21), the seat of said non-return valve (20) being formed in the piston head.

13. Pump-injector assembly for the supply of fuel-injection, internal combustion engines as claimed in claim 12), characterised in that said fuel chamber (18), formed in said extension (16), extends into an axial hole (18a) of the base (17) of the pump unit, which puts said chamber (18) in communication with an end chamber (19) mounting the injector unit (4).

14. Pump-injector assembly for the supply of fuel-injection, internal combustion engines as claimed in claim 7) or 13), characterised in that said injector unit (4) is directly connected with the pump unit (3) by the engagement of an extension (4a) of the same with said end chamber (19), preferably by simple screwing.

15. Pump-injector assembly, for the supply of fuel-injection, internal combustion engines as claimed in claim 7) or 13), wherein said injector unit (4) comprises a movable anchor (25), actuated by an electromagnet (26) against the action of a contrast spring (24) and which anchor moves a needle (28) closing a fuel injection nozzle (27), as well as a fuel supply chamber (29), characterised in that said supply chamber (29) is in direct, continuous communication with said fuel chamber (18) formed in the pump unit (3) by means of respective through-passages (22a, 25a).

Drawing